Sapphire deposits in China are mainly magmatic, pegmatite, metamorphic and placer (Pan Feng, Tang Lan, 2003).
1. Magmatic sapphire deposit
Magmatic sapphire deposits in China are mainly distributed near deep faults in the Pacific Rim structural belt along the southeast coast. The ore-bearing rocks are mostly Mesozoic and Cenozoic alkaline basalts, mainly alkaline olivine basalt and kyanite. Rocks are rich in aluminum and poor in silicon, and often show porphyritic structure, porphyritic structure, associated porphyritic structure, pore, almond-shaped structure and massive structure. The ore bodies are distributed in layers and lenses in basalt lava layers and rock necks, and are controlled by volcanic mechanism. Sapphire is a giant crystal, and sapphire crystals have columns, towers and barrels. The edge of the crystal is round and subangular, and there is a black film on the surface. The colors are dark blue, blue-black, blue, brown, green and yellow, a few are red, and some are two-color or variegated sapphires (blue/yellow, etc. ). The color band is developed, and the crystal is mainly translucent. Many mineral deposits have large crystals. Important producing areas are Changle in Shandong, Penglai in Hainan, Mingxi in Fujian, Liuhe in Jiangsu, Kuandian in Liaoning and Muling in Heilongjiang.
2. pegmatite sapphire deposit
The pegmatite sapphire deposit is located in the magmatic active zone in metamorphic or sedimentary rocks. Its ore-bearing rocks are distributed in the syenite belt, mainly syenite pegmatite and granite pegmatite, in which sapphire is produced in single crystal or continuous crystal. Sapphire crystals are columnar, waist-drum-shaped, light blue, off-white, bronze, brown, translucent-transparent, and colorful, with developed cracks. The variety is low-grade sapphire or starlight sapphire, represented by Jinping and Yunnan.
3. Metamorphic sapphire deposit
Metamorphic sapphire deposit is located in the regional metamorphic belt of orogenic belt or paleoplatform (shield). Ore-bearing rock bodies are distributed in aluminum-rich mixed gneiss, mainly corundum-biotite-feldspar (plagioclase) or adamellite-feldspar mixed gneiss, which often presents granite structure, pegmatite structure, gneiss structure, eyeball structure or banded structure. The rock is rich in aluminum, poor in silicon and low in calcium, and the ore body is layered and lenticular in mixed gneiss, which is in harmony with the occurrence of surrounding rock. Controlled by the horizon of aluminum-rich rocks and the degree of migmatization, sapphires are mostly distributed in the center of the eyeball or in the annulus, surrounded by feldspar. Corundum crystals are columnar, barrel-shaped, waist-drum-shaped, plate-shaped and so on. The colors are mostly blue-purple, brown, grayish green, bean blue and so on. , translucent and transparent, often with rutile, magnetite and other granular crystal inclusions, with twins and cleavage development, larger particles and low variety grade. Representative producing areas are sapphire deposits (spots) in Taihang Mountain in Hebei, Akto in Xinjiang, Alashan in Inner Mongolia, Lingbao in Henan and Foping in Shaanxi.
4. Placer sapphire deposit
The sand sapphire is controlled by the structural background of the primary deposit and the drainage structure (valley terrace, hillside, etc.). ). It is located in gravel layer and clayey gravel layer, and is produced in eluvial and alluvial deposits. Its structure is loose, and the ore body is banded, crescent-shaped and fan-shaped. Sapphire is unevenly distributed, and its quality is restricted by primary ore. Sapphire placers with representative origins in Changle, Shandong, Mingxi, Fujian and Penglai, Hainan.
(II) Characteristics of Changle Sapphire Primary Deposit
Changle sapphire primary deposit is a magmatic deposit, distributed in the basalt distribution area on the west side of the middle section of the Tan-Lu fault zone, located in the middle of the Shandong platform, belonging to Changle sag of Taiyi uplift in Luxitai anticline, which is one of the largest gem mines discovered in China at present. The formation of sapphire minerals in this area is closely related to the strong volcanic activity of Neogene basalt. Sapphire is mainly produced in alkaline olivine basalt and biscite with high Al2O3, TiO2 _ 2, poor SiO2 _ 2 and MgO, and megacrysts contain titanaugite, zircon, corundum, olivine and feldspar. Sapphire is often made into giant crystals, and the crystals are mostly columnar and tower-shaped. The edge of the crystal is round and sub-angular, and there is a black film on the surface. The colors are dark blue, blue-black, blue, brown, green and yellow, and there are also two-color or variegated sapphires (blue/yellow, etc. ). The ribbon is developed, mainly translucent. The crystal grain size is mostly between 5 ~ 10 mm, and some are larger than 30 mm. Most sapphire crystals are ring-shaped, and some sapphires can grind six starlight beams perpendicular to the C axis.