A Preliminary Study On Exhalative Hydrothermal Deposits In The Lucaogou Formation In Jimusar Sag, Permian, Zhunggar Basin

The Permian Lucaogou Formation is an important exploratory stratum of tight oil reservoir in Jimusar sag, Permian, Zhunggar basin. The exploratory stratum is a set of transitional rocks with chemical and mechanical sedimentary, which is characterized by magmatic clastic and exhalative hydrothermal deposits. The regional tectonic background of Jimusae sag with intracontinental downfault-rift setting from Late Carbonatiferous to Early-Middle Permian, which provides the canal makes hydrothermal fluid can reach earth surface and participate sedimentary process, thus constructs research area exhalative hydrothermal deposits association with characteristic. This paper explores the mineral type, lithologic features, sedimentary environment and formation mechanism of Jimusar sag by the research of mineralogy, petrology and geochemistry. In this study, we have obtained the achievements and recognitions as follows:(1)Mineralogical characteristics. This study obtains the mineralogy proof of hydrothermal action by discovers "hydrothermal mineral" magmatogenic calcite(?) for the first time. Besides, we preliminary analysis the morphological feature and formation mechanism of magmatogenic calcite(?). Lucaogou Formation lack for debris, the surface of mineral alastic is clean and with poor psephicity, the detrital components of Lucaogou Formation mainly consist of alkali feldspar and quartz, which reflects that Lucaogou Formation was formed in the lake basin rich in intraclast and lack for detrital material of terrigenous origin.(2)Material source characteristics. The Sr isotope composition of rocks in the Lucaogou Formation in Jimusar sag,87Sr/86Sr range from0.705286to0.705784and0.705486in average, is closed to the Sr isotope composition of mantle, wich reflects the lithogenous material of Lucaogou Formation is mainly originated from deep source, or deep source participated the sedimentary process at least.(3)Sedimentary environment characteristics. Lucaogou Formation in Jimusar sag was formed in weak reduction-weak oxidation saltwater lake, while the hydrothermal fluid intermittent participated the sedimentary process. The sedimentary stage of Lucaogou Formation in research area show the trends of temperature increases and salinity decreases, which may caused by the input process of fresh water at the later stage of Lucaogou Formation.