Apparently some of this "open cast" "underground" issue stems from MinAmb's interpretation of the wording of the concessions/contracts.

Venezuela offers two kinds of concession; alluvial or surface mining (used by the local small miners) and "hard rock" concessions mainly used by larger operators like KRY or GRZ where mining continues into the sub-surface rocks.

Apparently (I am not an expert in Spanish) the description used for the "hard rock" concession can also be interpreted as "vein mining" which of course is usually typically mined by underground methods. Ortega is hanging her hat on a literal interpretation of the wording to extrapolate that "vein mining" only allows underground operatons and excludes "open cast". However there is no specific "open cast" concession and the general industry use in the past has always considered that the "hard rock" concession refered to the whole ore body not the method of mining it.