Porphyry Mo Deposit Research Articles

Genesis and fluid evolution of the Yuku porphyry Mo deposit, East Qinling orogen, China

The Yuku is a large porphyry Mo deposit (1.5 Mt at 0.12% Mo) in the Luanchuan ore district of the East Qinling orogen, central China. The economic Mo ore bodies occur as veins, veinlets, and disseminated ore and are developed mainly within the late Mesozoic Yuku porphyritic granite. Molybdenum mineralization is generally associated with potassic and phyllic alteration. Hydrothermal processes in the Yuku deposit are divided into four stages: (I) a quartz–K‐feldspar–biotite ± pyrite stage, (II) a quartz–molybdenite ± pyrite ± K‐feldspar ± sericite stage, (III) a quartz–polymetallic sulphide stage, and (IV) a calcite ± quartz ± fluorite ± pyrite stage. The fluid evolution during these hydrothermal stages was constrained through systematic investigation of fluid inclusions (FIs) and H−O isotopes. Four types of primary or pseudosecondary FIs were recognized in hydrothermal quartz and calcite: two‐phase liquid‐rich inclusions (L‐type), two‐phase vapour‐rich inclusions (V‐type), halite‐bearing (hypersaline) inclusions (H‐type), and three‐phase CO2‐bearing inclusions (C‐type). FIs within Stages I–IV have homogenization temperatures of 375 to >550, 297–400, 198–298, and 149–188°C, with salinities of 0.53–13.18, 0.35–40.23, 5.11–11.81, and 5.71–9.73 wt% NaCl equiv., respectively. In Stage I, coexisting vapour‐rich (V‐type) and liquid‐rich (L‐type) FIs have similar homogenization temperatures (488 to >550°C) and distinct salinities, indicating fluid boiling during the formation of quartz–K‐feldspar–biotite veins at a pressure of 550–700 bar and a lithostatic depth of 2.3–2.8 km. In Stage II, FIs in quartz were also trapped under boiling conditions, as evidenced by coexisting hypersaline H‐type (34.13–40.23 wt% NaCl equiv.) and low‐salinity V‐type (0.35–2.24 wt% NaCl equiv.) inclusions, which formed at temperatures of 309–361°C and hydrostatic depths of 1.0–2.0 km, equivalent to pressures of 100–200 bar. During Stage III, the ore‐forming fluids were cooler (198–298°C) and more dilute (5.11–11.81 wt% NaCl equiv.) due to the involvement of meteoric water, with minimum trapping pressures estimated at <100–150 bar, corresponding to a hydrostatic depth of <1.0 km. In Stage IV, temperatures decreased further to 149–188°C, with lower salinities (5.71–9.73 wt% NaCl equiv.), indicating a post‐ore fluid stage. These data suggest that the mineralizing fluids forming the Yuku Mo deposit changed from early moderate‐ to low‐salinity CO2‐rich fluids in the H2O–NaCl–CO2 system that formed at high temperature and pressure, to late H2O–NaCl low‐salinity fluids that formed at low temperature and pressure. H−O isotopic compositions indicate that the mineralizing fluids had a dominantly magmatic signature but were diluted by meteoric waters. Combining our integrated analysis of the fluid evolution and deposit geology, we propose that fluid boiling and fluid–rock interaction, including intensive potassic alteration, changed the salinity and triggered CO2 escape, leading to a decrease in fO2 and an increase in the acidity of the ore‐forming fluids, which ultimately controlled the deposition of molybdenite in the Yuku Mo deposit.

Genesis of the Shiyaogou porphyry Mo deposit at East Qinling, China: Evidence from geochronological, fluid inclusion, geochemical whole-rock and isotope studies

The Shiyaogou deposit in Luanchuan County, China, is a large concealed porphyry Mo deposit within the East Qinling metallogenic belt (EQMB). Major and trace element analyses reveal that the host granite is defined by high silica (SiO2 = 71.56 to 75.25%) and alkali (Na2O + K2O = 6.91 to 7.88%) contents and has typical I-type characteristics. Zircons derived from the pluton yield U–Pb ages of 133.2 ± 1.1 Ma, indicating an early Cretaceous magmatic event in the EQMB. The εHf (t) values and TDM2 ages range from − 15.1 to − 11.2 and from 2.1 to 1.9 Ga, respectively, suggesting that the granite mainly originated from the lower crust melting with the involvement of mantle components. The mineralization process can be divided into three stages: (1) quartz + K-feldspar + pyrite + molybdenite; (2) quartz + pyrite + molybdenite; and (3) quartz + calcite veins. Three different types of fluid inclusions (FIs) are present in quartz veins: NaCl–H2O (W-type), CO2–H2O (C-type), and daughter mineral-bearing (S-type). Hematite is recognized as a daughter mineral in S-type inclusions of stage 1, whereas the daughter sulfide and reducing CH4 gases can be observed in the stage 2 quartz, suggesting that the ore-forming fluids were initially oxidizing and then evolved to more reducing conditions. The FIs in stages 1 mainly display Th above 428 °C with salinities up to 57.62 wt% NaCl eqv; in stage 2, the FIs display Th of 132–423 °C and salinities of 3.23–50.03 wt% NaCl eqv; in stage 3, the FIs homogenized in the range of 117–247 °C with low salinities of 2.74–8.95 wt% NaCl eqv. The coexisting W-, S- and/or C-type inclusions homogenized at similar temperatures, but contain different salinities during stages 1 and 2, suggesting that the fluids boiled during both stages. Our study reveals that the ore-forming fluids are magmatic in origin. These high-temperature magmatic fluids gradually evolved from high salinities and high CO2 contents to a mixture of magmatic and meteoric water with lower temperature, lower salinity, and lower CO2 content. The precipitation of Mo mainly resulted from the decreasing temperature and salinity. Additionally, the changes in pH and CO2 content due to boiling and the water–rock reaction could have contributed toward the precipitation of Mo.

Difference in the nature of ore-forming magma between the Mesozoic porphyry Cu-Mo and Mo deposits in NE China: Records from apatite and zircon geochemistry

Porphyry Cu-Mo and Mo deposits are the most important source of Mo in the world, but factors controlling their difference remain enigmatic. In recent years, many Mesozoic porphyry Cu-Mo and Mo deposits have been discovered in NE China, which provides a good opportunity to explore the difference between the Cu-Mo and Mo mineralization. In this region, porphyry Cu-Mo deposits (Wunugetushan, Jinchanggou) are distributed along the subduction zone, while the porphyry Mo deposits (Luming, Fu'anpu, Daheishan) are far away from the subduction zone. On the basis of whole rock geochemical studies, we present a comprehensive investigation on the apatite and zircon from Mesozoic typical porphyry Cu-Mo deposits and Mo deposits, in order to reveal the nature of parent magma constraints on Cu-Mo and Mo mineralization. Whole-rock geochemistry, in-situ apatite Sr-Nd and zircon Hf isotopic compositions from these granites in porphyry Cu-Mo and Mo deposits indicate that these granites originated from a juvenile crustal source. Apatites from the porphyry Cu-Mo mineralized granites show relatively high Cl and low F contents, accompanied by enrichment of fluid-mobile elements Ba and Sr, indicating that the magmatic source of porphyry Cu-Mo deposits were modified by subducted slab-derived fluids. In comparison, apatites from the porphyry Mo mineralized granites have high F and low Cl contents with correspondingly high F/Cl ratios, suggesting that these granites mainly formed in juvenile crustal dehydration self-metasomatism under the intra-continental environment. Additionally, apatites from porphyry Cu-Mo mineralized granites have higher OH contents than those from porphyry Mo mineralized granites, indicating that the original melt of porphyry Cu-Mo system was more hydrous, consistent with their higher (Ce/Nd)/Y and lower Dy/Yb ratios of zircon. It is here proposed that the formation of porphyry Cu-Mo deposits in NE China are related to partial melting of the juvenile crust, which metasomatized by slab-derived Cl-enriched fluids with carry significant amounts of Cu, whereas the porphyry Mo deposits are related to partial melting of juvenile crustal material with released F-enriched fluids by the dehydration of hydrous minerals.

The source, enrichment and precipitation of ore-forming elements for porphyry Mo deposit: Evidences from melt inclusions, biotite and fluorite in Dasuji deposit, China

The Dasuji ore deposit is a large-scale porphyry Mo deposit at the northern margin of the North China Craton, China. Four stages of hydrothermal veins were recognized in the deposit, from early to late: K-feldspar–quartz veins (stage 1), quartz–molybdenite veins (stage 2), quartz–carbonate–pyrite–galena–sphalerite veins and fluorite veins (stage 3), and carbonate–quartz ± fluorite veins (stage 4). The melt inclusions in the earliest K-feldspar–quartz veins retain information about the ore-forming magma. Melt inclusions in quartz were studied in detail to investigate the magmatic evolution. In chondrite- and primitive-mantle-normalized trace element diagrams, all the inclusions have negative Ba, Sr, and Eu, and positive Pb anomalies. The inclusions have uniform (La/Sm)N ratios, and Sr concentrations decrease with decreasing Ba content, indicating the magma experienced significant fractionation, particularly of plagioclase and biotite. With increasing SiO2, Mo concentrations gradually increased, whereas Cu concentrations first increased and then decreased, suggesting that magmatic evolution was beneficial for Mo, but not Cu, enrichment. This indicates that highly fractionated magmas are conducive to the formation of porphyry Mo ore deposits rather than Cu ore deposits. The high F contents in biotite (up to 4.03 wt%) and pervasive occurrence of fluorite are indicative of a high-F magmatic–hydrothermal system. The disappearance of magnetite means the decrease of oxygen fugacity during stage 2, which promotes molybdenite precipitation. The contents of trace elements in fluorite before the stage 4 changed little, indicating that the fluid system was closed prior to this stage. The highly fractionated granitic magmatic system with high oxygen fugacity and high fluorine content potentially contain new porphyry Mo deposit.

Fluid inclusion evidence for hydrothermal evolution of the Sadaigoumen porphyry Mo deposit on the northern margin of the north China Craton

The Sadaigoumen porphyry Mo deposit is located on the northern margin of the North China Craton (NCC). In this study, in situ fluid-inclusion analyses including microthermometry, laser Raman spectroscopy, and LA–ICP–MS microanalysis, as well as Quartz H–O isotopes are present to precisely constrain the hydrothermal evolution of the Sadaigoumen deposit. Five stages of hydrothermal activity are identified, with Stage 1 characterized by the development of magnetite with rare sulfide minerals; Stage 2 by K-feldspar as the typical vein mineral; Stage 3 by molybdenite mainly in veins; Stage 4 by the development of fluorite–quartz and quartz–pyrite veins; and Stage 5 by barren carbonate–quartz veins. Fluid inclusion types were distinguished based on petrographic observations and microthermometric analysis, and fluid compositions were detected by LA–ICP–MS. Microthermometric analyses indicate decreasing homogenization temperatures in primary fluid inclusions from Stage 1 to Stage 3. Intermediate-density fluids of stages 1 and 2 are characterized by high homogenization temperatures (420 °C–470 °C), moderate salinities (6.3–11.2 wt%), and high Mo contents (52–541 ppm). Hydrothermal evolution during Mo mineralization in Stage 3 is characterized by immiscible inclusion assemblages that formed through phase separation from intermediate-density fluid. Fluid inclusions of Stage 3 were trapped at pressures fluctuating around the two-phase fluid surface, leading to at least two fluid immiscible phases (373 °C–414 °C and 311 °C–341 °C). The Mo contents of fluid inclusions vary greatly in Stage 3, with Mo tending to be enriched in brine. In stages 4 and 5, fluids display characteristics that indicate mixing with meteoric water, with homogenization temperatures (<299 °C) and salinities (<5.8 wt%) decreasing together with Mo content. The Cs/(Na + K + Mn + Fe) ratios of fluid inclusions are stable from stages 1 to 4, indicating a constant supply of ore-forming fluids from an underlying, geochemically uniform magma chamber. The fluid inclusion data suggest that Mo and Cu in the initial exsolved fluids of the Sadaigoumen porphyry Mo deposit display different migration and precipitation progresses, which is of great significance to the study of the delicate ore-forming progress of porphyry Mo (–Cu) deposits in the northern NCC.

Magmatic Water Content and Crustal Evolution Control on Porphyry Systems: Insights from the Central Asian Orogenic Belt

Abstract Porphyry systems, the most important reserves of Cu and Mo with significant Au, are genetically linked to the emplacement of hydrous and oxidized intermediate to acidic magmas, in response to temporal and geochemical evolution of crust in orogenic terranes. In this study, comprehensive whole-rock and zircon geochemical and isotopic datasets of intermediate to acid igneous rocks were integrated to characterize the crustal evolution and metallogeny of porphyry deposits in the Central Asian Orogenic Belt (CAOB). The ore-forming porphyries of Cu ± Au ± Mo and Mo deposits have higher but largely overlapped ΔFMQ (the proxy for oxygen fugacity) with those of the barren igneous rocks. However, the ore-forming porphyries of Cu ± Au ± Mo deposits are characterized by distinctly higher whole-rock V/Sc and zircon Eu/Eu* (both are proxies for water content) than barren rocks. Furthermore, the V/Sc ratios positively correlate with the Cu tonnages of calc-alkali porphyry Cu deposits, suggesting that magmatic water contents may yield the first-order control on metal endowment. The general decrease of V/Sc from the Paleozoic to Mesozoic, combined with the negative correlation of V/Sc with K2O and SiO2, also indicates the gradual evolution of crust in CAOB clearly controls the end members of porphyry-type systems (i.e., Cu‒Au and Mo deposits). The crustal residence age (TRes, the time difference between Nd depleted-mantle model age and the crystallization age) of c. 500 Ma from the Nd isotopes is proposed as the threshold distinguishing porphyry Cu ± Au ± Mo (TRes &amp;lt; 500 Ma) and Mo deposits (TRes &amp;gt; 500 Ma) in the CAOB. The coupled zircon Hf isotopes and crustal thickness reveal that the fundamental crustal architecture in the eastern and western CAOB had been built by the Late Permian and Late Carboniferous, respectively, highlighted by the converging trends of εHf(t) commencing at c.250 Ma in the eastern segment and c.300 Ma in the western segment of CAOB, indicating reworking and homogenizing of juvenile crust after collision. In the eastern CAOB, porphyry Cu ± Au ± Mo deposits were formed by juvenile materials in thin island arcs, while porphyry Mo deposits were formed by reworked materials in the thickened orogenic crust after c.250 Ma. In the western CAOB, porphyry Cu deposits in the Balkhash region during the Late Carboniferous were formed in thickened continental crust (generally &amp;gt; 40 km), genetically linked to the culmination of world-wide magmatic addition rates (MARs) triggered by accelerated production of the juvenile crust, in contrast to the porphyry Cu ± Au ± Mo deposits formed in thin island arc (generally &amp;lt; 40 km) during the Early Paleozoic. This study tests the zircon ΔFMQ as proxy for fO2, and zircon Eu/Eu* and whole-rock V/Sc ratios as proxy for water content. It highlights that whole-rock V/Sc ratio is a favorable index for the Cu tonnages of porphyry Cu ± Au ± Mo deposits, and that the distinct porphyry-type mineralization in the CAOB is controlled by the crustal evolution reflected by crustal composition and thickness.

He, Ar, and S isotopic constraints on the origin of the Dasuji porphyry Mo deposit, China

The Dasuji Mo deposit lies on the northern margin of the North China Craton. Based on vein crosscutting relationships, mineral assemblages, and alteration characteristics, the formation of the deposit can be divided into four stages: K-feldspathization with minor Mo mineralization (stage 1), the main stage of Mo mineralization (stage 2), Pb–Zn mineralization (stage 3), and post-mineralization (stage 4). This paper presents new He–Ar–S isotopic data to constrain the origin of this deposit. Pyrite-hosted fluid inclusions yield 3He/4He ratios of 0.21–3.48 Ra (average = 0.96 Ra; Ra = 1.4 × 10−6) and 40Ar/36Ar ratios of 464.9–832.1 (average = 624.6), which indicate the ore-forming fluids were predominantly crust-derived with minor mantle-derived components. Molybdenite within the deposit contains 0.06–29 ppm Re, indicative of derivation from a crustal source. δ34S values of sulfide samples range from + 3.14 to + 6.84‰, with corresponding H2S δ34S values of stage 2 fluids of + 2.8‰ to + 3.1‰ and stage 3 fluids of + 4.9‰ to + 5.9‰. The δ34Sfluid values of stages 2 and 3 are + 3.1‰ to + 4.0‰ and around + 6‰, respectively. The escape of H2S during stage 2 was a key factor in increasing δ34Sfluid values, and contributed to the precipitation of sulfides.

Constraints on the Formation of the Giant Daheishan Porphyry Mo Deposit (NE China) from Whole-Rock and Accessory Mineral Geochemistry

AbstractThere are more than 80 porphyry (or skarn) Mo deposits in northeastern China with Jurassic or Cretaceous ages. These are thought to have formed mainly in a continental arc setting related to the subduction of the Paleo-Pacific oceanic plate in the Jurassic and subsequent slab rollback in the early Cretaceous. The Jurassic Daheishan porphyry Mo deposit is one of the largest Mo deposits in NE China, which contains 1·09 Mt Mo with an average Mo grade of 0·07 %. To better understand the factors that could have controlled Mo mineralization at Daheishan, and potentially in other similar porphyry Mo deposits in NE China, the geochemical and isotopic compositions of the ore-related granite porphyry and biotite granodiorite, and the magmatic accessory minerals apatite, titanite and zircon from the Daheishan intrusions, were investigated so as to evaluate the potential roles that magma oxidation states, water contents, sulfur and metal concentrations could have played in the formation of the deposit. Magmatic apatite and titanite from the causative intrusions show similar εNd(t) values from –1·1 to 1·4, corresponding to TDM2 ages ranging from 1040 to 840 Ma, which could be accounted for by a mixing model through the interaction of mantle-derived basaltic melts with the Precambrian lower crust. The Ce and Eu anomalies of the magmatic accessory minerals have been used as proxies for magma redox state, and the results suggest that the ore-forming magmas are highly oxidized, with an estimated ΔFMQ range of +1·8 to +4·1 (+2·7 on average). This is also consistent with the high whole-rock Fe2O3/FeO ratios (1·3–26·4). The Daheishan intrusions display negligible Eu anomalies (Eu/Eu* = 0·7–1·1) and have relatively high Sr/Y ratios (40–94) with adakitic signatures; they also have relatively high Sr/Y ratios in apatite and titanite. These suggest that the fractionation of amphibole rather than plagioclase is dominant during the crystallization of the ore-related magmas, which further indicates a high magmatic water content (e.g. &amp;gt;5 wt%). The magmatic sulfur concentrations were calculated using available partitioning models for apatite from granitoids, and the results (9–125 ppm) are indistinguishable from those for other mineralized, subeconomic and barren intrusions. Furthermore, Monte Carlo modelling has been conducted to simulate the magmatic processes associated with the formation of the Daheishan Mo deposit, and the result reveals that a magma volume of ∼280 km3 with ∼10 ppm Mo was required to form the Mo ores containing 1·09 Mt Mo in Daheishan. The present study suggests that a relatively large volume of parental magmas with high oxygen fugacities and high water contents is essential for the generation of a giant porphyry Mo deposit such as Daheishan, whereas a specific magma composition (e.g. with unusually high Mo and/or S concentrations) might be less critical.

The Giant Chalukou Porphyry Mo Deposit, Northeast China: The Product of a Short-Lived, High Flux Mineralizing Event

Abstract Whether giant porphyry ore deposits are the products of single, short-lived magmatic-hydrothermal events or multiple events over a prolonged interval is a topic of considerable debate. Previous studies, however, have all been devoted to porphyry Cu and Cu-Mo deposits. In this paper, we report high-precision isotope dilution-negative-thermal ionization mass spectrometric (ID-N-TIMS) molybdenite Re-Os ages for the newly discovered, world-class Chalukou porphyry Mo deposit (reserves of 2.46 Mt @ 0.087 wt % Mo) in NE China. Samples were selected based on a careful evaluation of the relative timing of the different vein types (i.e., A, B, and D veins), thereby ensuring that the suite of samples analyzed could be used to reliably determine the age and duration of mineralization. The molybdenite Re-Os geochronology reveals that hydrothermal activity at Chalukou involved two magmatic-hydrothermal events spanning an interval of 6.92 ± 0.16 m.y. The first event (153.96 ± 0.08/0.63/0.79 Ma, molybdenite ID-N-TIMS Re-Os age) was associated with the emplacement of a granite porphyry dated at 152.1 ± 2.2 Ma (zircon laser ablation-inductively coupled plasma-microscopic [LA-ICP-MS] U-Pb ages), and led to only minor Mo mineralization, accounting for &amp;lt;10% of the overall Mo budget. The bulk of the Mo (&amp;gt;90%) was deposited in less than 650 kyr, between 147.67 ± 0.10/0.60/0.76 and 147.04 ± 0.12/0.72/0.86 Ma (molybdenite ID-N-TIMS Re-Os ages), coincident with the emplacement of a fine-grained porphyry at 148.1 ± 2.6 Ma (zircon LA-ICP-MS U-Pb ages). The high-precision Re-Os age determinations presented here show, contrary to the finding of a number of studies of porphyry Cu and Cu-Mo systems, that the giant Chalukou porphyry Mo deposit primarily formed in a single, short-lived (&amp;lt;650 kyr) hydrothermal event, suggesting that this may also have been the case for other giant porphyry Mo deposits.

Age and Genesis of the Laodaizhanggou Pb-Zn-Ag Deposit in the Fudian Ore Field, Southern North China Craton: Implications for Regional Mineral Prospecting

The Fudian ore field in the southern North China Craton hosts the giant Donggou porphyry Mo deposit and several Pb-Zn-Ag vein deposits. Ore genesis of the Pb-Zn-Ag deposits and their relationships with the Donggou porphyry-related system are still controversial, which further restricts the regional prospecting and exploration. The Laodaizhanggou Pb-Zn-Ag deposit in the northwest of the ore field was focused in this study, to investigate its ore-forming age and genesis, and further to explore the implications for regional prospecting of Pb-Zn-Ag and Mo. The Pb-Zn-Ag veins at Laodaizhanggou are structurally controlled by the east-striking fault zones transecting the host volcanic rocks of Proterozoic Xiong’er Group. Field observations and textural relationships indicate that there are four paragenetic stages during ore-forming process, including the quartz-pyrite veins (stage I), siderite-polymetallic sulfide veins (stage II), ankerite-polymetallic sulfide veins (stage III), and quartz-calcite veins (stage IV). Ore-related sericite 40Ar/39Ar dating shows that the Pb-Zn-Ag mineralization at Laodaizhanggou was formed at 124.7±1.2 Ma. Carbonate minerals (siderite, ankerite, and calcite) have δ13CPDB values of −9.1‰ to −3.9‰ and δ18OSMOW of 12.1‰ to 15.6‰, corresponding to calculated values for the ore fluids of −8.0‰ to −2.8‰ and 4.9‰ to 10.1‰, respectively. These isotope values are in accordance with those of magmatic fluids. Sulfide minerals at Laodaizhanggou have δ34S values of 5.3‰ to 10.1‰, and galena separates have 206Pb/204Pb ratios of 17.380 to 17.458, 207Pb/204Pb ratios of 15.459 to 15.485, and 208Pb/204Pb ratios of 38.274 to 38.370. Both S and Pb isotope data of Laodaizhanggou are consistent with those of the Donggou porphyry Mo deposit and distal Sanyuangou and Wangpingxigou Pb-Zn-Ag deposits, suggesting they share a similar magmatic origin. However, the Laodaizhanggou deposit was not the distal product of the giant Donggou porphyry-related magmatic-hydrothermal system, as the former is about 7 Ma older than the latter. The ore-forming age of Laodaizhanggou is consistent with that of the phase 1 magmatism of Taishanmiao batholith, indicating the Laodaizhanggou deposit is genetically related to ca. 125 Ma magmatism in the area. Combined the geochronological and geochemical data on Laodaizhanggou and the regional geological setting, we propose that the fracture systems in the northeast of the Taishanmiao batholith are potential sites for prospecting Pb-Zn-Ag deposit and the deep part among Laodaizhanggou, Xizaogou, and Liezishan is a target for prospecting porphyry Mo deposit.

A Metamorphosed Au–Ag Deposit in the Precambrian of the Fennoscandian Shield: A New Conceptual Model

The Oleninskoe gold deposit is located in the northwestern part of the Kolmozero–Voron’ya greenstone belt (Kola Peninsula), in a sequence of amphibolite with granite porphyry sills. The sills are genetically connected with a big granodiorite- and granite-porhyry massif, which hosts the Pellapahk Cu–Mo porphyry deposit. The geochemical association of the Oleninskoe includes As, Pb, Ag, Cu, Sb, and Au; the Au/Ag ratio is less than 0.2. The ore is of very complex mineral composition (more than 50 mineral names of intermetallic compounds, sulfides, and sulfosalts are defined), with widespread Ag and Sb minerals. Fluid inclusions in quartz are of high salinity with anomalous concentration of minor elements. All these characteristics show that the deposit formed in an Early Precambrian porphyry-epithermal system. Then the deposit underwent metamorphism (lower amphibolite facies) in the Neoarchean and Paleoproterozoic, indicating the absence of chlorite and a scarcity of carbonates in metasomatic rocks, replacement of pyrite with pyrrhotite, and signatures of sulfide anatexis in ore. This is the first finding of this genetic type of gold deposits in the northern part of the Fennoscandian Shield.

Spatio-Temporal Shifts in Magmatism and Mineralization in Northern Colorado Beginning in the Late Eocene

AbstractMagmatism in northern Colorado beginning in the late Eocene is associated with the formation of Pb-Zn-Ag carbonate-replacement and polymetallic vein deposits, the onset of caldera-forming magmatism, and eventually, the formation of rift-related, F-rich Mo porphyries (“Climax-type” intrusions). We use high-precision U/Pb zircon geochronology to better evaluate the temporal framework of magmatism and mineralization in the region. Our results demonstrate that mineralization in the Leadville area occurred between 43.5 and 39.7 Ma and was followed by mesothermal mineralization in the Montezuma area at approximately 38.7 Ma. Mineralization is associated with a suite of approximately 43 to 39 Ma intermediate magmatic centers that extended from Twin Lakes through Montezuma. The oldest porphyries associated with F-rich Mo prospects and deposits (Middle Mountain; 36.45 Ma) intruded 900 kyr after the start of the ignimbrite flare-up in the region. Spatiotemporal analyses reveal that the pattern of magmatism shifted in orientation between 40 and 35 Ma. We propose a model wherein magmatism before 39 Ma was the result of fluids evolved from the subducted Farallon slab being focused through weak zones in the lithospheric mantle and into the lower crust. This was followed by a more diffuse and higher power melting event that corresponds to a distinct change in the spatial patterns of magmatism. Our data suggest that low-grade Mo porphyry deposits can form close in time to calderas. We hypothesize that the transition from subduction to extensional tectonics in the region was responsible for this more widespread melting and a distinct shift in the style of magmatic-hydrothermal mineralization.

Magma volume and timescales in the formation of porphyry molybdenum deposits: A case study from the Central Asian Orogenic Belt

Porphyry Mo deposits, as an important repository for molybdenum, are generally considered to have formed from the reworking of Mo-rich ancient crust. However, some of the giant porphyry Mo deposits in the Central Asian Orogenic Belt (CAOB) are thought to have been derived from juvenile crust. Here we evaluate the role of large volume magma chamber,and the timescales of magmatic differentiation and hydrothermal processes in the formation of porphyry Mo deposits. In our case study on the Donggebi porphyry Mo deposit along the southern part of the CAOB, the pressure-temperature conditions of crystallization of the ore-related intrusion are estimated as 1.2–1.8 kbar and 570–727 °C. Based on the sulfur content of apatite grains from the deposit, we estimate that a large magma volume (25–215 km3) was involved in the formation of the Mo resources (0.508 Mt) associated with the Donggebi porphyry Mo deposit. Quartz associated with mineralization in this deposit is identified as two types. Type-1 quartz displays wide and parallel zoning and preserves high Na, K and Ca contents whereas Type-2 displays narrow and subparallel zoning with low Na, K and Ca contents. The Type-1 quartz is likely to retain the magmatic information, whereas the Type-2 quartz possibly formed through metasomatic processes in the hydrothermal stage. We use Ti diffusion patterns in quartz coupled with TitaniQ thermobarometry to estimate the timescales of magma evolution and hydrothermal processes. The quartz residence in the magma chamber is estimated as 10,000 to 40,000 years while that related to hydrothermal fluids is relatively short (800 to 5000 years). Our results suggest that large volume magma chambers might be an essential requisite for the formation of porphyry Mo deposits, as against models that consider prolonged hydrothermal processes.

Genesis of the Nailenggele Mo-Cu-Pb-Zn polymetallic orefield in the Boluokenu Metallogenic Belt, Western Tianshan, China: Constraints from geochronology, fluid inclusions and isotope geochemistry

The Nailenggele orefield, located in the northwestern Chinese Tianshan Orogenic Belt, is composed of the Lailisigao’er Mo deposit, No. 3571 Cu prospect and Qixing Pb-Zn deposit. Lailisigao’er is a typical porphyry deposit with characteristic veinlet-disseminated ores and potassic, phyllic and propylitic alterations. No. 3571, situated in the peripheral of Lailisigao’er, is characterized by large amounts of oxidized ores at surface with limited intrusions outcropped. Qixing, about 3 km from Lailisigao’er, is characterized by quartz-sulfide veins controlled by fractures. This study aims to examine the genetic relationships between these deposits and/or occurrences, and discuss the significance for further exploration in the orefield and elsewhere in the region. LA-ICP-MS U-Pb dating on zircons from the ore-bearing porphyry in the Lailisigao’er deposit yielded an age of 367.5 ± 4.8 Ma. The molybdenite Re-Os and sphalerite Rb-Sr isochron ages recalculated from previously published data are 365.9 ± 2.1 Ma for Lailisigao’er and 362.0 ± 5.7 Ma for Qixing, respectively, suggesting that they are coeval and both related to the granodiorite porphyries. Three types of fluid inclusions occur in the Mo-bearing quartz from Lailisigao’er, including two-phase aqueous inclusions (Type I), solid mineral-bearing aqueous inclusions (Type II) and CO2-H2O inclusions (Type III). The total homogenization (Th) temperatures cluster from 260 to 320 °C (to liquid) for type I inclusions, 310 to 332 °C (to liquid) for type II inclusions, and 268 to 324 °C (to CO2 phase) for type III inclusions. The salinities are mainly in the ranges of 2.0–8.0, 32.9–42.0, and 1.4–5.5 wt% NaCleq for types I, II and III inclusions, respectively. By contrast, only type I inclusions were identified in the Pb-Zn-bearing quartz from Qixing, with Th values of 149–261 °C and salinities of 1.7–5.3 wt% NaCleq. The δ34SCDT values of hydrothermal sulfides from Lailisigao’er, No. 3571 and Qixing range from 2.8‰ to 4.0‰, 4.0‰ to 4.6‰ and 0.7‰ to 4.9‰, respectively. Sulfides from these three locations have uniform Pb isotopic compositions. The (87Sr/86Sr)0 ratios of fluid inclusions (average 0.70971) in Mo-bearing quartz at Lailisigao’er and sphalerite (average 0.71020) at Qixing are similar to those of Mo-mineralized porphyries (average of 0.70886) from Lailisigao’er. The δ18OH2O and δDH2O values of Pb-Zn-bearing quartz from Qixing are similar to those of Mo-bearing quartz from Lailisigao’er, both plotting close to the field of magmatic water but shifted toward the meteoric line. These geochronological, fluid inclusions and isotopic data suggest that the mineralization at different localities in the Nailenggele orefield constitutes part of an integrated magmatic-hydrothermal system centered on the Lailisigao’er porphyry Mo deposit, with the Qixing Pb-Zn polymetallic deposit representing a distal end-member. Both metals and sulfur were dominantly derived from porphyritic intrusions, whereas the ore-forming fluids were initially derived from the magmatic intrusions, with increasing involvement of meteoric water in time and distance from magmatic-hydrothermal center. Fluid immiscibility in the early stage and fluid mixing in the later stage, together with cooling, were responsible for ore precipitation. Based on this mineralization model, it is inferred that concealed porphyry Cu-Mo mineralization may be developed underneath the No. 3571 and Qixing.

Petrogenesis of the Quanzigou porphyry Mo deposit at the northern margin of the North China Craton: Constrains from geochronology, geochemistry, and Sr–Nd–Hf isotopes characteristics

The Quanzigou Mo deposit is located in the western portion of the northern margin of the North China Craton (NCC). The results of molybdenite Re–Os isotopes indicate that the mineralization occurred at 170.8 ± 2.0 Ma. It is coeval with the mineralization-related porphyritic biotite granite pluton and granite porphyry dykes of respectively 170.3 ± 1.1 Ma and 169.3 ± 1.0 Ma (zircon U–Pb ages). Thus, the Quanzigou deposit is confirmed to fill the gap of the regional early Yanshanian (i.e., Early–Middle Jurassic) porphyry Mo deposits in this study. Whole-rock εNd(t) (−12.09 to −9.72; mean = −10.80) and zircon εHf(t) values (−16.28 to −9.23; mean = −12.01) of the Quanzigou granites indicate that they originated from the lower continent crust involving some depleted mantle material. Zircon oxygen fugacity results (fO2) show that the mineralization-related granites are high magma fO2 with an average ΔFMQZr (departure from the fayalite–magnetite–quartz oxygen buffer) of +1.1 in the porphyritic biotite granite pluton and an average ΔFMQZr of +1.0 in the granite porphyry dykes, respectively. Because of the relative low-fO2 of the ancient lower continent crust, the high-fO2 source might be associated with continuously metasomatic fluids/melts from the high-fO2 lithospheric mantle, which was metasomatized by the fluids/melts of the preexisting high-fO2 sediments during the closure of the paleo-Asian Ocean. Therefore, the high-fO2 granites are formed during the tectonic setting of the post-collisional compression-to-extension transition caused by the continental collision between the Siberian plate and the NCC. Their high-fO2 characteristics were inherited from the early oceanic crust sediments during the closure of the paleo-Asian Ocean.

Genesis of the Lakang'e porphyry Mo (Cu) deposit, Tibet: Constraints from geochemistry, geochronology, Sr-Nd-Pb-Hf isotopes, zircon and apatite

The Lakang'e porphyry Mo (Cu) deposit, intermediate to large in size, is located in the eastern part of the southern Gangdese metallogenic belt. It is associated with a Miocene granodiorite porphyry (GDP). The alteration styles are mainly potassic and phyllic alteration, with minor argillic, chlorite, and carbonation alteration. In this study, we present whole-rock geochemical compositions, zircon LA-ICP-MS U-Pb data, zircon Hf isotope analyses, and zircon and apatite major and trace element compositions for the ore-bearing GDP and postmineralization quartz diorite porphyry (QDP) to constrain the formation of the Lakang'e Mo (Cu) deposit. The ore-bearing GDP, with a zircon U-Pb age of 13.83 ± 0.20 Ma, was intruded after mineralization by the QDP, which was emplaced at 13.00 ± 0.16 Ma. The GDP and QDP are high-K calc-alkaline series rocks with adakite-like features characterized by high contents of K2O and Al2O3, high Sr/Y ratios, strongly fractionated REE patterns, LILE enrichment, and HFSE depletion. The GDP and QDP have relatively low (87Sr/86Sr)i values (0.7051–0.7054) and high εNd(t) values (−0.87 to 0.59). Zircon grains from the QDP have high εHf(t) values (7.0–9.6), while zircon grains from the GDP show large εHf(t) variations ranging from −4 to 9.6, indicating that the magma source of the ore-bearing GDP included more continental crust than that of the postmineralization QDP. The zircon Ce4+/Ce3+ and Eu/Eu* ratios and apatite Mn and SO3 contents indicate that the postmineralization QDP had higher oxygen fugacity than the ore-bearing GDP. The oxygen fugacity of the ore-bearing magma present during apatite crystallization (generally below the Ni-Ni-O (NNO) buffer), was lower than that present during zircon crystallization (above the hematite-magnetite (HM) buffer). The F, Cl, and S contents in apatite show that the GDP and QDP were F and S rich and that the GDP had a higher F content than the QDP. A high oxygen fugacity, a F- and S-rich magma and a Mo-rich crustal source were the key factors for the formation of the Lakang'e porphyry Mo (Cu) deposit.

Mineralogy, mineral chemistry and thermobarometry of post-mineralization dykes of the Sungun Cu–Mo porphyry deposit (Northwest Iran)

Abstract The Sungun copper–molybdenum porphyry deposit is located in the north of Varzaghan, northwestern Iran. The Sungun quartz-monzonite is the oldest mineralized intrusive body in the region and was emplaced during the Early Miocene. Eight categories of the late and unmineralized dykes, which include quartz diorite, gabbrodiorite, diorite, dacite, microdiorite and lamprophyre (LAM), intrude the ore deposit. The main mineral phases in the dykes include plagioclase, amphibole and biotite, with minor quartz and apatite and secondary chlorite, epidote, muscovite and sericite. The composition of plagioclase in the quartz diorite dykes (DK1a, DK1b and DK1c) varies from albite-oligoclase to andesine and oligoclase to andesine; in the diorite, it varies from andesine to labradorite; in the LAM, from albite to oligoclase; and in the microdiorite (MDI), it occurs as albite. Amphibole compositions are consistent with classification as hornblende or calcic amphibole. Based on their AlIV value (less than 1.5), amphibole compositions are consistent with an active continental margin affinity. The average percentage of pistacite (P s) in epidotes formed from alteration of plagioclase and ferromagnesian minerals is 27–23% and 25–30%, respectively. Thermobarometric studies based on amphibole and biotite indicate approximate dyke crystallization temperature of 850–750℃, pressure of 231–336 MPa and high fO2 (&gt;nickel-nickel-oxide buffer). The range of mineral compositions in the postmineralization dyke suite is consistent with a genetic relationship with the subduction of the Neotethys oceanic crust beneath the continental crust of the northwest part of the Central Iranian Structural Zone. Despite the change from calc-alkaline to alkaline magmatism, the dykes are likely related to the late stages of magmatic activity in the subduction system that also generated the porphyry deposit.

Volatile components and magma-metal sources at the Sharang porphyry Mo deposit, Tibet

Volatiles in magmatic‐hydrothermal fluids play an essential role in the formation of porphyry ore deposits. Models of F, Cl and S partitioning between silicate melt, fluid and volatile-bearing minerals (biotite and apatite) in the magmatic system provide an opportunity to estimate halogen fugacity in the fluids and F-Cl-S concentrations in the ore-related magmas. This work integrates mineralogical and isotopic studies of multi-stage intrusions in the Sharang porphyry Mo deposit, with the aim of tracing the evolution of magmatic volatile components in the magmatic-hydrothermal system and elucidating the origin of magma and ores. Sharang apatite compositions in pre-ore and ore-forming intrusions were likely formed at different fractional crystallization stages from volatile-undersaturated to H2O-saturated melts. Magmatic fluids that equilibrated with pre-ore melts were HCl-rich, while the exsolved fluids from the granite porphyry were enriched in HF. Magmatic Cl-F-S contents varied accordingly, and above 700 °C, the felsic causative melts likely had high F (ca. 2700 ppm), low Cl (ca. 130 ppm) and high S contents (ca. 300 ppm). Fluid exsolution was likely the main control over a decrease in magmatic Cl concentrations, while the deep magma source chamber appears to have been recharged by a more mafic S-Cl rich magma at the time of quartz diorite emplacement, elevating the sulfur content of the magma. The magma and sulfides likely originated from subduction-modified mantle and Lhasa terrane basement, which were also responsible for the generation of a high-F, Mo-mineralizing magma.

Delineation of geochemical haloes using the developed zonality index model by multivariate and fractal analysis in the Cu–Mo porphyry deposits

Main aim of this study is to propose a developed zonality index for Cu–Mo porphyry deposits based on staged factor analysis with Number-Size (N–S) fractal model. This method was used in an Iranian porphyry system as named Serenu (SE Iran). The developed zonality index was a ratio between factors related to major and minor ore elements based on in-situ soil samples. In this study, two factors were extracted after three stages of factor analysis including F1-3 (Pb, Zn, Au, Ag, Mn, Cd, As) and F2-3 (Cu–Mo). Based on these factors, F1−3F2−3is determined as a developed zonality index. Furthermore, conventional zonality index was calculated on the basis of(Pb×Zn)(Cu×Mo). Then, these zonality indexes were classified by the N–S fractal modeling. Results obtained by the fractal modeling indicates that the main anomalies for the developed zonality index is correlated with plutonic units, mineralized rock samples and exploratory boreholes especially in the central and SE parts of the studied area. This methodology can be utilized for other types of ore mineralization.

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

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