Isotopic compositions of gangue versus ore minerals in the Upper Mississippi Valley zinc-lead district

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5025496

Brannon, J C; Podosek, F A ^[1]; McLimans, R K ^[2]

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1. Washington Univ., St. Louis, MO (United States). Dept. of Earth Planetary Sciences
2. E.I. DuPont de Nemours Co., Deepwater, NJ (United States). Jackson Research Lab.

Four successive stages of gangue calcite occur after sulfide mineralization in the Upper Mississippi Valley zinc-lead district. These are commonly interpreted to represent the waning stage of MTV mineralization, because of spatial association and a smooth transition of decreasing fluid inclusion temperatures from late stage sphalerite through calcites 2 to 4. U-Pb systematics in two calcite 2 crystals suggests an age of 162 Ma, with [mu] values sufficiently great (1,175 and 1,611) that the indicated age is insensitive to initial [sup 206]Pb/[sup 204]Pb. This age for calcite formation is [approx] 100 Ma after that of sulfide mineralization and thus represents recurrent fluid activity along fracture zones. Initial [sup 87]Sr/[sup 86]Sr isotopic composition for three calcite 2 crystals range from 0.70956--0.70961, consist with initial [sup 87]Sr/[sup 86]Sr in the 270 Ma sphalerites. The initial [sup 87]Sr/[sup 86]Sr for two calcite 3 crystals and one calcite 4 crystal range from 0.70845--0.70875, consistent with mid-Ordovician seawater and the host carbonates of that age. The authors propose a hypothesis which is consistent with the Sr and U-Pb isotopic data. 162 Ma ago fluids flushed the existing pore fluids (left over from 270 Ma MVT event) from carbonate strata and deposited calcite 2. Subsequently, additional fluids containing [sup 87]Sr/[sup 86]Sr consistent with that derived from mid-Ordovician carbonates deposited calcite 3 and 4. If this hypothesis is correct the paragenetic connection between ore and gangue mineralization at UMV is weak and geochemical study of the gangue minerals may provide only limited information about the fluid which formed the ores.

• OSTI ID: 5025496
• Report Number(s): CONF-9303210--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:3
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ALKALINE EARTH ISOTOPES
CALCITE
CARBONATE MINERALS
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPED COUNTRIES
GANGUE
GEOCHEMISTRY
GEOLOGIC DEPOSITS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
MINERALS
MISSOURI
NORTH AMERICA
RESIDUES
STRONTIUM ISOTOPES
USA