Ocorrência de minerais metálicos e de alteração nas minas Paredão e Olaria – Lavras do Sul - RS

Abstract

Lavras do Sul is a city known since the 18th century due to its gold occurrences. With the evolution the geology knowledge, it was found that the city’s deposits held another metals besides gold, as copper, lead, zinc and rare Earth Elements. It was able to analyze the occurrences of those metallic and other alteration minerals, aiming to present a model of the mineralogical assembly at the paredão and Olaria Mines, emphasizing the presence of REE. For that, it was made the bibliographical review of the area, followed by the study of drill holes provided by the Amarillo Gold company. It was selected some altered and mineralized samples to study at the petrographic microscope and the Scanning Electron Microscope (SEM). The presence of pyrite, chalcopyrite, galena (sulphides), barite (sulphate), sericite and sambornite (silicates) and also hematite and ilmenite (oxides) were found. In pyrite, it was found Rhenium, Dysprosium and silver traces, in chalcopyrite, Indium and Tantalum. In galena, Lanthanum and in sphalerite, Lanthanum and Gold. The barite presented Cerium, in sambornite, Tin and Lead, and also in sericite, Praseodymium. In hematite, lead was detected. The mineral assemblies and its interactions between some elements suggest the presence of fluids that percolate and altered the rock, depositing the metals that mainly entered the sulphide structure. The presence of REE is indicative of fluid characteristics with high temperatures and acidic pH. This alteration fluid was responsible for the formation of the deposit (Copper Porphyry or Epitermal) and the most common alteration zone found was the Sericitic, containing the mineral assembly Quartz-Sericite-Pyrite. It is suggested to be conducted further studies on the REE mineral contents.