Vein deflections and thickness variations of epithermal quartz veins as indicators of fracture coalescence

Epithermal quartz veins at the Broken Hills gold deposit, New Zealand, strike N-S and dip steeply westward. Small changes in the orientations of the three main lodes and associated mesoscopic veins define deflection lines that rake steeply in the vein plane. A method of constructing the opening vector from the three-dimensional geometry of a vein deflection is presented. The resulting vectors plunge steeply and are at low angles to the main veins and the deflection lines, indicating a large component of normal dip-slip shear during the opening of these veins. Vein thickness distributions are power-law, with similar fractal dimensions to previously reported values for non-stratabound vein arrays. The vein system at Broken Hills developed by linking of isolated extension-dominated shear veins with shear-dominated veins, generating sub-vertical and sub-horizontal fluid flow pathways.