 Bucket line dredges are more capable of handling boulders and timber than other forms of dredges such as suction cutters.A dredge may be designed to handle the particular conditions of the area to be mined, including the presence of boulders, timber, gravel, sands, hard bands and clays.Ore Tin ore occurs naturally as brown or black grains of free cassiterite (SnO2) and it is frequently found with the gravel in ancient or present creek beds where it was deposited by the alluvial action of running water after weathering from the original lode.