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Timing of orogenic gold mineralisation in northeastern Tasmania: implications for the tectonic and metallogenetic evolution of Palaeozoic SE Australia

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Bierlein, FP and Foster, DA and Gray, DR and Davidson, GJ (2005) Timing of orogenic gold mineralisation in northeastern Tasmania: implications for the tectonic and metallogenetic evolution of Palaeozoic SE Australia. Mineralium Deposita, 39 (8). pp. 890-903. ISSN 0026-4598

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Abstract

New 40Ar/39Ar data from sedimentary rockhosted orogenic gold deposits in northeastern Tasmania constrain most ore formation to between 395 Ma and 385 Ma. These 385-395 Ma ages for the formation of orogenic gold agree well with an inferred Early to Middle Devonian timing for peak deformation and folding across much of northeastern Tasmania. Data from micas within alteration halos in some deposits give dates of ~420-430 Ma; these dates confirm the occurrence of an earlier Silurian phase of deformation and suggest that at least some of the mineralisation was possibly generated during this event. Gold mineralisation hosted by Middle Devonian post-tectonic granites may be genetically related to magmatism following orogeny, but these deposits formed virtually synchronously with peak deformation-related systems. Early to Middle Devonian
deformation in northeastern Tasmania also reactivated
older structures in western Tasmania, and the formation
of quartz vein-hosted gold mineralisation there. Based on
geological, structural, tectonic and metallogenetic similarities, northeastern Tasmania is interpreted as a lateral equivalent of the turbidite-dominated fold-thrust belt of the western Lachlan Orogen. However, unlike Victoria, where the sedimentary rock sequence developed on oceanic crust, northeastern Tasmania was probably underlain
by thinned Proterozoic crust, either as part of a
promontory along the Gondwana margin or as a microcontinental fragment. This may have protected the
Palaeozoic succession from large-scale, pre-Devonian
orogeny, with collision not beginning until the Middle
Devonian. These variations in the structural and tectonic
evolution, and the timing of deformation and ore formation
can explain the difference in contained gold, and
the distribution and number of major orogenic gold
deposits within the Palaeozoic of northeastern Tasmania.

Item Type: Article
Keywords: orogenic gold, Mathina Group, Tasmania, geochronology ore genesis, slate belt gold, Beaconsfield, Mangana, Golden Ridge, Lyell field, Ar-Ar dating
Journal or Publication Title: Mineralium Deposita
Page Range: pp. 890-903
ISSN: 0026-4598
Identification Number - DOI: 10.1007/s00126-004-0458-4
Additional Information:

The original publication is available at www.springerlink.com

Date Deposited: 12 Sep 2007
Last Modified: 18 Nov 2014 03:22
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