Genesis of the Southeast Missouri lead deposits

Several barites from the lead-barite district in southeast Missouri contain between 1,170 and 1,688 ppm Sr. Their S7Sr/S6Sr ratios range from 0.7098 to 0.7118, in contrast to the values of 0.7082 to 0.7089 for the host carbonate rocks. The origin of barites is explained in terms of mixing of two isotopically and chemically different fluids. Four galenas from the Viburnum mine in Southeast Missouri provide a Rb-Sr age of 892 +_ 21 m.y. and an initial isotopic composition of 0.7104 +_ 0.0004, indicating the period of mineralization to be early Devonian. The Sr isotope data from a galena from the lead-barite district tend to indicate a similar age. Data from calcites in association with galenas from the Viburnum mine suggest that the Sr isotopic composition of the fluids varied appreciably during deposition of the ore.

Section: The Southeast Missouri Lead and Barite Deposits Associated Pmentioning

confidence: 99%

Strontium isotopic evidence for the origin of barites and sulfides from the mississippi valley-type ore deposits in southeast Missouri

Lange¹,

Chaudhuri²,

Clauer³

1983

“…Equilibrium between the ore fluids and carbonates in other Mississippi Valley-type deposits has been considered as evidence against an acidic pH of the ore fluids and for sphalerite precipitation by the addition of reduced sulfur from a separate source at the site of deposition rather than from one solution carrying both zinc and reduced sulfur (Anderson, 1975(Anderson, , 1983. Some possible mechanisms for the addition of reduced sulfur include mixing with an H2S-rich fluid (Beales and Jackson, 1966;Beales, 1975;Davis, 1977), thermal degradation of organic compounds (Skinner, 1967;Churnet and Misra, 1983), or reduction of sulfates (Barton, 1967;Hersch and Misra, 1979). However, ore fluids with pH values significantly less than neutral can be in equilibrium with carbonate minerals at appropriately high partial pressures of CO2.…”

Section: Discussionmentioning

confidence: 99%

Fluid inclusion study of the Gordonsville zinc deposit, central Tennessee

Gratz¹,

Misra²

1987

A complementary paragenetic and fluid inclusion investigation of the carbonate-hosted Gordonsville zinc deposit was undertaken to trace thermal and chemical evolution of the mineralizing fluid. The following paragenetic sequence was established from field and petrographic study: white (early) calcite-sphalerite-galena-fiuorite-white to lavender (main stage) calcite-barite-clear to amber (late stage) calcite. Sphalerite occurs in three textural varieties: disseminated (yellowish brown), massive (reddish brown), and vug fill (dark brown). The disseminated sphalerite, with somewhat lower Fe and Cd contents, may represent an earlier stage of mineralization, but its fluid inclusion characteristics are similar to the other two.Homogenization and freezing temperatures of two-phase (liquid q-vapor) inclusions show a pronounced change in the nature of mineralizing fluids between early-stage and late-stage minerals. The early-stage minerals (early calcite through main-stage calcite) precipitated from moderately hot (97ø-133øC) and highly saline Na-Ca-Mg-CI fluids (salinity 9,1-23 equiv wt % NaC1). Variations in homogenization temperatures of the early-stage minerals probably reflect periodic influx of basinal fluids of similar salinites. However, the lack of correlation between homogenization and freezing temperatures suggests, but does not prove, that fluid mixing was not the cause of precipitation of these minerals. The fluid inclusion data for sphalerite are consistent with its emplacement from a single solution carrying both zinc and sulfur, although the model remains untested without a knowledge of the pH of the Gordonsville ore fluid.The late-stage minerals (barite and late-stage calcite) precipitated from a fluid of somewhat lower temperature (96ø-122øC) but markedly lower salinity (7-9 equiv wt % NaC1), suggesting an influx of a more dilute fluid, probably heated meteoric water, at the end of main-stage calcite deposition.

“…This relationship is well developed in three stratigraphic packages in the United States, with indications of the relationship in other carbonate units. The presence of this spatial relationship in numerous carbonate units throughout North America suggests that regionally dolomitized areas have served as aquifers for mineralizing fluids or even that dolomitization of the limestone released many of the ore-forming elements to mineralizing fluids, as suggested by Davis (1977) for the Southeast Missouri lead district. These inferences are supported by the spatial relationship of MVT mineralization to dolomite fronts, but also by the regional similarity of mineralization within each of the stratigraphic packages.…”

Section: Relationship To Genesis Of Mvt Mineralizationmentioning

confidence: 94%

“…This relationship has been noted before, but it is not widely accepted as a primary ore control. For example, Davis (1977) demonstrates that mineralization occurs at the margin of dolomitization of the Bonneterre Formation in the Viburnum Trend of southeast Missouri. Fulweiler and McDougal (1971) and McCormick et al (1971) describe the relationship between dolomite (recrystallized from limestone) to ore-bearing structures in the East Tennessee district.…”

Section: Introductionmentioning

confidence: 99%

Dolomite Fronts and Associated Zinc-Lead Mineralization, Usa

Harper¹,

Borrok²

2007

This paper provides previously unpublished drill core and mapping evidence of the spatial relationship between regional dolomitization and Mississippi Valley-type (MVT) mineralization in the midcontinent of the United States. Dolomitization is discussed for several key carbonate units and their contained MVT mineralization. This more complete picture of the relationship between regional dolomitization and mineralization provides constraints on models for MVT mineralization and serves as an exploration guide for new deposits.