Crystallisation conditions (T, P, fO2) from mineral chemistry of Cu- and Au-mineralised alkaline intrusions in the Red River–Jinshajiang alkaline igneous belt, western Yunnan Province, China

The Oligocene Yao’an syenite porphyry, associated with gold mineralisation, and the Machangqing alkali granite porphyry–monzonite porphyry, associated with Cu mineralisation, belong to the Red River–Jinshajiang alkaline igneous belt that formed in a continental setting in southwestern China. A study of the mineral chemistry of major silicate minerals in these two mineralised intrusions provides insights into their overall crystallisation conditions. The temperature and pressure conditions, derived from amphibole–plagioclase and perthite–plagioclase geothermometry and Al-in-amphibole barometry, suggest that the Yao’an intrusion crystallised at around 820?±?50°C and 0.9–1.3 kbar, whereas the Machangqing intrusion crystallised at around 730?±?50°C and 2.2–2.8 kbar. The higher temperature and lower pressure of crystallisation for the Yao’an intrusion relative to the Machangqing intrusion indicates that it was emplaced at a shallower crustal level. Based on biotite composition, the two intrusions formed under imposed oxygen fugacities above the Ni–NiO buffer (NNO), and the Yao’an intrusion crystallised under more oxidising conditions than the Machangqing intrusion. The results show that the intrusions associated with Cu–Au mineralisation in the Red River–Jinshajiang alkaline igneous belt were emplaced at a relatively high fO₂, which, together with the weakly fractionated magma, favoured Au enrichment relative to Cu in the belt.     

Control of magmatic oxidation state in intracontinental porphyry mineralization: A case from Cu (Mo–Au) deposits in the Jinshajiang–Red River metallogenic belt,SW China

The Jinshajiang–Red River porphyry Cu (Mo–Au) metallogenic belt (JRMB) is the most important intracontinental porphyry Cu (Mo–Au) mineralizing zone in the Sanjiang region, southwest China. The belt contains a number of giant deposits, including Yulong (6.50 Mt Cu) and Beiya (315 t Au) in the northern and center parts, and several small deposits in the southern part (e.g., Tongchang, 0.03 Mt Cu + Mo; Chang'anchong, 0.04 Mt Cu + Mo; Habo, 0.57 Mt Cu + Mo; and Chang'an 31 t Au). In order to investigate the mechanisms controlling the variation in size of these deposits, the LA-ICP-MS zircon U–Pb dating, bulk-rock geochemistry, and zircon trace-element analyses have been performed on the mineralization-related porphyries from the Tongchang district. Zircon U–Pb dating yielded concordant ages of 34.2 ± 0.6 Ma (Tongchang), 33.7 ± 0.8 Ma (Chang’anchong), 35.7 ± 0.5 Ma (Habo) and 34.6 ± 1.2 Ma (Chang’an). These porphyries are peraluminous with relatively high potassium contents (K₂O: 4.2–5.7 wt%), and show shoshonitic affinities. Bulk rock Fe₂O₃/FeO ratios vary from 0.51 to 0.97, typical of moderately oxidized to strongly oxidized magmas. Zircon Ce⁴⁺/Ce³⁺ values vary between 25.9 and 371.8 with a mean of 129.3. The log(ƒo₂) values vary from −20.7 to −9.6, and plot within the range of FMQ (fayalite-magnetite-quartz oxygen buffer) to MH (magnetite- hematite oxygen buffer), indicating an oxidizing parental magma. The mineralized porphyries from the Yulong and Beiya deposits, which were previous considered to have formed under the same tectonic conditions as those in the Tongchang district, have higher mean zircon Ce⁴⁺/Ce³⁺ values of 249.4 and 399.5, suggesting that the oxygen fugacities of the porphyries in the Tongchang district is relatively lower. This might imply that oxygen fugacity is an important factor that led to the differentiation of deposit size in the JRMB, and that larger porphyry deposits are associated with more oxidized magmas.     

SHRIMP U–Pb and Ar–Ar geochronology of major porphyry and skarn Cu deposits in the Balkhash Metallogenic Belt,Central Asia,and geological implications

The Balkhash Metallogenic Belt (BMB) in Kazakhstan, Central Asia, with the occurrence of the super-large Kounrad and Aktogai, the large Borly porphyry Cu–Mo deposits, and the large Sayak skarn polymetallic ore-field, is one of the central regions of the Paleozoic Central Asian metallogenic domain and orogenic belt. In this study, newly obtained SHRIMP zircon U–Pb ages of nine samples and ⁴⁰Ar/³⁹Ar ages of six mineral samples (inclding hornblende, biotite and K-feldspar) give more detailed constraints on the timing of the granitic intrusions and their metallogeny. Porphyritic monzonite granite and tonalite porphyry from the Kounrad deposit yield U–Pb zircon SHRIMP ages of 327.3 ± 2.1 Ma and 308.7 ± 2.2 Ma, respectively. Quartz diorite and porphyritic granodiorite from the Aktogai deposit yield U–Pb SHRIMP ages of 335.7 ± 1.3 Ma and 327.5 ± 1.9 Ma, respectively. Porphyritic granodiorite and granodiorite from the Borly deposit yield U–Pb SHRIMP ages of 316.3 ± 0.8 Ma and 305 ± 3 Ma, respectively. Diorite, granodiorite, and monzonite from the Sayak ore-field yield U–Pb SHRIMP ages of 335 ± 2 Ma, 308 ± 10 Ma, and 297 ± 3 Ma, respectively. Hornblende, biotite, and K-feldspar from the Aktogai deposit yield ⁴⁰Ar/³⁹Ar cooling ages of 310.6 Ma, 271.5 Ma, and 274.9 Ma, respectively. Hornblende, biotite, and K-feldspar from the Sayak ore-field yield ⁴⁰Ar/³⁹Ar cooling ages of 287.3 ± 2.8 Ma, 307.9 ± 1.8 Ma, and 249.8 ± 1.6 Ma, respectively. The new ages constrain the timing of Late Paleozoic felsic magmatism to ∼336 to ∼297 Ma. Skarn mineralization in the Sayak ore-field formed at ∼335 and ∼308 Ma. Porphyry Cu–Mo mineralization in the Kounrad deposit and the Aktogai deposit formed at ∼327 Ma, and in the Borly deposit at ∼316 Ma. The Late Paleozoic regional cooling in the temperature range of ∼600 °C to ∼150 °C occurred from ∼307 to ∼257 Ma.     

Re–Os geochronology of Cu and W–Mo deposits in the Balkhash metallogenic belt, Kazakhstan and its geological significance

The Central Asian metallogenic domain (CAMD) is a multi-core metallogenic system controlled by boundary strike-slip fault systems. The Balkhash metallogenic belt in Kazakhstan, in which occur many large and super-large porphyritic Cu–Mo deposits and some quartz vein- and greisen-type W–Mo deposits, is a well-known porphyritic Cu–Mo metallogenic belt in the CAMD. In this paper 11 molybdenite samples from the western segment of the Balkhash metallogenic belt are selected for Re–Os compositional analyses and Re–Os isotopic dating. Molybdenites from the Borly porphyry Cu deposit and the three quartz vein-greisen W–Mo deposits—East Kounrad, Akshatau and Zhanet—all have relatively high Re contents (2712–2772 μg/g for Borly and 2.267–31.50 μg/g for the other three W–Mo deposits), and lower common Os contents (0.670–2.696 ng/g for Borly and 0.0051–0.056 ng/g for the other three). The molybdenites from the Borly porphyry Cu–Mo deposit and the East Kounrad, Zhanet, and Akshatau quartz vein- and greisen-type W–Mo deposits give average model Re–Os ages of 315.9 Ma, 298.0 Ma, 295.0 Ma, and 289.3 Ma respectively. Meanwhile, molybdenites from the East Kounrad, Zhanet, and Akshatau W–Mo deposits give a Re–Os isochron age of 297.9 Ma, with an MSWD value of 0.97. Re–Os dating of the molybdenites indicates that Cu–W–Mo metallogenesis in the western Balkhash metallogenic belt occurred during Late Carboniferous to Early Permian (315.9–289.3 Ma), while the porphyry Cu–Mo deposits formed at 316 Ma, and the quartz vein-greisen W–Mo deposits formed at 298 Ma. The Re–Os model and isochron ages thus suggest that Late Carboniferous porphyry granitoid and pegmatite magmatism took place during the late Hercynian movement. Compared to the Junggar-East Tianshan porphyry Cu metallogenic belt in northwestern China, the formation of the Cu–Mo metallogenesis in the Balkhash metallogenic belt occurred between that of the Tuwu-Yandong in East Tianshan and the Baogutu porphyry Cu deposits in West Junggar. Collectively, the large-scale Late Carboniferous porphyry Cu–Mo metallogenesis in the Central Asian metallogenic domain is related to Hercynian tectono-magmatic activities.     

Evolution of magmatic-hydrothermal system of the Kalaxiange’er porphyry copper belt and implications for ore formation (Xinjiang,China)

The Kalaxiange’er porphyry copper ore belt is situated in the eastern part of the southern Altai of the Central Asian Orogenic Belt and forms part of a broad zone of Cu porphyry mineralization in southern Mongolia, which includes the Oyu Tolgoi ore district and other copper–gold deposits. The copper ore bodies are spatially associated with porphyry intrusions of granodiorite, quartz diorite, quartz syenite, and quartz monzonite and have a polygenetic (polychromous) origin (magmatic porphyry, hydrothermal, and supergene). The mineralized porphyries are characterized by almost identical REE and trace element patterns. The Zr/Hf and Nb/Ta ratios are similar to those of normal granite produced through the evolution of mantle magma. The low initial Sr isotope ratio I_Sr, varying within a narrow range of values (0.703790–0.704218), corresponds to that of primitive mantle, whereas the εNd(T) value of porphyry varies from 5.8 to 8.4 and is similar to that of MORB. These data testify to the upper-mantle genesis of the parental magmas of ore-bearing porphyry, which were then contaminated with crustal material in an island-arc environment. The isotopic composition of sulfur (unimodal distribution of δ34S with peak values of − 2 to − 4‰) evidences its deep magmatic origin; the few lower negative δ³⁴S values suggest that part of S was extracted from volcanic deposits later. The isotopic characteristics of Pb testify to its mixed crust–upper-mantle origin. According to SHRIMP U–Pb geochronological data for zircon from granite porphyry and granodiorite porphyry, mineralization at the Xiletekehalasu porphyry Cu deposit formed in two stages: (1) Hercynian “porphyry” stage (375.2 ± 8.7 Ma), expressed as the formation of porphyry with disseminated and vein–disseminated mineralization, and (2) Indosinian stage (217.9 ± 4.2 Ma), expressed as superposed hydrothermal mineralization. The Re–Os isotope data on molybdenite (376.9 ± 2.2 Ma) are the most consistent with the age of primary mineralization at the Xiletekehalasu porphyry Cu deposit, whereas the Ar–Ar isotopic age (230 ± 5 Ma) of K-feldspar–quartz vein corresponds to the stage of hydrothermal mineralization. The results show that mineralization at the Xiletekehalasu porphyry Cu deposit was a multistage process which resulted in the superposition of the Indosinian hydrothermal mineralization on the Hercynian porphyry Cu mineralization.     

Relationships between porphyry Cu–Mo mineralization in the Jinshajiang–Red River metallogenic belt and tectonic activity: Constraints from zircon U–Pb and molybdenite Re–Os geochronology

The Jinshajiang–Red River porphyry Cu–Mo metallogenic belt is an important Cenozoic porphyry Cu–Mo mineralization concentrating zone in the eastern Indo‐Asian collision zone. New zircon U–Pb and molybdenite Re–Os ages and compilation of previously published ages indicate that porphyry Cu–Mo deposits in the belt did not form at the same time, i.e., the porphyry emplacement and relevant Cu–Mo mineralization ages of the Ailaoshan–Red River ore belt in south range from 36.3 Ma to 34.6 Ma, and from 36.0 Ma to 33.9 Ma, respectively, which are obviously younger than the porphyry emplacement ages of 43.8–36.9 Ma and the relevant Cu–Mo mineralization ages of 41.6–35.8 Ma of the Yulong ore belt in north. Tectonic studies indicated that the Jinshajiang fault system in north and Ailaoshan–Red River fault system in south of the Jinsjiang–Red river belt had different strike-slip patterns and ages. The right-lateral strike-slip motion of the Jinshajiang fault system initiated at ca. 43 Ma with corresponding formation of the Yulong porphyry Cu–Mo system, whereas the left-lateral strike-slip motion of the Ailaoshan–Red River fault system initiated at ca. 36 Ma with corresponding formation of the Ailaoshan–Red River porphyry Cu–Mo system. Therefore, the different ages of porphyry Cu–Mo systems, between in north and south of the Jinshajiang–Red River belt, indicate that the porphyry Cu–Mo mineralization is closely related to the divergent strike-slip movements between the Jinshajiang and Ailaoshan–Red River strike-slip faulting resulted from the Indo‐Asian collision. The tanslithospheric Jinshajiang–Red River faulting caused partial melting of the enriched mantle sources of alkali-rich porphyries by depressurization or/and asthenospheric heating, and facilitated the migration of alkali-rich magmas and the corresponding formation of alkali-rich porphyries and relevant Cu–Mo deposits in the belt.     

Petrogenesis of ore-bearing porphyry of a porphyry Cu deposit at Mujicun in the North China Craton and its geological implicationsSCIEI北大核心CSCD

国内外学者对发育于弧环境和碰撞造山环境的斑岩铜矿成岩机制已取得了深刻的理解,但对产出在克拉通内部的斑岩铜矿成岩机制在认识上还有所欠缺。本文报道了侵位于144Ma木吉村斑岩铜矿内的含矿闪长玢岩的岩石地球化学资料,以揭示木吉村斑岩铜矿的含矿斑岩成因。岩石地球化学资料显示:含矿闪长玢岩具有较低的(^(87)Sr/^(86)Sr)i值(0.70599~70690)和εNd(t)值(-19.4~-14.9),富集轻稀土元素(LREEs)和大离子亲石元素(LILEs),相对亏损元素Y和Yb。木吉村含矿斑岩与王安镇杂岩体镁铁质岩(辉石岩、角闪石岩、辉长岩、辉长闪长岩、安山岩)具有相似的微量元素配分模式、Sr-Nd同位素组成及亲EMⅠ地幔特征,这些岩浆岩呈现持续性的成份演化趋势,反映出它们的同源性。木吉村含矿斑岩及相关的镁铁质岩石具有相对较低的(^(87)Sr/^(86)Sr)i值(0.70564~706897)和εNd(t)值(-19.4~-13.8),显著区别于中上地壳同位素区域。含矿斑岩起源于伸展背景下富集地幔部分熔融形成的玄武质岩浆,其上升过程中遭受了一定程度的下地壳混染。玄武质岩浆在深部岩浆房发生堆晶作用形成具典型堆晶结构的角闪石岩等基性岩,随后在浅部岩浆房经历两阶段辉长岩-辉长闪长岩、安山岩-闪长玢岩系列分离结晶作用形成含矿斑岩。此过程可能是形成华北克拉通木吉村斑岩铜矿含矿斑岩的机制和动力诱因。     

Ni–Cu–(PGE) magmatic sulfide deposits in the Yangliuping area,Permian Emeishan igneous province,SW China

The Ni–Cu–PGE sulfide deposits in the Yangliuping area, SW China, are hosted in mafic–ultramafic sills. The four mineralized sills are located in the Yangliuping tectonic dome and intrude Devonian carbonaceous marble, graphitic schist. The sills are 200–300 m thick and 1,000–2,000 m in strike length and now consist chiefly of serpentinite, talc schist, tremolite schist, and meta-gabbro. Disseminated Ni–Cu sulfide mineralisation occurs in the serpentinite in the lower parts of the sills. Massive sulfide mineralisation is located in the base of the sills and in the footwall along fractures beneath the mineralized serpentinite. Although the sulfide ores have been modified by hydrothermal activity, there are relict cumulate textures in the disseminated sulfides indicating a magmatic origin for the ores. The Yangliuping Intrusions and the Dashibao Formation have similar primitive-mantle normalized trace element and platinum group element (PGE) patterns, indicating that they are derived from a common parental magma type. The positive correlation between Cu concentrations and Cu/Zr ratios of the Dashibao Formation basalts indicates that the chalcophile elements were removed before eruption. We propose that fractional crystallization of the Yangliuping magma accompanied by the introduction of S and CO₂ from the wall rocks caused the magma to become S-saturated leading to the segregation of magmatic sulfides that became enriched in Ni–Cu–(PGE). The sills acted as conduits for the overlying Dashibao Formation basalts with the sulfide liquid, along with early crystallizing olivine and pyroxene, segregating from the magma as it passed through the conduits prior to eruption.Editorial handling: H.E. Frimmel     

Geochemical constraints on Cu–Fe and Fe skarn deposits in the Edong district,Middle–Lower Yangtze River metallogenic belt,China

Copper and iron skarn deposits are economically important types of skarn deposits throughout the world, especially in China, but the differences between Cu and Fe skarn deposits are poorly constrained. The Edong ore district in southeastern Hubei Province, Middle–Lower Yangtze River metallogenic belt, China, contains numerous Fe and Cu–Fe skarn deposits. In this contribution, variations in skarn mineralogy, mineralization-related intrusions and sulfur isotope values between these Cu–Fe and Fe skarn deposits are discussed.The garnets and pyroxenes of the Cu–Fe and Fe skarn deposits in the Edong ore district share similar compositions, i.e., dominantly andradite (Ad_29–100Gr_0–68) and diopside (Di_54–100Hd_0–38), respectively. This feature indicates that the mineral compositions of skarn silicate mineral assemblages were not the critical controlling factors for variations between the Cu–Fe and Fe skarn deposits. Intrusions associated with skarn Fe deposits in the Edong ore district differ from those Cu–Fe skarn deposits in petrology, geochemistry and Sr–Nd isotope. Intrusions associated with Fe deposits have large variations in their (La/Yb)_N ratios (3.84–24.6) and Eu anomalies (δEu = 0.32–1.65), and have relatively low Sr/Y ratios (4.2–44.0) and high Yb contents (1.20–11.8 ppm), as well as radiogenic Sr–Nd isotopes (εNd(t) = − 12.5 to − 9.2) and (⁸⁷Sr/⁸⁶Sr)_i = 0.7067 to 0.7086. In contrast, intrusions associated with Cu–Fe deposits are characterized by relatively high Sr/Y (35.0–81.3) and (La/Yb)_N (15.0–31.6) ratios, low Yb contents (1.00–1.62 ppm) without obvious Eu anomalies (δEu = 0.67–0.97), as well as (⁸⁷Sr/⁸⁶Sr)_i = 0.7055 to 0.7068 and εNd(t) = − 7.9 to − 3.4. Geochemical evidence indicates a greater contribution from the crust in intrusions associated with Fe skarn deposits than in intrusions associated with Cu–Fe skarn deposits. In the Edong ore district, the sulfides and sulfates in the Cu–Fe skarn deposits have sulfur isotope signatures that differ from those of Fe skarn deposits. The Cu–Fe skarn deposits have a narrow range of δ³⁴S values from − 6.2‰ to + 8.7‰ in sulfides, and + 13.2‰ to + 15.2‰ in anhydrite, while the Fe skarn deposits have a wide range of δ³⁴S values from + 10.3‰ to + 20.0‰ in pyrite and + 18.9‰ to + 30.8‰ in anhydrite. Sulfur isotope data for anhydrite and sedimentary country rocks suggest that the formation of skarns in the Edong district involved the interaction between magmatic fluids and variable amounts of evaporites in host rocks.     

Water geochemistry and boron isotope in the Xijiang River,SW China

During the last decade boron isotopic compositions have been successfully used as a geochemical tracer in oceanic paleo-pH reconstruction and paleo-climatologic studies. All the pH-proxy investigations were based on the assumption that the boron concentra…     

Mineral chemistry and H–O–S–Pb isotopic compositions of skarn type copper deposits in the Jiurui district of the Middle-Lower Yangtze River metallogenic belt,Eastern China

The skarn type copper deposits are widespread in the Jiurui district in the Middle-Lower Yangtze River metallogenic belt. This paper reports a detailed study on mineral chemistry, and H, O, S and Pb isotopic compositions on skarn silicate and sulfide minerals in the three major skarn dominant deposits (Wushan, Dongleiwan and Dengjiashan). The Wushan skarn deposit is characterized with prograde garnet-dominated and clinopyroxene limited skarns with average andradite content of 83% and hedenbergite content of 10%, whereas the Dongleiwan and Dengjiashan deposits are featured with retrograde skarn alteration with abundant hydrous minerals such as epidote and chlorite. The garnet and clinopyroxene compositions show 59% andradite and 15% hedenbergite for the Dongleiwan skarns, and 43% and 22% for the Dengjiashan skarns respectively. The pistacite components (Ps value) defined as Fe^3 +/(Fe^3 ++ Al) and Fe^3 +/Fe^2 + value of epidote are 0.12 and 1.63 for the Wushan skarns, 0.30 and 32.73 for the Dongleiwan skarns, and 0.17 and 42.85 for the Dengjiashan skarns. It is suggested that the prograde skarn mineralization in the three deposits was all formed in a relatively oxidizing environment, with the Wushan showing the highest oxidation potential and the Dengjiashan having the least oxidation potential. However, in the retrograde skarns, the Dongleiwan and Dengjiashan deposits show higher oxidation potential than that of Wushan. The three deposits show similar sulfur isotopic compositions of − 2.9 to + 1.4‰ and similar lead isotopic compositions with ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of 17.900 to 18.205, 15.538 to 15.649 and 38.170 to 39.025, respectively. All the three deposits should have similar magmatic origin for the ore-forming materials based on their S and Pb isotopes. The oxygen isotopic compositions of the prograde and retrograde fluids in the three deposits show some differences, with δ¹⁸O_Fluid values of + 8.13‰ and + 7.81‰ for the Wushan, + 6.47‰ and + 2.33‰ for the Dongleiwan, and + 8.27‰ and + 4.43‰ for the Dengjiashan. But the hydrogen isotopic compositions are similar for the prograde (− 65 to − 31‰) and retrograde (− 64 to − 33‰) fluids. Therefore, the fluid origins and evolution may be different in each deposit. The hydrothermal fluids for the prograde skarns in all three deposits were likely derived from magmatic–hydrothermal sources, but the Dongleiwan and Dengjiashan show a higher proportion of meteoric water input in the retrograde stage. Considering the similar average prograde temperatures (574 to 560 °C) as calculated from coexisting garnet–clinopyroxene pairs, and similar retrograde temperatures (281 to 246 °C) as calculated from chlorite chemistry for the three deposits, we suggest that the trigger for deposition of sulfide ores in the Wushan garnet-dominated skarn deposit was mainly caused by system cooling with temperature drop along with magmatic intrusion and crystallization process. The Dongleiwan and Dengjiashan skarn deposits constitute a well developed retrograde skarn system with abundant epidote, chlorite, quartz and calcite, which probably caused by fluid mixing of high-temperature saline magmatic–hydrothermal fluids with cooler, oxidizing and dilute meteoric water.     

Geochronology and geochemistry of the Wunugetushan porphyry Cu–Mo deposit in NE china,and their geological significance

The Wunugetushan porphyry Cu–Mo deposit is located in the Manzhouli district of NE China, on the southern margin of the Mesozoic Mongol–Okhotsk Orogenic Belt. Concentric rings of hydrothermal alteration and Cu–Mo mineralization surround an Early–Middle Jurassic monzogranitic porphyry. The Cu–Mo mineralization is clearly related to the quartz–potassic and quartz–sericite alteration. Molybdenite Re–Os and groundmass ⁴⁰Ar/³⁹Ar of the host porphyry dates indicate that the ore-formation and porphyry-emplacement occurred at 177.6 ± 4.5 Ma and 179.0 ± 1.9 Ma, respectively. Geochemically, the host porphyry of the deposit is characterized by strong LREE/HREE fractionation, enrichment in LILE, Ba, Rb, U, Th and Pb, and depletion of HFSE, Nb, Ta, Ti and HREE. The Sr–Nd–Pb isotopic compositions of the porphyry display an varied initial (⁸⁷Sr/⁸⁶Sr)_i ratio, a positive ε_Nd(t) values and high ²⁰⁶Pb/²⁰⁴Pb_t, ²⁰⁷Pb/²⁰⁴Pb_t and ²⁰⁸Pb/²⁰⁴Pb_t ratios. These data indicate that the magmatic source of the host porphyry comprised two end-members: lithospheric mantle metasomatized by fluids derived from the subducted slab; and continental crust. We infer that the primitive magma of the host porphyry was derived from crust–mantle transition zone. Based on regional geology and geochemistry of the host porphyry, the Wunugetushan deposit is suggested to form in a continental collision environment after closure of the Mongol–Okhotsk Ocean.     

Geochronology,geochemistry, and mineralization of the granodiorite porphyry hosting the Matou Cu–Mo (±W) deposit,Lower Yangtze River metallogenic belt,eastern China

Porphyry and skarn Cu–Fe–Au–Mo deposits are widespread in the Middle and Lower Yangtze River metallogenic belt (MLYMB), eastern China. The Matou deposit has long been regarded as a typical Cu–Mo porphyry deposit within Lower Yangtze part of the belt. Recently, we identified scheelite and wolframite in quartz veins in the Matou deposit, which is uncommon in other porphyry and skarn deposits in the MLYMB. We carried out detailed zircon U–Pb dating and geochemical and Sr–Nd–Hf isotopic studies of the granodiorite porphyry at Matou to define any differences from other ore-related granitoids. The porphyry shows a SiO₂ content ranging from 61.85 wt.% to 65.74 wt.%, K₂O from 1.99 wt.% to 3.74 wt.%, and MgO from 1.74 wt.% to 2.19 wt.% (Mg^# value ranging from 45 to 55). It is enriched in light rare earth elements and large ion lithophile elements, but relatively depleted in Nb, Ta, Y, Yb and compatible trace elements (such as Cr, Ni, and V), with slight negative Eu anomalies (Eu/Eu^* = 0.88–0.98) and almost no negative Sr anomalies. Results of electron microprobe analysis of rock-forming silicate minerals indicate that the Matou porphyry has been altered by an oxidized fluid that is rich in Mg, Cl, and K. The samples show relatively low ε_Nd(t) values from −7.4 to −7.1, slightly high initial ⁸⁷Sr/⁸⁶Sr values from 0.708223 to 0.709088, and low ε_Hf(t) values of zircon from −9.0 to −6.5, when compared with the other Cu–Mo porphyry deposits in the MLYMB. Zircon U–Pb dating suggests the Matou granodiorite porphyry was emplaced at 139.5 ± 1.5 Ma (MSWD = 1.8, n = 15), which is within the age range of the other porphyries in the MLYMB. Although geochemical characteristics of the Matou and other porphyries in the MLYMB are similar and all adakitic, the detrital zircons in the samples from Matou suggest that Archean lower crust (2543 ± 29 Ma, MSWD = 0.25, n = 5) was involved with the generation of Matou magma, which is different from the other porphyries in the belt. Our study suggests that the Matou granodiorite porphyry originated from partial melting of thickened lower crust that was delaminated into the mantle, similar to the other porphyries in the MLYMB, but it has a higher proportion of lower crustal material, including Archean rocks, which contributed to the formation of the porphyry and related W-rich magmatic-hydrothermal system.     

Platinum-group elemental chemistry of the Baima and Taihe Fe–Ti oxide bearing gabbroic intrusions of the Emeishan large igneous province,SW China

Nickel-, copper-, and platinum group element (PGE)-enriched sulphide mineralization in large igneous provinces has attracted numerous PGE studies. However, the distribution and behavior of PGEs as well as the history of sulphide saturation are less clear in oxide-dominated mineralization. Platinum group elements of oxide-bearing layered mafic intrusions from the Emeishan large igneous province are examined in this study. Samples collected from the Baima and Taihe oxide-bearing layered gabbroic intrusions reveal contrasting results. The samples from Baima gabbroic rocks have low total PGE abundances (ΣPGE < 4 ppb) whereas the Taihe gabbroic rocks, on average, have more than double the concentration but are variable ranging from ΣPGE < 2 ppb to ΣPGE ∼300 ppb. The Baima gabbro is platinum-subgroup PGE (PPGE = Rh, Pt and Pd) enriched and iridium-subgroup PGE (IPGE = Os, Ir and Ru) depleted, with a distinct positive Ru anomaly on a primitive mantle normalized multi-element plot. The Taihe gabbros are also PPGE enriched but with negative Ru and Pd anomalies on a primitive mantle normalized multi-element plot. The PGE concentrations of Baima rocks are indicative of fractionation of a relatively evolved, mafic, S-undersaturated parental magma that was affected by earlier sulphide segregation. In contrast, the Taihe rocks record evidence of both S-saturated and S-undersaturated conditions and that the parental magma was likely emplaced very close to S-saturation. Comparisons of the platinum group element contents in the Emeishan flood basalts and the Emeishan oxide-bearing intrusions suggest that the PGE budget in a magma is not controlled by magma series (high-Ti vs. low-Ti), but very much by crustal contamination. The unlikelihood of substantial crustal contamination in the Taihe magma allowed the magma to remain S-undersaturated for a longer duration. PGE and sulphide mineralization was not identified in the Taihe intrusion but the presence of one PGE-enriched sample (Pt + Pd = ∼300 ppb) suggests that the parental magma likely did not experience sulphide segregation and is a potential target for further prospecting.     

Genesis of Luobuzhen Pb–Zn veins: Implications for porphyry Cu systems and exploration targeting at Luobuzhen-Dongshibu in western Gangdese belt,southern Tibet

Porphyry systems are known to form in magmatic arc environment and commonly include porphyry Cu, epithermal Pb–Zn–Au–Ag, skarn polymetallic mineralization, etc. The systems are rarely reported in collisional zones, such as the Gangdese belt in southern Tibet where many postcollisional porphyry copper deposits occurred. In addition, other types of mineral systems are rarely present except porphyry copper mineralization in the Gangdese belt. In this study, we present Pb–Zn-bearing quartz veins at Luobuzhen in the western Gangdese belt. The Luobuzhen Pb–Zn veins cross-cut dacite of the Linzizong Group with zircon U–Pb age of 50.1 ± 0.2 Ma and monzogranite with zircon U–Pb age of 17.1 ± 0.1 Ma. Ore minerals include sphalerite, galena, chalcopyrite, and pyrite; gangue minerals are quartz with minor chlorite and sericite. Primary fluid inclusions of quartz are liquid-rich, aqueous, and two-phase inclusions. The homogenization temperatures of these primary inclusions are moderate to high (267–400 °C), and salinities range from 8.9 to 18.4 wt.% NaCl equiv. Quartz has δ¹⁸O_SMOW values of 6.2–9.3‰, while sulfides have δ³⁴S_V-CDT values of −5.1‰ to 0.1‰, ²⁰⁶Pb/²⁰⁴Pb of 18.722–18.849, ²⁰⁷Pb/²⁰⁴Pb of 15.640–15.785, and ²⁰⁸Pb/²⁰⁴Pb of 39.068–39.560. These data suggest that magmatic fluids with contribution from meteoric water, magmatic sulfur, and lead derived from upper crust and metasomatized mantle by Indian continental materials would be critical for the Luobuzhen base metal mineralization.The Dongshibu area, located at ∼2 km east of the Luobuzhen, is characterized by high concentrations of Cu (up to 1450 ppm) and Mo (up to 130 ppm) of stream sediments, which is quite different from high concentrations in Pb, Zn, Ag, and Au shown in the Luobuzhen area. In addition, porphyry copper mineralization-related alteration and veins/veinlets occur in the Miocene monzogranite at Dongshibu. The monzogranite is characterized by high Sr/Y ratios, which are also shown on ore-forming intrusions in the Gangdese postcollisional porphyry copper deposits, and shows similar zircon Hf isotopes to the ore-related high Sr/Y intrusions from the Zhunuo porphyry copper deposit which is located ∼20 km northeast of the Luobuzhen-Dongshibu. A comprehensive analysis allows us to infer that the base metal veins at Luobuzhen are components of a porphyry Cu system with porphyry Cu mineralization likely present at Dongshibu and epithermal Au–Ag veins possibly occurring at Luobuzhen, which are indicative of the existence of porphyry copper systems in collisional zones. The potential porphyry Cu mineralization and epithermal Au–Ag veins should be targeted in future exploration at Luobuzhen-Dongshibu.     

Application of ASTER data for exploration of porphyry copper deposits: A case study of Daraloo–Sarmeshk area,southern part of the Kerman copper belt,Iran

The Cenozoic Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran is a major host to porphyry Cu ± Mo ± Au deposits (PCDs). Most known PCDs in the UDMB occur in the southern section of the belt, also known as the Kerman Copper Belt (KCB). Three major clusters of PCDs are distinguished in the KCB and include the Miduk, Sarcheshmeh and Daraloo clusters. The Daraloo and Sarmeshk deposits occur in a northwest–southeast-trending fault zone that is characterized by the presence of a narrow zone of alteration–mineralization that contains a series of Oligocene granitoids and Miocene porphyritic tonalite–granodiorite plutons that cut Eocene andesitic lava flows and pyroclastic rocks. Here we use various techniques, including different ratio images, minimum noise fraction, pixel purity index, and matched filter processing to process ASTER data (14 bands) and generate maps that portray the distribution of hydrothermal minerals (e.g., sericite, kaolinite, chlorite, epidote and carbonate) related to PCD alteration zones. In order to validate the ASTER data, follow-up ground proofing and related mineralogical work was done which, in all cases, proved to be positive. The results of this work have identified the regional distribution of hypogene alteration zones (i.e., phyllic, argillic, propylitic and silicic), in addition to areas of secondary Fe-oxide formation, which are coincident with known sites of PCDs. The regional distribution and extent of the alteration zones identified also highlighted the role of regional structures in focusing the mineralizing/altering fluids. These results demonstrate very convincingly that ASTER imagery that uses the appropriate techniques is reliable and robust in mapping out the extent of hydrothermal alteration and lithological units, and can be used for targeting hydrothermal ore deposits, particularly porphyry copper deposits where the alteration footprint is sizeable.