Mapping chromite deposits with audio magnetotellurics in the Luobusa ophiolite of southern Tibet

The exploration of podiform chromites in the Indus Yarlong Zangbo suture zone of southern Tibet has proved difficult in recent decades because most known deposits pinch out and then reappear in the same direction. A number of ground-based geophysical approaches, including gravity, magnetic, and controlled-source audio-frequency magnetotelluric methods have been applied to explore for these chromite deposits but have mostly failed to delineate prospective areas. We present a successful podiform chromite exploration case history that is based on audio magnetotellurics (AMT). More than 8,000 AMT stations were utilized in this study within a 10 km2 area of the ophiolite belt. Line separations were 80 m or 40 m and station separation was 20 m. We implemented Bostick conversion and non-linear conjugate gradient inversions were implemented for data interpretation, while two-dimensional (2D) resistivity sections and three-dimensional (3D) resistivity imaging were used to elucidate the inner structure and distribu...