Cobalt Ridge Deposit
The Cobalt Ridge Deposit (Cobalt Ridge) within Mt Gilmore hosts a unique cobalt dominant sulphide deposit. Drilling by Corazon at Cobalt Ridge has validated historical mining and exploration results and confirmed the presence of multiple zones of cobalt-copper-gold sulphide mineralisation. The mineralisation has been tested over 300 metres, remaining open and untested along strike and at depth.
The Main Cobalt Lode has been the primary target of the Company’s past drilling, as well as much of the historical drilling. This lode is up to 25 metres in true width and contains multiple narrow zones of higher-grade mineralisation, within a broad envelope of mineralisation.
Metallurgical testwork on this sulphide mineralisation has demonstrated exceptional recovery of cobalt, copper and gold from drill samples from simple flotation processing, with solvent extraction following standard pressure oxidation (POX), to deliver separate high-quality cobalt and copper sulphates suitable for use in lithium-ion batteries. Gold is captured separately from the POX residue.
Main Lode Drilling Program expands mineralised system at Cobalt Ridge
During the December 2018 quarter, Corazon announced additional assay results from its recent 21-hole, 2,967.65 metre drilling program, which was focused on the Main Lode at Cobalt Ridge. Numerous +1% cobalt assays were returned, with the best result being 5 metres @ 2.14% cobalt (ASX announcement 9th November 2018).
Commenting on the results, Corazon’s Managing Director Brett Smith said; “this drilling has returned exceptional results and has enabled us to gain a much higher-level geological understanding of the deposit. Our ongoing work should enable us to more accurately express the potential of the Cobalt Ridge deposit, which is our core aim, and we expect to be able to announce more about this in the coming weeks.”
The results from this program provided Corazon with a strong understanding of the controls on the mineralisation. significant intercepts are presented in Table 1, below. This data is being worked back into geological models for the Cobalt Ridge Main Lode and are also being used to identify priority drill target areas within parallel zones of mineralisation to the north and south of Cobalt Ridge.
Cobalt Ridge remains substantially under-drilled and there is demonstrated potential to define additional areas of mineralisation. The Cobalt Ridge Main Lode remains open in all directions and is only one of numerous parallel mineralised trends, defined by historical workings and broad-spaced drilling, that have yet to be targeted with resource definition drilling.
Table 1: Significant assay results of +1% “Cu EQ” from Cobalt Ridge drilling
Table 1 Notes – Cobalt intercept calculation parameters: Greater than or equal to 0.3m down hole thickness, greater than or equal to 0.05% Co, greater than or equal to 0.05% Co cut-off and less than or equal to 3m internal dilution. Assay values at “lower than” detection limits are attributed a value of 50% of that detection limit for interval calculations.
Copper equivalents: The composited value of the cobalt-copper-gold mineralisation is presented as percentage copper equivalents (CuEq%). These metals have been historically extracted from small scale mining at Mt Gilmore and it is the Company’s belief that the cobalt, copper and gold are recoverable. Metallurgical test work completed by the Company support these assumptions. CuEq% = Cu% + (Co% * 8.35) + (ppm Au * 0.63). Metal prices used are Cu US$6,319/t, Co US$52,750/t and Au US$1,233/oz.
Figure 1: Interpreted cross section for drill hole MCRC042
This drilling program identified dominant trends for the cobalt-copper-gold sulphides, as well as structures (faults and shears) that may control the location of the mineralisation. This data is being worked back into geological models for the Cobalt Ridge Main Lode and are also being used to identify priority target areas within parallel zones of mineralisation (Cobalt Ridge lookalike trends) to the north and south of Cobalt Ridge. As can be seen in Figure 1, the geochemical anomaly within the Cobalt Ridge area is much more substantial than just the Cobalt Ridge Main Lode.
Highly successful completion of Phase 3 Metallurgical Testwork
Corazon’s highly successful Phase 3 metallurgical testwork focused on defining down-stream concentrate processing options, and the results demonstrated exceptional recovery rates of cobalt, copper and gold from drill samples from the Cobalt Ridge Deposit, using conventional processing routes (ASX announcement 17 May 2018).
Conventional flotation testwork delivered a high-grade cobalt-copper-gold concentrate – of up to 7.38% Co – from high grade Cobalt Ridge samples, as well as excellent concentrate grades from lower low-grade samples (see Table 2);
Table 2: Phase 3 metallurgical sample and concentrate grade
The combination of high grade concentrates and very high recoveries delivered in the testwork provides Corazon with the opportunity to potentially either produce a high-value bulk concentrate for direct sale, or to develop an in-house down-stream processing plant.
The Company produced high-grade concentrates from simple flotation processing, with solvent extraction following standard pressure oxidation (POX), to deliver separate high-quality cobalt and copper sulphates. Gold is captured separately from the POX residue.
The mineralisation at Cobalt Ridge has several beneficial characteristics. A key advantage for the processing is the sulphide mineralisation at Cobalt Ridge, which allows for a smaller sulphide/metal concentrate to be produced prior to down-stream processing. This would likely significantly reduce the capital and operating costs of a down-stream plant, compared to having to process a bulk feed.
Down-stream testwork focused on the use of POX as the method for cobalt and copper extraction. POX was identified as the preferred process route due to its potentially lower cost, processing adaptability for variable mineralisation and its capacity to deliver environmentally stable and controlled waste products.
The POX testwork achieved excellent results, with up to 98.91% cobalt and 96.70% copper extraction. The solution from the POX underwent precipitation testing in order to assess metal removal, with solvent extraction testing being completed using conventional organics.
The testwork was managed by internationally recognised metallurgical consultants, METS Engineering and independently carried out at ALS Metallurgy in Balcatta, Western Australia.