The analysis of the studies into fracturing of Zhelezny pitwall rock mass over the period from 1989 to 2019 proves that planetary fracturing is represented by faults, carbonatite dykes and single fractures oriented in the same direction as the prevailing regional lineaments on the Kola Peninsula. Planetary fracturing is assumed as a system of regular-oriented fractures. The planetary fracturing also includes lineaments of tectonic origin. The scientists think the faults registered in the pitwall rock mass and codirectional with the lineaments will accompany mining operations down to the full depth of the pit, up to the full extraction of magnetite–apatite ore reserves. While preparing this article, the authors have collected, generalized and analyzed the data of geological and structural mapping implemented by VIOGEM’s experts over the period from 1989 to 2019. VIOGEM’s procedure of geological and structural mapping ensures continuous documentation of extensional tectonics at high referencing accuracy (to 50 cm), as well as determination of inaccessible azimuths and angles of fractures by remote assessment of their orientations in pit walls using a laser scanner and photographic techniques to study the structure of hard rock mass and the behavior of permanent benches.
This article presents the back-calculation data on bench deformations in open pit mine Zhelezny of Kovdor Mining and Processing Plant. The calculations are performed for 105 rock falls divided into six groups with respect to volume (m3): 0–200 is group 1; >200–500 is group 2; >500–1000 is group 3; >1000–5000 is group 4; >5000–10000 is group 5; >10000 is group 6. The computational method was the single-factor analysis of change in specific cohesion between the surfaces of deformation-limiting fractures. The internal friction angle is assumed to be constant as it is the least of all changeable and is correlatable with laboratory test data. Actual rock falls were simulated in GIS GEOMIX. The simulation correctness was ensured by the high-accuracy referencing and orientation measurements of fractures using 3D models constructed based on laser scanning and drone photography. For all sampled rocks, it is found that specific cohesion between fracture surfaces grows with increasing volume of rock falls. Specific cohesion in case of small volume rock falls (0–200 м3) in all types of rocks, except for olivinite, is approximately the same and ranges as 0.0021–0.011 MPa; for olivinite, this value is higher by 20 % at least. Higher rate slipping along fractures is typical of fenite (almost in all groups, specific cohesion is lower by 10–90 % than in other rock types), which is governed by supergene mineralization of fenites and by down water flow in fractures. The low and approximately equal values of specific cohesion (0.0058–0.0094 MPa) are observed in group 0–200 m3, which is conditioned by the action of blasting on deformation of benches. The study is carried out under State Contract No. 075-03-2020-474/1 от 05.03.2020.
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