Superconducting Quantum Interference Devices (SQUID) are excellent sensors for high-performance electromagnetic (EM) geophysical prospecting. The SQUID chips exhibit low magnetic field noise level of 3 fT/√Hz, and the swing of the SQUID V-Φ curve reaches ~150 μV. This characteristic enables broadband signal acquisition up to 3 MHz with a flat spectral response for the sensor.
The experimental configuration employed the short offset TEM (SOTEM) with the survey line 500-2000 m away from the electrical transmitting line. Quantitative comparative analysis of SQUID performance against conventional induction coil receivers (Phoenix V8 system) was conducted. Post-normalization data revealed the SQUID system achieved a noise floor of 0.02 nT/s, which was improved by two orders of magnitude compared to 3 nT/s for the coil receiver.
The geophysical explorations were carried out at more than 20 metallic deposits. A notable achievement was the successful identification of the gold-bearing structure concealed beneath approximately 200 m thick low-resistivity overburden. In the porphyry copper deposit exploration across ten parallel survey lines, the exploration result fitted the drilling data well until 2000 m depth. The maximal exploration depth of 3400 m was achieved at a deep-buried lithium brings according to the resistivity profiling map.
HTc SQUID is also fabracated by helium-ion-beam process with noise level of 100fT/√Hz. It will be a more convenient method for TEM prospecting.