Aluminum is a crazy thing. Run over an aluminum can with a lawnmower and you have just created a full spectrum of target responses. Throw in 4 decades of pulltabs and you got yourself a challenge. Depth of target is the best indication for me. I never find to much aluminum past 4 inches. When you go to pinpoint larger pieces of aluminum will show a larger contour. Most aluminum responds stronger for me in the 7.5 kHz frequency, but there is always exceptions. This is really a tough one to pin down. If your looking for gold you just have to dig it all for awhile and try to profile your location. Oh, and by the way. If you find the secret to differentiating aluminum please send me a PM. We would not want to let everyone know about this ...

Keep Swing'in
Jack