Porphyry Mo Deposit Research Articles

Formation of Large to Giant Porphyry Mo Deposits: Constraints From Whole-Rock and In Situ Mineral Geochemistry of Causative Magmatic Rocks in the Tongbai-Hong’an-Dabie Orogens, Central China

Formation of Large to Giant Porphyry Mo Deposits: Constraints From Whole-Rock and In Situ Mineral Geochemistry of Causative Magmatic Rocks in the Tongbai-Hong’an-Dabie Orogens, Central China

Discovery and Exploration of the Luming Porphyry Mo Deposit, Northeastern China: Implications for Regional Prospecting

Over the past two decades, significant deposit discoveries were made in Northeastern China, including the super-large Chalukou, Daheishan, and Luming porphyry Mo deposits. The discovery of the Luming deposit was accomplished through verification of stream sediment anomalies, with mineralization closely associated with early Jurassic monzogranite and granite porphyry. Previous studies primarily focused on the mineralization mechanisms of these deposits without adequately addressing the exploration methods and prospecting criteria. This study involved a comprehensive re-evaluation of geological observations, analysis of rock primary halo, gravity and magnetic surveys, and induced polarization surveys conducted during exploration campaigns at the Luming porphyry Mo deposit. The results suggest that hydrothermal breccias play a critical role in controlling the mineralization by forming a central low-grade core within the deposit while the Mo mineralization and hydrothermal alteration exhibit a donut-shaped distribution around it. The primary halo shows a distinct metal zonation moving from a central W-Bi-Mo-(Sb) to a peripheral Cu-Co-Ni and a distal Pb-Zn-Ag-In. The mineralization zone exhibits a low Bouguer gravity anomaly, negative magnetic anomaly, medium to low resistivity, and moderate to high chargeability, indicating the effectiveness of geophysical methods in defining the extent of the ore body. The Luming porphyry Mo deposit and distal skarn-epithermal Pb-Zn mineralization are parts of a porphyry-related magmatic-hydrothermal system. The results of this study offer valuable insights into the genesis of porphyry Mo deposits and their implications for prospecting in the forested region of Northeastern China.

Quartz fluid inclusions and trace elements in the Lailisigaoer porphyry Mo deposit, Western Tianshan, Xinjiang: Fluid evolution and metallogenic mechanism in magmatic-hydrothermal system

The Lailisigaoer deposit is a typical porphyry Mo deposit located in the late Paleozoic Boluokenu metallogenic belt of Western Tianshan, NW China. This study aims to understand molybdenum mineralization and the dynamics of magmatic-hydrothermal fluid within the porphyry system, focusing on fluid inclusion, cathodoluminescence textures, and trace elemental composition in various generations of quartz. Six vein types in the Lailisigaoer deposit are classified as comb quartz veins with unidirectional solidification texture (UST, QI), actinolite/biotite ± quartz veinlets (M-type, QII), quartz-chalcopyrite vein (A-type, QIII), quartz-molybdenite vein (B-type, QIV), quartz-pyrite vein (D-type, QV) and quartz-carbonate vein (E-type, QVI). Micro thermometry data indicate decreasing homogenization temperatures in primary fluid inclusions from UST to E-type veins. The magmatic-hydrothermal fluids associated with UST and M-, A-, B-, D-, E-type veins underwent a transition from high temperature (342–495℃), high-pressure (∼1.25 kb), and variable salinity (6.7–41.1 wt%NaCl) in the H2O-CO2-NaCl system to low-temperature (142–238℃), low-pressure (∼0.25 kb), and low-salinity (1.6–5.1 wt%NaCl) in the H2O-NaCl system. This evolution is reflected in the proportion of quartz with oscillatory zones decreasing and irregular quartz increasing, indicating a shift from turbulent to stable fluid conditions. Furthermore, a gradual reduction in Ti concentration (from 79 ppm in UST to 1.4 ppm in E-type quartz) suggests a decrease in fluid temperature during the magmatic-hydrothermal evolution. Mineralization primarily occurs in A- and B-type veins, with molybdenum precipitation attributed to fluid immiscibility in a medium–high temperature (240–368 ℃) and high pressure (∼0.95 kb) environment. The A-type veins (mean 31 ppm in Ti concentrations) consist of equigranular (dark-core) (QIII-1) and patchy inhomogeneous CL-gray quartz (QIII-2). The B-type veins (mean 24 ppm in Ti concentrations) are characterized by equigranular (bright-core) inhomogeneous quartz (QIV-1) with growth zones that are cemented by later mosaic homogeneous CL-gray quartz (QIV-2). Based on the quartz-Ti thermometer, the mineralized veins (A- and B-type) were confined to be formed at depths of 2.8–3.6 km, with molybdenum mineralization occurring at 3.4–3.6 km. Molybdenum mineralization initiates during the QIV-1 crystallization period in magmatic-hydrothermal fluids and terminates in the QV-2 generation.

Positive Δ199Hg anomalies in Mesozoic porphyry Mo deposits of Northeastern China and their implications to the metallogeny of arc-related hydrothermal systems at convergent margins

Mercury (Hg) isotopes display unique mass-independent isotope fractionation (MIF, reported as Δ199Hg), which is primarily generated via Hg photochemical processes in the land-ocean-atmosphere system. Magmatic and hydrothermal processes do not trigger MIF of Hg isotopes, therefore, Hg-MIF signals detected in deep reservoirs (mantle and crust) are theoretically sourced from recycled surface materials. Here, we observed positive Δ199Hg signals (0.10 ± 0.07‰, SD) in Mesozoic porphyry Mo deposits of NE China. These values correspond to the recently reported Δ199Hg signature of Mesozoic epithermal AuAg systems in NE China (Δ199Hg: 0.11 ± 0.07‰, SD), suggesting that both mineral systems receive large amounts of Hg from subducted marine materials, given that marine Hg has positive Δ199Hg composition. Our study thus provides novel geochemical evidence on the linkage between oceanic plate subduction and metallogeny of various hydrothermal systems at convergent margins. Subduction contributes large amounts of volatiles to arc magmas, which then release metal-rich magmatic-hydrothermal fluids of the porphyry to epithermal ore deposit spectrum.

U–Pb Ages and Whole-Rock and Zircon Geochemistry of Granitoids from the Zhireken Mo-Porphyry Deposit, Eastern Transbaikalia: New Insights into the Link to Mineralization

U–Pb Ages and Whole-Rock and Zircon Geochemistry of Granitoids from the Zhireken Mo-Porphyry Deposit, Eastern Transbaikalia: New Insights into the Link to Mineralization

U–Pb ages and whole-rocks and zircon geochemistry of granitoids from the Zhireken Mo-porphyry deposit, Eastern Transbaikalia: new insights into the link to mineralization

Жирекенское Mo-порфировое месторождение расположено в пределах Западно-Станового террейна Забайкальского сектора Монголо-Охотского складчатого пояса и приурочено к одноименной многофазной интрузии средне-позднеюрского возраста. Несмотря на длительную историю освоения месторождения, на сегодняшний день остается невыясненным целый ряд вопросов касательно магматизма и рудной минерализации. В частности, до сих пор не установлена рудопродуцирующая гранитоидная интрузия, с внедрением которой связано формирование месторождения. В исследовании представлены новые U-Pb LA-ICP-MS цирконовые возрасты, а также геохимический состав цирконов и магматических пород Жирекенского месторождения. Проведенные исследования показывают, что месторождение пространственно ассоциирует с серией интрузий высоко-K известково-щелочных — шошонитовых гранитоидов I-типа, внедрившихся в интервале 158–166 млн лет на постколлизионной стадии эволюции Монголо-Охотского океана. Последовательность внедрения включает биотитовые лейкограниты (U-Pb возраст ок. 164–166 млн лет) → биотит-амфиболовые граниты и гранодиориты (U-Pb возраст ок. 161–163 млн лет) → дайки гранит-порфиров (U-Pb возраст ок. 162–163 млн лет), лейкогранит-порфиров и (кварцевых) диорит-порфиров → дайки кварцевых монцонит-порфиров (U-Pb возраст ок. 158 млн лет). Полученные U-Pb возрасты и геологические взаимоотношения между гранитоидами и минерализацией предполагают, что внедрение рудогененирующей гранитоидной интрузии и формирование Mo-порфирового рудного штокверка на Жирекенском месторождении произошло в интервале 158–161 млн лет. Оценка рудного потенциала этих гранитоидов по комплексу геохимических валовых и минеральных (цирконы) индикаторов фертильности показала, что изученные интрузии не могут быть генетически связаны с порфировой минерализацией, поскольку являются производными слабоокисленных магм. Гранитоидная интрузия, с которой генетически связано молибденовое оруденение Жирекенского месторождения, либо не вскрыта, либо представлена породами, не охваченными настоящим и более ранними исследованиями.

Application of a Multifractal Model for Identification of Lithology and Hydrothermal Alteration in the Dasuji Porphyry Mo Deposit in Inner Mongolia, China

The Dasuji giant porphyry molybdenum deposit is one of the largest ore deposits recently discovered along the Yinshan–Yanshan–Liaoning molybdenum belt in China. Using this deposit along the Yinshan–Yanshan–Liaoning molybdenum belt as the study area, the present study proposed a two-stage approach aimed at marking out the hydrothermally altered anomalies in the study area for the guidance of future prospecting in other regions. First of all, the Principal Component Analysis (PCA) and specific Band Ratio methods were applied to the ASTER images from different acquisition dates to extract ferric oxides and hydroxyl alterations related to the porphyry molybdenum deposit. Then, the Fractal-Aided Anomaly-Overlaying Selection model was adopted to recognize two ferric and hydroxyl alteration layers for separating anomalies from the interferences caused by geology and random noise from the data. Furthermore, for lithological differentiation in the previously marked off area, the Random Forest Classifier (RFC) was applied to the composite data obtained via the ASTER, ETM, and DEM, and it is demonstrated that the DEM can significantly improve lithological mapping in areas with complex vegetation cover and topography. Based on field verification and comparison with geological maps, the research revealed that the suggested two-stage approach may effectively reduce erroneously recognized anomalies produced during the first stage while retaining ore-related anomalies for gigantic porphyry molybdenum deposit prospecting in the Dasuji area, which showed the good application potential of the proposed model to extract actual hydrothermally altered anomalies adopted for lithological discrimination and mapping.

Geochemical evolution of the REE-enriched Cave Peak porphyry Mo-deposit, Trans-Pecos Texas, USA

The Cave Peak deposit is a rift-related, breccia-hosted, fluorine-rich porphyry molybdenum deposit that is enriched in Nb, REE, and other critical minerals. Cave Peak is the easternmost member of a northwest-trending group of Paleogene intrusions in the Diablo Plateau along with the Marble Canyon stock, an unmineralized, petrogenetically related, compositionally zoned mafic alkaline pluton. The Cave Peak intrusions show within-plate geochemical affinity and is the product of a highly differentiated magma series. Curvilinear trends in Harker variation and trace element diagrams record magma differentiation from mafic to intermediate (44–69 wt% SiO2) to felsic (70–76 wt% SiO2) compositions at Marble Canyon and Cave Peak, respectively. Quartz syenite and monzonite from the Marble Canyon stock yielded zircon UPb ages of 36.2 ± 0.15 Ma and 36.1 ± 0.09 Ma, respectively. The youngest major intrusion at Cave Peak, an alkali feldspar granite porphyry, has a zircon UPb age of 34.8 ± 0.4 Ma, supporting that these intrusions represent a magma differentiation trend. The δ98Mo of Cave Peak molybdenites range between −0.39 ± 0.06 ‰ and + 0.52 ± 0.06 ‰ with a total Mo isotope range of 0.91 ‰. Cave Peak samples predominantly fractionated towards heavier δ98Mo. The Cave Peak data are distinctly heavier than data obtained from the nearby subduction-related Red Hills porphyry Cu deposit which has δ98Mo values of −0.25‰ to −0.51‰.

The geochronology, geochemistry, and petrogenesis of the Leimengou porphyries, Qinling Orogen: A case study of intrusions associated with a Dabie-type porphyry Mo deposit

The Leimengou giant Mo deposit is a porphyry system in the northeastern Qinling Orogen along the southern margin of the North China Craton, comprising orebodies hosted mainly in a multiphase porphyritic granitic to monzonitic pluton emplaced in the Taihua Supergroup. Zircons from the syn-ore porphyritic monzogranite (PMG) and the porphyritic K-feldspar granite (PKG) yielded U − Pb ages of 131.3 ± 1.0 Ma and 130.6 ± 0.9 Ma, respectively. The post-ore, quartz monzonite porphyry (QMP), has a weighted mean 206Pb/238U age of 124.6 ± 1.0 Ma (n = 14, 1σ, MSWD = 0.13). These ages constrain the Leimengou porphyry system to have formed between 132 and 124 Ma. The PMG and PKG have similar geochemical characteristics, i.e., high-K calc-alkaline affinity, negative εHf(t) values of − 25.1 to − 22.0 and − 25.1 to − 19.2, and TDM2 ages of 2.77–2.57 Ga and 2.76–2.40 Ga, respectively. The PKG has lower concentrations for Sr, Ba, and negative anomalies of δEu, and also has higher total REE values compared to the PMG. These anomalies are interpreted to reflect fractional crystallization involving plagioclase and biotite. The characteristics of the PKG support its derivation from an evolved magma, which likely facilitated the enrichment of Mo. Additionally, the Hf isotope data suggest that the Leimengou porphyry system had a composite source, with inputs from the North Qinling Accretion Belt, the North China Craton, and the mantle. Compared to the syn-ore PMG, the post-ore QMP exhibits lower (La/Yb)N ratios of 20.5–22.8, higher zircon εHf(t) values of − 19.7 to − 9.0, and younger TDM2 ages of 2.42–1.75 Ga. This suggests that the Leimengou porphyry Mo system formed during thinning of an overthickened orogenic crust during the tectonic transition from collisional compression to post-collisional extension. The productive intrusions at Leimengou and other porphyry Mo deposits of Dabie-type have average Nb/Zr ratios that are typically below 1. Moreover, the Rb/Sr ratios range from 0.1 to 1, further distinguishing these intrusions from the intrusions associated with Climax- and Endako-type Mo deposits.

The mobility of copper, zinc, molybdenum, and tungsten in subduction zone fluids

Porphyry-type ore deposits are closely associated with subduction zones, but the ultimate source of the metals in these deposits is still uncertain. To test whether aqueous fluids from the subducted slab may contribute to the metal enrichment, we investigated the partitioning of Cu, Zn, Mo, and W between saline aqueous fluids and the subducted basaltic crust at 2.5–3.0 GPa and 650–670 °C by experiments in piston cylinder presses. The bulk fluid/solid partition coefficients (Dfluid/solid) of Cu and Zn increase significantly with fluid salinity. For Cu, Dfluid/solid is less than 1 in a salt-free aqueous fluid, but at a salinity of 10 wt% NaCl, Dfluid/solid approaches 10. On the other hand, the Dfluid/solid of Zn is still below 0.4 even at the same salinity. Dfluid/solid of Mo is always relatively high (>4), with only a very slight enhancement by salinity at 2.5 GPa. The fluid/solid partition coefficient of W is close to 1 for a chloride-free fluid, but slightly decrease with increasing salinity. Overall, these experimental data show that saline aqueous fluids released from the basaltic layer of the subducted oceanic slab can effectively transport Cu and Mo and therefore enrich these two metals in the mantle wedge. This enrichment does not contradict the observation that Cu concentrations in primitive arc magmas and MORB are similar, since these concentrations may be controlled by a buffering sulfide phase. The enrichment of copper in the source then does not necessarily increase Cu concentrations in the melt, but it ensures that the copper-bearing sulfide phase is not exhausted during repeated melting events. For molybdenum, our data suggest that aqueous fluids from the slab are the major source of Mo in arc magmas. Due to the high pre-enrichment of Mo in some sediments, there may be a direct link between the types of subducted sediment and the location of porphyry Mo deposits. On the other hand, the contribution of slab fluids to the Zn budget of these magmas is likely negligible. The W partitioning data are consistent with isotopic evidence for the mobility of W in subduction fluids. Moreover, the behavior of Mo and W is strongly affected by the abundance of rutile in the solid residue. In a rutile-free lithology, not only Mo, but also W would strongly partition into the fluid. As some sediments may be highly enriched in W relative to the average mantle, fluids from such sediments may also produce a significant W enrichment in the mantle wedge, provided that the sedimentary residue is free of rutile.

Ore Genesis and the Magmatism of the Yuhaixi Mo(Cu) Deposit in Eastern Tianshan, NW China: Constraints from Geology, Geochemistry, Zircon U-Pb and Molybdenite Re-Os Dating

The Yuhaixi Mo(Cu) deposit is a new discovery in the eastern section of the Dananhu-Tousuquan island arc, Eastern Tianshan. However, the genesis of the Yuhaixi Mo(Cu) deposit is still not fully understood. The Yuhaixi intrusion is composed of monzonitic granites, diorites, granites, and gabbro dikes, among which disseminated or veinlet Mo and Cu mineralization is mainly hosted by the monzonitic granites. The LA-ICP-MS zircon U-Pb dating yields emplacement ages of 359.4 ± 1.6 Ma for the monzonitic granite, 298.8 ± 1.8 Ma for the diorite, and 307.0 ± 2.3 Ma for the granite. The Re-Os dating of molybdenite hosted by monzonitic granite yields a well-constrained 187Re-187Os isochron age of 354.1 ± 6.8 Ma (MSWD = 1.7) with a weighted average age of 344.5 ± 3.1 Ma. The Mo mineralization is closely associated with the Yuhaixi monzonitic granite. The Yuhaixi monzonitic granite rocks are characterized by high silica (SiO2 > 70 wt.%), low MgO (0.23–0.36), Ni, Cr contents, and they are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: e.g., K, Ba, Pb and Sr), and depleted in heavy rare earth elements (HREEs) and high field-strength elements (HFSEs: e.g., Nb, Ta and Ti). They are weak peraluminous and have high εHf(t) (11.37–17.59) and εNd(t) (1.36–7.75) values, and varied initial 87Sr/86Sr (0.7037–0.7128) values. The Yuhaixi post-ore granites exhibit similar geochemical and isotopic signatures to the Yuhaixi monzonitic granite. These characteristics suggest that the Yuhaixi felsic rocks are likely sourced from the partial melting of the juvenile lower crust. The Yuhaixi diorite has low SiO2, and K2O contents, relatively high Na2O, MgO (Mg# = 45–53) contents, and depletions in HFSE (e.g., Nb, Ta, and Ti). These geochemical features, coupled with isotopic data such as low initial 87Sr/86Sr (≤0.7043), high εNd(t) (2.5 to 3.0) and εHf(t) (≥11.6) values, and young Hf model ages, suggest that their parental magmas possibly originated from the partial melting of the depleted lithospheric mantle that was metasomatized by hydrous melts or fluids from the subducting oceanic plate. Integrating our new results with previous works on the Dananhu-Tousuquan island arc belt, we suggest that the Yuhaixi Mo(Cu)deposit is likely sourced from the juvenile lower crust, which was formed in an arc setting, where the bipolar subduction of the North Tianshan oceanic slab forms the Dananhu Tousuquan belt to the north and the Aqishan-Yamansu belt to the south. The eastern section of the Dananhu-Tousuquan island arc is a promising target for late Paleozoic porphyry Mo(Cu) deposits.

Distinctive Features of the Major and Trace Element Composition of Biotite from Igneous Rocks Associated with Various Types of Mineralization on the Example of the Shakhtama Intrusive Complex (Eastern Transbaikalia)

This article presents data on the composition of biotite from igneous rocks of the Shakhtama complex, which are associated with various types of mineralization in Eastern Transbaikalia: Au-Cu-Fe-skarn, skarn-porphyry, Mo-porphyry, rare-metal–greisen, Au-polymetallic and Au-Bi. The major element and halogen contents were determined by EPMA. The content of trace elements was determined by means of LA-ICP-MS. As a result, the specific traits of the composition of the biotite of igneous rocks associated with specific types of mineralization of the Eastern Transbaikalia were determined. The biotites of rare-metal–greisen deposits are characterized by the maximum content of fluorine (>2 wt. %) and low chlorine content (<0.04 wt. %). In addition, such biotites are characterized by high XFe (>0.47). Within Eastern Transbaikalia, igneous rocks developed at the Bystrinsky deposit are potentially ore-bearing for the “classic” porphyry type of mineralization. They have the highest values of IV(F/Cl) (4.9–7.1) and IV(F) (2–2.8) and the lowest values of Log(XMg/XFe) (0.1–0.4). The trace element composition clearly distinguishes biotites from rare-metal–greisen deposits and is identified by the highest contents (ppm) Ga > 65, Li > 600, Sn > 20, Mn > 2000, Cs > 50, Zn > 600. Biotites of Au-polymetallic and Au-Bi deposits occupy an average position between rare-metal–greisen and Mo-porphyry ones. Biotites of Mo-porphyry deposits differ in minimum values (ppm) of Sn < 3, Zn < 160, and low values of Li (150–290), V (290–440), and Ga (39–48). In general, the chemical composition of biotites shows that the degree of igneous rock fractionation of deposits increases in the series: porphyry–skarn–polymetallic–rare-metal.

Discovery, geological setting and mineralization of the Shuvuutai molybdenum deposit, central-southern Mongolia

We document the newly discovered Shuvuutai Molybdenum (Mo) porphyry deposit located in the central-east Mongolian volcanic/-plutonic belt of the southern Altaids. The deposit is characterized by quartz vein- and veinlet-disseminated-type Mo ore bodies mainly hosted in a Late Permian-Early Triassic granitic intrusion. In this study, we provide a detailed study that integrates detailed geology with petrographic, mineralogic, geochemical, and geochronologic date to determine the tectonic setting of the deposit. Fluid inclusion analysis is used to reconstruct the fluid evolution history of the Shuvuutai Mo mineralization system and to understand the origin of the deposit. The ore bodies occur mainly as veins, lenses, and pods in positions from inner intrusions through contact zones to the host rocks distal to causative intrusions. The host rocks are variable in lithology, including granites, porphyries, volcanic breccias and tuffs, and sedimentary rocks. Outward from ore bodies to host rocks, the wall rock alteration is zoned from potassic (K-feldspar-quartz-mica), through phyllic (quartz-sericite-chlorite-epidote), to propylitic or argillic alterations. Two samples from porphyry stock intrusions at Shuvuutai were selected for U–Pb zircon geochronology and trace element composition studies, including the ore-hosting monzodiorite porphyry and quartz syenite porphyry. Our new ages are consistent with, or slightly postdate published zircon U-Pb ages of early phase of monzodiorite porphyry (268–232 Ma) and the main phase of quartz syenite porphyry (251.6 ± 1.7 Ma). Hydrothermal mineralization generally includes four stages, from early to late, represented by (1) potassic feldspar-quartz veins or veinlets, (2) quartz-molybdenite stockworks, (3) quartz-sulfide stockworks, and (4) quartz ± carbonate veins or veinlets. The ore-forming fluids were initially magmatic in origin and show high-temperature and high-salinity, containing daughter mineral and CO2-bearing fluid inclusions; and eventually evolved to low-temperature, low-pressure, low-salinity and CO2-poor meteoric water. S isotopic compositions of sulfides from the Shuvuutai Mo porphyry deposit indicate that the source of the ore-forming material was derived from the felsic magma. The Central-Eastern Mongolian volcanic-plutonic belt continues from Mongolia into northeast China, where similar Mo deposits are not yet recognized, suggesting that a new exploration strategy, based on the characteristics and history of the Shuvuutai discovery, is needed for the Chinese segment of the Altaids.

A 2D seismic reflection dataset of the Caosiyao giant porphyry Mo deposit in the shallow coverage area in Jining, Inner Mongolia, China

AbstractProspecting for and exploiting buried mineral deposits is currently challenging. Given their high precision and resolution, reflection seismic methods might be useful in such applications involving deep mineral deposits. However, there are few open seismic datasets available from mineral deposit exploration, especially in hardrock environments. The world‐class Caosiyao porphyry Molybdenum deposit (1.76 Mt) in the Jining area of Inner Mongolia, China, is largely covered by loess layers, which poses challenges to its exploration. Seismic reflection surveys were conducted to help delineate the deep granite porphyry intrusions and associated orebodies. This paper presents the raw seismic reflection dataset from three profiles on the Caosiyao deposit area, which can be used as a standard dataset for reflection seismic processing in shallow coverage and hardrock areas. Situated at the juxtaposition of the Khondalite Belt and the Trans‐North China Orogen in the northern North China Craton, the Jining region hosts considerable known porphyry Mo deposits. As such, this open dataset can assist in research on deep geological structures and hence increase prospecting efficiency in geologically similar areas.

U-Pb and Re-Os geochronology and geochemistry of the Ulgen hidden porphyry Mo deposit in the Derbugan metallogenic belt (NE China): Insights into petrogenesis and tectonic setting

The Ulgen porphyry Mo deposit, recently discovered in the northeastern segment of the Derbugan metallogenic belt, NE China, is a large and hidden ore deposit. Investigation of this deposit provides insights into the geodynamic background and metallogenic mechanism of Mesozoic porphyry Mo deposits that are exposed elsewhere in NE China. The host rocks consist of muscovite monzonitic granite (MMG) and biotite granitic porphyry (BGP), which are intruded into Lower and/or Middle Jurassic intermediate-felsic volcanic-sedimentary rocks and pre-ore monzogranitic porphyry (MP). Zircon laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) U-Pb age dating indicates that the MMG and BGP were emplaced at 144.9 Ma and 144.7 Ma, ca. 14 m.y. younger than the intrusion age of MP (159.3 Ma). Molybdenite Re-Os isotopic dating indicates that Mo mineralization occurred at 144.9 Ma, almost simultaneously with the 145 Ma magmatic activity. Geochemically, all of the Ulgen granitoids are enriched in large ion lithophile elements (e.g., Rb, Th, U, and K) and light rare earth elements, and are depleted in high field strength elements (e.g., Nb, Ta, and Ti). The pre-ore MPs belong to I-type granites with moderately negative Eu anomalies (Eu/Eu* = 0.62−0.65), whereas the syn-ore MMGs exhibit S-type affinity with pronounced negative Eu anomalies (Eu/Eu* = 0.29−0.39). The ore-forming BGPs display adakite-like geochemical features in terms of high-Sr, low-Y, and low-Yb contents, and slightly negative Eu anomalies (Eu/Eu* = 0.72−0.74). All intrusive rocks have relatively low initial (87Sr/86Sr)i ratios (0.7044−0.7055) and positive εNd(t) values (+1.15 to +2.65), positive εHf(t) values (+4.0 to +9.4), young two-stage Nd and Hf model ages (tDM2(Nd) = 841−731 Ma, tDM2(Hf) = 943−604 Ma), and moderate (206Pb/204Pb)i (18.300−18.402), (207Pb/204Pb)i (15.557−15.564), and (208Pb/204Pb)i (38.180−38.307) ratios. Therefore, it is most likely that these intrusive rocks originated from a mixture of two sources of magma derived from the mantle and juvenile lower crust, in which there were variable degrees of the fractional crystallization of ilmenite, apatite, and plagioclase. Rather than the partial melting of oceanic slabs, the fractional crystallization of hornblende and accessory minerals (e.g., ilmenite and apatite) induces the adakitic geochemical signature of BGPs. Compared with the BGPs, the MPs had a relatively deeper magma source region, whereas the MMGs had a relatively shallower magma source region. The BGPs and the Mo-bearing fluids of the Ulgen deposit were most probably derived simultaneously from magma that was generated at an extensional setting following the closure of the Mongol-Okhotsk Ocean during the latest Jurassic. Enrichment of Mo by late-stage fractional crystallization most likely played an important role in concentrating Mo during the formation of the Ulgen hidden Mo deposit.

The Role of Reductive Carbonaceous Surrounding Rocks in the Formation of Porphyry Mo Deposits

Porphyry Mo deposits are the most important type of Mo resource. They result from a high oxygen fugacity of the parent magma, which acts as an effective indicator for evaluating the mineralization. In the ore-forming system of porphyry Mo deposits, sulfur exists mainly as sulfate in highly oxidized magma but as sulfide in ores. What triggers the reduction in the mineralization system that leads to sulfide precipitation has not yet been determined. Most of the previous studies have focused on the origin and evolution of the ore-forming parent magma, and the effects of reductive surrounding rocks on porphyry mineralization have been ignored. In this study, a comprehensive geological–geochemical investigation and review have been performed on the typical porphyry Mo deposits, the Nannihu-Sandaozhuang, Yuchiling, and Shapingou deposits in China, and the Mt. Emmons deposits in America. Black carbonaceous sedimentary layers commonly surround porphyry Mo ores, which are widely altered and discolored during mineralization. CH4 is commonly present in fluid inclusions in the main mineralization stage, and the δ13CV-PDB values of calcite and fluid inclusions from the altered surrounding rocks and ore minerals are generally low and significantly different from those of marine sedimentary carbonate rocks, indicating that the involvement of reductive components from carbonaceous surrounding rocks might be key to the redox state transformation leading to mineral precipitation. On the other hand, the CH4 produced by the thermal decomposition of organic matter or carbonaceous reaction with H2O can diffuse into the ore-forming system along the structural fractures and reduce the SO42− in the ore-forming hydrothermal fluids to form sulfide precipitation without direct contact between the intrusion and the carbonaceous surrounding rocks. Moreover, the CH4 content controls the location of the orebody formation with the high content producing orebodies mainly in the porphyry intrusion, while the low CH4 content results in the orebodies mainly occurring at the contact zone between the porphyry and carbonaceous surrounding rocks. Compared to the magmatic stage of mineralization, the involvement of reductive components in the carbonaceous surrounding rocks during the hydrothermal stage is more favorable for forming giant/large Mo deposits. The highly oxidized porphyry with reductive carbonaceous surrounding rocks or Fe-rich volcanic rocks offers a new indicator for efficiently evaluating porphyry Mo mineralization.

Tracing black shales in the source of a porphyry Mo deposit using molybdenum isotopes

Abstract Porphyry Mo deposits are important suppliers of molybdenum for industrial applications, but the origin and source of metals in these deposits remain debated. Here, we present Mo isotope data for Miocene mineralized porphyritic monzogranites (MPMs) and Paleocene barren biotite monzogranites and tuffs (BMTs) from the Bangpu porphyry Mo (Cu) deposit in the Gangdese metallogenic belt. The results show that the MPMs display radiogenic Sr and Pb isotopes and elevated δ98/95Mo (relative to NIST SRM 3134; +0.07‰–1.2‰) and Mo contents, which exceed the range of the depleted mantle. These characteristics cannot be attributed to surface weathering, hydrothermal alteration, magmatic differentiation, or partial melting but rather reflect the incorporation of Mo from black shales into their magma sources, as evidenced by the significant correlations between δ98/95Mo and εNd(t) and aluminum saturation index (ASI) values. In contrast, the BMTs display lower Mo and δ98/95Mo values than the mineralized samples, and their δ98/95Mo values display no correlations with radiogenic isotopes or ASI values. The contrasting characteristics of mineralized and barren samples provide strong evidence that the addition of black shales played an important role in the formation of the Bangpu porphyry Mo deposit. Our study thus establishes a possible link between porphyry Mo deposits and organic-rich sediments and highlights the great potential of Mo isotopes in studying porphyry Mo deposits.

Carbonatisation and overprinting mineralisation in Siah-Kamar porphyry molybdenum deposit, NW Iran

The Siah-Kamar porphyry Mo deposit (SKD) is located at the north-western termination of the Urumieh-Dokhtar magmatic arc and it is the only known porphyry Mo ore reserve in Iran. The SKD formed in two main mineralisation stages, at ~33–32 Ma (late-stage, disseminated) and ~ 29–28 Ma (late-stage, high-grade), within a context of a long-lived magmatism. We integrate results from the whole-rock geochemistry, the OC stable and Sr isotope systematics across the mineralised alteration zones with the available drilling data (ore element concentration) to define the ore-forming processes leading to Mo enrichment in the SKD. Our investigation shows that CO2 bearing magmatic fluids had the major role in both early and late-stage mineralisation. The Mo shows positive correlation with SiO2 content but a clear negative correlation with W, Cu, and S, due to a delayed precipitation of Mo during the early-stage mineralisation. The released fluids from the new acidic magmas and subsequent fluid-rock interaction in an open-system, primarily assisted by brittle fracturing, and accompanied by cooling and mixing with various amounts of meteoric water and fluid neutralisation, was responsible for the selective ore depletion and Mo-ore enhancement during carbonatisation along structurally-controlled pathways.

Genesis of the Questa Mo Porphyry Deposit and Nearby Polymetallic Mineralization, New Mexico, USA

Abstract The Oligocene Latir magmatic center in northern New Mexico is an exceptionally well exposed volcano-plutonic complex that hosts a variety of magmatic-hydrothermal deposits, ranging from relatively deep, F-rich porphyry Mo mineralization to shallower epithermal deposits. We present new whole-rock chemical and isotopic data for plutonic rocks from the Latir magmatic center, including extensive sampling of drill core samples of intrusive rocks from the Questa porphyry Mo deposit. These data document temporal chemical trends of porphyry-related mineralization that occurred after caldera-forming magmatism and during postcaldera batholith assembly. Silicic magmas were generated multiple times throughout the history of the Latir magmatic center, but few are associated with the formation of a mineral deposit. Whole-rock trace element ratios and Sr, Nd, and Pb isotope compositions vary throughout the protracted history of silicic magmatism. The caldera-forming ignimbrite and early phase of postcaldera intrusions are unmineralized, more enriched in high field strength elements, and generally contain less radiogenic Sr and Pb and more radiogenic Nd than later intrusions. The Questa porphyry Mo deposit formed immediately after the most isotopically primitive phase of the batholith was assembled, ruling out simple reworking of juvenile mantle-derived crust as the source for mineralizing magmas. Rhyolite dikes associated with polymetallic sulfide deposits intruded ~800 k.y. after Mo mineralization, and Nd isotope data indicate that these dikes are associated with different batches of magma and are unrelated to the Mo-mineralizing intrusions at the Questa mine. Together, these data indicate that the source of magmas changed significantly throughout the 10-m.y. history of the magmatic center. We assess multiple genetic models for porphyry-related magmatism against this data set, favoring models with discrete periods of magma genesis from a deep hybridized zone in the lower crust giving rise to the punctuated periods of mineralization. These observations suggest that the formation of mineral deposits within a central magmatic locus is likely the result of the piecemeal assembly of individual hydrothermal-magmatic systems, and that distal and younger polymetallic mineralization commonly observed near known porphyry deposits represents decoupled processes.

Magmatic to hydrothermal evolution of the Gaogangshan Mo deposit, NE China: Mineralogical insights from quartz

Integrated study on cathodoluminescence (CL) textures and compositions of quartz is proven to be an effective way to reconstruct the ore-forming conditions and processes of porphyry system under subduction tectonic setting. However, little relevant research has been conducted on collision-type porphyry deposits. The Gaogangshan deposit in the northern Lesser Xing'an Range, NE China, consists of typical collision-type porphyry Mo mineralization related to Permo-Triassic granitic intrusions. Ore-forming process is recorded by multiple generations of quartz, including pre-ore stage quartz with unidirectional solidification texture (UST), early ore-stage quartz-molybdenite veins with K-feldspar alteration halos (Q1), late ore-stage quartz-sulfides veins with sericite alteration (Q2), and post-ore stage quartz veins (Q3) associated with calcite and fluorite. Cathodoluminescent textures, trace elements and fluid inclusions in quartz reveal physicochemical conditions, evolution of ore fluids and the Mo mineralization process. The UST quartz and Q1 veins are dominated by CL-bright homogenous and/or granular mosaic textures, containing more Ti concentrations (average = 35–42 ppm) than Q2 and Q3 veins. The molybdenite-bearing Q2 veins are dominated by CL-gray granular and zonal textures, displaying less CL intensity and lower Ti concentrations (average = 16 ppm) than early-stage quartz. The Q3 veins have the lowest CL-intensity and the lowest Ti concentrations (average = 2.5 ppm) among all quartz types. Three types of inclusions are identified in above quartz samples, including liquid–vapor aqueous inclusions, CO2-bearing liquid–vapor aqueous inclusions and halite-bearing multiphase aqueous inclusions. The ore-forming fluids in ore-stage Q1 and Q2 veins are dominated by large salinity variation (2.3–38.9 wt% NaCl equiv.), CO2-bearing (4.2–8.9 mol%) two-phase aqueous inclusions with vapor volumetric proportions of 30–65%. Intersections of fluid inclusion isochores with Ti-in-quartz isopleths yield quartz formation conditions of ∼2.2 kbar at ∼640℃ for UST quartz, ∼1.25 kbar at ∼510℃ for Q1, ∼1.0 kbar at ∼440℃ for Q2, and ∼0.37 kbar at ∼220℃ for Q3. The Gaogangshan porphyry Mo deposit formed at depths of 3.8 to 4.7 km.