(Decent amounts of very fine gold can be "locked" into black sands concentrates like these.)
Although they can definitely be a hassle to deal with at times, black sand concentrates can contain as much as 20% of your total gold recovery. Some years ago, mining consultant Gilbert Trujillo came up with the following method for separating fine gold from its black sand or magnetite "shell:"
"Simple and Effective"
"The procedure I have used in processing black sands is simple and very effective. Because the shell is a physical bond rather than a chemical one, it can be removed rather easily. Most of the current methods being used today that treat the black sands with chemicals create environmental problems and, in most cases, are not cost effective."
"The process I use requires the black sands to be dried first, then run through an impact mill. If your impact mill is built to run wet, just dry the black sands afterward. I then run the material through a magnetic separation system."
(Note: An impact mill is a motorized device that reduces gold-bearing material down to 200-300 mesh for most small-scale operations. There are many "bench" impact mills designed out there these days but they can be very pricy. You'll probably need to recover around three troy ounces of microdot gold from those black sands of yours to pay for one of the nicer home models. J.R.)
("Bench" model impact mills.)
"Running the material through a magnetic separation system will give you two distinct classifications: 1) The gold in the non-magnetic group, and 2) the gold in the magnetic group. Once this is done, you can follow your normal black sand concentration method. You should get clean gold concentrates this way and increased gold recovery."
In my ever-so simplistic mind I see Gilbert's method as a four-step approach for processing black sand concentrates:
1) Dry your black sands (let's forget the wet-run approach for the sake of simplicity).
2) Run them through an impact mill down to the appropriate mesh.
3) Separate the black sands magnetically.
4) Process them for fine gold recovery using your standard method (i.e., "Blue Bowl," Miller Table, spiral wheel, mini-sluice, etc.)
(Fine gold recovery is what it's all about.)
By the way, I'm no expert on magnetic separation systems by any stretch. The crudest and most obvious "system" would be a large magnet. Alternately, I believe an electrostatic set up could be used. Undoubtedly however, there are probably a number of magnetic separation systems out there for sale...I'm just not familiar with any of them.
Anyhoo, there's food for thought here.
Best of luck.
If you liked this post, you may want to read: "A Nifty Little Item From Down Under"
(c) Jim Rocha (J.R.) 2013
Questions? E-mail me at firstname.lastname@example.org