Osisko Mining Corporation

• Geology

  The Archean Canadian Malartic gold deposit is located immediately south of the Larder Lake-Cadillac fault zone, in the Pontiac sub-province of the Superior Province, about 20 km west of Val d'Or, Quebec. The deposit is part of a 3000 metre-long, contiguous, east-west striking mineralized system that was historically mined by three independent underground operations. These were, from west to east: Canadian Malartic, Sladen Malartic and East Malartic. Total production (1935-1983) was approximately 4.22 million ounces, excluding the Barnat Mine, which was part of the Malartic gold camp but consisted of a separate deposit located within the Cadillac fault zone. The Canadian Malartic deposit was mined mostly by underground long-hole stoping methods between 1935-1965, the only underground bulk tonnage gold mine in Quebec. Total production was 9.9 Mt @ 3.37 g/t Au (1.08 M oz). Mining was limited to higher grade (> 3 g/t Au) mineralized zones along nine levels extending to a depth of 350 m.

  The deposit is of porphyry gold type. The majority of the mineralization in the system occurs as a continuous shell of fine disseminated native gold with 1-3% pyrite, hosted by altered clastic sediments of the Pontiac Group (turbiditic greywacke, mudstone and minor siltstone) overlying an epizonal dioritic porphyry intrusion. Mineralization also occurs in the upper portions of the porphyry body. Alteration in both porphyry and the metasediments consists of biotite-Kspar-carbonate (potassic alteration) with an overprint of fine-grained, replacement silicification. Highly silicified zones («cherts») are commonly brecciated. Late, coarse-grained, quartz-feldspar-muscovite veins cut and hematize the porphyry in the Canadian Malartic and Sladen Malartic mines. These veins remobilized gold to produce local, high grade (>10 g/t Au) stockworks with visible gold.

  The mineralized zones defined by Lac Minerals are all, with the exception of the Gilbert Zone, the surface expression of a much larger, low-grade, continuous porphyry gold system extending to a depth of 350 m, which includes the former Canadian Malartic mine. The mineralized shell, as defined from grades in historical and current drill holes of greater than 0.4 g/t Au over 20 m, has been traced on the property over an east-west strike length of 1200 metres and a width of 350 to 400 metres. True thickness varies from 60 metres to 270 metres, and gold grades vary from 0.5 g/t to 3 g/t Au over significant tonnages. Average grade for the deposit appears to be in the 1.0 to 1.3 g/t Au range. The system is open to the south and to the west.

  The F zone is the near-surface expression of the western extremity of the deposit. Mineralization in the F zone is hosted by an apophasis of the porphyry intrusion that reaches surface. The Wolf, F, A and P surface zones as defined by Lac Minerals now reflect a somewhat pointless nomenclature in light of the fact that they are part of a larger contiguous mineralized zone.

  The close association between voluminous, low-grade, disseminated gold mineralization and an epizonal, intermediate porphyry intrusion, as well as the presence of abundant potassic alteration, defines the Canadian Malartic deposit is an Archean porphyry gold system. The deposit is older than vein-type load gold deposits hosted within the Larder Lake-Cadillac Fault zone since it is truncated by the fault.

Canadian Malartic Maps»