Variation of Cl and SO3 Contents of Microphenocrystic Apatite in Intermediate to Silicic Igneous Rocks of Cenozoic Japanese Island Arcs: Implications for Porphyry Cu Metallogenesis in the Western Pacific Island Arcs

Abstract. Determinations of SO₃ and Cl contents of igneous accessory apatite were carried out on Late Cenozoic intermediate to silicic intrusive and volcanic rocks in the Japanese island arcs of the western Pacific rim including the southwestern Kuril arc (eastern Hokkaido), Northeast Japan arc (southwestern Hokkaido through northeastern Honshu to central Honshu), Izu‐Bonin arc, Kyushu‐Palau ridge, Southwest Japan arc (northern Kyushu) and northern Ryukyu arc (southern Kyushu). These were compared to those from the Western Luzon arc, Philippines, to better understand the metallogenesis of porphyry Cu deposits in the western Pacific island arcs. In addition, SO₃ and Cl contents of accessory apatite in the Cretaceous magnetite‐series granitic rocks in the Kitakami belt (northeastern Honshu) and the Miocene ilmenite‐series granitic rocks in the Outer Zone of Southwest Japan (southern Kyushu) were also examined. Microphenocrystic apatites in shallow intrusions associated with porphyry Cu deposits in the Western Luzon arc contain >0.1 wt% S as SO₃. Such high SO₃ contents of microphenocrystic apatite are a common characteristic of hydrous mag‐matism in the Western Luzon arc, from 15 Ma old tonalitic plutonic rocks of the Luzon Central Cordillera to present‐day volcanism at Mount Pinatubo. The accessory apatite in intrusive rocks associated with porphyry Cu deposits, especially those at the Santo Tomas II deposit, show significantly high Cl contents (>2 wt%). The SO₃ contents of microphenocrystic apatite in most of the hydrous silicic rocks along the volcanic front, in andesites related to native sulfur deposits, and in Miocene and younger shallow granitic intrusions in northeastern Honshu, are generally <0.1 wt%. On the other hand, the SO₃ contents of apatite in such rocks from eastern Hokkaido, southwestern Hokkaido, Izu, northern Kyushu and southern Kyushu are similar to those from the Western Luzon arc. The SO₃ contents of accessory apatite in the Cretaceous magnetite‐series granitic rocks in the Kitakami belt are variable, whereas those of the Miocene ilmenite‐series granitic rocks in southern Kyushu are extremely low. The Cl contents of accessory apatite in some rocks of the Northeast Japan arc, Izu‐Bonin arc and Southwest Japan arc are significantly high. In terms of the Cl and SO₃ contents of microphenocrystic apatite, Cenozoic Japanese arc magmatism show similarities with arc magmatism associated elsewhere with porphyry Cu mineralization, except for the most of northeastern Honshu of the Northeast Japan arc. Apatite commonly occurs as inclusions in other phenocrystic phases. Thus the variation in SO₃ contents of apatite is a feature of early stage magmatic differentiation. The SO₃ contents of microphenocrystic apatite are considered to reflect the redox state of the magma source region or fluids encountered during magma generation.     

Geochemical Characteristics of Intrusive Rocks, Southeastern Mindanao, Philippines: Implication to Metallogenesis of Porphyry Copper-gold Deposits

This paper describes petrologic and geochemical characteristics of intrusive rocks associated with porphyry copper deposits in south-eastern Mindanao, the Philippines, where the Kingking deposit is located. Intrusive rocks at the Kingking deposit, are classified into biotite-bearing diorite porphyry, hornblende diorite porphyry and diorite porphyry. Intrusive rocks in other areas in south-eastern Mindanao, including Batoto, Bukal, Maragusan, Masara, Amacan and Sumlog, are hornblende diorite porphyry and hornblende quartz diorite. They are adakitic in Sr/Y-Y diagram, but not in La/Yb-Yb diagram due to relatively low REE contents. The magmas are oxidizing as suggested by the high X_Mg of mafic silicate phenocrysts and SO₃ contents of microphenocrystic apatite. An Oligocene-Miocene diorite intrusive complex formed by calc-alkaline, hydrous, oxidizing magma is considered to be associated with porphyry-type copper-gold mineralization.     

斑岩型铜、金、钼矿床成岩成矿特征差异的原因和意义

文中简要总结了斑岩型金矿、铜矿和钼矿在产出的构造环境,岩石地球化学特征和出溶流体的温度、压力、盐度、蚀变等方面的异同点,重点从元素的地球化学性质、岩浆的源区和过程(熔体和流体演化)3个方面解释了上述差异。Au、Cu和Mo在地球化学性质尤其是亲硫性上的差异决定了元素在不同的大地构造环境下的岩浆作用过程中的分布、迁移和富集特征,最终控制了矿床的分布。岩浆的源区及其温压条件、熔体上升过程中矿物的分离结晶和中上地壳岩浆房内的演化程度控制了成矿岩浆的地球化学特征,进而影响其就位时的压力和温度,从而导致出溶流体在p-T-X上的变化。结合岩浆岩中大离子亲石元素和SiO2的含量,可以评估斑岩型矿床的类型：高的Rb含量是斑岩型钼矿的特征,高的Ba含量是斑岩型钼+铜矿的特征,高的Sr含量是斑岩型铜+金矿的特征。相对于俯冲环境,后俯冲环境下的成矿岩体具有更高的大离子亲石元素含量。矿区中酸性岩石的结构(斑状、似斑状、不等粒和等粒结构)可以用来初步指示成矿的潜力。     

Generation and Evolution of Ore Fluids for Porphyry Cu-Au Mineralization of the Santo Tomas II (Philex) Deposit, Philippines

Abstract: The Santo Tomas II (Philex) deposit is a porphyry Cu‐Au deposit, located in the southern part of the Baguio mineral district, Benguet Province, northern Luzon, Philippines. The Santo Tomas II deposit is associated with an intrusive complex consisting of four rock types that are distinguished based on petrography. They are 1) post‐ore clinopyroxene‐bearing hornblende andesite porphyry, 2) ore‐generating hornblende andesite porphyry, 3) hornblende quartz diorite porphyry and 4) porphyritic hornblende quartz diorite. K‐Ar age of hydrothermal biotitization was estimated to be 1.5±0.4 Ma. A number of intrusive bodies having broadly similar petrography and K‐Ar age occur in the vicinity of the Santo Tomas II deposit, such as at Clifton, Ligay (Binang), Bumolo (Waterhole) and Philex Main Camp areas. The intrusions at the Santo Tomas II deposit and in the vicinity are characterized by high X_Mg (Mg/[Mg+Fe] atomic ratio, about 0.7 or higher) of mafic silicate phenocrysts such as hornblende, and high sulfur contents (> 0.2 wt% as SO₃) in accessory microphenocrystic apatite, suggesting a highly oxidizing condition. Sulfur is accommodated dominantly as oxidized species since the crystallization of phe‐nocrysts. Sub‐dendritic rim of tremolitic amphibole on hornblende phenocryst in the ore‐generating andesite porphyry at the Santo Tomas II deposit suggests interaction of magma and aqueous fluid(s) exsolved due to decompression during intrusion. Dissemination of magnetite is associated with hydrothermal biotitization and is followed by sheeted and stockwork quartz veinlets having silician magnetite and rare titanohematite instead of Cu‐Fe sulfides. The silician magnetite‐rich quartz veinlet was formed at f_O2 near the hematite‐magnetite buffer at nearly magmatic temperature, where sulfur dominantly existed as oxidized species such as SO₂. Chalcopyrite and bornite, which commonly exhibit micrographic texture often accompanying Pd telluride and native gold/Au‐rich electrum, are associated with subsequent anhydrite (‐quartz) veinlets and stringers. Both intermediate solid solution (iss) and bornite solid solution (bnss) are thought to have coprecipitated primarily at above 500°C based on fluid inclusion microthermometry and sulfur isotope thermometry applied for anhydrite and associated chal‐copyrite and bornite. The initial iss is considered to have converted to chalcopyrite partly replacing bnss during cooling. The hypersaline polyphase fluid inclusions abundantly found in the sheeted and stockwork quartz as well as anhydrite veinlets with scarce gaseous inclusions suggest that they have been trapped in the two aqueous fluid immiscible region. The western Luzon arc associated with porphyry Cu mineralization is characterized by oxidized hydrous magmatism and shallow emplacement, and by the source of sulfur enriched in ³⁴S.     

Ages and petrogenesis of the late Triassic andesitic rocks at the Luerma porphyry Cu deposit,western Gangdese,and implications for regional metallogeny

The Tibetan Plateau is one of the most significant Cu poly-metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry Cu mineralization. This study investigates a new occurrence of Cu mineralization-related andesitic porphyries in the western domain of the Gangdese magmatic belt and assesses its petrologic, zircon U-Pb geochronology, whole-rock chemistry, and Sr-Nd-Hf-Pb isotope data. Zircon U-Pb dating of three ore-related porphyries yields crystallization ages of 212–211 Ma. These ages are consistent with previous molybdenite Re-Os dating, indicating a late Triassic magmatic and Cu mineralization event in the western Gangdese magmatic belt. Nb, Ta, and Ti depletion, Th and LREE enrichment, and high La/Yb and Th/Yb ratios in addition to high U/Yb ratios from zircons suggest that the magma was generated in an active continental arc setting. The porphyries have radiogenic isotopic compositions with (⁸⁷Sr/⁸⁶Sr)_i 0.70431–0.70473, ε_Nd(t) +1.1 to +3.8, (²⁰⁷Pb^/204Pb)_i 15.601–15.622, and (²⁰⁸Pb/²⁰⁴Pb)_i 38.450–38.693, as well as high positive zircon ε_Hf(t) values from +6.2 to +10.6 (mean value 8.3), corresponding to model ages (T_DM) ranging from 509 Ma to 819 Ma (mean 646 Ma). This suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment-derived melts during the subduction of the Neo-Tethys Ocean. The mineralization-related porphyries contain amphibole and epidote, as well as high whole-rock Fe₂O₃/FeO and zircon Ce⁴⁺/Ce³⁺ ratios, suggesting hydrous and highly oxidized parent magmas. Considering the existing Cu mineralization and highly oxidized magma of the well-preserved Triassic andesitic igneous rocks in the western Gangdese belt, the subduction-related continental arc magma system is favorable for subduction-related porphyry Cu deposits. The existence of Luerma porphyry mineralization demonstrates that there are at least five generations of porphyry Cu-(Mo-Au) mineralization in the Gangdese magmatic belt, which advances the timeframe of porphyry mineralization to the late Triassic.     

The Lamandau IOCG deposit,southwestern Kalimantan Island,Indonesia: Evidence for its formation from geochronology,mineralogy, and petrogenesis of igneous host rocks

The Lamandau region of Kalimantan Island, Indonesia is located in Sandaland, in the southern part of the Kuching tectonic belt. A series of Cenozoic epithermal gold deposits and Fe–Cu–Au deposits are located in the Kuching belt. The Lamandau Fe–Cu–Au deposit is hosted by diorite porphyry. In-situ zircon U–Pb dating of the diorite porphyry shows that it formed between 82.1 ± 1.7 Ma and 78.7 ± 2.3 Ma. Geochemical data indicate a depletion of high field strength elements (HFSE) in the diorite porphyry and related basalt is similar to that of arc-related igneous rocks. The diorite porphyry and basalt were probably derived from typical arc magmas related to continental margin subduction and thus are characterized by light rare earth element (REE) enrichment and HFSE depletion. The sub-chondritic Nb/Ta ratios for the basalt in the Lamandau region indicate that the subducted Pacific slab began partial melting at depths where amphibole was the major residual phase, with some residual rutile. The basalt was derived from a depleted mantle source. The composition of apatite and zircon in the diorite porphyry indicates that the dioritic magma was produced from the subcontinental mantle after it was metasomatized by slab-derived fluids. The magma had a high oxygen fugacity, thus and therefore it was particularly conducive to the precipitation of Cu, Au and other ore-forming elements. The composition of magnetite indicates that it was of volcanic origin. The magnetite has a low REE content, and a high Cu–Au content. The deposit may be classified as an IOCG mineral system. In summary, the ore-related diorite porphyry in the Lamandau region might have formed in an extensional environment during rollback of the subducting western Pacific plate. The convergent velocity between the Philippine Sea and Eurasian plates was at a minimum during the rollback, so that the margin of East Asian began to undergo rifting with associated magmatism.     

云南姚安Au-Pb-Ag矿床含矿富碱岩浆岩地球化学特征及岩石成因

通过锆石U-Pb定年、全岩主微量元素、Sr-Nd-Pb和锆石Hf同位素测试, 对滇西姚安Au-Pb-Ag矿床含矿正长斑岩和粗面岩的地球化学特征进行了分析, 系统探讨了其岩浆起源和演化过程.正长斑岩和粗面岩的锆石U-Pb年龄分别为33.8±0.42 Ma和33.9±0.60 Ma, 它们与同时代滇西镁铁质火山岩和煌斑岩具有相似的稀土和微量元素配分模式和Sr-Nd-Pb同位素组成, 而与区内同时代加厚地壳来源的富碱埃达克质岩石存在Sr-Nd-Pb-Hf同位素组成的明显差异.全岩SiO₂与主微量元素关系指示正长斑岩和粗面岩总体上可由矿区内同时代的基性岩浆岩分异演化而来, 表明它们与这些基性岩浆岩起源相似, 较高的Rb/Sr(≥ 0.1)和较低的Ba/Rb(< 20)比值, 指示其源区为富金云母富集地幔, 较低的εHf和古老的模式年龄暗示源区的交代富集发生在中元古代.姚安富碱岩浆活动与矿化关系密切.正长斑岩和粗面岩较滇西镁铁质火山岩和煌斑岩具有稍高的初始Pb同位素组成, 暗示岩浆可能遭受了地壳混染, 从而提高了母岩浆中的金属含量, 增强了岩浆成矿潜力; 适中的氧逸度利于Au富集; 角闪石分离结晶和较多黑云母发育指示母岩浆含水量较高, 利于成矿流体的形成.这些特征综合起来为矿化发育提供了有利条件.      

秦祁昆结合部瓦勒根金矿床含矿斑岩体岩石学和LA-ICP-MS锆石U-Pb年龄

秦祁昆结合部广泛发育中三叠世岛弧钙碱性岩浆作用,已发现大量与其相关的斑岩型—夕卡岩型铜金、铜钼和银铅锌多金属矿床。瓦勒根金矿床是近年来在该区新发现的一个斑岩型金矿床,矿区内出露有众多的石英斑岩和花岗斑岩,且均发育有金矿化,其中石英斑岩与金矿化关系更为密切。LA-ICP-MS锆石U-Pb年龄表明,花岗斑岩形成于中三叠世(237Ma),其中包含有丰富的晚古生代及元古宙继承性锆石。这一特征与区域上的斑岩型铜金矿床含矿岩体具有相似性。进一步说明,古特提斯洋在秦祁昆结合部发生向北消减所形成的岩浆捕获了早于三叠纪的壳源和幔源物质,从而形成了岛弧钙碱性岩浆及相关的斑岩型—夕卡岩型矿床组合。     

中国大陆环境斑岩型矿床：基本地质特征、岩浆热液系统和成矿概念模型

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.     

Origin of the Miocene porphyries and their mafic microgranular enclaves from Dabu porphyry Cu–Mo deposit,southern Tibet: implications for magma mixing/mingling and mineralization

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.     

Extent of underthrusting of the Indian plate beneath Tibet controlled the distribution of Miocene porphyry Cu–Mo ± Au deposits

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 εNd_i 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 εNd_i 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.     

An attempt to analyze the development of geology as a science

The Eocene (42 to 41 Ma) El Salvador porphyry copper deposit in the Indio Muerto district, northern Chile (26° 15′ S Lat.), formerly thought to have formed at the culmination of a 9-m.y. period of episodic magmatism, is shown by new mapping, U-Pb and K-Ar geochronology, and petrologic data to have formed during the younger of two distinct but superposed magmatic events-a Paleocene (～63 to 58 Ma) and an Eocene (44 to 41 Ma) event. In the district, high-K Paleocene volcano-plutonic activity was characterized by a variety of eruptive styles and magmatic compositions, including a collapse caldera associated with explosive rhyolitic magmatism (El Salvador trapdoor caldera), a post-collapse rhyolite dome field (Cerro Indio Muerto), and andesitic-trachyandesitic stratovolcanos (Kilometro Catorce-Los Amarillos sequence). Pre-caldera basement faults were reactivated during Paleocene volcanism as part of the collapse margin of the caldera. Beneath Cerro Indio Muerto, where the porphyry Cu deposit subsequently formed, the intersection of two major basement faults and the NNE-striking rotational axis of tilted ignimbrites of the Paleocene El Salvador caldera localized emplacement of post-collapse rhyolite domes and peripheral dikes and sills. Subsequent Eocene rhyolitic and granodioritic-dacitic porphyries intruded ~14 m.y. after cessation of Paleocene magmatism along the same NNE-striking structural belt through Cerro Indio Muerto as did the post-collapse Paleocene rhyolite domes. Eocene plutonism over a 3-m.y. period was contemporaneous with NW-SE-directed shortening associated with regional sinistral transpression along the Sierra Castillo fault, lying ～10 km to the east. Older Eocene rhyolitic porphyries in the Indio Muerto district were emplaced between 44 and 43 Ma, and have a small uneconomic Cu center associated with a porphyry at Old Camp. The oldest granodioritic-dacitic porphyries also were emplaced at ～44 to 43 Ma, but their petrogenetic relation to the rhyolitic porphyries and younger granodioritic-dacitic porphyries in the district is unclear. The main porphyry Cu-Mo-related granodioritic-dacitic stocks in Quebrada Turquesa on Cerro Indio Muerto intruded, cooled, and were mineralized within ～1 m.y. between 42 and 41 Ma. Volumetrically minor late- to post-mineral porphyries are slightly more mafic than earlier granodioritic-dacitic porphyries, a compositional trend possibly repeated on several scales and more than once over the 3-million-year Eocene magmatic history of the Indio Muerto district. This compositional trend requires either addition of basaltic material into an open-system silicic magma chamber or tapping of progressively deeper levels of a vertically zoned magma chamber. Eocene porphyry magmas were more hydrous and their residual source mineralogy richer in garnet than the relatively anhydrous Paleocene rocks, whose source was rich in pyroxene. The presence of inherited zircons in Paleocene and Eocene rocks requires interaction with crustal rocks of Paleozoic and/or Proterozoic age.

Paleocene and Eocene igneous rocks in the Indio Muerto district were emplaced during distinct magmatic-tectonic events that are unrelated, although spatially associated. The districtscale Paleocene and Eocene eruptive styles and geochemical and mineralogic characteristics mimic characteristics of similar-aged igneous rocks throughout northern Chile (20°30′ S Lat. to 27° S Lat.), attesting to the regional nature of the Paleocene and Eocene events. Porphyry Cu mineralization in the district furthermore is associated not only with an Eocene granodioriticdacitic (42 to 41 Ma) complex, but also with one of an older Eocene (44 to 43 Ma) rhyolitic porphyry, implying that a long period of precursor magmatism is not required for generation of the El Salvador porphyry Cu-Mo deposit. Rather, the episodic magmatism preceding porphyry Cu mineralization reflects repeated structural localization through time of superimposed highlevel volcano-plutonic complexes in an active magmatic arc.     

Petrogenesis and metallogenic setting of porphyries of the Duobuza porphyry Cu–Au deposit,central Tibet,China

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 ε_Nd(t), and positive ε_Hf(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 ε_Nd(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.     

新疆东天山地区延西铜矿床的地球化学、成矿年代学及其地质意义

延西铜矿床位于新疆东天山觉罗塔格地区北部的哈尔里克-大南湖岛弧带内,是延东-土屋斑岩型成矿带的西延部分。矿床的赋矿地层主要为石炭系企鹅山群,被含矿斜长花岗斑岩侵入。矿床中的主要岩石类型为安山岩、闪长玢岩以及斜长花岗斑岩,安山岩和闪长玢岩具有同源性及岛弧火山岩的特点,是主要的赋矿围岩;斜长花岗斑岩具有埃达克质岩石的特征,与成矿作用直接相关,其形成晚于安山岩、闪长玢岩。本文测得延西铜矿床辉钼矿Re-Os年龄为326.2±4.5Ma,可以代表其成矿年龄,与土屋-延东铜矿床322.7±2.3Ma的辉钼矿Re-Os年龄基本相同;包括延西铜矿床在内的土屋-延东斑岩型铜矿带成矿时代与成岩时代基本一致或稍晚。延西铜矿床具有斑岩型铜矿床的矿化和围岩蚀变特征,与土屋-延东斑岩型铜矿带内其它矿床均为中石炭世同源岩浆演化的产物,具有相似的成矿作用过程,成矿物质均为岩浆来源,这些矿床可能为同一岩浆活动在不同部位发生矿化的产物。延西铜矿床以及土屋-延东斑岩型铜矿带形成于东天山觉罗塔格地区晚古生代的挤压岛弧背景,应与哈尔里克-大南湖晚古生代岛弧的形成相伴,可能与康古尔塔格大洋板块向北部哈尔里克-大南湖岛弧的俯冲有关。     

黄岩海山链俯冲与吕宋岛斑岩铜金成矿

菲律宾吕宋岛上约5Ma以来的斑岩铜金矿床主要集中在北部的Baguio和Mankayan地区,它们在时空上与黄岩海山链密切相关。1907~2013年间的地震数据表明,在吕宋岛中部(16°N)附近存在地震稀疏带。吕宋岛上的斑岩铜金矿床分布在该地震稀疏带的两侧。收集到的相应时期埃达克岩的Sr/Y-(La/Yb)N、Sr/Y-Y和La/Yb-Yb图解表明,这些埃达克岩几乎都是洋壳部分熔融形成的。与吕宋岛北部侵入型埃达克岩相比,位于16°N附近的埃达克岩具有更高的Sr含量,这可能与南海古扩张脊俯冲撕裂形成的板片窗有关。斜长石是辉长岩的主要矿物之一,因此,撕裂的洋壳边缘的辉长岩层部分熔融,形成具有更高Sr含量的埃达克质岩浆。而位于吕宋岛南部Bataan弧中的埃达克质火山岩,可能是在南海古扩张脊俯冲之前形成的。根据已发表的斑岩铜金矿床数据,Mankayan地区的成矿年龄在约3.5~1.4Ma,Baguio地区的成矿年龄在约3.1~0.5Ma之间,有从北向南变年轻的趋势,这与黄岩海山链沿马尼拉海沟向南迁移一致。此外,吕宋岛北部Mt.Cagua到Baguio之间存在一个延伸了220km的第四纪火山活动的空隙,该区域大部分火山已经在中新世停止活动。这可能是黄岩海山链的俯冲使得俯冲倾角逐渐变缓、挤压加强而导致的。同时期的斑岩铜矿床正好分布在这一火山空隙中,是俯冲洋壳部分熔融的产物。     

Geochemical differences between subduction- and collision-related copper-bearing porphyries and implications for metallogenesis

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.     

斑岩铜-钼-金矿床：构造环境、成矿作用与控制因素

斑岩型矿床作为全球Cu、Mo、Au、Re等战略性矿产的主要来源，是国际矿床学界和矿业界长期关注的热点。最新研究表明，斑岩矿床既可以产于俯冲带岩浆弧环境，也可以产于与俯冲无关的非弧环境（主要包括碰撞造山环境、陆内造山环境以及活化克拉通边缘及内部），后者发育于中国大陆。文章在总结全球斑岩矿床时空分布规律的基础上，重点从成矿斑岩成因与成矿动力学机制、成矿金属来源、蚀变-矿化分带等方面，综述了2类斑岩矿床的研究进展，阐释并总结了控制斑岩成矿的主要因素与机制，以及相关研究方法。研究表明，全球斑岩矿床集中产于3大成矿域，形成时代以中、新生代为主。其中，环太平洋成矿域斑岩矿床时空分布不均，集中发育于美洲西海岸，主要形成于白垩纪以来较年轻的几个短暂时期；古亚洲洋成矿域斑岩矿床形成时间跨度于奥陶纪—早白垩世，具有“西Cu-Au东Cu-Mo、早Cu-Au晚Cu-Mo”的成矿特征；特提斯成矿域主要发育三叠纪以来的斑岩矿床，主体沿造山带分布，时间分布不均，同一构造带内发育不同时期的斑岩成矿作用；中国斑岩矿床与3大成矿域既显示出对应性，也有独特性和复杂性。弧环境成矿岩浆、金属Cu(Au)主要来源于交代地幔楔，大...     

新疆东天山多头山铁-铜矿区花岗岩类的年代学、地球化学、岩石成因及意义

多头山矿床是东天山阿奇山?雅满苏成矿带铁铜矿床的典型代表,矿床成因与区内岩浆岩有紧密联系。矿区出露的侵入岩主要有花岗斑岩、二长花岗岩、钾长花岗岩及英安玢岩。LA-ICP-MS锆石U-Pb年代学研究获得花岗斑岩、二长花岗岩及英安玢岩的年龄分别为316.3±8.1 Ma、318.3±3.0 Ma和197.2±3.5 Ma。花岗斑岩A/CNK介于0.82~1.01之间,显示偏铝质特征,为Ⅰ型花岗岩;同时样品富集大离子亲石元素Th、U、Pb,亏损高场强元素Nb、Ta、Ti,显示弧岩浆特征。钠质蚀变导致了花岗斑岩显示出富Na、贫K、Rb、Ca、Sr的特征。钠化花岗斑岩Nb/Ta为12.4~16.0,具有较高的ε_(Nd)(t)(5.76~6.24)值和较低的I_(Sr)值(0.70353~0.70532),与安第斯中生代岩基地球化学特征相似,结合样品中出现古老锆石的捕掳晶,表明其源区为新生的下地壳,混合有少量幔源物质,并伴随有地壳混染。二长花岗岩与钠化花岗斑岩具有相近的形成年龄和相似的地球化学特征,如Nb/Ta比值(14.2),亏损高场强元素、富集大离子亲石元素,同为准铝质(A/CNK=0.97)弧岩浆,暗示它们可能具有相似的源区。而早侏罗世的英安玢岩具有高Sr(552×10~(-6))含量和较高的Sr/Y(73.6)比值,显示出钙碱性埃达克岩的特征,同时样品具有较高的K_2O(3.27%)含量、Mg~#指数(55),表明其来源于拆沉下地壳的熔融并混有少量幔源岩浆。综合区域研究资料、年代学、地球化学及同位素特征,我们认为多头山所在的阿奇山?雅满苏成矿带可能是晚古生代洋壳向南俯冲至中天山地块之下形成的大陆边缘弧。     

Recycling of palaeo-Pacific subducted oceanic crust related to a Fe–Cu–Au mineralization in the Xu-Huai region of North Anhui-Jiangsu,East China: Geochronological and geochemical constraints

ABSTRACT

In this study, Early Cretaceous skarn deposits and genesis of their host diorite/monzodiorite porphyry in the Xuzhou-Huaibei (Xu-Huai) region, northern Anhui-Jiangsu have been discussed by detailed geochemical work. In-situ zircon U–Pb dating of the diorites related to Fe–Cu–Au deposits shows that they were formed between 131.4 ± 1.5 Ma and 130.8 ± 1.8 Ma. Geochemical data indicate a depletion of high field strength elements (HFSE) in the diorite porphyry with similarity to that of arc-related igneous rocks. The diorite porphyry was probably derived from typical arc magmas related to continental margin subduction characterized by light rare earth elements (LREEs) enrichment and HFSE depletion. REEs compositions of apatite in the diorite porphyry indicate that the dioritic magma was produced from the metasomatized subcontinental mantle by slab-derived fluids. The magma was proven to be a high oxygen fugacity; thus, it was particularly conducive to the precipitation of Fe, Cu, Au and other ore-forming elements. The δ³⁴S values of pyrite and chalcopyrite of Fe–Cu–Au ores range from ?0.2‰ to 2.8‰, indicating that the sulphur in the ore was probably derived from deep-seated magmas. Integrated with geochronological and geochemical analyses, we suggest that the Early Cretaceous igneous suites associated with Fe–Cu–Au deposits in the Xu-Huai region are related to recycling subduction of Pacific oceanic crust.     

Contributions of basaltic underplating to crustal growth in island arc and extensional tectonic settings in the Chinese Tianshan Orogenic Belt,NW China

A mafic–ultramafic intrusive belt comprising Silurian arc gabbroic rocks and Early Permian mafic–ultramafic intrusions was recently identified in the western part of the East Tianshan, NW China. This paper discusses the petrogenesis of the mafic–ultramafic rocks in this belt and intends to understand Phanerozoic crust growth through basaltic magmatism occurring in an island arc and intraplate extensional tectonic setting in the Chinese Tianshan Orogenic Belt (CTOB). The Silurian gabbroic rocks comprise troctolite, olivine gabbro, and leucogabbro enclosed by Early Permian diorites. SHRIMP II U-Pb zircon dating yields a 427 ± 7.3 Ma age for the Silurian gabbroic rocks and a 280.9 ± 3.1 Ma age for the surrounding diorite. These gabbroic rocks are direct products of mantle basaltic magmas generated by flux melting of the hydrous mantle wedge over subduction zone during Silurian subduction in the CTOB. The arc signature of the basaltic magmas receives support from incompatible trace elements in olivine gabbro and leucogabbro, which display enrichment in large ion lithophile elements and prominent depletion in Nb and Ta with higher U/Th and lower Ce/Pb and Nb/Ta ratios than MORBs and OIBs. The hydrous nature of the arc magmas are corroborated by the Silurian gabbroic rocks with a cumulate texture comprising hornblende cumulates and extremely calcic plagioclase (An up to 99 mol%). Troctolite is a hybrid rock, and its formation is related to the reaction of the hydrous basaltic magmas with a former arc olivine-diallage matrix which suggests multiple arc basaltic magmatism in the Early Paleozoic. The Early Permian mafic–ultramafic intrusions in this belt comprise ultramafic rocks and evolved hornblende gabbro resulting from differentiation of a basaltic magma underplated in an intraplate extensional tectonic setting, and this model would apply to coeval mafic–ultramafic intrusions in the CTOB. Presence of Silurian gabbroic rocks as well as pervasively distributed arc felsic plutons in the CTOB suggest active crust-mantle magmatism in the Silurian, which has contributed to crustal growth by (1) serving as heat sources that remelted former arc crust to generate arc plutons, (2) addition of a mantle component to the arc plutons by magma mixing, and (3) transport of mantle materials to form new lower or middle crust. Mafic–ultramafic intrusions and their spatiotemporal A-type granites during Early Permian to Triassic intraplate extension are intrusive counterparts of the contemporaneous bimodal volcanic rocks in the CTOB. Basaltic underplating in this temporal interval contributed to crustal growth in a vertical form, including adding mantle materials to lower or middle crust by intracrustal differentiation and remelting Early-Paleozoic formed arc crust in the CTOB.