The contracts keep 18 rigs in the field and increase the company's contracted work in hand total to $353 million.

SMS has been at Barrick's gold operations in Nevada since 2013 with a fleet of eight rigs at the Turquoise Ridge and Cortez Hill gold mines and the Goldrush project.

To fulfil the work order under the three-year contract extension SMS will bring in another two rigs at a fixed price for two years, to expand the fleet to 10.

SMS will also deploy more rigs to the Jundee mine in Western Australia after Northern Star increased the scope of work under the existing contract agreement.

The fleet of nine will increase steadily from July to October to 14 full-time underground diamond coring rigs, which will be a record for the company.

At Mount Monger in WA, SMS was selected as the preferred tenderer by Silver Lake to carry out underground diamond coring for a two-year spell.

The company will head to site in August with three rigs to drill at the Daisy Milano, Cock-eyed Bob and Maxwell's underground mines.

SMS managing director Kent Swick said the company was delighted to be deepening its relationships with existing clients and, in the case of the new work with Silver Lake, returning to a project where it had extensive experience.

"It is particularly pleasing that our international strategy is yielding significant results, with a third of our total deployed underground diamond drilling rigs now operating outside of Australia," he said.

"By the end of September, we will have at least 22 rigs operating in our international operations including the US, Portugal and Spain, all at major mines with tier one clients."