Big River Gold identifies commercial potential of mica by-product at Borborema gold project

Test work on Big River Gold’s (ASX: BRV) Borborema ore has revealed the commercial potential of generating mica as a by-product to gold production.

According to Big River, the test work has yielded “very positive” results on creating and selling mica as a by-product at Boreborema, which is located in north-eastern Brazil.

The Borborema orebody is estimated to contain about 30% auriferous mica, which could generate about 600,000t of the material at a 2 million tonne per annum throughput rate.

After processing via milling, cyanide leach and elution circuits, test work indicates the mica can be “readily separated” in a flotation stage to produce a product with “attractive commercial properties” including flake size.

However, further evaluation revealed magnetic separation as a “more effective” and “attractive” process route.

Mica is used in the volume filler market, particularly dark coloured polymers. It is also used in coatings for the paint market, where its anti-corrosive properties make it a key additive.

In 2018, a wet ground fine mic concentrate sold for US$300-500 per tonne (A$445-743/t).

Ongoing test work will involve creating a bulk mica product for customer evaluation as well as determining the key technical information for effective fine grinding of the product.

Big River will also investigate separating coarse flake phlogopite from the bulk concentrate for us e in specialist electronics and automotive sectors.

The company noted this coarse flake phlogopite can sell between US$200/t and US$1,000/t.

Borborema gold project

Although the mica material offers a commercial opportunity as a by-product, the primary focus at Borborema is gold.

Big River released a definitive feasibility study into the project late last year, which revealed a potential 10.2-year operation that would generate 729,000 ounces of gold.

Average gold production is estimated at 71,000oz per annum, with forecast all in sustaining costs of US$839/oz.

Capital expenditure to get the asset up and running is anticipated to total US$99 million, which includes US$11 million for contingencies.

Life of mine earnings before interest tax depreciation and amortisation is expected to reach US$527 million, with US$53.8 million (A$79 million) anticipated annually.

Borborema is underpinned by a resource of 20Mt at 1.22 grams per tonne gold for 784,000oz.