Summary:
The Coolgardie district is located on the western side of the Archaean Norseman-Wiluna Greenstone Belt within the Coolgardie Domain. Gold deposits in the Coolgardie district occur in a number of different host lithologies, including dolerites, gabbros, basalts, ultramafics and diorites. In the Tindals Mining Centre the gold deposits are hosted within basalt, ultramafic and diorite rock units. In the Greater Coolgardie area the gold deposits are hosted in dolerite, gabbro, basalt, ultramafic and, to a lesser extent, felsic intrusive rock units. At The Mount gold mine, near the town of Widgiemooltha, the deposit is hosted in basalt.
Greenfields deposit
The Greenfields deposit is located within the Greenfield dolerite sill within the Coolgardie Greenstone Belt.
There are three rock types present in the pit; dolerite (southwall), felsic volcaniclastics (footwall to mineralisation) andultramafics(North Wall). The mineralisation at Greenfields forms a conjugate set of steep and moderate dipping lodes.
The mineralisation at Greenfields averages 50m width and varies between 25 and +60m width. The mineralisation is primarily hosted by coarsely granophyric G2 gabbro near the contact with footwall Black Flag Group volcaniclastics). Gold at Greenfields is hosted by a well-developed stockwork of 1cm to +20cm wide quartz>>chlorite>pyrrhotite>carbonate veins with trace amounts of chalcopyrite and arsenopyrite.
The wall rock to the veins is commonly bleached over 0.2-0-.4m intervals.
Brilliant South deposit
The deposit lies on the western margin of the Archaean Norseman–Menzies Greenstone Belt. Host rocks at Brilliant are a sequence of Archaean Basalts and Ultramafics, which have been intruded by a suite of porphyry dykes (also described as granodiorites). The porphyries host the bulk of the mineralisation, occurring in two orientations:
1. Steeply dipping (70 -80°) with an average width of 3 to 4m(Historically conventional model used for this resource estimate),
2. Shallow east dipping (20 -40°) with average widths of up to 2-4m(not modelled at this time).
Mineralisation consists of a stock work of quartz / sulphide micro-veining and albitic alteration of the porphyry.
Dimensions
The Brilliant mineralisation has been modelled over 2 km strike length, the shoots have been interpreted from surface to approximately 600 m below surface (~ -180 mRL).
Bonnie Vale Quarry Lode deposit
Locally the geology of the deposit is dominated by the Bonnie Vale Tonalite, with an ultramafic to the east and west of the tonalite. This ultramafic has been logged as a carbonate altered ultramafic and described as a komatiite in Hallberg’s regional mapping. Mineralisation is hosted within large (strike lengths >300m) quartz reefs which range in thickness from centimetre scale to several metres. The known reefs strike sub-parallel to the edge of the tonalite, with the main orientations being an easterly dip (e.g. Westralia) or northeast (Bonnie Vale, Quarry Reef) of 40 to 60 degrees.
Historic underground works at Bonnie Vale have focused on extracting mineralised quartz reefs dipping at a 40°-45° angle. Current interpretation of an un-excavated quartz reef at Bonnie Vale also supports mineralised quartz veins dipping at 40°-45°.
Within the main mineralised lode, a ‘core’ domain of higher Au values closely associated with the quartz veining was interpreted. The boundary between the high-grade core and surrounding main mineralisation envelope was considered a hard boundary and no samples were shared between the two domains. The use of these domains controlled the limit of the high gold values encountered at Bonnie Vale.
Dimensions
The main Quarry Reef lode extends east south eastover a strike length of 500m and extends from about a depth of 70m below surface to approximately 550m below surface. The thickness of the main Quarry Reef lode varies from 2m to approximately 10m, with an average thickness of 4m.
CNX open pit
CNX is located on the north-west extension of the Three Mile Hill Open Pit which had historic production of 4.2 Mt @ 2.4 g/t Au for 324Koz. The strike of the Mineral Resource being reported is 700m and reported to a vertical depth of 230m from surface. The south-east extension of the mineralisation is cut off using an exclusion zone 97m north of the Great Eastern Highway centreline.
The main control on the bulk-style tabular mineralisation at CNX is the G2 Gabbro. Within the G2 Gabbro, 0.5cm to +5cm quartz-chlorite-sulphide veins form a series of stacked, shallow south-west dipping stockworks. Higher-grade mineralisation dips south-east within the G2 Gabbro and is characterised by sets of 5cm to 30cm-thick quartz-chlorite-sulphide veins.
Alicia - Empressa
The Alicia-Empress deposit is located approximately 3.5km due south of the Coolgardie townsite and 6.5km south southeast from Three Mile Hill (TMH).
The two deposits, Empress and Alicia, are interpreted as being the two distinct limbs of an antiform with the fold hinge forming a structurally complex deposit (Figure 10). Local geology consists of a quartz-bearing intrusive diorite between a mafic basalt hanging wall and komatiite footwall that displays distinctive spinifex texture. The majority of the gold mineralisation is hosted by the diorite intrusions and associated mm-cm scale quartz veins.
Big Blow – Happy Jack
The Big Blow mineralisation is predominantly hosted by a sub-vertical to steeply east-dipping 10-20m wide fault zone and associated breccia within the Burbanks Basalt. Both the Big Blow and Happy Jack structures have been intruded by north trending feldspar-hornblende porphyries of similar style to those associated with Brilliant. Happy Jack is sub-parallel to Big Blow and hosts lower grade though structurally analogous mineralisation also within the Burbanks Basalt.
Central Coolgardie Gold Project Stockpiles and Tails
The Coolgardie Gold Project hosts numerous historic mines with remnant low grade stockpiles and historic gold treatment areas including leach vats. Nine deposits of potential free dig mill feed were identified in the central part of the CGP for infill drilling and Mineral Resource estimation. The Dreadnought – Empress Low Grade Stockpile was targeted with 10 – 15m spaced RC drilling leading to IDS Mineral Resource estimation. Follow up campaigns of toll milling confirmed a very close reconciliation of mill production to the reported Mineral Resource.
The low-grade stockpiles comprise transitional and fresh rock material sourced from historic mining at Greenfields Open Pit and Tindals Underground. The tails vats comprise crushed/ground ore veins from a variety of sources including: Bayleys, Lindsays, Redemption, Queen of Sheba and Golden Bar.