Mine to Mill optimisation is not a recently developed concept. It is one which is finally gaining greater acceptance in the Australian Mining Industry, possibly as a consequence of the downturn in markets and certainly made possible by the development of tools and techniques to measure and predict performance of mining equipment and milling plants. Fragment size after blasting has a major bearing on the performance of all aspects of mining and a major influence on the economics of the mine and mill. The process to optimise fragmentation consists of identifying the key factors, measuring their sensitivity through a modelling and trialing program and conducting economic evaluations on the changes on both the mine and mill.
Management of the Ernest Henry copper-gold mine in Northern
Queensland, Australia, has espoused the Mine-to-Mill concept and is
actively pursuing excellence in blasting to drive down the total cost of mining. Ernest Henry has extremely hard, wet and heavily jointed geological conditions, and had high powder factors and a large percentage of oversize material reporting to the crusher or ROM
stockpile. A blasting improvement program was undertaken between
Ernest Henry Mining, Thiess Contractors and Orica Explosives to
optimise the ore size distribution, particularly the oversize component, as a step to reducing production costs. Measures of success included bringing the rock breaker back from double shifts to part-time operation and increasing direct dumping into the crusher from 70 per cent to 92 per cent.
Tools and technologies to predict and measure the performance of
individual blasts are needed before it is possible to optimise
fragmentation or the downstream processes. These include such
specialised Orica Explosives tools as SABREX, POWERSIEVE, and
POWERLINE and commercially available drill monitors. As important
are the more common still and video camera, borehole loggers,
measuring tapes, surveying equipment such as face profilers, and a
high-speed camera if possible. There are many tools which can be applied however it is rarely necessary or possible to use all of them due to time constraints and a point of diminishing returns. The critical point is knowing what the true parameters of the blast were compared to design - only then can the predictive tools be effectively utilised.
Stage one of the program has seen gradual improvement as the
understanding grew and practices have been implemented resulting in
reduced bridging in the crusher, geological mapping with respective blast designs and the oversize component under control. This paper is about a process approach which links tools and technology to understand the fragmentation drivers and then to optimising the size distribution.
The continuous improvement program continues...