New lead isotope determination from five Proterozoic sulfide deposits,Skellefte district,Sweden

Lead isotope analyses of 25 sulfide samples (galenas, iron sulfides, and sulfosalts) from five different mines of the Skellefte district, northern Sweden, demonstrate that the Pb-isotopic composition of galenas and other sulfides rich in lead varies between individual deposits within the district. This contrasts with many other base-metal districts, where ore lead is isotopically homogeneous on a regional basis. Although all of the Skellefte leads are depleted in ²⁰⁷Pb relative to average global lead evolution models, thus suggesting a large mantle-derived component in their sources, the Nasliden deposit lying at the contact of the host volcanic rocks and the overlying metasediments contains a significant component of crustal lead. It is concluded that while the Pb-isotope data are consistent with a volcanic exhalative origin of the ores of the Skellefte district, they also demonstrate that older crustal lead was incorporated into the sulfides during their emplacement and the subsequent period of magmatic and metamorphic activity which followed their deposition.     

Preservation of Palaeoproterozoic early Svecofennian structures in the Orijärvi area, SW Finland—Evidence for polyphase strain partitioning

The predominantly migmatitic Palaeoproterozoic Uusimaa belt preserves early lower-grade Svecofennian structures in the Orijärvi area in SW Finland. This study aims at explaining the deformational history responsible for its preservation and also at defining the age of the early Svecofennian deformation. Detailed structural analysis reveals that the preservation was enabled by polyphase strain partitioning, which initiated during the early Svecofennian D₂ deformation, 1875 Ma ago, as revealed by ion microprobe U–Pb data on zircons from granodioritic and intermediate syn-D₂ intrusive dykes. The D₂ structures were low-strain upright folds at high crustal levels and sub-horizontal high-strain folds at deeper crustal levels. The sub-horizontal D₂ structures were refolded into upright folds during the subsequent late Svecofennian D₃ deformation, whereas the upright D₂ structures behaved as almost rigid blocks that caused strain partitioning into high-strain zones along the block margins. This accounts for the low cumulative strain in specific parts of the Orijärvi area. Further strain partitioning during D₄ caused reverse dip-slip movements along regional-scale shear zones. Crustal depth controlled the metamorphic grade during D₂, when local migmatisation took place at deep crustal levels. Later metamorphic overprint during D₃ deformation is evident from post-D₂ growth of sillimanite and a second generation of andalusite.Similarities in the structural patterns between the Orijärvi area and the Tampere-Vammala area (100 km to the north) suggest that irrespective of the age of the later overprint, subsequent deformation was localised along the margins of the early formed upright domains, while the low-grade rocks within the domains were preserved.     

Deformation,metamorphism, and mobilization of Ni–Cu–PGE sulfide ores at Garson Mine,Sudbury

The Garson Ni–Cu–platinum group element deposit is a deformed, overturned, low Ni tenor contact-type deposit along the contact between the Sudbury Igneous Complex (SIC) and stratigraphically underlying rocks of the Huronian Supergroup in the South Range of the 1.85-Ga Sudbury structure. The ore bodies are coincident with steeply south-dipping, north-over-south D₁ shear zones, which imbricated the SIC, its ore zones, and underlying Huronian rocks during mid-amphibolite facies metamorphism. The shear zones were reactivated as south-over-north, reverse shear zones during D₂ at mid-greenschist facies metamorphism. Syn-D₂ metamorphic titanite yields an age of 1,849?±?6 Ma, suggesting that D₁ and D₂ occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to colinear L₁ and L₂ mineral lineations, indicating that the geometry of the ore bodies are strongly controlled by D₁ and D₂. Sulfide mineralization consists of breccia ores, with minor disseminated sulfides hosted in norite, and syn-D₂ quartz–calcite–sulfide veins. Mobilization by ductile plastic flow was the dominant mechanism of sulfide/metal mobilization during D₁ and D₂, with additional minor hydrothermal mobilization of Cu, Fe, and Ni by hydrothermal fluids during D₂. Metamorphic pentlandite overgrows a S₁ ferrotschermakite foliation in D₁ deformed ore zones. Pentlandite was exsolved from recrystallized polygonal pyrrhotite grains after cessation of D₁, which resulted in randomly distributed large pentlandite grains and randomly oriented pentlandite loops along the grain boundaries of polygonal pyrrhotite within the breccia ore. It also overgrows a S₂ chlorite foliation in D₂ shear zones. Pyrrhotite recrystallized and was flattened during D₂ deformation of breccia ore along narrow shear zones. Exsolution of pentlandite loops along the grain boundaries of these flattened grains produced a pyrrhotite–pentlandite layering that is not observed in D₁ deformed ore zones. The overprinting of the two foliations by pentlandite and exsolution of pentlandite along the grain boundaries of flattened pyrrhotite grains suggest that the Garson ores reverted to a metamorphic monosulfide solid solution at temperatures ranging between 550 and 600 °C during D₁ and continued to deform as a monosulfide solid solution during D₂.     

托莫尔日特金矿区韧脆性剪切带及其控矿作用

矿区位于近NW-NWW向展布的断裂带内,并严格受其控制.控矿断裂带为一条韧-脆性剪切带,其形成主要经历了早期韧性变形、晚期脆性变形及后期改造破坏3个阶段,叠加于早期韧性剪切带之上的晚期脆性破裂带,是矿脉的主要产出位置,成矿与断裂带的韧-脆性转换密切相关.矿体形成于韧-脆性剪切带的转换带附近,后期由于抬升剥蚀而出露地表.矿体分布可能具有"两层楼"式的垂直分带,上部为石英脉型金矿体,品位较高,但规模不大;下部为糜棱岩型金矿体,规模较大,但品位稍低.因此本区以后的找矿工作中应注意挖掘深部糜棱岩型金矿的潜力.     

智利Candelaria-Punta del Cobre铁氧化物铜金矿床地质和成矿作用

智利Copiapó附近海岸东部边缘有一宽5km、长20km的铁氧化物铜金矿床带,包括Candelaria矿床和位于其北东方向3km处的Punta del Cobre矿集区的中小型矿床。初步估计,该成矿带的铜矿石资源量可达7×108~8×10~8t(含铜量1%)。矿石矿物主要为黄铜矿、黄铁矿、磁铁矿、赤铁矿。矿石产状为脉状、角砾状、细脉状等。含矿围岩主要为Punta del Cobre组的火山岩及火山碎屑岩。该矿带中大部分大型矿脉位于北西—北北西向高角度脆性断层与块状火山岩和火山碎屑岩接触带交汇处。Candelairia矿区主要发育黑云母-钾长石±钙角闪石±绿帘石蚀变矿物组合。在Punta del Cobr矿集区,矿床深部的矿石围岩蚀变情况与Candelairia地区一致,但是浅部的矿石赋存于黑云母-钾长石或钠长石-绿泥石±方解石蚀变带中。     

The Palaeoproterozoic Kristineberg VMS deposit, Skellefte district, northern Sweden, part I: geology

The Kristineberg volcanic-hosted massive sulphide (VMS) deposit, located in the westernmost part of the Palaeoproterozoic Skellefte district, northern Sweden, has yielded 22.4 Mt of ore, grading 1.0% Cu, 3.64% Zn, 0.24% Pb, 1.24 g/t Au, 36 g/t Ag and 25.9% S, since the mine opened in 1941, and is the largest past and present VMS mine in the district. The deposit is hosted in a thick pile of felsic to intermediate and minor mafic metavolcanic rocks of the Skellefte Group, which forms the lowest stratigraphic unit in the district and hosts more than 85 known massive sulphide deposits. The Kristineberg deposit is situated lower in the Skellefte Group than most other deposits. It comprises three main ore zones: (1) massive sulphide lenses of the A-ore (historically the main ore), having a strike length of about 1,400 m, and extending from surface to about 1,200 m depth, (2) massive sulphide lenses of the B-ore, situated 100–150 m structurally above the A-ore, and extending from surface to about 1,000 m depth, (3) the recently discovered Einarsson zone, which occurs in the vicinity of the B-ore at about 1,000 m depth, and consists mainly of Au–Cu-rich veins and heavily disseminated sulphides, together with massive sulphide lenses. On a regional scale the Kristineberg deposit is flanked by two major felsic rock units: massive rhyolite A to the south and the mine porphyry to the north. The three main ore zones lie within a schistose, deformed and metamorphosed package of hydrothermally altered, dominantly felsic volcanic rocks, which contain varying proportions of quartz, muscovite, chlorite, phlogopite, pyrite, cordierite and andalusite. The strongest alteration occurs within 5–10 m of the ore lenses. Stratigraphic younging within the mine area is uncertain as primary bedding and volcanic textures are absent due to strong alteration, and tectonic folding and shearing. In the vicinity of the ore lenses, hydrothermal alteration has produced both Mg-rich assemblages (Mg-chlorite, cordierite, phlogopite and locally talc) and quartz–muscovite–andalusite assemblages. Both types of assemblages commonly contain disseminated pyrite. The sequence of volcanic and ore-forming events at Kristineberg is poorly constrained, as the ages of the massive rhyolite and mine porphyry are unknown, and younging indicators are absent apart from local metal zoning in the A-ores. Regional structural trends, however, suggest that the sequence youngs to the south. The A- and B-ores are interpreted to have formed as synvolcanic sulphide sheets that were originally separated by some 100–150 m of volcanic rocks. The Einarsson zone, which is developed close to the 1,000 m level, is interpreted to have resulted in part from folding and dislocation of the B-ore sulphide sheet, and in part from remobilisation of sulphides into small Zn-rich massive sulphide lenses and late Au–Cu-rich veins. However, the abundance of strongly altered, andalusite-bearing rocks in the Einarsson zone, coupled with the occurrence of Au–Cu-rich disseminated sulphides in these rocks, suggests that some of the mineralisation was synvolcanic and formed from strongly acidic hydrothermal fluids. Editorial handling: P. Weihed     

High-grade iron ore at Windarling, Yilgarn Craton: a product of syn-orogenic deformation, hypogene hydrothermal alteration and supergene modification in an Archean BIF-basalt lithostratigraphy

Banded iron formation (BIF)-hosted iron ore deposits in the Windarling Range are located in the lower greenstone succession of the Marda–Diemals greenstone belt, Southern Cross domain, Yilgarn Craton and constitute a total hematite–martite–goethite ore resource of minimum 52 Mt at 60 wt.% Fe (0.07 P). Banded iron formation is interlayered with high-Mg basalts at Windarling and precipitated during episodes of volcanic quiescence. Trace element content and the rare earth element (REE) ratios Y/Ho (42 to 45), Sm/Yb (1.5), together with positive La and Gd anomalies in ‘least-altered’ hematite–magnetite–metachert–BIF indicate the precipitation from Archean seawater that was fertilised by hydrothermal vent fluids with a basaltic HREE-Y signature. Hypogene iron ore in sub-greenschist facies metamorphosed BIF formed during three distinct stages: ore stage 1 was a syn- to post-metamorphic, syn-D₁, Fe–Ca–Mg–Ni–Co–P–REE metasomatism that produced local Ni–REE-rich Fe–dolomite–magnetite alteration in BIF. Hydrothermal alteration was induced by hot fluid flow controlled by brittle–ductile reactivation of BIF-basalt margins and crosscutting D₁ faults. The Ni–Co-rich content of dolomite and a shift in REE ratios in carbonate-altered BIF towards Archean mafic rock signature (Y/Ho to 31 to 40, Sm/Yb to 1 to 2 and Gd/Gd* to 1.2 to 1.4) suggest that high-Mg basalts in the Windarling Range were the primary source of introduced metals. During ore stage 2, a syn-deformational and likely acidic and oxidised fluid flow along BIF-basalt margins and within D₁ faults leached carbonate and precipitated lepidoblastic and anhedral/granoblastic hematite. High-grade magnetite–hematite ore is formed during this stage. Ore stage 3 hydrothermal specular hematite (spcH)–Fe–dolomite–quartz alteration was controlled by a late-orogenic, brittle, compressional/transpressional stage (D₄; the regional-scale shear-zone-related D₃ is not preserved in Windarling). This minor event remobilised iron oxides, carbonate and quartz to form veins and breccia but did not generate significant volumes of iron ore. Ore stage 4 involved Mesozoic(?) to recent supergene oxidation and hydration in a weathering environment reaching down to depths of ～100 to maximum 200 m below surface. Supergene ore formation involved goethite replacement of dolomite and quartz as well as martitisation. Important ‘ground preparation’ for supergene modification and upgrade were mainly the formation of steep D₁ to D₄ structures, steep BIF/basalt margins and particularly the syn-D₁ to syn-D₂ carbonate alteration of BIF that is most susceptible to supergene dissolution. The Windarling deposits are structurally controlled, supergene-modified hydrothermal iron ore systems that share comparable physical, chemical and ore-forming characteristics to other iron ore deposits in the Yilgarn Craton (e.g. Koolyanobbing, Beebyn in the Weld Range, Mt. Gibson). However, the remarkable variety in pre-, syn- and post-deformational ore textures (relative to D₁ and D₂) has not been described elsewhere in the Yilgarn and are similar to the ore deposits in high-strain zones, such as of Brazil (Quadrilátero Ferrífero or Iron Quadrangle) and Nigeria. The overall similarity of alteration stages, i.e. the sequence of hydrothermal carbonate introduction and hypogene leaching, with other greenstone belt-hosted iron ore deposits supports the interpretation that syn-orogenic BIF alteration and upgrade was crucial in the formation of hypogene–supergene iron ore deposits in the Yilgarn Craton and possibly in other Archean/Paleoproterozoic greenstone belt settings worldwide.     

Structural and gold mineralizing evolution of the world-class orogenic Mana district,Burkina Faso: Multiple mineralizing events over 150 million years

The Mana district, located in the northern part of the Birimian Houndé greenstone belt in western Burkina Faso, is a world-class Paleoproterozoic orogenic gold district (∼8 Moz) including five gold deposits (Fofina, Nyafé, Siou, Wona-Kona and Yaho). These deposits are located in specific lithostratigraphic domains, and gold is controlled by various structural features. Deposit- and regional-scale mapping, intrusion age and geochemistry, as well as airborne aeromagnetic and electrical resistivity geophysical data, were used to decipher the tectonic evolution of each gold deposit and the district. Five deformational and four gold mineralizing events were recognized.The first deformation event (D1_MD: E-W oriented shortening) affected the metamorphosed volcanic and sedimentary rocks of the Lower Birimian group. This early deformation episode was correlated with the formation of gently N-plunging folds (F_1MD) and N-S-striking thrusts faults coeval with emplacement of the pre- to synkinematic Wona-Kona and Siou plutons dated at ∼2172 Ma, under greenschist facies metamorphism. The quartz-carbonate veins (V_1MD) at Fofina and Siou formed during D1_MD at Eoeburnean time, manifesting the first gold event at approximately ∼2172 Ma.The following deformation event (D2_MD: E-W oriented extension) is associated with the deposition of the Upper Birimian group (Mana basin) overlying the Lower Birimian group. The geometry of the Mana basin is controlled by the Mana and Maoula shear zones. The Tarkwaian-type rock formation overlying the Upper Birimian group, controlled by the Wona-Kona and Siou shear zones, is constrained at the end of D2_MD or at the beginning of the D3_MD event with a maximum deposition age at ∼2113 Ma.The third deformation event (D3_MD: E-W to WNW-ESE transpression) affected the entire supracrustal rock. Such event is correlated with the formation of map-scale F_3MD folds and dextral shear zones during the Eburnean orogeny (∼2113–2090 Ma). A second gold mineralizing event occurred during D3_MD and is manifested by quartz-carbonate veins (V_3MD) and disseminated sulfides at the Yaho, Fofina and Nyafé and possibly Wona-Kona deposits.The fourth deformation event (D4_MD: NNW-SSE transpression) is correlated with sinistral shearing along the major transcurrent faults and the development of asymmetric NNE-striking folds (F_4MD) associated with vertical fold axes. Syn-D4_MD mineralization is characterized mainly by a strong silicification (Si_4MD) with disseminated pyrite and arsenopyrite along the Wona-Kona shear zone and by tiny quartz-carbonate veinlets (V_4MD). This event is considered the main gold-bearing event in the western margin of the Mana district.The fifth and last deformation event (D5_MD) is brittle in character and was responsible for the formation of E-W subvertical crenulation cleavages and reverse faults under overall N-S shortening. This late deformation event is tentatively associated with a last gold event recorded as free gold associated with muscovite in brittle fractures developed in competent orebodies at the Wona-Kona and Siou deposits. This event could be as young as ∼2022 Ma, the age obtained from Ar-Ar datation of muscovite-schists at the Wona-Kona deposit.Our main contribution is that we decipher multiple gold mineralizing events at the district scale based on deposit- and regional-scale mapping. It is interpreted that gold was introduced as early as ∼2172 Ma and possibly as late as ∼2022 Ma during at least 3 or even 4 shortening tectonic events in a timeframe not yet recognized at the district scale for all the Birimian belts.     

Ore deposit types and tectonic evolution of the Iberian Pyrite Belt: From transtensional basins and magmatism to transpression and inversion tectonics

A new interpretation of the structural evolution of the Iberian Pyrite Belt (IPB) and volcanogenic massive sulfide mineralization (VMS) is presented in this work, based on a review of the ore deposit types, the analysis of the hosting volcanic sequences and the tectonic evolution. The VMS deposits of the IPB are hosted by volcanic and siliciclastic rocks. Four main volcano-sedimentary sequences (VSC), from VSC₀ to VSC_3, have been assumed, the main deposits being located in the VSC₀ and at the top of the VSC₂.We have defined three main sectors oriented approximately E-W and hosting the VMS deposits. In the Northern sector, which is mostly located in Spain, graben basins and local pull-aparts are the main structures. In this sector, two belts can be distinguished, the deposits being located at the top of the VSC₂ felsic volcanism (Rio Tinto-type IPB deposits). In the Central sector, both in Spain and Portugal, half-graben basins are the most common structures, and the deposits are mostly located in the VSC₀ andesitic volcanic-sedimentary sequence (Tharsis-type IPB deposits). In the Southern sector, which is only located in Portugal, a graben basin with a pull-apart is again the main structure, and the deposits are located in black slates and at the top of a felsic volcanism, Strunian in age (VSC₀). The deposits located in graben basin with a pull-apart are essentially felsic volcanic-hosted with some siliciclastic material, mostly black shales. By contrast, those located in half-graben basins are mainly hosted by black-shales with minor amounts of andesitic rocks.The tectonic evolution shows that as a result of a counterclockwise rotation of the stress axes, the formation of the IPB and the associated ore deposits took place during several episodes, from transtension (with the development of both graben with pull-aparts and half-graben basins), through left lateral E-W shearing, to transpression. At the beginning of the transtensional process, several extensional, roughly E-W trending faults that developed graben and half-graben basins were generated and the first volcanic andesite-rhyolite rocks (VSC₀) formed. The Tharsis-type deposits, mainly hosted by black slates with some volcanic rocks, were formed in the Central sector while the Neves Corvo-type deposit, hosted by black slates and felsic volcanism formed in the Southern one. After a period characterized by barren mafic volcanism (VSC₁), a sinistral shear affected the previous fractures due to the stress axis rotation and felsic crustal volcanism started (VSC₂). Rhyolites and dacites were particularly abundant in two graben basins, which developed rollovers in pull-apart zones, forming the Rio Tinto-type deposits in the Northern sector. The thermal increase associated with VSC₀ and VSC₂ gave rise to the development of crustal-scale hydrothermal convective cells, which generated both types of deposits.After a barren VSC₃ felsic volcanism, subsequently, during the Variscan transpressional phase, the E-W extensional faults were reactivated as reverse faults, affecting the volcanic sequence (VSC₀ to VSC₃) as well as the interbedded sedimentary rocks (mostly black shales). As has been recognized at the Rio Tinto deposit, buttressing must have played a significant role in the geometry of inverted structures, and the VMS ores were intensely recrystallized.It should be emphasized that this new regional geological model for the IPB is an approach to provide a better insight into VMS deposits and could be a key-point for further studies, providing a new tool to improve knowledge of the VMS mineralizations and exploration guidelines elsewhere in the IPB.     

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.     

Comparison of the Typical Metallogenic Systems in the North Slope of the Tongbai‐East Qinling Mountains and its Geologic Implications

The Tongbai-East Qinling Mountains, an important part of the Central orogenic belt, is one of the most important metallogenic belts in China and contains lots of orogenic-type and VMS-type (Volcanogenic Massive Sulfide type) metallogenic systems. The Dahe and Shuidongling VMS-type Cu-Zn deposits, located in the Erlangping Group in Tongbai and East Qinling Mountains, respectively, show similar geological and geochemical features. The Huoshenmiao Formation in the East Qinling region and the Liushanyan Formation in the Tongbai region are spilite-keratophyre sequences occurring in the western and eastern sides of the Nanyang Basin, respectively, and are interpreted to be equivalent to each other. The orogenic-type Au-Ag deposits can be subdivided into two styles; namely, fault- or structure-controlled (e.g. Yindonggou) and stratabound (e.g. Poshan). The Poshan and Yindongpo orogenic-type Au-Ag deposits, whose ore bodies are strictly hosted in carbonaceous strata in the Tongbai Mountains, show obvious stratabound characteristics. Their ore-fluids are enriched in K+ and SO42? and are regarded as K+-SO42? types. The Pb-isotope ratios of sulfides of the ores are extremely uniform and significantly different from those of the tectonostratigraphic terranes of the Qinling orogens except for the ore-hosting strata of the Waitoushan Formation. The Yindonggou and Xuyaogou orogenic Au-Ag deposits in the East Qinling Mountains, whose ore bodies are hosted in the faults cutting the hosting strata or granite body, show fault-controlled characteristics. Their ore-fluids belong to the Na+-Cl? type. The Pb-isotope ratios of sulfides of ores are similar to those of the northern Qinling orogenic belt. The Waitoushan Formation, dominated by carbonaceous sericite-rich schists and only occurring in Tongbai region, should be detached from the Erlangping Group, which occurs both in the western and eastern sides of the Nanyang Basin. Future ore exploration in the Tongbai-East Qinling Mountains should focus on fault-controlled Au-Ag lodes.     

Deformation and mineralisation in the Scotty Creek Basin,Agnew district,Eastern Goldfields,Western Australia: evidence for D1- and D3-related gold mineralisation

Gold deposits in the Agnew district display markedly different structural styles. The Waroonga and Songvang deposits are hosted in layer-parallel extensional shears formed under highly ductile conditions. In contrast, the New Holland–Genesis deposits are shallow-dipping quartz-filled brittle fractures and breccia zones that cut across the tightly folded bedding and formed during east–west compression. It is difficult to attribute their formation to a single compressive event. The Waroonga and Songvang deposits formed during D₁ extension, uplift and exhumation of the Agnew granitic complex and formation of the Scotty Creek Basin at ca 2670–2660?Ma. The New Holland–Genesis deposits formed during east–west D₃ compression at about ca 2650–2630?Ma. An S₁ foliation wraps around the Agnew granitic complex and L₁ stretching lineations form a radial pattern around the granite, consistent with formation during D₁ uplift of the composite granite body. Uplift and erosion of granite bodies in the surrounding area provide a source for the granite clasts in the upper parts of the Scotty Creek Basin. As clasts in the basin are undeformed, no significant deformation occurred prior to the uplift and erosion of the source granites in this area. Syn-tectonic emplacement of the Lawlers Tonalite during formation of the Scotty Creek Basin at ca 2665?Ma may have provided a good heat/fluid source for the mineralising systems during the first gold event. The distribution of the large deposits along the western edge of the Agnew granitic complex indicates that the extensional shear along the granite contact is a first-order control on gold deposition by providing a conduit for rising hydrothermal fluids. The northerly trend of high-grade shoots in the Waroonga deposit coincides with early north-trending growth faults, which are also likely fluid conduits.     

Metamorphism of volcanogenic massive sulphide deposits in the Urals. Ore geology

The Urals VMS province comprises a broad spectrum of variably metamorphosed deposits, from unmetamorphosed to those without any primary ore textures, which are the results of high-grade metamorphic processes. Contact metamorphism near large granite and granodiorite plutons caused the most significant changes of ores, with coarse-grained to pegmatoidal ores with magnetite closest to its contact with the intrusion, followed by pyrrhotite-enriched copper ores, and more distal zinc (± Pb ± Ag) mineralisation. Koktau, Tarnyer and Vesenneye deposits are metamorphosed to the hornblende-hornfels and pyroxene-hornfels facies (t = 400–800 °C, P = 1–6 kbar). Metamorphism of Tash-Yar, Dzhusinskoe and Krasnogvardeiskoe deposits corresponds to the greenschist and albite-epidote-hornfels facies (t = 250–450 °C, P = 1–4 kbar).The regional metamorphism of VMS ores varies from prehnite-pumpellyite facies (t = 150–300 °C, P = 0.5–4 kbar) in the South Urals to the epidote-amphibolite and amphibolite facies (t = 400–600 °C (up to 700 °C), P = 1–6 kbar) in the Karabash area in the Middle Urals. In the Magnitogorsk zone, the metamorphism of host rocks and VMS bodies increases to the north, reaching its peak near the Ufa promontory of the East European platform. With increased metamorphism, the morphology of orebodies evolves from gently dipping thick lenses (Alexandrinskoe and Uzelga fields), to subvertical and folded (Uchaly and Novo-Uchaly deposits) and pseudomonoclinal steeply-dipping vein-like bodies (Karabash district).The massive sulphide transformation in PTX-gradient fields led to partial redistribution of ore material. An enrichment in Cu, Zn, Ag and Au, ± Pb occur in the uppermost parts of large steeply-dipping massive sulphide lenses in wide tectonic zones (e.g., Gai deposit) or as gold-sulphide disseminated bodies near large metamorphosed VMS lenses, distal to a granite pluton (Tarnyer deposit). Partial melting probably occurred in some highly metamorphosed deposits (Tarnyer, Koktau and Mauk). Redeposition of base metals sulphides (chalcopyrite, tennantite, sphalerite, ± bornite, galena), as well as the presence of “visible” gold and tellurides, took place during retrograde metamorphism, which produced a transfer of ore matter towards the low stress areas, such as the outer parts of shear zones, the uppermost parts of steeply-dipping ore lenses, pressure shadows, hinge zones of small folds, and small extension fractures (i.e., Alpine-type veins) in deformed ore body or its immediate surroundings.     

云南大平掌铜多金属矿床成矿作用

云南大平掌矿床位于澜沧江火山岩带的中南段,左侧是澜沧江和酒房深大断裂。矿区内发育一套形成于岛弧环境的上石炭统细碧-石英角斑岩系,矿体产于流纹质火山岩中,产状与火山岩一致。矿体分2类,上部为块状矿体,下部为细脉-浸染状矿体。矿床内热液蚀变发育,特别是浸染状矿体中更强,并从矿体中心向外侧形成分带。具工业意义的Cu、Pb、Zn等元素以硫化物形式产出。S、Pb、Sr、Nd等同位素成分表明,成矿物质来源于地幔-下地壳。尽管矿体受后期构造破坏强烈,但综合研究表明,该矿床仍具有世界上绝大多数火山成因块状硫化物矿床的共同性。它与区内类似矿床的差异性,为在该区寻找火山成因块状硫化物矿床开辟了新方向。     

The Boliden gold-rich volcanogenic massive sulfide deposit, Skellefte district, Sweden: new U–Pb age constraints and implications at deposit and district scale

The Boliden deposit (8.3 Mt at 15.9 g/t Au) is interpreted to have been formed between ca. 1894 and 1891 Ma, based on two new U–Pb ID-TIMS ages: a maximum age of 1893.9?+?2.0/?1.9 Ma obtained from an altered quartz and feldspar porphyritic rhyolite in the deposit footwall in the volcanic Skellefte group and a minimum age of 1890.8?±?1 Ma obtained from a felsic mass-flow deposit in the lowermost part of the volcano-sedimentary Vargfors group, which forms the stratigraphic hanging wall to the deposit. These ages are in agreement with the alteration and mineralization being formed at or near the sea floor in the volcanogenic massive sulfide environment. These two ages and the geologic relationships imply that: (1) volcanism and hydrothermal activity in the Skellefte group were initiated earlier than 1.89 Ga which was previously considered to be the onset of volcanism in the Skellefte group; (2) the volcano-sedimentary succession of the Vargfors group is perhaps as old as 1892 Ma in the eastern part of the Skellefte district; and (3) an early (synvolcanic) deformation event in the Skellefte group is evidenced by the unconformity between the ≤1893.9?+?2.0/?1.9 Ma Skellefte group upper volcanic rocks and the ≤1890.8?±?1 Ma Vargfors sedimentary and volcanic rocks in the Boliden domain. Differential block tilting, uplift, and subsidence controlled by synvolcanic faults in an extensional environment is likely, perhaps explaining some hybrid VMS-epithermal characteristics shown by the VMS deposits of the district.     

Fault-controlled sedimentation in a progressively opening extensional basin: the Palaeoproterozoic Vargfors basin, Skellefte mining district, Sweden

The Vargfors basin in the central part of the Skellefte mining district is an inverted sedimentary basin within a Palaeoproterozoic (1.89 Ga) marine volcanic arc. The fault-segmented basin formed from upper-crustal extension and subsequent compression, following a period of intense sub-marine volcanism and VMS ore formation. New detailed mapping reveals variations in stratigraphy attributed to syn-extensional sedimentation, as well as provenance of conglomerate clasts associated with tectonic activity at the transition from extension to compression. The onset of fan delta to alluvial fan sedimentation associated with basin subsidence indicates that significant dip-slip displacement accommodating rapid uplift of the intrusive complex and/or subsidence of the adjacent volcano-sedimentary domain took place along a major fault zone at the southern margin of the intrusive complex. Subsidence of the Jörn intrusive complex and/or its burial by sedimentary units caused a break in erosion of the intrusion and favoured the deposition of a tonalite clast-barren conglomerate. Clast compositions of conglomerates show that the syn-extensional deposits become younger in the south-eastern parts of the basin, indicating that opening of the basin progressed from north-west to south-east. Subsequent basin inversion, associated with the accretion to the Karelian margin, involved reverse activation of the normal faults and development of related upright synclines. Progressive crustal shortening caused the formation of break-back faults accompanied by mafic volcanic activity that particularly affected the southern contact of the Jörn intrusive complex and the northern contact of the Vargfors basin.     

Ore Genesis for Stratiform Ore Bodies of the Dongfengnanshan Copper Polymetallic Deposit in the Yanbian Area, NE China：Constraints from LA-ICP-MS in situ Trace Elements and Sulfide S–Pb Isotopes

The Dongfengnanshan Cu polymetallic deposit is one representative deposit of the Tianbaoshan ore district in the Yanbian area, northeast(NE) China. There occur two types of ore bodies in this deposit, the stratiform ore bodies and veintype ones, controlled by the Early Permian strata and the Late Hercynian diorite intrusion, respectively. Due to the ambiguous genetic type of the stratiform ore bodies, there has been controversy on the relationship between them and veintype ore bodies. To determine the genetic type of stratiform ore bodies, laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) in situ trace elements and S–Pb isotope analysis have been carried on the sulfides in the stratiform ore bodies. Compared with that in skarn, Mississippi Valley-type(MVT), and epithermal deposits, sphalerite samples in the stratiform ore bodies of the Dongfengnanshan deposit are significantly enriched in Fe, Mn, and In, while depleted in Ga, Ge, and Cd, which is similar to the sphalerite in volcanic-associated massive sulfide(VMS) deposits. Co/Ni ratio of pyrrhotites in the stratiform ore bodies is similar to that in VMS-type deposits. The concentrations of Zn and Cd of chalcopyrites are similar to those of recrystallized VMS-type deposits. These characteristics also reflect the intermediate ore-forming temperature of the stratiform ore bodies in this deposit. Sulfur isotope compositions of sulfides are similar to those of VMS-type deposits, reflecting that sulfur originated from the Permian Miaoling Formation. Lead isotope compositions indicate mixed-source for lead. Moreover, the comparison of the Dongfengnanshan stratiform ore bodies with some VMStype deposits in China and abroad, on the trace elements and S–Pb isotope characteristics of the sulfides reveals that the stratiform ore bodies of the Dongfengnanshan deposit belong to the VMS-type, and have closely genetic relationship with the early Permian marine volcanic sedimentary rocks.     

Origin of the Dachang gold deposit,NW China: constraints from H,O, S,and Pb isotope data

The Dachang gold deposit is located in the Late Triassic Songpan-Ganzi Fold Belt, NE Tibetan Plateau. Gold ore is concentrated as veins along secondary faults and fracture zones in the Bayan Har Group metaturbidites. No exposed felsic plutons are present in the vicinity of the deposit. The auriferous veins contain <15% sulphide minerals, mainly arsenopyrite, pyrite, and stibnite. Gold is commonly enclosed within arsenopyrite and pyrite. Typical alteration around the ore bodies includes silicification, sericitization, and weak carbonatization.

Gold-bearing quartz samples have δ¹⁸O values of 16.9–21.2‰ (V-SMOW) from which δ¹⁸O_H2O values of 6.2–9.6‰ can be calculated from the fluid inclusion temperatures (or 10.0 to 12.7‰ if we used the average arsenopyrite geothermometer temperature of 301°C). The δD values of fluid inclusions in quartz range from –90‰ to –72‰. δ³⁴S values of gold-bearing sulphides mainly range from –5.9‰ to –2.8‰ (V-CDT). Pyrite and arsenopyrite in ores have ²⁰⁶Pb/²⁰⁴Pb ratios of 18.2888 to 18.4702, ²⁰⁷Pb/²⁰⁴Pb ratios of 15.5763 to 15.6712, and ²⁰⁸Pb/²⁰⁴Pb ratios of 38.2298 to 38.8212. These isotopic compositions indicate that the ore-forming fluids were of metamorphic origin, and the S and Pb may have been derived from the host metaturbidites of the Bayan Har Group. The Dachang Au deposit has geological and geochemical features similar to orogenic gold deposits. We propose that the ores formed when the Songpan-Ganzi Fold Belt was intensely deformed by Late Triassic folding and thrusting. Large-scale thrusting resulted in regional allochthons of different scales, followed by secondary faults or fracture zones that controlled the ore bodies.     

铧厂沟金矿床区域韧性剪切带特征

首次对铧厂沟金矿床区域韧性剪切带进行了较为系统的研究。根据野外地质调查和室内显微构造分析 ,区内发育一条较大区域韧性剪切带 ,无论沿走向还是顺倾向均呈舒缓波状 ,强变形带和弱变形域呈镶嵌形式。区域韧性剪切带经历了右行—左行—右行多期 (次 )活动 ,剪切方位也多次变化 ;早期形成温度约 5 0 0℃ ,以右行剪切为主 ,古应力值大于 0 .0 75GPa。控矿韧脆性剪切带是区域韧性剪切带演化的产物 ,最终形成脆性断裂。区域韧性剪切作用控制矿床、矿带的分布 ,并使部分金从矿源层分溢出来 ,产生第一阶段金的富集。次级韧脆性剪切带 (控矿剪切带 )控制富矿体的分布。因此 ,铧厂沟金矿床可称为韧性剪切带型金矿床。另外 ,中 -下泥盆统三河口群第一岩段第一岩层 (D1 -2 SH1a)部分原岩有明显海底热水同沉积特征 ;在矿床之西万家山—张家山应注意寻找硅化石英粗糜棱岩型金矿石。     

Structural genesis of the Eunsan and Moisan low-sulphidation epithermal Au–Ag deposits, Seongsan district, Southwest Korea

The Seongsan district in the Jindo–Haenam basin of southwest Korea comprises Precambrian gneissic basement, overlain and intruded by Cretaceous volcanic (98–71 Ma) and plutonic (86–68 Ma) rocks, respectively. Haenam Formation volcanic and volcaniclastic rocks are the dominant rock type exposed in the district and are the main host to high-sulphidation (82–77 Ma) and low-sulphidation (79–73 Ma) epithermal deposits. The Eunsan and Moisan low-sulphidation epithermal deposits have similar vein mineralogy, zoned hydrothermal alteration mineral assemblages, structural framework and interpreted deformation events. These similarities suggest that they formed by district-scale hydrothermal fluid flow at about 77.5 Ma. At this time, ore fluid movement along subvertical WNW-trending faults was particularly focussed in dilatant fault bends, jogs, and at intersections with N-trending splays. At Eunsan, Au–Ag ore shoots coincide with these areas of structural complexity, whereas at Moisan, narrower ore zones correspond with several parallel, poorly connected veins. A secondary control on the location of ore zones is the intersection between mineralised WNW-striking structures and rocks of the Haenam Formation. The higher permeability and porosity of these rocks, in comparison with mudstones and siltstones of the underlying Uhangri Formation, resulted in the more efficient lateral migration of ore fluids away from subvertical faults and into wall rocks. The intersection between subvertical WNW-striking faults and the gently dipping Haenam Formation imparts a low angle SW plunge to both ore bodies. WNW-striking post-mineralisation faults displace ore zones up to 100 m and complicate the along-strike exploration and mining of WNW-trending ore zones. Future exploration strategies in the district involve the systematic testing of WNW-trending mineralised structures along strike from known deposits, with a particular emphasis on identifying structurally complex areas that experienced local dilation during the mineralisation event. Poorly exposed regions have historically been under-explored. However, based on the proposed exploration model for the Eunsan and Moisan deposits, these areas of poor outcrop are now considered important target areas for hidden ore bodies using ground-based geophysical exploration tools, such as seismic surveys.