Larvotto Resources says metallurgical engineering studies have shown it can double the process plant throughput at its Hillgrove gold-antimony operation in NSW up to 500,000 tonnes per annum, with only minimal upgrade and modification required.
The company says its plant’s capacity to produce gold concentrate and doré in conjunction with antimony concentrate can easily be increased by expanding the crusher feed rate from 220,000 tonnes per year. The study was undertaken by Mincore, a leading process engineering and EPC (engineering, procurement and construction) contractor.
Additionally, a complementary scoping study of historical gold and antimony production reveals that a high-grade gold concentrate can be produced by incorporating a new gravity separation module into the process stream. It would provide the potential to produce a high-grade gold concentrate of more than 150 grams per tonne gold.
The potential improvement in gold output contrasts sharply with historical concentrate grades from prior operations, which produced 50g/t gold. Management says the historical results were obtained from feed grades of about 1.5g/t gold.
Larvotto Resources managing director Ron Heeks said: “As expected, the Hillgrove Gold and Antimony Mine is shaping up to be an exciting opportunity that provides Larvotto Resources with a rapid pathway to production. Scoping level testwork undertaken on historical concentrate also indicates the multi gravity separator is a potential game changer for the Hillgrove Gold Mine.”
Management said a separate study conducted by AXT Automated Mineral Incubator Laboratory in Perth also support its potential for gold recovery improvement. AXT examined gold concentrate produced by previous project owner Red River Resources while treating low-grade ore stockpiles in 2022.
The study showed that even with the original Knelson concentrator – long regarded as the ultimate gold “catch-all” module to pick up gravity recoverable gold – in front of the flotation circuit, the original Hillgrove concentrates still retained about 13 per cent gravity-recoverable gold, typically bigger than 40 microns (0.04 mm) in size.
However, it also revealed that about 44 per cent of the remaining fine gold is smaller than 40 microns, while the balance comprises sulphide-hosted gold (40 per cent) and a small amount of non-sulphide or stibnite (antimony sulphide)-hosted gold.
The study found that Red River’s low gold recovery was due to its poor initial feed grade, which is far lower than that expected to be presented to the circuit by Larvotto.
It implies that improving gravity recovery, hence refining the gold float feed concentrate, and expanding the flotation circuit would result in a significant improvement in overall recovery.
Testwork also showed further improvement in the gravity gold recovery circuit would be possible using a multi-gravity gold separator (MGS), which is a more recent and less complex innovation than the Knelson concentrator. Management says the MGS is capable of recovering more than 70 per cent of the gold from the concentrate.
Other proposed upgrades and modifications with minimal flowsheet changes would entail the addition of a secondary crushing circuit, a small re-grind circuit and the provision of an additional fine ore storage bin. Management says major components of the secondary crushing circuit and most of the steelwork is already onsite.
The upshot of the study is that significant upgrades to plant processing throughput, recoveries and overall performance can be achieved with minimal additional cost to improve the winning of both antimony and gold from the ore. It would be expected to significantly decrease production costs, while increasing gold and antimony production.
Following the positive findings, Larvotto is now eyeing more detailed studies to refine the proposed measures and costs to more accurately gauge the likely economic benefits.
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By Doug Bright
