The use of automated core logging technology to improve estimation of fracture mineralogy and weathering for geotechnical index calculations

In underground mining, it is vitally important to characterise the rock mass conditions as they relate to ground support requirements. Rock mass characterisation is often achieved through the calculation of geotechnical indices. These indices reflect the properties affecting rock mass stability. Fracture parameters such as spacing, density, roughness and orientation are used to design appropriate ground support. The mineralogical properties within and immediately adjacent to fractures also affect the rock mass strength. Therefore, the relative hardness, thickness, and weathering of minerals along fractures are key input parameters in determining overall rock mass characteristics.

Commonly, geotechnical index parameters are collected manually by geotechnical engineers and geologists on drill core. Recent advances in automated core logging technology provide an opportunity to rapidly and consistently collect surface topography (3D laser height data) and mineralogical information (hyperspectral data) from drill core. From a combination of the 3D laser image data and a series of experience-based logical image processing steps, fracture surfaces can be automatically identified and extracted as a group of neighbouring pixels. The mineralogical data is co-registered with the 3D laser data, so the mineralogy of a pixel group representing a fracture can be queried. Mineral hardness and weathering effects can be estimated by analysing the mineralogy within and surrounding a fracture. Fracture fill thickness can be calculated using the number of pixels of each mineral across a fracture. The automated quantification of fracture fill characteristics ensures that these parameters are collected consistently, greatly improving the calculation of geotechnical indices.