Black Sands Processing & Content Assaying

Black Sands Processing & Content Assaying

It appears none of the gold prospectors spend nor time or money on assaying their black sands for gold value determination.

Instead, they use a rare earth magnet to tells them what is in there and see that most of the gold is magnetite with sometimes hematite.

What little remains goes under the microscope where I see that it is a mix of wolframite, scheelite and zircon.  Could there be some -100 mesh gold within the sands? Yep, but not enough to be worth any further effort. There have been a few cases of manganese dioxide coated gold. It is non-magnetic. Just smack it with a hammer. The gold will flatten and the MnO2 will spall off as a blue-black powder. MnO2 coated gold is uncommon except in a few sands

On some gold lease/claim there are the very occasional sample of MnO2 coating a piece of Gold.  The way to find it is to notice when some black particle acts a bit too heavy in the pan to be Hematite or Magnetite.

You may stumble onto small specimens in the spring and segregated them to play with later. The MnO2 coating had self powdered and fallen off the Gold (they were stored dry).

Would not even think of assaying (or refining) black sands.  Hematite and Magnetite are ~ 5.1 Specific Gravity and when classified to within 4 diameters of Gold are not a challenge for me to pan off.  Sometimes they can be a bit time consuming when larger batches need to be worked and the Gold is tiny but a NEO magnet makes it a lot easier to live with.

A Gold Hog multi sluice might be a good “Just in case” idea for those larger batches of concentrate.  The new multi sluice works, it is very effective (no more gold cube).

Most prospectors appear to process black sands with this method:  Shovel into your recovery sluice box and wash out the concentrates, periodically. into a “save” bucket.  Repeat that step for the whole time on the river.  At the end re-run your concentrates (slowly) through the same sluice box to reduce the ‘carry back bucket’ to a small load.  Classify out the oversized material and check (pan) that oversized material for nuggets.  Back at camp or home, pan out the resulting concentrates, in very small batches, down to just Gold. Use a sucker bottle to pull out only Gold.  If you happen to suck up some black sands use a Neo Magnet to remove them from the Gold.

What is this i hear about miners collecting buckets and drums of black sands with no ways to process them?
Yes they save them until you got buckets and then find someone with a miller table or such. you can recover _100 -200 mesh gold if you want to pay the price to recover it.  May be get a recovery of 0.01 grams per bucket there are folks that specialize in this type of fine recovery

As gold becomes increasingly more difficult to find, recovering gold from black sands sounds like it might just be a viable option, provided one can streamline a decent process and figure out how to discard all the waste. At least with black sands, many gardeners like them as they are. I don’t think they’d like the brown muck that comes from fracturing and processing the sands!

Then started reading another thread…about magnets. Then read more magnet threads. What about making a magnetic blanket to drag in a gold-bearing river? Then take the black sands (magnetite) and process them for any possible gold?

People save the black sands from their concentrates usually because they are just timid about panning the very small Gold out of the black sands (Hematite and Magnetite) in the concentrates.  Sometimes it is simply a case of creating an overwhelming volume of concentrates.  Experience allows you to skillfully work the Gold out of the concentrates and discard the Iron minerals (Hem and Mag) unless it is just too overwhelming.

There are various aids to make the process easier (sometimes longer, but easier).

For those on a shoestring, a pan is the least expensive way to recover the Gold from concentrates.  If there is a lack of experience there is always the option of buying equipment that will reduce the effort and shore up the lack of experience.  There are bowls, tables, mini sluices, even jigs and such to work the last bits of gold from your concentrates.  McBain was referring to that type solution for those who just don’t want to pan out the final Gold from their stockpile of concentrates.

I had mentioned Gold Hog Products “Multi Sluice” as an option.
For some it is worth the expense to process higher volumes of concentrates — for some not.

So, the bottom line here is that the first step in gold recovery is the concentrating that the sluice box provides (I have heard 20,000 to 1 as a ratio).  The final step is to remove the non-Gold components from the concentrates, leaving just the Gold.  How you do it is up to you.

Gold is NOT somehow ‘stuck’ to Black Sands (Hem and Mag).  It is just concentrated along with with the other heaviest things in the stream material.  Hem and Mag are about a Specific Gravity of 5.1+.  A little over five times the weight of water.  Gold is at a Specific Gravity of 19+ – NINETEEN or so times heavier than water.  The difference in weights (if you paid close attention in science class you might say “density” instead of ‘weight’) is what allows less dense non-Gold to wash through a sluice box while the much denser Gold is trapped and retained.

And yes, Iron oxide minerals are really good for garden plants — especially roses.

“Anybody knows how much gold is left (if any) in the actual ‘cleaned out’ black sands?”
It just depends on skill and experience in removing the black sands and leaving just the Gold.

Gold is not “stuck” to the magnetite/hematite. There might be some minute amount of gold that “could” be a part of the black sands. …Not riding along with, but more like as if sulfides. Had read several things that mentioned about heating black sands (from gold-bearing areas) and dropping them into water to fracture the sands and release any gold that might be there. Then there was also talk of using bleach and cider vinegar, as well as adding salt.

Hematite and Magnetite are separate Iron Oxide minerals – both black in color – with only a possibility of a few Gold atoms incorporated into the minerals.  As was mentioned previously, there is also a separate black mineral, Manganese Dioxide, (MnO2) which might coat an occasional Gold particle.

In the past there were various attempts to try, somehow, to process black sands – The first and easiest was crushing.

When a very tiny piece of Gold is crushed it flattens out to now become more visible.   The same happens to the infrequent MnO2 coated Gold piece.   Mistaking how the odd Gold suddenly became visible, folks assumed that ‘the black sands’ had somehow ‘locked up Gold that was not able to be seen before’  That is still a widely held misconception (except for the infrequent MnO2 coated Gold).

Now, another ‘technique’ for “breaking Gold out from black sands” was to heat the black sands to a very high temperature and then quickly dump it into Icy Cold Water.   Thermal Shock was supposed to ‘break the Gold out from the black sands’.  To a minor extent that worked but only on the MnO2 coated piece or pieces.  MnO2 is a brittle mineral and the thermal shock could, or might, chip some of it away from the Gold center.

Now think about this – There is “Bubba” with a coffee can full of VERY hot concentrates held in fireplace tongs about to briskly pour this glowing red mass directly from the wood stove into a bucket of water.   Envision a steam and sand filled volcano erupting right there in front of “Bubba”.  I mean a raging, billowing, mushroom cloud of steam, hot water and gritty, wet black sand flying EVERYWHERE with instant and substantial violence.
I didn’t find any Gold at all.  After I calmed down, I used my microscope to view the now “”Thermally Shocked Concentrates””.  After panning them down to a very small sample I found not one tiny speck.  The same went for crushing the black sands.

Now we proceed to chemicals.

Stay away from Mercury.  If you aren’t a skilled chemicals guy it will only sicken or kill you.  (That’s kill you forever – did I say that clearly enough?)   If you are a skilled chemicals guy then you already know what the dangers are.  The same goes for the other ‘High Personal Safety Risk’ chemical processes.

Pickle Juice – an absolutely marginal exercise, ultimately ending in futility.  Vinegar (Acidic Acid in weak strength) will VERY SLOWLY ‘eat’ Iron Oxides (rust, Hem or Mag) because it is an acid.  Salt (NaCl) or Chlorine Bleach will help speed up the action a tiny bit by slightly cleaning the surface of the Oxide particle.  Bottom line, it’s infinitely worse than watching paint dry.  The unintended consequence of using Pickle Juice, or other acids, is that they foul themselves out very quickly on the Iron – requiring unending repetitions over many months to remove the Iron Oxide sands.  The only good thing about Pickle Juice is that it’s cheap.

Other acids will also succumb to quickly being fouled by the Iron in the black sand oxides.

The bottom line here is that it really is best to just carefully pan down your ultra concentrates in very small increments and discard whatever isn’t Gold.  Using those other techniques will cost you $30 for every cent’s worth of gold.