Strip ratio problem for PCPG review course
Strip ratio problem
Surface mining of a coal seam involves many costs (e.g., removal of overburden, extraction of coal, transportation, reclamation). Suppose the economics limit mining to portions of the deposit with a 2:1 strip ratio (i.e., you can mine the coal as long as the overburden is not more than twice the thickness of the coal seam). Which portions of this map could be economically mined for a profit?
Answer - thinking about the problem
Just basic geologic awareness: Depth to the seam is equivalent to the thickness of the overburden.
Structural geology knowledge: Structural contours describe the spatial elevation (or depth relative to a surface datum) of features like the top of the coal seam. Isochore maps describe the vertical thickness of subsurface features – similar to isopach maps, but isochore maps measure vertical dimensions, and isopach maps measure thickness perpendicular to top and bottom surfaces.
Answer - step 1
1. Identify intersections where the depth (blue) is twice the thickness (red)
Answer - step 2
2. Connect these control points with a continuous boundary line that divides economic from subeconomic.
Answer - step 3 (final)
3. Determine which side of the boundary is economic vs. subeconomic by picking a random intersection of contours and calculating the depth:thickness ratio.
