The world-class Wona-Kona gold deposit,Burkina Faso

The world-class > 4 Moz Wona-Kona gold deposit is hosted within the Paleoproterozoic Birimian Houndé greenstone belt which is the most important gold mineralized belt in the western part of Burkina Faso, with a cumulative reserve of ~ 11 Moz. The mineralization consists of a pervasive silicification with disseminated pyrite–arsenopyrite crosscut by quartz–carbonate veinlets (1 to 10 cm wide) forming a vertical, thick (up to 40 m) and laterally extensive (5 km) northeast trending orebody hosted within a large (200 m wide) shear zone of regional extent. Gold occurs in association with 3 generations of pyrite and 2 generations of arsenopyrite. Free gold, interpreted as the last mineralizing event, occurs as late fracture filling in the pervasive silicification zone.     

Geodynamic settings for Paleoproterozoic gold mineralization in the Svecofennian domain: A tectonic model for the Fäboliden orogenic gold deposit,northern Sweden

Northern Sweden is currently experiencing active exploration within a new gold ore province, the so called Gold Line, situated southwest of the well-known Skellefte VMS District. The largest known deposit in the Gold Line is the hypozonal Fäboliden orogenic gold deposit. Mineralization at Fäboliden is hosted by arsenopyrite-rich quartz veins, in a reverse, mainly dip-slip, high-angle shear zone, in amphibolite facies supracrustal host rocks. The timing of mineralization is estimated, from field relationships, at ca. 1.8 Ga.The gold mineralization is hosted by two sets of mineralized quartz veins, one steep fault–fill vein set and one relatively flat-lying extensional vein set. Ore shoots occur at the intersections between the two vein sets, and both sets could have been generated from the same stress field, during the late stages of the Svecofennian orogen.The tectonic evolution during the 1.9–1.8 Ga Svecofennian orogen is complex, as features typical of both internal and external orogens are indicated. The similarity in geodynamic setting between the contemporary Svecofennian and Trans-Hudson orogens indicates a potential for world-class orogenic gold provinces also in the Svecofennian domain.The Swedish deposits discussed in this paper are all structurally associated with roughly N–S striking shear zones that were active at around 1.8 Ga, when gold-bearing fluids infiltrated structures related to conditions of E–W shortening.     

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.     

Geology and isotope geochemistry (C–O–S) of the Diyadin gold deposit,Eastern Turkey: A newly-discovered Carlin-like deposit

Diyadin mineralization is the first reported gold deposit located in a collisional tectonic environment in Eastern Anatolia. The mineralization is related to N–S and N10–20°W-trending fault systems and hosted within the Paleozoic metamorphic basement rocks of the Anatolide–Toride microcontinent. Calc-schist, dolomitic marble and Miocene and Quaternary volcanic rocks comprise the exposed units in the mineralized area. Geochemical signatures, alteration types and host rock characteristics of the Diyadin gold deposit resemble those of Carlin-type deposits. Mineralization is constrained by alteration of overlying volcanic rocks to younger than ~ 14 Ma (K–Ar).Carbon and oxygen stable isotope measurements of carbonate rocks were made on six drill holes (n = 81) with an additional four samples of fresh carbonate rocks from surface outcrops. Background carbonate rocks have δ¹³C_V-PDB ~ 1.8‰ and δ¹⁸O_V-SMOW ~ 27‰. Isotopically-altered host rock samples have decreased δ¹⁸O (down to ~+11.4‰) and variable δ¹³C (from − 3.6 to + 4.8‰). Postore carbonate veins and cave-fill material have distinctly different isotopic signatures, particularly carbon (from δ¹³C = + 8.4 to + 9.8‰). Whether this post-ore carbonate is simply very late in mineralization associated with the gold system, or is a completely different, younger system utilizing the same pathways, is unclear at present. Within the host rock sample set, there is no correlation between gold and δ¹³C, and a weak correlation between gold and δ¹⁸O, indicative of water–rock interaction and isotopic alteration. Both the isotopic data and structural mapping suggest that the main upflow zone for the deposit is near the northern portion of the drill fence. Additional data at multiple scales are required to clarify the relationship(s) between fluid flow and mineralization.     

In-situ LA–ICP–MS U–Pb geochronology and trace elements analysis of polygenetic titanite from the giant Beiya gold–polymetallic deposit in Yunnan Province,Southwest China

The Beiya gold–polymetallic deposit, located in the middle of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt, is one of the largest gold deposits in China. The mineralization mainly occurs in skarn along the intrusive contacts between the alkaline porphyries and Middle Triassic limestone. In this paper, we present U–Pb age as well as major and trace element geochemistry of titanite from the Beiya deposit, and distinguish the titanite into a magmatic- and a hydrothermal suite. Our study indicates that the titanite from the ore-related porphyry and from the mineralized skarn is texturally and geochemically very different. The euhedral, envelope-shaped titanite from the ore-related porphyry has lower FeO, F, HFSEs, Nb/Ta and Lu/Hf, together with higher TiO₂ and Th/U than the subhedral titanite from the mineralized skarn. The titanite from the porphyry also displays higher LREE/HREE and more subtle negative Eu anomaly than its mineralized skarn counterpart. This suggests a magmatic- and a hydrothermal origin for, respectively, the titanite from the ore-related porphyry and from the mineralized skarn. In-situ magmatic titanite U–Pb dating has yielded an Eocene age of 36.0 ± 5.9 Ma, consistent with the porphyry zircon U–Pb age (36.07 ± 0.43 Ma) obtained in previous studies. Hydrothermal titanite has yielded a weighted average ²⁰⁶Pb/²³⁸U age of 33.1 ± 1.0 Ma (MSWD = 2.0), which represents the age of the retrograde skarn alteration and the maximum age for the gold mineralization. Together with the previous molybdenite Re–Os age, we have further constrained the Beiya gold–polymetallic metallogeny to 33.1–34.1 Ma. The mineralization age is slightly younger than the porphyry emplacement, indicating that the Beiya metallogeny was likely to be a post-magmatic hydrothermal product of the Himalayan orogenic event. The REE characteristics of hydrothermal titanite also reveal that the ore forming fluids may have been derived from a highly oxidized magma.     

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.     

40Ar/39Ar dating of the Jiehe gold deposit in the Jiaodong Peninsula,eastern North China Craton: Implications for regional gold metallogeny

The Jiehe gold deposit, containing a confirmed gold reserve of 34 tonnes (t), is a Jiaojia-type (disseminated/stockwork-style) gold deposit in Jiaodong Peninsula. Orebodies are hosted in the contact zone between the Jurassic Moshan biotite granite and the Cretaceous Shangzhuang porphyritic granodiorite, and are structurally controlled by the NNE- to NE-striking Wangershan-Hedong Fault. Sulphide minerals are composed predominantly of pyrite with lesser amounts of chalcopyrite, galena, and sphalerite. Hydrothermal alteration is strictly controlled by fracture zones, in which disseminated sulfides and native gold are spatially associated with pervasive sericitic alteration. Mineralogical, textural, and field relationships indicate four stages of alteration and mineralization, including pyrite-bearing milky and massive quartz (stage 1), light-gray granular quartz–pyrite (stage 2), quartz–polysulfide (stage 3) and quartz–carbonate (stage 4) stages. Economic gold is precipitated in stages 2 and 3.The Jiehe deposit was previously considered to form during the Eocene (46.5 ± 2.3 Ma), based on Rb-Sr dating of sericite. However, ⁴⁰Ar/³⁹Ar dating of sericite in this study yields well-defined, reproducible plateau ages between 118.8 ± 0.7 Ma and 120.7 ± 0.8 Ma. These ⁴⁰Ar/³⁹Ar ages are consistent with geochronological data from other gold deposits in the region, indicating that all gold deposits in Jiaodong formed in a short-term period around 120 Ma. The giant gold mineralization event has a tight relationship with the extensional tectonic regime, and is a shallow crustal metallogenic response of paleo-Pacific slab subduction and lithospheric destruction in the eastern NCC.     

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.     

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.     

Contrasting mineralogical and processing potential of two mineralization types in the platinum group element and Ni-bearing Kapalagulu Intrusion,western Tanzania

The Kapalagulu layered ultramafic and mafic intrusion is emplaced between the Paleoproterozoic Ubendian basement and overlying Neoproterozoic Itiaso Group metasedimentary rocks, located near the western shore of Lake Tanganyika. High-grade platinum group element (PGE) mineralization (1–6 g/t Pt + Pd + Au) is associated with chromitite and sulfide-bearing harzburgite within the southeastern extension of the intrusion, known as the Lubalisi Zone, which is covered by a layer of nickel-rich (0.2–2%Ni) laterite regolith that contains linear areas of PGE mineralization.In the Lubalisi Zone, the mineralization may be divided into several significant geometallurgical domains: (a) high-grade PGE mineralization (1–6 g/t Pt + Pd + Au) associated with stratiform PGE reefs and chromitite seams within a harzburgite unit; (b) high-grade PGE mineralization (up to 12 g/t Pt + Pd + Au) associated with small bodies and veins of nickel massive sulfide within harzburgite below PGE-bearing reefs and chromitite seams; (c) low-grade PGE mineralization (0.1–0.5 g/t Pt + Pd + Au) associated with a sulfide-mineralized harzburgite unit above the PGE-bearing reefs; (d) laterite style residual PGE mineralization (0.2–4 g/t Pt + Pd + Au) associated with chromite concentrations in the saprolite and overlying red clay horizons of the laterite regolith; and (e) supergene Ni associated with the saprock and overlying saprolite clay.Mineralogical study of three samples from the PGE reef consisting of high grade PGE chromitite and harzburgite indicate that this mineralization will give a good metallurgical response to conventional grinding and floatation due to the relatively coarse-grained nature of the PGM (P80 from ∼37 to 52 µm), association with base metal sulfides, and unaltered gangue minerals (Wilhelmij and Cabri, 2016). In contrast, mineralogical and metallurgical study of the Ni and PGE mineralized laterite indicate that it cannot be processed using conventional mineral processing techniques but that a hydrometallurgical route should be used to recover the base and precious metals. Because any process is very much deposit-controlled, significant metallurgical and geometallurgical testing of mineralized samples, as well as pilot plant testing, will be required to arrive at feasibility studies.     

The Tasiast deposit,Mauritania

The Tasiast gold deposits are hosted within Mesoarchean rocks of the Aouéouat greenstone belt, Mauritania. The Tasiast Mine consists of two deposits hosted within distinctly different rock types, both situated within the hanging wall of the west-vergent Tasiast thrust. The Piment deposits are hosted within metasedimentary rocks including metaturbidites and banded iron formation where the main mineral association consists of magnetite-quartz-pyrrhotite ± actinolite ± garnet ± biotite. Gold is associated with silica flooding and sulphide replacement of magnetite in the turbidites and in the banded iron formation units. The West Branch deposit is hosted within meta-igneous rocks, mainly diorites and quartz diorites that lie stratigraphically below host rocks of the Piment deposits. Most of the gold mineralisation at West Branch is hosted by quartz–carbonate veins within the sheared and hydrothermally altered meta-diorites that constitute the Greenschist Zone. At Tasiast, gold mineralisation has been defined over a strike length > 10 km and to vertical depths of 740 m. All of the significant mineralised bodies defined to date dip moderately to steeply (45° to 70°) to the east and have a south–southeasterly plunge. Gold deposits on the Tasiast trend are associated with second order shear zones that are splays cutting the hanging wall block of the Tasiast thrust. An age of 2839 ± 36 Ma obtained from the hydrothermal overgrowth on zircons from a quartz vein is interpreted to represent the age of mineralisation.     

Geology,geochronology and fluid characteristics of the Pingqiu gold deposit,Southeastern Guizhou Province,China

The junction of the southeastern Guizhou, the southwestern Hunan, and the northern Guangxi regions is located within the southwestern Jiangnan orogen and forms a NE-trending ∼250 km gold belt containing more than 100 gold deposits and occurrences. The Pingqiu gold deposit is one of the numerous lode gold deposits in the southeastern Guizhou district. Gold mineralization is hosted in Neoproterozoic lower greenschist facies metamorphic rocks and controlled by fold-related structures. Vein types present at Pingqiu include bedding-parallel and discordant types, with saddle-reefs and their down limb extensions dominating but with lesser discordant types. The major sulfide minerals are arsenopyrite and pyrite, with minor sphalerite, galena, chalcopyrite, and rare pyrrhotite, marcasite, and tetrahedrite. Much of the gold is μm- to mm-sized grains, and occurs as fracture-controlled isolated grains or filaments in quartz, galena, sphalerite, pyrite, and wallrock.Three types of fluid inclusions are distinguished in hydrothermal minerals. Type 1 aqueous inclusions have homogenization temperatures of 171–396 °C and salinities of 1.4–9.8 wt% NaCl equiv. Type 2 aqueous-carbonic inclusions yield final homogenization temperatures of 187–350 °C, with salinities of 0.2–7.7 wt% NaCl equiv. Type 3 inclusions are carbonic inclusions with variable relative content of CO₂ and CH₄, and minor amounts of N₂ and H₂O. The close association of CO₂-rich inclusions and H₂O-rich inclusions in groups and along the same trail suggests the presence of fluid immiscibility. The calculated δ¹⁸O_H2O values range from 4.3‰ to 8.3‰ and δD_H2O values of fluid inclusions vary from −55.8‰ to −46.9‰. A metamorphic origin is preferred on the basis of geological background and analogies with other similar deposit types.Two ore-related sericite samples yield well-defined ⁴⁰Ar/³⁹Ar plateau ages of 425.7 ± 1.7 Ma and 425.2 ± 1.3 Ma, respectively. These data overlap the duration of the Caledonian gold mineralization along the Jiangnan orogen, and suggest that gold mineralization was post-peak regional metamorphism and occurred during the later stages of the Caledonian orogeny.Overall, the Pingqiu gold deposit displays many of the principal characteristics of the Bendigo gold mines in the western Lachlan Orogen (SE Australia) and the Dufferin gold deposit in the Meguma Terrane (Nova Scotia, Canada) but also some important differences, which may lead to the disparity in gold endowment. However, the structural make-up at deposit scale, and the shallow mining depth at present indicate that the Pingqiu gold deposit may have considerable gold potential at depth.     

Ore petrography and chemistry of the tellurides from the Dongping gold deposit,Hebei Province,China

The Dongping gold deposit is a mesothermal lode gold deposit hosted in syenite. The ore petrography and chemistry of the tellurides from the alteration zone of the deposit have been studied in detail using optical microscopy, scanning electron microscopy, electron probe micro-beam and X-ray diffraction facilities. The tellurides, consisting mostly of calaverite, altaite, petzite tellurobismuthite and tetradymite, are hosted irregularly in pyrite fractures and voids. In the ore bodies, the species and quantity of tellurides decrease from the top downwards, accompanied with lowering of gold fineness, and the existence of tellurides exhibits a positive correlation with gold enrichment. Mineral paragenesis and chemical variations suggest that during evolution of the ore-forming fluids Te preferably incorporated with Pb to form altaite, followed in sequence by precipitation of petzite, and calaverite when Ag has been exhausted, and the residue fluids were enriched in Au, giving rise to formation of native gold. Calculation with reference of the fineness of native gold coexisting with the tellurides indicates that at 300 °C, log f (Te₂) varied between − 8.650 and − 7.625. Taking account of the Au–Ag–Te mineral paragenesis, it is inferred that log ƒ (Te₂) varies from − 9.12 to − 6.43, log ƒ (S₂) − 11.47 to − 8.86. In consideration of the physicochemical conditions for formation of tellurides, with comparison to some known telluride deposits, it is suggested that high log ƒ (Te₂) is a key factor for high fineness of native gold as well as precipitation of abundant tellurides.     

The Hakkari nonsulfide Zn–Pb deposit in the context of other nonsulfide Zn–Pb deposits in the Tethyan Metallogenic Belt of Turkey

The Hakkari nonsulfide zinc deposit is situated close to the southeastern border of Turkey. Here both sulfide and nonsulfide Zn ≫ Pb ores are hosted in carbonate rocks of the Jurassic Cudi Group with features typical of carbonate-hosted supergene nonsulfide zinc mineralization. The regional strike extent of the mineralized district is at least 60 km. The age of the supergene deposit has not been determined, but it is probable that the main weathering happened during Upper Tertiary, possibly between Upper Miocene and Lower Pliocene. The Hakkari mineralization can be compared to other carbonate-hosted Zn–Pb deposits in Turkey, and an interpretation made of its geological setting. The zinc mineral association at Hakkari typically comprises smithsonite and hemimorphite, which apparently replace both sulfide minerals and carbonate host rock. Two generations of smithsonite are present: the first is relatively massive, the second occurs as concretions in cavities as a final filling of remnant porosity. Some zinc is also hosted within Fe–Mn-(hydr)oxides. Lead is present in cerussite, but also as partially oxidized galena. Lead can also occur in Mn-(hydr)oxides (max 30% PbO). The features of the supergene mineralization suggest that the Hakkari deposit belongs both to the “direct replacement” and the “wall-rock replacement” types of nonsulfide ores. Mineralization varies in style from tabular bodies of variable thickness (< 0.5 to 13 m) to cross-cutting breccia zones and disseminated ore minerals in pore spaces and fracture planes. At Hakkari a As–Sb–Tl(≫ Hg) geochemical association has been detected, which may point to primary sulfide mineralization, quite different from typical MVT.     

The Archean BIF-hosted Cuiabá Gold deposit,Quadrilátero Ferrífero,Minas Gerais,Brazil

The Cuiabá Gold Deposit is located in the northern part of the Quadrilátero Ferrífero, Minas Gerais State, Brazil. The region constitutes an Archean granite–greenstone terrane composed of a basement complex (ca. 3.2 Ga), the Rio das Velhas Supergroup greenstone sequence, and related granitoids (3.0–2.7 Ga), which are overlain by the Proterozoic supracrustal sequences of the Minas (< 2.6–2.1  Ga) and Espinhaço (1.7 Ga) supergroups.The stratigraphy of the Cuiabá area is part of the Nova Lima Group, which forms the lower part of the Rio das Velhas Supergroup. The lithological succession of the mine area comprises, from bottom to top, lower mafic metavolcanics intercalated with carbonaceous metasedimentary rocks, the gold-bearing Cuiabá-Banded Iron Formation (BIF), upper mafic metavolcanics and volcanoclastics and metasedimentary rocks. The metamorphism reached the greenschist facies. Tectonic structures of the deposit area are genetically related to deformation phases D₁, D₂, D₃, which took place under crustal compression representing one progressive deformational event (E_n).The bulk of the economic-grade gold mineralization is related to six main ore shoots, contained within the Cuiabá BIF horizon, which range in thickness between 1 and 6 m. The BIF-hosted gold orebodies (> 4 ppm Au) represent sulfide-rich segments of the Cuiabá BIF, which grade laterally into non-economic mineralized or barren iron formation. Transitions from sulfide-rich to sulfide-poor BIF are indicated by decreasing gold grades from over 60 ppm to values below the fire assay detection limit in sulfide-poor portions. The deposit is “gold-only”, and shows a characteristic association of Au with Ag, As, Sb and low base-metal contents. The gold is fine grained (up to 60 μm), and is generally associated with sulfide layers, occurring as inclusions, in fractures or along grain boundaries of pyrite, the predominant sulfide mineral (> 90 vol.%). Gold is characterized by an average fineness of 0.840 and a large range of fineness (0.759 to 0.941).The country rocks to the mineralized BIF show strong sericite, carbonate and chlorite alteration, typical of greenschist facies metamorphic conditions. Textures observed on microscopic to mine scales indicate that the mineralized Cuiabá BIF is the result of sulfidation involving pervasive replacement of Fe-carbonates (siderite–ankerite) by Fe-sulfides. Gold mineralization at Cuiabá shows various features reported for Archean gold–lode deposits including the: (1) association of gold mineralization with Fe-rich host rocks; (2) strong structural control of the gold orebodies, showing remarkable down-plunge continuity (> 3 km) relative to strike length and width (up to 20 m); (3) epigenetic nature of the mineralization, with sulfidation as the major wall–rock alteration and directly associated with gold deposition; (4) geochemical signature, with mineralization showing consistent metal associations (Au–Ag–As–Sb and low base metal), which is compatible with metamorphic fluids.     

The Cipoeiro gold deposit,Gurupi Belt,Brazil: Geology,chlorite geochemistry,and stable isotope study

The Cipoeiro gold deposit, located in the Gurupi Belt, northern Brazil, is hosted by tonalites of 2148 Ma. The deposit is controlled by splays related to the major strike-slip Tentugal shear zone, and at the deposit scale, the mineralization is confined to ductile–brittle shear zones. Mineralization style comprises thick quartz veins and narrow and discontinuous quartz-carbonate veinlets associated with disseminations in altered host rocks. The postmetamorphic hydrothermal paragenesis is composed of quartz, calcite, chlorite, white mica (phengite), pyrite, and minor albite. Electron microprobe analysis of chlorites reveals a relatively uniform chemical composition at depths of more than 100 m. The chlorites are characterized by (Fe + Mg) ratios between 0.37 and 0.47 and Al^IV ranging between 2.22 and 2.59 a.p.f.u. and are classified as Fe-chlinochlore. Temperatures calculated by applying the Al^IV contents of chlorites yield a relatively narrow interval of 305 ± 15°C. Stable isotope (O, H, C, S) compositions have been determined in silicate, carbonate, and sulfide minerals. The δ¹⁸O and δD values of the mineralizing fluid range from +2.4 to +5.7 and from −43‰ to −20‰, respectively, and are interpreted as having a metamorphic origin. The δ¹³C values of fluid CO₂ are in the range −10.7‰ to −3.9‰, whereas the fluid δ³⁴S is around 0‰. Carbon and sulfur compositions are not diagnostic of their sources, compatible as they are with mantle, magmatic, or average crustal reservoirs. The hydrothermal paragenesis, chlorite–pyrite coexistence, temperature of ore formation, and sulfur isotope evidence indicate relatively reduced fO₂ conditions for the mineralizing fluid. Geologic, chemical, and isotopic characteristics of the Cipoeiro deposit are compatible with the class of orogenic gold deposits.     

Ar-Ar ages of gold deposits in the Song Hien domain (NE Vietnam): Tectonic settings and comparison with Golden Triangle in China in terms of a single metallogenic province

The Song Hien rift basin is an important metallogenic area in NE Vietnam. This domain consists mainly of Triassic sulfide-rich black shale beds, which play a role as a sedimentary host for various mineral systems such as antimony, mercury and gold-sulfide deposits. Most of gold deposits are hosted in carbonaceous sedimentary rocks, however some deposits, which have similar characteristics, are hosted in fine-grained mafic magmatic rocks. An Ar-Ar isotopic dating of hydrothermal sericite from the sedimentary hosted Bo Va and Khung Khoang gold deposits and intrusion hosted orogenic Hat Han gold deposit yields plateau ages of 184.8 ± 2.1 Ma, 211.63 ± 2.3 Ma, and 209.12 ± 2.3 Ma, respectively. The obtained Ar-Ar ages convincingly show that the orogenic gold deposits in the Song Hien domain were formed in Late Triassic to Early Jurassic, while the age of the Bo Va deposit is at least older than 184.8 ± 2.1 Ma. Loss of argon by volume diffusion, supported by previously reported mineralogical and isotopic features of the Bo Va deposit may suggest that the Jurassic-Cretaceous (Yanshanian) tectonothermal events overprinted some deposits in the Song Hien domain. Formation of gold deposits in the Song Hien domain is linked to the same tectonic event as the Carlin-like gold deposits in SW China and is associated with an extensional tectonic regime that followed continental collision between the Indochina and South China Blocks. The similarity in geology setting and mineral composition of gold deposits of the Song Hien domain and the Golden Triangle region, as well as timing and kinematics of deformation, magmatic features, and stratigraphic sequence and bulk architecture, lead to conclusion that NE Vietnam and SW China is a single metallogenic zone. The study of gold deposits in Vietnam will provide a new data on the metallogenic history of this important part of SE Asia.     

The geology of the Morro Velho gold deposit in the Archean Rio das Velhas greenstone belt,Quadrilátero Ferrífero,Brazil

The Morro Velho gold deposit, Quadrilátero Ferrífero region, Minas Gerais, Brazil, is hosted by rocks at the base of the Archean Rio das Velhas greenstone belt. The deposit occurs within a thick carbonaceous phyllite package, containing intercalations of felsic and intermediate volcaniclastic rocks and dolomites. Considering the temporal and spatial association of the deposit with the Rio das Velhas orogeny, and location in close proximity to a major NNW-trending fault zone, it can be classified as an orogenic gold deposit. Hydrothermal activity was characterized by intense enrichment in alteration zones of carbonates, sulfides, chlorite, white mica±biotite, albite and quartz, as described in other Archean lode-type gold ores. Two types of ore occur in the deposit: dark gray quartz veins and sulfide-rich gold orebodies. The sulfide-rich orebodies range from disseminated concentrations of sulfide minerals to massive sulfide bodies. The sulfide assemblage comprises (by volume), on average, 74% pyrrhotite, 17% arsenopyrite, 8% pyrite and 1% chalcopyrite. The orebodies have a long axis parallel to the local stretching lineation, with continuity down the plunge of fold axis for at least 4.8 km. The group of rocks hosting the Morro Velho gold mineralization is locally referred to as lapa seca. These were isoclinally folded and metamorphosed prior to gold mineralization. The lapa seca and the orebodies it hosts are distributed in five main tight folds related to F1 (the best examples are the X, Main and South orebodies, in level 25), which are disrupted by NE- to E-striking shear zones. Textural features indicate that the sulfide mineralization postdated regional peak metamorphism, and that the massive sulfide ore has subsequently been neither metamorphosed nor deformed. Lead isotope ratios indicate a model age of 2.82 ± 0.05 Ga for both sulfide and gold mineralization. The lapa seca are interpreted as the results of a pre-gold alteration process and may be divided into carbonatic, micaceous and quartzose types. The carbonatic lapa seca is subdivided into gray and brown subtypes. Non-mineralized, gray carbonatic lapa seca forms the hanging wall to the orebodies, and is interpreted as the product of extreme CO₂ metasomatism during hydrothermal alteration. This dolomitic lapa seca ranges in composition from relatively pure limestone and dolomite to silty limestone and dolomite. The brown carbonatic and micaceous lapa secas are the host rocks to gold. These units are interpreted to correspond to the sheared and hydrothermal products of metamorphosed volcaniclastic and/or volcanic rocks of varying composition from dacitic to andesitic, forming various types of schists and phyllites. The high-grade, massive sulfide orebodies occur at the base of the gray carbonatic lapa seca. Both disseminated mineralization and quartz veins are hosted by micaceous lapa seca. The data are consistent with a model of epigenetic mineralization for the lapa seca, from a hydrothermal fluid derived in part from the Archean basement or older crust material.     

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.     

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.