Genesis Of Reedmergnerite In The Lower Permian Fengcheng Formation Of The Junggar Basin,NE China

The lower Permian Fengcheng Formation in the Mahu Sag of the Junggar Basin was developed in a volcanic-induced alkaline saline lacustrine evaporation environment,with deposition of thick-bedded sodium carbonates and high-quality source rocks,as well as the borosilicate reedmergnerite,which is a rare mineral globally but is very rich in the Fengcheng Formation,Its controlling factors are worthy of further study.The predecessors carried out a certain degree of research on the genesis of cloud salt and the significance of oil and gas exploration,and mainly focused on the genesis of the dolomite and the dolomite reservoir.The research on the large amount of salt minerals enriched in the Fengcheng Formation is less,Especially boron-containing minerals.Based on the analysis of cores,rock thin section,backscattered images,electronic probes,fluid inclusions,and boron isotope studies,this article attempts to explore the cause of the enrichment of reedmergnerite in the Fengcheng Formation.The main results were as follows:?1?Petrological and mineralogical studies have found that the reedmergnerit of the Fengcheng Formation in the Mahu Sag,Junggar Basin,develops in the center and slopes of the Mahu Sag.Reedmergnerit is the product of diagenesis,often replaces carbonate minerals,including shortite,eitelite,nurthupite,calcite,trona,and even barytocalcite.?2?The Fengcheng Formation in the Mahu Sag,Junggar Basin,is deposited in a volcanic-alkali lake evaporation environment.the?¹¹B values of reedmergnerite are-0.04?+2.58‰,which is consistent with the range of B isotopes of granite and basalt.Combining with the study of petrology,mineralogy,and its distribution law,it is believed that B of diagenetic reedmergnerite is inherited from hydrothermal fluid in the original sedimentary environment.?3?The homogenization temperature of the primary inclusions in the reedmergnerite ranged from 100 to 116°C.Previous synthetic experimental studies have found that,due to the limitations of temperature and pressure in surface or shallow burial processes,the source of boron in reedmergnerite was deep hydrothermal fluid in the original sedimentary environment,mainly in deep diagenetic environments?>3000 m?.This stage corresponds to the maturation stage of kerogen?4?The enrichment of reedmergnerite in the Fengcheng Formation in the Mahu Sag,Junggar Basin is mainly related to its strong volcano-hydrothermal background and long diagenetic time.The strong volcano-hydrothermal activity provides a material basis for the formation of sodal.A long diagenetic history guarantees sufficient burial depth and sufficient diagenetic temperature and pressure,so that the reedmergnerite is more fully accounted for carbonate minerals.