568 



UNITED STATES MINERAL RESOURCES 



accumulate in enormously high concentrations in 

 localized sites. 



Most of the scandium in the earth's crust is con- 

 tained in igneous rocks, where it is largely a trace 

 constituent of the ferromagnesian minerals. These 

 minerals may commonly contain 5-100 ppm SC2O3 

 (Frondel, 1968, p. 122). Pyroxenes, hornblende, and 

 biotite are the usual hosts for scandium; therefore, 

 rocks rich in these minerals, notably the mafic rocks, 

 will have the highest scandium contents. Analyses 

 of 76 samples of igneous and sedimentary rocks, 

 including nine composite samples, reported by Nor- 

 man and Haskin (1968), showed that the highest 

 scandium contents (30-40 ppm) are in basalts and 

 gabbros and the lowest (about 1 ppm) in nepheline 

 syenites and limestones. 



Scandium in the ferromagnesian minerals appar- 

 ently substitutes for iron in sites occupied by either 

 (Fe+^Al) or (Fe+^Mg). Scandium can also form 

 limited solid solution with Y+^, Al, the heavy lan- 

 thanides Er+^ to Yb+^ Ti+% Sn+S Zr+% and W+« 

 in certain geochemical environments. Where scan- 

 dium is substituting for higher valence ions, such 

 as Ti+* or W+^, a complex coupling mechanism in- 

 volving (Nb,Ta)+* and Fe+^ may be required for 

 charge balances in some minerals (Frondel, 1968). 



MINERALOGY 



Scandium is an essential constituent of very few 

 minerals and these are all very rare species. These 

 minerals are: 



Thortveitite (Sc,Y) SLO, 



Sterrettite (Kolbeckite) .Sc(POi)2H20 



Bazzite Be3(Sc,Al)2SieOi8 



Magbasite KBa(Al,Sc) (Mg,Fe)6Si,0=„F, 



Many additional minerals may contain scandium 

 in amounts that range from a few to thousands parts 

 per million through substitution by one or more of 

 the mechanisms mentioned above. In addition to 

 being found in the ferromagnesian minerals, scan- 

 dium is found in multiple-oxide minerals of the 

 rare earths, columbite, wolframite, cassiterite, beryl, 

 garnet, muscovite, and aluminum phosphate min- 

 erals. The scandium contents of these and many 

 other minerals have been reported by Neumann 

 (1961), Borisenko (1963), Vlasov (1964), Phan, 

 Foissey, Kerjean, Moatti, and Schieltz (1967), 

 Frondel, Ito, and Montgomery (1968), and Frondel 

 (1970a,b). Inasmuch as several of the minerals 

 that are scandium carriers are also important ores 

 of other elements, byproduct recovery is a distinct 

 possibility. 



TYPES OF DEPOSITS 



PEGMATITES 



Granitic pegmatites have so far been the only 

 source of the high-grade scandium ore mineral 

 thortveitite. Thortveitite-bearing pegmatites, known 

 from only a few places in the world, have been 

 mined for scandium in the Iveland-Evje district in 

 Norway and in Madagascar. 



In Norway, at least 10 pegmatites have produced 

 thortveitite, but the aggregate recovery by 1961 was 

 only about 50,000 grams (Neumann, 1961). The 

 Befanomo pegmatite in Madagascar, apparently ex- 

 hausted by 1955, supplied 38,000 grams (Murdock, 

 1963, p. 101). 



Neumann's (1961) study of the Norwegian peg- 

 matites shows that most of the scandium is con- 

 tained in iron minerals, chiefly biotite and ilmenite, 

 and that minerals from dikes in which thortveitite 

 is present are richer in scandium than those from 

 dikes without thortveitite. Neumann suggested that 

 a deficiency of divalent iron, for which scandium 

 commonly proxies, would favor the development of 

 thortveitite in a pegmatite. 



Quite similar observations were made by Phan, 

 Foissy, Kerjean, Moatti, and Schieltz (1967) from 

 their work on Madagascar pegmatites. They noted 

 that one rarely finds a rich scandium mineral if the 

 associated minerals are scandium poor and that one 

 can observe in the majority of mineral deposits the 

 following decreasing order of tenor: Thortveitite, 

 niobium-tantalum minerals (metamict minerals, 

 columbite-tantalite, ilmenorutile) , muscovite, gar- 

 net, beryl, and tourmaline. 



The only known occurrence of thortveitite in the 

 United States is in the Crystal Mountain fluorite 

 deposit in Montana (Parker and Havens, 1963). 

 This deposit, described by Taber (1952, 1953) and 

 by Weis, Armstrong, and Kosenblum (1958), con- 

 sists of tabular bodies of fluorite in coarse-grained 

 biotite granite that contains xenoliths of biotite- 

 quartz-plagioclase gneiss, hornblende-plagioclase 

 gneiss, and pegmatitic granite. Gangue minerals in 

 the fluorspar are altered feldspar, sericite, quartz, 

 and biotite. Massive quartz overlies the west out- 

 crop (Geach, 1963). Radioactive zones, such as de- 

 scribed by Weis, Armstrong, and Rosenblum (1958, 

 p. 20), lie along the margins of the fluorite bodies. 

 These zones consist largely of dark-purple fluorite 

 and contain considerable biotite. Accessory minerals 

 include sphene, quartz, oligoclase, apatite, green 

 amphibole, fergusonite, thorianite(?), and thortvei- 

 tite (Parker and Havens, 1963). 



Limited geologic information on the Crystal 

 Mountain deposit suggests a magmatic origin. One 



