Today I took my Whites GMT and Exterra 70 to some very hot ground in the gold feilds to see how each compared. I took 2 test nuggets one about point one of a gram and the other about half this size. The ground is very mineralised with hot rocks and conglomerate. I first tried the whites using a six inch eliptical dd coil. The machine was noisy but easily picked up both nuggets, the larger one at about three inches, smaller around 1.5inches. the signals were sharp an clear. the hot rocks and ground noises were easy to identify as they would fade out as you moved the coil slowly over them.I was able to run the machine in auto tracking at setting 8 out of ten in sensitivity with the V Sat at 10. the threshold was set very low almost silent. I didnt find any other gold but managed to find some very tiny bird shot which gave the obvious zip zip signal. Next I tried the Exterra 70 with the six inch DD coil. I ground balanced it, noise cancelled set the sensitivity at 25 in prospecting mode and in tracking .Then swung it over the two test nuggets, and got no response ! I tried ground balancing alongside the nuggets the swinging over them super slowly and once again no response. I turned the sensitivty up to 30 and tried again and I finally got a weak signal only on the bigger nugget, but the coil had to be just about touching it. I turned off tracking and manually adjusted the ground balance slightly positive, and then swung over the nuggets I got a weak signal from both nuggets but in the highly variable mineralised ground soon had to turn it back to tracking.I found that running on 30sensitivity wasnt practical in this area and had to turn the machine down to around 20 to get any reasonable level performance. I found when it did find a target the signal response was poor and could easily be missed in ground noises. To give you an idea of the ground conditions the ground balance reading on tracking stayed at around 11-13 mark. In mild ground it would be in the 60s. This was obviously an area and task out of the Exterras league, I am sure in milder ground conditions eg pipe clay heaps the Terra would pick up these tiny nuggets. Has anyone any tips on improving the Terra s performance in highly mineralised ground, I would be interested to try them out. Seeya Neilo
