High-grade iron ore at Windarling, Yilgarn Craton: a product of syn-orogenic deformation, hypogene hydrothermal alteration and supergene modification in an Archean BIF-basalt lithostratigraphy

The lower stratigraphy of Agnew-Wiluna greenstone belt is composed of two main elements; a mafic/komatiite domain and a felsic/komatiite/basalt domain. Previous stratigraphic models show the mafic domain overlying the felsic domain. Komatiites in the latter host the vast majority of the nickel sulphide endowment of the belt (>20 significant deposits) whereas those in the mafic domain contain 3 and 4 relatively small deposits. Recently published geochemical data from well-preserved mafic domain rocks exposed in the Agnew area opens up the possibility to match these units with mafic rocks within the more structurally disrupted felsic domain. Analytical data from basalts at the Cliffs and Mount Keith Ni deposits and from the Wiluna Au mine sequence show that these can be matched to the basalt sequence stratigraphically below the Agnew Komatiite at Agnew and also show that basalts previously thought to occupy different stratigraphic positions (Centenary Bore and MacFarlanes Basalts) are laterally equivalent but structurally displaced. The revised stratigraphic model together with available age dates show that komatiites in both domains, Mount Keith and Cliffs/Agnew Komatiites, are laterally equivalent and part of the 2705 Ma Kalgoorlie-Kurnalpi komatiite LIP. This greatly enhances the Ni prospectivity of komatiites within the mafic domain which, previously being thought younger, were historically considered less prospective. The footwall to the komatiite is composed of basalt (Never Can Tell Basalt, in the mafic domain) and felsic sequences (Mount Keith Dacite in the felsic domain) that are laterally separated but occupy the same stratigraphic position and together with the komatiite correlate with the Kambalda Sequence in the south of the Kalgoorlie Terrane. The oldest crystallisation ages from the Mount Keith Dacite are 2719–2725 Ma but whether these rocks belong to the Kalgoorlie or Youanmi Terrane is currently unknown. The Kalgoorlie-aged sequence has an unconformable contact with underlying Youanmi-aged sequence (the latter including dates of 2724–2729, 2734, 2749 Ma) composed of basalt, komatiitic basalt, komatiite and minor felsic volcanic (in decreasing stratigraphic order; felsic volcanics, Songvang Basalt, Hickies Bore Basalt, Donegal Komatiite, Butchers Well Basalt). The Youanmi sequence is exposed throughout the AWB, is present in the Leonora area to the immediate south and extends eastward to other areas within the northern part of the Kalgoorlie-Kurnalpi Terranes.

Felsic

Greenstone belt

Yilgarn Craton

10.1016/j.oreoa.2019.100001

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Citations (5)

BIF-hosted iron mineral system: A review

Ore Geology Reviews (2015)

Steffen Hagemann Thomas Angerer Paul Duuring Carlos Alberto Rosiére Rosaline Cristina Figueiredo e Silva

Banded iron formation

Hypogene

Iron ore

Supergene (geology)

Yilgarn Craton

Ore genesis

10.1016/j.oregeorev.2015.11.004

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Citations (139)

Supergene modification of magnetite and hematite shear zones in banded iron-formation at Mt Richardson, Yilgarn Craton, Western Australia

Ore Geology Reviews (2019)

Paul Duuring Steffen Hagemann Carsten Laukamp Laura Chiarelli

Hypogene

Banded iron formation

Greenstone belt

Yilgarn Craton

10.1016/j.oregeorev.2019.102995

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Citations (8)

Geochemistry of Greenstone Belt Rocks Around Kalikapur-Potka-Dabanka, Singbhum Craton, East Singbhum, Jharkhand

Anvesh M Reddy

The recent geochronological data clearly brings out the Mesoarchean craton geological situation where the IOG greenstone rocks and the earliest TTG rocks have very similar ages of ~3.5 Ga and thus represent a case similar to those seen in the very ancient greenstone – TTG belts around the world including those in the Barberton greenstone belt of South Africa, Pilbara in Australia and probably the older Isua supracrustals of Greenland. Any study of these Mesoarchaen rocks in general would directly indicate petrogenesis of the TTG and thus geodynamic processes leading to craton formation, sedimentation and early life evolution in favourable marine conditions. In particular, we wanted to test the hypothesis proposed earlier on the equivalence of these small, disrupted greenstone belts occurring at places even as enclaves within the younger Singhbhum granite phases (both SBG-A and SBG-B) to the IOG, despite the fact that the interbedded cherts clearly are carbonaceous rather than typically iron bearing BIF as seen in both the Badampahar and the Daitari greenstone –BIF units. It appears that the basalt-komatiite-chert sequence of this greenstone developed as a supracrustal unit in a continental arc type setting where the shallow marine environment supported earliest life. The similar δ13C values from both the basalt and chert strongly suggest that these constituted a cogent depositional unit with a high degree of basaltseawater interaction in the marine environment.

Greenstone belt

Yilgarn Craton

Banded iron formation

Source

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Citations (0)

Yandal greenstone belt, Western Australia: 12 million ounces of gold in the 1990s

Mineralium Deposita (1998)

G. Neil Phillips J.R. Vearncombe E. Eshuys

Greenstone belt

Mineral resource classification

10.1007/s001260050150