Results are in line with those produced in pre-feasibility test work but on a larger scale.
The quantity of material was upscaled by 50-times compared to the pilot trial with commercial-scale spirals used for the tests.
COB is encouraged by the positive results achieved and successful use of the commercial-sized spirals bodes well for commercial implementation of the circuit.
Shares were up more than 7% today to 14.5 cents.
Since completing the pre-feasibility study (PFS) in mid-2018, COB has been advancing the metallurgical program for the project.
This year the work has seen COB treat 45 tonnes (wet basis) of reverse circulation (RC) drill chips through a pilot-scale concentrate circuit at ALS Metallurgy in Burnie, Tasmania.
Samples of ore from the Pyrite Hill, Big Hill and Railway deposits were collected during the
2017 drilling campaign and stored in the core yard at Broken Hill prior to processing.
Deposit plan showing the location of drill holes which were the source of material for the test work.
Mass Weighted Average Cobalt Grades per 1-metre drill core interval samples.
As part of the 2017 scoping study and 2018 PFS, COB developed a simple circuit for upgrading the ore into a pyrite-concentrate prior to refining.
The key driver for the circuit selection, was to take advantage of the large (coarse) grained pyrite, and thereby minimise crushing and milling costs.
After extensive mineralogical characterisation and bench-scale evaluation of different concentrate methods, a combined gravity-flotation circuit was selected.
The ore was crushed/milled to 1mm topsize, and passed across gravity spirals, to produce a gravity concentrate.
Gravity rejects were size-classified and the fine fraction (nominally <125 um) sent to a flotation circuit for scavenging the remaining cobalt-pyrite.
In the current pilot-scale program, the circuit has been shown to be robust, with successful concentration of variable ore grades.
Overall deportment of cobalt, cobalt grade, and mass through the pilot-scale concentrate circuit.
Furthermore, the combination of two techniques - gravity and flotation - provides an effective method for treating ore samples which vary in particle size distribution.
These are two common hurdles for reliable concentrator operations.
Operating rougher spiral (left) and cleaner spiral, with ‘heavy’ pyrite concentrate being separated from ‘light’ feldspar/silica gangue.
- The overall recovery of cobalt was 90%, in-line with the PFS test work results.
- Cobalt grades in the gravity and flotation concentrates were remarkably similar, ranging from 4444ppm to 5075ppm. This confirmed that the cobalt content in the host pyrite mineral was consistent across the range of ore grade samples. Variations are likely due to differences in liberation of pyrite grains from the gangue feldspar/silicates.
- Tailings rejects typically graded 100–180ppm cobalt, which was close to the analysis detection limit of 100ppm cobalt (XRF method was used). Sub-samples have been sent for characterisation of acid-forming properties (Bureau Veritas Adelaide), and other sub-samples are being evaluated for incorporation into overall mine waste rock and process plant tailings management studies (ATC Williams).
- Optimisation of the classification step, and the possible inclusion of a regrind unit operation, may lead to improved cobalt recoveries. This will be considered in future test work programs.
Coarse tails accumulating in bulka bag (left), wet concentrate stored under water in plastic drum.
The simplicity of the circuit equipment and the robustness to account for low-average-high grade ore and variable particle size distributions, provides a strong foundation for the process plant operations.
The ability to upgrade the ore by concentration, while retaining about 90% of the cobalt and rejecting about 80% of the feed ore to tails, significantly reduces the capital and operating costs for a refinery.
Summary of campaigns and feed batch sizes.
COB is preparing detailed plans for continued pilot testing of the flowsheet. This will include the following steps:
- During 2H 2019, the 7–8 tonnes of concentrate produced from the pilot-trial, will be progressed through a pilot-scale furnace operated by ANSAC in Bunbury.
- Plans are being prepared for a second concentrate trial, utilising the remaining 40–45 tonnes of mineralised material stored at Broken Hill. This will focus on seeking improved recoveries via process optimisations.
- Engineering design work will now commence to update the PFS costings for the concentrate circuit.
- Geo-metallurgical studies will now commence, with a focus on linking in-ground ore characteristics to extractive mining techniques (blasting, load and haul), and crushing/milling requirements.