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Location: 340 Km W from Townsville, Queensland, Australia
Level 21, Matisse Tower 110 Mary StreetBrisbaneQueensland, Australia4000
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The main styles of gold mineralisation in the area are epithermal and meso-thermal systems, which are generally associated with multiple intrusive phases associated with the Robertson Fault Zone. Narrow-vein mining has also previously taken place within the Forsayth area along or adjacent to the fault traces. The Robertson Fault Zone is recognised as one of the main controlling features for mineralisation in the region. Gold mineralisation at Sherwood is a low-sulphidation, adularia-sericite type epithermal system genetically related to the emplacement of Permo-Carboniferous porphyritic rhyolite and andesite extrusives and intrusives. Most mineralisation occurs within the Robertson Fault Zone, at the intersection of the Robin Hood Fault and is spatially associated with (and often within) rhyolite. The mineralised zones are interpreted as boiling outflow zones, likely fossil geysers. The Agate Creek Fault forms the eastern boundary to mineralisation but remains open in all other directions and at depth. There are two principal mineralised areas currently identified at Sherwood and Sherwood West. Additional infill drilling from 2014 in the upper part of Sherwood has allowed a higher grade domain to be defined with confidence as a shallow NW dipping lens of mineralisation. The lens is 250 m long by 50 to 100 m wide and 2 to 8 m thick. Sherwood West is hosted within a brecciated rhyolite, infilling a thrust fault truncated in the north by the Zig Zag Fault. The faulting allowed for a rhyolite intrusion followed by fluid conduits of the active Permian epithermal plumbing system. At Sherwood West the known mineralised zone extends for over 1 km along strike and remains open to the south and at depth. There is also the potential for parallel repetitions of the currently known mineralized zone. Agate Creek mineralisation is epithermal is style and associated with quartz veining. Both grade and quartz logging are used to aid geological interpretation in additional to geological contacts between the rhyolite and granite which are proximal and parallel to the main mineralisation at Sherwood West and the upper mineralisation at Sherwood. Quartz veining is dominantly near horizontal at Sherwood and dip at 30º to the east at Sherwood West. Early interpretations included vertical veining along fault zones at Sherwood and Zig-Zag faults, however there is room to interpret these areas to low angle structures. Other vertical veins are present around Sherwood and could possibly contribute to mineralisation. Examination of core indicates here is mineralisation without evident quartz veining indicating some areas are more complicated. Mining undertaken on the upper high grade zone at Sherwood confirms a gentle dip to the east that is now defined by infill RC drilling completed since November 2014. The high grade zones displays a strong relationship to quartz veining though not all quartz is mineralised. Sherwood comprises mostly sub-horizontal quartz veins and mineralisation with the main zone containing veins spread over a core area of 370 m NE-SW by 300 m NW-SE by 300 m RL. It is bounded to the East by the Agate Creek Fault a vertical NNW-SSE system with some mineralisation. Sherwood West is predominately a single zone dipping 30° to the east and up to 750 m N-S by 350 m E-W and 20 m in vertical thickness. There are some minor horizontal veins in the hanging wall sequence and additional mineralisation near the Zig Zag Fault. Sherwood South comprises a few largely vertical veins is minor extent. 18 November 2021 - Gold mineralisation at Sherwood has previously been described as a low-sulphidation, adularia-sericite type epithermal system, genetically related to the emplacement of Permo-Carboniferous porphyritic rhyolite and andesite extrusives and intrusives. Beams et al (2019) commented “the boundary between epithermal per se and intrusion-related epizonal is not clear and is broadly based on visual observations of textures but both types have similar chemistry implying that epithermal deposits are part of the Intrusion-Related Epizonal System”.
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