Mining (Ruia mine project)
Figure 1 Pit wireframe as at April 2017
Ore is mined from two open pits that are along strike of the 60m wide shear hosted deposit. These two pits are encroaching toward each other and will ultimately become a single pit elongated along strike (Figure 1). For each pit, a simple end-on road follows the working benches, then 15m incremental push backs are developed from this initial pit towards the north. Ore and waste are relatively soft ‘free dig’ material; however ore hardness beyond the zone of weathering requires blasting. Drill holes are drilled at a burden and spacing of 3m with the blast working across the shear, establishing 6m benches. Pit 1(deepest pit) has so far been mined to 975 level, (Figure 2) and the deepest point is currently 26m below the natural surface. A waste intrusion (with a diagnostic dark green colour) acts as a marker horizon to demarcate high grade material (> 0.5g/t) from low grade, though fast leaching ore (averaging 0.3g/t) near pit boundary on the foot wall. However, geological guidance is key in determining both the northern and southern pit boundary during mining.
Figure 2 Pit contours as at April 2017 (in Surpac)
Prior to mining, sample rip lines and trenches are established across strike. Samples are taken at 1m intervals along each line/trench and these are used to delineate the ore body using both fire assay and bottleroll analyses. Blast hole chippings are also sampled to get a more accurate grade for the block drilled and blasted.
Production is planned at 100 000 tonnes/month of undiluted ore per month at a grade of 0.75 g/t. Fines generated during the materials handling process are stockpiled on the surface for processing in the techno-shift phase during which a CIP/CIL plant will be installed. Earth moving equipment comprises of a Volvo A35 articulated dump truck, two Volvo EC300 LD excavators, SDLG LG958L Front end loader and two 30 tonne SINO truck (Howo) tipper trucks. All this equipment is owner equipment. Blast hole drilling is done using a Chinese crawler rig.
Open pit mining is expected to be done up to 35 m, which is the depth of the oxidised zone.However, an economic pit depth will be calculated after the ore body is delineated in the second phase of drilling when the down deep potential of sulphide zones are established. Beyond the economic pit depth mining will be done through underground methods.