Molybdenum Mineralization Research Articles

Fluid inclusions and C-H-O-S isotope systematics of early Permian porphyry Mo mineralization of the West Junggar region, NW China: the Suyunhe example

ABSTRACTThe Suyunhe porphyry Mo deposit, located in the West Junggar terrane, is the largest molybdenum deposit found in Xinjiang to date, with a proven reserve of 0.57 Mt. The Suyunhe deposit is associated with Early Permian granitic rocks, which emplaced into the volcano-sedimentary sequences of the Middle Devonian Barluk Formation. Four metallogenic stages are identified in this study. Stage I is marked by the quartz-magnetite-K-feldspar±biotite±pyrite±molybdenite veins, which mainly occurred in the intensively potassic alternation zone and were formed at high temperature (>481°C), high salinity (58.6−65.18 wt.%), and relatively high oxygen fugacity conditions with a fluid system of NaCl-H2O-CO2. Stage II is the main metallogenic stage and develops numerous quartz-molybdenite±pyrite veins associated with muscovite–chlorite alteration, which were formed by immiscible fluids at medium-high temperature (210−427°C), medium-high salinity (43.36−49.90 wt.%), and relatively low oxygen fugacity conditions with the fluid system of NaCl-H2O-CO2-CH4-C2H6. After the main Mo-mineralization, quartz-polymetallic sulphides veins associated with quartz–sericite alteration were formed by fluids at medium-low temperature, low-salinity conditions with the fluid system of NaCl-H2O-CO2 in stage III. The following quartz-polymetallic sulphide veins are quartz-calcite±pyrite veins associated with calcite alteration, which were formed by fluids at low temperature and low-salinity conditions with a fluid system of NaCl-H2O in stage IV.The δ18O‰ values indicate that the ore fluids of stages I and II are dominated by magmatic water, whereas stages III and IV are dominated by meteoric water. A wide range of δ34S‰ values (−7.1 to 3.4‰) of sulphides between stages I and II indicates that increasing the reducibility plays an important role in molybdenum mineralization. The δ13CCH4 values suggest that CH4 of the ore fluids mainly results from the assimilation–contamination of carbonaceous country rocks, and partly derives from magma. However, the δ13CCO2 values suggest that CO2 of the ore fluids mainly originates from magma, and minor derives from wall-rocks as well as meteoric water.

Geochronology and fluid inclusion study of the Shabutai porphyry Mo deposit, Inner Mongolia

The Shabutai molybdenum deposit is a newly discovered deposit located in the northern part of the Xilamulun metallogenic belt. Molybdenum mineralization is distributed in granite porphyry and its exocontact zone is in the shape of quartz veins. The LA-ICP-MS zircon U-Pb age of ore-bearing granite porphyry is 140.1±0.7Ma with a MSDW of 0.078. The granite belongs to the high-K calc-alkaline series characterized by relatively high LREE, low HREE, depletion of Ti, Ba, and Nb, and a negative Eu anomaly. Mineralization evolution is divided into three stages: early, middle and late. The stages are characterized by potassium feldspar veins, quartz-potassium feldspar veins, and quartz veins in the early stage, quartz-molybdenite veins in the middle stage, and quartz-carbonate veins in the late stage. Ore minerals were mainly precipitated in the middle stage. Pure-vapor (PV), vapor-rich (V), liquid-rich (L), and daughter mineral-bearing (S) fluid inclusions were observed in the hydrothermal quartz. Homogeneous temperatures of fluid inclusions in the early stage ranged from 240°C to 420°C, with salinities ranging from 4.0 to 57.2wt.% NaCl eqv. The fluid inclusions contained hematite daughter minerals, indicating high oxygen fugacity conditions in the early stage. The temperatures of the fluid inclusions at the middle stage ranged predominantly from 200 to 300°C with a salinity range of 0.5–48.5wt.% NaCl eqv. The inclusions also showed high K ion content characteristics, both in the early and middle stage fluid. A drop in potassium concentration caused by potassic alteration created a favorable condition for Mo precipitation. The temperature range of the late-stage fluid inclusions was 160–307°C with salinities below 10.7wt.% NaCl eqv. According to Laser Raman microprobe data, CO2 occurred only in a few gas fluid inclusions, while most gases were H2O. Microthermometric analysis results suggested that fluid boiling was the main factor triggering molybdenite precipitate and forming the Shabutai molybdenum deposit.

Regional Metallogeny of Mo-Bearing Deposits in Northeastern China, with New Re-Os Dates of Porphyry Mo Deposits in the Northern Xilamulun District

With many new discoveries of giant Mo deposits in the past decade, northeastern China has become the largest molybdenum mineralization region in China. The Xilamulun district is in the southern part of northeastern China and contains 25 Mo deposits and prospects, dominantly of porphyry type. These deposits are mostly along the E-striking Xilamulun fault. Re-Os dating of hydrothermal molybdenite from four deposits in the northern Xilamulun district revealed mineralization ages of 137 to 129 Ma (129.4 ± 3.4 Ma for Aolunhua, 135.3± 2.6 Ma for Shabutai, 136.4 ± 0.8 Ma for Haisugou, and 136.1 ± 6.6 Ma for Banlashan), in general agreement with the crystallization ages of their host granitoids. The compilation of existing data on Mo-bearing deposits in northeastern China, including the new data of this study, shows that Mesozoic Mo deposits in this region have a wide range of ages, from ~250 to 90 Ma. We propose that they are linked to three tectonic-magmatic events: (1) Triassic Mo deposits (250–220 Ma) are mainly distributed along the E-trending Xilamulun fault and are related to postcollisional crustal extension following the final closure of the Paleo-Asian ocean; (2) Jurassic Mo mineralization (200–140 Ma) displays a clear younging trend from southeast to northwest, coincides with the regional magmatism trend, and is interpreted to be related to the northwestward flat-slab subduction of the Paleo-Pacific plate beneath the Eurasian continent that started in the Early Jurassic (ca. 200 Ma); (3) Cretaceous Mo mineralization (140–90 Ma) shows a reversed migration trend from northwest to southeast, and can be explained by the coastward migration of slab rollback related to lower crust delamination, asthenospheric upwelling, and lithospheric thinning in eastern China. The spatial-temporal distribution of Mesozoic Mo mineralization is important for regional metallogeny and exploration. Recently numerous epithermal Au (Cu, Mo) deposits have been recognized in the southeast margin of northeastern China. According to this study, we predict that hidden porphyry/skarn systems could be located beneath these epithermal deposits.

Porphyry Copper Discovery Beneath the Valeriano Lithocap, Chile

ABSTRACT Exploration for porphyry copper deposits beneath barren or poorly mineralized, advanced argillic lithocaps is becoming common­place; however, there have been few discoveries except in cases where the copper ± gold ± molybdenum mineralization has been partly exposed, typically as a result of partial lithocap erosion. At Valeriano, in the high Andes of northern Chile, completely concealed Miocene porphyry copper-gold mineralization was recently discovered beneath a lithocap. Here, the results of the staged drilling program that led to the discovery are summarized, with emphasis on the key geologic, alteration, and mineralization features that provided guidance. The final deep drill holes of the 16-hole program cut well-defined advanced argillic and sericitic alteration zones before entering chalcopyrite ± bornite–bearing, potassic-altered porphyry, with grades of 0.7 to 1.2% Cu equiv, at depths of ~1,000 to >1,800 m.

Zircon U[sbnd]Pb geochronology and isotopic geochemistry of the Tangjiaping Mo deposit, Dabie Shan, eastern China: Implications for ore genesis and tectonic setting

The Tangjiaping Mo deposit is located in the Dabie Shan in eastern China. Molybdenum (Mo) mineralization mainly occurs as veinlets in the Tangjiaping granite porphyry, which is featured by the development of potassic-silicic-, phyllic- and propylitic alterations. The Mo-mineralized granite porphyry yields a zircon UPb age of 118.1±0.8Ma (MSWD=1.6, 2σ, n=24), and may have formed under post-collision extensional tectonics after the Yangtze–North China collision. The Tangjiaping granite porphyry is characterized by the enrichments of LILEs and LREEs, depletions of Ba, Nb, Ta, Sr, P, Ti and HREEs, and negative Eu anomaly. Zircons from the granite porphyry yield negative εHf(t) of −15.3 to −9.9, with TDM2(Hf) ages of 1.80 to 2.14Ga. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb of the granite porphyry and its K-feldspar are 16.842–17.342, 15.388–15.439 and 37.706–38.260, respectively, while those of the sulfides are 17.090–17.832, 15.420–15.510, and 37.550–38.026, respectively. The δ34S of these sulfides exhibit a relatively narrow range of 3.2–4.9‰, with an average of 4.0‰. The HfPbS isotopic signatures indicate that the granite porphyry and the ore-forming materials at Tangjiaping were mainly derived from the partial melting of both the Southern Dabie Complex and the Precambrian basement of the North China Craton.

Low-salinity Liquid-rich Or Vapor-like Fluids in a Porphyry-type Mo Deposit, South Korea

AbstractSmall porphyry-type molybdenum (Mo) mineralization, the Geumeum deposit in the Gyeongsang Basin, South Korea, is associated with the crystallization of a Cretaceous granodiorite, exsolution of magmatic hydrothermal fluids, and related hydrofracturing. Quartz and molybdenite occur with minor amounts of uneconomic chalcopyrite, pyrite, sphalerite, and galena that precipitated from exsolved magmatic fluids and formed hydrothermal fissure-filling vein ores. Three distinct fluid inclusion assemblages responsible for the precipitation of molybdenite are present in the vein quartz. The earliest fluid is represented by low-salinity liquid-rich Type I fluid inclusions, which displayed homogenization temperatures ranging from 298 to 352 °C, and salinities from ∼0 to 9 wt.% NaCl equiv. The Type I inclusions were trapped in a liquid-stable, vapor-absent, one-phase field. The intermediate fluid is represented by CO2-bearing vapor-rich Type IV inclusions, generally showing no visible CO2 liquid phase. These CO2-bearing inclusions totally homogenized by vapor disappearance at 327∼340 °C or vapor bubble expansion at 327∼369 °C, exhibiting near-critical behaviors. The textural relationships and phase equilibria constraints indicate that the Type IV inclusions were derived from a single population, which formed as pressure and temperature fluctuated at near-critical conditions. The latest fluid can be represented by vapor-rich Type II fluid inclusions. No microthermometric data were obtained for these latest assemblages as no visible amounts of liquid phases are evident in small inclusions. Type III inclusions, which commonly refer to halite-bearing inclusions, are absent in the quartz veins studied. The oxygen and hydrogen isotopic fluid compositions of the vein quartz (δ18OSMOW = 4.3 to 6.9‰ and δDSMOW = −65 to −84‰ at 400 °C) is consistent with a magmatic origin with a possible slight influence from meteoric water. Molybdenum mineralization at Geumeum is a product of hypogene hydrothermal processes that were strongly fracture-controlled, highlighting the importance of low-salinity liquid-rich to vapor-like supercritical fluids for the mineralization. It seems likely that the magmas responsible for the formation of the deposit at Geumeum were emplaced at greater depths than those reported for economic porphyry copper deposits in the world. The deposit could thus have survived long periods of erosion, and represent the weakly mineralized “base” of porphyry systems in the Gyeongsang Basin, South Korea.

Recycling of subducted upper continental crust: Constraints on the extensive molybdenum mineralization in the Qinling–Dabie orogen

The Qinling–Dabie orogenic belt is the most important molybdenum ore belt in the world, with a proven reserve of over 9 million tons metal Mo. More than 92% of the reserves come from porphyry-skarn type deposits that are closely related to Late Mesozoic granite intrusions (158–101Ma) occurring mainly along the southern margin of the North China Craton, where the majority of the continental crust was formed before 2.5Ga with crustal Hf model ages of 2.8 to 3.2Ga. The granite intrusions, which consist mainly of granodiorite, monzogranite, and syenogranite, intrude an Archean to Paleoproterozoic basement. The granitic rocks are metaluminous to peraluminous with C/CNK values mostly in range of 0.9–1.2, commonly alkaline rich with high-K calc-alkaline and shoshonitic features. The linear trends of major and trace elements on Harker diagrams suggest a common magma source for the granitic rocks. Abundant inherited zircons with Neoproterozoic U–Pb ages and substantial younger crustal Hf model ages (averaging 2.4Ga and 2.0Ga for granitic rocks with U–Pb ages older and younger than 125Ma, respectively) demonstrate that these granitic rocks were probably derived from partial melting of the subducted northern Yangtze continental crust with Hf model age younger than 2.2Ga. Integrating the recent progresses in geological, geochronological, and geophysical investigations of the Qinling–Dabie orogenic belt, we propose that it is the conjunction of the decoupling of the subducted plate at the easternmost part and the slab rollback and subsequent breakoff at the westernmost part of the orogenic belt that resulted in the westward shallowing continental subduction along the Manlue suture at the southern margin of the Qinling–Dabie orogenic belt. This subduction took place during westward propagating continental collision in the Late Triassic and the prolonged relative rotation of the North China Craton and Yangtze Block that lasted until the Middle Jurassic.The molybdenum source for the extensive Mo mineralization in the Qinling–Dabie orogenic belt was most likely derived from Mo enriched components of subducted continental crust. The decoupling of the subducted plate that occurred in the easternmost part of the orogenic belt, where only less Mo-enriched components of the Yangtze Block have been subducted, may account for the lack of economically significant Mo mineralization there.

Geochemistry and Sr‐Nd‐Pb Isotopes of the Granites from the Hashitu Mo Deposit of Inner Mongolia, China: Constraints on Their Origin and Tectonic Setting

AbstractThe Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range, NE China. Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite. Sr‐Nd‐Pb isotopes of the intrusions show that the porphyritic syenogranite has initial 87Sr/86Sr ratios of 0.70418–0.70952, εNd(t) values of 1.3 to 2.1 (t=143 Ma), 206Pb/204Pb ratios of 19.191–19.573, 207Pb/204Pb ratios of 15.551–15.572, and 208Pb/204Pb ratios of 38.826–39.143. The monzogranite has initial 87Sr/86Sr ratios of 0.70293–0.71305, εNd(t) values of 1.1 to 2.0 (t=147 Ma), 206Pb/204Pb ratios of 19.507–20.075, 207Pb/204Pb ratios of 15.564–15.596, and 208Pb/204Pb ratios of 39.012–39.599. The calculated Nd model ages (TDM) for monzogranite and porphyritic syenogranite range from 866 to 1121 Ma and 795 to 1020 Ma, respectively. The granitic rocks in the Hashitu area have the same isotope range as granites in the southern parts of the Great Hinggan Range. The isotope composition indicates that these granites are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust. The integrating our results with published data and the Late Mesozoic regional tectonic setting of the region suggest that the granites in the Hashitu area formed in an intra‐continent extensional setting, and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere.

Oceanic anoxic events, subduction style and molybdenum mineralization

Nearly half of the world's Mo resources are hosted in Cenozoic porphyries along the east Pacific margin. In contrast, there are essentially no large Mo porphyry deposits along the west Pacific. We propose that this uneven distribution is mainly due to Oceanic Anoxic Events (OAEs) and the different subduction regimes in the eastern and western Pacific margins. Molybdenum is rare in the Earth, with an abundance of 50 ppb in the primitive mantle, and 0.8 ppm in the continental crust. Pre-enrichment is needed for such a moderately incompatible element to form porphyry Mo deposits. The oxidation–reduction cycle on the Earth's surface is the major process that concentrates Mo. Molybdenum was more intensively oxidized under high erosion rates during alternating high-atmospheric-CO2 and high-oxygen periods immediately before OAEs, resulting in high Mo concentrations in surface water and subsequently higher Mo concentrations in organic-rich sediments during the OAEs. Large amounts of Mo-enriched sediments formed on the Pacific Ocean floor during at least 9 major OAEs since the Late Jurassic. Given that Mo comes from chemical weathering, far more Mo-enriched sediment was available in the east Pacific because of the erosion of the continental arc. In contrast, due to backarc extension, erosions in the Western Pacific margin was less extensive, resulting in less Mo in OAE sediments on the Pacific Ocean floor. Importantly, the Eastern Pacific plate has been mostly subducted, with only Cenozoic crust left. During plate subduction, large amount of the Mo-rich sediments in the Eastern Pacific have been taken down to the mantle wedge. Subsequently these sediments were metamorphosed and then Mo was transferred to porphyry deposits through partial melting. In contrast, only a small amount of the sediment in the Western Pacific has been subducted, with most of the Jurassic and Cretaceous oceanic crust well preserved.Molybdenum deposits of the Eastern Pacific margin can be classified into three types: porphyry-Cu-Mo, high-F porphyry and low-F porphyry-Mo deposits. Large and superlarge porphyry-Cu-Mo deposits are usually associated with ridge subductions, and thus formed through partial melting of subducted oceanic crust and metamorphosed Mo-rich sedimentary material due to subduction erosion. The high-F porphyry-Mo deposits (e.g., Climax-type) were likely formed by partial melting of subducted and thus metamorphosed Mo-enriched sediments during slab rollback (usually associated with A-type granite). Low-F porphyry-Mo deposits were formed through direct partial melting of metamorphosed Mo-enriched sediments entrained into the mantle wedge through subduction erosion at slightly shallower depths (usually associated with arc granite). Porphyry-Cu (Au) deposits in the southwest Pacific margin are all associated with subduction of backarc basins younger than the last OAE (55.8 Ma). Therefore, porphyry Cu (Au) deposits in the southwest Pacific margin have no economic levels of Mo. The oxygen fugacity of northwest Pacific is lower than ΔFMQ +2, which inhibits the formation of porphyry deposits.

Evidence from pseudomorphous β-quartz phenocryst for decompression of rock-forming and ore-forming processes in Shapinggou porphyry Mo deposit

The Shapinggou porphyry molybdenum (Mo) deposit, located in Jinzhai County, Anhui Province, China, is the largest in the Qinling-Dabie Mo Metallogenic Belt. The intrusive rocks in the Shapinggou Mo ore district formed in the Yanshanian can be divided into two stages based on zircon U-Pb dating and geochemical features. This study focuses on the late stage intrusions (quartz syenite and granite porphyry), which are closely genetically related to molybdenum mineralization. Petrographic observations identified two quartz polymorphs in the quartz syenite and granite porphyry, which were derived from the same magmatic sources and similar evolutionary processes. The quartzes were identified as a xenomorphic α-quartz within quartz syenite, while the quartz phenocrysts within the granite porphyry were pseudomorphous β-quartz, characterized by a hexagonal bipyramid crystallography. The pseudomorphous β-quartz phenocrysts within the granite porphyry were altered from β-quartz through phase transformation. These crystals retained β-quartz pseudomorph. Combined with titaniumin- zircon thermometry, quartz phase diagrams, and granitic Q-Ab-Or-H2O phase diagrams, it is suggested that the quartz syenite and granite porphyry were formed under similar magmatic origins, including similar depths and magmatic crystallization temperatures. However, the α-quartz within quartz syenite indicated that the crystallization pressure was greater than 0.7 GPa, while the original β-quartz within the granite porphyry was formed under pressures between 0.4 and 0.7 GPa. The groundmass of the granite porphyry which formed after the phenocryst indicated a crystallizing pressure below 0.05 GPa. This indicates that the granite porphyry was formed under repetitive and rapid decompression. The decompression was significant as it caused the exsolution of the ore-forming fluids, and boiling and material precipitation during the magmatic-fluid process. The volumetric difference during the phase transformation from β-quartz to α-quartz caused extensive fracturing on the granite porphyry body and the wall rocks. As the main ore-transmitting and ore-depositing structures, these fractures benefit the hydrothermal alteration and stockwork-disseminated mineralization of the porphyry deposit. It is considered that the pseudomorphous β-quartz phenocrysts of the porphyritic body are metallogenic indicators within the porphyry deposits. The pseudomorphous β-quartzes therefore provide evidence for the formation of the porphyry deposit within a decompression tectonic setting.

Structural reconstruction and age of an extensionally faulted porphyry molybdenum system at Spruce Mountain, Elko County, Nevada

This study integrates a cross-sectional restoration of normal faults and porphyry-related hydrothermal alteration zones with six new U-Pb zircon dates to constrain the ages of mineralization and large-magnitude Cenozoic extension at Spruce Mountain, northeastern Nevada (USA). Paleozoic sedimentary rocks and sparse rhyolitic intrusive rocks host a porphyry molybdenum deposit dated as ca. 38 Ma that contains associated skarn, carbonate replacements, fissure veins, and jasperoid. At least six crosscutting sets of normal faults with variable dip directions (east, west, and north) and angles ( 60°) are identified at Spruce Mountain, reflecting overprinting phases of extension. Based on the restored cross section, normal faulting at Spruce Mountain resulted in ∼6.9 km (120%) of total extension and ∼35° of net eastward tilting. The first four fault sets, late Eocene (ca. 38 Ma) or older, collectively accommodate most of the total extension (∼5.4 km). Later faults probably were active in the Miocene and Quaternary. All restored faults had initial dips of 45° or greater, and the restored preextensional structure of Spruce Mountain consists of west-vergent folds and gentle westward dips of Paleozoic rocks. Spruce Mountain is classified as a rhyolitic porphyry Mo or Climax-type deposit, with extensive skarn. Eocene rhyolite porphyry dikes associated with porphyry Mo mineralization locally intrude the early generations of normal faults at Spruce Mountain. However, many normal faults also postdate molybdenum mineralization and have partially dismembered the system. Cross-sectional restoration of the postmineralization faulting suggests that the original deposit had an ∼6 km long by ∼3 km deep elliptical pattern with carbonate replacement deposits surrounding skarn.

Late Mesozoic molybdenum mineralization on Hainan Island, South China: Geochemistry, geochronology and geodynamic setting

Hainan Island has become an important molybdenum (Mo) producer in East China, with the proven and measured metal Mo reserves of >0.29Mt and >0.69Mt, respectively. The known Mo-related deposits and occurrence which genetically might be attributed to porphyry- and hydrothermal vein types are hosted predominantly within the Cretaceous granitoids. These granitoids belong to high-K calc-alkaline, metaluminous to weakly peraluminous I-type series, and have geochemical affinities to arc-related basalts as defined by SiO2 (57.40–77.34wt.%) and K2O (2.45–6.28wt.%) contents, A/CNK ratios (mostly 0.86–1.10), depleted K, Ba, Nb, Sr, P and Ti, and enriched Rb, Th, Pb, Zr and La, and LREE-enriched REE patterns (La/YbN=7.1–66.3) with pronounced negative Eu anomalies to no Eu anomalies (Eu/Eu*=0.35–1.08). The highly variable geochemical compositions might be linked to magmatic processes. The LA-ICP-MS U–Pb dating on zircon have revealed three stages of magma emplacement for the Cretaceous Mo-hosting granitoids during ca. 113–108Ma, ca. 100–94Ma and ca. 90–70Ma, respectively. The initial 87Sr/86Sr ratios (from 0.70567 to 0.71208) and ɛNd(t) values (from −3.9 to −6.9) suggest that the host granitoids were sourced from an enriched subcontinental lithospheric mantle that had been metasomatized by fluids and/or melts released from ancient, subducted oceanic crust under an extension-induced setting. This setting is most favorable to variable degree of magma mixing between mantle-derived and crust-derived melts.With the second event as most important and the third event likely recording the youngest Mo mineralization in East China, the Re–Os dating of molybdenite from two types of Mo deposits on Hainan Island has identified three Mo mineralizing events occurring at ca. 112Ma, ca. 106–95Ma and ca. 89–72Ma. They are consistent with the episodes of the Cretaceous magmatism. The Re concentrations of molybdenites and δ34S values of sulfides (1.36–5.73‰ and average 4.3‰) commonly indicate that the metal Mo is of hybrid origin between mantle and crust but with variable degree of hybridization. Given that the subduction of the Paleo-Pacific plate beneath the eastern Asian margin dominated the Late Mesozoic tectonism of South China, and that Hainan Island has been a part of the Cathaysia Block since Late Permian, the widespread Cretaceous extension and associated Mo mineralizing event(s) on Hainan Island might be a response to episodic rollback of the subducted slab, which led to the underplating of mantle-derived basaltic melts and associated deep crustal melting. Moreover, this tectono-magmatic scenario likely resulted in the migratory pluses of Mo metallogenesis and the change of metal Mo sources from northeast to southwest Hainan Island.

Magmatic sequences in the Halasu Cu Belt, NW China: Trigger for the Paleozoic porphyry Cu mineralization in the Chinese Altay–East Junggar

The Halasu porphyry copper belt situated in the East Junggar is one of the major porphyry copper belts in Xinjiang Uygur Autonomous Region, northwest China. Copper and molybdenum mineralization occurs as disseminated sulfides or veinlets mainly in granodiorite porphyry and diorite porphyry, with the intense development of zoned alteration from potassic, through sericitic to an outer zone of propylitic alteration.New LA–ICP-MS zircon U–Pb dating reveals that magmatism in the belt can be divided into three periods during the Middle Devonian and Early Carboniferous, namely the pre-mineralization stage of 390Ma, syn-mineralization stage of 382–372Ma, and post-mineralization stage of 350–320Ma. The syn-mineralization intrusions are calc-alkaline, whereas pre- and post-mineralization intrusions are shoshonitic and high-K calc-alkaline. The syn-mineralization intrusions are enriched in highly incompatible trace elements but depleted in Nb, Ta, Hf and Ti relative to the pre- and post-mineralization intrusions.Zircon trace elements analyses demonstrate a negative correlation between Ti-in-zircon temperatures and oxygen fugacity. Ore-bearing syn-mineralization granitoids are characterized by higher water content, oxygen fugacity and low temperatures with higher mineralization potential than pre- and post-mineralization ones. These characteristics, together with the geochemical signature of the intrusions, suggest that the ore-bearing porphyries are derived from relative high ƒH2O magma reservoir. The remarkably homogeneous Hf isotopic compositions (εHf(t)=8 to 13) from syn-mineralization intrusions span over 10m.y., suggesting the existence of a long-lived reservoir beneath Halasu belt during the Middle Devonian. All the intrusions have low initial 87Sr/86Sr values (0.703935 to 0.707172), high εNd(t) values (4.7 to 5.5) and young crustal model ages (650 to 750Ma). Combined with the mantle-derived Pb isotope characteristics, the Sr–Nd–Hf data suggest that the parental magma was probably derived from flat subduction triggered partial melting of juvenile crust generated during subduction–accretionary process with no significant input of old crust, whereas pre-mineralization and post-mineralization intrusions are supposed to emplaced in immature island arc setting and post-orogenic setting, respectively.

Investigating the Geochemical Model for Molybdenum Mineralization in the JEB Tailings Management Facility at McClean Lake, Saskatchewan: An X-ray Absorption Spectroscopy Study.

The geochemical model for Mo mineralization in the JEB Tailings Management Facility (JEB TMF), operated by AREVA Resources Canada at McClean Lake, Saskatchewan, was investigated using X-ray Absorption Near-Edge Spectroscopy (XANES), an elemental-specific technique that is sensitive to low elemental concentrations. Twenty five samples collected during the 2013 sampling campaign from various locations and depths in the TMF were analyzed by XANES. Mo K-edge XANES analysis indicated that the tailings consisted primarily of Mo(6+) species: powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3·8H2O), and molybdate adsorbed on ferrihydrite (Fe(OH)3 - MoO4). A minor concentration of a Mo(4+) species in the form of molybdenite (MoS2) was also present. Changes in the Mo mineralization over time were inferred by comparing the relative amounts of the Mo species in the tailings to the independently measured aqueous Mo pore water concentration. It was found that ferrimolybdite and molybdate adsorbed on ferrihydrite initially dissolves in the TMF and precipitates as powellite.

Zircon U–Pb and molybdenite Re–Os geochronology, Hf isotope analyses, and whole-rock geochemistry of the Donggebi Mo deposit, eastern Tianshan, Northwest China, and their geological significance

The geodynamic setting of Mesozoic magmatic rocks and associated mineralization in eastern Tianshan, Northwest China, are attracting increasing attention. The newly discovered giant Donggebi molybdenum deposit (0.508 Mt at 0.115% Mo) is located in the central part of eastern Tianshan, Xinjiang. The molybdenum mineralization was genetically associated with the Donggebi stock, comprised of porphyritic granite and granite porphyry. Secondary ion mass spectrometry (SIMS) zircon U–Pb dating constrains that the porphyritic granite and granite porphyry emplacement occurred at 233.8 ± 2.5 Ma and 231.7 ± 2.6 Ma, respectively. The Re–Os model ages of six molybdenite samples range from 235.2 to 237.0 Ma, with a weighted mean age of 236.1 ± 1.4 Ma, which is roughly consistent within errors with the zircon U–Pb ages, suggesting a Middle Triassic magmatic–mineralization event at Donggebi. Geochemically, the Donggebi granitoids are characterized by high SiO2 and K2O contents, with low MgO contents, belonging to high-K calc-alkaline granites. These rocks show pronounced enrichment in K, Rb, U, and Pb, and depletion in Sr, Ba, P, and Ti, with negative Eu anomalies (Eu/Eu* = 0.20–0.38). In situ Hf isotopic analyses of zircon from the porphyritic granite and granite porphyry yielded εHf(t) values ranging from +6.6 to +10.5, and from +5.5 to +10.1, respectively. The geochemical and isotopic data imply that the primary magmas of the Donggebi granitoids could have originated by partial melting of a juvenile lower crust that involved some mantle components. Combined with the regional geological history, geochemistry of the Donggebi granitoids, and new isotopic age data, we thus propose that the Donggebi molybdenum deposit was formed in the Middle Triassic, and occurred in an intracontinental extension setting in eastern Tianshan.

Petrology, geochemistry and zircon U–Pb and Lu–Hf isotopes of the Cretaceous dykes in the central North China Craton: Implications for magma genesis and gold metallogeny

The Trans-North China Orogen (TNCO), a Paleoproterozoic suture that amalgamates the Western and Eastern Blocks of the North China Craton (NCC), witnessed extensive magmatism and metallogeny during Mesozoic, associated with intraplate tectonics and differential destruction of the cratonic lithosphere. Here we investigate a suite of porphyry dykes surrounding the Mapeng batholith in the Fuping Complex within the TNCO in relation to the Mesozoic gold and molybdenum mineralization. The major element chemistry of these dykes show a range of SiO2 (57.92 to 69.47wt.%), Na2O (3.20 to 4.77wt.%), K2O (3.12 to 4.60wt.%) and MgO (0.51 to 3.67wt.%), together with high concentration of LREE and LILE, and relatively low contents of HREE and HFSE. The rocks display (La/Yb)N=13.53–48.11, negative Nb, Ta, Th, U and Zr anomalies, and distinctly positive Ba, K and Sm anomalies. The mineralogy and geochemistry of the porphyry dykes indicate the rocks to be high-K calc-alkaline, and I-type, with adakitic features similar to those of the adjacent Mapeng batholith. The source magma for these rocks was derived from a mixture of reworked ancient continent crust and juvenile mantle materials. The zircon U–Pb data from these rocks show ages in the range of 124 to 129Ma, broadly coinciding with the emplacement age of the Mapeng intrusion. The inherited zircons of ca. 2.5, 2.0 and 1.8Ga in the dykes represent capture from the basement rocks during melting. The zircon Lu–Hf isotopic compositions show negative εHf(t) values varying from −27.8 to −11.3, with Hf depleted model ages (tDM) ranging from 1228Ma to 1918Ma and Hf crustal model ages (tDMC) of 1905Ma to 2938Ma, suggesting that the Mesozoic magmatism and associated metallogeny involved substantial recycling of ancient basement rocks of the NCC. We present an integrated model to evaluate the genesis of the porphyry systems and their relation to mineralization. We envisage that these dykes probably acted as stoppers (impermeable barriers) that prevented the leakage and run-off of the ore-bearing fluids, and played a key role in concentrating the gold and molybdenum mineralization.

Geochemistry and Geochronology of the Shanggusi Granite Porphyry, East Qinling: Implications to Molybdenum Mineralization

Geochemistry and Geochronology of the Shanggusi Granite Porphyry, East Qinling: Implications to Molybdenum Mineralization

Geological Condition of Molybdenum Mineralization, Dongwuqi, Inner Mongolia

Geological Condition of Molybdenum Mineralization, Dongwuqi, Inner Mongolia

A biogeochemical orientation study in Mo skarn deposits, Jecheon district in Korea

A biogeochemical orientation survey was conducted in the vicinity of Mo skarn deposits in the Jecheon district in Korea. The main litholigies of the study area are Ordovician dolostone, limestone and calc-silicate rocks intruded by ‘Jurassic Jecheon biotite granite’. The skarn zones occur at the contacts of granite and limestone. Molybdenum mineralization occurs in fracture zones in skarns within the screen and in disseminated form. The skarn ore minerals are mainly molybdenite, scheelite, galena and chalcopyrite. The control area is Gwanak mountain where the Seoul National University is located and the geology consists of Jurassic granite with no Mo mineralization. Samples of soils and two plant species (Daimyo oak leaves/branches — Quercus dentata, and Sargent cherry leaves — Prunus sargentii) were collected from the target area and control area in May and June 2011, and analyzed for Mo and 59 other elements by ICP-MS. Each of three sampling lines was designed to cross over each orebody at 30m spacings in the study area and 10 sampling points were chosen randomly in the control area. The soil samples (n=36/10, target/control) collected from the target area show higher values of Mo (<0.1–38.7, median: 1.5ppm) than those from the control area (<0.1–3.2, median: 0.9ppm Mo). The concentration of Mo in plants (n=108/30, target/control) from the target area (0.51ppm in Q. dentata leaves, 0.19ppm in Q. dentata branches and 0.31ppm in P. sargentii leaves) is 1.5–5 times higher than that from the control area (0.16ppm in Q. dentata leaves, 0.04ppm in Q. dentata branches and 0.21ppm in P. sargentii leaves). The biological absorption coefficient (BAC) of Mo is generally high (Q. dentata leaves=1.4, Q. dentata branches=0.4 and P. sargentii leaves=1.2) and Mo content in soils and plants is strongly correlated. The geochemical variation patterns of Mo in plants are similar to those in soils, which suggest a corresponding Mo anomaly and enhanced contrast near the Mo orebodies. The three plant organs (Q. dentata leaves, branches and P. sargentii leaves) may be used as indicators for the biogeochemical prospecting of Mo.

Geochronology and geochemistry of the giant Qian'echong Mo deposit, Dabie Shan, eastern China: Implications for ore genesis and tectonic setting

The Qian'echong Mo deposit is a giant porphyry deposit in the Dabie Shan of eastern China. Molybdenum (Mo) mineralization mainly occurs as numerous veinlets in altered schists, with the development of potassic, phyllic, argillic, and propylitic alteration assemblages. A buried granite porphyry stock and locally exposed dikes are spatially and genetically related to the Mo mineralization. Zircon crystals from exposed quartz porphyry, rhyolitic porphyry, and granite porphyry dikes, as well as a buried granite porphyry dike yield weighted average 206Pb/238U ages of 128.9±1.1Ma (MSWD=0.30, 2σ, n=13), 127.42±0.94Ma (MSWD=0.58, 2σ, n=17), 127.44±0.98Ma (MSWD=1.6, 2σ, n=16), and 126.6±1.4Ma (MSWD=0.67, 2σ, n=15), respectively. The buried granite porphyry stock yields a zircon U–Pb weighted average age of 124.7±1.6Ma (MSWD=1.5, 2σ, n=16), which is slightly younger than the exposed dikes, but within error of the age of the buried granite porphyry dike. Five molybdenite samples from the ores yield Re–Os isotope ages of 123.31±1.02 to 128.49±1.40Ma, which are consistent with the U–Pb ages for the igneous rocks These age data constrain magmatic–hydrothermal activity at the Qian'echong Mo deposit to a period of about six million years from 129 to 123Ma. This period overlaps the recognized regional Mo mineralization event in the Dabie Shan of 142–111Ma, which took place during the post-collisional tectonism subsequent to amalgamation of the Yangtze and North China blocks.The Qian'echong granite porphyry stock and dikes have high contents of SiO2, K2O and Al2O3, and low contents of TiO2, MgO and CaO, showing a peraluminous high-K calc-alkaline to shoshonite affinity, with obvious LREE enrichment and a negative Eu anomaly. The rocks have a high initial 87Sr/86Sr of 0.70729 to 0.71788 and highly negative εNd(t) values of −16.2 to −26.1, with TDM2(Nd) ages of 2.24 to 3.03Ga. Their (206Pb/204Pb)t, (207Pb/204Pb)t, and (208Pb/204Pb)t values range from 16.017 to 16.701, 15.252 to 15.368, and 37.095 to 37.578, respectively. This Sr–Nd–Pb isotopic signature indicates that the causative granitic intrusions for the Qian'echong deposit were mainly melts with components of both the northern Dabie complex and the Taihua and Xiong'er Groups that are part of the Precambrian basement of the North China block. The melts were generated during the tectonic extrusion of the Dabie Shan and their emplacement onto the basement of the North China block. The Qian'echong Mo deposit is unique based upon the crustal source for the causative porphyry, localization of most mineralization in the surrounding schist country rocks, and the CO2-rich ore-forming fluid. Thus we propose the Qian'echong deposit to represent a new sub-type of porphyry Mo deposit, herein termed collisional- or Dabie-type porphyry deposit.