首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
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   

2.
The Um Samiuki Zn–Cu–Pb–Ag mineralisation, south Eastern Desert, Egypt is hosted by felsic volcanic rocks which form part of the 712-Ma-old, east-west-trending Shadli Volcanic Belt. Two major occurrences of massive sulphides are present at the top of rhyolitic breccia in the Western and Eastern mine areas. In each occurrence, a bornite-bearing zone is overlain by a pyrite-chalcopyrite-bearing zone and underlain by a disseminated, Cu-depleted zone. In the massive sulphide ore, sphalerite, chalcopyrite, pyrite, galena, bornite and tetrahedrite–tennantite are major minerals, whereas arsenopyrite, pyrrhotite, molybdenite and magnetite are accessory phases. Covellite and digenite are common secondary minerals. Bornite, tetrahedrite–tennantite and covellite contain high amounts of silver (averages of 1.97, 1.39 and 1.82 wt% respectively). Based on mineralogical balance calculations, bornite and covellite accommodate 80% of silver in the Um Samiuki deposit. Ag was incorporated in the crystal structure of the early-crystallised copper sulphides and sulphosalts and silver minerals. The temperature, sequential precipitation of the fluids and the structure of the crystallising phases control the distribution of silver. Post-depositional deformation and metamorphic processes caused liberation, remobilisation and redeposition of silver within the massive sulphides.Editorial handling: D. Lentz  相似文献   

3.
Detailed mineralogical and geochemical studies of the volcanogenic sulphide mineralization in the Spanish part of the Iberian Pyrite Belt (IPB) define two geochemical, mineralogical and spatial gold associations: (1) the Tharsis-Sotiel-Migollas type in which the gold is enriched with (Co?±?Bi) in the stockworks and interaction zones at the base of the massive sulphide mound; and (2) the Rio Tinto-Aznalcóllar-La Zarza type in which the gold is enriched in facies with a polymetallic (Zn?+?Ag?±?As?±?Tl?±?Hg) signature in a distal position or blocked beneath the massive sulphides. The first type is localized within a domain covering the southern half of the belt which is characterized by an abundance of sedimentary facies. The paragenesis shows that the gold association formed at high temperature (>300?°C) during the initial phases of massive sulphide genesis; the gold, which occurs in patches of very auriferous electrum (Au?>?75?wt.%), was transported by chloride complexes. The second type is found in the northern domain of the belt where volcanic facies are predominant. The paragenesis shows that the gold association formed at lower temperature (<280?°C) late in the massive sulphide genesis. This gold was transported by bisulphide complexes [Au(HS)2 ?] and is contained in Ag- and Hg-rich electrum (up to 61.0 and 30.5?wt.% respectively) and/or auriferous arsenopyrite (mean of 280?ppm Au), two mineral expressions that are able to coexist. It would appear that sulphur activity and oxygen fugacity were important factors in controlling the distribution of gold between the two host minerals and also in determining the Ag content of the electrum. This antithetic behaviour of the gold in the IPB reflects differences in the gold mineralizing fluids that may be due to the geologic environment; i.e. either dominantly sedimentary and acting as a mechanical barrier for gold bearing fluids, or dominantly volcanic and more open to seawater circulation. The fact that possible complications can occur during massive sulphide genesis, in response to the source and evolution of the fluids, raises the question of whether one or two gold influxes are involved. For example, the two gold associations could derive from a single gold influx, with remobilization and redistribution of the gold from the early (Co?±?Bi) facies giving rise to the later gold paragenesis of the (Zn?+?Ag?±?As?±?Tl?±?Hg) facies; this would not have occurred or would have been limited at the Tharsis-Sotiel-Migollas type orebodies. Alternatively, the two gold associations could reflect two separate evolutionary processes distinguished by the gold appearing either early or late in the hydrothermal fluids. Knowing the gold association of a massive sulphide deposit is an advantage when exploring for potential host facies.  相似文献   

4.
The Elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the Srena Gora metallogenic zone in Bulgaria. The gold-bearing massive sulphide mineralization is considered to be the product of an island arc volcano-plutonic process and hydrothermal activity that took place during the Late Cretaceous. In addition to the major gold-hosted opaque minerals such as pyrite, chalcopyrite, sphalerite and galena there are minor phases of tennantite, goldfieldite, Se-bearing aikinite, native silver and bornite in the massive sulphide lenses and stringer zones. Most of the sulphide minerals are Se-bearing. All of the six mineral assemblages that were deposited during the pyrite and copper-pyrite stages of mineralization are gold-bearing. The gold tenor as a rule is less than 1 g/t. Native gold and electrum occur as blebs or intergranular particles in the sulphide minerals. Gold in the early massive pyrite is of submicroscopic type (< 0,1 μm) and of colloidal ori-gin. Pyrite deformation and recrystallization in the temperature range 250°–160 °C has led to Au and Ag migration to cracks and grain boundaries of the sulphide minerals. As a result of these process the native gold and electrum grain size increases from submicroscopic (< 0,1 μm) in the early colloform pyrite to microscopic (0,1–100 μm) and macroscopic (> 100 μm) in the late gold-sulphide assemblages. The electrum fineness in 41 individually studied grains varies between 780 and 992‰ with a mean of 895‰. Native silver was found in association with bornite. Cu, Te, Sb and Bi are the most common trace-elements in gold and electrum. The Cu-Zn-Pb association is most important as a Au-Ag-carrier. A model for gold behaviour during sulphide deformation is proposed involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages. Received: 4 December 1995 / Accepted: 23 September 1996  相似文献   

5.
The Iberian type of volcano-sedimentary massive sulphide deposits   总被引：6，自引：0，他引：6  
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   

6.
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   

7.
Riebeckite-arfvedsonite amphiboles occur in very low-grade metamorphosed doleritic sills at various localities within the Iberian Pyrite Belt. The alkali-amphiboles grew during sub-solidus hydrothermal spilitization of basalt associated with submarine massive sulphide ore formation. The riebeckite-arfvedsonite is only very rarely preserved, being converted to albite-chlorite during regional metamorphism. In the South Portuguese zone Hercynian regional metamorphic grade increases in a northward direction from zeolite facies south of the Pyrite Belt through prehnite-pumpellyite facies to the greenschist facies in its northernmost zone. Compositional and mineralogical data indicate a geothermal gradient in the order of 40–50 °C/km.Volcanism in the Pyrite Belt is essentially representative of a bimodal association of twoleiitic to alkalic basalt and dacite/rhyolite. Geochemical data for the Pyrite Belt mafic meta-volcanics contrast with available data for subduction related volcanic suites in orogenic belts but exhibit similarities with the basaltic members of basalt-rhyolite associations found in areas of extensional tectonics. It is proposed that the Iberian Pyrite Belt volcanism represents magmatic activity in an intra-continental basin undergoing rifting during the late Devonian and lower Carboniferous times. On leave from: Mineralogia e Geologia, Faculdade de Ciencias, Lisboa-2, Portugal  相似文献   

8.
Heavy mineral separates of peat from a mineralotrophic bog contain sulphide minerals with distinctive textures. Pyrite framboids, consisting of spherical aggregates of subhedral pyrite crystals, are surrounded by a thin rim of chalcopyrite or a layer of massive marcasite. Clusters of framboids are cemented by covellite which also occurs as small idiomorphic grains, with rectangular or hexagonal outlines, surrounded by chalcopyrite. The sulphides appear to have resulted from discharge of groundwaters, enriched in copper from weathering of primary sulphides in bedrock and in iron by reduction of the till underlying the peat, into the hydrogen sulphide charged bog.  相似文献   

9.
Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn–Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe7S8, and its absolute magnetic susceptibility is 2.10− 3 SI/g. Ar–Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile–brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (206Pb/204Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (206Pb/204Pb  18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO2 conditions and neither a high temperature nor a low aH2S (below 10− 3) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds.Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.  相似文献   

10.
Short-wave infrared reflectance (SWIR) spectra obtained from a Portable Infrared Mineral Analyser (PIMA) were applied to map acidic mine soils at San Miguel massive sulphide deposit, Iberian Pyrite Belt, Spain. Field spectral measurements and laboratory analysis were performed on samples from 58 stations from two very polluted grounds. These analyses identified secondary and tertiary Fe-rich sulphate–hydrate minerals associated with the alteration of sulphide-bearing mine wastes and other associated infrared active minerals. The spectral absorption features for the pure salt types found in these areas allowed the preparation of a specific reference library for automatic mineral identification.Using this approach three separate zones around the sources of contamination have been discriminated: a “proximal” zone dominated by rozenite + hexahydrite, a “transitional” zone dominated by copiapite + coquimbite and a “distal” zone of hydronium–jarosite. An additional zone of “gypsum” was also recognized locally at the areas, where, last decade the neutralization of the acid soils with limestones was attempted.In addition to discriminating distinct mineralogical zones quantitative spectral data allowed contoured mineral maps to be produced that are comparable with the estimated mineralogical data obtained from conventional methods, such as XRD and field observations. These maps demonstrate that sulphate minerals were firstly formed by oxidation of the pyrite-rich ores followed by dissolution and precipitation involving a combination of oxidation, dehydration, and neutralization reactions.The study shows the potential of SWIR spectral analysis to identify and understand the distribution of efflorescent salts and other products of pyrite decomposition and provides a methodology to assist the research and monitoring of sources of environmental contamination.  相似文献   

11.
The Platreef unit of the northern Bushveld Complex comprises a diverse package of pyroxenites, peridotites and mafic lithologies with associated Ni–Cu–platinum-group element (PGE) mineralisation. Base metal sulphides (BMS) are generally more abundant in the Platreef than in other Bushveld PGE deposits, such as the Merensky Reef and the UG2 chromitite, but the Platreef, though thicker, has lower overall PGE grades. Despite a commonly held belief that PGEs are closely associated with sulphide mineralisation, a detailed study by laser ablation ICP-MS (LA-ICP-MS) on a core through the Platreef at Turfspruit suggests that this is not strictly the case. While a significant proportion of the Pd, Os and Ir were found to be hosted by BMS, Pt, irrespective of its whole-rock concentration, was not. Only at the top of the Platreef is Pt directly associated with sulphide minerals where Pt–Pd–(±Sb)–Te–Bi-bearing inclusions were detected in the chalcopyrite portions of large composite sulphides. In contrast, Pd, Os, and Ir occur in solid solution and as discrete inclusions within the BMS throughout the core. For Os and Ir, this is usually in the form of Os–Ir alloys, whereas Pd forms a range of Pd–Te–Bi–(Sb) phases. Scanning electron microscope observations on samples from the top of the core revealed the presence of ≤0.2-mm-long (PtPd)2(Sb,Te,Bi)2 michenerite–maslovite laths within the chalcopyrite portions of large composite sulphides. Additional Pt-bearing minerals, including sperrylite and geversite, and a number of Pd(–Te–Bi–Sb) minerals were observed in, or close to, the alteration rims of these sulphides. This textural association was observed throughout the core. Similar platinum-group minerals (PGMs) were observed within the felsic assemblages composed of quartz, plagioclase, alkali feldspar and clinopyroxene produced by late-stage felsic melts that permeated the Platreef. Many of these PGMs occur a significant distance away from any sulphide minerals. We believe these features can all be linked to the introduction of As, Sb, Te and Bi into the magmatic system through assimilation of sedimentary footwall rocks and xenoliths. Where the degree of contamination was high, all of the Pt and some of the Pd formed As- and Sb-bearing PGM that were expelled to the edges of the sulphide droplets. Many of these were redistributed where they came into contact with late-stage felsic melts. Where no felsic melt interactions occurred, the expelled Pt- and Pd-arsenides and antimonides remained along the margins of the sulphides. At the top of the Platreef, where the effects of contamination were relatively low, some of the Pt remained within the sulphide liquids. On cooling, this formed the micro-inclusions and blade-like laths of Pt–Pd–(Sb)–Bi–Te in the chalcopyrite.  相似文献   

12.
The Iberian Pyrite Belt (IPB), SW Iberian Peninsula, Spain and Portugal, one of the most famous and oldest mining districts in the world, includes several major concentrations of massive sulphides, unique on Earth (e.g., Riotinto, Neves Corvo), as well as a large number of smaller deposits of this same type. All these deposits, in spite of their general similarities, show significant differences in geological setting, age, relations to country rocks, hydrothermal alteration, mineralogy and geochemistry. As a consequence of a review of the available data in the IPB, together with new findings on volcanism, hydrothermal alteration and ore mineralogy, we propose a modified genetic scenario, that can account particularly for the diversity of the geological situations in which sulphide deposits occur, as well as for their mineralogical and petrological diversity. It is concluded that there is no direct genetic relationship between felsic volcanic activity and massive sulphide deposition in the IPB, and that most of the massive sulphide bodies, including all of the giant ones, are closely related to hydrothermal vents, being therefore proximal. The available isotopic data yield additional genetic information: (a) Homogeneous lead isotope values indicate a single (or homogenized) metal source; (b) sea and connate water are the fluid reservoirs for hydrothermal input, and (c) bacterial reduction of sulphur is the most probable cause of differences in δ34S between stockwork and massive sulphide mineralizations. Finally, current geodynamic models suggested for the IPB are discussed. It is suggested that an intracontinental, ensialic rift or pull-apart environment is the most probable genetic environment for the IPB mineralizations.  相似文献   

13.
It is of great importance to understand the origin of UG2 chromitite reefs and reasons why some chromitite reefs contain relatively high contents of platinum group elements(PGEs: Os, Ir, Ru, Rh,Pt, Pd) or highly siderophile elements(HSEs: Au, Re, PGE). This paper documents sulphide-silicate assemblages enclosed in chromite grains from the UG2 chromitite. These are formed as a result of crystallisation of sulphide and silicate melts that are trapped during chromite crystallisation. The inclusions display negative crystal shapes ranging from several micrometres to 100 μm in size.Interstitial sulphide assemblages lack pyrrhotite and consist of chalcopyrite, pentlandite and some pyrite. The electron microprobe data of these sulphides show that the pentlandite grains present in some of the sulphide inclusions have a significantly higher iron(Fe) and lower nickel(Ni) content than the pentlandite in the rock matrix. Pyrite and chalcopyrite show no difference. The contrast in composition between inter-cumulus plagioclase(An_(68)) and plagioclase enclosed in chromite(An_(13)), as well as the presence of quartz, is consistent with the existence of a felsic melt at the time of chromite saturation.Detailed studies of HSE distribution in the sulphides and chromite were conducted by LA-ICP-MS(laser ablation-inductively coupled plasma-mass spectrometry), which showed the following.(Ⅰ) Chromite contained no detectable HSE in solid solution.(Ⅱ) HSE distribution in sulphide assemblages interstitial to chromite was variable. In general, Pd, Rh, Ru and Ir occurred dominantly in pentlandite, whereas Os,Pt and Au were detected only in matrix sulphide grains and were clearly associated with Bi and Te.(Ⅲ)In the sulphide inclusions,(a) pyrrhotite did not contain any significant amount of HSE,(b) chalcopyrite contained only some Rh compared to the other sulphides,(c) pentlandite was the main host for Pd,(d)pyrite contained most of the Ru, Os, Ir and Re,(e) Pt and Rh were closely associated with Bi forming a continuous rim between pyrite and pentlandite and(f) no Au was detected. These results show that the use of ArF excimer laser to produce high-resolution trace element maps provides information that cannot be obtained by conventional(spot) LA-ICP-MS analysis or trace element maps that use relatively large beam diameters.  相似文献   

14.
The Filón Norte orebody (Tharsis, Iberian Pyrite Belt) is one of the largest pyrite-rich massive sulphide deposits of the world. The present structure of the mineralization consists of an internally complex low-angle north-dipping thrust system of Variscan age. There are three major tectonic units separated by thick fault zones, each unit with its own lithologic and hydrothermal features. They are internally organized in a hinterland dipping duplex sequence with high-angle horses of competent rocks (igneous and detritic rocks and massive sulphides) bounded by phyllonites. The mineralization is within the Lower Unit and is composed of several stacked sheets of massive sulphides and shales hosting a stockwork zone with no obvious zonation. The Intermediate Unit is made up of pervasively ankeritized shales and basalts (spilites). Here, hydrothermal breccias are abundant. The Upper Unit is the less hydrothermally altered one and consists of silicified dacites and a diabase sill. The tectonic reconstruction suggests that the sequence is inverted and the altered igneous rocks were originally below the orebody. Carbon, oxygen and sulphur isotopes in the massive sulphides and hydrothermal rocks as well as the mineral assemblage and the paragenetic succession suggest that the sulphide precipitation in the sea floor took place at a low temperature (<≈150?°C) without indication, at least in the exposed section, of a high-temperature copper-rich event. Sporadic deep subsea-floor boiling is probably responsible for the formation of hydrothermal breccias and the wide extension of the stockwork. Its Co-Au enrichment is interpreted as being related with the superposition of some critical factors, such as the relationship with black shales, the low temperature of formation and the boiling of hydrothermal fluids. The present configuration and thickness of the orebody is due to the tectonic stacking of a thin and extensive blanket (2–4?km2) of massive sulphides with low aspect ratio. They were formed by poorly focused venting of hot modified seawater equilibrated with underlying rocks into the seafloor. Massive sulphide precipitation took place by hydrothermal fluid quenching, bacteriogenic activity and particle settling in an unusual, restricted, euxinic and shallow basin (brine pool?) with a low detritic input but with important hydrothermal activity related to synsedimentary extensional faulting. Resedimentation of sulphides seems to be of major importance and responsible for the observed well-mixed proximal and distal facies. The tectonic deformation is largely heterogeneous and has been mostly channelled along the phyllonitic (tectonized shales) deformation bands. Thus, sedimentary and diagenetic textures are relatively well-preserved outside the deformation bands. In the massive sulphides, superimposed Variscan recrystallization is not very important and only some early textures are replaced by metamorphic/tectonic ones. The stockwork is much more deformed than the massive sulphides. The deformation has a critical effect on the present morphology of the orebody and the distribution of the ore minerals. This deposit is a typical example of the sheet-like, shale-hosted, anoxic, low temperature and Zn-rich massive sulphides developed in a ensialic extensional basin.  相似文献   

15.
The Heath Steele massive sulphide deposit in northern New Brunswick lies conformably within a sedimentary-volcanic sequence of probable Ordovician age which has been metamorphosed to the greenschist stage. The dominant sulphide mineral is pyrite, and the main economic minerals are sphalerite, galena, and chalcopyrite; the general grade of the ore is 5% Zn, 2% Pb, and 1% Cu.The distribution of Pb and Zn in acid volcanic rocks stratigraphically above the massive sulphides is compared with the distribution in similar rocks stratigraphically below the sulphides. Whereas there are discernable differences in the populations, there is also considerable overlap between them. To enable individual samples to be classified, linear discriminant functions were calculated for the two groups; Pb and Zn were found to be the most useful variables to separate the two populations. The functions were then tested on hanging wall and footwall samples not used in computing the functions. A halo region, extending about 1,200 ft above the sulphides and 4,000 ft along the same stratigraphic horizon as the sulphides was outlined by samples classified as “hanging wall”. Beyond the halo zone there is no significant difference in the distribution of Pb and Zn between the hanging wall and footwall acid volcanic rocks.The results demonstrate that rocks at Heath Steele, which show no evidence of mineralogical alteration attributable to mineralization, have a trace element halo of considerable extent spatially associated with the sulphides. If similar halos can be shown to be a general feature of massive sulphide deposits, the technique described should have wide application for exploration for deeply buried deposits of this type.  相似文献   

16.
This paper reports the occurrence of Tsumoite (a bismuth telluride) in the Heti Cu-Ni-PGM prospect, Gondpipri mafic-ultramafic complex, Central India. The Gondpipri complex consists of several tectonically dismembered gabbronorite-gabbro-anorthositic gabbro — olivine gabbro -websterite disposed in ～10 km long tonalite-trondhjemitegranodiorite (TTG) and charnockite-enderbite suite of rocks. The mineralization occurs in the sulphide zone hosted by gabbro variants. The host rocks have been deformed and metamorphosed to granulite grade and subjected to various degrees of hydrothermal alteration. The mineralization comprises chalcopyrite, pentlandite, pyrrhotite, cubanite, millerite, and pyrite. In addition to these, occur (1) tsumoite (2) PGM in the form of moncheite, merenskyite, Pd-mellonite, and Pt-Pd-Te-Bi-Fe-S alloy. The present study indicates that the mineralization occurs in two stages related to: (i) magmatic and (ii) hydrothermal remobilization and transport of Cu-rich sulphides, tsumoite and PGM, and their re-deposition in hydrosilicate alteration zones. It is possible that the mineralization at Heti formed at different stages of bismuth activity under variable fS2, T, and fTe2 conditions due to change in total concentration of Te and S and /or cooling. Since the role of S is limited, Te and cooling are important factor influencing mineralogy and composition of tsumoite and associated mineralization. Mineralization occurs in two different modes of occurrences. The early mineralisation occur as blebs, specks and dissemination of sulphides, viz. pyrrhotite, chalcopyrite, pentlandite and minor pyrite ± PGM, whereas later mineralisation occur as stringers, minor veins of sulphides viz. pyrite, millerite, cubanite, sijenite, tsumoite and ± PGM. Mineral assemblages and textural relationships at Heti has indicated precipitation of tsumoite and associated PGM along fractures and secondary silicates, which confirms their hydrothermal origin.  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.
A distinct vertical zonation very similar to that described for the Kuroko deposits of Japan, is displayed by both mineralogy and textures of sulphides from the Lahanos and Kzlkaya massive sulphide deposits of northeastern Turkey. A deeper erosional level is exposed at the Kzlkaya deposit, so that only remnants of the massive sulphide ore zone are present. The zonation is from an upper zone of massive Cu and Zn sulphides (black and yellow ore) with fine-grained, colloform, banded, framboidal, and spherulitic textures, downwards through an intermediate zone of low Cu-Zn massive pyrite with transitional textures, to a lower zone of stockwork and impregnated pyrite displaying euhedral, zoned textures. The fine-grained and colloform pyrite of the upper zones is progressively overgrown by, and recrystallized to, the massive and euhedral pyrite of lower zones. The original textures of these deposits are best preserved by pyrite. The previous interpretation of these textures, of sulphide deposition from colloidal solutions ponded by an impermeable pyroclastic horizon, is reexamined in the light of present observations. Although ultra-fine-grained sulphides, framboids, and radially-cracked spherules could have formed by replacement of pre-existing minerals by a colloidal solution, the colloform and banded textures are indicative of growth in open spaces. It thus seems likely that the fine-grained colloform sulphides, including chalcopyrite, sphalerite, and tennantite as well as pyrite, were initially deposited on or near the surface of the sea-floor. Additional evidence for this interpretation is seen in the progressive recrystallization of the sulphide textures to massive, much coarser, pyrite in the lower zones. This recrystallization may in part be due to diagenetic and hydrothermal processes operating after formation of the original layered sulphides. These conclusions are in agreement with those reached for the similar, but larger Madenköy deposit 100 km to the east.  相似文献   

19.
Monitoring of mine waste on sulphide deposits through hyperspectral remote sensing data contributes to predicting surface water quality, quantitatively estimating acid drainage and metal contamination on a yearly basis. The mineralogy of surface crusts loaded with highly soluble salts is a record of available humidity and temperature along the year. A temporal monitoring of salt efflorescence on mine wastes at a mine site in the Iberian Pyrite Belt (Spain) has been mapped in this work using hyperspectral airborne Hymap data. Climate change estimations are made based on oxidation stages derived from well-known sequences of minerals tracing sulphides oxidation intensity, using archive spectral libraries. Therefore, mine-waste weathering products of sulphide mapped from airborne hyperspectral remote sensing data can be used as a short-term record of climate change, providing a useful tool for assessing environmental geoindicators in semi-arid areas.  相似文献   

20.
The Mount Morgan Au-Cu pyritic massive sulphide deposit occurs in a north-trending belt of Middle Paleozoic volcanic rocks located in south-central Queensland. The host rocks for the deposit are a normal sequence of rhyolitic tuff that have a north-northwest regional strike and easterly dips of 20° to 30°. The tuff contains thin units of chert, jasperoid and carbonate.The Mount Morgan deposit was represented by a zone of sulphide mineralization 600 m long, 100–200 m wide and 300 m deep that transects stratigraphy and can be divided into: (1) an oxidized zone, characterized by a hematitic, Au-enriched gossan with minor stratiform sphalerite-argillite; and (2) a primary zone which can be subdivided into an upper zone of greater than 50% sulphide minerals (Main Pipe orebody), and a lower siliceous stockwork zone with approximately 20% sulphide minerals (Sugarloaf orebody). Pyrite is the most abundant sulphide mineral in both the upper and lower primary zones with lesser pyrrhotite and accessory chalcopyrite, sphalerite and gold. A zone of silicification forms an envelope around the orebody and extends stratigraphically downwards in a pipe-like zone for greater than 750 m. The orebody contained 67 Mt of 4.87 g/t Au and 0.70% Cu.The distribution and variation of between 7 and 29 elements and specific conductance were examined in 1252 samples of the host rocks taken from diamond drill core and surface outcrop. The host rocks in the immediate vicinity of the deposit are marked by the development of three distinct but overlapping chemical and mineralogical zones representing an outward progression from the most intensive to a less intensive alteration. A 50-m-thick siliceous inner zone of intensely altered rocks, depleted in all investigated elements except Si, surrounds the orebody. This zone passes outward into a 100-m-thick middle zone of dominantly sericite-pyrite characterized by high concentrations of K, Fe, Cu and Co. The sericite-pyrite zone, in turn, passes into an outer 100-m-thick chlorite zone with high Fe, Mg, Mn and Zn concentrations. High concentrations of H2O+ are associated with the sericite-pyrite zone and the chlorite zone. The alteration pipe underlying the Mount Morgan orebody is characterized by depletions in Na, Ca and K and enrichments in Fe and Mg. A non-economic pyrite body contained within the alteration pipe has spatially restricted enrichment halos of Fe, Mg, Zn, Cu and Co.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号