How are ore deposits found

From inside the earth: ores and solid metals

Copper was the first metal that humans discovered in the earth's crust. It could be shaped into simple tools or weapons and was so important that an entire epoch was named after it: the Copper Age. The tools got better when man mixed the copper with tin and thus invented the bronze. And when he learned to smelt iron, the triumph of metal tools finally began.

Unlike the core of the earth, the earth's crust consists largely of non-metals. Nevertheless, metals such as iron, aluminum, manganese and potassium can be found in their rock. Experts (geochemists) can determine exactly how often they occur. They found out that around seven percent of the earth's crust consists of iron.

Like most metals, iron occurs as a chemical compound with other elements, so-called ore. In order to extract iron from the ore rock, the ore rock is ground, mixed with coal and heated. Then a chemical reaction takes place that removes the other elements from the ore, leaving the pure, elemental iron.

On the other hand, some metals hardly combine with other elements. They therefore do not weather and occur in pure form in the earth's crust. These “solid metals” include gold, silver and platinum. Platinum and gold are also extremely rare: on average, gold is only contained in a ton of rock with an average of 0.001 grams. A place is only referred to as a deposit if it contains a thousand times the amount of gold - i.e. one gram of gold per ton of rock.

The "rare earth metals" are more common than gold or platinum. What sounds strange has a simple reason: These metals are considered rare because they do not form deposits of their own, i.e. they do not occur in concentrated form, but only in scattered areas. We are therefore also talking about spice metals. Their importance has increased significantly in recent years because they are required for the manufacture of electronic devices such as cell phones or computers.


It happened on January 24th of last year in a sawmill on the American River: While building a sawmill, James Wilson Marshall discovered a gold nugget. Although attempts were made to keep the find a secret, the story quickly got around: There is gold on the American River!

Soon the first gold prospectors from all over California were crowding the river. Thousands of workers in San Francisco quit their jobs and came to make their fortune on the riverside. But not only the inhabitants of the country were caught by the gold fever. More than 50,000 people from Mexico, Chile, China and especially from Europe poured into California and flooded the cities here. San Francisco in particular was bursting at the seams with the migration of peoples. In just one year since the first gold nugget was discovered, California's population has now grown fivefold.

The immigrants have great hopes, and the yield from panning for gold is often low. With a bit of luck you can earn a lot more here than a worker on the east coast receives as wages, but life in the gold rushes is expensive. Simple groceries have to be bought at exorbitant prices. An egg costs a dollar, a newspaper even ten! In addition, some gold miners celebrate their new wealth by gambling or with alcohol in the saloons. For some, the gold rush has already ended with a bad hangover.

Wash gold - how are you?

The technique of the Californian gold prospector is simple: The search doesn't take much more than a tin pan and a leather bag. Sand and silt from the river are shoveled into the pan. When the pan is swiveled, water and sand are washed up to the edge. Now it's getting exciting: with a lot of luck, small pieces of gold will flash at the bottom of the pan. Because they are heavier than the rest, they stayed in the middle. The gold pieces can be collected in a leather bag and you can move on to the next pan. Good luck!


Whether green emerald, blue sapphire or red ruby: we know precious stones as sparkling and particularly valuable pieces of jewelry. Gemstones are simply minerals. However, they must meet three requirements in order to be considered gemstones: They must be particularly rare, transparent and at the same time very hard.

Gemstones are created deep inside the earth under high pressure and at high temperatures. The hardest of them and at the same time the hardest known mineral is diamond. It is formed from a single element at a depth of around 150 kilometers at temperatures above 1200 degrees Celsius: carbon. Crystals usually develop from eight equilateral triangles, called octahedra. Other shapes such as cubes are also possible. The diamond gets to the surface of the earth by being thrown upwards together with the rising magma. The largest diamond ever found is the so-called "Cullinan". It was discovered in a South African mine in 1905 and weighed exactly 3106.75 carats in its raw state. This corresponds to a weight of 621.35 grams.

Whether diamond, amethyst, emerald or topaz - all gemstones differ from one another in terms of structure, composition and color. They only become particularly beautiful and shiny when they are cut. He lets the colors of the gemstones shine properly through a certain refraction of light.

In addition to precious stones, there are other gemstones in the earth's crust, such as blue lapis lazuli or green malachite. Although these are also very sought-after and beautiful, they are not transparent and are too common to be considered gemstones.

Treasures on the ocean floor

Hidden treasures rest deep down on the ocean floor. What is meant here is not the sunken prey of predatory seafarers; we're talking about raw materials that occur on the ocean floor.

One of these raw materials is methane hydrate. This flammable ice is stored on the sea floor at a depth of more than 500 meters. It was formed at low temperatures and under high pressure from water and methane, which are produced by certain single cells during the metabolism. In the estimated deposits of methane hydrate, more than twice as much carbon is bound as in all oil, natural gas and coal reserves on earth. However, whether it can contribute to our energy supply in the future is controversial. It is difficult to break down because it decomposes easily at higher temperatures, releasing methane. The danger here is that methane is a greenhouse gas. If too much of it gets into the atmosphere, it affects our climate and temperatures rise.

Another peculiar substance lies at the bottom of the Pacific at a depth of around 5000 meters: manganese nodules. These black lumps can be about the size of potatoes, and some even as large as heads of lettuce. As a raw material, they are of interest to humans because they contain large amounts of the metals manganese and iron. However, there are also high proportions of copper, nickel and cobalt in the wrinkled structures - metals that are required in the electrical industry and for steel production. Whether it is worth mining them still has to be researched: Although they have a much higher metal concentration than ore mines on land, the mining of manganese nodules is particularly complicated because of the great depths of the sea in which they occur.

Fossil fuels: petroleum, natural gas and coal

It is called black gold because of its color and because it is so valuable to us: We are talking about petroleum. The raw material was created 150 million years ago when dinosaurs still inhabited our planet. Today it is hard to imagine our everyday life without crude oil: We need it as fuel for vehicles, as heating material or as the basis for plastic.

The raw material for crude oil is plankton, which floated in the sea millions of years ago. The remains of these tiny sea creatures sank to the bottom and were hermetically buried under other layers of sediment, such as sand and clay. The remains decomposed and turned into digested sludge. More sediments were deposited above this, the weight of which pressed on the digested sludge. Under this pressure the temperature rose and the digested sludge chemically changed to a mixture of gaseous and liquid hydrocarbons: petroleum. Because it was lighter than water and the surrounding rock, it rose through pores and higher and higher until it hit an impermeable layer under which the viscous mass was collected: an oil reservoir was created.

Natural gas was also produced under conditions similar to those of oil. This is why both fuels are often found in one deposit. Natural gas is lighter, which is why it is stored above crude oil. Because both substances are fossil remains of marine organisms, they are referred to as "fossil" fuels.

Coal is one of the fossil fuels. It owes its origin to the remains of dead marsh plants. These formed increasingly thick layers of peat, over which sediments piled up. Under their weight, water, oxygen and other gases were pressed out of the peat layer, and the proportion of carbon increased. Over the millennia, the peat turned into lignite. If the sediment cover grew and the pressure continued, brown coal became fat or hard coal. In order to be able to use their stored energy, the coal deposits - also called coal seams - are extracted in mines.

The outermost shell of the earth

Like an egg from an eggshell, the earth is also surrounded by a hard shell. This outermost layer surrounds the earth's mantle and is called the earth's crust. If you compare the earth to a peach, the earth's crust is - in relative terms - as thick as its skin. Under continents it reaches an average of 40 kilometers deep, under the oceans it is only about seven kilometers.

Below is the outer part of the earth's mantle, which extends to a depth of around 100 kilometers. It is also solid, but consists of heavier rock. The earth's crust and this outermost part of the mantle together are also called the “lithosphere”. This solid layer of rock has broken into slabs of various sizes, which slowly drift around on the hot, viscous mantle of the earth.

Where the rock melt penetrates upwards from the hot earth's mantle, the earth's crust can break up. Then lava flows out, which becomes the new crust of the earth. This mainly happens where the plates of the lithosphere adjoin one another, such as on the mid-ocean ridges.

In Iceland, for example, these plate boundaries are easy to recognize: cracks and furrows run through the earth's crust, where the Eurasian and North American plates drift away from each other. There is also a plate boundary in the Mediterranean region. Because the African plate is pressing against the Eurasian plate here, there are many volcanoes in Italy and there are always earthquakes.

The crust is covered by the bottom. The soil of the land masses is formed from weathered rock and remains of animals and plants. The sea floor, on the other hand, develops from deposits such as clay and sunken remains of marine organisms. On the coasts, the sea floor also consists of deposited rubble that was removed from the mainland and washed into the sea.