Frotet Lake - Troilus Lake Area, Abitibi and Mistassini Territories Quebec Department of Natural Resources

RG 123(A) FROTET LAKE - TROILUS LAKE AREA, ABITIBI AND MISTASSINI TERRITORIES QUEBEC DEPARTMENT OF NATURAL RESOURCES

Honorable Daniel Johnson Paul-Emile Auger Minister Deputy Minister

GEOLOGICAL EXPLORATION SERVICE

Robert Bergeron, Director

GEOLOGICAL REPORT 123

FROTET LAKE - TROÏLUS LAKE AREA

Abitibi and Mistassini Territories

Daniel L. Murphy

QUEBEC. 1966 -

TABLE OF CONTENTS

Page INTRODUCTION 1

General statement 1 Location and accessibility 2 Field work and acknowledgements 2 Previous work 3 DESCRIPTION OF THE AREA 3 Settlement 3 Resources 4 Agriculture 4 Timber 4 Fish and game 4 Climate 4 Physiography 5 Topography 5 Drainage 5

GENERAL GEOLOGY 6 Regional geology 6 Local geology 6

PRECAMBRIAN 7 Pre-Broadback Group 7 General features 7 Volcanic rocks 8 Andesite 9 Basalt 10 Tuff and breccia 10 Sedimentary rocks 11 Graywacke-type rocks and argillite 12 Black slate and chert 13 Metamorphic rocks 14 Greenstone, phyllite and schist 14 Hornblende gneiss and amphibolite 15 Intermediate to ultramafic igneous rocks 17 General features 17 Altered peridotite 17 Gabbro 18 Diorite 19 Acid igneous rocks and related types 20 General features 20 Quartz diorite 20 Granodiorite 21

Ea at

Quartz monzonite 21 Granites 21 Gray gneissic granite 21 Pink to tan granite 22 Pegmatite and aplite 23 Porphyritic rhyolite 23 Transitional or hybrid rocks 23 Vein and replacement deposits 24 Basic dikes 26

CENOZOIC 27 Pleistocene and Recent 27 STRUCTURAL GEOLOGY 28 Regional structure 28 Local structure 28 Folds 28 Linear features 29

ECONOMIC GEOLOGY 30 Metallic deposits 30 Non-metallic deposits 31 Asbestos 31 Sand and gravel 31 Pegmatite dikes 32

REFERENCES CITED 32

ALPHABETICAL INDEX 33 LIST OF ILLUSTRATIONS

Ma p

No. 1572 Frotet Lake - Troilus Lake Area (in pocket)

Plates

I A morainal ridge 1/2 mile northwest of Chix lake.

II A - Lunate fractures in bedrock east of Domergue lake. Fracture axes trend S.40°W.

B - The weathered surface of fragmental greenstone on an island near the north shore of Frotet lake.

C - Andesitic pillow lava along the west shore of the southwest bay of Troilus lake.

III A - Plicated foliation resulting from shearing in volcanic rocks along the southwest bay of Troilus lake.

B - Quartz-filled fractures cropping out 3 1/4 miles southwest of Domergue lake.

C - Pink granite intruding banded hornblende gneiss along the north shore of Chix lake.

IV A - A porphyritic rhyolite dike cutting finely layered greenstone 1/4 mile west of the northeast arm of Domergue lake.

B - A basic dike intruding granite (gr), 3 miles northwest of Troilus lake along its outlet.

C - Xenoliths of altered hornblende gneiss (x) in granite, 4 1/8 miles northeast of Troilus lake.

Tables Pane 1 Table of formations 8 2 Partial Semi-quantitative analysis of typical carbonate vein material 26 - V - I Geological Report

FROTET LAKE - TROÎLUS LAKE AREA

Abitibi and Mistassini Territories

Daniel L. Murphy

INTRODUCTION

General Statement

The Frotet Lake - Troilus Lake area is underlain by a variety of rocks of Precambrian age. The principal types are sedimentary and volcanic units, partly or completely altered to greenstone, phyllite, schist and gneiss, which have been invaded by igneous intrusions ranging in composition from meta-peridotite to granite. A series of closely-spaced dikes, varying in texture from basalt to diabase and found only along the outlet of Troilus lake, are the youngest consolidated rocks. Much of the area is blanketed by a veneer of glacial material, the thickness and distribution of which are variable; the most extensive deposits are concentrated in the southern and northwestern parts of the area.

The map-area was the object of an intensive staking rush in late 1958 and early 1959 following the discovery of copper- and nickel- bearing boulders in the summer of 1956. By 1961 most claims had lapsed although several organizations had carried out evaluation programs and a small number of claim blocks remained in good standing. In the fall of that year, however, a significant copper sulfide discovery at the north end of Moléon lake generated renewed interest in the entire region. During the 1962 field season prospecting parties turned up a number of interesting showings. Most of them are concentrated to the west and northwest of Troilus lake in the contact zone bordering the granitic intrusions. At least one discovery was made a short distance south of Frotet lake at the edge of a small granite stock. Generally speaking, metallic mineralization consists of either iron or nickel sulfides disseminated in the basic to ultramafic igneous rocks or vein deposits marginal to the acid intrusions. - 2 -

Location and Accessibility

The Frotet Lake - Troilus Lake area is approximately 70 air- miles north of Chibougamau. It encompasses about 400 square miles including all of the area between latitudes 50°30' and 51°00' and longitudes 74°30' and 74°45'. Most of the map-area lies within Abitibi Territory although a small part near the southeast corner is east of the height-of-land and in Mistassini Territory. In terms of unsurveyed townships it covers nearly all of 1223 and 1323, major portions of 1123 and 1423, and small sections of 1122, 1222, 1322, and 1422.

Except for the fall freeze-up and spring break-up periods most of the area is readily accessible by float- or ski- equipped planes. The nearest base is at Caché lake, 7 miles south of Chibougamau. An alternative means of access is by a nearly week-long canoe trip from Chibougamau through lakes Waconichi and Mistassini followed by rather involved canoe and portage travel to the west by way of a network of smaller lakes. Indians from the Mistassini post generally use this route or the nearby Rupert river when trav- eling to their hunting and trapping grounds in northwestern Quebec.

Canoe travel within the area is confined principally to the central and north-central sections. Frotet lake is connected with Régnault and Moléon lakes by short, shallow waterways which are difficult to'navigate during periods of low water. Troilus lake, which dominates much of the northern part of the area, is connected with Frotet lake by a short river. Except for a single set of unnavigable rapids one can journey from lake to lake with ease. Entry to the south-central part of the area may be made by canoe along the small chain of lakes to the east of Domergue lake. Frequent portaging is necessary along this route when the water is low. The small lakes near the southeast corner,as well as those near the northern areal limits, are relatively isolated and can be reached most easily by small aircraft. The northwest corner of the area is accessible from the outlet of Troilus lake although water travel is partly obstructed by a stretch of closely-spaced rapids near the beginning of the river.

Field Work and Acknowledgements

The area was studied by the writer during the 1961 and 1962 field seasons. Geologic mapping was on a scale of 2 inches to the mile. The areal base map was constructed from a series of 1/2-mile-to-the-inch hydro- graphic sheets furnished by the Federal Hydraulic Resources Branch. A special map was prepared on a scale of 1 inch to 1,000 feet for the area just north of Domergue lake. It was used during an experimental geologic-geochemical project undertaken in 1961. Pace and compass traversing was done at not more than 1/2-mile intervals. In areas where exposures were sparse or the geology was complex, the traverses were more closely spaced. Vertical aerial - 3 - photographs and mosaics, processed by the RCAF, were used extensively during the actual field work and in the preparation of the geologic map. A special mosaic and its accompanying geologic overlay (Sheet 32J 10 and 15, Chibougamau Area) prepared by Hunting Technical and Exploration Services Ltd. during Operation Overthrust, provided the writer with a perspective of the regional geologic frame-work.

The writer was ably assisted during both field seasons by students and experienced bushmen. In 1961 C.J. Ritter and Ian Semple served as senior assistants, and W.M. Atkins and Florent Gauthier were junior assistants. Eugene Drouin and Dave Chiasson were employed as cook and canoeman, respectively. Georges Boiteau assisted in the geochemical aspects of the work in addition to performing his duties as a canoeman. E.H. Carlson was the assistant party chief during 1962. Guy Mondoloni and Clement Lamontagne served as junior assistants. J.E. Gagnon and Jimmy Meanscum were engaged as canoemen and Joseph Lafrance was the cook.

Previous Work

The Frotet Lake - Troilus area is part of a regional investigation undertaken by Kindle and Riley (1958). Their work was one of'several broad studies in a region extending from Lake Mistassini on the east to Lake Evans on the west (see Shaw, 1940a and 1940b). Earlier investigations by Bell (1902) and Cooke (1914) were confined to the western part of the belt. Moyer (1961) mapped the area bounded by latitudes 50030' and 50°45, North and longitudes 74000' and 74°15' West in 1960. He continued his work into the 15-minute quadrangle immediately to the west during the 1961 season. Separate preliminary reports on the area of investigation have been prepared by the writer (Murphy, 1962 and 1963).

DESCRIPTION OF THE AREA

Settlement

There are no permanent inhabitants in the present area. From late fall to early spring Indians from the Mistassini post and the Doré Lake settlement hunt and trap in the general region. During the remainder of the year groups of prospectors and field parties, sponsored by either mining companies or governmental agencies, carried out exploration and geologic work. Occasionally, core drilling programs have been undertaken during the winter months. Chibougamau, 70 miles to the south, is the nearest settled area of any size. A motor road between Saint-Félicien and Chibougamau was completed in 1950, following the general route of the Canadian National railway. - 4 -

Resources

Agriculture

The agricultural potential of the area is not high,owing to the short growing season, the poor quality of much of the soil, and the relative inaccessibility.

Timber

Much of the area is well forested although large sections of it have been destroyed by forest fires. Evergreens are the common trees and include black spruce, jack pine, balsam fir, and tamarack. Stands of white birch, poplar, and alder occur on the shaded, moist slopes of the hills, along some lake shores, and on the margins of streams. Most of the timber is not well enough developed to be classified as a potential source of lumber although much of it would be suitable for pulp wood. Any such exploitation would have to await the construction of adequate transportation facilities since there are no direct water-routes to the nearest settled areas.

Sphagnum moss and Labrador tea blanket the forest floor. Several varieties of grasses, shrubs and bushes grow in the lightly forested localities. Windfalls of dead timber cover most of the burnt-over areas although here and there the bedrock is well exposed.

Fish and Game

A variety of fish and wildlife inhabit the area. Several species of trout dwell in the cold, fast-moving streams and in the deep lakes. Pike and doré (wall-eyed or yellow pike) are abundant in lakes and large streams. Moose and a few caribou inhabit the area. The rocky areas, especially where blueberries are common, are favorite haunts of black bear. A number of small fur-bearing animals such as mink, beaver, otter, weasel, marten, muskrat and fisher are trapped by the Indians during the winter. Small flocks of black duck and golden-eye duck were seen during the field season. Spruce partridge and ruffed grouse are common in the forested areas.

Climate

The warm-weather term is rather short. Maximum annual temperatures in the 80°F. range generally occur from mid-July to early August. Water temperatures as high as 65°F. were recorded during the warmest periods. Scattered patches of ice begin to form on the fringes of the small lakes in late September, with the general freeze-up taking place in October or a little later. The spring break-up occurs usually in May. Winter temperatures average 300-40° below zero. - 5 -

Precipitation during the summer is sporadic and, at times, may be quite heavy. Daily showers of a few minutes duration are commonplace. Rain storms lasting for several days to a week or more may take place at any time during the summer. Accumulations of snow as much as 5 to 6 feet have been reported.

Physiography

Topography

The regional topography is characterized by glacially scoured, rocky hills of.moderate to low relief surrounded by lower lands filled with different kinds of glacial deposits. Swamps and lake-filled depressions, the direct result of the glacially deranged stream patterns, are widespread. When viewed on a broad scale, however, the skyline, despite the local relief, is quite even. Most of this part of the Precambrian shield has been interpreted as an elevated peneplain. The topographic irregularities produced by stream erosion subsequent to peneplanation and uplift were subdued by Pleistocene glaciation, which tended to bevel off the stream divides and fill the valleys.

The topography of the Frotet Lake - Troilus Lake area is quite varied. North of Frotet lake a strong northeasterly topographic "grain", reflecting the combined effects of bedrock structure, ice motion and post- Pleistocene erosion, is evident. South of the lake the structural trend is northwesterly. Northwest of Troilus lake, where different kinds of granite occur, the local relief is subdued. The glacial cover is extensive and only rarely do erosional remnants break the skyline. Prominent northeast-trending ridges border the eastern and southwestern shores of Troilus lake. These features are generally underlain by intermediate to ultramafic igneous rocks. Similar topographic anomalies occur south of Frotet lake, but there they strike northwesterly. In both general localities the adjacent lowland consists of volcanic and sedimentary rocks covered by glacial material. The relief gradually decreases southerly. South of Domergue,lake and along the southwestern border of the area the ground slopes gently south; here, an extensive cover of glacial debris overlies granitic bedrock.

Drainage

Nearly all of the area is drained by the Broadback River system. Waters in the west-central part empty westward into Regnault and Mol4on lakes,which in turn flow into Frotet lake and thence into Troilus lake. This latter body of water is tributary to the northern branch of the Broadback. Lakes and streams in the center and south drain into the Opataca- Cachisca-Comencho-Assinica chain of lakes, which is the headwaters of the southern branch of the system. Waters to the east of the height-of-land empty into a myriad of waterways tributary to Lake Mistassini. The southeast corner of the area is drained by the headwaters of Samuel-Bedard (North Brock) river. - 6 -

GENERAL GEOLOGY

Regional Geology

The Frotet Lake - Troilus Lake area is in the Timiskaming subprovince, a nearly triangular region bordered on the north by Eastmain river and on the southeast by the Grenville front. It extends beyond the western border of Quebec into Ontario. Although the term "greenstone" has been used to describe the lithology of the east-trending belts of rock and the term granite,to characterize the intervening areas, a variety of sedimentary, igneous and metamorphic rocks is present. In many places it is difficult to assign exact ages to the rocks. Hence, terms such as Keewatin-, Timiskaming-, and Huronian-type have been proposed to describe units which are similar to those found at the type sections, but not necessarily correlative with them.

Keewatin-type volcanics include basalts, andesites, dacites and rhyolites,together with their tuffaceous and brecciated counterparts. Impure sedimentary rocks are locally intercalated with these units. Intense deformation and alteration are evident in most places. Timiskaming-type rocks are principally conglomerates and graywackes which have been folded and metamorphosed together with the Keewatin-type volcanics in certain districts. Intrusives of the Timiskaming subprovince are varied, embracing the entire range from peridotitic to acidic types. Dresser and Denis (1944, pp. 62-71) recognize four groups which extend from Archean to Proterozoic in age. Sedimentary rocks, correlative with known Huronian units in Ontario, are present near the western provincial border. The section includes primarily conglomerates with minor argillite, graywacke, and impure quartzite. In addition to their lithologic character, Huronian rocks are further distinguished by the fact that they are relatively undeformed and lie unconformably above early-Precambrian rocks.

Local Geology

All of the bedrock is Precambrian in age. The oldest rocks embrace an extensive succession of impure sedimentary and volcanic rocks referred to as the Pre-Broadback Group by Kindle and Riley (1958). This group is part of an extensive belt which continues to the east, northeast and west of the present area. The rocks consist of andesitic and basic lavas,together with their pyroclastic counterparts and several varieties of clastic sedimentary rocks. Cherty beds are intercalated with the sedimentary units in some localities. Much of the group shows some degree of alteration. Its total thickness is unknown.

Sill-like masses of gabbro, and lesser amounts of serpentinized peridotite and diorite, intrude the Pre-Sroadback Group. Acidic igneous intrusions, in places having a well-developed gneissosity, postdate the intermediate to ultramafic rocks. Diabasic dikes cut the granites along the outlet - 7 - of Troilus lake. Metallic mineralization is associated with both the intermediate to ultramafic complex and the granitic rocks. Broad sections in the southern and northwestern portions of the area are overlain by till and flu- vioglacial material. Age relations among the aforementioned lithologic units are shown on the accompanying Table of Formations (Table 1). Transitional or hybrid rocks, including mixed intrusive and non-intrusive types and composite plutonic varieties, have been grouped together for the sake of discussion although their individual age relationships may differ.

The structural attitude of the rocks changes in going from north to south across the area. North of Frotet lake, foliation and bedding attitudes strike northeasterly and dip steeply to the west. Near the lake they trend nearly east and are vertical or dip steeply south. North- westerly strikes prevail southward and near vertical dips are the general rule, although near the southern areal border foliations strike about east and dip north. Shear zones and related displacement features parallel the regional strike of the rocks but joint attitudes span a range of values.

PRECAMBRIAN

Pre-Broadback Group

General Features

Rocks similar to those described by Kindle and Riley (1958) as belonging to the Pre-Broadback Group are the most widespread lithologic units in the area. They crop out in a roughly east-trending band and constitute much of the bedrock everywhere except in the northwest and southwest. Except for a northwesterly shift of the group contact northwest of Troilus lake, the limits indicated by Kindle and Riley (1958) compare closely with those determined by the writer. Included within the group, whose total thickness is unknown, are a variety of sedimentary and volcanic rocks all of which show some degree of alteration. For mapping purposes, rocks possessing a distinct greenish cast or micaceous character and a measurable foliation were considered as greenstones ur low-rank schists. In the absence of original structures and textures (bedding, pillows, etc.), it is impossible to determine the nature of the parent rocks where alteration has been intense.

Metamorphic effects range from the formation of minute, disseminated flakes of chloritic material and mica through the development of scattered veinlets of pure actinolite and chlorite to a complete transfor- mation of the rocks to schistose types rich in actinolite,epidote, chlorite and mica. Basic lavas and tuffs seem to have been the most sensitive to mineralogical and textural changes. In the following paragraphs mildly altered rocks which can be related to specific lithologic parentages are discussed separately. Field relations indicate that the development of greenstone and schists can be attributed to regional metamorphism, or to - 8 -

Table 1

TABLE OF FORMATION;

Recent CENOZOIC and Moraines, eskers, alluvial deposits Pleistocene

GREAT UNCONFORMITY

Basic Dikes Range in texture from diabase to porphyritic basalt

Vein and replacement deposits Transitional or hybrid rocks Porphyritic rhyolite Acid Igneous Rocks Pale to dark pink pegmatite and aplite and Light pink to tan biotite granite Related Types Gray, gneissic biotite granite Gray, hornblende quartz monzonite Gray, hornblende granodiorite

BRIAN Gray, hornblende quartz diorite

Intermediate to Diorite and meta-diorite Ultramafic Gabbro and meta-gabbro ECAM Igneous Rocks Meta-peridotite and serpentinite PR Metamorphosed sedimentary and volcanic rocks, including greenstone, phyllite, schist and gneiss Pre-Broadback Graywacke with minor argillite, black Group slate and chert Andesite, basalt and minor rhyolite together with their pyroclastic counterparts

cataclastic deformation, or to contact processes in the aureoles of the acidic intrusions. In many cases, the alteration appears to represent the combined influences of two or more of these processes.

Volcanic Rocks

Intermediate to basic flow rocks and tuffs are common southwest of Troilus lake and along the north shore of Frotet lake. Andesitic - 9 - varieties seem to be much more abundant than the basaltic types. Prior to metamorphism, however, basalts may have been more widespread because specimens of them in a number of cases are quite similar to hand specimens of greenstone and would have been identified as such in the field had they not been found associated with pillow structures.

A variety of primary structures can be observed in the lavas. Pillows, including both cuspate and, less commonly, bun types, are especially well developed in the andesite. Individual pillows are sheathed by narrow zones rich in dark green micaceous minerals. The foliation within the zones parallels the outline of the structures. Brecciated lava flow tops were observed here and there and, together with the pillow structures, served as useful guides to formation tops.

Andesite

Andesite is typically fine grained, tan weathering and medium greenish gray on fresh surfaces; broken surfaces have a distinctive conchoidal fracture. Locally, minute plagioclase phenocrysts are visible in hand specimens. Thin-section study indicates that a major part of the andesite has been subject to some degree of alteration. Non-porphyritic varieties consist of a felty aggregate of plagioclase, epidote group minerals and a chlorite-actinolite mixture. Plagioclase occurs as irregular microlites whose composition ranges from albite to andesine. The more sodic laths appear to be fresher and probably are of secondary origin, having developed at the expense of the intermediate types during alteration. Epidote and clinozoisite are the resultant products of a breakdown of the primary femic silicates and the plagioclase; they are quite fine grained and commonly appear in cloudy patches. Actinolite is pale green and shreddy to sub- acicular. Green chlorite, showing anomalous tobacco-brown interference colors in many cases, is usually disseminated and interstitial although parts of it are concentrated in plicated veinlets. At some localities small, ragged, olive-brown to light brown biotite grains occur with the chlorite. In such cases chlorite replaces the biotite. Sericite and kaolinite were observed in a few sections. The white mica is associated either with biotite, epidote, and chlorite or with kaolinite and clinozoisite. Variable amounts of rhombohedral carbonate material and quartz are widely scattered through the andesite. They occur as isolated pods or fracture fillings, either alone or intermixed. Textural relationships indicate that both minerals are largely replacements; in fact, strongly carbonatized specimens readily effervesce when treated with dilute hydrochloric acid. Some of the quartz, however, seems to be primary; consequently, some of the "andesite" could be more appropri- ately termed quartz.andesite or even dacite. Accessory minerals include anhedral sphene, subhedral grains of apatite, magnetite, pyrite, ilmenite- leucoxene and dusty limonite. Some of the pyrite, especially where it occurs in fine-grained clusters, appears to be the result of replacement. — 10 —

Porphyritic andesite crops out at several places near the eastern and southern shores of Troilus lake and along its outlet. Plagio- clase and hornblende are the principal phenocryst materials. Generally, the plagioclase phenocrysts are classed with the sodic labradorite,although the matrix feldspar is andesine. Zoning, where present, may be accentuated because of differential replacement by fine sericite and partly recrystallized clinozoisite. Poikilitic hornblende, containing included apatite and opaque oxides, occurs as prismatic crystals with irregular terminations. Some biotite has developed along grain margins and cleavage traces. Strongly resorbed quartz phenocrysts, with hornblende inclusions, were observed in a specimen taken from along the east shore of Troilus lake.

Basalt

As mentioned above, all the basalt shows the effects of low- grade alteration. It is fine grained and dark greenish gray. Weathered surfaces are light brown with a slight green cast. Most of the rock consists of a semi-felty aggregate of actinolitic hornblende and epidote-clinozoisite. The amphibole is fibrous to shreddy and green. Much of it is concentrated in subradiating clusters. Epidote minerals appear as cloudy, incipient subhedral crystals. Both components locally occur as fracture fillings. Plagioclase is difficult to distinguish from the finely disseminated quartz owing to its fine grain. It appears to represent the partly recrystallized sodic portion of the original plagioclase. Chlorite and sericite are widespread in small amounts. The chief accessory minerals are magnetite, zircon and apatite.

Tuff and Breccia

Pyroclastic rocks are intimately associated with the lavas. However, a scarcity of outcrops prohibited the use of such rocks in estimating the number of flow sequences in a particular locality. Fine-grained andesitic tuff is nearly indistinguishable from its lava counterpart. Coarser-grained types, in the absence of recognizable flow features, can be most easily distinguished from the lava on weathered surfaces where the crystal and rock fragments tend to weather differentially and stand out from the matrix. Gradations from volcanic tuff through contaminated or hybrid varieties to graywackes were found throughout the area. The effects of shearing are evident in most specimens of tuff.

Tuffs are fine to medium grained and greenish gray, and contain scattered crystal fragments of light green plagioclase. Most specimens have at least a faintly schistose texture. Microscopically, the plagioclase appears as angular to subhedral laths that are fractured or broken and corroded. Their average composition is about sodic andesine. Nearly all the plagioclase shows some incipient alteration to clinozoisite, sericite and clay. Epidotized, green hornblende in the form of irregular, partly resorbed crystals, was observed in a few of the thin-sections. Epidote- group minerals appear either as fractured grains or in aggregates of fine, semi-opaque grains. Fine-grained carbonate material, probably calcite, is concentrated in veinlets crosscutting the larger crystals or in small patches. Quartz, commonly with numerous inclusions, is rare. All the above minerals are set in a grayish green matrix rich in chlorite, epidote, olive-green biotite, plagioclase and quartz. In many cases the quartz and feldspar are concentrated in lenses between the large crystals and the schistose matrix. Magnetite, ilmenite (partly converted to leucoxene), and pyrite are the principal accessories.

Acid volcanic rock was observed only near the south end of Troilus lake. It is lighter in color and softer than the common andesitic type. Sericitization and epidotization have masked the original texture so that it is difficult to determine whether the original rock was a porphyritic lava or a crystal tuff. Quartz, orthoclase and, to a lesser extent, sodic plagioclase are the chief primary minerals. In addition to sericite and epidote, minor amounts of rhombohedral carbonate and pyrite make up the secondary fraction.

The mineralogy of some tuffs suggest that they may contain admixed sedimentary material. They generally contain a higher percentage of quartz both as fragments and in the groundmass and in places they have a definite detrital texture. The increase in quartz is commonly accompanied by an enrichment in clay minerals and micas.

Beds of volcanic breccia, intercalated with lava and tuff, crop out along the north shore of Frotet lake and on the near-shore islands. The breccia is composed of light greenish tan fragments up to 4 inches or more long embedded in a rudely schistose, medium to dark gray matrix. Weathered surfaces are rough since the fragments are more resistant than the groundmass. In thin-section, fragments consist of a foliated, very fine mixture of quartz, feldspar and poorly crystallized epidote. Scattered through the mixture are lenses composed of microcrystalline quartz, shattered and altered feldspar crystals, and concentrations of olive-green biotite. The semi-schistose groundmass material includes altered plagioclase, green biotite, chlorite, epidote-clinozoisite, actinolitic hornblende, and quartz. Contacts between fragments and groundmass are marked by concentrations of micaceous minerals and epidote.

Sedimentary Rocks

A variety of sedimentary rocks occurs in the Pre-Broadback Group. Although closely associated with the volcanic members of the group, they appear to be most abundant near the northwestern and southern limits of the band. The lithologic units include graywacke-type rocks, siltstones, argillite, black slate and chert. In many cases it is difficult to distinguish between sedimentary rocks and pyroclastic types. This was especially - 12 - true in the absence of diagnostic field relationships such as the association with known lavas. Tuffs were distinguished from graywackes on the basis of texture and mineralogy. If the larger grains appeared to have identifiable crystal outlines, the rock was classified as a tuff, whereas rocks with large, angular grains (microbreccia) were termed graywackes. Rocks which contained high percentages of quartz, both as fragments and as silty matrix, were considered to be sedimentary.

Graywacke-type Rocks and Aroillite

The term "graywacke-type" applies to clastic rocks which range from silt and sand sizes to pebble or very coarse sand sizes and are rich in quartz, feldspar and a mica-chlorite-clay mixture. Such rocks are commonly thickly bedded to almost massive, although,locally,beds ranging from a few inches to nearly a foot in thickness occur. The fresh rock is either greenish gray or slightly brownish gray. Gradations from graywacke, in the strict sense, and subgraywacke to micaceous quartz sandstones and siltstones were observed. Most graywacke-type specimens have been sheared, resulting in typical cataclastic types. Large grains are fractured and their borders are granulated. Matrix minerals tend to become concentrated in paper-thin streaks.

True graywacke is exposed at several places near the northwest part of Troilus lake. Quartz and feldspar, including plagioclase and some orthoclase, are the conspicuous detrital minerals. Quartz particles are angular and contain abundant inclusions. Many grains show strain lamel- lae. Blocky feldspar crystals are turbid because of kaolinization by weathering or partial replacement of secondary minerals such as sericite and clinozoisite. The matrix is rich in white mica, chlorite and silty quartz. Brown biotite, epidote, limonite and clay occur in lesser amounts. Many specimens contain fine-grained carbonate either as fracture fillings or in isolated pods. Accessory minerals include apatite, magnetite and pyrite.

Subgraywacke is a common rock in the vicinity of Domergue lake and to the southwest of Frotet lake. Quartz is the principal clastic mineral, comprising as much as 60% of the rock. Cloudy feldspar makes up 10-15%, or less. These minerals are enclosed in a paste-like matrix similar to that found in graywacke. Bluish gray quartz pebbles, generally not more than 1/2 inch long, show evidence of stretching and fracturing in hand specimen. The matrix minerals, chiefly sericite, chlorite and quartz, tend to be segregated into wavy masses that wrap around the individual pebbles. A zone of conglomeratic subgraywacke of indeterminate extent is exposed on a small island near the east end of Frotet lake. The ellipsoidal particles are composed of brownish gray chert and are set in a fine mica-chlorite- quartz groundmass. Parts of the zone are sheared; secondary quartz and calcite are the chief shear-filling minerals. - 13 -

Siliceous argillite and fine-grained sandstone were observed in the northwest part of the area between Troilus lake and the contact zone fringing the granitic intrusions. Similar types also appear along the peninsula in the northwest section of the lake. These rocks have a higher percentage of quartz, up to 70%. Feldspar is either absent or present only in minor amounts. The mineralogy of the cementing materials is similar to that found in the graywacke-type rocks. A number of specimens contain up to 10% carbonaceous matter.

Black Slate and Chert

Black slate is a distinctive although relatively limited lithologic unit. Exposures of it were seen in the central and northern parts of the area. Although two of the outcrops immediately north of Domergue lake were roughly along strike with each other and a third just a short distance farther north, the writer was unable to determine whether they are parts of the same unit or represent two or more separate formations. The slaty zones range from 1 foot to 2 feet thick at these localities. An 8-foot zone of interbedded black slate and siliceous argillite crops out on the peninsula in northwestern Troilus lake. Owing to its distinctive character the slate may, at a future date, serve as a structural guide once its stratigraphic relationships and distribution have been established.

Fresh hand specimens of slate are nearly massive although some are finely laminated. In all cases, however, the bedding has been accentuated by weathering processes as evidenced by regular tonal changes on the brown-weathered surfaces. Individual beds, rarely exceeding 1/2 inch or so across, are primarily the result of variations in the mineralogy and, to a lesser extent, differences in grain size. South of Frotet lake bedding is the result of variations in the quartz to graphite-clay ratios. Chlorite occurs as a fracture filling and in subradiating concentrations with quartz and sericite. Small amounts of fine-grained feldspar are scattered through the graphite-clay matrix. Elsewhere, bedding resulted from the combined effects of mineralogy and texture. In such cases, silt to fine, sand-sized quartz and feldspar, surrounded by sericite, chlorite, epidote and graphite, are intercalated with finer-grained aggregates of quartz, feldspar and micaceous minerals.

Several bands of white weathering chert crop out along the south shore of Frotet lake. The largest of the bands is 2 1/2 feet wide and is bordered by smaller, discontinuous cherty lenses. Most of the chert consists of a mosaic of fine quartz crystals. However, isolated quartz particles, probably relic sand-sized grains, and crosscutting fractures filled with quartzitic material occur in most specimens. Ferric oxide, the chief accessory material, is present both as coatings on quartz crystals and as a lining of fractures. - 14 -

Thinly banded, light tan weathering, greenish gray chert occurs along the east shore of Troilus lake near the abandoned Dauphine Mines drill camp. It is interbedded with mixed volcanic rocks. The lighter-colored bands, from 1/4 to 1/2 inch wide, consist of a cryptocrystalline mosaic of quartz. Alternating with these layers are slightly thicker ones containing epidote and chlorite in addition to quartz. Boundaries between the contrasting layers are generally enriched with the aforementioned green minerals. Dusty limonite, magnetite and trace amounts of apatite also occur. Much of the chert is cut transversely by irregular joints and microfaults filled with fine-grained epidote, pyrite and limonite.

Metamorphic Rocks

A large part of the volcanic and sedimentary rocks has been metamorphosed. As indicated above the intensity of metamorphism spans a broad range. Consequently, the resultant rocks differ widely in both mineralogy and texture. From previous descriptions of the volcanic and sedimentary units it is evident that some petrographers would regard many of them as low-grade metamorphic rocks. The writer feels, however, that in most cases recrystallization has been limited and the nature of the parent material is readily apparent. The term greenstone has been used in a liberal sense to apply to distinctly foliated green and grayish-green rocks of questionable parentage. Although this usage is contrary to established petrographic schemes of classification, it was necessary as a field expedient. Continued use of the term helped maintain continuity between the field and laboratory phases of the investigation. In a number of cases the probable antecedent rocks could be inferred with reasonable confidence from the mineral changes and, to a lesser extent, from textural features and relic structures. On the accompanying geologic map, therefore, the "greenstone" designation has been modified to indicate the probable original rocks. This method of notation was also used where small masses of sedimentary or volcanic rock occurred in extensive areas of greenstone, but could not be separated on the present scale of mapping.

Greenstone, Phyllite and Schist

Greenstone is a widespread rock unit in the Pre-Broadback Group. It is especially well developed where regional metamorphic processes have been augmented by either cataclastic or contact metamorphism. A pro- gressive change from slightly altered rock to greenstone can be observed as one approaches Frotet lake. This change is correlative with a gradual increase in the intensity of deformation. Comparable rock alteration occurs at the borders of the injected zones of contact aureoles.

Greenstones, apparently derived from igneous rocks, are fine to medium grained, rudely foliated, and dark greenish gray. Average specimens are composed of more than 50% poikiloblastic actinolite having inclusions of - 15 - fine quartz, plagioclase and opaque minerals. Commonly, the well-developed amphibole crystals are concentrated in subradiating clusters. Widely scattered xenocrystic(?) quartz grains and strongly epidotized plagioclase make up the remainder of the rock. The unusually high percentage of subhedral to anhedral sulfide and iron oxide crystals suggests that the actinolitic schists are metamorphosed lavas. •

The distinct layering in certain of the greenstones and their high proportion of quartz indicate that they may have been originally sedimentary rocks. A section of exceptionally well-banded greenstone is exposed about 1/4 mile west of the northeast arm of Domergue lake. In hand specimen, the rock is a deep grayish green and has a semi-phyllitic texture. Microscopically, the darker layers are composed of a fine-grained, well- foliated aggregate of olive-green hornblende and quartz in about equal proportions. Individual layers are usually 1 inch to 2 inches thick. Inter- calated with these layers are lighter-colored types rich in epidote-group minerals, green hornblende and quartz. Some of the clinozoisite, together with sericite and kaolinite, is concentrated in turbid, spotty masses which probably represent altered feldspar grains.

Calcareous greenstones are common units within the Pre- Broadback Group near the southeast arm of Frotet lake. The carbonate-rich zones appear either as uniform layers a foot to several feet wide alternating with non-calcareous beds or as pod-like masses randomly distributed through the greenstone. Differential weathering has produced a deeply pitted surface on the latter rocks. Calcareous bands are fine grained, massive, and greenish gray-brown. Quartz is the principal non-carbonate mineral. Rhom- bohedral carbonate, chiefly calcite, occurs in irregular patches throughout the rock; however, some of the calcite is confined to crosscutting veinlets and so is of secondary origin. The intervening layers of non-calcareous greenstone are greenish gray and are composed of fine-grained quartz, clinozoisite, and chlorite.

Light greenish gray, phyllitic to semi-schistose rocks, composed largely of quartz, sericite, chlorite and biotite,are common in the area south of Frotet lake. Most specimens consist of 50% or more quartz, which is concentrated in lensoidal masses and interweaving stringers of sericite and chlorite with lesser amounts of biotite and, in some places, hornblende. Accessory sulfides and oxides are widely disseminated.

Hornblende Gneiss and Amphibolite

Hornblende gneiss and amphibolite occur at several widely separated localities in the area. Certain of them resemble border alteration facies of the younger basic rocks although, with perhaps one exception, a genetic field relationship could not be established between the two rock groups. The rocks in question seem to occur along the margins of the - 16 -

Pre-Broadback band. Their proximity to the contact with the later granite complex suggests that they may be the end products of magnetic or meta- somatic activity. Alternatively, since the rocks represent a higher grade of metamorphism than the greenstones, phyllites and schists, they might be exposed parts of a yet to be recognized basement complex underlying the Pre-Broadback Group.

Hornblende gneiss is exposed along the north shore of Chix lake in the southeast section of the area, and amphibolite,at the northern end of Moléon lake just west of the area. The mineralogies of the rocks are rather similar; their differentiation is based on the presence of essential quartz in the gneiss but only accessory quartz in the amphibolite. Both rocks are medium grained and dark gray. The hornblendic gneiss shows a poorly developed compositional banding, whereas the amphibolite is rudely foliated with the light and dark minerals rather evenly distributed. Blue- green hornblende is the principal femic mineral; generally, it is subhedral and poikiloblastic with quartz the common included mineral species. Moderate to strongly sericitized plagioclase is the chief feldspar. Both the gneiss and the amphibolite have above average amounts of what normally are minor accessory minerals such as sphene, pyrite and magnetite. Minerals of the epidote group occur in scattered crosscutting veinlets at both localities.

Medium-grained, well-banded gneiss crops out in a northeasterly trending zone to the northwest of Troilus lake. Individual bands range from less than an inch to several inches thick. The gneissic effect has been produced by alternating light and dark bands. The darker types are rich in biotite, hornblende-pyroxene, and minor quartz and plagioclase. The biotite is olive-green and strongly pleochroic, and contains apatite and zircon inclusions. Bluish green prismatic crystals of hornblende show evidence of replacement by biotite. Subhedral to anhedral epidote, interstitial quartz and scattered grains of clinopyroxene (probably diopsidic augite) make up the remainder of the band. Light-colored bands consist largely of irregular- ly shaped quartz of variable size, blocky, slightly sericitized plagioclase, and some altered orthoclase. Biotite is subordinate and disseminated. Apa- tite, sphene and zircon are accessory and most common in the dark layers.

Epidotized hornblende gneiss locally occurs as xenoliths in the granite northwest of Troilus lake. It resembles the gneissic rocks described in the preceding paragraph although the foliation is as much schistose as it is gneissic and biotite is absent. Moreover, epidotization of both the hornblende and plagioclase is more intense. f

A morainal ridge Y2 mile north-northwest of Chix lake. Plate Il

A - Lunate fractures in the bedrock east of Domergue lake. Fracture axes trend S.40'W.

B - The weathered surface of fragmental greenstone on an island near the north shore of Frotet lake.

C - Andesitic pillow lava along the west shore of the southwest bay of Troilus lake. Plate Ill

/ ! ~

J ~- - r ~ , O..• ,• ~` "' ! 44 1 4 A - Plicated foliation resulting _ from shearing in volcanic rocks along the southwest -~ ~ if bay of Troilus lake.

r ~ ,,r

B- Quartz-filled fractures cropping out 31% miles southwest of Domergue . lake.

C - Pink granite intruding banded hornblende gneiss along the north shore of Chix lake. Plate IV

A-A porphyritic rhyolite dike cutting finely-layered greenstone '4 mile west of the northeast arm of Do- mergue lake.

B-A basic dike intruding granite (gr) 3 miles northwest of Troilus lake along its outlet.

C - Xenoliths of altered hornblende gneiss (x) in granite, 41/8 miles northwest of Troïlus lake. - 17 -

Intermediate to Ultramafic Igneous Rocks

General Features

Sill-like masses of intermediate to ultramafic igneous rocks occur throughout the area underlain by the Pre-Broadback Group. The principal rocks include serpentinized peridotitd, gabbro and diorite., They are quite resistant to erosion and, as a result, are common ridge-forming units. From a quantitative standpoint, gabbro is the most important member of the group. Serpentinized peridotite commonly is associated with the basic rock. Contacts between intrusive rocks and country rock are sharp and, locally, show some shear. The consistent parallelism between the trends of the masses and the regional strike of the adjacent rocks throughout the area indicates that intrusion took place during the latter stages of, or shortly after, deformation.

The mafic and ultramafic members of the group show varying degrees of magnetism. Consequently, their approximate distributions can be inferred with reasonable accuracy from aeromagnetic maps in localities where outcrops are scarce. The high magnetism of the altered peridotite appears to be related, at least in part, to the intensity of serpentinization - a breakdown of primary olivine to serpentine and secondary magnetite. In places, however, small segregations of primary magnetite do occur.

Gradations from gabbro to diorite are rather subtle. In many cases the designation of a specific rock name was arbitrary and depended upon the observer as well as the location of the exposure with respect to a magnetic anomaly. Thus, subsequent investigation may demonstrate that rocks originally referred to as diorites are actually gabbros and vice versa. For example, south of Frotet lake the individual intrusions, besides appearing to be more extensive than those to the north, are indicated chiefly as gabbroic types. Exposures here are generally less common than near Troilus lake. A detailed study of these masses would probably show that they are actually more complex than indicated on the map. Transitional relationships also exist between the gabbro and serpentinized peridotite. A genetic relationship among the members of the group is further indicated by their areal distributions. Many of the intrusions are obviously composite sills. They could well be the surface expression of more extensive intrusion at depth, and there is some indication of this in the apparent coalescence of the masses in certain localities such as to the southwest of Troilus lake.

Altered Peridotite

Excellent exposures of altered peridotite are found at the southwest end of Domergue lake, to the east of Frotet lake, and along an extensive ridge which parallels the eastern shore of Troilus lake. Smaller masses crop out to the northwest of Domergue lake and near the outlet of - 18 -

Troilus lake. The fresh rock is dark bluish to slightly greenish gray and fine grained. Highly serpentinized types have a distinct greasy luster. Weathered surfaces range from bright rusty brown to pale gray, and these colors are almost diagnostic. Originally, the peridotite was composed of olivine and pyroxene with lesser amounts of ore minerals. However, all of it has been converted into rocks in secondary magnesium-bearing minerals.

Antigorite appears as the principal mineral in the felty groundmass and in small crosscutting veinlets. In several of the thin- sections examined the former positions of olivine grains are indicated by ovoidal concentrations of fine-grained, secondary magnetite and serpentine which have definite crystal outlines. Magnesite and talc are also common replacement minerals although they are generally subordinate to the serpentine. Talc occurs in fine platy or fibrous aggregates many of which are subparallel. Many individual grains are bent. The distribution of talc shows some evidence of structural control. Fine- to medium-grained magnesite, largely filling fractures, is concentrated in small pods or in long narrow veinlets. Chlorite is the least common secondary silicate mineral. It appears either in small vermicular aggregates or in thin lenses. Very small amounts of relic olivine and pyroxene grains, sheathed by the previously described secondary minerals, can be found in many specimens. Primary magnetite, pyrrhotite, and pyrite are widely distributed although in some cases the distribution is obviously fracture controlled, indicating that parts of the metallics are late magmatic segregations. Most of the altered ultramafic rocks which are rich in talc and magnesite are favorably located with respect to acid plutonic masses, suggesting that hydrothermal processes rather than deuteric solutions may have produced these minerals. Similarly, the addition of alumina from extraneous sources may account for all or part of the chlorite development.

Gabbro

The gabbro ranges from medium to dark greenish gray and includes both fine- to medium-grained types. It consists of about equal proportions of dark plagioclase and an amphibole-pyroxene mixture. Variable amounts of magnetite and iron sulfides are distributed throughout. Weather- ed surfaces of the gabbro contain scattered dark green prismatic crystals surrounded by dull tan, feldspathic material. In places differential weathering has produced a knobby surface because of the greater resistance of the ferric components.

Thin-section study indicates that amphibole, principally actinolitic hornblende, is the common dark mineral. It occurs either as bent and locally fractured crystals with irregular ends or as randomly distributed microlites. Most of the hornblende is bright bluish green. In the large grains the coloration is uneven, indicating that most, if not all, of the hornblende is a replacement of pyroxene. In some sections the -19 - alteration has produced a mass of fine,shreddy to nearly acicular amphibole grains. Commonly, they are actinolitic rather than hornblendic types. Ves- tigial fragments of clinopyroxene, either augite or diopsidic augite, are rare. Relatively fresh pyroxene is common in the mafic gabbro associated with the altered peridotites. It is pale brown with a slight purplish tint and contains brown, acicular inclusions and dusty opaque material which give rise to a schiller effect. Secondary amphibole, usually bluish to olive- green hornblende, is a replacement along the interfaces of the pyroxene and plagioclase crystals. Hornblende is also an inclusion in plagioclase. Epidote is a common reaction product occurring between magnetite and plagioclase. Some of the mafic gabbro contains above average amounts of magnetite, the distribution of which is suggestive of a late stage segregation. Labra- dorite plagioclase, commonly containing microlitic hornblende, is the chief feldspar. Less calcic plagioclase occurs where zoisite minerals have developed at the expense of the labradorite. Quartz grains appear either singly or in small clusters. Unusually large amounts of quartz generally can be related to the hydrothermal processes associated with the younger acid intrusive rocks. Sulfide minerals, largely pyrite and pyrrhotite, are present as discrete, anhedral crystals or in fine-grained concentrations whose outlines suggest that originally they were single grains. Subhedral magnetite crystals are commonly rimmed by layers of ferric oxide.

Shearing in the gabbro has locally given rise to a rudely foliated schist. Bluish green, poikilitic hornblende, containing inclusions of quartz, plagioclase and opaque minerals, is in places concentrated in subradiating aggregates. Most of the plagioclase has been strongly epidotized. Quartz, sulfides, and opaque oxides occur in subordinate quantities.

Diorite

The diorite was grouped with the mafic and ultramafic rocks rather than with the younger acidic types because of their relations on the ground. Furthermore, much of the diorite shows evidence of alteration similar to that found in the contact zone of granitic rocks. All the alteration may not, however, be the result of external processes. Autometamorphism by residual solutions or shearing is apparently responsible for the changes in bodies of diorite which are not near the acid intrusions. Average specimens of diorite are medium to coarse grained and slightly greenish gray.

Diorite cropping out near the south shore of Frotet lake shows a high degree of alteration. Blue-green hornblende makes up 25-40% of the rock and is strongly epidotized; individual crystals have finely ser- rated terminations. In a few places, chlorite rather than epidote replaces the hornblende. Grains which were originally feldspathic contain little unaltered material; generally, they consist of lath-shaped masses of kaolinite, sericite and, locally, epidote-group minerals. Pyrite and leucoxenized ilmenite are present in accessory amounts. Parts of the exposure area are - 20 - traversed by shear zones usually less than a foot wide. The rock in the immediate vicinity of the zones is fine grained and distinctly schistose, and has a discontinuous compositional banding. Original fragments of diorite have been converted into flaky masses of epidote-clinozoisite, chlorite, and reddish brown biotite. Intercalated with these masses are segregations of fine-grained quartz, rhombohedral carbonate and microcrystalline sulfide minerals. These latter minerals appear to be, at least in part, shear fillings of introduced material.

Diorite is well exposed on the ridges to the southwest and east of Troilus lake, on the peninsula in the northwest section of the lake, and along the northwest shore. Most of it is similar to that which occurs to the south, although secondary biotite is more common. It appears as reddish brown, ragged crystals partly replacing hornblende. Poikilitic varieties contain inclusions of epidote.

Acid Igneous Rocks and Related Types

General Features

Acid to slightly intermediate intrusive rocks in the area include quartz diorite, granodiorite, quartz monzonite, at least two kinds of granite, pegmatite, aplite and porphyritic rhyolite. Rocks of the group are widespread along the margins of the Pre-Broadback band in the southern, southwestern and northwestern parts of the area. Smaller outcrops are found at several localities in the central part. The larger masses are surrounded by contact aureoles of irregular dimensions and variable compositions. Included in these zones are a number of transitional or hybrid rocks as well as vein and replacement deposits. Reconnaissance study indicates that even the small intrusive bodies are composite types. All of the rocks mentioned are apparently members of the same intrusive complex; in fact, they may even represent the later stages of an extensive magmatic period which commenced with the emplacement of the altered peridotite, gabbro and diorite.

Quartz Diorite

Small masses of quartz diorite were observed in central and north-central Tro!lus lake. In both cases the major segment of the intrusions is under the lake. Most of the rock is medium grained, equigranular and slightly greenish-gray; scattered exposures of a fine-grained, leucocratic variety occur along the approximate margins of the intrusive bodies.

Olive-green hornblende is the principal femic mineral. Generally, it shows good evidence of alteration to chlorite and/oi epidote, a feature that is readily visible in many places. The intensity ranges from marginal replacements to nearly complete transformations into fine- grained aggregates of these secondary minerals. Blocky to lath-shaped - 21 - andesine crystals are similarly altered. The chief alteration products are sericite, clinozoisite-zoisite, and kaolinite. Sodic plagioclase accompanies the alteration. Quartz appears as irregular grains interstitial to the other minerals. Some of the large grains show strain shadows. Accessory minerals are sphene, apatite, pyrite and magnetite.

Granodiorite

Medium-grained, light gray hornblende granodiorite crops out along the chain of lakes east of Domergue lake, about midway along the east shore of Regnault lake, and in the contact zone of a small intrusive body north of Domergue lake. Hornblende and, less commonly, biotite are the dark minerals. The hornblende is blue-green to bright olive. Parts of it have been replaced by epidote in some localities although elsewhere dusky green biotite is the chief alteration product. Primary biotite is locally converted into aggregates of chlorite-sphene-magnetite. Muscovite, after biotite, also occurs in these places. Oligoclase and orthoclase are strongly sericitized and kaolinized. Generally, the zonal structure of the plagioclase is evidenced by preferential alteration. Two generations of quartz are present at a number of places. Myrmekitic intergrowths with plagioclase are rare. Fresh microcline accompanies the secondary quartz. Apatite and sphene occur in accessory amounts.

Quartz Monzonite

Exposures of pale tan-weathering hornblende-quartz monzonite are common in the vicinity of Domergue lake. Bluish green hornblende prisms are locally twinned. Marginal and cleavage trace replacements of olive biotite, magnetite and sphene or epidote occur in most specimens, and there are similar alterations to chlorite. Orthoclase and oligoclase, the primary felsic minerals, are clouded by the development of fine-grained sericite and clay. Small amounts of primary quartz are disseminated. Microcline and secondary quartz crosscut and replace some of the primary silicate material. Apatite, allanite(?) and some of the sphene are the accessory minerals.

Granites

Gray Gneissic Granite

Medium-grained, gray subgneissic granite was recorded at several localities northwest of Troilus lake. The foliation parallels the regional structure of the Pre-Broadback rocks. Intrusive relationships indicate that it is older than the pink granite.

The principal femic component is dark olive, strongly pleochroic biotite, much of which is poikilitic with included apatite and quartz. Some of the mica grains contain minute zircon crystals surrounded by dark -22 - brown halos. Green, euhedral hornblende crystals occur in some specimens. The dark minerals are found either concentrated in paper-thin layers or intermixed with the quartzo-feldspathic minerals in bands an inch or more thick. Subhedral orthoclase and oligoclase are partly converted to kaolinite and sericite, with the plagioclase generally the more altered. Accessory amounts of apatite, sphene and opaque minerals are present.

Pink to Tan Granite

A pale pink to tan, medium-grained, equigranular biotite granite is the principal member of the intrusive complex. Extensive masses of it crop out to the northwest of Tro!lus lake and in the southern part of the area. It is the chief rock type in a small stock north of Domergue lake. Shreddy, green biotite is the primary femic mineral, generally occurring either in thin stringers or in small clots. Much of it has been partly altered to chlorite and very fine magnetite. Muscovite, largely derived from the breakdown of biotite, appears either as isolated, irregular crystals or in subradiating aggregates. Concentrations of subhedral to anhedral epidote, surrounded by biotite, are present locally. Orthoclase and oligoclase have been partly converted to a sericite-kaolinite mixture. Inclusions of quartz and mafic minerals appear in some of the plagioclase. Unaltered microcline replaces both feldspars as well as parts of the biotite and muscovite. Two generations of quartz can be recognized: an earlier one of about the same age as the orthoclase and oligoclase, and a later one which crystallized with the microcline. Subhedral sphene, apatite and magnetite are present in accessory amounts.

Pink gneissic granite underlies the ground to the south of Chix lake. The well developed gneissosity, which parallels the regional strike of the surrounding rocks, results from the preferred alignment of discontinuous biotite segregations and the streakiness of the quartzo-feldspathic material. The rock is quite similar in composition to the granite found elsewhere in the area except for the following notable difference. In addition to secondary microcline and quartz, which are widespread in all members of the group, the rock contains unaltered, second-generation orthoclase and plagioclase. Nearly all of the introduced quartz and feldspar is confined to veinlets paralleling the foliation. Many crystals are slightly bent and granulated.

A porphyritic facies of the pink granite crops out near the northeast corner of Frotet lake. Phenocrysts, averaging 1/2 to 1 inch long, consist of perthitic orthoclase with inclusions of sericitized feldspar, sphene and quartz. The matrix feldspar is a mixture of strongly altered plagioclase and orthoclase. Preferential sericitization and kaolinization has brought out the plagioclase zoning. Olive to brown biotite, rich in pleochroic halos with zircon centers, is altered to chlorite. Sphene and magnetite are accessory minerals. Perthitic microcline and secondary quartz replace all the aforementioned minerals in varying degrees. - 23 "-

Pegmatite and Aplite

Pegmatitic and aplitic dikes have intruded all of the previously described rocks. Usually, they are less than a foot wide and rarely are more than 100 feet or so long. Age relations between the aplite and the pegmatite are non-diagnostic.

The pegmatites are typically coarse-textured and consist largely of milky to light gray quartz and alkalic feldspar, parts of which are distinctly reddish or pinkish. The coloring is due to the presence of microcline. Books of medium- to coarse-grained biotite and, in some cases, muscovite occur in certain of the pegmatitic bodies. Many of the dikes have readily discernable bands resulting from a contrast between the fine- to medium-grained border facies and the coarser-grained internal layers.

Aplites are saccharoidal combinations of quartz, light- colored feldspar and small amounts of micaceous minerals. Granophyric and myrmekitic intergrowths of quartz and feldspar are present. A small dike, which intrudes the greenstone 2 1/4 miles northwest of Chix lake, has a rudely layered interior structure because of grain-size differences between successive bands. Moreover, a variation in the degree of alteration seems to coincide with the textural changes since the coarser feldspathic material is generally more highly sericitized than the fine-grained part. Epidote group minerals are the principal fracture filling materials at this locality.

Forphyritic Rhyolite

A few small porphyritic rhyolite dikes occur between the easterly and westerly bays of Domergue lake and to the north of the lake. Since the rhyolite intrudes only the Pre-Broadback Group its exact relative age is uncertain. The rock is fine grained and grayish tan. Orthoclase, the principal feldspar, occurs both as highly altered and corroded phenocrysts and as fine, sericitized crystals in the groundmass. Trace amounts of unaltered microcline also appear as a matrix material. Mottled, bluish green amphibole is the only ferric mineral; its size is intermediate between the common phenocrysts and the groundmass minerals. Quartz is found primarily in the matrix although scattered phenocrysts do occur.

Transitional or Hybrid Rocks

The effects of acidic intrusion can be observed in contact aureoles of irregular dimensions marginal to the igneous masses. For mapping and descriptive purposes only those rocks having more than 10% introduced material are classed as transitional. The textures and mineral compositions of the units within this group are quite varied and are dependent upon the nature of the host and guest materials as well as the intensity of pervasion. - 24 -

In a series of closely spaced outcrops in the area north of Domergue lake the writer was able to trace out a typical sequence of changes from granite through injection gneiss to greenstone with disseminated feldspar and quartz. Along the granite contact, which is gradational, only relic fragments of country rock in varying stages of assimilation can be seen. A short distance beyond, the gneissic rock shows good evidence of lit-par-lit injection of quartz and feldspar along foliation planes. Near the outer limits of the aureole the injection is confined to crosscutting dikes and veinlets. The fringe of the contact zone is marked by greenstone rich in finely dispersed quartz and pink microcline grains. Throughout the aureole, chloritization, epidotization, and minor amphibolization are the most obvious types of alteration seen in the femic minerals, whereas host-rock feldspars are replaced by sericite and clay.

A broadly similar sequence of changes was recorded along the outlet of Tro!lus lake. As the actual granitic contact is approached,the abundance of introduced quartzo-feldspathic material and the degree of host rock change progressively increase. Within a few hundred feet of the intrusive boundary the quartz stringers give way to small dikes and sills of granitic material and, eventually, only small lenses of "greenstone" can be observed here and there in the granite. Farther northwest along the outlet several xenoliths of hornblendic gneiss occur in the gray gneissic granite; both rocks are traversed by pink granite. As mentioned above, the inclusions could be either highly altered remnants of the Pre-Broadback Group or exposed pieces of an older basement complex.

A mottled pink and gray "granite" has developed where pink granite has intruded the gray granite, the quartz monzonite, the granodiorite or the quartz diorite. The mottling, commonly in the form of either disseminated pink feldspar crystals and/or clots of such material, has been accompanied by the development of chlorite and epidote from the primary femic minerals.

The effects of intrusion in the intermediate to ultramafic group of rocks are less apparent than in the other groups mainly owing to an absence of good exposures in key locations. The original amphibole in the gabbro has been converted to a fibrous actinolitic variety or to epidote. Labradorite has been replaced by clinozoisite-zoisite and a more sodic variety of plagioclase. Segregations of carbonate material are commonplace. Talc, magnesite and perhaps some of the chlorite in the altered peridotite may be the result of younger intrusive activity.

Vein and Replacement Deposits

Vein and replacement deposits, resulting from hydrothermal solutions and/or gaseous emanations related to the acidic plutons, are exposed at numerous localities along the margins of the contact. zones. They - 25 - consist largely of smoky to slightly milky quartz. Calcite is a common, although subordinate,non-metallic mineral in a few of the veins. Sulfides are ubiquitous, appearing either as separate grains or in small bleds. Pyrite and pyrrhotite are the chief metallic minerals; chalcopyrite, sphalerite, galena and specularite also occur. Most deposits are structurally controlled. Rarely does one find a fracture that does not contain some of the material mentioned. Replacement deposits, commonly related to minor drag-folds, are less abundant than the fracture fillings. Dimensions of individual bodies vary a great deal although most are only an inch or so thick and 5 to 10 feet long. A few quartz-iron sulfide veins, 1 foot to 2 feet wide and nearly 100 feet long, crop out along the shores of Troilus lake. Fracture-filling deposits have well defined contacts with the adjacent rocks and fairly uniform widths along strike. Some of the larger bodies, however, are branching and sinuous. Neither vein nor replacement deposits appear to favor a particular host rock.

Rudely tabular deposits of slightly ferroandolomite occur in the vicinity of Frotet lake. A 6 1/2-foot, steeply dipping mass of rusty brown weathering dolomite is exposed near the water's edge on the south shore of the lake. The rock is a fine- to medium-grained mosaic of dolomite containing innumerable quartz- and sulfide-bearing stringers, many of which have a preferential orientation parallel to the margins of the body. Discontinuous bands of chlorite-dolomite-sericite schist are scattered through the mass. The contacts with the overlying and underlying greenstone are gradational, being marked by 3- to 4-foot zones rich in carbonate and micaceous minerals. These transition zones are highly sheared. Thinner and less extensive concentrations of this type of material crop out on the nearby islands. Although originally they were thought to be carbonate-rich beds within the Pre-Broad- back Group (Murphy, 1962, pp. 3-4), these deposits are now interpreted as shear fillings. Their appearance in only the more highly deformed rocks of the area, as well as a decided parallelism between their attitudes and those of nearby shear zones, can be most easily accounted for by an epigenetic origin.

A partial, semi-quantitative analysis of typical carbonate vein material is listed in Table 2: - 26 -

Table 2

PARTIAL SEMI-QUANTITATIVE ANALYSIS OF TYPICAL

CARBONATE VEIN MATERIAL

Calcium 10 - 50 Magnesium 5 20 Iron 1 - 5 Manganese 0.005 - 0.05 Silicon, Sodium 0.001 . - 0.01 Strontium Aluminum 0.005 - 0.05 Lead, Copper 0.001 - 0.01 Rare Earths not detected

Analyst Z. Katzendorfer, Quebec Department of Natural Resources

Basic Dikes

Reddish brown weathering basic dikes cut the granites 3 miles northwest of Tro!lus lake along its outlet. On the accompanying geologic map these intrusions have been indicated as a single body although they vary from a swarm of closely spaced dikes, averaging less than 15 feet wide, to a single mass 150 to 200 feet across with scattered subsidiary dikes along its margins. The dike system was traced for nearly 2 miles along strike. Similar basic dikes are widely known to the south of the map-area (Kindle and Riley, 1958).

The small dikes are composed of dark greenish gray to nearly black, holocrystalline basalt. Portions of the basalt are porphyritic. Subhedral, corroded plagioclase, ranging from calcic andesine to sodic labradorite, occurs both as phenocrysts and matrix material. Anhedral augite, the chief dark mineral, although some orthopyroxene is present, appears as a common phenocrystic mineral and in the matrix. Some of the pyroxene has been converted either to blue-green hornblende or to a very fine-grained mixture of chlorite and hornblende. Spotty alterations of plagioclase to sericite and kaolinite were noted in a few sections. Similarly, other portions of the feldspar, in addition to the primary femic minerals, have been altered to epidote-group minerals. Late stage, anhedral quartz is widespread. Pyrrhotite and titaniferous magnetite, partly converted to leucoxene, are the accessory components.

The large dikes generally show a well developed transition in grain size from basalt and porphyritic basalt along the chilled margins to diabase in the centers. In addition to having a subophitic texture, the mineralogy of the diabasic portion differs slightly from the basalt in some -27- respects. Nearly all the plagioclase falls within the sodic labradorite range. Furthermore, some of the clinopyroxene appears to be pigeonite rather than augite.

CENOZOIC

Pleistocene and Recent

The map-area is part of an extensive, imperfectly developed till plain which covers much of this part of Quebec. Where deposition by the ice cap was incomplete the glacially modified topography is primarily controlled by the bedrock. The features which make up the till plain are both glacial and glacio-fluviatile. In most localities the two are so intermingled that it is difficult to separate them.

The southern, southwestern and northwestern parts of the area are covered by a fairly continuous blanket of glacial material. Except for several prominent eskers and scattered morainal ridges, most of the glacial debris lacks topographic structure. The drift lithology is related to the local bedrock since most of the material comprising it was derived from nearby sources. This is particularly true of the angular boulders that commonly appear in small concentrations. Such concentrations have been recorded on the accompanying geologic map as they give some idea of the bedrock composition in places where the overburden is continuous. Recognizable deposits of moraine are confined principally to the preglacial valleys. Eskers, some of which are rather large and well developed, are generally discontinuous. One of them traverses the southeast section of the area and can be followed discontinuously beyond the map limits for nearly 50 miles. Evidence of ice scouring is uncommon. Rocks cropping out near Domergue lake and along the shores of Frotet lake contain lunate fractures which indicate that the direction of ice movement was S.40°W. paralleling the southwest grain of the regional topography. Glacial striations are common on the scoured bedrock in the northwest part of Tro!lus lake. Two sets of glacial striae were found on an island near the northwest corner of the lake. The older set trends S.45°E. and is cut by a younger one that strikes S.400W.

Post-glacial features are ill-defined since the recent drainage has not yet become integrated with the surface conditions. Generally, the stream courses wander into and out of the numerous lakes and have short tributaries. Interstream areas are swampy because of the damming effects of the glacial deposits. The large lakes and waterways that are in contact with the bedrock are exceptions. Many of them have forms which seem to indicate structural and bedrock control. A number of beaches fringing the large lakes are overlain by linear accumulations of boulders and cobbles resulting from ice heaving and the lowering of lake levels during times of low rainfall. - 28 -

STRUCTURAL GEOLOGY

Regional Structure

The Pre-Broadback rocks are part of an extensive volcanic- sedimentary-greenstone band which extends from Lake Mistassini on the east to Lake Evans and perhaps beyond, on the west. The width of the band is quite irregular,ranging from a mile or so to as much as 30 miles. Its sinuous character appears to be the result of erosion and partial engulfment by younger igneous intrusions. Similar trough-like bands of these rocks are found to the south near Chibougamau and to the north along Eastmain river.

Generally speaking, the non-intrusive rocks strike east or nearly so; however, in places, northeasterly or northwesterly structures are evident. Northeasterly structures are common near the eastern end of the Lake Evans - Lake Mistassini band. They reflect the influence of the Gren- ville trend which dominates the Precambrian rocks between Lake Mistassini and the St. Lawrence. Elsewhere, local effects of granitic intrusion have complicated the structural pattern.

Local Structure

Folds

The attitudes of foliation and bedding planes differ throughout the area. North of Frotet lake they strike northeast and are either steeply dipping to the northwest or vertical. In the vicinity of the lake they swing to nearly east-west positions. The dips here are vertical although steep dips to the south are common along the south shore of the lake. This attitude prevails for a short distance to the south and is gradually superseded by northwesterly-striking foliations with vertical to steep southerly and, in some places, northerly dips. Foliations strike about east and dip to the north near the southern border. An obvious north to northeasterly structural trend is present near the western limits of the area. In all the sections mentioned, the abrupt and local reversals in dip suggest that tight, nearly isoclinal folds are present. However, the absence of easily recognizable marker beds in the Pre-Broadback Group makes it difficult to delineate fold axes. Intense shearing, especially near Frotet lake, has produced secondary foliations which depart markedly from the general trends mentioned.

The foregoing structural pattern indicates that the Pre- Broadback rocks have been complexly deformed. Unfortunately, only a small number of fold axes could be recognized. Two roughly east-trending synclines, separated by a small anticline, were identified a short distance north of Chix lake near the southern limits of the Pre-Broadback Group. The most southerly downwarp is probably continuous with the syncline between Guiguet -29- and Oudiette lakes. Two northerly-trending folds occur to the west of Chix lake. At least 10 folds, several of which are discontinuous, have been recognized to the north of Frotet lake. All trend northeast. This unequal distribution of recognized folds within the area is more apparent than real since exposures of bedrock are more abundant to the north of Frotet lake than to the south of it. A more detailed investigation would uncover a number of additional folds in any one section of the area because, in all probability, local marker beds would be recognized. Over much of the area fold structures are not evident on the ground although photolinear study has outlined what appear to be the noses of plunging folds. Good examples can be seen to the west of Domergue lake and to the northwest of Tro!lus lake.

The over-all structural pattern of the area indicates the presence of a broad fold whose east-west axis is approximately coincident with Frotet lake. Aeromagnetic maps support this interpretation. South of Frotet lake the dominant trend of the rocks is southeast to east, whereas to the north of the lake it is southwest. Moreover, there is a definite increase in the intensity of cataclastic deformation as one approaches this apparent axis. The presence of a gabbroic phacolith, based on limited exposures but a reasonably definite magnetic anomaly, indicates that the fold developed prior to the emplacement of the ultramafic to intermediate rocks. Numerous, tightly compressed secondary flexures are superimposed on the broad fold.

Linear Features

Cataclastic deformation accompanied the folding but it is hard to relate the individual breaks to specific folds. Many of the more extensive linear structures, though difficult to detect on the ground, are quite apparent on aerial photographs. They appear either as tonal lineaments in the vegetation and soil cover or as topographic alignments.

Shears are evident throughout the area as narrow, linear to slightly curved zones of crushed and highly fractured rock. Commonly, these zones are filled with vein matter such as quartz, feldspar, carbonates, and ore minerals. Shear zones range in width from less than a foot to several feet with the wider zones generally containing highly altered, angular fragments of country rock. Most of the breaks could be traced for only a few tens of feet before they passed under the overburden. A distinct parallelism exists between the trends of recorded shear zones and the prominent lineaments seen on aerial photographs, suggesting that, at least in places, they are one and the same. An excellent example of this relationship is just south of Domergue lake.

Faults are difficult to recognize because of the absence of distinct reference beds within the Pre-Broadback. Group and the lower relief throughout much of the area. Two high-angle gravity faults were observed near the east end of Frotet lake. Slickenside measurements indicate that the net - 30 - slip was normal to the strike of the faults. Local bands of brecciated and mylonitized rock, indicative of faulting, occur at numerous places near Frotet lake. These zones,as well as the observable faults,parallel nearby photogeologic lineaments suggesting that faults are commonplace.

Joints are steeply dipping to vertical and occur either singly, in pairs, or in groups of three or more. In general, they trend northeasterly or northwesterly. At several localities in the area joints appear in close association with small granitic dikes which appear to be joint fillings. This relationship indicates both pre-intrusive and post- intrusive joint development.

ECONOMIC GEOLOGY

Metallic Deposits

Interest in the Frotet Lake - Troilus Lake area was initially aroused by the discovery of copper- and nickel-bearing boulders in the summer of 1958. Since that time it has waxed and waned,depending upon the number of discoveries made during any one field season. The apparent widespread distribution of metallic minerals offers a number of target localities. Promis- ing surface showings of base metals discovered in the past few years alone. attest to the area's potential. From a purely economic standpoint the geo- graphic location of the area, less than 100 miles from Chibougamau, further enhances its value because of the relatively low exploration costs.

The metallic mineralization seems to be related to two separate periods of metallization, but it is difficult to say which of the two has the greater economic potential. The earlier period is marked by the formation of iron and nickel sulfides either as disseminations or as segregations during the consolidation of the basic to ultramafic igneous rocks. Pyrite and pyrrhotite are by far the most common minerals although minor pentlandite does occur. Generally, the sulfides are sparsely disseminated; however, minute blebs and small fracture fillings are found locally. A series of dimethyl glyoxime spot tests failed to reveal significant amounts of nickel. Although chromite was not positively identified, a detailed study of the ultramafic bodies would be justified to determine their value as a potential source of this mineral.

Solutions and/or gaseous emanations related to the younger igneous activity gave rise to widespread mineralization along the fringes of the contact zones and beyond. Rarely does one find a fracture in these areas that does not carry some quartz, sulfides, and occasional calcite. Pyrite is exceptionally common, whereas sparse amounts of chalcopyrite were recorded in a number of localities, especially just north of Domergue lake, in the vicinity of Chix lake and along the shores of Troilus lake,as well as to the northwest of it. Locally, pyrrhotite is associated with the pyrite. - 31 -

Clusters of galena and sphalerite crystals,together with oxidized molds of these minerals,were found in a few small shears immediately north of Domergue lake. Malachite coats some of the shear surfaces in this general location. Fine-grained specularite occurs in some of the greenstone along the southeast arm of Frotet lake. Molybdenite-bearing float was seen along the west shore of Troilus lake, north of the entrance to the southwest bay. The host rock is a fine-textured, light-colored facies of the quartz diorite. Molybdenite grains are fine and evenly distributed through the rock.

A limited amount of reconnaissance geochemical work was undertaken in conjunction with the geologic study to the south of Frotet lake during 1961. It consisted largely of soil and water testing for total heavy metals although stream sediments were analysed in selected localities. Commercially prepared field kits were used for all tests. In view of the broad nature of the work only a few very generalized opinions can be given. Approximately 18 above-background values were recorded in the soils covering the area between Frotet and Domergue lakes; only four were found to the south, two of which occur in the vicinity of Chix lake. The actual significance of this distribution of values is difficult to assess, however; the thickness of the glacial cover is undoubtedly a contributory factor. Glacial deposits are continuous to the south of Domergue lake. Water testing may prove to be a useful prospecting tool in this part of the province if the veneer of glacial material is not too thick. Above normal water values were obtained at a dozen or so sites north of Domergue lake. In practically every case the abnormal concentration of heavy metals could be traced with reasonable cer- tainty to a nearby mineralized vein. Stream sediment. values were erratic and did not correlate well with the results of the soil and water tests.

Non-metallic Deposits

Asbestos

Deuteric and/or hydrothermal alteration of the ultramafic intrusive bodies has produced rocks which are rich in serpentine. Generally the serpentine is fine grained and occurs as a felty groundmass - although locally parts of it are concentrated in fractures. Reconnaissance examinations failed to disclose chrysotile deposits that would be considered of economic grade by present-day standards. However, just the presence of altered peridotitic rocks, which account for 93% of the world production of asbestos, is very significant. Detailed studies may reveal commercial deposits of asbestos. - 32 -

Sand and Gravel

The unconsolidated glacial deposits constitute an important potential source of material for construction purposes. No attempt was made by the writer to evaluate the engineering properties of the materials. Under certain conditions the well-sorted sands and gravels of the eskers might be used as concrete aggregate. Till, constituting the bulk of the glacial deposits, could be used either as fill or as a surfacing material for secondary roads.

Pegmatite Dikes

The only pegmatite dikes found in the area are simple types although more complex ones are known to occur in this region. Lithium-bearing dikes have been studied southwest of the area, a short distance north of Assinica lake. They are large, having widths measurable in tens of feet, and seem to be concentrated in a swarm. Pale green spodumene is the principal lithium mineral although small amounts of triphylite are also present. Quartz, a variety of alkalic feldspars and radiating aggregates of tourmaline make up the remainder of the dike rock. Beryl crystals occur in a few of the dikes. Similar pegmatites have been reported at McAdam lake, immediately west of the map-area.

The presence of complex dikes in the region is encouraging. Although only lithium-rich pegmatites have been recognized so far, there is a good possibility that other types may also occur. It is common knowledge that such intrusives are important sources of a variety of industrial minerals. -33-

REFERENCES CITED

BELL, R. (1902) - Report on the Geology of the Basin of Nottaway River, with a Map of the Region: Geol. Sur. Canada, Ann. Rept., Vol. XIII, 1900, Pt. K, Map 702 (777)

COOKE, H.C. (1914) - An Exploration of the Headwaters of the Broad- back or Little Nottaway River, Northwestern Quebec, with Map No. 2284: Geol. Sur. Canada, Sum. Rept., 1912, pp. 337-341.

DRESSER, J.A. (1944) - Geology of Quebec, Vol. II: Descriptive Geology: and DENIS, T.C. Que. Dept. Mines Geol. Rept. 20, 544 p.

KINDLE, E.D. (1958) - Brock River, Abitibi and Mistassini Territories and RILEY, G.C. and Abitibi County, Quebec: Geol. Sur. Canada, Map 106OA.

MOYER, P.T. (1961) - Preliminary Report on St-Urcisse Area, Mistassini Territory: Que. Dept. Nat. Res. Prelim. Rept. 460.

M'Ji?PHY, D.L. (1962)- Preliminary Report on Frotet Lake Area, Abitibi and Mistassini Territories: Que. Dept. Nat. Res. P.R. No. 476.

MURPHY, D.L. (1963) Geology of the Troilus Lake Area, Abitibi Ter- ritory: Que. Dept. Nat. Res. P.R. No. 508.

SHAW, G. (1940a)- Assinica Lake, Que: Geol. Sur. Canada, Paper 1+0-20, Prelim. Map.

SHAW, G. (1940b) -Mishagomish Lake, Quebec: Geol. Sur. Canada, Paper 40-21, Prelim. Map.

ALPHABETICAL INDEX

,Paqe a e Actinolite 9,14 Dacite 6,9 Activity in area 3 Denis, T.C. - Allanite 21 Ref. to work by 6 Aluminum 26 Dikes 23,26,32 Amphibole 10,15,18,23,24 Diorite 6,17,19,20 Amphibolite 15,16 Dresser, J.A. - Andesite 6,9,10,26 Ref. to work by 6 Antigorite 18 Drouin, Eugéne - Apatite .. 9,10,12,14,16,21,22,23 Cook for field party 3 Aplite 20 Argillite 6,11,13 Epidote ... 9,10,11,12,16,19,20,23 Augite 19,26 Atkins, W.M. - Feldspar 11,12,13,22,23 Junior assistant 3 Ferric oxide 13 Ferroandolomite 25 Basalt 6,9,10 Flow rocks 8 Bell, R.- Formations, Table of 8 Ref. to work by 3 Fur-bearing animals 4 Beryl 32 Biotite .. 10,11,12,16,20,21,22,23 Gabbro 6,17,18,20 Boiteau, Georges - Gagnon, J.E. - Acknowledgement to 3 Canoeman for party 3 Galena 31 Calcite 11,15,25 Gauthier, Florent - Calcium 26 Junior assistant 3 Canoe travel 2 Glacial cover 5 Carbonate 9,11,15 Glacial striae 27 Carlson, E.H. Gneiss 16 Assistant party chief 3 Granite 20,22,24 Chalcopyrite 30 Granodiorite 20,21 Chert 11 Graywacke 6,12 Chiasson, Dave - Graywacke-type rocks 11,12 Canoeman for party 3 Greenstone 7,14,15 Chlorite 9,10,11,12,13,18,20,22,24 Chrysotile 31 Hornblende 10,11,15,16,18,19,20,21 Clinozoisite 9,11,15,20,21 Hunting Technical and Conglomerates 6 Exploration Services 3 Cooke, H.C. - Huronian rocks 6 Ref. to work by 3 Copper 1,26 Ilmenite 9,11,19

-35-

page Lam Intrusive rocks 20 Oligoclase 21,22,23 Iron 1,26 Olivine 18 Iron sulfides 18 Orthoclase 11,12,21,22 Orthopyroxene 26 Kaolinite 9,15,21,22 Oxides 15,19 Katzendorfer, Z. - Analyst 26 Pegmatite 20,23,32 Keewatin-type volcanics 6 Peridotite 6,17,18,20 Kindle, E.D. - Plagioclase 9,10,11,12,16 ,19,26,27 Ref. to work by 3,6,7,26 Phyllites 16 Post-glacial features 27 Labrador tea 4 Pre-Broadback rocks 28 Labradorite 24,26 Precipitation in area 5 Lafrance, Joseph - Pyrite ... 9,11,12,18,19,21,24,30 Cook for party 3 Pyroclastic rocks 10 Lamontagne, Clement Pyroxene 16,18,19,26 Junior assistant 3 Pyrrhotite 18,24,26,30 Lead 26 Leucoxene 9,11,26 Quartz 9,11,12,13,15,16,19,21 Limonite 9,12,14 23,32 Lithium 32 Quartz diorite 20 Quartzite 6 Magnesite 18,24 Quartz monzonite 20,21 Magnesium 26 Magnetite 9,10,11,12,14,18,19 Rare earths 26 21,22,26 Rhyolite 6,20,23 Malachite 31 Riley, G.C. - Manganese 26 Ref. to work by 3,6,7,26 Meanscum, Jimmy - Ritter, C.J. - Canoeman for party 3 Senior assistant 3 Mica 9,11,21 Microcline 21,22,23 Sandstone 13 Mineralization 1,30 Schists 7 Mclybdenite 31 Sedimentary rocks 6,11,14 Mondoloni, Guy - Semple, Ian - Junior assistant 3 Senior assistant 3 Moyer, P.T. - Sericite .... 9,10,11,12,15,21,22 Ref. to work by 3 Shaw, G. - Muscovite 21,22,23 Ref. to work by 3 Murphy, D.L. - Silicon 26 Ref. to previous work by •• 3,25 Siltstones 11 Slate 11,13 Nickel 1 Sodium 26 -36-

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Specularite 31 Timiskaming-type rocks 6 Sphagnum moss 4 Tourmaline 32 Sphalerite 31 Traversing in area 2 Sphene 9,16,21,22 Triphylite 32 Spodumene 32 Tuff 8,10,12 Strontium 26 Structural attitude of rocks ... 7 Volcanic rocks 8,11,14 Subgraywacke 12 Sulfides 1,15,19,25 Zircon 10,16 Talc 18,24 Zoisite 21 -