Mercier, J-P, van As, A, Carlson, C & Tumur-Ochir, B 2018, 'Microseismic monitoring of the Oyu Tolgoi Hugo North Lift 1', 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. 823-834, https://doi.org/10.36487/ACG_rep/1815_65_Mercier
(https://papers.acg.uwa.edu.au/p/1815_65_Mercier/)
Abstract: Oyu Tolgoi is a copper–gold mine in the South Gobi region of Mongolia located approximately 550 km south of the capital Ulaanbaatar, near the Chinese border. The Oyu Tolgoi mine is expanding underground to exploit the Hugo North deposit, one of several large-scale orebodies of the Oyu Tolgoi complex. The Hugo North deposit extends over 900 m vertically, from 500 to -400 MASL (670 m below the surface to 1,570 m below the surface), and is approximately 1,800 m long and 500 m wide. Mining of the Hugo North deposit will be done in stages using block caving. In the first stage, referred to as Lift 1, the top 400 m of the orebody will be mined.
A microseismic monitoring system comprising 128 triaxial sensors is currently being commissioned to cover the Hugo North Lift 1 cave and the critical infrastructure underground. The purpose of the microseismic system is to provide information on the cave growth, and monitor and evaluate the seismic risk around the mine. The cave area is, to a large extent, covered by an array of 90 triaxial sensors installed and grouted in 
15 deep boreholes that surround the orebody. The boreholes are drilled from surface and vary in length between approximately 80 and 1,250 m. Additional sensors are deployed underground in a series of short boreholes.
The commissioning and the operation of the Hugo North Lift 1 microseismic monitoring system pose significant challenges. Installing seismic sensors in 127 mm diameter (PQ) boreholes of more than 1,000 m is not trivial, and had, as far as we know, never been achieved before in a mining context.

Keywords: microseismic, monitoring, geotechnical, block caving, drilling, sensor installation