Stable Isotope Geochemistry of the Ulldemolins Pb-Zn-Cu Deposit (SW Catalonian Coastal Ranges, Spain)

Geologica Acta, Vol.10, Nº 2, June 2012, 145-157 DOI: 10.1344/105.000001707 Available online at www.geologica-acta.com Stable isotope geochemistry of the Ulldemolins Pb-Zn-Cu deposit (SW Catalonian Coastal Ranges, Spain) 1 2 3 1 4 P. ALFONSO C. CANET J.C. MELGAREJO J.M. MATA-PERELLÓ A.E. FALLICK 1 Departament d’Enginyeria Minera i Recursos Naturals, Universitat Politècnica de Catalunya (UPC) Av. de les Bases de Manresa 61-73, 08242 Manresa, Barcelona, Spain. Alfonso E-mail: [email protected] 2 Departamento de Recursos Naturales, Instituto de Geofísica, Universidad Nacional Autónoma de México Ciudad Universitaria, Del. Coyoacán, México DF, 04510, Mexico 3 Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona (UB) c/ Martí i Franquès, s/n, Spain 4 Isotope Geosciences Unit, Scottish Universities Environmental Research Centre East Kilbride, Glasgow, G75 0QF, Scotland (UK) ABS TRACT The Pb-Zn-Cu deposit of Ulldemolins occurs within the Carboniferous sedimentary series of the southernmost Catalonian Coastal Ranges. It consists of sulphide-bearing calc-silicate assemblages, with epidote, Ca-amphiboles and Ca-garnet, which develop selectively along a dolomicrite bed near the contact with a granite porphyry. Two mineralisation styles can be differentiated: a) banded and b) irregular. Fluid inclusions and stable isotope compositions of sulphur in sulphides (sphalerite, galena and chalcopyrite) and carbon and oxygen in carbonates (calcite and dolomite) were studied in order to constrain the genesis and the source of mineralizing fluids. Fluid inclusions in sphalerite and calcite are aqueous, liquid+vapour and have a salinity between 1.2 and 7.2 wt% 34 NaCl eq. and homogenization temperatures in the range of 273º to 368ºC. The δ S(V-CDT) values in the banded mineralisation are mostly between –1.5 and +2.1‰, and those from the irregular mineralisation are between –1.1 and +20.5‰. These δ34S values of the banded mineralisation are in agreement with a magmatic origin of sulphur. 18 In addition, the δ O(SMOW) values of hydrothermal calcite, from +6.9 to +12.5‰, are consistent with a magmatic origin of the fluids that formed the banded ore deposit. Later, a new input of fluids interacted with the previously formed mineral assemblages and modified part of the deposit, leading locally to an irregular skarn mineralisation. KEYWORDS Ore deposits. Skarn. Calcsilicates. Stable isotopes. Fluid inclusions. INTRODUCTION of stratiform and banded base metal occurrences, which were ascribed to the sedimentary-exhalative The southern Catalonian Coastal Ranges include type (SEDEX; Melgarejo, 1992; Canet, 2001; Alfonso several ancient mining areas, most of them consisting et al., 2002; Canet et al., 2005). of Pb-Zn vein deposits hosted by Paleozoic rocks. These deposits have produced more than 1Mt of The studied deposit is located about 3Km to the NE ores since Roman times. Moreover, the Silurian and of the village of Ulldemolins, at 41°20’12”N-0°54’15”E, Carboniferous sedimentary series contain several tens in the vicinity of the Mas del Bessó farm (Fig. 1, 2). The 145 P. ALFONSO e t a l . Stable isotope geochemistry of the Ulldemolins deposit supergene ores (secondary Cu carbonates) were mined GEOLOGICAL SETTING during the Eneolithic (Vilaseca, 1973). These mines were also operative during short periods in the Middle Ages. The Catalonian Coastal Ranges consist of a Hercynian Later, in the XIX century, these mines were known as the folded basement unconformably covered by Mesozoic Minas San Antonio, but the fine grain size and complex sedimentary rocks (Fig. 1). The basement is formed by early character of the ores prevented their metallurgical Cambrian to Devonian sedimentary rocks unconformably processing, and thus giving up mining works. However, followed by a turbiditic Carboniferous Culm sequence the banded morphology of the deposit induced the Real (Melgarejo, 1992; Sanz-López et al., 2000). Compañía Asturiana de Minas to explore it during the 1960s, establishing about 250,000 tons of an average grade At the base of the Carboniferous sequences a cherty of 2.5wt% Pb, 2.5wt% Zn, 0.5wt% Cu, 80ppm Ag and unit (up to 10m thick) occurs; it has been attributed to the 500ppm Cd, after a drilling survey of the reserves. Tournaisian. The Culm facies, up to 2000m-thick (Anadón et al., 1985), contains several sedimentary exhalative Pb- For a long time, the deposit has been considered as Zn-Cu-Ag occurrences (Melgarejo, 1992; Canet, 2001). It an example of the SEDEX type, owing to its apparent starts with the coarse-grained Bassetes Unit, ~400m thick, stratiform morphology (Melgarejo, 1992). Otherwise, which is composed of greywackes and conglomerates, considering the extensive development of calc-silicates in with interstratified olistoliths of chert and limestones. On this deposit, Canet (2001) suggested that the deposit could the basis of its conodont fauna, this informal unit, which be an example of “inhalites” produced by replacement of contains the massive sulphide ore body of L’Argentera limestone bodies. This study presents data on the geology, (Alfonso et al., 2002), has a Visean age (Anadón et al., fluid inclusions and stable isotopes of the Ulldemolins 1985). The following Ulldemolins Unit has a similar deposit. The principal goals of the study are to determine thickness and is essentially pelitic, with minor interbedded the origin of the ore-forming fluids, and to elucidate the sandstones (Sáez, 1982). It also contains limestone genesis of the deposit. olistoliths and minor trachytes (Melgarejo, 1992). This unit contains the Pb-Zn-Cu sulphide deposits of Ulldemolins and L’Alforja, and is Visean to Lower Namurian in age (Sáez, 1982). Spain Poblet Zn-Cu-Pb (-PGE) Ulldemolins Pb-Zn-Cu (-W) The Hercynian orogenesis affected the Paleozoic series throughout the development of two episodes of folding and thrusting accompanied by very low-grade regional des de Pra yes ntan metamorphism. The first deformation produced NNW- Mu SSE trending folds and thrusts with vergence to the WSW, whereas the second one produced folds and thrusts with L’Alforja vergence to the ENE. L’Alforja Zn-Pb-Cu L’Aleixar Post-tectonic, Late Hercynian calc-alkaline granitic Gratallops stocks, ranging from quartzdiorite to leucogranite, Reus Bellmunt intruded the Hercynian sequences (Melgarejo and Ayora, 1984). Granite to tonalite porphyries crosscut all the L’Argentera Zn-Pb-Cu above-mentioned Paleozoic series and granitic rocks. The Mediterranean Sea intrusive rocks are Permian in age, according to Rb-Sr 0 5 Km dating (Enrique and Debon, 1987), and produced contact metamorphism from pyroxene to amphibole hornfels Graben fill sediments (Neogene) Post-Hercynian veins facies. Some Late Hercynian NNW-SSE and NE-SW Carboniferous hosted Foreland basin sediments (Paleogene ) base metal deposits wrench faults have been reactivated as normal faults during Silurian hosted Mesozoic sedimentary cover (Triassic-Jurassic) base metal deposits the Alpine orogenesis, acting as conduits for hydrothermal Late Hercynian granitoids (Permian) Faults fluids and producing Ba-Pb-Zn-Cu-Ni-Co-Ag veins Carboniferous (Canals and Cardellach, 1997). Devonian Pre-Hercynian metasediments Silurian METHODS AND CONDITIONS OF ANALYSIS Cambrian (?) FIGURE 1 Geological map of the southern Catalonian Coastal Ranges, The extensive outcrops of the deposit and a complex with the location of the main base metal sulphide occurrences. system of trenches and galleries favoured a detailed Geologica Acta, 10(2), 145-157 (2012) 146 DOI: 10.1344/105.000001707 P. ALFONSO e t a l . Stable isotope geochemistry of the Ulldemolins deposit sampling. The samples have been studied in polished (1992) and Hall et al. (1994); powder combustions were thin sections using a standard petrographic microscope. performed similarly and purified SO2 was analyzed on a Scanning electron microscope (SEM) images and VG-SIRA II mass spectrometer. The results are given as qualitative analyses were produced using a Cambridge d34S‰ values relative to the Vienna-Canyon Diablo Troilite Stereoscan 120 equipment, at the Serveis Cientificotècnics (V-CDT) standard. The lateral resolution of the laser de la Universitat de Barcelona. The samples were examined beam is about 250mm; the analytical precision is within in the backscattered electron mode (BSE). The mineral ±0.2‰ at 1. Additional samples were analysed by mass chemistry of silicates (epidote, chlorite, Ca-amphibole, Ca- spectrometry using a Delta C Finnigan MAT continuous garnet and feldspars), sulphides (sphalerite), and carbonates flow isotope-ratio mass spectrometer with an elemental (calcite and dolomite), was quantitatively obtained with analyzer, a TC-EA according to the method of Giesemann a CAMECA SX-50 electron microprobe at the Serveis et al. (1994). These analyses were carried out at the Serveis Cientificotècnics of the Universitat de Barcelona. Cientificotècnics of the Universitat de Barcelona. Microthermometric measurements were performed on Six representative samples of hydrothermal carbonates a Linkam THMS-600 stage. Calibration was made with were selected for carbon and oxygen isotope analyses. Three standard compounds between -56.6ºC and 308.9ºC. The samples of carbonates are comprised of dolomite from the precision was ±0.2ºC for the freezing measurements and dolostone of the banded mineralisation and another three ±1ºC for the heating measurements. These ice melting are made up of calcite from the irregular mineralisation. temperatures

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