The Gold of Sudan: From Cosmic Origins to River and Desert Mines

SadaNews - Gold is a cosmic element; millions or billions of years before the Earth existed, gold atoms formed during some of the most violent events in the universe. Astronomers believe that heavy elements, such as gold, are formed during the explosion of massive stars or when neutron stars collide, resulting in intense nuclear reactions.

These cosmic phenomena disseminate gold atoms into space, and by the time our solar system was born about 4.6 billion years ago, tiny traces of gold had mingled with the dust surrounding the sun, which would eventually form the planets.

The Cosmic Visitor

As the Earth formed, some of this primordial gold, alongside other heavy metals, was drawn by gravity into the molten iron core of the Earth.

In fact, scientists estimate that a quantity of gold sank into the Earth's core during its formation that would cover the entire planet with a layer 4 meters thick.

However, not all the gold is confined to the depths of the core; today, the Earth's crust contains quantities of it, albeit very small. But why does the crust contain any gold at all if much of it sank to the center? The answer lies in a subsequent cosmic event.

After the Earth formed hundreds of millions of years later, a torrent of meteors rained down on the planet during a period known as the "Late Heavy Bombardment." These meteors were stained with small amounts of gold and other precious metals, and when they struck the Earth, they added a layer of those metals to the mantle and crust.

Geochemical evidence supports this idea; the abundance of gold in the upper layers of the Earth is tens to thousands of times higher than expected.

Nevertheless, gold is rare in the Earth's crust: about 5 parts per billion on average. To illustrate this: if you have a ton of ordinary rock, you would be lucky to find just a few milligrams of gold in it.

Ancient Geology

Because gold is so diluted, nature requires special conditions to concentrate it in rich deposits. Fortunately for gold prospectors, such conditions exist on our planet, where gold tends to occur in two main forms in the Earth's crust: primary deposits confined to rocks and secondary deposits scattered in soil and waterways.

Deep within the Earth, heat and pressure cause water to circulate through rock fractures, and these hot, mineral-rich liquids can dissolve tiny amounts of gold and transport it. When the hot liquids move to cooler areas, gold can precipitate (i.e., come out of solution) and crystallize in the fractures, alongside other minerals such as quartz and sulfides.

Over time, this process forms veins of gold-bearing quartz that seep through the host rocks.

Gold in these veins may not be immediately visible to the naked eye; it may be distributed as microscopic particles. However, sometimes, visible lumps and flakes of gold can be found embedded within quartz.

Geologists also realize that gold can concentrate within specific types of volcanic (formed when magma makes its way to the Earth’s surface or near it and cools rapidly) or metamorphic rocks (which change in composition and texture due to heat and pressure within the Earth’s crust without fully melting), such as 'greenstone' belts, which are relatively ancient, greenish rocks.

Of course, the matter is more complex than that, but the summary is that once a gold vein or rock is exposed at the surface, erosion begins, as wind and water gradually break down the rocks, liberating the gold.

Because gold is extremely dense (19 times heavier than water) and chemically inert, liberated gold particles do not drift far from their source. Flowing water in rivers carries away light sand and silt, but heavy gold particles tend to settle in place when the current slows down.

Over thousands of years, this weathering process concentrates gold in specific locations, such as in river bends or banks, or in natural slopes and cracks of stream beds, or at waterfalls. The result is placer deposits (alluvial), a layer of sand or gravel containing scattered flakes or lumps of gold.

In fact, placer gold can be found in large or small lumps, but even small specks glisten among the sands after being naturally mined by geology. Indeed, many gold rushes throughout history began with the discovery of easily extracted placer gold deposits in streams.

In summary, the geology of the Earth provides two main types of gold deposits for miners, as previously mentioned. The first is lode deposits (primary sources where gold exists in rocks that need to be extracted and crushed), and the second is placer deposits (secondary concentrations of free gold particles that can be sifted from the sediment).

The Inert Treasure

Historically, both types of gold have been important. For example, the ancient Egyptians mined to extract gold from quartz veins, but they, alongside many subsequent peoples, also recognized the importance of sifting river deposits for free gold.

Gold's chemical inertness means it remains metallic and shiny even after eons underground, and unlike iron, it does not rust. This durability is why gold is sometimes found in its completely natural form, shining like the sun, without any intervention.

But it is not that simple; finding gold is only half the story, and turning ores and placer into pure metal is the other half. Gold that is made into a ring or necklace goes through a long journey of mining, extraction, and refining to reach its final form.

In placer deposits, mining can be as simple as collecting the sediment with a shovel and sifting it in a river; sifting is a traditional technique still used today, where the miner moves a pan of gravel with water. Because gold is heavy, the flakes settle to the bottom of the pan while lighter sand washes away.

In contrast, for primary deposits (hard rock), mining is harder, as miners must extract the gold-bearing rocks from the ground, either by open-pit mining if the ore is close to the surface, or by digging an underground tunnel if its veins are deep. They may need to extract tons of rock from massive open pits to reach gold veins.

After that, the gold-rich rock is crushed into small pieces to start extracting gold from it.

Once the rock is turned into powder, the goal is to separate the fine gold particles from the surrounding minerals. In ancient times, simple methods based on sifting and washing were employed, and these methods are still used today, though chemical methods have been added for finer extraction; however, some of these are toxic and harmful to the environment, but are still used.

The process does not stop there; there are several complex refining processes that ultimately lead to smelting, which produces impure gold ingots, often containing about 90% gold, which needs further purification. The molten gold is heated to a high temperature, and a stream of chlorine gas is pumped through it.

Chlorine reacts with contaminants like iron, lead, and zinc, turning these impurities into chloride compounds (like iron chloride) that form a scum on the molten gold, leaving the pure substance at the bottom.

Removing the chloride scum yields gold that is about 99.5% pure, but believe it or not, this purity still requires further chemical processes (the "Wohlwill" electrolysis process) for even more refinement for some clients. However, a gold purity of 99.5% is perfectly sufficient for most practical uses.

The final step is to turn gold into forms that people can wear or use. Pure 24-carat gold is shiny yellow metal, but it is also very soft for most jewelry, making it bend or scratch easily. For this reason, nearly all gold jewelry is made from gold alloys mixed with a little copper, silver, or other metals to increase their hardness.

For example, 18-carat gold (common in high-quality jewelry) consists of 75% gold and 25% other metals, while 14-carat gold contains about 58% gold.

By mixing metals, artisans can also produce gold in various colors (like white gold or rose gold). Thus, refined gold alloys are melted and cast into the desired shapes, whether they are rings, necklaces, or bracelets, or are shaped into coins and standard ingots.

Gold in Sudan

After solidifying the understanding of gold in general, let us now focus on Sudan, a country that has become one of the most important sources of gold in Africa in recent years.

Sudan's connection to gold dates back to ancient times when the Kingdom of Northern Nubia was famous for its gold deposits, and the name "Nub" itself means "gold" in the local Nubian language.

The ancient Egyptians and the Kingdom of Kush extracted gold from the deserts of Sudan and its riverbeds for thousands of years. Today, Sudan is the third-largest gold producer in Africa, reflecting the rich geology beneath its sands, and to understand it, let's learn a little about types of rocks.

Imagine the Earth's crust, that top layer of our planet, like a house with solid foundations. Sudan is like that house, standing above an ancient rock foundation called the Nubian Shield; these are rocks that formed long ago (before the Cambrian period about 550 million years ago) and are naturally rich in minerals. Where is gold found within this "foundation"? Often in three main places:

In Rusty Covers Over Ancient Deposits

The first location is the eroded "Gossan" deposits in the northeast of the country, particularly the area of Ariab in the Eastern Desert. Gossan is a hard rock layer near the surface that appears rusty red, orange, and yellow; it is the