Namibian rosin deposit

The deposit is located about 65km northeast of Swakopmund in namib desert, the western coast of Namibia. According to the diwa theory, the tectonic position belongs to the western end of the Damara diwa area in the African crust. The average uranium grade of the deposit is 0.04%, which belongs to low-grade ore. Uranium is uniformly embedded in Baigangyan, which is called "porphyry" uranium deposit. The total reserves of the deposit are relatively large, about 6.5438+0.4 million tons U3O8. The ore body is exposed to the surface and the mining conditions are favorable. The mine has an annual output of two or three thousand tons of metallic uranium.

The discovery of mineral deposits has experienced a long history. As early as the 1920s, titanomagnetite was discovered in the Rosin Yingshi pegmatite. 1954, Henno Martin demarcated the Swakop area according to the titanomagnetite given to him by local immigrants. 1955 ~ 1958 Smith. D.A.M explored the area and found many narrow pegmatite ore belts containing uranium. Later, due to the low grade of uranium, it was considered to have no industrial significance. In 1970s, J.W.Von Backstrom( 1970, 1974), J. Berning (1976) and V. Ruzicka (1975) successively described this kind of deposit. In the process of revealing mineral deposits in 1970s, uranium reserves increased by leaps and bounds and became a new and important type of uranium deposits.

The host rocks of the deposit are Baigangyan, Wen Xiang granite and biotite granite. They are the products of strong folding, metamorphism and partial granitization of Neoarchean basement rocks. There are three rock series in the mining area, namely Abbabis rock series, Noxibu rock series and Damara rock series from old to new. The Ababis rock series formed in the Neoarchean geosyncline stage include granular quartzite, dolomite marble and calcareous silicate, as well as biotite schist and biotite amphibole schist. Granite and pegmatite intruded before Neoproterozoic Noxibu rock series and Damara rock series were deposited. The age of granite and pegmatite is 1000 ~ 800 Ma, accompanied by folding and metamorphism. When pegmatite intrudes into biotite enrichment area, it is often rich in uranium. Noxibu rock series and Damara rock series are in a continuous whole relationship, which consists of biotite schist, marble, calcareous silicate and quartzite with chronological and feldspar, covering the basement in an unconformity form. Granite and pegmatite also intrude into these two rock series, and remain in pegmatite only in the form of xenoliths of various sizes and in the form of NE-trending, southeast dip and 70-degree dip angle. The pegmatite has an age of 5 100 Ma and belongs to alkali feldspar. Because biotite is often a secondary component, local prospectors call it Baigangyan, which is also the host rock of the deposit.

Therefore, there are two periods of Baigangyan in Luoxin mining area. The first stage was formed in 1000 ~ 800 Ma, mainly mineralized by rare metals, which was the product of the early and middle diwa stage. The second stage was formed in 5 100 Ma, characterized by uranium mineralization, and was the product of the middle and late stage of structural-magmatic activation in diwa stage. The two phases of Baigangyan are not related in space (Figure 4- 1 and 2).

Baigangyan containing uranium mineralization is a kind of light-colored coarse-grained granite, which occurs in the environment of strong metamorphism and fault structure destruction. Baigangyan is basically consistent with regional foliation and foliation, but the dip angle changes greatly. Most of them are bedrock-shaped and small.

Figure 4- 1 Geological Plan of Luoxin Deposit

(according to D. Schmidt)

1 ~ 1 1. Damara system: 1. Biotite cordierite-garnet syenite schist, constructed in Hermas; 2. Marble under construction in 2.Villevich, with silicon interlayer; 3. Chusai built moraine; 4. Gneiss, quartzite, conglomerate and marble are built in Rosin; 5. Hahn builds gneiss and amphibolite; 6. Idusis builds gneiss; 7. The construction of quartzite and gneiss by Idusis; 8.Abbabis eyeball sillimanite and chronological feldspar gneiss; 9. Coarse basalt in Kalu Port; 10. pegmatite granite; 1 1. Granite gneiss, granite and migmatite; 12. Fault zone; 13. The uranium deposits in pegmatite are irregular and dome-shaped. Mineralized Baigangyan is homogeneous in composition and exists in the main rock with great changes in composition in the form of veins. The main uranium ore in the ore is crystalline uranium ore, the particle diameter ranges from several microns to 0.3 mm, and it exists in quartz, feldspar and biotite. Because the crystalline uranium ore particles are very small, it is difficult to identify with the naked eye. According to the research of S.A.Hiemstra( 1969), crystalline uranium accounts for 55%, niobium titanium uranium accounts for 5%, and secondary uranium minerals such as β-uranium amphibole, copper-like uranium mica, water-like uranium amphibole, uranium amphibole, potassium vanadium uranium, thorium lead uranium and lead uranium account for about 40%. These secondary uranium deposits are distributed along the joints and cracks between feldspar and biotite. Crystalline uranium deposits are attached to quartz, biotite and feldspar in the form of particles, or appear as single particles. In addition to uranium minerals, zircon and monazite are closely associated with crystalline uranium deposits, and a small amount of pyrite, chalcopyrite, molybdenite, ilmenite, celestite, chalcocite and titanium dioxide are associated with magnetite, fluorite and hematite. Nicolayson L.O.( 1962) determined the ages of crystalline uranium, titanomagnetite and biotite, and determined that the metallogenic age of Baigangyan and uranium was 5 10Ma-40Ma, which was equivalent to the metallogenic age during the eastern tectonic movement in Hugary.

Figure 4-2 Profile of Luoxin Deposit

1. Uranium-bearing Baigangyan; 2. Upper marble; 3 ~ 6. Rosin Group: 3. Conglomerate; 4. schist; 5. Gneiss; 6. Lower marble; 7 ~ 10.Knaum group; 7. biotite amphibole schist; 8. Upper pyroxene amphibole gneiss; 9. Pyroxene garnet rock; 10. pyroxene amphibole gneiss

Mineralized Baigangyan belongs to a part of the mixed metamorphic rock belt, and has the structure of granite, pegmatite and fine grained rock. It is integrated with gneiss, schist and marble with strong folds in the upper part of Precambrian, and the local unconformity accounts for it. It can be considered that Baigangyan belongs to metamorphic origin. In addition, only Baigangyan contains primary uranium minerals, which are uniformly distributed in the form of accessory minerals. J Berning (1976+0976) pointed out that this mineralized baigangyan is syntectic. Mineralization is only locally enriched in some sections of Baigangyan, indicating that melting occurred in the section with high uranium content in Precambrian bedrock, and the melting made Baigangyan invade the caprock upward.

Baigangyan secondary uranium deposit is a kind of dewdrop that condenses on the bare surface of Baigangyan in desert area at night, seeps into the ground, and the uranium mineralization on the surface is leached out, which precipitates and forms enrichment in favorable structural spaces such as joints, cracks and crevices among mineral particles, and is superimposed on the existing endogenous uranium mineralization. Therefore, the deposit was formed by the preconcentration of uranium in Precambrian sedimentary-diagenetic period and Baigangyan uranium formed by Caledonian granitization, which almost represents the industrial enrichment of bioleaching superimposed uranium. It has experienced many exogenous and endogenous uranium mineralization processes, and then formed a polygenetic compound uranium deposit. Unfortunately, the data of uranium mineralization age in sedimentary diagenetic period and leaching period have not been published publicly. However, from the distribution characteristics of uranium mineralization and the proportion of endogenetic uranium and secondary uranium formed by leaching is close to half, there is enough evidence to show that Luoxin deposit is a typical polygenetic compound uranium deposit.