Crater Gold Mining Limited announced the results of ongoing metallurgical test work on graphite mineralisation from the Golden Gate Graphite Project at Croydon in North Queensland. Encouraging flotation test work results were obtained for a 7-stage cleaner concentrate from a 850 micron composite sample. There was very little coarse material present and insufficient of the finer grained fractions remaining to enable microscopic examination of the graphite product.

The lack of coarse grains was surprising as previous petrological examination had indicated the presence of graphite flakes from fine sizes, up to, and exceeding 500 microns. It was therefore decided to run the test work again using composite samples of 100% passing 1.0mm and 1.4mm. Graphite recoveries to the rougher concentrates of 77.4% and 78.7% respectively were achieved, but the graphite grades of the final concentrate products were low at 25.8% and 25.7%.

Both sample rougher concentrates were then sized and found to have a good spread of grain sizes from + 500 microns to minus 25 microns. However, microscopic examination of these fractions revealed a surprising result, with the graphitic material appearing as sub-rounded clusters or nodules, rather than an expected size range of traditional flake material. This examination also showed that the coarser grain sizes were composed of graphite nodules, gangue minerals and un-separated graphite/gangue grains.

The individual coarse graphite grains identified in the thin section petrology were not present in this test. To investigate this matter further, it was decided to select a 1.0mm composite sample for more detailed metallurgical testing. This involved preparing a 7-stage cleaner concentrate rather than a 4-stage rougher concentrate that was previously used.

This new test work involved less vigorous progressive regrinds for the cleaner concentrate stages. A high-grade final concentrate of 96.4% graphite was achieved, but the graphite recovery to the final concentrate was only 60.2%. Sizing of the cleaner concentrate product indicated that most of the graphite was ultra-fine grained with 95.4% being less than 53 microns and 73.4% being less than 25 microns.

It was then decided to attempt to optimise the 1.0mm composite sample flotation test work by using only a 3 minute bead mill polish time for all of the cleaner concentrate stages. This optimisation attempt resulted in a final concentrate grade of 95.3% graphite, with the graphite recovery to the final concentrate much higher at 78.9%. This result indicates that optimisation is heading in the right direction.

The Company is confident that further optimisation will achieve higher graphite recovery and final product purity. Sizing of the graphite concentrate also indicated that most of the graphite was ultra-fine grained with 90.5% being less than 53 microns and 66.6% being less than 25 microns. The minus 25 micron, minus 38 to +24 micron and the minus 53 to + 38 micron graphite concentrates from the optimised 1.0mm composite sample were then examined at high magnification via a Scanning Electron Microscope (SEM).

This revealed that the graphite in all three ultra-fine grain sizes was present as platy flake. This has raised optimism that the graphite, being mostly ultra-fine grained and present as platy flake, may potentially be amenable to production of high value products and in particular battery anode material. Future metallurgical test work will concentrate on investigating these possibilities at a specialised metallurgical test laboratory.