In-situ stress characteristics and fracture stability analysis of a gold-copper deposit in the Duolong ore concentration area,Northern Xizang
To assess the current in-situ stress state and fracture stability of a gold-copper deposit in the Duolong ore concentration area,Northern Xizang,the hydraulic fracturing method and impression orientation method were employed alongside the HYF-3 single and dual-circuit in-situ stress testing system.This approach facilitated the measurement of in-situ stress across three boreholes at depths ranging from 171.90 m to 751.40 m.A total of 1 397.20 m of drilling was conducted,which included in-situ stress measurements for 14 sections and maximum horizontal principal stress direction measurements for 3 sections.Utilizing the measured in-situ stress data,the variation patterns of in-situ stress and lateral pressure coefficients with depth were established,and a regional fracture stability analysis was performed.The results indicate that the stress field in the study area is predominantly influenced by horizontal tectonic stress,with maximum and minimum horizontal principal stresses(S H and S h)ranging from 7.55 MPa to 31.94 MPa and 6.61 MPa to 20.36 MPa,respectively.The vertical principal stress(S v)ranges from 4.56 MPa to 20.29 MPa,with all stress components showing a linear increase with depth.The in-situ stress structure is primarily characterized by S H＞S h＞S v,indicating a reverse fault-type stress state.Predictive analysis based on the measured data suggests that the transition depth of the stress structure is approximately 746.18 m,below which the stress structure displays a strike-slip fault-type stress state.The maximum horizontal principal stress direction in the study area ranges from N14.30° E to N33.34° E,with a predominant northeast orientation.The distribution pattern of the lateral pressure coefficient(K)with depth indicates that the influence of horizontal tectonic stress is stronger in the shallow crust than at greater depths,gradually diminishing as depth increases.The fitting results for the horizontal stress coefficient(K Hh)and the horizontal shear stress intensity index(μm)reveal that while the overall horizontal shear stress intensity in the study area is relatively low,it is significantly higher in Area A compared to Area B.Utilizing the Coulomb sliding friction criterion and assuming a critical friction coefficient(μ)of 0.6 for the fracture surfaces,the analysis of regional fracture stability suggests a low level of stress accumulation in the study area.The current in-situ stress state has not reached the critical threshold necessary to induce fracture instability and sliding.Instability and sliding of the fracture zone would only become likely if μ were to decrease to 0.2.
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