From mining to striking, understanding the entire minting process
Though easier than producing coins, manufacturing gold and silver bullion bars is still a tedious and complex process. By understanding the various steps that go into producing a single precious metal bar, you can gain a greater appreciation for your investment and the reason behind bullion premiums.
While other minting and purification methods exists, the process outlined below is the most common.
Step 1 - Mining and Extraction
First, the metal needs to be located and extracted.
In the past, hydraulic mining was used to move and separate gold from deposits with high pressure water jets. Nowadays, gold and silver ore is typically mined from the ground using explosives and other techniques.
Four common ways to mine precious metals from the earth are placer, hard rock, by-product, and processing gold ore:
Placer - This method makes use of metal detection, dredging, panning, sluicing, and cradling. It is typical for amateur miners and utilizes water plus gravity to segregate the metal from other materials.
Hard rock - In this technique, miners use open wells or underground tunnels to retrieve gold from rocks. Most mines worldwide use this traditional system.
By-product - Similar to hard rock mining, except the precious metal is not the target. The principal purpose of such operations is to mine copper, gravel, or sand (although sizeable quantities of gold and silver make this procedure a lucrative endeavor).
Ore processing - A majority of mining operations avoid ore processing because yield is extremely low and the method is expensive. It also causes extensive damage to the environment. With this chemical process, workers use cyanide and crush the rocks containing smidgens of gold.
Once mined, the gold or silver then has to be extracted from the rock deposit through a multi-step process involving crushing the sediment to the size of sand grains. After applying a chemical solution to the ore in a process known as “leaching,” the mixture is heated in a smelter to 1600 degrees Celsius (2,912 degrees Fahrenheit). The gold, which is a heavier element, then sinks to the bottom and is removed from the “slag.”
Step 2 - Refining and Pouring
Refining is the next step in the production of gold and silver bars.
It entails the removal of impurities that remain after the process of smelting. Workers in refineries combine chemicals with pressure and extremely high temperature to purify gold and silver in a large furnace.
Thanks to advanced technology, manufacturers are now capable of producing a premium quality of gold and silver bars. Electro-refining involves separation of impurities by means of electricity charged through immersion of adulterated silver in acidic solution. The process generates very pure metal for monetary and industrial purposes.
Most major bullion manufacturers purify the metal through one of two processes:
Electrolysis - Also known as the “Wohlwill Process,” electrolysis is when the metal is first cast into bars which are used as anodes in an electrolyte consisting of gold chloride and/or hydrochloric acid. When the electric current passes through the gold or silver, 99.99% pure metal is deposited at the cathode. This deposit is then washed, dried, melted, and poured into bars.
Pyrometallurgical chlorination - Also known as the “Miller Process,” pyrometallurgical chlorination is when chlorine gas is pumped into molten bullion. Base metals react with the chlorine to form chlorides, which either evaporate or rise to the surface to form a slag. Once purple fumes of chloride begin to appear, it is a sign that the metal has reached around 99.5 to 99.7 percent purity and the process is complete.
Regarding silver, workers commonly use a different method of purifying and separating the metal from lead known as the “Parkes Process.” This method is a pyro-metallurgical technical means of extracting the ore from the lead and is different from the manual process, commonly used back when there was no modern equipment. Factory laborers had to pour the thawed silver into dies before removing the cooled ingots or silver bars. Some factories still use this obsolete approach which results in bars with uneven surfaces.
Once the purification is accomplished, some laborers bring the samples to a laboratory for testing or assays prior to measurement. Gold and silver must be 99.9% pure. Workers melt the gold and silver bullion in metal or ceramic containers before casting them in ingot molds. They cut the metals into pieces or melt them prior to pouring. Experts conduct an assay or analysis to measure and examine the composition of precious metals. This is the most effective approach in finding out if bars manufactured in mints adhere to standards of purity and content.
Bullion manufacturers and mints can make poured bars from precious metals like gold, silver, palladium, and platinum. The melting point of 24-karat gold is approximately 1,945 degrees (Fahrenheit). Pure silver requires a lower temperature of only 1,761 degrees (Fahrenheit) to melt, making it less complicated for mints to produce poured silver compared to gold.
Step 3 - Pressing and Striking
Next, pressed gold bars are made from the high quality poured gold bars.
Gold and silver refiners must use expensive metal to produce pressed bars, which allows mints to have more control regarding consistency and quality. It is the main reason manufacturers and mints opt for this technique.
This process involves using high-powered machinery for cutting and stamping the metal into pressed bars. First, the refined liquid metal is poured into a casting machine which forms long, thin bars. These bars are then pressed multiple times in a rolling mill until they reach their approximate correct thickness. Softening, or “annealing,” of the strips may be needed at this time.
Next, the strips are formed into the exact thickness desired using a precision machine known as a gauging mill. Blanks are then punched from the strips and heated in a furnace until softened. Once weighed and tested, the blanks are polished, cleaned, and finally struck (like coins) with a die. Blanks that do not pass quality control are recycled.
For striking, extremely high pressure is applied to the blank and the mirror design is stamped into it. The stamped bar is then inspected and shipped, thus completing the process.
Pretty cool, right?
Why Invest in Gold and Silver Bars?
If you want to buy .999 fine gold bars or silver bars, we invite you to see what we have in stock today. Many precious metals investors prefer bars to coins because they are easier to stack, and most carry a lower premium than their sovereign coin counterparts.
At Provident Metals, we offer gold and silver bars in a variety of sizes, ranging from 1 gram to 100 ounces, and everything in between.