The first undercut blast was ahead of schedule and marks the first step to starting production.

The Grasberg Block Cave underground mine officially began its production phase September 12 with the successful initiation of the first undercut blast.

The blast was in one of three undercut areas required to start the ramp up in production. Blasting of the other two areas will begin in the coming months.

“This is our first step to a producing mine and comes after a tremendous effort by the GBC team to build the world’s biggest underground bock cave mine,” said Mick Garbellini, Senior Manager-Grasberg Block Cave.



Initiated two weeks ahead of schedule, the first undercut blast is a major milestone for a project that began in September 2004 with the development of the tunnels that accessed the Grasberg ore body.

The undercut level sits above the extraction and haulage levels and is used to fracture the ore that will be drawn down through draw bells on the extraction level below.

“The fracturing of the ore on the undercut levels begins a caving sequence that allows gravity and ground pressures to continuously feed the ore onto the extraction level,” said Brian Clark, PTFI’s Executive Vice President-Operations. “The early startup of our ore-handling systems and the blasting of the undercut on schedule will help ensure a successful, productive startup of the GBC Mine."

While ore is not expected to be drawn through the draw points until January 1, 2019, the preconditioning, or fracturing, of the ore is the first step toward production."

“In my view, undercutting is the most important step to starting production, because it’s really critical to get it right,” said Nick Pascoe, Manager-Grasberg Block Cave Engineering. “If you do it well, it allows you to focus on production. If you get it wrong, you potentially can have all sorts of issues down the line.”

Though the undercut and extraction levels of the GBC mine are similar to other PTFI block cave mines, the way ore is moved in the haulage level has gone from road to rail. Rather than haul trucks delivering the ore to a conveyor system that feeds the concentrator, GBC has an electrified train.

All levels and the ore flow system currently are in operation, with continued commission efforts underway. 

At full production, the GBC mine will yield between 130,000 and 160,000 tons per day, Clark said.

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