Browsing by Author "Spencer, L"

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    The Kulumadau epithermal breccia-hosted gold deposit, Woodlark Island, Papua New Guinea
    (AusIMM, 2015-03-18) Burkett, D; Graham, IT; Spencer, L; Lennox, P; Cohen, D; Zwingmann, H; Lau, F; Kelly, BFJ; Cendón, DI
    The Kulumadau deposit represents an intermediate-sulfidation epithermal gold deposit (3.8 Mt at 2.3 g/t, Ag:Au = 1). Mineralisation is primarily confined to hydrothermal breccias within preexisting fault zones, where it is disseminated throughout a hydrothermal matrix comprising chlorite-quartz-adularia-illite-I/S clays-calcite-pyrite. The host sequence represents numerous mid-Miocene pyroclastic flow eruptions within a tectonically active emergent shallow marine to subaerial depositional setting. Subsequent growth faulting was responsible for debris avalanches, which were subsequently cut by reverse faults. Faults were exploited by hydrothermal fluids, with the heightened porosity at the juncture between faults and debris material facilitating boiling of the ore constituents. Fluid inclusion studies suggest that fluid mixing between meteoric fluids and magmatic fluids, accompanied by boiling, were the primary mechanisms for gold deposition. The occurrence of anhydrite/gypsum as late-stage veins and their sulfur and oxygen isotopic values indicate post-mineralisation mixing of sea water with hydrothermal fluids.
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    Stratigraphy and age-dating of the Kiriwina Formation,Woodlark Island, Papua New Guinea
    (Australian Geosciences Council, 2012-08) McGeeney, D; Graham, IT; Cohen, DD; Spencer, L; Jacobsen, GE; Williams, A
    The Upper-Pleistocene Kiriwina Formation (KFm) of Woodlark Island, Papua New Guinea, is a complex, largely transitional shallow marine to near-shore terrestrial sedimentary unit. This study provides the first detailed analysis of the KFm on any KFm hosting island of the Solomon Sea. Highly elevated Au contents (up to 10 ppm) occur within various sub-units. The KFm covers most of the island’s surface, has a thickness of 0–90m, and unconformably overlies the mid-Miocene Okiduse Volcanics that host carbonate-base metal-Au epithermal mineralization. The formation has undergone rapid horizontal and vertical changes in the sedimentary environment and style; individual units and subunits occur as repeated lenses of conglomerates, gritstones, beach sands, silts, lagoonal clays, and mixed clays/carbonates. The KFm is capped by porous and permeable shallow marine limestones, which in places have undergone karst development. Detailed mapping indicates previously unknown near-shore terrestrial subunits that may comprise a large part of the sequence. Andesitic fragments are widely dispersed throughout each member and subunit. The main clay in the Talpos Marine Clay Member is nontronite, an Fe-rich smectite. New C14 radiometric age-dating has determined the KFm to be 47,130–60,300 yrs BP at Kulumadau and > 70,000 yrs BP at Busai. These ages were used as a basis to determine an average uplift rate of 1.06m/1000 years.