Wang, Yamei; Forster, David; Cronin, Dan; Montgomery, Karen; Blevin, Phil
1Geological Survey of New South Wales, Department of Regional NSW, Maitland, Australia
This study summarises previous exploration in the Mount Adrah area and presents the results of new petrographic, sulfur isotopic and HyLogger™ hyperspectral analyses of intrusion-related gold mineralisation centred on the Hobbs Pipe intrusion at Mount Adrah, New South Wales. The work was conducted as part of the five-year East Riverina Mapping Project, which improved geological understanding to aid mineral exploration and enable informed land use decisions in the region.
The Hobbs Pipe deposit contains about 770 000 oz of gold and is interpreted to be an intrusion-related gold deposit. Two main styles of mineralisation are present: disseminated pyrite–gold, developed within a cylindrical, zoned intrusion (Hobbs Pipe); and narrow, high-grade gold reefs located nearby. Drillhole GHD009 (total depth 1,312 m) provides a representative section through the Hobbs Pipe deposit and associated rocks.
Reconnaissance petrology was undertaken on twenty thin sections collected from drillhole GHD009. Three main phases have been identified: a felsic monzogranite core, an intermediate quartz monzodiorite to diorite outer core, and an intermediate–mafic diorite to gabbro rim. Disseminated pyrite-gold mineralisation in the Hobbs Pipe deposit is mainly hosted in the felsic monzogranite core.
Twenty-eight sulfur isotope results were obtained; twenty-seven from drillhole GHD009 and one from White Deer Reef, intersected in drillhole GHD011. δ34S results mainly fall within a relatively narrow range and suggest a single, magmatic-dominated source of sulfur.
HyLogger™ hyperspectral analysis of drillhole GHD009 was conducted at the WB Clarke Geoscience Centre, Londonderry, New South Wales. Chlorite, white mica and dark mica type all show mineralogical changes near lithological contacts and/or alteration which relates to gold mineralisation.
The geology and alteration assemblages in conjunction with new petrology, hyperspectral data and sulfur isotopes suggest that both the disseminated mineralisation within the core of the intrusive stock and the distal high-grade gold-bearing reefs are related to the same mineralising event, and probably the same fluid source.
Dr Yamei Wang has broad experience in minerals exploration. She also has a strong academic background, with a PhD in structural geology. She joined Geological Survey of NSW in February 2019 and her current role is Senior Geoscientist in Mining & Exploration Assessment team in the Survey.