3D Analysis of Structures at the Kambalda Nickel Mines, Western Australia

Abstract

The Kambalda Nickel Mines are a type example of massive nickel sulphide deposits located in the 2.7 Ga Archaean Eastern Goldfields Province, Yilgarn Craton, Western Australia. Nickel sulphide deposits are hosted in embayments, known as troughs, in the contact between Lunnon Basalt and the overlying Kambalda Komatiite. This contact is structurally complex as a result of several phases of compressive deformation after ore formation. The troughs and the orebodies they host define a linear pattern, trending NNW-SSE sub-parallel to each other and the regional structural trend. I This thesis proposes a new model for the origin of these troughs which is based on a comparison with extensional structures seen in the Holocene volcanic fissure swarms of Iceland. It is argued that Kambalda ore troughs were originally similar extensional structures formed synvolcanically during a previously undocumented early extensional event. This early extension created the NNW-SSE tectonic grain that characterises the eastern portion ofthe Yilgarn Craton. The model is developed to explain unusual thrust structures on the Kambalda Dome. These thrusts represent footwall shortcuts formed during subsequent compressive deformation which partially inverted the original graben bounding faults. However three-dimensional kinematic modelling of the Kambalda Dome and Tramways fold-thrust structures suggests they are not inversion anticlines above the regional scale BoulderLefroy Fault. The relationship between these structures and the Boulder-Lefroy Fault remains ambiguous. It is suggested that the regional Foster, Tramways and Democrat-Republican thrusts are thick-skin structures, hence precluding models invoking a regional thrust duplex. The new model presented in this thesis for the early structural history of the Kambalda area provides an explanation for many of the geologic features observed today in the Kambalda area