Au-Pd mineralization and ore-forming fluids of the Bleïda Far West deposit (Anti-Atlas, Morocco)

Abstract

Research subject. Au-Pd mineralization of the Bleïda Far West deposit, represented by an unusual association of palladium gold, minerals of the Pd-Bi-Se system, as well as silvery gold and minerals of the Pd-Bi-Te system. The deposit is localized in the Neoproterozoic volcanic rocks of the central Anti-Atlas (Morocco).Methods. A chemical analysis of minerals was carried out at the Center for Collective Use of Multielement and Isotopic Studies of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk, Russia) using the electron probe microanalysis (EPMA) method. Fluid inclusions were studied using cryometry and homogenization using a THMSG-600 microthermochamber. The composition of the gas phase and the determination of the solid phases of the inclusions were carried out by Raman spectroscopy. The qualitative chemical composition of fluid inclusion salts was determined by the EPMA method.Results and conclusions. It is suggested that palladium gold and minerals of the Pd-Bi-Se system were formed under the conditions close to those during the formation of Au-Pd infiltration deposits in Brazil, while silvery gold and minerals of the Pd-Bi-Te system could be formed under the conditions similar, but not identical, to the formation conditions of Au-Pd low-temperature mineralization in porphyry deposits. According to the study of fluid inclusions in quartz and calcite, Au-Pd mineralization was formed at temperatures from 384 to 75°C with the participation of homogeneous or heterophasic CaCl2-NaCl highly saline hydrothermal solutions at a depth of 2.8–2.7 km. Minerals of the Pd-Bi-Se system, previously unknown in Bleïda Far West ores, were found in association with native gold: osterboshite (Pd, Cu)7Se5, paladsite (Pd17Se15), (Au,Ag)Se, padmaite PdBiSe, native Se, as well as a number of unidentified phases – Pd2BiSe, Pd3BiSe, Pd4BiSe and Pd5BiSe.