Minelab X-Terra 705 Black Sand Feature

I just stumbled upon a pritty cool feature. I was going along a wash and hit the ground balance button to see what reading I was getting and noticed if I kept the ground balance reading display on and scanned the area it would make a unique ping pong tone over black sand. I checked the area in prospect and coin mode and none of them made that tone. I was able to follow the entire path of the black sand in that area. Pritty cool feature that I had no idea about. Anyway just wanted to share that with you all.