The gold mineralization in the Central Aldan ore district is genetically related to potassic calc-alkaline and alkaline magmatism dated at 115–150 Ma.The objective of this study is to establish the age of hydrotherma...The gold mineralization in the Central Aldan ore district is genetically related to potassic calc-alkaline and alkaline magmatism dated at 115–150 Ma.The objective of this study is to establish the age of hydrothermal processes that accompanied the formation of Au-Te mineralization at the Samolazovsky Deposit.Based on the isotope-geochemical study of zircons from quartz-feldspar metasomatic rocks of the deposit,the granitoids and charnokites of the Nimnyr Complex(1900–1960 Ma)at the contact with the Yukhta monzonite-syenite massif(~127 Ma)were studied.Zircon U-Pb dating was performed on a SHRIMP-II ion microprobe,and rare-earth and trace elements analyses of zircon were carried out in the same craters by secondary-ion mass spectrometry on a Cameca IMS-4f ion microprobe.It is revealed that the studied zircons have heterogeneous structures:dark core and lighter rim,which differ greatly in isotope-geochemical parameters.Zircon rims are cut by a network of fractures,extending into the central part of zircon grains.The rims yield a subconcordant age of 1937±24 Ma,with an average total REE content of 550 ppm,which corresponds to the formation age of the Nimnyr Complex.All zircon cores yield a discordant age of 83±11 Ma and are characterized by a higher total REE content(~1812 ppm),as well as higher contents of U and non-formula elements(Ca,Sr,and Y)with respect to rims,due to the effect of fluid on zircons.Despite the limited number of zircon grains,the additional geochronological study of zircons from syenites of the ore-bearing Ryabinovy Massif has revealed the presence of two distinct age clusters:~125–138 and 76–83Ма.The older ages of zircons from syenites are typical for the Central Aldan ore district.Until now,there is still no explanation for an age range(76–83 Ma)of single zircon grains from ore-bearing syenites of the Ryabinovy Massif.The obtained data suggest that the processes of activation(the effect of fluid)within the Central Aldan ore district continued until Late Mesozoic.With regards to the equivocal geotectonic position of the Mesozoic potassic magmatism in the study area and its high metallogenic potential,there exists an absolute necessity to determine the geochronological age of the rock formations.Therefore this study presents the Late Cretaceous geochronological data for the first time which can constrain the time-frame for the formation of gold-bearing magmatic and metasomatic rocks of the Aldan ore district.展开更多
基金This study was supported by the Russian Foundation of Basic Research(RFBR)(No.16-35-00334 mol_a)a state contract of the Institute of Precambrian Geology and Geochronology of Russian Academy of Sciences(No.0153-2019-0002).
文摘The gold mineralization in the Central Aldan ore district is genetically related to potassic calc-alkaline and alkaline magmatism dated at 115–150 Ma.The objective of this study is to establish the age of hydrothermal processes that accompanied the formation of Au-Te mineralization at the Samolazovsky Deposit.Based on the isotope-geochemical study of zircons from quartz-feldspar metasomatic rocks of the deposit,the granitoids and charnokites of the Nimnyr Complex(1900–1960 Ma)at the contact with the Yukhta monzonite-syenite massif(~127 Ma)were studied.Zircon U-Pb dating was performed on a SHRIMP-II ion microprobe,and rare-earth and trace elements analyses of zircon were carried out in the same craters by secondary-ion mass spectrometry on a Cameca IMS-4f ion microprobe.It is revealed that the studied zircons have heterogeneous structures:dark core and lighter rim,which differ greatly in isotope-geochemical parameters.Zircon rims are cut by a network of fractures,extending into the central part of zircon grains.The rims yield a subconcordant age of 1937±24 Ma,with an average total REE content of 550 ppm,which corresponds to the formation age of the Nimnyr Complex.All zircon cores yield a discordant age of 83±11 Ma and are characterized by a higher total REE content(~1812 ppm),as well as higher contents of U and non-formula elements(Ca,Sr,and Y)with respect to rims,due to the effect of fluid on zircons.Despite the limited number of zircon grains,the additional geochronological study of zircons from syenites of the ore-bearing Ryabinovy Massif has revealed the presence of two distinct age clusters:~125–138 and 76–83Ма.The older ages of zircons from syenites are typical for the Central Aldan ore district.Until now,there is still no explanation for an age range(76–83 Ma)of single zircon grains from ore-bearing syenites of the Ryabinovy Massif.The obtained data suggest that the processes of activation(the effect of fluid)within the Central Aldan ore district continued until Late Mesozoic.With regards to the equivocal geotectonic position of the Mesozoic potassic magmatism in the study area and its high metallogenic potential,there exists an absolute necessity to determine the geochronological age of the rock formations.Therefore this study presents the Late Cretaceous geochronological data for the first time which can constrain the time-frame for the formation of gold-bearing magmatic and metasomatic rocks of the Aldan ore district.
