Distinguishing basinal- and magmatic-hydrothermal IOCG deposits, Cloncurry District, Northern Australia

Oliver, Nicholas H.S., and Rubenach, Michael J. (2010) Distinguishing basinal- and magmatic-hydrothermal IOCG deposits, Cloncurry District, Northern Australia. In: Proceedings of the 10th Biennial Meeting of the the SGA 2009 (2) pp. 647-649. From: Smart Science for Exploration and Mining: 10th Biennial Meeting of the SGA 2009, 17-20 August 2009, Townsville, QLD, Australia.

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Abstract

We recognise two distinctive styles of IOCG deposits in the Cloncurry District of the Proterozoic Mount Isa Block. The earliest (Osborne) type (1680 to 1600 Ma) is dominated by basinal and/or metamorphic fluids, deformed ores in shear zones, sodic-calcic alteration, intra-basinal metal and sulphur sources, and chemically favourable ore hosts. Fluid circulation was likely driven by extensional shearing or convection and magmatic heat inputs, and there a genetic connection to the region's large Pb-Zn ± Ag deposits (Cannington, Mt Isa Pb-Zn) is possible. The later (Ernest Henry) type (c. 1530 Ma) shows potassic alteration, and co-precipitated magnetite and calcite in milled breccia. Geochemical data indicate mixtures of mantle or magmatic fluids with sedimentary formation waters (or their metamorphosed equivalents), and an abundance of CO₂₋ and Cl+F-bearing fluids. These formed primarily by release of fluids, S and probably metals from crystallizing A-type granitoids and tholeiitic gabbros via fluidised breccia pipes, and have likely parallels with Olympic Dam and other large to giant IOCGs worldwide hosted in milled hydrothermal breccias. Fluidisation occurred by violent release of overpressured fluids across permeability barriers near intrusions, carrying volatiles and cm- to m-scale rock fragments upwards, and forming ore deposits in cooling and de-pressurising dilatant structural traps.

Item ID: 22960
Item Type: Conference Item (Research - E1)
ISBN: 978-0-9805-5868-5
Keywords: Mount Isa, breccia, basin, copper, gold, fluidisation, CO2
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Date Deposited: 15 Aug 2012 05:48
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 50%
04 EARTH SCIENCES > 0403 Geology > 040312 Structural Geology @ 50%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840102 Copper Ore Exploration @ 33%
84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840104 Iron Ore Exploration @ 33%
84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840105 Precious (Noble) Metal Ore Exploration @ 34%
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