Forecast changes of the piezometric surface of the Metegero-Ichersky aquifer system in the Internationalniy mine (Yakutia)

Abstract

Introduction: To compensate for the retired capacities of the Internationalniy mine, it is planned to remove pit reserves under the protection of artificial pillar supports. The safety of underground mining below the bottom of the quarry is directly affected by the Metegero-Ichersky confined aquifer system (MIXAS) and soluble rocks in the underlying rock mass. This requires developing a waterproofing system in the mine considering the peculiarities of the geological structure and hydrogeological conditions of the Internationalniy diatreme. Superficial, underground, and combined waterproofing methods were considered. The main purpose of the research was to study the positions of the levels of the Metegero-Ichersky aquifer system after the advance dewatering systems started to operate in the field. Methodology: By means of numerical modelling and the MODFLOW GMS program various alternatives of drainage systems were studied with the help of a planned model under pressure-pressureless filtration modes in the MIXAS. According to the plan, the Metegero-Ichersky aquifer system is assumed to be piece-wise homogeneous, in the cross section it was presented as a single aquifer with averaged filter coefficients. The forecast was conducted under the conditions of reinjection of the brine from the Internationalniy mine into the structure of the Western fault. In this case, the reinjection flow rate was assumed to be equal to the inflow of drainage wells. Results and discussion: It was found that the surface dewatering by means of drainage wells does not pro-vide complete drainage of the MIXAS in the area of the ore body. The residual levels may be removed by up-holes from the horizon of 145 m. It was revealed that it is reasonable to drain the MIXAS from the underground mine workings of the horizons of +85, ±0, and -145 m in three stages: the dewatering of confined static reserves of the MIXAS from the horizon of ±0 m by down-holes; the dewatering of the unconfined MIXAS by down-holes from the horizon of +85 m; the removal of residual water by up-holes from the horizon of -145 m. It was determined that the mine drainage almost to the bottom of the MIXAS is provided by the operation of inclined up-holes constructed from the drainage roadway at the horizon of -145 m. Conclusions: According to the results of prediction modelling, all investigated alternatives will result in the decrease in the level of groundwater at the site of mining operations almost to the bottom of the MIXAS. Multivariate technical, economic, and hydrogeological calculations proved the practicability of the under¬ground method of protecting the mine from brine which was adopted at the site and which involved constructing a ring water-drainage roadway and inclined up-holes at the horizon of -145 m.