Geochronology and Ore Mineralization of the Dzheltula Alkaline Massif (Aldan Shield, South Yakutia)

摘要

The Dzheltula alkaline massif is located in the Tyrkanda ore region of the Chara-Aldan metallogenic zone of the Aldan-Stanovy Shield (South Yakutia). The region contains separate placer gold objects, which are being explored at the present time, and ore-bearing Mesozoic alkaline intrusions, which are weakly studied due to their poor accessibility. The Dzheltula massif (DM) is the largest exposed multiple-ring intrusion within the Tyrkanda ore region; therefore, it is considered as a typical object for geological, petrological, geochronological, and metallogenic studies. The DM consists of five magmatic phases of syenite composition. Ar-40-Ar-39 dating has established that the crystallization age of the oldest phase, the leucocratic syenite porphyry (pulaskite), is 121.1 +/- 1.3 Ma. The crystallization age of the cross-cutting phases represented by syenite-porphyry dikes (laurvikites and pulaskites) ranges from 120.1 +/- 2 to 118.3 +/- 2.1 Ma. The youngest phase of the massif, trachyte, crystallized at 115.5 +/- 1.6 Ma. According to the mineralogical and geochemical studies, two types of ore mineralization, namely gold and uranium-thorium-rare-earth (U-Th-REE), are established within the DM. The gold mineralization was found in the quartz-chlorite-pyritized metasomatites. It is confined to the NNE- and NNW-trending fault zones and coincides with the strike of the syenite porphyry dike belt. Uranium-thorium-rare-earth mineralization has been established in the quartz-feldspathic metasomatites localized in the outer contact of the massif. The juxtaposition of mineralization of different types in some zones of the Dzheltula syenite massif significantly increases the ore potential of the studied object within the Tyrkanda ore region.