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1.
Most porphyry Cu deposits in the world occur in magmatic arc settings and are formed in association with calc-alkaline arc magmas related to subduction of oceanic lithosphere. This contribution reviews a number of significant porphyry Cu deposits in the eastern Tethyan metallogenic domain. They widely occur in a variety of non-arc settings, varying from post (late)-collisional transpressional and extensional environments to intracontinental extensional environments related to orogenic and anorogenic processes. Their spatial–temporal localization is controlled by strike–slip faults, orogen-transverse normal faults, lineaments and their intersections in these non-arc settings. These deposits are dominated by porphyry Cu–Mo deposits with minor porphyry Cu–Au and epithermal Au deposits, and exhibit a broad similarity with those in magmatic arcs. The associated magmas are generally hydrous, relatively high fO2, high-K calc-alkaline and shoshonitic, and show geochemical affinity with adakites. They are distinguished from arc magmas and/or oceanic-slab derived adakites, by their occurrence as isolated complexes, high K2O contents (1.2–8.5%), and much wider range of εNd(t) values(? 10 to + 3) and positive εHf(t) values (+ 4.6 to + 6.9). These potassic magmas are most likely formed by partial melting of thickened juvenile mafic lower-crust or delaminated lower crust, but also involving various amounts of asthenospheric mantle components. Key factors that generate hydrous fertile magmas are most likely crust/mantle interaction processes at the base of thickened lower-crust in non-arc settings, rather than oceanic-slab dehydration (as in arc settings). Breakdown of amphibole in thickened lower crust (e.g., amphibole eclogite and garnet amphibolite) during melting is considered to release fluids into the fertile magmas, leading to an elevated oxidation state and higher H2O content necessary for development of porphyry Cu–Mo–Au systems. Copper and Au in hydrous magmas are likely derived from mantle-derived components and/or melts, which either previously underplated and infiltrated at the base of the thickened lower crust, or were input into the primitive magmas by melt/mantle interaction. In contrast, Mo and (part of the) S in the fertile magmas are probably supplied by old crust during melting and subsequent ascent.  相似文献   

2.
大陆碰撞成矿作用:I.冈底斯新生代斑岩成矿系统   总被引：12，自引：3，他引：9  
火山岩浆弧和大陆碰撞带是产出巨型斑岩矿床的两类重要环境.岩浆弧环境的斑岩铜矿成矿理论业已建立,而大陆碰撞环境的斑岩矿床则研究薄弱.在青藏高原,印度-亚洲大陆碰撞导致了大规模斑岩成矿作用,在主碰撞期(65～41 Ma)发育沙让式斑岩Mo矿和亚贵拉式斑岩-矽卡岩型Pb-Zn-Mo矿床,在晚碰撞期(40～26 Ma)形成明则式斑岩Mo矿和努日式斑岩-矽卡岩型Mo-W-Cu矿床,在后碰撞期(25-13Ma)产生驱龙式斑岩Cu-Mo矿床.这些矿床构成了3条规模不等的成矿带,分别发育在冈底斯的北带(中拉萨地体)、南带(泽当弧地体)和中带(南拉萨地体).冈底斯含矿斑岩系统通常为多期多相浅成侵入杂岩体.含矿斑岩以高K为特征,多为高K钙碱性岩和钾玄岩系列.含Cu斑岩以二长花岗斑岩为主,显示埃达克岩地球化学亲和性,含Mo斑岩以花岗斑岩为主,显示大陆壳成因特点.微量元素和Sr Nd Hf同位素地球化学研究表明,含Cu斑岩来自碰撞加厚的西藏镁铁质的新生下地壳(如角闪榴辉岩),早期卷入新生下地壳的幔源物质及硫化物的重熔为斑岩岩浆提供了部分金属Cu、Au和S;含Mo 岩浆来自古老的西藏镁铁质下地壳(如角闪岩)的部分熔融,金属Mo主要来自古老地壳物质的贡献.冈底斯含矿斑岩均含有不同成分的微粒镁铁质包体(MME),并显示典型的长英质与镁铁质岩浆混合特征.以MME为代表的含Cu富H2O幔源岩浆,或底侵于冈底斯地壳底部,为下地壳熔融提供了热和H2O,或注入长英质岩浆房,为斑岩系统提供了部分金属cu和S,并提升了岩浆氧逸度.冈底斯斑岩岩浆热液-成矿系统受控于斑岩就位的地壳环境.在斑岩体侵位的花岗岩基环境,其良好的封闭性导致热液流体(岩浆出溶)以斑岩岩株为核心向外扩散,形成环状蚀变分带,并主要在钾硅酸盐化带发生Cu-Mo矿化;在碎屑岩-碳酸盐建造环境,碳酸盐建造发生矽卡岩化和金属淀积,不透水的细碎屑岩层阻挡热液流体扩散,热液矿化围绕斑岩体发育,形成斑岩型Mo-矽卡岩型Pb-Zn Mo或Mo-W-Cu 成矿系统;在层火山沉积环境,良好的封闭盖层导致岩浆流体与天水强烈混合以及混合流体的长距离侧向流动,发育大面积蚀变岩盖,形成上部浅成低温热液Au Cu和下部斑岩型Cu-Mo成矿系统.结合区域构造岩浆分析,笔者认为,发育于冈底斯碰撞带3个不同碰撞期的幔源岩浆上侵-下地壳部分熔融岩浆浅成侵位-斑岩成矿系统,受控于印度-亚洲大陆三阶段碰撞的不同深部过程,据此提出了大陆碰撞过程中斑岩型矿床的地球动力学模型.  相似文献   

3.
Porphyry Cu (–Mo–Au) deposits occur not only in continental margin–arc settings (subduction-related porphyry Cu deposits, such as those along the eastern Pacific Rim (EPRIM)), but also in continent–continent collisional orogenic belts (collision-related porphyry Cu deposits, such as those in southern Tibet). These Cu-mineralized porphyries, which develop in contrasting tectonic settings, are characterized by some different trace element (e.g., Th, and Y) concentrations and their ratios (e.g., Sr/Y, and La/Yb), suggesting that their source magmas probably developed by different processes. Subduction-related porphyry Cu mineralization on the EPRIM is associated with intermediate to felsic calc-alkaline magmas derived from primitive basaltic magmas that pooled beneath the lower crust and underwent melting, assimilation, storage, and homogenization (MASH), whereas K-enriched collision-related porphyry Cu mineralization was associated with underplating of subduction-modified basaltic materials beneath the lower crust (with subsequent transformation into amphibolites and eclogite amphibolites), and resulted from partial melting of the newly formed thickened lower crust. These different processes led to the collision-related porphyry Cu deposits associated with adakitic magmas enriched by the addition of melts, and the subduction-related porphyry Cu deposits associated with magmas comprising all compositions between normal arc rocks and adakitic rocks, all of which were associated with fluid-dominated enrichment process.In subduction-related Cu porphyry magmas, the oxidation state (fO2), the concentrations of chalcophile metals, and other volatiles (e.g., S and Cl), and the abundance of water were directly controlled by the composition of the primary arc basaltic magma. In contrast, the high Cu concentrations and fO2 values of collision-related Cu porphyry magmas were indirectly derived from subduction modified magmas, and the large amount of water and other volatiles in these magmas were controlled in part by partial melting of amphibolite derived from arc basalts that were underplated beneath the lower crust, and in part by the contribution from the rising potassic and ultrapotassic magmas. Both subduction- and collision-related porphyries are enriched in potassium, and were associated with crustal thickening. Their high K2O contents were primarily as a result of the inheritance of enriched mantle components and/or mixing with contemporaneous ultrapotassic magmas.  相似文献   

4.
侯增谦  杨志明 《地质学报》2009,83(12):1779-1817
中国大陆环境斑岩型矿床包括斑岩型Cu(-Mo、-Au)、斑岩型Mo、斑岩型Au和斑岩型Pb-Zn等矿床类型,主要产出于青藏高原大陆碰撞带、东秦岭大陆碰撞带和中国东中部燕山期陆内环境,在地球动力学背景、深部作用过程、岩浆起源演化、流体与金属来源等方面与岩浆弧环境斑岩型矿床存在重要差异.在大洋板块俯冲形成的岩浆弧,主要发育斑岩Cu-Au矿床或富金斑岩Cu矿(岛弧)和斑岩Cu-Mo及斑岩Mo矿床(陆缘弧).相比,在大陆碰撞带,晚碰撞构造转换环境发育斑岩Cu、Cu-Mo和Cu-Au矿床,矿床受斜交碰撞带的走滑断裂系统控制,后碰撞地壳伸展环境则主要发育斑岩Cu-Mo矿床,矿床受垂直于碰撞带的正断层系统控制;在陆内造山环境,早期发育斑岩Cu-Au矿床,晚期发育斑岩Pb-Zn矿床,它们主要沿古老的但再活化的岩石圈不连续带分布,受网格状断裂系统控制;在后造山(或非造山)伸展环境,则大量发育斑岩Mo矿和斑岩Au矿,它们则主要围绕大陆基底-克拉通(或地块)边缘分布,受再活化的岩石圈不连续带控制.大陆环境斑岩Cu(-Mo,-Au)矿床的含矿斑岩多为高钾钙碱性和钾玄质,以高钾为特征,显示埃达克岩地球化学特性.岩浆通常起源于加厚的新生镁铁质下地壳或拆沉的古老下地壳.上地幔通过三种可能的方式向岩浆系统供给金属Cu(和Au):①提供大批量的幔源岩浆并底垫于加厚下地壳底部,构成含Cu岩浆的源岩;②提供小批量的软流圈熔体交代和改造下地壳,并诱发其熔融;③与拆沉的下地壳岩浆熔体发生反应.大陆环境含Mo岩浆系统高SiO_2、高K_2O,岩相以花岗斑岩为主,花岗闪长斑岩次之,既不同于Climax型,又有别于石英二长斑岩型Mo矿床,岩浆起源于古老的下地壳.金属Mo主要为就地熔出,部分萃取于上部地壳.大陆环境含Pb-Zn花岗斑岩多属铝过饱和型,与S型花岗岩相当,以高δ~(18)O(>10‰)和高放射性Pb为特征,Sr-Nd-Pb同位素组成反映其来源于中下地壳的深熔作用,金属Pb-Zn主要来源于深融的壳层.大陆环境含Au岩浆系统以富B花岗闪长斑岩为主,常与矿前闪长岩密切共生.Sr-Nd-Pb同位素显示,含Au岩浆主要来源于上部地壳,但曾与幔源岩浆发生相互作用.金属Au部分来源于上地壳,部分来源于地幔岩浆.大陆环境斑岩型矿床显示各具特色的蚀变类型和蚀变分带,其中,斑岩型Cu(-Mo,-Au)矿热液蚀变遵循Lowell and Guilbert模式;斑岩型Mo矿主要发育钙硅酸盐化、钾硅酸盐化和石英-绢云母化;斑岩型Pb-Zn矿主要发育绿泥石-绢云母化和绢云母-碳酸盐化,缺乏钾硅酸盐化;斑岩型Au矿强烈发育中度泥化.斑岩型矿床的成矿流体初始为高温、高fO_2、高S、富金属的岩浆水,由浅成侵位的长英质岩浆房在应力松弛环境下出溶而来,晚期有天水不同程度地混入.Cu、Mo、Pb-Zn通常沉淀于流体分相和流体沸腾过程中,而Au则主要沉淀于岩浆-热液过渡阶段.  相似文献   

5.
初论大陆环境斑岩铜矿   总被引：43，自引：1，他引：42  
世界范围内大型-巨型斑岩铜矿多数产于岩浆弧（岛弧、陆缘弧）环境,含矿斑岩岩浆起源与大洋板块的俯冲作用有关。综合研究了与大洋板块俯冲无关、产于中国大陆环境的若干大型-巨型斑岩铜矿。研究发现,这些大陆环境的斑岩铜矿,虽然其基本地质特征与岩浆弧环境斑岩铜矿具有广泛的类似性,但其动力学背景、含矿斑岩性质、岩浆起源演化、金属富集过程及其构造控制机制却独具特色。这些大陆环境斑岩铜矿至少可产出于4类环境：晚碰撞走滑环境、后碰撞伸展环境、后造山伸展环境和非造山崩塌环境。大陆环境含矿斑岩以高钾质为特征,多具高钾钙碱性和钾玄质特征,通常显示埃达克岩地球化学亲和性。其岩浆通常起源于加厚的新生镁铁质下地壳或拆沉的古老下地壳。陆间碰撞期的地壳大规模增厚以及其后的软流圈上涌和岩石圈拆沉,是形成含矿岩浆的主导性机制。含矿岩浆的金属初始富集通常经历两阶段过程：（1）幔源物质直接供给金属阶段;（2）伴随含水、高氧逸度埃达克质岩浆演化金属富集阶段。在第一阶段,幔源物质主要通过两种形式供给金属：（1）以幔源组分为主的新生下地壳直接熔融;（2）拆沉下地壳熔融产生的埃达克质熔体与地幔岩石圈发生水/岩反应。在第二富集阶段,下地壳角闪榴辉岩熔融过程中角闪石大量分解产生富水的、高度氧化的埃达克质熔体,其分异演化使金属元素作为不相容元素得以在残浆中富集。大陆环境含矿斑岩的浅成侵位主要受大规模走滑断裂系统、切割造山带的断裂系统和基底线性断裂构造控制。与走滑断裂系统相伴发育的走滑拉分盆地、切割造山带的张性断裂与平行造山带的逆冲断裂带交汇部位以及不同方向的线性断裂构成的棋盘格子构造,常常控制斑岩岩浆-热液系统的空间定位。  相似文献   

6.
作为贱金属主要来源的斑岩铜矿床，大多数产出于大陆边缘和岛弧环境。普遍认为，被俯冲洋壳板片释放流体交代的地幔楔部分熔融形成的玄武质岩浆，在相对封闭系统结晶分异和／或同化混染形成含铜长英质岩浆。然而，我们的研究表明，在西藏碰撞造山带，发育一条具有巨大成矿潜力的中新世斑岩铜矿带，含铜斑岩具有埃达克岩地球化学特性，来源于被加厚的藏南镁铁质下地壳，但俯冲的新特提斯洋壳板片部分熔融也不能完全被排除。斑岩铜矿形成于陆-陆后碰撞伸展时期(13～18Ma)，即青藏高原迅速抬升之后。横切碰撞造山带的南北向正断层系统，类似于岛弧环境下的横切弧的断层系统，成为埃达克质斑岩岩浆快速上升和就位的通道与场所，并使岩浆热液系统中大量的含矿流体充分地分离而成矿。  相似文献   

7.
Miocene igneous rocks in the 1,600 km-long E–W Gangdese belt of southern Tibet form two groups separated at longitude ～89° E. The eastern group is characterized by mainly intermediate–felsic calc-alkaline plutons with relatively high Sr/Y ratios (23 to 342), low (87Sr/86Sr)i ratios (0.705 to 0.708), and high εNdi values (+5.5 to ?6.1). In contrast, the western group is characterized by mainly potassic to ultrapotassic volcanic rocks with relatively high Th and K2O contents, low Sr/Y ratios (11 to 163), high (87Sr/86Sr)i ratios (0.707 to 0.740), and low εNdi values (?4.1 to ?17.5). The eastern plutonic group is associated with several large porphyry Cu–Mo ± Au deposits, whereas the western group is largely barren. We propose that the sharp longitudinal distinction between magmatism and metallogenic potential in the Miocene Gangdese belt reflects the breakoff of the Greater India slab and the extent of underthrusting by the Indian continental lithosphere at that time. Magmas to the east of ～89° E were derived by partial melting of subduction-modified Tibetan lithosphere (mostly lower crust) triggered by heating of hot asthenospheric melt following slab breakoff. These magmas remobilized metals and volatile residual in the crustal roots from prior arc magmatism and generated porphyry Cu–Mo ± Au deposits upon emplacement in the upper crust. In contrast, magmas to the west of ～89° E were formed by smaller volume partial melting of Tibetan lithospheric mantle metasomatized by fluids and melts released from the underthrust Indian plate. They are less hydrous and oxidized and did not have the capacity to transport significant amounts of metals into the upper crust.  相似文献   

8.
This paper reviews the tectonic, magmatic, and metallogenic history of the Tethyan orogen from the Carpathians to Indochina. Focus is placed on the formation of porphyry Cu ± Mo ± Au deposits, as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region. Relatively little is known about the history of the Paleotethys ocean, which opened and closed between Gondwana and Eurasia in the Paleozoic, and few ore deposits are preserved from this period. The Neotethyan ocean opened in the Permian–Early Triassic as the Cimmerian continental fragments (the cores of Turkey, Iran, Tibet, and Indochina) rifted from the northern Gondwana margin and drifted northwards. These microcontinents docked with the Eurasian margin at various points in the Mesozoic and Cenozoic, and formed a complex archipelago involving several small back-arc basins and remnants of the Paleotethyan ocean. The main Neotethyan ocean and these smaller basins were largely eliminated by collision with India and Africa–Arabia in the early Eocene and early-mid Miocene, respectively, although Neotethyan subduction continues beneath the Hellenic arc and the Makran.The majority of porphyry-type deposits are found in association with Neotethyan subduction (mainly in the Mesozoic and Paleogene), and syn- to post-collisional events in the mid-Paleogene to Neogene. They are found throughout the orogen, but some sections are particularly well-endowed, including the Carpathians–Balkans–Rhodopes, eastern Turkey–Lesser Caucasus–NW Iran, SE Iran–SW Pakistan, southern Tibet, and SE Tibet–Indochina. Other sections that appear barren may reflect deeper levels of erosion, young sedimentary cover, or lack of exploration, although there may also be real reasons for low prospectivity in some areas, such as minimal subduction (e.g., the western Mediterranean region) or lithospheric underthrusting (as proposed in western Tibet).Over the last decade, improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction-related are in fact broadly collision-related, some forming in back-arc settings in advance of collision, some during collision, and others during post-collisional processes such as orogenic collapse and/or delamination of subcontinental mantle lithosphere. While the formation of subduction-related porphyries is quite well understood, collisional metallogeny is more complex, and may involve a number of different processes or sources. These include melting of: orogenically thickened crust; previously subduction-modified lithosphere (including metasomatized mantle, underplated mafic rocks, or lower crustal arc plutons and cumulates); or upwelling asthenosphere (e.g., in response to delamination, slab breakoff, back-arc extension, or orogenic collapse).The most fertile sources for syn- and post-collisional porphyry deposits appear to be subduction-modified lithosphere, because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events, and retain the oxidized and relatively metalliferous character of the original arc magmatism. Unusually metallically enriched lithospheric sources do not seem to be required, but the amount of residual sulfide phases in these rocks may control metal ratios (e.g., Cu:Au) in subsequent magmatic hydrothermal ore deposits. Relatively Au-rich deposits potentially form in these settings, as observed in the Carpathians (e.g., Roşia Montană), Turkey (Kisladag, Çöpler), and Iran (Sari Gunay, Dalli), although the majority of syn- and post-collisional porphyries are Cu–Mo-rich, and resemble normal subduction-related deposits (e.g., in the Gangdese belt of southern Tibet). This similarity extends to the associated igneous rocks, which, being derived from subduction-modified sources, largely retain the geochemical and isotopic character of those original arc magmas. While still retaining a broadly calc-alkaline character, these rocks may extend to mildly alkaline (shoshonitic) compositions, and may display adakite-like trace element signatures (high Sr/Y and La/Yb ratios) reflecting melting of deep crustal garnet amphibolitic sources. But they are otherwise hard to distinguish from normal subduction-related magmas.Small, post-collisional mafic, alkaline volcanic centers are common throughout the orogen, but for the most part appear to be barren. However, similar rocks in other post-subduction settings around the world are associated with important alkalic-type porphyry and epithermal Au ± Cu deposits, and the potential for discovery of such deposits in the Tethyan orogen should not be overlooked.  相似文献   

9.
The Shakhtama Mo–Cu porphyry deposit is located within the eastern segment of the Central Asian Orogenic Belt, bordering the southern margin of the Mongol–Okhotsk suture zone. The deposit includes rocks of two magmatic complexes: the precursor plutonic (J2) and ore-bearing porphyry (J3) complexes. The plutonic complex was emplaced at the final stages of the collisional regime in the region; the formation of the porphyry complex may have overlapped with a transition to extension. The Shakhtama rocks are predominantly metaluminous, I-type high K calc-alkaline to shoshonitic in composition, with relatively high Mg#, Ni, Cr and V. They are characterized by crustal-like ISr (0.70741–0.70782), relatively radiogenic Pb isotopic compositions, εNd(T) values close to CHUR (−2.7 to +2.1) and Nd model ages from 0.8 to 1.2 Ga. Both complexes are composed of rocks with K-adakitic features and rocks without adakite trace element signatures. The regional geological setting together with geochemical and isotopic data indicate that both juvenile and old continental crust contributed to their origin. High-Mg# K-adakitic Shakhtama magmas were most likely generated by partial melting of thickened lower crust during delamination and interaction with mantle material, while magmas lacking adakite-like signatures were probably generated at shallower levels of lower crust. The derivation of melts, related to the formation of plutonic and porphyry complexes involved variable amounts of old Precambrian lower crust and juvenile Phanerozoic crust. Isotopic data imply stronger contribution of juvenile mantle-derived material to the fertile magmas of the porphyry complex. Juvenile crust is proposed as an important source of fluids and metals for the Shakhtama ore-magmatic system.  相似文献   

10.
斑岩Cu-Mo-Au矿床:新认识与新进展   总被引：59，自引：0，他引：59  
侯增谦 《地学前缘》2004,11(1):131-144
斑岩型矿床作为一种最重要的铜钼和铜金矿床类型一直得到人们的普遍重视 ,近些年来又取得了重要研究进展 ,主要体现在 5个方面 :①岛弧和陆缘弧是斑岩型矿床产出的重要环境 ,但大陆碰撞造山带也具有产出斑岩型矿床的巨大潜力。按矿床产出的构造环境 ,可以分为弧造山型斑岩矿床和碰撞造山型斑岩矿床 ;②弧造山型含矿斑岩主要为钙碱性和高钾钙碱性 ,而碰撞造山型含矿斑岩则主要为高钾钙碱性和橄榄安粗质 (shoshonitic)。两种环境的含矿斑岩多具有埃达克岩 (adakite)岩浆亲合性 ,但前者主要来源于俯冲的大洋板片 ,后者主要来源于碰撞加厚的下地壳。大洋板片的部分熔融缘于俯冲角度的平缓化 ,而加厚下地壳的熔融起因于俯冲大陆板片的断离 (slabbreakoff) ;③在弧造山环境 ,大洋俯冲板片的膝折 (kink)或撕裂 (slabtear)不仅导致俯冲角度变缓 ,而且引起弧地壳耦合变形 ,产生切弧断裂 ,控制斑岩铜系统的时空分布。俯冲板片撕裂引发软流圈上涌 ,诱发大洋板片熔融 ,产生含矿岩浆 ;④在碰撞造山环境 ,大陆俯冲板片的裂离导致软流圈上涌 ,向下地壳注入新生物质 ,并诱发下地壳物质熔融 ,产生含矿岩浆。碰撞后地壳伸展形成横切碰撞带的正断层系统 ,为斑岩侵位提供运移通道 ,并导致岩浆流体大量分凝和铜钼金淀积。不论  相似文献   

11.
The origin of magmas that are linked to economic mineralization in porphyry deposits formed in continental collisional belts is controversial. In this paper, we studied the mafic microgranular enclaves (MMEs) and their host monzogranite porphyries (HMPs) from the Dabu porphyry Cu–Mo deposit in southern Tibet. Zircon SHRIMP U–Pb ages indicate coeval formation for the MMEs and HMPs in middle Miocene time (~15 Ma). The MMEs have high Mg# (50.7–60.8), low SiO2 (53.2–62.5 wt.%), and high Cr (95–175 ppm) contents, with positive εHf(t) values ranging from +3.4 to +9.4. These results, along with the presence of phlogopite, suggest that the MMEs were most likely generated by partial melting of a metasomatic lithospheric mantle source region. The HMPs have high Sr/Y (88.2–135.7), La/Yb (25.0–31.9) ratios, and moderate Mg# (46.2–49.3) values. They have the same εHf(t) values (+3.3 to +7.7) with arc-like Palaeogene rocks. The HMPs also show typical arc magma characteristics such as enrichment in LILEs (e.g. Rb, Ba, Sr, and K) and depletion in HFSEs (e.g. Nb, Ta, Ti, Zr, and P). These results suggest a possible origin involving high-pressure remelting of thickened lower crustal arc cumulates related to earlier Neo-Tethyan subduction. The lower crustal arc cumulates dominated by garnet-bearing amphibolite facies could be the potential copper sources of the Dabu porphyry Cu–Mo deposit. Underplating of the mantle-derived mafic magmas could have provided heat input for melting of the hydrous lower crust. Reaction between the mafic and felsic magmas might have further increased Cu concentrations and contributed to subsequent mineralization.  相似文献   

12.
Understanding the geochemical behavior of chalcophile elements in magmatic processes is hindered by the limited partition coefficients between sulfide phases and silicate melt, in particular at conditions relevant to partial melting of the hydrated, metasomatized upper mantle. In this study, the partitioning of elements Co, Ni, Cu, Zn, As, Mo, Ag, and Pb between sulfide liquid, monosulfide solid solution (MSS), and hydrous mantle melt has been investigated at 1200 °C/1.5 GPa and oxygen fugacity ranging from FMQ−2 to FMQ+1 in a piston-cylinder apparatus. The determined partition coefficients between sulfide liquid and hydrous mantle melt are: 750–1500 for Cu; 600–1200 for Ni; 35–42 for Co; 35–53 for Pb; and 1–2 for Zn, As, and Mo. The partition coefficients between MSS and hydrous mantle melt are: 380–500 for Cu; 520–750 for Ni; ∼50 for Co; <0.5 for Zn; 0.3–6 for Pb; 0.1–2 for As; 1–2 for Mo; and >34 for Ag. The variation of the data is primarily due to differences in oxygen fugacity. These partitioning data in conjunction with previous data are applied to partial melting of the upper mantle and the formation of magmatic-hydrothermal Cu–Au deposits and magmatic sulfide deposits.I show that the metasomatized arc mantle may no longer contain sulfide after >10–14% melt extraction but is still capable of producing the Cu concentrations in the primitive arc basalts, and that the comparable Cu concentrations in primitive arc basalts and in MORB do not necessarily imply similar oxidation states in their source regions.Previous models proposed for producing Cu- and/or Au-rich magmas have been reassessed, with the conclusions summarized as follows. (1) Partial melting of the oxidized (fO2 > FMQ), metasomatized arc mantle with sulfide exhaustion at degrees >10–14% may not generate Cu-rich, primitive arc basalts. (2) Partial melting of sulfide-bearing cumulates in the root of thickened lower continental crust or lithospheric mantle does not typically generate Cu- and/or Au-rich magmas, but they do have equivalent potential as normal arc magmas in forming magmatic-hydrothermal Cu–Au deposits in terms of their Cu–Au contents. (3) It is not clear whether partial melting of subducting metabasalts generates Cu-rich adakitic magmas, however adakitic magmas may extract Cu and Au via interaction with mantle peridotite. Furthermore, partial melting of sulfide-bearing cumulates in the deep oceanic crust may be able to generate Cu- and Au-rich magmas. (4) The stabilization of MSS during partial melting may explain the genetic link between Au-Cu mineralization and the metasomatized lithospheric mantle.The chalcophile element tonnage, ratio, and distribution in magmatic sulfide deposits depend on a series of factors. This study reveals that oxygen fugacity also plays an important role in controlling Cu and Ni tonnage and Cu/Ni ratio in magmatic sulfide deposits. Cobalt, Zn, As, Sn, Sb, Mo, Ag, Pb, and Bi concentrations and their ratios in sulfide, due to their different partitioning behavior between sulfide liquid and MSS, can be useful indices for the distribution of platinum-group elements and Au in magmatic sulfide deposits.  相似文献   

13.
江南造山带东段燕山晚期含钨的东源岩体与非含钨的旌德岩体、桃岭岩体,其地球化学特征具有埃达克质岩的亲缘性,是先前(新元古代)交代的岩石圈地幔发生部分熔融底侵到壳幔过渡带附近,导致加厚下地壳发生部分熔融的产物,可能与少量的幔源岩浆发生岩浆混合作用。含矿岩体与非含矿岩体存在不同的Sr-Nd同位素组成,表明含矿与非含矿岩体具有不同的源区。锆石LA-ICPMS定年显示含矿的东源岩体侵位时间147 Ma,非含矿岩体侵位时间140 Ma。含矿岩体的副矿物组合以独居石+辉钼矿+白钨矿+白钨矿+电气石为特征。岩体中富含成矿元素、富挥发分、富钾,黑云母中富F、低Fe和fO2,斜长石以钠长石为主,均可作为含矿花岗(斑)岩体的重要地球化学参数。  相似文献   

14.
Given that the Duobuza deposit was the first porphyry Cu–Au deposit discovered in central Tibet, the mineralization and mineralized porphyry in this area have been the focus of intensive research, yet the overall porphyry sequence associated with the deposit remains poorly understood. New geological mapping, logging, and sampling of an early granodiorite porphyry, an inter-mineralization porphyry, and a late-mineralization diorite porphyry were complemented by LA–ICP–MS zircon dating, whole-rock geochemical and Sr–Nd isotopic analyses, and in situ Hf isotopic analyses for both inter- and late-mineralization porphyry intrusions. All of the porphyry intrusions are high-K and calc-alkaline, and were emplaced at ca. 120 Ma. The geochemistry of these intrusions is indicative of arc magmatism, as all three porphyry phases are enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. These similar characteristics of the intrusions, when combined with the relatively high (87Sr/86Sr)i, negative εNd(t), and positive εHf(t) values, suggest that the magmas that formed the porphyries were derived from a common source region and shared a single magma chamber. The magmas were generated by the mixing of upwelling metasomatized mantle-wedge-derived mafic magmas and magmas generated by partial melting of amphibolite within the lower crust.The inter-mineralization porphyry has the lowest εNd(t) and highest (87Sr/86Sr)i values, suggesting that a large amount of lower-crust-derived material was incorporated into the melt and that metals such as Cu and Au from the enriched lower crust were scavenged by the parental magma. The relative mafic late-mineralization diorite porphyry phase was formed by the residual magma in the magma chamber mixing with upwelling mafic melt derived from metasomatized mantle. The magmatic–hydrothermal evolution of the magma in the chamber released ore-forming fluid that was transported mainly by the inter-mineralization porphyry phase during the mineralization stage, which ultimately formed the Duobuza porphyry Cu–Au deposit.These porphyritic intrusions of the Duobuza deposit have high Mg# and low (La/Yb)N values, and show some high LILE/HFSE ratios, indicating the magma source was enriched by interaction with slab-derived fluids. Combined with age constraints on the regional tectonic evolution, these dating and geochemical results suggest that the Duobuza porphyry Cu–Au deposit formed in a subduction setting during the final stages of the northward subduction of the Neo-Tethyan Ocean.  相似文献   

15.
The Miocene porphyry Cu–(Mo) deposits in the Gangdese orogenic belt in southern Tibet were formed in a post-subduction collisional setting. They are closely related to the Miocene adakite-like porphyries which were probably derived from a thickened basaltic lower crust. Furthermore, mantle components have been considered to have played a crucial role in formation of these porphyry deposits (Hou et al. Ore Geol Rev 36: 25–51, 2009; Miner Deposita doi:10.1007/s00126-012-0415-6, 2012). In this study, we present zircon Hf isotopes and molybdenite Re–Os ages on the newly discovered Gangjiang porphyry Cu–Mo deposit in southern Tibet to constrain the magma source of the intrusions and the timing of mineralization. The Gangjiang porphyry Cu–Mo deposit is located in the Nimu ore field in the central Gangdese porphyry deposits belt, southern Tibet. The copper and molybdenum mineralization occur mainly as disseminations and veins in the overlapped part of the potassic and phyllic alteration zones, and are predominantly hosted in the quartz monzonite stock and in contact with the rhyodacite porphyry stock. SIMS zircon U–Pb dating of the pre-mineral quartz monzonite stock and late intra-mineral rhyodacite porphyry yielded ages of 14.73?±?0.13 Ma (2σ) and 12.01?±?0.29 Ma (2σ), respectively. These results indicate that the magmatism could have lasted as long as about 2.7 Ma for the Gangjiang deposit. The newly obtained Re–Os model ages vary from 12.51?±?0.19 Ma (2σ) to 12.85?±?0.18 Ma (2σ) for four molybdenite samples. These Re–Os ages are roughly coincident with the rhyodacite porphyry U–Pb zircon age, and indicate a relatively short-lived episode of ore deposition (ca. 0.3 Ma). In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS indicate that the ε Hf(t) values of zircons from a quartz monzonite sample vary from +2.25 to +4.57 with an average of +3.33, while zircons from a rhyodacite porphyry sample vary from +5.53 to +7.81 with an average of +6.64. The Hf data indicate that mantle components could be partly involved in the deposit formation, and that mantle contributions might have increased over time from ca. 14.7 to 12.0 Ma. Combined with previous works, it is proposed that the Gangjiang deposit could have resulted from the convective thinning of the lithospheric root, and the input of upper mantle components into the magma could have played a key role in the formation of the porphyry deposits in the Miocene Gangdese porphyry copper belt in the Tibetan Orogen.  相似文献   

16.
We investigate the geology of Altar North (Cu–Au) and Quebrada de la Mina (Au) porphyry deposits located in San Juan Province (Argentina), close to the large Altar porphyry copper deposit (995 Mt, 0.35% Cu, 0.083 g/t Au), to present constraints on the magmatic processes that occurred in the parental magma chambers of these magmatic-hydrothermal systems. Altar North deposit comprises a plagioclase-amphibole-phyric dacite intrusion (Altar North barren porphyry) and a plagioclase-amphibole-biotite-phyric dacite stock (Altar North mineralized porphyry, 11.98 ± 0.19 Ma). In Quebrada de la Mina, a plagioclase-amphibole-biotite-quartz-phyric dacite stock (QDM porphyry, 11.91 ± 0.33 Ma) crops out. High Sr/Y ratios (92–142) and amphibole compositions of Altar North barren and QDM porphyries reflect high magmatic oxidation states (fO2 = NNO +1.1 to +1.6) and high fH2O conditions in their magmas. Zones and rims enriched in anorthite (An37–48), SrO (0.22–0.33 wt.%) and FeO (0.21–0.37 wt.%) in plagioclase phenocrysts are evidences of magmatic recharge processes in the magma chambers. Altar North and Quebrada de la Mina intrusions have relatively homogeneous isotopic compositions (87Sr/86Sr(t) = 0.70450–0.70466, εNd(t) = +0.2 to +1.2) consistent with mixed mantle and crust contributions in their magmas. Higher Pb isotopes ratios (207Pb/204Pb = 15.6276–15.6294) of these intrusions compared to other porphyries of the district, reflect an increase in the assimilation of high radiogenic Pb components in the magmas. Ages of zircon xenocrysts (297, 210, 204, 69 Ma) revealed that the magmas have experienced assimilation of Miocene, Cretaceous, Triassic and Carboniferous crustal rocks.Fluids that precipitated sulfides in the Altar deposit may have remobilized Pb from the host rocks, as indicated by the ore minerals being more radiogenic (207Pb/204Pb = 15.6243–15.6269) than their host intrusions. Au/Cu ratio in Altar porphyries (average Au/Cu ratio of 0.14 × 10?4 by weight in Altar Central) is higher than in the giant Miocene porphyry deposits located to the south: Los Pelambres, Río Blanco and Los Bronces (Chile) and Pachón (Argentina). We suggest that the increase in Au content in the porphyries of this region could be linked to the assimilation of high radiogenic Pb components in the magmas within these long-lived maturation systems.  相似文献   

17.
初论陆-陆碰撞与成矿作用——以青藏高原造山带为例   总被引：54，自引：9，他引：45  
青藏高原碰撞造山带以其成矿规模大、形成时代新、矿床类型多、保存条件好诸特征而被誉为研究大陆成矿作用的天然实验室。文章基于青藏高原已有的矿产勘查与研究成果,概述了大陆碰撞过程中的主要成矿作用及其成矿带的时空分布,初步分析了陆一陆碰撞所造就的成矿背景和成矿环境以及控制成矿作用的关键地质过程．并草拟了可供今后研究的工作模型。初步研究认为,始于60Ma的印度大陆与亚洲大陆碰撞至少形成了3个重要的控矿构造单元,即雅鲁藏布江以北的主碰撞变形带,雅鲁藏布江以南的藏南拆离-逆冲带和高原东缘的藏东构造转换带。主碰撞变形带以巨大规模的地壳缩短、双倍地壳加厚、大规模逆冲系和SN向正断层系统发育为特征,控制了冈底斯斑岩铜矿带(含浅成低温热液金矿)、安多锑矿化带和风火山铜矿化带及腾冲锡矿带的形成及分布;藏南拆离一逆冲带由藏南拆离系(STDS6)和一系列北倾的叠瓦状逆冲断裂带构成,控制了藏南变质核杂岩型金矿化、热液脉型金锑矿化和蚀变破碎带型金锑矿化的形成;藏东构造转换带以发育大规模走滑断裂系统、大型剪切带、富碱斑岩带和走滑拉分盆地为特征,控制了玉龙斑岩铜矿带、哀牢山和锦屏山金矿带及兰坪盆地银多金属矿带的分布。按成矿系统的基本思想,初步将青藏高原碰撞造山带的成矿作用划分为3个成矿巨系统：大陆俯冲碰撞成矿巨系统、陆内走滑一剪切成矿巨系统和碰撞后伸展成矿巨系统。在大陆俯冲碰撞阶段,主要发育与流体迁移汇聚和排泄有关的锑金铜热液成矿系统和碰撞期花岗岩岩浆．流体锡稀有金属成矿系统;伴随陆．陆碰撞而发生的陆内走滑．剪切作用,主要导致了走滑拉分盆地银多金属热液成矿系统、斑岩型铜钼金成矿系统和剪切带型金成矿系统的形成;在碰撞后伸展阶段,主要发育受SN向正断层系统控制的斑岩铜矿成矿系统、浅成低温热液金矿成矿系统和热水沉积铯锂硼金属成矿系统。在此基础上,初步提出了碰撞造山带成矿作用的构造控制模型。  相似文献   

18.
The Duolong porphyry Cu–Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au) was recently discovered in the southern Qiangtang terrane, central Tibet. Here, new whole‐rock elemental and Sr–Nd–Pb isotope and zircon Hf isotopic data of syn‐ and post‐ore volcanic rocks and barren and ore‐bearing granodiorite porphyries are presented for a reconstruction of magmas associated with Cu–Au mineralization. LA–ICP–MS zircon U–Pb dating yields mean ages of 117.0 ± 2.0 and 120.9 ± 1.7 Ma for ore‐bearing granodiorite porphyry and 105.2 ± 1.3 Ma for post‐ore basaltic andesite. All the samples show high‐K calc‐alkaline compositions, with enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE: Cs and Rb) and depletion of high field strength elements (HFSE: Nb and Ti), consistent with the geochemical characteristics of arc‐type magmas. Syn‐ and post‐ore volcanic rocks show initial Sr ratios of 0.7045–0.7055, εNd(t) values of −0.8 to 3.6, (206Pb/204Pb)t ratios of 18.408–18.642, (207Pb/204Pb)t of 15.584–15.672 and positive zircon εHf(t) values of 1.3–10.5, likely suggesting they dominantly were derived from metasomatized mantle wedge and contaminated by southern Qiangtang crust. Compared to mafic volcanic rocks, barren and ore‐bearing granodiorite porphyries have relatively high initial Sr isotopic ratios (0.7054–0.7072), low εNd(t) values (−1.7 to −4.0), similar Pb and enriched zircon Hf isotopic compositions [εHf(t) of 1.5–9.7], possibly suggesting more contribution from southern Qiangtang crust. Duolong volcanic rocks and granodiorite porphyries likely formed in a continental arc setting during northward subduction of the Bangong–Nujiang ocean and evolved at the base of the lower crust by MASH (melting, assimilation, storage and homogenization) processes. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
中国斑岩铜矿与埃达克(质)岩关系探讨   总被引：16，自引：2，他引：14  
对比研究了中国26个主要斑岩铜矿的地球化学特征和年代学,结果表明其中25个矿床与埃达克(质)岩有成因联系,且多数与玄武质下地壳熔融形成的埃达克岩(C型)有关,现有数据表明土屋-延东和普朗斑岩铜矿可能与俯冲板片熔融形成的埃达克岩(O型)有关。容矿斑岩的初始锶值为0.7034～0.7090,均大于洋中脊玄武岩和亏损地幔的初始锶值,多数与EMI的初始锶值接近,推测其源区或源岩主要为玄武质下地壳,少数为洋中脊玄武岩,并受到中、上地壳不同程度的混染,这与两类埃达克岩的源区基本一致。虽然埃达克质岩浆具有形成斑岩铜矿的巨大潜力,但并非所有埃达克岩都能成矿,不同岩体需具体分析。  相似文献   

20.
The Dexing porphyry Cu–Mo–Au deposit in east China (1,168 Mt at 0.45 % Cu) is located in the interior of the South China Craton (SCC), made up of two lithospheric blocks, the Yangtze and Cathaysia blocks. The Cu–Mo–Au mineralization is associated with mid-Jurassic granodioritic porphyries with three high-level intrusive centers, controlled by a series of lineaments at the southeastern edge of the Yangtze block. Available age data define a short duration (172–170 Ma) of the felsic magmatism and the mineralization (171?±?1 Ma). The deposit shows broad similarities with deposits in volcanoplutonic arcs, although it was formed in an intracontinental setting. Porphyries associated with mineralization are mainly granodiorites, which contain abundant phenocrysts (40–60 %) and carry contemporaneous microgranular mafic enclaves (MMEs). They are mainly high-K calc-alkaline and show geochemical affinities with adakite, characterized by relatively high MgO, Cr, Ni, Th, and Th/Ce ratios. The least-altered porphyries yielded relatively uniform ε Nd(t) values from ?0.9 to +0.6, and wide (87Sr/86Sr)i range between 0.7046 and 0.7058 partially overlapping with the Sr–Nd isotopic compositions of the MMEs and mid-Jurassic mafic rocks in the SCC. Zircons from the porphyries have positive ε Hf(t) values (3.4 to 6.9), and low δ18O values (4.7 to 6.3?‰), generally close to those of depleted mantle. All data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components (e.g., Neoproterozoic mafic arc magmas), triggered by invasion of contemporaneous mafic melts at Dexing. The MMEs show textural, mineralogical, and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas. These MMEs usually contain magmatic chalcopyrite, and have original, variable contents of Cu (up to 500 ppm). Their geochemical characteristics suggest that they were derived from an enriched mantle source, metasomatized by Proterozoic slab-derived fluids, and supplied a part of Cu, Au, and S for the Dexing porphyry system during their injection into the felsic magmas. The 171?±?1 Ma magmatic-hydrothermal event at Dexing is contemporaneous with the mid-Jurassic extension in the SCC, followed by 160–90 Ma arc-like magmatism in southeastern China. With respect to the tectono-magmatic evolution of the SCC, the emplacement of Cu-bearing porphyries and the associated Cu mineralization occurred in response to the transformation from a tensional regime, related to mid-Jurassic extension, to a transpressional regime, related to the subduction of the Paleo-Pacific oceanic lithosphere.  相似文献   

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