 INCO's 1991 proof-of-concept study in Sudbury, Ontario, Canada sensed a 1750-meter-deep nickel deposit.Falconbridge followed with a feasibility study in 1996 that accurately located two Ni-Cu mineralized zones at about 800 m and 1350 m depth.Since then, both major and junior mining companies are increasingly using MT and audio-magnetotellurics (AMT) for both brownfields and greenfields exploration.