Bourlamaque batholith and its gold potential, Val d'Or, Quebec

CIM Bulletin, Vol. 82, No. 922, 1989

Mehmet F. Taner, Consulting Geologist, and Pierre Trudel, Ecole Polytechnique

The metamorphosed mineralized Archean Bourlamaque batholith, dated at 2710 +5-4 Ma, is a homogeneous body, composed mainly of quartz diorite; it is cut by late dioritic, mafic and aplitic dykes, and contains metasomatized ultramaflc xenoliths. A geochemical investigation confirms the calc-alkaline affinity of the batholith, and the REE profiles are similar (La/Yb = 3.9 to 8.1) to those of the intermediate to felsic metavolcanic rocks at Val d'Or into which the batholith was intruded and to those of the calc-alkaline members of the Blake River Group at Rouyn. Gold distribution within the batholith is heterogeneous and anomalous. Although the background Au content of the batholith is estimated to be 3.2 ppb Au by RNAA, the estimated median gold content of the batholith is 10 ppb (with P84 = 32 and P16 = 3.1 ppb), much higher than that of "normal" granites (1 to 5 ppb Au). The gold mineralization exhibits a close relationship with shear zones (e.g. Belmoral Mine) or with diorite dykes (e.g. Sullivan, Perron and Courvan mines). The following sequence of geological events is proposed: (1) pretectonic emplacement of the batholith, which is cogenetic with its volcanic host rocks; (2) regional metamorphism and deformation with localized shearing; and (3) hydrothermal alteration and quartz veining. We conclude that: (1) the Bourlamaque batholith is a gold-enriched intrusion, and (2) the determination of average gold content may be an effective method for distinguishing "sterile" intrusions from those with potentials for gold mineralization.

Keywords: Mineral exploration, Gold distribution, Bourlamaque batholith, Petrography, Geochronology, Geochemistry, Abitibi volcanic belt