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Compilation Geology, Pelican Narrows (63M) and Amisk Lake (63L) by R. Macdonald

The writer spent 9 days in the summer based on Pelican Narrows, mainly investi­ gating the following:

1. Psammitic sillimanite-bearing rocks in the Kipaligan area, to explore the feasibility of stratigraphically sub-dividing this unit along the lines adopted else­ where for Sickle Group rocks (Gilboy, 1976 and various Manitoba authors). 2. Supracrustal rocks arou~d the western margin of the Sahli granite, with a view to tracing possible lithostratigraphic units through Jan Lake to the units mapped in the Lirnestone-Tulabi Lakes area farther south (Macdonald and Posehn, 1976) .

Insufficient time was spent on problem 1 for conclusions to be drawn and the remainder of this account concerns problem 2.

The generally well foliated to moderately layered medium-grained f elsic gneisses (Q) mapped around the northern nose of the Sahli granite in the Pelican Narrows area (Macdonald, 1974) are associated with massive ma.fie rocks (M) and a few t hin pelitic layers (P) . Exposures of this composite tnit (QM) along the well foliated contact with the Sahli granite show waxy feldspars and other features indicating t he granu­ lite faci es. A kilometre or two aw&y from the contact towards the settlement of Pelican Narrows the unit is progressively affected by anatexis. In t he islands southwest of Pelican Narrows the anatectite comprises a biotite granodiorite c on­ taining well rounded mafic xenoliths. Examples of intermediate stages between the parent QM composite unit and this anatectic assemblage abound in the area. The anatectic zones appear to trace intermittently further southwest down the east side of Pelican Lake t o Jan Lake where migmatites and anatectites are extremel y abundant. The QM unit also traces through into Jan Lake to form a closed domal structure around the granite at McMillan Point (Pyke, 1964) and around the granitoid on Harper I sland (Kirkland 1958). The quartz monzonite mapped by Pyke (1964) north of the McMillan Point granitoid is also a complex of the QM unit in various degr ees of anatexis.

A belt of predominently ma fic (hornblendic) rocks lies along the western side of the QM Unit connecting southwards across the narrows to Jan Lake and apparently connecting farther south with the Tul abi Lake hornblendic rocks (Macdonald and Posehn, 1976). This belt - which includes rocks mapped in the Sandy Nar rows area by Sibbald (in press) as interlayered arnphibolites , hornblende gneisses and quartzo- feldspathic gneisses - contains distinctive, and probably mappable, metamorphosed subunits - 52 -

~esembling tuffs,agglomerates and flows . At a point about one kilometr e east of Richardson Island, anatectic felsic and ma f ic rocks are cut by massive mafic sills.

The granitoid rocks in the core of the McMillan Point dome contain garnet and resemble some parts of the Sahli granite. Brief inspection of the Harper Island granite revealed granitoids of more alaskitic aspect .

Synthesis

A broadly coherent stratigraphic succession may exist in the area under review:

Unit 2. (M) Mafic gneisses, including tuffs, agglomerates and f lows, with some felsic and pelitic layers Unit 1 . (QM) Felsic gneisses with widespread mafic (hornblendic layers and minor pelites and semipelites

Unconformity (deformed)

Sahli granite (possibly equivalent t o the McMillan Point and Harper Island granitoids)

Unit 1 i s anatectic in many places, generall y and apparent ly at a consistent stratigraphic level above the presumed unconformity. Mafic sills cut and probably comprise much of the mafic component of Unit 1. The lower part of the pr oposed broad succession is af fected by granulite faci e s metamorphism, as is the Sahl i granite.

The Sahli granite has been dated a t approximatel y 2340 1 30 m. y . usi ng the Rb/Sr isochron method (Bell and Ma cdonald, in prep. ) and is provisionally considered t o be basement to the contiguous supracrus tal units, including t he afore- mentioned Units l and 2.

The question r emains open as to whethe r the supracrustal rocks Units 1 and 2 are equivalent to the late-Archean Hansen Lake vol canics (Coleman, 1970), in which case the Sahli Granite age i s an "updated age", or whether Units l and 2 are Apheb ian and related to the Flin Flon - Amisk volcanic assemblages.

The compilation of sheet area 63M is sche duled f or completion when map sheet ar ea 63M-14 (W) is mapped in 1978.

References

Coleman, L.C . (1970) : Rb/Sr isochron s for some Precambrian rocks i n t he Hanson Lake ar ea, Saskat c hewan; Canadian Journ . Earth Sci. , Vol. 7, 338-345.

Kirkland, S.J.T. (1958): The Geo logy of the Deschambault Lake Area (East Half) , Saskatchewan, Sask. Dept. Mineral Resources, Rept. No. 31 . - 53 -

Gilboy, C.F. (1976): Reindeer Lake South (SE) Area in Summary of Investigations 1976 by the Saskatchewan Geological Survey, Sask. Dept. of Mineral Resources.

Macdonald, R. (1974): Pelican Narrows (West) area, in Annual Summary of Field Investigations by the Saskatchewan Geological Survey 1974, Sask. Dept. Mineral Resources.

Macdonald, R. and Posehn, G.A. (1976) : Re-investigation of the Pickerel River and Limestone-Tulabi Lakes area, in Summary of Investigations 1976 by the Saskatchewan Geological Survey 1976, Sask. Dept. Mineral Resources.

Pyke, M.W. (1966): The Geology of the Pelican Narrows and Birch Portage Areas, Saskatchewan, Sask. Dept. Mineral Resources, Rept . No . 93.

Sibbald, T.I. l. (in press): The Geology of the Sandy Narrows (East) area, Sask. Dept. Mineral Resources, Rept . No. 170 .

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