Firstly, that the grades for zinc and copper were excellent when carried out by IGME and Outukumpu, and Secondly, that with advances in technology over the last 20 years, the exploration potential may be greater than initially thought.

Source: https://investingnews.com/hispania-resources-announces-the-preparation-of-its-three-year-exploration-program-at-las-herrerias-on-the-puebla-de-la-reina-property-in-spain/