Geology and Structure, Orion Mine (No. 8 Zone), Val d'Or District, Quebec

Exploration & Mining Geology, Vol. 1, No. 3, 1992

YVON TRUDEAU, Les mines Selbaie, Joutel, Quebec, Canada, and, DENIS RAYMOND SOQUEM, Sullivan, Quebec, Canada

The Orion gold mine, located 7 km northeast of the town of Malartic, Quebec, was discovered in mid-1985. Underground exploration was undertaken in 1986 leading to commercial production in 1988. The upper part of the orebody was exploited above the 125 m level and a total of 131 090 t at an average grade of 5.31 g/t gold were extracted. This paper describes the authors' current knowledge and interpretation of the geology, gold distribution, and structure of the Orion No. 8 ore zone deposit. The deposit is an epigenetic lode gold occurrence somewhat unique in that both quartz-vein type and pyritic type of gold ore occur side-by-side. It is located within the Marban-Norlartic Deformation Corridor (MNDC) formed during a first deformation stage (D{). The MNDC is a well-defined regional structural feature in the Val d'Or - Malartic mining camp. Primary gold mineralization is associated with the D, event and is represented by pyritized, silicified and brecciated basaltic lavas enclosed by ultramafic flow units. The ore zone is concordant with the MNDC. Felsic intrusions are spatially related with the ore zone, but their role in the genesis of the ore has yet to be defined. A second deformation event (D^ resulted in local folding, a second schistosity (82) and reverse faulting. Gold remobilization, the formation of the gold-bearing quartz breccia and the emplacement of the main quartz vein at the No. 8 zone deposit were associated with this event.