| The approximately E-W-trending Quruqtagh block, is located in the northeast part of the Tarim craton, where Precambrian rocks are widely exposed. The Quruqtagh block is composed of an older metamorphic crystalline basement and a younger sedimentary cover consisting of strata from the middle Neoproterozoic to Phanerozoic. Therefore, Precambrian gold deposits and their relationship to Precambrian tectonic-magmatic events are very importants to understand the geological evolution of the Quruqtagh block. However, being harsh natural conditions, inconvenient traffic and the resulting lack of geological research, ore deposits geological characteristics and its genetic type are not well known, much less studies on ore-forming fluids.The Dajingou gold deposit, located in the central Quruqtagh block, is a key gold deposit to understand the Precambrian evolution and metallogeny.The goldmineralization here occurs in primarily within tectonic fracture zone with banded (garnet-contained) migmatizated geniss of the Xiaojingou formation from the Paleoproterozoic Hongliugou Group as the principal host rock. The sulfide mineral assemblage is dominated by electrum, pyrite, and chalcopyrite, withminor limonites. Alteration includes silicification, sericitization, chloritization and carbonatization.Metallogenic fluid characters and ore-forming processes of this deposit are valuable to reveal the developmental characters of Precambrian gold deposit and metallogenic potential. Based on extensively petrographic observation on fluid inclusion in the gold-contained quartz veins from the Dajingou gold deposit, microthermometry studies were conducted to investigate characters and evolution processes of the ore-forming fluid. As we known, most fluid inclusion in our samples are liquid-rich two phase gas-liquid inclusions, occasionally pure liquid or gas inclusions. These liquid-gas phase inclusions could be divided to Ⅰ-type (low temperature and high salinity), Ⅱ-type (low temperature and low salinity), Ⅲ-type (low-middle temperature and salinity) and IV-type (high temperature and low-middle salinity inclusions). Homogenization temperatures of these fluid inclusions are varied from 75℃ to 255℃, while their salinity are varied from 0 to 13.0 wt% NaCl, and no obvious linear relationship between their temperature and salinity was found. Our results show the fluid regime of the Dajingoud gold deposit is typical low salinity fluid system, similar to the orogenic metamorphic fluids.Hydrogen and oxygen isotope analysis for samples from the gold-contained quartz veins indicate that, ore-forming fluids of the Daigingou deposit were major of metamorphic origin fluid mixed with a small amount of meteoric water. Hydrothermal zircons from post-mineralization quartz veins were analysesed and yield a U-Pb Age at 795±20Ma, which is conincident with the Ar-Ar age of sericite from gold-contained greisen ore (isochron age of 833.3±7.9, plateau age of 829.4± 4.8Ma). Therefore, we argued that the mineralization of the deposits are in the middle of Neoproterozoic, coeveal with the widely developed tectono-magmatic events occurred in the northern Tarim attending the assembly of Rodinia. Comprehensive ore deposits geology, fluid inclusions, hydrogen and oxygen isotopes and metallogenic chronology, we suggest that the Daigingou gold deposit are orogenic gold deposit, which was formed in the middle Neoproterozoic (～830Ma) druing the asssembly of the Rodinia. |
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