A GEOCHEMICAL ANALYSIS OF ABSAROKA VOLCANICS FROM DEAD INDIAN HILL, NORTHWEST WYOMING

Dead Indian Hill is a Laramide monocline overlain by Heart Mountain Fault blocks and Eocene volcanic rocks in northwest Wyoming, northeast of the Absaroka Range. It is part of the potassium-rich eastern belt of the Absaroka volcanic province. Quantitative data for 35 samples, 14 from the top of Dead Indian Hill and 21 from a volcanic ridge approximately 1 mile away, suites 1 and 2 respectively, were analyzed using x-ray fluorences and x-ray diffraction to obtain major and trace element abundances, as well as mineralogical composition and abundances for the two different rock suites. Point counting and petrographic hand sample descriptions were undertaken to complement the quantitative analyses. Results show that suite 1 are tracheyandesites and suite 2 are dacites with overlap in both suites. The mineral assemblage plagioclase, sanidine, augite, montmorillinite, edenite, and quartz dominate both suites. The chemical variance between the two suites is small enough to assume that they were emplaced a similar way at a similar time. Comparison to published data for four major volcanic centers in the area suggest that the volcanics present at Dead Indian Hill are most similar to those at Sunlight Volcano and are therefore likely to have the same source.