A secondary geological vein, fault, or dyke that intersects the primary mineral lode at an angle. A cross-course often displaces the main lode, causing a fault heave that forces miners to search for the continuation of the ore. They can also act as channels for groundwater, making them hazardous to breach underground.
Heard on the job
We lost the copper seam when we hit a barren quartz cross-course, so we're driving a drift to find the offset.