Evaluation of the effect of wider-spaced layouts in recovery for high column block caves

Authors: Paredes, P Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2205_27

Cite As:
Paredes, P 2022, 'Evaluation of the effect of wider-spaced layouts in recovery for high column block caves', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 393-416, https://doi.org/10.36487/ACG_repo/2205_27



Abstract:
Block caving has historically been the preferred underground solution to mine large, low-grade deposits (Laubscher 1994; Brown 2007; Chitombo 2010; Flores 2014). However, the caving industry has entered a less certain environment where some of the caving options are showing not to be fully suitable to achieving the envisaged low cost and high productivity (Flores 2019). This environment includes extreme conditions, i.e. deeper and blind deposits (>1,400 m from surface), lower grade, harder and heterogeneous rock masses, and higher in situ stress regimes (Flores 2019). It is well understood that the major drawback of block caving is the high upfront capital cost and long lead time required to establish the cave. Establishment time and cost is exacerbated by increasingly complex orebodies at depth, including depth related issues such as low grades, strength/stress ratios, material handling costs and heat, among others (Flores 2014; Chitombo 2018; Ferguson et al. 2018; Flores 2019). The underground materials handling system and the footprint development and setup can represent above 50% of the direct capital cost for a new block (Paredes 2021). In this context, cave layout and materials handling system design are key levers to reduce tunnelling and timing requirements to establish a block caving operation. By reducing the overall tunnelling scope to establish a cave, the total exposure to risk of people and equipment, and establishment cost and timing can be consequently reduced. Based on a critical literature review, one of the main gaps identified to enable the implementation of wider-spaced layouts (i.e. layouts that have wider spacing of extraction and drawpoint drives) that can be less intensive in development, is that: current methods to assess the gravity flow outcomes of block cave layouts in early engineering stages are based on physical experiments and empirical methods developed for low column heights in the 1990s and early 2000s. However, since then there has been significant progress in physical and numerical modelling of gravity flow, which can be used to quantify recovery and interaction for high column caves using wider-spaced layouts. Thus, this work aims to quantify the effect in recovery of widespaced layouts for deep and high-column caves based on mine data and the current state-of-the-art in flow modelling. This consisted of conducting a back-analysis of the Cadia East Mine data to understand the gravity flow behaviour and main flow parameters of a high column cave mine, with the aim to use these as the basis to quantify the effect in recovery of wide-spaced layouts using numerical and physical modelling. Subsequently, physical and numerical modelling (using both Cellular Automata and Kinematic approaches) was conducted to understand the effect on interaction and recovery of wider-spaced layouts and identify any potential fatal flaws. Results show that no fatal flaw in terms of interaction and recovery was identified by increasing drawpoint spacing beyond current industry practices, which presents an opportunity to evaluate wider-spaced layouts that are less intensive in development for deep and high column caves.

Keywords: block caving, mine design, drawpoint spacing

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