GEM2-A

GEM-2A Specifications

Total length and weight 643 cm (21.1 ft); 120kg (250 lbs.)

Tow cable length 35 m (120 ft); diameter 2.54 cm (1 inch)

TX-RX separation 510 cm (16.7 ft)

Coils configuration Horizontal coplanar

Transmitter current 60 amp RMS max

Transmitter moment 500 Am² at 330 Hz; 160 Am² at 1 kHz

16 Am² at 10 kHz; 4 Am² at 40 kHz

Power supply 28 VDC

Frequency range 300 Hz to 48 kHz

Number of frequencies Programmable (typically 5)

Sampling rate 30 samples/sec for all used frequencies

GEM-2A is a programmable, broadband EM sensor for geologic investigation, groundwater survey, and mineral exploration. The system utilizes a single set of transmitter-receiver coils for all frequencies, rendering an advanced HEM system with high sensitivity, light weight, and minimal drift. The system upload (frequencies, powerline monitoring, etc.) and data download are done by WinGEM software operating in Windows. With a mouse click, WinGEM also converts GEM-2A data to apparent conductivity at each frequency and to apparent susceptibility at the lowest frequency.

GEM-2A Data from a Kimberlite Pipe

Apparent conductivity maps. The prominent high in the center, elongated N-S, is the northern extension of a kimberlite pipe. Also shown is an apparent susceptibility map computed at 1,325 Hz. The total field magnetic map is shown for comparison.

Electromagnetic Induction Spectroscopy (EMIS)

Each mineral deposit, depending on its bulk electrical conductivity and magnetic susceptibility, should exhibit a unique frequency dependence in its inphase and quadrature responses. EMIS is a method of identifying a particular geologic body based on its broadband EMI spectrum. In the example below, Points A and B are on a kimberlite pipe, but Points C and D are not.