Orogenic Au Deposits Research Articles

The Khangalas Orogenic Au Deposit, Yana–Kolyma Metallogenic Belt (Northeast Russia): Structure, Ore Mineral and Isotopic (O, S, Re, Os, Pb, Ar, and He) Composition, Fluid Regime, and Formation Conditions

The Khangalas Orogenic Au Deposit, Yana–Kolyma Metallogenic Belt (Northeast Russia): Structure, Ore Mineral and Isotopic (O, S, Re, Os, Pb, Ar, and He) Composition, Fluid Regime, and Formation Conditions

New insights into the metallogenic genesis of the Xiadian Au deposit, Jiaodong Peninsula, Eastern China: Constraints from integrated rutile in-situ geochemical analysis and machine learning discrimination

The genesis of the Mesozoic Au deposit within the Jiaodong Peninsula is debated, with vague connections to magmatism, deep-source metamorphic devolatilization, or the involvement of mantle materials over the long term. This study presents an integrated investigation involving textures, in-situ geochemical analysis, and machine learning discrimination of the rutile of the Xiadian Au deposit at the northwest Jiaodong Peninsula, aiming to provide metallogenic insights. Rutile is distinguished into three types: Type 1 rutile formed in the pre-ore stage is fine-grained and replaces and coexists with relict titanite, with euhedral crystal and being homogeneous and dark BSE response. Type 2 and type 3 rutile exhibit subhedral and anhedral crystals and are associated with quartz-sericite-pyrite alteration. The former has low W contents and is dark BSE response, while the latter is brighter in BSE and exhibits pronounced fragmentation and erosion. Chemical trends indicate the elemental substitution mechanism within rutiles from early to later stages: (Nb, Ta)5+ + (V, Fe, Al, Cr)3+ ↔ 2Ti4+ to 2(V, Fe, Al, Cr)3+ + W6+ ↔ 3Ti4+. Elevated concentrations of trivalent iron ions due to elevated oxygen fugacity of the ore-forming fluids are more likely to have contributed to this change, rather than the increment of W content. This may induce the destabilization of gold-sulfur complexes and contribute to gold mineralization. Machine learning models, including Extreme Randomized Tree (ET), Support Vector Machine, and Naive Bayes classifiers, were trained using a collected dataset containing 6598 rutile geochemistry data. These models consistently classify Xiadian rutile as the hydrothermal origin and having affinity to orogenic Au deposit. The SHapley Additive exPlanation (SHAP) framework was used to explain the discrimination criteria for the best-performing ET models. It revealed that elements such as Y, Ta, Mo, Sn, W, and Nb significantly contribute to classifying Xiadian rutile as affiliated with orogenic Au deposit. Further mass balance calculations with titanite, the predominant precursor Ti-bearing mineral of rutile, suggest that the W content in rutile is controlled by ore-forming fluids, likely having a deep source. In contrast, elements like Y, Mo, Cr, Nb, and Ta are influenced by leaching or re-equilibration with host rocks. Collectively, deep geodynamic processes likely provide major Au mineralization-related materials and fluids, while elemental leaching or re-equilibration with shallow crust rocks near fluid pathways influences the geochemical characteristics of the Xiadian gold system.

Gold Mineralization, Hydrothermal Alteration, and Li Isotope Fractionation at Cochenour Orogenic Gold Deposit, Red Lake, Canada

Abstract Lithium isotopes have been used to study subduction zones, continental weathering, and magmatic–hydrothermal transitions, but little is known about their behavior in metasomatic footprints surrounding hydrothermal ore deposits. Although minerals such as biotite, chlorite, and white micas may sometimes be characteristic of Au mineralization, they are not truly diagnostic given that they also usually occur outside the ore zones. Here, whole rock δ7Li compositions are measured in samples from drill core cutting through metasomatized basalts from the Cochenour orogenic Au deposit, Red Lake, Canada, to verify whether Au ore-related biotite, chlorite, white micas, and quartz have specific δ7Li signatures. Laser ablation ICP-MS maps show 1000–1100 ppm Li in biotite, 200–600 ppm in chlorite, and 20–100 ppm in white mica. In the ‘arsenopyrite-bearing replacement-style’ alteration and mineralization, Au is associated with arsenopyrite, pyrrhotite, and chalcopyrite in the ore zone, but is more concentrated in white mica than in sulfides outside the ore zone. In the cross-cutting ‘quartz-actinolite vein-style’ alteration and mineralization, Au is distributed with chalcopyrite and arsenopyrite in the selvages of the veinlets, but is associated with pyrite, calcite, and biotite outside the ore zone. Mass balance calculations suggest that Au ore-related biotite, chlorite, white mica, and quartz have δ7Li values of ∼+4‰, ∼0 to +2‰, ∼−2‰, and ∼+6 to +12‰, respectively. This is explained by Li isotopic fractionation occurring during the retrograde sequence of auriferous biotite-chlorite-white mica alteration and the late auriferous quartz vein event, identified in the present samples as well as in the Red Lake-Campbell mine complex and the Red Lake greenstone belt. In the ‘arsenopyrite-bearing replacement-style’ alteration, the intercorrelation of δ7Li and Au and their correlation over distance show greater amounts of Au in biotite-enriched rocks, where biotite has δ7Li values of ∼+4‰. Such values indicate a mantle source for the early biotite-related auriferous fluid at Red Lake.

Geology, fluid inclusions, mineral and (S-O) isotope chemistry of the Badran orogenic Au deposit, Yana-Kolyma belt, eastern Siberia: implications for ore genesis

The Badran orogenic gold deposit is located in the Yana-Kolyma belt, Eastern Siberia; it has proven reserves of ∼9.3 t of gold and an average grade of 7.8 ppm. The total gold production at the Badran deposit since 1984 amounts to ∼34 t. Despite many years of study, the origin of the gold deposits of the Yana-Kolyma metallogenic belt, one of the world’s largest belts, and the Badran deposit is controversial. Synthesis of regional geology and geology of the Badran deposit, fluid inclusion analysis, mineral and (S-O) isotope chemistry defines the genetic model, origin of fluids, and source of metals in the evolution of the ore-forming system, equivalent to other orogenic gold deposits on the margin of the Siberian craton. The deposit is localized in the Upper Triassic clastic rocks and is controlled by the NW-trending thrust. Polyphase mineralization occurs as disseminated arsenian pyrite and arsenopyrite ores with invisible gold, quartz veins with native gold and Fe, Pb, Zn, Cu sulfides and sulfosalts of orogenic type, and locally post-ore Ag, Sb-bearing minerals and Hg epithermal features. The quartz veins with native gold were formed from low-medium saline (1.5–10 wt% NaCl eq.) aqueous-carbonic fluids boiling at temperatures of 290°C to 210 °C and pressures of 300–250 to 125 bar. The δ34S values of pyrite and arsenopyrite vary from −1.1‰ to +2.4‰, with an average of +0.4‰; the δ18О of quartz from +15.1‰ to +17.5‰ at constant δ18ОH2O about +7.5‰ (±1.0‰). High contents of As (up to 2.4 wt%) and Co/Ni ∼ from 0.3 to 9.9 in pyrite of proximal alteration are typical for hydrothermal systems. The results obtained confirm that the ore-forming fluids did not have a single origin, but were formed from a mixture of subcontinental lithospheric mantle and metamorphic sources. The subcrustal lithospheric mantle was fertilized in the time preceding mineralization (Late Jurassic) and was derived directly from the down-going subduction slab and overlying sediment wedge at the closure of the Oymyakon Ocean.

Age and petrogenesis of ore–forming volcanic–subvolcanic rocks in the Yidonglinchang Au deposit, Lesser Xing’an Range: Implications for late Mesozoic Au mineralization in NE China

The age and petrogenesis of volcanic–subvolcanic rocks associated with Au mineralization of the recently discovered Yidonglinchang Au deposit in the Lesser Xing’an Range provide insights into late Mesozoic Au metallogenesis in NE China. In this paper, we report zircon U–Pb chronological and Hf isotopic, whole–rock geochemical, and Sr–Nd isotopic data of the andesite porphyry and quartz diorite porphyry from the Yidonglinchang Au deposit. Zircon U–Pb dating shows that the andesite porphyry and quartz diorite porphyry associated with Au mineralization were formed at 101 and 99–97 Ma, respectively, suggestive of an early Late Cretaceous Au mineralization event in the Lesser Xing’an Range. Whole–rock geochemical data reveal that they have low SiO2 contents (59.87–61.48 % and 55.91–63.22 %, respectively) and high Mg# values (41.5–55.4 and 43.2–61.3, respectively). In addition, these rocks are enriched in large–ion lithophile elements (e.g., K, Rb, and Ba) and depleted in high–field–strength elements (e.g., Nb, Ta, P, Ti, Zr, and Hf). The rocks have slightly negative to positive zircon εHf(t) values (−2.3 to 5.7) and negative whole–rock εNd(t) values (−3.3 to −2.9), indicating a metasomatized mantle source with some contamination by crustal materials. Combined with regional magmatic and metallogenic characteristics, we conclude that the Au mineralization at Yidonglinchang formed as a result of early Late Cretaceous magmatic–hydrothermal activities. Previously obtained data show that the orogenic Au deposits in the northern NE China formed mainly during the Early Cretaceous, earlier than the late Early Cretaceous to Late Cretaceous epithermal Au deposits in the eastern NE China. The formation of the late Mesozoic Au mineralization in the northern and eastern NE China was likely controlled by distinct tectonic settings. During the late Early to early Late Cretaceous, the rollback of Paleo–Pacific oceanic slab beneath eastern NE China generated an extensional setting that led to large–scale magmatism and associated Au mineralization.

Late Mesozoic tectonic evolution and thermal history in the northeast Xing'an Block, NE China: Implications for gold mineralization and preservation

Late Triassic–Jurassic orogenic and Early Cretaceous epithermal Au deposits are significant producers of Au, Ag, and potentially critical elements (e.g., Te, Se and Sb) in the North Heilongjiang Belt in the Xing'an Block, NE China. However, the preservation mechanism of these Au deposits associated with tectonic evolution is unclear. Here, we conducted zircon U–Pb, sericite Ar–Ar, zircon and apatite (U–Th)/He dating as well as whole‐rock geochemistry in the Xing'an Block. Zircon U–Pb dating shows the ages of 174.1 ± 2.4 Ma for the granodiorite, 169.9 ± 1.6 Ma for the tonalite, 154.0 ± 2.0 Ma for the monzogranite and ca.122 Ma for the diorite. Sericite Ar–Ar dating presents plateau and isochron ages of 163.2 ± 1.8 Ma and 163.4 ± 2.8 Ma. The average apatite (U–Th)/He (AHe) and zircon (U–Th)/He (ZHe) ages from the Jurassic rocks have the ranges of ca. 146–89 Ma and ca. 150–116 Ma and from the Cretaceous are ca. 109–76 Ma and ca. 117–111 Ma, respectively. The Early‐Middle Jurassic intrusions are featured by the tonalite‐trondhjemite‐granodiorite (TTG) rock type. Late Jurassic monzogranite has the geochemical signature of adakitic rocks. The Early Cretaceous granitoids are classified as volcanic arc granites with a part of the Early Cretaceous granodiorite featured by adakitic. These new results reveal five group ages associated with tectonic evolution, Au mineralization and the preservation of the Au deposits. (i) Magmatic events were related to the subduction of the Mongolia‐Okhotsk Ocean during the Early Jurassic (ca. 177–170 Ma) and then the compressional settings with regional deformation (ca. 167–163 Ma). (ii) Thickening crust and orogenic Au mineralization were related to the closure of the Mongolia‐Okhotsk Ocean (ca. 154–145 Ma). (iii) The transformation was from compressional to extensional settings followed by exhumation during the Early Cretaceous (ca. 145–120 Ma), which is the factor of the exhumation of the orogenic Au deposits formed from the Late Triassic to Late Jurassic. (iv) Epithermal Au–Ag mineralization was associated with an extension related to the subduction of the Palaeo‐Pacific Plate (ca. 120–100 Ma). (v) Thermal history shows one thermal event during the Late Cretaceous (ca. 89–76 Ma). The Au deposits have been preserved since the Late Cretaceous.

Gold mineralization related to rifting of the Rodinia surpercontinent: As gauged from the Dongyuan Au deposit, Jiangnan orogen, China

Abundant orogenic gold (Au) deposits, widely distributed in medium to low-grade metamorphic rocks, formed episodically since the Middle Archean. Orogenic Au mineralization waned during the Neoproterozoic era, although Neoproterozoic orogenies were prevalent. The Jiangnan Orogen, South China, as part of the sutures uniting the Rodinia (Meso- and Neoproterozoic) supercontinent, is situated between the Cathaysia and Yangtze blocks. Many orogenic Au deposits, such as the Wan’gu, Huangjindong, Dongyuan, and Jinshan Au deposits, are located in the northeastern section of the Jiangnan Orogen. The orebodies of the recently discovered Dongyuan deposit display a horizontal zonation, as follows: a peripheral quartz–chlorite–sulfide–calcite (ankerite, manganocalcite, and calcite) veinlets/veins and a central sulfide (mainly arsenopyrite) veinlets/veins. The former veinlets/veins also contain a small amount of albite, scheelite, TiO2 minerals, xenotime, and monazite. Compared with the other orogenic Au deposits, arsenopyrite from the Dongyuan Au deposit is characterized by enrichment of Sb–Co–Cd–Ag element assemblages. Based on the electron microprobe and Raman analyses, TiO2 mineral grains, including anatase, rutile, and anatase–rutile intergrowths, are present in the Au veins. In contrast with previous studies, TiO2 minerals (anatase and rutile) have a nearly consistent concentration range of each element detected, which taken together can be used for constraining fluid sources of ores. TiO2 minerals with enriched V–Fe assemblages, combined with initial 187Os/188Os ratio (0.64 ± 0.11) of arsenopyrite, reflect that the Dongyuan Au veins were probably precipitated from a metamorphic fluid. The Liyangdou biotite granodiorite and Donggang granite, located about one kilometer north and six kilometers south of the deposit, have LA-ICP-MS U–Pb zircon ages of 803 ± 3.4 Ma and 814 ± 3.4 Ma, respectively. The analysis of five arsenopyrite samples selected from the Dongyuan Au veins yields an isochron age of 744 ± 36 Ma (with an initial 187Os/188Os ratio of 0.64 ± 0.11 (2σ) and MSWD = 30). We found that the Dongyuan Au mineralization was later than the peripheral Neoproterozoic magmatic activities and metamorphic events of country rocks. Combined with previous studies, the Dongyuan deposit was formed in the tectonic setting of Rodinia supercontinent rifting, after the Neoproterozoic collision event in the Jiangnan Orogen, which likely triggered orogenic Au mineralization.

Gold metallogeny in Iran; implications for gold exploration and conceptual modelling

Significant progress in the classification, definition and understanding of the main Au deposit types could significantly aid improvements in Au exploration. Because of the wide occurrence of Au in the central part of the Tethyan Eurasian Metallogenic Belt, Iranian structures composed of more than 17 zones (arcs and blocks) are considered as having one of the largest Au reserves in the Middle East. Without attempts at understanding the tectono-magmatic evolution of Iran and the geodynamic settings of Au deposition, the establishment of a reliable predictive exploration model for Au-type deposits in Iran and other parts of the world will be unsuccessful. By considering a total of 33 Au deposits and prospects in Iran, a mineralization sequence is revealed from orogenic and volcanogenic massive sulfide (VMS), orogenic, Carlin-type, epithermal/porphyry Cu–Au/skarn, epithermal/iron oxide–copper–gold (IOCG). The trend of deposition gradually changes in the SW–NE axis to intrusion-related, epithermal and porphyry Cu–Au deposits at the Urumieh–Dokhtar Magmatic Arc (UDMA) and post-arc magmatism. VMS deposits occur adjacent to the NE Zagros Fold and Thrust Belt, at the Sanandaj–Sirjan Zone. The Zagros Orogeny and associated post-collisional magmatism at UDMA host many porphyry, epithermal and intrusion-related Au deposits, with a major magmatism peak in the Miocene. This work reveals that orogenic and Carlin-type Au mineralization are linked genetically. After each associated subduction for Palaeotethys (286–215 Ma) and Neotethys (210–68 Ma) in Iran, VMS and orogenic Au-deposits are formed in the border of the subduction (±obduction) zone. The porphyry, intrusion-related, epithermal and IOCG mineralization are emplaced in appropriate formations and structures during collision and post-collision processes.

Au-Bi-Te(-Cu) Mineralization in the Wawa Gold Corridor (Ontario, Canada): Implications for the Role of Bi-Rich Polymetallic Melts in Orogenic Au Systems

The Wawa Gold Corridor, a series of Archean orogenic Au deposits in the Michipicoten greenstone belt, Canada, comprises two styles of Au mineralization: (1) syn-deformation gold associated with pyrite and arsenopyrite; and (2) late- to post-deformation gold associated with chalcopyrite and Bi-Te(-S) phases. Through petrographic and mineral–chemical analysis, it was determined that gold in the latter assemblages precipitated from Bi-rich polymetallic melts during hydrothermal overprinting of the earlier Au-As-S mineralization; this event was likely driven by the emplacement of Archean lamprophyres. The formation and evolution of these melts was governed by fluid–pyrite reaction interfaces, where the bulk composition of the melts was broadly controlled by the trace-element chemistry of the sulphide minerals in the local host rocks. This suggests that the melt-formation event involved mobilization of existing metal endowments related to early Au events, rather than addition of new Au, Bi, and Te. Thus, the deposition of high-grade Au by Bi-rich melts was dependent on pre-existing sulphide mineralization, both as a source of metals and as micro-environments that stabilized the melts. The paragenesis documented in the Wawa Gold Corridor (i.e., early hydrothermal Au-As-S mineralization and late melt-related Au-Bi-Te mineralization) has been previously recognized in numerous other orogenic and non-orogenic Au deposits. Herein, it is suggested that this apparent consistency in the timing of melt events across multiple systems probably reflects the physicochemical conditions (i.e., fO2-aH2S) of orogenic fluids being incompatible with molten Bi. Bi-rich polymetallic melts are hence unlikely to form primary Au mineralization in orogenic systems but can, however, have a significant impact on the ultimate deposit-scale distribution of Au via secondary mobilization and enrichment.

Nature of fluid and genetic affiliation of the Bakoshi-Kundila Au deposit, Nigeria: Evidence from trace elements in hydrothermal quartz

The Bakoshi-Kundila Au deposit is located in the Nigerian Shield in West Africa. In this deposit, Au-bearing pyrite contains inclusions of Au-rich hydrothermal quartz. Whether or not this co-precipitation relationship of quartz and pyrite is cogenetic and related to the gold fluid remains untested. The deposit's genetic affiliation is controversial. This study reports the results of textural and in situ chemical compositions of hydrothermal quartz, and sheds light on fluid composition, element substitutions into quartz structure, and inferred the deposit genetic type. We grouped the quartz into four generations: Qz1 and Qz2 (vein-type) and Qz3 and Qz4 (wallrock-type). The Qz2 is deformed, overprinted by late-stage fluid activity. The Qz1 is rich in Ga and Sr but poor in Al and Fe than Qz3 and Qz4: average Ga in ppm (Qz1 – 0.62, Qz3 – 0.08, Qz4 – 0.15), Sr (Qz1– 26.7, Qz3 – 4.59, Qz4 – 5.78), Al (Qz1– 16.7, Qz3 – 82.8, Qz4 – 136), Fe (Qz1– 131, Qz3 – 144, Qz4 – 133). However, the contents of low melting point chalcophile elements (LMCE) are higher and overlapped between Qz1 and Qz3 than those from Qz4: average Au in ppm (Qz1– 33.9, Qz3 – 38.2, Qz4 – 7.83), Cu (Qz1 – 13.1, Qz3 – 14.8, Qz4 – 5.95), Bi (Qz1 – 3.48, Qz3 – 0.25, Qz4 – 0.51). The LMCE in Qz1 displayed covariant relationships with Au (but poorly defined in Qz3 and Qz4), suggesting the likely presence of Au-Ag-(±Te)-bearing phases like petzite and argentum. Aluminum is the main trivalent element substituting Si4+ in Q3 and Qz4, whereas Fe3+ in Qz1. The charge-balanced cations are Li+, Na+, and K+ in Qz3 and Qz4, whereas Sr2+ in Qz1. The Al and Ti contents (in ppm) are higher and more variable in Qz3 (Al: 5.97–374, avg 82.8; Ti: 2.69–12.5, avg 6.60) and Qz4 (Al: 8.13–792, avg 136; Ti: 7.64–72.0, avg 20.2), which may imply fluctuation in fluid pH. These element concentrations are lower and less variable in Qz1 (Al: 5.25–47.8, avg 16.7; Ti: 3.41–18.0, avg 5.43), suggesting a less acidic and probably stable pH condition during its precipitation. The Qz1 has a lower average content (in ppm) of compatible elements (K – 15.7, Fe – 13.1, Ti – 5.43) than Qz3 (K – 25.9, Fe – 144, Ti – 6.60) and Qz4 (K – 63.0 Fe – 133, Ti – 20.2), implying that Qz3 and Qz4 precipitated at a higher temperature than Qz1. However, the contents of the incompatible elements (e.g., P, Ge, Rb, and Li) are not enriched in the supposed lately-formed Qz1 over Qz3 and Qz4, which is inconsistent. The inconsistency is also true between the wallrock type, with lower contents in low-temperature Qz3 than in high-temperature Qz4. Thus, temperature is considered not a major controlling factor during the formation of Bakoshi-Kundila quartz; instead, the pH condition and fluid-rock reaction are favored. The Bakoshi-Kundila quartz has Al-Ti contents akin to quartz from orogenic Au deposits.

Genetic link between orogenic Au and porphyry Cu ([sbnd]Au) mineralization in the Dananhu Arc, NW China: Evidence from geochronology, geochemistry, and Sr–Nd–Hf isotopes of the Tudunbei Au deposit

The late Paleozoic Chinese Tianshan is characterized by large volumes of arc-related magmatic rocks, and numerous associated orogenic Au and porphyry Cu (Au) deposits. The link between these two deposit styles, however, is ambiguous. Here, we present zircon U–Pb–Hf isotopes, bulk-rock geochemistry, and sericite 40Ar/39Ar geochronology from the newly discovered Tudunbei Au deposit located east of the Tuwu–Yandong porphyry Cu (Au) ore district in the Dananhu Arc, Chinese North Tianshan, and combine this with previously published geochronological and geochemical data to characterize the genetic relationship between orogenic Au and porphyry Cu (Au) mineralization. Our new UPb zircon ages indicate that the wall rocks of the Tudunbei Au deposit formed during the Carboniferous between 337 and 314 Ma (K-feldspar granite: 334.8 ± 1.9 Ma, basaltic tuff: 336.6 ± 4.0 Ma, quartz diorite: 316.0 ± 1.8 Ma, gabbroic diorite: 318.3 ± 1.8 Ma, and gabbro: 314.3 ± 1.8 Ma). These wall rocks are enriched in light rare earth elements and large ion lithophile elements (e.g., Ba, U, and Pb), and depleted in high field strength elements (e.g., Nb, Ta, and Ti). Given the absence of Precambrian basement rocks in the Chinese North Tianshan, and the depleted NdHf isotope compositions (εHf(t) = 12.12–14.98; εNd(t) = 5.77–7.06) of the wall rocks, their young Hf model ages (350–510 Ma), the lack of inherited zircons, and their enrichment in Na2O (2.84–4.73 wt%) relative to K2O (0.43–2.40 wt%), it is suggested that they formed in an oceanic arc environment. One sericite sample selected from an auriferous quartz vein yielded 40Ar/39Ar plateau ages of 260.6 ± 1.1 Ma, which is representative of the gold mineralization age. Given the abundance of gold in the Carboniferous wall rocks of the Tuwu–Yandong porphyry Cu (Au) ore district, the similarity in the timing of its magmatism with Tudunbei, and the geochemical–isotopic (Sr–Nd–Hf) similarity of their wall rocks, it is inferred that the gold in the Tudunbei deposit was remobilized from pre-existing gold in the Carboniferous wall rocks during regional metamorphism and deformation.

Using pyrite composition to track the multi-stage fluids superimposed on a porphyry Cu system

Abstract The Yulekenhalasu porphyry Cu-Mo deposit (0.2 Mt Cu at 1.04 wt% and 0.012 Mt Mo at 0.06 wt%) is located in the Devonian Halasu copper belt, East Junggar block, northwest China. At Yulekenhalasu, Cu and Mo mineralization commonly occurs as disseminated sulfides or veinlets in porphyry-related alteration zones. Five alteration stages have been identified, including porphyry-type alteration, i.e., sodic-calcic (stage I), potassic (stage IIa), propylitic (stage IIb), and phyllic (stage III) alteration, and widespread late Cu sulfide-bearing veins (stage IV) cross-cutting porphyry-type alteration, plus a post-ore fault-controlled argillic alteration (stage V). Stages IV and V have overprinted porphyry-type alteration (stages I–III). Anomalous concentrations of trace elements in stage IIb pyrite (e.g., Ti, Zr, Gd, and Hf) are due to the presence of micro-inclusions (e.g., zircon and rutile) in the low-temperature (~200 °C) propylitic zone. Cu, Ag, Co, and Mn, occurring as stoichiometric substitutions or as tetrahedrite inclusions in overprinting stage IV pyrite, were sourced directly from the primary hydrothermal fluid. The enrichment of distal pathfinder elements (e.g., Cr, Au, and Tl) in overprinting stage V pyrite was caused by a low-temperature (~160 °C) hydrothermal event related to regional orogenic Au mineralization. The spatial variation of Se/S in pyrite among various paragenetic stages were influenced by changes in the hydrothermal fluid composition and temperature, with the latter having the effect of decreasing pyrite Se/S. Lower Se concentrations in pyrite of stages IIb and III close to the orebody are explained by relatively higher temperatures in the locus of mineralization. This may provide a potential vectoring tool to mineralization using pyrite geochemistry in porphyry deposits. Systematic thermodynamic calibrations were applied to pyrite compositions to fingerprint the corresponding Se/S and Co/Ni ratios of fluids and further to develop a complete metallogenic model for Yulekenhalasu. The Devonian diorite porphyry generated fluids that produced the early porphyry-type alteration. High Co/Fe (average ~1 × 10–4) and Ni/Fe (average ~3 × 10–6) ratios of fluid for late Cu sulfide-bearing veins, combined with higher Se/S (average ~6 × 10–7) than orogenic Au deposits (average ~3 × 10–8), indicate that the fluids possibly derived from a Late Devonian-Carboniferous mafic intrusion. Argillic alteration assemblages forming at ca. 280 Ma host pyrite relatively enriched in Au (average 0.1 ppm, with native gold inclusions). Therefore it is likely related to a regional orogenic gold mineralizing event in the Early Permian that overprinted Devonian mineralization. Although spatially contiguous, hydrothermal alteration and hypogene mineralizing stages identified herein represent discrete episodes of hydrothermal activities at Yulekenhalasu. The multi-stage alteration features observed at Yulekenhalasu may provide insights into the complete evolutionary history of Paleozoic porphyry Cu deposit systems in the Central Asian orogenic belt. This study contributes to a better understanding of the metallogenic and exploration models of porphyry Cu deposits overprinted by multi-stage hydrothermal events, which is economically important in Phanerozoic orogenic belts.

Linking Pacific Plate formation and Early Cretaceous metallogenic response on the circum-Pacific continental margins

Hydrothermal mineralization along the circum-Pacific continental margin is genetically linked to the motions of the Pacific Plate. Compiled geochronological results of ore deposits, coupled with the newly reconstructed geometry of the late Early Cretaceous subduction zones in East China, North America, and the Central Andes using GPlates and I2VIS software, were applied to investigate the relationships between mineralization and Pacific Plate formation. The ∼120-m.y.-old orogenic Au provinces in East China and North America are related to transpression caused by high-rate oblique subduction with intermediate−high dip angles of the Izanagi and Farallon plates, respectively. In contrast, the ∼105-m.y.-old porphyry-epithermal belt in Southeast China was produced by oblique subduction of the Izanagi Plate with low−intermediate subduction rates and intermediate−high dip angles. In the Central Andes, the oblique subduction of the Farallon Plate with low−intermediate rates and low dip angle accounted for iron oxide−copper−gold ore (IOCG) deposit mineralization in South Peru at ca. 110 Ma; whereas the high rate and low dip-angle subduction of the paleo-Phoenix Plate, which caused mild compression, was responsible for Fe, porphyry Cu, and IOCG mineralization in North Chile at ca. 110 Ma. The late Early Cretaceous metallogenic response in the circum-Pacific region coincides with superplume events that triggered the significant growth of the modern Pacific Plate. The forward simulations reveal that different subsequent styles of subduction and associated magmatism are likely responsible for the distinct mineralization types present in the region, including orogenic Au, porphyry-epithermal, Fe, and IOCG deposits. The precise dynamics of the subduction zone determined by this study led to the improved metallogenesis models in the Pacific margin.

Metallogeny in the Bangong–Nujiang belt, central Tibet, China: A review

The Bangong–Nujiang metallogenic belt consists of scattered Tethyan oceanic blocks, mainly distributed underneath the margins of the Qiangtang and Lhasa terranes in central Tibet. A new world-class metallogenic belt has been reported in this region recently, based on the geological mapping and ore deposit prospecting over the last two decades. It currently comprises inferred resources of 30 Mt Cu and 500 t Au, together with several Cr–Ni, Fe, and W (Mo) resources, forming a significant potential area for future mineral exploration. These metals are mainly hosted in porphyry copper, skarn copper, skarn iron, orogenic gold, quartz-vein tungsten, and ophitic chromite deposits. The mineral deposits in the Bangong–Nujiang metallogenic belt have been widely recognized in different localities, including the southern edge of the southern Qiangtang block, part of the north Lhasa block, and even part of the central Lhasa block, indicating they were formed in variable geological settings, from the initial opening, subduction, and collision to the extension of the Bangong–Nujiang Ocean. Specifically, five major tectonic events contributed to mineralization, including the stage 1 (240–165 Ma) initial opening of the Bangong–Nujiang Ocean, stage 2 (165–145 Ma) oceanic subduction, stage 3 (145–100 Ma) close of the ocean, stage 4 (100–65 Ma) continent–continent collisional orogenesis, and stage 5 (65–0 Ma) post-orogenesis. At stage 1, Cr–Ni deposits were formed during the initial opening of the ocean; porphyry–epithermal Cu (Au), skarn Fe, and minor orogenic Au deposits were formed at stage 2 and stage 3; a younger pulse of a few porphyry–skarn Cu ± Mo and orogenic Au deposits were formed during stage 4; finally, W(Mo) deposits were generated in stage 5. In general, porphyry Cu systems, orogenic Au, and skarn Cu polymetallic deposits that occurred in the subduction and post-collision settings related W(Mo) deposits have the most potential for future exploration. An in-depth investigation of several scientific problems, such as addressing the tectonic setting, magmatism, and metallogeny of this region and genetic linkage of these deposit preservations to plateau uplift, is essential for the future success of exploration in the Bangong–Nujiang metallogenic belt.

Scheelite trace element compositions: A robust new tool for mineral exploration

Scheelite is a widespread accessory tungstate mineral that contains a variety of trace elements. Scheelites from the major types of magmatic-hydrothermal mineral deposits (86 deposits, including quartz-vein and greisen, porphyry, skarn and orogenic Au deposits) have been collected and analyzed using laser ablation-inductively coupled plasma mass spectrometry (3270 data, including 584 analyses). Discriminant analysis using Mo, Sr, Nb, La, Ce, Eu, Dy, Yb, Y, Ta, Pb, (Ce/Yb)N, (La/Sm)N, (Gd/Yb)N, Eu anomaly, Ce anomaly, (La/Yb)N, LREE/HREE, Y/Ho and Mo + Sr + Nd + rare-earth elements (REE) + Y + Ta + Pb reveals that scheelites from different mineral deposits can be distinguished. Scheelites from quartz-vein and greisen deposits have high total contents of trace elements that partition onto the Ca sites (Mo, Sr, Nd, REE, Y, Ta, Pb). Scheelites from the porphyry W ± Cu ± Mo deposits, which have been studied in this work, are characterized by low Mo and positive Eu than scheelites from porphyry Cu ± Mo deposits. This indicates that large scale tungsten deposits are related to reduced hydrothermal fluids, in contrast to the oxidized fluids associated with porphyry Cu ± Mo deposits. Scheelites from skarn W ± Sn ± Mo deposits typically exhibit a wide range of Y/Ho ratio and a higher sum of the elements Mo, Sr, Nd, REE, Y, Ta, and Pb compared to that from the skarn Cu ± Mo ± W deposits, indicating that increased amount of fluorine probably leads to large-scale W, Mo, and Sn mineralization during magmatic-hydrothermal processes. Scheelites from the greisen W-Sn polymetallic deposits tend to have more restricted Sr compositions and Eu anomalies than those from the quartz vein W-Sn deposits, as well as relatively high Gd, Tb, Dy and Ho contents, which coincide with extensive hydrothermal alteration, indicating intense fluid-rock interaction during mineralization. Using Discriminant projection analysis (DPA), scheelites from many ore deposits can be readily separated from each other. This study demonstrates that heavy-mineral scheelite grains collected during regional geochemical surveys are effective in identifying specific types of buried mineral deposits in potential mineralization area. Scheelite geochemistry with DPA provides an effective guidance for mineral exploration.

Origin of Disseminated Gold-Sulfide Mineralization from Proximal Alteration in Orogenic Gold Deposits in the Central Sector of the Yana–Kolyma Metallogenic Belt, NE Russia

The Yana–Kolyma metallogenic belt, NE Russia, is a world-class gold belt with resources numbering ~8300 tons of gold. The belt is localized in the central part of the Verkhoyansk–Kolyma orogen, formed by a collage of diverse terranes. The Tithonian-to-Early-Cretaceous orogenic gold deposits are hosted in a sequence of Permian–Triassic and Jurassic clastic rocks and altered Late Jurassic andesite, dacite, granodiorite, trachyandesite, and trachybasalt dykes. High-fineness gold (800–900‰) in quartz veins and invisible gold in disseminated arsenian pyrite-3 (Py3) and arsenopyrite-1 (Apy1) are present in ores. Here, we present new data about microtextures; the chemical composition and stable sulfur isotopes of auriferous pyrite-3 and arsenopyrite-1 from proximal alterations in sediment-hosted (Malo–Taryn, Badran, Khangalas); and intrusion-hosted (V’yun, Shumniy) orogenic Au deposits in the central sector of the Yana–Kolyma metallogenic belt to better constrain the ore-forming process and tracking their evolution. Detailed petrography defined the following generations of pyrite: syn-sedimentary/diagenetic Py1, metamorphic Py2 and hydrothermal Py3, and Apy1. Hydrothermal Py3 and Apy1 are localized in the proximal pyrite–arsenopyrite–sericite–carbonate–quartz alteration in ore zones and make a major contribution to the economic value of the veinlet-disseminated mineralization with “invisible” gold in the orogenic deposits of the Yana–Kolyma metallogenic belt. Electron microprobe analysis (EMPA) of Py3 in both types of deposits shows concentrations of As (up to 3.16 wt%), Co, Ni, Cu, Sb, and Pb. Py3 in intrusion-hosted orogenic gold deposits reveals elevated concentrations of Co (up to 0.87 wt%), Ni (up to 3.52 wt%), and Cu (up to 2.31 wt%). The identified negative correlation between S and As indicates an isomorphic substitution of sulfur by As1−. Py3 from igneous rocks is characterized by a high degree of correlation for the pairs Fe2+→ Co2+ and Fe2+→ Ni2+. For hydrothermal Apy1, Co (up to 0.27 wt%), Ni (up to 0.30 wt%), Cu (up to 0.04 wt%), and Sb (up to 0.76 wt%) are typomorphic. According to atomic absorption spectrometry, the concentration of Au in Py3 reaches 159.5 ppm; in Apy1, it reaches 168.5 ppm. The determination of the precise site of the invisible gold within Py3 and Apy1 showed the predominance of solid-solution Au+ in the crystal lattice. The values of δ34S in Py3 and Apy1 (from −6.4 to +5.6‰, mean value of about +0.6‰), both from sediment-hosted and from intrusion-hosted deposits, display a relatively narrow range and are characteristic of the hydrothermal ore stage. Our analytical results showed no systematic differences between the chemical and stable sulfur isotope compositions of both auriferous pyrite-3 and arsenopyrite-1 from the proximal alteration in sediment-hosted (Malo–Taryn, Badran, Khangalas) and intrusion-hosted (V’yun, Shumniy) orogenic Au deposits, indicating that the primary source of sulfur, gold, and mineralizing fluids was likely from subcrustal and metamorphic systems in the Late-Jurassic-to-Early-Cretaceous Verkhoyansk–Kolyma orogen.

Orogenic Au deposits with atypical metal association (Cu, Co, Ni): Insights from the Pohjanmaa Belt, western Finland

The Laivakangas Au-Cu metallogenic area is characterised by orogenic Au deposits with both Au-only and with atypical (Au ± Cu, Co, Ni) metal associations. Here we study and compare four examples to better constrain the parameters controlling enrichment in base metals in addition to Au. We selected two typical Au-only deposits, the Laivakangas and the Huhta deposits and two orogenic Au deposits with atypical metal association, the Jouhineva Au-Cu-Co-Ag and the Kurula Au-Co deposits. All four deposits record multiple successive mineralisation events with local variations in their respective metal association. Two auriferous mineralisation events are identified, (1) a ubiquitous As-Au-(Co, Ni) event close to peak metamorphism (620–430 °C) where Au occurs either as invisible Au in arsenides or as inclusion in arsenopyrite; (2) a later Cu(-Au)-rich sulfide event on the retrograde path where Au locally occurs as free, native grains along with chalcopyrite. From S isotope studies of the sulfide and sulfarsenide minerals and relations between the deposits and surrounding rocks, we propose that the variation in metal association of the ore fluid is linked to the diversity of lithologies involved in metamorphic fluid production. Multi-event hydrothermal mineralisation and relatively reduced redox conditions appear critical to increase the Au endowment in a deposit and to introduce atypical metals. Results of this study provide a new comprehension of the variability of metal association in orogenic Au deposits of the Laivakangas Au-Cu metallogenic area and elsewhere.

Contribution of Triassic Tectonomagmatic Activity to the Mineralization of Liziyuan Orogenic Gold Deposits, West Qinling Orogenic Belt, China

The Western Qinling orogenic belt (WQOB) is one of the most important prospective gold districts in China, with widely distributed Indosinian intermediate–acidic intrusions. The Liziyuan Au deposit is a representative orogenic deposit in the northern WQOB, hosting several sections spatially associated with igneous rocks. The Au deposit is hosted by meta-sedimentary volcanic rocks of the Cambrian–Ordovician Liziyuan Group and the Tianzishan monzogranite. Two periods, including five stages of mineralization, are recognized in this area: an early metamorphic mineralization period (PI), including quartz–pyrite (Stage I) and banded quartz–polymetallic sulfide (Stage II) veins, and a later magmatic mineralization period (PII) including quartz–K-feldspar–pyrite–molybdenite veins (Stage III), quartz–polymetallic sulfide–chlorite ± calcite veinlets and stockwork (Stage IV), and late calcite–quartz veinlets (Stage V). Geochronological studies indicate a SHRIMP zircon U-Pb age of 236.1 Ma for the Tianzishan monzogranite, and our published ages of ore-bearing diorite porphyrite of the Suishizi section and granite porphyry of the Jiancaowan section being 213 and 212 Ma, respectively. Pyrites formed in association with PI and PII mineralization have well-defined Rb–Sr ages of 220 ± 7.5, 205.8 ± 8.7, and 199 ± 15 Ma, with close temporospatial coupling between mineralization and magmatism. The δ18O and δD values of fluid inclusions in Stage IV auriferous quartz veins range from −0.03‰ to +5.24‰ and −93‰ to −75‰, respectively, suggesting that mineralizing fluid was likely of magmatic origin. Three distinct ranges of δ34S values are identified in the studied sections (i.e., 7.04‰–9.12‰, −4.95‰ to −2.44‰, and 0.10‰–3.08‰), indicating a source containing multiple sulfur isotopes derived from magmatic and metamorphic fluids. The Liziyuan Au deposit is thus likely an orogenic deposit closely related to magmatism. Geochemical characteristics indicate that Tianzishan monzogranite is adakitic and was derived from thickened lower crust during Triassic orogenesis. The ore-bearing diorite porphyrite and granite porphyry formed in a post-collision extensional setting. Together with previous geological and geochemical data, our results indicate that the Liziyuan orogenic Au deposit was formed by early collisional–compressional metamorphism and late post-collision extensional magmatic fluids related to the evolution of the WQOB.

Trace Element Characteristics of Tourmaline in Porphyry Cu Systems: Development and Application To Discrimination

AbstractSamples of tourmaline supergroup minerals from seven mineralized porphyry systems (Cu ±Au, ±Mo) that include Casino (Yukon, Canada), Coxheath (Nova Scotia, Canada), Donoso breccia (Chile), Highland Valley Copper (British Columbia, Canada), New Afton (British Columbia, Canada), Schaft Creek (British Columbia, Canada), and Woodjam (British Columbia, Canada) were examined to characterize their trace element signatures and to evaluate discriminating variables that distinguish them from tourmaline supergroup minerals forming in other environments. Trace element analyses, conducted via LA-ICP-MS, reveal striking similarities in trace element character among the mineralized environments examined in contrast to those considered to be barren. Key concentrations of elements (Sr, Pb, Zn, Cu, and Ga) and select element ratios (Sr/Pb and Zn/Cu) are useful discriminators. These discriminators are presented and compared to that of tourmaline supergroup minerals forming in other geologic environments. The tourmaline supergroup minerals from porphyry systems are characterized by high Sr/Pb values (avg: 297) and relatively low Zn/Cu (avg: 4.8) values. A ternary plot of Sr/Pb–Zn/Cu–Ga is effective in distinguishing porphyry-related tourmaline supergroup minerals. Compared to porphyry grains, tourmaline supergroup minerals derived from felsic pegmatites have lower Sr/Pb values (avg: 2.91) and higher Zn/Cu values (avg: 472); those from orogenic Au deposits have high Sr/Pb (avg: 193) similar to porphyries but intermediate Zn/Cu (avg: 223) and lower Ga (avg: 43 ppm); and those considered metamorphic (greenschist to amphibolite) form in the center of the ternary. An effective approach for discrimination was developed utilizing an understanding of both intrinsic and extrinsic controls. More broadly, this work has implications for using tourmaline supergroup minerals recovered from surficial sediments to identify prospective areas for further porphyry exploration.

Mineralogical, lithogeochemical and sulfide trace element characteristics of the Hirvilavanmaa Au-only and the base metal-rich Naakenavaara orogenic gold deposits in the Central Lapland belt, northern Finland

The Hirvilavanmaa (Au-only) and Naakenavaara (Cu-Co-Au-Ni) deposits, located only 5 km apart in the Paleoproterozoic Central Lapland belt (CLB) in northern Finland, represent two types of orogenic gold mineralization that dominate the CLB: (1) Au-only and (2) Au with atypical metal association, respectively. In this study, we compare these deposits in order to pinpoint the origin of differences in their metal associations. The pyrite-rich Hirvilavanmaa and the pyrrhotite- and chalcopyrite-rich Naakenavaara deposits are hosted primarily by ultramafic metavolcanic and metasedimentary rocks respectively. Similarities in the deposits include pre-ore albitization of host rocks and ore mineralization-related carbonate and chlorite alteration and quartz‑carbonate veins. Ore-related sericite and biotite alteration is prominent only at Naakenavaara. Pyrite and chalcopyrite from the two deposits have a distinct trace element geochemistry; pyrrhotite from Naakenavaara hosts significant Co and Ni concentrations. At Hirvilavanmaa, three pyrite generations with distinct Co/Ni ratios represent the gradual evolution of ore deposition. Hirvilavanmaa can be confidently classified as an orogenic Au deposit with evidence pointing to a mafic metavolcanic rock source for the ore-forming components. At Naakenavaara, our results reveal a complex evolution involving two distinct but spatially coincident mineralizing events. The earliest base metal-rich event started as Co-rich and gradually developed into the main Cu-rich stage; two pyrite types (mean Co/Ni ratios of 12.5 and 762 respectively) are associated with these stages. Subsequently ore zones were overprinted locally by an orogenic Au event that deposited pyrite with low Co/Ni ratios (mean of 0.3). The presence of late gold deposition overprinting earlier base metal-rich ore fits with observations from other base metal‑gold deposits from northern Finland.