Masters Theses

Date of Award

6-1984

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Kula C. Misra

Committee Members

Otto Kopp, Hap McSween

Abstract

Pyrite and pyrrhotite were analyzed for 7 trace elements in 59 samples by laser microprobe spectrographic analysis. The concentrations of Co, Ni, Mn, Pb, Ti, Sn and Ag in pyrite and pyrrhotite were determined. This is the first attempt to analyze pyrrhotite using a laser microprobe. Frequency distribution plots of all of the trace elements from both pyrite and pyrrhotite show that the trace elements approach a log-normal distribution rather than an arithmetic-normal distribution. The trace element distribution patterns in the sulfide minerals were examined with respect to effects of metamorphism and ore genesis.

The spatial distribution of trace elements in the sulfide phases from the country rocks (Ocoee Gorge) to the orebodies show definite patterns which can be explained by mobilization of trace elements along with other sulfide constituents during prograde metamorphism. The trace element contents of the sulfides in the Calloway and Cherokee orebodies are quite different. This may be explained by the presence of two distinct ore horizons related to the original syngenetic deposition of the ore. Variations in the trace elements in the sulfides from the hanging wall to the footwall indicate that the orebodies may be zoned. The patterns observed are in good agreement with bulk assay data and may be related to hydrothermal processes during the formation of the orebodies lying horizontally within a sedimentary pile. The reversal of some of the trends in the Cherokee orebody indicate that the Cherokee orebody is overturned. The trace elements in pyrite and pyrrhotite showed several trends from the upper to the lower levels of the Galloway orebody. These patterns may represent lateral zoning in the original orebody subsequently modified by metamorphism. Pyrite from the Cherokee orebody and the country rocks show the highest and lowest Co contents and Co:Ni ratios, respectively. This data along with bulk Zn and Cu assays and strati graphic relationships, indicate that the Cherokee orebody may have formed during an earlier and possibly higher tempera ture phase of ore deposition than the Galloway orebody. Co and Ni data for pyrite plot near the boundary between sedimentary/syngenetic and volcanogenic massive sulfide deposits, suggesting a mixed genetic environment.

The trace element data suggest that the Ducktown deposits had a complex history and cannot be explained by any single genetic model. Early deposition of syngenetic (premetamorphic) massive sulfide lenses occurred away from any volcanic center. Subsequent prograde metamorphism produced mobilization of sulfide constituents, including trace elements, from the country rocks into the orebodies. This process may have added significant amounts of sulfide material and produced one of the largest massive sulfide deposits in the world.

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