Alma Metals (ASX:ALM) is immediately advancing towards Prefeasibility Studies after completing a Scoping Study assessing the technical and economic viability for large-scale open pit mining of the Briggs Copper Project.
The company says the Scoping Study has given it and the joint venture partner Canterbury Resources (ASX:CBY) confidence that Briggs represents an “excellent opportunity” for a future large-scale, low-cost open-pit copper mine in central Queensland.
On this basis, the project is moving straight to a PFS to assess an aspirational 30 million tonnes per annum open pit operation – initially comprising drilling to enhance and expand the mineral resource estimate (MRE); more detailed metallurgical studies to optimise the process flowsheet; and additional evaluation of a molybdenum circuit and the use of coarse-particle flotation technology.
Mining Plus was engaged to study potential open pit mining operations at the Briggs Copper Project on an owner-operated basis, and to provide capital and operating cost estimates and a conceptual project layout.
The mining study scope included preliminary pit shell optimisation using Whittle software, incorporating economic inputs provided by Alma Metals and Ausenco and geotechnical parameters defined by Mining Plus.
Conceptual project layout included the open pit, haul roads, ROM pad, comminution circuit, concentrator and supporting site infrastructure including workshop and administrative buildings.
Alma Metals Managing Director Frazer Tabeart says the results of the Scoping Study confirm a strongly held belief that “Briggs represents an outstanding opportunity to build a large-scale copper mine in central Queensland at a time when copper supply is under severe global pressure”.
“We will focus on further drilling aimed to significantly increase resource confidence and enhance planned prefeasibility studies, which will include several promising areas already identified for value addition,” Tabeart says.
Right location
Briggs is located in central Queensland, 60km to the south-west of the industrial port city of Gladstone, within proximity to a major infrastructure corridor, which includes multiple high-voltage power lines, a heavy haulage railway, multiple gas pipelines, and the Dawson Highway.
Exploration and evaluation at Briggs is being funded and managed by Alma under an earn-in joint venture agreement with Canterbury Resources.
Alma has earned a 51% JV interest and can increase this to 70% through further expenditure of $7 million by 30 June 2031. The project then becomes a contributing, unincorporated joint venture with standard proportional funding and dilutionary provisions.
Canterbury Managing Director Grant Craighead says Briggs represents an outstanding opportunity to build a large-scale copper mine in central Queensland at a time when copper supply is under severe global pressure.
“Key drivers of these encouraging results are the excellent metallurgy, economies of scale and favourable location of the project,” Craighead says.
“Drilling is ongoing, aimed at increasing resource confidence as part of our Prefeasibility Studies which include several promising areas identified for value addition.”
Mineral resource estimate
At Briggs, copper, molybdenum and silver mineralisation is hosted by early Triassic (ca. 248 Ma) porphyritic granodiorite intrusions that were emplaced into older Devonian volcanic rocks and volcanoclastic sediments.
The intrusions are multiphase, and form three distinct bodies that form elongated, north-south trending bodies with a vertical to steep northeast dip, extending over a strike length of more than 2km.
Mineralisation occurs in disseminations and vein stockworks containing quartz, chalcopyrite, minor molybdenite, potassium feldspars and locally anhydrite in both the porphyritic granodiorites and in the surrounding volcanic sediments.
The MRE was last updated in April 2025. Resource classification categorised material as indicated where drill spacing was less than 80m between lines and inferred where greater than 80m.
Metallurgical test-work for Briggs was conducted by Auralia Metallurgy under the supervision of Scott Dalley Francks. Comminution tests indicate that the mineralisation is hard to very hard and moderately abrasive. The results indicate that both SABC (SAG Mill + Ball Mill) or HPGR (High Pressure Grinding Rolls) comminution circuits would be suitable for this type of mineralisation.
Flotation testwork achieved recoveries of 93-96% copper in batch rougher flotation tests. Results were insensitive to primary grind size (150-212 µm).
Cleaner and recleaner re-grind and flotation achieved 88-89% overall copper recovery in batch flotation tests. Subsequent locked cycle flotation tests improved overall recovery to 93-95% at 23-29% copper grade.
Analysis of the locked cycle test concentrates revealed clean, marketable concentrates. Minor concerns were raised over levels of fluorine, silica and alumina in the volcanic-sediment master composite, but these are considered likely to reduce to acceptable levels with more efficient cleaning of the final concentrates.
A conceptual process flowsheet comprises primary/secondary crushing followed by SAG/ball mill grinding (SABC) to P80 212µm, rougher flotation, regrind, and cleaner/recleaner stages.
Ausenco reviewed the testwork results and conceptual flowsheet and provided advice on equipment sizing and plant layout.
Alma and Canterbury say capital and operating cost estimates were provided by Ausenco via industry benchmarking for similar scale projects in similar jurisdictions with similar mineralisation types (particularly with regards to hardness).
Write to Adam Orlando at Mining.com.au
Images: Alma
