Surface deformation was detected over a dewatered Carlin Trend underground mining operation utilizing longhole stoping methods, and there was evidence that it was caused by mine dewatering and/or underground mining. A numerical modeling study investigated the mechanism(s) producing subsidence, and InSAR data was used as the main calibration dataset. The findings of this case study include: surface deformation is likely the result of coupled mining-induced and aquifer deformation; geologic factors form controls on the surface pattern of deformation; and rock mass yielding likely produced higher strain magnitudes over stoping. This case study provides the first published example of coupled mechanism subsidence, and has implications for understanding ground behavior and mine design at similar Carlin-style deposits. It also provides a methodology for investigating the mechanism(s) of deformation when they are unclear, complex, or caused by multiple processes.

1. INTRODUCTION

Subsidence is defined as a lowering of the ground surface, and can result from multiple types of subsurface ground behavior. Two common causes of subsidence include aquifer-system compaction, caused by lowering the groundwater table, and underground mining.

Subsidence is a potential concern in an underground mining environment due to the impacts it can have on the rock mass surrounding excavations. However, the risk to excavations cannot be assessed until the cause(s) of the subsidence are understood.

Subsidence was detected by InSAR methods in the region of the Leeville underground mining complex between 2004 and 2015. Leeville underground operations are located on the Carlin Trend in northern Nevada, include extraction of multiple tabular orebodies, and primarily utilize longhole stoping methods with backfill. It was unclear whether the subsidence was caused by mine dewatering or underground mining, as both activities were taking place simultaneously and there was potential evidence for both aquifer compaction and mining subsidence affecting ground behavior. Therefore, an investigation was undertaken to determine the cause of the observed surface deformation.

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