Serpentine is mainly composed of ultrabasic magma (peridotite, pyroxene, etc.). ), its mineral composition is mainly serpentine. The alteration that formed this rock is usually called serpentine.
Serpentine is generally yellow-green to dark green, black when it contains magnetite and chromite, and reddish brown when it contains limonite. Sometimes, due to different shades of color, mottled patterns are formed, which are very similar to snakeskin, hence the name snake pattern. Dense and massive, soft and slightly slippery. The mineral composition is mainly composed of various serpentine, including serpentine, fibrous serpentine, colloidal serpentine and sericite. Secondary minerals include magnetite, chromite and ilmenite. Olivine and pyroxene can appear as residual crystals, and there are a few amphibole, talc, actinolite and tremolite in fashion. Cryptocrystalline texture, under the microscope, is a fiber-crystal structure or a scale-crystal structure, and sometimes you can see a network ring structure, metamorphic structure and so on. The structures are mostly dense blocks, strips and breccia.
The formation of serpentine in ultrabasic rocks is mainly the result of hydration, silicification and carbonation of iron and magnesium minerals such as olivine and pyroxene under the action of heated liquid. In addition, dolomite limestone and dolomite can also form serpentine under hydrothermal action.
In the serpentine process of ultrabasic rocks, useful elements such as iron, nickel, cobalt and platinum were found. , is often substantial. In addition, non-metallic minerals such as asbestos, talc and magnesite can be formed, and serpentine itself is also a good fertilizer raw material.
Serpentine is widely distributed in Inner Mongolia, Qilian Mountains, Qinling Mountains, Tibet, Yunnan and western Sichuan.
2. Qingpanyan
Pan Qingyan is a green massive rock formed by the dissolution of intermediate-basic volcanic rocks, subvolcanic rocks and pyroclastic rocks in gas and water. The formation process of greenschist is called greenschist.
Pan Qingyan is generally gray-green to dark-green, with aphanitic-medium-fine-grained crystal structure, sometimes with mottled structure and residual pyroclastic structure. Most of these structures are blocky and breccia-like. Mineral components mainly include actinolite, chlorite, epidote, albite, quartz, carbonate minerals, etc., and often contain a certain amount of pyrite. Because of the high content of green minerals, rocks are green.
In the process of Pan Qing's diagenesis, firstly, pyroxene and amphibole in the original rock were eroded into actinolite and chlorite, then plagioclase was metasomatism, decomposed into albite, chlorite and epidote, and timely and carbonate minerals were precipitated. H2O, CO2 and H2S are important "reactants" for the above mineral changes. Water mainly promotes the formation of chlorite, epidote and actinolite in the reaction process; Carbon dioxide promotes the formation of carbonate minerals such as calcite and dolomite. The reaction of H2S with iron can directly produce pyrite. At the same time, some metal elements such as gold, copper, lead, zinc, silver, iron and so on. It can form a medium-low temperature hydrothermal deposit. Pan Qingyan is also one of the typical altered rocks in the porphyry Cu-Al-Au deposit, which is often associated with sulfide recrystallization polymetallic deposits. Therefore, diagenesis in Pan Qing is an important prospecting indicator.
3. Yunyingyan
Greisen is formed by metasomatic alteration of granite under the action of high temperature gas-water hydrothermal solution, and is mainly composed of muscovite and quartz in mineral composition. The formation of greisen is called greisenization.
Maronite is generally light gray, grayish green, light pink, etc. , with medium-coarse grained granulite structure, scaly granulite structure and metasomatic texture, massive structure. The mineral composition is mainly composed of mica (muscovite, lepidolite and zinc mica) and quartz. The seasonal content is generally above 50%, and mica can reach 40%. In addition, there are often volatile minerals such as topaz, tourmaline, fluorite, beryl and apatite. Sometimes there are rutile, arsenopyrite, pyrite, molybdenite, cassiterite, wolframite and other metal minerals.
The process of transforming granite into greisen is that biotite, plagioclase and orthoclase in the original rock are replaced by gas and water solution successively, and then transformed into muscovite and quartz. The general procedure of its change is that biotite first becomes hydrobiotite or chlorite, then becomes muscovite, and sometimes it can also be directly changed into muscovite. Plagioclase first becomes albite, epidote and sericite, and also becomes a collection of sericite and timing, and finally becomes muscovite and timing. When metasomatism is strong, potash feldspar can also be transformed into quartz and mica. Because of the direct participation of volatile components (OH, f, b, etc.). Topaz, tourmaline and fluorite often appear in the process of greisenization.
In the process of mineral transformation, the migration law of elements is that all or most of Mg, Ca, K and Na in the original rock are taken away, while Ti, Si and al are relatively stable, and Fe is partly taken away in most cases. The elements brought in from the solution are lithium, phosphorus, fluorine, boron, sulfur, H2O and metal elements such as tungsten, tin, molybdenum, bismuth, copper and lead. The increase of timely content in greisen is not caused by SiO2 _ 2, but by the decomposition and precipitation of aluminosilicate minerals.
Feldspar is the main prospecting indicator of tungsten-tin deposits. Feldspar is widely distributed in granite distribution areas in Jiangxi, Hunan, Guangdong, Guangxi and other provinces (regions) in China, which contains a large number of tungsten-tin ores and rare earth elements such as beryllium, bismuth, molybdenum, niobium and tantalum.
4. Chrysotile sericite
The colors of topaz sericite (topaz fine-grained rock) are usually white, light gray, light green, green, red and light yellow. Because the original rock mineral illusion and original rock fabric often remain in the metasomatic alteration process, there are often residual structures, such as residual granite structure, residual porphyritic and porphyritic structure, residual fine-grained structure and residual structure similar to the original rock. Those with strong alteration can form scaly or granular scaly metamorphic structures, banded metamorphic structures, granulite structures and massive structures.
The main mineral components of rocks are Yingshi, sericite (muscovite) and pyrite. , sometimes containing a small amount of carbonate (ankerite and calcite). Feldspar is only a residual mineral, and sericite is the largest, which is often irregularly distributed on a large scale (up to 0.5mm), followed by timely content; The total amount of carbonate and sulfide can reach10% ~ 20% at most; Pyrite usually forms a large (5 mm) cube. Therefore, chalcopyrite sericite is a fine-grained crystalline massive rock composed of sericite, quartz, carbonate (ankerite) and pyrite, which is characterized by a single cubic pyrite crystal, sulfides (chalcopyrite, sphalerite and galena) and gold mineralization.
Pyrite sericite is named according to the main mineral composition, and it can only be named if pyrite is more than 5%. It is an altered rock produced by hydrothermal replacement of intermediate-acid and neutral magmatic rocks, metamorphic rocks and argillaceous sedimentary rocks with similar compositions at medium and low temperatures (300 ~ 400℃). According to the lithologic characteristics and formation environment, it is a transitional type between quartzite and secondary quartzite.
Topaz sericite often occurs near the two sides of the corresponding pulse, which is a near-pulse alteration and generally symmetrical. The alteration near the vein is strong, and the further away from the vein, the weaker the rock alteration, and finally the transition to the original rock without alteration.
The shape and width of pyrite sericitized rocks are controlled by structural fractures. The more complex the shape of the vein wall, the more the number of veins and the wider the alteration zone. Chrysotile sericite is one of the main prospecting indicators of gold-bearing veins, and sometimes it is also the altered surrounding rock of tin, molybdenum and polymetallic deposits.
5. Secondary quartzite
Secondary quartzite is formed by hydrothermal replacement of intermediate-acid volcanic rocks, subvolcanic rocks and pyroclastic rocks near the surface by sulfur-containing steam ejected from volcanoes, and its mineral composition is mainly chronological. The process of forming such rocks is called secondary quartzitization.
Secondary quartzite is generally light gray, dark gray or grayish green. Cryptocrystalline texture, massive structure. Under the microscope, it is a fine-grained crystal structure, and sometimes embryo-speckled structure and residual ripple structure can be seen. The mineral components are mainly aluminum-rich minerals such as timely (usually as high as 70% ~ 75%), sericite and alunite, kaolinite, andalusite, pyrophyllite and diaspore. The secondary minerals are corundum, topaz, tourmaline and chlorotopaz. Sometimes it also contains a small amount of pyrite, hematite, rutile, barite and natural sulfur.
The formation process of secondary quartzite is mainly due to the action of gas-water solution, which brings out the oxides of sodium, potassium, magnesium and calcium in the original rock, and relatively stable oxides of silicon, titanium and aluminum are relatively enriched, thus forming stable mineral time and some aluminum-rich minerals such as corundum and andalusite. Components brought in from gas-water solution include H2O, CO2, S, F, Cl, P, B and various heavy metal elements, which can form topaz, chlorotopaz, tourmaline, alunite and metal minerals.
Secondary quartzite is mainly produced in Mesozoic and Cenozoic subvolcanic rocks, volcanic rocks and pyroclastic rocks, and less in Paleozoic. Secondary quartzite is widely distributed in Mesozoic volcanic rocks along the southeast coast of China, mainly related to some nonmetallic minerals, such as alunite, kaolinite, pyrophyllite, diaspore, corundum, andalusite and so on. The largest alunite mining area in China is Fanshan, Pingyang, Zhejiang, and its main seam is alunite secondary quartzite. Secondly, the metal minerals related to secondary quartzite are gold, silver, copper polymetallic, antimony, arsenic and rare radioactive elements.