Summary:
Cue Gold Operations is located in the Achaean Murchison Province, a granite-greenstone terrane in the northwest of the Yilgarn Craton. Greenstone belts trending north-northeast are separated by granite-gneiss domes, with smaller granite plutons also present within or on the margins of the belts.
The CGO lies within the northern part of the province, which is an area dominated by northeast trending supracrustal greenstone sequences within the Archaean Murchison Supergroup.
The greenstone belts comprise tholeiitic and high-Mg basalts, komatiites and other ultramafic volcanics, mafic and ultramafic intrusives (dolerites, gabbros, dunites), felsic and intermediate volcanics and metasediments including banded iron formations.
The Cue Gold Operations can be subdivided into four major geological domains: Big Bell, Cuddingwarra, Day Dawn and Tuckabianna.
Big Bell
The Big Bell project area is located at the southern end of a narrow northeast-trending greenstone belt, (informally referred to as the Big Bell Greenstone Belt), which adjoins the larger Meekatharra - Mount Magnet Greenstone Belt. The belt has a strike length of 33 km and a width of 1.5 km at Big Bell and is bounded to the east and west by granite intrusions.
The Big Bell Greenstone Belt is comprised of variably altered and intensely sheared, northnortheast-trending amphibolites and felsic schists. The muscovite and biotite-altered rocks hosting gold mineralisation at Big Bell are informally referred to as the Big Bell Mine Sequence. The greenstone belt can be divided into three domains separated by two major regional fault zones (Barnes, 1996). The eastern domain (mostly amphibolite), the central domain (quartzofeldspathic and biotite schists which host the Big Bell Mine Sequence), and the western domain (dominated by amphibolite). The metamorphic grade within the greenstone belt is mid to upper amphibolite facies (Phillips, 1985).
Mineralisation at Big Bell is hosted within a shear zone and is associated with the postpeak metamorphic retrograde assemblages (Smith, 1998). Stibnite, native antimony and trace arsenopyrite are disseminated through the K-feldspar-rich lode schist. These are intergrown with pyrite and pyrrhotite, which are noted in most rocks of the Mine Sequence, and chalcopyrite (Barnes, 1996). Mineralisation outside the typical Big Bell host rocks (KPSH), for example 1,600N and Shocker, also display a very strong W-As-Sb geochemical halo (Barnes, 1999).
Along strike to the south of Big Bell the lithological host of the mineralisation is variable, although still restricted to the altered biotite or quartzofeldspathic schist. At Little Bell and Big Bell South, better gold mineralisation is found on the hanging wall (BISH) and to a lesser degree the footwall (KPSH) contacts of the mineralisation observed at Big Bell.
Cuddingwarra
The Cuddingwarra project area is located within the Archaean Meekatharra-Wydgee Greenstone Belt. The greenstone belt is comprised of thick sequences of mafic and ultramafic rocks, with banded iron formation and felsic volcanic rocks. Felsic porphyries have intruded the layered sequence. Deeper crustal shear zones (such as the Cuddingwarra Shear) and secondary structures have been influential in gold deposition (Barber, 2013).
The Cuddingwarra Project area encloses three lithological sequences, generally separated from each other by sub-concordant strike faults trending northerly to northnortheast.
• A high-Mg basalt and basalt sequence in the west.
• Intercalated komatiites and high-Mg basalts with minor tholeiitic basalts and dolerite in the centre of the project area.
• A sequence of sediments and volcaniclastics in the east.
Day Dawn
The Day Dawn project area is situated within the Meekatharra-Wydgee Greenstone Belt, in the Murchison Province of the Archaean Yilgarn Craton of Western Australia (Myers, 1992). Within the Day Dawn project area, the Greenstone Belt consists of intrusive and extrusive mafic and ultramafic units, felsic volcanics and volcaniclastics, sediments and quartz-haematite banded iron formation (BIF) belonging to the Gabanintha Formation, one of four laterally extensive litho-stratigraphic formations comprising the Luke Creek Group (Martin, 1993b). The Gabanintha Formation overlies sedimentary rocks of the Golconda Formation.
The Great Fingall Dolerite (GFD) hosts the major gold mineralisation of the Greenstone Belt, including the following deposits within the project tenements (from north to south).
The GFD is a large differentiated tholeiitic sill striking 30° (MGA) and dipping 70° to the NW and is approximately 530 m thick. It is truncated to the north-east by a gabbroic intrusion and a post-folding tonalite, and to the south-west it is progressively attenuated by and brought into parallelism with the N-S Cuddingwarra Shear Zone (CSZ). The GFD hosts numerous quartz vein gold deposits attributed to dilatational strain. This strain appears to have been induced by refracted N-S late-stage regional cross fractures.
The GFD unit is bounded by less competent basalts. Dilation of refracted regional fault structures within the dolerite has created sites favourable for quartz accumulation and gold mineralisation.
Tuckabianna
The Tuckabianna project area lies in the Archaean Murchison Province within a northeasttrending supracrustal greenstone sequence comprising various volcanic, intrusive and sedimentary rocks that form part of the Luke Creek Group. Mineralisation is concentrated within the lower formations of the Group (Golconda Formation and Gabanintha Formation), which dominate the greenstone belt in the district (Watkins and Hickman, 1990).
The supracrustal rocks were broadly divided into two associations separated by a major fault zone, the Tuckabianna Shear Zone, and intruded by post-tectonic granitoids. Association 1 rocks to the east of the shear zone comprise numerous BIF beds interlayer with mafic and ultramafic volcanic and intrusive rocks, which have been deformed into an asymmetric syncline referred to as the Kurrajong syncline. Association 2 rocks are located to the west of the Tuckabianna Shear Zone and consist of felsic rocks of the Eelya complex and mafic and ultramafic volcanic rocks.
Association 2 is characterised by an almost complete absence of BIF sediments. The Tuckabianna Shear Zone (also referred to as the Comet-White Well Shear Zone) is a broad, 1 to 2 km wide, north-northeast trending zone of intense deformation and alteration stretching the entire 30 km length of the Tuckabianna project area. The shear zone is a portion of the much larger Mount Magnet-Meekatharra Shear Zone, which extends at least 180 km between these two main mining centres and beyond. The shear zone is very poorly exposed and marked by deep weathering. Also present are north - north-northwest trending faults and shear zones with displacements of up to several hundred metres.