Toronto-based RPA (Roscoe Postle Associates) was acquired by UK-based Scott Wilson Group in 2006, then bought out and reprivatised by management in 2011.

SLR's move on RPA follows ERM's acquisition of Australia-based CSA Global in July this year.

RPA has about 60 staff, including geological, mining and metallurgical consultants, and offices in Toronto, Denver and London. The company becomes part of SLR's existing mining and minerals arm.

The companies said they'd collaborated on client projects for several years and "together we will now be able to offer our clients in the mining sector a complete service extending from value creation and generation through resource and reserve work to environmental and social risk and liability management".

SLR CEO Neil Penhall said the company's fourth acquisition this year reflected "the confidence both we and our new investors, Charterhouse Capital Partners, have in the market and the opportunities to provide world-class environmental solutions and advice to our clients".