Discussion and Reply Llandovery‐Ludlow graptolites from central Victoria: New correlation perspectives of the major formations |
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| Authors: | A H M VandenBerg A C Sandford R B Rickards |
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| Institution: | 1. Department of Natural Resources and Energy , Geological Survey of Victoria , PO Box 500, East Melbourne, Vic., 3001, Australia;2. Department of Earth Sciences , University of Melbourne , Parkville, Vic., 3052, Australia;3. Department of Earth Sciences , University of Cambridge , Downing Street, Cambridge, CB2 3EQ, UK |
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| Abstract: | The Kambalda Ni province, located in the Archaean Norseman‐Wiluna greenstone belt of Western Australia, boasts the largest known concentration of komatiite‐associated magmatic Fe–Ni–Cu sulfide deposits. These are found as long, linear massive to disseminated bodies at the base of a thick komatiite sequence. The sulfide bodies are closely associated with, or contained within, trough structures at the contact with the underlying basaltic unit. In this study, the McComish Prospect, located 40 km south of Kambalda at Tramways, was studied to assess the relationships between volcanic facies, mineralisation and trough structures. The rocks in this region have variably experienced four phases of deformation, upper greenschist ‐ lower amphibolite facies metamorphism, granitoid intrusion, and subsequent alteration. Relict igneous textures are locally preserved at McComish, however, enabling the evaluation of existing geological models and interpretations. The McComish trough is considered to be entirely structural in origin and unrelated to primary volcanic processes (e.g. thermal erosion). The association of volcanic textural facies in individual flow units, and the distribution of flow units across the trough is more complex than predicted by prevailing models, suggesting an alternative komatiite lava emplacement mechanism. Results are consistent with the proposal that komatiites did not flow turbulently as widely accepted, nor did they cool by vigorous convection. Alternatively, the lavas were emplaced as inflated, lobate basalt pahoehoe‐like flows. Although Fe–Ni–Cu sulfide mineralisation at McComish is most likely volcanic in origin, its present distribution appears to be structurally controlled or modified. The zone of weakly to strongly disseminated sulfides at the base of the komatiite sequence is thickened adjacent to a major north‐northwest‐trending fault on the western margin of the trough. This fault is interpreted to have been a fluid conduit, remobilising the ore during metamorphism and deformation. |
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| Keywords: | Archaean Kambalda komatiite nickel sulfides volcanology |
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