Massive Sulfide Ores in the Iberian Pyrite Belt: Mineralogical and Textural Evolution

Abstract

The Iberian Pyrite Belt (IPB) is recognized as having one of the major concentrations of volcanogenic massive sulfide (VMS) deposits on Earth. Original resources of about 2000 Mt of massive sulfides have been reported in the province. Recent classifications have considered the IPB deposits as the bimodal siliciclastic subtype, although major differences can be recognized among them. The main ones concern the hosting rocks. To the north, volcanic and volcaniclastic depositional environments predominate, whereas to the south, black shale-hosted VMS prevail. The mineral composition is quite simple, with pyrite as the main mineral phase, and sphalerite, galena, and chalcopyrite as major components. A suite of minor minerals is also present, including arsenopyrite, tetrahedrite-tennantite, cobaltite, Sb-As-Bi sulfosalts, gold, and electrum. Common oxidized phases include magnetite, hematite, cassiterite, and barite. The spatial relationship between all these minerals provides a very rich textural framework. A careful textural analysis reported here leads to a general model for the genetic evolution of the IPB massive sulfides, including four main stages: (1) Sedimentary/diagenetic replacement process on hosting rocks; (2) sulfides recrystallization at rising temperature; (3) metal distillation and sulfides maturation related to late Sb-bearing hydrothermal fluids; and (4) metal remobilization associated with the Variscan tectonism. The proposed model can provide new tools for mineral exploration as well as for mining and metallurgy.Minerals 2019, 9, 653 2 of 20 structural and tectonic settings; genetic models; the origin of mineralizing fluids; and economic aspects related to resources, reserves, tonnages, and ore grades.In spite of the enormous amount of published research, the generation of massive sulfide deposits in the IPB remains controversial. At least a part of this issue is due to a generalized tendency to assimilate the ore genesis in the IPB to classic genetic models for VMS deposits which are based on present comparables (i.e., black smokers, brine pool). A general review of published proposals for the generation of VMS in the IPB is detailed below. Geodynamic interpretations suggest that during the Late Devonian-Mississippian the IPB was affected by a period of regional extension with the breakdown and compartmentation of Late Devonian homogeneous basin and the beginning of the volcanic activity [26,27]. This paleogeographic environment favored the generation of hydrothermal systems, and the formation of the massive sulfide deposits [10]. According to Barriga [28] and Barriga and Fyfe [29], mineralizing fluids derived from seawater were equilibrated with underlying volcanic, volcanoclastic, and sedimentary rocks. These fluids were expelled on the seafloor where massive sulfide formed below a sealing chert layer that promoted ore precipitation but inhibited oxidation and dispersion. Based on Pb isotope analyses, Marcoux et al. [30] showed a homogenized metal source. Sáez et al. [11,23,31] and Almodóvar et...

Pyrite Varieties at Pobeda Hydrothermal Fields, Mid-Atlantic Ridge 17°07′–17°08′ N: LA-ICP-MS Data Deciphering

“…Quantitative LA-ICP-MS analyses of trace elements ( 51 V, 52 Cr, 55 Mn, 59 Co, 60 Ni, 65 Cu, 66 Zn, 75 As, 77 Se, 95 Mo, 107 Ag, 111 Cd, 118 Sn, 121 Sb, 125 Te, 182 W, 197 Au, 205 Tl, 208 Pb, 209 Bi, 232 Th, and 238 U) were carried out on a New Wave 213-nm solid-state laser microprobe coupled to an Agilent 7700 quadrupole ICP-MS housed at the Federal Scientific Centre of UB RAS. The analyses were performed by ablating spots ranging in size from 35 to 60 µm.…”

“…Obviously, this element is expelled from pyrite during recrystallization from porous to massive microtextures (e.g., [18]). In other MS systems, this involves the formation of arsenopyrite (e.g., [60]).…”

Some Experiences of Resistivity and Induced Polarization Methods on the Exploration of Sulfide: A Review

“…In the Iberian Pyrite belt, in Bathurst districts in Canada and Kuroko province of Japan, sulfide observed as volcano-sedimentary stratigraphic layers for being closely associated with volcanic lavas and pyroclastic rocks. They have formed a different relative participation of sedimentary/bacterio-genic and hydrothermal processes (Boulter, 1996; Barrie & Hannington, 1999;Sáez et al, 1999;Lentz & McCutcheon, 2006;Lentz, Thorne, & Beal, 2009;Walker, 2010;Piercey, Peter, & Herrington, 2015;Almod et al, 2019). VMS deposits (Sulfide in mafic or felsic hosted or occur as intercalation of basalts) are characterized by high electrical conductivity, high chargeability bordering zones, and sediments (such as graphitic shales) are more conductive than the associated volcanic host (Tavakoli et al, 2016b).…”

Natural and anthropic pollution episodes during the Late Holocene evolution of the Tinto River estuary (SW Spain)

“…The Tinto estuary is one of the most polluted fluvial-estuarine systems in the world, with very high concentrations of heavy metals (mainly As, Cu, Pb and Zn) due to acid mine drainage processes (Lottermoser 2010, Muñoz et al 2017. The hydrographic basin of this river includes the Iberian Pyrite Belt, one of the largest volcanogenic massive sulphide provinces on Earth, with original resources of about 2000 Mt (Almodóvar et al 2019). The exploitation of these deposits began during the Tartessian period (~4.5 kyr BP), with mining of precious metals and copper (Tornos 2008).…”