Analysis On Metallogenic Regularity Of Geothermal Resources In Tianjin From The View Of Geochemistry

In this paper, we selected West Tuanbo Area, Beichen Area and Dasi-haihe Education Park as thethree key areas and analysis the metallogenic regularity of geothermal fluid in Tianjin from a viewof geochemistry. We mainly discuss the hydrogeochemical characteristics and regularity, and thenanalyzed the flow direction and the recharge source to describe the spatial distribution rule ofwater chemical field characterization.The geothermal resources in the key areas belong to sedimentary basin type faulted depression oflow medium temperature geothermal resources. From the ancient world to the Cenozoicsedimentary reservoir formation water series, it can be divided into porous reservoirs typeand karst fissure type reservoirs. Porous reservoir includes Minghuazhen and Guantaoreservoir; karst fissure type reservoir includes Ordovician, Kantake Changping formation andJixian Wumishan formation. Different reservoirs, the formation development situation are alsodifferent. In Tianjin area, Neogene and bedrock geothermal fluids have obvious horizontal zoningregularity in water chemistry. From north to south, the TDS of geothermal fluid graduallyincreased and the water quality types is from gradually by sodium bicarbonate type to chloridetype with complex components. With the analysis of the diagram of TDS and reservoir burieddepth, we found the pore type of geothermal fluid mineralization and buried depth is positivelycorrelated. The deeper of the reservoir, the higher temperature makes the more chemical elementssoluble in geothermal fluids, which leads to the increased of TDS. From the Na-K-Mg equilibriumdiagram, we found that compared to other reservoirs, the fissures are more developed inOrdovician. So in the vertical direction it is recharged by the overlying and underlyingreservoirs, especially in the vicinity of some deep fault, there maybe havelarge runoff channels. We can use HCO3-Cl-SO4equilibrium diagram to get the chemical type ofgeothermal fluids to infer lithology and karst fissuresis are not the main factors which caused thewater quality difference in the key areas. Using geothermometers, we also inferredthe temperature range is about73DEG to125deg in key areas of Ordovician geothermal fluids.In addition, we collected a large amount of isotopic data of geothermal fluid, rain waterand surface water. The application of isotopic geochemical method can solve the originand genesis of geothermal fluid qualitatively or quantitatively and distinguish the rechargesource area and the recharge altitude. In Tianjin area, the age of fluids in Minghuazhen reservoir is16.83~20.47Ka, the age of Ordovician reservoir is15.15~20.33Ka, the age ofWumishan reservoir is19.43~27.35Ka. The reservoir of Cangxian uplift area in Tianjin belongedto the "ancient" water supply. The geothermal fluid of the southern plain area is supplied by thefluids of northern mountains, which formed of the precipitation transporting a long distance.