Zhengzhou Dixiang Technology Co., Ltd. Kou Wei December 2020
( This article is purely a reading note and excerpt, as a sub-section of mineral knowledge for understanding)
Third, several kinds of chalcedoli associated with SiO2
1. Vein quartz
Vein quartz is a collection of quartz (SiO2), which is formed by the hot water solution of SiO2 secreted by underground magma in the rock cracks, the Mohs hardness is greater than 7, the specific gravity is about 2.65, the melting point is above 1700 °C, and it is dense and lumpy. Vein quartz is often symbiotic with crystal, its ore body is mostly veined, chicken nest-like, lens-like, some are bifurcated, several meters to hundreds of meters long, tens of centimeters to tens of meters thick, the scale is mainly small, all produced in metamorphic rocks, garnet tectonic fissures or both contact zones belong to primary ore.
2. Quartz vein
Quartz veins are actually a collection of veined quartz minerals and should be attributed to the concept of rock. Quartz veins are intrusive rocks produced in the form of veins produced by acidic magmas that are intrusively consolidated along tension faults, and their composition is silica. Quartz veins are filled with ore-bearing magma or hydrothermal fluids that penetrate upward along fault zones and fault levels and condense, and may form ore bodies together with aggregates of other metallic minerals and altered surrounding rocks.
Diabase intrusive limestone surrounding rock appears quartz veins, basalt magma in the rapid rise of intrusion into shallow limestone in the process of intrusion depth is shallower than gabbro, crystallization rate is faster than gabbro, so the formation of smaller particles than gabbro diabase, in the magma intrusion to the shallow layer, the cooling process often forms SiO2-rich aerothermal fluid, these hydrothermal fluids seep into the fissures of the rock cooling crystal, so the formation of quartz veins.
3. Quartz gravel (rock)
Quartz gravel belongs to the secondary gravel type quartz, endowed with the fourth series of residual slopes - the bottom of the slope alluvial sediment accumulation, above the erosion surface of the bedrock, in a layered distribution, commonly known as "stone shed", thickness of 0.1-1 meters, with the change of ancient terrain. The composition of quartz gravel is mainly veined quartz, a small amount of quartzite, pegmatite, siliceous rock, etc., with a diameter of generally 2-10 cm, disorderly and disorderly, sub-angular.
4. Silicification
Silicification refers to the action of rocks under the action of hydrothermal fluid, producing altered minerals containing quartz, chalcedony, opal, and jasper. Under hydrothermal conditions from high to low temperatures, various rocks can be silicified. Silicification may take a long time, and the quartz particles go from small to large: the degree of crystallization varies from other shapes to self-shapes. According to the thermodynamic equilibrium factors, temperature, pressure, concentration and chemical component activity and chemical potential, etc., the percolation and diffusion accounting are determined, so as to form fine veins and impregnation-like confessional forms. Generally, silicified rocks generated by alteration (quartzization) low-temperature hydrothermal fluid are often composed of fine-grained quartz or cryptocrystalline chalcedony and amorphous opal, jasper-like. Silicified rocks generated by high and medium temperature hydrothermal fluids are mainly composed of quartz.
5. Siliconized belt
The silicification belt (silicification fracture zone) is a geological body composed of multiple siliceous breccia mass that are not connected to each other, and is a group of explosive breccia mass formed by magma gas and some magmatic materials that produce sharp explosions under closed reduction conditions. Silicification zones of various sizes are often developed along the fault zone, and the structural structure of silicified rocks in the fault zone is varied, and the degree of silicification is not equal, including strong silicified rocks, weak silicified rocks, and residual silicified rocks. The silicification belt is an excellent ore-controlled geological body, and the main minerals related to it are copper, molybdenum, tungsten, lead, zinc, uranium, gold, antimony, mercury, fluorite, pyrite, hematite, piezoelectric crystal and barite.