Structural, mineralogical, and paleoflow velocity constraints on Hercynian tin mineralization: the Achmmach prospect of the Moroccan Central Massif

Abstract

International audienceThe Achmmach tin mineralization (NE of theMoroccan Central Massif) is associated with tourmaline-richalteration halos, veins, and faults hosted in sandstones andmetapelites of the Upper Visean-Namurian. These depositsare reported to be late Hercynian in age and related to theemplacement of late-orogenic granite not outcropping in thestudied area. Structural and paragenetic studies of theAchmmach tin deposit were conducted in order to establisha general model of the mineralization. From field constraints,the late Hercynian phase is marked by a transition fromtranspression to extension with deformation conditions evolvingfrom ductile to brittle environments. The transpression(horizontal shortening direction roughly trending E-W) is coevalwith the emplacement of the first tourmaline halos alongseveral conjugated trends (N070, N020, and N120).Thereafter, a tourmaline-rich breccia formed in response tothe fracturing of early tourmaline-altered rocks.Subsequently, during the extensional phase, these structureswere reactivated as normal faults and breccias, allowing theformation of the main tin mineralization (cassiterite) associatedwith a wide variety of sulfides (arsenopyrite, chalcopyrite,sphalerite, galena, pyrrhotite, bismuthinite, pyrite, and stannite). This evolution ends with fluorite and carbonate deposition.The hydrothermal fluid flow velocity, calculated byapplying statistical measures on the tourmaline growth bands,varies with the lithology. Values are lower in metapelites andhigher in breccia. In the general evolution model proposedhere, tourmaline alteration makes the rock more competent,allowing for brittle fracturing and generation of open spacewhere the main Sn mineralization was precipitated

Deciphering fluid flow at the magmatic-hydrothermal transition: A case study from the world-class Panasqueira W–Sn–(Cu) ore deposit (Portugal)

“…In this study, the mean fluid flow velocity deduced from veins tourmalines (10 -4 m.s -1 ) is high and close to values obtained with the same method in the same type of deposit by Sizaret et al, (2009) and Mahjoubi et al, (2016), and suggests an efficient metal transport in veins. Considering a porous media with an averaged porosity of 1%, the conversion of this mean velocity to a Darcy velocity (VDarcy = V*porosity) gives a value of 10 -6 m.s -1 .…”

Tourmaline from the Solnechnoe tin deposit, Khabarovsk Krai, Russia

“…Tourmaline-supergroup minerals are typical of greisen, intrusion-related and porphyry tin deposits (Kuzmin et al ., 1979; Gorelikova, 1988; Wright and Kwak, 1989; Mlynarczyk and Williams-Jones, 2006; Baksheev et al ., 2009; Jia et al ., 2010; El Mahjoubi et al ., 2016; Codeço et al ., 2017). Tourmaline is characterised by a wide variety of chemical substitutions; therefore, different substitutions could be expected in tourmalines of different genesis.…”

Sulfide and Fluoride Mineralization of the NNE Region of Achemmach (Central Morocco): Paragenetic Sequences and Pyrrhotite-Sphalerite Geothermometry Constraints

“…The Cambrian formations are composed of a carbonates-based platform and volcano-detrital sediments. The Ordovician is represented by detrital deposits (shales, sandstones and quartzites) in a shallow marine platform-type environment [9,10]. The Silurian is characterized by a glacio-eustatic transgression, producing black graptolitic pelites and carbonates.…”