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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, Miscel laneous Report"li7-4.

The steadily growing demand for rare earth elements (REE) and yttrium (Y) in petroleum cracking catalysts, the electronics industry, and the manufacture of super conductors, permanent magnets, ceramics, glass and metal alloys indicates that these elements are worthy of exploration attention. The purpose of this paper is firstly to illustrate the character, variety and distribution of REE occurrences in general, and particular ly in northern Saskatchewan, and secondly to fulfill a demand from the mineral industry for information on these REE occurrences.

The Rare Earth Elements

Rare earth eleme nts, or the lanthanide series, constitute a group of 15 element s (16 including yttr ium) beginning with lanthanum (atomic no. 57) and ending with lutecium (atomic no. 71) (Table I). Although generally more abundant than e lements such as gold, silver and uranium (Mason, 1966), REE rarely form distinct minerals in nature, occurring instead in trace amounts in over 250 minerals, of which 54 are designated as lanthanide minerals (Valasov, l 966).

Despite their relative abundance, there are only three major ore minerals for REE and Y: monazite,

bastnasite and xenotime. Monazite, a REE- Y -Th phospha te, contains up to 70 percent RED (rare earth oxide), 7 percent ThO and 2 percent Y z03. Bastnasite is a rare earth fluorocarbonate which contains up to 75 percent RED and minor Y z03. Xenotime is a yttr ium phosphate, which contains up to 60 percent Yz03 and is more enriched in the 'heavy' REE, dysprosium (Dy, atomic no. 66) to lutecium (Anstett, 1986). Both monazite and bastnasite are 'light' REE enriched.

Minor ore minerals include apatite, allanite, brockite , crandalite, euxeni te and loparite.

Until recently, monazite was the principal source of REE. It occurs in many geological environments, being most prominent in felsic igneous rocks such as granites and pegmatites. Most monazite is extracted from heavy mineral beach sands as a byproduct of sands mined for ilmenite, rutile, cassiterite, zircon or gold. The principal mining areas are along the coasts of Austra lia, Brazil, India, South Africa and the United States.

Xenotime generally occurs in the same environments as monazite. Like monazite, it is a byproduc t of placer mining, in part icular the tin placers of Malaysia and China (Anstett, 1986).

Table l - Rare Earth Element Abundance in Chondrites, the Crust and Some Camnon Rocks. Values are i n ppm.

Atomic No.

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

Element

Lanthan1111 Cerium Praseodymi1111 Neodymi um Promethi 001

Samarium Europi1111 Gadolinium Terbium Dysprosi um Holmium Erbi1111 Thul i1111 vtterbium Lutetil.m

lfrom Haskin et al. ( 1968) 2f rom Krauskopf (1979)

S~ol

La Ce Pr Nd Pm Sm Eu Gd Tb Oy Ho Er Tm Yb Lu

Average Chondritesl

.30 ± .06

.84 ±. 18

. 12 ± .02

.58 ± . 13

. 21 ± .04 .074 .t .015 .32 ± .07

. 049 .t .010

. 073 ± .014 .21 ± .04

.033 ± .007 . 17 ± .03

. 031 ± .005

Average Average Average Crus t 2 Granites2 Shales2

35 55 40 70 90 70 8 10 9

30 35 30

7 9 7 1.2 1.0 1.4 7 8 6 1 1.5 1 6 6.5 5 l.5 2 1.5 3.5 4. 5 3.5 0.5 0.06 0.06 3.5 4.0 3.5 0.6 o. 7 0.6

Average Basalts2

10 30 4

20

05 1.5 6 0.8 4 l j

.05 2.5 .05

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Bastnasite occurs in veins and as disseminations in carbonatite intrusions (e.g., Mountain Pass, California); quartz veins cutting micaceous schist and quartzite (Burundi); epithermal fluorite veins and breccia fillings in Permian sandstones (New Mexico); and associated with iron ore minerals (China). Bastnasite has now replaced monazite as the principal source of REE. The Mountain Pass deposit, which contains reserves of }.6 million tons, produces 50 percent of the world's annual REO production (Anstett, 1986). The Chinese iron deposits may contain as much as }6 million tons RED (ibid.), but these deposits have yet to be developed.

ln Canada, REE have been produced as a byproduct of uranium mining in the Elliot Lake region (Anstett, 1986). Other Canadian reserves of REE and yttrium include Highwood Resources Ltd.'s beryllium - yttrium - rare earths - niobium deposit 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.

Saskatchewan Rare Earth and Yttrium Occurrences

There are more than 40 reported REE-bearing mineral occurrences in northern Saskatchewan (Fig. l), the majority of which occur in high-grade gneiss terrains surrounding the Athabasca Basin. They can be subdivided into the following five types: l) pegmatite-granite association; 2) metadetrital; }) allanite veins; 4) detrital heavy mineral sands in the Athabasca Group; and 5) diagenetic-hydrothermal associated with unconformity - type uranium deposits.

Pegmatite-Granite Association

Most occurrences in Saskatchewan belong to the pegmatite-granite type; the majority are believed to have formed by anatectic processes. They consist predominantly of monazite with rare or minor xenotime associated with biotite -rich segregations in pegmatites or restites of the enclosing high-grade gneisses. Allanite, apatite, zircon and uraninite may also be associated with this type of occurrence. Available assays typically range from 0.008 to 2.0 percent total REO, but south of Alces Lake in the Beaverlodge region, two monazite -bearing pegmatite occurrences contain up to 16 percent RED (Robinson, 1955; Assessment File 74N09-0020, Saskatchewan Energy and Mines, Regina).

Two other significant occurrences include Kulyk Lake and J ahala, both of which were originally discovered as uranium prospects. At Kulyk Lake, located 1 km west of Middle Foster Lake, massive monazite occurs in pegmatitlc, graphic and aplitic

granite dykes which intrude high-grade gneisses of the Wollaston Domain (Mawdsley, 1957; Watkinson and Mainwaring, 1976; Assessment File 74Al2-0005, Saskatchewan Energy and Mines, Regina). There is mineralogica1 zoning from Fe-Ti oxides to monazite to minor concentrations of apatite in a zone less than 5 cm thick and approximately 15 m long.

The J aha la prospect, located 8 km east of Hunter Bay, Lac La Range, occurs in a zoned pegmatite sill intruding amphibolitic metasediments (Mawdsley, 1954; Ford, 1955; Forsythe, 1981; Sabina, 1987). Uraninite is accompanied in this occurrence by monazite, allanite, apatite, zircon and xenotime. Dark brown monazite crystals, up to l cm long, are associated with massive biotite selvages of the border zone (Ford, 1955) and are also reported to occur in the intermediate phase of the pegmatite (Mawdsley, 1954). Estimates of the volume of

r-· I I j 1 ·

I I I ,..j I I x I.

.. 2 . • 3 . • 4 . u 5.

D Phanerozoic

D Athobosca Grot1 p (Heli k ion)

D Pr, -Athabcuca baumenf

I ~r I I I I

O !1 0 ,oo 1)0 200 ... ~~-....____._......._..........1._._.,.J

Figure 1 - Distribution of reported rare earth element and yttrillll occurrences in northern Saskatchewan. Occurrence types: 1, pe!Jllcltite-<;1ranite association; 2, ~tadetrital; 3, allanite veins; 4, heavy mineral layers in the Athabasca Group; and S, diagenetic-hydrothermal type associated with unconfonnity urani1111 depos its. Place names ~ntioned in text include: A, Alces lake; AR, Archie Lake; B, Birch Portage; c, Cluff Lake; CB, Collins Bay; CL, Cigar Lake ; CP, Cup Lake; O, Dawn lake; E, Eagle Point; F.F . , Flin Flon; J, Jahala; K, Kulyk Lake; L, Lyle Lake; M, Maurice Bay; ML, Mclean Lake; MR, McArthur River; N, Nisikkatch-Hoidas Lakes; R, Rabbit Lake ; U.C. , Uranium City; and Z, Zoo Bay.

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REE-bearing minerals present and geochemical analyses are not available for the J ahala or Kulyk Lake occurrences.

Several occurrences with interesting mineralogical associations include:

l) a monazite-bearing syenitic pegmatite closely associated with the Lyle Lake nepheline syenite (MacDougall, this volume);

2) beryliferous pegmatites in the Birch Portage area, 50 km west of Flin Flon, some of which contain accessary monazite (Radcliffe and Campbell, l 965; Pyke, 1966; Sabina, 1987); and

3) a group of radioactive pegmatites in the Cup Lake area which generally contain less uranium than thorium; uraninite, molybdenite, fluorite and allanite have been identified, as well as niobium-tantalum values (Munday, 1977; Thomas, 1983).

REE occurrences associated with pegmatites are typically found as a result of uranium exploration due to the radioactivity of thorium in monazite and/or allanite. As thorium is commonly more abundant than uranium in these occurrences, they have attracted little attention, and consequently are rarely if ever checked for REE.

Metadetrital

An ilmenite-monazite occurrence in Archean granulite facies metasedimentary gneisses at Archie Lake, 30 km east-southeast of Uranium City (Fig. 1), is believed to represent a metamorphosed heavy mineral accumulation (Harper, 1986, 1987). Ilmenite, monazite and trace amounts of zircon and gold occur in layers 0.1 to 10 cm thick within a 5 to 6 m thick stratabound zone that has been traced over a strike length of 600 m. Radioactive anomalies along strike from the main occurrence suggest the possibility of further extensions to the zone or additional 'heavy mineral' lenses. Assays of material from the main zone range from 0.1 to 15. 7 percent total REO (Assessment Files 7405-0038, -0053, and -0059, Saskatchewan Energy and Mines, Regina) and locally TiOz exceeds 17 .0 percent. Several other ilmenite-monazite occurrences exist in the surrounding area (Harper, l 983b, 1986). Undoubtedly other meta-detrital occurrences exist elsewhere in the Saskatchewan Shield.

Allanite Veins

A unique group of allanite-apatite veins occur in the Nisikkatch - Hoidas Lakes area, 40 km northeast of Uranium City (Fig. I). The veins, which cut granulite and retrogressed granulite facies gneisses, are found in a zone up to 10 km long. Mineralogical zoning is common and includes

calcite, barite, hyalophane (Ba-feldspar), amphibole and pyroxene (Hogarth, 1957). Grab samples have given assays of up to 12 percent total REO (Assessment File 74013-000 I, Saskatchewan Energy and Mines, Regina).

Heavy Mineral Layers in the Athabasca Group

Athabasca Group sandstones and conglomerates contain heavy mineral layers, especially in the dominantly conglomeratic basal section. Detrital zircon, monazite and xenotime have been identified in some places (e.g., Maurice Bay (Harper, 1978, in prep.); Cluff Lake (Pagel, pers. comm.); Zoo Bay (No. 1149, Saskatchewan Mineral Deposits Index, Regina)); however, these layers remain essentially untested for REE-bearing paleoplacer deposits.

Diagenetic-Hydrothermal Type

The association of REE and Y with the Athabasca Basin unconformity uranium deposits is only beginning to be appreciated. For example, strongly altered clay-enriched Athabasca Group sandstones above the Mcclean Lake uranium deposits contain up to 10 percent Y, present in masses of xenotime and goyasite in the clay (Wallis et al, 1985). Xenotime and goyasite are also associated with uranium mineralization in the McArthur River area, located northeast of Key Lake (Hubregtse and Sopuck, 1987). Yttrium geochemical anomalies, ranging from three to seven times background, occur above the Cigar Lake and Dawn Lake uranium deposits (Clark, l 987), and elevated Y concentrations exist at the Rabbit Lake, Collins Bay and Eagle Point deposits (Ruzicka, 1986). Locally at Cluff Lake and Maurice Bay, REE are progressively enriched along with uranium (Harper, l 983a and unpublished data). The association of these occurrences with Athabasca Basin unconformity uranium deposits suggests a potential for "unconformity-type" diagenetic-hydrothermal Y and REE ore.

Conclusion

Rare earth elements occur in diverse geological settings, any of which could contain ore-grade material. The growing awareness of the important industrial uses of REE and Y, coupled with a steadily increasing demand, will undoubtedly lead to increased exploration attention. A variety of REE and Y exploration targets exist in northern Saskatchewan, with a good potential for the discovery of economic concentrations of these elements. ·

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