Passive Seismic Monitoring of Mine-scale Geothermal Activity: A Trial at Lihir Open Pit Mine

Abstract

The Lihir open pit mine in Papua New Guinea is located inside an old volcano where geothermal activity is strongly present. Outbursts of hot water and steam into the mining areas were a major safety concern. Passive seismic monitoring was carried out at the mine to investigate whether the geothermal activities could be detected and located using microseismic techniques in a mining environment. In this trial, sixteen triaxial geophones which can withstand temperature up to 200°C were used and installed in four deep boreholes inside the pit. The microseismic events were discriminated using the STA/LTA triggering criterion. During 6 weeks of monitoring, more than 17,000 events were recorded. Approximately 12% of the events showed harmonic vibration characteristics similar to those observed in other geothermal and volcanic areas, suggesting that the geothermal activity inside the pit was captured by the microseismic monitoring system. More than 75% of the events present both P and S waves and they were interpreted to be associated with rock fracturing due to stress release near the bottom of the pit. Many geothermal-type events were located in areas where shear events occurred, implying that the detected geothermal events were not far from the mining area below the pit and they may also be associated with mining. The borehole installation of the geophones significantly reduced the interference of mining noise and achieved good observation of the seismic events. However, equipment installation requires great attention as the geophones may be destroyed due to unexpected rising temperature within the boreholes.

Dynamic modelling of a mining-induced fault slip

“…Seismic waves arising from seismic events that take place in underground mines can be detected by means of seismic monitoring systems installed in underground mines and/or near the ground surface. Seismic source parameters are computed on the basis of wave forms recorded by the seismic monitoring systems and used for understanding seismic activities (Bischoff, Cete, Fritschen, & Meier, 2010;Domanski & Gibowicz, 2008;Holub, 1996;Luo, Creighton, & Gough, 2010;Sileny & Milev, 2008;Urbancic & Trifu, 1998;Urbancic & Trifu, 2000). More importantly, seismic source parameters can be also computed based on results obtained from numerical analysis.…”

Experimental Study on Stress Evolution and Microseismic Signals under Vibration Conditions of Coal during Excavation and Subsequent Waiting Time

“…As the technology has matured, the microseismic technique has become the fundamental monitoring approach for mine safety and ground control. Luo et al studied the roof fracture process and stability using the microseismic method [8]. Mansurov analyzed the microseismic data gathered by North Ural Bauxite Mines.…”