Material composition and geological-structural position of gold-bearing hydrothermal-metasomatic formations of the Anabar river basin (northeast of the Siberian Platform)

We study mineralogical features of the gold-bearing hydrothermal-metasomatic formations of the Anabar region. Their main substrate is represented by fractured near-fault dolomites of the Anabar formation of the Cambrian age. We have found, for the first time, hydrothermalites developed on the slightly cemented fine-pebble quartz conglomerates of the Early Permian age in the core of exploration wells. Furthermore, we have identified two types of metasomatic rocks: quartz-potassium feldspar and jasperoid. We have revealed that the main ore minerals were galena and pyrite with different ratios by sites. The disseminated galena was the main ore mineral at the «Billyakh» and «Kurung Yuryakh» sites, and pyrite – at the «Sredny Mayat» site. At the «Sources of the Mayat» site, where sulfidized rocks were studied from a depth of more than 25 m, the main ore mineral was pyrite, which had a veinlet and continuous nature of development. Gold was identified in the form of small particles in the carbonate and siliceous substrate of hydrothermal-metasomatic formations at all sites. The lithological factor was one of the leading factors for the ore formation due to the presence of near-fault highly permeable fractured carbonate and slightly cemented terrigenous rocks. The structural control of the studied ore occurrences was determined by their localization in the Mayat-Logoy and Dogoy-Kuoy faults of the Molodo-Popigay system of discontinuous faults. We assume a two-stage formation of the gold ore occurrences. During the first stage, the ore components in the form of primary hydrothermal-sedimentary ores in the near-fault zones were formed. The second stage was related to the processes of the Mesozoic tectonic-magmatic activation when the intrusion of basite dikes initiated the mobilization of ore components. The gold-sulfide occurrences were formed in the near-fault zone as a result of silicic-potassic metasomatosis of the Cambrian carbonate and Permian terrigenous rocks.

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