BRAZILIAN CHRYSOCOLLA CHARACTERIZATION

Silica and silicate phases constitute by far the largest part of the earth’s crust and mantle. Intensive fundamental research in silicates has been carried out for many years due to their intrinsic properties. Chrysocolla mineral, Cu2H2Si2O5 (OH)4, is found in a relatively few localities associated with other copper ores and it has been subject of few studies, especially studies related to dating.
In this paper, a Chrysocolla sample extracted from a mine located at the Governador Valadares city, Minas Gerais, Brazil, was firstly characterized by spectrometry techniques, optical absorption (OA), XRD and ICP-MS. The X-ray diffraction (XRD) spectrum has proved our sample is a crystal one without incrustation. ICP-MS analyses were performed on liquid subsamples, with the aid of nitric acid and hydrofluoric acid through a microwave-assisted-digestion. Results reveal this mineral has high content of Fe and Mn and it had suffered a natural chemical leaching.
A dating study was also done. For this purpose two additional techniques were employed: EPR (Electron Paramagnetic Ressonace) and TL (thermoluminescence). The content of Fe and Mm had no effect on the EPR signal. A large accumulated dose of approximately 1.7 kGy has been detected, and due to the content of U, a large annual dose of 10.9 mGy yielded an age of (156.88 ± 16).103 years. To cross check this result, TL dating was also carried out. The additive method after adjusting with the saturation equation yielded an accumulated dose about 1.4 kGy that corresponds an age of (129.8 ± 11).103 years. The ages obtained are agreeable with areas formed by Quaternary deposits. To understanding about the process of geological formation in the region of the city of Governador Valadares in Minas Gerais additional data are needs.