Three-dimensional shear zone and joint geometry and permeability in the Sigma Gold mine, Canada

摘要

We have prepared a 3D-CAD representationof the mineralized shear zones in the Sigma mine, indicating that these are splays of transpressional shears. Individual splays are continuous for up to sixhundred meters, but dilatd and vein-infilled, once highly permeable splay atches are much smaller (10-400m, avg. 25m). Gold-mineralized parts of these patches have a size of 10-80 meters and a distorted disc shape. Gold-mineralized subhorizontal joints are mechanically associated with the splays and occur predominantly along their tiplines. The high-permeability patch-normal spacing and teh number of patch intersections indicates clustering and hydrologic interactions among patches. Gold grade is highest where high-permeability patches intersect. While compacted mineralized fault-breccias and fractures document the transient permeability of teh shear zones, these structures originated, were sealed and re-opened episodically at fixed locations relative to their host structures. This indicates that high-permeability patches are largely stationary over the course of the mineralising event.