Correlation of permeability with weathering of crystalline rock core from South Korea

Abstract:

In this study, we examine the role that weathering plays in the permeability of crystaline rocks. A total of 40 drillcore samples for two crystalline rock types (granite (n = 21), gneiss (n = 19)) were taken from Daejeon and Andong, South Korea and used to identify the contribution of weathering to rock-matrix permeability. Each sample was collected at 50 m intervals in the borehole of 1 km depth. Ten types of weathering indices including Ruxton Ratio (RR), Weathering Index of Parker (WIP), Vogt’s Residual Index (VRI), Chemical Index of Alteration (CIA), Harnois’s Chemical Index of Weathering (CIW), Plagioclase Index of Alteration (PIA), the Silica-Titania Index (STI), Chemical Weathering Indices (CWI), Sesquoxide Content (SOC), and Weathering Potential Index (WPI) were calculated for the drillcore samples. The indices values were in the ranges: RR 3.2 - 5.6; WIP 4270.3 - 6995; VRI 0.9 - 4.7; CIA 51.3 - 64.9; CIW 55.3 - 80.0; PIA 51.5 - 73.7; STI 71.9 - 84.6; CWI 14.4 - 31; SOC 13.8 - 25.7. Permeability for the two rock types were measured and ranged from 4.0 × 10^-22 to 3.62 × 10^-18. We used t-test to evaluate an association between permeability and weathering at a significance level of 0.05. Among the weathering indices evaluated here, the significance levels of RR, VRI, STI, CWI, and SOC were determined under 0.05. As the permeability increased, the weathering indices also tended to increase.The results showed the permeability of the drillcore samples is affected by chemical weathering and alteration of the minerals by water-rock reaction.