Ciyaobao uranium deposit in Ningxia

(0 140 10 of 208 Brigade of Baotou Nuclear Industry, Inner Mongolia)

The discovery of Ciyaobao uranium deposit has gone through several stages, such as comprehensive mapping research, uranium resources investigation and evaluation, regional evaluation, preliminary investigation and general survey. The ore-bearing layer of the deposit is the lower member of Zhiluo Formation of Middle Jurassic. The ore body is distributed in the north-south direction, with a length of 7km and a width of 100 ~ 400m, which is simple in shape, controlled by interlayer oxidation zone and obvious in structural ore control. It belongs to interlayer oxidation zone sandstone uranium deposit.

[Keywords:] Ciqibao; Interlayer oxidation zone; Sandstone type uranium deposit

Ciyaobao uranium deposit, located in lingwu city, Ningxia Hui Autonomous Region, is distributed in the north-south direction, controlling the ore belt area of 9km2. The deposit is located at the intersection of G20 National Highway and G30/KLOC-0 National Highway, with convenient transportation. This is the landscape of desert hills.

1 discovery and exploration process

Ciyaobao uranium deposit was discovered in 2002 by the No.208 Brigade of the Nuclear Industry on the basis of studying and mapping uranium metallogenic conditions in Ciyaobao area in the north of Ordos Basin, based on the front of interlayer oxidation zone between Yan 'an Formation and Zhiluo Formation delineated by it, taking in-situ leachable sandstone-type uranium deposit as the main prospecting type, and through several stages of uranium resources investigation and evaluation, regional evaluation, pre-investigation and general survey.

Comprehensive mapping and research of 1. 1

In 2002, in view of the discovery of Zaohuohao uranium deposit in the north of Ordos Basin, in order to further expand the uranium prospecting achievements in Ordos Basin, the middle Jurassic Zhiluo Formation and the middle Jurassic Yan 'an Formation in the western margin of the basin have the characteristics of shallow burial, and the No.208 Nuclear Industry Brigade systematically collected basic geological data and borehole data in the western margin of the basin. It has undertaken the project "Study and Mapping of Uranium Mineralization Conditions in Ciyaobao Area in Northern Ordos Basin" issued by China Nuclear Geology Bureau [1], further determined that the prospecting targets in Ciyaobao area are middle Jurassic Yan 'an Formation and Zhiluo Formation, delineated the leading edge of interlayer oxidation zone in the sand bodies of lower Yan 'an Formation, upper Yan 'an Formation and lower Zhiluo Formation respectively, and predicted the type I metallogenic prospect of gravel well in Ciyaobao-Zhiluo Formation.

1.2 investigation and evaluation

From 2003 to 2005, the project "Investigation and Evaluation of In-situ Leached Sandstone Uranium Resources in Northern Ordos Basin" was issued by China Geological Survey, organized and implemented by China Geological Bureau of Nuclear Industry, and undertaken by No.208 Brigade of Nuclear Industry. According to the technical idea of "overall evaluation of regional uranium metallogenic environment and drilling verification in key areas", the verification work is mainly carried out in Ciyaobao area, with a drilling workload of 2300m and five boreholes. The lower member of Zhiluo Formation in Ciyaobao-Qingshuiying-Fengjigou area further delineates a large interlayer oxidation zone, which is more than 80 kilometers long and generally 3 kilometers wide. It is further determined that the Zhiluo Formation of Middle Jurassic is the main prospecting target layer in Ciyaobao area on the western margin of the basin, and the type I uranium metallogenic prospect area of Ciyaobao is divided.

1.3 regional evaluation

In 2005-2006, the No.208 Brigade of the Nuclear Industry undertook the project "Regional Evaluation of Yindong Area in Northern Ordos Basin1∶ 250,000 Uranium Resources" issued by the Geological Bureau of China Nuclear Industry [3], and proposed that the thrust belt in the western margin of Ordos Basin has the basic geological conditions for sandstone-type uranium deposits with interlayer oxidation zone, and the prospecting horizons are mainly the Zhiluo Formation (J2z) and the Yan 'an Formation (J2Z) in the middle Jurassic. The technical route is determined as "regional development, moderate pursuit and key breakthrough", controlling the front of interlayer oxidation zone in Qingshuiying, Ciyaobao, Gravel Well and Majiatan Zhiluo Formation, and taking into account the exploration of interlayer oxidation zone in Yan 'an Formation and Yanchang Formation. In the past two years, 34 boreholes have been drilled, and the drilling workload is 1 1300m, which confirms the genesis of Ciyaobao and Fengjigou uranium deposits.

1.4 Pre-inspection

From 2007 to 2008, the No.208 Brigade of the Nuclear Industry undertook the project of "uranium prospecting in Yindong area in northern Ordos Basin" issued by the Geological Bureau of China Nuclear Industry [4], and followed the technical idea of "regional development, moderate pursuit and key breakthrough" to further control the frontier of interlayer oxidation zone of Zhiluo Formation in Qingshuiying-Majiatan area, taking into account the exploration of interlayer oxidation zone of Yan 'an Formation and Yanchang Formation. In the past two years, we have put into drilling 15300m, and drilled 32 holes. The front line of interlayer oxidation zone of Zhiluo Formation in Ciyaobao section is mainly controlled, the favorable uranium mineralization position is properly dissected, and the medium-sized sandstone uranium deposit in Ciyaobao is preliminarily determined.

1.5 Census

20 10-20 12 The 208th Brigade of the Nuclear Industry undertook the project of "Uranium Survey in Yindong District, lingwu city City, Ningxia" issued by China Nuclear Industry Geology Bureau [5]. The drilling workload is 19000 m, and 39 boreholes are drilled, which roughly identifies the shape, occurrence and spatial distribution of ore bodies, and further confirms the sandstone in Ciyaobao.

2 the basic characteristics of deposits

2. 1 structural features

Ciyaobao uranium deposit is located in Majiatan fault zone in Majiatan-Tianshuibao section of fold thrust belt in the western margin of Ordos Basin, with complex geological structure (Figure 1). Influenced by Yanshan movement, there were many folds and faults in Yindong area in Mesozoic. The associated scale of faults and folds is large, and the general direction of structural line is NNW [6].

Liu Ma fault: it is the eastern boundary fault of Majiatan coal mining area, and it is a first-class main reverse fault zone, with northwest strike and west dip of the reverse fault, with dip angle of 50 ~ 70, fault distance > 1000 m and extension 15km in the area. Located in the east of Ciyaobao uranium deposit, this structure is the main ore-controlling fault structure of Ciyaobao uranium deposit and the local drainage channel of uranium-bearing and oxygen-bearing groundwater of ore-forming fluid.

Figure 1 Structural Outline of Ciyaobao Uranium Deposit

(According to the geological records of Ningxia, 1990)

1-Lower Cretaceous; 2- Upper Jurassic; 3- Middle Jurassic; 4- Upper Triassic; 5- Middle Triassic; 6— Parallel unconformity interface of strata; 7— unconformity interface of stratum angle; 8- anticline; 9— Syncline; 10- thrust fault and secondary fault; 1 1- Ciyaobao uranium deposit; 12- place names

Yuanyanghu-Fengjigou anticline: it is the main ore-controlling fold structure of the deposit, showing north-south direction and north-south direction, about 60km long. The west wing of the anticline is steep and the east wing is gentle, and uranium mineralization is generally located in the east wing of the fold structure (Figure 2).

The fold structures around Ciyaobao uranium deposit are generally 10 ~ 20km long and only 5km wide, and most of them are inclined to the north. The west wing of anticline is often broken and incomplete, with narrow exposure and steep dip angle; Syncline structure is the opposite. Folds are all composed of Mesozoic. The axis of syncline is mostly Upper Jurassic Anding Formation and Lower Cretaceous Zhidan Group, and the core of anticline is mostly Middle Jurassic Zhiluo Formation or Upper Triassic Yanchang Formation.

Distribution map of target sand body, interlayer oxidation zone and ore body in Ciyaobao uranium deposit.

1- Middle Jurassic Zhiluo Formation; 2-Middle Jurassic Yan 'an Formation; 3- Industrial uranium mine; 4-Mineralized pores; 5— Abnormal hole; 6— No ore holes; 7-exploration line and number; 8- anticline; 9- Presumption of fault; 10-the front of interlayer oxidation zone; 1 1- formation parallel unconformity line; 12- uranium ore body; 13 —— thickness contour line of braided river sand body in the lower member of Zhiluo Formation (m)

2.2 Formation characteristics

The sedimentary cover of Ciyaobao uranium deposit is composed of Mesozoic and Cenozoic, with Triassic, Jurassic and Cretaceous as the main sedimentary bodies. The middle Jurassic Zhiluo Formation can be divided into the lower member and the upper member (J2z2), and the lower member (J2z 1) belongs to braided river deposit (Figures 3 and 4), which is the ore-bearing horizon of the deposit.

Fig. 3 Histogram of Sequence Division of Zhiluo Formation in Ciyaobao Uranium Deposit

(According to Guo, 2006, it has been revised)

1-gravelly coarse sandstone; 2- coarse sandstone; 3- medium sandstone; 4— Fine sandstone; 5— Siltstone; 6— argillaceous sandstone; 7— Carbonaceous mudstone; 8— Mudstone; 9- rise for half a week; 10-drop by half a week

Schematic diagram of uranium body profile in Ciyaobao uranium deposit.

1- Upper member of Zhiluo Formation of Middle Jurassic; 2- Upper submember of lower member of Zhiluo Formation of Middle Jurassic; 3- Lower submember of the lower member of Zhiluo Formation of Middle Jurassic; 4- Middle Jurassic Yanan Formation; 5- sandstone; 6— Mudstone and siltstone; 7— Stratigraphic and lithologic boundaries; 8— Parallel unconformity boundary; 9— Profile direction; 10- number of holes; 1 1- interlayer oxidation zone; 12- uranium ore body

The lithology of the lower member of Zhiluo Formation in Ciyaobao uranium deposit is mainly medium sandstone and medium coarse sandstone, which constitute 3 ~ 5 incomplete positive rhythmic layers from bottom to top. The top mudstone and siltstone are not developed, but can be seen in the drilled core. The thickness of sand body is generally between 40 ~ 60m. The distribution of sand bodies has the following characteristics: the thickness of sand bodies is thin in the north, and gradually thickens to the south, 20 ~ 40m in the north and 60 ~ 80m in the south. The isoline trend is roughly east-west, from north to south, and the sand body is thin and thick. The areas with thin sand body thickness are mostly located on both sides of the river, and the areas with large sand body thickness are located in the river.

2.3 Hydrogeological characteristics

The sand body in the lower member of Zhiluo Formation of Middle Jurassic is a mineral-bearing aquifer, and its thickness gradually increases from north to south. The ore-bearing aquifer in the anticline core on the west side of the deposit is exposed to the surface, and the buried depth of the aquifer roof gradually increases eastward. The maximum buried depth of the aquifer roof exposed on the east side is 532.0m, and the dip angle is about 6 ~ 7. The roof and floor structure of the ore-bearing aquifer is stable, with single-hole water inflow 182.40m3/d, unit water inflow of 0.054 l/s·m, and permeability coefficient of the ore-bearing aquifer of 0. 17m/d ... The ore-bearing aquifer has large single-hole water inflow, good water abundance and good permeability.

2.4 Development characteristics of interlayer oxidation zone

Interlayer oxidation zone is developed in braided channel sand body of the lower member of Zhiluo Formation in Ciyaobao uranium deposit. Influenced by the faults and folds in the western thrust belt and the modern watershed in the east, the distribution characteristics of interlayer oxidation zone are complex and generally develop from west to east. Interlayer oxidation develops along the eastern and western wings of the anticline core and from the northern end to the southern end of the anticline. The front line of the oxidation zone generally extends in a serpentine north-south direction, and the southern end protrudes in a long hook shape. The interlayer oxidation zone in the east wing of the anticline is well developed, which roughly controls the length of the leading edge of the oxidation zone from north to south by about 15km. The interlayer oxidation zone is irregularly serpentine along the strike, with a long extension distance and a short extension distance along the dip (Figure 2). Ciyaobao uranium deposit belongs to a typical interlayer oxidation zone, which can be divided into complete oxidation zone, transition zone and reduction zone. Uranium bodies are spatially distributed in the oxidation-reduction transition zone.

2.5 characteristics of ore bodies

The uranium body of Ciyaobao uranium deposit extends irregularly from south to north in the plane (Figure 2). The thickness of the ore body in the north of the deposit is small, and the thickness of the ore body in the south is large. Ore bodies are mainly plate-shaped in profile, and a few are spiral (Figure 4). Uranium ore bodies are distributed in the sand body of the lower member of Zhiluo Formation, generally in the middle and lower part of the 40m thick sand body, and the ore bodies are located at the top and bottom of yellow sandstone, close to the front of oxidation zone. The elevation at the bottom of the ore body tends to increase to the south and decrease to the north. The ore body is deep in the north and shallow in the south. The average elevation of the bottom of the main ore body is 965.4 1m, which is lower in the north and higher in the south. The average buried depth of the main ore body is 406.24m (table 1).

Table 1 Characteristics of Buried Depth and Elevation of Main Orebodies in Ciyaobao Uranium Deposit

The change of ore body grade has no obvious regularity, and the overall performance is high grade near the front edge of interlayer oxidation zone. The parts with high uranium content per square meter of ore body often correspond to the parts with large thickness of ore body, and the areas with high uranium content per square meter are mostly distributed near the front edge of interlayer oxidation zone (Table 2).

Table 2 Variation characteristics of thickness, grade and uranium content per square meter of main ore bodies in Ciyaobao uranium deposit

2.6 ore characteristics

The uranium ores in Ciyaobao uranium deposit are mainly medium-grained, medium-grained and coarse-grained sandstone. The ore industry type is mainly uranium-bearing clastic rock with low content of characteristic minerals; The mineral composition of ore basically maintains the main composition of surrounding rock; Uranium ore is mainly pitchblende, with a small amount of uranium ore and secondary uranium ore, and uranium is mostly distributed in matrix and cement in a dispersed adsorption state (Figure 5).

3 Main achievements and innovations

3. 1 main achievements

Ciyaobao sandstone uranium deposit occurs in the thrust fold belt on the western edge of Ordos Basin. According to the general industrial indicators of in-situ leachable sandstone-type uranium deposits, uranium resources have reached a medium scale.

2) The lithologic and lithofacies characteristics of the target layer and the development characteristics of the oxidation zone are roughly identified. The lower member of Zhiluo Formation of Middle Jurassic is the main ore-bearing stratum of Ciyaobao uranium deposit, and the sand body of the target stratum is braided river deposit, with medium-coarse grained feldspathic sandstone as the main ore-bearing rock. The front of the control interlayer oxidation zone is about 15km long from north to south and about 3km wide from east to west. The uranium ore belt is about 7km long and100 ~ 400 m wide along the strike.

Fig. 5 Uranium-bearing minerals and adsorbed uranium minerals.

(According to Fang Xiheng, 2006)

3) The hydrogeological characteristics of the deposit are roughly identified, and the Zhiluo Formation is divided into an aquifer. The ore-bearing aquifer (the lower member of Zhiluo Formation) is dominated by coarse clastic rocks with good permeability and large water inflow.

4) The characteristics of ore bodies and ores have been roughly ascertained, and the ore bodies are pie-shaped and crescent-shaped, and the ore bodies are scattered; The ores are mainly medium-grained, medium-coarse grained and coarse grained sandstone; Uranium is mainly pitchblende, with a small amount of uranium ore and secondary uranium ore, and uranium is mostly distributed in matrix and cement in the state of dispersion and adsorption.

3.2 Main innovation points

1) established the metallogenic model of Ciyaobao uranium deposit. The metallogenic model of Ciyaobao uranium deposit is multi-stage and multi-stage, which is mainly divided into three stages (Figure 6).

Fig. 6 Metallogenic model diagram of Ciyaobao uranium deposit

(According to Guo, 20 10, modified)

1-Lower Cretaceous; 2- Upper Jurassic Anding Formation; 3- Middle Jurassic Zhiluo Formation; 4- Middle Jurassic Yanan Formation; 5- Triassic; 6- Carboniferous-Permian; 7- Lower Paleozoic; 8- Precambrian (metamorphic rocks); 9- Hercynian uranium-rich granite; 10- migration direction of surface uranium; 11-migration direction of uranium during denudation and leaching; 12- stratum boundary; 13- thrust fault; 14- denudation structural morphology; 15-Angle unconformity; 16-gravel; 17-Carboniferous coarse sandstone; 18— mudstone; 19- coal seam; 20— Uranium ore bodies (coiled and lenticular)

Jurassic —— Early stratum preconcentration and later stratum folding and denudation stage: Due to denudation transportation, acid magmatic rocks and other substances eroded by Yinchuan ancient uplift in the source area were transported to this area and deposited in the form of braided river, forming sandstone in the lower member of Zhiluo Formation. This process took place in the early Middle Jurassic. Yanshan movement caused Yinchuan and Liupanshan areas to uplift strongly and thrust eastward, accompanied by the appearance of fold structures. At this time, the north-south structure of Yindong area was basically finalized. Later, due to denudation and transportation, the terrain was leveled, and local sand bodies were exposed as skylights, which created conditions for uranium enrichment in the future.

Cretaceous-early Cretaceous sedimentary caprock and late Cretaceous denudation and oxidation stage: the strong thrust and folding of Jurassic Yanshan movement made the Cretaceous cover the underlying strata widely with angular unconformity. Late Cretaceous became an important development period of interlayer oxidation zone in Yindong area. Oxygen-containing and uranium-containing water replenished by erosion source and atmospheric precipitation permeates downward along the exposed area of anticline core. During the infiltration process, the ore-forming materials in surrounding rock are continuously dissolved, forming interlayer oxidation zone. The seepage of interlayer water has not only recharge conditions, but also discharge conditions. It is generally believed that the buried faults in the north-south direction are local drainage sources, while the Ordos Basin and the Yellow River are regional drainage areas in different periods.

Cenozoic-main uranium mineralization stage: before the formation of Yinchuan fault depression and Helanshan uplift belt, it was a new important uranium mineralization process, and Paleocene, Eocene and Miocene were important uranium mineralization periods. At this stage, the interlayer oxidation zone and mineralization formed in the early stage further developed and superimposed with new mineralization. Combined with uranium mineralization age analysis, uranium mineralization in Yindong area can be divided into three stages: 59.2 ~ 5 1 Ma, 2 1.9 Ma and 6.8 ~ 6.2 Ma. It can be seen that the uranium mineralization age of Ciyaobao uranium deposit is relatively new, mainly Paleogene Paleocene and Eocene, followed by early and late Miocene.

2) Ciyaobao uranium deposit is a sandstone-type uranium deposit found in thrust belt and compression belt, which breaks through the previous understanding that it is difficult to form sandstone-type uranium deposits in thrust belt and compression belt.

4 Development and utilization status

The technical and economic conditions of in-situ leaching mining of Ciyaobao uranium deposit have not been evaluated.

5 concluding remarks

The industrial uranium mineralization of Zhiluo Formation in the periphery of Ciyaobao uranium mine is developed, and Yan 'an Formation also has a good uranium metallogenic environment and broad metallogenic space, so the uranium prospecting work in the periphery of Ciyaobao uranium mine should be strengthened.

In the combination of short-axis anticline and water-conducting fault in Ciyaobao area, what role the fault structure plays in the process of uranium mineralization, whether it is the drainage channel of uranium mineralized groundwater and other issues need to be further studied, and the uranium mineralization model needs to be further improved.

refer to

Kuang, et al. Study on uranium metallogenic conditions and metallogenic prognosis in Ciyaobao area in northern Ordos Basin [R]. 208 Brigade of Nuclear Industry, 2002:5-35.

Yang Jianxin, Kang Shihu, et al. Investigation and evaluation of in-situ leachable sandstone-type uranium resources in northern Ordos Basin [R]. No.208 Brigade of Nuclear Industry, 2005: 12- 189.

Liu Zhonghou, Wang Yongjun, et al. Regional evaluation of1∶ 250,000 uranium resources in Yindong area of northern Ordos Basin [R]. No.208 Nuclear Industry Brigade, 2006:11.

Liu Zhonghou, Wang Yongjun, et al. Pre-exploration of uranium deposits in Yindong area of northern Ordos Basin [R]. 208 Brigade of Nuclear Industry, 2008:13-11.

Wang Yongjun, Gao Long, et al. General survey of uranium deposits in Yindong area, lingwu city, Ningxia [R]. No.208 Brigade of Nuclear Industry, 2012:12-108.

Guo. Tectonic evolution and sandstone-type uranium mineralization in the western margin of Ordos Basin [D]. Geological Bureau of China Nuclear Industry, 20 10: 13-24, 168.

Significant progress and breakthrough in uranium exploration in China —— Examples of newly discovered and proven uranium deposits since the new century.

[Author] Wang Yongjun, male, born in June, 1974, 165438, master, senior engineer. 1997 joined the work, engaged in uranium geological exploration for a long time, and served as the project leader. Won the ministerial-level scientific and technological progress award and the national defense scientific and technological progress award 1 respectively.