Abstract Renewed gold exploration in the Carolina slate belt of North and South Carolina that led to the discovery of the Ridgeway gold mine (#5 on Figure 1) by Amselco (now Kennecott) began at about the same time as the last Geological Society of America field trip to focus on southeastern metal deposits. That trip occurred in the fall of 1980 as part of the national GSA meeting in Atlanta, Georgia (Bell, Carpenter, and Feiss, 1980). On that trip at stop 8, Henry Bell described abundant hydrothermal alteration similar to the Haile and Brewer mines in an area with no known gold mines. He noted that auger cuttings from a hole drilled by the South Carolina Geological Survey in the 1960’s near stop 8 at Mount Rehovah church contained 0.06 ppm gold and 220 ppm copper in the upper 9 feet of rock and 10 ppm molybdenum from 30-40 feet. Because the values decreased with depth, the gold was attributed to surface enrichment (Bell, 1976). Samples collected by Bell (1976) of small drainage basins in the region contained up to 1000 ppm tin in heavy mineral concentrates that were also anomalous in gold, boron, lanthanum, niobium, beryllium, and copper (Figure 16 of Bell, Carpenter, and Feiss, 1980). Bell et al. (1980) stated “Geochemical data suggest that this region is on the periphery of an area having many of the ore-bearing characteristics of the Haile and Brewer mines” Stop 8 was only hundred’s of feet west of the present site of the

Abstract Highly evolved alkaline/peralkaline igneous rocks host deposits of rare earth elements (REE), including Y as well as Zr, Hf, Nb, Ta, U, and Th. The host rocks spanning from silica-undersaturated (nepheline syenites) to silica-oversaturated (granites) occur in intraplate tectonic environments, mainly in continental settings and are typically associated with rifting, faulting, and/or crustal extension. They range in age from Neoarchean/Paleoproterozoic to Mesozoic, but several significant deposits are of Mesoproterozoic age. The deposits/prospects can be subdivided into three types. The first is hosted by nepheline syenitic rocks of large, layered alkaline intrusions where the mineralization commonly occurs in layers rich in REE-bearing minerals, which mostly show cumulate textures (e.g., Thor Lake/Nechalacho, Canada; Ilimaussaq, Greenland; Lovozero, Russia; Kipawa, Canada; Norra Kärr, Sweden; Pilanesberg, South Africa). The second type includes mineralization in peralkaline granitic rocks where REE-bearing minerals are usually disseminated. The mineralization is typically hosted by pegmatites (including the Nb-Y-F type), felsic dikes, and minor granitic intrusions (e.g., Strange Lake, Canada; Khaldzan-Buregtey, Mongolia; Ghurayyah, Saudi Arabia; Bokan, Alaska, United States). The third type is disseminated, very fine grained, and hosted by peralkaline felsic volcanic/volcaniclastic rocks, mostly of trachytic composition (e.g., Dubbo Zirconia and Brockman/Hastings, Australia). The bulk of the REE is present in ore/accessory minerals which in some mineralized zones, particularly in cumulate rocks from alkaline complexes, can reach >10 vol %. Mineralization is composed of a variety of REE-bearing minerals, which frequently show complex replacement textures. They include fluorocarbonates, phosphates, silicates, and oxides. Economically most important are bastnäsite, monazite, xenotime, loparite, eudialyte, synchysite, and parasite. Many other minerals are either sparse or it is difficult with present technology to profitably extract REE from them on a commercial scale. Compared to carbonatite-hosted REE deposits, the REE mineralization in alkaline/peralkaline complexes has lower light REE concentrations but has commonly higher contents of heavy REE and Y and shows a relative depletion of Eu. Elevated concentrations of U and Th in the ore assemblages make gamma-ray (radiometric) surveys an important exploration tool. The host peralkaline (granitic, trachytic, and nepheline syenitic) magmas undergo extensive fractional crystallization, which is protracted in part due to high contents of halogens and alkalis. The REE mineralization in these rocks is related to late stages of magma evolution and typically records two mineralization periods. The first mineralization period produces the primary magmatic ore assemblages, which are associated with the crystallization of fractionated peralkaline magma rich in rare metals. This assemblage is commonly overprinted during the second mineralization period by the late magmatic to hydrothermal fluids, which remobilize and enrich the original ore. The parent magmas are derived from a metasomatically enriched mantle-related lithospheric source by very low degrees of partial melting triggered probably by uplift (adiabatic) or mantle plume activity. The rare metal deposits/mineralization related to peralkaline igneous rocks represent one of the most economically important resources of heavy REE including Y. In addition to REE, some of these deposits contain economically valuable concentrations of other rare metals including Zr, Nb, Ta, Hf, Be, U, and Th, as well as phosphates.

Abstract Sandstone-hosted deposits mined primarily for their uranium content also have been a source of vanadium and modest amounts of copper. Processing of these ores has also recovered small amounts of molybdenum, rhenium, rare earth elements, scandium, and selenium. These deposits share a generally common origin, but variations in the source of metals, composition of ore-forming solutions, and geologic history result in complex variability in deposit composition. This heterogeneity is evident regionally within the same host rock, as well as within districts. Future recovery of elements associated with uranium in these deposits will be strongly dependent on mining and ore-processing methods.

Abstract The criticality of metals (the quality, state, or degree of being of the highest importance) is of increasing concern as populations and wealth increase and as mineral extraction follows. Many characteristics are involved in determining criticality, and those involving geology are among the most important. We discuss the state of knowledge of mineable resources across the periodic table, and how those determinations factor into criticality evaluations. We then illustrate criticality evaluations of the copper ore group elements for the specific example of the UK. Given the importance of the ore metals over the long term, we argue that efforts on the part of the geological community to update and maintain criticality-related information deserve much more attention than they are now receiving.