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1.
The low-grade base metal sulphide Cu–Zn–Pb and Fe mineralization of Qandil Series develop in shear zones that occur in formations of the north-western part of the Zagros Orogen. This sulphide mineralization occurs either as quartz vein type or disseminated type associated with metamorphic rocks (marbles and phyllites). This study aims to characterize these sulphide-rich ores by means of their mineralogical and geochemical features, including also the features of the corresponded host formations and those of marbles (calcitic and dolomitic) and phyllites. Petrographical data indicate the presence of Cu, Zn, Pb and Fe sulphides in hydrothermal quartz (±calcite) veins of different generations. Geochemical data of surface samples indicate enrichment of Cu and Fe in shear zones with low concentrations in Zn and Pb. The REE data indicate that the genesis of these sulphide ores took place in a hydrothermal system and was generally attributed to high temperature (> 250 °C).The mineralization seems to be fault-controlled, which is favoured by the significant tectonic deformation of the area.  相似文献   

2.
Gold bearing metavolcanics of Gadag Gold Field (GGF) are represented by mafic (metabasalt, metabasaltic andesite), intermediate (metaandesite) and felsic (metadacite, metarhyolite) rocks. Mafic metavolcanic rocks are low-K Fe-rich tholeiites and were derived by partial melting of the upper mantle sources with high Fe/Mg ratios and low M values. Intermediate and felsic metavolcanics were formed by remelting of these tholeiites mainly in crustal regimes. Although a complete sequence of metavolcanic rocks from mafic to intermediate to felsic fractions occurs, these products were not the result of differentiation from a single magma, crustal contamination was involved in the formation of intermediate and felsic rocks. A clear gap in the chemical composition as well as index of differentiation among the mafic, intermediate and felsic fractions indicate that these metavolcanics constitute a typical bimodal character. It is suggested that these metavolcanics were emplaced in an active continental margin or a continental island arc setting. The petrogenetic processes of formation of Fe-rich tholeiites that evolved in an active continental margin or a continental island arc setting could have provided a favourable geochemical environment for gold mineralisation under the conditions of deformation and metamorphism.  相似文献   

3.
The c. 1.9 Ga old Stollberg sulphide and Mnrich skarn iron ores and sulphide ores in Bergslagen, south-central Sweden are hosted by hydrothermally altered and metamorphosed felsic volcanic and volcaniclastic rocks. The ores are underlain by comformable alteration zones characterized by albite-gedrite-quartz and biotite-muscovite-plagioclase-K-feldspar-quartz +/– garnet assemblages. The present mineralogies are interpreted as medium-grade metamorphic equivalents to the original alteration mineral assemblages. PT-conditions during prograde regional metamorphism are semiquantatively determined to be 510 to 560 °C at approximately 3 kbar. With increasing modal content of gedrite and biotite in the alteration zones, the Mg/Fe ratios and XMg's in octahedral positions of these minerals also increase. In the gedrite-bearing strata, whole-rock Mg/Fe ratios remain constant, whereas in the biotite-rich unit the wholerock Mg/Fe trend is parallel to that of the biotites.The trends in the metamorphic mineral composition are interpreted to be a product of original changes in fluid composition during the evolution of a sub-seafloor hydrothermal system. During the initial stage of alteration, Fe-Mn-rich fluids altered the rocks, and during a later stage, the fluids became more Mg-rich, possibly due to entrainment of fresh seawater, and the alteration zones became relatively more Mg-rich. Sulphide precipitation was contemperaneous with Mg metasomatism, suggesting base metal precipitation was a function of the mixing of cool seawater with hydrothermal fluid. It is proposed that early hydrothermal alteration was associated with the deposition of areally extensive Fe-oxide formation, and that Mg metasomatism defines a second stage of hydrothermal activity during which sulphide mineralization overprinted the earlier formed Fe-oxide deposit.  相似文献   

4.
The Dalradian and Ordovician–Silurian metamorphic basement rocks of southwest Scotland and Northern Ireland host a number of base‐metal sulphide‐bearing vein deposits associated with kilometre‐scale fracture systems. Fluid inclusion microthermometric analysis reveals two distinct fluid types are present at more than half of these deposits. The first is an H2O–CO2–salt fluid, which was probably derived from devolatilization reactions during Caledonian metamorphism. This stage of mineralization in Dalradian rocks was associated with base‐metal deposition and occurred at temperatures between 220 and 360°C and pressures of between 1.6 and 1.9 kbar. Caledonian mineralization in Ordovician–Silurian metamorphic rocks occurred at temperatures between 300 and 360°C and pressures between 0.6 and 1.9 kbar. A later, probably Carboniferous, stage of mineralization was associated with base‐metal sulphide deposition and involved a low to moderate temperature (Th 70 to 240°C), low to moderate salinity (0 to 20 wt% NaCl eq.), H2O–salt fluid. The presence of both fluids at many of the deposits shows that the fractures hosting the deposits acted as long‐term controls for fluid migration and the location of Caledonian metalliferous fluids as well as Carboniferous metalliferous fluids. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

5.
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   

6.
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   

7.
Zn-bearing minerals that act as indicator minerals for base metal sulphide mineralization from the Proterozoic Betul Belt, central India with special emphasis on their genetic significance have been discussed. Sulphide mineralisation is hosted by the felsic volcanic rocks and has similarities with volcanic-hosted massive sulphide deposits in other parts of the world. Synvolcanic hydrothermal alteration is crudely zoned with an inner high Mg-Ca core and an outer wider envelop of Al-Fe rich mineral assemblage. Most of the prospects have strata bound, moderately to steeply dipping, multiple, sub-parallel sheet like ore bodies composed of disseminated and semi-massive to massive ores. Zn-bearing spinel, staurolite, biotite and ilmenite typically occur within the foot-wall alteration zones in close proximity to the sulphide mineralization. Zincian spinel is ubiquitous irrespective of the nature of alteration zone. Zincian staurolite is nearly absent in Mg-Ca alteration zones but commonly present in Al-Fe alteration zone along with zincian ilmenite. Zn-bearing biotite in intimate association with zincian spinel is generally found in Mg-Ca alteration zone and in the transition to Al-Fe alteration zone. Most of these indicator minerals can be considered as products of desulphidation of sphalerite during metamorphism. Mechanisms other than desulphidation like formation of gahnite by overstepping of the zinc saturation limit of biotite during retrogression to chlorite and formation of zincian staurolite at the expense of gahnite is also recorded. Field presence of these minerals has immense significance in exploration in Betul Belt as they occur in close spatial relationship with the sulphide rich zones and therefore act as direct vectors to ore.  相似文献   

8.
Thin- to medium-bedded, stratiform calc-silicate deposits (banded skarns) are a peculiar, but important, component of the supracrustal successions in the Palaeoproterozoic Bergslagen mining district of central Sweden. They are referred to as ??skarn-banded leptites?? in the literature and are common in areas and at stratigraphic levels that contain iron oxide and base metal sulphide deposits. The stratigraphic hanging wall of the stratabound Ryllshyttan Zn?CPb?CAg + magnetite deposit at Garpenberg, contains approximately 100?C150?m of interbedded aluminous skarn beds and rhyolitic ash-siltstones. The skarn beds are mineralogically variable and dominantly composed of grandite, spessartine, epidote, actinolite, quartz, clinopyroxene, and locally magnetite. Integrated field-mapping, and whole-rock lithogeochemical, microscopic and mineral chemical analyses suggest that the stratiform skarn beds are the products of at least two discrete hydrothermal events and subsequent metamorphism. The first event comprised accumulation in a quiescent subaqueous environment, below wave base, of calcareous and ferruginous sediments rich in Fe, Mn, Ca, and Mg. These chemical sediments were deposited concurrently with rhyolitic ash-silt sedimentation, thus forming a (now metamorphosed) laminated calcareous Fe formation with both a detrital rhyolitic component and rhyolitic siltstone interbeds. Positive Eu-anomalies and negative Ce-anomalies for normalized rare earth element analyses of skarn beds suggest that the iron may have been derived from exhalation of hot and reduced hydrothermal fluids, which upon mixing with more oxidized seawater, precipitated Fe oxides and/or carbonates that settled from suspension to the seafloor. The size of the positive Eu-anomalies of the chemical sediments are modified by the content of rhyolitic volcaniclastic material, which has a negative Eu anomaly, such that positive Eu-anomalies are only observed in skarn beds that possess a minor volcaniclastic component. Subsequently, the calcareous Fe formations were subjected to post-depositional alteration by hydrothermal fluids, locally yielding more manganoan and magnesian assemblages. The Mn-alteration is manifested by lateral gradations from epidote-grandite-clinopyroxene±magnetite rocks into significantly more Mn-rich quartz-spessartine rocks and massive andradite rocks over distances of less than 10?cm within individual skarn beds. Magnesian alteration is manifested by the development of discordant zones of pargasite para-amphibolites and formation of stratiform pargasite rocks texturally similar to the interlaminated grandite-epidote-ferroan diopside rocks. The latter increase in abundance towards the Ryllshyttan deposit and are associated with pre-metamorphic/pre-tectonic K?CMg?CFe±Si alteration (now biotite-phlogopite-garnet-cordierite-pargasite rocks) that is related to base metal mineralization. The zone of Mn- and Mg-altered skarn beds extends beyond the zone of pervasive K?CMg?CFe±Si alteration around Ryllshyttan. This suggests that the skarn bed progenitors, or their sedimentary contacts against rhyolitic ash-siltstones, acted as conduits to outflowing hydrothermal fluids. The chemical and mineralogical imprint, imposed on affected beds by alteration, may serve as indicators of proximity to intense K?CMg?CFe±Si alteration envelopes around other base metal sulphide deposits in Bergslagen. The last recorded event comprised syn-tectonic veining of competent massive andradite skarn beds. The veins contain quartz-albite-epidote-ferroan diopside-actinolite assemblages.  相似文献   

9.
南秦岭古生代热水沉积盆地与热水沉积成矿   总被引：7，自引：1，他引：7       下载免费PDF全文
扬子地块北部被动边缘的南秦岭古生代沉积盆地中,发育一套自早古生代—中生代以来的碳酸盐岩夹细碎屑岩沉积建造,形成规模巨大独具特色的以铅锌金为主的多金属成矿带。伸展构造体制下形成的裂陷或断陷型盆地中,正常水成沉积与热水沉积同盆共存。正常水成沉积中叠加的热水沉积是一个"突发事件或灾变事件",具有特殊的物质组成和产态。通过对区内沉积成矿盆地的识别、分级,二级沉积盆地中边缘部位常发育多个三级构造热水沉积成矿盆地,它受控于沉积盆地中的同生断裂,具有沉积岩相、热水沉积岩组合、显著成矿作用及物化探异常广布的特点。三级构造热水沉积成矿盆地是矿床定位的构造空间,四级热水沉积洼地为矿体(矿层)的容纳空间。区内热水沉积岩主要为重晶石(毒重石)岩、硅质岩、钠长石岩和铁碳酸盐岩类,铅锌重晶石等矿产多产于热水沉积岩中或上盘。热水沉积形成一般由早期的热水喷发交代→主期热水喷流→晚期热水喷气演变。早期的热水喷发交代往往沿矿液喷发通道,形成网脉状、角砾状矿化;主期热水喷流主要形成多金属及热水喷流相,形成块状、条带状、层纹状矿石或热水沉积岩;晚期热水喷气主要形成浸染状矿石和热水喷气岩石。  相似文献   

10.
The Ishpeming Greenstone Belt is an Archean belt in the southern part of the Canadian Shield in the Upper Peninsula of Michigan, U.S.A. Two volcanic cycles are preserved in it. The oldest formation, and basal to the first cycle (the Kitchi Schist), consists of mafic metavolcanics, has a major serpentinized ultramafic body near its base, and grades upward to a coarse felsic volcanic breccia at the top of the cycle. This unit in turn is overlain by a sequence of mafic flows that grades upward to interbedded mafic flows and exhalites of the Mona Schist. This sequence has been intruded by the Dead River Pluton.The Ishpeming Greenstone Belt probably represents the keel of a previously much more extensive Greenstone Belt.Gold mineralization occurs associated with mafic basaltic volcanic rocks and serpentinized ultramafics low in the succession, and with carbonate-rich quartz-chlorite-sericite schists and exhalites higher in the sequence. No mineral deposits are now being exploited here.  相似文献   

11.
Three types of tourmaline occurrence have been identified in the area of Bin Yauri, Nigeria, mesothermal lode-gold mineralization. These are: (1) stratabound tourmalinites in pelitic metasediments, (2) tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks, (3) tourmaline in auriferous quartz and quartz-carbonate veins. Although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion, geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source. Two stages of tourmalinization are envisaged. The earlier (ca. 1100 Ma) involved syngenetic-diagenetic formation of tourmalinites, while the later (ca. 500 Ma) involved epigenetic (hydrothermal) tourmaline-gold mineralization, possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline-rich rocks or tourmalinites. Electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl-dravite solid solution series. Plots involving FeO, MgO, and/or Al2O3 from these analyses are used to constrain the sources and processes of tourmalinization. Two metallogenic implications are derived from this study. One is that, although the tourmalinites are barren of gold and base metal mineralization, their occurrences nevertheless encourages exploration for syngenetic-exhalative massive sulphide deposits in the region. The other implication applies to the potential use of tourmaline in deciphering the physico-chemical conditions of gold-mineralizing fluids in the Bin Yauri area.  相似文献   

12.
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.
The volcanic-hosted massive sulphide (VHMS) deposits in the Eastern Desert of Egypt (e.g., Um Saki deposit) are associated with Precambrian coarse acid pyroclastic rocks. The upper contacts of the massive sulphide body are sharp and well-defined; while the keel zone to the mineralization is always associated with pervasive alteration, characterized by the presence of septechlorite and talc, associated with variable amounts of carbonate and tremolite. On the other hand, the economic talc deposits in Egypt are hosted intensively altered volcanic rocks. Besides talc, chlorite, carbonates and tremolite that occur in variable amounts in these deposits, anomalously high concentrations of gold are also present.The present study showed that alterations in the talc deposits of Darhib, El Atshan, Abu Gurdi, Egat, Um Selimat and Nikhira are similar to those occurring in the keel zone underlying the VHMS of Um Samuki and that the chemical modifications due to alteration processes (additions of Mg, Fe, Mn and Ca coupled with depletions in silica, alkalies, alumina and titanium) are comparable, even the host rocks are different, thus reflecting a genetic relationship. It is suggested that, the examined localities of talc deposits are hosted in the intensively altered volcanics in the keel zones of volcanogenic massive sulphide deposits. Recently, detailed geophysical prospecting program, including electric (resistivity, self-potential and induced polarization), electromagnetic and magnetic methods, was carried out at Darhib, Abu Gurdi and Um Selimat talc deposits. The quantitative interpretation of these geophysical measurements revealed the presence of subsurface bodies of sulphides. The present distribution of talc and allied minerals in Darhib, El Atshan, Abu Gurdi, Egat, Um Selimat and Nikhira could be explained by a tectonic process in which the coarse acid pyroclastic rocks with massive sulphides have tilted in such way that the footwall rock alterations (talc and allied minerals) are exposed on the present-day surface at these localities. Structural studies are currently under way in an attempt to explain the deformation regime that led to the present situation of talc deposits.Two distinct spatial and mineralogical associations of gold mineralization could be identified in the volcanogenic massive sulphide deposits and their footwall alterations (the keel zone) in the Eastern Desert of Egypt. These are (1) gold–silver–zinc association, and (2) gold–copper association. In the former, gold grades are very low and silver is anomalous. This association occurs typically in the upper levels of the VHMS deposit where low-temperature sulphides are abundant. Gold was deposited because of the mixing between the ascending hot solutions and the sulphate-rich seawater. The upper levels of Um Samuki sulphide body represent this association. Gold–copper association, on the other hand, typically occurs in the footwall altered rocks (the keel zone) and the lowest parts of the massive sulphide body. Gold grades reach up to 5.54 ppm, but the average is 1 ppm. Silver is very low, usually in the range of 4–10 ppm. Lead usually, but not always, accompanies gold in this association. Deposition of gold probably took place due to decreasing of temperature and/or increasing pH of the ascending hot brines. The keel zones at Darhib, Abu Gurdi, El Atshan, Um Selimat, Nikhira and Egat talc mines better represent this association.  相似文献   

14.
The Cu-Sb-Pb polymetallic vein deposit is hosted by metavolcanics rocks of the Gawuch Formation at the Kaldom Gol area of the northwest Kohistan arc terrain in northern Pakistan. The mineralization is closely associated with the dioritic to granodioritic rocks of the Lowari pluton, which was intruded into the Gawuch metavolcanics. Details of ore characterization and processes of ore genesis of this evidently hydrothermal mineralization are not well documented. Integrating petrographic, mineral-chemical and isotopic investigations, this study aims to comprehend the source of hydrothermal fluids, geochemical evolution, mineral inclusions and physicochemical conditions of the Cu-Sb-Pb polymetallic vein deposit in Gawuch metavolcanics in the Kohistan arc terrain in northern Pakistan. The mineralization is distinguished into three types of ore-gangue associations: Type Ia, Type Ib, and Type II. The textural study revealed two pyrite generations: (i) Py1 displaying euhedral to subhedral habits and containing scarce inclusions, and (ii) Py2 occurring as anhedral grains hosting abundant inclusions. Type Ia is characterized by Py1 associated with abundant quartz (Qz) showing comb texture, sericite (Ser), and minor chlorite (Chl). Type Ib comprises Qz + Ser + Chl and Py2, chalcopyrite (Ccp), and magnetite (Mag). Type II is represented by mosaic quartz, rhombic adularia, and bladed calcite, and the ore minerals fahlore and galena. Alteration zones composed of Qz-Ser ± Chl and Qz-Ser-Chl, surround Type I (a, b) and Type II veins, respectively. Fahlore and galena mostly replace pyrite of Type Ia and chalcopyrite of Type Ib. In addition, malachite, azurite, hematite and covellite occur as secondary (supergene) minerals. The Co/Ni ratios (>1) of Kaldom Gol pyrites suggest that the ore-forming fluids were hydrothermal in origin and Py1 and Py2 solidified at 221–304 °C and 225–261 °C, respectively. The LA-ICP-MS time-resolved depth profiles confirm the existence of sphalerite, and chalcopyrite inclusions in pyrite (Py1 and Py2) and millerite, bravoite, vaesite, Au-tellurides, native Au and galena inclusions in chalcopyrite and fahlore. Sulfur isotope compositions of pyrites (δ34S = Py1, −0.58 to +2 ‰; δ34S = Py2, −0.24 to +2.04 ‰) indicate that the ore-forming fluids were derived from magmatic source (s). The mineral assemblage, hydrothermal alterations, textures, temperature and δ34S of pyrites suggest that the Cu-Sb-Pb polymetallic mineralization at Kaldom Gol represents an intermediate-sulfidation type of epithermal deposit.  相似文献   

15.
国外铁氧化物铜-金矿床的特征及其研究现状   总被引：22，自引：0，他引：22  
铁氧化物铜-金矿床是一类具许多共同特征但成因联系不太密切的矿床类型，近来已成为国外铜-金勘探的主要矿床类型之一。该类矿床以矿石中含有大量的铁氧化物（磁铁矿或赤铁矿）且伴有很强的区域性钠（-钙）质蚀变为特征，可以产于元古代克拉通内或新生代大陆边缘岛弧环境，其周围具火成岩或含蒸发盐层，时空上与之有关的侵入岩为磁铁矿系列花岗岩，矿化主要产于近区域主断裂的羽状次级断裂中。部分该类矿床的形成与一定的主岩类型有关，而多数矿床可能由高盐度 H2O-CO2-盐混合流体的不混溶作用形成，且矿化通常与钾化有关。对成矿流体是主要来自岩浆还是受围岩控制尚有争论，成矿模式有蒸发盐来源模式、外来流体加热模式和岩浆-热液流体模式。但对部分该类矿床详细的流体包裹体和稳定同位素研究表明成矿流体主要源于岩浆。对该类矿床进行地球物理勘探需要考虑磁铁矿、硫化物和Cu-Au矿化之间的相互关系。在我国开展对该类矿床的研究将有益于发现新的铜资源基地。  相似文献   

16.
Throughout Earth??s history, all volcanogenic massive sulfide (VMS)-hosting environments are associated with specific assemblages of mafic and felsic rocks with distinct petrochemistry (petrochemical assemblages) indicative of formation at anomalously high temperatures within extensional geodynamic environments. In mafic-dominated (juvenile/ophiolitic) VMS environments, there is a preferential association with mafic rocks with boninite and low-Ti tholeiite, mid-ocean ridge basalt (MORB), and/or back-arc basin basalt affinities representing forearc rifting or back-arc initiation, mid-ocean ridges or back-arc basin spreading, or back-arc basins, respectively. Felsic rocks in juvenile oceanic arc environments in Archean terrains are high field strength element (HFSE) and rare earth element (REE) enriched. In post-Archean juvenile oceanic arc terrains, felsic rocks are commonly HFSE and REE depleted and have boninite like to tholeiitic signatures. In VMS environments that are associated with continental crust (i.e., continental arc and back-arc) and dominated by felsic volcanic and/or sedimentary rocks (evolved environments), felsic rocks are the dominant hosts to mineralization and are generally HFSE and REE enriched with calc-alkalic, A-type, and/or peralkalic affinities, representing continental arc rifts, continental back-arcs, and continental back-arcs to continental rifts, respectively. Coeval mafic rocks in evolved environments have alkalic (within-plate/ocean island basalt like) and MORB signatures that represent arc to back-arc rift versus back-arc spreading, respectively. The high-temperature magmatic activity in VMS environments is directly related to the upwelling of mafic magma beneath rifts in extensional geodynamic environments (e.g., mid-ocean ridges, back-arc basins, and intra-arc rifts). Underplated basaltic magma provides the heat required to drive hydrothermal circulation. Extensional geodynamic activity also provides accommodation space at the base of the lithosphere that allows for the underplated basalt to drive hydrothermal circulation and induce crustal melting, the latter leading to the formation of VMS-associated rhyolites in felsic-dominated and bimodal VMS environments. Rifts also provide extensional faults and the permeability and porosity required for recharge and discharge of VMS-related hydrothermal fluids. Rifts are also critical in creating environments conducive to preservation of VMS mineralization, either through shielding massive sulfides from seafloor weathering and mass wasting or by creating environments conducive to the precipitation of subseafloor replacement-style mineralization in sedimented rifts. Subvolcanic intrusions are also products of the elevated heat flow regime common to VMS-forming environments. Shallow-level intrusive complexes (i.e., within 1?C3?km of the seafloor) may not be the main drivers of VMS-related hydrothermal circulation, but are likely the manifestation of deeper-seated mantle-derived heat (i.e., ~3?C10?km depth) that drives hydrothermal circulation. These shallower intrusive complexes are commonly long-lived (i.e., millions of years), and reflect a sustained thermally anomalous geodynamic environment. Such a thermally anomalous environment has the potential to drive significant hydrothermal circulation, and, therefore multi-phase, long-lived subvolcanic intrusive complexes are excellent indicators of a potentially fertile VMS environment. The absence of intrusive complexes, however, does not indicate an area of low potential, as they may have been moved or removed due to post-VMS tectonic activity. In some cases, shallow-level intrusive systems contribute metals to the VMS-hydrothermal system.  相似文献   

17.
The Penjom Gold Mine is located 30 km from the Bentong-Raub Suture at the western boundary of the Central Belt in Peninsular Malaysia. Gold mineralization hosted within the vein system is associated with pyrite, arsenopyrite, and minor base metals including galena. Trace element and lead isotope analysis was undertaken on nine samples that represent two stages of galena formed during two tectonic events. Both the Pb isotopes and the trace elements show that the first stage galena within the mineralized areas at the footwall has different geochemical characteristics compared with galena in non mineralized areas in the hanging wall, suggesting that galena crystallized from two different ore fluids and probably at two different times. Higher Te, Se and Bi in the galena from the mineralized area may indicate hydrothermal fluids that migrate through the structural conduit and leached out the metal along the pathway that consist of dominant carbonaceous unit. The Pb isotopic ratio composition are transitional between the bulk crustal growth and an upper crustal growth curve, indicating that derivation was from arc rocks associated with continental crust or a crustal source that includes arc volcanic and old continental sedimentary rocks.  相似文献   

18.
Although the term orogenic gold deposit has been widely accepted for all gold-only lode-gold deposits,with the exception of Carlin-type deposits and rare intrusion-related gold systems,there has been continuing debate on their genesis.Early syngenetic models and hydrothermal models dominated by meteoric fluids are now clearly unacceptable.Magmatic-hydrothermal models fail to explain the genesis of orogenic gold deposits because of the lack of consistent spatially- associated granitic intrusions and inconsistent temporal relationships.The most plausible,and widely accepted,models involve metamorphic fluids,but the source of these fluids is hotly debated.Sources within deeper segments of the supracrustal successions hosting the deposits,the underlying continental crust,and subducted oceanic lithosphere and its overlying sediment wedge all have their proponents.The orogenic gold deposits of the giant Jiaodong gold province of China,in the delaminated North China Craton,contain ca.120 Ma gold deposits in Precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization.The only realistic source of fluid and gold is a subducted oceanic slab with its overlying sulfide-rich sedimentary package,or the associated mantle wedge.This could be viewed as an exception to a general metamorphic model where orogenic gold has been derived during greenschist- to amphibolite-facies metamorphism of supracrustal rocks:basaltic rocks in the Precambrian and sedimentary rocks in the Phanerozoic.Alternatively,if a holistic view is taken,Jiaodong can be considered the key orogenic gold province for a unified model in which gold is derived from late-orogenic metamorphic devolatilization of stalled subduction slabs and oceanic sediments throughout Earth history.The latter model satisfies all geological,geochronological,isotopic and geochemical constraints but the precise mechanisms of auriferous fluid release,like many other subduction-related processes,are model-driven and remain uncertain.  相似文献   

19.
Summary The stratiform massive Zn-Pb sulphide Rosebery deposit of western Tasmania is hosted by metamorphosed deformed acid volcanics and sediments of the Cambrian Mt. Read Volcanics. Tourmalinite, a boron-rich siliceous sulphide facies iron formation, overlies and occurs as an exhalite facies equivalent of the massive sulphides. The orebody is partially replaced by post deformation tourmaline-bearing pyrrhotite-pyrite rocks associated with an alteration facies comprising magnetite-pyrite-tourmaline-phlogopite and the host metavolcanics are transgressed by quartz-tourmaline veins and tourmaline-filled joints. Tourmalinite and tourmaline in alteration zones are associated with other base metal deposits in the area. Tourmaline also occurs as fault-fill and in granitic rocks and associated Sn-W mineralization nearby. Tourmaline associated with the Cambrian massive sulphides is schorl > dravite in contrast to schorl in the Devonian granites.It is suggested that boron was an integral part of the ore fluids at Rosebery which precipitated tourmaline in exhalites immediately after and distal to the mineralization event. Tourmaline from the tourmalinite exhalites appears to have derived from submarine hydrothermal precipitation. Joint- and fracture-fill tourmaline could have derived from remobilization from tourmalinites during Devonian tectonism, however, it is more probable that these discordant tourmaline-bearing veins, tourmaline in the post-cleavage Rosebery Fault and tourmaline-bearing pyrrhotite-pyrite replacement of the Rosebery orebody derived from Devonian granite at a shallow depth which has been intersected in drilling. Tourmaline replacement associated with discordant structures is no different in composition from that from tourmalinites associated with the orebody and hence has undergone re-equilibration with the host rocks during multiple events of deformation and metamorphism associated with Devonian tectonism. In contrast, the composition of tourmaline from the Devonian granites is markedly different from that of the Rosebery area.
Zusammenfassung Die stratiforme, massive Zn-Pb-Sulfidlagerstätte Rosebery in West-Tasmanien sitzt in metamorphen und deformierten sauren Vulkaniten und Sedimenten der Kambrischen Mt. Read Vulkanit-Serie auf. Turmalingesteine treten im Hangenden dieser Serie auf. Sie stellen eine Bor-reiche Eisenformation in silizuiumreicher Sulfidfazies dar und sind als das exhalative Äquivalent der massiven Sulfide anzusehen. Der Erzkörper wird teilweise von postdeformativen Turmalin-fährenden Pyrrhotin-Pyrit-Gesteinen verdrängt, die mit einer Alterationsfazies, bestehend aus Magnetit-Pyrit-Turmalin-Phlogopit, assoziiert sind. Die erzfährenden Metavulkanite werden von Quarz-Turmalin-Gängen und Turmalinadern durchschlagen. Turmalingesteine wie auch Turmalin in Alterationszonen kommen auch mit anderen Buntmetall-Vererzungen des Arbeitsgebietes vor. Turmalin tritt weiters in Störungszonen, in Graniten und in an diese gebundenen Sn-W Mineralisationen auf.Der mit den kambrischen, massiven Vulkaniten assozierte Turmalin ist ein Schörl > Dravit, während in den devonischen Graniten Schörl dominiert. Es ist anzunehmen, daß Bor einen integralen Anteil der Erzlösungen in der Rosebery-Lagerstätte darstellt. Aus diesen ist Turmalin exhalativ, kurz nach der Sulfidmineralisation distal gebildet worden. Es zeigt sich, daß der Turmalin aus submarin hydrothermalen Absätzen herzuleiten ist. Gangturmaline könnten durch Remobilisation der Turmalingesteine während devonischer Deformation entstanden sein. Es scheint jedoch wahrscheinlicher, daß diese diskordanten Gänge, wie auch der Turmalin in der Rosebery-Störung und die Turmalin-führenden Pyrrhotin-Pyrit-Verdrängungen aus dem devonischen Granit stammen. Verdrängter Turmalin, assoziiert mit diskordanten Strukturen, zeigt in seiner Zusammensetzung keinerlei Unterschiede zum Turmalin in Turmalingesteinen aus dem Erzkörper. Im Zuge mehrphasiger, devonischer Deformation und Metamorphose ist es somit zu Reäquilibrierung des Turmalins mit dem Trägergestein gekommen. Die Zusammensetzung des Turmalins in den devonischen Graniten unterscheidet sich deutlich von der des Rosebery-Gebietes.
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20.
The Mangalur greenstone belt of Dharwar Craton, South India, is an Archaean schist belt dominated by metavolcanic rocks. The gold mineralization occurs within the metavolcanics and the fabric, mineralogy and geochemistry of these host rocks indicate that they were tholeiitic basalts regionally metamorphosed under medium to low-grade greenschist facies. The basic metavolcanic rocks occur as tholeiitic metabasalts and amphibolites. The rocks have undergone some fractionation and appear to be derived from melts generated by 10 to 25% melting of the mantle at depths 30 to 35 km around temperature 1200°C and pressure 12 kb. The source of gold is mainly in the basalts and not in the surrounding granites.  相似文献   

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