Resource World Magazine

70 www.resourceworld.com F E B R U A R Y / M A R C H 2 0 1 7 Eldorado is a leading low cost gold producer with mining, development and exploration operations in Turkey, Greece, Romania and Brazil. TSX: ELD | NYSE: EGO eldoradogold.com The Company's success to date is based on a low cost strategy, a highly skilled and dedicated workforce, safe and responsible operations, and long-term partnerships with the communities where it operates. sierrametals.com TSX: SMT BVL: SMT A POLYMETALLIC PRODUCER with exciting RESOURCE GROWTH POTENTIAL 3 MINES 2 COUNTRIES 1 SOLID INVESTMENT OPPORTUNITY for unstable ground, whereas, modern ground support has changed to mecha- nized support such as rock bolts, screen and shotcrete. Wide veins and larger ore zones can now be completely mechanized for drilling, blasting, ground support and mucking. More precise long hole drilling and smaller mechanized equipment is now allowing many narrow veins to convert to safer sub level long hole mining instead of the more labour intensive conventional shrinkage and cut and fill mining methods. Development of an underground mine is more complicated than an open pit and requires different experience and equip - ment plus different design depending on whether a shaft, adit or decline (sloping tunnel) is the main means of access. If the mine access is via an adit or decline, then this is easier to get started, requires less equipment, expertise, less development to open up the first stopes for mining and less capital. Once the first stopes are developed, the decline can continue downwards, opening up new stopes after production commences. If a shaft needs to be sunk instead of a decline, then a headframe needs to be constructed with a hoist installed. The shaft needs to be sunk and equipped for a man cage and skip for ore and waste. As it is difficult to sink the shaft while the mine is operating and it is expensive to setup for deepening the shaft, the initial sinking will often be to a depth that allows mining for the first five to ten years, which is a large, initial capital outlay. If a decline is required as well, then there is an additional expense, but with the benefit that mining of ore can start as soon as the first few months of ore have been developed from the decline. Subsequently, the shaft can continue sink - ing while the plant is already processing ore from the mine. In conjunction with the main accesses, other development will be required for ventilation and a secondary means of egress. The crushing and processing facil - ity is constructed based on the testing, flow sheet and design determined in the FS. Processing of the ore starts with understanding the mineralogy, then metal- lurgical testing for crushing, grinding and recovery of the metals and treatment/man- agement of the tailings. The metallurgy is extremely important and lack of sufficient testing up front has been the demise of a number of projects. Most deposits require one or two stages of crushing and sometimes a third stage, with at least one crusher in closed circuit, via screening to provide a feed to the grinding circuit of one quarter inch to half inch size. However, if semi-autogenous grinding (SAG) is used, the ore feed to the SAG from primary crushing may be six inch, thus eliminating the need for secondary crush - ing prior to the SAG Mill. Conventional grinding using a rod mill or ball mill will also be used, or some combination, to MININGWORLD

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