GEOCHEMISTRY OF CRITICAL MINERALS IN BLACK HAWK DISTRICT MINE WASTES, GRANT COUNTY, NEW MEXICO

The modern world relies on critical minerals for everything from smartphones to electric vehicles. Critical minerals are non-fuel minerals that are essential to the U.S. economy and national security whose supply chain may be disrupted. Mine wastes could be potential sources of critical minerals that need to be classified based on their mineralogy, geochemical characterization, and critical minerals estimation. The Black Hawk district in Grant County, New Mexico has been classified as an arsenide five-element vein deposit containing Ag, Ni, Co, As, U, and Bi as well as some other local minerals such as Pb, Cu, Zn, W, and Sn. Many of these are critical minerals. The district produced Ag, Cu, Pb, Au, and some W and fluorite from 1881 to 1960. Therefore, the district could be a potentially important source of critical minerals. The purpose of this project is to characterize and estimate the critical minerals in the Black Hawk district mine wastes and determine the acid-generating potential. Following the USGS sampling procedure based on geological evidence and sampling statistics, samples are collected from mine waste rock piles (dumps). Comparison of the geochemistry of ore and waste samples shows that Ag, Co (highest content in ore is 5690 ppm and in waste 29275 ppm), Ni (highest content in ore is 72400 ppm and in waste 2128.5 ppm), As (highest concentration in waste samples is 490 ppm), and Zn (in ore is above 1% and in waste the highest value is 8463.5 ppm) are more elevated in ore samples than in waste samples. However, Cu is more elevated in waste sample than in ore samples, and Pb concentration is above 1% in both. While Ag is more abundant in ore samples, its concentration is more than 200 ppm in some Alhambra waste samples. In addition, Ag and Co values are higher in fine (less than 2 mm) samples than in coarse (over-sieved, greater than 2 mm) samples. Analyzing the geochemistry of different particle size fractions shows that Ag, Co, Bi, As, Cu, Li, Ni, Pb, and Rb concentrations increase in the finer size fractions (the finer, the higher value). The paste pH and fizz tests showed that the pH of mine waste samples is approximately neutral, and these samples are non-acid-generating and can be used as back-fill materials.