Summary:
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 region has been extensively studied, 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. It is a suite of anastomosing sub-parallel shears that together comprise a major terrane-scale structure. The Zuleika Shear Zone hosts many of the active mines at Mungari including Frogs Legs, East Kundana Joint Venture and Kundana Underground. Two major mineralised shears within the zone have been identified as the Strzelecki and K2 shears with high-grade gold mineralisation which host laminated quartz veins.
The Carbine Thrust corridor intersects the Zuleika Shear in the north of the tenement package. The CarbineZuleika area geology is predominantly a sedimentary sequence known as The Black Flag Group containing volcaniclastic and deep marine sediments. The two major mineralised planes in the Carbine area, the Carbine thrust and Lincancabur Fault, host 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 on the Fault. Mineralisation related to the Carbine Thrust is typically observed as brecciated, coarse crystalline veins and laminated veins similar to those seen in the Zuleika Shear Zone observed in the Lincancabur Fault. The Anthill deposit lies to the east of Paradigm on the Zuleika Sheer mineralisation is defined as stockwork veining in an altered pillow basalt.
The Kunanalling Shear Zone also hosts significant gold mineralisation with Cutters Ridge being mined currently and advanced projects including Rayjax, Castle Hill and Kintore. The Kunanalling Shear Zone (KSZ) is a transcrustal feature that cuts through anticlinal fold hinges in the Coolgardie North region. The area has been intruded by conformable syntectonic dolerites, gabbros and stocks of monzogranitic, tonalitic, and granodioritic composition. Gold mineralisation is hosted in areas of high strain and in and around felsic intrusives.
The interpreted lithology models are constructed based on geological logging of drill holes and geological mapping. The interpretations involve extensive review of logging data, drill chips if retained, drill core, historical sections and maps and core photographs. Wireframes representing different lithological units and regolith domains are generated in geological modelling software. Wireframes are generated by implicit and explicit modelling methods. Wireframes are peer reviewed before being finalised for further estimation work.
Structures logged and mapped include brittle, brittle-ductile and ductile features as well as lithological and bedding contacts. Structural measurements are routinely obtained from orientated drill core, underground and open pit mapping. Routine Geotechnical logging is done by field technicians and geologists. Logging is on a per metre basis and includes percentage core recovery, percentage RQD, fracture count, and an estimate of hardness. The geotechnical data is entered into the database. Interpreted surfaces are generated by implicit and explicit modelling methods. Wireframes are peer reviewed.
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.