Natural copper family

This family includes natural copper, natural silver, natural gold and other minerals. The elemental state of gold is its main existing form in nature. In addition, only a small amount of gold appears in the form of telluride. Silver or copper rarely exists in elemental form, and they usually form sulfides and other compounds.

Copper-copper

Equiaxed crystal system with crystal parameters; Symmetric Fm3m. Aerospace group Fm3ma0 = 0.3908nm; Z=4。

Composition and structure Pyrite usually contains a small amount of silver, bismuth, mercury, arsenic and antimony. The atomic radius of copper is so small that it can form a solid solution with gold only at high temperature. Gold and copper can form intermetallic compounds, such as Cu-Au (copper-gold mine). The structure of natural copper is copper type.

The morphology is usually irregular dendritic (Figure 7-2), flaky or dense block.

Figure 7-2 Morphology of Natural Copper

A- native copper is dendritic; B— Natural Copper (Museum of Minerals, Harvard University, USA)

(According to Herbert et al., 1977)

Physical properties: the fresh surface is copper red, the streaks are copper red and have metallic luster. Usually the surface is oxidized to black and dull. Strong ductility, serrated fracture and hardness of 2.5 ~ 3; The density is 8.95g/cm3.

The identification features are copper red, hackly fracture, high density and strong ductility.

The genesis and occurrence of native copper are formed under the reducing conditions of various geological processes. Natural copper of hydrothermal origin often coexists with zeolite and calcite in the form of loose dyeing. The genesis of native copper, which is filled in the pores of basalt and coexists with minerals such as zeolite and prehnite, is related to volcanic hydrothermal process. Natural copper of sedimentary origin is found in sedimentary rocks rich in organic matter. Natural copper is most commonly found in the oxidation zone of copper-bearing sulfide deposits. The copper sulfate solution formed by oxidation of copper-bearing sulfide minerals is reduced by other sulfates or sulfides, namely cuso 4+2feso 4→Cu+Fe2(SO4)3.

The main use is copper ore, and natural copper occupies a very secondary position. At present, copper sulfide is the main copper ore for extracting copper. The biggest use of copper is mainly for electric wires. It is also widely used to make alloys, such as brass (copper-zinc alloy), bronze (copper-tin-zinc alloy) and German silver (copper-nickel-zinc alloy). The contribution of copper to modern civilization is second only to that of iron.

Natural gold

Equiaxed crystal system with crystal parameters; Symmetry m3m. Aerospace group Fm3ma0 = 0.4070nm; Z=4。

Composition and structure Au and Ag form a complete solid solution series, and most gold contains Ag. When the silver content reaches or exceeds 20%, this alloy is called silver-gold mine. Natural gold can contain a small amount of copper and iron, and a small amount of bismuth, lead, tin, zinc and platinum. The purity or purity of gold is expressed as 1000. Since most gold contains 10% of other metals, the optimum purity is generally 900. The structure of gold is copper type.

The morphology is a dispersed granular or irregular dendritic aggregate (Figure 7-3). Occasionally, large pieces appear, commonly known as gold nuggets.

Figure 7-3 Natural Gold Forms

A- twisted natural gold octahedral crystal; B- gold is dendritic; C- natural gold (sample from Yekaterinburg, Russia)

(According to Klein et al., 2007)

Physical properties are golden yellow, and with the increase of Ag content in its composition, the color gradually turns pale yellow. The stripe color is the same as the color, and the content of Ag can be determined according to the depth of the stripe color. Metallic luster. The hardness is 2.5-3; Strong ductility, the density is19.3g/cm3.

The identification features are golden yellow, mottled, low hardness, high density, strong ductility and no discoloration after burning.

Genesis and occurrence state The abundance of natural gold in the crust is 0.004× 10-6, which is a rare element. It mainly occurs in gold-bearing quartz veins caused by high and medium hydrothermal fluids, or in altered rocks and volcanic rocks in medium and low temperature hydrothermal deposits related to volcanic hydrothermal processes. As for the migration form of gold in hydrothermal solution, it is generally believed that it migrates in the form of Na3Au S3 soluble complex. For example, the symbiosis of hydrothermal natural gold and pyrite is the result of the following reactions: 2Na3AUS3+3FeCO3 → 2AU+3FeS2+3Na2CO3. Under exogenous conditions, natural gold is often enriched to form important placer gold deposits. Many provinces and regions in China have natural gold producing areas, among which primary deposits are famous in Shandong and other places, while placer gold deposits are most distributed in Jinsha River, Heilongjiang and Yuanshui River Basin in Hunan.

Natural gold is almost the only source of gold. The world market takes gold as the currency calculation standard, so the amount of gold reserves in the national treasury is of great significance. In modern technology, electronic components are made of ultra-fine pure gold wires, and high-temperature heat insulation reflector and infrared heater reflector are made of gold-plated films. In addition, gold can also be used to prepare various alloys and parts of cutting-edge technical equipment.

nugget

The mineral composition of gold nuggets is usually natural gold, timely and other minerals. The shape is irregular block. Some people call it nugget because it looks like a dog's head. Some people call it horseshoe gold because it looks like horseshoe; But most people generally call this natural massive natural gold nugget. Gold bullion is rare and hard to get, but because of its high value, it is regarded as a treasure among treasures. The discovery of gold bullion is often accidental, and once it is discovered, it will often cause social sensation. According to statistics, there are about 8000 ~ 10000 gold nuggets in the world that are larger than 10 kg. The largest number is Australia, accounting for 80% of the total number of Goldnuggets. The largest gold nugget weighs 235.87 kilograms and is also produced in Australia. In the history of human gold mining, China is also one of the countries where many gold nuggets have been found. The middle and lower reaches of Zishui River Basin in Hunan Province are rich in gold deposits in China. In addition, gold nuggets have also been found in White County, Sichuan Province, Nanzheng County, Ankang City, Shaanxi Province, Huma County, Heilongjiang Province, huadian city City, Datong County, Qumalai County, Zhaoyuan City, Shandong Province, and zunhua city City, Hebei Province. About one thousand pieces in all.