Reportaje sobre el oro en las minas de Asturias, España - Gold in Spain

Reportaje sobre las minas de oro de Asturias, muy interesante.

+++ ORO NATIVO +++

El oro nativo es un mineral de la clase de los minerales elementos, y dentro de esta pertenece al llamado “grupo del cobre”.
Fue descubierta en tiempos prehistóricos, siendo nombrada en español del latín aurus.
Es en su mayor parte oro puro -más del 99%-, comúnmente con impurezas de plata, cobre, hierro y mercurio,​ más raramente con otros muchos elementos, que cristaliza en el sistema cristalino cúbico o isométrico.
Forma dos series de solución sólida, una de ellas en la que la sustitución gradual del oro por plata, perfectamente mezclables al tener tamaño parecido y cristalizar ambos en sistema isométrico, va dando minerales intermedios con distintas proporciones:​ cuando ambos elementos se encuentran entre un 20% a 80% se denomina a este mineral crisoargirita o electrum, si el oro es más de 80% se denomina oro-argentífero y si el oro es menos del 20% se denomina plata-áurica. Una segunda serie es la que forma con la sustitución de oro por paladio, que suele llevar impurezas de platino.
Se encuentra ampliamente extendido por todo el mundo en muy pequeña cantidad en rocas de diversos tipos, así como en el agua marina. Aparece en vetas de origen epitermal por fumarolas, típicamente en vetas de cuarzo con pirita y otros minerales sulfuros y telururos; también en rocas pegmatitas volcánicas y depósitos de rocas metamórficas de contacto, a veces en pláceres de ríos en forma de pepita de oro.
Suele encontrarse asociado a otros minerales como: pirita, calcopirita, arsenopirita, pirrotina, silvanita, krennerita, calaverita, altaíta, tetradimita, scheelita, ankerita, turmalina o cuarzo.
Usos industriales: conductor eléctrico, recubrimientos reflectantes, en joyería y objetos decorativos, en electrónica e industria aeroespacial por su conductibilidad, como patrón monetario, etc.

--- ENGLISH ---

Gold is a chemical element with symbol Au (from Latin: aurum) and atomic number 79. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element.
It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).
Gold is thought to have been produced in supernova nucleosynthesis, from the collision of neutron stars, and to have been present in the dust from which the Solar System formed. Because the Earth was molten when it was formed, almost all of the gold present in the early Earth probably sank into the planetary core. Therefore, most of the gold that is in the Earth's crust and mantle is thought to have been delivered to Earth later, by asteroid impacts during the Late Heavy Bombardment, about 4 billion years ago.
Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects, giving rise to the term acid test. Gold also dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction.
Historically, the value of gold was rooted in its relative rarity, easy handling and minting, easy smelting and fabrication, resistance to corrosion and other chemical reactions (nobility) and its distinctive color. As a precious metal, gold has been used for coinage, jewelry, and other arts throughout recorded history. In the past, a gold standard was often implemented as a monetary policy, but gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after 1976.
A total of 186,700 tonnes of gold exists above ground, as of 2015.
The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity have led to its continued use in corrosion resistant electrical connectors in all types of computerized devices (its chief industrial use). Gold is also used in infrared shielding, colored-glass production, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine. As of 2016, the world's largest gold producer by far was China with 450 tonnes.

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