Microstructural timing of the Rosebery massive sulphides, Tasmania: evidence for a metamorphic origin through mobilization of disseminated base metals |
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Authors: | D. G. A. M. AERDEN |
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Affiliation: | Geology Department, James Cook University of North Queensland, Townsville, Qld 4811, Australia |
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Abstract: | Microstructural timing relationships indicate that the Rosebery massive sulphide ore, western Tasmania, Australia, formed by metasomatic replacement of 'sericite' schist during a Devonian deformation event (D3). This interpretation is contrary to earlier volcanogenic-based interpretations, but accords with the discordant position and inferred structurally controlled emplacement of the orebody. The main timing criteria are: overprinting of S3 by the late ore minerals, replacement textures in undeformed mineral parageneses, and a D3 structural control from the microscopic to the macroscopic scales. The consistent observation of these criteria in the orebody and the complete lack of pre-D3 ore argue against in situ dissolution of a primary orebody and local redeposition of sulphides by replacement. D3 deformation at Rosebery is inferred to have been characterized by heterogeneous cleavage-parallel extension, which resulted in localized microfracturing and selective replacement of zones of maximum strain rate. Continuous shifts in the strain-rate distribution pattern during progressive mineralization led to the compositional ore banding. Published Pb-isotope data point towards a Cambrian source rock for the orebody. This suggests a metamorphogenic origin by regional-scale dissolution of dispersed volcanogenic metals, focused solution transfer and concentrated redeposition in a structural trap. |
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Keywords: | massive sulphides metamorphic ore deposits metasomatic replacement ore genesis syntectonic sulphides Tasmania |
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