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Metals rarely occur in nature in a “pure” state. Most are firmly bound within other rocks as ore minerals. Many of these deposits formed deep within the Earth under extreme heat and pressure.
Most ore deposits originated through magmatic processes. As molten magma cooled, ore minerals crystallised and became concentrated (magmatic segregation). Other deposits formed from so-called hydrothermal solutions: hot water dissolved metallic compounds from the surrounding rock and redeposited them as they cooled — usually in fissures, crevices or the adjacent host rock. This process created the characteristic ore veins. Ore deposits are still forming today — for example, on the ocean floor. In areas of volcanic activity, hot, metal-rich solutions rise from below and meet cold seawater. As a result, metal sulphides precipitate. These submarine springs are known as “Black Smokers”.
Ores can also form through sedimentation, when metal-bearing muds accumulate on the ocean floor. In other cases, weathering leaves behind sparingly soluble ore minerals, which gradually segregate. When ore minerals and metals are concentrated by flowing water and changing currents due to their specific gravity, such deposits are known as “placer deposits”.
How a deposit originally formed is not always easy to determine, as tectonic movement can carry it deep into the Earth’s crust. High pressure and temperature alter the rocks and ore minerals: they recrystallise and develop new structures and textures. Such deposits are referred to as metamorphic, and their original formation is often difficult to reconstruct.
The mineralisation at the Telfer Weißen/Cime Bianche di Telves mountain, located between the fractions of Ridnaun/Ridanna and Pflersch/Fleres, represents such metamorphic non-ferrous metal deposits. The prevailing ore minerals are sphalerite, galena (lead glance), pyrrhotite and chalcopyrite. The stratiform occurrence of the mineralisation suggests a submarine origin with subsequent hydrothermal redistribution — similar to