Active (swelling) clay minerals play predominate role in defining properties of clay based slurry, such as particle agglomeration, slurry rheology and tailing deposit permeability. They affect processes like extraction, flotation, flocculation, thickening, hydrotransportation and sedimentation. Impacts of clays span different mineral sectors including potash, kimberlites and oil sands operations. Research in this area shows that the presence of active clays, such as smectite can significantly increase solids settling times, which can have a significant impact on water recycle and tailings management processes. Understanding the types and amounts of clay in mineral ores and tailings enables more effective process design and control. The talk will present the impacts different clay types have on mining operations and the sort of variation that can be seen within a single ore deposit. Methods for defining clay content, including X-Ray Diffraction and Methylene Blue Index (MBI) as a measure of clay activity will be discussed.