Unplanned fall at 315 blk intersection 9 So. haulage. Approx. 28' by 21' by 11' high. Multiple slips in rubble, including small amounts of slicken-sided shale, and a large amount of white chalky/talc-like powder, that was very slick, allowing separation in rock strata above the anchorage. No problems with training, PPE, mining machines or compliance issues.