Caracterização de componentes ambientais através de parâmetros geoquímicos no depósito Três Estradas, Lavras do Sul - RS

Abstract

The carbonatites are rocks that form deposits of high economic interest. These rocks are hosts of elements of extreme importance for the industry, especially phosphorus, rare earth elements and niobium, which has been encouraging more and more mining companies to seek this type of deposit. The studied area covers the Três Estradas carbonatite, located in the municipality of Lavras do Sul, approximately 30 km southwest of its urban perimeter. In recent years, this deposit has been the subject of research for host phosphate mineralization, present mainly in the mineral apatite and used for the production of fertilizers. This carbonate deposit presents as expected, high concentrations of phosphorus, values that are more expressive in its weathering zone due to a secondary supergenic enrichment. This study seeks to understand how the formation of this deposit affected the natural components of this region (water, soil and stream sediments). The sampling prioritized points inside and outside the deposit area for later comparison of the results. The soil samples and stream sediments were submitted to mineralogical and chemical composition analyzes through the X-ray fluorescence spectrometry and X-ray diffraction tests at the Laboratório de Geoquímica – CPGq - of UFRGS Geoscience Institute. For water samples, acidity, alkalinity and detection of the elements calcium and phosphorus were performed on the chemistry laboratory of UNIPAMPA. The results indicated important positive anomalies in the soil sample 05S for the elements iron, calcium, phosphorus, yttrium, strontium, zirconium, zinc and niobium, implying that this soil had an important carbonatite contribution in its formation process. The concentration of these elements was the main compositional modification that the intrusion caused in the soil. The other samples kept less expressive values for these elements, especially those located outside the deposit area. The stream sediment sample 03SC presented anomalous contents for some elements in common with the sample 05S, indicating that it also had an important contribution from the carbonatite body. The opposite occurs with the sample 05SC, like calcium, phosphorus, zirconium and niobium, indicating that it also had an important contribution from the carbonatite body. The opposite occurs with the sample 05SC, which presented the lowest grades mainly for the elements iron, phosphorus, yttrium, nickel, copper, zinc and niobium. Water samples 02A, 03A and 04A had high values of alkalinity and phosphorus. The samples located in the most distant regions of the body presented the lowest concentrations of phosphorus. In these areas the deposit contribution in the studied components seems to be greatly reduced or even absent.