Porphyry Cu-Au Mineralization Research Articles

A New Anisotropic Singularity Algorithm to Characterize Geo-Chemical Anomalies in the Duolong Mineral District, Tibet, China

With the increasing exploitation of mineral resources by humans, exploring non-traditional areas for hidden resources such as deep earth and sediment-covered regions has become a significant challenge in the field of mineral exploration. Geochemical data, as a crucial information carrier of geological bodies, serves as one of the direct and effective sources for quantitative analysis of regional geological evolution and mineralization prediction studies. It plays an indispensable role in geographic information system (GIS)-based mineral exploration. Due to the neglect of spatial distribution characteristics and the variability of statistical features with spatial metrics in traditional statistical methods, this paper employs fractal/multifractal and the local singularity analysis to identify geochemical anomalies from background and characterize geochemical distributions associated with porphyry Cu-Au mineralization in the Duolong mineral district, Tibet, China. A novel algorithm for estimating the singularity index, which takes anisotropy into consideration, is proposed and practically applied to the Duolong district. By comparing with the isotropic singularity index, this new method objectively identifies anisotropic geochemical signatures and investigates non-linear behaviors of ore-forming elements, making it more practical and effective in geo-anomaly extraction. Furthermore, the current method is capable of indicating variations in geochemical distributions at different scales through directional arrows marking analytical windows. The summed-up direction of these multi-scale vectors effectively demonstrates migration trends of ore materials at each location within the study area. The new method can pinpoint the location of ore-forming element accumulation and migration directions, unlocking valuable insights from complex datasets. This promises to revolutionize our understanding of how minerals are formed and distributed within the Earth’s crust.

Petrogenesis and geochronology of the bronze fox porphyry Cu-Au deposit: Implications for the geodynamic evolution of the Gurvansaykhan Island arc, southern Mongolia

ABSTRACT A diversity of Devonian-Carboniferous volcanic arcs and granitoid intrusions are exposed in the Gurvansaykhan arc terrane of southern Mongolia. Several giant porphyry Cu-Au-Mo deposits are associated with intrusions within these arcs. The Bronze Fox deposit located in the central part of the Gurvansaykhan arc terrane is an example of a potentially economic deposit with affinity of adakite-like granitoid porphyry (i.e. 428 Mt grading 0.26% to 0.30% Cu for up to 2,437 Mlb of copper and 0.84 Moz gold). The genesis and magmatic evolution of the causative rocks of the Bronze Fox porphyry Cu-Au hosting rocks are poorly understood, and different models are still under debate. In the current study, we present new field observations and petrographic, geochemical, and geochronological data to describe the magmatic evolution and geodynamic settings. In addition, the mineral chemical data are reported from some selected rock-forming minerals to identify crystallization conditions of the studied rock suites by employing geothermobarometric methods. Zircon chronological data reveal the emplaced age at 331 ± 3.4 Ma for the volcanic lava, followed by mineralized granodiorite and monzodiorite with intruded ages of 326.5 ± 3.4 Ma and 326.5 ± 2.7 Ma, respectively. The studied intrusive and extrusive rocks are high-K-alkaline and metaluminous, characterized by high Mg#. They are enriched in large ion lithophile elements (Sr and Ba) and light rare earth elements (LREEs) and depleted in high field strength elements (Nb, Ta, and Ti) and heavy rare earth elements (HREEs). The highly mineralized granodiorite intrusion yields zircon crystallization temperatures ranging from 631.8 to 779.4°C, and the monzodiorite intrusion, which contains relatively low-grade mineralization, has a wider range (599.0 to 803.4°C). The formation pressures of the former range from 0.5 to 0.2 kbar, which is equivalent to a depth of 1.38 km based on amphibole geochemical calculations. The results of mineral chemistry indicate that the unmineralized diorite unit was formed under medium pressure (~50 MPa) and high temperature (~750°C) at depths of 6.8 to 7.5 km. Similarities in geochemistry and petrographic features suggest that the igneous rocks probably originated from a similar magma source (i.e. from the melting of ancient oceanic crust and sediments) but experienced different degrees of partial melting or mixing with lower juvenile crust melts. The estimated fO2 values obtained by amphibole chemistry in the granodiorite and quartz diorite of the Bronze Fox copper-gold mineralization range from −13.0 to −11.8 and −13.2 to −10.8, respectively, confirming that these igneous rocks probably crystallized under relatively oxidized conditions above the nickel-nickel oxide (NNO) buffer. Such results yield an overall range between NNO +2.6 and NNO +1.4, which are characterized by high oxygen fugacities and high Ce4+/Ce3+ ratios that reflect oxidizing magma, thus indicating quite promising potential for porphyry Cu-Au mineralization in the region. Based on the findings of this work, we suggest a new tectonic model of arc magmatism that is a response to the subduction of the Paleo-Asian Ocean in the early Carboniferous period.

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 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 multiple mineralizations and geodynamic settings of the Laozuoshan Cu–Au deposit in the Jiamusi Massif, NE China: Zircon U–Pb geochronological, elemental and Hf isotopic geochemical evidence

Situated in the centre of the Jiamusi Block, the Laozuoshan deposit is a large-sized deposit with composite of vein and lenticular Au orebodies and veinlet-disseminated Cu-Au orebodies. It is characterized by two types of mineralization, skarn Au mineralization and porphyry Cu-Au mineralization. The former occurs along the contact zone between granodiorite and Proterozoic metamorphic rocks in the eastern and central ore zones, while the latter is hosted in granodiorite porphyry and diorite in the western ore zone. In this study, we present the results of geochronological and geochemical analyses of these rocks which show the following features. (1) Zircon U–Pb dating results show that the ages of granodiorite, diorite and granodiorite porphyry are 264.6±2.6 Ma, 103.2±1 Ma and 104.6±1.8 Ma, respectively. (2) Whole-rock elemental compositions indicate that the granodiorite shows potassium-rich adakitic rock properties, and the diorite has typical island arc calc-alkaline magmatic properties. They are all characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs). (3) The in-situ Hf isotope analysis results show that the granodiorite and diorite have εHf(t) values of −3.7 to −8.7 and −0.4 to 10.7, respectively, corresponding to TDMC ages of 2040–2500 Ma and 630–1650 Ma, respectively. These results indicate two periods of mineralization in the Laozuoshan deposit. Skarn mineralization occurred in the late Permian and was a result of metasomatism between partial melting magma that originated from thickened Paleoproterozoic lower crust and Proterozoic marble. Porphyry mineralization took place in the Early Cretaceous and was a result of the shallow emplacement of mid-Neoproterozoic mantle-derived magma with the addition of crustal materials. In terms of geodynamic settings, skarn Au and porphyry Cu-Au mineralization occurred in a compressional setting formed during the gradual closure of the Paleo-Asian Ocean, and a crustal-thinning setting formed from Eurasian Plate-ward subduction, retreating, and rollback of the Paleo-Pacific Plate, respectively.

Porphyry Cu-Au prospectivity modelling using semi-supervised learning algorithm in Dehsalm district, eastern Iran

Porphyry Cu-Au prospectivity modelling using semi-supervised learning algorithm in Dehsalm district, eastern Iran

The Late Triassic-Jurassic magmatic belt and its implications for the double subduction of the Neo-Tethys Ocean in the southern Lhasa subterrane, Tibet

The southern Lhasa subterrane (SL), located between the Yarlung-Tsangpo Suture Zone and the Luobadui-Milashan Fault, preserves a complete Late Triassic-Jurassic magmatic record related to Neo-Tethys Ocean evolution. Therefore, the SL is key to understanding the geodynamic processes occurring during the controversial early-stage evolution of this ocean. Here, we present new zircon U–Pb data and a detailed synthesis of geochronological, geochemical, and Sr-Nd-Pb-Hf isotope data from Late Triassic-Jurassic igneous rocks in the SL to constrain the early-stage evolution of the Neo-Tethys Ocean. The data suggest that these igneous rocks can be divided into two groups. Group 1 magmatism lasted from ca. 243 Ma to 145 Ma, with three stages at ca. 243–200 Ma, 199–165 Ma, and 164–145 Ma, and is characterized by high positive εHf(t) and εNd(t) values and low (206Pb/204Pb)t, (207Pb/204Pb)t, and (208Pb/204Pb)t values. Group 2 magmatism lasted from ca. 225 Ma to 160 Ma, with two stages at ca. 225–190 Ma and 189–160 Ma, and is characterized by lower εHf(t) and εNd(t) values and higher (206Pb/204Pb)t, (207Pb/204Pb)t, and (208Pb/204Pb)t values than Group 1. We suggest that the Triassic-Jurassic magmatic belt in the SL was controlled by double subduction; the Group 1 igneous rocks formed in an intraoceanic arc setting, while the Group 2 igneous rocks formed in a continental margin arc setting. An integrated interpretation of magmatism, ophiolites, sedimentary rocks, and metallogenesis within the SL constrains the geodynamic processes that occurred during the early-stage tectonic evolution of the Neo-Tethys Ocean as follows. (1) During the Middle-Late Triassic, the initiation of intraoceanic subduction between Gondwana and the SL produced the ~243–200 Ma magmatism of Group 1. Subsequently, a new continental margin subduction system formed on the southern margin of the SL, which induced the ~225–190 Ma magmatism of Group 2. (2) With ongoing subduction, slab roll-back of the intraoceanic subduction system resulted in the ~199–165 Ma magmatic flare-up of Group 1. Additionally, slab roll-back of the continental margin subduction system resulted in extension of the overriding plate and formed the ~189–160 Ma magmatic flare-up of Group 2. (3) Finally, the slab roll-back associated with intraoceanic subduction transitioned to flat subduction and produced the 164–145 Ma magmatism of Group 1, and porphyry Cu-Au mineralization developed during the stress transition period. In summary, the double subduction system in the early-stage evolution of the Neo-Tethys Ocean controlled the tectonic, magmatic, and metallogenic events in the SL.

Nature and Origin of Zoned Polymetallic (Pb-Zn-Cu-Ag-Au) Veins from the Bingham Canyon Porphyry Cu-Au-Mo Deposit, Utah

Abstract Polymetallic veins (Pb-Zn-Cu-Ag-Au) at the world-class Bingham Canyon, Utah, porphyry Cu-Au-Mo deposit have long been recognized, but poorly understood. They are laterally zoned outward from the center of the porphyry deposit transitioning from Fe-Cu to Pb-Zn-Cu-Ag-Au mineralization. Physical and chemical characterization of these polymetallic veins provide insight into the origin, timing, and controls of ore deposition. These sheared, sulfide-rich, NE/SW- trending veins are dominated by pyrite and multiple generations of quartz, with lesser amounts of other sulfide and gangue minerals. Gold (0.27–4.61 ppm) provides the most value to the ore, though the veins contain substantial Cu and Ag as well. Host rocks include Eocene monzonite and Paleozoic limestone and quartzite—all of which can contain economic ore lodes. Associated alteration is predominantly sericitic and argillic, with mineralization in wall rocks restricted to 1.5 m from the vein margins. Mineral assemblages vary with distance from the center of the main porphyry Cu-Au-Mo deposit and the modal abundances are dependent on the host rock. The appearance of both galena and sphalerite (and tennantite to an extent) occur along a boundary that creates a halo around the center of the associated porphyry deposit. This is accompanied by a shift in metal ratios and an increased concentration of chalcophile trace elements in sulfides from the polymetallic veins as determined by electron microprobe analyses (EMPA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Significant hosts of Ag include galena and tennantite, and Cu is hosted primarily in chalcopyrite, tennantite, and sphalerite. The main host of Au could not be determined, but Au could be focused along fractures or hosted in inclusions found in pyrite. The δ34S values of vein pyrite have a narrow range (2.3–3.4‰) suggestive of a magmatic source, whereas δ18O of quartz is more variable (11.5–14.0‰). These values are similar to several other polymetallic vein deposits associated with porphyry Cu deposits. This can be explained by fractionation of magmatic fluids at lower temperatures (350°–250°C) and/or mixing with exchanged 18O-rich meteoric water. Ore grades (Cu, Ag, Au) improve with distance from the center of the porphyry deposit; however, this is accompanied by higher concentrations of deleterious elements (e.g., Pb, As, Bi) for downstream processing. These polymetallic veins were created sequentially throughout the formation of the deposit. Initial joints in the sedimentary rocks probably formed as a result of emplacement of a barren equigranular monzonite intrusion, with continued dilation and propagation in all host rocks with each subsequent intrusion. The northeast orientation of the joints was controlled by the regional stress field, which is more apparent distal to the center of the Bingham deposit. Vein mineralization appears to postdate all intrusions and the porphyry Cu-Au mineralization; however, it may be related to the late fluids responsible for Mo mineralization in the main porphyry orebody that followed intrusion of the quartz latite porphyry. Quartz-sericite-pyrite mineralization associated with the veins precedes galena-sphalerite-pyrite mineralization. This was followed by late precipitation of chalcopyrite and tennantite and late normal faulting.

Genesis of the Xiaoyuzan epithermal Au deposit in the Yelimodun volcanic basin, Western Tianshan, China: Constraints from geology, geochronology, isotopes and mineralogical compositions

The Tulasu and Yelimodun volcanic basins are two important Au districts in the northwestern Chinese Western Tianshan. Two large Au deposits have been discovered in the Tulasu basin, whereas only small-sized Au deposits and prospects, including the Xiaoyuzan deposit, were found in the Yelimodun basin. The purpose of this study is to examine the genesis of the Xiaoyuzan deposit and its implications for further exploration through geological, geochronological, geochemical and mineralogical studies of the host rocks and ores. The orebodies are mineralized veins and veinlets and are structurally controlled by NW- and NNW-trending faults within the Lower Carboniferous Dahalajunshan Formation volcanic rocks (DF). Sulfides are abundant (10–20 vol%) in the ores and consist of pyrite, sphalerite, galena, chalcopyrite and minor tetrahedrite. Electron microprobe analysis (EMPA) indicates that pyrite and sphalerite are both auriferous. Three ore-forming and alteration stages were distinguished: (I) quartz-pyrite stage with silicification and propylitization, (II) quartz-polysulfide stage with silicification and phyllic alteration, and (III) quartz-carbonate stage with carbonatization.The mineralization age is constrained to 357–331 Ma by a LA-ICP-MS U-Pb age of 357.3 ± 4.0 Ma for zircon from the ore-hosting tuff and the unconformably overlying Lower Carboniferous Aqialehe Formation containing fossils of the Visean period. The zircons from the tuff have highly positive εHf(t) values ranging from 5.9 to 10.1, indicating a magma source of depleted mantle with limited crustal contribution. The values of δ18OH2O-VSMOW calculated from δ18Oquartz and δDH2O-VSMOW measured from fluid inclusions of stage II quartz range from −4.0‰ to −2.9‰ and −117‰ to −109‰, respectively. The values of δ13CCO2 calculated from δ13Ccal and δ18OH2O calculated from δ18Ocal range from −1.6‰ to −1.4‰ and −9.8‰ to −2.7‰, respectively. The in-situ δ34S values range from 2.6‰ to 3.7‰ for pyrite and 2.7‰ to 4.1‰ for sphalerite, respectively. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of pyrite vary from 18.196 to 18.253, 15.564 to 15.642, and 38.063 to 38.300, respectively, similar to those of ore-hosting DF and granites from the Tulasu-Yelimodun volcanic belt. The above geochemical characteristics suggest that the ore-forming fluids were mixtures of magmatic and meteoric waters, and the metals and sulfur may have been derived partly from magmatic fluids generated from the hidden causative intrusions and partly from the hosting volcanic rocks. These, together with high sulfide abundance and development of sulfide assemblages representing intermediate-sulfidation state, suggest that Xiaoyuzan is an intermediate-sulfidation epithermal Au deposit. Considering the limited erosion for the Au mineralization within the interior of Yelimodun basin and close spatio-temporal relationship between intermediate-sulfidation and porphyry mineralization, it is inferred that there may be concealed porphyry Cu-Au mineralization underneath the Xiaoyuzan deposit and its vicinity.

Genesis of Cretaceous igneous rocks and its related large scale porphyry Cu-Au mineralization in Chating, the Middle-Lower Yangtze River Metallogenic Belt: The geochemical constrains

The newly discovered large Chating porphyry Cu–Au deposit is associated with early Cretaceous intrusive rocks in the Middle-Lower Yangtze River Belt (MLYRB), eastern China. Two types of intrusive rocks in the Chating area have been identified, i.e., the quartz-diorite porphyry, related to the Cu–Au mineralization, and the diorite porphyry that is ore-barren. Zircon LA–ICP–MS U–Pb dating yields 145–136 Ma for the Chating intrusions. They both belong to High-K calc-alkaline series, with enrichments of large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletions of high field-strength elements (HFSEs) and heavy rare earth elements (HREEs), and no or slightly negative Eu anomalies. The quartz-diorite porphyry shows high Sr contents and Sr/Y ratios; low MgO, Cr and Ni contents; medium (La/Yb)N and Mg# (34.6–54.6) and low K2O/Na2O (<1) values; decoupling of Sr/Y and (La/Yb)N; and low Th/U (3.49–6.08) values, thus exhibiting characteristics of slab-derived adakitic rocks. In addition, it has slightly enriched Sr–Nd–Hf isotopes ((87Sr/86Sr)i = 0.70655–0.70717, εNd(t) = −6.9 to −8.8, and εHf(t) = −7.6 to −10.6) and high radiogenic Pb isotopes ((206Pb/204Pb)i = 18.22–18.70, (207Pb/204Pb)i = 15.63–15.66 and (208Pb/204Pb)i = 38.49–38.97), reflecting the involvement of subducted sediments in the magma source. Therefore, the fertile quartz-diorite porphyry was most likely generated by the partial melting of the slab-derived, subducted sediments and a partial degree of metasomatized mantle-derived magma with crustal assimilation. As to the barren diorite porphyry, it has similar Sr–Nd–Pb isotope and trace element features as the fertile adakitic samples. However, it shows relatively lower SiO2 contents; high contents of MgO (3.89–4.06 wt%), Cr and Ni (avg. 47.6 ppm and avg. 15.01 ppm); high Mg# (51.2–69.8); and more enriched Hf isotope characteristics (−8.5 to −12.9), which imply that this barren diorite porphyry could be generated from the partial melting of enriched metasomatised lithospheric mantle assimilated with old continental crust materials. The δ34S values of the pyrite and chalcopyrite of the ores in Chating indicate a magmatic-derived source, resembling other porphyry-skarn Cu–Au deposits in the MLYRB. The fertile Qtz-diorite porphyry adakitic rocks are characterized by higher oxygen fugacities than the barren diorite porphyry, which are closely related with the partial melting of the subducted oceanic slab in an oxidizing environment, thus making them favorable for Cu–Au mineralization.

Early sulfide saturation is not detrimental to porphyry Cu-Au formation

AbstractOre-forming magmas are commonly considered to have been unusually metal rich. Because Cu and Au are strongly chalcophile, early sulfide saturation has been regarded as detrimental to porphyry Cu-Au mineralization. Here we demonstrate, based on amphibole-rich cumulate xenoliths and amphibole megacrysts from the Tongling porphyry(-skarn) Cu-Au mining district in southeastern China, that this view is not necessarily correct. Age data combined with petrological and geochemical evidence suggest that the mineralizing magmas at Tongling underwent significant fractional crystallization of amphibole, clinopyroxene, and magmatic sulfides in the middle to lower crust. The fact that the silicate melts nevertheless were able to produce substantial porphyry(-skarn) Cu-Au deposits implies that the formation of metal-rich cumulates at depth was not detrimental to their fertility. On the contrary, the common association of porphyry Cu (Au, Mo) deposits with high-Sr/Y magmas suggests that amphibole fractionation at depth even promotes the mineralization potential, despite the likely loss of metals.

Petrogenesis and geochronology of Cenozoic intrusions in the Poboya and Sassak gold and copper districts in Western Sulawesi, Indonesia: Implications for the mineralization processes and magma sources

This paper presents petrographic, geochemical and geochronological data for intrusions that area spatially related to gold and copper mineralization in the Poboya and Sassak areas in western Sulawesi. These data coupled with previous studies are then used to discuss the implications for the mineralization processes and magma sources. In the Poboya area, gold-bearing quartz veins are related to high-K calc-alkaline granitoids that display a reduced nature, whereas in Sassak area porphyry Cu-Au mineralization is associated with monzonitic intrusions intruded by gabbroic and syeno-dioritic intrusions. Granitoids from Poboya have a metaluminous to mildly peraluminous character (mol. Al2O3/mol. CaO + Na2O + K2O = 1.0–1.04) and include both I-type and S-type varieties. The Poboya and Sassak intrusions have Rb-Sr isotopic ages of 3.94 ± 0.03 Ma, 2.97 ± 0.05 Ma and 10.7 Ma ± 0.11 Ma, respectively, which are interpreted to closely approximate the time of emplacement into their country rocks. Zircon U-Pb dating of gabbro and diorite from the Sassak area yielded crystallization ages of 10.8 ± 0.16 Ma and 10.6 ± 0.19 Ma, respectively. New Sr isotopic data (87Sr/86Sr ratios >0.709) are consistent with previous data obtained from the central and northern parts of western Sulawesi, Gondwana-derived Mesozoic granitoids and enriched-mantle or lower crustal equivalents are the most likely magma sources for the Poboya and Sassak igneous rock suites, respectively. The Poboya deposit is interpreted to represent the distal part of a reduced intrusion-related gold system.

Multiple episodes of Late Paleozoic Cu-Au mineralization in the Chatkal-Kurama terrane: New constraints from the Kuru-Tegerek and Bozymchak skarn deposits, Kyrgyzstan

The Chatkal-Kurama terrane is the most fertile region for porphyry-skarn Cu-Au mineralization (~31 Mt Cu and 2300 t Au) in the West Tianshan, even though in the Chatkal range of Kyrgyzstan only limited studies have been conducted. We present the first robust geochronological and geochemical data for the important Kuru-Tegerek and Bozymchak skarn Cu-Au mineralization and related magmatism in the Chatkal region. Consistent zircon SHRIMP U-Pb and molybdenite Re-Os ages reveal that the Kuru-Tegerek skarn Cu-Au deposit formed at about 325 Ma (zircon U-Pb, 326 ± 3 Ma; molybdenite Re-Os, 323 ± 2 Ma), and the Bozymchak skarn Cu-Au deposit formed at about 305 Ma (zircon U-Pb, 304 ± 2 Ma; molybdenite Re-Os, 305 ± 3 Ma). The new ages, in combination with previous data, suggest four pulses of Cu-Au mineralization and related magmatic events in response to changing dynamic settings. The ca. 325 Ma Kuru-Tegerek in the NE Chatkal is associated with low- to medium-K calc-alkaline tonalite porphyry derived from Precambrian continental crust (εNdt = −16.3 to −20.0, T2DM = 2.4–2.7 Ga) in an early subduction stage. The ca. 315 Ma time slice records the peak of tremendous porphyry Cu-Au mineralization (Kal’makyr and Sarycheku) and voluminous magmatism with high-K calc-alkaline to shoshonite series rocks of mixed origin of continental crust and metasomatized mantle-derived that denote a compressive regime due to flat subduction. The ca. 305 Ma Bozymchak Cu-Au skarn deposit is also associated with a high-K calc-alkaline intrusion (granodiorite porphyry) and supposedly marks the cessation of supra-subduction magmatism. The Early Permian Kochbulak high sulfidation epithermal Au deposit is related to a stratovolcano setting that is closely associated with post-collisional shoshonitic rocks related to slab breakoff. Collectively, the Cu-Au mineralization in the Chatkal-Kurama terrane formed during a 30 My period related to multiple magmatic pulses in a geodynamic setting evolving from early over peak to late subduction to post-collisional slab breakoff.

Modeling geochemical anomalies of stream sediment data through a weighted drainage catchment basin method for detecting porphyry Cu-Au mineralization

Stream sediment surveying is a geochemical sampling method which is typically applied in the preliminary stages of mineral prospecting. Both continuous and discrete mapping approaches have been proposed to delineate geochemical anomalies at large scales using stream sediment samples. We aim to enhance the efficiency of a recent discrete mapping method called Weighted Drainage Catchment Basin (WDCB) which is independent of sampling sites and density, and has an advantage given that samples may not be uniformly distributed throughout the study area. The Enhanced WDCB (E-WDCB) method can be applied to calculate the weight of each catchment basin using different geochemical parameters such as factor scores. Our study focuses on the factor analysis of three datasets from the Bathurst region, New South Wales, Australia, with different numbers of samples. Different associations of the elements revealed by the factor analysis show that such analyses highly depend on the contributing samples and elements. We propose the Catchment Basin Score (CBS) index to delineate the suitability of sampling in each catchment basin. This index can also be applied to integrate the components resulting from several multivariate analyses on different datasets in a same area. The prediction-area plots show that our proposed method is able to predict a higher percentage of porphyry CuAu occurrences in a smaller area compared to other canonical methods, e.g. the median of factor scores in each catchment basin. We demonstrate that prospective areas for porphyry CuAu mineralization using the proposed discrete mapping method are also well correlated with volcanic and intrusive rocks.

Petrogenesis of Cenozoic high–Sr/Y shoshonites and associated mafic microgranular enclaves in an intracontinental setting: Implications for porphyry Cu-Au mineralization in western Yunnan, China

Cenozoic high–Sr/Y shoshonites in western Yunnan, China, are spatially and temporally associated with porphyry deposits and mafic volcanic rocks that formed at a post–collisional setting. However, the petrogenesis of these rocks and the origins of the associated mineralization remain unclear. Here we present new geochemical data for the high–Sr/Y shoshonites and associated mafic microgranular enclaves (MMEs) in the Jinshajiang–Ailaoshan mineralization belt, which formed as a result of India–Asia collision during the Cenozoic. Both fertile and barren shoshonitic porphyries were emplaced during the Eocene–Oligocene (32–37 Ma) and are characterized by enrichment in large–ion lithophile elements (LILE), depletion in high field strength elements (HFSE), high K2O (4–6 wt%), Sr contents (674–1370 ppm), and low Y contents (7–18 ppm). The barren Zhanhe, Yongsheng, Songgui, and Jianchuan, and fertile Machangqing (Cu–Au–Mo mineralization) porphyry intrusions have variable zircon εHf(t) values of −6 to +9 and old TDM2 ages of 1433 to 900 Ma. However, the barren Shigu porphyry intrusion yields relatively positive zircon εHf(t) values (−4 to +8) and younger TDM2 ages (903–631 Ma). These features indicate that the Shigu intrusion was derived from late Permian juvenile lower crust, and the other high Sr/Y shoshonites were derived mainly from Neoproterozoic juvenile lower crust. Fertile and barren porphyries have variable whole–rock εNd(t) values (−5 to −0.7) and (87Sr/86Sr) i ratios (0.70595–0.70788) that are within the range of coeval mafic magmas in western Yunnan. The MMEs comprise mafic enclaves and andesitic enclaves that formed during the Eocene (34–35 Ma) and have spheroidal shapes, igneous textures and contain acicular apatites. This indicates that the MMEs are globules of coeval mafic magma that was injected into and mixed with the host shoshonitic magma. The enclaves show low TiO2 contents (0.7–0.8 wt%), high MgO (6–9 wt%), Cr (184–450 ppm) and Ni contents (98–157 ppm), positive LILE anomalies, marked negative HFSE anomalies, a narrow range of εNd(t) values (−1.2 to −0.6), and (87Sr/86Sr) i values of 0.70556–0.70635. The andesitic enclaves show adakitic geochemical affinities and have similar zircon εHf(t) values (−2.7 to +2.5) to the host porphyries, whereas, the mafic enclaves have relatively negative zircon εHf(t) values (−8.7 to +1.5), similar to enriched mantle. These evidences suggest the high−Sr/Y shoshonites were produced by partial melting of juvenile lower crust mixed with ultrapotassic or potassic mafic magmas as represented by the andesitic enclaves. The mafic enclave melts were derived from enriched mantle metasomatized by slab–derived fluids, which elevated the Mg#, Cr, Ni contents of the host porphyries at Machangqing, Zhanhe and Yongsheng.Zircon saturation temperatures (TZr) of the high–Sr/Y shoshonitic rocks range from 735 to 777 °C and indicate the shoshonites were derived mainly from water–fluxed melting of lower crust. The Manchangqing fertile intrusion had a high oxidation state (zircon Ce4+/Ce3+ = 38–180, average = 91) and was derived by mixing between juvenile lower–crustal melts and voluminous coeval lamprophyres. In contrast, the barren Jianchuan, Songgui, Shigu, Yongsheng and Zhanhe high–Sr/Y shoshonites formed by partial melting of juvenile lower crust and some mixing with mafic lavas, and are characterized by low oxygen fugacity (zircon Ce4+/Ce3+ = 0.5–77, average = 20). As such, we suggest the mafic magmas triggered water–fluxed, moderate–degree partial melting of the lower crust and caused amphibole breakdown during melting. This process could not provide enough water for the formation of porphyry Cu-Au deposits in western Yunnan, and therefore formed low–fO2, relatively low–H2O, and barren high–Sr/Y magmas. However, ultrapotassic magmas (e.g., lamprophyres) with high H2O are able to trigger intense water–fluxed, partial melting of metal–fertilized lower crust, which generated high–fO2, relatively high–H2O, fertile, high–Sr/Y shoshonitic magmas in this intracontinental setting.

Apatite and zircon geochemistry of Jurassic porphyries in the Xiongcun district, southern Gangdese porphyry copper belt: Implications for petrogenesis and mineralization

The Xiongcun district, a unique area where oxidized porphyry copper-gold deposits (OPCD) and reduced porphyry copper-gold deposits (RPCD) coexist, is located in the central part of the Gangdese porphyry copper belt (GPCB) in Tibet, China, and hosts the only known mineralization related to the Neo-Tethyan oceanic subduction. Apatite and zircon major and trace elements, in situ oxygen isotopes in zircon from fertile quartz diorite porphyry (QDP) of the No. I deposit, fertile hornblende quartz diorite porphyry (HQDP) of the No. II deposit, and barren hornblende quartz diorite porphyry with coarse quartz eyes (QQDP) in the Xiongcun district were determined by EPMA, LA-ICP-MS, and SHRIMP II ion microprobe to investigate the petrogenesis, magma oxidation state, and mineralization differences between the No. I and No. II deposits, as well as the potential of apatite as a metallogenic indicator. The results from this study show that a combination of REE, Ti, oxygen isotopes, and the Th/U ratios in zircon and REE as well as Sr in apatite can be used to track the magma compositions and crystallization histories in porphyry systems. Multiple indicators, including the apatite SO3 content, apatite Mn oxybarometer, and zircon Ce4+/Ce3+ ratio, indicate that (1) the parental magmas of fertile QDP and HQDP containing Cu and Au mineralization were more reduced than that of barren QQDP; (2) despite barren QQDP having higher oxygen fugacity than QDP and HQDP, the lower Cu and water contents in the magma result in a lower potential for ore formation; and (3) the similar oxidation states of QDP and HQDP show that the mineralization differences between RPCD (No. I deposit) and OPCD (No. II deposit) were not caused by the oxidation states of the magmas but were likely caused by the different processes of hydrothermal fluid evolution. Apatite grains from fertile porphyries (QDP and HQDP) have much higher Cl/F ratios than those from barren porphyry (QQDP), indicating that the Cl/F ratio of apatite can be used as a proxy for porphyry Cu-Au mineralization related to the Jurassic porphyry intrusions in the Gangdese porphyry copper belt.

Fractal/multifractal analysis in support of mineral exploration in the Duolong mineral district, Tibet, China

The study area, Duolong mineral district, Tibet, China is not a well-developed area but has received attention in recent years due to its considerable production of Cu-Au resources. This paper utilizes fractal/multifractal analytical techniques to gain insights to the geological environment, metallogenesis of ore deposits, as well as mineral exploration in this area. Porphyry Cu-Au mineralization related elements and fault-activity indicator elements from stream sediments geochemical data are integrated by log-ratio transformation-based principal component analysis, the results of which are further analyzed by singularity theory and spectrum-area model. Identified geochemical anomalies spatially coincident with structural framework are not only suggestive of the presence of mineralization but also suggest genetic relationship between mineralization and regional fault structures. The usefulness of the singularity theory and spectrum-area model, as two mature and effective geo-information extraction methods in the fractal/multifractal context, is compared based on their theoretical foundations and practical applications. It was found that, in the study area, the spectrum-area model is more effective for characterizing self-similar spatial patterns caused by specific geological processes, while the singularity theory can inform about geochemical behaviours of elements or element associations reflecting a series of geological processes. Compared to the results of the singularity technique, the results of spectrum-area modeling results, especially the geochemical background patterns, are more robust for interpreting structural framework and metallogenic background of the area. This study infers mesh-like structural control on porphyry mineralization, and identified background geochemical patterns of multi-element association by fractal/multifractal analyses further provide indirect and/or proxy geo-information of the mesh-like structure to support of mineral exploration in the Duolong mineral district.

Constraints of magmatic oxidation state on mineralization in the Beiya alkali-rich porphyry gold deposit, western Yunnan, China

The Beiya gold deposit is the biggest Cenozoic gold deposit in the Jinshajiang-Ailaoshan alkali-rich porphyry metallogenic belt within the Sanjiang region. Porphyry intrusions are widely distributed at the Beiya deposit. In this study, we investigate the lithological and geochemical characteristics of the Beiya alkali-rich porphyries and compare zircon Ce4+/Ce3+ ratio and magmatic oxygen fugacity (fO2) of the ore-bearing and ore-barren porphyries. The research shows that the ore-bearing intrusion is monzogranite porphyry in the area of Wandongshan, Hongnitang and their surrounding ore blocks. The intrusions have similar U-Pb zircon ages of ∼36 Ma, and all the porphyries display patterns of enriched LREEs and depleted HREEs. The ore-bearing monzogranite porphyry is characterized with high zircon Ce4+/Ce3+ ratio (average of 80) and high fO2 value (average of △FMQ = +3.7), whereas the ore-barren monzogranite porphyry and granite porphyry are characterized by much lower zircon Ce4+/Ce3+ ratios (average of 24 and 20, respectively) and low fO2 values (average of △FMQ = +1.2 and △FMQ = −0.5, respectively). This indicates that the ore-bearing porphyry intrusions had much higher fO2 of magma than the ore-barren porphyry intrusions. We suggest that oxidized magmas are more favorable to porphyry Cu-Au mineralization under the intra-continental and collisional settings, which is similar to that in arc environments. Such a conclusion may potentially be used in regional exploration for porphyry Cu-Au deposits.

Early Cretaceous high-Mg adakites associated with Cu-Au mineralization in the Cebu Island, Central Philippines: Implication for partial melting of the paleo-Pacific Plate

Early Cretaceous arc volcanic rocks, diorite intrusions and an associated large porphyry deposit occur in the Cebu Island, Central Philippines. In this paper, we studied the diorite porphyries associated with Cu-Au mineralization in the Kansi region, where Early Cretaceous arc volcanic rocks are widely distributed. Zircon U-Pb age reveals that the diorites were formed at ca. 110Ma, close to the formation age of Lutopan diorites in the famous Atlas porphyry Cu-Au deposit (109–101Ma), and younger than those of the arc volcanics in this region (126–118Ma). The Kansi diorites and Lutopan diorites are both calc-alkaline high-Mg adakites with high Sr/Y ratios. Their major elements define similar variation trends in Harker diagrams, suggesting that they were probably generated from a uniform source but experienced different degree of partial melting or fractional crystallization. The Kansi diorites are characterized by LREE enrichment, HREE depletion, no Eu negative anomaly, with enrichment of Pb, Sr, Zr and Hf and depletion of Nb, Ta, and Ti. They are probably generated by the partial melting of subducted oceanic crust, followed by a certain degree of mantle interaction and crustal contamination. The highly depleted Sr-Nd-Pb-Hf isotopes of the Kansi diorites are close to the Amami Plateau basalt and tonalite, indicating the dominance of a Pacific-type MORB in the source. The Cu-Au mineralization-related Kansi diorites are characterized by high oxygen fugacities more than ΔFMQ +2, indicating quite a good potential for porphyry Cu-Au mineralization in the region. Finally, in our tectonic model, the successive generation of arc volcanic rocks and adakites in the Cebu Island are responses to the subduction and rollback of the paleo-Pacific Plate to the proto-Philippine Sea Plate (PSP) in the Early Cretaceous.

Geology and District-Scale Setting of Tilted Alkalic Porphyry Cu-Au Mineralization at the Lorraine Deposit, British Columbia

Lorraine is a copper-gold porphyry deposit (6.4 Mt indicated resource at 0.61% copper and 0.23 g/t gold, and 28.8 Mt inferred resource at 0.45% copper and 0.19 g/t gold) in north-central British Columbia—one of the youngest known alkalic porphyry deposits within the Triassic-Jurassic Quesnel arc. The deposit is hosted by the Early Jurassic Duckling Creek Syenite Complex, an alkalic multiphase intrusive dike complex of pyroxenite, syenite, and monzonite composition. The southern part of the complex hosts numerous copper-gold porphyry prospects in addition to Lorraine; together, they constitute the Duckling Creek district. Main-stage Cu-Au porphyry mineralization at Lorraine is hosted by phase 1 of the Duckling Creek Syenite Complex, an SW-dipping, early intrusive suite of silica-undersaturated pyroxenites and syenites. Mineralized zones are up to 2.5 km long by 500 m wide, in the form of northwesterly elongate, SW-dipping panels that generally parallel the phase 1 intrusive contacts. Mineralization is attributed to “blind” porphyries within the phase 1 sequence, which was tilted after main-stage mineralization. Copper sulfides define deposit-scale zonation patterns of bornite-chalcocite cores rimmed by chalcopyrite-rich and outer, weakly developed pyrite-dominated domains. Alteration patterns and intensity are consistent across mineralized zones. Strong, pervasive K-feldspar-biotite (potassic) core zones are rimmed by albite-diopside-magnetite (calc-potassic) alteration that is pervasive near the center of the zones, but varies laterally outward to vein-style alteration. Pervasive albite alteration (sodic) is locally present and is interpreted to be an early alteration event. Mineralization at Lorraine has been cut by later phases of the Duckling Creek Syenite Complex. A second cycle of pyroxenite-syenite-monzonite intrusion (phase 2) is mineralogically similar to phase 1, but is unmineralized and has vertical intrusive contacts that strike northwest. A change to late, silica-saturated intrusions is marked by subvertical phase 3 silica-saturated leucosyenite and pegmatite dikes. U-Pb zircon and Ar-Ar geochronology constrain the timing of main-stage mineralization at Lorraine to an approximately 1.5 m.y. interval between 180 Ma and 178.5 Ma. Phase 1 intrusions are as old as 181.68 ± 0.95 Ma based on an Ar-Ar age on biotite from pyroxenite, but may range to as young as 180.2 ± 0.28 Ma based on a U-Pb zircon age from a mineralized phase 1 syenite. The upper age limit for mineralization is 178.75 ± 0.21 Ma, based on U-Pb data for a postmineral phase 2 syenite. An alternate interpretation considers the presence of zircon antecrysts in an analyzed phase 1 rock, which leads to a more narrow time window of 0.31 m.y. that includes phase 1 intrusion, main-stage porphyry mineralization, and structural tilting, which was followed by phase 2 intrusion. Magmatic and hydrothermal activity in the Lorraine area persisted until at least 176 Ma, based on the U-Pb zircon age of 176.77 ± 0.36 Ma from a phase 3 leucosyenite dike, and a late biotite-albite-apatite vein with an Ar-Ar biotite age of 175.21 ± 0.91 Ma. Several intrusive-hosted porphyry prospects within the Duckling Creek district share mineralogical and alteration characteristics, as well as relative igneous paragenesis, with Lorraine. The model for magmatic and hydrothermal development at Lorraine may broadly be applied to the district as a whole, providing a geologic framework upon which to base future exploration in the district.