(1) Electron probe analysis

Focus on the selection of DL18, DL15, and DL32 bubble-shaped, massive rhodochrosite ores and large rhodochrosite ores in the PD1200 tunnel of Songtao Datangpo Joint Venture Plant. The Dm4 sample from the dolomite mound at the bottom of the Liangjiehe Formation on the Maomaoyan section in Tangpo was sliced ??and processed into an electron microscope based on thin section identification. It was then examined at the National Institute of Geological Processes and Mineral Resources of China University of Geosciences (Wuhan). Key laboratories conduct electron probe microanalysis. Specifically, the JXA-8100 electron probe microanalysis system produced by Japanese technology JEOL Co., Ltd. is used. The accessories are the MonoCL3+ cathodoluminescence system of the American GATA company and the X-ray energy spectrometer of the American Noran company. Through electron probe microscopic analysis of the above-mentioned cold seep carbonate rocks (rhodochrosite and dolomite) in the early South China Period, a preliminary understanding and grasp of their material composition and structural characteristics were obtained.

1. Chalcedony

Through electron probe analysis of a bubble wall in the DL18 bubble rhodochrosite ore sample, the bubble wall is composed of SiO2 (Figure 3-29, Figure 3-30). After further rock and mineral identification and analysis, the mineral composition of the bubble wall is chalcedony.

In addition, the mineral distribution of SiO2 component can also be seen in the rhodochrosite mineral (Figure 3-31), which is different from the chalcedony production form of the bubble wall. Specifically, it is distributed irregularly in rhodochrosite. Its mineral form is in the form of quartz or chalcedony or other forms, which remains to be further studied. Due to the irregular shape of the output, its formation time should be at the same time or later than the formation of rhodochrosite.

Figure 3-29 Electron probe image of the bubble structure and probe analysis results of the bubble wall (DL18 sample)

Figure 3-30 Further enlarged electron probe image of the bubble wall and probe analysis results of bubble walls (DL18 sample)

Figure 3-31 Electron probe image of rhodochrosite ore and probe analysis results of quartz minerals (DL15 sample)

Note: The light-colored mineral in the electron probe image is pyrite, the dark gray mineral is rhodochrosite, and the black irregular-shaped mineral is quartz

2. Strawberry-shaped pyrite

Strawberry pyrite is commonly distributed in rhodochrosite. On the outside of the SiO2 (chalcedony) bubble wall in the DL18 sample, more strawberry-shaped pyrite distribution can be seen (Figure 3-32). However, it is worth noting that pyrite is distributed outside the bubble structure, but there is no pyrite distribution inside the bubble or in the bubble wall.

Figure 3-32 Image and electron probe analysis results of strawberry-like pyrite in rhodochrosite ore (DL18 sample)

Electronic probe analysis results show: strawberry-like pyrite The material composition of silica is not single. It often contains SiO2 particles or silicate particles inside, with irregular shapes and sizes ranging from 5 to 15 μm (Figure 3-33, Figure 3-34).

Figure 3-33 Image and electron probe analysis results of strawberry-shaped pyrite in rhodochrosite ore (DL15 sample)

3. Strawberry-shaped pyrite and chalcedony bubbles Wall contact relationship

The contact surface between the strawberry pyrite and the bubble wall with chalcedony composition is not smooth, and the mineral composition near the contact zone is relatively complex (Figure 3-35). The distribution of apatite and plagioclase can be seen locally (Figure 3-36, Figure 3-37).

Figure 3-34 Image of strawberry-shaped pyrite in rhodochrosite ore and electron probe analysis results (DL18 sample)

Figure 3-35 Chalcedony bubbles in rhodochrosite ore Mineral image and electron probe analysis results between the wall (black part) and pyrite (white part) (DL18 sample)

Figure 3-36 The outer side of the chalcedony bubble wall and the yellow part between the walls of rhodochrosite ore Apatite image between iron ores and electron probe analysis results (DL18 sample)

Figure 3-37 Image of plagioclase locally distributed near strawberry-like pyrite in rhodochrosite ore (dark color part) and electron probe analysis results (DL18 sample)

4. Rhodochrosite and rhodochrosite

Through electron probe analysis, it was found that rhodochrosite is in the form of microscopic "spherules" "shaped, about 5 to 20 μm in size, lighter in color, and smooth in shape. Most of them have 1 to 2 layers of ring structure, similar to the characteristics of "thin-skinned ooids".

Some of the spherules are embedded together to form relatively large and complex microscopic "spherulites", but with a smooth appearance; while the matrix of the cemented rhodochrosite microscopic "spherulites" is darker rhodochrosite (picture 3-38). Electron probe composition analysis was carried out on the matrix - rhodochrosite (Figure 3-38Pt1) and the microscopic "spherules" of rhodochrosite (Figure 3-38pt2), and it was found that the manganese content of the microscopic "spherulite"-shaped rhodochrosite It is obviously higher in manganese content than the matrix - rhodochrosite.

Paleonatural gas seepage and manganese ore mineralization - taking the Nanhua Period "Datangpo style" manganese deposit in eastern Guizhou as an example

Figure 3-38 Microscopic "spherulite" shape Images of rhodochrosite (light color) and rhodochrosite (dark color) (DL18 sample) |pt1—electron probe analysis results of rhodochrosite (upper right picture);pt2—electron probe analysis results of rhodochrosite (lower right picture)< /p>

Further magnification of the microscopic rhodochrosite "spherulites" revealed that the surface of the "spherulites" is generally surrounded by a light-colored thin shell, and inward is a circle of roughly equal thickness but darker color. Surrounded by, and further inward, the color is lighter and the composition is more uniform. The outer light-colored thin shells of the composite "pellets" are connected to form a knotted edge. One of the rhodochrosite microscopic "spherules" with a long axis of 20 μm, in addition to the above-mentioned ring structure, was found to have an irregularly shaped core. The outer layer of the core is a thin dark ring layer, and the inner part is lighter in color. , the composition is relatively uniform (Figure 3-39a). An electron probe was used to analyze the microscopic content change characteristics of manganese along the long axis of the large microscopic "spherulite". It can be found that the manganese content in the core of the "spherule" is significantly lower than that of the outside, but the manganese content in the core is lower than that of the calcite. The matrix content of manganese ore is high (Figure 3-39b). The core may be an algal biodegradation, and rhodochrosite "pellets" may gradually grow along this biodegradation. Therefore, this structure of rhodochrosite is likely to be a typical structural feature of algal organisms. In addition, the phenomenon of growth of quartz grains wrapped by rhodochrosite can also be seen (left picture in Figure 3-39).

Figure 3-39 Microscopic "spherulite" internal layer structure of rhodochrosite (a) and the change curve of Mn content in the "spherulite" (b)

Note :aThe black oval particles in the upper right corner of the picture are quartz, and the quartz particles are wrapped by rhodochrosite (DL18 sample)

5. The relationship between pyrite, quartz and albite

< p>Through electron probe analysis of the Datangpo DL32 rhodochrosite sample, it was found that there are inclusions of quartz minerals in the pyrite crystals in the rhodochrosite. Quartz inclusions in pyrite are round in shape, 3 to 5 μm in size, as shown in Figure 3-40. In addition, albite inclusions are also found in pyrite crystals. Albite is also round in pyrite, with a size of 3 to 4 μm and a darker color (Figure 3-40b). Albite is also distributed in rhodochrosite, but its shape is irregular (Figure 3-41pt2).

6. The relationship between pyrite and rhodochrosite

Pyrite is usually produced in microscopic "spherulite" rhodochrosite. Through electron probe analysis of the Datangpo DL18 rhodochrosite sample, rhodochrosite mineral inclusions were found in the pyrite mineral crystal (Figure 3-42), indicating that the formation of pyrite and rhodochrosite may have occurred at the same time. of. The gray microscopic "spherulite" mineral in the photo is rhodochrosite, the gray-white mineral is pyrite, and the black irregular-shaped mineral is quartz (SiO2).

Figure 3-40 The relationship between pyrite and quartz particles in rhodochrosite (DL32 sample)

Figure 3-41 Pyrite crystals (white mineral) in DL32 rhodochrosite sample ) Electron probe images of albite inclusions (black particles)

Figure 3-42 Electron probe images and analysis of the interrelationships of minerals such as rhodochrosite, pyrite, quartz (SiO2) Results

7. The microscopic pore structure in dolomite is similar to the bubble structure in rhodochrosite

By analyzing the dolomite at the bottom of the Liangjiehe Formation on the Maomaoyan section of Datangpo, Songtao Electron probe analysis of sample Dm4 in Qiu Zhong found that the dolomite has a microscopic hole structure similar to the bubble structure in rhodochrosite, which is consistent with the large number of macroscopic hole structures and tent structures found in the dolomite hill. match. The microscopic hole structure is generally 20 to 100 μm in size and has certain directional characteristics (Figure 3-43).

The above-mentioned characteristics of the microscopic pore structure in dolomite are consistent with Chen Duofu et al. (2002) who collected cold spring carbonate rock samples from the submarine natural gas seepage system in the GC238 block in the Gulf of Mexico and used optical The upper surface of the carbonate crust found in these cold seep carbonate rocks when observed with a microscope and an electron scanning microscope (Figure 3-44) shows that micropores of ~10 μm are surrounded by euhedral calcite arranged in a certain direction. The characteristics are very similar. These calcite crystals may be formed by the combination of CO2 released from micropores and Ca in seawater [9].

Further magnified observation of the microscopic pore structure in the Dm4 dolomite sample revealed that there is also a pore wall structure composed of dark minerals around the pore structure, with a thickness of 5 to 20 μm. Through electron probe analysis, the dark pore walls contain a high level of Si and may be composed of albite (Figure 3-45). This is consistent with the bubbles in the rhodochrosite ore in the black manganese-bearing rock series at the bottom of the overlying Datangpo Formation. The wall is somewhat similar. As mentioned before, the bubble walls in rhodochrosite ore are composed of SiO2 (chalcedony). This has shown that there is some kind of genetic connection and similar formation mechanism between the two. The mineral composition filled in the microscopic pores of dolomite is relatively complex, including dolomite, quartz, plagioclase and other minerals.

Figure 3-43 Electron probe photos of microscopic holes in dolomite hills (Dm4 dolomite sample) (JXA-8100 State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan))

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Figure 3-44 SEM image of the natural upper surface of modern cold seep carbonate rock [14]

8. Two types of dolomite with higher Ca content and higher Mg content

Further electron probe analysis was conducted on the Dm4 sample of the dolomite mound at the bottom of the Liangjiehe Formation on the Maomaoyan section of Datangpo, and it was found that the dolomite is composed of two types of dolomite: the darker one and the higher Mg content. It is composed of dolomite and dolomite with lighter color and higher Ca content. The content of dolomite with higher Mg content in dolomite is obviously higher than that of dolomite with higher Ca content, and the latter is mostly distributed near holes and in the gaps of the former (Figure 3-46, Figure 3-47). This is very similar to the composition of rhodochrosite and rhodochrosite in rhodochrosite. The rhodochrosite with higher calcium content cements the microscopic "pellets" of rhodochrosite with higher manganese content. Therefore, similar to the hole structure in dolomite and the bubble structure in rhodochrosite, the dolomite at the bottom of the Liangjiehe Formation is composed of two types of dolomite with higher Mg content and higher Ca content, which is similar to that of the Datangpo Formation. The basic characteristics of the rhodochrosite at the bottom, which are composed of rhodochrosite and rhodochrosite, are also very similar, further illustrating the similarity in the formation mechanisms of the two. However, due to the occurrence of a certain geological event, Mg was replaced by Mn, and the cold seep carbonate rock deposition mainly composed of dolomite became the cold seep carbonate rock deposition mainly composed of rhodochrosite.

Figure 3-45 Images and electron probe analysis results of microscopic pore structures in dolomite (Dm4 sample)

(2) Scanning electron microscope analysis

Select two electron microscopes of vesicular rhodochrosite and massive rhodochrosite samples, DL18 and DL15, from the PD1200 tunnel of Songtao Datangpo Area Joint Factory, and conduct them at the State Key Laboratory of Geological Processes and Mineral Resources of China University of Geosciences (Wuhan) Scanning electron microscope analysis (Figure 3-48).

Figure 3-48 mainly shows the backscattered electron image of the rhodochrosite sample, and the three-dimensional image is the secondary electron image. Because it is a polished thin section, the three-dimensional effect of the secondary electron image is not ideal, but it still clearly shows structural features such as rhodochrosite, rhodochrosite, pyrite, and bubble-like structures. Combined with the analysis of electron probe results, the microscopic "spherulite" structure characteristics of rhodochrosite in the scanning electron microscope photos are very clear. The lighter colors are rhodochrosite "spherulites", and the darker ones indicate higher Mg and Ca content. The calcium rhodochrosite, cemented rhodochrosite "pellets" (Figure 3-48, a, b, c, d); the pyrite mineral is filled between the rhodochrosite "pellets" (Figure 3-48, d) , the crystal shape is not obvious, and may be formed at the same time as rhodochrosite; the second is distributed along the outside of the bubble wall, the crystal shape is slightly better, and is mostly distributed at the fracturing deformation at both ends of the bubble (Figure 3-48, h, i), its formation may It is later than the pyrite filled between the rhodochrosite "pellets"; the flattened bubble structure is roughly parallel to the texture of the rhodochrosite layer, and cracks formed during the flattening of the bubbles can be seen inside the bubble structure. Note that cracks are limited to the development and distribution inside the bubbles.

Figure 3-46 Structural image and electron probe analysis results of dolomite (Dm4 sample)

(3) Mineral composition characteristics

Nanhua, eastern Guizhou region Thin-section identification and electron probe microscopic analysis of two types of cold seep carbonate rocks, namely rhodochrosite of the Datangpo Formation and dolomite of the Liangjiehe Formation, show that the mineral composition of rhodochrosite is relatively simple, mainly composed of rhodochrosite and calcium rhodochrosite. It is composed of magnesium-calcium rhodochrosite, manganite and a small amount of manganese dolomite, manganese calcite, etc., containing a small amount of clay minerals, organic carbon and authigenic minerals such as pyrite, quartz, apatite, barite, chlorite; debris Minerals include plagioclase, albite, zircon, quartz, etc. (Table 3-2). The mineral composition of the Liangjiehe Formation dolomite is mainly dolomite, which can be divided into two stages of dolomite with relatively high magnesium content and relatively high calcium content. In addition, because it is in the development period of the Sturtian Ice Age, the dolomite contains more terrigenous clastic minerals.

Figure 3-47 Structural image and electron probe analysis results of dolomite (Dm4 sample)

Figure 3-48 Bubble-shaped and massive rhombus in Songtao Datangpo Joint Venture Plant Scanning electron microscope photos of manganese ore (DL18, DL15 samples)

Table 3-2 Statistical table of mineral content of rhodochrosite ore in eastern Guizhou Province Unit: %

Note: ++ means the content is 1% ~5%; + is about 1%; - is less than 1% or occasionally seen.

*Other minerals include iron and manganese oxides, ankerite, feldspar powder and clay rock debris.

1. Rhodochrosite

Phase analysis of rhodochrosite samples from Datangpo, Yanglipzhang and Dawu mining areas in northeastern Guizhou Province shows that [81, 93] (Table 3-3): Regardless of whether the Mn content of the ore is high or low, Mn is overwhelmingly distributed in rhodochrosite minerals (accounting for about 90%). Followed by pyromanganite (accounting for about 6% to 9%) and manganese calcite (accounting for about 1% to 4%). The Mn content in high-valent manganese compounds and manganese silicate is less than 0.5%. Through electron probe and scanning electron microscopy analysis, it has been known that rhodochrosite has a microscopic spherulite structure, with a diameter of generally 2 to 25 μm. There are often 1 to 3 concentric layers inside the spherules, which resemble ooids (see Figure 3-39). . Sometimes several pellets gather together to form clot-like aggregates of different sizes, irregular shapes, and no traces of abrasion and transportation. After electron probe analysis of the pellets and cement, it was found that there are differences in the mineral composition of the two. The pellets are composed of rhodochrosite, while the cement is rhodochrosite (see Figure 3-38). These rhodochrosite pellets should be algae biological structures. By measuring the manganese content of a larger rhodochrosite pellet along its diameter, it was found that the manganese content in the center of the pellet was slightly lower than the manganese content on both sides (see Figure 3-39 ), further indicating that it is caused by algae. In addition, quartz is occasionally found in the center of the pellet, and rhodochrosite grows along it to form a circle.

Table 3-3 Phase analysis results of rhodochrosite ore from Songtaoyang Lizhang. Unit: %

Continued table

According to the data of Datangpo Associated Plant Thin-section microscopic identification and electron probe analysis of the bubbly rhodochrosite ore (DL18 and DL15 samples) in the PD1200 tunnel revealed that the material making up the bubble wall is chalcedony, and the chalcedony has a roughly vertical circumferential radial structure (see Figure 3-15) , the pores are filled with asphalt; electron probe analysis of the Liangjiehe Formation dolomite (Dm4 sample) on the Maomaoyan section of Datangpo also found a large number of tiny pores (see Figure 3-43), with sizes ranging from 20 to 50 μm. The pore walls are albite, and there are plagioclase, quartz and other minerals in the pores (see Figure 3-45), which are very similar to the micropores found in SEM images of the surface of modern cold seep carbonate rocks [9].

2. Carbonaceous

In thin sheets, it is a black opaque pollution-like substance with irregular shape. It can be produced with rhodochrosite and become a component of rhodochrosite pellets, and can also be mixed with illite. It is widely distributed in rhodochrosite ore, with a content of 10% to 20%, but the distribution is uneven. Carbon-rich and carbon-poor often form a lamellar structure of alternating light and dark.

3. Illite

The illite content in rhodochrosite ore is unstable, generally between 5% and 40%, and decreases with the increase of manganese content, showing microscopic scales. Like aggregates, sometimes arranged in a directional manner. Interacting with carbonaceous organic matter to form a rhodochrosite lamina structure.

4. Pyrite

There are two types of pyrite in rhodochrosite ore: one is strawberry pyrite, which is an aggregate of microscopic spheroidal pyrite. , 2 to 10 μm in diameter, mostly disordered internally, with a content of 5% to 10%, uneven distribution, and often concentrated in a certain part of the ore, such as the outside of the bubble wall in bubbly rhodochrosite. In pyrite, primary quartz or albite can be seen growing with it (Figure 3-40, Figure 3-41, Figure 3-42); the second is crystallized pyrite, mostly in the form of euhedral or semi-euhedral crystals. Star points are scattered in rhodochrosite, 3 to 25 μm, and the content is unstable, ranging from trace to 15%. However, it is not closely related to the original structure of rhodochrosite ore. Sometimes it can be densely packed into thin strips and is produced in rhodochrosite ore. middle.

5. Pyromanganite

In rhodochrosite ore, star-shaped fine crystals of pyromanganite can sometimes be seen, 2 to 5 μm in size, often occurring together with pyrite. Because its particle size is too small, its exact morphology and characteristics are difficult to determine.

6. Asphalt

It is mainly distributed in the bubbles in rhodochrosite ore. At the same time, dispersed bitumen is also occasionally seen in rhodochrosite ore. The asphalt is surrounded by a "shell" composed mainly of chalcedony, ankerite, magnesium-manganese calcite, etc., that is, a bubble wall. The long axis of the bubbles is distributed parallel to the rhodochrosite bedding, does not cut through the microlayers, and is flattened by the later diagenetic compaction. Due to the compressive stress, the asphalt in the bubbles often develops roughly perpendicular to the long axis of the bubbles. Or oblique cracks, the cracks are also filled with minerals such as chalcedony, ankerite, and magnesium-manganese calcite. The organic carbon content of asphalt in bubbles is as high as 44.2% [81].

7. Quartz

Quartz can be seen in rhodochrosite ore as clean, transparent and other-shaped crystal grains, which are distributed among the microscopic spherules of rhodochrosite or wrapped in pyrite crystals. In the grain.

8. Apatite

One of the main characteristics of the Nanhua Period "Datangpo-style" manganese deposits is the relatively high phosphorus content. After electron probe analysis, apatite was found to be distributed in rhodochrosite ore, which is the main phosphorus-containing mineral in rhodochrosite ore. Apatite has extremely fine particle size and is distributed in microscopic granular form between rhodochrosite pellets and is accompanied by quartz.

Other heavy minerals mainly include rutile, tourmaline, zircon, anatase, etc., with a total content of only about 1%. Scattered in the ore, often associated with quartz dust.