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Pyotr Paderin, A.P. Karpinsky Russian Geological Research Institute (VSEGEI) (Russian Federation)
Oleg Petrov, A.P. Karpinsky Russian Geological Research Institute (VSEGEI) (Russian Federation)
Vasily Proskurnin, A.P. Karpinsky Russian Geological Research Institute (VSEGEI) (Russian Federation)
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1. Taimyr carbonatite province has total extent more than 600 km. Earlier, carbonatites were distinguished as the Devonian sedimentary or Early Triassic metasomatic carbonate formations, which control the uranium and thorium-uranium fluorite-barite-rare earth mineralization. This work raises the problem of volcano-plutonic origin of carbonate massifs with gold-bearing polymetallic-sulphide mineralization in close association with subalkalibasite-alkalisyenite intrusions of Na series. Newly formed carbonatite bodies occur among the Upper Paleozoic rocks and have injection contacts. Rocks are characterized by massive, brecciated, sometimes fluidal, porphyry and spotted structures. Predominance of fluorine-boron-albite and barium-strontium- bearing carbonate rocks is noteworthy. Overall, more that 50 minerals are described.
2. For identifying the genetic nature of carbonate ore-bearing rocks, VSEGEI laboratories carried out studies, which determined stable features of different genesis of carbonate formations. In particular, in the course of thermobarogeochemical studies, the investigated samples based on fluid inclusions clearly fall under primary sedimentary and magmatic carbonate rocks. It has been established that carbonatites of "volcano-plutonic" genesis derived from "boiling" fluids at a temperature, at least, 420°Ñ and pressure about 2.5 kBar. Local zircon analysis at SHRIMP-II installation allowed drawing the age boundary of injection carbonatite bodies formation at the level of the Middle Triassic and zircon growth time at the Jurassic/Cretaceous boundary.
3. The obtained results point to a peculiar type of carbonate rocks differing markedly from the -known classic carbonatites associated with alkali-ultrabasite massifs. Taking into account the leading role of the hot spot of Taimyr in the formation of carbonatites of the Maymetch-Kotuj and Taimyr Provinces as well as the obtained, the following evolution model of carbonatite formation can be predicted: local uplift of the mantle substrate in a hot spot in the Triassic causes a successive magmatism gradation from ultramafic-alkaline with classic carbonatite differentiates to subalkalinegabbro-alkalisyenite-granosyenite with crust type carbonatites up to formation of surface volcanogenic carbonatite facies which in Na composition correspond to calcareous lavas which are close to the effusives of modern Oldoinio-Lengai Volcano in Tanzania. According to this, the mineralization type changes both horizontally and vertically across the magmatic column: from high-temperature apatite-magnetite with Òà, Nb, Zr to gold-bearing polymetallic-sulphide with Tl, Ñd medium-temperature and barite-fluorite-rare earth (La, Ce, Nd) low-temperature.
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