Formation And Occurrences Of Laumontite And Related Minerals In The Carolinas And Virginia, Middle Mesozoic Zeolite Facies Metamorphism Southern Appalachian Piedmont Donald R. Privett, P.G. S.T.A. R. Environmental 1 Circle Street Great Falls, SC 29055 ABSTRACT A 175 -150 Ma hydrothermal zeolite grade metamorphic event altered most pre-Jurassic rocks in the southern Appalachian Piedmont from south central Georgia to southern Virginia. Laumontite fills fractures and replaces plagioclase in exposed and in drilled and cored subsurface rocks. A swarm of 200 Ma northwest/north striking diabase dikes were injected and basalt flowed into into rift valleys during initial Atlantic rifting, followed by filling of half grabens with immature clastic sediments. Fractures (joints and faults) served as conduits for calcium-saturated warmed water that crystallized laumontite, prehnite, calcite and other zeolites. This period of zeolite grade thermal alteration metamorphism is widespread. GENERAL GEOLOGY Piedmont Neoproterozoic and Paleozoic igneous, metamorphic, and Triassic igneous and sedimentary rocks of the Southern Appalachians were subjected to a period of zeolite grade thermal metamorphism about 175- 150 Ma evidenced by the widespread zeolite occurrences in older and younger intrusive and in older metamorphosed (mostly diorites and granites) intrusive host rocks, Figure 1 is a tectonic map (Hatcher, et. al., 2007) showing the area geologic structures. ZEOLITE PARAGENESIS Zeolite grade thermal metamorphism refers to the crystallization of fracture - filling and replacement zeolites and prehnite in host rocks. The zeolite facies is considered to represent a transitional from hydrothermal metamorphism and to encompass all mineral, textural, and chemical changes resulting from hot waters, steam or/and gas. Laumontite and other zeolites have been the subject of theoretical considerations and experimental limit determination (Coombs, 1952) ( Thompson, 1971, Frost, 1980, Loui, 1971) plus detailed paragenesis studies (Boles and Coombs, 1977 and Suranam, 1973). Still there is considerable disparity between theoretical and experimental temperature and pressure limits, and the independently determined substantially lower temperatures of natural formation. Complex ever-changing variables lower and inhibit formation. Zeolites occur in the geothermal areas of Iceland, (Kristmannedottir and Tomanson,1978), (Mehegan, Robinson and Delaney, 1982) and in metamorphic rocks of California, (Madsen, and Murata, 1970) and New Zealand thermal areas (Barnes, 1977). Boles and Coombs (1977) summarized the parameters thought to control the temperature and pressures of formation of zeolites. Experimentally determined temperatures are both higher and lower than values obtained under natural conditions. Fluid pressure gradients, CO2 and H2O, activities of CO2, H20, ratio of water and CO2, the permeability, nucleation and reaction kinetics, oxygen fugacity and presence of additional ions can alter the temperatures of formation. Stability limits determined vary widely; Loui (1971) obtained upper limits of 230º – 325º at 0.5 kb, while Thompson (1971) obtained values of 250º at 2.75 kb. The lower limit is in even greater conflict with natural occurrences. Loui (1971) obtained values of 150º - 200º C at 1 kb where p f = p t the lowest recorded temperature of formation is 43º C (McCulloh, 1981) for laumontite that crystallized on rocks exposed at the Suspe Hot Springs, California. Temperatures of 50º C for laumontite, 90º C for prehnite (Boles and Coombs, 1977) and 104º C (Castino and Sparks, 1974) have been estimated for laumontite in buried sedimentary rocks. Siki, (1969)
Transcript
Formation And Occurrences Of Laumontite And Related Minerals In The Carolinas And Virginia, Middle Mesozoic Zeolite Facies
Metamorphism Southern Appalachian PiedmontDonald R. Privett, P.G. S.T.A. R. Environmental
1 Circle Street Great Falls, SC 29055
ABSTRACT
A 175 -150 Ma hydrothermal zeolite grade metamorphic event altered most pre-Jurassic rocks in the southern Appalachian Piedmont from south central Georgia to southern Virginia. Laumontite fills fractures and replaces plagioclase in exposed and in drilled and cored subsurface rocks. A swarm of 200 Ma northwest/north striking diabase dikes were injected and basalt flowed into into rift valleys during initial Atlantic rifting, followed by filling of half grabens with immature clastic sediments. Fractures (joints and faults) served as conduits for calcium-saturated warmed water that crystallized laumontite, prehnite, calcite and other zeolites. This period of zeolite grade thermal alteration metamorphism is widespread.
GENERAL GEOLOGY
Piedmont Neoproterozoic and Paleozoic igneous, metamorphic, and Triassic igneous and sedimentary rocks of the Southern Appalachians were subjected to a period of zeolite grade thermal metamorphism about 175-150 Ma evidenced by the widespread zeolite occurrences in older and younger intrusive and in older metamorphosed (mostly diorites and granites) intrusive host rocks, Figure 1 is a tectonic map (Hatcher, et. al., 2007) showing the area geologic structures.
ZEOLITE PARAGENESIS
Zeolite grade thermal metamorphism refers to the crystallization of fracture - filling and replacement zeolites and prehnite in host rocks. The zeolite facies is considered to represent a transitional from hydrothermal metamorphism and to encompass all mineral, textural, and chemical changes resulting from hot waters, steam or/and gas.
Laumontite and other zeolites have been the subject of theoretical considerations and experimental limit determination (Coombs, 1952) ( Thompson, 1971, Frost, 1980, Loui, 1971) plus detailed paragenesis studies (Boles and Coombs, 1977 and Suranam, 1973). Still there is considerable disparity between theoretical and experimental temperature and pressure limits, and the independently determined substantially lower temperatures of natural formation. Complex ever-changing variables lower and inhibit formation.Zeolites occur in the geothermal areas of Iceland, (Kristmannedottir and Tomanson,1978), (Mehegan, Robinson and Delaney, 1982) and in metamorphic rocks of California, (Madsen, and Murata, 1970) and New Zealand thermal areas (Barnes, 1977).
Boles and Coombs (1977) summarized the parameters thought to control the temperature and pressures of formation of zeolites. Experimentally determined temperatures are both higher and lower than values obtained under natural conditions. Fluid pressure gradients, CO2 and H2O, activities of CO2, H20, ratio of water and CO2, the permeability, nucleation and reaction kinetics, oxygen fugacity and presence of additional ions can alter the temperatures of formation. Stability limits determined vary widely; Loui (1971) obtained upper limits of 230º – 325º at 0.5 kb, while Thompson (1971) obtained values of 250º at 2.75 kb. The lower limit is in even greater conflict with
natural occurrences. Loui (1971) obtained values of 150º - 200º C at 1 kb where p f = p t the lowest recorded temperature of formation is 43º C (McCulloh, 1981) for laumontite that crystallized on rocks exposed at the Suspe Hot Springs, California. Temperatures of 50º C for laumontite, 90º C for prehnite (Boles and Coombs, 1977) and 104º C (Castino and Sparks, 1974) have been estimated for laumontite in buried sedimentary rocks. Siki, (1969)
reported 75º + 5° C for laumontite formed in hot springs. Using calcite fluid inclusions Meghan, Robinson and Delaney (1982) determined that laumontite filled amygdules in lava flows in Iceland formed at 140º - 200º C.
LAUMONTITE DISTRIBUTION
Laumontite has been identified from over 100 separate locations in relatively unweathered outcrops and in rock exposed in foundations, trenches, quarries, mined caverns, and in cores from borings for power plants and cuttings from water wells and exploratory test wells. Table 1 and Figure 2 shows the general geographic area of interest and earlier referenced laumontite occurrenses. The geographic distribution of additional laumontite in the Carolinas, Georgia and Virginia is shown in Table 2 and Figure 3.
Laumontite is present in the majority of rock exposed in the Piedmont region. Table 1 shows the previously reported occurrences. It occurs in gneisses of the Inner Piedmont; metamorphosed and unmetamorphosed igneous rock and metasedimentary rocks of the Charlotte Belt (Privett, 1974a) and the Kings Mountain Belt; metavolcanic and metasedimentary rock of the Carolina Slate Belt and Triassic - Jurassic sedimentary and igneous rocks.
The discovery of laumontite in the buried Triassic rocks and in cored basement below the Triassic of South Carolina and south central Georgia suggest that laumonatization is even more extensive, here, laumontite fills amygdules and replaces plagioclase in a 184 +/- 3 my basalt from Dorchester county, S.C. (Gotten et.al.,1983) and is present in Triassic sedimentary and older igneous rocks from South Central Georgia (Chowns and Williams,1983).
OCCURRENCE
Laumontite occurs as: (1) single pink and white euhedral crystals in druses and incompletely filled veins where it crystallized on host rock, prehnite, epidote and quartz (Figure 4), (2) veinlets of matted interpenetrating crystal aggregates filling single and multiple narrow fractures and joints (Figure 5) and (3) common replacement of plagioclase forming partial to complete "mosaic pseudomorphs" of laumontite after plagioclase which are composed of minute laumontite crystals and albite (Figures 6 ). Laumontite is identified by microscopic study; in diffuse plane light laumontized plagioclase (Figure 7A and B) displays a mottled texture (Figure 8 A and B )) and polysynthetic twinning of plagioclase is destroyed; partly replaced plagioclase retains its twinning; however, it is mottled. Laumontite imparts a pinkish color to the altered and replaced plagioclase. This color change is a good indication and appears to be directly proportional to the intensity of laumonatization. The sequence is shown by partly replaced laumontite; calcite fills the interior of the vein. Coarse grained microscopic crystals of laumontite under crossed polars (Figure 9) display a somewhat wavy extinction. Rock cores (Figures 10 and 11) contain replacement and fracture filling laumontite.Intenesly altered rocks are sometimes veined with laumonitite-calcite (Figure 12 and 13). Fine grained replacement and fracture filling laumontite (Figure 14) in outcrop and on an exposed weathered surface of saprolite. (Figure15). Coarsly crystallized white laumontie (Figure 16) on broken rock surface.
The x-ray reflections (Table 3) vary with the relative humidity; therefore. the material is best described as laumontite-leonhardite. It is mottled. Laumontite readily dehydrates to leonhardite unless the sample is kept under conditions of 100% relative humidity. Partial re-hydration of leonardadite to laumontite can be observed under the polarizing microscope when a sample is placed in water.
ORIGIN
Tectonic activity about 175 -150 my, in the Triassic and Jurassic consisted of the separation of the continents following the breakup of Pangea. This tectonism fractured old weaker shears, formed new joints and faults. Siliceous cataclasite bodies and quartz mylonites formed in stressed rocks. Immature clastics were deposited in subsiding half grabens and [generation of basaltic magmas and intrusion of diabase dikes and basaltic to diabase sills. Basalt flows are present in Triassic sedimentary rock. Heated circulating groundwaters probably mixed with hydrothermal solutions fluids reacted with plagioclase to form prehnite and laumontite. The excessive calcium reacted with silica to produce the fracture filling laumontite and calcite with lower temperatures other zeolites crystalllized. Two generations of diabase dikes are evident; suggesting that igneous activity persisted as
the stress changed. As temperatures subsided, other zeolites crystallized. This period of zeolite grade thermal alteration metamorphism is widespread in rocks of the southern Appalachians especially Charlotte Terrane.
ACKNOWLEDGEMENTS
I thank Dr. Robert D. Hatcher, Jr.,UT Distinguished Scientist and Professor of Geology, Department of Geological Sciences, University of Tennessee Knoxville, Tennessee for his insightful and complete review of my manuscript and preparation of Figures 1, 2 and 3.
Table I SUMMARY OF PREVIOUSLY REPORTED LAUMONTITE OCCURRENCES
Location Host Rocks types of laumontite*
Other zeolites Other Secondary Minerals
References
FF R D
Near Durham, NC Metamorphosed greenstone and crystal tuffs
x Furbish, 1965
Foote mine Cleveland County, NC
Spodumene pegmatites and amphibolites
x x prehnite and about 80 secondary minerals
White, 1969
Nello Teer Quarry, Durham, NC
Diabase sill (Triassic)sedimentary rocks
x x Furbish, 1972
Near Great Falls, southeastern Chester, Co., SC
meta-adamellite x x epidote Privett, 1973a
Western Rowan Co.,NC (Woodleaf Quarry)
Diorite intruded by 300 ma. adamellite
x x x stilbite,chabazite heulanditescolecite
prehnite, calcite epidote, flourite
Privett, I973b
Southern Fairfield Co., SCV.C. Summers plant
almandine amphibolite ? (no Probe) and granodiorite
x chlorite South CarolinaGas and Electric,1977
Near Apex, Wake Co., NC
Diabase dikes and Triassic sedimentary rocks
x x harmontoneheulandite
barite and saponite Ragland, 1977
Eastern Cherokee Co., SC
Rhyolites and felsic gneiss x x x calcite,epidote, chlorite
Privett, 1974b
Eastern Fairfield Co., SC
Granite and hornblendegneiss and 300 m.y. adamellite
x x epidote, calcite chlorite Law Engineering,1975
Near Tirzah NorthCentral York Co.,SC
Metadiorite, diorite, mafic dikes and Triassic diabase dikes
x x stilbite prehnite, epidote Butler, 1976
North Central York Co., SC (Catawba)
Meta-adamellite and metamorphosed mafic dikes (532 m.y.)
x x x heulandite quartz Bobyarchick and Glover, 1979
Monticello Reservoir6 km. south of V.C. Summer N. P.
quartz monzonite x Secor, 1982
Dorchester Co, SC CC# 1
early Jurassic basalt x x Gotfried, 1983
South central Georgia diabase, sandstone and felsic volcanics
x x x prehnite, epidote pumpellite
Chones and Williams,1983
Old Pineville Quarry, York Co. SC
metagabbro x heulandite stilbite
calcite prehnite epidote Butler, 1983
Iredell Co., NC between I- 40 and US 64/70.
schist x quartz prehnite Milton, 1981
Brevard Zone near Atlanta Chattahochee Tunnel, Cobb County, Ga
amphibolite grade gneiss and schist crosscuts regional foliation.
x x (1).quartz-calcite-chlorite assemblagelater laumontite, prehnite, calcite and (2).orange staining of albite and replacement of biotite by chlorite.
Burnley, P.C. , et.al., 2008
Keystone Blue quarry, northeastern Georgia
Elberton fine-grained biotite granite cut by dikes of pegmatitic granite and diabase.
chabazite and the radiating zeolite ? stilbite ,fine-grained individual crystals 0.1 to 1.0 mm, well crystallized
fluorite-chlorite- pyrite-quartz, and calcite
Bulger, Dan, et.al., 2008
*FF = Fracture filling R=Replacement D= Druse
Table 2. Summary of Additional Laumontite Occurrences
LocationType oflaumontite
Other Zeolites and Secondary Minerals
Host Rock FF R D
McGuire Nuclear Sta. and Cowans Ford Dam Foundation borings northwestern Mecklenburg and Lincoln Co., NC, Duke Power core repository.
Metadiorite x x epidote
Pineville Quarry southern Mecklenburg Co., NC off Hwy. 51 rock core. Duke Power core repository.
Gabbro metagabbro x x prehnite, calcite
Boring, N.E. Gaston Co. NC .2 mi. east of US 16 on the Catawba River (Riverbend) Duke Power core repository
Medium-grained blue-gray biotite adamellite
x x prehnite
Arrowood Quarry 0.4 mi; east I-77 Mecklenburg Co. NC, Duke Power core repository
Metagabbro x x epidote calcite
Hyco Reservoir, Person Co. NC (road below dam) hornblende schist cut by small pegmatites
x x x
Whitnel Quarry near Lenior, Caldwell Co., NC Hornblende gneiss x Epidote calciteHickory Quarry 0.5 mi. north US 321, 0.8 mi. East County Road 1536, Catawba Co. NC
Augen granite gneiss and pegmatites
x epidote calcite
Quarry off SC 901, northeastern Fairfield Co. biotite gneiss and porphyry dikes
x x epidote
Borrow Pit off SC 72, S.W. Chester Co. SC also in roadcuts for new bridge 2007.
Metagranite and mafic dikes x x prehnite epidote
Borings North Cabarrus, Northeastern Rowan, Davidson, Davie, Guilford, Stokes and Alamance counties,NC 52 occurrences, Duke Power core repository,
Granite, diorite sheared igneous rocks; metasedimentary and metavolcanic rocks.
x x x prehnite, calcite, epidote
South Boston, VA. hornblende gneiss cut by pegmatites
x x stilbite, epidote, calcite
Boring Rock Hill Printing, White St. Rock Hill, SC, Duke Power core repository.
Metadiorite x x epidote
Apt. Complex off SC 161,Rock Hill, SC. Metadiorite x epidoteGreat Falls, SC, Chester County Rd. borrow pit. metagranite x xNorth Quarry, west of Winston-Salem, Forsythe Co. NC.
Foliated granite to hornblende gneiss
x x calcite, epidote
Stokesdale Quarry 1 mile west NC 158 Guilford Co. NC.
Biotite-hornblende gneiss cut by mafic dikes
x chabazite, stilbite, calcite
Jamestown Quarry, off County road 1147, 1.5 miles east of I-85. Guilford Co. NC.
Hornblende gneiss and metagranite
X x x stilbite, heulandite, quartz calcite
Lexington Quarry off county Road 1646, 0.7 mi. east US 52 Davidson Co. NC.
Adamellite cutting metadiorites and amphibolites
x x x prehnite, epidote, calcite
Churchland pluton-Davie andDavidson Counties, NC Duke Power core repository,
Albite granite - (300 m.y.)27 separate borings[
x x prehnite, epidote
Boring Marshall Steam Station off Hwy. 150 eastern Catawba Co. NC, Duke Power core repository.
Metadiorite x x prehnite, epidote
Smith Grove Quarry, Davie Co. NC Gabbro-diorite x x prehnite, epidoteCentral Rock Products Quarry, east 421. central Guilford Co. NC
MetagraniteGranodiorite
x
Pomona Quarry south 1-40 at end of Co. Road I539.
Chlorite schist and granite gneiss
x stilbite, calcite
Inactive quarry, Kings Creek, western York, Co., SC
metadiorite x epidote
4 borings near Kings Creek eastern Cherokee Co. , SC (across creek from above), Duke Power core repository
metadiorite x x prehnite, calcite
*FF = Fracture filling R=Replacement D= Druse
Table 3X-Ray Diffraction Powder Data laumontite-leonhardite
I II III IV whkl(s) dA I dA I dA I dA I dA I110 9.52 84 9.50 100 9.46 100 9.44 100 9.43 78200 6.98 80 6.84 90 6.84 80 6.83 75 6.83 s6201 6.23 w 6.19 10 6.20 W 6.18 10 6.18 w111 5.05 18 5.04 10 5.04 10 5.04 20 5.04 18220 4.74 30 4.73 30 4.72 30 4.72 14 4.72 16221 4.52 25 4.49 27 4.49 15 4.49 22 4.49 32130 4.17 100 4.16 95 4.16 100 4.15 100 4.15 100131 3.77 w 3.78 w 3.77 w 3.77 18 3.76 w401 3.67 28 3.66 40 3.56 30 3.65 56 3.66 42002 3.52 56 3.51 55 3.51 40 3.50 60 3.51 94131 3.41 16 3.41 10 3.41 10 3.41 16 3.40 26312 3.37 w 3.35 w W 3.36 40 3.36 34040 3.27 50 3.28 50 3:27 50 3.27 60 3.27 63311 3.20 18 3.21 38 3.20 25 3.19 60 3,20 45330 3.16 32 3.17 20 3.15 25 3.15 32402 3.07 15 3.09 w420 3.04 46 3.03 40 3.03 40 3.03 40 3.03 45240 2.97 W 2.96 W 2.95 W 2.95 w511 2.88 24 2.89 30 2.88 25 2.87 25 2.88 38422 2.80 12 2.79 12 2.80 W 2.79 22 2.80 w331.512 2.63 w 2.60 25 2.63 w 2.64 W 2.64 w241 2.58 28 2.57 w 2.57 20 2.57 30 2.57 34132 2.54 w222,203 2.52 14 2.52 w 2.52 w601,441 2.44 26 2.45 30 2.44 25 2.44 43403 2.39 16 2.39 w151 2.36 24 2.36 w 2.36 15 2.36 23250 2.27 12 2.29 w 2.27 10 2.27 w622 2.22 w 2.21 w 2.22 w 2.22 w060 2.18 14 2.19 25 2.18 w333,620 2.16 30 2.15 15 2.15 20 2.15 28
I. Euhedral white crystal on diorite. Woodleaf (luarry. Rowan CountyII Pink asicular crystals, Lexin9ton Quarry, Davidson County, North CarolinaIII. Laumontite, pink asicular crystals from -790 feet in well drilled in East Spencer,
Rowan County, NC, Isenhour Brick and Tile Company.IW Leonhardite. Madsen and Murata, 1970, p. 193W Laumontite, LIou, 1971, p. 386.(s) after Liou, 1971, p. 386.
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Figure 1. Geologic Provinces SC, NC, Va., and Ga. Hatcher, Tectonic index map, 2007.
Figure 4. Carse-grained white laumontite on fracture in diorite, Woodleaf Quarry, Rowan County, NC.
Figure 5. Brecciated diorite with vein filled by white calcite and pink laumontite.
Lexington Quarry, Davidson County, NC
6A
6B
Figure 6A and B “Pseudomorph” of laumontite after plagioclase, displaying the typical mottled mosaic texture seen in plane light.
Figure 7 Texture of partly laumonitized plagioclase in quartz monzonite, mottled texture, center unaltered. Plane light.
Lexington Quarry, Davidson County, NC
Figure 8 A and B. Texture of partly laumontized plagioclase in quartz monzonite, Lexington Quarry Davidson County, NC. The plagioclase crystal in the center bottom still retains twinning while twinning is nearly destroyed in the
more completely altered crystal at the right. A. plane light. B. crossed polars
