Bench Testing of Gold
In order to bench/lab test for gold you will need to place the detector on a table and place one of the smaller coils on it. In order to do this you will need to follow the manufacturer’s instructions in order to adjust it to the all-metal mode of operation. If it only works in the discriminate mode, make sure that no discrimination whatsoever is used. Set the audio threshold so that you can only hear a very dim sound and you will need to make sure to take all the metal off of your hands and arms like rings and watches, jewelry etc.
You should then move a sample of ore over the search coil and pay attention to the outcome. if the sample of ore does not have a high proportion of metal in a way that is detectable, you will be able to hear the sound increase as you pass the sample over the coil. If the sound however, dies out when the ore sample is passed over the coil, it means it has a predominance of mineral or magnetic iron. The ore sample could still have metal, but it means it has more mineral than metal in it.
Something that should be kept in mind is that whenever you do these types of tests, you should always use a good high quality metal detector. You should get a detector that has a true non motion all metal mode or a discriminate mode with factory calibrated metal and mineral discriminator at its zero control setting.
You can try to get ahold of some samples of silver, gold ore, galena and some normal rocks. By doing your bench tests you will become familiar with the type and amount of response to low grade ores as well as high grade ores. Besides that, a lot of types of ore do not give a response to metal detectors. Only the samples that have metal in the conductive from and do not have enough amounts to interfere the electromagnetic field will give a response to even a quality detector.
For instance, some big sized garnets will respond as mineral due to the fact that garnet has enough magnetic iron to respond. When you are checking samples that have had a metal response, you will usually observe a metallic look on the inside. When samples that look metallic but respond as mineral are slabbed or sawed, you will usually notice a streak of magnetic iron on the inside. Due to the fact that there was enough iron to supersede the small amount of metal, the sample responds as mineral.