The Aguablanca Cu-Ni(PGE) ore is a case of an intraplutonic ore deposito It is hosted by mafic and ultramafic cumulates of the Aguablanca Stock, which is part of the larger calcalkaline Santa Olalla Plutonic Complex of 359±18Ma age (Rb-Sr whole rock determination). Primary mineralization consists of pyrrothite, pentlandite and chalcopyrite and resulted from the crystallization of an inmiscible sulfiderich liquid. Several stages of hydrothermal alteration are superimposed. Isotope work on the host igneous rocks (Sr, Nd) and the ore (S), suggests that contamination with a crustalsource took place at some depth before final emplacement of the plutons (ε Nd360= -5.8 to -7.2; Sr(360) = 0.7082 to 0.7103; (δ14S(sulfides) near + 7.4‰). Assimilation - fractional crystallization (AFC) processes are invoked to explain de chemical variability of magmas

Casquet, César

Eguiluz, L.

Galindo Francisco, Mª del Carmen

Tornos Arroyo, Fernando

Velasco Roldán, Francisco

The Aguablanca Cu-Ni(PGE) ore is a case of an intraplutonic ore deposito It is hosted by mafic and ultramafic cumulates of the Aguablanca Stock, which is part of the larger calcalkaline Santa Olalla Plutonic Complex of 359±18Ma age (Rb-Sr whole rock determination). Primary mineralization consists of pyrrothite, pentlandite and chalcopyrite and resulted from the crystallization of an inmiscible sulfiderich liquid. Several stages of hydrothermal alteration are superimposed. Isotope work on the host igneous rocks (Sr, Nd) and the ore (S), suggests that contamination with a crustalsource took place at some depth before final emplacement of the plutons (ε Nd360= -5.8 to -7.2; Sr(360) = 0.7082 to 0.7103; (δ14S(sulfides) near + 7.4‰). Assimilation - fractional crystallization (AFC) processes are invoked to explain de chemical variability of magmas.El yacimiento de Cu-Ni(PGE) de Aguablanca constituye un caso de mineralización intraplutónica
alojada en los acumulados máficos y ultramáficos del Plutón de Aguablanca. Este plutón pertenece al
Complejo Plutónico de Santal Olalla de Cala, cuya edad, establecida por el método Rb-Sr en roca total,
es de 359±18Ma. La mineralización primaria consiste en pyrrotina, pentlandita y calcopirita y se formó
por cristalización de un líquido sulfurado, inmiscible con el magma silicatado. Además, se han reconocido
varias etapas de alteración hidrotermal superpuestas. La composición isotópica de las rocas ígneas (Sr,
Nd) Y de la mineralización (S), sugiere que tuvo lugar contaminación con corteza continental a cierta
profundidad, previa al emplazamiento definitivo de los plutones (ε Nd360= -5.8 a -7.2; Sr(360) = 0.7082 a 0.7103; (δ14S(sulfuros) aprox. + 7.4‰). 
 La diversificación química de los magmas se explica por una
combinación de procesos de asimilación y cristalización fraccionada (AFC).Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Docta Complutense

GEOGACETA,24, 1998 The Aguablanca Cu-Ni(PGE) intraplutonic ore deposit (Extremadura, Spain). Isotope (Sr, Nd, S) consfraints on the source and evolution of magmas and sulfides La mineralización intraplutónica de Cu-Ni(PGE) de Aguablanca (Exlremadura). Aportaciones de la geoquÍmica isotópica (Sr, Nd y S) con respecto a la fuente y evolución de los magmas y sulfuros. C.Casquetl, L.Eguiluz2, C. Galindo1, F.Tornos3, F.Velasco4 1 Opto. de Petrología y Geoquímica, Facultad de Geología, Universidad Complutense, 28040 Madrid, Spain. 2 Opto. de Geodinámica, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain. 3 Instituto Tecnológico Geominero de España, Rios Rosas 23, 28003 Madrid, Spain. 4 Opto. de Mineralogía y Petrología, Universidad del País Vasco, Apdo 644, 48080 Bilbao, Spain. Abstract The Aguablanca Cu-Ni(PGE) ore is a case of an intraplutonic ore deposito It is hosted by mafic and ultramafic cumulates of the Aguablanca Stock, which is part of the larger calc-alkaline Santa Olalla Plutonic Complex of 359±18Ma age (Rb-Sr who/e rock determination). Primary mineralization consists of pyrrothite, pentlandite and chalcopyrite and resulted from the crystallization of an inmiscible sulfide-rich Iiquid. Several stages of hydrothermal alteration are superimposed. Isotope work on the host igneous rocks (Sr, Nd) and the ore (S), suggests that contamination with a crustalsource took place at some depth before final emplacement of the plutons (e Nd360 = -5.8 to -7.2; Sr(360) = 0.7082 to 0.7103; 8 4S(5Ulfides) near + 7.4%0). Assimilation - fractional crystallization (AFC) processes are invoked to explain de chemical variability of magmas. Resumen El yacimiento de Cu-Ni(PGE) de Aguablanca constituye un caso de mineralización intraplutónica alojada en los acumulados máficos y ultramáficos del Plutón de Aguablanca. Este plutón pertenece al Complejo Plutónico de Santal Olalla de Cala, cuya edad, establecida por el método Rb-Sr en roca total, es de 359±18Ma. La mineralización primaria consiste en pyrrotina, pentlandita y calcopirita y se formó por cristalización de un líquido sulfurado, inmiscible con el magma silicatado. Además, se han reconocido varias etapas de alteración hidrotermal superpuestas. La composición isotópica de las rocas ígneas (Sr, Nd) Y de la mineralización (S), sugiere que tuvo lugar contaminación con corteza continental a cierta profundidad, previa al emplazamiento definitivo de los plutones (eNd360 = -5.8 to -7.2; Sr(360) = 0.7082 a 0.7103; 8 4S(5ulluro5) aprox. + 7.4%¡¡). La diversificación química de los magmas se explica por una combinación de procesos de asimilación y cristalización fraccionada (AFC). Geogaceta, 24 (1998), 71-74 ISSN: 0213683X Introduction The Aguablanca Cu-Ni(PGE) ore is a massive intraplutonic sulfide deposit hosted by mafic cumulates of the Aguablanca stock. It is located in SW Spain in Extremadura, very close to the boundary with the Sevilla and Huelva provinces (Fig.1). The deposit is not exposed on the surface and was discovered after a regional geochemical prospection survey carried out by Presur, a Spanish public company, and subsequently drilled and evaluated by Atlantic Copper Holding S.A., venture-joined with the former. The deposit is pipe~like and subvertical, extending downward for more than SOOm, with a thickness of 60 to 100m (Lunar et al., 1997), and is found at few tens of meters from the northern contact of the stock. Host rocks here are marb1es and cale silicate rocks replaced by a massive Ca-skarn formed mainly by garnet, clinopyroxene and scapolite (Casquet, 1980). Noril'sk, Rana and Monchegorsk, and the favorable potentiality offered by neighbouring areas make this deposit an interesting target for research. This is the first ore deposit of this type to be found in Spain. Although it is a small deposit, the similarities with other world c1ass Ni-Cu(PGM) deposits such as Geological setting The Santa Olalla Plutonic Complex (SOPC) was emplaced in the southern limb of the large Monesterio Antiform, into low-grade metavoleanics and meta-sedimentary rocks of Upper Precam-brian-Lower Cambrian age. To the south it ends abruptly against the Zufre Fault (Fig.1). The Monesterio Antiform is part 71 GEOGACETA.24, 1998 N A o 2/<m e A: Aguablanca T: Teuler 0 (5§JI f32l • l1mI O o. ru t:] 0 lZl Quatemary Llmestones Skam Gabbros Diorites Tonalltes Granites Roof Pendants RhyoJltes Shales SOC: Santa Olalla del Cala Fig.l. Sketclty geological map of tite Santa Olalla Plutonic Complexo Esquema geológico del Complejo Plutónico de Santa Olalla. of the Ossa-Morena Zone, which is one ofthe subdivisions ofthe Hesperian Mas-sif as recognized by Lotze (1945). Regio-nal schistosity and bedding wraps around the pluton. However, in detail, discordan-ces are common, suggesting that an ear-lier stage of forcefull intrusion and/or ba-lloning was followed by stoping. The lat-ter is indicated by the abundance of roof pendants in the central part of the massif. An aureole of contact metamorphism is well developed around the SOPC with temperature reaching Hyperstene Horn-fels facies conditions. The igneous rocks The SOPC consists of two main epizonal zoned plutons, the Main Santa Olalla Pluton and the Aguablanca Stock (AS), as well as many felsic dykes and small satellite grallltlc bodies. Emplacement took place at depth of 2-4km (0.5-lkb) according to Casquet (1980, 1982). The Main Santa Olalla Pluton is the largest intrusion. Compositional zoning of the pluton is pronunced with amphibole-biotite quartz diorites merging into tonalites and these in turn 72 into granodiorite-monzogranites towards the pluton center (Velasco, 1976, Casquet, 1980). Transitions are gradational. The AS is a small body in the northern part of the SOPC, in contact with the regional host rocks. It is also zoned with cumulates, largely norites, gabbronorites and websterites, that grade into amphibole-biotite diorites in the coreo Sulfide mineralization is hosted by the cumulates. Chemically two main groups of rocks can be distinguished in the SOPC: 1) the AS cumulates and 2)the Main Igneous Sequence(MIS), forrned by the rest of the AS and the Main Santa Olalla Pluton rocks. The first, show Si02 contents of 48-57% and are low in ~ O «0.7%) reflecting small amounts of biotite. High contents of Ni (300-450ppm) and er (740-1200ppm) have been found in the AS cumulates. The MIS consists of metaluminous Hy+Q normative rocks with Si02 contents of 55-69% (excluding the small granitic intrusions) and KzD values of up to 5% Ranges of Rb and Sr contents in the Main Igneous Sequence are 45-135ppm and 225-360ppm respectively. The MIS is a case of a calcalkaline K20-rich association (Casquet, 1980). The ore The mineralization consists mainly of pyrrhotite, pentlandite and chalcopyrite. Textural evidence suggests that several stages of mineral formation were involved in the formation of this ore deposit. The first, probably the consequence of crystallization of an in miscible sulfide-rich liquid, gave rise to massive coarse grained (0.2-3mm) pyrrhotite with fine (50-100 )..lm) flame-like exsolutions of pentlandite (Nio.3leo.27S0.45) and chalcopyrite intergrowths. Sulfides are interstitial to cumulus silicates. This stage is roughly synchronous or sligthly younger, than the crystallization of silicates (pyroxenes and plagioclase mainly) and magnetite. A second stage is evidenced by a new generation of coarse grained recrystallized pyrrhotite (without pentlandite exsolutions), chalcopyrite and pentlandite (NiOo.24Feo.25S0.51) that replace the earlier sulfides. Minor amounts of mackinawite, rutile and cobaltite were also forrned at this stage. A third stage is represented by the transformation of pentlandite to violarite along grain boundaries and fractures, and the growth of pyrite and new chaIcopyrite and pyrrhotite. FinaIly marcasite forrned as late replacements of pyrite and pyrrhotite. Postmagmatic sulfides might be related to relatively low-temperature alteration processes as suggested by the complementary replacement of igneous mineral s by biotite, actinolite, epidote and sericite, among others. The relationships between endo and exo-contact (skarns) alterations are not precisely known as yet. . Lunar et al., (1997) have described PGE rninerals sllcl1 as sperrylite dr kiÓhenerite associate4 topyrrhoÜte. Ho\vevetthe pie~ise signifi~anceof these PGM i~ st111 uIlknown. ~s()tope work Sexteen igneous rocks were chosen for Rb-Sr and Sm-Nd isotope determina-tions. Rb-Sr results are portrayed in the form of an isochron diagram in Fig.2. The N d-isotope composition expressed as eNd360 values (MIS rocks only), range from -5.8 to -7.2. The analytical methods and the data-reduction issues involved are described in Galindo et al.(1994). Mo-reover, twenty five sulfur isotope deter-mination were made on sulfides, particu-larly chalcopyrite, pyrrhotite; pentlandite and pyrite fram the Aguablanca ore and the nearby Cala Fe-(Ca) skarn. The isoto-pe composition of sulfur in ore sulfides is very similar in a11 samples with a mean close to +7.4%~334Scp=+7.2 to +7.7%0; S34S =+7.1 to 7.8%0' 334S =+7.4%0). po 'pent Discussion Origin and evolution of the SOPC magmas Fig.2, shows an 87Sr/86Sr - 87Rb/86Sr isochron plot ofMIS rocks. An errochron of359±18Ma with a MSWD (Mean Stan-dard Weigthed Deviation) of 17.1 can be fitted to these rocks. The resulting initial Sr-isotope composition is 0,7092. The Sr-isotope composition of the sope igneous rocks at a reference age of 360 Ma ranges from 0.7082 to 0.7103. Aguablanca cumulates show a very small range of Sr(360) values (0.7082-07084) whilst most the Main Igneous Sequence rocks show values between 0.7090 and 0.7094. The large MSWD of the MIS isochron plot suggests that causes other than analytical error must be involved in the dispersion of isotopic compositions, either primary compositional heterogeneities or secondary subsolidus alteration. Low-T alteration, although usually weak is GEOGACETA.24. 1998 -------------------.------------------------------------------~ 0.7180 -----_._-------------------¡ lo. ti) <D '" 1: ti) ",-" ",. 0.7170 --0.7160 --0.7150 0.7140 0.7130 -0.7120 0,7110 0.7100 Age: ~54* 17 !VI!! I.rt: Ol709328:tO,000194 !VISWO::: 18.f· ... . ~-----------~--------~~-----~----------~ O.S 1 87Rb/~6Sr 1,9 2 '-------,-------------------------_._-------Fig.2. Isochron diagram of the Main Igneous Sequence rocks of the Santa OIalla Plutonic Complexo Diagrama isócrpna de las Rocas. Ígneas de la Secuencia Principal del Complejo . Plutónico de Santa Olalla. always present in these rocks. Model ages (T DM(360) calculated after the method of Borg et al.(1990) range from 1.57 to 1.67 Ga. The Sr and Nd isotope evidence suggests that a source rich in radiogenic Sr and poor in Light REE elements, relative to a depleÜ:d mantle, was probably involved in the composition of the SOPC magmas,Moreover Nd-model ages suggest that this component was a continental crust containing old resident Nd. The existence of a circa 2 Ga basement in the Ossa Morena zone has been convincingly argued by Nagler (1990). Strontium and Nd-isotope composition of the magmas can be modelled in terms of assimilation-fractional crystallization (AFC) processes (D¡; Paolo, 1981). Early crystallization of ortopyroxene in a deep magma chamberaccompanied by assimilation of crustal material could lead to an evolution of Sriniti,l compositions from those shown by. the cumulates to those of the MIS magmas. Moreover, the fairly uniform Sr-isotope c()mposition et mast of the MIS magmas can be explained by further fractional crystallization of plagiOclase at lower pressure accompanied-· by minor assimilation of crustal material (De Paolo, 1981), probably at or near the final emplacement leve!. Likewise the Nd-isotope composition of MIS magmas, which also is very uniforrn, was probably contro11ed by amphibole fractionation. Plagioclase and amphibole have high crystal-melt partion coefficents for Sr and Nd respectively. This interpretation contradicts the magma mixing hypothesis proposedbyBatemán etal. (1992) :tor the MIS rocks. The fact that supracrustal biotite-rich metamorphic xenoliths are the only foreign material recognized in these rock;' suggests that AFC processes took place in the upper crust, probably at its base. Why magmas with Sriniti,l signatures lower that 0.708 have not been found probably is the consequence of earlier cumulates, richer in olivine, having been left behind during magma displacement from the deep magma chamber to the fi-nal emplacement leve!. Constraints on the source and evolution of the ore The S-isotope composition values of the ore sulfides are larger than those typical of juvenile sulfur (0±3%0 ; Ohmoto, 1986). However they are close -within the error limits- to the upper end of 334S values of igneous rocks with a strong crustal component (-1 to +7%0 ; Sasaki and Isihara, 1979; Matthai et al., 1995). It is interesting to remark here that sulfide mineralizations hosted by Upper Precambrian to Lower Paleozoic slates in the Iberian Massif -probably derived 73 GEOGACETA,24. 1998 from remobilization of sedimentary sulfur- show 834S values between +7 and +21 %0 . At Mina Sultana, a Cu-Au ve in hosted by MSOP tonalites near the western contact of the SOPC, vein sulfides have 834S values of + 1 0.4 to +14.4%0 (Tornos and Velasco, 1997). In consequence, we think that sulfur in the Aguablanca ore evidences a mixing between a juvenile igneous component and a crustal sulfur in a proportion close to 1: 1 (sulfurization; Cheney & Lange, 1967). This conc1usion is reinforced by few preliminary 207Pbj206Pb values obtained in this ore (¡.t=9.6-9.8) (Tornos and Chiaridia, umpub.data). The origin of crustal sulfur, whether derived from reduction of sulfates or biogenic is still uncertain. The solubility of sulfur in basic magmas is very small (Ohmoto, 1986). Exsolution of the S-rich 1iquid fram the contaminated magma prabably took pla-ce as a consequence of either decreasing temperature, increasing silica activity during differentiation, increasing oxygen fugacity or by a combination of them (Carmichael el al., 1974), during ascent fram the deep magma chamber to the fi-nal emplacement level of the pluton (2-4km). Constraints on the age of the sope The errochron age of 359±18Ma refe-rred to aboye must be taken with caution because of the large age error, and the fact that mixing with a crustal contaminant could pravoke a departure fram the hori-zontal of the 87Sr/86Sr - 87Rb/86Sr line at time t=O. To check for the latter an inde-pendent age determination has been at-tempted using the K-Ar method on whole rocks. Four determinations have given the following values: 307, 325, 348 and 373 Ma, which are cooling ages. The last two 74 values are well within the error limits of the errochron age. In consequence we think that 359±18Ma, i.e., Middle Devo-nian to Early Carboniferaus, is a reasona-ble estimate of the emplacement age of the MSOP. Younger K-Ar ages are proba-bly representative of the late low-T alte-ration event shown by these rocks. The age of the early regional low-grade metamorphism has been estimated by Galindo el al. (1988) at 385±I1Ma. Moreover Schafer (1990) quotes a zircon age of 379Ma from a Pulo de Lobo domain granite and relates it with the amalgamation of the Ossa Morena Zone to the South Portuguese Zone, in the course of the Acado-Hercynian Orogeny (Quesada, 1989). In consequence the intrusion of the SOPC prabably took pla-ce late in this geodynamic scenario. Acknowledgements The radiogenic isotope work was carried out by one of us (C.G.) in 1992 at the NIGL (Keyworth, U.K.). We acknowledge advice by Dr Bob Pankhurst of the British Antarctic Survey. We are also grateful to Mr Angel Canales of Presur. Finnancial support was pravided in part by Spanish grants AMB92-0918-C02-01 and DGES96-0135. K-Ar work was camed out at the Geochronology and Isotope Geochemistry Center of the Complutense University. References Bateman,R., Martín,M.P., Castro,A., (1992): Lithos, 28,111-131. Borg,S.G., DePaolo,D.J., Smith,B.M., (1990): Jour. Geophys. Res., 95, 6647-6667. Carmichael,I.S.E., Turner, F.J., Verhoo-gen, J. (1974): Igneous Petrology, Ed. McGraw-Hill Inc., 739 págs. Casquet,C., (1980): Tesis Doctoral, Universidad Complutense de Madrid, 300 págs. Casquet,C.,(1982): R.Acd. Ci. Ex. Fis. Nat.Madrid, 76, 333-363. Cheney,E.S. and Lange,I.M. (1967): Mineralium Deposita, 2, 80-94. DePaolo,D.J., (1981): Earth Planet. Sci.Letters, 53, 189-202. Galindo,C., Casquet,C., Portugal-Ferreira,M., Regencio Macedo,C.A. (1988): In: Geología de los granitoides y rocas asociadas del Macizo Hespéri-co, Ed.Rueda, 385-392. Galindo,C., Tornos,F., Darbyshire, D.P.F., Casquet,C. (1994): Chem. Geol., 112,351-364. Lotze, F. (1945): Geotekt.Forsch., 6,78-82. Lunar,R., Ortega,L., Sierra,J., García Palomero,F., Moreno,T., Prichard,H. (1997): In Mineral Deposits, Papu-nem (ed.), Balkema Rotterdam, 463-466. Ntigler,T. (1990): Tesis Doctoral. Swiss Federal Inst. of Technology Zurich, 141 págs. Matthai,S.K., Henley,R. w., Heinrich, C.A. (1995): Econ. Geol., 90-8, 2133-2142. Ohmoto,H. (1986): In: Stable Isotopes in High Temperature Geological Pro-cesses, Reviews in Mineralogy, Ed. ASM,491-555. Quesada, C. (1989): 28th Intern.Geol. Congress Washington De. Abstracts, 24-27. Sasaki,A., Isihara,S. (1979): Contrib. Mineral. Petrol., 68,107-115. Schtifer,H.J. (1990): Tesis Doctoral, Swiss Federal Institute of Technolo-gy Zurich, 153 págs. Tornos,F., Velasco,F. (1997): Informe Interno, Serv.Doc.lTGE. Velasco, F., (1976): Tesis Doctoral, Universidad de Bilbao, 290 págs. 

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The Aguablanca Cu-Ni(PGE) intraplutonic ore deposit
(Extremadura, Spain). Isotope (Sr, Nd, S) consfraints on the
source and evolution of magmas and sulfides

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The Aguablanca Cu-Ni(PGE) intraplutonic ore deposit

(Extremadura, Spain). Isotope (Sr, Nd, S) consfraints on the

source and evolution of magmas and sulfides

The Aguablanca Cu-Ni(PGE) intraplutonic ore deposit (Extremadura, Spain). Isotope (Sr, Nd, S) consfraints on the source and evolution of magmas and sulfides

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