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1.
The Iberian Pyrite Belt, located in the SW Iberian Peninsula, contains many Paleozoic giant and supergiant massive sulphide
deposits, including the largest individual massive sulphide bodies on Earth. Total ore reserves exceed 1500 Mt, distributed
in eight supergiant deposits (>100 Mt) and a number of other smaller deposits, commonly with associated stockwork mineralizations
and footwall alteration haloes. Massive sulphide bodies largely consist of pyrite, with subordinated sphalerite, galena and
chalcopyrite and many other minor phases, although substantial differences occur between individual deposits, both in mineral
abundance and spatial distribution. These deposits are considered to be volcanogenic, roughly similar to volcanic-hosted massive
sulphides (VHMS). However, our major conclusion is that the Iberian type of massive sulphides must be considered as a VHMS
sub-type transitional to SHMS.
This work is an assessment of the geological, geochemical and metallogenic data available up to date, including a number of
new results. The following points are stressed; (a) ore deposits are located in three main geological sectors, with the southern
one containing most of the giant and supergiant orebodies, whereas the northern one has mainly small to intermediate-sized
deposits; (b) ore deposits differ one from another both in textures and mineral composition; (c) Co and Bi minerals are typical,
especially in stockwork zones; (d) colloidal and other primary depositional textures are common in many localities; (e) a
close relation has been found between ore deposits and some characteristic sedimentary horizons, such as black shales. In
contrast, relationships between massive sulphides and cherts or jaspers remains unclear; (f) footwall hydrothermal alterations
show a rough zoning, the inner alteration haloes being characterized in places by a high Co/Ni ratio, as well as by mobility
of Zr, Y and REE; (g) 18O and D values indicate that fluids consist of modified seawater, whereas 34S data strongly suggest the participation of bacterial-reduced sulphur, at least during some stages of the massive sulphide
genesis, and (h) lead isotopes suggest a single (or homogeneized) metal source, from both the volcanic piles and the underlying
Devonian rocks (PQ Group).
It is concluded that, although all these features can be compatible with classical VHMS interpretations, it is necessary to
sketch a different model to account for the IPB characteristics. A new proposal is presented, based on an alternative association
between massive sulphide deposits and volcanism. We consider that most of the IPB massive orebodies, in particular the giant
and supergiant ones, were formed during pauses in volcanic activity, when hydrothermal activity was triggered by the ascent
and emplacement of late basic magmas. In these conditions, deposits formed which had magmatic activity as the heat source;
however, the depositional environment was not strictly volcanogenic, and many evolutionary stages could have occurred in conditions
similar to those in sediment-hosted massive sulphides (SHMS). In addition, the greater thickness of the rock pile affected
by hydrothermal circulation would account for the enormous size of many of the deposits.
Received: 8 September 1998 / Accepted: 4 January 1999 相似文献
2.
3.
Two small to medium sized massive sulphide deposits, Las Herrerías and La Torerera, located in the Iberian Pyrite Belt (IPB) are examined from a geological and palynostratigraphic perspective. The palynological assemblages are assignable to the Retispora lepidophyta–Verrucosisporites nitidus (LN) miospore Biozone (Latest Devonian: Latest Famennian/Strunian) of Western Europe. This age permits correlation with some of the main massive sulphide deposits dated so far in the region (viz., Tharsis, Aznalcóllar, Sotiel-Coronada or Neves-Corvo), and validates once again the hypothesis that a single mineralizing event was responsible for the genesis of most of the IPB’s massive sulphide deposits. The present study confirms that palynostratigraphy is an invaluable high-resolution biostratigraphic tool in the IPB, applicable to dating, correlation and ore-exploration. 相似文献
4.
F. Velasco J. Sánchez-España A. J. Boyce A. E. Fallick R. Sáez G. R. Almodóvar 《Mineralium Deposita》1998,34(1):4-18
The sulphide deposits of the Iberian Pyrite Belt (IPB) represent an ore province of global importance. Our study presents
113 new sulphur isotope analyses from deposits selected to represent the textural spectrum of ores. Measured 34S values range from −26 to +10‰ mostly for massive and stockwork ores, in agreement with data previously published. In situ
laser 34S analyses reveals a close correlation of 34S with texture. Primary diagenetic textures are dominated by relatively low 34S (−8‰ to −2‰), whereas stockwork feeder textures are dominated by higher 34S (∼+3‰ to +5‰). Intermediate textures (mainly coarse textures in stratiform zones) have intermediate 34S, although they are mostly dominated by the high 34S component. Rare barite has a homogeneous 34S around +18‰, which is consistent with direct derivation from Lower Carboniferous seawater sulphate. A dual source of sulphide
sulphur in the IPB deposits has been considered. A hydrothermal source, derived from reduction of coeval seawater sulphate
in the convective systems, is represented by sulphide in the feeder zones. Here variations in 34S are caused by variations in the extent of the sulphate reduction, which governs the SO4:H2S ratio. The second end-member was derived from the bacterial reduction of coeval seawater sulphate at or near the surface,
as reflected in the primary textures. A distinct geographical variation in 34S and texture from SW (more bacteriogenic and primary textures) to NE (more hydrothermal textures and 34S) which reflects a variation in the relative input of each source was likely controlled by local geological environments.
Given that the sulphur isotope characteristics of the IPB deposits are unlike most VMS and Kuroko deposits, and noting the
dominance of a mixed reduced sedimentary and volcanic environment, we suggest that the IPB could represent an ore style which
is intermediate between volcanic and sedimentary hosted massive sulphide types.
Received: 8 October 1997 / Accepted: 14 May 1998 相似文献
5.
The original stratigraphic relationships and structure of VMS deposits are commonly obscured by deformation. This can also affect their economic significance, as shown by several Iberian Pyrite Belt (IPB, SW Iberia) examples. The contrasting rheologic properties of the different lithologies present in an orebody (massive sulphide, feeder stockwork, alteration envelope, volcanic and sedimentary rocks) play a major role in determining its overall behaviour. Variscan thin-skinned tectonics led to stacking of the massive pyrite and stockwork bodies in duplex structures, resulting in local thickening and increased tonnage of minable mineralization. Furthermore, differential mechanical behaviour of the different sulphide minerals localised the detachments along relatively ductile sulphide-rich bands. The result was a geochemical and mineralogical reorganisation of most deposits, which now consist of barren, massive pyrite horses, bounded by base metal-rich ductile shear zones. Metal redistribution was enhanced by mobilisation of the base metal sulphides from the initially impoverished massive pyrite, through pressure-solution processes, to tensional fissures within the already ductile shear zones. In NW Iberia, VMS deposits were also strongly overprinted by the Variscan deformation during emplacement of the Cabo Ortegal and órdenes allochthonous nappe complexes, but no stacking of the orebodies was produced. Original contacts were transposed, and the orebodies, their feeder zones and the country rock acquired pronounced laminar geometry. In lower-grade rocks (greenschist facies, Cabo Ortegal Complex), solution transfer mechanisms are common in pyrite, which remains in the brittle domain, while chalcopyrite shows ductile behaviour. In higher-grade rocks (amphibolite facies, órdenes Complex), metamorphic recrystallisation overprints earlier deformation textures. The contrasting behaviour of the IPB and NW Iberian deposits is explained by key factors that affect their final geometry, composition and economics, such as pre-deformation structure, size and mineralogical composition of the orebody and associated lithologies, temperature, crustal level, deviatoric stress and availability of a fluid phase during deformation and the style and rate of deformation. 相似文献
6.
G. R. Almodóvar R. Sáez J. M. Pons A. Maestre M. Toscano E. Pascual 《Mineralium Deposita》1997,33(1-2):111-136
The Aznalcóllar mining district is located on the eastern edge of the Iberian Pyrite Belt (IPB) containing complex geologic features that may help to understand the geology and metallogeny of the whole IPB. The district includes several ore deposits with total reserves of up to 130 Mt of massive sulphides. Average grades are approximately 3.6% Zn, 2% Pb, 0.4% Cu and 65?ppm Ag. Mined Cu-rich stockwork mineralizations consist of 30?Mt with an average grade of 0.6% Cu. Outcropping lithologies in the Aznalcóllar district include detrital and volcanic rocks of the three main stratigraphic units identified in the IPB: Phyllite-Quartzite Group (PQ), Volcano-Sedimentary Complex (VSC) and Culm Group. Two sequences can be distinguished within the VSC. The Southern sequence (SS) is mainly detritic and includes unusual features, such as basaltic pillow-lavas and shallow-water limestone levels, the latter located in its uppermost part. In contrast, the Aznalcóllar-Los Frailes sequence (AFS) contains abundant volcanics, related to the two main felsic volcanic episodies in the IPB. These distinct stratigraphic features each show a different palaegeographic evolution during Upper Devonian and Lower Carboniferous. Massive sulphides occur in association with black shales overlying the first felsic volcanic package (VA1) Palynomorph data obtained from this black shale horizon indicate a Strunian age for massive sulphides, and consequently an Upper Devonian age for the VA1 cycle. Field and textural relationships of volcanics suggest an evolution from a subaerial pyroclastic environment (VA1) to hydroclastic subvolcanic conditions for the VA2. This evolution can be related to compartmentalizing and increasing depth of the sedimentary basin, which may also be inferred from changes in the associated sediments, including black shales and massive sulphides. Despite changes in the character of volcanism, the same dacitic to rhyolitic composition is found in both pyroclastic and subvolcanic igneous series. The main igneous process controlling chemical variation of volcanics is fractional crystallization of plagioclase (+accessories). This process took place in shallow, sub-surface reservoirs giving rise to a compositional range of rocks that covers the total variation range of felsic rocks in the IPB. The Hercynian orogeny produced a complex structural evolution with a major, ductile deformation phase (F1), and development of folds that evolved to thrusts by short flank lamination. These thrusts caused tectonic repetition of massive and stockwork orebodies. In Aznalcóllar, some of the stockwork mineralization overthrusts massive sulphides. These structures are cut by large brittle overthrusts and by late wrench faults. The original geometric features of massive sulphide deposits correspond to large blankets with very variable thicknesses (10 to 100?m), systematically associated with stockworks. Footwall rock alteration exhibits a zonation, with an inner chloritic zone and a peripheral sericitic zone. Silicification, sulphidization and carbonatization processes also occur. Hydrothermal alteration is considered a multi-stage process, geochemically characterized by Fe, Mg and Co enrichment and intense leaching of alkalies and Ca. REE, Zr, Y and Hf are also mobilized in the inner chloritic zones. Three ore types occur, both in stockworks and massive sulphides, named pyritic, polymetallic and Cu-pyritic. Of these, Cu-pyritic is more common in stockworks, whereas polymetallic is prevalent in massive sulphides. Zoning of sulphide masses roughly sketches a typical VHMS pattern, but many alternating polymetallic and barren pyritic zones are probably related to tectonics. Although the paragenesis is complex, several successive mineral associations can be distinguished, namely: framboidal pyritic, high-temperature pyritic (300?°C), colloform pyritic, polymetallic and a late, Cu-rich high-temperature association (350?°C). Fluid inclusion data suggest that hydrothermal fluids changed continuously in temperature and salinity, both in time and space. Highest Th and salinities correspond to inner stockworks zones and later fluids. Statistic population analysis of fluid inclusion data points to three stages of hydrothermal activity, at low (<200?°C), intermediate (200–300?°C) and high temperatures (300–400?°C). 34S values in massive sulphides are lower than in stockwork mineralization suggesting a moderate bacterial activity, favoured by the euxinoid environment prevailing during black shale deposition. The intimate relation between massive sulphides and black shales points to an origin of massive sulphides by precipitation and replacement within black shale sediments. These would have acted both as physical and chemical barriers during sulphide deposition. Hydrothermal activity started during black shale deposition, triggered by a rise in thermal gradient due to the ascent of basic magmas. We suggest a three-stage genetic model: (1) low temperature, diffuse fluid flow, producing pyrite-bearing lenses and disseminations interbedded with black shales; locally, channelized high-T fluid flow occurs; (2) hydrothermal cyclic activity at a low to intermediate temperature, producing most of the pyritic and polymetallic ores, and (3) a late high-temperature phase, yielding Cu-rich and Bi-bearing mineralization, mainly in the stockwork zone. 相似文献
7.
The Rammelsberg polymetallic massive sulphide deposit was the basis of mining activity for nearly 1000 y before finally closing
in 1988. The deposit is hosted by Middle Devonian pelitic sediments in the Rhenohercynian terrane of the Variscan Orogen.
The deposit consists of two main orebodies that have been intensely deformed. Deformation obscures the original depositional
relationships, but the regional setting as well as the geochemistry and mineralogy of the mineralisation display many characteristics
of the SHMS (sediment-hosted massive sulphide) class of ore deposits. Rammelsberg is briefly compared to the other massive
sulphide deposits in the European Variscan, including Meggen and those deposits in the Iberian Pyrite Belt.
Received: 28 September 1998 / Accepted: 5 January 1999 相似文献
8.
《Applied Geochemistry》2000,15(9):1265-1290
Massive sulphide deposits of the northern Iberian Pyrite Belt (IPB) are mainly hosted by felsic volcanic rocks of rhyolitic to dacitic composition. Beneath most of the massive ores of this area (e.g., Concepción, San Miguel, Aguas Teñidas Este or San Telmo deposits) there is usually a wide hydrothermal alteration halo associated with stockwork-type mineralization. Within these alteration envelopes there are two principal rock types: (1) chlorite-rich rocks, linked to the inner and more intensely altered zones and dominantly comprising chlorite+pyrite+quartz+sericite (+carbonate+rutile+zircon+chalcopyrite), and (2) sericite-rich rocks, more common in the peripheral zones and showing a dominant paragenesis of sericite+quartz+pyrite+chlorite (+carbonate+rutile+zircon+sphalerite). Mass-balance calculations comparing altered and least-altered felsic volcanic rocks suggest that sericitization was accompanied by moderate enrichment in Mg, Fe and H2O, with depletion in Si, Na and K, and a slight net mass loss of about 3%. Chloritization shows an overall pattern which is similar to that of the sericitic alteration, but with large gains in Fe, Mg and H2O (and minor enrichment in Si, S and Mn), and a significant loss of Na and K and a minor loss of Ca and Rb. However, chloritization has involved a much larger net mass change (mass gain of about 28%). Only a few elements such as Nb, Y, Zr, Ti, P and LREE appear to have remained inert during hydrothermal alteration, whilst Ti and Al have undergone very minor mobilization. The results point to the severity of the physico-chemical conditions that prevailed during the waxing stage of the ore-forming hydrothermal systems. Further, mineralogical and geochemical studies of the altered footwall rocks in the studied deposits indicate that hydrothermal ore-bearing fluids reacted with host rocks in a multi-stage process which produced a succession of mineralogical and chemical changes as the temperature increased. 相似文献
9.
R.A. Koski 《Journal of Geochemical Exploration》1983,19(1-3)
Massive and stockwork Fe-Cu-Zn (Cyprus type) sulphide deposits in the upper parts of ophiolite complexes represent hydrothermal mineralization at ancient accretionary plate boundaries. These deposits are probable metallogenic analogues of the polymetallic sulphide deposits recently discovered along modern oceanic spreading centres. Genetic models for these deposits suggest that mineralization results from large-scale circulation of sea-water through basaltic basement along the tectonically active axis of spreading, a zone of high heat flow. The high geothermal gradient above 1 to 2 km deep magma chambers emplaced below the ridge axis drives the convective circulation cell. Cold oxidizing sea-water penetrating the crust on the ridge flanks becomes heated and evolves into a highly reduced somewhat acidic hydrothermal solvent during interaction with basaltic wall-rock. Depending on the temperature and water/rock ratio, this fluid is capable of leaching and transporting iron, manganese, and base metals; dissolved sea-water sulphate is reduced to sulphide. At the ridge axis, the buoyant hydrothermal fluid rises through permeable wall-rocks, and fluid flow may be focussed along deep-seated fractures related to extensional tectonic processes. Metal sulphides are precipitated along channelways as the ascending fluid undergoes adiabatic expansion and then further cooling during mixing with ambient sub-sea-floor water. Vigorous fluid flow results in venting of reduced fluid at the sea-floor/sea-water interface and deposition of massive sulphide. A comparison of sulphide mineralization and wall-rock alteration in ancient and modern spreading centre environments supports this genetic concept.Massive sulphide deposits in ophiolites generally occur in clusters of closely spaced (< 1–5 km) deposits. Individual deposits are a composite of syngenetic massive sulphide and underlying epigenetic stockwork-vein mineralization. The massive sulphide occurs as concordant tabular, lenticular, or saucer-shaped bodies in pillow lavas and pillow-lava breccia; massive lava flows, hyalcoclastite, tuff, and bedded radolarian chert are less commonly associated rock types. These massive sulphide zones are as much as 700 m long, 200 m wide, and 50 m thick. The pipe-, funnel-, or keel-shaped stockwork zone may extend to a dehpth of 1 km in the sheeted-dike complex. Several deposits in Cyprus are confined to grabens or the hanging wall of premineralization normal faults.Polymetallic massive sulphide deposits and active hydrothermal vents at medium- to fast-rate spreading centres (the East Pacific Rise at lat. 21°N, the Galapagos Spreading Centre at long. 86°W, the Juan de Fuca Ridge at lat. 45°N., and the Southern Trough of Guaymas Basin, Gulf of California) have interdeposit spacings on a scale of tens or hundreds of metres, and are spatially associated with structural ridges or grabens within the narrow (< 5 km) axial valleys of the rift zones. Although the most common substrate for massive sulphide accumulations is stacked sequences of pillow basalt and sheet flows, the sea-floor underlying numerous deposits in Guaymas Basin consists of diatomaceous ooze and terrigenous clastic sediment that is intruded by diabase sills. Mound-like massive sulphide deposits, as much as 30 m wide and 5m high, occur over actively discharging vents on the East Pacific Rise, and many of these deposits serve as the base for narrow chimneys and spires of equal or greater height. Sulphides on the Juan de Fuca Ridge appear to form more widespread blanket deposits in the shallow axial-valley depression. The largest deposit found to date, along the axial ridge of the Galapagos Spreading Centre, has a tabular form and a length of 1000 m, a width of 200 m, and a height of 30 m.The sulphide assemblage in both massive and vein mineralization in Cyprus type deposits is characteristically simple: abundant pyrite or, less commonly, pyrrhotite accompanied by minor marcasite, chalcopyrite, and sphalerite. With few exceptions, the composition of massive sulphide ranges from 0.3 to 5 wt. % Cu, from 0.1 to 3 wt. % Zn, from 0.5 to 30 ppm Au, and from 1 to 50 ppm Ag. The only common gangue minerals — quartz, chlorite, calcite, and gypsum generally make up less than 10 percent of the massive zone.Sulphide assemblages in massive sulphide samples recovered from the Juan de Fuca Ridge (abundant sphalerite, wurtzite, and pyrite; minor marcasite, chalcopyrite, and galena), East Pacific Rise (abundant sphalerite, pyrite, and chalcopyrite; minor wurtzite, marcasite, and pyrrhotite), and Guaymas Basin (abundant pyrrhotite and sphalerite; minor chalcopyrite) contrast with ophiolitic deposits. Bulk analyses of two zinc-rich sulphide samples from the Juan de Fuca Ridge yield the following average values: Zn, 56.6 wt. %; Cu, 0.2 wt. %; Pb, 0.15 wt. %; Fe, 4.9 wt. %; Ag, 260 ppm; and Cd, 775 ppm. Other minerals precipitated with sulphides at hydrothermal-vent sites include anhydrite, barite, gypsum, Mg-hydroxysulphate-hydrate, talc, sulphur, and amorphous silica.Massive sulphide lenses in some Cyprus-type deposits are underlain by a silica-rich zone consisting of massive quartz, opaline silica, red jasper, or chert mixed with disseminated and veinlet Fe-Cu-Zn sulphides. Some deposits are overlain by ochre, a gossanous Mn-poor Fe-rich bedded deposit composed of goethite, maghemite, quartz, and finely disseminated sulphide. In the Solomon Islands, ochre is overlain by siliceous sinter containing anhydrite, barite, and sulphide; the sinter contains anomalous Ag, Au, Cu, Zn, and Hg, and grades upward into Fe-rich chert and manganiferous wad. Amorphous Fe-Mn deposits (umber) and Mn-bearing chert enriched in Ba, Co, Cu, Ni, Cr, Pb, and Zn are common features near the top of ophiolite sequences. Although their genetic relation to sulphide mineralization is uncertian, they probably formed during off-axis hydrothermal discharge.At modern, medium-rate spreading centres, thin blankets of unconsolidated hydrothermal sediment have been observed near hydrothermal sulphide deposits. Basalt fragments recovered with massive sulphide from the Juan de Fuca Ridge have surfaces coated with smectite, magnetite, hematite, opaline silica, and Fe---Mn-oxyhydroxides. Sediment mounds composed largely of nontronitic clay and hydrated Fe and Mn oxides, and more distal metalliferous (Fe, Mn, Cu, Ni, Pb, Zn) sediment on the flanks of ceanridges, are also products of off-axis hydrothermal processes.Pillow lavas, diabase dikes, and gabbro in ophiolite sequences, and deeper, layer 2 basalt and diabase recovered from oceanic ridges, are altered to greenschist-facies assemblages (albite + chlorite + actinolite ± sphene ± quartz ± pyrite) during high-temperature sub-sea-floor hydro-thermal metamorphism near the axis of spreading. Chemical changes in the wall-rock during this large-scale sea-water/rock interactive episode depend on the water/rock ratio and temperature but generally include gains in Mg, Na and H2O and losses of Ca. Subsequent low temperature sea-water/rock interaction away from the axis of spreading results in fracture-controlled zeolitefacies alteration, characterized by smectite, caledonite, zeolite, calcite, prehnite, hematite, marcasite, and pyrite. This retrograde alteration involves increases in total Fe, K, and H2O and decreases in Mg and Si in the wallrock; Ca may be lost or gained.Wall-rock alteration in Cyprus type stockwork zones is more striking, in that the basalt and diabase between veins of Fe---Cu-Zn sulphides, quartz, and chlorite have undergone partial to complete conversion to fine-grained aggregates of quartz + chlorite + illite + pyrite; kaolinite and palygorskite may be present in minor amounts. Calcium and Na are strongly depleted; K, Al, Ti, Mn, and Ni are leached to a lesser extent; and Fe, S, Cu, Zn, and Co are strongly enriched in the wall-rock underlying massive sulphide. Mafic rocks at depth in the volcanic pile may be enriched in K, Rb, and Li, and depleted in Cu, Co, and Zn. Lavas lateral to and overlying massive sulphide mineralization may have low concentrations of Cu and high concentrations of Zn and Co relative to background levels.Mutual consideration of hydrothermal sulphide deposits and associated wall-rock alteration in ophiolites and at modern oceanic spreading centres can provide useful criteria for the development of regional exploration models for ophiolitic terrains. 相似文献
10.
The Ordovician Zn–Pb–Cu massive sulphide ore deposits of the Bathurst mining camp share many features with those of the Devonian/Carboniferous Iberian pyrite belt, particularly the tendency to large size (tonnage and metal content); shape, as far as can be determined after allowing for deformation; metal content, particularly Fe/Cu, Pb/Zn and Sn; mineral assemblages (pyrite + arsenopyrite ± pyrrhotite and lack or rarity of sulphates); sulphide textures (particularly framboidal pyrite); lack of chimney structures and rubble mounds; irregular metal or mineral zoning; and the low degree of zone refining compared to Hokuroku ores. The major differences between the provinces are the lack of vent complexes and the presence of Sn–Cu ores in the Iberian pyrite belt. There are also similarities in the geological setting of the two camps: both lie within continental terranes undergoing arc-continent and continent–continent collision, and in each case massive sulphide mineralisation followed ophiolite obduction; the ore deposits are associated with bimodal volcanic rocks derived from MORB and continental crust and marine shales; and mineralisation was locally accompanied or followed by deposition of iron formations.Fluid inclusion data from veins in stockworks from at least six of the Iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline, ore-forming fluids (brine pools), and it is suggested that most of the major features of the Bathurst deposits can be explained by similar processes. The proposed model is largely independent of ocean sulphate and O2 content, whereas low values of each are requisites for the current, spreading-plume model of sulphide deposition in the Bathurst camp. 相似文献
11.
E. Marcoux 《Mineralium Deposita》1997,33(1-2):45-58
Lead isotope analyses were performed on 26 polymetallic massive sulphide deposits of the Iberian Pyrite Belt, as well as on overlying gossans and associated volcanic rocks. All the massive sulphide deposits (except for Neves-Corvo), and nearly all the volcanic rocks show very similar isotopic compositions grouped around 18.183 (206Pb/204Pb), 15.622 (207Pb/204Pb) and 38.191 (208Pb/204Pb), indicating that most of the ore deposit lead was derived from the same continental crust environment as the associated volcanic rocks. The isotopic compositions are representative of the average south Iberian crust during the Devonian to Early Carboniferous (Dinantian), and their constancy implies a homogenization of the mineralizing fluids before the deposition of the massive sulphides from hydrothermal fluids circulating through interconnected regional fracture systems. This isotopic constancy is incompatible with multiple, small, independent hydrothermal cells of the East Pacific Rise type, and fits much better with a model of hydrothermal convections driven by “magmatic floor heating”. Neves-Corvo is the only south Iberian massive sulphide deposit to have a heterogeneous isotopic composition with, in particular, a highly radiogenic stanniferous ore (206Pb/204Pb of the cassiterite is >18.40). A model of lead mixing with three components is proposed to explain these variations: (1) one derived from the Devonian to Early Carboniferous (Dinantian) continental crust that generated all the other massive ores; (2) an Eohercynian stanniferous mineralization partly remobilized during the formation of the massive sulphides, but independent of them; and (3) a Precambrian continental crust component. The juxtaposition of three different sources places Neves-Corvo in a specific paleogeographic situation that could also explain its mineralogical specificity. The geodynamic context that best explains all the obtained isotopic results is one of an accretionary prism. The fact that lead isotope signatures of the gossans are almost identical to those of the underlying massive sulphides means that this technique could be a useful exploration tool for the Iberian Pyrite Belt. 相似文献
12.
John C. Volesky Robert J. Stern Jan M. Peter Daniel Layton-Matthews Sarah Rice 《International Geology Review》2017,59(16):1975-2002
The Wadi Bidah Mineral District of Saudi Arabia contains more than 16 small outcropping stratabound volcanogenic Cu–Zn–(Pb) ± Au-bearing massive sulphide deposits and associated zones of hydrothermal alteration. Here, we use major and trace element analyses of massive sulphides, gossans, and hydrothermally altered and least altered metamorphosed host rock (schist) from two of the deposits (Shaib al Tair and Rabathan) to interpret the geochemical and petrological evolution of the host rocks and gossanization of the mineralization. Tectonic interpretations utilize high-field-strength elements, including the rare earth elements (REE), because they are relatively immobile during hydrothermal alteration, low-grade metamorphism, and supergene weathering and therefore are useful in constraining the source, composition, and physicochemical parameters of the primary igneous rocks, the mineralizing hydrothermal fluid and subsequent supergene weathering processes. Positive Eu anomalies in some of the massive sulphide samples are consistent with a high temperature (>250°C) hydrothermal origin, consistent with the Cu contents (up to 2 wt.%) of the massive sulphides. The REE profiles of the gossans are topologically similar to nearby hydrothermally altered felsic schists (light REE (LREE)-enriched to concave-up REE profiles, with or without positive Eu anomalies) suggesting that the REE experienced little fractionation during metamorphism or supergene weathering. Hydrothermally altered rocks (now schists) close to the massive sulphide deposits have high base metals and Ba contents and have concave-up REE patterns, in contrast to the least altered host rocks, consistent with greater mobility of the middle REE compared to the light and heavy REE during hydrothermal alteration. The gossans are interpreted to represent relict massive sulphides that have undergone supergene weathering; ‘chert’ beds within these massive sulphide deposits may be leached wall-rock gossans that experienced silicification and Pb–Ba–Fe enrichment from acidic groundwaters generated during gossan formation. 相似文献
13.
双峰式火山岩与块状硫化物矿床 总被引：13，自引：0，他引：13
双峰式火山岩不仅是火山成因块状硫化物矿床中最常见的含矿岩石组合，而且也是研究其古成矿地质背景和成矿作用的主要依据之一。笔者收集了我国以及世界一些著名火山成因块状硫化物矿床和矿带的含矿建造资料，其中包括含矿建筑的岩石组合、形成时代和层序、火山岩的岩石组合和岩石化学、产出的大地构造环境等等。整理结果表明，双峰式火山岩是火山成因块状硫化物矿床的最佳含矿岩石组合；它们主要产五各个时期的造山火山岩类，产生了有利成矿组分浓集的巨大热液循环系统及适宜原（海水深度和封闭条件良好的）含矿流体集积的沉陷盆地（裂谷），从而为成群成带的VHMS型矿床的形成提供了有利的地质环境。 相似文献
14.
We present the first platinum group elements (PGE) data on seven massive sulfide deposits in the Iberian Pyrite Belt (IPB), one of the world largest massive sulfide provinces. Some of these deposits can contain significant PGE values. The highest PGE values were identified in the Cu-rich stockwork ores of the Aguas Teñidas Este (Σ PGE 350 ppb) and the Neves Corvo (Σ PGE 203 ppb) deposits. Chondrite normalized PGE patterns and Pd/Pt and Pd/Ir ratios in the IPB massive, and stockwork ores are consistent with the leaching of the PGE from the underlying rock sequence. 相似文献
15.
Since lenses of chert are common within the volcano-sedimentary succession hosting the massive sulphide deposits of the Iberian Pyrite Belt (Spain and Portugal), we examined numerous chert occurrences, both petrographically and geochemically, to test their possible value for massive sulphide exploration. The chert is found at two main lithostratigraphic levels (upper and lower) that are also interpreted as massive-sulphide bearing. In both cases the chert is located at the top of acidic volcanic sequences or in the associated sediments; we have not been able to observe the relationships between massive sulphides and chert, but some of the large orebodies of the Province (Lousal, La Zarza, Tharsis, Planes-San Antonio body of Rio Tinto, Neves) are described as being locally capped by chert facies. Four main types are recognized among the chert and associated facies: (1) red hematitic chert?±?magnetite; (2) radiolarian and/or sedimentary-textured (conglomeratic) chert with hematite and/or Mn oxides; (3) pale sulphidic chert; (4) rhodonite and/or Mn carbonate?±?magnetite facies. In the Spanish part of the Province the radiolarian chert is confined to the upper level; the distribution of the other types appears to be haphazard. The hydrothermal origin of the South Iberian chert is shown by its high Fe-Mn and low Co-Ni-Cu contents. The presence of small positive Ce anomalies indicates a shallow marine environment (shelf or epicontinental sea), which is consistent with the volcanological and sedimentological data. The chert was emplaced below the sea floor through chemical precipitation and/or through alteration and replacement of the country rock, residual traces of which are ghost phenocrysts and high Al, Ti and rare earth contents. Macro- and microscopic relationships indicate that the oxide facies (hematite?±?magnetite) formed first, probably providing a protective insulating cover against the marine environment and enabling an evolution towards sulphide facies; a phase of Mn?carbonate and silicate + quartz?±?chlorite + sulphides appears to be even later. It was not possible, through discrimination, to isolate a chert that could be considered as representing a lateral marker of massive sulphides; moreover, both field observations and geochemical data seem to indicate a relative independence of this siliceous sulphide hydrothermal activity from the hydrothermal activity giving rise to the massive sulphides. Such is also indicated by the lead isotopic signature of the chert, which is appreciably more radiogenic than that of the massive sulphides; the lead enrichment in the sulphidic chert facies indicates the participation of a different source (sediments, sea water) from that of the massive sulphides. The hypothesis of an independent hydrothermal “chert” event can thus be envisaged, wherein the chert reflects submarine low-temperature hydrothermal activity that is most apparent during a “break” within the volcano-sedimentary succession and which may locally have competed with the high-temperature hydrothermal activity giving rise to the massive sulphides. The interest of the chert thus rests in its palaeodynamic significance, as a marker of periods of volcanic quiescence, and in its possible role as a protective insulating cap favourable to the deposition of massive sulphides. 相似文献
16.
A new interpretation of the structural evolution of the Iberian Pyrite Belt (IPB) and volcanogenic massive sulfide mineralization (VMS) is presented in this work, based on a review of the ore deposit types, the analysis of the hosting volcanic sequences and the tectonic evolution. The VMS deposits of the IPB are hosted by volcanic and siliciclastic rocks. Four main volcano-sedimentary sequences (VSC), from VSC0 to VSC3, have been assumed, the main deposits being located in the VSC0 and at the top of the VSC2.We have defined three main sectors oriented approximately E-W and hosting the VMS deposits. In the Northern sector, which is mostly located in Spain, graben basins and local pull-aparts are the main structures. In this sector, two belts can be distinguished, the deposits being located at the top of the VSC2 felsic volcanism (Rio Tinto-type IPB deposits). In the Central sector, both in Spain and Portugal, half-graben basins are the most common structures, and the deposits are mostly located in the VSC0 andesitic volcanic-sedimentary sequence (Tharsis-type IPB deposits). In the Southern sector, which is only located in Portugal, a graben basin with a pull-apart is again the main structure, and the deposits are located in black slates and at the top of a felsic volcanism, Strunian in age (VSC0). The deposits located in graben basin with a pull-apart are essentially felsic volcanic-hosted with some siliciclastic material, mostly black shales. By contrast, those located in half-graben basins are mainly hosted by black-shales with minor amounts of andesitic rocks.The tectonic evolution shows that as a result of a counterclockwise rotation of the stress axes, the formation of the IPB and the associated ore deposits took place during several episodes, from transtension (with the development of both graben with pull-aparts and half-graben basins), through left lateral E-W shearing, to transpression. At the beginning of the transtensional process, several extensional, roughly E-W trending faults that developed graben and half-graben basins were generated and the first volcanic andesite-rhyolite rocks (VSC0) formed. The Tharsis-type deposits, mainly hosted by black slates with some volcanic rocks, were formed in the Central sector while the Neves Corvo-type deposit, hosted by black slates and felsic volcanism formed in the Southern one. After a period characterized by barren mafic volcanism (VSC1), a sinistral shear affected the previous fractures due to the stress axis rotation and felsic crustal volcanism started (VSC2). Rhyolites and dacites were particularly abundant in two graben basins, which developed rollovers in pull-apart zones, forming the Rio Tinto-type deposits in the Northern sector. The thermal increase associated with VSC0 and VSC2 gave rise to the development of crustal-scale hydrothermal convective cells, which generated both types of deposits.After a barren VSC3 felsic volcanism, subsequently, during the Variscan transpressional phase, the E-W extensional faults were reactivated as reverse faults, affecting the volcanic sequence (VSC0 to VSC3) as well as the interbedded sedimentary rocks (mostly black shales). As has been recognized at the Rio Tinto deposit, buttressing must have played a significant role in the geometry of inverted structures, and the VMS ores were intensely recrystallized.It should be emphasized that this new regional geological model for the IPB is an approach to provide a better insight into VMS deposits and could be a key-point for further studies, providing a new tool to improve knowledge of the VMS mineralizations and exploration guidelines elsewhere in the IPB. 相似文献
17.
The Spanish-Portuguese Pyrite Belt covers a large area in the SW part of the Iberian Peninsula from Seville to the westcoast of Portugal. Total reserves of aprox. 1.000 million tons of massive sulphide ores have an average content of 46% S, 42% Fe, and 2–4% Cu+Pb+Zn. The stratiform sulphide deposits and accompanying manganese mineralizations are of synsedimentary-exhalative origin. They occur in a Lower Carboniferous, geosynclinal, volcanic-sedimentary rock sequence, strongly folded during the Hercynian Orogeny. A brief outline of the regional geology of this ore province is given, and the geology of three mining districts is described: Lousal (Portugal), La Zarza and Tharsis (Huelva Province, Spain). A close relationship between sulphide and manganese ores with the submarine, acid alkaline volcanism is emphasized. Solfataric activity is responsible for the formation of sulphides in the final stages of volcanic extrusions. The ore concentration in big deposits (ore-lenses with up to 100 million tons of massive sulphides) has been due to inflows of sulphide muds and/or detrital sulphides into newly formed depressions of a contineously changing seafloor topography due to volcano tectonic movements. 相似文献
18.
V. Oliveira J. Matos M. Bengala N. Silva P. Sousa L. Torres 《Mineralium Deposita》1997,33(1-2):170-187
Gravimetry was the main exploration method used in this high risk area to the north of the Grândola fault, in the Iberian Pyrite Belt (IPB). It showed several targets, among which the Valverde-Lagoa Salgada area stood out. Here, in August 1992, a polymetallic massive sulphide orebody was found, named Lagoa Salgada. According to the geological characteristics of the area and to the nature of the surveyed targets, other exploration techniques were used, namely: geology, magnetometry, resistivity, electrical sounding, magneto-telluric, seismic and mechanical drilling. The deposit was found under a Tertiary cover, 128?m in depth, complete with a 15?m thick gossan, caused by paleoalteration, with a supergene enrichment zone. This gossan gave way to massive sulphides, with intersections, at times, exceeding 60?m. They are limited towards the footwall by an important fault with strong associated kaolinization, which is interpreted as a reverse fault, placed on the inverse limb of an anticlinal structure. Throughout the deposit, the chemical composition of the mineralization showed great variation reaching significant values of Zn, Pb, Sn, Cu, As, Hg, Sb, Cd, Au and Ag. In the initial phase the deposit has an estimated tonnage of 5?Mt. It is related to a large gravity anomaly with the general orientation NW-SE, which was investigated by 15 boreholes made by the Instituto Geológico e Mineiro. The drilling cut an important volcanic centre of an acid to intermediate nature, around which intense hydrothermal activity was associated with contemporaneous sulphide mineralization. The gravity anomaly has two nuclei, a NW and a central one, about 450?m apart, where a pyrite orebody with polymetallic sulphides and stockwork sulphide mineralization are developed. This discovery led to an extensive exploration project that confirmed the mining potentialities of the NW sector of the IPB, to the north of Grândola fault, where previously no polymetallic sulphide occurrences were known. 相似文献
19.
《Geodinamica Acta》2013,26(3):117-137
In the Ligurian Alps (South-Western Italian Alps), Zn-Pb deposits occur within late Palaeozoic meta-sedimentary units belonging to the Briançonnais Zone near Casario (Tanaro valley). Different types of sulphide-rich, lens-shaped mineralizations are recognized: sphalerite-galena massive sulphide bodies, pyrite-rich lenses and sulphide-rich quartz–carbonate-chloritoid granofels. Sulphide lenses and host rocks are affected by at least three ductile deformation phases and by a polyphase alpine metamorphism, whose climax conditions are estimated, based on P-T pseudosection calculations, at T = 300-325 °C and P = 0.55-0.60 GPa. In all the mineralized lenses the ore minerals are represented, in variable amount, by Fe-poor sphalerite, galena, pyrite and arsenopyrite (± tetrahedrite, chalcopyrite and pyrrhotite); the gangue consists of quartz, carbonate (sideritemagnesite ± rhodochrosite s.s.), Fe-chloritoid, muscovite-phengite and chlorite. The mineralizations are associated with chloritoid – carbonate micaschists displaying a finely bedded texture, with sharp between-bed compositional contrast, which suggests their exhalative origin. In spite of the tectono-metamorphic overprint, some pre-metamorphic features of the hydrothermal system are still recognized, like relics of the hydrothermal feeding system, primary growth textures and sulphide-rich microbreccias. These massive sulphide lenses, which share many characters with the SEDEX deposits, testify to the occurrence of an exhalative event of Upper Carboniferous age previously unrecognized in the Ligurian Briançonnais Unit. 相似文献
20.
Vein-related data have been collected around the giant Rio Tinto orebody in southern Spain within the root zones of the massive sulphide deposits. Here, we report the main results of this study, concerning the geometry of the stockwork and the conditions of formation. Although field and thin-section studies have shown that a wide range of vein configurations exist, from micro cracks (fluid-inclusion planes) to large paleo-flow channels, two groups seem to dominate. The first corresponds to small, constricted micro cracks and capillary-flow channels, now mainly filled with quartz, whereas the veins of the second group have large widths, are continuous over several meters and are filled with quartz and sulphides. Most are tension veins and only very few (<0.1%) show evidence of shearing. The pyrite-dominated variety (i.e., pyrite?>?quartz) tends to post-date the quartz-dominated veins (quartz?>?pyrite). The vein-thickness and -spacing distribution is modal rather than logarithmic, and their densities are not fractal, but are characterized by a Poisson distribution. From the immediate sub-surface zone to more than 100?m below the base of the massive sulphide deposits, most hydrothermal quartz-sulphide stockwork veins are sub-parallel to the base of the massive sulphide deposit. The assumption that the base of this deposit corresponds to a paleo-horizontal plane, implies that most veins were sub-horizontal. This is particularly evident for small veins, but the larger ones can be strongly oblique to the base of the deposit. The hydrothermal fluids that generated the massive sulphide deposits and underlying stockworks, were very saline and probably underwent sub- or super-critical phase separation in the root zones of the system. This phase separation was the probable mechanism producing the periodic over-pressures of at least 20 MPa that were necessary to generate the sub-horizontal veins of the stockworks. 相似文献