Chromites mapping using geophysical methods proved difficulty during the past several decades, because most Chromites are feature as podiform deposits which always pinch out and reappear in the same survey line. Several ground-based geophysical methods including: Microgravity, Magnetic and Controlled Source Audio MagnetoTelluric (CSAMT) have been used for chromites mapping. However, the result did not satisfy the need of the mining geologists. A successful case history of chromites mapping using induced polarization method based on spread spectrum technology in Luobusa Ophiolite, Southern Tibet, is presented in this paper. Wireless Sensor Network (WSN) based electromagnetic system (SinoCGI) is used for the data acquisition, which is its first time using in China. Luobusa chromites mine is one of the chromites deposits with maximum mineral production in China. But drilling and ground-based geophysical exploration did not meet the good deposit for sustainable yield in the past several years. Experiment measurement in the lab indicates that the chromites samples and its host rocks sample characterize by different rock apparent resistivity and chargeability. Based on this, we conduct induced polarization method based on spread spectrum technology to map the potential favorite deposit. We carried out around 500 IP scanning stations and three 2-D IP sounding profiles in the working area with acreage of 0.5 square kilometer. The favorite chromites deposits which features as conduct and low polarizability has been mapped. Four boreholes have been drilled to verify the ore delineation by IP method, three of them met chromites, the other one met chromites mineralization. The result gives a new recognition on geophysical methods to chromites mining geologists in China.

Southwestern Tibet plays a crucial role in the protection of the ecological environment and biodiversity of Southern Asia but lacks energy in terms of both power and fuel. The widely distributed geothermal resources in this region could be considered as potential alternative sources of power and heat. However, most of the known geothermal fields in Southwestern Tibet are poorly prospected and currently almost no geothermal energy is exploited. Here we present a case study mapping the Mapamyum (QP) geothermal field of Southwestern Tibet using audio magnetotellurics (AMT) and magnetotellurics (MT) methods. AMT in the frequency range 11.5-11,500 Hz was used to map the upper part of this geothermal reservoir to a depth of 1000 m, and MT in the frequency range 0.001-320 Hz was used to map the heat source, thermal fluid path, and lower part of the geothermal reservoir to a depth greater than 1000 m. Data from 1300 MT and 680 AMT stations were acquired around the geothermal field. Bostick conversion with electromagnetic array profiling (EMAP) filtering and nonlinear conjugate gradient inversion (NLCGI) was used for data inversion. The AMT and MT results presented here elucidate the geoelectric structure of the QP geothermal field, and provide a background for understanding the reservoir, the thermal fluid path, and the heat source of the geothermal system. We identified a low resistivity anomaly characterized by resistivity in the range of 1-8 Ω·m at a depth greater than 7 km. This feature was interpreted as a potential reflection of the partially melted magma in the upper crust, which might correlate to mantle upwelling along the Karakorum fault. It is likely that the magma is the heat source of the QP geothermal system, and potentially provides new geophysical evidence to understand the occurrence of the partially melted magmas in the upper crust in Southwestern Tibet.

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