Summary:
The Youanmi Project straddles a 40km strike length of the Youanmi Greenstone Belt, lying within the Southern Cross Province of the Archaean Yilgarn Craton in Western Australia. The greenstone belt is approximately 80km long and 25km wide, and incorporates an arcuate, north-trending major crustal structure termed the Youanmi Fault Zone. This structure separates two discordant greenstone terrains, with the stratigraphy to the west characterised by a series of weakly deformed, layered mafic complexes (Windimurra, Black Range, Youanmi and Barrambie) enveloped by strongly deformed, north-northeast trending greenstones.
Gold mineralisation is developed semi-continuously in shear zones over a strike length of 2,300m along the western margin of the Youanmi granite.
Gold is intimately associated with sulphide minerals and silicates in zones of strong hydrothermal alteration and structural deformation. Typical Youanmi lode material consists of a sericite- carbonate- quartz- pyrite- arsenopyrite schist or mylonite which frequently contains significant concentrations of gold, commonly as fine, free gold particles in the silicates, occluded in sulphide minerals and in solid solution in arsenopyrite. The lodes contain between 10% and 25% sulphide, the principal species being pyrite (10% to 20%) and arsenopyrite (1% to 5%).
There are a series of major fault systems cutting through the Youanmi trend mineralisation that have generated some significant off-sets.
The Youanmi Deeps project area is subdivided into three main areas or fault blocks by crosscutting steep south-east trending faults; and these are named Pollard, Main, and Hill End from south to north, respectively.
Granite hosted gold mineralisation occurs at several sites, most notably Grace and the Plant Zone Prospects. Gold mineralization occurs as free particles within quartz-sericite altered granite shear zones.
The Commonwealth-Connemarra mineralised trend is centred 4km northwest of the Youanmi plant. The geology comprises a sequence of folded mafic and felsic volcanic rocks intercalated with BIF and intruded by granite along the eastern margin. Gold mineralisation is developed over a 600m strike length, associated with a north-trending and steeply west-dipping shear zone that traverses the northwest-trending succession.
Dimensions
Ninety-four mineralised lodes have been modelled, along 2.2km of strike length, comprising the Main Lode and associated footwall and hanging wall lodes along the main trend corridor. The maximum depth of the Main Lode interpretation is to approximately -600mRL, 1,060m below the natural surface. The Main Lode is continuous down the dip for this length; other lodes have much more restricted down-dip extents.
Satellite lodes (26) from the 2024 MRE have been incorporated without change as no recent work has been undertaken in these areas.
The hanging wall and footwall lodes are predominantly 0.5m-2m thick, while the Main Lode is generally in the order of 1m-3m thick, but locally exceeds 10m.