REE and Nd-isotope evidence for the origin of siderite from the Jebel Awam deposit (Central Morocco)

Abstract

REE contents and Nd-isotope ratios were determined in siderite ores from the “Filon du Signal” and the “Filon Sud” of the Pb–Zn–Ag mineralization of the Jebel Awam deposit, central Morocco. The deposit was formed by the intrusion of granites into the Lower Paleozoic metasedimentary basement probably by 280 Ma. The REE contents in the siderites allow for discrimination between the two veins, likely reflecting different concentrations in the mineralizing fluids. All siderites display positive Eu anomalies, indicating that the parent fluids were metamorphogenic. Assuming a common origin of the fluids, the higher REE contents and higher LREE/HREE ratios of FS siderites compared to FdS siderites suggest that the FS fluids were hotter and more acidic. The ɛ Nd and the 147Sm/ 144Nd ratios of the siderites range from − 5.97 to − 7.74, and from 0.172 to 0.183, respectively, and are statistically irrespective of sample provenance. The homogeneous isotopic data prevent use of the data for age-determination purposes, but they support the common origin of the mineralizing fluids. Moreover, since the siderites exhibit ɛ Nd 280 Ma comprised between the values of the basement schists and the granites, this supports a hydrothermal origin for the mineralizing fluids, which acquired Sm and Nd by leaching both lithotypes. These conclusions, corroborating earlier information provided by Sr isotopes, demonstrate the potential of Nd isotopes and REE as geochemical tracers in the study of hydrothermal deposits.