海相钾盐矿床溶滤卤水找钾指标体系:以川东北天星桥构造寒武系深部地下卤水为例

Index System for Potassium Prospecting in Marine Potash Deposits:A Case Study of Cambrian Deep Brine from Tianxingqiao Structure of Northeast Sichuan in China

长期工作成果显示我国现阶段常用的找钾指标Br×10^(3)/Cl值偏低.创新性地应用"以古验古"的溶滤实验与地质统计法厘清了海相蒸发盐盆地找钾指标体系,充分考虑了不同地质年代海水成分的变化,也可克服"将今论古"应用于现代海水在等温等压条件下实验数据的不足.通过对世界上典型钾盐矿床的石盐、含钾石盐及钾盐(含光卤石)进行溶滤实验,并结合前人海水及海相卤水的蒸发实验成果,总结了海相钾盐矿床溶滤卤水找钾指标体系:Br×10^(3)/Cl、K×10^(3)/Cl、K/Br重量比及nNa/nCl、nMg/nCl摩尔浓度比等.以天星桥构造寒武系深部地下卤水为例,分析其Br×10^(3)/Cl、K×10^(3)/Cl、K/Br重量比及n Na/n Cl、n Mg/n Cl等找钾指标与δD、δ^(18)O特征,认为天星桥构造寒武系深部地下卤水的水化学特征与溶滤卤水一致,与沉积卤水有较大差异,其δD、δ^(18)O投点均靠近大气降水线.因此,综合分析认为该区卤水属于溶滤卤水,且有溶解含钾石盐甚至是溶解钾盐的可能性.该成果对评价研究区地下卤水钾资源具有重要意义,也为在该区寻找寒武纪固体钾盐矿提供了新依据.

Through summary of long-term work,it is found that the value of Br×10^(3)/Cl,which is commonly used,is low.In this paper,it innovatively clarifies the index system for potassium prospecting of marine evaporative basin by using the"ancient test"leaching experiment and geological statistics method.This method fully considers the changes of seawater composition in different geological years and can also overcome the insufficiency of data for applying modern seawater under isothermal and pressure conditions.Through the leaching experiment of rock salt,potassium-bearing salt and potassium salt(including carnallite)of the typical potash deposits in the world,and combining the previous evaporation experiment results of sea water and marine brine,the index system for potassium prospecting in mineral deposit:Br×10^(3)/Cl,K×10^(3)/Cl,K/Br,nNa/nCl,nMg/nCl,is summarized.This study aims to trace the origin of the brine which is Cambrian deep brine from Tianxingqiao structure of Northeast Sichuan Basin by analyzing its hydrochemical characteristics(weight ratios of Br×10^(3)/Cl,K×10^(3)/Cl and K/Br,and molar ratios of nNa/nCl and nMg/nCl).The results show that the hydrochemical characteristics andδD andδ^(18)O values of the brine from Tianxingqiao are similar to those of the brine from dissolution and that of the salt precipitates,but have distinct difference from that of the primary brine.Therefore,it is believed the formation brine from Tianxingqiao is sourced from meteoric water and the brine salinity come from saliferous strata,which might come from the dissolution of halite beds or even the sylvinite beds.This finding is in contrast to the previous studies which held that the brine is primary brine.This study provides new and important information for searching potash deposits in this area.