ABSTRACT

Three different types of secondary coronas developed around monazite-(Ce) were discovered in altered metavolcanic rocks closely associated with the Palaeoproterozoic apatite-iron oxide ore deposit in Grängesberg, Sweden. All three types of reaction coronas include fluorapatite that is either rimmed by allanite-(Ce), REE-fluorocarbonate(s), or hingganite-(Y). The latter mineral has not been previously observed among monazite breakdown products. A unique feature of the described reaction coronas around monazite is their spatial proximity to each other, not exceeding a few hundreds of micrometres. We infer that the observed, strongly contrasting monazite breakdown assemblages highlight the presence of a heterogeneous fluid that mediated these microscale decomposition reactions. Thus, it is emphasized that metasomatic fluid variability in natural systems may often be too large to be predicted and reproduced experimentally.

摘要

在与瑞典 Grängesberg 的古元古代磷灰石-氧化铁矿床密切相关的蚀变变质火山岩中发现了三种不同类型的围绕独居石 (Ce) 形成的次生日冕。所有三种类型的反应电晕都包括氟磷灰石，其边缘是由阿兰石-(Ce)、REE-氟碳酸盐或hingganite-(Y) 包围的。在独居石分解产物中以前没有观察到后一种矿物。独居石周围所描述的反应日冕的一个独特特征是它们在空间上彼此接近，不超过几百微米。我们推断，观察到的、强烈对比的独居石分解组合突出了介导这些微尺度分解反应的异质流体的存在。因此，