Saskatchewan Geological Society Special Publication Number 14: MINEXPO'96 SYMPOSIUM - Advances in Saskatchewan Geology and Mineral Exploration , Proceedings of a Symposium, Saskatoon, Saskatchewan 21 - 22 November, 1996. Editors: K.E. Ashton and C.T. Harper, 1999 .
B. Gold in Saskatchewan: Deposits and Deposit Settings, Pages 62 - 70 .

Lithostructural Setting of the Contact Lake Gold Deposit: Controls on Vein Formation and Ore Distribution

Christopher B. Lee and R. Gwilym Roberts
Department of Geological Sciences, University of Waterloo, Waterloo, ON N2L 3G1

The Contact Lake deposit is hosted by the Bakos structure, which transects the granitic core of the composite Little Deer Lake pluton. The principal ore zones in the deposit occur at the intersection of the Bakos structure with a north-trending felsic dyke. There are four episodes of veining and hydrothermal alteration, of which the last three involved the emplacement of gold, with the bulk of the gold emplaced during the second episode. Each hydrothermal event is associated with a structural event, all of which postdate a regionally penetrative, peak metamorphic, deformation fabric.

The geometry of the vein structures produced during the first two events is lithologically controlled. Within the dyke, brittle structures predominate, and consist of breccia arid stockwork veins. Granite-hosted veins are controlled by more ductile-dominated deformation and consist of replacement vein networks and sheeted extensional veins. Structures associated with the third and fourth episodes of vein emplacement consist of shear and extensional veins associated with ductile-dominated deformation, and brittle, fracture-fill veins, respectively. All structures associated with veining are offset by minor brittle faults.

Deformation and vein emplacement were developed during a protracted period of north-northwest-south-southeast shortening, coupled with steeply-plunging, west-southwest extension. The felsic dyke acted as a competent layer enclosed in less competent granite, and caused a refraction of the shears into a dilational, releasing bend geometry. Brittle deformation enhanced the permeability of the dyke during the early stages of deformation and gold emplacement, and consequently, it is preferentially mineralized.