SOURCE OF SCHEELITE IN THE TURBIDITE-HOSTED OROGENIC AU DEPOSITS OF OTAGO, NEW ZEALAND: AN INTEGRATED METAMORPHIC SOURCE MODEL EXPLAINING THE PRESENCE OR ABSENCE OF SCHEELITE IN TURBIDITE-HOSTED OROGENIC AU DEPOSITS Ben J. Cave (BSc. Honours, University of Adelaide) ARC Centre of Excellence in Ore Deposits (CODES) School of Physical Sciences (Earth Sciences) Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy University of Tasmania May, 2016 Declaration This thesis does not contain any material that has been accepted for degree or diploma by the University or any other institution, except where it has been duly acknowledged in the thesis. To the best of the author's knowledge it also contains no previously published material written by another person, except where it is acknowledged in the text of the thesis. Ben J. Cave Date: Ct-o9- 2o({, B.J. Cave ii Authority of Access The publisher of the papers comprising Chapter 7 (The Canadian Mineralogist) and Chapter 8 (Mineralium Deposita) holds the copyright for that content, and access to the material should be sought from the respective journals. The remaining non published content of the thesis may be made available for loan and limited copying and communication in accordance with the Copyright Act 1968. B.J. Cave iii Statement of Co-authorship The following people and institutions contributed to the publication of work undertaken as part of this thesis: Ben Cave, University of Tasmania = Candidate Aleksandr Stepanov, University of Tasmania = Author 1 Dave Craw, University of Otago = Author 2 Ross Large, University of Tasmania = Author 3 Jacqueline Halpin, University of Tasmania = Author 4 Jay Thompson, University of Tasmania = Author 5 Iain Pitcairn, Stockholm University = Author 6 Sean Johnson, University of Tasmania = Author 7 Chris White, Nova Scotia Department of Natural Resources = Author 8 Stafford McKnight, Federation University Australia = Author 9 Author details and their roles: Paper 1, Release of Trace Elements through the Subgreenschist Facies Breakdown of Detrital Rutile to Metamorphic Titanite in the Otago Schist, New Zealand: Located in Chapter 7 Candidate was the primary author (75%) and combined with authors 1, 2, and 3 contributed to the idea, its formalization, and development (15%). Author 4 provided U-Pb B.J. Cave iv geochronological ages for zircons, and assisted in the refinement and presentation ( I 0%). Author 5 assisted in the refinement of the methodology section (5%). Paper 2, A Metamorphic Mineral Source for Win the Turbidite-hosted Orogenic Au Deposits of the Otago Schist, New Zealand: Located in Chapter 8 Candidate was the primary author (80%) and combined with authors 2, 3, 6, and 7 contributed to the idea, its formalization, and development (15%). Author 5 assisted in the refinement of the methodology section (5% ). Paper 3, The Source of Win Turbidite-hosted Orogenic Au Mineralization: Implications for Metamorphic Processes and Metal Sources in the Meguma and Bendigo-Ballarat Terranes: Located in Chapter 9 Candidate was the primary author (80%) and combined with author 3, 8, and 9 contributed to the idea, its formalizationand development (15%). Author 5 assisted in the refinement of the methodology section (5%). We the undersigned agree with the above stated "proportion of work undertaken" for each of the above published (or submitted) peer-reviewed manuscripts contributing to this thesis: Ross Large Leonid Danyushevsky Primary Supervisor Co-Supervisor/ Head of Earth Sciences School of Physical Sciences School of Physical Sciences University of Tasmania University of Tasmania B.J. Cave v Abstract The Otago Schist in the South Island of New Zealand is a Mesozoic-aged accretionary belt comprised predominately of metaturbiditic graywackes and argillites, with subordinate metabasic horizons and ultramafic slices. A complete crustal section is exposed from prehnite-pumpellyite facies on the flanks to upper greenschist facies (biotite-garnet-albite) in the center of the belt. Quartz veins are abundant throughout the schist, some of which are enriched in a variety of metals including W, Au, As, Ag, Hg, and Sb. Historically, W (scheelite; CaWO4) has been exploited from some of these veins, with in excess of 3,000 tons of scheelite concentrate having been produced. Previous research on metal sources for these deposits has defined the sources for most of these metals. Sources are well-constrained for Au, As, Ag, Hg, and Sb, with the metamorphic recrystallization of sedimentary pyrite (to metamorphic pyrrhotite) having been shown to mobilize these metals. The source for W, however, has not been constrained. The primary aim of this thesis is to investigate the source of W (scheelite) in the turbidite-hosted orogenic Au deposits of the Otago Schist. Major lithologies have been sampled and analyzed from the lowest metamorphic grade to the highest metamorphic grade observed in the Otago Schist. Combined laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) traverses, images, and spot analyzes, show that detrital rutile is the most important host mineral for W in the subgreenschist facies rocks, and that its prograde metamorphic recrystallization to titanite releases significant amounts of W. Mass balance calculations indicate that this mineral reaction has potential to mobilize over 1,100 tons of W from every 1 km3 (0.41 g of W per ton of rock) of subgreenschist facies rock metamorphosed to greenschist facies conditions. Scheelite development closely follows the progression of this W-liberating reaction, with early formation of scheelite micrograins B.J. Cave vi within the fabric of the rock evolving to locally and regionally sourced scheelite-bearing veins. Scheelite is present in the Otago Schist in two major vein forms, that is, syn- metamorphic and late-metamorphic veins. Syn-metamorphic veins sampled at Fiddlers Flat and Lake Hāwea show distinct differences in chemical composition to scheelite from late metamorphic veins at the Macraes Mine, with the Macraes scheelite being enriched in REEs, Y, and Sr. This enrichment in the Macraes scheelite is likely sourced from the breakdown of the Ca-silicate minerals epidote and titanite by the ore forming fluid. Tungsten enrichments (in the form of scheelite) are common in Archean to Cenozoic aged turbidite-hosted orogenic Au deposits, worldwide. The source model developed for the W-bearing turbidite-hosted orogenic deposits of the Otago Schist was evaluated through investigating the source and mobilization mechanism in two additional turbidite-hosted orogenic Au provinces, one containing orogenic Au mineralization with associated subordinate W (Meguma Terrane, Canada) and the other containing orogenic Au mineralization without associated W (Bendigo-Ballarat Terrane, Australia). Similar to the Otago Schist, in both of these terranes, detrital rutile is the most important host mineral for W in the lowest metamorphic grade rocks, and its prograde metamorphic recrystallization (to ilmenite) releases significant amounts of W (1.9 g and 0.18 g of W per ton of rock, Meguma Terrane and Bendigo-Ballarat Terrane, respectively). This release of W in the Meguma Terrane is likely the source of W in the orogenic Au deposits. The lack of W in the orogenic Au deposits of the Bendigo-Ballarat Terrane possibly reflects the Au in these deposits as being sourced from lower greenschist facies metasediments (Castlemaine metasediments), and further potentially precludes previous models that have suggested source rocks for Au in these deposits as being either Castlemaine metasediments at the upper greenschist- amphibolite transition or underlying Cambrian metavolcano-sedimentary rocks. However, the lack of scheelite in the Bendigo-Ballarat Terrane could also result from other factors, such as B.J. Cave vii variations in the conditions of formation of the mineralized veins (P, T, pH, redox, host-rock composition) that may not favor the transport and/or precipitation of W. These factors were unable to be resolved in this study. The results presented within this thesis support recent models for turbidite-hosted orogenic Au mineralization, whereby prograde metamorphic recrystallization of diagenetic or detrital metal-rich mineral phases [pyrite to pyrrhotite, Au, As, Ag, Hg, and Sb; rutile to titanite or ilmenite (this study), W] can release significant amounts of these metals into the concurrently developing metamorphic fluids that can be subsequently focused into regional structures and form orogenic Au ± W deposits. Acknowledgements I would like to thank my family, girlfriend Georgia, and friends, for their constant support and encouragement over the 3.5 years, which has been instrumental in my ability to produce this completed thesis. Georgia is additionally thanked for her invaluable assistance in the field. My supervisory team consisting of Professor Ross Large, Professor Leonid Danyushevsky, and Dr Aleksandr Stepanov, are thanked for their constant support and guidance. Likewise, Professor Dave Craw at the University of Otago, New Zealand, and Dr Iain Pitcairn at the University of Stockholm are thanked for sharing their enthusiasm, as well as immense wealth of knowledge of the geology of the Otago Schist. I am indebted to Al Cusion and Michelle Chapple-Smith at the UTAS lapidary who consistently produced perfect laser mounts, which was fundamental for this research. Mr Jay Thompson, Dr Sarah Gilbert, and Dr Ivan Belousov are thanked for their assistance with LA- B.J. Cave viii ICP-MS analyzes, as is Dr Karsten Goemann and Dr Sandrin Feig for their assistance with SEM work. Advice and samples provided by Dr Chris White, Professor Rebecca Jamieson, and Mr Stafford McKnight, is acknowledged and proved invaluable for this research. In addition, I am extremely thankful for the scheelite samples provided by Ms Lauren Farmer (via Dave Craw), which were instrumental in unravelling the story behind the source of W in the Otago Schist. Funding for this research, for which I am extremely thankful, was provided by a University of Tasmania, Centre of Excellence post-graduate grant, and a Society of Economic Geology, Student Research Grant (SRG_15-28) from the Newmont Mining Corporation.