The signals you get are likely a false positive, you must understand that there are likely alot of minerals in that sample all of them likely (traces)the predominating mineral would be iron,but the copper, and what ever else is in that sample will disrupt a magnetic field that could to the machine resemble gold, these machines are not 100 percent spot on,you must also understand that minerals are formed in a geological soup,and when cooled and solidified there are varying ratios of metals,all of which disrupt magnetic fields which send your machine singing, you can't assume any signal is definitely a positive for whatever its reading,