Summary:
The Kundana deposits are hosted by a structurally prepared sequence of sediments, volcaniclastics, mafic and ultramafic volcanic and intrusive rocks typical of the greenstone sequences in the Archaean Yilgarn Block. The deposits are spatially associated with the cratonscale Zuleika Shear Zone. The Zuleika Shear Zone represents the boundary between the Coolgardie domain to the west and the Ora Banda domain to the east.
The Mungari Operation lies within the Kalgoorlie Terrane of the Wiluna-Norseman Greenstone Belt, part of the greater Archaean Yilgarn Craton of Western Australia. The host rocks date to 2.7 billion years with the main episode of deformation, granitoid intrusion, metamorphism, and gold mineralisation between 2.66 to 2.64 billion years. The structural framework can be summarised by 5 major events (gold mineralisation associated with D3 & D4):
D1e - Early extension – Syn-volcanic emplacement if komatiite and basalt sequences;
D1 - Broad upright folding and north-south directed thrusting;
D2 - ENE – WSW shortening resulting in significant regional folding;
D3 - Activation north-northwest trending shear zones (including the Zuleika Shear);
D4 - North-northeast brittle faults, offsetting the stratigraphic sequence and mineralisation.
The Kalgoorlie Terrane comprises five major stratigraphic successions; (from oldest to youngest) lower basalt, komatiite, upper basalt, felsic volcanic and sedimentary, and a polymictic conglomerate. The terrane is highly folded and disrupted by faults and major shear zones; the rocks are metamorphosed to greenschist facies with local areas metamorphosed to amphibolite facies, associated with deformation and granitoid intrusion.
The Zuleika Shear Zone, Kunanalling Shear Zone and Carbine Thrust Zone are the dominant corridors of mineralisation at Mungari.
The Zuleika Shear Zone is the major structural element of the area and hosts two major mineralised shears (Strzelecki and K2 shears) with high-grade gold mineralisation hosted in laminated quartz veins.
The Carbine Thrust corridor intersects the Zuleika Shear in the north of the tenement package and hosts the Carbine thrust and Lincancabur Fault, defined by brecciated and laminated veins respectively, with high-grade gold mineralisation. The Carbine and Phantom deposits are associated with the Carbine Thrust, while the Paradigm deposit is hosted by the Lincancabur Fault. The Anthill deposit lies to the east of Paradigm on the Zuleika Shear and mineralisation is defined as stockwork veining in an altered pillow basalt.
The Kunanalling Shear Zone also hosts significant gold mineralisation with Cutters Ridge and Rayjax being mined recently and advanced projects including Castle Hill and Kintore.
A regolith model was generated to aid estimating density, geological domains and targeting supergene gold horizons. The interpreted regolith model was constructed based on geological logging of drill holes and geological mapping. Historically mined open pits were also referenced. Regolith zones are well developed with secondary enrichment of gold (supergene gold) remobilised to geochemical horizons documented within the regolith profile.
Mineralisation and alteration models were constructed based on geological logging of drill holes and geological mapping. Mineralisation is characterised as orogenic, narrow vein gold deposits and, mineralised alteration envelopes, stockworks and mineralised intrusives and supergene enrichment horizons.
Orogenic, narrow vein gold mineralisation is typically hosted within brittle (extension vein arrays and breccias), brittle-ductile (laminated veins) and ductile (shear zones) structural zones and typically exhibit a sodic and potassic alteration assemblage, proximal to the structure. Alteration minerals include: sericite epidote, chlorite and albite, muscovite and biotite. Gold mineralisation is often observed in conjunction with sulphide crystals such as pyrite, pyrrhotite, arsenopyrite, galena and sphalerite. Visible gold has been observed in drill core and rock exposures.