Rio Tinto Group, the world’s third- largest mining company, said its Bunder project in India is the world’s biggest diamond discovery in the past 10 years.  “It’s in a pre-feasibility study right now so a major drilling program is under way to define the resource,” Eric Finlayson, the London-based company’s head of exploration, said today in an interview in the city. “A mining lease has been applied for so we are waiting on that. It’s the largest diamond discovery in the last 10 years.”