THESE TERMS GOVERN YOUR USE OF THIS DOCUMENT

Your use of this Ontario Geological Survey document (the “Content”) is governed by the terms set out on this page (“Terms of Use”). By downloading this Content, you (the “User”) have accepted, and have agreed to be bound by, the Terms of Use.

Content: This Content is offered by the Province of Ontario’s Ministry of Northern Development and Mines (MNDM) as a public service, on an “as-is” basis. Recommendations and statements of opinion expressed in the Content are those of the author or authors and are not to be construed as statement of government policy. You are solely responsible for your use of the Content. You should not rely on the Content for legal advice nor as authoritative in your particular circumstances. Users should verify the accuracy and applicability of any Content before acting on it. MNDM does not guarantee, or make any warranty express or implied, that the Content is current, accurate, complete or reliable. MNDM is not responsible for any damage however caused, which results, directly or indirectly, from your use of the Content. MNDM assumes no legal liability or responsibility for the Content whatsoever.

Links to Other Web Sites: This Content may contain links, to Web sites that are not operated by MNDM. Linked Web sites may not be available in French. MNDM neither endorses nor assumes any responsibility for the safety, accuracy or availability of linked Web sites or the information contained on them. The linked Web sites, their operation and content are the responsibility of the person or entity for which they were created or maintained (the “Owner”). Both your use of a linked Web site, and your right to use or reproduce information or materials from a linked Web site, are subject to the terms of use governing that particular Web site. Any comments or inquiries regarding a linked Web site must be directed to its Owner.

Copyright: Canadian and international intellectual property laws protect the Content. Unless otherwise indicated, copyright is held by the Queen’s Printer for Ontario.

It is recommended that reference to the Content be made in the following form: , . ; Ontario Geological Survey, , p.

Use and Reproduction of Content: The Content may be used and reproduced only in accordance with applicable intellectual property laws. Non-commercial use of unsubstantial excerpts of the Content is permitted provided that appropriate credit is given and Crown copyright is acknowledged. Any substantial reproduction of the Content or any commercial use of all or part of the Content is prohibited without the prior written permission of MNDM. Substantial reproduction includes the reproduction of any illustration or figure, such as, but not limited to graphs, charts and maps. Commercial use includes commercial distribution of the Content, the reproduction of multiple copies of the Content for any purpose whether or not commercial, use of the Content in commercial publications, and the creation of value-added products using the Content.

Contact:

FOR FURTHER PLEASE CONTACT: BY TELEPHONE: BY E-MAIL: INFORMATION ON The Reproduction of MNDM Publication Local: (705) 670-5691 Content Services Toll Free: 1-888-415-9845, ext. [email protected] 5691 (inside Canada, United States) The Purchase of MNDM Publication Local: (705) 670-5691 MNDM Publications Sales Toll Free: 1-888-415-9845, ext. [email protected] 5691 (inside Canada, United States) Crown Copyright Queen’s Printer Local: (416) 326-2678 [email protected] Toll Free: 1-800-668-9938 (inside Canada, United States)

LES CONDITIONS CI-DESSOUS RÉGISSENT L'UTILISATION DU PRÉSENT DOCUMENT.

Votre utilisation de ce document de la Commission géologique de l'Ontario (le « contenu ») est régie par les conditions décrites sur cette page (« conditions d'utilisation »). En téléchargeant ce contenu, vous (l'« utilisateur ») signifiez que vous avez accepté d'être lié par les présentes conditions d'utilisation.

Contenu : Ce contenu est offert en l'état comme service public par le ministère du Développement du Nord et des Mines (MDNM) de la province de l'Ontario. Les recommandations et les opinions exprimées dans le contenu sont celles de l'auteur ou des auteurs et ne doivent pas être interprétées comme des énoncés officiels de politique gouvernementale. Vous êtes entièrement responsable de l'utilisation que vous en faites. Le contenu ne constitue pas une source fiable de conseils juridiques et ne peut en aucun cas faire autorité dans votre situation particulière. Les utilisateurs sont tenus de vérifier l'exactitude et l'applicabilité de tout contenu avant de l'utiliser. Le MDNM n'offre aucune garantie expresse ou implicite relativement à la mise à jour, à l'exactitude, à l'intégralité ou à la fiabilité du contenu. Le MDNM ne peut être tenu responsable de tout dommage, quelle qu'en soit la cause, résultant directement ou indirectement de l'utilisation du contenu. Le MDNM n'assume aucune responsabilité légale de quelque nature que ce soit en ce qui a trait au contenu.

Liens vers d'autres sites Web : Ce contenu peut comporter des liens vers des sites Web qui ne sont pas exploités par le MDNM. Certains de ces sites pourraient ne pas être offerts en français. Le MDNM se dégage de toute responsabilité quant à la sûreté, à l'exactitude ou à la disponibilité des sites Web ainsi reliés ou à l'information qu'ils contiennent. La responsabilité des sites Web ainsi reliés, de leur exploitation et de leur contenu incombe à la personne ou à l'entité pour lesquelles ils ont été créés ou sont entretenus (le « propriétaire »). Votre utilisation de ces sites Web ainsi que votre droit d'utiliser ou de reproduire leur contenu sont assujettis aux conditions d'utilisation propres à chacun de ces sites. Tout commentaire ou toute question concernant l'un de ces sites doivent être adressés au propriétaire du site.

Droits d'auteur : Le contenu est protégé par les lois canadiennes et internationales sur la propriété intellectuelle. Sauf indication contraire, les droits d'auteurs appartiennent à l'Imprimeur de la Reine pour l'Ontario. Nous recommandons de faire paraître ainsi toute référence au contenu : nom de famille de l'auteur, initiales, année de publication, titre du document, Commission géologique de l'Ontario, série et numéro de publication, nombre de pages.

Utilisation et reproduction du contenu : Le contenu ne peut être utilisé et reproduit qu'en conformité avec les lois sur la propriété intellectuelle applicables. L'utilisation de courts extraits du contenu à des fins non commerciales est autorisé, à condition de faire une mention de source appropriée reconnaissant les droits d'auteurs de la Couronne. Toute reproduction importante du contenu ou toute utilisation, en tout ou en partie, du contenu à des fins commerciales est interdite sans l'autorisation écrite préalable du MDNM. Une reproduction jugée importante comprend la reproduction de toute illustration ou figure comme les graphiques, les diagrammes, les cartes, etc. L'utilisation commerciale comprend la distribution du contenu à des fins commerciales, la reproduction de copies multiples du contenu à des fins commerciales ou non, l'utilisation du contenu dans des publications commerciales et la création de produits à valeur ajoutée à l'aide du contenu.

Renseignements :

POUR PLUS DE VEUILLEZ VOUS PAR TÉLÉPHONE : PAR COURRIEL : RENSEIGNEMENTS SUR ADRESSER À : la reproduction du Services de Local : (705) 670-5691 contenu publication du MDNM Numéro sans frais : 1 888 415-9845, [email protected] poste 5691 (au Canada et aux États-Unis) l'achat des Vente de publications Local : (705) 670-5691 publications du MDNM du MDNM Numéro sans frais : 1 888 415-9845, [email protected] poste 5691 (au Canada et aux États-Unis) les droits d'auteurs de Imprimeur de la Local : 416 326-2678 [email protected] la Couronne Reine Numéro sans frais : 1 800 668-9938 (au Canada et aux États-Unis)

ONTARIO DEPARTMENT OF MINES

HON. G. C. WARDROPE, Minister D. P. DOUGLASS, Deputy Minister J. E. THOMSON, Director, Geological Branch

Geology of Eastern Lac des Mille Lacs Area

District of Thunder Bay

By L. KAYE

Geological Report 48

TORONTO 1967 Crown copyrights reserved. This book may not be reproduced, in whole or in part, without the permission of the Ontario Department of Mines.

Publications of the Ontario Department of Mines and pricelists

are obtainable through the

Publications Office, Ontario Department of Mines Parliament Buildings, Queen©s Park Toronto, Ontario, Canada.

Orders for publications should be accompanied by cheque, or money order. payable in Canadian funds to Treasurer of Ontario. Stamps are not acceptable.

2,000—Ell—1967 CONTENTS PAGE Abstract...... iv Introduction...... l Present Geological Survey...... l Acknowledgments...... 2 Means of Access...... 2 Previous Geological Work...... 3 Topography and Drainage...... 3 Natural Resources and Development...... 3 General Geology...... 3 Age Correlation...... 4 Table of Formations...... 5 Metasedimentary Group...... 6 Metavolcanic Group...... 10 Acid Metavolcamcs...... 10 Basic Metavolcanics...... 11 Acid Hypabyssal Intrusive Rocks...... 16 Early Basic Intrusive Rocks...... 17 Granitic Intrusive Rocks...... 18 Northern Granodiorite Complex...... 18 Southern Granite Complex...... 19 Migmatitic Rocks...... 19 Mafic Xenolith-GranitJc Complexes...... 19 Amphibplite-Granitic Gneiss Complexes...... 19 Late Basic Intrusive Rocks...... 20 Pleistocene...... 20 Recent...... 21 Structural Geology...... 22 Folds...... 22 Faults...... 24 Economic Geology...... 25 Recommendations for Prospectors...... 27 Selected References...... 28 Index...... 29

Figure and Photographs PAGE Figure l Key map showing location of report-area...... iv Photo l Intraformational conglomerate (Metasedimentary Group); Bolton Bay...... 7 Photo 2 Thinly bedded metasediments; Bolton Bay...... 7 Photo 3 Weathered joints in tuffaceous metasediments; Bolton Bay...... 8 Photo 4 Migmatitic biotite-quartz paraschist; boudinage structures; erratic block...... 9 Photo 5 Silicic flow breccia; north acid metavolcanic band...... 11 Photo 6 Silicic flow breccia; south acid meta volcanic band...... 12 Photo 7 "Pseudo-pillows"; on island southeast of Hook Island...... 13 Photo 8 Flattened vesicular pillow lavas; on island south of Rabbit Island...... 14 Photo 9 Flattened pillow structures; on mainland east of Hook Island...... 15 Photo 10 Undeformed pillow lavas; Lac des Mille Lacs...... 15 Photo 11 Highly sheared basalt (chloritic schist); Bolton Bay...... 16 Photo 12 Gabbroic xenolith intruded by granodiorite; island north of Rabbit Island...... 20 Photo 13 Pleistocene glacial deposits; Pine Point, Lac des Mille Lacs...... 21 Photo 14 Folded bedding in metasediments (Metasedimentary Group); Bolton Bay...... 23 Photo 15 Large cleavage mullions in biotite-quartz paraschist...... 23 Photo 16 Tight fold in biotite-quartz paraschist; Kashabowie Lake...... 24 Photo 17 Breccia zone; Bolton Bay gold prospect...... 26

Geological Maps (back pocket) Map 2104 (coloured,) Bolton Bay Sheet, Lac des Mille Lacs. Scale, l inch to J^ mile. Map 2105 (coloured) Portage Bay Sheet, Lac des Mille Lacs. Scale, l inch to ^ mile.

in ABSTRACT This report describes the general, structural, and economic geology of the eastern Lac des Mille Lacs area, District of Thunder Bay.

Figure 1—Key map showing location of map-area. Scale 1 inch to 50 miles.

The bedrock is entirely Precambrian; it is overlain, with great uncon formity, by extensive Pleistocene glacial deposits. The oldest rocks, consisting mainly of biotite-quartz paraschists, are placed in a metasedimentary group that was formerly classified as Couchi- ching in age. The upper part of this group contains an intraformational conglomerate, a banded magnetite iron formation, and tuffaceous sedi mentary rocks, which grade into or interfinger with silicic tuffs belonging to stratigraphically younger metavolcanics. The rocks of the Metavolcanic Group that were formerly classified as Keewatin in age consist of acid and basic ^flows and pyroclastic rocks, and are intruded by acid hypabyssal and basic intrusive rocks. Granitic rocks form two major complexes: an early syntectonic northern granodiorite batholith, and a late-tectonic to post-tectonic southern granite complex. The late granite is injected lit par lit into biotite-quartz paraschist ("Couchiching") to form migmatite, which underlies much of the area south of the Quetico Fault. The metasediments and metavolcanics are isoclinally folded through out; some outcrops are affected by small-scale second folds. A major "break", the Quetico Fault, strikes east-west across the area and, in the west, separates the Metasedimentary Group from the Metavolcanic Group. No mineral production has been recorded from the area, but there has been some investigation of gold and iron (magnetite) occurrences.

IV Geology of Eastern Lac des Mille Lacs Area District of Thunder Bay

By L. Kaye1

INTRODUCTION

This report describes the geology of an area about 300 square miles in the District of Thunder Bay. It includes the eastern part of Lac des Mille Lacs, and is bounded approximately by latitudes 48042©N and 48056©N, and longitudes 900ll©W and 90038©W. The centre of the report-area is about 65 miles north west of the cities of Fort William and Port Arthur. The report-area straddles a belt of metamorphosed sedimentary and volcanic rocks that extends 140 miles westward to the Rainy Lake Basin. West of the report-area, the belt includes the gold deposits at Sapawe and the iron deposits at Atikokan. No mineral production has been recorded within the area mapped, but in 1938 T. L. Tanton, on G.S.C. Maps 338A and 432A, reported gold to have been found in three locations. During the 1964 field season, redis covery of gold at one of these locations on Bolton Bay was the focus of restaking by several prospectors. Records of prospecting in the early part of the century are lacking. In 1953 the Resources Development Department of Canadian Pacific Railway Co. prospected and geologically mapped part of the Lac des Mille Lacs greenstone belt. In 1954, Block No. 2, the property of Abitibi Power and Paper Company Limited2, was geologically mapped for the company by C. C. Ruston and Associates, who also made a ground geophysical survey and assessment of the iron formation (magnetite) on the property. In an area in the metavolcanics south of Rabbit Island, exploration that included ground geophysical surveys and diamond-drilling was carried out by Phelps-Dodge Corporation Limited in 1962.

Present Geological Survey. The present survey was made in the summer of 1964. The most detailed mapping was along the volcanic-sedimentary belt. A study of the air photographs for the area yielded much accurate information on the positions and accessibility of rock outcrops. Because the rock outcroppings along the shoreline of Lac des Mille Lacs are numerous, detailed mapping of exposures was comparatively easy. The intricate indented northern shoreline of the lake permitted rapid reconnaisance mapping of the granitic rocks that underlie the northern third of the report-area. Pace-and-compass traverses inland were conducted across-strike at ^-mile intervals in the metavolcanics, and at ^-mile intervals in the metasedimentary 1 Department of Geology, Carleton University, Ottawa. Manuscript received by Chief Geologist 7 April 1965. 2The name of this company was changed to Abitibi Paper Company Ltd. in December 1965. l Eastern Lac des Mille Lacs and granitic rocks in the south half of the area. Private motor-roads in Block No. 2, east of Lac des Mille Lacs, were used for a rapid reconnaissance, which defined the main lithological boundaries and the eastward continuation of the metavolcanic belt. Geological data were plotted in the field on acetate sheets (Perfatrace) fitted over vertical air photographs (scale, l inch to J^ mile). The field data were traced on plastic foil (Cronaflex) basemaps (scale, l inch to J^ mile) pre pared by the Cartographic Unit of the Ontario Department of Mines from maps of the Forest Resources Inventory of the Ontario Department of Lands and Forests. Aeromagnetic maps on a scale of l inch to l mile, released jointly by the Ontario Department of Mines and the Geological Survey of Canada, cover the area (see Selected References, p. 28). The geophysical information provided by these maps was used in many instances to find geological boundaries obscured by water or overburden. O. D. M. preliminary uncoloured geological maps that covered most of the report-area are given in the list of Selected References on p. 28. The final maps (Nos. 2104 and 2105, in back pocket) are reproduced on a scale of l inch to J^ mile.

Acknowledgments. The author was ably assisted in the field by C. E. Blackburn, A. L. Barker, J. W. D. Sheldon, and D. R. Hahn. Mr. Blackburn, as senior assistant, carried out independent mapping during the season. The author gratefully acknowledges the valuable assistance and many courtesies extended to the party by Deputy Chief Ranger L. W. Reid and his staff of the Ontario Department of Lands and Forests, Upsala. Thanks are due to A. Leeyus and C. Korpi, proprietors of Pine Point Resort, for assistance and for the use of their facilities during most of the season. W. G. Edwards1 supplied helpful infor mation. The author is especially grateful to Abitibi Paper Company Ltd. for per mission to use its private road system in Block No. 2, and to refer to the company©s own geological report of that area. Discussions with E. G. Pye, Resident Geologist, Port Arthur, on problems pertaining to the geology of the area were most helpful.

Means of Access. The report-area lies south of the main line of the Canadian Pacific railway, and the Trans-Canada Highway, No. 17. Highway 11 is about 3 miles south of the south boundary of the report-area. The Fort William- Atikokan line of the Canadian National railway crosses the extreme southwest corner of this area (see Map 2104). Pine Point, the geographical centre of Lac des Mille Lacs, can be reached by a 17-mile gravel motor-road that joins Highway 17 four miles east of Upsala, a village and C.P.R. station 90 miles northwest of Port Arthur; there is direct access to the lake from Highway 17 at Savanne. A third of the area is under water; this permits ready access by float- equipped aircraft and small boats. Kashabowie Lake can be reached from Highway 11, or from Lac des Mille Lacs via a l-mile road portage at Portage *W. G. Edwards, prospector, Savanne, Ontario. Bay. A gravel motor-road joins Little Athelstane Lake, in the southeastern part of the report-area, to Highway 11. In the eastern part of the report-area (Map 2105), Block No. 2 is served by a system of private motor-roads of Abitibi Paper Company Ltd.

Previous Geological Work. The general geology was first described by W. Mcinnes (1897). The report-area is included in a G. S. C. geological map, No. 432A, by T. L. Tanton, published in 1938 on a scale of l inch to 4 miles. M. W. Bartley (1945) has reported on the geology of Lac des Milles Lacs. Map 2104 adjoins, on its west side, Ontario Department of Mines Map 2022, Western Lac Des Milles Lacs area, by T. N. Irvine (1963); on its south side, it ties onto Ontario Department of Mines Map 2036, Burchell Lake area, by P. E. Giblin and Preliminary Map P.223, Shebandowan Lake (West) area, by J. M. Hodgkinson. The Atikokan-Lakehead sheet, O.D.M. Map 2065, covers the report-area.

Topography and Drainage. The area is a peneplain with a maximum relief of 100 to 200 feet; the average elevation is about 1,600 feet above sea-level. In general, ridges and valleys conform to the regional foliation trends of the bedrock lithology and structure. Those parts underlain by massive granite intrusions are characterized by irregularly shaped hills. The configuration of many of the larger lakes is partly controlled by the bedrock geology. Bolton Bay of Lac des Mille Lacs is underlain by foliated rocks of a major syncline; the south shore of Bolton Bay is a linear feature associated with the east-west major (Quetico) fault. Lac des Mille Lacs is a comparatively shallow lake, with depths rarely exceeding 60 feet; it contains hundreds of rocky islands, many of which are covered with sand and boulder drift. On the mainland, glacial debris (sand and boulder moraine) has greatly modified the topography and drainage patterns. Much of the area, particularly the northeastern part, is covered by muskeg and swamp. The height-of-land passes south of Bolton Bay, between Lac des Mille Lacs and Kashabowie Lake and north of Athelstane Lake, in the southeastern part of the report-area. Lac des Mille Lacs drains westward into the Seine River system; Athelstane Lake drains southward through Kashabowie and Shebandowan lakes to Lake Superior.

Natural Resources and Development. Much of the area is covered by a thick forest; the principal trees are spruce, jackpine, balsam, poplar, cedar, and white birch. Lumbering is conducted on timber-cutting concessions in the eastern part of the report-area in Block No. 2, which is owned by Abitibi Paper Company Ltd. The larger lakes are well stocked with pike and pickerel. Lac des Mille Lacs is the focus of a seasonal influx of tourists for whom the facilities of six established tourist resorts are available. Commercial fishing is done on a minor scale. Moose and deer are frequently seen; beaver are still sought after by local trappers. GENERAL GEOLOGY Ontario Department of Mines Atikokan-Lakehead sheet, O.D.M. Map 2065, shows the relationship of the report-area to the regional geology. Eastern Lac des Mille Lacs

The bedrock of the area is entirely Precambrian in age; it is overlain, with great unconformity, by extensive Pleistocene glacial deposits and Recent sand and swamp. The exposed Precambrian rocks fall into the following major subdivisions: 1. A metasedimentary group lithologically similar to rocks previously assigned to the Couchiching Series. 2. A metavolcanic group lithologically similar to rocks previously assigned to the Keewatin Series. 3. Basic intrusions and their metamorphic derivatives. 4. Granitic rocks. The Metasedimentary Group, the oldest rocks, consists mainly of biotite- quartz paraschist. The upper part of the group contains an intraformational conglomerate, a banded magnetite iron formation, and interbedded quartzo- feldspathic, pelitic, and tuffaceous sedimentary rocks. The metasediments are in gradational and interfingering contact with silicic tuffs belonging to the Metavolcanic Group, which forms a central east-west belt through the area. The metavolcanic rocks consist of silicic flow breccia, rhyolite, acid pyroclastic rocks, and basaltic lavas that are massive, foliated, and pillowed; the basaltic lavas include interbeds of tuff and agglomerate. The metasedimentary and metavolcanic rocks are isoclinally folded through out; some outcrops are affected by small-scale second folds. In the west the contact between the two groups is along the Quetico Fault, an east-west "break" across the report-area. The metavolcanics are intruded by basic intrusive rocks occurring as small elliptical masses that are commonly concordant with the regional foliation. Late diabase dikes are rare. Granitic rocks form two major complexes: an early syntectonic north granodiorite batholith and a late-tectonic to post-tectonic south granite complex. Granite is injected lit par Ut into biotite-quartz paraschist of the Metasedi mentary Group to form migmatite, which underlies much of the area south of the Quetico Fault. Age Correlation Tanton (G. S. C. Map 432A) showed that the belt of metamorphosed sedimentary and volcanic rocks mapped in the report-area extends westward 140 miles to the Rainy Lake Basin. The early workers who mapped parts of the belt adopted a time-stratigraphic terminology (system, series, stage) and classified the rocks in terms of time-stratigraphic units. In the Rainy Lake area, Lawson (1914) applied the term Couchiching Series to the metasediments, and Keewatin Series to the metavolcanics. Tanton (G. S. C. Map 432A) applied these names to the entire belt. In this report and on the accompanying maps, rock-stratigraphic units have been used. The Metasedimentary Group of rocks is lithologically equivalent to the Couchiching Series, and the Metavolcanic Group is litholog ically equivalent to the Keewatin Series. Both groups are Early Precambrian in age. No attempt was made to correlate later intrusive rocks in the area with the time-units (Laurentian, Algoman, Keweenawan) formerly used in govern ment geological reports. The Table of Formations shows the relative ages of the intrusive rocks. TABLE OF FORMATIONS

CENOZOIC Recent: Swamp, stream, and lake deposits. Pleistocene: Sand, gravel, and boulders.

Unconformity PRECAMBRIAN Late Basic Intrusive Rocks: Metadiabase (dikes).

Intrusive Contact

Migmatitic Rocks:1 Amphibolite-granitic gneiss complexes, mafic xenolith-granitic com plexes. Granitic Intrusive Rocks: Pink pegmatitic granite. White muscovite granite pegmatite, white muscovite granite, red hornblende granite, quartz syenite, pink biotite granite, biotite leucogranite. Granodiorite, granodiorite gneiss, quartz diorite, quartz diorite gneiss.

Intrusive Contact

Early Basic Intrusive Rocks: Metadiabase porphyry, metadiabase, metadiorite, metagabbro, meta- pyroxenite.

Intrusive Contact

Acid Hypabyssal Intrusive Rocks: Rhyolite (quartz) porphyry, rhyolite (quartz feldspar) porphyry, aplite (dikes).

Intrusive Contact

Metavolcanic Group: Basic Meta volcanics: Basalt (metabasalt), pillowed basalt, gabbroic lava, porphyritic basalt, vesicular basalt, amygdaloidal basalt, agglomerate, tuff, chloritic schist. Acid Meta volcanics: Rhyolite, porphyritic (quartz) rhyolite, porphyritic (quartz) rhyo dacite, silicic flow breccia, silicic tuff, silicic agglomerate.

Fault, Gradational or Interfingering Contact (Local Unconformity)

Metasedimentary Group: Biotite-quartz schist, biotite-feldspar-quartz schist, phyllitic schist, meta-argillite, quartzite (chert), tuffaceous schist, conglomerate, magnetite iron formation, garnet-hornblende schist, migmatitic biotite-quartz schist.

©Within northern granitic complex only. Eastern Lac des Mille Lacs

Metasedimentary Group Included in this group are the metamorphosed sedimentary rocks, mainly biotite-quartz paraschist, which underlie much of the south half of the report- area. The upper part of the sedimentary succession is characterized by an intraformational conglomerate, a magnetite-quartz iron formation, and a complex interbedded succession of biotite-feldspar-quartz paraschist, and thinly banded pelitic, cherty, and tuffaceous metasediments. The Metasedimentary Group consists predominantly of biotite-quartz schist and biotite-feldspar-quartz schist, the metamorphic derivatives of grey wacke and feldspathic greywacke. Typically, they are uniform, very fine grained, weakly schistose rocks. Weathered surfaces are buff to dark-brown and often have a sandy appearance; fresh surfaces are grey to dark-brownish-grey. In thin section, flaky biotite porphyroblasts show a marked planar parellilesm defining the foliation. The biotite is distributed evenly within an aggregate of very fine-grained (0.05 to 0.1 mm.) quartz and plagioclase. The biotite ranges from olive-green to reddish-brown. Pale-green hornblende is often present, and the plagioclase is mainly oligoclase. Metamorphism has destroyed primary sedimentary structures. Concentra tions of biotite in thin layers are often apparent in outcrops and may indicate relict bedding. Toward the northern part of the metasedimentary belt, where relict bedding is more distinct, graded bedding and crossbedding structures are more numerous. The rocks of the Metasedimentary Group are delimited on the north by the overlying Metavolcanic Group. In the western part of the report-area, the two groups are in sharp contact for 10 miles along the Quetico Fault (see Faults, p. 29). Eastward from Bolton Bay, the contact follows the N700E trend of the metavolcanic belt, away from the east-striking Quetico Fault, and the metased iments are in gradational and interfingering contact with silicic tuffs of the Metavolcanic Group. Near the contact with the overlying metavolcanics, sedimentary layering is well defined; biotite-feldspar-quartz paraschist is interbedded with thinly banded phyllitic schist, meta-argillite, quartzite (recrystallized chert), meta- conglomerate, magnetite-quartz iron formation, and metamorphosed tuff. The beds range in colour from light-grey or buff, to black or dark-brown. Where the beds attain a thickness of several feet they usually consist of coarse-grained quartzo-feldspathic clastic fragments (weathered to a light colour) with abundant angular quartz granules. The thickness of individual finer-grained and aphanitic layers is measured in inches. An intraformational conglomerate layer is traceable for a strike-distance of 9 miles, from Bolton Bay where it is 50 feet thick, to Glen Lake where it is about 200 feet thick. The conglomerate consists of pebbles and cobbles of biotite-quartz schist, quartzite, and miscellaneous material derived from the older Metasedimentary Group. Boulders are rarely over 12 inches in size and are more common in the Glen Lake area. The pebbles and cobbles are stretched and flattened parallel to the schistosity; they are concentrated in distinct layers several feet thick, between which the pebble density is low. The matrix material is highly schistose and consists of fine-grained quartz, plagioclase, biotite, and ODM7423

Photo 1—Intraformational conglomerate (Metasedimentary Group). Dip is northward. Note flattened pebbles and cobbles. Fine grooves on surface of outcrop are glacial striae. Northern point of island (approximately Lot. N48"47' 20", Long. W900 25'05") at mouth of Bolton Bay.

ODM7424 Photo 2—Thinly bedded metasediment*. South shore of Bolton Bay. 7 Eastern Lac des Mille Lacs

ODM7426 Photo 3—Weathered joints in tuffaceous metasediment*. Small island near south shore of Bolton Bay.

abundant angular coarse granules of quartz. Thin sections show that a con siderable part of the matrix includes muscovite, carbonate, chlorite, garnet idioblasts, and minor amounts of hematite and pyrite. About 550 feet south of the conglomerate, a dark-green chloritic rock forms a layer about 50 feet thick, which extends from the west shore of Portage Bay to Bolton Bay. The rock is partly tuffaceous in origin. Weathered surfaces are pitted and display abundant lapilli-size fragments; deep weathered open joints are common. Thin sections of this rock show that it consists of angular to subangular lithic inclusions of diabasic basalt in a matrix of abundant chlorite, pale-brown biotite, muscovite, saussurite, carbonate, euhedral (idio blastic) garnet, and tourmaline. 8 ODM7427 Photo 4—Migmatitic biotite-quartz paraschist; with granite (light) infected parallel to bedding foliation in metasediment; (dark). Note boudinage structures in the granite. Photo of erratic block (in-place) west of Magnus Lake.

The boundary of the magnetite-quartz iron formation on Map 2105 is derived from aeromagnetic data, which show that it extends from the west boundary of Block No. 2, eastward for at least four miles. Where it is seen in outcrops, the iron formation appears to be about 200 feet thick; it lies strati- graphically above the conglomerate horizon and dips at about 700 to the north. The iron formation consists of very thin (0.1 to 5.0 mm.) alternating bands of fine-grained magnetite and quartz. In thin section, the quartz contains dusty magnetite and is probably a recrystallized chert. The iron formation is flanked by a zone of garnet (almandine) -hornblende schist and was probably formed within a restricted sedimentary basin. Where biotite-quartz paraschist is migmatized, it has been mapped as a separate lithological unit within the group. Migmatites are characterized by granite layers along bedding and schistosity planes in paraschist; evidently the granite was injected. Rock exposures showing more than 10 percent granitic injections are described as migmatitic biotite-quartz schist. These rocks are mainly found as zones within the granite complex south of the Quetico Fault. Within these zones, and elsewhere as xenoliths in the granite, outcrops of unmigmatized biotite-quartz schist are commonly found. Apparently the south limits of the Metasedimentary Group extends beyond the south boundary of the report-area. North of the Quetico Fault, rocks of the Metasedimentary Group are conspicuously unmigmatized, except locally in the Athelstane Lake area where lit par Ut migmatization is associated with younger white muscovite granite intrusions. Eastern Lac des Mille Lacs

Metavolcanic Group The Metavolcanic Group of rocks forms a central east-trending belt, which has an average width of three miles. The belt continues eastward from Lac des Mille Lacs and extends beyond the east boundary of the map-sheet (Map 2105). This extension is shown on an insert on Map 2105. The group consists of a complex succession of deformed acid and basic volcanic rocks that have undergone low-grade metamorphism.

Acid Metavolcanics The acid metavolcanics consist of the metamorphic equivalents of por phyritic (quartz) rhyolite, rhyolite, silicic flow breccia, tuff, agglomerate, and silicic tuff. Except for the silicic tuff, which forms part of the contact zone with the Metasedimentary Group, these rock types lie within three separate parallel bands, each of which is about 2,500 feet wide. The centre and south bands are on the north and south limbs of a major isoclinal syncline. Structural and stratigraphic evidence suggests that a single acid volcanic layer has been tectonically repeated within the metavolcanic belt. From their stratigraphic position the acid volcanics represent an early phase of volcanism in the report- area. (See Photo 5, p. 11) Porphyritic (quartz) rhyolite is typically an aphanitic light-grey to green- grey rock that weathers to a whitish-grey. Commonly, these rhyolitic flows are intensely sheared, and they are now "quartz-eye" sericite schists that are extremely fissile and dull waxy-yellow. A thin section of a typical and relatively unsheared waxy-greenish-grey porphyritic (quartz) rhyolite, from an island ^ mile southwest of Rabbit Island, shows that the rock is composed of micro crystalline sericite, carbonate, feldspar, and quartz, with scattered fine-grained albite. Subhedral to euhedral porphyritic quartz grains (2.0 to 3.0 mm.), show a "corroded" lobe texture common to acid volcanic flows. Rhyolitic flows commonly grade into silicic flow breccia. Silicic flow breccia is conspicuous where exposed on water-washed islands and along the shoreline of Lac des Mille Lacs. Characteristically, these rocks consist of rhyolitic fragments that are elongate, angular and subangular, and that weather to a light colour; these fragments are in all sizes up to blocks over three feet long. The fragments are set in a light-grey fine-grained schistose matrix of a similar rhyolitic composition. They are usually aligned parallel or subparallel to the schistosity. On the mainland south of Shaft and Tunnel islands, a band of silicic flow breccia is over 1,000 feet thick. The southern third of this band consists of reddish rhyolitic breccia fragments included in a dark-greenish-grey dacitic matrix. The origin of the flow breccia rocks is uncertain; they may have been formed by extreme autobrecciation of highly viscous acid flows or, possibly, they are tectonic breccias. On the larger islands in Lac des Mille Lacs, 3,000 feet southeast of Hook Island, porphyritic (quartz) rhyolite, porphyritic (quartz) rhyodacite, and coarse silicic flow breccia are interbedded with sheared basic (greenstone) pillow lavas. One unusual band, over 100 feet thick, consists predominantly of "pseudo-pillows", light-grey silicic ellipsoids up to 2 feet in size with dark-grey rims of lapilli-size pyroclastic fragments. 10 ODM7428

Photo 5—Silicic flow breccia; north acid metavolcanic band. Large island, 3,000 feet south of Tunnel Island.

Crystal tuff is exposed on a small island, about 2,000 feet southwest of Rabbit Island. The tuff is light-grey on fresh surfaces and weathers to a distinctive creamy-white. The exposure is part of a tuffaceous zone that is at least 200 feet thick. Microscopic study shows that the rock consists of sub angular plagioclase (An6o) and quartz in a schistose sericitic matrix. The contact between the Metavolcanic Group and the Metasedimentary Group in the south limb of the major syncline is marked by a transition zone composed, for the most part, of silicic tuff.

Basic Metavolcanics The basic metavolcanics consist mainly of lava flows, which were originally basaltic in composition. The rocks have been subjected to low-grade meta morphism and exhibit a mineral assemblage characteristic of the greenschist facies. The reconnaissance nature of the mapping and the extensive cover of Pleistocene sediments and water prevented the tracing of individual flows over any considerable distance. Individual flows are foliated, uniform, and massive, or exhibit primary flow structures. Pillow lavas are common and conspicuous, particularly in the south half of the metavolcanic belt. Amygdaloidal and porphyritic lavas, although not ubiquitous, are often found in several distinctive broad zones and, discretely, in minor flows. Thin beds of basic tuff and agglo merate are frequently interbedded with the lava flows. The lavas range from light-grey to dark-green-in-colour; typically, they weather to various shades of green or brown. In thin sections, the mineral assemblage in these rocks is characterized by an abundance of the green 11 Eastern Lac des Mille Lacs

ODM7429 Photo 6—Silicic flow breccia; south acid metavolcanic band. Large island, 3,000 feet southeast of Hook Island. minerals (amphibolite-actinolite, chlorite, and epidote). The rocks are usually designated as greenstone in the field. Strongly sheared basic lavas are usually intensely carbonatized and are now chlorite-sericite-carbonate schists. Indivi dual flows range in texture from aphanitic to coarse-grained; typically, they are fine-grained and equigranular. Often they exhibit a relict diabasic texture. Gabbroic lavas may represent the central parts of flows or, possibly, feeder pipes and fissures. Thick pillow lava flows alternate with massive flows in the south half of the metavolcanic belt. Some of the flows appear to be up to 200 feet thick. Most of the pillow structures are highly vesicular, and frequently the tops of the flows may be determined from the shapes of the pillows. Pillows of all sizes up to 4 feet across were seen. 12 ODM7430 Photo 7—"Pseudo-pillows". Light-coloured silicic ellipsoids with dark rims of lapilli-tuff, Large island, 3,000 feet southeast of Hook Island.

The mapping bf outcrops shows that the main pillow lava zone is about a mile wide and lies within a large isoclinal syncline, a major structural element defined by reliable pillow top determinations. The shape of the pillows and the degree to which they have been deformed is related to their position within the fold and the concomitant intensity of tectonic shearing. In the core of the syncline deformed pillows are stretched and flattened in the plane of the schistos ity (axial-plane foliation). Commonly, as the result of intense shearing, pillow rims and other primary flow structures have been obliterated, and the rocks exhibit every gradation from recognizable schistose volcanic flows to chloritic schist. Away from the hinge-area of the fold, the pillows are relatively un- deformed. (See Photo 8, p. 14) Linear zones of chloritic schist are commonly distributed within the south half of the metavolcanic belt. These schists are highly carbonatized or anker- itized and are probably in the cores of smaller (parasitic) folds of similar trend (east to east-northeast) to that of the major syncline. Relatively undeformed pillow lavas are exposed on the mainland west of Birch Narrows in the western part of the report-area (Map 2104), where they strike in a northward direction. These, and a thin flow of southward-facing undeformed pillows on Tunnel Island, were the only pillow lavas seen in the north half of the metavolcanic belt. In the amygdaloidal lavas the amygdules consist of calcite, calcite and quartz, and epidote and chlorite. The calcite usually weathers out leaving a pock-marked surface. Quartz, and quartz-carbonate veins and stringers are commonly found in the foliated greenstones. Locally, the flows are silicified 13 Eastern Lac des Mille Lacs

ODM7431 Photo 8—Flattened vesicular pillow lavas; on north limb of major syncline. Tops are in the left of photo, Small island in Lac des Mille Lacs, 2,000 feet south of Rabbit Island. and brecciated, notably along the shouth shore of Bolton Bay in the vicinity of the Quetico Fault. Strongly sheared zones may contain sulphides, usually in the form of minor disseminations and stringers of pyrite and pyrrhotite. Occasionally, pillow rims may be entirely replaced by pyrite. Two minor occurrences of iron formation in lava flows were seen. The largest exposure is an outcrop 8,000 feet south of Birch Narrows and about 600 feet north of the Quetico Fault. The iron formation consists of small discon tinuous bands and fragments of magnetite and chert contained within a zone 50 feet thick. Efforts to trace this zone were unsuccessful. A smaller exposure of a similar type of iron formation is present on a small island in Lac des Mille Lacs, 1,200 feet southwest of Case Island. 14 O DM7432

Photo 9—Pillow lavas; section showing flattened pillow structures. Cigarette lighter indicates approximate scale. Mainland, 2,600 feet east of Hook Island, Lac des Mille Lacs.

ODM7433 Photo l O—Undeformed pillow lavas. Southeast shore of Lac des Mille Lacs. 15 Eastern Lac des Mille Lacs

ODM7434 Photo 11—Highly sheared basalt (chloritic schist). North shore of Bolton Bay.

Acid Hypabyssal Intrusive Rocks Rhyolitic intrusive rocks are often found as narrow sills and, rarely, as dikes intruding greenstone. They are similar in appearance and lithology to the porphyritic (quartz) rhyolite flows with which they may be easily confused. A porphyritic (quartz) rhyolite band, 30 feet thick, that strikes eastward across Shaft and Tunnel islands is interpreted as a flow, but may possibly be a shallow sill intrusive into basalt. A rhyolite (quartz feldspar) porphyry dike intrudes pillow lavas 4,000 feet southwest of Rabbit Island. The dike strikes northeast and is considerably more than 50 feet thick. No other rhyolite dikes with as definite discordant contact relationships were seen. Elsewhere within the basic lavas, many of the narrow zones of sericite-quartz schist are the schistose derivatives of rhyolitic intrusive sills. 16 Rhyolite (quartz) porphyry, which outcrops along the shoreline of Lac des Mille Lacs, 4,000 feet northeast of Hook Island, is probably part of a volcanic plug. The rock is relatively unsheared; thin sections show that it consists of coarse phenocrysts of quartz, muscovite, and calcite in a microcrystalline groundmass of quartz, feldspar, white mica, epidote, and chloritic pseudomorphs. The coarser quartz grains are often milky-blue in colour. In the eastern part of the report-area (Map 2105), a few aplitic dikes intrude metavolcanic pillow lavas and metasedimentary hornblende schist in the vicinity of the iron formation.

Early Basic Intrusive Rocks Included in this group are mafic-rich intrusive rocks that are older than the granitic plutonic rocks and younger than the metavolcanics in age. They include a variety of rock types mapped separately as metadiorite, metadiabase, metagabbro, and metapyroxenite. The bulk of these rocks exist as small stocks, sills, and dikes; they commonly form elongate bodies, less than 1,000 feet thick, concordant with the main foliation trends. Except for a few small gabbroic stocks in the vicinity of the iron formation and some metadiabase dikes in biotite-quartz schist north of Glen Lake, no mafic rocks were found to intrude rocks of the Metasedimentary Group. Metapyroxenite is exposed along the south shore of Case Island and along the southeast shore of Rabbit Island. The area underlain by the metapyroxenite is indicated on the aeromagnetic map as a conspicuous anomaly, and this anomaly shows that the rock forms an elongate body about 1,000 feet wide and 2 miles long. It is evident on the accompanying maps that the metapyroxenite has intruded between the basic metavolcanics and the northern contact of the central acid metavolcanic band. The original pyroxene and olivine minerals have been altered, and the rock is now composed essentially of actinolite and chlorite. In outcrops, the metapyroxenite is a massive medium-grained greenish-black rock. Microscopic study of two typical specimens shows that the rock consists of 50 percent actinolite, 40 percent chlorite, 5 to 10 percent magnetite, and minor amounts of chromite, ilmenite, carbonate, and epidote. The actinolite forms ragged flakes and fibrous tuffs after pyroxene, and granular pseudomorphs after olivine. Most of the rocks mapped as metagabbro are massive, dark-green to black, and fine-grained to medium-grained; they commonly exhibit a relict intergranular or subdoleritic texture. In thin sections, the metagabbros are seen to consist largely of hornblende and highly saussuritized plagioclase; carbonate, epidote, uralite, chlorite, apatite, and magnetite are common accessory minerals. Several elongate metagabbro intrusions parallel the trend of the Rabbit Island meta pyroxenite. One such intrusion crosses the core of the major isoclinal syncline, just north of Bolton Bay. Near the westward attenuation of the central acid metavolcanic band, a narrow lens of metagabbro intrudes along the southern contact, between porphyritic (quartz) rhyolite and basic metavolcanics. Metadiabase is relatively less altered than metagabbro and usually exhibits a coarser, more distinct ophitic texture. Metadiabase is commonly found as small stocks and sills and, less commonly, as dikes. Contacts with the country rock are usually sharp. In the field, the distinction between metadiabase and 17 Eastern Lac des Mille Lacs metagabbro is often arbitrary, particularly where outcrops are small, or con tacts are obscured. A relatively large mass of metadiabase is exposed along the shoreline of the mainland west of Case Island. The metadiabase is intruded by narrow dikes and stringers of pink pegmatitic granite. Metadiorite intrusions are more commonly found in the western part of the metavolcanic belt; they are usually in the form of dikes or small stocks. The metadiorite is a medium-grained relatively fresh-looking rock; under the micro scope it is seen to consist of green hornblende and moderately saussuritized plagioclase. Quartz is often present in moderate amounts. Metadiabase porphyry, though rare in its occurrence, is a distinctive rock type found in the eastern part of Lac des Mille Lacs. The rock exhibits abundant euhedral phenocrysts of saussuritized plagioclase, in a dark medium- grained diabasic matrix. A metadiabase porphyry dike, 15 feet wide, intrudes basic metavolcanics on the north shore of Shelter Bay. Metadiabase porphyry is also seen at Pine Point, as a large xenolithic mass caught up in the northern granodiorite.

Granitic Intrusive Rocks Granitic intrusive rocks are the most abundant rock type underlying the map-area. They are separated into two major complexes that differ in com position, structure, and association. Most of the area north of the metavolcanic belt is occupied by granodiorite and quartz diorite. In the south half of the report-area, granite intrudes rocks of the Metasedimentary Group and underlies most of the area south of the Quetico Fault. Irvine (1963, p. 16, 17) has recognized a similar compositional difference in the geographical distribution of the granitic rocks that exist immediately west of the report-area.

Northern Granodiorite Complex The northern granodiorite is massive or weakly foliated and medium- grained to coarse-grained in texture. Fresh surfaces are grey or greenish-grey; weathered surfaces are buff-greenish-grey. Hornblende and biotite may locally constitute up to 30 percent of the rock giving it a decidedly "hybrid" aspect in the field. The biotite is commonly in the form of coarse euhedral crystals and flakes, which impart a spotted or mottled appearance to the rock. Microscopic examination of representative granodiorite specimens shows that these rocks contain 16 to 35 percent quartz, 45 to 65 percent plagioclase (basic oligoclase-andesine), 5 to 15 percent biotite, and 5 to 10 percent hornblende; potash feldspar (microcline) is present but rarely exceeds 15 percent of the rock. The plagioclase is commonly zoned and partly altered to saussurite; the quartz shows undulatory extinction and is strained. Accessory minerals are epidote, chlorite, apatite, sphene, magnetite or ilmenite, and muscovite. Granodiorite grades locally into quartz diorite where there is a decrease in the potash feldspar content and a greater abundance of andesine. The contact with the metavolcanic rocks either is sharp or is an irregular zone of multiple granodiorite dike intrusions. In the northwestern part of the report-area (Map 2104), dikes of coarse-grained pink granite intrude the granodiorite. 18 Southern Granite Complex Most of the area south of the Quetico Fault is underlain by medium-grained to coarse-grained biotite leucogranite. In the mapping, the granites were sub divided on the basis of colour, which ranges from white to pink or, less com monly, red. Under the microscope, the granites are mineralogically similar and consist of microcline, plagioclase (albite-oligoclase), quartz, and the accessory minerals, biotite, apatite, and muscovite. The plagioclase is com monly clouded and slightly saussuritized. Quartz syenite is associated with the relatively less common occurrences of red hornblende granite. The emplacement of the granite south of the Quetico Fault was largely controlled by pre-existent structures in the older metasedimentary rocks. The granite is commonly injected lit par lit into steeply dipping foliation planes (bedding and schistosity) of the isoclinally folded metasedimentary rocks to form migmatitic biotite-quartz schists. In the Kashabowie Lake area the cores of small tight folds in biotite-quartz schist (see Photo 16) are cross-grained leuco granite dikes from which apophyses diverge and pass along bedding foliation planes. The granite was thus emplaced after main folding of the rocks of the Metasedimentary Group. Within the areas dominated by lit par Ut migmatitic biotite-quartz schist, elongate granite masses are generally concordant with the regional foliation trends. Elsewhere, the granite assumes batholithic proportions. North of the Quetico Fault, a pink biotite granite stock intrudes unmig- matized metasedimentary rocks in the Henderson Lake area. The distribution of exposures indicates that the Henderson Lake pluton is roughly circular and 2 miles in diameter. The northwestern part of the Athelstane Lake area is underlain by massive coarse-grained white to grey muscovite granite. The rock is composed of microcline-perthite, quartz, muscovite, and minor amounts of garnet and tourmaline. Pegmatitic phases of the muscovite granite are common; the long axes of some feldspar crystals are up to a foot long, and some of the white mica sheets are several inches in size.

Migmatitic Rocks Mafic Xenolith-Granitic Complexes Within the northern granodiorite mass there are areas that contain xeno- lithic remnants of older metavolcanic or basic intrusive rocks. The large size and angular blocky nature of the xenoliths suggests magmatic stoping by the invading granodiorite. The migmatitic complexes show up as slight anomalies on the aeromagnetic map in contrast to the characteristic "lows" of the uncon- taminated granodiorite, and have been separated on this basis in the mapping.

Amphibolite-Granitic Gneiss Complexes Also separated lithologically are the amphibolite-granitic gneiss complexes that underlie a considerable part of the northern area. These rocks are character ized by an amphibolitic content of up to 80 percent. They are strongly foliated and commonly exhibit /*/ par lit interbanding of hornblendic with quartzo- 19 Eastern Lac des Mille Lacs

O DM7435 Photo 12—Gabbroic xenolith (dark) intruded by granodiorite (light). Part of mafic xenolith-granitic complex. Island in Lac des Mille Lacs, north of Rabbit Island. feldspathic material. The amphibolite-granitic gneiss grades into a gneissic phase of the granodiorite; the contacts between the two rock types, as shown on the coloured geological maps, Nos. 2104 and 2105, are arbitrary.

Late Basic Intrusive Rocks Included in this group are the few metadiabase dikes that intrude the granitic rocks in the north half of the report-area. The dikes generally strike north and are rarely more than 50 feet wide. In composition and texture, late diabase intrusions do not appear to differ from the early metadiabase intrusions (discussed under Early Basic Intrusive Rocks). Along the north shore of Shaft Island, a number of metadiabase dikes are bordered by several feet of massive white quartz along contacts with granodiorite. Metadiabase found within the northern granodiorite complex appears in many places to be in the form of "late" dikes, but these dikes are usually intruded by the granodiorite. Pleistocene Pleistocene deposits of glacial origin are widespread throughout the report- area. Postglacial reworking has considerably modified the earlier drift pattern. The dominant terrane type is sandy boulder moraine. Glaciofluvial and outwash deposits are common. Most of the bedrock east of Lac des Mille Lacs is mantled by a thick cover of sandy gravel and boulder drift. Glacial striae, chattermarks, and ice-grooving are more commonly seen in the sedimentary 20 ODM7436 Photo 13—Pleistocene glacial deposits. Interfingering glaciofluvial and outwash facies. Note crossbedding structures. Pine Point, Lac des Mille Lacs.

and volcanic rocks. Glacial striae show variations in the direction of ice- movement in a range between S5 0W and S350W; the three dominant trends are S50-100W, S15 0-200W, and S35 0W. Outcrops showing several ages of striae are numerous.

Recent * Recent deposits consist of beach sands and gravels, sand bars, clays, and muskeg and swamp accumulations. Sand and gravel beaches are found on many of the bays and islands of Lac des Mille Lacs. 21 Eastern Lac des Mille Lacs

STRUCTURAL GEOLOGY

FOLDS At least two periods of folding affected the rocks of both the Metasedimentary and Metavolcanic groups. During the earlier deformative phase (Fi), the rocks were isoclinally folded. A large FI isoclinal fold is the major structural feature in the map-area. Reliable pillow top determinations show that this structure is an isoclinal syncline, overturned slightly to the south; the fold-axis is horizontal. The axial trace of the fold trends approximately N700E and lies within the main pillow lava band; as the result of duplication the lava band attains widths up to 8,000 feet. The axial plane of the fold is parallel to bedding foliation; a com parison of the strike of the conglomerate horizon-marker with the axial trace of the fold clearly shows this relationship. The major synclinal fold is more than 10 miles long, and extends from the northwest corner of Block No. 2, through the southeastern part of Lac des Mille Lacs, to Bolton Bay where it is truncated by the east-west-striking Quetico Fault. Axial plane cleavage (Si foliation) is developed most strongly in the hinge- area of the major syncline where the rocks are highly schistose. That they have been subjected to intense tectonic deformation is shown by flattened pillows, elongate flow breccia fragments, flattened pebbles of the intraformational conglomerate of the Metasedimentary Group and the development of chloritic and sericitic schists from the original lava flows. Axial lineations (Li) associated with FI folds are obscure. Vertical fine lineations on flattened pillows in the lavas suggest that the direction of tectonic transport has been normal to the horizontal fold axis and parallel to the axial plane of the major fold. Other zones of fissile intensely schistose metavolcanic rocks are probably the cores of smaller parasitic folds of similar trend to that of the major structure. The hinges of these smaller folds and the hinge of the major synclinal fold have been obliterated. Small folds (F2), which are apparent in outcrops, fold the earlier axial plane schistosity (Si) and belong to the later phase of structural deformation. Along the north shore of Bolton Bay the hinges of small open F2 folds in crumpled greenschist form a lineation (L2) that plunges to the west at about 400. Near the west boundary of the report-area (Map 2104), on an island in Baril Bay 400 feet north of the Quetico Fault, chloritic schist is similarly folded. Evidence of F2 folding of the metasediments is based mainly on fine L2 crinkle lineations in phyllitic slates and schists that are seen along the south shore of Bolton Bay. These lineations plunge S500-650W at 300-400 and cross the FI foliation trend at a small angle. On an island (position given in caption of Photo 1) at the mouth of Bolton Bay in Lac des Mille Lacs, about 600 feet south of the conglomerate mentioned in Photo l, small FI folds in the metasedi- mentary rocks plunge S65 0W at about 35 0 (see Photo 14). On the east shore of Kashabowie Lake, opposite Lily Bay, small tight FI folds in biotite-quartz schist (see Photo 16) plunge westward at about 25 0. The similar orientation of these FI folds and that o\ the L2 lineations suggests that first and second folds are almost co-axial. In the amphibolite-granitic complex north of the main metavolcanic belt, small open folds with subhorizontal axes are common; the significance of these folds is obscure. 22 ODM7437 Photo 14—Folded bedding in metasediment* (Metasedimentary Group); fold belongs to first period (Fi) of deformation. Biotite-quartz paraschist (light), tuffaceous paraschist (dark). Fold plunges westward at about 350, indicated by pencil. Note small cleavage mullion* along bedding contact. Photo taken approximately 600 feet south of Photo 1 on small island at mouth of Bolton Bay.

ODM7438 Photo 15—Large cleavage mullions in biotite-quartz paraschist, associated with fold shown in Photo 14. View from same position described for Photo 14. Pencil shows approximate scale. 23 Eastern Lac des Mille Lacs

ODM7439 Photo 16—Tight fold (Fi) in biotite-quartz paraschist of the Metasedimentary Group. Granite dike crosses core of fold. Also note granite apophyses from dike intrude along bedding planes in the metasediment;. Fold plunges westward at 250. East shore of Kashabowie Lake, opposite Lily Bay.

Top determinations based on current bedding and grain gradation are commonly used in Precambrian metamorphic terranes to interpret gross geologi cal structure. Within the report-area, it is apparent that top determinations based on such features can only relate to local folds and provide misleading information if applied directly to the interpretation of major geological structures.

FAULTS The Quetico Fault is a prominent east-west "break" through the report-area; it is probably an extension of the fault believed by Hawley (1929, p. 1-58) to exist in the Sapawe Lake area. The actual fault was not seen by the author, but its presence is assumed from the following evidence. Metavolcanic and metasedimentary rocks are in sharp contact along the Quetico Fault for 10 miles in the western part of the report-area. The major syncline (discussed under Folds) is truncated by the Quetico Fault along the south shore of Bolton Bay; in this vicinity metabasalt is, in many places, seen to be silicified and brecciated. From Bolton Bay to Little Athelstane Lake, the area south of the Quetico Fault is underlain by massive biotite leucogranite and red granite, and Ut par lit migmatized paraschist. North of the fault, granitic intrusions are con spicuously absent except for the unique circular Henderson Lake granite pluton and the probably younger white muscovite granite. The rocks of the Meta sedimentary Group north of the Quetico Fault are mainly unmigmatized 24 biotite-quartz schist. Lit par lit migmatization north of the Quetico Fault is seen only in the Athelstane Lake area, where it is associated with the white muscovite granite. Red granite and quartz syenite intrude basic metavolcanics in two places only: (1) along the south shore of Bolton Bay, within 100 feet of the Quetico Fault, where schistose metabasalt is impregnated along schistosity planes by red granite and quartz syenite; and, (2) in the band of metabasalt, less than 1,000 feet thick, that extends from Trout Bay (of Kashabowie Lake) to Little Athelstane Lake. Of note is the lithological similarity of the rocks in the two places described above and the unique position of the Trout Bay-Little Athelstane Lake metabasalt band isolated within Couchiching-type meta- sedimentary rocks and in direct line of projection of the Quetico Fault. The evidence strongly suggests that the Trout Bay-Little Athelstane Lake metabasalt is a slice or wedge of the Metavolcanic Group caught up in a zone of dislocation along the Quetico Fault. The author tentatively favours a sinistral (south side east) movement along the Quetico Fault. This would account for the 10-mile horizontal displacement of the southern metavolcanic rocks from the main metavolcanic belt on the north side of the fault. East of Trout Bay, the metavolcanic slice is offset in several places by a later system of crossfaults. A fault system is represented on the maps by two strong faults that strike approximately N300E. One of these, the Tunnel Island Fault, lies within a shear zone in porphyritic (quartz) rhyolite on a small island 250 feet west of Tunnel Island. The shear zone strikes N250E and dips 600NE. Small folds within the shear zone are Z-shaped in profile and plunge 700NE. Map 2104 shows that the granodiorite on the west side of the fault is displaced southward for a distance of almost a mile. This displacement is sinistral, and is not in accord with a dextral sense of movement suggested by the Z-shaped folds within the fault zone. Immediately east of the fault, the strike of the silicic flow breccia band swings north-northeast. On the basis of the foregoing evidence, it is possible that the Tunnel Island Fault is associated with a large fold belonging to the later F2 phase of deformation. The Tunnel Island Fault occurred before and independently of the movements associated with the Quetico Fault. The main evidence for the Hook Island Fault is a fractured and sheared zone that is exposed along the shoreline of Lac des Mille Lacs, half a mile northeast of Hook Island. Rhyolite (quartz) porphyry is strongly fractured for a width of 30 feet, adjacent to a carbonatized shear zone which strikes N300E. The shear zone contains minor amounts of disseminated pyrrhotite and molybdenite. The Hook Island Fault may extend southwest into the main basic metavolcanic belt, where it may prove to be of economic significance.

ECONOMIC GEOLOGY Tanton (G.S.C. Map 432A) recorded three occurrences of gold, one on the east side of Case Island, and two on the north side of Bolton Bay. No trace of any workings was found at the Case Island locality. The occurrences at Bolton Bay are in a silicified breccia zone, which was traced by the author for 880 feet. The zone is about 35 feet wide and has been explored by shallow 25 Eastern Lac des Mille Lacs

O DM7440 Photo 17—Bolton Bay gold prospect. Breccia zone with stringers and pods of quartz (light). Photo taken at one of larger trenches.

trenches. The breccia zone strikes N75 0E, and for much of its extent is in a rhyolite flow or intrusive sill that follows a contact between pillow lavas on the north and massive basic metavolcanics on the south. At its east end, the breccia zone includes a band of sheared agglomerate consisting of light-coloured fragments in a chloritic matrix. About 150 feet south of the agglomerate, a strongly sheared zone in basic metavolcanics strikes N450E and is probably a fault that may cross and offset the main brecciated zone. The breccia zone contains, in places, up to 60 percent quartz as small veins, stringers, and pods. No visible gold was found by the author. Where exposed in trenches, the breccia contains coarse disseminations of chalcopyrite in amounts up to 5 percent of the rock. Assays of grab samples, taken by the author from one of the larger trenches, yielded a trace of gold and silver. During the 1964 field season, the zone was restaked by A. J. Leeyus, I. A. McLeod, and W. G. Edwards; Mr. Edwards1 reported that assays of mineralized samples, taken from the trenches in the breccia zone, yielded 0.2 to 1.74 ounces of gold per ton, 0.08 to 4.16 ounces of silver per ton, and about 1.0 percent copper. A strongly brecciated zone in basic metavolcanic rock and porphyritic (quartz) rhyolite is exp6sed along the northwest shore of Tunnel Island. Pyrite cements and replaces the breccia fragments and matrix of the rock; minor amounts of pyrrhotite and chalcopyrite are also present. Assays of grab samples taken by the author from this zone yielded traces of gold, silver, and nickel. The zone is capped by a gossan that is several inches thick. XW. G. Edwards, prospector, Savanne, Ontario. 26 Several small gossans and rusty zones were seen along the shoreline of Lac des Mille Lacs. These are commonly associated with brecciated and sheared rhyolite, which contains sulphide minerals, usually pyrite and pyrrhotite, as stringers and disseminations. Disseminations and narrow stringers of pyrite are commonly found in sheared metabasalts. Rusty pyritized zones in sheared pillow lavas within the major synclinal fold are particularly well exposed on waterworn islands in Lac des Mille Lacs. On several islands on the north and south limbs of the synclinal fold, the rims of sheared pillows have been completely replaced by massive pyrite. Narrow quartz veins and stringers, commonly found in the foliated meta basalts, are usually unmineralized; assays of vein material occasionally yield a trace of gold and silver. A small exposure with minor amounts of copper-bearing minerals (malachite, chalcopyrite, and bornite) was found at the contact between silicic flow breccia and metabasalt, near an intrusion of metagabbro. This exposure is one mile due south of Tunnel Island; an assay of a grab sample yielded 0.3 percent copper and a trace of gold. Minor amounts of molybdenite and pyrrhotite were found as disseminations in a sheared carbonatized fault zone on the mainland, half a mile northeast of Hook Island. Molybdenite was also found as disseminations in a narrrow quartz vein on the mainland, 1,000 feet north of the Hook Island Fault. No economic minerals were found in the metasedimentary rocks. A grab sample taken by the author from the banded magnetite iron formation and analyzed by the Laboratory Branch of the Ontario Department of Mines was found to contain: total iron, 38.80 percent; silica, 36.09 percent; phosphorus pentoxide, 0.27 percent; titanium oxide, 0.21 percent; sulphur, none.

RECOMMENDATIONS FOR PROSPECTORS The most favourable areas for future exploration are: 1. Within the central acid metavolcanic band, and in the vicinity of its southern contact with basic metavolcanics. Rhyolitic rocks have responded to structural deformation by fracturing and shearing, and could prove to be favourable host rocks for mineralizing solutions. 2. Shear zones in pillow lavas on the north and south limbs of the major syncline. 3. In the vicinity of the fault zone northeast of Hook Island and along its assumed southeast projection into the main basic meta- volcanic belt.

27 Eastern Lac des Mille Lacs

SELECTED REFERENCES Texts Bartley, M. W. 1954: Exploration report on the Lac des Mille Lacs area; Dept. of Industrial Development, Canadian Pacific Railway Co., Jan. 28, 1954. (Reference copy on file at Ontario Dept. Mines Library, Toronto.) Giblin, P. E. 1964: Geology of the Burchell Lake area; Ontario Dept. Mines, Geol. Rept. No. 19. Hawley, J. E. 1929: Geology of the Sapawe Lake area; Ontario Dept. Mines, Vol. 38, pt.6, p. 1-58. (Pub lished 1930) Irvine, T. N. 1963: Western Lac des Mille Lacs area; Ontario Dept. Mines, Geol. Rept. No. 12. Lawson, A. C. 1914: The Archaean geology of Rainy Lake re-studied; Geol. Surv. Canada, Memoir 40. Mcinnes, W. 1897: Report on the geology of the area covered by the Seine River and Lake Shebandowan map-sheets comprising portions of Rainy River and Thunder Bay districts, Ontario; Geol. Surv. Canada, Annual Report, Vol. X (new series), pt. H. (Published 1899) Perdue, H. S. 1938: Couchiching, Kashabowie Lake, Ontario; Journal of Geology, Vol. 46, p.842-867.

Maps Geol. Surv. Canada Map 338A. Shebandowan area, District of Thunder Bay, Ontario. Provisional edition with marginal notes. Scale l inch to l mile. Geology by T. L. Tanton. (Pub lished 1938) Map 432A. Quetico sheet, (East Half), Thunder Bay and Rainy River districts, with marginal notes. Scale l inch to 4 miles. Geology by T. L. Tanton. (Published 1938) Ontario Dept. Mines Map 2065. Atikokan-Lakehead sheet; Geol. Compilation Series. Scale l inch to 4 miles. (Published 1965) Map P.177 (prelim, map). Lakehead-Shebandowan sheet. Geological compilation by E. G. Pye and K. G. Fenwick. Scale l inch to 2 miles. (Published 1963) Map P. 187 (prelim, map). Lac des Isles sheet. Geological compilation by E. G. Pye and K. G. Fenwick. Scale l inch to 2 miles. (Published 1963) Map P.223 (prelim, map). Shebandowan Lake (West) area sheet. Geology by J. M. Hodgkinson. Scale l inch to J^ mile. (Published 1963) Map P.260 (prelim, map). Birch Narrows sheet. Geology by L. Kaye. Scale l inch to ^ mile. (Published 1964) Map P.261 (prelim, map). Rabbit Island sheet. Geology by L. Kaye. Scale l inch to ^ mile. (Published 1965) Map P.262 (prelim, map). Henderson Lake sheet. Geology by L. Kaye. Scale l inch to *A mile. (Published 1965) Map P.263 (prelim, map). Argon Lake sheet. Geology by L. Kaye. Scale l inch to M mile. (Published 1965) O.D.M.-G.S.C. Aeromagnetic maps: No. 1102G, Shebandowan Lakes; No. 1103G, Savanne; No. 1112G, Huronian; No. 1113G, Bedivere Lake. Scale l inch to l mile. Ontario Dept. Mines-Geol. Surv. Canada. (Published 1961)

28 Index

PAGE PAGE Abitibi Paper Co. Ltd...... 2, 3 Economic geology...... 25-27 Access...... 2 Edwards, W. G...... 2, 26 Acid hypabyssal rocks...... 16 Acid metavolcanics...... 10, 11 Acknowledgments...... 2 Faulting...... 24, 25 Age correlation...... 4 Folding, notes and photos...... 22-24 Agglomerate...... 11, 26 Formations, table of...... 5 Amphibolite...... 19 Amygdaloidal lavas...... 11, 13 Garnet-hornblende schist...... 9 Ankeritized rocks...... 13 Geology, economic...... 25-27 Aplite...... 17 Geology, general...... 3-21 Athelstane Lake...... 3 Geology, structural...... 22-25 Rocks...... 9, 19, 25 Glacial deposits. See also Pleistocene. Photo...... 21 Baril Bav, folding near...... 22 Glen Lake, rocks near...... 6, 17 Barker, A. L...... 2 Gneiss, granitic...... 19 Bars, sand...... 21 Gold...... 25-27 Basalt...... 8 Granite...... 9, 19, 24, 25 See also Metabasalt. Injection, photos...... 9, 24 Basic intrusions...... 17, 18, 20 Granitic rocks...... 18, 19 Basic metavolcanics...... 11-14 See also: Granite. Beaches...... 21 Granodiorite. Bedding...... 6 Granodiorite...... 18 In metasediments, photo...... 7 Faulted...... 25 folding in, photo...... 23 Photo...... 20 Biotite-quartz schist...... 6, 9, 19, 25 Gravel...... 20, 21 Folding in, notes and photos...... 22-24 Greenstone. See Basic metavolcanics. Photo...... 9 Birch Narrows, rocks near...... 13, 14 Hahn, D. R...... 2 Blackburn, C. E...... 2 Henderson Lake, rocks near...... 19 Block No. 2, rocks...... 9 Hook Island: Folding...... 22 Fault...... 25, 27 Bolton Bay...... 3 Rocks near...... 10, 17 Faulting...... 24 photos...... 12, 13, 15 Gold occurrence, notes and photo...... 25, 26 Hypabyssal rocks. Rocks...... 6, 8, 14, 17, 25 See Acid hypabyssal rocks. folding in, photos...... 23 photos...... 7, 16 Intrusive rocks...... 16-19 Bornite...... 27 Iron formation...... 6, 9, 14, 27 Boudinage structure, photo...... 9 Breccia, flow: Faulted...... 25 Jointing, weathered, photo...... 8 Gold in, notes and photo...... 26 Notes and photos...... 10-12 Kashabowie Lake...... 2 Rocks near...... 19 Carbonatized rocks...... 12, 13 folding in...... 22 Mineralized...... 25, 27 photo...... 24 Case Island: Keewatin Series...... 4 Gold occurrence...... 25 Rocks near...... 14, 17, 18 Lac des Mille Lacs...... 3 Chalcopyrite...... 26 Glacial deposits, photo...... 21 Chert. See Quartzite. Rocks...... 10, 17 Chlorite schist...... 13, 16, 22 mineralized...... 27 Chromite...... 17 photos...... 15, 21 Cleavage mullions, photos...... 23 See also Bolton Bay. Conglomerate, intraformational...... 6 Lapilli-tuff, photo...... 13 Photo...... 7 Lava flows. See Basic metavolcanics. Contact, mineralized...... 27 Leeyus, A. J...... 2, 26 Copper...... 26, 27 Leucogranite...... 19 Couchiching Series...... 4 Lily Bay: Crossbedding in glacial deposits, photo...... 21 Rocks, folding in...... 22 Crystal tuff...... 11 photo...... 24 Little Athelstane Lake...... 2 Drainage...... 3 Rocks...... 24, 25 29 Eastern Lac des Mille Lacs

PAGE PAGE Magnetite...... 17 Portage Bay...... 2 See also Iron formation. Rocks...... 8 Magnus Lake, rocks, photo...... 9 Prospecting, recommendations for...... 27 Malachite...... 27 "Pseudo pillows"...... 10 Map, geological, coloured...... back pocket Photo...... 13 Mapping methods ...... 1,2 Pyrite...... 14, 26, 27 McLeod, I. A...... 26 Pyrrhotite...... 25, 27 Meta-argillite...... 6 Metabasalt...... 25 Quartz, massive...... 20 Faulted...... 24 Quartz diorite...... 18 Sulphides in...... 27 Quartz syenite...... 19, 25 Metaconglomerate...... 6 Quartz veins...... 13, 27 Metadiabase...... 17, 20 Mineralized...... 26, 27 Metadiorite...... 18 uartzite...... 6 Metagabbro...... 17 uetico Fault...... 3, 6, 24, 25 Metapyroxenite...... 17 e Metasediments: Rabbit Island, rocks near...... 10, 11, 16, 17, 20 Folding in...... 22 Photo...... 14 photos...... 23 Recent deposits...... 21 Jointing in, photo...... 8 References, selected...... 28 Petrology and photos...... 6-9 Reid, L. W...... 2 Meta volcanics: Rhyolite. See Porphyritic (quartz) rhyolite. Folding in...... 22 Petrology and photos...... 10-14 Sand beaches...... 21 Migmatitic rocks...... 9, 19 Savanne...... 2 Photo...... 9 Schists, folding in...... 22 Mica, white...... 19 Sericitic schist...... 10, 22 Molybdenite...... 25, 27 Shaft Island, rocks...... 10, 16, 20 Moraines, boulder...... 20 Shearing in metavolcanics, photo...... 16 Muscovite granite...... 19, 25 Sheldon, J. W. D...... 2 Shelter Bay, rocks...... 18 Natural resources...... 3 Silver...... 26 Nickel...... 26 Slate, phyllitic...... 22 Sulphides...... 14, 27 See also: Chalcopyrite. Outwash deposits...... 20 Pyrite. Photo...... 21 Pyrrhotite. Surveys, geological ...... 1,3 Phyllitic schist...... 6 Syncline...... 13 Pillow lava: See also Folding. Folding in...... 22 Notes and photos...... 11-15 Topography...... 3 Pine Point...... 2 Trout Bay (Kashabowie Lake), rocks...... 25 Glacial deposits, photo...... 21 Tuffaceous rock...... 6, 8, 11 Rocks...... 18 Folding in, photo...... 23 Pleistocene deposits...... 20 Jointing in, photo...... 8 Plug, volcanic...... 17 Tunnel Island: Porphyritic lava...... 11 Fault...... 25 Porphyritic metadiabase...... 18 Rocks near...... 10, 13 Porphyritic (quartz) rhyodacite...... 10 mineralized...... 26, 27 Porphyritic (quartz) rhyolite...... 10 photo...... 11 Faulted...... 25 Intrusive...... 16, 17 Xenoliths...... 9, 18, 19 gold in...... 26 Photo...... 20

30

Map 2104 Bolton Bay Sheet Lac des Mille Lacs

ONTARIO DEPARTMENT OF MINES HON. G. C. WARDROPE, Miniatrr of Mi*m D. P. Douglass. Deputy Minitter M. E. Huml. ttorrtt,*. t

s INWOOD TOWNSHIP JOYNT K TOWNSHIP

Scale, l inch lo 50 miles

H.T.S. reference 52 B/9, 52 6/10, 52 B/15, 52 B/16

LEGEND

CENOZOIC* RECENT Swamp, stream, lake deposits. PLEISTOCENE Sand, gravel, boulders, clay. UNCONFORMITY PRECAMBRIAN** LATE BASIC INTRUSIVE ROCKS

© © 8a Metadiabase (dikes).

INTRUSIVE CONTACT M1GMATIT1C ROCKS 7a Amphibolite-granitic gneiss com plexes.**** 7b Mafic xenolith -granitic complexes.****

GRANITIC INTRUSIVE ROCKS*** 6a Biotite leucogranite. 6b Red hornblende granite, quartz syenite. 6c White muscovite granite pegmatite, white muscovite granite. 6d Pink biotite granite. 6e Granodiorite; granodiorite gneiss; quartz diorite; quartz diorite gneiss. 6f Pink pegmatitic granite. INTRUSIVE CONTACT EARLY BASIC INTRUSIVE ROCKS*** 5a Metadiorite, metadiabase, metadia- base porphyry. 5b Metagabbro. 5c Metapyroxenite. INTRUSIVE CONTACT ACID HYPABYSSAL INTRUSIVE ROCKS 4a Aplite (dikes).f 4b Rhyolite (quartz) porphyry, rhyolite (quartz feldspar) porphyry. INTRUSIVE CONTACT METAVOLCANIC GROUP BASIC METAVOLCANICS*** 3a Basalt (metabasalt), gabbroic lava. 3b Tuff, agglomerate. 3c Pillowed basalt. 3d Vesicular, and amygdaloidal basalt. 3e Porphyritic basalt. 3f Chloritic schist. ACID METAVOLCANICS*** 2a Rhyolite, porphyritic (quartz) rhyo lite, porphyritic (quartz) rhyodacite. 2b Silicic flow breccia. 2c Silicic tuff, silicic agglomerate, FAUUT, GRADATIONAL. OR INTERFINGERING CONTACT METASEDIMENTARY GROUP*** la Conglomerate. 1b Biotite-quartz schist, phyllitic schist, meta-argillite, quartzite (chert), tuffaceous schist. 1c Garnet-hornblende schist.f 1d Magnetite iron formation.f 1e Biotite-quartz schist, biotite-feld- spar-quartz schist. 1f Migmatite biotite-quartz schist.

AO Silver. Au Gold. Cu Copper. Mo Molybdenum.^ g Quartz. S Sulphide mineralization. DES

"Unconsolidated deposits. Cenozoic deposits are represented by the lighter coloured and uncoloured parts of the map.

""Bedrock geology. Outcrops and inferred extensions of each rock map unit are shown respectively in deep and light tones of the same colour. Where in places a formation is too narrow to show/ colour and must be represented in black, a short black bar appears in the appropriate block.

***The rocks in these groups are subdivided litho- logically and the order does not imply age relation ships within each group.

****Ooes not include migmatized metasediments of the metasedimentary group. f These rocks are mapped on the companion sheet.

S Occurs only on companion sheet.

SYMBOLS

Glacial striae.

Small rock outcrop.

Boundary of rock outcrop,

CeoTi.., cal boundary, approximate.

Magnetic contour, value in gammas.

Strike and dip;direction of top unknown.

Strike and dip; top in direction of arrow.

Strike and vertical dip; top in direction of arrow.

Strike and dip of overturned bedding; beds face in direction of arrow and dip in direction of loop. Direction (arrow) in which beds face; direction of dip unknown. Bolton Bay

Direction (arrow) in which inclined beds face as indicated by cross bedding.

Direction in which lava {lows face as indicated by shape of pillows.

Syncline, trace of axial plane.

Direction of plunge of fold axis, crest line or trough line.

Strike and dip of schistosity.

Strike of vertical schistosity.

Strike of schistosity, dip unknown.

Strike and dip of gneissosity.

Strike of vertical gneissosity.

Stratiform foliation, inclined.

Stratiform foliation, vertical.

Lineation (plunge known, plunge un known).

Drag-folds. (Arrow indicates direction of plunge).

Fault, indicated or assumed; arrows indicate horizontal movement.

Veins, width in inches.

Muskeg or swamp.

Railway.

Electric power transmission line.

Other road.

Trail, portage, winter road.

Building. Map 2104

Depth of overburden in feet. BOLTON BAY SHEET

Magnetic attraction. Lac des Mille Lacs

Township boundary, with mile post, ap THUNDER BAY DISTRICT proximate position only. Scale 1:31,680 or l Inch to V2 Mile

SOURCES OF INFORMATION

Geology by L Kaye and assistants, 1964. Geology is not tied to surveyed lines.

Maps and plans of mining companies.

Ontario Department of Mines and Geological Survey of Canada Aeromagnetic Maps, 1102G, 11Q3G, 1112C, 1113G.

Map 432A Quetico, East Half, Geological Survey of Canada, 1938.

Exploration Report by M. W. Bartley, C.P.R., 1954.

Preliminary Maps: Scale of 1 inch to X mile. P260 Birch Narrows, 1964; P261 Rabbit Island, 1965; P262 Henderson Lake, 1965; P263 Argon Lake, 1965, Scale of 1 inch to 2 miles. PJ87Lac des Isles, 1963; P177Lakehead-Shebandowan, 1963.

Cartography by R. G. Curtis and J. A. Be/bin, Ontario Department of Mines, 1965.

Base maps derived from Forest Resources Inventory Maps, with additional information by L. Kaye, 1964.

Magnetic declination approximately 3" East, 1960. Map 2105 \ Portage Bay Sheet Lac des Mille Lacs

ONTARIO DEPARTMENT OF MINES HON. O. C. WARDROPE, Minister of Mines D. P. Douglass, Deputy Minister M. E. Hurst, Director, Geological Branch

Scale l inch to 50 miles

N.T.S. reference 52 B/9, 52 B/16

LEGEND

CENOZOIC* RECENT Swamp, stream, lake deposits. PLEISTOCENE Sand, gravel, boulders, clay, UNCONFORMITY

PRECAMBRIAN** LATE BASIC INTRUSIVE ROCKS

Indian ReservelNo. 22 A l 8a Metadiabase (dikes).

INTRUSIVE CONTACT GOODFELLOW MIGMATITIC ROCKS 7a Amphibolite-granitic gneiss com plexes**** 7b Mafic xenolith -granitic complexes.****t

GRANITIC INTRUSIVE ROCKS*** 6a Biotite leucogranite. 6b Red hornblende granite, quartz syenite. 6c White muscovite granite pegmatite, white muscovite granite. 6d Pink biotite granite. 6e Granodiorite; granodiorite gneiss; quartz diorite; quartz diorite gneiss. 6f Pink pegmatitic granite.f INTRUSIVE CONTACT EARLY BASIC INTRUSIVE ROCKS*** 5a Metadiorite, metadiabase, metadia- base porphyry, 5b Metagabbro. 5c Metapyroxenite. INTRUSIVE CONTACT ACID HYPABYSSAL INTRUSIVE ROCKS 4a Aplite (dikes). 4b Rhyolite (quartz) porphyry, rhyolite (quartz feldspar) porphyry. INTRUSIVE CONTACT METAVOLCANIC GROUP BASIC M ETA VOLCANICS*** 3a Basalt (metabasalt), gabbroic lava. 3b Tuff, agglomerate. 3c Pillowed basalt, 3d Vesicular, and amygdaloidal basalt. 3e Porphyritic basalt. 3f Chloritic schist. ACID METAVOLCANICS*** 2a Rhyolite, porphyritic (quartz) rhyo lite, porphyritic (quartz) rhyodacite. 2b Silicic flow breccia. 2c Silicic tuff, silicic agglomerate. FAULT, GRADATIONAL, OR INTERFINGERING CONTACT METASEDIMENTARY GROUP*** 1a Conglomerate. 1b Biotite-quartz schist, phyllitic schist, meta-argillite, quartzite (chert), tuffaceous schist. 1c Garnet-hornblende schist. 1d Magnetite iron formation. 1e Biotite-quartz schist, biotite-feld- spar-quartz schist. 11 Migmatitic biotite-quartz schist.

AO Silver. Au Gold. Cu Copper. Mo Molybdenum. q Quartz. S Sulphide mineralization.

* Unconsolidated deposits. Cenozoic deposits are represented by the Ijghter coloured and uncoloured parts of the map,

**Bedrock geology. Outcrops and inferred extensions of each rock map unit are shown respectively in deep and tight tones of the same colour. Where in places a formation is too narrow to show colour and must be represented in black, a short black bar appears in the appropriate block.

***The rocks in these groups are subdivided litho- logically and the order does not imply age relation /XL -4ft ships within each group.

****Does not include migmatized metasediments of the metasedimentary group.

j-These rocks are mapped on the companion sheet.

SYMBOLS

Glacial striae.

BLOCK No. 2 Small rock outcrop.

Boundary of rock outcrop.

Geological boundary, approximate.

Magnetic contour, value in gammas.

Strike and dip; direction of top unknown.

Strike and dip; top in direction of arrow.

Strike and vertical dip; top in direction of arrow.

Strike and dip of overturned bedding; beds face in direction of arrow and dip in direction of loop.

Direction (arrow) in which beds face; A direction of dip unknown.

Direction (arrow) in which inclined beds face as indicated by cross bedding.

Direction in which lava flows face as indicated by shape of pillows.

Syncline, trace of axial plane.

Direction of plunge of fold axis, crest line or trough line.

ATHELSTA NE Strike and dip of schistosity.

Strike of vertical schistosity.

Strike of schistosity, dip unknown.

Strike and dip of gneissosity.

Strike of vertical gneissosity.

Stratiform foliation, inclined.

Stratiform foliation, vertical.

Lineation (plunge known, plunge un known).

Drag-folds. (Arrow indicates direction of plunge).

Fault, indicated or assumed; arrows indicate horizontal movement.

Veins.

Muskeg or swamp.

Railway,

Electric power transmission line.

Other road.

Trail, portage, winter road.

Building.

Depth of overburden in feet. Map 2105 PORTAGE BAY SHEET Magnetic attraction. Township boundary, with mile post, ap Lac des Mille Lacs proximate position only. THUNDER BAY DISTRICT

Scale 1:31,680 or l Inch to V2 Mile

Chains 80______60______40______20 O

Metres 1000

SOURCES OF INFORMATION

Geology by L Kaye and assistants, 1964. Geology is not tied to surveyed lines.

Maps and plans of mining companies.

Ontario Department of Mines and Geological Survey of Canada Aeromagnetic Maps, 1102G, 1103G, 1112G, 1113G.

Map 432A Quetico, East Half, Geological Survey of Canada, 1938.

Exploration Report by M. W. Bartley, C.P.ft., 1954.

Preliminary Maps: Scale of 1 inch to X mile. P260 Birch Narrows, 1964; P261 Rabbit Island, 1965; P262 Henderson Lake, 1965; P263 Argon Lake, 1965. Scale of 1 inch to 2 miles. P187Lac des Isles, 1963; P177 Lakehead-Shebandowan, 1963.

Cartography by R. G. Curtis and J. A. Belbin, Ontario Department of Mines, 1965.

Base maps derived from Forest Resources Inventory Maps, with additional information by L. Kaye, 1964.

Magnetic declination approximately 3" East, 1960.