The geochemistry and mineralogy of the Gies gold-silver telluride deposit, central Montana

Abstract

In order to better characterize and classify the three major intrusive rock types that crop-out in the immediate vicinity of gold-silver telluride mineralization, major and trace element compositions and mineral compositions were determined. Mineral compositions were obtained on an automated ARL-SEMQ electron microprobe housed in the Department of Geological and Atmospheric Sciences at Iowa State University. On-line ZAF corrections employed the MAGIC IV program utilizing the method of Bence and Albee (1968). For native elements, sulfides, sulfosalts, and tellurides in veins, operating conditions were an accelerating voltage of 25 KV, and a sample current of 20 nA on a Faraday cup. For silicates and carbonates, the accelerating voltage and sample current was 20 KV and 15 nA, respectively. Native gold, silver, and tellurium, natural and synthetic sulfides and sulfosalts, synthetic tellurides, and natural silicates were used as standards. The quartz monzonite porphyry at Elk Peak, although relatively poorly exposed, appears to consist of only one intrusion. It comprises a groundmass of intergranular feldspars and hornblende with accessory amounts of diopside, sphene, calcite, magnetite, and pyrite. The phenocrysts are up to 3 cm in length and consist, in order of abundance, plagioclase (An27 to An^^), alkali feldspar (Or^^ to Org^), ferro-pargasitic hornblende and quartz. Mineral compositions for feldspar and amphibole are given in Tables 1 and 2. 1. Data shown in this table are average values of each individual samples. For complete analyses, see Appendix. course of my Ph. D. study at Iowa State University. I also acknowledge my graduate