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Project 8: Reindeer Lake South (SE Quarter)

Reconnaissance Geological Mapping of 640-1,2,7 and 8

by C. F. Gil boy

2 The geology of a 3500 km area centred about Kyaska Lake, 220 km northeast

of La Ronge, has been mapped at a scale of 1:100,000. Rock exposure and access

by float-equipped plane are excellent except in the southern part of the region,

south of the Cree Lake moraine, which was reached by helicopter,

A total of 280 lake sediment samples has been collected for base metal and

uranium analysis. Almost all are from the southwest, where the predominant bed­

rock is hornblende-bearing gneiss.

General Geology

Precambrian metasediments, generally known as the Kisseynew Gneisses, under­

lie most the area. In nearby areas to the east, geologists of the Manitoba Mines

Branch have recognized two distinctive groups within the Kisseynew Gneisses: the

Burntwood River Supergroup and the overlying Sickle Group (Lenton, 1975; McRitchie,

1974, 1975; Zwanzig and Wielezynski, 1975) both of which are represented in the

map-area. The main criteria used on the present survey to distinguish between

them were:-

Burntwood River Supergroup

i) Predominantly composed of pelites and hornblende-bearing gneisses

ii) Mobilizate generally white in colour

iii) Magnetite lacking, aeromagnetic intensities less than 3500 gammas except over hornblende-bearing gneisses of the southwest

iv) Graphite generally visible in handspecimens from pelitic units

Sickle Group

Predominantly composed of arkosic psarnmites and semipelites

Mobilizate generally pink in colour

Magnetite commonly present, aero­magnetic intensities generally greater than 3500 gammas

Graphite absent

No evidence of an unconformity between the groups was found.

Plutonic rocks are largely confined to the south and southeast, where compo­

sitionally uniform gneisses, in many places with poorly developed foliation,are

probably derived from intrusive batholiths.

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Pegmatite is an ubiquitous minor intrusive phase, most commonly as segregated

mobilizate in pelites and semipelites. Thin amphibolitic bands present in both

Burntwood River Supergroup and, more commonly, Sickle Group metasediments are

possibly derived from basic dykes and sills.

All Precambrian rocks have been intensely deformed and metamorphosed to the

upper amphibolite/lower granulite facies.

Main features of the Quaternary geology include the east-west trending Cree

Lake moraine and four esker systems flanked by glaciofluvial and gravel deposits.

All observed glacial striae indicate ice movement from 010°-030°.

Burntwood River Supergroup

Mappable subdivisions have been made mainly on the basis of a mineralogically

or texturally characteristic rock-type distinctive of, or dominant within, parti­

cular units. In detail, there is much interbanding of the units, and their

stratigraphic or structural sequence has not been established.

Pelitic and semipelitic biotite-garnet gneisses (la) are the most common rock­

type. They are fine- to medium-grained, and typically contain 15-20 percent

biotite, 5-10 percent well shaped garnet crystals, 1-2 mm in diameter, and traces

of graphite. Very rarely is there less than 20 percent white garnetiferous

pegmatitic mobilizate present in outcrops of unit la. Cale-silicate boudins are

locally abundant.

Pelitic biotite-garnet-graphite gneisses (lb) are similar to unit la, but

additionally contain several percent readily visible graphite.

Recrystallized feldspar-porphyroblastic biotite ±garnet± graphite rocks

(le) are gradational variants of units la and lb. They are massive to well

foliated, medium-grained, and contain numerous white feldspar porphyroblasts

1-10 cm across. Garnet attains 1 cm in diameter and is rimmed by biotite. Blocks

and lenses of unaltered la and lb are generally included; in places they show

relative rotation, indicating mobilization of the recrystallized rock unit.

Pegmatitic sweats are rare in comparison with units la and lb.

Pelitic biotite-garnet-cordierite ± sillimanite gneisses (ld) crop out north­

west and south of Shaw Lake. They are intermixed with la gneisses. Garnet

crystals tend to be large, up to 1 cm across. Pale to moderate blue cordierite.

weakly pinitized, forms patches as much as 3 cm in diameter which are mainly

concentrated in pegmatitic mobilizate. Fibrolitic sillimanite is sparsely

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contained as minute lenses within the gneissic restite.

Pelitic biotite ± sillimanite gneisses (le) are well lineated, coarse­

grained rocks possessing 25-30 percent biotite. They are found in the Ky3ska

Lake - Pagato Lake - Kamatsi Lake region. Fibrolitic sillimanite, where present,

is streaked out in foliation planes in minor amounts; it has largely retrogressed

to produce large flakes of muscovite which cut across the biotite schistosity.

Pelitic biotite gneisses (lf) differ from unit le only in being finer

grained and generally in having less than 20 percent mobilizate. They are

complexly interbanded with units la and/or le.

Semipelitic and pelitic biotite-graphite gneisses (lg) are medium-grained

rocks with 15-20 percent biotite and about 1-10 percent graphite. They are

particularly well developed towards the contact with Sickle Group gneisses in the

vicinity of Wapus Lake.

Hornblende-bearing gneisses (lh) crop out in the Todd Lake area of the south­

west, south of Fleming Bay, and in places along the Burntwood River Supergroup/

Sickle Group contact in the Wapus Lake - Kamuchawie Lake region. The gneisses

especially vary in the typ e , proportions and amounts of mafic minerals present.

Four sub-units are indicated in places on the geological map:

Biotite-hornblende ± diopside ± garnet gneisses (lha) in which biotite is

more abundant than hornblende and the total mafic content reaches up to 30 percent;

Hornblende-biotite ± diopside ± garnet gneisses (lhb) in which hornblende

exceeds biotite;

Hornblende± diopside ± garnet gneisses (lhc) in which hornblend e generally

forms 30-80 percent of these medium- to coarse-grained, pink or white rocks, and

Banded hornblende gneisses (lhd) in which melanocratic hornblende-rich

layers alternate with leucocratic bands, 1-10 cm in width, composed of diopside

and feldspar or of quartz and feldspar; these gneisses typically crop out imme­

diately below the contact with the Sickle Group.

Quartzitic and arkosic psamrnites (lj) form generally unmapped lenses, a notable

exception being the calcareous quartzitic psamrnite immediately north and northeast

of Deep Bay.

Sickle Group

Essentially the same succession of units is present as described by Zwanzig

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and Wielezynski (1975) from the Kamuchawie Lake area:

Semipelitic and psammitic hornblende and hornblende-biotite gneisses (2a)

crop out at the base of the Sickle Group. The total mafic content of these medium­

grained, in places flaggy, pinkish to greenish rocks varies from 5-30 percent.

Scattered magnetite grains less than 1 mm across are common.

Psammitic and semipelitic biotite gneisses (2b) are medium- to fine-grained

pale pink to pinkish-grey rocks containing 5-20 percent biotite. Magnetite grains

are usually visible.

Semipelitic and psammitic biotite-sillimanite gneisses (2c) form the upper­

most unit of the Sickle Group. They are medium-grained pink rocks with 10-15 per­

cent biotite and trace-5 percent sillimanite typically concentrated into faserkiesel

with lengths of up to 15 cm and widths of about 1 cm.

Burntwood River Supergroup - Sickle Group contact

The contact between the two groups is well exposed on the south side of the

island 1 km east of Frost Island at the south end of Kamuchawie Lake. Vertically

dipping pelitic sillimanite-bearing biotite gneiss, unit le, of the Burntwood

River Supergroup is in contact with a 15 m-wide band of white quartzo-feldspathic

gneiss, unit lj, which contains less than 5 percent mica and several concordant

5 to 10 cm-wide layers of melanocratic amphibolite. The quartzo-feldspathic gneiss

is in contact with a 3 m-wide horizon of fine-grained semipelitic biotite schist,

unit lf. This in turn is in contact with pinkish medium-grained amphibole gneiss,

unit 2a, of the Sickle Group which here has no recognizable basal conglomerate.

Contacts of these units and their foliations are concordant.

Intrusive rocks*

Granitoid rocks of probable intrusive origin underlie much of the southern

and southeastern part of the map-area. Most are gneissose and, apparently

possessing low ratios of potassium feldspar to plagioclase, are tonalitic and

granodioritic orthogneisses.

The following rock-types, whose relative ages have not yet been determined,

have been distinguished on the map:

* The classification recommended by the IUGS Subcommission on the Systematics of Igneous Rocks has been adopted (Streckeisen, 1976).

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Waxy-looking metatonalite and metadiorite (3) form a band with an outcrop

width of up to 5 km flanked by smaller bands and lenses. The unit has been traced

from Harriott Lake southeastwards to the southern boundary of the map-sheet.

They comprise homogeneous well foliated medium-grained brown-weathering rocks

typically containing small feldspar porphyroblasts which rarely exceed 1 cm in

length, up to 25 percent finely granular biotite, and variable amounts of quart z .

Garnet and/or amphibole is locally present. Fine-grained relatively biotite-rich

xenolithic patches of questionable origin have been observed in several outcrops .

Pegmatitic veining is almost entirely absent; this is in strong contrast with

adjacent pelitic gneisses.

Metatonalite and metagranodiorite (4) respectively white or pale pink in

colour, are uniform medium-grained weakly foliated xenolithic gneisses in which

there are numerous 1 cm-long feldspar porphyroblasts. Biotite makes up 10-25

percent of the gneisses; amphibole is patchily distributed in the meta-granodior ite .

Metamonzogranite and metasyenogranite (5) are pink weakly foliated to mass i ve

rocks containing 5-20 percent biotite and, rarely, amphibole; feldspar porphyro­

blasts are developed in some plutons of this unit.

Metagabbro (6) is a scarce medium- to coarse-grained homogeneous equigranu l ar

weakly foliated rock composed of white feldspar and 30-40 percent mafics, amphi bole

generally being dominant over biotite. Metagabbro forms small elliptical masses

and sills 10-50 m wide.

Pegmatite (7) although the commonest intrusive rock in the area rare ly

constitutes a mappable unit. It contains accessory biotite, muscovite, garnet ,

sillimanite, tourmaline and/or magnetite.

Structure and metamorphism

The earliest recognizable thermotectonic event (D1

) produced the gneissic

foliation (s1

) seen in all rock-types except most pegmatites. No folds attr i bu-

table to this event have been identidied.

Tight isoclinal folds (F2

) deform s1

. Macroscopic F2

folds are common

throughout the area. Megascopic F2

folds have been distinguished only in the

extreme east, where they trend N-S, and northeast, where they trend E-W. The

variation in trend results from later deformation. F2-folding has produced

interbanding of rock units of the Burntwood River Supergroup and the Sickle Group ,

~here complete successions in the latter group are not developed, shearing on F2

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fold limbs was probably responsible. Sillimanite faserkiesel in unit 2c have major

axes parallel to the axial planes (S 2) of F2 minor folds. Mineral lineations,

mullions and boudins (L2) have been generated parallel to F2

hinges.

NE- and ENE- trending folds (F 3), particularly well developed at the south

end of Kamuchawie Lake, clearly refold F2 structures. Crenulation cleavage (S3

)

is conunon in F3 hinge zones along with linear fabrics (L3

) parallel to F3

hinges.

F3 folds account for most closures seen on the map.

Northerly trending folds (F4) in the east have combined with F3

folds to give

a dome-and-basin interference pattern. An intense N-S fracture system readily

observed on aerial photographs of the north end of Kamuchawie Lake possibly re­

presents an F4 axial planar fabric; no such fabric has been recognised in outcrop.

Numerous lineaments traceable for many km along strike are conspicuous on

aerial photographs. However lithological offset or brecciation to which faulting

could be attributed has not been noted. The three main trends are: N-S, NNW-SSE

and NW-SE, with other lineaments oriented NNE-SSW to NE-SW and E-W.

Metamorphic grades in the upper amphibolite facies prevailed during and

following n1

and n2

. Considerable quantities of mobilizate were produced by

partial melting of the original sediments. Growth of most metamorphic miner3ls,

including garnet, sillimanite, cordierite, biotite and amphibole, took place

during and after n2

. The characteristic waxy colour of some metatonalitic and

metadioritic rocks (unit 3) suggests that lower granulite facies conditions were

locally attained. F3

and F4 folds probably formed while temperatures throughout

most of the area were still very high as there is neither intense nor widespread

retrograde metamorphism. Growth of biotite, amphibole, quartz and feldspar

took place locally during n3

• Large randomly oriented flakes 1-5 mm across of

muscovite ar e c ommon in coarse-grained sillimanite-bearing biotite gneisses of

unit le.

Economic Geology

Most of the areas underlain by pelites of the Burntwood River Supergroup or

by orthogneisses are of little economic interest and have attracted little

attention from industry.

Exploratory work has, however, been carried out as follows:

a) Deep Bay - Gladman Lake area. Augustus Exploration conducted some

prospecting and located several small copper showings in 1960. Sherritt Gordon

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Mines Ltd. (1965) submitted records of 6 diamond drillholes that were sunk into

conductive horizons in pelitic metasediments. No economically significant

sulphide mineralization was encountered, but visual estimates of up to 60 percent

graphite were reported from within the uppermost 21 m of DDH 3 from CBS 756. Part

of the area was covered by a photogeologic evaluation commissioned by Great Plains

Development Co. of Canada Ltd. in 1966. Superior Graphite Co. (1974) has re­

examined the more highly graphitic area drilled by Sherritt Gordon.

b) Wapus Lake - Dumont Lake area. The earliest work on record was performed

by Columbia Metals Exploration Co. Ltd. (1955-7) over a weakly radioactive zone in

pegmatite. Augustus Exploration prospected about 80 km2 in 1960, finding a few

minor copper and molybdenum occurrences. Considerable interest was shown by

Sherritt Gordon Mines Ltd. (1965, 1970) in molybdenum and sulphide mineralization

in amphibole gneisses at the south end of Dumont Lake; their drilling results

indicated that the concentration of molybdenum and base metals is too low and

scattered to be viable.

c) Kamatsi Lake area. An airborne geophysical survey was flown for Straus

Exploration Inc. in 1970; several conductors were outlined; there is no account

of any follow-up work.

d) Todd Lake - Harriott Lake area . Ground electromagnetic surveys, trenching

and some drilling was undertaken in 1970 and 1971 on behalf of Straus Exploration

Inc. Copper mineralization giving assays of up to 0.75 percent Cu was reported

from garnet± cordierite ± sillimanite pelite in the nose and adjacent limbs of

the Pistol Lake antiform . South of Todd Lake, eight electromagnetic anomalies

warrenting further investigations were found, but appear not to have been followed-

up.

The entire map-area was covered by a joint Federal-Provincial lake sediment

sampling programme in 1974 (Hornbrook et al, 1975). No outstanding anomalies were

found for any of the 12 chemical variables analysed.

During the present survey, no new mineralized outcrops of possible economic

importance were noted. However, initial results from a lake sediment sampling

project give several extremely high nickel values (5000 and 1900 ppm) from Todd

Lake and its immediate neighbourhood; these outline a target area worthy of

further examination. The bedrocks are hornblende and hornblende-biotite gneisses

(units lhb, lhc) in which a few low-value disseminated pyrrhotite occurrences

have been observed. Pearson (1972, 1973) has suggested that these amphibole­

bearing rocks are an extension of the Amisk Group which mainly contains rocks

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of volcanic origin.

References

Hornbrook, E.W.H., Garrett, R.G., Lynch, J.J. and Beck, L.S. (1975): Regional lake sediment reconnaissance data, east-central Saskatchewan; Geol. Surv. Can ., Open File Rept. 266.

Lenton, P.G. (1975): Geology of the McKnight Lake area; Man. Mines Br.; Geol. Paper 2/75, pp. 16-18.

McRitchie, W.D. (1974): The Sickle-Wasekwan debate, a review; Man. Mines Br.; Geol. Paper 1/74.

(1975): Russell Lake south; Man. Mines Br.; Geol. Paper 2/75. pp. 19-21.

Pearson, D.E. (1972): The location and structure of the Kisseynew Gneiss domain of northern Saskatchewan; Can. Jour. Earth Sci. Vol. 9, pp. 1235-1249.

(1973): The geology of the Scimitar Lake area (east half), Saskatchewan Dept. Mineral Res., Rept. 156.

Streckeisen, A. (1976): To each plutonic rock its proper name; Earth Sci. Rev., 12; pp. 1-33.

Zwanzig, H.V. and Wielezynski, P. (1975): Geology of the Kamuchawie Lake area; Man. Mines Br.; Geol. Paper 2/75, pp. 12-15.