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 was discovered within the Mesoproterozoic age Fraser Zone (about 425km long by 50km wide) of the Albany-Fraser Orogen. The Fraser Zone is fault bound by the Biranup Zone to the northeast and the Nornalup Zone to the southeast. The Arid Basin sequence of rocks is the basement to the Fraser Zone, and the Snowys Dam Formation of the Arid Basin is the basement rock package in the Nova-Bollinger area. During the first phase of the Albany-Fraser Orogen at around 1.30 billion years ago, mafic, ultramafic and granitic intrusions were emplaced penecontemporaneously with the granulite facies metamorphism of the regional stratigraphy, which is interpreted to have occurred 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 local Nova-Bollinger region are consistent with the geological literature’s descriptions of the Snowys Dam Formation and include pelitic to psammitic gneisses, a local carbonate unit, along with metamorphosed mafic-ultramafic (MUM) and volcaniclastic rocks. The NovaBollinger 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 about 2.4 by 1.2km in plan and up to 450 metres (m) 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 an up to a 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.
Nova-Bollinger’s Ni+Cu+Co sulphide mineralisation is associated with the Nova Gabbro mafic magmatic conduit, from which the sulphide mineralisation is interpreted to have precipitated and accumulated within the conduit and the fracture zones surrounding this source ‘chonolith’ 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 (comprising olivine crystals in sulphide matrix), stringer sulphides in metasediments, and disseminated and blebby textures in gabbroic units.
Nova-Bollinger’s massive sulphide mineralogy is dominated by the mineral pyrrhotite (80 to 85% by volume), with minor pentlandite (10 to 15%) and lesser chalcopyrite (5 to 10%). Concentrations of up to 5% magnetite also occur locally within more massive sulphide 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. Copper is hosted by the chalcopyrite.
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 180m, thickness of 10 to 20m and north-south width of up to 80m.