Pure and simple: a practical guide to predicting ore body geometry in shear zones

Several types of ore deposit are commonly hosted within shear zones. Understanding the kinematics of such shear zones is critical to exploration and exploitation of shear-zone hosted deposits. In the last decade, it has been increasingly realised that natural shear zones involve combinations of pure and simple shear, which substantially changes the interpretation of shear zone fabrics from the simple shear zone model that was previously in widespread use. Shear zones can be divided into two types: simple shear dominated and pure shear dominated. In the first case, lineation is sub-parallel to the shear direction, but the shear direction in the second case is perpendicular to the lineation. The two types of shear zone can be distinguished in the field using this criterion. Ore bodies in the first case may be parallel or perpendicular to the lineation; in the second case they will only be parallel to the lineation. These simple guidelines have important applications to exploration and resource estimation for shear zone hosted deposits that do not have significant structural complications.