HR: 1340h
AN: V13D-1583    [Abstracts]
TI: Geochemistry of the ~2.7 Ga Prohibition Banded Iron Formation, Meekatharra, Western Australia
AU: * González-Álvarez, I
EM: ignacio@mercatorgold.com.au
AF: Mercator Gold Australia Pty Ltd., PO Box 1256 Canning Bridge, Perth, WA 6153, Australia
AU: Thébaud, N
EM: Thebaud@mercatorgold.com.au
AF: Mercator Gold Australia Pty Ltd., PO Box 1256 Canning Bridge, Perth, WA 6153, Australia
AU: Hollingsworth, D
EM: David@mercatorgold.com.au
AF: Mercator Gold Australia Pty Ltd., PO Box 1256 Canning Bridge, Perth, WA 6153, Australia
AB: At ~2.7 Ga a large quantity of continental crust was generated coinciding with a world-wide vast formation of Iron-bearing sedimentary rocks. The key depositional mechanism for iron during that time is part of an unsettled long-standing debate.
Trace elements and particularly rare earth elements (REE) have been extensively applied as a proxy to approach the origin of these iron-bearing sedimentary formations. Accordingly, this study presents novel geochemical data from the Prohibition banded iron-formation (BIF) in Meekatharra, Western Australia, and its wrapping sedimentary package.
The Meekatharra area belongs to the Murchison Domain that is part of the Youanmi Terrane in the Yilgarn Craton. The Youanmi Terrane is composed of north-trending greenstone belts separated by extensive granite and granitic gneiss. Lava flows at the Meekatharra-Mt Magnet Greenstone Belt has been dated at 2.7 Ga. Stratigraphically the Prohibition BIF is enclosed within a sedimentary package of volcanoclastic siltstone and fine- grained sandstone bounded by mafic chlorite-schist. Samples were collected from diamond drill core at the BIF outcrop in the Prohibition gold mine pit, comprising the iron-bearing sedimentary unit and the volcanoclastic envelope associated.
Samples were normalized to bulk continental crust values. BIF samples display Fe₂O₃ content from 27 to 42wt%, featuring: (1) flat REE patterns systematically depleted between ~0.2-0.6; (2) slight negative Ce depletion; (3) positive Eu anomaly; and (4) large Cu, As and Sb positive anomalies up to 2.5, 62 and 7 respectively; whereas samples from the sedimentary volcanoclastic unit grouped at two populations: (1) with depleted REE profiles, La/Lu = 0.17-0.34, and V, Sc, Co, Cr and Ni enrichment; and (2) with concave REE patterns due to middle REE lower values accentuated by Eu depletion at ~0.8, coupled with La/Lu = 0.8-1. Both populations display Cu, As and Sb positive anomalies up to 5, 60 and 6 correspondingly.
The geochemical fingerprint of the Prohibition BIF strikingly mimics its ~2.8 Ga BIF counterpart at the Sukumaland greenstone belt of Geita, Tanzania; interpreted as the result of mixing of hydrothermal and clastic sources. Conversely, stratigraphic observations coupled with petrological observations could envision a diagenetic component in the formation of the Prohibition iron-bearing sedimentary unit. Further geochemical study is being carried out to determine if there is any geochemical signature that could constrain the genetic processes involved.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1039 Alteration and weathering processes (3617)
DE: 1051 Sedimentary geochemistry
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting