Abstract

The occurrence and distribution of fracture-filling material within the Eye–Dashwa granite indicate that the dominant fracture system formed shortly after emplacement and cooling of the pluton at 2678 ± 67 Ma. Subsequent reactivation of these ancient fractures was accompanied by sequentially younger and lower temperature filling materials. These reopened ancient fractures are best developed in the upper 300–400 m of the rock mass and are commonly conduits for present-day groundwater flow.Multiple linear regression analysis performed on the geological variables defined from boreholes ATK-1, -2, -3, -4, and -5 identified a highly significant correlation between a number of these variables and hydraulic conductivity values measured in 25 m test sections of the boreholes. The correlation is expressed asgraphichere log Kerm is the log of hydraulic conductivity; log(DEPTH) is the log-transformed depth to the lower end of the packer interval; log(CLAY) is the log-transformed frequency of clay-filled fractures per 25 m interval; log(VEIN) is the log-transformed frequency of veins per 25 m interval. The equation has a multiple r value of 0.82, explains 67% of the variance of hydraulic conductivity, and has a random exceedence probability (Q) of 9 × 10−12 (i.e., it is highly significant).The predictive capability of the regression design was tested with seven new test data and found to be a valid estimator of the hydrogeological conditions within these test intervals.

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