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Hydrothermal and metamorphic fluid-rock interaction associated with hypogene “hard” iron ore mineralisation in the Quadrilátero Ferrífero, Brazil: implications from in-situ laser ablation ICP-MS iron oxide chemistry

Citation

Hensler, A-S and Hagemann, SG and Rosiere, CA and Angerer, T and Gilbert, S, Hydrothermal and metamorphic fluid-rock interaction associated with hypogene 'hard' iron ore mineralisation in the Quadrilatero Ferrifero, Brazil: implications from in-situ laser ablation ICP-MS iron oxide chemistry, Ore Geology Reviews, 69 pp. 325-351. ISSN 0169-1368 (2015) [Refereed Article]

Copyright Statement

© 2015 Elsevier

DOI: doi:10.1016/j.oregeorev.2015.02.023

Abstract

In-situ laser ablation ICP-MS analyses on iron oxides in itabirite and iron ore from the Quadrilátero Ferrífero (Brazil) reveal a wide range in trace element abundances (e.g., average concentrations in hematite: Al = 40–2200 ppm, Mg = 1–930 ppm, Mn = 5–540 ppm, Ti = 3–500 ppm, V = 2–390 ppm, Cr = 1–98 ppm, As = 0.5–60 ppm). The chemistry of early hematite stages is mostly inherited from host rock and precursor magnetite, e.g., Mn concentrations correlate with bulk Mn content in itabirite. With progressive iron ore formation and modification, external fluids play a more prominent role. This is reflected by REE-Y switching from seawater-like Y/Ho ratios (> 44) in early-, to more chondrite-like Y/Ho ratios (< 34), in late-hematite stages, likely due to fluid–rock reactions with country rocks (e.g., phyllites) or exchange with magmatic hydrothermal fluids.

The following ore formation stages and key processes, supported by mineral scale mass balance calculations, are constrained: (1) martitisation, cogenetic with gangue leaching, is driven by large volumes of oxidising, Si-undersaturated fluids resulting in an absolute depletion of Mg, Mn, Al, Ti, Ni and Zn, and enrichment of Pb, As, LREE and Y; (2) the formation of granoblastic hematite and locally microplaty hematite represents a largely isochemical recrystallisation of magnetite and/or martite accompanied by a depletion of Mg and Y and an elevated Ti mobility at the mineral scale; and (3) precipitation of schistose and vein-hosted specular hematite along shear and fracture zones is driven by an external Fe–Si-rich hydrothermal fluid likely under high fluid/rock ratios.

Item Details

Item Type:Refereed Article
Keywords:LA-ICP-MS, iron ore, hematite, magnetite, itabirite, iron oxide, laser ablation ICP-MS
Research Division:Earth Sciences
Research Group:Geochemistry
Research Field:Exploration Geochemistry
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Mineral Exploration
Objective Field:Iron Ore Exploration
UTAS Author:Gilbert, S (Ms Sarah Gilbert)
ID Code:100504
Year Published:2015
Web of Science® Times Cited:15
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2015-05-18
Last Modified:2016-05-24
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