Examinantion of the geological set up and rock mass characteristics of Nchanga underground Mine in order to optimize draw of' the Feldspathic-Quartzite'(TFQ) Ore in the caved areas

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Hakakwale, Bornwell
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Nchanga Underground Mine applies a variant of block cave mining to exploit the massive copper ore deposits with generally low ore grades fairly distributed within the orebody. Mining activities date as far back as 1937 when underground production commenced. Traditional block caving mining method is in use where the Jackhammers are used to drill the rock. Jumbo drifter machines are then used to drill long holes for caving. The ore is then caved and channeled through a series of transfer chutes and later hauled to shaft hoisting facilities to surface. Block cave mining has proved to render a solution to massive orebody mining worldwide especially with low grades due to, mainly, its low mining costs (i.e. high profitability), high productivity per man-shift and generally safety advantages as one ‘does not re-enter’ the caved stopes. However, the major challenge faced with block cave mining is ore dilution as waste rock gets caved along with the ore. The Nchanga sedimentary copper orebody comprises mainly of two major limbs of the orebody, i.e. the Lower Orebody (LOB) and the Upper Orebody (UOB). The minor limb, the Intermediate Orebody (IOB), exists between the LOB and UOB in some areas but is generally very thin. The two are separated by a weak but thick layer of banded sandstone (BSS). The upper orebody is made up of ‘The Feldspathic-Quartzite’ (TFQ) copper mineralized rock unit. During extraction of the ore, the LOB is drawn up to the point where the recovery reaches the BSS material. Once all the production drifts reach their draw into the BSS layer, the block is declared exhausted. This leaves out the copper mineralization in the TFQ above the BSS. This project intended to examine the ore potential in the TFQ copper ore above the BSS layer as well as the BSS tonnage to be removed to recover this remnant ore. This has been achieved by reviewing the ground conditions of the old exhausted areas (rock mass characteristics), support requirements as well as draw parameters to enhance optimized recovery of ore left in the TFQ. An economic analysis of the project has shown that a breakeven copper market price of US$5,737.22 per tonne above which the project becomes viable has been determined. The project objective to optimize draw of ‘TFQ’ ore in the caved areas of Nchanga has been achieved: BSS pulling to commence with from down-dip drifts and end with up-dip drifts in a block. The project should be embarked upon speedily to take advantage of the currently high copper prices.
Rock Mechanics , Mining Engineering