Geology,geochronology, geochemistry and ore genesis of the Wangu gold deposit in northeastern Hunan Province,Jiangnan Orogen,South China

The Wangu gold deposit in northeastern Hunan, South China, is one of many structurally controlled gold deposits in the Jiangnan Orogen. The host rocks (slates of the Lengjiaxi Group) are of Neoproterozoic age, but the area is characterized by a number of Late Jurassic–Cretaceous granites and NE-trending faults. The timing of mineralization, tectonic setting and ore genesis of this deposit and many similar deposits in the Jiangnan Orogen are not well understood. The orebodies in the Wangu deposit include quartz veins and altered slates and breccias, and are controlled by WNW-trending faults. The principal ore minerals are arsenopyrite and pyrite, and the major gangue minerals are quartz and calcite. Alteration is developed around the auriferous veins, including silicification, pyritic, arsenopyritic and carbonate alterations. Field work and thin section observations indicate that the hydrothermal processes related to the Wangu gold mineralization can be divided into five stages: 1) quartz, 2) scheelite–quartz, 3) arsenopyrite–pyrite–quartz, 4) poly-sulfides–quartz, and, 5) quartz–calcite. The Lianyunshan S-type granite, which is in an emplacement contact with the NE-trending Changsha-Pingjiang fracture zone, has a zircon LA-ICPMS U–Pb age of 142 ± 2 Ma. The Dayan gold occurrence in the Changsha-Pingjiang fracture zone, which shares similar mineral assemblages with the Wangu deposit, is crosscut by a silicified rock that contains muscovite with a ca. 130 Ma ⁴⁰Ar–³⁹Ar age. The gold mineralization age of the Wangu deposit is thus confined between 142 Ma and 130 Ma. This age of mineralization suggests that the deposit was formed simultaneously with or subsequently to the development of NE-trending extensional faults, the emplacement of Late Jurassic–Cretaceous granites and the formation of Cretaceous basins filled with red-bed clastic rocks in northeastern Hunan, which forms part of the Basin and Range-like province in South China. EMPA analysis shows that the average As content in arsenopyrite is 28.7 atom %, and the mineralization temperature of the arsenopyrite–pyrite–quartz stage is estimated to be 245 ± 20 °C from arsenopyrite thermometry. The high but variable Au/As molar ratios (>0.02) of pyrite suggest that there are nanoparticles of native Au in the sulfides. An integration of S–Pb–H–O–He–Ar isotope systematics suggests that the ore fluids are mainly metamorphic fluids originated from host rocks, possibly driven by hydraulic potential gradient created by reactivation of the WNW-trending faults initially formed in Paleozoic, with possible involvement of magmatic and mantle components channeled through regional fault networks. The Wangu gold deposit shares many geological and geochemical similarities as well as differences with typical orogenic, epithermal and Carlin-type gold deposits, and may be better classified as an “intracontinental reactivation” type as proposed for many other gold deposits in the Jiangnan Orogen.     

Geochronological and mineralogical constraints on mineralization of the Hetai goldfield in Guangdong Province,South China

The Hetai goldfield, located in the southern segment of the Qinzhou Bay-Hangzhou Bay Juncture Orogenic Belt (QHJB), is the largest concentration of gold deposits in Guangdong Province, South China. The gold mineralization is hosted within the late Neoproterozoic to early Paleozoic Yunkai Group and strictly confined to mylonite (ductile shear) zones. The nature of the structural control of mineralization, in particular the role of ductile versus brittle deformation and their ages, which remain unclear despite numerous previous studies, are examined in this paper through an integrated study of geochronology and mineralogy.Lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism, but the majority of the ores are associated with brittle deformation features. In combination with macroscopic and microscopy observations on shear fabrics, LA-ICP-MS U-Pb dating on zircons of hydrothermal origin from mylonites suggests that the Hetai goldfield was subjected to two shearing events: an early sinistral ductile shearing at ca. 240 Ma, and a late dextral ductile-brittle shearing at ca. 204 Ma (Indosinian). These ages are ca. 90–30 Ma older than the previously published gold mineralizing ages of ca. 175–152 Ma (Yanshanian), suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation. This inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite (ca. 350–290 °C), chlorite (ca. 260–230 °C), and sphalerite (ca. 230–170 °C) intergrown with native gold, which are considerably lower than that for the ductile deformation (500–300 °C or higher). Based on these data, we propose that the gold mineralization in the Hetai goldfield predominantly occurred during the Yanshanian event, and only minor gold mineralization and associated sulfidation took place during the earlier Indosinian ductile deformation.     

Geochemistry,petrogenesis and tectonic setting of Neoproterozoic mafic–ultramafic rocks from the western Jiangnan orogen,South China

The Jiangnan orogenic belt (JOB) has been interpreted as a suture zone between the Yangtze craton and Cathaysian terranes in South China. The Neoproterozoic mafic–ultramafic rocks are extensively exposed in the western JOB, providing an ideal opportunity to study the Neoproterozoic assembly and tectonic evolution of South China. We present integrated field and geochemical studies including LA-ICP-MS zircon U–Pb dating, and whole-rock major and trace element and Sm–Nd isotope analyses of the Neoproterozoic mafic–ultramafic rocks exposed in the northern Guangxi Province, South China. Geochronological results show that the magmatic events took place in two distinct periods: the early Neoproterozoic (861–834 Ma) and the late Neoproterozoic (770–750 Ma). Early Neoproterozoic ultramafic rocks of the Sibao Group have positive ε_Nd(t) values (+ 2.7 to + 6.6) whereas mafic rocks exhibit negative ε_Nd(t) values (− 5.8 to − 0.9). The basaltic rocks show TiO₂ contents of 0.62–0.69 wt.% and Mg-number of 59–65, and also display an enrichment of light rare earth elements (LREEs) and pronounced negative Nb, Ta and Ti anomalies on chondrite- and primitive mantle-normalized diagrams, consistent with subduction-related geochemical signatures. Late Neoproterozoic rocks of the Danzhou Group show ε_Nd(t) values (− 1.23 to + 3.19) for both ultramafic and mafic rocks. The basaltic rocks have TiO₂ contents of 1.01–1.33 wt.% and Mg-number of 57–60, and have a mixture of MORB- and arc-like geochemical affinities, inferred to have formed in an extensional arc environment. Geochemical signatures suggest that all rock types in this study were derived from subarc mantle wedge sources and underwent various degrees of crustal contamination. Thus, we suggest that subduction may have continued to ca. 750 Ma in the western JOB, implying that the amalgamation event between the Yangtze craton and Cathaysian terranes was later than 750 Ma.     

Cenozoic metallogeny of Greece and potential for precious,critical and rare metals exploration

The Cenozoic metallogeny in Greece includes numerous major and minor hydrothermal mineral deposits, associated with the closure of the Western Tethyan Ocean and the collision with the Eurasian continental plate in the Aegean Sea, which started in the Cretaceous and is still ongoing. Mineral deposits formed in four main periods: Oligocene (33–25 Ma), early Miocene (22–19 Ma), middle to late Miocene (14–7 Ma), and Pliocene-Pleistocene (3–1.5 Ma). These metallogenic periods occurred in response to slab-rollback and migration of post-collisional calc-alkaline to shoshonitic magmatism in a back-arc extensional regime from the Rhodopes through the Cyclades, and to arc-related magmatism along the active south Aegean volcanic arc. Invasion of asthenospheric melts into the lower crust occurred due to slab retreat, and were responsible for partial melting of metasomatized lithosphere and lower crustal cumulates. These geodynamic events took place during the collapse of the Hellenic orogen along large detachment faults, which exhumed extensive metamorphic core complexes in mainly two regions, the Rhodopes and the Cyclades. The detachment faults and supra-detachment basins controlled magma emplacement, fluid circulation, and mineralization.The most significant mineralization styles comprise porphyry, epithermal, carbonate-replacement, reduced intrusion-related gold, intrusion-related Mo-W and polymetallic veins. Porphyry and epithermal deposits are commonly associated with extensive hydrothermal alteration halos, whereas in other cases alteration is of restricted development and mainly structurally controlled. Porphyry deposits include Cu-Au-, Cu-Mo-Au-Re, Mo-Re, and Mo-W variants. Epithermal deposits include mostly high- and intermediate-sulfidation (HS and IS) types hosted in volcanic rocks, although sedimentary and metamorphic rock hosted mineralized veins, breccias, and disseminations are also present. The main metal associations are Cu-Au-Ag-Te and Pb-Zn-Au-Ag-Te in HS and IS epithermal deposits, respectively. Major carbonate-replacement deposits in the Kassandra and Lavrion mining districts are rich in Au and Ag, and together with reduced intrusion-related gold systems played a critical role in ancient economies. Finally hundreds of polymetallic veins hosted by metamorphic rocks in the Rhodopes and Cyclades significantly add to the metal endowment of Greece.     

Paleogene magmatism and gold metallogeny of the Jinping terrane in the Ailaoshan ore belt,Sanjiang Tethyan Orogen (SW China): Geology,deposit type and tectonic setting

The Jinping terrane is situated in the southern segment of the Ailaoshan ore belt, Sanjiang Tethyan Orogen (SW China). The Paleogene intrusions in Jinping consist of syenite porphyry, fine-grained syenite and biotite granite stocks/dikes, and contain relatively low TiO₂ (0.21–0.38 wt%), P₂O₅ (0.01–0.35 wt%), and high Na₂O (2.00–4.62 wt%) and K₂O (4.48–7.06 wt%), belonging to high-K alkaline series. Paleogene gold mineralization in Jinping comprises four genetic types, i.e., orogenic, alkali-rich intrusion-related, porphyry and supergene laterite. The NW–NNW-trending faults and their subsidiaries are the major ore-controlling structures. The orogenic Au mineralization, dominated by polymetallic sulfide-quartz veins, occurs in the diorite and minor in Silurian-Devonian sedimentary rocks. It contains a CO₂-rich mesothermal fluid system generated from the mixing of mantle-derived fluids with crustal-derived metamorphic fluids, and the ore-forming materials were upper crustal- or orogenic-derived. The alkali-rich intrusion-related Au mineralization is hosted in the Ordovician-Silurian sedimentary rocks and minor in the Paleogene alkaline intrusions, and the Au orebodies occur predominantly in the alteration halos. It contains a CO₂-bearing, largely metamorphic-sourced mesothermal fluid system, and the ore-forming materials were derived from the ore-hosting rocks and minor from the alkali-rich intrusions. The porphyry Cu-Mo-Au mineralization occurs in the granite/syenite porphyries and/or along their contact skarn, with the mineralizing fluids being magmatic-hydrothermal in origin. The former two hypogene Au mineralization types in Jinping were mainly formed in the late Eocene (ca. 34–33 Ma) and slightly after the porphyry Cu-Mo-Au mineralization (ca. 35–34 Ma), which is coeval with the regional Himalayan orogenic event. Subsequent weathering produced the laterite Au mineralization above or near the hypogene Au orebodies.     

The Guelb Moghrein Cu–Au deposit: Neoarchaean hydrothermal sulfide mineralization in carbonate-facies iron formation

The Guelb Moghrein copper–gold deposit in the Islamic Republic of Mauritania reopened in 2006 and has produced copper concentrate and gold since then. The deposit is hosted in Neoarchaean–Palaeoproterozoic Fe–Mg carbonate-dominated metamorphic rocks interpreted as carbonate-facies iron formation. It forms tabular orebodies controlled by shear zones in the hanging wall and footwall of this meta-iron formation. Copper and gold are hosted in a complex sulfide ore in tectonic breccia replacing Fe–Mg carbonate and magnetite. Hydrothermal monazite dates the mineralization at 2492 ± 9 Ma. Two types of aqueous fluid inclusions suggest fluid mixing at 0.75–1.80 kbar and ~ 410 °C as the mineralization and precipitation mechanism, which is temporally coincident with regional retrograde metamorphism at 410 ± 30 °C (garnet-biotite). Distal alteration zones are enriched in K, Rb and Cu, whereas orebodies are depleted in K, Rb, Sr and Ba. The copper–gold mineralization at Guelb Moghrein formed during retrograde shearing in metamorphic rocks and contemporaneous hydrothermal alteration. The stable isotope signature of alteration and ore minerals suggest an external crustal fluid source. Fluids were focused in the reactive and competent meta-iron formation. Potassium alteration, magnetite and copper–gold mineralization suggest an IOCG mineral system akin similar deposits in Australia and Brazil.     

40Ar/39Ar geochronological constraints on the formation of the Dayingezhuang gold deposit: New implications for timing and duration of hydrothermal activity in the Jiaodong gold province,China

China's largest gold resource is located in the highly endowed northwestern part of the Jiaodong gold province. Most gold deposits in this area are associated with the NE- to NNE-trending shear zones on the margins of the 130–126 Ma Guojialing granite. These deposits collectively formed at ca. 120 ± 5 Ma during rapid uplift of the granite. The Dayingezhuang deposit is a large (> 120 t Au) orogenic gold deposit in the same area, but located along the eastern margin of the Late Jurassic Linglong Metamorphic Core Complex. New ⁴⁰Ar/³⁹Ar geochronology on hydrothermal sericite and muscovite from the Dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 ± 4 Ma and is the earliest important gold event that is well-documented in the province. The Dayingezhuang deposit occurs along the Linglong detachment fault, which defines the eastern edge of the ca. 160–150 Ma Linglong granite–granodiorite massif. The anatectic rocks of the massif were rapidly uplifted, at rates of at least 1 km/m.y. from depths of 25–30 km, to form the metamorphic core complex. The detachment fault, with Precambrian metamorphic basement rocks in the hangingwall and the Linglong granitoids and migmatites in the footwall, is characterized by early mylonitization and a local brittle overprinting in the footwall. Gold is associated with quartz–sericite–pyrite–K-feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault. Our results indicate that there were two successive, yet distinct gold-forming tectonic episodes in northwestern Jiaodong. One event first reactivated the detachment fault along the edge of the Linglong massif between 134 and 126 Ma, and then a second reactivated the shears along the margins of the Guojialing granite. Both events may relate to a component of northwest compression after a middle Early Cretaceous shift from regional NW–SE extension to a NE–SW extensional regime.     

Gold occurrences of the Archean North Atlantic craton,southwestern Greenland: A comprehensive genetic model

The North Atlantic craton of southwestern Greenland hosts several orogenic gold occurrences, although, to date, none is in production. Four gold provinces are distinguished and include Godthåbsfjord, Tasiusarsuaq, Paamiut, and Tartoq. In the Godthåbsfjord gold province, the hypozonal gold occurrences are aligned along the major ca. 2660–2600 Ma Ivinnguit fault. Orogenic gold mineralization correlates temporally with, and is related to, ductile deformation along this first-order structure. The northern part of the Tasiusarsuaq gold province is characterized by small hypozonal gold occurrences that are controlled by 2670–2610 Ma folds and shear zones. Auriferous fluids were focused into the structures in both gold provinces during west-directed accretion of the Kapisilik terrane (2650–2580 Ma) to the already amalgamated terranes of the North Atlantic craton. In the southern part of the Tasiusarsuaq gold province, hypozonal gold mineralization is hosted in back-thrusts (Sermilik prospect) and thrusts (Bjørnesund prospect) that formed at 2740 Ma and 2860–2830 Ma, respectively. The deformation is related to the ca. 2850 Ma accretion of the Sioraq block and the Tasiusarsuaq terrane, and the 2800–2700 Ma accretion of the Tasiusarsuaq terrane and the Færingehavn and Tre Brødre terranes.Mesozonal orogenic gold mineralization is hosted in an accretionary complex in the Paamiut and Tartoq gold provinces. Gold occurrences cluster over a strike extent of approx. 40 km in thrusts and complex strike-slip settings in lateral ramps. The timing of the E-vergent terrane accretion in both areas is unknown, and could either be at ca. 2850 Ma or 2740 Ma. In the eastern part of the Paamiut gold province, quartz veins and associated alteration zones were overprinted by granulite facies metamorphism and show evidence for partial melting. These outermost parts of the accretionary complex were involved in burial-exhumation tectonics during crustal accretion.Mainly three different orogenic stages related to gold mineralization are distinguished in the North Atlantic craton between ca. 2850 Ma and 2610 Ma. These are generally accretionary tectonic episodes, and gold mineralization is hosted either in reactivated fault systems between terranes or accretionary complex structures along the deformed cratonic margin. The larger orogenic gold occurrences formed at ca. 2740–2600 Ma that appears to be a period of orogenic gold mineralization globally, although significant gold resources in the North Atlantic craton have yet to be identified.     

Structural evolution of the Mokrsko-West,Mokrsko-East and Čelina gold deposits,Bohemian Massif,Czech Republic: Role of fluid overpressure

The studied Mokrsko-West (90–100 t Au), Mokrsko-East (30 t Au) and Čelina (11 t Au) deposits represent three spatially and genetically interrelated deposits of supposed affiliation to the intrusion-related gold deposit type. The deposits differ in their dominant host rocks, which are represented by ca 354 Ma old biotite tonalite (Mokrsko-West) and Neoproterozoic volcanic and volcanosedimentary rocks (Mokrsko-East, Čelina). Another difference lies in the style of veining — densely spaced networks of 0.1–5 mm thin veins (Q₂) within the tonalite, compared to thick (usually 5–20 cm; Q_1–2) and widely spaced veins within the Neoproterozoic rocks.Five generations of quartz veins, referred to as Q₀ through Q₄ were distinguished: Q₀ veins are the oldest and ore-barren, Q₁ veins mark the onset of the Au-ore formation, Q₂ veins its culmination and Q₃ veins its fading. Late quartz gangue (Q₄) is associated with uneconomic Ag–Pb–Zn vein-type ores hosted by calcite–barite–(quartz) veins.Quartz vein thickness (~ 0.3 to ~ 300 mm), spacing (~ 3 mm to ~ 500 mm), distribution, and related extensional strain (ca. 3–25%) evolve systematically across the studied ore district, reflecting both the major host rock and other tectonic factors. Detailed study of vein dimension parameters (thickness, length, width, aspect ratios) allowed estimation of the probable depth of the fluid source reservoir (~ 2 km or ~ 4 km) below the present surface. The depth to the fluid source seems to increase through time, being the shallowest for the Q₀ veins and the deepest for the Q₂ veins. Two independent methods of estimating fluid overpressure are discussed in the paper. Fluid overpressure during vein formation decreases from the Q₀ through the Q₂ veins, from 10 to 4 MPa or from 26 to 10 MPa, depending on the assumed tensile strength of the tonalite (5.5 and 15 MPa, respectively).The origin of joints and veins is discussed in terms of the stress orientation and crack-seal and crack-jump mechanisms. Field relationships unambiguously indicate that the veins hosted by Neoproterozoic rocks originated by reopening of the pre-existing extension joints (J₁) due to fluid overpressure. The origin of the densely-spaced thin veins (Q₂) hosted by the tonalite at the Mokrsko-West deposit is, however, less certain. It is probable that the tonalite was already affected by microfracturing analogous to the J₁ joints prior to the formation of quartz veins.The formation of the Q_1–2 veins at the Mokrsko-East deposit was constrained by the Re–Os dating of molybdenite to 342.9 ± 1.4 Ma. The ore-bearing hydrothermal system is thus ca 12 Ma younger than the tonalite that hosts the Mokrsko-West deposit. A similar ca 15–2 Ma difference between the age of the host-intrusion and the age of the hydrothermal event was encountered in several other gold deposits in the vicinity of the Central Bohemian Plutonic Complex. Two hypotheses to explain this are discussed in the paper.     

Late Permian–Triassic metallogeny in the Chinese Altay Orogen: Constraints from mica 40Ar/39Ar dating on ore deposits

The Central Asian Orogenic Belt (CAOB) constitutes the largest Phanerozoic accretionary orogen on Earth. It extends over 5000 km and hosting numerous metal deposits. The Chinese Altay Orogen, an important element of the CAOB, hosts abundant Devonian (ca. 410–370 Ma) deposits. The ⁴⁰Ar/³⁹Ar dating of seven mica separates from the representative samples syngenetic with orogenic-type mineralization is summarized to record a poorly studied Permian to Triassic metallogenic episode in the Chinese Altay Orogen. The Kelan and Maizi basins in the Chinese Altay Orogen, which likely represent an arc accretionary complex, contain a series of polymetallic lode deposits hosted in low-grade metamorphic volcano–sedimentary rocks. Two muscovite and five biotite separates were obtained from the ore-forming veins paragenetically associated with Au-bearing polymetallic sulfides in the Keketale Pb–Zn, Wulasigou Cu, Tiemurt Pb–Zn, Dadonggou Pb–Zn and Sarekuobu Au deposits. These separates yielded ⁴⁰Ar/³⁹Ar plateau ages ranging from 260 Ma to 205 Ma. Integration of these results with other published geological and geochronological data indicates that the Au–Cu–Pb–Zn mineralization post-dated the final CAOB assembly, with fluid movement and mineralization possibly driven by regional metamorphism and deformation. It is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the CAOB results into the formation of the deposits.     

Age and petrogenesis of the Neoproterozoic Chon-Ashu alkaline complex,and a new discovery of chalcopyrite mineralization in the eastern Kyrgyz Tien Shan

Neoproterozoic volcanics and granitoids formed at Rodinia margins within a time span of 880 Ma–700 Ma, are well-documented in many terranes of the southern Central Asian Orogenic Belt (CAOB). Ages younger than 550 Ma corresponding to the opening of the Terskey Ocean are also common. However, so far, there were very few published ages in the range 700 Ma–550 Ma from the Kyrgyz Tien Shan. In this paper we present new data for the alkaline Chon-Ashu complex emplaced at the end of the Cryogenian Period of the Neoproterozoic (850–635 Ma, Gradstein et al., 2012). The alkaline complex intrudes the Precambrian metamorphic rocks north of the Nikolaev Line which separates the Northern and Middle Tien Shan terranes in the eastern Kyrgyzstan. The undeformed shallow level alkaline rocks range from olivine gabbro to nepheline and cancrinite syenites and leucosyenites. The differentiated rock assemblage can be explained by fractional crystallization of high-silica mineral phases which drives nepheline-normative melts away from the silica saturation boundary. The alkaline rocks of Chon-Ashu are enriched in LILE and HFSE indicative of their origin from lithospheric mantle. An age of 678 ± 9 Ma (U–Pb, SHRIMP) was obtained for a protolith of country gneiss, and an age of 656 ± 4 Ma was obtained for the crosscutting alkaline rocks of the Chon-Ashu complex. Seven zircon grains recovered from gneiss and alkaline rocks had bright overgrown rims which yielded a cumulative age of 400 ± 8 Ma. A metamorphic event, followed by uplift and emplacement of shallow level alkaline complex, constrains the geodynamic setting. Alkaline rocks usually form in an extensional setting and originate from lithospheric mantle. The 690 Ma xenoliths of mafic granulite from the NW Tarim have been interpreted to originate by mafic underplating. This mafic underplating may have been responsible for metamorphism in the middle crust prior to emplacement of the Chon-Ashu complex. The 670 Ma–630 Ma period of extension and emplacement of enriched alkaline rocks can be also traced on a regional scale through southern Kazakhstan and the northern Tarim. We tentatively interpret these events as a result of mafic underplating and subsequent rifting related to the break-up of Rodinia. During field work at Chon-Ashu, rich chalcopyrite mineralization has been discovered in carbonate veinlets in leucosyenite alkaline dikes and has also been found in the adjacent Cambrian gabbro and granites shown on the map as undivided Devonian–Silurian. Stockwork mineralization predominates though disseminated mineralization is also present. The Cu content reaches 16,184 ppm and is associated with elevated concentrations of Pb, Zn and Ag. The polyphase structural evolution of the area suggests that mineralization could have formed in several genetically unrelated stages. Based on structural and mineralogical evidence we tentatively relate the earliest stage of chalcopyrite mineralization to the late magmatic CO₂-rich fluids emanating from the Cryogenian alkaline complex. The Early Devonian thermal event registered by growth of new zircon at 400 Ma has important metallogenic implications on a regional scale. However the origin of two zones of alteration in the undivided Silurian–Devonian granites is ambiguous because their age was not determined geochronologically. The 522 ± 4 Ma Cambrian gabbro of the Tashtambektor Formation is strongly foliated along the splays of the Nikolaev Line, indicating a Hercynian origin of the fabric. Superimposed mineralized stockwork postdates the foliation and suggests a late-Hercynian age of mineralization in gabbro. The new data enable a reassessment of the metallogenic potential of the Eastern Kyrgyz Tien Shan. Presence of not eroded high-level mineralized Neoproterozoic alkaline intrusions points to a previously underestimated metallogenic potential of pre-Hercynian granitoids which may host preserved porphyry systems, skarns and shear-related mineralization. Finally, the Devonian magmato-metamorphic event which caused formation of a number of ore deposits in central Kyrgyzstan and Kazakhstan could also create potential exploration targets in eastern Kyrgyzstan.     

U–Pb SHRIMP monazite ages of the giant Morro Velho and Cuiabá gold deposits,Rio das Velhas greenstone belt,Quadrilátero Ferrífero,Minas Gerais,Brazil

U–Pb SHRIMP results of 2672 ± 14 Ma obtained on hydrothermal monazite crystals, from ore samples of the giant Morro Velho and Cuiabá Archean orogenic deposits, represent the first reliable and precise age of gold mineralization associated with the Rio das Velhas greenstone belt evolution, in the Quadrilátero Ferrífero, Brazil. In the basal Nova Lima Group, of the Rio das Velhas greenstone belt, felsic volcanic and volcaniclastic rocks have been dated between 2792 ± 11 and 2751 ± 9 Ma, coeval with the intrusion of syn-tectonic tonalite and granodiorite plutons, and also with the metamorphic overprint of older tonalite–trondhjemite–granodiorite crust. Since cratonization and stable-shelf sedimentation followed intrusion of Neoarchean granites at 2612 + 3/− 2 Ma, it is clear that like other granite–greenstone terranes in the world, gold mineralization is constrained to the latest stages of greenstone evolution.     

The Mokrsko-West gold deposit,Bohemian Massif,Czech Republic: Mineralogy,deposit setting and classification

The Mokrsko-West deposit is unique among European Variscan gold deposits from the points of view of both the structure (an approx. 200 m thick complex of sheeted, several mm-thick, densely spaced quartz veins) and the economic viability (gold reserves of about 100 t). The deposit is hosted mainly by tonalite of the calc-alkaline Sázava tonalite suite (ca. 354 Ma) of the Central Bohemian Plutonic Complex. Mineralization is characterized by quartz-dominated gangue, no visible hydrothermal alteration, low sulfide content, high fineness native gold accompanied by maldonite, aurostibite, native bismuth and numerous Bi–Te–(S) phases. Five mineralogical stages are described in great detail. Arsenopyrite and chlorite thermometers, mineral phase stabilities and published isotope and fluid inclusion data are used to reconstruct the temperature and compositional evolution of the system. The role of liquid bismuth in the sequestration of gold is also discussed.The deposit shares the features of both orogenic gold (ORG) and intrusion-related gold (IRG) deposits. The IRG model is advocated by close spatial association between the ore zone and the tonalite host-intrusion, by the absence/scarcity of hydrothermal alteration, by the Au–Bi–Te–As elemental association and by marked thermal gradients from the early to late mineralization stages. The ORG model is advocated by an approx. 15–10 Ma gap between the intrusion of the tonalite-host and the ore formation, by isotope and geochemical evidence for a key role of metamorphic fluids in the mobilization and transfer of many elements/species (inclusive S and Au). The apparently ambiguous classification of the deposit can most probably be attributed to deposit formation at a depth of ≥ 9 km and to setting of the deposit at/inside a large-scale plutonic complex with multiple and prolonged tectonic and intrusive activity.     

Geochemical and geochronological constraints on the formation of shear-zone hosted Cu–Au–Bi–Te mineralization in the Stanos area,Chalkidiki, northern Greece

Copper–gold–bismuth–tellurium mineralization in the Stanos area, Chalkidiki Peninsula, Greece, occurs in the Proterozoic- to Silurian-aged Serbomacedonian Massif, which tectonically borders the Mesozoic Circum-Rhodope metamorphic belt to the west and crystalline rocks of the Rhodope Massif to the east. This area contains the Paliomylos, Chalkoma, and Karambogia prospects, which are spatially related to regional NW–SE trending shear zones and hosted by marble, amphibolite gneiss, metagabbro, and various muscovite–biotite–chlorite–actinolite–feldspar–quartz schists of the Silurian Vertiskos Unit. Metallic minerals occur as disseminated to massive aggregates along foliation planes and in boudinaged quartz veins. Iron-bearing sulfides (pyrite, arsenopyrite, and pyrrhotite) formed prior to a copper-bearing stage that contains chalcopyrite along with galena, sphalerite, molybdenite, and various minerals in the system Bi–Cu–Pb–Au–Ag–Te. Fluid inclusion homogenization temperatures of primary aqueous liquid–vapor inclusions in stage I quartz veins range from 170.1 °C to 349.6 °C (peak at ~ 230 °C), with salinities of 4.5 to 13.1 wt.% NaCl equiv. Calculated isochores intersect P–T conditions associated with the upper greenschist facies caused by local overpressures during late-stage tectonic movement along the shear zone in the Eocene, which produced stretching and unroofing of rocks in the region. Values of δ³⁴S for sulfides in the Stanos shear zone range from 2.42 to 10.19‰ and suggest a magmatic sulfur source with a partially reduced seawater contribution. For fluids in equilibrium with quartz, δ¹⁸O at 480 °C varies from 5.76 to 9.21‰ but does not allow for a distinction between a metamorphic and a magmatic fluid.A ¹⁸⁷Re–¹⁸⁷Os isochron of 19.2 ± 2.1 Ma for pyrite in the Paliomylos prospect overlaps ages obtained previously from intrusive rocks spatially-related to the Skouries porphyry Cu–Au, the Asimotrypes Au, and the intrusion-related Palea Kavala Bi–Te–Pb–Sb ± Au deposits in northern Greece, as well as alteration minerals in the carbonate-replacement Madem Lakkos Pb–Zn deposit. Ore-forming components of deposits in the Stanos area were likely derived from magmatic rocks at shallow depth that intruded an extensional shear environment at ~ 19 Ma.     

Genesis of Neoproterozoic Au-bearing volcanogenic sulfides and quartz veins in the Ar Rjum goldfield,Saudi Arabia

The Ar Rjum goldfield is an example of late Neoproterozoic Au mineralization that is hosted by submarine arc assemblage and syn-anorogenic intrusive rocks. Apart from ancient workings, recent exploration in the goldfield defined three main targets along 3 km N–S corridor (Um Na'am, Ghazal and Wasema), and indicated that Wasema alone hosts 11.8 Mt @ 2.5 g/t Au. The majority of gold and sulfide mineralization is confined to diorite, where gold content increases with shearing, pyrite–sericite–carbonate alteration and development stockworks of quartz–carbonate–pyrite veins and stringers. Generally, the concentration of gold increases in the diorite samples that experienced variable degrees of hydrothermal alterations near local shear zones. Anomalous gold content (up to 11.76 g/t) in some metachert is the result of the remobilization of volcanogenic lattice-bound (refractory) Au into free Au due to post-metamorphic hydrothermal alterations. The chemistry of pyrite from the mineralized veins and stringers indicates considerable amounts of gold that reaches ~ 0.3 wt.%.Chlorite that co-exists with pyrite in the hydrothermally altered metavolcanics is mostly sheridanite with up to ~ 25 wt.% FeO^t and minor amounts of ripidolite. Chlorite geothermometry suggests that two temperature ranges affecting the area. The first temperature range (290–334 °C) is consistent with regional greenschist facies metamorphism, and the second (306–355 °C) is interpreted to be related to recrystallization-submarine hydrothermal alteration related to the gold mineralization. Stable isotope (δ³⁴S, δ¹⁸O and δ¹³C) data suggest an original volcanogenic arc signature that has been slightly modified by low-grade metamorphism, and finally by the late interaction of hydrothermal fluids. Ore evolution model for the Ar Rjum goldfield includes seafloor sulfide alteration, several deformation episodes and intrusive effects, and in this context the ore resulted from the reduction of seawater sulfates. The gold-rich veins interpreted as orogenic lode deposits are confined to localized shear zones in a syn-orogenic diorite.     

Neoproterozoic magmatic events in the South Qinling Belt,China: Implications for amalgamation and breakup of the Rodinia supercontinent

Neoproterozoic magmatic rocks in the South Qinling Belt of China provide important clues for understanding the mechanism and timing of the amalgamation and breakup of the Rodinia supercontinent. Here we report new geochemical and high-precision LA-ICP-MS zircon U–Pb–Hf isotopic analyses on magmatic suites from the Liuba and Zhashui areas in the South Qinling Belt. Our data show that the crystallization ages of the granitic intrusions from Tiefodian and Tangjiagou in the Liuba area are 863 ± 22 Ma and 794 ± 11 Ma, respectively, whereas those of the dioritic and gabbroic intrusions at Chishuigou in the Zhashui area are 925 ± 28 Ma and 832.6 ± 4.0 Ma, respectively. The diorites at Chishuigou display arc-related geochemical affinity, characterized by strong depletion in Nb, Ta, P and Ti, and enrichment in large-ion lithophile elements (i.e., Rb, Ba, Th and U), indicating a subduction-related arc setting at ca. 925 Ma. The Tiefodian granitic rocks have high SiO₂ (68.46–70.98 wt.%), Na₂O (3.87–4.51 wt.%), and low K₂O (1.34–2.61 wt.%) contents with TTG affinity. However, their Cr, and Ni contents and Cr/Ni, Nb/Ta ratios are similar to those of continental crust, and together with high negative ε_Hf(t) values (− 4.87 to − 14.84), suggesting a continental margin arc at ca. 863 Ma. The gabbros at Chishuigou have high TiO₂ content (2.74–3.14 wt.%), Zr/Y (3.93–4.24), Ta/Yb (0.19–0.25) ratios and low Zr/Nb ratios (11.37–13.17), similar to the features of within-plate basalts, indicating an intra-continental rift setting at ca. 833 Ma. The granitoids at Tangjiagou exhibit enrichment of LREE, K and Pb, and depletion of Nb, Ta, P and Ti, suggesting an extensional tectonic environment at ca. 794 Ma.The results indicate that Neoproterozoic magmatic rocks in the South Qinling Belt formed before ca. 833 Ma and might represent the amalgamation of the Rodinia supercontinent in an arc-related subduction environment, whereas the magmatic events with the peak ages at ~ 740 Ma during ca. 833–680 Ma represent the breakup of Rodinia. Integrating our new data with those from previous works, we propose a new tectonic model for the evolutionary history of the South Qinling Belt in the Neoproterozoic, including four key stages: 1) an ocean that separated the South Qinling Belt and the Yangtze Block in the Early Neoproterozoic (ca.1000–956 Ma); 2) bidirectional subduction of the oceanic lithosphere during ca. 956–870 Ma; 3) subduction and collision between the South Qinling Belt and the Yangtze Block during ca. 870–833 Ma, thus suggesting that the South Qinling Belt was as a part of the Yangtze Block from this period; and 4) intra-continental rifting during ca. 833–680 Ma, although the blocks were not entirely rifted apart.     

Genesis of the Yuanlingzhai porphyry molybdenum deposit,Jiangxi province,South China: Constraints from petrochemistry and geochronology

The newly discovered Yuanlingzhai porphyry molybdenum (Mo) deposit in southern Jiangxi province belongs to the group of Mo-only deposits in the Nanling region. The mineralization developed at contact zones between the Yuanlingzhai granite porphyry and Neoproterozoic metamorphic rocks of the Xunwu Formation. Precise LA–MC–ICPMS zircon U–Pb dating of the Yuanlingzhai porphyry, as well as the adjacent western Keshubei and eastern Keshubei granites, yielded ages of 165.49 ± 0.59 Ma, 159.68 ± 0.43 Ma, and 185.13 ± 0.52–195.14 ± 0.63 Ma, respectively. Molybdenite Re–Os isochron ages of the ores are 160 ± 1–162.7 ± 1.1 Ma, which is consistent with the age of large-scale W–Sn deposits in South China. The Yuanlingzhai porphyry is characterized by high K₂O, P₂O₅, and A/CNK (1.33–1.59), and low CaO and Na₂O. The rock shows relatively enriched LREE without significant Eu anomalies (Eu/Eu^* = 0.80–0.90). Geochemical and mineralogical characteristics indicate that the ore-hosting porphyry is a typical S-type granite generated from the partial melting of crustal material with only minor mantle contribution. Both Harker and evolutionary discrimination diagrams indicate that the Yuanlangzhai and western Keshubei granites are not products of co-magmatic evolution. The Keshubei granites and Xunwu Formation were not significant sources for the components in the porphyry mineralization, but the Yuanlangzhai granite may have supplied some ore-forming material. However, the main ore-forming material was carried by fluids from deep sources, as demonstrated by fluid inclusion and stable isotope data from the molybdenum deposit. The Mo porphyry deposit formed in an extensional setting, and was possibly associated with Jurassic subduction of the Izanagi Plate.     

Three successive Proterozoic island arcs in the Northern Arabian–Nubian Shield: Evidence from SIMS U–Pb dating of zircon

Four isolated metamorphic complexes located within post-collisional granitoids occupying up to 70% of the total area, were distinguished in Sinai (Egypt) and Elat area (southern Israel), the northernmost part of the Arabian–Nubian Shield. The metamorphic rocks include metasediments, felsic and mafic metavolcanic rocks intruded by granitic, dioritic, and gabbroic plutons, all subjected to penetrative deformation.We present new SIMS U–Pb dating of zircons from 13 rock units comprising metasediments, volcanic rocks, gneisses and plutons from three metamorphic complexes (Sa'al, Feiran–Solaf, and Kid). In addition we present a SIMS U–Pb titanite age of a granitic gneiss previously dated using zircon. On the basis of the new and published U–Pb data, three successive Meso- to Neoproterozoic island arcs formed during a period of ca. 500 My are recognized. The Sa'al arc (represented by the oldest arc rocks in the ANS) evolved from 1.03 to 0.93 Ga (100 My); the Feiran–Elat arc developed from ca. 870 to 740 Ma (130 My), and the Kid arc formed from ca. 640 to 620 Ma (20 My). Evidence for an older, ca. 1.1 Ga, pre-Sa'al island arc was established from the zircon xenocryst population, though no exposures of rocks of this age were found. In the Sa'al and Kid arcs both volcanic and sedimentary rocks are preserved, whereas in the Elat–Feiran arc volcanic rocks are missing. We suggest that at ~ 700 Ma the Elat−Feiran arc was subjected to rifting that resulted in separating of the Qenaia block and its movement to the SE.     

Phanerozoic continental growth and gold metallogeny of Asia

The Asian continent formed during the past 800 m.y. during late Neoproterozoic through Jurassic closure of the Tethyan ocean basins, followed by late Mesozoic circum-Pacific and Cenozoic Himalayan orogenies. The oldest gold deposits in Asia reflect accretionary events along the margins of the Siberia, Kazakhstan, North China, Tarim–Karakum, South China, and Indochina Precambrian blocks while they were isolated within the Paleotethys and surrounding Panthalassa Oceans. Orogenic gold deposits are associated with large-scale, terrane-bounding fault systems and broad areas of deformation that existed along many of the active margins of the Precambrian blocks. Deposits typically formed during regional transpressional to transtensional events immediately after to as much as 100 m.y. subsequent to the onset of accretion or collision. Major orogenic gold provinces associated with this growth of the Asian continental mass include: (1) the ca. 750 Ma Yenisei Ridge, ca. 500 Ma East Sayan, and ca. 450–350 Ma Patom provinces along the southern margins of the Siberia craton; (2) the 450 Ma Charsk belt of north-central Kazakhstan; (3) the 310–280 Ma Kalba belt of NE Kazakhstan, extending into adjacent NW Xinjiang, along the Siberia–Kazakhstan suture; (4) the ca. 300–280 Ma deposits within the Central Asian southern and middle Tien Shan (e.g., Kumtor, Zarmitan, Muruntau), marking the closure of the Turkestan Ocean between Kazakhstan and the Tarim–Karakum block; (5) the ca. 190–125 Ma Transbaikal deposits along the site of Permian to Late Jurassic diachronous closure of the Mongol–Okhotsk Ocean between Siberia and Mongolia/North China; (6) the probable Late Silurian–Early Devonian Jiagnan belt formed along the margin of Gondwana at the site of collision between the Yangtze and Cathaysia blocks; (7) Triassic deposits of the Paleozoic Qilian Shan and West Qinling orogens along the SW margin of the North China block developed during collision of South China; and (8) Jurassic(?) ores on the margins of the Subumusu block in Myanmar and Malaysia. Circum-Pacific tectonism led to major orogenic gold province formation along the length of the eastern side of Asia between ca. 135 and 120 Ma, although such deposits are slightly older in South Korea and slightly younger in the Amur region of the Russian Southeast. Deformation related to collision of the Kolyma–Omolon microcontinent with the Pacific margin of the Siberia craton led to formation of 136–125 Ma ores of the Yana–Kolyma belt (Natalka, Sarylakh) and 125–119 Ma ores of the South Verkhoyansk synclinorium (Nezhdaninskoe). Giant ca. 125 Ma gold provinces developed in the Late Archean uplifted basement of the decratonized North China block, within its NE edge and into adjacent North Korea, in the Jiaodong Peninsula, and in the Qinling Mountains. The oldest gold-bearing magmatic–hydrothermal deposits of Asia include the ca. 485 Ma Duobaoshan porphyry within a part of the Tuva–Mongol arc, ca. 355 Ma low-sulfidation epithermal deposits (Kubaka) of the Omolon terrane accreted to eastern Russia, and porphyries (Bozshakol, Taldy Bulak) within Ordovican to Early Devonian oceanic arcs formed off the Kazakhstan microcontinent. The Late Devonian to Carboniferous was marked by widespread gold-rich porphyry development along the margins of the closing Ob–Zaisan, Junggar–Balkhash, and Turkestan basins (Amalyk, Oyu Tolgoi); most were formed in continental arcs, although the giant Oyu Tolgoi porphyry was part of a near-shore oceanic arc. Permian subduction-related deformation along the east side of the Indochina block led to ca. 300 Ma gold-bearing skarn and disseminated gold ore formation in the Truong Son fold belt of Laos, and along the west side to ca. 250 Ma gold-bearing skarns and epithermal deposits in the Loei fold belt of Laos and Thailand. In the Mesozoic Transbaikal region, extension along the basin margins subsequent to Mongol–Okhotsk closure was associated with ca. 150–125 Ma formation of important auriferous epithermal (Balei), skarn (Bystray), and porphyry (Kultuminskoe) deposits. In northeastern Russia, Early Cretaceous Pacific margin subduction and Late Cretaceous extension were associated with epithermal gold-deposit formation in the Uda–Murgal (Julietta) and Okhotsk–Chukotka (Dukat, Kupol) volcanic belts, respectively. In southeastern Russia, latest Cretaceous to Oligocene extension correlates with other low-sulfidation epithermal ores that formed in the East Sikhote–Alin volcanic belt. Other extensional events, likely related to changing plate dynamics along the Pacific margin of Asia, relate to epithermal–skarn–porphyry districts that formed at ca. 125–85 Ma in northeastmost China and ca. 105–90 Ma in the Coast Volcanic belt of SE China. The onset of strike slip along a part of the southeastern Pacific margin appears to correlate with the giant 148–135 Ma gold-rich porphyry–skarn province of the lower and middle Yangtze River. It is still controversial as to whether true Carlin-like gold deposits exist in Asia. Those deposits that most closely resemble the Nevada (USA) ores are those in the Permo-Triassic Youjiang basin of SW China and NE Vietnam, and are probably Late Triassic in age, although this is not certain. Other Carlin-like deposits have been suggested to exist in the Sepon basin of Laos and in the Mongol–Okhotsk region (Kuranakh) of Transbaikal.     

The Niassa Gold Belt,northern Mozambique – A segment of a continental-scale Pan-African gold-bearing structure?

The Niassa Gold Belt, in northernmost Mozambique, is hosted in the Txitonga Group, a Neoproterozoic rift sequence overlying Paleoproterozoic crust of the Congo–Tanzania Craton and deformed during the Pan-African Orogeny. The Txitonga Group is made up of greenschist-facies greywacke and schist and is characterized by bimodal, mainly mafic, magmatism. A zircon U–Pb age for a felsic volcanite dates deposition of the sequence at 714 ± 17 Ma. Gold is mined artisanally from alluvial deposits and primary chalcopyrite-pyrite-bearing quartz veins containing up to 19 ppm Au have been analyzed. In the Cagurué and M’Papa gold fields, dominantly N–S trending quartz veins, hosted in metagabbro and schist, are regarded as tension gashes related to regional strike-slip NE–SW-trending Pan-African shear zones. These gold deposits have been classified as mesozonal and metamorphic in origin. Re–Os isotopic data on sulfides suggest two periods of gold deposition for the Cagurué Gold Field. A coarse-crystalline pyrite–chalcopyrite assemblage yields an imprecise Pan-African age of 483 ± 72 Ma, dating deposition of the quartz veins. Remobilization of early-formed sulfides, particularly chalcopyrite, took place at 112 ± 14 Ma, during Lower Cretaceous Gondwana dispersal. The ～483 Ma assemblage yields a chondritic initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.123 ± 0.058. This implies a juvenile source for the ore fluids, possibly involving the hosting Neoproterozoic metagabbro. The Niassa Gold Belt is situated at the eastern end of a SW–NE trending continental-scale lineament defined by the Mwembeshi Shear Zone and the southern end of a NW–SE trending lineament defined by the Rukwa Shear Zone. We offer a review of gold deposits in Zambia and Tanzania associated with these polyphase lineaments and speculate on their interrelation.