"A study of the occurrence of nickel and cobalt in the Southeast Missouri Mining District has revealed several significant geochemical trends and mineralogical relationships. Regional geochemical studies indicate that the greatest concentration of nickel and cobalt occurs in the Fredericktown area. Mines in the Viburnum Trend also have significant concentrations of these metals. Studies of the Viburnum Trend have established that both nickel and cobalt decrease in concentration southward from the Magmont mine to the Brushy Creek mine, increase at the Fletcher mine, and decrease again at the Sweetwater mine.
A detailed geochemical study of the Buick mine has shown that this same decrease southward is more pronounced at the mine level and that copper trends very closely mimic those of nickel and cobalt. The north-south zoning is also substantiated by an observed decrease in silicification from north to south within the Magmont and Buick mines. Studies of the individual ore bodies reveal differences in metal zoning which indicate that they may not be contemporaneous.
Nickel/cobalt ratios also show significant patterns. For the Viburnum Trend, the nickel/cobalt ratio gradually increases southward from the Magmont mine to the Brushy Creek mine, then decreases southward from the Fletcher mine to the Sweetwater mine. A vertical cross section of one high cobalt-nickel zone within the Buick mine indicates that nickel/cobalt ratios also increase toward the center of the zone.
An ore microscope and microprobe study reveals that although siegenite is the dominant nickel-cobalt mineral present in the ores, four other thiospinel minerals occur: carrollite (Co₃S₄), nickelean carrollite ((Co,Ni,Cu)₃S₄), fletcherite ((Co,Ni,Cu)₃S₄) and polydymite (Ni₃S₄). The nickel sulfides bravoite ((Ni,Fe)S₂), vaesite (NiS₂) and millerite (NiS), and the nickel arsenide gersdorffite (NiAsS) are also present.
Thiospinel composition varies dramatically within the district. Paragenetic studies of deposits in host rocks ranging in age from Precambrian to Upper Cambrian have shown that the strati graphically lowest thiospinels are the most cobalt-copper-rich and nickel-poor. Stratigraphically higher thiospinels have an increasing nickel content and a decreasing cobalt content.
Studies of Buick polydymite indicate that it formed by supergene alteration of millerite late in the mineralizing sequence of the ores. Furthermore, this alteration appears to have occurred subsequent to the major stage of octahedral galena deposition but immediately preceeding the deposition of cubic galena.
Nickel/cobalt ratios and concentration gradients support a duel source for these metals, a major source in proximity to the Magmont mine and a less important source near the south end of the Viburnum Trend. Geochemical and mineralogical studies are consistent with a model which postulates that early cobalt-copper-rich hydrothermal fluids generated from basement sources near the Viburnum Trend migrated easterly and mixed with basin derived, lead-zinc-rich brines at or near the present site of the ore deposits. With time, the nickel content in the hydro- thermal solutions increased and copper and, to a lesser extent, cobalt decreased. During the waning stages of mineralization, supergene fluids significantly altered the character of the mineralizing solutions as evidenced by concurrent dissolution and silicification"--Abstract, page iii.
Hagni, Richard D.
Grant, S. Kerry
Sorrell, Charles A.
Geosciences and Geological and Petroleum Engineering
Ph. D. in Geology and Geophysics
University of Missouri--Rolla
xiii, 217 pages
© 1981 David Ray Jessey, All rights reserved.
Dissertation - Restricted Access
Geochemistry -- Missouri
Geology -- Missouri
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Jessey, David Ray, "An investigation of the nickel-cobalt occurrence in the Southeast Missouri Mining District" (1981). Doctoral Dissertations. 119.
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