Anctil Lake

Regional Settings

The Lac Anctil property is located in the northeast part of the Archean Greenstone Belt of the Abitibi Sub-province, in the Superior Province of the Canadian Shield. This area belongs to the Northern Volcanic Zone of Chown et al (1992) which exposes the eldest rocks of the Abitibi Sub-province (2,730 – 2,710 Ma).

The property is part of the southern band of the Chibougamau-Matagami belt, so called the Caopatina-Quévillon greenstone belt (MB 90-01). The region comprises a synclinal structure (Druillettes synclinal) and an anticlinal structure (Opawica anticline) both oriented N090° to N100°. The heart of the anticline is occupied by the Opawica Pluton, a tonalitic (syn-volcanic) pre-kinematic age. The Druillettes synclinal is made up of sequences of volcano-sedimentary rocks from the Obatogamau and Caopatina Formations. It is bordered to the northwest by a mylonitic band associated with the Guercheville fault which lies approximately 1.3 kilometres north of the property. To the north, the synclinal of Druillettes is bordered by the gneiss of the Lapparent Complex, to the northeast by the tonalitic syn-tectonic pluto of Rachel and to the west by the post-tectonic La Ronde Pluton (MB 90-01). The Obatogamau and Caopatina Formations are located at the very base of the 1^st volcanic cycle of the Chapais-Chibougamau area (MM 89-03).

Rocks from the Chibougamau-Matagami greenstone belt were deformed and metamorphosed by two orogens. The earlier Kenorean orogen (2800-2600 Ma), was a three phase regional deformation that resulted in large E-W domes & basins structures and associated E-W, SE and NE regional fault systems. The Grenville orogen (1300-1000 Ma), on the other hand is responsible for the NNE regional fault system visible on the regional geology map.

Several intrusions are present in the surroundings of the Anctil Lake property. The Rachel pluton is a syntectonic tonalite, located to the north of the property. The La Ronde pluton is a syntectonic monzonite, located to the west. The Opawica River Complex is similar to the Doré Lake anorthositic Complex and consists of a banded intrusion with an anorthositic level at its base, surmounted by a 900 metres thick gabbro-ferropyroxenite level. The Opawica Pluton is a 500 m to 3.5 km wide intrusion lying in the heart of the Opawica River Complex. It’s composed of tonalite, quartz-diorite and QFP dykes (Midra, 1989).

The metamorphic grade of the Caopatina-Quévillon belt is of greenshist facies, locally reaching the amphibolites facies near the Grenville front and along deformational corridors and intrusion margins. 

Property Geology

The Anctil Lake property is located over a section of basalts from the Obatogamau Formation, mostly composed of massive and pillowed basalts of tholeiitic affinity. 3% to 20% plagioclase feldspar megacrysts can be observed locally (MB 90-01). In this area, the basalts are squeezed between the Rachel pluton to the NE and the La Ronde pluton to the SE. Mafic volcanoclastites, gabbro sills, wacke horizons and massive felsic volcanics are also observed in intercalations within basalts of the Obatogamau formation.

The property is located over the Druillettes syncline which is overfolded to the north and plunges to the east. The Guercheville fault zone crosses the property in a northwest/southeast direction and corresponds to a series of parallel shear zones limited to a corridor less than 1 km wide. This structure is parallel to the regional schistosity and possesses a distinct magnetic signature, marked by the presence of numerous Input anomalies.

The schistosity on the Anctil Lake property is sub-vertical and moulded around the La Ronde pluton (MB 90-01). In this area, the stratigraphy and regional schistosity of the volcanics are parallel, which is generally the case in the Obatogamau Formation. Metamorphism is at the greenschists grade. More details on the Mina Lake property are presented in Amrhar & Rioux (2017 – GM 70966).

Metallogeny

The mining district of Chapais-Chibougamau has for long been known as “the shear zone hosted deposits region” and produced approximately 1.2M tons of copper, 3.7M oz of gold, 20.9M oz of silver, 115,000 kg of zinc and 4,000 kg of lead (MB-96-14). The region is host to several types of deposits and showings within a wide variety of geological context. The Caopatica Segment is host of the principal gold producing mine in the district, the Joe Mann mine. It is also host of two past producing gold deposits (Lac Shortt and Lac Bachelor mines), and of one past producing Zn-Pb-Ag deposit, the Coniagas mine.

Following Brochu & Hamel-Hébert (BG 2023-06), deposit types that are the most likely to be found in this area include 1) Orogenic Gold associated to the Guercheville shear corridor, 2) VMS or vein-type synvolcanic mineralization hosted in felsic or mafic volcanics, associated with positive Mag and EM anomalies (Fenton deposit style), and 3) Gold associated with hydrothermalism of felsic to intermediate late intrusives (Drouet Pluton).

The Guercheville corridor represents the first-class metallotect for both Au and base metals mineralization in the area of the property. This regional structure hosts several showings and deposits, the most important one being the former Joe Mann mine located some 70 kilometres ESE of the Anctil Lake property, with a historical production of 4,289,221 tonnes of ore at 7.56 g/t Au and 0.23% Cu (GM 70966).

Works of the Quebec Ministry of Energy and Natural Resources (BG 2023-06) recently defined several favorable potential horizons for both Au and Cu mineralizations within the Obatogamau basalts. On the regional geology map, Cu-favorable horizons appear in strike to the SE with the Anctil Lake property.

On the Anctil Lake property, the Lac Anctil “A” mineralization can be described as blebs of pyrite in quartz veins within sheared basalts of the Obatogamau formation. The Lac Anctil “A” zone, as defined by Diagnos following the 2008 summer exploration program, can be described as an area of approximately 500 meters long by 200 meters wide (GM 64963) following the regional schistosity, in which anomalous gold values (>10 ppb) were obtained in quartz veins. The highest assay value of this zone is 3.96 g/t Au over 0.3 m.

The Lac Anctil “A-2” showing is located approximately 1.3 km NE of the Lac Anctil “A” zone. This showing comes from a grab sample taken from the hinge of a fold on a strong IP axis (GM 64964), and which returned 0.49 g/t Au. The mineralization is described as trace amounts of sulfides in a folded rock containing silicified horizons.