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1.
The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest.The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle Tianshan to the south. It is part of a Hercynian orogen with three distinct E-W-trending tectonic belts: the Devonian-Early Carboniferous Tousuquan-Dananhu island arc on the north and the Carboniferous Aqishan -Yamansu rift basin to the south, which are separated by rocks of the Kanggurtag shear zone. The porphyry deposits, dated at 322 Ma, are related to the late evolutionary stages of a subduction-related oceanic or continental margin arc. In contrast, the skarn, gold, and magmatic Ni-Cu deposits are associated with post-colli-sional tectonics at ca. 290-270 Ma. These Late Carboniferous - Early Permian deposits are associated with large-scale emplacement and eruption of magmas possibly caused by lithosphere delamination and rifting within the East Tianshan.  相似文献   

2.
《International Geology Review》2012,54(11):1311-1358
Molybdenum exploration activity in China has accelerated tremendously during the past decade owing to the continuous, increasing demand for Earth resources. China possesses the largest Mo reserves in the world (exceeding 19.6 Mt). The major ore deposits are of porphyry, porphyry–skarn, skarn, vein, and sedimentary types. Porphyry molybdenum deposits contain 77.5% of the Chinese Mo reserves, with lesser amounts in porphyry–skarns (13%), skarns (5.1%), and veins (4.4%). Exploitation of sedimentary-type molybdenum deposits thus far has been uneconomical. The six Mo provinces are in the Northeast China, Yanliao, Qinling–Dabie, middle–lower Yangtze River Valley, South China, and Sanjiang areas. We recognize six ore-forming periods: (1) Precambrian (>541 Ma), (2) Palaeozoic (541–250 Ma), (3) Triassic (250–200 Ma), (4) Jurassic–Early Cretaceous (190–135 Ma), (5) Cretaceous (135–90 Ma), and (6) Cenozoic (55–12 Ma). The abundance of Mo ore deposits in China reflects the occurrence of multiple periods of tectonism, involving interactions between the Siberian, North China, Yangtze, India, and Palaeo-Pacific plates. Precambrian molybdenum deposits are related to Mesoproterozoic volcanism in an extensional setting. Palaeozoic Cu–Mo deposits are related to calc-alkaline granitic plutons in an island arc or a continental margin setting. Triassic Mo deposits formed in the syn-collision–postcollision tectonic setting between the Siberian and North China plates and between the North China and Yangzi plates. Jurassic–Early Cretaceous molybdenum deposits formed along the eastern margin of Asia and are associated with the palaeo-Pacific plate-subduction tectonic setting. Cretaceous Mo deposits are related to high-K calc-alkaline granitic rocks and formed in a lithospheric thinning setting. Cenozoic molybdenum deposits formed in a collision setting between the Indian and Eurasian continents and the subsequent extensional setting.  相似文献   

3.
This paper models the physico-chemical conditions of a Neoarchæan to Palæoproterozoic marine basin in which the sedimentary sequence of BIF, Fe and Mn ores of the Lake Superior-type formed. The model is based on Eh-pH diagram stability fields for Fe, silica and Mn solubilities (taken from the literature) and on field observations of the lithological sequences. BIF formation took place in epicontinental marine basins with free access to the ocean. The main Fe source for BIF formation was ocean enriched with about 6–10 ppm ferrous Fe of hydrothermal geochemical affinity. Land-derived Fe influxes into the BIF-forming basins certainly contributed, but the lack of clastic sedimentation precludes estimation of element budgets. The main silica source for formation of chert layers is sea water. If silica was precipitated by evaporation, the silica concentration of the BIF-forming sea must have been close to saturation (15–20 ppm). Biogenic silica concentration from a possible silica undersaturated sea may not be excluded. These inferred BIF-forming conditions fit the global occurrence of Lake Superior-type BIF in general, whereas special sedimentary environments were probably responsible for the formation of highly enriched laminated Fe ore at the Maremane Dome and in the Sishen-Kathu mining district in Griqualand West, and for the FeMn ores in the Kalahari field. Formation of laminated Fe ore in the Maremane Dome and in the Sishen-Kathu areas were restricted to local deeps within the BIF basins, caused by karst collapse in the underlying Campbellrand dolomites. In such deeps, increased pH values relative to the normal BIF-forming sea caused sufficiently increased silica solubility, resulting in the almost exclusive sedimentation of colloidal Fe precipitates.In the Kalahari field, the BIF sedimentation pile became silica-depleted when approaching the Mn layers. This was genetically controlled by the increased pH of sea water and increased silica solubility. Under such increased pH conditions, Mn oxides become stable for precipitation if minimum Mn activity is achieved in the sedimentary basin. The sedimentation sequence of low silica BIF - kutnahoritic BIF - jacobsitic BIF - braunitic Mn ore can be explained, using combined Eh-pH diagrams, as reflecting a precipitation path of increasing redox potential in a pH environment slightly above 9. These conditions were achieved by closing the access of the basin to the open ocean, resulting in the reduction of water level by evaporation and thereby increasing salinity and pH. Precipitation of low silica BIF followed and, in the presence of sufficient Mn activity with increasing Eh in the precipitating water stratum, deposition of the Mn mineral associations occurred.  相似文献   

4.
1 Introduction The association of massive Fe-Ni-Cu sulfides andchromite is a very unusual feature of podiformchromitites occurring in mantle tectonites of ophioliticcomplexes. It has only been described in theSoutheastern Desert, Egypt, where sulfides a…  相似文献   

5.
Base metal deposits in western Cuba belong to the SEDEX type, as defined by Carne and Cathro (1982). The age of the mineralisation is Jurassic. The host rocks of the deposits are gritstones, sandstones and black shales, with no igneous rocks involved. Sulphur isotopic data from pyrite and chalcopyrite indicate a biogenic and magmatic origin, at least for part of the Cuban sulphides. The inferred tectonic setting of these deposits is that of a passive continental margin. The Pb-Zn-Cu mineralisation in Cuba is hosted in the siliciclastic sedimentary rocks of the San Cayetano Formation (Lower-Upper Jurassic in age), which indicates derivation of quartzose grains from recycled orogen source areas, related to either the Grenville or Pan African granitic-metamorphic belts. Received: 7 January 1997 / Accepted: 25 September 1997  相似文献   

6.
Magnesite is relatively frequent as a mineral, there are, however, only two types of economically important deposits:The world's largest reserves are found in deposits of theVeitsch type. These are strata-bound lensoid and nearly monomineralic bodies consisting of coarsely crystalline »spar« magnesite hosted by marine platform sediments. Conspicuous are sedimentary and diagenetic features of the magnesite bearing suites, which indicate formation within a subtidal, evaporitic environment closely associated with sabkhas, mudbars or other inter- to supratidal highs. The coarse crystallinity of these magnesites is a product of diagenesis.As spar magnesites as a rock are mainly characterized by diagenetic features it is now often concluded that the main phase of magnesium concentration would also have taken place during late diagenesis or early metamorphism from fluids formed by these processes. In that case, their origin would be by hydrothermal replacement.Contrary to this trend it is here concluded by integrating important data that Veitsch type magnesites are essentially ofsyngenetic origin. A genetic model is presented, which stresses their kinship with shallow water marine chloride type evaporites.Deposits of cryptocrystalline magnesite of theKraubath type are much smaller and less frequent than spar magnesites, although they are quite important because of their high quality product. Deposits include veins and stockworks of snow-white magnesite in ultramafic country rocks.Genetic models of Kraubath type magnesites include the extremes of supergene alteration versus hypogene-hydrothermal formation. In this paper, arguments are discussed which favour the second interpretation, illustrated by a model asSynearsurface epithermal deposits.
Zusammenfassung Magnesit ist zwar ein relativ häufiges Mineral, seine wirtschaftlich bedeutenden Lagerstätten erscheinen aber nur in zwei Typen:Die größten bergbaulichen Reserven liegen imVeitsch Typ vor, das sind schichtgebundene, linsige Körper von nahezu monomineralischem, grobkristallinem »Spatmagnesit« in marinen Plattformsedimenten. Besonders auffällig sind charakteristische sedimentäre und diagenetische Merkmale dieser Lagerstätten und ihrer Nebengesteine, welche insgesamt auf Bildung in einem subtidalen, evaporitischen Milieu in enger Nachbarschaft zu naheliegenden Sabkhas oder Schlammbänken und anderen inter- bis supratidalen Hochzonen verweisen.Daß Spatmagnesite ihre Hauptprägung offenbar während der Diagenese erfahren führt dazu, daß heute auch die erstmalige Konzentration des Mg in den Lagerstätten in diese Phase verlegt wird. Daraus ergäbe sich eine hydrothermal-metasomatische Entstehung durch Fluide, deren Herkunft zur Zeit meist in Zusammenhang mit diagenetischen oder metamorphen Prozessen gebracht wird.Im Gegensatz zu diesem Trend wird hier auf Grund einer Zusammenschau aller wesentlichen Daten zu diesen Lagerstätten eine im wesentlichensyngenetische Entstehung der Spatmagnesite vertreten. Es wird ein Modell vorgestellt, in dem die Ähnlichkeit mit chloridischen Seichtwasserevaporiten betont ist.Ogerstätten von kryptokristallinem Magnesit desKraubath Typs sind seltener und relativ klein, doch infolge der Rohstoffqualität besonders gesucht. Es sind Gänge und oberflächennahe Stockwerkkörper von schneeweißem Magnesit in ultramafischen Nebengesteinen, der oft kolloforme, selten auch faserige Texturen zeigt.Genetische Modelle der Bildung solcher Magnesitlagerstätten liegen zwischen den unvereinbaren Extremen einer supergenen Entstehung durch Verwitterung und einer hypogen-hydrothermalen Bildung. Es werden Argumente für das zweitgenannte Modell angeführt, wobei auffällige Parallelen zuoberflächennahen, epithermalen Lagerstätten festgestellt werden.
Résumé Bien que la magnésite soit un minéral relativement fréquent, elle ne constitue que deux types de gisements d'importance économique:Le premier est le type Veitsch dont les gisements comportent les plus grandes réserves de magnésite du monde. Il s'agit de corps lenticulaires «strata-bounds», formés de magnésite grossière («spathique») presque monominérale et contenus dans des sédiments marins de plate-forme. Diverses structures sédimentaires et diagénétiques dans les roches de ces séries indiquent une formation dans un milieu sub-évaporitique, en association étroite avec des sabkhas, des «mud bars» et d'autres milieux inter- à supratidaux. La cristallinité grossière de ces magnésites est d'origine diagénétique. Comme ces magnésites spathiques portent surtout l'empreinte du stade diagénétique, on tend aujourd'hui à rapporter aussi à ce stade la phase principale de concentration du Mg. Ceci impliquerait une formation par métasomatose hydrothermale de carbonates pré-existants, les fluides responsables de ce métasomatisme étant d'origine diagénétique ou métamorphique.Contrairement à ce modèle courant, et se basant sur une revue de l'ensemble de données actuelles, on conclut ici que les magnésites du type Veitsch sont essentiellement d'origine sédimentaire. L'auteur présente un modèle génétique qui fait appel à une relation étroite avec des évaporites marines du type chloruré.La deuxième source économique de magnésite est représentée par les gisements du type Kraubath, dont les réserves sont beaucoup moins importantes mais la qualité supérieure comparées à celles des magnésites spathiques. Il s'agit de filons et Stockwerks de magnésite d'un blanc de neige dans des roches ultramafiques.Les interprétations génétiques avancées pour les gisements du type Kraubath comportent des modèles extrêmes: origine par altération supergène d'une part et formation à partir des fluides hydrothermaux d'autre part. Les arguments discutés dans la présente note sont en faveur de la deuxième interprétation; ils sont illustrés par un modèle de gisements épithermaux peu profonds.
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7.
Data on the distribution of radiolarians and planktonic and benthic foraminifers are obtained for the first time from the Alan-Kyr Section (Coniacian–Campanian), in the central regions of the Crimean Mountains. Radiolarian biostrata, previously established from Ak-Kaya Mountain (central regions of the Crimean Mountains) were traced: Alievium praegallowayi–Crucella plana (upper Coniacian–lower Santonian), Alievium gallowayi–Crucella espartoensis (upper Santonian without the topmost part), and Dictyocephalus (Dictyocryphalus) (?) legumen–Spongosaturninus parvulus (upper part of the upper Santonian). Radiolarians from the Santonian–Campanian boundary beds of the Crimean Mountains are studied for the first time, and Prunobrachium sp. ex gr. crassum–Diacanthocapsa acanthica Beds (uppermost Santonian–lower Campanian) are recognized. Bolivinoides strigillatus Beds (upper Santonian) and Stensioeina pommerana–Anomalinoides (?) insignis Beds (upper part of the upper Santonian–lower part of the lower Campanian) are recognized. Eouvigerina aspera denticulocarinata Beds (middle and upper parts of the lower Campanian) and Angulogavelinella gracilis Beds (upper part of the upper Campanian are recognized on the basis of benthic foraminifers. These beds correspond to the synchronous biostrata of the East European Platform and Mangyshlak. Marginotruncana coronata-Concavatotruncana concavata Beds (Coniacian–upper Santonian), Globotruncanita elevata Beds (terminal Santonian), and Globotruncana arca Beds (lower Campanian) are recognized on the basis of planktonic foraminifers. Radiolarian and planktonic and benthic foraminiferal data agree with one another. The position of the Santonian–Campanian boundary in the Alan-Kyr Section, which is located stratigraphically above the levels of the latest occurrence of Concavatotruncana concavata and representatives of the genus Marginotruncana, is refined, i.e., at the level of the first appearance of Globotruncana arca. A gap in the Middle Campanian–lower part of the upper Campanian is established on the basis of planktonic and benthic foraminifers. The Santonian–Campanian beds of the Alan-Kyr Section, on the basis of planktonic foraminifers and radiolarians, positively correlate with synchronous beds of the Crimean-Caucasian region, and beyond. Benthic foraminifers suggest a connection with the basins of the East European Platform.  相似文献   

8.
Black shales and massive sulfides represent reduced lithofacies that require isolation from oxic environments to be preserved. This, together with the sedimentary affinity of both lithofacies, can explain their common concurrence in the geologic record. The present study is based on the comparison of Rammelsberg in Germany, Tharsis in Spain, and Draa Sfar in Morocco, three massive sulfide deposits closely associated with black shales that are distributed along the European and North African Variscan orogen. The study entails geochemical, biostratigraphic, and stratigraphic analyses of the black shale sequences hosting the three deposits and mineralogical and textural analyses of the sulfides. All three deposits were formed in immature, tectonically unstable basins within an active continental margin or continental magmatic arc. Their stratigraphic records consist of a sequence of black shales enclosing massive sulfides and variable proportions of bimodal volcanic and subvolcanic rocks. The major differences among the three deposits concern the size, composition, and mineralogy. Regarding age, they are diachronous and younger southward: Rammelsberg is middle Eifelian, Tharsis latest Famennian, and Draa Sfar late Viséan. The study of redox conditions of the paleoenvironment using organic and inorganic proxies highlights similarities and significant differences among the three ore-hosting basins during massive sulfide and black shale deposition. The black shales generally display low Corg and high Stot contents. At Rammelsberg, the Stot/Ctot ratios provide values typical for normal Middle Devonian marine environments, which suggests that the original reactive organic C is now fixed in carbonates. At Tharsis, most of the samples have Corg >1 and Stot/Corg values equivalent to those of Devonian?CCarboniferous normal marine sediments. However, some pyritic hanging-wall samples have Corg <1 and Stot up to 5?wt.%, suggesting the epigenetic addition of HS?. The Stot/Corg ratio for the Draa Sfar samples resembles that of Middle Carboniferous normal marine environments. Geochemical inorganic proxies used to define the environmental conditions include the enrichment factors of U (UEF) and Mo (MoEF) together with V/Cr and V/(V?+?Ni) ratios. Footwall shales at Filón Norte (Tharsis) show positive and eventually elevated UEF and MoEF values, which suggests anoxic conditions, whereas at Rammelsberg and Draa Sfar oxic bottom water is indicated. The relations V/Cr and V/(V + Ni) in all three cases point to a redox boundary near the sediment?Cwater interface, although at Tharsis some samples indicate anoxic/euxinic conditions (i.e., V/(V + Ni) >0.9). Regarding the environmental conditions of the source areas, feldspar illitization and selective depletion in Na and Ca occurred at the three studies sites. Available sulfur isotopic data from the Rammelsberg and Tharsis sulfide ore indicate that biogenic reduction of marine sulfate was a major sulfur source during massive sulfide generation. Nevertheless, a hydrothermal sulfur source has also been detected. At Rammelsberg, this is indicated from the polymetallic sulfides that replace sedimentary and diagenetic pyrite. At Tharsis, the bacteriogenic sulfur signature is also restricted to sulfide with less evolved textures, whereas a hydrothermal source is more evident in sulfides showing evidence of recrystallization. Both geochemical and isotopic data suggest that the bacteriogenic reduction process was inhibited by rapid burial. The sedimentation rates calculated for Rammelsberg, Tharsis, and Draa Sfar were in the range 7?C13, 8?C14, and 19?C27?cm/ka, respectively. Continuous sedimentation of black shale favored the isolation of the massive sulfides and organic material from bottom waters and hence favored their preservation. Accordingly, the relationships between black shales and massive sulfides are considered to be casual. Nevertheless, the tectono-sedimentary evolution of each basin controlled the deposition of both black shales and massive sulfides and the parameters that favored their coeval deposition.  相似文献   

9.
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10.
We collected groundwaters in and around a large (313 Mt at 1.08% Cu and 0.3% cutoff) undisturbed porphyry copper deposit (Spence) in the hyperarid Atacama Desert of northern Chile, which is buried beneath 30–180 m of Miocene piedmont gravels. Groundwaters within and down-flow of the Spence deposit have elevated Se (up to 800 μg/l), Re (up to 31 μg/l), Mo (up to 475 μg/l) and As (up to 278 μg/l) concentrations compared to up-flow waters (interpreted to represent regional groundwater flow). In contrast, Cu is only elevated (up to 2036 μg/l) in groundwaters recovered from within the deposit; Cu concentrations are low down gradient of the deposit. The differential behavior of the metals/metalloids occurs because the former group dissolves as anions, enhancing their mobility, whereas the base metals dissolve as cations and are lost from solution most likely through adsorption to clay surface exchange sites and through formation of secondary copper chlorides, carbonates, and oxides. Most groundwaters within and down-flow of the deposit have Eh–pH values around the FeII/FeIII phase boundary, limiting the impact of Fe-oxyhydroxides on oxyanions mobility. Se, Re, Mo, and As are all mobile (with filtered/unfiltered samples ～ 1) to the limit of sampling 2 km down gradient from the deposit. The increase in ore-related metals, metalloids, and sulfate and decrease in sulfate–S isotope ratios (from values similar to regional salars, + 4 to + 8‰ δ34SCDT to lower values closer to hypogene sulfides, + 1 to + 4‰ δ34SCDT) is consistent with active water–rock reactions between saline groundwaters and the Spence deposit. It is likely that hypogene and/or supergene sulfides are being oxidized under the present groundwater conditions and mineral saturation calculations suggest that secondary copper minerals (antlerite, atacamite, malachite) may also be actively forming, suggesting that supergene and exotic copper mineralization is possible even under the present hyperarid climate of the Atacama Desert.  相似文献   

11.
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12.
The Suwałki anorthosite massif, located in extreme northeast Poland beneath more than a kilometer of Phanerozoic cover, hosts major Fe-Ti-V deposits. These deposits, discovered in 1962, are contained in Fe and Ti oxide minerals that coexist with subordinate quantities of Fe, Cu, Ni, and Co sulfides in massif-style anorthosites, norites, and gabbronorites. Accessibility and other considerations preclude development of this natural resource in the present economic climate. Detailed work by Polish geologists during the last 35 years provides a sound geologic framework for this Re-Os study of the age and origin of oxide and sulfide deposits associated with a major, but lesser known anorthosite massif. Rhenium and osmium abundances and Os isotopic compositions were measured for nine sulfides and four titanomagnetites from the Suwałki anorthosite massif. The titanomagnetites are over an order of magnitude lower in Re (0.4–1.5 ppb) and Os (0.036–0.144 ppb) concentrations than co-precipitated pyrrhotite, pyrite, and chalcopyrite that yield consistent concentrations for Re (30–55 ppb) and Os (1–6 ppb). Parallel lines connecting co-existing titanomagnetite and sulfides have slopes of ∼1 on Re versus common Os concentration plots, indicating that both Re and Os behave similarly during crystallization in their high preference for any sulfide phase over magnetite. Samples from three deposits within the anorthosite massif were analyzed. An age of 1559 ± 37 Ma (n=10) with an initial 187Os/188Os of 1.16 ± 0.06 for the Jezioro Okrągłe and Krzemianka deposits is essentially identical to an age of 1556 ± 94 Ma (n=3) for the Udryń deposit. Udryń, however, yielded a marginally lower initial 187Os/188Os of 0.87 ± 0.20. The high initial 187Os/188Os combined with the Proterozoic Re-Os age indicates that the source for Suwałki oxides-sulfides is older crust, and hypothetically, could involve Archean rocks. An average crustal value of 50 for 187Re/188Os yields a 2777 Ma age for Suwałki source rocks. Widespread Phanerozoic cover severely limits knowledge of basement rocks in Poland, however, and no Archean rocks are known in the immediate region. More likely, 187Re/188Os ratios may be higher than average continental crust, reflecting mafic crust in the source, and may move the source age for Suwałki anorthosite and mineral deposits toward younger values that easily include ∼2.0 Ga Proterozoic rocks. This more favorable case also accommodates Paleoproterozoic Nd model ages. Regardless of Archean or Proterozoic source age, the high initial 187Os/188Os ratios derived from the Re-Os isochron indicate that the source for the oxide-sulfide mineral deposits is more likely the crust and not the mantle. Given that these deposits are clearly magmatic, the Re-Os results add a new dimension to the long-standing “origin of anorthosite” problem, implying a crustal source for the anorthosite as well. The 1559 Ma Suwałki age is compatible with a well-exposed east-west band of 1530-1660 Ma rapakivi granite-anorthosite magmatism to the immediate north, transecting western Russia, southern Finland, Estonia and Latvia, and central Sweden. In particular, the age and isotopic character of Suwałki are not unlike those of the well-studied Salmi rapakivi granite-anorthosite batholith in western Russia (Karelia). Received: 4 December 1998 / Accepted: 11 November 1999  相似文献   

13.
The “Americano do Brasil” Complex (ABC) is part of a cluster of coeval synorogenic mafic–ultramafic intrusions emplaced during the Brasiliano/Pan-African Orogenic Cycle in Brazil. The medium-sized ABC consists of interlayered dunite, peridotite, websterite, and gabbronorite. High Fo values of olivine (up to Fo88) and the crystallization sequence of the ABC (Ol + Chr ≥ Ol + Opx + Chr ≥ Cpx + Opx ≥ Opx + Pl + Cpx ≥ Opx + Pl + Cpx + Ilm + Mag) suggest crystallization from tholeiitic high-MgO parental magmas. Light rare earth element (REE)-enriched mantle-normalized REE profiles and εNd(T) values of +2.4 for cumulate rocks from the ABC suggest a depleted mantle source for the parental magma. The ABC Ni–Cu sulfide deposit (3.1 Mt at 1.12 wt.% Ni and 1.02 wt.% Cu) consists of three distinctively different orebodies (S1, S2, and G2). The S2 orebody, an unusual occurrence of stratiform massive sulfide hosted by dunite and peridotite in the interior of a layered intrusion, results from sulfides accumulated at the transient base of the magma chamber following a new influx of parental magma. The G2 orebody has an irregular and roughly cylindrical shape, consisting mainly of net-textured sulfides. The G2 orebody is hosted by peridotite and pyroxenite and located stratigraphically below the S1 orebody. S2 and G2 orebodies are characterized by low Cu/Cu + Ni ratios (mainly below 0.4). The S1 orebody, hosted by websterite and gabbronorite in the more fractionated sequence of the ABC, is a cluster of several irregular discontinuous orebodies of Ni–Cu disseminated sulfides. The sulfides of the S1 orebody have high Cu/Cu + Ni ratios (mainly between 0.5 and 0.8) and are highly depleted in PGE. The S1 orebody is interpreted to result from a later event of sulfide segregation in the magma chamber, possibly following the event that originated the G2 orebody. The bulk of δ34S values for sulfides of the ABC orebodies and their host rocks fall in the range of 0 ± 2‰. Higher δ34S values (between 3‰ and 5‰) are restricted to pyrite from xenoliths of gneiss located close to the S1 orebody and sulfides from the S1 orebody. Crustal xenoliths and chemical data (lithogeochemistry and sulfur isotope composition) provide evidence of crustal contamination of the igneous rocks hosting the S1 orebody, suggesting that sulfur saturation was induced by contamination with sulfide-bearing crustal rocks. The ABC deposit is an example of Ni–Cu sulfide mineralization hosted by synorogenic mafic–ultramafic intrusions. The S2 orebody is the first documented example of an economic stratiform massive sulfide orebody located within layered intrusions, expanding the opportunities for exploration of Ni–Cu sulfides in orogenic regions worldwide.  相似文献   

14.
《China Geology》2022,5(4):595-613
By the end of 2020, 83 silver deposits (or ore occurrences), including four super-large-scale deposits, nine large-scale deposits, 33 medium-scale deposits and 37 small-scale deposits or ore occurrences, have been proved. The amount of silver metal exceeds 86000 t with average grade of 100 g/t, which makes Daxing’ anling region one of the the most important silver ore belt in China. However, the metallogenic characteristics and metallogenesis need to be clarified. The silver deposits in the study area are classified into three main types, which are magmatic hydrothermal vein type, continental volcano-subvolcanic type and skarn type, respectively. The supergiant deposits include the Shuangjianzishan deposit (silver metal amount of 15214 t with average grade of 138 g/t), the Baiyinchagandongshan deposit (silver metal amount of 9446 t with average grade of 187 g/t), the Huaobaote deposit (silver metal amount of 6852 t with average grade of 170 g/t), and the Fuxingtun deposit (silver metal amount of 5240 t with average grade of 196 g/t). The silver deposits are mainly distributed in the central and south of the Daxing’anling area, and mainly formed in the Yanshanian period. The silver polymetallic deposits in the Daxinganling area are significantly controlled by regional faults and the junction zone of volcanic rock basins and their margins. The north-east trending deep faults are the most important ore-controlling structures in this area. The distribution of silver polymetallic deposits along the main faults is obvious, and the intersection area of multiple groups of faults often form important mine catchments. The Permian is the most important ore-bearing formation in this area, but some important silver polymetallic deposits occur in Mesozoic volcanic basins or pre-Mesozoic strata. The magmatic rocks related to mineralization are mainly intermediate acidic or acidic intrusions, intermediate acidic lavas, pyroclastic rocks, and small intrusions of ultra-shallow or shallow facies of the Yanshanian Period. The mineralization element combination is mainly determined by the elemental geochemical background of surrounding rocks or source layers. In addition, the type of deposit, the distance from the mineralization center, and the degree of differentiation of ore-forming rock mass are also important influence factors. The article analyzes the prospecting prospects of each silver deposit type in the study area, discusses the relationship between mineralization center and deep prospecting, and proposes that porphyry silver deposits should be paid attention to. In the prospecting and exploration of silver deposits, comprehensive evaluation and multi-target prospecting need to be strengthened because silver can coexist or be associated with a variety of metals.©2022 China Geology Editorial Office.  相似文献   

15.
ABSTRACT

The east–central part of Jilin Province, NE China, hosts an important polymetallic metallogenic district that contains more than 10 recently discovered large-, medium-, and small-scale Mo deposits. The Mo deposits in this area include porphyry-, skarn-, and quartz vein-type mineralization, of which the porphyry-type deposits dominate. Few studies of these mineralization-related granitoids have been undertaken. Here, we present the results of a systematic regional survey of the geochemistry and geochronology of Mo mineralization-related granites in this area. Zircon U–Pb dating of the Fuanpu, Jidetun, Shuangshan, and Jiapigou granites, all of which are associated with Mo mineralization, yielded weighted mean 206Pb/238U ages of 167.05 ± 0.81, 170.91 ± 0.83, 183.8 ± 1.1, and 182.3 ± 2.2 Ma, respectively, indicating that these plutons were emplaced during the Early–Middle Jurassic. They have SiO2 = 62.59–73.5 wt.%, Al2O3 = 13.74–16.19 wt.%, and K2O/Na2O = 0.8–2.18. Chemically, they are metaluminous to peraluminous and belong to the high-K calc-alkaline to shoshonitic series. Moreover, they are enriched in large ion lithophile elements and light rare earth elements, and are depleted in high field strength elements, which are characteristics of I type granite. Whole rock Sr–Nd–Pb isotopic compositions of these granitoids are similar (initial 87Sr/86Sr = 0.70404 to 0.70554; εNd(t) = –0.9 to 2.4; (206Pb/204Pb)t = 15.549–15.567, (207Pb/204Pb)t = 18.035–18.530, (208Pb/204Pb)t = 37.966–38.229) and altogether suggest that the magmas from which the Mo deposits were generated originated from the mantle or juvenile crust. Combining our results with regional Jurassic tectonic setting, we conclude that the mineralization of these granitoids reflected Pacific plate subduction which induced magma underplating and promoted the remelting of the juvenile crust, resulting in voluminous granitic magma.  相似文献   

16.
Two epithermal gold deposits (Kartaldağ and Madendağ) located in NW Turkey have been characterized through the detailed examinations involving geologic, mineralogical, fluid inclusion, stable isotope, whole-rock geochemistry, and geochronology data.The Kartaldağ deposit (0.01–17.65 ppm Au), hosted by Eocene dacite porphyry, is associated with four main alteration types with characteristic assemblage of: i) chlorite/smectite–illite ± kaolinite, ii) quartz–kaolinite, iii) quartz–alunite–pyrophyllite, iv) quartz–pyrite, the last being characterized by three distinct quartz generations comprising massive/vuggy (early), fine–medium grained, vug-lining (early), and banded, colloform, comb (late) textures. Observed sulfide minerals are pyrite, covellite, and sphalerite. Oxygen and sulfur isotope analyses, performed on quartz (δ18O(quartz): 7.93 to 8.95‰ and calculated δ18O(H2O): − 7.95 to 1.49‰) and pyrite (δ34S(pyrite): − 4.8‰ and calculated δ34S(H2S): − 6.08 to − 7.20‰) separates, suggest a meteoric water source for water in the hydrothermal fluid, and an igneous source for the sulfur dissolved in ore-related fluids. Microthermometric analyses of primary fluid inclusion assemblages performed on quartz (late quartz generation) yield temperatures (Th) dominantly in the range of 245–285 °C, and generally low salinity values at 0 to 1.7 wt.% NaCl eq. Based on the quartz textures and the associated base metal concentrations, along with fluid inclusion petrography, the early vug-lining quartz is considered to have been associated with the mineralization possibly through a boiling and a late mixing process at > 285 °C.The Madendağ deposit (0.27–20.60 ppm Au), hosted by Paleozoic mica schists, is associated with two main alteration types: sericite–illite–kaolinite, and quartz–pyrite dominated by two distinct quartz generations i) early colloform, comb and banded quartz and ii) late quartz, forming the cement in hydrothermal breccia. Whereas oxygen isotope analyses of quartz (δ18O(quartz): 9.55 to 18.19‰ and calculated δ18O(H2O): − 2.97 to 5.54‰) suggest varying proportions of meteoric and magmatic sources for the ore bearing fluid, sulfur isotope ratios (δ34S(pyrite): − 2.2‰ and calculated δ34S(H2S): (− 3.63) to (− 3.75) ‰) point to an essentially magmatic source for sulfur with or without contribution from sedimentary sources. Microthermometric analysis carried out on primary fluid inclusion populations of a brecciated sample (early quartz), give a temperature (Th) range of 235–255 °C and 0.0 to 0.7 wt.% NaCl eq. salinity. Based on the textural relationship, base metal and high gold contents, the ore precipitation stage is associated with late stage quartz formation via a possible boiling process.The presence of alunite, pyrophyllite and kaolinite, vuggy quartz and covellite suggest a high-sulfidation type of epithermal deposit for Kartaldağ. On the other hand, Madendağ is identified as an adularia-sericite type owing to the presence of significant sericite, neutral pH clays (mostly illite, chlorite/smectite, and kaolinite), low temperature quartz textures (e.g., colloform, comb, and banded quartz), and limited sulfide minerals.Given the geographical proximity of Kartaldağ and Madendağ deposits, the similar temperature and salinity ranges obtained from their fluid inclusions, and the similar ages of igneous rocks in both deposits (Kartaldağ: 40.80 ± 0.36 to 42.19 ± 0.45 Ma, Madendağ: 43.34 ± 0.85 Ma) the mineralizing systems in both deposits are considered to be genetically related.  相似文献   

17.
Please refer to the attachment(s) for more details  相似文献   

18.
The Song Hien rift basin is considered to be one of the most important regions of gold mineralisation in North East Vietnam. A number of gold deposits in the Song Hien rift basin are hosted in Triassic and Devonian sedimentary formations of the basin. The largest among them are the Bo Va, Tham Riem and Khung Khoang deposits. The Bo Va deposit is hosted in carbonaceous sedimentary rocks of Triassic age, whereas the Tham Riem and Khung Khoang deposits are hosted in carbonaceous sedimentary rocks of Devonian ages. Based on the mineral composition of the ores, the deposits can be divided into to two types: (i) pyrite dominated and (ii) pyrite-arsenopyrite dominated. The Khung Khoang is of the first type and the Bo Va and Tham Riem deposits belong to the second type. The isotopic composition of pyrite and arsenopyrite in the Tham Riem deposit however, is close to that for the ores of the Bo Va deposit. The δ34S value for pyrite ranging from −3.7‰ to −7.4‰ and for arsenopyrite ranging from −3.2‰ to 7.4‰. The δ34S of pyrite in the ore from the Khung Khoang deposit however, has a much heavier isotopic composition of +18.9 to +20.2‰. A narrow range of the variation of sulfur isotopic composition of pyrite and arsenopyrite, the presence of visible gold as inclusions, the presence of chalcopyrite, sphalerite and other inclusions in arsenopyrite and pyrite, the large size of the grains of major ore minerals allow us to assume that the primary gold ores of the Bo Va and Tham Riem deposits underwent metamorphic transformations. The absence of arsenic, antimony, mercury and other characteristic elements in the ores of the Khung Khoang deposit, and substantially heavier isotopic composition of sulfur similar to the sulfur isotopic composition of marine sulfates in the Devonian, allow us to assume another source of the ore components, not connected with the Triassic sedimentary rocks of the Song Hien rift.  相似文献   

19.
Vein-type, structurally controlled Cu–Au mineralisation hosted by turbidites of late Silurian to earliest Devonian age, forms an important resource close to the eastern margin of the Cobar Basin. Here we report 103 new sulfur isotope analyses, together with homogenisation temperatures and salinity data for 545 primary two-phase fluid inclusions for the mineralised zones from the central area of the Cobar mining district. A range in δ34S values from 3.8 to 11.2‰ (average 7.9‰) is present. Sulfur is likely to have been derived from rock sulfur/sulfide in basin and basement rocks, but there may be an additional connate-derived component. Homogenisation temperatures (Th) for inclusion fluids trapped in quartz and minor calcite veins range from near 150°C to 397°C. Fluid inclusions are characterised by a low CO2 content and low, but variable salinities (2.1–9.1 wt% NaCl equivalent). Generations of inclusion fluids correspond to six paragenetic stages of vein quartz deposition and recrystallisation at the Chesney mine. Primary fluid inclusions in the first two stages were subjected to re-equilibration resulting from increased confining pressure. Their Th range (151–317°C) is considered a minimum for the temperature of these fluids. Sulfide and gold deposition at Chesney appears to be related to fluids of moderately high Th (range 270–397°C) associated with the final paragenetic stage. Th for the ore-related fluids may be close to the solvus of the H2O–NaCl–CO2 system and hence near trapping temperatures. Late-stage entry of a hot, moderately saline ore-forming fluid is implicated as the origin of the Cu–Au mineralisation. However, comparison with geochemical data for the vein-style Zn–Pb–Ag deposits at Cobar demonstrates that differences in metal content for individual zones cannot be attributed to major differences in fluid temperature or salinity. Rather, these differences are probably due to variations in source-rock reservoirs and structural pathways along which the ore-forming fluids moved.  相似文献   

20.
The history of eolian dust deposition in northern China has been traced back to 22 million years ago （Ma） and the combination of different eolian formations provides a nearly continuous terrestrial climate record since the early Neogene. The spatial distribution of environmental indicators define a roughly EW zonal climate pattern in Asia throughout the Paleogene, attributable to a circulation pattern dominated by a Planetary Wind System （PWS）. A major rearrangement occurred near the Miocene/Oligocene boundary, characterized by a replacement of the zonal PWS by a monsoon circulation similar to that of the present day. This event is also marked by the onset of loess deposition in northern China. The Asian summer monsoon was likely rather weak during the Paleogene. The loess deposition and formation of numerous well-developed paleosols since the Early Miocene indicate that the following features of the modem-day circulation already existed 22 Ma ago： sizeable deserts in the Asian inlands as dust sources, the winter monsoon as dust carrier, and an energetic summer monsoon as a supply of moisture. Uplift of the Himalayan-Tibetan complex and changes in land-sea distribution were likely responsible for these joint changes in circulation and aridity. From 22 to 6 Ma, loess accumulation rates were much lower, suggesting moderate levels of ar/dity and winter monsoon strength. Evolution of the aridity was not strongly correlative with the cooling trends indicated by marine oxygen isotope records, suggesting a smaller impact of global cooling on drying of the Asian interior during this time interval. However, the general aridification history since about 6 Ma matches the ongoing high-latitude cooling and the consequent expansion of Arctic sea-ice/ice sheets. Some increases in aridification also coincide with proposed uplift of portions of the Tibetan Plateau.  相似文献   

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