Authors: Morrison, DM

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Morrison, DM 2022, 'Value-production systems for block caving mines', in Y Potvin (ed.), Caving 2022: Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 355-368,

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Block caving mines produce the lowest grade ore in the metal mining industry and more than any other, they must begin to focus on producing ‘value’ rather than tonnes. Block caving involves no primary blasting or backfilling, so the first step in reducing operating cost is to improve coarse ore haulage. Batch load–haul–dump (LHD) haulage is slow and expensive; it uses six times more fuel (energy) than is required to move the ore (LHD mass is three times the payload plus return). Batch haulage leaves broken ore in active drawpoints untouched 90% of the shift and doubling the speed of the LHD only reduces this to 80%. All other industrial processes moving low-value product to the customer use the cheapest possible technique – a conveying system of some kind. A steel conveying system such as presented here can move ore 80% of the shift, at three times the speed and 20% of the energy of LHDs, around 100 times more effective (8 × 3 / 0.2) than batch haulage. The second step in improving value production is to increase the ore grade. Recent oresorting techniques identifying the most valuable component of the ore stream have been proven effective in surface mines. Upgrading techniques in underground mines need a process to dispose of the reject material. Removing waste from the ore-flow system is easier in a conveying system amenable to sizing, and inline ore crushing facilitates the removal of waste from the ore stream. Boreholes and raisebore holes can elevate the crushed reject material above the haulage level for storage and disposal in mined out voids. Waste rock can be consumed in cemented backfill or in loose waste rock voids above and behind the production front. Early removal of negative-value material (zero value, absorbing cost) from the ore-flow has to be balanced against the cost of processing zero-value material through the entire beneficiation process and tailings storage. This is especially important for shaft mines where hoisting waste rock prevents hoisting ore. Even if only 20% of the waste rock can be consumed in mine voids, the implementation underground of low-energy, low-cost, continuous, autonomous ore haulage systems shifts the cost-benefit from high-volume production to high-value production.

Keywords: metal demand, value production, ore haulage, ore upgrading, waste rock diversion, autonomous systems, lower cut-off grade, non-mining technology, cultural change

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