Ore-hosting Porphyry Research Articles

Ore genesis and fluid evolution of the Sandaozhuang supergiant W-Mo skarn deposit, southern margin of the North China Craton: Insights from scheelite, garnet and clinopyroxene geochemistry

The Sandaozhuang deposit (0.55 Mt WO3 at 0.112% and 0.75 Mt Mo at 0.109%), located in the southern margin of the North China Craton, is one of the largest W-Mo deposits in the world. This study carried out in-situ elemental analyses on skarn minerals, as well as elemental and Sr-Nd isotopic analyses on scheelites from the deposit, to constrain the metal source and fluid evolution of the deposit. Three generations of scheelite (Sch A to C) were identified based on petrographic observations, including prograde skarn and diopside-plagioclase hornfels-hosted Sch A, retrograde skarn-hosted Sch B, and quartz vein-hosted Sch C. Varieties of REE patterns in the scheelite are mainly controlled by different substitution mechanisms and crystallization of REE-enriched skarn minerals. The Mo contents decrease from early generation Sch A (1.57–24.45%) to Sch B (0.19–1.52%) and finally to Sch C (0.20–0.97%), and Eu anomalies of scheelite change from negative to positive and then back to negative values. The Sandaozhuang deposit is characterized by Mg-rich clinopyroxene (Di40-81Hd17-47), and grossularite–andradite (And22–89Gro6-77), similar to well-studied oxidized W skarn deposits worldwide, but the andradite contents of one garnet grain in the late prograde stage, decrease from the core (84.09%) to rim (75.12%). Composition changes of scheelite and garnet indicate that the ore-forming fluids changed from oxidized to reduced state in the skarn stage then to oxidized state in the quartz-sulfide stage, and the variations in redox state favoured the muti-stage Mo mineralization. The relatively uniform Y/Ho ratios of the Nannihu granite porphyry and scheelite imply that the ore-forming fluids are mainly derived from the porphyry. Scheelites from Sandaozhuang are characterized by low εNd(t) values (−14.7 to − 11.8), which are consistent with those for the Nannihu granite porphyry. Such a coincidence indicates that ore-forming fluids were mainly derived from the ore-hosting porphyry. However, the initial 87Sr/86Sr ratios of scheelites (0.7158–0.7295) are significantly higher than those of the Nannihu granite porphyry and other granites in the Luanchuan ore district (0.7047–0.7098), indicating that the Neoproterozoic Luanchuan Group with radiogenic Sr isotopic compositions contributed to tungsten mineralization, and the intense fluid-rock interaction between the ore-forming fluids derived from the granite porphyry and the Luanchuan Group country rocks may play an important role in tungsten mineralization.

The Mesozoic magmatic, metamorphic, and tectonic evolution of the eastern Gangdese magmatic arc, southern Tibet

ABSTRACTMagmatic arcs are natural laboratories for studying the growth of continental crusts. The Gangdese arc, southern Tibet, is an archetypal continental magmatic arc that formed due to Mesozoic subduction of the Neo-Tethyan oceanic lithosphere; however, its formation and evolution remain controversial. In this contribution, we combine newly reported and previously published geochemical and geochronological data for Mesozoic magmatic rocks in the eastern Gangdese arc to reveal its magmatic and metamorphic histories and review its growth, thickening, and fractionation and mineralization processes. Our results show that: (1) the Gangdese arc consists of multiple Mesozoic arc-type magmatic rocks and records voluminous juvenile crustal growth. (2) The Mesozoic magmatic rocks experienced Late Cretaceous granulite-facies metamorphism and partial melting, thus producing hydrous and metallogenic element-rich migmatites that form a major component of the lower arc crust and are a potential source for the Miocene ore-hosting porphyries. (3) The Gangdese arc witnessed crustal thickening and reworking during the Middle to Late Jurassic and Late Cretaceous. (4) Crystallization-fractionation of mantle-derived magmas and partial melting of thickened juvenile lower crust induced intracrustal chemical differentiation during subduction. We suggest that the Gangdese arc underwent the following main tectonic, magmatic, and metamorphic evolution processes: normal subduction and associated mantle-derived magmatism during the Late Triassic to Jurassic; shallow subduction during the Early Cretaceous and an associated magmatic lull; and mid-oceanic ridge subduction, high-temperature metamorphism and an associated magmatic flare-up during the early Late Cretaceous, and flat subduction, high-temperature and high-pressure metamorphism, partial melting, and associated crust-derived magmatism during the late Late Cretaceous. Key issues for further research include the temporal and spatial distributions of Mesozoic magmatic rocks, the evolution of the components and compositions of arc crust over time, and the metallogenic processes that occur in such environments during subduction.

Petrogenesis of ore-hosting porphyry in the Gelouang gold deposit, West Qinling and its geological implications

Petrogenesis of ore-hosting porphyry in the Gelouang gold deposit, West Qinling and its geological implications

Petrogenesis of Eocene mineralized porphyry in Bijiashan, eastern margin of Tibet Plateau: Constraints from geochronology, geochemistry and Hf isotopes

The Ailaoshan-Jinshajiang porphyry belt located in the Sanjiang area of eastern Tibetan Plateau is one of the major polymetallic metallogenic belts in China. However, the nature and genesis of magmatic intrusions associated with the porphyry copper mineralization in this belt remain contentious. Here we focus on the Bijiashan Deposit, one of the large-scale porphyry copper deposits in this area, to gain insights on the host rock, petrogenetic mechanism, tectonic setting based on geochemistry, zircon UPb geochronology and LuHf isotopic compositions. Zircon UPb dating of the ore-hosting porphyry yielded an age of 35.6 ± 0.2 Ma. The major elements of the porphyry show wide range in SiO2 (58.33–70%), high K2O (2.83–8.85%) and Na2O + K2O (mostly>8%), and moderate range in A/CNK (0.56–1.17). Our data suggest that the porphyry belongs to high-Kcalc-alkaline-alkaline and metaluminous-peraluminous series. The trace elements are characterized by enrichment in K, Rb, Ba, La and Nd, but depletion in Ta, Nb, P and Ti, and enrichment in LREE but depletion in HREE with LREE/HREE of 9.78–20.10. The main intrusion associated with mineralization corresponds to alkali-richA-type granitoid, with high TFeO (0.49–3.4%), low Na2O/K2O (0.23–1.62), and high 1000*Ga/Al (2.17–2.64 except 1.57), and right-declinedREE patterns. However, some of the geochemical features also are consitent with the typical characteristics of C-adakite rocks, including high contents of Al2O3 (13.49–16.12%) and Sr (>400 ppm), lower MgO (mostly <3%), depleted Y (<18 ppm) and Yb (<1.9 ppm), and slightly negative Eu anomalies (δEu = 0.83). The zircon εHf (t) values show a wide range from negative to positive (−13.65 to 2.60) with TDMC varying from 947 Ma to 1982 Ma, suggesting that the Eocene porphyries were derived from the partial melting of the lower crustal materials, together with the addition of mantle source materials. Combined with the regional geological evolution, our study suggests that the ore-hosting porphyry formed under a setting of post-collisional crustal extension. Following the collision between the Indian and Eurasian plates, the stress relaxation resulted in extension and magma emplacement along major faults and the copper polymetallic mineralization formed along the Chenghai-Binchuan Fault.

Recognition of Late Ordovician Yudai porphyry Cu (Au, Mo) mineralization in the Kalatag district, Eastern Tianshan terrane, NW China: Constraints from geology, geochronology, and petrology

Although the Eastern Tianshan terrane in Xinjiang, NW China, occupies a critical position in the Central Asian Orogenic Belt (CAOB), the early Paleozoic tectonic evolution and mineralization history of this terrane remain ambiguous. The Yudai deposit is a newly discovered porphyry Cu (Mo, Au) deposit in the Kalatag district of the Dananhu island arc, a key area containing early Paleozoic rocks in the Eastern Tianshan. This paper reports the geologic characteristics, molybdenite Re–Os ages, zircon LA-ICP-MS U–Pb ages, and geochemical and Lu–Hf isotopic findings regarding the ore-hosting porphyries in the Yudai deposit.The Yudai ore-hosting porphyries include an early diorite porphyry and a late quartz diorite porphyry. Alteration and mineralization have formed distinct zones around the quartz diorite porphyry, with disseminated, vein, or veinlet Cu (Mo, Au) mineralization types mainly related to potassic alteration (e.g., biotite, magnetite, and quartz), typical of a porphyry Cu deposit.Two molybdenite samples have an Re–Os weighted mean age of 449.5±4.2Ma and exhibit high Re contents (2624 to 4704ppm), indicating a mantle component. The observed mineralization was probably related to the quartz diorite porphyry, which yielded a mean zircon 206Pb/238U age of 452.7±2.8Ma.The rock samples from the two porphyries mainly plot in the diorite field, show metaluminous to weak peraluminous features, and belong to tholeiitic to calc-alkaline series, with K2O/Na2O ratios of 0.16–0.34 and Mg# values of 44.2–50.3. The samples also exhibit steep chondrite-normalized rare earth element and relatively flat heavy rare earth element patterns (indicating residual amphibole), with positive Eu anomalies (Eu/Eu∗=1.09–1.45). The samples are enriched in large-ion lithophile elements relative to high-field-strength elements, typical of arc magma. In addition, the rocks show adakitic features (Sr/Y=47.8–73.5) and present high Ba/Th and low Th/Nb ratios (indicating slab fluids). The zircons from the quartz diorite porphyry mainly yield high εHf(t) values (13.5–14.7) and very young two-stage Hf model ages (TDM2=494–556Ma), consistent with a depleted mantle origin.Combined with the arc tectonic setting, we propose that the ore metals and ore-hosting porphyries at Yudai were predominately derived from the partial melting of the amphibole-bearing and fluid-rich Kangguer Ocean slab that was subducted northward beneath the Dananhu island arc in the Late Ordovician. Therefore, the evolutionary history of the Dananhu island arc can be traced back to the Late Ordovician; the Yudai deposit is the first age-constrained early Paleozoic porphyry Cu deposit in the Eastern Tianshan terrane; and the early Paleozoic was an important epoch of mineralization on this terrane.

Geochronology, redox-state and origin of the ore-hosting porphyry in the Tongkuangyu Cu deposit, North China Craton: Implications for metallogenesis and tectonic evolution

Tongkuangyu Cu deposit, located at the southern edge of the North China Craton, is hosted by a suite of sedimentary-magmatic rocks. Genesis of this giant ore deposit has been debated for over half a century. New data from geochronological, geochemical and isotopic analyses on the ore-hosting monzogranitic porphyries are presented. Seventy four zircon U-Pb dates by laser ablation ICPMS suggest that the porphyries were emplaced at ca. 2180Ma. Geochemically, they show transitional features between typical Archean TTG and sanukitoid, e.g. displaying sodium enrichment with elevated K contents, and exhibiting strong REE fractionation with elevated HREE, Mg, Cr contents. Ti-in-zircon thermometer reveals a crystallization temperature of 675±16°C. Cerium anomalies in zircons indicated that the porphyry magmas have low oxygen fugacity of 0.5 log unit below the fayalite-magnetite-quartz buffer (ΔFMQ −0.5). Zircons from the porphyries have ɛHf(t) values of −4.9 to 2.5 with two-stage depleted mantle model ages of ∼2.8Ga, which point to a magma source resembles the newly-discovered 2.7Ga TTGs and diorite in this region. Zircons from the porphyries are slightly more enriched in 18O than that of mantle zircons, with δ18O values of 5.2–5.9‰ (averaging 5.6±0.1‰). Geochemical modeling suggests that the porphyry magmas were likely sourced from melting of the 2.7Ga diorite leaving behind hornblende and biotite as residues, with minor contribution (<20%) from juvenile, mantle-derived materials. The reducing nature of the porphyry magmas makes them incapable of sequestering sufficient Cu and S, thus rendering them unsuitable for porphyry-style copper mineralization. By tentative inference, we suggest that magmatic sulfide in the porphyries may have acted as a reducing agent to precipitate copper from the ore-forming fluids. Combining the above evidence and previous interpretations, we propose a tectonic evolution model envisaging an oceanic subduction at ∼2.7Ga, followed by a continental collision at ∼2.5Ga, and ended up with an extension at ∼2.2Ga.

Geochemistry and fluid characteristics of the Dalli porphyry Cu–Au deposit, Central Iran

The Miocene Dalli porphyry Cu–Au deposit in the central part of Urumieh–Dokhtar magmatic arc is the first reported Au-rich porphyry Cu deposit in the Zagros orogenic belt. The Cu–Au mineralization is mainly hosted in diorite and quartz diorite intrusions, presenting as numerous veinlets in the altered wall rocks, with potassic, phyllic, and propylitic alteration developed. Based on the mineral assemblages and crosscutting relations of veinlets, hydrothermal mineralization–alteration occurred in at least three stages, characterized by veinlets of (1) Qtz+Kfs+Mag±Ccp, (2) Qtz+Py+Ccp±Bn±Cv±Cc and, (3) Qtz+Chl+Bt. The ore-bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas, including LREE fractionated pattern, strong enrichment in LILE (Cs, Rb, Ba, Pb, and U), and depletion of HFSE, with marked negative Ti and Nb anomalies. The adakite-like ore-hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of Y and Eu/Eu∗ with increasing SiO2 content, respectively. Moreover, they exhibit a significant increasing trend of Sr/Y with decreasing of Y, which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma. A relatively flat HREE pattern with low Dyn/Ybn and Nb/Ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust. Based on the phase assemblages confirmed by detailed laser Raman spectroscopy analyses and proportion of solid, liquid, and gaseous components, five types of fluid inclusions were recognized, which are categorized as; (1) liquid-rich two phase (liquidH2O+vaporH2O) (IIA), (2) vapor-rich two phase (vaporH2O/CO2+liquidH2O) (IIB), (3) high saline simple fluids (IIIA; liquidH2O+vaporH2O+Hl), (4) high saline opaque mineral-bearing fluids (IIIB; liquidH2O+vaporH2O+Hl+Hem+Ccp+Py) and (5) multi-phase type (IIIAB; liquidH2O+vaporH2O+Hl+Anh+Hem+Mag+Ccp). In early stage veins, the homogenization temperature of multiphase inclusions as high as 620°C, with corresponding salinities of up to 75wt.% NaCl equivalent represent the initial ore-forming fluids. From early to late stage veins, the gradual decrease of homogenization temperature of saline inclusions (IIIAB, IIIA, and IIIB) from 620 to 340°C (corresponding salinities of 75–35wt.% NaCl equivalent) may reflect fluid boiling and mixing of the early magmatic fluids with circulating groundwater. The common association of hematite and anhydrite daughter phases with the most primitive inclusions (IIIAB) in early-stage veins and the lack of CO2-bearing inclusions in the middle to late stage veins reveal CO2 content and oxygen fugacity of the fluids was significantly decreased from early to main stage of sulfide mineralization (second generation of veins). It seems that magnetite crystallization and CO2-escape have a decisive role in oversaturation of S2− and subsequent rapid and large-scale precipitation of sulfides in second generation of veins at the Dalli deposit.

Genesis of the Yuanlingzhai porphyry molybdenum deposit, Jiangxi province, South China: Constraints from petrochemistry and geochronology

The newly discovered Yuanlingzhai porphyry molybdenum (Mo) deposit in southern Jiangxi province belongs to the group of Mo-only deposits in the Nanling region. The mineralization developed at contact zones between the Yuanlingzhai granite porphyry and Neoproterozoic metamorphic rocks of the Xunwu Formation. Precise LA–MC–ICPMS zircon U–Pb dating of the Yuanlingzhai porphyry, as well as the adjacent western Keshubei and eastern Keshubei granites, yielded ages of 165.49±0.59Ma, 159.68±0.43Ma, and 185.13±0.52–195.14±0.63Ma, respectively. Molybdenite Re–Os isochron ages of the ores are 160±1–162.7±1.1Ma, which is consistent with the age of large-scale W–Sn deposits in South China. The Yuanlingzhai porphyry is characterized by high K2O, P2O5, and A/CNK (1.33–1.59), and low CaO and Na2O. The rock shows relatively enriched LREE without significant Eu anomalies (Eu/Eu*=0.80–0.90). Geochemical and mineralogical characteristics indicate that the ore-hosting porphyry is a typical S-type granite generated from the partial melting of crustal material with only minor mantle contribution. Both Harker and evolutionary discrimination diagrams indicate that the Yuanlangzhai and western Keshubei granites are not products of co-magmatic evolution. The Keshubei granites and Xunwu Formation were not significant sources for the components in the porphyry mineralization, but the Yuanlangzhai granite may have supplied some ore-forming material. However, the main ore-forming material was carried by fluids from deep sources, as demonstrated by fluid inclusion and stable isotope data from the molybdenum deposit. The Mo porphyry deposit formed in an extensional setting, and was possibly associated with Jurassic subduction of the Izanagi Plate.

Origin of the Yinshan epithermal-porphyry Cu–Au–Pb–Zn–Ag deposit, southeastern China: insights from geochemistry, Sr–Nd and zircon U–Pb–Hf–O isotopes

The Yinshan deposit is a large epithermal-porphyry polymetallic deposit, and the timing and petrogenesis of ore-hosting porphyries have been hotly debated. We present new results from geochemical, whole-rock Sr–Nd and zircon U–Pb–Hf–O isotopic investigations. Zircon U–Pb data demonstrate that the quartz porphyry, dacitic porphyry, and quartz dioritic porphyry formed at ˜172.2 ± 0.4 Ma, ˜171.7 ± 0.5 Ma, and ˜170.9 ± 0.3 Ma, respectively. Inherited zircon cores show significant age spreads from ˜730 to ˜1390 Ma. Geochemically, they are high-K calc-alkaline or shoshonitic rocks with arc-like trace element patterns. They have similar whole-rock Nd and zircon Hf isotopic compositions, yet an increasing trend in ϵNd(t) and ϵHf(t) values typifies the suite. Older (inherited) zircons of the three porphyries display Hf compositions comparable to those of the Jiangnan Orogen basement rocks. In situ zircon oxygen isotopic analyses reveal that they have similar oxygen isotopic compositions, which are close to those of mantle zircons. Moreover, a decreasing trend of δ18O values is present. We propose that the ore-related porphyries of the Yinshan deposit were emplaced contemporaneously and derived from partial melting of Neoproterozoic arc-derived mafic (or ultra-mafic) rocks. Modelling suggests that the quartz porphyries, dacitic porphyries, and quartz dioritic porphyries experienced ˜25%, ˜10%, and ˜10% crustal contaminations by Shuangqiaoshan rocks. Our study provides important constraints on mantle–crust interaction in the genesis of polymetallic mineralization associated with Mesozoic magmatism in southeastern China.

LINKING Cu MINERALIZATION TO HOST PORPHYRY EMPLACEMENT: Re-Os AGES OF MOLYBDENITES VERSUS U-Pb AGES OF ZIRCONS AND SULFUR ISOTOPE COMPOSITIONS OF PYRITE AND CHALCOPYRITE FROM THE IJU AND SARKUH PORPHYRY DEPOSITS IN SOUTHEAST IRAN

The Kerman copper belt in Iran contains a number of important porphyry copper deposits, including Sarkuh and Iju. Molybdenite Re-Os isotope dating of the Sarkuh and Iju porphyry copper deposits shows that mineralization occurred at 15.14 ± 0.08 and 9.8 ± 0.06 Ma, respectively. Compared with the previous Re-Os dating of molybdenite in the region, it is revealed that Cu mineralization was an ongoing process in an arc setting during the Miocene. The available zircon dates of the granitic rocks from the Sarkuh (15.18 ± 0.43 Ma) and Iju (9.27 ± 0.50 Ma) porphyry copper deposits indicate that the mineralization occurred contemporaneously with the emplacement of collision-related ore-hosting porphyries. The Re content (1,715.40 ppm) of molybdenite and the δ^(34)S_(CDT) values (0.05‰) of pyrite-chalcopyrite from Iju are consistent with its origin of sulfur and metals from a dominantly mantle source. However, the lower Re content (302.21 ppm) of molybdenite and higher δ^(34)S_(CDT) values (3.20‰) of pyrite-chalcopyrite from Sarkuh suggest additional contributions from crustal materials. It is likely that the younger porphyry copper deposits in the Kerman copper belt, such as Iju, are related to the greater contribution of postcollisional mantle-derived magmas, while the older deposits (e.g., Sarkuh) were formed during the collisional event at the Oligocene-Miocene interval where the magma had some additions from the lower crustal melts generated during crustal thickening.

Lead isotope signatures of the igneous rocks and porphyry copper deposits from the Kerman Cenozoic magmatic arc (SE Iran), and their magmatic-metallogenetic implications

Copper deposits in the Kerman Cenozoic magmatic arc (KCMA) of Iran are genetically related to Miocene porphyries. The porphyries and their associated Cu deposits were intruded and emplaced into Eocene volcanic-sedimentary successions. Lead isotope compositions of the Eocene volcanic rocks exhibit homogeneous, non-radiogenic values ( 206Pb/ 204Pb = 18.40 to 18.49, 207Pb/ 204Pb = 15.41 to 15.48, and 208Pb/ 204Pb = 38.15 to 38.36). In contrast, the Miocene ore-hosting porphyries and associated sulfide minerals also show a relatively radiogenic and homogenous Pb-isotopic values with orogen character ( 206Pb/ 204Pb = 18.52 to18.60, 207Pb/ 204Pb = 15.58 to 15.64, and 208Pb/ 204Pb = 38.57 to 38.80). The shift in the Pb-isotopic composition of igneous rocks with time towards higher Pb-isotopic values precludes derivation of the ore-hosting porphyries from a reservoir of similar composition to those in the Eocene volcanic rocks. The non-radiogenic Pb-isotope signature of the Eocene volcanic rocks indicates an origin from subduction-related mantle-derived magmas, whereas the higher Pb-isotopic values of the Miocene ore-hosting porphyries suggest an increasing involvement of crustal materials (with lower U/Pb ratios than the upper crust) in the source region of these rocks. Combining the Pb-isotope data with petrogenetic considerations suggests derivation of the middle Miocene ore-hosting porphyries from a mixed reservoir with slightly radiogenic Pb values, such as a hybridized lower continental crustal source. This source probably formed because of the involvement of Cretaceous–Oligocene subduction-related mantle-derived mafic magmas at the base of arc crust. The contribution of the Miocene collision-related mantle-derived mafic magma in melting of the hybridized lower continental crust caused generation of the middle Miocene porphyries, hosting large copper deposits with the least 206Pb/ 204Pb ratios among other porphyries. The higher 206Pb/ 204Pb ratios of the late Miocene–Pliocene porphyries hosting small copper deposits, as well as barren porphyries, may reflect a decreasing involvement of collision-related mantle-derived mafic magma in the source of the late Miocene–Pliocene porphyries. The overall similarity in Pb-isotope values between sulfide minerals and ore-hosting porphyries suggests a magmatic source for most of the Pb and possibly other metals. The more radiogenic isotopic ratios of some late sulfide minerals suggest an insignificant metal contribution from an external source such as local country rocks during hydrothermal circulation.

U–Pb SHRIMP geochronology of Th-poor, hydrothermal monazite: An example from the Llallagua tin-porphyry deposit, Bolivia

In situ U–Pb SHRIMP analysis of hydrothermal monazite virtually free of Th and poor in U (<0.2 ppm Th, 40–103 ppm U) from the world-class Llallagua tin porphyry deposit in Bolivia defines a mineralization age of 23.4 ± 2.2 Ma (MSWD 0.48) confirming earlier K–Ar sericite alteration age data. These ages are, however, in contrast with a weighted mean single crystal 207Pb/ 206Pb evaporation age of 39.3 ± 6.0 Ma, and a related Pb–Pb inverse isochron age of 42.4 ± 4.0 Ma (MSWD 0.66) on zircon from a post-porphyry dike, as well as with an earlier single crystal Sm–Nd apatite isochron age. Our data points to a significant time gap between emplacement of the ore-hosting porphyry intrusion (magmatism) and its hydrothermal overprint (tin mineralization), suggesting long-lived magmatic-hydrothermal activity in this part of the Andean back-arc crust. The decoupling of porphyry magmatism and hydrothermal activity may explain the unusual occurrence of relatively little fractionated felsic rocks together with extensive tin mineralization. Our study demonstrates the usefulness of the application of the U–Pb SHRIMP method to direct age determination of ore mineralization using Th-poor hydrothermal monazite even when dealing with geological young events. The common assumption of synchronous magmatism and hydrothermal ore formation in porphyry systems may not always be warranted.