The history of gold mining

The history of gold mining is as old as man’s.

There is no doubt that gold was one of the first metals known to primitive man. After all, it exists in nature in an elemental state. Its connection with primitive cultures is evidenced by the fact that crude gold ornaments have been found among the remains of all prehistoric peoples. Of course, it is not known how, why, where and when gold was first mined. On the other hand, the reasons for gold mining are known: the precious metal occurs naturally in nature, has a permanent bright yellow shine, is easy to work with and can be combined with other metals relatively easily. It has always been the ideal material. No wonder gold was one of the first metals to be processed.

The first finds

The oldest finds of processed gold were discovered in Bulgaria and estimated at 4,600 to 4,300 BC. These are 3,000 works made of gold, including jewelry and animal replicas. There is further evidence of gold in the form of jewelry from Eastern and Central Europe from the fourth millennium and increasingly from the third millennium. Even then, people understood the special value of gold. The former high culture of Egypt in particular saw gold as a symbol of power. They were the first people to make significant use of gold. Archaeological evidence shows that the yellow metal was used as early as 3,100 BC. was quite widespread. And that despite the fact that silver was more expensive and rarer back then. The yellow precious metal outshined silver, whether as a sacrificial offering or as a piece of jewelry. Huge idols and even chariots were made of gold. Due to its properties, gold became a symbol of eternity. The Egyptians had almost everything made out of gold. Even if one can only guess how gold was mined at the beginning of gold processing, experts are sure that the precious metal was first mined in water.

First was panning for gold

Gold was more common in nature than it is today. Pure panning for gold was also significantly more productive than one can imagine today. Rock, sand or mud were filtered and pre-cleaned. Then it was swung around in containers until the gold had separated from the dirt. As people’s metropolitan areas expanded over time, so did the demand for gold. Only with the advent of the Egyptian high culture was gold also extracted by mining. Thus, gold was no longer just washed, but also dug afterwards. It is not known when the first separation of gold-bearing ores took place. What is known, however, is that thousands of slaves had to dig up the gold, which was still relatively easy to mine, every day.

Slaves were used to extract gold

The Greek historian Diodorus Siculus, who lived between 60 B.C. and 30 B.C. lived, described Egyptian mining and thus produced the first historical sketch of gold mining. Siculus wrote of the agonizing and barbaric procedure:
“The miners follow the direction of the metallic threads in their work and are aided by the light of lamps in the subterranean darkness. The stones are carried outside, where they are broken and broken up into small fragments. The workers never stop torturing themselves. They are constantly forced to work through mistreatment and lashes.”

Children also had to serve

As was customary at the time, child slaves were also used: “Even children are not spared. Some are sent to carry the blocks of stone, others to break them into pieces. The fragments are taken out by older craftsmen, over 30 years old, and crushed in iron mortar. The fragments thus crushed are then found in mills turned by women and older men. Two or three people work in each mill. It is impossible to describe the suffering of these unfortunates. Exposed to the cold and the rain naked, they are not allowed to rest. There is no pity, neither for a weak woman nor for an old man on the brink of the grave; nor for the sick who may become victims of the fever. They are all hit indiscriminately with repeated blows until they die of their ailments on the spot where they worked.”

Origins of gold mining more than 5,000 years ago

The actual processing of the ore was primitive, but still ingenious. After the ore was crushed into powder, it was spread on wide, slightly inclined tables, and a stream of water running over the tables eroded the earthen materials from the gold. This process was repeated several times by the workers. They then rubbed the pulverized ore with their hands for some time, and then wiped it with small sponges to remove the impurities that water alone could not remove. In this way the gold dust became clean and shiny. The gold could then be further processed by goldsmiths for all performances. Egyptian goldsmiths also smelted ores to separate the metals within. They use refractory clay blast tubes to heat the furnace. It is estimated that approximately 6.7 million ounces of gold were mined from the Eastern Desert gold bearing deposits.

And today?

Gold mining has changed significantly over the centuries. Chemistry and mining gradually developed and so did the processing of gold. The precious metal cannot be produced synthetically, so gold is extracted from nature as it has always been. In the 19th and 20th centuries there were many gold booms across the planet. The gold rush had broken out. Countless gold digging sites are now deserted steppes or tourist resorts. The sources of gold production dried up. Today there are still many gold mines, but drilling for gold is very expensive and technically advanced. Because gold veins are no longer developed in large quantities in the water or in the obvious nature. The mining companies have to dig deeper and deeper. The amount of gold per tonne of ore is also decreasing. In some places, one gram per tonne of gold is enough to justify mining. At the deepest drilling site in the world, gold is being drilled around 4,000 meters below the surface of the earth in South Africa. In order to open up new sources of gold, gold producers have to invest a lot. It takes a few years of exploration and drilling to guess whether a gold mine will be profitable. As already mentioned, the chemistry for separating gold and ore has also evolved. There is still the classic way of gold mining: gold panning. Today, gold panning is used little or not at all to extract gold. It only serves as a step before the actual procedure. Rock, sand or mud are filtered and pre-cleaned. After that they are processed further. Only in the Amazon are companies still panning for gold, but not in the adventurous sense of panning gold in special pans. Here, the gold is separated from the rock at high pressure. This method then leaves behind a barren lunar landscape. Widespread processes for gold extraction are therefore the amalgam process and cyanide leaching.

Amalgam procedure

When gold is extracted using the amalgam process, sludge and rock sands that contain gold are pre-washed or ground and intensively mixed with liquid mercury. The smallest grains of gold mix with the liquid mercury and combine with it. Gold and mercury form a silver-colored alloy, the amalgam. The amalgam settles on the bottom and can be easily removed. In the next step, it is heated to 360 degrees. The mercury, with its very low melting and boiling point, goes into the gaseous state at this temperature (sublimation) and what remains is the raw gold. Releasing mercury into the environment causes major problems because it accumulates.

Cyanide leaching

If soil contains at least 0.9 grams of gold per ton, it is economically viable for cyanide leaching. In gold mining, the rocks are first ground and stacked. An oxygen-containing sodium cyanide solution then seeps through the dust-fine rock. However, the gold, which is actually very inert, forms a complex compound with the cyanide. Now bound, the gold flows into catch basins as a gold cyanide complex. It is a highly toxic leachate. The solution is filtered and precipitated by adding zinc dust. The resulting brown sludge becomes raw gold through reduction. The cyanide-containing residue is not nearly as stable as the mercury residue and decomposes after some time.

Dangerous Production

Both processes are dangerous for humans and the environment. Mercury is toxic. Since it evaporates quickly, the heavy metal can be inhaled unnoticed. Direct skin contact should also be avoided. Mercury vapors are produced in dangerous concentrations even at low temperatures. Even intensive one-time contact can lead to complaints. The worst consequences of long-term contact are severe stomach and intestinal colic and bloody diarrhea, kidney failure, serious damage to the central nervous system and side effects such as motor disorders or weight loss. Dissipated into the soil, it damages the soil and the river basins. Mercury accumulates in fish, which eat various species of animals and also serve as food for humans. A whole kilogram of mercury is required to extract just one gram of gold.
Since the cyanide lye has to be stored outdoors due to its large quantities, this is dangerous for people and the environment, e.g. due to possible ruptures in the basin. If you come into contact with hydrocyanic acid, this can lead to death in seconds. In 2000 in Romania in Baia Mare and in 2011 in Turkey’s Kütahya there were serious accidents. One result in 2000 was a contaminated Danube and extensive environmental damage.

Precious metal recycling

The largest gold miners are China (440 tons of gold in 2017), Australia (300t) and Russia (255t). However, since gold is not an element that decomposes or becomes worthless after being damaged and used, it can be reused. The process is called precious metal recycling. Around 1,200 tons of gold are extracted from old gold every year. Old gold refers to the precious metal that has already been used. Whether in jewellery, in technology or as dental gold. Separators such as the Norddeutsche Edelmetall Scheideanstalt are responsible for precious metal recycling. The modern industrial methods of a refinery are the extraction of gold in the anode slime process and by aqua regia separation.

Gold extraction using the anode slime method

The anode slime process is a modern recycling process. This method is the most common today. The electrochemical method offers the possibility of obtaining particularly pure precious metal and is environmentally friendly in its implementation, since toxic substances such as mercury or cyanide are not used. In order to obtain the precious metal in its pure form, it is electrolytically separated. Ions migration is triggered in a liquid electrolyte by means of a defined current via two electrodes, cathode and anode. The impure metal is used as an anode. A solution of a salt of the metal in question serves as the electrolyte. The opposite charge of the two electrodes causes the gold ions to collect on the cathode, and anode sludge is formed as they pass through the electrolyte. The tramp elements from the impure anode dissolve or fall as a fine powder. The sludge as well as the cathode deposits contain the coveted precious metal in pure form. After washing, drying and melting, the reprocessable raw material gold is obtained. This electrochemical cleaning is also called electrolytic refining .

Gold recovery by aqua regia

For gold, which is metallic or in the form of an alloy, there are wet-chemical processes with the solution using aqua regia. Since gold is not attacked by most acids, particularly strong and oxidizing acids are needed to dissolve gold. Aqua regia consists of hydrochloric acid and nitric acid in a ratio of 3 to 1. Gold oxidizes in this solution even at room temperature. The dissolved gold becomes gold tetrachloride acid and must then be separated from other metals in the separation process. You work with extremely reactive and concentrated acids. The processes are demanding and require both special reactors and the know-how of experienced chemists.