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USGS2021

Toward an effective global green economy: The Critical Minerals Mapping Initiative (CMMI)

Global population growth, economic development and the accelerating pace of technological innovation are driving increased demand for non-fuel mineral commodities that are vital for emerging and low-carbon technologies. Examples of such commodities include cobalt and graphite for rechargeable batteries, tellurium in thin-film solar photovoltaics and rare earth elements (REE) in permanent magnets, electronics and medical technologies. These commodities are known as critical elements and/or minerals (collectively referred to as critical minerals), with the term critical used to define not only their importance for new technologies, but also their demand and vulnerability to supply disruption. The demand for critical minerals is likely to continue to grow, but supply is not assured. Therefore, national strategies in Australia, Canada, United States and elsewhere (e.g. Europe: Wittenberg et al. 2021) are being developed to encourage exploration and production, including resolving the geological processes responsible for their enrichrichment into viable ore deposits. In 2019, Geoscience Australia (GA), the Geological Survey of Canada (GSC) and the United States Geological Survey (USGS) formed the Critical Minerals Mapping Initiative (CMMI) to undertake research to develop a better understanding of critical mineral resources in known deposits, determine the geological controls on critical mineral distribution for deposits currently producing by-products, and identify new sources of supply through mineral prospectivity mapping and resource assessment.

SGA News↗
USGS2026

The mineral chemistry networks of tin and tungsten reflect metallogenic eras of the Mesozoic

Continental remobilization is a crucial driver of metallogenesis and the formation of ore deposits. Some of the world’s largest mineral deposits of the economically valuable elements tin (Sn), tungsten (W), gold (Au), copper (Cu), lead (Pb), and zinc (Zn) formed during the Mesozoic Era. Additionally, the chemistry and distribution of the elements Sn and W have been investigated in previous studies to understand planetary formation and differentiation processes. These two elements are largely co-located during certain South China Mesozoic metallogenic events but are not co-located during other time periods in the same regions. Here, we investigated the mineral chemistry network similarities and dissimilarities of Sn and W to understand their mineral formation and distribution during the Mesozoic Era and throughout Earth history. Mineral chemistry network community detection analysis and electronegativity associations among mineral constituent elements of Sn minerals and W minerals indicate that the elements have similar chemistry among their oxide minerals. However, Sn forms a much wider range of minerals that also contain S compared to W, which occurs in a limited number of S-containing minerals. The divergent constituent element interactions among S-containing Sn minerals and W minerals reflect the redox sensitivity and importance of oxygen (O) fugacity in Sn mineral formation. Conversely, extensive W mineral deposits are known to form at both high and low O fugacities. The similarities and differences between the mineral chemistry networks of Sn and W reflect the mineral distribution of the two elements in the Sn-W mineralization event from 160 to 139 Ma vs. the Sn–uranium (U) mineralization event from 125 to 98 million years ago (Ma). The mineral chemistry and distribution of Mesozoic Sn and W deposits illustrate the contrasting importance of redox and O fugacity on the mineral formation of different elements, and the dynamic crustal evolution that took place during this period of Earth history.

Geosciences↗
USGS2007

Geology and Mineral Resources of the East Mojave National Scenic Area, San Bernardino County, California

From our evaluations that largely used model-based criteria, we conclude that much of the East Mojave National Scenic Area (EMNSA) contains significant indications of epigenetic mineralization of various types. Economically significant concentrations of many metals may possibly remain to be discovered in many parts of the EMNSA (see also Wetzel and others, 1992). We have discussed specific types of metallic deposits that are known to be present in the EMNSA. Some mountain ranges that have widespread occurrences are the Providence Mountains, Clark Mountain Range, Ivanpah Mountains, and New York Mountains; the area of Hackberry Mountain is included in a tract that is judged to be favorable for the discovery of epithermal, volcanic-hosted gold deposits (pl. 2). These ranges make up a broad, roughly north-south-trending region in the central part of the EMNSA. Much less endowed with known occurrences of all of the various types of deposits considered above are the Granite Mountains, the central parts of the Piute Range, the Fenner Valley area, the general area of Cima Dome, the Cima volcanic field, and areas west to Soda Lake. We have attempted to make some judgments concerning the gravel-covered areas in the EMNSA (pl. 3), including the areal extent of bedrock apparently covered only by thin veneers of gravel. But few data are available to us for the overwhelming bulk of the covered areas. The presence of any mineralization, the type of mineralization, and the extent and intensity of mineralization in the covered areas is essentially unknown. The likelihood is high, however, that those areas in the EMNSA covered only by a thin cap of gravels could host mineralization similar to that known in the adjoining mountain ranges. Most buried epigenetic-mineral deposits do not respond to standard geophysical methods, particularly at the coarse spacing of the data-collection points available for our evaluation. Restricting judgments concerning the presence of undiscovered metal resources in the EMNSA only to currently known types of deposits and to regionally representative tonnages for such deposits would undoubtedly yield small estimates for volumes of many metals that might be exploited. Metals from most newly discovered, base- and ferrous-metal deposits of the types presently known in the EMNSA probably would be insignificant from the standpoint of national needs. For example, copper from a newly discovered skarn deposit in the EMNSA would have roughly a 25 percent chance of being in excess of approximately 10,000 tonnes contained Cu, if the grade-and-tonnage distribution curves of Jones and Menzie (1986b) for copper skarns are applicable to copper skarn in the EMNSA. Most copper in the United States is produced in the Southwest from much larger open-pit operations than those associated with the typical copper skarn; the former operations exploit large-tonnage porphyry-type systems. Historically, the EMNSA has been the site of minor production of many metals from a large number of sites. Since 1985, however, a small number of sites in the EMNSA whose gold production and reserves are much greater than that of the preceding discoveries have been developed (see U.S. Bureau of Mines, 1990a). Nonetheless, widespread distribution of numerous types of deposits (including copper skarn, lead-zinc skarn, tin-tungsten skarn, polymetallic vein, gold-silver quartz-pyrite vein, low-fluorine porphyry molybdenum, gold breccia pipe, and volcanic-hosted gold) that are petrogenetically associated with igneous rock in many parts of the EMNSA is indicative of a metallogenic environment that may be the site of future discoveries of mineral-deposit types that are not now recognized by the exploration community. The science, art, and, yes, even luck of exploration procedures continually evolve, and this evolution is one of the most important aspects of currently employed methods of exploration (Bailly, 1981; Hutchinson and Grauch, 1991).

Miscellaneous Field Studies Map↗
USGS2021

Porphyry and epithermal mineral deposits

Porphyry and epithermal mineral deposits form large economic ore bodies that provide the global economy with copper, molybdenum, gold, silver and other byproducts (Re, Te, Se). They form in the upper crust and are related to sulfur- and water-rich intermediate to silicic magmatic sources of hydrothermal fluids that move upward and produce extensive hydrolytic and alkali wall-rock alteration, quartz veins, and sulfides. Porphyry-type deposits are formed above magma chambers where fluids hydrofracture rock at 700–350 °C and at pressures ranging from supra-lithostatic to supra-hydrostatic. The depth of formation ranges from 2 to 10 km and influences orebody geometries and the types and mineralogy of veins, sulfides and wall-rock alteration. The temporal evolution of hydrothermal events is documented by cross-cutting veins and is commonly characterized by a decline in fluid temperature and concordant evolution from potassic alteration to sericitic alteration, with attendant increase in sulfidation state of copper-iron sulfides. In some localities porphyry copper deposits transition upwards to lower temperature base metal lodes (350–200 °C) and eventually the formation of near surface (<1.5 km depth) intermediate- and high-sulfidation epithermal deposits (~300–120 °C). Extensional environments are often characterized by porphyry molybdenum and low-sulfidation epithermal deposits. In the base metal lode and epithermal environments, mixtures of magmatic and meteoric fluids produce ore fluids at hydrostatic pressures that advect freely both vertically and laterally along permeability provided by faults, joints, and porous lithologies. Wall-rock alteration ranges from hydrolytic to alkali-carbonate, and from high- to low-sulfidation state sulfide assemblages, respectively. In porphyry, base metal lode, and epithermal environments, geology and the zonation of wall-rock alteration, veins, sulfide assemblages, and metals are useful for exploration.

Book chapter↗
USGS2007

The Russell gold deposit, Carolina Slate Belt, North Carolina

Gold deposits have been mined in the Carolina slate belt from the early 1800s to recent times, with most of the production from large mines in South Carolina. The Russell mine, one of the larger producers in North Carolina, is located in the central Uwharrie Mountains, and produced over 470 kg of gold. Ore grades averaged about 3.4 grams per tonne (g/ t), with higher-grade zones reported. The Russell deposit is interpreted to be a sediment-hosted, gold-rich, base-metal poor, volcanogenic massive sulfide deposit in which gold was remobilized, in part, during Ordovician metamorphism. The ore was deposited syngenetically with laminated siltstones of the late Proterozoic Tillery Formation that have been metamorphosed to a lower greenschist facies. The Tillery Formation regionally overlies subaerial to shallow marine rhyolitic volcanic and volcaniclastic rocks of the Uwharrie Formation and underlies the marine volcanic and sedimentary rocks of the Cid Formation. Recent mapping has shown that a rhyolitic dome near the Russell mine was extruded during the deposition of the lower part of the Tillery Formation, at about the same time as ore deposition. Relict mafic, rock fragments present in the ore zones suggest contemporaneous bimodal (rhyolite-basalt) volcanism. The maximum formation age of the Russell deposit is younger than 558 Ma, which is similar to that of the larger, well known Brewer, Haile, and Ridgeway deposits of South Carolina. Gold was mined from at least six zones that are parallel to the regional metamorphic foliation. These strongly deformed zones consist of northeast-trending folds, high-angle reverse faults, and asymmetric doubly plunging folds overturned to the southeast. The dominant structure at the mine is an asymmetric doubly plunging anticline with the axis trending N 45?? E, probably related to late Ordovician (456 ?? 2 Ma) regional metamorphism and deformation. Two stages of pyrite growth are recognized. Stage 1, primary, spongy pyrite, is present in thin massive sulfide layers parallel to bedding and intergrown with pyrrhotite, chalcopyrite, sphalerite, and sparse arsenopyrite. Stage 2, secondary pyrite, is present as euhedral, idiomorphic rims on spongy pyrite and as veinlets that parallel the regional foliation. Stage 1 pyrite was deposited syngenetically or diagenetically during or soon after sedimentation. Stage 2 pyrite overgrowths and veins resulted from recrystallization or remobilization of stage 1 pyrite, probably during deformation related to Ordovician regional metamorphism. It is proposed that the spongy texture of the stage 1 pyrite represents nucleation and growth of pyrite on organic matter, possibly of bacterial origin. Other textures, such as geometric voids in spongy pyrite, As-rich zones surrounding central voids, 60-??m ring structures composed of spongy pyrite, and layers of spongy pyrite interlayered with bedding laminations, also appear to indicate replacement of organic matter by pyrite. Stage 1 pyrite contains up to 0.06 wt percent gold. The ??34S values of pyrite in and near pyritic ore (3.5-4.5???), in the rhyolite dome (5.1-5.4???) and in the Tillery Formation (5.9-6.2???) are interpreted to reflect mixing of sulfur derived from igneous and seawater sources. Whole-rock ??18O values of nearby unaltered mudstone are about 11 per mil whereas those from altered mudstone at the deposit are 7.4 to 10.6 per mil. The lower ?? 18O values are interpreted to indicate possible high-temperature exchange between relatively low ??18O hydrothermal fluids and the wall rocks. Gold, As, K, and Mo are enriched relative to the regional background in both the ore zones and in pyrite veins and disseminations in the nearby rhyolite dome, suggesting a possible genetic link between the rhyolitic volcanism and the gold mineralization. ?? 2007 Society of Economic Geologists, Inc.

Economic Geology↗
USGS1953

Reconnaissance of superficial phosphate deposit near Minas, Uruguay

The phosphate deposit in Uruguay described here is of interest primarily because it is believed to be a superficial deposit that resulted from the action of guano on volcanic rock. Even though some of the rock contains as much as 30 per cent P206, it is unavailable as a source of fertilizer because the phosphate is combined with aluminum and iron as variscite and strengite, and possibly other equally insoluble minerals. © 1953 Society of Economic Geologists, Inc.

Economic Geology↗