A knowledge of the geomechanical properties of the rock mass is a critical requirement for improving almost all mining processes, from geotechnical design, drilling and blasting through to mineral processing. Current methods used to obtain this data such as mapping, core drilling, chip sampling, and geophysical techniques are expensive, yield limited results, are time-consuming, and valuable time is lost in the planning process during the analysis of the data. Estimating rock properties on-line and in real time simply by analysing the response of key drilling parameters to the rock mass is not new, and the technique has been used successfully for many years in the petroleum industry. However, until recently, attempts to obtain reliable and repeatable correlations between these parameters and rock properties in mining have proven to be only partially successful. This paper describes recent advances in the technology and its application at two of the largest open pit mines in South Africa. The data density and quality, and speed with which the rock property data is generated, offers tremendous potential for increasing the efficiency of mining operations by improving numerous short-range planning decisions. Most importantly, the technology provides information at a far lower cost, at greater density and, in some cases, more accurately than conventional methods such as core logging and mapping. The paper describes the geotechnical and other related improvements that are possible from using rock property data generated by the many large production drill rigs that have been equipped at these two mines during the past four years.

INTRODUCTION

In the mine-to-mill process the nature of the rock mass has a critical impact on almost all the operations, from drilling through blasting, loading, transportation, crushing, grinding, concentration, and waste disposal. However, crucial mine planning decisions are usually made based on a very limited knowledge of the rock mass prior to blasting. Any techniques that are able to provide additional information on the condition and content of the rock mass ahead of mining would therefore be highly desirable and realize considerable value through the optimization of these processes. For example, detailed knowledge of ore boundaries acquired during normal percussion drilling activities would offer substantial mine planning advantages. Drilling and blasting is another example that would clearly benefit from advance information on rock mass properties. The traditional means of obtaining such information is through exploratory drilling, analysis of the rock cores recovered, and geological/geotechnical face mapping. The disadvantages of these methods are clear; disruption to mining activities, time taken to obtain and analyse the samples, additional cost of drilling, loss of core in fractured material, damage to core making an assessment of fracturing difficult, and very sparse sample of data, among many others. Various methods have been used over the years in an attempt to obtain this information as far ahead of mining as possible, with varying degrees of success.

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