MIM production accent shifts to underground operations

Staff Reporter

At December’s official opening of the $153 million Newlands underground mine, an upbeat prediction from Nick Stump, chief executive of mine operator MIM Holdings Ltd, put future output from the Newlands complex at 7 million tonnes per annum.

This is a far cry from current production levels of about 4.5mt and would boost total production from the Newlands-Collinsville-Abbot Point operations (NCA) owned by MIM (75%) and Itochu Coal Resources of Australia Pty Ltd (25%), to 16mtpa. It signals the start of a significant shift in the balance of MIM’s coal exports from open pit to underground sourcing, and further reinforces the company’s confidence in its revitalised coal business.

With the Oaky North longwall commencing operation last month and much improved performances from Oaky Creek No.1 and the Alliance longwall in 1998, MIM is on track to surpass 12mt of underground coal production this year. Workforce reductions and the increased production levels have put the company in a position to become one of Australia’s lowest-cost coal exporters.

However, first it must prove that significant improvements in its operating performance can be sustained. With a lot of focus now on underground mines, operating risks have increased. This is something that has already been demonstrated at Newlands.

An existing opencut mining site, the new area being mined by longwall has a total resource of 42mt. The area is geologically “disturbed” in that it is characterised by major thrust faults, including a system of monoclines with parallel faulting and folding, and in areas, reverse thrust faulting. Most longwall blocks in Newlands’ mine plan are known to have some faulting — generally not more than about half seam height.

When mining started in block S4 in August last year management believed the block was clear of unmineable faults.

Mike Ryan, NCA’s general manager, said minor faults which had shown up during gateroad development had been anticipated in the 1.8km block, but were thought to be about 0.5m in total displacement. “Surface drilling had not shown up any major faulting within the block,” Ryan said. “We also did a rim survey after developing the block so we were confident that any faulting we’d find in there would be quite small.”

However, by mid-September additional, carefully targeted drilling indicated the block contained an unmineable fault of greater than 8m displacement. Consequently mining ceased after only 271m of retreat.

“We relied heavily on the rim survey result and the evidence we saw in the maingate and tailgate which both indicated the faults would be small,” Ryan said. “The surface drilling which was really quite intense had missed the almost vertical fault, which pretty much ran parallel to the monocline. With the benefit of hindsight I suppose we could have used a 3D seismic survey a couple of years ago. And in fact that’s what we’re doing with the northern blocks where we’re about 70% complete with a major 3D seismic survey.”

Although S3 roadway development had already been completed by mid-September, conveyors and services had not been installed as the changeover had been planned for June 1999. Consequently, it was not until early December that the longwall recommenced.

Ryan told Australia’s Longwalls that as crews were still in “learning mode”, progress on block S3 since mining began late last year had been relatively slow. A minor thrust fault of about 1.5m was successfully negotiated, however, it delayed production somewhat. At press time the mine was operating at full capacity of about 19,000t per day — about the expected throughput for this stage of development.

The extraction height limit on the longwall equipment is 4.35m and coal is cut at this height in unfaulted sections. Where faulting occurs extraction heights can drop below the 4m mark.

Apart from the mine’s geological challenges, management has been waging something of a running battle with new sensitive equipment which has caused major problems with the communication and electrical control systems on the longwall face and the conveyors. Additionally, problems with conveyor belt tensioning devices have caused substantial downtime. Ryan said debugging of the system was ongoing.

Problems aside, Newlands has a lot to be proud of. Development has been a feature of the mine and for the half year to December 1998 development crews achieved an average of 16.2m per unit shift, putting development three blocks ahead of the operating panel. In 1998 a single shift achieved a remarkable 83.7m. “To do that everything had to be perfect, although there was 20 minutes of downtime,” Ryan said.

Newlands is one of a new breed of coal mines with an enterprise agreement which eliminates demarcation between miners, and performance appraisals linked to remuneration. Since MIM took control of the mine in August 1997 and employed the previous contractor’s workforce under new terms and conditions, there have been no industrial disputes. Ryan spoke of a harmonious workforce characterised by high levels of communication and interaction between management and the workforce. What partly underpins such openness is the fact that as a steaming coal mine Newlands has to be cost-driven and losing precious production time on industrial disputes could easily chew big chunks out of Newlands’ margins.

The mine currently achieves 136 operating hours per week with a total workforce of 150. From March 1 it went to a seven-days-a-week operation. Monday through Friday the day and night shifts each work 10 hours, leaving a four-hour maintenance gap while on Saturday and Sunday production crews work two 12-hour shifts.

Safety performance at Newlands has been extremely good and is managed under NOSA guidelines. In a mine with moderate propensity to spontaneous combustion and methane gas, mine monitoring is an important safety issue and Newlands has in place a sophisticated AMR system with 20 sample points and comprehensive management and response plans developed. The ventilation shaft is 5m in diameter and 220m deep.

Newlands expects to produce 7 mt of product coal this year from a combination of underground and opencut sources and mine management are optimistic about the future.

“The equipment and the people have the capacity to produce excellent results but we have a geologically disturbed area and we are learning quickly how to deal with the disturbed geology,” Ryan said.

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