Determination of in-situ stress from oriented core

This paper presents the results of a program of determining the current in-situ stress based on testing under cores taken from exploration drilling. The analysis of the results uses the deformation rate technique (DRA) developed by Yamamoto and published in 1990. The results when rotated into the appropriate direction are confirmed in direction and magnitude by two independent stress measurement programs using Hydraulic Fracture. Work has also been undertaken to confirm the technique with CSIRO Hollow Inclusion (HI) tests. The initial testing which established the veracity of the method was undertaken in May 2002. Confirmatory testing of previously tested under cores was completed in August 2004. These tests not only showed the current in-situ stress, but also confirmed the Kaiser Effect stresses measured by the Acoustic Emission (AE) technique, as well as revealed the maximum load that the samples had been tested. Six independent test programs have been undertaken using different personnel and different laboratories to confirm that the approach is robust, simple and elegant. The results are also supported by a tectogenetic study (after Bogacz et al. 2002) undertaken for the site. The results confirm a low stress field for the proposed mine, when combined with the tectogenetic study they provide an understanding of the local tectonic regime responsible for the mineralizing event hence provide a guide to exploration potential. The in-situ stress determined from these tests is not the Kaiser Effect (KE) although the KE can be measured from the procedure as noted by Yamamoto in 1990. Using the knowledge that the stress is locked into the sample, it can be demonstrated that other methods such as AE also measure the same effect but with considerably less reliability. The maximum stress measured from the tests undertaken on diamond drill core is a function of the orientation of the hole and the in-situ stress. This is demonstrated in the paper. The stress measurement technique is independent of elastic theory and can be shown to work on samples previously tested. That is, it is a non destructive test.