Base and precious metal mineralization in Middle Jurassic rocks of the Lesser Caucasus: A review of geology and metallogeny and new data from the Kapan,Alaverdi and Mehmana districts

The polymetallic Cu–Au–Ag–Zn ± Pb, Cu–Au and Cu deposits in the Kapan, Alaverdi and Mehmana mining districts of Armenia and the Nagorno–Karabakh region form part of the Tethyan belt. They are hosted by Middle Jurassic rocks of the Lesser Caucasus paleo-island arc, which can be divided into the Kapan Zone and the Somkheto–Karabakh Island Arc. Mineralization in Middle Jurassic rocks of this paleo-island arc domain formed during the first of three recognized Mesozoic to Cenozoic metallogenic epochs. The Middle Jurassic to Early Cretaceous metallogenic epoch comprises porphyry Cu, skarn and epithermal deposits related to Late Jurassic and Early Cretaceous intrusions. The second and third metallogenic epochs of the Lesser Caucasus are represented by Late Cretaceous volcanogenic massive sulfide (VMS) deposits with transitional features towards epithermal mineralization and by Eocene to Miocene world-class porphyry Mo–Cu and epithermal precious metal deposits, respectively.The ore deposits in the Kapan, Alaverdi and Mehmana mining districts are poorly understood and previous researchers named them as copper–pyrite, Cu–Au or polymetallic deposits. Different genetic origins were proposed for their formation, including VMS and porphyry-related scenarios. The ore deposits in the Kapan, Alaverdi and Mehmana mining districts are characterized by diverse mineralization styles, which include polymetallic veins, massive stratiform replacement ore bodies at lithological contacts, and stockwork style mineralization. Sericitic, argillic and advanced argillic alteration assemblages are widespread in the deposits which have intermediate to high-sulfidation state mineral parageneses that consist of tennantite–tetrahedrite plus chalcopyrite and enargite–luzonite–colusite, respectively. The ore deposits are spatially associated with differentiated calc-alkaline intrusions and pebble dykes are widespread. Published δ³⁴S values for sulfides and sulfates are in agreement with a magmatic source for the bulk sulfur whereas published δ³⁴S values of sulfate minerals partly overlap with the isotopic composition of contemporaneous seawater. Published mineralization ages demonstrate discrete ore forming pulses from Middle Jurassic to the Late Jurassic–Early Cretaceous boundary, indicating time gaps of 5 to 20 m.y. in between the partly subaqueous deposition of the host rocks and the epigenetic mineralization.Most of the described characteristics indicate an intrusion-related origin for the ore deposits in Middle Jurassic rocks of the Lesser Caucasus, whereas a hybrid VMS–epithermal–porphyry scenario might apply for deposits with both VMS- and intrusion-related features.The volcanic Middle Jurassic host rocks for mineralization and Middle to Late Jurassic intrusive rocks from the Somkheto–Karabakh Island Arc and the Kapan Zone show typical subduction-related calc-alkaline signature. They are enriched in LILE such as K, Rb and Ba and show negative anomalies in HFSE such as Nb and Ta. The ubiquitous presence of amphibole in Middle Jurassic volcanic rocks reflects magmas with high water contents. Flat REE patterns ([La/Yb]_N = 0.89–1.23) indicate a depleted mantle source, and concave-upward (listric-shaped) MREE–HREE patterns ([Dy/Yb]_N = 0.75–1.21) suggest melting from a shallow mantle reservoir. Similar trace element patterns of Middle Jurassic rocks from the Somkheto–Karabakh Island Arc and the Kapan Zone indicate that these two tectonic units form part of one discontinuous segmented arc. Similar petrogenetic and ore-forming processes operated along its axis and Middle Jurassic volcanic and volcanosedimentary rocks constitute the preferential host for polymetallic Cu–Au–Ag–Zn ± Pb, Cu–Au and Cu mineralization, both in the Somkheto–Karabakh Island Arc and the Kapan Zone.     

The trinity pattern of Au deposits with porphyry,quartz–sulfide vein and structurally-controlled alteration rocks in Ciemas,West Java,Indonesia

The Ciemas gold mining area is located in the Sunda arc volcanic rock belt, West Java, Indonesia. Ore bodies are associated with Miocene andesite, dacite and quartz diorite porphyrite. To constrain ore genesis and mineralization significance, a detailed study was recently conducted examining these deposits, which included detailed field observation, petrographic study, petrochemistry, sulfur isotope analyses, zircon U–Pb dating, and fluid inclusion analysis. The results include the following findings. 1) Ore types have been identified as porphyry, a quartz–sulfide vein, and structure-controlled alteration rocks. 2) In host rocks, zircon LA–ICP-MS U–Pb dating of quartz diorite porphyrite, amphibole tuff breccia and andesite yield ages of 17.1 ± 0.4 Ma, 17.1 ± 0.4 Ma and 17.5 ± 0.3 Ma, respectively. 3) Fluid inclusions in the quartz from ore are given priority to liquid and gas–liquid phases, and their components are of the NaCl–H₂O system with homogenization temperatures of 240–320 °C, salinities of 14–17%, densities of 0.85–0.95 g/cm³, and fluid pressure values between 4.1 and 46.8 MPa, corresponding to metallogenic depths from 150 to 1730 m. Fluid characteristics are identified as similar to those of high sulfur epithermal deposits. 4) The sulfur isotopic compositions are notably uniform, the δ³⁴S values of wall rocks range from 3.71 to 3.85‰, and the δ³⁴S values of ores vary from 4.90‰ to 6.55‰. The sulfur isotopic composition of ores is similar to that of the wall rocks, indicating a mixed origin of mantle with a sedimentary basement. 5) The trace element patterns of different ore types are similar, which indicates that they originate from the same source. Au deposits primarily occurred during the late magmatic activity. Finally, we have set up the regional metallogenic model, confirming that this gold deposit in the Sunda arc volcanic rock belt belongs to a metallogenic system from porphyry to epithermal type.     

Genesis of the Zhengguang gold deposit in the Duobaoshan ore field,Heilongjiang Province,NE China: Constraints from geology,geochronology and S-Pb isotopic compositions

The Zhengguang gold deposit in the Duobaoshan ore field, hosted in volcanic rocks of the Middle Ordovician Duobaoshan Formation, is one of the largest gold deposits in the Northeastern Great Xing’an Range of the Central Asian Orogenic Belt (CAOB). The deposit comprises the No. I, II and III ore zones with a total resource exceeding 35 tonnes of Au, 100,000 tonnes of Zn and 100 tonnes of Ag. A genetic relationship between gold mineralization and concealed tonalite porphyry is inferred based on the characteristics of cryptoexplosive breccia and hydrothermal alteration indicative of porphyry-type and epithermal mineralization. Zircon LA-ICPMS U-Pb dating reveals that the tonalite porphyry was emplaced at 462.1 ± 1.8 Ma (Middle Ordovician). The δ³⁴S_V-CDT values of sulfide minerals range from −3.0‰ to −1.7‰ with an average of −2.33‰, indicating that sulfur was mainly derived from a magmatic source. The Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb ranging from 17.572 to 17.629, ²⁰⁷Pb/²⁰⁴Pb from 15.424 to 15.486, and ²⁰⁸Pb/²⁰⁴Pb from 37.206 to 37.418) suggest a major mantle component for Pb and, by inference, for other ore metals. Therefore, we suggest that the ore-forming elements in the Zhengguang gold deposit may be related to the mantle-sourced tonalite porphyry. On the basis of the geological characteristics and geochemical signatures documented in this study, we conclude that the Zhengguang gold deposit was formed in a porphyry to epithermal transitional environment associated with the concealed tonalite porphyry, as part of the Duobaoshan porphyry-epithermal ore system that is related to the subduction of the Paleo-Asian Ocean during the Ordovician.     

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.     

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.     

Recognition of Yanshanian magmatic-hydrothermal gold and polymetallic gold mineralization in the Laowan gold metallogenic belt,Tongbai Mountains: New evidence from structural controls,geochronology and geochemistry

The Laowan metallogenic belt in China is an important metallogenic belt within the Tongbai orogenic belt, and contains the medium-sized Laowan and Shangshanghe gold deposits, the small Huangzhuyuan lead–zinc–silver–gold deposit and some gold and Cu–Pb occurrences. These deposits are hosted in Mesoproterozoic plagioclase amphibolite (or schist) and mica-quartz schist. The gold ores are mainly quartz veins and veinlets and disseminated altered ores. Subordinate ore types include massive sulfides and breccias. The Laowan gold deposit is characterized by three right-stepping en-echelon fracture-controlled alteration zones that dip gently to the south and includes disseminated, sheeted and stockwork ores. These lodes were formed by the interaction of ore-forming fluid with foliated-to laminated cataclasite within the transpressional faults. The Shangshanghe gold deposit is characterized by parallel ore lodes that dip steeply to the north, and includes quartz veins and breccias in addition to ores in altered wallrocks. These lodes were formed by focusing of fluids into transtensional faults. These ore controlling faults displaced early barren quartz veins 10 m horizontally with a dextral sense of motion. The ore-hosting structures at the Laowan and Shangshanghe deposits correspond to the P and R-type shears of a brittle dextral strike-slip fault system, respectively, which make angles of about 15° and − 15° to the Laowan and Songpa boundary faults. The ore-controlling fault system post-dated formation of a ductile shear zone, and peak regional metamorphism. This precludes a genetic relationship between hydrothermal mineralization and regional metamorphism and ductile shear deformation. These gold deposits are not typical orogenic gold deposits. The metallogenic belt displays district-scale-zoning of Mo → Cu–Pb–Zn–Ag → Au relative to Songpa granite porphyry dike zone, suggesting the mineralization may be closely related to the granite porphyry. Measured δ³⁴S of sulfides and δ¹⁸O and δD of fluid inclusion waters in auriferous quartz also are consistent with a magmatic source for sulfur and ore fluids. The similarity of Pb isotope ratios between the ores and Yanshanian granitoids suggests a similar source. As the age (139 ± 3 Ma) of granite porphyry obtained by zircon U–Pb isotope overlaps the mineralization age (138 ± 1 Ma: Zhang et al., 2008a), the gold and polymetallic metallogenesis of the Laowan gold belt has close spatial, temporal and possibly genetic relationships with Yanshanian high level magmatism.     

Geochemical,fluid inclusion and isotopic (O,H and S) constraints on the origin of Pb–Zn ± Au vein-type mineralizations in the Eastern Pontides Orogenic Belt (NE Turkey)

The mineralization area (Altınpınar, Torul–Gümüşhane) is situated in the Southern Zone of the Eastern Pontides Orogenic Belt (EPOB), which is one of the important metallogenic provinces in the Alpine–Himalayan belt and is intruded by the late Carboniferous granitic rocks (Gümüşhane Granitoid), an early to middle Jurassic volcano-sedimentary unit consisting mainly of basaltic–andesitic volcanic and pyroclastic rocks (Şenköy Formation) and Eocene basaltic–andesitic volcanic rocks (Alibaba Formation). The studied Pb–Zn ± Au mineralizations are related to silica veins ranging from a few millimeters to a maximum of 40 cm in thickness and are localized within fracture zones developed along the contact between the Gümüşhane Granitoid and Şenköy Formation. Silicic, sulfidic, hematitic, argillic, intense chloritic and carbonate alteration are the most common types from the fault lines toward the outer zones. Cavity filling and banded structures are widely observed. The mineral paragenesis comprises galena, sphalerite, pyrite, chalcopyrite, tennantite and quartz. Mineral chemistry studies indicate that ion exchange occurs between Zn and Fe in sphalerites, and the Zn/Cd ratio of sphalerites varies between 50.65 and 144.64. The homogenization temperatures measured from fluid inclusions vary between 170 °C and 380 °C, especially between 250 °C and 300 °C, and the wt.% NaCl eqv. salinity of ore-forming fluids is between 2.4 and 7.3 (4.7 on average), supporting an epithermal system in their origin. The values of sulfur isotopes, which are obtained from pyrite and galena minerals, range between − 8.3‰ and − 2.3‰, indicating that sulfur, which enables mineral formation, originates from magmatic genesis. The average formation temperature of the ore is 317 °C as determined with a sulfur isotope geothermometer. The values of oxygen and hydrogen isotopes vary between 8.5‰ and 10.2‰ and − 91‰ and −73‰, respectively. With regard to the compositions of oxygen and hydrogen isotopes, fluids comprising the mineralization are formed by the mixture of magmatic water and meteoric water. This situation is supported by the fact that the increase in the homogenization temperature indicates dilution with surface water but depends on the increase in the salinity of fluid inclusions. Considering all the data, it is clear that the studied mineralization is an epithermal vein-type mineralization that is related to granitic magmas.     

Geological characteristics and metallogenesis of iron deposits in western Tianshan,China

The western Tianshan metallogenic belt is one of the most significant polymetallic iron metallogenic belts in China. Important advances have been achieved recently in iron exploration in the Awulale Mountain in western Tianshan, China. These newly-discovered iron deposits are mainly hosted in the basic-medium andesitic lavas and volcaniclastics, often comprising a number of high-grade ores. Magnetite is predominated in ore mineral assemblages, and pyrite, chalcopyrite, pyrrhotite or sphalerite increase in certain deposits. Wallrock alterations are intensively developed, exemplified as sodic–calcic and potassic alterations which display in different patterns as country rocks and ore-controlled structures vary. Skarn assemblages are commonly developed in ore districts like Beizhan, Dunde and Chagangnuoer, and pyroxene + albite + K-feldspar − epidote + actinolite alterations are dominated around ore bodies in Zhibo deposit, whereas the Shikebutai deposit develops alteration assemblages comprising of jasper, barite, sericite, and chlorite. Thus, iron deposits can be divided into three types including volcanic-sedimentary type, volcanic magmatic-hydrothermal type and iron skarn type. Our preliminary interpretation about the tectonic background of this iron mineralization in this area is in the late stage of a collisional–accretional orogenic belt around Carboniferous, with some extrusional–extensional tectonic transition locally. Iron mineralization is likely to have a close genetic relationship with volcanic–subvolcanic activity, syn- or slightly post- the volcanism which took place besides continental arc. Volcanic eruption contributes to majority of mineralizing iron, with minor extracted from hydrothermal replacement from wall rocks.     

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.     

Application of ASTER data for exploration of porphyry copper deposits: A case study of Daraloo–Sarmeshk area,southern part of the Kerman copper belt,Iran

The Cenozoic Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran is a major host to porphyry Cu ± Mo ± Au deposits (PCDs). Most known PCDs in the UDMB occur in the southern section of the belt, also known as the Kerman Copper Belt (KCB). Three major clusters of PCDs are distinguished in the KCB and include the Miduk, Sarcheshmeh and Daraloo clusters. The Daraloo and Sarmeshk deposits occur in a northwest–southeast-trending fault zone that is characterized by the presence of a narrow zone of alteration–mineralization that contains a series of Oligocene granitoids and Miocene porphyritic tonalite–granodiorite plutons that cut Eocene andesitic lava flows and pyroclastic rocks. Here we use various techniques, including different ratio images, minimum noise fraction, pixel purity index, and matched filter processing to process ASTER data (14 bands) and generate maps that portray the distribution of hydrothermal minerals (e.g., sericite, kaolinite, chlorite, epidote and carbonate) related to PCD alteration zones. In order to validate the ASTER data, follow-up ground proofing and related mineralogical work was done which, in all cases, proved to be positive. The results of this work have identified the regional distribution of hypogene alteration zones (i.e., phyllic, argillic, propylitic and silicic), in addition to areas of secondary Fe-oxide formation, which are coincident with known sites of PCDs. The regional distribution and extent of the alteration zones identified also highlighted the role of regional structures in focusing the mineralizing/altering fluids. These results demonstrate very convincingly that ASTER imagery that uses the appropriate techniques is reliable and robust in mapping out the extent of hydrothermal alteration and lithological units, and can be used for targeting hydrothermal ore deposits, particularly porphyry copper deposits where the alteration footprint is sizeable.     

Mineral chemistry and geochemical behavior of hydrothermal alterations associated with mafic intrusive-related Au deposits at the Atud area,Central Eastern Desert,Egypt

Vein-type gold deposits in the Atud area are related to the metagabbro–diorite complex that occurred in Gabal Atud in the Central Eastern Desert of Egypt. This gold mineralization is located within quartz veins and intense hydrothermal alteration haloes along the NW–SE brittle–ductile shear zone, as well as along the contacts between them. By using the mass balance calculations, this work is to determine the mass/volume gains and losses of the chemical components during the hydrothermal alteration processes in the studied deposits. In addition, we report new data on the mineral chemistry of the alteration minerals to define the condition of the gold deposition and the mineralizing fluid based on the convenient geothermometers. Two generations of quartz veins include the mineralized grayish-to-white old vein (trending NW–SE), and the younger, non-mineralized milky white vein (trending NE–SW). The ore minerals associated with gold are essentially arsenopyrite and pyrite, with chalcopyrite, sphalerite, enargite, and goethite forming during three phases of mineralization; first, second (main ore), and third (supergene) phases. Three main hydrothermal alteration zones of mineral assemblages were identified (zones 1–3), placed around mineralized and non-mineralized quartz veins in the underground levels. The concentrations of Au, Ag, and Cu are different from zone to zone having 25–790 ppb, 0.7–69.6 ppm, and 6–93.8 ppm; 48.6–176.1 ppb, 0.9–12.3 ppm, and 39.6–118.2 ppm; and 53.9–155.4 ppb, 0.7–3.4 ppm, and 0.2–79 ppm for zones 1, 2, and 3, respectively.The mass balance calculations and isocon diagrams (calculated using the GEOISO-Windows program) revealed the gold to be highly associated with the main mineralized zone as well as sericitization/kaolinitization and muscovitization in zone 1 more than in zones 2 and 3. The sericite had a higher muscovite component in all analyzed flakes (average X_Ms = 0.89), with 0.10%–0.55% phengite content in wall rocks and 0.13%–0.29% phengite content in mineralized quartz veins. Wall rocks had higher calcite (CaCO₃) contents and lower MgCO₃ and FeCO₃ contents than the quartz veins. The chlorite flakes in the altered wall rocks were composed of pycnochlorite and ripidolite, with estimated formation temperatures of 289–295 °C and 301–312 °C, respectively. Albite has higher albite content (95.08%–99.20%) which occurs with chlorite in zone 3.     

Evolution of hydrothermal fluids of HS and LS type epithermal Au–Ag deposits in the Seongsan hydrothermal system of the Cretaceous Haenam volcanic field,South Korea

The Haenam volcanic field was formed in the southern part of the Korean peninsula by the climactic igneous activity of the Late Cretaceous. The volcanic field hosts more than nine hydrothermal clay deposits and two epithermal Au–Ag deposits. This study focuses on the relationship between hydrothermal clay alteration and epithermal Au–Ag mineralization based on the geology, alteration mineralogy, geochronology, and mineralization characteristics.These clay and epithermal Au–Ag deposits are interpreted to have formed by the same hydrothermal event which produced two distinct types of mineral systems: 1) Au-dominant epithermal Au–Ag deposit and 2) clay-dominant hydrothermal clay deposit. The two types of mineral systems show a close genetic relationship as suggested by their temporal and spatial relationships. The Seongsan hydrothermal system progressively evolved from a low-intermediate sulfidation epithermal system with Au–Ag mineralization and phyllic alteration to an acid–sulfate high-sulfidation system with Au–Ag mineralization and/or barren advanced argillic/argillic alteration. The Seongsan system evolved during post volcanic hydrothermal activity for at least 10 Ma in the Campanian stage of the late Cretaceous.The Seongsan hydrothermal system shows the rare and unique occurrence of superimposed high to low (intermediate) sulfidation episodes, which persisted for about 10 Ma.     

The Engineer Mine,British Columbia: An example of epithermal Au-Ag mineralization with mixed alkaline and subalkaline characteristics

The Engineer Mine epithermal precious metal deposit in British Columbia, Canada, is related to Eocene Sloko-Skukum-Group (SSG) volcanism and, according to previous studies, contains roscoelite in intimate association with electrum. Roscoelite, a vanadian mica, is considered characteristic of low-sulfidation epithermal deposits related to alkaline magmatism. This contradicts the fact that the SSG volcanics are subalkaline. In order to address this ambiguity and to accurately classify the style of epithermal mineralization at the Engineer Mine we conducted detailed petrographic, mineralogical, geochronological, fluid inclusion, and stable isotope studies.The principal ore assemblage of the Engineer Mine epithermal veins precipitated in response to boiling during a hydrothermal event at 49.90 Ma ± 0.25 Ma. During this event electrum, arsenopyrite, pyrite ± chalcopyrite ± sphalerite ± löllingite ± tetrahedrite-group phases ± allargentum ± acanthite ± hessite ± dyscrasite ± stibarsen ± galena and an unidentified Ag-rich phase were deposited in conjunction with amorphous silica, platy and rhombic calcite, K-feldspar, and vanadian illite. Fluid inclusion and stable isotope data suggest that the ore-forming fluid was boiling at ∼220 °C during vein mineralization and had an isotopic composition derived from local meteoric water. Based on these results the Engineer Mine is classified as an epithermal low-sulfidation deposit, which shares similarities with alkaline and subalkaline epithermal low-sulfidation deposits. This is attributed to the fact that the SSG volcanic rocks are borderline subalkaline to alkaline in character and that the sedimentary host rocks are vanadium-bearing. These sedimentary rocks contributed the bulk of the vanadium to the Engineer Mine epithermal system. The presence of roscoelite at the Engineer Mine could not be confirmed during this study. The mica referred to as roscoelite in previous publications instead is vanadian illite. To our knowledge the only alkaline low-sulfidation epithermal precious metal deposit that contains V-mica which exclusively qualifies as true roscoelite is the Porgera deposit, Papua New Guinea.     

Genesis of the giant Zijinshan epithermal Cu-Au and Luoboling porphyry Cu–Mo deposits in the Zijinshan ore district,Fujian Province,SE China: A multi-isotope and trace element investigation

The Zijinshan ore district occurs as one of the largest porphyry-epithermal Cu–Au–Mo ore systems in South China, including the giant Zijinshan epithermal Cu–Au deposit and the large Luoboling porphyry Cu–Mo deposit. The mineralization is intimately related to Late Mesozoic large-scale tectono-magmatic and hydrothermal events. The Cu–Au–Mo mineralization occurs around intermediate-felsic volcanic rocks and hypabyssal porphyry intrusions. In this study, we summarize previously available Re–Os isotopes, zircon U–Pb age and trace elements, and Sr–Nd–Pb isotope data, and present new Pb–S and Re–Os isotope data and zircon trace elements data for ore-related granitoids from the Zijinshan high-sulfidation epithermal Cu–Au deposit and the Luoboling porphyry Cu–Mo deposit, in an attempt to explore the relationship between the two ore systems for a better understanding of their geneses. The ore-bearing porphyritic dacite from the Zijinshan deposit shows a zircon U-Pb age of 108–106 Ma and has higher zircon Ce⁴⁺/Ce³⁺ ratios (92–1568, average 609) but lower Ti-in-zircon temperatures (588–753 °C, average 666 °C) when compared with the barren intrusions in the Zijinshan ore district. Relative to the Zijinshan porphyritic dacite, the ore-bearing granodiorite porphyry from the Luoboling deposit show a slightly younger zircon U–Pb age of 103 Ma, but has similar or even higher zircon Ce⁴⁺/Ce³⁺ ratios (213–2621, average 786) and similar Ti-in-zircon temperatures (595–752 °C, average 675 °C). These data suggest that the ore-bearing magmatic rocks crystallized from relatively oxidized and hydrous magmas. Combined with the high rhenium contents (78.6–451 ppm) of molybdenites, the Pb and S isotopic compositions of magmatic feldspars and sulfides suggest that the porphyry and ore-forming materials in the Luoboling Cu–Mo deposit mainly originated from an enriched mantle source. In contrast, the ore-bearing porphyritic dacite in the Zijinshan Cu–Au deposit might be derived from crustal materials mixing with the Cathaysia enriched mantle. The fact that the Zijinshan Cu–Au deposit and the Luoboling Cu–Mo deposit show different origin of ore-forming materials and slightly different metallogenic timing indicates that these two deposits may have been formed from two separate magmatic-hydrothermal systems. Crustal materials might provide the dominant Cu and Au in the Zijinshan epithermal deposit. Cu and Au show vertical zoning and different fertility because the gold transports at low oxygen fugacity and precipitates during the decreasing of temperature, pressure and changing of pH conditions. It is suggested that there is a large Cu–Mo potential for the deeper part of the Zijinshan epithermal Cu–Au deposit, where further deep drilling and exploration are encouraged.     

The Late Paleozoic porphyry–epithermal spectrum of the Birgilda–Tomino ore cluster in the South Urals,Russia

The Birgilda–Tomino ore cluster in the East Uralian zone, South Urals, Russia, hosts a variety of Late Paleozoic porphyry copper deposits (Birgilda, Tomino, Kalinovskoe, etc.), high- and low sulfidation epithermal deposits (Bereznyakovskoe, Michurino), and skarn-related base metal mineralization (Biksizak) in carbonate rocks. The deposits are related to quartz diorite and andesite porphyry intrusions of the K–Na calc-alkaline series, associated to a subduction-related volcanic arc. We report microprobe analyses of ore minerals (tetrahedrite–tennantite, sphalerite, Bi tellurides and sulfosalts, Au and Ag tellurides), as well as fluid inclusion data and mineral geothermometry. On the basis of these data we propose that the Birgilda–Tomino ore cluster represents a porphyry–epithermal continuum, with a vertical extent of about 2–3 km, controlled by temperature decreases and fS₂ and fTe₂ increase from deeper to shallow levels.     

Gold mineralization in the Jiangnan Orogenic Belt of South China: Geological,geochemical and geochronological characteristics,ore deposit-type and geodynamic setting

Located in the southeastern margin of the Yangtze Block and generally interpreted as the Neoproterozoic collisional product of the Yangtze with the Cathaysia Blocks of South China, the Jiangnan Orogenic Belt (JOB) contains a number of gold (Au) (-polymetallic) ore deposits and mineral showings, mostly hosted by Neoproterozoic low-grade metamorphic volcaniclastic and sedimentary rocks. The mineralization styles mainly include auriferous quartz veins and disseminated mineralization in altered mylonite and cataclasite that are developed along shear zones, fracture zones and inter- or intra-formational fault zones closely related to regional folding and shearing deformation. Three gold mineralizing epochs are recognized in the JOB. The ca. 423–397 Ma mineralization was associated with the early Paleozoic tectonothermal event(s), which induced widespread emplacement of Silurian S-type granites, low-grade metamorphism and enrichment of gold in the Neoproterozoic rocks (i.e., forming Au source beds). The second Au mineralization epoch, occurring at ca. 176–170 Ma (Jurassic), was related to the subduction of the Paleo-Pacific plate beneath the South China continental margin. The third and most important Au mineralization epoch took place at ca. 144–130 Ma (early Cretaceous), when a Basin-and-Range tectonic pattern was developed, characterized by NE–NNE-trending strike-slip faults, granitic domes and metamorphic core complexes (MCC), and basins filled with red bed lithologies. C, H, O, He-Ar, S and Pb isotopic and fluid-inclusion data suggest that the ore fluids were predominantly metamorphic and/or magmatic, with variable input of mantle-derived fluids and the progressive involvement of meteoric waters in the later stages of mineralization. Ore materials were mostly contributed by the Neoproterozoic source beds, plus a possible contribution from mantle- or magma-derived components. The Au (-polymetallic) deposits in the JOB, particularly those formed in the early Cretaceous, share many geological and geochemical features with the orogenic-type and Carlin-type deposits. In the context of tectonic evolution of South China, the gold mineralization in the JOB may be considered an “intracontinental reactivation type”, characterized by synchronous development of Au–polymetallic mineralization, reactivation of stuctures developed in Neoproterozoic metamorphic rocks, and widespread granite emplacement in the late Mesozoic.     

Geology,geochemistry, and geochronology of Fe-oxide Cu (± Au) mineralization associated with Şamlı pluton,western Turkey

The Şamlı (Balıkesir) Fe-oxide Cu (± Au) deposit, one of several iron (+ Cu ± Au) deposits in western Turkey, is hosted by porphyritic rocks of the multi-phase Şamlı pluton and metapelitic–metadiabasic rocks of Karakaya Complex. Two successive mineralization events are recognized in the area as; i) early magnetite and sulfide and ii) late hematite–goethite-native copper (± Au). Alteration associated with the mineralization in Şamlı is characterized by four distinct mineralogical assemblages. They are, in chronological order of formation, (1) plagioclase–early pyroxene (± scapolite), (2) garnet–late pyroxene, (3) chlorite–epidote, and (4) chalcedony–calcite alteration. Geochemical, isotopic (Sr, Nd, O, S) and geochronological (Ar–Ar) data from alteration and magmatic rocks suggest a temporal and genetic link between the multiphase Şamlı pluton and the hydrothermal system that controls the Fe-oxide-Cu (± Au) mineralization. ⁴⁰Ar/³⁹Ar geochronology on hornblende and biotite separates of the Şamlı pluton yielded an age range between 23.20 ± 0.50 and 22.42 ± 0.11 Ma, overlapping with ⁴⁰Ar/³⁹Ar age of 22.34 ± 0.59 Ma from alteration.The close spatial and temporal associations of Şamlı mineralization with porphyritic intrusions, pervasive Ca-rich alteration (calcic plagioclase, andraditic garnet, diopsidic pyroxene, scapolite, and epidote) are considered as common features akin to calcic assemblages in typical IOCG deposits. Besides abundant low-Ti (≤ 0.5%) magnetite/hematite, high Cu–moderate Au (up to 8.82 ppm) association, structural control and lithologic controls of mineralization, low S-sulfide content (chalcopyrite > pyrite) in the deposit; and the derivation of causative magma from subduction-modified subcontinental lithospheric mantle under a transpressional to transtensional regime, are collectively considered as the features in favor of IOCG-type mineralization for the Şamlı deposit.     

Geological setting of the Wassa gold deposit,SW Ghana

Including past production, current indicated and inferred resources, Wassa is a 5 Moz poly-deformed early-orogenic gold deposit located on the eastern flank of the Ashanti Belt, in southwest Ghana. It is hosted by metamorphosed volcanic, intrusive and sedimentary rocks of the Sefwi Group (ca. 2260–2160 Ma). Early mineralization has an Eoeburnean age (2164 ± 22 Ma, Re–Os on pyrite) and is characterized by quartz veins, by a carbonate alteration of the host rocks, and by deformed gold-bearing pyrite. Remobilization of this gold occurred during the late stages of the Eburnean Orogeny (~ 2.1 Ga) and is associated with quartz-carbonate veins with visible gold and euhedral pyrites.     

Geological,geochemical, and geochronological characteristics of Weilasituo Sn-polymetal deposit,Inner Mongolia,China

The recently discovered Weilasituo Sn-polymetal deposit is located in the southern part of the Great Xing'an Range of Inner Mongolia, NE China, which is belonged to the eastern part of the Central Asian Orogenic Belt (CAOB). Sn-polymetal mineralization is closely related to the emplacement of the Early Cretaceous fine- to medium-grained quartz porphyry. Three types of mineralization have been recognized at Weilasituo with the disseminated and stockwork Sn-polymetal mineralization mainly hosted by the quartz porphyry, the vein-type Sn-polymetal mineralization hosted by NE-trending and WE-trending fractures and faults in the upper and outer part of the porphyry, and breccia mineralization occurred within a steep cryptoexplosive breccia pipe. The ore-related alteration typically consists of Na-Ca-Sr alteration and greisen.In order to understand the petrogenetic link between the Sn-polymetal mineralization and the host quartz porphyry, this paper presents new whole-rock geochemistry for the quartz porphyry, EPMA analysis of ore and gangue minerals, and in situ U-Pb dating of cassiterite. The Laser Abrasion Multiple Collector Inductively Coupled Plasma Mass Spectrometer (LA-MCICP-MS) cassiterite U-Pb dating yields two well-defined isochron ages of 138 ± 6 Ma for disseminated ore and 135 ± 6 Ma for the vein-type ore, which could be regarded as the ore-forming age. The cassiterite U-Pb ages (ca. 138–135 Ma) determined in this study, together with previous data, reveals the close temporal and genetic relationship between the mineralization event and the emplacement of the quartz porphyry.The quartz porphyry is characterized by high SiO₂, Na₂O, and A/CNK values (1.09–1.21). REE tetrad effect combined with extremely high Rb/Sr, K/Ba ratios and low K/Rb, Zr/Hf, La/Nb, La/Ta and Eu/Eu* ratios indicate that the quartz porphyry is a highly fractionated peraluminous I-type granite that is hydrothermally altered. Low εNd(t) values of 4.27–0.28 and the two-stage depleted mantle Nd model ages (T_2DM = ca. 1279–908 Ma) for the quartz porphyry, are similar to granites in Precambrian microcontinents of the eastern part of the Central Asian Orogen (CAOB). This suggests that the quartz porphyry was derived from the remelting of juvenile crust and Precambrian rocks in an extensional setting. Therefore, the highly fractional crystallization and magmatic-hydrothermal interactions of the quartz porphyry have contributed to the formation of the Weilasituo Sn-polymetal deposit.