Summary:
The vast majority of the mineralisation at the Project is hosted within the altered parts of the sheared ultramafic rocks. Pyrrhotite and arsenopyrite are the main sulphides with occasional pyrite and rare chalcopyrite or pentlandite. The areas with the highest gold grades are associated with arsenopyrite. Metallurgical tests of the mineralised sections carried out by Lakefield Research Limited (Lakefield, 1999b) indicated that the gold is free in form. Gold mineralisation occurs in zones of variable thickness, with average widths of 10 m, and is nearly continuous along 2 km of strike.
Gold at the Project is linked with an assemblage of sulphides and oxides in ultramafics and granite. Opaque minerals include trace to minor quantities of pyrrhotite, arsenopyrite, chalcopyrite, pentlandite, galena, sphalerite, magnetite, ilmenite and rutile. Sulphide growth may be in the form of vein fills, massive aggregates, clusters, blebs, stringers and fine or coarse disseminations in ultramafics or granite veins. There appears to be a progression from syntectonic to late-tectonic growth, with at least two phases of sulphide and oxide growth. The non-opaque minerals are amphibole, chlorite, mica, serpentine, talc and quartz. Pyrrhotite, arsenopyrite, coarse grained pyrite, chalcopyrite, sphalerite and minor pentlandite are the principal sulphides; the chief observation being (but not always) an increase in grain size and abundance, both absolute and relative, in host rocks near granite veins.
The gold mineralisation at the Project is associated with sulphides, hosted in metamorphosed ultrabasic rocks intruded by tourmaline-bearing granites that are closely associated with albitite dykes. The ultramafics consist of amphibole (tremolite, actinolite), chlorite, phlogopite, talc, some carbonate and the sequence is moderately to highly silicified.
The widespread silicification is accompanied by ubiquitous magnetite precipitation. The sulphide association is pyrrhotite, pyrite (the two alternating in dominance), arsenopyrite and minor- to-trace chalcopyrite, niccolite and gersdoffite. Magnetite and minor haematite are the main oxides
The mineralisation being targeted by Aureus comprises typical Upper Archaean to Lower Proterozoic greenstone belt-hosted lode gold mineralisation. These deposits are often referred to as orogenic and are characterised by the presence of a combination of gold-quartz veins and disseminated mineralisation.
Archaean orogenic deposits are typically hosted in greenstone belts comprising meta-volcano sedimentary supracrustal assemblages, together with coeval calc-alkaline granitoid intrusions. The gold mineralisation is typically hosted in moderate to steeply dipping quartz-dominated shear zones with associated extensional vein systems and is considered to be coeval with the syntectonic stages of the orogeny and related to periods of crustal shortening at 8 km -15 km depth. Structures are typically formed at, or close to, contacts between rock types of contrasting competencies, and mineralisation is often localized at bends or splay intersections in the shear system.