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Geochemical evolution of the banded iron formation-hosted high-grade iron ore system in the Koolyanobbing greenstone belt, Western Australia

Citation

Angerer, T and Hagemann, SG and Danyushevsky, LV, Geochemical evolution of the banded iron formation-hosted high-grade iron ore system in the Koolyanobbing greenstone belt, Western Australia, Economic Geology, 107, (4) pp. 599-644. ISSN 0361-0128 (2012) [Refereed Article]

Copyright Statement

Copyright 2012 Society of Economic Geologists, Inc.

DOI: doi:10.2113/econgeo.107.4.599

Abstract

The banded iron formation (BIF)-hosted iron ore deposits in the lower greenstone succession of the Koolyanobbing greenstone belt, 50 km north of Southern Cross in Western Australia, are a ∼200 Mt high-grade Fe (>58%) pre-mining resource and represents one of the most important iron ore districts in the Yilgarn craton. Four hypogene alteration (ore-forming) stages and one supergene upgrading event took place: (1) During ore stage 1, LREE-depleted, transition metal-enriched, Mg-Fe (±Ca) carbonates replaced quartz in BIFs. The deposit-scale alteration was most likely induced by devolatilization of sea-floor-altered, Ca-Si-depleted mafic rocks in the vicinity of the BIF during early regional (syn-D 1), very low to low-grade metamorphism and was most strongly developed on reactivated BIF-basalt contacts. (2) Ore stage 2 involved the formation of patchy magnetite ore by a syn-D 2 to-D 4 dissolution of early carbonate. Enrichment of Fe 2O 3total in magnetite iron ore was by a factor of 2 to 2.4, and compatible trace elements in magnetite, such as Ga, V, and Al, were immobile. A subdeposit-scale ferroan talc-footprint proximal to magnetite iron ore in the largest deposit (K deposit) was associated with ore stage 2 and resulted from dissolution of magnesite due to reaction with silica in the BIF under greenschist facies conditions and potentially high fluid/rock ratio. (3) Magnetite growth, during ore stage 3, forming granular magnetite-martite ore is related to a subsequent hydrothermal event, occurring locally throughout the belt, especially in D 2b faults. (4) Ore stage 4 was associated with Fe-Ca-P-(L)REE-Y-enriched hydrothermal fluids, possibly from a magmatic source such as the postmetamorphic Lake Seabrook granite that crops out about 10 km west of the Koolyanobbing deposits and at the southern margin of the greenstone belt. These Ca-enriched fluids interacted with distal metamorphosed mafic rock and influenced the BIF-ore system in a small number of deposits. They were channelled through regional D 4 faults and caused specularitedolomite- quartz alteration, resulting in Fe grades of up to 68%. (5) Supergene upgrade (ore stage 5) by (further) gangue leaching in the weathering zone was most effective in carbonate-altered BIFs and magnetite ore. This process, together with supergene martitization and goethite replacement of magnetite, led to the formation of high-grade, locally (at K deposit) high P goethite-martite ore. At Koolyanobbing, the two geochemically distinct stages of Archean carbonate alteration clearly controlled the formation of hypogene magnetite-specularite- martite-rich ore and recent supergene modification, including the further upgrade of Fe ore. © 2012 by ECONOMIC GEOLOGY.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Ore Deposit Petrology
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Mineral Exploration
Objective Field:Iron Ore Exploration
Author:Danyushevsky, LV (Professor Leonid Danyushevsky)
ID Code:81488
Year Published:2012
Funding Support:Australian Research Council (CE0561595)
Web of Science® Times Cited:25
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2012-12-10
Last Modified:2014-04-30
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