WORLD-FIRST FIELD TRIAL OF ‘IN-SITU’ GOLD EXTRACTION PROCESS

 

A new, environmentally friendly process developed by Australia’s CSIRO, to extract gold without mining, is to be field tested for the first time - with a South Australian gold deposit chosen as the test site.

The breakthrough in-situ process - which may reduce the need for conventional, expensive open-cut mining techniques – is being taken forward through a collaboration agreement between the CSIRO and ASX-listed minerals explorer, Minotaur Exploration Limited (ASX: MEP).

Minotaur announced today that a 15-month program of field trials to confirm the process concept will take place at its Tunkillia gold deposit in the Gawler Craton, south of Tarcoola.

“The process has the potential to revolutionise the way we normally mine near surface weathered (or ‘oxide’) gold deposits, while at the same time delivering potential massive cost savings for the owners of oxide gold resources,” Minotaur’s Managing Director, Mr Andrew Woskett, said.

He said the process is specifically designed to treat oxide gold occurrences, as distinct from sulphide (or ‘primary’) gold systems.

Successful demonstration of the process at the field scale could open up the potential for any similar oxide gold deposits to be brought into production at low capital and operating costs, compared to traditional mining and processing methods.

The process involves installation of a conventional groundwater recovery bore field and injection of an appropriate solution (“lixiviant”) into the host rock. The lixiviant dissolves the gold in the rock and the gold in solution travels through the rock mass to be recovered, to surface, via nearby extraction wells, as ‘pregnant’ solution.

This differs markedly from conventional heap leach gold operations which require the ore to be mined, crushed and stockpiled on surface (as ‘heaps’) prior to irrigation with a cyanide solution.

The CSIRO has developed a non-cyanide solution that, when injected into the host rock, is expected to cause minimal alteration to groundwater chemistry. The field trials will focus on determining key objectives: the transmission characteristics of the lixiviant through the host orebody; groundwater modification; gold recovery rates and; economic feasibility of the in-situ gold recovery process.

A range of environmentally acceptable lixiviants has been trialled in the laboratory by CSIRO, with promising results. Groundwater at the Tunkillia test site is restricted in distribution, is highly saline and is not fit for human or stock consumption. The tests are expected to demonstrate no material detrimental impact on the quality of the groundwater.

Significantly, the process negates the need for traditional reliance on cyanide in solution to liberate gold from ore, thereby minimising hazardous material consumption and potential site contamination.

It obviates the need for pre-stripping, drill and blast, open-cut mining, crushing and grinding circuits, cyanide leach systems, waste dumps and tailings dams.

Mr Woskett said the process is not dissimilar to the in-situ extraction methods successfully employed for over a decade by the uranium sector – a process, until now, not able to be applied to gold as a non-cyanide based solvent had not been previously identified.

“Successful results from the lixiviant leach trials are expected to show that operating and capital investment costs are substantially lower, and implementation timelines much shorter, than for conventional gold mining and processing installations,” Mr Woskett said.

“The in-situ recovery process could potentially make many low grade oxide gold deposits economic to extract.”