Rio Tinto’s copper leaching technology venture, Nuton, has invested $25-million in McEwen Copper, which is advancing a copper project in Argentina.

The investment forms part of the third and final tranche of a previously announced placement offering, in which the McEwen mining subsidiary raised $81.85-million.

The third tranche also included $1.85-million from other investors.

Nuton acquired 2.5-million common shares at $10.00 each, for post-closing ownership of 9.73%.

McEwen Copper also entered into a collaboration agreement with Nuton to advance its understanding of the potential application of heap leach technology its Los Azules project.

Leaching has many potential economic and environmental benefits over a conventional milling scenario, including lower water and energy consumption, no large tailings storage facility or dam, and typically lower capital and operating costs.

“Los Azules is among the largest undeveloped copper assets in the world. We recognise the potential opportunity of using Nuton Technologies to produce copper in greater amounts, more rapidly, and with less impact on the environment and water resources,” said McEwen Copper CEO Rob McEwen.

Rio Tinto CEO of Copper Bold Baatar added that the agreement would allow the group to evaluate the potential to commercially deploy its innovative Nuton Technologies for copper leaching in the planned development of Los Azules.

“Our Nuton Technologies have the capacity to unlock increased copper production for Rio Tinto and our partners, with a low carbon footprint and leading environmental performance.”

McEwen Copper and Nuton would undertake copper leach testing using Nuton Technologies with samples from Los Azules.

McEwen Copper granted exclusivity to Nuton for one year in the area of novel, patented or trade secret leaching technology, while it will continue its independent test work and studies using conventional leach technologies.

Nuton will have the right to select one nominee who will be appointed as a director or observer to the board of McEwen Copper. This right will continue for as long as Nuton holds greater than 7.5% of the issued and outstanding shares of McEwen Copper.

The agreement also dictates that McEwen Copper and its controlling shareholders will not complete a liquidity event, such as the planned initial public offering (IPO), until after March 31, 2023.

McEwen Copper has agreed to limit related party transactions in certain situations until the earlier of the planned IPO (or alternative liquidity event) or Nuton ceasing to hold 7.5%.

Los Azules has an estimated copper resource of 10.2-billion pounds at a grade of 0.48% copper in the indicated category, and an additional 19.3-billion pounds at a grade of 0.33% copper in the inferred category.