Modern Mining September 2018

ZINC/LEAD

transporting the ore to surface; and backfilling of extracted pro- duction areas. UDF is a top down min- ing method where a cement ed pas t e tailings backfill is used in com- bination with steel reinforcing, providing suffi- cient fill strength to allow mining to occur directly beside and below t h e f i l l . Th e method permits min- ing in low strength rock types and provides for improved control of work areas.

The process plant has a small footprint and maxi- mises the local landform to achieve efficiency within the process.

Among the benefits of UDF are engineered roof support and safe mining conditions in weak orebodies. The continuous filling system prevents ground relaxation and subsidence on surface while the selective mining method allows for separation of ore and waste with minimal dilution. The method also allows potential for future extraction of lower grade material as metal prices rise. The use of tailings for backfill reduces tailings storage on surface. The mineable ore zone at Tala Hamza extends from around 0 mRL to minus 365 mRL. The flat plunge and variable nature of the orebody is such that mining shapes vary sig- nificantly with depth. Ore zone strength is relatively weak, varying from less than 5 MPa to an average of 25-30 MPa. Extraction is planned to be via four lifts (‘panels’). Each panel is made up of a series of 5 m high slices (‘flitches’) which vary from 30 m x 50 m to 500 m x 300 m in surface area. The flitches are in turn divided into up to five ‘districts’. Each district will be mined by jumbo in blocks of 3 000 to 6 000 tonne stopes, some- times referred to at other operations as ‘cells’. This will be done by developing 5 m wide ore drives up to 50 m long and, depending upon the local rock quality, stripping up to 10 m wide. Each cell will be filled with steel-rein- forced cemented paste-fill before mining the production block alongside. Flitches are expected to be mined in a down- wards or ‘underhand’ progression to allow working under an engineered roof. Ore from the Tala Hamza deposit can be treated with conventional froth flotation to produce high-grade zinc and lead concentrates. The bond ball mill work indices of samples

and exploration both within the existing exploration area and further afield in a highly prospective emerging mining country which is looking to diversify from oil and gas.” The project surface footprint has been sig- nificantly reduced in size from the 2010 DFS. The land needing to be acquired for surface infrastructure has been minimised, without reducing flexibility for expansion. The mineralisation at Tala Hamza is approx- imately 650 m across strike, 600 m down-dip, typically 150 m thick and located between 120 m and 680 m below surface. Overall, the mineralisation plunges approximately 20 deg to the south-east. The deposit has a mineral resource of 53 Mt (at a cut off of 3,0 % Zinc Equivalent (Zn.eq) including an indicated resource of 44,2 Mt. Total ore (material mined at a project evalua- tion cut-off grade of 4,4 % Zn.eq) is 25,9 Mt at 6,3 % Zn and 1,8 % Pb with a nominal mine production rate of 1,32 Mt/a and an estimated mine life of 21 years (23 years includ- ing pre-production). The deposit remains open to the east and south-east, allowing the potential to expand production without reducing mine life. As mentioned above, the mining method now envisaged for the exploitation of the deposit is Underhand Drift and Fill. Activities include: development of the mine access (via a decline) and supporting infrastructure; min- ing of the ore using conventional drill and blast; loading the ore into mining trucks and

24  MODERN MINING  September 2018