There have been many questions about how to get gold out of black sand. I thought I would post a method that I use on cleaning up on my 6" Dredge. I clean up the top of my sluice box everyday and the rest of the sluice box when it is needed. One problem I see with a lot of new miners is they clean up too often and this takes away from the time the could be dredging and finding more gold. If you have the sluice on your dredge set up so that the gravel is not getting too full between the rifles and not running so fast that it sweeps the rifles, then once a day clean up is all you should need on most store bought dredges. The perfect set up for the sluice is so you have about one quarter inch of carpet showing between the gravel of the middle riffle of the sluice and the one below it. Now dredge all day.
After dredging all day I empty my dredge into a large wash tub. I then screen those concentrates using a 20 mesh screen into a 5 gallon bucket. I then pan the concentrates that did not go through the 20 mesh screen while down at the river (looking for nuggets of course). Any gold found in the concentrates that were to large to fit through the 20 mesh screen, I put in a vial. I then put a shovel sluice (a Keene or Le Trap sluice works well) inside the dredge sluice so that the shovel sluice is close to the header box or jet flare (Note: This only works on 5" and larger dredges). I use a modified Keene A-52 sluice. It has some NoTrax matting glued in the top to catch fine gold. I then start the engine on the dredge at idle so the water runs down the shovel sluice. I adjust the engine so that the water flow is swift enough to wash out light sand and still save all of the black sand and gold. The out put of the shovel sluice goes back into the dredge sluice and there are still several riffles in the dredge sluice that will catch any flour gold that happens to escape (this will remain until the next time I dredge). I then scoop the concentrates that I screened into the shovel sluice. When all concentrates are ran. I then empty the shovel sluice into a 5 gallon bucket. I then have <20 mesh extreme concentrate.
To do the final cleanup I use a panning wheel and a micro sluice. You can also pan down to get to the last of the impurities. These impurities usually consist of a small amount of black sand, a few iron rocks, and pieces of lead.
There are many ways to go about doing this final cleanup. Personally, in general cleanup I like to stay away from the use of mercury, as there is a faster way without it. I also like to stay away from the use of nitric acid because its usually not needed either. There are times when the use of mercury and nitric acid can help speed thing up. Usually though, I can do the final cleanup without them.
(1) Dry out the gold by pouring it into a metal pan and heating it over a stove outside. Don't get it so hot that any pieces of lead which are still with the gold will melt. Heat it up just hot enough to dry it out. It is a good idea to stay upwind anytime you put gold in a pan and heat it up. Mercury attaches itself to gold in different amounts. Often it's there but you can't see it. When heating the gold to certain temperature, the mercury vaporizes off. These vapors are very dangerous. So it is good practice to heat your gold outside and downwind of you, even when heating it up just enough to dry it out. Also, the pan you use for heating up gold during cleanup should be used only to cleanup, not for cooking. I use a portable hot plate for this.
(4) By lightly blowing over the gold, you can finish extracting the rest of the impurities. If you can locate a very fine screen you can use it to separate the smaller pieces of gold and impurities from the larger ones just after drying it out. This speeds the process up a bit.
(5) Put your gold back in the metal pan, take it outside and heat it up, hotter this time, in order to vaporize any further mercury for the gold. This will bring your gold back to the basic deep rich beauty which we love.
(6) Now you can put it in a bottle. If you want to sell it keep it dry, but if it is for show put water in the bottle to keep it beautiful. The water will also prevent the glass vial from breaking due to the weight of the gold.