沉积岩容矿天青石矿床的发育特征与成因综述

Characteristics and genesis of sediment-hosted celestite deposit:An overview

沉积岩容矿的天青石矿床是锶最主要的来源。文章对全球该类矿床的资料进行了系统梳理,对矿床的发育特征和成因进行了综述和探讨。研究显示:①该类矿床的产出与含石膏或硬石膏的蒸发盐密切相关,或赋存在碳酸盐岩-蒸发岩沉积建造中,或出现在蒸发岩底辟环境;②多数为后生成因,表现为富锶流体交代石膏或硬石膏,或富锶流体与富硫酸盐流体混合、充填开放空间;少数矿床为同生成因,天青石直接从蒸发环境的水体中沉淀出;③后生天青石矿床中的锶可以来自不同途径,包括盆地流体与富钙矿物相互作用萃取的锶、碳酸盐岩重结晶过程文石转变为方解石或硬石膏转变为石膏释放的锶;同生天青石矿床中的锶来自沉积水体本身,沉积源区岩石提供了锶;④天青石中的硫来源于围岩地层中的石膏或硬石膏,有些矿床中的硫来自发生过硫酸盐还原作用后的(溶解的)石膏/硬石膏,而在个别矿床中,还原硫氧化成硫酸盐提供了部分硫;⑤一些天青石矿床中出现有铅锌硫化物,两者可以有成因关系,也可以无成因关系;⑥少数天青石矿床中重晶石含量较高,与高Ba/Sr流体与富硫酸盐流体混合有关。天青石从低钡流体中结晶时,钡在流体中含量的震荡变化会导致SrSO_(4)-BaSO_(4)固溶体的形成,从而使天青石出现环带或出溶结构。

Sediment-hosted celestite deposits are the principle sources of the world’s strontium resources.Based on the data of celestite deposits worldwide,this study presents an overview of the ore characteristics and genesis.①Deposits are hosted by gypsum-or anhydrite-bearing evaporite,either by carbonate-evaporite sedimentary sequences or by evaporite diapirs;②Mineralization is mostly epigenetic,characterized by strontium-rich fluids replacing gypsum or anhydrite or by open-space filling through mixing of strontium-rich fluids with sulfate-rich fluids;a few of deposits are syngenetic with celestite deposition in evaporative environments;③Strontium in epigenetic celestite deposits can be obtained via interaction between basinal fluids and Ca-rich minerals,conversion of aragonite to calcite during diagenetic recrystallization of carbonate sediments,or transformation of anhydrite to gypsum during hydration;strontium in syngenetic celestite deposits derives from water in sedimentary systems with the ultimate source being the provenance of sediments;④Sulfur in celestite derives mainly from gypsum or anhydrite within host rocks but some of the(dissolved)gypsum or anhydrite have suffered from sulfate reduction;oxidation of reduced sulfur may contribute sulfur to celestite in a few of deposits;⑤Zinc and lead sulfides occur in some celestite deposits where celestite and sulfides have genetic links or not;⑥High Ba/Sr ratio of mineralizing fluid is responsible for high abundance of barite in a few of celestite deposits.Variation in Ba concentration in low Ba concentration of mineralizing fluid can form SrSO_(4)-BaSO_(4) solid solution in celestite and consequently generate oscillatory zonation or exsolution texture.