Project 8318 Pelican Narrows Project by L. 0. Craig 1. Discussion

Transcription

1 Project 8318 Pelican Narrows Project by L. 0. Craig 1 'Ihe Pelican Narrows Project study area is indicated on the location map. Field work took place in t\\o parts of the Pelican Narrows map sheet area 62M-2(W) (Figs. 1 and 2). A geological map of the Pelican Narrows map sheet produced by the Saskatchewan Geological Survey (Macdonald, 1974, 1975) was used as a basis for the present investigation, with revisions as i ndicated by the author's observations. Table 1 is a provisional Sl.lITTllary of the stratigraphy, structural history and metamorphism of the area, Deformational History The structural features of the area are illustrated in Fig. 3. 'Ihe earliest deformational event recognized in the area (D1), is displayed by unit Is, which is strongly foliated. 'Ihe adjacent intrusive unit Gd shows a rroderate to strong foliation coplanar with the layers in unit Is. 'Ihe foliation planes produced by D1 are designated S1. 'Ihe S1 surface presently strikes east-west and dips to the north, This s1 surface has been folded and possibly tilted by later events, The secord deformational event produced a strong and pervasive effect upon the area, forming a S2 foliation and L2 lineation in the Sahli granite as well as in units Gg and Ga, and induced F2 folds in the other units. 'Ihese F2 folds are corrm::,nly associated with an S2 axial plane foliation which is most evident in unit (;b. F2 folds are open and plunge rroderately towards the north arxl northeast. The third arxl last deformational event produced the intense folding and mylonitization in unit A. 'Ihe 83 layering planes in the mylonite strike north-northeast ard dip steeply to the east. 'Ihe associated F3 folds have shallow-plunging hinges and irregular axial planes. The F3 deformation was associated with or followed by a lowering luniversity of Saskatchewan. Project received field logistical support from Saskatchewan Energy and Mines. of metamorphic grade. J'djacent to a zone of S3 mylonite, hornblende gneisses contain idiomorphic grains of chlorite. Geochronology Che whole-rock rubidium-strontium isochron has been previously determined from the area (Bell and Macdonald, 1982). The samples analyzed were collected from the northern part of the Sahli granite at the location indicated in Fig. 1. The isochron indicates an age of Ma. In the vicinity of the sample location, the Sahli granite has been extensively to partially recrystallized and shows a strong F1 foliation. An initial 87sr;86sr ratio of suggests that the Sahli granite contains a significant cojtiix)nent of older crustal material. The Sahli granite could be older than the indicated age due to possible disturbance of the isotope systems by recrystallization of feldspars and the growth of new biotite, both of which appear to be related to the o 2 event. It is reasonable to assume that the biotite gneiss unit Bp is part of the Kisseynew Gneisses which are considered to be Aphebian. Since the D2 event has affected the Bp gneisses, this sets a maximum age for the D2 deformation. Discussion Units Q and Bg are the oldest rock units in the area. The presence of quartz-rich bands suggests a possible sedimentary origin. These units appear to wrap around the Sahli granite and connect with less defonned gneisses to the south of the granite, which are also considered to be metasedirnentary. However, unit Q has been repeatedly deformed and recrystallized, and possibly contains a significant amount of unrecognized igneous material. No original sedimentary structures remain, with the possible exception of some of the larger scale layering. Fig. 4 is a map of an outcrop of unit Q gneiss, the location of which is indicated in Fig. 1. The Sahli granite (Units Go and Ga) intrudes unit Q gneiss. Although inclusions are hard

2 to recognize because of the effects of the s2 deformation, one clear example of an inclusion of Q gneiss in Sahli granite was found. Textures and structures in the northern part of the sahli granite are dominated by D2 fabrics and structures. 'lbe present S2 foliation was produced by granulation and recrystallization of feldspars and the growth of new biotite. 'lbe southern portion of the Sahli granite has been much less affected by the D2 i,,, ' LAKE:_', Seale I :50,000 55'03' 102'45' Figure 1 - Structures in the Sahli granite. Lithological units and some structural symbols adapted from Macdonald (1974): Q Quartzofeldspathlc gnelsse11: granoblastic to granitoid, layered and foliated, commonly containing layers and lenses of mafic gneiss; probably derived from felsic metasediments. Bg Blotlle-garnet-sltllmanlte-cordlerlte gneiss: commonly with quartz, feldspar,± garnet.± cordierite layers and metamorphic segregations, locally graphitic; probably derived from pelitic metasediments. Md Maflc dyke or other small intrusive body. Ga Granltold garnet-blotlte gneiss: with strong to moderate foliation, locally containing corroded chnopyroxene and traces of orthopyroxene. Gg Garnet-cllnopyroxene-orthopyroxene-hornblende gneiss: weakly layered and foliated, locally migmatitic, colour index varies from 5 to 15 percent. Gd Intermediate granllold rock: foliated grey to white, includes migmatites with hornblende gneiss paleosome. Is Rock: strongly foliated to laminated, fine to medium grained, intermediate colour index. Bp Blotlte gneiss+ garnet: medium grained, strongly foliated and layered to massive, commonly containing quartz and quartz feldspar segregations, commonly gradational into Qp. Op Felslc gnelh: commonly containing traces of calc-silicate minerals. A Mylonlllc gnelh: strongly folded, containing lenses of units Bp, Op and Gd, together with coarse-grained granite and pegmatite... f boundary uncertain due to interfolding of units

3 ,o, ss' 1.:._,,-,o,,-::c;:"-:--:-,1,,\i,l.-;:--I, -"', >,,,_J ", -,,, t: \,., l, \ "\,,..,,.., A;?, >. ' C. ;., ':) '..;: < '; --- \ :,-,:; :; Opr '",.P -- ' --,:. ---,._ - I : - i'',,..,.,. -, J\ ;: 9 F15 J?r.o., (".-':';., \'--,..)- L _ ; ELICA!,!,ARROWS,,-- lh lk4b -.,,..... ;...., - - :' _.3 km Bp -----t- <!Eji ;>t: ft(:::..,... '.'.::"' -...,"\, I ': o I j,.--.,\...,.,,......::-... ';..._...,,.,.- :;; :-!,:--\ <,. <.._.-,. _oc;., S.'? --':.-:d..," ) Gd ""-.--. w"- ::-- t.. \"-,.'\,' \,,: ',-<. -j-'l.{.. ". -:,-r4' < -- --,.,:.,,.-,J: r - -,.. 1\,'.'l,::r.. """-. -- ' ' -- -,:,:)' :::f -,-".-, ;,,.;,;,c:;fl:\ } ' _;,...(,.,i'. CC' -,, j<, 'f '.' Gd \\ t l j \ \,. I "!-,,.)1...\ l r;; """" u"'.....,,,_..,'i '(!,,... l< '!'' 'e v"' \t,.,.. J I. '...,; r ,.,. :,. u ' :. -, '""".. ',, " ', J < U ' "' BA ' i_:\ "!(.:::,'.::, I,:::-J",...,\\...-.,\..\ _,\:"'...:.._"'.,<,,...,::.: \,b,..,,,. '::;s. }>\ vcv:, ; --,, - :.,,,,--,. :.- >.,t--- -=--' L t< :',: \ 1020$S '10 S ln,1ctura l Symb<Mi Lo, ro u.-,on.,.., fvl<::lhut' "' Cc,p)ano, f,:,l!qt... Ql'ld _..,,. fonoiiofl <Wl,I:,.,'-:> IC- Foldl!O"Q# 'cld0ll<11l p;o-. '.::2 l1 r,11 " "" " flq l,:;11...,...,.. -""vlon.... 8o,.-,d r, 10,,, ;- f-t>cr,or or"'' SI r,,n,:,i:i J,'<1,.., e>log,1 l',a.,.. &11, it:1., Co:>la-.o ;p.' '" " 10,.. l :i-21,tn:wr!qc --- p.,;.-d )2 lo'll ;,'.,ort,.-.d A.Pf<Oo-- "r<>o;ibll,02,40 45 s, 13 3.s N Figure 2 - Geology of the Wunehikun Bay area. Lithological units adapted from Macdonald (1974). Refer to Fig. 1 tor explanation of units and symbols,

4 Table 1 - Provisional Summary of Stratigraphic Units, Deformation. Metamorphism and Geochronology Stratigraphy, Wunehikun Bay Area Stratigraphy, Sahli Granite Area Deformational Events Metamorphi c Events Geochronology Oz Md dykes? , F3, Ch lorite growth 53 my lonite iri uni t A 03, Fz, Biotite-garnet Sz foliation assemb l age in L2 liheation unit Ga Bp & Qp 9neisses Aphebian Md dykes Uncc,nformi ty Unit Is , S1 foliation - and my l on ites Gd possible intrusion (relation uncertain ) Sah 1 i grani te Gg, (Ga) Qpx, Cpx, garnet assemblage Intrusion c. 2.4 Ma -- Older gneisses Q, Bg Older gnei sses Q, Bg poss i bly Archean 103'13' l02 '20 ' 55'20'-t-- -= '20',,,,,.,.---, I, ,,- \ \ \,,,,,, ATTITTI BLOCK ', w z w...j 0 Kllol'lttm Kllolntt,es Figure 3 Regional setting o f struc tural features in the Pelican Narrows area. See text for designation of structural elements.

5 deformation. Fig. 5 is a detailed map of a group of particularly well exposed outcrops at the southwest corner of Sahli Lake. Orthopyroxene arrl clinopyroxene in these outcrops are noderately fresh. '.Ihe rcx::ks have a granular texture and only a weak and irregular foliation. Economic Geol ogy Unit Bp and gneisses north of Wunehikun Bay contain layers bearing disseminated iron sulphides arrl graphite. 'Ihese layers are associated with calc-silicate minerals and are rrore s iliceous than normal. Large IT] Felsic gneiss - [TI Laminated mafic lli] Massive maf ic []] Pegmatite 0. :.o : Layer Frost heaved rock 0 5 metres Fold hinge Minor fault figure 4 Detailed map of a felsic gneiss outcrop (unit Q o n Fig. 2).

6 , l, J,_ Migmatite-number ffi is colour index Rodded intrusive Mafic sill Fe lsic vein Pegmatite [2J Mofic boudin Gradotional boundary 0 I 1p metres ' patches of sandy till in the area irrrnediately nor th of WUnehikun Bay contain s ignificant quantities of iron-stained cobbles. 'lhe iron sulphide- and graphite-bearing gneisses strike eastward into unit A where they occur in lenses as t ectonic relics. In the rrore highly deformed parts of unit A, the graphite is concentrated along S3 planes. Although only iron sulphides were seen in outcrops visited, many sulphide-bear ing l ayers beneath the t ill have not been examined. Jlcknowledgments 'Ibi s project is supported in part by the Saskatchewan Department of Energy and Mines. The project i s being supervised by Dr. E. G. Nisbet who receives a NSERC operati ng grant. L. O. Craig received support for 1983 under a Northern Field Research grant. '!be Saskatchewan Mini ng Developnent Corporation contributed to this research by providing accomodation in the field for a ten-day period in '!he authors wish t o thank Dr. M. R. St auffer for his assistance. References Bell, K. and Macdonald, R. (1982) : Geochronol ogical calibration of the Precarrbrian Shield in Saskatchewan; in Sumnary of Investigations 1982, Sask:-Geol, Surv., p Macdonald, R. (1974) : Pelican Nar rows (west) area: reconnaissance geological survey of 63M-2 (W); in Sl.llllTlary of Investigations 1974, Sask. Geol:-surv., p (1975) : Compil ation geology, Pelican Narrows (63M) and Ami sk Lake (63L) ; in S1..1T111ary of Investigations 1975, Sask. Geol. Surv., p Figure 5 - Detailed map of an area of Sahli granite (unit Gg on Fig. 1).

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