(1. Shaanxi Nuclear Industry Group 224 Brigade Co., Ltd., xi 'an, Shaanxi 7 10024 2. Shaanxi Nuclear Industry Group 218 Brigade Co., Ltd., xi 'an 7 10024, Shaanxi)
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0+0 rock mass
Huichizi rock mass is exposed in the north and southwest of the mining area, and is in intrusive contact with the stratum of the third lithologic member of Qinling Group. Lithology is dominated by biotite diorite granite, light red-grayish white, medium-fine grained-medium grained granite structure and gneiss structure. The main minerals are plagioclase, plagioclase, potash feldspar, Yingshi and a small amount of biotite, and the auxiliary minerals are zircon, apatite, monazite and garnet. U-Pb isotopic age of granular zircon is 465Ma. The Rietmann index of chemical composition of Huichizi rock mass is 1.67, which belongs to calc-alkaline granite. Rich in silicon and alkali, Na2O content is greater than K2O content, Na2O +K2O content is less than 7%, aluminum is supersaturated, low in uranium and high in thorium, and the Th/U ratio is large (Table 4).
Fig. 3 Geological schematic diagram of Xiaohuacha uranium deposit.
Table 4 Chemical Composition (wB) of Huichizi Rock Mass and Gaoshangou Rock Mass
Gaoshangou rock is exposed in Gaoshangou area in the southeast of the mining area, with an exposed area of about 5.45km2, which is in intrusive contact with the stratum of the third lithologic member of Qinling Group, and the lithology of the contact part with Huichizi rock mass is in gradual transition. The lithology is Baigang adamellite, with potash feldspar belt developed at the edge, and the rock is light red-grayish white, with medium-grained and coarse-grained granite structure. The edge is dominated by gneiss structure, the gneiss is basically consistent with the stratum occurrence, and the central part is dominated by massive structure. Main mineral components: albite, potash feldspar, microcrystalline feldspar, microcline and timing; The content of dark minerals is low, mainly biotite; The accessory minerals are zircon, apatite, monazite and garnet. The U-Pb isotopic age of granular zircon is 423Ma. The Rietmann index of chemical composition of Gaoshangou rock strain is 1.72, which belongs to calc-alkaline granite. Rich in silicon and alkali, K2O content is greater than Na2O content, Na2O+K2O content is greater than 7%, aluminum is supersaturated, low in uranium and high in thorium, and the Th/U ratio is small.
2.2.3.2 dike
The dike in the mining area is mainly biotite granite pegmatite dike, and a small amount of biotite granite pegmatite dike is distributed near the core of Miaoping syncline in the mining area. The biotite granite pegmatite dike is the main uranium mineralization rock in the mining area, mainly distributed in the contact zone outside the rock mass, and the U-Pb isotopic age of granular zircon is 405Ma. The characteristics of pegmatite dikes of mineralized biotite granite are as follows:
(1) Geological characteristics
Five veins I, II, III, IV and V are delineated in Xiaohuacha uranium belt, in which vein II is mainly mineralized vein rock. Mineralized dikes are distributed in the third lithologic member of Qinling Group within 0 ~ 100 m from the contact zone outside the south wing of Miaoping syncline, which are parallel to each other. The vein is 300 ~ 3400 meters long and 2 ~ 25 meters wide, and it tends to the northeast with an inclination angle of 60 ~ 80. Its spatial form is veined and layered, and there are phenomena such as expansion, contraction, branching and compounding along the dip and strike, among which there are often metamorphic rock residues of different sizes and shapes. The mixed dyeing zone develops along the vein edge, with a mixed dyeing bandwidth of 5 ~ 20 cm, rich in massive and veinlets biotite and silicified development.
(2) Petrological characteristics
Mineralized biotite granite pegmatite is locally rich in massive biotite and pig liver chromophore massive plagioclase. The medium-coarse grained texture, massive structure and accessory mineral composition show the petrological characteristics of molybdenite (Table 5).
Table 5 Mineral composition of biotite granite pegmatite
The petrochemical characteristics of mineralized biotite granite pegmatite are high mass fraction of dark components (Fe2O3+FeO +M nO +M gO), minimum A/CNK, minimum Na2O +K2O, maximum K2O/Na2O, and maximum Fe2O3 and FeO (Table 6).
Table 6 Characteristics of mass fraction and chemical composition of biotite granite pegmatite
(3) Radiogeochemical characteristics
The pegmatite of ore-bearing biotite granite is characterized by high uranium content and thorium-uranium ratio less than 1 (Table 7).
Table 7 Contents of radioactive elements in biotite granite pegmatite
Trace element mantle standard spider web diagram The curve of ore-bearing biotite pegmatite is obviously enriched with Zr and Mo elements (Figure 4).
Fig. 4 standard spider web diagram of trace element mantle
The average fluorine content of non-mineralized dikes is 237× 10-6, that of mineralized dikes is 4 13× 10-6, and that of ore bodies is 1602× 10-6. The F content of non-mineralized dikes, mineralized dikes and industrial ore bodies is relatively large.
2.2.4 Metamorphism and Wall Rock Alteration
The main metamorphic period in the mining area is the middle and late Jinning. A uranium-rich layer dominated by biotite plagioclase gneiss was formed in the third lithologic member of Qinling Group by metamorphism in the middle and late Jinning period. Metamorphic formation is biotite plagioclase-granulite formation, and metamorphic facies is low amphibolite-high amphibolite facies.
The surrounding rock alteration in the mining area is not developed.
2.2.5 Characteristics of radioactive physical field of the deposit
The anomalous halo of 1) uranium in the surface energy spectrum is distributed along the dense areas of biotite granite pegmatite dikes, mainly in the outcrops of biotite granite pegmatite dikes such as valleys and ridges, which roughly reflects the scope of uranium mineralization.
2) The distribution direction of surface gamma anomalies is basically the same as that of uranium-bearing biotite granite pegmatite, and most of them are distributed in a point or intermittent way along the outcrop of ravine biotite granite pegmatite. The surface gamma value of uranium-bearing biotite granite pegmatite is higher than that of unmineralized biotite granite pegmatite.
3) The abnormal distribution of activated carbon mostly develops along the ravine and rock cracks on both sides, and the distribution direction of abnormal halo of activated carbon is basically the same as that of biotite granite pegmatite.
2.3 Ore body geology
2.3. 1 ore body characteristics
Xiaohuacha uranium deposit has delineated six uranium bodies, which mainly occur in biotite granite pegmatite dikes II and III in Magou section, among which KT2- 1 and KT2-2 are the main ore bodies. Except KT4 ore body, other ore bodies are blind. The ore body is veined and lenticular. The length of ore body is generally 80 ~ 3 10 m, with a maximum of 440 m; The depth extension is generally 3 1 ~ 202 m, and the maximum is 837 m; Generally, the thickness is 0.50 ~ 10.3 1m, the maximum is 14.72m, and the coefficient of variation of thickness is 56% ~ 105%, so the thickness is relatively stable. The grade of ore body is generally 0.0340% ~ 0.1.61.5%, with a maximum of 0.2395%, and the coefficient of variation is 1.8% ~ 93%, indicating uniform mineralization. The uranium grade of the deposit is 0.0805%, which belongs to low-grade industrial ore. The occurrence of ore body is consistent with vein rocks, with strike 1 10 ~ 1300 and dip angle of 38 ~ 72 (Table 8) [4] 424.
Table 8 List of main ore body characteristics of Xiaohuacha uranium deposit
Ore quality
(1) Mineral composition of ore
The uranium minerals in the ore industry are mainly crystalline uranium, followed by a very small amount of pitchblende [3]. The main gangue minerals are chronological and plagioclase, followed by biotite. Metal minerals include pyrite, magnetite, limonite and molybdenite. The accessory minerals are mainly apatite, zircon and monazite (Figure 5).
(2) Ore texture and structure
The ore texture is mainly medium-coarse grained granite texture, followed by pegmatite texture, with graphic texture and porphyritic granite texture locally. The ore structure is dominated by massive structure, with some porphyritic schistose structure and banded structure (Figure 6 ~ Figure 9).
(3) Occurrence and physical properties of crystalline uranium deposits.
Crystalline uranium deposits have completely authigenic granular structure and disseminated structure, which are dispersed or disseminated, accounting for more than 60% of mineral particles, and a small part of them occur in rock-forming minerals. When the ore is rich in biotite and plagioclase, most crystalline uranium deposits occur between biotite and plagioclase particles. When the content of biotite and plagioclase is low, it appears between plagioclase and timely particles.
Crystalline uranium deposits are highly radioactive and are black and equiaxed. The crystal forms are mainly cubic and underdeveloped octahedron, and a few are long granular, thick plate or irregular. The particle size is 0. 1 ~ 0.3mm, and the maximum is1mm. The stripes are black and green. The fracture is shell-shaped, with resin luster or asphalt luster. Mohs hardness is 5 ~ 6, and Vera hardness is 348kg/mm2. The density is 9.47 g/cm2. The secondary change is very weak.
Fig. 5 backscattering image of core slice electron probe
Crystalline uranium exists in the interior of potash feldspar (Kf) and in the cracks between K feldspar (Q) and K feldspar (Kf). Crystalline uranium (Ur) is closely related to zircon, molybdenite (Mot) and monazite (Monz).
Fig. 6 Granite pegmatite type uranium deposit
Fig. 7 Uranium ore rich in biotite
Fig. 8 Enriched feldspar-type uranium ore
Uranium ore rich in biotite and plagiogranite pegmatite.
(4) Ore type
According to the host rocks of the ore body, the natural type of uranium in Xiaohuacha uranium deposit is low-grade granite pegmatite type uranium deposit (Figure 6); When the ore is rich in massive biotite or brownish-red plagioclase, it is a medium-grade granite pegmatite ore (Figure 7 and Figure 8), which is locally distributed in low-grade uranium ore. At the same time, granite pegmatite is rich in massive biotite and brownish-red plagioclase (Figure 9), and it is occasionally found in low-grade uranium ore [5].
The uranium ore in Xiaohuacha uranium deposit is a high silicate uranium ore with low content of fluorite and other characteristic minerals.
(5) Chemical composition of ore
The chemical composition of biotite granite pegmatite uranium ore in Xiaohuacha uranium deposit is shown in Table 9, which has the following characteristics:
Table 9 Chemical Composition of Xiaohuacha Uranium Ore (wB)
1) The ore is rich in silicon, alkali, potassium and aluminum.
2) The content of basic components (Fe, Ti, M g, M n, Ca) in high uranium grade granite pegmatite ore is relatively high, which is related to the rich biotite minerals and feldspar minerals in the ore.
3) The Fe2O3/FeO value of the ore is 1.08 ~ 1.49, which indicates that the uranium deposit was formed in a low oxygen fugacity environment.
4) The content of acid-consuming chemical components in the ore is low, which is suitable for acid leaching.
2.4 Ore-controlling factors and prospecting indicators
2.4. 1 ore-controlling factors
1) Strata and lithologic ore control: The deposit, occurrence and anomalies of Chenjiazhuang-Guangshigou granite pegmatite uranium deposit are located in the third lithologic member of Qinling Group (Figure 2), and the ore bodies in the mining area are mainly distributed in biotite gneiss, and the mineralization intensity of thick amphibole lenses is weakened. The uranium bodies in Chenjiazhuang-Guangshigou granite-pegmatite type uranium deposit are all found in biotite granite-pegmatite dikes within 200m of the inner and outer contact zones of crust-mantle mixed source rocks such as Huanglongmiao, Luoziping and Huichizi (Figure 2), and uranium mineralization in massive biotite granite-pegmatite dikes is better (Figure 5-8).
2) Structural ore control: the watershed and Luanzhuang deep fault control the distribution range of deposits, occurrences and anomalies in Chenjiazhuang-Guangshigou granite pegmatite uranium deposit area; Luanzhuang-Wuguanhe buried fault controls the occurrence position of uranium ore bodies; The uranium ore body east of Luanzhuang-Wuguanhe buried fault occurs in the mineralized biotite pegmatite vein in the contact zone outside the rock body. The uranium ore body on the west side of Luanzhuang-Wuguanhe buried fault occurs in the mineralized biotite pegmatite vein in the contact zone inside and outside the rock mass. The fold wing of the mining area controls the distribution of pegmatite veins and ore bodies of biotite granite, and the mineralization veins and uranium bodies of the mining area are located in the fold wing. In the mining area, the occurrence of mineralized biotite granite pegmatite dike is consistent with that of rock mass interface, and uranium ore bodies occur in the parts where the interface between mineralized biotite granite pegmatite dike and rock mass fluctuates and the occurrence changes from steep to slow.
2.4.2 Exploration marks
1) biotite granite pegmatite located in the external contact zone of rock mass is the main rock for uranium mineralization.
2) The biotite granite pegmatite is dominated by medium-coarse grained texture, and pegmatite texture is occasionally seen in some areas. Abundant massive biotite, reddish brown plagioclase, apatite and monazite are the petromineralogical indicators of uranium ore bodies.
3) High uranium content, low thorium content and thorium-uranium ratio less than 1 are the radioactive parameters of mineralized biotite granite pegmatite.
4) The content of SiO2 _ 2 in biotite granite pegmatite vein decreases, and the total amount of rare earth elements increases, especially the content of heavy rare earth elements increases, and the Eu loss is strong, δ EU < 0.25, which is the chemical symbol of rare earth elements in mineralized biotite granite pegmatite.
5) The high content of molybdenum, zirconium and fluorine in dikes is a geochemical indicator of mineralized biotite granite pegmatite.
6) The biotite granite pegmatite with high surface gamma value located in the composite part of activated carbon, uranium with surface energy spectrum and radioactive hydrochemical anomalies within the halo range of uranium deposits is mineralized biotite granite pegmatite.
7) The place where the occurrence of pegmatite dike of undulated biotite granite changes from steep to slow may be the structural sign of uranium mineralization.
2.5 Mineral processing and smelting performance
Guangshigou uranium deposit, which is the same type as Xiaohuacha uranium deposit, has completed the experimental study on conventional stirring leaching, gravity concentration and heap leaching of uranium ore. The technical indexes in table 10 confirm that the granite pegmatite type uranium ore is easy to leach and gravity separation [5].
Table 10 Metallurgical Test Results of Guangshigou Uranium Deposit
3 Main achievements and innovations
3. 1 main achievements
Medium-sized uranium deposits have been identified, and it is expected that 1 large uranium deposits will be identified through general survey in the next 2-3 years.
3.2 Main innovation points
1) puts forward that the uranium mineralization of this deposit is located in the contact zone outside 100m rock, which is controlled by biotite granite pegmatite dike, and uranium is positively correlated with the enrichment degree of massive biotite, massive brownish-red feldspar, apatite and zircon, and summarizes the petromineralogy, radioactive geochemistry, rare earth elements, trace elements and radioactive geophysical and geochemical prospecting indicators of mineralized dike rocks, so as to provide a basis for future prospecting.
2) The viewpoint that the contact surface of rocks and the occurrence of dikes control ore is put forward. When the concave surface of rock contact surface changes, the shape of mineralized pegmatite dike is wavy, and the occurrence from steep to slow is the occurrence position of uranium ore body.
3) A new idea of gravity separation and preconcentration+stirring leaching of crystalline uranium concentrate is put forward, and the test results of Nelson's new high-efficiency gravity separation equipment are obtained, which puts forward new ideas and achievements for improving the economic benefits of granite pegmatite uranium deposits.
4 Development and utilization status
At present, it is still in the general survey and has not yet been developed and utilized.
5 concluding remarks
5. 1 Follow-up exploration needs scientific and technological research.
1) Explore the new technology of detecting, locating and exploring the spatial position of granite pegmatite dikes, roughly find out the spatial occurrence position of pegmatite dikes, and provide a basis for revealing the engineering layout of middle and deep ore bodies.
2) Through the research of metallurgical technology and comprehensive utilization technology, the problem of low economic value of this type of low-grade ore can be solved, and the development benefit of this type of deposit can be improved, and further research and improvement can be made on selective gravity preconcentration-conventional stirring leaching of crystallized uranium concentrate-leaching solution separation and enrichment-alkali precipitation production 11product or extraction separation and enrichment-precipitation production1. Through the study of process mineralogy, the occurrence and enrichment of titanium, iron and gallium in the enrichment process of crystalline uranium ore, the feasibility of comprehensive utilization of titanium, iron and gallium in gravity separation and preconcentration process is studied.
5.2 Exploration prospect
The total predicted amount of Xiaohuacha uranium deposit in the shallow 500m is 4796t, and the general survey has confirmed that the medium-sized uranium deposit is not closed in the deep part of the ore body. In the 20 13 general survey, three layers of industrial ore bodies have been drilled in Majiacha area outside the city, and biotite granite pegmatite dikes with good matching with radioactive anomalies have been circled in Miaogou area (Figure 1). It is estimated that more than 3000t tons of large-scale uranium resources can be discovered in 2 ~ 3 years.
5.3 Development prospect
1) The prospective resources of Xiaohuacha uranium deposit have reached the scale of large-scale deposits, and the ore bodies are mainly distributed in the range of 640m in length and 60 m in width 160m in No.7 to No.24 exploration lines of the deposit, with concentrated ore bodies, simple mining technical conditions and low mining cost. The natural and industrial types of ore are basically the same as those of Guangshigou uranium deposit. Compared with the experimental indexes of beneficiation and metallurgy of Guangshigou uranium deposit, it has good beneficiation and metallurgy performance and low processing cost.
2) The mining area is located in the forest area, and there are no residents and cultivated land within 2km of Fiona Fang. There are abundant clear water resources 2 kilometers outside the mining area, and township roads have reached 2 kilometers outside the mining area, and the external environment for development is good.
refer to
[1] Luo Zhongxu, Shayazhou, Zhang Zhanshi, et al. Research report on enrichment regularity and metallogenic prospect prediction of granite pegmatite uranium deposits in Feng Dan area [R]. China Bureau of Nuclear Geology, 2008.
Feng, Jiao, Zhang, et al. Relationship between evolution characteristics of Caledonian magmatic rocks and uranium mineralization in northern Feng Dan [J]. World Nuclear Geology Science, 201,(4):202-207.
Feng, Zhang, Jiao, et al. Characteristics and prospecting direction of granite pegmatite uranium deposits in Feng Dan area, Shaanxi Province [J]. Northwest Geology, 2013,46 (2):159-165.
Feng, Cheng Dejing, Zhang, et al. Uranium survey report in Xiaohuacha area, Shangnan County, Shaanxi Province [R]. Brigade 224, Geological Bureau of Shaanxi Nuclear Industry, 20 13.
Cui Shuanfang, Feng, Pu, et al. Experimental research report on gravity separation of Guangshigou uranium mine in Shangnan County, Shaanxi Province [R]. Shaanxi Nuclear Industry Group Co., Ltd., 20 14.
Significant progress and breakthrough in uranium exploration in China —— Examples of newly discovered and proven uranium deposits since the new century.
[Author Brief Introduction] Gao Ming, male, born in 1958, is a professor-level senior engineer, majoring in mineral geology. He is currently the chief engineer of the 224 Brigade of Shaanxi Nuclear Industry Geological Bureau, and has been engaged in the prospecting and exploration of solid minerals for a long time.