How to do Fire Assay

    Fire assay has been in use for thousands of years and still stands the test of time as the standard method to value noble metals. A lot of attention has been given to "micron gold" or "colloidal gold". A cold hard fact of this type of gold requires a lot of material to make even one ounce. Generally, much more ore than an independent operator is equipped to move.

    Fire assay has been in use for thousands of years and still stands the test of time as the standard method to value noble metals. A lot of attention has been given to "micron gold" or "colloidal gold". A cold hard fact of this type of gold requires a lot of material to make even one ounce. Generally, much more ore than an independent operator is equipped to move. No machine, recovery process, or chemical method will produce any gold if there is not enough values to collect it from the ore.

    How to Measure for Gold

    Most assay samples tend to be high-graded and do not represent the ore body. A serious independent miner needs a consistent ore that will run around one ounce per ton to make any profit. It is a fact that there is gold in water and most sands, including black sands. However, the cost of equipment, mining and refining is often more than the values that can be recovered.

    Platinum group metals (PGM) are very rare, but they do show up in micro amounts in many ores and sands that have iron content. These traces are more of a problem than they are of any commercial value. It should be noted that the PGM's mines in South Africa move 12 tons of material to recover just one ounce of PGM's. Assay definitions imply that only ore is assayed, as opposed to samples of rock. Tens of thousands of samples and other mineral matter are submitted to assay laboratories annually. Only a fraction of then turn out to have economic meaning.

    Arguments contend that a fire assay is not applicable to Colloidal or Micron gold are:

    1. The particles are so small they vaporize or burn off.
    2. Small particles of gold float on the surface and stay in the slag.
    3. Interfering elements mask the gold.

    Gold does burn into the air, plus will go into the crucible or remains in the slag are factors that can be seen when the torch assay method is used. There is no good evidence that elements mask the gold.

    Ores that do not assay well.

    1. Ores with high sulfur or copper content may or may not assay. The results will depend on how much sulfur and other impurities are in the ore and the method used to assay it.
    2. Ores containing high base metals, lead, nickel, tin, copper and etc. will assay, but are difficult to handle so the results can generally be inaccurate.
    3. Placer gravels contain mostly free gold and may assay very high or not at all depending on the sands that were selected to assay. Even when concentrated the results may not represent the true value of the placer location. Placer values are generally given in dollars per yard of material to avoid this problem.
    4. Some minerals of gold require a special process to determine any value. Some Platinum Group Metals (PGM) are assayed with nickel as the collector. Standard assay litharge will collect only 3 of the PGM's while nickel will collect all 6, plus the gold. However, high copper content in the sample can give a false reading. In addition, the nickel must be eliminated from the sample.