- 82 - Rare Earth Elements and their Occurrence in Northern Saskatchewan by C.T. Harper Harper, C. T. (1987) : Rare earth elements and their occurrence in northern Saskatchewan; in SIM!milry of Investigations 1987, Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report"li7 -4. The steadily growing demand for rare earth bastnasite and xenotime. Monazite, a REE- Y -Th elements (REE) and yttrium (Y) in petroleum phosphate, contains up to 70 percent RED (rare cracking catalysts, the electronics industry, and the earth oxide), 7 percent ThO and 2 percent Y z03. manufacture of super conductors, permanent Bastnasite is a rare earth fluorocarbonate which magnets, ceramics, glass and metal alloys indicates contains up to 75 percent RED and minor Y z03. that these elements are worthy of exploration Xenotime is a yttrium phosphate, which contains up attention. The purpose of this paper is firstly to to 60 percent Yz03 and is more enriched in the illustrate the character, variety and distribution of 'heavy' REE, dysprosium (Dy, atomic no. 66) to REE occurrences in general, and particularly in lutecium (Anstett, 1986). Both monazite and northern Saskatchewan, and secondly to fulfill a bastnasite are 'light' REE enriched. demand from the mineral industry for information on these REE occurrences. Minor ore minerals include apatite, allanite, brockite , crandalite, euxenite and loparite. The Rare Earth Elements Until recently, monazite was the principal source of REE. It occurs in many geological environments, Rare earth elements, or the lanthanide series, being most prominent in felsic igneous rocks such as constitute a group of 15 elements (16 including granites and pegmatites. Most monazite is yttrium) beginning with lanthanum (atomic no. 57) extracted from heavy mineral beach sands as a and ending with lutecium (atomic no. 71) (Table I). byproduct of sands mined fo r ilmenite, rutile, Although generally more abundant than elements cassiterite, zircon or gold. The principal mining such as gold, silver and uranium (Mason, 1966), REE areas are along the coasts of Australia, Brazil, rarely form distinct minerals in nature, occurring India, South Africa and the United States. instead in trace amounts in over 250 minerals, of which 54 are designated as lanthanide minerals Xenotime generally occurs in the same (Valasov, l 966). environments as monazite. Like monazite, it is a byproduct of placer mining, in particular the tin Despite their relative abundance, there are only placers of Malaysia and China (Anstett, 1986). three major ore minerals for REE and Y: monazite, Table l - Rare Earth Element Abundance in Chondrites, the Crust and Some Camnon Rocks. Values are i n ppm. Atomic Element S~ol Average Average Average Average Average No. Chondritesl Crust2 Granites2 Sha les2 Basalts2 57 Lanthan1111 La .30 ± .06 35 55 40 10 58 Cerium Ce .84 ±. 18 70 90 70 30 59 Praseodymi1111 Pr . 12 ± .02 8 10 9 4 60 Neodymi um Nd .58 ± . 13 30 35 30 20 61 Promethi 001 Pm 62 Samarium Sm . 21 ± .04 7 9 7 05 63 Europi1111 Eu .074 .t .015 1.2 1.0 1.4 1. 5 64 Gadolinium Gd .32 ± .07 7 8 6 6 65 Terbium Tb . 049 .t .010 1 1.5 1 0.8 66 Dysprosi um Oy 6 6.5 5 4 67 Holmium Ho . 073 ± .014 l.5 2 1.5 l 68 Erbi1111 Er .21 ± .04 3.5 4. 5 3.5 j 69 Thul i1111 Tm .033 ± .007 0.5 0.06 0.06 .05 70 vtterbi um Yb . 17 ± .03 3.5 4.0 3.5 2.5 71 Lutetil.m Lu . 031 ± .005 0.6 o. 7 0.6 .05 lfrom Haskin et al. ( 1968) 2f rom Krauskopf (1979) - 83 - Bastnasite occurs in veins and as disseminations in granite dykes which intrude high-grade gneisses of carbonatite intrusions (e.g., Mountain Pass, the Wollaston Domain (Mawdsley, 1957; Watkinson California); quartz veins cutting micaceous schist and Mainwaring, 1976; Assessment File and quartzite (Burundi); epithermal fluorite veins 74Al2-0005, Saskatchewan Energy and Mines, and breccia fillings in Permian sandstones (New Regina). There is mineralogica1 zoning from Fe-Ti Mexico); and associated with iron ore minerals oxides to monazite to minor concentrations of (China). Bastnasite has now replaced monazite as apatite in a zone less than 5 cm thick and the principal source of REE. The Mountain Pass approximately 15 m long. deposit, which contains reserves of }.6 million tons, produces 50 percent of the world's annual REO The J aha la prospect, located 8 km east of Hunter production (Anstett, 1986). The Chinese iron Bay, Lac La Range, occurs in a zoned pegmatite sill deposits may contain as much as }6 million tons intruding amphibolitic metasediments (Mawdsley, RED (ibid.), but these deposits have yet to be 1954; Ford, 1955; Forsythe, 1981; Sabina, 1987). developed. Uraninite is accompanied in this occurrence by monazite, allanite, apatite, zircon and xenotime. ln Canada, REE have been produced as a byproduct Dark brown monazite crystals, up to l cm long, are of uranium mining in the Elliot Lake region associated with massive biotite selvages of the (Anstett, 1986). Other Canadian reserves of REE border zone (Ford, 1955) and are also reported to and yttrium include Highwood Resources Ltd.'s occur in the intermediate phase of the pegmatite beryllium - yttrium - rare earths - niobium deposit (Mawdsley, 1954). Estimates of the volume of at Thor Lake in the Northwest Territories (James, 1986) and a columbium - fluorite - zirconium - beryllium - Y-rich gadolinite deposit near Strange Lake in northeastern Quebec (Hedrick, 1985; Anstett, 1986). A production decision is expected for the Thor Lake deposit by the end of 1987. ~Ir I I Saskatchewan Rare Earth and Yttrium Occurrences I I There are more than 40 reported REE-bearing mineral occurrences in northern Saskatchewan (Fig. l), the majority of which occur in high-grade r-· gneiss terrains surrounding the Athabasca Basin. I They can be subdivided into the following five I types: l) pegmatite-granite association; 2) j metadetrital; }) allanite veins; 4) detrital heavy 1 · mineral sands in the Athabasca Group; and 5) I diagenetic-hydrothermal associated with I unconformity-type uranium deposits. ,..jI Pegmatite-Granite Association II x I. .. 2 . • 3. Most occurrences in Saskatchewan belong to the • 4. pegmatite-granite type; the majority are believed u 5. to have formed by anatectic processes. They D Phanerozoic consist predominantly of monazite with rare or Athobosca Grot1 p minor xenotime associated with biotite-rich D (Heli kion) segregations in pegmatites or restites of the D Pr,-Athabcuca baumenf enclosing high-grade gneisses. Allanite, apatite, O~ ~-....____!1 0 ._......._..........1._,oo 1)0 ._.200,.J ... zircon and uraninite may also be associated with this type of occurrence. Available assays typically Figure 1 - Distribution of reported rare earth element range from 0.008 to 2.0 percent total REO, but and yttrillll occurrences in northern Saskatchewan. south of Alces Lake in the Beaverlodge region, two Occurrence types: 1, pe!Jllcltite-<;1ranite association; 2, monazite-bearing pegmatite occurrences contain up ~tadetrital; 3, allanite veins; 4, heavy mineral layers to 16 percent RED (Robinson, 1955; Assessment in the Athabasca Group; and S, diagenetic-hydrothermal File 74N09-0020, Saskatchewan Energy and Mines, type associated with unconfonnity urani1111 deposits. Regina). Place names ~ntioned in text include: A, Alces lake; AR, Archie Lake; B, Birch Portage; c, Cluff Lake; CB, Two other significant occurrences include Kulyk Collins Bay; CL, Cigar Lake ; CP, Cup Lake; O, Dawn lake; Lake and J ahala, both of which were originally E, Eagle Point; F.F . , Flin Flon; J, Jahala; K, Kulyk discovered as uranium prospects. At Kulyk Lake, Lake; L, Lyle Lake; M, Maurice Bay; ML, Mclean Lake; MR, located 1 km west of Middle Foster Lake, massive McArthur River; N, Nisikkatch-Hoidas Lakes; R, Rabbit monazite occurs in pegmatitlc, graphic and aplitic Lake ; U.C. , Uranium City; and Z, Zoo Bay. - 84 - REE-bearing minerals present and geochemical calcite, barite, hyalophane (Ba-feldspar), amphibole analyses are not available for the J ahala or Kulyk and pyroxene (Hogarth, 1957). Grab samples have Lake occurrences. given assays of up to 12 percent total REO (Assessment File 74013-000 I, Saskatchewan Energy Several occurrences with interesting mineralogical and Mines, Regina). associations include: l) a monazite-bearing syenitic pegmatite closely Heavy Mineral Layers in the Athabasca Group associated with the Lyle Lake nepheline syenite (MacDougall, this volume); Athabasca Group sandstones and conglomerates contain heavy mineral layers, especially in the 2) beryliferous pegmatites in the Birch Portage dominantly conglomeratic basal section. Detrital area, 50 km west of Flin Flon, some of which zircon, monazite and xenotime have been identified contain accessary monazite (Radcliffe and in some places (e.g., Maurice Bay (Harper, 1978, in Campbell, l 965; Pyke, 1966; Sabina, 1987); and prep.); Cluff Lake (Pagel, pers. comm.); Zoo Bay (No. 1149, Saskatchewan Mineral Deposits Index, 3) a group of radioactive pegmatites in the Cup Regina)); however, these layers remain essentially Lake area which generally contain less uranium untested for REE-bearing paleoplacer deposits. than thorium; uraninite, molybdenite, fluorite and allanite have been identified, as well as niobium-tantalum values (Munday, 1977; Diagenetic-Hydrothermal Type Thomas, 1983). The association of REE and Y with the Athabasca REE occurrences associated with pegmatites are Basin unconformity uranium deposits is only typically found as a result of uranium exploration beginning to be appreciated. For example, strongly due to the radioactivity of thorium in monazite altered clay-enriched Athabasca Group sandstones and/or allanite. As thorium is commonly more above the Mcclean Lake uranium deposits contain abundant than uranium in these occurrences, they up to 10 percent Y, present in masses of xenotime have attracted little attention, and consequently and goyasite in the clay (Wallis et al, 1985).