Highgrade iron ore at Windarling Yilgarn Craton

Authors: Thomas Angerer Steffen G Hagemann Leonid Danyushevsky

Publish Date: 2012/12/04

Volume: 48, Issue: 6, Pages: 697-728

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Abstract

Banded iron formation BIFhosted iron ore deposits in the Windarling Range are located in the lower greenstone succession of the Marda–Diemals greenstone belt Southern Cross domain Yilgarn Craton and constitute a total hematite–martite–goethite ore resource of minimum 52 Mt at 60 wt Fe 007 P Banded iron formation is interlayered with highMg basalts at Windarling and precipitated during episodes of volcanic quiescence Trace element content and the rare earth element REE ratios Y/Ho 42 to 45 Sm/Yb 15 together with positive La and Gd anomalies in ‘leastaltered’ hematite–magnetite–metachert–BIF indicate the precipitation from Archean seawater that was fertilised by hydrothermal vent fluids with a basaltic HREEY signature Hypogene iron ore in subgreenschist facies metamorphosed BIF formed during three distinct stages ore stage 1 was a syn to postmetamorphic synD1 Fe–Ca–Mg–Ni–Co–P–REE metasomatism that produced local Ni–REErich Fe–dolomite–magnetite alteration in BIF Hydrothermal alteration was induced by hot fluid flow controlled by brittle–ductile reactivation of BIFbasalt margins and crosscutting D1 faults The Ni–Corich content of dolomite and a shift in REE ratios in carbonatealtered BIF towards Archean mafic rock signature Y/Ho to 31 to 40 Sm/Yb to 1 to 2 and Gd/Gd to 12 to 14 suggest that highMg basalts in the Windarling Range were the primary source of introduced metals During ore stage 2 a syndeformational and likely acidic and oxidised fluid flow along BIFbasalt margins and within D1 faults leached carbonate and precipitated lepidoblastic and anhedral/granoblastic hematite Highgrade magnetite–hematite ore is formed during this stage Ore stage 3 hydrothermal specular hematite spcH–Fe–dolomite–quartz alteration was controlled by a lateorogenic brittle compressional/transpressional stage D4 the regionalscale shearzonerelated D3 is not preserved in Windarling This minor event remobilised iron oxides carbonate and quartz to form veins and breccia but did not generate significant volumes of iron ore Ore stage 4 involved Mesozoic to recent supergene oxidation and hydration in a weathering environment reaching down to depths of ∼100 to maximum 200 m below surface Supergene ore formation involved goethite replacement of dolomite and quartz as well as martitisation Important ‘ground preparation’ for supergene modification and upgrade were mainly the formation of steep D1 to D4 structures steep BIF/basalt margins and particularly the synD1 to synD2 carbonate alteration of BIF that is most susceptible to supergene dissolution The Windarling deposits are structurally controlled supergenemodified hydrothermal iron ore systems that share comparable physical chemical and oreforming characteristics to other iron ore deposits in the Yilgarn Craton eg Koolyanobbing Beebyn in the Weld Range Mt Gibson However the remarkable variety in pre syn and postdeformational ore textures relative to D1 and D2 has not been described elsewhere in the Yilgarn and are similar to the ore deposits in highstrain zones such as of Brazil Quadrilátero Ferrífero or Iron Quadrangle and Nigeria The overall similarity of alteration stages ie the sequence of hydrothermal carbonate introduction and hypogene leaching with other greenstone belthosted iron ore deposits supports the interpretation that synorogenic BIF alteration and upgrade was crucial in the formation of hypogene–supergene iron ore deposits in the Yilgarn Craton and possibly in other Archean/Paleoproterozoic greenstone belt settings worldwideThis work has been funded and logistically supported by Cliffs Natural Resources Asia Pacific Iron Ore Ltd The project was initiated by Nick Payne and Dave Fielding whose foresight and trust in using applied science as an aid for exploration is highly appreciated The authors are grateful for the support from Cliffs Exploration/Resource Development team Many thanks go to Andrew Ryan Principal Exploration Geologist and Rene Schellekens Senior Mine Geologist at Cliffs’ Windarling operation for the logistical support and discussions in the mines and to Peter Fey who mapped Windarling region Sarah Gilbert from CODES University of Tasmania is greatly acknowledged for her inductions at the Laser ablation system We very much appreciate the thorough reviews of Carlos Rosière and Alexandre Raphael Cabral whose critique significantly improved the manuscript

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