Porphyry Systems Research Articles

Redox conditions, compositional parameters, and indirect subduction-related source of Cretaceous Sn and Cu–Mo fertile post-subduction granites in the Yidun Terrane of eastern Tibet

The metal and sulfur fertility of granite magmas that formed in post-subduction settings, the key processes that led to their contrasting associated polymetallic mineral deposits, and their post-subduction source remain obscure. The Yidun Terrane, eastern Tibet, extends for 500 km and can be divided into the northern Yidun Terrane (NYT) and southern Yidun Terrane (SYT) based on distinctive magmatic source affinities and related mineral deposits. The NYT has several 103–93 Ma granite plutons and associated magmatic-hydrothermal vein-type Sn–Pb–Zn–Ag polymetallic deposits, such as the giant Xiasai deposit. In contrast, the SYT granites host the Xiuwacu porphyry Mo–W deposit (88–84 Ma) and several porphyry or porphyry–skarn-type Cu–Mo deposits (85–78 Ma), such as Relin, Hongshan and Tongchanggou. The contrasting nature of the causative Cretaceous post-subduction granites and their source is determined from their whole-rock and isotope geochemistry, zircon trace-element concentrations, and biotite and amphibole mineral chemistry. Based on these parameters, the NYT Sn–Pb–Zn–Ag deposits are associated with highly fractionated, reduced ilmenite-series granites derived from a relatively dry magma that formed via mixing between amphibolite-derived and greywacke- and orthogneiss-derived metasomatized crustal melts. In contrast, the SYT Mo–W deposits are associated with strongly- to moderately-evolved and fractionated, oxidized intermediate-series granites. The SYT Cu–Mo deposits are related to more hydrous and less fractionated magnetite-series granites. The granites associated with both Mo–W and Cu–Mo deposits in the SYT were generated by partial melting of metasomatized ancient mafic-intermediate lower continental-crust with variable contributions of metasomatized mantle components. However, there is only evidence for the presence of garnet as a residual phase in the magmatic source of the SYT Cu–Mo-bearing granites. The different magma sources were important in determining the redox state of the Yidun granite magmas, providing a fundamental control on the behaviour of metals and sulfur in fractionating melts and dictating the contrasting polymetallic compositions of causative magmatic-hydrothermal fluids and resultant mineral deposits. The source regions of the granites are thus the primary control on the spatial distribution of the Sn–Pb–Zn–Ag, Mo–W, and Cu–Mo belts in the Yidun Terrane. Although not derived during subduction, as for most Cenozoic porphyry systems, the Yidun deposits are indirectly related to subduction via the metasomatism and fertilization of the mantle lithosphere and lower crust during the earlier subduction phase. The anomalous preservation of Cretaceous porphyry systems in the Yidun Terrane relates to their proximity to the margin of the Yangtze Craton, whose thick buoyant lithosphere inhibited exhumation and erosion.

Рудно-метасоматическая зональность молибден-порфировой системы Аксу (Северо-Восток Азии)

The article presents the data from a comprehensive study of the Aksu Mo-porphyry system metasomatites (Korkodon-Nayakhan magmatic activation zone). The halo of metasomatic changes around the porphyry system, associated with the tectonic-block structure of the territory, is shown to be asymmetric. The core of the system is brought to the surface and located in a halo of kalifeldspar- muscovite metasomatites; the northwestern block is elevated and characterized by high-temperature epidote-biotite and epidote-pyroxene propylites, while in the southeastern block there is a consistent transition from kalifeldspar-sericite metasomatites to fragments of argillisite ones. The established zoning is confirmed by geochemical associations and mineralization types from the northwest to the southeast: in the northwest, Au-Bi (As, Cu) at the Solnechnoye ore occurrence; in the center, Mo (Cu, Au) at the Aksu deposit; in the southeast, Ag-Pb-Zn (Cu, Bi, As, Au) at the Vysokoye ore occurrence.

Porphyry indicator zircons (PIZ) and geochronology of magmatic rocks from the Malmyzh and Pony Cu-Au porphyry ore fields (Russian Far East)

New data obtained by petrographical, geochemical and U-Pb geochronological studies of magmatic whole rock and zircon samples from the Malmyzh and Pony gold-copper porphyry ore fields are discussed. The trace elements distribution patterns (REE + Y, Hf, Ti, U, Th, Pb) in zircons have been measured by SIMS SHRIMP-IIe instrument in the same spots as for local U-Pb age dating. Geochronological data show a matching Cenomanian crystallization age of the Malmyzh and Pony magmatic rocks: 99–97 and 93 Ma, respectively. ∑REE in zircons from the Malmyzh granitoids varies from 217 to 1,158 ppm, Y – from 718 to 732 ppm, Hf – from 4,524 to 4,928 ppm, Ti – from 4.1 to 16.6 ppm, Pb – from 1.2 to 1.6 ppm, U – from 89 to 112 ppm, Th – from 58 to 76 ppm. Geochemical characteristics of zircons from the Pony monzodiorite-porphyry differ significantly from the Malmyzh granitoid zircons. Concentrations of most trace elements in the Pony zircons, especially LREE and MREE, as well as Y, Pb, U, Th, and Ti are two–three times higher than in zircons from the Malmyzh granitoids. Temperature of zircon crystallization of the Malmyzh granitoids revealed by «Ti in zircon» thermometer is estimated at 680–700 °C, whereas temperature of zircon crystallization of the Pony monzodiorite-porphyry is approximately 784 ± 15 °C. Fertility assessment of magmatic rocks from the Malmyzh and Pony ore fields is based on geochemical characteristics of zircons like Eu/Eu* vs. Dy/Nd and Eu/Eu* vs. (Ce/Nd)/Y plots. These characteristics show that zircons from the Malmyzh granitoids fall into the field of fertile porphyry systems, whereas zircons from the Pony monzodiorite-porphyry plot within the field of barren suites. Comparative analysis of studied samples from the Malmyzh and Pony ore fields with magmatic rocks from porphyry deposits worldwide aids our understanding of the geodynamic framework of their formation and establishes links to adakitic granitoids generated under similar conditions. This result can be utilized during prognostic and metallogenic considerations not only within the limits of Sikhote-Alin territory but also within the whole Russian Far East region.

Fluid inclusion evidence for the magmatic-hydrothermal evolution of closely linked porphyry Au, porphyry Mo, and barren systems, East Qinling, China

Abstract The Xiong’ershan district in central China hosts broadly coeval porphyry Au (Qiyugou deposit), porphyry Mo (Leimengou deposit), and barren (Huashan pluton) systems. The key controls on the ore potential and different mineralization styles in these systems are not well understood, with first-order differences in fluid chemistry and melt sources being the main alternatives. The fluid inclusion characteristics of all three porphyry systems have been studied using an integrated approach that combines field geology, petrography, microthermometry, and laser ablation–inductively coupled plasma–mass spectrometry analysis of single fluid inclusions. The results permit a reconstruction of the magmatic-hydrothermal evolution of the ore-forming fluids, and to elucidate whether specialized hydrothermal fluids strongly enriched in ore metals (i.e., Mo, Au, Cu) were essential to form the economically significant deposits. The fluid compositions across the three hydrothermal stages from the Qiyugou Au deposit remain approximately the same over time, suggesting that progressive magma fractionation, fluid-rock reaction along fluid path, and mineral precipitation had a limited effect on fluid composition. The syn-ore stage fluids of the Leimengou Mo deposit are characterized by higher Cs/Na, Sr/Na, and B/Na, but lower K/Na and Cl/Na ratios, and also have salinities and homogenization temperatures distinct from the earlier fluids. This demonstrates that Mo mineralization was caused by a second pulse of fluid input from a highly fractionated felsic magma subsequent to the pre-ore stage. At the Huashan barren pluton, fluids from phase II have higher Cs/Na, B/Na, Li/Na, and Rb/Na ratios with lower homogenization temperatures than fluids occurring in porphyritic rocks of phase III, reflecting a higher degree of magma fractionation of this plutonic complex. The Huashan pluton does not host economic mineralization which is likely caused by the low ore metal tenor, inefficient fluid extraction from the melt, or the flat-roof geometry preventing accumulation of a large volume of fluid in the apical part. The Au tenor of the Qiyugou deposit was most likely contributed by mantle-derived material of higher Mg/Na, Fe/Na, Pb/Na, and Zn/Na ratios. Taken together, the metal charged magmatic-hydrothermal fluids, steeply dipping geometry, and small volume of the porphyry stocks all suggest that a much larger magma chamber feeding the porphyry systems should be present at deeper levels with good potential for Mo mineralization below the current level of exposure at Qiyugou deposit.

Vertical evolution of Ag-Pb-Zn-(Cu)-Mo in porphyry system: A case study from the Laochang deposit, SW China

Distal massive sulfide Ag-Pb-Zn mineralization is commonly associated with proximal porphyry Mo-(Cu) systems, but the vertical evolution of Ag-Pb-Zn-(Cu)-Mo distribution within porphyry systems remains poorly understood and documented. The Laochang deposit located in the southeastern Sanjiang metallogenic belt, SW China contains both the massive sulfide Ag-Pb-Zn-(Cu) and porphyry-skarn Mo-(Cu) mineralization (1737 t Ag@222 g/t, 0.51 Mt Pb@5.1 wt%, 0.34 Mt Zn@3.1 wt%, 117, 800 t Mo@0.15 wt%, and 0.1 Mt Cu@0.2 wt%), thus representing an excellent case study. The Laochang deposit is mainly hosted in early Carboniferous volcanic rocks, late Carboniferous to early Permian carbonate rocks, and links with Eocene granite porphyry. Here, we report Rb-Sr age of sphalerite and pyrite from the massive sulfide Ag-Pb-Zn-(Cu) ores, zircon U-Pb age for the granite porphyry, C-O isotopes of hydrothermal calcite, and S-Zn isotopes of sulfide minerals to reveal the vertical distribution of Ag-Pb-Zn-(Cu)-Mo mineralization in porphyry system. The sulfides Rb-Sr age (45.1 ± 3.6 Ma) is similar to the zircon U-Pb age (44.6 ± 0.2 Ma), indicating the Ag-Pb-Zn-(Cu) mineralization has a genetic link with the granite porphyry and formed in the same system as the porphyry-skarn Mo-(Cu) mineralization. Furthermore, the C-O isotopic compositions of the hydrothermal calcite suggest a diminishing contribution of the host rocks and an increasing input of the meteoric water in the hydrothermal fluids from deep to shallow. The S-Zn isotopic compositions of the sulfide minerals indicate a magmatic source of the ore-forming elements. The δ34S values decrease, and the δ66Zn values increase with elevated levels of sampling depth, implying a Rayleigh fractionation process. This means fluids and late-stage sulfides evolved toward isotopically lighter sulfur and heavier zinc isotopes. Hence, we propose that the Laochang deposit is a porphyry system comprising distal Ag-Pb-Zn-(Cu) and proximal Mo-(Cu) mineralization. In addition, the sulfur and zinc isotopic systematics observed in this study provides a new insight into the mineralization processes of the porphyry-distal systems.

Generation of the Giant Porphyry Cu-Au Deposit by Repeated Recharge of Mafic Magmas at Pulang in Eastern Tibet

Abstract The giant Pulang porphyry Cu-Au district (446.8 Mt at 0.52% Cu and 0.18 g/t Au) is located in the Yidun arc, eastern Tibet. The district is hosted in an intrusive complex comprising, in order of emplacement, premineralization fine-grained quartz diorite and coarse-grained quartz diorite, intermineralization quartz monzonite, and late-mineralization diorite porphyry, which were all emplaced at ca. 216 ± 2 Ma. Mafic magmatic enclaves are found in both the coarse-grained quartz diorite and quartz monzonite. The well-preserved primary mineral crystals in such a systematic magma series (including contemporaneous relatively mafic intrusions) with well-defined timing provide an excellent opportunity to investigate upper crustal magma reservoir processes, particularly to test the role of mafic magma recharge in porphyry Cu formation. Two groups of amphibole crystals, with different aluminum contents, are observed in these four rocks. Low-Al amphibole crystals (Аl2О3 = 6.2–7.6 wt %) with crystallization temperatures of ~780°C mainly occur in the coarse-grained quartz diorite and quartz monzonite, whereas high-Al amphibole crystals (Al2O3 = 8.0–13.3 wt %) with crystallization temperatures of ~900°C mainly occur in the fine-grained quartz diorite and diorite porphyry. These characteristics, together with detailed petrographic observations and mineral chemistry studies, indicate that the coarse-grained quartz diorite and quartz monzonite probably formed by crystal fractionation in the same felsic magma reservoir, whereas the fine-grained quartz diorite and diorite porphyry formed from relatively mafic magmas sourced from different magma reservoirs. The occurrence of mafic magmatic enclaves, disequilibrium phenocryst textures, and cumulate clots indicates that the coarse-grained quartz diorite and quartz monzonite evolved in an open crustal magma storage system through a combination of crystal fractionation and repeated mafic magma recharge. Mixing with incoming batches of hotter mafic magma is indicated by the appearance of abundant microtextures, such as reverse zoning (Na andesine core with Ca-rich andesine or labradorite rim overgrowth), sharp zoning (Ca-rich andesine or labradorite core with abrupt rimward anorthite decrease) and patchy core (Ca-rich andesine or labradorite and Na andesine patches) textured plagioclase, zoned amphibole, high-Al amphibole clots, skeletal biotite, and quartz ocelli (mantled quartz xenocrysts). Using available partitioning models for apatite crystals from the coarse-grained quartz diorite, quartz monzonite, and diorite porphyry, we estimated absolute magmatic S contents to be 20–100, 25–130, and >650 ppm, respectively. Estimates of absolute magmatic Cl contents for these three rocks are 1,000 ± 600, 1,800 ± 1,100, and 1,300 ± 1,000 ppm, respectively. The slight increase in both magmatic S and Cl contents from the premineralization coarse-grained quartz diorite magma to intermineralization quartz monzonite magma was probably due to repeated recharge of the relatively mafic diorite porphyry magma with higher S but similar Cl contents. Mass balance constraints on Cu, S, and Cl were used to estimate the minimum volume of magma required to form the Pulang porphyry Cu-Au deposit. Magma volume calculated using Cu mass balance constraints implies that a minimum of 21–36 km3 (median of 27 km3) of magma was required to provide the total of 2.3 Mt of Cu at Pulang. This magma volume can explain the Cl endowment of the deposit but is unlikely to supply the sulfur required. Recharge of 5–11 km3 of diorite porphyry magma to the felsic magma reservoir is adequate to account for the additional 6.5–15 Mt of S required at Pulang. Repeated diorite porphyry magma recharge may have supplied significant amounts of S and some Cl and rejuvenated the porphyry system, thus aiding formation of the large, long-lived magma reservoir that produced the porphyry Cu-Au deposit at Pulang.

Multiple tectonic-magmatic Mo-enrichment events in Yuleken porphyry Cu-Mo deposit, NW China and its’ implications for the formation of giant porphyry Mo deposit

The Yuleken porphyry Cu-Mo deposit located in the Chinese Altay-East Junggar, a section of the Central Asian Orogenic Belt, the world's largest Phanerozoic subduction-accretionary orogen, witnessed the multistage tectonic-magmatic evolution and mineralization from arc to syn- and post-collision environment over a time span of about 52 Ma. Four types of molybdenite have been distinguished: (1) primary magmatic-hydrothermal, undeformed molybdenite in porphyry, (2) recrystallized molybdenite associated with ductile deformation, (3) recrystallized, intrafoliational molybdenite, and (4) fracture-related hydrothermal molybdenite, and these are characterized by decreasing Re abundances from magmatic to hydrothermal conditions. Individual molybdenite types are non-stoichiometric and exhibit the following negative correlation between the Mo and Re contents:Re (apfu) = −0.0026 Mo (apfu) + 0.00268.This trend reflects successive stages of tectonic-hydrothermal events from a magmatic island-arc to a post-collisional setting. These repetitive mineralization events produced Mo enrichment and higher overall Mo grade of the Yuleken deposit, and are recorded in progressively decreasing Re concentrations in molybdenite. Statistical evaluation of Mo and Re abundances in giant to small porphyry deposits worldwide also indicates that decreasing Re in molybdenite will lead to lower overall Re resource (in a single deposit) and to greater overall Mo resource (in the same deposit). Multiple mineralization processes related to repetitive tectonomagmatic episodes in large porphyry Mo deposits that display Re depletion in molybdenite suggest that reworking of mantle-derived porphyry systems by successive events of crustal growth may be the responsible for Mo enrichment and higher overall Mo ore grade, and eventually produce giant porphyry molybdenum deposits.

Trace Element Geochemistry of Chalcopyrites and Pyrites from Golpu and Nambonga North Porphyry Cu-Au Deposits, Wafi-Golpu Mineral District, Papua New Guinea

Studying elemental geochemistry of hypogene sulphides can discriminate the hydrothermal fluids responsible for ore formation. To determine whether Golpu porphyry Cu-Au deposits are related to the Nambonga North porphyry system which is located 2.5 km apart in the Wafi-Golpu Mineral District, Papua New Guinea, we compare the trace element compositions of drill core chalcopyrites and pyrites analysed using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS). The results for the Golpu chalcopyrites revealed high concentrations of Au, As, Se, Mo, Sb, Te and Bi and lower concentrations of Ag and Zn compared to those from Nambonga. Pd and Pt were below the detection limit in chalcopyrites for both deposits. The results for the Golpu pyrites indicated high concentrations of Pt, Au, Se, Mo, Sb, and Te and lower concentrations of Cu, Zn, As, Ag, Pb, Pd and Bi compared to those from Nambonga North. Au concentrations in the pyrites from both the porphyry deposits were higher compared to chalcopyrites, which mean that pyrite is the Au-bearing sulphide responsible for the higher Au content. In contrast, Cu values in pyrites from Nambonga North are higher than those from Golpu. Overall, it is envisaged that the ore fluids were exsolved at different times during the evolution of both porphyry deposits, although these porphyry centres may be related in space and time.

Geochemistry of Rhenium and Other Trace Elements in Molybdenite, Sar Cheshmeh Porphyry Cu‐Mo Deposit, Iran

AbstractLA‐ICP‐MS analysis of molybdenite from the Sar Cheshmeh porphyry Cu‐Mo deposit (PCD), Iran, shows moderate concentration of Re (average ∼207 ppm) and low concentration of chalcogenides (average of Pb + Te + Bi, ∼31 ppm) as well as metalloids (average of As + Sb + Ge, ∼4.5 ppm). The early‐formed quartz–molybdenites associated with potassic alteration are characterized by moderately low concentration of Re (21–215 ppm with an average of 83 ppm), whereas the transitional quartz–molybdenite veins related to the sericitic stage of mineralization contain more Re (62–465 ppm, with an average of 207 ppm). In contrast, the late‐formed quartz–molybdenite veins associated with phyllic alteration show the highest concentration of Re (up to 1273 ppm with an average of 395 ppm). Gradual increase in Re content of molybdenites deposited throughout the evolution of the porphyry system is probably related to elevated ƒO2 and acidic conditions of the ore fluids governing the transitional and late stage of mineralization, when compared to the moderately low ƒO2 and basic conditions of the ore fluids precipitating the low‐Re molybdenites associated with potassic alteration. The mixed mantle/crustal source of the ore‐related magma and its fractionated composition in Sar Cheshmeh are consistent with magmatic conditions for the formation of Mo‐rich and Re‐poor PCDs in the world.

Stream Sediment Datasets and Geophysical Anomalies: A Recipe for Porphyry Copper Systems Identification—The Eastern Papuan Peninsula Experience

Airborne magnetic and radiometric datasets have, over the past few years, become powerful tools in the identification of porphyry systems which may host economic porphyry copper–gold–molybdenum ore bodies. Magnetisation contrasts with the unaltered host rocks, coupled with the elevated radiometric signature, compared to the host rock, makes identification of large-scale porphyry copper systems possible. Integrating these two different datasets with stream sediment data and other geochemical exploration methods results in a higher degree of confidence. Stream sediment data were analysed to see the distribution of copper and gold elements throughout the study area, located within the Eastern Papuan Peninsula of Papua New Guinea. Airborne geophysics data over the same area were also processed for magnetic and radiometric responses. The processing of the magnetic data revealed several magnetic anomalies related to concealed intrusive rock units, with associated radiometric signatures. The distribution of gold and copper anomalism was correlated with the geology and geophysical signatures. Results indicate varying degrees of correlation, with some areas showing a strong correlation between gold/copper occurrence and geophysical signatures, compared to other areas. Some factors that we believe impact the level of correlation may include tectonic history, volcanic cover, and weathering patterns. We recommend caution when applying multi-data exploration for porphyry copper systems.

Erratum to: Crustal Source of Pb and S at the Yubileynoe Porphyry Gold Deposit (Southern Urals, Kazakhstan): High Precision Pb–Pb and δ34S Data

The Yubileinoe large gold deposit, located at the southern end of the Magnitogorsk megazone, is the only known representative of the Au–porphyry systems in the Southern Urals. It is genetically related to granitoids formed in a suprasubduction setting under mature oceanic island arc environment/setting. The obtained isotope (Pb–Pb and δ34S) data indicate the input of mineral-forming components into the Au–porphyry system of the deposit, mainly from granitoid melts, confirming a common source of ore material and ore-bearing granitoids. The geochemical and isotopic characteristics of granitoids indicate the leading role in their genesis of the crustal source, which is considered Late Precambrian continental crust.

Petrochronology of hydrothermal rutile in mineralized porphyry Cu systems

Hydrothermally formed rutile is a common mineral in porphyry Cu (-Au-Mo) deposits and has the potential to provide versatile information about the physical-chemical conditions and timing of mineralization. In this study, we investigated the trace element composition and U-Pb dates of hydrothermal rutile by LA-ICP-MS together with its petrographic context, in four well-studied porphyry systems: Batu Hijau (Indonesia), Bingham Canyon (USA), El Salvador (Chile) and Northparkes (Australia). A similar sequence of rutile generations occupying comparable textural positions was found to be common to all investigated deposits. We particularly focused on the most common rutile generation that is formed by the breakdown of biotite and temporally closely associated with mineralization as demonstrated by intergrowth relationships between individual, blocky rutile grains and Cu-Fe sulfides as well as cathodoluminescence imaging of mineralized quartz veins. Compositionally, rutile shows large trace element variations within and among the porphyry deposits, indicating that the compositions of both the local host rock and the fluid phase influence that of hydrothermal rutile. In comparison with non-hydrothermal rutile of various petrogenetic origins, rutile from porphyry Cu deposits show characteristic differences regarding their Sn, W, Si and Fe concentrations, indicating that rutile might be used to fingerprint porphyry-style mineralization. Due to its temporal link to Cu mineralization, texturally controlled in-situ U-Pb dating of blocky rutile grains by LA-ICP-MS provides the possibility to directly determine the absolute timing of Cu mineralization. Despite variable incorporation of initial Pb in the investigated hydrothermal rutile, we obtained robust lower intercept U-Pb dates that overlap within uncertainty with previously obtained mineralization ages for all four deposits, including those based on high-precision (ID-TIMS) zircon dating of bracketing porphyry intrusions. This demonstrates that rutile can be used to accurately predict the age of porphyry Cu deposit formation and with a precision better than 1.5% relative for deposits older than ca. 10 million years.

Distribution of indium, germanium, gallium and other minor and trace elements in polymetallic ores from a porphyry system: The Morococha district, Peru

We report indium, germanium, gallium, and other minor and trace elements contents in sphalerite, chalcopyrite, galena, and tetrahedrite-tennantite occurring in skarn and skarn-free (“Cordilleran”) polymetallic mantos and vein ore bodies in the Miocene porphyry-related Morococha District, Central Peru. Among the investigated minerals, LA-ICP-MS measurements indicate that In and Ga concentrate mostly in sphalerite (Inter-Quartile Range [IQR] 217–2.7 ppm and up to 4608 ppm In; IQR 61–2.0 ppm and up to 2137 ppm Ga) and chalcopyrite (IQR 109–32 ppm and up to 1070 ppm In; IQR 62–1.5 ppm and up to 630 ppm Ga). In coeval generations of sphalerite and chalcopyrite, the contents of In and Ga in sphalerite are at least two times higher than in chalcopyrite. Germanium content is generally low in the four analyzed minerals (IQR 1.2–0.19 ppm), although late Fe-poor sphalerite may yield much higher values (IQR 129–74 ppm).Certain trace element contents appear to correlate with (i) the evolving characteristics of the hydrothermal fluids during individual mineralization events, and (ii) the location of the studied ore bodies relative to the hydrothermal feeders. The highest In values in sphalerite are found in high-sulfidation assemblages in Cordilleran polymetallic veins and, with lower amounts, in low-sulfidation assemblages in skarn bodies. In intermediate-sulfidation assemblages in Cordilleran mineralization, In content decreases from early to late generations of sphalerite, while that of Ge increases. Spatial trace-element trends in Cordilleran veins and replacement bodies formed during the so-called “Morococha district-scale polymetallic event” include, from porphyry-distal to porphyry-proximal locations: i) In and Cu, and to a lesser extent Ga, enrichment in sphalerite; ii) Se and Hg enrichment and Sn and Ag depletion in chalcopyrite; iii) In enrichment in galena; and iv) Ag depletion in tetrahedrite-tennantite.Our dataset suggests that In is incorporated in the sphalerite crystal lattice via coupled substitutions involving Cu and subordinately also Sn and Ag. Availability of Cu in the mineralizing fluids is therefore key to In enrichment in sphalerite. Progressive dilution of metal-rich magmatic-hydrothermal fluids and Cu precipitation probably account for the progressive In depletion in distal-to-porphyry Zn-Pb-Ag and Ag-Pb Cordilleran polymetallic mineralization and in late sphalerite generations in intermediate-sulfidation assemblages.

Evolution of the gold (copper) mineralization in the porphyry stock and the related skarn zones and epithermal veins in the Astarghan area, NW Iran: Evidence from fluid inclusion, mineral chemistry and sulfur isotope analyses

The Astarghan area in northwest Iran (~50 km north of Tabriz) represents an excellent example of coexisting and associated skarn, porphyry and epithermal mineralizations of copper and gold. This contribution aims to study the geology, alteration and mineralization in these deposits, as well as the occurrence of gold and its host minerals, and present the physico-chemical characteristics of ore-forming fluids and the sulfur origin, in order to get a better understanding of development and evolution of these mineralizations. The Astarghan porphyry stock (Oligo–Miocene) intruded the upper Cretaceous flysch-type sedimentary sequence (calcareous sandstone and limestone with intercalations of siltstone, shale and marl) and brought about metamorphism and metasomatism along the contact. The Cu–Au mineralization in the Astarghan area occurred mainly in three forms: (1) skarn patches along the contact (Zone A), (2) stockwork-type and disseminated porphyry mineralization within the potassic (at Kaghdara and Boiokwari areas) and phyllic (at Sildirimdara area) alteration zones (Zone B), and (3) native gold-bearing low-sulfidation epithermal veins within the argillic alteration zone at Nowrozkala area (Zone C). The micro-thermometric studies on the porphyry-type Kaghdara potassic alteration zone showed that homogenization temperatures for liquid-rich and vapor-rich 2-phase, as well as halite-bearing multiphase inclusions range about 160–420 °C, 220–460 °C, and 320–580 °C, respectively. Salinities of the 2-phase and multiphase inclusions have ranges of 5–25 and 40–70 wt% NaCleq., respectively. However, fluid inclusions present in the epithermal veins of Nowrozkala are mainly liquid-rich 2-phase, and their homogenization temperature and salinity values lie within the ranges of 118–325 °C and 0.6–7.4 wt% NaCleq., respectively. The approximate estimated depth of the sulfide and gold mineralization in the porphyry system ranges from 1.6 to 2.5 km, and in the epithermal system is < 0.9 km. The sulfur isotopic analysis of pyrite from the porphyry and epithermal mineralizations in the potassic alteration zone at Kaghdara and argillic alteration zone at Nowrozkala indicate that the δ34S values (–0.1 to –0.3 and –0.5 to –1.1‰, respectively) are close to the range of magmatic sources. Finally, electron probe micro-analyses indicate that besides independent particles of 50–200 μm in the epithermal veins, gold is mainly hosted by tetrahedrite within the porphyry-related phyllic alteration zone, but especially stibnite within the epithermal veins; these minerals, as well as epithermal polyhedral pyrites contain native gold inclusions.

Are Vapor-Like Fluids Viable Ore Fluids for Cu-Au-Mo Porphyry Ore Formation?

Abstract Ore formation in porphyry Cu-Au-(Mo) systems involves the exsolution of metal-bearing fluids from magmas and the transport of the metals in magmatic-hydrothermal plumes that are subject to pressure fluctuations. Deposition of ore minerals occurs as a result of cooling and decompression of the hydrothermal fluids in partly overlapping ore shells. In this study, we address the role of vapor-like fluids in porphyry ore formation through numerical simulations of metal transport using the Gibbs energy minimization software, GEM-Selektor. The thermodynamic properties of the hydrated gaseous metallic species necessary for modeling metal solubility in fluids of moderate density (100–300 kg/m3) were derived from the results of experiments that investigated the solubility of metals in aqueous HCl- and H2S-bearing vapors. Metal transport and precipitation were simulated numerically as a function of temperature, pressure, and fluid composition (S, Cl, and redox). The simulated metal concentrations and ratios are compared to those observed in vapor-like and intermediate-density fluid inclusions from porphyry ore deposits, as well as gas condensates from active volcanoes. The thermodynamically predicted solubility of Cu, Au, Ag, and Mo decreases during isothermal decompression. At elevated pressure, the simulated metal solubility is similar to the metal content measured in vapor-like and intermediate-density fluid inclusions from porphyry deposits (at ~200–1,800 bar). At ambient pressure, the metal solubility approaches the metal content measured in gas condensates from active volcanoes (at ~1 bar), which is several orders of magnitude lower than that in the high-pressure environment. During isochoric cooling, the simulated solubility of Cu, Ag, and Mo decreases, whereas that of Au reaches a maximum between 35 ppb and 2.6 ppm depending on fluid density and composition. Similar observations are made from a compilation of vapor-like and intermediate-density fluid inclusion data showing that Cu, Ag, and Mo contents decrease with decreasing pressure and temperature. Increasing the Cl concentration of the simulated fluid promotes the solubility of Cu, Ag, and Au chloride species. Molybdenum solubility is highest under oxidizing conditions and low S content, and gold solubility is elevated at intermediate redox conditions and elevated S content. The S content of the vapor-like fluid strongly affects metal ratios. Thus, there is a decrease in the Cu/Au ratio as the S content increases from 0.1 to 1 wt %, whereas the opposite is the case for the Mo/Ag ratio; at S contents of &amp;gt;1 wt %, the Mo/Ag ratio also decreases. In summary, thermodynamic calculations based on experiments involving gaseous metallic species predict that vapor-like fluids may transport and efficiently precipitate metals in concentrations sufficient to form porphyry ore deposits. Finally, the fluid composition and pressure-temperature evolution paths of vapor-like and intermediate-density fluids have a strong effect on metal solubility in porphyry systems and potentially exert an important control on their metal ratios and zoning.

Tracking fluid mixing in epithermal deposits – Insights from in-situ δ18O and trace element composition of hydrothermal quartz from the giant Cerro de Pasco polymetallic deposit, Peru

Ore precipitation in mineral deposits formed in the upper parts of a porphyry system, at shallow crustal level (< 1.5 km), such as epithermal Au-Ag-(Cu)-(As) and polymetallic deposits is often triggered by fluid cooling and/or mixing between fluids from different sources. Commonly, in such deposits, two main fluid sources are identified a deeply sourced magmatic fluid and a shallow meteoric water stored in a surficial aquifer. Oxygen and hydrogen isotope compositions of gangue and alteration minerals using conventional bulk isotopic methods support the existence of mixing between these two fluid types. However, bulk isotope analysis provides only limited information on the exact mixing mechanisms and on the changing proportions of the involved fluids. Due to their high spatial resolution, SIMS in-situ oxygen isotope and LA-ICP-MS trace element analyses, in transects across growth zones of single crystals are adequate tools to trace the dynamics of this fluid mixing. In this study, in-situ SIMS oxygen isotope and LA-ICP-MS trace element analyses were performed on 10 selected quartz crystals from the giant Cerro de Pasco porphyry-related epithermal polymetallic deposit in central Peru. The results, combined with previous microthermometric and LA-ICP-MS fluid inclusion studies on the same or equivalent crystals, allow quantifying and documenting the mixing between different types of fluids that formed the large Cerro de Pasco epithermal polymetallic deposit. The δ18Oquartz values range between 4‰ and 20‰ and display variations up to 11.5‰ inside single crystals that cannot be only, nor mainly ascribed to fluid temperature changes. Rather, these variations record variable mixing proportions of a rising moderate-salinity magmatic fluid with a δ18OH2O around 10‰ and a low-salinity fluid with a δ18OH2O between 0 and 4‰, the latter stored below the paleo-water table. Each analyzed quartz crystals also display important variation of their trace element content, with Al (43 to 2098 ppm), Li (0.7 to 18 ppm), Ge (1.1 to 24ppm) and Ti (0.8 to 10 ppm). These variations do not systematically correlate with oxygen isotope compositions. This suggests that quartz trace element content is controlled by a complex interplay of fluid composition, temperature, pressure, and growth rate. Application of published Ti-in-quartz geothermometers on quartz grains from which the precipitation temperature is well constrained by fluid inclusion microthermometry, shows that it can lead to overestimation or underestimation of precipitation temperatures by more than 50 °C.The obtained δ18Oquartz patterns measured along profiles in the studied quartz crystals, and less clearly the in-situ trace element compositions, reveal abrupt changes and suggest that mixing between magmatic and surface-derived low-salinity fluids was not a continuous process. It rather took place through the influx of multiple short-lived pulses of magmatic fluid into the surface-derived low-salinity fluid surface aquifer.

Chemistry of rock-forming silicate and sulfide minerals in the granitoids and volcanic rocks of the Zefreh porphyry Cu–Mo deposit, central Iran: Implications for crystallization, alteration, and mineralization potential

Abstract Cu–Mo mineralization and associated hydrothermal alteration zones in the Zefreh porphyry Cu–Mo deposit are a result of the emplacement of the early Miocene granodioritic-to-granitic porphyritic intrusions into the Eocene volcanic rocks (dacites, pyroclastic rocks, and andesitic lavas) during active subduction along the Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran. The compositions of rock-forming minerals, such as plagioclase, amphibole, and biotite, in the granitoids of the Zefreh magmatic suite are used to determine temperature and oxygen fugacity in the magma during crystallization and emplacement. Plagioclase is locally unaltered and ranges widely in composition with reverse, normal, and oscillatory zoning, but there is no evidence of excess aluminum. Primary calcic amphiboles in the granodiorite porphyry are mainly magnesio-hornblende with high Mg#’s. The crystallization temperature of the granodiorite is in the range of 765–867 °C (average 821 ± 28 °C for amphibole–plagioclase geothermometer) and 706–861 °C (average 808 ± 35 °C for amphibole alone). Whereas, the zircon saturation temperature for the Zefreh granodiorite is lower and ranges from 724° to 733 °C (average 729 ± 4 °C). Biotites in the least-altered granodiorite and in the potassic alteration are Mg-rich and Ti-poor, and mainly fall within the fields of phlogopite and re-equilibrated primary biotite, because of their low TiO2 contents (2.7–4.5 wt%, average 3.5 wt%). Copper and molybdenum in the Zefreh porphyry deposit appear to have been transported by Cl-rich hydrothermal fluids as chloride complexes, based on the calculated halogen fugacity ratios of the fluid in equilibrium with hydrothermal biotite that range from 5.0 to 5.4 for log (ƒH2O)/(ƒHF), 4.3 to 4.8 for log (ƒH2O)/(ƒHCl), and –2.0 to –1.4 for log (ƒHF)/(ƒHCl). The calculated fugacity ratios indicate that the biotites equilibrated with hydrothermal fluids that varied in composition, including oxygen, sulfur, and halogen fugacities. The intercept values for biotites from the Zefreh porphyry Cu–Mo deposit [IV(F) = 1.9 to 2.2 and IV(Cl) = –4.8 to –4.3] correspond to those from other well-known porphyry Cu–(Mo–Au) deposits worldwide [IV(F) = 1.5 to 2.8 and IV(Cl) = –5.0 to –3.5]. On the other hand, hydrothermal chlorite and epidote in the propylitically altered granodiorite of the Zefreh deposit are more Fe-rich and Mn-poor than those in some mineralized porphyry systems. The calculated temperatures of chlorite formation by the geothermometer of Cathelineau (1988) are all similar (300–330 °C), suggesting the potassically altered granodiorite was also affected by later, cooler hydrothermal fluids associated with the distal propylitic alteration zone. Disseminated chalcopyrite in the matrix of the potassically and propylitically altered granodiorite hosts as much as 1.3 wt% Zn and 0.1 wt% As. Based on whole-rock and mineral compositions, we conclude that the Zefreh magmatic system is similar in many regards to subduction-related ore systems, but it is unlikely to host a major porphyry Cu–Mo deposit.

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.

Factors controlling the formation of large porphyry Cu deposits: A case study from the Jiurui ore district of Middle-Lower Yangtze River Metallogenic Belt using in situ zircon and apatite chemistry from syn-mineralization intrusions

The geological processes leading to the formation of porphyry Cu deposits have been well studied and documented. However, the major factors controlling the scale of mineralization resulting in giant ore deposits, remain poorly understood. In this study, we evaluate the compositions of zircon and apatite from syn-mineralization intrusions associated with two porphyry Cu deposits (Chengmenshan and Xiangutai) in the Jiurui ore district of the Middle-Lower Yangtze River Metallogenic Belt, in an attempt to reveal the possible role of mantle-contribution to ore-forming materials in controlling metal endowment in porphyry systems. The Chengmenshan and Xiangutai deposits share similar characteristics including age of formation and type of host-rocks but with different Cu endowment. Chengmenshan (2.6 Mt at grade 0.8%) is classified as well-endowed whereas Xiangutai (280,000 t at grade 0.5%) is poorly-endowed. New laser ablation ICP-MS U-Pb ages of zircon from the Chengmenshan intrusions are between 144.8 ± 1.4 Ma and 147.3 ± 1.2 Ma. These ages are similar to the U-Pb ages for the Xiangutai intrusions (146.1 ± 1.3 Ma to 149.3 ± 1.1 Ma). Both Chengmenshan (average 699 °C) and Xiangutai (average 692 °C) intrusions have similar calculated Ti-in-zircon temperatures for magma crystallization and both are inferred to have crystallized from highly oxidized magmas on the basis of calculated values of Ce/Ce*, Eu/Eu* and Ce(IV)/Ce(III) in zircon and Mn in apatite. Water contents of magma are both high and similar based on zircon trace element ratios. However, the average εHf(t) value (−3.2) of zircon from the Chengmenshan intrusions is much higher than the Xiangutai (−13.2). Furthermore, the Chengmenshan apatites show lower 87Sr/86Sr ratios (0.70780 to 0.70909, average 0.70842) than those from the Xiangutai intrusion (0.70964 to 0.71061, average 0.71017). Intrusions associated with both deposits share a similar age and physio-chemical characteristics (e.g. log (fO2), T, water content) but have different magmatic sources. This suggests that the contribution of mantle material is a controlling factor in the formation of large porphyry Cu deposits in the Jiurui ore district and even in the whole metallogenic belt.

Unravelling the hydro-mechanical evolution of a porphyry-type deposit by using vein structures

The Permian San Pedro Cu-(Mo) deposit consists of a porphyry system with associated polymetallic veins in the San Rafael Massif, Argentina. This deposit resulted from the emplacement of a dioritic - tonalitic subvolcanic stock into the Early Permian Choiyoi volcanic rocks. Veins and veinlets linked to the hydrothermal alteration stages (potassic, phyllic and carbonitization) show different attitudes and are predominantly steeply dipping; sequentially, they fill four fracture systems: stockwork (potassic), dilatant WNW- & ENE-trending shear-compressional fractures (phyllic), NNE- & ~NS-striking tensional and shear-extensional fractures (phyllic), and NW/NNW- & WNW-trending tensional and shear-extensional fractures (carbonitization). Because of mechanical anisotropies of the host-rock, alteration telescoping, presence of hydrothermal fluids, thermodynamic constraints, and waning orogenic conditions, vein/veinlet overprinting is conspicuous. Focused hydrothermal fluid flow promoted episodic hydraulic reactivation and hydraulic fracturing, and reveals that differences in vein fabrics do not necessarily represents veins emplaced under different stress regimes. Based on the study of the structure of the area (including available geophysical maps) and its kinematics, the control of structures during vein emplacement, the vein/veinlet overprint sequence, and the thermo and physical conditions at the time of vein emplacement (using fluid inclusion data), it was possible to identify, characterize and track the changing hydro-mechanical evolution of this deposit as well as the progressive exhumation of the area during the time of vein emplacement.