Oceana Gold Waihi North Project Waihi North Project Geochemical Assessment – Geochemistry of Tailings and Overburden, Treatment and Mitigation Revision 0 – 17-Jun-2022 Prepared for – Oceana Gold (New Zealand) Limited – Co No.: 2274246 5 AECOM 2.0 Geology and Mineralogy 2.1 Local Geology The mineralised rock types at Waihi, to be encountered in Martha, Gladstone and Wharekirauponga, have been divided into the following main groups: • Andesite Host Rock, which primarily consists of fine to medium porphyritic andesite flows with varying degrees of clay alteration and silicification. Also included within this category are volcanic ash and tephra deposits stratified within the main body of the andesite host rock. This host rock is prevalent throughout the wider area. Characteristic alteration assemblages include quartz, albite, adularia, calcite, pyrite, illite, chlorite, interlayered illite-smectite, and chlorite-smectite clays extending over tens of metres laterally from major veins. There is also an association of quartz, interlayered chlorite-smectite (corrensite) and chlorite, producing a distinctive pale green colouration. The system is locally oxidised to depths in excess of 350 m below ground level along fractures. • Quartz Andesite, which is the dominant host lithology for the Martha Vein system and in the Union Hill epithermal vein system which includes the Trio, Amaranth, and Union veins. This lithology is described as a quartz-feldspar phyric andesite lava. • Hydrothermal Vent Breccia, which is found at shallow levels (above 1000 m RL, mine datum) as NNE - SSW elongated funnel-shaped vents comprising variously clay to quartz altered breccias with variably milled clasts of all pre / syn-mineral lithologies, including vein quartz. These have formed through phreatic eruptions in shallow levels of an active hydrothermal system and vent to the surface forming tuff rings of the vent ejecta. • Rhyolite Host Rock, the WUG ore body is situated in rhyolitic deposits that are predominantly volcanoclastic breccias with some massive lava. The rhyolite is typically intensely silicified with secondary remineralisation of quartz. This hydrothermal alteration and deposition of heavy metals and associated mineralisation is associated with multiple faults in the area. Ignimbrite, dacite, volcanic ash, and alluvial sediments overlie the andesite. These rocks were formed subsequent to the epithermal activity that resulted in mineralisation phase and previous analyses have confirmed that these rocks are Non-Acid Forming (NAF). Further drill core logs show no hydrothermal alteration or visible sulphides. The various mining areas of WNP form part of the greater Waihi epithermal vein system. The Waihi vein system, including Martha Hill, Union Hill, Favona, and Correnso, has been interpreted as being located within a series of sub-regional scale NE-trending grabens. The quartz andesite unit attains thicknesses in excess of 400 m in the Union Hill – Waihi East area with only minor variation in texture or modal composition. The quartz andesite is overlain by a fine-grained tuff, which forms a distinctive marker horizon and is overlain in turn by a series of feldspar-phyric andesite flows and volcaniclastics. The geology and mineralogy of the Gladstone area, as with the greater Waihi epithermal vein system, is expected to be generally consistent with that encountered in the existing Martha, Favona, Trio, and Correnso mines with the exception of the greater influence of the breccias which overlie the andesite rock in the GOP. The lower mafic content of the rhyolitic host material around the Wharekirauponga ore body will influence the rock mineralisation to a limited degree. These rhyolites are intruded through and underlain by andesitic material. The Golden Cross mine is close to the Wharekirauponga ore body however data from this site is not considered in this assessment due to differences in the host rock (rhyolite versus andesite) and the alteration associated with these two ore bodies.
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