Putting the Minelab GPZ 7000 to the GOLD test

Well, the much anticipated GPZ 7000 has finally been released, and while some users put their name down for one before they really knew any info, others have been waiting patiently for more info to emerge, mainly performance reports from the field. In my opinion, a gold detector should be judged by its ability to find the gold that is still in the ground, so that’s what I did; just put my harness on, switched on the GPZ and went swinging in spots where I have found gold previously. Now, if you are hoping to hear about all the ounce plus pieces I found to date, well then you can stop reading now. It is still early days, and South Australia is generally gold poor, and the Adelaide Hills even more so. With only 3 public areas available to swing a gold detector, you can imagine they’ve copped a fair hammering, so in saying that, I wasn’t sure what to expect in terms of finds with the GPZ 7000. Fingers crossed that larger nugget with my name on it is waiting for me across the border. But before I get onto the field results, I just want to say a few words about the new Search Modes and the audio.

Gold Mode & Ground Type

In an attempt to simplify the operation of the unit, and allow the user to select the best settings for the conditions, Minelab have done away with having 8 different soil/timings options as found on the GPX5000 and have introduced a new selection method: Gold Mode & Ground Type. The Gold Mode function has three options: High Yield, General, Extra Deep, and the Ground Type has three options: Normal, Difficult, Severe (being a setting of its own). This gives the user seven Search Mode combinations to detect in for different tasks and ground conditions. Here is a brief overview of the various combinations:

High Yield/Normal – For very mild ground, this is what you want to be using!

General/Normal – In mild to Medium soils, this will provide excellent depth on most gold sizes

Extra Deep/Normal – The best depth combination available for very large gold, but only for milder soils

High Yield/Difficult – For finding the greatest number of targets in mineralised soils

General/Difficult – A good all round setting for most medium – high mineralised ground. Runs smoother and provides a slight depth increase over High Yield on larger gold.

Extra Deep/Difficult – This is a specialty setting for maximim depth in high mineralised soils

Severe – Use this on the worst ground conditions, for maximum performance on common gold sizes

Audio

The general audio of the GPZ 7000 is something that I really like. At first I struggled with the often complex target signals, but once you get used to the “Zed” language, it is very good. While larger targets at medium depth sound pretty much like a GPX series machine, the general tone of the audio is more crisp – it seems more closely related to the SDC2300. Identifying ground noises is much the same as with any of the MPS machines, but one thing I have been repeatedly fooled on is when in the Normal ground settings, a deeply buried nugget can sound the same as a charcoal hot spot. The response is broad and mellow but with a definite start and end. By allowing the auto tracking to do its work, by sweeping over the target area a few times you can often identify if it’s a ground noise or not, but as always – if in doubt, dig it out! Scraping a few inches of top soil off will soon clarify the situation.

So what I have done, is to break up my experiences with the unit in relation to differing levels of ground mineralisation.

Mild/Medium Mineralised Ground

So what would I class as Mild/Medium mineralised ground? If you are familiar with a GPX, you’ve probably come across areas where you are using Fine Gold and Enhance with a mono coil, and the machine is purring along. You “think” you can switch into Normal or Sensitive Extra so you try it, but after 20 mins remember how much you hate digging ground noises, so it’s back to Fine Gold. This is very common for me here in SA, and I know quite a few spots in Victoria that are the same. Pale clays, shale, a sprinkling of iron stone, with a generally mild appearance to the eye, but some nasty stuff going on underneath. In these types of soils with the GPZ 7000, you will want to be in General/Normal for maximum depth, or High Yield/Difficult for really good depth and still excellent sensitivity. Which option you go for will really come down to the exact ground type, the general size of gold in the area, and the EMI levels present. I have found that while the High Yield/Difficult combo will generally run smoother than General/Normal, it can pick up hot rocks in certain areas, and can be more susceptible to EMI.

In one gully, that is a perfect example of mild/medium mineralisation, I had tried to use monoloop coils here on numerous occasions with a SD2100, GP extreme and GP3500, without success. Only 1 time when the ground was really dry did I feel it was working well enough, but I still didn’t find any gold. I’d for some reason given up on this area for some years, but decided to give it another look with the SDC2300. In one afternoon, I was rewarded with 6 nuggets for over 3 grams. The nuggets were coated in ironstone and had a smooth waterworn appearance. I made the assumption that they would have been easy to find with the GPX5000 in Fine Gold, so soon returned with an arsenal of coils including a 15×12” Commander Mono and 16” Nugget Finder Mono. The result? The machine performed beautifully with both coils, but I didn’t find any colour.

With a GPZ7000 looking at me, waiting for my decision on where to swing the beast, I decided to go back to the same gully, but my plan was to first use the SDC2300 to see if I missed anything. I worked hard for 2 hrs and was rewarded with two tiny bits. Okay, time to get serious I thought, so put the SDC away and strapped on the Zed. Long story short, the 7000 performed flawlessly in High Yield/Difficult, Sens 8, and I managed 4 nuggets, ranging from 0.2 – 1.4 grams. The 1.4 grammer was literally 40cm away from one of the SDC finds, so must’ve been just out of range for the 2300. I also found several other junk targets at depth which proved the GPZ was seeing targets the other detectors had overlooked.

My gold tally with these two combos gives a clear advantage to the High Yield/Difficult combo, but the finds made in General/Normal (when the ground has been suitable) have been more impressive. I know it is early days, but I predict that the General/Normal combo is going to be responsible for some brilliant nugget finds in parts of NSW, quieter ground areas in VIC, and in generally quieter ground found in New Zealand, Brazil, Mongolia and the USA. There is also the combo of Very Deep/Normal, but I haven’t yet spent too much time in this mode, but if you know of a spot that has produced big gold and the soil is very mild, you should be on your way now!

Very Mild Ground

In very Mild ground, High Yield/Normal is the ticket. In the few patches I have gone over with very mild ground, predominantly quartz wash with scattered charcoal and only a sprinkling of ironstone, High Yield/Normal has been truly impressive. One spot in particular has produced a lot of gold, and has been hit hard with all manner of Minelab PI’s. Taking the “Zed” here was an eye opener. I set it to High Yield, Low Smoothing, Target Volume 11, Sensitivity 6 and began searching. My first 3 signals were nuggets from 0.8g – 1.4 grams and all were DEEP. As night fell I strapped on a head lamp and continued searching and was rewarded with another 4 nuggets, all around the same weight.

On a subsequent trip to the same area I chose a different spot further downslope as it had deeper ground. I first used my GPX5000 with 16” NF mono and Sensitive Extra, trying to maximise depth and sensitivity. After 2 hrs I got 1 nugget. I then strapped on the GPZ, and being a very hot and windy day the EMI was much worse than the previous session, which forced me to use High Audio Smoothing. The unit was now purring, but I did a test on the nugget I found with the GPX5000, and I found that by going back to Low Smoothing and dropping the Gain to 5 gave much better results. At first I was struggling to get any targets, but I started a loose grid and eventually found a piece of gold directly under a layer of charcoal. 2 m away was another bit, then 3 metres downslope I got a bigger piece and they just kept coming. I ended up with 9 bits of hackly, iron encrusted nuggets. I was sold.

Hot Ground

In really hot ground you have a few options at your disposal: Severe, Extra Deep/Difficult, and General/Difficult. Severe is the most stable, still has surprisingly good sensitivity, but won’t punch very deep. I liken it to Sensitive Smooth on the GPX units. Extra Deep/Difficult is also quite stable depending on the ground, will punch to great depths on larger targets, but Sensitivity to small targets is diminished. My deepest target with the GPZ so far was using the Extra Deep/Difficult combo, and I was surprised when a blob of lead came out the hole. I wouldn’t use this as a primary search mode, but if you have a suspicion that big gold may be lurking, it is definitely worth a go.

Difficult/General is the happy medium setting. It handles most mineralised spots very well, still has the capability to ping nuggets down to 0.2 gram, and will go surprisingly deep. I used the Difficult/General mode in a heavily worked area of diggings in Victoria and spent 3 hrs digging plenty of bullets and lead shot, a few 2 ft holes (unfortunately for junk) and also picked up 3 nuggets for my trouble. What impressed me the most was the sensitivity and depth I was achieving at the same time – the GPZ 7000 will prove to be a fantastic patch hunter.

Warts and all?

Okay, well no review is ever taken seriously if it is all peaches and cream, so there has to be some negatives……doesn’t there? Yes, as always, one thing can’t be the best at everything. Here’s a couple of downers:

– The coil is a touch heavy. The unit does balance nicely, and the Pro-swing takes a lot of the weight, but this doesn’t help you when lifting the coil over obstacles or doing side walls etc. On flat open terrain it’s very comfortable. If you are working undulating terrain, then the supplied swing arm is a massive plus. The only problem I have here is where to put your pick, as the GPZ will detect it if it’s anywhere below chest height!! Probably a good time to mention – leave the baby picks at home!

– The DOD configuration of the coil is good for getting extra ground coverage at depth like a conventional DD coil, which is fine in open terrain where you can swing left to right (did I mention this is going to be a great patch hunter ). However, the beauty of a round monoloop coil is that it has equal sensitivity around the rim of the coil, so you can swing it left and right, push it under a stump, guide it around tussocks etc. and you don’t have to think about the search pattern.

Considering I do a lot of my detecting in harvested forest areas, as well as overgrown old diggings, I won’t be offloading my GPX just yet, as the ability to select the right coil for the task is still a big plus. With this in mind, and the fact that most of the gold here is well under the 2 gram mark, I will be eagerly awaiting some coil options for the GPZ 7000. In the meantime, I have plenty of spots to revisit that are nicely suited to the 14” Super D.

In Summary

So how would I summarize the performance of the machine? Well, if you’ve used a SDC2300, try to imagine it with a 14” DD coil without any loss in sensitivity. It is great on the porous, prickly, ironstone encrusted and specimen gold at greater depth, but the GPZ’s field is still tickling the ground at a deeper level looking for the bigger lumps. Yes everyone likes to find big gold, but the thing I hate is coming home empty handed. The SDC2300 proved that you can find gold on a regular basis, even if the pieces are quite small, at the end of the day gold is gold and it all adds up. The GPZ 7000 has also proven to have the capability to find gold regularly, but the general size of the pieces are a lot bigger, and judging by the size of some of the holes I have dug, it will prove to be quite capable on larger lumps at depth.

Well I hope this review has given you some useful information, and I will be keeping you up to date with any tips & tricks as I get more time behind the wheel.

Happy Prospecting

Nenad Lonic