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Gazley M.F.,CSIRO | Gazley M.F.,Victoria University of Wellington | Vry J.K.,Victoria University of Wellington | Millet M.-A.,University of Cardiff | And 3 more authors.
Australian Journal of Earth Sciences | Year: 2016

The Plutonic Well Greenstone Belt (PWGB) is located in the Marymia Inlier between the Yilgarn and Pilbara cratons in Western Australia, and hosts a series of major Au deposits. The main episode of Au mineralisation in the PWGB was previously interpreted to have either accompanied, or shortly followed, peak metamorphism in the late Archean at ca 2650 Ma with a later, minor, event associated with the Capricorn Orogeny. Here we present new Pb isotope model ages for sulfides and Rb–Sr ages for mica, as well as a new 207Pb–206Pb age for titanite for samples from the Plutonic Gold Mine (Plutonic) at the southern end of the PWGB. The majority of the sulfides record Proterozoic Pb isotope model ages (2300–2100 Ma), constraining a significant Au mineralising event at Plutonic that occurred >300 Myr later than previously thought. A Rb–Sr age of 2296 ± 99 Ma from muscovite in an Au-bearing sample records resetting or closure of the Rb–Sr system in muscovite at about the same time. A younger Rb–Sr age of 1779 ± 46 Ma from biotite from the same sample may record further cooling, or resetting during a late-stage episode of metasomatism in the PWGB. This could have been associated with the 1820–1770 Ma Capricorn Orogeny, or a late-stage hydrothermal event potentially constrained by a new 207Pb–206Pb age of 1725 ± 26 Ma for titanite in a chlorite–carbonate vein. This titanite age correlates with a pre-existing age for a metasomatic event dated at 1719 ± 14 Ma by U–Pb ages of zircon overgrowths in a sample from the Marymia Deposit. Based on the Pb-isotope data presented here, Au mineralising events in the PWGB are inferred to have occurred at ca 2630, 2300–2100 Ma, during the Glenburgh and Capricorn orogenies, and 1730–1660 Ma. The 2300–2100 Ma event, which appears to have been significant based on the amount of sulfide of this age, correlates with the inferred age for rifting of the Marymia Inlier from the northern margin of the Yilgarn Craton. The texturally-later visible Au may have been deposited during the Glenburgh and Capricorn orogenies. © 2016 Geological Society of Australia.


Bernau R.,University of Southampton | Roberts S.,University of Southampton | Richards M.,Equinox Minerals PLC | Richards M.,Barrick Australia Pacific Ltd | And 3 more authors.
Mineralium Deposita | Year: 2013

The Lumwana Cu (± Co ± U) deposits of NW Zambia are large, tabular, disseminated ore bodies, hosted within the Mwombezhi Dome of the Lufilian Arc. The host rocks to the Lumwana deposits are two mineralogically similar but texturally distinct gneisses, a granitic to pegmatitic gneiss and a banded to augen gneiss which both comprise quartz-feldspar ± biotite ± muscovite ± haematite ± amphibole and intervening quartz-feldspar ± biotite schist. The sulphide ore horizons are typically developed within a biotite-muscovite-quartz-kyanite schist, although mineralization locally occurs within internal gneiss units. Contacts between the ore and host rocks are transitional and characterized by a loss of feldspar. Kinematic indicators, such as S-C fabrics and pressure shadows on porphyroblasts, suggest a top to the north shear sense. The sulphides are deformed by a strong shear fabric, enclosed within kyanite or concentrated into low strain zones and pressure shadows around kyanite porphyroblasts. This suggests that the copper mineralization was introduced either syn- or pre-peak metamorphism. In addition to Cu and Co, the ores are also characterized by enrichments in U, V, Ni, Ba and S and small, discrete zones of uranium mineralization, occur adjacent to the hanging wall and footwall of the copper ore bodies or in the immediate footwall to the copper mineralization. Unlike typical Copperbelt mineralization, unmineralized units show very low background copper values. Whole rock geochemical analyses of the interlayered schist and ore schist, compared to the gneiss, show depletions in Ca, Na and Sr and enrichments in Mg and K, consistent with replacement of feldspar by biotite. The mineral chemistry of muscovite, biotite and chlorite reflect changes in the bulk rock chemistry and show consistent increases in XMg as the schists develop. δ34S for copper sulphides range from +2. 3 ‰ to +18. 5 ‰, with pyrite typically restricted to values between +3. 9 ‰ and +6. 2 ‰. These values are atypical of sulphides precipitated by bacteriogenic sulphate reduction. δ34S data for Chimiwungo (Cu + Co) show a broader range and increased δ34S values compared to the Malundwe (Cu) mineralization. The Lumwana deposits show many characteristics which distinguish them from classical Copperbelt mineralization and which suggests that they are formed by metasomatic alteration, mineralization and shearing of pre-Katangan basement. Although this style of mineralization is reported elsewhere in the Copperbelt, sometimes associated with the more widely reported stratiform ores of the Lower Roan, none of the previously reported occurrences have so far developed the tonnages of ore reported at Lumwana. © 2012 Springer-Verlag.


Smith G.B.,Barrick Australia Pacific Ltd | Butcher R.J.,Barrick Australia Pacific Ltd | Uzbekova A.,Barrick Australia Pacific Ltd | Mort E.,Caterpillar Inc. | Clement A.,WesTrac Pty Ltd
11th AusIMM Underground Operators' Conference 2011, Proceedings | Year: 2011

Barrick (Australia Pacific) Limited initiated a trial of Caterpillar's Minegem autonomous loader technology in 2009 at the Kanowna Belle mine in Kalgoorlie. Autonomous loader technology offers the potential to improve loader productivity, reduce operating costs and improve safety through removing personnel from the mine operating environment. This paper discusses the implementation of the technology at the mine site, the data collected during the trial and quantifies the benefits of using automated loader technology in comparison with teleremote loader operation. The lessons learned from the trial and work planned for the future in respect of this technology is also discussed.


Fallon M.,Barrick Australia Pacific Ltd | Porwal A.,Curtin University Australia | Guj P.,Curtin University Australia
Ore Geology Reviews | Year: 2010

The Plutonic Marymia Greenstone Belt is the sixth largest gold camp in Western Australia. Quantitative estimates of the residual endowment of this greenstone belt based on Zipf's Law indicate that the belt contains between 5.5 and 5.9. Moz of gold in undiscovered deposits larger than 0.1. Moz, including six undiscovered deposits ranging in size between 0.7. Moz and 0.4. Moz and another six undiscovered deposits ranging between 0.3. Moz and 0.2. Moz, in addition to several smaller deposits. GIS-based prospectivity analyses using weights-of-evidence and logistic regression models were undertaken to delineate prospective areas where these yet-to-be-discovered deposits could be spatially located. This knowledge will be critical in guiding future exploration programs in the Plutonic Marymia Greenstone Belt. © 2010.


Gazley M.F.,Barrick Australia Pacific Ltd | Gazley M.F.,Victoria University of Wellington | Duclaux G.,CSIRO | Fisher L.A.,CSIRO | And 6 more authors.
Transactions of the Institutions of Mining and Metallurgy, Section B: Applied Earth Science | Year: 2012

The amphibolite-facies metabasaltic rocks of the Mine Mafic Package at Plutonic Gold Mine, Western Australia, contain an estimated endowment of 10·5 Moz of Au. A preliminary study based on portable X-ray fluorescence (pXRF) analyses identified a geochemical stratigraphy which strongly controlled the location of Au mineralisation. The present study incorporates a significantly larger pXRF dataset and presents the data in a three-dimensional framework. This dataset allows an investigation of the mineralogy of Au mineralisation with varying geochemical associations across the deposit. Historically, high As content in the mill feed resulted in poor metallurgical performance. Seamless data integration of the pXRF dataset allows for recognition of the different styles of Au mineralisation based on Au/As ratios, and visualisation of the distribution of these different mineralogical associations in three dimensions. This work enables us to better predict the As concentration of underground ore blocks, and to be proactive in optimising the mill configuration to improve metallurgical performance. © 2012 The Australasian Institute of Mining and Metallurgy Published by Maney on behalf of the Institute of Materials, Minerals and Mining and The AusIMM.


Gazley M.F.,Barrick Australia Pacific Ltd | Gazley M.F.,Victoria University of Wellington | Duclaux G.,CSIRO | Fisher L.A.,CSIRO | And 6 more authors.
8th International Mining Geology Conference 2011, Proceedings | Year: 2011

The amphibolite-facies metabasaltic rocks of the Mine Mafic Package at Plutonic Gold Mine, Marymia Inlier, Western Australia, contain an estimated total endowment of 12.2 Moz of Au, which includes 4.71 Moz of past production and 2.77 Moz of reserves and resources; the remainder comprises lower-grade inventory. Over 65 000 multi-element analyses of whole-rock core and face channel samples from the underground workings of the deposit have been collected by portable X-ray fluorescence (pXRF) using a handheld Innov-X Omega pXRF unit. The analyses were performed on pulverised samples through paper bags, and were corrected using a pulverised, matrix-matched, reference standard. This method of data correction compares favourably with conventional XRF analyses performed on the same samples. A preliminary study based on pXRF analyses from a small number of drill holes found that a geochemical stratigraphy was evident in the pXRF data, and that this stratigraphy strongly controlled the location of Au mineralisation. The present study incorporates a much larger pXRF data set that samples a greater volume of diamond drill core and face channel samples and presents the data in a three-dimensional (3D) framework. This data set allows an investigation of the mineralogy of Au mineralisation with varying geochemical associations across the deposit. Historically, there has been a strong relationship identified between As and Au, which has caused issues with metallurgical performance, rendering some areas of the deposit only marginally economic. Utilising seamless data integration of the pXRF data set allows for recognition of the different styles of Au mineralisation using elemental concentrations and ratios from the multi-element analyses (Au:As, Au:As:Cu, As:Cu vs. K:V), and to visualise the distribution of these different mineralogical associations in 3D. The results of the 3D modelling and geochemical characterisation of the different styles of Au mineralisation are currently the focus of an extensive metallurgical testing program, the preliminary results of which are presented here.


Gazley M.F.,Victoria University of Wellington | Gazley M.F.,Barrick Australia Pacific Ltd | Vry J.K.,Victoria University of Wellington | Boorman J.C.,Victoria University of Wellington
Journal of Metamorphic Geology | Year: 2011

The metamorphosed mafic rocks of Archean greenstone belts host major orogenic gold deposits, and may record information about changing pressure-temperature (P-T) conditions that could contribute to understanding of Archean geodynamic processes. Until recently, it was difficult to obtain good constraints on pressure and temperature from these rocks. Here we present results of P-T pseudosection calculations in the NCFMASHTOS (Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O-SO2) system, using as an example typical amphibolite facies metabasaltic rocks from the Plutonic Gold Mine in the Neoarchean Plutonic Well Greenstone Belt (PWGB), Marymia Inlier, Western Australia. The pseudosections together with observed mineral compositions and mineral assemblages in the rocks are used to argue that a previously unrecognized steep pressure increase (from ∼3-4kbar at ∼500°C to ≥8kbar at ∼600°C) accompanied metamorphism to peak temperatures. The P-T data presented here could be the result of either horizontal or vertical tectonics. Existing models for the early evolution of the PWGB involve nappe stacking supported by relatively cold strong crust, with little overall change in thickness. While the available evidence from the study area and the wider region is not yet sufficient to confirm whether the peak metamorphic conditions were attained by horizontal or vertical tectonic means, the P-T data presented here can provide region-specific constraints for computer modelling that may provide a more definite answer in the future. © 2011 Blackwell Publishing Ltd.


Gazley M.F.,Victoria University of Wellington | Gazley M.F.,Barrick Australia Pacific Ltd | Vry J.K.,Victoria University of Wellington | du Plessis E.,Barrick Australia Pacific Ltd | Handler M.R.,Victoria University of Wellington
Journal of Geochemical Exploration | Year: 2011

Stratigraphy, structure and host-rock chemistry are dominant controls on the location of Au in Archaean greenstone-hosted Au deposits, but the stratigraphy in such deposits is seldom obvious due to the monotonous nature of the host rocks or pervasive alteration associated with Au mineralisation. Portable, hand-held, X-ray fluorescence (pXRF) spectrometry provides a method to rapidly collect large amounts of whole-rock geochemical data that can yield new insights into both stratigraphy and Au localisation. Here we present results of pXRF analyses of samples from a representative section through Au-mineralised amphibolite-facies metabasaltic rocks at Plutonic Gold Mine, Western Australia. These data illustrate a geochemical stratigraphy in which individual lava flows can be identified on the basis of element concentrations. The most evolved basalts are at the structural base of the succession, and the least evolved at the top of the sequence, confirming previous geochemical interpretations and textural evidence that the sequence is overturned, and demonstrating for the first time that the presented section does not involve significant structural repetition. In conjunction with Au assay data, the pXRF data reveal that Au commonly occurs along basalt flow boundaries. The elemental concentration data clearly demonstrates for the first time the stratigraphic control on Au mineralisation that is not readily apparent at the macroscopic level. The methods described in this paper are readily applied, and have the potential to enhance the understanding of otherwise unclear stratigraphy and its control on mineralisation in many different types of deposits worldwide. © 2011 Elsevier B.V.

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