(Shaanxi Xianyang Institute of Nuclear Industry 203 7 12000)

.

The ore belt of the lower member of Zhiluo Formation in the east wing of Fengjigou anticline is 65438±0.0km long, and it runs nearly north-south. The ore belt in the west wing of the anticline is 0.3 km long, with a northeast-southwest trend. There are four nearly north-south uranium belts in the upper section of Zhiluo Formation in the east wing of the anticline, with a length of 0.4 km.

At present, the discovered uranium mineralization (bodies) are mainly plate-shaped ore bodies, followed by coiled ore bodies, mainly developed in Zhiluo Formation, and plate-shaped and lenticular ore bodies are developed in all ore-bearing layers (Figure 1, Figure 2).

Figure 1 Jinjiaqu Section of Hui 'anbao Deposit 13 Geological Profile of Exploration Line

1- four yuan; 2— Upper member of Zhiluo Formation; 3-Lower member of Zhiluo Formation; 4— Yan 'an Formation; 5- sandstone; 6— Mudstone; 7- Geological boundary; 8— Boreholes and their number; 9-oxidation zone front; 10- gamma curve; 1 1- uranium ore body; 12- uranium mineralization

Fig. 2 Geological profile of Fengjigou section 133 exploration line of Huianbao deposit.

1- four yuan; 2— Upper member of Zhiluo Formation; 3. Lower member of Ziluo Formation; 4— Yan 'an Formation; 5- sandstone; 6— Mudstone; 7- Geological boundary; 8— Boreholes and their number; 9-oxidation zone front; 10- gamma curve; 1 1- uranium ore body; 12- uranium mineralization

2.3.2 Ore body grade, thickness and buried depth

The variation range of ore body thickness is 1.00 ~ 6.20 m, with an average of 3.66m and a coefficient of variation of 0.50, which belongs to medium variation. The variation range of uranium content per square meter is 1.0 1 ~ 3.49 kg/m2, with an average value of 1.84kg/m2 and a coefficient of variation of 0.45. Generally speaking, the uranium content per square meter has little change and is relatively stable. The range of grade change is 0.0 120 ~ 0.0385%, with an average of 0.0230% and a coefficient of variation of 0.36. The grade changes stably and belongs to low-grade ore.

2.4.7 Metallogenic Age

The isotopic ages of 10 ore samples belong to Cenozoic. The apparent ages of U-208 Pb in the northern area of Ciyaobao are 59.2Ma and 2 1.9Ma, respectively, belonging to Paleogene Paleocene and early Neogene Miocene. The apparent ages of U-208Pb in the southern area of Hui 'anbao are 6.2Ma and 6.8Ma, respectively, belonging to Neogene Late Miocene.

3 Main achievements and innovations

3. 1 further clarified the anticline shape, stratigraphic occurrence and fault structure characteristics of Jinjiaqu and Fengjigou sections.

The identification and study of Jinjiaqu Fault (F3) have given us a new understanding of the structure, strata and the distribution of interlayer oxidation zones in Jinjiaqu area. F3 is not just a fault, but a pile of faults. Due to F3 recoil and translation, Yan 'an Formation and Zhiluo Formation overlap in some sections of the east wing of Jian 'erzhuang anticline. In the later period, uranium-bearing and oxygen-bearing groundwater migrated laterally along the axis and east wing of Jianerzhuang anticline, forming three sets of oxidation zones and uranium mineralization in the lower member of Zhiluo Formation and Yan 'an Formation.

3.2 The distribution characteristics of interlayer oxidation zone and uranium ore zone in Jinjiaqu and Fengjigou sections are further clarified.

Around the axis and the east and west wings of a large anticline in Huianbao area, large-scale interlayer oxidation occurred in the upper and lower parts of Zhiluo Formation, and moderate interlayer oxidation occurred in Yan 'an Formation. Oxidized sandstone is mostly light yellow, light yellow and brownish yellow, with light red locally, mainly limonite, followed by hematitization. The interlayer oxidation zone I in the lower member of Zhiluo Formation on the upper wall of F3 in the east wing of Jianerzhuang anticline in Jinjiaqu section is 5.4km long, nearly north-south and developing eastward. The interlayer oxidation zone Ⅱ of the lower member of the footwall Zhiluo Formation in F3 is long 10km, trending northeast-southwest and developing eastward. The interlayer oxidation zone ⅲ of Yan 'an Formation is 2.4km long, showing northwest-southeast-north-south trend and developing eastward. The oxidation zone in the west wing of the southern tip of Jianerzhuang anticline is 1.4km long and develops westward. The oxidation zone of the lower member of Zhiluo Formation in the east wing of Fengjigou anticline in Fengjigou section is 5km long, nearly north-south and developing eastward. The oxidation zone of the upper member of Zhiluo Formation is 65438±0.4km long, which runs nearly north-south and develops eastward. The oxidation zone of the lower member of Zhiluo Formation in the west wing of the anticline is 3km long, nearly north-south and developing westward.

Interlayer oxidation zones I, II and III in Jinjiaqu profile control uranium ore zones I, II and III respectively. The uranium belts in the upper and lower parts of Zhiluo Formation in the east and west wings of Fengjigou anticline are also controlled by interlayer oxidation zones.

3.3 The metallogenic characteristics, ore-controlling factors and metallogenic model of sandstone-type uranium deposits in fault fold zone are summarized.

Metagenetic uranium mineralization in the fault fold belt not only has some characteristics of sandstone-type uranium deposits in typical interlayer oxidation zone, such as being mainly controlled by interlayer oxidation zone, front mineralization, zoning of macro, micro and trace elements in the oxidation zone, but also has its own particularity, such as the main role of structure and bidirectional oxidation mineralization. Sandstone-type uranium mineralization in fault-fold belt has the characteristics of thick sand body, short-distance bidirectional runoff of groundwater and formation of multiple complex local hydrodynamic systems. Interlayer oxidation in the east and west wings of anticline has the characteristics of multi-stage, two-way development, multi-layer, large oxidation depth, short dip extension, large vertical and horizontal thickness variation, poor continuity and weak hydrolytic corrosion. Uranium mineralization has the characteristics of multi-stage, low grade, small thickness, dispersed mineralization, many layers, large depth, strong wing mineralization, weak front mineralization, poor vertical and horizontal continuity of mineralization and strong post-ore transformation.

Anticlinorium is the main and direct factor controlling interlayer oxidation zone and uranium mineralization, and faulting can promote uranium mineralization. Uranium mineralization is obviously controlled by the interlayer oxidation zone developed in two directions on the east and west wings of the anticline. Under the background of anticlinorium and fault structure, several relatively independent groundwater dynamic systems play an important role in controlling uranium mineralization.

In addition, uranium mineralization is closely related to reducing substances such as carbon and pyrite, and oil-gas reduction and hydrothermal transformation are involved in uranium mineralization.

The characteristics and spatial distribution of uranium mineralization in Huianbao area show that uranium mineralization in this area is a unique sandstone-type uranium deposit in the local interlayer oxidation zone controlled by the structural background of fault fold zone. The formation has gone through six stages: early and middle Jurassic sedimentary preconcentration stage, late Jurassic structural framework formation and phreatic uranium oxide enrichment stage, late Cretaceous-Oligocene interlayer oxidation main mineralization stage, mineralization stop stage, Miocene interlayer oxidation secondary mineralization stage, Pliocene local oil and gas and hydrothermal transformation stage.

3.4 provides an example for searching for sandstone-type uranium deposits in tectonic active areas.

Typical interlayer oxidation zone sandstone-type uranium deposits occur in Mesozoic-Cenozoic basins with secondary orogenic structural background and gently inclined slopes. The tectonic setting of Huianbao area is located in Majiatan fault zone on the western edge of Ordos Basin. According to the classical theory and evaluation criteria of hydrogeologic uranium deposits, fault fold zone is not conducive to epigenetic uranium mineralization. In recent years, under the guidance of "looking for relatively gentle structural parts in tectonic active areas", we have continuously enriched the theory of sandstone uranium mineralization, implemented in-situ leaching sandstone-type medium-sized uranium deposits, and explored and confirmed that epigenetic uranium mineralization in fault-fold zones has some characteristics of typical interlayer oxidation zone sandstone-type uranium deposits, but it also has its own particularity.

The sedimentary and tectonic evolution in Hui 'anbao area shows that although this area is located in the tectonic active area of the western margin fold fault zone, it has experienced multi-stage tectonic movement and transformation, forming anticlinorium and syncline, and the structural pattern is relatively complex, which leads to the lack of regional tectonic slope zone in this area. However, from the analysis of tectonic evolution and tectonic action mode, the tectonic framework of the north-south fold belt in this area was mainly formed in the third act of Yanshan movement (JBOY3), while the subsequent fourth and fifth acts of Yanshan movement and Himalayan movement were mainly differential uplift movements in this area, with no strong horizontal compressive deformation, and were in a relatively gentle and stable period of structure. The distribution of Jurassic in ore-bearing strata is mainly controlled by wide and gentle folds and fault structures, and there is a relatively stable monoclinic structure area. At the same time, the uplift and denudation since the Yanshanian movement in the IV and V episodes exposed the Jurassic in the core of the anticline, which provided favorable conditions for the infiltration and leaching transformation of atmospheric precipitation and uranium-bearing groundwater into ore-bearing beds (sand bodies), and the uranium-bearing oxygen-bearing water oxidized along the aquifer to form an interlayer oxidation zone.

The front belt of the thrust nappe structural belt is a favorable area for uranium mineralization. A series of imbricate recoil faults are developed in the front belt, and uranium mineralization is concentrated near the upper and lower walls of the easternmost recoil fault. In the later stage, the leading edge zone is dominated by differential uplift movement, which is in a relatively stable vertical lifting state. After strong deformation, the leading edge zone is in a relaxed state, which makes the groundwater transform the target layer deeper and more thoroughly. It is these imbricate recoil faults (F 1, F3) distributed in the easternmost part of the front belt of thrust nappe that make the target layer thrust upward, close to the surface, and have hydraulic contact with groundwater, leading to interlayer oxidation and uranium mineralization.

3.5 Expand the prospecting field and vision.

In the early days, it was thought that uranium mineralization only occurred in the lower member of Zhiluo Formation in the east wing of anticline. In recent years, we have discovered industrial ore belts in the west wing of anticline, the upper member of Zhiluo Formation and Yan 'an Formation.

4 Development and utilization status

At present, the technological test and feasibility evaluation of special industrial utilization of this deposit have not been carried out. Judging from the geological data ascertained at present, the deposit is generally low in grade, deep in burial, thin in thickness and has a general development and utilization prospect.

refer to

Institute of Nuclear Industry 203 [1]. Study on ore-controlling factors and prospecting direction of uranium deposits in the fault-fold belt in the southwest margin of Ordos basin [r] .19989.999999899997

Sun Yat-sen University. Mesozoic-Cenozoic tectonic evolution in western Ordos Basin and its relationship with sandstone-type uranium mineralization [R].2007.

Guo. Mesozoic-Cenozoic tectonic evolution and uranium mineralization in the western margin of Ordos Basin [J]. Uranium Geology, 20 10, 26 (3): 137- 143.

Li Baoxia. Characteristics of uranium mineralization in Huianbao area, western margin of Ordos Basin [J]. Uranium Geology, 2010,26 (4): 201-207.

Yellow. Metallogenic characteristics, metallogenic model and prospecting prospect of sandstone-type uranium deposits in China paleointerlayer oxidation zone [J]. Uranium Geology, 2007,23 (1): 7-16.

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

[Author] Li Baoxia, male, born in 1962, is a researcher-level senior engineer. 1983 graduated from Guilin Institute of Metallurgical Geology and has been engaged in uranium geological exploration and scientific research for a long time. The projects he presided over and participated in won many national, ministerial and bureau awards, published papers and translated many articles.