Cu-Mo Deposit Research Articles

Distribution characteristics and influencing factors of rhenium concentrations in molybdenite from the porphyry Cu-systems: A review

金属铼（Re）是支撑航空航天等高科技产业高质量发展的重要原材料，具不可替代性。研究表明，世界上绝大部分的Re都赋存在斑岩型矿床的辉钼矿之中，且Re含量在矿床、矿石、矿物颗粒等不同尺度上均存在较大差异，但目前学术界对导致这些差异的影响因素尚不清楚。本文通过对全球斑岩型Cu（Mo）、Mo（Cu）矿床中Mo品位、辉钼矿的微量元素组成和Re-Os年龄、成矿岩体的化学组成、Sr-Nd同位素等数据的汇总，深入探讨了影响该类矿床辉钼矿中Re含量变化的主要因素。结果显示，Re含量与矿床中钼的平均品位呈负相关，地幔物质的加入可能是形成高Re辉钼矿的基础。本研究证实，辉钼矿Re含量与其成矿时代不具耦合关系，并且Re的含量与辉钼矿沉淀的位置、以及辉钼矿多型之间亦无明显相关性，而可能与成矿岩体的成分、岩浆分异程度、成矿流体的性质、热液蚀变及表生作用过程有关。;As one of key metals, rhenium (Re) is extensively used in high-tech fields such as aerospace due to its refractory geochemical properties, which is irreplaceable. Previous studies have shown that most of Re in the world is concentrated in molybdenite of porphyry Cu-Mo deposits, but Re concentrations vary significantly on the scale of ore deposits, samples and even individual molybdenite particles. At present, understanding of such difference is still unclear. Based on the data of molybdenum grades, trace elements contents of molybdenite, molybdenite Re-Os ages, lithogeochemical and Sr-Nd isotopic compositions of porphyry Cu(Mo) and Mo(Cu) deposits in the world, key factors of affecting Re concentrations in molybdenite from porphyry deposits are discussed. The results show that Re concentrations are negatively correlated with the average molybdenum grades, and mantle-derived component input may be in favor of high Re molybdenite formation. This study confirmed that there were no direct relationships between Re concentrations of molybdenite and metallogenic ages of porphyry deposits, molybdenite precipitation locations, and molybdenite polytypes. In contrast, rhenium concentrations in molybdenite may be related to the compositions of ore-forming rocks, magmatic differentiation degree, nature of ore-forming fluids, hydrothermal alteration and supergenesis.

Evolution of Multistage Hydrothermal Fluids in the Luoboling Porphyry Cu-Mo Deposit, Zijinshan Ore Field, Fujian Province, China: Insights from LA-ICP-MS Analyses of Fluid Inclusions

Abstract The Luoboling Cu-Mo deposit, with 1.4 million tons (Mt) Cu and 0.11 Mt Mo, is the largest porphyry deposit in the Zijinshan district of southeast China. Mineralization at Luoboling is divided into premineralization, synmineralization, and late-mineralization stages. Consistent Cs/(Na + K) ratios in fluid inclusions suggest that the mineralizing fluids originated from a common source—the Luoboling granodiorite porphyry. The absence of initial supercritical fluid inclusions and abundant coexisting vapor and brine fluid inclusions imply that the fluids exsolved at low-pressure two-phase conditions, with temperatures of 250° to 600°C and salinities of 30 to 60 wt % NaCl equiv (brines) and <10 wt % NaCl equiv (vapors). The deposit formed at ~120 to 800 bar, corresponding to the depths of ~1.2 to 3.2 km (assuming a transition from lithostatic to hydrostatic load). Metals such as Mo (up to 77 ppm), Pb (up to 8,800 ppm), Zn (up to 13,000 ppm), and Ag (up to 130 ppm) migrated mainly in brines. Although vapor inclusions have high concentrations of Cu (up to 20,000 ppm), hypersaline fluid was the major medium for Cu transport and precipitation. The successive precipitation of Mo and Cu occurred when fluids cooled to ~500°C and ~350° to 450°C, respectively. The late-stage quartz-pyrite veins with phyllic alteration were formed by Cu-rich magmatic hydrothermal fluids. The Zijinshan epithermal Cu-Au deposit and the Luoboling porphyry Cu-Mo deposit originated from independent hydrothermal systems. Nonetheless, the increasing trends of Pb, Zn, and Ag concentrations in different stage inclusions from Luoboling imply potential for distal Pb-Zn-Ag mineralization.

Flotation Separation of Chalcopyrite and Molybdenite Assisted by Microencapsulation Using Ferrous and Phosphate Ions: Part I. Selective Coating Formation

Porphyry Cu-Mo deposits, which are the most important sources of copper and molybdenum, are typically processed by flotation. In order to separate Cu and Mo minerals (mostly chalcopyrite and molybdenite), the strategy of depressing chalcopyrite while floating molybdenite has been widely adopted by using chalcopyrite depressants, such as NaHS, Na2S, and Nokes reagent. However, these depressants are potentially toxic due to their possibility to emit H2S gas. Thus, this study aims at developing a new concept for selectively depressing chalcopyrite via microencapsulation while using Fe2+ and PO43− forming Fe(III)PO4 coating. The cyclic voltammetry results indicated that Fe2+ can be oxidized to Fe3+ on the chalcopyrite surface, but not on the molybdenite surface, which arises from their different electrical properties. As a result of microencapsulation treatment using 1 mmol/L Fe2+ and 1 mmol/L PO43−, chalcopyrite was much more coated with FePO4 than molybdenite, which indicated that selective depression of chalcopyrite by the microencapsulation technique is highly achievable.

Identifying hydrothermal quartz vein generations in the Taiyangshan porphyry Cu-Mo deposit (West Qinling, China) using cathodoluminescence, trace element geochemistry, and fluid inclusions

Porphyry-style mineralization is characterized by superposition of multiple generations of quartz growth, punctuated by dissolution and juxtaposed within a single vein. Such superposition inevitably obscures temporal relationships between quartz formation, alteration events, and fluid inclusion assemblages (FIAs), and consequently complicates the interpretation of fluid origin and evolution. Very detailed information of these relationships recorded within hydrothermal quartz from the Taiyangshan porphyry Cu-Mo deposit (NW China) is obtained using integrated cathodoluminescence (CL) imaging, trace element analyses, and fluid inclusion petrography.The CL characteristics range from bright blue-CL quartz (Q1) associated with early high-temperature potassic alteration, to dark blue-CL quartz (Q2) broadly coinciding with metal precipitation, to post-ore dull red-CL fine-grained, anhedral, and recrystallized quartz (Q3) subgrains. Early bright blue-CL quartz (Q1) crystals, generally at the edges of stockwork veinlets close to wallrock, are characterized by oscillatory growth zoning, and exhibit alignment of primary, equant-shaped, brine-bearing FIAs along the banded growth zones. Later dark blue-CL quartz (Q2) crystals are generally euhedral in shape and grow with c-axes pointing inward to the vein center. They exhibit well-defined, but rarely preserved, growth zones truncating Q1 and crystal terminations projecting into pyrite and chalcopyrite in the vein center although they are not spatially associated with sulfides. These vein features clearly indicate that Q2 crystals grow into an open cavity or fracture during the ore precipitation. This is also evident by coexisting, secondary, irregular-shaped, liquid-rich inclusions and vapor-rich inclusions along fractures transecting Q1 oscillatory growth bands. The coexistence of hypersaline and vapor-rich inclusions moreover provides unequivocal evidence for phase separation during mineralization. Dull red-CL quartz (Q3) crystals appear to coincide with or follow sericitic alteration, and cut and encompass preexisting Q1 and Q2 crystals. They spatially associated with sulfides. The Q3 grains contain rare well-defined FIAs, but show scattered, secondary, irregular-shaped, low-salinity aqueous inclusions with small- to medium-sized vapor bubbles (10–30 vol%), as well as complex fluid inclusions that have migrated to the margins of anhedral Q3 subgrains due to quartz dissolution and recrystallization.Formation of early blue-CL Q1 and Q2 crystals at moderate temperatures are consistent with enrichment of Ti in the quartz lattice compared to neighboring younger Q3. The Q2 crystals are typified by elevated concentrations of Al and K concentrations when compared to Q1 and Q3. The substitution of Ti4+ for Si4+ in the tetrahedral sites of quartz leads to an increased CL intensity from Q1, to Q2, and then to Q3 corresponding to a decrease in quartz precipitation temperature. Ore deposition, recorded by integration of CL textures, FIAs petrography, and trace element variations in Q2, in the Taiyangshan porphyry Cu-Mo deposit must have occurred over a significant change in physicochemical conditions. This suggests that phase separation due to fluid cooling/pressure drops during the transition from lithostatic to hydrostatic regimes is critical to porphyry mineralization. We further propose a complex hydrothermal quartz vein formation history involving multiple fluid inclusions under varying pressure and temperature conditions.

Occurrence and Distribution of Silver in the World-Class Río Blanco Porphyry Cu-Mo Deposit, Central Chile

Abstract Porphyry Cu-Mo deposits (PCDs) are the world’s major source of Cu, Mo, and Re and are also a significant source of Au and Ag. Here we focus on the world-class Río Blanco PCD in the Andes of central Chile, where Ag is a by-product of Cu mining. Statistical examination of an extensive multielemental inductively coupled plasma-mass spectrometry data set indicates compositional trends at the deposit scale, including Ag-Cu (r = 0.71) and Ag-In (r = 0.53) positive correlations, which relate to Cu-Fe sulfides and Cu sulfosalts in the deposit. Silver is primarily concentrated in Cu ores in the central core of the deposit, and significant variations in the Ag concentration are related to the different hydrothermal alteration types. The concentration of Ag is highest in the potassic core (avg 2.01 ppm) and decreases slightly in the gray-green sericite (phyllic) zone (avg 1.72 ppm); Ag is lowest in the outer propylitic alteration zone (avg 0.59 ppm). Drill core samples from major hydrothermal alteration zones were selected for in situ analysis of Ag and associated elements in sulfide and sulfosalt minerals. To ensure representativeness, sample selection considered the spatial distribution of the alteration types and ore paragenesis. Chalcopyrite is the most abundant Cu sulfide in Río Blanco, with Ag concentration that ranges from sub-parts per million levels to hundreds of parts per million. The highest concentration of Ag in chalcopyrite is associated with the high-temperature potassic alteration stage. Bornite is less abundant than chalcopyrite but has the highest Ag concentration of all studied sulfides, ranging from hundreds of parts per million up to ~1,000 ppm. The Ag concentration in bornite is higher in lower-temperature alteration assemblages (moderate gray-green sericite), opposite to the behavior of Ag in chalcopyrite. Pyrite has the lowest Ag content, although concentrations of other critical elements such as Co, Ni, and Au may be significant. The highest Ag concentrations, i.e., thousands of parts per million up to weight percent levels, were detected in late-stage Cu sulfosalts (enargite, tennantite, and tetrahedrite). The Ag content in these sulfosalts increases with increasing Sb concentrations, from the Sb-poor enargite to the Sb-rich tetrahedrite. The earliest Ag mineralization event is related to the potassic alteration stage represented by early biotite and transitional early biotite-type veinlets and where the predominant sulfides are chalcopyrite and bornite. Silver mineralization during this stage was predominantly controlled by crystallization of Cu-Fe sulfides. The second Ag mineralization event at Río Blanco is associated with the transitional Cu mineralization stage, which is represented by the gray-green sericite alteration (C-type veinlets). In this alteration type, Ag was partitioned preferentially into chalcopyrite, bornite, and to a lesser extent pyrite. The last Ag mineralization event is related to the late quartz-sericite alteration stage, characterized by D- and E-type veinlets with pyrite-chalcopyrite and enargite-tennantite-tetrahedrite. Our data indicate that Ag was associated with several Cu mineralization episodes at Río Blanco, with Ag concentration apparently controlled by cooling, changes in pH, fO2 and fS2 of the hydrothermal fluids, and the intensity of alteration. Overall, our results provide information on critical metal partitioning between sulfides, plus the distribution of critical element resources at the deposit scale. Knowledge of the mineralogical occurrence of critical metals in PCDs is necessary to better assess their resources and evaluate the potential for their recovery.

Protolith-controlled superposition of Sn-(W) and Cu-Mo mineralization: Examples from the Jurassic and Cretaceous granite-related mineralization in the coastal region of southeastern China

Sn (W) and Cu-Mo have distinct geochemical behaviors during magmatic evolution, thus these two group deposits are seldom superposed. Specially, the Mesozoic granite-related Sn-W/W-Sn and Mo-Cu/Cu-Mo deposits in south China are spatial overlapped, with some are even temporal-coincided. To reveal the factors controlling the distribution and the locally coeval occurrence of different mineralization types, here we compared the ages, sources compositions, and tectonic settings of the Jurassic Zijinshan Sn-rich granite, the Jurassic Gutian porphyry Mo-Cu deposit, and the Cretaceous Luoboling porphyry Cu-Mo deposit from the southeastern (SE) China. The results indicate that the Jurassic Sn-W and Mo-Cu rich magmas were derived from Paleoproterozoic meta-sedimentary and meta-basaltic rocks, respectively, through partial melting (>850 °C) along the suture zones triggered by asthenospheric upwelling in the intra-plate extensional setting. The Cretaceous porphyry Cu-Mo deposit was formed by water-flux melting (<800 °C) of the mantle wedge metasomatized by the fluids derived from the subducted Paleo-Pacific plate. A protoliths-controlled distribution model was proposed, namely that during Jurassic, the suture zones, where were the ancient continental margins containing both meta-sedimentary and meta-basaltic rocks, favored heat input from upwelling mantle and high temperature melting, which consumed the both protoliths to form W-Sn and Mo-Cu rich magmas in the same region; shift in tectonic setting from intra-plate extension to subduction during Cretaceous, introduced mantle or juvenile crust-derived materials to source, therefore formed Cu-Mo deposits superposing the Jurassic W-Sn and Mo-Cu ores in SE China.

Laser-Raman spectral analysis of the Baoxingchang Cu-Mo deposit, Yunnan Province, SW China

Baoxingchang Cu-Mo deposit is one of several Cu-Mo-(Au) polymetallic deposits have been found in the Tethys metallogenic province. Laser-Raman spectral analysis shows that the vapour-phase components of fluid inclusions in quartz are mainly composed of water vapour and a little CO2, while the fluid-phase components contain Na+ and Cl− metallogenic fluid, which generally belongs to a NaCl-H2O system. In conclusion, the characteristics of fluid inclusions in porphyry-type Cu-Mo polymetallic deposits in Baoxingchang are closely related to multi-stage intrusions along the Jinshajiang-Red River shear zone.

Protracted Magmatism and Mineralized Hydrothermal Activity at the Gibraltar Porphyry Copper-Molybdenum Deposit, British Columbia

Abstract The Gibraltar Cu-Mo deposit, with a total tonnage of 3.2 million tons (Mt) Cu, is located in the Canadian Cordillera and hosted by the Late Triassic Granite Mountain batholith. The batholith formed through multiple intrusions of tonalitic rocks over a period of ~25 m.y. beginning at 229.2 ± 4.4 Ma in the Quesnel island arc before the accretion of the arc to the North American continent. Late in its evolution, Cu fertile magmas intruded in the center of the batholith, during at least three events from 218.9 ± 3.1 to 205.8 ± 2.1 Ma. The fertile magmas were hotter and more mafic than older barren magmas. They generated magmatic-hydrothermal activity, forming potassic alteration and white mica alteration, and produced Cu mineralization as chalcopyrite-quartz veinlets and disseminated chalcopyrite. Zircon in the Cu-bearing tonalite intrusion (218.9 ± 3.1 Ma) shows high Ce4+/Ce3+ (681 ± 286 [2σ], n =15) compared to those from older barren intrusions (129 ± 56 [2σ], n = 118). Oxidation conditions for parental magmas are calculated using the compositions of zircon and amphibole. The magmas for Cu-bearing intrusions have an average of fayalite-magnetite-quartz buffer (FMQ) +1.7 ± 0.7 (2σ, n = 73), whereas those for older barren intrusions have slightly lower fO2 (avg FMQ +1.3 ± 0.5 [2σ], n = 108), although the values are overlapping for the two. The bulk rocks of Cu-bearing tonalite intrusions in the Granite Mountain batholith have low Sr/Y ratios (&amp;lt;22) independent of the degrees of alteration. The low ratios are also reflected by low Sr/Y in zircon, suggesting that the low Sr/Y ratios of bulk rocks represent those of unaltered rocks. The values are low compared to those associated with many other porphyry Cu deposits globally. The data suggest that igneous rocks elsewhere with low Sr/Y in bulk rocks may have a potential to host economic Cu deposits. Ratios of Ce/Nd and Ce/Ce* (=Ce/((NdN)2SmN)) in zircon are positively correlated with the Ce4+/Ce3+ in zircon from the Granite Mountain batholith. Since the former two ratios can be obtained solely from zircon composition, these ratios from detrital zircon may be useful in evaluating the occurrences of oxidized intrusions in regional mineral exploration.

Late Mesozoic magmatism at Xiaokelehe Cu[sbnd]Mo deposit in Great Xing'an Range, NE China: Geodynamic and metallogenic implications

Multiphase Late Mesozoic magmatism is clearly recorded at the Xiaokelehe porphyry CuMo deposit in NE China, including the syn-ore granodiorite porphyry, and post-ore diorite, gabbro, monzonite (porphyry), and granite porphyry. In this study, we present new geological, LA-ICP-MS zircon UPb geochronological and geochemical data on these intrusive units to unravel the tectonic evolution of the Late Mesozoic Great Xing'an Range (GXR). Zircon UPb dating indicates that the multiphase magmatism extended from the Late Jurassic to Early Cretaceous, i.e., 149.4 ± 4.0 Ma (diorite), 148.9 ± 1.4 Ma (granodiorite porphyry), 146.9 ± 4.1 Ma (monzonite), 140.6 ± 3.8 Ma (gabbro), and 139.9 ± 4.3 Ma (monzonite porphyry).Geochemical data indicate that the syn-ore granodiorite porphyry is adakie-like, featured by relatively LILE-enrichments (Rb, Ba, K, Pb, LREEs), high Sr contents (1065–1130 ppm), and elevated Sr/Y (129.9–171.8) and (La/Yb)N (35.12–47.07) ratios, but with HFSE-depletions (Nb, Ta, Ti, HREEs), low Y (6.2–8.7 ppm) and Yb (0.48–0.67) contents. The granodiorite porphyry has relatively higher Mg# values (41–47), depletion of Nb and Ta, low Cr (29.0–31.0 ppm) and Ni contents (9.4–12.6 ppm), as well as enriched SrNd isotope features, indicating that the granodiorite porphyry was derived from an enriched mantle (garnet-bearing) refertilized by subduction-related melts in a post-collision setting, and the magmas were subsequently fractionated during their ascent. The diorite and gabbro may have also derived from the refertilized lithospheric mantle (but without garnet), whereas the monzonite and its porphyry were derived from the lower crust at >40 and < 40 km depths, respectively. Meanwhile, fractionation and crustal assimilation have been important for the diorite, gabbro, and monzonite (porphyry) formation. Combined our study with published ones, we concluded that: (1) the Mongol-Okhotsk Ocean was finally closed in the GXR before the Late Jurassic; and (2) Late Mesozoic magmatism and porphyry CuMo mineralization in the GXR likely occurred in the compressive-to-extensional transition after the collision between the Mongol-SinoKorea and Siberia plates.

Re-Os Ages for the Kourki Porphyry Cu-Mo Deposits, North West Niger (West Africa): Geodynamic Implications

The study area is located at the southern end of the Gorouol greenstone belt, northwestern Niger. This region contains significant deposits of Copper and Molybdenum hosted in intrusive rocks metamorphosed in the green shale facies. This deposit was previously considered a porphyry system of Copper (Cu) and Molybdenum (Mo) without having been the subject of advanced research. The objective of this study is to confirm or refute this hypothesis and to date the mineralisation in an absolute manner in order to readjust the mineralising episode in the history of the West African Craton. The methodology used within the framework of this study is the isotopic dating by the Re-Os method carried out on the pyrites of the host rock. The results of this analysis give an age range between 2158 ± 50 Ma and 2110 ± 51 Ma for the Cu-Mo mineralisation. This age range represents the West African Craton scale to an episode of magmatic accretion. During this accretion, the subduction phenomena between the Crusts (Oceanic and Continental) would have been favourable for the formation of the Cu and Mo mineralisation of Kourki.

Late Paleozoic metallogenesis and evolution of the Chinese Western Tianshan Collage, NW China, Central Asia orogenic belt

The Chinese West Tianshan has a prominent position in China, with respect to mineral resources and mineral production including copper, nickel, molybdenum, iron, gold, zinc and many other mineral resources. These resources are represented by a vast array of mineral systems and deposit styles in their respective terranes spanning the Precambrian and Phanerozoic geological history. These mineral systems include VMS iron–zinc, orogenic gold, magmatic copper-nickel, porphyry copper and copper–molybdenum, and epithermal gold deposits. Some of the deposits are large and superlarge including the well-known Axi gold and Dunde iron-zinc deposits, the Zhibo, Chagangnuoer, Beizhan iron deposits, and the Katebahasu gold deposit. Apart from the above-mentioned giant deposits, several others are poorly known and/or unknown to western geoscience. The study of these mineral systems can significantly contribute to our further understanding of the metallogeny of cratons and orogenic belts, orogenic collages, and anorogenic settings. This provides additions to, and further development of, existing classifications and genetic models of mineral systems, allowing researchers to elucidate unknown or poorly studied mineral systems and formation styles found in the Chinese West Tianshan, and to discover some other important styles that appear to be missing, although they are present in other regions with similar geological and tectonic settings.Based on the study of the of the West Tianshan domain, five types of endogenous metal deposits are identified: (1) Magmatic Cu-Ni deposits; (2) Porphyry Cu-Mo deposits; (3) VMS iron deposits; (4) Epithermal Au deposits; and (5) Orogenic Au-Cu deposits. Tectonically, the development of these metal deposits was closely associated with accretionary and convergent processes that occurred in the Chinese western Tianshan collage. The formation of the deposits involved three main stages, briefly described as follows: The Jingbulake intrusion associated with the Cu-Ni deposits suggests subduction of the South Tianshan oceanic lithosphere beneath the YCTB. During the Early to Late Carboniferous, the north-dipping subduction led to the development of porphyry Cu-Au deposits, epithermal gold deposits and VMS iron deposits. In the earliest Late Carboniferous, the south Tianshan oceanic crust was probably consumed, leading to the collision between the YCTB and the Tarim Craton. The large suites of granites were widely distributed in the NTAS and YCTB, accompanied by the formation of orogenic Au-Cu deposits.

The role of early sulfide saturation in the formation of the Yulong porphyry Cu-Mo deposit: Evidence from mineralogy of sulfide melt inclusions and platinum-group element geochemistry

Sulfide melt inclusions enclosed in silicate minerals have been observed in many oxidized Cu-bearing porphyries. The origin of such sulfide melt inclusions could bear critical information of metal enrichment or depletion during magma evolution of porphyry systems. The giant Yulong porphyry Cu-Mo deposit in eastern Tibetan Plateau consists of a series of felsic intrusions, among which the mineralized Yulong intrusion emplaced at a late stage of the magmatic activity. This study reports detailed texture and composition of sulfide melt inclusions from barren and mineralized intrusions, as well as platinum-group elements of these intrusions, to evaluate potential role of early sulfide saturation in the porphyry mineralization system. These sulfide melt inclusions, occurring as globules or droplets, are preserved in zircon, amphibole and quartz grains. Most of them are composed of a major phase of pyrrhotite and minor pyrite, chalcopyrite and pentlandite. Smooth boundaries between these phases suggest the origin of fractionation from sulfide melt upon cooling. Small amounts of Cu and Ni are heterogeneously distributed in the pyrrhotite. The sulfide melt inclusions could be observed in both the pre- and syn-mineralization intrusions at Yulong, indicating that sulfide saturation had commonly occurred during magma evolution. Magnetite mineral inclusions could be observed in zircon and amphibole grains as well. The mineral assemblage of magnetite + pyrrhotite + pyrite of the mineral inclusions constrains the Yulong magmatic system to redox conditions near the magnetite-pyrite/pyrrhotite buffer and above the fayalite/ magnetite-quartz buffer (FMQ). High Eu/Eu* values (0.56–0.78) of the hosting zircons and high calculated ΔNNO values (>0.5) of the hosting amphibole indicate highly oxidized nature of the parental magma.Both pre- and syn-mineralization intrusions have low PGE contents (Pt = 0.04 to 0.17 ppb, Pd = 0.19–0.60 ppb) with compositions plotting in the Au-poor porphyry Cu fields in discriminating diagrams. Early sulfide saturation may have been reached and small amounts of sulfides have been segregated from magma. Most PGEs and Au but little Cu have been removed from the evolved magma because the partition coefficient of Cu between sulfide and silicate melt is about two orders of magnitude lower than PGE or Au. As a consequence, the evolved magma would have high Cu but very low PGE and Au, resulting in the Au-poor porphyry Cu mineralization at Yulong.

Texture and geochemistry of multi-stage hydrothermal scheelite in the Tongshankou porphyry-skarn Cu-Mo(-W) deposit, eastern China: Implications for ore-forming process and fluid metasomatism

Abstract Scheelite from the Tongshankou porphyry-skarn Cu-Mo(-W) deposit occurs mainly as disseminated grains in the altered granodiorite porphyries at depth (Sch A), in the skarn coeval with retrograde alteration (Sch B) and in distal quartz veins crosscutting marbles (Sch C). Cathodoluminescence (CL) responses within a single Sch A grain reveal two subtypes: CL-clear Sch A-I and CL-turbid, densely veined Sch A-II. The CL contrast, coupled with geochemical data, suggest Sch A-I was metasomatized to form Sch A-II. CL images reveal that Sch A-I, Sch B and Sch C are all homogenous, with blue luminescence and are depleted in heavy rare earth elements (HREE), indicating a primary origin. However, Sch A-II is characterized by higher contents of light REE and heavy REE as well as higher Sr isotopes (0.7080–0.7100) than the primary scheelite (&amp;lt;0.7080). These differences indicate that Sch A-II formed through dissolution-reprecipitation. The Sr isotopes of the primary scheelite (0.7073–0.7078) are generally consistent with those of the mineralized granodiorite porphyries (0.7061–0.7063) and mafic enclaves (0.7058–0.7073). The granodiorite porphyries contain low tungsten contents (3–11 ppm), whereas high tungsten contents were detected in mafic enclaves (48–75 ppm). The coexistence of mafic enclaves and tungsten mineralization at depth, and their consistent Sr isotopes, indicates that the interaction of mafic enclaves and exsolved magmatic fluids from the granodiorite porphyries may have played an important role in the extraction of tungsten from the mafic enclaves and formation of scheelite mineralization. Our work shows that scheelite geochemistry can be used to trace the mineralizing conditions but the compositions may be significantly modified during the ore-forming process. Thus, detailed textural relationships should be investigated before using scheelite geochemistry to constrain the hydrothermal fluids and ore genesis.

Epidote Trace Element Chemistry as an Exploration Tool in the Collahuasi District, Northern Chile

AbstractThe Collahuasi district of northern Chile hosts several late Eocene-early Oligocene world-class porphyry Cu-Mo deposits, including Rosario, Ujina, and Quebrada Blanca deposits, and associated high-sulfidation epithermal mineralization at La Grande. Mineralization is hosted by intermediate to felsic intrusive and volcanic rocks of the upper Paleozoic to Lower Triassic Collahuasi Group, which experienced lower greenschist facies regional metamorphism prior to mineralization. Extensive hydrothermal alteration zones surround the porphyry and epithermal deposits, associated with hypogene ore-forming processes. However, outside of the observed sulfide halo the limits of geochemical anomalism associated with mineralization are difficult to define due to mineralogical similarities between weak, distal propylitic alteration and regional metamorphism affecting the host rocks.Recent advancements in laser ablation-inductively coupled plasma-mass spectrometry analysis of epidote from hydrothermal alteration zones around porphyry and skarn deposits have shown that low-level hypogene geochemical anomalies can be detected at distances farther from the center of mineralization than by conventional rock chip sampling. Selective analysis of propylitic epidote from the Collahuasi district indicates that anomalous concentrations of distal pathfinder elements in epidote, including As (&amp;gt;50 ppm), Sb (&amp;gt;25 ppm), Pb (&amp;gt;100 ppm), and Mn (&amp;gt;5,000 ppm), were detectable 1.5 to 4.0 km from deposit centers. Significantly, the concentrations of these trace elements in epidote were obtained from samples that contained whole-rock concentrations of &amp;lt;25 ppm As, &amp;lt;2 ppm Sb, &amp;lt;100 ppm Pb, and &amp;lt;5,000 ppm Mn. Systematic increases in Cu, Mo, and Sn concentrations in epidote near deposit centers, and corresponding decreasing As, Sb and Pb concentrations, also provide effective tools for assessing the fertility and locating the centers of porphyry mineralization. In addition, anomalous concentrations in epidote of Cu (up to 1 wt %) and Zn (up to 6,000 ppm) effectively discriminate epidote associated with high-sulfidation epithermal veins in the Collahuasi district (e.g., La Grande, Poderosa-Rosario) from alteration associated with porphyry mineralization.

Using Mineral Chemistry to Aid Exploration: A Case Study from the Resolution Porphyry Cu-Mo Deposit, Arizona

AbstractThe giant, high-grade Resolution porphyry Cu-Mo deposit in the Superior district of Arizona is hosted in Proterozoic and Paleozoic basement and in an overlying Cretaceous volcaniclastic breccia and sandstone package. Resolution has a central domain of potassic alteration that extends more than 1 km outboard of the ore zone, overlapping with a propylitic halo characterized by epidote, chlorite, and pyrite that is particularly well developed in the Laramide volcaniclastic rocks and Proterozoic dolerite sills. The potassic and propylitic assemblages were overprinted in the upper parts of the deposit by intense phyllic and advanced argillic alteration. The district was disrupted by Tertiary Basin and Range extension, and the fault block containing Resolution and its Cretaceous host succession was buried under thick mid-Miocene dacitic volcanic cover, obscuring the geologic, geophysical, and geochemical footprint of the deposit.To test the potential of propylitic mineral chemistry analyses to aid in the detection of concealed porphyry deposits, a blind test was conducted using a suite of epidote-chlorite ± pyrite-altered Laramide volcaniclastic rocks and Proterozoic dolerites collected from the propylitic halo, with samples taken from two domains located to the north and south and above the Resolution ore zone. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data of epidote provided indications of deposit fertility and proximity. Competition for chalcophile elements (As, Sb, Pb) between coexisting pyrite and epidote grains led to a subdued As-Sb fertility response in epidote, consistent with epidote collected between 0.7 and 1.5 km from the center of a large porphyry deposit. Temperature-sensitive trace elements in chlorite provided coherent spatial zonation patterns, implying a heat source centered at depth between the two sample clusters, and application of chlorite proximitor calculations based on LA-ICP-MS analyses provided a precisely defined drill target in this location in three dimensions. Drilling of this target would have resulted in the discovery of Resolution, confirming that epidote and chlorite mineral chemistry can potentially add value to porphyry exploration under cover.

Chemical Variations in Hydrothermal White Mica Across the Highland Valley Porphyry Cu-Mo District, British Columbia, Canada

Abstract Hydrothermal white mica in the Highland Valley district, British Columbia, is present in high-temperature alteration assemblages in early halo veins and in intermediate-temperature sericitic alteration assemblages in D-type veins. Pale-gray white micas characterize early halo veins in the Valley and Bethsaida zone porphyry Cu-Mo deposits, whereas pale-green white micas form texturally similar vein halos along the margin of the Valley deposit and at the Alwin vein. White micas in the Bethlehem porphyry Cu-Mo deposit form part of a sericitic alteration assemblage associated with D-type veins that overprinted K-silicate–altered rocks. Cation compositions in white micas indicate phengitic compositions trending toward aluminoceladonite. Pale-gray phengitic white micas intergrown with bornite-chalcopyrite-molybdenite contain elevated Na, indicating higher formation temperatures than those that characterize phengitic white micas formed during hydrolytic alteration. Bethlehem phengitic white micas have cation compositions similar to those of pale-green phengitic white micas at the Valley deposit margin, Bethsaida zone margin, and the Alwin vein. The Al-OH absorption wavelengths in pale-gray phengitic white micas are shorter than in pale-green phengitic white mica or phengitic white mica in the sericitic assemblage. In the phengitic white micas, alkali elements substituting in the interlayered site are positively correlated, whereas higher-valence elements substituting into the octahedral site show a greater variability. The data confirms that hydrothermal white-mica chemistry varies between paragenetic stages of a porphyry Cu deposit and between multiple porphyry deposits in a district.

Molybdenum isotopic fractionation in the Tibetan Yulong Cu-Mo deposit and its implications for mechanisms of molybdenite precipitation in porphyry ore systems

Large variations in Mo isotopes (up to ~2‰ δ98Mo) of molybdenite from many porphyry ore deposits have been reported. However, the mechanisms of Mo isotopic fractionation and their implications for mineralization processes remain poorly understood. Here we report contrasting Mo isotopes of molybdenite formed in two discrete, successive mineralizing stages of the giant Yulong porphyry Cu-Mo deposit in eastern Tibet which, when combined with available fluid inclusion data and high-precision molybdenite Re-Os ages, provide a better understanding in the mechanisms of Mo isotopic fractionation and molybdenite precipitation. The initial ore-forming fluids of both mineralizing stages at Yulong exsolved from magmas as a single-phase, intermediate-density fluid, which subsequently separated into coexisting brine and vapor phases upon ascent and decompression. The relatively uniform Mo isotopes (δ98Mo = 0.03–0.18‰) of the early Cu-Mo stage is consistent with the precipitation of molybdenite from relatively stagnant, high-density brines at shallow levels after phase separation. In contrast, the large spread of Mo isotopes (δ98Mo = −0.16–0.60‰) of the transitional Mo stage requires a process similar to instantaneous Rayleigh fractionation and suggests molybdenite precipitation from rapidly ascending single-phase fluids before phase separation in deep parts of the deposit . These arguments imply that the amount of Mo precipitation from the single-phase fluids likely determines the degree of Mo isotopic fractionation. Further quantitative modeling results suggest that the relatively large Mo isotope variation of molybdenite in many porphyry ore deposits may be simply explained by the precipitation of significant amount of Mo from the initial single-phase fluids. Therefore, apart from the precipitation of molybdenite with economic importance from metal-enriched brines that condensed from the single-phase fluids, the direct precipitation of molybdenite from the single-phase fluids may represent another significant mechanism of molybdenite precipitation in porphyry ore systems.

Ore genesis of skarn mineralization in continental collision orogens: A case study from the Pusangguo Co-bearing Cu–Pb–Zn deposit in Tibet

The Gangdese belt in southern Tibet, is renowned for hosting numerous collision-related porphyry Cu-Mo deposits. The recent discovery of Pusangguo Co-bearing Cu–Pb–Zn skarn deposits is the first reported Co-bearing deposit in Gangdese belt as well as in Tibet. Researches on the geological and metallogenic characteristics of Pusanguo indicate that this Co-bearing Cu-Pb-Zn deposit was formed in a collisional setting. We document mineralogy, fluid inclusion studies, and H–O–S–Pb isotope systematics of the skarns and ores of the Pusangguo deposit. Intense endoskarn alteration, dominated by green and pink epidote and quartz, is widely disseminated throughout the host granodiorite as well as in veinlets. Exoskarn alteration is characterized by the presence of prograde grandite (andradite32–100 and grossular0–68) with minor pyroxene (diopside0–46, hedenbergite38–74, and johannsenite1–62). Retrograde epidotes from both the endoskarn and exoskarn show a narrow range of Fe3+/(Fe3+ + Al) ratios (0.25–0.34). Ore minerals include chalcopyrite, sphalerite and galena, with lesser pyrite, pyrrhotite, bornite, Co minerals and falkmanite.Four paragenetic stages of skarn formation and ore deposition are recognized in the Pusangguo Cu–Pb–Zn deposit: prograde (stage I), retrograde (stage II), early sulfide (stage III), and late sulfide (stage IV). Fluid inclusions in all stages are dominated by two-phase liquid-rich (type L) inclusions. During the major phase of mineralization (stage III), fluid inclusions formed at low temperatures (180–240 °C) and with low salinities (0.5–8.6 wt% NaCl equiv.). This is in contrast to other skarn deposits within the Gangdese porphyry copper belt (e.g., the Zhibula, Jiama, and Bangpu deposits) that formed from highly saline fluids at high temperatures. Hydrogen-Oxygen isotopic values obtained from garnet, epidote, quartz and calcite are δDH2O = −179‰ to − 213‰ and δ18OH2O = −9.1‰ to 9.3‰, whereas S-Pb isotopic values for sphalerite, chalcopyrite, pyrite and galena are δ34S = −1.0‰ to 1.2‰, estimated δ34Sfluid = −0.05‰. Such data are indicative of ore-forming fluids and metals that originated from a magmatic–hydrothermal source related to granodiorite emplacement during the Miocene post-continental collision. Extensive mixing between the magmatic-hydrothermal and meteoric fluids led to the co-precipitation of Cu, Pb and Zn minerals from low-salinity fluids at relatively low temperatures. The Pusangguo Co-bearing Cu-Pb-Zn skarn deposit shows consistent features with other (porphyry-related) skarn deposits in the Gangdese belt, except for relatively low temperature and salinity. The research is of great significance for understanding cobalt as an associated mineral in the Gangdese sulfide skarn deposit in Tibet.

Distinctive geochemical features of biotite types from the subeconomic Sonajil porphyry-type Cu deposit, northwestern Iran: Implications for analysis of porphyry copper deposit mineralization potential

The geochemical characteristics of four biotite types comprising least-altered magmatic biotite (LA-Mbt), least-altered equilibrated magmatic biotite (LA-Eq Mbt), equilibrated magmatic biotite (Eq-Mbt), and secondary hydrothermal biotite (S-Hbt) types from a subeconomic low-grade porphyry Cu system named Sonajil are compared with the economic high-grade Sungun porphyry Cu-Mo deposit situated in the Western Alborz-Azerbaijan structural zone of Iran; the proximity of the two porphyry copper deposits helps to evaluate mineralization potential of the intrusive bodies. The classification scheme for biotite types is based on petrographic data, back-scattered electron images, and compositional attributes. Whereas both of the S-Hbt types at Sonajil and Sungun are related to the overlapping alteration zones of high potassic / low phyllic, the S-Hbt types at Sungun are Mg-rich and fall within the compositional field confined by two endmembers of eastonite and phlogopite. The S-Hbt types at Sonajil are Fe-rich plotting in the compositional field enclosed by two endmembers of eastonite and siderophyllite. The mean of MgO, MnO, TiO2, Na2O, SiO2, and F (wt%) contents of the biotites help in characterizing the geochemical features of the mineralized magmatic rocks contrasted with subeconomic intrusions. Biotite types of the Sungun Porphyry stock display much higher SO3 contents (0.06 wt% on average) compared to those of biotite types of the Sonajil Porphyry stock (<0.01 wt% on average). Fluorine contents (0.9 wt% F on average) in the Sungun Porphyry biotites are the highest ones, whereas the biotite types of the Sonajil Porphyry stock have 0.8 wt% F (on average). Biotite types of the Sonajil and Sungun Porphyry stocks exhibit approximately equal Cl contents (0.15 wt% on average). Magmatic biotites of the productive Sungun Porphyry stock were characterized by higher temperatures (760 °C on average) compared to those of unproductive Sonajil Porphyry stock (747 °C on average). The LA-Mbt types of the Sonajil Porphyry point to oxygen fugacities (ƒO2) with values ranging from 10−16.27 to 10−14.40 bars, while LA-Mbt types at Sungun deposit were formed under oxygen fugacities between 10−15.4 to 10−13.8 bars. There is a positive correlation between the amount of Cu (wt%) in the Porphyry stocks and the wt% SO3 in the biotites of Porphyry stocks. The hydrothermal fluids related to alteration zones in the subeconomic Sonajil have approximately the same range of log(ƒH2O)/(ƒHCl) and log(ƒHF)/(ƒHCl) values to those of fluids associated with other economic deposits, such as Los Pelambres and Casino. Therefore, it can be recommended that evaluating of log(ƒH2O)/(ƒHCl) and log(ƒHF)/(ƒHCl) ratios of fluids in equilibrium with biotites alone cannot be a discriminating parameter. Confirmation by SO3 (wt%) content of the biotite types, by linkage between SO3 content of biotites and Cu grade, by halogen (wt% F and Cl) chemistry of biotite types, by halogen intercept values of F, Cl, and F/Cl, and by hydrothermal fluid halogen fugacity ratios, all illustrate the capacity of SO3 content (wt%) of biotites to be a reliably exploration index and highlight the critical role of fluorine compared to chlorine in discrimination of unproductive and productive porphyry Cu systems.

Petrogenesis and Geological Implications of the Oligocene Mingze monzodiorites, Southern Lhasa

The Mingze Cu-Mo deposit is located in the southern margin of the Lhasa block of the Himalayan Tibetan Plateau. Here, we report the geochronological and geochemical data from Mingze monzodiorites, which hosts the Mingze deposit. Zircon dating indicates that the Mingze monzodiorites were emplaced at ca. 31 Ma (i.e., the Oligocene). The monzodiorites have variable SiO2 and MgO contents, strongly negative high field-strength element (HFSE, such as Ta, Nb, Zr and Hf) anomalies on the normalized trace element diagram and show uniform (87Sr/86Sr)i (0.7066–0.7076), εNd(t) (−2.50 to −4.04) and εHf(t) (+1.50 to +7.50). Their geochemical compositions are different from coeval (40–30 Ma) adakite-like rocks but comparable to coeval mafic enclaves and gabbros. We propose that Mingze monzodiorites were derived from partial melting of the lithospheric mantle, which previously metasomatized by the subducted Indian continental plate that probably subducted into the overlying mantle. The concurrency of the genetically related mafic enclaves and associated intermediate to mafic rocks implies the heterogeneity of the Lhasa lower crust.