The Volcanic-Hosted Massive Sulphide Deposits of the Iberian Pyrite Belt Review and Preface to the Thematic Issue
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Mineralium Deposita (1998) 33: 2±30 Ó Springer-Verlag 1998 ARTICLE J.M. Leistel á E. Marcoux á D. Thie blemont á C. Quesada A. Sa nchez á G.R. Almodo var á E. Pascual á R. Sa ez The volcanic-hosted massive sulphide deposits of the Iberian Pyrite Belt Review and preface to the Thematic Issue Received: 4 April 1996 / Accepted: 10 April 1997 Abstract The Iberian Pyrite Belt (IPB) has, over the comparable to those of mantle-derived basalts emplaced past decade, been an area of renewed mining activity in extensional tectonic settings, and the associated acidic and scienti®c research that has resulted in a wealth of rocks were produced by melting of a basic crustal new data and new geological and metallogenic concepts protolith at low- to medium-pressures and a steep geo- that are succinctly presented in this Thematic Issue. The thermal gradient, thus, the sulphide-bearing volcano- reason for this interest in the IPB, which forms part of sedimentary sequence diers strongly from recent the Hercynian orogenic belt, is that its Late Devonian to arc-related series. It is considered here that the tectonic Middle Carboniferous rocks host a huge quantity of setting was extensional and epicontinental and that it volcanic-hosted massive sulphide (VMS) mineralization developed during the Hercynian plate convergence, that (1700 Mt of sulphides, totalling 14.6 Mt Cu, 13.0 Mt culminated in thin-skinned deformation and accretion of Pb, 34.9 Mt Zn, 46100 t Ag and 880 t Au). The miner- the South Portuguese terrane to the Iberian Paleozoic alization and its environment display a number of typ- continental block. ical signatures that can be related to the mineralogy and zoning of the sulphide orebodies, to the lead isotopes of Resumen (translated by E. Pascual) Durante la de cada the mineralization, to the geochemical and mineralogical pasada, la Faja Pirõ tica Ibe rica (FPI) ha sido un a rea de variations in the hydrothermal alteration halos sur- actividad minera e investigacio n cienti®ca renovadas, lo rounding the orebodies, to the geochemical characteris- que ha conducido a la obtencio n de nuevos datos y tics of the bimodal volcanics hosting the VMS, to the conceptos geolo gicos y metaloge nicos, que se exponen complex structural evolution during the Hercynian sucintamente en este Nu mero Especial. La razo n de este orogeny, to the presence of palaeofaults and synsedi- intere s en la FPI, que forma parte del cinturo n or- mentary structures that acted as channels and discharge oge nico hercõ nico, es que sus rocas, cuyas edades abar- traps for the metalliferous ¯uids, and to the gossans can desde el Devo nico tardõ o al Carbonõ fero Medio, developed over VMS. Discriminant geological criteria albergan una enorme cantidad de mineralizaciones de have been deduced for each domain which can be helpful sulfuros masivos ligados a vulcanismo (1700 millones de in mineral exploration, complementing the more tradi- toneladas de sulfuros, que totalizan 14,6 Mt de Cu, 13,0 tional prospecting techniques. Although the question of Mt de Pb, 34,9 Mt de Zn, 46100 toneladas de Ag y 880 the IPB's geodynamic setting is still under debate, any toneladas de Au). Las mineralizaciones y su entorno interpretation must now take into account some incon- muestran signaturas que se pueden relacionar con la trovertible constraints: for example, the geochemical mineralogõ a y la zonacio n de las masas de sulfuros, con characteristics of a large part of the basic lavas are los iso topos de plomo de la mineralizacio n, con las variaciones en los halos de alteracio n hidrotermal alre- dedor de las mineralizaciones, con los caracteres geo- quõ micos de las rocas volca nicas bimodales que albergan Editorial handling: DR los sulfuros masivos, con la compleja evolucio n tecto - J.M. Leistel á E. Marcoux (&) á D. Thie blemont nica del conjunto durante la orogenia hercõ nica, con la BRGM, DR/MGG, BP 6009, 45060 Orle ans Cedex 2, France existencia de paleofallas y estructuras sinsedimentarias C. Quesada á A. Sa nchez que actuaron como canales y trampas de descarga para ITGE, Rõ os Rosas n°23, 28003 Madrid, Spain los ¯uidos metalõ feros y los gossans que se desarrollaron sobre los sulfuros. Se han deducido criterios geolo gicos G.R. Almodo var á E. Pascual á R. Sa ez Geologõ a y Minerõ a, Universidad de Huelva, La Ra bida, discriminantes para cada a rea de conocimiento, que 21819 Palos de la Frontera (Huelva), Spain pueden ser u tiles para la exploracio n minera, 3 complementando las te cnicas ma s tradicionales de pro- Tharsis (mined for pyrite by Minas de Tharsis and for speccio n. Aunque la cuestio n del entorno geodina mico gold from the Filo n Sur gossan by Caledonia). The only de la FPI todavõ a es materia de debate, cualquier in- mine in Portugal is Neves-Corvo which is being worked terpretacio n tiene que tener ahora en cuenta algunas by Somincor. restricciones incontrovertibles: por ejemplo, los car- It was the 1977 discovery of Neves-Corvo with its Cu- acteres geoquõ micos de una gran parte de las rocas ba - and Sn-rich orebodies that led to renewed exploration sicas son comparables a los de basaltos derivados del interest in the area. This deposit was a major discovery, manto y emplazados en entornos tecto nicos ex- not only because Neves-Corvo is a deep blind deposit, but because the richness of the deposit showed that the tensionales, y las rocas a cidas asociadas se produjeron a Iberian Pyrite Belt still contains major economic metal partir de un protolito cortical ba sico, a presiones bajas o potential; subsequent renewed exploration has already intermedias y asociadas a un abrupto gradiente te rmico. resulted in further orebodies being discovered. The other Por consiguiente, la secuencia vulcanosedimentaria que interesting aspect of the mining revival is that the Iberian contiene los sulfuros masivos di®ere claramente de las Pyrite Belt has also become a major ®eld area for world- series recientes relacionadas con entornos de arco. wide scienti®c research, research that has harvested a Consideramos aquõ que el entorno tecto nico fue exten- wealth of new data, that has given rise to new metallo- sional y epicontinental y que tuvo lugar durante la genic concepts, and that has led to revised geological convergencia de placas hercõ nica, que culmino en de- interpretations not only of this province, but of the en- formacio n ``thin-skinned'' y acrecio n del terreno con- tire Western Hercynides. stituõ do por la Zona Sudportuguesa al bloque con- The few reviews dealing with the mineralization of tinental paleozoico ibe rico. the Iberian province include that of Pinedo Vara (1963), who made an exhaustive and invaluable compilation for the Spanish part of the belt, and more recently those of Introduction Carvalho et al. (1976a), Routhier et al. (1980), IGME (Instituto Geologico y Minero de EspanÄ a 1982b), Bar- The Iberian Pyrite Belt (IPB), with more than 80 known riga (1990) and Leistel et al. (1994). And two synthesis deposits containing >1700 Mt of sulphide ore (mined papers on the IPB massive sulphide mineralizations by and reserves), is one of the largest (if not the largest) of Sa ez et al. (1996a, b) will be published soon. Finally, the the world's massive sulphide provinces (see Table 1, IPB within the South Portuguese Zone is also well de- Plates I and II). Mining has been active in the belt since scribed in a volume dedicated to the geology of the Pre- the Chalcolithic era with the result that today almost all Mesozoic basement of Iberia (Dallmeyer and Martõ nez- the outcropping and near-surface deposits are exhausted Garcõ a 1990). and mineral prospecting must now orientate itself to- The articles prepared for this Thematic Issue present wards ®nding deeper orebodies. The fact that pyrite is results that have been obtained over the past ®ve years. no longer used as a raw material for manufacturing Several concentrate on detailed descriptions of individ- sulphuric acid, combined with the rather poor known ual deposits, such as Aznalco llar-Los Frailes (Al- base-metal content of the deposits, has resulted in many modo var et al.), Tharsis (Tornos et al.), and Lagoa mines closing over the last two decades. Only ®ve mine Salgada (Oliveira et al.). Others are based on regional- sites are still active in the belt today. Four of these are in or deposit-scale thematic studies, such as mineralization Spain: Sotiel-Migollas (mined by Almagrera S.A. of the in the Western Hercynides (Lescuyer et al.), structural Teneo Group), Aznalco llar-Los Frailes (mined by Ap- reinterpretation of the province (Quesada), geochemis- irsa of the Boliden Group), Rio Tinto (mined for gold try of the sulphide-bearing lavas (Thie blemont et al.), from the gossan, by Minas de Rõ o Tinto S.A.L.) and lead isotopic analyses of the mineralization (Marcoux), Table 1 Comparison of ore and metal tonnages (mined + re- from Franklin and Thorpe 1982; Chartrand and Cattalani 1990; serves) in the massive sulphide provinces of Australia, Canada, and Kerr and Gibson 1993; Barret and MacLean 1994; for Iberia see the Iberian Peninsula (for Australia data mainly from Green 1990; Table 2) Large 1992; Barley 1992; Berry et al. 1992; for Canada data mainly Country n Size Cu Pb Zn Ag Au (Mt) (Mt) (Mt) (Mt) (t) (t) Australia (Archean to Permian) 30 334.9 4.2 4.1 12.8 13447 578 Mount Read Belt-Tasmania (Cambrian) 6 148.6 1.5 2.5 6.1 7423 156 Canada (Superior Province ± Archean) 87 769.0 11.8 0.6 25.9 28359 712 Abitibi (Archean) 40 500.3 9.9 0.4 18.2 20919 656 Rouyn-Noranda+Val d'Or (Archean) 20 394.3 5.8 0.0 6.2 5590 596 Iberian Peninsula (Pyrite Belt) 85 1765.0 14.6 13.0 34.9 46188 887 (Devonian to Carboniferous) Neves Corvo 1 261.5 3.44 0.6 3.74 2977 n = number of deposits 4 gold distribution in the massive sulphides (Leistel et al.), Plate I Location map of deposits in the Spanish part of the Iberian a study of the cherts (Leistel et al.), geometry and genesis Pyrite Belt.