Azure Minerals’ small-scale open pit at Oposura finds high-grade zinc, lead mineralisation

The first phase of Azure Minerals’ (ASX: AZS) small-scale program at the Oposura zinc-lead-silver mine in Mexico has extracted near-surface, high-grade, massive zinc and lead sulphide mineralisation.

Since July, an estimated 6,100 tonnes of ore at grades of 13.4% zinc and 10.7% lead has been mined and stockpiled at Oposura, located in the northern, mining-friendly state of Sonora.

Tonnage and grades significantly exceeded average figures of 5.1% zinc and 2.6% lead for the East Zone open pit mine as estimated in Oposura’s 2018 scoping study.

The stockpile included approximately 2,100t of ultra-high-grade ore at 24% zinc and 18.3% lead.

Managing director Tony Rovira said it was an “impressive start” to the small-scale mining program.

“To be getting more tonnes and much higher grades than we had expected gives us great confidence in the project as we advance Oposura toward large-scale mining and on-site processing,” he said.

Mr Rovira said wet commissioning of the toll treatment processing plant was due to start this month under a toll treatment agreement with the nearby the nearby San Javier sulphide flotation processing plant but was delayed due to an extended refurbishment program.

Processing has since commenced.

Mine plan

Mining at Oposura comprised a starter open pit to exploit easily-accessible, high-grade massive sulphide mineralisation from the East Zone mineral resource.

The material occurs at, or very close to, surface and in some places, had already been fully exposed by historical prospecting activities.

Overburden comprised weathered rock which was removed by a bulldozer and excavator and required minimal drilling and blasting, ensuring low mining costs.

Initially, the open pit was designed to extract 1,000t of ore before moving into an underground mining phase.

However once mining commenced, significantly more ore at higher grades was identified than originally estimated by mineral resource drilling.

In light of the lower mining costs and higher production rates associated with open pit mining compared to underground, Azure opted to extend the open pit phase.

Underground operation

Within the open pit, the relatively flat-lying, high-grade massive sulphide zone varied in thickness up to 4m and demonstrated “excellent continuity” of the overall mineralised horizon and the internal high-grade, massive sulphide zones.

Within the western part of the open pit, 2,100t of ultra-high-grade massive sulphide ore was mined at a combined 42.3% zinc and lead, with some parts of the zone containing zinc and lead grades exceeding a combined 50%.

This ultra-high-grade ore was stockpiled separately as a potential direct shipping ore (DSO) product.

Azure said open pit activities enabled the western pit wall to be cut back to provide a stable face for portal access for the planned underground operation.

Underground development will be carried out in ore to offset establishment costs prior to selectively mining the high-grade ore zone using a room and pillar method.

Ore processing

Oposura ore throughput is scheduled to start in the December quarter and continue into 2020.

Azure will produce separate zinc and lead-silver concentrates and expects to sell them on the spot market to locally-based metals traders or smelters, several of which have already expressed strong interest.

When delivered, positive cashflow will support funding of the definitive feasibility study into a large- scale mining and on-site processing operation and provide general working capital.

At midday, shares in Azure were trading 21.05% higher at $0.23.