Log in

View Full Version : Metal Detecting for Placer Nuggets of Galena



Robert
06-19-2012, 05:01 PM
Does anyone have experience detecting for placer nuggets of galena around the Yukon/Alaska?

Bob(AK)
06-19-2012, 10:00 PM
I don't believe a detector will pick up on galena, but perhaps someone else knows for sure. May depend on how much silver is in the specimen

Walt_Anchorage
06-20-2012, 06:49 AM
Galena is the main ore of lead. You can detect lead so you may be able to detect Galena? Just a guess. If I have detected galena I probably thought it was a hot rock and tossed it.

Reno Chris
06-20-2012, 07:27 AM
OK - Some facts about how metal detectors work:
Metal detectors respond to things if they have magnetic or electrical properties.
Metals conduct electricity, so they respond to the magnetic field of the metal detector.
Magnetite has magnetic properties so it affects the magnetic field of the detector and causes a response.
Things like turquoise or chrysocolla have copper in them and copper is a fine conductor, but these minerals have no electrical or magnetic properties, so your detector wont see them. Quartz, feldspar, mica - same thing - they don't conduct electricity or have their own magnetic properties, so the detector ignores them - in spite of the fact that feldspar and mica contain aluminum and aluminum is a decent conductor.
Galena is a semi-conductor, basically a poor conductor. So it has poor electrical response. Impurities affect just how poor the response actually is, so conductivity varies from mining district to mining district. We cant tell the original poster how well his galena will respond. It has no magnetic properties. A PI detector wont see it because it is such a poor conductor. Just like any metallic target, size matters. As with gold, tiny flakes are harder to detect than giant multi-ounce nuggets. Bigger chunks of galena located near the surface may respond weakly to a VLF - depending on the impurities you have in your galena. Fist sized chunks would be a lot easier to detect than marble sized pieces. Pea sized chunks should be near impossible. Scattered bits of galena disbursed through ore will not respond well at all. If I wanted to look for galena, I'd test specimens from the mine I was looking at on a detector and see. Probably a sensitive high frequency detector like a GB2 or Gold Master type would be best. Test it at home and see how well it works. If I had no test specimens, I'd go get some, but I would not count on the metal detector working very well for placer galena. Some other minerals like arsenopyrite are much better conductors. One of the best non-metal, natural mineral conductors is the copper mineral cuprite.

Robert
06-20-2012, 03:02 PM
Thanks for the great answer Reno Chris!

tvanwho
06-20-2012, 04:15 PM
I've got many pounds of galena at home that I found detecting around old lead mine diggings of SW Wisconsin. Some farmers west of Dodgeville,Wisconsin in the 1800's, would dig for lead as a sideline to farming.One chunk of galena was an 8 pound slab .The metal was inside a cow patty shaped brownish limestone rock right on the edge of one of the old dig holes. I would have walked right over it had my Tesoro Lobo not screamed. I had a crystal of the galena assayed years ago as an old time gold prospector guy in Arizona told me that galena doesn't usually sound off on a detector unless it has a high silver content? My assay came back as showing 2.5 ounces a ton of Silver in the galena crystal.....AND another surprise....0.13 ounce a ton for GOLD.
0.13 ounces a ton doesn't sound like much but them Carlin belt open pit gold mines in Nevada I hear have to mine 100 tons of ore to get 1 ounce of gold so my galena is 13 times richer in gold, or at least that one specimen anyway.
Ps, my Lobo with either 3x7 or 9x8 coil or MXT with 9x6 coil could pick up peanut shell size to 8 pound chunks of Galena at 0-14 inches deep ( my Lesche digger would fit in some of the holes I dug for comparison) , could even hear them inside the host rock with or without headphones. Just crank up the detector volume loud as you can stand it.I have gone over spots 5 times and still get more specimens every time listening for faint bumps in the threshold sound.If the faint sound gets better after you kick away some dirt, you best dig like a dog as it will be another piece of galena.
My old Garrett Infinium PI detector refused to make even a whisper sound in an air test over a full peanut butter jar of these galena specimens, several pounds worth in fact.
I was thinking galena nugget detecting would be good experience to have for when it comes time to head to the Gold Fields to metal detect for more valuable nuggets.


-Tom, now if Chris would just share with us how he recovers crystals from solid rock with hand tools without breaking them ? And is it possible to tell in advance if there is a Vug or pocket of crystals close to a single exposed crystal, Chris?
Pss,Chris, tell us about geodes? How do you break /cut them open and is it possible to tell how large an opening is inside the ball shaped rock by shaking it or ? Geodes are all over in central Indiana gold bearing creeks.

Reno Chris
06-20-2012, 08:01 PM
how he recovers crystals from solid rock with hand tools without breaking them?
Normally crystals fully encased are of low quality. When I have to break out crystals I use hammer, chisel and tile nippers.

And is it possible to tell in advance if there is a Vug or pocket of crystals close to a single exposed crystal, Chris?
Only by hefting - a hollow rock is lighter than a solid one.

How do you break /cut them open?
With a diamond saw. Much neater that way.

and is it possible to tell how large an opening is inside the ball shaped rock by shaking it or?
As noted above, geodes are lighter than solid rock, the greater the difference (ie, the lighter it is) generally the larger the void.

Minermike
06-20-2012, 10:52 PM
Use a diamond saw. Many, many opal miners have lost hundreds if not thousands of dollars, by hitting a rock with a hammer. Keep your cool and take it home to cut on a diamond saw.

Minermike
06-24-2012, 11:38 PM
When I was opal mining in Coober Pedy, our standard practice was to drill 8 holes 3 ft. long by 1 inch, in a drive. This was loaded with 2 sticks of jelly per hole and lit by hand. The opal level was on top of the drive, if this level dropped and formed a pocket of good opal , the result could be a lot of powder with colour. It did not happen to me but it did happen to some miners that could have been digging for weeks and getting nothing. Tales from the past.