Geology
Historical drilling campaigns have enabled a detailed study of the geology to be undertaken. Profiles of the ore environment along the entire strike length of the known mineralization at Mt Thirsty are substantially consistent. The following represents a typical laterite profile developed within the ore environment:
• Lateritic scree/veneer 0-0.5m thick. In the breakaway areas this veneer is up to 15m thick;
• Powdery limonitic clay (“upper saprolite”) 10-35m thick, average 25m thick, with minor occurrences of chalcedonic quartz;
• Puggy smectitic clay (“lower saprolite”) 5-25m thick, average 12m thick, with common chalcedony + magnesite. Relict orthocumulate textures are visible; and
• Underlying metaperidotite which is moderately serpentinised with a dominant composition of antigorite, chlorite, magnesite and magnetite.
Contacts can be sharp or gradational over a few metres. Concentration of Ni and Co can occur at all oxidation boundaries as sub horizontal to weakly karstaform lenses. However the main zones of high grade cobalt/nickel are concentrated at the interface between the upper and lower saprolite horizons. The ore zone is generally visible as a layer of manganese oxides black to grey in colour.
The approximate breakdown of ore within the profile is:
Laterite/Ferricrete 2-3%
Upper saprolite 80-85%
Lower saprolite 10-15%
Moderately oxidized saprolite 2-3%
The host metaperidotite is in sharp contact with metagabbro to the east of the resource and is marked by a north-south orientated creek. The metagabbro is completely devoid of mineralization. It has been postulated that the metagabbro has acted as a weathering barrier or dam to the existing Co/Ni mineralization and has aided in the concentration and development of the resource. Further exploration for new ore zones should be concentrated adjacent to this contact to the south.
Laterite Profiles: Wet and Dry Laterites
