The mine and plant were re-started in the first half of 2019. The underground mine which is accessed through an incline ramp is currently entering the 3rd level. The mine operates with Fermel equipment and hauls about 12 000 tonnes of ore to the Crusher. The zinc, lead and slivers grades vary across the mine.
The Plant was constructed by EPC contractor, Bond Equipment and completed in March 2019. The first production was achieved in May. The plant aims to produce Zn concentrate above 48% and Lead concentrate above 55%. The first 200 ton sales of Lead concentrate was shipped in August and the first 1000 tonnes of Zinc was sold in September. The company have off-take contracts in place to sell to Europe and Asia.
The detailed process is as follows: The plant circuit is a conventional crushing, grinding, flotation operation, for a lead/zinc orebody.
- Ore from the run-of-mine pad is fed by front end loader to a bin, vibrating feeder and grizzly, which feeds a jaw crusher. The crushing plant is a two-stage unit with intermediate screening and the ability to reject coarse, potentially waste, material. An impact crusher was chosen as the second stage to take advantage of the high reduction ratio to provide suitable feedstock for the small-scale ball mill. Impact breakage suits grain boundary cleavage and avoids ‘squashing’ softer minerals like galena. Surge storage is handled via a fine ore bin and overflow stockpile.
- The flotation circuit provides flexibility to deal with both elevated head grades and circuit modifications. The circuit was designed to maximise the use of gravity, reducing the need for pumps and increasing the ability of the plant to deal with variability. The lead roughers and lead cleaner capacity can cope with elevated head grades. The lead rougher tails form the feed to the zinc conditioner. The zinc roughing cells are conservative to allow for easy reconfiguration should a larger scavenging duty be required which builds up a recirculating load and thereby reduce the actual residence time. The zinc cleaner circuit incorporates a re-grind facility to complete the effective liberation of the available sphalerite particles.
- An opportunity was taken to modify the original design of laying out the flotation circuit in a terraced format, into a large steel, multi-level structure. This new layout will have significant benefits when in operations but resulted in a small delay in the delivery of this portion of the plant as the logistics around the installation of this structure and plant equipment also took a little longer than originally planned.
- The final concentrates are fed onto horizontal belt filters, which also allows considerable air-drying time. The lead concentrate is packaged into bulk bags to minimise any open piles and either load a container on-site or transport the bags to Walvis Bay to load the containers. The zinc concentrate is directly loaded onto trucks or bulk loaded into plastic-lined containers on site.
- A tailings thickener reduces water consumption. A large internal paddock was established to compartmentalise the initial tailing in order to maximise the water return capabilities. This paddock has sufficient capacity for the first year’s production.
- The company employs about 150 staff. More information can be obtained from the NLZM website.