Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/121346
Type: Thesis
Title: Mineralogy and Geochemistry of Iron-Oxides in Precambrian Banded Iron Formations of the Middleback Ranges, South Australia
Author: Keyser, William Mark
Issue Date: 2019
School/Discipline: School of Chemical Engineering and Advanced Materials
Abstract: The Gawler Craton in South Australia is host to hundreds of Fe-rich deposits of varying types, most well-known are those of iron-oxide copper gold (IOCG) type within the ~1.6 Ga Olympic Cu-Au Province. However, only iron ore deposits of the Archean-aged Middleback Ranges (Eyre Peninsula) belt are unequivocally recognized as being banded iron formation (BIF)- derived. Although other deposits are alleged to be of BIF origin, their formation remains illconstrained. Petrography and geochemistry of iron-oxides from the Middleback Ranges are studied at various scales of observation to constrain ore formation in BIFs from a terrane with a protracted geological history. The age, petrography and geochemistry of granites and mafic lithologies associated with the ores are used to constrain ore formation from deposition to ore enrichment. Several Fe-rich prospects from different parts of the Gawler Craton are studied in further detail to test the reliability of iron-oxides to track ore formation. Petrography and trace elements signatures of iron-oxides from deposits along the Middleback Ranges indicate domain heterogeneity throughout the belt with respect to depositional environment and interaction with fluids of both granitic (U, W, Sn) and mafic affiliation (Cr, Ni, Zn). The discovery of U-bearing hematite in BIF ores is followed by LAICP- MS U–Pb dating in one prospect, Iron Count. The age (~1790 Ma) is concordant with monazite ages in the same sample and coincident with emplacement of the adjacent Wertigo Granite. This proves the reliability of hematite for dating the overprinting events that contributed to upgrading of BIF to ore. Archean ages are documented from SHRIMP dating of zircon in granites (3.0-3.24 Ga) adjacent to ore along the belt and for amphibolites (~2.5 Ga) within the BIFs. The youngest age (~780 Ma) is obtained from dolerites crosscutting the ores, the first confirmation of Gairdner-affiliated dikes in the Eyre Peninsula. This supports an Archean environment of BIF deposition post-dating the granite basement and contemporaneous with mafic magmatic activity. The youngest tectono-magmatic event is also recorded by U–Pb dating of Iron Knight hematite (~680 Ma). Alkali-calcic alteration of granites, typical of ~1.6 Ga Hiltaba granitoids, gives indication for undiscovered IOCG mineralization. Iron-oxides from the Island Dam prospect within the Olympic Cu-Au Province show both BIFlike and IOCG (W-Sn-rich) signatures. The ore is associated with actinolite skarn formed on behalf of ~1.75 Ga Wallaroo volcano-sedimentary formation, with carbonate- and Fe-rich horizons affected by emplacement of Hiltaba-aged granitoids. High-grade, Zr- and Ti-rich hematite from Peculiar Knob deposit (Mount Woods Inlier, northern Gawler Craton) was studied from micron- to nanoscale. Baddeleyite (nm-wide needles in hematite) accounts for high-Zr (up to 650 ppm) in hematite whereas interstitial zircon gives an age of ~1.74 Ga, concordant with the Kimban Orogeny. The ore, previously considered BIF, is re-interpreted as a metamorphosed Fe-rich sediment with detrital titanomagnetite sourced from mafic rocks, and also featuring a Hiltaba overprint (W-, Nb-, Sb- , Sn-rich rims in hematite). Whereas BIF-hosted iron-oxides share generic characteristics, the transformation from BIF to ore must be understood in the context of the local geological setting underpinned by sound petrographic characterization at appropriate scales. The petrographic and geochemical approach used here, combined with hematite dating, can be used to understand ore genesis. Bridging micron- to nano- scales of observation gives insights into trace element incorporation into, and later release from, iron-oxides.
Advisor: Ciobanu, Cristiana
Cook, Nigel
Ehrig, Kathy
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering and Advanced Materials, 2019
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
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