Granodiorite Porphyry Research Articles

Increasing sulfur and chlorine contents in ore-forming magmas: The key to Pulang porphyry Cu-Au formation, SW China

The giant Pulang porphyry Cu-Au district (446.8 million tonnes at 0.52% Cu and 0.18 g/t Au) is located in the southern Yidun terrane of the Sanjiang (Three-river) region, southwest China. It has six phases of porphyry intrusions: premineralized fine-grained quartz diorite (FQD) and coarse-grained quartz diorite porphyry (CQD), the main synmineralized quartz monzonite porphyry (QMP), and late synmineralized granodiorite porphyry (GP), diorite porphyry (DP), and aplite. New zircon U-Pb ages for the premineralized FQD and late synmineralized GP, DP, and aplite are 226.3 ± 2.6 Ma (MSWD = 1.9), 216.4 ± 1.0 Ma (MSWD = 2.0), 216.0 ± 1.1 Ma (MSWD = 1.7), and 216.0 ± 1.5 Ma (MSWD = 1.7), respectively. All Pulang porphyry rocks have high whole-rock Sr/Y ratios (37.8–184) with minor or no negative Eu anomalies (0.73–1.04), and are characterized by high large-ion-lithophile-element (LILE: Th, U, Ba, Rb) abundances and low high-field-strength-element (HFSE: Nb, Ta, Ti, Zr, Hf).Zircons from premineralized FQD and synmineralized GP, DP, and aplite rocks have consistently high EuN/EuN* ratios (mostly > 0.4). The magmatic oxygen fugacity calculated from zircon compositions, show that the FQD (ΔFMQ = 1.59 ± 0.43), GP (ΔFMQ = 1.52 ± 0.18), DP (ΔFMQ = 1.52 ± 0.30), and aplite (ΔFMQ = 1.75 ± 0.60) were all derived from moderately oxidized magmas. Magmatic water contents estimated from amphibole compositions and the extensive presence of amphibole phenocrysts suggest that H2O contents are >4 wt%. Together with the published results for premineralized CQD and main synmineralized QMP, it is concluded the causative magmas for the six porphyry phases at Pulang were all relatively oxidized and hydrous.The difference between premineralized FQD and CQD and synmineralized QMP, GP, and DP are reflected in magmatic chlorine and sulfur contents. To minimize the effect of hydrothermal alteration, the apatite microphenocrysts enclosed by least altered phenocrysts were selected for analyses. The Cl contents of magmatic apatite microphenocrysts from the synmineralized QMP (avg = 0.340 ± 0.192, n = 26), GP (avg = 0.317 ± 0.151, n = 21), and DP (avg = 0.179 ± 0.112, n = 18) are significantly higher than those from the premineralized FQD (avg = 0.046 ± 0.032, n = 9) and CQD (avg = 0.043 ± 0.034, n = 13). Similarly, the SO3 contents of igneous apatite microphenocrysts from the synmineralized QMP (avg = 0.259 ± 0.156, n = 25), GP (avg = 0.203 ± 0.163, n = 20), and DP (avg = 0.306 ± 0.173, n = 18) are higher than those from the premineralized FQD (avg = 0.181 ± 0.136, n = 10) and CQD (avg = 0.085 ± 0.068, n = 6). The S-Cl contents of synmineralized melts estimated from apatite S-Cl compositions are higher than those of premineralized magmas, suggesting that the elevated magmatic S-Cl contents in the synmineralized porphyries might have been important for Cu-Au mineralization. This was likely due to S-Cl rich mafic magma recharge, supported by the presence of abundant mafic magmatic enclaves in the synmineralized QMP.

LA-ICP-MS trace element analysis of pyrite from the Dafang gold deposit, South China: Implications for ore genesis

The Dafang is a hydrothermal gold deposit (6 t Au with an average grade of 1.8 g/t) in periphery of the Sn-Cu metallogenic system in Nanling Range in south China. This deposit locates in the contact zone between late Jurassic granodiorite porphyry and late Paleozoic limestone as well as the fractures of them. The mineralization comprises three stages, pyrite + arsenopyrite ± chalcopyrite + quartz (I), pyrite + arsenopyrite + gold + calaverite + sulfosalt ± sphalerite ± galena + quartz (II), and pyrite + arsenopyrite + quartz + calcite (III). Pyrite is the dominant gold-bearing mineral, which can be classified into three generations (Py1 to Py3), corresponding to three ore stages (Stage I to Stage III), respectively. Different stage pyrites show textural homogeneity in both reflected light and backscattered electron images. In addition, the LA-ICP-MS results show that all pyrites have relatively low Au concentrations (0.17 ppm for Py1, 0.48 ppm for Py2 and 0.58 ppm for Py3), and trace element mapping for Py1 demonstrate oscillatory zoning patterns for Au, As, Sb, Te, Co, and Ni. Compared to Py2 and Py3, Py1 has higher Co, Ni, Cu, Pb, Zn, Ag, and Te contents, but lower Au and Tl contents. Gold contents for all stage pyrite plot well below the solubility limit for gold in arsenian pyrite, indicating that invisible gold occurs as Au1+ in the pyrite lattice. Silver occurs mainly as Ag-bearing sulfosalt inclusion or galena micro-inclusion in pyrite, while Pb and Zn as galena and sphalerite micro-inclusions in pyrite. Trace element mapping yields that Au-rich zone coincides well with As rich zones, demonstrating that the occurrence of As in pyrite promotes the enrichment of lattice gold. From Stage I to Stage III, the decrease of Co and Ni contents indicates the decrease of the ore-fluid temperature, and the change of Se and Te contents suggests the fO2 increased from Stage I to Stage II and then decreased to Stage III. The Co and Ni contents suggest that all studied pyrite is dominantly of hydrothermal origin. Combined geological and mineralogical evidences indicate that the Dafang gold deposit is an epithermal Au deposit.

The geochemistry and geochronology of Permian granitoids from central Inner Mongolia, NE China: Petrogenesis and tectonic implications

Permian granitoids have been identified in the Zhalageamu district, Inner Mongolia, NE China, which provide an excellent opportunity to constrain the tectonic evolution of the Central Asian Orogenic Belt (CAOB). In this study, we determined the zircon UPb ages of the quartz diorite, granodiorite porphyry, diorite porphyry and granite porphyry at Zhalageamu. These ages are 269.5 ± 1.8, 261.4 ± 1.9, 256.4 ± 2.0 and 255.2 ± 2.0 Ma, respectively. The granitoids have high contents of SiO2 (61.95–75.41 wt%) and Al2O3 (11.87–15.88 wt%), and their A/CNK ratios range from 0.91 to 1.44. Their Na2O + K2O contents range from 6.04 to 9.28 wt% and help classify them as having calc-alkaline to high-K calc-alkaline affinity. The low P2O5 contents of the quartz diorite, diorite porphyry and granite porphyry and their decrease with increasing SiO2, in combination with low 10,000*Ga/Al ratios (1.51–2.58) and Zr + Nb + Ce + Y contents (128–264 ppm) identify them as I-type granitoids, whereas the strongly peraluminous character of the granodiorite porphyry classifies it as an S-type granite. These I-type granitoids are characterized by an enrichment in large ion lithophile elements (LILE; e.g., Rb, Ba and Th) and a depletion in high field strength elements (HFSE; e.g., Nb, Ta and Ti). This, and their weakly negative Eu anomalies on chondrite-normalized REE diagrams, are features of typical arc magmatic rocks. The ɛNd(t) values and initial 87Sr/86Sr ratios range from 2.9 to 4.2 and 0.7010 to 0.7039, respectively, and both sets of values point to a mantle source. Hafnium isotopic analysis of quartz diorite yielded positive εHf(t) values of 8.5–12.3 and young two-stage Hf model ages (TDM2) of 0.51–0.72 Ga, suggesting a juvenile crustal source. These features are similar to those of locally occurring coeval volcanic arc rocks, indicating that the Zhalageamu granitoids mostly formed by partial melting of juvenile mantle-derived crust. Our geochemical and Sr-Nd-Hf isotopic data show that the Zhalageamu granitoids were generated in a subduction setting related to the northward subduction of the Paleo-Asian Ocean.

Texture and Geochemistry of Scheelites in the Tongshankou Deposit in Daye, Hubei, China: Implication for REE Substitution Mechanism and Multistage W Mineralization Processes

The Tongshankou skarn deposit in the Edong ore district is a typical metasomatic deposit associated with adjacent granodiorite porphyry and carbonate rocks. Using comprehensive microscopic observations, mineralogical and geochemical analysis, scheelite grains in the skarns can be classified into three major types, showing multi-stage mineralization characteristics. In the redox fluid environment, scheelites that occur with garnets usually have affinity to garnets, while in later skarn phases others exist with oxides and sulfides. They can be subdivided by trace elements, such as Nb and Eu, to discuss the detailed ore-forming process. Scheelites have three typical substitution mechanisms including: 2Ca2 + ⇌ REE3 + +Na+ (1); Ca2 + + W6 + ⇌ REE3 + +Nb5+(2); and 3Ca2 + ⇌ 2REE3++ □Ca (□Ca = Ca site vacancy) (3). Plagioclase or various hydrothermal stages can cause Eu anomalies to fluctuate from positive to negative, and these processes can cause particular zonation in W and Mo contents in scheelites. This study highlights the use of texture and geochemistry of scheelites in skarn deposits, depicting the W mineralization processes.

Magmatic controls on the mineralization potential of a porphyry Cu system: The case of Jurassic Tongshan skarn Cu deposit in the Qin–Hang Belt, South China

The Qin–Hang suture belt in South China formed during the Neoproterozoic amalgamation between the Cathaysia and Yangtze blocks. There are several Jurassic porphyry–skarn Cu deposits in this region, and the factors controlling the mineralization potential remain unclear. This study reports geochemical data for the Tongshan skarn deposit and zircon trace element data for five porphyry- or skarn-type Cu deposits in this region, in order to identify geochemical indexes for the mineralization potential of the ore-related intrusions. A garnet U–Pb age (170 Ma) for the Tongshan skarn indicates that Cu mineralization occurred in the Middle Jurassic, which is consistent with the zircon U–Pb ages (173 Ma–171 Ma) of the host granodiorite porphyries. Granodiorite porphyry samples from the Tongshan deposit have moderately high SiO2 contents (64.4–65.0 wt%), low MgO contents (1.39–1.47 wt%), and high (La/Yb)N ratios (14.7–16.8), typical of low-Mg adakitic rocks. The whole-rock geochemistry, bulk Earth-like εNd (t) values (–1.5 to –1.6) and positive zircon εHf(t) values (+2.7 to +6.0), corresponding to two-stage Hf model ages of 1014–832 Ma, suggest the porphyries were derived from thickened juvenile lower crust initially generated during Neoproterozoic amalgamation. In addition, the porphyry samples have arc-like geochemical characteristics (Nb–Ta–Ti depletion), low Th/Yb ratios (average = 4.7), high Ba/Th ratios (average = 346), zircon Eu/Eu* values (average = 0.71) and 10000×(Eu/Eu*)/Y values (average = 6.80), and moderate zircon Ce/Ce* values (average = 705) and Ce/Nd ratios (average = 17.1). These features demonstrate that the parental magmas of the porphyries were formed by melting of a mantle wedge.That had been metasomatized by moderately oxidized slab-derived fluid near a Neoproterozoic subduction zone. Previous studies suggest porphyries from large to giant deposit (e.g., Dexing and Yinshan) have similar two-stage Hf model ages and were derived from Neoproterozoic juvenile crust. But these porphyries have higher whole–rock Th/Yb ratios and zircon Ce/Ce* and Ce/Nd values than those of intrusions from medium-sized deposits (e.g., Tongshan, Chuankeng and Jiande). This indicates that the magma source of the former may have been distant from the trench in the Neoproterozoic, and formed by melting of a mantle wedge that had been metasomatized by highly oxidized slab-derived melt. Our results and previously published data indicate that the Neoproterozoic two-stage Hf model ages of the intrusions are positive indicators of Jurassic Cu mineralization, and granitoids with relatively high Th/Yb ratios and zircon Ce/Ce* and Ce/Nd values likely have more potential to form large to giant Cu deposits.

Platinum-group elements and gold distribution in ores of the Haftcheshmeh porphyry Cu-Mo-Au deposit, NW Iran

The Haftcheshmeh porphyry Cu-Mo-Au deposit is located in the Arasbaran metallogenic belt, northwest Iran, with mineralization occurring mainly in gabbro-diorite and granodiorite porphyry. Pyrite and chalcopyrite are the most abundant sulfides that occur as disseminated and veinlet type ores in the potassic alteration zone. Platinum-group elements (PGEs), Au, and Cu concentrations of selected pyrite- and chalcopyrite-bearing samples were analyzed using in situ LA-ICP-MS and bulk rock Lead Fire Assay. Relatively high contents of PGEs and other precious elements are present in sulfide minerals, especially in pyrite that is the principal carrier of these elements in the deposit. Palladium is the most abundant of the PGEs in the sulfides. The contents of Pd are systematically higher than Pt in this deposit, consistent with other porphyry deposits, although Os, Rh, and Ir abundances are in general equal to or below the limits of detection in pyrite and chalcopyrite. The most important factors related to potential PGEs and chalcophile elements enrichment in the Haftcheshmeh deposit is the oxidized mafic endmember components of source magmas, i.e., high ƒO2 conditions, possibly with a semi-metal collector melt involved, and the high saline magmatic hydrothermal fractionation process. All these mechanisms seem to have enhanced the concentration of PGEs, Au, and other chalcophile metals. PGEs and other chalcophile elements were transported by exsolved high-T, saline magmatic hydrothermal fluids and then low T reaction and reduction to enhance saturation of sulfide phases during mineralization associated with potassic alteration.

Magmatic constraints on the Ermi porphyry copper mineralization, Northeast China: Evidence from zircon U-Pb geochronology, whole-rock geochemistry and Sr-Nd-Hf isotopic geochemistry

The Ermi porphyry Cu deposit (PCD), located on the northeastern margin of the North China Craton (NCC), is a medium-sized PCD with a reserve of > 0.11 Mt and an average grade of 0.6% Cu. Copper mineralization occurs mainly within the intrusions of quartz diorite, granodiorite, granodiorite porphyry and granite porphyry. To reveal the magmatic contributions to mineralization, we conducted zircon U-Pb dating and element geochemical and Sr-Nd-Hf isotope analyses of mineralized intrusions at Ermi on the basis of field and petrographic observations. The zircon LA-ICP-MS U-Pb ages of quartz diorite, granodiorite, granodiorite porphyry and granite porphyry are 95.0 ± 1.0 Ma (n = 16, MSWD = 0.97), 94.2 ± 1.4 Ma (n = 15, MSWD = 0.93), 93.9 ± 1.2 Ma (n = 19, MSWD = 0.22) and 92.0 ± 1.2 Ma (n = 18, MSWD = 0.41), respectively. All of these intrusive rocks belong to metaluminous, calc-alkaline I-type granites. They exhibit high 87Sr/86Sr(t) values (0.7075 to 0.7084), low negative εNd(t) values (-16.7 to −12.6), and variable but mainly negative εHf(t) values (-12.4 to −6.4), with corresponding TDM2(Hf) ages of 2.1 ~ 2.7 Ga. These findings indicate that the initial magma originated from the partial melting of the Archean lower crust of the NCC. Combined with the dynamic background of the study area, we believe that they formed in an active continental margin environment related to the rollback of the subducting Paleo-Pacific slab in the Cretaceous. The oxygen fugacity (fO2) values estimated from rare earth element (REE) and Ti concentrations in zircons show that: The fayalite-magnetite-quartz buffer (ΔFMQ) values of the quartz diorite and granodiorite are −2.6 and 0.87, respectively. The ΔFMQ values of the granodiorite porphyry and granite porphyry are 2.68 and 2.13, respectively. The high oxygen fugacity promoted the enrichment of Cu and other ore-forming elements in the magma. However, the results of estimating crustal thickness from the (La/Yb)N ratio of magma show that the Ermi PCD formed under the condition of a thinned or shallow lower crust (<25 km). Thinned continental crust may lack massive sulfide accumulation and is not conducive to the large-scale storage and accumulation of fertile magmas in the middle or upper crust, which may limit the mineralization scale of the Ermi PCD.

The multiple mineralizations and geodynamic settings of the Laozuoshan Cu–Au deposit in the Jiamusi Massif, NE China: Zircon U–Pb geochronological, elemental and Hf isotopic geochemical evidence

Situated in the centre of the Jiamusi Block, the Laozuoshan deposit is a large-sized deposit with composite of vein and lenticular Au orebodies and veinlet-disseminated Cu-Au orebodies. It is characterized by two types of mineralization, skarn Au mineralization and porphyry Cu-Au mineralization. The former occurs along the contact zone between granodiorite and Proterozoic metamorphic rocks in the eastern and central ore zones, while the latter is hosted in granodiorite porphyry and diorite in the western ore zone. In this study, we present the results of geochronological and geochemical analyses of these rocks which show the following features. (1) Zircon U–Pb dating results show that the ages of granodiorite, diorite and granodiorite porphyry are 264.6±2.6 Ma, 103.2±1 Ma and 104.6±1.8 Ma, respectively. (2) Whole-rock elemental compositions indicate that the granodiorite shows potassium-rich adakitic rock properties, and the diorite has typical island arc calc-alkaline magmatic properties. They are all characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs). (3) The in-situ Hf isotope analysis results show that the granodiorite and diorite have εHf(t) values of −3.7 to −8.7 and −0.4 to 10.7, respectively, corresponding to TDMC ages of 2040–2500 Ma and 630–1650 Ma, respectively. These results indicate two periods of mineralization in the Laozuoshan deposit. Skarn mineralization occurred in the late Permian and was a result of metasomatism between partial melting magma that originated from thickened Paleoproterozoic lower crust and Proterozoic marble. Porphyry mineralization took place in the Early Cretaceous and was a result of the shallow emplacement of mid-Neoproterozoic mantle-derived magma with the addition of crustal materials. In terms of geodynamic settings, skarn Au and porphyry Cu-Au mineralization occurred in a compressional setting formed during the gradual closure of the Paleo-Asian Ocean, and a crustal-thinning setting formed from Eurasian Plate-ward subduction, retreating, and rollback of the Paleo-Pacific Plate, respectively.

Early Mesozoic crustal evolution in the NW segment of West Qinling, China: Evidence from diverse intermediate–felsic igneous rocks

Continental convergent margins are commonly considered as significant sites for understanding crustal reworking and growth, but the geodynamic processes involving crustal growth remain highly debatable. Triassic intermediate–felsic intrusive rocks are widespread in the northwestern segment of the West Qinling orogenic belt on the NE Tibetan Plateau. These rocks well document the evolution of one branch of the Paleo-Tethys oceans (i.e., the A'nyemaqen Ocean) in East Asia. Here we present a comprehensive study of zircon UPb and LuHf isotopic data, along with whole-rock elemental and SrNd isotopic data to decipher the origins of intermediate–felsic intrusions and crustal evolution of the West Qinling in the Triassic. Two episodes of magmatism were detected in this study, i.e., the early high-Mg diorite porphyry–granodiorite–granodiorite porphyry assemblage (Episode #1, ~244–230 Ma), followed by a later monzogranite–granodiorite–granite porphyry assemblage (Episode #2, ~228–203 Ma). These two episodes of magmatism are interpreted as products related to oceanic subduction and continental collision, respectively. In Episode #1, the mafic magmatic enclaves were mainly mantle-derived and were indicative of magma mixing. The high-Mg diorite porphyries were likely derived from partial melting of the mantle wedge metasomatized by sediment-derived melts, whereas the coeval granodiorites and granodiorite porphyries mainly originated from partial melting of amphibolites with significant addition of mantle-derived components. By contrast, the granodiorite porphyries in Episode #2 probably originated from the lower crust-sourced melts with insignificant mantle contribution. The contemporaneous granodiorites and monzogranites were generated by partial melting of the crustal amphibolites or metagreywackes. The proportion of positive zircon εHf(t) values decreased from Episode #1 to Episode #2, indicating a decreasing tendency of the mantle or juvenile component contribution. Our study suggests that the addition of mantle-derived magmas to the continental crust during oceanic subduction processes played an important role in crustal growth.

Geology, fluid inclusion and H-O-S-Pb isotope study of the Ganhegou epithermal gold deposit in Yanbian, NE China: Implications for ore genesis and mineralization process

• Ganhegou deposite is a typical low-sulfidation epithermal gold deposit. • The ore-forming fluids were derived from intermediate-acid magmatic water. • The ore-forming materials were derived from Neoproterozoic juvenile lower crust . • Twice boiling are the main mechanism for the precipitation of precious elements. The Yanbian mining district is located at the eastern end of the Central Asian orogenic belt and northeast of the western Pacific continental margin metallogenic belt. It is a porphyry-epithermal Cu-Au mining district related to Mesozoic continental volcanic eruptions and hypabyssal magmatism. To explore the genesis and mineralization process of epithermal gold deposits, we conducted a systematic study of the geology, fluid inclusions and H-O-S-Pb isotopes of the Ganhegou gold deposit, which is expected to be revealed as a medium-sized deposit in the latest exploration. We found the following: (1) The deposit occurs in Early Cretaceous continental andesites of the Jingouling Formation and granodiorite porphyry. The ore belts are controlled by NW-trending volcanic faults. The mineralization process can be divided into the quartz-hematite-arsenopyrite-pyrite stage (I), grey-white quartz-pyrite stage (II), smoky quartz-polymetallic sulfide stage (III), milky quartz-adularia stage (IV) and carbonate stage (V). Gold precipitated in stage III. (2) Vapour-rich-, liquid-rich-, pure-liquid- and pure-vapour-type FIs developed in quartz in stages II, III and IV, and the average homogenization temperatures in these stages are 325 ℃, 273 ℃ and 229 ℃, respectively. The ore-forming fluids belonged to the H 2 O-NaCl ± CO 2 system. (3) The δ 18 O H2O and δD H2O values of stage II-IV range from −9.9 to −5.2‰ and −121.9 to −119.8‰, respectively, indicating that the ore-forming fluids were driven by intermediate-felsic magmatic water and mixed with meteoric water during mineralization. (4) The δ 34 S values of pyrite in stages II and III range from −5.8 to −3.4‰, whereas the values of 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb are 15.529–15.551, 18.239–18.257 and 38.075–38.153, respectively, implying that the ore-forming materials were derived from Neoproterozoic lower crust. These characteristics indicate that Ganhegou is a low-sulfidation epithermal gold deposit. Mineralization occurred via several main processes: (i) The ore-forming fluids migrated along volcanic faults to suitable positions driven by intermediate-felsic magmatic water. (ii) In stage I, the quartz-arsenopyrite-hematite assemblage formed under relatively high oxidation conditions. (iii) In stage II, the pyrite-hessite-galena-quartz veins formed in the near-neutral environment, which was slightly reduced relative to that of stage I due to the fluid boiling. (iv) In stage III, the gold-bearing quartz veins formed due to the fluid boiling and mixing. (v) In stage IV, the precipitation of quartz-adularia-pyrite veins occurred under near-neutral conditions (pH≈5). (iv) Small-scale carbonate veinlets formed in stage V, signalling the end of mineralization.

Genesis of the Yanghuidongzi Cu deposit, NE China: Constraints from H-O-Pb isotopic compositions and geochronological study

• The Yanghuidongzi Cu deposit classified as a porphyry type Cu deposit. • H-O isotopes indicate a mixing of magmatic water and meteoric water for ore fluids. • Pb-Re isotopes indicated a deep seated magma mixed with crustal materials for ore metals. • The Yanghuidongzi Cu deposit formed during Early Jurassic . The newly-discovered Yanghuidongzi porphyry Cu deposit is located in the southeastern part of Heilongjiang Province in NE China and represents one of the rare Jurassic porphyry Cu deposits within the easternmost segment of the Central Asian Orogenic Belt (CAOB). The Cu mineralization occurs as veins and disseminations hosted by granodiorite porphyry, associated with typical porphyry copper deposit alteration zoning, which is characterized by from an inner K-silicate zone through to a quartz–sericite zone to an outer propylitic zone, the K-silicate alteration and quartz–sericite alteration are closely related to mineralization. LA-ICP-MS zircon U-Pb data, sericite Ar-Ar and Molybdenite Re-Os data, and H-O and Pb isotopic compositions are used to constrain the ore-forming age and genesis of the Yanghuidongzi Cu deposit. LA-ICP-MS U-Pb dating of zircons from three granodiorite porphyry samples yielded weighted mean 206 Pb/ 238 U ages of 194.3 ± 1.2 Ma, 192.0 ± 2.0 Ma, and 194.6 ± 2.1 Ma respectively, whereas zircon U-Pb age of granodiorite in the study area yielded weighted mean 206 Pb/ 238 U age of 199.5 ± 1.5 Ma that are interpreted to be the emplacement age of these intrusions. 40 Ar- 39 Ar dating of sericite from a quartz-pyrite vein and a quartz-polymetallic sulfide vein yielded plateau ages of 193.9 ± 2.1 Ma and 193.6 ± 1.9 Ma, respectively, whereas five molybdenite samples yielded a Re-Os isochron age of 194.8 ± 2.1 Ma, with a weighted mean model age of 193.6 ± 1.2 Ma. Mineralization ages are consistent with the emplaced ages of the granodiorite porphyry within the analytical uncertainties, indicating that the Cu mineralization is genetically related to the granodiorite porphyry. The fluid δ 18 O fluid and δ 18 D fluid values range from −4.22‰ to 6.5‰ and from −92.8‰ to −65.7‰, respectively, indicating that the ore fluids were mixtures of magmatic and meteoric water. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb values of the pyrite and chalcopyrite are 17.547–18.327, 15.446–15.505, and 37.408–38.113, respectively, suggesting a common, magmatic source for the sulfur. Taking Re (6.75–29.53 ppm) data into consideration, the sources of ore-forming materials may be from a mixture of crustal and mantle sources. Combining our new data with the Jurassic regional tectonic setting, the Yanghuidongzi Cu deposit and the related granitoids formed in a compressional tectonic setting are associated with the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.

Genesis of the Gongpoquan porphyry Cu deposit in Beishan Orogen, NW China: Evidence from geochronology, fluid inclusions, H–O–S isotopes, and sulfides trace element

• The Gongpoquan porphyry Cu deposit is located in the Beishan Orogen, NW China. • Muscovite 40 Ar/ 39 Ar dating yielded Early Devonian (404.0 ± 2.2 Ma) mineralization age. • Ore fluid was magmatic-sourced with more meteoric water input toward late stage. • Fluid mixing and boiling were likely effective mechanism for Cu ore precipitation. • The Devonian mineralization was likely related to Paleo-Tianshan Ocean sbuduction. The Gongpoquan is a representative porphyry Cu deposit in the Beishan Orogen, which is located between the Tarim–North China Craton and South Mongolia. The mineralization is associated with dacite porphyry and granodiorite porphyry, and occurs as veins/veinlets, and disseminations. The mineralization can be divided into three stages: (I) quartz–sericite/muscovite–K-feldspar ± chalcopyrite/bornite veins associated with phyllic alteration, (II) quartz–K-feldspar–chalcopyrite/bornite/pyrite veins/veinlets associated with propylitic alteration, and (III) quartz–calcite ± pyrite ± epidote veins. The mineralizing fluids are characterized by intermediate-low temperatures (peak at 210 to 220 °C), intermediate-low salinities (peak at 1.5 to 5.5 wt% NaCl eqv.), and belong to a H 2 O–NaCl–CO 2 ± CH 4 ± N 2 system. Oxygen and hydrogen isotope data indicate that stage I and II fluids were dominantly magmatic-sourced, with increasing meteoric water input toward stage III. Stage I and IIa-b chalcopyrite, bornite, and sphalerite have in situ δ 34 S values of −9.0 to −2.4‰, indicating a magmatic sulfur origin. The chalcopyrite has largely similar contents of Ti, Ge, As, Sn, Sb, and Se across stage I to III, and the contents are higher than those of bornite and sphalerite. This indicates that sulfide formation are controlled by intermediate-low temperatures with no mineral textural modification or chemical remobilization throughout the mineralization. Muscovite 40 Ar/ 39 Ar dating of stage I vein in the granodiorite porphyry ore host yielded an Early Devonian age of 404.0 ± 2.2 Ma (MSWD = 0.40), indicative of the close temporal with the Gongpoquan arc granitoids formed during the Paleo-Tianshan Ocean subduction.

Chemistry of rock-forming silicate and sulfide minerals in the granitoids and volcanic rocks of the Zefreh porphyry Cu–Mo deposit, central Iran: Implications for crystallization, alteration, and mineralization potential

Abstract Cu–Mo mineralization and associated hydrothermal alteration zones in the Zefreh porphyry Cu–Mo deposit are a result of the emplacement of the early Miocene granodioritic-to-granitic porphyritic intrusions into the Eocene volcanic rocks (dacites, pyroclastic rocks, and andesitic lavas) during active subduction along the Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran. The compositions of rock-forming minerals, such as plagioclase, amphibole, and biotite, in the granitoids of the Zefreh magmatic suite are used to determine temperature and oxygen fugacity in the magma during crystallization and emplacement. Plagioclase is locally unaltered and ranges widely in composition with reverse, normal, and oscillatory zoning, but there is no evidence of excess aluminum. Primary calcic amphiboles in the granodiorite porphyry are mainly magnesio-hornblende with high Mg#’s. The crystallization temperature of the granodiorite is in the range of 765–867 °C (average 821 ± 28 °C for amphibole–plagioclase geothermometer) and 706–861 °C (average 808 ± 35 °C for amphibole alone). Whereas, the zircon saturation temperature for the Zefreh granodiorite is lower and ranges from 724° to 733 °C (average 729 ± 4 °C). Biotites in the least-altered granodiorite and in the potassic alteration are Mg-rich and Ti-poor, and mainly fall within the fields of phlogopite and re-equilibrated primary biotite, because of their low TiO2 contents (2.7–4.5 wt%, average 3.5 wt%). Copper and molybdenum in the Zefreh porphyry deposit appear to have been transported by Cl-rich hydrothermal fluids as chloride complexes, based on the calculated halogen fugacity ratios of the fluid in equilibrium with hydrothermal biotite that range from 5.0 to 5.4 for log (ƒH2O)/(ƒHF), 4.3 to 4.8 for log (ƒH2O)/(ƒHCl), and –2.0 to –1.4 for log (ƒHF)/(ƒHCl). The calculated fugacity ratios indicate that the biotites equilibrated with hydrothermal fluids that varied in composition, including oxygen, sulfur, and halogen fugacities. The intercept values for biotites from the Zefreh porphyry Cu–Mo deposit [IV(F) = 1.9 to 2.2 and IV(Cl) = –4.8 to –4.3] correspond to those from other well-known porphyry Cu–(Mo–Au) deposits worldwide [IV(F) = 1.5 to 2.8 and IV(Cl) = –5.0 to –3.5]. On the other hand, hydrothermal chlorite and epidote in the propylitically altered granodiorite of the Zefreh deposit are more Fe-rich and Mn-poor than those in some mineralized porphyry systems. The calculated temperatures of chlorite formation by the geothermometer of Cathelineau (1988) are all similar (300–330 °C), suggesting the potassically altered granodiorite was also affected by later, cooler hydrothermal fluids associated with the distal propylitic alteration zone. Disseminated chalcopyrite in the matrix of the potassically and propylitically altered granodiorite hosts as much as 1.3 wt% Zn and 0.1 wt% As. Based on whole-rock and mineral compositions, we conclude that the Zefreh magmatic system is similar in many regards to subduction-related ore systems, but it is unlikely to host a major porphyry Cu–Mo deposit.

Petrogenesis and oxygen fugacity of the Xintian complex associated with the Naozhi-Xintian porphyry–epithermal system in the Yanbian area, NE China

• The Xintian complex is associated with a telescoped porphyry-epithermal system. • Influxes of mafic melts into felsic melts result in the emplacement of this complex. • High oxidation state and magmatic water are conducive to the Cu–Au mineralization. The Naozhi polymetallic veins classified into the intermediate-sulfidation (IS) type and the 2 km northwest Xintian porphyry Cu–Mo ore occurrence in the Yanbian area, Northeast China, constitute a telescoped porphyry-epithermal system. IS veins are surrounded by Early Jurassic granodiorite stocks (189 ± 1 Ma; zircon U-Pb ) and Early Cretaceous andesite lava (128 – 130 Ma; zircon U-Pb ). They are partially covered by younger pyroclastic rocks dated at 108 ± 2 Ma (Zircon U-Pb ). The Xintian occurrence is connected in space and time with an intrusive complex including five sequential phases from gabbro diorite and granodiorite stocks through diorite porphyry dykes to granodiorite porphyry and granite porphyry stocks, with indistinguishable ages within errors (128 ± 1 Ma to 126 ± 1 Ma zircon 206 Pb/ 238 U by laser ablation inductively coupled plasma mass spectrometry). The broad compositional variations (eg., 52.24 – 69.23 wt% SiO 2 ) of the complex and the igneous mafic microgranular enclaves (MMEs) hosted by granodiorite stocks are likely responses to inputs of hot mafic melts into a shallow felsic magma chamber. Based on the trace element contents of zircons, the redox conditions during the crystallization of zircon minerals in equilibrium with the melts are evaluated by calculating the FMQ values. The early mafic phase (gabbro diorite; FMQ 4.60 ± 1.33) is more oxidized than later phases (granodiorite, diorite porphyry, granodiorite porphyry, and granite porphyry) with FMQ values of 1.70 ± 1.80 to 2.28 ± 2.36. The highly oxidizing conditions of associated magmas, as well as high magmatic water contents (>4%) because of ubiquitous biotite and amphibole in this complex, are conducive to escape of primary volatiles from shallow, fertile porphyry magmas, with consequent ore deposition in structurally optimal positions at Naozhi-Xintian.

Himalayan Miocene adakitic rocks, a case study of the Mayum pluton: Insights into geodynamic processes within the subducted Indian continental lithosphere and Himalayan mid-Miocene tectonic regime transition

AbstractThe Himalayan Orogen is a typical continental collision orogenic belt that formed during India-Asia collision. The orogeny involved a transition in tectonic regime, which led to E-W–trending extension during the middle Miocene. At the same time, widespread post-collisional adakitic magmatism occurred in southern Tibet, particularly in the Lhasa Terrane, and these rocks provide a valuable record of the collisional geodynamic processes within the lithosphere. Few studies have focused on the middle Miocene adakitic rocks of the Himalayan Orogen, so further research is required to constrain their origin and geodynamics. This study presents new geochronological and geochemical data, including the whole rock Sr-Nd and zircon Hf isotopic compositions from the Mayum pluton in the Mayum-Gong Tso area, Northern Himalaya. Zircon U-Pb ages show that the Mayum granodiorite porphyries crystallized at 16.67 ± 0.14 Ma (mean square weighted deviation [MSWD] = 0.82, n = 29) and 16.68 ± 0.16 Ma (MSWD = 1.13, n = 28), indicating that they formed during the middle Miocene. The major and trace element characteristics are as follows: SiO2 = 65.79–67.31 wt%, Al2O3 = 15.28–16.00 wt%, MgO = 1.77–1.89 wt%, Y = 12.0–13.5 ppm, Yb = 0.11–0.99 ppm, Sr = 719–822 ppm, (La/Yb)N = 21.89–27.02, Sr/Y = 56.1–65.5, and the rocks have weak negative Eu anomalies (Eu/Eu* = 0.76–0.85), indicating that they are adakitic rocks and show high Sr-Ba granite affinity. The Mayum granodiorite porphyries have high K2O contents (3.42–3.65 wt%), Na2O (3.76–4.04 wt%), and K2O/Na2O ratios of 0.91–0.95, indicating a high-K calc-alkaline affinity. All samples are enriched in large-ion lithophile elements and depleted in high field strength elements. The initial 87Sr/86Sr ratios are 0.709262–0.709327 and εNd(t) values are −6.36 to −7.07, which correspond to two-stage Nd model ages [TDM2(Nd)] of 1405–1348 Ma. In situ zircon Lu-Hf isotopic compositions are variable, with 176Hf/177Hf ratios of 0.2823845–0.282824, εHf(t) values of −13.37 to +2.17, and two-stage Hf model ages [TDM2(Hf)] of 1704–841 Ma. These geochemical and Sr-Nd-Hf isotopic characteristics indicate that the Mayum granodiorite porphyries may be derived from partial melting of the subducted Indian thickened ancient mafic lower crust (∼92%) mixed with depleted mid-ocean ridge basalt mantle material input (∼8%) slightly. Crust-mantle interaction was induced by asthenospheric upwelling followed by the underplating of the Himalayan lower crust beneath Southern Tibet during the middle Miocene in response to significant changes in the geodynamics of the India-Asia collisional orogen. These deep geodynamic processes reflect the break-off or rollback of the subducted Indian continental slab, which caused asthenospheric upwelling, the input of juvenile heat, and the addition of depleted mantle material. This study indicates that the middle Miocene Himalayan adakitic rocks, which include the Miocene Yardoi two-mica granite, Gyangzê granite porphyry dike, Bendui two-mica granite, Langkazi enclave, Kuday dacitic dike, Lasa pluton, and Mayum pluton, form a belt of adakitic rocks in the Northern Himalaya to the south of the Indus-Tsangpo Suture Zone. These adakitic rocks have similar temporal and spatial distributions, geochemical features, and Sr-Nd isotopic compositions, indicating that their petrogenesis and geodynamic settings were similar. At that time there was widespread initiation of N-S–trending rifting, exhumation of central Himalayan eclogites, and large changes in the compositions of Himalayan leucogranites in the Himalayan Orogen. These can be attributed to significant changes in the characteristics of the subducted Indian continental lithosphere during the middle Miocene. The middle Miocene Himalayan adakitic rocks provide valuable insights into this transition in the tectonic regime and deep geodynamic processes.

New constraints on the source of the Late Jurassic granodiorites from Gutian porphyry Cu–Mo deposit in the southeast coastal area, South China

The Gutian porphyry Cu–Mo deposit, which is localized at the Southeast Coastal Metallogenic Belt (SCMB) in South China, is a newly identified porphyry Cu deposit occurring as part of a granodioritic igneous complex. We report new zircon U–Pb, in–situ apatite Sr–Nd, zircon Hf–O isotopic, and rock geochemical data for the early stage granodiorite, granodioritic porphyry (P1) and mineralization-related granodioritic porphyry (P2) of the Gutian complex, so as to constrain the magmatic sources of the Late Jurassic porphyry Cu deposit and crust–mantle interaction during the Late Jurassic. Zircon U-Pb dating yielded weighted-mean ages of 161.0 ± 1.7 Ma (n = 22; MSWD = 0.42) for the granodiorite and 159.9 ± 1.9 Ma (n = 23; MSWD = 0.37) for the granodioritic porphyry (P2). The granodioritic complex is featured by the increased Sr level, reduced Y level, great (La/Yb)N and Sr/Y ratios, indicating adakitic affinity. Both intrusions exhibit homogeneous enriched Sr–Nd–Hf isotopic compositions ((87Sr/86Sr)i = 0.7084–0.7099; εNd(t) = –10.3 to –7.8; εHf(t) = –13.1 to –8.8, and high δ18O values of 6.96‰ to 9.29‰ with an average at 7.92‰. Hf model ages (T2DM) vary from 1.76 to 2.03 Ga with a peak at ca. 1.85 Ga. The similar emplacement ages and isotopic compositions suggest that both intrusions formed from a common magmatic source: Paleoproterozoic thickened lower crust with ~ 20% garnet-bearing amphibolite. As suggested by Nb/Ta and Nb/U ratios, Mg# values, and the isotopic data of binary mixing models Hf–O and Sr–Nd, ca. 30–40% of mantle-derived magma may have been added to the source region (HfM/HfC = 0.2). This result was verified by the increased εHf(t) and decreased δ18O values than those of Paleoproterozoic juvenile material (εHf(106 Ma) = –24.7; δ18O values of ca. 8‰ to 10‰, with a peak value of 8.55‰). The geochemical characteristics are similar to arc magmas and this, and the coeval syenites and basalts, indicate that the mantle would have been metasomatized by a subduction-related component during the Middle to Late Jurassic. The Gutian granitoids are part of a Jurassic magmatic arc and are the product of the crust-mantle interaction resulting from paleo-Pacific subduction, which is the most important dynamic process for porphyry deposits in Late Mesozoic Southeastern Coastal area.

Geochronological and geochemical constraints on the genesis of the Tieshan complex in the Edong district, Eastern China with implications for Fe and Cu skarn mineralization

Fe and Cu skarn deposits constitute the most important skarn type worldwide, whereas the controlling factors that lead to the difference in metal associations remain not well known. The Fe- and Cu-hosting Tieshan complex in the Edong district provides a good opportunity for comparative study on the genetic differences between Fe and Cu skarn deposits. In this study, integrated studies of geochronology, geochemistry and Sr-Nd-Hf isotope compositions were conducted on the complex. LA-ICP-MS zircon U-Pb dating results show that the Tieshan complex was emplaced in the time interval of 135 ± 3 to 144 ± 1 Ma. Multiphase rocks from the complex can be broadly subdivided into two suites. The Fe-Cu-related suite, which consists of diopside diorite, quartz diorite, quartz diorite porphyrite and porphyritic granodiorite, possesses low SiO2 (53.5–67.1 wt.%), K2O (2.44–3.53 wt.%) and Rb (45−83 ppm) contents, but high Sr (1132−2684 ppm), Ba (1073−1656 ppm) contents and negligible Eu anomalies, with very high Sr/Y (>90) ratios, similar to typical high Ba-Sr granitoids. The rock suite has initial 87Sr/86Sr values of 0.70648 to 0.70737, εNd(t) values of −12.3 to −8.2 and εHf(t) values of −16 to −7, comparable to values of the Early Cretaceous mafic rocks in the Edong district and adjacent areas, indicating that it might be largely derived from an enriched lithospheric mantle source, along with minor involvement of lower-crustal components. By contrast, the Fe-related suite, which is composed of quartz diorite, quartz diorite porphyrite and granodiorite porphyry, is characterized by relatively high SiO2 (63.0–71.0 wt.%) and K2O contents (3.36–5.53 wt.%), and a wide range of Sr (158−1135 ppm), Ba (762−1366 ppm) contents and Sr/Y (11–99) ratios. In combination with the presence of abundant inherited zircon grains, the lower εNd(t) (−12.4 to −9.3) and εHf(t) (−25 to −15) values indicate a greater degree of lower-crustal contribution for the Fe-related suite. In addition, the calculated zircon Ce (Ce/Ce* and Ce4+/Ce3+) and Eu (Eu/Eu*) anomalies suggest that the Fe-Cu-related suite has much higher oxygen fugacity (fO2) than the Fe-related suite. This study highlights fO2 and fractionation degree of magma as useful indicators for differentiating Fe and Cu skarn mineralization.

Young Silicic Magmatism of the Greater Caucasus, Russia, with implication for its delamination origin based on zircon petrochronology and thermomechanical modeling

Several kilometers of rapid uplift in the past 2–3 million years in the Greater Caucasus in Russia has produced world-class exposures of Pliocene-Pleistocene age granites and ignimbrites at the Tyrnyauz and Chegem volcanic centers just to the east of Europe's highest mountain and active volcano, Mount Elbrus. This represents one of the world's best-preserved examples of silicic magmatism in a continental collision environment. We report results of a multi-method zircon petrochronologic (U--Pb, O--Hf isotopes, trace elements) investigation of six ignimbrites, lavas, and associated granodioritic porphyries from these localities. We observe two pulses of magmatism at 2.92 and 1.98 Ma related to Chegem and Tyrnyauz, respectively. High precision CA-ID-TIMS dating of zircons from the top and bottom of the Chegem ignimbrite and its associated porphyry yield indistinguishable age spectra recording 160 kyr of magma assembly and differentiation, with 2.9181 ± 0.0014 Ma eruption age as is constrained by the youngest dated zircon population. Together with overlapping O and Hf isotopic values, this suggests that they represent a large volume of pre-eruptively homogenized magma with ~20% crystals. Zircons have isotopically diverse cores (δ18O = +3.4–6.7‰, εHf = +0.8 to +5.6) while the rims (+5.75 ± 0.20‰, εHf = 3.3 ± 0.7) are in isotopic equilibrium with associated unaltered glass and major phenocryst phases. The neighboring and younger ignimbrites and granites of the nearby Elbrus and Tyrnyauz centers have overlapping higher δ18O and lower εHf zircon values and cluster narrowly in age around 1.98 Ma, suggesting a common source for all these ignimbrites, likely in the Tyrnyauz area. Isotopic data for Chegem, Elbrus and Tyrnyauz zircons and rocks require the contribution of a high proportion (25–55%) of Paleozoic crust to magma petrogenesis.The origin of sudden spikes of voluminous silicic magmatism is further investigated using thermomechanical modeling of the collisional environment. We show that the voluminous silicic volcanism at Chegem, Tyrnyauz and Elbrus is best explained by heating of the lower crust by asthenospheric upwelling after a relict slab detached and sank into the mantle at approximately 5 Ma. This timing is coincident with both the beginning of rapid uplift of the Greater Caucasus and initiation of major volcanism. After this initial melting, continuing delamination of the lithosphere and lower crust from the subducting plate produced broad mantle melting and basaltic volcanism, potentially explaining continued regional-scale magmatism in both the Greater and Lesser Caucasus.

Petrogenesis and geodynamic setting of the Late Carboniferous granodiorite porphyry in Miaoergou pluton, southern West Junggar

位于西准噶尔南部的庙尔沟岩体主体由碱长花岗岩和少量紫苏花岗岩组成。本文在前人工作基础上，以岩体东南边缘新发现的花岗闪长斑岩为研究对象，开展岩石学、年代学和Hf同位素以及全岩地球化学研究，确定花岗闪长斑岩形成时代、揭示岩石成因类型及源区属性、探讨其与碱长花岗岩和紫苏花岗岩岩浆演化成因联系及其形成的深部动力学过程。锆石U-Pb定年结果显示，花岗闪长斑岩形成于317.4±1.9Ma，为晚石炭世早期岩浆活动的产物，明显早于紫苏花岗岩（~307Ma）和碱长花岗岩（~303Ma）。岩石地球化学数据表明，花岗闪长斑岩具有较高硅、中等铝，贫钙、铁、镁，富集Rb、K、Th、U，强烈亏损Nb、Ta、Ti的特征，为钙碱性弱过铝质I型花岗岩；紫苏花岗岩更多的表现出钙碱性-高钾钙碱性镁质I型紫苏花岗岩特征；碱长花岗岩为碱性准铝质-弱过铝质A型花岗岩。锆石Hf同位素分析结果表明，花岗闪长斑岩、紫苏花岗岩和碱长花岗岩均具有高正的ε_Hf（t）值（+11.6~+15.8）和年轻的二阶段模式年龄（325~600Ma），表明其原始岩浆主要起源于亏损地幔新衍生的年轻地壳物质。综合分析认为，庙尔沟岩体花岗闪长斑岩形成于晚石炭世早期洋壳俯冲背景，由底侵的、受流体交代的幔源基性岩浆与其诱发的年轻下地壳酸性岩浆在深部混合而成。紫苏花岗岩和碱长花岗岩形成于弧后伸展背景，前者是伸展初期继续底侵于下地壳的幔源玄武质岩浆降温释放大量的水和热诱使早期侵位于下地壳的镁铁质岩石再次发生部分熔融的产物，后者是伸展后期大规模软流圈地幔上涌底垫加热年轻中下地壳使其部分熔融而成。;The Miaoergou pluton, located in southern West Junggar, is mainly composed of alkali-feldspar granites with small amount of charnockites. On the basis of previous researches, this paper mainly focuses on the newly discovered granodiorite porphyry in southwestern margin of the Miaoergou pluton. A comprehensive study of petrographical, zircon U-Pb geochronological and in-situ Hf isotopic, whole-rock geochemical analyses were carried out to determine its diagenetic age and reveal the petrogenesis, the nature and composition of the magma source of this porphyry, and furthermore, to discuss the genetic relationships among the granodiorite porphyries, alkali-feldspar granites and charnockites and their geodynamic processes. LA-ICP-MS zircon U-Pb dating for the granodiorite porphyry yielded crystallization age of 317.4±1.9Ma, defining an early Late Carboniferous magmatic event in southern West Junggar, which is significantly earlier than the ages of charnockites (~307Ma) and alkali-feldspar granites (~303Ma). The geochemical characteristics indicate that the studied granodiorite porphyries belong to cal-alkaline weakly peraluminous I-type granite, and are characterized by slightly high silicon, medium aluminum, but low ferrum, calcium and magnesium, and also enrichment in Rb, K, Th, U with pronounced negative Nb, Ta and Ti anomalies. The charnockites possess calc-alkaline to high-K calc-alkaline magnesian I-type charnockite affinities, which were previously considered A-type granites by some geologists, while alkali-feldspar granites belong to alkaline metaluminous to weakly peraluminous A-type granites. In-situ zircon Hf isotope analyses show that these granites have high positive ε_Hf(t) values (+11.6~+15.8) and very young two-stage Hf model ages of 325~600Ma, indicating that the magma was sourced from juvenile crust originated from depleted mantle during the Late Neoproterozoic to Early Carboniferous period. In association with previous analysis, it is proposed that the Miaoergou granodiorite porphyries were formed in an oceanic crust subduction setting during early Late Carboniferous. They are probably the products of the acidic magma formed by partial melting of the juvenile lower crust and mixed with the underplated basaltic magma derived from the fluid metasomatic mantle wedge in the deep crust to some extent. Both the charnockites and alkali-feldspar granites were formed in a back-arc extensional setting related to the northwestward subduction of the Junggar oceanic crust. The charnockites may be generated by re-melting of juvenile lower crust mafic rocks, probably triggered by addition of water and heat released from cooling of underplated depleted mantle-derived basaltic magma during the incipient rifting stage of the back-arc basin, and the alkali-feldspar granites may be generated by partial melting of the juvenile middle-lower crust induced by the large-scale upwelling of asthenosphere during the later stage of the back-arc extension.

Geochronological framework and coexisting Sn-Cu mineralization of Jinkeng Sn-Cu deposit in eastern Guangdong, China

金坑Sn-Cu矿床是粤东地区新发现的典型Sn-Cu共生矿床。矿区发育花岗闪长斑岩、中粗粒黑云母花岗岩和细粒花岗岩等多种侵入岩以及高基坪组火山岩，而这些岩石的年代学格架，及其与成矿过程关系还不清楚。因此，本文以粤东地区新发现的金坑铜锡矿床为研究对象，系统开展不同岩性侵入岩锆石和矿石锡石的U-Pb年龄测定，旨在浅析Sn-Cu共生成矿机制和成矿背景。结果表明，矿区中粗粒黑云母花岗岩和细粒花岗岩的锆石U-Pb年龄为145.2±1.2Ma和144.1±2.2Ma，这些年龄与该矿床的锡石U-Pb年龄（144.2±5.6Ma）在误差范围内一致，表明区内中粗粒黑云母花岗岩和细粒花岗岩与锡矿成矿关系密切。此外，获得花岗闪长斑岩U-Pb年龄为147.4±1.1Ma，且花岗闪长斑岩和高基坪组火山岩具有较高Cu含量，表明Cu可能来自于这两类岩石。结合前人研究成果，我们认为早白垩世矿区内发生了含锡中粗粒黑云母花岗岩和细粒花岗岩的侵位，其分异出富锡的还原性流体由于物理化学条件的变化析出了锡石；随着水岩反应的进行，流体萃取了围岩中的Cu、Pb、Zn等成矿元素，随着流体温度、盐度的持续下降，Cu、Pb、Zn和剩余的Sn在构造带内析出沉淀，从而造成了Sn-Cu共生成矿。;The Jinkeng Sn-Cu deposit is a typical coexisting Sn-Cu deposit newly discovered in the eastern Guangdong Province. Volcanic rocks of Gaojiping Formation and various intrusive rocks including granodiorite porphyry, biotite granite and fine-grained granite are developed in the mining area. However, the geochronology of these rocks and their relationship with mineralization are still unclear. In this paper, we systematically determined the U-Pb ages of zircon and cassiterite from different intrusive rocks or ore body from the Jinkeng Sn-Cu deposit, in order to investigate the mechanism of coexisting Sn-Cu mineralization and metallogenic setting. Zircon U-Pb dating of the biotite granite and fine-grained granite in the Jinkeng deposit yielded concordant ages of 145.2±1.2Ma and 144.1±2.2Ma, consistent with the cassiterite U-Pb age (144.2±5.6Ma), indicating a genetic link between the biotite granite and fine-grained granite and the Sn mineralization. In addition, the granodiorite porphyry with a U-Pb age of 147.4±1.1Ma and the volcanic rocks of the Gaojiping Formation having high Cu contents, likely suggesting a Cu source. Combined with the previous studies, we propose the Sn-bearing granite intruded during the Early Cretaceous in the mining area, and then evolved high-Sn fluids resulted in cassiterite precipitation due to the change of physicochemical conditions. With the progress of fluid-rock reactions, Cu, Pb and Zn were extracted from the surrounding rock by fluid. Cu, Pb, Zn and remaining Sn precipitated coevally in the structures with the decrease of fluid temperature and salinity, which resulted in coexisting Sn-Cu mineralization.