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.
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