Gold Assay Techniques

(A paragraph taken from our short paper "Introduction to Cluster Interference and co-bonding in Mineral Resource Evaluation", Article titled "Cluster Compound Ores" by Robert Bishop)

I like to divide precious metal ores into three categories for practical reasons in terms of the processing needed to recover the values. The last two are not considered to be ores by the mainstream mining industry. (1) Conventional ores having metallic values in quartz, calcite and/or sulfides, and as chemical concentrations in sulfides. This type responds to standard assay methods and is easy to identify with many process methods available to extract the values economically. The second type is (2) abnormal cluster compound ores made up of metals, semi-metals, and non-metals found with high concentrations of iron. Compositional analysis of materials hosting these values may show only abundant iron. Even non-metals and semi-metals like sulfur and arsenic, respectively can remain undetected. Under the right redox conditions smelting or roasting can cause these elements to break down and express themselves in their normal molecular forms. The precious metals usually remain alloyed in this material in their cluster forms. Occasionally they are found in a normal state after these treatments, but this is rare. The physics and chemistry of cluster science examines the behavior and phenomenon of these microcrystalline forms of matter. The third category involves a close association with the cluster compounds that interfere with the expression of the precious metals normal properties. Precious metals can be in a metallic form as discrete particles or as normal ions in a gold mineral (i.e. gold telluride, arsenopyrite) adjacent to and bonded to minerals composed of cluster compounds. These are (3) conventional-abnormal-cluster compound ores. When the interfering mineral is removed, the normal behavior of the precious metal is allowed to express itself. This is why pretreated ores can give higher assays than raw ore.

Measure out a 10% salt (NaCl) concentration and saturate the sediments with the solution. A 1% Na-Hypochlorite or bleach with pH on the alkaline side (8-14) pH can be maintained by lime additions. Chlorine vapors stay in solution at this pH range. Hypochlorite electro potential discharges more efficiently on the alkaline side. Only microscopic gold will dissolve in this relatively mild solution. Gold larger than 10 microns should be dissolved on the acid side with ORP>950 mV. Submerged leaching with good circulation can complete in a matter of hours.

RIP - resin-in-pulp

Add resin to pulp and agitate by shaking or swirling or use a gentle mechanical stirring (slow paddles opposed to high speed prop) - A variation is to decant the solution then add the resin collector. Rinse the pulp at least once to pick up residual pregnant leach values.

In-Line-Cannister

Pump solution through PVC pipe with appropriate nylon or polypropylene screen mesh to hold resins in place. One or two teaspoons resin may be enough. Low cost marine 12 VDC bilge pumps will stand up to the corrosion for test purposes.--Five gallon buckets or square containers can hold gravels for leach testing. Use plastic plumbing, valves, hoses and connectors to complete vat circuit.

Resins

High-base anion exchange resins or neoprene foam can be used once to selectively recover gold.

Resin Ashing & Cupelling

Slowly heat to char in stainless steel bowl. Then slowly burn with cover on to carbon-ash mixture (50-50). Cupel in lead foil to gold bead.

Leaching mineral concentrates at pH 1 or above separates iron from good values. Precipitation at this pH is selective for precious metals over base metals and iron.

Try to use the minimum amount of collector metal in cupellation. Think of the cupel as a small smelt to produce dore. Lead and cupels are inexpensive materials that can be used in production.

Can you combine the cupel ingredients in a small crucible and fire to a dore finish?