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The Coompana Province: Regional Context

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The Coompana Province: Regional Context The Coompana Province Regional Context R.A. Dutch Coompana Exploration Release Areas Industry Information Session, Tonsley, May 2016 The Coompana Province • Covers an area of approximately 200 000 km2, straddling the border between South Australia and Western Australia • Bound to the west by the Mundrabilla shear zone, the north by the Musgrave Province, the east by the Gawler Craton and likely extends off shore to the continental margin Arunta Province Musgrave Province Yilgarn Craton Coompana Province AFO Gawler Craton Department of State Development 2 The Coompana Province • There are no known exposed basement rocks of the Coompana Province, with the region being extensively covered by sediments of the Officer, Denman, Bight and Eucla basins Department of State Development 3 The Coompana Province • Due to the often unknown thickness of cover in many places, and the lack of exploration or stratigraphic drilling, very little is known about the basement units Currently • 6 cored basement intersections • 8 percussion basement intersections Mulyawara 1 • 4 intersections into younger basalt Kutjara 1 Lake Maurice E FOR 010 Adi 1 Ooldea 1, 2 & 3 FOR 011 FOR 008 BN 1 & 2 Nullarbor Plains 7 FOR 012FOR 004 CD 1KN 1 Guinewarra Bore Malabie 1 Alballa-Karoo Eucla 1 Potoroo 1 – Off shore Department of State Development 4 Regional Time-Space Plot Department of State Development 5 Regional Time-Space Plot Department of State Development 6 Regional Time-Space Plot Department of State Development 7 Oceanic pre-cursors • No direct evidence of rocks of this age • Based on isotopic and geochemical arguments (Kirkland et al. 2014) iHf Plot Coompana-Musgrave-St Peter Suite 0.2825 West Musgraves East Musgraves 0.2823 St Peter Suite Coompana Evolution Curve 0.2821 Linear (DM) 0.2819 176Hf/177Hf initial 0.2817 0.2815 800 1000 1200 1400 1600 1800 2000 2200 Department of State Development Age (Ma) 8 Oceanic pre-cursors Arunta Province Musgrave Province Yilgarn Craton Coompana Province AFO Gawler Craton Department of State Development 9 1610 event – Arc magmatism • Core from the Coompana Province has magmatic crystalisation ages between ~1640-1604 Ma • These ages are identical to ages from the eastern Musgrave Birksgate Complex and the St Peter Suite in the southern Gawler Craton • Lithologies range from gabbroic to granitic Department of State Development 10 1610 event – Arc magmatism • Each of these suites are Calc-alkaline, metaluminous, medium to high- K suites. • All show strong AFC trends with systematic trends in the major elements suggesting they are co-magmatic controlled predominantly by fractionation processes Department of State Development 11 1610 event – Arc magmatism • Similarly each suite displays strong enrichments in LILE/HFSE and LREE/HREE typical of subduction settings. • They plot within the Volcanic Arc Granite field of the Nb v Y plot of Pearce et al. Department of State Development 12 1610 event – Arc magmatism • They have juvenile Nd isotopic signatures with a trend to more radiogenic compositions suggesting minimal evolved crustal contamination and a significant new mantle input 10.00 5.00 0.00 -5.00 eNd St Peter Suite Gairdner Dolerite -10.00 Musgrave Province Coompana Province -15.00 -20.00 600 800 1000 1200 1400 1600 1800 2000 2200 Department of State Development 13 Age (Ma) 1610 event – Arc magmatism Arunta Province Musgrave Province Yilgarn Craton Coompana Province AFO Gawler Craton Department of State Development 14 1500 event • Poorly constrained event, known only from 3 drill holes (FOR10, FOR12 & Mallabie 1) • Spatial extent within Coompana Province not known. Apparently confined to Coompana Province Arunta Province Musgrave Province Yilgarn Craton Coompana Province AFO Gawler Craton Department of State Development 15 1500 event • These rocks range in composition from monzonitic to granitic • They are extensively deformed Department of State Development 16 1500 event • Geochemically these rocks form 2 series • A medium-K, calac-alkali and magnesian suite • A high-k to shoshonitic, magnesian to slightly ferroan suite Department of State Development 17 1500 event • These granites are comparatively enriched in Ti, Na, K, P, Zr, Nb and LREE with relative depletions of Ca and Sr • They are Peraluminous to Metaluminous and have REE patterns typical of A-Type granites Department of State Development 18 1500 event • They plot as transitional A-type to A-type field and generally within the WPG field on a Nb v Y plot of Pearce et al. Department of State Development 19 1500 event • Isotopically these rocks could be derived from re-working of the 1610 Ma protoliths but also run to more radiogenic compositions suggesting a new juvenile input • The A-Type charachteristics but the magnesian compositions suggest an oxidized and hydrated crustal source. • Potentially reflects high temperature melting of juvenile mafic arc-related crust during extensional collapse or a potential back-arc setting? 10.00 5.00 0.00 -5.00 eNd St Peter Suite Gairdner Dolerite -10.00 Musgrave Province Coompana Province -15.00 -20.00 600 800 1000 1200 1400 1600 1800 2000 2200 Department of State Development 20 Age (Ma) Maralinga event (~1200-1120 Ma) Arunta Province • Corresponds to a major thermal event effecting the entire region between the NAC, WAC and SAC. Arunta Province Musgrave Province Yilgarn Craton Coompana Province AFO Gawler Craton Department of State Development 21 Maralinga event (~1200-1120 Ma) • Synchronous with the Musgravian Orogeny and Stage 2 of the AFO • Recognised as an extended period (~100 Myr) of elevated geothermal gradients and HT to UHT metamorphism • Represents a major period of predominantly felsic magmatism including the Esperance Supersuite (AFO), Pitjantjatjara Supersuite (Musgraves) and the Moodini Supersuite (Coompana and Madura Provinces) • This magmatism is diverse ranging from in-situ anatectic melts to high- T melting of the lower crust. • In the north western Coompana (FOR010 and FOR011), extensive partial melting of subduction enriched lithosphere led to voluminous mafic – felsic shoshonitic magmatism Department of State Development 22 Maralinga event (~1200-1120 Ma) • These granites are typically high-K to shoshonitic, ferroan, A-type magmas enriched in TiO2, P2O5, REE and HFSE and fall within the WPG field of a Nb v Y plot of Pearce et al. Department of State Development 23 Maralinga event (~1200-1120 Ma) • The shoshonitic units are similarly enriched in TiO2, P2O5, LILE, HFSE and LREE but tend to more magnesian compositions. • A constant Eu/Eu* suggests either relatively oxidized (wet?) conditions or no feldspar fractionation. High La/Yb, Gd/Yb and Sr/Yb suggest a deep melt source with residual garnet but not plagioclase Department of State Development 24 Maralinga event (~1200-1120 Ma) • Isotopically these rocks could be derived from re-working of the 1610 Ma protoliths but also run to more radiogenic compositions suggesting a new juvenile (asthenospheric?) input. • The extensive melting, crustal anatexis and HT to UHT metamorphism, and wide spread occurance of this event suggests major extensional destabilization of the lithosphere and asthenospheric upwelling. • This event likely led to cratonisation of the Coompana/Madura Provinces and halted the closure between the WAC and SAC 10.00 5.00 0.00 -5.00 eNd St Peter Suite Gairdner Dolerite -10.00 Musgrave Province Coompana Province -15.00 -20.00 600 800 1000 1200 1400 1600 1800 2000 2200 Department of State Development 25 Age (Ma) ~800 Ma basaltic magmatism • Basaltic volcanics (intrusives?) are intersected in a number of holes around the Coompana magnetic anomaly • This basalt overlies the Mesoproterozoic basement and sits below the cover sequences of the Loongana Fm and Madura Fm • The relationship between these basalts and the remnantly magnetized intrusions is unclear Department of State Development 26 ~800 Ma basaltic magmatism • The basalts are variably altered • 2 pt Sm/Nd mineral isochrons give an age on the basalt in CD1 between 842 ± 11 Ma and 963 ± 26 Ma with a weighted average age of 859 ± 69 Ma • This is within error of other Neoproterozoic mafic suites including the Gairdner Dolerite and Amata Dolerite Department of State Development 27 ~800 Ma basaltic magmatism Arunta Province Musgrave Province Yilgarn Craton Coompana Province AFO Gawler Craton Department of State Development 28 ~800 Ma basaltic magmatism Geochemically the basalts are enriched in Fe and generally tholeitic in composition There are 2 chemical subsets • A med to low-K suite with relatively flat, mantle like REE similar to the Amata Dolerite and part of the Gairdner Dolerite • A high-K suite with relatively enriched LREE and LILE and relative depletions in HFSE Department of State Development 29 ~800 Ma basaltic magmatism • Isotopically these rocks could be derived from re-working of the 1610 Ma protoliths but also run to less radiogenic compositions suggesting possible evolved crustal contamination, perhaps derived from the Gawler Craton • The geochemical similarities with the subduction modified 1610 Ma crust and the high- KFe Moodini SS suggest a significant crustal component in these melts and likely reflect re-working of a mafic lower crust 10.00 5.00 0.00 -5.00 eNd St Peter Suite Gairdner Dolerite -10.00 Musgrave Province Coompana Province -15.00 -20.00 600 800 1000 1200 1400 1600 1800 2000 2200 Department of State Development 30 Age (Ma) Geodynamic setting ~1950 Ma – Oceanic crust development as the SAC (Mawson Continent) continued rifting off the NAC and WAC At ~1640 –
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