(1. China Geo University (Wuhan), Wuhan 430000; 2. Guangdong Nuclear Industry 293 Brigade, Guangzhou 5 10800)
This paper reviews the discovery and exploration process of Huzi uranium deposit in Guangdong Province, summarizes its geological characteristics, comprehensively analyzes the new breakthrough in understanding and practice of silicified zone type, "intersection type" and alkali metasomatism type, and puts forward that a series of gently inclined ore-controlling structures in Huzi uranium deposit are the secondary structures formed by the interaction of footwall of Xiazhuang fault, which is the focus of silicified zone type uranium exploration. It is considered that the ore-controlling function of basic dikes related to "intersection" uranium mineralization is mainly the control of structural faults, and the so-called "intersection" ore-controlling essence is the special performance of uranium mineralization in silicified zone through "interface effect"; According to the relationship between the distribution of uranium deposits and mineralization points in Xiazhuang ore field and the spatial output of late intrusive rocks and the characteristics of alkali metasomatic uranium mineralization, the viewpoint that the formation of late intrusive rocks is closely related to alkali metasomatic uranium mineralization is put forward.
[Keywords:] gently inclined ore-controlling structure; "intersection" uranium mineralization; Interface effect
1 discovery and exploration process
Huzi uranium deposit is located in the middle of Xiazhuang ore field in Guangdong Province. It was discovered in the 1950s. When the team first entered this area for a general survey, they found some anomalies. Experts sent by the Soviet Union to support China's uranium prospecting believe that it has a certain prospecting prospect. Then, focusing on area 6009, the tunnel is divided into north section (main section) and south section (steep cliff section) for tunnel exposure, and three-layer tunnels are built respectively. Therefore, it is considered that the ore bodies are scattered and small in scale. In the 1980s, uranium prospecting at the "crossroads" of the ore field developed rapidly, and the 293rd Brigade of Guangdong Nuclear Industry resumed the exposure and evaluation of the intersection of silicified zone and diabase in the east and south of the area. However, due to the small scale of ore body, slow development of achievements and great adjustment of geological work, exploration work was suspended again.
In 2005, the Geological Bureau of China Nuclear Industry implemented the strategy of "big base" and carried out the "Study on the exploration planning and deployment of the big base of uranium resources in Xiazhuang minefield". Study on exploration planning and deployment of large-scale uranium resource base in xia zhuang mine field in 2009.
The No.293 Brigade of Guangdong Nuclear Industry studied the ore-controlling laws and prospecting potential of various uranium mineralization types in the ore field, and combined with the mine investigation, formulated the deployment plan of "expanding the group in the north and south". According to the deployment plan, in 2006, Huzi area was selected as a distant scenic spot to carry out the project demonstration, and the idea of finding large mines and rich mines was put forward, focusing on the structure of large ore fields and large alteration fields. Because of the existence of Xiazhuang fault zone and No.6009 ore-bearing structural zone in Huzi area, which belongs to the intersection of ne-trending anomaly and NW-trending anomaly of airborne gamma-ray spectrum, the ore-forming hydrothermal activity is strong and has good prospecting prospects. Gong Zhigen and Li, who worked in the 293rd Brigade of Guangdong Nuclear Industry, also encouraged the younger generation. As long as the innovative ideas are carefully investigated, there will be new breakthroughs in this regard.
In 2006-2008, the Geological Bureau of China Nuclear Industry carried out the project "Uranium Survey in Huzi Area of Xiazhuang Orefield in wengyuan county, Guangdong Province". Firstly, exploration is carried out in the fault depression area composed of Xiazhuang fault zone and zone 6009. The properties of Xiazhuang fault and its leading role in mineralization are analyzed and studied, and the mechanical properties of No.6009 belt and its controlling role on ore bodies are analyzed and studied. Deep ore bodies are found, and uranium resources are growing rapidly.
In 2009, the preliminary work results were summarized in stages, and we think that there is a great prospect for finding rich ore in the eastern part of the mining area. After 20 10 ~ 20 12 exploration, it is found that there are abundant shallow ore bodies at the intersection of NNE structural group and diabase. After drilling control, 39 ore bodies were delineated, and the exploration results were remarkable, and a medium-sized uranium deposit was confirmed.
During the whole exploration process, Guangdong No.293 Nuclear Industry Brigade cooperated with China Geo University (Wuhan) to study the relationship between deformation and alteration of rock mass structure and uranium mineralization, and cooperated with Sun Yat-sen University to study granite remelting and uranium mineralization, and put forward the idea of prospecting along the source bed-along the granite remelting interface-along the upper structure of the remelting interface uplift area. Through engineering verification, the overall distribution and connection of ore bodies have been solved, alkali metasomatic uranium mineralization has been discovered in the area, and the prospecting results have been consolidated.
2 The basic characteristics of the mining area
Xiazhuang ore field is located at the junction of the Caledonian of Hunan, Guangxi and Guangdong and the West Indosinian depression of Beihai after Fujian and Jiangxi, and belongs to the tongue-shaped projection in the middle of Nanling metallogenic belt and the eastern part of Guidong rock mass. The ore field rocks are mainly composed of Indosinian granite. Luxi rock mass, coarse-grained porphyritic biotite granite, exposed in the south of the ore field; Xiazhuang rock mass, medium-grained porphyritic biotite granite, exposed in the middle of the ore field; Maofeng rock mass exposed in the north of the ore field is fine-grained mica granite. The rock structure of each rock mass is obviously different, but the boundary between rock masses is irregular. The ore field is sandwiched by Huangpi fault and Ma Shishan fault, and the NE-trending fault and the nearly EW-trending diabase formation are equidistantly distributed and interwoven with each other, forming a checkerboard lattice structure framework to control uranium production in the ore field (Figure 1).
Huzi uranium deposit is located in the middle of the ore field, and medium-grained porphyritic biotite granite is mainly exposed in the mining area. The basic structural framework of the mining area consists of Xinqiao-Xiazhuang fault zone in the northeast, zone 6009 and Huangpi-Zhangguangying diabase formation in the northwest. The NNE-Dongxiazhuang fault zone is the main ore-controlling structure of the ore field, which tends to be near due east and controls the distribution of uranium deposits. It has been found that uranium deposits are mainly distributed in the east (upper wall). Belt 6009 is the main ore-controlling structure, which tends to the west; Belt 6009 and Xinqiao-Xiazhuang fault zone form a small fault depression area, which belongs to a part of the fault depression area composed of Xinqiao-Xiazhuang fault zone and 102- Shijiaowei fault zone (Figure 1). Secondary parallel zones are developed in the fault depression area, and the exposed zones are 207, 205, 204, 20 1. With the development of the exposure work, the concealed secondary parallel zones are gradually discovered. The material composition of the fault zone is complex, and it is filled with many kinds of microcrystals such as syenite, pyrite, hematite, fluorite and calcite. In particular, a good industrial uranium ore body has been formed at the composite site where the NE-trending structure meets the nearly EW-trending diabase vein (Figure 2).
Huzi uranium mineralization mainly includes silicified zone type and "intersection type". Silicified zone type ore bodies are strictly controlled by silicified fault zones, and the occurrence of ore bodies is basically consistent with structural zones. It is mainly distributed in structural zones such as 6009, 6009- 1 ~ 6009- 19, and is a concealed uranium ore body. Twenty-five ore bodies have been discovered, with the vertical depth 100 ~ 400 m and the lowest exposed elevation of 50 m. The strike length of ore body is generally 100 ~ 200m, and the average grade of ore body is 0.09 1%. The ore bodies are distributed in geese formation groups, and most of them are tabular and lenticular. The "intersection" uranium ore body is controlled by the composite trajectory of the intersection of silicified fault zone and diabase, and the size of the ore body is closely related to the trajectory surface. The strike length of ore bodies is generally close to the width of diabase, mostly 10 ~ 30m. Its dip extension is generally 5 ~ 10 times of strike extension. At present, it has been revealed that the controlled vertical depth is mostly 100 ~ 300 m, the shallowest outcrop is 70m, and 3 1 ore body has been discovered. "Intersecting" uranium ore bodies are rich in grade, with an average grade of 0. 18 1%.
Figure 1 Geological Schematic Diagram of xia zhuang Ore Field
1-Upper Cretaceous; 2- Devonian; 3- CAMBRIAN; 4- dacite porphyry; 5- Fine-grained muscovite granite; 6— Medium-fine grained mica granite; 7— Lithofacies dividing line; 8- diabase vein; 9- silicided zone; 10- timely pulse; 1 1- ductile shear zone; 12- deposit and its number; 13- Small deposit and its number; 14- occurred; 15- residential area; 16- huzi uranium deposit
Fig. 2 Geological schematic diagram of Huzi uranium deposit
1-syenite; 2- Fine-grained muscovite granite; 3- medium grained porphyritic mica granite; 4- diabase vein; 5- silicified fault zone; 6- altered cataclastic rock belt; 7- Uranium deposit; 8- uranium anomaly
3 Main achievements and innovations
3. 1 The discovery of gently inclined concealed ore bodies reveals the ore-controlling law of the secondary structure in the fault depression zone and broadens the idea of further blind exploration.
3. 1. 1 Discovery and characteristics of gently inclined concealed ore bodies
The surface geophysical and geochemical exploration of fault zone 6009 in Huzi uranium deposit is good, but the mineralization is poor. According to the previous tunnel construction, the ore body is discontinuous and pinches out deeply. After re-demonstration and comparative analysis of the occurrence law of Xinqiao uranium ore body found in Xinqiao fault depression zone, it is considered that the 6009 fault zone should not exist in isolation, but should be studied as a whole with the Xiazhuang fault zone on the west side, and should be studied as a part of the large fault depression zone composed of Xinqiao-Xiazhuang fault zone and 102- Shijiaowei fault zone in the ore field (mentioned earlier). Through engineering verification, from shallow to deep, there is a group of concealed NE-NE gentle structures on the upper wall of No.6009 fault zone, which is generally 50m long and1~ 5m wide, with an occurrence of 65 NW ∠ 30, which is echelon-like and densely distributed, all with ore bodies or mineralization, and the included angle between the axes of core mineralized layers is generally 70 (Figure 3). Because the ore bodies are short, the ore bodies with the engineering spacing of 100 m× (100 ~ 50) m discovered in the early stage cannot be connected. After the profile is densified, the ore body output law can be displayed and the resources increase rapidly.
Fig. 3 Section of Exploration Line 25 of Huzi Uranium Deposit
1- medium grained porphyritic biotite granite; 2- silicified zone; 3- silicified cataclastic rocks; 4-Complete drilling and numbering; 5— Industrial ore bodies; 6- mineralized zone; 7— Abnormal area
3. 1.2 genetic analysis of ore-controlling structure of gently inclined concealed ore bodies
This group of structures is distributed in the clamping position between the 6009 belt and the Xinqiao-Xiazhuang fault zone. Since the Xiazhuang fault is a left normal fault and the No.6009 fault zone is a right reverse fault, the stress effect formed by the No.6009 fault and the Xiazhuang fault can be analyzed according to their properties, as shown in Figure 4. On the vertical map, we can see that the footwall of Xiazhuang fault is relatively uplifted, giving the footwall an upward friction. Because this force is different at different heights of the fault plane, it can be seen from the horizontal schematic diagrams of Xiazhuang fault and No.6009 fault that the movement of the right plate relative to the left plate gives the left plate a force in the southwest direction, which helps to form a secondary structure intersecting with the main structure at a low angle (Figure 4b), which is consistent with the gentle structure in the NE-NE direction found in exploration. Therefore, it can be inferred that the interaction between the upper and lower plates of Xiazhuang fault is the embryonic stage of the formation of NE-NE gentle structure, and fault 6009 is in the horizontal direction. By studying the formation stress of this group of structures and combining with the exploration results (Figure 3), it can be known that the faults of this group have the characteristics of equal spacing and nearly parallel distribution in vertical and horizontal directions, and the spacing will decrease with the weakening of structural stress.
Schematic diagram of tectonic stress analysis of gently inclined ore-controlling structure.
1- gently inclined structural belt; 2- diabase vein; 3- the (relative) movement direction of geological blocks; 4- Direction of Force
3. 1.3 Exploration ideas for gently inclined concealed ore bodies
Huzi uranium deposit belongs to a part of a large-scale fault depression zone composed of Xinqiao-Xiazhuang fault zone and 102- Shijiaowei fault zone, accounting for about one-fifth of the longitudinal length of the fault depression zone. The discovery of NE-NE trending flat uranium ore bodies in the hanging wall of the 6009 belt verifies the speculation that there are a series of secondary ore-bearing structures in the fault depression zone, which shows to some extent that the fault depression zone has the potential to form large-scale uranium deposits except the 6009 belt and the Xinqiao-Xiazhuang fault zone.
3.2 The discovery of ultra-rich "intersection" uranium ore bodies has once again become the focus of ore field exploration, which has enhanced the confidence of ore fields in finding large and rich ores.
3.2. 1 ultra-rich "intersection" uranium ore body and its characteristics
The exploration of Xiazhuang "intersection" uranium ore field has experienced a breakthrough from the initial negative evaluation of "shallow dispersion and small scale" to the positive evaluation of "shallow enrichment and easy separation". The identified resources account for 40% of the total uranium resources in the ore field, and the average grade of 40% "intersecting" ore bodies reaches 0.3%, so the ore is easy to be mined and selected. Because intersecting uranium ore bodies are produced in groups at a long distance, a lot of work needs to be done to achieve a certain degree of exploration control in an exploration area. How to improve the prospecting efficiency and economic benefits has become a difficult problem in the exploration of intersecting uranium bodies. In the past exploration process, we have been exploring hard with the innovative spirit of "picking sesame seeds and holding watermelons".
During the exploration of Huzi uranium deposit, there is only slight mineralization on the surface at the intersection of zone 205 and diabase. After engineering exposure, the ultra-rich uranium ore body A205- 1-3 (intersection type) was discovered several tens of meters below the surface. The ore body is tabular, extending 10m, with a buried depth of 45m, an average thickness of 0.82m and an average grade of 65438. The discovery of ultra-rich uranium ore bodies strongly shows that "intersection" uranium mineralization has the potential to form rich uranium deposits, and finds a new way to find such ore bodies in the future.
Fig. 5 section of 205 ~ 19 exploration line of huzi uranium deposit.
1- medium grained porphyritic biotite granite; 2- diabase; 3- silicided zone; 4- altered cataclastic rocks; 5-Complete drilling and numbering; 6- Description of ore bodies; 7- Sample section
3.2.2 Preliminary analysis on the formation mechanism of ultra-rich "intersection" uranium ore bodies
The temperature of inclusions in ore-controlling structures is measured, and combined with the previous research on metallogenic temperature [1], it is concluded that the temperature during metallogenic period is
Previous studies have shown that basic dikes in Xiazhuang ore field are closely related to uranium mineralization [2]. However, the previous research on the basic dikes in Xiazhuang ore field is still insufficient, and there are great disputes on lithology [3 ~ 6]. Previous scholars believed that the mineralizer ∑CO2 provided by intermediate-basic dikes was closely related to uranium mineralization [7]; It is considered that mantle fluid plays an important role in uranium mineralization in the study area [8 ~ 10]. Some scholars have also proved this through the study of H and O isotopes [4,11]; Uranium comes from the surrounding rocks of hydrothermal system [12 ~ 13], and from the leaching of uranium from basement rocks and surrounding rocks of the crust by mantle fluid [10, 14 ~ 16]. Combined with the latest research results, from the (Fe3++Fe2++Ti)-Al-M g diagram (Figure 6a, internal data), it can be seen that some points are in the range of high-alumina tholeiite and some points are in the range of high-iron tholeiite, which can be considered as the result of strong silicification and alkali metasomatism of the samples. In the K2O-Na2O diagram (Figure 6b, internal data), the ore sample points are in the range of potassium, and the non-ore sample points are in the range of sodium.
Fig. 6( Fe3++Fe2++Ti)-Al-M g diagram and K2O-Na2O diagram
Umk-ultrabasic komatiite; Bk- basaltic komatiite; HMT-high magnesium tholeiite; Hft-high iron tholeiite; High alumina tholeiite
Because silicification is closely related to uranium mineralization, the evolution of matter is analyzed with SiO2 as abscissa and other major elements as ordinate. The uranium-rich intermediate-basic dikes with strong wall rock alteration were taken out from the borehole, and compared with the samples of non-mineralized intermediate-basic dikes on the surface, so as to study the variation law of major elements in the mineralization process of intermediate-basic dikes. The results show that both Fe3 ++ and Fe2 ++ decrease with the increase of silicification degree (Figure 7), and iron ions decrease with the increase of mineralization degree, which is related to the fading and alteration of mineralization profile, indicating that some iron ions are lost due to leaching. It is not because Fe2+ reduces hexavalent uranium, fe3++ significantly increases and Fe2+ decreases, while the total amount of iron ions remains unchanged. In contrast, CaO and M gO gradually decrease with the increase of silicification degree (figure omitted), which shows that CaO, M gO and SiO2 have a trade-off relationship in composition during mineralization and have no direct influence on mineralization. With the intensification of silicification, potassium oxide and sodium oxide increase rapidly (Figure 8), and the content of potassium oxide increases more obviously, thus revealing the role of "alkalization" in mineralization. Potassium metasomatism is the main factor, and the formation of extra-rich ore bodies may be related to silicification and superposition of potassium.
3.2.3 Exploration ideas of ultra-rich "intersection" uranium deposits
To sum up, it is considered that the extremely rich "intersection" uranium ore body is preliminarily considered that the intermediate-basic dikes are more likely to fracture under the action of tectonic stress to form the migration channels and precipitation sites of ore-forming materials, and the genesis may be that the superimposed silicon-rich and alkali-rich hydrothermal solution is mineralized in a specific geochemical environment on the basis of the conventional "intersection" uranium mineralization, and the specific metallogenic mechanism needs to be discussed. It is worthy of affirmation that the occurrence of ultra-rich "intersection" uranium ore bodies is consistent with that of conventional "intersection" uranium ore bodies, so the exploration idea should be changed from the intersection of existing silicified belts and intermediate-basic dikes to the intersection of silicon-rich and alkali-rich hydrothermal migration and accumulation.
Fig. 7 diagrams of Fe3+-SiO2 and Fe2+-SiO2.
Fig. 8 Diagram of K2O-silica and Na2O- silica
According to this idea, according to the relationship between structural deformation and alteration of rock mass and uranium mineralization, as well as the study of granite remelting and uranium mineralization, it is proposed to look for ore along the source bed-along the granite remelting interface-along the upper structure of the remelting interface uplift area. The ore-controlling essence of "intersection" uranium mineralization is a special form of mineralization by silicon-rich and alkali-rich hydrothermal solution through "interface effect" Maofeng rock mass in the northern part of the ore field is formed by alkali-rich magmatism, and the cave of the rock mass is the gathering area of alkali-rich hydrothermal solution.
High-temperature alteration (greisenization, pegmatization and K-Na metasomatism) is generally developed in the west of Xiazhuang ore field, and K-Na metasomatic uranium mineralization (early uranium mineralization) is generally disseminated along the boundary of rock mass, which may be related to the fact that the magma forming rock mass in the west is alkaline or rich in fluorine ions. It is speculated that the boundary of rock mass has a certain control effect on mineralization, which can be considered as a new mineralization type in Xiazhuang ore field. The exploration depth of this kind of uranium mineralization on the surface can reach below -500 m [17], which indicates that there is still enough uranium exploration potential space in Xiazhuang ore field.
4 Development and utilization status
Compared with the neighboring mining areas, Huzi deposit is an easy-to-mine uranium deposit with good mining conditions and simple beneficiation and metallurgy performance. The deposit has entered the stage of detailed investigation and has been included in the mining plan.
5 concluding remarks
The discovery and expansion of Huzi uranium deposit is a new achievement of Xiazhuang uranium ore field, especially the discovery of gently inclined concealed ore bodies and the discovery of ultra-rich "confluence" uranium bodies, which provide theoretical and geological basis for a new round of prospecting in Xiazhuang ore field. Due to the limited workload, the exposure of mineralization points is still insufficient, and new breakthroughs and progress are needed.
refer to
Pan, Cao, Guan Taiyang, et al. Geochemical study of fluid inclusions in Xiazhuang uranium ore field [J]. Uranium Geology, 2007,23 (5): 257-261.
Hu. Metallogenic mechanism of XW uranium deposit. Journal of Chengdu Institute of Geology [J], 1989, (3): 1-9.
Hu, Jin Jingfu. Genesis of lamprophyre in granite in eastern Guangxi [J]. Mineral rocks, 1990, 10 (4): 1-7.
Wang Zhengqi, Li Ziying, Wu Lieqin, et al. Geochemical evidence of mantle-derived uranium mineralization-taking Xiazhuang Xiaoshui confluence uranium deposit as an example [J]. Uranium Geology, 20 10/0,26 (1): 24-34.
Zhu Ba, Ling, Shen Weizhou, et al. Isotopic geochemistry of Shituling uranium deposit in northern Guangdong [J]. Deposit Geology, 2006,25 (1): 71-82.
, Zhang, Zhang Zuhuan, et al. Study on the relationship between dark dikes and uranium mineralization [J]. Deposit Geology, 199 1, 10 (4): 359-369.
, Hu, Shang, et al. Study on carbon and oxygen isotopic composition of calcite in 302 uranium deposit and its metallogenic dynamic background [J]. Acta Minerala Sinica, 2008,28 (4): 413-420.
Du Letian. Significance of mantle fluid [J]. Structure and Mineralogy, 1989, 13 (1): 97-99.
Du Letian. Geochemical Principles of Hydrocarbon Alkaline Fluids-Further Discussion on Hydrothermal and Magmatic Processes [M]. Beijing: Science Press,1996:165-2301.
[10] Du Letian. Basic metallogenic regularity and general hydrothermal mineralization of hydrothermal uranium deposits in China [M]. Beijing: Atomic Energy Press, 2001:57-110, 15 1-237.
[1 1], Shen Weizhou, Ling, et al. Mantle fluid and uranium mineralization: taking Shixian uranium mine in Xiazhuang ore field as an example [J]. Geochemistry, 2003, 132(6):520-528.
Li Xueli, Sun Zhanxue, zhou wenbin. Paleohydrothermal system and uranium mineralization [M]. Beijing: Geological Publishing House, 2000.
Shao Fei. Low temperature hot water in Xiangshan ore field and its relationship with uranium mineralization [J]. Earth Science —— Journal of China Geo University, 2005,30 (2): 206-210.
[14], Jiang,, et al. Deep fluid metallogenic system [M]. Wuhan: China Geo University Press, 2005.
[15], Liu. Simulation experiment of uranium mineralization in granite [J]. Frontier of Earth Science (China Geo University (Beijing), Peking University), 2009,16 (1): 99-113.
[16] Ni, Hu, Jin Jingfu.302 Vertical zoning model of hydrothermal mixing and boiling in uranium deposits [J]. Uranium Geology, 1994, 10(2):70-77.
Feng Zhijun, Huang Hongkun, Zeng, et al. Geological basis of deep prospecting in Xiazhuang ore field and its periphery [J]. Uranium Geology, 20 1 1, 27 (4): 22 1-224.
Significant progress and breakthrough in uranium exploration in China —— Examples of newly discovered and proven uranium deposits since the new century.
[Author] Lai Zhongxin, male, born in 1963, is a senior engineer. 1984 graduated from the Department of Geology, East China Institute of Geology, majoring in general survey and exploration, and obtained a master's degree from China Geo University (Wuhan) on 20 10. Now he is the chief engineer of Guangdong Nuclear Industry 293 Brigade. He presided over the exploration of 1 large, 2-medium and 5-small uranium deposits, presided over or participated in the completion of 5 special studies, worked out the exploration plan for the large-scale base of uranium resources in Xiazhuang ore field, organized and implemented geological projects and personnel training projects, and achieved remarkable results and prospecting benefits.