Expressão dos elementos de terras raras nas rochas encaixantes do campo pegmatitíco do Licungo-Zambézia

Abstract

The Licungo Pegmatitic Field (CPL) consists of an aggregate of structurally controlled pegmatitic bodies embedded in schist, granite-gneissic and amphibolite rocks on the eastern bank of the Licungo River, in the Mocuba District, Zambézia Province. These pegmatites are of the rare earth class and NYF family and contain rare earth elements, which are important resources in the current global context of technological development and energy transition. The aim of this study is to assess the occurrence and forms of occurrence of rare earth elements in the host rocks proximal to the pegmatitic intrusion. In addition, rare earth elements, particularly light earth elements (LRE), related to felsic rocks and which, through fractionation, could concentrate these LRE in the host granitoids of Licungo are considered. Since REEs are of geological importance, they were used to study the differentiation processes of host rocks. To this end, the chemical composition of REEs in the host rocks was determined based on inductively coupled plasma mass spectrometry (ICP-MS) and the concentration of major elements (silica) based on X-ray fluorescence at the National Laboratory of Energy and Geology (LNEG). Binary and spider diagrams were constructed to study geochemical trends using the CGDKit software. Thin section samples were also used for petrographic characterization in order to identify accessory minerals that concentrate REEs. From observations of felsic rocks, it was observed that the mineralogy of the rocks is formed essentially by plagioclase, quartz, microcline, amphibole biotite and accessory minerals, notably chlorite, titanite, allanite and opaque minerals. Titanite and sphene are possibly the main causes of the high levels of RLTE in the felsic host rocks. From the projection and interpretation of the diagrams based on the compositional data, it can be seen that the felsic host rocks underwent two evolutionary events that were manifested in the distribution of REE, namely, fractional crystallization and, later, the reopening of the system driven by the installation of the Licungo pegmatites. IVAlthough several REE host minerals are found in the Licungo pegmatites, their occurrence in the host rocks is rare. Only allanite and titanite were observed, in a single pegmatitic body. It should be noted that although the chemical results show ETR concentrations in most samples, the minerals containing these elements are found in reduced percentages, suggesting that the crystallization levels of these host rocks have not been reached, unlike what happens with the Licungo pegmatites(TRADUÇÃO COSSA)