Abstract

Analyses of fluid inclusion leachates indicate that the composition of the ore-forming fluids of the Viburnum Trend was similar to that of typical oil-field brines. Relatively elevated K (super +) /Na (super +) values (0.034-0.15, by weight) of the ore-forming fluids may reflect interaction of the fluids with granitic basement or with arkosic sediments. Br (super -) /Cl (super -) values (0.0042-0.0051, by weight) of the fluid inclusions in octahedral galena crystals are greater than that of present-day seawater (0.0035) and suggest that the brines from which the octahedral galenas were deposited originated as evaporated seawater. Br (super -) /Cl (super -) values (0.00125-0.0022) of the fluids from which the cubic galenas were deposited are significantly lower than that of present-day seawater, suggesting that much of the salinity of these fluids was derived from the dissolution of halite. 87 Sr/ 86 Sr ratios of 0.7097 to 0.7102 were determined for fluid inclusion leachates from a sample of cubic galena.A rough correlation between the isotopic composition of lead and sulfur persists in galenas throughout the Viburnum Trend. The general trend of the isotopic data can be explained in terms of the mixing of two end members, one containing isotopically heavy sulfur and less radiogenic lead, the other containing isotopically light sulfur and more radiogenic lead. The isotopic composition of lead and sulfur in octahedral galenas is closer to that of the first end member; the isotopic composition of lead and sulfur in cubic galenas is closer to that of the second end member. The isotopic composition of the less radiogenic (normal) lead component is similar to that of lead in oil-field brines. The more radiogenic lead component has a composition that is consistent with a source 1.0 to 1.2 Ga in age. The origin of the sulfur in both end members appears to have been marine sulfate.The results of various age determinations on the ores, the physical attributes required of the source basin, and the similarity between the composition of the ore-forming fluids and present-day Arkoma basin brines suggest that the Arkoma-Ouachita basin was the source of the ore-forming fluids during the later Carboniferous or the Early Permian. Correlation of the isotopic composition of lead and sulfur in the galenas strongly suggests that these elements were transported together in solution. Available geologic and geochemical data appear to be most consonant with the sulfate reduction model for ore deposition.

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