Abstract

Samples of mineralized jasperoid from the central part of the Taylor silver mining district, near Ely, Nevada, and of unmineralized jasperoid from outlying bodies exhibit characteristics that seem to be useful as guides to the center of mineralization and also to clarify the genesis of the ore deposits. The most reliable indicators of proximity to mineralization centers are a change in color of jasperoid bodies from dominantly brown to dominantly dark gray, an increase in the grainsize and in the abundance of vugs in the matrix quartz, and an increase in the ratio of copper to chromium. The presence of relict sulfides disseminated in the matrix quartz of the jasperoid and the tendency for the concentrations of all the ore metals to fluctuate together in a series of samples taken across a mineralized body of jasperoid suggest that the ore metals were introduced before jasperoid formation ceased and that the ore metals and jasperoid are penecontemporaneous. Both silica and metals are inferred to have been derived from a buried stock that underlies the district. Maps of anomalies for the ore metals suggest the possibility of an eastern extension of the main mineralized area and of small separate centers of mineralization in both the northern and southern parts of the district.The ores of this district are unusual in that they consist largely of jasperoid containing abundant tiny disseminated grains of ore and gangue minerals, although there are also a few bodies of coarse-grained ore in the jasperoid. These jasperoid ores are most abundant in the central part of the district, grading outward into unmineralized jasperoid.The ore-bearing jasperoid in the central part of the Taylor district plus the wide distribution of apparently unmineralized bodies of jasperoid around it (Drewes, 1967, p. 80-82) prompted the present study. The primary objective of this investigation was to describe this unusual type of ore and to find out which properties of these outlying bodies of barren jasperoid change systematically toward the boundaries of the area of intense mineralization. The detection of these properties might be useful as prospecting guides. Other objectives were to see whether the patterns of minor-element distribution in the jasperoid offered clues to the position of a probable buried intrusive parent stock for the dikes, the siliceous alteration, and the ore metallization and to compare the suite of anomalous trace elements, which characterize mineralized jasperoid of the Taylor district, with those of jasperoid samples collected from other nearby mining districts and areas of siliceous alteration.

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