The construction milestone is part of the critical sequence to first ore and follows BHP announcing 50% of project completion last year.
South Flank project director Richard Gerspacher said the project team had worked extremely hard to get the project to this position.
"Based on the project routines and the culture we've created, I am confident that the project will continue to proceed in a positive manner as we work towards first ore," he said.
When fully operational, South Flank will be one of the largest iron ore processing hubs in the world.
It is being developed as a replacement for BHP's 80Mtpa Yandi iron ore mine.
This project includes an 80 million tonne per annum crushing and screening plant, an overland conveyor system and rail loading facilities.
Fluor is providing the engineering, procurement and construction management services on South Flank.
South Flank engineering and procurement work is being performed from BHP's office in Perth with Fluor working with BHP as an integrated team.
Fluor previously managed the feasibility study for the project before being awarded the follow-on construction and project management scope.
Over the life of the project it is expected more than 9000 people will be engaged in the South Flank work force.
Construction started in July 2018 and first ore production is expected in 2021.
Fluor mining and metals business president Tony Morgan called the integrated team approach on this project "pioneering" and said it was a truly collaborative effort.
"We are extremely proud of what we have been able to accomplish with BHP on this project, including our commitment to achieve diversity through the hiring of indigenous and local team members," he said.