CRITICAL METALS IN THE SHAWANGUNK MINING DISTRICT

The U.S. is in desperate need of a domestic supply of critical minerals, but new mines can often take up to a decade to get up and running. A quicker and possibly cheaper alternative would be to reexamine old mines and their tailing piles. The Shawangunk mines located in Ulster County, Sullivan County, and Orange County New York are great examples of locations where historic mining for zinc and lead left tailings piles, pits and trenches behind that may have critical minerals left behind. When the Shawangunk mines were running from the 1700’s until the end of World War 1 the metals that were in demand were different than the ones of today. The original mines focused on lead and at the end on zinc. Textural analyses of samples indicated a more complex set of precipitation behavior than simple brecciation and primary veins. Most samples showed co-precipitation of sphalerite and chalcopyrite at the Shawangunk mine with galena sometimes being contemporaneous while other times appearing later in the paragenetic sequence. Chalcopyrite is predominantly absent at other mine locations. Preliminary bulk rock geochemistry shows small amounts of Ag, As, Co, and Ga. and significant amounts of Cu, Zn, and Pb. Sphalerite appeared to be optically zoned, but neither the geochemistry nor the backscattered electron images showed signs of any zonation. One possible explanation is the “optical” zoning was related to fluid inclusion assemblages. Samples tended to either be zinc-dominated or lead-dominated but had economic quantities (>5 wt.% in “waste” rocks) of those two metals, respectively. The zinc-dominated samples had higher levels of Cu, Ga, Co, Cd, As, In, and Hg. Lead-dominated ones had higher levels of Ag and Sb. However, electron microprobe analyses found that contrary to expectations, sphalerite was host of the Co, Ag, and As, while galena had higher levels of Ga, and chalcopyrite and pyrite hosted the As and some Ga.