North Narrabri in detail

THE drift and skyline conveyors are being commissioned at Whitehaven Coal’s upcoming North Narrabri longwall operation in the Gunnedah Basin of New South Wales, with first coal on track for February.
North Narrabri in detail North Narrabri in detail North Narrabri in detail North Narrabri in detail North Narrabri in detail

The Narrabri box cut.

Blair Price

Presenting at the recent eighth Annual Longwall Conference, North Narrabri mine manager Matthew Klein said the last of the three 1100m long drifts will be complete in February, when there will be two continuous miners in operation.

Commissioning of the crusher and reclaim equipment is expected this month, while the train load-out is due in November and coal roadway development is to start in December.

Klein also detailed equipment specs, including the longwall equipment to be supplied by Bucyrus, which is capable of being retrofitted for the longwall top coal caving (LTCC) system of mining.

He said the longwall will use Bucyrus’ IMAR-based automation, have two-leg 1378-tonne shields, an EL3000 shearer, and a 3500 tonnes per hour armoured face conveyor.

For development, the project already has its three Joy 12CM series of continuous miners completed and onsite, with Klein saying four roof-bolting and two rib-bolting rigs are installed on each machine.

Klein expects the roadway conditions to be quite good and said the Hoskinsons Seam has strength ranges of 30-35 megapascals.

Seven mains headings will be developed and roadways are expected to be developed at a height of about 3.5m.

The seam has an average thickness of 9m but mining will target the bottom section for low-ash, low-sulfur coal for thermal and pulverised coal injection coal markets.

Klein said the depth of cover will range from 180m to the pit bottom area to around 350m inbye of the mains, while the deepest area of the future mine is expected to have a depth of cover of some 400m.

The mine plan is quite simple, with the longwall blocks to be 300m wide.

The first longwall block will be 2000m long, while panels 9 to 23 will be 4000m long, with Klein expecting more than 6 million tonnes in those blocks at the extraction height of 4.2m.

On using LTCC, Klein said the seam could potentially be fully or about 90% extracted using those techniques, but it would require a major upgrade from the proposed wash plant.

He added it would be necessary to gain some mining experience and an understanding of how the goaf behaved to see if it was conducive to LTCC mining.

Two roadheaders are in use for the drifts, while two jumbos are being used to blast the drifts through a sill.

For the ventilation shaft and associated gear, the mine will have a 200m deep, 5m internal diameter lined shaft using main fans capable of 450 cubic metres per second, and powered by an 11-kilovolt substation and switchgear.

An AirLiquide nitrogen inertisation plant will help address spontaneous combustion risks.

Over the mining lease, a seam gas content ranging from 5.0-8.5cu.m per tonne has been identified, with the gas estimated to be 90% carbon dioxide and calculated to have an outburst threshold of 6cu.m/t.

Klein said the majority of lease would require pre-drainage just for outburst management alone.

The mine will have a ventilation circuit of up to 450cu.m per second capacity and rear of longwall block exhaust shafts.

For pre-drainage, Narrabri will have a surface-to-inseam program of the pit bottom, and SIS drilling is currently underway for Tailgate 1 and Maingate 1.

Conventional inseam cross-block drilling will also be used to pre-drain the longwall blocks.

For post-drainage, goaf drainage holes of 0.3m diameter with 200m spacing are planned.

On the surface, Klein said Whitehaven owns all but three properties over the lease and negotiations have advanced on two, while the third property covers an area that will be developed much later in the mine’s life.

The first longwall is planned to start in February 2011 with a production target of 6 million tonnes per annum of saleable product, while Klein said the marketable reserves were more than 100Mt for Narrabri North.

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