Geology of Pythonga Lake Area (DP-151)

Documents complémentaires / Additional files Licence / License I MINISTERE DE L'ÉNERGIE ET DES RESSOURCES ,B DIRECTION GENERALE DE L'EXPLORATION GÉOLOGIQUE ET MINERALE ~ PYTHONGA LAKE AREA J.H. Bourne 1970 DP-151 GM-28638 OPEN FILE MANUSCRIPT Gouvernement du Québec DEPARTMENT OF NATURAL RESOURCES GEOLOGICAL EXPLORATION SERVICE GEOLOGY OF PYTHONGA LAKE AREA Preliminary report by James Bourne PUBLIC Ministère des Richesses Naturelles, Québec SERVICE DE LA DOCUMENTATION TECHNIQUE 2 5 MAI 1973 Date: ~ Quebec No GM: 1970 INTRODUCTION The Lac Pythonga area lies between 76°00W•and 76°30'W, and between 46°15'N and 46°30'N, and includes Artois and }3eliveau Townships as well as parts of Boureogne, Perche, Isle-De-Prance, Angoumois, Egan, Souchette, Church and Aunis Townships. Maniwaki Township, most of which also lies within the area delimited above, is an Indian Reservation and was not mapped. Thus the mapping covered a surface area of some 345 square miles. LOCATION AND ACCESS The Town of Maniwaki (population 9,000) is located approximately 1 mile east of the eastern boundary of the area. The geographic centre of the area, Turtle Lake, is 16 miles from Maniwaki by road. There are two main access roads into the area,-: one from the Town of Gracefield, and the other from,Maniwaki. Both Maniwaki and Gracefield are located on the paved Provincial Highway #11, and are 84 and 57 road miles north of Hull respectively. There are numerous bush roads which have been built and are maintained by the Canadian International Paper Company (C.I.P.) C.I.P. Route 1.1-: Runs between Eagle Depot and Maniwaki, following the Eagle River for some 15 miles. C.I.P. Route 12-: Goes to the northwest corner of the area, passing by Turtle Lake and several others. C.I.P. Route 35-: Runs from Eagle Depot up the west shore of Lac Pythonga, and out of the area to the northwest: C.T.P. Route 36-: Runs southwest from route 35 and effectively côvers the southwest corner of the area. In the southeastern part of the area the main access road runs into the interior' from Messines or Parley. In the northeast part of the area a well graded provincial road, (known locally as the Montcerf Road) has been built from Maniwaki. Numerous secondary roadslead into the larger lakes. The following important lakes are all accessible by road. Depot Lake Harding Lake Doyle Lake Kingsbury Lake Lac Pythonga Turtle Lake Lac David Green Lake Inman Lake Lac Cairine Lac Hel'ene Petit Lac-Aux-Cedres Lac Jean Grand. Lac-Aux-Cedres An excellent road map of this area is available through the C.I.P. office in Maniwaki. Drainaçse& Physiography With the exception of a very few streams, all streams drain into the Eagle River. Several streams develop drainage areas of considerable size before they themselves empty into the Eagle River. The western part of the area is in large part drained by the Hibou and Turtle Rivers. Relief in the area is less than 400' locally, usually in the order of 150'.Hills are for the most part rounded and valleys filled with glacial debris. 3 Two broad physiographic provinces can be outlined, the Gatineau Valley which is in. general a broad sand-filled plain underlain by •marble, and'the highlands to the west of it which form the hilly hinterland and out of which drain all the major streams. Elevations vary from a low of 550' in the extreme eastern part of the area along the Desert River to a high of 1592' in the north- western corner of the area east of Lac David. The average elevation rises from 800' in the east to 1100' in the west. GEOLOGIC COLUI4N Tectonic Unit Dominant Category Number Lithology Syn and Post- 11 quartz veins Grenville Orogeny 10 lamprophyre intrusive rocks 9 diabase 8 diorite 7 granite 6 pegmatite 5 white rock Grenville Group 4 biotite - feldspar gneiss metasedimentary 3 marble rocks pre - Grenville 2 calc - silicate Group basement rocks if amphabolite 1 o le garnet (sillimanite) gneiss p.,ld biotite gneiss ôlc hornblende - biotite gneiss üilb granite gneiss la green rock complex 0 m GEOLOGY - INTRODUCTION In the legend the writer has placed the rock units inte different "tectonic categories". In 'so doing he is following the practice established by Wynne-Edwards (1966, 1969) of mapping in this part of the Grenville Province. The proof that this concept is valid could best be arrived at by obtaining a number of Rb-Sr whole rock age determinations from each tectonic category which would then set out a rough time sequence of events. No such project has been attempted for this part of Quebec. However, in adjacent parts of Ontario such an investigation is being conducted, (Krogh et al (1968); Davis et al (1967, 1969)) and has established a geochronologic framework for the Grenville Province of Ontario. Baer (1969), on the . basis of large scale mapping in both Ontario and this area of Quebec under consideration felt that a correlation of the rocki across the river into adjacent western Quebec was possible, and divided up the rocks of western Quebec into three "blocks" each of which is envisaged to he of different primary age. The contact between his "Algonkin" and "Gatineau" blocks passes through the Lac Pythonga area and should, therefore, divide the rocks into groups of different age which, following the terminology of Wynne-Edwards, are, here called "tectonic categories" and are listed below, Tectonic Rock Types'Involved Category III sy - and post - Grenville orogeny intrusive rocks II Grenville Group metasâdimentary rocks and associated rocks I a "pre - Grenville Group" basement complex According to this concept, the rocks of tectonic category I are considered to have been in a gneissic condition when the limestones, aluminous shales which were destined to become the Grenville Group, were laid down. The rocks of category I are then considered to have been through 2 complete orogenic episodes, while those of category II have experienced only 1. The rocks of category III are intrusive rocks which are massive or at most slightly foliated and must have been emplaced after most of the movement associated with the Grenville Orogeny had taken place. Krogh's and Davis'. work on the handed paragneisses of the French River area of Ontario gave a value of m.y, for those rocks which Baer tentatively correlates with tectonic category I, while Silver & Lumbers (1965) report a value of 1310± 15 m.y, for the Tudor metavolcanics which are considered to underlie the Grenville Group marbles and thus place a maximum age on them and on tectonic category II. Finally, Doig and Barton (1968) have determined the age of some of the fresh intrusive rocks in the Maniwaki area. Their results show that although these rocks are generally post - Grenville Orogeny in age, they are nevertheless. still Precambrian. The rocks were divided into the above tectonic categories• on the basis of association. For instance, only rocks which were observed to have a widespread and intimate association with the white to pinkish marbles of the Grenville Group were assumed to be members of the Grenville Group as well. The same technique was applied to the basement rocks, using as a point of departure the acceptance of the large-region of biotite gneisses and hornblende gneisses as being part of the basement. For all it's faults, it is felt that this technique is justifiable simply for economic reasons. Baer (1969) has shown that many of the major mineral deposits of the Grenville Province, particularly zones of uranium mineralization, are located near the contact between tectonic categories I and II, It is, therefore, hoped that this style of mapping will be useful for subsequent mineral exploration. Basement Complex (unit 1) The 'Basement Complex' is a term used to describe all rocks (except pegmatites) which are believed to have been in a gneissic condition at the time when the Grenville Group of metasediments were laid down. This term, therefore, covers a vast variety of rock types, including microcline-bearing gneisses of granitic composition, biotite-plagioclase gneisses, biotite-hornblende gneisses, amphibolites and quartzo-feldspathic gneisses. All these rocks are readily recognizable at any one particular locality, but it is very difficult to trace these rocks for any great distance. It is probable that there is a gradation of composition along strike so that two outcrops, both of which are along strike with each other may be quite different lithologically. This feature is common in other parts of the Grenville Province where the structural geology has been carefully worked out - for example see Martignole & Schrijver (1970). The result of this is that the spatial distribution pattern of the various gneisses is quite irregular and their structures difficult to determine. Because of this problem, all gneisses believed to belong to this tectonic category, except those with a highly distinctive bulk composition, were classified as one unit, and tin different lithologic varieties indicated by means of subunits. Where possible zones of relatively constant lithology were delimited. In the following short description, the principal lithologic units are described. Green Rock Complex (unit la) These rocks form a quantitatively minor group of rocks in the extreme western part of the area. The best exposures of this unit are in fact just outside the area mapped, just west of the western end of Lucy Lake. Two. subunits of unit 1 have been recognized in the field - homogenous charnockite (?) and layered gneisses. Both have a colour which sets them apart immediately from all 'other rocks in the area - namely the pea-soup green colour.

Load more