Altamira Gold Corp. (TSX-V:ALTA, OTC:EQTRF) said it has received impressive results from a metallurgical leach test on a drill core composite sample from the recent Maria Bonita discovery at its Cajueiro project in the northern state of Brazil.
The Vancouver, British Columbia-based company said the tests complement results released on March 1, 2023, using the conventional cyanide leach technology.
Altamira said that after the completion of holes MBA001-MBA004, a composite sample of fresh rock mineralization was prepared from assay sample coarse rejects, returned from the analytical lab. The sample weighed 5 kilograms (kgs) and consisted of 15 subsamples of individual core intervals.
The company sent the samples to Clean Mining and the test work was done at SGS Australia and CSIRO labs in Australia using a proprietary thiosulphate leach technique developed by Clean Mining, a subsidiary of Clean Earth Technologies (CET), based in Singapore.
Cyanide leaching is the traditional method to extract low-grade gold. However, Thiosulphate leaching offers a more environmentally benign route to gold extraction, said the company.
Altamira noted that compared with earlier results for metallurgical characterization for Maria Bonita mineralization, the thiosulphate leach gave high recoveries, marginally higher than those for conventional cyanide leaching.
“A 24-hour agitated leach test using the thiosulphate leach agent, at a grind size of 80% passing 75µm, recovered 92% of total gold content,” said the company.
The head grade of the sample treated compares well with the original assays of the diamond drill composites making up the sample. The original assays from the drill samples gave 1.07 grams per ton (g/t) gold, while the Clean Mining lab head grade (500g sample) gave 1.04 g/t gold, noted the company.
In addition, the Clean Mining leach test resulted in a back-calculated head grade of the sample (after leaching) of 1.10 g/t gold (1,000g of leach test sample). The results underline the consistency of the mineralization, pointed out Altamira.
A cyanide leach test was also conducted in parallel using the same grind and leach time and yielded a gold recovery of 91%. The results correlate very well with recently announced cyanide leach tests carried out in the test-work lab in Brazil, which also returned an average cyanide leach gold recovery of 91% for primary mineralized material from Maria Bonita.
Very positive
In a statement, Altamira CEO Michael Bennett said: "We are pleased to receive this very positive result, which underlines the potential for a non-cyanide process route to be technically highly competitive with conventional cyanide leaching at our Cajueiro project.”
“Our previous work with Clean Mining on oxide material from the existing Cajueiro resources, gave similar highly encouraging results, and we have now achieved high recoveries with primary material from the new Maria Bonita discovery. This initial test creates a strong option to now evaluate the application of both the Clean Mining and conventional cyanide leach technologies to a start-up heap leach project."
Meanwhile, consulting metallurgist Ian Gordon Hall Dun, who has 45 years of experience as a metallurgist in Brazil noted that at this initial stage, the results provide “higher gold recoveries” than conventional cyanide leach at low reagent consumption rates, which is a “very positive initial result.”
“We will further develop this option through testing both the Clean Mining and conventional cyanide leach routes for heap leaching conditions," Dun added.
Santa Helena drill results
Altamira also provided drill results from its Santa Helena project in the Brazilian state of Mato Grosso. The company said that 23 diamond drill holes totaling 3,615 meters (m) were completed on 8 separate targets identified by a combination of soil sampling, geological mapping, and reviews of artisanal miners' workings.
Altamira highlighted that final drill results from a series of reconnaissance drill holes completed during 2022 at the Santa Helena project returned several notable intercepts including 0.8m at 44.8 g/t gold and 0.9m at 10.4 g/t gold.
Investors can find Notable drill results received from the scout drilling program here.
Contact the author Uttara Choudhury at uttara@proactiveinvestors.com
Follow her on Twitter: @UttaraProactive