June 2003

New gold targets in the Chibougamau area
Characterization of mineral occurrences

Patrick Houle
Géologie Québec

Most mineral occurrences in the western part of the Chibougamau Pluton are characterized by the presence of a shear zone, accompanied by strong sericitization. This sericite generally occurs as crystals aligned parallel to the shearing direction. Since known showings are currently found in all phases of the Chibougamau Pluton, and even in meladiorite and quartz diorite intrusive breccias, the type of host rock does not appear to be a determining criteria in the search for new mineral occurrences. Different types of veins were emplaced in the shear zones, as a result of several distinct phases of injection. Quartz remains the dominant mineral in these veins. In addition to quartz, the veins may contain the following minerals: carbonate, tourmaline, chlorite, sericite, fuchsite, epidote, albite, pyrite, chalcopyrite, sphalerite, magnetite, silver and gold. Native gold was observed in a few showings. Some showings exhibit weak hematization of plagioclase grains, possibly related to the presence of major NE faults, such as the Scott lake fault.

As an exploration guide, mineralized shear zones may be grouped into two preferential directions, namely NW to NNW (PDF Format, 84 kb) and NNE to NE (PDF Format, 85 kb).

A compilation of previous work conducted in the western part of the Chibougamau Pluton shows that most of this work was performed on mineral occurrences associated with NNE to NE-oriented shear zones. However, very little work has been conducted on showings hosted in NW to NNW shear zones. The Silver Tower showing (PDF Format, 84 kb) , associated with a NW to NNW shear, is an excellent example. It is defined by quartz veins with pyrite, sphalerite, chalcopyrite and gold mineralization (grab sample: 24.0 g/t Au, 0.80% Cu, 1.10% Zn and 9.4 g/t Ag). This mineralization, emplaced in the tonalite, is characterized by the presence of a shear zone (N330º) about 2 to 3 m wide. Previous work carried out on this showing includes EM geophysical surveys and surface sampling in a trench. Recently, in the fall 2002, in the vicinity of the showing, an induced polarization survey delineated a NW-trending conductor that extends for at least 1.8 km. The conductor is then disturbed by a series of late NNE to NE faults (C. Claveau, personal communication, 2003).

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