GBF has worked at Silver Lake's Mount Monger operations in Western Australia's Goldfields since 2014, providing mining services to the Daisy Complex, Cock-eyed Bob and Maxwells mines.
It is expected the work will be extended for a further three years from March 1, while GBF will also develop Silver Lake's new Santa mine.
Silver Lake and GBF will now negotiate the formal mining services agreement, with finalisation expected in March.
Macmahon CEO and managing director Michael Finnegan said the company was pleased to receive the letter of intent.
"The new work is an important milestone in our strategy to further expand in the underground market, and demonstrates the value in our GBF acquisition," he said.
"We are looking forward to working closely with Silver Lake on this project and building on our relationship with this key client."
Macmahon acquired GBF for $48 million last year.
Shares in Macmahon closed at 29c yesterday, valuing the company at $2.15 billion.