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. 26

Fig. 2. Principal metallogenetic provinces in the Iberian Meseta.

schists) does in fact recall the black quartzites and cherts of the orebody. Bama. Sulphide mineralization is found in other Silurian black in this well (Chabod Serie Negra (unless they are metamorphosed places structure as et al.. 1976).

cherts). At Arinteiro and Bama the mineralization is linked to a

At Fornás three stacked lenses of disseminated to fairly particular level of garnet amphibolite 20-80 m thick. The

million massive sulphides (pyrrhotite with chalcopyrite and pyrite), three sulphide deposits add up to almost 25 tonnes of of Cu (White. 1977a). The together 30 m thick by a strike length about 200 m, are copper ore reserves grading 0.66",, enclosed with sharp contacts in unmineralized garnet amphi- Fornás ore is much more massive than Arinteiro and Bama.

S for Arinteiro bolite. They total 750,000 tonnes grading 1.02% Cu. Arin- grading 20 30% S as against 5-7% (N. Rho-

teiro is much den, coram.), is still diluted a larger orebody of pyrrhotite with chalcopyrite pers. but moderately by gangue andjjyrite disseminatedin garnetamphibolite in the east flank minerals such as anthophyllite or gedrite and other silicates, of an anticlinorium. The west flank contains a similar with little garnet (Ypma. 1966). 27

From their field aspect and their simple composition (iron called flysch-like (as also the fossiliferous Middle Cambrian

sulphide with chalcopyrite and little else), these deposits of southeast-central Portugal and southwest Spain) - and

to be stratabound appear original syngenetic cupriferous represent the infilling of a large, fairly deep basin. The

pyrite mineralizations in submarine mafic volcanics. Sub- fossiliferous Cambrian of the northern and southern Meseta

under in sequent recrystallization high-grade conditions caused was largely deposited shallow waters and it shows a much

the of the coarse grain sulphides, destroying any original greater development of carbonates.

and depositional structures textures, and the alteration to Characteristic for the Beira Schists and coeval formations

pyrrhotite of original thin pyrite. are interbedsof quartz conglomerates made

As the ore-bearing amphibolites of the Ordenes of rounded of and complex pebbles quartz quartzite. with rare clasts of

are mafic to intermediatemetavolcanics interbedded among black quartzite and chert derived from the Serie Negra. metasediments. the Fornás, Arinteiro and Bamba deposits Characteristic too. and like the quartz conglomerates useful

be classified as to the Besshi of may belonging type volcano- for correlation purposes, are amphibole schists of mineralization discussion of genie sulphide (see sulphide- Garbenschiefer type. They occur as thin beds of metamor-

classification under Lower deposit Carboniferous base-metal phosed impure calcareous sediments, consisting of quartz,

sulphides). calcic plagioclase and amphibole (often hornblende) poikil-

oblasts, frequentlyaccompanied by garnetand other silicates. CAMBRIAN They have been described from the Beira Schists in Portugal

(Schermerhorn. 1956) and from similar successions in Spain

The Cambrian of the Iberian Meseta is generally thick 1969 (his 5 shows very (Capdevila, fig. a rock entirely similar to

and Cambrian is well in volcanism developed,especially south Schermerhorn's fig. 13): Martinez Carda. 1973: Martínez

Portugal and southwest García & Spain. Nicolau. 1973); these rocks are of interest because The LowerCambrian (Georgian) is a sandy-slaty sequence they host scheelite mineralizations (see be-

with limestone-dolomite is a level in its upper part that thick low).

and continuous in the south, thinning northwards and thick- The Olio de is Sapo a sequence in which coarse in the northern Meseta (Schermerhom, 1955; ening again augengneisses are dominant,mostly consisting of metamor- Julivert et al.. Schmitz 1974; & Walter. 1974; Walter & phosed feldspathic sediments, with interbedded felsic meta- Schmitz. 1975). This carbonate level is interbedded locally volcanics. This formation is exposed in northwest and central with mafic or felsic volcanics (Guillou, 1971a; It is Vázquez Spain. a lateral equivalent of Cambrian and Beira Schist

Guzman & Fernández Pompa, and volcanics are also 1976), rocks, and may extend into the basal Ordovician. Olio de

the in found near base of the Cambrian several places. Less levels Sapo-like rocks occur at lower too, though their

carbonates, the Cándana Limestone, occur in the important relationship to the Serie Negra is not always clear.

lower part of the Lower Cambrian in northwest Spain. The Olio de Sapo constitutes a regional lithofacies largely The Middle Cambrian of (Acadian) consists slates and made of the freshly eroded debris ofPrecambrian porphyritic sandstones and contains spilites and some felsic volcanics. Its went granites. deposition on from the early Cambrian or Where still the present, UpperCambrian (Potsdamian) shows earlier into the Ordovician, indicating the continuous exis-

a sandstone-slate lithology. Fossiliferous Cambrian out tence this crops during period of a granitic source area within the in south Portugal, south Spain and northwest Spain. In Hercynian geosyncline.

addition, the Beira Schists and the Olio de Sapo Formation

are here regarded, in common with and Thus sedimentation many Spanish Hercynian géosynclinal starts with a

as Cambrian Portuguese geologists, essentially successions. great thickness of terrigenous elastics, mostly

The Beira Schists of Portugal and equivalent for- sand and clay, deposited during the Late Precambrian and

mations in Spain vast tracts in the central and western Cambrian. However, occupy basin configuration was not uniform Meseta. The name Beira Schist Formation, or Beira Schists the extent of the over Meseta. One or more geanticlinal ridges for short, is to be since it has clear preferred priority (Xistos exposing older Precambrian basement shed feldspathic detri- das Beiras. Formaçâo Xistosa da Beira: 1907); this Delgado, tus into the basin, and shallow-water conditions prevailed formation has also become known as 'xistograuváquico', an during most ofthe Cambrian along the northern and southern

not in accordance with equivocal designation modern litho- edges of the Meseta. Here carbonate deposition

stratigraphical nomenclature. The Beira Schists and coeval attained great importance during part of the Lower Cam- formations in Spain (such as the Valdelacasa Series, the brian.

VillalbaSeries, the Porto Series and the upper Alcudiense) are The Cambriancarbonate rocks and the associated minera-

generally unfossiliferous. but other arguments show their lizations are economically important. Thoughvery extensive,

equivalence to, at least, the Middle and Lower Cambrian the terrigenous elastics making up most of the fossiliferous

(Schermerhorn, 1955. 1956; Bard et al.. 1972; Martínez Cambrian, the Beira Schists and the Olio de Sapo do not García, 1973; Ribeiro, 1974) and locally they confor- contain mineral pass syngenetic deposits of any significance.

mably into the basal Ordovician (A. Ribeiro, the pers. comra.). Locally quartz conglomerates are auriferous: Ta- overlie Serie They Negra rocks, and the precise main refers to to chronostratig- (1971) grades up 16 g/t Au in the Valle de ofthe raphical age junction between Serie Negraand the Beira Alcudia in southern Spain. The slates, sandstones, schists and

Schists or the fossiliferous Lower Cambrian is still uncertain. gneisses are quarried to some extent to provide local building The Beira like the Schists (and equivalent), Serie Negra, and roadmaking material, but it is the Lower Cambrian

consist mostly of interbedded slates and - often limestones greywackes and marbles that are extensively exploited as 28

ornamental and for industrial in south Por- Pn-Zn in the carbonates stone purposes sulphides are widespread near the

tugal, northwest and southwest Spain. top of the Lower Cambrian in the southwest Meseta. In south

Local sedimentary differentiationto magnesium-rich rocks Portugal a Lower Palaeozoic lead-zinc-magnetite

within the Lower Cambrian carbonates has led to the for- belt (Faixa Zincífera e Magnetítica Alentejana,also known

mation of several i in northwest been m a g n e s t e deposits as Faixa Zincífera, or Zinc Belt, for short Fig. 3) has

Spain. The largest is worked at Pacios near Incio (Lugo defined and thoroughlyexplored by the Serviço de Fomento

province) and is one ol the two active magnesite mines in the Mineiro (Andrade, J969, 1972; Goinhas. 1971; Carvalho et

Peninsula. Here the magnesite is associated with dolomites al., 1971a, b). This metallogenetic province continues into

belonging to the Cándana Formation and is of lagoonal southwest Spain (Guillou, 1971). Here stratabound sulphide al., origin (Doval et 1977). mineralizationsoccur as disseminations near or at the top of

the carbonate horizon in the Lower upper part of the

Cambrian schee lite Cambrian (Upper Georgian), and as massive bodies at the

Scheelite has been found disseminated in the thin layers of base of disconformably overlying volcanics which also con-

called of in the tain The amphibole schist (sometimes quartzite gneiss) magnetite orebodies. age ofthese volcanics is not yet

Beira Schistsand equivalent sequences, as south ofSalamanca known with certainty. In the opinion of the Serviço de

in western Spain (Pellitero, Arribas & Saavedra. 1976). Fomento Mineiro geologists they are Lower Silurian (or at

Though formerly ascribed to the epigenetic Sn-W minerali- most Upper Ordovician), and the Middle and Upper Cam-

zation generated by the Hercynian granites, discussed later, brian and the Ordovician are lacking in the Zinc Belt

occurrences such as near Castro Daire in northern Portugal (Goinhas, 1971; Carvalho et al., 1971a, b; Carvalho, 1976a).

where scheelite is found dispersed in hornblende schist (out- According to others the volcanism could be Middle Cambrian

side the granite contact aureoles) over a strike length exceed- (Andrade, 1972; Guillou, 1971a). We will follow S. F. M.

the Belt ing 400 metres (Schermerhorn. 1956. p. 77, 537) lead to opinion and regard Zinc as a metallogeneticprovince

reinterpretation as a syngenetic mineralization in marly where mineralizations dating from different epochs have

sediments.This problem will be examined when reviewing the become superposed. All rocks and ores have been strongly

the similar scheelite occurrences in Silurian calc-silicate rocks. folded and metamorphosed during Hercynian orogeny. The carbonate level, here mostly dolomitic, is uniquein the

Cambrian lead-zinc sulphides whole Late Precambrian-Palaeozoicsuccession of the south-

The Lower Cambrian carbonates form an important metal- west Meseta: it is a marker horizon and by dint of its

lotect for Pb-Zn mineralization. In west and northwest Spain. singularity reliably correlated with the less metamorphosed

Lower carbonates Upper and Georgian limestones carry syngenetic fossiliferous Upper Georgian nearby in southwest

stratiform base-metal mineralizations sometimes associated Spain (Carvalhosa, 1965).

with and of Mon- There two of minerali- antimony traces mercury (Guillou, 1971a; are types sulphide

The seur. 1977). These are considered by Guillou to represent zation in this mineral belt. most frequent type, found

marine concentrations of elements leached and transported at Preguiça. Ficalho, Balsa and other prospects, consists of strataboundaccumulations of marmatitic from a weathered landmass. sphalerite, argenti-

Rubiales in northwest Spain (Piedrafita del Cebrero, ferous galena and pyrite in siliceous metadolomitehorizons,

Lugo province), a recent discovery, is a zinc-lead mine. The with the sulphides mostly forming veinlets along microfrac- silicified ore is found in limestonesalternating with mudstone tures. The other type, found at Algares, comprises massive

layers, in the dragfolded east limbof an anticline. Reserves are orebodies discussed under Silurian metallization. At Vila

at least 12 million tonnes grading8.1",, Zn and 1.5% Pb(2.5- Ruiva, near Preguiça, and elsewhere, primary sulphides were

3"„ Pb has also been quoted) with some Cu and Ag (White, weathered, leached and rcdeposited on a karst surface de-

1977b). veloped in the Cambrian carbonates, possibly during the

Tertiary. The ore consists ofiron oxides and calamine, that is.

zinc oxides, silicates and carbonates, such as smithsonite,

Zn and descloizite Pb hydrozincite 5 (C0 3) 2 (OH) 6 (Zn, Cu)

(V0 4) (OH).

The disseminated sulphides in the dolomites of the Zinc

Belt are thought to be synsedimentary mineralizations unre-

lated to volcanism. Later remobilization caused redistri-

bution of the sulphides in veinlets following cracks in the

dolomites, accompanied by silicification and redolomiti-

zation.

In the continuation of the Zinc Belt in southwest Spain the

same two types of sulphide mineralization occur. According

to Guillou (1971b) Pb and barite occur disseminated in

Cambrian dolomites, accompanied by subordinate Zn and

little Cu, Ag, Sb, while the overlying volcanics(felsic pyroclas- contain tics) sulphide lenses (pyrite with pyrrhotite, mag-

Fig. 3. The South-Portuguese zinc-magnetite belt. After Goinhas netite, sphalerite, chalcopyrite and galena) associated with

(1971). carbonate and chert lenses. Guillou concludes to a syngenetic 29

origin of both mineralizations: were is worked Cu, Pb, Sb. Hg and Ba copper sulphides by opencast and underground with the carbonates the of the deposited at top Lower mining, producing Fe and Cu. The magnetite ore forms Cambrian carbonate level, with the metals deriving from conformable levels and lenses and is banded (5-30 cm), with weathered land while abundant, masses, Zn - locally else- layers and zones rich in pyrite and chalcopyrite. The deposit - where almost is volcanogenic. in lacking occurs interbedded limestone-quartzite-slate country rock

and is associated with much skarn, near granite.

in All all. the age difference between the Cambriandolomites The origin of the mineralization in this belt is uncertain.

and the volcanics, whether overlying Silurian, Ordovician or Many authors favour a pyrometasomatic mode of formation,

even Middle Cambrian, seems sufficiently significant that, with the iron and the sulphides deriving from intruding

taken with their different modes of the but together occurrence, magma, a syngenetic sedimentary or volcanic origin

of mineralization must to different two types belong two modified by later metamorphism caused by granite intrusion

periods of deposition and represent different environments. has also been defended (Doetsch. 1967). In favour of synge-

Cambrian and carbonates are a metallotect for lead-zinc ore, netic deposition is the occurrence of minor iron ore as folded

n seems likely that the end of the period of Lower Cambrian the Elsewhere there layers older than granites. are strong signs carbonate sedimentation became favourable for the de- of epigenetic mineralization,such as the formation of mineral- position of terrigenous-sedimentary lead and zinc sulphides. ized skarns in a carbonate horizon that outside the contact

Concentration instead of of Pb Zn in aureole consists of dissipation and the rather pure limestone only. More study is Cambrian sea could have been brought about by suitable needed.

sedimentary and palaeogeographical configurations.

Early Palaeozoic chromium Cambrian (?) mercury Ultramafic rocks, the of source chromium, are rare in the At in southwest Usagre Spain (near Burguillos del Cerro) was Meseta. be They can divided into two groups: 1) the Early a mine working stratiform cinnabar - mercury impregnations Palaeozoic ultramafics peridotites and serpentinites that three horizons in Lower Cambrian along limestones, accom- occur associated with mafic rocks and paragneisses in a panied by cinnabar veinlets; other minerals included pyrite, of number high-grade massifs in the northwest corner of the

galena, barite and It is not certain chalcopyrite. quartz. Meseta (Fig. 2), and 2) ultramafics occurring associated with whether this mineralization is syngeneic or epigenetic, mafic intrusives and extrusives of ages varying from Early to the Cambrian. Guzman and Fernández postdating Vázquez Late Palaeozoic; these are on a discussed later page. think it Pompa (1976) well be of pre-orogenic and In the northwest may age Meseta are found the Cabo Ortegal. related to volcanism. with subsequent remobilization due to Santiago de Compostela (only mafics exposed), Sobrado. Hercynian tectonism. Mellid and Lalin mafic-ultramafic complexes in Galicia, and

the Bragança (or Bragança-Vinhais) and Moráis mafic-

ultramafic complexes in Trás-os-Montes (northeast Por-

Cambrian iron tugal). The best known is the Cabo Ortegal complex which No important iron mineralizationis found in the Cambrianor consists of amphibolite, granulite and eclogite-facies ultra- supposed Cambrian of the northern and central mafics. mafics sequences and paragneisses. These complexes are mush- Meseta. However, iron assumes considerableeconomic intrusions and signi- room-shaped they are seen as mantle diapirs ficance in the south. whose emplacement was attended by high-grade metamor-

In southwest Spain a magnetite belt extends from and various phism other effects (van Calsteren et al., 1979).

near Córdoba to south of Badajoz (Vázquez Cuzmán & The ultramafic rocks (lherzolite, harzburgite and dunite) are

FernandezPompa. 1976). continuing in in the Elvas mantle. Portugal derived from the Rb-Sr whole-rock isochron dating of region (Fig. 2). In this metallogenetical province Cabo magnetite Ortegal Iherzolites indicates that intrusion took place of skarn Lower deposits type occur in Cambrian carbonates about 500± 100 Ma Calsteren ago (van et al., 1979). h aureoles of vv ii i n the contact Hercynian to granites quartz Little chromite occurs in these complexes, most perhaps in diorites. northeast Portugal where the Abessedo mine in the Thus, in central the Elvas region of Portugal, near Spain, massif has Bragança produced some thousands of tonnes of the Alagada deposit of stratiform magnetite bodies, totalling ore during the last world war. Extraction was on a small scale

one million tonnes at Fe, SiO, and 40",, 12% 0.73",, S, is and no chrome mines are working any more, for the chro- enclosed in Lower Cambrian marbles, calcsilicate hornfelses mitite deposits are small, irregular and mostly rather low- and skarns in with contact a Hercynian granite (Carvalho et grade. al., 1971a: Carvalho. 1976a). The chromitc occurrences in the Braganea and Moráis

In Spain several iron mines are found in this belt (San complexes in Portugal have been described by Cotelo Neiva

Guillermo near Monchi Jerez de los Caballeros, near Bur- (1947a). C'hromitite is present as vaguely bounded pockets, guillos del Cerro, Cala, Teuler, The is etc.). ore magnetite, lenses and layers in peridotite and serpentinite. The Abessedo

sometimes hematiteand siderite, and mine rarely averages 48-52",, worked chromitite pockets 40 Cr grading 48",, 20,; Fe, with sulphur and silica as principal impurities (1% S or some to 1500 ehromite. pockets yielded up t In these ores over); the is (Doetsch, chromite phosphorus content negligible 1967). is associated with serpentinized olivine. The most important is Cala, with hundred deposit over a Platinum occurs as minute inclusions in chromite (Cotelo

million tonnes of Here reserves. magnetite associated with Neiva. 1947a. b). 30

ORDOVICIAN

of During the Upper Cambrian a phase folding, tilting, uplift

and erosion, often called the Sardic phase, affected the

which Cambrian over a considerable part of the Meseta, after

the Ordovician transgressed (Schermerhorn, 1955, 1956).

Thus the Cambrian-Ordovician junction is conformable,

disconformable or unconformable in different localities.

The Lower Ordovician generally begins with quartzites that

in reach a few hundred metres thickness, locally underlainby

conglomerate. This level is the so-called ArmoricanQuartzite,

well developed in central and west Iberia but thinning out in

southern Spain and Portugal, where Silurian overlies Cam-

brian carbonates,and in north Portugal and northwest Spain. interbedded volcanics. In a few places the quartzites enclose

of dark trilobite The quartzites are followed by a sequence slates, and the Upper Ordovician contains slates, sandstones

and locally limestones. Felsic and mafic volcanism took place

of during the deposition of these sequences. Towards the end

the Ordovician tectonic movements caused local uplift and

the Ordovician-Silurian emergence, and junction, though Fig. 4. Distribution ofLower Ordovician ironstone deposits around mostly conformable, can be locally disconformable or even an emerged landmass in the northwest Meseta. Stippled: zone in unconformable. During the late Ordovician some granites ironstone hatched: which occurs; probable land during Ordovician. east-central Por- and peralkaline massifs were emplaced in After Ribeiro (1974). tugal and western Galicia (Priem et al.. 1970).

Ordovician iron

and The Lower Ordovician quartzites of the northwest Meseta proportions of siliceous and aluminous gangue, are in often enclose stratabound marine-sedimentary iron-ore de- characterized by phosphorus contents, apatite and col-

that exceed 1967; Carvalho. posits, especially near or at their top (Ribeiro & Rebelo, 1971 ; lophane, may 0.8",, (Doetsch,

Armengot de Pedro & Campos Julia, 1971; Ribeiro. 1974). 1976a).

Ponferrada in northwest They show a sedimentary facies indicating deposition in a The largest deposits are near Spain

shallow (Coto Vivaldi, Coto Wagner mines) and Moncorvo and epicontinental sea and owe their existence to the

sometimes that arose as a result of the Marâo in north Portugal. The ore is mostly oxidic. palaeogeographicalconfiguration

tectonic movements The sideritic or chamositic. Guadramil in northeast Portugal is a Upper Cambrian (Sardic phase).

deposit of oolitic siderite in this horizon. The Marâo mine northwest corner of the Meseta remained as an emergent

landmass Lower exploited magnetite interbedded at the top of the quartzites during the Ordovician while around it the less eroded and in the overlying slates; the ore is metamorphic (Priem, Ordovician quartzite transgressed over more or

The iron-ore Lower 1962). Cambrian strata. deposits in the Ordo-

in north- vician surround this landmass, to Ribeiro and By far the largest occurrence isMoncorvo according

since and Ribeiro the for the iron east Portugal, which has been intermittently worked Rebelo (1971) ( 1974), source area

be 1.5 think have been leached from weathered the 13th century and is to developed into a million tpy which they may exceed million mafic rocks 4). producer in the near future. The reserves 550 (Fig.

be billion (J. A. Rebelo, The iron in coastal waters, mostly oxides, in tonnes and may as high as one tonnes precipitated as

the is low Fe) and silicate or carbonate, on local physi- pers. comm.) though average grade (36% places as dependent the phosphorus content (0.4-0.5%) troublesome. The main cochemical conditions. After some current transport, the ore

deposit is 8 km long by 1 km wide and occurs in the north became concentrated in local accumulations. for limbof the Moncorvo synclinorium. A smaller deposit, 0.5 by Spain has no large iron ore production, unlike instance

Sweden or Russia. The mine, the 1 km in size, is found in a syncline nearby. These deposits have France. largest Marquesado

been in the southeast, 3 million tonnes of folded and suffered regional andcontact metamorphism open pit produces per year from The ore is mainly hematitic. ore in Triassic' limestones, reserves during the Hercynian orogeny. hematite-goethite Fe. including spéculanteand martite, and rather siliceous. Below estimated at 100 million tonnes grading 55-56",, Spanish

80-100 indicate decline in iron ore a depth of m magnetite predominates (Rebelo, pers. production figures a output:

comm). Banded ore/quartzite alternations are frequent. The 7,684,000 t ore (50% Fe) was produced in 1976, 10.8",, below

the 1974 orebodies occur as distinct levels in the upper part of 1975 production, itself 4.3",, below (Mining Mag.,

Armorican into 51,989 t he- quartzite formation and pass laterally quart- August 1977). Portugal produced magnetite,

matiteand in 1977 (Bol. Minas (Lisboa), zites. They were deposited in a shallow sea, apparently as ferromanganeseore

crossbedded iron oxide sands (Thadeu, 1952, 1965a). The December 1977). These figures illustrate the potential impor-

of the Ordovician iron ores of northwest Spain and north Portugal tance within the Iberian context Moncorvo orebody

with its reserves. are low to medium grade (up to 55% Fe), contain varying enormous 31

Ordovician antimony releasing mercury preconcentrated by adsorption in Ordo-

In northwest Spain antimony has been mined from several vician carbonaceous muds and transporting it into overlying

small associated with Ordovician Silurian the and rede- deposits Upper (Ashgill) sands where mercury was trapped

carbonate lenses. This is interpreted as a synsedimentary posited by sulphidization. Maucher (1976) considers such an

in mineralization a shallow-marineenvironment, remobilized and a volcanic for the origin unlikely proposes source Hg.

and The redistributed during the Hercynian orogeny. origin of the Sb could be sought in earlier Ordovician volcanism. Silurian base-metal sulphides and magnetite

with pedological concentration during subsequent emer- In the lead-zinc-magnetite belt of south Por-

and the coast erosion gence, redeposition along following tugal (Fig. 3) and southwest Spain, as discussed, massive

(Guillou. 1969, 1971a). and sulphide magnetite orebodies occur associated with

volcanics overlying the Lower Cambrian carbonate level.

SILURIAN These in south volcanics, Portugal, are greenstones or green-

schists (intermediate to mafic metavolcanics) enclosing

The Silurian of the Meseta This usually presents a monotonous lenses of marbles and calcschists. formation passes up

facies of dark graptolite slates with frequent interbeds of into felsic metavolcanics, likewise associated with calcareous sandstone, limestone and black chert (lydite). The Upper metasedimentsbut not containing orebodies.

Silurian often is In south the Lower Silurian Al A 1 zinc south sandy. Portugal is the g a r e s prospect in Portugal the two

highly volcanic, with abundant levels of mafic and felsic types ofsulphide mineralizationcharacteristic of this metallo-

extrusives. In northeast and northwest the belt Portugal Spain genetic (see above) are met with: in depth, beneath a

Silurian is thick developed as a eugeosynclinal facies of flysch- gossan, a massive pyritic mineralization overlies a dissemi-

type turbidites. greywackes and slates containing black chert nated Pb-Zn mineralization. The first consists of banded to

layers, with plentiful felsic and mafic volcanics. almost massive orebodies made mostly of pyrite, with sub-

Near the base ofthe Silurian iron ordinate barite, occur important mercury, pyrrhotite, magnetite, sphalerite, and some

and base-metal mineralizations.At levels higher stratabound chalcopyrite and galena. These occur at the base of pre- scheelite is found. sumably Silurian greenstones (intermediate to mafic meta-

The Silurian-Devonian junction is generally a little dis- tuffs) which rest on Lower Cambrian dolomites containing

turbed transition. sphalerite, pyrite and galena veinlets (Andrade. 1969;

Goinhas, 1971; Carvalho et al.. 1971a, b).

Silurian mercury: Almadén Magnetite occurs disseminatedand as massive lenses

The celebrated mercury deposit of Almadén (i.e. 'the in the intermediate to mafic metavolcanics and has been mine' in Arabic) is by far the largest and richest known Hg worked in several small mines in south Portugal (Nogueirinha accumulation on earth. It is a stratiform mineralization and Monges near Montemor-o-Novo, Alvito, Pedrógao,

of three most consisting cinnabar-impregnated quartzite layers, Orada and others) the important ofwhich was Orada

each about 10 m thick, within the formationknown where quartzite (Fig. 3) mining ceased in 1971 (its original reserves were - as 'cuarcita del criadero' (ore-deposit quartzite). This two million tonnes quart- Carvalho, 1971, 1976a). Magnetite may zite horizon is the host of the ore at Almadén and several much be accompanied by pyrite, locally plentiful, and pyrrhotite

smaller occurrences in the area. (Carvalho. 1971; Carvalho et al.. 1971a. b). The largest

The at Almadén reached (cinnabar and known grade 20",, Hg orebody reached 30 m thickness by a length of about native mercury) in some places in the richest lodes. Even richer 250 m.

is the recently (1975) discovered cinnabar deposit of El The polymetallic pyritic lenses at the base of the

Entredicho, 17 km from Almadén, where ore consisting of greenstones and the magnetite-pyrite-pyrrhotite lenses within 50",, cinnabar (Bol. Geol. Minero (Madrid), vol. 89, the occurs greenstonesare now mostly regarded assyngenetic exhala-

1978, The worked p. 188). average grade of the Almadén ore tive-sedimentary deposits (Andrade, 1969. 1972; Carvalho, the first of this during quarter century was 8"„ Hg, around 1971. 1976a; Carvalho et al., 1971a, b).

1940 it was still 6-7",, Hg and it is now around 1.5",,. No other mercury deposit anywhere has ever approached these ex- The Maria Luisa mine near La Nava in the Sierra

rich Almadén tremely grades. accounts for 18",, of world Morena is an old cupriferous pyrite exploitation now worked for with mercury production. copper goldand silver as byproducts. The ore consists The cuarcita del criadero is by analogy considered to be of of pyrite with chalcopyrite and sphalerite, and in places Silurian the Almadén Early (Valentian) age. In area, mafic magnetite and pyrrhotite. The minerals are concentrated in volcanism started before the deposition of this quartzite bands parallel to the metamorphic layering in the host rocks formation and continued afterwards the Silurian and and during (greenstone, jasper schist). Detailed studies of the com- Devonian. plex paragenetical relationships by Vázquez Guzman (1972, The cinnabar, native and 1974) accompanied by quicksilver some revealed the existence of syngenetic sulphide and pyrite, shows features its in- mineralizations sedimentary indicating early magnetite on which an epigenetic sulphides- troduction, before diagenesis (Saupé, 1976). Saupé suggests a magnetite assemblage has been superposed through skarn- direct genetic relationship between the Hg mineralizationand type (re)crystallization (with diopside, actinolite and epidote)

the Silurian volcanism which reached its greatest development caused by diorite intrusions. in the mineralized area, in the sense that the Lower Silurian Maria Luisa and other occurrences in the same region

volcanic activity set into motion the convection of solutions originated as submarine exhalative-sedimentary sulphide ac- 32

tin cumulations in volcanic horizons and associated jaspers: panying may be of sedimentary or volcanic origin.

too However, though the Silurian contains volcanics in the locally the jaspers contain manganese ore. The age of

of the scheelite beds, this is not for the Cambrian. It these ores is uncertain since their host rocks have not yet been vicinity so

Middle Devonian is difficult to the of dated. They were regarded as to Upper by moreover explain preference syngenetic sediments. is needed. Vázquez Guzman and Fernández Pompa (1976). Other au- tungsten for marly More study

Monseur thors, such as (1977), favour a Cambrian age. Still,

of these DEVONIAN since the syngenetic stratiform ores occurrences are

least volcanic-associated) sul- clearly a volcanogenic (or at

phide-oxide mineralization,of the type foundin the lead-zinc- Over most of the Meseta the Devonian presents a variable

Lower facies of interbedded sandstones, shales and magnetite belt, a Silurian age seems possible. epicontinental

carbonates not attaining any great thickness.

In Galicia, the metasedimentsand meta volcanics surrounding In northeast Portugal and part of northwest Spain the Devonian is and in the the Cabo Ortegal mafic-ultramafic complex, formerly a flysch-type greywacke-slatc sequence

thought to be Precambrian, have recently been shown to be of southwest Meseta (the Iberian Pyrite Belt) it consists of

Devonian shales with and limestone beds. Silurian and, possibly, age (Martinez Garcia et al., monotonous quartzite rare

mafic, 1975; van der Meer Mohr. 1975). In the Moeche area and Devonian volcanism, mostly is rare. No important

elsewhere in the same zone occur small stratiform massive to mineral deposits are associated with the Devonian.

disseminated orebodiescontainingpyrite, hematite and chal-

EARLY TO MIDDLE CARBONIFEROUS copyrite, interbedded among Silurian metasediments and

metavolcanics.

After the the Devonian lull, Carboniferous gave rise to

Asbestos (tremolite-actinolite) has been worked on a extensive mineral resources of some importance in the Iberian

in Devonian-Carboniferous small scale in the Arado do Castanheiro mine near Portel economy. At the boundary the

Meseta became differentiatedinto a central block which south Portugal, in a small mass of serpentinized ultramafics large

associated with metaspilites belonging to the presumably emerged and two flanking troughs in which subsidence and

continued. The central block the Silurian greenstone formation overlying the Cambrian car- sedimentation englobes

bonates (Gaspar, 1971; Carvalho et al., 1971b). West Asturian-Leonese, the Central Iberian and the Ossa-

Morena Zones. The flanking troughs are the Cantabrian

Silurian scheelite Zone in northern Spain and the South Portuguese Zone in

As mentioned above, scheelite disseminations are found in south Portugal and southwest Spain (Fig. 2). These external

cale-silicate interbeds (amphibole schists: originally impure basins are secondary geosynclines that were to a large extent

marls) in the greywacke-slate sequence of the Beira Schists in fed by detritus from the central block, a geanticlinal source

northern Portugal and western Spain. Similar tungsten mine- area. This block is composite, containing internal basins,

ralization occurs in the calc-silicate intercalations in the thoughthe Upper Palaeozoic sediments here deposited do not

Silurian greywacke-slate facies of northeast Portugal and reach the great thicknesses attainedby contemporarystrata in

adjacent Spain (L. Ribeiro, 1971). the flanking troughs in northern and southwest Iberia.

However, the Silurianmetacalcareous interbeds containing As a result, marine Carboniferous up to and including

the this mineralization are unlike the amphibole schists of the Westphalian strata is well represented in Cantabrian

in from Chain and the South Zone. In the Cantabrian Beira Schists aspect: they range fine-grained, thinly Portuguese

Lower banded rocks consisting of quartz, intermediate plagioclase Chain the Carboniferous is very thin, a condensed

and varying amounts of garnet, actinolite-tremolite,epidote- marine succession of shales and limestones not bearing

such mineral The South Zone, on the other group minerals, sulphides and other minerals as diopside resources. Portuguese

(Sousa, 1975: Noronha, 1976) to skarns (L. Ribeiro, 1971). hand, is the site ofthe Pyrite Belt geosyncline and here a thick

in Cambrian and into Scheelite may be of wider distribution eugeosynclinal sequence was laid down, divided three

intercalations conformable Devonian shales and the Silurian metamarly than was previously sup- groups. quartzites.

overlain Low- posed. Carvalho (1971) refers to the occurrence of some Phyllite-Quartzite Group, are conformably by

dispersed scheelite in Silurian calc-silicate hornfelses near the er Carboniferous volcanics and sedimentsof Tournaisian and

old Orada iron mine in south Portugal. Early Visean age, the Volcanic-Siliceous Complex which

In northeast Portugal the Cravezes scheelite prospect hosts the Pyrite Belt mineralization. It is covered confor-

a thick barren of turbidite is being actively explored. Mineralizationextends over three mably by flysch sequence grey-

calc-silicate horizons up to 34 m thick and up to 2.5 km long wackes and shales, the Culm Group which ranges from the

(Sousa. 1975; Viegaset al., 1976). Provisional tenors obtained Upper Visean into the Westphalian A in south Portugal.

then by surface sampling before drilling started are as follows: Géosynclinal deposition was brought to an end by

1.43-3.2 W0 that is 1134-2538 W. and 420-770 (Schermerhorn. 1971a: Carvalho et al., 1971b. 1976). kg/t 3. ppm orogeny Sn. ppm

It seems likely that most of the tungsten in these marls is Early Carboniferous base-metal sulphides: the Iberian Pyrite

It syngenetic. may have been deposited as scheelite or, as Belt

The Noronha (1976) proposes, originally dispersed tungsten may Iberian Pyrite Belt (Fig. 5) is a metallogeneticprovince of

been remobilized have by metamorphism to produce polymetallic pyrite deposits, copper and copper-zinc dissemi-

In either scheelite. case the syngenetic tungsten and accom- nations, some copper veins and manganese orebodies. oc- 33

Fig. 5. Geology and major pyritite deposits in the Iberian Pyrite Belt. Note regular spacing of the large deposits. Adapted from Carvalho et al.

(1976).

km 30 km wide. here diabase and cupyingazone230 long by up to Mining sills), sulphide deposits manganese ore deposits.

The the is goes back forat least 30 centuries, at first for copper and noble sulphide mineralization and most of manganese

metals, since 1866 also for sulphur, with iron and other metals genetically linked to the felsic volcanism in the geosyneline Madel, Carvalho a byproduct. Annual production of pyrite ore is 2.5 3 million (Schermerhorn. 1971a; Strauss & 1974; et

double al.. 1976; Strauss el al.. 1977). tonnes but new projects in Spain and Portugal aim to

this figure. The Spanish Pyrite Belt contains five large pyrite The pyrite deposits of this belt are lenticular or sheetlike

three Zarza occurrences of which are large mines, Tharsis, La bodies conformably interbedded among volcanics and/or

sediments: felsic onto shales and Rio Tinto, while Aznalcóllar will soon enter production they overlie volcanics or overstep

and Sotiel Coronada is still under study. In addition there are and siliceous slates (dust tuffs) or may be wholly enclosed in

several smaller workings. In the Portuguese Pyrite Belt three shales, as at Tharsis. The felsic important occurrences, together with some smaller ones, are, volcanism was explosive, along submarinestrike

or have been, worked: Aljustrel, Sao Domingos and Lousal. fissures (Schermcrhorn, 1976). and generated mostly sub-

is from flow with few Most The annual production of Aljustrel to be raised aqueous tuffs, lavas and breccias. pyrite

300.000 to 2 million tonnes. occurs at or near the top of felsic piles: it was produced at the

ofthe Iberian of end of when the waned. The Iberian Pyrite Belt is the type area type an eruptive cycle explosive activity In

volcanogenic polymetallic pyritic deposits (as discussed at the each mining centre the mineralizationis related to aneruptive

end of this section). These are stratiform, associated with centre and occurs at one. or rarely more, stratigraphie levels.

felsic with small When felsic each have its volcanism and are composed of pyrite two cycles are present, may pyritic

and other mineralization, proportions of chalcopyrite, sphalerite, galena so there will be two ore levels (Strauss &

minerals. Massive pyritic deposits of this and other types Madcl. 1974; Ramirez Copeiro del Villar. 1976). However, the

consist of p y r i t i t e (Schermerhorn, 1970). timing of sulphide deposition varies between centres: it is of sediments The Volcanic-Siliceous Complex consists relatively early, Tournaisian, in some mines, and rather late.

( including prominent jaspers), felsic volcanics (largely quartz- Lower Visean, in others where microfossils in associated

keratophyric tuffs), maficvolcanics (spilite lavas and tuffs and limestones permit dating, as at Sotiel Coronada. As a result. 34

the local volcanic and ore stratigraphie columns cannot be and still to be discovered, and applying Zipfs law. the total

correlated from mine to mine: detailed stratigraphy at Rio amount of sulphide deposited in the Iberian Pyrite Belt will

Tinto is quite differentfrom Tharsis to the west or Aznalcóllar have been somewhat over 2 billion tonnes.

to the east. This fact has sometimes been ignored. The distributionof this enormousamount over the 230 km

The orebodies be divided into autochthonous of the may length Pyrite Belt presents a regular rather than a

and allochthonous deposits. Some of the pyritite random pattern. The large pyritite deposits are isolated:

where the bodies enclosed in felsic volcanics are autochthonous, as at other orebodics are foundin same area they are very

Rio which is that overlie feeder A lie Tinto, to say they zones, now much smaller. plot of the large deposits shows them to at

stockwork pipes strongly alteredby chloritizationand silicifi- roughly similar intervals (Fig. 5). The Neves-Corvo prospect,

cation (Strauss & Madel. 1974; Williams et al.. 1975). This is a large blind orebody was only discovered in 1977. and the

relatively rare in the Pyrite Belt where most pyritite has apparent lack of significant mineralization in the interval

between suffered some transport during or shortly after its original Aljustrel and Sao Domingos, which seemed twice as

the the normal strike precipitation on seafloor as a very fine-grained pyritic large as distance between comparable

mud. subsequently consolidating elsewhere as allochthonous pyritite bodies elsewhere in the Pyrite Belt, was an incentive to

stratiform The is and that thus deposits. pyritite usually thinly rhythmi- prospecting in area. It seems that large accumu-

bedded, in the autochthonous of tonnes cally except deposits overlying lations pyritite. 20 million and over, were only

their own feeders. The frequent occurrence of internal struc- produced at distances between 23 and 35 km. La Zarza and sediment tures denoting primary movement, such as small Sotiel are separated by 12 km only but this is across the strike cut-and-fill. and in folded and the distance slump structures, low-angle crossbedding a strongly area original must have

graded bedding, together with the varying lithological en- been at least twice that amount. Between the major deposits

vironmentof the orebodies. from volcanic to sedimentary, led numerous small deposits were generated in the Spanish Pyrite

to the recognition of allochthonous pyritic masses mobilized Belt but not curiously enough in the Portuguese halfof

and redeposited by gravity flow at some distance downslopc this orefield where only a few small occurrences are known

from the feeder vents (Schermerhorn, 1970, 1971b). The beside the four large deposits. is first the seafloor around exhalative There four main of pyritite precipitated on are alignments sulphide mineralization

orifices is in as a sulphide gel containing pore water (seawater). along the strike. The most northerly alignment Spain and

Thixotropic gel-sol transformation causing liquefaction of comprises several small to medium-sized deposits such as

sulphide muds is the mobilizationmechanism,and the gravity Concepción. The next alignment joins Rio Tinto. La Zarza

gradient existing on the slopes ofsubmarine volcanoes sets the and Sao Domingos. The third alignment has A/nalcóllar.

times The instable mass in motion. This process, many repeated, Sotiel, Tharsis and Aljustrel. southernmost alignment is

the well-bedded produces allochthonous pyritite lenses. Far- in Portugal and runs through Lousal and Neves.

thest travelled, away from the volcanic feeder vents, are the

orebodies overlying sediments on the basin floor. Thus there Very approximately, the known pyritite reserves of 620

is from All a gradation proximal to distal pyritite deposits. million tonnes present the following average composition:

Pyrite Belt pyritite is exhalative-sedimentary in the sense that sulphur 46 "„

it laid down chemical sediment, was originally asa iron 40 "„

namely a hydrothermal surface precipi- copper 0.7%

then be t a t e. The transported allochthonous pyritite may zinc 2.9% termed exhalative-resedimented since it has been redeposited lead 1.1% at some distance from the site of primary precipitation. arsenic 0.6%

Usually the autochthonous pyritite bodies are large single gold 0.8 g't lenses sheets, Rio Tinto et al., or as at (Williams 1975) or La silver 30 g/t

Zarza (Strauss & Madel, 1974) while the allochthonous

deposits often occur in clusters: five pyritite lenses at Tharsis The remainder is largely siliceous, chloritic and carbonate

North and eighteen at Lousal (Strauss & Madel, 1974). gangue: as the high sulphur content shows, most pyritite in The Iberian Belt Pyrite contains several pyritite deposits of this province is massive sulphide ore of high purity.

accumulations in In the is giant size, the largest sulphide the world. the very large deposits copper tenor low. 0.3-0.7",,.

Most Rio Tinto important was where owing to folding and though zinc can be relatively high, up to 4-5",,. It appears to be and subsequent uplift erosion most of the original deposit has a geochemical law in the Pyrite Belt that pyritite bodies been removed. had folded It been into an anticline, with exceeding 30 million tonnes, or over 40 m thickness, do not

in tenors pyritite left the northand south limbsand as a gossan on its contain over 0.7",, Cu. Higher copper occur in smaller Reconstitution crest. by unfolding yields an original pyritite orebodies (up to 2"„ Cu) and locally as oreshoots in larger sheet measuring approximately 4.5 km long by 1.5 km wide pyritite masses. and to 80 m thick 1971b). This leads to up (Schermerhorn, an Vázquez Guzman (1976) has established that primary

of billion tonnes. and hematite, with siderite. original tonnage roughly three-quarter magnetite together some appear

in the Belt total in of Present reserves Pyrite 620 million tonnes small quantities in pyritite. especially in the northern part (Carvalho et al., 1976). Largest are the reserves of Aljustrel the Spanish Pyrite Belt. (250 million tonnes) and Tharsis (130 million tonnes) while

Rio 55 The dissemi- Tinto still has million tonnes. Taking into account the massive sulphides may be associated with amount of pyritite removed by erosion, extracted by mining nated sulphides constituting syngenetic (pre-folding) 35

or epigenetic (post-folding) stoekwork ores underlying mixture of juvenile sulphur associated with the felsic vol- stratabound pyritite deposits, or syngenetic ores in hanging canism and of sulphur derived from seawater sulphate.

slates. contain wall or footwall tuft's and These may workable Seawater in circulating as pore water the tuff piles building the of and and reach proportions chalcopyrite. sphalerite galena, submarine volcanoes and participating in convective hy- - This of mineralization sulphides dilu- drothermal large tonnages. type systems driven by magmatic heat, would supply - ted by volcanic material at the source is common though the sulphate sulphur component. The Iberian ore carries an

not often economic. wide extremely range of metals (Schermerhorn, 1971b): tin,

for is instance, widespread, occurring as cassiterite. sometimes

accompanied by stannite (Aye & Picot. 1976). The source of Of considerable and explorational metallogenetic interest are the metals would be volcanic too, either directly from the two lithofacies that chloritite and accompany pyritite: jasper. magmatic residue or by leaching from volcantes.

C h i named 1 o r i t t e, first studied and at Aljustrel. consists As the is the end geology shows, pyritite deposited at of a of mostly a fine-grained chlorite aggregate contain- volcanic from generally cycle, hydrothermal solutions discharging on ing disseminated sulphides and sometimes carbonate; it the seafloor and volumes of may building up large very pure

grade into chloritic tuffs. When cleaved it could be, and has active sulphides. During volcanism the hydrothermal process

been, mistaken for black slate. Chloritite be bodies may found cannot take place without interruptions and the sulphides in the footwall or sometimes in the hanging wall of pyritite produced are scattered. Moreover, the mineralizing fluids

deposits, and reach 50 m thickness. At Aznalcóllar may a bringing the sulphides were accompanied by solutions from massive pyritite orebody is overlain tuffaceous chloritite which chlorite by and silica were deposited, within the vents

carrying copper-zinc sulphides. Chloritite (chloritization and mostly occurs near silicification of footwall tuffs) or on the

or at the of In a similar periphery an orebody. peripheral surface (primary chloritite and jasper). The Mg. Fe and Si position, generally beyond the and ore boundary slightly needed for these processes are likely to be of volcanic origin

higher are jasperlenses, silica rocks contain- stratigraphically, too, either directly or indirectly.

ing some chloriteand but pyrite mostly poor or lacking in iron The mafic volcanism of the Pyrite Belt mafic to in-

oxides, unlike the red or black to - jaspers unrelated sulphide termediate spilites and diabases is completely distinct from mineralization. the felsic volcanism, showing no transitions. Though the

Pyrite, chlorite and silica are associated, as mafics intimately are likely to be mantle-derived, such an origin seems bodies of pyritite, chloritite and jasper, or intergrown and less probable for the felsic volcanics, and the few known initial

even interlaminated.This association is the 87 8b widespread world Sr/ Sr ratios favour a crustal origin (Schermerhorn, 1976).

over, a volcano constituting genie sulphide- fsuch is the then the and metals 1 case, sulphur brought up by chlorite-silica association. the either have magmas an origin in remelted Precambrian Chlorite and silica accompany sulphide precipitation both rocks, or have been transferred from mantle-derived mafic

as subsurface replacements in the feeder zones underneath to felsic magma ascending deep-crustal magmas, a problem

autochthonous and as surface of pyritite deposits accompanying awaiting resolution. Either type source involves a pre-

autochthonous and allochthonous Chloritization pyritite. existing sulphur-metals concentration, to explain the vast and silicification of footwallrock in alterationpipes is caused tonnage of Pyrite Belt deposits. by syngenetic hydrothermal activity around the feeder chan-

nels below the seafloor on which pyritite was deposited. Such

replacement bodies show irregular, discordant Chlo- to shapes. According their volcanic environment there can be distin- ritite and jasper on the seafloor, deposited as volcanogenic guished three types of volcanogenic poly- muds (they may grade into tuff) and metallic transported downslope p y r i t i c deposits, grading from massive with allochthonous along pyritite masses, are stratiform, (pyritite) to disseminated.

concordant bodies. Chloritite deposits were formed im- The is found - 1. Cyprus type in the mafic ( s p i 1 i

mediately preceding, and sometimes the of lavas i succeeding, phase tic) at the top of o p h o 1 i t c complexes. sulphide precipitation, while the jasper represents siliceous The best known example is Cyprus and similar deposits have precipitation occurring slightly later in and travel- been described from Newfoundland sequence, and elsewhere. This type ling farther out. represents polymetallic sulphide mineralizationin an oceanic

environment, outside continentalplates.

2. The Iberian is f 1 type linked to submarine e s i c

Pyritite originates through an interaction between volcano- volcánica (often quartz keratophyres) and it comprises genie emanations and seawater that rise the gives to pre- most of the important pyritite deposits through time and of cipitation colloidal on the seafloor sulphides (pyritite may space, the Iberian Belt. This including Pyrite type may be show colloform gel textures). There is a whole found original range along or within continentalplates. of possibilities between the of volcanic heat here, extremes 3. The B e s s h is with - i type associated n o n only plus seawater all the of supplying components pyritite. ophiolite mafic and intermediate vol- and of seawater chill hot only serving to upwelling ore ca n i c s, along or within continental plates.

solutions wholly of volcanic to origin, precipitate pyritite. Though the Iberian type is sometimes called the Kuroko it However, appears likely, in the of data on the type, the kuroko form light ores a subtype of infrequent occurrence isotopic constitution ofsulphur at Rio Tinto (Williams et al., and smalltonnage. Briefly, the differences between

1975) and a the elsewhere, that the sulphur in pyritite represents Kuroko and Iberian types are as follows: 36

mineralizationis restricted in timeand took 1. Kuroko-type space. place in an oxidizing environment, after pyritite de- - (Miocene in unlike the Iberian - Japan), widespread type (from position underreducing conditions had ceased or else at

the Archean all the world): distance on, over some from the centres of sulphide accumulation.

2. Kuroko small, 10 million Because the available exhalative deposits are exceptionally over Mn. an product, was not

tonnes; absorbed by sulphide precipitation, as was iron, it entered 3. Kuroko is black of' ore, consisting mostly sphalerite, seawater to be dispersed, presumably as a colloidalhydrosol. and barite. with little and this is from the volcanic galena pyrite chalcopyrite: Transport away sources under the in-

of flucence of not base-metal-carrying pyritite such as makes up the bulk gravity and sea currents did not lead to complete the Iberian type deposits: dispersal by dilutionwith seawater, for no thin extensive beds

4. Oko, the of the yellow pyrite-chalcopyrite ore (pyritite) underly- manganese ore are known. Rather, manganese deposits

ing most kuroko ore, is less well developed than kuroko, is form lenses strung out along a favourablehorizon. Accumu-

often bounded kuroko. and is with sharply against coarser-grained lation of manganese mineral gels, together silica gels

than most In bodies of the Iberian the must pyritite. pyritite type producing jasper, therefore have depended on mass

transition from a copper-rich lower to a zinc-lead-rich upper transport and settling in situ.

part of the deposit takes place gradually:

5. Abundantbariteand kuroko and MIDDLE gypsum accompany may CARBONIFEROUS

even be more important than the sulphides but are rare

elsewhere; Within the Westphalian the break takes place that separates 6. Kuroko is associated with lava domes and tuff breccias géosynclinal from orogenic evolution in the Hercynian se-

formed by vent explosions; true tuff is extremely rare. In the quence, and mainly syngenetic from mainly epigenetic mine-

Iberian Pyrite Belt tuff is the normal felsic rock, tuff breccias ralization episodes.

and are infrequent lavas are rare; Tectonic movements largely ofepeirogenic character made

7. Every lava dome in the Kuroko province has its kuroko their influence felt at various times during the development of

and allochthonous kuroko has not been the deposit, transported Hercynian geosyncline. leaving their traces as more or less

in black over great distances; kuroko is very rarely found a widespread disconformitiesandunconformities. They did not

shale environment, As unlike the Pyrite Belt where even very involve Meseta-wideorogenic deformation. we have seen,

be in large deposits may sited shales. one of these tectonic phases, acting at the end of the

Devonian, caused emergence of the central Meseta block and

in and Copper veins have been worked at many places subsidence of the Cantabrian and South Portuguese external

near the Pyrite Belt: they are crosscutting epigenetic quartz geosynclines. This phase is sometimes equated with the

veins containingchalcopyrite and some other minerals, and Bretonian orogeny and considered to be the first Hercynian

are post-orogenic since they cut folded,cleavedand metamor- orogenic phase. Succeeding phases are largely of the nature of

Culm the This phosed strata, youngest Pyrite Belt group. epeirogenic movements, as for instance the uplift during the mineralization could well have Visean of the originated by remobilization source area in the southwest part of the central

of cupriferous pyritite in depth. block that gave rise to the deposition of the thick widespread

Culm group in the South Portuguese Zone, the second most

Early Carboniferous manganese extensive sedimentary unit, after the Beira Schists, in the

Manganeseore deposits are far more numerous than sulphide Meseta.

in the Iberian Belt much When full-scale in with occurrences Pyrite though always orogeny set the Hercynian main

smaller: extensive manganese mineralization was much more phase, orogenic development superseded géosynclinal sedi- but less intensive than mineralization. pyritite The total mentation in the two external remnants of the Hercynian

of amount manganese ore produced in this belt is about 5 geosyncline, the Cantabrian and South Portuguese Zones.

million tonnes, from a few hundred occurrences. The last

mines abandoned the were some years ago. Hercynian orogeny: main phase Where found in the neighbourhood of pyritite. as at The main Hercynian folding took place during the West-

than the Aljustrel. manganese deposits are slightly younger phalian (Schermerhorn, 1956, 1971a). The evidence for this sulphide mineralization. Most of them have been mined for is principally of two kinds: firstly, everywhere in the Meseta oxides, derived from secondary manganese rhodochrositeand the older géosynclinal formations up to and including the rhodonite in often associated with Visean depth. They are jasper and Namurian (where present) were folded before the lenses. deposition of the continentalcoal-bearing Middle to Upper The manganese deposits originated through seafloor pre- Carboniferous strata (mostly Upper Westphalian and Ste- of oxides, cipitation volcanogenic manganese hydroxides and phanian). themselves deformed by later Hercynian phases. carbonates, probably as a gel. Later metamorphic recrystalli- Secondly, this folding was accompanied by the development zation formed rhodonite, braunite. and other of and spessartite cleavage closely followed in many places by regional minerals (Thadeu, 1965; Carvalho et al.. 1971b. 1976; Cra- metamorphism. migmatization and the emplacement of the mer, 1976). Older Granites. widespread Many of these have been ra-

The orebodies are small in comparison not manganese only diometrically dated and their average age is around 300 Ma.

associated with the to the pyritite masses same volcanism but that is approximately Middle Westphalian (Mendes, 1968; ako to deposits elsewhere. Their Priem al., 1970; Leutwein manganese deposition as et et al., 1970: van Calsteren et al., chemical sediments fed from a volcanic-hydrothermal source 1979). 37

The succession of Hcrcynian phases and how they affected vician and Toumaisian granites are much rarer and arc not

unfolded or already consolidated regions is of importance in associated with mineralization.

the genesis of the Hercynian epigenetic mineral deposits. The designation of Older and Younger Granites serves to

Without entering into detail, it may be mentioned that the situate the two suites in time: it must be realized that either

in structural history of the Hercynian folding phases is still far group contains units varying texture, structure, mine-

from worked This is having been satisfactorily out. to a large ralogy, composition and environment. The distinction be-

extent to and due the prevalence of coaxial refolding the tween the two suites, based on crosscutting relationships, is a

scarcity of time horizons that can be used to distinguish valid one as radiometric dating all over the Meseta has shown.

between discrete phases. It is therefore difficult to assess the The Older Granites have been equated with an alkaline suite,

extent of deformational and whether pre-main phase episodes as leucogranites. in contrast to the Younger Granites as a

they involved epeirogenic or true orogenic movements. So far, calcalkaline suite (Capdevila. 1969; Oen Ing Soen, 1970;

it of the Meseta but appears that the large-scale fold structures Capdevila et al.. 1973) this chemical subdivision only

were laid out during the main phase, possibly starting during applies locally in the northwestern Meseta (Floor, 1970).

some local earlier folding. Later tectonic phases consisted of Elsewhere, as in south Portugal and south Spain, the Older

block movements affecting crust that had already been Granites often are calcalkaline rocks. Moreover, in the

in consolidated by main-phase folding, cleavage, metamor- northwestern Meseta also many Older Granites arc rich

phism and granite intrusion. These later phases only caused biotitc and show calcalkaline tendencies, with plagioclasc as

their true foldingin post-main phase sediments, and effect on calcic as andesineand evenlabradorite(Schermerhorn,1956).

the earlier of formations was tightening main phase folds and Also, many YoungerGranites show an alkaline, leucogranitc

differential vertical movements giving rise to faulting and trend, containing abundant albite and moscovite.

horst-and-graben tectonics. Granites were emplaced over the width of the Hercynian

the Zone Pervasive folding and shearing, with development of orogen in the Iberian Peninsula,from the Cantabrian in

cleavage, was only associated with the main phase, possibly in the north to the South Portuguese Zone in the southwest several Thisis illustrated the deformationof the subphases. by (according to Capdevila et al. ( 1973) granites are lacking in the

pre-main phase granites of Lower Carboniferous and Upper latter zone but this is erroneous: granites (granodiorite to

Ordovician become age which have gneissose (Priem et al., quartz diorite) occur in the Spanish Pyrite Belt). They arc

1970). The Older Granites, associated with the main phase, most abundant in the central block.

have not suffered similar tectonization, though they were The Older Granites are late-syntcctonic to post-tectonic

subjected to later Hercynian phases. Thus only the main- with reference to the Hercynian main phase, show concordant

phase deformationwas forceful enough to shear and gneissify to crosscutling relationships with their country rock (mostly massifs. schists), often of granite occur in areas medium to high-graderegional

metamorphism. may be associated with extensive migmati-

Westphalian talc zation, and range from gabbroic to granitic with quart/ At diorite Puebla de Lillo in León, the main talc producer in Spain. and granodiorite most common. They often show an

Namurianlimestone, the 'caliza de montaña", has been locally alkaline character, with albitic plagioclase. and they contain

transformed into talc by dolomitization and later silica biotite and muscovite. the latter frequently abundant. Yet

metasomatism during low-grade regional metamorphism calcalkaline rocks with oligoclasc to andesine and little or no

when silica derived from adjacent detrital sediments was muscovite are also known, especially in the southern Meseta.

redistributed; most talc is found near the contact with In the northwest Meseta fine to mediumgrained two-mica shales & Rodas. overlying Westphalian (Galán-Huertos granodiorites and granites arc common but sparsely to fully

1973). porphyritic rocks are found too. These granites often arc

As talc such, this important deposit may be classified as one leucocratic, containing rather less dark constituents than the

of the few metamorphic mineral deposits in the Iberian YoungerGranites, but the Older Granites also include rather Peninsula. Moreover, since the regional metamorphism is of dark varieties, not only leucogranites. In south Portugal and

this is the talc south Westphalian age. the age of too. Spain occur much more mafic Older Granites ranging from gabbros and diorites to granites; most frequent are

Hercynian Older Granites quartz diorites (tonalités) and granodiorites. Radiometric

Granite took in various the determined plutonism place episodes during ages by Mcndes( 1968) are mostly around 303 Ma

Priem Hercynian cycle (Mendes. 1968; et al.. 1970): but a few older (about 360 Ma) and younger (280 Ma) rocks

are present as well.

87 86 1. Late Ordovician 460 430 Ma The initial Sr, Sr ratios in the Older Granites of the

2. Ma Meseta between 0.709 values Early Tournaisian ca. 350 range mainly and 0.711; lower

Ma 3. Westphalian ca. 300 are rare but higher values are not infrequent.

4. Earliest Autunian ca. 280 Ma

MIDDLE TO UPPER CARBONIFEROUS The Westphalian and Autunian granites are distinguished

as Older and Younger Granites (Schermerhorn. 1956). a Géosynclinal sedimentationand the deposition ofsyngeneic and distinction originally based on structural relationships mineral resources came toan end with the onset of Hercynian later al.. 1970). After confirmed by radiometric dating (Priem et orogeny. the main Hercynian deformationhad run its These two suites present different characteristics. The Ordo- course, with widespread metamorphism and the emplacement 38

Ma the Meseta had 1976 well of world fluorite derives from of the Older Granites about 300 ago, or over 6"„ output)

become an emerged consolidated massif and the Upper this district.

Middle Carboniferous is characterized by continental deposits and The Lower Permian starts with a basal breccia on

coal measures. Carboniferous limestones and other rocks, on which sandy

breccia and Over most of the Meseta Upper Carboniferous and Per- limestones, dolomitesand sandstones follow.The by fluorite. According mian strata were laid down in isolated post-orogenic basins overlying sediments are impregnated

in these in- Forster this is stratabound minerali- formed by block movements. The sequences to (1974) a syngenetic

shallow-marine tramontane troughs characteristically start with orogenic zationof Lower Permian age, originated on a and the fluorite conglomerates derived from adjacent rising blocks and fur- shelf along a shoreline. The clastic material

ther contain shales and sandstones in continental to paralic derive from the emerged Cantabrian hinterland in the south,

The sediments contained facies, with coal seams. Some volcanism occurred locally. where the Palaeozoic already relatively

Puertollano coalfield in south-central Spain and some other much fluorite. However. García Iglesias (1978) admits an

basins also contain oil shales. epigenetic mode of origin for these fluorite deposits.

from The ages of thesesequences mostly range Westphalian D to Upper Stephanian and Autunian;some are Westphalian Hercynian Younger Granites

B (Ortuño, 1970; Wagner, 1971). The Younger Granites are late-syntectonic to post-tectonic the deformational These basins are numerous in Spain and Portugal and some with respect to Upper Stephanian phase worked for coal. Most caused of and older of them have been or are still being (this phase compression Stephanian

mines, is the central Asturian and took before the of the important, with many large synclines place just deposition

thick. Lower intruded all kinds of earlier rocks, Coalfield where the Upper Carboniferous is very Autunian). They

Older Spanish coal and anthracite output (excluding lignite) was including Granites, and form mostly crosscutting

11.9 million tonnes in 1977. Portugal produced 195,000 massifs. The YoungerGranites are largely calcalkaline rocks, and tonnes of anthracite in 1977. ranging in composition from gabbroic to granodioritic

granitic, but they are commonly granitic. Theirplagioclase is

later to andesine and the mica is biotite Hercynian orogeny: phases generally oligoclase mostly radioac- deformation can only be with less muscovite. Thesegranites are rich,in The ages of the later Hercynian usually monazite, xenotime, orthite) unlike worked out in areas where datedCarboniferous and Permian tive accessories (zircon,

An most (Schermerhorn, 1956) and be formations are present. unconformity usually separates Older Granites may

Stephanian B/C from earlier formations, due to tectonic associated with abundant pegmatites and aplites. Coarse

of the Autunian biotite with abundant movements Early Stephanian age. Similarly, porphyritic granite potash feldspar batholiths. in Portugal lies on folded and cleaved older Palaeozoic rocks megacrysts is common and forms large is the of but was itself folded and deformed, indicating a terminal A widespread phenomenon development potash

Granites Hercynian phase of post-Autunian age. As the Autunian feldspar megacrysts in cquigranular Older or earlier

consists largely of orogenic conglomerates, tectonic move- Younger Granites in the vicinity of porphyritie Younger

Granites, described fe ld- ments must have taken place shortly before their deposition, a process as potash-

the Late West- h i of earlier later that is, during Stephanian. Folded Upper spa t i 7. a t o n by granites (Scher-

and merhorn. This is a evidenced the phalian, Stephanian Autunian conglomerates may carry 1956). secondary process by distribution clasts from metamorphic and granitic rocks but have not irregular of newly crystallized potash feldspar fabric element themselves been regionally metamorphosed; the Younger megacrysts as an inhomogeneous superim-

consolidation texture of Granites cut the Westphalian and Stephanian, but not the posed on the homogeneousoriginal

Autunian. the affected older granites. Moreover, megacryst density

varies with the distance from the adjacent Younger Granite.

PERMIAN The megacrysts are few and far between in the distal facies of

potash-feldspathization, giving rise to sparsely porphyritie

The Permian of the Meseta continues the deposition of granite. They increase in abundance towards the adjacent or

continental facies in intramontane basins, though coal is underlying YoungerGranite next to which the proximal facies

is both much rarer. Most of it is Lower Permian, the Upper Permian of highly porphyritie granite developed. Apparently

in metasomatic introductionof deduced from modal being unknown Portugal and very rare in Spain. The potash (as and of Permian basins were formed by late-Hercynian epeirogenic analyses) metamorphic rearrangement already present chemical block movements and have themselves been deformed and potash feldspar (as deduced from analyses: Brink. the role. and the folded by the latest Hercynian movements. As a result, 1960) play a Potash-feldspathization accom-

Permian is covered disconformably to unconformably by panying processes of decalcification of plagioclase to albite

Triassic sediments, at the close of the Hercynian cycle. and muscovitization are contact-metamorphic effects exerted

by large intruding masses of Younger Granites.

Autunian stratabound fluorite Two aspects of the mcgacrysl development in older granites the In northern Asturia a fluorite mineralization is found in a need to be considered here. First, process ultimately

which must be Permotriassic basin developed on folded, eroded and plana- generates porphyritic granites distinguished

ted Carboniferous and older strata. This mineralization is from primary, magmatic porphyritic granites. Second, this

worked in several mines, together with vein deposits, and type of megacryst production in Older Granites or earlier effect of most of the Spanish fluorite production (275.000 tonnes in YoungerGranites is a contact neighbouringYounger 39

Granites and as such often coincides with close Sn-W minerali- Portugal indicated a spatial relationship with the coarse

zation. Thus Brink (1960) mapped a large area of equigra- porphyritic and related granites of the Younger Granite suite. nularOlder Granite in which of Hence two zones megacryst develop- a genetic link was deduced and the mineralization was

ment also sites of are tungsten mineralization which he dated as belonging to the consolidationperiod of the parent

ascribed to a buried Younger Granite. to granites, which is say Autunian. 87 86 Initial Sr/ Sr ratios in the Younger Granites vary from Later investigations in Galicia (Ypma, 1966; Capdevila, about 0.705 to higher values. Their abundant and varied indicated with 1969) a relationship two-mica granites re-

mineralization- in contrast to the Older Granites - seems to garded as Older Granites. For the northeast corner of

indicate a different in levels different mode source deeper or a Portugal, in eastern Trás-os-Montes, Ribeiro (1968) claimed of generation. The Older Granites often aluminous that are more tin-tungsten deposits were associated with two-mica

than the Granites as is Younger brought out by their higher granites (belonging to the Older Granite suite) emplaced into

normative corundum contents (Priem, 1962), indicative of the cores of antiforms originated during Westphalian oro-

sialic assimilation. In western the other hand, Spain, on occur geny. These deposits are quartz veins and some aplite veins the cordierite-bearing granites assigned to Younger Granites filling tension fractures normal to the antiformaxis. However, whose high alumosilicatecontent is ascribed to assimilation in the supposedassociation of tin-tungsten lodes with the Older

middle crustal levels & Bea, 1976). (Ugidos Granites, indicating an earlier episode of mineralization,has

been criticized (Conde et al.. 1971;Thadeu. 1973. 1977)and to

Autunian tin and tungsten date it has not been confirmed.

Historically the Iberian Peninsula has since pre-Roman times Could there have been two episodes of epigenetic tin-

been tin an important source of from lodes and placers in tungsten mineralization in the northwest Meseta, producing Galicia and northern Portugal. and ofidentical To this Spain Portugal are very deposits aspect'? answer question care must

minor tin in 1977 t producers now: Spain's output was 800 tin be taken not to confuse nature and age of the mineralizing

concentrate (containing 427 t tin metal) and Portugal pro- granites.

duced 369 t concentrate (at Sn), about a In the first much has 70",, together quarter place, too been made of a supposed

of British mine and a half ofworld production percent output. contrast between (older) two-mica granites and (younger) However. is with biotite Portugal an important tungstenproducer, granites, leading in some cases to incorrect assignment

1010 t W (metal contained in concentrates) in 1977 the first in of the of muscovite-bearing granites to group Older Granites.

Europe and no. 10 in the world, world is contributing 2.25",, to Muscovite a mineral occurring abundantly in the Younger

output. In 1974 the were Portuguese tungsten reserves put at Granites, and muscovitization. even greisenization of Older

10,0001 W. or ofworld the U.S. 0.53",, reserves, by Geological by Younger granites took place (Schermerhorn. 1956. p. 244). 350 W Survey. Spain produced t (metal content) in 1977. Secondly, the two-mica granites associated with Sn-W Modem of the tin and study tungsten ore deposits in the deposits in northern Portugal and Galicia show medium-

Meseta starts with Cotelo Neiva Tin is found (1944). in grained, mostly non-porphyritic textures, but "similar tex-

granites, and tures do Hercynian pegmatites, aplites, greisens hy- not signify similar ages" (Schermerhorn, 1956, p.

drothermal veins and stockworks, and derived from 249). quartz Medium-grained muscovite-bearing granites occur these are post-Hercynian eluvial and alluvial deposits. The among both the Older and Younger Granites, and the same main tin mineral is cassiterite; stannite and other for though rarer goes porphyritic granites. Such was confirmed by a study

minerals in occur, they are not worked. Tungsten deposits are of an area northernmost Portugal: Farinha Ramos et al.

hydrothermal quartz veins, stockworks and replacement (1972) showed the existence of two granitic cycles separated bodies with wolframite and scheelite mostly, as economic by a tectonic phase which caused deformation in the older

minerals, and furthermore stratabound scheelite dissemi- Either granites. cycle displays an identical succession from

nations which as we have well be of seen may syngenetic coarse porphyritic granites over medium-grained non- There also eluvial and origin. occur post-Hercynian alluvial porphyritic granites to fine-grained granites, and either cycle of little contains calcalkaline deposits significance. as well as alkalinerocks. Mineralization

The Sn and W lodes are found in a from is related to the zone stretching younger granites.

Galicia over northern Portugal and western Spain into Firm evidence as to age is provided only by the Younger

southern 2), which is to Granites Spain (Fig. say, mostly the Central where they intrude folded Stephanian strata; the

Iberian Zone of the new tectonic subdivision of the Iberian associated pegmatites, aplites, greisens and quartz veins

Massif or Meseta Julivert et al. (1974). mines Sn and W minerals by Working are bearing occur either withinthese granites lound in Galicia, Asturia, northern Portugal and western or in their country rock which consists of contact-

Spain. Most of the rocks outcropping in this zone are either metamorphosed sediments and potash-feldspathized and

Hercynian granites or Beira Schists and their equivalents, muscovitized Older Granites (Schermerhorn, 1956). The

with a lesser radiometric proportion ofOrdovician and Silurian rocks, and dating of these Younger Granites (Priem et al..

some strata of other 1970) defines ages. equally the Autunian age of these slightly

Except forthe tin and tungstenplacers and the stratabound younger mineralizations. For the Older Granites this kind of

scheelite, the tin and associated evidence is not available; tungsten deposits are closely unfortunately no supposedly

in and time with and are stanniferous Older Granites have space Hercynian granites endogenic yet been dated by a Rb-Sr ores. isochron.

The al. age of this epigenetic granite-bound tin-tungsten Conde et (1971)point out that the porphyritic granites characteristic mineralization has been in dispute. Studies in northern of Sn-W mineralization in most ol' northern 40

Portugal almost disappearin the northernmost regions where I. Disseminations

disseminated in muscovite or the ore deposits are associated with medium-grained two- cassiterite granite greisen

mica alkaline granites surrounded by contact-metamorphic II. Pegmatites aureoles. Furthermore, de Boorder (1965) has shown that a. cassiterite pegmatites with little or no tungsten

batholiths in b. wolframite with little or no cassiterite the coarse porphyritic granite forming large pegmatites

III. tes northern Portugal may grade into medium-grained two- A pi i mica granite. a. cassiterite aplites b. wolframite aplites

Whether Sn-W veins associated with two-mica granites IV. Quartz veins (with stock works and of breccia supposedly belonging to the Older Granites are really pipes)

two conditions. First there must a. cassiterite veins with little Westphalian age depends on or no tungsten be evidence that the spatially associated granite is truly the b. cassiterite-wolframite (and/or scheelite) veins

wolframite veins with little or no cassiterite parent granite of the ore, for Older Granites often are hosts to c. ore veins that in reality emanate from an underlyingYounger d. scheelite veins with little or no wolframite or cassiterite

Granite. Second, the spatially associated granite must be an V. Metasomatic skarns

scheelite skarns Older Granite, that is, its age must be radiometrically ascer- a. tained. b. wolframite-scheeliteskarns

this evidence is the As long as not forthcoming hypothesis

Excluded are the Cambrian and Silurian metamorphic of an older, Westphalian episode of Sn-W mineralization remains unconfirmed and, in the light of other evidence, scheelite skarns (reaction skarns) since their metallization

to be much older. doubtful. Incidental mineralizationmay have occurred but no appears

formationof economic is known important ore significance as

is In as in greisens are of frequent yet. This evidence the following. the first place, Conde Tin disseminations

but do not often constitute et al. (1971) and Thadeu (1973) point out, no Sn-W veins, occurrence large masses. Normally whether or not related to the Older Granites, are cut by later tin has been concentrated in late-stage fluids which became

and has YoungerGranites or their pegmatites, aplites and other veins. segregated in pegmatites and vein deposits only rarely

since it entirerock This is strong negative evidence the very widespread impregnated masses.

and or sometimes YoungerGranites very frequently intrude Older Granites Late-stage fine-grained granites aplogranites

economic their country rock. Secondly, even though there are minera- carry sufficient dispersed cassiterite to warrant

structural extraction. The and Nb- logical. petrographical and differences, as group Columbite-tantalitealso occurs. Sn characteristics, between the Older and Younger Granites Ta minerals are in some cases found finely disseminated

(Schermerhorn. 1956; Floor, 1970: Oen Ing Soen, 1970; through the rock, in other cases they are associated with of this kind of tin is Capdevila et al., 1973) the Sn-W deposits cannot be differen- quartz veinlets. The grade ore variable

tonne tiated on this basis. Thus Conde et al. (1971) and Thadeu between 0.3-2 kg cassiterite per (A. Arribas, pers.

Thus, at Penouta (Orense district, ( 1973) concludein favour of a single period ofmineralization comm.). Galicia) a

is which In addition,another argument supporting this view is that the kaolinized greisen granite" (Gumiel, 1978) worked 0.4 cassiterite. At Westphalian and Stephanianconglomerates carrying clasts of yields kg/t Golpejas near Salamanca a similar is mined and several other of Older Granites and metamorphic rocks have not been found granite occurrences

tin in to contain cassiterite or other detritus indicative of an disseminated mineralizationsare known Spain (Arribas, important mineralization associated with these granites. 1978).

Tin pegmatites contain albite. quartz, potash

and muscovite main minerals with Tungsten is more abundant than tin in this Sn-W province. feldspar as cassite-

rite, tourmaline, and in The two metals mostly occur jointly, forming Sn-W deposits, beryl, apatite sulphides accessory Wolframite but there also are some deposits in which only one of these amounts. is rare; however, a few pegmatites carry

wolframite but no cassiterite. metals is present, with the other absent or appearing in trace

Tin as distinct from the barren pegmatites of amounts. Byproducts of the Sn-W mines include copper, pegmatites, silver (both from chalcopyrite), niobium and tantalum (in simple mineralogy, show very complex mineral assemblages, columbite-tantalite) and formerly bismuth and lithium as with the minerals listed above accompaniedby plentiful rarer

in ofthese contain well. I 1 m e n i t e is recovered together with cassiterite from minerals trace amounts. Many pegmatites

alluvial tin deposits in Portugal (which produced 367 t fine-grained aplitic portions (pegmaplites of some authors).

u ilmenite concentrate ' Ti0 in 1976 and 175 t in The tin pegmatites have in the past been worked extensively (50 o 2) 1977); however, this mineral derives not from the tin lodes but from for cassiterite, with columbite-tantálite,wolframiteand other

ceased, the the Hercynian granites in which it is almost the only oxidic ore byproducts, but exploitation has mostly as grade mineral (Schermerhorn, 1956). in pegmatites is generally lower than in veins.

with the In some abundant, in the Serra de The Sn-W lodes are associated especially Younger regions pegmatites are as where cassiterite and columbite- Granites, notably the coarse porphyritic and related granites, Arga (northern Portugal) veins studied Cotelo Neiva as is discussed below. The Sn-W-bearing pegmatites, aplites, tantalite-bearing were by (1954).

The tin fields of the Amarante in northern greisens and quartz veins are found in the vicinity of" the pegmatite region

have been described these contacts of these granite massifs. Portugal by Maijer (1965); peg-

be follows: contained 0.1-0.3 cassiterite. The deposits may grouped according to type as matites wt % 41

Some attain considerable dimensions: pegmatites the La- of a subhorizontal vein system, Borralha has two breccia pipes tin gares pegmatite (Cotelo Nei va, 1944;Schermerhorn. 1956) and is exceptionally rich in molybdenum, and Barruecopardo

is one kilometre long and to 12 m thick. The is scheelite up grade was a vein system, not wolframite like the other two.

0.09-0.1 wt cassiterite; the % concentrate produced by the The Panasqueira mine in central Portugal produces mine contained in addition columbite-tantalite Lagares 2% wolframite and cassiterite concentrates and since 1962 also and 0.1",, wolframite. argentiferous chalcopyrite concentrates; the recovery ofspha-

lerite is being studied. Mine statistics show thatbetween 1934

Tin and less and tungsten aplites are much frequent 1970 56,960 t wolframite concentrate, 3.984 t cassiterite

than tin and do not attain similar pegmatites sizes: they have concentrate and 2,848 t chalcopyrite concentrate have been been worked on a small scale only. These rocks are muscovite produced (Reis, 1971 ). Although the overall ratio is cassiterite

aplites generally bearing some and tourmaline, they contain 1% of wolframite output, the tin percentage has since 1960 disseminated cassiterite finely occasionally accompanied by dropped to 1-2%, again rising to 4-5% during the last few

wolframite and/or wolframite 1977 sulphides: some aplites carry years. Production in was 1287 t wolframite concentrate

only; some aplites show greisenization (Schermerhorn, 1956). of (75% Portuguese output; however, in 1975 it was 1742 t),

1176 t chalcopyrite concentrate and 58 t cassiterite con-

Where both and mineralized veins pegmatites quartz are centrate (16"„ of Portuguese output).

developed there exists a tin zonation from pegmatites and/or Panasqueira mineralization consists of subhorizontal wolf-

tin-bearing veins inside or just quartz outside the granite ramite-cassiterite-sulphide-bearing quartz veins. The mine-

contact to tungsten veins at some distanceoutside the ralized is the granite. area large: underground workings cover 3 by 3.4

Though the different of ore veins into each other km. It types grade lies in Beira Schist country, largely within a zone of

no transition is known between or and contact pegmatites aplites spotted phyllites. This metamorphism is due to a quartz veins 1965b, 1973). (Thadeu, buried granite whose roof has been intersected underground

and in boreholes. A dome of greisen (greisenized granite) Quartz veins carrying cassiterite and/or wolframite roughly 150 m in diameter rises about 120 m above the

and the most scheelite constitute ore exploited by mines. As a irregular roof of a much larger granite massif (Fig. 6). The rule cassiterite-quartz veins occurring inside granite to pass roof rocks range from more or less strongly greisenized cassiterite-wolframite veins across the contact and these to to granite muscovite-quartz greisen and belong to an unde- wolframite veins outside the granite. Sulphides accompany formedpost-tectonic massif (Clark, 1964, 1970; Conde et al., this mineralization, in the especially tin-tungsten and tungsten 1971). The greisen carries arsenopyrite, chalcopyrite, spha- zones. Thadeu out that marmatiteand (1973) points arseno- lerite and a little cassiterite and is itself cut by the mineralized

tend to be pyrite concentrated in the zone where cassiterite veins. The quartz greisen dome is capped by about 15 m of and wolframite occur jointly. Pyrite, pyrrhotite and chalco- massive which quartz was deposited in the space left by pyrite but become are present too quantitatively more impor- sagging due to contraction of the dome rock. tant in the outer of wolframite veins where marmatite zone The ore veins are to 200 m long and up average 30 cm thick, and decrease. arsenopyrite rarely exceeding one metre. They mostly dip gently at 5-20° The veinsoften followexisting joints, especially SW, SE or NW: moderate cross-joints to steep SE dips occur locally. («(joints) and also in schistose cleavage planes country rock. The most common minerals are wolframite, arsenopyrite. Often too are somewhat later than the and they jointing chalcopyrite, pyrite, pyrrhotite, sphalerite (marmatite) and exhibit strikes and Subhorizontal veins at siderite. Less diverging dips. as abundant are cassiterite. apatite, marcasite,

Panasqueira are rare: the veins generally show very moderate muscovite, fluorite, topaz, tourmaline, galena and calcite. to Stockworks as at and in steep dips. Bejanca (Sn W) Minerals present in small quantities include stannite. molyb- northern usually occur Portugal in greisens (Cotelo Neiva, denite, bismuth, bismuthinite, cubanite, freibergite and other 1944). silver minerals, beryl and others. The most abundant mineral

was in after Veining many cases accompanied or preceded by quartz is arsenopyrite (Reis. 1971). The cassiterite greisenization of the host rocks in of the generally narrow zones content veins increases in depth and towards the along the vein contacts. In contrast, the of The veins development granite. display muscovite-tourmalineselvages and greisen borders in the wall rocks of pegmatites and aplites is greisenized borders. rarely seen, as distinguished from internal in these Greisenization greisens preceded mineralization. Based on four K- bodies. Greisen borders, often attended minerali- Ar determinations by some age of muscovites from Panasqueira grei- zation, are best in granites, much less in and veins developed so sens ore which yielded identical results, Clark ( 1970) sedimentary host rocks where tourmalinization and other concluded that greisenization and hydrothermal minerali- alterations are more common (Schermerhorn, 1956; Thadeu, zation took in a brief place period, possibly less than one 1965b). million years.

Metasomatic replacement ore (cassiterite and wolframite) The veins follow existing flat-lying joints (Fig. 6) which is occurs as small bodies associated with vein minerali- unusual for locally tin-tungsten vein mineralization. These joints zation (Thadeu & Aires Barros, 1973). have been may produced as subhorizontal fractures resulting The three most important vein deposits in the Iberian from subvertical pressure release caused by slight sagging of Peninsula are the tungsten producers Panasqueira and the underlying large granite mass when it contracted during Borralha in Portugal and in western consolidation. Barruecopardo Spain. As has been noted, shrinking of the greisen They not at all alike: are Panasqueira presents the peculiarity dome, a small protuberance on the roof of the main granite 42

the with Fig. 6. Section through the Panasqueira vein system and greisen-granite dome its quartz cap (black). After Beralt Tin and Wolfram Portugal. S.A.R.L.

that filled The mass, left a space was by hydrolhermal quartz. orogenic phase during the Westphalian. at least two tectonic joints formed due to pressure release as here suggested, phases of an epeirogenic, block-faulting nature ensued, dur-

latent the and the Late possibly remained until forced open by overpressured ing Early Stephanian (Schermerhorn. 1956).

solutions from which the vein minerals hydrothermal were causing elevation of areas outside the basins in which the

deposited. Stephanian deposits were laid down, hence strong erosion and

Hydrothermal mineralization took place in various stages denudation.The Stephanian conglomerates in Portugal con-

(Orey. 1967). According to Kelly (1974). study of the fluid tain plentiful detritus derived from the Older Granites in- inclusions in the vein quartz shows that the ore fluids were hot truded shortly beforeand from regional-metamorphic schists

(80-325 C) and fairly saline (3-10 wt "„ equivalent NaCI) likewise formed shortly before, during the Westphalian. This while mineralization took place within 1.5 km of the con- indicates a high rate of erosion and denudationin the uplifted

surface. Stable temporaneous ground isotope data indicate a source areas of the Stephanian. It thus is perfectly possible for for the in the formed surface juvenile origin sulphur sulphides during an Upper Westphalian-Stephanian erosion to trun- the main stage of mineralizationbut a shallow source for late- cate Beira Schists at a deep level after removal of several

The shallowness of Panas- stage sulphur; the carbonates contain a substantial pro- kilometres of overlying strata. portion of organic carbon; and the hydrothermal fluids queira mineralization hence is not inconsistent with a deep appear to have been predominantly magmatic during the stratigraphie-structural level of emplacement.

of some minerals but mixtures of and h mine deposition meteoric The B o r r a 1 a in northernmost Portugal, the magmatic during the deposition of others (Rye & Kelly. second largest tungsten deposit in the Peninsula, produces

1974). wolframite, scheelite and argentiferous chalcopyrite con-

Fluid inclusions in the apatite accompanying the minerali- centrates. Together with Panasqueira it accounts for about

of An zation indicate that it was deposited at temperatures in or 90% Portuguese tungsten output. extensive /one of tin

above the °C' 280 veins slightly range of 230-315 (peaking at °C) and tungsten adjoins a massif of porphyritic granite

of about 3 the from fluids showing a salinity 11 wl ",, equivalent regarded as parent magma; cassiterite veins near this

NaCl. in vein minerals veins The fluid inclusions later (siderite. granite pass outwards to wolframite (with some

Iluorite. calcite and others) reveal a systematic decline of scheelite) that arc worked at Borralha. The country rock is temperature to below 70 C. granite and Silurian schists (Conde et al.. 1971 ).

Kelly's assessment of the depth of mineralization entails The lodes, up to 1.5 m thick, form anextensive, very regular that the have risen less than 1.7 km E veins underlying magma must to system of to ESE trending mineralized quartz dipping below the surface. This in turn implies, first, a very high level at25 30 N,45-60 Nand50 N(Noronha, 1974:Noronha& of emplacement but that is not unusual for the Younger Saavedra, 1975). Two large breccia pipes, one of them granites and. second, strong denudation.The granite intruded outcropping, the other blind, are cemented by ore-bearing

blind 415 into folded and cleaved Beira Schists. Before erosion, this quartz. The recently discovered pipe contains ppm

overlain Ordovician. Silurian and Devonian (in and 1300 sequence was by W. 980 ppm Mo molybdenite) ppm Cu (in

combined thickness 500 As strata to a certainly exceeding m. chalcopyrite) (F. Noronha. pers. coram.). mentioned in section, tectonic differentiation veins a preceding at The carry wolframite and sulphides (mainly chalco-

of the Carboniferous raised minerals, the beginning the central Iberian pyrite and pyrite) as principal accompanied by block above sea level and erosion started. After the main molybdenite, scheelite (and rare powellite). marmatite. arse- 43

nopyrite. other sulphides, tourmaline,white mica, apatite and wolframite, pyrite and some chalcopyrite; cassiterite and carbonates al. 1971; Noronha & Saavedra, (Conde et 1975). molybdenite are present in trace amounts. offluid the led Noronha Study inclusions in vein quartz ( 1974) The stockwork occurs in a granite described as a two-mica

to admit a temperature of formation in the order of 280- adamellite in which pronounced microclinization of biotite under 350 C a pressure around 1000 at. and plagioclase took place, and Pellitero et al. (1975, 1976)

estimated this from relate the Noronha pressure value figures pub- tungsten mineralizationto this process. They note a

lished Russian workers. However. Amossé (1976) has by positive correlation between potash feldspar content and ore.

evolved a new method of measuring the pressure ofcrystalli- hence they infer that the tungsten was extracted from the zation: lattice variationin wolframite beforeand afteranneal- surrounding granite itself during microclinization: scheelite

ing at high temperatureto remove strain is measured by X-ray precipitated insteadofwolframite because the replacement of

methods, and from this value and the compressibility coef- plagioclase by microcline released calcium. However, it also

ficient of wolframite the of be seems that of older pressure crystallization can possible potash-feldspathization an by an derived the solid Thus Amossé arrived using state equation. at underlying younger granite took place and that shear zones in a of 1500 bar for wolframite formation Borralha. the pressure at older granite provided pathways for mineralizing so-

this value the the Using to correct homogenization temperature lutions related to younger granite. The presence of of the fluid inclusions in the quartz host of the ore, he predominant scheelite is most unusual in this type of minerali- estimated that the Borralha wolframite difficult was deposited at zation and to explain on either hypothesis. Because

temperatures between 325 and 430 C, the temperature gra- microclinization of plagioclase is widespread in the Meseta dient correlated with distance from being a breccia pipeas 'hot granites, scheelite ought to be rather more abundant than

of mineralization. centre' wolframite, which is not the case. In fact. Barruecopardo is

Noronha's and Amossé's for the if taken figures pressure, unique, the more so because of its large size. as load pressure, would indicate that mineralization took Skarn-type scheelite-wolframite min- of place at a depth roughly 3.8 km, respectively 5.7 km. eralization is linked to the occurrence of calcareous Further, according to Noronha and Saavedra (1975) the beds in the Beira Schists and Silurian country rock of the

Silurian at host rocks of the ore deposits were metamorphosed Younger Granites. As we have seen, formerly such minerali- a of temperaturein the order 650 C under a pressure of 4.5-5 zation was uniformly regarded as due to epi'genetic in-

kbar. This is to of troduction equivalent a depth 17-19 km. Given a oftungsten. It has recently become recognized that

the Middle Westphalian age of mctamorphism. it meansthat syngenetic tungsten exists in Cambrian and Silurian calc-

20 the time during the 30 million years separating of meta- silicate beds, especially where they are found outside the

and the time ofmineralization of morphism some 12 14 km granite contact aureoles, such as the occurrence cited under overburden removed erosion, of was by at a rate 400 700 m the heading Cambrian scheelite.

millimetre per million years or less than a a year. Such does Within the contact aureoles such occurrences have been

not in appear impossible a tectonically active environment of metamorphosed to reaction skarns. and these are hard to

block-faulting. Still, the depth of mineralization deduced distinguish from contact-metasomatic skarns (or tactites) in

from the above pressure figures seems rather high. But if it is which the scheelite has'been produced from introduced admitted, in view the of presence of breccia pipes, that the tungsten and sedimentary lime. Normally the syngenetic pressure under which wolframite formed was a scheelite in hydraulic deposits are poor sulphides and lack wolframite overpressure exceeding the lithostatic pressure, hence not while the metasomatic scheelite deposits contain both sul-

correlatable with then the of depth, depth mineralizationwas phides and wolframite. even less, say one or two km as at Panasqueira, and this entails In the Covas mining district situated in the extreme an even greater rate of erosion, almost reaching a millimetrea northwest corner of Portugal, several scheelite deposits, the

most year. important among them being Valdarcas, are

These calculations incidentally tend to confirm the view associated with a very extensive skarn horizon developed on

Conde et al. (1971) that the mineralization of Ordovician expressed by top quartzite in a large anticline near two emanated the Youn- from a porphyritic granite belongingto intrusive granites; many barren aplitic pegmatites (pegmap-

Granite suite. Older Granite would have intruded not ger An lites) occur in the area.The skarn consists of calcite, grossular- long after the regional metamorphism had run its course, rich garnet, diopside. vesuvianite. actinolite-tremolite. horn- when at the and little erosion could have taken place surface, but blende other minerals. The mineralized skarn zones the Borralha ore veins could not have formedat a depth of 10 contain in addition scheelite. ferberite (pseudomorphosing km or over. Hence this mineralization too is related to the scheelite), wolframite, plagioclase (albite to labradorite).

Granites and of Autunian fluorite, Younger age. apatite, a little quartz and much pyrrhotite. with

arsenopyrite. pyrite and other sulphides. Wolframite prefers In the is the scheelite Spain largest tungsten producer the zonesrich in sulphides where scheelite is rare and scheelite stockwork of the mine Barruecopardo open-cast prefers the zones in which calc-silicates prevail (Bayer. 1968:

northwestof Salamanca, near the frontierwith Portugal. This Conde et al.. 1971). occurrence is a system of subvertical The worked 8 parallel NNE-trending orebody at Valdarcas was a lens up to in thick veins 0.5-15 thick, in (Pel- and averaging cm developed granite about 100 m long that contained two kinds of ore: calc- litero et al.. 1975).This stockwork is over 3 km 200 m silicate-rich long by scheelite ore ("skarn ore') and sulphidic (mainly wide and 100 The veins m deep (Arribas. 1978). are minera- pyrrhotite) wolframite ore with scheelite and ferberite after

lized scheelite and with subordinate ferberitic The by arsenopyrite scheelite. sulphide ore formedthe main mass; calc-silicate 44

occurred as a bed 1.5-2 thick in the wall of the ore m hanging does occur, it is distinctly rare in comparison to other

sulphide lens. The grade of the Valdarcas ore was 2.5-5 kg Hercynian tin-tungstenbelts in Europe (Schermerhorn, 1956.

1971. Tourmaline, the wolframite-scheelite per tonne ore. or 0.18-0.25",, WO, p. 536. 560; Conde et al., p. 41). on

(Bayer, 1968), that is 0.14-0.20",, W. other hand, is abundant, mostly in the wall rocks of the lodes

Bayer (1968) envisages the sequences of mineralization at where tourmalinites may have formed. Also, unmineralized

Valdarcas as follows: an intercalationofeither marl or a mafic tourmalinepegmatites and aplites are widespread, and tour-

rock folded and the eruptive was metamorphosed to amphi- maline frequently occurs in quartz veins and on joint planes.

bolite with the facies crystallization of diopside, hornblende, Apatite is very frequent too in the tin and tungsten deposits.

be plagioclase and possibly also grossular-rich garnetand vesu- Among the sulphides, marmatiteappears to more plentiful

vianite. The tungsten is of syngenetic origin, preconcentrated than it is. for instance, in the lodes of Cornwall.

in as volcanogenic scheelite a mafic lava or tuff: below this Some occurrences show enrichment in certain elements.

the lava a submarine iron-sulphide containing some copper, zinc Thus Borralha tungsten deposit is relatively rich in and arsenic existed. During metamorphism and aplite-peg- molybdenum as compared to other occurrences. Lithium is

matite emplacement the iron sulphide became pyrrhotite and locally plentiful in cassiterite veins, for example in western

the mobilized in the scheelite in metamafic horizon was part Spain (see next section). and redeposited as wolframite in the sulphide lens.

In contradistinction. Conde et al. ( 1971 ) consider the skarn Autunian beryl, columbite-tantalite, lithium andfeldspar

to be metasomatizcd limestone, since borings revealed its Minerals containing Be, Nb-Ta and Li. together with feld-

limestone its in passage to crystalline limestone, and this by spar, are won from pegmatites the Iberian tin-tungsten

reactivity channeled the mineralization which is a normal province. A great variety of iron-manganese and other wolframitic mineralization the of these generated by Covas granite. phosphates occur in many pegmatites(Corrcia Neves.

Thadeu (1973) further remarks that volcanics are lacking in I960).

this region. Beryl and columbite-tantalite can be by- The of Covas tungsten deposits are unique in the Peninsula. products tin mining but pegmatites rich in beryl or

Their association with Ordovician calc-silicates sets them columbite-tantaliteand manganese phosphates contain little

apart from the scheelite orebodies in Cambrian or Silurian or no cassiterite (Correia Neves. 1960; Thadeu. 1965. 1973.

host of is rocks. The presence a vast amount of pyrrhotite 1977; Conde et al.. 1971). The Mangualdc pegmatite in

lack unusual. The of cassiterite in the very closely associated northern Portugal has been worked for beryl and feldspar; it

carried lithium aplitic pegmatites seems curious, especially as cassiterite does a little cassiterite and iron, manganese and

occur in pegmatites near the Covas granite. phosphates (Jesus. 1933).

Lithium minerals appear in pegmatites and aplites in

Tin and tungsten lodes ofgranitic descent are characterized by- Galicia, north Portugal and western Spain. Moreover,ambly-

apical deposition, that is. during consolidation of the gonite and montebrasite-bearing cassiterite-quarlz veins oc-

parent granite (which need not be their actual granitic host cur locally in western Spain (Weibel. 1955).

rock) the metalliferous fluids move upwards, not sidewards, Portugal lOOOt Li 0)in 1977asa produced lepidolite! 1.5",, 2 and accumulate in the roof of the pluton. Hence the richest byproduct offeldspar exploitation (Bol. Minas (Lisboa). Dec. concentrations tin-tungsten are found over unexposed shal- 1977). low granites or over gently dipping granite contacts. Deeply Usually lepidolite is the common Li -mineral in pegmatites

eroded granites with steep contacts are unfavourable explo- (Conde et al.. 1971 ). and lepidolite pegmatites, often cassiter-

ration targets in contradistinctionto contact-metamorphosed ite-bearing as well, are widespread, but amblygoniteand other

with little sedimentary or older granite areas or no younger minerals also occur. Henscn (1967) described an extensive

wide granite outcropping. zone 600 m by 15 km long of metalliferous pegmatite

Tin and tungsten became concentrated by crystal fractio- veins in micaschist in Galicia. These have been mostly mined

halidc- for in nation processes in the granite magmas in volatile-rich cassiterite (up to 0.2 wt "„) and some for beryl; addition. enriched hydrothermal fluids, together with several other late- Li-minerals (spodumene and petalite), columbite-tantalite. stage constituents, including those causing greisenization. phosphates and many other minerals occurred.

However, mineralization is fre- furthermore the greisenized granite lacking Pegmatites are most important source of

and and metallization linked to and in the Peninsula. quent, greisenization are a feldspar quartz Spain pro-

but certain extent not inseparably. duced 70,000 t feldspar in 1974 (no. 9 in world production) and

When fissures the crossing granite-wall rock contact are Portugal 28.000 t. However, in 1977 Portuguese production this late opening at stage they become mineralized,producing had declined to 10,803 t feldspar (and 103,565 t quartz).

high-grade low-volume lodes. Tungsten penetrates farther into the wall rocks than tin which is less mobile in this Autunian gold and silver

within the Gold have been situation. Retention of stanniferous fluids granite and silver, likecoppcr. tin and lead, won in the roof zone, in the absence oflate-stage fissuring or because the Iberian Peninsula since before the Romans. Both vein and earlier veins close, disseminated originates low-grade high- placer gold were exploited. No gold or silver mines are active

volume cassiterite in in deposits greisenized granite, as at Pe- anymore Spain; these metals are still being won as by- nouta in northwest or in western from other and silver from Spain Golpejas Spain. products ores (gold cupriferous

the Iberian and their lastly, tin-tungsten province presents certain sulphide deposits gossans (Cerro Colorado in the

it For characteristics setting apart. instance, though topaz Pyrite Belt accounts for 90",, of Spanish gold output) and 45

silver from lead sulphide deposits; with the planned increase gold-bearing older ores were deposited during fracturing of of production of these ores gold and silver output will mount the Older Granite, and the undeformed later mineralsformed too: from these sources Spain produced 320 kg Au and 671 Ag during a posterior episode of vein dilation. in Calzado, to t Still, the vein dextral wrench 1970 and expects (Prado 1973) produce 6 Au Campo was emplaced along a and 170 t Ag in 1980). The Jales mine in northern Portugal is fault according to Portugal Ferreira (1971), and recurrence of the only active gold-silver mine in the Iberian Peninsula, and minor movements during mineralization could well account for of Portuguese output of gold and silver as sulphide concentrate the deformation the older minerals. Because the gold grading 133.8 g/t Au and 377.8 g/t Ag was 2,0211 in 1977 (Bol. mineralization is clearly associated with wall rock alterations

is mine Minas (Lisboa), December 1977). This a very old ofthe type generally caused by YoungerGranites and because

it in affected remarkable for the enormous extent of the Roman workings. occurs an area by potash feldspathization

A formerly important gold-silver district is situated in generated by underlying Younger Granite, it seems more northwest Spain (Galicia, Asturia and León) and northern likely that this mineralizationtoo is genetically linked to the

Portugal. In this area numerous gold-silver-arse- Younger Granites. no p y r i t e veins have been worked. Gold veins in

Galicia occur within and around granitic plutons and contain Another type of gold mineralization is represented by

disseminated gold and arsenopyrite in association with pyrite, pyrrhotite, gold, as described by Harris (1978) for

altered of the chalcopyrite, bismuth and bismuthinite; silver is also present the highly portions Salave granodiorite stock in

(Armengot de Pedro & Campos Julia, 1971). Asturia, a Hercynian intrusion of Younger Granite age

is The Jales minein northern Portugal has been described (Harris, pers. comm.). The gold associated with arseno- by Brink (I960) and Portugal Ferreira (1971). Here gold- pyrite, pyrite, stibnite, some molybdenite and traces of

Beira and Alteration of the silver-arsenopyrite-quartz vein systems occur in Schists, sphalerite galena. granodiorite pro-

Ordovician, Silurian and Older Granite country rock, in an duced a complex zonation: from the unaltered granodiorite area where this granite has been potash-feldspathized. that is. towards the highly altered mineralizedrock, igneous texture is plentiful have in it. Na and C0 increase and SiO, potash feldspar megacrysts developed progressively destroyed, 2

decreases. which is ascribed to the contact-metamorphic effects of an Peripheral molybdenite-bearing quartz veins may

Granite. The Gralheira remobilized Mo and Si0 from the altered auri- underlying porphyritic Younger represent 2 ferous veins, no longer in exploitation, trend WNW and are sited in bodies. This occurrence is a prospect and this means basal and that the Salave mineralization Ordovician metaquartzites schists. Somewhatmore may prove to be economic and northwards is the Tres Minas occurrence of disused gold furtherthat this type of gold deposit may be present elsewhere workings in Silurian schists. To the south is the long Campo too.

vein (Minas dos Mouros) which produces gold and silver. It

NE and trends across the contact between Older Granite and Autunian antimony gold

Beira Schists and reaches 1 m thickness. In the same area of Antimoniferous veins occur in northern Portugal, northwest

Beira Schists are small cassiterite deposits. and western Spain and. to a. lesser extent, in south Portugal.

The grade of the ore extracted from the Campo vein was They are most abundant in the so-called 'antimonybelt' (faixa

1970 Ferreira. 1971 The is 14g,tAuin (Portugal ). gold mostly antimonifera) in northern Portugal, a southeast-trending associated with arsenopyrite. also with pyrite and to a lesser zone lying east and southeast ofOporto that reaches some 30

with km in extent younger sulphides (chalcopyrite. galena and length by a width of up to 10 km. Here auriferous of sphalerite). Jalesproduction silver is two or three times gold antimony veins, of which the largest was the Alto do Sobrido production and the silver is contained in tetrahedrite as- mine, have been worked for gold by the Romans. The veins

the rather in in the district sociated with galena. were poor gold but rich stibnite and

The Older Granite wall rock of the Campo vein has suffered was an important antimony producer during the second half microclinization of and microcline has been of the plagioclase, last century; it is now inactive. introduced into the schist wall rocks as well: Brink attributes The host rocks of the veins are mostly Beira Schists and this to metasomatic introductionofpotash feldspar from the Ordovician quartzites and slates, more rarely Silurian slates ore-bearing solutions which also caused muscovitization, and Carboniferous conglomerates, in the limbs of the large silicification. sulphidization and tourmalinization. Valongo anticline. The Sb-Au vein mineralization is of

Granite Younger age (Portugal Ferreira, 1971; Portugal The gold-silver veins of the northwest Meseta are generally Kerreira et al.. 1971). In this area occur furthermore Sb-Pb regarded as Hereynian deposits but theirprecise age is still not and Pb-Zn-Ag vein mineralizations.. clear. The Sb- Some authors (Cerveira. 1952) see these veins as directly Au mineralizationoccurs in quartz veins of varying related to the Hereynian tungsten mineralization, based on trends, most frequently ENE-WSW (following dextral the in reach mineralization presence of wolframite or scheelite gold mines. Brink's wrench faults), that 2.5 m thickness. The consists of (1960) opinion was that there exists no connection between stibnite, berthierite. gold, pyrargyrite. pyrite, and the two mineralizations: the gold and silver belong to an locally galena, sphalerite and arsenopyrite (Portugal Ferreira, earlier, quite separate phase ofore deposition possibly related 1971). to the Older Granites. He argued that the older minerals in the The origin of the mineralization is uncertain: it has been

Campo vein are deformed while the younger minerals are not; ascribed to the Younger Granites, to later hydrothermal also, the wolframite veins in the area show no signs of activity and to remobilization ofantimony in older sediments

deformation. Brink therefore concluded that the cataclastic or volcanics. 46

Stibnite veins carrying some gold and silver, emplaccd in are richly mineralized and they reach several kilometers

the local equivalent of the Beira Schists, have also been length. The mineralization consists of galena and sphalerite,

worked in the de southern with Valle Alcudia in Spain (Crespo. pyrite, chalcopyrite, carbonates and quartz (Ovtracht &

1972). Tamain, 1973).

et - Gumiel al. (1976) described an occurrence of 110 The richest lead district, between 1875 and 1920 the most

stibnite-scheelite veins in trending Devonian limestone, the productive leadfield in the world, lies at the east end of the

San in Antonio mine near Albuquerque western Spain; these Sierra Morena: the Linares and La Carolina

authors a late At the assigned juvenile epigenetic, Hercynian origin orefields. beginningof the century, when Spain was the this mineralization, to which they related to an antimoni- second largest lead producer in the world (after the U.S.A.), ferous belt the traversing western Meseta in a NW-SE with for instance 265.500 t lead ore (60-80% Pb) in 1905. this direction from Oporto to Valdepeñas. region supplied nearly half of the Spanish lead ore output Other vein antimony mineralizations in northern and from some 1300 mines (Ahlburg, 1907;Azcárate & Arguelles.

southern and western much less At three veins Portugal Spain are impor- 1971). present are still being worked in the

tant. Linares field and three others in the La Carolina field (Ríos

Quartz-stibnite veins containing some sulphides in trace Aragües. 1977).

amounts are in of Linares fairly frequent southern Spain where they have North a granite massif in the eastern con-

been mined on a small scale in Ciudad Real province and tinuationof the Los Pedroches batholithcontainsNE to NNE

elsewhere, and locally in northwest Spain. trending veins of great extent ( 12 km for the Arrayanes vein,

ofthe richest lead veins veins one known anywhere). The carry and later and silver Autunian lead, zinc galena (with 160-250g/t Ag) and lesser amounts ofsphalerite,

in Epigenetic lead and lead-zinc veins, argentiferous, are and in a part pyrite chalcopyrite quartz-barite-carbonate gangue.

in the Meseta. Their is not evident and A vertical zonation exists: from the widespread age always surface down lo 100 m

some are leadand certainly post-Hercynian. depth copper are present; 100 150 m: a barren zone:

The richest and most famous lead province of the Meseta is 150-300 m: a rich in lead: 300 400 zone very m: a poor zone;

in the eastern Sierra Morena of central southern below 400 m: the lead tenor increases again (Ovtracht &

Spain (Fig. 2). Here metalliferous lodes, especially lead and Tamain. 1973).

argentiferous lead veins, that have been worked since North of La Carolinaextends pre- a mineralized areaconsisting

Roman times are found in the Los Pedroches batholith and of veins in the Santa Elena granite (the Santa Elena deposits),

the it. This batholith is area north and east of a very large and to the west, first, the Los Guindosdeposits and then the El

elongated. WNW-trending massifcomposed of various types Centenillo deposits, where ESE. respectively NNE trending

of intrusive granite and granodiorite (Ovtracht & cross Tamain, lead veins Ordovician or Silurian country rock contact- 1973). Its precise age is not known; some 50 km to the north is metamorphosed by underlying granite. Argentiferous galena the small Fontanosas stock, a late or to 1500 constitutes post-tectonic grano- (up g/t Ag) the ore, accompanied by

diorite (containing andesine and some cordierite) that has and sphalerite, pyrite quartz-ankerite-barite gangue (Ov- 87 86 been dated at 302 ± 10 Ma with an initial Sr/ Sr ratio of tracht & Tamain. 1973).

0.7099 well with the (Leutwein et al.. 1970). This age accords Except for the Valle de Alcudia, all these mineralizations

and initial strontium ratios measured for Older associated with age isotope are granite: however, an important lead field,

Graniteselsewhere in the Meseta. However, this result neither the San Quintín (Villamayor de Calatrava) vein system, is in dates the Los Pedroches rocks nor the ore veins in the area! Alcudian country rock north ofthe Valle de Alcudia, far from

The Los Pedroches batholithcontains several and tungsten granite (Crespo, 1972). The veins trend E-W and are minera-

tin mined in former Cassiterite- lized some occurrences, days. by highly argentiferous galena (up to 3500 g/t Ag), black

veins, cassiterite greisens, and in wolframite-arsenopyrite-quartz sphalerite, pyrite somechalcopyrite quartz gangue with

wolframite and scheelite found in and pegmatites pegmatites are rare carbonate very rare barite (Ovtracht & Tamain.

the central part of the massif; farther west only tungsten 1973).

occurs and the east of the massif has part some wolframite, in Ovtracht and Tamain ( 1973),as does Crespo ( 1972),relate

scheelite. the southern contact places accompanied by along the Cu, Pb and Sb mineralizations in the Sierra Morena to the

(Ovtracht & Tamain, 1973). Los Pedroches batholith, more particularly one of its phases,

The batholith also encloses number of a biotite a large copper porphyritic granite (rather a granodiorite, as an-

veins ( chalcosite-chalcopyrite-carbonate-quartz veins) desine exceeds potash feldspar in amount). The minerali- in its and especially eastern part, a lesser number of lead veins zation is zoned, with Cu nearest to the granite and Pb farther in silver: 170-250 Lead veins Sn and (galena poor g/t Ag). are more out. W are related to a fine-grained two-mica granite. in the Lower Carboniferous frequent slates and greywackes These are late Hercynian mineralizations: the veins are

the north side of the batholith. the covered on Along contact occur Bi- by barren Triassic sediments (Tamain, 1968: Az-

veins. cárate & Ni-Co-Ag-Au Arguelles. 1971). The Linares mineralization is North of batholith the and parallel to it extends the Valle de thought to be associated with the Linares granite, and the

Alcudia, a broad plain where the Alcudiense (Beira Schists) Santa Elena, La Carolina and neighbouring mineralizations

Here outcrops. lead veins are abundant (Crespo, 1972). with the Santa Elena granite (Tamain, 1968; Ovtracht &

Just south of the central part of the batholith is the Tamain. 1973).

El Soldado-Las Morras important orefield, a vein system In northern Portugal two types of lead-zinc

following NE and ESE to E-W directions; only the NE veins mineralization of different ages are distinguished: the first 47

in the and veins that type occurs area southeast of Oporto where several quartz dolomite of these they were deposited mines worked argentiferous lead-zinc veins of small extent, from hot fluids at temperatures above 100 C. mostly emplaced in metamorphic Beira Schists. The best This type of epigenetic hydrothermal mineralization is known of these is the Terramonte mine, active until recently tectonically controlled: ore deposition took place in fault

is is (see hereafter). This type characterized by a very complex zones belonging to a regional system and not linked to

of mineral assemblage, by high silver tenors, by the presence granites (Thadeu. 1951. 1973). Evidently the veins are post-

is Granite in that Permian high-temperature ferriferous sphalerite (marmatite) which Younger age. meaning they are or

the earlier in paragenetical sequence than galena, and by younger. Because they are related to regional fracturation

it considered be common presence of cataclastic textures; is to they were assigned an Alpine age by Thadeu (1951). From of late Hercynian age. fission track dating ofthe thermal history of the apatite in the

The second type, occurring over a large area in northern tungsten-tin veins of Panasqueira. Kelly and Wagner (1977)

Portugal, has a simple mineral assemblage, shows low silver infer that the lead veins are either late Jurassic ( 152 Ma) or late

later in in Jurassic thermal tenors, has sphalerite than galena sequences and does Cretaceous (79 Ma) age. Either a event not display deformed textures although the mineralization would have reheated the apatite to temperatures above generally follows faults; it is of post-Hercynian, probably 150 C followed by slow steady cooling or this event would

For mild mostly Mesozoic, age (Thadeu, 1973, 1977). complete- have been followed by rapid cooling and a second ness' sake this type, though post-Hercynian. is briefly re- thermal event (not exceeding 150 C) in Cretaceous times. viewed afterwards. Kelly and Wagner prefer the last interpretation and correlate

The first type is exemplified by the Terramonte the lead mineralization with it, while they relate the late deposit southeast of Oporto, worked between 1966 and the Jurassic event to the 'early rifting of the Atlantic'. The early middle of 1973. The orebody was a steep NE vein, 6 14 m history of the opening of the North Atlantic Ocean started

with thick, and much faulted and brecciated due to wrench fault continentalstretching, fracturing and rifting. The age of and movements. At first the ore graded 4.16 % Pb, 3.35 % Zn this initial period was discussed by Schermerhorn et al. (1978)

1 SO but these values in later 2.0 Pb. who concluded that well have in g t Ag decayed years to ",, rifting may begun Early to 3.0 % Zn and 100 g/t Ag (Portugal Ferreira, 1971). Middle Triassic times. Continental separation accompanied

Theore was mostly galenaand sphalerite (marmatiterich in by seafloor spreading and the generation of oceanic crust

Cd: the minor started the 3 kg/t Cd in zinc concentrate) accompanied by during Early Jurassic, about 180 Ma ago. These

amounts of pyrite, marcasite, chalcopyrite. arsenopyrite. events are too early to be correlated with the fission-track bournonite and sulphosalts such as jamesonite and bou- timings of lead vein emplacement. However, somewhat later

in langerite a quartz gangue with carbonates. The main silver- during the spreading stage, the Messejana Doleriteintruded, a minerals and with 2) intrusion bearing ore were freibergite pyrargyrite very long dyke system ( Fig. emplaced by multiple

some miargyrite, polybasite and argentite (Gaspar. 1967). mainly during the Early and Middle Jurassic (Schermerhorn

Based on sulphur isotope ratios determinedon some galena et al., 1978). The Late Jurassic event recorded by Kelly and and sphalerite samples, indicating a juvenile source for the Wagner may be correctable with later doleriteactivity; also, the late Cretaceous much took in sulphur, Gaspar (1967) suggested a plutonic hydrothermal during igneous activity place origin for this deposit. Portugal, especially along the Atlantic coast, and post-

Hercynian lead mineralization in the interior of the Meseta

Lead-zinc well date from this time. needed. veins ofthe second type are numerous in the Beira might More study is

Baixa region of northern Portugal, emplaced in Beira Schists

and granite host rocks. They consist of galena and sphalerite Silver was an important byproduct of many leadmines in

latter small the (the not everywhere present ) and varying amounts Spain, rarely inPortugal. Owing to supergene enrichment, of and of lead veins such those of Guadalcanal pyrite and chalcopyrite, with quartz, barite carbonate upper parts as and

Seville gangue (Thadeu. 1951. 1977). Silver contents were low. None Cazalla northeast of yielded important quantities of of these deposits was large and exploitation has long since native silver and silver sulphides. come to an end. Only one vein system consisted of true silver ore: at

The follow and fractures H i d veins steep to vertical faults e n e 1 a e n c i n a. about 90 km NE of Madrid (Fig. 2). mainly trending NNE to NE and ENE to E. three silver veins in gneiss and schist have been mined; they

The old C e i f e mine worked a lead vein near Penamacor contained silver sulphosalts such as freieslebenite. miargyrite, in Here NE in Beira Schists and in north Portugal. a crush zone was stephanite argyrite a gangue of barite, quartz and mineralized with the of four stockworks. The siderite Cávala Laborde. development (Ahlburg. 1907; y 1953). largest was 90 m long, 20 m wide and slightly over 100 m deep. These stockworks were formed by veinlets chiefly of galena Autunian phosphate

dolomite, calcite and in in and small amounts of barite, pyrite, Epigenetic phosphate deposits occur many places

(Thadeu, 1951). western and of some sphalerite. No quartz was present Spain (Estremadura) adjacent areas east-

The tungsten-tin veins at Panasqueira arc cut by later faults central Portugal (Alto Alentejo and Beira Baixa). In Estre-

the and madura. between Cáceres and trending N S and ENE WSW. and fault gouge Logrosán. these deposits have breccia have been mineralized by lenses of undeformed been worked since 1864 until fairly recently; the largest mine dolomite-calcite-ankerite Aldea Moret. There containing galena and sphalerite was occur quartz veins mineralized by

(Thadeu. 1951). Kelly and Wagner ( 1977)estimated from the fine-grained apatite (often called phosphorite, that is. col-

of and in the in the in slate proportion gas liquid fluid inclusions lophane. essentially cryptocrystalline apatite) granite, 48

or limestone host rocks, and furthermore pipe-like bodies in The southern part of the Beja eruptive complex in south

limestones (near Cacera cassiterite-bearing amblygonite Portugal consists mainly of gabbrosanddiorites with volcanic

veins 1955) have been mined; these to rocks; associated with these (Weibel, clearly belong rocks occur serpentinites. In this

the tin Farther southeast, the Namurian lime- paragenesis). area folded Upper Devonian limestones show minor copper

stones the Morena northwest of Belmez coalfield in the Sierra and nickel mineralizationsthat arc considered to derive from

of Córdoba containphosphorite-calcite veins and pockets (no leached ultramafics (Batista et al.. 1976). Pyroxenile. peri-

quartz) which have been exploited during the second halfof dotitc and dimite associated with gabbro intrusive into

the last century. Cambrian carbonates occurs in east-central Portugal (NE

The Aldea Moret minesouthwest of Cáceres worked the frontier with Alentejo) near Spain (Gonçalves. 1971).

a large quartz-apatite vein down to a depth of 180 m. The vein. Nickeliferous veins are furthermore known to occur in the

800 m and 12 m thick, Devonian limestone Cabo long I cut Ortegal area in Galicia (Armengot de Pedro& Campos

of (Weibel. 1955). Julia. 1971). None these mineralizationsare of economic

Near Elsewhere the veins formed swarms. Logrosán a NE- significance.

SW quartz-apatite (phosphorite) vein swarm in Beira Schists

reached 4 km width; of the veins, the Constanza vein. nickel one Late to post-Hercynian epigenetic copper, cobalt, and

0.60-7 m thick, was over 6 km long. bismuth

As these veins in Portugal and Spain are known to cut Epigenetic metalliferous veins and replacements unaffected

Younger Granites, they must be of Autunian or youngerage. by exogenic deformation and often following Hercynian

There be little doubt of the in the can that many quartz-apatite veins faults are widespread Meseta. They frequently show no

of and related to the obvious are hydrothermal origin Hercynian relationship to graniteand they tend to occur in more

granites because of their paragenesis. From such veins in or less well-defined metalliferous provinces. Pb, Zn and Cu

Portugal, C'otelo Neiva et al. ( 1952) describe perthitic ortho- deposits are most frequent. Co-Ni-Bi-quartz-carbonate veins

clase. muscovite, arsenopyrite and other minerals. These are foundalong the borders of the Los Pedroches batholith in

authors propose a pegmatitic-hydrothermal origin from re- southern Spain (Crespo. 1972: Arribas. 1978). Veins carrying

the in sidual fluids derived from Hercynian granite magmas. Co-Ni arsenides Galicia and elsewhere are considered

Also. Schneider (1951) distinguished pegmatitie. pneuma- related to Hercynian granite magmatism.

tolytic and hydrothermal phases during the formationof the Co-Ni-Cu veins and replacement deposits in dolomitized

Portuguese apatite-quartz veins. In favour of a directly Namurian limestones in León, formerly mined, contain

granite-related origin is the fact that apatite is a common villamaninite (Cu, Ni, Co. Fe) (S. Se) named after 2,

mineral in the Younger Granite pegmatites and tin-tungsten Villamanin in this area, together with chalcopyrite. linnaeite.

veins. pyrite, bravoite. niccolite and other sulphides and secondary

On the other hand. Ahlburg (1907) refers to the finding of minerals (Ypma et al.. 1968; Arribas. 1978).

phosphorite-encrusted bone breccias in the Constanza vein, Copper veins are widespread especially in south Portugal

to the alteration and of the and southwest impregnation by apatite granite Spam, as in the Los Pedroches batholith or in

wall the rocks of the veins, and to the occurrence of phosphate Iberian Pyrite Belt, discussed on previous pages. Their with nodules in slates associated the limestones in the Cáceres mineral assemblage is simple: chalcopyrite may be accom-

district. In his the mineralization opinion phosphate is very panied by pyrite, by tennantite/tetrahedrite or by galena and

the consists of young. sphalerite; gangue quartz and carbonate. In

It circulation of meteoric seems to me that waters could well south Portugal several copper veins have been exploited, for have immobilizedand redeposiled apatite at some later date, instance the Aparis occurrence, a system of veins following when erosion and had down the level of the shear planation cut to faults in greywackes and slates. The fissures were filled veins. primary by carbonates (mainly dolomite,ankerite and calcite). quartz

and some chlorite.The mineralizationconsists ofchalcopyrite

Late Palaeozoic chromium and nickel with some pyrite rich in arsenic and minor arsenopyrite.

Apart from the mafic-ultramafie complexes in Galicia and pyrrhotite, marcasite, sphalerite, galena and other minerals

Trás-os-Montes. discussed under Early Palaeozoic chro- (Gaspar. 1968). Copper veins containing uranium minerals

mium, much smaller ultramafic occurrences are found as are known in central and southern Spain (Ahlburg, 1907:

differentiatesofmafic rocks locally in the west, southwest and Arribas, 1978).

south Meseta. Unimportant chromium and nickel minerali- These veins postdate the main folding and regional meta-

zations associated with some of these rocks. then are morphism. so are post-Westphalian. but exact age

North of Córdoba in southern Spain. Upper Palaeozoic, remains unknown. Carboniferous possibly Lower slates contain an alignment of

serpentinite bodies associated with spilites and diabases: the Late Hercynian ferromanganese

contain disseminated chromite. Southwest of the Belt in south serpentinites some magnetite Pyrite proper Portugal lies a

and pentlandite (Crousilles et al., 1976). large structure, the Cereal anticlinorium (Fig. 5), in Lower Small ultramafic bodies, mostly serpentinized, occur as Carboniferousvolcanics and sediments much like the Volcan-

local differentiation the Palaeozoic of products among Early ic-Siliceous Complex the Iberian Pyrite Belt. Here occur a

and in the southwestern number of (Cambrian Silurian) spilites Meseta large ferromanganese veins, of which two are still

and the Lower (Caspar. 1971). Carboniferous spilites and being worked. These veins reach 18 m thick by up to 5 km long diabases of the Iberian Pyrite Belt (Strauss et al., 1977). and they follow NE SW fractures dipping 40 70 SE. They 49

consist of quartz with iron-manganese oxides (lepidocrocite out mines,and 15001 U exploitable at up to SI 30/kg U ($50/lb

and mostly) which are to derive by U 0 ) by leaching of low-grade ores grading less than 425 pyrolusite thought 3 8

from siderite. superficial oxidation primary manganiferous ppm U) (Uranium Resources. Production and Demand,

is Mn and Fe. In addition the veins OECD The average grade 8"„ 43",, December 1977. Nuclear Energy Agency and IAEA,

OECD, thus holds of the world's carry barite and in places base-metal sulphides as well. In Paris). Portugal 0.4%

1977, 30,2501ferromanganese (7.7% Mn. 40.5",, Fe) and 5901 uranium reserves. The 68001 U reserves embrace 112 deposits; barite were produced. however, only 15 deposits contribute 80",, of the reserves and

is ascribed late This hydrothermal epigenetic paragcnesis to one, Nisa, has 1884 t U or 27.7",, of the total (Matos Dias,

Hercynian magmatic activity (Carvalho et al.. 1971b: Car- 1976).

valho. 1976a. b). In Portugal uranium extraction is in the hands of the Junta

de Energía Nuclear which operates several mines in the

Autunian (?) mercury Urgeiriça and Guarda areas, with a totaloutput of 87.61 U in

In the is the Central Asturian coalfield several small mercury- 1976 and 66.3 t in 1977; production being stockpiled.

arsenic found between uranium 207 t U 0 in 1976 and occurrences, formerly mined, are Spanish production was 3 8

Mieres and Pola de Lena, south of Oviedo. Cinnabar 201 t U 0 in 1977. Two state entities exploit uranium mines as- 3 8

sociated with realgar, orpiment, arsenopyrite (in considerable in Spain. The main producer is a state company. Empresa

amounts: arsenic was formerly produced in this field), various Nacional del Uranio S.A. (Enusa) which in 1977 produced

other and carbonate or occur 132 t U 0 from its mine near Ciudad (which has sulphides quartz gangue along 3 8 Rodrigo

fractures and joints and also as impregnations in mostly reserves in excess of 10,000 t). The remainder of Spanish

Westphalian sandstones, conglomerates, limestonesand even uranium output stems from mines belonging to the Junta de

U coal seams. Ore grades averaged 0.2 Hg and 0.5 1.2",, As. Energía Nuclear. „

These occurrences, of which the most important is the M ieres In 1977 the Spanish uranium ore reserves at up to $80/kg U

mineralization, form NNE some 16 km U 0 ) stood at 6800 t U in the reasonably assured a alignment long ($30/lb 3 8

Their and is 8500 U (Anger et al.. 1968). age origin uncertain. category plus another t estimated additional re-

sources, totalling 15,300 t U; for the cost range $80-l-30/kg U - Autunian (?) epigenetic fluorite and barite no figures were given (Uranium Resources, Production and

Quartz veins carrying sphalerite, galena and other sulphides Demand, December 1977. OECD Nuclear Energy Agency

and rich in fluorite are found in the southern Meseta. The and IAEA, OECD, Paris). Like Portugal. Spain has 0.4% of fluorite mine El Chaparral near Cerro Muriano in south world reserves.

Spain exploits two long steep veins reaching 30 m thick and The majority of the uranium deposits of the Meseta are

trending 110 -120 and 060 respectively. The veins run in situated within or near Younger Granites. The intragranite ,

granite and the surrounding gneiss country rock. They are deposits are veins, and the deposits around the granites, veins with much fluorite and the aureoles, veins and dissemi- quartz some sulphides, mainly mostly within contact are

sphalerite with pyrite, galenaand a littlechalcopyrite: barite is nations. There is generally a clear tectonic control in that the

lacking. veins and disseminations follow shears, faults and shatter

Barite this fracturation has veins formerly worked in small mines are likewise zones. As for the Pb-Zn veins been

the mineralization most abundant in the southern Meseta but also occur in assigned an 'Alpine' age and was con-

central and northwest Spain. sidered to be Alpine too. that is. Tertiary. It now seems likely

These veins are undeformed and cut deformed strata and that it is largely of Mesozoic age.

of Hercynian granites, hence their age is late Hercynian or The main zone of uranium deposits economic impor-

possibly post-Hercynian. tance stretches from northern and central Portugal over

western Spain into southern Spain (where deposits in the

Remobilized Autunian uranium have Pedroches batholith been worked) up to the Guadal-

Uranium deposits in Hercynian rocks of the Iberian Meseta quivir fault.

are numerous in the eastern parts of north and central The U r g e i r i ç a mine in north Portugal exploited uran- iferous Portugal and west and south Spain. jasper veins in granite; ore extraction has ceased and

In 1907 the Urgeiriça deposit in northern Portugal was the deposit is now worked solely by leaching (the applicability

this discovered and itwas worked for radium from 1913 until 1944 of method was discovered when 5000 tonnes of ore

uranium extraction took 0.5 in when over (Matos Dias, 1976). "„ U,0 were the open during four grading 8 stockpiled

in 1955 Systematic prospecting for uranium inPortugal began years, when it had lost about 70% of the contained uranium the due the by Junta deEnergia Nuclear, a state organization, leading to winter rains). Mineralization is controlled by an to the of four hundred of which ENE wrench fault thick. discovery nearly deposits 7.5 km long with a crush zone 1 -10 m about one hundred offer economic potential. In Spain exten- Workable uranium mineralizationextends over a distance of

sive of 1300 prospecting has likewise resulted in the discovery m along this zone and consists mainly of pitchblende in

uranium with promising deposits. jasper gangue some pyrite or marcasite (Cameron, 1960:

In 1977 thePortuguese uranium ore reserves recoverable at Portugal Ferreira, 1971).

up to S 130/kg U ($50/lb U 0 ) were assessed at 91501 U (6800 The Ni sa prospect, discovered in 1957 during a scintillo- 3 8 t U of 425 meter reasonably assured reserves (at a cutoff grade ppm survey, is by far the largest uranium deposit inPortugal.

t U It U) minable at to U ($30/lb U 0 ), 850 consistsof disseminations crush zones in the up $80/kg 3 8 irregular along

of recoverable at up to $80/kg U by in situ leaching worked- contact-metamorphosed Beira Schist wall rock of the coarse 50

porphyritic Nisa granite, a Younger Granite, which contains U O sericitization of 3 s ) by and the breakdown biotite would

several other uranium The uraniumorebodies in the deposits. release enough U and Fe to account for the uranium deposits crush zones extend to a depth of 25 metres. Autunite and the wall rock alteration (Cameron, 1960). Radiometric

predominates, accompanied uranium 20< 238 207 235 207 208 by other phosphates dating (using Pb 7U Pb and Pb me- , /U /'Pb

and rare and black oxides pitchblende (Portugal Ferreira. thods) of some Portuguese pitchblendes resulted in two

1971). of 80 groups ages: + 20 Ma, 83 ±8 Maand 190±10Ma,and

Of the same the type are orebodies in the Ciudad this fits the Upper Cretaceous and Triassic planation periods (Mina Fé, Mina Rodrigo region Esperanza and others) in (Matos Dias & Soares de Andrade, 1970; Portugal Ferreira. western Spain, which the largest economic In represent uranium 1971). post-Hercynian times strong erosion cut down to concentration in Spain. The mineral is the principal ore pitch- expose Hercynian granites, and during a long phase of blende, accompanied by its alteration conditions favourable products (gummite. planation were for prolonged leaching

etc.), some and a of pyrite gangue consisting quartz, jasper, and redistribution of uranium. Another major episode of barite, chalcedony, calcite and fluorite (Arribas. 1960, 1975; erosion and planation occurred during the Cretaceous.

Fernández Polo, 1970). Il thus appears likely that while the deposition of the The and mode of of these origin deposition uranium uranium orebodiestook largely place in Mesozoic times, their deposits has been diversely interpreted. Originally regarded as source is to be sought in the Younger Granites; hence these

Hercynian endogenic hydrothermal mineralizations it was deposits consist of remobilized Autunian uranium.

soon realized that factors exogenic must have played a role.

Matos Dias and Soares de Andrade (1970) classify the SYNTHESIS

Portuguese uranium ore occurrences as concordant and

disconcordant (discordant to Ferreira. according Portugal Various m etallogenetic provinces a n d 1971) far the known concordant deposits; so only deposit epochs have been outlined in the foregoing; especially consisted of uranium phosphate impregnations in lacustrine significant and productive because of exceptionally strong sandstones in the Urgeiriça The disconcordant de- region. concentration of ore elements are (Fig. 2):

make posits up the remainder: they are veins and dissemi- nations (with Portuguese reserves evenly distributedbetween 1. the skarn iron province of the magnetite belt in the Ossa-

the two Matos Dias, 1976) and are associated with the Morena in Lower Zone, Cambrian carbonates as stated,

Younger Granites. The vein embrace veins with these deposits deposits may be syngenetic. as reaction skarns, and/or veins with and jasper gangue, milky smoky quartz gangue, epigenetic. as metasomatic skarns.

quartz-limonite breccias and weathered mafic dykes; they 2. the Lower Ordovician ironstone marine-sedimentary pro- show mainly NE trends. In dissemination uranium vince in the northwest deposits Meseta, fringing an emergent landmass

minerals altered - impregnate granite or metasedimentary wall these are syngenctic deposits.

rock. Wall rock alteration (sericitization, hematization and 3. the Lower Silurian mercury province of the Almadén area limonitization) is characteristic. Hematized have in south granite may Spain a syngenetic deposit that may be wholly suffered desilicificationtoo (Juntade 1968). have Energía Nuclear, volcanogenic or may a sedimentary source with de- This classification seems applicable to the Spanish Meseta position activated by volcanic heat.

deposits as well. the 4. Lower Carboniferous polymetallic pyritite province of The uranium minerals are pitchblende, black oxides, cof- the Iberian - Pyrite Belt in the southwest Meseta syngenetic finite, and diverse coloured silicates gummite such as uran- volcanogenic massive sulphides. ophane, phosphates torbernite. (autunite, sabugalite etc.) and 5. the Lower Permian tin-tungsten province of the northwest sulphates (uranopilite and zippeite). Pyrite and/or marcasite and central Meseta mostly epigenetic granite-bound de-

are frequent, other sulphides appear in minor amounts and posits.

calcite and other carbonates are infrequent. 6. the Permian lead province of the eastern Sierra Morena in

None of the known U extends - mineralizations to any great south Spain epigenetic lead-zinc veins.

not depth, even pitchblende (max. 50 m generally).

Apart from their close association In terms spatial with Younger of tectonic environment we find much Granites the uranium deposits also a to display relationship varying settings of mineralization. The iron ore of the old planation surfaces in central and northern Portugal and magnetite belt, if would have syngenetic, been deposited on a controlled they are by shears, faults and fractures marked by Lower Cambrian carbonate shelf, developed during a major

tectonized zones. lull in the clastic infilling of the Cambrian geosyncline

Matos Días and Soares de Andrade (1970) Meseta. present the covering the The Lower Ordovician iron ores accu-

model: uranium following genetical was leached circulat- mulated in shallow water a at by along coastline the end of a

meteoric waters from the ing YoungerGranites which are rich transgression phase. Almadén was The mercury deposited on in radioactive elements 1960) and Silurian (Cameron, accumulated in a platform during an episode of mafic volcanism. The the soil on Mesozoic planation surfaces. Afterwards uran- Pyrite Belt is the only major orefield developed outside the iferous solutions from these infiltrated central block, in the preconcentrations southwestern geosyncline, when ten- joints, fractures, breccias and mafic in the bedrock movements dykes and sional during the early Carboniferous set off deposited uranium minerals in intense volcanism. open spaces. felsic and mafic The tin-tungsten ores are

to calculations, of removal a quarter of the associated with the second episode of major granite intrusion.

uranium content (stated to veins late- original average about 47 ppm The lead-zinc followed to post-orogenic shear faults. 51

the The There is no obvious metallogenetic zonation, and uplift of the central block eventually gave rise to folding, distribution of these major ore provinces, let alone the with the folds spilling over into the marginal troughs. As a

be the immense variety of minor deposits, cannot adequately result, vergence is to north in the northern Meseta and to explained by plate-margin tectonics involving subduction, the southwest in the southwest. Most ofthe folding took place collision, arcs etc. Local strong subsidence, block-faulting, during the main orogenic phase, during the Westphalian. geanticlinal uplift and emergence, as well as well-developed Though some folding and refolding occurred afterwards, later volcanism ranging from mafic to felsic. characterize the tectonism was mainly of the nature of wrench-faulting and history of the Meseta and indicate differentialvertical move- block-faulting. ments and crustal tension. The tectono-sedimentary facies The ascent of hot mantle material into the lower crust and their palaeogeographical control plus the symmetrical caused extensive remelting of lower to middle crustal levels,

Meseta in outer in the structure of the (as expressed two geosyn- resulting generation of the Older Granite magmas. At a clines central block, in level, in the middle to crust, the or foredeeps flanking a large rising higher upper riseofgeotherms outwards verging folds and thrusts and in the abundance of over the mantle domes originated regional metamorphism, granites in the central block) produce a pattern consistent locally passing to migmatization and anatexis. The Older with an intraplate environment where orogenic evolution is Granite magmas gained the higher crustal levels somewhat controlled by vertical tectonics and great magmatic activity later. Almost no important mineral deposits of metamorphic that find their origin in the underling mantle. The broad origin are known and none derive from migmatization and framework of Hercynian mineralization anatexis, nor are the Older Granites associated with much is within-plate, not plate-margin. mineralization. This means that the crustal level where they

originated lacked ore elements in sufficient concentration.

Twenty million years later, however, a new granite magma

Mantle activity below the Meseta all through the Hercynian intruded the earlier granites and their country rock: the cycle is indicated by strong volcanicity in almost all periods Younger Granites which are distinguished from the Older trom the Late Precambrian on. by repeated intrusion of Granites by a higher content in radioactive minerals and by granitic magmas, and by tectono-sedimentary differentiation their mineralization. into a mosaic of subsiding, stableand rising palaeogeographi- Shortly afterwards the consolidated crust of the Meseta, cal units. composed offolded and variably metamorphosed strata and

I interpret this in the following terms. Mantle upwellings vast granitic massifs, was faulted and fractured. No large below the affected the crust offsets and Hercynian orogen by producing occur the faults probably arose from uneven uplifts and by generating fractionates that rose through the stresses set up in a rigid crustal slab in response to slight crust as volcanic and plutonic magmas. Some mantle diapirs movements in the underlying mantle. Thus channelways were

to the came pierce the crust, forming mafic-ultramafic com- opened to post-granitic hydrothermal solutions from which plexes of the northwest corner of the Meseta (van Calsteren, epigenetic vein minerals precipitated, some of them ofgranitic

1977). derivation, the others produced by near-surface recycling. One of period uplift and related tectonism took place This completes a broadoutlineof framework and evolution towards the end of the Cambrian.Over most of the Meseta the of mineralization during the Hercynian cycle in the Iberian

Cambrian strata (including Beira Schists and equivalents) Meseta. Now let us look at some deposits and their possible emerged and became variably eroded; locally they were sources in more detail. folded. It seems likely that this resulted from heightened mantle the ultramafic First activity: diapirs of the northwest date the part played by v o 1 c a n i s m in metallic sulphide, from this time, as does the uplift of this corner of the Meseta sulphide-oxide and oxide mineralization. and its the Ordovician 4). Thus the The of the Cambrian lead-zinc that emergence during (Fig. origin sulphides occur

Early Ordovician iron deposits laid downaround the emerged as disseminations in carbonates in the northwest and south- area owe their mantle convection. As west ultimately origin to Meseta, is obscure since theyare not obviously related to mantle diapirism and the ascent of fractionated magmas voleanism, unlike the massive base-metal sulphides of the continued in the northwest, the surrounding zone subsided pyritite type. For the Pb-Zn mineralizationsof the northwest and the Ordovician, Silurian and Devonian Meseta, strongly, Upper such as Rubiales, Guillou (1971a) infers an exogenic flysch a facies with the of the was deposited, contrasting platform source metals, onan adjacent weatheredcontinent. The facies in the dominantelsewhere Peninsula. same explanation may also hold for the lead-zinc belt in south

At the it beginning of" the Carboniferousthe Meseta became Portugal, though may be noted that voleanism took place in differentiated into a central block with rising tendencies and the southwest Meseta during the deposition ofthe carbonates. two Iberian marginal basins. The emergence of the central The ore of the magnetite belt, if Cambrian and synsedimen-

well block coincides with the emplacement of the Tournaisian tary. may be volcanogenic.as its composition (high S, low granites 350 Ma and the of the extensive and its at ca. eruption Pyrite P) association with copper sulphides in economic

Belt felsic the Tournaisian and earliest amounts does favour volcanism during not a purely sedimentary origin. Visean. The other The central block was the site of' metamorphism and stratiform base-metal sulphide mineralizations granite intrusion. This to indicate the slow rise of the Late Precambrian appears (or Silurian) copper sulphides magma underneath this block, while the adjacent secondary in Galicia, the Silurian deposits in the northwestern and geosynclines of the Cantabrian and South Portuguese Zones southern Meseta and the Lower Carboniferous Iberian Pyrite subsided. Belt were deposited during important volcanic episodes and 52

submarine middle and crustal are exhalativc-sedimentary (and resedimented) from upper levels, since the Older Granites

The ores. volcanism was attended by hydrothermal activity on which consist of' rcmelted middle crust - and also the

the seafloor and sulphides were precipitated around sub- Hercynian géosynclinal rocks and their basement (which we

know its marine vents. from detritus in the geosyncline). that is, the upper

The Late Precambrian in Galicia and the Silurian in these if deposits crust are poor constituents. Besides, the Older

with and the sulphides are associated mafic volcanics. felsic Granites could not extract these elements from their parent

volcanism taking place in these epochsis barren. However, the material or from the overlying crustal levels through which

much more important Lower Carboniferous sulphides (and they rose, how could the Younger Granites do so?

the manganese) of the Pyrite Belt are related to felsic vol- Second, the Younger Granites are a very diverse suite,

the mafic canism. and contemporaneousmafic volcanism is practi- much more so than the Older Granites, and range from

cally barren. There is thus an evolution from mafic to felsic rocks to calcalkaline and alkaline granites, including grei-

ore-element carriers. Even a or This indicates differentiationin the magmas as though greater sens. strong magma and

be derived fractional smaller part ofthe sulphur in these sulphides may supports an origin by crystallization from more

from seawater sulphate, the metals must be largely or entirely mafic material without significant crustal contamination.

I of juvenile origin. deduce this from the contrast between This material may have been derived by partial melting from

On the mantle it contemporaneous ore-bringing and barren volcanics. a ultramafic upper or may have constituted the

scale there is or between lower larger contemporaneity nearly so crust. The latter possibility is considered unlikely

is felsic and mafic magmas but their metalliferous potential because mafic or intermediate crustal materials such as

different in On a smaller scale, basalts would be too in elements of the Sn-W completely any one epoch. poor ore group.

mineralization occurs during only one or at most a few Besides, the enormous heat transfer leading to regional

volcanic and is linked to few of episodes during a period only a metamorphism and granite intrusion over the width of the

Meseta 700 km the erupting volcanics. The other rocks in the volcanic piles orogen 600 requires a vast source such

is mantle It are barren. If volcanic heat were all that needed to mobilize as canonly be provided by the appears that mantle and redistribute metals contained in in seawater. contempo- material, possibly a derived mafic magma, ascending into the

volcanics or in basement rocks, the crust and heat caused raneous resulting ore introducing melting on a vast scale of

would be the volcanics. not the crust above it. thus the Older Granite dispersed through highly con- generating magmas. centrated at one particular level in one particular place. Hence The Younger Granites are then to be seen as later con-

the metals must have a and have become taminated fractionates of deep-seated origin the mafic magma, slowly growing

in concentrated one particular magma phase, by differen- into large magma blisters in the deep crust. The Younger

tiation. this be mantle Granites, on view, may of derivation, including of 1 assimilated Next the role p u t o n i s m. Leaving aside the Brag- crustal material.

anca. Cabo Ortegal and other mafic-ultramafic complexes Next, the source of the metals, which has been dis-

their with minor chrome deposits, most endogenic minerali- puted. Notably the main source of the tin and tungsten and of zation is linked of the four to only one or more Hercynian the accompanying metals has been sought in sedimentary

granite suites: the Younger Granites (the magnetite belt preconcentration in géosynclinal sediments, with the intrud-

constitutes a doubtful case: if the iron ore deposits are not ing granite magmas extracting, concentrating and redeposit-

syngeneic but epigenetic, they are skarns generated by ing the metals. Thus Ypma (1966) suggested that tin and other

metasomatic introduction of ore elements from the granitic metals would have been present in sedimentary formationsin

in that the of this the the magmas area age possible granite-bound crust, entering ascending magmas. For tungsten the

be the is metallization would the age of granites, and this age is matter more complicated than for tin since sedimentary

still unknown). tungsten is known in the Meseta: it seems likely that the

The Younger-Granite-bound endogenic mineralization tungsten disseminations in Cambrian and Silurian metamor-

be divided can into the following groups: Sn-W and related phic marly beds are syngenetic stratiform deposits, because of

elements (Nb, Ta, Mo. Be. Li): Au-Ag: Sb-Au. Part ofthe Pb- their extent; latercontact or regional metamorphism induced

Zn-Ag mineralizationbelongs here too. and the U minerali- local concentration into skarn-type pockets. The source of

zation derives from these is this metallization this granites. Why tungsten remains problematical: the scheelite may be a

linked to the YoungerGranites and what is the source of this mechanical sediment ofplacer type, eroded from pre-existing

and the associated elements? or else it have magma ore deposits, may formed as an exhalativeproduct,

First, the contrast between the Younger trapped in marly sediments. and the Older Granites Cambrian and Silurian as regards as- syngeneic tungsten has been pro- sociated mineralization indicates that posed as a preconcentrated source for the later epigenetic their sources are different. This provides im- deposits associated with the Hercynian granites, for instance

constraints the of the of portant on source region Younger through anatexis tungsten-bearing Cambrian or Silurian

Granites and their If the Older Granites strata to a mineralized ores. represent yield magma (Noronha, 1976).

recycled middle crust, then the YoungerGranites must derive However, Older Granitesare mostly not associated with tin

still from deepercrustal levels or. ultimately, from the mantle. and tungsten mineralization but Younger Granites breaking

the been tin Though Younger Granite magma may have water- through them are. When the and tungsten associated with

- undersaturated.it was not a dry one. The ore elements and the latter granites have been deposited in granite that is to

volatiles in the the in (especially F and CI to act as tin carrier ions) say, ore-bearing YoungerGranite has not been contact

Younger Granites can hardly be explained by assimilation with Cambrian or Silurian sediments then these metals 53

must certainly derive from deeperlevels even than the middle has been proposed as a possible origin for the Almadén

crust where the Older Granites originated by anatexis. mercury; 3) by volcanic or plutonic magmas from lower

the crustal - base- [f Younger Granites stem from fractionated mantle- or upper mantle levels this is the case for the

if the and associated elements of Late Precambrian. Silurian and derived magma, and Sn ore metal sulphide deposits

the could not have been collected from crustal rocks, because Carboniferousage, for the volcanogenic iron deposits, and for

Older Granitesfailed to do so, then these metals too must have the granite-bound mineralization of the Sn-W province.

be made for that It lineaments were instrumental in a mantlesource. Evidently anexception must seems very likely that part of the tungsten minderalization that represents Cam- localizing mineralization. Overall structural control of min-

eral in the Meseta - in brian and Silurian syngenetic stratabound scheelite deposits. deposits may have been exerted this - Still, most of the Sn, W, Nb, Ta, Mo. Be, Li. U, Au, Ag and intraplate setting by deep crustal zones of structural direct from the and related elements may have been brought up weakness that acted as channelways to magmas ore mantle. On this heretical note we conclude this section. solutions. Local structural control became pronounced in the

case of the late Hercynian and post-Hercynian vein deposits.

elements have [fit is ofthe To sum up, ore been derived 1) by weather- considered that major, economically important

from the surface of of the Peninsula the of Almadén is ing, leaching or other exogenic processes deposits only mercury - the crust this was probably the origin of the large ironstone associated with mafic volcanism, while metals of the Pyrite

the Belt deposits of Ordovician age in northwest Meseta and and the tin-tungsten province are related to felsic lead-zinc volcanic volcanism and it is clear that felsic possibly of the Cambrian ores: 2) by or plutonism. magmas played

Plutonic heat from pre-existing rocks in the upper crust - this a more important role than mafic magmas.

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