Authors: Davies, AGL; Hamilton, DB; Clayton, MA

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Davies, AGL, Hamilton, DB & Clayton, MA 2018, 'Understanding and managing surface subsidence at New Gold's New Afton block cave operation', in Y Potvin & J Jakubec (eds), Caving 2018: Proceedings of the Fourth International Symposium on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 675-688,

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New Gold’s New Afton Mine is a 6 million tonne per year operating mine located 8 km outside of Kamloops, British Columbia, Canada. After ~17,700 m of decline access, underground ancillary and footprint development, the first drawbell was blasted in September 2011. The ore being mined is a copper–gold porphyry deposit situated within the Iron Mask batholith complex, bounded by two major subvertical fault structures, and plunges to the southwest. Determining the key components and driving mechanisms of surface subsidence is vital when considering potential impact on critical surface infrastructure. This paper will examine a number of fundamental learnings, starting from the initial feasibility study design assumptions through to actual cave behaviour and observed surface subsidence. As is the case in most start-up operations, early numerical modelling studies and inputs are often data poor and multiple assumptions need to be made. Furthermore, continuous and accurate calibration is required as subsidence evolves over time. This can be achieved through a better understanding of the regional geological model, and use of surface, subsurface and deep-seated instrumentation methods. At New Afton, we embarked upon an intensive instrumentation and drilling program to better understand the regional geological model and rock mass behaviour mechanisms, and their associated subsidence impacts.

Keywords: block caving, subsidence, numerical modelling, instrumentation

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