Nickel in chalcopyrite – Bingham District, Utah: Supplement 18 from "Trace elements in sulfide minerals from the Central Mining District, New Mexico and the Bingham Mining District, Utah" (Thesis)

A total of 143 samples of chalcopyrite, 230 samples of sphalerite, and a few samples of other hydrothermal minerals from the Central and Pinos Altos mining districts of New Mexico, and the Bingham mining district of Utah, have been analyzed spectrographically for trace element content. Most of the sphalerites have also been analyzed for iron content by an x-ray fluorescence method. For many elements, variations within single crystals and within mines show no correlation with variations of other elements in the sulfides, indicating that several factors, not temperature alone, are of importance in determining the trace element content of sulfides. Changes in the composition of the hydrothermal fluid with time and position are believed to be the most important causes of variations in the sulfides, but temperature and lack of equilibrium are also believed to be significant. In the chalcopyrite and sphalerite from both districts the trace element contents are found to fall readily into two or more groups as defined by trace element content. The groups can generally be distinguished geographically and also show geologic and mineralogic differences, although enough similarities exist among groups in the Central mining district to conclude that temperature and other environmental factors are not the primary cause for the grouping, but that the differences probably existed in the hydrothermal fluids before they reached the site of deposition. The trace element content of sphalerite from the Central mining district shows a poorly developed but distinct lateral zoning away from the Hanover-Fierro and Santa Rita stocks. This zoning in trace element content is accompanied by an increase in the Pb/Zn ratio and an increase in the average silver content of the ores. A similar zoning may exist in the trace element content of chalcopyrite from this district and in the trace element content of sphalerite from the Bingham mining district. In addition, a poorly developed vertical zoning in the trace element content of sphalerite appears to exist within one ore shoot at Bingham. Either a temperature gradient or concurrent progressive changes in the composition of the hydrothermal fluid and the site of deposition are suggested as possible causes for the zonal relations found. Study of variability of trace element content of chalcopyrite, and sphalerite within mining districts indicates that four or more properly selected samples are necessary to obtain a valid mining district average for use in regional studies such as that made by Burnham (1955). The large variability of iron content of sphalerite within districts, mines, and even veins and single crystals is believed to result in part from variations in temperature, in part from lack of equilibrium between the sphalerite and the adjacent minerals and fluid during deposition, and in part from equilibrium with pyrite rather than pyrrhotite. It is suggested that the iron content of sphalerite is most correctly interpreted to give a minimum temperature of deposition of the sphalerite; that is, the temperature of deposition was at least as high as the value indicated by the iron content on the solvus of the FeS-ZnS system