Porphyry Mo Deposit Research Articles

Ore-Forming Fluids of the Aleksandrovskoe and Davenda Deposits (Eastern Transbaikalia)

A study of the composition of fluid inclusions in ore minerals of the Davenda Mo–porphyry deposit and the Aleksandrovskoe sulfide–quartz–gold ore deposit, as well as of fluid inclusions in minerals of igneous rocks, showed that ore-forming fluids inherit the salt and gas composition of magmatic fluids generated during crystallization of ore-bearing rocks of the Amudzhikan–Sretensky Igneous Complex, which formed simultaneously with the Au and Mo mineralization. The gold-bearing sulfide–quartz veins of the Aleksandrovskoe deposit formed with the participation of two types of hydrothermal fluids, differing in the composition of salts and the gas phase: homogeneous Ca–Na chloride fluids with CO2 and heterophasic Na–K–Fe-chloride fluids, which indicates two sources of ore-forming fluids during the formation of Au-mineralization. Na–K–Fe-chloride fluids in terms of salt and gas composition were similar to the ore-forming fluids of the Mo-mineralization of the Davenda deposit. Ore-forming Ca–Na-chloride with CO2 The fluids of the Aleksandrovskoe field are comparable in salt and gas composition with the magmatogenic fluids of quartz diorite porphyries and diorite porphyrites. Ore forming Na–K–Fe carbonate-chloride fluids of the Davenda and Aleksandrovskoe deposits show great similarity in composition to magmatic fluids of granite porphyry and emphasize the genetic identity of Mo mineralization in both deposits. The data obtained confirm the widespread opinion that a genetic relationship exists between gold mineralization and dikes of intermediate and mafic composition, and molybdenum–porphyry mineralization with granite–porphyry of the Amudzhikan–Sretensky Igneous Complex. The real agents of this genetic link are metalliferous magmatogenic fluids, the salt and gas composition of which inherit ore-forming fluids. The formation depth of productive ore mineral assemblages in veins of the Aleksandrovskoe and Davenda deposits is estimated at 7.9–7 and 8–6.3 km, respectively, which is not typical of porphyry deposits, the formation of which is characterized by shallower depths.

Zircon U–Pb and molybdenite Re–Os dating and geological implications of the Shimadong porphyry molybdenum deposit in eastern Yanbian, northeastern China

The Shimadong porphyry Mo deposit is located in eastern Yanbian, in the eastern part of the north margin of the North China craton, northeastern China. Here, we present the whole-rock major and trace elements, zircon U–Pb and Hf isotope data, and molybdenite Re–Os data for the Shimadong deposit. The porphyry was emplaced at 163.7 ± 0.9 Ma and the mineralization at 163.1 ± 0.9 Ma, suggesting that the mineralization was associated with the emplacement of the Shimadong porphyritic monzogranite. The porphyritic monzogranite had high SiO2 (70.09–70.55 wt%) and K2O + Na2O (7.98–8.27 wt%) contents and low MgO (0.51–0.53 wt%), TFeO (2.4–2.47 wt%), CaO (2.19–2.26 wt%), and K2O/Na2O (0.8–0.82) contents. The porphyry was rich in large ion lithophile elements Rb, Ba, K, and Sr, depleted in high-field-strength elements Y, Nb, Ta, P, and Ti, without significant Eu anomaly (δEu = 0.86–1.00), and depleted in heavy rare earth elements with light rare earth elements/heavy rare earth elements = 18.25–20.72 and (La/Yb)N = 27.10–34.67. These features are similar to those of adakitic rocks derived from a thickened lower crust. Zircon εHf(t) values for the porphyritic monzogranite ranged from –19.2 to 6.3, and the two-stage Hf model ages (TDM2) were 2421–811 Ma. These data indicate that the primary magma of the Shimadong porphyritic monzogranite was mainly derived from partial melting of the thickened lower crust consisting of juvenile crust and pre-existing crust. Combined with the results of previous studies, our data suggest that the Shimadong porphyry Mo deposit was emplaced along an active continental margin related to the westward subduction of the paleo-Pacific Plate.

Petrogenesis and Mo prospecting significance of Sadaigoumen granites on the northern margin of the North China Craton

The Sadaigoumen porphyry Mo deposit lies on the northern margin of the North China Craton. Molybdenum mineralization occurs mainly as veins and veinlets, or is disseminated within alkali feldspar granite and granite porphyry, which yield weighted-mean 206Pb/238U ages (±2σ) of 243.7 ± 1.6 to 242.2 ± 2.0 Ma and 240.0 ± 1.7 Ma, respectively. ReOs dating of molybdenite from Stage 3 mineralization yields an isochron age of 238.0 ± 1.9 Ma. The Sadaigoumen ore-related granites have petrological, mineralogical, and geochemical characteristics of I-type granite. Ore-related granites exhibit low (87Sr/86Sr)i ratios of 0.710256–0.711463, negative εNd(t) values of −16.4 to −15.4 with corresponding TDM2 (Nd) ages of 2061–1870 Ma, and negative εHf(t) values of −21.2 to −11.2 with corresponding TDM2 (Hf) ages of 2614–1983 Ma, indicating that the primary magma was derived by partial melting of ancient lower crust. In chondrite- and primitive-mantle-normalized trace element diagrams, the Sadaigoumen ore-related granites are characterized by moderate enrichment of light rare earth elements (REE) relative to heavy REE, moderate to strong negative Nb, Ta, Zr, Hf, and Ti anomalies, and increasing Rb/Sr ratios with decreasing Sr content, all attributed to fractional crystallization. Fractionation of amphibole, muscovite, and possibly minor biotite and garnet (and/or zircon) produced the variations in most elements. Together with the regional geology, the data imply that the Sadaigoumen ore-related granites and corresponding mineralization formed in a syn-collision to post-collision transitional setting during the Early–Middle Triassic. These fractionated Triassic alkaline granites or syenogranites potentially contain new porphyry Mo deposits.

Sulfide S and Pb Isotopic Constraint on the Genesis of Diyanqinamu Mo-Pb-Zn Polymetallic Deposit, Inner Mongolia, China

The Great Hinggan Range (GHR) hosts many large Mo deposits and vein-type Pb-Zn deposits and is one of the most important polymetallic metallogenic belts in China. Although Mo and Pb-Zn deposits are locally closely related in space in the GHR, it is disputed whether the Mo and Pb-Zn deposits have a genetic relationship. The Diyanqinamu Mo deposit located at the middle part of the northern GHR is a Late Jurassic large porphyry Mo deposit and closely adjacent by vein-type Pb-Zn deposit. In this work, we discussed the relationship between Mo and Pb-Zn deposits in Diyanqinamu mine based on the data of S and Pb isotopic geochemistry and geological information. In this mine, the Mo deposit is concentrated in the southern area with a distance of 500 m to the vein Pb-Zn deposit. The δ34SCDT values of the galena and sphalerite from the Mo deposit range from +1.73‰ to +7.29‰ with average of +5.04‰. By contrast, δ34SCDT values of the galena and sphalerite from the Pb-Zn deposit, ranging from +2.38‰ to +5.46‰ with average of +4.04‰, is similar to that of the Mo deposit. The formation temperatures of the Pb-Zn deposit calculated based on the sulfur isotope balance fractionation between sphalerite and co-existed galena range from 220 °C to 315 °C (average 247 °C), which is lower than that of the Mo mineralization (292–510°C). Pb isotopic results show that the 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the Pb-Zn deposit range from 18.326–18.364, 15.541–15.589, and 38.054–38.214, respectively, which are slightly higher than those of the Mo deposit ranging from 18.287–18.331, 15.532–15.569, and 38.034–38.139, respectively. In the 206Pb/204Pb˗207Pb/204Pb diagram, sulfides sampled from the Mo and Pb-Zn deposits overlapped with each other and formed a linear distribution, indicating that they are derived from a mixed metal source with more external contribution to the Pb-Zn mineralization. This mixed signal is further confirmed by the geologic facts that the host rocks of the vein-type Pb-Zn deposit have abnormally high contents of Pb, Zn, and Ag, and experienced strong hydrothermal alteration. Combined with the ore geology, mineral assemblage, and isotopic geochemistry of the two types of mineralization, we propose that the Mo and Pb-Zn deposits in the Diyanqinamu mine represent different faces of the same porphyry system. This Mo-Pb-Zn metallogenic system would provide important clues on further prospecting of Mo and Pb-Zn resources in the GHR.

Petrogenesis and tectonic setting of igneous rocks from the Dongbulage porphyry Mo deposit, Great Hinggan Range, NE China: Constraints from geology, geochronology, and isotope geochemistry

The Dongbulage porphyry Mo deposit is a recently discovered deposit located in the Huanggang–Ganzhuermiao polymetallic metallogenic belt of Inner Mongolia, NE China. Here, we present zircon U–Pb ages and Hf isotopic compositions, and whole-rock geochemical and Sr–Nd–Pb isotopic data, for magmatic rocks associated with Mo mineralisation to constrain the age and petrogenesis of these rocks. The rocks are dominated by mineralised granite porphyries, quartz-monzonites, and rhyolite. Zircon U–Pb dating shows that the ore-bearing granite porphyries have ages of 154.4 ± 3.5, 155.4 ± 1.1, and 158.7 ± 0.6 Ma, the quartz-monzonites have ages of 157.8 ± 1.6 and 166.5 ± 1.3 Ma, and the rhyolite has an age of 172.9 ± 3.0 Ma. The granite porphyries and rhyolites are characterised by high K2O and SiO2 contents, enrichment in light rare-earth elements, strong negative Eu anomalies, and pronounced depletion in Ba, Nb, Ta, Sr, P, and Ti. The quartz-monzonites show enrichment in large-ion lithophile elements (Rb and K), are depleted in heavy rare-earth elements, Nb, Ta, Sr, P, and Ti, and exhibit weak negative Eu anomalies. All of the rocks have low initial 87Sr/86Sr (0.7022–0.7064) and εNd(t) values (−3.62 to + 3.99), positive εHf(t) values (+1.1 to + 13.8), and young two-stage Nd and Hf model ages (TC DM(Nd) = 623–1240 Ma and TC DM(Hf) = 305–1108 Ma, respectively). Whole-rock Pb isotopic compositions show a narrow range of values, with 206Pb/204Pb = 18.314–19.116, 207Pb/204Pb = 15.573–15.595, and 208Pb/204Pb = 38.731–39.296, which, together with their Sr–Nd–Hf isotopic compositions, indicate the dominance of a mantle source component. The isotopic data suggest that the Dongbulage magmatic rocks were derived from partial melting of juvenile lower crust. The granite porphyries are highly evolved I-type magmas with geochemical characteristics similar to those of porphyry granitoids associated with Mo mineralisation in the Great Hinggan Range. On the basis of the regional geology and geochemistry, we suggest that the Dongbulage porphyry Mo deposit formed in a subduction setting associated with southward subduction of the Mongol–Okhotsk oceanic plate.

Fluid inclusion and H–O isotope study of the Jiguanshan porphyry Mo deposit, Xilamulun Metallogenic Belt: implications for characteristics and evolution of ore-forming fluids

We studied the fluid inclusions of the Jiguanshan Mo deposit in China, which is a large porphyry deposit located in the southern Xilamulun Metallogenic Belt. The irregular Mo ore body with various types of hydrothermal veinlets is hosted by Late Jurassic granite porphyry. Intense hydrothermal alterations in the deposit from the core to margin are silicification–potassium feldspar alteration, pyrite–quartz–sericite–fluorite alteration, and propylitic alteration. Based on the mineral assemblages and crosscutting relationships of ore veins, the ore-forming process were divided into three stages and two substages: quartz–pyrite veins (stage I) associated with potassic alteration; quartz–molybdenite–chalcopyrite–pyrite veins (substage II-1) and quartz–molybdenite–fluorite veins (substage II-2) associated with phyllic alteration; and fluorite–quartz–carbonate veins (stage III) with carbonation. Five major fluid inclusions (FIs) types were distinguished in the quartz associated with oxide and sulfide minerals, i.e. polyphase brine (Pb-type), opaque-bearing brine (Ob-type), solid halite (S-type), two-phase aqueous (A-type), and vapor (V-type) inclusions. The FIs of stage I were composed of liquid-rich S-, A-, and V-type FIs with homogenization temperatures and salinities of 490 to 511 °C and 8.9 to 56.0 wt% NaCl equiv., respectively. The FIs of substage II-1 are composed of Pb-, Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 352 to 460 °C and 3.7 to 46.1 wt% NaCl equiv, respectively. The FIs of substage II-2 are Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 234 to 309 °C and 3.7 to 39.2 wt% NaCl equiv, respectively. The FIs of stage III are A-type FIs with homogenization temperatures and salinities of 136 to 172 °C and 1.1 to 8.9 wt% NaCl equiv, respectively. Fluid boiling, which resulted in the precipitation of sulfides, occurred in stages I and II. The initial ore-forming fluids of the Jiguanshan deposit had high temperature, high salinity, and belonged to an F-rich NaCl ± KCl–H2O system. The fluids gradually evolved to low temperature, low salinity, and belonged to a NaCl–H2O system. Studies of the hydrogen and oxygen isotope compositions of quartz (δ18OH2O = − 7.3 to 6.3‰, δDH2O = − 104.3 to − 83.3‰) show that the ore-forming fluids gradually evolved from magmatic water to meteoric water.

Identifying mineral prospectivity using seismic and potential field data in the Hongniangyu district, Inner Mongolia, China

Since the discovery of several large porphyry Mo deposits (>0.1 Mt Mo) in the Jining region of Inner Mongolia, China, during the past decades, the area has been receiving wide interest for mining activities. However, mineral exploration in this area is challenging because most of it is thickly covered by Cenozoic sediments. Geophysical surveys, especially the seismic method, are becoming increasingly important for investigating deep-seated ore-controlling structures (e.g., porphyry granites, faults and even orebodies), supporting the discovery of buried ore deposits. Recently, potential field data and seismic reflection data have been acquired for the Hongniangyu area, south of Jining region. In this study, we mainly use seismic reflection and potential field data to obtain subsurface geological model in support of mineral exploration targeting. Gravity and magnetic data were firstly used for spatial analysis of mineral system by mapping the distribution of the faults, concealed granites, and the sedimentary basin (through wavelet analysis, tilt angle, and Euler deconvolution). To address the common problem of low signal-to-noise ratio of seismic reflection data obtained in hard-rock terranes, we applied a sophisticated workflow including refraction static correction, noise filtering, surface-consistent deconvolution, and velocity analysis. The obtained post-stack migrated seismic profile clearly imaged the geometry of the concealed graben located at the north end of the Datong Basin, and the South-East dipping Kouquan normal fault controls the depression of the graben and offsets Cenozoic sediments by several hectometers up to ~500 m. Joint modeling of seismic, gravity and magnetic data further provided evidence of the three buried belts of granites. Intriguingly, one of the concealed granitic belts located in the north of Hongniangyu area was found to have both significant chargeability and Mo geochemical anomalies, indicating a high potential of hosting porphyry-type Mo ore deposits. As expected, Mo and W mineralized cores were discovered in this target area but limited to only one deep drilling hole. The presented results provide the geological framework of Hongniangyu district and guidelines for delineating new potential Mo mineralization in the Jining region.

Geochemistry and Crystallization Conditions of Magmas Related to Porphyry Mo Mineralization in Northeastern China

AbstractTo better understand processes leading to porphyry Mo deposit formation, the metal content, volatile content, and crystallization conditions of melt inclusions from pre- and synmineralization intrusions in six porphyry(-skarn) Mo deposits of northeastern China (Aolunhua, Hashitu, Lanjiagou, Songbei, Wanbaoyuan, and Yangjiazhangzi) were investigated by means of laser ablation-inductively coupled plasma-mass spectrometry and electron microprobe analysis. The ore-forming silicate melts were one to four times more evolved than average granite with 1 to 7 ppm Mo. The ore-related intrusions crystallized predominantly at 760° to 690°C and 3.7 to 1.0 kbar, except for the one at Hashitu, which crystallized at 770° to 740°C and lower pressures (2.0–1.0 kbar). Fertile silicate melts at Hashitu contain up to 0.4 wt % F, 0.03 to 0.09 wt % Cl, 5.0 to 7.0 wt % H2O, 10 to 24 ppm Cs, and 200 to 500 ppm Rb, whereas those at Yangjiazhangzi and Wanbaoyuan contain less Cs (3–6 ppm and 5–7 ppm, respectively), less Rb (180–220 ppm and 200–240 ppm, respectively), and negligible F (<0.15 wt %) but have similar Cl (0.03–0.05 wt %) and H2O (5.3–6.5 wt % and 4.0–5.2 wt %, respectively) contents. Calculated melt viscosities in fertile magmas (log η = 4.3–6.1 Pa s) are at the lower end of the values reported for felsic melts at the same temperature.Comparison between syn- and premineralization intrusions in individual deposits reveals that the ore-related intrusions were similarly evolved and had similar Mo contents and crystallization conditions as the nonmineralizing intrusions. The only difference is that the premineralization intrusions tend to occur as batholiths. The key to porphyry Mo mineralization lies in the focusing of fluid into and through a small rock volume on the top of the intrusion.For the studied porphyry Mo deposits, the mineralizing magmas are all Mo poor, indicating Mo enrichment is not required to form porphyry Mo deposits. Metal endowments in porphyry Mo deposits have no direct relationship with the composition and crystallization condition of mineralizing melts but are linked with the fluid flux released from the underlying magma chamber through a cupola.

The formation mechanism of reduced porphyry Mo deposits in the West Junggar region, Xinjiang: The Suyunhe example

Some porphyry Mo deposits with relatively reduced ore assemblages, characterized by high reduced gases (e.g. CH4) and a lack of magnetite and hematite, are generally considered as the reduced porphyry Mo deposits. Nevertheless, the role of oxygen fugacity (fO2) in controlling Mo enrichment and precipitation of molybdenite in such reduced porphyry Mo deposits is poorly understood. The Suyunhe reduced porphyry Mo deposit with a Mo metal reserve of 0.57Mt at an average grade of 0.05–0.09%, located in the West Junggar terrane in Xinjiang, is associated with Early Permian granitic rocks, which emplaced into the volcano-sedimentary sequences of the Middle Devonian Barluk Formation. In this study, we report that the variation of magmatic fO2, the possible mechanism of Mo enrichment, and the contributions of the reduced gases or matter to molybdenite precipitation. Results indicate that the primitive magma is still oxidized with fO2 > NNO (Ni–NiO oxygen buffer), but it is then reduced due to contamination by the reduced sequences. Furthermore, the decreasing magmatic fO2 does not significantly prevent the enrichment of Mo metals during magmatic evolution. By contrast, the evolved parental magma, characterized by highly differentiated and fluorite-rich, is responsible for improving Mo concentration of melts. Most of reduced gases are derived from decomposition of organic matter occurring in the reduced volcanic sedimentary rocks of Barluk Formation. More importantly, these reduced gases (e.g. CH4) play a role in molybdenite precipitation, which may effectively improve the efficiency of metal precipitation.

The Late Early Cretaceous Mo Mineralization in the South China Mo Province: Constraints from U–Pb and Re–Os Geochronology of the Lufeng Porphyry Mo Deposit

Compared to other Mo provinces, few studies focused on the South China Mo Province (SCMP), especially for Early Cretaceous Mo mineralization. The Lufeng porphyry Mo deposit in the SCMP is characterized by disseminated and veinlet‐type mineralization in granite porphyry, gneiss, and rhyolite. In this study, six molybdenite samples yield a Re–Os isochron age of 108.0±1.8 Ma, which is consistent with the zircon U–Pb age of the granite porphyry (108.4±0.8 Ma). The coincidence of magmatic and hydrothermal activities indicates that Mo mineralization was associated with the intrusion of granite porphyry during the late Early Cretaceous. A compilation of U–Pb and Re–Os chronological data suggests that an extensive and intensive Mo mineralization event occurred in the SCMP during the late Early Cretaceous. The marked difference in molybdenite Re contents between Cu‐bearing (85–536 ppm) and Cu‐barren (1.3–59 ppm) Mo deposits of the late Early Cretaceous indicates that the ore‐forming materials were derived from strong crust–mantle interactions. Together with regional petrological and geochemical data, this study suggests that late Early Cretaceous Mo mineralization in the SCMP occurred in an extensional setting associated with the roll‐back of the Paleo‐Pacific slab.

Ore genesis and tectonic setting of the Laojiagou porphyry molybdenum deposit, Inner Mongolia, China: evidence from geology, fluid inclusions, H–O isotopes, zircon U–Pb geochronology, and geochemistry

The Middle Triassic Laojiagou porphyry Mo deposit is located in the Xilamulun metallogenic belt, along the northern margin of the North China Craton (NCC). Molybdenum mineralization is associated with a monzogranite porphyry and occurs primarily in quartz veins and veinlets hosted in wall rocks affected by potassic, silicic, sericitic, and propylitic alteration. The ore-forming process is divided into three stages, characterized by veinlets comprising molybdenite + pyrite + quartz (stage I), pyrite + chalcopyrite + molybdenite + quartz (stage II), and pyrite + quartz (sulfide-poor) (stage III). We identify three fluid inclusion types in quartz grains: carbonic (C-type), liquid-rich two-phase (L-type), and rare vapor-rich two-phase (V-type) inclusions. Microthermometric results indicate that an initial high-temperature (> 350 °C) and low-salinity (< 10 wt% NaCl equiv.) CO2-rich fluid evolved to a low-temperature (< 280 °C) and CO2-poor fluid, comprising dominantly of meteoric water. Hydrogen and oxygen isotopes indicate that initial ore-forming fluids were magmatic and became progressively mixed with meteoric water (stage I δ18OH2O = 4.4–4.8‰ and δDH2O = − 105.8 to − 101.5‰). Zircon U–Pb dating indicates that the monzogranite porphyry formed at 232.2 ± 3.6 Ma (MSWD = 0.88). The porphyry has high SiO2, K2O, and Al2O3 and low MgO and CaO concentrations and is classified as high-K calc-alkaline and weakly peraluminous. All samples are enriched in light rare earth and large-ion lithophile elements and depleted in high-field-strength elements. Our results indicate that the Laojiagou porphyry Mo deposit formed in the Middle Triassic, associated with post-orogenic extension following closure of the Palaeo-Asian Ocean.

The Lavrion Pb-Zn-Ag–Rich Vein and Breccia Detachment-Related Deposits (Greece): Involvement of Evaporated Seawater and Meteoric Fluids During Postorogenic Exhumation

AbstractThe formation of ore deposits in the Lavrion Pb-Zn-Ag district was associated with Miocene detachment that accommodated orogenic collapse and exhumation of high-grade nappes across the ductile-brittle transition. This district consists of (1) low-grade porphyry Mo style, (2) Cu-Fe skarn, (3) high-temperature carbonate replacement Pb-Zn-Ag, and (4) vein and breccia Pb-Zn-Ag mineralization. The vein and breccia mineralization locally contains high-grade silver in base metal sulfides that are cemented by fluorite and carbonate gangue. The rare earth element contents of these gangue minerals, chondrite-normalized patterns, and fluid inclusion studies suggest that they precipitated from a low-temperature hydrothermal fluid. Primary and pseudosecondary fluid inclusions in fluorite and calcite are characterized by a wide range of homogenization temperatures (92°–207°C) and salinities of up to 17.1 wt % NaCl equiv. Secondary fluid inclusions only represent &lt;5 vol % of the total fluid trapped. Fluids extracted from inclusions in fluorite have values of δD = –82.1 to –47.7‰ (Vienna-standard mean ocean water [V-SMOW]) and δ18O = –10.4 to –5.1‰ (V-SMOW). These data and low ratios of Cl/Br measured by crush-leach analyses for fluids in fluorite (102–315) and calcite (162–188) are compatible with the ore fluid being the result of mixing of meteoric water with evaporated seawater. These data suggest that fluids leading to the deposition of late Pb-Zn-Ag–rich vein- and breccia-style mineralization in Lavrion were related to circulation of mixed evaporated seawater and meteoric fluids that was enhanced by brittle deformation. This contrasts with the fluids of magmatic origin related to the formation of low-grade porphyry Mo, Cu-Fe skarn, and high-temperature carbonate replacement deposits spatially related to the Plaka granodiorite.

Source and Tectonic Setting of Porphyry Mo Deposits in Shulan, Jilin Province, China

The Shulan area in Jilin Province is a part of the Lesser Xing’an–Zhangguangcai Range polymetallic ore belt, which is an important Cu–Mo ore region of northeast China. The discovery of three large Mo ore deposits (Fu’anbu, Chang’anbu, and Jidetun) highlights its potential for porphyry Mo ore deposits. Here we investigated the tectonic setting and mineralization of Mo ore deposits in the Shulan area, based on comparative study of the Fu’anbu, Chang’anbu, and Jidetun deposits. The ore-controlling structures are NE–SW- and NW–SE-trending faults. The main ore mineral in all three deposits is molybdenite. The ore bodies are all hosted in granites, have a stratiform or lenticular shape, and have strongly altered wall rocks. These observations indicate the Mo deposits in the Shulan area are typical porphyry Mo deposits. All were formed during the early Yanshanian (199.6–133.9 Ma). Biotite adamellites from the Chang’anbu deposit yield a U–Pb age of 182.10 ± 1.20 Ma. Molybdenites from the Fu’anbu and Jidetun deposits have Re–Os isochron ages of 166.9 ± 6.7 and 169.1 ± 1.8 Ma, respectively. Quartz and ore minerals were analysed for H–O and S–Pb isotopes, respectively. The results suggest the ore-forming materials were predominantly of upper-mantle origin, with secondary contributions from the lower crust. The ore-hosting granites have high concentrations of SiO2 (66.67–75.43 wt.%) and Al2O3 (12.91–16.44 wt.%), low concentrations of MgO (0.09–1.54 wt.%), and Ritman index (σ = K2O + Na2O)2/(SiO2 − 43)) ratios of 2.09–2.57. The granites are enriched in large-ion lithophile elements and depleted in high-field-strength elements, and have negative Eu anomalies. The ore-hosting rocks are geochemically similar to granites in northeastern China that were generated in a collisional orogeny. We conclude that early Yanshanian (199.6–133.9 Ma) mantle–crust-derived magmatism caused by the subduction of the Palaeo-Pacific Plate was the main source of Mo deposits in the Shulan area.

Zircon U–Pb and molybdenite Re–Os geochronology and whole‐rock geochemistry of the Baishan porphyry Mo deposit: Insights into Triassic mineralisation and tectonic setting in the eastern Tianshan, NW China

The Baishan Mo deposit in the eastern Tianshan Mountains is representative of the local metallogenic Triassic Mo belt. In this study, the geological characteristics, petrography, and geochemistry of the granite porphyry and the Mo deposit were examined using zircon U–Pb dating, molybdenite Re–Os isotope dating, whole‐rock geochemistry, and fluid inclusions. Results show that the crystallisation age of the Baishan granite porphyry is 229.8 ± 1.4 Ma and the Re–Os age of molybdenite in the ore body quartz vein is 225.0 ± 1.2 Ma. Therefore, the ore formed basically at the same time as diagenesis in the Late Triassic. The Baishan granite porphyry has high levels of Si, Al, and alkalis (K2O + Na2O = 5.72–8.88%) and low levels of Mg. The differentiation index is high (81.68–91.20), while the aluminium saturation index is low, indicating that the pluton belongs to metaluminous–weak peraluminous highly fractionated I‐type granite. The rock is also enriched in light rare earth elements (LREE) and large‐ion lithophile elements but depleted in heavy rare earth elements (HREE) and high‐field‐strength elements, with a distinct differentiation between LREEs and HREEs. δEu is weakly negative. The high Sr/Y and La/Yb ratios indicate geochemical characteristics similar to adakite rocks. The formation of the deposit is closely related to Mo‐rich, low‐salinity (1.23‐ to 9.73‐wt.% NaCl eqv.), and medium‐ to low‐temperature (91–280°C) magmatic fluid in the plate extension setting. The magma was derived from partial melting of thickened lower crust and possibly mixed with intrusive mantle‐derived magma. The ore‐forming fluids were uplifted, transported, mixed with meteoric water, and precipitated to form the Mo ore.

Mineral chemistry of magmatic and hydrothermal biotites from the Bangpu porphyry Mo (Cu) deposit, Tibet

The Bangpu deposit, located in the eastern part of the Gangdese porphyry copper belt, Tibet, is a porphyry Mo (Cu) deposit in a continental collisional orogenic belt. The Mo (Cu) mineralization occurs mainly in monzogranite porphyry, whereas the Cu (Mo) mineralization occurs mainly in diorite porphyry. Most magmatic and hydrothermal biotites from the Bangpu deposit are Mg-rich, plotting in the phlogopite and Mg-biotite compositional fields. The Bangpu magmatic biotite has high BaO (>0.1 wt%) and TiO2 (>3 wt%), while the hydrothermal biotite has low BaO (<0.1 wt%) and TiO2 (<3 wt%). Hydrothermal biotite from the Bangpu Mo (Cu) mineralization system has higher Al2O3, SiO2, MgO, K2O, Na2O and F contents and lower TiO2, FeOtot, MnO and Cl contents than hydrothermal biotite from the Cu (Mo) mineralization system. Crystallization temperatures range from 757 °C to 827 °C and 687 °C to 740 °C for magmatic biotite in monzogranite porphyry and biotite monzogranite, respectively. Hydrothermal biotite geothermometry yields a temperature range from 362 °C to 547 °C for the Mo (Cu) mineralization system and 302 °C to 410 °C for the Cu (Mo) mineralization system. Calculated oxygen fugacity, relative F and Cl contents, and fugacity ratios indicate that the Cu (Mo) and Mo (Cu) mineralization systems formed from different magmatic-hydrothermal fluids. The Mo (Cu) mineralization system formed from F-rich high oxygen fugacity (above NNO) magmatic-hydrothermal fluids favorable for extracting Mo from the melt and transporting Mo, whereas the Cu (Mo) mineralization system formed from Cl-rich high oxygen fugacity (above NNO) magmatic-hydrothermal fluids favorable for extracting Cu from the melt and transporting Cu. The Bangpu porphyry Mo (Cu) deposit is the result of two different superimposed magmatic-hydrothermal fluids.

Fluid Inclusions and S–Pb Isotopes of the Reshui Porphyry Mo Deposit in East Kunlun, Qinghai Province, China

The Reshui porphyry Mo deposit is located in the East Kunlun orogenic belt (EKOB). Molybdenum mineralization is distributed in monzogranite and porphyritic monzogranite rocks, mainly presenting as various types of hydrothermal veinlets in altered wall rocks, and the orebodies are controlled by three groups of fractures. In this paper, we present the results of fluid-inclusion and isotopic (S and Pb) investigations of the Reshui Mo deposit. The ore-forming process of the deposit can be divided into three stages: an early disseminated molybdenite stage (stage 1), a middle quartz–molybdenite stage (stage 2) and a late quartz–polymetallic sulfide stage (stage 3). The alteration was mainly potassic and silicic in stage 1, silicic in stage 2, and sericitic and silicic in stage 3. Five types of fluid inclusions (FIs) can be distinguished in quartz phenocrysts and quartz veins, namely W, PL (pure liquid inclusions), PV (pure gas inclusions), C (CO2 three-phase inclusions), and S (daughter mineral-bearing inclusions). The homogenization temperatures of fluid inclusions belonging to stages 1 to 3 are 282.3–378 °C, 238.7–312.6 °C and 198.3–228 °C, respectively. The fluid salinities at stages 1 to 3 are 4.65–8.14% NaCl eq., 4.34–42.64% NaCl eq., and 3.55–4.65% NaCl eq., respectively. The fluids of this deposit were generally moderate–high temperature and moderate–low salinity and belong to the H2O–NaCl–CO2 ± CH4 system. The temperature and pressure changed considerably between stage 2 (high–medium-temperature) and stage 3 (low-temperature). The evidence for ore-forming fluids containing different types of coexisting inclusions in stage 2 and a decrease in the fluid temperature from stage 2 to stage 3 indicate that fluid boiling and fluid mixing were the main mechanisms of ore precipitation. The sulfide 34SV-CDT values range from 4.90‰ to 5.80‰, which is characteristic of magmatic sulfur. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are 18.210–18.786, 15.589–15.723, and 38.298–39.126, respectively. These lead isotopic compositions suggest that the ores were mainly sourced from crustally derived magmas, with minor input from the mantle. The fluid inclusions and S–Pb isotopes provide important information on the genesis of the Reshui porphyry Mo deposit and indicate that the Triassic has high metallogenic porphyry potential in the EKOB.

Highly differentiated juvenile crust-derived magmas linked with the Xilekuduke porphyry Mo (Cu) deposit in East Junggar, NW China

The East Junggar region links the Kazakhstan-Junggar plate with the Siberian Craton along the western part of the Central Asian Orogenic Belt. Among the major ore deposits in this region, the Xilekuduke molybdenite deposit is a unique example of Mo-dominated porphyry. Molybdenum and copper mineralization here occur as disseminated sulfides or veinlets mainly in granite porphyry and monzogranite, with a prominent alteration from an inner potassic, through sericitic to an outer propylitic zone. Zircon LA-ICP-MS U–Pb ages indicate that the granite porphyry and monzogranite were emplaced at 326.4 ± 2 Ma and 328.2 ± 1.8 Ma respectively. Both rocks show enrichment in light rare earth elements (LREE), and Rb, K, Sr, Hf, Zr, but depletion in Nb, Ta, Ti and P, suggesting magma generation in a post-collisional setting. A relatively high oxidation state is inferred from zircon δCe values and oxygen fugacity of parental magma. The ore hosted intrusions also show high Differentiation Index (DI), indicating a highly oxidized parental magma and prolonged differentiation process. The range of zircon εHf (t) values (+11.5 to +17), young zircon Hf model ages, and consistent but slightly low zircon δ18O values (+4.84 to +5.20), together with the range of Mg# (35–53), suggest derivation of the parental magma through partial melting of juvenile crust with minor contribution from mantle components and sediments. We propose that melting of juvenile oceanic components at depth with high degree of differentiation played a significant role in generating the Mo mineralization in Xilekuduke deposit within a post-collisional setting in the East Junggar domain.

Rhenium abundance in molybdenites: a case study on vein-type Cu-Mo-Au mineralisation in the Qarachilar area, Sungun porphyry Cu and Siah Kamar porphyry Mo deposits, NW Iran

The vein-type Cu-Mo-Au mineralisation in Qarachilar, the Sungun porphyry Cu deposit (PCD) and the Siah Kamar porphyry Mo deposit (PMD) are all located at the northwestern end of the Neo Tethys-related Urumieh–Dokhtar volcano-plutonic belt of Iran. Re contents of molybdenite samples from the Qarachilar, Sungun and Siah Kamar deposits are about 112.67–462 ppm, 53.24–252.29 ppm, and 10.44–41.05 ppm, respectively. Re contents of the first two deposits fall in the range of PCDs, while those of the latter are lower and correspond to PMDs. The relatively high Re content of the Qarachilar and Sungun molybdenites can be explained considering the low abundance of molybdenite, a mantle-dominated source for ore materials and the incorporation of oxidized and acidic hydrothermal fluids with high f Cl. The high abundance of molybdenite in the Siah Kamar PMD has resulted in volume dilution of Re. Furthermore, occurrence of the main ore within the potassic alteration zone and, hence, the alkaline nature of the responsible fluids in this zone have also affected the Re content of molybdenites. Variations of the Re content in different veins/veinlets showed a negative relationship with the formation temperature of these veins, and a positive/negative relationship with the acidity/alkalinity of the hydrothermal fluids, while the grain size of molybdenites showed a positive relationship.

Insights into the formation of the Dasuji porphyry Mo deposit (North China Craton) gained from mineral chemistry data

The Dasuji Mo deposit is located within the northern margin of the North China Craton. Based on vein cross-cutting relationships, mineral assemblages and alteration characteristics, the formation of the deposit can be divided into four stages: stage 1, consisting of two vein types developed in deep, is characterized by K-feldspathization with minor molybdenum mineralization; stage 2, containing four distinct vein types, is the main stage of molybdenum mineralization accompanied by sericitization and silicification; stage 3 is involved in lead-zinc mineralization associating with carbonatization and fluorination; and stage 4 is characterized by no mineralization. This paper presents new mineral (magnetite, rutile, molybdenite, and pyrite) chemistry data that provide new insights into the formation of this deposit. The magnetites within veins in the deposit have chemical compositions that are indicative of a magmatic origin, suggesting that these magnetites hosted in quartz were captured from syn-mineralization granites in the area. Molybdenite W, Pb, Zn, and Cu concentrations increase with the decreasing temperature of formation, suggesting the initiation of W, Pb, Zn, and Cu precipitation at the end of the second stage of mineralization. The stage 3 pyrite within the deposit contains the highest concentrations of Pb, Zn, and Cu, consistent with the Pb–Zn–(Cu) mineralization that formed during this stage. The majority of the F ion deposition occurred at the end of stage 3, and the fluids associated with stage 4 were meteoric water dominated.

Plate subduction, oxygen fugacity, and mineralization

Plate subduction is the largest natural factory that processes elements, which controls recycling and mineralization of a variety of elements. There are three major ore deposit belts in the world: the circum-Pacific, the central Asian, and the Tethys belts. All the three belts are closely associated with plate subductions, the mechanism remains obscure. We approached this problem from systematic studies on the behaviours of elements during geologic processes. This contribution summaries the recent progress of our research group. Our results suggest that porphyry Cu deposits form through partial melting of subducted young oceanic crust under oxygen fugacities higher than ΔFMQ ∼+1.5, which is promoted after the elevation of atmospheric oxygen at ca. 550 Ma. Tin deposits are associated with reducing magmatic rocks formed as a consequence of slab rollback. The Neo-Tethys tectonic regime hosts more than 60% of the world’s total Sn reserves. This is due to the reducing environment formed during the subduction of organic rich sediments. For the same reason, porphyry Cu deposits formed in the late stages during the closure of the Neo-Tethys Ocean. Tungsten deposits are also controlled by slab rollback, but is not so sensitive to oxygen fugacity. Subduction related W/Sn deposits are mostly accompanied by abundant accessory fluorites due to the breakdown of phengite and apatite. Decomposition of phengite is also significant for hard rock lithium deposits, whereas orogenic belt resulted from plate subduction promote the formation of Li brine deposits. Cretaceous red bed basins near the Nanling region are favorable for Li brines. Both Mo and Re are enriched in the oxidation-reduction cycle during surface processes, and may get further enriched once Mo-, Re-enriched sediments are subducted and involved in magmatism. During plate subduction, Mo and Re fractionate from each other. Molybdenum is mainly hosted in porphyry Mo deposits and to a less extent, porphyry Cu-Mo deposits, whereas Re is predominantly hosted in porphyry Cu-Mo deposits and sedimentary sulfide deposits.