Changes in the seismic energy flow when mining deep levels (the Apatite Circus deposit, Khibiny Massif)

Abstract

The study is aimed at assessing the changes in seismic energy flow as mining operations advance to deep levels as exemplified by the Apatite Circus apatite-nepheline deposit (Khibiny Massif), which underground reserves are difficult to develop due to the presence of the nearby Rasvumchorr Plateau deposit, which is mined using the open-pit method. Underground mine workings and open-pit walls are located in the bordering area. A large number of fractures and tectonic faults are exposed in this area, which become waterlogged when the snow thaws. As a result, the stress-and-strain state of certain rock mass sections (mainly the tectonic fault zones) changes, which generally affects the seismic settings of the deposits. Along with transition of the mining operations to greater depth, an increase is observed in the number of seismic events and their energy in the lower levels of the mine. Also the fracturing processes in the overhand part of the rock mass are reflected in seismicity activation. The paper presents maps showing the spatial distribution of the seismic energy flows of various events across the mine field as mining progresses to greater depth. It has been established that there exist areas of increased level of seismic energy flow distribution, corresponding to the compressive strain zones (two lower levels, where intensive mining is in progress) and tensile strain zones in the overhand part of the rock mass ( the top third layer), where a gradual collapse of the near-surface area of the mass occurs.