The Geochemistry and Petrography of Some Veins and Wallrocks Hosting Gold and Silver in the Republic District, Northeastern Washington
"Sixty-four rock samples were collected from mineralized and unmineralized areas around five gold-silver lode mines in the Republic district. The five mines were the Knob Hill, Mountain Lion, Morning Glory, Flagg Hill and Golden Valley. Samples were obtained from veins (quartz, carbonate and banded quartz-carbonate), wallrocks (andesite, trachyandesites and monzonite), and country rocks (pyroxene--hornblende andesite, trachyandesite and quartz latite). All samples were analyzed for major and minor oxides and selected trace elements. Thirty-four samples were examined petrographically. Hydrothermal alteration products of wallrocks were either quartz-sericite ±clays and sulfates or chlorite-pyrite-calcite. Country rocks were altered deuterically in part. Chemical and petrographic classifications of the host rocks were therefore imprecise. Chemical data reported by Ikramuddin and others (1983) for unaltered Sanpoil Volcanics were used to establish background geochemical values. Altered volcanic rocks are enriched in Si, K, Ag, As, Au, Li, Rb and Sb and depleted in Al, Fe, Ca, Na, Mn, Ba, F, Sr and Zn compared to unaltered rocks. Se is detected only in volcanic-hosted veins at lower topographic intervals. K, As, Au, Rb and Sb are enriched in altered volcanic rocks found at the highest topographic positions. The five mines are classified tentatively according to their vertical posi-tions on the zoned model epithermal precious metals systems proposed by Buchanan (1981) and White (1981), as follows: Mountain Lion - the uppermost portion of the precious metals horizon (PMH), the Knob Hill - the full PMH, the Flagg Hill - the lower portion of the PMH and the Morning Glory and Valley - intermediate positions in the PMH. Enrichment of Au at concentrations>20 ppb coupled with Ag/Au ratios