摘要
大石桥菱镁矿区诸矿床已初步查明为蒸发沉积成岩-热液交代富集型,本文进一步研究热液的物质来源。该区青山怀矿床的菱镁矿及蚀变白云岩的稀土总丰度、铺和重稀土均高于未蚀变白云岩。后者的稀土型式反映沉积成因,菱镁矿和蚀变白云岩则反映热液富集交代型式,热液为混合岩化热液。自元古宙混合岩的强烈蚀变中获得稀土,并从长石中获得Eu,并与蚀变混合岩达到稀土平衡。由含碱氯化络合物搬运,在循环过程中淋滤了围岩(白云岩)的物质。菱镁矿通过品格收容和晶问沉淀捕获稀土。显示了高浓度卤水在搬运、沉淀过程中的稀土分馏。物质来源主要来自混合岩,次为白云岩。
The dolomites, wall rocks of the Dashiqiao magesite deposit, containing diageneric micro-magnesitic matter have undergone low-grade regional metamorphism and are dated at 1450Ma. The deposit is in a spacial connection with proterozoic migmatite.
The total REE contents and Eu and HREE concentrations, of magnesite and altered dolomite are all elevated in comparison with those of unaltered dolomite. The REE patterns of the latter indicate its sedimentary origin, while those of the magnesite and altered dolomite suggest their hydrothermal origin. The probadle source rock is the Proterozoic migmatite which shows a REE pattern similar to those of magnesites. The rock contains strongly sericitized feldspars and altered amphiboles and is capable of liberating Eu and HREE. The ore solution would leach materials from dolomite during its circulation. The REE might be transported in the form of alkali chloride complexes. The capture of REE by magnesite might occur in the way of either accommodation of REE to the crystal lattice or precipitation as trace elements in the interstices of crystals. In summary,the REE mobility due to the formation of the deposit reflects the REE fractionation during the transportation and deposition of alkali brines enriched in REE from a certain open system.
In view of the precedent hypothesis that the origin of the deposits is due to evaporation sedimentation-diagenesis followed by hydrothermal enrichment, the author further puts forwards a thoughtful idea, i. e. the origin of evaporation sedimentation-diagentic reformation-migmatized hydrothermal enrichment.
出处
《地质论评》
CAS
CSCD
北大核心
1990年第1期31-41,共11页
Geological Review
