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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 by 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 on FROTET LAKE - TROÎLUS LAKE AREA Abitibi and Mistassini Territories by 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 vol- canic units, partly or completely altered to greenstone, phyllite, schist and gneiss, which have been invaded by igneous intrusions ranging in composi- tion 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 ultra- mafic 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 north- ern 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 as- sistants. Eugene Drouin and Dave Chiasson were employed as cook and canoe- man, 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 inves- tigation 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.

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