Hu Kai deposit is located in the southeast of athabasca basin, about 200km north of Lalange town in northern Saskatchewan, with the geographical coordinates of N57°2″ "and W105 40". It is a uranium-nickel deposit completely covered by athabasca Group or Quaternary ice deposit. The geotectonic position of the deposit was attributed to canadian shield by Canadian geologists, and according to the diwa theory, it can be attributed to the wollaston dome in the diwa area of athabasca in the North American crust. The average grade of uranium (U3O8) in this deposit is 2%, and its reserve is 73,900 tons.
The Hu Kai deposit was discovered by the German company Uranerz in 1975. A series of comprehensive methods were applied to the discovery and expansion of the deposit, mainly including tracing the source of radioactive boulders, surface glacier geology, geochemistry, geophysics and core drilling. Geologists from Canada, the United States, Germany and other countries, such as volz Di, Kocher, Dahlkamp, Rusika, have made in-depth research on the Hu Kai deposit. Different scholars divide it into different types, some are sedimentary deposits, some are metamorphic deposits or hydrothermal deposits, and only a few mathematicians think it is a multi-stage genetic deposit. Liu Xiang, one of the authors of this book and a senior engineer, visited the deposit and other important unconformity uranium deposits in athabasca Basin in 1995, collected some latest geological data, and re-recognized the deposit by applying diwa theory and its polygenetic compound metallogenic theory. The author thinks that the genesis of the deposit is complex, so some experts emphasize one aspect and others emphasize another, which leads to a great gap in understanding the genesis of the deposit. In fact, the deposit is a typical polygenetic compound deposit.
2. Geological characteristics of the deposit and its multi-genetic basis.
1) mining strata and ore-bearing surrounding rocks
The strata in Hu Kai area are composed of Archean, Proterozoic and Mesoproterozoic. The oldest strata in Hu Kai area are Archean granite gneiss and migmatite, which constitute dome-shaped complex. Proterozoic Wollaston Group is unconformity covered on Archean strata, extending in northeast dome shape, distributed around Archean uplift, and the strata are strongly folded (Figure 5-38).
Wollaston Group is a set of metamorphic sedimentary rocks, belonging to a part of crystalline basement. The regional metamorphism occurred during Hudson orogeny (1735Ma) and was influenced by the strong ancient weathering before the deposition of Mesoproterozoic athabasca Group. Wollaston Group is mainly composed of biotite-plagioclase-cordierite gneiss, garnet-syenite-feldspar-cordierite gneiss, graphite schist, biotite-rich schist, amphibole, coarse-grained anatexic migmatite and granite pegmatite. Mesoproterozoic athabasca Group was deposited on the crystalline basement, which was unconformity with continental clastic sediments. The formation consists of basement conglomerate, fan conglomerate and timely sandstone. The bottom strata are bedrock fragments, some of which are strongly weathered, indicating that bedrock weathering occurred before sandstone deposition in athabasca Group. The grain size of timely sandstone gradually becomes finer upward. The total thickness of this stratum group in the mining area is 60m.
Uranium mineralization occurs directly in the unconformity between the Mesoproterozoic athabasca Formation and the underlying Proterozoic Wollaston Group (Figure 5-39). The main ore bodies occur in graphitized metamorphic sedimentary argillaceous rocks (gneiss) of wollaston Group in the basement below the unconformity surface, but the mineralization only extends to about 150m below the unconformity surface (Figure 5-39). Some ore bodies occur in gravelly sandstone and coarse sandstone of athabasca Group above unconformity surface.
Figure 5-38 Geological Map of Hu Kai Deposit
1. athabasca group; 2. Proterozoic gneiss and schist; 3. Archaean migmatite and gneiss; 4. Tectonic fracture zone: a. Based on geophysical data; 6. measurement; 5. Graphite conductive area; 6. Assumed complex boundary; 7. Deposition bed; G. Geithner orebody; Delman orebody
2) Tectonic morphology and metallogenic structure
The regional structure of the deposit has the characteristics of multiple structural layers. Granite gneiss and granite of Archean Tajin Group are the oldest structural layers in this area. The tectonic layer was finally formed in the Kenolan orogeny (2480Ma), representing the product of the pre-geosyncline stage. The wollaston Group, Truyiqiao Lake Group and Multi-island Group in the Afro-Proterozoic are composed of metamorphic sedimentary rocks from the sub-shelf to the geosyncline, which constitute the second structural layer in this area and become a part of the crystalline basement in this area. The formation of this tectonic layer finally reached the Hudson orogeny (1735Ma), representing the product of geosyncline stage. The terrigenous clastic rocks, Devonian and Cretaceous of Manting Formation (1630Ma) and athabasca Group (1350ma) in the middle Proterozoic Hailiki period constitute the youngest structural layers in this area, representing the products of diwa stage. In addition, there may be a short platform stage in Late Proterozoic (1735 ~ 1630м a).
The main structural features of Hu Kai area are Archean granite and granite gneiss as the core, which are covered with folded metamorphic sedimentary rocks of Wollaston Group (Figure 5-40). The regional trend of schistosity and bedding is northeast-southwest Fault structures are developed in the mining area, with the largest scale and the widest distribution, showing NE-SW direction. In the mining area, this group of faults tend to be NW-trending, with an inclination of 50 ~ 70. The nearly north-south post-athabasca fault is also well developed, which crosses the previously formed northeast fault. Both fault systems have vertical fault distances. In the Geithner orebody, the southeast fault block descends by 40m (Figure 5-4 1). In the northeast part (Delman ore body), the fault zone is more complicated than its southwest extension (Geithner ore body) (Figure 5-42). On the profile of the mining area, Paleoproterozoic unconformity structures are widely developed and have become one of the important ore-controlling factors.
The formation of fault structure in mining area is obviously divided into two stages. The first stage was the return stage of the Paleoproterozoic Afibian geosyncline, which formed NE-trending folds, schists and a series of NE-trending shear fault zones. The structural rocks of the shear fault zone are mainly mylonite with ductile shear properties, and iron-bearing chloritization and kaolinite are the most direct surrounding rocks for uranium mineralization, with high-grade uranium and nickel mineralization. The second stage is the fault structure after the formation of athabasca Group in Mesoproterozoic and later. It is mainly manifested in cutting the NE-trending faults and nearly N-S-trending faults of athabasca Group, and activating the pre-existing faults for many times, so that some pre-existing faults cut through the strata deposited in the Mesoproterozoic Diwa Basin (Figure 5-42) and are superimposed on the ductile shear zone of the pre-existing basement, which has the characteristics of brittle faults.
Figure 5-39 Schematic diagram of cross-section of Delman and Geithner ore bodies
1. Glacier deposit; 2. athabasca sandstone; 3. Afribia base; 4. Sandstone uranium deposits; 5. Basement uranium ore; 6. Failure
The ore-forming structures of uranium-nickel deposits in Hu Kai are mainly Paleoproterozoic unconformity structures and NE-SW shear fault zones superimposed on NE-trending schists, and a few small-scale ore bodies are related to nearly N-S fault zones.
3) Magmatic rocks in the mining area
Magmatic rocks are not developed in the mining area, but diabase veins with diwa stages and stages have been invaded in athabasca Basin. The first diabase vein emplacement was found in the sandstone of athabasca Group in Kelihu area adjacent to Hu Kai area, and its K-Ar age was 1230ma (Burwash, 1962). The second diabase vein emplacement was discovered in the Carswell area in the west of the basin, with K-Ar ages of 938Ma and 33Ma, respectively (according to Trewblay of the Canadian Geological Survey, unpublished). These two diabase vein intrusions are very close to the main metallogenic age of Hu Kai deposit or other uranium deposits in athabasca basin. Therefore, the author thinks that uranium deposits in athabasca Basin may not be closely related to magmatism as most scholars think, but may be closely related to hydrothermal activities related to deep magmatism, such as multi-stage diabase dike intrusion in diwa period, which is worth further exploration.
Figure 5-40 Geological Interpretation of Zimmer Lake-Lake Kay Basement in Canada
1. Archean paleocore; 2. Affibia sedimentary metamorphic rocks; 3. The approximate boundary of the south of athabasca Formation; 4. failure; 5. Freeze the uplifted boulder; 6. Mineralization; 7. Bedrock outcrop; 8, the main electromagnetic wave conductor with magnetic inclination and letter display; 9. Use numbers
The secondary electromagnetic wave conductor or strip shown; 10.Afibia syncline axis; 1 1. anticline axis; 12. Synclinal axis
Fig. 5-4 1 Geological Profile of Central Gaina Ore Body
1. Sand and fine gravel layer; 2. boulder ore body; 3. Glacier sediments; 4. massive and disseminated ore bodies; 5. Physical and chemical fields; 6. Sandstone buildings in athabasca; 7. pegmatite; 8. Graphite gneiss; 9. biotite-bearing gneiss
Figure 5-42 Profile of Derman Ore Body
(According to F.J. Dahlkamp 1978)
1. Ice water deposits sand and gravel; 2. Ore bodies; 3. Shear band; 4. Built in athabasca; 5. Graphitized gneiss; 6. biotite gneiss
4) Ore body shape and surrounding rock alteration near the mine.
Hu Kai deposit is composed of two main ore bodies, namely, Gaina ore body and Delman ore body, both of which are concealed ore bodies. The two ore bodies occur in the same NE-trending shear fault zone. The length of the fault zone is more than 6km, and the total length of uranium mineralization is more than 5km, which has been partially eroded by glaciers. The ore body extends along the shear fault zone to below the unconformity surface120m, showing a simple lenticular shape. Geithner orebody has a total length of1500m and a width of10 ~ 90m, which can be divided into two parts. The northern ore body is 800 meters long and 10 ~ 50 meters wide, and mineralization usually occurs 50 ~ 80 meters below the surface. In the core over 0.3m in length, the grade of U3O8 and Ni is as high as 45%. The southern ore body is 600 meters long, with an average width of 15 meters, and the Delman ore body is about 1400 meters long and 10-200 meters wide, with a maximum downward extension of 160 meters, and it is located at 60- 140 meters below the surface. The core is Most ore bodies occur in iron chloritization and kaolinite mylonite in graphite metamorphic argillaceous rocks of wollaston Group, and a few occur in sandstone of athabasca Group.
There are two types of alteration in mining areas, the first is related to mineralization, and the second is caused by weathering. Weathering alteration includes sericitization and Fe-Mg chloritization. This alteration also exists in mylonite, but it quickly becomes gneiss with only weak shearing. Its chemical and mineral composition is basically the same as that of non-fragmented weathered gneiss far away from the ore belt, and usually contains no ore.
Alteration closely related to mineralization can be divided into two types: iron chloritization and kaolinite. Iron chloritization is iron-rich chlorite produced in mylonite, which is mainly composed of dark green iron-rich (magnesium-free) chlorite and a small amount of kaolinite. Kaolinitization occurs in grayish white mylonite dominated by kaolinite. In some cases, it is completely composed of kaolinite, with calcite and siderite veinlets locally developing and passing through the ore body. According to Di, during the formation of iron chloritization and kaolinite related to mineralization, almost all the primary cations in the host rocks directly containing ore migrated, and kaolinite and iron chlorite were considered as the products of strong tectonic deformation zone. Then hydration alteration occurs, which recrystallizes kaolinite and iron chlorite. Kaolinization and iron chloritization obviously occur after regional weathering and are closely related to uranium mineralization (Figure 5-43).
Figure 5-43 Vertical Profile of Hu Kai Deposit
(According to F.J. Dahlkamp 1978)
1. Glacier deposit; 2. athabasca sandstone; 3. substrate; 4. Ore bodies; G. Geithner orebody; D. Delman ore body; Glaciation formed the skylight in the basement.
5) Mineral composition
The main ore-forming elements in the ore are uranium and nickel. Uranium exists in the form of oxides and silicates, nickel exists in the form of sulfides and thioarsenides, and secondary minerals include copper, lead and zinc, as well as molybdenum. According to the generation sequence of minerals, Dahlkamp can be divided into five mineralization stages, and the occurrence sequence of ore minerals is shown in Figure 5-44. De et al. think that ore minerals can be divided into early mineral groups in basement mylonite and graphitized gneiss and late mineral groups in overlying athabasca Group.
The ore minerals in basement mylonite are α-U3O7 (called "square" crystalline uranium ore), uranium ore and fumed pitchblende, nickel-nickel ore, goethite, nickel-arsenic ore, orthorhombic nickel ore, galena, galena, pyrite and white iron ore, and a small amount of chalcopyrite, celestite and sphalerite. Arsenide, nickel-nickel ore, arsenite and orthoarsenite of α-U3O7 and nickel do not exist in sandstone.
The adjacent graphite schists do not contain uranium minerals, but may contain a small amount of nickel arsenic, nickel iron ore or goethite locally. This mineralization may be caused by (initial) metamorphism (Tilsley, 1979).
Uranium deposits in athabasca Group are mainly found in intergranular spaces of sandstone, and also found in some places of synchronous intergranular spaces. These intergranular spaces have good original roundness and secondary (newer) synchronous edges. In some places, the late mineralization (especially goethite) is limited to the fault surface.
Figure 5-44 * * mineral generation and generation sequence diagram
The most important uranium ore in bedrock is a-U3O7 ("Square Crystalline Uranium Ore"), which fills the cracks in blocks, or distributes in thin films along the cleavage plane of layered silicate, or produces colloidal lumps and well-developed autogenous crystals, and then oxidizes along the surface and contraction cracks of α-U3O7 to form soot-like pitchblende.
Nickel arsenate and α-U3O7 are formed at the same time, and they are authigenic and sometimes banded, and coexist with uranium, other nickel minerals and gangue minerals in banded form. Late nickel arsenic replaced other nickel minerals except goethite.
Galena-iron-nickel ore was also formed in the first stage of mineralization. Together with α-U3O7, it appears as inclusion in authigenic nickel arsenite. The orthorhombic arsenic-nickel deposit may also be formed in the early metallogenic stage and replaced by nickel-nickel ore along the fault.
Nickel exists as spherical particles, which can be explained by Ni3As2. Nickel ore is closely related to grey pitchblende and has become the cause of other nickel ores.
Uranite and pitchblende belong to a relatively young genetic stage, and are found as concentric symbionts in metamorphic sedimentary rocks in Africa or in gaps between other minerals.
A few but locally enriched ore components are pyrite, white iron ore, chalcopyrite, galena and sphalerite. Ore bodies in metamorphic sedimentary rocks are locally cut by many calcite and siderite veins. Apart from the above minerals, there are basically no other minerals, especially gangue minerals.
6) Metallogenic age of the deposit
The uranium and lead isotopic analysis data of main ores in Hu Kai deposit show that the deposit has four main metallogenic ages, namely 1228 ~ 160ma (crystalline α-U3O7), 960 ~ 9 18ma and 370Ma (gray pitchblende in basement rocks) and 250 ~ 60ma.
3. Formation conditions of ore deposits
Graphitized gneiss in Proterozoic Wollaston Group metamorphic rock series is the main ore-bearing rock. The uranium content of unaltered graphite and garnet argillaceous gneiss in this area is 12 ~ 17g/t, and Canadian scholars believe that the original rock of this rock series is a set of argillaceous rocks. Du Letian (1996) thinks that its protolith is a set of strata rich in uranium and containing carbon (graphite), carbonate, flint and sulfide, which is called uranium-rich C-Si mudstone series in uranium geology in China. We agree with Du Letian that this rock series in China is often rich in elements such as U, Ni, As, Co, Cu, Mo and Au. This can explain the enrichment of U, Ni, As, Cu and Mo in Hu Kai deposit. Accordingly, the author thinks that the uranium source mainly comes from the uranium-rich carbonaceous siliceous mudstone series in the basement of the basin. In addition, the Archean granite gneiss and granite in the area have high uranium content, and the sandstone of athabasca Formation has high uranium content and good permeability, which can provide some uranium sources. Therefore, the uranium source of this deposit should be multi-source.
The metallogenic temperature of main mineralization can be inferred from mineral thermometer. There is pyroxenite-nickel ore in the ore, the upper limit of its stable temperature is137℃ 6℃, and the lower limit of the stable temperature of tetragonal α-U3O7 is 135℃. Based on this, the temperature of ore-forming solution in the main mineralization period can be accurately determined as 135 ~ 137℃. According to the data of F. Dahlkamp (1978), the δ34S/32S ratio of nickel sulfide in ore ranges from+1.0 ‰ ~+10 ‰, which indicates that the ore-forming solution forming Hu Kai deposit has the characteristics of multiple sources of sulfur.
4. Evolution of uranium mineralization
Based on the analysis of the stratigraphic and structural characteristics in Hu Kai area and the understanding of the structural evolution of athabasca Basin (see the sedimentary profiles of Canadian Central Lake and West Lake for details), the author thinks that Hu Kai area has also experienced Archean pre-geosyncline stage, Proterozoic geosyncline stage, Mesoproterozoic short platform stage and Mesoproterozoic diwa stage. The outstanding feature of its tectonic evolution is that the platform stage is short and the diwa stage lasts about 65.438+0.6 billion years. Uranium mineralization is closely related to tectonic evolution. In addition, before discussing the evolution of uranium mineralization in Hu Kai deposit, the main ore-controlling characteristics of Hu Kai deposit are summarized:
(1) mineralization occurs directly in the Mesoproterozoic unconformity contact zone between the athabasca Group and the underlying crystalline basement, and the mineralization only extends to about 150m below the unconformity, and the main mineralization is generally within 20m below the unconformity.
(2) Orebodies mainly occur in the NE-SW shear fault zone.
(3) Before mineralization, the main changes were sericitization and chloritization, which were confined in the ancient weathering crust and produced by ancient weathering; Iron chloritization and kaolinite closely related to uranium-nickel mineralization are obviously formed by ore-bearing thermal fluids.
(4) There are two main types of mineralization. The ancient (1228Ma) uranium oxide and nickel sulfide are confined to crystalline substrates. Young (< 300Ma) mineral assemblages containing U-Ni occur in overlying sandstone of athabasca Group, which may be formed by mineralization and reactivation in basement rocks.
The above characteristics show that the formation of uranium-nickel deposits in Hu Kai mainly experienced the following metallogenic evolution processes:
(1) sedimentary mineralization
It is mainly the formation of Carboniferous-siliceous mudstone series in Paleoproterozoic geosyncline stage, which hAs high components such as U, Ni, As, Cu, Pb, Zn, Mo and organic carbon, leading to the initial enrichment of elements such as U and Ni in sediments, with an average uranium content of 50g/t, laying a foundation for transformation and remineralization.
② Metamorphic mineralization
Hudson orogeny in the return stage of geosyncline leads to the deterioration of sedimentary rock series rich in uranium, nickel, arsenic and carbon, which leads to the activation and migration of uranium and re-precipitation in local carbon-rich sections, forming uranium pre-enrichment. At this time, cubic uranium was formed.
(3) Tectonic-magmatic activation mineralization
Hu Kai deposit is obviously controlled by Mesoproterozoic unconformity and NE-trending shear fault zone, because tectonic activation not only provides power for uranium activation and migration, but also is the migration channel of uranium-bearing solution and reducing gas and the precipitation place of uranium. Magmatic activation can also provide energy and rich mineralizers for uranium migration, and drive the activation and migration of ore-forming materials. The main industrial metallogenic period of Hu Kai deposit (1228Ma) is basically consistent with the intrusion age of diabase wall formed in the diwa stage of Kelihu, which is a strong evidence.
(4) Leaching mineralization
In Hu Kai area, there are usually several meters to tens of meters thick paleoweathering crust under the Mesoproterozoic unconformity surface, which indicates that uranium migrated and enriched near the unconformity surface after a short platform stage before the diwa period.
(5) Late reformation and mineralization.
In the late diwa stage, the uranium-bearing and oxygen-bearing aqueous solution flowing downward through the athabasca Group of the caprock can also transform the pre-existing uranium ore bodies and enrich the superimposed ore bodies. There are abundant ores in the deposit, some of which were formed much later than sedimentary caprocks, and the δ34S/32S ratio of ores changed greatly, which provided a basis for this argument.
To sum up, all kinds of mineralization in different evolution stages have played an important role in the formation of Hu Kai deposit, which has the obvious characteristics of multiple metallogenic stages, multiple material sources, multiple ore-controlling factors and multiple genetic types, and is a typical polygenetic compound uranium-nickel deposit.