At our November meeting we saw a video about black sand removal from concentrates. The information spoke of screening your material to -20 to make clean-up easier. That is, a screen that has 20 openings per square inch and anything that goes through the screen is classified as -20. I want to add a personal note to that information.
We have all sampled a new area by tossing a shovel full of bank material into a pan and washing it to determine if we want to spend more time in that location. This allows us to "wash off the rocks," moss, clay, and whatever else needs washing. No doubt this is a good idea . . . for the first pan. It will give you a visual of everything that was in the material and an indication of gold values in that area.
After that initial sample, it's time to get busy and move material quickly. The more dirt moved, the more gold recovered. With that in mind, I like to use the standard 1/4-inch screen (4 holes per square inch), the one that fits on top of a five-gallon bucket. Here is my procedure:
- Fill the bucket with water.
- Place a shovel full of material in the screen. The material will now be sitting in the water. If not, add more water.
- Shovel more water over the material.
- Grasp the screen and bucket and shake back-and-forth to allow the water to rinse over the material.
- You have now washed any gold off the rocks and you can break up moss and clay.
- Discard the larger material ONLY after you have checked for those big nuggets.
- Repeat the procedureuntil you have a bucket full of -1/4-inch material.
At this point, one can run the material through a sluice, wheel, or pan. Whatever method you choose, you are running 1/4-inch material. I have decided that I am going to classify my material at least one more time, to -20, before running it. Here's why:
- From my experience, Colorado gold is usually much smaller than 1/4-inch.
- In fact, I believe that it is even smaller than 120.
- That means any 120 gold in my pan/wheel/sluice hasto compete with the 1/4-inch material in order to be trapped in my equipment.
- If I don't classify it again, it's like trying to save a marble when panning with oranges; you're going to loose more than you save.
My plan is this:
I should save time and effort because I will be runing similar-sized material, less of it, and it should be richer.
- First, screen the bank material to -14-inch until I have two or three buckets full.
- Second, screen the -1'4-inch material through a #20 screen.
- Third, pan or sluice what I estimate will be slightly less than one full bucket of material.