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Off Grid

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About Off Grid

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    gold prospecting, geology, hard science
  • Gear Used:
    GB, GB2, Garrett ATX, Keene backpack dredge/highbanker

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  1. Magnetite quartzite would be my my guess especially if you are in Michigan. Several images on Google
  2. To GB's questions hopefully the attached Excel file (to make a long story even longer) clears things up and you can make your own plots and interpretations. A straight line on a log-probability plot tells me I likely got everything because alluvial minerals are log-normally distributed. It's a bit like quantum mechanics! Nobody knows why it works but the overwhelming evidence shows that it does work. When you don't get a straight line it can indicate several things, as I try to explain, but an apparent excess of large nuggets from a thick profile would suggest to me I'm missing small nuggets.
  3. And then of course you also have Croc Diamonds...... As every self-respecting local in N.E. Angola knows all this stuff about diamonds forming at huge depths and temperatures is just BS and diamonds are really made in the heads of crocodiles. It stands to reason after all.. diamonds are found in rivers and crocs live in rivers. Croc dies, decomposes and his diamonds stay in the river. Nevertheless it came as a big surprise one day back in the '80's when the diamond security police carried a large sack into the plant office and dumped a very decomposed croc on the floor and asked the manag
  4. Hopefully this won't sound too propeller-head but, hey, data is data! I guess the data in the video would show that (all other parameters being equal) detection depth follows something close to a weight to the inverse sixth power rule. That's the theory I got courtesy of MineLab and what my own checks seem to indicate. I confess that once I get a good signal I'm in too much of a hurry to dig it to measure the depth correctly but, yes, about 100% <6"! But I do have all the weights and the other issue that bugs me is "have I got everything?". Found this post from Aussie on the subje
  5. I couldn't agree more with the sentiments expressed in the video but I'd like to see the data for, say, deeper than 6" plotted as nugget weight versus depth. Might be asking too much to color code the data points by detector/coil combo's!
  6. I hunt gold on dry land hillsides with generally low mineralization but some very mineralized fossil black-sand bearing sandstones and wet clay after (very infrequent) rain. My GB2 struggles with these and I figured I needed a PI. I agonized long and hard over whether to buy the ATX or the GPX 5000 and in the end got the ATX (in 2019) given the large price differential and low performance differential between the machines. I had not seen Steve's 2014 review until this post but his experience mirrors mine exactly. It's a great machine but the bad ergonomics are a huge downside particularly if
  7. Yes, I'm based in Africa but it's a big place so there's no one answer as to why no posts? Yes, there's Internet but it varies from 5G to 0G depending which country and where in the country you are. There is activity, Google "metal detecting/South Africa" and you'll get hits . Google "metal detecting/Equatorial Guinea" and you won't. My guess is that there's a booming gold detecting scene in lode gold places like Ghana, Mali and southern Ethiopia around Lega Dembi but it's all under the radar. But these are places you might not want to go or at least send your mother-in-law first to chec
  8. At an SG of 2.65 it has to be mainly quartz and it does look like a quartz-rich igneous or metamorphic rock. My guess is that it has a disseminated conductor as a minor component that's causing the response. Maybe a graphitic gneiss or something granitic with some sulfide a.k.a. "hot rock". Steve has an old post from Dove Creek Alaska showing quartz monzonite and great chunks of gold running through it. You might get lucky.......
  9. It looks like magnetite to me. There's some tests you can do in the link below. A meteorite would generally have a melted look to the surface skin. If you have a gas torch heat some powder to red heat. If it cools to a red color and loses its magnetism it was magnetite and is now hematite. https://meteorites.asu.edu/meteorites/how-can-i-find-a-meteorite
  10. Being a data-junkie sorta guy I put together the attached comparisons for my GB2 versus my ATX. Hope it helps. I think the "Buried" data is the most useful. The rig is a PVC conduit pipe buried at a 1:10 slope in slightly iron-stained dry quartz sand. I push nuggets down it until I achieve whatever threshold signal I'm looking for. The depth is a tenth of the distance down pipe. I bought the ATX because it's cheaper than a Minelab and I was really surprised that the ATX really didn't give me more depth than the GB2 but I was a newbie on the ATX when I did all this. In the field I've yet t
  11. Steve Thanks for the links. I liked the tow coil post. Basically an airborne system flying at zero feet! My ground is too rugged for that but I recall that an early base metal EM system had the operator wearing a 5-6 foot coil like a giant hula hoop. One for the back-burner.... Next trip I'll blow the dust off my GB Mk1 for which I have a 14" aftermarket coil, pay attention to ground balance and give no-motion a shot over a hammered patch.
  12. My first post here, coil-related, so I hope it's not too off topic. Two more spanners... First off I hunt residual gold mostly, not transported alluvial stuff and until I started nugget hunting a lot two years back I always thought that the term "gold patch" was just that, a term. To my surprise I've found that nuggets cluster really tightly. Although the district is a few square miles patches are no more than a hundred square yards with a whole lot of nothing between patches. So I tend to visit a patch multiple times. 1st pass-discovery, 2nd pass- move all the rocks, 3rd pass buy a PI an
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