On 12/10/21 20:41, Don Y wrote:> On 10/12/2021 6:15 AM, Martin Brown wrote: >> On 12/10/2021 12:53, Don Y wrote: >>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>> a couple of guys hunting for gold deposits with the sorts of metal >>> detectors you'd look for trinkets on a sandy beach. >>> >>> And, apparently, *finding* same! (gold just lying around in >>> surface rock outcroppings? who'd guessed!) >>> >>> But, they each used detectors with small diameter (10"?) coils. >> >> 8-10" is about the sweet spot for a coil that is easy to work with and >> sensitive enough. Modern metal detectors can distinguish ferrous from >> non-ferrous metals which is a big help finding precious metals. >> >> I have yet to see one that can recognise and ignore coke can ring pulls. > > What originally caught my attention (I had just turned on the TV > in order to watch a movie/DVD and hadn't yet switched the video source) > was that they were out in the wilderness -- grass, trees, shrubs, > etc. I am used to seeing folks combing beaches for lost wedding rings, > etc. > > "What the hell are they looking for out there??" > > I would imagine they got fewer false positives simply because > it didn't appear that there was any sign of "civilization", nearby. > > [But, I only saw the last 2-3 minutes when they found a nugget and > congratulated themselves]But there were previous generations of miners there, so they detect bullets and staples!
Metal detectors
Started by ●October 12, 2021
Reply by ●October 12, 20212021-10-12
Reply by ●October 12, 20212021-10-12
On 10/12/2021 1:22 PM, Tom Gardner wrote:> On 12/10/21 20:41, Don Y wrote: >> On 10/12/2021 6:15 AM, Martin Brown wrote: >>> On 12/10/2021 12:53, Don Y wrote: >>>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>>> a couple of guys hunting for gold deposits with the sorts of metal >>>> detectors you'd look for trinkets on a sandy beach. >>>> >>>> And, apparently, *finding* same! (gold just lying around in >>>> surface rock outcroppings? who'd guessed!) >>>> >>>> But, they each used detectors with small diameter (10"?) coils. >>> >>> 8-10" is about the sweet spot for a coil that is easy to work with and >>> sensitive enough. Modern metal detectors can distinguish ferrous from >>> non-ferrous metals which is a big help finding precious metals. >>> >>> I have yet to see one that can recognise and ignore coke can ring pulls. >> >> What originally caught my attention (I had just turned on the TV >> in order to watch a movie/DVD and hadn't yet switched the video source) >> was that they were out in the wilderness -- grass, trees, shrubs, >> etc. I am used to seeing folks combing beaches for lost wedding rings, >> etc. >> >> "What the hell are they looking for out there??" >> >> I would imagine they got fewer false positives simply because >> it didn't appear that there was any sign of "civilization", nearby. >> >> [But, I only saw the last 2-3 minutes when they found a nugget and >> congratulated themselves] > > But there were previous generations of miners there, so > they detect bullets and staples!Dunno. All I saw looked pretty overgrown, flat terrain. E.g., you visit a "spent" mine in the US and you'll likely see the tailings piled outside. It's obvious that a mine was (is) there. Even if any structures (typ wood) have long since given up their ghosts.
Reply by ●October 12, 20212021-10-12
On 12/10/2021 20:44, Don Y wrote:> On 10/12/2021 9:23 AM, Joe Gwinn wrote: >> On Tue, 12 Oct 2021 14:15:33 +0100, Martin Brown >> <'''newspam'''@nonad.co.uk> wrote: >> >>> On 12/10/2021 12:53, Don Y wrote: >>>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>>> a couple of guys hunting for gold deposits with the sorts of metal >>>> detectors you'd look for trinkets on a sandy beach. >>>> >>>> And, apparently, *finding* same! (gold just lying around in >>>> surface rock outcroppings? who'd guessed!)They must have known enough about the geology to be in about the right place then.>>>> But, they each used detectors with small diameter (10"?) coils. >>> >>> 8-10" is about the sweet spot for a coil that is easy to work with and >>> sensitive enough. Modern metal detectors can distinguish ferrous from >>> non-ferrous metals which is a big help finding precious metals. >>> >>> I have yet to see one that can recognise and ignore coke can ring pulls. >>> >>>> Wouldn't a larger diameter give greater soil penetration? >>>> Are tehre other reasons why a small coil might be prefered >>>> (easier to carry?) >>> >>> That and being able to get a better fix on the target. The sensitivity >>> to objects in the ground extends a couple of coil diameters outwards in >>> all directions. How deep in depends also on how wet the soil is. >> >> Yes. >> >> For those that want to dig deeper, so to say, google on "pulse >> induction metal detector" without the quotes. > > The question has more to do with the apparent lack of a *need* to > sense deeper. That gold could be found within inches of the > surface.If there is gold about there are often deposits in mineralised quartz veins too if you know where to look. Likewise in the gravel of streams. Some people are just lucky like with the ~5kg Mojave nugget. https://en.wikipedia.org/wiki/Mojave_Nugget> Gold mines that I've visited were deep underground...Mineable quality gold ore is uncommon. They follow any seams they can find until it runs out (same applies to most other ore bodies). -- Regards, Martin Brown
Reply by ●October 12, 20212021-10-12
On 10/12/2021 2:28 PM, Martin Brown wrote:> On 12/10/2021 20:44, Don Y wrote: >> On 10/12/2021 9:23 AM, Joe Gwinn wrote: >>> On Tue, 12 Oct 2021 14:15:33 +0100, Martin Brown >>> <'''newspam'''@nonad.co.uk> wrote: >>> >>>> On 12/10/2021 12:53, Don Y wrote: >>>>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>>>> a couple of guys hunting for gold deposits with the sorts of metal >>>>> detectors you'd look for trinkets on a sandy beach. >>>>> >>>>> And, apparently, *finding* same! (gold just lying around in >>>>> surface rock outcroppings? who'd guessed!) > > They must have known enough about the geology to be in about the right place then.No doubt! I was surprised that it would be that near the surface. And, to wonder how they *knew* it would be there! (Did someone, someday, just happen to look down and say, "My! There's a gold nugget by my left foot!" And, thereafter, the area known for "gold just lying around"? If so, why is there *still* any left to be found -- if it was common knowledge!)>>>>> But, they each used detectors with small diameter (10"?) coils. >>>> >>>> 8-10" is about the sweet spot for a coil that is easy to work with and >>>> sensitive enough. Modern metal detectors can distinguish ferrous from >>>> non-ferrous metals which is a big help finding precious metals. >>>> >>>> I have yet to see one that can recognise and ignore coke can ring pulls. >>>> >>>>> Wouldn't a larger diameter give greater soil penetration? >>>>> Are tehre other reasons why a small coil might be prefered >>>>> (easier to carry?) >>>> >>>> That and being able to get a better fix on the target. The sensitivity >>>> to objects in the ground extends a couple of coil diameters outwards in >>>> all directions. How deep in depends also on how wet the soil is. >>> >>> Yes. >>> >>> For those that want to dig deeper, so to say, google on "pulse >>> induction metal detector" without the quotes. >> >> The question has more to do with the apparent lack of a *need* to >> sense deeper. That gold could be found within inches of the >> surface. > > If there is gold about there are often deposits in mineralised quartz veins too > if you know where to look. Likewise in the gravel of streams.Yes. But in streams, one usually "pans" for the gold.> Some people are just lucky like with the ~5kg Mojave nugget. > > https://en.wikipedia.org/wiki/Mojave_Nugget > >> Gold mines that I've visited were deep underground... > > Mineable quality gold ore is uncommon. They follow any seams they can find > until it runs out (same applies to most other ore bodies).Again making the "just lying around" all the more interesting! <shrug> Someday, I'll stumble on the show, again (unless it was a "special") and see what more there is to it...) [Amusingly, many TVs don't include a "guide" feature. They will tell you what is playing, currently, on the channel you are watching but not what will be aired next -- or two hours hence. Or, what's on the *other* channels. (Yes, I'm sure there are TVs that *do* offer this feature; our previous one did -- but none of the three that we currently have). And, it's too much of a hassle to power on the DVR to consult *it's* guide... OTOH, we rarely watch broadcast TV -- treating the TV as a large monitor, instead, for viewing movies -- so no real loss!]
Reply by ●October 12, 20212021-10-12
On 12/10/2021 17:28, Don Y wrote:> On 10/12/2021 5:11 AM, Clive Arthur wrote: >> On 12/10/2021 12:53, Don Y wrote: >>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>> a couple of guys hunting for gold deposits with the sorts of metal >>> detectors you'd look for trinkets on a sandy beach. >>> >>> And, apparently, *finding* same! (gold just lying around in >>> surface rock outcroppings? who'd guessed!) >>> >>> But, they each used detectors with small diameter (10"?) coils. >>> >>> Wouldn't a larger diameter give greater soil penetration? >>> Are tehre other reasons why a small coil might be prefered >>> (easier to carry?) >> >> Idle speculation on my part, but I'd think that a larger coil would >> encompass a larger search volume and would require a larger nugget to >> give the same response as a smaller coil with a smaller nugget, >> percentage wise. > > Yes, but you could tweek the rest of the electronics, accordingly, > to improve the sensitivity (?) > >> The detectorists probably know the likely size range of nuggets. >> Small deep ones can't be detected, and large deep ones don't occur. > > I'm not sure small deep ones *cant* be detected. That's the point. > > OTOH, your point wrt the hunters knowing the likely sizes of > stuff they will find is probably true -- for their locale. > > (the whole idea of gold being accessible so close to the > surface was interesting... what other ores can be similarly > located?) >A former colleague and his friend (from the UK) went gold prospecting in Australia a couple of years ago for a couple of months. They did it for fun, a holiday, but also with a sense of well, you never know... As it happens, they found about enough gold to buy food and beer. Their trip was arranged through an agency. I do wonder if said agency distributes gold throughout their prospecting area. Maybe it's all just an easter egg hunt. -- Cheers Clive
Reply by ●October 12, 20212021-10-12
On 12/10/21 22:59, Don Y wrote:> On 10/12/2021 2:28 PM, Martin Brown wrote: >> On 12/10/2021 20:44, Don Y wrote: >>> On 10/12/2021 9:23 AM, Joe Gwinn wrote: >>>> On Tue, 12 Oct 2021 14:15:33 +0100, Martin Brown >>>> <'''newspam'''@nonad.co.uk> wrote: >>>> >>>>> On 12/10/2021 12:53, Don Y wrote: >>>>>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>>>>> a couple of guys hunting for gold deposits with the sorts of metal >>>>>> detectors you'd look for trinkets on a sandy beach. >>>>>> >>>>>> And, apparently, *finding* same! (gold just lying around in >>>>>> surface rock outcroppings? who'd guessed!) >> >> They must have known enough about the geology to be in about the right place >> then. > > No doubt! I was surprised that it would be that near the surface. > And, to wonder how they *knew* it would be there! > > (Did someone, someday, just happen to look down and say, "My! There's > a gold nugget by my left foot!" And, thereafter, the area known for > "gold just lying around"? If so, why is there *still* any left to > be found -- if it was common knowledge!)According to school geography lessons, the importance of Kiirunavaara was discovered when someone found his steel knife was attracted to the ground. I've never understood why gold (and similar) elements, which were produced in supernovae, aren't evenly distributed lone atoms.
Reply by ●October 12, 20212021-10-12
On Wednesday, 13 October 2021 at 09:05:09 UTC+11, Clive Arthur wrote:> On 12/10/2021 17:28, Don Y wrote: > > On 10/12/2021 5:11 AM, Clive Arthur wrote: > >> On 12/10/2021 12:53, Don Y wrote: > >>> I caught the tail end (last 2-3 minutes) of a TV show which depicted > >>> a couple of guys hunting for gold deposits with the sorts of metal > >>> detectors you'd look for trinkets on a sandy beach. > >>> > >>> And, apparently, *finding* same! (gold just lying around in > >>> surface rock outcroppings? who'd guessed!) > >>> > >>> But, they each used detectors with small diameter (10"?) coils. > >>> > >>> Wouldn't a larger diameter give greater soil penetration? > >>> Are tehre other reasons why a small coil might be prefered > >>> (easier to carry?) > >> > >> Idle speculation on my part, but I'd think that a larger coil would > >> encompass a larger search volume and would require a larger nugget to > >> give the same response as a smaller coil with a smaller nugget, > >> percentage wise. > > > > Yes, but you could tweek the rest of the electronics, accordingly, > > to improve the sensitivity (?) > > > >> The detectorists probably know the likely size range of nuggets. > >> Small deep ones can't be detected, and large deep ones don't occur. > > > > I'm not sure small deep ones *cant* be detected. That's the point. > > > > OTOH, your point wrt the hunters knowing the likely sizes of > > stuff they will find is probably true -- for their locale. > > > > (the whole idea of gold being accessible so close to the > > surface was interesting... what other ores can be similarly > > located?) > > > A former colleague and his friend (from the UK) went gold prospecting in > Australia a couple of years ago for a couple of months. They did it for > fun, a holiday, but also with a sense of well, you never know... > > As it happens, they found about enough gold to buy food and beer. Their > trip was arranged through an agency. I do wonder if said agency > distributes gold throughout their prospecting area. > > Maybe it's all just an easter egg hunt. > > -- > Cheers > CliveAbout 30 years ago on a camping trip to Laanecoorie in the Victorian (Australia) gold region we met a local who showed us a nugget he found with a metal detector which was remarkably puck-shaped (approx 5cm dia x 1 cm thick). This is the general region where the Welcome Stranger was discovered after all: https://en.wikipedia.org/wiki/Welcome_Stranger His technique (on his own property of course!) was to scan the area of interest with the detector then scrape ~30cm of soil off with a bulldozer & repeat. I can't remember now how deep he went or the total area he covered - seem to think it was an acre or two at least... -- Cheers, Chris.
Reply by ●October 12, 20212021-10-12
In article <sk537r$kfq$2@dont-email.me>, Tom Gardner <spamjunk@blueyonder.co.uk> wrote:>I've never understood why gold (and similar) elements, >which were produced in supernovae, aren't evenly >distributed lone atoms.They probably started out that way, when Earth formed via accretion from the original dust cloud. Gold and other heavy elements (e.g. uranium) would have been distributed fairly evenly and randomly in the silicate rocks of the mantle and crust. Since then, hydrothermal effects have done their magic. Hot, circulating fluids dissolve minerals (even noble elements like gold), and the minerals can precipitate out in interesting ways, forming veins and other ore bodies. https://www.nature.com/articles/nature.2013.12615 reports an interesting "take" on the precipitation process - it may occur _very_ rapidly when pressure on a sub-surface fault is released suddenly during an earthquake.
Reply by ●October 13, 20212021-10-13
On 10/12/2021 3:46 PM, Tom Gardner wrote:> On 12/10/21 22:59, Don Y wrote: >> On 10/12/2021 2:28 PM, Martin Brown wrote: >>> On 12/10/2021 20:44, Don Y wrote: >>>> On 10/12/2021 9:23 AM, Joe Gwinn wrote: >>>>> On Tue, 12 Oct 2021 14:15:33 +0100, Martin Brown >>>>> <'''newspam'''@nonad.co.uk> wrote: >>>>> >>>>>> On 12/10/2021 12:53, Don Y wrote: >>>>>>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>>>>>> a couple of guys hunting for gold deposits with the sorts of metal >>>>>>> detectors you'd look for trinkets on a sandy beach. >>>>>>> >>>>>>> And, apparently, *finding* same! (gold just lying around in >>>>>>> surface rock outcroppings? who'd guessed!) >>> >>> They must have known enough about the geology to be in about the right place >>> then. >> >> No doubt! I was surprised that it would be that near the surface. >> And, to wonder how they *knew* it would be there! >> >> (Did someone, someday, just happen to look down and say, "My! There's >> a gold nugget by my left foot!" And, thereafter, the area known for >> "gold just lying around"? If so, why is there *still* any left to >> be found -- if it was common knowledge!) > > According to school geography lessons, the importance > of Kiirunavaara was discovered when someone found his > steel knife was attracted to the ground. > > I've never understood why gold (and similar) elements, > which were produced in supernovae, aren't evenly > distributed lone atoms.Why aren't celestial bodies perfectly round (oblate) orbs? Why Les Alpes and The Mariana Trench?
Reply by ●October 13, 20212021-10-13
On 10/12/2021 3:05 PM, Clive Arthur wrote:> On 12/10/2021 17:28, Don Y wrote: >> On 10/12/2021 5:11 AM, Clive Arthur wrote: >>> On 12/10/2021 12:53, Don Y wrote: >>>> I caught the tail end (last 2-3 minutes) of a TV show which depicted >>>> a couple of guys hunting for gold deposits with the sorts of metal >>>> detectors you'd look for trinkets on a sandy beach. >>>> >>>> And, apparently, *finding* same! (gold just lying around in >>>> surface rock outcroppings? who'd guessed!) >>>> >>>> But, they each used detectors with small diameter (10"?) coils. >>>> >>>> Wouldn't a larger diameter give greater soil penetration? >>>> Are tehre other reasons why a small coil might be prefered >>>> (easier to carry?) >>> >>> Idle speculation on my part, but I'd think that a larger coil would >>> encompass a larger search volume and would require a larger nugget to give >>> the same response as a smaller coil with a smaller nugget, percentage wise. >> >> Yes, but you could tweek the rest of the electronics, accordingly, >> to improve the sensitivity (?) >> >>> The detectorists probably know the likely size range of nuggets. Small deep >>> ones can't be detected, and large deep ones don't occur. >> >> I'm not sure small deep ones *cant* be detected. That's the point. >> >> OTOH, your point wrt the hunters knowing the likely sizes of >> stuff they will find is probably true -- for their locale. >> >> (the whole idea of gold being accessible so close to the >> surface was interesting... what other ores can be similarly >> located?) > > A former colleague and his friend (from the UK) went gold prospecting in > Australia a couple of years ago for a couple of months. They did it for fun, a > holiday, but also with a sense of well, you never know...IIRC, the folks on this show had aussie accents (but I'm not an expert on accents -- other than my own)> As it happens, they found about enough gold to buy food and beer. Their trip > was arranged through an agency. I do wonder if said agency distributes gold > throughout their prospecting area. > > Maybe it's all just an easter egg hunt.Too funny! But, stranger things have been known to happen! I recall a show where a guy sat in a field of clover and periodically pulled up a four-leaf-clover -- disproving the myth of their scarcity. Maybe it's just a matter of BELIEVING that you will find something...?
