Boundary Identification and Surface Updates Using MWD

In the banded iron formation-hosted iron ore deposits in the Hamersley Range of Western Australia, the stratigraphic boundaries are generally modelled using data from exploration drilling. Accurately identifying the locations of boundaries is important when modelling and mining ore deposits. Exploration drilling typically has a coarse horizontal spacing (~ 50 m), resulting in inaccuracies in the modelled boundaries on a bench scale. Measure-while-drilling (MWD) data from blast holes has a much denser spacing (~ 5–7 m), and can be used to locally update boundaries with a finer resolution. However, MWD measures the relative effort required to drill through the rock, and this does not directly correlate to the boundaries. Also, MWD measurements can be affected by factors such as blast damage, end-of-hole effects, different equipment, equipment wear, and settings and drill operators. Therefore, an accurate method of identifying the boundary points in the MWD was required. MWD data produces a signal that is significantly different from those in geophysical logs, without areas that can be clearly related to a single rock type, and the data is significantly noisier. Identifying boundary points in the MWD required initial preprocessing and cleaning of the data, including thresholding and applying a continuous wavelet transform. The cleaning allowed a boundary to be more clearly observed visually and reduced the number of incorrect boundary identifications. A Gaussian process (GP) model was trained to successfully identify the transition between the unmineralised West Angelas Shale and mineralised ore. The MWD-based boundary points were then used to train a surface GP to fit the boundary. When boundary points from multiple blasts were used, the GP surface produced a reasonable surface with more detail than the initial, exploration-based surface. Therefore, the GP surface can potentially be used to update geological boundaries in the deposit model to increase their accuracy within localised areas.