Reporting on metalurgical tests using drill core composite samples from its Brazilian development project, Altamira Gold said it obtained good results from a nonconventional leaching method that eliminates the need for cyanide.

Altamira Gold, a Canadian junior focused on exploration and development of gold projects in western central Brazil, recently received comparative results of an initial metallurgical leach characterization test using an unconventional technology on a drill core composite sample of primary mineralization from its Maria Bonita drill target at the Cajueiro project in Para state.

The company said the information complements other test results released earlier this year that used conventional cyanide leach technology. The current test was conducted at SGS Australia and CSIRO laboratories in Western Australia using a proprietary thiosulphate leach technique developed by Clean Mining, a subsidiary of Clean Earth Technologies (CET), based in Singapore. CET is commercializing a non-cyanide approach to leaching of gold ores that was originally developed in Australia by CSIRO. 

According to Altamira, a 24-hr agitated leach test using the thiosulphate leach agent, at a grind size of 80% passing 75µm, recovered 92% of total gold content. A cyanide leach test was also conducted in parallel using the same grind and leach time and yielded a gold recovery of 91%. These results, said the company, correlate well with recently announced cyanide leach tests carried out in Brazil, which also returned an average cyanide leach gold recovery of 91% for primary mineralized material from Maria Bonita.

For the Clean Mining leach test, 31.2 g of clean leach reagent (CLR), equivalent to 20 g of reagent per liter of liquor) and 5.6 g of clean leach enhancer (CLE) equivalent to 3.7 g of reagent per liter of liquor were added. The concentration of reagents and the pH were monitored for the duration of the test. After 48 hours of leaching, the pulp was filtered and washed with three displacements of water.

The results indicate consumption of 3.59 kg/t of CLR and 0.36 kg/t of CLE and an average gold recovery of 92.1% within 24 hours. Clean Mining noted, “The ore has shown low reagent consumption, high gold recovery and fast leaching kinetics.”

The company’s consulting metallurgist, Ian Gordon Hall Dun, observed, “This leach test supports the concept of Altamira utilizing a non-cyanide route to gold recovery for the Maria Bonita project. 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.”

The company said it next plans to investigate crushing and grinding characteristics, the amenability of both conventional cyanide and thiosulphate leach to the dynamics to heap leaching and further evaluation of agitated leach using both reagent options.

In related developments, Clean
Mining formed a partnership in late 2022 with MCT Group, a specialist provider of construction chemicals, under which MCT Group will manufacture Clean Mining’s patented non-toxic reagent. Also in 2022, CET signed an MOU to establish a working relationship with Gekko Systems to pursue project opportunities combining CET’s technologies and reagents while utilizing Gekko’s Inline Leach Reactor (ILR) and associated modular mineral processing equipment.