ERM didn't disclose an acquisition price for CSA, which is headquartered in Western Australia.

CSA is the world's second ranked consulting firm for resource reports, and fifth ranked for reserve reports, produced over the past five years for public-listed mining and exploration companies, according to RSC Mining and Mineral Exploration Services/Opaxe data.

As well as geological services, CSA provides a range of expert technical and management consulting services, and independent corporate advice to mining and exploration companies, and financial and legal groups. It has more than 100 consultants in offices in Australia, Asia, South Africa, Europe, Russia, the Middle East and North America.

ERM generated gross revenues in its FY18 of more than US$900 million (down from a peak this decade of $945 million) and has circa 5000 employees in more than 160 offices worldwide.

The company has completed a string of acquisitions in North America, Europe and Australia since 2010, and has an existing presence in the mining market through its environmental, health, safety, risk and social impact advisory businesses.

Toronto-based OMERS Private Equity bought previous PE owner Charterhouse Capital Partners out of ERM in mid-2015.

"At a time when our clients in the mining sector face major challenges on numerous fronts from investors, customers and broader public sentiment, the acquisition of CSA Global further strengthens ERM's capability to help our mining clients address their most complex challenges whether that be their business strategy, highly technical exploration or operational issues,"ERM CEO Keryn James said in a statement.

Long-time CSA managing director Jeff Elliott said the combination would "enhance what we are each doing in the mining sector".

"It is a very good strategic fit, both culturally and operationally; our mining services are complementary across geographies, clientele and capabilities," he said.