New Mexico Geological Society Annual Spring Meeting — Abstracts

Abstract

Arsenide five-element vein deposits are high grade silver veins (1000’s g/ton of silver) with significant cobalt, nickel, bismuth, and arsenic along with other elements such as U, Cu, Pb, Zn, Sb, and Hg; many of these elements are critical minerals important for the economic and national security of the United States. These deposits are distinctive due to the unusual combination of elements with varying chemical properties not commonly found together. Arsenide five-element veins typically host Ag, Bi, and As as native elements, while Co and Ni occur as arsenides and/or sulfides. The Black Hawk district in the Burro Mountains, Grant County, New Mexico contains arsenide five-element vein deposits and historically, has been a significant producer of silver, with approximately 1,286,000 million ounces extracted between 1881 and 1960, along with other metals such as Cu, Pb, Au, tungsten, and fluorite.

This study presents analysis of petrographic descriptions, mineralogy, and paragenesis of samples collected from the Black Hawk district using petrography, geochemistry results and microprobe analysis. Samples were obtained from drill core and hand samples from underground at the Black Hawk mine and include fresh and altered host rocks and mineralized veins and breccia. A total of 48 samples were prepared into polished sections and thin sections for detailed petrographic and mineral analysis, with a subset of three thin sections selected for Electron Microprobe Analysis (EPMA). Gangue minerals predominantly comprise calcite, dolomite, and quartz, with quartz displaying early and late occurrences. Ore minerals, including native metals (Ag) and arsenides, exhibit complex paragenetic relationships, suggesting a sequential deposition pattern. Gangue minerals quartz and carbonates dominate early and late-stage mineralization, hosting micro-inclusions of hematite. Late-stage minerals include native silver, base-metal sulfides, and sulfosalts. Electron Microscopy Analysis showed the chemical diversity of sulfarsenides and highlighted enrichment in U, particularly in niccolite nodules. Whole rock geochemical analyses provided insights into major, minor, and trace element compositions. Based on mineralogy and chemistry results Black Hawk district samples are elevated in critical minerals such as arsenic, cobalt, barium, copper, nickel, and zinc. The study enhances understanding of arsenide five-element vein deposits, shedding light on its complex textures and mineral assemblages of these potentially important sources of critical minerals.