Herencia Resources said its potential joint venture partner OZ Minerals had discovered the target area of its Guamanga project in northern Chile could be larger than first anticipated.Australian mining group OZ Minerals is conducting due diligence at Guamanga with a view to taking a controlling stake in the iron oxide copper gold project. It has told AIM-listed Herencia that it now wants to expand the project area and it has started buying additional exploration licenses.Herencia's Managing Director Graeme Sloan said: "OZ Minerals believe that Guamanga has the potential to be bigger than first thought. They are aiming to expand the joint venture area and bring it within the umbrella of the agreement with Herencia."He said that while due diligence was taking a little longer than initially anticipated he believed the outcome would be "a significant positive for all parties."Shares in Herencia were up 4.0% at 0.64p at 09:01 on Friday.TB