Review of the Burra Mine Project 1980-2008
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Minerals and Energy (M&E) Division geochronologist Anthony Reid has determined an age of 797 ± 5 Ma on samples of the enigmatic Burra porphyry collected by M&E geologist John Drexel almost 30 years ago during detailed mapping of the Burra open cut. The U/Pb age was obtained from subhedral to euhedral zircon crystals of igneous origin with no evidence of contamination, overgrowth or transport. The Burra orebody and its geological relationships have been re-examined by John Drexel, Wolfgang Preiss and Wayne Cowley, firstly to compile all mapping data into a publicly available data set and, secondly, to formalise the definition of the distinctive tuffaceous siltstone–dolomite–limestone sequence into which the porphyry and its associated mineralisation has been intruded. Wolfgang Preiss, during regional mapping of the BURRA 1:250 000 geological map with Wayne Cowley, had previously recognised the siltstone–dolomite–limestone package as a distinctive, mappable stratigraphic unit within the otherwise dominantly dolomitic Skillogalee Dolomite. Detailed mapping by John Drexel and Wayne McCallum in the open cut and petrological examination by AMDEL petrologist Andrew Kemp and M&E petrologist Mike Farrand in the 1980s have demonstrated both K-feldspar-rich and albite-rich tuffaceous units. Compilation of all field and petrological data, and now revelation of the porphyry age, provide the opportunity to define this stratigraphic unit as the Kooringa Member (Preiss et al., in prep.). Extraction of zircons from these tuffaceous units for U/Pb dating is planned to establish a depositional age for the Skillogalee Dolomite. Copper mineralisation at Burra has long been linked to hydrothermal alteration associated with intrusion of the porphyry. Previously these were thought to have been emplaced long after Delamerian folding of the host sedimentary rocks. The newly determined age convincingly demonstrates that these events occurred soon after deposition of the host and that there is stratigraphic control on mineralisation. The Kooringa Member should therefore be regarded as a prime copper exploration target in the Adelaide Geosyncline, but its true extent has yet to be mapped. Reference: Preiss, W.V., Drexel, J.F., Reid, A. and Cowley, W.M., in prep. The Kooringa Member — a tuffaceous siltstone–dolomite–limestone sequence hosting the Burra copper mineralisation in the Skillogalee Dolomite. MESA Journal. |
Abstract from Review of the Burra Mine Project, 1980-2008: a progress report (.html)
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- Page Last Modified: November 8, 2011