U16 Critical Mineral Resources of the United States—Vanadium Shale-Hosted Vanadium Deposits Vanadium-rich metalliferous black shales occur primarily in late Proterozoic and Phanerozoic marine successions. The term shale is used here broadly to include a range of carbonaceous rocks that include marls and mudstones. These finegrained sedimentary rocks were deposited in epeiric (inland) seas and on continental margins. They typically contain high concentrations of organic matter (greater than 5 percent) and reduced sulfur (greater than 1 percent; mainly as pyrite), as well as a suite of metals, such as copper, molybdenum, nickel, PGEs, silver, uranium, vanadium, and zinc (Desborough and others, 1979; Coveney and Martin, 1983; Coveney and others, 1992; Hatch and Leventhal, 1992; Piper, 1999). Concentrations regularly exceed 0.18 percent V2 O5 and can be as high as 1.7 percent V2 O5 . Vanadiferous black shales are commonly found with phosphorite deposits and marine oil shales and, in North America, are marine equivalents of coal-bearing cyclothems. Well-characterized vanadiferous black shales include the Woodruff Formation in Nevada (Desborough and others, 1979), the Meade Peak Phosphatic Shale Member of the Phosphoria Formation in Idaho and Wyoming (McKelvey and others, 1986; Love and others, 2003), the Mecca Quarry Shale Member of Illinois and Indiana (Coveney and others, 1987), the Doushantuo Formation in Hubei Province in southern China (Fan and others, 1992), and portions of the Toolebuc Formation in Queensland, Australia (Lewis and others, 2010). Although these black shales have long been recognized as potential sources of vanadium, they are not currently exploited. Project development is underway at the Gibellini vanadium prospect in Nevada (Woodruff Formation), and if production begins, it will be the first primary shalehosted producer of vanadium in the United States. The Julia Creek deposit (Toolebuc Formation) is also in the planning stages. The Green Giant deposit in southern Madagascar (Energizer Resources, Inc., 2013) consists of metamorphosed vanadiferous shale that extends for at least 21 km along strike and is reported to contain about 350,000 metric tons of V2 O5 (table U1; fig. U1). The ultimate source of vanadium in metalliferous black shales is dissolved vanadium in seawater (Breit and Wanty, 1991; Piper, 1994). Whereas the specific mechanisms of enrichment are disputed, all require the reduction of dissolved V5+ (Breit and Wanty, 1991), which is the predominant redox state in the oceans (Collier, 1984). Vanadium is used by various phytoplankton species (Robson and others, 1986; Moore and others, 1996), and sedimentation of phytoplankton debris likely acts as a minor source of vanadium in black shales (Piper, 1994). In oxygen-deficient bottom waters and pore waters, dissolved vanadium is reduced to particle-reactive V4+ and is incorporated into the sedimentary fraction (Wehrli and Stumm, 1989). Further reduction to V3+ requires the presence of dissolved aqueous sulfide (H2 S) and promotes the incorporation of vanadium into sedimentary organic matter and authigenic clays (Lewan and Maynard, 1982; Lewan, 1984; Breit and Wanty, 1991). Vanadium concentrations correlate with organic carbon in black shales, suggesting that vanadium is incorporated into organic matter upon burial (Breit and Wanty, 1991). Black shales that have been buried to depths sufficient to pass through the oil window typically produce petroleum that has high vanadium concentrations (Lewan and Maynard, 1982; Lewan, 1984). Conversely, vanadium can become incorporated into illite upon burial (Peacor and others, 2000). Because no modern analogues for vanadiferous black shales are known, the processes of vanadium enrichment are not well understood. Vanadium-rich black shales of North America occur in Devonian to Permian marine successions. Black shale of the Upper Devonian Woodruff Formation (Nevada) contains 0.5 to 1.2 percent V2 O5 in unaltered rocks containing high concentrations of organic matter (greater than 10 percent) (Desborough and others, 1979, 1981). Oxidized zones of the Woodruff Formation contain 1.1 to 1.4 percent V2 O5 , reflecting secondary enrichment of vanadium during oxidation; the principal vanadium mineral in the oxidized shales is metahewettite (CaV6 O162 • H2 O). Vanadiferous black shales are also found with Pennsylvanian cyclothems of North America (Coveney and Martin, 1983; Coveney and others, 1987; Coveney and Glascock, 1989; Hatch and Leventhal, 1992). These typically thin, metalliferous black shales occur throughout the midcontinent region. The Mecca Quarry Shale of Illinois and Indiana is conspicuously rich in various metals, including vanadium, with concentrations of up to 10,000 ppm (Coveney and Martin, 1983). These concentrations of vanadium exceed that of many VTM deposits; however, because the Mecca Quarry Shale is only a few tens of centimeters thick, it is not considered an economically viable vanadium resource (Coveney and Martin, 1983). Vanadium enrichments in the Mecca Quarry Shale could be related to the action of basinal brines, similar to processes that concentrate lead-zinc in Mississippi Valleytype (MVT) deposits (Coveney and Glascock, 1989), although direct evidence for this mineralizing process is lacking. The Permian Phosphoria Formation in Idaho and Wyoming contains a world-class phosphate deposit that also includes vanadium-rich strata (McKelvey and others, 1986; Piper, 1999). The black-shale interval within the Meade Peak Phosphatic Shale Member contains an average of 1.2 percent V2 O5 (Piper, 1999) and, since the early 1940s, has been considered a potential economic source of vanadium (Love and others, 2003). In the 1960s, vanadium and uranium were produced from ferrophosphorus, a byproduct of an elemental phosphorus plant in southeastern Idaho (McKelvey and others, 1986). The occurrence of vanadium-rich shale with black-shale-hosted phosphorite deposits is common worldwide and suggests that steep and (or) fluctuating redox gradients existed within bottom waters and pore waters of the sedimentary basin (Piper, 1994). The Julia Creek deposit in the Cretaceous Toolebuc Formation in Queensland, Australia, is an example of a vanadium-rich oil shale (Riley and Saxby, 1982; Patterson, Ramsden, and others, 1986). The oil shale was deposited in a shallow, epicontinental sea under reducing bottom water Geology U17 conditions that promoted the enrichment of vanadium. Concentrations range from 0.1 to 1.0 percent V2 O5 . Other known vanadium-rich (greater than 0.17 percent V2 O5) oil shales include the Mississippian Heath Formation in Montana (Desborough and others, 1981; Derkey and others, 1985) and the Cretaceous La Luna Formation, which is a major petroleum source rock in Colombia and Venezuela (AlberdiGenolet and Tocco, 1999). Associated metals.—Vanadium-rich black shales commonly contain high contents of other metals, such as silver, barium, cobalt, copper, molybdenum, nickel, phosphorus, PGEs, uranium, and zinc. Well-characterized deposits include the following (metals associated with vanadium are in parentheses): Julia Creek (molybdenum) in Queensland, Australia (Lewis and others, 2010); Nick (nickel, PGEs, and zinc) in Yukon Territory, Canada (Hulbert and others, 1992); and Viken (molybdenum, nickel, phosphorus, and uranium) and Häggån (uranium, molybdenum, and nickel) in Sweden (Hallberg, 2012; Aura Energy, 2012). As reported by Coveney and others (1992), carbonaceous and phosphatic black shales of Cambrian age in China, which have reported values exceeding 4 percent V2 O5 , contain exceptionally high grades of nickel (from 2 to 4 percent) and molybdenum (>2 percent), and high concentrations of PGEs (20 to 80 parts per billion for platinum and palladium combined). Although vanadium has not been recovered from these strata, molybdenum and nickel have been mined on a small scale in China since about 1985. Metamorphosed sulfide- and phosphate-rich black shale in southwestern Catalonia, Spain, contains unusually high concentrations of vanadium and chromium (as silicates and oxides) together with palladium and platinum minerals (Canet and others, 2003). The Talvivaara deposit in Finland has elevated contents of vanadium (averages 600 ppm) (Loukola-Ruskeeniemi and Heino, 1996; Loukola-Ruskeeniemi and Lahtinen, 2013), and until recently, was mined for cobalt, copper, nickel, and zinc, all of which were extracted using a bioheapleach mineral processing method (Jowitt and Keays, 2011; Saari and Riekkola-Vanhanen, 2012; LoukolaRuskeeniemi and Lahtinen, 2013). Vanadium is not currently recovered by this process, however. Vanadate Deposits Vanadates of lead, zinc, and copper (vanadinite and minerals of the descloizite-mottramite series) form in the oxidized zones of base-metal deposits, especially in areas of arid climate and deep oxidation (Fischer, 1975a). The copper-lead-zinc vanadate ores in the Otavi Mountainland of northern Namibia were once considered to be among the largest vanadium deposits in the world, with an estimated resource of several million metric tons (Boni and others, 2007). Other areas with known vanadate deposits include Angola, South Africa, Zambia (Broken Hill district, now known as the Kabwe Mine), and Zimbabwe (fig. U1). Small deposits occur in Argentina, Mexico, and the United States (Arizona, California, Nevada, and New Mexico), but are unlikely ever to be economically significant resources. Vanadates as a supply of vanadium essentially ceased in 1978 when the last producing vanadium mine at Berg Aukas (Otavi Mountainland) in Namibia was closed. Vanadate minerals and wulfenite (a lead molybdate mineral) within these deposits form crusts on open cavities or are intergrown with residual clays (Fischer, 1975a). The vanadate ores in the Otavi Mountainland occur in collapse breccias and solution cavities related to karst development in Neoproterozoic carbonate rocks of the Otavi Supergroup and are spatially associated with primary sulfide orebodies within the carbonate strata (Boni and others, 2007). Mottramite and copper descloizite are particularly abundant around copper sulfide deposits (Tsumeb type), whereas descloizite occurs in areas surrounding primary sphalerite-willemite (a zinc silicate mineral) orebodies (Berg Aukas type). Vanadate deposits are secondary accumulations that form during supergene processes. The vanadate ores of the Otavi Supergroup are interpreted to have formed during several stages, preferentially within a karstic network. The vanadate ores, formed by low-temperature fluids related to weathering, are clearly distinct in age from that of the associated primary sulfide concentrations (Boni and others, 2007). The source of vanadium in such deposits is most likely the surrounding country rocks, especially shales (Fischer, 1975a), or in the case of the Otavi Mountainland deposits, mafic rocks of the older Paleoproterozoic basement (Boni and others, 2007). Other Magmatic-Hydrothermal Vanadium Resources Some magmatic-hydrothermal niobium-titanium deposits contain elevated concentrations of vanadium. Deposits at Potash Sulphur Springs (also called Wilson Springs) in Arkansas were the most important sources of vanadium in North America in the 1970s and 1980s, and nearly 4.3 million metric tons of 1.2 percent V2 O5 was produced. By 1990, all the mines at Wilson Springs were closed (Howard and Owens, 1995). The deposits are located within secondary enrichment zones and fenite that formed during and after intrusion of syenite and mafic alkalic igneous rocks (McCormick, 1978). The Wilson Springs deposits host a variety of vanadiumbearing minerals (Howard and Owens, 1995), including several minerals specific to these deposits (table U2). Adjacent carbonatite and alkaline igneous complexes at the Christy deposit within the Magnet Cove complex in Arkansas have high concentrations of vanadium together with titanium, niobium, and (or) rare-earth elements (Verplanck and Van Gosen, 2011; Flohr, 1994), and carbonatites and related rocks in Kenya are enriched in vanadium (Barber, 1974). Typical vanadium concentrations in such deposits are about 1 percent and are contained in magnetite and titanium minerals. At Magnet Cove and Wilson Springs, sodic pyroxene and magnetite contain up to 3.19 and 1.43 weight percent V2 O3 , respectively, and high concentrations occur in goethite (Flohr, 1994; Howard and Owens, 1995). Several other deposit types contain vanadium concentrations that are noteworthy, but all are presently uneconomic and U18 Critical Mineral Resources of the United States—Vanadium are unlikely to be considered vanadium resources in the future. For example, heavy-mineral-concentrate samples from iron ores (Kiruna-type apatite-magnetite deposits) in Sweden and Chile have reported high concentrations (1,000 to 2,000 ppm) of vanadium (Nyström and Henríquez, 1994) and iron oxide mineral separates (magnetite and hematite) from such deposits contain up to 0.479 weight percent vanadium (Dupuis and Beaudoin, 2011). Vanadium concentrations of a few tenths of a percent are also common in titanium-bearing minerals, such as rutile and brookite (table U2) in some epithermal gold-silver and porphyry copper deposits (Fischer, 1973). For example, porphyry deposits in Australia contain rutile with vanadium contents of 0.2 and 1.3 weight percent (Scott, 2005), and rutile from the Pebble porphyry deposit in Alaska has vanadium concentrations that average 6.3 weight percent (Kelley and others, 2011). Even iron-rich minerals that do not contain titanium, such as magnetite and hematite, in some porphyry deposits contain elevated concentrations (up to 0.619 weight percent) of vanadium (Dupuis and Beaudoin, 2011). In some gold-quartz veins, especially those containing gold-telluride minerals, roscoelite and other vanadium-bearing minerals are common as fine-grained intergrowths with quartz and other gangue minerals (Richards, 1995). In the Tuvatu gold-telluride deposit in Viti Levu, Fiji, vanadium occurs in roscoelite together with karelianite, vanadian muscovite, titanium-free nolanite, vanadian rutile, schreyerite, and an unnamed vanadium silicate mineral (Spry and Scherbarth, 2006). Rutile in the Tuvatu deposit contains up to 5.2 weight percent V2 O3 ; roscoelite contains 32.71 weight percent V2 O3 , which is among the highest reported vanadium value for roscoelite from an epithermal gold-tellurium deposit (Spry and Scherbarth, 2006). The source of the vanadium is probably magnetite-bearing mafic alkalic igneous rocks that are spatially associated with the gold ores (Spry and Scherbarth, 2006). Fossil Fuels Vanadium closely correlates with organic carbon and, therefore, is enriched in many oil shales. It follows that significant amounts of vanadium are available for commercial use as a byproduct of petroleum, and minor amounts are produced as byproducts of coal and tar sands (Breit, 1992; Polyak, 2012, 2013). At least 10 percent of the world’s supply of vanadium comes from coal, crude oil, and petroleum (Polyak, 2012, 2013). The highest concentrations of vanadium are in heavy crude oils (Breit, 1992). Most of the world’s heavy oil and vanadiferous petroleum resources are located in Venezuela. These oilfields contain consistently high (up to 1,400 ppm) concentrations of vanadium (Kapo, 1978). Other oils with greater than 50 ppm vanadium are produced in Iran and Japan, and from several fields within the United States, including Alaska, Arkansas, California, Louisiana, Mississippi, Oklahoma, Texas, and Wyoming. Vanadium is recovered from oil by processing ash generated in thermoelectric powerplants, petroleum coke residues generated during refining of heavy oils, and residues plated onto catalysts (Breit, 1992). Vanadium abundances in ashes formed by burning coals generally range from 0.01 to 0.3 weight percent, with some as high as 8 percent (Reynolds, 1948). The lowest values are contained in coals formed from subaerial plant material; the highest concentrations are in marine sapropelic coals (Breit, 1992). Although China is the only producer of vanadium from coal, coal deposits in Venezuela contain high vanadium contents. The average vanadium content of coal in the United States is 20 ppm (Swanson and others, 1976). Tar sands are large deposits of bitumen or extremely heavy crude oil. The sands were originally named for those in the Athabasca region in northeastern Alberta, Canada, and tar sand deposits in this region are the best known examples in the world. Other documented occurrences are in Alabama, Alaska, California, Kansas, Kentucky, Oklahoma, Missouri, New Mexico, Texas, and Utah in the United States (Wever and Kustin, 1990), and in other countries, such as Jordan (Breit, 1992; Dill and others, 2009). The oil sands consist of a mixture of crude bitumen (a semisolid form of crude oil), silica sand, clay minerals, and water. Production of refinery-grade oil from the tar sand deposits generates a substantial amount of petroleum coke fly ash that may contain appreciable amounts of valuable metals, such as nickel, titanium, and vanadium. The amount and form of vanadium varies, depending on the nature of the sands. Tar sands in the Athabasca region average several hundred ppm vanadium, whereas other localities contain lower concentrations (Wever and Kustin, 1990; Breit, 1992).
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