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The United States (US) has sufficient geological endowment in active metal mines to reduce the nation’s dependence on critical mineral imports. Demand is increasing for cobalt, nickel, rare earth elements, tellurium, germanium, and other materials used in energy production, semiconductors, and defense. This study uses a statistical evaluation of new geochemical datasets to quantify the critical minerals that are mined annually in US ores but go unrecovered. Ninety percent recovery of by-products from existing domestic metal mining operations could meet nearly all US critical mineral needs; one percent recovery would substantially reduce import reliance for most elements that we evaluated. Policies and technological advancements can enable by-product recovery, which is a resource-efficient approach to critical mineral supply that reduces waste, impact, and geopolitical risk. 

Abstract The Battle Mountain mining district of north-central Nevada hosts a variety of gold deposit types, including Cu-Au porphyries and skarns, polymetallic veins, and sedimentary rock-hosted disseminated Au deposits. This study examines intrusions in the northern part of the district, with a focus on those spatially associated with the sedimentary rock-hosted disseminated Au deposits. We identify three periods of magmatism in the district using zircon U-Pb geochronology—Jurassic (~162 Ma), Cretaceous (~97–92 Ma), and Eocene (~40–39 Ma)—which we attribute to magma periodically exploiting a structural fabric that developed over a Late Proterozoic rift structure. New district-scale geophysical surveys support this process; aeromagnetic data reveal large positive anomalies that we interpret to represent batholiths that grew through repeated injections of magma during the Cretaceous and Eocene. Sedimentary rock-hosted Au deposits are generally located at the margins of these anomalies, suggesting that mineralizing fluids utilized the fracture networks that developed where the rheologic contrast between igneous stocks and the surrounding country rock is most pronounced. Apatite and zircon (U-Th)/He thermochronology identifies district-wide cooling during the Eocene, even at deposits that lack causative Eocene intrusions. We interpret this Eocene date population to represent heating and subsequent cooling from widespread hydrothermal fluid flow, as the (U-Th)/He dates overlap with the formation of Eocene magmatic-hydrothermal Au deposits elsewhere in the Battle Mountain district (e.g., Converse, Buffalo Valley, Elder Creek, Copper Basin, Copper Canyon) and predate rapid exhumation. Time-temperature thermal models on (U-Th)/He aliquots and an absence of alteration zonation constrain fluid temperatures to <210°C during this period. Based on the spatial association with inferred large batholiths at depth and the fluid temperature constrained by thermal modeling, we interpret that Eocene magmatism contributed fluids and heat (and possibly metals) to the sedimentary rock-hosted disseminated Au deposits in the northern Battle Mountain district. 

Abstract The Battle Mountain mining district in north-central Nevada hosts a variety of magmatic-hydrothermal ore deposits, as well as sedimentary rock-hosted Au deposits that lack a conclusive relationship to magmatism. Mining of the sedimentary rock-hosted deposits has been primarily limited to oxidized zones, so there is little information available about the hypogene sulfide characteristics and mineralizing processes. Marigold mine is located in the northern Battle Mountain mining district and comprises multiple deposits, including the Red Dot deposit. The Red Dot deposit includes a mineralized sulfide zone recently intersected by deep drill holes, which provides an opportunity to examine hypogene mineralization styles and relationships. At Red Dot, early-stage pre-ore pyrite is enriched in Hg and Ni but contains less As than ore-stage pyrite and little to no Ag or Au. Ore-stage quartz lacks fluid inclusions but produces a yellow cathodoluminescence response typical of low-temperature hydrothermal environments. Ore-stage pyrite occurs as arsenian pyrite rims enriched in Au, As, Ag, Cu, and Sb that overgrow pre-ore pyrite; these rims have δ34S stable isotope values consistent with porphyry pyrite elsewhere in the district. Alteration styles include decarbonization, carbonation, sericitization, silicification, sulfide precipitation, and oxidation. The absence of zonation in the alteration styles suggests Red Dot is distal to any causative porphyry stock. District aeromagnetic data indicate an absence of any buried igneous bodies beneath Marigold, providing additional evidence that Red Dot is distal to any magmatic-hydrothermal fluid source. Red Dot is ideally situated along a complex structural network capable of focusing fluids from laterally distant sources into the host rocks repeatedly through time. Cretaceous magmatic-hydrothermal fluids related to the emplacement of the Trenton Canyon Stock or local quartz monzonite dikes at Marigold mine may have caused the early-stage alteration and sulfide mineralization at Red Dot. The early-stage alteration and sulfide mineralization could also be attributed to the emplacement of felsic dikes at the Lone Tree and Trenton Canyon Au deposits during the Eocene. Apatite and zircon (U-Th)/He data support an Eocene formation age for ore-stage quartz and pyrite. The alteration styles, ore-stage sulfide textures, geochemical signature, base metal and Au mineralization, and distal nature of Red Dot most closely resemble the Cove deposit, 25 km to the south. At Cove, overprinting polymetallic and Carlin-like Au mineralization are genetically related to Eocene magmatic-hydrothermal fluids. We suggest that Red Dot represents a similar expression of magmatic-hydrothermal mineralization, but at a greater distance from the causative intrusion and in different host rocks that underwent ideal preparation for interaction with mineralizing fluids.