jasong

"Learn the rules like a pro, so you can break them like an artist". - Picasso Aphorisms like "dig it all", "low and slow", etc are good for people detecting club claims, heavily worked areas, old patches, etc. For those detecting a wide range of different environments and doing exploration, it's often more about figuring out when and where to break the rules and how to adapt to changing, new environments in order to maximize yield (aka - your total gold take per unit time spent).

Quickest test for magnetite is just putting a magnet to it and seeing if it's attracted.

It changes by location/environment. Sometimes the presence of sulfides mean that the gold is also locked up in the sulfides themselves (and not in nugget form or large enough to be nuggets). But then other times it doesn't - I optioned a mining project to an exploration company where my initial discovery was a large series of stacked quartz veins containing chalcocite, and those same veins also had visible gold in them, a short distance away there was some large pocket gold which was discovered using a metal detector. The bonanza grade gold was all surface or near surface occurrence. The only way to find out is just to swing the coil over the area and see. 🙂 Doing some sample panning, looking at the ore under a magnifying loupe, maybe cutting a few ore samples to get a fresh face to magnify, these can helpful to know if free gold is showing up or not to begin with.

Simon's comment there would be the #1 determining factor in a machine for me, if I was getting one for working bedrock. Working hot basalts and serpentines or magnetite laden areas? PI 100%, wouldn't pull my hair out with a VLF in that terrain. Low mineral granites, gneiss, sandstones? 800 or 900 would be my first choices - looking at one or the other of those right now for working non-river bedrock/lode zones.

I totally forgot about this detector. I hope they come out with one still. All I need is: light, fast, quiet (EMI), external speaker, and a little more sensitive than a 5000 so I can hit the buried sub-0.1 nugget leads while exploring. Make it $2k And I'll ditch my 6000 and use this all day as an exploration/prospecting machine and never look back, I need an excuse to stop using ML products, still pissed about the 6000 honestly and how they treated the EMI issues and fix "rollout" that I had to force for them. Plus I just don't trust the 6 anymore either. I had a bad experience with Nokta when they first rolled out the FORS Core, 3 of mine failed in a row and I just gave up and threw it in the closet. Willing to try again.

Either galena or chalcocite probably. Lead and copper sulfides. Maybe hematite, but less likely. Chalcocite can hit quite hard on a VLF detector and sound much like gold. I've found both occurring in gold areas in the past. Galena and chalcocite should have a faint odor of sulfur if you crush/scrape some of the rock, hematite will not smell of sulfur. If smelling of sulfur, a density test will tell the difference as galena is 7.6g/cc and chalcocite is 5.6g/cc.

Horn coral fossils

Are you aiming to cover ground or aiming for depth on patches? Seems to me those large drag coils are mostly for depth on patches and not ground coverage, especially not being towed. But maybe I misunderstand them due to not having used one. I tried a 25" round and gave that up as too large for exploration because it was slower to swing and produced too many spurious signals that caused lots of lost time investigating, and investigating each target was laborious due to coil size. So one even larger seems like it may come with the same problems for covering lots of ground. You probably already know about these NF 30x7" Patch Pros and eliminated them, but here's one if not - swiped this from Rob's site. I haven't tried one my self so take what I say with a hefty grain of salt. If ground coverage is the key and not depth, then more elliptical is better (large swath coverage, but skinny so quicker to locate targets, less EMI per area swath coverage). This one has the area equivalent to a 15" round roughly, so the EMI should be about equal too, and a 15" is ok for exploration IMO. The EMI/spurious signals on coils like 20 or 25" rounds increase quite a lot (especially on uneven ground where the coil is at an angle)...on a big drag coil it seems like you might be chasing ghosts often all day, and that means less ground coverage. Just a guess though, I could be totally wrong. And we definitely have worse EMI issues here so that may just be a big problem for us and not for you. The other consideration is if you are working salt ground then you want to minimize your total coil area too, and in those cases and extreme elliptical shape is the best too since total coil area is small relative to swath coverage. Just another thought to toss out there anyways.

I've never built or run one myself. I hope I can meet up with Chet again sometime and check one of his out or maybe give it a go in person and learn a bit more. Until then I can't really comment with much useful. I definitely relate to the "big country" issue though. It can be an overwhelming amount of land to cover. Barring a better solution, the only ways to tackle it for me have come down to 3 things basically: speeding up by using a lightweight, quiet, fast detector (I've posted about this technique a ton, but it's not for everyone granted). Geologic/topographic indicators. And using an ATV to speed up movement between low probability zones, as well as to do a lot of scouting by eye first. I'd say at least 50% of my field prospecting in big country now is standing on my ATV while driving and just looking at the ground with my eyes, or getting from the most likely place to the next most likely quick without walking or detecting in between. I'm missing a lot, but I'm also usually only spending time detecting in the most probable spots when there is just too much ground to feasibly detect. I'd love for there to be a better solution...starting to look unlikely we'll get one though.

The one I used in my pic is 365nm. Yours is about the most gemmy one I've seen from Wyoming, probably worth prospecting for a lode source on that. Most the WY rubies I've found or seen have been very low quality - shattered and bad color. This UV flashlight I have is crazy powerful, I'm going to take it camping this summer and do a few night scouting trips just out of curiosity. That red stands out so starkly it seems if there were rubies around they'd be pretty easy to spot. It's easy to tell the difference between that red and the reds from calcite.

Interesting Jim...yes mine came from Wyoming too, though not from any of the diamond areas in the Green River basin. I can't quite say where this one came from yet, but I hope to be able to write a bit more about it in the future as there are some other pretty interesting things associated with it. Yours is an interesting one though...pictures can be deceiving so maybe I'm not looking at it right, but it appears to have a semi-defined hexagonal form? If so, I would lean more corundum - probably ruby - than garnet. I don't think garnet fluoresces under UV much either. I think you got an interesting one there...it's more gemmy than mine is too.

Can't miss that red glow... Granted this one is tiny and not really gem color. Was storing some samples and checking them out in the microscope first, and decided to run the UVBeast flashlight over them. This one came from a place with no known ruby occurences, didn't expect to see this turn up. It could also be spinel, but no known occurences of that where this came from either. Might be worth running a UV light over panning/sluicing concentrates for people that have them. Never know what you might find...

I wasn't really shooting for any kind of accurate number, I just wanted to show the physical relationship between coil inductance, material permeability and number of turns in a quick example. Just to show one might be able to replace some amount of copper wire with a lesser weight of ferrite. No clue though. I guess it would really need to be something done via experiment, or done in EM finite element analysis modelling software though to know if it worked. Hysteresis as well as localized magnetic flux concentration around the ferrite might make this infeasible in a PI, GPZ maybe not? The flux concentration effect might be interesting to experiment with too though on it's own for various reasons too. I guess I'll chunk it onto the log pile of ideas I'll never get around to actually trying. 😄 One of these days I'd like to get back into electronics again, just no time now.

I don't mean a solid ferrite core, I just mean adding some small amount of ferrite to make up for the inductance loss resulting from subtracting some coil turns. Maybe even just using ferrite powder in a paint as shielding instead of graphite paint could be enough, no idea. A little bit of highly permeable material can raise the inductance quite a lot. Permeability of air = 1. Permeability of ferrite can be around 1500. So for a solenoid inductance would be something like this: So adding a ferrite core would increase the inductance 1500 times over a foam/air core, which is way too much because we'd need to subtract a substantial amount of windings to get back down to 300mH. But if you just added a small bit of ferrite so that the entire coil "sees" an average permeability increase of maybe 25 (since much of the foam or air will still be permeability = 1, the total permeability will depend on the size of the ferrite), then you could remove quite a lot of copper. The ferrite might actually weigh less than the copper did, and the coil could be lighter? Less turns will mean less resistance, so the remaining turns could be downsized in gauge diameter to increase resistance again, and this too would save weight. Just a quick example: Foam core, 1 cm thickness, 10cm coil radius (8 inch wide) means you need 275 turns of copper to equal roughly 300mH. Conversely, add a bit of ferrite in some way or form to increase permeability to 25, at least in terms of what the detector sees (this would be a small amount of ferrite) and now that same coil dimension only needs 55 turns of copper. (I have no clue if this is close or far from actual ML coil turns, I'm just using a generic example with the formula above) In this example the ferrite would probably weigh less than the 220 turns of copper removed from the coil since the ferrite permeability is 1500, you wouldn't need to cover the entire core to reach an average permeability of 25. No idea if that would work or if the hysteresis curve of the ferrite would screw the detector sensitivity up. Curious though. A high permeability material with a slim hysteresis curve might exist?

In the case of the smaller coils lacking space for the windings, is it possible to get rid of some windings and then raising the coil inductance back to 300mH via the inclusion of a small bit of ferrite or even iron to boost it back to spec? Maybe using the ferrite for shielding in some way too such as powdered ferrite paint instead of powdered graphite paint (2 birds, one stone)? Permeability of ferrite is like 1500x that of air, foam, etc so it shouldn't take much to raise the total coil inductance - at least in terms of the inductance the detector sees. If that works, would adding materials with varying degrees of magnetic permeability to increase inductance be a potential experiment to reduce winding weights and thus total coil weights too? Or would those materials themselves have a negative effect on the detector operation/ground balance/etc? I wonder if in some way this is one reason the ferrite was included with the GPZ due to some kind of design considerations like this? Slightly smaller diameter wire could be used to increase the coil resistance if reducing the turns/wire length threw it out of a critically damped state and introduced ringing? Or I assume they are designed to be critically damped anyways, but I guess I'm not sure. I've never built coils for detectors, but I find it interesting to think of experiments to try to potentially improve upon them. It's educational to see some discussion of it here.