Using ghost rock weathering as a new tool for quarry management

Although karstic weathering (sensu lato) is a major concern for the exploitation of limestone quarries, the importance, spatial extension, and intensity of this natural phenomenon are rarely investigated because of the lack of applicable technique to assess these variables other than subsurface geophysical exploration methods. Here, we propose to use the intrinsic property of ghost-rock weathering, tectonic control, to predict the degree and type of weathering of the reserve of two contiguous limestone quarries in the Tournai area (western Belgium). First, we revised the macrotectonic setting of these quarries, creating five tectonic entities. Then, we built an extensive fracture database (1357 ‘events’), recording fracture direction, dip, width, height, mineralization, and weathering. Then, we calculated a “Sterile Index” that is a simple function of the relative occurrence and mean width of karstified fractures. The rose diagrams of fracture orientations are contrasted between tectonic entities and so are the intensity and the dominant type of weathering: tectonic entities with widely dispersed fracture directions are significantly more weathered than entities with narrowly dispersed rose diagrams. Preliminary tests indicate fracture orientation and weathering are consistent within the tectonic entities, allowing extrapolation to quarries reserves. Ultimately, this technique can be used to predict the rock waste volume of the quarries reserves (when combined with geophysical exploration methods) and manage the development of the quarries accordingly.