Geology of the Hanson Lake Area (Part of NTS 63L-10) 1

R.O. Maxeine?-, T.1./. Sibbald, and B.R. Watters2

Maxeiner, R.O., Sibbald, T.1.1., and Watters, B.R.(1993): Geology of the Hanson Lake area (part of NTS 63L-10); in Summary of Investigations 1993, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 93-4.

During the past summer the authors collaborated in 1 :20 000 scale mapping in the western part of the Han­son Lake area. The work represents the continuation of a project that was initiated in 1989 which contributed to the revisional geological mapping of the Flin Flon Do­main and Hanson Lake Block along the Shield margin (Project Seagull). Project Seagull ls a component of a larger national mapping project (NATMAP).

Geologically the Hanson Lake area (Figure 1) lies within the Hanson Lake Block of the Reindeer Zone of the Trans-Hudson Orogen. The Block comprises both Archean and Lower Proterozoic elements; the former represented by the charnockitic Sahli granite and the MacMillan Point granite and the latter by a mixed se­quence of volcanic, volcaniclastic, and sedimentary su­pracrustal rocks, which were intruded by hypabyssal to plutonic rocks of a wide compositional range. Hanson Lake is dominated by the presence of a mixed suite of felsic to mafic metavolcanics and lesser metasedi· ments. To the north and west, these abut the Jackpine Lake-Tulabi Lake migmatitic gneisses of granodioritic to tonalitic composition and of uncertain origin (Byers 1957; Coleman et al. 1970; Sibbald 1989; Maxeiner et al. 1992). South of Hanson Lake, the Precambrian Shield is overlain by Ordovician clean quartz sand­stones of the Winnipeg Formation and dolomites of the Red River Formation.

Age dating of the Shield rocks has provided the follow­ing time markers in the study area. Early Rb-Sr dating by Coleman (1970) indicated a whole rock age of 2375 ±30 Ma for the supracrustal rocks. This was sub­sequently discredited by Bickford et al. (1986), who dated an intrusive quartz-feldspar porphyry from the Hanson Lake metavolcanics at 1888 ±12 Ma by the U­Pb zircon method. A rhyolite from the upper part of the volcanic succession has recently provided a more pre­cise U-Pb zircon age of 1875 ±1 Ma (Heaman et al., this volume). This is similar to a U-Pb zircon age of 1886 ±2 Ma for a rhyolite of the Amisk Group in the Flin Flon Domain (Gordon et al., 1990). The Finger penin­sula granite, which intrudes the metavolcanic assem­blage, yields a U-Pb zircon age of 1844 ±12 Ma (Bick­ford et al., 1987). A migmatitic hornblende-plagioclase­quartz diorite gneiss from the northern end of Jackpine Lake provided a preliminary U-Pb zircon age of 1830 ±28 Ma (Mock and Bickford, 1992) which may date peak metamorphism and/or migmatization within the

Jackpine Lake gneiss dome. Another sample of migma­titic hornblende-plagioclase gneiss, also collected from the northern end of Jackpine Lake, yielded a U-Pb zir­con age of 1827 ±4 Ma (Mock, internal progress report 1993). The beryliferous pegmatites from the Jackpine Lake gneiss dome, which are essentially undeformed and clearly post-tectonic, produced a whole rock Rb-Sr age of 1760 Ma (Coleman, 1970). Further sampling was completed in 1993, in conjunction with the Royal Ontario Museum, in order to more clearly define the age and duration of volcanism, the age of metamor­phism and deformation, and the relationship of the Jack­pine Lake gneisses to the structurally overlying su­pracrustal rocks.

Regional metamorphism reached amphibolite facies grade. Within metasedimentary rocks from the northern part of the area, middle amphibolite facies conditions are indicated by a mineral paragenesis containing bi­otite+muscovite+quartz+sillimanite+almandine-garnet (Maxeiner et al., 1992). In the south, the stable mineral paragenesis is represented by chlorite+white mica+ andafusite, and is indicative of upper greenschist facies metamorphism.

Two significant base metal deposits are known at Han­son Lake. The Western Nuclear Mine, in operation from 1967-69, was a Pb-Zn massive sulphide deposit. The mine produced 147,300 tonnes of ore, with grades of 5.83 percent Pb, 9.99 percent Zn, and 0.51 percent Cu. Silver and gold were recovered as by-products. The Mcllvenna Bay deposit has estimated reserves of 13.08 million tonnes of ore, with grades of 4.95 percent Zn, 1.26 percent Cu, 0.53 git Au, and 24.3 git Ag (CAMECO, annual report, 1992). A detailed description of the deposit and an account of its discovery can be found elsewhere (Sibbald, 1989; Koziol and Osta­povitch, 1990). Numerous base metal showings are pre­sent in the Hanson Lake area, the more promising of which have been described in earlier papers (Maxeiner and Watters, 1991, 1992). Additional mineral prospects include the Side Lake copper showing, located at the north end of Side Lake and the Jackpine Cu-Zn show­ing, situated southwest of Jackpine Lake.

1. Previous Work

Mapping was first carried out at a scale of 1 :126,720 by Wright and Stockwell (1934) for the Geological Survey

{1) This project was funded in 1993 by both federal and provincial components of the Canada-Saskatchewan Partnership Agreement on Mineral Development 1990-95.

(2) Department of Geology, University of Regina, Regina, Saskatchewan, S4S OA2.

40 Summary of Investigations 1993

LEGEND

OROOVICIAN

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llfflllJSM: ROCICS:

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Figure 1 - Simplified geological sketch map of the Hanson Lake area. JLA=Jackpine Lake Antiform, TLA=Tulabl Lake Antiform.

Saskatchewan Geological Survey 41

of Canada. A more detailed map of the district, at a scale of 1 :31,680, was compiled by Byers in 1957 for the Saskatchewan Department of Mineral Resources. Both the geology and the geochemistry of the Hanson Lake area were described by Coleman et al. (1970), who also produced a map at a scale of 1 :15,84~. A Ph.D. thesis by Gaskarth (1967) formed the basis of this publication. Lithogeochemical studies have been un­dertaken by Parslow and Gaskarth (1986). The most re­cent work was carried out by Sibbald (1989), Lewry (1990), Maxeiner and Watters (1991 , 1992), Maxeiner et al. (1992), and an unpublished M.Sc. thesis by Maxe­iner (1993).

2. Description of Major Rock Types

a) Mafic Metavolcanic Rocks

Rocks of mafic composition comprise pillowed and mas­sive amygdaloidal flows and richly garnetiferous, granu­lar amphibolites surrounding the gneiss domes. Mafic and intermediate volcanic and volcaniclastic rocks make up from 1 O to 20 percent of the volcanic se­quence in the Hanson Lake area, mostly in the west.

Mafic flow rocks, which are dark green to black, with white to light green mottling, and very fine to fine grained, occur as a fairly extensive unit that extends from the mine road, south of Nicu Lake, to Fly Lakes. The unit is heterogeneous and, in most outcrops, the rocks are strongly rodded and characteristically exhibit pitted weathering. The rock has a calc-silicate lithology, containing hornblende, diopside, plagioclase, carbonate, ±quartz, ±garnet. The mafic mineral content generally exceeds 35 percent. The texture is partly amygdaloidal, partly fragmental, and partly massiv~. In sever~I out­crops within the unit southwest of N1cu Lake, pillow structure was identified and in consequence the rocks are interpreted as subaqueous basaltic flows.

Massive, partly amygdaloidal fine-grained, dark grey to dark green mafic rocks occur in a number of s1:1a11 units, most commonly along and west of the.mine road. The rock is in part hornblende porphyroblast1c and lo­cally contains numerous round diopside pods, u~ t.o 40 cm in maximum dimension. One small subunit 1s gametiferous (3 to 5 percent}, shows faint compo~i­tional layering, and is partly fragmental. These units are interpreted as amygdaloidal basaltic flows and minor vol­caniclastics.

Richly garnetiferous amphibolites occur in several u~its along Highway 106, sandwiched between the Jackpine Lake and the Tulabi Lake gneiss domes, and partly ~ur­rounding the former. They are dark green to black, fine to medium grained, highly recrystallized, tectonically laminated, and in part compositionally layered. Essen­tial minerals comprise plagioclase, hornblende, garnet (locally 5 to 10 percent, up to 5 cm diameter), ~iot.ite and, locally, white feldspar porphyroblasts. Maf1c min­eral content ranges from 40 to 45 percent. The large garnets have extensive, and generally symmetrical quartz-feldspar pressure shadows. It is believed that

42

these rocks represent recrystallized and highly strained equivalents of mafic volcanics and volcaniclastics.

b) Intermediate Metavolcanlc Rocks

Volcaniclastics of intermediate composition, including crystal tufts, heterolithic tuff breccia, and intermediate to mafic granular amphibolites, are also fairly uncommon in the Hanson Lake area. They are generally dark green to black, fine grained, thinly bedded to thinly lami­nated and occur as several long, narrow units northeast of Fly Lakes extending towards Nicu lake. Major min­eral constituents are plagioclase, hornblende, garnet, ±biotite, ±magnetite, ±quartz. Mafic mineral content var­ies from 15 to 30 percent. A local variant containing rel­ict feldspar crystals and numerous large porphyroblastic garnets is interpreted as an andesitic crystal luff. To the north, it grades laterally into intermediate amphibolites, which are also feldspar-phyric, fine to medium grained, and tectonically laminated. Where these rocks are pre­sent on the southern and eastern flank of the Jackpine Lake gneiss dome, they contain from 2 to 3 percent gar­net, are commonly injected by quartz-feldspar±hom- _ blende ' lits of tonalitic leucosome and cut by late grani­tic pegmatite.

Embedded within the dacitic volcanic assemblage are several small, apparently folded units of heterolithologi­cal andesitic tuft breccia. These rocks are dark grey­green, inequigranular, locally feldspar-phyric, weakly laminated and contain lapilli-sized mafic, and less abun­dant, lithic fragments. They comprise plagioclase, horn­blende, biotite±garnet and mafic mineral content ranges from 20 to 25 percent. The unit is volcaniclastic in origin and might have been deposited as a pyroclastic flow. In part the rocks are closely associated and intercalated with minor mafic volcanics and volcaniclastics.

c) Felsic Metavolcanic Rocks

An effort was made to try and differentiate between three kinds of felsic metavolcanic rocks in the field. Dacilic, rhyodacitic, and rhyolitic rocks were subdivided on the basis of their colour, mafic mineral content, and mineralogy, a sometimes very difficult undertaking.

Dacltlc rocks form the predominant volcanic compo­nent in the Hanson Lake area. They are grey, fine- to very fine-grained, often monotonous .felsic rocks conta.in­ing from 5 to 15 percent mafic constituents. Some var~e­ties are fragmental, with lapilli-sized and larger, monoh­thological fragments, and locally with well preserved centimetre scale flow-banding. Dacitic volcanics also oc­cur as massive feldspar-phyric flow rocks, with from 3 to 1 O percent plagioclase phenocrysts .up to 2 f!lm in maximum dimension. Locally these unrts are thickly bed­ded and interlayered with minor rhyodacitic fragmental intervals. Sandwiched between the gneiss domes and closely associated with intermediate and mafic amphibo­lites, are granular rocks of dacitic composition, contain­ing tonalitic lits, which lack any primary features due to strong deformation and recrystallization. Rocks of daci­tic composition contain plagioclase, K-feldspar, quartz, biotite±garnet±sericite±magnetite±hornblende. Quartz

Summary of Investigations 1993

and feldspar may occur as phenocrysts. Garnet forms subhedral pink porphyroblasts up to one centimetre in diameter. The garnet content of the dacitic rocks is highly variable and probably reflects differences in pri­mary compositional variation, rather than superimposed alteration, unless garnet is in excess of 5 percent and associated with amphibole. The dacitic rocks are inter­preted as a complex succession of volcaniclastic rocks, massive volcanic flows, and intercalated epiclastic mate­rial. Highly strained and recrystallized felsic rocks are in­terpreted as high grade equivalents of these dacitic vol­canics and volcaniclastics.

Rhyodacitic rocks, which contain thin subordinate rhy­olite layers, occur in several small units west of the mine road. They are light grey to pink on weathered sur­face, aphanitic to fine grained, and occasionally micro­porphyritic, with sporadic quartz phenocrysts, pinhead garnet and also visible magnetite crystals; often they are feldspar-phyric, and in some outcrops fragmental, containing lapilli-sized fragments of rhyolite. Quartz, pla­gioclase, K-feldspar, biotite±garnet±magnetite are the major mineral constituents; mafic mineral content typi­cally varies from 3 to 5 percent. The rocks are inter­preted as dominantly pyroclastic in origin.

Rhyolitic metavolcanics occur predominantly in the eastern part of the area (Sibbald, 1989), but also form two small units east and northeast of Nicu Lake. The rhyolitic volcanics are light pink to white, aphanitic to fine grained, poorly layered to unlayered, and locally ex­hibit fine millimetre-scale contorted lamination and centi­metre-scale compositional variations, both of which have been interpreted as flow banding. The rocks are microporphyritic, with up to 5 percent euhedral to subhe­dral quartz and microcline phenocrysts, ranging from 0.2 to 2 mm in maximum dimension. The groundmass is extremely fine grained to aphanitic and is made up of quartz, K-feldspar, plagioclase, muscovite±biotite±mag­netite; mafic mineral content does not generally exceed 3 percent.

Felsic volcanic rocks, surrounding Parrex Bay, Mine Bay, and continuing into Mcllvenna Bay in the south, are interpreted as the marginal zones of an inferred len­ticular rhyolite dome. These marginal zones are formed by volcaniclastic flow deposits. The core of the rhyolite dome is situated near Parrex Bay and is believed to rep­resent the upper levels of an eruptive centre, marking the final stage of volcanic activity in the Hanson Lake area. The dome is surrounded by elastic aprons, repre­senting fragmentary debris shed from the dome. The elastic material making up the aprons would appear to have accumulated in a subaqueous environment, as it is now represented by proximal quartz-eye schist that grades distally into sillimanite schist and layered chert, which are in part intercalated metagreywacke. Volcanic breccia is common within rocks of the felsic dome and comprises large irregular blocks of flow-banded rhyolite contained in a fine-grained, sericitized felsic matrix. Pri­mary features are often preserved and the presence of spherulites within the rhyolitic blocks indicates that, in part at least, eruption was subaerial (Cas and Wright, 1987). Spherulites, comprising radiating aggregates of quartz and feldspar, are arranged in parallel bands mim-

Saskatchewan Geological Survey

icking primary flow banding. The spherulites are typi­cally somewhat elongated, due to weak deformation.

d) Metasedimentary rocks

A Polymictic conglomerate was identified as a mappa­ble unit in exposures along the mine road. The rock is poorly sorted and matrix supported, containing a variety of lithic clasts and quartz pebbles. The clasts are typi­cally sub-angular to well rounded and from 2 to 10 cm in diameter, although numerous smaller fragments, which are from 1 to 2 mm in diameter, are also present. The clasts are contained in a fine-grained matrix of inter­mediate composition, made up of plagioclase, horn­blende, quartz±biotite±garnet; mafic mineral content of the matrix varies from 15 to 20 percent. In places, the rocks are finely laminated and openly folded. The con­glomerate is surrounded by rocks of volcanic and vol­caniclastic origin.

Psammitic greywacke, exposed on Young Peninsula and on islands in the main basin of Hanson Lake, is lat­erally transitional into, and overlies, calc-silicate rocks (i.e. east of the calc-silicate unit of Young Peninsula). The unit was also mapped to the east of Agnew Bay and at the north end of the main lake in association with a mafic wacke (Maxeiner et al., 1992). Poorly de­veloped graded bedding indicates that the unit east of Young Peninsula is east facing. Some interlayered bands are extremely quartz-rich and medium grained, others comprise pelitic metasedimentary rocks and mafic wackes. Clast supported conglomerate beds, with elongated quartz-eyes and lithic 'eyes' several centime­tres in maximum dimension, are uncommon. The clasts comprise coalescent quartz, single crystals of amphi­bole, fragments of amphibolite, and heavily altered feld­spar minerals. In general, the greywackes have quartzofeldspathic matrices and their mineralogy com­prises quartz, feldspar, biotite, muscovite, garnet (1 to 5 percent), magnetite (1 percent) and minor sillimanite. Pelitic intervals within the greywacke are characterized by assemblages containing garnet, sillimanite, staurolite, biotite, and white mica, together with minor amounts of sphene, tourmaline, and opaque minerals.

Greywacke also occurs interlayered with silicate facies iron formation and garnetiferous 'granodiorites', in a unit that extends from Fly Lakes to Nicu Lake and farther north. Here it is a delicately layered, dirty grey, domi­nantly fine-grained, equigranular quartz-rich metasedi­ment. Layering is preserved on a 1 to 100 cm scale with quartzofeldspathic layers predominating over am­phibole-biotite-rich layers and garnet-rich layers.

Mafic wacke, a fine-grained amphibolite of mafic to in­termediate composition, is exposed at the northern end of Young Peninsula. The rocks are dark grey to green, medium-grained, fairly heterogeneous on a large scale, and comprise plagioclase, hornblende, biotite, and quartz; mafic mineral content varies between 20 and 40 percent, typically averaging about 30 percent. Small, elongated hornblende porphyroblasts, often defining a stretching lineation, are commonly present. Although in individual outcrops the amphibolite appears fairly homo­geneous with an apparent lack of primary textural tea-

43

tures, field relationships suggest that the unit is a sedi­mentary rock derived from partially reworked volcanics, rather than a juvenile volcanic rock. Intercalation with sil­limanite schists and psammitic greywacke on a metre scale provides evidence for this proposed sedimentary origin. These intercalations are especially abundant to­wards the top of the amphibolite unit and along the northeastern edge of the area mapped.

Cale-silicate rocks outcrop along the eastern shore of Young Peninsula where they extend over a strike length of 2 km. They also form thinner discontinuous unmappa­ble units with the psammitic greywacke. Outcrops on Young Peninsula have a fragmental appearance, as large lenses of medium-grained, unfoliated rock are in­tercalated with fine-grained, micaceous, highly foliated bands. Elongated carbonate lumps are also abundant and are usually weathered out, leaving empty, lens­shaped pockets. Local psammitic layers within the calc­silicate rocks grade laterally into typical greywackes. The composition of the rock varies considerably on a metre scale, some parts being enriched in amphibole, and others in plagioclase and diopside. In general, calc­silicate rocks are grey to light green, medium to coarse grained, massive to poorly bedded; plagioclase, horn­blende, diopside, actinolite, and carbonate are essential constituents and sphene, zircon, apatite, sericite, and epidote are accessory minerals. The entire unit is inter­preted as epiclastic.

Mixed metasedimentary rocks outcrop along the north­eastern shore of Agnew Bay and can be traced over a north-south strike length of almost 2 km, and possibly also extends to the south through Agnew Bay. The as­semblage comprises garnet-mica schist, sillimanite schist, cherty quartzite, and garnet-diopside-amphibole rock, and is locally intruded by ultramafic rocks. As the various subunits cannot usually be traced over any great distance, all were incorporated into a single unit. From west to east (i.e. stratigraphically upwards) the as­semblage grades from the pelitic schists into the cherty quartzite, and garnet-diopside-amphibole gneiss.

The pelitic schists are grey to light brown, fine-grained and locally fragmental with subordinate quartz pebbles and lithic clasts. Main constituents are quartz, mica (20 percent), and feldspar±garnet±sillimanite (faserkie­sel).

Cherty quartzite is white to light grey, occasionally grass green, and aphanitic to very fine grained. Other than quartz, constituent minerals are white and green mica (fuchsite ?)±galena±sphalerite. The rocks are com­positionally laminated on a millimetre- to centimetre­scale.

Garnet-diopside-amphibole rock is closely associated with cherty quartzite. It is dark grey to dark green, fine to medium grained, and contains abundant hornblende, diopside, garnet±feldspar±cummingtonite-grunerite± mica±staurolite±sillimanite. Subtle layering and lamina­tion has been documented in a number of outcrops. Sul­phides, mainly sphalerite, galena and pyrrhotite, are dis­seminated or enriched in parallel bands. Anthophyllite­cordierite-bearing schists, accompanied by minor pyr-

44

rhotite and chalcopyrite, were identified in one location within this subunit. MnO values within the garnet-diop­side-amphibole rock are anomalously high (4 wt.%). This entire assemblage is interpreted to represent alumi­nous shales grading upward with decreasing sedimenta­tion rates into cherty iron formation exhalite.

Several units of lean, partly banded iron formation are recognized, particularly in the lower part of the sedimen­tary package overlying the volcanics. A thin unit over­lies the hydrothermal alteration halo exposed on north­ern Bluebird Island (Maxeiner and Watters, 1992). As noted above, iron formation is also interbedded with greywacke in the Fly-Nicu lakes area. Silicate-facies iron formation dominates, with varying proportions of ox­ide-facies and sufphide-facies developed. The rocks are massive and rusty brown to dark dirty grey on weath­ered surface and contain abundant garnet (spessartine­rich), amphibote (commonly cummingtonite-grunerite se­ries), chert, biotite, lumps of quartz and feldspar, and sulphides. Anomalously high manganese concentra­tions (up to 9 wt.%) are typical of the Bluebird Island unit. Occasionally, bands of dacitic mineralogy are inter­calated and are believed to represent tuffaceous inter­vals. Similar rocks have been described in the nearby Limestone Lake area (Adamson, 1988).

e) Intrusive rocks

Biotite granite forms three major intrusive bodies in the area; one on Finger Peninsula, one to the east of Side Lake and another one to the southeast of Bad Car­rot Creek. The granites are medium to coarse grained, equigranular, pink to fight grey, homogeneous, gener­ally weakly foliated, and contain quartz, microcline, or­thoclase, plagioclase, biotite, ±hornblende, ±muscovite, minor calcite and sericite, and accessory phases of apa­tite, zircon, and epidote. Mafic mineral content is less than 10 percent. Locally, granite contains xenoliths of mafic country rocks and is cut by numerous fate granitic pegmatites.

Quartz-feldspar porphyry forms relatively large intru­sive bodies notably east of Agnew Bay, west of Parrex Bay, and northeast of Mine Bay. Several smaller intru­sions are also recognized (Sibbald, 1989; Maxeiner and Watters, 1991). In outcrop, the rocks are dark-grey, fine to medium grained and inequigranular, with numerous euhedraf to subhedral phenocrysts of orthoclase and to lesser extent pfagioclase, averaging 2 to 3 mm maxi­mum dimension. Elongated eyes of coalescent quartz or iridescent blue quartz phenocrysts are also present, but are usually less abundant than feldspar. The matrix of the rock is very fine grained, consisting of quartz, po­tassium feldspar, pfagioclase, and biotite. White mica occurs as a postkinematic mineral. Accessory phases are epidote and apatite.

Garnetiferous quartz porphyry represents a second type of porphyry which is exposed at the south end of Bluebird Island and on several islands in Bertrum Bay. The fine-grained, weakly foliated matrix of the rock is quartz-rich and partly recrystallized, with microcfine, pla­gioclase, and biotite as main constituents. Garnet por­phyrobfasts are always present, but rarefy exceed 3 per-

Summary of Investigations 1993

cent, as are 'eyes' of coalescent quartz which are typi· cally elongated and stretched within the schistosity. Feldspar phenocrysts are absent.

Quartz-diorlte is medium-grained, homogeneous, light to medium grey and outcrops at the southern end of Bad Carrot Lake, as well as in several locations of lesser significance. Feldspar (dominantly plagioclase), quartz, biotite±hornblende are major constituent miner­als; mafic mineral content is approximately 15 percent. Composition varies from quartz diorite to granodiorite. Field relations show that these rocks crosscut the sur­rounding dacites; they might possibly be the feeder dikes for these volcanics.

Diorlte is medium grained, grey to green, and homoge­neous; it forms the marginal phase of granitic intrusions northwest of Bad Carrot Lake and west of Bertrum Bay, as well as small bodies elsewhere. A sill of micropor­phyritic diorite occurs along the eastern shore of Young Peninsula and extends for a distance of 8 km from the northern end of Hanson Lake, almost to its southern ter­mination. Where it is relatively weakly deformed, this particular unit is characterized by a very fine-grained groundmass of plagioclase, hornblende, and biotite con­taining euhedral phenocrysts of plagioclase and horn­blende up to 3 mm in size; the latter has been partially retrogressed to biotite. The mafic mineral content is be· tween 15 and 30 percent.

Metagabbro occurs as marginal phases to the Side Lake granite, as discrete units east of Nicu Lake, south· east of Fly Lakes and east of Parrex Bay, and as small units associated with ullramafic bodies throughout the area. Typically these are several distinct leucocratic to melanocratic intrusive phases. The rocks are medium to coarse grained, dark grey to dark green and quite uni­form, containing hornblende and plagioclase as princi­pal minerals, and biotite and/or garnet as minor constitu­ents; pyrite and chalcopyrite are locally present. The mafic mineral content ranges from 30 to 60 percent. Characteristically, gabbroic rocks feature large porphy­roblastic hornblende crystals, which locally contain relict pyroxene cores. In places, the gabbro contains xeno­liths of country rock.

Ultramafic rocks were identified in several locations and are usually associated with gabbro. They comprise fine- to coarse-grained, pale green to dark green, mas­sive amphibolites, comprising hornblende, other amphi­boles±diopside±biotite±plagioclase. One thin section shows relict olivine 'spots'. The mafic mineral content exceeds 90 percent. These ultramafic rocks are inter­preted as peridotitic intrusions.

Epldote-magnetite ultramafic rock ('skarn') is a fine­to medium-grained, dark green to black, massive amphi· bolite, containing hornblende, plagioclase, magnetite (approximately 5 percent), and epidote (approximately 5 percent). Magnetite and epidote occur as highly elon­gated streaks and lenses. Mafic minerals comprise greater than 60 percent.

Pyroxenite forms two bodies in the area; one occurs at the northern end of Fly Lakes, the other forms a small

Saskatchewan Geological Survey

unit exposed along Highway 106. The pyroxenite is coarse to very coarse grained, deeply weathered, homo­geneous and massive. It is dark brown to dark red on weathered surface, and dark green to black on fresh surface and comprises dominant pyroxene (diopside and augite), hornblende, plagioclase±magnetite. Mafic mineral content is in excess of 90 percent.

Mafic dike rock outcrops as a single large unit, trend· ing north-south, be1Ween Nicu Lake and Geol Lake. and as countless other small mafic dikes that are unmappa­ble. All these bodies have cross-cutting relationships. They are fine to medium grained, dark grey, equigranu­lar and homogeneous and are made up of plagioclase, hornblende, biotite±garnet±magnetite. Their mafic min­eral content exceeds 30 percent.

f) Jackpine Lake and Tulabi Lake Gneisses

These gneisses are compositionally variable from quartz diorite to granodiorite to tonalite, although on av­erage they comprise pink to grey, medium- to coarse­grained biotite and biotite-hornblende granodiorite and granodiorite gneisses. Mineralogically they contain pla­gioclase, quartz, K-feldspar, biotite, hornblende±mag· netite±muscovite. The mafic mineral content is gener­ally between 5 and 15 percent.

The Jackpine Lake gneisses are a highly heterogene­ous assemblage, with strong textural and compositional variations from outcrop to outcrop. They are distinctly migmatized; partial melting has occurred throughout the gneiss dome producing several different phases of melt fraction. Some of these are at least syn- to post tec­tonic. Partly, the granodiorite/tonalite is megacrystic, with up to 50 percent large plagioclase crystals. In a number of outcrops of the Jackpine Lake gneisses, large K-feldspar crystals (5 to 15 cm) are present within the granodiorite. They may represent clasts or relict K· feldspars derived from disrupted early pegmatite. Fre­quently, the gneisses contain bands, schollen and rafts of amphibolite, which are quite variable in composition. Such amphibolite 'inclusions' are interpreted as dis· rupted mafic dikes and xenoliths of mafic country rocks. Characteristic migmatitic features such as ptygmatic folding, schlieren development, agmatite, and isolated folds are found throughout.

The Tulabi Lake granodiorite and granodiorite gneisses are significantly more homogeneous south of High-way 106 and over large areas comprise variable foli· ated biotite±hornblende granodiorite which is cut by sev­eral generations of simple granite pegmatite sheets. The contact with the Hanson Lake metavolcanics is not a sharp break, but is marked by an interlayering of vol­canics and intrusive sheets of granodiorite over several tens of metres. As a result, screens of supracrustals are incorporated within the granodiorite complex, one example with particular continuity being the silicate fa­cies iron formation interlayered with quartz-rich grey­wacke traceable from Chip Lake to Fly Lakes. Grano­diorite and granodiorite gneisses within metres of the contact with these rocks are typically garnetiferous, con­taining up to a few percent ruby red garnet. Similar gametiferous, mainly tonalitic gneisses, form well de-

4 5

fined outcrop areas in the centre of the Jackpine Lake dome.

Jackpine Lake and Tulabi Lake gneisses are incorpo­rated within the high-strain zone (Lewry's 'Pelican Slide': Lewry, 1990) which follows Highway 106 from Winteringham Lake to south of the Hanson Lake turn­off. The shear zone rocks are layered hornblende grano­diorite gneisses. They are blastomylonites exhibiting granular groundmass fabrics, within which winged por­phyroclasts and rounded megacrysts of K-feldspar and plagioclase are preserved.

'Granite' Pegmatite of several generations intrudes the Jackpine Lake and Tulabi Lake gneisses. The youngest pegmatites, occurring in the central part of the Jackpine Lake dome, are beryliferous, and clearly post-date all the tectonic activity in the area (MacDougall, 1991). Pegmatite is also abundant in the supracrustal rocks ad­jacent to the dome and in association with granitic intru­sions. Mappable bodies of white 'granite' pegmatite, which appear to be essentially undeformed, occur at the north end of Hanson Lake, where they intrude me­tasedimentary rocks overlying the metavolcanic assem­blage. They are mineralogically simple, comprising quartz, feldspar±biotite±muscovite.

3. Structural Geology

In the Hanson Lake volcanics, foliation (schistosity) trends uniformly north·south and dips steeply east or west. Major lithological volcanic units appear to trend sub·parallel to the regional foliation and there is no clear evidence that large scale folding has resulted in repetition. Where preserved, primary compositional lay­ering in the dacitic volcanics is openly to isoclinally folded by small scale, northerly trending folds. Fold axes and axes of elongation of fragments mostly plunge moderately to the south. Faulting and shearing have played a major role in the structural history of the west­ern Hanson Lake area and have led to the development of an extremely complex and broken up map picture. This, combined with the initial variability of a succession of volcanic and volcaniclastic rocks, explains the discon­tinuity of many of the exposed units.

In the Jackpine Lake gneiss dome the structural geol­ogy is much more complex. At least two folding events are recognized which deform the alternating migmatitic banding of granoblastic leucosomal melt, early pegma· tile, and amphibolite. Locally, superposition of folds gives rise to Type I and Type Ill interference patterns (Ramsay and Huber, 1987). Thus, at least two deforma­tional events post-date the earliest phase of partial melt­ing on an outcrop scale. The large, northerly trending Jackpine Lake dome possibly represents a third event, as Type Ill interference patterns are described as occur­ring all around the nose of this antiformal structure (Coleman et al., 1970). That partial melting outlasted this latest phase of folding is illustrated by leucosomal material forming parallel to the north-trending told axial planes and crosscutting minor folds of this age in the antiform core.

46

The relationship between the Jackpine Lake gneisses (and by implication the Tulabi gneisses) and the struc­turally overlying metavolcanic belt is not understood. Current hypotheses entertain both 'allochthonous' and 'autochthonous' settings. The former envisages the for­mation of the gneiss complex and the volcanic assem­blage at different structural levels and the later juxtaposi­tion of the two along a high-strain zone, thereby making them unrelated in terms of their age. The highly strained nature of the margin, the relative confinement of partial melting to the gneiss domes, and the different styles of deformation in the domes as compared to the volcanics, all seem to support such an interpretation.

The latter anticipates granodiorite was emplaced in a more or less 'autochthonous' environment; in this case the granodiorite would have to yield a younger age than the volcanics which it intrudes. The intrusive nature of granodiorite into the metavolcanics, the presence of a band of greywacke and lean iron formation along the eastern flank of the Tulabi Lake gneisses, and the oc­currence of lits, a possible product of restricted partial melting, in the immediate country rocks surrounding the Jackpine gneiss dome support the 'autochthonous' the­ory. As was discussed in the introductory part of this pa­per, ages from the Jackpine Lake gneisses are equivo­cal. The latest dating, however, indicates a U-Pb age of around 1830 Ma for a migmatitic hornblende-plagio­clase gneiss ; this age might reflect the latest partial melting event rather than provide the age of the original granodiorite.

4. Geochemistry

Analytical data for some 600 samples from the Hanson Lake area are available (Parslow and Gaskarth, 1986). In the area mapped this summer, some 200 samples of the metavolcanics were matched to sample locations from this open file report. Analyses of these samples were used to determine the geochemical characteristics of the volcanic assemblage. Comparison was made with data from the eastern half of the area.

Several geochemical plots (Figures 2, 3, 4, and 5) illus­trate the geochemical trends for the volcanics in the west half of the Hanson Lake area (i.e. west of the mine road). In previous publications, it was reported that the Hanson Lake volcanics were generated in a subduction related environment similar to modem island arcs, that the volcanic pile is generally eastward facing and has tholeiitic, calc-alkaline and alkaline components preserved (Parslow and Gaskarth, 1986; Maxeiner et al., 1992; Maxeiner, 1993).

The present study supports and improves on these ear­lier ideas. Rocks of true basic composition, in terms of Ti versus Zr ratio, are relatively rare in the western part of the area (Figure 2). In terms of total Fe plus Ti con­centration, however, the rocks of the western area have somewhat elevated concentrations over their eastern counterparts, as illustrated on a Jensen cation plot (Fig­ure 3). The elevated Fe plus Ti values allow classifica­tion of the mafic, intermediate, and part of the dacites as tholeiitic. Rhyodacite and rhyolite are calc-alkaline,

Summary of Investigations 1993

1 .000 I 10 100

Zr (ppm)

.. 1

I

I I

1.0IJO

Figure 2 -A plot of Ti versus Zr (Pearce and Norry, 1979) sepa­rates evolved from unevolved basic rocks and discriminates be­tween arc lavas and within plate lavas in the western Hanson Lake area.

Fe+ Ti

/\ I \

JX~allc ---1 / \ ' : :::::ed'°le / \

7 I \ ! ' Tnoleiilic ,

// . • ,J •~~~)SK~. I Basaltic ,\,' i ~Vr:i: ~ • •"'( ~Komat1ite

/~·,. • . Cale-alkal ine \ \ I : 'Ultramatic \ \\,

; ::...._ .· ' Komatilte

Al Mg

Figure 3 - A Jensen cation plot after Jensen (1976) differenti­ates between calc-alkaline and tholeiitic lavas in the western Hanson Lake area. Only rocks of sub-alkaline affinity can be used on this plot.

as is the bulk of felsic rocks in the eastern part of the area (Maxeiner et al., 1992). A plot of Si02 versus Zr!Ti02 illustrates the spread from subalkaline basaltic to rhyolitic samples (Figure 4), with simultaneous enrich­ment of both silica and the Zrffi02 ratios. Figure 5 is a plot incorporating only elements which are generally considered to be immobile (e.g. Pearce and Cann, 1973; Winchester and Floyd, 1977) and it indicates, when compared to Figure 4, that the rocks were partly silicified after crystallization. Rocks which were mapped as rhyodacite in particular seem to have been affected by silicification, an observation which is consistent with some of the field interpretations. In many cases, units of rhyodacitic composition seemed to be situated paral­lel to major late faults which are commonly associated with late K-feldspar, epidote and quartz veining, and are

Saskatchewan Geological Survey

so ,.-I RH YOltTE

RHVODACIH

70 I OACITE

~ 1 . Q 60 1

ANlESITE ..,, / (/) .

so I S'JB-ALKALINF SAS ALT

. , . . , . ·~ ,: ,. - - -.. ·· • -"-, "'- ....... ~Yr,·ft"v • .

~ )( ~ ... ~-!· ~ -~~' ~ A'- ., )K ~ ., BASANITE ,( A"' .'

TRACHYTE

PHONOUTE

;( :1§1: )( I ::K mafic • mlermediate • telsic . ·.. . 11

40 Q _()()l 001 0 . 1 1

Zr/TiO,

Figure _4 - A plot of Si02 versus ZrfTiD2 (Winchester and Floyd, 1977) is taken as a geochemical discrimination diagram for the rocks of the western Hanson Lake area.

\ CO~ENOITE / ..

I ,'. mafic . • int~ diate _"_'._•lsic I "'-. f

RHYOUTE """ /

PHONOUTE

O 1 I RHYODACITE · ... . >~--

O I DACITE • \ ~ :· i -----,,,, ____ TR ACHYTE

~ ANDESITE ""··:;;~:: ••• ·J, .. TAA~~~: J )- .

0.01 I .,J!~\ • . ;/ I

- - - . . !j;' I I IINO(SITF; } ',.;;:. I BASANITF

I BASALT 'llfll.~ 'j( I NEPHELINITF

0 .001 I 0.01

· · .. · · ~~ :,,: i ALKALl,A<SALT

I

Sl..B·ALKAI INE BASALT I

0.1 NbN

10

Figure 5 - A plot of ZrfTiD2 versus Nb!Y (Winchester and Floyd, 1977) is taken as a geochemical discrimination diagram for the rocks of the western Hanson Lake area. The ratio of Zr!Ti02 is taken as a measure of the degree of differentiation, whereas the Nb!Y ratio is indicative of the degree of alkalinity.

believed, therefore, to represent silicified dacites rather than primary rhyodacites. Three samples of rhyolite from east of Nicu Lake are much different in their geo­?hemistry to the rhyolites from Mine Bay/Parrex Bay be­ing much less evolved and, consequently, are believed to have formed at a different time, presumably earlier, in the volcanic history of the area.

The geochemical characteristics of the volcanics mapped during the past summer indicate that they are generally somewhat less evolved than those occurring in the eastern portion of the Hanson Lake area. There­fore, the previously established model, in which the Han­son Lake volcanics are regarded as broadly east-fac­ing, is still believed to be valid. It is apparent now, how­ever, that felsic volcanics represent an integral part of both the eastern and western parts of the Hanson Lake area. Previous interpretations assumed that much of

47

the volcanic succession west of the mine road was dominated by intermediate to mafic volcanics (Coleman et al., 1970; Parslow and Gaskarth, 1986).

5. Economic Geology

Base me~al showings and deposits, as previously re­ported (Sibbald, 1989; Koziol and Ostapovitch 1990· Maxeiner and Watters, 1991, 1992), are abundant in' the Hanson Lake area. In addition to important deposits such as the Mcllvenna Bay deposit and the Western Nu­clear Mine, and important showings such as the Young Pros~ect, Bluebird Prospect, and Zinc prospect, other sho"'."1ngs that were encountered during the past sum­mer include the Jackpine Lake showing and the Side Lake showing. In addition, several areas of weakly to moderately altered volcanics were seen, particularly in the southeastern part of the area. They include se­quences of felsic, aluminous schists, and areas of gar­net-amphibole alteration similar to the one described on Blue_bir?_lsland ~Max~ine! and Watters, 1991); however, no significant mmerahzat1on was found in association with alteration.

6. Acknowledgments

Funding for this study was provided by the Geological S~rvey o_f Canada and by Saskatchewan Energy and Mines. Field and other logistical support was granted by Saskatchewan Energy and Mines and the Geological Survey of Canada. R.M. would like to thank Dave Thomas and Tom Sibbald for their insights during the field season.

7. References

Adamson, D.W. (1988): Volcanogenic mineralization in the Limestone Lake area, Saskatchewan, Canada; unpubl. Ph.D. thesis, Univ. Aston, Birmingham, 238p.

Bickford, M.E., Van Schmus, W.R., Collerson, K.D., and Mac­donald, R. (1987): U-Pb zircon geochronology project new results and interpretation; in Summary of Investigations, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 87-4, p76-79.

Bickford, M.E., Van Schmus, W.R., Macdonald, R., Lewry, J.F:, and Pearson, J.G. (1986); U-Pb zircon geochronology proJect for the Trans-Hudson: Current sampling and recent results;. in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86·4, p101-107.

Byers, A.A. (1957): The geology and mineral deposits of the Hanson Lake area; Sask. Dep. Miner. Resour., Rep. 30, 47p.

Cas, A.A. F. and Wright, J.V. (1987): Volcanic Successions, Modern and Ancient; Allen and Unwin Ltd., London, 528pp.

Coleman, LC. (1970) Rb-Sr isochrons for some Precambrian rocks in the Hanson Lake area, Saskatchewan; Can. J. Earth Sci., v7, p338-345.

Coleman, LC., Gaskarth, J.W., and Smith, J.R. (1970): Geol­ogy and geochemistry of the Hanson Lake area, Saskatch­ewan; Sask. Research Council, Rep. 10, 156p.

48

Gaskarth, J.W. (1967): Petrogenesis of Precambrian rocks in the Hanson Lake area, east-central Saskatchewan· un-publ. Ph.D. thesis, Univ. Sask. '

Gordon, T.~., Hunt, P.A., Bailes, A.H., and Syme, E.G. (1990): U-Pb wcon ages from the Flin Flon and Kisseynew belts, Manitoba: Chronology of crust formation at an Early Pro­terozoic accretionary margin; in Lewry, J.F. and Stauffer, M.A. (eds.), The Early Proterozoic Trans-Hudson Orogen of North America, Geol. Assoc. Can., Spec. Pap. 37 p177· 199. ,

Jens_en, LS. (1976): A new cation plot for classifying subalka­l1c volcanic rocks; Ont. Geol. Surv., Misc. Pap. 66, 22p.

Koziol, M. and Ostapovitch, G. (1990): The Mcllvenna Bay de­posit-a case history; in Beck. L.S. and Harper, C.T. (eds.), Modern Exploration Techniques, Sask. Geol. Soc., Spec. Publ. 10, p54-69.

Lewry, J.F. (1990): Bedrock geology, Tulabi-Church Jakes area: De~vation and significance of porphyroclastic gneisses 1n the southern part of the Pelican Window; in Summary of Investigations 1990, Saskatchewan Geologi­cal Survey, Sask. Energy Mines, Misc. Rep. 90-4, p36·43.

MacDougall, D.G. (1991 ): Rare element pegmatites in the Han­son Lake pegmatite field; in Summary of Investigations 1991, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 91-4, p118·127.

Maxeiner, R.O. (1993): Geochemistry, petrography, and metal­Jogenesis in the Hanson Lake area; unpubl. M.Sc. thesis, Univ. Regina, 217p.

Maxeiner, A.O. and Watters, B.R. (1991 ): Mineralization and associated alteration in !he western Hanson Lake area; in Summary of Investigations 1991, Saskatchewan Geologi· cal Survey, Sask. Energy Mines, Misc. Rep. 91-4, p109-117.

____ (1992): Alteration in the Hanson Lake area: A me­tasomatic evaluation; in Summary of Investigations 1992, S~skatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 92-3, p66-71.

Maxeiner, A.O., Watters, B.R., and Sibbald, T.1.1. (1992): New implications for geochemistry and metamorphism in the Hanson Lake area; in Summary of Investigations 1992, S~skatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 92-4, p72-7B.

Mock, T.D. and Bickford, M.E. (1992): Field and isotopic study of late, undeformed pegmatites and leucogranites in the Glennie ~omain and the Hanson Lake Block; in Summary of lnvest1ga!1ons 1992, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 92-4, p57-60.

Parslow, G.R. and Gaskarth, J.W. (1986}: Geochemistry of the Hanson Lake area; Sask. Energy Mines, Open File 86-1, 107p.

Pearce, J.A. and Cann, J.R. (1973) Tectonic settings of basic volcanic rocks determined using trace element analyses; Earth Planet. Sci. Lett., v19, p290-300.

Pearce, J.A. and Norry, M.A. (1979): Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks; Contrib. Mineral. Petrol., v69, p33-47.

Ramsay, J.G. and Huber, M.I. (1987): The Techniques of Mod­ern Structural Geology, Vol. 2, Folds and Fractures· Aca-demic Press, London, 264pp. '

Summary of Investigations 1993

Sibbald, T.1.1. (1989): Base metal deposits and geology of the Early Proterozoic Hanson Lake Metavolcanics; in Sum­mary of Investigations 1989, Saskatchewan Geological Sur· vey, Sask. Energy Mines, Misc. Rep. 89-4, p66-70.

Saskatchewan Geological Survey

Winchester, J.A. and Floyd, P.A. (1977): Geochemical discrimi­nation of different magma series and their differentiation products using immobile elements; Chem. Geel., v20, p325·343.

Wright, J.F. and Stockwell , C.H. (1934): West half of the Amisk Lake area, Saskatchewan; Geo!. Surv. Can., Surnm. Rep. 1933, Part C, p12·22.

49