Guidebook to the Socorro area, New Mexico

Compiled by Virginia T. McLemore and Mark R. BowieNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801

24th annual meeting of the Clay Minerals Society

and

36th annual Clay Minerals Conference

Guidebook for the 1987 conference

SOCORRO 1987

NEW MEXICO INSTITUTE OF MINING & TECHNOLOGYLaurence H. Lattman, President

NEW MEXICO BUREAU OF MINES & MINERAL RESOURCESFrank E. Kottlowski, Director

George S. Austin, Deputy Director

BOARD OF REGENTS

Ex Officio

Garrey E. Carruthers, Governor of New Mexico

Alan Morgan, Superintendent of Public Instruction

AppointedGilbert L. Cano, President, 1985-1989, Albuquerque

Lenton Malry, Sec./Treas., 1985-1991, Albuquerque

Robert 0. Anderson, 1987-1993, Roswell

Donald W. Morris, 1983-1989, Los Alamos

Steve Torres, 1967-1991, Albuquerque

BUREAU STAFF

Full TimeORIN J. ANDERSON, Geologist DARRELL DAUDE, Computer Operator IRE A N L . RAE , Drafter

RUBEN ARCHULETA, Technician II Lois M. DEVLIN, Director, Bus./Pub. Office MARSHALL A. REITER, Senior Geophysicist

AL BACA, Crafts Technician ROBERT W. EVELETH, Mining Engineer JACQUES R. RENAULT, Senior Geologist

NORMA L. BACA, Secretary/Receptionist ROUSSEAU H. FLOWER, Emeritus Sr. Paleontologist JAMES M. ROBERTSON, Senior Economic Geologist

JAMES M. BARKER, Industrial Minerals Geologist MICHAEL J. GOBLA, Manager, Inf. Ctr. SYLVEEN E. ROBINSON-COOK, Geologist

ROBERT A. BIEBERMAN, Senior Petrol. Geologist MICHAEL J. HARRIS, Metallurgist GRETCHEN H. ROYBAL, Coal Geologist

DANNY BORROW, Geologist JOHN W. HAWLEY, Senior Env. Geologist CINDIE SALISBURY, Scientific Illustrator IMARK R. BOWIE, Research Associate CAROL A. FLIELLMING, Editorial Secretary DEBORAH A. SHAW, Assistant Editor

LYNN A. BRANDVOLD, Senior Chemist GARY D. JOHNPEER, Engineering Geologist WILLIAM J. STONE, Senior Hydrogeologist

RON BROADHEAD, Petroleum Geologist ANNABELLE LOPEZ, Staff Secretary SAMUEL THOMPSON III, Senior Petrol. Geologist

MONTE M. BROWN, Drafter DAVID W. LOVE, Environmental Geologist REBECCA J. TITUS, Drafter

FRANK CAMPBELL, Coal Geologist JANE A. CALVERT LOVE, Associate Editor JUDY M. VAIZA, Executive SecretaryANNETTE G. CARROLL, Admin. Secretary I CECILIA ROSACKER MCCORD, Technician I MANUEL J. VASQUEZ, Mechanic

STEVEN M. CATTIER, Postdoctoral Fellow CHRISTOPHER G. MCKEE, X-ray Laboratory Technician ROBERT H. WEBER, Emeritus Senior Geologist

RICHARD CHAMBERLIN, Economic Geologist VIRGINIA MCLEMORE, Geologist DONALD WOLBERG, Vertebrate Paleontologist

CHARLES E. CHAPIN, Senior Geologist LYNNE MCNEIL, Technical Secretary ZANA G. WOLF, Staff Secretary

RICHARD R. CHAVEZ, Assistant Head, Petroleum NORMA J. MEEKS, Accounting Clerk—Bureau MICHAEL W. WOOLDRIDGE, Chief Sci. Illustrator

KEVIN H. COOK, Research Associate ROBERT M. NORTH, Economic Geologist–Mineralogist JIRI ZIDEK, Chief Editor–Geologist

RUBEN A. CRESPIN, Garage Supervisor BARBARA R. POPP, Biotechnologist

Research AssociatesCHR IS T INA L . BA L K , NMT JEFFREY A. GRA MBLING, UNM JOHN R. MACMILLAN, NMT

WILLIAM L. CHENOWETH, Grand Junction, CO JOSEPH HARTMAN, Univ. Minn. HOW A RD B. N ICKE LSON , Carlsbad

PAIGE W. CHRISTIANSEN, Kitty Hawk, NC DONALD E. HATTIN, Ind. Univ. LLOYD C. PRAY, Univ. Wisc.

RUSSELL E . CLEMONS, NMSU ALONZO D. JACKA, Texas Tech. Univ. A L L A N R . S A N F O R D , NM T

WILLIAM A. COBBAN, USGS DAVID B. JOHNSON, NMT JOHN H. SCHILLING, Nev. Bur. Mines & Geology

AUREAL T. CROSS, Mich. St. Univ. WILLIAM E. KING, NMSU WILLIAM R. SEAGER, NMSU

MARIAN GALUSHA, Amer. Mus. Nat. Hist. DAV ID V. LEMONE, UTEP RICHARD H. TEDFORD, Amer. Mus. Nat. Hist.

LELAND H. GILE, Las Cruces A. BYRON LEONARD, Kansas Univ. JORGE C. TOVAR R., Petroleos Mexicanos

Graduate Students

DONA L D BA R R IE JOAN GABE LMAN RIC HA R D P . LO Z INS KY

MA RGA RE T BA RROLL RICHARD HARRISON B R U C E M A R R O N

PAUL BAUE R TI M Huns WILLIAM MCINTOSH

Plus about 50 undergraduate assi stants

Original Printing 1987

Published by Authority of State of New Mexico, NMSA 1953 Sec. 63-1-4Printed by University of New Mexico Printing Plant, October 1987Available from New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801

Preface

Welcome to Socorro! The roadlogs in this guidebookwere written primarily for the field trips of the 24thannual meeting of the Clay Minerals Society and the36th annual Clay Minerals Conference held in So-corro, New Mexico, October 19-22, 1987. With per-mission, the authors have drawn freely on appropriateparts of published roadlogs from field trips in andaround Socorro hosted by the New Mexico GeologicalSociety (Foster and Luce, 1963a, b; Weber and Willard,1963; Smith et al., 1983) and the New Mexico Bureauof Mines and Mineral Resources (Chapin et al., 1978a).Nomenclature and correlation of Cenozoic strata fol-lows that established by Osburn and Chapin (1983a,b). Radiometric ages of major ash-flow tuffs and re-lated cauldron collapse events were updated by highprecision 40Ar/39Ar dating by McIntosh et al. (1986).

This guidebook is organized into three parts: 1) anintroduction to the Socorro area; 2) roadlogs, and 3)short papers that supplement the field trips. Theroadlogs have been divided into three trips. The pre-meeting field trip on Sunday, October 18, 1987 (Trip1), is to examine clays in the Luis Lopez and PopotosaFormations and to see manganese mineralization inthe Luis Lopez mining district. The mid-meeting tripon Tuesday, October 20, has been divided into Trips2a-d because of its length. We will examine clays andsoils of the La Jencia and Socorro Basins (Rio Grandevalley) and drive through a structurally complex sec-tion of Paleozoic rocks on the east side of the RioGrande and into the Jornada del Muerto. At the endof the day we will tour the Bosque del Apache Na-

tional Wildlife Refuge. In case of inclement weather,the mid-meeting trip will consist of Trips 2a, 3, 2c,and 2d (in that order). Nearby attractions and daytrips for spouses, family, and friends of conferenceparticipants are described in the introduction. We hopeyou enjoy your stay in Socorro and get the oppor-tunity to visit other areas of the Southwest.

Acknowledgments—We are grateful to the follow-ing people for their assistance: Charles Carroll (Bu-reau of Land Management), Gretchen Roybal(NMBMMR), George Austin (NMBMMR), Linda Frank(NMIMT), and Frank Kottlowski (Director, NMBMMR).Numerous people in addition to the field trip leadershave spent years studying the geology in the Socorroarea (C. E. Chapin, C. T. Smith, G. R. Osburn, J. R.MacMillan, M. N. Machette, W. J. Stone, S. E. Hook,and others), and their work is cited where appropriateand gratefully acknowledged. Technical assistance byShawn Leppert and Linda Frank is appreciated.

Virginia T. McLemoreGeologist, NMBMMRField Trip Chairman

Field Trip Committee:Mark R. Bowie

John W. HawleySocorro Richard M. ChamberlinMay 1987 James L. Post

iv

Contents

IntroductionPhysiographic and geographic setting ....................................................................................................................................... 6Climate, vegetation, and wildlife .........................................................................................................................................6City of Socorro .................................................................................................................................................................................................. 7New Mexico Institute of Mining and Technology ...........................................................................................................................8

Mining—past and present ............................................................................................................................................. 10Regional attractions ....................................................................................................................................................... 11

Fort Craig ............................................................................................................................................................................11Very Large Array ................................................................................................................................................................11Water Canyon and Langmuir Laboratory ................................................................................................................ 11Salinas National Monument ..............................................................................................................................................12Albuquerque ....................................................................................................................................................... 12

RoadlogsUse of roadlogs .......................................................................................................................................................................... 12

TRIP 1—Roadlog from Socorro to Blue Canyon area of Socorro Peak, to US-60 clay pit,and to Luis Lopez manganese district .................... R. M. Chamberlin, V. T. McLemore, M. R. Bowie, and J. L. Post 15

TRIP 2a—Roadlog from Socorro to Sedillo Hill andto Escondida .................................................................................. R. M. Chamberlin, V. T. McLemore, M. R. Bowie, and J. W. Hawley 22

TRIP 2b—Roadlog from Escondida to Pueblito, Loma de las Carias,and junction of county road A-129 and US-380 near Carthage(including a stop at Arroyo del Tajo interpretive site) J W. Hawley, V. T. McLemore, and M. R. Bowie 25

TRIP 2c—Roadlog from junction of county road A-129 and US-380 west to Carthageand San Antonio J W. Hawley, V. T. McLemore, and M. R. Bowie 33

TRIP 2d—Roadlog from San Antonio to Bosque del ApacheNational Wildlife Refuge and return to Socorro V T. McLemore, M. R. Bowie, and J. W. Hawley 38

TRIP 3—Roadlog from Socorro to San Antonio, Carthage,and Bingham Post Office V T. McLemore, M. R. Bowie, and J. W. Hawley 40

Roadlog references and additional reading ............................................................................................................................. 44

ArticlesClay mineralogy of selected sedimentary and volcanic rocks, Socorro County,

New Mexico ........................................................................................................... M. R. Bowie and V. T. McLemore 46Geomorphic evolution and soil-geomorphic relationships in the Socorro area,

central New Mexico .................................................................................................................... D. B. McGrath and J. W. Hawley 55Mineralization in the Luis Lopez mining district, Socorro County, New Mexico—

a summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. M. North and V. T. McLemore 68

Glossary ............................................................................................................................................................................................................74

6

Introduction

Socorro (pronounced so Kor' ro) is an old city, richin heritage and history. The word "Socorro," whichis Spanish for help or aid, was given by Don Juan de(Mate in June 1598 to a nearby Piro Indian pueblobecause the Indians provided his expedition with food.Socorro has since been under the authority of theSpanish, Mexican, and American governments.

Socorro has numerous attractions, including the NewMexico Institute of Mining and Technology, San Mi-guel mission church, and numerous buildings remi-niscent of times past. The Very Large Array (VLA)radio telescope research facility lies about 50 miles tothe west via US-60. Socorro will be the headquartersfor the Very Large Baseline Array (VLBA) radio tele-scope facility in the near future. The Bosque del ApacheNational Wildlife Refuge is about 18 miles to the southand will be visited on Trip 2d.

The Socorro area reveals a complex geologic historystrongly influenced by leaky crustal flaws, initiallyformed as wrench faults, and later reactivated by ep-isodes of crustal shortening, translation of micro-plates (Colorado Plateau) and crustal stretching alongthe Rio Grande rift. Mining and exploitation of naturalresources has played a vital role in Socorro's devel-opment, from early activities of the Native Americans(who were attracted to the area by warm fresh-watersprings), to the silver boom of the 1880's, to modern-day quarrying of perlite and road metal. This guide-book describes some of the area's attractions and pro-vides detailed roadlogs for the conference trips thatexamine the geology and mineral resources of theSocorro area.

Physiographic and geographic settingSocorro, at an elevation of 4,620 ft, lies near the

center of New Mexico in the Mexican Highland sec-tion of the Basin and Range physiographic province(Hawley, 1986), a region of distended continental crustcharacterized by a series of gently sloping alluvium-filled basins separated by complexly faulted moun-tains or uplifts. Socorro is situated along the Rio Grande(Fig. 1), which flows along a series of linked structuralbasins that compose the Rio Grande rift from south-ern Colorado to El Paso, Texas. The Socorro Basin isseparated from the stark, desolate plains of the Jor-nada del Muerto Basin to the east by picturesquehills and mesas of the Loma de las Canas and Carth-age areas (Trips 2b, 2c, and 3). The Jornada del Muerto(journey of the dead man) provided a treacherousshortcut for travelers going from Las Cruces (about150 miles south of Socorro) to Santa Fe (about 135miles north of Socorro). It was a waterless stretchand an area prone to attacks by Apache Indians;hundreds of travelers perished along this desolateroute.

The western edge of the Socorro Basin is borderedby (from north to south) the Lemitar Mountains (el-evation 7,929 ft), Strawberry Peak (elevation 7,012 ft),Socorro Mountains (elevation 7,284 ft), and the Chu-padera Mountains (elevation 6,179 ft). La Jencia Basin(elevation 6,090 ft; Trip 2a) lies to the west of thesemountains. The Magdalena Mountains, rising to over

10,000 ft, can be seen on the southwestern skylinefrom Socorro.

Climate, vegetation, and wildlifeSocorro has a mild semiarid to arid climate with a

wide range of precipitation, temperature, and evap-oration rates due to local topographic differences. Theaverage annual precipitation is less than 10 inches,but annual precipitation can deviate from the averageby as much as 50%. Precipitation is primarily fromrainfall during summer and early fall storms, and itincreases with increasing elevation. Total averagesnowfall in the winter months is approximately 6-7inches, and the amount of snowfall also increaseswith increasing elevation. The higher parts of theMagdalena Mountains retain snow throughout thewinter months, in contrast to the Rio Grande valleywhere snow melts within a few days.

Daily temperatures in Socorro range from an av-erage low of 23°F in January to an average high of93°F in July. Temperature variations between day andnight can be as high as 40°F. Radiation and cold-airdrainage at night can cause temperature inversionsin the valley bottoms, where frost may form in thevalleys at night, but temperatures are above freezingon the higher slopes.

Evaporation is influenced by temperature, wind ve-locity, and relative humidity. Evaporation in Socorrotypically exceeds precipitation, especially in summermonths, resulting in depletion or complete evapo-ration of local ponds, springs, and watering holes.

Vegetation and wildlife distribution in the Socorroarea, as elsewhere in New Mexico, is dependent uponrainfall, altitude, and temperature. Along the RioGrande and major arroyos, thick woods or bosquesof cottonwood, saltcedar, willows, and Russian oliveprovide excellent cover, feed, and nesting for wildlife,such as mule deer, coyote, bobcat, gray fox, jackrab-bits, cottontail rabbits, dove, quail, roadrunners (NewMexico's state bird), hawks, ravens, and varioussongbirds, rodents, and reptiles, including the poi-sonous diamond-backed rattlesnake. Rare, endan-gered species such as the bald eagle and peregrinefalcon may be encountered along the river and arro-yos. During winter months, the Rio Grande valley isthe home of numerous migratory birds such as snowgeese, Canadian geese, ducks, sandhill cranes, andthe rare and endangered whooping cranes. The Bos-que del Apache National Wildlife Refuge (Trip 2d)offers an excellent view of the habitat of the lowerelevations.

As one moves upslope and away from the river,the vegetation changes and is more typical of whatone would expect to find in a desert. Vegetation inthe Socorro area is typical of that found in the upperChihuahuan Desert where creosotebush, mesquite,and various grama grasses predominate. Cacti speciesare varied and plentiful; more than 60 species arefound in New Mexico. In the Socorro area, the cane(cholla) and pancake (prickly pear) cacti are the most

common. The trees along the Rio Grande have givenway in the desert to dwarf and scrubby juniper (cedar)and pirion (pine) trees. The yucca is common in thisarea as well. Similar species of wildlife inhabit boththe Rio Grande valley and the adjacent desert. How-ever, in the Jornada del Muerto one can encounterherds of antelope and wild horses.

In the higher elevations of the Magdalena Moun-tains, various coniferous and deciduous trees formactual forests that abound with wildlife. The juniperand pirion also occur in this area as tall trees, quitedifferent from their brothers in the lower desert re-gions. Wildlife species seen in the lower regions, aswell as elk, bighorn sheep, and wild turkey are foundin the higher elevations.

City of SocorroVery little is known about the Socorro area before

the expedition of Don Juan de Oriate in 1598. At thattime the area was inhabited by the Piro Pueblo Indianswho based their economy on agriculture and tradingwith other Pueblo Indians. Several pueblo ruins andnumerous petroglyphs and pictographs remain todaythroughout the Socorro area (see Trip 2b for a visit toa pictograph site).

Spanish missionaries established a church at a Piropueblo, known by the Spanish as Socorro, sometimebetween 1615 and 1626. The mission church becamethe center of the pueblo, similar to other pueblos inthe Rio Grande valley. During the Pueblo Revolt of1680, the Piro Indians at Socorro remained friendlywith the Spanish and together they abandoned So-corro and fled south. They resettled along the lowerRio Grande in Texas where the town of Socorro delSur remains today.

It wasn't until the early 1800's that Socorro wasre-established although Don Diego de Vargas recon-quered New Mexico in 1693 (Simmons, 1983). Fre-quent raids by Indians remained a serious problem.A small group of Spaniards applied to the Spanishcrown for a land grant in 1817. The mission churchwas rebuilt during this time on top of the ruins of theoriginal building. Many of the massive adobe wallsremaining from the original church were used in re-building. Since its completion in 1821, the church hasbeen known as San Miguel. The church was remod-eled in the early 1900's and again in 1973 to its presentform (Fig. 2). From the time of resettlement to the1870's, Socorro

7

remained a quiet, poor Spanish community that grewslowly. Its development was hindered by raiding In-dians, mostly Apaches. The change from Spanish toMexican rule in the 1820's and then from Mexican toAmerican rule in 1847 made very little difference tothe people of Socorro. Socorro County was created in1852 by the New Mexico Territorial Legislature withSocorro as the county seat. Fort Craig was commis-sioned in 1854 to subdue the Indians and then wasabandoned in 1885 once this was accomplished.

Between 1867 and 1890, Socorro was the center ofa rich silver-mining district (Eveleth, 1983). Unprec-edented growth followed. The Atchison, Topeka andSanta Fe (AT&SF) Railroad came to Socorro in 1880,and the stage was set for boom times. In 1882 Socorrowas incorporated, and the Billing smelter (later theRio Grande Smelting Co.) was built in 1883 to processthe rich ores brought from the Magdalena district bymule and ox wagon trains. Later a spur of the AT&SFRailroad into Magdalena would facilitate transporta-tion of the Magdalena ore to Socorro. The SocorroFire Clay Works on Cuba Road began manufacturingbricks for the smelter and later for homes and otherbuildings in Socorro. The original county courthousewas built in 1884 with local brick. During this periodthe Illinois Brewery, the first beer brewery and iceplant in the territory, and the Golden Crown FlourMill were built. The Garcia Opera House (Fig. 3) wasbuilt about 1886 with an open trussed roof systemsupporting a pitched roof and tilted walls. Three ho-tels served Socorro at the time: the Park, Grand Cen-tral, and Windsor; only portions of the Park Hotelremain today.

The end of the boom period came in 1893 with thedemonetization of silver resulting in a dramatic de-cline of silver mining in the area. A series of naturaldisasters followed. A devastating flood hit Socorro onJuly 30, 1895, and decimated the lower section of town.Near the train depot the water level reached four feet.A minor earthquake hit Socorro in 1906. Over theyears floods and droughts continued to plague thecity.

In 1908, Col. Ethan William Eaton completed re-modeling on his adobe house to prevent damage byearthquakes. He installed rods through the adobe wallsand through the exterior vertical boards. The rodswere secured on the inside with bolts and the outsidewith star washers to help distribute the load (Conron,1980); the Eaton house still remains today.

Progress was slow after the boom period. Agricul-

ture became the important means of livelihood in thearea. Electricity came to town in 1910, and New Mex-ico entered the Union as a state in 1912. The firstocean-to-ocean highway (present-day US-60) passedthrough Socorro in 1910 and helped to revitalize thetown. As a result of this major highway, the Val VerdeHotel was built in 1919 and became a popular socialgathering site until just before World War II. The ValVerde has since been renovated and part of it hasbeen reopened as a restaurant adjacent to small shopsand offices (Fig. 4).

The years since World War II have brought steadygrowth to Socorro, mainly in response to the growthof New Mexico Tech. Renovation of historic buildingshas become popular and some results are seenthroughout the town (Fig. 5).

New Mexico Institute of Miningand Technology

New Mexico Institute of Mining and Technology(NMIMT) or New Mexico Tech (Fig. 6) is a small stateinstitution specializing in instruction and research inphysical science and mineral engineering. The collegewas founded in 1889 as the New Mexico School ofMines as a result of extensive mining in the region.The name was changed in 1960 by an amendment tothe State Constitution in recognition of its new func-tions and an enlarged organization. New Mexico Techconsists of four divisions: 1) the College, 2) the NewMexico Bureau of Mines and Mineral Resources, 3)the Research and Development Division, and 4) theNew Mexico Petroleum Recovery Research Center.

The College Division consists of undergraduate andgraduate programs in basic sciences, computer sci-ence, mathematics, technical communication, andmineral engineering, which are supported by hu-manities, social science, and military science courses.New Mexico Tech is accredited by the North CentralAssociation of Colleges and Secondary Schools as adoctoral-degree-granting institution.

New Mexico Bureau of Mines and Mineral Re-sources (NMBMMR) is the official state agency re-sponsible for conducting investigations of geology andmineral resources in New Mexico. Information gen-erated by the staff and associates is provided to thepublic through maps, publications, and direct re-sponse to inquiries. Publications are available at thePublications Office in Workman Center. Other infor-

mation is available through the Bureau's GeotechnicalInformation Center.

The NMBMMR Mineral Museum in Workman Cen-ter is definitely worth a visit. The museum containsmore than 10,000 display and study specimens. Thedisplay collection, with more than 2,000 minerals fromNew Mexico, the rest of the United States, and theworld, can be viewed from 8:00 a.m. to 5:00 p.m.,Monday through Friday. The study collection con-tains more than 6,000 specimens and is available tothe public for inspection during regular office hours.A micromount collection, where small crystals aremounted in 1 x 1 inch boxes for viewing with a bi-nocular microscope, is also available for examination.

There are four organized components of the Re-search and Development Division (RDD): 1) the Geo-physical Research Center (GRC), 2) the Terminal EffectsResearch and Analysis group (TERA), 3) the NewMexico Mining and Mineral Resources Research In-stitute (NMMMRRI), and 4) the Center for ExplosivesTechnology Research (CETR). RDD was establishedin 1946 in Albuquerque and was moved to Socorro in1949. The GRC supports research in atmosphericphysics and chemistry, air quality, geophysics, andhydrology. The Langmuir Laboratory for Atmo-spheric Research, located in the nearby MagdalenaMountains, is also supported by the GRC. The TERAgroup supports research in ordnance and transpor

tation safety and operates the RDD machine shop.NMMMRRI provides research and education in thefields of mining and extractive metallurgy. CETR isRDD's newest group and was established in 1983 topromote research in new materials, explosive devices,rock-blasting techniques, and energetic materials.

The Petroleum Recovery Research Center (PRRC)conducts basic and applied research on enhancementtechniques for recovery of petroleum and natural gas.

10

New Mexico Tech was selected for the home of thePRRC because Tech is the only institution in the statethat grants degrees in petroleum engineering. Inter-action between the division and the department isextensive.

Socorro is also the home of the New Mexico Techgolf course, which is recognized as one of the best18-hole courses in the state. The annual Hilton Openand the Chili Chase tournaments are held here.

The Macey Theater/Conference Center (Fig. 7) at-tracts meetings of all types and hosts many fine artsevents. It is located on the northern edge of the cam-pus.

Mining—past and presentOnce the Apaches were subdued in the mid-1800's

by troops stationed at Fort Craig, prospectors begansearching the hills in earnest for gold, silver, and othermetals. Lead and silver were discovered in the Mag-dalena Mountains in 1866, and by 1876 mines in theMagdalena (Kelly), Socorro Peak, and Water Canyondistricts were producing (Fig. 8, Table 1). Actual pro-duction figures from most of these districts are sketchy,but much more than 30,000 oz of gold and more than

4.8 million oz of silver were produced from SocorroCounty (North, 1983; North and McLemore, 1986).

Socorro became the center of these silver-rich dis-tricts. The Torrance stamp mill and the New Orleansand La Joya smelters initially processed the ore, butin 1883 the Billing smelter went on line and soon wasprocessing ore from throughout the Southwest. It isestimated that $18 million worth of lead, silver, andgold were smelted at this plant from 1883 through1894 (Eveleth, 1983).

Coal and limestone were mined at Carthage (Trips2c and 3) as feedstock for the Billing smelter and lateras heating fuel. Total coal production through 1964 isestimated at more than 1.8 million tons. An unknownquantity of reserves is still present at Carthage. Quar-ries in the Popotosa and Luis Lopez Formations nearSocorro (Trips 1 and 2a), in the Sandia Formation atArroyo de la Presilla (near Stop 2-3, Trip 2b), and inthe southern Lemitar Mountains supplied clay to thelocal brick plant. Bricks were used in the smelter andin buildings in town. Most of the fluxing ore wasimported from Mexico.

The end of the mining boom commenced in 1893and 1894 with 1) a duty increase on the Mexican flux-ing ore and 2) a steady decrease in demand for silver

11

(Eveleth, 1983). The Billing smelter closed in October1894. The closing of the plant crippled the economyof Socorro. Socorro's population in 1890 was 2,300,but by 1900 it had dropped to 1,500.

In the 1900's, mining of gold, silver, and other met-als occurred sporadically throughout Socorro County(North, 1983; North and McLemore, 1986). Mines inthe Magdalena and Water Canyon districts continuedsporadic production until the early 1980's. Other dis-tricts produced ore until the 1950's. Exploration forprecious metals continues today.

Mines from Socorro County have also yielded bar-ite, fluorite, manganese, uranium, and vanadium.Barite was produced from several areas in the 1970'sand milled at Pueblito (Trip 2b). Perlite, a hydratedrhyolitic glass capable of expansion upon heating,was discovered in the Socorro Mountains in the 1960'sand is being produced currently. Perlite is used pri-

TABLE 1—Mining districts in Socorro County, New Mexico.Numbers are keyed to Fig. 8.

Volcanic epithermal deposits

1 Abbe Spring Cu, Ag (Ba)2 Bear Mountains (Cu, Ag, Sb)3 Cat Mountain Cu, Au, Ag4 Council Rock Pb, Ag (Ba)5 Goldsboro Au, Ag6 Hop Canyon (Mill Canyon) Cu, Pb, Au, Ag (Zn,

Ba, U)7 North Magdalena (Silver Hill) Pb, Ba, Cu, V, Ag

(Zn)8 Rosedale Au, Ag (F)9 San Jose Cu, Pb, Zn, Au, Ag

10 San Lorenzo Cu, Ag (U)11 Socorro Peak Pb, Ag (Ba, F)12 Taylor (Ojo Caliente #2) Cu, Pb, Ag

Carbonate-hosted deposits

13 Magdalena (Kelly) Ag, Au, Zn, Pb, Cu(F, Ba)

14 Water Canyon Ag, Au, Cu, Pb, Zn(Mn)

Stratabound, sedimentary copper deposits

15 Chupadero Cu, Ag (U)16 Rayo (Cu, Ag)17 Scholle Cu, Ra, Pb, Ag, Au

(U, V)

Sedimentary-hydrothermal barite-fluorite-galena18 Hansonburg Pb, F, Ba, Cu, Ag,

Au19 Joyita Hills Pb, F, Ag (Cu)20 Lemitar Mountains Cu, Pb, Ba, Ag (F,

Zn, U, V)21 Mockingbird Gap Pb, Ag (Cu, Ba, F,

Zn)22 Fra Cristobal Mountains (Cu, Pb, Ag, Au, F,

Ba, Mn)Precambrian23 Chupadera Mountains (Au, Ag, Cu, Pb,

(Coyote Hills) Zn, Ba)24 Ladron Mountains U, Cu, Pb, Ag, F

(Zn, Ba)

Manganese deposits25 Luis Lopez Mn (Au, Ag, Zn, W)

marily in building materials (e.g., wallboard) and asa filter aid. New Mexico is the leading producer ofperlite in the United States. Sand and gravel are theonly other raw materials currently produced in So-corro County. They are quarried from Quaternarygravels along the Rio Grande valley.

Regional attractions

Fort Craig

Fort Craig is located 25 mi south of Socorro, but iscurrently closed to the public until restoration of thefort is completed. The site is administered by the U.S.Bureau of Land Management (BLM); guided tours ofFort Craig are provided periodically by BLM person-nel.

The fort was commissioned in 1854 to provide pro-tection from hostile Indians. It was named for CaptainLouis S. Craig of the 3rd Infantry who was killed inCalifornia in 1852. At the beginning of the Civil War,Colonel E. R. S. Canby ordered Fort Craig to bestrengthened (Wilson and Bieberman, 1983), therebymaking it the second largest fort in New Mexico. FortUnion near Las Vegas, New Mexico, was larger andserved as the main supply point for the entire South-west. The first Civil War battle in New Mexico wasfought at Val Verde in 1862; Confederate forces werevictorious. However, the Confederates failed to cap-ture Fort Craig. They were finally defeated later thatyear at Glorieta Pass, between Santa Fe and Las Vegasand forced to retreat to Texas. After the Civil War thefort continued to provide protection from the ApacheIndians. It was abandoned in 1885.

Very Large Array

The Very Large Array (VLA) is an astronomical ob-servatory operated by the National Radio AstronomyObservatory and is located on the San Agustin Plainsabout 50 mi west of Socorro on US-60. Twenty-sevengiant, dish-shaped radio telescopes, each weighing235 tons and standing 100 ft high, make up one ofthe world's largest astronomical observatories. Theyare linked electronically to form, in effect, a single,large radio telescope. Each antenna is computer-con-trolled and collects incoming radio signals and sendsthem to a central computer where they are processed.By using many antennae, VLA researchers can makedetailed, high resolution pictures of extremely faintnear- and far-distance celestial objects. The VLA, oneof the most powerful radio telescopes in the world,operates 24 hours a day, 7 days a week. The visitorcenter contains several displays about radio astron-omy and the operation of the VLA. A walking tourtakes visitors around the central portion of the ob-servatory, including the control and computer rooms,the antenna assembly building, the service area, andthe closest of the antennae.

Water Canyon and Langmuir LaboratoryWater Canyon is a popular picnic and camp site in

the Magdalena Mountains. It is located about 20 miwest of Socorro on the road that leads to LangmuirLaboratory. The laboratory, which was built in 1963

12

at an elevation of 10,630 ft, is used for research inatmospheric physics and was named in honor of thelate Dr. Irving Langmuir, Nobel Prize winner for re-search in cloud physics and weather modification atNew Mexico Tech, 1946-1957. In cooperation with theGoddard Space Flight Center of NASA and New Mex-ico Tech, the Joint Observatory for Cometary Re-search was built at the site in 1973.

Salinas National MonumentSalinas National Monument, which is about 60 mi

northeast of Socorro near Mountainair, includes theruins of three Indian pueblos—Abo, Quarai, and GranQuivira—and their nearby 17th century Spanish mis-sion ruins. The National Park Service headquarters isin the historic Shaffer Hotel in Mountainair and housesa museum display and audiovisual program. Parkpersonnel present excellent seminars describing theIndian culture, history, and subsequent influence bythe Spanish. The pueblo of Abo (10 mi west of Moun-tainair) was fully settled by A.D. 1150 along a majorIndian trade route. Spanish records and the extensiveruins suggest that Abo was one of the largest com-munities in central New Mexico. Gran Quivira is about33 mi southeast of Abo (25 mi southeast of Moun-tainair) and was first occupied by at least A.D. 700.Mission activity began with the construction of SanIsidro church in 1629. Quarai, which is 8 mi north ofMountainair (33 mi north of Gran Quivira), was a

thriving community by A.D. 1300. The Nuestra Sen-ora de la Purisima ConcepciOn de Cuarac church wasconstructed about 1630. All three sites were aban-doned during the 1670's and 1680's. Today, preser-vation and excavation of the ruins, including churches,Indian rooms, and kivas, can be seen along trails ateach of the three sites.

AlbuquerqueNew Mexico's largest city, Albuquerque, lies about

75 mi north of Socorro, also on the Rio Grande. TheVilla of Alburquerque was established at Old Town in1706 by the colonial governor Don Francisco Cuervoy Valdez. The villa was named after the Duke of Al-burquerque and Viceroy of New Spain. The "r" in thesecond syllable was dropped by 19th century English-speaking people. Today, Old Town Plaza is a popularattraction where Indian vendors display their waresalong sidewalks in front of the many shops and res-taurants. The Indian Pueblo Cultural Center, the Al-buquerque Museum, and the Natural History Museumare near the Old Town Plaza area. Sandia Peak Tram-way, the world's longest, spans 2.7 mi from the foot-hills of the Sandia Mountains (elevation 10,378 ft). Anexcellent panoramic view of the Albuquerque area canbe seen from the Summit House and restaurant at thetop. The geology of the Albuquerque area, includingthe route of the tramway, is described by Kelley (1982)in NMBMMR's Scenic Trip No. 9.

Roadlogs

Use of roadlogs

The following series of roadlogs point out geologicfeatures, historical information, and other items ofinterest in and around Socorro. Passenger cars can beused on all trips; however, travel on dirt roads in Trips1 and 2b is not advised during wet weather. Manyfeatures can be seen while driving, but please do nottry to read the logs while driving! Have a passenger

read the logs or pull over in a safe place to read andobserve. A few stops include short walks. Dress ap-propriately for the weather, carry water, and bewareof snakes. Odometers on different vehicles often donot agree, so allow for differences at major landmarks."Where to look" is usually given in clock-face termi-nology: 12:00 is straight ahead, 9:00 is due left, and3:00 is due right. Stratigraphic nomenclature is givenin Table 2.

13

TABLE 2—Stratigraphic nomenclature for the Socorro area (from Osburn and Chapin, 1983a, b; Osburn and Lochman-Balk, 1983; Hook, 1983; Osburn, 1984;McIntosh et al., 1986). Ages in parentheses are approximate ranges; ages in brackets are from one or more age dates.

Geologic age Geologic unit Thickness (ft) General lithology

CenozoicQuaternary undifferentiated alluvial, eolian, basin floor, and

piedmont depositsvariable unconsolidated sands, silts, and grav-

elsQuaternary–Tertiary

Pliocene–Upper Santa Fe Group

Pleistocene Sierra Ladrones Formationincludesbasalt of Sedillo Hillbasalt of Socorro Canyon [4.1 ± 0.3 m.y.]basalt of San Acacia

0-1000 poorly indurated fanglomerates inter-tonguing mudstone and siltstone;basalt flows

Miocene Popotosa Formationincludes

basalt of Broken Tank basalt ofBear Canyon Socorro PeakRhyolite [7-12 m.y.]

0-3000 lower unit is well indurated mudflowdeposits overlain by red and greenplaya shales; fanglomerates, mud-stones, and sandstones interfin-gered with local volcanic deposits

Magdalena Peak Rhyolite [14.8 m.y.]basalt of Kelly Ranchbasalt of Council Rock [17.4 m.y.]rhyolite of Water Canyon Mesa [20.5± 0.8 m.y.]

Oligocene South Canyon Tuff [27.36 m.y.] 0-650 ash-flow tuffLa Jara Peak Basaltic Andesite 0-1100 basaltic andesite flowsLemitar Tuff [27.97 m.y.] 0-400 ash-flow tuffLa Jencia Tuff [28.7 m.y.] 0-500; ..-2500 ash-flow tuffVicks Peak Tuff [28.46 m.y.] 0-800 ash-flow tuffLuis Lopez Formation

includes rhyolite of Cook Spring0-3500 rhyolite lavas and domes, intermedi-

ate lavas, ash-flow tuffs, and sedi-mentary rocks including mudstones

Hells Mesa Tuff [32.04 m.y.[ 0-800; >3000 ash-flow tufftuff of Granite Mountain 0-200 ash-flow tuffDatil Group

Spears Formation [33.1-39.6 m.y.] 0-3000 volcaniclastic rocks and lavas, andes-itic

Eocene Baca Formation (37-41 m.y.) 0-1000 red to buff sandstones and claystoneswith minor conglomerates

MesozoicCretaceous Crevasse Canyon Formation 0-1115 mudstone, sandstone, and siltstone

with some coalsGallup Sandstone (89-88 m.y.) 0-110 sandstoneD–Cross Tongue of Mancos Shale (90-89 m.y.) 50-300 noncalcareous shale with some lime-

stoneTres Hermanos Formation (93-90 m.y.) 190-300Fite Ranch Sandstone Member 75-90 sandstone

Carthage Member 100-150 predominantly shale and severalsandstones; coal

Atarque Sandstone Member 10-100 sandstoneRio Salado Tongue of Mancos Shale 200 basal limestone overlain by calcareous

and noncalcareous shalesTwowells Tongue of Dakota Sandstone 0-100 sandstoneslower part of Mancos ShaleDakota Sandstone (95-93 m.y.)

0-450 shalessandstone with interbedded shale and

local coal

Triassic Dockum GroupChinle Formation 0-550 maroon and gray shales and siltstones

with local sandstonesSanta Rosa Sandstone 200-250 red sandstones with interbedded shales

and siltstonesPaleozoic

Permian Bernal Formation 0-100 mudstone and siltstone with minorsandstone

San Andres Limestone 20-60 limestone and dolostone with gyp-sum, siltstone, and shale

Glorieta Sandstone 0-115 cliff-forming quartzose sandstone withlocal siltstones

Yeso FormationJoyita Member 0-160 quartzose sandstone with local silt-

stoneCallas Member 0-300 gypsum, limestone, and siltstone

Torres Member 100-600 interbedded sandstone, shale, gyp-sum, and limestone

Meseta Blanca Member 130-400 sandstone with minor siltstone andshale

Abo Formation 0-1000 dark reddish brown sandstone, shale,and siltstone

Trip 1:Socorro Peak area and

Luis Lopez manganese district

Roadlog from Socorro to Blue Canyon areaof Socorro Peak, to US-60 clay pit, and to

Luis Lopez manganese district.

by Richard M. Chamberlin, Virginia T. McLemore, Mark R. Bowie, and James L. PostNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801 and California State University, Sacramento, CA 95819-2694

Sunday, 18 October 1987

Assembly point: Macey Center, New Mexico Techcampus

Departure time: 1:00 p.m.Distance: 23.4 miStops: 3

Summary

This half-day excursion provides a brief introduc-tion to the geologic and tectonic setting of two dif-ferent types of clay deposits as well as the hydrothermalmanganese deposits found on the periphery of theSocorro Mountains. As shown in Figure 9, the north-trending basins and ranges of the Socorro region (in-cluding Socorro Peak) are predominantly tilted faultblocks (half basin, half uplift) formed by westwardextension of the continental crust along the Rio Granderift. Twentieth century uplift, historic seismicity, ther-mal springs, and high-heat flow in the Socorro Peak-Socorro Basin area are reasonably attributed to anactive sill-like magma body, about 11 mi below theRio Grande valley, and numerous dike-like bodies about2.5-8.5 mi below Socorro Peak (Sanford, 1983).

The 2,000-ft escarpment forming the east face ofSocorro Peak represents a late-stage tilted-fault-blockuplift within the Rio Grande rift. Less than 7 m.y.old, the Socorro-Lemitar uplift has disrupted an earlyclosed basin of the rift known as the Popotosa Basin.Silicic lava flows and domes, that now form the sky-line west of "M" Mountain, were erupted, episod-ically, onto the playa floor of the Popotosa Basin from12 to 7 m.y. ago. Claystones of the upper PopotosaFormation (Fig. 10) lack sufficient strength to supportthe flanks of the uplifted lava flows. The SocorroMountains are therefore surrounded by a hummockyapron of Pleistocene landslide blocks, composition-ally equivalent to lava flows found immediately up-slope.

The bold cliffs on the east face of Socorro Peak (be-low the "M") are formed by extremely well indurateddebris-flow deposits of the lower Popotosa Formation

(Figs. 10, 11). These coarse matrix-supported clastioccur as thick wedges in narrow strike valleys (3 mwide) adjacent to low-angle early rift faults. A widspread angular unconformity at the base of the Ppotosa (20-30°) and abrupt thickness variationsunderlying ash-flow tuff sheets indicate that dominstyle crustal extension began along the rift axis abo29 m.y. ago.

Thermal springs flowing from the east flank of tSocorro Mountains lie at the intersection of the rangbounding fault zone and the Socorro transverse shezone—a broad domain boundary separating westertilted fault blocks on the north from easterly tiltfault blocks on the south (Fig. 9).

The relatively young Socorro Mountain block trasects the northeastern topographic wall and structumargin of the 32-m.y.-old Socorro cauldron (Fig. 9)

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5

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hee-arly

ed

n-ral.

The uplift thus provides a cross-section-like view ofthe cauldron margin. Pennsylvanian limestones (Ma-dera Formation) in the middle slope of Socorro Peakdefine the structurally high rim of the cauldron; anda large rhyolite lava dome in the caldera moat (northof Blue Canyon) is considered to mark a point on thering-fracture zone. Moat deposits, collectively as-signed to the Luis Lopez Formation, thin abruptly byat least 700 ft, northward across the buried rim of theSocorro cauldron.

The middle Tertiary caldera complex southwest ofSocorro and the area of strong domino-style extensionalong the axis of the rift are superimposed on a late

Laramide (Eocene) transpressional welt locally boundby right-lateral wrench faults (Fig. 9). The Socorroregion can be considered a relatively soft (warm) zonein the continental lithosphere that has been periodi-cally squeezed, transposed, intruded, and stretchedbetween two relatively rigid (cold) microplates, rep-resented by the Colorado Plateau and the Great Plainsprovinces (Fig. 9). More details on the geology andtectonic setting of this area are by Chapin et al. (1978b),Chamberlin (1980, 1981, 1983), and Chamberlin andOsburn (1986).

16

19

TotalMilage

0.0 Drive west on Canyon Road at intersectionwith Campus Drive. Macey Center on rightand Petroleum Recovery Research Center (KellyBuilding) on left. Drive past green oasis of theNew Mexico Tech golf course. As much as1,000 ft of water-saturated sands deposited bythe ancestral Rio Grande underlie much of theSocorro Basin. Shallow wells in this unit canproduce 1,000 gpm, enough for golfers,farmers, and other Socorroans whoappreciate greenery. Machette (1978) namedthese fluvial sands and intertonguingpiedmont-slope deposits (shed from modernranges) the Sierra La- drones Formation(Fig. 10; Table 2). 0.1

0.1 Slow, duck crossing. 0.30.4 Tech Physical Plant on right. 0.20.6 Security check point just west of drainage bot-

tom. Passage into this explosives-testing arearequires being with a leader familiar with safetyprocedures and a visitor's pass from TERA(Terminal Effects Research and Analysis group).This drainage is part of the Socorro flood-con-trol ditch, which diverts runoff from the So-corro Mountains northward around the city.0.4

1.0 "M" Mountain and Socorro Peak (with radiotowers) on crest of range at 1:30 (Fig. 11). Blue-green propylitized ash-beds near foot of rangeat 12:00 give Blue Canyon its name. Small cutat 12:15, in the same unit of altered pyroclas-tics, was a clay pit of the Socorro Fire ClayWorks at the turn of the century (1880-1920).Cottonwood trees and water-storage tank at11:00 to 11:15 are natural and manmade in-dications of thermal springs (90°F) that pro-vide a large part of Socorro's water supply.The springs are located where the range-bounding fault cuts moat deposits of the So-corro cauldron and intersects a transverse shearzone of the Rio Grande rift. The transverseshear zone represents reactivation of an an-cient crustal flaw, the Morenci lineament ofChapin et al. (1978b), within the strongly ex-tended axial zone of the rift. 0.9

1.9 Pass under telephone wires. Approachingmountain front. 0.1

2.0 STOP 1-1. Turn right onto dirt road leadingto TERA storage area. Park and walk upslopeabout 200 yds to old clay pit. Clay (see pp. 48-49) was mined from this pit during the late1800's and early 1900's to produce fire bricksat the Socorro Fire Clay Works. Talmage andWootton (1937, p. 69) described clays from thispit as "kaolinitic material . . . derived from arhyolite flow"; and also stated that "Bricks madefrom it are buff-colored and very hard." Recentanalyses by J. L. Post have shown that thisaltered rhyolite contains abundant 1M illite andabout 8% K20. The best illite material is foundin the wash to the south of the pit. Concen-trations of 6-11% K20 are widespread in Oli-gocene volcanic rocks to the north and west

of Socorro. This large region of potassium me-tasomatism has been interpreted as both a fos-sil geothermal system (D'Andrea-Dinkelmanet al., 1983) and alternatively as diagenetic al-teration by alkaline waters descending into thevolcanic section from playa deposits in the early-rift Popotosa Basin (Chapin and Lindley, 1986).

Near the entrance to the pit, weathered sur-faces reveal blocky fragments of altered pum-ice that show flattened and elongated vesiclestypical of a viscous foam. In unweathered pitwalls this altered pumice breccia looks rela-tively massive; it is broken only by joint-likefracture sets and discontinuous silica veinlets.Only the weathered pumice blocks and sparseandesitic lithic fragments in the pit walls attestto its pyroclastic origin.Retrace route to campus. 2.0

4.0 At junction of Canyon Road and Campus Driveturn right onto Campus. Pass Kelly Building(Petroleum Recovery Research Center) on rightand New Mexico Bureau of Mines and MineralResources on left. At junction of Campus andNeel (2-way stop), bear right and follow roadto 4-way stop. South Hall Dormitory onleft. 0.5

4.5 Stop sign. Junction of Leroy Place and NeelSt. Continue straight. 0.5

5.0 Stop sign. Junction of Neel St., Fisher Ave.,Grant Ave., and Blue Canyon Rd. Continuestraight onto Grant Ave. 0.2

5.2 Stop sign. Junction of Grant Ave. and US-60.Bear right onto US-60. 0.2

5.4 Junction of US-60 and Spring St. Continuestraight. 0.4

5.8 Railroad crossing, Grefco spur of the AT&SF.Ascend hill onto remnant of mid-Pleistocenefan surface. Stockpiles of manganese concen-trates on the right. 0.4

6.2 Socorro High School on left. 0.46.6 Socorro General Hospital on left. 0.97.5 Entrance on right to Grefco perlite operation.

Commercial perlite is hydrated volcanic glass, usuallyof rhyolitic composition, which can be expanded whenheated, producing a lightweight, nearly inert product.Perlite is used as a lightweight aggregate inconstruction products (wallboard) and as filter aids.New Mexico is the leading producer of perlite in theU.S. The Grefco perlite deposit was the principle do-mestic source of perlite during the infant years of theindustry (Weber and Austin, 1982). The Socorro per-lite deposit is the youngest of a series of siliceous lavadomes (the Socorro Peak Rhyolite) guided to the sur-face by the deep plumbing of the Morenci lineament(transverse shear zone) and north-trending faults ofthe rift. This high-silica (78% SiO2) rhyolite dome isabout 7.4 m.y. old, as determined by K-Ar dating ona whole-rock sample (Osbum and Chapin, 1983a). 0.1

7.6 Bridge across concrete ditch that diverts waterfrom Socorro Canyon southward into Arroyode la Matanza; milepost 136. Light-coloredsands of the ancestral Rio Grande exposed ateastern base of ridge. These beds form the

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oldest part of the Sierra Ladrones Formationfluvial facies and intertongue westward withpiedmont-slope alluvium. Pale-red, ledge-forming outcrops of fanglomerate are pied-mont facies of Sierra Ladrones Formation shedfrom the eastern Magdalena Range. This Plio-Pleistocene basin-fill unit is the youngest for-mation of the Santa Fe Group in the Socorro-Albuquerque Basin area (Machette, 1978). 0.3

7.9 Milepost 136. Stockpiles of manganese con-centrates on left. Spur at 3:00 of lower Plioceneolivine basalt; flat-topped basalt overlies SierraLadrones Formation and is distinctly offset byrange-bounding fault zone. 0.4

8.3 Piedmont fault scarp at apex of Pleistocenealluvial fan at mouth of Socorro Canyon. Re-current movement on this range-bounding faultoffsets the late Pleistocene terrace (fore-ground) about 10 ft, middle Pleistocene gravels(9:00) about 100 ft, and the Pliocene basalt flow(3:00) by at least 200 ft. 0.4

8.7 Foundations of old Great Lakes Carbon perlitemill on Pleistocene arroyo terrace to the right.Waste dumps of perlite fines (white) at 3:00.1.1

9.8 Milepost 134; bend in road. At 1:30, hum-mocky landslide blocks of basalt are derivedfrom Black Mountain (mesa on skyline). Un-usually large exposure of red Popotosa clay-stones in north wall of Socorro Canyon at 2:00.Incompetent Popotosa claystones underlie allof the landslide terrane below Black Mountain;this is the same basalt flow that rests on theancestral Rio Grande deposits at the mountainfront. See pp. 49-51 for description of Popo-tosa clay mineralogy. 1.2

1.0 Crossing east boundary fault of ChupaderaRange. Roadcut in deposits of rhyolitic tufffaulted against underlying porphyritic andesitelavas, all part of the Luis Lopez Formation(Oligocene). The formation is the collectivename for the heterogeneous moat fill of theSocorro cauldron. The white rhyolitic tuff hasbeen zeolitically altered (clinoptilolite). 0.4

1.4 Roadcut on left of variegated red and greengypsiferous mudstone and clay and inter-bedded thin basaltic flow or sill(?). 0.4

1.8 Milepost 132. Crossing fault contact betweenPopotosa Formation on east and volcanic moatdeposits (Luis Lopez Formation) on west. 0.1

1.9 Bridge over Box Canyon; milepost 131. Enteringlarge roadcut in Luis Lopez Formation dikes andtuffs, which are overlain by red debris- flowdeposits and fanglomerates of lower PopotosaFormation (Fig. 12). 0.4

12.3 STOP 1-2. Caution! High-speed traffic trav-eling downhill. Clay pit on left (Fig. 13). Turnleft into pit and park. Variegated red, green,and gray beds are in upper Popotosa Forma-tion. The contact between the upper and lowermembers of the Popotosa Formation is con-cealed in the valley to the east. Talmage andWootton (1937) reported that experimentalbricks, made from red clays scattered around

the Socorro Mountains (Popotosa claystones),are hard and chocolate brown. Roadcuts alongUS-60 provide some of the best exposures ofthese red gypsiferous claystones, which areotherwise exposed mostly in deep gullies re-cently cut into the landslide terranes. Samplesfrom the US-60 clay pit have been identifiedas a diverse mixture of dominantly illite andmixed-layer illite smectite, with minor chloriteand sodium smectite (see pp. 46-54). This di-versity probably reflects the detrital origin ofthese clays derived from a large watersheddraining the southeast margin of the ColoradoPlateau and the Magdalena-Bear Mountainsuplift (Fig. 9).Return to US -60, turn right. 0.1

12.4 Turn right onto dirt road. Road is on lowermember of Popotosa Formation. 0.2

12.6 Cattleguard. Andesitic lava forming ridge onleft . 0.2

21

12.8 Discontinuous playa beds of Popotosa in road-cuts on right. 0.1

12.9 Road junction. Turn left into arroyo leadinginto Box Canyon to the north. 0.1

13.0 Optional stop at arroyo. Park on northeast sideof arroyo and walk down arroyo to Bear (Box)Canyon to examine the breached margin of avolcanic vent in the Luis Lopez Formation,exposed in west (left) wall of canyon (Fig. 14).White beds below cliff are tuffs, mudflows,and sandstone; purple andesitic cinders formwall of vent.Return to vehicles. Ascend hill. 0.8

13.8 Pit on left exposes minor manganese miner-alization. 0.1

13.9 Pit on left . 0.114.0 Road junction. Take right fork uphill. South

Canyon Tuff forms top of hill at 9:00. Mosthills from 11:00-12:00 in middle skyline are"sea" of intracaldera Hells Mesa Tuff on re-surgent dome of Socorro cauldron. 0.3

14.3 Rhyolite intrusion forms south wall of canyonat 10:00-11:00. Notch of Black Canyon at 9:00formed by thick andesite lava flow stronglytilted to east. The Gloryana mine is on top ofthe hill at 3:00. 0.1

14.4 STOP 1-3. Turn around and park. Dumps ofGloryana mine are visible on top of the hill tothe west. Mineralization at the Gloryana is inthe South Canyon Tuff. Below, to the east, arepits and dumps of the Grand Canyon minewhere manganese mineralization is in basalticandesite lavas. To the south, cuts of the Towermine are in the Lemitar Tuff. "Rats hair" psi-lomelane [(Ba,K,Mn,Pb,Co)Mn,0,„•H,0], afelty manganese mineral, occurs along frac-tures and can occasionally be found by break-ing open large boulders. Other manganeseminerals include pyrolusite (Mn02), crypto-melane (KMn R0,), hollandite (BaMn 80,,),among other manganese oxides. Black andwhite calcite and rhodochrosite are also found.For more information see pp. 68-73.

The Gloryana mine lies on the eastern edge of the28.8 m.y. old Sawmill Canyon cauldron, where thecauldron cuts across the resurgent core of the Socorrocauldron (Fig. 9). Jasperoidal silica veinlets and younger

(crosscutting) manganese-calcite veinlets in theGloryana pit are hosted by the 27.4-m.y.-old SouthCanyon Tuff. Conformable to unconformable rela-tionships below the South Canyon Tuff locally definethe older Sawmill Canyon caldera margin. In the LuisLopez mining district, jasperoidal silica is commonlyassociated with Oligocene caldera structures and earlyrift faults of late Oligocene to early Miocene age. Incomparison, manganese and manganiferous calcitemineralization is commonly associated with late-stagerift structures and locally cuts late Miocene rhyolitelavas. These relationships suggest that the cross-cutting veinlets in the Gloryana pit represent twolong-lived hydrothermal systems—the older one ac-tive from about 32 to 20 m.y. ago and the youngerone active from about 12 to 7 m.y. ago.

"Rats hair" psilomelane may be found in pocketsalong manganese veinlets that are not associated withcalcite. Good luck! 9.0

23.4 Retrace route back to Socorro.

22Trip 2a:

Socorro Canyon area and Sedillo Hill

Roadlog from Socorro to Sedillo Hill and to Escondida

by Richard M. Chamberlin, Virginia T. McLemore, Mark R. Bowie, and John W. HawleyNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801

Tuesday, 20 October 1987

Assembly point:

Departure time:Distance:Stops:

Macey Center, New Mexico Techcampus8:00 a.m.26.2 mi1

Summary

The first part of this field trip will be to ascendSedillo Hill into the La Jencia Basin, west of Socorrofor an overview of the regional geology. We will ex-amine a red argillic soil profile developed on alluvial-fan deposits of the Sierra Ladrones Formation. Thesoils are developed in a stable zone on the axis of thetilted Socorro—La Jencia block. The trip offers an ex-cellent view of the Socorro transverse shear zone andmorphology of the Rio Grande rift. An optional stopcan be made to examine the Socorro Canyon fault,which offsets arroyo terrace gravels of middle and latePleistocene age. The roadlog ends at Escondida, northof Socorro; Trip 2b begins there.

TotalMileage

0.0 Junction of US-60 and Spring St. Continuestraight on US -60. 0.4

0.4 Railroad crossing, Grefco spur of the AT&SF.Ascend hill onto remnant of mid-Pleistocenefan surface. Stockpiles of manganese concen-trates on the right. 0.4

0.8 Socorro High School on left. 0.41.2 Socorro General Hospital on left. 0.92.1 Entrance on right to Grefco perlite operation.

Commercial perlite is hydrated volcanic glass, usu-ally of rhyolitic composition, which can be expandedwhen heated, producing a lightweight, nearly inertproduct. Perlite is used as a lightweight aggregate inconstruction products (wallboard) and as filter aids.New Mexico is the leading producer of perlite in theU.S. The Grefco perlite deposit was the principle do-mestic source of perlite during the infant years of theindustry (Weber and Austin, 1982). The Socorro per-lite deposit is the youngest of a series of siliceous lavadomes (the Socorro Peak Rhyolite) guided to the sur-face by the deep plumbing of the Morenci lineament(transverse shear zone) and north-trending faults ofthe rift. This high-silica (78% Si02) rhyolite dome isabout 7.4 m.y. old, as determined by K—Ar dating ona whole-rock sample (Osburn and Chapin, 1983a). 0.1

2.2 Bridge across concrete ditch that diverts waterfrom Socorro Canyon southward into Arroyo

de la Matanza; milepost 136. Light-coloredsands of the ancestral Rio Grande exposed ateastern base of ridge. These beds form theoldest part of the Sierra Ladrones Formationfluvial facies and intertongue westward withpiedmont-slope alluvium. Pale-red, ledge-forming outcrops of fanglomerate are pied-mont facies of Sierra Ladrones Formation shedfrom the eastern Magdalena Range. This Plio-Pleistocene basin-fill unit is the youngest for-mation of the Santa Fe Group in the Socorro-Albuquerque Basin area (Machette, 1978,1982). 0.3

2.5 Milepost 136. Stockpiles of manganese con-centrates on left. Spur at 3:00 of lower Plioceneolivine basalt; flat-topped basalt overlies SierraLadrones Formation and is distinctly offset byrange-bounding fault zone. 0.4

2.9 Optional stop. Piedmont fault scarp at apexof Pleistocene alluvial fan at mouth of SocorroCanyon. Recurrent movement on this range-bounding fault offsets the Pleistocene terrace(foreground) about 10 ft, middle Pleistocenegravels (9:00) about 100 ft, and the Pliocenebasalt flow (3:00) by at least 200 ft. 0.4

3.3 Foundations of old Great Lakes Carbon perlitemill on Pleistocene arroyo terrace to the right.Waste dumps of perlite fines (white) at 3:00.1.1

4.4 Milepost 134; bend in road. At 1:30, hum-

it

nrse

spr

ootde

mocky landslide blocks of basalt are derivedfrom Black Mountain (mesa on skyline). Un-usually large exposure of red Popotosa clay-stones in north wall of Socorro Canyon at 2:00.Incompetent Popotosa claystones underlie allof the landslide terrane below Black Mountain;this is the same basalt flow that rests on theancestral Rio Grande deposits at the mountainfront. See pp. 49-51 for description of Popo-tosa clay mineralogy. 1.2

5.6 Crossing east boundary fault of ChupaderaRange. Roadcut in deposits of rhyolitic tufffaulted against underlying porphyritic andes-ite lavas, all part of the Luis Lopez Formation(Oligocene). The formation is the collectivename for the heterogeneous moat fill of theSocorro cauldron. The white rhyolitic tuff hasbeen zeolitically altered (clinoptilolite). 0.4

6.0 Roadcut on left of variegated red and greengypsiferous mudstone and clay and inter-bedded basalt flow or sill(?). 0.4

6.4 Milepost 132. Crossing fault contact betweenPopotosa Formation on east and volcanic moatdeposits (Luis Lopez Formation) on west. 0.1

6.5 Bridge over Box Canyon; milepost 131. Enter-ing large roadcut in Luis Lopez Formation dikesand tuffs, which are overlain by red debris-flow deposits and fanglomerates of lower Po-potosa Formation (Fig. 12). 0.4

6.9 Clay pit on left. See Trip 1, Stop 1-2 and Fig.13 (p. 20) for description. Roadcuts ahead inPopotosa Formation. 1.0

7.9 Ascending Sedillo Hill. Sierra Ladrones fangravels capping Popotosa playa fades on right.Basalt-capped hills in right foreground. Mag-dalena Mountains form skyline ahead. 1.9

9.8 STOP 2-1. Top of Sedillo Hill. Park in rest areato the right.

This site is at the south end of La JenciaBasin on a high-level remnant of the piedmontplain that extends from the base of the Mag-dalena Mountains. To the northwest of thispoint, the plain is cut by late Quaternary pied-mont fault scarps (Machette, 1986).

Figure 15 shows the location of major points ofnterest and is keyed to the following outline of fea-ures west of the Rio Grande:

1) The peak of the Ladron Mountains on theorthern skyline, elevation 9,176 ft, is on Precambrianocks with Upper Paleozoic rocks forming the westernlopes of the uplift. Use this peak as 12:00 for ori-ntation in locating the features seen from this stop.

2) Red Mountain at 12:15 is a hogback on the westlope of Lemitar range. Basal debris flows of the Po-otosa Formation rest on upper Oligocene volcanicocks and dip about 30° westward into La Jencia Basin.

3) Polvadera Mountain (peak formed by 32-m.y.-ld Hells Mesa Tuff) at 12:30-12:45 is the high pointf the Lemitar Range. Field relationships suggest thathe Lemitar uplift was forming throughout Popotosaeposition (Miocene time), but major topographicxpression of the uplift occurred after 7 m.y. ago.

4) Just to the right of the Lemitar Mountains at

12:45 is Strawberry Peak, an 11.8-m.y.-old rhyodacitedome and remnant flow. The vent is on the southeastside of the peak.

5) At 2:00 rhyolite to rhyodacite flows and domeslead up to Socorro Peak and bury the northern So-corro cauldron margin.

6) Flat-topped rhyodacite lava flow, just left of 3:00,occurs at the same elevation as Black Mesa, which ledto earlier interpretations that it was a dome truncatedby a Pliocene erosion surface. Vertical columnar jointsperpendicular to flat cooling surface and an equiva-lent flat-topped flow overlapped by 11-m.y.-old rhy-olite (on Socorro Peak) refute the earlier interpretations.

7) Note west dips in 4-m.y.-old basalt of SedilloHill at 1:30 in foreground. This flow remnant is northof the transverse shear zone and is being rotated west-ward with the Socorro Peak block.

8) Basalt on Black Mesa, immediately right of 3:00and lying on the shear zone, is nearly horizontal.

9) Resurgent dome of Socorro cauldron at the northend of the Chupadera Mountains at 4:00-5:00.

10) Basalt of similar age and position to the SedilloHill unit caps high mesas at 5:30 on west flank ofChupadera Mountains.

11) From 6:00-8:30 a field of east-tilted blocks ofupper Miocene rhyolite lavas equivalent to those onSocorro Peak forms the eastern foothills of the Mag-dalena Range.

12) Timber Peak—South Baldy—South Canyon areaof the Magdalena Mountains at 8:30-9:00 is west ofSocorro cauldron margin and forms the north marginof the Sawmill Canyon cauldron.

24

13) North Baldy area of Magdalena Mountains andnorthwest margin of Socorro cauldron is at 9:30-10:00on the skyline beyond the mouth of Water Canyon.The light-colored rocks just south of North Baldy arehydrothermally altered Hells Mesa Tuff abutting againstthe topographic wall of the cauldron. Mudflow de-posits of andesitic debris are interbedded in the HellsMesa Tuff at this locality.

14) Precambrian rocks are exposed along the north-eastern front of the Magdalena Range from 10:00-10:30.

15) Bear Mountains at 10:45-11:00 form the north-west border of La Jencia Basin. Hells Mesa overlook-ing the Rio Salado valley forms the prominent peakat the north end of the Bear Range.

16) High mesas (including Sierra Lucero) of thesoutheastern Colorado Plateau margin are on the dis-tant skyline at 11:00-11:30, northwest of Ladron Peak.

17) A COCORP (Consortium for Continental Re-flection Profiling) seismic profile from east of Mag-dalena to Sedillo Hill closely parallels US-60 in thebasin northwest of this stop. The profile indicates astructurally complex sub-fill basin floor.

18) A shallow dike-like magma body appears tounderlie this tour stop at a depth of about 3 mi (San-ford, 1978, 1983).

Looking east of the Rio Grande through the gapbetween Socorro Peak and Black Mesa, Abo Pass isat 2:30 on the far skyline between the Manzano Range(north) and Los Pinos Mountains (south). South ofBlack Mesa, Chupadera Mesa is on the distant skylineat 3:30. Slopes east of these uplifts (Sacramento sec-tion of the Basin and Range physiographic province)are transitional to the Great Plains province—PecosValley section. The lower chain of mesas, cuestas, andhills from 2:30-4:00 (just east of the river valley) com-poses the Loma de las Callas uplift (Trip 2b). Thesehighlands form the eastern border zone of the rift.They are composed mostly of complexly faulted Penn-sylvanian and Permian rocks, capped by San Andresand Yeso Formations. The Mesozoic—lower Tertiarysection and at least 2,000 ft of Oligocene volcanic rockshave been stripped by erosion associated with upliftof the blocks. Thick sections of Mesozoic and lowerTertiary sedimentary rocks are preserved only indownfaulted blocks in the Carthage area (4:00) andon the eastern flank of the Joyita Hills (2:30). The eastside of the Rio Grande rift is structurally higher thanthe west side through most of its length.

High ranges visible to the southeast beyond thenorthern end of Jornada del Muerto Basin includeSierra Oscura at 3:45-4:15 beyond Cerro Colorado andthe northern San Andres Mountains at approximately5:00. If you had been standing here at 5:29 a.m. onJuly 16, 1945, you would have seen the blinding flashof light and the mushroom cloud from the first atomicbomb detonated at Trinity site at the base of the Os-cura Mountains.

Examine soil developed in Sierra Ladronesfan alluvium (see pp. 55-67).Return to Socorro by retracing roadlog. Anexcellent view to the east of Rio Grande val-ley . 10.2

20.0 Junction of Spring St. and US-60. Turn right

onto Spring St. 0.620.6 Turn right at traffic light onto California St. 0.821.4 Enter 1-25 ramp. (Trip 3 roadlog south to San

Antonio begins here.) Stay in left lane and get on1-25 north. Continue straight on 1-25 on lowfan-terrace surface bordering the RioGrande floodplain. 3.2

24.6 North exit 150 to Socorro. Continue north on1-25 across Rio Grande floodplain. Socorro Peakis at 9:00; Strawberry Peak is at 10:00; Polva-dera Peak (highest point in Lemitar Moun-tains) is at 11:00; Ladron Mountains are at 12:00;Loma de las Callas are at 3:00 across Rio Grande.The geology of Socorro Peak is discussed inTrip 1 (pp. 15-21).

Tertiary volcanic strata in the LemitarMountains generally dip 45-70° to the west.This strong westerly rotation of Tertiary andunderlying Paleozoic strata (paraconformable)are the most obvious indication of 100-200%domino-style extension since 29 m.y. ago(Chamberlin, 1983).

The east side of the Lemitar Mountains (Pol-vadera Peak) consists of Precambrian granites,schists, pegmatites, diabase dikes, and Or-dovician carbonatite dikes (McLemore, 1987).Near the south end of the Lemitar Mountains,80 ft of Mississippian and 1,000 ft of Penn-sylvanian rocks overlie the Precambrian. Shalefrom the Pennsylvanian Sandia Formation (600ft thick) was mined in the late 1800's for brickmanufacture at the Socorro Fire Clay Works.Just below Polvadera Peak, about 400 ft of grayPennsylvanian limestones (Madera Forma-tion) and 150 ft of Sandia Formation uncon-formably overlie reddish-orange Precambriangranite. A Late Mississippian to Early Penn-sylvanian thrust fault caused this change instratigraphic relationships (Chamberlin, 1983,fig. 1). A typical 4,000-ft-thick outflow volcanicsection (Fig. 10) unconformably overlies thePennsylvanian rocks. Near the north and southends of the Lemitar uplift, strongly tilted fanand playa deposits of the Popotosa Formationare exposed. West of the ridge, topped by Pol-vadera Peak, Precambrian, Pennsylvanian, andTertiary volcanic rocks are repeated by a majorlow-angle normal fault (rotated early rift fault)to form a dual hogback range. Permian bedspredominate in the Loma de las Callas (eastof the river) accompanied by some Precam-brian and Pennsylvanian strata in small faultslices (see Trip 2b). 1.4

26.0 Bridge over Nogal Arroyo and Socorro diver-sion channel. Bluffs across the river are red-dish Sierra Ladrones beds capped with valley-fill alluvium and eolian sand. Excellent viewto the west of the large landslide area on thenorth side of Socorro Peak. Hills ahead arealluvial fill. 0.2

26.2 Take exit 152 at Escondida turnoff. End of Trip2a. Trip 2b roadlog begins here with mileage0.0.

25

Trip 2b:Loma de las Callas area

Roadlog from Escondida to Pueblito, Loma de las Callas,and junction of county road A -129 and US-380

near Carthage(including a stop at Arroyo del Tajo interpretive site)

by John W. Hawley, Virginia T. McLemore, and Mark R. BowieNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801

Tuesday, 20 October 1987

Distance: 36.4 miStops: 2

Summary

Loma de las Callas separates the Socorro Basin ofthe Rio Grande valley from the Jornada del MuertoBasin. We travel from 1-25 at Escondida (which meanshidden in Spanish) and cross the Rio Grande at Pue-blito to view interfingering relationships of piedmontdeposits shed from the east side of the valley withaxial river sands of the ancestral Rio Grande. At STOP2-2 we will examine the Sierra Ladrones gravels andpedogenic calcrete (petrocalcic horizon). At STOP 2-3 (lunch stop) we will examine the Arroyo del Tajointerpretive site, where pictographs, presumably fromthe Piro Pueblo Indians, can be seen on the canyonwalls. The entire route passes through excellent ex-posures of the red, orange, pale-yellow, and gray bedsof the Abo, Yeso, Glorieta, and San Andres Forma-tions, spectacular views reminiscent of scenes on theColorado Plateau. The route ends in the Jornada delMuerto; Trip 2c begins there.

TotalMileage

0.0 Stop sign at intersection of 1-25 exit 152 andNM-408. Turn right on NM-408 and continueeast into village of Escondida. 0.2

0.2 Turn sharp left (north). Route skirts westernedge of Rio Grande floodplain. Holocene fanalluvium of small tributary arroyos overlapsand intertongues with axial-river deposits inthis area. 0.2

0.4 Bluffs and hillslopes to left veneered with val-ley-fill alluvium and colluvium of late Qua-ternary age. These gravelly deposits form adiscontinuous cover on a stepped sequence ofvalley-border erosion surfaces cut on Santa FeGroup—Sierra Ladrones Formation basin fill.The Sierra Ladrones is of Plio-Pleistocene age

and comprises two major facies: 1) piedmontalluvium, predominantly derived from bed-rock and older basin fill exposed in flankingmountain uplifts; and 2) a basin-floor fluvialfacies, here primarily deposits of the ancestralRio Grande. The river-channel and floodplaindeposits, mainly sand and rounded pebblegravel with local silt-clay beds, intertongue withgravelly alluvial-fan deposits of distal pied-mont facies. The middle to upper Quaternaryvalley fill in this area also exhibits complexintertonguing of tributary (arroyo) alluviumand axial-river deposits. Note irrigation canal

2

6

and farmland on right. Primary crops grownin the Socorro area are corn and alfalfa; othercrops include permanent pasture, chili, mel-ons, onions, blue corn, and a limited amountof grapes, wheat, barley, and soybeans. 0.4

0.8 Sierra Ladrones fluvial sands and gravels withripup clasts of fine-grained sediments exposedin cuts to left. 0.7

1.5 Pueblito Point. Turn right, cross irrigation canaland AT&SF tracks, and continue east acrossRio Grande floodplain. Recent test drilling atSan Acacia (10 mi to north) and water-well logsin this area (Clark and Summers, 1971) indi-cate that upper Quaternary fill of the innerriver valley ranges from about 70 to 110 ft thick.Below a thin surface layer of clay and silt, thevalley-fill section is mainly sand with clay-siltand pebble-gravel lenses. Pebble-to-cobblegravel is common in lower part of the section.These river-channel deposits are unconform-able on upper Santa Fe basin fill in mostplaces. 0.2

1.7 County park at Escondida Lake to left; crossmain river conveyance channel. Two -lanebridge ahead. 0.1

1.8 Crossing Rio Grande. 0.22.0 End of pavement. Note prominent, stepped

sequence of valley-border geomorphic sur-faces rising east of the Rio Grande floodplain.The lowest surface, about 30 ft above the val-ley floor and of late Holocene age, is formedby coalescent arroyo-mouth fans. Throughoutthe Rio Grande valley during much of Holo-cene time, fans of tributary arroyo systemsprograded over marginal floodplain areas.When the laterally shifting river channel im-pinges on these deposits, truncation of distal-fan segments produces low scarps such as theone crossed by the tour route ahead. 0.25

2.25 Top of hill. Pueblito ahead; roadcuts in Hol-ocene alluvial-fan deposits capped with recentcar bodies. Pueblito is a very old communitythat formerly consisted of many houses, smallfarms, and vineyards. The route of the na-tion's first transcontinental highway (ocean-to-ocean highway) was established throughPueblito in 1911 and crossed the Rio Grandenear the present bridge (Henderson, 1956;McKee and Wilson, 1975; Smith et al., 1983).Abandoned barite mill at 11:00 on top of hill.0.05

2.3 Turn right (south) on Bosquecito Road alongeastern edge of Rio Grande floodplain. 0.3

2.6 Bluffs to left capped with upper Pleistocenegravelly alluvium and Holocene eolian sandthat mantle stepped sequence of valley-bordersurfaces cut on fluvial facies of Sierra LadronesFormation. The surface just east of the road,about 90 ft above floodplain, is underlain byintertonguing axial-river deposits and oldertributary-fan gravels. Archeological sites oc-cur on top of many of these hills. 0.7

3.3 Road junction. Turn left through cattleguardand continue east up valley of Arroyo del Co-

yote on graded BLM Quebrados Road. Routefor next 1.8 mi is on Holocene arroyo-terraceand channel deposits, which form youngervalley fill. Fluvial and alluvial-fan facies of oldervalley fill and the Sierra Ladrones Formationare exposed in roadcuts and valley wallsahead. 0.6

3.9 Older valley-fill deposits exposed in high arroyocuts to right appear to be graded to an ances-tral river base level about 90 ft above modernfloodplain. 0.3

4.2 Roadcut to left in older valley-fill alluvium.0.5

4.7 Approximate eastern limit of ancestral RioGrande (fluvial) facies in Sierra Ladrones For-mation. 0.25

4.95 Roadcut and valley-wall exposures of reddish-brown conglomeratic sandstones and mud-stones of Sierra Ladrones piedmont facies aheadon left and right. 0.35

5.3 Crossing Arroyo del Coyote. Sierra Ladronespiedmont facies exposed in valley walls to left.0.2

5.5 Cattleguard. Route ascends ridge. Roadcut inpiedmont facies of Sierra Ladrones Formation.0.7

6.2 Top of hill at road junction. Keep left on mainroad. Cerrillos del Coyote at 12:00 capped bySan Andres Limestone and Glorieta Sand-stone with lower slopes cut in Yeso Formation(Fig. 16). Ridge on skyline at 1:00 is an upliftedfault block that exposes upper arkosic lime-stone member of Madera Formation. Roadcutsahead in uppermost Sierra Ladrones pied-mont facies. 0.1

6.3 High ridge on skyline at 2:30-3:30 consists ofgently folded lower gray limestone member ofMadera Formation; the lower slopes and west-erly exposures are Sandia Formation. Beds oneastern shoulder of ridge are overturned towest and are upper arkosic limestone memberof Madera Formation. 0.1

6.4 Trail to right leads to Bursum "Spring" (Ojode Amado), a favorite swimming hole andpicnic area in wet years. It is not a spring buta plunge pool beneath an overhanging cliffformed by steeply east-dipping, overturnedlimestone beds of Pennsylvanian age. 0.1

6.5 Road junction. Keep left on main road. Road

27

to right leads to Minas del Chupadero copperprospects, a stratabound, sedimentary copperdeposit consisting of malachite, azurite,chalcanthite, and chalcocite in interbeddedcarbonaceous shales and limestones of upperarkosic limestone member of Madera Forma-tion (Jaworski, 1973). 0.6

7.1 Contact of Santa Fe (Sierra Ladrones) fanglom-erate with Abo Formation in valley wall to left.Continue up hill. 0.1

7.2 Top of hill. Cuts ahead in Abo Formation mud-stone and sandstone; clay mineralogy is de-scribed on pp. 50, 52. Peaks of Cerrillos delCoyote (11:00-1:00) capped with San AndresLimestone and Glorieta Sandstone. 0.2

7.4 Road to left and right. Route for next 0.6 miin Abo Formation. 0.6

8.0 Side road on right. Roadcuts to east of junctionare in gypsiferous Torres Member of Yeso For-mation; road has crossed a major north-trend-ing fault. 0.05

8.05 Crossing Yeso-Abo contact ahead. Complexfaulting in this area has formed slivers of sev-eral stratigraphic units. Pennsylvanian lime-stones of upper arkosic member of the MaderaFormation at 1:00-2:00. A major north-north-east-trending fault juxtaposes Pennsylvanianrocks on east against Abo red beds on west.0.35

8.4 The broad slope at 9:30 is broken by four thin,cliff-forming units of the Yeso, Glorieta, andSan Andres Formations, which are not in properstratigraphic order, thus indicating possibleimbricate structure on a low-angle fault. 0.1

8.5 Cross arroyo and major north-northeast-trending fault at mile 8.05. 0.1

8.6 Small gullies to right over next mile are erodedalong minor north-trending faults with a fewtens of feet displacement. The road is entirelyin Pennsylvanian shale of upper arkosic mem-ber of Madera Limestone. 0.4

9.0 Ridge to left is upper arkosic member of Ma-dera Limestone, but is lower in section thanshale on which road is built. Another north-trending fault cuts through saddle ahead andpasses east of steep, west-dipping limestonebeds behind you at 6:00. 0.2

9.2 Cross saddle and fault. Lowest massive lime-stone cliff on right is Council Spring Lime-stone of Thompson (1942), equivalent to partof arkosic limestone member of the MaderaFormation (Wilpolt and Wanek, 1951). TheCouncil Spring Limestone hosts sedimentary-hydrothermal galena-fluorite-barite depositsin the Hansonburg (Bingham) mining districtapproximately 30 mi to the east (Trip 3). 0.05

9.25 Massive west-dipping limestone at 12:00 isnarrow west-tilted fault block of uppermostpart of arkosic limestone member of MaderaFormation with reddish, arkosic conglomer-ates of Bursum Formation to east and lowerpart of arkosic limestone member in valley towest. On skyline is north end of Loma de lasCatias. Note low-angle faulting with SanAndres Limestone resting on tilted GlorietaSandstone and units of the Yeso Formation.

0.359.6 Cross arroyo. Outcrops to right across arroyo

are arkosic conglomerates of Bursum Forma-tion. The fault, which bounds the east side ofthe tilted block discussed at mile 9.2, crossesroad in this vicinity. 0.05

9.65 Cattleguard. 0.059.7 Road junction. Keep right on main road. 0.1

9.8 Blocky outcrops at 2:00 are slivers of BursumFormation along fault that splits and outlinestilted Madera block at mile 9.2. Road is onBursum Formation for next 0.5 mi, then crossescontact with Abo Formation. Beds dip gentlyto east. 0.5

10.3 Arroyo crossing. Drainage through water gapon right superimposed in fault block in Ma-dera Formation. See article on pp. 46-54 fordiscussion of clay mineralogy. 0.2

10.5 Road is now on lower Abo Formation. 0.611.1 Cross northeast-trending fault with lower Abo

beds to west and Bursum arkosic conglom-erates to east. Outcrops on hills to east areupper Abo Formation. Cross arroyo. 0.25

11.35 Cross another arroyo. Good exposures of ar-kosic conglomerates and purple shales of Bur-sum Formation in arroyo bank. Road is againon Bursum Formation. 0.5

11.85 Contact of Bursum Formation and arkosicmember of Madera Formation in gully to rightof road. 0.4

12.25 Mesa on eastern skyline capped by limestonesin lower part of Torres Member of Yeso For-mation. Rounded yellowish-red, cliff-formingsandstone beds are Meseta Blanca Member ofYeso Formation. Road is on Abo Formationand follows a south-trending strike valley,which eroded along beds that are overturnedto east and dip steeply to west. As the roadprogresses south, sandstone and mudstonebeds of Abo Formation in right-hand bar ditchgradually steepen and become vertical. 0.6

12.85 Sandstones and mudstones of Abo Formationin right-hand bar ditch now dip vertically. Ridgeto left is in Yeso Formation. 0.5

13.35 At 12:30, thin-bedded red and gray sandstonesand mudstones of uppermost Abo Formationdip 30°W and are overturned (Fig. 17). Verticalbuff-colored sandstone ridges at 12:00 areMeseta Blanca Member of Yeso Formation.0.3

13.65 Cross north fork of Arroyo del Tajo. 0.113.75 Cross northeast-trending fault with lower

limestone bed of Torres Member of Yeso For-mation faulted against uppermost Abo For-mation; Torres on left and Abo on right. 0.1

13.85 Cross arroyo. Water gap to right exposes largeoverturned (to east) anticline in upper part ofarkosic member of Madera Formation. Mag-dalena Range and South Baldy Peak on skylineto the west. At 1:00, Meseta Blanca Memberof Yeso Formation is overlain by first limestonebed of Torres Member. 0.4

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FIGURE 17-Small syncline on top of knob (Torres Member of YesoFormation) near mile 13.35, looking south. Overturned beds ofAbo Formation to right of knob.

14.25 Cross south fork of Arroyo del Tajo. 0.214.45 Fault in arroyo at 9:00 with gypsum and lime-

stone beds of upper part of Torres Member ofYeso Formation downfaulted against lower-most Torres units. 0.3

14.75 Tightly contoured beds of lowermost lime-stone in Torres Member at 3:00. Beds formingbattlement on skyline are overturned to eastand dip sharply west. 0.2

14.95 Lowermost limestone beds of Torres Memberof Yeso Formation at 1:00 are overturned (al-most recumbent) and dip gently west. 0.1

15.05 Cross arroyo. Ascend steep grade across west-dipping Yeso strata capped with carbonate-ce-mented piedmont gravel of upper Sierra Lad-rones Formation. 0.15

15.2 Road junction. Turn sharp right. Continue weston high piedmont surface described at STOP2-2 (mile 15.65). 0.2

15.4 Cattleguard. Socorro Peak at 2:00; ChupaderaMountains lower ridge at 10:00 to 12:00; sky-line formed by Magdalena Mountains. 0.2

15.6 Gate on right to STOP 2-3 (entry 17.5). Con-tinue ahead to STOP 2-2. 0.05

15.65 STOP 2-2. Turn around and park at road junction.After an introduction to the geologic andgeomorphic setting, walk down road on leftto roadcut exposure of Sierra Ladrones gravelsand pedogenic calcrete (petrocalcic horizons;see pp. 55-67).

Panoramic view (west at 12:00), Socorro cauldron(Trip 1), and geomorphic surfaces-ChupaderaMountains are at 11:30-12:30; marked break at 12:15with flat-topped mesa in background is Nogal Can-yon. South end of San Mateo Range (Vicks Peak) onskyline behind and south of Nogal Canyon. Socorroand Socorro Peak are at 2:30. Topographic margin ofnorth side of Socorro cauldron exposed on SocorroPeak below the "M" (Trip 1); topographic margin ofsouth side of Socorro cauldron marked by highestpoint at south end of Chupadera Mountains (11:00).The distended Socorro cauldron has a north-southdiameter of about 12 mi and an extended east-westdimension of 18-20 mi. A resurgent dome in Socorrocauldron makes up the northern part of Chupadera

Mountains at about 1:00. Low areas between resur-gent dome and north and south topographic marginscompose the moat of Socorro cauldron and are un-derlain by a complex series of rhyolitic domes, flows,local ash-flow tuffs, and various types of breccias andvolcaniclastic rocks, collectively known as Luis LopezFormation. High point of Magdalena Range on sky-line from 12:30-2:00 is within both the Socorro caul-dron and a younger, nested, Sawmill Canyon cauldron.

The stop is on a high-level piedmont surface cappedwith gravelly alluvium and now deeply incised by thevalley of Arroyo de las Canas; note surficial zone ofpedogenic calcrete. The basal contact of the alluvialdeposits on deformed beds of the San Andres andYeso Formations can be seen in upper valley walls tothe south and east. The gravel cap locally includesfan and channel-fill deposits up to 100 ft thick, as wellas thin alluvial veneers on extensive rock pediments.This surface appears to be one of the oldest and high-est members of stepped sequence of surfaces gradedto the ancestral Rio Grande.

Reconnaissance geomorphic investigations in thisarea by NMBMMR staff document the presence of atleast three major valley-border surfaces between thislevel and the Holocene fills of larger arroyo valleys.These geomorphic surfaces of both erosional and con-structional origin have been tentatively correlated withthe Tio Bartolo, Valle de Parida, and Canada Marianastepped sequence of Kirk Bryan (1932) and CharlesDenny (1941). Elevations of projected surface profilesabove the present floodplain approximate the ances-tral river base levels suggested by Denny (1941) andSanford et al. (1972): Tio Bartolo-200-225 ft, Valle deParida-100-180 ft, and Canada Mariana-40-90 ft.The high-level piedmont surface at this stop, infor-mally designated "Las Carias surface" by W. Stoneand L. Fleischhauer, appears to grade to a river-baselevel more than 300 ft above the modern valley floor.However, this surface has been offset (down-to-west)by a rift-boundary fault located about 1.5 mi to thewest. Projected base-level estimates of older membersof the valley-border sequence may be considerably inerror due to faulting and tectonic warping. The grav-elly alluvium with pedogenic calcrete that caps the"Las Carias" surface is included in the youngest pied-mont facies of Sierra Ladrones Formation and is prob-ably of early to middle Pleistocene age (>0.5 m.y.).

Return to vehicles and retrace route to STOP2 -3. 0.05

15.7 Turn left through gate and continue north-west across "Las Carias" surface. 0.7

16.4 At 1:00 orange-brown hills of Precambrian Tajogranite are overlain by dark beds of SandiaFormation (Fig. 18). Route descends from "LasCarias" surface to lower valley-border erosion-surface complex (possible fault offset). 0.8

17.2 Steep downgrade. Crossing major boundaryfault zone of Rio Grande rift. Hillslopes to westare cut of upper Santa Fe Group basin fill (SierraLadrones Formation). Veneers of gravelly al-luvium and colluvium cap mid-to-late Qua-

29

ternary valley-border erosion surfaces. 0.317.5 STOP 2-3 at windmill—lunch. Discussion of

panoramic view and examination of Arroyodel Tajo interpretive site.

Follow the trail downhill and across thearroyo for about 0.2 mi to the Arroyo del Tajointerpretive site, which consists of a group ofpictographs—pictures painted on rock by Na-tive Americans, probably the Piro Pueblo In-dians.

Panoramic view: Socorro Peak ("M" Mountain) towest (12:00); Magdalena Mountains on southwesternskyline. To the east at 5:00 are orange-brown hills ofthe Precambrian Tajo granite (Fig. 19). During the late1970's, the granite and adjacent rock was explored foruranium (McLemore, 1983). Uranium mineralizationwith fluorite occurs along fractures. Barite and fluo-rite veins are common along the western fault contactwith the Santa Fe Group; some barite and fluoritewere mined.

Fire clay was produced from several stratigraphichorizons in the Sandia Formation (Pennsylvanian) atthe Houlett deposit (2.5 mi to the north) for brickmanufacture at the Socorro Fire Clay Works duringthe late 1800's (Talmage and Wootton, 1937). Threecarloads of clay were shipped to the International BrickCo. in El Paso, Texas, in 1910 and three carloads wereshipped to the Denver Fire Clay Co. in Denver, Colo-rado, between 1910 and 1920 (J. Van Sandt, writtencomm. 1964). The clay mineralogy of this site is de-scribed on pp. 50, 52-53.

Arroyo del Tajo interpretive site (Fig. 20) was dis-covered by Robert Weber, NMBMMR, and has beenexamined by the National Park Service for possiblepreservation. The National Park Service concludedthat any high technological preservation methodswould accelerate deterioration. Please use caution inexamining this site and do not touch the paintingsbecause they are extremely fragile. Despite adminis-tration by the U.S. Bureau of Land Management asan Area of Critical Environmental Concern (ACEC)and a special management area, some vandalism ofthe site has occurred.

Although interpretation of this site is controversial,it is almost certainly of Piro origin. The Piro Pueblo

30

Indians were an agriculture-based people and had 12-44 settlements along the Rio Grande during the late1500's. The closest known pueblos to this site are nearLuis Lopez and in Socorro, both on the west side ofthe Rio Grande (Cordell and Earls, 1983). The pop-ulation of the Piro Indians declined during the 1640'sand 1650's due to an influx of European diseases,including smallpox, and to raids and massacres byApache Indians. Many Piros also died of starvationand famine resulting from severe draughts during the1660's. The Piros did not participate in the PuebloRevolt of 1680; most left for the south with the Span-iards.

The pictographs (Fig. 21) are on the north side ofArroyo del Tajo in a natural amphitheater with ex-cellent acoustics that may have been used as a teach-

FIGURE 21—Pictographs at the Arroyo del Tajo interpretive site.

ing area. Interpretations of the paintings suggest that

they are of post-Spanish contact (A.D. 1540-1680), asevidenced by pictures of a goat and horse.

Early Piro history is depicted in these scenes ac-cording to various interpretations. Some figures arepainted white, symbolizing light-skinned Indians,whereas others are red, symbolizing dark-skinned In-dians. There was a war between the two peoples asshown by swords and other instruments of warfare.Legend suggests the dark-skinned Indians, ancestorsof modern Indians, overcame the light-skinned In-dians. Other figures represent medicine men and gods.A painted face encircled with dots may represent theGod of Nature.

Retrace roadlog to gate and Quebrados Roadjunction at mile 15.2. 1.8

19.3 Gate. Turn left. 0.219.5 Cattleguard. 0.219.7 Junction of Quebrados Road. Turn right. Route

continues east across "Las Catias" surface rem-nant, then drops abruptly into upper valley(cationcito) of Arroyo de las Carias. 0.25

19.95 Road bends right and begins descent into Ojode las Carias, a spring high in carbonate andsulfate, which feeds Arroyo de las Catias inthe reach visible on the right. Narrow zone ofstrong deformation noted at mile 14.75 con-tinues beneath Sierra Ladrones Formation onwhich we are driving and crosses Arroyo delas Catias below the recent sand dunes andpiedmont gravels visible on south side ofarroyo. Note well-developed pedogenic cal-crete (Bkm horizon) in upper part of piedmontgravel deposit, which is about 50 ft thick here.The base of the Sierra Ladrones Formation isa nonpedogenic conglomeratic calcrete. 0.1

20.05 Caution: steep grade. On skyline, the Glori-eta—San Andres contact is visible at 12:00 atcolor break; dark brownish-gray limestone isabove and buff to gray-white sandstone is be-low. Pinkish sandstone and mudstone ex-posed here and there beneath buff sand is theJoyita Member of Yeso Formation and is par-tially interbedded with it. 0.05

20.1 Roadcut in basal Sierra Ladrones Formationconglomerate that is angularly unconformableon Yeso Formation. 0.05

20.15 Roadcuts on left after bend in road exposeTorres Member of Yeso Formation. See pp. 50,52 for description of clay mineralogy. Notelaminated gypsum beds in Torres Mem-ber. 0.2

20.35 Cross Arroyo de las Caftas. As road ascendssouth bank note successive limestone units inTorres Member. These beds cannot be used asmarkers because they are lithologically verysimilar and contain little or no fossils. Gravellyalluvium caps terraces above inner arroyo val-ley at 12:00-3:00. 0.75

21.1 Cattleguard. Route ahead ascends east-dip-ping Yeso section to another remnant of the"Las Callas" surface. 0.3

21.4 Cuts in veneer of Sierra Ladrones gravel, with

31

pedogenic calcrete, at edge of "Las Canas" sur-face remnant. Note extensive cover of Holo-cene eolian sand. Route for next 5 mi crossesdissected piedmont erosion surface (rock ped-iment) cut across deformed beds of upper Pa-leozoic section. 0.25

21.65 Limestone beds with interbedded gypsum,siltstone, and mudstone of Torres Member of

Yeso Formation on either side of road. 0.522.15 Road turns to follow strike of Yeso beds. 0.5522.7 Cross arroyo. 0.1522.85 Slow: steep grade ahead. Driving on small

gravel-capped remnant of "Las Carias" surfacewith well-developed pedogenic calcrete. Roadcontinues to follow strike of Yeso beds. Notelocal gypsum outcrops. 0.3

23.15 Cross arroyo. East-dipping limestones of TorresMember of Yeso Formation on right. 0.2

23.35 Red sandstones and mudstones from 9:00-12:00are a fault block of Abo Formation. Contortedbeds of Torres Member of Yeso Formation at3:00-4:00 dip steeply west. 0.3

23.65 Entering San Antonio 71/2 min quadrangle.0.4

24.05 Good exposure of limestones in Torres Mem-ber of Yeso in canyon to right. 0.3

24.35 Another remnant of "Las Carias" surface withgravelly pedogenic calcrete and sample site isdescribed on p. 63, Table 6. Good exposuresof Cafias and Joyita Members of Yeso Forma-tion overlain by Glorieta Sandstone and SanAndres Limestone on north end of mesa at9:30-11:30. 0.1

24.45 Westward dip slope of San Andres Mountainsin distance at 11:00, Little San Pasquel Moun-tain at 11:30, eastward dip slope of Fra Cris-tobal Mountains at 12:00. 0.3

24.75 Slow. Downgrade. 0.325.05 Cross arroyo. A spectacular buckle-type fold

is exposed downstream along the arroyo walls(Smith et al., 1983, stop 5). 0.05

25.1 Catt leguard. 0.625.7 Road crosses northwest-trending fault that

juxtaposes lower Abo Formation on southwestagainst middle part of Torres Member of YesoFormation on northeast. 0.5

26.2 Road on right. Hills of tilted Madera lime-stones on right. 0.8

27.0 Cattleguard. Route ahead curves to eastthrough water gap (north fork of San PedroArroyo) and across southern part of Loma delas Carias uplift. Road on Abo Formation withexposures of channel sandstone to eithers ide. 0.15

27.15 Cross arroyo. Stratigraphic section from 11:00-12:00 is Joyita Member of Yeso Formation atbase of slope, overlain by Glorieta Sandstone(light colored in lower half, reddish near top),which, in turn, is overlain by San AndresLimestone on upper slopes (Fig. 22). 0.2

27.35 Outcrops along arroyo to left contain grada-tional contact of Abo Formation and MesetaBlanca Member of Yeso Formation in zone of

FIGURE 22-Southern part of Loma de las Carias at mile 27.15.

green mudstone and siltstone. Contact crossesroad near this point. 0.4

27.75 Entering Canon Agua Bueno 772 min quad-rangle. Fault block of Abo at 10:00. 0.2

27.95 Cross arroyo. Abo Formation in arroyo bot-toms. 0.1

28.05 Cross fault described at mile 25.7. Abo For-mation is to southwest, Torres Member of YesoFormation to northeast. 0.05

28.1 Arroyo crossing. Entering zone of complexstructure including low-angle faulting in slopefrom 2:00-2:30. 0.5

28.6 Red beds on steep slope to right are TorresMember of Yeso Formation. Massive outcropnear crest is San Andres Limestone. A low-angle fault separates these units. 0.3

28.9 Entering flat-floored valley. Rocks from 7:30-10:30 are Glorieta Sandstone and San AndresLimestone in upper plate above low-angle fault(some imbricate faulting in upper plate). Val-ley floor is underlain by red mudstones andsandstones of the Chinle Formation (Triassic)and a small amount of overlying buff to whiteDakota Sandstone (Upper Cretaceous) at 1:00.The Cretaceous rocks are downfaulted againstYeso Formation to south along same north-west-trending fault as miles 25.7 and 28.05.Low-angle faults are also present from 3:00-4:30 beneath San Andres Limestone. (Thisshallow valley in Triassic and Cretaceous rockssurrounded by topographically higher Per-mian rocks suggests that the Permian mightbe thrust again over younger units with thethrust somewhat modified by later fault-ing.) 0.6

29.5 Road bends to left. Good exposures of ChinleFormation red beds in roadcuts and gul-lies. 0.2

29.7 Road tops divide between north fork and AguaBueno forks of San Pedro Arroyo. Jornada delMuerto and distant Oscura Mountains at 12:00-1:00. Note thin cap of gravelly alluvium onhigh pediment surfaces flanking hills to northand south. 0.5

30.2 Unusual buff to yellow-gray sandstone inter-bedded in Chinle Formation on left. Paleo-weathering zone? 1.1

31.3 Cattleguard. Road continues on Chinle For-mation. 0.3

32

31.6 Road junction. Gonzales well and old ranchhouse 0.3 mi via left fork. Possible weatheringprofile on Chinle Formation in roadcut at 6:30.Continue southeast on main road across up-per valley of Canon Agua Bueno arroyo. Ridgesahead and to left capped with mid-Pleistocenealluvial fill of Jornada del Muerto Basin. 0.2

31.8 Cross arroyo. Route ahead on thin upper Qua-ternary valley-fill deposits. 0.1

31.9 Cross arroyo. Approaching Jornada del Muertoclosed basin. 0.4

32.3 Route ascends to Jornada del Muerto Basinsurface. Thick gravelly fill is fan-piedmont fa-cies of Sierra Ladrones Formation (here mostlymiddle Pleistocene) with discontinuous ve-neer of upper Quaternary alluvium and eoliandeposits. 0.1

32.4 Broad plains of northern Jornada del MuertoBasin from 10:00 to 2:00 (elevation 5,400-4,700ft) are about 500 ft above the floor of the RioGrande valley.

The Jornada del Muerto extends southward fromChupadera Mesa to Las Cruces and the Desert Projectarea (Gile et al., 1981). It was named "journey of thedeadman" because hundreds of people perished en-route from Chihuahua to Santa Fe due to lack of waterand attacks by Apache Indians (Pearce, 1965). OscuraMountains are on the skyline at 12:30-1:30, Mocking-bird Gap is at 3:00, northern San Andres Mountainsand Salinas Peak are at 2:00-2:30. The regional dipshifts from eastward in the Oscura Mountains to west-ward in the San Andres Mountains across Mocking-bird Gap. The Bliss Sandstone and the rest of thelower Paleozoic section present in southern NewMexico pinch out at the south end of the OscuraMountains. Layered rocks overlying Precambrian rockson the crest of the Oscura block are Pennsylvanian—

Permian limestones, mostly Missourian, Desmoines-ian, and Virgilian in age. Scars near the lower northend of the Oscura block are mines in the Hansonburgbarite-fluorite-galena district. 0.432.8 Road junction. Continue straight ahead. Cross

divide ahead between Rio Grande drainage(Arroyo Agua Buena) and internal drainage ofJornada Basin.

Jornada surface drainage is southward to alarge playa that was formerly inundated bypluvial Lake Trinity (Neal et al., 1983). Ground-water discharge from northern Jornada area iswestward to Rio Grande valley (Weir, 1965).Hogbacks of Oligocene volcanic strata at 10:00may be underlain by a low-angle listric fault.The beds dip 40-50°W in the eastern hogback,generally steeper than underlying Paleozoicand Mesozoic rocks. The western hogbacksdip much more gently than the eastern onesand, locally, dip either east or west. Localizedareas of steeply dipping beds such as thesesuggest listric faulting. 0.3

33.1 Road junction. Turn right (south) on gradedroad (county road A-129). Route descendsgentle piedmont slope graded to Jornada delMuerto Basin floor. Conical hills at 12:00 areOligocene volcanic rocks (mainly andesitic la-vas of Spears Formation) at north end of WhiteSands Missile Range. White buildings at 11:00are Stallion Site Range Station, the securityand tracking headquarters for the north endof the missile range. 3.2

36.3 Cattleguard. 0.136.4 Cattleguard and junction with US-380. Turn

right. End of Trip 2b. Trip 2c begins here atmileage 0.0

33Trip 2c:

Carthage area

Roadlog from junction of county road A -129 and US-380west to Carthage and San Antonio

by John W. Hawley, Virginia T. McLemore, and Mark R. BowieNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801

Tuesday, 20 October 1987

Distance: 24.1 miStops: 2

Summary

This trip takes us from the Jornada del Muerto (endof Trip 2b) west along US-380 through the structurallycomplex Carthage coal field. At STOP 2-4 we willexamine a roadcut exposing the Triassic Chinle For-mation—Dakota Sandstone (Cretaceous) contact. Anexcellent calcic soil profile on top of the Sierra La-drones Formation can be viewed at STOP 2-5. Theunconformity between the Sierra Ladrones Formationand the Gallup Sandstone is beautifully exposed atthis stop. The route continues west into San Antoniowhere it joins Trip 2d.

TotalMileage

0.0 Junction of county road A-129 (dirt) and US-380. 0.3

0.3 Buried archeological site at north edge of high-way. Thin surficial deposits of Holocene ageunconformably overlie thick calcic horizon ofpaleosol on Jornada surface. 0.35

0.65 Milepost 11. Cross divide between Jornada andRio Grande (San Pedro Arroyo) drainage ba-sins. 0.15

0.8 Roadcut in gravels of Baca and Spears For-mations dips about 40° east. Baca conglom-erates (Eocene) at west end of cut containPrecambrian, Paleozoic, and some Mesozoicclasts that were transported eastward from aLaramide uplift, now mostly downfaulted be-neath the Rio Grande rift (Cather, 1983). Sev-eral fossil teeth (Titanotheres, etc.) recoveredin the Carthage area indicate a Bridgerian pro-vincial age for the lower part of the Baca (Lucaset al., 1982; Lucas, 1983). The Baca—Spearscontact, which is placed at the first occurrenceof Tertiary volcanic clasts (here mainly plagio-clase-rich andesitic rocks), is exposed aboutmidway in the outcrop. Volcanic clasts in-crease gradationally over 15-30 ft until almostall clasts are volcanic. 0.7

1.5 Junction with county road A-137 on Baca For-mation. Crossing covered contact (late Qua-ternary val ley f il l) ahead between BacaFormation and underlying Upper Cretaceousrocks. Route for next 4.5 mi is mainly on Cre-taceous strata that dip predominantly southand east and are cut by numerous north-trending faults. See map (Fig. 23) for details.

At 9:00 are old dumps and tipples of Hart and Hil-ton coal mines, the northeasternmost coal producersin the Carthage mining district (Fig. 24; Osburn, 1983).The Hilton mine (marked by reddish dumps behindtipples) closed before 1920. The Hart mine was op-erated until 1967; in later years it was operated by A.B. Baca of Socorro under the name Carthage mine.Some coal was used by the Santa Fe Railroad and fordomestic use in Socorro and San Antonio, but mostwas shipped to Socorro, El Paso, and Chihuahua assmelter fuel. A. B. Baca supplied coal to the steamplant at New Mexico Tech until 1953 and to Albu-querque Public Schools until 1967.

The mines were developed in a 4-ft-thick coal bedin the lower part of the Crevasse Canyon Formation(Upper Cretaceous). The mine site currently consistsof a westward-sloping, timbered decline, a loadoutfacility, small buildings, mine dumps, and a railroadgrade that marks the eastward terminus of the NewMexico Midland Railroad. Westward mine develop-ment was halted at a north-trending fault that juxta-poses the Crevasse Canyon Formation and the Carth-age Member of the Tres Hermanos Formation. 0.1

34

1.6

1.7

FIGURE 23—Geologic map

Milepost 10. Ridge from 12:30 to 2:00 formon west-dipping Atarque Sandstone—the bamember of the Tres Hermanos Formation (Table 2, pp. 13-14, for stratigraphic nomeclature). The Atarque is a regressive, coastbarrier sandstone that ranges up to 75 ft thin the Carthage area (Hook et al., 1983).consists of an alternating sequence of massi3-4-ft-thick beds of flat to low-angle crobedded sandstones, and 2-3-ft-thick, fingrained, burrowed and bioturbated sanstones that weather to form minor reentranAt 3:00 the Atarque is faulted against the FRanch Sandstone Member of the Tres Hmanos Formation to the east and this, in tuis faulted against the Baca Formation. 0.1

Dip slope on Atarque Sandstone Member3:00; dip flattens immediately westwaHighway crosses the axis of a small synclwhere soft, paludal shales and thin splay aoverbank sandstones of the Carthage Memboverlie the Atarque Sandstone Member. Lcally, the Carthage Member is 115 ft thick. A

9:00, immediately south of the highway, areversal takes place in the Atarque. This cha

S

Crevasse Canyon Formation Ga l lup Sands tone

D -Cross Tongue of the Mancos

- Fite Ranch Sandstone Member

Car t hag e M emb er

Atarque Sandstone Member

Lower part of the Mancos Shale

Da kota Sandstone Ch in le Fo rma t io n

mi I0

V2 km I0

KEYQ young valley al luvium

T - Sierra Ladrones FormationT - Baca Formation

Q

Cretaceous

Tres Hermanos

F o rm at i o n

Triassic

K

K

K

K

K

K

K

K

Tic

of the Carthage area (by Osburn, 1983).

edsalseen-al-ickIt

ve,ss-e-d-ts.iteer-rn,

atrd.inendero-tdipnge

in attitude from westward dippingthe highway to eastward dipping souhighway reflects influence of the sythe north and drag folding to the soutalso indicate that on the north side ofway the fault is offset to the east anddrag folding is seen in the Atarque SSouth of the highway the fault trendsouth and the Atarque and lower paCarthage Member are in fault contactCrevasse Canyon Formation; vertication is approximately 500 ft. 0.1

1.8 Fite Ranch Sandstone Member of Trmanos Formation along north side oway. This unit represents transgressivpart of Tres Hermanos. The type secFite Ranch Sandstone Member is 2 mi twest in sec. 17, T5S, R2E (Hook et alwhere it is 72 ft thick. Along the higis about 66 ft thick; the basal 40 ft is mof a lower, grayish-orange, fine-grained

hale

uaternary

Tertiary

vy

slb

cc

g

md

thf

t hC

tha

m1

d

north ofth of thencline toh. It maythe high-thus no

andstone.s north–rt of thewith the

l separa-

es Her-f high-

e uppertion of

o south-., 1983),hway, it

ade upsand-

35

FIGURE 24—Dumps and tipples of Hart and Hilton coal mines,looking south.

stone, mottled, and bioturbated in its lowerportion and containing Lopha bellaplicata (ma-rine oyster) in middle and upper parts. Theupper Fite Ranch Sandstone Member (Hooket al., 1983) is 20 ft of white to grayish-yellow,fine-grained, unfossiliferous sandstone. A 5-ft-thick, moderate yellowish-brown sandstoneforms the distinctive top of the Fite RanchSandstone Member. This bed has been inter-preted as a disconformity based on missingfaunal zones and presence of phosphatizedinternal molds of bivalves, gastropods, andammonite chambers (Hook et al., 1983). Lophabellaplicata also occur in this bed. 0.2

2.0 Contact between Atarque and Carthage Mem-bers on south side of highway. Carbonaceousshales and siltstones form base of CarthageMember here. East-dipping Atarque Forma-tion is present in roadcut immediately to righton west limb of syncline. 0.05

2.05 Highway descends into valley developed onlower part of Mancos Shale. Valley fill is ofHolocene and latest Pleistocene age. 0.25

2.3 Railroad bed formerly serving Carthage mineon left. Rails were removed between 1935 and1940 and shipped to Japan as scrap. Excellentbricks of several colors were made in Socorrofrom clay from the Cretaceous units in theCarthage area (Talmage and Wootton, 1937).During the 1930's, Mr. B. H. Kinney had a fewshipments of clay sent to his New Mexico ClayProducts Co. plant in Albuquerque. Some claywas also used in a small roofing-tile plant atSan Antonio during the 1930's (Talmage andWootton, 1937). 0.1

2.4 Road to left leads to Carthage cemetery andtownsite. Sandstone ledge capping cliff at 9:00is Gallup Sandstone (Kg). Coal dump is fromManilla mine where a coal seam about 50 ftabove the Gallup was exploited. Wastes weretrammed north from the mine and dumpedover Gallup cliff. Highway crosses north-trending fault. Light-colored Bridge CreekLimestone beds of the Mancos Shale on east(upthrown) block are in fault contact withD-Cross Tongue of Mancos Shale on west

(downthrown) block. The Atarque Sandstone

Member, which lies approximately 164 ftstratigraphically above Bridge Creek beds, ispresent on ridge at 3:00 and caps knob at 9:00.Coal dumps at 10:00-11:00. 0.1

2.5 Brown sandstone flatirons on dip slope at 3:00are top of Fite Ranch Sandstone Member.0.25

2.75 An erosion surface developed on D-CrossTongue of Mancos Shale is seen on both sidesof road. At 9:00 note upper half of D-Cross,containing very large calcareous concretionsand overlain by Gallup Sandstone. At 3:00 notedip slope on uppermost distinctive brown bedof Fite Ranch Sandstone Member of Tres Her-manos Formation. 0.2

2.95 Highway crosses north-trending fault; aban-doned coal mine at 9:00. All three members ofTres Hermanos Formation are exposed in as-cending order south of highway along west(upthrown) side of fault, which here cuts outcoal-bearing Crevasse Canyon Formation. Ar-cheological sites dating back to Old Carthage(late 1800's) throughout the area. 0.1

3.05 Atarque Sandstone Member caps ridge thatparallels highway on south. Old railroad gradealong north side of highway is on dissectedvalley-fill alluvium of Holocene age. At 3:00note dip slope formed on highly fractured andhematite-stained Dakota Sandstone. Strikevalley ahead cut in lower part of MancosShale . 0 .25

3.3 Bridge Creek Limestone beds of Mancos Shaleform a light-colored zone in a low ridge alongthe south side of the highway. Associated withthe limestone beds, which individually rangefrom 1 to 6 inches thick, are numerous thin,white- to orange-weathering bentonites fromwhich selenite crystals commonly weather out.These beds mark a transgressive maximum ofthe shallow seaway. The Sciponoceras gracile(ammonite) zone in lower part of this calcar-eous interval was previously designated as theCenomanian—Turonian boundary; this bound-ary has now been moved up several faunalzones. Also present in lower half of BridgeCreek Limestone beds are the guide fossil Py-chodonte newberryi (oyster) and ammonites Me-toicoceras geslinianum and Euomphaloceras(kanabiceras) septemseriatum. The uppermostBridge Creek Limestone contains Inoceramusmytiloides (clam) and other fossil debris. Fossilagate wood is found throughout the area. Thecalcareous interval represented by the BridgeCreek Limestone is about 50 ft thick. 0.15

3.45 Old railroad grade passes through water gapin Dakota Sandstone hogback at 3:00. BridgeCreek Limestone beds parallel highway onsouth; Atarque Sandstone Member caps ridgebeyond. 0.2

3.65 At 9:00 the south-dipping Atarque is cut outby a sinuous, northwest-trending fault. Dipslope of Dakota Sandstone on right forms east-trending hogback. 0.25

36

FIGURE 25-Roadcut at mile 4.1 (Stop 2-4) exposing contact be-tween Chinle Formation on left and Dakota Sandstone on right(south side of highway).

3.9 Milepost 8. Highway crosses fault betweenDakota Sandstone (Cretaceous) on east andChinle Formation (Triassic) on west. 0.2

4.1 STOP 2 -4. Roadcut exposes Chinle-Dakotacontact on left (Fig. 25). White, clayey zone atbase of Dakota may represent Morrison-likebeds (Jurassic) or a weathering zone at top ofTriassic. See pp. 50-52 for a synopsis of theclay mineralogy of this outcrop. A major high-angle fault at west end of roadcut on right (Fig.26) juxtaposes Triassic mudstones (Chinle For-mation) against conglomeratic calcrete of up-per Santa Fe Group. 0.1

4.2 Cut in sands and clays of Sierra Ladrones For-mation. Prepare for sharp left turn ahead. 0.3

4.5 Turn left onto Fite Ranch Road (Socorro Countyroad A-153). Cuts ahead in soft mudstonesand sandstones of Sierra Ladrones Formation.These beds are distal piedmont facies and in-tertongue 1 to 2 mi to west with fluvial (an-cestral Rio Grande) facies. 0.3

4.8 At 10:00-11:00 are isolated remnants of SierraLadrones conglomerates (Santa Fe Group)resting on lower part of Mancos Shale. Onskyline beyond is dip slope of Dakota Sand-stone passing under buff to gray MancosShale. 0.2

5.0 West-dipping Sierra Ladrones sandstone to left.For more information see Smith et al. (1983,stop 6). 0.25

5.25 Tres Hermanos Sandstone to left capped byprominent ledge of dark-brown sandstone.Many minor faults offset this unit. Note changein strike, which now is southeast, rather thaneast as seen to the north. 0.2

5.45 Valley to left now cut in upper D-Cross Tongueof Mancos Shale. Ridge on skyline (10:00-11:30) is capped by Gallup Sandstone atbase of Mesaverde Group. Ascend windingroad to Jornada del Muerto Basin floor. 0.1

5.55 Crossing unconformable contact of Sierra La-drones piedmont facies on Gallup Sandstoneand D-Cross Tongue (Fig. 27). Basal Santa Febeds are locally well cemented with calcite de-rived from ground water that previously cir-

FIGURE 26-Roadcut at mile 4.1 (Stop 2-4) exposing a high-angle

fault between Chinle Formation on right and Santa Fe Group onleft (north side of highway).

culated above basin fill-bedrock contact. Coaldumps to left. 0.3

5.85 STOP 2-5. Examine soil profile on top of SierraLadrones Formation and unconformity be-tween Gallup Sandstone and Sierra LadronesFormation (see pp. 55-67 for more informa-tion). After stop, turn around and return toUS-380. 1.35

7.2 Turn left on US-380 and continue west downvalley of San Pedro Arroyo. Quarries in SanAndres Limestone on hillside to far north (Fig.28). Limestone was used in the smelters inSocorro during the late 1800's. 0.2

7.4 Crossing San Pedro Arroyo. The distal-pied-mont facies of Sierra Ladrones Formation iswell exposed in valley wall from 9:00-11:00.Bluffs flanking arroyo valley are capped withthin deposits of eolian sand and older valleyfi l l . 1.2

8.6 Bridge. Milepost 6. 0.59.1 Gray-brown sand and reddish clay of Sierra

Ladrones fluvial facies exposed in arroyo bankto right. The belt of intertonguing distal-pied-mont and fluvial facies, first observed alongArroyo de la Parida (Trip 2b), continues souththrough this area and extends southeastward

FIGURE 27-Unconformity between Sierra Ladrones Formation(upper beds) and Gallup Sandstone, at mile 5.55 (just before Stop2-5).

37

FIGURE 28—Limestone quarries as seen from Fite Ranch Road FIGURE 29—Thick bed (about 15 ft) of gravelly pumice interbedded(looking north at mile 7.2). with Santa Fe Group fluvial units, looking west about 1 mi north-

east of mile 10.9.

across the northern Jornada del Muerto Basin.Route ahead on arroyo terraces capped withmiddle to upper Quaternary alluvium. 0.8

9.9 Bridge. Conglomeratic sandstone, pebbly sand,and minor clay and mudstone of Sierra La-drones fluvial facies is well exposed south ofSan Pedro Arroyo for next 1.1 mi. 0.2

10.1 Sands of Sierra Ladrones fluvial facies withveneer of arroyo-terrace gravel in roadcutsahead. The thin terrace fill probably correlateswith deposits of lowest major valley-bordersurface of Pleistocene age (Canada Marianasurface of Denny, 1941). 0.8

10.9 Bridge over San Pedro Arroyo. Fluvial sandand clay of Sierra Ladrones Formation ex-posed in valley wall to left. Route for next 1.4mi on Holocene arroyo terrace and fan de-posits, with low bluffs to right underlain bymiddle to upper Pleistocene valley fill. A largedeposit of volcanic ash and gravelly pumice(mostly pebble to cobble size) approximately1 mi to northeast is derived from Cerro ToledoRhyolite and basal Bandelier Tuff of the JemezMountains (Fig. 29; Izett et al., 1981). Thispumice mass is interbedded with the fluvialfacies and was probably emplaced as a unitduring a catastrophic Rio Grande flood some-time between 1.4 and 1.1 m.y. ago. Olderarroyo-fan and terrace deposits in this area aregraded to ancestral river-base levels from 60to 180 ft above the present valley floor. 0.9

11.8 Bosquecito road to right. Route descends fan

of San Pedro Arroyo, which has progradedonto the Rio Grande floodplain during middleto late Holocene time. 0.4

12.2 San Pedro townsite to left on toe of arroyo-mouth fan. Route ahead descends to RioGrande floodplain. 0.5

12.7 East end of Rio Grande bridge. 0.813.5 Cross AT&SF Railroad (Albuquerque—El Paso

line) at west edge of floodplain. Route ascendsHolocene fan of Nogal Canyon drainage andenters San Antonio. The town is named for amission founded in 1629 by Fray Antonio deArteaga and Fray Garcia de Francisco de Zuniga(Pearce, 1965) and is the birthplace of hotelentrepreneur Conrad Hilton. A small roofingplant operated intermittently during the 1930's(Talmage and Wootton, 1937); two or three menoperated a small kiln to produce tile from locala d ob e c l a y an d s h a l e f ro m C ar t h ag e .0.3

13.8 Junction with NM-1 and Owl Bar ahead. Southmargin of Socorro cauldron in southern Chu-padera Mountains is to the west. Pleistocenepiedmont and valley-border surfaces, gradingeastward from base of Chupaderas to bluffsalong Rio Grande, are offset by several faultsthat trend south—southeast toward this areafrom the foot of Socorro Peak (Sanford et al.,1972). 0.5

14.3 Junction of US-380 and NM-1. Turn left. Endof Trip 2c. Trip 2d begins here at mileage 0.0.

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Trip 2d:Bosque del Apache National Wildlife Refuge

Roadlog from San Antonio to Bosque del ApacheNational Wildlife Refuge and return to Socorro

by Virginia T. McLemore, Mark R. Bowie, and John W. HawleyNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801

uesday, 20 October 1987

istance: 41.8 mitops: 1 (tour loop)

Summary

Bosque del Apache (woods of the Apache) Nationalildlife Refuge was established in 1939 on the Riorande as a refuge and breeding ground for water

owl and other wildlife. The 57,191-acre park providesabitat for about 295 different bird species, includinghe endangered bald eagle, peregrine falcon, andhooping crane, and over 400 different mammals,

eptiles, and amphibians. Water is diverted from ir-igation channels or pumped from wells to create tem-orary ponds and marshes during the winter whereirds can nest and feed. During the summer months,he ponds are drained and the water is used for ag-iculture. About 1,400 acres of farmland provide sup-lemental food for the wildlife.The Bosque consists of a 15-mi tour loop, open to

he public throughout the year from 30 minutes beforeunrise to 30 minutes after sunset. Two hiking trails,he Bosque trail (1.75 mi) and the marsh walk (0.75i), provide an opportunity to view wildlife more

losely. The Bosque also includes 30,287 acres of wil-erness for day hikes for the more hardy individualho wants to observe wildlife.

Totalileage

0.0 Junction of US-380 and NM-1 in San Antonio.Continue south on NM-1. 0.6

0.6 Foundations on right side of road are all thatremain of the Hilton store, boyhood home ofhotel entrepreneur Conrad Hilton. Railroadstation foundation on left. Route continues onRio Grande floodplain. 0.95

1.55 Former Mex—Tex barite-fluorite mill on left.These ores were mined from the Hansonburgmining district , Oscura Mountains nearBingham (Trip 3). Low bluffs to right are un-derlain by terrace and fan gravels of middleto late Pleistocene age that are inset against

fluvial sand and gravel of the Sierra LadronesFormation. 2.7

4.25 Enter Bosque del Apache National WildlifeRefuge. Little San Pascal Mountain at 11:00.0.6

4.85 Milepost 12. Chupadera Mountains at 1:00.High peak at 1:30 is capped by dark-coloredA—L Peak tuff, erupted from cauldrons in theMagdalena area. The underlying light-col-ored, poorly welded tuffs dip southeast andrest on silicified Mississippian sandstones andlimestones, which, in turn, overlie Precam-brian granites and schists. The Precambrianrocks form low, rounded foothills at 1:30 to3:00. The light-colored tuff unit probably ac-cumulated in pre-existing topographic lowsbecause the densely welded A—L Peak tuff restsdirectly on Paleozoic rocks just to south.

Approximately 1,500-2,000 ft of the Oligo-cene volcanic section is missing in this area.Possible causes are: 1) erosion along the southmargin of the Sawmill Canyon cauldron be-fore eruption of the A—L Peak tuff and/or 2)

38

39

the existence of a Laramide uplift that wasbeveled to its Precambrian core by the lateEocene erosion surface but that remained top-ographically high until middle Oligocene time.Transport directions in arkosic channel sandsof the Baca Formation (Eocene) north of Mag-dalena indicate a source region for Precam-brian detritus somewhere to the south-southeast.

Note basalt-capped mesa at 2:30 on crest ofChupadera Mountains in saddle at head of •valley. This unit may be correlative with the4-m.y.-old basalt of Sedillo Hill seen on Trip1. 2.35

7.2 AT&SF Railroad crossing. Note dissected fansand pediments extending from ChupaderaMountains. Higher ridges to the southwest .underlain by deformed piedmont and basin-floor facies of the Popotosa Formation (lower'Santa Fe Group). 1.6

8.8 STOP 2-6. Headquarters of the Wildlife Ref-uge. Turn right and continue to Visitors Cen-ter parking area. Following visit to refugeheadquarters and museum, continue on tourloop of refuge east of NM-1 (tour loop mapavailable at entrance). After tour, retrace routeto San Antonio. 22.8

31.6 San Antonio at junction of NM -1 and US-380.Turn left. 0.4

32.0 Turn right (north) onto access ramp of I-25. 0.4

32.4 Roadcuts and arroyo exposures from here toSocorro show complex intertonguing of pied-mont-gravel and fluvial-sand facies. Units makeup youngest Santa Fe basin fill (Sierra La-

drones Formation) and middle to upper Pleis-tocene valley fill. 1.5

33.9 Milepost 141. Magdalena Range on westernskyline. Socorro Peak at 11:00 and Ladron Peakon distant skyline behind Lemitar Mountainsat 11:30. Basalt of Sedillo Hill (4 m.y.) capsmesa in moat of Socorro cauldron at 10:30.Piedmont fault scarp at 11:00 shows displace-ment of youngest Santa Fe and older valley-fill units. 1.0

34.9 Milepost 142. Relay tower on left. High hills,mesas, and cuestas on skyline east of RioGrande (Loma de las Cafias uplift) consistmostly of Permian (San Andres, Glorieta, andYeso) formations (Trip 2b). Pliocene to lowerPleistocene fluvial and piedmont facies of up-per Santa Fe Group crop out in bluffs andbenches that form eastern border of river val-ley. 2.3

37.2 Underpass; Luis Lopez Road. 1.638.8 Milepost 146. Socorro airport on left. Crossing

Socorro Canyon fan. The surface here is prob-ably of pre-Wisconsin, late Pleistocene age.1.2

40.0 Bridge over Arroyo de la Matanza. Exposuresof upper Santa Fe Group basin fill overlain byfan gravel in arroyo and gravel pit to left. 0.2

40.2 Take exit 147. 0.740.9 Enter Socorro. 0.741.6 Railroad crossing, Grefco spur of the AT&SF.

0.241.8 Intersection of California and Spring Streets,

junction of US-60 and US-85 (business 1-25).End of log.

Trip 3:Carthage, Jornada del Muerto, and Bingham

Roadlog from Socorro to San Antonio, Carthage,and Bingham Post Office

by Virginia T. McLemore, Mark R. Bowie, and John W. HawleyNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801

Tuesday, 20 October 1987 (if it rains)

Distance: 37.5 miStops: 1

Summary

Trip 3 is the reverse log of Trip 2c, starting in So-corro and traveling south on 1-25 to San Antonio.From San Antonio, the route progresses east throughthe Carthage coal field and into the Jornada del MuertoBasin as far east as Bingham. Geology of the Carthagearea is shown in Figure 23 (p. 34).

TotalMileage

0.0 South end of Socorro at ramp to 1-25. Proceedsouth on 1-25. 0.5

0.5 Bridge over Arroyo de la Matanza. Exposuresof upper Santa Fe Group basin fill overlain byfan gravel in arroyo and gravel pit to right. 0.4

0.9 Socorro airport on right. Crossing SocorroCanyon fan. The surface here is probably ofpre-Wisconsin, late Pleistocene age. 1.9

2.8 Underpass; Luis Lopez Road. 2.25.0 Relay tower on right. High hills, mesas, and

cuestas on skyline east of Rio Grande (Lomade las Canas uplift) consist mostly of Permian(San Andres, Glorieta, and Yeso) formations(Trip 2b). Pliocene to lower Pleistocene fluvialand piedmont facies of upper Santa Fe Groupcrop out in bluffs and benches that form east-ern border of river valley.

Roadcuts and arroyo exposures from hereto San Antonio show complex intertonguingof piedmont-gravel and fluvial-sand facies.Units make up youngest Santa Fe basin fill(Sierra Ladrones Formation) and middle to up-per Pleistocene valley fill. 3.0

8.0 Turn right at San Antonio (exit 139). Continueinto San Antonio on US-380. San Antonio isnamed for a mission founded in 1629 by FrayAntonio de Arteaga and Fray Garcia de Fran-cisco de Zufiiga (Pearce, 1965) and is the birth-place of hotel entrepreneur Conrad Hilton.Route descends on Holocene fan surface gradedto Rio Grande valley floor. 0.6

40

8.6 Junction with NM-1 and Owl Bar ahead. Con-tinue east on US-380. Bosque del Apache Na-tional Wildlife Refuge is south on NM-1 (Trip2d). 0.3

8.9 Cross AT&SF Railroad (Albuquerque-El Pasol ine) at west edge of Rio Grande flood-plain. 0.7

9.6 West end of Rio Grande bridge. 0.610.2 San Pedro townsite to right on toe of arroyo-

mouth fan. Route ahead ascends fan of SanPedro Arroyo, which has prograded onto theRio Grande floodplain during middle to lateHolocene time. 0.4

10.6 Bosquecito road to left. Ahead on the left, mid-dle to upper Pleistocene fan alluvium is ex-posed in arroyo walls. Higher ridges to thenorth are eroded on fluvial sand and gravelof the Sierra Ladrones Formation. A large de-posit of volcanic ash and gravelly pumice(mostly pebble to cobble size) approximately1 mi to northeast is derived from Cerro ToledoRhyolite and basal Bandelier Tuff of the JemezMountains (Fig. 29, Trip 2c, p. 37; Izett et al.,1981). This pumice mass is interbedded with

41

the fluvial facies and was probably emplacedas a unit during a catastrophic Rio Grandeflood sometime between 1.4 and 1.1 m.y. ago.Older arroyo-fan and terrace deposits in thisarea are graded to ancestral river-base levelsabout 60 to 180 ft above present val leyfloor. 0.9

11.5 Bridge over San Pedro Arroyo. Fluvial sandand clay of Sierra Ladrones Formation ex-posed in valley wall to right. Sands of SierraLadrones fluvial facies with veneer of arroyo-terrace gravel in roadcuts ahead. Loma de lasCatias on skyline at 11:00 (Trip 2b). 1.0

12.5 Culvert. Route ahead on terrace capped witholder valley-fill alluvium. 0.4

12.9 Bridge. 0.813.7 Gray-brown sand and reddish clay of Sierra

Ladrones fluvial facies exposed in arroyo bankto left. The belt of intertonguing distal-pied-mont and fluvial facies, first observed alongArroyo de la Parida (Trip 2b), continues souththrough this area and extends southeastwardacross the northern Jornada del Muerto Ba-sin. 0.5

14.2 Bridge. Milepost 6. 1.215.4 Crossing San Pedro Arroyo. The distal-pied-

mont facies of Sierra Ladrones Formation iswell exposed in valley wall to south (red toyellowish-brown beds) and is capped with thindeposits of eolian sand and older valley-fillalluvium, commonly with multiple buried soils(Trip 2c, Stop 2-5, p. 36). 0.2

15.6 Fite Ranch Road on right (Socorro County roadA-153-Trip 2c, Stop 2-5). Continue east onUS-380. Quarries in San Andres Limestone at10:00 (Fig. 28, p. 37). Limestone was used inthe smelters in Socorro during the late 1800's.The San Andres Formation caps the high ridgeat 9:00. 0.4

16.0 Roadcut exposes Chinle-Dakota contact onright (Trip 2c, Stop 2-4; Figs. 25, 26, p. 36).White, clayey zone at base of Dakota may rep-resent Morrison-like beds (Jurassic) or aweathering zone at top of Triassic. The claymineralogy of this outcrop is described on pp.50-52. A major high-angle fault at west end ofroadcut on left (Fig. 26, p. 36) juxtaposes Trias-sic mudstones against conglomeratic calcreteof upper Santa Fe Group. 0.1

16.1 Crossing fault between Dakota Sandstone(Cretaceous) on east and Chinle Formation(Triassic) on west. Dip slope of Dakota Sand-stone ahead on left forms east-trending hog-back. Route continues up strike valley cut inlower Mancos shale, with thick fill of Holoceneand latest Pleistocene age. 0.4

16.5 Old railroad grade passes through water gapin Dakota Sandstone hogback at 9:00. Railroadbed formerly serving Carthage mine on left.Rails were removed between 1935 and 1940and shipped to Japan as scrap. Atarque Sand-stone Member caps ridge on southern skyline.Ridge on left formed on west-dipping AtarqueSandstone-the basal member of Tres Her-

manos Formation (see Table 2, pp. 13-14, forstratigraphic nomenclature). The Atarque is a

regressive, coastal-barrier sandstone that rangesup to 75 ft thick in the Carthage area (Hooket al., 1983). It consists of an alternating se-quence of massive, 3-4-ft-thick beds of flat tolow-angle crossbedded sandstones, and 2-3-ft-thick, fine-grained, burrowed and biotur-bated sandstones that weather to form minorreentrants. Bridge Creek Limestone beds ofthe Tres Hermanos Formation (Mancos Shale)form a light-colored zone in a low ridge alongthe south side of the highway. Associated withthe limestone beds, which individually rangefrom 1-6 inches thick, are numerous thin,white- to orange-weathering bentonites fromwhich selenite crystals commonly weather out.These beds mark a transgressive maximum ofthe shallow seaway. The Sciponoceras gracile(ammonite) zone in lower part of this calcar-eous interval was previously designated as theCenomanian-Turonian boundary; this bound-ary has now been moved up several faunalzones. Also present in lower half of BridgeCreek Limestone beds are the guide fossil Py-chodonte newberryi (oyster) and ammonites Me-toicoceras geslinianum and Euomphaloceras(kanabiceras) septemseriatum. The uppermostBridge Creek Limestone contains Inoceramusmytiloides (clam) and other fossil debris. Fossilagate wood is found throughout the area. Thecalcareous interval represented by the BridgeCreek Limestone is about 50 ft thick. 0.5

17.0 Coal mine dump on right. Atarque SandstoneMember caps ridge at 11:00; old railroad gradecrosses highway. 0.15

17.15 Highway crosses north-trending fault. All threemembers of Tres Hermanos Formation are ex-posed in ascending order south of highwayalong west (upthrown) side of fault, whichhere cuts out coal-bearing Crevasse CanyonFormation. 0.15

17.3 Milepost 9. Surface developed on D-CrossTongue of Mancos Shale is seen on both sidesof road. At 3:00 note upper half of D-Cross,containing very large calcareous concretionsand overlain by Gallup Sandstone. At 9:00 notedip slope on uppermost distinctive brown bedof Fite Ranch Sandstone Member of Tres Her-manos Formation. 0.15

17.45 Highway crosses north-trending fault. Light-colored Bridge Creek Limestone beds of theMancos Shale on east (upthrown) block are infault contact with D-Cross Tongue of MancosShale on west (downthrown) block. The Atar-que Sandstone Member, which lies approxi-mately 164 ft stratigraphically above BridgeCreek beds, is present on ridge at 9:00 andcaps knob at 3:00. 0.05

17.5 Road to right leads to Carthage townsite andcemetery. Sandstone ledge capping cliff at 2:00is Gallup Sandstone (Kg). 0.4

17.9 Roadcut in Atarque Sandstone. East-dippingAtarque is present in roadcut immediately to

42

left on west limb of syncline. 0.0517.95 Contact between Atarque and Carthage Mem-

bers on south side of highway. Carbonaceousshales and siltstones form base of CarthageMember here. 0.15

18.1 Fite Ranch Sandstone Member of Tres Her-manos Formation along north side of high-way. This unit represents transgressive upperpart of Tres Hermanos. The type section ofFite Ranch Member is 2 mi to southwest insec. 17, T5S, R2E (Hook et al., 1983) where itis 72 ft thick. Along the highway, it is about66 ft thick; the basal 40 ft is made up of a lower,grayish-orange, fine-grained sandstone, whichis mottled and bioturbated in its lower portionand contains Lopha bellaplicata (marine oyster)in its middle and upper parts. The upper FiteRanch Sandstone Member is 20 ft of white tograyish-yellow, fine-grained, unfossiliferoussandstone. A 5-ft-thick, moderate yellowish-brown sandstone forms the distinctive top ofFite Ranch Member. This bed has been inter-preted as a disconformity based on missingfaunal zones and presence of phosphatizedinternal molds of bivalves, gastropods, andammonite chambers (Hook et al., 1983). Lophabellaplicata also occur in this bed. 0.1

18.2 Dip slope on Atarque Sandstone Member at9:00; dip flattens immediately westward.Highway crosses the axis of a small synclinewhere soft, paludal shales and thin splay andoverbank sandstones of the Carthage Memberoverlie the Atarque Sandstone Member. Lo-cally, the Carthage Member is 115 ft thick. At3:00, immediately south of the highway, a dipreversal takes place in the Atarque. This changein attitude from westward dipping north ofthe highway to eastward dipping south of thehighway reflects influence of the syncline tothe north and drag folding to the south. It mayalso indicate that on the north side of highwaythe fault is offset to the east and thus no dragfolding is seen in the Atarque Sandstone. Southof the highway the fault trends north-southand the Atarque and the lower part of Car-thage Member are in fault contact with theCrevasse Canyon Formation; vertical separa-tion is approximately 500 ft. 0.1

18.3 At 9:00 the Atarque is faulted against Fite RanchSandstone Member of the Tres Hermanos For-mation to the east and this, in turn, is faultedagainst the Baca Formation. 0.1

18.4 At 3:00 are old dumps and tipples of Hart andHilton coal mines, the northeasternmost coalproducers in the Carthage mining district (Fig.24; Osburn, 1983).

The Hilton mine (marked by reddish dumps behindtipples) closed before 1920. The Hart mine was op-erated until 1967; in later years it was operated by A.B. Baca of Socorro under the name Carthage mine.Some coal was used by the Santa Fe Railroad and fordomestic use in Socorro and San Antonio, but mostwas shipped to Socorro, El Paso, and Chihuahua assmelter fuel. A. B. Baca supplied coal to the steamplant at New Mexico Tech until 1953 and to Albu-

querque Public Schools until 1967.The mines were developed in a 4-ft-thick coal bed

in the lower part of the Crevasse Canyon Formation(Upper Cretaceous). The mine site currently consistsof a westward sloping, timbered decline, a loadoutfacility, several small buildings, mine dumps, and arailroad grade that marks the eastward terminus ofthe New Mexico Midland Railroad. Westward minedevelopment was halted at a north-trending fault thatjuxtaposes the Crevasse Canyon Formation and theCarthage Member of the Tres Hermanos Forma-tion. 0.05

18.45 Milepost 10. 0.0518.5 Junction of US-380 and A-137. Continue on

US-380. Crossing covered contact between BacaFormation and underlying Upper Cretaceousrocks. 0.6

19.1 Roadcut in gravels of Baca and Spears For-mations that dip about 40° east. Baca conglom-erates (Eocene) at west end of cut containPrecambrian, Paleozoic, and some Mesozoicclasts that were transported eastward from aLaramide uplift, now mostly downfaulted be-neath the Rio Grande rift (Cather, 1983). Sev-eral fossil teeth (Titanotheres, etc.) recoveredin the Carthage area indicate a Bridgerian pro-vincial age for the lower part of the Baca (Lucaset al., 1982; Lucas, 1983). The Baca-Spearscontact, which is placed at the first occurrenceof Tertiary volcanic clasts (here mainly plagio-clase-rich andesitic rocks), is exposed aboutmidway in the outcrop. Volcanic clasts in-crease gradationally over 15-30 ft until almostall clasts are volcanic. 0.3

19.4 Milepost 11. Top of hill. Road descends intothe Jornada del Muerto Basin. This basin ex-tends southward to Las Cruces and northwardto the Los Pinos Mountains and ChupaderaMesa. It was so named because hundreds ofpeople perished en route from Chihuahua toSanta Fe due to lack of water and attacks byApache Indians (Pearce, 1965). ChupaderaMesa is at 11:00-12:00; Oscura Mountains,12:00-2:00; Mockingbird Gap, 2:00. 0.6

20.0 Junction of county road A-129 and end of Trip2b. 0.9

20.9 STOP 3-1. Historical marker at junction withNM-525 to Stallion Site, White Sands MissileRange. Trinity Site, location of the world's firstnuclear test is about 20 mi to the southeast.Pluvial Lake Trinity, described by Neal et al.(1983), flooded the Jornada Basin floor southof Trinity Site during Pleistocene pluvial pe-riods. Salinas Peak, in the northern San AndresRange at 2:30, is capped by an aphanitic rhy-olite sill of Tertiary age intruded into Penn-sylvanian rocks. 0.6

21.5 Ruins of Carthage Post Office and Store. 5.827.3 Milepost 19. Hansonburg mining district at 1:00

in the Oscura Mountains. Lower red hills at2:00 are in Abo Formation. 3.4

43

30.7 Rest stops ahead. Recent sand dunes have beenpartially stabilized by vegetation. 1.7

32.4 Roadcuts in limestone of San Andres Forma-tion. Roadcuts ahead in Glorieta Sandstoneand gypsum of the Yeso Formation. 3.1

35.5 Roadcuts in San Andres Formation ahead.Cross west flank of small syncline. 2.0

37.5 Bingham. Hansonburg mining district to right(Fig. 30). Roadcuts in Abo Formation ahead.See pp. 50, 52 for description of clay miner-alogy.

End of roadlog.Retrace route back to Socorro or continue onUS-380 to Valley of Fires field trip (Allen andKottlowski, 1981). FIGURE 30—Looking east at the Hansonburg mill and dumps of

barite-fluorite-galena mines.

A

B

B

C

C

C

C

C

C

*

C

C

C

C

C

C

D

D

E

F

F

4

Roadlog references and additional reading (*)

llen, J. E., and Kottlowski, F. E., 1981, Roswell-Ruidoso-Valleyof Fires, including trips to Lincoln, Tularosa, and BottomlessLakes State Park: New Mexico Bureau of Mines and MineralResources, Scenic Trip 3, 3rd edition, 96 pp.auch, J. H. A., 1982, Geology of the central area of the Loma delas Carias quadrangle, Socorro County, New Mexico: Unpub-lished M.S. thesis, New Mexico Institute of Mining and Tech-nology, 116 pp.ryan, K., 1932, Pediments developed in basins with throughdrainage as illustrated in the Socorro area, New Mexico (abs.):Geological Society of America Bulletin, v. 43, pp. 128-129.ather, S. M., 1983, Laramide Sierra uplift-evidence for majorpre-rift uplift in central and southern New Mexico: New MexicoGeological Society, Guidebook to 34th Field Conference, pp. 99-101.hamberlin, R. M., 1980, Cenozoic stratigraphy and structure ofthe Socorro Peak volcanic center, central New Mexico: Unpub-lished Ph.D. dissertation, Colorado School of Mines, Golden,495 pp.; New Mexico Bureau of Mines and Mineral Resources,Open-file Report 118, 532 pp., 3 pls.hamberlin, R. M., 1981, Cenozoic stratigraphy and structure ofthe Socorro Peak volcanic center, central New Mexico-a sum-mary: New Mexico Geology, v. 3, no. 2, pp. 22-24.hamberlin, R. M., 1983, Cenozoic domino-style crustal extensionin the Lemitar Mountains, New Mexico-a summary: New Mex-ico Geological Society, Guidebook to 34th Field Conference, pp.111-118.hamberlin, R. M., and Osburn, G. R., 1986, Tectonic framework,character, and evolution of upper crustal extensional domains inthe Socorro area of the Rio Grande rift, New Mexico: ArizonaGeological Society Digest, vol. XVI, p. 464.hapin, C. E., 1983a, Selected tectonic elements of the Socorroregion: New Mexico Geological Society, Guidebook to 34th FieldConference, p. 97.Chapin, C. E., editor, 1983b, Socorro region II: New Mexico Geo-

logical Society, Guidebook to 34th Field Conference, 344 pp.hapin, C. E., Chamberlin, R. M., and Hawley, J. W., 1978a, So-corro to Rio Salado; in Hawley, J. W. (compiler), Guidebook toRio Grande rift in New Mexico and Colorado: New Mexico Bu-reau of Mines and Mineral Resources, Circular 163, pp. 121-137.hapin, C. E., Chamberlin, R. M., Osburn, G. R., White, D. W.,and Sanford, A. R., 1978b, Exploration framework of the Socorrogeothermal area, New Mexico; in Chapin, C. E., and Elston, W.E. (eds.), Field guide to selected cauldrons and mining districtsof the Datil-Mogollon volcanic field, New Mexico: New MexicoGeological Society, Special Publication No. 7, pp. 114-129.hapin, C. E., and Lindley, J. I., 1986, Potassium metasomatismof igneous and sedimentary rocks in detachment terranes andother sedimentary basins-economic implications: Arizona Geo-logical Society Digest, vol. XVI, pp. 118-126.lark, N. J., and Summers, W. K., 1971, Records of wells andsprings in the Socorro and Magdalena areas, Socorro County,New Mexico, 1968: New Mexico Bureau of Mines and MineralResources, Circular 115, 51 pp.onron, J. P., 1980, Socorro, a historic survey: University of NewMexico Press, Albuquerque, 124 pp.ordell, L. S., and Earls, A. C., 1983, Piro Pueblo excavation: NewMexico Geological Society, Guidebook to 34th Field Conference,pp. 63-64.'Andrea-Dinkelman, J. F., Lindley, J. I., Chapin, C. E., and Os-burn, G. R., 1983, The Socorro K2O anomaly-a fossil geothermalsystem in the Rio Grande rift: New Mexico Geological Society,Guidebook to 34th Field Conference, pp. 76-77.enny, C. S., 1941, Quaternary geology of the San Acacia area,New Mexico: Journal of Geology, v. 49, pp. 225-260.veleth, R. W., 1983, Gustav Billing, the Kelly mine, and the greatsmelter at Park City, Socorro County, New Mexico: New MexicoGeological Society, Guidebook to 34th Field Conference, pp. 89-95.erguson, C. A., 1986, Geology of the east-central San MateoMountains, Socorro County, New Mexico: New Mexico Bureauof Mines and Mineral Resources, Open-file Report 252, 135 pp.,4 maps.oster, R., and Luce, P., 1963a, Road log A, Socorro northward toValencia County line via Interstate 25, U.S. 85, and U.S. 60: NewMexico Geological Society, Guidebook to 14th Field Conference,pp. 6-12.

Foster, R., and Luce, P., 1963b, Road log D, Socorro to Sierra Countyline, via U.S. 85: New Mexico Geological Society, Guidebook to14th Field Conference, pp. 26-30.

Gile, L. H., Hawley, J. W., and Grossman, R. B., 1981, Soils andgeomorphology in the Basin and Range area of southern NewMexico-guidebook to the Desert Project: New Mexico Bureauof Mines and Mineral Resources, Memoir 39, 222 pp.

Hawley, J. W., 1986, Physiographic provinces; in Williams, J. L.(ed.), New Mexico in maps, 2nd edition: University of New Mex-ico Press, Albuquerque, pp. 23-31.

*Hawley, J. W., and Parsons, R. B., 1984, Glossary of selectedgeomorphic terms for western soil surveys: West National Tech-nical Service Center, U.S. Soil Conservation Service, Portland,Oregon, 31 pp.

Henderson, E., 1956, U.S. 60: Arizona Highways, v. 32, no. 5, pp.12-31.

Hook, S. C., 1983, Stratigraphy, paleontology, depositional frame-work, and nomenclature of marine Upper Cretaceous rocks, So-corro County, New Mexico: New Mexico Geological Society,Guidebook to 34th Field Conference, pp. 165-172.

Hook, S. C., Molenaar, C. M., and Cobban, W. A., 1983, Stratig-raphy and revision of nomenclature of upper Cenomanian toTuronian (Upper Cretaceous) rocks of west-central New Mexico;in Hook, S. C. (compiler), Contributions to mid-Cretaceous pa-leontology and stratigraphy of New Mexico-part II: New MexicoBureau of Mines and Mineral Resources, Circular 185, pp. 7-28.Izett, G. A., Obradovich, J. D., Naeser, C. W., and Cebula, G. T.,1981, Potassium-argon and fission-track zircon ages of Cerro To-ledo Rhyolite tephra in the Jemez Mountains, New Mexico: U.S.Geological Survey, Professional Paper 1199-D, pp. 37-43.

Jaworski, M. J., 1973, Copper mineralization of the Upper MoyaSandstone, Chupadera mines area, Socorro County, New Mex-ico: Unpublished M.S. thesis, New Mexico Institute of Miningand Technology, Socorro, 102 pp.

Kelley, V. C., 1982, Albuquerque, its mountains, valley, water, andvolcanoes, 3rd edition: New Mexico Bureau of Mines and MineralResources, Scenic Trip 9, 106 pp.

*Kuellmer, F. J., editor, 1963, Socorro region: New Mexico Geolog-ical Society, Guidebook to 14th Field Conference, 240 pp.

*Lasky, S. G., 1932, The ore deposits of Socorro County, NewMexico: New Mexico Bureau of Mines and Mineral Resources,Bulletin 8, 139 pp.

Lucas, S. G., 1983, The Baca Formation and the Eocene-Oligoceneboundary in New Mexico: New Mexico Geological Society,Guidebook to 34th Field Conference, pp. 187-192.

Lucas, S. G., Wolberg, D. L., Hunt, Adrian, and Schoch, R. M.,1982, A middle Eocene titanothere from the Baca Formation,south-central New Mexico: Journal of Paleontology, v. 56, pp.542-545.

Machette, M. N., 1978, Preliminary geologic map of the Socorro1° x 2° quadrangle, central New Mexico: U.S. Geological Survey,Open-file Report 78-607, scale 1:250,000.

Machette, M. N., 1982, Quaternary and Pliocene faults in the LaJencia and southern part of Albuquerque-Belen Basins, NewMexico-evidence of fault history from fault-scarp morphologyand Quaternary geology: New Mexico Geological Society, Guide-book to 33rd Field Conference, pp. 161-169.

Machette, M. N., 1986, History of Quaternary offset and paleo-seismicity along the La Jencia fault, central Rio Grande rift, NewMexico: Bulletin of the Seismological Society of America, v. 76,no. 1, pp. 259-272.

McIntosh, W. C., Sutter, J. F., Chapin, C. E., Osburn, G. R., andRatte, J. C., 1986, A stratigraphic framework for the eastern Mo-gollon-Datil volcanic field based on paleomagnetism and high-precision 90ArP9Ar dating of ignimbrites; a progress report: NewMexico Geological Society, Guidebook to 37th Field Conference,pp. 183-195.

McKee, J. D., and Wilson, S., 1975, Leave the back of garage andturn left: New Mexico Architecture, v. 17, no. 6, pp. 11-19.

McLemore, V. T., 1983, Uranium in the Socorro area, New Mexico:New Mexico Geological Society, Guidebook to 34th Field Con-ference, pp. 227-233.

McLemore, V. T., 1987, Geology and regional implications of car-

4

45

bonatites in the Lemitar Mountains, central New Mexico: Journalof Geology, v. 95, pp. 255-270.

Neal, J. T., Smith, R. E., and Jones, B. F., 1983, Pleistocene LakeTrinity, an evaporite basin in the northern Jornada del Muerto,New Mexico: New Mexico Geological Society, Guidebook to 34thField Conference, pp. 285-290.

*Nieman, C. L., 1972, Spanish times and boom times-toward anarchitectural history of Socorro, New Mexico: Socorro CountyHistorical Society, Inc., v. 6, 100 pp.

North, R. M., 1983, History and geology of the precious metaloccurrences in Socorro County, New Mexico: New Mexico Geo-logical Society, Guidebook to 34th Field Conference, pp. 261-268.

North, R. M., and McLemore, V. T., 1986, Silver and gold occur-rences in New Mexico: New Mexico Bureau of Mines and MineralResources, Resource Map 15, 32 pp., scale 1:1,000,000.

Osburn, G. R., compiler, 1984, Socorro County geologic map: NewMexico Bureau of Mines and Mineral Resources, Open-file Re-port 238, 14 pp., 1 map, scale 1:200,000.

Osburn, G. R., and Chapin, C. E., 1983a, Nomenclature for Ce-nozoic rocks of northeast Mogollon-Datil volcanic field, NewMexico: New Mexico Bureau of Mines and Mineral Resources,Stratigraphic Chart 1, 7 pp., scale 1:1,000,000.

Osburn, G. R., and Chapin, C. E., 1983b, Ash-flow tuffs and caul-drons in the northeast Mogollon-Datil volcanic field-a sum-mary: New Mexico Geological Society, Guidebook to 34th FieldConference, pp. 197-204.

Osburn, G. R., and Lochman-Balk, C., 1983, Stratigraphic nomen-clature chart: New Mexico Geological Society, Guidebook to 34thField Conference, p. 98.

Osburn, J. C., 1983, Coal resources of Socorro County, New Mexico:New Mexico Geological Society, Guidebook to 34th Field Con-ference, pp. 223-226.

*Patterson, S. H., and Holmes, R. W., 1965, Clays; in Mineral andwater resources of New Mexico: New Mexico Bureau of Minesand Mineral Resources, Bulletin 87, pp. 312-322.

Pearce, T. M., 1965, New Mexico place names, a geographical dic-tionary: University of New Mexico Press, Albuquerque, 187 pp.Sanford, A. R., 1978, Characteristics of Rio Grande rift in vicinityof Socorro, New Mexico, from geophysical studies; in Hawley,J. W. (compiler), Guidebook to Rio Grande rift in New Mexicoand Colorado: New Mexico Bureau of Mines and Mineral Re-sources, Circular 163, pp. 116-121.Sanford, A. R., 1983, Magma bodies in the Rio Grande rift in central

New Mexico: New Mexico Geological Society, Guidebook to 34thField Conference, pp. 123-125.

Sanford, A. R., Budding, A. J., Hoffman, J. P., Alptekin, 0. S.,Rush, C. A., and Topozada, T. R., 1972, Seismicity of the RioGrande rift in New Mexico: New Mexico Bureau of Mines andMineral Resources, Circular 120, 19 pp.

Simmons, M., 1983, The refounding of Socorro, 1816: New MexicoGeological Society, Guidebook to 34th Field Conference, pp. 83-84.

Smith, C. T., Osburn, G. R., Chapin, C. E., Hawley, J. W., Osburn,J. C., Anderson, 0. J., Rosen, S. D., Eggleston, T. L., and Cather,S. M., 1983, First day road log from Socorro to Mesa del Yeso,Joyita Hills, Johnson Hill, Cerros de Amado, Lomas [sic] de lasCarias, Jornado [sic] del Muerto, Carthage, and return to Socorro:New Mexico Geological Society, Guidebook to 34th Field Con-ference, pp. 1-28.

Talmage, S. B., and Wootton, T. P., 1937, The non-metallic mineralresources of New Mexico and their economic features (exclusiveof fuels): New Mexico Bureau of Mines and Mineral Resources,Bulletin 12, 159 pp.

Thompson, M. L., 1942, Pennsylvanian system in New Mexico:New Mexico Bureau of Mines and Mineral Resources, Bulletin17, 90 pp.

Weber, R. H., and Austin, G. S., 1982, Perlite in New Mexico; inAustin, G. S. (compiler), Industrial rocks and minerals of theSouthwest: New Mexico Bureau of Mines and Mineral Resources,Circular 182, pp. 97-101.

Weber, R. H., and Willard, M. E., 1963, Road log C, Socorro west-ward to Catron County line via U.S. 60: New Mexico GeologicalSociety, Guidebook to 14th Field Conference, pp. 20-25.

Weir, J. E., Jr., 1965, Geology and availability of ground water inthe northern part of the White Sands Missile Range and vicinity,New Mexico: U.S. Geological Survey, Water-Supply Paper 1801,78 pp.

Wilpolt, R. H., and Wanek, A. A., 1951, Geology of the regionfrom Socorro and San Antonio east to Chupadera Mesa, SocorroCounty, New Mexico: U.S. Geological Survey, Oil and Gas In-vestigations Map OM-121, scale 1:63,360.

Wilson, S., and Bieberman, R. A., 1983, The Civil War in NewMexico-tall tales and true: New Mexico Geological Society,Guidebook to 34th Field Conference, pp. 85-87.

vFSvwrofBtasC27eMa3

foot(ottvb

Clay mineralogy of selected sedimentary andvolcanic rocks, Socorro County, New Mexico

by Mark R. Bowie and Virginia T. McLemoreNew Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801

AbstractOriented slide semi-quantitative x-ray diffraction (XRD) analyses of the <2 micron-size fraction

of selected sedimentary rocks from Socorro County, New Mexico, were undertaken to examinetemporal and lateral trends in their clay mineralogy and to ascertain whether variations in detritalclay mineral deposition or diagenetic processes are responsible for sharp color differences betweenbeds and within individual beds of the same rock units. Claystones from the playa fades of thePopotosa Formation (Miocene) southwest of Socorro consist dominantly of either illite or dioctahedralsodium smectite (montmorillonite). Variations in clay mineralogy are reflected in color differencesof the rock. The observed clay mineralogy may be the product of potassium metasomatism of detritalclay minerals.

The D-Cross Tongue of the Mancos Shale (Cretaceous) near Carthage is illitic, with lesser mixed-layer illite/smectite (I/S) and kaolinite. Also near Carthage, white kaolinitic claystones previouslyassigned to the base of the Cretaceous Dakota Sandstone may represent a zone of weathering atthe top of the Chinle Formation (Triassic). Varicolored Chinle claystones immediately underlyingthe Dakota are also kaolinitic but grade downward into mostly I/S and illite-bearing purple and grayclaystones. Different-colored sandy claystones of the Torres Limestone Member of the Yeso Formation(Permian) in the Loma de las Calias are uniformly illitic with lesser, subequal amounts of chloriteand kaolinite. Varicolored claystones and sandstones of the Abo Formation (Permian) in the Lomade las Cafias and east of Bingham consistently contain subequal amounts of illite and chlorite.Carbonaceous claystones of the Sandia Formation (Pennsylvanian) at the Houlett fireclay depositin the Loma de las Cafias are uniformly dominantly kaolinite with subordinate I/S and illite. Theconsistency of the clay mineralogy of the Yeso, Abo, and Sandia sediments vertically and throughseveral color variations suggest that most of the clays are detrital and were little affected by diageneticprocesses that changed the original color of the sediments.

Randomly oriented pressed powder XRD analyses of the <2 micron-size fraction of an alteredrhyolite tuff from the Luis Lopez Formation (Oligocene) revealed that it consists dominantly of 1Millite, a polytype which, experimentally, forms at less than 350°C.

IntroductionSedimentary rocks from the Sandia Formation (Pennsyl-

anian), the Abo and Yeso Formations (Permian), the Chinleormation (Triassic), the Dakota Sandstone and Mancoshale (Cretaceous), the Popotosa Formation (Miocene), andolcanic rock from the Luis Lopez Formation (Oligocene)ere sampled in Socorro County, New Mexico, in prepa-

ation for semi-quantitative x-ray diffraction (XRD) analysesf the <2 micron-size fraction (Fig. 1). Altered rhyolite ash-low tuff from the Luis Lopez Formation was collected inlue Canyon near the base of Socorro Peak. Claystones in

he Popotosa Formation were sampled in roadcuts and inpit along US-60 southwest of Socorro. Claystones, silt-

tones, and sandstones from the Sandia, Abo, Yeso, andhinle Formations were sampled along the traverses of Tripsb, 2c, and 3 (this volume) in the Loma de las Cafias aboutmi east of Socorro and in roadcuts along US-380 from just

ast of Bingham to about 7 mi east of San Antonio. Theancos Shale was sampled in a roadcut on the Fite Ranch

bout 0.5 mi south of US-380 near Stop 2-5 of Trip 2c (p.6).The purpose of the semi-quantitative analyses is several-

old: 1) to supplement the rock descriptions in the roadlogsf this guidebook, 2) to identify the clay mineral assemblagef the <2 micron-size fraction of the rocks and to determinehe relative abundances of the major clay mineral groupsillite, smectite, mixed-layer clay minerals, chlorite, and ka-lin) present, 3) to examine vertical and lateral trends inhe clay mineralogy of the rock units, and 4) to ascertainhe origin of sharp, distinct color differences (notably redersus green or gray) between beds and within individualeds of the rock units. Are the color variations controlled

by differences in clay mineralogy? Are they the result of theinfluence of local oxidizing or reducing conditions duringdeposition of the sediments? Are they a product of diagen-esis?

Previous studiesVery few investigations have assessed clay resources in

New Mexico. Talmage and Wootton (1937) briefly describedclay occurrences, production, and commercial uses in thestate. Patterson and Holmes (1965) updated this earlier re-port. An unpublished manuscript by Van Sandt (1964) pro-vides descriptions of refractory clay occurrences in Arizonaand New Mexico; several are in the Socorro and Carthageareas. Van Sandt also tested physical and chemical prop-erties of the clays to evaluate their refractory qualities.

Burlbaw and Siemers (unpubl. report 1975), Cappa (un-publ. report 1975), and Domski (unpubl. report 1987) per-formed semi-quantitative XRD analyses of the major claymineral groups in selected Pennsylvanian, Permian, andTertiary rocks in Socorro County and surrounding areas.Brenner-Tourtelot and Machette (1979) and Asher-Bolinder(1982) analyzed the mineralogy of claystones and alteredair-fall tuffs in the Popotosa Formation by XRD and chem-ical methods. The data generated by the above workerscomplement data presented in this paper.

Historical production and utilizationIn New Mexico, clay deposits have been used since pre-

historic times by Native Americans for making pottery and

46

48

building homes. Native Americans were making crude adobebricks when the Spanish first entered the region. Most ofthe clay material was extracted from alluvial deposits alongmajor rivers and arroyos. Even today, many New Mexicansuse local clay material to produce adobe brick. Numeroushomes and buildings in Socorro County, including the his-toric San Miguel Church at Socorro (see fig. 2 on p. 7), arebuilt of adobe (Conron, 1980). Adobe construction remainsa very popular form of architecture because it is aestheticallypleasing, inexpensive, and a good insulator. Adobe brickmaking and adobe construction in New Mexico are dis-cussed by Smith (1982). Clay minerals, most commonly il-lite-group clays and kaolinite, are the chief binders in adobebrick.

In the late 1800's and early 1900's, common brick and firebrick were manufactured by the Socorro Fire Clay Works.Common brick was produced from a mixture of local alluvialclay material and fireclay. Fire brick was made from fireclayobtained from several localities in Socorro County (the fol-lowing letters are keyed to Fig. 1): A) Sandia Formation,southern Lemitar Mountains 10 mi northwest of Socorro,B) Sandia Formation, near the head of Arroyo de la Presilla6 mi east of Socorro, C) Popotosa Formation, Socorro Moun-tains immediately west and southwest of Socorro, D) LuisLopez Formation, Socorro Mountains, and E) Cretaceousunits, Carthage coal field (Talmage and Wootton, 1937; VanSandt, 1964). Exact production statistics are not known al-though the brick industry was an important contributor toSocorro's economy around the turn of the century. Firebrick was used under boilers in several smelters in theSouthwest, including the Billing smelter in Socorro (Tal-mage and Wootton, 1937). Common brick was later usedin many buildings in Socorro.

A small roofing-tile plant in San Antonio operated inter-mittently during the early 1900's. The three-man operationused local adobe material and sometimes clay from Car-thage to make the tiles. Some Carthage clay was also shippedto Albuquerque by the New Mexico Clay Products Com-pany who experimented with admixtures of Carthage andAlbuquerque clays in the manufacture of brick and tile (Tal-mage and Wootton, 1937).

Experimental procedureFresh select grab samples of a particular zone in outcrop

or channel samples of a vertical interval of outcrop werecollected for this study. In particular, different-colored bedswithin the rock units were sampled to determine if the colorvariations are due to variations in clay mineralogy or dep-ositional or diagenetic processes.

Oriented (sedimented) clay slides were prepared for XRDanalyses by immersing the samples in distilled water in abeaker and allowing the coarse material to settle, leaving aresidual <2 micron-size fraction at the top of the suspen-sion. An eye dropper was then touched to the surface ofthe suspension, and the drawn sample was transferred toa petrographic slide where it was allowed to dry at roomtemperature. Samples that did not disperse after severalcycles of immersion and mixing in distilled water were wetground in a mortar and pestle, and if they remained floc-culated, they were treated with a few drops of ammoniumhydroxide (NI-140H) and remixed. All samples dispersedbefore or during this stage of preparation.

A Rigaku Geigerflex diffraction unit with Ni-filtered CuKa,( =1.5418 A) radiation was used for the XRD analyses. FiveXRD traces (scans) were run on each slide using the samemachine settings. Initially, the oriented, untreated slideswere continuously scanned at 2° 20/min between 2° 20 and38° 20. When both kaolinite and chlorite were present in asample, a scan from 24° 20 to 26°/20 was run at a slowerscan speed to help distinguish between the 002 kaolinite

reflection at 24.9° 20 and the 004 chlorite reflection at 25.1°20.

All slides were then placed in an ethylene glycol chamberfor 24 hours. Glycolation caused expansion of smectite andinterstratified smectite layers within mixed-layer clay min-erals and shifts in reflection positions of the untreated, ori-ented slide traces, which aided in their identification. Theglycolated slides were continuously scanned with the dif-fractometer between 2° 20 and 15° 20. The same slides werethen heated at 375-380°C for 30 minutes in a Blue M Lab-Heat Muffle Furnace. They were scanned with the diffrac-tometer between 7.5° 20 and 9.5° 20, then between 2° 20and 15° 20 immediately after removal from the furnace sothat the scan passed over the 10-A peak while the slide wasstill hot. The scan between 2° 20 and 15° 20 was used todemarcate background scatter on the diffractograms and,subsequently, to determine the relative intensity of the 10Apeak. Any enhancement of the 10-A peak by heating wasattributed to the collapse of interstratified smectite layerswithin illite/smectite mixed-layer minerals (Austin andLeininger, 1976).

The semi-quantitative XRD analyses were performed us-ing equations developed by G. S. Austin (written comm.1987; Table 1) to determine the relative abundance of themajor clay mineral groups. This method is based on theheights of 001 peaks above background and quantifies themajor clay mineral groups to parts in 10.

A <2 micron-size fraction of altered rhyolite tuff from theLuis Lopez Formation was analyzed by randomly orientedpowder XRD using a Phillips Norelco diffraction unit withNi-filtered CuKa, radiation at 40 kv and 20 ma from 3° to65° 20, a vertical goniometer, a graphite crystal mono-chrometer, and receiving and scattering slits of 1/2° and 4°,respectively.

49

Clay mineralogy of the rock unitsLuis Lopez Formation

The Luis Lopez Formation consists of intermediate tomafic lavas and flows and volcaniclastic sedimentary rocksemplaced as moat-fill in the Socorro cauldron (Chamberlin,1980; Osburn et al., 1981; Eggleston, 1982; Osburn andChapin, 1983). An altered rhyolite ash-flow tuff of the LuisLopez was sampled from a clay pit in sec. 16, T3S, R1W inBlue Canyon on the eastern flank of the Socorro Mountains(Fig. 1; Trip 1, Stop 1-1, p. 19). Clay (altered tuff) from thispit was previously described as kaolinitic (Talmage andWootton, 1937, p. 69), but recent randomly oriented pressedpowder XRD analyses by G. S. Austin and J. L. Post (writtencomm. 1987) of the <2 micron-size fraction of the tuff revealthat it consists dominantly of 1M illite (Fig. 2), a polytypewhich, experimentally, forms at temperatures less than 350°C(Yoder and Eugster, 1955; Austin et al., 1987).

The sampled tuff lies within a large zone in which Oli-gocene and early Miocene volcanic and sedimentary rockshave been pervasively altered by potassium metasomatism(D'Andrea-Dinkelman et al., 1983; Chapin and Lindley, 1986).Within this zone, volcanic rocks commonly contain 5-11%K20. Unaltered tuffs outside the zone average less than 5%K20. Chemical analyses of the illite in the clay pit in BlueCanyon by J. L. Post (written comm. 1987) indicate that itcontains about 8% K20. Whole rock x-ray fluorescence anal-yses by the authors of the same illitized tuff indicate thatit contains about 4-5% K20 (Table 2).

The large zone of potassium metasomatism has beeninterpreted both as a fossil geothermal system (D'Andrea-

TABLE 2-Whole rock x-ray fluorescence analyses of two samplesof altered rhyolite ash-flow tuff from the Luis Lopez Formationin a clay pit, sec. 16, T3S, R1W, Blue Canyon, SocorroMountains. -, analyzed for but not found. Sample numbers referto locations on Fig. 1.

Oxide Sample MI Sample M2

Si02 69.2 68.7

Al203 14.6 15.2Fe203 (total Fe) 2.29 2.42MnO 0.03 0.02TiO2 0.15 0.15MgO 2.09 1.79CaO 1.52 1.03Na20 1.42 1.47K20 4.36 5.04P20,LOI 5.00 4.68

Total 100.66 100.50

Dinkelman et al., 1983) and, alternatively, as a zone of di-agenetic alteration by alkaline solutions descending into theburied Oligocene and early Miocene volcanic and sedimen-tary section from an alkaline, saline-lake system of the Po-potosa (Miocene) Basin (Chapin and Lindley, 1986). Thislatter low-temperature alteration is analogous to diageneticreactions in alkaline saline-lake environments common toTertiary basins of the Basin and Range Province (Hay, 1966,1978; Sheppard and Gude, 1968; Surdam and Sheppard,1978). The abundance of the relatively low-temperature 1Millite polytype in the altered tuff in Blue Canyon lends sup-port to the low-temperature alkaline solutions theory.

Popotosa FormationThe Popotosa Formation represents early basin fill of the

Rio Grande rift and consists of intertonguing fanglomer-ates, alluvium, and playa deposits (Denny, 1940; Bruning,1973; Chapin and Seager, 1975; Brenner-Tourtelot andMachette, 1979; Asher-Bolinder, 1982). A nearly continuous100-ft section of the playa facies is exposed in two roadcutsand a clay pit (see fig. 13 on p. 20) sampled along US-60southwest of Socorro (Fig. 1). The clay pit sediments arethe lowest stratigraphically, and the samples from the northside of the highway are the highest stratigraphically in thissection. The results of the semi-quantitative XRD analysesof the Popotosa and the other sedimentary units in thisstudy are in Table 3. The variegated green claystones of thepit contain dominantly illite and mixed-layer illite/smectite(I/S). The claystone from the middle of the pit face (sample27) consists wholly of I/S and illite. The claystone from thetop of the face (sample 6) is dominantly illite with minor 1/S and chlorite. Sample 1, a select grab sample of greenclaystone, contains mostly illite and US with minor chloriteand dioctahedral sodium smectite (montmorillonite). Ka-olinite was not found in the pit.

Brown and gray variegated, gypsiferous claystones fromthe playa facies on the south side of US-60 (Trip 1, mile11.4 on p. 20) have different clay mineral suites from oneanother. Both are dominantly illitic, but the brown samplecontains more I/S and kaolinite than the gray sample, whichcontains more dioctahedral sodium smectite (montmoril-lonite) and chlorite.

Five samples from a 60-ft exposure of the playa facies onthe north side of US-60 (Fig. 3; Trip 1, mile 9.8 on p. 20)have a generally uniform clay mineral suite. Except sample31, the samples are dominantly dioctahedral sodium smec-tite (montmorillonite) with little or no illite, I/S, chlorite,and kaolinite. Sample 31, a red claystone between gypsi-ferous siltstone beds, is mostly dioctahedral sodium smec-

50

TABLE 3—Results of semi-quantitative XRD analyses of the <2 micron-size fraction of sedimentary rocks from Socorro County. Dataare in parts in 10 and were calculated using the equations in Table 1. In general, samples are listed, from top to bottom, in descendingstratigraphic order at each outcrop. I, illite; NaSm, sodium smectite; I/Sm, mixed-layer illite/smectite; C, chlorite; K, kaolinite; gyp,gypsiferous; sltst, siltstone. Sampling procedure described in text. Sample numbers refer to locations on Fig. 1.

Sample Formation Location

1 Popotosa 36 T3S R2W(clay pit)

6 Popotosa 36 T3S R2W(clay pit)

27 Popotosa 36 T3S R2W(clay pit)

2 Popotosa 31 T3S R1W(S side US-60)

3 Popotosa 31 T3S R1W(S side US-60)

29 Popotosa 33 T3S R1W 2E(N side US-60)

31 Popotosa 33 T3S R1W 5E(N side US-60)

28 Popotosa 33 T3S R1W 3E(N side US-60)

23 Popotosa 33 T3S R1W 4E(N side US-60)

30 Popotosa 33 T3S R1W 1W(N side US-60)

5 Mancos 17 T5S R2E(Fite Ranch)

24 Dakota 8 T5S R2E(US-380)

21 Dakota/Chinle 8 T5S R2E(US-380)

15 Chinle 8 T5S R2E(US-380)

17 Chinle 8 T5S R2E(US-380)

18 Chinle 8 T5S R2E(US-380)

14 Chinle 8 T5S R2E(US-380)

20 Chinle 8 T5S R2E(US-380)

22 Yeso 19 T3S R2E(Loma de las Carias)

12 Yeso 19 T3S R2E(Loma de las Canas)

13 Yeso 19 T3S R2E(Loma de las Canas)

4 Abo 23 T2S R1E(Loma de las Cafias)

7 Abo 23 T2S R1E(Loma de las Cafias)

26 Abo 23 T2S R1E(Loma de las Canas)

11 Abo 31 T2S R2E(Loma de las Canas)

16 Abo 31 T2S R2E(Loma de las Canas)

25 Abo 31 T2S R2E(Loma de las Canas)

8 Abo 8 T5S R6E(US-380)

9 Abo 8 T5S R6E(US-380)

10 Abo 8 T5S R6E(US-380)

19 Abo 8 T5S R6E(US-380)

44 Sandia 2 T3S R1E(Houlett deposit)

43 Sandia 2 T3S R1E(Houlett deposit)

42 Sandia 2 T3S R1E(Houlett deposit)

41 Sandia 2 T3S R1E(Houlett deposit)

Sample description

green, select

green, select, top

green, select, midwall

red, select, lower gyp sltst bed

red, channel, between sltst beds

red, channel, upper gyp sltst bed

green, select, between gyp sltst beds

red, channel, below gyp sltst beds

brown, select

white, clayey zone, channel

white, clayey zone and top of Chinle, channel

green, select, 1 ft below white, clayey zone

purple, channel, 5 ft below white, clayey zone

purple, channel, 30 ft below white, clayey zone

gray, select, 35 ft below white, clayey zone

purple, select, 40 ft below white, clayey zone

green, channel

red, select

white, channel

red, select

gray, select

red, channel

gray and minor red, select

red and minor gray, select

red, channel

green, select

red, select

brown, channel

red, channel

brown, select

dark gray, select, from mine dump

dark gray, select

dark gray, channel

I NaSm I/Sm C K5

7

4

1

0

0

3

1

6

2

1

0

0

0

0

4 1 3 1 3

4 3 0 2 1

0 10 0 0 0

1 3 3 0 2

1 9 0 0 2

1 9 0 0 1

1 5 1 1 1

5 1 2 1 2

1 0 1 0 7

1 2 3 0 3

1 0 8 0 1

1 2 1 1 5

3 1 6 0 0

3 1 2 2 1

2 0 7 0 0

5 1 1 2 1

4 0 1 3 2

4 1 0 3 3

3 0 1 3 3

3 0 1 3 4

2 0 1 2 6

3 1 0 4 2

3 0 1 3 2

3 0 1 3 3

3 0 2 3 1

3 0 2 3 2

4 0 2 3 1

4 0 3 2 1

1 1 2 0 6

2 0 3 0 5

2 0 2 0 6

2 0 3 0 5

brown, select

gray, select

51

FIGURE 3—Looking northwest from US-60 at exposure of the playafades of the Popotosa Formation at the base of the Socorro Moun-tains.tite, US, and kaolinite with lesser illite. The green claystone(sample 23) has a clay mineral assemblage that is very sim-ilar to the red claystones from this outcrop.

Generally, there is little variation vertically in the claymineralogy within each outcrop, but there is a significantdifference between the clay mineralogy of the red claystonesand siltstones in the exposure on the north side of US-60and that of the green, brown, and gray claystones in theexposures on the south side of US-60 and in the clay pit.The samples from the north side of the highway are dom-inantly smectitic (sodium montmorillonite) and contain lit-tle illite, whereas samples from the other two exposures areillitic and 1/S-bearing but generally contain little smectite(Table 3).

The color of the claystones, therefore, seems to be areflection of the clay mineralogy. But why does the claymineralogy differ between the three outcrops? Several ex-planations are possible, based on whether the observed claymineral assemblages are detrital, authigenic, or both. It isdifficult to discern from semi-quantitative analyses whetherthe clays are detrital or authigenic. A scanning electron mi-croscopy study of the morphological characteristics andspatial and paragenetic relationships of the clays wouldhelp resolve this problem.

If the clays are detrital, their varying abundance betweenthe outcrops may be the result of variable detrital inputfrom lithologically different source areas surrounding theplaya. Picard and High (1972) examined the clay mineralsuite of 40 mostly Recent lakes and found that lacustrincdeposits are characterized by diverse clay mineral assem-blages that reflect source materials and climate. These de-posits are generally dominated by illite, smectite, and US.Droste (1961a) studied the clay mineralogy of sediments in45 playas of the Mojave Desert. He found illite and mont-morillonite in each playa and determined that they com-posed at least 70% of the clay minerals present. Chloriteand kaolinite were in the sediments of less than half of theplayas and accounted for generally less than 30% of the clayminerals present. The clay mineralogy of desert saline sed-iments in southern California is controlled almost entirelyby the composition of the source rocks surrounding thebasins and there is little evidence that any of the clays areunstable in the saline-lake environment (Droste, 1961a, b).

Similarly, the clay mineral assemblage of the Popotosaplaya facies may be detrital, unaltered, and a reflection ofthe composition of the surrounding source rocks. However,these clays may be, in part, authigenic. If they were notaltered in the playa proper, they may have been alteredafter burial by continued exposure to potassium metaso-matic alkaline and saline solutions percolating downwardinto the subsurface from a younger playa.

Domski (unpubl. report 1987) performed semi-quantita-

tive XRD analyses of the <2 micron-size fraction of Popo-tosa early basin fanglomerate and immediately overlyingplaya sediments. His playa samples were collected from thesame exposures where we collected ours. The two fanglom-erate samples both consist wholly of illite (seven parts in10) and L'S (three parts in 10). The illite content progres-sively decreases upsection from the fanglomerate samplesthrough the playa samples until dioctahedral sodium smec-tite (montmorillonite) becomes the dominant species. Thistrend is also apparent from our analyses (Table 3). The highillite content of the fanglomerate may indicate an initiallyhigh detrital illite influx. In contrast, it may be the result ofillitization of smectite by potassium metasomatizing fluids.Domski (unpubl. report 1987) found that the amount ofUS is constant through the sampled vertical interval. Henoted that the I/S is randomly interstratified and that theamount of illite in it decreases with depth, from about 20%in the uppermost playa samples, to about 50% in the playasamples nearest the contact with the underlying fanglom-crate, to about 90% in the fanglomerate samples. This trendis, most likely, the result of increasing illitization of smectitewith depth by potassium metasomatizing fluids percolatingdownward through the subsurface, and is probably not aresponse to varying detrital influx over time.

Mancos Shale

The D-Cross Tongue of the Mancos Shale (Cretaceous) isa transgressive marine shale sequence that is up to 300 ftthick in the Carthage area (Hook, 1983). A brown, silty shalein the D-Cross was sampled in a roadcut on the Fite Ranch(Fig. 1; Trip 2c, between miles 5.45 and 5.55 on p. 36; fig.1-64.4 of Smith et al., 1983). It consists mostly of illite withlesser, subequal amounts of US, kaolinite, dioctahedral so-diu smectite (montmorillonite), and chlorite (Table 3).

Chinle FormationIn the Carthage area, the Chinle Formation (Triassic) con-

sists dominantly of nonmarine claystone with thin, discon-tinuous sandstone, siltstone, and conglomerate interbeds.No single unit is traceable for more than several tens of feet(Smith, 1983). The upper 463 ft is dominated by reddish-brown and gray-red claystones with thin intraformationalconglomerates and sandstones (Hunt and Lucas, 1987). Avertical interval from a white, clayey zone at the base ofthe unconformably overlying Dakota Sandstone (Creta-ceous) to about 40 ft below the Chinle-Dakota contact wassampled in a roadcut along US-380 about 2 mi west ofCarthage (Fig. 1; Trip 2c, mile 4.1 and fig. 25 on p. 36).

The white, clayey zone was previously assigned to thebase of the Dakota but may, alternatively, represent Mor-rison-like beds (Jurassic) or a weathering zone at the topof the Triassic (Smith, 1983). It consists dominantly of ka-olinite with minor illite and US (Table 3). A channel sampleof claystone (sample 21) from the base of the white, clayeyzone 2 ft into the top of the Chinle is mostly kaolinite andL'S with lesser dioctahedral sodium smectite (montmoril-lonite) and illite. A select grab sample of green claystone(sample 15) 1 ft below the white, clayey zone is dominantlyL'S, similar to the purple claystones (samples 18, 20) down-section. A channel of silty claystone (sample 17) about 5 ftbelow the white, clayey zone is dominantly kaolinite withminor dioctahedral sodium smectite, illite, US, and chlorite.A channel of purple claystone about 30 ft below the white,clayey zone, and a select grab sample of purple claystoneboth consist dominantly of liS with minor illite. A selectgrab sample of gray claystone (sample 14) consists of sub-equal amounts of illite, US, and chlorite with lesser sodiumsmectite and kaolinite. The widely variable colors of theclaystones may, in part, reflect differences in clay miner-

52

alogy. They may also be attributable to oxidation-reductionprocesses active when meteoric waters, percolating down-ward along fractures and bedding planes, reacted with py-rite or organic acids.

The high I/5 and illite content of the purple and grayclaystones (samples 18, 14, 20) in the Chinle Formation isrepresentative of the terrestrial origin of the unit. The highkaolinite content of the white, clayey zone (samples 24, 21)suggests that it may represent a zone of weathering. Ka-olinite formation is favored in non-marine to near-shore,well-leached environments in the presence of fresh to acidicsolutions. The uppermost Chinle was deposited in a ter-restrial, near-shore environment.

Yeso FormationThe Yeso Formation (Permian) consists of sandstones,

shales, limestones, dolomite, and evaporites representinglittoral and near-shore deposits between underlying con-tinental deposits of the Abo Formation and overlying ma-rine carbonates of the San Andres Formation. In SocorroCounty the Torres Limestone Member of the Yeso Formationconsists of limestone, sandstone, siltstone, claystone, bree-ch), and gypsum (Smith, 1983). Sandy claystone of the TorresMember was sampled in the Loma de las Carias in a roadcutin sec. 19, T3S, R2E (Fig. 1; Trip 2b, mile 20.15 on p. 30).The three claystone samples are white, red, and green (Table3). They are all dominantly illite with lesser chlorite andkaolinite and little or no sodium smectite and 1,'S. The uni-formity of the clay mineralogy vertically and through thecolor variations suggests that the clays are detrital and werelittle affected by the diagenetic processes that induced colorchanges in the sediments, probably reaction of oxygenatedmeteoric waters with local pyrite and organic debris.

Abo Formation

In Socorro County the lower Permian Abo Formation isuniformly very dark reddish brown, fine-grained sand-stones with interbedded claystones, siltstones, and arkoses,and a few coarser-grained channel sandstones in the lowerpart of the section (Smith, 1983). They represent continentalsediments deposited on a gently, southerly sloping alluvialplain. The Abo conformably overlies the near-shoreishelfsediments of the Bursum Formation and grades upwardinto the near-shoredittoral Yeso deposits.

Abo claystone and fine-grained sandstone were sampledin two roadcuts in the Loma de las Carias (Trip 2b, miles7.2 and 10.5 on p. 27) and in a roadcut along US-380 2 mieast of Bingham (Trip 3, mile 37.5 on p. 43; Speer et al.,1983). Gray, green, and brown color hands, which cut acrossprimary sedimentary structures, were selectively sampled(Figs. 1, 4). The Abo rocks consistently contain high, sub-equal amounts of illite and chlorite with little or no sodiumsmectite (Table 3). The kaolinite content varies significantly(between one and six parts in 10), and the US content variesslightly between the outcrops. The clay mineralogy gen-erally changes little vertically within each outcrop, regard-less of the color of the sediments. This uniformity and thelateral consistency of the clay mineralogy between outcropssuggests a detrital origin for much of the clay minerals. Thevariable kaolinite contents are ascribed to locally variabledetrital influx from the source areas. Like the Chinle andYeso sediments in Socorro County, the Abo sediments ap-parently were little affected by diagenetic processes re-sponsible for color changes of the sediments. The gray,green, and brown stringers, transverse to the primary bed-ding, most likely represent conduits for diagenetic fluidsand were variably colored by reduction of pyrite and or-ganic debris.

In studying the clay mineralogy of the Abo in the Sac-ramento Mountains farther south, Cappa (unpubl. report

FIGURE 4—Looking north at claystones and sandstones of the AboFormation along US-380 east of Bingham. Note clay-rich stringerstransverse to primary bedding.

1975) noted lateral variations in kaolinite/illite content ratiosof the sediments. The kaolinite illite ratios decreased towardthe marine basin to the south. Cappa attributes this to ka-olinite being less stable in the near-shore environments thanin the inland environments and/or "degraded" illite trans-ported from the inland environments being "regraded" byuptake of potassium in the near-shore, more saline envi-ronments.

Burlbaw and Siemers (unpubl. report 1975) performedsemi-quantitative XRD analyses of Pennsylvanian and lowerPermian units north of our sample localities, in the JoyitaHills at the southern end of the Los Pinos Mountains, So-corro County. They observed a very uniform clay miner-alogy of Abo claystones vertically and laterally. The averageof the clay mineral assemblages of the claystones in thisarea is three parts in 10 illite, two parts in 10 US, four partsin 10 chlorite, and two parts in 10 kaolinite, with no smec-tite. These values are strikingly similar to our results (Table3).

Burlbaw and Siemers (unpubl. report 1975) noted thatthe first appearance of chlorite in the regressive sequence

from the marine Pennsylvanian Sandia and Madera For-mations to the lower Permian Bursum (transitional) andAbo (continental) Formations is in the Abo, and, conse-quently, can be a useful stratigraphic indicator. Chloriteformation and preservation is favored by mild leaching con-ditions and an abundance of magnesium (Grim, 1968; Keller,1970). The high chlorite content of the Aho here suggeststhat it was deposited in a semiarid, foreshore environment.

Sandia FormationIn Socorro County, the Sandia Formation (Pennsylvanian)

consists of a basal conglomerate with chert boulders in aquartz-arenite matrix overlain by interbedded siltstones,quartz arenites, thin-bedded carbonaceous claystones, andthin limestones (Smith, 1983). These sediments were de-posited in marine, near-shore/shelf environments. Thelimestones contain a diverse fauna of brachiopods, crinoids,corals, and gastropods. Dark-gray and brown carbonaceousclaystones were sampled in the Loma de las Carias at theHoulett fireclay deposit (see discussion for Trip 2b, mile17.5 on p. 29; Van Sandt, 1964), which was exploited in thelate 1800's by the Socorro Fire Clay Works for brick making(Figs.. 1, 5). The clay mineralogy is uniformly dominantlykaolinite with lesser IiS and illite, regardless of the color ofthe sediments (Table 3). Little sodium smectite and no chloriteare present. The consistency of the clay mineralogy verticallyand through the color variations suggests that the clays aremostly detrital and were not significantly affected

FIGURE 5—Dark-colored, carbonaceous claystones of the SandiaFormation at the Houlett fireclay deposit in the Loma de las Canas.

by diagenetic solutions responsible for color changes in thesediments.

Burlbaw and Siemers (unpubl. report 1975) analyzed dark-gray to black carbonaceous shales of the Sandia in the JoyitaHills by semi-quantitative XRD and found that they consistevenly of L'S and illite vertically and laterally. No kaolinite,smectite, or chlorite was found. The Sandia sediments inthe Joyita Hills were deposited shoreward of those in theLoma de las Callas. Apparently, for reasons not known, thedepositional conditions favored the deposition and pres-ervation of illite nearer the shore and kaolinite basinward.

ConclusionsThe primary conclusions reached from the semi-quanti-

tative XRD analyses of the <2 micron-size fraction of theselected sedimentary rocks in Socorro County are:

1) Claystones from the playa fades of the PopotosaFormation (Miocene) southwest of Socorro consistdominantly of either illite or dioctahedral sodiumsmectite (montmorillonite). Variations in the ob-served clay mineralogy are reflected in color differ-ences of the rock. After burial, the original clay mineralassemblage may have been potassium metasornatizedby alkaline solutions descending into the subsurfacefrom a younger playa.

2) The D-Cross Tongue of the Mancos Shale (Cre-taceous) near Carthage is dominantly illite, with lesserVS and kaolinite.

3) Near Carthage, white kaolinitic claystones pre-viously assigned to the base of the Dakota Sandstone(Cretaceous) may represent a weathering zone at thetop of the Chink Formation (Triassic). VaricoloredChink claystones immediately underlying the Dakotaare also kaolinitic, but they grade downsection intodominantly IIS and illite-bearing purple and gray clay-stones. The variable colors of the claystones may, inpart, reflect differences in clay mineralogy, but wereformed, most likely, by oxidation-reduction processesactive when meteoric waters, descending along frac-tures and bedding planes, reacted with pyrite ancLororganic acids.

4) Sandy claystones in the Torres Limestone Mem-ber of the Yeso Formation (Permian) in the Loma delas Canas are illite with lesser, subequal amounts ofchlorite and kaolinite. The clay mineralogy is uniformthrough color variations of green to red to white.

5) Claystones and fine-grained sandstones of theAbo Formation (Permian) in the Loma de las Canas

53

and along US-380 east of Bingham uniformly consistof subequal amounts of illite and chlorite, regardlessof the color of the sediments. Gray, green, and brownstringers, which cut across primary sedimentarystructures, have clay mineral assemblages similar tothe host sediments.

6) Bark-gray and brown carbonaceous claystonesof the Sandia Formation (Pennsylvanian) at the Hou-lett fireclay deposit in the Loma de las Canas are uni-formly mostly kaolinite with lesser US and illite.

7) The consistency of the clay mineralogy of theYeso, Abu, and Sandia sediments vertically and throughwide-ranging color variations suggests that most ofthe clays are detrital and were not significantly af-fected by diagenetic processes that changed the orig-inal color of the sediments.

AcknowledgmentsWe wish to thank the New Mexico Bureau of Mines and

Mineral Resources, in particular, Drs. Frank Kottlowski,Director, and George Austin, Deputy Director, for sup-porting this work. Kent Cadey prepared oriented slide sam-ples for x-ray analyses. George Austin ran the randomlyoriented pressed powder XRD analyses of the tuff from theLuis Lopez Formation. Chris McKee, NMBMMR x-ray lab-oratory, ran the Socorro Mountain samples on the x-rayfluorescence.

ReferencesAsher-Bolinder, S., 1982, Lithium-rich tuffs in the Popotosa For-

mation, New Mexico; in Austin, G. S., compiler, Industrial rocksand minerals of the Southwest: New Mexico Bureau of Minesand Mineral Resources, Circular 182, pp. 73-76.

Austin, G. S., Glass, H. U., and Hughes, R. E., 1987, Determinationof polytype structure of some "1Md" illitic clays; in preparation.

Austin, G S., and Leininger, R. K., 1976, Effects of heat-treatingmixed-layer illite-smectite as related to quantitative clay mineraldeterminations: Journal of Sedimentary Petrology, v. 46, pp. 206-2 1 5 .

Brenner-Tourtelot, E. F., and Machette, M. N., 1979, The miner-alogy and geochemistry of lithium in the Popotosa Formation.Socorro County, New Mexico: U.S. Geological Survey, Open-fileReport 79-839, 23 pp.

Bruning, J. E., 1973, Origin of the Popotosa Formation, north-central Socorro County, New Mexico: Unpublished Ph.D. dis-sertation, New Mexico Institute of Mining and Technology, So-corro, 132 pp.; New Mexico Bureau of Mines and MineralResources, Open-file Report 38, 142 pp.

burlbaw, J., and Siemers, T., 1975, Clay mineralogy of Pennsyl-vanian and lower Permian beds, Joyita bills, Socorro County,New Mexico, unpublished report.

Cappa, J. A., 1975, Clay mineral assemblage variations in the lowerPermian sedimentary rocks of the Sacramento Mountains, NewMexico, unpublished report.

Chamberlin, R. M., 1980, Cenozoic stratigraphy and structure of

the Socorro Peak volcanic center, central New Mexico: Unpub-lished Ph.D. dissertation, Colorado School of Mines, Golden,495 pp.; New Mexico Bureau of Mines and Mineral Resources,Open-file Report 118, 532 pp.

Chapin, C. F., and Lindley, J. I., 1986, Potassium metasomatismof igneous and sedimentary rocks in detachment terranes andother sedimentary basins—economic implications: Arizona Geo-logical Society Digest, v. 16, pp. 118-126.

Chapin, C. E., and Seager, W. R., 1975, Evolution of the Rio Granderift in the Socorro and Las Cruces areas: New Mexico GeologicalSociety, Guidebook to 26th Field Conference, pp. 297-321.

Conran, I. P., 198(1. Socorro, a historic survey: University of NewMexico Press, Albuquerque, 124 pp.

D'Andrea-Dinkelman, J. F., Lindley, J. 1., Chapin, C. E., and Os-burn, G. R., 1983, 'Me Socorro K:0 anomaly—a fossil geothermalsystem in the Rio Grande rift: New Mexico Geological Society,Guidebook to 34th Field Conference, pp. 76-77.

Denny, C. S., 1940, Tertiary geology of the San Acacia area, NewMexico: Journal of Geology, v. 48, pp. 73-106.

54

Domski, P., 1987, The clay mineralogy of the Popotosa Formationas a funct ion of the imposed geochemical parameters, unpub-lished report.

Droste, J. B., 1961a, Clay minerals in the playa sediments of theMojave Desert, California: California Division of Mines, SpecialReport 69, 21 pp.

Droste, J. B., 196th, Clay minerals in the sediments of Owens,China, Searles, Panamint, Bristol, Cadiz, and Danby Lake Basins,California: Geological Society of America Bulletin, v. 72, pp. 1713-1721.

Eggleston, T. L., 1982, Geology of the central Cluipadera Moun-tains, Socorro County, New Mexico: Unpubl ished M.S. thes is ,New Mexico Inst i tute of Mining and Technology, Socorro, 155pp.; New Mexico Bureau of Mines and Mineral Resources, Open-file Report 141, 162 pp.

Grim, R. E., 1968, Clay mineralogy: McGraw-Hill, Inc., New York,2nd ed., 596 pp.

Hay, R. L., 1966, Zeoli tes and zeolitic reactions in sedimentaryrocks: Geological Society of America, Special Paper 85, 130 pp.

Hay, R. L., 1978, Geologic occurrence of zeolites; in Sand, L. B.,and Mumpton, F. A. (eds.), Natural zeolites-occurrence, prop-erties, use: Pergamon Press, New York, pp. 135-143.

Hook, S. C., 1983, Stratigraphy, paleontology, depositional frame-

work, and nomenclature of marine Upper Cretaceous rocks, So-corro County, New Mexico: New Mexico Geological Soc iety,Guidebook to 34th Field Conference, pp. 165-172.

Hunt, A. P., and Lucas, S. G.. 1987, Triassic stratigraphy, Carthage

area, Socorro County, New Mexico and the southeasternmost

outcrops of the Moenkopi Formation (abs.): New Mexico Geo-

log ica l Soc ie ty, Proceed ings o f 1987 Annual Spr ing Meet ing,

p. 47.

Keller, W. D., 1970, Environmental aspects of clay minerals: Journalof Sedimentary Petrology, v. 40, pp. 788-813.

Osborn, G. R., and Chapin, C. E., 1983, Ash-flow tuffs and caul-drons in the nor theas t Mogo l lon-Dati l vo lcanic f ie ld -a sum-mary New Mexico Geological Society, Guidebook to 34th FieldConference, pp. 197-204.

Osburn. G. K.. Petty, D. M., and Chapin, C. E., 1981, Geology ofthe Molino Peak quadrangle, Socorro-Magdalena area, SocorroCounty, New Mexico: New Mexico Bureau of Mines and MineralResources, Open-file Report 139a, 24 pp.

Patterson, S. H., and Holmes, R. W., 1965. Clays; in Mineral and

water resources of New Mexico: New Mexico Bureau of Mines

and Mineral Resources, Bulletin 87, pp. 312-322.Picard, M. D., and High, L. K., Jr., 1972, Criteria for recognizing

lacustrine rocks; in Rigby, J. K. , and Hamblin, W. K. (eds.),Society of Economic Paleontologists and Mineralogists, SpecialPublication No. 16, pp. 108-145.

Sheppard, R. A., and Gude, A. J., 111,1968, Distribution and genesis

of authigenic silicate minerals in tuffs of Pleistocene I.akeTecopa,lnyo County, Cali fornia: U.S. Geological Survey, ProfessionalPaper 597, 38 pp.

Smith, C. T., 1983, Structural problems along the east side of theSocorro constriction, Rio Grande rift: New Mexico GeologicalSociety. Guidebook to 34th Field Conference, pp. 103-109.

Smith, C. T., Oshurn, G. R., Chapin, C. E., Hawley, J. W., Osburn,

J. C., Anderson, 0. J., Rosen, S. D., Eggleston, T. I.., and Cather,

S. M., 1983, First day road log from Socorro to Mesa del Yeso,Joyita Hil ls, Johnson [til l, Cerros de Amado, Lomas [sic] de las

Jornado [sic] del Muerto, Carthage, and return to Socorro:New Mexico Geological Society, Guidebook to 34th Held Con-ference, pp. 1-28.

Smith, E. W., 1982, Large-scale adobe-brick manufacturing in NewMexico; in Austin, G. S. (compiler), Industrial rocks and minerals

of the Southwest: New Mexico Bureau of Mines and Mineral

Resources, Circular 182, pp. 49-56.Speer, S. W., Broadhead, R. F., and Kottlowski, F. E., 1983, Road

log-second day-Socorro to Bingham, Bent, and to the northernSacramento Mountains; in Guidebook for field trip to the Abured beds (Permian), central and south-central New Mexico: Ros-well Geological Society and New Mexico Bureau of Mines andMineral Resources, pp. 15-44.

Surdam, R. C., and Sheppard, R. A., 1978, Zeolites in saline, al-kaline-lake deposits; in Sand, L. B., and Mumpton, F. A. (eds.),Natural zeolites-occurrence, properties, use: Pergamon Press,New York, pp. 145-174.

Talmage, S. B., and Wootton, T. P., 1937, The non-metallic mineralresources of New Mexico and their economic features (exclusiveof fuels): New Mexico Bureau of Mines and Mineral Resources,Bulletin 12, 159 pp.

Van Sandt, J., 1964, Refractory clays of Arizona and New Mexico:U.S. Bureau of Mines, unpubl ished manuscr ipt.

Yoder, H. S., and Eugster, H. P., 1955, Synthetic and natural mus-covites: Geochimica et Cosmochimica Ada, v. 8, pp. 225-280.

55

Geomorphic evolution and soil-geomorphic relationshipsin the Socorro area, central New Mexico

by Daniel B. McGrath' and John W. Hawley''Camp, Dresser & McKee, Inc., Denver, Colorado 80202 and 'New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801

IntroductionThe tour stops on Trips 2a-d of the 1987 Clay Minerals

Society annual meeting (this volume) offer excellent vantagepoints for reviewing the late Cenozoic geomorphic evolu-tion of the Socorro area. This region is the site of pioneeringstudies on desert-basin geomorphology and hydrogeologyby Kirk Bryan (1938) and his students. Much of the earlygeomorphic research in this area was done by Denny (1940,1941) and Wright (1946). Recent detailed studies have beenmade by Machette (1978a, b, c, 1986), and Love and Young(1983). Regional overviews include reports by Hawley et al.(1976), Hawley (1978), and Machette (1985). Machette's workdeals not only with geomorphology and late Cenozoic geol-ogy, but also with soil-geomorphic relationships and soilstratigraphy. Unpublished work by R. M. Chamberlin onthe geology of the Socorro area provided much of the sub-surface information and structural interpretations used inpreparation of the diagrammatic cross section of the RioGrande valley (Fig. 1).

Most of the clay mineral analyses and interpretations ofsoil-clay mineral genesis presented in this paper were doneby D. B. McGrath as part of a special graduate researchproject at New Mexico Tech in 1985. Additional informationon soil-clay mineral distribution and genesis has been pro-vided by B. G. Jones as part of a clay minerals class project(New Mexico Tech, 1987). The soil survey of Socorro Countyhas been completed recently by the U.S. Soil ConservationService and cooperators in other federal and state agencies,but it is still unpublished. However, the soil survey manu-script is available for review and was also utilized in thepreparation of this paper.

Geomorphic settingintermontane basin tills and associated geomorphic sur-

faces of the Socorro area are excellent examples of upperCenozoic deposits and arid to semiarid landscapes in theMexican Highland section of the Basin and Range Province(Hawley, 1986a, b). Major mountain and basin landformsare volcano-tectonic features of the Rio Grande rift sub-province (Chamberlin, 1981; Chapin, 1983) that essentiallyformed by the early Pliocene (4 to 5 m.y. ago). The bulk ofthe intermontane basin fill (Santa Fe Group) was emplacedby early Pleistocene (>0.75 m.y.), and erosional valleys ofthe Rio Grande and major arroyo tributaries have only de-veloped in the past half million years. Early rift-basin de-posits comprise bolson fill and interbedded volcanics of lateOligocene and Miocene age (lower Santa Fe Group-Popo-tosa Formation) and are, for the most part, deeply buriedby younger basin and valley fills. The older deposits arebest exposed in structural uplifts in and adjacent to moun-tain ranges west of the Rio Grande and are derived fromgeologic terranes partly obliterated by subsequent tecton-ism, volcanism, erosion, and burial. Widespread playa-lakedeposits in bolson-floor fades assemblages demonstrate thata regional system of through drainage was not present dur-ing Miocene and late Oligocene time.

In terms of hydrologic and biologic environments, the

physiographic setting during ()Bo-Pleistocene time was

probably quite similar to that of the late Quaternary. Pa-leontological evidence and "caldc" paleosols associated withburied and relict geomorphic surfaces indicate that pre-vailing climates were semiarid to arid. The stratigraphicrecord in the form of basin and valley fills clearly showsthat ephemeral, high-gradient streams (commonly fan dis-tributaries) dominated piedmont-slope depositional envi-ronments, while a perennial, low-gradient fluvial system(the ancestral Rio Grande) and local playa lakes occupiedbasin floors.

The diagrammatic cross section (Fig. 1) from La JenciaBasin (Trip 2a, Stop 2-1—"Sedillo I sill" surface) across theRio Grande valley to the Loma de las Canas (Stop 2-2—"Las Callas" surface) illustrates the complex history of basinformation and filling as well as the episodes of middle tolate Quaternary valley entrenchment. The earliest ancestral-river deposits (early Pliocene, -.3.5 to 4.5 'my.), which formthe lower part of the Sierra Ladrones Formation (upperSanta Fe Group) of Machette (1978b, c), were probably firstemplaced along the western margin of the basin (Fig. 1,unit 1). They are now partly incorporated in the upliftedSocorro Mountain block (north of Socorro Canyon; Fig. 1).Sierra Ladrones fluvial sands, exposed along lower Arroyode la Parida near Pueblito (Trip 2b, mi 2.25, p. 26), containa Blancan vertebrate fauna of late Pliocene to early Pleis-tocene age (more than 1.5 m.y.; Tedford, 1981). This unit((?) on Fig. 1) is extensively preserved in bluffs east of theRio Grande and intertongues with fan deposits of the east-ern piedmont facies of the Sierra Ladrones Formation (seenat Stops 2-2 and 2-3 along Arroyo de las Catlas and Arroyodel Tajo). Between 1.5 and 0.5 m.y. ago the ancestral rivercontinued to deliver sandy sediments to an aggrading cen-tral basin floor (Q) on Fig. 1). Volcanic ash and pumice fromcaldera-forming and intra-caldera eruptions in the JemezMountains of northern New Mexico are present in upperSierra Ladrones fluvial deposits at at least two sites in theSocorro area (Izett et al., 1981). These tephra lenses weredeposited by air-fall and debris-flow mechanisms betweenabout 1.5 and 1.1 m.y. ago during the early Pleistocene.

Geologic and soil-geomorphic studies throughout the Al-buquerque to El Paso reach of the upper Rio Grande valleyindicate that culmination of basin filling and the end ofSanta Fe Group deposition occurred about 0.4 to 0.5 m.y.ago (Hawley et al., 1976; Hawley, 1978; Gile et al., 1981;Machette, 1985). The "Sedillo Hill" (Stop 2-1, p. 23) and"Las Cafias" (Stops 2-2 and 2-3, pp. 28, 36) geomorphicsurfaces west and east of the river valley, respectively, ap-proximate the ultimate level of piedmont-slope aggradationin the La Jencia, Socorro, and Jornada del Muerto Basins.These surfaces appear to correlate with the Llano de Al-buquerque and Jornada I-Lower La Mesa geomorphic sur-faces in the Albuquerque and southern Jornada Basins. Thehistory of late stages of basin filling was complicated byrecurrent structural deformation (Machette, 1978a, 1986), aswell as by shifts in paleohydrologic regimes and effective-ness of vegetation cover.

The present Rio Grande valley (s on Fig. 1), is a narrowerosional feature of a river system that is just beginning to

57

entrench itself in an enormous volume of ancient fluvialdeposits (upper Santa Fe Group). A stepped sequence ofgraded ("valley-border") surfaces flanking the modernfloodplain, and an erosion surface about 100 ft below thevalley floor represent at least four major episodes of river-valley entrenchment. Each of these episodes was followedby long intervals of partial valley backfilling or relativelysteady-state conditions with respect to local floodplain baselevel. Times of widespread valley incision appear to cor-relate with major expansions of pluvial lakes and alpineglaciers in the eastern Basin and Range and Southern RockyMountain provinces (e.g., parts of marine-oxygen-isotopestages 2, 6, 8, 12-14). The extensive remnants of "valley-border" surfaces in this region represent long periods ofrelative base level stability and surface aggradation subse-quent to the major episodes of valley entrenchment (Haw-ley et al., 1976). These depositional periods probably reflectenvironments between full-glacial substages when smallertributary drainage systems delivered more sediment to val-ley floors and adjacent piedmont slopes than master streamscould remove from the upper Rio Grande Basin (parts of0-isotope stages 1, 3-5, 7, 9-11).

Some principles of soil developmentin an arid to semiarid area

of central New MexicoThe basic principle of soil development in arid and semi-

arid regions is that precipitation does not remove free cat-ions from the soil during most years. Thus, the soil solutionbecomes concentrated and alkaline. Weathering proceedsat an extremely slow rate. Gile (1975, 1977), Gile and Gross-man (1979), and Gile et al. (1981) provide a large amountof information on soils and soil-geomorphic relations in thearid to semiarid Desert Project region of south-central NewMexico. The following brief overview covers general soil-forming factors and diagnostic-horizon characteristics in theSocorro area. Preliminary data on clay minerals in soils ofmid-Pleistocene surfaces (Stops 2--1, 2 2, and 2-5) will alsobe discussed.

Basin and valley fills of the Socorro area are derived fromcarbonate rocks (partly dolomitic), sandstone, mudstone,and gypsite of Paleozoic age, Mesozoic sandstone and mud-stone, and Cenozoic volcanic and nonmarine sedimentaryrocks. The upper Tertiary Quaternary stratigraphic recordcomprises alluvial, colluvial, lacustrine, and eolian sedi-ments as well as basaltic and silicic volcanics deposited ina tectonically active, intermontane basin and stream-valleysetting.

Topographic features range from broad, relatively un-dissected floors and piedmont slopes, in basins still notintegrated with the Rio Grande valley system, to dissected"valley-border" terrains with large local relief and extensiveareas of active erosion and sedimentation. Throughout theHolocene the broad Rio Grande valley floor has been thesite of active channel and floodplain aggradation, with al-luvial fans of tributar v-arrovo systems encroaching on thefloodplain margins.

The Rio Grande valley and higher intermontane basinsurfaces of the Socorro area have an arid to semiarid climatewith mean annual precipitation of about 8-13 inches (20-33 cm) and mean annual temperature of about 50-61 F (10-16'C). Soil and temperature classes include the thermic tomesic transition, and soil-moisture regimes range from aridic(torric) to ustic to possibly xeric. The arid to semiarid. thermicto mesic, and aridic to ustic transitions at this latitude (34'north) occur in the 5,000-6,000 ft (1,524 1,829 m) range.Cooler and moister conditions existed during Wisconsinand earlier Pleistocene glacial-pluvial stages. Xeric moistureregimes may have been prevalent due to shifts from sum-mer-fall-dominant to winter-spring-dominant precipita-

tion. Interglacial temperature and moisture regimes are typ-ified by the warm-dry Holocene and Sangamon intervals(past 10,000 yrs and about 120 to 130 ka, respectively; 0-isotope stages 1 and 5e) are probably not typical of long-term Quaternary environments in this part of the Basin andRange Province (Spaulding, 1984; Van Devender, 1985).

The present vegetative cover is dominated by desert shrubs,grasses, annuals, cacti. and trees of the pifion-juniper zone.During the Pleistocene glacial-pluvial intervals grasslandsand mixed forest-grassland were much more extensive atlowland sites. Faunal influence on pedogenesis includessubsurface activity of insects and burrowing vertebrate forms;ubiquitous soil microorganisms also play a major, but oftenpoorly documented, role in desert soil formation.

Tour stops on Trips 2a and 2b emphasize ancient soillandscapes on relict geomorphic surfaces that have beenessentially stable for hundreds of thousands of years. Soilsexamined are associated with piedmont slopes that repre-sent culminating stages of early to middle Pleistocene basinaggradation (upper Santa Fe Group-Sierra Ladrones For-mation deposition). These geomorphic surfaces, informallydesignated "Sedillo Hill" and "Las Cafias" (Fig. 1) includedeeply dissected fans and rock pediments that predate mid-to late-Pleistocene entrenchment of the present river-valleysystem.

Surface soil horizons in arid and semiarid parts of theSocorro area tend to 1) be low in organic matter except onhigher undissected basin surfaces, 2) have variable (alkalineto slightly acid) soil solutions, 3) be easily eroded at manysites with sparse vegetative cover, 4) have a thin surfacecrust at such sites, 5) be exposed to extreme temperaturevariations, and 6) receive atmospheric fallout (aerosol con-tributions). Subsurface horizons have fewer oscillations intemperature and soil solution, but are wetted to differentdepths by each precipitation event. Calcite precipitates inthe subsurface of all arid-region soils. Clay translocationoccurs, as evidenced by the strong argillic horizon at Stop2-1, but secondary carbonate commonly disrupts argillansor engulfs argillic horizons. Clay neoformation is possibleif soil solution exists for a long enough time at great enoughconcentrations. Some common horizonation sequences ob-served are shown in Figure 2. For additional explanationon soil-horizon and fabric nomenclature, see Soil SurveyStaff (1975, 1981), Brewer (1976), and Cornell UniversityAgronomy Department (1986).

FIGURE 2—Parent material (C), with continuedaddition of aerosols to a stable geomorphic sur-face, transforms to cambic (Bw) to calcic (Bk) to

petrocalcic (Bkm) horizons, or from cambic (Bw)to argillic (Bt) to argillic overprinted with calcic(Btk) to petrocalcic (Btkm) horizons, or directly tocalcic (Bk) to petrocalcic (Bkm) horizons.

Pedogenic horizonsof carbonate accumulation

caliche is the common term used to describe near-surface

accumulations of secondary calcium carbonate of bothpedogenic and nonpedogenic origin in the AmericanSouthwest (Bretz and Horberg, 1949; Aristarain, 1970; Reeves,1970; Gardner, 1972; Frye et al., 1974). Nonpedogenic va-

58

rieties formed mainly by precipitation of calcite by deeplypercolating subsurface water in both the vadose and un-derlying saturated (ground-water) zones. Many fanglomerates, conglomerates, and sandstones in the upper SantaFe Group basin-fill sequence have been cemented by thisprocess, and, where exposed, may be misinterpreted aspedogenic carbonate horizons. These rocks are also tran-sitional to travertine deposits in areas of active or priorspring discharge (Bachman and Machette, 1977; Barker, 1983;Carlisle et al., 1978).

Bates and Jackson (1980) define calcrete as a "calcareousduricrust" and a duricrust as "a general term for a hard crust. . . or layer in the upper horizons of a soil in a semiaridclimate." Calcrete (Lamplugh, 1902; Goudie, 1973) is nowcommonly used as a synonym for indurated forms of calichein the southwestern United States (McGrath and Hawley,1985; Machette, 1985; Sowers, 1985). The general term "cal-cic soil," introduced by Bachman and Machette (1977), refersto all soils with readily identifiable amounts of illuvial car-bonate in the B-horizon position, whether nonindurated orindurated (Bk and Bkm horizons; previously designatedBca, Cca. and Ccam horizons). Soils with calcic and petro-calcic horizons, as well as weaker accumulations of sec-ondary carbonate, are included in the broad "calcic soil"category (Machette, 1983; Gile, 1987).

Gile (1961, 1975, 1977) and Gile et al. (1965, 1966) devel-oped many of the fundamental principles of carbonate ho-rizon genesis and classification in soils of arid and semiaridregions. Their model for soil-carbonate accumulation is de-scribed by a bimodal, four-stage (1-IV), morphogenetic se-quence for both gravelly and nongravelly parent sediments(Gile et al., 1966). Bachman and Machette (1977), and Ma-chette (1985) expanded this scheme to a six-stage morpho-genetic sequence, with stages V and VI used to characterizevery strong and morphologically complex pedogenic cal-cretes (caprock caliches) of the American Southwest. Thisscheme, as adapted by McGrath and Hawley (1985) is pre-sented in Table 1.

Stages I and II are initial phases of soil-carbonate illu-viation and result in the formation of weaker Bk horizonsthat usually are not diagnostic in soil classification. Non-indurated carbonate accumulations that qualify for calcichorizon designation commonly exhibit stage III morphol-ogy. A nearly continuous fabric of carbonate-coated clastsand carbonate-filled voids (K-fabric of Gile et al., 1965) andinitial development of irreversible cementation (induration)characterize late stage HI. This incipient phase of petrocalcichorizon and calcrete formation may be followed by stageIV, which is characterized by an indurated layer of dense,multiple-laminar K-fabric that caps the massive to nodular"carbonate-plugged" horizon. Stage IV marks the initial for-mation of "caliche profile" as defined by Lovelace (1972).Stage V includes development of a thicker "caprock caliche"layer, with several multiple-laminar subhorizons, followedby initial fracturing of this zone and development of coarse-platy structure and zones of brecciation andlor dissolution.Recementation of hrecciated material and solution-roundedfragments to form a pisolitic fabric and additional cycles ofbrecciation and cementation occur in stage VI. Very longintervals of soil-landscape stability (>10' to 10' yrs) andmajor changes in paleohydrologic conditions are reflectedin the thickness and complexity of the caprock layer incalcretes with stage V and VI morphology.

Soils with petrocalcic horizons, marking the stage III toIV transition, are widely developed on Pleistocene geomor-phic surfaces in this region while "calcic soils" with weakerexpression of pedogenic carbonate (stages Ito III) are nearlyubiquitous (Machette, 1985). Petrocalcic horizons (pedo-genic calcretes) with stage IV to V morphology are locallypresent ("Las Callas" surface, Stop 2-2), but only on sur-faces of mid-Pleistocene or older age (e.g., La Mesa and

TABLE 1—Stages of carbonate accumulation in gravelly and non-gravelly morphogenetic sequences of calcrete development.

Diagnostic carbonate morphology

NongravellyGravelly sequence sequence

Weakes texpress i on Thi n , d i sc ont in Few f i l a ments or ofmacroscopic car uous coatings on faint coatings on pedb o n a t e g r a v e l c l a s t s s u r f a c e s

IICarbona te s egrega Cont i nuous coa t Few t o common

tions separated by ings on clasts, some noduleslow-carbonate fab interdast fillingsric

IIICarbonate essen Many interpebble Many nodules andt i a l l y c o n t i n u o u s ; f i l l i n g s i n t e r n o d u l a r f i l l i n g sp lugged hor iz onforms in last part Upper part of horizon essentially plugged

IVLaminar horizon Indurated laminar horizon over pluggeddevelops over horizon; thin upper zone of platy structureplugged horizon; over zone with massive to nodular struc-incipient calcrete ture; grades downward into gravelly orformation; forms nongravelly material with stage III mor-caprock layer up to phology; incipient "caliche profile" of Love-0.5 m thick lace (1972) and pedogenic calcrete

VMultiple laminar Thick, well-indurated upper horizon; platyhorizon develops in to tabular structure with multiple laminarupper part of pro internal fabric; zones of dissolution, brec-file; incipient devel ciat ion, and recementation locally present;opment of degra dry hulk densities up to 2.2 grcm'

dational features;forms caprock layerup to 2 in thick

VIBrecciation, disso Very thick, well-indurated, upper horizon;lution and recemen tabular to platy structure, with pisolitic andtation of upper, multilaminar internal fabric; secondary sil-multilaminar hori ica common; dry hulk densities 2.2-2.7 gizon; mult ip le gen cm'erations of calcreteformation and deg-radation; forms cap-rock layer up to 4 mthick

Jornada 1 surfaces of the Desert Project area; Gile and Gross-man, 1979; Gile et al., 1981). Stage VI calcretes are almosteverywhere restricted to soils whose formation started inPliocene to late Miocene time (1.7 to 7 m.y. ago). The onlyextensive soil landscape (relict and buried) that is preservedin the Southwest is on the Southern High Plains (LlanoEstacado) of Texas and New Mexico. However, ancient soilswith stages V and VI carbonate morphologies are locallypreserved throughout the Basin and Range Province fromTrans-Pecos Texas and New Mexico to southern Nevada(Bretz and Horberg, 1949; Gile, 1961; Reeves, 1970; Gardner,1972; Lattman, 1973; Machette, 1985). In addition to citedpublications, recent theses by McGrath (1984), Sowers (1985),and Chitale (1986) give an excellent overview of currentresearch on pedogenic calcretes.

Clay minerals in mid-Pleistocene soilsof the Socorro area

Clay minerals in horizons of carbonate accumulation insoils of the American Southwest have received much atten-

Stage and generalcharacter

59

tion since early studies of Desert Project calcretes by VandenHeuval (1966). Of particular interest are authigenic clays ofthe smectite, illite-smectite (US), and palygorskite-sepiolite(chain-lattice or hormite-clay) groups that commonly occurin both soils and alkaline-lake deposits of the Basin andRange Province, Southern Great Plains l'rovince, and else-where in arid and semiarid regions of the world (Parry andReeves, 1968; Martin-Vivaldi and Robertson, 1971; Gardner,1972; McLean et al., 1972; Papke, 1972; Frye et al., 1974;Bachman and Machette, 1977; Post, 1978; Bigham et al.,1980; Hay and Wiggins, 1980; Khoury et al., 1982; Jones,1983; Birkeland, 1984; McGrath, 1984; Sowers, 1985). Modelsof clay mineral neoformation and transformation in "calcicsoils" of arid and semiarid regions are outlined briefly inTable 2.

The relative depletion of sepiolite and palygorskite, par-

ticularly sepiolite, with increasing amounts of smectite andassociated expansive clays in pedogenic calcretes has beenobserved by many workers including Frye et al. (1974),Yaalon and Wieder (1976), Bachman and Machette (1977),Bigham et al. (1980), and Jones (1983). Jones (1983) and mostother workers (Table 2) consider that neoformation (directprecipitation) of chain-lattice clays can occur in dry-landsoils where controlling geochemical parameters (soil-waterpH, magnesium, and silica activities, etc.) are at optimumlevels. Jones (1983) concluded that the formation of I'S in-tergrades or interstratifications in pre-existing smectite hascompeted with neoformation of chain-silicate phases in aridpedogenic environments.

Frye et al. (1974), Bachman and Machette (1977), and

TABLE 2—Models of sepiolite and palygorskite formation in soils of arid and semiarid regions—an overview.

Researcher(s) Models and regions Researcher(s) Models and regions

Formed penecontemporaneously withcalcic and petrocalcic horizon develop-ment by an unknown mechanism andwas later mechanically concentratedwithin dissolution voids during wetterperiods.Desert Project area, southern New Mex-ico

1) detrital component of the parent ma-terial,

2) mechanically infiltrated clay derivedfrom colian additions,

3) transformational products fromchemical weathering of detrital min-erals,

4) "Chemical precipitation of dissolvedimpurities from evaporating rainwater in the soil. -

Mormon Mesa area, southeastern Ne-vada

Transformational product occurring inassociation with volcanic ash.

Texas High Plains

Neoformation (direct precipitation) ofpalygorskite is possible (if appropriatesoil solution exists) in a thin surficial layercharacterized by infrequent saturation.Apparent palygorskite-gypsum rela-tionship noted by Eswaran and Bar-zanji.Middle East, Australia

Transformation of detrital smectite topalygorskite; in the lower part of cap-rock caliche profiles in a high magne-sium environment; locally associated withformation of opal.

Southern Great Plains

Neoformation of palygorskite with Mgsupplied by weathering of Mg-carbon-ates. "The montmorillonite Ito] paly-gorskite transformation, provided ad-ditional Mg is available, seems to be adistinct possibility. . ." Possible rela-tionship between pedogenic gypsum andpalygorskite.Israel

Mineral transformation over hundredsof thousands of years of geologic timeand increasing content of calcium car-bonate; smectite or mixed-layer clays al-ter to palygorskite and then to sepiolite.American Southwest

Pedogenic palygorskite formed (via thesoil solution) at the expense of smectitesinherited from the underlying forma-tion.Saudi Arabia

Palygorskite precipitates directly fromsolution in near-surface materials.

Overview of arid regions

Neoformation of sepiolite and especiallypalygorskite can occur; however, theseminerals appear to be actively degradingto mixed-layer clays and poorly crystal-lized material in present-day environ-ments.Semiarid Texas High Plains

Sepiolite is the result of precipitation fromsolution.American Southwest

1) Neoformation by direct precipita-tion,

2) dissolution of mixed-layer kerolite/stevensite via a dilute ground water.

Southwestern Nevada

Inherited from colian additions.

Saudi Arabia

Neoformation of chain-silicate clays incalcic soils by direct precipitation; pro-cess enhanced by presence of dolomiticsedimentary and silicic volcanic rocks andcalcareous sepiolitic aerosols.

Southwestern Nevada

Neoformation model supported.

Australia; overview of arid-zone soils

Palygorskite formation occurred beforeor penecontemporaneous with calichi-fication; with increased degree of calichedevelopment, the carbonate replaces thepalygorskite.North Africa

Vanden Heuvel (1966)

Gardner

McLean et al.

E

(19Singer and Norrish

Frye et al.

Yaalon andWieder (1976)

Bachman andMachette (1977)

Elprince et al. (1979)

Singer (1979)

Bigham et al. (1980)

I lay and Wiggins (1980)

Khoury et al. (1982)

Viani et al. (1983)

Jones (1983)

Norrish and Pickering(1983)

Paquet (1983)

swaran andBarzanji

74)

"Hormites" form by precipitation (neo-formation) in a caliche after an indura-t ion threshold is exceeded becausemoisture is available over a longer time,during which reactions can occur.Southern Great Plains

McGrath (1984)

60

Bigham et al. (1980) found an increase of palygorskite withdepth in well-developed calcic and petrocalcic horizons ofthe New Mexico-western Texas region; and they also foundsepiolite to be most abundant in the middle to lower ho-rizons of the pedons examined. Bachman and Machette(1977) presented a general mineral transformation model inwhich smectite or US transforms to palygorskite, which inturn is converted to sepiolite. Occurrence of the latter min-eral is associated with very ancient soil landscapes and depthzones in petrocalcic horizons where calcium carbonate pre-cipitation and soil-water infiltration are most active. Bighamet al. (1980) point out the sepiolite and palygorskite do notappear to be stable in modern semiarid environments ofthe Texas High Plains. The geochemical and morphologicalimplications of their work are that these minerals are ac-tively degrading to less well structured IIS and poorlycrystallized material. However, they do not argue againstneoformation of pedogenic sepiolite and, especially, paly-gorskite at other places or times.

Profiles of five representative "calcic soils" at or near Stops2-1, 2-2, and 2-5 are described in Tables 3-7 (pedons la,lb, 2a, 2h, and 3). Figures 3-6 are photographs that illus-trate soil-geomorphic and stratigraphic relationships at thefield trip stops (pedons la, lb, 2a, and 3). Preliminary inter-pretations of x-ray diffraction (XRD) analyses of samplesfrom the Paleargids and Paleorthids described at or nearStops 2-1, 2-2, and 2-5 are given in Table 8 (pedons la, 2a,2h, and 3, respectively). Field and laboratory methodologyare discussed below. Inferred distribution of smectite, illite,

chlorite, kaolinite, sepiolite, and palygorskite clays, aswell as quartz and dolomite, are presented in this table. Itmust he re-emphasized that these interpretations are verypreliminary and may be significantly modified during fu-ture, more detailed investigations. However, the chain-sil-icate (hormite) clays are definitely a substantial componentof well-developed soil carbonate horizons that were sam-pled for this study. The preliminary XRD data on sepioliteoccurrence is also supported by use of methyl orange (methoddescribed by Hay and Wiggins, 1980; McGrath, 1984; andSowers, 1985) for rapid field (and laboratory) identificationof major zones of sepiolite accumulation in strong soil-car-bonate horizons.

The mineralogical contrast between soils of the "SedilloHill" (Stop 2-1) and "Las Callas" (Stops 2-2 and 2-5) geo-morphic surfaces is striking, particularly when data onsmectite and mixed-layer L'S clays are compared with in-formation on sepiolite and palygorskite (Table 8). Whileboth soil landscapes (Figs. 1, 3-6) have been in a relictsurface position for about 0.5 m.y., the long-term paleo-climatic setting of the "Sedillo Hill" surface (I.a Jencia Basin,elev. _6,000 ft, 1,829 m) is distinctly less arid and coolerthan the "Las Can as" surface (Socorro and Jumada Basins,elev. L5,000 ft, 1,524 m). Furthermore, the "Sedillo Hill"surface at Stop 2-1 is underlain by basin fill derived pri-marily from silicic volcanic rocks, and dynamic aerosol com-ponents of soil parent materials appear to be very low incarbonates relative to nearby valley and basin areas. Majorsoils in the vicinity of Stop 2-] (Figs. 3 and 4; Tables 4 and5) have thick, noncalcareous zones in the upper A and (ar-gillic) B position where pH is commonly neutral to slightlyacid.

Contrasting soil landscapes of the "Las Callas" surfacearea, east of the Rio Grande (Figs. 1, 5, and 6) are underlainby basin fill derived from sedimentary and local volcanicterranes that mainly contribute fragments of limestone, do-lomite, and calcareous clastic rocks to soil parent materials.Atmospheric additions are also more calcareous in the So-corro Basin area, particularly east (seasonally downwind)of the Rio Grande; and the soil solution is significantly morealkaline than in the southern La Jencia Basin (Fig. 1; Stop2-1). It has also been noted that beds of volcanic ash and

TABLE 3—Field morphological description of Paleargid (pedon la)

at Stop 2-1 (p. 23).

Classification: Ustollic Paleargid; clayey, mixed, mesic

Location: NW'14, NE' /4, SW' /4, sec. 27, T3S, R2W; in roadcuton west side of US -60 at crest of Sedillo Hill (10mi west of Socorro)

Geomorphic "Sedillo 11111" (early middle Pleistocene)surface (age):Land form: piedmont slope, medial position; relict alluvial

fanSlope: 4 percent (eastward)Elevation: 6,095 ft (1,858 in)material:Parent Sierra Ladrones Formation, upper piedmont fa-

cies; fine loamy to gravelly fan alluvium, primar-ily derived from silicic volcanic terrane (mid-Ter-tiary) in east-central Magdalena Mountains; withcalcareous aerosol contributions.

Vegetation: grasses, cacti, annualsDescribed by: D. A. McGrath (7/26/85)

Sampled by: D. A. McGrath (7i26/85)Horizon

A 0-10 cm; dark brown (7.5YR 4i4) silt loam, darkbrown (7.5YR 213) moist; weak granular and finesubangular blocky; soft; noncalcareous; few rootsto many roots under grass bunches; clear, smoothboundary.

BAt 10-27 cm; reddish brown (5YR 4/4) silty clay, darkreddish brown (5YR 34) moist; weak mediumsubangular blocky, breaking into moderate veryfine angular blocky; very hard; noncalcareous; fewfaint clay films; 10 percent ash-flow-tuff frag-ments; many tine to medium roots; clear, smoothboundary.

Btkl 27-41 cm, dark red (2.5YR 3/6) clay; weak mediumsubangular blocky, breaking into moderate veryfine angular blocky; very hard; effervesces strongly;distinct clay films on ped faces and rock frag-ments; carbonate rinds coat clay-film-coated rockfragments; 10 percent ash-flow-tuff fragments;clear, smooth boundary.

Btk2 41-55 cm; red (2.5YR 4/6) gravelly clay, dark red(2.5YR 3/6) moist; moderate medium subangularblocky; very hard; very plastic; effervesces vio-lently; distinct clay films on pod faces and rockfragments; common carbonate nodules; 20 per-cent ash-flow-tuft fragments, few medium roots;

abrupt, wavy boundary.Btk3 (K) 55-79+ cm; pink (5YR 74) clay yellowish red (5YR

5/6) moist; massive; very hard to indurated (cal-crete); plastic; effervesces violently; 60 percent ar-gillic fragments engulfed by carbonate along pedfaces; plugged with secondary carbonate; fewmedium roots.

Remarks: Calcic horizon, with late stage 111 carbonate mor-phology (Gile et al., 1966) below 55 cm. Prelimi-nary interpretation of clay mineral distributionby D. A. McGrath and G. S. Austin (Table 8).

pumice, derived from caldera-forming eruptions in north-ern New Mexico (Izett et al., 1981), and from elsewhere inthe western United States (Hawley et al., 1976; Hawley,1978; Izett, 1981), are common constituents of axial-riverand piedmont facies of the upper Santa Fe Group. Thesedeposits include the upper Sierra I.adrones Formation inthe Socorro Basin.

The clay mineral assemblages in soils described in thispaper are quite similar to occurrences discussed by otherworkers who have dealt with soil-clay relationships in sim-ilar geomorphic and geologic settings (Table 2). The workof Jones (1983) and Bigham et al. (1980) is particularly per-tinent to the interpretations of preliminary data on soil-

FIGURE 3—"Sedi l lo Hi l l" geomorphic surface and Paleargid so il landscape at Stop 2area of east-central Magdalena Mountains. Piedmont-s lope facies of uppermost Sierr8" person) exposed in US-60 roadcut.

a

p

b

5stvfon

7csr3b

9civvfcpk

1cifvocbc

1CntgcmIpmascgMS

61

telv thick clay films on faces of peds; 45 percent

ebbles and 5 percent cobbles; neutral; clear, wavy

oundary.

8-76 cm; dark red (2.5YR 3/6) very gravelly clay;trong medium angular blocky structure part ingo strong fine angular blocky, very hard, f i rm,ery sticky, and very plastic; few fine and very

ine roots; continuous, thick clay f i lms on facesf peds; 35 percent pebbles and 5 percent cobbles;eutral; clear, wavy boundary.

6-91 cm; red (2.5YR 4/6) gravelly clay; strong,oarse prismatic structure; very hard, firm, veryticky, and very plastic; few fine and very fineouts; continuous thick clay films on faces of peds;5 percent pebbles; mildly alkaline; abrupt, wavyoundary.

1-130 cm; yellowish red (5YR 5/6) very gravellylay; moderate medium prismatic structure part-ng to common fine and very fine angular blocky;ery hard, firm, very sticky, and very plastic; fewery f ine and fine roots; continuous thick c layilms on faces of peds; effervesces violently, withalcium carbonate occurring as soft masses; 45ercent pebbles and 5 percent cobbles; mildly al-aline; clear, wavy boundary.

30-157 cm; yellowish red (5YR 5/6) very gravellylay; moderate medium prismatic structure part-ng to moderate fine subangular blocky; very hard,irm, very sticky, and very plastic; few fine andery fine roots; many moderately thick clay fi lmsn faces of peds; 50 percent pebbles and 5 percentobbles; effervesces violently, with calcium car-onate occurring as soft masses; mildly alkaline;lear, wavy boundary.

57-188 cm; very grave l ly loamy sand.ontiguous pedons show apparent cyc l ic alter-ation (wave length of about 2 in, amplitude lesshan 1 m) between very grave l ly c lay and lowravelly to gravelly clay zones. Horizons of soil-arbonate accumulation below 76 cm are muchore prominent in the less gravelly clay zones.

nterpreted by J. W. Hawley (8/25/77) as a relictatterned-ground feature, possibly related to for-er gilgai microrelief and action of expansive clayss suggested by Yaalon and Kalmar (1978). Theite may also have been affected by freeze-thawondit ions dur ing middle and late Ple istocenelacial stages. Laboratory data available from Newexico State University Agricultural Experimenttation and U.S. Soi l Conservation Service.

-1 (p. 23). V iew to west toward Sixmile Canyona Ladrones Formation and Paleargid pedon la (5 '

mineralogy obtained in this study. The dominance of VSand illite, and the presence of smectite and kaolinite, inupper soil horizons sampled at Stop 2-1 (Tables 3 and 8,pedon la) agree with observations on clay mineral occur-rence in other areas with similar climate and soil-geo-morphic settings (Gile and Grossman, 1979; Nettleton andBrasher, 1983). The upper (A, 13t, l3tk) horizons of soils ofthe "Sedillo Hill" surface do not appear to be sites where"neoformational" or "transformational" processes have ledto genesis of chain-lattice clays. However, positive (methylorange) tests for sepiolite have been obtained from pedo-genic calcretes that locally occur in areas of soil-landscapedissection and soil-profile truncation contiguous to the Stop2 1 study area (Table 3, pedon la). At these places alongthe rim of the Rio Grande valley, the soil microclimate isdistinctly drier than in adjacent undissected areas (well il-lustrated by pedon lb in Table 7) where an ancient soillandscape is well preserved (also see Gile et al., 1981, pp.99-102).

The following scenario for genesis of chain-lattice claysin pedogenic calcretes of the "Las Car'las" geomorphic sur-face (Tables 5-7, pedons 2a, 2h, and 3) is in essential agree-ment with models described by Jones (1983) in southernNevada and McGrath (1984) in the Southern High Plains.Calcic-petrocalcic horizon sequences (late stage III andstronger carbonate morphologies) serve as holding tanksfor a concentrated soil solution. It is inferred that the chain-lattice clays form after the carbonate cementation (incipientinduration) threshold has been crossed. When the solution

63

30-50 cm; pale brown (10YR 6i3) gravelly clay

loam; yellowish brown (10YR 5/4) moist; weaksubangular blocky; soft; effervesces violently; 3-mm carbonate rinds on gravel clasts, which in-clude calcrete fragments; few fine and mediumroots; clear, smooth boundary.50-60 cm; light gray (10YR 7/2) gravelly clay loam,yellowish brown (10YR 514) moist; weak suban-gular blocky; hard; effervesces violently; 3-mmcarbonate rinds on gravel clasts, which includecalcrete fragments; few fine and medium roots;abrupt, smooth boundary.60-61 cm; white (10YR 9.11) laminar calcrete crust;pale brown (10YR 6/3) moist; very well indurated;effervesces violently; solution-cupped limestonefragments; some 2-mm brown siliceous bands; se-piolitic; abrupt, smooth boundary.

61-86 cm; white (10YR 8/1) very gravelly calcrete,pale brown (10YR 6/3) moist; well indurated; ef-fervesces violently; plugged and cemented withsecondary carbonate; sepiolitic; common frag-ments of dolomite and mudstone; some dolomitefragments fractured and recemented by pedo-genic calcite; clear, smooth boundary.86-180 cm; pinkish white (7.5YR 8/2) very gravelly

loam with indurated nodular calcrete zones, lightbrown (7.5YR 6/4) moist; massive; partly indurated;effervesces violently; plugged with secondarycarbonate; sepiolitic in upper part; commonfragments of mudstone and dolomite.180-245 cm; pink (7.5YR 714) gravelly sandy clayloam; brown (7.4YR 514) moist; massive; soft; ef-fervesces strongly; non-sepiolitic. Upper part ofveneer of gravelly alluvium (upper Sierra Lad-rones Formation-piedmont facies) that caps LasCamas geomorphic surface (pediment phase).I'etrocalcic horizon with stage IV carbonate mor-phology (tile et al., 1966) 60-86 cm. l'reliminaryinterpretation of clay mineral distribution byID. A. McGrath and G. S. Austin (Table 8).

sepiolite neoformation would occur. Chain-lattice clays, ratherthan the ubiquitous smectites, form because of the low pMg.The necessary Mg could be supplied by degradation ofphyllosilicates, volcanic ash, and/or other detrital minerals.However, if the parent sediment (including aerosol contri-butions) contained a significant dolomite component, thenthe Mg supply problem would be greatly simplified. FreeCa in solution would precipitate on the existing calcite re-sulting in a still greater degree of induration and calcretedevelopment. Free Ca" would be obtained from dissolutionof detrital carbonates and the weathering of other Ca-bear-ing materials.

Free Si in the system not used in clay neoformation wouldprecipitate as an independent opal phase (opal—CT). How-ever, this phase has not been observed in "Las Calias" pe-dons. If volcanic ash, even in relatively small increments,were to be deposited on the surface, or if a grassland soilwas buried or climatically altered, with resulting dissolutionof opal phytoliths, then silica cementation of the subsoilmight also be expected. The necessary Si could also beobtained from the degradation of clay phyllosilicates or de-trital primary silicates. If a trend of decreasing feldspar/quartz ratio with increasing degree of calcrete developmentis observed in future studies, an inference could be madethat Al" would also be available for clay neoformation.Another possible Al" source would be from degradationof phyllosilicates. Thus, Al' liberated in the system wouldbe readily available for clay neoformation when a flux ofthe other necessary cations existed. With increasing age ofthe deposit and advancing stages of diagenesis and pedo-genesis, the probability of more than one of the above eventsoccurring would be increased greatly.

Methodology

Samples were collected from hand-dug excavations inroadcut and natural exposures, and pedons were describedusing standard U.S. Cooperative Soil Survey nomenclature(Soil Survey Staff, 1981). Samples were air-dried and in-durated samples were ground to pass a 60-mesh sieve. Car-bonates were destroyed by placing approximately 20 g ofsample in 150 ml of 10 percent acetic acid (HOAc; McLeanet al., 1972). Samples were washed (by decantation) untildispersion occurred. Dispersion was aided by adding 5 mlof 5 percent sodium hexametaphosphate. Clay was ex-tracted based on a settling time of 45 minutes per cm for<2µm-sized particles. Clay extract volume was controlledby using 10 percent CaC1 to induce flocculation. Sampleswere oriented using the filter membrane peel technique ofDreyer (1973).

X-ray diffraction (XRD) was conducted on the Rigaku dif-fractometer at the New Mexico Bureau of Mines and MineralResources. The machine was operated at a speed of 4°/minute with a time constant of 0.2. Occasional powder sam-ples were examined from 2-50° 20. Oriented clay slides wereexamined from 2-32° 20. Ethylene glycol solvated slideswere examined from 2-15° 20, with the glycolation obtainedby allowing the samples to remain in a room-temperaturedesiccator containing ethylene glycol. Glycolated slides wereexposed to 350°C temperatures for one hour then examinedfrom 8-10° 20 immediately upon removal from the ovenand then examined from 2-15° 20 (Austin and Leininger,1976). Clay minerals were identified with the aid of pro-cedures described by Brindley (1980), Brown (1980), andBrown and Brindley (1980).

66

Ack now le dgme nt s

As s i s tance by George Aus t i n , R i cha rd Chambe r l i n , Geo f -

f r e y J o ne s , Dav i d L ov e , V i r g in i a M c L e m o r e , and De bo r ah

Shaw i n p r e pa r a t i o n o f t h i s p ape r i s g r a t e f u l l y a c k no w l -

edged.

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Dreyer, J. 1., 1973, The preparation of oriented clay mineral spec-imens for XRD analysis by a filter-membrane peel technique:American Mineralogist, v. 58, pp. 553-554.

Elprince, A. M., Mashady, A. S., Aba-Husayn, M. M., 1979, Theoccurrence of pedogenic palygorskite (attapulgite) in Saudi Ara-bia: Soil Science, v. 128, pp. 214-218.

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Gardner, L. R., 1972, Origin of the Mormon Mesa caliche, ClarkCounty , Nevada: Geo log ica l Soc ie ty o f Amer ica, Bu l le t in 83,pp. 143-156.

Gile, L. H., 1961, A classification of ca horizons in soils of a desertregion, Dona Ana County, New Mexico: Soil Science Society ofAmerica Proceedings, v. 25, pp. 52-61.

Gile, I.. II., 1975, Holocene soils and soil-geomorphic relations inan ar id region of southern New Mexico: Quaternary Research,v. 5, pp. 321-360.

Gi le, L. H., 1977, Holocene soi ls and so i l -geomorphic re lat ions in

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Gile, L. H., 1987, Book review of Weide, D. L. (ed.), Soils andQuaternary geology of the southwestern United States: Quater-nary Research, v. 27, pp. 335-336.

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Gile, L. H., Hawley, J. W., and Grossman, R. B., 1981, Soils andgeomorphology in the Basin Range area of southern New Mex-ico -gu idebook to the Deser t P ro jec t : New Mex ico Bureau o fMines and Mineral Resources, Memoir 39, 222 pp.

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Hawley, J. W. (compi ler), 1978, Guidebook to Rio Grande r i ft inNew Mexico and Colorado: New Mexico Bureau of Mines andMineral Resources, Circular 163, 241 pp.

Hawley, J. W., 1986a, Physiographic provinces of New Mexico; inWil liams, J. L. (ed.), New Mexico in maps: Univers ity of NewMexico Press, Albuquerque, pp. 28-31.

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1981, Potassium-argon and fission-track ages of Cerro ToledoRhyolite tephra in the Jemez Mountains, New Mexico: U.S. Geo-logical Survey, Professional Paper 1199-D, pp. 37-43.

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Khoury, H. N., Eber l, D. D., and Jones, B. F., 1982, Or ig in ofmagnesium clays from the Armagosa Desert, Nevada: Clays andClay Minerals, v. 5, pp. 327 336.

Lamplugh, G. W., 1902, Calcrete: Geological Magazine, v. 9, p. 75.Lattman, L. H., 1973, Calc ium carbonate cementat ion of al luv ialfans in southern Nevada: Geological Society of America Bulletin,v. 84, pp. 3013-3028.Love, D. W., and Young, J. D., 1983, Progress report on the late

Cenozoic geologic evolut ion of the lower Rio Puerco: New Mex-ico Geological Society; Guidebook to 34th Field Conference, pp.277-284.

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Lovelace, A. D., 1972, Aggregate resources in central eastern NewMexico: New Mexico Geological Society, Guidebook to 23rd FieldConference, pp. 187-191.

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6

ineralization in the Luis Lopez mining districtSocorro County, New Mexico—a summary

by Robert M. North and Virginia T. McLemore

New Mexico Bureau of Mines and Mineral Resources Socorro, New Mexico 87801

IntroductionThe Luis Lopez mining district,. located southwest ofocorro, was one of the largest manganese producers inew Mexico. Manganese oxides occur along fractures and

reccia zones in Tertiary volcanic rocks. By 1957, total pro-uction from this district amounted to about 97,000 shortons of concentrate that averaged 41% Mn and 18,000 shortons of crude ore that averaged 28% Mn (Farnham, 1961;

illard, 1973; Eggleston et al., 1983a). Production continuedto the 1970's; however, figures are not available. Produc-

ion was by both underground and open pit methods.This report is a summary of published accounts describing

he geology and mineralization in the district as well asbservations by the authors. For more detailed information,he reader is referred to the references cited.

GeologyThe Luis Lopez mining district is located near the north-

ast edge of the mid-.Tertiary Datil-Mogollon volcanic field.he geology of the area is dominated by silicic ash-flow tuffsrupted from a number of mid-Tertiary cauldrons (Fig. 1).he district is located within the eastern portion of the Socor-

o cauldron, a mid-Tertiary volcanic feature subsequentlyodified by late Tertiary extension. The Socorro cauldronas formed approximately 32.04 m.y. B.P. (McIntosh et al.,986; 'Art'Ar on sanidine) by the explosive evacuation of aigh-level silicic magma chamber; the pyroclastic debris be-ame the hells Mesa Tuff. The roof of the magma chamberubsided as material was erupted, resulting in a volcanicollapse basin (Fig. 2). The gradual subsidence allowed theccumulation of a thick sequence of Hells Mesa Tuff withinhe cauldron (cauldron facies) as compared to the outflowheet (outflow facies), which spread for several tens of kilo-eters around the cauldron (Osburn, 1983). Continued sub-

idence caused oversteepened cliffs to form, which periodi-ally spilled into the cauldron and became interbedded withhe tuff. At some point, the central portion of the fractured,ubsiding block was forced upward. This is known as aesurgent dome, resulting in a topographically high centralection surrounded by a moat, which in this case, was subse-uently filled by about 1,000 m of volcaniclastic sediments,hyolite domes and flows, and local ash flows known as theuis Lopez Formation (Chamberlin, 1980; Eggleston, 1982).The eastern margin of the Sawmill Canyon cauldron isear the western edge of the mining district. The Sawmillanyon cauldron is a small cauldron nested within the muchrger Socorro cauldron (Fig. 3). La Jencia Tuff was formedy the contemporaneous eruption of the Sawmill Canyon-agdalena cauldrons about 28.78 m.y. B.P. (Osburn andhapin, 1983a; McIntosh et al., 1986). The outflow facies of

a Jencia Tuff is preserved within the margins of the Socorroauldron south of the Luis Lopez district. Later, the I .emitaruff probably erupted from a cauldron in the northern Sanateo Mountains about 27.97 m.y. B.P. (Osburn and Cha-

in, 1983a; McIntosh et al., 1986), and partially filled theoat of the Sawmill Canyon and Socorro cauldrons (Eggles

on, 1982; Eggleston et al.. 1983b). The South Canyon Tuff,lso probably erupted from the northern San Mateo Moun-

tains, overlies the Lemitar Tuff and hosts some mineraliza-tion in the northern part of the district. McIntosh et al. (1986)reported an age of 27.36 m.y. B.P. for the South CanyonTuff. Mid- to late-Tertiary extension of up to, perhaps, 100%has modified the cauldron, burying its eastern rim in the RioGrande rift and exaggerating the east-west dimension (Fig.3). The approximate present outline of the cauldron is 16 mifrom north to south and 22 mi from east to west (Osburn andChapin, 1983b).

StructureThe structure of the Luis Lopez district is dominated by

cauldron structures and faulting and tilting related to regionalextension. Pre-volcanic structure is dominated by a transverseshear zone (Precambrian wrench fault?) of the Morencilineament north of the district (Chapin et al., 1978). Thiszone of crustal weakness, locally referred to as the Socorrotransverse shear zone, is the focus for the repeated volcan-ism and high heat flow in the area. The zone is expressed atthe surface by a change in the regional dip of the volcanicrocks from west- north of the zone to east-south of the zone(Chapin et al., 1978).

Regional extension related to the Rio Grande rift beganabout 31 m.y. B.P. (Aldrich et al., 1986), shortly after theeruption of the Socorro cauldron, contemporaneous withthe eruption of the Sawmill Canyon-Magdalena cauldrons.High-angle, normal faults were formed, resulting in east-dipping fault blocks in the Luis Lopez mining district. Thedip of the fault blocks increases from about 20 to 70° fromsouth to north in the district, probably indicating a greaterdegree of extension in the northern part of the area (Eggles-ton, 1982). In some cases, the original high-angle faultsmight he rotated to lower angles as extension continues andsubsequently cut by high-angle faults. Structure of this typeis referred to as domino-style crustal extension because incross section it resembles toppled dominoes (Chamberlin,1983).

MineralizationMineralization in the district occurs along joints, minor

faults, and in breccia zones related to faulting and perhaps inbreccias formed by hydrothermal explosive events (T. L.Eggleston, pers. comm. 1987). At the MCA (Red Hill) mine,mineralization occurs along steeply dipping parallel struc-tures in the Hells Mesa Tuff, which strike north to N20°Wand have small displacements. At the Nancy and Towermines, the major mineralization is along parallel structuresin the Lemitar Tuff, South Canyon Tuff, and basaltic ande-site striking N15'W to N30°W (Eggleston et al., 1983a, b).

The mineralization has not been dated, but structuralevidence cited by Chamberlin (1980) suggests an age of 3 to 7m.y. B.P., possibly associated with rhyolitic volcanism andhigh heat flow on Socorro Peak, north of the district. Indi-vidual veins of manganese oxides vary from less than 1 cm to

8

69

Fc

Fp

Santa Fe Group

CITertiary infrusives

Younger ash-flow tuffs

Luis Lopez FormationQ

t

Caldero Collapse Breccias(Tnb on cross section)

L H e l l s M e s a l u f f

A

Ty

Tz

1115

ITd Datil Group

H Paleozoic undivided

i.2 Precambrian undivided

red altered zone .

IGURE 1—Generalized geologicermission.)

e,

map and cross section of the

Luis Lopez mining district and vicinity. (From Eggleston, et al .,19831;: used with

70

nearly 1 m. The breccia zones consist of tuff fragmentscoated by manganese oxides and cemented by manganeseoxides and!or calcite.

MineralogyThe mineralogy of the veins has been the subject of con-

siderable discussion and debate. The hard manganese ox-ides have been commonly referred to as psilomelane. Thismaterial is a mixture of acicular manganese oxides, mostcommonly hollandite (Ba(Mn -1,Mn '2)8016), a monoclinic(pseudotetragonal) mineral with a structure related to theruffle group. Commonly, the last stage of manganese miner-alization is a fine-grained aggregate of intertwining crystalsresembling black velvet (Fig. 4). Among mineral collectorsthis material is referred to as "rat's hair" psilomelane. Otherend-members with a structure related to the ruffle groupinclude cryptomelane (K(Mn -4,Mn - - ,)8016; monoclinic,pseudotetragonal) and coronadite (Pb(Mn '1,1vin -2)8016;tetragonal?). Pyrolusite (Mn02) is also probably present.Using high-resolution transmitted electron microscopy,Turner and Buseck (1979) showed that individual crystalfibers from the district are composed of single unit-cell layersof romanechite (BaMn 2Mns

4016(OH)4; monoclinic) randomlydistributed within a dominant hollandite crystal lattice. Usingelectron microprobe analysis, Modreski (1983) showed thematerial to be chemically zoned from nearly pure barium-manganese oxide, with some potassium (5-15 mole percentcryptomelane with no lead), to coronadite (20 weight percentPhO). Willard (1973) reported microprobe

71

FIGURE 3—Approximate location of mid-Tertiary cauldrons in the Socorro area. 1, Socorro cauldron; 2, Sawmill Canyon cauldron; 3,Magdalena cauldron. The Socorro transverse shear zone separates two structural domains with rocks north of the zone dipping west andsouth of the zone dipping east. (From °shun' and Chapin, 1983a).

analyses, which indicated the banded material (Fig. 5)showed as much chemical variation along the bands asacross them. lie concluded that the banding is due to physi-cal, not chemical, changes during deposition. Because of thisuncertainty, psilomelane is probably the best name for thematerial, keeping in mind that it is most often hollanditewith a unit-cell of crvptomelane, coronadite, and!orromanechite thrown in here and there, perhaps admixedwith pyrolusite. The common gangue minerals include cal-cite, quartz, hematite, and barite.

Trace-element chemistryTrace-element studies of the Luis Lopez manganese de-

posits have shown that the manganese veins contain con-siderable amounts of some interesting trace elements. Themost detailed geochemical study of the ore is the unpub-lished report of Willard (1973; Table 1), who reported avariety of minor and trace elements from the district. Lead,due to the presence of coronadite, is widespread in thedistrict. Tungsten, in concentrations between 0.1 and 0.3percent, is common in the district (Willard, 1973; Norman etal., 1983). Silver and gold have been detected in severalsamples (Table 1). Other elements generally present include

FIGURE 4—Scanning Electron Microscope photo of "rat's hair"psilomelane from the Nancy mine. Field of view is approximately0 .18 mm by 0.23 mm. (Photo try Mar tha Cather . )

72

FIGURE 5—Banded, hard manganese oxides (psilomelane). Mate-rial of this type has been found to he dominately hollandite with

intergrown cryptomelane and coronadite. Sample is 6 cm wide.

arsenic, antimony, beryllium, nickel, cobalt, strontium, and

thall ium (Wi l lard, 1973). Molybdenum is errat ic in the d is -

tr ic t. ranging from undetectab le to nearly 0.2%.

Genesis of the depositsThe Luis I.opez deposits have been descr ibed as an oxi -

dized epithermal system (Norman et al., 1983). The main

manganese deposits in the district are adjacent to a large area

of red alterat ion (oxid ized iron) super imposed on a large

area of potassium metasomatism. The potassium metaso-

mat ism has resulted in replacement of plag ioc lase by K -

fe ldspar (adular ia?) and is thought to represent a wide -

spread fossi l hydrothermal system associated with r ift ing

(D 'Andrea-D inke lman et a l . , 1983). The K 2 0 anoma ly i s

Miocene or younger , and the minera l izat ion at Luis Lopez

and the silver-lead epithermal mineralization in the Socorro

Peak distr ict may be parts of this fossil geothermal system.

The red, a l tered rock is dep le ted in manganese and is

thought to he the source of the element in the adjacent Luis

Lopez deposits. Manganese ( 1.2) was leached and oxidized

from the altered rocks by hydrothermal solutions and depo-

sited in open fractures and breccias adjacent to the altered

area (Eggleston et al ., 1983a; Fig. 6). Flu id inclus ion and

stable isotope analyses of the manganese ores indicate that

the main minera l izat ion in the d ist r ic t was formed from

bo i l ing ; low-sa l in i t y so lu t ions between 175 and 375°C

formed approximate ly 500 in beneath the sur face (Norman

et al., 1983).

Future potentialAs long as imports are stable, it is doubtful that the Luis

Lopez ores wi l l be mined again for manganese. Current ly,the United States imports 100% of its manganese needs, 73%coming from Gabon, Brazi l, and South Afr ica (Jones, 1987).In the event that the import sources were cut off, mining ofsea- f loor nodules would probably be as att ract ive as re -opening the mines of the Luis Lopez district exclusively formanganese. However, some of the trace elements in the oreare interest ing. Metal lurgical studies on the ore may discov-

TABLE 1—Trace elements in the Luis Lopez mining district (from

Willard, 1973).

AnalyticalRange method

Element

PbBa

FeCuZnNiCo

MoKSr

AsSbTI

0.001-20% atomic absorption5.0-19% atomic absorption1.0-10% atomic absorption

0.8-0.58%0-0.13% atomic absorptionatomic absorption

0-0.014% atomic absorption

0-0.070% atomic absorption

0-1.7% atomic absorption

0-0.181% atomic absorption

0-2.0% atomic absorption

0 0.1% atomic absorption

0.7-1.5% spectrographic

0-0.7% spectrographic

0-0.7% spectrographic0.003-0.007% spectrographic

0.03-0.15% spectrographic

0.03-1.5% spectrographic0.00-0.02 oziton fire assay

(0.68 ppm)f i re assay

0.00-3.30 oz/ton(113 ppm)

er ways to recover some of the more abundant or va luabletrace elements such as tungsten, si lver, and perhaps evengold (Ahmad, 1972).

Norman et al. (1983) stated that it is unlikely to find pre-cious- or base-metal sulfide mineral izat ion below the man-ganese oxide veins. They c i ted the lack of organic com-pounds and H2S in the fluid inclusions, and they also notedthat the manganese mineral izat ion is at the bo i l ing leve l inthe system, a level at which precious meta ls are found inmany epithermal systems (Buchanan, 1981). However, theydo suggest that a si lver base-metal deposit similar to theHardshel l depos i t in the Patagonia Mounta ins of Ar izonacould underlie the manganese oxide veins of the Luis Lopez

district. This is a rather unlikely possibility. The 1 lardshell

deposit is thought to have formed from the in-situ oxidationof a manganese sulf ide (albandite) -base-meta l sulf ide de-posit (Koutz, 1984). No evidence of any sulf ide mineral iza-t ion has been found at Lu is Lopez. A lso, the Hardshe l lm inera l i zat ion is probably par t o f a Laramide porphyry -copper system (Keith et al., 1983), a much different geologicsett ing than the mid-Tert iary Luis Lopez distr ict. This doesnot preclude some type of base- or precious-metal miner-alization at depth, but it is unlikely that anything similar toHardshe l l w i l l be found .

Acknow ledgme ntsThe manuscr ip t was reviewed by Dr. Ted L. Eggles ton ,

and discussions with him aided the authors in understand -ing the geology of the distr ict. The New Mexico GeologicalSociety k indly a l lowed the reproduction of several f iguresfront their Guidebook to the 34th Field Conference, SocorroRegion II.

ReferencesAhmad, U. M. U., 1972, Recovery of manganese and by-products

from manganese ores in Socorro County, New Mexico: Unpub-lished M.S. thesis, New Mexico Institute of Mining and Technolo-

gy, 91 PP.Aldrich, M. J., Jr., Chapin, C. E., and Laughlin, A. W., 1986, Stress

history and tectonic development of the Rio Grande rift, NewMexico: Journal of Geophysical Research, v. 91, no. 86, pp. 6199-6211.

Buchanan, L. J . , 1981, Precious metal deposits associated with vol-

canic environments in the Southwest; in Dickinson, W. R., and

Payne, W. D. (eds.), Relations of tectonics to ore deposits in thesouthern Cordillera: Arizona Geological Society Digest, v. 14, pp.237-262.

73

Chamberlin, R. M., 1980, Cenozoic stratigraphy and structure of theSocorro Peak volcanic center, central New Mexico: UnpublishedPh.D. thesis, Colorado School of Mines, 495 pp.; New MexicoBureau of Mines and Mineral Resources, Open-file Report 118,532 pp.

Chamberlin, R. M., 1983, Cenozoic domino-style crustal extensionin the Lemitar Mountains, New Mexico—a summary: New Mex-ico Geological Society, Guidebook to 34th Field Conference, pp.111-118.

Chapin, C. E., Chamberlin, R. M., Osburn, G. R., White, D. W.,and Sanford, A. R., 1978, Exploration framework of the Socorrogeothermal area, New Mexico; in Chapin, C. E., and Elston, W. E.(eds.), Field guide to selected cauldrons and mining districts ofthe Datil-Mogollon volcanic field New Mexico: New MexicoGeological Society, Special Publication 7, pp. 115-129.

D'Andrea-Dinkleman, J. F., Lindley, J. 1., Chapin, C. E., andOsburn, G. R., 1983, The Socorro K2O anomaly—a fossil geo-thermal system in the Rio Grande rift: New Mexico GeologicalSociety, Guidebook to 34th Field Conference, pp. 76-77.

Eggleston, T. L., 1982, Geology of the central Chupadera Moun-tains, Socorro County, New Mexico: Unpublished M.S. thesis,New Mexico institute of Mining and Technology, 164 pp; NewMexico Bureau of Mines and Mineral Resources, Open-file Report141, 162 pp.

Eggleston, T. I.., Norman, D. 1., Chapin, C. E., and Savin, S., 1983a,Geology, alteration, and genesis of the Luis Lopez manganesedistrict, New Mexico: New Mexico Geological Society, Guidebookto 34th Field Conference, pp. 241-246.

Eggleston, T. I.., Osburn, G. R. „ind Chapin, C. E., 1983b, Third dayroad log from Socorro to San Antonio, Nogal Canyon, ChupaderaMountains, Luis Lopez manganese district, and the MCA mine:New Mexico Geological Society, Guidebook to 34th Field Confer-ence, pp. 61-81.

Farnham, L. L., 1961, Manganese deposits of New Mexico: U.S.Bureau of Mines, Information Circular 8030, 176 pp.

Jones, T. S., 1987, Manganese; in Mineral commodity summaries,1987: U.S. Bureau of Mines, Government Printing Office,Washington, D.C., pp. 98-99.

Keith, S. B., Gest, D. E., DeWitt, E., Toll, N. W., and Everson, B. A.,

1983, Metallic mineral districts and production in Arizona: Arizo-na Bureau of Geology and Mineral Technology, Bulletin 194, 58pp., scale 1:1,000,000.

Koutz, F. R., 1984, The Hardshell silver, base-metal, manganeseoxide deposit, Patagonia Mountains, Santa Cruz County, Arizo-na—a held trip guide; in Wilkins, J., Jr. (ed.), Gold and silverdeposits of the Basin and Range Province, western U.S.A.: Arizo-na Geological Society Digest, v. 15, pp. 199-217.

McIntosh, W. C., Sutter, J. F., Chapin, C. E., Osburn, C. R., andRatte, J. C., 1986. A stratigraphic framework for the easternMogollon-Datil volcanic field based on paleomagnetism andhigh-precision 41Art39Ar dating of ignimbrites—a progress report:New Mexico Geological Society, Guidebook to 37th Field Confer-ence, pp. 183-195.

Modreski, P. J., 1983, Manganese oxides (psilomelane) from SocorroCounty, New Mexico (abs): New Mexico Geology, v. 5, no. 4, p.84.

Norman, D. 1., I3azrafshan, K., and Eggleston, T. L., 1983, Miner-alization of the Luis Lopez epithermal manganese deposits inlight of fluid inclusion and geologic studies: New Mexico Geolo-gical Society, Guidebook to 34th Field Conference, pp. 247-251.

Osburn, G. R., 1983, Ash-flow tuffs, ignimbrites, cauldrons, andcalderas: New Mexico Geological Society, Guidebook to 34th FieldConference, pp. 66-67.

Osburn, G. R., and Chapin, C. E., 1983a, Nomenclature for Ceno-zoic rocks of northeast Mogollon-Datil volcanic field, New Mex-ico: New Mexico Bureau of Mines and Mineral Resources, Strati-graphic Chart 1.

Osburn, G. R., and Chapin, C. E., 1983b, Ash-flow tuffs and caul-drons in the northeast Mogollon-Datil volcanic field—a sum-mary: New Mexico Geological Society, Guidebook to 34th FieldConference, pp. 197-204.

Turner, S., and Buseck, P. R., 1979, Manganese oxide tunnel struc-tures and their intergrowths: Science, v. 203, pp. 456-158.

Willard, M. E., 1973, Geology of Luis Lopez manganese district,New Mexico: New Mexico Bureau of Mines and Mineral Re-sources, Open-file Report 186, 81 pp.

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74

Glossary

lluvial fan—body of stream, sheetwash, and debris-flowdeposits whose surface forms the segment of a cone thatradiates downslope from the point where a streamemerges from a narrow valley or canyon onto a plain.

lluvium—unconsolidated elastic material deposited byrunning water, including various mixtures of gravel,sand, silt, and clay.

mmonite—extinct marine invertebrate related to the pre-sent-day chambered nautilus.

ndesite—volcanic rock intermediate in composition be-tween rhyolite and basalt.

nticline—archlike fold in which strata dip in opposite direc-tions from a common ridge or axis.

rroyo—flat-floored and steep-walled channel or gully of anephemeral stream, usually dry but can be transformedinto a temporary watercourse or short-lived torrent afterheavy rainfall.

sh—fine pyroclastic material that is less than 4.0 mm indiameter.

asalt—fine-grained, dark-colored volcanic rock composedchiefly of calcium-rich plagioclase, pyroxene, and olivine.asement—the oldest rocks recognized in a given area;usually a complex of Precambrian igneous and metamor-phic rocks underlying l'aleozoic and younger sedimentaryformations.ed—thin layer of rock, usually sedimentary or pyroclastic.reccia—coarse-grained, elastic rock composed of very

angular fragments; may be sedimentary, volcanic, or tec-tonic in origin.

alcrete—see caliche.aliche--a common term, used in Hispanic North America,for a prominent zone of secondary carbonate accumula-tion in surficial materials of semiarid to arid areas formedby both geologic and pedogenic processes; finely crystal-line calcium carbonate forms a nearly continuous surface-coating and void-filling medium in parent sediments androcks; cementation ranges from weak and discontinuousto well-indurated (calcrete) forms; and accessory cementsmay include other carbonate, silicate, and sulphateminerals.

lastic—rock and mineral fragments (clasts) derived frompm-existing rocks and transported from their place oforigin by water, wind, ice, volcanic, or mass-wasting pro-cesses.

olluvium—unconsolidated elastic material deposited onand at the base of steep hillslopes and mountain fronts bymass wasting and unconcentrated runoff.

onglomerate—clastic sedimentary rock composed pre-dominantly of rounded to subangular gravel, cementingminerals, and lesser amounts of sand, silt, and clay.

ontact—the place or surface where two different kinds ofrocks meet.

ike—tabular igneous intrusion that cuts across the planarstructures of surrounding rocks.ip—the angle that a bed or fault plane makes with animaginary horizontal plane.ome—round or elliptical upwarp of strata.

xtrusive rock—volcanic rock emplaced on the surface of theearth.

ault—fracture in rocks along which the two sides havemoved relative to each other.

low unit—group of sheets or beds of lava that were formedby a single eruption.

old—archlike or troughlike undulations of rocks best seen

in layered rocks; usually caused by compressional forcesin the earth's crust.

formation—the fundamental unit in rock stratigraphic clas-sification; a mappable body of rock characterized by litho-logic homogeneity or distinctive lithologic features that isprevailingly, but not necessarily, tabular.

fossil—identifiable remains or traces of an ancient animal orplant preserved in rock.

gabbro—dark-colored, medium- to coarse-grained igneousrock consisting mainly of pyroxene and calcium plagio-clase.

granite—light-colored, medium- to coarse-grained intrusiveigneous rock consisting chiefly of orthoclase, sodium-plagioclase, and quartz with minor mica.

gypsum—common evaporite mineral used in making plas-ter of Paris (Ca504 • 2H20).

igneous rock—rock formed by solidifying and crystallizingfrom magma within the earth's crust (plutonic) or fromlava and pyroclastic material on the earth's surface (vol-canic).

intrusive rock—body of igneous rock that penetrated pre-existing rocks as magma and cooled within the earth'scrust.

laccolith —concordant, usually lenticular, igneous instru-sion with known or assumed flat floor and a postulateddike-like feeder somewhere beneath its thickest point.

Laramide—of or relating to mountain-making (orogenic)movements in late Mesozoic and early Cenozoic time,approximately 75-40 m.y. ago in New Mexico.

lava—magma or molten rock that has reached the surface.limestone—sedimentary rock composed of calcium carbo-

nate; the consolidated equivalent of calcite mud, cal-careous sand, or shell fragments.

magma—the molten rock material that forms igneous rockswhen it cools.

mesa—isolated, nearly flat-topped, upland mass standingdistinctly above the surrounding country and hounded bysteeply sloping scarps; in Hispanic North America theterm is also used for broad alluvial terraces and erosionalbenches that occur as intermediate platforms borderingstream valleys and canyons; Spanish for table.

metamorphic rock—sedimentary or igneous rock that hasbeen altered chemically and structurally by extreme heatand pressure, causing new structures and minerals toform.

monzonite—grayish, medium- to coarse-grained intrusiverock consisting of approximately equal amounts of ortho-clase and plagioclase with minor biotite and hornblende.

paleontology—the study of fossils, their environment, and therecord of evolutionary development.

pediment—broad, gently sloping erosion surface developed atthe foot of a receding hillslope or mountain front; thesurface may be essentially hare, exposing rocks that ex-tend beneath adjacent uplands, or it may be thinly man-tled with alluvium and colluvium.

petroglyphs—figures and inscriptions pecked, carved, orhammered into rock surfaces.phenocryst—conspicuous, relatively large crystal, inset in amore finely crystalline groundmass of an igneous rock.

pictograph—picture painted on a rock and used as a sign.piedmont slope—the dominant gentle slope at the foot of a

mountain, including footslope erosion surfaces (pedi-

75

ments) and constructional surfaces (fans, coalescent fans,and alluvial plains).

pluton—large igneous intrusion formed at depth in thecrust.

porphyry—igneous rock consisting of distinct crystals (phe-nocrvsts) set in a very fine crystalline base or groundmass.

pyroclastic—pertaining to clastic materials produced by ex-plosive aerial ejection of rock and mineral particles from avolcanic vent.

rhyolite—light-colored, silicic, very fine grained volcanicrock; extrusive equivalent of granite.

sandstone—clastic sedimentary rock composed predomi-nantly of sand grains, cementing minerals, and lesseramounts of silt, clay, and gravel.

sedimentary rock—indurated deposit of clastic particles,chemical precipitates, and organic remains; primarilymaterial transported by water, wind, or ice, or mass-wasting processes.

semiarid—type of climate characterized by 10-20 inches ofannual rainfall and high evapotranspiration.

shale—clastic sedimentary rock, composed of induratedclay-silt mixtures, that tends to split apart easily into verythin layers.

sill—tabular igneous intrusion that parallels the planarstructure of surrounding rocks.

siltstone--clastic sedimentary rock composed predominant-ly of particles between 0.062 and 0.004 mm in diameter.

stock—large, irregular igneous intrusion that cuts throughsurrounding rocks.

stratification—recognizable parallel beds of considerablelateral extent in sedimentary formations.

stratigraphic column—list of formations, by age, that com-pose the geologic history of an area. syncline—trough-like fold in layered rocks.

talus—sloping heap of coarse rock fragments at the foot of acliff or steep slope.

tectonic—pertaining to the forces involved in, or the result-ing structure of, the broader deformational features of theupper part of the earth's crust.

terrace—one of a series of level surfaces in a stream valley,elongated more or less parallel to the stream channel,representing the dissected remnant of an abandonedfloodplain or valley floor produced during a former stateof erosion or deposition.

tipple—apparatus by which loaded cars (as with coal ormineral ore) are emptied by tipping, sometimes includingan elevated trackway upon which the cars are run fortipping.

unconformity—surface of erosion or nondeposition repre-senting an undocumented period of geologic time andhence a gap in the stratigraphic record.

volcano—localized vent in the earth's crust from which mol-ten or hot rock and gases issue; a hill or mountain com-posed wholly or in part of the material ejected from such avent and often having a crater at its top.