Cu-Au Deposit Research Articles

Constraints from in-situ Rb-Sr dating on the timing of tectono-thermal events in the Umm Farwah shear zone and associated Cu-Au mineralisation in the Southern Arabian Shield, Saudi Arabia

• In-situ Rb-Sr dating constrains tectonic and igneous events in mineralised systems. • Umm Farwah Major Shear Zone was developed between 671 Ma and 631 Ma. • Ablah pegmatite was emplaced following the shear zone between 626 and 611 Ma. • Greisen and Cu-Au deposits in the Mount Ablah were formed due to two separate hydrothermal events. Constraining the tectonic history and timing of major shear zone structures in the Arabian Shield is critical for better understanding of the origin, tectonic history and distribution of ore deposits within this Precambrian crystalline crustal block. Here, we used a novel in-situ Rb-Sr dating of micas and K-feldspar to constrain the age of the Umm Farwah Shear Zone, which represents a regional tectonic feature that extends about 200 km across the southern part of the Arabian Shield. We also constrain the timing of Mount Ablah mineralisations which are exposed within the Umm Farwah Shear Zone and contains two styles of mineralisations including a greisen and Cu-Au mineralisation. These ore deposits are hosted in a pegmatite body that formed during the development of the Umm Farwah Shear Zone. Two main groups of muscovite (i.e., Group I and Group II) and K-feldspar mineral phases were identified based on ages and elemental variations in the mineralised zone and the host rocks. Results of in-situ Rb-Sr dating in the above K-rich minerals show that the Umm Farwah Shear Zone was initiated at ca. 651 Ma, and the emplacement of the Mount Ablah pegmatite occurred between 626 and 611 Ma, followed by the formation of greisen at 601 ± 12 Ma. In-situ Rb–Sr data also highlight a younger ‘alteration’ event occurred at ca. 556 ± 23 Ma, which partially reset the Rb–Sr system in the pegmatite and may thus reflect hydrothermal circulation event or overprint due to formation of Cu-Au mineralisation.

Perspective of Permian porphyry Cu-Au mineralization in Chinese Western Tianshan: Constraints from sulfide Re-Os dating and trace element study of the Kuruer deposit, Xinjiang

Western Tianshan along the southwestern Central Asian Orogenic Belt is well-endowed with epithermal and porphyry Au-Cu deposits. The Kuruer Cu-Au deposit, recently discovered in the eastern part of Western Tianshan, represents a transition from a high-sulfidation epithermal to a porphyry system. In this contribution, we explored the capacity of chalcopyrite to record direct mineralization time and fluids evolution in the Kuruer deposit, by presenting Re-Os isotopic data and the concentration range of 16 trace elements obtained through LA-ICP-MS. The chalcopyrite Re-Os isochron age of 256 ± 12 Ma (MSWD = 2.6) is comparable within error with the U–Pb age of the ore-causative albite porphyry which demonstrates a Permian porphyry-epithermal system instead of the previously proposed Carboniferous epithermal mineralization. The initial 187Os/188Os ratio of 0.81 ± 0.17 for chalcopyrite implies mixing between crust and mantle. Both pyrite and chalcopyrite can host trace elements in considerable amounts, where pyrite primarily hosted Co, As, Au, V, and Bi, but chalcopyrite concentrated more Zn, Cd, In, Sn, Sb, Mo. The study also highlighted systematic variation of trace element concentrations and Cd/Zn ratios in chalcopyrite and pyrite that can be powerful indicators of fluid phase separation and fluid mixing with meteoric water.

Fluid Inclusion Study of Epithermal Quartz Veins from the Kyaukmyet Prospect, Monywa Copper-Gold Ore Field, Central Myanmar

The Kyaukmyet prospect is located near the main ore bodies of the Kyisintaung and Sabetaung high-sulfidation Cu-Au deposits, Monywa copper-gold ore field, central Myanmar. Lithologic units in the research area are of mainly rhyolite lava, lapilli tuff and silicified sandstone, mudstone and siltstone units of Magyigon Formation which hosted to be polymetallic mineralization. Our field study recorded that epithermal quartz veins are hosted largely in rhyolite lava and lapilli tuff units. Those quartz veins show crustiform, banded (colloform), lattice bladed texture and comb quartz. The main objectives of the present research in which fluid inclusion studies were considered to conduct the nature, characteristics and hydrothermal fluids evolution from the epithermal quartz veins. In this research, there are three main types of fluid inclusions are classified according to their phase relationship (1) two-phase liquid-rich inclusions, (2) the coexisting liquid-rich and vapor-rich inclusions, and (3) only vapor-rich inclusions. Microthermometric measurements of fluid inclusions yielded homogenization temperatures (Th) of 148–282 °C and final ice-melting temperature (Tm) of -0.2°C to -1.4°C . The value of (Tm) are equal to the salinities reaching up 0.35 to 2.07 wt % NaCl equiv. respectively. Estimation formation temperature of the quartz veins provide 190°C and 210°C and paleo-depth of formation are estimated to be between 130m and 210m. Petrography of fluid inclusion and microthermometric data suggest that fluid boiling as well as mixing processes were likely to be happened during the hydrothermal fluid evolution at the Kyaukmyet prospect. According to the characteristics of many parameters including petrography of fluid inclusion, microthermometric data, paleo-depth, evidence of quartz vein textures and types of hydrothermal alteration from the Kyaukmyet prospect allows to interpret these data to be the low-sulfidation epithermal system.

A comprehensive overview on the origin of intrusive rocks and polymetallic mineralization in the Tongling ore-cluster region, lower Yangtze River Metallogenic Belt: Geological and geochemical constraints

The Tongling ore-cluster region is one of the most important Cu-Au polymetallic producers in the famous Lower Yangtze River Metallogenic Belt (LYRMB) in eastern China. The Cu-Au polymetallic ore deposits can be divided into four types, i.e., skarn, strata-bound hydrothermal, porphyry, and cryptobreccia, closely related to the Late Jurassic to Early Cretaceous magmatism. We summarize the geology of the Mesozoic Cu-Au deposits in Tongling, eastern China, and revisit the age distributions and geochemical characteristics of associated Mesozoic intrusions, by integrating a large number of published geochemical data (including major and trace elements for both early-stage and late-stage intrusions, whole-rock Sr-Nd-Pb isotopes, and zircon U-Pb age and Hf isotopes for early-stage intrusions), to reveal their sources and genesis.According to the U-Pb ages of intrusions, the main magmatic events in the area can be divided into two stages, i.e., 152–135 Ma and 135–124 Ma, respectively. The early-stage magmatism mainly produced Cu-Au mineralization-related dioritic intrusions, including pyroxene diorite-pyroxene monzodiorite, quartz diorite-quartz monzodiorite, and granodiorite, showing unobvious geochronological order. Geochemical data of Late Jurassic-Early Cretaceous intrusions from the early-stage magmatism suggest that they are all derived from a similar source composed of different proportions of slab-derived melt, metasomatized lithospheric mantle, and a lesser content of lower crust materials. Among them, the key differences lie in that more lower crust materials are incorporated in the source of intermediate-felsic rocks compared to intermediate-basic rocks. The late-stage magmatism produced a wide variety of rocks (diorite porphyry, syenite porphyry, granite porphyry, monzonite, and granite porphyry), which are related to Pb-Zn deposits. The late-stage igneous rocks may evolve from the early-stage rocks and have experienced fractional crystallization of apatite, ilmenite, and other minerals. Both early and late-stage magmatic events in the Tongling region were formed in the subduction setting, and corresponding to compression and extensional setting, respectively.Besides, the H-O isotopes of different kinds of minerals suggest that the ore-forming fluids of most ore deposits were mainly derived from the magma and mixed with a small amount of meteoric water in the late-stage mineralization. The S isotopes of sulfides show that the ore-forming materials come from the magma, accompanied by the addition of original sediments.

Crustal magnetotelluric imaging of a Paleoproterozoic graphitic suture zone, Curnamona Province, Australia

The Curnamona Province is a Paleoproterozoic to Mesoproterozoic domain that hosts the Broken Hill Pb-Zn ore body and a number of IOCG type Cu-Au deposits, but is mostly covered in Neoproterozoic to Quaternary cover. Three-dimensional resistivity modelling of 55-km gridded long-period (0.1–0.0001 Hz) magnetotelluric (MT) data collected as part of the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) previously revealed the presence of the Curnamona Conductor that exhibits extremely low resistivities <1 Ω.m at upper-crustal depths (<15 km) which has a lateral extent of >200 km in a north–south orientation. The conductor appears to dip to the west, centred under the large igneous province Benagerie Suite Volcanics with resistivity ∼10–100 Ω.m in a broader lower crustal region. To yield higher resolution of the Curnamona Conductor, a 56-site broadband (200–0.001 Hz) MT transect was undertaken with 2 km spacing. The east- west line intersected the observed conductive structures orthogonally. We show consistency between long-period MT AusLAMP 3D models, and new 2D and 3D broadband MT inversions, but with higher spatial and vertical resolution compared to the AusLAMP model.The linearity, depth extent and western dipping morphology of the Curnamona Conductor is remarkably similar to other Paleoproterozoic conductors in Australia along the eastern margin of the Mount Isa Province in northern Australia, and the eastern margin of the Gawler Craton in southern Australia. Plate reconstructions of Paleoproterozoic Nuna supercontinent suggests that these now disparate continental cratons were originally contiguous, with extensive subduction along their eastern margin between 2200 and 1850 Ma. Marine sedimentation in accretionary wedges prior to continental collision occurred during the Lomagundi-Jatuli Event, which recorded a global increase in δ13C (2300–2000 Ma) with a significant increase in burial of organic carbon. We argue that these Paleoproterozoic conductors thus represent graphitic suture zones that are uniquely representative of a time of enhanced carbon burial in Earth’s history.

Pyrite geochemistry and its implications on Au-Cu skarn metallogeny: An example from the Jiguanzui deposit, Eastern China

Abstract Trace element geochemistry of pyrite is widely used to monitor ore-forming processes of various types of deposits, but its application to skarn mineral systems is not well constrained due to the multi-stage nature and complex associated mineral assemblages for skarn-type pyrite. The Jiguanzui skarn Au-Cu deposit in the Middle-Lower Yangtze River Valley Metallogenic Belt (Eastern China) is characterized by abundant pyrite that formed in the main-ore (Py1), late-ore (Py2), and post-ore (Py3) stages, which makes it ideal for unraveling skarn ore-fluid evolution. Specifically, Py1 is composed of quartz–pyrite (Py1a), quartz–calcite–pyrite (Py1b), quartz–sericite–pyrite (Py1c), quartz–chlorite±epidote–pyrite (Py1d), and quartz–K-feldspar–pyrite (Py1e), among which Py1a is the most widespread. Py2 comprises calcite–pyrite (Py2a) and calcite–K-feldspar–pyrite (Py2b), and Py3 comprise bird’s-eye pyrite (Py3a) and fingerprint-like pyrite (Py3b). The varying Co/Ni ratios (mostly &amp;gt;2) and coexistence with hydrothermal minerals (quartz, calcite, K-feldspar, chlorite, and epidote) reveal the hydrothermal origin of Py1 and Py2. The Co/Ni (0.97–7.30), Cu/Ni (8.94–186), and As/Ni (0.80–11.7) ratios, and the high trace-element contents indicate that Py3a may have been genetically linked to the waning magmatic-hydrothermal system and increasing meteoric fluid influx. Py1 generally has higher Co-Ni-Se but lower Zn-As-Mo contents than Py2. Py1 in the orebodies also has higher Cu-Au contents than Py2, consistent with the formation of Py1 during the main Au-Cu ore stage. During the ore-fluid evolution, meteoric water input and abundant galena formation in the late-ore calcite-sulfide stage may have controlled the decreasing Se-Co-Ni contents from Py1 to Py2, while the fluid cooling and pH rise (caused by acidic fluid-carbonate rock reactions) may have increased the As-Zn-Mo contents from Py1 to Py2. Py1a in the orebodies has higher As-Ag-Te, but lower Co-Ni-Se contents than Py1a in the wallrocks. The decompression and phase separation (fluid boiling) by extensive hydraulic fracturing may have caused the higher temperature, pH, and fO2 for the Py1a-forming fluids in the orebodies (than those in the wallrocks). Such fluid physicochemical differences may have been the main controlling factor on trace element spatial variations of Py1a. More importantly, the spatial variation of these trace elements in Py1a provides insights for using pyrite trace element geochemistry in skarn mineral exploration.

The genesis and mineralization process of Xiaobaliang VHMS Cu-Au deposit, Central Asian Orogenic Belt: Constraints from the pyrite geochemistry and zircon geochronology

The Xiaobaliang Cu-Au deposit is located in the Hegenshan ophiolite complex belt of the western Xing’an–Mongolia Orogenic Belt (XMOB). Strata-bound sulfide ores are discovered within the Carboniferous volcanic tuff, with the oxidized Au-Cu ores at the top and Cu (-Au) sulfide ores at the bottom. Zircon U-Pb dating on volcanic tuff has yielded a concordia age of 326 ± 3 Ma (n = 21, MSWD = 5.6). Four types of pyrite have been identified, including lamellar pyrite (Py1) in the wall rocks, framboidal pyrite (Py2) in the Zn-rich massive ores, colloform pyrite (Py3) in the massive Cu ores, and euhedral pyrite (Py4) in the fractured Cu ores. Chalcopyrite comprises two types: early massive chalcopyrite aggregates (Cp1) and late chalcopyrite veinlets (Cp2). Here we present the in situ trace elements and sulfur isotopes analyses of different sulfide generations. Elements like Se (44.1 ppm), Co (227 ppm) and Cu (3211 ppm) are enriched in pyrites from Cu ores (Py3&Py4), whereas the pyrites from altered rocks (Py1) take high Mn (5027 ppm), Ti (134 ppm), V (13.0 ppm), Ni (41.9 ppm) and Au (5.07 ppm) concentrations. Similar elemental patterns are observed in chalcopyrite analyses where Co (312 ppm), Se (566 ppm) and Te (31.5 ppm) are enriched in massive Cu ores (Cp1), but Mn (147 ppm), V (174 ppm) and Ti (42.2 ppm) contents are mainly concentrated in chalcopyrite veinlets (Cp2). In situ S isotope analyses exhibit a large variation in Py1 (−30.70 to −1.50‰) and Cp2 (−7.81 ∼ −4.50‰) but are constant in Py2, Py3, Py4 and Cp1 (0.44 to 3.15 ‰). The high Co/Ni ratios and relatively lower δ34S values in Py1 suggest a diagenetic environment where the lower-temperature and extremely reduced conditions facilitate the enrichment of Mn, V and Au. The progressive enrichment of Sn, Te, Bi, Se and Cu in hydrothermal Py3 and Py4 then points out the rising of temperature in the weakly reduced environment. The negative sulfur isotopes in altered rocks (Py1) and fractured ores (Cp2) point out the contribution of the volcanic-sedimentary sequence. These compositional features, combined with sulfur isotopes, have demonstrated that Cu was mainly derived from magmatic-hydrothermal fluids whereas Au was released from Au-rich sediments on the seafloor. The Xiaobaliang Cu-Au deposit belongs to a Cyprus-type VHMS deposit formed in the Carboniferous extensional setting.

Melt volatile budgets and magma evolution revealed by diverse apatite halogen and trace elements compositions: A case study at Pulang porphyry Cu-Au deposit, China

Apatites those shielded as inclusions in igneous minerals are avoided of diffusion effects associated with evolving melts and can record the original volatile and trace element evolutions of the magma. Volatile and trace element compositions of apatites enclosed in high-Al, medium-Al, low-Al amphibole, magmatic biotite, plagioclase, and groundmass from ores, quartz monzonite porphyry (QMP) and its mafic microgranular enclaves (MMEs), and pre-ore coarse-grained quartz diorite porphyry (CQD) were present to evaluate the magmatic processes in the formation of Pulang porphyry Cu-Au deposit. All apatite inclusions are magmatic fluorapatites and occur as early-crystallization phases (940–980 °C), followed by the crystallization sequence of high-Al amphibole, medium-Al amphibole, magmatic biotite, plagioclase, low-Al amphibole (altered medium-Al amphibole) with fluctuating ƒO2 conditions. Compared to the low SO3 (<0.27 wt%) concentrations of other apatites inclusions in fertile QMP, the biotite-hosted apatites retain an abnormal SO3 (0.15–1.01 wt%) and Cl (0.08–0.71 wt%) enrichment. Estimates of sulfur and chlorine concentrations using partitioning models for apatite in QMP return similar features, where the biotite-hosted apatites yield highly variable melt S (315–2025 ppm) and Cl (0.1–1.2 wt%) contents. The presence of biotite-hosted S-Cl enriched apatites with overgrowth texture, together with the resorbed medium-Al amphiboles in QMP, both suggest that they have crystallized from an extra sulfur supplement process caused by the injection of a series of S-Cl enriched magma, and even subsequent remelting of the preexisting dioritic batholith and its interior apatites. Such magma processes further account for the fluid exsolution and alteration from medium-Al amphiboles to low-Al ones. Whereas, those from the barren CQD systematically returns normal SO3 (0.18–0.70 wt%) and Cl (0.03–0.51 wt%) concentrations with estimates of melt S (335–1321 ppm) and Cl (0.1–0.5 wt%) contents exhibiting features of typical arc basalts (300–1000 ppm; 0.01–0.85 wt%, respectively). Although the acicular apatite of MMEs has normal SO3 contents (0.19–0.37 wt%), its abundance also confirm an extra sulfur supplement process. The altered apatites of both QMP and CQD showing pitted surface with visible voids and LREE-rich mineral inclusions return low SO3 (<0.06 wt%) and Cl (<0.22 wt%) concentrations, indicating that these elements were depleted during potassic and phyllic alteration.Given that Sr/Y ratios (2.21–3.62) of apatite at Pulang do not vary significantly with changing melt composition (Mg = 119.1–528.8 ppm), the Sr/Y and Eu/Eu* ratios of apatite from QMP have confirmed a water-rich, oxidized magma origin, whereas the CQD are originated from a water-poor, reduced source. Besides, the hydrothermal alteration possibly accounts for the abnormally increased Ce/Ce* ratios of altered apatites from CQD and decreased Sr/Y ratios of the low-Al amphibole-hosted apatite from QMP. Therefore, using trace elements as indicators for petrogenetic studies would be more robust for those apatites enclosed in igneous minerals. Our studies demonstrate that apatite inclusions can be linked to discrete periods in the crystallization history of its host phases, thus providing insight into the magma evolution process.

Petrogenesis and metallogeny of the Dongguashan Cu-Au deposit in the Tongling ore-cluster region, the Lower Yangtze River Metallogenic Belt: Constraints from geochemistry and geochronology

The Dongguashan Cu-Au deposit located in the eastern portion of the Tongling mining district, the Lower Yangtze River Metallogenic Belt (LYRB), Eastern China is a typical one associated with the Qingshanjiao quartz monzodiorite, including porphyry, skarn, and stratabound ores. In order to constrain the petrogenesis of the intrusive rocks and associated Cu-Au mineralization, detailed analyses of the zircon geochronology and geochemistry, whole-rock geochemistry and Sr-Nd-Pb isotopes, and zircon Lu-Hf isotopes were performed. Magmatic zircons from quartz monzodiorite yield U-Pb ages of 136–138 Ma, revealing their formation ages of early Cretaceous. Geochemical characteristics of the quartz monzodiorites (SiO2 = 63.6–66.2 wt%, high Sr, low Y and Yb concentrations) discriminate their adakitic affinity. They are enriched in LILE and LREE, depleted in HFSE and HREE, and has no or slightly negative Eu anomalies. These geochemical characteristics indicate that the monzodiorites may be primarily derived from the magma mixing of mantle- and LCC-derived melts. The relatively low εNd(t) values (−11.7 to −10.7) and high (87Sr/86Sr)i ratios (0.7075 to 0.7078) may be plausibly interpreted by contamination of enriched mantle materials and/or continental crust. The high radiogenic Pb isotopes with (206Pb/204Pb)i = 17.98–18.09, (207Pb/204Pb)i = 15.51–15.53, and (208Pb/204Pb)i = 38.18–38.26 plot in the field of MORB, near the intersection of EM-1 and EM-2, and are considerably different from those of the upper and lower continental crust and the Dabie adakites, which exclude major contamination from the continental crust. Ti-in-zircon temperatures and calculated Ce4+/Ce3+ values fall within the field between MH and FMQ. The results indicate that the intrusive rocks and associated large-scale Cu-Au mineralization in the Dongguashan deposit are resulted from the magma mixing of mantle- and LCC-derived melts. in a lower magma temperature, yet higher fO2 and water content environment.

Copper recycling and redox evolution through progressive stages of oceanic subduction: Insights from the Izu-Bonin-Mariana forearc

Addition of subducted materials from the slab to the mantle wedge is often thought to elevate the oxygen fugacity of arc magmas and also to fertilize the mantle wedge in metals for subduction-related Cu-Au deposits. However, it remains controversial if slab-driven metal addition is effective and whether it occurs at all stages of subduction. The Izu-Bonin-Mariana (IBM) forearc preserves a full record of arc development from the initiation of subduction of the Pacific plate to mature arc volcanism. Here, we study the ore-forming and redox-sensitive metal Cu and its isotopes (δ65Cu) in the type-locality forearc basalts (FABs), boninites and high-Mg andesites from the IBM forearc, as well as MORBs from the East Pacific rise. Overall, the FABs display variably high Cu contents and MORB-like δ65Cu, consistent with limited Cu isotopic fractionation during partial melting of typical MORB mantle sources. Beginning with the boninites, the magma products from the IBM record strong slab signals, high water contents and high fO2 (ΔFMQ > +1). However, the oxidized, hydrous boninites and subsequent high-Mg andesites display low Cu contents, and mantle-like Cu/Sc ratios and δ65Cu, with no clear indication of the addition of Cu from the slab. The boninites show noticeably lower TiO2, Yb and Cu contents than the FABs, consistent with refractory mantle sources. Combined with available data from boninites and arc basalts worldwide, our results lead to a general conclusion that subducted oceanic slabs from initial to mature subduction contribute little Cu to the mantle wedge. This is further supported by the compiled Cu contents of arc peridotites. Adding Cu-poor, water-rich slab melts to the mantle wedge at any stage of Pacific oceanic subduction causes limited release of Cu, which remains trapped predominantly by reduced sulfides in the subducting slab. This likely reflects the overall reducing nature of slab materials added to the mantle wedge. However, we propose that the subsequent reaction of such reducing, hydrous slab melts with peridotites and flux melting produce oxidized primitive arc magmas deep in the mantle wedge. The reactive process promotes sulfide dissolution and metal release from the mantle wedge itself to oxidized arc magmas with high sulfur solubility, which explains the inheritance of mantle-like δ65Cu and the sulfide-undersaturated early-stage evolution in boninites and arc basalts. This study elucidates the role of subducted oceanic slabs in metal transfer and redox evolution and implies no significant Cu enrichment in the metasomatized mantle sources of magmatic arcs.

Hydrothermal evolution and mineralization of the Pulang porphyry Cu-Au deposit in the Sanjiang Tethys, Southwest China: Constraints from fluid inclusions and D-O-S isotopes

Pulang is the largest porphyry Cu-Au deposit that formed in the Late Triassic and is located in the eastern Tethys. Its ore-forming fluids and mineral assemblages show some reducing characteristics. Magma and fluid are two key parameters in porphyry mineralization. Studies have shown that syn-mineralization quartz monzonite porphyries have higher oxygen fugacities, which are conducive to mineralization. However, this does not answer the question of why the deposit has reducing characteristics, which should be positively related to fluid activity. Based on detailed geologic observation, hydrothermal evolution and ore-forming process have been divided into three successive periods, namely, pre-mineralization, syn-mineralization (subdivided into three stages, including early-, inter-, and late-mineralization, corresponding to stage 1, 2, and 3 veins), and post-mineralization, in the Pulang deposit. The corresponding fluid inclusions and sulfur isotopic compositions of sulfides are studied on this basis. The results show that the salinity ranges of the stage 1 and stage 2 veins are larger, which indicates that fluid immiscibility may exist. Pyrrhotite is developed in some of the stage 2 veins, and their fluid inclusions contain CH4. However, CH4 was not found in fluid inclusions in veins that do not contain pyrrhotite. The homogenization temperatures and salinities of the fluid inclusions decrease gradually, and the hydrogen and oxygen isotopes gradually approach the meteoric water line overall, from premineralization to postmineralization. Furthermore, sulfur isotopes of pyrrhotite are the highest, indicating a possible additional source of sedimentary sulfur. That is, the ore-forming fluids were dominated by magmatic water, and meteoric water was added in the late stage as the fluid evolved. The trend of the Heishuitang fault is consistent with the extension of the main ore body in the mining area. Because the strata is affected by faults, the strata acts as a good channel for meteoric water. Meteoric water was added to the magmatic fluid after extraction and carried organic matter from the Tumugou Formation and along the cracks. The fluid was mixed, and the ore-forming elements were effectively precipitated in a reducing environment. Therefore, pyrrhotite and CH4 occur in some veins. That may be why the Pulang deposit is giant.

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 &amp;gt;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.

Genesis and fluid evolution of the Huangtan Au-Cu deposit in the Kalatag district, Eastern Tianshan, NW China: Constraints from geology, geochronology, fluid inclusions, and H-O-S-Pb isotope geochemistry

The newly discovered Huangtan Au-Cu deposit is located in the central Dananhu - Tousuquan arc of Eastern Tianshan, southern Central Asian Orogenic Belt (CAOB). It is the first Au-dominated volcanogenic massive sulfide (VMS) polymetallic deposit in the Eastern Tianshan. Veinlet-disseminated and massive orebodies are hosted within Early Silurian pyritic phyllic tuff and volcanic breccia and controlled by a secondary fracture zone of the Kalatag fault with extensive hydrothermal alteration. Four primary alteration/mineralization stages have been recognized as follows: (1) Early ore stage (S1), forming mainly ore-barren fine quartz veins with minor gold-bearing sulfides; (2) main ore stage (S2), forming mainly thick quartz veins with abundant coarse-grained subhedral pyrite (S2-1), and plentiful chalcopyrite, sphalerite, barite and Au-bearing sulfide veins (S2-2); (3) late ore stage (S3), which is characterized by plenty of barren quartz–calcite veins with few sulfides; and (4) supergene stage (S4), accompanied by abundant oxide mineralization, including malachite, jarosite and other supergene minerals. From S1 to S3, microthermometric data of fluid inclusions show homogenization temperatures of 263–379 °C (mean = 308 °C), 188-292 °C (mean = 240 °C), and 118-198 °C (mean = 158 °C), respectively, and salinities of 5.3–14.2 (mean = 10.8) wt.% NaCl equiv., 2.8–10.7 (mean = 7.6) wt.% NaCl equiv., and 0.3–14.1 (mean = 2.6) wt.% NaCl equiv., respectively. The ore-forming fluids are characterized by middle-low temperature, low salinity, relatively reduced condition, and an H2O-NaCl ± CO2 ± CH4 system.The δ34S values (−5.25‰ to 0.50‰) and Pb isotopic ratios (206Pb/204Pb = 17.868–19.495, 207Pb/204Pb = 15.446–15.575, and 208Pb/204Pb = 37.350–38.491) suggest that the ore-forming materials came predominantly from a deep-seated magma source with a minor contribution of lower continental crust. The δ18OH2O and δDV-SMOW values of fluid inclusions in each metallogenic stage range from −6.1 to 5.6‰ and −66.8 to −53.9‰, respectively, suggesting the dominant role of magmatic water mixed with convectively circulating heated seawater during fluid evolution. Fluid cooling dilution, local boiling, and fluid mixing were considered as the main mechanisms of metal precipitation. The 40Ar-39Ar plateau age of hydrothermal muscovite from the late ore stage (S3) is 414.4 ± 0.4 Ma, which represents the upper limit age of shallow hydrothermal alteration and Au-Cu mineralization. It is also consistent with the Early Silurian polymetallic metallogenic event in the Kalatag district. The auriferous Huangtan and adjacent Cu-Zn-rich Huangtupo VMS deposits show obvious ore-forming element differences, and constitute a unique VMS metallogenic system in the Eastern Tianshan Orogenic Belt (ETOB), which provides an important research object and new insight for ore prospecting in the peripheral Gobi Desert area.

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.

The volcanogenic perspective on the world-class Chapada Cu-Au deposit in Central Brazil revisited

The Chapada deposit, located in the Neoproterozoic intraoceanic Mara Rosa Magmatic Arc, is a low-grade, world-class metallic concentration with a minimum endowment of 3.78 Mt Cu plus 7.76 Moz Au. Ore consists of pyrite-chalcopyrite disseminated mainly in early Neoproterozoic biotite-rich schist pertaining to a mafic-dominated volcanic-sedimentary sequence intruded by 884 to 865 Ma-old gneissic diorite-tonalite. The deposit was metamorphosed and isoclinally folded in a fold-and-thrust system under upper amphibolite facies conditions at 760-730 Ma, and underwent further metamorphism and deformation under greenschist facies conditions at 630-600 Ma, leading to difficulties to unravel its nature. Pre-metamorphic hydrothermal alteration includes an ore-bearing potassic biotitic core with haloes of phyllic (muscovite-pyrite-rich), argillic (quartz-muscovite-kyanite-bearing), advanced argillic (quartz-kyanite-rich), and propylitic (amphibole-epidote-bearing) alteration. Based on these features –– along with the identification of A- and D-type veinlets, and sulfur isotope results close to zero per mil - Chapada has been considered a porphyry-type deposit. This conception, from 1986, has gained general acceptance, whereas another early proposition, from 1989, of a volcanogenic nature for Chapada, has been practically dismissed. Nonetheless, the geologic setting of Chapada is permissive for volcanogenic deposits. Considering this, the volcanogenic perspective on Chapada is re-evaluated here. The exercise has been carried out by scrutinizing essential attributes of volcanogenic deposits searching for features comparable to those of Chapada. The outcome is that the evidence leading to the acceptance of the porphyry model for Chapada applies equally to support a volcanogenic interpretation. This situation probably reflects a shallow-crustal, sub-volcanic environment, where both deposit types share attributes as, e.g., epithermal-style high-sulfidation alteration. The picture obtained allows for the working hypothesis that a volcanogenic relationship exists between epidote-rich amphibolite source rocks in the west, and quartzitic cap rocks in the east, of Chapada to produce disseminated ore, with accompanying K-Al-Si-propylitic alterations and a magnesian zone made up by early-recognized gedrite-staurolite rocks. The situation envisaged is that ore deposition occurred in sub-seafloor conditions from a poorly focused hydrothermal upflow discharge of fluids from a convective system with magmatic contribution. The volcanogenic model for Chapada is reinforced by the recent discovery of active submarine volcanogenic Cu-Au systems with high-sulfidation silica-aluminous alteration, by the incidence of equally high-aluminous alteration in the 40 km-distant VMS-affiliated Zacarias Au-Ag-Ba deposit, and by the localization of the deposit in a regional zone of alteration, with a suggested exhalative contribution, that seems to fit the concept of favorable, or equivalent, ore horizon.

Hydrothermal monazite trumps rutile: Applying U-Pb geochronology to evaluate complex mineralization ages of the Katbasu Au-Cu deposit, Western Tianshan, Northwest China

Abstract The Tianshan orogenic belt hosts several world-class gold deposits and is one of the largest gold provinces on Earth. The Katbasu Au-Cu deposit in the Chinese Western Tianshan is hosted in a granite intrusion. Previous researchers have shown that the main gold ores formed much later than the ore-hosting granite. However, the formation age of Cu mineralization and its possible link to Au mineralization remain poorly understood. This paper reports detailed mineralogical studies, combined with zircon U-Pb, in situ hydrothermal monazite as well as rutile U-Pb ages to constrain the timing of Cu mineralization and its possible link to Au mineralization. The two main ore types in the Katbasu deposit include Cu-Au ores with pyrite-chalcopyrite veins that crosscut the granite and Au ores with massive pyrite and quartz as the main minerals. The Cu-Au ores are spatially associated with diorite that intruded the granite, and they are overprinted by massive gold ores. Detailed mineralogical studies show that chalcopyrite is the main Cu-bearing mineral in the Cu-Au ores, and it is closely associated with some native gold, monazite, and rutile. Secondary ion mass spectrometer (SIMS) U-Pb dating of zircon grains from the ore-hosting granite and mafic enclave yielded concordant ages of 354.1 ± 1.6 and 355.8 ± 1.7 Ma, respectively. The diorite that intruded the granite has a zircon U-Pb age of 352.0 ± 3.2 Ma. The trace element compositions of the monazite suggest they were formed by hydrothermal fluids rather than inherited from the ore-hosting granite. Hydrothermal monazite coexisting with chalcopyrite and native gold yielded a concordant age of 348.7 ± 2.3 Ma, and the W-rich hydrothermal rutile grains associated with the chalcopyrite yielded a U-Pb age of 345 ± 27 Ma, indicating an early Cu-Au mineralization event prior to the major Au mineralization (ca. 323–311 Ma). The formation time of early Cu-Au mineralization is consistent with the emplacement age of the diorite and may be of magmatic-hydrothermal origin, whereas the main Au has no genetic associations with magmatic rocks in the ore district and may belong to the orogenic type. Monazite geochronology provided a more reliable age constraint than rutile in the Katbasu Au-Cu deposit, and we suggest hydrothermal monazite has advantages over rutile in dating the complex mineralization ages of gold deposits.

Fluid inclusions, isotopes and mineralogy of the Kuruer epithermal Cu-Au deposit, Chinese Western Tianshan: Implications for ore genesis and exploration

The Kuruer Cu-Au deposit is located in the Wusun Range of Yili Block, Chinese Western Tianshan, where numerous epithermal Au, skarn Fe-Cu and porphyry Mo-Cu deposits have been recognized. Petrography, fluid inclusions, S-Pb-H-O isotopes, field emission-scanning electron microscopy (FE-SEM) plus energy dispersive spectrometer (EDS) and electron microprobe analysis (EMPA) have been carried out to constrain the genesis of the Kuruer deposit and its implication for further exploration. The minerlization is hosted by volcanic rocks and occur as veins and veinlets structurally controlled by NW-trending faults. Three ore-forming stages were recognized, including quartz-sulfides-bismuth-gold stage (I), quartz-chalcopyrite stage (II) and calcite-chlorite-chalcopyrite stage (III).Six types of fluid inclusions were identified in stage I quartz, including monophase vapor inclusions (type 1), liquid-rich biphase inclusions (type 2), vapor-rich biphase inclusions (type 3), H2O-rich CO2-H2O triphase inclusions (type 4), CO2-rich CO2-H2O triphase inclusions (type 5) and solid halite-bearing triphase inclusions (type 6), whereas only type 2 inclusions were recognized in stage II quartz and stage III calcite. Types 2, 3, 4 and 6 inclusions in stage I have homogenization temperature (Th) ranges of 184–359 °C, 209–252 °C, 250–319 °C and 229–263 °C, with salinity ranges of 4.1–8.5 wt% NaCleq, 5.9–6.9 wt% NaCleq, 1.0–6.0 wt% NaCleq and 32.7–33.9 wt% NaCleq, respectively. Type 2 inclusions in stages II and III have Th varying from 144 to 212 °C and 114 to 163 °C, with salinities of 0.2–6.7 wt% NaCleq and 0.1–3.1 wt% NaCleq, respectively.The in-situ δ34S values of sulfides in stage I range from −4.66 to 0.34‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of stage I chalcopyrite vary from 18.295 to 18.954, 15.568 to 15.673 and 38.109 to 38.817, respectively, which are consistent with those of Early Carboniferous Dahalajunshan Formation volcanic rocks and granitoids from the Wusun Range. The values of δ18OH2O-VSMOW calculated from δ18Oquartz and δDH2O-VSMOW of stage I quartz range from 0.0 to 2.4‰ and −118.6 to −109.3‰, respectively. These isotopic compositions indicate that both metals and sulfur were sourced from the hosting volcanic rocks and hidden causative pluton, while the initial ore-forming fluids were magmatic in origin, with increasing involvement of meteoric water with time.Evidence from mineralogy, mineral geochemistry and fluid inclusions indicates that the initial fluid phase separation triggered the precipitation of “invisible” gold within pyrite and chalcopyrite during stage I. Subsequently, the decrease of fS2 due to the escape of H2S(g) and sulfide precipitation and cooling caused the formation of liquid bismuth from solutions. The bismuth melts have scavenged Au in situ from the residual solutions, resulting in the formation of Bi-Au inclusions within the fractures and intergranular spaces of earlier pyrite. For stages II and III, dilution and cooling due to input of meteoric water facilitated the chalcopyrite precipitation. The Kuruer Cu-Au deposit is classified as a subepithermal mineralization associated with porphyries. Porphyry Cu-Au mineralization could have developed beneath the Kuruer and its vicinity.

The Glafirinskoe and related skarn Cu-Au-W-Mo deposits in the Northern Altai, SW Siberia, Russia: Geology, igneous geochemistry, zircon U-Pb geochronology, mineralization, and fluid inclusion characteristics

The Glafirinskoe and related skarn Cu-Au (+Mo, W) deposits represent an Early Paleozoic (Late Cambrian to very early Ordovician) mineralization in the Altaid Belt, also known as the Central Asian Orogenic Belt. They are associated with multiphase plutons of high-K calc-alkaline to shoshonitic rocks that are related to a low-degree partial melting of metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal ?) magma chamber and then by magma fractionation and emplacement at shallower crustal levels. Isotopic U-Pb zircon dating of the igneous rocks yields early Ordovician (ca. 480–478 Ma and 483 Ma) age. These rocks were emplaced in a continental magmatic arc after the Late Cambrian collision, in a post-collisional setting involving the stall and break-off of the subducting slab during the Late Cambrian to Early Ordovician.The deposits comprise prograde and retrograde skarns that are characterized by abundant andradite-rich garnet, which defines their oxidized type. Wider zones of potassic (quartz-K-feldspar) and calc-potassic (quartz-K-feldspar-calcite-garnet) alteration occur in the igneous rocks, with their further overprint by propylitic (with abundant scapolite) and phyllic (carbonate-phyllic) alteration. All these alteration assemblages bear abundant chalcopyrite and minor bornite. Phyllic alteration assemblages also contain various As, Sb, Pb, Zn, Co, Ni sulfides and sulfosalts, tellurides, Bi minerals, and native Au. Scheelite and/or molybdenite are locally present in some mineralized zones. The Cu-Au-Mo(-W) mineralization occurs as skarn orebodies that are spatially associated with porphyry-style alteration assemblages reflecting the high exploration potential for additional, but concealed, skarn-porphyry Cu-Au-Mo deposits in the vicinity.The retrograde skarn and potassic (calc-potassic) alteration assemblages were formed from high temperature (570–580 °C), high salinity, aqueous chloride magmatic-hydrothermal fluid, with its boiling and phase separation indicating hydrostatic conditions at a relatively deep (~6 km) skarn-porphyry environment. Propylitic alteration assemblages were formed at lower temperatures (~380–420 °C) from a Ca-Na-chloride, low salinity (~8 wt% NaCl-eq.) magmatic-hydrothermal fluid. Fluid inclusions in minerals from phyllic alteration assemblages indicate the influx of a CO2-rich fluid at about 270–290 °C and 1400 ± 50 bars and subsequent mixing with more saline (20 wt% NaCl-eq.) and cooler (~240 °C) hydrothermal fluids.

Inherited source affinity of Li and Hf isotopes for porphyry copper deposits from subduction and collisional settings

Porphyry Cu deposits can be classified at the global scale as oceanic subduction- and continental collision-types based on their tectonomagmatic settings. In order to further characterize the possible differences in the geochemical and isotopic features of these two types of porphyry Cu deposits, Li-Hf isotopes were investigated together with bulk rock major/trace element concentrations and geochronology, for porphyritic granitoids related with four porphyry Cu deposits. The Baogutu porphyry Cu-Au deposit, Xinjiang Province, China, and the Atlas porphyry Cu-Au deposit, Philippines, are taken to represent the oceanic subduction-type, whereas the Demingding porphyry Cu-Mo deposit, Tibet Province, China, and the Grasberg porphyry Au-Cu deposit, Indonesia, are taken as proxies for the continental collision-type. The Li isotopic compositions of the Baogutu granodiorite shows a limited range of + 3.2 to + 6.5‰ (avg. + 4.6 ± 1.7‰, n = 13) in δ7Li values, whereas the diorite from Atlas have δ7Li values of + 2.6 to + 7.7‰ (avg. + 5.9 ± 2.8‰, n = 16), i.e., slightly higher than the Baogutu granodiorites, probably reflecting the involvement of subducted marine sediments. The relatively homogeneous and MORB-like δ7Li values (~+3 to 5‰) of the Baogutu and Atlas porphyries, together with depleted zircon εHf(t) values for Baogutu (+11.8 to + 17.5, avg. + 14.5, n = 19) and Atlas (+7.1 to + 10.6, avg. + 9.0, n = 40), are suggestive of an affinity with oceanic plate, and/or partial melting of the mantle wedge in response to oceanic subduction. By contrast, the δ7Li values of the Demingding monzogranite and quartz porphyry, and the Grasberg quartz monzodiorite vary more broadly, ranging from −0.7‰ to + 10.3‰ (avg. + 2.5 ± 5.9‰, n = 19) and from −0.3 to + 7.3‰ (avg. + 3.7 ± 4.6‰, n = 8), respectively. These two localities also show variable zircon εHf(t) values ranging from −5.4 to + 5.7 (avg. + 2.8, n = 20) and from −20.0 to −1.0 (avg. −10.7, n = 42), respectively. The large variations of δ7Li and εHf(t) values at Demingding and Grasberg are generally similar to those of mid- to lower continental crust (δ7Li ~+3.3‰ and εHf(t) −20.0 to + 5.7), and are thus consistent with their source regions, which are interpreted to reflect continental collisional settings. The Li-Hf isotopic compositions of the four porphyry intrusions show that tectonic settings have dominant effects on the Li-Hf isotopic compositions of the related magmatic rocks, prior to any redistribution by porphyry Cu deposits-related hydrothermal alterations, suggesting that Li-Hf isotopes systematics can partly act as tracers of the source regions related to tectonic settings.

The geophysical signature of Oyut deposits, Oyu Tolgoi, Mongolia

The well-known Oyu Tolgoi Cu-Au group deposits can be divided into three main deposits: Hugo Dummett deposit (Hugo North and Hugo South), Oyut deposits (South Oyu, Southwest Oyu and Central Oyu), and Heruga deposit in the south. These deposits sit along 26 km long, north-northeast trending belt termed as the Oyu Tolgoi trend. This paper reviews investigations on geophysical signatures of the South Oyu, Southwest Oyu and Central Oyu deposits and compares geophysical models of the mineral deposits with their lithology, alteration, mineralization, and structures. A variety of datasets including induced polarization, ground magnetic, gravity survey are used in the study and generated inversion products of ground magnetic and gravity data with integrated interpretation. Typical responses from the Oyut deposits are: up to 0.1 mGal positive gravity anomaly above background, 100–200 nT low or high magnetic anomaly compared to background depending on the geological situations, and from 12 mV/V to 30 mV/V chargeability anomalies and low resistivity signatures from 100 ohm.m to 400 ohm.m. The interpreted geological-geophysical models of porphyry Cu-Au deposits presents in this study have emphasis on integrated interpretation of geophysical techniques, and inversions of gravity and magnetic data in gold rich porphyry copper system.