Summary:
The Elizabeth Creek project, of which MG14, Cattle Grid South and Emmie Bluff are part, sits in the Stuart Shelf within the broader Olympic Copper Province in South Australia.
The Elizabeth Creek Project is situated within flat-lying volcano-sedimentary sequences of the Stuart Shelf (Precambrian to Neoproterozoic), overlying the eastern part of the Archaean age Gawler Craton in South Australia, specifically within the Olympic Copper Province. The province forms an approximate north-northwest trending feature, hosting a number of polymetallic iron oxide copper gold (IOCG) deposits.
The volcano-sedimentary units are part of the Neoproterozoic Wilpena and Umberatana groups, which unconformably overlie the older (Meso-Palaeoproterozoic) Pandurra Formation. The formation has been uplifted, forming a large horst structure that directly underlies the Project area (the Pernatty Upwarp).
Mineralisation
The Elizabeth Creek Project is known to host three major distinct mineralisation styles:
• Iron oxide copper gold (IOCG) mineralisation, which is known from the Emmie IOCG deposit;
• Zambian-style sediment-hosted copper-cobalt mineralisation, which is the principal focus of this Scoping Study; and
• Cattle Grid-type copper breccia mineralisation such as Cattle Grid South, which has historically been the source of historical copper production in the area.
Zambian-style mineralisation, as the name suggests, is best compared to the large shale hosted copper-cobalt deposits known from central Africa, or the central European kupferschiefer deposits. At Elizabeth Creek, large-scale Zambian-style copper-cobalt-silver mineralisation is known from three deposits: MG14 and Windabout are shallow (20– 30m and 55–80m deep, respectively), metallurgically similar, and will be mined as open pits; Emmie Bluff is a larger, deeper (approximately 400m) deposit and will be mined using underground methods.
Each deposit consists of an isolated embayment of Tapley Hill Formation shale onlapping onto the Pernatty Upwarp. Mineralisation across all three deposits has similar basic characteristics and consists of (broadly speaking) two relatively narrow stratiform lodes at the upper and lower contacts of the dolomitic black shales and dolostones of the Tapley Hill Formation. These two lodes typically come together to form a single, thicker lode at the edges of the deposit, where the grades can be materially higher than in surrounding areas.
The dominant copper sulphides are chalcocite, bornite and chalcopyrite, with all three varying in abundance from sample to sample. Minor covellite, sphalerite and galena are known. Cobalt is generally found as Carrollite, a copper-cobalt sulphide with the formula CuCo2S4.
Mineralisation at Cattle Grid South is geochemically similar to that at the other deposits, but is expressed slightly differently. Mineralisation at the Cattle Grid Deposit (of which Cattle Grid South is an extension) is expressed as a series of fracture filling veins (average 2mm thick) within the Cattle Grid breccia, which forms a blanket following the Pandurra palaeotopography, averaging 4.5m thick and approximately 1400m x 600m in area.
There is a vertical zoning in the mineralisation texture, an upper zone of open space filling is more intensely brecciated and more richly veined by copper sulphides, in the lower fracture zone the intensity of brecciation and fracturing diminishes, with a consequent decrease in the frequency and width of sulphide veins. Jointing continues beneath the permafrost breccia layer, and some joints are weakly mineralised up to 140m depth.
Mineralogy has been determined by historical petrology reports of the Cattle Grid deposit, which is laterally zoned with a chalcopyrite core to the northwest, rimmed by bornite on the southeast and in turn rimmed by chalcocite extending out from the deposit. Cattle Grid South is principally located within this outer chalcocite dominated zone.
Galena and sphalerite commonly occur as an outer zone around other sulphide masses, Carrollite occurs as minute inclusions in bornite, and also as relict corroded grains in chalcocite and sphalerite. Vertical mineral zoning is very irregular, in general a pyrite/chalcopyrite rich band occurs at the top of the mineralised zone grading to a chalcocite/bornite assemblage to the lower sections of the mineralised body, sphalerite and galena occur usually in the upper portion of the mineralisation.
The study is based on four Mineral Resource Estimates.
Three broadly geologically consistent Mineral Resource Estimates (shale hosted, stratiform copper-cobalt-silver deposits of the central African or Kupferschiefer style). They are:
- Emmie Bluff: A roughly triangular lens of Tapley Hill Formation shale extending from the northern boundary of Coda’s tenure, with a maximum width of approximately 2.9 km east-west and a north-south extent of approximately 2.4 km. The upper lode varies in thickness from 1 m to 22 m, whereas the lower lode is inconsistent, varying from absent to approximately 8 m.
- Windabout: A flat, tabular, triangular shaped sheet of Tapley Hill Formation, extending approximately 2 km east-west and 1 km north-south, with an upper lode varying in thickness between 2 m and 8 m at a depth between 55 m and 85 m, whereas the lower lode varies from 2 m to 6 m.
- MG14: A tabular, horizontal, triangular shaped sheet of Tapley Hill Formation, extending approximately 1.4 km east-west by 0.4 km north. The upper lode of the deposit is 3–8 m thick and is located approximately 20–25 m below the surface, whereas the lower lode is narrow and inconsistently mineralised.
One geologically distinct variant on sediment hosted mineralisation,( breccia sandstone-hosted copper- cobalt-silver) deposit:
- Cattle Grid South: Cattle Grid South breccia mineralisation is approximately 1.4km (east-west) by 750m (north-south) by 15m (thickness), and is hosted in a palaeopermafrost breccia of the basalt Whyalla Formation and upper Pandurra Formation sandstones. This formation unconformably overlies the Meso/Palaeoproterozoic Pandurra Formation due to local uplifting associated with the Pernatty Upwarp. This unconformity, as well as structures associated with the Pernatty Upwarp, represent the most likely fluid flow pathways associated with the emplacement of metal-bearing sulphides. Cattlegrid Breccia mineralisation closely resembles mineralisation in the Main Open Cut, East and West Lagoon, House and Gunyot resources found approximately 2-4 km to the north and east, also within the broader Elizabeth Creek project tenure. These deposits are considered by Coda to be genetically related to, but geologically distinct from, the shale-hosted Zambian-style copper-cobalt deposits which host the majority of the copper known to exist at Elizabeth Creek (MG14, Windabout and Emmie Bluff). While Coda considers it very likely that the two deposit types formed from the same fluid at the same time, differences in the host rock produced two highly distinct deposit types with different chemistry, morphology and metal distribution, with material implications for mining and metallurgy.