Geology, paragenesis, and alteration patterns of the E1 group of iron oxide-Cu-Au deposits, Cloncurry district, northwest Queensland, Australia

Case, George, Chang, Zhaoshan, Lilly, Richard, Blenkinsop, Thomas, and Huizenga, Jan Marten (2014) Geology, paragenesis, and alteration patterns of the E1 group of iron oxide-Cu-Au deposits, Cloncurry district, northwest Queensland, Australia. In: Abstracts from the 2014 Conference of Economic Geologists. From: SEG 2014 Conference: Building Exploration Capability for the 21st Century, 27-30 September 2014, Keystone, CO, USA.

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The Proterozoic E1 Group of iron oxide-Cu-Au deposits, composed of E1 North, East, and South, is located 8 km east of the world-class Ernest Henry IOCG deposit in the Cloncurry district of northwest Queensland, and contains estimated resources of 48 Mt averaging 0.72% Cu and 0.21 g/t Au. The E1 Group has been recently discovered below 20-50 m of Mesozoic sedimentary rocks near the world-class Ernest Henry IOCG, but its relationship to that deposit is not clear. Modelling of drill data indicates that the orebody is stratigraphically controlled within a series of folded, discontinuous metatuff, metasiltstone, marble and metapsammite lenses intercalated with metabasalt and glomerophyric metaandesite. The metaandesite is likely equivalent to the intermediate volcanic rocks hosting the Ernest Henry deposit. The E1 North orebody is controlled by a NW-plunging antiform, with mineralization occurring in a single major, discontinuous metatuff lens on the east limb, and in two discontinuous metatuff lenses on the west limb. The west limb of the antiform is truncated by Corella Breccia, and the east limb continues to the southeast to form the west limb of the E1 South synform. The E1 South orebody is comprised of three discontinuous lenses within this synform, with the upper lenses hosted in metasiltstone and the lowermost lens hosted in metatuff continuing from the E1 North antiform east limb. The uppermost ore lens of E1 South grades into barren carbonaceous metapelite, and the entire E1 South system is truncated to the southeast by the Mount Margaret Fault Zone. E1 East ores are hosted in two steeply east-dipping lenses of metasilts intercalated with metabasalt and surrounded by Corella Breccia. E1 Group mineralization is characterized dominantly by fine (0.05 mm) to coarse (3 mm)-grained layer-controlled magnetite-chalcopyrite-pyrite±Fe-Mn-carbonate±barite±fluorite±biotite±albite±chlorite±apatite±arsenopyrite±pyrrhotite±monazite (tr.) ±coffinite (tr.) ±uraninite(tr.) replacement of layered metatuff and metasilt, and matrix-controlled replacement of volcaniclastic metatuff, associated with Fe-Mn-carbonate-quartz-barite-fluoritealbite-chalcopyrite-magnetite-biotite-chlorite-apatite veining. Very high-grade ores (>2% Cu) typically exhibit a massive texture which completely overprints earlier layering. This replacementdominated mineralization style is substantially different from that of the hydrothermal brecciahosted Ernest Henry orebody. The E1 paragenetic sequence is comprised of four major stages: 1) Sodic-calcic: albite-quartzhematite±actinolite±magnetite; 2) Potassic(-Fe): K-feldspar-biotite-magnetite; 3) Ore stage A: magnetite-Fe-carbonate-chalcopyrite-pyrite-quartz-barite-fluorite-biotite (±Ba-Cl)-chloriteapatite-muscovite (±Ba)-monazite; and 4) Ore stage B: Mn-(Fe)-carbonate-barite-fluorite-chalcopyrite-pyrite-quartz-sericite-arsenopyrite-pyrrhotite. Stage 1 and 2 alterations are heavily overprinted by mineralization, and are most visible immediately outside the orebody and within and proximal to the Corella Breccia. Stages 3-4 carbonate veins, accompanied by chlorite and sericite alteration, are widespread throughout the mine lease, but are most prevalent outside the orebody in the more brittle metabasalts, metaandesites and Corella Breccia. In the west limb of the E1 North antiform the carbonate veins contain abundant apatite, magnetite, and pyrite, forming a magnetic and Fe-P-rich geochemical anomaly extending 150-200m southwest from the orebody. The E1 Group and Ernest Henry share a similar paragenetic sequence of early sodic (-Ca), intermediate potassic (-Fe), and late mineralization alteration, suggesting a similar genetic origin. The reason(s) for differing mineralization styles between the two systems, despite being hosted in similar rock types, is under investigation.

Item ID: 43685
Item Type: Conference Item (Abstract / Summary)
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Date Deposited: 19 Jul 2016 03:36
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840199 Mineral Exploration not elsewhere classified @ 100%
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