geochemical features of the massive sulfide (cu...

Per. Mineral. (2002), 71, 1,27-48

PERIODICO di MINERALOGIAestablished in 1930

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An International Journal ofMINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY,ORE DEPOSITS, PETROLOGY, VOLCANOLOGY

and applied topics on Environment, Archaeometrv and Cultural Heritage

Geochemical features of the massive sulfide (Cu) metamorphoseddeposit of Arinteiro (Galicia, Spain) and genetic implications

SILVIA SERRANTI I*, VINCENZO FERRINI2, UMBERTO MASI2,

MASSIMO NICOLETTI) and LOUIS N. CONDE4

1* Dipartimento di Ingegneria Chimica, dei Materiali, Materie Prime e Metallurgia, Universita di Roma «La Sapienza»,Via Eudossiana 18,00184 Roma (Italy)

2 Dipartimento di Scienze della Terra, Universita di Roma "La Sapienza" - P.le Aldo Moro, 5 - 00185 Roma (Italy)) CNR, Centro di Studio del Quaternario e dell'Evoluzione Ambientale, c/o Dipartimento di Scienze della Terra,

Universita di Roma "La Sapienza" - P.le Aldo Moro, 5 - 00185 Roma (Italy)4 Departamento de Ciencias da Terra, Universidade de Coimbra - Coimbra (Portugal)

Submitted, July 2001 - Accepted, October 2001

ABSTRACT. - Major and trace element contents insulfide ores, gangue minerals and rock samples fromthe Arinteiro deposits hosted in metaophiolites ofwestern Galicia were determined. S isotope ratios ofselected sulfides were also analysed.

Polymetallic orebodies, represented by abundantpyrrhotite, subordinate chalcopyrite and sphalerite,and rare pyrite, underwent metamorphicrecrystallization, probably during the last stage ofthe Hercynian orogenesis as suggested by the K/Arradiometric ages ascertained on host rocks (261 275 ± 20 Ma). Recrystallization took place at about400°C and 5.5 kbar, log aS2 was generally -7 atm orlower, log am was about -30 atm, and pH rangedmainly from 4.4 to 4.9.

The Co/Ni values and Se contents of the sulfidesare consistent with the inferred volcano-sedimentaryorigin of the deposit, and 834S (about 0 %0) indicatesthat the source of S was magmatic.

Comparisons of the Arinteiro deposit with similardeposits of corresponding origin and metamorphicrank shows the typical characteristic of the former dominant pyrrhotite and rare pyrite - indicating thegreatly reduced conditions of hydrothermal fluids,due to interaction with organic matter.

RIASSUNTO. - Sono stati dosati i contenuti deglielementi maggiori e in traccia nei solfuri, nei

Corresponding author. E-mail: [email protected]

minerali di ganga e nelle rocce incassanti di duecorpi minerari polimetallici di Arinteiro, ricorrenti inun complesso ofiolitifero metamorfosato dellaGalizia occidentale. Sono stati inoltre determinati irapporti isotopici dello zolfo di solfuri selezionati.

I corpi mineralizzati, la cui paragenesi e costituitada abbondante pirrotina, subordinate calcopirite eblenda, e scarsa pirite, si sono sviluppati a seguito diprocessi di ricristallizzazione, probabilmente durantegli ultimi stadi dell' orogenesi ercinica comesuggeriscono Ie datazioni radiometriche KIAr (261 275 ± 20 Ma) ottenute sulle rocce incassanti. Laricristallizzazione ha avuto luogo a circa 400°C e 5,5kbar, il log aS2 e variato da -7 atm a valori pilinegativi, il log am si e mantenuto intorno a -30 atme, infine, il pH ha oscillato tra 4,4 e 4,9.

I rapporti Co/Ni e gli elevati tenori di Se deisolfuri sono in accordo con la supposta originevulcano-sedimentaria della mineralizzazione, inaccordo con la quale e anche la composizioneisotopica dei solfuri (834S ~ 0 %0) che indica unasorgente tipicamente magmatica per 10 S.

Il confronto con depositi simili per genesi e gradometamorfico mostra che il deposito di Arinteiro sidistingue per l' insolita abbondanza della pirrotinarispetto alla pirite, caratteristica questa che potrebberiflettere condizioni molto riducenti dei fluidiidrotermali a causa dell' interazione con materiaorganica.

28 S. SERRANTI, V. FERRINI, U. MASI, M. NICOLETTI and L. N. CONDE

KEY WORDS: polymetallic mineralization,geochemistry, Arinteiro, Spain, metamorphosedophiolites.

INTRODUCTION

Within the framework of a research projectconcerning the geochemistry of ore deposits inthe western Iberian peninsula, this paper dealswith the polymetallic (mainly Cu) deposit ofArinteiro, in western Galicia, Spain. Thisdeposit, which until 1992 was the largest ofthose occurring in Paleozoic ophiolites insouth-western Europe, is contained in apoly metamorphic complex of LowerPalaeozoic or Precambrian (?) age,overthrusting a segment of Hercynian Europe(Badham and Williams, 1981; Williams1983a). Study of ore and rock samplesprovided information about the maingeochemical features and origin of the deposit.Lastly, its geochemical characteristics werecompared with those of other deposits ofsimilar genetic type and metamorphic ranklocated in Newfoundland, Scandinavia andNamibia, aimed at providing a deeper insightinto the origin of the Arinteiro deposit.

GEOLOGICAL SETTING AND SAMPLING

The Arinteiro deposit is located about 15 kmeast of Santiago de Compostela in westernGalicia, north-western Spain (Fig. 1). Thisregion is essentially composed of Hercyniangranitoids overthrust by polymetamorphiccomplexes of Lower Paleozoic-Precambrian (?)age. The Arinteiro deposit lies within theOrdenes Sedimentary Complex, whichmetamorphosed during the Hercynian and isbordered discontinuously by metabasites, whichmay represent dismembered relics of ophiolites(Badham and Williams, 1981). According toArps et al. (1977), the Arinteiro deposit belongsto the Santiago Unit, which represents the upperpart of the ophiolitic sequence (Badham andWilliams, 1981). The composition and grainsize of the metabasites, probably ocean-floor

basalts (Badham et al., 1985), are extremelyvariable. They are mainly represented byhornblende-plagioclase amphibolites withscarce garnet (almandine), salite and quartz and,subordinately, amphibolites withcummingtonite and biotite. The host rocks showcompositional variations with respect to theunaltered amphibolites of the Santiago Unit,reflecting differences already existing in therocks prior to metamorphism and essentiallydue to alterations by mineralizing fluids(Williams, 1983a). In fact, unlike commonamphibolites, the host rocks are relatively Capoor and contain gedrite and cummingtonite,which are characteristic of amphibolitesassociated with sulfide mineralizations (Spearand Schumacher, 1982).

The Santiago Unit hosts two differenttypes of sulfide mineralization, bothclosely concordant with rock schistosity. Onetype is represented by the Arinteiro s.s.and Barna orebodies (Fig. 1), with pyrrhotiteand chalcopyrite disseminated in acoarse-grained rock composed of almandine,gedrite and quartz. The other type, somekilometres westwards within a largermetabasite outcrop, is formed of two relativelysmall orebodies of massive sulfides, Fornasand Manoca, composed of pyrrhotite,subordinate chalcopyrite, and scarce pyriteand sphalerite.

At the moment of sampling (1989) only theFornas and Barna orebodies (l and 20 millionmetric tons, 1-2 % and 0.5 % Cu, respectively)were exploited. The Fornas massive orebody iscomposed of several intensely deformed andrecrystallized lenses, located in the hinges ofisocline folds and showing sharp contacts withthe garnet amphibolitic wallrocks. The Barnadisseminate orebody is about 10 km longand 20-80 m thick, and is also located in thehinges of isocline folds of garnet amphibolites,grading outwards to hornblende-plagioclaseamphibolites. The amphibolites show thin (1-5ern), locally more abundant, calcite layers up to20 m far from the orebody. The contactbetween amphibolites and calcite layerssometimes shows evidence of metamorphic

Geochemicalfeatures of the massive sulfide (Cu) metamorphosed deposit ofArinteiro (Galicia, Spain) ... 29

0Ultramatic rocks

Metasedimcntarv rocksL- IOrthogneiss .and Granite

X Mine

Low metamorphic gradeCJPrecambrian to

Devonian sedimentary rocks

D Metasedimentary rocksand orthogneiss

~ Foliation"'--""Thrust

o km 3

Others

gGabbro

"-< Fault

tN

Fig. I - Lower left: map of Spain showing Santiago de Compostela area. Upper left: geological sketch map of NW Spain(western Galicia), showing location of Arinteiro deposit (white box). Upper right: geological sketch-map of area ofArinteiro deposit, with locations of disseminate orebodies of Arinteiro s.s. and Barna, and massive orebodies of Fornas andManoca (modified after Williams, 1983a).

reactions, i.e., presence of diopside,grossularite, epidote, clinozoisite andwollastonite. According to Williams (1983a),the Barna disseminate orebody is the stockworkof the smaller massive orebody of Fornas,which formed on the seafloor.

With the assistance of the geological staff ofthe Arinteiro mining company, more than 20representative samples (with dimensions ofabout 3 dm- each) of bulk ores, and mineralizedand unmineralized rocks from both Fornas andBarna mines were collected for this study.

ANALYTICAL METHODS

A minerographic study of all collectedsamples was carried out by reflected and

transmitted-light microscopy. The compositionof the main minerals was determined byelectron microprobe lEOL lXA 50 A (EDSLink). Eighteen sulfide separates were alsoselected from the samples and analysed formajor and trace elements by atomic absorptionspectrophotometry. Separate purity (about98%) was checked by XRD analysis, whichshowed no evidence of extra-mineral phases inthe diffraction patterns of each mineral,because no extra-peaks higher than 3 o withrespect to the background were observed. TheS isotopic composition of the sulfide separateswas also analysed according to standardprocedures, and results are expressed as per milunits against the eDT standard. Lastly, tenhost-rock samples from the Barna orebodywere analysed for major and trace elements by


atomic absorption spectrophotometry. Twosamples of the latter group were also examinedto verify their K-Ar radiometric ages, followingthe method of Nicoletti and Petrucciani (1977).Details of the laboratory standards used, decayconstants and error calculations are given inAkinci et al. (1991).

ANALYTICAL RESULTS

Mineral and rock microscopy

Fornas

The massive mineralization is composed ofpyrrhotite, subordinate chalcopyrite, scarcepyrite and sphalerite, and quartz and chlorite asgangue minerals. Pyrrhotite, which turned outto be hexagonal by XRD analysis, occurs asirregular lumps, often fractured and infilled by

quartz. Chalcopyrite and sphalerite formirregular masses around pyrrhotite;chalcopyrite may also occur as exsolution blebsin sphalerite (Fig. 2). Both pyrrhotite andchalcopyrite often replace wallrock silicates(Fig. 3). Two generations of pyrite wereidentified in a few samples: pyrite I occurs insamples GA-3-3 and GA-4-2 as cubic andsubhedral porphyroblasts of various size,intensely fractured and infilled by quartz,amphiboles, pyrrhotite, sphalerite andchalcopyrite (Fig. 4); pyrite II, derived from thetransformation of pyrrhotite, occurs only insample GA-4-2. Etching of pyrite-I crystalswith cone. HN03 showed growth structure; thedifficulty lay in deciphering when growthactually occurred (Craig and Vokes, 1993).Alteration of pyrrhotite into pyrite II startsfrom the rim towards the centre of the crystal(Fig. 5).

Fig. 2 - Photomicrograph showing sphalerite (sph) with chalcopyrite blebs, chalcopyrite (cpy) and an amphibole relic(amph) from Fornas orebody (sample GA-lB-3; reflected light).


Fig. 3 - Photomicrograph showing amphibole (amph) corroded and replaced by pyrrhotite (po) and chalcopyrite (cpy) fromFornas orebody (sample GA-2-1; reflected light).

Fig. 4 - Photomicrograph showing subhedral pyrite I (py) porphyroblasts, fractured and replaced by chalcopyrite (cpy), in amass of pyrrhotite (po) from Fornas orebody (sample GA-4-2; reflected light).


Fig. 5 - Photomicrograph showing pyrrhotite (po), transformed into pyrite II (py) from rim towards centre of crystal,chalcopyrite (cpy) and sphalerite (sph) from Fornas orebody (sample GA-4-2; retlected light).

Textural relationships show that pyrite Icrystallized earlier than pyrrhotite, and wasfollowed by crystallization of chalcopyrite andsphalerite; lastly, pyrrhotite was occasionallytransformed into pyrite II.

The bulk ore samples contain a number ofsilicate relics either as «rolled-ball» clusters(Williams, 1983b) or disseminated singlecrystals, intensely deformed and often replacedby sulfides. These silicates are represented, inorder of decreasing abundance, by amphiboles(gedrite, cummingtonite, hornblende),chloritized biotite, plagioclase and, only insample GA-3-3, staurolite. Rutile and gahnite(the latter only in sample GA-3-3) sometimesoccur. Rutile and staurolite are present as roundinclusions within the other minerals, mainlyamphiboles. Gahnite, a common mineral inmetamorphosed sulfide deposits, probablyderived from the reaction of sphalerite andgedrite (Williams, 1983b).

Bama

The amphibolites host sulfides, mainlydisseminated and subordinately in the form oflayers together with quartz and carbonates,alternate with layers of severely fracturedgarnets. In the latter case, sulfides are eitherinterstitial to amphibole crystals (Fig. 6),infillthe cracks of garnet porphyroblasts togetherwith quartz, or form veinlets parallel to therock schistosity, together with quartz, chloriteand carbonates (Fig. 7). Sulfides may replaceamphiboles, especially when the latter areintensely deformed and broken. Sulfides arerepresented by pyrrhotite, subordinatechalcopyrite, very rare pyrite, and sphalerite.Pyrrhotite is sometimes included inchalcopyrite. Cubic pyrite and sphalerite occuras small grains only in sample GA-15-1.Among gangue minerals, quartz formsprismatic subhedral crystals of various sizes,showing undulated extinction under crossed

Geochemical features of the massive sulfide (Cu) metamorphosed deposit ofArinteiro (Galicia, Spain) ... 33

Fig. 6 - Photomicrograph showing disseminate pyrrhotite (po) and chalcopyrite (cpy) in amphibole (amph) lenses withrutile (ru) from Bama orebody (sample GA-18; retlected light).

amph

Fig. 7 - Photomicrograph showing a veinlet of pyrrhotite (po) and chalcopyrite (cpy) parallel to amphibole (amph)elongation from Bama orebody (sample GA-12-1 ; reflected light).


nicols. Chlorite occurs as either small, oftenfibrous laths, or parallel, radiated clusters,lining the fractured silicates, together withsulfides, carbonates and quartz.

Textural relationships show that pyrrhotitewas deposited before chalcopyrite. As regardssphalerite and pyrite, there is no clearindication of their paragenetic position in thesequence because of their scarcity. Quartz wasdeposited together with sulfides, followed bycarbonates and chlorites.

Bama host rocks

These show oriented porphyroblastic fabricand a nematoblastic matrix, and are composedof quartz, garnet and amphiboles interbeddedwith scarce plagioclase and biotite. Rutile,ilmenite, sphene and apatite are minorminerals. Garnet (almandine), occurring asisolated idio- and subidio-porphyroblasts, isintensely fractured and dismembered, thecracks being infilled with quartz, subordinatechlorite and biotite. Both grain size andabundance of garnet decrease with distancefrom the ores. Amphiboles, often altered tochlorite, form clusters of oriented, prismatic tofibrous crystals. Gedrite is more abundant thancummingtonite, but hornblende is the mainamphibole in the wallrocks, far from the ores.Quartz occurs as crystals of various sizes andmay form veinlets oriented parallel to the rockschistosity. The rare plagioclase is oligoclaseand the biotite is generally altered to chloriteand greatly deformed.

Geochemistry

Table 1 shows major and trace elementcontents in the main minerals, table 2 gives theS-isotope composition of selected sulfideseparates, table 3 lists element contents in theBama host rocks, and table 4 displays the K-Arradiometric ages of host-rock samples fromBama.

Fornas

As usual, pyrrhotite shows less Fe and,conversely, more S (average variation about2% for each element) than the stoichiometricmineral. It also contains high Cu (x = 1,894ppm), subordinate Se, Co, Zn and Ni (x = 316,214, 117 and 104 ppm, respectively), low Pband As (x = 53 and 49 ppm) and scarce Mn, Vand Cd (x = 20, 19 and 7 ppm).

Chalcopyrite and pyrite I are generally nearlystoichiometric. Chalcopyrite also showsmoderate Se and As (x = 243 and 133 ppm),and low Cd, Mn, Pb, Co, Ni and V (x =68, 68,49, 39, 32 and 21 ppm). Pyrite I contains highCo and Cu (x = 1,999 and 1,490 ppm),subordinate Se and Zn (x = 301 and 266 ppm),low As and Pb (x =68 and 57 ppm) and scarceNi, V, Mn and Cd (x = 19,16,12 and 7 ppm).

Sphalerite, especially when associated withpyrite, shows a clear Zn (x = 8.6%) deficiencywith respect to stoichiometry. In contrast, itcontains significant Fe (x = 7.8 %) andsometimes Cd and Mn (x = 1.2 and 0.3%).

Chlorite is pycnochlorite transitional tobrunsvigite, according to Hey's (1954)classification.

Lastly, the 834S ranges of pyrite I (-0.4 to+0.7%0), pyrrhotite (-0.6 to + 0.9 %0) andchalcopyrite (-0.2 to -0.7 %0) are narrow andoverlapping, indicating lack of isotopicequilibrium among the three sulfides (Ohmotoand Rye, 1979). However, as the isotopicfractionation of a given mineral pair correlatesnegatively with temperature, the similar Sisotope ratios may reflect high temperatures offormation.

Bama

As at Fornas, pyrrhotite shows less Fe and,conversely, more S (average variation of 2.8%for each element) than the stoichiometricmineral.

Chalcopyrite and pyrite, both from sampleGA-15-1, are nearly stoichiometric.Chalcopyrite also shows high Zn (1,775 ppm),subordinate Se and As (296 and 104 ppm), lowCo, Mn, Ni and Pb (x =65, 54, 54 and 37 ppm)and scarce V and Cd (21 and 7 ppm).


TABLE 1Major contents (mass %)of the main mineral phases of the Arinteiro deposit determined by microprobe

analyses. The stoichiometric compositions are written within brackets. n number ofsignificant analyses(>2a/total); a = analytical error; s. d. = standard deviation. Also shown are trace-element contents (ppm) insulfides from Fornas and chalcopyrite ofsample GA-15-1 from Bama determined by atomic absorption. nd =

below detected limit. The figures underlined are excluded from averages.

FORNAS

PYRRHOTITE(S = 36.5%;Fe = 63.5%)

mean± s. d. n I 32 a (%)

S 38.63± 1.00 32 0.20Fe 61.31 ±0.46 32 0.46

SAMPLE Cu Zn Co Ni Pb Mn V Cd Se As Co/Ni

GA-I-A 1342 48 400 101 60 17 19 7 320 37 3.96GA-2-1 2164 120 143 108 46 17 17 7 359 37 1.32GA-3-5 2664 196 135 109 51 21 21 8 282 245 1.24GA-4-1 5010 253 382 95 49 17 17 8 321 nd 4.02GA-5-1 1112 41 121 105 198 20 20 6 292 86 1.15GA-5-2 2190 45 100 104 58 20 20 6 323 85 0.96mean 1894 117 214 104 53 19 19 7 316 49 2.11s. d. 646 90 138 5 6 2 2 1 27 37 1.46

CHALCOPYRITE(S = 35.0%;Fe = 30.4%; Cu = 34.6%)

mean ± s. d. n/32 a(%)

S 34.53± 1.15 32 0.19Fe 30.58± 0.24 32 0.35Cu 35.08± 1.15 32 0.52

SAMPLE Zn ZnS (%) Co Ni Pb Mn V Cd Se As Co/Ni

GA-I-A 15558 2.33 44 37 43 81 29 64 480 163 1.19GA-IB-l 14278 2.14 37 34 42 89 38 77 198 50 1.09GA-IB-3 14934 2.23 40 31 84 42 23 64 168 159 1.29GA-4-1 15561 2.33 37 32 33 77 29 66 199 146 1.16GA-4-3 17257 2.56 37 28 43 54 18 70 168 149 1.32mean 15518 2.32 39 32 49 68 27 68 243 133 1.21s. d. 1108 0.16 3 3 20 20 8 5 134 47 0.09


Table 1: CONTINUED

PYRITE I(S =53.5%; Fe 46.5%)

mean ± s. d. n/8 S (%)

S 54.07 ± 0.30 8 0.22Fe 45.98 ± 0.25 8 0.40

SAMPLE Cu Zn Co Ni Pb Mn V Cd Se As Co/Ni

GA-2-1 515 203 2487 21 46 10 17 6 256 57 118.43GA-2-3 913 83 2042 15 48 13 15 5 316 100 136.13GA-3-4 1178 501 1827 22 65 ill 17 9 363 52 83.05GA-3-5 1866 315 1566 18 72 12 17 8 250 39 87.00GA-4-2 2450 98 1505 19 52 12 16 8 316 58 79.21GA-5-1 2020 393 2569 16 61 14 16 4 306 102 160.56mean 1490 266 1999 19 57 12 16 7 301 68 110.73s. d. 738 167 453 3 10 1 1 2 42 26 33.20

SPHALERITE(S =32.9%; Zn 67.1%)

mean ± s. d. n I 24 o (%)

S 33.24 ± 1.41 24 0.18Zn 58.51 ± 1.59 24 0.76Fe 7.81 ±0.41 24 0.22Cd 1.23 ± 0.25 8 0.30Mn 0.32 ± 0.05 10 0.11Cu 0.70 ± 0.19 6 0.25

PYCNOCHLORITE(Si02 =28.32%; A120 3 = 19.03%; FeO = 14.85%; Fe203 = 1.19%; MgO =23.72%; H2O 12.10%)

mean ± s. d. n III cr (%) mean ± s. d. n 111

Si02 28.33 ± 0.69 11 0.09 Si 5.68 ± 0.10 11A120 3 19.17 ± 1.06 11 0.10 Al (IV) 2.32 ± 0.10 11FeO 17.68 ± 1.34 11 0.20 Al (VI) 2.18±0.13 11MgO 22.55 ± 1.12 11 0.15 Mg 6.72 ± 0.28 11H2O 11.80 ± 1.31 11 Fe 2.96 ± 0.25 11

GEDRITE CUMMINGTONITE

mean ± s. d. n/5 o (%) mean ± s. d. n/6 o (%)

Si02 47.91 ± 0.34 5 0.12 SiO') 54.92 ± 0.81 6 0.12Ti02 0.29 ± 0.06 2 0.06 AI203 2.69 ± 0.75 6 0.07AI203 11.99 ± 0.77 5 0.09 FeO 14.07 ± 1.04 6 0.18FeO 13.97 ± 0.27 5 0.18 MnO 0.44 ± 0.06 6 0.08MgO 20.99 ± 0.55 5 0.14 MgO 23.87 ± 0.85 6 0.15CaO 0.59 ± 0.06 5 0.05 CaO 0.48 ± 0.06 6 0.05Na20 1.51 ± 0.13 5 0.12 Na')O 0.75 ± 0.13 6 0.11H2O 2.41 ± 0.25 5 Hi) 2.78 ± 0.51 6


Table 1: CONTINUED

HORNBLENDE BIOTITE


Si02 46.72 ± 1.37 6 0.12 Si02 39.31 ± 0.25 3 0.11Ti02 0.55 ± 0.11 6 0.07 Ti02 1.22 ± 0.05 3 0.08A120 3 12.90 ± 1.53 6 0.09 A120 3 17.31 ± 0.23 3 0.10FeO 8.76 ± 0.86 6 0.15 FeO 8.93 ± 0.17 3 0.16MgO 15.90 ± 1.13 6 0.14 MgO 18.41 ± 0.13 3 0.14CaO 10.43 ± 0.34 6 0.09 Na20 0.65 ± 0.06 2 0.11Na20 1.83±0.19 6 0.12 K20 8.65 ± 0.06 3 0.09K20 0.14 ± 0.03 4 0.05 H2O 5.55±0.19 3H2O 2.79 ± 0.99 6

STAUROLITE GAHNITE


Si02 28.29 ± 0.25 4 0.10 A120 3 59.11 ± 1.53 5 0.13Ti02 0.65 ± 0.12 4 0.06 FeO 5.84 ± 0.21 5 0.15A120 3 54.38 ± 0.33 4 0.14 MgO 3.39 ± 0.33 5 0.11FeO 7.15±0.17 4 0.15 ZnO 32.27 ± 0.80 5 0.49ZnO 6.92 ± 0.40 4 0.27MgO 3.57 ± 0.23 4 0.10

BAMA

PYRRHOTITE(S =36.5%; Fe =63.5%)

mean ± s. d. n I 20 c (%)

S 39.23 ± 0.19 20 0.19Fe 60.60 ± 0.41 20 0.45

CHALCOPYRITE(S =35.0%; Fe =30.4%; Cu =34.6%)

mean ± s. d. n I 20 o (%)

S 34.87 ± 0.32 20 0.18Fe 30.43 ± 0.16 20 0.35Cu 34.49 ± 0.60 20 0.50

SAMPLE Zn Co Ni Pb Mn V Cd Se As Co/Ni

GA-15-1 1775 65 54 37 54 21 7 296 104 1.20


Table 1: CONTINUED

PYRITE SPHALERITE(S =53.5%; Fe =46.5%) (S =32.9%; Zn =67.1 %)


S 52.68 ± 0.33 4 0.21 S 33.30 ± 0.13 4 0.18Fe 46.99 ± 0.53 4 0.40 Zn 56.53 ± 0.74 4 0.73

Fe 8.22 ± 0.23 4 0.22

CALCITE SIDERITE(CaO =56.0%; CO2 =44.0%) (FeO =62.0%; CO2 =38.0%)

mean ± s. d. n/lO o (%) mean ± s. d. n/3 o (%)

CaO 52.89 ± 1.77 10 0.19 FeO 41.65 ± 1.61 3 0.21MnO 1.41 ± 0.81 10 0.04 MgO 13.86 ± 1.70 3 0.15MgO 0.27 ± 0.21 10 0.05 MnO 2.35 ± 0.53 3 0.09FeO 0.57 ± 0.52 10 0.09 CaO 0.84 ± 0.74 3 0.07CO2 44.75 ± 1.57 10 CO2 41.56 ± 0.26 3

RIPIDOLITE(Si02 =26.45%; A1203 =20.88%; FeO =21.28%; Fe203 =2.82%;

MgO =17.04%; MnO =0.44%; H20 =11.09%)

TYPE A

mean ± s. d. n /10 o (%) mean ± s. d. n/lO

Si02 26.80 ± 0.42 10 0.09 Si 5.27 ± 0.05 10A1203 23.49 ± 0.36 10 0.10 Al (IV) 2.74 ± 0.05 10FeO 16.18 ± 0.59 10 0.19 Al (VI) 2.70 ± 0.04 10MgO 22.17 ± 0.47 10 0.14 Mg 6.50 ± 0.12 10H2O 11.31 ± 0.88 10 Fe 2.66 ± 0.10 10

RIPIDOLITE(Si02 =26.45%; AI203 =20.88%; FeO =21.28%; Fe203 =2.82%;

MgO =17.04%; MnO =0.44%; H20 =11.09%)

TYPEB

mean ± s. d. n/2 o (%) mean ± s. d. n/2

Si02 25.56 ± 0.43 2 0.09 Si 5.31 ± 0.04 2A1203 21.41 ± 0.54 2 0.10 Al (IV) 2.69 ± 0.04 2FeO 27.62 ± 0.74 2 0.20 Al (VI) 2.56 ± 0.13 2MgO 14.29 ± 1.01 2 0.15 Mg 4.43 ± 0.27 2H2O 10.84 ± 0.63 2 Fe 4.80 ± 0.16 2


Table 1: CONTINUED

DAPHNITE(Si02=22.27%; AI20 3 21.40%; FeO =43.01 %;

MgO 2.35%; MnO =0.05%; H2O 10.21%)

mean ± s. d. n/5 s (%) mean ± s. d. n/5

Si02 22.64 ± 0.30 5 0.09 Si 5.08 ± 0.07 5A120 3 21.90 ± 0.62 5 0.10 Al (IV) 2.92 ± 0.07 5FeO 38.23 ± 0.55 5 0.20 Al (VI) 2.87 ± 0.08 5MgO 5.36 ± 0.25 5 0.15 Mg 1.79 ± 0.08 5H2O 11.79 ± 0.73 5 Fe 7.17±0.13 5

GEDRITE CUMMINGTONITE


Si02 43.71 ± 0.24 5 0.11 Si02 53.40 ± 0.95 3 0.12Ti02 0.19 ± 0.05 3 0.07 AI20 3 2.54 ± 1.34 3 0.07AI20 3 16.79 ± 0.71 5 0.10 FeO 20.67 ± 1.48 3 0.20FeO 20.66 ± 0.28 5 0.21 MnO 0.35 ± 0.11 3 0.08MgO 14.72 ± 0.27 5 0.13 MgO 20.17 ± 0.94 3 0.13CaO 0.27 ± 0.06 5 0.04 CaO 0.93 ± 0.88 3 0.05Na20 1.56 ± 0.07 5 0.11 H2O 2.10 ± 0.97 3H2O 2.17 ± 0.20 5

HORNBLENDE ALMANDINE

mean ± s. d. n/3 c (%) mean ± s. d. n/8 cr(%)

Si02 44.00 ± 0.45 3 0.11 Si02 38.11 ± 0.90 8 0.11Ti02 0.58 ± 0.06 3 0.07 AI20 3 22.36 ± 0.35 8 0.10AI20 3 16.07 ± 0.70 3 0.09 FeO 31.35 ± 1.91 8 0.25FeO 12.74 ± 0.22 3 0.17 MnO 0.93 ± 0.39 8 0.09MgO 11.99 ± 0.56 3 0.12 MgO 6.66 ± 0.89 8 0.10CaO 10.36 ± 0.21 3 0.09 CaO 2.41 ± 1.69 8 0.06Na20 1.74 ± 0.20 3 0.11K20 0.18 ± 0.01 2 0.04H2O 2.11 ± 0.46 3

Sphalerite from sample GA-15-1 containsless Zn (x = 10.6%) than the stoichiometricmineral and has significant Fe (x = 8.2%).

According to Hey's (1954) classification,three types of chlorite were identified in thesamples. Two types are ripidolites, hereaftercalled ripidolite-A and ripidolite-B (the latteronly found in sample GA-15-1), characterizedby lower and higher Fe/Fe--Mg ratios,

respectively; the third type (only in sampleGA-20-2) is daphnite. On the whole, Barnachlorites are distinguished from Fornaschlorites because of their comparatively greatercontents of FeO and less MgO.

Two types of carbonates were detected:calcite, and a Mg-rich siderite (sideroplesite,Deer et al., 1963). This latter is present only insample GA-15-1.


TABLE 2

S-isotope composition expressed in %0 against theeDT standard for selected sulfide separates from the

Fornas orebody, and chalcopyrite GA-15-1 fromthe Bama orebody.

SAMPLE ()34S

py GA-2-1 +0.7py GA-2-3 -0.4py GA-3-4 + 0.1py GA-3-5 + 0.1py GA-4-2 - 0.1

mean +0.08

pO GA-1-A - 0.6pO GA-1B-3 -0.1pO GA-2-1 +0.9pO GA-3-5 +0.6pO GA-5-1 0.3po GA-5-2 - 0.6

mean +0.05

cpy GA -l-A - 0.2cpy GA -lB-3 -0.4cpy GA -4-1 -0.2cpy GA -15-1 - 0.7

mean -0.38

Lastly, the 834S of chalcopyrite from sampleGA-15-1 is -0.7 %0, similar to the values of theFornas chalcopyrites.

Composition and radiometric age ofBama hostrocks

The wide compositional range correlateswith the ample mineralogical range.Comparisons with unmineralized rocks fromthe same area (Williams, 1983a) shows that thestudied samples are enriched in Fe, Cu, Pb, Zn,Cd, As, Co and Se, and depleted to variableextents in Ca, Sr, Ni, K, Na and Mg.

The K/Ar radiometric ages of two samplesare 261 ± 20 and 275 ± 20 Ma. These agesoverlap within analytical error.

DISCUSSION

K-Ar radiometric ages ofBama host rocks

Radiometric ages indicated that themetamorphic recrystallization of the Arinteiroores occurred during the last stage of theHercynian orogenesis.

Mineral and rock composition

As evident from field geology, regionalmetamorphism reached the amphibolitic stage.In particular, the presence of staurolite suggeststemperature not less than 500 aC, and thecrystallization of almandine at this temperatureimplies that pressure was higher than 4 kbar(Winkler, 1976). During metamorphism, theores recrystallized and, althoughmetamorphism was essentially isochemical(Williams, 1983a), element redistributionamong minerals may have occurred. In thisview, we examine the distribution of Co and Nibetween pyrite and pyrrhotite, as these sulfidesgenerally show similar Co/Ni inunmetamorphosed deposits (Campbell andEthier, 1984), whereas Co and Ni arepreferentially concentrated by pyrite andpyrrhotite, respectively, in metamorphoseddeposits (Bralia et al., 1979). Table 1 showsthat these pyrites and pyrrhotites have Co/Niratios (x = 111 and 2, respectively) consistentwith metamorphic redistribution.

Se contents in pyrrhotite and pyrite I aresimilar and generally higher than those inchalcopyrite. This pattern is consistent with thelate crystallization of chalcopyrite with respectto pyrrhotite and/or pyrite I, and supports theobservation that Se contents in sulfides do notvary during regional metamorphism(Wedepohl,1974).

The high Cu contents in pyrrhotite and pyriteI from Fornas are consistent with the high Cuconcentration in the mineralizing fluids, provenby the deposition of chalcopyrite afterpyrrhotite and pyrite. Moreover, at Fornas thepresence of both chalcopyrite exsolution blebsin sphalerite and significant ZnS in

C1noa"~~;:;.l::l

~§~

'"TABLE 3~

Major- (mass %) and trace- (ppm) element contents in Bama amphibolitic host rocks determined by atomic absorption. nd = below detection limit. ::s-no

The figures underlined are excluded from averages. :::ll::l

'":::.Sample Fe Mg Na Ca K Mn Cu V Zn Co Pb Li Ni Sr Ba Cd Rb Se As Co/Ni I~

S;GA-1O-2 13.52 3.46 1.22 0.13 0.04 1505 854 559 1053 92 75 95 34 27 nd 16 4 122 97 2.71 ~no

GA-11-2 14.13 3.33 0.21 0.25 0.05 1951 2214 534 127 110 184 16 26 21 163 4 6 115 39 4.23 RGA-12-1 9.91 4.19 1.52 0.28 0.12 819 322 741 376 78 57 70 23 58 161 4 8 121 27 3.39GA-13-1 11.38 4.47 1.05 0.29 0.07 2189 431 621 247 84 66 43 27 45 53 4 8 124 97 3.11

:::l~

GA-15-2 11.95 5.38 0.29 0.16 0.02 760 78 705 525 84 65 27 22 23 nd 8 6 145 39 3.82l::l:::::

GA-16-3 9.43 0.73 0.06 0.08 0.04 1238 741 257 70 54 23 9 32 12 nd 3 2 65 nd 1.69§'\:i

GA-17-1 10.61 2.40 0.93 0.20 0.10 2521 1127 367 281 72 76 28 27 35 269 6 8 92 78 2.67 ::s-a'"GA-19-1 7.47 0.50 0.04 0.16 0.02 859 683 312 64 40 62 6 16 10 nd 6 1 52 nd 2.50 no~

GA-20-1 11.10 1.98 2.26 0.08 0.03 1392 3911 425 259 93 48 39 31 41 nd 10 10 73 39 3.00 ~

~GA-21-1 10.44 3.41 0.57 3.32 0.07 3566 606 379 426 78 98 16 58 29 nd 4 6 88 28 1.34 a

~.

mean 10.99 2.99 0.82 0.18 0.06 1680 1210 490 264 79 63 35 30 30 7 6 100 44 2.85 Its. d. 1.94 1.50 0.72 0.08 0.03 892 1156 167 160 20 21 28 11 15 4 3 30 35 0.88~.(3

Gs,;:;.£S.

~:::.2-

.,J:::..I-'


TABLE 4

K-Ar radiometric ages ofBama amphibolitic host rocks.

SAMPLE

GA-17

GA-20

rad 40Ar/g

1.118 x 10-6

1.121 x 10-6

1.763 x 10-6

rad 40Ar %

9.5%10.5%

12.0%

K (mass %)

0.100.10

0.03

t ± e (Ma)

275 ± 20261 ± 20

265 ± 15

chalcopyrite suggests that the deposition ofchalcopyrite and sphalerite overlapped to someextent. Unlike the case at Fornas, at Barna nodata on Cu contents in pyrrhotite and pyritewere available, as separates of these sulfideswere not obtained. However, the deposition ofchalcopyrite indicates that, also at Barna, thefluids were Cu-rich,

The high Zn in Barna chalcopyrite isconsistent with the relatively high Znconcentration in the mineralizing fluids, asproven by the deposition of sphalerite afterchalcopyrite in both localities.

Fe contents in sphalerite are similar to thosein sphalerite of pyrrhotite-rich deposits (Craiget al., 1984).

The higher Fe contents in Barna chlorite thanin Fornas chlorite probably reflect thecomparatively higher Fe contents in the Barnafluids. In general, chlorite composition reflectsthe compositional range of the mineralassemblage (Bryndzia and Scott, 1987;Mignardi et al., 1997). Thus, at Barnaripidolite-A is associated with pyrrhotite andchalcopyrite and ripidolite-B with pyrite andsphalerite; and daphnite occurs with pyrrhotite,chalcopyrite, quartz and carbonates.

As well as chlorite, gedrite and hornblendefrom Barna contain more FeO and, conversely,less MgO than the corresponding Fornassilicates. This is consistent with the fact thatgedrite probably occurred because of thereaction of quartz and chlorite in the presenceof a little Na20 at temperatures between 550and 700°C and pressures of 1-2 kbar (Spearand Gilbert, 1982).

Lastly, enrichment of the Barna amphibolitic

host rocks in Fe, Cu, Pb, Zn, Cd, As, Co and Seis explained by sulfide dissemination.Depletion in Ca, Sr, Na, K, Mg and Ni wascaused by chloritization of hornblende andbiotite operated by mineralizing fluids.

Physical-chemical conditions ofore formation

Taking into account atomic Fe % inpyrrhotite (47 %) associated with pyrite,temperatures of formation of 400 ± 80 and 400± 50°C may be calculated for the Fornas andBarna ores, respectively (Arnold, 1962). Thesetemperatures are too high for sulfidescrystallizing in an ophiolitic environment(Lydon, 1988) but are fully consistent withmetamorphic recrystallization, being lowerthan the peak temperature. Moreover, takinginto account the relationship of IVAI contents inchlorite with temperature (Cathelineau andNieva, 1985), because the average IVAIcontents in Fornas pycnochlorite and Barnaripidolite-A are 2.32 and 2.74, respectively,temperatures of 265 ± 10 and 310 ± 10°C maybe calculated for these minerals, respectively.These values are reasonable, as they fall withinthe range for chlorite from similarmineralizations.

Using the relationship between pressure andFeS contents in sphalerite (Hutchison andScott, 1981), as the Fornas and Barnasphalerites contain 13.5 and 14.2 FeS %,respectively, pressures between 5.3 and 5.5kbar may be calculated. These values areconsistent with those estimated from themetamorphic mineral assemblage.

Assuming t = 400°C, and taking into


account atomic Fe contents in pyrrhotite (47%)and FeS contents in sphalerite (13.5 and 14.2 %at Fornas and Barna, respectively), it iscalculated that log aS2 ranged initially between-7 and -8, and then decreased to more negativevalues as the mineralizing process evolved(Fig. 8).

Lastly, Fig. 9 shows that pH was lower than4.9 at t = 350°C and log am was about - 30atm, considering the association of pyrrhotite,pyrite and chalcopyrite, together with 034S(Tab. 2). At Barna, the pH was occasionallyhigh enough to allow carbonates to bedeposited in layers with sulfides and quartz.

e

Origin of the deposit

Although the values of the Co/Ni values ofpyrite may not be original because of possibleredistribution of the two elements withpyrrhotite during metamorphism, they areplotted together with the pyrrhotite values inFig. 10, in which the genetic fields for thesesulfides are shown for comparison (Bajwah etal., 1987; Brill, 1989). The Co/Ni values ofchalcopyrite are also plotted, although there isno information in the literature on thebehaviour of the two elements in chalcopyritewith respect to other coexisting sulfides during

-5

NCI'I

ceo.....

-10

-IS

Fig. 8 - Sulfur activity as a function of temperature, sulfide stability, Fe (atomic %) pyrrhotite composition and FeS (mole%) composition of sphalerite in equilibrium with pyrite in Fe-Zn-S system (modified after Barton and Toulmin, 1966, andBarton and Skinner, 1967). Black circle: probable conditions of pyrite and pyrrhotite deposition at Fornas and Barna; blackarrow: variations in aS2 and T with evolution of mineralizing process.

44 S. SERRANTI, V. FERRINI, U. MASI,M. NICOLETTI and L. N. CONDE

24,..-----,.----,.--r--.,...----r----,----,

Ql

o"'l~U "iiiU

I

8632 ~---'------'--'---'---JJ.----'-------'-----'-

2

E....~

~28

0eu

0')

.2

30

pH

Fig. 9 - Cu-Fe-S-O system and mineral stability at about 350°C (modified from Norman and Sawskins, 1985). Solid linemarked [0]: 034S of sulfides precipitated from solutions, in which OL34S LS = 0 %0, ionic strength = I, LS = 0.0 Imole/kgH2() (Ohmoto, 1972). Black area: probable values of pH and log a02 for ore formation at Fornas.

metamorphism. Fig. 10 shows that the threesulfides show Co/Ni values characteristic ofmassive hydrothermal volcanogenic sulfides.Together with the high Se contents (Anderson,1969), this supports the pre-metamorphic originof the deposit (Badham and Williams, 1981), asalso suggested by 834S (Tab. 2), indicating thatS is typically magmatic in origin (Ohmoto andRye, 1979). There is also evidence thatmetamorphic recrystallization did not alter theoriginal S isotopic signature, in agreement withthe above inference of metamorphism havingacted as a closed system (Williams 1983a).

Lastly, it is interesting to compare the mainfeatures of the Arinteiro deposit with those ofother massive sulfide deposits hosted in

pillowed metabasalts of amphibolitic facies.For this, three deposits were selected: GullPond, Newfoundland (Bachinski, 1978),Sulitjelma, Scandinavian Caledonides (Cook etal., 1990, 1993), both of Lower Palaeozoic age,and Matchless, Namibia (Klemd et al., 1987,Cook et al., 1994), Upper Proterozoic. Thedominant sulfide in these deposits is pyrite,accompanied by minor hexagonal pyrrhotite,chalcopyrite and sphalerite. Pyrrhotite is moreabundant than pyrite only in some sectors ofthese deposits. In addition, a common featureto all these deposits is the scarcity or even theabsence of galena, indicating that, if this sulfidewas involved in remobilization processes, itwas deposited elsewhere (Cook et al., 1994).

Geochemicalfeatures of the massive sulfide (Cu) metamorphosed deposit ofA rinteiro (Galicia, Spain) ... 45

100001000

• pyrrhotite• pyriteA chalcopyrite

100

Ni (ppm)

I

I magmaticI

I

\"- f"".,

1\ /

1\~ /

/.-~

/,/

.- t - --/

/'

/

/

~~~"-;

.'/

.~' GO »:

I\\

\.

"-

"-<,

~

10e:'~

O~~

'<'~~,

.'/

.~'GO

10

100

1000

10000

oU

Ea.a.-

Fig. 10 - Plot of Co and Ni contents in iron sulfides and chalcopyrite from massive orebody of Fornas. Fields forvolcanogenic pyrite and chalcopyrite (dashed area) also shown for comparison (data from Brill, 1989, and Bajwah et al.,1987).

Of the three deposits, Gull Pond is the onemost similar to Arinteiro, partly because of theclose 8345 (Bachinski, 1977). However,Arinteiro is distinguished from the above threedeposits mainly because pyrrhotite is thedominant sulfide throughout the mineralization.According to Bralia et al. (1979) and Craig andVokes (1993), increasing metamorphic P-Tconditions favour the transformation of pyriteinto pyrrhotite. This may therefore explain whyArinteiro contains abundant pyrrhotite,although the scarce pyrite does not show

optical evidence of incipient transformation.However, it does not explain why the otherdeposits of similar metamorphic rank have onlya little pyrrhotite. Neither can the presence ofabundant pyrrhotite in Arinteiro be explainedby any of the reasons proposed by Plimer andFinlow-Bates (1978), i.e. the old age of thedeposit, formation on the ocean floor, or themagmatic source of 5. In fact, for instance, allthe above deposits are old, especiallyMatchless. In contrast, according to Peter et al.(1987), the occurrence of pyrrhotite instead of

46 S. SERRANTl, V. FERRINI, U. MASI, M. NICOLETTI and L. N. CONDE

pyrite in a volcano-sedimentary deposit reflectsthe extremely reduced state of hydrothermalfluids caused by interaction with sediments richin organic matter. This suggestion may apply tothe Arinteiro deposit.

CONCLUSIONS

The Paleozoic polymetallic metamorphoseddeposit of Arinteiro in western Galicia containspyrrhotite, subordinate chalcopyrite, scarcepyrite and sphalerite. The hosting rocks areamphibolitic metabasites, composed of gedrite,hornblende, almandine, minor staurolite andalbite-oligoclase. Their chemical compositionreflects pre-metamorphic alterations operatedby mineralizing fluids. Field geology suggeststhat the deposit formed from hydrothermalfluids on the sea floor.

The Arinteiro deposit is composed of fourorebodies, Arinteiro s.s., Manoca, Fornas andBarna. The minerographic and geochemicalfeatures of selected samples from the massiveorebody of Fornas and the disseminate orebodyof Barna are studied in this paper.

The textural features of the Fornas massiveores indicate that pyrite was the first sulfide tocrystallize, followed by pyrrhotite, chalcopyriteand sphalerite. Pyrrhotite was lateroccasionally turned into pyrite II. At Barna, theparagenetic sequence of the disseminate ores issimilar, but the very low abundances of pyriteand sphalerite do not provide clearcutinformation on the crystallization of thesesulfides with respect to that of pyrrhotite andchalcopyrite.

The calculated crystallization temperaturesfor both pyrrhotite and pyrite probably rangedaround 400°C, fitting the hypothesis that orerecrystallization occurred during the Hercynianmetamorphism. The calculated temperature forchlorite is lower (310-265°C), consistent withthe late crystallization of this mineral withrespect to most sulfides in the twomineralizations. Using sphalerite asgeobarometer, a pressure of about 5.5 kbar wascalculated, consistent with the metamorphic

media. Log aS2 ranged from -7 atm to morenegative values, log am ranged around -30 atm,and pH was probably between 4.4 and 4.9. AtBarna, pH was occasionally high enough toallow carbonates to be deposited, together withsulfides and quartz.

Although the Arinteiro deposit underwentmetamorphism with possible elementredistribution between coexisting sulfides, theCo/Ni values of pyrrhotite suggest affinity withpyrrhotite in hydrothermal vein deposits, inagreement with the inferred origin based onfield geology. The high Se contents in thesulfides support the non-sedimentary origin ofthe deposit, as also proven by S isotopiccompositions indicating the magmatic origin ofS. These suggestions are consistent withgenetic inferences based on field relationships.

The host rocks of the Barna mineralizationyielded K/Ar radiometric ages between 261and 275 ± 20 Ma, which are similar withinanalytical error, and indicate that metamorphicrecrystallization took place during the last stageof the Hercynian orogenesis.

Lastly, comparisons of the Arinteiro depositwith other massive sulfide deposits ofcorresponding genetic type and metamorphicrank from Newfoundland, ScandinavianCaledonides and Namibia, ranging in age fromPrecambrian to Lower Palaeozoic, highlight thepeculiarity of the Arinteiro deposit,characterized by pyrrhotite dominating overpyrite. This feature may be explained by thegreatly reduced conditions of hydrothermalfluids, due to interaction with organic matter.

ACKNOWLEDGEMENTS

The authors thank the Rio Tinto Mining Companyfor authorizing sampling for this study, and the CNRand JNICT for having provided funds for the minevisit, within the framework of scientific co-operationagreements between Italy (through the Centro diStudio per gli Equilibri Sperimentali in Minerali eRocce) and Portugal (through the Departamento deCienci as da Terra, Universidade de Coimbra,Coimbra). MURST supplied financial support(60%). The authors also appreciated the carefulsuggestions and recommendations of twoanonymous referees. Thanks also go to Mr. Guido

Geochemical features of the massive sulfide (ell) metamorphosed deposit ofArinieiro (Galicia, Spain},.. 47

Aurisieehio and Dr. Lucio Martarelli for their help inatomic absorption and electron microprobe analyses,respectively.

REFERENCES

AKINCI O.T., BARBIERI M., CALDERONI G., FERRINIV., MASI D., NICOLETTI M., PETRUCCIANI C. andTOLOMEO L. (1991) - The geochemistry ofhydrothermally-altered rocks of the LowerVolcanic Cycle from the Eastern Pontides(Trabron, NE Turkey), Chern. Erde, 51, 173-186.

ANDERSON C.A (1969) - Massive sulphide depositsand volcanism. Eeon. Geol., 64, 129-146.

ARNOLD R.G. (1962) - Equilibrium relationsbetween pyrrhotite and pyrite from 325° to 743°C", Eeon. Geol., 57, 72-90.

ARPS C.E.S., VAN CALSTEREN P.W.c., HILGEN J.D.,KUIJPER R.P., and DEN TEX E. (1977) - Maficand related complexes in Galicia: An excursionguide. Leidse. Geol. Med., 51, 63-94.

BACHINSKI D.J. (1977) - Sulfur isotopiccomposition of ophiolitic cupriferous iron sulfidedeposits, Notre Dame Bay, Newfoundland. Eeon.Geol., 72, 243-257.

BACHINSKI D.J (1978) - Sulfur isotopiccomposition of thermally metamorphosedcupriferous iron sulfide ores associated withcordie rite-anthophyllite rocks, Gull Pond,Newfoundland. Eeon. Geol., 73, 64-72.

BADHAM J.P.N. and WILLIAMS P.l. (1981)Genetic and exploration models for sulfide ores inmetaophiolites, Northwest Spain. Eeon. Geol., 76,2118-2127.

BADHAM J.P.N., WILLIAMS P.J. and WRAITH D.(1985) - Geochemical characterization ofmetabasites in N. Portugal and significance forCu-Fe sulphides. Studia Geol. Sa1matieensia, 20,19-44.

BAJWAH Z.D., SECCOMBE P. K. and OFFLER R.(1987) - Trace element distribution; Co:Niratios and genesis of the Big Cadia iron-copperdeposit, New South Wales, Australia. Mineral.Dep., 22, 292-300.

BARTON P. B. and TOULMIN P. (1966) - Phaserelations involving sphalerite in the Fe-Zn-Ssystem. Eeon. Geol., 61,815-850.

BARTON P. B. and SKINNER BJ. (1967) - Sulfidemineral stabilities. In BARNES H.L. (ed.),«Geochemistry of hydrothermal ore deposits»,236-333, Holt, Rinehart and Winston.

BRAILIA A, SABATINI G. and TROJA P. (1979) - Arevaluation of the Co/Ni ratio in pyrite asgeochemical tool in ore genesis problems.

Mineral. Dep., 14, 353-374.BRILL B. A (1989) - Trace-element contents and

partitioning of elements in ore minerals from theCSA Cu-Pb-Zn deposit, Australia. Can. Mineral.,27,263-274.

BRYNDZIA L.T. and SCOTT S. D. (1987) Application of chlorite - sulfide - oxide equilibriato metamorphosed massive sulfide ores, SnowLake, Manitoba. Eeon. Geol., 82, 963-970.

CAMPBELL P. A and ETHIER V.G. (1984) - Ni andCo in pyrite and pyrrhotite from the Faro Sullivanorebodies. Can. Mineral., 22, 503-506.

CATHELINEAU M. and NIEVA D. (1985) - A chloritesolid solution geothennometer. The Los Azufres(Mexico) geothermal system. Contrib. Mineral.Petrol., 91, 235-244.

COOK N. J., HALLS C. and KASPERSEN P.O. (1990)- The geology of the Sulitjelma ore field,Northern Norway - Some new interpretations.Eeon. Geol., 85, 1720-1737.

COOK N. J., HALLS C. and BOYLE A.P. (1993) Deformation and metamorphism of massivesulphides at Sulitjelma, Norway. Mineral. Mag.,57,67-81.

COOK N. J., MEMD R. and OKRUSCH M. (1994) Sulphide mineralogy, metamorphism anddeformation in the Matchless massive sulphidedeposit, Namibia. Mineral. Dep., 29, 1-15.

CRAIG J.R., LJOKJELL P. and VOKES P.M. - (1984)Sphalerite compositional variations in sulfide oresof the Norwegian Caledonides. Eeon. Geol., 79,1727-1735.

CRAIG J.R., and VOKES F.M. (1993) - Themetamorphism of pyrite and pyritic ores: anoverview. Mineral. Mag., 57,3-18.

DEER W.A, HOWIE R.A and ZUSSMAN M.A (1963)-Rockforming minerals. Vol. 1-5, London.

HEY M.H. (1954) - A new review of the chlorites,Mineral. Mag., 30, pp.277-292

HUTCHISON M.N. and SCOTT S.D. (1981) Sphalerite geobarometry in the Cu-Fe-Zn-Ssystem. Eeon. Geol., 76,143-153.

KLEMD R., MAIDEN K.J. and OKRUSCH M. (1987) The Matchless copper deposit, SouthWest Africa/Namibia : a deformed andmetamorphosed massive sulfide deposit. Eeon.Geol., 82,587-599.

LYDON J.W. (1988) - «Volcanogenic massivesulphide deposits. Part 2: genetic models»,Geosei. Can., 15, n. 1, 155-181.

MIGNARDI S., FERRINI V., MASI D., NICOLETTI M.,CONDE L.N. and DE SOUSA M.B. (1997) Significance of muscovite and chloritecompositions from the hydrothermal wolframitedeposits of Panasqueira and Vale das Gatas(Portugal) and hints for ore exploration. Chern.


Erde 57, 337-349.NICOLETTI M. and PETRUCCIANI C. (1977) - «Il

metodo KIAr: mo difiche metodologiche alprocesso di estrazione dell'argon», Rend. Soc. It.Mineral. Petrol., Vol. 33, pp. 45-48

NORMAN D.J. and SAWSKINS F.l. (1985) - TheTrib ag breccia pipes: Precambrian Cu-Modeposits, Batchawena Bay, Ontario. Econ. Geol.,80, 1593-1621.

OHMOTO H. (1972) - Systematics of sulfur andcarbon isotopes in hydrothermal ore deposits.Econ. Geol., 67, 551-578.

OHMOTO H. and RYE R. D. (1979) - Isotopesof sulfur and carbon. In: Barnes H.L.(ed.) Geochemistry of hydrothermal ore deposits.(2nd edition), Wiley and Sons, New York,509-567.

PETER r. M., MCCONACHY T. F. and SCOTT S. D.(1987) - A geological and geochemicalcomparison of hydrothermal vent deposit in thesouthern trough of Guaymas basin, Gulf ofCalifornia and I ION, East Pacific Rise. In: Recenthydrothe rmal mineralization at seafloorspreading center: tectonic, petrologic andgeochemical constraints. Mineral. Expl. Inst., 87(1), Progr. and Abs., 35-37.

PLIMER 1. R. and FINLOW-BATES T. (1978) Relationship between primary iron sulphidespecies, sulphur source, depth of formation and

age of submarine exhalative sulphide deposits.Mineral. Dep., 13,399-410.

SPEAR F.S. and GILBERT C.M. (1982) - Amphibolesin metamorphic rock compositions. In: VeblenD.R. and Ribbe P.H (eds.). Reviews inMineralogy. Amphiboles: Petrology andexperimental phase relations, 9B, Mineral. Soc.Am., 268-278.

SPEAR F.S. and SCHUMACHER C.M. (1982) Orthoamphibole and Cummingtonite Amphiboles:Origin of cordierite - anthophyllite rocks. In:Veblen D.R. and Ribbe P.H (eds.). Reviews inMineralogy: Amphiboles: Petrology andexperimental phase relations, 9B, Mineral. Soc.Am., 160-163.

WEDEPHOL K.H. (1974) - Handbook ofgeochemistry. Springer Verlag, Berlin.

WILLIAMS P.l. (1983a) - The genesis andmetamorphism of the Arinteiro-Bama Cu deposits,Santiago de Compostela, Northwestern Spain.Econ. Geol., 78, 1689-1700.

WILLIAMS P.l. (1983b) - The mineralogy andmetamorphism of some gahnite-bearing silicateinclusions in massive sulphides from Fornas, NWSpain. Mineral. Mag., 47 (2), 233-235.

WINKLER R.G.F. (1976) - Petrogenesis ofmetamorphic igneous rocks (4th ed.), SpringerVerlag, New York, 334 pp.

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