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ord to the iseJOHN RAKOVAN
Department o f Geo logyMiami University
Oxford Ohio 4 5 0 5 6rakovaj f@muohio .edu
Figure1.Galena crystal, 3.2 cm across, with ch alcopyrite anddolomite. Brushy Creek mine, Viburnum Trend, ReynoldsCounty, Missouri. Dan Weinrich specimen and photo.
MississippiValley-Type Deposi ts ississippi Valley-type deposits, commonly referredto as MVTs, are hydrothermal lead-zinc ore depos-its that are characterized by (1) low-temperature forma-tion (50-200''C, but usually 100-150C), (2) epigenetic(forming after) emplacement within restricted dolstone orlimestone strata of sedimentary basins (i.e., stratigraphicallycontro lled), (3) precipitation from highly saline brines, and(4) the presence of barite and /or Ouorite gangue m ineraliza-tion (Leach an d Sangster 1993; Sangster, 1995; Misra 1999;Leach et al. 2001). They are also typically found far from,and lack a genetic relationship to, igneous activity or igne-ous rocks (Heyl 1983; Sverjensky 1986). Althoug h they arefound around the globe, the MVTs within the MississippiRiver drainage basin are the largest and v^-ere the first to bestudied in detailthus the origin of their name.
MVT deposits host a large proportion of Earth's econom-ic zinc and lead and are thus of great societal importance.The most abundant minerals in MVTs are sphalerite andgalena (the ores of zinc and lead respectively), barite, fluo-rite, calcite, and dolomite. Several other minerals arc foundin substantial quantities; quartz and pyrite are also com-mon gangue minerals and some deposits or districts (i.e.,Viburnum Trend) host significant copper mineralization.Although the mineralogy is rather simple, the paragenesis(time sequence of mineral formation) can be complex, withmultiple precipitation and dissolution events. Althoughtypically present in small amounts, many other miner-
Dr. John Rakovan, an executive editor o/Rocks Minerals ,isaprofessor of mineralogy and geochemistry at Miami Universityin Oxford Ohio.
igure2 .Calcite, doub ly termin ated crystal 7 cm long ,Milliken (Sweetwater) mine. Viburnum Trend, ReynoldsCounty, Missouri. Dan Weinrich specimen and pho to.
als may also be found in MVT deposits. An example is inthe Viburnum Trend, where minerals of minor abundanceinclude anilite, arsenopyrite, bornite, carroUitc, chalcopyrite,enargite, gersdorffite, millerite, polydymite, siegenite (inexceptional specim ens), tennantite, vaesite, and o thers.MVT deposits tend to occur in clusters (forming adis-trict at the margins of sedimentary basins, and they are inti-mately associated with the evolution of these basins. Mostdistricts cover hundreds, and in some cases thousands, ofsquare kilometers (Misra 1999). It has long been suggestedthat MVTs are the result of huge hydrothermal systemsinvolving massive quantities of fluids that have traveled
hu nd reds of kilom eters. Recent studies have even suggesteda relationship to major tectonic events that may supply adriving force for these hydrologic systems, although this isstill an issue of some debate (Leach et al.2001;Bradley andLeach 2003;Kesler et al. 2004; Bradley ct al. 2004).Well-known examples of MVT deposits include the PinePoint d istrict. Northwest Territories, Canada; the Cornwallisdistrict, C anada; the U pper M ississippi Valley district . UnitedStates (Wisconsin, Iowa, and Illinois); the Vibu rnum Trend,southeast M issouri, United States; the O ld Lead Belt, south-east Missouri, United States; the Central Tennessee district.United States (Elmwood-Gordonsville); the Eastern Tennes-
see district. Un ited States; the Tri-State district, Un ited States(Missouri, Kansas, and Oklah oma); the Silesia-Cracow dis-trict, Poland; the Cevennes region of southern France; theVolume 8 1 January/February 2006 69
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igur 3 Sphalerite on Kosiclare sandstone,Rosiclare level, "bu tter knife" pod, Dentonmine, Ozark-Mahoning Company, HarrisCreek district, southern Illinois. Specimenis 3X7X11.6 cm, main crystal 1.8 x 2.5 cm;mined March 1986. Ross C. Lillie specimen(#1288), Jeff Scovil ph oto .
igur 4 Barite on fluorite, Rosiclarelevel, main orebody, Denton mine, Ozark-Mahon ing Com pany, Harris Creek dis-trict, southern Illinois. Specimen is2x 2.7X3.3 cm, m ain crystal 2 x 2.7 cm; m ined1982.Ross C. Lillie specimen (#0352),Jeff Scovi] photo.
igur 5.Galena on tluo rite, R osiclarelevel, "wafer" pod, D enton mine,Ozark-Mahoning Company, HarrisCreek district, southe rn Illinois.Specimen is 3.2 x 4.5 x 7 cm, m aincrystal 3.1 cm; mined ca. 1988. RossC. Lillie specim en (#1969), Jeff Scovilphoto. Figure7 Calcite on fluorite,"St. Louis" level, Annabel Lee mi ne,Ozark-Mahoning Company, HarrisCreek district, southern Illinois.Specimen is 3.5 x 7.6 x 10 cm, m aincalcite crystal 8.5 cm; minedSeptember 1988.Ross C . Liiliespecimen (#1170), Jeff Scovil photo.
igur 6 Fluorite on barite, Rosiclarelevel, Minerva N o. mine, Ozark-Mahoning Company, Cave-in-Rockdistrict, southern Illinois. Specimenis 3.5X 5 X6 cm, main crystal 2.5 cm;mined April 1993. Ross C. Lilliespecimen (#0759), Jeff Scovil photo.
Reocin deposit in northern Spain; El Abadekta, Morocco;Vazante, Brazil; San Vicente, Peru; and the Sorby J-Iil s,Coxco, and Lennard Shelf districts, Australia. MVT depositshave been the source of some of the world's best galena,sphalerite, barite, fluorite, and calcite specimens, amo ng oth-ers. To learn more about some of these deposits and theirmineralogy see Lillie (1988), Lasmanis (1989), Fisher (2004),and Locock, Mussieux, and Tyson (2006, this issue).
Although MVTs share the common features listed above,if one looks in detail at these deposits it becomes apparentthat there is a great diversity in their characteristics (i.e., theratio of lead to zinc, the do min ant gangue minerals, the exactstyle of emplacement, trace-element and isotope chemistry,and so on) and possibly in their origins. The differencesand similarities have been the subject of numerous studies,and many scientists have grouped MVTs into subclasses,whereas others have considered diversity as one of the char-acteristic features of these deposits. A common division of
different MVT deposits (Leach and Sangster 1993) includesthe lead-rich subtype (e.g., the Ozark districts of the Vibur-num Trend; Zn/Pb = 0.25-0.8), the zinc-rich subtypes (e.g.,the Tri-State district; Zn/Pb = 16), and the fluoritic subtype(e.g., the Illinois-Kentucky fluorspar district).
In the fluoritic subtype, fluorine concentrations are sohigh that fluorite is the dominant gangue mineral or maybe present in economic concentrations as an ore ot fluorine(used in steel manufacturing, toothpaste, drinking watersupplies, hydrofluoric acid, fluorochloro-hydrocarbons, andso forth). Indeed, the Illinois-Kentucky fluorspar districtproduced 75 percent of the fluorite mined in the UnitedStates during the twentieth century. This is in contrast tothe scarcity or absence of fluorite in many MVTs. The sourceof the anomalously high concentrations of fluorine in thesedeposits has been a topic of serious interest and debate andmay be related to igneous activity in some districts (Plum-lee, Goidhaber, and Rowan 1995; Partey et ai. 2004). Othe r
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districts that have been classified as this subtype includethe Penninesin theUnited Kingdom (Fisher 2004)and theHansonburg mining district and related depositsoftheRioGrande Rift, NewMexico, United States [Dem ark 2003]}.The features thatset thefluoritic subty pe apart from typicalMVT deposits (fluorine con centration, the possible relation-shiptoigneous activity, andso on) are distinct enough thatsome authors consider themaseparate typ eofdeposit (e.g.,Hansonburg mining district; McLemoreetal. 1998).
ACKNOWLEDGMENTSI would liketothank Kendall HauerandAndrew Sicrccfortheirhelpful reviews and comments. I am also grateful to Jeff Scovil,Ross Lillie,andDan W einrichfortheir helpand forph otographs.REFERENCESBradley, D.C and D. L.Leach.2003.Tectonic controlsofM issis-sippi Valley-type lead-zJnc m ineralization inorogenic forelands.MineraliiimDeposita38:652-67.BradleyD.C, D. L.Leach,D.Symons,P.Emsbo,W. Premo , G. Breit,
andD.F. Sangster. 200 4. Replytodiscussionon tectoniccon-trolsofMississippi V alley-type le;id-zinc mineralization in oro-genic forelands byS.E. Kesler,).TChesley,|.N. Christenscn,R.D.Hagni, W. Heijlen,J. R.Kyle, K.C.Misra,RMuchez,and R.van derVoo. MincraliumDeposita 39:515-19.Demark, R. S.2003.Fluoritc fromtheBlanchard mine g roup.Rocks&Minerals78:380-89.Fisber, J. 2004. Fluorite fromtheNor thern Pennines orefield, Eng-land.Rocks6~Minerals79:378-98.Heyl,A. V. 1983. Geologic charncteristicsoftbree major MississippiValley type district.s.InInternationa conferenceonMississippiVal-leytype lead-zincdeposits:Proceedings vohinie,ed. G. Kisvarsanyi,et al., 27-60. RoUa: UniversityofMissouriRolla Press.Kesler,S.E.,). T. Chesley,] .N. C bristensen, R. D. Hagni,W. Heijlen,
|. R. Kyle, K. C. Misra, P.Mu chez, and R. van derVoo. 2004. Dis-cussionof tectonic controlsofMississippi Valley-type lead-zincmineralization in orogenic forelands hyD.C.Bradleyand D. LLedch.Mineraliiim Deposita 39:512-14.Lasmanis, R. 1989. Galena from Mississippi Valley-type deposits.Rocks&Minerals64:11-34.Leacb,D. L., and D.F.Sangster. 1993. Mississippi Valley-type lead-zincdeposits. Geological Association o( Canada special paper 40,Leacb,D. L, D.C. Bradley, M. Lewchuck,D. T. A.Symons,J.Brannon,and G. de M iirsily. 200i . Mississippi Valley-type lead-zinc dep ositsthrough geological time: Implications from recent age-datingresearch.M/M[T(I(I IDeposita 36:711^0.Lillie,R. 1988. Harris Creek fluorspar district, Hardin County, Illi-nois.Rocks&Minerals63:210-26.Locock, A.,R.Mussieux,and R. Tyson. 2006. Mineralsof thePinePoint lead-zinc deposits.Rocks&Minerals8:24-33.McLetnore, V.T., T. H.Giordano,V W.Lueth,and J. C.Witcher.1998, Originof barite fluorite-galana deposit in the RioGrandeRift, NewM exico.InNewMexicoGeological Societyguidebookvol. 49, 251-64.Misra, K.C. 1999.Understanding mineraldeposits.Boston, MA:Klu-wer Academic Publishers.Partey, F.,F..Widom,V.Lucth, S. Lev,and |.Rakovan. 2004. Tracingthe sourceoffluorinein thefluorite mineralizationoftbe South-ern Rio Grande Rift,InN\V Regional Geological Societyof AmericaMeeting abstracts with program,vol. 36,22-23. Apaperontbiswork has been submittedtoEconomic Geology.Plumlee, G. S., M. B.Goldhaber, andE. L. Rowan.1995. The potentialroleof tnagmatic gasesin tbegenesisof Illinois-Kentucky fluor-spar deposits: Implications from chemical reaction path model-ing.Economic Geology 90:999-1011.Sangster, D.F, 1995. M ississippi Valley-tj'pe lead-zinc.InGeologyofCanadian mineral deposit types,ed. O. R. Eckstrand,W. D. Sinclair,and R.1.Thorpe,253-61.Ottawa: Geological SurveyofCanada.Sverjensky, D. A. 1986.Genesis of Mississippi Valley-type lead-zinc deposits. Annual Reviewof Earthand Planetary Science14:177-99. J
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