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1.
Placing ore formation within the overall tectonic framework of an evolving orogenic system provides important constraints for the development of plate tectonic models. Distinct metallogenic associations across the Palaeozoic Lachlan Orogen in SE Australia are interpreted to be the manifestation of interactions between several microplates and three accretionary complexes in an oceanic back-arc setting. In the Ordovician, significant orogenic gold deposits formed within a developing accretionary wedge along the Pacific margin of Gondwana. At the same time, major porphyry Cu-Au systems formed in an oceanic island arc outboard of an evolved magmatic arc that, in turn, gave rise to granite-related Sn-W deposits in the Early Silurian. During the ongoing evolution of the orogen in the Late Silurian to Early Devonian, sediment-hosted Cu-Au and Pb-Zn deposits formed in short-lived intra-arc basins, whereas a developing fore-arc system provided the conditions for the formation of several volcanogenic massive sulphide deposits. Inversion of these basins and accretion to the Australian continental margin triggered another pulse of orogenic gold mineralisation during the final consolidation of the orogenic belt in the Middle to Late Devonian. 相似文献
2.
斑岩铜矿主要产于聚合板块的上盘 ,是岛弧和活动大陆边缘花岗岩质岩浆 -热液系统 (其中包括火山作用 )演化的产物 ,从斑岩铜矿带与近同期陆相火山岩的关系来看 ,可以归纳为 2种 :一种是斑岩铜矿床或矿田内有同期或稍早期的陆相火山活动 ,例如江西银山、内蒙古乌努格吐山和安徽沙溪等 ;另一种是斑岩铜矿床或矿田内缺少同期陆相火山活动 ,仅见到浅成 -超浅成侵入活动 ,例如江西德兴和西藏玉龙等。斑岩铜矿与陆相火山岩有关的矿床之间具有一定的联系 ,例如有时二者晚期都常发育浊沸石化和硅化 ,常与金等矿化伴生 ,以及常伴随爆破角砾岩和火山口陷落等。环太平洋带、古特提斯带和中亚 -蒙古带为世界斑岩铜矿最发育 ,地质工作最为活跃的地区。中国北部相当于中亚 -蒙古带的一部分 ,东部相当于环太平洋带的一部分 ,西南部相当于特提斯带的一部分 ,集中了许多聚合板块 ,随着洋盆的消减和陆 -陆碰撞的造山作用具有很长的构造 -岩浆 -热液活动的历史(其中包括陆相和海陆交互相火山活动 ) ,故找寻评价斑岩铜矿很有前景。文中重点讨论了东天山、德兴和冈底斯地区同时代的陆相火山活动与斑岩铜矿的关系 ,通过这一讨论 ,为斑岩铜矿的找寻与评价提供了依 相似文献
3.
About three quarters of superlarge porphyry copper deposits throughout the world occur along the eastern Pacific basin rim, most of which were formed during the Mesozoic-Cenozoic. Porphyry copper deposits often occur in the upper parts of a subduction zone and in a within-plate orogenic belt. Some porphyry copper deposits are inconsistent with plate subduction with respect to their formation time, and most of them in the world are associated with tensional environment. Metallogenic porphyries originated from the mantle, and the involvement of the lower-crust or oceanic crust materials have played an important role. Based on the geochemical characteristics and tectonic settings of the ore-bearing porphyries in the Gandise and Yulong metallogenic zones, it is proposed that delamination may be the important mechanism of formation of porphyry copper deposits. 相似文献
4.
About three quarters of superlarge porphyry copper deposits throughout the world occur along the eastern Pacific basin rim, most of which were formed during the Mesozoic-Cenozoic. Porphyry copper deposits often occur in the upper parts of a subduction zone and in a within-plate orogenic belt. Some porphyry copper deposits are inconsistent with plate subduction with respect to their formation time, and most of them in the world are associated with tensional environment. Metallogenic porphyries originated from the mantle, and the involvement of the lower-crust or oceanic crust materials have played an important role. Based on the geochemical characteristics and tectonic settings of the ore-bearing porphyries in the Gandise and Yulong metallogenic zones, it is proposed that delamination may be the important mechanism of formation of porphyry copper deposits. 相似文献
5.
Gaku Kimura Yujin Kitamura Asuka Yamaguchi Jun Kameda Yoshitaka Hashimoto Mari Hamahashi 《Island Arc》2019,28(5)
The belt boundary thrust within the Cretaceous–Neogene accretionary complex of the Shimanto Belt, southwestern Japan, extends for more than ~ 1 000 km along the Japanese islands. A common understanding of the origin of the thrust is that it is an out of sequence thrust as a result of continuous accretion since the late Cretaceous and there is a kinematic reason for its maintaining a critically tapered wedge. The timing of the accretion gap and thrusting, however, coincides with the collision of the Paleocene–early Eocene Izanagi–Pacific spreading ridges with the trench along the western Pacific margin, which has been recently re‐hypothesized as younger than the previous assumption with respect to the Kula‐Pacific ridge subduction during the late Cretaceous. The ridge subduction hypothesis provides a consistent explanation for the cessation of magmatic activity along the continental margin and the presence of an unconformity in the forearc basin. This is not only the case in southwestern Japan, but also along the more northern Asian margin in Hokkaido, Sakhalin, and Sikhote‐Alin. This Paleocene–early Eocene ridge subduction hypothesis is also consistent with recently acquired tomographic images beneath the Asian continent. The timing of the Izanagi–Pacific ridge subduction along the western Pacific margin allows for a revision of the classic hypothesis of a great reorganization of the Pacific Plate motion between ~ 47 Ma and 42 Ma, illustrated by the bend in the Hawaii–Emperor chain, because of the change in subduction torque balance and the Oligocene–Miocene back arc spreading after the ridge subduction in the western Pacific margin. 相似文献
6.
G. P. Glasby 《Island Arc》1996,5(4):396-406
Abstract Mass balance calculations indicate that the potential supply of metals resulting from subduction of oceanic crust and sediment far exceeds that required for mineralization in island ares. Subduction of oceanic crust is more important than that of sediment in supplying these metals and the subduction of manganese nodules makes only a negligible contribution. The nature and extent of mineralization in island ares therefore depend on the nature, geometry and rate of subduction. In the Pacific, two types of subduction system occur: the high-stress (Chilean) type, characterized by shallow subduction and the formation of porphyry copper deposits in andesitic ares, and the low-stress (Mariana) type, characterized by deep subduction and the formation of Kuroko deposits in the back-arc basin, and porphyry copper and epithermal gold deposits in the island are. Kuroko deposits are analogous to the epithermal deposits but are formed from saline hydrothermal fluids under much higher hydrostatic pressure. 相似文献
7.
8.
Thermal consequences of the formation of a slab window beneath the Mid-Cretaceous southwest Japan arc: A 2-D numerical analysis 总被引：1，自引：0，他引：1
Abstract The development of voluminous granitic magmatism and widespread high-grade metamorphism in Mid-Cretaceous southwest Japan have been explained by the subduction of a spreading ridge (Kula–Pacific or Farallon–Izanagi plate boundaries) beneath the Eurasian continent and the formation of a slab window. In the present study, the thermal consequences of the formation of a slab window beneath a continental margin are evaluated through a 2-D numerical simulation. The model results are evaluated by comparison with the Mid-Cretaceous geology of southwest Japan. Of particular interest are the absence of an amphibolite- to granulite-facies metamorphic belt near the Wadati–Benioff plane, and significant melting of the lower crustal-mafic rocks sufficient to form a large amount of granitic magma. Because none of the model results simultaneously satisfied these two geological interpretations, it is suggested that subduction of plate boundaries in Mid-Cretaceous southwest Japan was not associated with the opening of a slab window. According to previous studies, and the results of the present study, two different tectonic scenarios could reasonably explain the geological interpretations for Mid-Cretaceous southwest Japan: (i) The spreading ridge did not subduct beneath the Eurasian continent, but was located off the continental margin, implying the continuous subduction of very young oceanic lithosphere; (ii) ridge subduction beneath the continental margin occurred after active spreading had ceased. Consequently, in both tectonic scenarios, the subduction of plate boundaries at the Mid-Cretaceous southwest Japan was not associated with a slab window, but very young (hot) oceanic lithosphere. 相似文献
9.
Kerrich Robert Goldfarb Richard Groves David Garwin Steven Jia Yiefei 《中国科学:地球科学(英文版)》2000,43(1):1-68
There are six distinct classes of gold deposits, each represented by metallogenic provinces, having 100's to >1000 tonne gold production. The deposit classes are: (1) orogenic gold; (2) Carlin and Carlin-like gold deposits; (3) epithermal gold-silver deposits; (4) copper-gold porphyry deposits; (5) iron-oxide copper-gold deposits; and (6) gold-rich volcanic hosted massive sulfide (VMS) to sedimentary exhalative (SEDEX) deposits. This classification is based on ore and alteration mineral assemblages; ore and alteration metal budgets; ore fluid pressure(s) and compositions; crustal depth or depth ranges of formation; relationship to structures and/or magmatic intrusions at a variety of scales; and relationship to the P-T-t evolution of the host terrane. These classes reflect distinct geodynamic settings. Orogenic gold deposits are generated at mid-crustal (4–16 km) levels proximal to terrane boundaries, in transpressional subduction-accretion complexes of Cordilleran style orogenic belts; other orogenic gold provinces form inboard, by delamination of mantle lithosphere, or plume impingement. Carlin and Carlin-like gold deposits develop at shallow crustal levels (<4 km) in extensional convergent margin continental arcs or back arcs; some provinces may involve asthenosphere plume impingement on the base of the lithosphere. Epithermal gold and copper-gold porphyry deposits are sited at shallow crustal levels in continental margin or intraoceanic arcs. Iron oxide copper-gold deposits form at mid to shallow crustal levels; they are associated with extensional intracratonic anorogenic magmatism. Proterozoic examples are sited at the transition from thick refractory Archean mantle lithosphere to thinner Proterozoic mantle lithosphere. Gold-rich VMS deposits are hydrothermal accumulations on or near the seafloor in continental or intraoceanic back arcs.
The compressional tectonics of orogenic gold deposits is generated by terrane accretion; high heat flow stems from crustal thickening, delamination of overthickened mantle lithosphere inducing advection of hot asthenosphere, or asthenosphere plume impingement. Ore fluids advect at lithostatic pressures. The extensional settings of Carlin, epithermal, and copper-gold porphyry deposits result from slab rollback driven by negative buoyancy of the subducting plate, and associated induced convection in asthenosphere below the over-riding lithospheric plate. Extension thins the lithosphere, advecting asthenosphere heat, promotes advection of mantle lithosphere and crustal magmas to shallow crustal levels, and enhances hydraulic conductivity. Siting of some copper-gold porphyry deposits is controlled by arc parallel or orthogonal structures that in turn reflect deflections or windows in the slab. Ore fluids in Carlin and epithermal deposits were at near hydrostatic pressures, with unconstrained magmatic fluid input, whereas ore fluids generating porphyry copper-gold deposits were initially magmatic and lithostatic, evolving to hydrostatic pressures. Fertilization of previously depleted sub-arc mantle lithosphere by fluids or melts from the subducting plate, or incompatible element enriched asthenosphere plumes, is likely a factor in generation of these gold deposits. Iron oxide copper-gold deposits involve prior fertilization of Archean mantle lithosphere by incompatible element enriched asthenospheric plume liquids, and subsequent intracontinental anorogenic magmatism driven by decompressional extension from far-field plate forces. Halogen rich mantle lithosphere and crustal magmas likely are the causative intrusions for the deposits, with a deep crustal proximal to shallow crustal distal association. Gold-rich VMS deposits develop in extensional geodynamic settings, where thinned lithosphere extension drives high heat flow and enhanced hydraulic conductivity, as for epithermal deposits. Ore fluids induced hydrostatic convection of modified seawater, with unconstrained magmatic input. Some gold-rich VMS deposits with an epithermal metal budget may be submarine counterparts of terrestrial epithermal gold deposits. Real time analogs for all of these gold deposit classes are known in the geodynamic settings described, excepting iron oxide copper-gold deposits.
相似文献10.
V. P. Trubitsyn 《Izvestiya Physics of the Solid Earth》2006,42(2):93-113
The present Pacific Ocean differs significantly in its structure and evolution from the expanding Atlantic Ocean. The Pacific is asymmetric. Its mid-ocean ridge is located not along its median line but is closer to South America and adjoins North America. The Pacific is surrounded by a ring of subduction zones but has marginal seas only at its Eurasian margins. After the breakup of Pangea, the Atlantic began to open and the Pacific began to close. This paper examines the evolution of the Pacific Ocean and, in particular, the formation mechanisms of its present structures. Numerical modeling of the long-term drift of a large continent is performed, with the initial position of the continent corresponding to the state after the breakup of the supercontinent. At first the continent, driven by the nearest descending mantle flow, begins to approach a subduction zone. Since the mantle flows beneath a large continent have different directions, its velocity is a few times lower than that of the mantle flows near the subduction zone. As a result, a zone of extension arises at the active continental margin and a fragment is broken off from the continent; this fragment rapidly moves away and stops above the descending mantle flow as in a trap. A marginal sea forms at the active continental margin. The continent continues its slow movement toward the subduction zone. The oceanic lithosphere, which earlier sank vertically, begins to descend obliquely. This evolutionary stage corresponds to the present position of Eurasia. The modeling shows how the interaction of the continent with the mantle causes the subduction zone to roll back toward the ocean. Subsequently, the continent nevertheless catches up with the subduction zone, and they move together for a while. The marginal sea then closes and high compressive stresses arise at the active continental margin. This state corresponds to the present position of South America. During the subsequent drift, the continent together with the subduction zone reaches the mid-ocean ridge and partially overrides it. This state corresponds to North America, which was the first to break off from Pangea and passed through the stages of both Eurasia and South America. The large and slowly moving Eurasia, which formed only at the time of Pangea, is still in the first evolutionary stage of the Pacific Ocean closure. 相似文献
11.
New multichannel seismic reflection data provide information on the stratigraphic framework and geologic history of the forearc basin west of central Sumatra. We recognize six seismic-stratigraphic sequences that reflect the Cenozoic history and development of the outer continental shelf and forearc basin southeast of Nias Island. These sequences indicate several episodes of uplift of the subduction complex and filling of the forearc basin.Early in the development of this margin, Paleogene slope deposits prograded onto the adjacent basin floor. Onlapping this assemblage are two units interpreted as younger Paleogene(?) trough deposits. Uplift associated with rejuvenation of subduction in the late Oligocene led to erosion of the Sumatra shelf and formation of a regional unconformity.The early Miocene was a period of significant progradation. A Miocene limestone unit partly downlaps and partly onlaps the older Paleogene deposits. It is characterized by shallow shelf and oblique progradational facies passing into basin floor facies. A buried reef zone occurs near the shelf edge. The cutting of an erosional unconformity on the shelf and slope in late Miocene/early Pliocene time culminated this episode of deposition.In the late Pliocene, a large flexure developed at the western boundary of the basin, displacing the outer-arc ridge upward relative to the basin. Over 1 km of Pliocene to Recent sediment was deposited as a wedge in the deep western portion of the basin landward of the outer-arc ridge. These deposits are characterized by flat-lying, high-amplitude, continuous reflections that overstep the late Miocene unconformity. Up to 800 m of shallow-water limestone have been deposited on the shelf since mid-Pliocene time. 相似文献
12.
HOU Zengqian QU Xiaoming WANG Shuxian DU Andao GAO Yongfeng & HUANG Wei . Institute of Mineral Resources Chinese Academy of Geological Sciences Beijing China . National Center of Geoanalysis Chinese Academy of Geological Sciences Beijing China . Shijiazhuang College of Economy Shijiazhuang China . Xizang Bureau of Geology Mineral Resources Lhasa China 《中国科学D辑(英文版)》2004,47(3)
It is recognized that there are at least two sorts of significant environments for porphyry copper deposits, i.e. magmatic arcs and collisional orogens[1 4]. The deposits in the former environments are exampled by the circle-Pacific porphyry copper belt, such as An-dean-type deposits, which mainly formed in the period of the Andean tectonic cycle characterized by trans- pressional and transtensional movements along the arc-parallel strike-slip fault zone in the Late Eo-cene-Early Oligocene[5… 相似文献
13.
Ridge collision and in situ greenstones in accretionary complexes: An example from the Late Cretaceous Ryukyu Islands and southwest Japan margin 总被引：1，自引：0，他引：1
Abstract Mélange units containing greenstones are common throughout the Cretaceous-Miocene Shimanto Supergroup in the Ryukyu Is and southwest Japan. Most greenstones in the accretionary complex originated in oceanic spreading ridges and seamounts, and they formed far from the convergent margin. Some mélange-like units in the supergroup, however, contain greenstones that were extruded upon and intruded into unconsolidated fine-grained terrigenous clastic sediments. It is inferred that eruption of the in situ greenstones resulted from igneous activity in the trench area. Geochemical signatures indicate that the greenstone protoliths were similar to mafic lavas generated at spreading ridges. Fossil ages of the strata containing in situ greenstones become younger over a distance of 1300 km eastward from Amami-Oshima (Cenomanian-Turonian) in the Ryukyu Is to central Japan (Late Maestrichtian-earliest Paleocene), implying that a site of igneous activity in the trench area migrated eastward along the Ryukyu Is and southwest Japan margin. Plate reconstructions of the northwest Pacific Ocean suggest the presence of the Kula-Pacific ridge near Late Cretaceous to early Paleogene Japan. In this context, it is suggested that the greenstones formed in response to Kula-Pacific ridge-forearc collision.
Ancient ridge-forearc collisions are best recognized by the presence of mid-ocean ridge basalt (MORB) extruded on sediments inferred to have accumulated in the trench area. Diachronous occurrences of the strata associated with these MORB in an orogenic belt are useful for documenting the ridge collision through time. 相似文献
Ancient ridge-forearc collisions are best recognized by the presence of mid-ocean ridge basalt (MORB) extruded on sediments inferred to have accumulated in the trench area. Diachronous occurrences of the strata associated with these MORB in an orogenic belt are useful for documenting the ridge collision through time. 相似文献
14.
Studies of late Tertiary silicic volcanic centres in the Western and Eastern Cordilleras of the Central Andes show that three volcanic environments are appropriate sites for mineralization: (1) ring-fracture extrusions post-dating large calderas; (2) similar extrusions within ignimbrite shields; and (3) isolated, small silicic volcanoes. Subvolcanic tin mineralization in the Eastern Cordillera is located in silicic stocks and associated breccias of Miocene age. The Cerro Rico stock, Potosi, Bolivia, contains tin and silver mineralization and has an intrusion age apparently millions of years younger than that of the associated Kari Kari caldera. Similar age relationships between mineralization and caldera formation have been described from the San Juan province, Colorado. The vein deposits of Chocaya, southern Bolivia, were emplaced in the lower part of an ignimbrite shield, a type of volcanic edifice as yet unrecognized in comparable areas of silicic volcanism. The El Salvador porphyry copper deposit, Chile, is related to silicic stocks which may have been intruded along a caldera ring fracture. Cerro Bonete, Chile, provides a modern example of the volcanic superstructure which may have overlain isolated mineralized stocks and breccia pipes such as that of Salvadora at Llallagua, Bolivia.Existing models for the genesis of porphyry copper deposits suggest that they formed in granodioritic stocks located in the infrastructure of andesitic stratovolcanoes. Sites of porphyry-type subvolcanic tin mineralization in the Eastern Cordillera of Bolivia are distinguished by the absence of such andesitic structures. The surface expression of a typical subvolcanic porphyry tin deposit was probably an extrusive dome of quartz latite porphyry, sometimes related to a larger caldera structure. Evidence from the El Salvador porphyry copper deposit in the Eocene magmatic belt in Chile suggests that it too may be more closely related to a silicic volcanic structure than to an andesitic stratovolcano.The dome of La Soufriere, Guadeloupe is proposed as a modern analog for the surface expression of subvolcanic mineralization processes, the phreatic eruptions there suggesting the formation of hydrothermal breccia bodies in depth. Occurrence of mineralized porphyries, millions of years after caldera formation, does not necessarily indicate that intrusions and mineralization are not genetically related to the sub-caldera pluton, but may be a consequence of the long thermal histories (1–10 million years) of the lowermost parts of large plutons. Caldera formation can only inhibit mineralization by dispersal of ore metals when these are of magmatic origin, and ignimbrites should not be taken as being unlikely to be associated with porphyry mineralization. Whether ore metals are of wall rock or magmatic origin, the key to understanding the relationships between silicic volcanism and mineralization lies in the fractionation of trace elements within large zoned magma chambers during their igneous history, and their subsequent hydrothermal migration. Small, highly mineralized intrusions formed late in a caldera cycle (such as the Cerro Rico) may be due to the introduction of fresh supplies of mafic magma into the lower parts of the main pluton. 相似文献
15.
Modern collisional orogens represent the natural laboratory for the study of metallogeny in continental collision zones. The Pyrenees, Alps, Zagros and Himalaya are all associated with Neo-Tethyan subduction and represent the youngest collisional orogens on Earth. Here, we compare these four orogens in terms of their composition, architecture, tectonic evolution, and metallogenic systems. The four orogens can be divided into simple and composite types. Simple orogens are represented by the Pyrenees and the Alps, and are characterized by narrow linear shapes in plain view and symmetric structures in cross-section, are free of arc magmatism, and are associated with the Mississippi Valley Valley-type Pb-Zn and orogenic gold deposits. The mineral deposits that form in these simple collisional orogens are generally related to processes that occur in the middle and upper crust. In contrast, composite orogens, as exemplified by the Zagros-Iranian and Himalayan-Tibetan Plateaus, are associated with broad orogenic plateaus in plain view and asymmetrical structures in cross-section, record extensive arc magmatism in continental margins, and are associated with a variety of deposit types including carbonatite-related rare earth element (REE), porphyry Cu-Mo, orogenic Au, Mississippi Valley type Pb-Zn, and detachment-fault-related polymetallic deposits. Although the subduction of Neo-Tethys oceanic crust occurred before the creation of simple collisional orogens in the Pyrenees and the Alps, these areas do not show the record of continental arc magmatism. In contrast, the composite collisional orogens are associated with the development of huge continental margin arcs prior to continental subduction, and the subduction was followed by reactivation of the subduction-modified arc lithospheric material, generating the ore-forming systems in these regions. 相似文献
16.
E. Julius Dasch 《Physics of the Earth and Planetary Interiors》1974,9(3):249-258
Under the auspices of the International Decade of Ocean Exploration, scientists from Oregon State University and the Hawaii Institute of Geophysics, along with representatives from the several South American countries which border the Nazca Plate, are intensively studying the origin and economic importance of metalliferous sediments which form extensive deposits on and near the East Pacific Rise. The sediments, enriched in iron, manganese, copper, nickel, zinc, silver, molybdenum, and lead are mineralogically and chemically similar to deposits cored by the “Glomar Challenger”, implying a common origin. The metalliferous sediments are especially abundant in an extensive basin, the Bauer Deep, which occurs about 800 km east of the East Pacific Rise. Elemental and isotopic data, supported by geologic information provided by cores and by geophysical instrumentation, suggest that the enriched elements in the sediments originate by the interplay of volcanism and sea water, by precipitation from sea water alone, and perhaps by the influence of deep-ocean physical processes acting on detritus transported from the continents or from the basaltic East Pacific Rise.An additional objective of the project is to define the possible relationship between marine metalliferous sediments of the plate to ore deposits of the Andean Cordillera. As pointed out by several writers, much of the earth's economic mineralization occurs along zones of convergence between subducted oceanic crust, including metalliferous sediments if present, and continental margins. Field and geochemical techniques are being applied to determine if sediments are in fact subducted beneath the Andean margin, and if they are remobilized into the continental ore deposits of the Andes. Isotopic tracers may prove most useful in testing this relation. Before the model can be tested rigorously, one must know not only the important chemical parameters of the ocean sediment that may be subducted, but also those of the pertinent rock and ore bodies of the South American Cordillera. 相似文献
17.
E.V. Grill R.L. Chase R.D. MacDonald J.W. Murray 《Earth and Planetary Science Letters》1981,52(1):142-150
Crusts composed of nontronite and ferromanganese oxides were recovered from Explorer Ridge, a spreading ridge segment in the northeastern Pacific Ocean located off the west coast of Canada. The chemical and mineralogical composition of the crusts closely resembles that of the mound-like hydrothermal deposits recently discovered at the FAMOUS site on the Mid-Atlantic Ridge and on the Galapagos spreading centre. Compositional anomalies suggest that the crusts are precipitates of hydrothermal vent solutions which were ejected discontinuously and subsequently mixed with seawater. 相似文献
18.
The paper briefly describes the characteristics of the Chilean porphyry copper deposits, emphasizing the volcanic characteristics observed in the youngest ore bodies. Mention is made of the polymetallic ore bodies that are associated with rhyolitic porphyries intruding Jurassic sedimentary formations in the north of Chile, and the similarities and differences between the Chilean porphyry coppers and the Bolivian tin-bearing porphyries are pointed out.The models proposed by Sillitoe (1972), Brousse and Oyarzún (1971), and Mitchell and Garson (1972), are discussed and a new model is proposed agreeing with that of Mitchell and Garson for the genesis of the tin-bearing porphyries (the transportation of Sn as volatile halogenide by F liberated in the Benioff zone), but suggesting different generating mechanism for the porphyry coppers and polymetallic deposits related with porphyries. This mechanism, as a part of the global tectonic model, is based on the separation at depth of hydrogen sulphide from pyrite and water introduced with the upper layers of the lithospheric plate. The ascending migration of H2S to high levels in the crust would be responsible for the porphyry copper mineralization by segregating sulphides of Fe, Cu, Mo and other sulphophile metals contained in the calc-alkaline magmas, brines, or sedimentary-volcanic formations intruded by the porphyries. The excess of H2S would give rise to the formation of sulphur deposits normally present in the volcanic belt situated along the same line but at a higher level than those of the emplacement of porphyry coppers.The generation of copper and tin-bearing porphyries would be a consequence of the upward migration of volatile substances from different depths in the subduction zone, which explain its different emplacement with regards to the continental margins. 相似文献
19.
Liangyi Meng 《中国科学D辑(英文版)》1997,40(3):225-231
The copper deposits in the mid-lower reaches of the Changjiang River consist mainly of porphyry, skarn and massive sulphide
deposits. According to the geological background, the types of ore deposits and the mineralization, the metallogenic model
of the copper deposits is discussed. It is pointed out that the ore-forming hydrothermal fluids came mainly from magmatic
water and were related to the intermediate-acid intrusions, and that the formation of skarn arid massive sulphide deposits
coincided with the mineralization of porphyry deposits.
Project supported by Doctorate Foundation of the State Education Commission of China. 相似文献
20.
The aim of this work is to introduce the application of the fuzzy ordered weighted averaging method as a straightforward knowledge‐driven approach to explore porphyry copper deposits in an airborne prospect. In this paper, the proposed method is applied to airborne geophysical (potassium radiometry, magnetometry, and frequency‐domain electromagnetic) data, geological layers (fault and host rock zones), and various extracted alteration layers from remote sensing images. The central Iranian volcanic–sedimentary belt in Kerman province of Iran that is located within the Urumieh–Dokhtar (Sahand–Bazman) magmatic arc is chosen for this study. This region has high potential of mineral occurrences, especially porphyry copper, containing some active world‐class copper mines such as Sarcheshmeh. Two evidential layers, including the downward continued map and the analytic signal of such filtered magnetic data, are generated to be used as geophysical plausible traces of porphyry copper occurrences. The low values of the resistivity layer acquired from airborne frequency‐domain electromagnetic data are also used as an electrical criterion in this study. Four remote sensing evidential layers, including argillic, phyllic, propylitic, and hydroxyl alterations, are extracted from Advanced Spaceborne Thermal Emission and Reflection Radiometer images in order to map the altered areas associated with porphyry copper deposits. The Enhanced Thematic Mapper plus images are used to map iron oxide layer. Since potassium alteration is the mainstay of copper alteration, the airborne potassium radiometry data are used. Here, the fuzzy ordered weighted averaging method uses a wide range of decision strategies in order to generate numerous mineral potential/prospectivity maps. The final mineral potential map based upon desired geo‐data set indicates adequately matching of high‐potential zones with previous working mines and copper deposits. 相似文献