Первый слайд презентации
Radiogeochemical specialization of the Late Jurassic and Cretaceous intrusive complexes of the Kolyma. Autor : Vorobev Iurii V. Scientific supervisor: PhD Kashkevich Marina P.
The structure of the presentation Relevance of the research Purpose of the research Research methodology Main results Conclusion
The depletion of the reserves of the Kolyma placer deposits made the search for primary gold deposits actual. Intrusive complexes are key to formation of gold deposits in the region. Determining the type of complex at the stage of airborne geophysical work will significantly increase the efficiency of prospecting work. The ability to record metasomatic processes by radio- geochemical zoning will make it possible to identify the type of predicted ore objects. Relevance of the research Practical F undamental Establishing a relationship between the composition of intrusive formations and metasomatic changes with radio-geochemical characteristics.
The object of research are the igneous complexes of the Kolyma. Purpose of the research Tasks: Create a database of the main igneous complexes of the Kolyma based on the available geological, geochemical and geophysical information ; Classify complexes using ARC technology, based on modern airborne gamma-spectrometric data Conduct radiogeochemical analyzes of samples taken during the 2019-2020 work. Correlate radio geochemical classification and important characteristics of igneous complexes ; The aim is to establish the radio-geochemical specialization of petrotypes of the main igneous complexes and to find out the relationship between the composition of the complexes and the radio-geochemical specialization.
Creation of digital models of K, U, Th concentrations according to modern AGS surveys. Isolation of the correlated component using the ARC technology. Determination of specialization within the known contours of intrusive massifs. Establishing correlations with the available characteristics. Research methodology
Main resalts U ncorrelated potassium component U ncorrelated uranus component U ncorrelated thorium component Correlation tables
Conclusion From east to west, the contents of U and Th increase over large massifs. Moreover, the nature of radioactivity, including for the host sedimentary rocks, gradually changes from significantly potassium to significantly uranium. In the case of sedimentary rocks, this pattern as a whole reflects the change of Permian deposits to Triassic from southwest to northeast. As for the intrusive massifs, this pattern does not correlate with the belonging of the arrays to different complexes. Perhaps this is due to a different level erosional cut. A common feature of all large intrusions is the presence of lateral radiogeochemical zoning. Regardless of belonging to a particular complex along the periphery of the massif, in the endocontact zone, the thorium-potassium nature of radioactivity, which indicates a partial removal of uranium from here. Younger intrusions of the Neorchansk and Magadan complexes are generally more radioactive than intrusions the rest of the complexes, which corresponds to the geochemical criteria for the distribution of radioactive elements. Abnormal values on Vetrenskaya area are the Professorsky massifs (U content up to 10.5 10-4 %) and Western Butugychag ( Th content up to 44 · 10-4%)). Intrusive massifs assigned to the same complexes have different specialization. Siberdyk complex : massifs of Malye Porogov, Yaryga, Siberdyk-3 and Siberdyk-4, - K, K- Th specialization, Siberdyk-1, Siberdyk-2, Pravo-Obinsky - mostly U ( Th -U); Magadan complex: Victory - K (U-K) specialization, stock Professorial U specialization; Neorchan complex - Western Butugychag - Th specialization, Eastern Butugychag - K (K- Th, U-K). Rocks of the same intrusion phase belonging to different massifs can have different specializations. For example, the Bolshoi Chalbykan stock and the southern block of the Ship massif are composed of granodiorites of the 4th intrusion phase, however in the radiogeochemical field, the rocks of the first intrusion have Th -U specialization, and the rocks of the second, U-K. Such differences indicate metasomatic processing of rocks.
Conclusion The heterogeneity of the massifs belonging to the same complex is also emphasized by the difference in useful fossils. So, for example, in Western Butugychag, rich deposits of U and Sn have been discovered and are being developed, and the points of Mo mineralization are confined to the East. In addition, in the southern part of Eastern Butugychag there is an area (about 0.5 - 0.6 km in diameter) with underlined uranium ((6.5-7.5) 10-4%) and thorium (( 15–16) · 10-4%) components, which may also indicate the presence of promising mineralization. According to the theoretical regularities of the distribution of U, Th, and K, with an increase in silicic acidity, contents of Th and U. Similarly, with increasing alkalinity, but the Th / K bond is more rigid than U / K, therefore an increase in concentrations is accompanied by an increase in the Th / U ratio. Also, for large multiphase differentiated intrusions of granitoids are characterized by an increase in the content of U and Th from early phases to later and from inner facies to marginal facies. For rocks of the Korabl massif, the first condition is fulfilled in the series: diorite ≈ monzodiorite - granodiorite, second: diorite - granodiorite ≈ monzodiorite, third: diorite - granodiorite - monzodiorite. For example The Ship massif shows that an increase in the content of Th and U occurs in the series granodiorite (phase 4) - diorite (phase 3) - monzodiorite (phase 6), an increase in Th / U in the series granodiorite - monzodiorite - diorite. Such inconsistencies in correlations is associated with the redistribution of matter, which indicates a significant metasomatic processing. High content of uranium (7.72 10-4%) and low for igneous rocks thorium-uranium (1.89) rock ratio Professorial stock can serve as a direct indication that the rocks of this stock have been subjected to strong metasomatic changes. According to the PI map, points of mineralization were found on the territory of the stock development Mo and Au. The combination of these features indicates the possibility of detecting hydrothermal deposits. greisen, gold-quartz formations.