Modelamiento de fragmentacion

Blast Fragmentation Modelling of the Codelco-Andina Open Pit Expansion
F. Mardones
GeoBlast S. A., Chile

C. Scherpenisse
GeoBlast S. A., Chile

I. Onederra
The University of Queensland, Sustainable Minerals Institute, W H Bryan Mining and Geology Research Centre, Qld 4072 Australia ABSTRACT: In large scale metalliferous mining, there is significant evidence to suggest that by providingan appropriate size distribution to crushing and grinding circuits, a measurable increased throughput and/or reduced power draw can be obtained. Tailoring blast designs to suit specific fragmentation requirements is now common place at both the pre-feasibility and feasibility study stages. This is particularly the case when significant increases in ore production rates are being considered. As partof the feasibility study of the open pit expansion project of Codelco’s Andina operation, a comprehensive blast monitoring program was conducted in the currently mined secondary ore domains of the “Don Luis” pit. The objective of this program was to calibrate and implement a site specific blasting model to enable the prediction of fragmentation trends in the deeper, more competent ore zones, alsoreferred to as primary rock domains. This paper gives a brief description of the blast fragmentation monitoring program conducted and discusses the calibration and application of a stochastic blast fragmentation modelling framework. Results from several simulations have highlighted the key differences in fragmentation if current blast designs are applied in the more competent primary rockdomains. A number of blast design options have been evaluated and recommendations made in order to achieve specific ore handling and processing targets.

1 INTRODUCTION Blasting activities in major mining operations have been placing significant emphasis on the ability to tailor fragmentation to improve downstream processes. In many of these operations, the impact of fines has been clearly identified.At the conceptual and feasibility stages, fragmentation modelling studies which support future Mine to Mill strategies can be conducted through the calibration of empirical models using existing data; and if need be, through the implementation of specific trials. An important pre-requisite is the adequate classification and characterisation of the blasting domains of interest. As part of thefeasibility study of the open pit expansion project of Codelco’s Andina operation, a comprehensive blast monitoring program was conducted in the currently mined secondary ore domains of the “Don Luis” pit. The objective of this program was to calibrate and implement a site specific blasting model to enable the prediction of fragmentation trends in the deeper, more competent ore zones

2 DESCRIPTIONOF BLASTING DOMAINS The main geotechnical units forming the core of the mining environment of current and future operations at Andina have been grouped into Primary Rock, Secondary Rock and Riolite and Dacite chimneys. This study is mainly concerned with the calibration of an empirical fragmentation model in secondary rock and simulations in primary rock. Primary rock masses have been described as“hard” and competent with well healed gypsum or Anhidrite filled fractures, typical RMR values are in the range of 60 to 80. Secondary rock masses can also be described as “hard”, however fractures are generally open and hence reduce the competency of the rock mass with characteristic RMR values in the range of 42 to 50. Relevant to blast fragmentation modelling is the degree of in situ fracturing.As shown in Figure 1, total spacing statistics derived from fracture frequency data show that the degree of fracturing is clearly more intense in the secondary rock mass domains. Results from the available core logging data indicated that total fracture spacing may be as wide as 0.4 m in the secondary domain and 0.91 m in the primary rock domain. The analysis shows that the variability in...