RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES6002, doi:10.2205/2007ES000285, 2008
[14] Statistical data analysis of a section of the database related to carbonatites was carried out by the method of correlation and factorial analysis. The highest values of pair correlation coefficients were close to those significant for selection of about 150 objects (+0.38 - between the summarized iron reserves and phosphorus pentoxide and integral tectonic indices). The higher level of correlations was revealed between the summarized ore reserves of sub-provinces and the parameters of their tectonic control.
[15] On analyzing small samples of several large massifs (for example, Maimecha-Kotuiskaya), separate significant correlations of iron reserves, uranium octoxide and phosphorus pentoxide were established (correlation coefficients +0.6 and more) with the massifs position related to rift structures and with a number of controlling lineaments. It has to be mentioned that the results obtained confirm a correlation between carbonatite magmatism and riftogenic structures. At the same time, since it was not the relation of the number of the massifs with other structures that was analyzed, but a dependency of the level of their ore content on the tectonic and structural factors of localization, this relation turned out to be weaker, because the concentration of ore components in carbonatite complexes was determined by other factors as well. The factorial analysis appeared to be more efficient, including the multiple regression method, allowing to obtain a set of predicting evaluating criteria. On the basis of the obtained regression dependencies of the information criteria (parameters of the massifs) and their ore content a prognostic evaluation of the content of various ore types for the majority of the massifs was made. The correlation coefficients (pair correlation) of the predicted reserves to the real ones turned out to be quite high (0.51-0.71). The obtained estimations of factor loadings showed that informative geological parameters and corresponding indicators of reserves concur with each other when there is a connection between them. A significant connection of the iron and phosphorus reserves with the massifs position within the limits of rift zones in intersection nodes with lineaments of different orientation, and also a connection of niobium and rare-metal ores with several structural-morphological types of mineralization, characteristic for multiple-phase long-term forming complexes, was established. A positive connection between these ore reserves and the volume of siderite and ankerite carbonatites in the massifs was also noted.
[16] For the study of evolution of the productive ultrabasic alkaline and carbonatite magmatism in time the reserves were summarized and geological characteristics of the massifs were averaged according to the main geological epochs. Reserves of uranium, thorium, zirconium and rare-metal ores for convenience of comparison were increased several times. Together with the volumes of development and correlations of the volumes of ultrabasic alkaline and carbonatite magmatism the fascial structure of the massifs was examined. It is related to the level of erosive truncation of the massifs and to the great extent determines the type of their ore content as a result of the vertical ore zoning of these complexes. The maxima of manifestation of ultrabasic alkaline and carbonatite magmatism were established to occur in the Middle Proterozoic, Palaeozoic, with the absolute maximum in the Mezozoic. The peaks of manifestation of the carbonatite phase (by the area of exposure and by its relative amount in the massifs), that took place in the Early and Late Proterozoic age, and also in Mezozoic, correspond to the maxima of summarized reserves of niobium-iron-phosphorus ores and to the great extent of the uranium, thorium, fluorite, polymetallic, tantalum, phlogopite-vermiculite, rare-metal and titanium mineralization. Wide development of ijolites in palaeozoic complexes correlates with the maximum of reserves of apatite ores, formed during that epoch. The content of iron ore reserves in the massifs increases with growing relative volumes of ultrabasic rocks.
[17] A more precise evaluation of a correlation between the geological parameters, averaged in accordance to geological epochs, and of the ore content was implemented with the help of factorial analysis - by maximum-likelihood method using varimax rotation. The weight of factors, determined as their contribution to mutability of properties, decreases from first to fourth factor. A sign of factor loadings allows to determine groups, directly or inversely related to mineralization of parameters. In our opinion, in geological respect the first is related to the size of massifs and the area of carbonatite phase in them, and also to the development of siderite carbonatites. It determines the scale of mineralization (increased reserves) of many types of ores. Their significant positive factor loadings are shown in the first factor's column (first of all, iron, titanium, vermiculite, boxites). Siderite carbonatites determine the development of torium mineralization. The second factor is slightly less significant and is connected to a higher role of ankerite carbonatites in the massifs at a small share of calcite differences. It determines the development of niobium and rare-metal, and in some cases polymetallic mineralization (Beloziminsky massif can serve as an example). The third factor is determined by the prevalence of ultramafite phase of the ancient massifs with considerable erosion truncation, where shallow phase is missing. This factor determines the development of uranium, copper and tantalum mineralization. The fourth factor results from prevailing ijolitic phase in the massifs. It determines the development of phosphorus, complex iron-phosphorus with niobium, phlogopite and circonium mineralization.
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[19] Therefore, the described variants of statistic analysis of ore-bearing parameters of carbonatite complexes are characterized by good convergence of results. The main conclusion of research related to this section of the database is the possibility of reliable prediction of ore content of carbonatite complexes based on an informative set of criteria, including both structural-tectonic and magmatic parameters of the massifs (depending on the types of mineralization). Very interesting statistical data on the evolution of ore-bearing alkaline ultrabasic magmatism were obtained for the first time.
Citation: 2008), Analysis of evolution and ore-bearing factors of rare-metal carbonatites and diamondiferous kimberlites, Russ. J. Earth Sci., 10, ES6002, doi:10.2205/2007ES000285.
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