Characteristics Of Salt-bearing Series In Eastern Sichuan Basin And Research On Homogenization Temperature Of The Fluid Inclusions In Salt

Potassium is one of important shortage mineral in China. Finding potassium salt deposit is an urgent task in front of our geologists. There is a wide evaporite salt era in China from Sinian to Quaternary. Sichuan basin is an important marine salt basin in China, which was divided into six salt period from middle-lower Triassic Series Jialingjiang Formation. There is a salt zone in eastern Sichuan basin which was divided into11salt basins. Rock salt has precipitated and potassium minerals were found at period of T1j4in eastern Sichuan where has a good prospect for potassium. In recent years, polyhalite was found in the salt bed of T1j4-2in Changpeng third well, this has brought new clues for the work of looking for potassium.This paper researched on Changping third well. We find out salt mineral characteristics and distribution in salt bed of Triassic system, divide the sedimentary cycle of salt, summarize geochemical characteristics of the salt layer, discuss the causes of salt-bearing series, and we also reseach homogenization temperature of the fluid inclusions in the salt precipitated both in laboratory and the Changping third well.We found many mineral in salt-bearing series of Changping third well including anhydrite, halite, polyhalite, calcite, dolomite, pyrite, which consists the section features of dolomite-anhydrite halite/polyhalite-anhydrite. The gross thick of rock salt is52.37m in the salt bed which was divided into three beds. From the mineral assemblages, we found that evaporation concentration degree of brines of Ⅲ salt bed much higher than that of Ⅰ and Ⅱ salt bed. Small granular polyhalite distributes as layers in salt bed, which is thought that precipitated when brines evaporating. Banana leaf-shaped polyhalite is thought that formed by recrystallization.We divided salt beds into three sedimentary cycles of salt, every cycle includes several secondary cycles which consist by rock stratum of anhydrite-rock salt-anhydrite and dolomite-anhydrite. The cycles indicate that water concentration change frequently when it evaporating.There is a high coefficient of Br*1000/Cl in salt layers in Changping third well with the section of0.2-0.48, which should have precipitated magnesium salt. Coefficient of Br*1000/Cl at start of every salt layers has an abnormally high amount which was thought cause by brines from basin inside or secondary basin surrounding flowing in.We carried out the experiments of homogenization temperature of the fluid inclusions in the salt precipitated both in laboratory and the Changping third well, proved that’cooling nucleation method’ is feasible, verified that the information carried by all-liquid primary fluid inclusions of salt could reflect the depositional conditions. We also improved experiment procedure and drew the conclusion that rock salt in Changping third well was precipitated in the hot weather conditions through applying’cooling nucleation method’into rock salt in Changping third well.