GEOLOGICAL AND GEOCHEMICAL EVALUATION OF A Cu-Au-W DEPOSIT IN THE FERRIS MOUNTAINS, WYOMING

This study focuses on a copper deposit in the Archean Ferris Mountains plutonic suite in south-central Wyoming. Previous exploration of the Ferris Mountains deposit in the 1970s described it as a copper porphyry deposit with high-grade quartz-sulfide veins with up to 10,000 ppm of copper, and disseminated copper reaching 1,800 ppm (Master, 1977). A USGS study reported veins with copper concentrations from 7,000-20,000 ppm, along with other anomalous mineralization of silver, lead, and gold (Mitchell & Neubert, 1988). This study aims to identify the deposit type, mineralization history, and economic viability of this deposit.

The Ferris Mountain plutonic suite is made up of predominantly porphyritic granite, that is intruded by undeformed pegmatitic dikes and mafic dikes. Initial field observations find that porphyritic granite is hydrothermally altered with intense k-feldspar and chlorite alteration near high-grade quartz sulfide veins. Alteration intensity decreases with distance away from these veins. Copper mineralization is identified in quartz veins hosting pyrite, chalcopyrite, and bornite. Abundant scheelite was found adjacent to the quartz veins indicating tungsten mineralization. Disseminated copper mineralization is observed but follows the alteration trend of decreasing with distance from the veins. We will present bulk rock geochemical data from veins and plutonic host rock to quantify the concentrations of copper and other viable critical minerals, such as tungsten. Detailed petrography will be presented to describe mineralization and hydrothermal phases, and electron microscopy will be used to quantitatively assess mineralogy. Together the data will help identify diagnostic features that define the deposit type and assess its economic viability. By establishing a deposit model, the project will guide future mineral exploration in the region.