Análise química de micas e classificação petrogenética de pegmatitos das províncias da Zambézia e Manica

Abstract

The work aimed to determine the elements La, Nd, Sm, Nb, Ti, Li and Rb in 15 samples of lepidolites and muscovites using the respective levels to classify petrogenetically the pegmatites according to the LCT families (enriched in Li, Cs and Ta) and NYF (enriched in Nb, Y and F). The samples were taken in the provinces of Manica and Zambezia. The elements La, Nd, Sm, Nb, Ti were determined by X-ray fluorescence (XRF), at the Mozal quality control laboratory, for which the device was calibrated with 10 reference materials. The Li element was determined by photometry of flame (FC) and Rb by atomic absorption spectrophotometry with flame atomization (FAAS). The samples were solubilized in an acidic mixture (HNO 3, HClO 4 and HF, concentrated) hot. For the control of the results obtained by XRF, two reference materials, GH and SARM 1, both granites. Good accuracy and precision were obtained for all elements, using SARM 1, with% error and% RSD values ranging from 0.92 to 5.5 and 0 to 12.9 respectively. Exception was for the Sm element with % RSD of 47, which may be related to the fact that only one reading was done. For the reference material GH, good accuracy and precision were obtained in determining the Nd, Sm, Nb and Ti elements with% error and% RSD values ​​ranging from 10 to 20 and from 0.0 to 20 respectively. The determination of La revealed precision and accuracy with a value of % RSD of 47 and% of error of 60, with the low content of the element in the material of reference is at the origin of the result obtained. In the samples,% RSD values ​​between 0.0 to 20.1 were obtained for all elements, revealing good precision, except for La and Nd, in sample M6707, with% RSD values ​​of 47 and 28 respectively. For the element Sm in sample M6182, a high value of% RSD (47) was obtained, a very linked anomaly probably to the manual homogenization process of the sample. The precision and accuracy of FAAS method in determining the Rb, using the GH reference material were good with% RSD values ​​of 1.6 and error% of 8.7. All samples showed good accuracy in determining Rb with% RSD values ​​ranging from 0.0 to 11.4. For Li good accuracy by the FC method it was obtained with a value of% error of 14.0 with the reference material GH. In all samples, measurements showed good accuracy with% RSD values ​​between 0.0 and 9.6, except for sample M6673 with a% RSD value of 50. The samples revealed high levels in Li, Rb, Cs (the levels in Cs were not determined at work, having extracted from studies on pegmatites) and low levels of Ti and Nb. The brands geochemical findings after analysis of lepidolites and muscovites suggest that pegmatites from which the samples were taken are from the LCT pegmatitic family. (TRADUÇÃO NOSSA)