Wednesday, December 6, 2023

Confusion over Phikwe tremors

By Bonnie Modiakgotla

The earth tremors experienced in Selebi Phikwe have caused the Botswana government a great deal of anxiety, and have largely been blamed on the flooding of some BCL mine shafts.

“Based on the timing of the reports of the tremors, it is my ministry’s view that the flooding of the South East Extension and number one shaft are the major cause of tremors,” said minister of Mineral Resources, Green Technology and Energy, Eric Molale, when addressing parliament on Friday.

Molale’s findings are premised on anecdotal evidence, and are yet to confirmed by a complete scientific research. “Our reasoning is that in the period that the shafts were regularly dewatered, we did not receive any reports of tremors, neither did we experience any tremors,” he said.

A week earlier, Molale told parliament that he cannot authoritatively conclude that the tremors are caused by the flooding of shafts, and disclosed that he is still awaiting a professional report from the Botswana Geoscience Institute who are onsite to determine the cause of the tremors.

In the latest revelation, the minister said expert opinion points to the possibility that water from the flooding of shafts has seeped through rock joints – and as it percolates through the rocks, it increases pressure from, resulting in dislodgement of rocks which fall in the void.

“The dislodging and falling of rocks release energy that turns into movement. If the amount of energy is too high, it may transfer into the surface in the form of tremors and central seismicity,” said Molale.   

The phenomena of seismicity are generally associated with closed deep underground mines similar to BCL mine, said the minister, also adding that it usually occurs when the water is accumulated in the void created by the large removal of masses of rock which manifest in stresses and strains on the mine shafts.

“The preliminary assessment conducted by the Department of Mines and Botswana Geoscience Institute concluded that further scientific investigations and monitoring are required to establish causes, location, magnitude, intensity, frequency and risk arising out of these tremors,” the minister said.

Based on the findings, Molale’s ministry engaged Open House Management Solutions, a consulting company to conduct a scoping study of the tremor incidences. The purpose of the study was to familiarize the consultant with the area of incident, also to agree on the term of reference and prepare a detailed investigation going forward, explained the minister.

“The broad study should assist us to assess the potential hazard of the seismic activity to people, property and even the mining infrastructure itself,” he said.

“As mitigation against these tremors, it is my ministry’s intention, the legal process permitting, to start pumping water out of those shafts as soon as possible.”

According to Molale, the dewatering process will be monitored by the geo-technical expert to determine the impact on the tremors, with the hopes that it will lead to reduction of the earthly movement in Selebi Phikwe. In addition, the Botswana Geoscience Institute and Department of Mines will remain onsite to assess the “evolving public safety issues and advise accordingly in areas where cracking of houses has been recorded”.

The disclosure by the minister regarding the tremors in on the backdrop of strained relations between him and the court appointed BCL liquidator, Nigel Dixon-Warren, who is accused of flooding some shafts despite direct instructions not to do so.

“We had said that flooding of the shaft will actually compromise the quality of the asset. It wasn’t more about the envisaged earthquake but now we have this collateral damage and it has caused us a lot more anxiety,” said Molale.

Dixon-Warren has strongly rejected the claims, insisting that he is not damaging the mine, nor decreasing its value and the decision to flood certain areas of the mine was done in consultation with experts ÔÇô who all supported the decision. The areas that are currently being flooded are the number one and the South East Extension (SEE) Shafts.

“The Board of BCL itself declared that the SEE was to be abandoned and as at date of liquidation, and had flooded to 1540mL following the fatal accident. Both 1 Shaft and SEE had limited life of mine left and were of poor grades. SEE is a very difficult and costly area to mine, due to the depth and distance from surface,” Dixon-Warren said in an emailed statement to Sunday Standard.

The liquidator said he took the decision to dewater SEE to carry out an assessment of all mining areas to determine which ones are potentially viable and those that are not going to be mined again. Following the assessment, a decision to abandon and flood shaft one up to 450mL and SEE up to 1000mL.

“This decision took in to account the economics, mining and engineering issues, costs of keeping these areas open and environmental issues. Experts in all of these areas were consulted before the decision was taken,” said Dixon-Warren.

He confirmed that Molale had requested he reverse the dewatering of SEE, and he advised the minister that funding to do that will be required, and based on advice provided to the liquidator, there was no prudent rationale to do so. Dixon-Warren also revealed that he has not been provided with additional funding by Government since September 2017 to fund the care and maintenance of the mines, quipping that he has limited funds available.

“It can be argued that by reducing the costs of dewatering unviable areas of the mines, the value of the mines themselves has improved given the cost of care and maintenance has been reduced,” he said.

Responding to allegations that flooding of shafts might be the cause of tremors, the former KPMG partner said there is no evidence yet that links the flooding of parts of the mine to the tremors, and added that there is some evidence that tremors began before the flooding commenced.

“I will not speculate as to the cause of the tremors except to say that underground mines can cause seismic and acoustic activities when underground rock moves or settles due to mother nature,” he explained. “This is a common occurrence with underground mines around the world ÔÇô often old mining areas collapse naturally, and this can cause some noise or movements.  We are not aware of any safety issues at the mines as a result of these events.”

Dixon-Warren disclosed that proper monitoring equipment will be installed at the mines and around Selebi Phikwe so that scientific data can be collected and assessed, with the report coming out two weeks after the conclusion of the field work.

“Only when the scientific data has been gathered will we be able to make an assessment as to what is the cause of the tremors.”


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