June 2003

New gold targets in the Chibougamau area
Economic geology

Patrick Houle
Géologie Québec

Most Cu-Au deposits in the Chibougamau mining camp are hosted in NW-SE shear zones (mine shear) within the meta-anorthosite along the northern DLC. These zones are interpreted as synvolcanic structures that were reactivated by regional deformation (Kirkham et al., 1998). From 1954 to the end of 1997, eleven (11) ore deposits were mined in NW-SE shear zones, for a total production of 31.7 million short tons of ore at a grade of 1.76% Cu and 2.26 g/t Au. Historically, mines in the lac Doré and lac Chibougamau area have yielded a total production of 46.9 million short tons of ore at a grade of 1.74% Cu and 2.19 g/t Au, amounting to a little over 1.6 billion pounds of copper and 3.1 million ounces of gold (PDF Format, 65 kb).

Similarly, there are many other examples of gold deposits associated with granitoid intrusions in the Abitibi geological Subprovince. Among these, the Bourlamaque batholith in the Val-d’Or area hosts several gold deposits along its margins. Furthermore, the Belmoral mine (1,710,102 t at 6.46 g/t Au) is hosted in a shear zone within the Bourlamaque batholith, in a setting similar to what is observed in the western part of the Chibougamau Pluton.

In addition, late orogenic gold-bearing quartz veins in the Rouyn-Noranda mining district are largely hosted in Archean tonalitic plutons of the Blake River Group. For example, the Silidor mine (2.95 million tonnes at 5.1 g/t Au) is a 900-m-long ore zone oriented N330º/55ºE, with a vertical extension of 900 m and an average width of 3.5 m. It is enclosed in a strongly hematized trondhjemite of the Powell Pluton. The Silidor deposit is the result of several vein-filling episodes, which took place throughout the evolution of a fault network with normal or reverse movements (Carrier et al., 2000). NW to NNW-oriented lode gold deposits in the Powell Pluton therefore appear to be similar in many ways to NW to NNW structures in the western part of the Chibougamau Pluton.

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