Mining takes place in a structurally complex zone between two major north-south trending faults: the De Bron/Homestead Fault in the west and the Saaiplaas Fault in the east. The orebody has been subjected to severe deformation and contains numerous folds (anticlines and synclines) as well as an abundance of smaller faults. The dip of the reef bands is very variable – from 45 degrees to the east, adjacent to the western side of the lease, to less than two degrees in parts of the southern area.

Production is hosted within two quartz pebble conglomerate bodies, developed above unconformity surfaces, the Basal and the B reefs. Approximately 80% of the centares (1 centare = 1 square metre) are from the Basal Reef horizon and 20% from the Basal B Reef horizon.

The primary facies of Basal Reef intersected at Masimong 5 Mine is the Black Chert facies. It comprises two upward fining cycles. The lower one has a small to medium pebble conglomerate at its base, overlain by a grey ortho-quartzite. The upper unit consists of a pyrite-rich grit. The upper cycle tends to erode large segments of the Lower higher grade cycle in the south-west, with resultant lower values. Towards the east of the shaft, it appears that only the upper unit is present. Carbon is almost always present on the bottom contact of the lower cycle of the black chert facies.

The B3 facies of the B-Reef comprises polymictic medium to large pebble-supported conglomerates, with porphyry clas ........

Masimong is a single-shaft operation, which exploits two reef horizons, the Basal and B reefs at 1 650m to 2 010m below surface. Masimong exploits the Basal Reef and B Reef, using a conventional tabular narrow-reef stoping method.

Masimong mines at moderate depths of between 1 650m and 2 010m below surface. The reef horizon is accessed by means of conventional grid development. The Basal Reef, which accounts for approximately 80% of the on-reef production profile, is mined by the open and undercut method, depending on whether the reef is overlain by shale. The B Reef, making up the remaining 20% of the on-reef production profile, is located approximately 120m stratigraphically above the Basal Reef, which necessitates separate infrastructure (footwall development).

The presence of the upper shale marker, approximately 20m thick below the B Reef, strains the development rates of the B Reef, requiring drop raising for holing on all boxholes. In addition, all on-reef development must be conducted by means of wide raising. Despite the marginality of the orebody and the current economic environment, current mine reserves give a life expectancy of two years, mainly due to the successful accessing of known value trend extensions.

The underground infrastructure is that of a mature, low-cost mining operation approaching the end of its economic life. The only undeveloped area of any economic significance lies to the south and south-east of the shaft in g ........

Ore Reception:
The use of parallel processing starts at the ore receive bin, where there are two unloading stations for the railcars that bring the ore in from the various shafts and rock dumps. A unique feature of the Plant is the Ore Reception facility, which has been designed to eliminate dead storage space, a serious constraint in railway ore storage bins. Ore is transported by rail to the Plant. The railway hoppers discharge individually into one of the two concrete, rail-lined inverted cones, 12m in diameter and 8m deep. The apex of the cone is 57o. The ore is rapidly withdrawn from the apex of the cone via a shuttle belt feed conveyor feeding onto a main silo feed conveyor. The twelve ore storage silos are constructed from concrete and are also rail-lined. Each silo has a live storage of approximately 3 000 tons. Ore is discharged onto the mill feed conveyor via a pneumatically-operated Langlaagte chute. When filled to full capacity, the twelve ore silos provide approximately 60 hours storage for the six Run-of-Mine (ROM) mills.

There are six parallel and independent milling lines with each one having a conveyor running underneath 2 silos (A and B) and taking the ore up into one of the six run-ofmine (ROM) mills. Generally, ore is drawn only from one of the two silos for each mill whilst the other is being filled with ore. Hence, one silo is discharging onto the mill feed belt, and the other refilled.

Milling:
The ore is taken up the slow-moving conveyers from underneath the silos and discharged directly into the feed hopper for the ROM (Run Of Mine) mills. Fully autogenous (FAG) milling is a milling process in which the entire ROM ore stream is fed directly into the mills. The grinding media is generated within the mill from suitably sized pieces of ROM ore itself, supplemented by waste rock dump material. The feed rate to the mills is between 90 and a 100t/h.

The milling circuit consists of six single stage ROM mills that are controlled on maximum power, utilising programmable logic controllers (PLCs). Variations in mill load are measured by load cells situated under the outlet trunnion bearings. Each ROM mill is 4.9m diameter by 10m long and powered by 3.3MW motors and grinds the ore to between 68 and 73% minus 75µm.

For control purposes, the mill feed belts and the mill discharge pumps both have variable speed drives. Each mill is in closed circuit with a 1200mm primary cyclone with mass flow measurement on the feed. The primary cyclone overflow is screened on a 600µm linear screen for the removal of coarse woodchips and tramp steel. This has the purpose of preventing gold losses and carbon contamination in the downstream CIP circuit. Cyclone overflow, which has a low density, is pumped out to the thickeners. The current cyclone overflow size is 68% at -75µm.

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