I can only think of two obvious things that spring to mind,...

I can only think of two obvious things that spring to mind, firstly it could be directly drilling related (either significant assays from a drillhole completed earlier or an obviously mineralized drill hole with visible high grade mineralization) or secondly - something that affects the timing or progress of the drilling (could be anything from additional drill rig to possible geotechnical issues such as collapse or flooding of a drill drive access or drill cuddy resulting in a delay to the drilling).