Amalgamation and panning have been used traditionally to treat gold ores and some metallurgists consider important to perform these tests in order to have a preliminary idea of levels of free gold present in the sample. Take the sample of gold ore, weigh, and then reduce in size (weight and mesh). The assay sample should weigh at least 100 grams and should pass at least a 100-mesh screen. Take care that all scales pass the screens used.
In order to amalgamate the sample weigh out five charges (100 grams each) of the 40-mesh lot, and place in bottles provided for the purpose with 10 grams of mercury, and 150 mL of water; and agitate for 30 minutes. Separate the mercury by panning and transfer to a porcelain dish, dry with filter or blotting paper. Place the thoroughly dry mercury in a crucible in which 20 grams of lead have been placed. Add to the crucible a charge consisting of 30 grams of litharge, 10 grams of soda, 5 grams of borax glass, and 0.5 grams of argol, and silver enough to part the gold. Fuse the charge very slowly, starting with a slow temperature in the furnace or if using a muffle, one that has not yet become red and has a good draught through it to prevent the escape of fumes into the room. This point is important in order to avoid the release of vapor of mercury into the room. When fusion is quiet, pour and cupel the resulting lead button. Part and weigh the gold. This part must be performed by experienced metallurgists.
The contents of the bottles are to be panned separately and then together. Pour the contents of one bottle into a gold pan, add water if necessary, and wash by giving the pan a vibratory motion as in vanning, washing off the light particles of gangue and leaving only the mercury and the heavy portion of the ore, as black sand, sulphides, etc. The light portion of the ore should be washed into a pan or vessel of somewhat larger size than the gold pan. Repeat the panning of the mercury and concentrates in order to separate the mercury. If the mercury is floured, add a small globule of liquid sodium amalgam. Treat the contents of the other bottles in the same way. The light portion or tailings of the several bottles may be poured into the same vessel. Re-pan this material to make sure that no mercury or sulphides have escaped. If any is recovered, add to the amount recovered before.
Treat the collected mercury as directed above. Allow the tailings to settle, pour off the surplus water, and dry by any convenient means. When dry, weigh, pass through a 100-mesh screen, mix well and assay. Wash the heavy material or concentrates into a small porcelain pan, or if more convenient on to a batea. Examine under a magnifying glass or low power microscope, and note the different kinds of sulphides or other constituent, and the approximate amount of each.
The test results will give the following information: assay value of ore in ounces, and dollars and cents per ton; gold amalgamated in ounces, and dollars and cents per ton; assay value of concentrates in ounces, and dollars and cents per ton; assay value of tailings in ounces, and dollars and cents per ton; percentage of gold amalgamated; total gold contents in comparison with assay value; percentage and different kinds of sulphides or other heavy; and presence of free gold.