"Geochemical characteristics of Early Cretaceous shales from Las Pavas mining title in the Western Emerald Belt, Colombia"

Abstract

The Colombian Early Cretaceous rocks in the Eastern Cordillera Basin have been of particular relevance for geoscientists since those rocks host the worldwide famous emerald deposits that have been the subject of several studies. This study is centered on the Las Pavas emerald mining title where 19 samples were collected to obtained detailed elemental geochemistry analysis using several techniques such as X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The mineralogy along with the major, trace and rare earth (REE) elements concentrations were analyzed, according to their distribution, enrichment and depletion within the samples studied. Results obtained in samples collected inside Las Pavas mine, show negatives anomalies of SiO2, TiO2, Al2O3 and K2O and high concentrations of MnO, MgO and CaO contrasting with higher concentrations of the same major elements from outcrops. Trace elements Be, V, Cr, Rb, Sc, Cs, Ba, Y, Co, Cu, Ga, Pb, Th, U, Zr, Hf, Nb and, W are enriched in the outcrop sections (Itoco and Las Pavas) compared to the tunnels. Itoco samples present the highest concentrations of REE followed by Las Pavas and finally the tunnel samples. Regarding the mineralogy, high contents of albite, calcite and dolomite provide the evidence of the albitization and carbonation processes that affected the country rocks. Thus, samples within the tunnels that are closer to the emerald mineralization, show negative anomalies of some major, trace and rare earth elements along with a characteristic mineralogy compared to outcropping samples.