Iron-oxides constrain BIF evolution in terranes with protracted geological histories: The Iron Count prospect, Middleback Ranges, South Australia

摘要: Abstract When studied at appropriate scales of observation and using complementary methods, the intrinsic textural geochemical complexity iron-oxides can provide unparalleled insights into evolution iron ore resources from banded formation deposition to formation. Iron Count is one >20 deposits prospects within Archean Middleback Ranges belt, South Australia, in which BIFs ores display variable trace element signatures. Integrated petrography, iron-oxide laser-ablation mapping geochemistry, in-situ dating BIF-derived was undertaken assess whether features observed samples this representative prospect might be attributed localized superimposed overprint processes. The consists a West East ridge, each characterized by sequence overprints expressed as interconversions between iron-(hydr)oxides accompanying variation concentrations. Pseudomorphic replacement early magnetite hematite (martite), followed iron-hydroxides recognized Ridge. Further are veining, brecciation crystallization (micro)platy rich granitophile elements (Sn, Mo, W, U). Martitization Ridge accompanied enrichment Zn, Co Ni martite. Subsequent recrystallization martite/iron-hydroxides granoblastic marked Ti, Ta, Nb, REE elements, co-crystallization REE-minerals. This hematite, similarly these elements. Enrichment Ti interpreted infer highly saline fluids generated interaction evaporite-bearing sedimentary rocks granite-derived fluids. Post-Archean Australian Shale-normalized REY fractionation trends consistent with precipitation iron-rich minerals mixture anoxic seawater hydrothermal vent Analogous lack signature. Contrasts two ridges combination loss primary signature due severe overprinting Ridge, lateral marine depositional environment. Results validate hypothesis that signatures seen throughout belt results tectono-magmatic events have locally affected deposit. Despite undergoing different sequences ore-forming stages, well possibly distinct environments, share common overprint, dated here ~1790 Ma U Pb geochronology co-existing monazite xenotime. age considered represent timing ore-hosting rock. Such interpretation supported showing coincident ages for Wertigo Granite Myola Volcanics, occur proximal were emplaced/erupted during intracontinental rifting. approach here, combining geochemistry generically applicable other or analogous terranes elsewhere.