Advantage of a small (or large) DD coil on variable ground.
Not long ago I was out detecting an area not far to the north east of Ararat in Victoria, I have found good gold close to surface scattered over a wide area. There is evidence that there was substantial surfacing done most likely in the rushes of the 1850’s. No gold was found in the deep surfaced area’s but it was found up near the edges of where the cutting meets with the original ground level and beyond on the eastern side of the ground. It is probable that the gold came from the small mountainous country on the eastern side of the diggings.
I was using a small eight inch mono coil and it was a little noisy on this ground but over two detecting days I found just over an ounce of gold as small water washed pieces.
There are some wash area’s that have been dug into on the side that made a lot of ground noise when the mono coil was pushed into the cut out part of the ground, if there were small nuggets in this cut out I would not of been able to hear them as a good target response and definitely missed any gold that was there.
On a third visit to the site I brought with me a small 10 x 5 inch DD type coil that I wanted to use over the variable ground, I was using my trusty Minelab GPX 4500 in all instances and found that I could increase the input gain by around 20% and not have much, if any increase in ground noise. I pushed the DD coil into the opening on the side of the cut and straight away I had a weak but repeatable signal, I had the detector in Enhance mode as I was only looking for small gold. I moved the coil in the cut to a quiet section and fast tracked the detector in the cut and locked it into fixed ground balance, then moved the coil towards the target and I now has two distinct signals.
I believed that the signals were coming from the top of the cut and thus started scraping out the small rounded rocks and clay, as in the picture two lovely gold nuggets were found.
The other gold was found at the sloped part of a cut out that went towards the side of the cut were it was the close to original ground but a a few inches below. I have previously worked this area with a selection of mono type coils and though I was using a modded detector the ground noise here was a lot more than I have found at other sites close by.
In this type of ground the DD coil has proven that it has a place in the detecting world, nearly every prospector that I see are stuck in the mindset of using mono coils and in some instances missing out on gold in noisy ground.
Since I started detecting in 1980 most of my gold has been found in noisy ground and for the last ten or so years I have been using mono coils from 6 inch to 48 inch monsters.
This brings me to think that I need to go over all the old ground using a DD coil of various sizes, crank up the gain as a DD will allow the use of more gain and will also allow the use of a higher sampling speed on the pulse induction detectors as ground noise is greatly reduced. I should Note that my GPX 4500 is not factory standard as it has extra adjustments that help with optimising for coil size and gold depth and size. The same detecting techniques can be generally be used with a standard detector with no problem.