VCMSM Report 5 - Re-Os geochronology of Victorian mineral occurrences.
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Product description:Executive Summary:As part of the Developing Victoria's Critical Minerals Initiative, new pre-competitive geoscience has determined the age of gold, gold-antimony, gold-molybdenum, gold-silver, and gold-silver-copper mineralisation from mineral occurrences from central-west, central and northeast Victoria. These ages are important inputs for mineral systems analyses and prospectivity studies as they provide insights into the temporal and spatial distribution of mineralisation events. Results from Glenlyle in the Grampians-Stavely Zone are consistent with gold-silver mineralisation occurring at approximately the same time as the formation of the Thursday’s Gossan copper-gold-silver deposit circa (ca.) 505 Ma within the same belt of Cambrian volcanic arc rocks (the Stavely Arc). Ages from the Stawell, Bendigo and Melbourne zones add further weight to the interpretation that gold mineralisation in west-central and central Victoria was introduced in two main events at ca. 445 Ma and ca. 380-370 Ma, during and just after the culminations of the Benambran and Tabberabberan orogenies respectively. The first mineralisation event occurred in the absence of magmatism and was therefore most likely orogenic, related to prograde regional metamorphism associated with crustal thickening which, in the western Lachlan Orogen, was centred on the Bendigo Zone, but extended into the adjacent Stawell Zone in reactivated structures. The new data confirms the widespread geographic extent of orogenic gold mineralisation of this age across the Bendigo Zone including under cover, and that multiple separate deposits of this age and of Stawell mine-style occur in the western Stawell Zone, localised within the eastern Moornambool Metamorphic Complex (the Moyston Fault hanging wall high strain zone). The second event appears more complex and may contain both orogenic and intrusion-related components. An initial, likely orogenic component appears to have produced gold ± antimony mineralisation associated with crustal shortening, while subsequent intrusion-related components are characterised by a polymetallic assemblage that includes gold, which formed in a different stress-field. The new data confirms that the geographic distribution of this overall event is widespread, likely covering the entire Melbourne Zone and at least the eastern half of the Bendigo Zone, including areas under cover. The new age data combined with field relationships suggests that the early orogenic component of the ca. 380-370Ma event is likely to be mainly preserved in metasedimentary rocks since it appears to predate final emplacement of the largest intrusions. Timing of the later intrusion-related component means that mineralisation of this style may occur in both metasediments and large felsic intrusions. Results from the Omeo Zone are consistent with gold-silver-copper mineralisation at Granite Flat being intrusion-related. Other intrusions of this age and chemistry in this region may have comparable prospectivity. This report demonstrates the power of the rhenium-osmium (Re-Os) geochronometer as a tool to establish robust mineralisation ages, while highlighting the value of collecting multiple samples containing ample sulphide volume and ideally more than one sulphide phase to maximise the chances of generating a successful age. Bibliographic Reference: Waugh, S.A.F., Creaser, R.A., Cairns, C.P., Duncan, R.J. & Cayley, R.A., 2024. Re-Os geochronology of Victorian mineral occurrences. Victoria's Critical Minerals and Strategic Materials Report 5. Geological Survey of Victoria, Department of Energy, Environment and Climate Action, Melbourne, 58 pp. Download: The downloadable version of this report is supplied as (PDF 22 MB) and Attachment 1 (XLS/ODS 28KB). | ||||||
