Preliminary results on magma fertility related to Au-Cu mineralization in north Queensland, Australia

Transcription

1 Subproject #3: Magma fertility, petrogenesis and geodynamic setting of Carboniferous and Permian magmatic complexes Preliminary results on magma fertility related to Au-Cu mineralization in north Queensland, Australia Helge Behnsen, Carl Spandler, Zhaoshan Chang, Isaac Corral, Bob Henderson EGRU, JCU 27 May 2015 Townsville, Queensland, Australia Overview: Aims of the project Location of study area / sampling strategy Alteration of collected samples Application of Bob Loucks magma fertility schemes Preliminary observations and forward program

2 Aims of this project and methods: 1) Proof of concept and application or modification of existing magma fertility schemes o Comparison between samples from the Mt. Carlton deposit and the same volcanic sequence (Lizzie Creek Volcanics) away from mineralization 2) Feed magma fertility concept(s) into subproject #9 to develop a tool to identify potential future exploration targets for this type of mineralization in North QLD (or even internationally) Location: Townsville Mt. Carlton

3 Sampling strategy: Lionel Diggings Samples close to Mt. Carlton HS mineralization (n=23); 22 for WR geochem. 22 for thin sections 6 zircon U-Pb dating Pinnacle completed + 4 underway Gold Creek PIMA analyses Samples away from mineralization (n=25); 25 for WR geochem. 25 for thin sections (waiting for return) 10 zircon separations underway Sullivans Reward Quartz Hill Mt Dillon Castle Capsize Strathmore Herbert Creek Boundary Mt Carlton Ortiz BV8 Boundary Power Line Oakey Creek Matrimony ridge Mt Abbot Otter ridge Collinsville Stockyard Creek The Springs Bee Hill Delta Beta BV5 Bowhunters Sansons Mt Pool Euri Creek Motley Hill Top Mount Vista Ridge Albion Southern Robard Creek Delvin Pocket Map courtesy of Ian Withnall (2015) Local Stratigraphy A conceptual model: Morrison, 2010

4 Wall rock and mineralization ages at Mt Carlton district: Zircon U-Pb LA-ICP-MS; this study Zircon, SHRIMP, literature Mo Re-Os; Capsize porphyry; this study Alunite Ar-Ar; V2; this study Trachyte Capsize, late-mineral Below V2 Age (Ma) Basement granitoid Chang, 2015 Lizzie Creek Volcanic Group Porphyritic intrusions in Lizzie Creek volcanics Alteration of samples: Mt Carlton samples: Least altered samples selected; most altered by montmorillonite, chlorite, based on PIMA; 3 samples have disseminated pyrite, analysis Rhyodacite porphyry; Lower R - unit Altered rhyodacite; Upper R - unit Collinsville sample suite not altered

5 Magma fertility Applying Louck s ideas: Bob Loucks proposed a magma fertility scheme to differentiate between fertile and barren Cu and Au ore forming arc magmas (Loucks, 2014) Favourable magmatic rocks for Cu ore: Sr/Y > 35 V/Sc > x wt.-% SiO 2 (SiO %) Magma fertility Applying Louck s ideas: Loucks, 2014 Modified after Loucks, 2014

6 Magma fertility Applying Louck s ideas: Loucks, 2014 Modified after Loucks, 2014 Preliminary Observations: Bob Loucks fertility scheme for Cu-Au ore generally works, with fertile magma having higher Sr/Y, V/Sc Exact boundary in this district is slightly different compared to the global dataset; local variation

7 Forward Program: Purpose Better correlate samples from proximal / distal locations Method U-Pb zircon dating of undated intrusives/volcanic rocks close to and away from mineralization (LA-ICP-MS) Understand the magma evolution of the Lizzie Creek Volcanic suite in the chosen district Understand the redox conditions of the melt where Fe2O3/FeO ratios are affected by alteration Analyse Hf isotope compositions of zircons (LA-ICP-MS) Ce4+/Ce3+ ratios and Eu3+/Eu2+ ratios of zircons (LA-ICP-MS) WR major and trace elements of the Collinsville samples away from mineralization were obtained only 7 days ago; more examination of data to extract information Literature: Le Bas, M.J., Le Maitre, R.W., Streckeisen, A. and Zanettin, B. (1986). A Chemical Classification of Volcanic Rocks Based on the Total Alkali Silica Diagram. Journal of Petrology, Vol. 27, Part 3, pp Morrison, G. (2009). Exploration Potential in the Mt Carlton Area. Klondike Exploration Services. Company Report. Loucks, R.R. (2014). Distinctive composition of copper ore forming arcmagmas. Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia, 61:1, Allen, C.M., (2000). Evolution of a post batholith dike swarm in central coastal Queensland, Australia: arc front to backarc?. Lithos, 51, pp Thank you very much!

8 Acknowledgements Evolution Mining; Roric Smith, Genesio Circosta, David Hewitt, Mick Pocock, Tyron Edgar, Jim Dugdale, Ned Howard, Matthew Obiri-Yeboah Geological Survey of Queensland; Vladimir Lisitsin, Courteney Dhnaram Glencore Coal JCU Mineral Separation Lab (MSL) and Advanced Analytical Centre (AAC), U Michigan Ar-Ar lab and U Alberta Re-Os lab JCU research team Slides not showed

9 Magma fertility Applying existing ideas: Applying Phil Blevin s approach (Blevin et al., 1996) Using the oxidation state of the magma Geochemistry Major elements:

10 Lithology examples: Massive, dacitic lava; C - unit Altered rhyodacite; Upper R - unit Rhyodacite porphyry; Lower R - unit Massive, andesitic lava; Z - unit Morrison, 2010