Summary:
The Nova Operation comprises an underground mine consisting of two orebodies, Nova and Bollinger. The Nova and Bollinger zones are now recognised as a single continuous deposit known as Nova-Bollinger.
Nova-Bollinger is within the 425 by 50km wide, Mesoproterozoic-age Fraser Zone of the Albany-Fraser Orogen. The Fraser Zone is fault bounded by the Biranup Zone to the northeast and the Nornalup Zone to the southeast. The Arid Basin forms the basement to the Fraser Zone and the Snowys Dam Formation of the Arid Basin is the basement package in the Nova-Bollinger area. During the first phase of the Albany-Fraser Orogeny at around 1.30Ga, mafic, ultramafic, and granitic intrusions were emplaced penecontemporaneously with the granulite facies metamorphism of the regional stratigraphy, which was occurring at crustal depths of 28 to 35km below surface. This zone is now characterised by gneissic fabrics, complex refolding and major mylonitic zones.
The rocks within the Nova-Bollinger region are consistent with the regional descriptions of the Snowys Dam formation and include pelitic to psammitic gneisses, a local carbonate unit, along with metamorphosed mafic-ultramafic (MUM) and volcanoclastic rocks. The Nova-Bollinger MUM sill complex that hosts Nova-Bollinger’s Ni-Cu-Co sulphide mineralisation is a doubly plunging synform, where a magnetite-bearing footwall gneiss has been identified as the cause of ‘The Eye’ magnetic feature. The MUM sill complex is a dish-shaped package 2.4 by 1.2km in plan and up to 450m in thickness. The rocks of the complex range in mineralogy from peridotite to pyroxenite, to gabbronorite and norite, with both sharp and gradational contacts between different intrusive phases. An upper and lower intrusion are recognised with the lower ‘Nova Gabbro’ intrusion intimately associated with the Ni-Cu-Co sulphide mineralisation. The mine area is covered by up to 3m thick regolith and/or transported cover, with oxidation of sulphides in fresh rock down to depths of 20m in the western end of the Nova area.
As noted above, Nova-Bollinger’s Ni-Cu-Co sulphide mineralisation is associated with the Nova Gabbro mafic magmatic conduit, from which the sulphide mineralisation precipitated and accumulated within the conduit and the fracture zones surrounding this source intrusion. The Nova Gabbro and associated sulphide mineralisation is interpreted to have been emplaced in a dynamic environment, at peak metamorphism, with most of the sulphide mineralisation remobilised into structures and/or fracture zones surrounding the mineralising intrusion. There are several mineralisation styles in Nova-Bollinger, ranging from massive sulphide accumulations, breccias, net-textured zones (olivine and sulphide matrix), stringer-sulphides in metasediments, and disseminated and blebby textures in gabbroic units.
Nova-Bollinger’s massive sulphide mineralogy is dominated by pyrrhotite (80 to 85%), minor pentlandite (10 to 15%) with lesser chalcopyrite (5 to 10%). Concentrations of up to 5% magnetite also occur locally within more massive sulphides zones. Cobalt is strongly and positively correlated with nickel as both elements are found concentrated in pentlandite, albeit both also occur in minor concentrations in solid solution with pyrrhotite.
Dimensions:
- The Nova area mineralisation commences from 40m below surface and extends to 470m below surface.
- The Nova area extents are about 650m (northeast to southwest) and about 300m (northwest to southeast).
- The Bollinger mineralisation abuts the Nova zone and starts at about 360m below surface (highest point) and extends to about 425m below surface.
- Bollinger has areal extents of about 300m long (north) and ranges from 125m to 400m wide (east).
- The Nova and Bollinger zones are joined by an interpreted narrow east-west trending feeder ‘Mid’ zone that has a length of about 180mm, thickness of 10 to 20m and north-south width of up to 80m.