Hydrothermal alteration and mineralisation characteristics at Anabama Hill: a porphyry Cu-Mo prospect in the Delamerian Orogen, South Australia

Wei Hong1,2,3, Adrian Fabris2,3, Stacey Curtis2,3, Rian A. Dutch2,3

1 Department of Earth Sciences, School of Physical Sciences, The University of Adelaide, Adelaide, SA, Australia, 5005, 2 Geological Survey of South Australia, Department for Energy and Mining, 11 Waymouth Street, Adelaide, SA, Australia, 5001, 3 Mineral Exploration Cooperative Research Centre (MinEx CRC)

The Delamerian Orogen is the oldest component of the Phanerozoic Tasmanides and is argued to have constituted a Proterozoic continental rift margin overprinted by convergent, west-dipping subduction since the Cambrian (Foden et al., 2020). It has experienced a complex geological history that includes deformation, metamorphism and magmatism from the middle Cambrian (ca. 520 Ma) to early Ordovician (ca. 480 Ma), involving of the emplacement of a series of I-type, S-type and A-type granitoids. Magmatic-hydrothermal Cu-Mo mineralisation in the Delamerian Orogen was first identified in the 1970s, and related Cu-Mo occurrences include the Anabama Hill, Blue Rose, Netley Hill, Cronje Dam-Oak Dam, and Bendigo, situated along the eastern margin of the Adelaide Fold Belt. This belt forms part of a Cambro-Ordovician arc that extends southeast into Victoria (e.g., Thursday’s Gossan Cu deposit) and northeast into New South Wales (e.g., Loch Lilly-Kars Cu prospect), respectively.

The Anabama Hill Cu-Mo prospect is located in the northeast part of the Delamerian Orogen and associated with the Anabama Granite that has limited surface outcrop. Recent geophysical investigations shows that it is a NE-trending large batholith, with an estimated subsurface area > 50 km2. A granodiorite pluton is the major component of this batholith, which was intruded by quartz diorite and monozogranite. Minor components include microgranodiorite, dacite porphyry, and lamprophyre dikes as identified in seven legacy diamond drill cores. These magmatic facies were emplaced into a Neoproterozoic sedimentary sequence composed of mica schists, tillites, quartzites, and siltstones. Only a Pb-Pb plateau zircon age of 485 ± 4 Ma is currently available for the granodiorite (Nasev, 1998). Extensive pyrite-muscovite-quartz alteration prevails in the granodiorite, diorite and monzogranite, which is capped by a 50m-thick weathering zone consisting of kaolinite, montmorillonite, jarosite and goethite. The pyrite-muscovite-quartz zone extends intermittently downwards for more than 700 meters, and occurs commonly as multiple veins and veinlets. Epidote-quartz-magnetite-pyrite veinlets contain chalcopyrite and/or molybdenite disseminations and are overprinted by the pyrite-muscovite-quartz veins. Euhedral, coarse-grained molybdenite, pyrite and muscovite typically occur along fractures or as disseminated patches within massive quartz (> 1m wide). Narrow K-feldspar-quartz veinlets (several cm in width) cut the diorite porphyry and equigranular granodiorite and generally occur below the intense muscovite-dominated alteration zone. Copper grade in the muscovite-rich altered zone range from 0.17% to 0.38%, whereas Mo contents increase from 2-10 ppm in the granodiorite up to 620 ppm in the muscovite-rich assemblages. Epidote-chlorite alteration generally develops in a peripheral domain, extending a few hundred metres laterally from the Cu and Mo anomalies. The granodiorite, monzogranite and diorite have mostly undergone selective epidote-chlorite replacement. Locally, epidote, chlorite, pyrite and minor quartz and magnetite assemblage develop intensely and occur as thick veins (1 to 30 cm wide) that truncate the intrusive facies. Epidote and chlorite mineral chemistry are used to further characterise alteration patterns and assess mineralisation fertility of the Anabama Hill prospect and broader Cu-Mo porphyry-style mineralisation potential of the Delamerian Orogen, which forms part of ongoing research of the Mineral Exploration Cooperative Research Centre and Geological Survey of South Australia.


Biography

Wei Hong is currently a postdoc researcher in the University of Adelaide and embedded researcher in GSSA and MinEx CRC, conducting research on assessing mineralisation potential in the Delamerian Orogen. He completed his PhD in 2017 on Tasmanian granite and related Sn-W mineralisation and following two-year postdoc at CODES. 

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