Gold Panning
suggested grade levels: K- 4
view Idaho achievement standards for this lesson

Procedure:
1. First fill the pan level full or slightly heaping with placer material.
2. Submerge the pan in water, preferably still water 6 to 10 inches deep.
3. Carefully and slowly stir the contents of the pan with both hands so as to totally saturate the material with water. It is extremely important at this stage to break up all dirt clods and dissolve the clay.
4. While the pan is held in a flat position under water, shake the pan in a circular or back-and forth manner. The purpose of the shaking is to stratify the contents of the pan in layers so that the heavier minerals are concentrated on the bottom and the lighter material moves upwards.
5. A 16-inch pan full of water-saturated gravel may weigh as much as 30 pounds or more. For this reason the work can be lightened if the pan is worked under water.
6. The pan is tilted so that the less dense material can be floated over the edge of the pan.
7. The gold and other heavy minerals will work downward and concentrate at the edge of the flat pan bottom.
8. Continue to shake the pan in a circular motion under water or with water in it. Then repeat the tilting action so as to wash or float off the light surface layers.
9. Finally the pan contents are reduced to the heavy mineral concentrates and any gold present can readily be seen. Many beginners worry that their style is faulty and that they are losing gold; however, if normal amounts of heavy minerals or black sands are recovered, then it is quite likely that the gold which has a much higher density would also be saved.

Capacity of the Gold Pan
Panning is the most arduous and lowest capacity method that may be used to wash gold from placer gravel. Because an accomplished panner can only wash 8 to 10 pans per hour, the method is not suitable for anything but high-grade gravels. Such high-grade material generally occurs only at bedrock or in crevices. A 16-inch gold pan level full of dry gravel will weigh approximately 22 pounds. However the weight may be more or less depending on the amount of moisture and the size and type of material. Typically, one cubic yard of bank gravel weighs 33oo pounds. Depending on the type of placer material 150 to 180 pans are normally equivalent to one cubic yard. If a person is able to pan at the rate of 10 pans per hour, it is possible to pan about 1/2 cubic yard per day. Under exceptional conditions, such as an experienced panner working with clean gravel, it is possible to pan up to one cubic yard in a day.

Separation of Black Sands from Gold
Nuggets and small particles of gold of sufficient size should be picked out with tweezers and placed in a vial. There are several different methods or combinations of methods for separating the remaining fine gold from the black sand concentrate. Transfer the concentrates to a smaller pan and continue to manipulate the pan in the manner described above until the black sands are separated. This procedure should be done above another pan so that if gold is lost, it can be recovered. If the concentrates are dried, the black sands can be separated either by a magnet or by blowing. Magnetite commonly represents up to 90 percent of the heavy mineral concentrate. Several drops of mercury can be placed in the concentrates and the remaining fine gold amalgamated. If the colors are very fine, the added time and effort to recover them may not be worthwhile. For example, the Snake River gold in southern Idaho is so fine that several hundred colors may only be worth one cent. Pans with copper bottoms may be used for the amalgamation process. First the copper bottom is abraded with emery paper and then, using a device other than your hand, coated with a clean shiny surface of mercury. Gold in the concentrates is picked up by contact with the mercury surface. Only fine material should be used in the pan as coarse concentrates will grind off the mercury. As amalgam collects on the bottom of the pan, it should be scraped off with a scraper made of iron. You should always use extreme caution when working with mercury. Take particular care not to touch mercury with your hands or breathe its vapors.

Amalgamators
Rusty gold or gold partly coated by iron oxide does not amalgamate completely because the mercury cannot make complete contact with the gold. To remedy this problem, the heavy mineral concentrates with the gold must be agitated to clean the gold. Mechanical amalgamators are normally used to treat rusty gold. Most amalgamators consist of a cast iron container in which the concentrates are placed. A rock tumbler will work well for small samples. Water, one or two percent mercury, caustic soda and steel balls are combined with the concentrates. As the container is turned slowly for several hours, the steel balls provide a grinding action to clean the gold. Finally the gold, amalgam and mercury are recovered by panning. A small concrete mixer serves very satisfactorily as an amalgamator. Such a device can handle 50 to 100 pounds of concentrate, one or two pounds of mercury and a few cobbles or steel balls together with water. Generally about an hour is sufficient to complete the amalgamation process.

Cleaning Amalgam
Amalgam is first separated from the black sands by carefully washing with a gold pan. The amalgam or impure mercury is then squeezed manually through a tight cloth such as canvas, chamois skin or buckskin. The process is best done under water to avoid losing mercury. The cleaned mercury still contains a small amount of gold which will increase its reactivity with gold. After squeezing, the stiff, pasty amalgam may still contain up to 75 percent mercury with the balance in gold and silver.

Separating Gold from Amalgam
Gold may be recovered from amalgam by several different methods. The selection of a particular method is based on convenience or the need to recover the mercury. If it is unnecessary to recover the mercury, the simplest method is to volatilize the mercury, by heating the amalgam. In this method, the mercury is placed on a clean iron surface and heated to 675 degrees Fahrenheit, a temperature at which mercury vaporizes. Mercury vapor which may appear as a heavy white vapor, is extremely dangerous and should not be inhaled.

Potato Method
The potato method is commonly used by prospectors because it is both simple and allows part of the mercury to be recovered. The following procedure is used:
1. A large potato is cut in half.
2. On one half, a recess is hollowed out which is larger than the amount of amalgam.
3. The amalgam is placed on a clean sheet of iron such as a pan suitable for heating.
4. The potato is placed over the amalgam and then heat is applied below the sheet of iron.
5. After 15 to 20 minutes of heating, the mercury will be driven off into the potato and the gold will be left in the hollow of the potato.
6. The mercury can then be recovered by crushing and panning the potato.

Nitric Acid Method
The amalgam is placed in a beaker with a 1 to 1 solution of nitric acid and water which is heated until the mercury is dissolved. After the mercury is dissolved, the gold sponge can be washed in water. Finally the gold may be annealed in a porcelain crucible.

Retorting
Retorting of amalgam to recover gold requires the most elaborate equipment but allows all the mercury to be saved. A retort is basically a pipe-shaped device in which the amalgam is placed in the end that is heated to vaporize off the mercury. The mercury vapor then moves through a condenser pipe where it cools and condenses back to liquid mercury.

Related Lesson Topics:
Mining: Mining