Ore Geology Reviews 80 (2017) 377–405
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Mineralogical evolution of the Las Cruces gossan cap (Iberian Pyrite Belt): From subaerial to underground conditions Lola Yesares a,⁎, Reinaldo Sáez a, Gabriel Ruiz De Almodóvar a, José Miguel Nieto a, Carmelo Gómez b, Gobain Ovejero c a b c
Department of Earth Sciences, University of Huelva, Avenida de las Fuerzas Armadas, S/N, 21071 Huelva, Spain Geological Area, Mining Drepartment of Cobre Las Cruces S.A., Ctra. SE-3410, Km 41,100, 41860 Gerena, Seville, Spain Cobre Las Cruces S.A., Ctra. SE-3410, Km 41,100, 41860 Gerena, Seville, Spain
a r t i c l e
i n f o
Article history: Received 13 November 2015 Received in revised form 16 May 2016 Accepted 20 May 2016 Available online 1 June 2016 Keywords: Massive sulfide deposit Weathering Gossan Iberian Pyrite Belt Mineral chemistry Sulfide Sulfosalt
a b s t r a c t The Las Cruces VMS deposit is located at the eastern corner of the Iberian Pyrite Belt (SW Spain) and is overlain by the Neogene–Quaternary sediments of the Guadalquivir foreland Basin. The deposit is currently exploited from an open pit by Cobre Las Cruces S.A., being the supergene Cu-enriched zone the present mined resource. The Las Cruces orebody is composed of a polymetallic massive sulfide orebody, a Cu-rich stockwork and an overlying supergene profile that includes a Cu-rich secondary ore (initial reserves of 17.6 Mt @ 6.2% Cu) and a gossan cap (initial reserves of 3.6 Mt @ 3.3% Pb, 2.5 g/t Au, and 56.3 g/t Ag). The mineralogy of the Las Cruces weathering profile has been studied in this work. Textural relationships, mineral chemistry, deposition order of the minerals and genesis of the Las Cruces gossan are described and discussed in detail. A complex mineral assemblage composed by the following minerals has been determined: carbonates such as siderite, calcite and cerussite; Fe-sulfides including pyrite, marcasite, greigite and pyrrhotite; Pb–Sb sulfides and sulfosalts like galena, stibnite, fulöppite, plagionite, boulangerite, plumosite, and the jordanite– geocronite series, Ag–Hg–Sb sulfides and sulfosalts including miargyrite, pyrargyrite, sternbergite, acanthite, freibergite, cinnabar, Ag–Au–Hg amalgams; and Bi–Pb–Bi sulfides and sulfosalts such as bismuthinite, galenobismutite, others unidentified Bi–Pb-sulfosalts, native Bi and unidentified Fe–Pb–Sb-sulfosalts. Remains of the former oxidized assemblage appear as relicts comprised of hematite and goethite. Combining paragenetic information, textures and mineral chemistry it has been possible to derive a sequence of events for the Las Cruces gossan generation and subsequent evolution. In that sense, the small amount of Feoxyhydroxides and their relict textures replaced by carbonates and sulfides suggest that the gossan was generated under changing physico-chemical conditions. It is proposed that the Las Cruces current gossan represents the modified residue of a former gossan mineralization where prolonged weathering led to dissolution and leaching out of highly mobile elements and oxidation of the primary sulfides. Later, the gossan was subject to seawater-gossan interaction and then buried beneath a carbonated-rich cover. The basinal fluids-gossan interaction and the equilibration of fluids with the carbonated sediments brought to the carbonatization and sulfidation of the gossan, and thus to the generation of Fe-carbonates and Pb–Sb-sulfides. The Las Cruces mineral system likely represents a new category within the weathering class of ore deposits. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Gossan deposits derived from the supergene alteration of massive sulfide deposits have been documented from many different metallogenetic provinces (e.g., Lachlan Fold Belt, Australia (Scott et al., 2001); Bathurst Mining Camp, Canada (Boyle, 1994); Golden Grove District, Australia (Mann, 1984; Smith and Sing, 2007); Khomas Schist Belt, ⁎ Corresponding author. E-mail address:
[email protected] (L. Yesares).
http://dx.doi.org/10.1016/j.oregeorev.2016.05.018 0169-1368/© 2016 Elsevier B.V. All rights reserved.
Namibia (Andrew, 1984); Iberian Pyrite Belt (Capitán, 2006; Velasco et al., 2013). Commonly, the surface exposition of sulfide-rich deposits involves mineralogical and chemical alteration of the protores, remobilization of metals and their reprecipitation in secondary Feoxyhydroxides-sulfate-rich bearing mineralizations (Mann, 1984; Boyle, 1994). As a general rule, these deposits depict a well-defined internal zonation resulted from the geochemical and mineralogical transformations during leaching (Scott et al., 2001; Taylor, 2011). The mobility of metals and mineralogical changes of sulfide deposits during weathering have been widely investigated (Andrew, 1980; Taylor et al.,
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1984; Thornber, 1985; Scott et al., 2001). Properties controlling the mobility and aqueous geochemistry of Fe, Cu, Zn, Pb, Au and Ag have been described by Mann and Deutscher (1980), Mann (1984) and Thornber (1985). In addition, weathering profiles are also well known due to their high concentration in precious metals, which may concentrate to form economic ores (Boyle, 1979; Webster and Mann, 1984; Groen et al., 1990; Benedetti and Bouleguè, 1991; Gray, 2001; Hough et al., 2009; Fairbrother et al., 2012; Reith et al., 2012). Numerous studies have shown that major mineralogical features in gossan caps concerns with precipitation of newly-formed oxyhydroxides, oxides, sulfates, oxy-sulfates, sulfo-arsenates, arsenates, halides, native metals and phyllosilicates after leaching its protores, under acidic and oxidizing conditions. Common minerals in supergene profiles include: goethite, hematite, pyrolusite, rutile, cassiterite, cuprite, tenorite, barite, anglesite, alunite, chalcanthite, jarosite, argentojarosite, plumbojarosite, beudantite, scorodite, chlorargyrite, iodargyrite, bromargyrite, native gold, native silver, halloysite, chrysocolla and delafossite (Scott et al., 2001; Freyssinet et al., 2005; Capitán, 2006; Koski, 2012; Velasco et al., 2013). Many efforts have been put on the generation mechanisms of oxides and sulfates in weathering profiles in order to elucidate how metals are redistributed within the supergene deposits (Taylor et al., 1984; Thornber, 1985; Bigham et al., 1996; Dutrizac and Jambor, 2000; Capitán et al., 2000). Many other investigations have been devoted to the study of Au and Ag mineralogy, in order to understand their mobilization and fixation during the weathering of primary deposits (Webster and Mann, 1984; Stroffregen, 1986; Groen et al., 1990; Benedetti and Bouleguè, 1991; Gray, 2001; Freyssinet et al., 2005; Fairbrother et al., 2012; Reith et al., 2012). The generation of volcanic-hosted massive sulfides (VHMS) in the Iberian Pyrite Belt (IPB) has been related to the palaeogeographic evolution of the IPB Basin at the uppermost Devonian, and more specifically to the breakup of the basin in response to the onset of the Variscan orogeny (Moreno et al., 1996). The subsequent uplift of the Variscan chain drove to the erosion and exhumation of part of the IPB during the upper Oligocene-lower Miocene (Essalhi et al., 2011; Velasco et al., 2013). The aerial exposition of large amounts of massive sulfide deposits resulted in the generation of supergene profiles, including gossan caps and cementation zones. These have been targeted for Cu and precious metals in the IPB for more than five millennia (Nocete et al., 2005). Due to the long history of base and precious metal production in the IPB, only few gossan caps have remained well preserved. This explains the scarcity of publications on the genesis of IPB supergene profiles. Of these, most are focused on the reserves, metallurgy and mining features of economic gossans (García Palomero et al., 1986; Viñals et al., 1995; Sanchez et al., 1996; Roca et al., 1999). The available data indicate that, as a whole, the IPB gossans show general features comparable to weathering profiles of other massive sulfides (Andrew, 1980; Taylor, 1984; Scott et al., 2001). Some examples of well-studied gossans in the IPB are: San Miguel (Álvaro and Velasco, 2002); Riotinto (Williams, 1950; Amorós et al., 1981; Arribas, 1998); and Tharsis (Capitán et al., 2003; Capitán, 2006). General reviews on the IPB gossans are published by Kosakevitch et al. (1993, 1994), Viallefond (1994) and Velasco et al. (2013). According with all these authors the main features of the IPB gossan are: (i) major mineralogy consisting of oxidized facies including goethite, hematite, minerals of the jarosite group, and quartz; (ii) main textures including massive, boxwork, colloform and open space fillings; and (iii) common development of vertical zonation with three clearly discernible horizons: a lower zone composed by goethite and quartz with jarosite, an intermediate zone comprised of goethite, quartz and hematite, and an upper zone dominated by hematite and quartz (Velasco et al., 2013). In contrast, the features exhibited by Las Cruces weathering profile do not match any of these general patterns (Yesares et al., 2015a). Las Cruces is a currently exploited volcanic-hosted massive sulfide deposit at the eastern end of the IPB, about 24 km NW of Seville (SW
region of the Iberian Peninsula), that is covered by a detrital and carbonate sequence, 150 m thick, consisting of sediments of the Guadalquivir foreland Basin. The deposit includes a polymetallic massive sulfide orebody, a Cu-rich stockwork (initial reserves of 4.5 Mt of Cu-rich ore @ 3.3% Cu and 20.7 Mt of polymetallic-rich ore @ 4.2% Zn and 2% Pb; Doyle et al., 2003) and an overlying supergene profile, which includes the Cu-rich secondary ore (initial reserves of 17.6 Mt @ 6.2% Cu) and the gossan cap (initial reserves of 3.6 Mt @ 3.3% Pb, 2.5 g/t Au, and 56.3 g/t Ag) (Cobre Las Cruces S.A. data updated on May 11, 2015). The Las Cruces deposit was recently subject to several research papers mainly focused on the supergene profile (Knigth, 2000; Capitán, 2006; Blake, 2008; Tornos et al., 2014; Yesares et al., 2014, 2015a,b). These include the description of its geological, structural, mineralogical and geochemical features, as well as the discussion on different hypotheses regarding its genetic conditions. The most noticeable gossan features are the absence of internal structure, and the unusual mineralogy, which includes newly formed siderite, calcite, Fe-sulfides and galena, with goethite and hematite as minor components. According to these attributes, Knigth (2000) proposed a genetic model for the Las Cruces Cu-rich secondary mineralization involving: 1) the oxidation of primary sulfides during the last stages of the hydrothermal oreforming system and; 2) a later fluctuation of the geothermal gradient in relation to the tectonic burial and uplifting events affecting the deposit after its genesis. Capitán (2006) suggested that the evolution of the Las Cruces gossan was controlled by the Miocene transgressive–regressive episodes in the area. Yesares et al. (2014, 2015b) reported several supergene precious metals mineralizations within the supergene profile and proposed two different mechanisms for Au and Ag mobilization and concentration. Blake (2008) and Tornos et al. (2014) proposed that the unusual features of the Las Cruces gossan were related to bacteriogenesis processes. Finally, Yesares et al. (2015a) reported mineralogical and geochemical data on the whole deposit and proposed a genetic model for the supergene profile linking its evolution to the interaction between the gossan and the sedimentary cover. Although the genesis of the Las Cruces gossan has been highly debated in recent times, no detailed mineralogical studies, nor mineral chemistry and mineral association descriptions were present so far. In consequence, the present study aims to fill this knowledge gap and describes comprehensively the unusual mineralogy of the Las Cruces weathering profile. This work provides the first mention of the occurrence of newlyformed carbonates, sulfides and sulfosalts, previously unreported in gossanous deposits. The geology, mineralogy and mineral chemistry of the Las Cruces gossan has been evaluated, in order to obtain information on the mineral evolution sequence and on the distribution of ore minerals. The mineral chemistry and textural descriptions of these minerals can offer valuable information about their physico-chemical conditions of formation, thus contributing to a better understanding of the Las Cruces metallogenic evolution. 2. Geological background 2.1. Iberian Pyrite Belt The Iberian Pyrite Belt is recognized as one of the most prolific massive sulfide provinces in the world (Leistel et al., 1998; Sáez et al., 1999). It is located at the southwestern corner of the Iberian Peninsula, forming a band circa 230 km long and 40 km wide, that extends from the surroundings of Seville, in Spain, to southern Lisbon, in Portugal (Fig. 1). The IPB is the largest of the three domains comprising the South Portuguese Zone, and the southernmost zone in the Iberian Variscan Massif. It has been interpreted as a tectonostratigraphic terrane sutured to the Iberian Massive during Variscan times (Leistel et al., 1998, and references therein). The stratigraphic succession of the IPB is composed by sedimentary and igneous rocks of Middle Devonian–Pennsylvanian age, arranged in
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Fig. 1. Geologic map of the South Portuguese including the location of the Las Cruces deposit in the Iberian Pyrite Belt (modified from Saéz, 2010).
three main lithostratigraphic units. From the footwall to the hanging wall these are: the Givetian–Famennian pre-volcanic Phyllite–Quartzite Group, the late-Famennian–early Visean Volcano–Sedimentary Complex, and the Visean–Bashkirian post-volcanic Culm Group (Schermerhorn, 1971). The limits of the three units are depositional, although locally they are masked by tectonic. The massive sulfide deposits are included within the Volcano–Sedimentary Complex ranging in age from Late Famennian to early Visean (Nesbit et al., 1999; Nieto et al., 2000; Barrie et al., 2002; González et al., 2002). The massive sulfides occur as lenses associated mostly with felsic-volcaniclastic and/or black shale sequences (Saéz et al., 1996). During the Variscan orogeny, the IPB was intensely deformed following a thin-skinned tectonic style characterized by stacking of tectonic slices, folding, and very low grade metamorphism (Silva et al., 1990). The deformation was polyphasic, including three main stages. During Bashkirian times the first deformation stage (Schermerhorn, 1971; Silva et al., 1990) produced the main regional structures and the stacking of tectonic slices. The second and third stages, both distensive, are responsible of a late phase of Variscan faulting (Simancas, 1983). The older stage comprised a N–S fault system while the younger one produced an E–W set and a conjugated NNW/SSE and NE/SW system. 2.2. Weathered deposits in the Iberian Pyrite Belt Supergenesis in the IPB began during the upper Oligocene-lower Miocene (Essalhi et al., 2011; Velasco et al., 2013) as a consequence of the exhumation and surface exposition of some massive sulfide deposits. Under arid and semiarid climatic conditions, the weathering of these massive sulfides derived in the generation of gossan caps (Velasco et al., 2013). Some examples of gossans in the IPB are seen at Tharsis, Riotinto, San Miguel and São Domingos (García Palomero et al., 1986; Arribas, 1998; Capitán, 2006). According to Capitán (2006) and Velasco et al. (2013) the IPB gossans commonly consist of goethite, hematite, quartz and jarosite as the main forming minerals. These are distributed along three horizons: i) the lowermost horizon, composed by goethite with minor jarosite
and enriched in S, As, P, Pb, Sn, Sb, Ag and Au; ii) the intermediate horizon, volumetrically constituting the major part of the gossan, and largely comprised by goethite, that involves strong S and As depletion, and heavy and precious metals; iii) and the upper horizon, located near the surface, strongly leached and mostly composed of hematite and quartz. 2.3. Post-Variscan sedimentary cover The Neogene transgression buried the south and western parts of the IPB under the post-Alpine sediments of the Guadalquivir and Sado basins in Spain and Portugal, respectively (Strauss and Madel, 1974; Abad, 2007). Las Cruces and Lagoa Salgada represent cases of recently discovered massive sulfide deposits hidden below such Neogene–Quaternary sedimentary cover (Fig. 1). The sedimentary record of the Guadalquivir Basin, unconformably overlying the Palaeozoic basement in the region, mostly consists of a carbonate and detrital sequence. In the Las Cruces area this sedimentary cover is approximately 150 m thick and can be divided in two conformable formations. The Niebla Fm (the lowermost one) consists of a 5– 15 m thick wedging southward sequence of calcarenites and basal conglomerates, which has been interpreted to represent the continental to shallow marine transition. The overlaying Arcillas de Gibraleón Fm consist of a 100–150 m thick sequence of marls and silts, with glauconiterich sand beds predominantly at the base. The subsequent formations of the Guadalquivir Basin (e.g. Arenas de Huelva, and Arenas de Bonares Fms) are absent in the study area (González-Delgado et al., 2004). 3. Samples and analytical methods The geological observations presented here have been carried out during the excavation of the open pit. Up to 325 samples, which encompass all the differentiable lithofacies of the weathering profile, were collected during the first three mining stages of the open pit. Additional samples have been obtained from drill cores and blast holes conducted by Cobre Las Cruces S.A. during further exploration, evaluation and
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production stages. The samples were processed using the equipment located at the University of Huelva. In order to study the whole rock mineralogy of the weathering profile, 150 samples were investigated by X-ray diffraction (XRD) using a Broker D8 Advance Powder Diffractometer with Cu–Kα radiation. In addition, 20 more XRD analyses were conducted to confirm the identification of specific minerals (e.g. greigite, pyrrhotite and anatase). These minerals were previously separated by handpicking under a binocular microscope. Up to 193 samples from the whole gossan cap were prepared as thin polished sections for petrographic studies. Among them, 96 samples were used for detailed mineralogical studies by JEOL scanning electron microscope coupled with energy dispersive spectroscopy (SEM–EDS) (JMS-5410 equipped with a microanalyzer Link Oxford and Fei-QUANTA 200 equipped with a microanalyzer EDAX Genesis 2000). Twenty five polished sections containing carbonates, Feoxyhydroxides, sulfides and sulfosalts were selected for electron microprobe analyses (EPMA). The chemical compositions were determined using a JEOL JXA-8200 Super Probe Electron Probe Micro-Analyzer. The measurements were performed on carbon-coated polished sections using an acceleration voltage of 20 kV, 20 nA beam current, 30 s counting time for the peak and 10 s for the background. The analysis spots were selected using the backscattered electron (BSE) images. Concentrations of FeO, CaO, MgO, MnO2, SrO, BaO, CuO, ZnO, PbO, TiO2, CuO and ZnO in carbonates and Fe-oxyhydroxides and Ag, Sb, Mn, Cd, Bi, As, Sn, Co, Se, Ni, Au, Cu, Zn, Fe, Pb, Hg, Au and S elements in sulfides and
sulfosalts were determined by wavelength-dispersive spectroscopy (WDS). Up to 77 successful EPMA analyses of carbonates, 32 of oxyhydroxides, 122 of sulfides and sulfosalts have been obtained. Routine data reductions, including full matrix (ZAF) corrections, were performed. The Eh-pH diagrams of the Fe, Pb, Ag and Sb systems were calculated using “MEDUSA” code and “HYDRA” database (Puigdomènech, 2010). 4. Geology of the deposit The Las Cruces VMS deposit is located at the eastern margin of the IPB, beneath a thick sequence (140–150 m) of carbonate-rich detrital sediments of the post-Alpine (Neogene–Quaternary) Guadalquivir Basin (Fig. 1). The ore deposit is hosted by a thick sequence of black shales, felsic volcanics and volcaniclastic rocks, and extends E–W more than 1 km, dipping circa 35° to the north (Fig. 2). The ore concentrations consist of a 60–100 m thick polymetallic massive sulfide body, surmounting a copper rich-pyritic stockwork mineralization. The upper part of the massive sulfides consists of a supergene profile including a gossan mineralization, above a copper-rich cementation zone (Figs. 2, 3a and b). Three deformation stages have been recognized in the Las Cruces deposit. The main structural feature includes the stacking of several tectonic slices demarcated by low-angle subhorizontal trending faults associated with the main Variscan deformation phase in the IPB (Silva et al., 1990). These were responsible for the shearing of the orebody
gossan
S
N
primary sulfides
stockwork Cu-rich secondary ore
gossan
Cu-rich secondary ore
E
W
primary sulfides
stockwork Fig. 2. 3D model to the Las Cruces deposit, including both views to the West (above) and to the South (below).
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a E
W -110m
marls late variscan fault (F1)
D
gossan
glauconitic sands -115m
pyritic sands gossan -120m secondary enrichment zone
b marls
gossan
black shale detachment level
pyritic sands
c
basal conglomerate
d
Fig. 3. Overviews of the Las Cruces outcrops at the Open Pit. (a) View of the Las Cruces open pit; (b) NE–SW section of the open pit first mining stage, showing the gossan and massive sulfides crosscutted by a late Variscan fault (F1), the contacts of the gossan with the massive sulfides (below) and with the sedimentary cover (above); (c) East and west faces showing gossan in sharp contact with massive sulfides; and (d) Basal conglomerate including gossan pebbles in a glauconitic sand matrix.
and the stacking of several massive sulfide sheets detached along the black shale hosting horizons. Las Cruces area is crosscut by a subvertical faults system associated with late-Variscan deformation. These faults were reactivated during the Alpine cycle producing a significant control in the distribution of the secondary mineralization (Fig. 3a and b) (Yesares et al., 2015a). The primary deposit is mostly made of pyrite and minor sphalerite, chalcopyrite and galena. Tetrahedrite–tennantite, arsenopyrite, and
several Bi- and Pb-sulfosalts are common accessory minerals. The primary orebody shows features similar to other massive sulfide deposits in the IPB as shape, mineralogical composition and textural relationships (Sáez et al., 1999). The cementation zone overlays the primary mineralization (Figs. 2, 3a and b) and consists of a 50 m thick lens preferentially developed through higher permeability zones associated with late Variscan subvertical faults (Yesares et al., 2015a,b). From the hanging wall to
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the footwall, the cementation zone includes a lens of barren pyritic sands, up to 5 m thick, underlain by a 50 m thick lens of copper-rich supergene mineralization mainly composed of chalcocite, djurleite, digenite, covellite and minor enargite and bornite. In addition, precious metals-rich mineralized breccias have been identified in association with subvertical faults. This mineralization is mainly composed of pyrite, proustite, pyrargyrite, cinnabar and native gold (Yesares et al., 2015b).
preserved, the observed kinematic markers (Figs. 3c and 5e) suggest that this black shale horizon represents the detachment surface of a thrust fault active during the main Variscan deformation phase (Yesares et al., 2014). The black shale horizon acted as a redox front during weathering. Compositionally, it includes remnant minerals such as quartz, monazite, barite and newly-formed phyllosilicates of the smectite and kaolinite groups, as well as native Hg (Fig. 5f). It also includes Fe-sulfides, galena, Ag-sulfides, cinnabar and Au–Ag–Hg amalgams (Yesares et al., 2014).
4.1. Gossan The gossan cap ranges from 0 to 20 m in thickness, being thicker at the central and western parts of the deposit, and gradually thinning to the east due to the erosion predating the deposition of the Neogene cover (Figs. 2, 3a and b). The cap exhibits at the bottom a sharp horizontal contact with the massive sulfides. Only in areas cut and brecciated by vertical faults, the contact with the cementation zone is transitional (Fig. 3b and c). The upper limit of the gossan is marked by an erosive-discordant contact with the sedimentary cover (Fig. 3b). The base of the sedimentary pile includes 5–15 m of conglomerates with gossan pebbles (Fig. 3b and d), which indicates that the supergene process in Las Cruces predates the transgressive Tortonian deposits (Moreno et al., 2002). The Las Cruces gossan cap shows unique characteristics including high precious metals grades, high mineralogical and geochemical variability, both vertical and laterally, and absence of internal structure. Nevertheless, the most remarkable feature differencing the Las Cruces weathering profile from other known gossans consists in its unusual mineralogical composition. While carbonates (i.e. calcite and siderite) and newly-formed reduced phases, including Fe-sulfides and galena are the major components of the gossan, common oxidized phases are scarce. Four different facies have been identified according to the mineralogical and textural features: - Fe-oxyhydroxide facies: This is a minor facies pervasively distributed through the gossan, and alternating with carbonate facies (Fig. 4a– d). It is mostly comprised of goethite, hematite, smectite and kaolinite (Fig. 4a–d). The subordinated mineralogy consists of variable amounts of residual phases such as quartz, barite, rutile, cassiterite and newly-formed minerals including native elements, precious metals and siderite. The main textural patterns in the Fe-oxide facies include primarily gossan relicts, dissolution-replacement and colloform textures. - Siderite facies: This represents the most abundant facies, which is mostly composed of masses of siderite heterogeneously distributed throughout the profile (Fig. 4d–f). Its distribution is controlled by the major NNW/SSE subvertical fault (F1). This fault crosscuts the whole supergene profile affecting the cementation zone, the gossan and the sedimentary cover (Fig. 3b). Besides siderite, the facies also includes subordinated Fe-oxyhydroxides (Fig. 4d and f). - Carbonate-sulfide facies: This facies mainly comprises late-deposited masses of calcite with siderite, cerussite, galena, Fe-sulfides (Fig. 5a–d) and subordinated Pb–Sb-sulfosalts, Bi-sulfides and sulfosalts. As for the siderite-dominated facies, this one is located in the neighbourhood of the F1 fault. The connection between the gossan and the sedimentary cover across the subvertical fault system is suggested by the common occurrence of mineralized Miocene microforaminifera in the deepest levels of the gossan, as components of the fault breccia (Fig. 3b). The spatial relationship between the siderite and carbonate-sulfide facies indicates that the calcitedominated facies represents the last void- and fracture-filling (Fig. 5b and d). - Leached black shales facies: This facies is observed in a 5–15 cm thick horizon of black shales located between the barren pyritic sands and the base of the gossan (Figs. 3c and 5e). Although the original lithology is strongly leached and the primary features are poorly
5. Mineralogy 5.1. Oxyhydroxides Goethite and hematite have been identified in the Las Cruces gossan mainly as botryoides, radial growths and acicular aggregates, always in close association with siderite (Fig. 6a–c). Two Fe-oxyhydroxide generations have been identified. The first generation consists of isolated fragments of massive goethite and/or hematite enclosed in younger siderite (Fig. 6d and e). The fragments range in size from few μm to 3 mm, exhibiting corroded boundaries and siderite replacement. They occur as scarce isolated relicts unevenly dispersed throughout the gossan (Fig. 4a and f). The second generation of Feoxyhydroxides occurs as colloform microbands (micrometric-sized) of alternating siderite and/or hematite (II) and goethite (II). Apparently, Fe-oxyhydroxides and siderite are genetically related (Fig. 6f–h). They commonly fill open spaces mainly in the siderite facies (Fig. 4e and f). Textural evidence indicates that the first and second generations of Fe-oxyhydroxides are not coeval, although their compositions are quite similar. In Table 1 and Appendix 1 the chemical composition of the different Fe-oxyhydroxides generations is shown. Both generations of goethite are relatively homogeneous, although the Pb content in goethite I (0.33 wt. % PbO) is slightly lower than in goethite II (up to 1.08 wt. %). Furthermore, hematite I is enriched in Ti and depleted in Cu and Zn relative to hematite II.
5.2. Carbonates The carbonate suite is comprised of siderite, calcite and cerussite. These minerals occur with a wide range of grain sizes, between few μm to 1 cm, and a large variability of textures such as: colloform, alternating microbands, open spaces filling, massive, microcrystalline and euhedral aggregates (Fig. 6e–l). Two main carbonate generations have been identified in these ores. The oldest generation (I) occurs as microbands of siderite and Fe-oxyhydroxides forming the above-described botryoidal textures (Fig. 6f–h). The second generation of carbonates (II) consists of siderite, calcite and minor cerussite, all sealing fractures. These are observed as microcrystalline and/or coarse euhedral aggregates always associated with a wide range of sulfides and sulfosalts (Fig. 6h–l). The carbonates I are widely and unevenly distributed throughout the gossan linked to carbonate-sulfide facies mainly as siderite masses (Fig. 4e and f). Carbonates II are associated to fracture-related breccias of late-Variscan faults (Fig. 5a–d). These carbonate-rich fractures show a continuous filling from the walls to the core, being usually calcite the latest precipitated phase. The compositional data from both generations of carbonates are shown in Fig. 7 and listed in Table 2 and Appendix 2. Siderite of the carbonate generation I shows a relatively high Pb content (1.28 PbO wt.% in average) and variable Ca, Mg and Mn contents. The youngest carbonate generation can be subdivided in Fe-rich and Ca-rich carbonates. Siderite in the second carbonate generation shows lower Pb amounts (0.51 PbO wt.% in average) than siderite I and variable Mg and Mn contents.
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Fe-oxyhydroxide facies
Fe-oxyhydroxide facies
3cm
a
1cm
Fe-oxyhydroxide facies
b
carbonate-sulfide facies
Fe-oxyhydroxide facies 1cm
cc
1cm
dd
siderite groundmasses
siderite groundmasses
goethite
20cm
ee
5cm
ff
Fig. 4. Facies of the Las Cruces gossan. (a) Fe-oxyhydroxide facies composed by goethite and hematite; (b) Fe-oxyhydroxide facies formed by colloform goethite; (c) Fe-oxyhydroxide facies comprised of massive goethite; (d) Transitional contact between Fe-oxyhydroxide and siderite; (e) and (f) Siderite facies composed by massive siderite and Fe-oxyhydroxiderich fragments.
5.3. Fe-sulfides Fe-sulfides occur in carbonate-sulfide facies and leached black shales (Fig. 5a–f). These sulfides represent quite common newly-formed minerals in the gossan, and are mostly associated with carbonates, galena, Ag-sulfides and sulfosalts (Fig. 8a–d). Fe-sulfides usually occur within the carbonate matrix as micrometer-to-millimetre-sized crystals. These show a wide variety of intricate textures such as radial aggregates, veinlets and euhedral crystals (Figs. 8a–d, 9a–d). The Fe-sulfides assemblage is mainly composed of pyrite and minor greigite, pyrrhotite and marcasite (Fig. 9, Table 3 and Appendix 3). Pyrite has stoichiometric composition, with low concentrations of trace elements (e.g.: Ag, Sb, Bi, As, Co, Se, Ni and Cu).
Greigite has major elements contents ranging between 52.8–58.15 Fe wt.% and 38.94–42.48 S wt.%; it is also slightly enriched in trace elements such as Sb, Bi, As and Co. It has also a remarkable amounts of precious metals (values up to 0.07 Au wt.% and 7.79 Ag wt.%). Fe and S contents in pyrrhotite range from 59.32 to 59.77 Fe wt.% and from 37.1 to 37.16 S wt.%, respectively. There are no significant chemical differences between trace elements contents in greigite and pyrrhotite. 5.4. Galena Galena is one of the most common newly-formed sulfides in the Las Cruces gossan. It is mainly linked to the carbonate-sulfides facies and leached black shales (Fig. 5a–f). Galena shows a wide range of textures and grain sizes, and an intricate relationship with other gossan minerals
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Fe-sulfides + galena + Pb-Sb sulfosalts
glauconitic sands -115m siderite
-120m calcite late-groundmasses
aa
late calcite
1cm
b
carbonate-sulfide facies py+po
sd+gn
carbonate-sulfide facies
siderite facies
sd+gn
1cm
ccc
2cm
dd
leached black shale horizon
Hg
leached black shale horizon
2cm
ee
1cm
f
Fig. 5. Facies of the Las Cruces gossan. (a) Carbonate-sulfide facies formed by late calcite replaced massive siderite; (b) Carbonate-sulfide facies comprised of newly-formed sulfides and calcite geodes; (c) Carbonate-sulfide facies composed by fractures filling of sulfides and carbonates; (d) Carbonate-sulfide facies formed by fractures filling of coarse aggregates of euhedral siderite and aggregates of fine galena; (e) Sheared black shale level which separates gossan and the secondary enrichment zone; and (f) Hg-rich leached black shale horizon.
(Fig. 8e–l). Overall, galena shows textures such as infilling of fractures, aggregates and veinlets (Fig. 8e–g). The most abundant textural pattern of galena consists of very fine skeletal branched crystals, 3–40 μm thick (Fig. 8i–l). These structures show morphologies that range from reticular to lobate, depending on the degree of crystals development (Fig. 8i– l). These growths are usually embedded into carbonates, mainly in calcite and siderite (Fig. 8e–l). The textural relationship between galena and carbonates is complex. Although both phases generally appear as simplectitic intergrowths or filling fractures and cavities (Fig. 8e–i), calcite and/or siderite occasionally seem to occur somewhat later as overgrowths on galena or cyclically, in multiple stages (Fig. 8j and k). Moreover, galena is commonly closely associated with other sulfides and sulfosalts, showing textures such as: inclusions in later Pb–Sb sulfides, galena rims on Fe-sulfides, fine aggregates linked to Pb–Sb and Ag-sulfosalts, and
myrmekitic-like intergrowths with Pb-halides (Figs. 8g,h, 10a,b and 11a–c). Galena is also associated with mimetite and pyromorphite. The EPMA data on galena reveal quite homogeneous compositions (Table 4 and Appendix 4). It is enriched in other base metals and semimetals (e.g.: Fe, Cu, Zn, Sb and As), and depleted in common trace elements including Ag, Bi, Cd and Se.
5.5. Stibnite, Pb–Sb-sulfosalts and Fe–Pb–Sb-sulfosalts Sulfides and sulfosalts of the Pb–Sb–Fe system are commonly associated to the latest stages of the Las Cruces gossan evolution. These minerals show a wide compositional range including sulfides as stibnite and galena, sulfosalts such as fulöppite, plagionite, boulangerite,
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qtz gt I hem I gt I
gt I
smec
100µm
a
10µm
b
20µm
c
hem II gt I gt I
sd hem I sd
sd I
sd
sd I sd 0.5mm
d
50 µm
e
sd I qtz
sd II
gt II
10µm
gn
gt I
f
sd II gn
qtz sd II gt II gt II+sd I 10µm
sd I
g
250 µm
h
0.5mm
i
qtz gn
gt II gt II sd II
sd II sd II
gt II
10µm
j
100µm
k
10µm
l
Fig. 6. Back Scattered Electron (BSE) images on samples of the Las Cruces gossan. (a) Colloform hematite I (hem I) enclosed in Fe-rich smectite (smec); (b) Acicular aggregates of fine goethite I (gt I); (c) Acicular aggregates of fine goethite I (gt I) including residual quartz grains (qtz); (d) and (e) Relicts of massive hematite I (hem I) and goethite I (gt I) cemented by corroded siderite I (sd I); (f) and (g) Microbands of alternating siderite I (sd I), hematite II (hem II) and goethite II (gt II); (h) Microbands of alternating siderite (sd I) goethite (gt II) and microcrystalline siderite II (sd II) filling voids; (i) Siderite II (sd) veinlet sealing microfisures on residual quartz (qtz). Siderite II include fine aggregates of galena (gn); (j) Microcrystalline siderite II (sd II) filling voids in colloform goethite (gt II); (k) Coarse aggregates of euhedral siderite II (sd II); and (l) Interstitial galena (gn) aggregates including a euhedral crystal of siderite II (sd II) which in turn include goethite II (gt II) remnants.
plumosite, the jordanite–geocronite series and other unidentified Fe– Pb–Sb-sulfosalts (Figs. 10a–e, 11a–d, Table 5 and Appendix 5). The Pb–Sb–Fe assemblage has been recognized in the carbonate– sulfides facies (Fig. 5a–d), showing also a very close relationship with galena (Figs. 10a,b, 11a–c). Sulfides and sulfosalts show complex textural features such as: micron-sized veinlets in carbonate matrix, euhedral aggregates of 5–10 μm size in calcite crystals, fine radial growths (few
μm in size) embedded in calcite, and coarse grains filling fractures (Figs. 10a–c, 11a–d). Complex textural relationships have been observed between sulfides and sulfosalts of the Pb–Sb–Fe suite. These phases occur as micron-sized crystal aggregates filling open spaces in calcite I. The observed textural relationship suggests an intergrowth between sulfides and sulfosalts (Figs. 10a–c and 11a–d). In addition, Miocene microforaminifera have been observed enclosed in the Pb–Sb
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Table 1 Summary of goethite and hematite EPMA analysis of the Las Cruces gossan (% oxide). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown. MnO2
MgO
CaO
CuO
ZnO
PbO
SrO
BaO
gt I: goethite enclosed in siderite II (n = 7) Min 74.873 0.133 Max 82.029 0.430 Mean 78.327 0.251 Std. Dsv. 2.684 0.117
0.069 0.869 0.272 0.290
0.013 0.106 0.057 0.037
0.045 0.475 0.223 0.167
0.050 0.267 0.132 0.082
0.052 0.864 0.372 0.324
0.028 0.998 0.339 0.363
0.000 0.054 0.025 0.022
0.025 0.095 0.067 0.027
76.166 83.644 79.880 2.857
hem I: hematite I enclosed in siderite II (n = 5) Min 89.091 0.126 Max 93.243 0.236 Mean 91.253 0.187 Std. Dsv. 1.672 0.046
0.005 0.034 0.021 0.012
0.000 0.020 0.012 0.007
0.056 0.690 0.304 0.299
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.358 3.138 1.507 1.092
0.000 0.032 0.009 0.014
0.000 0.147 0.049 0.064
92.446 94.267 93.276 0.814
0.000 0.178 0.050 0.052
0.030 0.277 0.121 0.074
0.006 0.209 0.098 0.067
0.000 0.095 0.028 0.035
0.025 3.126 1.083 0.929
0.000 0.014 0.002 0.004
0.000 0.175 0.045 0.053
75.854 88.949 80.590 3.906
hem II: botroidal hematite interbedded with siderite I (n = 10) Min 88.355 0.000 0.000 0.000 Max 98.365 0.211 0.086 0.056 Mean 91.164 0.097 0.036 0.023 Std. Dsv. 2.886 0.080 0.034 0.023
0.042 0.562 0.177 0.167
0.000 0.060 0.031 0.025
0.000 0.455 0.099 0.137
0.332 1.098 0.701 0.282
0.000 0.012 0.002 0.004
0.000 0.158 0.054 0.065
89.228 100.093 92.345 3.087
(% oxide)
Fe2O3
TiO2
gt II: botroidal goethite interbedded with siderite I (n = 10) Min 73.901 0.000 0.026 Max 87.305 0.101 0.092 Mean 79.128 0.044 0.054 Std. Dsv. 4.091 0.041 0.021
MgO+MnO
Carbonate I Carbonate II
FeO
CaO
Fig. 7. Composition of carbonates in the FeO–CaO–MgO + MnO ternary diagram. Two clusters corresponding to composition of siderite and calcite.
Total
sulfosalts masses that fill fractures affecting low and intermediate gossan levels (Fig. 10d and e). Pb–Sb–Fe sulfides and sulfosalts have been characterized by EPMA (Fig. 11, Table 5 and Appendix 5). In general, stibnite is fairly pure, although its Fe content is remarkably high, up to 0.31 wt. %. The Pb–Sb-sulfosalts suite includes several species such as: compounds of the jordanite–geocronite series, plumosite, boulangerite, plagionite and fulöppite. Although all these minerals are relatively depleted in trace elements, some differences should be noted. Significant trace elements include Fe, with slightly high values in all analyses. Plumosite is the richest in Fe among the Pb–Sb-sulfosalts, with a mean value of 2.84 wt.%. Arsenic mean concentration ranges from 0.03 wt.% in plumosite to 7.85 wt.% in jordanite. In general, the Pb– Sb-sulfosalts are impoverished in other common trace elements including Se and Bi. The composition of Fe–Pb–Sb sulfosalts is characterized by a wide variation in major elements contents. These range between 9.78– 23.01 Fe wt.%, 46.4 to 61.5 Pb wt.%, 0.66–14.13 Sb wt.% and 16– 24.75 S wt.%. Other trace elements are also highly variable (e.g.: As, Cd, Bi, Cu and Se).
Table 2 Summary of siderite EPMA analysis of Las Cruces gossan (% oxide). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown. (% oxide)
FeO
CaO
MgO
MnO2
SrO
BaO
CuO
ZnO
PbO
TiO2
Total
sd I: botroidal siderite interbedded with goethite-hematite II (n = 14) Min 46.984 2.004 0.632 0.000 Max 59.191 5.884 5.641 0.367 Mean 51.204 3.666 1.833 0.150 Std. Dsv. 3.066 1.408 1.297 0.159
0.000 0.089 0.026 0.029
0.000 0.162 0.064 0.062
0.000 0.078 0.015 0.023
0.000 0.092 0.028 0.033
0.000 4.816 1.286 1.826
0.000 0.174 0.055 0.058
54.499 63.247 57.803 2.852
sd II: filling fractures and associated with Fe-sulfides and Pb-sulfides (n = 50) Min 41.842 0.216 0.080 0.000 Max 65.619 8.674 7.385 1.721 Mean 49.289 4.631 2.295 0.161 Std. Dsv. 5.006 2.141 1.901 0.347
0.000 0.095 0.018 0.021
0.000 0.356 0.070 0.088
0.000 0.308 0.034 0.055
0.000 0.235 0.041 0.058
0.000 5.648 0.516 1.107
0.000 0.239 0.030 0.046
52.987 66.746 56.890 2.612
cc II: filling fractures and associated with Fe-sulfides and Pb-sulfides (n = 13) Min 0.015 51.123 0.025 0.125 Max 0.655 60.641 0.220 0.616 Mean 0.242 53.653 0.110 0.308 Std. Dsv. 0.177 2.913 0.069 0.143
0.006 0.199 0.124 0.051
0.000 0.068 0.020 0.024
0.046 0.495 0.307 0.158
0.000 0.098 0.052 0.034
0.000 0.095 0.043 0.035
0.000 0.051 0.018 0.018
52.443 61.531 54.840 2.751
L. Yesares et al. / Ore Geology Reviews 80 (2017) 377–405
smec
387
qtz sd II sd II
sd II po
50µm
a
sd II
grei
gn
py
100µm
b
py
gt II
c
25µm
sd II
sd II gn
sd II gn
sd II
po gn py
10µm
d
e
10µm
100µm
sd II
gn
f
gn
nad po gn
sd II
g
25µm
cal II
10µm
gn
h cal II
cal II
i
cal II
gn
10µm
10µm
gn
j
10µm
k
10µm
cal II
l
Fig. 8. BSE images of Las Cruces gossan showing: (a) Intergrowth between siderite II (sd II) and acicular aggregates of pyrrhotite (po) replacing Fe-rich smectite (smec); (b) Pyrite (py) sealing veinlets in microcrystalline siderite II (sd II); (c) Euhedral greigite (grei) crystals associated with fine aggregates of galena (gn); (d) Pyrrhotite (po) aggregates replacing pyrite (py) relicts; (e) Cross-section of siderite II (sd) vein crosscutting massive goethite I (gt I). Siderite II include aggregates of skeletal galena (gn); (f) Cross-section of galena (gn) vein crosscutting siderite II (sd II); (g) Fragment composed from boundary to core of nadorite (nad) partially replaced by galena (gn), and symplectitic intergrowth between galena and siderite II (sd II) as last precipitate; (h) Galena (gn) rims along pyrrhotite (po) boundaries and as fine idiomorfic mycrocrystals, both intergrowing with siderite II (sd II); (i) Symplectic intergrowth between skeletal galena (gn) and calcite II (cal II); (j) Euhedral galena (gn) crystals enclosed in calcite II (cal II); (k) Skeletal galena (gn) crystals included in calcite II (cal II); (l) Skeletal branched crystals of galena (gn).
5.6. Ag-sulfides and sulfosalts Ag-sulfides and sulfosalts are also widely distributed, but concentrated mostly in the lower gossan, linked to the leached black shale horizon (Figs. 3c and 5e). In the upper gossan they have been recognized as minor phases associated with carbonate-related facies (Fig. 4e and
f). Both Ag-sulfides and sulfosalts are closely associated with galena, cinnabar and Fe-sulfides (Figs. 10f,g and 12a–d). In the leached black shales, the Ag-assemblage appears in coarsely disseminated grains (50 μm–1 mm) enclosed within the clay-rich matrix. Common textures include: interstitials fillings, intergrowths, mainly with cinnabar, and Ag-sulfides rims around pyrite grains (Figs. 10f,g, 12a and b). Ag-
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grei
po
55 53 Pyrite
51
py
49
sd II
S wt.%
47 200µm
a
25µm
45 Greigite
b
43 41
po
39
sd II
Pyrrhotite
py
37
gn
35 45
50
55
60
25µm
65
po
25µm
c
Fe wt. %
d
Fig. 9. Fe-sulfides composition and their common associations and textures. (a) Pyrrhotite (po) replacing a pyrite (py) crystal; (b) Greigite (grei) replacing colloform siderite II (sd II); (c) Pyrrhotite (po) with galena (gn) rims, both intergrown with siderite II (sd II); and (d) pyrrhotite (po) aggregates replacing pyrite (py) relicts.
sulfides and sulfosalts occurring in the upper gossan show smaller grain sizes (b 0.5 μm). They are embedded within the oldest generation of carbonates and are also closely associated with late galena and Fe-sulfides (Fig. 12c and d). The composition of Ag-sulfides and sulfosalts is summarized in Fig. 12, Table 6 and Appendix 6. The Ag-assemblage is mainly comprised of miargyrite, pyrargyrite-proustite, sternbergite, acanthite and freibergite. However, whereas miargyrite shows variation in the content of Fe, As, Se and Zn, pyrargyrite has variable Sb, Fe and Pb concentrations, and sternbergite shows variation in the content of Sb, Pb and Zn.
show constant and slightly high contents of Sb, Cd, Fe and Se. Furthermore, bismuthinite show variable amounts of As, Pb and Cu. Unidentified Bi–Pb-sulfosalts are less common. EPMA analysis on these minerals depicts a fairly constant stoichiometric Bi:Pb:Sb:S ratio of 1:1:1:4 that is inconsistent with the published composition of Biminerals (Moëlo et al., 2008). These phases show variable and relatively high contents of Ag, Fe, As, Se and Cu. 5.8. Gold and mercury minerals The gold occurrence in the Las Cruces gossan has been detailed by Yesares et al. (2014, 2015b). Based on the host lithology and particle composition gold occurs as two types of minerals: Au–Ag–Hg amalgams linked to the leached black shales of the lower gossan, and as high fineness gold particles related to the Fe-oxyhydroxide facies in the upper gossan (Figs. 4a–c and 5e). Au–Ag–Hg amalgams currently appear as coarsely disseminated grains (50–250 μm in size), filling open spaces in black shales and, in minor extent, as fine skeletal aggregates (b 5 μm) overgrowing sulfides (Fig. 10j). The amalgams are closely associated with native Hg (Fig. 5f), Ag-sulfides, sulfosalts and cinnabar, and, in minor extent, with galena and pyrite (Fig. 10j). Gold related to Fe-oxyhydroxide facies occurs as coarsegrained (50–250 μm) particles of high fineness coexisting with Fe-oxides, Pb-halides and galena (Fig. 10k). This gold particles concentration reaches peak values higher than 100 ppm Au (whole rock analysis) in the upper part of the weathering profile. Hg-minerals always form part of the precious metals assemblage, preferentially in the lower gossan (Fig. 5e). Cinnabar, amalgams and
5.7. Bi-sulfides and sulfosalts Bi-sulfides and sulfosalts are rare in the Las Cruces gossan, although some of them have been identified. The Bi-assemblage is scarcely and unevenly dispersed in the upper gossan, where it is related to the Feoxyhydroxides facies. Bi-minerals mostly occur as filling of veinlets and/or as finely disseminated aggregates of crystals, b50 μm thick, that fill voids in goethite and hematite (Fig. 10h and i). Native Bi, Bi-sulfides and sulfosalts have never been observed associated with other common sulfide minerals in the Las Cruces gossan. Among the Bi-sulfides and sulfosalts suite, bismuthinite is the most common mineral, but galenobismutite and other unidentified Bi–Pbsulfosalts are also present (Table 7 and Appendix 7). The compositions of the Bi-minerals are comparable. Bismuthinite and galenobismutite
Table 3 Summary of Fe-sulfides EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown. wt.%
Mn
Cd
Bi
As
Sn
Co
Se
Ni
Au
Cu
Zn
Ag
Sb
Total
Pyrite (n = 4); Fe1.09 S2.00 Min 49.954 47.852 Max 51.369 48.360 Mean 50.632 48.097 Std. Dsv. 0.581 0.208
S
Fe
0.000 0.006 0.003 0.003
0.000 0.000 0.000 0.000
0.037 0.080 0.058 0.018
0.058 0.095 0.077 0.015
0.012 0.018 0.015 0.002
0.056 0.087 0.072 0.013
0.084 0.100 0.093 0.007
0.025 0.045 0.035 0.008
0.000 0.000 0.000 0.000
0.000 0.015 0.010 0.007
0.000 0.000 0.000 0.000
0.756 1.010 0.883 0.104
0.000 0.021 0.013 0.009
99.699 100.372 99.992 0.292
Greigite (n = 10); Fe3.17 S4.00 Min 38.948 52.806 Max 42.489 58.157 Mean 40.739 55.629 Std. Dsv. 1.202 2.192
0.000 0.026 0.006 0.008
0.000 0.095 0.020 0.030
0.000 0.141 0.055 0.045
0.023 0.939 0.322 0.342
0.000 0.013 0.003 0.005
0.046 0.097 0.070 0.016
0.000 0.030 0.013 0.012
0.000 0.017 0.005 0.008
0.000 0.075 0.027 0.027
0.000 0.062 0.020 0.019
0.000 0.082 0.020 0.026
0.000 7.798 2.272 2.971
0.000 0.682 0.168 0.211
98.091 100.895 99.408 0.820
Pyrrhotite (n = 5); Fe0.73 S0.99 Min 37.101 59.323 Max 37.167 59.779 Mean 37.133 51.005 Std. Dsv. 0.028 0.172
0.000 0.026 0.005 0.005
0.048 0.119 0.031 0.027
0.000 0.141 0.048 0.011
0.389 0.939 0.300 0.071
0.000 0.041 0.008 0.018
0.026 0.097 0.065 0.027
0.000 0.100 0.033 0.008
0.000 0.045 0.013 0.000
0.000 0.075 0.016 0.004
0.000 0.062 0.015 0.006
0.000 0.082 0.013 0.000
0.000 7.798 1.616 0.109
1.258 1.395 0.409 0.052
98.407 100.895 92.632 0.225
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cal II
bou
cal II
cal II
pla
pla pla
gn
pla gn
10µm
a
10µm
smec microforaminirefa
non
cal II
b
10µm
c
jor ci
py
jor
microforaminifera
pyr
40µm
d
10µm
e
10µm
f
stb bs
Bi
pyr+ci
py
gt I mi gt I
g
10µm
25µm
h
10µm
i
ap non
Au Au-Ag-Hg amalgam hem 100µm
j
10µm
k
25µm
l
Fig. 10. Reflected light and BSE images of Las Cruces gossan. (a) Plagionite (pla) euhedral crystals associated with galena (gn) aggregates filling fractures in calcite II (cal II); (b) Calcite II (cal II) intergrown with euhedral aggregates of plagionite (pla) and fine galena crystals (gn); (c) Calcite II (cal) including euhedral aggregates of plagionite (pla) with very fine boulangerite (bou) inclusions; (d) and (e) Calcite II (cal II) breccia with voids filled by massive jordanite (jor). The massive jordanite includes Fe-smectite microforaminifera from the overlaid sediments; (f) Pyrargyrite (pyr) and cinnabar (ci) filling voids in pyrite (py); (g) Massive stembergite (ste), miargyrite (mi), pyrargyrite (pyr) and cinnabar (ci) cementing pyrite (py) fragments; (h) Native Bi included in goethite I (gtI) aggregates; (i) Bismuthinite (bs) veins crosscutting massive goethite I (gt I); (j) Au–Ag–Hg amalgams filling cavities in pyrite (py) and galena (gn) matrix; (k) Coarse gold particle; (l) Apatite (ap) aggregates associated to colloform hematite (hem).
imiterite, the principal phases identified, have been investigated with optical microscopy and SEM-EDS. Cinnabar and imiterite occur as euhedral aggregates and/or filling veinlets in the leached black shales at the lower gossan. Their grain sizes are highly variable, ranging from few microns to near 1 mm (Figs. 10f,g, 12a and c). Hg-sulfides occur intimately associated with Ag-sulfides and sulfosalts, developing mutual intergrowths and/or overgrowth (Figs. 10f,g, 12a and c).
5.9. Other minerals Other minor minerals identified in the Las Cruces weathering profile consist of phyllosilicates belonging to the smectite and kaolinite groups, zircon, monazite and anatase (SEM-EDS analysis). Phyllosilicates occur associated with the leached black shale horizon and the Fe-oxyhydroxide facies. The leached black shale horizon is
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Sulfides
Sb2S3
Pb-Sb-Sulfosalts
pla
cal II
gn
gn
Pb-Fe-Sb-Sulfosalts Reference compositions
stbn
pla
sd II
50µm
a
Fulöppite
25µm
b
sd II Plagionite
ful
Plumosite
pla
Boulangerite
gn
Jordanite
cal II 25µm
PbS
c
25µm
d
FeS2
Fig. 11. Pb–Fe–Sb sulfides and sulfosalts composition and their common associations and textures. (a) Stibnite (stbn) filling voids in siderite II (sd II). Porfidoblastic Stibnite crystal showing plagionite (pla) inclusions which in turn includes earlier galena (gn); (b) Galena (gn) rims on plagionite (pla), both enclosed in calcite II (cal II); (c) Fulöppite with galena (gn) inclusions filling voids in siderite II (sd II); and (d) Plagionite (pla) euhedral aggregates filling fractures in calcite II (cal II).
mostly composed of kaolinite (Fig. 5e), which represents the hosting matrix for amalgams and Ag-sulfides (Figs. 10g,j and 12a,b). In the Feoxyhydroxide facies, the phyllosilicates appear mainly as Fe-rich smectite, which is compositionally close to common nontronite. These smectite group minerals mainly occur in semimassive gossan developed over sulfide-rich host rock. The nontronite-like mineral is intimately associated with Fe-oxyhydroxides and with minor extent to siderite and apatite (Fig. 10l). Monazite and zircon have been identified at the base of the gossan, in relation to the leached black shale horizon. They occur as fine-sized remnants embedded into the kaolinite matrix (Fig. 5e). However, other primary preserved minerals, like fine-grained quartz, barite and cassiterite, are dispersed through the whole weathering profile. Anatase occurs also preferentially at the base of the gossan and in relation to the leached black shale horizon (Figs. 3b,c and 5e). It generally occurs as small crystals (5–75 μm) associated with residual phases, such as monazite and zircon, included within a smectite–kaolinite-rich matrix (Fig. 5e). In addition, apatite, quartz, barite and cassiterite have been also identified as relict phases.
6.1. Oxide association It is mainly characterized by relicts of former goethite and hematite enclosed within the newly-formed carbonate matrix (Figs. 6d,e, 13 and Table 8). To a lesser extent, the oxide association also include phyllosilicates of the kaolinite and smectite groups (Fig. 10l), minor oxidized minerals including oxyhalides as nadorite (Fig. 8g), phosphates such as monazite and pyromorphite, phospho-arsenates of the apatite group, including Cl-apatite and mimetite (Fig. 10l), and native metals such as Au and Bi (Fig. 10h and k). This mineral association typically occurs in the Fe-oxyhydroxide facies (Fig. 4a–c) and it is better preserved far away the Alpine rejuvenated late-Variscan faults (Fig. 3a and b). It is interpreted as a relict of the first stage of the gossan formation. This mineral assemblage is coeval with the weathering of the primary sulfide deposit. The occurrence of gossan pebbles within the basal conglomerate of the sedimentary cover indicates that supergene stage at Las Cruces predates Tortonian (Fig. 3d) (Moreno et al., 2002). This is consistent with age proposed for the exhumation and subaerial exposure of the massive sulfide deposits and the subsequent generation of gossan caps in the IPB (Essalhi et al., 2011). Unlike other known gossan in the IPB and elsewhere, the Las Cruces gossan lacks other common supergene-related minerals (mainly sulfates). Even so, according with the mineralogical composition and textural relationships recognized in the oxidized gossan remnants, the generation of the Las Cruces supergene profile can be assumed to be similar to other weathered sulfide deposits in the IPB (Capitán, 2006; Velasco et al., 2013) and elsewhere (Scott et al., 2001; Sillitoe, 2005). Some common gossan constituents, such as sulfates, arsenates and sulfoarsenates (Dutrizac and Jambor, 1987), have been formed during
6. Discussion: Mineral evolution The mineralogy of the Las Cruces gossan confirmed the occurrence of a complex sequence of mineralogenetic processes that can be summarized by three mineral associations (Fig. 13 and Table 8). The first stage is related to the deposit exhumation and weathering. And the last two stages are linked to the burial of the deposit beneath the sediments of the Guadalquivir Basin.
Table 4 Summary of galena EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown. wt.%
Pb
S
Mn
Cd
Bi
Fe
As
Ag
Se
Sb
Ni
Cu
Zn
Total
0.000 0.008 0.002 0.003
0.000 0.119 0.038 0.039
0.000 0.048 0.009 0.017
0.030 1740 0.913 0.605
0.012 0.662 0.224 0.245
0.000 0.063 0.007 0.016
0.000 0.077 0.032 0.024
0.000 1394 0.331 0.475
0.000 0.095 0.012 0.024
0.000 1014 0.128 0.251
0.000 0.844 0.160 0.264
84.889 102.810 98.215 5449
Galena (n = 16); Pb0.99 S1.00 Min Max Mean Std. Dsv.
83.582 87.125 85.322 1336
13.025 13.989 13.424 0.295
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Table 5 Stibnite, Pb–Sb–Fe–sulfides and sulfosalts EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown. wt.%
Pb
Fe
Sb
As
S
Bi
Cu
Ag
Zn
Au
Sn
Se
Mn
Cd
Co
Ni
Total
69.211 71.525 70.379 0.831
0.000 0.116 0.029 0.043
27.537 28.741 28.392 0.422
0.000 0.074 0.028 0.030
0.000 0.054 0.025 0.022
0.000 0.014 0.005 0.006
0.000 0.015 0.006 0.007
0.000 0.006 0.001 0.002
0.000 0.421 0.308 0.153
0.000 0.033 0.015 0.015
0.000 0.024 0.009 0.011
0.000 0.065 0.027 0.032
0.000 0.028 0.009 0.014
0.000 0.009 0.002 0.003
96.748 100.266 98.771 0.832
Jordanite (n = 4;) Pb14.34 (As4.61 Sb2.40)7.01 S23 Min 67.075 0.150 6.309 7.288 Max 67.874 0.207 7.177 8.474 Mean 67.507 0.172 6.673 7.853 Sta. Dsv. 0.334 0.027 0.386 0.487
16.470 16.920 16.743 0.202
0.000 0.016 0.005 0.008
0.000 0.043 0.016 0.020
0.000 0.017 0.006 0.009
0.000 0.021 0.008 0.012
0.000 0.036 0.014 0.017
0.000 0.000 0.000 0.000
0.000 0.048 0.016 0.024
0.000 0.011 0.004 0.006
0.000 0.055 0.018 0.028
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
97.142 100.445 98.776 0.580
Plumosite(n = 5); (Pb1.79 Bi0.04)1.83 (As0.02 Sb1.96)1.98 (S4.99 Se0.01)5 Min 45.276 0.544 32.204 0.306 20.289 0.000 Max 50.192 5.851 32.204 0.316 21.608 2.716 Mean 46.936 2.846 30.202 0.219 20.156 1.144 Sta. Dsv. 2.485 2.323 1.672 0.167 1.641 1.303
0.000 0.023 0.008 0.011
0.000 0.000 0.000 0.000
0.021 0.046 0.023 0.022
0.000 0.000 0.000 0.000
0.000 0.197 0.086 0.097
0.000 0.279 0.114 0.133
0.000 0.010 0.003 0.005
0.000 0.136 0.063 0.071
0.000 0.013 0.004 0.007
0.000 0.024 0.009 0.011
97.769 102.571 101.284 0.844
Boulangerite (n = 2); (Pb5.09 Bi0.04)5.09 (As0.08 Sb3.76)3.84 S11 Min 55.742 0.775 24.078 0.287 18.382 Max 56.236 1.472 24.556 0.395 19.016 Mean 55.989 1.124 24.317 0.341 18.699 Sta. Dsv. 0.349 0.493 0.338 0.076 0.448
0.000 0.000 0.000 0.000
0.000 0.036 0.018 0.025
0.000 0.000 0.000 0.000
0.000 0.001 0.001 0.001
0.000 0.000 0.000 0.000
0.000 0.164 0.082 0.116
0.000 0.005 0.003 0.004
0.000 0.000 0.000 0.000
0.000 0.123 0.062 0.087
0.000 0.033 0.017 0.023
0.000 0.000 0.000 0.000
98.202 101.280 100.129 0.402
Geocronite (n = 5); Pb13.46 (As1.82 Sb4.87 )6.69 S23 Min 62.210 0.233 10.888 1.974 Max 67.333 2.238 16.716 4.075 Mean 64.860 1.061 13.790 3.178 Sta. Dsv. 2.280 0.805 2.438 0.907
16.631 17.765 17.153 0.521
0.000 0.056 0.020 0.025
0.000 0.053 0.026 0.020
0.000 0.022 0.006 0.010
0.000 0.029 0.015 0.015
0.000 0.018 0.005 0.008
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
91.703 108.127 100.042 0.569
Plagionite (n = 3); (Pb4.50 Bi0.07)4.57 Sb8 S17 Min 35.156 0.374 38.126 0.000 Max 40.342 0.973 41.260 0.079 Mean 37.768 0.729 39.411 0.032 Sta. Dsv. 2.594 0.340 1.766 0.046
21.434 22.595 22.020 0.581
0.000 1.719 0.688 0.992
0.000 0.010 0.004 0.006
0.000 0.070 0.028 0.040
0.000 0.006 0.002 0.003
0.000 0.011 0.006 0.006
0.000 0.170 0.068 0.098
0.000 0.100 0.040 0.058
0.000 0.000 0.000 0.000
0.000 0.055 0.022 0.032
0.000 0.010 0.004 0.006
0.000 0.007 0.003 0.004
94.716 105.916 99.199 0.966
Fuloppite (n = 8); (Pb2.82 Ag0.01 Bi0.17)3.00 (As0.04 Sb7.7)7.74 S15 Min 26.612 0.054 43.276 0.000 23.074 Max 30.236 1.566 48.424 0.692 23.865 Mean 28.541 0.885 45.726 0.170 23.397 Sta. Dsv. 1.251 0.549 1.742 0.249 0.275
0.032 6.046 1.778 2.020
0.000 0.055 0.025 0.020
0.000 0.294 0.059 0.104
0.000 0.037 0.013 0.015
0.000 0.015 0.005 0.006
0.000 0.321 0.113 0.142
0.000 0.067 0.026 0.033
0.000 0.002 0.001 0.001
0.000 0.133 0.029 0.047
0.000 0.030 0.006 0.011
0.000 0.032 0.006 0.011
92.962 110.137 99.442 0.641
Pb–Fe-sulfosalts; (n = 21) Min 46.402 9.788 Max 61.501 23.017 Mean 51.337 16.770 Sta. Dsv. 4.259 2.624
0.000 1.179 0.411 0.317
0.000 4.211 0.550 1.026
0.000 0.157 0.040 0.057
0.000 0.040 0.013 0.012
0.000 0.033 0.004 0.008
0.000 0.103 0.015 0.028
0.000 0.500 0.076 0.118
0.000 0.005 0.001 0.002
0.000 0.192 0.049 0.060
0.000 0.035 0.011 0.011
0.000 0.017 0.002 0.004
72.194 132.853 99.364 1.490
Stibnite (n = 7); Sb1.95 S3 Min 0.000 0.000 Max 0.000 0.589 Mean 0.000 0.316 Sta. Dsv. 0.000 0.209
0.661 14.137 6.286 2.859
0.230 4.057 2.360 1.508
16.004 24.751 22.611 2.258
the first stage of the gossan evolution, but were subsequently dissolved due to the loss of chemical stability under changing redox conditions (Bigham and Nordstrom, 2000; Dutrizac and Jambor, 2000). The oxidation of pyrite-rich primary sulfides under subaerial conditions was followed by the precipitation of minerals of the jarosite group, beudantite, scorodite and oxyhydroxides (Thornber, 1985; Capitán et al., 2003; Koski, 2012). Moreover, in the Las Cruces gossan, phosphates, halides, phyllosilicates and native metals also crystallized at this early oxidative stage. The precipitation of sulfates, sulfoarsenates and Fe-oxyhydroxides assemblages during the generation of the primary gossan involved high fluid oxidation state and very low pH (ph ≈ 3) (Fig. 13 and Table 8) (Bigham and Nordstrom, 2000; Craw et al., 2002). As quoted above, pyromorphite, mimetite and nadorite have been recognized in the Las Cruces gossan (Fig. 8g) (Yesares et al., 2015b). Common halides in other IPB gossans, such as chlorargyrite, iodargyrite and Hg-sulfohalides (Viñals et al., 1995; Sanchez et al., 1996; Capitán, 2006; Velasco et al., 2013) have not been observed at Las Cruces. These phases could have been formed at this stage but dissolved afterwards (Yesares et al., 2014, 2015b). The occurrence of nadorite, mimetite and pyromorphite together with the palaeogeographic location of Las Cruces during the Tortonian suggest the interaction of seawater or connate marine fluids with the gossan.
Extreme weathering conditions, suggested by the reported mineralogical assemblage (ph ≈ 3 and Eh N 0.5 V) (Fig. 13 and Table 8), favoured strong oxidative dissolution, leaching of sulfides and release of the most mobile metals (e.g.: Cu, Zn) out of the weathering system (Thornber, 1985; Curtis, 2003; Sillitoe, 2005). These conditions also led to the precipitation of sulfates, arsenates, sulfoarsenates, oxides and phosphates (Jambor et al., 2000; Dutrizac and Jambor, 2000; Capitán et al., 2003; Koski, 2012), enhancing the fixation of the less mobile elements in the system (e.g.: Pb, Sn, Au, Ag, As, Sb, Ti, Bi) (Mann and Deutscher, 1980; Nieto et al., 2003; Freyssinet et al., 2005). In that sense, metal and semimetal content in Fe-oxyhydroxides was controlled by environmental physico-chemical conditions (Forbes, 1974; Liu et al., 2014). According to this, microprobe analyses on goethite I show significant high content of Pb, Cu, Zn, Ti, Mn and Ca (Table 1 and Appendix 1) indicating the fixation of some elements from fluids via adsorption and/ or coprecipitation in weathering conditions (Dzombak and Morel, 1990; Rose and Bianchi-Mosquera, 1993). Under such conditions the capacity of Fe-oxyhydroxides to trap metal is enhanced by the stability of sulfates (see Swedlund et al., 2009 and references therein). This mineral composition for goethite and hematite is in agreement with results from other IPB gossans where high leaching conditions have been proposed (Capitán, 2006; Velasco et al., 2013). Besides, although the mobility of Pb, As and Sb is limited in supergene environments, the chlorine supply
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Sb2S3-As2S3
Sb2S3-As2S3
Miargyrite
Miargyrite
Pyrargyrite
Pyrargyrite Imiterite
Sternbergite
Cinnabar
Ag2S
Pyrite & Pyrrhotite
Sternbergite
HgS
Greigite
Ag2S
FeS2 stb
mi
Sb2S3-As2S3 ci
50µm
Miargyrite
a stb
10µm
b gn
sd II
ci
py
pyr
ac
Pyrargyrite
sd II
Sternbergite
Galena
Ag2S
PbS mia+gn
ac 250µm
50µm
c
d
Fig. 12. Ag–Fe–Hg–Sb sulfides and sulfosalts composition and their common associations and textures. (a) Cinnabar (ci) crystals enclosed in massive acanthite (ac); (b) Interstitial association of massive pyrargyrite (pyr) + miargyrite (mi) + sternbergite (stb) including corroded fragments of pyrite (py); (c) Cinnabar (ci) crystals enclosed in acanthite (ac) and sternbergite (stb); and (d) Miargyrite (mi) and galena (gn) aggregates cemented by siderite II (sd II).
into the Las Cruces system, suggested by the nadorite, mimetite and pyromorphite assemblage, could contribute to its partial mobilization (Fig. 8g). The precious metals mobility and concentration are also related to these processes. Precious metals could be transported via chloride
complexes and precipitated as coarse gold particles associated to Feoxyhydroxides (Fig. 10k) (Yesares et al., 2014, 2015b). These geochemical patterns have been previously described in the Las Cruces deposit by Yesares et al. (2015a).
Table 6 Summary of Ag-sulfides EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown. Samples
Ag
Sb
S
Bi
As
Sn
Pb
Co
Se
Mn
Ni
Au
Cu
Zn
Total
0.249 4.937 3.033 2.667
0.000 0.090 0.036 0.052
0.000 0.297 0.119 0.171
0.000 0.017 0.007 0.010
1.244 3.162 2.031 1.079
0.000 0.011 0.004 0.006
0.000 0.003 0.001 0.002
0.000 0.038 0.018 0.019
0.000 0.029 0.012 0.016
0.000 0.302 0.128 0.165
99.647 101.703 100.823 1.113
Pyrargyrite (n = 8); (Ag3.15 Fe1.19)4.34 (Sb0.62 As0.22)0.84(S2.89 Se0.11)3 Min 34.277 38.127 16.571 0.000 0.061 0.000 Max 36.924 46.328 22.842 0.127 1.971 0.396 Mean 35.398 42.246 21.148 0.057 0.561 0.176 Std. Dsv. 1.062 2.502 2.094 0.046 0.640 0.179
0.000 0.172 0.034 0.061
0.000 2.538 0.831 1.111
0.000 0.000 0.000 0.000
0.000 0.350 0.070 0.124
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.000 0.009 0.002 0.003
0.000 0.014 0.006 0.006
0.000 0.018 0.007 0.008
99.423 101.852 100.592 0.867
Sternbergite (n = 12); Ag0.91 (Fe2.00 Zn0.01)2.01 S3 Min 29.998 0.000 30.440 0.000 Max 33.545 0.855 32.296 0.155 Mean 32.087 0.230 31.356 0.047 Std. Dsv. 1.102 0.280 0.600 0.044
0.000 0.037 0.007 0.011
0.000 0.121 0.025 0.042
0.013 0.045 0.032 0.009
0.004 0.650 0.136 0.178
0.000 0.014 0.005 0.005
0.000 0.014 0.004 0.005
0.000 0.042 0.010 0.013
0.036 0.372 0.149 0.097
0.000 1.737 0.252 0.500
98.967 102.053 100.836 0.993
Miargyrite (n = 3); (Ag0.99 Fe0.03)1.02 Sb1.04 S2 Min 61.405 13.568 15.064 0.005 Max 63.022 14.448 18.656 0.033 Mean 62.309 14.004 17.023 0.017 Std. Dsv. 0.854 0.440 1.856 0.015
Fe 0.589 3.532 1.950 1.506
34.691 38.885 36.588 1.056
0.025 0.239 0.106 0.077
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Table 7 Summary of Bi-sulfides EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown. wt.%
Ag
Sb
Cd
Bi
Fe
As
Pb
Co
Se
S
Ni
Au
Cu
Zn
Total
77.450 80.694 79.325 1.779
1.109 1.680 1.392 0.286
0.033 0.152 0.089 0.060
0.135 2.552 1.142 1.341
0.000 0.014 0.006 0.008
0.224 0.348 0.280 0.065
19.146 19.360 19.264 0.111
0.000 0.021 0.011 0.011
0.000 0.000 0.000 0.000
0.090 0.133 0.110 0.022
0.000 0.003 0.002 0.002
101.905 102.989 102.360 0.598
Galenobismutite (n = 3); (Pb0.29 Bi1.55)1.84 (S2.99 Se0.02)3 Min 0.000 0.265 0.135 67.256 Max 0.065 0.452 0.164 68.262 Mean 0.033 0.355 0.151 67.659 Std. Dsv. 0.033 0.094 0.016 0.580
0.258 1120 0.741 0.457
0.030 0.090 0.062 0.031
11.257 12.690 11.856 0.793
0.000 0.004 0.002 0.002
0.158 0.462 0.326 0.159
19.025 20.248 19.522 0.695
0.000 0.007 0.003 0.004
0.000 0.000 0.000 0.000
0.095 0.187 0.150 0.052
0.000 0.000 0.000 0.000
99.850 101.204 100.624 0.734
Bi–Pb-sulfosalts (n = 3) Min 0.146 21.358 Max 0.224 22.963 Mean 0.180 22.185 Std. Dsv. 0.042 0.806
1.662 2.121 1.883 0.231
0.250 0.618 0.419 0.189
32.765 33.259 32.980 0.264
0.000 0.037 0.015 0.021
0.185 0.338 0.246 0.088
19.890 20.860 20.455 0.537
0.000 0.000 0.000 0.000
0.000 0.008 0.003 0.005
0.053 0.137 0.093 0.042
0.000 0.017 0.009 0.009
99.178 101.192 100.112 1.029
Bismuthinite (n = 3); Bi1.88 (S2.99 Se0.01) Ʃ3 Min 0.000 0.111 0.146 Max 0.062 0.851 0.307 Mean 0.025 0.431 0.230 Std. Dsv. 0.036 0.397 0.081
0.000 0.096 0.038 0.055
21.326 21.740 21.542 0.209
6.2. Carbonate-oxide association This association mainly occurs in the siderite facies (Fig. 4e and f). Unlike the Fe-oxyhydroxide facies, the siderite facies is located near to Alpine rejuvenated late-Variscan faults, decreasing away from such faults (Fig. 3a and b). In consequence, this association is interpreted as a fault-controlled carbonatization of the early gossan. This association consists of a first generation of siderite and a second generation of hematite and goethite (Fig. 6f–h). It also includes carbonates such as calcite and cerussite as minor components. Fine alternation of goethite II-hematite II and siderite I are the commonest textural feature. Such texture records the changing chemical conditions of the weathering fluids during mineral precipitation (Fig. 6f–h). Precipitation of goethite can occur under a relatively wide range of pH–Eh conditions (pH N 3; Eh N − 0.2), while siderite only forms under a very restricted set of pH–Eh (pH ≈ 7; Eh ≈ 0) (Fig. 13 and Table 8). The stability of goethite is strongly affected by changes in the physical-chemical conditions. Fine alternation of siderite-goethite is therefore indicative of oscillations in the pH–Eh conditions (alternating goethite II-hematite II + siderite I) (Fig. 6f–h) and progressive alkalinisation of the system, as siderite always filled the central cores (Fig. 6h–j). Its genesis was proposed to be in relation to the burial of the deposit under the Guadalquivir Basin sediments (Figs. 3a,b, 13 and Table 8) (Yesares et al., 2014, 2015a,b). The burial of the weathered massive sulfide body beneath the carbonate-rich sediments caused progressive changes in the hydrogeological flow pattern and pH–Eh conditions. As the whole supergene profile remained below the redox front, the Eh conditions progressively decreased. The Alpine tectonic cycle reactivated the late Variscan faults, producing highly permeable zones from where the pervasive basinal fluids circulated at the sediment-gossan interface (Fig. 3b). These basinal fluids reached to the former weathered profile buffered to weakly alkaline conditions by the carbonated sediments (around the siderite buffer in the goethite stability field), and slightly reduced due to the rise of the redox front. The new conditions resulted in the progressive carbonatization of the gossan, as evidenced by the association oxyhydroxides-siderite (Fig. 6f–j). These changes in the pH–Eh conditions increased the solubility of the Feoxyhydroxides (Grivé et al., 2014) favouring its dissolution. Besides, the partial reduction of Fe3+ to Fe2+ and the increase of the CO2 activity enhanced the sideritization of the former gossan. The change in the pH–Eh conditions also led the progressive destabilization of the sulfates, arsenates and sulfoarsenates formed in the early weathering stages (Dutrizac and Jambor, 2000; Jambor et al., 2000). The progressive dissolution of these minerals promoted the release of elements previously fixed by these minerals (e.g.: Pb). Such elements
were partially included in the newly-formed mineral assemblage (siderite I + Fe-oxyhydroxides II). For example, goethite II incorporated more Pb than goethite I due to its higher Pb sorption capacity under nearly neutral conditions (Abel-Samad and Watson, 1998; Bigham and Nordstrom, 2000) (Table 1 and Appendix 1). However, hematite II, which precipitated under similar conditions, included minor Pb amount owing to its lower sorption capacity (Byong-Hun et al., 2004). Due to their high solubility, Cu and Zn are also poorly represented in the minerals of the carbonate-oxide association (Mann and Deutscher, 1980; Thornber, 1985) (Tables 1, 2, Appendices 1 and 2). Goethite II and hematite II are also depleted in Ca, Mg and Mn (Table 1 and Appendix 1), because there are crystal-chemical limitations to incorporate all available Ca, Mg and Mn during the crystallization of carbonates (Table 2 and Appendix 2).
6.3. Carbonate-sulfide association This association is linked to the carbonate-sulfide facies (Fig. 5a–d), and is always related to late-Variscan–Alpine subvertical faults (Fig. 3b) and to the leached black shales at the gossan base (Figs. 3d and 5e). The carbonate-sulfide association consists of a second generation of carbonates, including calcite as dominant mineral, and siderite and cerussite as subordinate ones (Figs. 6i–l). This later stage of carbonate formation is commonly associated with sulfide minerals, including Fesulfides, galena, stibnite, Pb–Fe–Sb-sulfosalts, Ag-sulfides and sulfosalts, Bi-sulfides and sulfosalts (Figs. 8, 9, 10a–g, 11–13 and Table 8). Three carbonate-sulfides assemblages have been identified. These are: (i) siderite II + Fe-sulfides (± galena); (ii) calcite II + galena (±stibnite ± Pb-Fe sulfosalts ± Fe-sulfides); and (iii) Ag-sulfides and sulfosalts + cinnabar + galena (± Fe-sulfides ± siderite II ± calcite II). These minerals always occur filling gaps (Fig. 5b–d). In veins and geodes the composition of carbonates evolves from siderite at the selvages to calcite in the cores. Although textural relationships between carbonates and sulfides are very complex, both seem to be roughly co-genetic. Supporting textural evidences include: intergrowth and overgrowth between siderite and Fe-sulfides; simplectitic intergrowths between galena and calcite and/or siderite; and intergrowth and overgrowth between Pb–Sb-sulfosalts and galena (Figs. 8, 9, 10a-d, 11, 12 and Table 8). The close relationship between sulfides and later carbonates, and the connection of the mineralization with Alpine rejuvenated late-Variscan faults (Fig. 3b) enhance the potential role of the sedimentary cover in the genesis of carbonate-rich associations. The suggested connection of the gossan with the sedimentary cover is reinforced by the occurrence of Miocene microforaminifera in the Pb–Sb sulfosalts inside the carbonated gossan (Fig. 10d and e).
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Fig. 13. Mineral sequence of the Las Cruces gossan. On the right, the changing Eh–pH conditions of the evolving system.
If compared with the carbonate-oxide association, the carbonatesulfide association and its textural features imply the evolution to more reducing conditions (Eh b 0) under variable pH (Fig. 13 and Table 8), as well as a source for the reduced sulfur supply. The siderite stability is strongly constrained to nearly neutral pH and Eh conditions (pH ≈ 7; Eh ≈ 0), whereas that of calcite involves relatively higher pH (pH N 7) and a wide range of Eh conditions (Eh N − 0.2) (Kinniburgh and Cooper, 2004). Compared with the carbonate-oxide association, the minerals forming the carbonate-sulfide
association involve the progressive alkalinization from pH ≈ 7 to pH N 7, and a gradual decrease of the redox conditions from Eh ≈ 0 to Eh b − 0.2 (around the pyrite and galena stability fields) (Fig. 13 and Table 8). These changing environmental conditions are consistent with the generation of the previously described sulfides and sulfosalts associations (Fig. 10a–e, 11–13 and Table 8), which are stable within this range of conditions. The reported carbonatization of the Las Cruces gossan had never been observed (Fig. 13 and Table 8) in gossans developed under
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Table 8 Summary of mineral associations from the Las Cruces gossan. AssociationI (Upper Oligocene-Lower Miocene) Tectonic uplifting, deposit exhumation and gossan formation
System Conditions pH<5; Eh>0.5 V Metals released from primary sulfides, weathering and enrichment of the least mobile elements in the gossan
Newly-formed minerals Fe-sulfates Fe-oxyhydroxides Pb-sulfates Nadorite Au-native Ag-halides Ag-sulfates Bi-native Smectites Kaolinites
Association II (Miocene-Pliocene) Ore burial under carbonate-rich sedimentary cover
System conditions pH~7; Eh~0 V Migrating solutions buffered and progressive gossan carbonatization
Newly-formed minerals Fe-oxyhydroxides Anatase Siderite Calcite Cerussite
Association III (Miocene-Pliocene) Ore burial under carbonate-rich sedimentary cover
System conditions pH~7; Eh~-0.25 V Migrating solutions buffered and progressive gossan carbonatization and reduction
Newly-formed minerals Siderite Calcite Cerussite Galena Pyrite Greigite Marcasite Pyrrhotite Marcasite Pyrargyrite Miargirite Acanthite Sternbergite Cinnabar Amalgams Stibnite Pb-Sb-sulfosalts Pb-Fe-Sb-sulfosalts Bi-sulfidesand sulfosalts Bi-sulfosalts
subaerial conditions in the IPB (Capitán, 2006; Velasco et al., 2013) or elsewhere (Taylor, 2011; Scott et al., 2001; Freyssinet et al., 2005). In this sense, the Las Cruces gossan is a unique mineralization-type known up to date. Subsequent change of the redox condition resulted in the precipitation of a second generation of siderite associated with Fe-sulfides and galena (Figs. 8, 9, 13 and Table 8). As the pH–Eh stability field of siderite is very restricted (pH ≈ 7; Eh ≈ 0) (Fig. 13 and Table 8) and is also limited to low sulfur activity (Pye, 1984; Curtis and Spears, 1968), the expected Fe-assemblage is siderite + Fe-monosulfides (Pye et al., 1990; Sagnotti et al., 2005). This association consists of intergrowths of greigite and/or pyrrhotite in massive siderite. It occurs as fracture filling and shows textures such as euhedral aggregates and radial crystals (Fig. 8a). In some cases, the precipitation of siderite + Fe-monosulfides has been attributed to microbially-mediated processes, such as sulfate reduction and anaerobic oxidation of methane. These processes have been proposed by Larrasoaña et al. (2007) for authigenic greigite and pyrrhotite formed in marine sediments, and by Tornos et al. (2014) for Las Cruces. However, the preservation of greigite and pyrrhotite is limited by the sulfur activity (Liu et al., 2004; Kao et al., 2004). Femonosulfides are pyritized if the reduced sulfur concentration increases, as suggested by the precipitation of galena, stibnite and Pb– Fe–Sb sulfosalts, associated with the Fe-monosulfides, in the carbonate-sulfide association (Figs. 8c,h, 9c, 13 and Table 8). Moreover, although greigite and pyrrhotite have been recognized in the Las Cruces weathering profile, the main Fe-sulfide in the carbonate-sulfide
association is pyrite rather than monosulfides. The observed textural pattern suggests a crystallization sequence consisting on pyrite → pyrrhotite/greigite → siderite (Figs. 8d and 9a). Precipitation of pyrite as the first Fe-bearing mineral in this sequence suggests a sudden increase in the availability of reduced sulfur, as well as a progressive increase in reactive iron and CO2 activity, in order to reach the siderite stability. In that case, siderite will only precipitate when the sulfur concentration of the mineralizing solution had been significantly reduced by precipitation of galena or Fe-sulfides (Sagnotti et al., 2005). This is consistent with the pH–Eh changes that produced the dissolution of the early gossan oxyhydroxides and sulfates (Dutrizac and Jambor, 2000; Jambor et al., 2000). Remobilization of accessory elements at this stage is also evidenced by the trace elements content in Fe-sulfides. The analyzed pyrites show homogeneous compositions depleted in trace metals, whereas greigite and pyrrhotite display a relative high content in Ag, Sb, As and Au (Table 3 and Appendix 3). This compositional evolution in the pyrite → pyrrhotite/greigite sequence also involves dissolution of less stable minerals from the early gossan, and metals fixation in Fe-sulfides stable under the new system conditions. As a general rule, mature gossans developed under subaerial conditions show very low sulfur content. The average sulfur depletion ratio for gossan in the IPB, relative to primary massive sulfides, has been reported as 1/27 (Velasco et al., 2013) with peak values up to 1/54 for the Tharsis gossan (Capitán, 2006). At Las Cruces, the average sulfur depletion ratio is 1/14 (Yesares et al., 2015a). Therefore, the sulfate dissolution that took place during the gossan carbonatization stage could not
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release enough sulfur for the precipitation of sulfides and sulfosalts. This geochemical/mineralogical evolution suggests an extra sulfur source. The Miocene marine incursion (Abad, 2007) and the connate fluids from the sedimentary pile covering the Las Cruces area, appear as the most plausible candidates for this sulfur supply (Yesares et al., 2015a). This sulfur source is consistent with the published δ34S data for the sulfides of the Las Cruces weathering profile (Tornos et al., 2014), which match the Miocene marine sulfur isotopic composition (Hoefs, 1987). The input of marine sulfur under reduced conditions (within the siderite and calcite stability field) increases the sulfidization of fluids making the system suitable for galena precipitation. The source for Pb could be the gossan itself, because it is widely accepted that, compared with the primary mineralization, weathering profiles are enriched in Pb, as Pb-sulfates and Pb-oxides, due to its low mobility under acidic and oxidizing conditions (Thornber, 1985). In that sense, the Pb enrichment factor of 1.5 measured in Las Cruces (Yesares et al., 2015a) is akin to the factor of 1.4 reported for the Tharsis gossan (Capitán, 2006), and with the average value calculated for the IPB gossans (Velasco et al., 2013). Thereby, the change in the pH–Eh conditions led the dissolution of Pb-rich oxidized minerals generated in the early gossan stage. As a consequence of the low stability of Pb-rich oxidized minerals in slight alkaline and reduced conditions (Dutrizac and Jambor, 2000; Jambor et al., 2000), the Pb was dissolved and subsequently fixed by galena during the generation of the carbonate-sulfide association. This is consistent with the main Pb crystallization sequence recognized in Las Cruces gossan: nadorite → galena → cerussite/calcite/siderite (Fig. 8g). This crystallization sequence suggests high oxidizing fluids and high Cl activity during an early stage linked to the seawater-gossan interaction. This led the generation of Cl-rich minerals such as nadorite, mimetite and pyromorphite (Fig. 8g). Later change of redox conditions and the increase in reduced sulfur activity produced galena in myrmekitic intergrowth with nadorite (Fig. 8g). The maximum of reduced sulfur activity was constrained by the galena + Pb–Fe–Sb sulfosalts equilibrium. Galena has stoichiometric composition. Only the high concentration in Fe and Sb (Table 4 and Appendix 4) are probably derived from Fe–Sb-bearing sulfide microinclusions. Furthermore, the galena textures are also evocative of these processes. In that sense, a wide range of galena textures have been identified in the Las Cruces gossan (Fig. 8e–l), including the fine skeletal branched crystals as the most common one (Fig. 8i–l). These galena textures denote rapid mineral growth along corners and edges, usually resulting from sulfur and lead supersaturation in the solution (Ramdohr, 1980). Unbranched bacteriomorphic crystals of galena, as reported by Tornos et al. (2014), have not been observed in the studied samples. Finally, the decrease of Eh and the low concentration of sulfur in a progressively more alkaline depositional environment resulted in the generation of simplectitic intergrowths of galena and carbonates (Fig. 8g and i). Precipitation of cerussite, calcite or siderite associated with galena depends on cation availability (Fe, Pb and Ca) and pH–Eh conditions. Unlike siderite, calcite is stable under high fluid sulfidization conditions, but its stability requires more alkaline conditions (Kinniburgh and Cooper, 2004). Increase of Ca activity and calcite precipitation at the end of each ore deposition stage suggests the progressive rise of pH and Ca activity in the mineralizing fluids that reached the replacement front. Thereby, precipitation of siderite requires interaction between basinal carbonate-rich fluids and Fe-oxyhydroxides of the original gossan, whereas predominance of Ca-rich carbonates suggests major influence of the overlying marls. The chemical composition of the different carbonate generations also provides genetic links between the different mineralization stages. If comparing with siderite I, the compositional variations of the second carbonate generation reflects an increase in the relative proportions of Ca, Mg and Mn from siderite I to siderite II, and finally to calcite II (Table 2 and Appendix 2). Thus, carbonates II, incorporated progressively more Ca, Mg and Mn, elements that were previously dissolved from the carbonates of the overlaying sediments and introduced into the gossan system via the Alpine rejuvenated subvertical faults (Fig. 3a and b). All these data strength the model in
which carbonatization and sulfidization of the Las Cruces gossan took place in an open system strongly controlled by the overlying sedimentary cover. This open system is seemingly incompatible with the pure biogenic model (bioreactor) proposed by Tornos et al. (2014) for the socalled “black-rock” and “red-rock” of the Las Cruces weathered cap. The latest evolution of the Las Cruces gossan is characterized by precipitation of Ag–Hg–Pb–Sb–Bi-bearing sulfides and sulfosalts (Fig. 13 and Table 8). According to the minerals composition, textural relationships and distribution throughout the weathering profile three main mineralogical/geochemical associations have been differentiated for this stage. These are: (i) Pb–Fe–Sb(± As); (ii) Ag–Hg–Pb–Fe– Sb(±As); and (iii) Bi–Pb–Sb. The Pb–Fe–Sb (±As) association is composed of stibnite, fulöppite, plagionite, boulangerite, plumosite, jordanite–geocronite and some unidentified Fe–Pb–Sb-sulfosalts (Fig. 11). All these minerals are systematically associated with galena, calcite and minor Fe-sulfides (Figs. 10a–c and 11). These minerals are widespread throughout the weathering profile and occur both as filling late-veinlets (Fig. 5b–d, 10d and e) or as overgrowths of former sulfides embedded within the carbonate matrix (mainly calcite) (Figs. 10a–c and 11). EPMA analysis of Pb–Sbsulfosalts indicates variable amounts of Fe content as the main minor element (Table 6 and Appendix 6). The erratic composition of the Fe–Pb– Sb-sulfosalts (Fig. 11, Table 6 and Appendix 6) could be associated with an unidentified Fe–Pb–Sb-sulfosalt or with submicroscopic inclusions of different mineral species (Fig. 11). The interpretation of these sulfosalts is problematic, mainly because this kind of mineral assemblages are commonly described for hydrothermal-related deposits and its compositional variability is generally related to the system temperature (Seal et al., 1992; Normand et al., 1996; Radosavljević et al., 2015). The maximum temperature reported for the Las Cruces supergene profile had been 100 °C (Knigth, 2000), so these thermodynamic models are inapplicable. The formation of sulfosalts in low temperature systems is a poorly understood process, nevertheless textural evidences point to these minerals as formed by the same processes and under the same conditions than galena and Fe-sulfides. The Ag–Hg–Pb–Fe–Sb (±As) association consists of miargyrite, pyrargyrite, sternbergite, acanthite, freibergite, cinnabar, imiterite, Ag– Au–Hg amalgams, pyrite, galena and minor siderite (Fig. 12). The close textural relationships between these minerals (e.g.: Ag-sulfides intergrowths and overgrowths with cinnabar, pyrite or galena) (Figs. 10f,g and 12) suggest a co-genetic origin. This mineral association is mainly located at the lower gossan, in association with the leached black shale horizon (Figs. 3c and 5e) and embedded within a kaolinite-rich matrix. To a lesser extent, this association is also found at the upper gossan, in relation to carbonate-sulfide facies (Fig. 5a–d) and enclosed within siderite crystals (Fig. 12c and d). Analytical data of these Ag-sulfides and sulfosalts display highly variable metal content (Fig. 12, Table 6 and Appendix 6) and are characterized by a high concentration of Fe, Pb, Se and Sb. The whole Ag–Hg–Pb–Fe–Sb (±As) association involves enrichment of Ag, Au, Hg, Sb, Pb and S in the lower gossan probably as result of a later remobilization of the sulfates, arsenates and halides that formed beneath the sedimentary cover during the early gossan development. This Ag–Hg assemblage had never been reported in gossan caps, although it has been described as common in cementation zones within supergene profiles (Greffié et al., 2002; Belogub et al., 2008; Koski, 2012). Concerning to the Bi–Pb–Sb association, it is comprised mainly of native Bi and minor bismuthinite, galenobismutite and some unidentified Bi–Pb-sulfosalts (Fig. 10h,i, Table 7 and Appendix 7). These are mostly recognized in the Fe-oxyhydroxides facies at the upper gossan (Fig. 4a–c), being clearly later than their hosting oxides (e.g.: veinlets and fills of open spaces in goethite and hematite) (Fig. 10h and i). The analyzed Bi-sulfides and sulfosalts exhibit a consistent metal content (Table 7 and Appendix 7), with Cd, Fe and Se as the most abundant trace metals. This involves enrichment in the upper gossan linked to the formation of early gossan minerals, and subsequent in situ remineralization, as reduced phases, during the gossan evolution
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beneath the sedimentary cover. The initial enrichment stage has been described in others weathering profiles (Taylor et al., 1984; Thornber, 1985), including those in the IPB (Capitán, 2006). In general, composition and distribution of sulfides and sulfosalts within the Las Cruces weathering profile suggest fixation of Ag, Hg, Au and S as sulfates, sulfo-arsenates and amalgams at the lower gossan, whereas at the upper gossan, Bi, Cd and Se were fixed as native Bi, oxides and oxyhydroxides during an early gossan development. Further changes in redox conditions during later stages of the gossan evolution involved reductive dissolution and in situ reprecipitation as sulfides and sulfosalts. The distribution pattern of these elements along the supergene profile resembles that reported in other gossans in the IPB (Capitán, 2006; Velasco et al., 2013) and elsewhere (Freyssinet et al., 2005). By contrast, the Pb–Sb bearing minerals, concentrated due to the entrance of carbonate-rich fluids through permeable subvertical fractures, were dispersed across the entire supergene profile during later stages, once beneath de sedimentary cover. Gossan caps usually show similar geochemical behaviour for As and Sb, suggesting comparable enrichment factors for both elements (Scott et al., 2001; Boyle, 2003; Capitán, 2006). It is worthy to note that, contrary to others known gossan, the Las Cruces weathering profile displays disparate As and Sb distributions. High Sb enrichment, mainly fixed by stibnite and Pb–Fe–Sb sulfosalts, occurs in the vicinity of the Alpine rejuvenated late-Variscan faults, whereas the underlying cementation zone, also controlled by these subvertical fractures, is enriched in As associated with Cu–As sulfosalts (Yesares et al., 2015a) and Ag–As sulfosalts (Yesares et al., 2015b). The mobilization of As down to the cementation zone and the concentration of Sb in the gossan are mainly related to the rejuvenation of the system through subvertical faults under reduced and alkaline conditions. 7. Conclusions The mineral associations forming the Las Cruces weathering profile differ from other known gossans in the IPB and elsewhere. The complex mineralogical sequence of events recognized in the Las Cruces weathering profile can be explained using three mineral associations: (1) The first association consists of early gossan relicts related to the subaerial weathering of primary sulfides. These relicts include Fe-oxyhydroxide-rich fragments dispersed through the weathering profile, mineralogically and geochemically similar to those described in other supergene profiles. (2) The second mineral association includes a first generation of siderite and a second generation of hematite and goethite. These
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minerals are linked to the carbonatization process that took place when the former gossan buried below carbonate-rich sediments. (3) The third association consists of a sulfide-rich generation linked to the late stage of carbonate precipitation. It is mainly formed by calcite and a sulfide-dominated assemblage including Fe-sulfides, galena, stibnite, Pb–Fe–Sb-sulfosalts, Ag-sulfides and sulfosalts, Bisulfides and sulfosalts.
The interaction of gossan with seawater after the upper Miocene sea level rise is proposed as the most likely scenario for these newly formed mineral associations. Precipitation continues beneath the sedimentary cover by interaction with sulfide-rich and reduced basinal fluids. The mineral distribution and compositional variability suggest that carbonatization and sulfidization were systematically controlled by the reactivation of late Variscan subvertical faults during the Alpine orogeny. Secondary permeability associated with these faults provided the pathways for basinal fluids migration and its interaction with the oxidized gossan. Early sideritization and later calcite-sulfide mineralization are related with this stage. It could be assumed that the mineralogical transformations in the Las Cruces supergene profile resulted from the diagenetic alteration (sensu stricto) of the former gossan. This is suggested by the relationship between the gossan and the overlying Neogene carbonate-rich sedimentary cover. In that sense, the whole processes involved in the modification of the early gossan include: remobilization of the mineralizing fluids depending on the fluctuations of the water table; dissolution and mobilization of carbonates; reductive dissolution of the early gossan minerals; and precipitation of newly formed phases stable with the new system conditions. Finally, the peculiar mineralogical features of the Las Cruces weathering profile, as described in this research, argue that this mineral system can be assigned to a separate category in the gossans ore systems.
Acknowledgments This research is a contribution to projects P–S Anoxia (CGL201130011) and Metodica (CGL2010-21956-C02-02), which are supported by the Spanish government. The authors thank Cobre Las Cruces S.A. for the field assistance and the ongoing collaboration. We are also grateful to Felipe González for his constructive language suggestions to improve the manuscript.
Appendix 1. Goethite and Hematite EPMA analysis of the Las Cruces gossan (% oxide). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown
(% oxide)
MnO2
MgO
CaO
CuO
ZnO
PbO
SrO
BaO
Total
gt I: goethite enclosed in siderite II 1-1 82.029 0.133 1-2 77.040 0.200 1-3 74.873 0.430 1-4 75.954 0.158 1-5 78.265 0.259 1-6 79.215 0.357 1-7 80.667 0.157 Min 74.873 0.133 Max 82.029 0.430 Mean 78.327 0.251 Std. Dsv. 2.684 0.117
Fe2O3
TiO2
0.156 0.069 0.122 0.095 0.117 0.078 0.869 0.069 0.869 0.272 0.290
0.013 0.074 0.106 0.025 0.037 0.045 0.097 0.013 0.106 0.057 0.037
0.045 0.475 0.187 0.075 0.087 0.258 0.359 0.045 0.475 0.223 0.167
0.050 0.189 0.267 0.068 0.083 0.102 0.114 0.050 0.267 0.132 0.082
0.214 0.159 0.052 0.864 0.698 0.086 0.358 0.052 0.864 0.372 0.324
0.282 0.18 0.028 0.158 0.284 0.095 0.998 0.028 0.998 0.339 0.363
0.035 n.d. 0.013 0.025 0.048 0.054 n.d. 0.000 0.054 0.025 0.022
0.045 0.086 0.088 0.095 0.067 0.074 0.025 0.025 0.095 0.067 0.027
83.002 78.472 76.166 77.517 79.944 80.364 83.644 76.166 83.644 79.880 2.857
hem I: hematite I enclosed in siderite II 1-1 89.091 0.126 1-2 93.243 0.224
0.034 0.005
n.d. 0.020
0.071 0.056
n.d. n.d.
n.d. n.d.
3.138 0.636
n.d. 0.032
n.d. 0.051
92.459 94.267
(continued on next page)
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(continued) (% oxide)
Fe2O3
TiO2
MnO2
MgO
CaO
CuO
ZnO
PbO
SrO
BaO
Total
1-3 1-4 1-5 Min Max Mean Std. Dsv.
91.258 92.540 90.306 89.091 93.243 91.253 1.672
0.158 0.204 0.236 0.126 0.236 0.187 0.046
0.015 0.029 0.025 0.005 0.034 0.021 0.012
0.015 0.014 0.012 0.000 0.020 0.012 0.007
0.500 0.690 0.064 0.056 0.690 0.304 0.299
n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. 0.000 0.000 0.000 0.000
1.265 0.358 1.656 0.358 3.138 1.507 1.092
n.d. n.d. n.d. 0.000 0.032 0.009 0.014
n.d. n.d. 0.147 0.000 0.147 0.049 0.064
93.211 93.835 92.446 92.446 94.267 93.276 0.814
gt II: botroidal goethite interbedded with siderite I 2-1 74.590 n.d. 0.035 2-2 76.255 0.075 0.043 2-3 78.165 0.025 0.059 2-4 73.901 n.d. 0.027 2-5 80.825 0.084 0.069 2-6 79.452 n.d. 0.057 2-7 87.305 0.067 0.059 2-8 81.769 0.072 0.062 2-9 80.255 n.d. 0.026 2-10 75.816 0.101 0.092 Min 73.901 0.000 0.026 Max 87.305 0.101 0.092 Mean 79.128 0.044 0.054 Std. Dsv. 4.091 0.041 0.021
0.026 0.016 0.035 0.069 0.014 0.007 0.016 n.d. 0.059 0.178 0.000 0.178 0.050 0.052
0.055 0.075 0.095 0.068 0.179 0.030 0.105 0.159 0.102 0.277 0.030 0.277 0.121 0.074
0.092 0.126 0.185 0.209 0.070 0.116 0.006 0.068 0.037 0.052 0.006 0.209 0.098 0.067
n.d. 0.026 0.046 n.d. 0.095 n.d. n.d. 0.075 n.d. n.d. 0.000 0.095 0.028 0.035
0.987 0.025 1.256 3.126 0.093 1.64 1.217 0.174 0.856 0.469 0.025 3.126 1.083 0.929
n.d. n.d. n.d. n.d. n.d. 0.014 n.d. n.d. n.d. n.d. 0.000 0.014 0.002 0.004
0.069 n.d. n.d. n.d. 0.003 0.045 0.175 0.032 n.d. 0.04 0.000 0.175 0.045 0.053
75.854 76.640 79.865 77.400 81.432 81.361 88.949 82.412 81.335 77.025 75.854 88.949 80.590 3.906
hem II: botroidal hematite interbedded with siderite I 2-1 90.368 n.d. n.d. 2-2 90.684 0.042 n.d. 2-3 91.448 n.d. n.d. 2-4 91.152 0.035 0.009 2-5 89.831 0.041 0.039 2-6 88.531 0.190 0.064 2-7 88.355 0.126 0.086 2-8 98.365 0.165 0.013 2-9 89.611 0.142 0.078 2-10 88.906 0.211 0.053 Min 88.355 0.000 0.000 Max 98.365 0.211 0.086 Mean 91.164 0.097 0.036 Std. Dsv. 2.886 0.080 0.034
n.d. n.d. n.d. n.d. 0.016 0.056 0.027 0.045 0.016 0.056 0.000 0.056 0.023 0.023
0.074 0.044 0.042 0.097 0.066 0.339 0.095 0.562 0.086 0.117 0.042 0.562 0.177 0.167
n.d. n.d. 0.049 0.055 0.015 n.d. 0.056 0.037 0.042 0.060 0.000 0.060 0.031 0.025
0.021 0.077 0.029 n.d. n.d. 0.014 0.025 0.455 0.032 0.080 0.000 0.455 0.099 0.137
0.954 0.889 0.715 1.098 1.015 0.693 0.458 0.452 0.38 0.332 0.332 1.098 0.701 0.282
n.d. n.d. n.d. n.d. 0.012 n.d. n.d. n.d. n.d. 0.003 0.000 0.012 0.002 0.004
n.d. 0.111 0.158 0.004 0.02 n.d. n.d. n.d. 0.043 0.149 0.000 0.158 0.054 0.065
91.417 91.847 92.441 92.450 91.055 89.886 89.228 100.093 90.430 89.967 89.228 100.093 92.345 3.087
n.d.: not detected.
Appendix 2. Siderite EPMA analysis of the Las Cruces gossan (% oxide). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown
(% oxide)
FeO
CaO
MgO
MnO2
SrO
BaO
CuO
ZnO
PbO
TiO2
Total
0.367 0.362 0.292 0.028 0.266 0.015 0.011 0.303 0.331 n.d. 0.028 0.009 n.d. 0.020 0 0.367 0.150 0.159
0.070 0.029 0.040 n.d. 0.089 n.d. n.d. 0.042 n.d. n.d. 0.022 n.d. 0.038 n.d. 0 0.089 0.026 0.029
0.018 n.d. 0.089 0.148 0.162 n.d. 0.118 0.008 n.d. 0.070 0.018 n.d. 0.096 0.136 0 0.162 0.064 0.062
0.005 n.d. n.d. 0.007 n.d. 0.017 0.044 0.012 n.d. n.d. 0.078 n.d. n.d. n.d. 0 0.078 0.015 0.023
0.054 n.d. n.d. 0.047 n.d. 0.092 0.025 n.d. n.d. n.d. n.d. 0.002 0.050 0.080 0 0.092 0.028 0.033
n.d. 0.033 0.005 0.086 0.017 0.959 0.050 0.397 n.d. 4.693 0.426 4.816 0.481 3.789 0 4.816 1.286 1.826
0.024 0.066 0.043 0.059 n.d. 0.148 n.d. 0.174 n.d. 0.028 0.121 0.017 n.d. 0.023 0 0.174 0.055 0.058
55.563 55.814 55.965 54.499 55.887 63.218 55.466 56.601 63.247 59.404 60.090 58.045 55.479 57.816 54.499 63.247 57.803 2.852
sd II: filling fractures and associated with Fe-sulfides and Pb-sulfides 1-1 54.271 0.506 0.562 0.009 1-2 41.842 7.259 4.006 n.d. 1-3 42.980 7.749 7.385 0.006 1-4 45.000 6.452 6.527 0.014 1-5 43.299 7.576 7.253 n.d. 1-6 54.451 1.414 0.564 0.037 1-7 50.730 3.432 1.317 0.388
n.d. 0.053 n.d. n.d. n.d. n.d. 0.009
0.047 0.167 n.d. n.d. n.d. 0.046 n.d.
0.068 0.040 n.d. n.d. n.d. 0.040 0.016
0.048 0.058 n.d. n.d. n.d. 0.130 n.d.
0.188 0.032 n.d. n.d. n.d. 0.109 n.d.
n.d. n.d. n.d. n.d. n.d. 0.007 0.005
55.699 53.457 58.120 57.993 58.128 56.798 55.897
sd I: botroidal siderite interbedded with goethite–hematite II 1-1 49.137 4.392 1.496 1-2 49.611 4.276 1.437 1-3 48.229 5.694 1.573 1-4 47.807 3.956 2.361 1-5 50.765 3.274 1.314 1-6 59.191 2.164 0.632 1-7 51.626 2.552 1.040 1-8 46.984 5.884 2.797 1-9 51.626 5.649 5.641 1-10 51.783 2.004 0.826 1-11 54.535 3.793 1.069 1-12 50.184 2.079 0.938 1-13 51.543 2.156 1.115 1-14 50.063 2.890 0.815 Min 46.984 2.004 0.632 Max 59.191 5.884 5.641 Mean 51.204 3.666 1.833 Std. Dsv. 3.066 1.408 1.297
L. Yesares et al. / Ore Geology Reviews 80 (2017) 377–405
399
(continued) (% oxide)
FeO
CaO
MgO
MnO2
SrO
BaO
CuO
ZnO
PbO
TiO2
Total
1-8 1-9 1-10 1-11 1-12 1-13 1-14 1-15 1-16 1-17 1-18 1-19 1-20 1-21 1-22 1-23 1-24 1-25 1-26 1-27 1-28 1-29 1-30 1-31 1-32 1-33 1-34 1-35 1-36 1-37 1-38 1-39 1-27 1-28 1-29 1-30 1-31 1-32 1-33 1-34 1-35 1-36 1-37 1-38 1-39 1-40 1-41 1-42 1-43 1-44 1-45 1-46 1-47 1-48 1-49 1-50 Min Max Mean Std. Dsv.
50.005 45.495 45.603 45.072 48.611 50.020 56.233 48.971 47.115 47.118 44.740 43.248 43.975 44.661 45.408 45.076 44.341 46.005 46.230 65.619 64.331 47.542 62.128 47.720 43.749 45.464 47.311 44.845 45.357 47.880 49.095 49.314 51.843 53.767 47.713 55.357 53.473 45.440 47.313 51.438 49.903 49.041 54.842 47.087 47.048 46.015 44.990 51.899 49.317 50.142 51.519 54.683 50.702 56.889 49.979 55.088 41.842 65.619 49.289 5.006
4.690 6.490 6.422 6.995 3.189 3.542 0.216 2.814 6.375 5.651 6.260 5.569 6.686 6.811 6.381 6.341 6.890 6.608 5.137 0.446 0.302 4.284 0.732 4.567 8.674 7.199 4.333 6.924 7.091 5.253 6.318 3.258 3.557 4.555 6.767 4.002 4.264 4.284 6.145 1.273 2.577 6.137 4.210 3.648 5.883 5.278 5.084 3.355 3.880 3.969 3.407 3.243 3.717 0.317 4.336 1.416 0.216 8.674 4.631 2.141
1.311 2.358 2.249 1.990 2.413 1.909 0.909 6.134 1.309 1.698 3.093 3.801 3.339 6.762 6.162 6.664 6.792 1.418 0.994 0.151 0.080 1.395 0.127 1.459 2.081 1.941 1.478 1.809 2.032 1.884 1.087 0.806 1.025 1.055 1.099 0.944 1.083 2.338 1.519 0.619 1.270 1.195 1.036 2.277 2.067 2.899 3.072 1.375 2.207 1.656 1.383 1.197 2.121 0.579 1.713 0.716 0.080 7.385 2.295 1.901
0.108 0.074 0.066 0.056 0.011 0.004 0.020 0.042 0.015 n.d. 0.080 0.017 n.d. n.d. 0.024 0.025 0.010 1.045 1.183 0.017 0.032 0.450 0.021 1.531 0.323 0.401 1.721 0.401 0.027 0.025 0.007 0.056 0.004 n.d. 0.005 n.d. n.d. n.d. 0.048 n.d. 0.062 0.036 n.d. 0.022 0.025 0.043 0.147 0.046 n.d. n.d. n.d. 0.006 0.036 n.d. n.d. n.d. 0 1.721 0.161 0.347
0.017 0.024 0.005 0.025 0.006 0.001 n.d. n.d. 0.054 n.d. 0.095 0.046 n.d. n.d. n.d. n.d. n.d. 0.014 0.047 0.042 0.007 0.032 0.019 n.d. n.d. 0.028 0.051 n.d. 0.057 0.006 0.026 0.053 0.049 n.d. n.d. 0.009 0.060 0.015 0.033 0.008 0.010 0.002 0.018 0.005 0.021 0 0.027 0.024 0.004 n.d. 0.054 n.d. n.d. 0.019 n.d. 0.021 0 0.095 0.018 0.021
0.106 0.104 0.172 0.259 0.199 0.080 n.d. n.d. 0.132 0.356 0.162 0.305 0.243 n.d. n.d. n.d. n.d. n.d. 0.032 0.075 0.031 n.d. 0.067 0.019 0.111 n.d. 0.045 n.d. 0.224 0.055 0.066 n.d. n.d. n.d. n.d. n.d. 0.045 0.238 0.192 0.044 0.026 0.007 n.d. 0.066 0.127 0.043 0.004 n.d. 0.027 n.d. n.d. 0.155 0.080 0.018 n.d. n.d. 0 0.356 0.070 0.088
0.087 0.011 n.d. 0.048 0.057 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.019 n.d. n.d. n.d. n.d. 0.047 n.d. 0.308 0.191 0.084 0.202 0.022 0.091 n.d. n.d. 0.028 n.d. 0.037 0.008 n.d. n.d. n.d. n.d. 0.009 0.047 0.074 n.d. n.d. 0.105 0.081 0.027 n.d. 0.063 0.008 0.025 n.d. 0.022 n.d. 0.002 n.d. n.d. n.d. 0.005 0.020 0 0.308 0.034 0.055
0.013 0.158 0.116 0.006 n.d. n.d. n.d. n.d. n.d. n.d. 0.066 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.029 0.004 0.172 0.031 n.d. 0.079 n.d. 0.014 n.d. 0.056 0.105 0.196 0.067 0.024 0.113 0.089 n.d. n.d. 0.028 0.008 0.036 n.d. 0.107 0.142 n.d. 0.088 0.004 0.055 0.235 n.d. n.d. n.d. 0.021 n.d. n.d. n.d. n.d. 0.141 0 0.235 0.041 0.058
0.031 0.196 0.288 0.200 0.005 0.045 n.d. n.d. 0.058 0.073 n.d. 0.001 n.d. n.d. n.d. n.d. n.d. 0.081 0.037 0.037 0.093 0.026 0.053 0.060 0.081 0.069 0.071 0.047 0.100 0.374 0.097 5.648 0.289 0.138 0.101 0.137 0.269 3.483 0.384 4.810 2.787 0.005 1.031 2.968 0.038 0.423 1.118 0.067 0.009 0.017 0.064 0.287 1.094 0.162 0.121 n.d. 0 5.648 0.516 1.107
n.d. 0.051 0.046 n.d. 0.015 0.024 n.d. n.d. n.d. 0.025 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.007 0.163 0.047 0.239 n.d. 0.113 n.d. n.d. 0.015 n.d. 0.031 n.d. 0.048 n.d. n.d. 0.062 0.109 0.038 0.146 0.075 0.040 0.036 n.d. 0.019 0.027 0.126 n.d. 0.035 0.051 n.d. n.d. 0.024 n.d. 0.045 0.032 n.d. n.d. n.d. 0.003 0 0.239 0.030 0.046
56.368 54.961 54.967 54.651 54.506 55.625 57.378 57.961 55.058 54.921 54.496 52.987 54.262 58.234 57.975 58.106 58.033 55.225 53.852 66.746 65.478 53.844 63.462 55.457 55.110 55.131 55.010 54.141 54.993 55.758 56.771 59.159 56.942 59.713 55.723 60.604 59.344 55.920 55.706 58.192 56.866 56.673 61.290 56.161 55.311 54.815 54.702 56.766 55.490 55.784 56.495 59.603 57.750 57.984 56.154 57.405 52.987 66.746 56.890 2.612
cc II: filling fractures and associated with Fe-sulfides and Pb-sulfides 1-1 0.117 52.639 0.030 0.170 1-2 0.245 51.273 0.162 0.391 1-3 0.367 52.543 0.053 0.287 1-4 0.655 51.567 0.062 0.374 1-5 0.356 52.555 0.103 0.177 1-6 0.285 51.376 0.025 0.125 1-7 0.025 52.789 0.157 0.285 1-8 0.345 51.123 0.027 0.302 1-9 0.117 52.758 0.156 0.133 1-10 0.159 51.357 0.054 0.291 1-11 0.202 54.016 0.220 0.236 1-12 0.015 60.641 0.187 0.616 1-13 0.075 58.397 0.164 0.492 Min 0.015 51.123 0.025 0.125
0.143 0.199 0.157 0.125 0.126 0.129 0.174 0.159 0.136 0.136 0.121 0.006 0.045 0.006
n.d. 0.031 n.d. 0.002 0.035 0.052 0.068 0.036 n.d. 0.005 n.d. n.d. n.d. 0
0.401 0.495 0.358 0.384 0.268 0.486 0.476 0.426 0.221 0.321 0.061 0.046 0.121 0.046
0.019 0.062 0.065 0.049 0.057 0.068 0.098 0.035 0.088 0.095 n.d. 0.003 0.026 0
0.014 0.049 0.075 0.095 0.085 0.065 0.025 0.025 0.036 0.085 n.d. n.d. n.d. 0
0.011 0.008 0.035 0.051 n.d. n.d. 0.024 n.d. 0.045 0.032 n.d. 0.017 n.d. 0
53.544 52.915 53.940 53.364 53.762 52.611 54.121 52.443 53.690 52.535 54.856 61.531 59.320 52.443
(continued on next page)
400
L. Yesares et al. / Ore Geology Reviews 80 (2017) 377–405
(continued) (% oxide)
FeO
CaO
MgO
MnO2
SrO
BaO
CuO
ZnO
PbO
TiO2
Total
Max Mean Std. Dsv.
0.655 0.242 0.177
60.641 53.653 2.913
0.220 0.110 0.069
0.616 0.308 0.143
0.199 0.124 0.051
0.068 0.020 0.024
0.495 0.307 0.158
0.098 0.052 0.034
0.095 0.043 0.035
0.051 0.018 0.018
61.531 54.840 2.751
n.d.: not detected.
Appendix 3. Fe-sulfides EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown
wt.%
Ag
Sb
Mn
Cd
Bi
As
Sn
Co
Se
Ni
Au
Cu
Zn
Fe
S
Total
Pyrite 1-1 1-2 1-3 1-4 Min Max Mean Std. Dsv.
0.882 1.010 0.756 0.883 0.756 1.010 0.883 0.104
0.015 n.d. 0.021 0.018 n.d. 0.021 0.013 0.009
0.006 n.d. n.d. 0.006 n.d. 0.006 0.003 0.003
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
0.037 0.057 0.080 0.058 0.037 0.080 0.058 0.018
0.077 0.095 0.058 0.077 0.058 0.095 0.077 0.015
0.018 0.012 0.015 0.015 0.012 0.018 0.015 0.002
0.056 0.075 0.087 0.073 0.056 0.087 0.072 0.013
0.084 0.100 0.095 0.093 0.084 0.100 0.093 0.007
0.045 0.036 0.025 0.035 0.025 0.045 0.035 0.008
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
0.015 n.d. 0.014 0.015 n.d. 0.015 0.010 0.007
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
48.065 48.360 47.852 48.092 47.852 48.360 48.097 0.208
50.529 49.954 51.369 50.617 49.954 51.369 50.632 0.581
99.829 99.699 100.372 99.982 99.699 100.372 99.992 0.292
Greigite 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 Min Max Mean Std. Dsv.
0.079 n.d. 0.027 n.d. n.d. 0.033 1.173 4.304 7.798 6.051 n.d. 7.798 2.272 2.971
0.682 0.027 0.005 n.d. n.d. n.d. 0.081 0.108 0.248 0.178 n.d. 0.682 0.168 0.211
n.d. 0.003 n.d. 0.026 0.004 n.d. n.d. n.d. 0.011 n.d. n.d. 0.026 0.006 0.008
n.d. 0.095 0.030 0.009 n.d. n.d. 0.015 n.d. n.d. n.d. n.d. 0.095 0.020 0.030
0.141 0.020 0.111 0.058 n.d. 0.026 0.014 0.070 0.033 0.052 n.d. 0.141 0.055 0.045
0.127 0.100 0.288 0.160 0.916 0.939 0.023 0.108 0.124 0.116 0.023 0.939 0.322 0.342
0.013 n.d. n.d. n.d. n.d. n.d. n.d. 0.012 n.d. n.d. n.d. 0.013 0.003 0.005
0.055 0.077 0.078 0.049 0.082 0.046 0.069 0.066 0.097 0.082 0.046 0.097 0.070 0.016
0.030 0.003 n.d. 0.016 0.002 0.024 n.d. 0.005 0.026 0.016 n.d. 0.030 0.013 0.012
0.017 n.d. n.d. 0.016 n.d. n.d. 0.014 n.d. n.d. n.d. n.d. 0.017 0.005 0.008
n.d. n.d. n.d. 0.021 0.021 0.038 n.d. 0.039 0.075 0.057 n.d. 0.075 0.027 0.027
0.011 0.001 n.d. 0.012 0.011 0.009 0.008 0.018 0.062 0.040 n.d. 0.062 0.020 0.019
0.013 0.007 0.082 n.d. n.d. 0.029 n.d. 0.029 n.d. n.d. n.d. 0.082 0.020 0.026
55.354 57.993 57.663 58.157 57.370 56.867 53.070 53.936 52.806 53.371 52.806 58.157 55.629 2.192
40.870 41.110 41.096 40.782 42.489 41.736 41.833 39.396 38.948 39.172 38.948 42.489 40.739 1.202
99.392 99.436 99.380 99.306 100.895 99.747 98.300 98.091 100.228 99.134 98.091 100.895 99.408 0.820
Pyrrhotite 3-1 3-2 3-3 3-4 3-5 Min Max Mean Std. Dsv.
0.031 n.d. n.d. 0.250 n.d. n.d. 7.798 1.616 0.109
1.395 1.344 1.370 1.258 1.357 1.258 1.395 0.409 0.052
0.007 n.d. 0.010 n.d. n.d. n.d. 0.026 0.005 0.005
0.119 0.073 0.096 0.095 0.048 0.048 0.119 0.031 0.027
0.018 n.d. n.d. 0.024 0.015 n.d. 0.141 0.048 0.011
0.455 0.389 0.422 0.578 0.458 0.389 0.939 0.300 0.071
n.d. 0.041 n.d. n.d. n.d. n.d. 0.041 0.008 0.018
0.059 0.097 0.078 0.026 0.047 0.026 0.097 0.065 0.027
0.017 n.d. n.d. n.d. n.d. n.d. 0.100 0.033 0.008
n.d. n.d. n.d. n.d. n.d. n.d. 0.045 0.013 n.d.
0.010 n.d. n.d. n.d. n.d. n.d. 0.075 0.016 0.004
n.d. 0.014 n.d. n.d. n.d. n.d. 0.062 0.015 0.006
n.d. n.d. n.d. n.d. n.d. n.d. 0.082 0.013 n.d.
59.779 59.323 59.551 59.489 59.657 59.323 59.779 51.005 0.172
37.101 37.126 37.114 37.157 37.167 37.101 37.167 37.133 0.028
98.991 98.407 98.640 98.877 98.749 98.407 100.895 92.632 0.225
n.d.: not detected.
Appendix 4. Galena EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown
wt.%
Ag
Sb
Mn
Cd
Bi
Fe
As
Pb
Se
S
Ni
Cu
Zn
Total
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Min Max
n.d. n.d. 0.063 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.007 0.063
0.113 0.159 1.394 1.258 0.966 0.427 n.d. 0.058 0.005 0.01 n.d. 0.025 0.035 0.072 0.013 0.025 0.331 1394
n.d. n.d. 0.007 n.d. 0.007 0.003 0.001 n.d. 0.007 n.d. 0.003 n.d. n.d. 0.008 n.d. n.d. 0.002 0.008
n.d. n.d. 0.119 0.095 0.008 0.001 0.072 0.087 0.027 0.024 0.034 0.015 n.d. n.d. 0.066 0.025 0.038 0.119
n.d. n.d. n.d. n.d. n.d. 0.048 0.045 0.025 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.009 0.048
1.545 1.602 0.03 0.1 0.121 0.6 1.392 1.258 1.74 1.68 0.942 0.958 1.12 0.99 0.285 0.299 0.913 1740
0.065 0.012 0.013 0.158 0.043 0.074 0.126 0.152 0.07 0.081 0.061 0.053 0.625 0.514 0.662 0.645 0.224 0.662
87.125 87.025 84.671 84.258 85.145 84.019 87.025 87.102 86.751 86.255 85.025 84.854 83.582 83.812 83.815 84.624 85.322 87.125
0.077 0.035 0.03 n.d. 0.063 n.d. 0.022 0.039 0.052 0.034 0.028 0.059 0.045 0.021 n.d. n.d. 0.032 0.077
13.325 13.123 13.989 13.258 13.719 13.494 13.125 13.245 13.844 13.459 13.667 13.52 13.159 13.334 13.23 13.025 13.424 13.989
0.008 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.014 0.095 0.012 0.095
n.d. n.d. 0.015 0.085 n.d. 0.095 n.d. n.d. 0.038 1.014 n.d. n.d. n.d. n.d. 0.034 0.012 0.128 1014
0.029 0.29 n.d. n.d. 0.006 n.d. 0.704 0.844 0.006 n.d. n.d. n.d. 0.098 0.063 n.d. n.d. 0.160 0.844
102.287 102.246 100.268 99.212 100.078 98.761 102.512 102.81 102.54 102.557 99.76 99.484 98.664 98.814 98.119 98.75 98.215 102.810
L. Yesares et al. / Ore Geology Reviews 80 (2017) 377–405
401
(continued) wt.%
Ag
Sb
Mn
Cd
Bi
Fe
As
Pb
Se
S
Ni
Cu
Zn
Total
Mean Std. Dsv.
0.000 0.016
0.000 0.475
0.000 0.003
0.000 0.039
0.000 0.017
0.030 0.605
0.012 0.245
83.582 1336
0.000 0.024
13.025 0.295
0.000 0.024
0.000 0.251
0.000 0.264
84.889 5449
n.d.: not detected.
Appendix 5. Sulfides and sulfosalts EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown
wt.%
Pb
Fe
Sb
As
S
Bi
Cu
Ag
Zn
Au
Sn
Se
Mn
Cd
Co
Ni
Total
Stibnite 1 2 3 4 5 6 7 Min Max Mean Sta. Dsv.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
0.347 0.201 0.201 0.364 0.589 0.557 n.d. 0.000 0.589 0.316 0.209
69.603 70.940 70.940 69.923 70.532 69.211 71.525 69.211 71.525 70.379 0.831
0.116 n.d. n.d. n.d. n.d. n.d. 0.027 0.000 0.116 0.029 0.043
28.714 28.646 28.646 28.430 27.537 28.533 28.741 27.537 28.741 28.392 0.422
n.d. n.d. n.d. 0.040 0.014 0.074 0.054 0.000 0.074 0.028 0.030
n.d. 0.043 0.043 0.004 0.008 0.054 0.017 0.000 0.054 0.025 0.022
0.006 n.d. n.d. n.d. 0.008 0.014 n.d. 0.000 0.014 0.005 0.006
n.d. 0.011 0.011 n.d. 0.015 n.d. n.d. 0.000 0.015 0.006 0.007
n.d. n.d. n.d. n.d. n.d. n.d. 0.006 0.000 0.006 0.001 0.002
n.d. 0.413 0.413 0.421 0.364 0.421 0.323 0.000 0.421 0.308 0.153
n.d. 0.028 0.028 n.d. 0.009 n.d. 0.033 0.000 0.033 0.015 0.015
n.d. 0.024 0.024 n.d. 0.004 n.d. 0.006 0.000 0.024 0.009 0.011
n.d. 0.065 0.065 n.d. 0.044 n.d. n.d. 0.000 0.065 0.027 0.032
n.d. 0.028 0.028 n.d. n.d. n.d. n.d. 0.000 0.028 0.009 0.014
n.d. n.d. n.d. 0.001 0.001 n.d. 0.009 0.000 0.009 0.002 0.003
98.317 99.586 99.586 98.353 98.069 97.744 100.266 96.748 100.266 98.771 0.832
Jordanite 1 2 3 4 Min Max Mean Sta. Dsv.
67.622 67.522 67.075 67.874 67.075 67.874 67.507 0.334
0.169 0.150 0.150 0.207 0.150 0.207 0.172 0.027
6.420 6.648 7.177 6.309 6.309 7.177 6.673 0.386
7.826 7.288 8.474 7.766 7.288 8.474 7.853 0.487
16.920 16.833 16.844 16.470 16.470 16.920 16.743 0.202
n.d. n.d. 0.016 n.d. 0.000 0.016 0.005 0.008
n.d. 0.043 n.d. 0.010 0.000 0.043 0.016 0.020
n.d. n.d. 0.017 n.d. 0.000 0.017 0.006 0.009
n.d. 0.021 n.d. n.d. 0.000 0.021 0.008 0.012
0.009 n.d. 0.036 n.d. 0.000 0.036 0.014 0.017
n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
0.048 n.d. n.d. n.d. 0.000 0.048 0.016 0.024
0.011 n.d. n.d. n.d. 0.000 0.011 0.004 0.006
0.055 n.d. n.d. n.d. 0.000 0.055 0.018 0.028
n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
98.788 98.291 99.570 98.419 97.142 100.445 98.776 0.580
Plumosite 1 2 3 4 5 Min Max Mean Sta. Dsv.
45.840 44.668 45.446 50.192 45.276 45.276 50.192 46.936 2.485
5.851 2.868 0.573 1.390 0.544 0.544 5.851 2.846 2.323
28.353 27.723 31.542 29.188 32.204 32.204 32.204 30.202 1.672
0.058 0.316 0.316 0.002 0.306 0.306 0.316 0.219 0.167
18.135 21.608 20.647 18.650 20.289 20.289 21.608 20.156 1.641
1.420 2.716 0.013 n.d. n.d. 0.000 2.716 1.144 1.303
0.023 n.d. 0.003 n.d. n.d. 0.000 0.023 0.008 0.011
n.d. n.d. n.d. n.d. 0.255 0.000 0.000 0.000 0.000
0.027 n.d. n.d. 0.046 0.021 0.021 0.046 0.023 0.022
n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
0.197 0.122 n.d. n.d. n.d. 0.000 0.197 0.086 0.097
0.279 0.127 n.d. n.d. n.d. 0.000 0.279 0.114 0.133
n.d. 0.010 n.d. n.d. n.d. 0.000 0.010 0.003 0.005
0.104 0.136 n.d. n.d. n.d. 0.000 0.136 0.063 0.071
0.013 n.d. n.d. n.d. n.d. 0.000 0.013 0.004 0.007
0.007 0.024 n.d. n.d. n.d. 0.000 0.024 0.009 0.011
99.599 99.583 97.635 99.420 97.769 97.769 102.571 101.284 0.844
Boulangerite 1 55.742 2 56.236 Min 55.742 Max 56.236 Mean 55.989 Sta. Dsv. 0.349
0.775 1.472 0.775 1.472 1.124 0.493
24.556 24.078 24.078 24.556 24.317 0.338
0.287 0.395 0.287 0.395 0.341 0.076
19.016 18.382 18.382 19.016 18.699 0.448
n.d. n.d. 0.000 0.000 0.000 0.000
n.d. 0.036 0.000 0.036 0.018 0.025
n.d. n.d. 0.000 0.000 0.000 0.000
n.d. 0.001 0.000 0.001 0.001 0.001
n.d. n.d. 0.000 0.000 0.000 0.000
n.d. 0.164 0.000 0.164 0.082 0.116
n.d. 0.005 0.000 0.005 0.003 0.004
n.d. n.d. 0.000 0.000 0.000 0.000
n.d. 0.123 0.000 0.123 0.062 0.087
n.d. 0.033 0.000 0.033 0.017 0.023
n.d. n.d. 0.000 0.000 0.000 0.000
99.314 100.168 98.202 101.280 100.129 0.402
Geocronite 1 2 3 4 5 Min Max Mean Sta. Dsv.
67.222 67.333 63.673 62.210 64.036 62.210 67.333 64.860 2.280
0.530 0.233 2.238 1.331 0.621 0.233 2.238 1.061 0.805
11.689 10.888 14.460 15.176 16.716 10.888 16.716 13.790 2.438
4.075 3.809 2.599 3.743 1.974 1.974 4.075 3.178 0.907
16.816 16.834 17.626 17.765 16.631 16.631 17.765 17.153 0.521
n.d. 0.056 n.d. 0.028 n.d. 0.000 0.056 0.020 0.025
0.015 n.d. 0.053 0.026 0.037 0.000 0.053 0.026 0.020
n.d. 0.022 n.d. n.d. n.d. 0.000 0.022 0.006 0.010
0.029 n.d. n.d. 0.021 0.028 0.000 0.029 0.015 0.015
n.d. n.d. 0.018 n.d. n.d. 0.000 0.018 0.005 0.008
n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
99.802 98.864 100.596 100.225 99.357 91.703 108.127 100.042 0.569
Plagionite 1 2 3 Min Max Mean Sta. Desv.
40.342 37.844 35.156 35.156 40.342 37.768 2.594
0.953 0.973 0.374 0.374 0.973 0.729 0.340
38.126 38.283 41.260 38.126 41.260 39.411 1.766
n.d. 0.079 n.d. 0.000 0.079 0.032 0.046
21.434 22.043 22.595 21.434 22.595 22.020 0.581
n.d. 1.719 n.d. 0.000 1.719 0.688 0.992
0.010 n.d. n.d. 0.000 0.010 0.004 0.006
n.d. n.d. 0.070 0.000 0.070 0.028 0.040
n.d. 0.006 n.d. 0.000 0.006 0.002 0.003
0.009 0.011 n.d. 0.000 0.011 0.006 0.006
n.d. 0.170 n.d. 0.000 0.170 0.068 0.098
n.d. 0.100 n.d. 0.000 0.100 0.040 0.058
n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. 0.055 n.d. 0.000 0.055 0.022 0.032
n.d. 0.010 n.d. 0.000 0.010 0.004 0.006
n.d. 0.007 n.d. 0.000 0.007 0.003 0.004
99.902 99.889 99.011 94.716 105.916 99.199 0.966
Fuloppite 1 2
30.236 27.703
1.424 0.054
43.645 48.424
0.284 n.d.
23.291 23.865
1.642 0.264
0.020 0.055
n.d. n.d.
n.d. 0.029
0.011 n.d.
n.d. 0.321
n.d. 0.067
n.d. 0.002
n.d. n.d.
n.d. n.d.
n.d. 0.032
100.238 99.992
(continued on next page)
402
L. Yesares et al. / Ore Geology Reviews 80 (2017) 377–405
(continued) wt.%
Pb
Fe
Sb
As
S
Bi
Cu
Ag
Zn
Au
Sn
Se
Mn
Cd
Co
Ni
Total
3 4 5 6 7 8 Min Max Mean Sta. Dsv.
28.553 27.778 29.619 28.181 26.612 29.882 26.612 30.236 28.541 1.251
0.355 1.114 1.566 0.551 0.810 1.354 0.054 1.566 0.885 0.549
47.209 46.654 44.968 45.707 43.276 45.675 43.276 48.424 45.726 1.742
n.d. n.d. n.d. 0.031 0.692 n.d. 0.000 0.692 0.170 0.249
23.590 23.083 23.182 23.526 23.074 23.421 23.074 23.865 23.397 0.275
0.055 0.032 0.514 2.326 6.046 0.824 0.032 6.046 1.778 2.020
0.005 0.044 0.012 0.042 0.021 n.d. 0.000 0.055 0.025 0.020
n.d. n.d. n.d. n.d. 0.294 n.d. 0.000 0.294 0.059 0.104
0.037 n.d. n.d. 0.023 0.006 n.d. 0.000 0.037 0.013 0.015
n.d. n.d. 0.006 0.007 0.015 n.d. 0.000 0.015 0.005 0.006
0.229 0.263 n.d. n.d. n.d. n.d. 0.000 0.321 0.113 0.142
0.064 0.062 n.d. n.d. n.d. n.d. 0.000 0.067 0.026 0.033
n.d. 0.001 n.d. n.d. n.d. n.d. 0.000 0.002 0.001 0.001
0.027 0.133 n.d. n.d. n.d. n.d. 0.000 0.133 0.029 0.047
0.030 n.d. n.d. n.d. n.d. n.d. 0.000 0.030 0.006 0.011
n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.032 0.006 0.011
99.352 98.629 99.335 99.740 99.008 100.332 92.962 110.137 99.442 0.641
14.268 21.969 19.742 9.788 16.121 16.422 16.503 16.103 16.827 16.748 16.687 16.443 23.017 18.062 16.959 17.628 15.694 15.572 16.251 15.664 16.430 9.788 23.017 16.770 2.624
2.336 0.661 5.356 9.151 6.233 5.468 4.493 4.952 3.972 3.973 5.364 7.008 8.480 14.137 9.506 9.238 6.672 6.614 5.058 6.352 4.746 0.661 14.137 6.286 2.859
0.332 0.230 2.014 0.329 3.520 3.621 3.739 3.326 3.838 4.057 3.620 3.064 0.525 0.633 0.282 0.321 3.433 3.304 3.355 2.851 3.606 0.230 4.057 2.360 1.508
20.036 16.004 20.762 20.571 24.462 24.657 24.751 24.111 24.642 23.817 23.891 23.801 21.358 19.712 24.210 24.540 23.868 22.879 24.145 23.660 23.430 16.004 24.751 22.611 2.258
n.d. 0.065 0.016 n.d. 0.253 0.207 0.573 0.625 0.605 0.753 0.317 0.297 0.008 1.179 0.066 0.662 0.503 0.432 0.757 0.376 0.573 0.000 1.179 0.411 0.317
n.d. 0.022 0.309 1.524 n.d. n.d. 0.003 0.015 0.018 0.003 0.032 0.098 0.028 0.018 2.068 4.211 0.005 0.031 n.d. 0.035 0.025 0.000 4.211 0.550 1.026
n.d. n.d. n.d. 0.026 n.d. 0.035 n.d. n.d. 0.154 n.d. 0.157 0.115 n.d. n.d. n.d. 0.032 0.049 n.d. 0.045 0.152 n.d. 0.000 0.157 0.040 0.057
0.008 0.040 0.014 0.025 0.020 0.010 n.d. 0.015 n.d. 0.033 n.d. 0.011 n.d. 0.006 n.d. n.d. 0.006 0.032 0.008 n.d. 0.013 0.000 0.040 0.013 0.012
n.d. n.d. 0.033 n.d. n.d. 0.003 0.001 0.011 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.009 n.d. 0.013 0.000 0.033 0.004 0.008
n.d. 0.021 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.103 0.070 0.051 n.d. n.d. n.d. n.d. n.d. 0.000 0.103 0.015 0.028
0.500 n.d. 0.157 0.073 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.064 0.103 0.161 0.182 n.d. n.d. n.d. n.d. n.d. 0.000 0.500 0.076 0.118
0.005 n.d. 0.003 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.005 n.d. 0.002 n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.005 0.001 0.002
0.120 0.122 n.d. n.d. 0.135 n.d. n.d. 0.079 n.d. n.d. n.d. n.d. 0.074 0.119 n.d. 0.046 0.192 0.040 n.d. n.d. n.d. 0.000 0.192 0.049 0.060
0.002 0.015 0.005 0.004 0.035 0.006 0.003 0.022 0.025 n.d. n.d. n.d. 0.015 0.010 0.028 0.027 n.d. 0.007 0.007 0.007 n.d. 0.000 0.035 0.011 0.011
n.d. n.d. n.d. 0.017 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.004 0.011 0.006 n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.017 0.002 0.004
98.141 99.326 97.879 100.514 100.937 100.812 99.957 99.352 99.859 99.221 100.463 100.496 99.883 99.492 101.251 103.219 98.541 98.221 97.827 97.684 97.423 72.194 132.853 99.364 1.490
Pb–Fe-sulfosalts 1 61.501 2 61.353 3 50.005 4 59.480 5 50.601 6 50.644 7 50.471 8 50.860 9 50.580 10 50.626 11 50.901 12 50.180 13 47.028 14 46.402 15 48.508 16 47.602 17 48.874 18 49.852 19 49.018 20 49.157 21 49.211 Min 46.402 Max 61.501 Mean 51.337 Sta. Dsv. 4.259 n.d.: not detected.
Appendix 6. Ag-sulfides EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown
wt.%
Ag
Sb
S
Bi
Fe
As
Sn
Pb
Co
Se
Mn
Ni
Au
Cu
Zn
Total
Pyrargyrite 1-1 1-2 1-3 Min Max Mean Std. Dsv.
62.692 61.405 63.022 61.405 63.022 62.309 0.854
13.568 14.448 13.987 13.568 14.448 14.004 0.440
17.674 18.656 15.064 15.064 18.656 17.023 1.856
0.033 0.010 0.005 0.005 0.033 0.017 0.015
1.509 0.589 3.532 0.589 3.532 1.950 1.506
4.795 4.937 0.249 0.249 4.937 3.033 2.667
n.d. 0.090 n.d. 0.000 0.090 0.036 0.052
n.d. n.d. 0.297 0.000 0.297 0.119 0.171
0.017 n.d. 0.001 0.000 0.017 0.007 0.010
1.345 1.244 3.162 1.244 3.162 2.031 1.079
n.d. n.d. 0.011 0.000 0.011 0.004 0.006
0.003 n.d. n.d. 0.000 0.003 0.001 0.002
0.038 n.d. 0.013 0.000 0.038 0.018 0.019
0.029 n.d. 0.002 0.000 0.029 0.012 0.016
n.d. 0.034 0.302 0.000 0.302 0.128 0.165
101.703 101.413 99.647 99.647 101.703 100.823 1.113
Miargyrite 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 Min Max Mean Std. Dsv.
35.861 34.357 36.766 34.455 36.924 35.243 34.894 34.277 34.277 36.924 35.398 1.062
38.127 42.046 46.328 44.831 40.567 42.429 41.466 42.208 38.127 46.328 42.246 2.502
22.169 22.275 16.571 20.892 21.845 22.830 22.842 22.639 16.571 22.842 21.148 2.094
0.053 0.086 0.044 0.127 n.d. 0.038 0.099 n.d. 0.000 0.127 0.057 0.046
1.971 0.064 0.491 0.468 0.073 0.061 0.306 0.146 0.061 1.971 0.561 0.640
0.389 0.179 n.d. 0.396 n.d. 0.016 0.339 0.044 0.000 0.396 0.176 0.179
0.172 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.172 0.034 0.061
2.403 0.768 0.065 n.d. n.d. n.d. n.d. 2.538 0.000 2.538 0.831 1.111
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
0.350 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.350 0.070 0.124
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.000 0.000 0.000
n.d. n.d. n.d. n.d. n.d. n.d. 0.009 n.d. 0.000 0.009 0.002 0.003
0.004 0.008 0.014 0.008 n.d. 0.012 n.d. n.d. 0.000 0.014 0.006 0.006
n.d. 0.018 0.012 n.d. 0.014 0.009 n.d. n.d. 0.000 0.018 0.007 0.008
101.510 99.801 100.291 101.177 99.423 100.638 99.955 101.852 99.423 101.852 100.592 0.867
Sternbergite 3-1 3-2 3-3 3-4 3-5 3-6
31.509 33.369 33.545 33.285 29.998 31.555
0.324 0.024 0.108 0.133 0.855 0.165
31.232 31.124 31.249 31.265 31.011 32.282
0.031 0.009 0.028 0.036 0.098 0.034
36.401 35.546 35.888 36.561 34.691 37.350
0.128 0.048 0.174 0.026 0.225 0.109
0.037 n.d. 0.010 n.d. 0.017 n.d.
n.d. n.d. n.d. n.d. 0.121 n.d.
0.035 0.039 0.039 0.039 0.030 0.023
0.038 0.024 0.034 0.027 0.004 0.051
n.d. n.d. 0.007 0.001 0.012 n.d.
0.005 n.d. 0.005 n.d. 0.005 0.002
0.019 n.d. n.d. n.d. 0.005 n.d.
0.157 0.110 0.038 0.195 0.114 0.036
n.d. n.d. n.d. n.d. 1.737 0.013
99.996 100.293 101.125 101.635 98.967 101.635
L. Yesares et al. / Ore Geology Reviews 80 (2017) 377–405
403
(continued) wt.%
Ag
Sb
S
Bi
Fe
As
Sn
Pb
Co
Se
Mn
Ni
Au
Cu
Zn
Total
3-7 3-8 3-9 3-10 3-11 3-12 Min Max Mean Std. D(wt.%). sv.
31.305 32.241 32.050 31.355 31.957 33.504 29.998 33.545 32.087 1.102
0.656 0.045 n.d. 0.051 n.d. n.d. 0.000 0.855 0.230 0.280
31.926 31.219 32.296 30.513 30.440 31.697 30.440 32.296 31.356 0.600
0.026 0.155 n.d. 0.060 0.020 0.011 0.000 0.155 0.047 0.044
36.290 36.100 37.419 38.885 37.013 36.509 34.691 38.885 36.588 1.056
0.118 0.025 0.025 0.239 0.042 0.067 0.025 0.239 0.106 0.077
n.d. n.d. n.d. n.d. n.d. n.d. 0.000 0.037 0.007 0.011
0.092 n.d. n.d. 0.012 n.d. n.d. 0.000 0.121 0.025 0.042
0.045 0.013 0.031 0.034 0.037 0.028 0.013 0.045 0.032 0.009
0.004 0.150 0.069 0.650 0.129 0.076 0.004 0.650 0.136 0.178
0.014 n.d. n.d. 0.005 0.011 n.d. 0.000 0.014 0.005 0.005
n.d. 0.011 n.d. n.d. n.d. 0.014 0.000 0.014 0.004 0.005
0.005 n.d. 0.013 0.017 0.042 n.d. 0.000 0.042 0.010 0.013
0.161 0.372 0.118 0.086 0.245 0.051 0.036 0.372 0.149 0.097
n.d. 0.011 0.032 n.d. n.d. 0.003 0.000 1.737 0.252 0.500
100.756 100.368 102.053 101.953 99.936 101.960 98.967 102.053 100.836 0.993
n.d.: not detected.
Appendix 7. Bi-sulfides EPMA analysis of the Las Cruces gossan (wt.%). Basic statistic parameters (minimum, maximum, mean and standard deviation) are shown
wt.%
Ag
Sb
Cd
Bi
Fe
As
Pb
Co
Se
S
Ni
Au
Cu
Zn
Total
Bismuthinite 1-1 1-2 1-3 Min Max Mean Std. Dsv.
0.062 n.d. n.d. 0.000 0.062 0.025 0.036
0.851 0.23 0.111 0.111 0.851 0.431 0.397
0.307 0.146 0.244 0.146 0.307 0.230 0.081
77.45 80.694 80.336 77.450 80.694 79.325 1.779
1.109 1.68 1.38 1.109 1.680 1.392 0.286
0.033 0.076 0.152 0.033 0.152 0.089 0.060
2.552 0.336 0.135 0.135 2.552 1.142 1.341
0.014 n.d. n.d. 0.000 0.014 0.006 0.008
0.224 0.348 0.255 0.224 0.348 0.280 0.065
19.146 19.36 19.306 19.146 19.360 19.264 0.111
0.021 0.013 n.d. 0.000 0.021 0.011 0.011
n.d. n.d. n.d. 0.000 0.000 0.000 0.000
0.133 0.106 0.09 0.090 0.133 0.110 0.022
0.003 n.d. 0.002 0.000 0.003 0.002 0.002
101.905 102.989 102.011 101.905 102.989 102.360 0.598
Galenobismutite 2-1 n.d. 2-2 0.035 2-3 0.065 Min 0.000 Max 0.065 Mean 0.065 Std. Dsv. 0.033
0.342 0.2645 0.452 0.265 0.265 0.452 0.094
0.164 0.159 0.135 0.135 0.135 0.164 0.016
68.262 67.256 67.26 67.256 67.256 68.262 0.580
1.12 0.258 0.95 0.258 0.258 1.120 0.457
0.09 0.03 0.07 0.030 0.030 0.090 0.031
11.385 11.257 12.69 11.257 11.257 12.690 0.793
0.004 n.d. n.d. 0.000 0.004 0.004 0.002
0.391 0.158 0.462 0.158 0.158 0.462 0.159
19.063 20.248 19.025 19.025 19.025 20.248 0.695
0.007 n.d. n.d. 0.000 0.007 0.007 0.004
0.000 0.000 0.000 0.000 0.000 0.000 0.000
0.187 0.184 0.095 0.095 0.095 0.187 0.052
n.d. n.d. n.d. 0.000 0.000 0.000 0.000
101.015 99.8495 101.204 99.850 99.850 101.204 0.734
Bi–Pb-sulfosalts 3-1 0.146 3-2 0.224 3-3 0.158 Min 0.146 Max 0.224 Mean 0.180 Std. Dsv. 0.042
22.285 22.963 21.358 21.358 22.963 22.185 0.806
n.d. 0.096 n.d. 0.000 0.096 0.038 0.055
n.d. 21.326 21.58 21.326 21.740 21.542 0.209
2.121 1.662 1.85 1.662 2.121 1.883 0.231
0.618 0.357 0.25 0.250 0.618 0.419 0.189
32.765 33.259 32.852 32.765 33.259 32.980 0.264
n.d. 0.037 n.d. 0.000 0.037 0.015 0.021
0.186 0.338 0.185 0.185 0.338 0.246 0.088
19.89 20.776 20.86 19.890 20.860 20.455 0.537
n.d. n.d. n.d. 0.000 0.000 0.000 0.000
0.008 n.d. n.d. 0.000 0.008 0.003 0.005
0.053 0.137 0.085 0.053 0.137 0.093 0.042
0.009 0.017 n.d. 0.000 0.017 0.009 0.009
99.821 101.192 99.178 99.178 101.192 100.112 1.029
n.d.: not detected.
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