W^ord to the Wise

JOHN RAKOVANDepartment of Geology

Miami UniversityOxford, Ohio 45056

rakovajf@muohio.edu

Figure 1. Galena crystal, 3.2 cm across, with chalcopyrite anddolomite. Brushy Creek mine, Viburnum Trend, ReynoldsCounty, Missouri. Dan Weinrich specimen and photo.

MississippiValley-Type Deposits

M 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°-150°C), (2) epigenetic(forming after) emplacement within restricted dolstone orlimestone strata of sedimentary basins (i.e., stratigraphicallycontrolled), (3) precipitation from highly saline brines, and(4) the presence of barite and/or Ouorite gangue mineraliza-tion (Leach and 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). Although they arefound around the globe, the MVTs within the MississippiRiver drainage basin are the largest and v̂ -ere the first to bestudied in detail—thus 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, is aprofessor of mineralogy and geochemistry at Miami Universityin Oxford, Ohio.

Figure 2. Calcite, doubly terminated crystal 7 cm long,Milliken (Sweetwater) mine. Viburnum Trend, ReynoldsCounty, Missouri. Dan Weinrich specimen and photo.

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 specimens), tennantite, vaesite, and others.

MVT deposits tend to occur in clusters (forming a dis-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 traveledhundreds of kilometers. 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 district. Northwest Territories, Canada; the Cornwallisdistrict, Canada; the Upper Mississippi Valley district. UnitedStates (Wisconsin, Iowa, and Illinois); the Viburnum Trend,southeast Missouri, United States; the Old Lead Belt, south-east Missouri, United States; the Central Tennessee district.United States (Elmwood-Gordonsville); the Eastern Tennes-see district. United States; the Tri-State district, United States(Missouri, Kansas, and Oklahoma); the Silesia-Cracow dis-trict, Poland; the Cevennes region of southern France; the

Volume 81, January/February 2006 69

Figure 3. Sphalerite on Kosiclare sandstone,Rosiclare level, "butter knife" pod, Dentonmine, Ozark-Mahoning Company, HarrisCreek district, southern Illinois. Specimenis 3 X 7 X 11.6 cm, main crystal 1.8 x 2.5 cm;mined March 1986. Ross C. Lillie specimen(#1288), Jeff Scovil photo.

Figure 4. Barite on fluorite, Rosiclarelevel, main orebody, Denton mine, Ozark-Mahoning Company, Harris Creek dis-trict, southern Illinois. Specimen is 2 x 2.7X 3.3 cm, main crystal 2 x 2.7 cm; mined1982. Ross C. Lillie specimen (#0352),Jeff Scovi] photo.

Figure 5. Galena on tluorite, Rosiclarelevel, "wafer" pod, Denton mine,Ozark-Mahoning Company, HarrisCreek district, southern Illinois.Specimen is 3.2 x 4.5 x 7 cm, maincrystal 3.1 cm; mined ca. 1988. RossC. Lillie specimen (#1969), Jeff Scovilphoto.

Figure 7. Calcite on fluorite,"St. Louis" level, Annabel Lee mine,Ozark-Mahoning Company, HarrisCreek district, southern Illinois.Specimen is 3.5 x 7.6 x 10 cm, maincalcite crystal 8.5 cm; minedSeptember 1988. Ross C. Liiliespecimen (#1170), Jeff Scovil photo.

Figure 6. Fluorite on barite, Rosiclarelevel, Minerva No. 1 mine, Ozark-Mahoning Company, Cave-in-Rockdistrict, southern Illinois. Specimenis 3.5 X 5 X 6 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, among 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 dominant 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). Other

70 ROCKS & MfNERALS

districts that have been classified as this subtype includethe Pennines in the United Kingdom (Fisher 2004) and theHansonburg mining district (and related deposits of the RioGrande Rift, New Mexico, United States [Demark 2003]}.The features that set the fluoritic subtype apart from typicalMVT deposits (fluorine concentration, the possible relation-ship to igneous activity, and so on) are distinct enough thatsome authors consider them a separate type of deposit (e.g.,Hansonburg mining district; McLemore et al. 1998).

ACKNOWLEDGMENTSI would like to thank Kendall Hauer and Andrew Sicrcc for their

helpful reviews and comments. I am also grateful to Jeff Scovil,Ross Lillie, and Dan Weinrich for their help and for photographs.

REFERENCESBradley, D. C, and D. L. Leach. 2003. Tectonic controls of Missis-

sippi Valley-type lead-zJnc mineralization in orogenic forelands.Mineraliiim Deposita 38:652-67.

Bradley D. C, D. L. Leach, D. Symons, P. Emsbo, W. Premo, G. Breit,and D. F. Sangster. 2004. Reply to discussion on "tectonic con-trols of Mississippi Valley-type le;id-zinc mineralization in oro-genic forelands" by S. E. Kesler,). T Chesley, |. N. Christenscn, R.D. Hagni, W. Heijlen, J. R. Kyle, K. C. Misra, R Muchez, and R.van der Voo. Mincralium Deposita 39:515-19.

Demark, R. S. 2003. Fluoritc from the Blanchard mine group. Rocks& Minerals 78:380-89.

Fisber, J. 2004. Fluorite from the Northern Pennines orefield, Eng-land. Rocks 6~ Minerals 79:378-98.

Heyl, A. V. 1983. Geologic charncteristicsoftbree major MississippiValley type district.s. In Internationa! conference on Mississippi Val-ley type lead-zinc deposits: Proceedings vohinie, ed. G. Kisvarsanyi,et al., 27-60. RoUa: University of Missouri—Rolla Press.

Kesler, S. E.,). T. Chesley, ]. N. Cbristensen, R. D. Hagni, W. Heijlen,

|. R. Kyle, K. C. Misra, P. Muchez, and R. van der Voo. 2004. Dis-cussion of "tectonic controls of Mississippi Valley-type lead-zincmineralization in orogenic forelands" hy D. C. Bradley and D. LLedch. Mineraliiim Deposita 39:512-14.

Lasmanis, R. 1989. Galena from Mississippi Valley-type deposits.Rocks & Minerals 64:11-34.

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 Miirsily. 200i. Mississippi Valley-type lead-zinc depositsthrough geological time: Implications from recent age-datingresearch. M/M[T(I(I»»I Deposita 36:711^0.

Lillie, R. 1988. Harris Creek fluorspar district, Hardin County, Illi-nois. Rocks & Minerals 63:210-26.

Locock, A., R. Mussieux, and R. Tyson. 2006. Minerals of the PinePoint lead-zinc deposits. Rocks & Minerals 8:24-33.

McLetnore, V. T., T. H. Giordano, V W. Lueth, and J. C. Witcher.1998, Origin of barite fluorite-galana deposit in the Rio GrandeRift, New Mexico. In New Mexico Geological Society guidebook,vol. 49, 251-64.

Misra, K. C. 1999. Understanding mineral deposits. Boston, MA: Klu-wer Academic Publishers.

Partey, F., F.. Widom, V. Lucth, S. Lev, and |. Rakovan. 2004. Tracingthe source of fluorine in the fluorite mineralization of tbe South-ern Rio Grande Rift, In N\V Regional Geological Society of AmericaMeeting, abstracts with program, vol. 36, 22-23. (A paper on tbiswork has been submitted to Economic Geology.)

Plumlee, G. S., M. B. Goldhaber, and E. L. Rowan. 1995. The potentialrole of tnagmatic gases in tbe genesis of Illinois-Kentucky fluor-spar deposits: Implications from chemical reaction path model-ing. Economic Geology 90:999-1011.

Sangster, D. F, 1995. Mississippi Valley-tj'pe lead-zinc. In Geology ofCanadian mineral deposit types, ed. O. R. Eckstrand, W. D. Sinclair,and R. 1. Thorpe, 253-61. Ottawa: Geological Survey of Canada.

Sverjensky, D. A. 1986. Genesis of Mississippi Valley-type lead-zinc deposits. Annual Review of Earth and Planetary Science14:177-99. J

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