South Africa Region
South Deep is designed to access and exploit one of the largest gold ore bodies in the world. Its rebasing process has a strong operational process to deliver ramp-up, sustained steady state production and targeted cash-flow.
- Dividing the ore body into a series of mining blocks, to allow the operation to be suitably focused (Current Mine, NoW, SoW W and SoW E)
- Conducting geotechnical modelling to determine layouts of increased stability and lower seismic risk. These changes include – change from low-profile destress to high-profile destress, changes to the destress pillar layout to larger rectangular yielding pillars and migrating from primary and secondary stoping to sequential stoping
- General improvements in operational efficiencies such as: maintenance, backfilling and drill and blast
- Putting the focus on open stoping as the primary method of increasing production
- Capacity and productivity analysis
- Ore handling facilities and potential bottlenecks
- Compliance to plan and reconciliation
- Risk and mitigation
- Assessment of growth capital infrastructure
- Requirements for ventilation/refrigeration, ore handling, pumping, backfill, electrical and workshop
In February 2017, Gold Fields delivered the revised plan, termed the rebase plan, to the market.
This plan defines the updated Mineral Reserve and LoM plan for South Deep and incorporates all recent revisions and improvements in mine design, production scheduling and geotechnical parameters.
|General location||South Deep Gold Mine is situated in the magisterial districts of Westonaria and Vanderbijlpark (Gauteng province), some 45km south-west of Johannesburg at latitude 26º 25’ south and longitude 27º 40’ east. It is accessed via the N12 provincial road between Johannesburg and Potchefstroom.|
|Licence status and holdings||The conversion of the old order mining right to a new order mining right, as required in terms of the Minerals and Petroleum Resources Development Act, No 28, 2002 (the MPRD Act), was approved in July 2010. The aerial extent of the South Deep lease area is 4,268ha. All required authorisation has been obtained and is in good standing.|
|Operational infrastructure and mineral processing||The workings are accessed from the surface through two shaft systems, the Twin Shaft
Complex (main and ventilation shafts), of which the main shaft comprises a single-drop to a
depth of 2,998m, the vent shaft to 2,947m and the South Shaft Complex, which is a subvertical
system (four shafts) to 95 level at a depth of 2,786m.
The mine is divided into three main areas:
South Deep Gold Mine operates one on-property gold plant. The comminution circuit comprises two stage milling with a free gold recovery circuit. Gold recovery is carried out using a conventional leach/carbon-in-pulp (CIP) circuit. Final product from both the free gold and CIP circuits is smelted into bullion.
|Tailings storage facility||South Deep Gold Mine utilises one tailings storage facility (TSF) known as the Doornpoort TSF. The TSF footprint is designed to accommodate the LoM tonnage excluding backfill. The first phase of the dam was completed in 2011 and the top of the starter wall will be reached by mid-2018. Based on the current plan Phase 2 TSF infrastructure expansion will be required in 2021.|
|Climate||No extreme climate conditions are experienced that may affect mining operations. The regional climate is classified as Cwb (warm temperature; winter dry; warm summer) under Köppen-Geiger climate classification.|
|Deposit type||Intermediate to deep-level gold mine (> 2,000m below surface) exploiting auriferous palaeoplacers (reefs), namely the conglomerates that comprise the Upper Elsburg Reefs of the Mondeor Formation and the Ventersdorp Contact Reef (VCR).|
|LoM||It is estimated that the current Mineral Reserves will be depleted in 2095 (79 years).|
|Environmental, health and safety||South Deep reports its level of compliance in respect of its Social and Labour Plan and Mining Charter commitments on an annual basis. Furthermore, during Q3 2016, a compliance inspection was conducted by the Department of Mineral Resources (DMR) on the title conditions contained in South Deep’s new order mining right. No material issues were noted and South Deep has not received any further formal communications from the DMR. An amendment to the current approved water use licence was submitted during May 2015. Approval is still pending. A consolidated EMP (current EMPs were approved in 2010 and 2012) was submitted for approval during Q4 2016. The mine’s safety and environmental management systems are OHSAS 18001 and ISO 14001 certified. The mine is certified in compliance with the International Cyanide Management Code (ICMC).|
Brief history of South Deep
Commercial production of the Western Areas Gold Mine commenced in September 1951. In 1990, Western Areas Gold Mining Company Limited (WAL) shareholders approved the transfer, cession and assignment of certain land and mineral rights to South Deep Exploration Company Limited in exchange for its shares. WAL and South Deep Exploration Company Limited merged on 1 January 1995. Development of 95 Level across to the planned collar position of Twins commenced.
On 1 April 1999, the Placer Dome/Western Areas (PDWA) joint venture (JV) was formed and in February 2000, the name of the mine was changed to South Deep Gold Mine. Sinking of the ventilation shaft was completed to 95 level in 2001 and the main shaft to 110 level in 2002, concurrently a 7,200tpd capacity mill was commissioned. The Twin Shaft Complex was officially opened on 4 February 2005.
Barrick Gold Corporation acquired a majority interest in Placer Dome Inc. on 20 January 2006 and Gold Fields acquired Barrick’s 50% JV interest in the PDWA JV on 1 December 2006. In April 2007, Gold Fields acquired all remaining WAL shares and consequently owned 100% of South Deep Gold Mine at that time. All conventional mining was stopped in 2008 and commenced low profile mechanised distress.
A new-order mining right was granted to South Deep in 2010, including the area known as Uncle Harry’s. During 2011, Newshelf 899 (Proprietary) Limited (Newshelf) was established, which holds a 100% interest in South Deep gold mine. Newshelf is a 90% subsidiary of GFI and the remaining 10% is held by outside shareholders as part of the Broad-based Black Economic Empowerment (BBBEE) transaction.
The mine converted from low-profile to high-profile mechanised destress in 2015. The corridor span was decreased from 240m to 180m resulting in an increase in the number of mining corridors from four to six.
South Deep presented the rebase plan to the market in February 2017, incorporating the work and recommendations of the Geotechnical Review Board (GRB), together with expert input from specialist consultants on the other key areas of the plan.
Key developments and material issues
South Deep experienced a landmark year during 2016, with improvements recorded in almost every aspect of the mine. Organisational capacity, mine design and planning, production output and mining quality have significantly improved. South Deep developed a rebased production plan, which includes improvements in the full mining value chain together with higher confidence scheduling parameters. The plan reflects improved overall confidence in terms of mine design, scheduling and operational execution and is supported by realistic and risk-adjusted inputs that have been peer reviewed by external consultants and experts. These improvements lay the foundation for a robust production ramp-up phase and solid ~ten-year plan that focuses on maximising delivery from the ore body in the Current Mine and NoW areas, before establishment of SoW.
The capacity and skills to drive continuous business improvement have been embedded at the mine, in conjunction with the necessary management capability, so that the productivity, efficiency and quality drivers needed to realise the ramp-up and steady state production are delivered.
South Deep has a similar risk profile to other deep level operations; however, due to its ore body geometry, its mining methods are unique. As future lessons are learned, it is expected the mining methods will require ongoing optimisation and refinement to ensure that full site potential is achieved. The high-profile destress method was successfully implemented during 2016, with all destress activities conducted utilising this method by quarter three 2016. Further enhancements were also made to this mining method driven by upgraded geotechnical and production efficiency parameters. The revised design includes:
- Twin access to each of the destress cuts, elimination of trucks in the stoping horizon with improved ore-flow design, engineering infrastructure and ventilation flow
- Larger yielding pillars (rib pillars) in the destress area and reduced corridor spans resulted in a ‘stiffer’ support system that reduces convergence and therefore reduces the seismic risk
- The rib pillar design has reduced the requirement for backfill during the destressing phase
- The long-hole stoping sequence will be changed from a primary-secondary extraction strategy to a sequential method to further improve the geotechnical stability and maximise extraction
The mine continued to refurbish and build on its infrastructure platform, including the shaft, ore-handling facilities, backfill, ventilation and refrigeration infrastructure. Significant investment was made in skills development with core training programmes for engineering and mining personnel. In addition, outsourced equipment maintenance was implemented to improve fleet maintenance capacity, while also transferring higher technical skills to the organisation.
Over the past two years energy release rates have reduced, as a result of the improvements made in yield pillar design and the geometry of the destress mining front. The seismicity associated with the advance of the destress cuts is comparable with other deep level mines.
Plan of the South Deep mining area