New Mexico Geological Society Annual Spring Meeting — Abstracts

Five-element style deposits are unusual hydrothermal systems that are typically characterized by a nickel-cobalt-arsenic-silver-bismuth metal assemblage. This mineralization is often represented by abundant native silver, arsenic, or bismuth, and followed by nickel, cobalt, and iron arsenides (skutterudite, safflorite, nickeline, rammelsbergite, and lollingite). The Black Hawk district in Grant County, New Mexico is one of the few examples of this mineralization style in the United States. Despite differences in formation temperature, depth of emplacement, and host rocks between five-element style deposits worldwide, there are commonalities in mineralogy, ore texture, and composition. A detailed exploration of the native metal and arsenide phases was performed to compare ore forming fluids between systems and the effects on styles of mineralization and paragenesis, as well as to aid in broader classification of the deposit style. Mineralogy and mineral relationships of the Black Hawk District and the Cobalt-Gowganda district, Canada, are characterized by reflected light petrography, scanning electron microscopy, X-ray diffraction, and electron microprobe analysis. Despite these two deposits having very similar genetic relationships, 5-element style mineralization occurring in relation to calc-alkaline bodies intruding into Proterozoic bedrock, there are notable differences in the abundances of cobalt, antimony, and uranium, as well as the ratio of metal to arsenic of the major arsenide phases. Mineralogical phase diagrams were generated to better understand the driving processes and evolution of these systems, and to use the relationships between nickel, cobalt, and iron to reflect the formation conditions through native metal and arsenide precipitation.