Preliminary 3-D geological model of the Kalgoorlie region, Yilgarn Craton, Western Australia, based on deep seismic-reflection and potential-field data

The granite-greenstone terranes of the Eastern Goldfields Province, Yilgarn Craton, Western Australia, are a major Australian and world gold and nickel source. The Kalgoorlie region, in particular, hosts several world-class gold deposits. To attempt to understand why these deposits occur where they do, it is important to understand the crustal architecture in the region and how the major mineral systems operate in this architecture. One way to understand these relationships is to develop a detailed 3-D geological model for the region. The best method to map the 3-D geometry of major geological structures is by acquisition and interpretation of seismic-reflection profiles. To contribute to this aim, a grid of deep seismic-reflection traverses was acquired in 1999 to examine the 3-D geometry of the region in an area including the Kalgoorlie mineral region and mineral fields to the north and west. This grid was tied to the 1991 regional deep seismic traverse and 1997 high-resolution seismic profiles in the same region. The grid covers an area measuring approximately 50 km wide by 50 km long and extended to a depth of approximately 50 km (below the base of the crust in this region). The resulting 3-D geological model was further constrained by both surface geological data and geophysical interpretations, with the seismic interpretations themselves also constrained by gravity and magnetic modelling. The 3-D model was used to investigate the geometric relationships between the major faults and shear zones in the area, the relationship between the granite-greenstone succession and the basement, and the spatial relationships between the greenstones and the granites. Interpretation of the grid of seismic lines and construction of the 3-D geological model confirmed the existence of the detachment surface and led to the recognition that the granite-greenstone contact usually occurs at a much shallower level than the detachment. Also, west-dipping faults in the vicinity of the Golden Mile, including the Abattoir Shear through to Boulder-Lefroy Fault, appear to be more important than previously thought in controlling the structure of that area. An antiformal thrust stack occurs beneath a triangle zone centred on the Golden Mile. The Black Flag Group was deposited in a probable extensional setting, and late extension was also probably more important than previously thought. The granite-gneiss domes were uplifted by the formation of antiformal thrust stacks at depth beneath them.