have been prospecting in an area with a lot of old gold mines in North Queensland using a Nox 800. Generally the area is benign, being on gold 1 and sensitivity of around 20.in an area of about 3x3 km. I was Detecting in one area when the nox went into high level chatter. One next to Creek and one in the creek. Both areas were about 4x4 m, once I moved the detector away from the area every thing became normal with chatter normal. I noticed some black sands in this area. Could a concentration of this be causing the chatter.