Off Grid

Jeff Thanks these comparisons. I know Steve and others have cautioned about comparitive tests in the past, and with good reason, but some data is always better then no data. I recall you had good things to say about the Legend some time back so I've decided to get one to back up (or take over from) my trusty GB2 that at 71 kHz probably has left stuff in the ground in my patches. One question. What is the makeup of the AZ dirt that you used? It looks like weathered granite wash to me. If you were to run a fridge magnet over it what percentage of magnetics would you get? Other stuff?? I was thinking of trying to replicate it, see if I get your results, run the GB2 over it and then add to your data. Be a while, mid-year or so. Of course there's probably someone down the street from you with a GB2 already 🙂.`

Why did you choose the ATX rather than the Axiom? If you are going to try out an Infinium coil with the ATX make sure there is zero cable movement relative to the coil. The slightest movement will make the coil noisy (as I found out. 101 stuff I know, 😬). After fixing that snafu if anything the Axiom was quieter than the closed ATX DD.

Search "mylonite textures" on Google and have a look at the images.

My GB2 with the 10" coil is still my workhorse detector and I never used the 6" until recently. The 6" did find very small gold in an area that the 10" no longer produced from. Say, another 2grams from where the 10" had found forty. I think the main reason for the extra was the 6" could get into spots the 10" couldn't. Prior to the GB2 I had the original GB with the 6" and the 14" and my limited experience with that was that, all other things being equal, any depth gain from the larger coil was more than offset by the fact that in patch hunting it was, on average, further off the ground to avoid legions of small bushes and rocks. If you are in WA say detecting a gravel strewn billiard table I guess that wouldn't matter as much. I've thought about getting a 14" for the GB2 as well but when the price delivered South Africa isabout 3x US price I'm not that interested. The theoretical depth gain over the 10" is about 5% (15% over the 6"). A lot less than than scan height loss. Yes, you can kick the rocks aside at a huge loss in ground covered per day. In my case I'm not usually short of ground to cover but I am short of time and energy. I do have the 13" DD on my ATX and so far I never found anything with it that the GB2 10" couldn't also detect but I do have bone dry, low mineral, thin soil. Perfect for the GB2. My advice? Take the wrapping off your 10" coil and try it on an area the 6" thas already thrashed. If that works buy the 14". If that doesn't work let me know and maybe I'll buy it off you. Put it in a padded envelope and post it. There's a 25% chance it won't get stolen en route. Glad to hear there's still GB2 believers out there. I was getting lonely.

Probably vesicular basalt with zeolite crystals

Are they more sensitive than even a GB2 with the 6" coil and running at 71 kHz ?? I thought that, because of the frequency, the GB2 was hard to beat on very small gold.

I'd leave it be Steve. I've had a shot are identifying the specimen once or twice. They can be interesting to the person responding and maybe educational. I still cringe when, as a geologist, I overthought one post that turned out to be quartz 🤐

Reg, these days there are likely more expat South Africans in Aussie than there are left in South Africa so there can't be a butcher far from you that doesn't stock biltong and/or droewors (dried sausage). Ambrosia! Suspend disbelief and try some. Ostrich if you can get it. On my trips (usually about a week and under pretty rough conditions) I tend to pack a couple of whole salamis, sardines, hard boiled eggs, oranges and dried fruit for the field. The biltong has usually disappeared within 200km of leaving home. Pasta and a variety of bottled sauces for camp. Always open to other ideas.....

If the density is correct then my guess would be impure barite. If you have access to a really hot flame, like a brazing torch, stick a corner of your rock into it. If you get a pale green flame it's barite. If your density is high then maybe magnesite (3-3.2).

Boot nails are one thing but I figure that firing off No.5 birdshot in gold-bearing areas should be a capital offence.

Thanks for the post Phrunt. I was really interested to see the incremental finds from this patch. The nuggets look more elluvial than alluvial; is that so? Any idea to what extent the extra finds were due to the 6000 & 7000 seeing deeper in previously searched ground, the size of the patch expanding over time or something else?

Thanks for these replies, very useful. Like much else, this topic was all done and dusted long before I joined the forum. Being a retro sort and a GB-junkie it looks like I need to add a GB Pro to my collection.

This recent video features the Nemo. If I were 20 years younger I'd be tempted but dry-land detecting is my limit these days. They earn every gram they find.

I don't recognize the detector but I do recognize the general setup. They are probably chasing vein gold. If it was alluvial under thick overburden you'd see it blocked out into little squares. The first guy down to the gravel wins as he's tempted to skim his neighbours reserves. Of course they are aware of this so it only works when the gravel is below the water table (I'm not kidding). Take a deep breath dive, grab gravel, surface, repeat to fill bucket. Sniping Africa-style. It's a measure of desperation I guess. At one locality in Angola back in the day some genius decided to make an underwater crosscut with predictable results. The whole digging was then abandoned because of the dead spirits.

It's an enduring mystery to me why anyone in their right mind would take jewelry to the beach in the first place.

Full disclosure here, I'm a data junkie, but whenever I see reference to hot ground I wonder if anyone has ever put together a simple method of measuring hotness? I guess that would be in WA if anywhere? I realize that there's many factors involved as Minelab's great introduction below discusses. If you set aside salt beaches and wet clay and just consider dry-land detecting would the percentage of magnetite, or whatever a magnet picks up (ilmenite, maghemite) be a reasonable measure of hotness? If so, what percentages would constitute low mineralization thru hot mineralization ? https://www.minelab.com/__files/f/11043/KBA_METAL_DETECTOR_BASICS_&_THEORY.pdf

I've hunted through the various press releases on this and have yet to see anything that gives the actual composition of the minerals. Has anybody had better luck on what's so new? I assume they are likely some new iron-nickel alloy or maybe iron and/or nickel with a new crystal form?

Ever since I read Steve's comment that Africa is Garrett's real target market for the Axion I've been really curious as to exactly where they hope to sell large volumes? At the nominal Rand price that Phrunt posted (I thought they were about R80k) they would have to be smoking something if they hope to sell volumes in South Africa. In Zimbabwe there are other constraints as a friend who has a small hard rock operation pointed out to me recently: "I have to admit I’ve hardly used my GPX5000, apart from time constraints there is no law in our gold fields and it is potentially dangerous for a white man to walk around the bush detecting. We’ve had two murders and one decapitation in the district in the last year, all gold related." What he does use his 5000 for is to scan the end-of-shift miners when they exit the shaft for high-grade "souvenirs" there's a lot of those. Theft is an endemic issue all over Africa so that's maybe what Garrett are thinking of? But a hand-held wand is good enough for that as I found out at Ashanti back in the day. Somehow a piece of high-grade had fallen into my overalls during a field trip and the wand picked it up right away. Everybody else on the visit seemed to have had the same issue with hitch-hiking rocks 😬

Quite a while back I decided to follow in Steve's footsteps and made up own ATX-lite. That being the ATX box as supplied but slung from my left shoulder using an old laptop bag sling + an Infinium 10x5 DD mounted on an old Gold Bug shaft. The main reason being to reduce the weight on by right arm and increase detecting time between cramps. I don't like the bungee Garrett supplies with the ATX. The ATX-lite set up is a bit clunky as the box swings around a bit on the sling but I like the ability to play with sensitivity, threshold, ground balance on the go. The Infinium coil on the GB shaft is just perfect. Even lighter than the GB2. Of course in the meantime Garrett developed the Axion which (for a price) makes my mods redundant and it looks like I have the smallest niche setup in detecting history with a total addressable market of 1! N.B. In due course I'd be interested to know how what the Axion can do that the ATX can't do on dry land. Anyway, just got back from a trip where I was lucky enough to find a new patch (on the last day of course!) and try out the ARX-lite against my work-horse GB2 with 10" and 6" coils. I probably have a few hundred hours on the GB2 by now and maybe 50-100 on the ATX original and ten on the Lite. To be fair I think my conditions are just about perfect for the GB2. A few inches of bone dry soil over sandstone and siltstone. Close to zero magnetite but I must do a test next time. It's hard to get scientific when there's nuggets to be found. No EMI at all, not even 1 bar on the mobile. Very few hot rocks but the sound is real distinctive (like a cracked bell). I run the GB2 on sensitivity 7-8 , low mineralization setting, audio boost. Ground reject about 6.5. The ATX-lite sensitivity around 10. Headphones on both machines (Garrett as supplied & a beat up old Phillips on the GB2). Seventeen nuggets, 9.5g total. Largest 3g but most cluster around 0.3g. Most I found with the 6" GB2 coil (that happened to be on the machine) but mid-afternoon I switched to the 10" to cover more ground. It worked just as well. I am biased towards the GB2 as we are old friends and the iron discrimination saves me lots of work. Every time I've dug something that sounds like iron on the GB2 that's what it was. So, it just so happened that the GB2 tended to be the first pass machine and found all the nuggets. Those I then checked with the ATX/Infinium also registered except maybe the very smallest (0.25g). Next time I promise to resist the temptation to dig before I've swung both machines over the same patch and note ATX signal strength but it's a long, long drive and next year only. What I can say is that the Infinium coil balances easily and is very quiet (once I taped the cable down and stopped it swinging about). Low knock sensitivity. The iron-grunt check is pretty reliable (it sounds just like a hippo if that means anything west of the Atlantic?). I did find small boot nails with the ATX when on first pass but iron-check is more subtle than GB2 iron discrimination. All in all I think I have two great and inexpensive machines but I just don't need PI under those dry conditions. I just need more hours on PI to get my comfort levels up. That said, when it rains and the soil turns to clay it's a different story and the 71k GB2 just crashes and burns. There is another Fe-rich area where the ATX has the edge but I just haven't found gold with either. Yet.

To my surprise Google had quite a lot on dry jigs. Take a look at this YouTube and be sure to read all the comments, 'Fraid there's some not so good news in there. But it sounds like the guy has already been down the road you are contemplating. My gut feel is that it's a stretch but give your dry blower a shot first.

That's a tough one. Dry panning for gold when the density contrast is 19 to 2.6 is one thing but when it's 4 to 2.6 that's something else. When I was doing diamond exploration back in the day we used hand jigs. Not much more than a 1/2 mm classifying screen that you move (jig) an inch up and down in a bucket of water, say, twice a second. Yeah, it takes practice but the guys who did it day after day got really good! We were looking for garnet and ilmenite diamond indicators though. The attached gives you the idea. It's not rocket-science. You do need to classify the material first (+1mm -5mm?) and a minimal amount of water. Maybe classify it, bag it and haul it to somewhere with water? It's hard work so the dry washer sounds worth trying. Spike a sample with a couple of sapphires first and see if you lose them! Also, like gold, diamonds will be on bedrock. You can throw away everything except the last inch. Let me know how it goes.

If you have those kinds of depths to bedrock from surface then I guess you really need to permit the right area 😠 This is a useful intro to mapping bedrock https://www.guidelinegeo.com/bedrock-mapping/ What is the bedrock? If there is a density contrast between that and the gravels a gravity survey might work. You'd be amazed what a gravity meter can do but it's specialist operation.

Drilling has to achieve two things, be technically capable of sampling of what you are interested in and give you a big enough sample to give you a reasonable estimate of the grade of what you are interested in. Alluvial gold just has to be the second hardest kind of deposit to evaluate with drilling on both counts. The hardest being alluvial diamonds. High value, low concentration, particulate deposits need large samples and core won’t give you that on both counts. Unstable ground and small samples. On top of that the values aren’t spread evenly, they are in small, relative to realistic drill spacing, bedrock trap sites. That’s a nightmare to get a grade for. From my reading of this thread the deposit seems to be thick, consolidated but uncemented gravel. Coring that won’t work technically or statistically but certain types of piling augers might. The simplest might be to rent a large diameter auger attachment if you have a backhoe and it’s not running gravel. Large meter-diameter Caldwell bucket-augers worked very well on diamond gravels during my misspent youth but you need flat ground and even then, more than 50% of holes in a rich (on average) deposit would be barren. Gold would be more forgiving statistically if it’s fine gold but any boulder will stop you dead technically. Personally, I would give any kind of drilling a miss. Somewhere around page 50 of this thread there was a discussion on using geophysics to narrow the search. With dry gravels and a big hardness contrast with bedrock both reflection seismics and ground-penetrating-radar (GPR) would give useful information and are cheap and fast (well, compared to drilling that is!). Site investigation or “hammer seismics” isn’t much more than a steel plate, a sledgehammer and a guy with muscles as a seismic source plus a string of geophones on the ground. It’ll give you an averaged picture of what the bedrock is doing. Maybe a kilometre a day depending on terrain. OK for a general work program but I doubt it would have the resolution to find a kettle. GPR would find a kettle and looks like a no-brainer viewed from the other side of the Atlantic! A site investigation contractor should be able to do both. Thumb suck cost? $5k for a couple of days and interpretation? Then you start digging. Good luck 😊

Thank you for a really great story. Reminds me of a Jack London book (?) on the Klondyke my father had, thick, mismatched, yellowed pages and all. Set me on the road to a geological career I've never regretted. I guess that detectors won't be much use is pothole country given their relative depth limitations compared to a pothole. Have you used or considered using Ground Penetrating Radar in your current efforts? For that matter has anybody else on the forum used GPR as a companion to detectors? I've considered it but it's a big investment. In the US there should be contractors to use. It should work a treat on dry gravels over irregular bedrock which you seem to have. GPR is the go-to approach for dry-land, alluvial diamonds in Africa.

Thanks for this KDOCAC. Now I know that I've been in the right ball-park, maybe a tad generous (land owner not claim title), but it has made for a lasting, friendly relationship. I'll take that.......