STRUCTURAL SETTING AND STYLE OF GOLD-BEARING SHEAR ZONES IN THE BELLETERRE DISTRICT, TEMISCAMINGUE, QUEBEC

Greenschist facies metavolcanics of the Belleterre district are hetero geneously deformed and obliquely cut by two types of gold-bearing stri ke-slip shear zones that overprint fabrics developed during a regime o f prominent shortening and subvertical elongation. Type 1 shear zones, consisting of conjugate ductile-brittle shear zones developed in isot ropic gabbro sills, are marked by a mylonitic schistosity. Shear zones and gold-bearing quartz veins of the major set strike east-west and h ave a prominent dextral shear sense. Type 2 shear zones contain two co planar sets of shear zones developed in strongly foliated metavolcanic s; an early contractional dextral set and a late extensional sinistral set. Typically, both sets lack conjugate arrangement but are characte rized by an opposite sense of horizontal displacement parallel to the boundaries. This intricate geometry may be due to a shear-sense revers al on shear zone boundaries as a result of two successive shear increm ents during a bulk non-coaxial deformation. Despite this complex kinem atic history, the plunge of orebodies in type 2 shear zones shows a si mple geometric relationship to the slip direction: these are perpendic ular to the slip direction along the host shear zone. Consequently, th e orientation and plunge of ore shoots can be predicted from knowledge of the internal kinematics of gold-bearing shear zones of the area at an early stage of exploration programs.