Project 8836

Glennie-Kisseynew P-T Study 1988: Fieldwork and Preliminary Results 1

Dexter Perkins2

Perkins, D. (1988): Glennie·Kisseynew P·T study 1988: fieldwork and preliminary results, in Summary of Investigations 1988, Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report 88·4.

During August 1987, preliminary fieldwork was con· ducted in the Pelican Narrows area of northeastern Sask­atchewan (Figure 1). Analytical results and application of some conventional geothermobarometers indicate that the rocks have retained chemical signatures of high­grade metamorphism. A joint venture agreement be­tween the University of North Dakota and Saskatchewan Energy and Mines was negotiated. The goal was to in· vestigate the pressures and temperatures of metamor· phism recorded by rocks in a 5000 km2 area centred around Pelican Lake.

1. Region of Interest

The area covered by field work during 1988 is approx­imately rectangular. The northern border coincides with the Churchill River system (Ourom, lskwatam, Wintego, Pita and Sokatisewin Lakes); the southern border fol­lows a line connecting Brownell, Deschambault and Jan Lakes. To the west, the area extends to Trade and Sad­ler Lakes; the easternmost samples were collected along the road connecting Pelican Narrows to Sandy Falls.

Because metamorphosed granites and basalts tend to be of little use in determining metamorphic pressures and temperatures, emphasis was placed on the study of metasedimentary rocks. Based on the compilation map of Macdonald (1981) and, to a lesser extent, the more detailed work of several other workers (including Kirkland, 1957, 1958, 1976a, 1976b; Johnson, 1966; Pyke, 1966; Sibbald, 1978; Scott, 1981), important metasedimentary areas were identified. Outcrops were visited via air and water, and over 800 samples were col· lected from approximately 20 different lakes and rivers. Thin sections are presently being made for about 200 samples. Garnet and biotite have already been semi­quantitatively analyzed in about 25 sections, using EMPA to calculate metamorphic temperatures.

2. Lowest Grade Rocks

The rocks collected vary in metamorphic grade from greenschist to granulite facies. The lowest grade rocks were collected just east of the trace of the Tabbernor Fault on the shores of Ourom, Manawan and Wood Lakes. In outcrop, some of these lowest grade rocks ap­pear little deformed or metamorphosed, but thin sec-

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G ~Sadler Wood

~ Vincent Cl. C>

Stauroli1e

Brownell

Deschambault

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1 Figure 1 - Pelican Narrows area, showing lakes visited during the summer of 1988. Solid line represents the trace of the Tab· bemor Fault; dashed lines are roads.

tions reveal the presence of metamorphic chlorite, mus­covite and andalusite. Andalusite was observed in out­crop at three locations: 1) 2.5 km southeast of the Wood Lake Indian Reservation, 2) in the woods ap­proximately 3 km east of Piney Lake, and 3) at the southernmost end of Pelican Lake near the portage to Deschambault Lake. Andalusite, staurolite and quartz coexist at the Piney Lake locality, suggesting metamor· phic pressure and temperature of about 3 kbar and 550°C (Thompson, 1976; Winkler, 1979). Staurolite­quartz assemblages were also found in the vicinity of Brownell and Staurolite Lakes. However, at those loca­tions the stable Al~iOs polymorph is sillimanite, sug­gesting pressures in excess of 3 kbar at 525 to 600°C (Holdaway, 1971).

(1) Joint venture project wtth partial support provided by the Ganada-Saskalchewan Sut>sldary Agreemenl on Mineral Development 1984-69 (2) Department ol GeolOgy and Geologlcal Engineering, University of North Dakota, Grami ForkS, North Dakota 58102

32 Summary of Investigations 1966

3. Highest Grade Rocks The highest grade rocks encountered are garnet-sil­limanite-bearing Kisseynew gneisses. These gneisses must have formed at temperatures in excess of 6QO•C and at pressures of 4 to 7 kbar. Only two samples of sil­limanite-bearing Kisseynew gneiss have been identified so far. More will probably be found when all the thin sec­tions are made. The general appearance of the Kissey­new gneiss suggests uniform metamorphic conditions across most of the northeastern portion of the study area.

Sillimanite has also been found in other lithologic units. In particular, one sample collected near Palf Lake and another from an outcrop between Vincent and Staurolite Lakes appear to contain visible sillimanite. Garnet is ab­sent in both specimens.

4. Regional Variation in Grade Based upon some key minerals and assemblages, some of which were summarized above, it appears that metamorphic grade is relatively uniform to the east of the Tabbernor Fault, but changes rapidly over short dis­tances near the Tabbernor Fault and in metasediments associated with greenstone units to the west of the fault. Such variations in grade may be primary, due to varia­tions in pressure and temperature at the time of meta­morphism, but may also be due to postmetamorphic tec­tonism. There are many examples of high-strain zones which may represent postmetamorphic deformation. More detailed mapping is needed.

5. Geothermometry Semiquantitative analyses of garnet and biotite were ob­tained from about 25 thin sections. The distribution of Fe and Mg between coexisting garnet and biotite was used to deduce metamorphic temperatures (Perchuk and Lavrent'eva, 1983). The specifics of these results must be regarded with caution inasmuch as the analyses are attended by rather large uncertainties. High­quality analyses will be obtained this winter.

The preliminary results (Figure 2) are sufficiently reliable, however, to suggest attainment of metamorphic temperatures in excess of 625 to 650°C to the east of the Tabbernor Fault, and in the range 550 to 600.C to the west. The results also suggest that there are no major regional variations in metamorphic temperatures other than those associated with the fault. It is particular­ly interesting to note that there appears to be no "ther­mal high" associated wrth the orthopyroxene-bearing Sahli Granite unit between Mirond and Pelican Lakes. If detailed geothermometry supports this observation, it suggests metamorphic (re)equilibration after emplace­ment of the Sahli Granite.

6. Ongoing Work During the winter of 1988-89, all thin sections will be made and quantitative analyses of key minerals will be

Saskatchewan Geological Survey

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Figure 2 - Gamet-biotite temperatures based on the calibra­tion of Perchuk and Lavrent'eva (1983). For clarity, a few calcu­lated tempertures have b6en omitted from the centre of the area, as they fall in the same range. Solid line represents the trace of the Tabbemor Fault.

obtained. Several different geothermometers and geobarometers, based primarily on equilibria involving garnet, biotite, cordierite and sillimanite, will be applied. Once those results have been obtained, plans for the next field season will be made.

7. References Holdaway, M. J. (1971): Stability of andalusite and the

aluminosilicate phase diagram; Am. J. Sci., v271, p97-131.

Johnson, R.L. (1966): The geology of the Nemei Lake area (west half); Sask. Dep. Miner. Resour., Rep. 107, 24p.

Kirkland, S.J.T. (1957): The geology of the Manawan Lake area (north half); Sask. Dep. Miner. Resour., Rep. 27, 12p.

Kirkland, S.J.T. (1958): The geology of the Deschambault Lake area (east half}, Saskatchewan; Sask. Dep. Miner. Resour., Rep.31, 16p.

Kirkland, S.J.T. (1976a): The geology of the Marchel-Win­tego - Sandy Bay area, Saskatchewan; Sask. Dep. Miner. Resour., Rep.172, 12p.

Kirkland, S.J.T. (1976b}: The geology of the Manawan Lake area (south half), Saskatchewan; Sask. Dep. Miner. Resour., Rep.175, 14p.

Macdonald, R. (1981}: Compilation bedrock geology: Pelican Narrows and Amisk Lake areas; in Summary of Investiga­tions 1981, Sask. Geol. Surv., p.16-23.

33

Perchuk, LL. and Lavrent'eva, 1.V. (1983): Experimental inves­tigation of exchange equilibria in the system cordierite-gar­net-biotite; in Saxena, S.K.(ed.), Kinetics and Equilibrium in Mineral Reactions; Springer-Verlag, New York, p111-129.

Pyke, M.W. (1966) : The geology of the Pelican Narrows and Birch Portage areas, Saskatchewan; Sask. Dep. Miner. Resour., Rep. 93, 68p.

Scott, 8.P. (1981): Geology of the Maynard Lake- Sandy Nar­rows (west} area; Sask. Dep. Miner. Resour., Rep. 186, 26p.

Sibbald, T.1.1. (1978): Geology of the Sandy Narrows (east) area, Saskatchewan; Sask. Dep. Miner. Resour., Rep .170, 49p.

Thompson, A.B. (1976): Mineral reactions in pelitic rocks: I. prediction of P-T-X(Fe-Mg} phase relations; Am. J . Sci., v276, p401 -454.

Winkler, H.G.F. (1979): Petrogenesis of Metamorphic Rocks (5th ed.) ; Springer-Verlag, New York; 348p.

Summa,y of Investigations 1988