Nouvelles subdivisions de la Formation de Gilman, Groupe de Roy, région de Chibougamau, sous-province de l'Abitibi, Québec : résultats préliminaires

Abstract

The Gilman Formation (Roy Group) is located on the southern fl ank of the Chibougamau syncline, at the eastern end of the Archaean Abitibi Subprovince, and holds potential for volcanogenic massive-sulphide deposits. Recent geological mapping and compilation work has led to a proposed new subdivision of this formation. The David Member (lower Gilman Formation) contains tholeiitic, mas- sive to pillowed mafi c lavas, with minor fl ow breccia and hyaloclastite. The Allard Member (middle Gilman Formation) contains minor transitional to calc-alkaline mafi c lavas at its base, overlain by inter- mediate calc-alkaline volcaniclastic rocks (containing clasts of chert with varying amounts of sulphides, and mafi c to intermediate lavas), plagioclase-phyric crystal tuff, and rhyodacite. The Bruneau Member (upper Gilman Formation) is composed of tholeiitic, massive to pillowed mafi c lavas, with lenses of volcaniclastic rocks and spherulitic rhyolite.

The Lemoine Auriferous Volcanogenic Massive Sulfide Deposit, Chibougamau Camp, Abitibi Greenstone Belt, Quebec, Canada: Geology and Genesis

“…This contact is more Leclerc et al (2011), D-G. Mortensen (1993). Modified from Leclerc et al (2008Leclerc et al ( , 2011 or less parallel to stratigraphy. The Lemoine Member is composed of at least ten volcanic and intrusive units (Fig.…”

“…The age of the footwall quartz and feldspar porphyry, which is possibly intrusive, and the age of the Hanging-wall quartz and feldspar porphyry unit both give a minimum age constraint on the effusive rocks of the Lemoine Member, which are therefore older than ~2725.7 Ma (min age of the Doré Lake Complex), and perhaps older than 2731.6 Ma (max age of the footwall porphyry). Elsewhere in the region, felsic rocks of the Waconichi Formation, including stratigraphic equivalents to the Lemoine Member, have been dated at ~2728 Ma (Scott Member, 2728.2 ± 0.8 Ma, Leclerc et al, 2008), suggesting that the Lemoine deposit has an age of approximately 2728 Ma.…”

Geology, Alteration, and Origin of Archean Au-Ag-Cu Mineralization Associated with the Synvolcanic Chibougamau Pluton: The Brosman Prospect, Abitibi Greenstone Belt, Canada

“…The host rocks of the Brosman prospect belong to a younger cycle (third cycle in Leclerc et al, 2012) of volcanism (~2720−2705 Ma; Daigneault et al, 2004;Pilote and Guha, 2006;Leclerc et al, 2008) that is interpreted as being the result of an emerging volcanic arc built on the products of the older volcanic rocks (Daigneault et al, 2004). The lowermost part of the younger volcanic cycle consists of mafic flows and sills that are overlain by an assemblage of intermediate to felsic flows, sills, and volcaniclastic deposits that are considered as remnants of variably preserved volcanic edifices (Couture, 1986;Pilote, 1986;Côté-Mantha, 2009).…”

“…The lower part of the volcanic succession was deposited during a first cycle of volcanism dated at ~2730 to 2720 Ma by Daigneault et al (2004), Pilote and Guha (2006), and Leclerc et al (2008) that resulted in the formation of extensive subaqueous basalt plain. Much older volcanic rocks have recently been dated in the region and the 2730 to 2720 Ma volcanic rocks are now rather considered part of a second volcanic cycle by Leclerc et al (2011Leclerc et al ( , 2012.…”

Potential-field modelling of the prospective Chibougamau area (northeastern Abitibi subprovince, Quebec, Canada) using geological, geophysical, and petrophysical constraints

“…The Roy Group is overlain by the sedimentary units of the Opémisca Group. The Roy Group consists of volcanic cycle 1, which is dominated by mafic lava flows, and volcanic cycle 2, which consists of mafic to felsic lava flows and pyroclastic rocks (Allard 1976;Gobeil and Racicot 1983;Allard and Gobeil 1984;Daigneault and Allard 1987;Leclerc et al 2017).…”