The study of gold deposits in Australia
June 18, 2005
Field works
The object of the study was the middle part of the gold deposit in Big Nugget Hill, Australia, which stretches to the north-west for many tens of kilometers with width of 50 to 300 meters.
The study aimed at contouring of gold-bearing quartz bodies at the depths of 50-100 meters using GROT-10 and GROT-11 georadars and assessing the capabilities of GPR to find and follow steeply dipping wiry bodies in the contrast flooded geological medium with significant anthropogenic disturbances.
The ore zone is composed of quartz stem reef occupying the central part that goes on the flanks to the zone of small wiry reefs of the same composition. The transition zone is gradual. The ore adjoining soils are argillic with iron accumulation. Host rocks - carbonaceous shales with mist sulfides. The ore formation - gold-quartz.
Fig. 1. Radargram.
The radargram on Fig. 1 was received during the coverage of the track transversely to the ore zone using GROT-11 GPR with a 4-meter antennas. That equipment allowed scanning the ore body to the full visible depth. Red indicates the maximum value of the amplitude of the reflected signal.
Fig. 2. Radargram.
The radargram on Fig. 2 was received during the coverage of the track transversely to the ore zone using GROT-10 GPR with 1.5-meter antennas. Red indicates the maximum value of the amplitude of the reflected signal.
Fig. 3. The trace and the radargram with maximum of the amplitudes of the reflected signal marked red. GPR data from GROT-11 provided using GROTDATA processing software produced by Timer CJSC.
Figure 3 shows that the gold reef can be traced to a depth of 80 meters, then the signal is attenuating. Analysis of the radargrams shows that the soil moisture significantly affects the received signal and it is an indirect sign of the quartz reef localization.
Fig. 4. The radargram of the track crossing gold-bearing reef, and two signal traces from the 8th and 12th meters of the track.
The radargram of the gold deposit on the Fig. 4 was detected from 10 to 28 meter of the track with penetration depth of 80 meters. There is a marked difference between the GPR data obtained on the track points corresponding to the loam (the trace on the left, from the 8th meter of the track) and the gold-bearing reef (the trace on the right, from the 12th meter of the track). Moist loamy soils have higher conductivity causing transformation of the received signal where additional low-frequency components appear.
As a result of the GPR research on site there were inhomogeneities revealed such as tectonic faults, ferruginization zones, quartz reefs, including the reef adjoining zones of crushing and argillic alteration.
The gold-quartz deposits were located and contoured at the depths of up to 80 meters. The expected capacity of the horizontal reefs including adjoined zones ranges from 3 meters on the southern and northern flanks to up to 10-15 meters in the center. The gold content ranges from 1.5 to 120 g/m.
Thus, the differences in the dispersion of media with different conductivity allow contouring the gold deposits using the GPR.