LEIDSE GEOLOGISCHE MEDEDELINGEN, Deel 52, 1-7-1981 Aflevering 1, pp. 23-56, Framework and evolution of Hercynian mineralization in the Iberian Meseta BY L.J. G. Schermerhorn Abstract The Hercynian cycle, starting in Late Precambrian times and terminated at the end ofthe Palaeozoic, is associated in the Iberian Peninsula with the the deposition of a wide variety of metallic and nonmetallic mineral resources. The most famous of these are the base-metal sulphides of Iberian Pyrite Belt (Rio Tinto and other deposits), tin and tungsten (Panasqueira), and mercury (Almadén). The of the the accumulation of depositional stage Hercynian cycle saw syngenetic mineral deposits, resulting from the interplay of palaeogeographical, sedimentary and volcanic controls. During and after the following orogenic stage, epigenetic minerals originated through magmaticactivity, mostly as direct deposits from magmatic-derived fluids and also indirectly through thermal activation of existing rock. In both stages felsic magmatismwas the dominant agent of mineralization, both for the moreimportant volcanogenic and for the plutonic mineral deposits. Framework and evolution of Hercynian mineralization are defined by the geotectonic intraplate — not plate-margin - setting ofthe Meseta and by its palaeogeographicaland structural developmentduring the cycle, modified by regional and local factors, foremost among which are volcanic and plutonic heat and mass transfer. the Metallogeneticprovinces and epochs are distinguished, metallotects outlined, and possible sources for introduced ore elements discussed. Contents Introduction 24 Middle Carboniferous 36 (jcotcctonic and structural setting 24 Hcrcynian orogeny: the main phase 36 Westphalian talc 37 Late Precambrian 24 Hercynian Older Granites 37 Late Precambrian (?) copper sulphides 24 Middle to Upper Carboniferous 37 Cambrian 38 27 Hercynian orogeny: later phases Cambrian scheelite 28 Cambrian lead-zinc sulphides 28 Permian 38 38 Cambrian (?) mercury 29 Autunian stratabound fluorite Cambrian iron 29 Hcrcynian Younger Granites 38 Early Palaeozoic chromium 29 Autunian tin and tungsten 39 Autunian beryl, columbite-tantalite, lithium and feldspar . 44 Ordovician 3D Autunian gold and silver 44 Ordovician iron 30 Autunian antimony and gold 45 Ordovician antimony 31 Autunian and later lead, zinc and silver 46 Autunian phosphate 47 Silurian 31 Late Palaeozoic chromium and nickel 48 Silurian Almadén 31 cobalt, nickel and mercury: Late to post-Hercynian epigenetic copper, Silurian base-metal sulphides and magnetite 31 bismuth 48 Silurian scheelite 32 Late Hercynian f'erromanganese 48 AuUinian 49 (?) mercury Devonian 32 Autunian (?) epigenetic fluorite and baritc 49 Remobilized Autunian uranium 49 Early to Middle Carboniferous 32 EarlyCarboniferous base-metal sulphides: the Iberian Pyrite Synthesis 50 Belt 32 Carboniferous 36 References 53 Early manganese *) Prof. Dr. L. J. G. Schermerhorn, Institut für Mineralogie, Freie Universitàt Berlin, Takustrasse 6. D-1000 Berlin 33. B.R.D. 24 INTRODUCTION change from one zone to another but tend to remain constant withineach that the zone, is, along strike. The zones represent The Iberian Peninsula is well endowed with mineral resources, not only differentpalaeogeographical domains and different a ofwhich created the large part were during Hercynian cycle, stratigraphie and sedimentary facies but also more or less that the is. geological cycle of sedimentation,magmatism and different tectonic, metamorphic and magmatic styles together tectonism leading to the ter- - up Hercynian orogeny which with different mineralizations(Fig. 2 this figure follows the minates the cycle at the end of the Palaeozoic (Fig. I). The adaptation by Julivert et al. (1974) of Lotze's original Iberian Meseta, or Hesperic Massif, occupying a large part of scheme). the Peninsula, was consolidated the The during Hercynian oro- Hercynian geosyncline in Iberia was a multiplex, It is the site of a ofmetallic and geny. great variety nonmetallic ceaselessly shifting assemblage of subsiding basins, more or mineral deposits. Three world-famous Iberian ores belonging less stable platforms and geanticlinal uplifts, evidencing the mind: to Hercynian cycle spring to the base-metal sul- pronounced vertical mobility of the basement underlying the ofthe Iberian Belt, with Rio most Positive phides Pyrite Tinto as their geosyncline. epeirogenic movements in a region at celebrated the belt, with Panas- In representative, tin-tungsten one time may turn to negative soon after, and so on. the queira as most important tungsten mine outside the Far formation thicknesses between consequence, can vary greatly and the of Almadén. East, mercury regions. Moreover, volcanism took place in all periods from Two factors dominate the context of mineral the deposition in Precambrian and Cambrian on (Fig. 1 ). the Iberian Peninsula during the Hercynian cycle. They are, first, the long-drawn evolution of the Hercynian geosyncline. LATE PRECAMBRIAN starting in Late Precambrian times, with volcanism occurring throughout, and, second, extensive granitic intrusion. The Hercynian cycle in the Iberian Peninsula begins when the The depositional stage, when the geosyncline Hercynian geosyncline formedand sedimentationstarted, on was being filled, the for the accumulation of a floor ofolder Precambrian rocks, provided setting some time during the Late syngenetic mineral resources, ranging from sedimentary iron- Precambrian. stone to the Precambrian in volcanogenic polymetallic sulphides. During Upper strata crop out several places in the o r o e n the earlier were Meseta. In the south known subsequent g i e stage deposits they are generically as the 'Serie deformed, and intruded. The metamorphosed deformed Negra', a slate-grcywacke succession containing thin la vers rocks served hosts to wide and géosynclinal as a range of epi- and lenses ofblack quartzites cherts, and some limestone. genetic mineraldeposits, from bariteand fluorite to the famed intermediate of the Locally volcanics appear at the top Iberian tin and lodes. The mineral tungsten géosynclinal sequence (Vegas, 1974). The Serie Negra is overlain by the deposits are the result of the interplay of palaeogeographical. Lower Cambrian, and the junction is conformable, discon- sedimentary and volcanic controls, and the and Ibrmable orogenic or locally even unconformable. Similar slate-grey- minerals wacke successions postorogenic arose from magmatic activity, directly appear elsewhere in the Meseta below as or contain felsic plutonic deposits indirectly through thermal activation Cambrian or probable Cambrian beds and may of materials. Thus were a volcanics at their existing produced great variety ol' or near top. Little is known as yet of the mineral deposits, some of them on a grand scale indeed: the relationship between the Upper Precambrian successions and Iberian Belt contains the Pyrite largest massive sulphide the older schists and gneisses of the crystalline basement to the bodies in the world, the Panasqueira mine is the largest Hercynian geosyncline. tungsten producer in Europe, and Almadén is by far the No syngenetic mineralizationshave been recorded from the vastest mercury concentration known. Upper Preeambrian (meta) sediments, and their slate-grey- Hercynian géosynclinal and orogcnic evolution in Europe wacke lithology often called flysch-like does not favour and North Africa is of different than the evolution of the of a type occurrence synsedimentary ores of any importance. the Alpine and other to Nor orogens related lithosphère sub- are important orebodics known from the volcanic duction, this is still though an endlessly debated point. This intercalations, with the possible exception of the copper however difference is undeniable as it makes itself fell in a deposits at Arinteiro and Fornás. number of is the ways, one of which scarcity of Hercynian ultramafic rocks and in the absence of true Late Precambrian particular (?) copper sulphides that is. ophiolite, oceanic crust complexes. As a result, the The A r i n t e i r o and Fornás cupriferous pyrrhotite minerals associated with ultramafic magmatism. such as the deposits near Santiago de Compostela in Galicia, in exploi- ores ofnickel and chromium, in the Iberian are rare Meseta. tation since 1975, are metamorphosed sulphide lenses in- terbedded with garnetiferous amphibolites in the polymeta- and The Geotectonic structural setting morphic Ordenes complex. rocks and ores underwent The volcanic and tectonic sedimentary, history of the Meseta polyphase deformation and were metamorphosed to the during the Precambrian and Palaeozoic is very complex and hornblende granulite facies, suffering rétrogradation to the has not yet been completely unravelled. There is a cleareut amphibolitc facies (van Zuuren. 1969). The Ordenes complex zonation the trend. across orogenic Lotze's well-known consists of paragneiss and schist (mostly original greywackes subdivision into six which has suffered little zones change in according to vanZuuren ( 1969))enclosing amphibolites in the the 34 since it first Julivert al. lower levels. Its years was propounded. et ( 1974) age is considered to be probably Late out that the of these is Precambrian (E. Den Tex, comm.). The point significance zones essentially pers. occurrence of palaeogeographical: sedimentary facies and thicknesses thin beds of black quartzite (van Zuuren's graphite-bearing 25 Fig. 1. Generalized section illustrating timing and evolution of mineralization in the Iberian Meseta.