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This rare and precious metal came about the same way as all other chemical elements: because of nuclear fusion. “During the formation of the Solar System, 15 billion years ago, the nuclei of hydrogen and helium atoms, the simplest elements, combined at very high temperatures, giving rise to more complex elements, such as gold”, says the geologist Roberto Perez Xavier, from the State University of Campinas (Unicamp). On Earth, formed 4.5 billion years ago, gold appeared in the form of atoms housed in the structure of other minerals. But the amount is very small. To give you an idea, in the Earth’s crust – the most superficial layer of the planet – out of every billion atoms, only five are gold. The deposits appeared millions of years ago, created by the action of geological processes that modified the face of the earth’s surface, such as volcanoes and erosion.
The result is that gold can now be found and extracted both from underground mines – up to 1.5 kilometers deep – and from open-air mines and prospecting – where the metal is removed just 50 meters from the surface – or even from the a river bed. When a rock containing gold is found, it needs to be chemically treated for the mineral to separate from other elements. “In the deposits, the concentration of gold is only a few grams per ton extracted”, says Roberto. It is no wonder that world production is small: around 2,500 tons per year. To find new gold deposits, geologists need an arsenal of information. “First, satellite images indicate, on the ground, either geological faults or the presence of certain minerals and rocks that indicate the occurrence of a deposit. Afterwards, it is necessary to carry out a geological mapping of the region, with the collection of samples of rocks, soil and sediments to analyze the areas that may have the metal. If there is any certainty, it’s time to drill the ground. Then, a good dose of luck also helps”, says Roberto.