Basinal Brines at the Origin of the Imiter Ag-Hg Deposit (Anti-Atlas, Morocco): Evidence from LA-ICP-MS Data on Fluid Inclusions, Halogen Signatures, and Stable Isotopes (H, C, O)—A Discussion

Abstract

We congratulate Essarraj et al. (2016) for their paper on the polymetallic Ag-Hg Imiter deposit (Anti-Atlas, Morocco), which is one of the most intensely investigated yet still discussed mineral deposits in term of ore genesis. In their contribution, Essarraj et al. have employed fluid inclusion, halogen, and isotopic analyses in an attempt to constrain the genesis of the Imiter Ag-Hg deposit. It is through detailed geochemical studies such as this that the origin(s) of this world-class orebody will be deciphered. Their contribution represents a significant advance in the investigation of polymetallic hydrothermal deposits of the Anti-Atlas. However, we feel compelled to stress certain problems with their interpretation. Important geologic attributes of the Imiter deposit have been documented by numerous workers (Ouguir et al., 1994; Pasava, 1994; Baroudi et al., 1999; Cheilletz et al., 2002; Essarraj et al., 2005; Barral et al., 2011; Levresse et al., 2005, 2016). However, there is a lack of direct age information to constrain the timing of hydrothermal activity and duration of vein filling during the silver mineralizing event(s). This age uncertainty has resulted in the proposal of several conflicting models involving different fluid sources and genetic processes that have been ignored by Essarraj et al. In their contribution, Essarraj et al. relate the genesis of silver ore at Imiter to a single, regional-scale hydrothermal circulation of basinal brines but do not mention preexisting models that emphasize the polyphase character of the mineralization. The authors point out the role of Triassic evaporitic brines and development of the Central Atlantic magmatic province as the main ore-forming processes that triggered formation of the Imiter Ag-Hg ores. Key evidence for their proposed model is based on the Late Permian and Triassic ages of Borisenko et al. (2014) that were determined on a …