GPZ 19 compared to GPZ 14 - Nugget Dig!

Like all things new, it takes time for results to feed back into the general community. Overall, there have been some very good reports from people using the GPZ 19 coil. Early adopters who have been tough enough to brave the heat of summer here in Australia have been reaping the rewards, as well as fast-tracking their experience levels for when the weather cools off, come Easter time…

Late last year, on Christmas Eve, I woke to a cool morning with cloud cover and some spare time on my hands, so I got up before the sun and headed for one of my test patches in one of the Clermont General Permission areas here in Central QLD. (You can find maps of these General Permission areas and access requirements on the Queensland government website: https://www.qld.gov.au/recreation/activities/fossicking/central-gold/)

My chosen location has produced a lot of gold for me over the years and is one of my favourite sites to test new equipment, as I am extremely familiar with the area. Finding gold there with new equipment means there is an improvement in performance over what I’ve used previously, especially due to the intimate knowledge I have of this site.

This location is extremely variable and mineralized. The old-timers potholed and surfaced it back in the late 1860’s and, since the advent of metal detectors, it has continued to produce ‘sluggy’ gold to this day, particularly since the SD 2000 was released in 1995. I first started testing metal detectors here in 1996 and have revisited the location hundreds of times over the years, the most productive years for me being with the GPX-4500 and the Enhance timings.

On this occasion, I had a clear goal in mind: I was chasing the deeper more solid nuggets, so to that end, I was prepared to only get one signal all morning or even no targets at all. For heavy ‘shotty’ gold General/Difficult is the GO-TO mode: it provides a clear advantage over High Yield/Difficult in noisy variable ground and is the mode I HIGHLY recommend for GPZ 7000/GPZ 19 users in Victoria and W.A. where:

• the gold-bearing soil can be deep;
• surface minerals are highly mineralized and variable;
• the gold tends to be heavy and solid in nature.

General/Difficult tends to ‘kick in’ on nugget sizes from around 10 grams and up, depending on shape and depth.  Conversely, High Yield is very good at detecting the tiny nuggets and specimen gold. 

It took me four hours to lock onto a suspect target response at the base of a tree right up under the edge of an old boy’s digger hole. Initially the response was extremely faint, just like someone twanging the surface tension of water without breaking through, causing a ripple like waver in the threshold that would not go away. After digging away and widening the hole, the signal improved and I soon realized this was a golden opportunity to compare the GPZ 14 coil against the GPZ 19, so I went back to the 4x4 and grabbed the smaller coil and my smartphone so I could film the event. Holding a smartphone, whilst swinging the GPZ 19 one-handed, is no easy task, so I apologize for the shaky footage! It is also very hard to convey the distances of the coil sweep over the target when filming from above, but experienced users should be able to easily see the differences between the modes and coils.

What is of particular importance is the performance difference between the two coil sizes. Minelab have claimed an “Average 30%” depth advantage of the GPZ 19 coil over the GPZ 14. In this case the video easily shows the depth advantage, which, in some cases, can be a lot more! You will notice in the edit I have not cut the “swing over target” footage when comparing modes except between coil changes. The comparison footage is shown in real time without edits.
(I would also like to point out that even though General/Normal was providing a reasonable signal response, the Normal Ground Type is not really practically usable at this specific site due to the extreme variableness of the ground.)

All modes were individually Ferrite balanced and a local Ground Balance (GB) was also achieved. My preferred method is to ‘pump’ the coil between changing modes. This is to fine tune the GB which was set in Auto. In situations like this, once it’s been decided to dig, I highly recommend operators to pre-configure the USER button of the GPZ 7000 to the Ground Balance function and once balanced, FIX the GB by placing it in Manual. If you pay careful attention to the footage you can hear the Auto GB taking the edge off the target response after repeated swinging of the coil. This is especially noticeable with the GPZ 19 coil and the settings that produced the weakest signal response.

So take a look at the video! I got a massive ‘buzz’ out of the difference in signal response between the two coil sizes…

If I’d only had the GPZ 14 coil on that day, that nugget would still be in the ground. It makes me wonder what else I‘ve missed at other locations around Australia!

The nugget was recovered at 22+ inches depth, weighed in at touch over 26-grams and was a beautiful water-worn crystalline “Herring Bone” nugget. A few days after Christmas I returned to the location and scored a fantastic 30-gram piece right out in the open with dig holes all around. I know for a fact that I have had my GPZ 14 coil over this exact ground, and only very recently. The signal was a real eye popper and what I would call an easy “dig me” response; more proof the GPZ 19 coil is providing an ‘edge’ over the GPZ 14 when the gold is present. On New Year’s Day I returned in 40 degree Celsius temperature and ‘nailed’ a solid little 12-gram slug at reasonable depth, taking my total for 12 hours detecting at this location to a tad over 2-ounces!

The GPZ 19 coil requires commitment and an understanding of the right locations required to see its advantages, it is not a prospecting tool to improve coverage unless you’re strong of arm. The real benefits are in the deeper soils, chasing the ‘sluggy’ pieces. However, I’ve also done well in High Yield chasing large specimen gold and Enrichment type deposits. In Normal Ground Type and quieter soils, it is mind-boggling how deep the GPZ 19 detects and also surprising how sensitive it still is on the smaller stuff, but it does require INPUT AND EFFORT from the operator to achieve these results. I’ll be swinging the GPZ 19 coil a lot more this coming winter – will you?

Jonathan Porter

Aurum Australis

To read more about the GPZ 19 Super-D coil, click here.