Exploration had indicated that cap rock was relatively uniform in thick
ness and that copper mineralization was gradational. The pit limits were to
be assay boundaries rather than geological features, and it was decided that
they could be set by consideration of a line rather than a volume, thus
reducing the calculations required.
Before acceptable theoretical slope lines were established, certain con
ditions were assumed. On the basis of experience at Castle Dome mine, it was
decided that benches 45 feet high would be satisfactory and that a back slope
of 45° could be safely maintained.