Aluminum silicate-bearing rock and its relation to gold mineralization; Bousquet Mine, Bousquet Township, Quebec

CIM Bulletin, Vol. 76, No. 850, 1983

R.I. VALLIANT, \Long Lac Mineral Exploration Ltd. Reno, Nevada, R.L BARNETT and R.W. HODDER, Geology Department, University of Western Ontario, London, Ontario

Rocks with abundant aluminum silicate minerals occur in two ways adjacent to stratabound pyritic gold occurrences within mafic tuffs at the Bousquet Mine, Abitibi Belt, Quebec: 1) A weakly laminated rock composed of quartz, muscovite, andalusite, kyanite, pyrite, pyrophyilite, diaspore and chlori-toid is discordant within tuff footwall to a pyritic gold occurrence and is traversed locally by quartz-kyanite veinlets. This rock is SiO2-, Al2O3- and K2O-rich relative to enveloping tuff, although abundances are erratic. Abundances of CaO, MgO, Na2O, MnO and TiO2 are minor, especially where compared to the enveloping tuff. Trace amounts of gold are present throughout the rock.2) A rock composed essentially of quartz, muscovite, andalusite, pyrite, paragonite, pyrophyilite, pyrrhotite and diaspore is laminated and concordant in the hanging wall of pyritic gold occurrences. Abundances of Al2O3, K2O and locally SiO2, Na2O and total iron are greater than those within enveloping tuff, whereas CaO, MgO and MnO abundances are less than those within enveloping tuff. The interpretation is that both rocks containing the aluminum silicate minerals andalusite, kyanite, pyrophyilite and diaspore are tuff altered through the ascent and deposition of hydrothermal fluids on the seafloor during volcanism and syngenesis of the pyritic gold occurrences. Type 1 developed from tuff through leaching by the ascending hydrothermal fluids which fed the exhalations responsible for the pyritic gold bodies. Type 2, hanging-wall concordant aluminous rock, resulted from alteration of tuff at the seafloor by downward percolation and circulation of dense exhaled fluid which did not disperse into the sea water. This is essentially a seafloor weathering. Recognition of aluminous rocks is a useful focus to exploration and in evaluation of specific targets as to their gold-bearing potential. Type 1 is footwall to and Type 2 is hanging wall to gold-bearing pyritic bodies.

Mots Clés: Gold deposits, Abitibi gold deposits, Aluminous rocks, Mineralization, Bousquet Mine, Blake River Group, Stratiform deposits, Hydrothermal alteration, Mineral analyses.