Date of Award
1988
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
Archean volcanic and plutonic rocks in Bousquet Township, Quebec, host gold orebodies. Gold ore is within pyroclastic andesite and rhyolite lava as concordant native gold- and electrum-bearing lenses of disseminated coarse and polygonal pyrite with minor base metal sulphide minerals, flanked by idioblastic manganiferous garnet and andalusite porphyroblasts. There is manganiferous ilmenite in the garnet and garnet-bearing and andalusite-bearing rocks have REE abundances similar to adjacent non-garnet and andalusite-bearing rock. Gold ore in plutonic rocks occurs as variably discordant veins within porphyritic tonalite. All the gold orebodies are foliated by schistosity S{dollar}\sb1{dollar} defined by ripidolite and muscovite, and show shape alignment L{dollar}\sb1{dollar} on S{dollar}\sb1{dollar}. Regionally, rocks have primary structure, idioblastic hornblende, biotite and clinozoisite porphyroblasts, intermediate plagioclase, S{dollar}\sb1{dollar}, and shape alignment L{dollar}\sb1{dollar} of minerals and clasts on S{dollar}\sb1{dollar}.;Coarse and polygonal pyrite grains with very fine grained native gold and electrum, manganiferous ilmenite occupied by garnet, idioblasticity of garnet and andalusite in wall rock to the gold concentrations, the assemblage of hornblende, biotite, clinozoisite and intermediate plagioclase and preserved primary structure regionally indicate recrystallization of the gold concentrations with their immediate wall rock plus surrounding rocks during low pressure metamorphism transitional between the greenschist and amphibolite facies. Ripidolite and muscovite in S{dollar}\sb1{dollar} and L{dollar}\sb1{dollar} within both gold concentrations and host rocks indicates concomitant recrystallization and flattening during retrogressive metamorphism to the lower greenschist facies. Hence, concentration of gold predates peak low pressure metamorphism.;Similar REE abundances of garnet-bearing and andalusite-bearing wall rock to gold concentrations suggests manganese metasomatism and relative enrichment in silica and aluminum in the manner of an argillic alteration, respectively. This along with andesite and rhyolite host rock and associated gold and pyrite with small base metal content, suggests initial concentration of gold in an epithermal-like hydrothermal system by boiling of a metamorphogenic fluid liberated through devolatilization of rock subsided toward synvolcanic magma during the low pressure metamorphism. Gold was subsequently moved into dilatent and discordant fractures during plutonism.
Recommended Citation
Stone, William Edward, "Nature And Significance Of Metamorphism In Gold Concentration, Bousquet Township, Abitibi Greenstone Belt, Northwest Quebec" (1988). Digitized Theses. 1755.
https://ir.lib.uwo.ca/digitizedtheses/1755