Bull. Minéral.
(19 79), 102, 569-576.
Significance of fluid phases associated with shear zone Cu-Au mineralisation in the Doré lake complex, Chibougamau, Quebec
by Jayanta GUHA (*), Jacques LEROY (**) and Denise GUHA (*),
(*) Sciences de la Terre, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada. (**) Équipe de recherche «Équilibres entre fluides et minéraux »,
E. N. S. G. -C. R. P. G., C. O. n° 1, 54500 Vandœuvre-lès-Nancy, France.
Signification des phases fluides associées à la minéralisation à Cu-Au sur zone cisaillée dans le complexe du lac Doré, Chibougamau, Québec.
Introduction
The Henderson ore bodies have been shown to be pre-or synmetamorphic in origin where fluids played a major role in the shaping of the ore body (Guha and Koo, 1975 ; Leroy et Guha, 19 77). This study was undertaken to investigate the nature of the fluids that were involved during the ore deposition. The project forms a part of a continuing study contri¬ buting to the understanding of the metallogenetic processes of the Chibougamau mining camp.
Regional and local setting of the ore bodies
The Henderson ore bodies are one of the so called «shear zone type » Cu-Au mineralisation of the Chi¬ bougamau mining camp which is situated roughly between longitudes 740 and 64° W and latitudes 490 and 50° N.
Geologically the district lies within the Superior Province of the Canadian shield at the eastern ex¬ tremity of the Archean Abitibi greenstone belt. The Gren ville Front demarcates its eastern limit. The rocks were subjected to the Kenoran Orogeny, charac¬ terised by greenschist facies of metamorphism and less commonly the amphibolite facies.
The greenstone assemblage of the Chibougamau district is composed of volcano-sedimentary rocks and related mafic to ultramafic intrusions and a
«granitic assemblage of felsic plutonic rocks » (Du¬ quette, 1970).
The host rock for the ore bodies is the Doré Lake complex which is a stratiform intrusive within the greenstone assemblage (Allard, 1970). The lower anorthosite zone of this complex is the host rock for the Cu-Au ore bodies found in the Doré Lake complex. The lower anorthosite zone comprises repetitions of anorthosite and gabbroic anorthosite grading into gabbro. The greenschist facies of metamorphism altered the original plagioclase to albite/zoisite and the intercumulus pyroxene and ilmenite to chlorite and leucoxene respectively. Only a few small lenses of anorthosites have been left untouched by meta¬ morphism .
The major regional structures are east-west trending folds, and faults and shear-zones. The regional structu¬ ral pattern of the area is dominated by a major anti¬ cline whose core is occupied by the Chibougamau Pluton which intrudes the lower anorthosite zone of the Doré Lake complex. The Pluton is a complex multiphase intrusion varying from meladiorite to quartz porphyry.
The lower anorthosite zone of the Doré Lake complex contains a number of Cu-Au deposits within shear-zones similar to the Henderson ore bodies. However, there is one striking difference between the Henderson deposit and the others. There is no close spatial dyke-ore relationship in the Henderson ore bodies but it is a characteristic feature in the
