Stable isotope geochemistry and Re–Os ages of the Yinan gold deposit,Shandong Province,northeastern China

The Yinan gold deposit in the Luxi area of Shandong Province in northeastern China is a skarn-type ore deposit. In this article, we present results from sulphur, lead, carbon–oxygen, and helium–argon isotope chemistry to characterize the ore genesis and source features. We also present rhenium–osmium ages from molybdenite to evaluate the timing of ore formation. The δ³⁴S values of pyrite from the ore deposit range from 0.7‰ to 5.60‰ with a mean at 2.70‰, close to mantle and meteorite sulphur. Among Pb isotopes, ²⁰⁶Pb/²⁰⁴Pb values range from 18.375 to 18.436, ²⁰⁷Pb/²⁰⁴Pb values from 15.694 to 15.8, and ²⁰⁸Pb/²⁰⁴Pb values from 38.747 to 39.067. The δ¹³C values of calcite associated with the ores range from ?0.2‰ to ?0.5‰ and their δ¹⁸O values show variation from 9.4‰ to 12.6‰, suggesting a mixed fluid source. The ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of fluids trapped in pyrite are in the range of 0.27–1.11 Ra and 439.4–826, respectively, with calculated proportion of the mantle-derived He ranging from 3.25% to 14.03% and atmosphere argon ranging from 35.8% to 67.3%. The data suggest that the ore-forming fluids were derived from the crust and were mixed with a distinct contribution of mantle helium. The Re and Os values vary from 32 × 10^?6 to 93.02 × 10^?6 and from 0.01 × 10^?9 to 0.34 × 10^?9, respectively. The model ages of molybdenite range from 126.96 ± 1.82 Ma to 129.49 ± 2.04 Ma, with a weighted mean age of 128.08 ± 0.75 Ma and isochron age of 130.3 ± 3 Ma. These ages are close to the age of the associated quartz diorite porphyrite pluton, suggesting a close relationship between Cretaceous magmatism and metallogeny in NE China. A comparison of the Yinan gold deposit in the Luxi area with those of the Jiaodong area shows that the contrast in metallogenic features between the two are linked with the tectonic and geodynamic history.     

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.     

Fluid inclusion geochemistry and Ar–Ar geochronology of the Cenozoic Bangbu orogenic gold deposit,southern Tibet,China

Located along the southern part of the Yarlung Zangbo suture zone in southern Tibet, Bangbu is one of the largest gold deposits in Tibet. Auriferous sulfide-bearing quartz veins are controlled by second- or third-order brittle fractures associated with the regional Qusong–Cuogu–Zhemulang brittle-ductile shear zone. Fluid inclusion studies show that the auriferous quartz contains aqueous inclusions, two-phase and three-phase CO₂-bearing inclusions, and pure gaseous hydrocarbon inclusions. The CO₂-bearing inclusions have salinities of 2.2–9.5% NaCl_eq, and homogenization temperatures (Th) of 167–336 °C. The δD, δ¹⁸O, and δ¹³C compositions of the Bangbu ore-forming fluids are − 105.5 to − 44.4‰, 4.7 to 9.0‰ and − 5.1 to − 2.2‰, respectively, indicating that the ore-forming fluid is mainly of metamorphic origin, with also a mantle-derived contribution. The ³He/⁴He ratio of the ore-forming fluids is 0.174 to 1.010 R_a, and ⁴⁰Ar/³⁶Ar ranges from 311.9 to 1724.9. Calculations indicate that the percentage of mantle-derived He in fluid inclusions from Bangbu is 2.7–16.7%. These geochemical features are similar to those of most orogenic gold deposits. Dating by ⁴⁰Ar/³⁹Ar of hydrothermal sericite collected from auriferous quartz veins at Bangbu yielded a plateau age of 44.8 ± 1.0 Ma, with normal and inverse isochronal ages of 43.6 ± 3.2 Ma and 44 ± 3 Ma, respectively. This indicates that the gold mineralization was contemporaneous with the main collisional stage between India and Eurasia along the Yarlung Zangbo suture, which resulted in the development of near-vertical lithospheric shear zones. A deep metamorphic fluid was channeled upward along the shear zone, mixing with a mantle fluid. The mixed fluids migrated into the brittle structures along the shear zone and precipitated gold, sulfides, and quartz because of declining temperature and pressure or fluid immiscibility. The Bangbu is a large-scale Cenozoic syn-collisional orogenic gold deposit     

‘Indicator’ carbonaceous phyllite/graphitic schist in the Archean Kundarkocha gold deposit,Singhbhum orogenic belt,eastern India: Implications for gold mineralization vis-a-vis organic matter

Carbonaceous rocks in the form of graphitic schist and carbonaceous phyllite are the major host rocks of the gold mineralization in Kundarkocha gold deposit of the Precambrian Singhbhum orogenic belt in eastern India. The detection of organic carbon, essentially in the carbonaceous phyllite and graphitized schist within the Precambrian terrain, is noted from this deposit. A very close relationship exists between gold mineralization and ubiquitous carbonaceous rocks containing organic carbon that seems to play a vital role in the deposition of gold in a Precambrian terrain in India and important metallogenetic implications for such type of deposits elsewhere. However, the role played by organic matter in a Precambrian gold deposit is debatable and the mechanism of precipitation of gold and other metals by organic carbon has been reported elsewhere. Fourier transform infrared spectroscopy (FTIR) results and total organic carbon (TOC) values suggest that at least part of the organic material acted as a possible source for the reduction that played a significant role in the precipitation of gold. Lithological, electron probe analysis (EPMA), fluid inclusions associated with gold mineralization, Total Carbon (TC), TOC and FTIR results suggest that the gold mineralization is spatially and genetically associated with graphitic schist, carbonaceous phyllite/shale that are constituted of immature organic carbon or kerogen. Nano-scale gold inclusions along with free milling gold are associated with sulfide mineral phases present within the carbonaceous host rocks as well as in mineralized quartz-carbonate veins. Deposition of gold could have been facilitated due to the organic redox reactions and the graphitic schist and carbonaceous phyllite zone may be considered as the indicator zone.     

He–Ar isotope geochemistry of iron and gold deposits reveals heterogeneous lithospheric destruction in the North China Craton

The North China Craton (NCC) provides a classic example for extensive destruction of the cratonic lithosphere. The Mesozoic magmatism which contributed to the decratonization of the NCC was also accompanied by the formation of a variety of mineral deposits. In order to gain further insights into the cratonic destruction process, typical iron and gold deposits are investigated here. Helium–argon isotopic data on pyrite, from typical skarn iron deposits of the Beiminghe and Fushan in the Han-Xing district of the central NCC, and the Linglong and Canzhuang gold deposits in the Jiaodong district in the eastern NCC, are presented in this paper. The ³He/⁴He, ⁴⁰Ar/³⁶Ar and ⁴⁰Ar/⁴He ratios show generally uniform patterns within the individual deposits and reveal a complex evolutionary history of the ore-forming fluids with varying degree of crust–mantle interaction. The ore-forming fluids associated with the gold mineralization at the Jiaodong mine have higher content of fluids of mantle origin with mantle helium ranging from 1.24% to 18.02% (average 6.73%; N = 18). In contrast, the ore-forming fluids related to the iron ore deposits contain less mantle contribution with mantle helium ranging from 0.12% to 4.96% (average 1.29%; N = 10). Our results suggest complex and heterogeneous crust–mantle processes associated with the magmatism and metallogeny, where the lithosphere of the eastern NCC was subjected to more extensive thinning and destruction as compared with that in the western part, consistent with the observations from geophysical studies in the region. Our study demonstrates that fluids associated with the Mesozoic metallogenic processes in the NCC provide useful insights into the geodynamics of destruction and refertilization of the cratonic lithosphere.     

Comparison of petrology and isotope geochemistry of the Bulka peridotite–gabbro massif and granitoids of the Kyzykchadra complex (West Sayan)

The study provides new petrologic and isotope geochemical data for rocks of the 465 ± 5 Ma Bulka massif (Borodina et al., 2011). The primary amphibole from granitoid stocks cutting across the layered series of the massif yielded an Ar–Ar age of 415.9 ± 3.7 Ma. The rocks of the Bulka massif have ¹⁴³Nd/¹⁴⁴Nd ratio of 0.513243 and εNd (Т) values of +12.00. The granitoids have ¹⁴³Nd/¹⁴⁴Nd ratios between 0.512919 and 0.512961 and εNd (Т) values between +8.03 and +9.25. The Nd isotope composition indicates that the rocks of the Bulka massif and granitoids were derived from a depleted mantle source. Depletion of the rocks of the massif in LILE, LREE, and HFSE over LILE is inherited from the mantle source, which has geochemical signatures of N-MORB and subduction-related components. Granitoids are metaluminous I-type granites, which were probably generated either by differentiation of intermediate to mafic mantle-derived magmas or by melting of metabasites. The rocks of the granitoid stocks are characterized by enrichment in LILE and LREE and depletion in HFSE over LILE, which suggests derivation from arc-related parental magmas.     

Stable isotope (O and C) geochemistry of non-sulfide Zn–Pb deposits; case study: Chah-Talkh non-sulfide Zn–Pb deposit (Sirjan,south of Iran)

The study of oxygen and carbon isotopic ratios has gained importance to determine the origin of ore-bearing fluids, carbon origin, and also to determine the formation temperature of non-sulfide Pb and Zn minerals. In order to determine the origin of fluids and carbon existing in Zn carbonate minerals in Chah-Talkh deposit, initially the amounts of δ¹⁸O_SMOW and δ¹³C_PDB changes in various zinc minerals in important deposits in Iran and the world were studied, and then by comparing these values in Chah-Talkh deposit with those of other deposits, the origin of fluids responsible for ore forming, carbon, and formation temperature of Chah-Talkh deposit was determined. The range of δ¹⁸O_SMOW changes in smithsonite mineral in non-sulfide lead and zinc deposits varies from 18.3 to 31.6 ‰, and δ¹⁸O_SMOW in hydrozincite mineral varies from 7.8 to 27 ‰. Due to the impossibility of smithsonite sampling from Chah-Talkh deposit (due to it being fine-grained and dispersed), hydrozincite minerals which have high isotopic similarities with smithsonite are used for the isotopic analysis of carbon and oxygen. The range of δ¹⁸O_SMOW changes in hydrozincite mineral of Chah-Talkh deposit varies from 7.8 to 15.15 ‰, which places in the domain of metamorphic water. The extensiveness of δ¹⁸O_SMOW changes in Chah-Talkh indicates the role of at least two fluids in the formation of non-sulfide minerals. The obtained formation temperature of non-sulfide minerals (hydrozincite) in Chah-Talkh deposit is 70 to 100 °C, which indicates the role of metamorphic fluids in the formation of deposit. Complete weathering of sulfide minerals to a depth of 134 m confirms the role of rising metamorphic fluids in the formation of non-sulfide minerals. The δ¹³C_PDB values of Chah-Talkh deposit are set in the range of atmospheric CO₂ and carbonate rocks, in which the existence of atmospheric CO₂ indicates the role of atmospheric fluids, and the existence of carbonate carbon rock indicates of the role of metamorphic fluids in the precipitation of non-sulfide Zn minerals.     

Geochemistry and isotope systematics of calc-alkaline volcanic rocks from the Saar-Nahe basin (SW Germany) – implications for Late-Variscan orogenic development

Late Carboniferous (300–290 Ma) calc-alkaline basalts, andesites, and rhyolites typical of volcanic arc settings occur in the intermontane Saar-Nahe basin (SW Germany) within the Variscan orogenic belt. The volcanic rock suite was emplaced under a regime of tensional tectonics during orogenic collapse and its origin has been explained by melting of mantle and crust in the course of limited lithospheric rifting. We report major, trace and rare-earth-element data (REE), and Nd-Pb-Sr-O isotope ratios for a representative sample suite, which are fully consistent with an origin closely related to plate subduction. Major and trace element data define continuous melt differentiation trends from a precursor basaltic magma involving fractional crystallization of olivine, pyroxene, plagioclase, and magnetite typical of magma evolution in a volcanic arc. This finding precludes an origin of the andesitic compositions by mixing of mafic and felsic melts as can be expected in anorogenic settings. The mafic samples have high Mg numbers (Mg# = 65–73), and high Cr (up to 330 ppm) and Ni (up to 200 ppm) contents indicating derivation from a primitive parental melt that was formed in equilibrium with mantle peridotite. We interpret the geochemical characteristics of the near-primary basalts as reflecting their mantle source. The volcanic rocks are characterized by enrichment in the large ion lithophile elements (LILE), negative Nb and Ti, and positive Pb anomalies relative to the neighboring REE, suggesting melting of a subduction-modified mantle. Initial _Nd values of −0.7 to −4.6, Pb, and ⁸⁷Sr/⁸⁶Sr_(t) isotope ratios for mafic and felsic volcanics are similar and indicate partial melting of an isotopically heterogeneous and enriched mantle reservoir. The enrichment in incompatible trace elements and radiogenic isotopes of a precursor depleted mantle may be attributed to addition of an old sedimentary component. The geochemical characteristics of the Saar-Nahe volcanic rocks are distinct from typical post-collisional rock suites and they may be interpreted as geochemical evidence for ongoing plate subduction at the margin of the Variscan orogenic belt not obvious from the regional geologic context. Received: 3 August 1998 / Accepted: 2 January 1999     

Sulfur isotope characteristics of the Archean Cu–Zn Gossan Hill VHMS deposit, Western Australia

Gossan Hill is an Archean (∼3.0 Ga) Cu–Zn–magnetite-rich volcanic-hosted massive sulfide (VHMS) deposit in the Yilgarn Craton of Western Australia. Massive sulfide and magnetite occur within a layered succession of tuffaceous, felsic volcaniclastic rocks of the Golden Grove Formation. The Gossan Hill deposit consists of two stratigraphically separate ore zones that are stratabound and interconnected by sulfide veins. Thickly developed massive sulfide and stockwork zones in the north of the deposit are interpreted to represent a feeder zone. The deposit is broadly zoned from a Cu–Fe-rich lower ore zone, upwards through Cu–Zn to Zn–Ag–Au–Pb enrichment in the upper ore zone. New sulfur isotope studies at the Gossan Hill deposit indicate that the variation is wider than previously reported, with sulfide δ³⁴S values varying between −1.6 and 7.8‰ with an average of 2.1 ± 1.4‰ (1σ error). Sulfur isotope values have a broad systematic stratigraphic increase of approximately 1.2‰ from the base to the top of the deposit. This variation in sulfur isotope values is significant in view of typical narrow ranges for Archean VHMS deposits. Copper-rich sulfides in the lower ore zone have a narrower range (δ³⁴S values of −1.6 to 3.4‰, average ∼1.6 ± 0.9‰) than sulfides in the upper ore zone. The lower ore zone is interpreted to have formed from a relatively uniform reduced sulfur source dominated by leached igneous rock sulfur and minor magmatic sulfur. Towards the upper Zn-rich ore zone, an overall increase in δ³⁴S values is accompanied by a wider range of δ³⁴S values, with the greatest variation occurring in massive pyrite at the southern margin of the upper ore zone (−1.0 to 7.8‰). The higher average δ³⁴S values (2.8 ± 2.1‰) and their wider range are explained by mixing of hydrothermal fluids containing leached igneous rock sulfur with Archean seawater (δ³⁴S values of 2 to 3‰) near the paleoseafloor. The widest range of δ³⁴S values at the southern margin of the deposit occurs away from the feeder zone and is attributed to greater seawater mixing away from the central upflow zone. Received: 10 June 1999 / Accepted: 28 December 1999     

Structural geochemistry of gold mineralization in the Linglong-Jiaojia district, Shandong Province, China

The Linglong-Jiaojia district is one of the most important regions containing gold deposits in China. These gold deposits can be divided into: a) the pyrite-gold-quartz vein type (Linglong type), which is controlled by brittle-ductile to ductile deformation structures, and b) the alteration-zone type (Jiaojia type), characterized by small veinlets, or the disseminated type recognized in brittle shear zones. Lode gold deposits in the Jiaojia area occur in NE brittle fracture zones, formed in a dominantly simple shear deformation regime, mainly in thrust attitude with a minor sinistral strike slip component. In the Linglong area, the lode gold deposits are located at the intersection of three types of structures: NNE and NE brittle-ductile fault zones and the ENE ductile reverse shear zone in the south of the area. The structural characteristics of these brittle shear zones are consistent with a tectonic NNW-SSE principal stress field orientation. Similar stresses explain the ENE Qixia fold axes, the Potouqing and several other ENE reverse ductile shear zones elsewhere in the region, the Tancheng-Lujiang fault zone and its subsidiaries in the vicinity of the Linglong-Jiaojia district, as well as the southern ENE suture zone north of Qingdao. Therefore these structural systems occurred as part of different major tectonic events under NNW-SSE compression principal stress fields in the area. Gold deposits are hosted in smaller-scale structures within the brittle fault zones and brittle-ductile shear zones. Although ore bodies and, on a smaller scale, quartz ore veins often seem to be randomly oriented, it is possible to explain their distribution and orientation in terms of the simple shear deformation process under which they were developed. The progressive simple shear failure is characterized by various fracture modes (tension and shear) that intervene in sequence. The tension and shear fractures are influenced by the stress level (depth of burial beneath the paleosurface) in their structural behavior, show variable dilatancy (void openings) and extend on all scales. By making use of these characteristics, a progressive failure analysis can be applied to predicting the shape and extent of ore bodies as well as the styles of mineralization at any given location.     

Helium, lead and sulfur isotope geochemistry of the Gejiu Sn-polymetallic ore deposit and the sources of ore-forming materials

Studies on the helium, lead and sulfur isotopic composition were performed of the Gejiu super-large Sn-polymetallic ore deposit. The results indicated that the ore-forming materials came from different sources and the deposit is a product of superimposed mineralization. The deposit is characterized by multi-source and multi-period mineralization, which experienced submarine hydrothermal deposition and Late Yanshanian magmatic hydrothermal mineralization. It is held that the Gejiu super-large Sn-polymetallic ore deposit is a multi-genesis deposit.     

REE and isotope (Sr,S, and Pb) geochemistry to constrain the genesis and timing of the F–(Ba–Pb–Zn) ores of the Zaghouan District (NE Tunisia)

The F–(Ba–Pb–Zn) ore deposits of the Zaghouan District, located in NE Tunisia, occur as open space fillings or stratabound orebodies, hosted in Jurassic, Cretaceous and Tertiary layers. The chondrite-normalized rare earth element (REE) patterns may be split into three groups: (i) “Normal marine” patterns characterizing the wallrock carbonates; (ii) light REE (LREE) enriched (slide-shaped) patterns with respect to heavy REE (HREE), with small negative Ce and Eu anomalies, characteristic of the early ore stages; (iii) Bell-shaped REE patterns displaying LREE depletion, as well as weak negative Ce and Eu anomalies, characterizing residual fluids of subsequent stages. The ⁸⁷Sr/⁸⁶Sr ratios (0.707654–0.708127 ± 8), show that the Sr of the epigenetic carbonates (dolomite, calcite) and ore minerals (fluorite, celestite) are more radiogenic than those of the country (Triassic, Jurassic, Cretaceous, lower Miocene) sedimentary rocks. The uniformity of this ratio, throughout the District, provides evidence for the isotopic homogeneity and, consequently, the identity of the source of the mineralizing fluids. This signature strongly suggests that the radiogenic Sr is carried by Upper Paleozoic basinal fluids.The δ³⁴S values of barite, associated to mineralizations, are close to those of the Triassic sea water (17‰). The δ³⁴S values of sulfide minerals range from − 13.6‰ to + 11.4‰, suggesting two sulfur-reduced end members (BSR/TSR) with a dominant BSR process.Taking account of the homogeneity in the Pb-isotope composition of galenas (18.833–18.954 ± 0.001, 15.679–15.700 ± 0.001 and 38.690–38.880 ± 0.004, for the ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios respectively), a single upper crustal source for base-metals is accepted. The Late Paleozoic basement seems to be the more plausible source for F–Pb–Zn concentrated in the deposits. The genesis of the Zaghouan District ore deposits is considered as the result of the Zaghouan Fault reactivation during the Late Miocene period.     

New data on ore geochemistry of the Rodionovskoe gold–quartz deposit,Northeast Russia

The enrichment of gold–quartz ores from the Rodionovskoe deposit in chalcophile elements (Au, Ag, As, Sb) is established. The ores are characterized by small negative Eu anomalies and low REE contents, which are typical of magmatic fluids. Slight enrichment of ores in Bi is evidence of the possible involvement of magmatic fluid in ore formation, which may have been superimposed on early metamorphic quartz veins and veinlets. The variously oriented REE patterns also indicate the presence of another magmatic fluid source, which could be related to the post-ore granitic intrusion. These results generally confirm the metamorphic–magmatic model of the formation of the gold–quartz deposits of the Yana–Kolyma belt. Our data are of practical interest for regional metallogenic forecasts, search, and evaluation of gold deposits.     

Ore fluid geochemistry of the Jinlongshan Carlintype gold ore belt in Shaanxi Province, China

THEJINLONGSHANGOLDOREBELTINZHEN’ANCOUN TY,SOUTHERNSHAANXIPROVINCE,ISLOCATEDINTHEWEST ERNQINLINGGOLDPROVINCE(NO.16INFIG.1;CHEN YANJINGETAL.,2004).ITWASDISCOVEREDINTHEDEVO NIANSTRATAINTHELATE1980S).ITSGEOLOGICALSETTING ANDMETALLOGENICEVOLUTIONARESIMILARTOT…     

Sulfur isotope and fluid inclusion geochemistry of metamorphic Cu–Au vein deposits,central Cobar area,NSW, Australia

Vein-type, structurally controlled Cu–Au mineralisation hosted by turbidites of late Silurian to earliest Devonian age, forms an important resource close to the eastern margin of the Cobar Basin. Here we report 103 new sulfur isotope analyses, together with homogenisation temperatures and salinity data for 545 primary two-phase fluid inclusions for the mineralised zones from the central area of the Cobar mining district. A range in δ³⁴S values from 3.8 to 11.2‰ (average 7.9‰) is present. Sulfur is likely to have been derived from rock sulfur/sulfide in basin and basement rocks, but there may be an additional connate-derived component. Homogenisation temperatures (T_h) for inclusion fluids trapped in quartz and minor calcite veins range from near 150°C to 397°C. Fluid inclusions are characterised by a low CO₂ content and low, but variable salinities (2.1–9.1 wt% NaCl equivalent). Generations of inclusion fluids correspond to six paragenetic stages of vein quartz deposition and recrystallisation at the Chesney mine. Primary fluid inclusions in the first two stages were subjected to re-equilibration resulting from increased confining pressure. Their T_h range (151–317°C) is considered a minimum for the temperature of these fluids. Sulfide and gold deposition at Chesney appears to be related to fluids of moderately high T_h (range 270–397°C) associated with the final paragenetic stage. T_h for the ore-related fluids may be close to the solvus of the H₂O–NaCl–CO₂ system and hence near trapping temperatures. Late-stage entry of a hot, moderately saline ore-forming fluid is implicated as the origin of the Cu–Au mineralisation. However, comparison with geochemical data for the vein-style Zn–Pb–Ag deposits at Cobar demonstrates that differences in metal content for individual zones cannot be attributed to major differences in fluid temperature or salinity. Rather, these differences are probably due to variations in source-rock reservoirs and structural pathways along which the ore-forming fluids moved.     

Geology,geochronology, and Hf isotope geochemistry of the Longtougang skarn and hydrothermal vein Cu–Zn deposit,North Wuyi area,southeastern China

The recently discovered Longtougang skarn and hydrothermal vein Cu–Zn deposit is located in the North Wuyi area, southeastern China. The intrusions in the ore district comprise several small porphyritic biotite monzonite, porphyritic monzonite, and porphyritic granite plutons and dikes. The mineralization is zoned from a lower zone of Cu-rich veins and Cu–Zn skarns to an upper zone of banded Zn–Pb mineralization in massive epidote altered rocks. The deposit is associated with skarn, potassic, epidote, greisen, siliceous, and carbonate alteration. Molybdenite from the Cu-rich veins yielded a Re–Os isochron age of 153.6 ± 3.9 Ma, which is consistent with U–Pb zircon ages of 154.0 ± 1.3 Ma for porphyritic monzonite, 154.0 ± 0.8 Ma for porphyritic biotite monzonite, and 152.0 ± 0.8 Ma for porphyritic granite. Geological observations suggest that the Cu mineralization is genetically related to the porphyritic biotite monzonite and porphyritic monzonite. All the zircons from intrusive rocks in the ore district are characterized by ε_Hf(t) values between − 13.41 and − 4.38 and Hf model ages (T_DM2) between 2054 and 1482 Ma, reflecting magmas derived mainly from a Proterozoic crustal source. Molybdenite grains from the deposit have Re values of 14.6–27.7 ppm, indicative of a mixed mantle–crust source. The porphyry–skarn abundant Cu and hydrothermal vein type Pb–Zn–Ag deposits in the North Wuyi area are related to the Late Jurassic porphyritic granites and Early Cretaceous volcanism, respectively. The Late Jurassic mineralization-related granites were derived from the crustal anatexis with some mantle input, which was triggered by asthenospheric upwelling induced by slab tearing during oblique subduction of the paleo-Pacific plate beneath the South China block, and the Early Cretaceous mineralization-related granitoids mainly from crust material formed within a series of NNE-trending basins during margin-parallel movement of the plate.     

Pb–Pb isotopic systematics of orogenic gold deposits of the Baikal–Patom fold belt (Northern Transbaikalia,Russia) and estimation of the role of neoproterozoic crust in their formation

The paper reports the results of Pb isotope study of several gold deposits of the Russia’s largest metallogenic province of Northern Transbaikalia. Potential sources of the ore material are considered by the example of new and previously published Pb–Pb data on nine deposits and occurrences of different scales. The comparison of Pb–Pb isotope-geochemical characteristics of ores, Paleozoic granitoids, as well as metamorphic pyrite from barren metasedimentary sequences shows that the Neoproterozoic terrigenous–carbonate rocks of the Baikal–Patom fold belt (BPB) served as the main source of lead and other components in the mineral-forming systems of the deposits. Significant variations of Pb isotope ratios typical in general of the considered deposits of the BPB reflect the initial isotopic heterogeneity of Pb source. This heterogeneity is caused by mixing of two geochemical types of continental crust during sedimentation: old (Early Precambrian) crust of the Siberian craton with long-term geochemical evolution and newly formed Late Precambrian crust. Pb–Pb data serve in support of the hydrothermal–metamorphogenic hypothesis of the formation of gold deposits of the BPB.