1. Understanding the complexity of uranium mineralization
Classification of uranium deposits of the fourth genetic type. The research shows that it is impossible to use the unit metallogenic theory of traditional mineral deposit science to classify the genesis in the past because of the complex characteristics of multi-material sources, multi-metallogenic structural stages or multi-stages and multi-genetic processes. It not only has the characteristics of endogenous deposits, but also has the signs of exogenous deposits. Only by dividing the fourth type of deposits can the problem of deposit classification be solved.
2. Emphasize the importance of comprehensive observation and comprehensive research.
The polygenetic compound uranium deposit has the characteristics of endogenesis and exogenesis. Only by comprehensive observation and comprehensive research can we make a comprehensive and complete evaluation of the characteristics of the deposit. If we only emphasize certain characteristics and signs from one side, it is often difficult to reflect objectivity and the understanding of each family cannot be unified. For example, when we studied carbonate uranium deposits in the early 1980s, we conducted sedimentology research, and reached the conclusion that lithofacies palaeogeography controlled the deposits, and the conclusion that sedimentary-diagenetic deposits were formed. Structural workers have seen that mineralization is restricted by fault structures, hydrothermal alteration is related to the distribution of endogenetic uranium mineralization, and they have an understanding of hydrothermal or hydrothermal mineralization. Some people see that the deposit is superficially enriched and the physical properties of the ore are loose, emphasizing leaching mineralization and concluding that the deposit is the cause of leaching; Later, karst scientists saw that karst caves were developed and karst breccia was widely distributed in carbonate areas, which was related to the distribution of uranium mineralization, and concluded that karst caves were sedimentary-diagenetic-mineralized. People who hold various views have their own observation facts and basis, and all have their own correct side. However, it is often difficult to draw a more objective conclusion if we comprehensively evaluate the genesis of the deposit based on our own observations, even deny the facts and basis observed by others, or ignore the facts and basis discovered by others.
3. The necessity of applying the viewpoint and research method of metallogenic evolution.
Due to the formation of polygenetic compound uranium deposits, they have often experienced multi-stage or multi-stage tectonic activities, and have multi-source and multi-genesis mineralization, which belongs to the cumulative superimposed metallogenic model and mechanism. It is necessary to study them with the viewpoint and method of metallogenic evolution. In particular, it is necessary to point out the research and determination of the main metallogenic tectonic stages, the main metallogenic uranium sources and the main genetic processes. Judging from the studied polygenetic compound uranium deposits, the tectonic magmatic activity in diwa stage plays an extremely important role in the formation and location of large and super-large polygenetic compound uranium deposits. Diwa stage from geosyncline to platform to diwa, or from geosyncline to diwa. Therefore, it is of special significance to study the polygenic uranium mineralization in diwa period and diwa area.
4. Expand the research field and prospecting direction.
Due to the structural evolution of polygenetic compound uranium deposits, the source of polymetallic substances and the organic superposition of various causes, the research contents and fields of such deposits are far more than those formed by unit metallogenic theory. In the direction of prospecting, the prospecting ideas are expanded, and the ore-controlling factors of various stages, various uranium sources and various genesis are analyzed, which is of great significance to the research of finding large and super-large multi-genetic composite uranium deposits.
The practical significance of studying polygenetic compound uranium deposits is embodied in the economic significance of the study. The large and super-large uranium deposits found at home and abroad are rich in ore grade and reserves, and most of them belong to polygenetic complex formation. Studying the formation conditions, metallogenic characteristics and identification marks of this kind of deposits is helpful to guide geological prospecting personnel to find this kind of deposits quickly and economically. In recent years, the discovery of the super-large polygenetic compound uranium deposit at the Olympic Dam in Australia has attracted worldwide attention.
Regarding the relationship between polygenetic compound deposits and super-large deposits, Chen published his paper "Polygenic compound deposits and super-large deposits" at the 9th International Conference on the Genesis of Deposits (IAGODW4) on 1994. He pointed out that polygenetic compound deposits are usually beneficial to become large and super-large deposits because of their complex characteristics and comprehensive formation history. In fact, it is known that many large and super-large deposits are formed in this way. The formation process of multi-genetic large and super-large deposits can generally be divided into three stages: gestation, birth and gestation, which provide congenital, imminent and acquired conditions for such deposits in turn: that is, on the basis of pre-existing deposits or source beds (rocks), on the basis of geological-geochemical environment in the main formation period of the deposits, and on the condition of superimposed transformation or transformation after the main formation period. Diwa area is the structural area with the best chance to form multimorphic super-large deposits, and it is also the area with the best prospecting prospect. In diwa area, the structural transition zone (transition zone in evolution stage and transition zone in structural zoning) is the most favorable priority target area in time and space. Specifically, the temporal and spatial distribution law of multi-genesis compound large and super-large deposits is controlled by many factors, such as stratabound, rock-bound, structural control and so on.
Chen's above discussion is completely applicable to the relationship between polygenetic compound uranium deposits and super-large uranium deposits. The polygenetic compound uranium deposit is indeed closely related to the super-large uranium deposit in time and space and genesis. As we all know, most of the large and super-large uranium deposits discovered so far in Australia, Canada, Russia, Kazakhstan, Ukraine, Germany, France and some countries in Eastern Europe belong to polygenetic compound uranium deposits. On the other hand, although the scale of composite uranium deposits is very large or very large, it is rare, but it is obviously different in order of magnitude from large and super-large deposits with single genesis.
Super-large uranium deposits, like polygenetic compound uranium deposits, are not formed by one mineralization, but are the result of multi-stage, multi-source, multi-genesis and multi-ore-controlling factors. Usually, it is the cumulative process of multiple mineralization such as original enrichment, pre-enrichment, superimposed enrichment and industrial enrichment, but there are also main metallogenic facts of main stage, main stage, main source, main genesis and main ore-controlling factors. For example, Mary-Kathleen uranium deposit in Australia used to regard the main mineralization of the deposit as contact metasomatic mineralization, so it was classified as contact metasomatic deposit type when it was studied by unit mineralization theory in the past. Another example is the Waitwatersrand uranium and gold mine in South Africa. In the past, it was thought that the main mineralization of the deposit was ancient placer mineralization. It was thought that after the formation of the basic outline of the deposit, although it was influenced by metamorphism, it led to some transformation and enrichment, but it retained the characteristics of ancient placer, so some people insisted on calling it ancient placer. In fact, these two deposits have experienced the integration stages of original enrichment and pre-enrichment in the process of accumulation and superposition of the above mineralization, and the main mineralization is the industrial enrichment ore after pre-enrichment and hydrothermal superposition, both of which belong to polygenetic compound deposits.
Super-large uranium deposits and polygenetic compound uranium deposits are mostly the comprehensive results of multi-stage tectonic or multi-stage tectonic magmatism and multi-stage and polygenetic mineralization. Diwa area is formed by at least two tectonic stages: geosyncline and platform, or directly evolved from geosyncline area. The geological structure and metallogenic events experienced in this structural area are complex, and the metallogenic evolution is relatively sufficient, which is the basic structural unit most conducive to the formation of super-large uranium deposits and polygenetic compound uranium deposits. In particular, the transitional period and transitional structure in diwa area, that is, the transitional turning period between stages of evolution and the transitional interface of structural zoning, are the most concentrated space-time location areas for the formation of super-large uranium deposits and polygenetic compound uranium deposits, and naturally become the priority target areas for prospecting. Some super-large uranium deposits, such as the Zhongxihu deposit and the Iger deposit in athabasca, Canada, are concentrated in the marginal transition zone of the Mesoproterozoic diwa basin in athabasca.