Geological Setting of Sediment-hosted Copper Mineralization in the Janice Lake Area, Wollaston Domain 1

G.D. Delaney, R.O. Maxeiner, M.L. Rawsthome 2, J. Reid 3, R. Hartlaub, and P. Schwann

Delaney, G.D., Maxeiner, A.O., Rawsthorne, M.L., Reid, J., Hartlaub, R. , and Schwann, P. (1995): Geological setting of sediment­hosted copper mineralization in the Janice Lake area, Wollaston Domain; in Summary of Investigations 1995, Saskatchewan Geo­logical Survey. Sask. Energy Mines, Misc. Rep. 95-4.

The Janice Lake area contains the most significant con­centration of sediment-hosted copper showings yet known in the Wollaston Domain (Scott, 1973; Coombe, 1994; Delaney, 1994). During the summer of 1995, a detailed study was completed of the geological setting and nature of the sediment-hosted copper occurrences near Janice Lake (NTS 74A-14 and -15), eastern Wol­laston Domain (Figure 1 ). The investigation was supple­mented by reconnaissance studies by the senior author in the Thompson River area, Alexander Lake map sheet (NTS 74H-2), to the north of NTS 74A-15.

Current mapping, which adjoins detailed mapping dur­ing 1994 of the area southwest of Janice Lake (De­laney, 1994), involved the participation of a number of workers. R.O. Maxeiner mapped the area between Bur­bidge Lake and southwestern extent of 1994 mapping and studied diamond drill core from holes drilled in 1993 by Noranda Exploration Inc. between Burbidge and Janice lakes. M. Rawsthorne mapped the area of the Rafuse and Kaz showings; J. Reid completed de­tailed (1:100 and 1:500) maps of the Genie Showing; R. Hartlaub mapped an area northeast of Janice Lake and southwest of the Kaz and Rafuse showings; and P. Schwann completed a detailed map of the discovery outcrops of the Jansem 1 Showing. Rawsthome's work will form the basis of a dissertation in the M.Sc. Mineral Exploration Program at the University of Leicester. Reid's work is for an undergraduate research project at the University of Regina.

This report, which builds on the senior author's 1994 re­port, is accompanied by two 1:10 000 maps that include a revised version of the 1994 mapping and detailed maps of the Jansem 1, Jansem 2, and Genie copper showings. Jansem 2, discovered by the senior author in 1994 (Delaney, 1994}, is the largest exposed copper oc­currence in the Janice Lake area.

Mapping was facilitated by a cut grid established in the early 1990s by Noranda Exploration Inc. Walking away from the cut grid is extremely arduous because of dense new growth and windfall in old burn. Hip chains were used to establish mini grids on the Jansem 1 and 2 as well as the Genie showings. Exposed outcrop is about 15 percent and erratic in distribution.

1 . Previous Work

The area is described in early reconnaissance geologi­cal maps prepared by the Geological Survey of Canada (McMurchy, 1936; Rice, 1951). In 1969, Rath (1969; Rath and Morton, 1969) completed an M.Sc. thesis in­vestigation of the petrology and base metal mineraliza­tion in the Janice Lake area. In 1971 , Scott (1973) mapped the west half of the Pendleton Lake map area (NTS 7 4A-15W) at a scale of 1 :63,360; Scott also pre­pared detailed geological maps of the Janice and Rafuse showings. In 1975, Ray ( 1980) mapped the Al­exander Lake map area {74H-2) to the northwest of the Pendleton Lake map area at a scale of 1:100 000 as part of a geological mapping program that included NTS 74A-15E and -16 and 74H-1 and -2. Subsequently in 1976, Ray (19n) mapped the Burbidge Lake map area (NTS 74A-14) as part of a 1:100 000 geological mapping program that also included NTS map sheets 74A-13 and 74H-3 and -4. In 1977, Coombe briefly stud­ied the Kaz copper occurrence as part of an investiga­tion of base metal mineralization in the Wollaston Domain (Coombe, 1977, 1994}. The Janice Lake area is also covered in 1 :250 000 compilation bedrock geol­ogy (Ray, 1983) and metallogenic (Scott, 1986) maps for the Foster Lake NTS map-area (7 4A). In 1984, the area was included in a regional lake sediment and water geochemical survey completed by the Geological Survey of Canada (1984, 1988}. Reports by Coombe Geoconsultants Ltd.(1991} and Coombe (1994) summa­rized the characteristics of some of the Cu occurrences.

2. Regional Geological Setting

The Janice Lake area lies near the southeastern side of the Wollaston Domain (Figure 1; Lewry and Sibbald, 1977), a northeast-trending, generally tightly folded lin­ear belt of siliciclastic metasediments and minor meta­volcanics segmented by interfolded remobilized Archean granitoids (Money, 1968, Money et al., 1970; Ray, 1979; Lewry and Sibbald, 1979, 1980; Ray and Wanless, 1980; Lewry, 1981; Stauffer, 1984). The do­main is bounded on the southeast by the Needle Falls Shear Zone (Munday, 1974; Ray, 1974; Lewry and Sib­bald, 1980; Stauffer and Lewry, 1988) which is "inter-

(1) Saskatchewan Project F.105 is a continuation of Project A.1 2b initiated under the canada-Saskatchewan Partner.ihip Agreemenl on Mineral Development 1990-95; funding in 1995 was under the Saskatchewan Energy and Mines Geoscience Program.

(2) Department of Geology, Leicester University. University Road, Leicester, LE1 7RH, United Kingdom. (3) Department of Geology. University of Regina, Regina, SK S4S OA2.

30 Summary of Investigations 1995

105"

ATHABASCA

BASIN

km

Legend

Ma jor plu!on

f-~~ ..... ~J Undivided gronitoids

~ Sandstone / conolomerote ~ Alhobosco Basin r:']:"'"1 Arkose /conglomerate L_J:J Wol laston

~?~:j Peli te Wolloston

~ Grey_wocke, pel ite ~ semi pthte

Figure 1 - Major lithostructural elements in the central part of the Precambrian Shield of northern Saskatchewan (from Figure 1 of Delaney, 1993; modified after Macdonald and Broughton, 1980).

Saskatchewan Geological Survey 31

preted as either a late-tectonic oblique collisional struc­ture or as the result of counterclockwise oroclinal rota­tion of the southern part of the (Trans-Hudson) Orogen" (Stauffer and Lewry, 1993, p1338; Lewry et al., 1994). Although metamorphic grade is lower amphibolite facies along parts of the west side of the Needle Falls Shear Zone it increases rapidly to the west to upper amphibo­lite-granulite facies (Munday, 1978; Lewry et al., 1978). The western boundary with the Mudjatik Domain which forms the high-grade core of the Cree Lake Zon~. is marked by a change in structural style from linear to ar­cuate. Compositionally heterogeneous granitoid rocks predominate and supracrustal rocks are subordinate. Relationships between the supracrustal rocks in the Mudjatik Domain and the Wollaston Domain are equivo­cal (Bickford_ e~ al., 1994). Some workers have argued that t~e MudJatl_k supracrustals are structurally continu­ous with tho~e in the Wollaston Domain (Munday, 1978; Lewry and Sibbald, 1980). Others have suggested that there is a major tectonic break between the Mudjatik and Wollaston domains (Annesley and Madore, 1989).

On a broad scale, the Lower Proterozoic supracrustal rocks of the Wollaston Domain are divisible into two dis­tinct assemblages (Ray, 1979):

1) Coarse elastic facies and locally intercalated minor volcanics of c~>ntinental tholeiitic affinity (Fossenier, 1995; Fosserner et al., this volume), occurring in nar­row discontinuous strips along the southeastern mar· gin of the domain, have been interpreted as depos­ited along a rift margin corresponding broadly to the Needle Falls Shear Zone (Coombe, 1979; Ray, 1979; Lewry et al., 1981). Although Ray (1979) pro­posed grouping these rift margin rocks into his Nee­dle Falls Group, it has been argued (Lewry, 1981 ; Delaney, 1993) that there are sufficient distinctions from area to area to preclude this grouping.

2) The Daly Lake Group of Money (1966, 1968) or Wol­laston Group of Ray (1979), which is widespread west of the Needle Falls Shear Zone, consists of a basal pelite overlain and in part intercalated with a thick succession of arkose that locally contains calc­silicate lenses. As reported here for the first time a thick fanglomerate in the succession marks at le~st a local unconformity and major episode of uplift.

Throughout much of the Wollaston Domain two main episodes of deformation are distinguished (Lewry and Sibbald, 1980). The first event, 01, is attributed to ther­mal reworking of basement and the emplacement of gneiss domes to a level at or near the contact between basement and lower Proterozoic cover. 01 formed a pr?minent_fo!iation that is typically parallel to original lay­ering and 1s interpreted to have paralleled the basement­cover contact. The second major event refolded o 1 structures into tight northeast-trending, commonly dou­bly plunging folds. As this corresponds to 03 deforma­tion in the adjacent Mudjatik Domain, that designation w~s applied in the Woll~ston Domain. Other, generally minor post-03 deformahons are recognized locally such

32

.. ~ ... ·--·- - ~--~·-·-·--·-····· -- -~-~--·.

as in the Duddridge-Meyers lakes area (Coombe, 1978; Delaney, 1993), the Pendleton Lake area (Scott 1973) and the Hidden Bay area (Wallis, 1971). '

3. Overview of Local Geology

T_he Janice Lake area is underlain by a thick succes­~1on of ~ortheast-trending, generally northwest-young-1~9. variably deformed and metamorphosed arkose, siltstone, conglomerate, semipefitic, and calc-sificate­bearing rocks with minor pelite (Figure 2). Abrupt facies ch~nges are common. Metamorphism has resulted in variable degrees of recystallization and partial melting although primary structures and textures are preserved at many localities. This assemblage has been intruded by pegmatite and granitoid veins.

The rocks exhibit fabrics and structures related to at least _the thre~ ~pisodes of folding. These include a prominent fohat1on (S1) with no recognizable associated folds, small-scale and focally large-scale tight folds that plunge shallowly to both the northeast and southwest and small-scale folds that plunge shallowly to moder- ' ately in directions between west and southwest. The a~ea_ is dissected by northeast-trending and northwest­d1pp1ng reverse faults including the Burbidge Lake Shear Zone, a major reverse fault that repeats part of the sequ~nc_e. Later north- to north-northwest-trending, steeply dipping, brittle-ductile sinistral faults are also pre­sent.

More than twenty copper occurrences are hosted either In fanglomerate of the Janice Lake Formation or more commonly in the overlying Rafuse Lake Formation.

4. Description of Formations

The sedimentary succession has been divided into seven formations. Scott's (1973) "Daly Lake Group-type Rocks", which correspond approximately to the base, has been superseded and divided into the Janice Lake Formation (a succession of fangfomerate, conglomer­ate, arkose and minor pelite} and the Rafuse Lake For­mation (a mixture, of variably argillaceous fine-grained siliciclastic sediments, conglomerate, and calc-sificate breccia). The northeast-trending Burbidge Lake Shear Zone r~p?ats part of ~hese basal sequences and sepa­rates distinct successions on each side of the fault. These formations are overlain by five unnamed forma­tions composed of arkose with intercalated wacke, ark­ose, mixed siliciclastic-calc-silicate rock, and arkose with intercalated quartz arenite and psammopelitic gneiss. Gradational to abrupt facies changes are com­mon in many of these formations (Figure 3).

a) Janice Lake Formation

The name Janice Lake Formation is proposed for the basal unit. The sequences differ on either side of the Burbidge Lake Shear Zone, as indicated in the table of members below (oldest at the base):

Summary of Investigations 1995

LEGEND

0 Burbidge Lake Shear Zone (BLSZ)

~ Formation rq (arkase / quart z crenite)

m Formotion re (orkose I co lc silicate rock)

CJ Formations r2 and r.3 (orkose I wacke)

Rafuse Lake Formation

~ Undivided

~ Arkose

lllll!II Wacke

Janice Lake Formation

JLo ( tonglornerale)

JLro (co ng lomera te end sandstone)

Jl.rop (conglom era te , sands tone and org illite).

~ Forma tion np (psamrnopelit,c gneiss )

105"00'

t:. Copper Occurrences

1. Juno 2. Sunshine (boulder lroin) 3. WS- 1 (boulder train) 4. Rafuse Zone 4 5. Rafuse Zone 5 6. Rafuse Zone 2 7. Rafuse Zone 3 8. Rafuse 9. Rafuse Zone 6 10. RS3 11. RS 12. RSl 13. Kwest 14. Kaz 15. Breezy ( boulder t rain) 16. Janice Nor1 h

0 1.0 2.0 3 .0 17. Janice (Jan) 18. JS

km 19. JS3 20. JS2 21. Jens em 2 22. Jansem 1 23. JS4 24. Genie

Figure 2 - Geological sketch map of the Janice Lake area showing the location of mineral occurrences.

Saskatchewan Geological Survey 33

. . . . . . . . . .

0 0 0 0 0 C

Rock Types

~ Strongly 1heared rocks

LJ Quartzite

EJ Calc-ailicate rocl<

[] Arkoae .

~ C11lc-silk:ate breccla

B Conglometal•

[GJ Fangloln«ate

~ Pellte

~ Psammopefite

1200

800

400

0

Formation r2

----~ - Rafuse Lake Fonnatton --- -- -- - - - -·D. "· 0 .. (,::: JLo

o ooooc JLto

Janice Lake Formation

JLtop

Figure 3 - Schematic cross-section of the sedimentary succession northwest of the Burbidge Lake Shear Zone in the Janice Lake and Burbidge Lake area and southeast of the Burbidge Lake Shear Zone in the Genie Lake area.

Northwest of Burbidge Lake Shear Zone

Conglomerate (Jlo2)

Fanglomerate (Jlo)

Southeast of Burbidge Lake Shear Zone

Fanglomerate (Jlo)

Conglomerate with intercalated arkose (JLro)

lnterbedded arkose, conglomerate and argillite (Jlrop)

Conglomerate, Grit, Sandstone, and Argillite (subunit Jlrop)

The type area for this member is southeast of the Bur­bidge Lake Shear Zone from Janice Lake. It is at least 400 m thick, has been traced for about 3.5 km along strike and apparently continues to both the northeast and southwest of the mapped area. The unit comprises a northwest-dipping and younging sequence of interbed­ded conglomerate, grit, fine sandstone, and argillite. Ar­gillite is intercalated in fine sandstone as single to more commonly sets of buff grey weathering laminae, typi­cally a few millimetres thick, mantled by 1 to 2 cm wide maroon coloured bands. Some argillite laminae are tee-

34

tonically dismembered and deformed into tight to isocli­nal small-scale folds. Conglomerate, in beds up to 2 m thick, is characterized by an intact framework of pebble­sized fragments of fine sandstone, argillaceous sand­stone, and siltstone. Clasts are commonly ellipsoidal due to extreme flattening in the plane of foliation (Fig­ure 4). Grit forms grey to maroon grey weathering beds 10 cm to 1 m thick containing granule-sized fragments of fine sandstone, siltstone, and quartz, and rare pebble­sized clasts of fine sandstone in a disrupted framework of sand-sized quartz and feldspar. The light grey weath­ering sandstone commonly occurs in sets of thin to me­dium beds that vary from homogeneous to those with paper thin, even parallel, and rare cross laminae. The base of the member was not observed. The upper con­tact is gradational and is set above the uppermost argil­lite lamination.

Conglomerate, Sandstone, and Grit (Unit Jlro)

Like Unit Jlrop, the type area for this member is south­east of the Burbidge Lake Shear Zone from Janice Lake and it also has been traced for about 3.5 km along strike apparently continuing to both the northeast and southwest of the mapped area. In the type area, this 500 m thick member comprises several thickening

Summary of Investigations 1995

Figure 4 - Arkose and conglomerare of Unit JLrop of the Janice Lake Formation. Bedding dips and youngs to the north· west; the prominent S1 foliation, defined by the planar align­ment of flattened clasts, dips steeply to the southeast.

and coarsening upward cycles of sandstone, minor grit, and conglomerate which overall define a large-scale coarsening and thickening upward succession. The up­per contact of the unit is placed at the base of the thick overlying fanglomerate member (subunit Jlo).

Fanglomerate (Unit JLo)

Although the fanglomerate member occurs both north­west and southeast of the Burbidge Lake Shear Zone, the best exposures are southwest of Janice Lake and consequently this was chosen as the type area. Map­ping by Scott (1973) indicated that the unit extends to both the western and northern boundaries of the Pendle­ton Lake map sheet (NTS 74A-15W), but was not distin· guished during previous mapping of the Burbidge Lake map sheet (Ray, 1977; NTS 74A-14) to the west, nor the Alexander Lake map sheet (Ray, 1980; NTS 74 H-2) to the north. Detailed mapping in 1994 (Delaney, 1994) and this past summer revealed that fanglomerate and associated conglomerate member (Unit JLo2) ex­tends for at least 5 km southwest into the Burbidge Lake map area. Reconnaissance mapping this past summer also revealed that fanglomerate extends for at least 8 km northeast of the Pendleton Lake map-sheet (NTS 74A-14) into the Thompson River area of the Alex­ander Lake map-sheet, defining a total strike length of at least 35 km.

Northwest of the Burbidge Lake Shear Zone, the fan­glomerate has an apparent thickness of about 1.4 km. The true thickness is probably somewhat less as the member is cut by a series of northwest-trending reverse faults.

Southeast of the Burbidge Lake Shear Zone, in addition to a 220 m thick sequence overlying subunit Jlro, fan­glomerate also occurs as tabular and wedge-shaped bodies intercalated in the overlying Rafuse Lake Forma­tion.

Saskatchewan Geological Survey

In most exposures, the fanglomerate is distinctively weathered to a mottled maroon, buff, and light grey. Much of the unit is massive and has a poorly sorted framework of angular to subangular fragments, that range from a few centimetres to as much as a metre or more across, in a matrix of fine- to locally medium­grained quartz and feldspar (Figures 5 and 6). The most abundant fragments are buff-weathering arkose containing maroon hematitic laminations. Massive, buff or grey weathering sandstone is a minor clast type. Rare, commonly pebble-sized clasts include: white­weathering very fine-grained felsite, pink-weathering, fine- to medium-grained quartz porphyroblastic granitoid or grit, and grey to dark grey weathering, well-rounded quartz and quartzite. Within the massive sequence are layers of variable thickness displaying an intact frame­work of better sorted clasts that typically range from 2 to 4 cm in diameter. Some of these layers are crudely graded. Rare 10 to 15 cm thick cross-laminated sand channels consistently indicate younging to the north­west.

Figure 5 - Moderately foliated fanglomerate of the Janice Lake Formation, southwest of Janice Lake. Note the large block of arkose, with hematitic laminae, to the left of the scale.

Figure 6 - Fanglomerate of the Janice Lake Formation, Thompson River area. Note the angular cobble of laminated arkose to the right of the scale.

35

Secondary phases in the Fanglomerate: The fanglom­erate member has been affected by a number of secon­dary processes that probably included late diagenetic alteration, metamorphic recrystallization, and syn- to post-tectonic development of partial melt segregations. In some areas, such as northeast of Janice Lake, these secondary processes have been responsible for the complete replacement of all clasts. Three types are rec­ognized:

1} In many outcrops the recrystallization of matrix and parts of clasts to a fine-grained granoblastlc mosaic of mostly quartz and feldspar impart a matrix-sup­ported character to the conglomerate {Figure 7).

2) The production of amoeboid-shaped bodies ranging in diameter from a few centimetres to several tens of centimetres of medium- to coarse-grained clots of quartz, amphibole, and specularite, and in some lo­calities, fine- to medium-grained black spinal in a matrix of fine- to medium-grained, and typically white-weathering plagioclase.

3) The production of blotchy maroon weathering patches of fine· to medium-grained feldspar and mi­nor hematite containing disseminated amphibole.

The fanglomerate is variably deformed. In some parts clasts are moderately to strongly rodded, and else­where there is a weak to locally very strong foliation de· fined by the degree of flattening of clasts {Figure 8). Approaching the Burbidge Lake Shear Zone, on the northwest side, the intensity of foliation progressively in· creases to the point where clasts are smeared out, al­most beyond recognition, except for the presence of variegated maroon-weathering and the rare highly strained clast.

The contact between fanglomerate of the Janice Lake Formation and the overlying Rafuse Lake Formation is apparently sharp northwest of the Burbidge Lake Shear Zone. Southeast of it, fanglomerate is interfingered, but with relatively sharp contacts, with siltstones of the over­lying Rafuse Lake Formation.

Figure 7 • Fanglomerate of the Janice Lake Formation, south­west of Janice Lake, in the vicinity of the Jansem 2 Showing. Note the large angular block of laminated arkose and recrystal· lized, fine-grained matrix in the vicinity of the scale.

36

Polymictlc Conglomerate (Unit Jlo2)

Adjacent to the northeast arm of Burbidge Lake, a vari· ant of the Janice Lake fanglomerate is a light to me­dium grey weathering conglomerate characterized by rounded pebble· and cobble-sized clasts of grey quartz, quartzite, wacke, arkose, and pink granitoid. The clasts form a poorly sorted, disrupted framework in a fine- to medium-grained, biolite-bearing, 'non-mottled', and re­crystallized quartzofeldspathic matrix. The conglomer­ate is massive to moderately foliated and weakly lineated, with a maximum clast elongation of 1 :5. An as­sociated pink to grey, fine-grained felsic rock might rep­resent recrystallized and albitized conglomerate, inter­bedded homogeneous arkose, or an aplitic intrusive.

The polymictic conglomerate occurs on both sides of the Burbidge Lake Shear Zone, but its full distribution has not been mapped. The contact between the con­glomerate and the fanglomerate members is not ex· posed but probably interfingers.

b) Rafuse Lake Formation

The name Rafuse Lake Formation is proposed for the unit overlying the Janice Lake Formation. As this forma­tion hosts several copper occurrences in the area north· west of the Burbidge Lake Shear Zone, it was examined in detail. Southwest of Janice Lake, the for· mation extends for more than 7 km towards Burbidge Lake, but is generally poorly exposed there, and the de­scription of the formation in this area derives mostly from a detailed study of the drill core from holes drilled by Noranda Exploration Inc. Northeast of Janice Lake, the formation is somewhat better exposed and the de­scription in that area derives from outcrop obseivations. Southeast of the Burbidge Lake Shear Zone, the forma­tion is poorly exposed except in the vicinity of Genie Lake.

Figure 8 • Strongly deformed fanglomerate of the Janice Lake Formation, Thompson River area.

Summary of Investigations 1995

Area Southwest of Janice Lake

Southwest of Janice Lake, the Rafuse Lake Formation is about 400 m thick and comprises mostly arkose with subordinate wacke, conglomerate, calc-silicate breccia, and a fine-grained felsic rock. The unit is highly vari­able, both along and across strike (Figure 9).

Arkose (Unit RLra)

About 60 percent of the Rafuse Lake Formation is a grey, buff, pink to light maroon weathering, in part mot­tled, fine-grained, thin to medium bedded "arkose". Out­crop exposures typically contain pink-green blebby patches of feldspar speckled with fine- to medium­grained hornblende. Blotchy patches of varying size and shape comprise medium- to coarse-grained quartz, magnetite, hornblende, and spine! in a matrix of fine­grained, white-weathering plagioclase. In drill core, the arkose is a grey, pinkish grey to pink, fine- to very fine­grained, quartzofeldspathic rock containing biotite and epidote in concentrations that range from less than 5 percent to as much as 10 percent. Locally layers con­tain as much as 15 percent fine- to medium-grained hornblende. Other minerals include muscovite, specular hematite, magnetite, and actinolite. The rock is massive to well foliated and appears in part to be recrystallized. Primary bedding was rarely observed.

SW

Wacke (Unit RLw)

Grey to greenish grey, fine- to very fine-grained, mas­sive to well-foliated wacke constitutes about 7 percent of the formation. This monotonous, recrystallized rock is composed of plagioclase, quartz, biotite (10 to 15 per­cent), and epidote (5 to 10 percent). Disseminated mag­netite or hematite, 1 to 2 mm in diameter and forming about 3 percent of the rock, is common. Hornblende and actinolite are minor constituents. The mafic mineral content varies. Locally, wacke grades imperceptibly into grey argillaceous arkose. Approximately 1 O percent of the Rafuse Lake Formation is characterized by interca­lated medium to very thickly bedded arkose, argil­laceous arkose, and wacke.

Conglomerate (Unit RLo)

Pebble and cobble conglomerate make up about 12 per­cent of the Rafuse Lake Formation. The unit has been observed in outcrop only in the vicinity of the Janice Showing where parts of it host copper mineralization. The rocks are light grey to buff, in part mottled maroon weathering, very heterogeneous, and massive to well fo­liated. Clasts range in size from pebbles to cobbles, are subangular to subrounded and dominantly arkosic. The conglomerate appears to be matrix-supported, but this appearance may be due to extensive recrystallization and other secondary phases {see below) which hinders the recognition of clasts, particularly in drill core. Miner­als present include feldspar, quartz, and biotite (<5 per-

NE JS-2 JS - 3

Showing Showing JS

S howing Jani ce

Showing

Forrna hon r2 ln fercolo led ~:.=-=--------.-. ---==-~=-=:-==-.==~=-==~!3-~2-==~=--======

~:·. - ~_-.:::..::....-~ -- -- -- -- · - -- ~ - 93-1 4 _-- · ·- · -- · -- ·· - -· •

Hori.-zontal S cale: L..-

Vertical Exag9eration: fOx

5 00 rn

Arkose & Cong lomerate

gfil Wocke

R af use Lake Forma tion

f':_Cl Intercalated [ \ (j Wocke & Ar kose

I~ Cole - silica te b recc io

[] Quartz - orenite

Wocke

[. J Arkose

J anice Lak e Formati on

(~ Fonglomerale

Figure 9 - Schematic cross-section of the Rafuse Lake Fonnation southwest of Janice Lake. Indicated are t~e locatiorys of No­randa Exploration Inc. 's 1993 drill holes. Copper-bearing intersections are coloured black; the numbers beside these md1cate per­cent Cu and thickness of the mineralized intersection in metres.

Saskatchewan Geological Survey 37

cent), with minor amounts of hornblende, magnetite, and specular hematite.

Secondary Features of Units RLra, RLw, and RLo

A number of secondary features have been recognized:

1) Areas of pink-green mottling are common and char­acteristically invade the rock along irregular cross­cutting 'fronts'. The pink areas comprise homogene­ous, fine- to very fine-grained feldspar with 5 to 15 percent hornblende porphyroblasts 1 to 1 O mm in di­ameter. These are believed to be a product of feld­spathization (afbite, orthoclase or microcline), with accompanied development of minor carbonate phases. This alteration postdates deposition of the arkose, but predates thermotectonism as shown by the existence of hornblende porphyroblasts, is at least in part affected by deformation, and may be late-diagenetic.

2) Deep maroon mottling, due to hematization, is possi­bly the relict of late-diagenetic alteration.

3) Late quartz-feldspar-hornblende-hematite blebs and veins which are generally massive to poorly foliated.

4) Copper and silver mineralization in the form of chal­cocite, native copper, and in rare cases chalcopy­rite. The relationship between copper mineralization and the other secondary phases is not known.

Cale-silicate Breccia (Unit RLcbx}

Cale-silicate breccia forms about 5 percent of the Rafuse Lake Formation. A lenticular body of variable thickness is exposed in several outcrops northwest of the 41 +OON baseline of the Noranda Exploration grid be­tween cross lines 53+00E and 62+00E. The breccia contains 1 to 10 cm wide, subangular to subrounded, buff to white weathering fragments composed mostly of plagioclase. These form an intact to disrupted frame­work in a matrix of greenish light grey weathering, fine­to medium-grained plagioclase containing disseminated and patchy concentrations of medium- to coarse­grained actinolite and diopside. Disseminated specu­larite occurs locally in the matrix.

In drill core intersections, cafc-silicate breccia is mottled grey, green to pink, fine to medium grained, very hetero­geneous, and massive to moderately foliated. The unit comprises fragments of pink, fine-grained quartz and feldspar, forming 50 to 80 percent of the rock, which are set in a green, medium- to coarse-grained diopside­actinolite-plagioclase-biolite-quartz matrix. The rock ap­pears to be neither epiclastic nor cataclastic in origin. It cannot be a sedimentary breccia as the elastic appear­ance seems to be the product of alteration; neither can it be a fault breccia as the subunit occurs quite exten­sively along distinct sedimentary horizons over dis­tances of tens of kilometres. The breccia is possibly an altered and metamorphosed derivative of evaporites.

38

Fe/sic Rock (Unit RLfel)

Near Burbidge Lake, the Rafuse Lake Formation con­tains a narrow unit of pink to buff, fine-grained falsie rock. The rock is very homogeneous, massive and fea­tureless, and may be a recrystallized granoblastic ark­ose or an aplogranite.

Area Northeast of Janice Lake

Northeast of Janice Lake, the Rafuse Lake Formation contains many of the same members as in the south­western area, but in significantly different proportions.

Mottled Arkose (Unit RLra)

The mottled arkose is a pink to maroon to buff to light grey mottled weathering, recrystallized, fine-grained quartzofeldspathic rock. Texture and composition vary. Primary structures such as laminae are extremely rare. The content of biotite, feldspar, and quartz. the main components, is variable. The more argillaceous varie­ties contain as much as 15 percent biotite, but other parts are composed mostly of quartz and only minor feldspar.

Three secondary phases are common:

1) Light grey to white, oval to irregular-shaped bodies, 5 to 50 cm in diameter, composed of coarse-grained quartz with feldspar and minor amphibole, magnetite or specularite.

2) Pink to maroon, 5 to 25 cm wide irregularly-shaped bodies of fine- to medium-grained feldspar contain­ing disseminated fine- to medium-grained amphibole.

3) Light grey to white, fine- to medium-grained quartz­feldspar bodies forming a pseudo matrix and elon· gate structures 1 to 3 cm thick and 1 to 15 cm long.

With increasing intensity of foliation, the secondary phases are progressively flattened in the plane of folia­tion. In places, where there is a high concentration of the oval- to blebby-shaped quartz-feldspar bodies, the arkose has the mistaken appearance of a conglomer­ate, and in fact in many of the copper showing expo­sures in the Rafuse Lake area, previous workers (i.e. Scott, 1973) interpreted these rocks to be conglomerate.

Wacke (subunit RLw)

Subunit RLw, which typically weathers dull grey to buff, is a fine-grained quartzofeldspathic rock that contains 10 to 15 percent biotite and minor amphibole. Vari­ations in the amount of biotite, feldspar, and amphibole content are common. The same three secondary phases are present as found in the altered arkose mem­ber. In addition, quartz is found both as tightly folded veins and in clots 1 to 15 mm across.

Semipelite (subunit RLsp)

Subunit ALsp has only been observed north of baseline 60+00N, between lines 112+00E and 113+00E on the Noranda Exploration Inc. grid. It is a dull grey to buff

Summary of Investigations 1995

weathering, fine-grained quartzofeldspathic rock that dis­plays gneissic compositional layering commonly 1 to 2 mm thick. The member is distinguished from wacke by the gneissic texture and a biotite content of about 30 percent.

Two secondary phases have been distinguished:

1) Light grey to white, fine- to medium-grained quartz and feldspar-rich bodies forming planar features typi· cally 1 to 6 mm thick, extending for more than a me­tre parallel to foliation.

2) Pink to maroon, fine- to medium-grained feldspar bodies containing disseminated fine to medium­grained amphibole, typically 1 to 6 mm thick, extend· ing for more than a metre parallel to foliation.

Cale-silicate Breccia (Unit RLcbx)

Pink, buff, and green mottled weathering calc-silicate breccia has only been observed north of baseline 60+00N between lines 11 3+00E and 114+00E on the Noranda Exploration Inc. grid. Like its counterpart south· west of Janice Lake, the main fragments are sub­rounded to angular and composed of fine-grained feldspar which ranges in diameter from less than 1 to 10 cm. Ellipsoidal-shaped quartz fragments are a minor component and angular arkose fragments ranging in size from 20 to 50 cm are exceedingly rare. The matrix consists of fine-grained amphibole, quartz, and diop­side; epidote coats joint surfaces.

Hornblende-plagioclase Granulite (Unit RLhpg)

Hornblende-plagioclase granulite underlies a small area on the west side of Kaz Lake. This member, a fine- to medium-grained quartzofeldspathic rock composed of quartz (40 to 50 percent), hornblende (20 to 40 per­cent), and plagioclase (15 to 30 percent), typically weathers speckled dull grey. Disseminated and blebby magnetite are a minor component, as are clots of me­dium- to coarse-grained amphibole 5 mm to 1 O cm in di­ameter. Irregular-shaped bodies of medium- to coarse-grained feldspar containing clots of amphibole and magnetite are common. The member grades into the altered arkose and wacke, structurally above and below this unit, respectively.

Previously interpreted as a doleritic rock by Noranda Ex­ploration Inc., Unit RLhpg is now considered to derive from calcareous arenite or siltstone, on the basis of the gradational boundary between the overlying and under­lying units.

Area Southeast of the Burbidge Lake Shear Zone

With the exception of the area south of Genie Lake, ex­posed rock is exceedingly sparse southeast of the Bur­bidge Lake Shear Zone. Much of the Rafuse Lake Formation, here, apparently comprises variably argil· laceous siltstone and wacke with minor calc-silicate breccia, and interfingered wedges and tabular bodies of fanglomerate of the Janice Lake Formation.

Saskatchewan Geological Survey

Siltstone and Wacke (subunit RLsw)

Subunit RLsw is a 500 to 900 m thick member compris­ing light grey, dark grey, and brownish grey weathering, variably argillaceous siltstone and wacke. The se­quence is strongly foliated and varies from homogene­ous to alternating more to less argillaceous laminae and thin beds. Some parts of the member contain concentra­tions of elliptical quartz blabs aligned and flattened par­allel to foliation locally deformed into tight small-scale folds. A light grey weathering, fine-grained quartzofeld­spathic granitoid, occurring locally in this succession, al­most entirely assimilates the siltstone and wacke. In the upper part of this member, blebs and veinlets of amphi· bole and epidote, mantled by pink feldspar are com­mon. Rock in this part weathers with a distinct ribbed aspect.

Cale-silicate Breccia (Unit RLcbx)

The Rafuse Lake Formation contains at least one nar­row layer of calc-silicate breccia similar to that north of the Burbidge Lake Shear Zone. Associated with the breccia in some areas is a greenish grey weathering, fine- to medium-grained quartzofeldspathic rock contain­ing disseminated and clotted concentrations of fine- to coarse-grained amphibole.

c) Formations Above the Rafuse Lake Formation

The Rafuse Lake Formation is overlain on both sides of the Burbidge Lake Shear Zone largely by arkosic rocks of Formations r2, r3, re, and rq, and by the psammopeli­tic gneiss, Formation np. Rock exposure is very poor on the southeast side of the zone.

Although the contact between the Rafuse Lake Forma­tion and the Formation r2 arkose is not exposed, the base of Formation r2 (close to Janice Lake) is defined in Noranda Exploration Inc. drill core intersections by about an 80 m thick interval of homogeneous, greenish grey, fine-grained wacke containing 20 percent biotite and epidote. To the southwest, towards Burbidge Lake, Formation r2 grades into the arkosic Formation r3.

Arkose with Intercalated Wacke (Formation r2)

Arkose is intercalated with wacke in Formation r2. The arkose, which most commonly occurs in sets of several beds, is thin to medium bedded, buff to light grey weath­ering, and contains 1 to 2 cm thick bedding-parallel ma­roon weathering layers and lenses. Scarce cross beds and scour surfaces consistently indicate tops to the northwest. In places, the arkose beds are intercalated with 1 to 2 cm thick layers of brownish grey weathering wacke or pelite laminae. Elsewhere, thin to medium bed· ded arkose occurs in intervals a few to several metres thick. These are separated by brownish grey weather· ing wacke beds containing vague internal laminae. Some of the wacke contains abundant medium- to coarse-grained quartz lenses mantled by fine-grained quartz-feldspar haloes which are oriented both parallel and oblique to foliation.

39

Southeast of the Burbidge Lake Shear Zone rocks in­cluded in Formation r2 comprise a heterogeneous se­quence of arkose, siltstone, wacke, and calc-silicate­bearing varieties of these rocks. Arkose is typically light grey weathering and thin bedded; primary structures such as cross laminae are rare and, where present, consistently indicate younging to the northwest. An ex­ception is the peninsula at the southwest end of Genie Lake which is underlain by a thick bedded sequence of light grey weathering arkose with some maroon colour banding and large-scale cross-bedded channel struc­tures.

Arkose (Formation r3)

Towards Burbidge Lake, Formation r2 grades laterally into Formation r3, a relatively clean, buff to light grey weathering, very fine-grained granoblastic arkose that is medium to thick bedded, fairly monotonous, and mas­sive to weakly foliated. Biotite and minor hornblende comprise less than 5 percent of the rock, which is in part cut by quartz-feldspar-hornblende-hematite segre­gation veins and clots. The formation grades into overly­ing calc-silicate arkose (Formation re).

Arkose Containing Intercalated Cale-silicate Horizons (Formation re)

An approximately 600 m thick sequence of intercalated arkose, siltstone, psammopelite, and calc-silicate rock extends at least 10 km northeast from the large penin­sula on the northeast shore of Burbidge Lake. The con­tact with the underlying r2 and r3 formations is gradational and is marked by the first calc-silicate layer. Much of the formation comprises 1 to 2 m thick layers of thin to medium-bedded, light grey weathering arkose locally containing foliation-parallel maroon grey colour laminations.

The calc-silicate layers are greenish grey to green weathering, 3 to 8 cm thick, and occur singly or in groups of beds. The calc-silicate minerals, which in­clude actinolite, diopside, epidote, and calcite, comprise up to 50 percent of these layers, and are particularly abundant to the northwest, i.e. the top of the formation. The actinolite occurs as medium to coarse grains in a matrix of white weathering, fine-grained quartz and feld­spar. Psammopelite is a minor component. The rocks are weakly to well foliated and strongly lineated, and in part are pitted due to rodding and differential weather­ing of calcite-rich areas.

Arkose with Intercalated Quartz-arenite (Formation rq)

Three outcrops constrain an approximately 300 m thick unit of intercalated arkose and quartz-arenite overlying Formation re to the northeast of Burbidge Lake. This for­mation, which is thin to thick bedded and weakly to strongly foliated, comprises light grey to buff, very fine­grained to fine-grained arkose (80 percent); grey, very fine-grained quartz-arenite (15 percent); and brown to grey, fine-grained argillaceous (biotite 5 to 10 percent) arkose (5 percent).

40

Psammopelitic Gneiss (Formation np}

Formation rq is structurally overlain by psammopelitic gneisses on the northwest shore of Burbidge Lake. These rocks are brown, buff to grey weathering, fine- to medium-grained gneisses to schists, and quite distinc­tive in appearance in comparison to the other forma­tions. Foliation is well developed and the rocks are recrystallized, granoblastic, and in part migmatized. Abundant tight to isoclinal folds occur on a 20 cm scale. These folds, combined with injection of pink granitic melt material parallel to the axial planes, have produced a very heterogeneous outcrop appearance. The gneis­sosity is defined by alternating layers of pinkish brown, medium-grained quartzofeldspathic melt material and fine- to medium-grained schistose psammopelite con­taining up to 20 percent biotite. In places the rock has a 'nutty' appearance, due to the presence of large white plagioclase porphyrobfasts up to 2 cm in size and equally large faserkiesel aggregates. Other minerals in­clude magnetite, hematite, and muscovite. Cordierite oc­curs in late quartzofeldspathic sweats.

d) Mylonites and Protomylonites of the Burbidge Lake Shear Zone

The Burbidge Lake Shear Zone, defined by the north­east-trending linear lake-filled valley between the north­east arm of Burbidge Lake and Janice Lake, is underlain by generally heterogeneous quartzofeldspa­thic rocks designated as Unit qfx. These are all very highly strained and generally dip from 70 to 80° to the northwest. With the exception of a few areas, such as adjacent to the small lake northeast of Burbidge Lake, exposure is sparse.

The quartzofeldspathic rocks at the southwest end and along much of the southeast side of the topographic lineament defining the shear zone are white to buff weathering and very fine grained. Paper-thin tectonic laminations, produced by ribboning of quartz, have been isocfinally folded on a 10 cm scale and shear bands are developed locally.

On the southeast side of Janice Lake, the shear zone comprises a foliated sequence of alternating 1 O cm thick, fine-grained, buff weathering quartzofeldspathic rocks and grey, fine-grained, biotite-quartz-feldspar rock.

At the northeast end of Janice Lake, the quartzofeldspa­thic rocks are weathered maroon, grey striped, and probably derived from conglomerate.

To the northwest, there is a progressive decrease in strain from mylonite into recognizable fanglomerate of the Janice Lake Formation. Although outcrop is sparse to the southeast of the shear zone, this contact is also apparently characterized by a gradual decrease in strain.

5. Depositional Setting Redbed arkose fragments, of the type found in fanglom­erate at the base of the succession in the Janice Lake

Summary of Investigations 1995

area, are considered by Walker (1989} to have been de­posited as first cycle sediments containing iron-bearing labile minerals in an arid to semi-arid environment. Early diagenetic alteration of these sediments to red· beds followed by induration, preceded an episode of normal or listric faulting probably in a tensional and pos­sible rift setting, and is believed to have been followed by the deposition of the fanglomerate (Figure 10).

Northwest of the Burbidge Lake Shear Zone, the thick, poorly sorted succession of Janice Lake fanglomerate, characterized by large angular fragments and an abun­dance of hematitic laminated arkose fragments, was probably deposited in an arid to semi-arid environment as proximal alluvial deposits flanking the uplifts (Bull, 1972; Miall, 1981; Rust and Koster, 1984}. Fanglomer­ate was reworked, at least locally, in a braid

NW

plain/braided river environment which deposited the con­glomerate of the JLo2 member.

In contrast, southeast of the Burbidge Lake Shear Zone, where the Janice Lake Formation is a coarsening and thickening upward succession of pelite, arkose, con­glomerate and fanglomerate containing several coarsen­ing upward subcycles, spasmodic rejuvenation in the area of uplift and basinward progradation of the alluvial fans are indicated.

With completion of the Janice Lake events and as tec­tonic activity in the area of uplift subsided or the fault scarps migrated into the hinterland, the depositional re­gime recorded by the Rafuse Lake Formation and suc­ceeding formations suggest an evolution to a shallow to emergent marginal marine or lacustrine regime. This

SE

Rock Types

quartz~e

arkose with calc-sllicate layers

catc-slllcate breccla

siltstone /wacke

r:::::, ~

[gJ ~ ~

conglomerate

fanglomerate

arkose

Figure 10 - Sketch illustrating inferred post-depositional relationships between the various rock units and copper mineralization in the area southwest of Janice Lake.

Saskatchewan Geological Survey 41

was characterized by abrupt facies changes including, at least locally, conditions favorable for the formation of evaporites preserved as the calc-silicate breccia. More distal facies were deposited in the area that now lies southwest of the Burbidge Lake Shear Zone. The Baja Peninsula at the north end of the Gulf of California is a modern setting (Walker, 1967, 1989) with many deposi­tional similarities to the sequence on the southeast side of Janice Lake.

Janice Lake fanglomerates have been traced northeast of Janice Lake to the Thompson River in the adjacent Alexander Lake map sheet (NTS 74H-2}. There the fan­glomerates overlie a succession of cordierite- and sillimanite-bearing psammopelitic and pelitic schists and gneisses flanking the southwest end of the Johnson River Inlier, a remobilized Archean granitoid (Ray, 1980). The Daly Lake Group of Money (1966, 1968) and the Wollaston Group of Ray (1979) which overlie Archean basement, have been described as consisting of a basal pelitic sequence overlain in tum by, and in part Intercalated with, a thick succession of arkose lo­cally containing intercalated calc-silicate rocks. Recogni­tion of a thick sequence of fanglomerate in the Janice Lake-Thompson River areas suggests that, at least lo­cally, in the Wollaston basin there were periods of uplift and tectonic instability during deposition of equivalent sediments.

6. Structural Geology The present area has been affected by at least three episodes of deformation:

1) The first episode of deformation produced the promi­nent foliation (81) common throughout the bedded sediment as well as locally within the conglomerate. In the bedded sediments, this foliation parallels origi­nal compositional layering. Primary sedimentary structures such as cross-bedding, grading, and scour surfaces, although not abundantly preserved, have been found throughout much of the succes­sion on both sides of the Burbidge Lake Shear Zone. These structures consistently indicate young­ing to the northwest. No related small-scale folds have been distinguished. The foliation producing event, labeled as 01 , has been identified throughout much of the Wollaston Domain, and is believed to be related to the thermal reworking of the basement and the emplacement of gneiss domes to levels near the basement cover contact (Lewry and Sib­bald, 1980).

2) The second recognized deformational event re­folded or compressed the 01 structures into gener­ally tight, northeast-trending, and commonly doubly· plunging folds. This event corresponds to 03 defor­mation in the adjacent Mudjatik Domain. Evidence

42

of 03 in the Janice Lake area includes the local de­velopment of a subvertical, northeast-trending, pene­trative foliation, strong rodding of clasts on the west side of the conglomerate, and small-scale tight folds that plunge shallowly to the northeast and south­west (Figure 11 ). These last-mentioned structures are particularly abundant in the more argillaceous

units of the Rafuse Lake Formation where they are defined by tightly folded quartz blebs (Figure 12). The only example of large scale 03 folds are the S folds on the northeast side of Janice Lake (Figure 2).

3) Small-scale folds which plunge shallowly to moder­ately in directions that vary between the southwest and west are attributed to a third 04 deformation.

The sedimentary succession is cut and partially re­peated by the Burbidge Lake Shear Zone, a major northeast striking reverse fault that dips 70° to 80° to the northwest. A prominent mineral lineation on the folia­tion surfaces of this structure has a mean plunge of 68° towards 294° (Figure 13). Northwest of the shear zone, fanglomerate of the Janice Lake Formation is dissected by a set of narrow northeast-striking reverse faults that typically plunge at about 50° to the northwest (Figure 14). Millimetre-scale ductile shear zones mimic the larger structures.

The study area is also cut by a series of large-scale, north-northwest-trending, brittle sinistral faults such as the one that trends through Janice Lake. Displacement is a few tens to a maximum of about two hundred me­tres. Locally, such as in the Genie Lake area, small­scale structures mimic the large structures (Figure 15). These small-scale structures are typically a few tens of metres long, range in width from a few millimetres to 1 or 2 m and have small displacements. These structures are part of a late sinistral fault system recognized along much of the east side of the Wollaston Domain (Scott, 1973).

D 0

D D

N

+

o Smol I sca le folds o Mean L1neat 1on

Number of Samp le Po ints Mean L1neotion Azimuth Mean L1neot 1on Plunqe

D

18 228 7 2"l 9

Figure 11 • £qua/ area stereonet plot of small-scale folds in the Rafuse Lake Formation southeast of Rafuse Lake.

Summary of Investigations 1995

0

N

0 0

+

o Smal I Scal e Fol ds o Mean L1neat ian

Number of Sampl e Po ints Mean L1neati on Az imuth Mean L1 neat 1an Plunqe

55 5"1 . '1 17 7

Figure 12 - Equal area stereonet plot of small-scale folds in the Rafuse Lake Formation near Genie Lake.

N

o Miner a l L1neot 1ans o Mean l ineat1 on

Number of Samp le Po, nts 23 Mean l 1neat1 on Az imut h 29~.2 Mean l 1neot1 on Plunge 58 0

Figure 13 - Equal area stereonet plot of mineral lineations in the Burbidge Lake Shear Zone.

Saskatchewan Geological Survey

Figure 14 - Northeast-trending, northwest-plunging reverse fault cutting fanglomerate (Unit JLo) of the Janice Lake Forma­tion.

N

0

+ a 0

0

0

a

0 a

a

a Smol I scale late fau lts Number of Samp le Points 18

Figure 15 - Equal area stereonet plot of poles to planes of small-scale brittle faults in the Genie Lake area.

7. Mineralization

0

Highlights of the mineral exploration history are summa­rized in Delaney (1994). Other key sources of informa­tion include published reports of Scott (1973), Coombe (1977, 1994), and Coombe Geoconsuftants Ltd. (1991). Information is also contained in the Mineral Assessment files of Saskatchewan Energy and Mines.

43

a) Descriptions of New Mineral Occurrences

The Jansem 1 and 2 copper occurrences were discov­ered during traverses in 1994 (Delaney, 1994), and they were evaluated in the field this summer. The Ge­nie Showing, discovered by Noranda Exploration Inc. in 1993, was also mapped and sampled in detail this sum­mer, as no previous published information about this showing was available.

Jansem 1 (UTM 500360 m E, 6300960 m N)

A detailed scale map of the showing is contained in the map package that accompanies this report.

Location: This showing is best exposed in a group of outcrops along the southeast side of a southwest-trend­ing ridge of glacial drift, located along the extension of Noranda Exploration Inc. grid line 68+00E at 36+25N. Copper mineralization has also been discovered in three other outcrops 60 to 100 m to the south.

Description of Rock Types: Jansem 1 is hosted in fan­glomerate of the Janice Lake Formation. On the basis of textural relationships, three subdivisions are distin­guished in the main exposures:

1) The area west and southwest of, and structurally be­low, the mineralized zone is underlain by maroon, grey, and white mottled weathering, poorly sorted polymictic conglomerate typical of the fanglomerate member of the Janice Lake Formation. Clasts which compose 30 to 40 percent of the rock lie in a recrys­tallized fine- to medium-grained quartzofeldspathic matrix. White weathering, fine-grained quartzofeld­spathic rock is the main clast type; other clasts in­clude grey recessive weathering wacke containing 15 to 20 percent biotite and laminated salmon weathering arkose. Rounded quartz clasts are rare. Clasts are generally pebble to cobble size, although those of laminated arkose are as much as 1 m wide. Amoeboid-shaped bodies to 0.5 m in diameter containing clots of coarse grained quartz, and fine­to medium-grained spinal in a matrix of plagioclase and minor magnetite are scattered throughout this unit and the one described subsequently.

2) Underlying the mineralized zone, the rock is mottled salmon, buff and light grey weathering, and consists of foliation-parallel blebby patches of salmon to or­ange weathering, fine- to medium-grained feldspar containing amphibole and magnetite in a ground­mass of fine- to medium-grained quartz, feldspar, and magnetite. Other than rare blocks of laminated arkose, primary features are absent and much of the rock appears to have been recrystallized.

3) A grey, recessive weathering rock comprises mainly fine- to medium-grained quartz-feldspar with minor biotite. A faint laminated appearance is defined by foliation-parallel concentrations of quartz grains. Scattered throughout are blebby patches of quartz, feldspar, and amphibole. The rock is cut by irregular lenses and sharp-walled veins of quartz-feldspar pegmatite. The two small copper-bearing outcrops, 60 m south of the main outcrop area, are weathered

44

to a mottled green, whereas the outcrop 100 m to the south is mottled maroon, grey, and brown weath­ering and contains some original clasts.

Character of mineralization: Three varieties of copper mineralization are distinguished:

1 ) Disseminated to clotted, generally fine-grained sooty chalcocite with malachite and azurite developed on fracture surfaces. Along the southeastern side of the main outcrop area this chalcocite-bearing phase is about 40 m long and 7 m wide and dips under over­burden. This zone, occurs in subdivision 1 above the conglomerate. Grab samples have assayed as much 5.49 percent Cu and 0.44 oz/ton Ag. A red­dish brown weathering rind is developed over areas of high-chalcocite content. The zone is open in an arcuate area between the northeast and south. Al­though no outcrops were discovered to the north­east, a chalcocite-bearing outcrop 100 m to the south suggests the zone is at feast 100 m wide.

2) Scattered small clots of malachite. On the northwest side of the chalcocite zone is an irregular zone char­acterized by scattered millimetre-scale malachite stains on weathered surface. Grab samples contain on average about 0.04 percent Cu.

3) Drab to emerald green weathering feldspar-rich blabs in a light grey to buff light grey weathering fine-grained groundmass of quartz and feldspar. Two small outcrops about 60 m south of the discov­ery outcrop are characterized by drab to emerald green-weathering foliation-parallel blebs a few centi­metres long in a matrix of fine- to medium-grained, buff light grey weathering, recrystallized quartz and feldspar. Grab samples from these outcrops con­tained 0.029 and 0.008 percent copper; one of these samples (9522-223) contained 1.25 percent lead.

Jansem 2 (UTM 501229 m E, 6301521 m N)

A detailed scale map of the showing is contained in the map package that accompanies this report.

Location: The Jansem 2 Showing is located about one kilometre west of the southwest end of Janice Lake in a northeast-trending valley. An approximately 50 m high cliff bounds the showing immediately to the southeast. The copper-bearing zone, about 325 m long and trend­ing at about 60°, is exposed in scattered outcrops com­prising about 15 percent of the area. The showing is open to both the northeast and southwest as these areas are devoid of outcrop.

Description of Rock Types: Jansem 2 is hosted in magnetite-bearing, mottled maroon, buff, and light grey weathering, variably altered and recrystallized fanglom­erate of the Janice Lake Formation. In the high-grade parts, the host rock contains foliation-parallel pink to salmon feldspar blebs. These are typically a few centi­metres long and 1 to 2 cm wide and occur in a light grey to buff, fine- to medium-grained groundmass of quartz, feldspar, and minor biotite and magnetite.

Summary of Investigations 1995

Primary clasts are more common in outcrops that are weakly mineralized or contain no visible copper miner­als. The fanglomerate is polymictic and poorly sorted. Common clasts comprise white to salmon weathering, fine-grained, and maroon-laminated arkose. Angular, cobble- to boulder-sized clasts of laminated arkose oc­cur rarely, as also do pink quartzofeldspathic grit or gra­nitoid, and pebble-sized quartz clasts.

Northwest of the showing, the conglomerate is hematite­bearing and weathers a distinctive mottled maroon and light grey. Here again, the conglomerate has a poorly sorted framework of angular to subangular pebble- to boulder-size clasts which include some blocks of hema­titic laminated arkose up to one metre wide. Secondary phases appear to have partially assimilated the clasts, at least locally. These secondary phases consist of ma­roon grey weathering, fine-grained quartz and feldspar containing disseminated specularite, and light grey weathering, fine- to medium-grained quartz with subordi­nate feldspar.

Character of Mineralization: Four varieties of copper mineralization are recognized:

1) Clotted to disseminated fine-grained chalcocite and minor native copper in mottled pink, salmon, and light grey weathering recrystallized fanglomerate. An emerald green mineral tentatively identified as antlerite and less common malachite are secondary copper minerals. This mineralization underlies a northeast-trending, 125 m long and 10 to 15 m wide, high-grade zone from which grab samples have yielded up to 4.11 percent Cu and 1.13 oz/ton Ag. Other chalcocite-bearing outcrops occur north­east of the high-grade zone and in sparse outcrop near the southwest end.

2) Drab to emerald green weathering, fine-grained feldspar-rich blebs typically a few centimetres long and 1 to 2 cm thick aligned parallel to foliation in a buff light grey weathering, fine-grained groundmass of quartz and feldspar. The foliation-parallel green blotches, which average 2 by 5 cm, are due to a dusting of very fine-grained antlerite. Grab samples of locally associated chalcocite have assayed as much as 0.65 percent Cu and as little as 0 .08 per­cent Cu. The green mottled-weathering phase is generally irregularly distributed. Some outcrops ap­pear to mantle the structural hanging wall and a pos­sible stratigraphic footwall of the high-grade chalco­cite zone near the center of the showing.

3) Sparse small clots of antlerite and or malachite. This phase is common in many outcrops particularly in the structural hanging wall to the high-grade chal­cocite zone near the center of the showing.

4) Quartz feldspar pegmatites characterized by green weathering feldspar and less commonly blebs of chalcocite. Although common in copper-bearing ar­eas, in at least one outcrop at 10+90NE on the Jan­sem 2 grid, a 25 cm wide greenish grey weathering pegmatite vein containing chalcocite cuts unmineral­ized conglomerate. A grab sample from this dyke as­sayed 0 .889 percent Cu and 0.22 oz/ton Ag, possi-

Saskatchewan Geological Survey

bly indicating the presence of an adjacent covered high-grade zone.

Genie (UTM 502810 m E, 6300480 m N)

A detailed scale map of the showing is contained in the map package that accompanies this report.

Location: The center of the Genie copper showing is lo­cated about 450 m southeast of Genie Lake at 17+95N on line 83+50E on the Noranda Exploration Inc. grid system. Copper minerals occur in a series of outcrops over an area about 150 m long and 25 m wide. One large trench, as well as some smaller trenches have been blasted out by Noranda Exploration Inc.

Description of Rock Types: Copper is hosted in a nar­row arkosic unit in a thick succession of light to dark grey, brownish grey weathering, strongly foliated, mas­sive to laminated, variably argillaceous siltstone of the Rafuse Lake Formation. Some parts contain concentra­tions of elliptical quartz blebs aligned and flattened par­allel to foliation and locally deformed into tight small-scale F3 folds that plunge shallowly to the north­east or less commonly to the southwest. Locally, such as in the footwall to the mineralized zone, the siltstone has been variably assimilated by a light grey, buff or rusty pink weathering, fine-grained, quartzofeldspathic granitoid phase.

The 20 m thick 'arkosic' host to the mineralization com­prises three types:

1) 'Clean' arkose. A homogeneous, foliated pink to grey weathering, fine-grained rock composed mostly of quartz and feldspar, with biotite and amphibole as minor components.

2) Siliceous arkose. An apparently discontinuous unit, about 1.5 m wide, of light grey to grey weathering, fine- to medium-grained quartzofeldspathic rock characterized by resistant millimetre-size blabs of quartz which impart a knobby-weathering appear­ance.

3) Mixed unit. A heterogeneous mixture of white, pink, and buff brown weathering arkose, siliceous arkose and fine-grained quartzofeldspathic granitoid.

The rock types described in the preceding paragraphs are cut by two phases of pegmatite: 1) salmon weather­ing quartz-feldspar-tourmaline pegmatite in veins up to 50 cm wide and 2) white weathering quartz-feldspar­mica-tourmaline pegmatite in veins up to 5 m wide. An apparently discontinuous sill of light grey weathering, fine-grained quartzofeldspathic rock containing millime­tre quartz eyes, possibly a falsie volcanic, was also re­corded.

Structure: The supracrustal succession hosting the Ge­nie Showing contains a prominent northeast-trending S1 foliation that dips steeply to the southeast. A weak second penetrative foliation is locally oriented oblique to the first foliation. Quartz blabs in siltstone have been de­formed into small-scale Z folds that generally plunge shallowly to the northeast or less commonly southwest

45

(Figure 11 ). Pegmatites are deformed into S folds that plunge shallowly northeast. These folds are related to the D3 deformation. Rocks in the vicinity of the Genie Showing are also cut by north-northwest-trending small­scale sinistral brittle faults.

Character of mineralization: Copper occurs in variable concentrations over a strike length of 150 m in all three phases of the arkose. 'Clean' arkose in the central part contains the highest grades. Copper minerals include chalcocite, bornite, chalcopyrite, malachite, azurite, and trace covellite. Chalcocite and bornite occur as fine­grained disseminations. The chalcopyrite, bornite, mala­chite, and azurite occur along fractures.

b) Summary and Interpretation of Janice Lake Area Copper Deposits

Over twenty occurrences of in situ copper mineraliza­tion as well as some unsourced mineralized boulder trains have now been found in the Janice Lake area. These are associated with a thick redbed fanglomerate sequence and overlying mixed siliciclastic sediments, deposited in an arid or semi-arid environment adjacent to a zone of normal or listric faulting. Cale-silicate brec­cia lenses occurring in the sequence immediately overly­ing the conglomerate and reports of scapolite in thin sections of some samples from the conglomerate (Scott, 1973), are evidence of evaporitic conditions dur­ing part of this depositional regime.

The greatest concentration of copper occurrences is in rocks of the Rafuse Lake Formation northwest of the Burbidge Lake Shear Zone (Figure 2) . Most of these are hosted in arkose, but some are also hosted in fan­glomerate of the Janice Lake Formation. In the former host, such as between Janice and Rafuse lakes, copper occurs near the contact with wacke locally.

The mineralized zone has a strike extension of at least 8 km. In the area between Janice and Rafuse lakes, the zone has been deformed into large-scale S folds that plunge gently to the southwest. Data provided by Noranda Exploration Inc. revealed that magnetic and IP anomalies associated with the mineralized zone are also folded, supporting an early origin for mineralization.

Southeast of the Burbidge Lake Shear Zone, only two copper occurrences have been identified: the Genie (in the Rafuse Lake Formation) and the Juno (in fanglomer­ate of the Janice Lake Formation). Host rocks of all cop­per occurrences are magnetite-bearing. Adjacent unmineralized conglomerate or bedded siliciclastic sedi­ment commonly contain hematite. Zoning has been documented for some of the occurrences.

Previous workers favored hydrothermal (Scott, 1973), syngenetic (Rath, 1969) or diagenetic (Coombe, 1994) origins for copper deposits in the Janice Lake area and have made comparisons to apparently similar deposits elsewhere, such as those in the Udokan area of east­ern Siberia (Rath, 1969). This report highlights the simi­larity of many features of the copper occurrences in the Janice Lake area to those common to sediment-hosted

46

stratiform copper deposits (Kirkham, 1989; Brown, 1992).

c) Mineral Potential of the Janice Lake Area

The Janice Lake area is considered to be a sediment­hosted stratiform copper environment of significant eco­nomic potential. Although more than twenty showings of copper mineralization have been found there, these dis­coveries are grouped in a relatively small area, parts of which have yet to be thoroughly explored. With a cou­ple of exceptions, all of these occurrences lie northwest of the Burbidge Lake Shear Zone in apparently more proximal facies of the Janice Lake and Rafuse Lake for­mations.

Mapping this summer has revealed that fanglomerate of the Janice Lake Formation and an associated polymic­tic conglomerate extend both southwest of the Janice Lake area into the adjacent Burbidge Lake map sheet area for at least 5 km and northeast into the Alexander map sheet for at least 8 km for a total strike length of at least 35 km. Much of this northeastern extension is drift covered and has yet to be thoroughly evaluated for cop­per mineralization. Fanglomerate records a major and previously unrecognized period of intrabasinal uplift dur­ing deposition of Lower Proterozoic sediments in the Wollaston Domain and defines a significant copper met­allotect.

8. Acknowledgments

Wayne Darch and Don Dudek of Noranda Exploration Inc. are thanked for their insightful discussions of the ge­ology and mineral occurrences of the Janice Lake area and for providing access to confidential data. Field visits and the ensuing frank discussions with Rod Kirkham and Tom Sibbald are gratefully acknowledged. Doug Harvey provided invaluable help during mapping.

9. References Annesley, I.A. and Madore, C. (1989): The Wollaston Group

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Bull, W.B. (1972): Recognition of alluvial fan deposits in the stratigraphic record; in Recognition of Ancient Sedimentary Environments. Soc. Econ. Paleontol. Mineral., Spec. Publ. No. 16, p63-83.

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Summary of Investigations 1995

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Summary of Investigations 1995