Boab holds 75% of the Sorby Hills lead-silver project with 25% partner Henan Yuguang.

Under the contract scope GRES will go 50% bigger than previously planned with a 2.25 million tonne per annum processing plant and other infrastructure for the project.

The parties will work toward a commercial agreement and contract award in the lead up to Boab's expected final investment decision on Sorby Hills in the coming months, before moving to ratify the EPC contract.

GRES acting managing director Tony Patrizi said it was exciting to be working on the important regional project.

"We are cognisant of the economic and social benefits the project will deliver to Kununurra and east Kimberley regions and we are eager to play our part to bring the project to fruition," he said.

"We look forward to working with Simon [Noon] and his team to finalise detailed design of the process plant in the coming months and commencing long lead procurement and construction activities in due course."

Boab Metals managing director and CEO Simon Noon said having GRES on board would complement the project delivery team and add value to the project.

He said the engineering firm won a highly competitive EPC tender process that drew strong submissions from a range of leading engineering firms, with the tendered prices an outstanding result given the inflationary economic environment.