Zn Pb Ag
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The Rubiales Pb-Zn ore deposit is located in the Lugo Province of Galicia, Spain, 140 km SE of La Coruna and 125 km SE of Oviedo (#Location; 42° 33' 53"N, 7° 10' 9"W).
The deposit is situated in the arcuate Westasturian-Leonese zone, of the Hercynian Chain in the Iberian Peninsula (Julivert et al., 1972). This zone trends from north-south in the north to SE towards the core of the peninsula. Three different stratigraphic domains have been recognised in this zone, i). the Navia; ii). Mondoñedo; and iii). Caurel domains. Rubiales is hosted within the Mondoñedo domain. The stratigraphic succession in this domain can be summarised as follows, from the base (after Arias et al., 1991):
Villalba series - slate and greywacke;
Candana Group ~1100 m thick - comprising ~400 m of quartzite, overlain by ~375 m of slate and carbonate rocks and ~325 m of quartzite;
Transition Series ~810 m thick - which is the main host to mineralisation at Rubiales, and is composed of three members,
• Lower Transition, ~300 m thick - mainly dark grey, generally sandy slates with a dew limestone and quartzitic intercalations that are a few tens of cm to a few metres in thickness;
• Middle Transition ~385 m thick - alternating layers of blue limestone and green slate and lesser quartzite in beds that are also a few tens of cm to a few metres in thickness;
• Upper Transition ~125 m thick - blue limestone, grey and cream dolomites and light green dolomitic slates with some quartzite intercalations.
Vegadeo Formation ~390 m thick - divided into three members,
• Lower Vegadeo Member, ~135 m thick - dark blue nodular or oolitic slate with fine intercalations of green slates and sandstones,
• Middle Vegadeo Member, ~210 m thick - alternating cream and dark blue dolomites and light blue limestones with fine intercalations of green slates and sandstones,
• Upper Vegadeo Member, ~45 m thick - limestones and dark blue to black calc-schists.
Lower Ordovician to Middle Cambrian
Cabos Series ~1100 m thick - comprising a lower ~650 m of slate, overlain by ~300 m of sandstone, passing upwards into quartzite.
Luarca Formation ~100 m thick comprising a lower quartzite continuous with the upper Cabos Series, overlain by slates.
Garganta Formation ~100 m of slates, continuous with the upper facies of the Luarca Formation.
The Westasturian-Leonese zone has been affected by three folded Carboniferous deformation phases (Bastida et al., 1986). D1 resulted in a large recumbent east-verging folds with an associated cleavage or schistosity. D2 produced a generation of thrusts and associated shear zones, the most significant of which is the Mondoñedo that resulted in the eastward thrusting of the Mondoñedo domain over the Navia domain. This phase was accompanied by minor folds, often non-cylindrical and locally sheath like, as well as a new cleavage, usually crenulated. D3 produced open folds and a crenulation cleavage. Metamorphism is generally low grade, with medium to high grade facies near the base of the Mondoñedo domain (Arias et al., 1991).
The shallow plunging Rubiales orebody was emplaced within and adjacent to a subvertical silicified shear zone, close to intersections with extensional faults. It occurs along the eastern limb of the Baralla syncline, hosted within the tightly folded middle and upper members of the Transition Series. The deposit is a vertical lenticular mass trending at 330°. Its length is about 1200 m in a north direction by 600 m down dip and has an average thickness of 30 m. To the south of the main deposit, within the same shear zone, low grade mineralisation is also found in the Lower Vegadeo Member (Arias et al., 1991).
The orebody is made up of a series of sub-vertical lens of scattered, stringer to massive sulphides, composed of sphalerite, galena, pyrite and minor chalcopyrite and pyrrhotite in a mainly jasperoid (quartz) gangue. The mineralogy of the deposit is simple, with 99% of the sulphides beng sphalerite and galena in a ratio of 7 to 1. The remaining 1% is mainly pyrite and chalcopyrite with traces of pyrrhotite. The deposit shows a large aureole of hydrothermal alteration which Arias et al. (1991) regard to to be the result of three consecutive processes: i). sericitisation of slates and 'ankeritisation' of limestones; ii). silicification of ankeritic rocks producing jasperoids; and iii). chloritisation of the lower part of the deposit (Arias et al., 1991).
Jasperoid (especially its early ankerite-altered portions) is the product of hydrothermal silicification of limestone. Lesser volumes of the same ore mineral assemblage are found as veins and veinlets in the schist envelope around the carbonate host rocks. Zn and Pb mineralisation with low Ag is notable for its high Hg content (0.16% Hg in sphalerite). Initial low (250 to 150°C) hydrothermal temperatures were followed by subsequent metamorphism (Arias et al., 1991).
The sphalerite is of two types, i). dark sphalerite, which is the most abundant and is found throughout the deposit. It is dark brown, and medium to coarse grained occurring in veins and jasperoids, with rare inclusions, generally of pyrite and chalcopyrite in the upper parts of the deposit and pyrrhotite in some other locations, ii). light coloured sphalerite, with similar morphological characteristics and occurring in the same hosts as the dark variety of the mineral (Arias et al., 1991).
Since the deposit was discovered in 1967 by Exminesa, there has been controversy concerning its origin. Two hypotheses have been considered so far: i). a metamorphosed and remobilised sediment hosted "sedex" model formation (Gilissen 1977; Vazquez 1987); and ii). a hydrothermal origin in a shear zone during the Hercynian Orogeny (Merayo et al., 1984; Arias 1988). According to Arias et al. (1991), the characteristics of the deposit favour the latter.
The mine has closed due to bad ground conditions.
The pre-mining resource of 18.6 Mt @ 7.3% Zn, 1.3% Pb, 13 g/t Ag contained 1.358 Mt Zn; 0.2418 Mt Pb; 242 t Ag; 289 t Cd; and 356 t Hg (Arias et al., 1991).
The most recent source geological information used to prepare this summary was dated: 1991.
Record last updated: 30/11/2015
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Arias, D., Suarez, O., Corretge, L.G., Fernandez-Jardon, L. and Perez-Cerdan, F., 1991 - Structure, hydrothermal alteration and composition of the Rubiales Pb-Zn orebody (Lugo, Spain): Genetic model: in Mineralium Deposita v.26, pp. 199-210|
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