Gold and uranium deposits in the Witwatersrand Basin are hosted by quartz-pebble conglomerates, which are generally less than 2 m in thickness and developed on laterally continuous unconformity surfaces. These reefs are generally characterised by shallow dips of between 10° to 25° and thicknesses of 1.0 m to 2.5 m that make them suitable for exploitation by means of typical narrow stoping techniques.

The gold deposits of the Witwatersrand Basin are considered to be associated with coalesced fluvial braidplains, where gold was concentrated within braided stream gravels developed on unconformities which have been correlated around the basin.

Most early theories on the origin of gold believed the gold to be deposited syngenetically (placer theory) with the conglomerates or by epigenetic means (hydrothermal origin), but subsequent research by Kirk et al (2004) concluded that metamorphism caused the post depositional local redistribution of gold (modified placer theory).

Generally, gold occurs in native form often associated with pyrite (less commonly pyrrhotite) and carbon, with quartz as the main gangue mineral.

At Blyvoor, two economic placer horizons have been exploited. These are namely the Carbon Leader and Middelvlei Reefs and occur in quartzites of the Main Reef Conglomerate Formation of the Johannesburg Subgroup of the Central Rand Group. The auriferous conglomerates dip uniformly at 22°S.

The Carbon Leader is a high grade, predominantly thin (<40 cm) carbon-rich reef and is the principle economic horizon at Blyvoor. The origin of the carbon is in debate as to whether it originated hydrothermally or from algae. Within the deeper southern section of the Mine, carbon is scarcer and hence likely responsible for the decline in grade.

In the western area, the Carbon Leader is eliminated by a northwest-southeast striking, 1,900 m wide erosional channel. The erosion channel is truncated to the north by the Master Bedding Fault. Its eastern boundary is well defined by mining, while the western boundary is less certain and has only been defined by drilling.

The Carbon Leader is divided into seven facies areas, namely F1 to F7, based on channel width and carbon content. Four types of Carbon Leader are recognised:-
• carbon seam;
• channel reef;
• thin single reef; and
• thick single reef.

Grade generally decreases down dip (south) and towards the west associated with a reduction in carbon.

The Middelvlei Reef is the second economic horizon at Blyvoor and lies stratigraphically 50 m to 75 m above the Carbon Leader. Towards the south, the separation increases due to a minor angular unconformity. The Middelvlei Reef is characterised by lower grades than the Carbon Leader. Owing to the variable payability and presence of sedimentologically controlled pay shoots, the Middelvlei Reef has been mined in scattered payable areas and is present over the whole lease area.

On the Middelvlei Reef, facies areas have similarly been identified using grade, channel direction and reef characteristics.

The mining strategy for the Blyvoor Mine is to extract both the Carbon Leader Reef and Middelvlei Reef utilising the No. 5 Shaft Complex via conventional ledging and opening up to the required stoping width of 160 cm for Selective Blast Mining (SBM). The first month of production on each panel will consist of conventional ledging (approximately 8 m linear advance) and conventional opening-up from a 117 cm stoping width to the planned SBM stoping width of 160 cm.

It is expected that a 2 m linear face advance will be required to open-up the stoping width from 117 cm to 160 cm (43 cm). The conversion to SBM stoping will require an additional 4 m linear face advance using conventional stoping, to create sufficient volume in the back area for waste packing once SBM commences. It has been estimated that 50% of the waste within the 4 m advance will be packed, and the remaining 50% will contribute to dilution.

There after SBM stoping will be implemented. Some of the targeted workings cannot currently be accessed and opening-up with re-equipping will be required prior to mining.

Planned mining will initially take place between 15 Level and 27 Level. A ramp up of 17 months has been planned to reach steady state production of approximately 20,000 m², which equates to approximately 40 ktpm. This production rate will be sustained for a period of 15 months followed by a second ramp up. The second ramp up to a steady state production rate of approximately 40,000 m², which will produce approximately 80 ktpm, has been planned over a 12-month period.

The production rate was determined by Blyvoor Gold and is a realistically achievable rate considering the current infrastructure. The initial production rate is limited by the capacity of cage hoisting and the requirement to install a mid-shaft loading station.

Opening-up and re-equipping has advanced sufficiently for development and early stoping to commence on 15 and 27 Levels. The aim is to produce at the initially planned production rate of 20,000 m², from these levels, allowing ample time for opening-up and re-equipping on other levels which are required to sustain the planned 40,000 m² per month. The No. 5A Sub-vertical shaft is currently flooded up to 10 m above 29 Level. Dewatering as well as opening-up and re-equipping will be required, prior to the commencement of production on and below 29 Level.

The shaft pillars have been included in the updated Mineral Resources and Mineral Reserve estimation. Mining of the shaft pillar areas will be subject to a geotechnical study and specific rock engineering recommendations for mining the shaft pillars.

The current mining infrastructure, namely the existing main surface shaft (No. 5 Shaft), underground subshafts (No. 5A Sub-vertical Shaft and No. 1A Sub-vertical Shaft and orepass system, existing footwall drives and crosscuts will be utilised as access to the workings. All the existing excavations required to access the underground workings (stopes and development ends) have been, or will be, refurbished as necessary to provide safe access for men and material.

Men and material will be transported via No. 5 Shaft and No. 5A Sub-vertical Shaft. Ore will be transferred via the orepass system located at No. 1A Sub-vertical Shaft down to 27 Level and cross-trammed to No. 5A Sub-vertical Shaft. Initially ore will be hoisted to 15 Level via cage hoisting, where the ore is then crosstrammed to No. 5 Shaft and hoisted to surface. Once the No. 5A Sub-vertical shaft rock winder and 27.5 Level mid-shaft loading station has been commissioned, the No. 5A Sub-vertical Shaft orepass system will be utilised from where the ore is hoisted to 14 Level and then transferred to No. 5 Shaft loading station by way of an existing conveyor installation and hoisted to surface.

SBM (Selective Blast Mining) makes use of milli-second sequential blasting technology to separate the valuable reef material from waste rock in the blasting operation at the stope faces in the mining of tabular ore bodies. In resue mining or SBM, the waste rock is thrust blasted by creating a 'secondary footwall' above or below the reef and advancing the blast in the waste region by one meter per blast. The reef above the true footwall or below the hanging wall is then lifted or dropped and collected. The ore is shattered but not displaced and only the reef material is transported to the surface. The principle of this mining method is stowing or packing of waste material in the mined-out area behind the advancing stope face.

The mining method that will be employed at the No. 5 Shaft Complex will consist of a month of conventional ledging (approximately 8 m linear advance) and conventional opening-up from a 117 cm stoping width to the planned SBM stoping width of 160 cm.

It is expected that a 2 m linear face advance will be required to open-up the stoping width from 117 cm to 160 cm (43 cm). The conversion to SBM stoping will require an additional 4 m linear face advance using conventional stoping, to create sufficient volume in the back area for waste packing once SBM commences. It has been estimated that 50% of the waste within the 4 m advance will be packed, and the remaining 50% will contribute to dilution.

Conventional mining is a mining method whereby the drilling is conducted by means of handheld hydropower drills. The cleaning of the stopes is conducted by face, strike gully and centre gully scraping into orepasses that are connected to the underlying crosscut.

The first activity is to support the area, followed by drilling, blasting and finally cleaning. The support of the area is required to ensure safe working conditions. The support of the face includes the installation of roof bolts, the installation of mine poles with jack pots and the placement of timber packs. The drilling of the face is conducted by handheld hydropower rock drills. After drilling the holes are charged with explosives and blasted at the end of the shift. Cleaning of the blasted face is conducted with face scrapers scraping into the gully. The gully is cleaned by scraping the ore towards the raise, into an orepass. The orepass is connected to a crosscut from where the ore is loaded into hoppers. The battery powered loco trams the material towards the loading station located at the shaft.

A single panel layout will be utilised. Each crew is anticipated to achieve an overall face advance of 16 m/month and 14 m/month for conventional and SBM stoping, respectively. Drilling and blasting activities will be conducted on dayshift with nightshift performing cleaning activities.

RoM will be conveyed from the shaft into the plant feed silo or added with a front-end loader (“FEL”) via a static grizzly into the primary jaw crusher. A heavy-duty apron feeder extracts material from the silo and discharges it into a jaw crusher. The jaw crusher product is conveyed to the secondary screen which returns the oversize to the cone crusherand discharges the undersize onto the product conveyor running to the crushed ore silo’s. The cone crusher product is also discharged onto the secondary screen feed conveyor.

The crushing circuit throughput is enough to accommodate higher ore throughput, it only needs to run for longer. The hours of operation need to be increased from 12 to 18 hours per day, and the circuit should run 7 days per week instead of 5. A second RoM bin will be be added to enable a larger buffer between the crushing plant and the ore hoisting operations.

Crushed ore can be discharged into either one of the two crushed ore silos. Each silo is however dedicated to one mill via an apron feeder and conveyor belt. The mills have a trommel discharge that removes scats and wood chips. The two mills discharge into a common sump from where the slurry is pumped to either a cyclone cluster or a Falcon Screen. The cyclone cluster returns the oversize material to the mills while the Falcon screen protects the gravity concentrator from blockage by larger material. The Falcon concentrator’s tails are returned to the mill sump while the concentrate flows straight into the gold room for further processing. The cyclone overflow is first passed over a linear trash screen before being sent to the conditioning tank.

The two 900 kW mills that are currently installed have a specified throughput of 32.5 tph, and a third 14’ x 21’ mill will be added to increase the milling throughput to the required 128 tph. This mill will be fed with a new apron feeder and conveyor system. The new sump pumps will pump to an existing cyclone and another new pump will discharge onto an existing Falcon screen. The underflow from the screen will feed the existing Falcon concentrator.

The plant was designed with a total RoM feed capacity of 40 ktpm and an expansion to 80 ktpm is planned. The upgraded plant will follow the same process flow as the existing plant with some of the circuits only being expanded. The flowsheet does also accommodate the addition of surface stockpiles directly into the crushing circuit or sluicing of fine material into the classification circuit. The addition of these sources is however not planned, but they remain available in case of emergency and are useful during the start-up and commissioning phase.

The recovery method is the most widely used for processing hard rock ore that does not have significant preg-robbers. The circuit is the same as the old plants that treated this ore, and the recovery performance is expected to be similar.

Construction of the plant was recently completed, and the plant is currently being ramped up to full capacity of 40 ktpm.

Ore slurry from the milling section is added to a ........