1. Fundamental knowledge relating to Raw Gold and Refining.
Mining Process
Gold mining is carried out on a small scale by individual prospectors (e.g. in various West African
Countries, and also in Brazil) and on a large scale in underground mines (e.g. in South Africa) and in
open pit mining (e.g. in the United States and Canada).
The simplest method of gold mining is panning which involves filling a circular dish with gold-bearing
sand or gravel, holding it under a stream of water and swirling it. The lighter sand and gravel is
gradually washed off, leaving the gold particles near the centre of the pan. More advanced hydraulic
gold mining consists of directing a powerful stream of water against the gold-bearing sand or gravel.
For river mining, elevator dredges are used, consisting of flat-bottomed boats which use a chain of
small buckets to scoop up material from the river bottom and empty it into a screening barrel. The
material is rotated in the barrel as water is directed on it. The gold-bearing sand sinks through perfo-
rations in the barrel and drops on to shaking tables for further concentration.
There are two main methods for the extraction of gold from ore. There are the
processes of amalgamation and cyanidation.
The process of amalgamation is based on the ability of gold to alloy with metallic mercury to form
amalgams of varying consistency, from solid to liquid. The gold can be fairly easily removed from the
amalgam by distilling off the mercury.
The amalgamation process is rare today, except in small scale mining, because of environmental con-
cerns.
The process of cyanidation is based on the ability of gold to form stable water-soluble double salt
KAu(Cn)2 when combined with potassium cyanide in association with oxygen. The pulp resulting from
the crushing of gold-ore consists of larger crystalline particles, known as sands, and smaller amor-
phous particles, known as silt. The sand being heavier is deposited at the bottom of the apparatus
and allows solutions (including silt) to pass through. The gold extraction process consists of feeding
finely ground ore into a leach tub and filtering a solution of potassium or sodium cyanide through it.
The silt is separated from the gold cyanide solution by adding thickeners and by vacuum filtration.
Heap leaching in which the cyanide solution is poured over a levelled heap of coarse ore, is becoming
more popular, especially with low grade ores and mine tailings. In both instances the gold is recov-
ered from the gold cyanide solution by adding aluminium or zinc in a separate operation, concen-
trated acids create a reaction to dissolve the zinc or aluminium, leaving behind the solid gold.
Under the influence of carbonic acid, water and air, as well as the acids present in the ore, the cya-
nide solution decomposes and gives off hydrogen cyanide gas. In order to prevent this, alkali is added

2. (lime or caustic soda). Hydrogen cyanide is also produced when acid is added to dissolve the alumin-
ium or zinc.
Another cyanidation technique involves the use of activated charcoal to remove the gold. Thickeners
are added to the gold cyanide solution before slurring with activated charcoal in order to keep the
charcoal in suspension. The gold-containing charcoal is removed by screening and the gold extracted
using concentrated alkaline cyanide in alcoholic solution. The gold is then recovered by electrolysis.
The charcoal can be reactivated by roasting and the cyanide can be recovered and reused.
Both amalgamation and cyanidation produce metal that contains a considerable quantity
of impurities. The gold content rarely exceeds fineness 900 per 1,000 (90%) unless it is fur-
ther electrolytically refined in order to produce a degree of fineness of up to 999.8 per 1,000 and
more, but for this is required to add pure gold until the gold-content is at minimum 95%.
Gold is recovered further as by-product from the smelting of copper, lead and other metals.
Gold refining processes
99.5% Purity and/or 99.99% Purity.
Refining
Gold extracted by amalgamation or cyanidation contains a variety of impurities, including zinc, cop-
per, silver, and iron. Two methods are commonly employed for purification: the Miller process and
the Wohlwill process. The Miller process is based on the fact that virtually all the impurities present
in gold combine with gaseous chlorine more readily than gold does at temperatures equal to or
greater than the melting point of gold. The impure gold is therefore melted and gaseous chlorine is
blown into the resulting liquid. The impurities form chloride compounds that separate into a layer on
the surface of the molten.
The MILLER CHLORINATION PROCESS (patented in Britain in 1867) is an industrial-scale chemical,
pyrometallurgical process whereby either gold ore or dore gold is heated in furnace crucibles.
The process is able to separate gold from impurities by using chlorine gas which is added to the cru-
cibles once the gold is molten. Chlorine gas does not react with gold but will combine with silver and
base metals to form chlorides. Once the chlorides have formed they float to the surface as slag (salt)
or escape as volatile gases. The surface melt and the fumes containing the impurities are collected
and further refined to extract the gold and silver. It was invented by Francis Bowler Miller.
This process which can take up to 90 minutes, produces gold which is at least 99.5% pure with silver
being the main remaining component. This gold can be cast into bars as 99.5% + gold purity meets
the minimum London Good Delivery requirements of the London Bullion Market Association.

3. (400 OZ Bars – minimum 350 fine troy ounces and maximum 430 fine troy ounces. Please compare to
GLD rules).
The WOHLWILL PROCESS (patented in Hamburg, Germany, in 1874, introduced 1878) is an industrial-
scale electrochemical process used to refine gold to the highest degree of purity (99.999%). However
some customers such as jewelers and other industrial end users require gold that is almost 100%
pure, so further refining is necessary. In this case, gold using the Miller process (minimum 99%, low-
er percentages of gold in the anode will interfere with the reaction, especially when the contaminat-
ing metal is silver or one of the platinum group elements) is cast into anodes which are then further
processed by an electrolytic process by the other common refining process the Wohlwill process .
The cathodes for this reaction are small sheets of pure (24k) gold sheeting or stainless steel. Current
is applied to the system, and electricity travels through the electrolyte or chloroauric acid.
The final product is 99.999% pure gold sponge that can then be melted to produce various end prod-
ucts in 99.99% by add-on of silver suited to the needs of the customer.
When highest purity gold is not required, refiners often utilize the Miller process due to its relative
ease, quicker turnaround times, and because it does not tie up the large amount inventory of gold in
the form of chloroauric acid which the Wohlwill process permanently requires for the electrolyte.
99.5% - 400-OZ Bars need to be priced recognizably lower than 99.99% Bullion Bars in 1g up to
1,000g for further it is not required to have an exact weighing in the hot status during casting.
Resumption:
Raw Gold:
1. Gold dore is unlikely to be at gold contents higher than 92%.
2. Gold Dore is an amalgamation of Gold, Silver, Copper and PGM (Platinum Group Metals)
3. FA. Busch is a recognized Amalgam recycling Comp. producing Gold purities of 95% and for-
warding such to refineries providing the Wohlwill Process.
Bullion Gold:
400 – OZ Bars are produced generally by the Miller Process and are varying from minimum 350 fine
troy ounces and maximum 430 fine troy ounces providing purities of min. 99.5% so are still to be
refined further by the Wohlwill Process. Such Gold is to be priced lower than 99.99% Investor Bars
from 1g up to 1,000g.