A Mine's fastest way out of the (re)starting blocks

Published: 01 May 2017 | SA Mining

Flickers of rising demand in some commodity markets are good news for mines under care-and-maintenance, raising hopes for a return to production.

However, the start-up process is complex and demands meticulous planning, according to global engineers and scientists at SRK Consulting.

"Potentially time-consuming legal compliance issues include environmental permissions and labour regulations," says SRK principal mining engineer Joseph Mainama, "but equally important are risk factors relating to legal agreements, safety and health, stakeholder expectations, infrastructure and water management."

The environmental and social impacts of mining are growing in importance, and the related regulations are becoming steadily tighter, states SRK environmental consultant and closure specialist James Lake.

"It is no longer acceptable, for instance, to place an operation onto care-and­-maintenance indefinitely. Projects on a care-and-maintenance programme  need to  be updated and annually reportedon; permission to remain so lapses after five years, although there is an option for renewal," explains Lake.

He recommends that- as per legislative requirements - an environmental audit be conducted to determine the risk factors and their impacts beforehand, allowing time limitations to be reviewed on authorisations such as water use licences.

"Environmental reporting is also vital to remain compliant with the legal requirements that the mine commits to in  its environmental management plan, water use licence and record of decisions. Without these, the start-up of production could be delayed."

COMMUNITIES AND STAFF

The socio-economic impact of a mine closure - even temporarily - is potentially devastating for the wellbeing of the local community. Forward planning, and leveraging the company's social and labour plan (SLP) and corporate social investment programmes, could help to sustain economic activity around the mine, to retain the scarceskills that would be needed when production resumes.

"Carefully managing the social impact issues allows a mine to hold on to the reputational capital it has built up over years of engagement with its communities and employees," says Lake.

This links to human resources issues, where legal compliance is a key factor.

"Putting a mine under care-and­-maintenance usually results in people being laid off, and procedures have to be followed in terms of Section 189 of the Labour Relations Act;' explains Allan Labrum, legal advisor at SRK. "Staffing requirements to manage the site during care-and­maintenance should also be planned with the eventual start-up in  mind."

AGREEMENTS  AND CONTRACTS

A range of other contracts will have to be addressed, including those with service providers and suppliers, as well as off-take agreements with customers, adds Labrum.

"The mine's contracts may contain provision for suspension of services, although there may be limits to the duration  of such suspension. Termination of contracts might be considered, but, once again, the implications need to be carefully weighed if this could lead to delays in re-engaging these services at a later stage; the mine may have to embark on new tender processes for the services required."

He notes that force majeure provisions - which could exempt both parties from liability or obligation - would not apply if the mine's decisions were driven by a decline in commodity prices.

MINE PLANS AND MINING

In terms of mining and surveying, mine-to-sales tonnage and mineral reconciliations should be conducted, and the final face positions surveyed, notes Mainama.

"It is imperative that the mine plans are updated with the latest information," he says.

Before mining can resume in an underground operation, though, rock-mass failure could be addressed by installing renewed support, in line with the mine's geotechnical  engineering standards.

''Collapsed excavations underground could result in remedial support operations that can hamper production start-up," asserts Shaun Murphy, principal rockare growing in importance, and the related engineering consultant at SRK. ''It is worth remembering that this time-dependent rock­ mass failure continues during the care-and­-maintenance period, as there is no ongoing rectification of hazardous situations, as is the case during normal mining operations. Before start-up, the installed support has to be supplemented to help control this deterioration."

For deep-level mines, which are associated with the incidence of seismicity, monitoring should continue during the care­ and-maintenance phase, highlights Murphy. For open-pit operations, slope monitoring and inspections should also continue to assess the stability of the slopes duringroutine maintenance of in-pit infrastructure such as pumps, crushers, conveyors and switchgear.

''Further, site-specific risk assessments should consider how geotechnical conditions - geology, weathering, groundwater and rock-mass conditions - will change when the pit is placed on care-and-maintenance, and what the resulting change in the pit stability or risk level will be," he states.

INFRASTRUCTURE

On the engineering side, a number of aspects need to be considered when putting an underground mine onto care-and­-maintenance in a way that allows relatively quick start-up, adds SRK principal mechanical engineer Chris Smythe.

"Winders must be kept in working condition, which means keeping up with statutory maintenance and examination provisions," notes Smythe. ''In generaI, monthly and annual examinations will have to be carried out as normal, but exemption may be obtained to extend daily examinations to weekly, and weekly to monthly."

He warns that winder ropes should not be removed, as this would prevent shaftexaminations from taking place. Shafts should be maintained in operation for dewatering purposes and for access for essential maintenance.

"Shafts can only be abandoned if it is certain that they will no longer be required;' he explains. However, the relicensing of abandoned  shafts is difficult, time-consuming and costly."

Smythe emphasises the need to keep the mine and installed infrastructure dry, with underground pumping equipment properly maintained to protect fixed equipment from deterioration; fixed equipment should be started up or rotated manually as appropriate.

Closed mines on the Reef have been devastated by the incursion of "zama zamas'' - illegal miners - and the theft of equipment, heightening the importance of security and access control; without an effective strategy to safeguard instalied infrastructure, start-up would be severely delayed by first having to restore equipment and facilities.

VENTILATION, HEALTH AND SAFETY

Ensuring a safe environment in underground mines that are to be placed on care-and­ maintenance requires a systematic approach to closing down the ventilation, contends Jacques van Eyssen, associate ventilation and occupational hygiene consultant to SRK. He recommends a pre-closure risk assessment,in which the establishment of procedures must comply with the Mine Health and Safety Act (Act No 29 of 1996); this includes a record of airflow quantities, and the monitoring of underground gases and temperatures, as well asthe position of auxiliary fans, ventilation columns, valves, refuge bays, doors, regulators and other equipment.

"A schematic layout should be compiled, indicating the airflow requirements and critical ventilation equipment needed to be operational during the care-and-maintenance period," says Van Eyssen. ''The critical tasks to prepare the shaft for this programme should be defined, and the procedures have to be approved and signed off by the Department of Mineral Resources (DMR)."

He notes that it is likely that most of the auxiliary fans will not be operational if the mine remains closed for longer than a couple of years, so these should be stopped and reclaimed. Temporary seals should be installed as close as possible to the shaft station areas.

"The underground environment of the shaft area should be monitored, and reports -  including safety reports- submitted to the DMR at required intervals. Fridge plants, bulk air coolers and other related equipment should be maintained duringcare-and­ maintenance, and all reclaimed fans must be refurbished and stored under roof to ensure availability for start-up."

The areas identified for production after care-and-maintenance have to be examined and declared safe before employees can enter the mine, he adds.

WATER

The management of water on mines is also a key aspect duringthe care-and-maintenance phase, as the aim is to avoid flooding and equipment damage, as well as to prevent pollution of water should it reach the pit or underground workings.

''Reduced water use on surface means that higher amounts of water pumped from underground may need to be treated or reused elsewhere;' explains Peter Shepherd, partner and principal hydrologist at SRK.

Shepherd states that the water in a closed mine's pollution control dam would  need to be treated before it could be discharged from the site; so, an extensive clean-up of the site after the care-and-maintenance phase may be necessary to ensure that the runoff is relatively clean.

''Polluted areas such as wash-bays and workshops should also be isolated from the remainder of the site, so that the clean run­ off is not unnecessarily polluted," he says.

METALLURGY  AND PROCESS

The process plant on a mine site is a significant capital investment, so it warrants careful attention and monitoring to ensure it can be successfully recommissioned after a period on care-and-maintenance.

''The first step is clearly to shut down the plant in an orderly fashion - stopping the feed to front-end unit processes, and then steadily emptying and stopping downstream unit processes," notes minerals processing consultant Vic Hills. "Emptying and cleaning procedures can then follow, depending on the nature of the process material."

To facilitate quick start-up, mechanical and electrical equipment should be prepared for non-operation in terms of its manufacturers' specifications, while the condition of lubricants left in the equipment should be monitored. Vessels and equipment processing toxic or corrosive material would have to be emptied and decontaminatedin terms of safety and health codes of practice.

"It is likely that large rotating equipment such as mills and longkilns will have to be regularly rotated to avoid mechanical deformation or bearing damage," says Hills.

TAILINGS

A tailings storage facility (TSF) presents a potential risk to the environment longafter tailings deposition has ceased.

''Under care-and-maintenance, the physical and geochemical risks need to be monitored and managed," says SRK principal and partner Angus Bracken. ''This would include the maintenance of the drainage infrastructure, the top surface freeboard,  and the access and security infrastructure. It would also involve managing the erosion of outer slopes, and the monitoring of the phreatic surface, surface pool, drain flows and geochemistry of ground and surface water in the vicinity of the facility. Particular attention should be given to the condition of a TSF during and after high rainfall events."

REQUIREMENTS, ROLES AND RESPONSIBlLITIES

To tie the whole care-and-maintenance programme together - and to help to expedite restarting production - Mainama recommends compiling a document that reports on all of the requirements of the exercise.

''This document will become useful in future, when there is need to revisit the decisions made earlier. All disciplines involved in the mining operation should codify their requirements, and outline the various roles and responsibilities. Drawing on our range of mining-related expertise, SRK provides key discipline-specific guidelines for a programme that allow the mine to get back into production smoothly and without delay," says Mainama. •

/sites/default/files/File/South-Africa/pressreleases/2017/May_2017/SA_Mining_A_mines_fastest_way_out_of_the_restarting_blocks_01May17.pdf
 

 

 

 


 

SRK Africa