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Polymetallic Mineralisation in the Chillagoe District of North-East Queensland: Insights Into Base Metal Rich Intrusion-Related Gold Systems

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Polymetallic Mineralisation in the Chillagoe District of North-East Queensland: Insights Into Base Metal Rich Intrusion-Related Gold Systems ResearchOnline@JCU This file is part of the following reference: Lehrmann, Berit (2012) Polymetallic mineralisation in the Chillagoe district of north-east Queensland: insights into base metal rich intrusion-related gold systems. PhD thesis, James Cook University. Access to this file is available from: http://eprints.jcu.edu.au/29094/ The author has certified to JCU that they have made a reasonable effort to gain permission and acknowledge the owner of any third party copyright material included in this document. If you believe that this is not the case, please contact [email protected] and quote http://eprints.jcu.edu.au/29094/ Polymetallic mineralisation in the Chillagoe district of north-east Queensland – insights into base metal rich intrusion-related gold systems Thesis submitted by Berit Lehrmann (Dipl. Min.) May 2012 for the degree of Doctor of Philosophy in the School of Earth & Environmental Sciences James Cook University STATEMENT OF ACCESS I, the undersigned, author of this work, understand that James Cook University will make this thesis available for use within the University Library and, via the Australian Digital Theses network, for us elsewhere. I understand that, as an unpublished work, a thesis has significant protection under the Copyright Act and, I wish this work to be embargoed until May 31st, 2013. After which date I do not wish to place any further restriction on access to this work. All users consulting this thesis will have to sign the following statement “In consulting this thesis I agree not to closely paraphrase it in whole or in part without the written consent of the author; and make proper public written acknowledgement for any assistance that I have obtained from it.” 23/05/2012 i STATEMENT OF SOURCES DECLARATION I declare that this thesis is my own work and has not been submitted in any form for another degree or diploma at any university or other institution of tertiary education. Information derived from the published or unpublished work of others has been acknowledged in the text and a list of references is given. 23/05/2012 ii ELECTRONIC COPY I declare that the electronic copy of this thesis provided to the James Cook University Library is an accurate copy of the print thesis submitted, within the limits of the technology available. 23/05/2012 iii STATEMENT OF CONTRIBUTIONS Financial contributions included: . Living stipend and research scholarship from Kagara Ltd & Mungana Goldmines Ltd . James Cook University Graduate Research School Grant 2009 . James Cook University School of Earth and Environmental Sciences grant 2010 General contributions of others included: . Prof. T.G. Blenkinsop: supervision throughout the second half of the PhD project and revision of all chapters . Dr. A.I.S. Kemp: supervision throughout the second half of the project including help in redesigning the project, LA-ICP-MS analysis and revision of some chapter drafts . Prof. N.H.S. Oliver: supervision throughout the first half of the project, help in designing the project and assistance in the field . Dr. M.J. Rubenach: supervision throughout the first half of the project and assistance in the field . Dr. K.L. Blake, Dr. J. Whan, Dr. S. Askew: technical assistance during EMP & CL analysis (chapters 3, 4, 5 and 6) at the Advanced Analytical Centre, James Cook University, Townsville . Dr. Y. Hu: technical assistance during LA-ICP-MS analysis (chapter 4, 5 and 6) at the Advanced Analytical Centre, James Cook University, Townsville . Dr. M. Norman: Re-Os isotope analysis (chapter 5) at the Research School of Earth Sciences, Australian National University, Canberra . Mr Darren Richardson: preparation of all polished thin and thick scetions . SGS Townsville mineral laboratory assay analysis (chapter 5) iv ACKNOWLEDGEMENTS First I would like to thank Kagara Ltd and Mungana Goldmines Ltd for their financial support, logistic support to and from Chillagoe as well as access to the property, samples and data. I greatly appreciate all the help and support given to me by the geologists, field assistants and other company members from the exploration team, the Townsville office and other persons up in Chillagoe and for sharing their thoughts and knowledge about the deposits and geology. Thanks in particular to Charlie Georgees, Ian Morrison, John Nethery, Robert Henry, Kay Mathews, Rowena Duckworth, and the hard core ‘fieldi’ crew Kevin, James, Ewen, Macca and Mervin. I am grateful to Prof. Tom Blenkinsop for redesigning the project and his constructive criticisms, improvements and patience during the revision of all chapter drafts. I also acknowledge Dr. Tony Kemp for redesigning the project, his help during LA-ICP-MS analysis and revision of some chapter drafts. Prof. Nick Oliver and Dr. Mike Rubenach are thanked for their help in getting the project started and providing assistance in the field. Technical support by Dr. Kevin Blake (EMP, CL), Dr. Yi Hu (LA-ICP-MS), Dr. Jen Whan (EMP, CL), Dr. Shane Askew (EMP, CL) at the AAC-JCU (Townsville) and Re-Os isotope analysis by Dr. Marc Norman (Research School of Earth Sciences, Australian National University, Canberra) is gratefully acknowledged. I also would like to thank Darren Richardson (Ingham Petrographics) for the preparation of thin and thick sections. Thanks also to everyone else in the SEES & AAC department in particular Glen Connolly, Beth Moore, Judy Botting, Judith Casey for all the help they provided and Clive Grant and Robert Scott for solving numerous computer license and field trip tracker issues. Finally, I would like to thank the many people far away from home for their constant encouragement, support and patience. v ABSTRACT The Chillagoe district, located in northeast Queensland, is host to several polymetallic mineral deposits, which comprise three major metallogenic commodities: 1. Cu-Au, 2. Zn-Pb-Cu and 3. Sn-W-Mo. Metals such as W, Mo, Bi, Te, (± As, Sb) vary in concentrations within and between deposits. The deposits occur in a wide range of styles such as porphyries, breccias, skarns, and veins. Previous workers suggested that granites related to four igneous supersuites of the Permo-Carboniferous Kennedy Igneous Province were the source of the diverse metal commodities, whereas the calc-alkaline, metaluminous to weakly peraluminous, I-type, weakly oxidised to reduced, compositionally evolved nature of the oldest supersuite suggests that it alone could be the source for the polymetallic deposits. The mineralisation could be recognised as having affinities to intrusion-related gold deposits (IRG), adding to the increasing number of such systems recognised within the Tasmanides of eastern Australia. Although an IRG system could explain the polymetallic nature of the deposits in general, the economic grade of base metals hosted by deposits of the Chillagoe district is quite unusual for an IRG system. This thesis investigated three polymetallic deposits (Recap, Mungana and Red Dome) of the Chillagoe district by combining petrographical, electron-microprobe (EMP), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and radiogenic isotope studies (Re-Os, U-Pb and Lu-Hf) in order to improve the understanding of the metal diversity of IRGs, and provide insights into the processes of magma formation and evolution related to such systems. Petrographical studies showed that skarn formation at all three deposits is very similar and show no differences to the processes in other intrusion-related skarn systems. Mineralisation on the other hand differs regarding their major commodities, with Redcap and Mungana being base metal dominant, but also hosting minor gold mineralisation, whereas Red Dome is dominated by copper mineralisation and also comprises gold mineralisation and a very minor base metal commodity. The difference in the metal commodities and economic grade was caused by the emplacement of two compositionally different magmatic phases. The primary magmatic event (~ 326-320 Ma), characterised by weakly reduced and strongly fractionated rocks, provided the metallogenic diversity typical for an IRG system with some of the metals being incorporated into silicate phases (Sn, Zn) and As-Cu-Sb sulphide minerals (Au). The second magmatic event (more oxidised and less fractionated, ~312-305 Ma) caused remobilisation of metals related to the primary event, as well as adding S and possibly Zn, Cu, Pb to the system at Redcap and Mungana, whereas at Red Dome in addition to the sulphur, Cu and maybe Au was introduced. vi Studies of the mineral chemistry showed that composition of garnets and sphalerite have the potential to be used as exploration tool to locate causative intrusions. Due to the complexity of the systems investigated here, the concept should be tested again to establish its use in other multiphase IRG systems. Trace element concentrations and radiogenic isotope data (Lu-Hf) of zircons on the other hand showed that the diverse metallogeny of the IRG systems can be linked to the most fractionated phase in the magmatic system, with the magma originally being derived from a crustal metasedimentary source (in Chillagoe: ~2.0-2.5 Ga). The great advantage of determining such information from zircons rather than from whole rock data is that the latter can become easily affected by metamorphism, (hydrothermal) alteration and/or weathering, whereas physico- chemically robust zircons preserve their primary information. vii TABLE OF CONTENTS STATEMENT OF ACCESS……………………………………………………………………...i STATEMENT OF SOURCES…………………………………………………………………...ii
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