Sajuu. The problem is....you will never know what the target is until it is in your hand. That means you have to dig it to know for sure. Wasted time or not. That is all part of the "game."You can choose to walk away from a junk sounding target but you will not know if it is junk or not unless you dig it. I dig all signals & I still get blown away by signals that sound so much like junk but have turned out to be gold. That is why I dig every thing....because you just dont know & cant tell 100% by the sound of the signal alone. I have also dug many junk targets, & once out of the ground & rescanned before back filling, have got a nice mellow gold signal. The junk signal masking the good mellow signal that was gold. Has happened to me so many times. So I just dig them all.
The problem with discrimination in a dedicated gold machine is that gold by its very nature is never of the same purity from goldfield to goldfield. Unlike coin & relic machines that have a much more accurate discrimination ability which I believe comes down to them running at lower frequencies than gold machines, but also due to the objects that those detectors are used to hunt for. Coins are all made from a known amount & mix of metals. Usually non magnetic, Except our stupid new New Zealand coinage which has an iron content. So coin machines discrimination has been calibrated on known metal content & coin size. Hence they can even tell you what the coin is & how deep its. Unlike gold out in nature. Being mixed with different & varying amounts of other metals & impurities. Copper & silver being the most common but also others. Gold & ironstone are often together...so what is the discrimination going to tell you about that mix?? It is the variation of the amounts of other metals/impurities mixed in with the gold from nugget to nugget that is the problem with accurate discrimination. One of the very first objects of gold that I found when starting out with my GP 3000, with DD coil & in discrimination mode was an old rusty nail. The detector was blanking out in discrimination, but because I was learning the detector & wanting to get familiar with the different sounds....even objects of discrimination, was to dig every signal. That nail was jammed in a crevice in the bedrock in a shallow creek & coated with flakes of gold caught up in the rust halo of the nail. From that day on I have dug every thing. Dont use DD coils & always detect in no discrimination. I moved on from the 3000 to a 4500. Still have my 4500 but I am full time on the Zed at the moment.
Technology is what it is at the moment on gold detectors. The Minelab Pi's do have a discrimination ability with DD coils. But I think you will find that the more successful operators dont detect in discrimination & dig every thing. I also believe the discrimination circuitry takes away a bit of grunt from the depth & sensitivity of the detector & so you arent getting full depth & sensitivity on those slightly deeper bits of gold. You want all the depth & sensitivity that your detector has the capability of giving you. The discrimination in the detectors is programmed to be on the cautious side & when dealing with gold not worth the risk of walking away from gold because the detector is telling you it is iron....it just may not be. Some VLF gold detectors have an iron probability form of discrimination & VDI number read outs. The VLF's lack the depth of the Pi's. An accurate 100% trustable discrimination in gold machines is still a thing of the future. At the moment it comes down to your choice to dig a signal or not. I know I will keep on digging them all.
Knowing how to operate your detector to its full potential in any goldfield situation & digging all signals is what will lead you to success.....at the present point in time.
Good luck out there