Water may have contributed to a series of roof falls at Crinum

SOJITZ Blue’s Crinum underground coal mine in Queensland is believed to have experienced roof falls while it was in care and maintenance before being sold by the BHP Billiton-Mitsubishi Alliance in 2019.
Water may have contributed to a series of roof falls at Crinum Water may have contributed to a series of roof falls at Crinum Water may have contributed to a series of roof falls at Crinum Water may have contributed to a series of roof falls at Crinum Water may have contributed to a series of roof falls at Crinum

Construction, Forestry, Mining and Energy Union district president Stephen Smyth believes Crinum had geotechnical issues after it went into care and maintenance.

The mine experienced a roof fall late on Tuesday night that took the life of one Mastermyne contract worker and seriously injured another.

Construction, Forestry, Mining and Energy Queensland president Stephen Smyth told Australia's Mining Monthly the mine had a history of problems.

"I believe that the mine did experience some geotechnical issues," he said.

"This area of the mine - as I believe it - had experienced roof falls after it had stopped mining coal. The area was sealed up."

It is understood the two men were carrying out roof support works when the roof fall in the conveyor drift occurred.

Queensland resources minister Scott Stewart said a thorough investigation of the causes of the incident would be carried out by the Queensland Mines Inspectorate.

CFMEU Queensland District vice-president Shane Brunker told the Courier Mail the two men were in a man basket when the mine caved in.

"I'm not 100% sure on what duties they were performing," he reportedly said.

"I've been informed that they were just installing new roof bolts as they were making their way back into the mine, but that hasn't been confirmed yet."

Brunker said union check inspectors were attending the site and would undertake a thorough, independent investigation.

He said that may have damaged layers of rock at the mine.

Crinum North along with Centennial Coal's Springvale colliery in New South Wales were chosen by ACARP for a study on estimating the height of longwall mining-induced fracturing and the height of complete groundwater drainage in 2017.

ACARP said the impact of fracturing on drainage was a contentious issue, with some misconceptions and misunderstandings apparent among practicing engineers and groundwater modellers.

"As the Australian mining industry operates under strict environmental accountability, the ability to reliably predict and manage mining-induced water inflows and aquifer interference is critically important," it said.

"With the introduction of longwall top coal caving in several mines in Australia in recent times, this knowledge gap in estimating the extent of strata fracturing has significantly widened - creating extra demand for rigorous study and the development of more sophisticated and reliable assessment tools.

"We selected Crinum North and Springvale collieries as project sites for the availability of extensive hydrogeological data, comprehensive monitoring data and past studies."

The extent of mining-induced subsurface deformation, fracturing, surface subsidence and aquifer interference is largely controlled by local lithological conditions, mining methods and mine layouts.

ACARP said to effectively assess the impact of mining on groundwater it was imperative to develop methods and tools that - unlike empirically based strata desaturation height-estimation methods - could properly consider all influence factors and accurately predict strata deformation and subsequent fracturing, particularly connective fracturing, in varied hydrogeologic environments.

Brunker said there was water in the rest of the mine and dewatering was progressing in order to restart production by Christmas.

"This is an old working area," he reportedly said.

"This is where the belt road, where the conveyor belt used to bring all the coal out of the mine.

"The pit has been closed for 14 years, and it was flooded with water, so you don't know what that's impacted on the strata."

During the first half of FY2021, Mastermyne successfully re-entered the underground mine workings in conjunction with Queensland Mines Rescue to re-establish ventilation and verify the underground conditions.

The mine remained in care and maintenance awaiting the final investment decision to begin underground production after Sojitz bought it from BMA for $100 million.

"It's well before 2015 when that particular operation shut, so after five or 10 years of dormant position of that underground you don't know what the condition of that place is," Sojitz CEO Cameron Vorias told ABC.

The site comprises the Crinum underground mine, Gregory open cut mine, undeveloped coal resources and on-site infrastructure including a coal handling and preparation plant, maintenance workshops and administration facilities.

Gregory Crinum mine's capacity was 6 million tonnes of hard coking coal per annum when production ceased and it was placed into care and maintenance in 2016.

BMA made the decision to sell the mine after a detailed review that concluded there was potential for another party to realise greater value at the mine.

A team effort by Sojitz personnel from its Gregory, Minerva and Meteor Downs South mines was required to bring the Crinum CHPP back to close to optimum production in 2019.