New Mexico Mineral Symposium — Abstracts

The use of semimetal-bearing sulfides as petrologic tools has not yet been applied in most ore-deposit studies although ore deposits containing sulfosalts or semimetal sulfides have been located and symbolized by deposit type. This compilation of sulfosalt localities and the plotting of relative abundances of arsenic, antimony, and bismuth have been done to test the usefulness of these minerals and elements as ore-deposit and metallogenic indicators.

Gross distribution of the semimetals follows closely the general distribution of metallic ore deposits related to Laramide and Cenozoic volcanism. However, certain semimetal elements appear confined to particular tectonic environments. Bismuth displays an affinity for continental crust areas, especially in spacial relation to exposed Precambrian rocks. Antimony, although widely distributed, is concentrated in areas of crustal thinning (i.e., the Great Basin and Rio Grande rift). Arsenic is the most widely distributed semimetal element, but interestingly occurs in high crustal deposits not necessarily related to magmatism (e.g., sandstone uranium deposits of the Colorado Plateau).

Semimetal distribution in particular ore-deposit environments is fairly consistent and often zoned, indicating possible geochemical factors unique to each deposit type. Bismuth is most commonly found in pegmatites (bismuthinite), porphyry coppers, and skarns (Pb-Ag-Bi sulfosalts). Bismuthinite also is found in epithermal gold veins, usually with other semimetal phases absent. Antimony is most often associated with epithermal veins (tetrahedrite and polybasite) and hot-spring deposits (pyrargyrite and stibnite) and in massive sulfides(tetrahedrite). Arsenic species are found in skarns (arsenopyrite), veins (arsenopyrite, pearceite, and proustite), stratabound deposits (arsenopyrite and tennantite), and the upper zones of porphyry coppers (enargite).

The details of sulfosalt geochemistry and tectonics are still poorly known and are subject to continuing study. This relatively simple treatment of the data does reveal potential in the field of semimetal geochemistry, perhaps converting sulfosalts from mineralogic curiosities to interpretive tools.