巴西Paraná和Bahia地区滑石矿床的地质特征与成因模式

本文总结了巴西两个最重要的滑石产地,Parana和Bahia区中滑石矿床的地质特征,并探讨了这些矿床的可能成因。巴西的滑石在世界滑石储量与产量中占有十分重要的地位。巴西Parana和Bahia区的滑石矿主要产于前寒武纪地体中。尽管该区的滑石具有不同的地质产状,与变质火山岩和变质沉积岩共生的滑石最为重要。其他类型的滑石,如与镁铁质-超镁铁质岩共生的、在花岗岩与白云质大理岩接触带的、在花岗岩体中呈包体或顶垂体状的、则相对不重要。在巴西与岩浆活动有关的滑石矿化主要发生在前寒武纪(Bahia区)和白垩纪(Parana区)。滑石的成因模式主要有两类:一为与岩浆热液有关的热液交代成矿模式,另一是起源于盆地热卤水的变质流体交代成矿模式。其中后一种成因模式可用来解释巴西的大多数大型滑石矿床,同时也适用于其他地区,如中国辽宁和乌拉尔南部的滑石成矿。

Geologic characteristics and genetic models for the talc deDosits in Parana and Bahia. Brazil

This paper summarized geological characteristics of talc deposits from the two most important talc production districts (Parana and Bahia) in Brazil, and discussed their possible genetic models. The Brazilian participation in the world rank of reserves and production of talc played an important role. The talc deposits in the states of Parana and Bahia are mostly occurred in Precambrian terrains. Although there are many different occurrences of talc ores, those associated with metavolcanic and metasedimentary rock sequences are the most important type. Other types such as those associated with mafic-ultramafic rocks and in the contact between granites and dolomitic marbles or enclaves and roof pendants in granites are less significant. In Brazil magmatic activities leading to talc formation happened during Precambrian (at Bahia) and Cretaceous (at Parana ) times. There are two major genetic models related to the formation of talc deposits. One is hydrothermal metasomatism related to magmatic-derived fluids and another is hydrothermal replacement of metamorphic fluids that possibly derived from formation brines. The latter model may account for most of the large talc deposits in Brazil and elsewhere such as in Liaoning (China) and South Ural.