191 / 2023-09-05 14:32:40

3D fracture simulation in the Gejiu tin district (southwest China) using GEOFRAC for exploring vein structure

Discrete fracture network, three-dimensional simulation, geostatistics, orebody shape, fault distribution

Fracture is an essential factor controlling mineralization and ore distribution in metallic deposits. Fracture also affects the mechanical stability of drifts. A plausible three-dimensional discrete fracture network (DFN) was constructed using GEOFRAC, a geostatistical method of conditioning directions (strikes and dips) and locations of sample fractures. The northern part of the Gejiu tin district, southwest China, was selected, using 10 212 fractures sampled on drift roofs at five different levels and along a 5463 m length. Critical parameters of this DFN are fracture density, direction, and the connective condition of discs that form a fracture plane. The simulated fractures were verified by good correspondence of their directions with those of the sample fractures; furthermore, continuous fractures longer than 1 km matched the faults observed in outcrops. The most notable result was clarification of fracture control by the orebody shape: simulated gentle fractures (30° dips or less) formed layered orebodies and created boundaries between each layer, while steep fractures (60° dips or more) displaced the layers by acting as faults. Such fault-type fractures and the densely fractured portions require caution with respect to mining safety. It was concluded that GEOFRAC is useful for three-dimensional DFN modeling in underground mines.



Almost current DFN methods randomly assign locations and directions of simulated fractures using a probabilistic function obtained from sampled fracture data, which results cannot reflect the spatial characteristics of locations and directions of actual fractures. To address this problem, the GEOFRAC (GEOstatistical FRACture) simulation method can be used to construct a plausible DFN using actual locations and directions of sample fracture data. GEOFRAC uses ordinary kriging (OK), sequential Gaussian simulation (SGS), and principal component analysis (PCA) to incorporate spatial correlation structures of locations and directions of sample fractures. The study aimed to construct a plausible DFN of the Gaosong field in southwestern China using the GEOFRAC method to clarify the relationship between fracture distribution and orebody formation. The GEOFRAC method used was verified in three ways: agreement of general trends in directions of simulated fractures with those of sample fractures; positional correspondence of the continuous fractures with the known faults, despite no use of actual fault information; and geometrical characteristics of the horizontal orebodies extended along a gentle, continuous fracture plane and displaced vertically at the four steep fractures. The GEOFRAC method is confirmed by this study as a powerful tool to produce a plausible DFN that can help to identify control of fractures on an orebody geometry and contribute to the exploration of new deposits. The GEOFRAC method also has application in mining safety, by predicting locations of fault-type fractures accompanying weak zones and densely fractured portions with many fractures in narrow spaces.