Search

[Display omitted] • The Woxi deposit is featured by coenriched Au-Sb-W elemental association. • The Au, Sb, and W occurred mainly as invisible gold, stibnite, and scheelite. • Transition of fluid-rock interaction to phase separation caused ore precipitation. • Dissolution-reprecipitation process facilitate coenriched Au-Sb-W metallogenesis. It is well-known that tungsten and antimony are commonly enriched in the gold deposit and occur as Au-Sb or Au-W deposits. However, the Woxi deposit, located in the West Jiangnan Orogen of South China, is remarkably co-enriched in the Au-Sb-W elemental association. This deposit is characterized by multistage Au mineralization and reactivation of structures developed in the Neoproterozoic metamorphic rocks, but the detailed mechanism of its co-enriched Au-Sb-W metallogeny is still unclear. Here, we perform detailed petrographic observations and ore mineral textural and pyrite compositional analyses by using SEM and LA-ICP-MS to constrain ore-forming physiochemical conditions and to decipher the Au-Sb-W metallogenic mechanism in the Woxi deposit. The Woxi deposit consists of nine auriferous quartz lodes in the shape of stratiform, tabular, and lenticular, which are surrounded by alteration halos in the Neoproterozoic slate. These orebodies are distributed along the bedding-parallel fracture zones of the EW-striking and N -dipping in the purplish red slate of the Madiyi Formation, below the regional EW-striking Woxi fault. Four stages of hydrothermal mineralization and alteration processes could be recognized in the Woxi. Stage 1 occurs in bleached slate, and consists of euhedral, porous, and coarse auriferous pyrite (Py1), with slight arsenopyrite, siderite, and rutile. Stage 2 mainly consists of subhedral to euhedral and compositional zoning auriferous pyrite (Py2) and scheelite (Sch1), with slight wolframite and apatite hosted in quartz veinlets and native gold enclaved in Sch1. Stage 3 is characterized by scheelite (Sch2) and stibnite, with slight native gold and dendritic-shaped anhedral auriferous pyrite (Py3) hosted in quartz veins. Stage 4 features a quartz-calcite-barite-chlorite mineral assemblage that occurred as veinlets, or in the pressure shadows of Py1. Gold is mainly incorporated in the three stages (S1 to S3) of arsenian pyrite (Py1to Py3) as invisible gold and, to a lesser extent, formed visible native gold at late S2 and S3, tungsten mineralization occurs mainly as scheelite (Sch1) and wolframite at S2, with a minor amount of scheelite (Sch2) at S3, and antimony mineralization is mainly occurred as stibnite at S3. Furthermore, invisible gold most likely occurs as nanoscale particles of Au-Bi-Pb-bearing tellurides in Py1, and may be hosted in the structurally bounded lattice of Py2 and Py3.The SEM study presents highly developed dissolution-reprecipitation microstructures in hydrothermal minerals, such as pyrite, arsenopyrite, wolframite, scheelite, and apatite. Mineral paragenesis and pyrite trace element signatures suggest the ore fluid is characterized by elevated f O2 , low pH and high temperature in S1, decreased f O2 , medium pH and medium temperature in S2, and elevated f O2 , high pH and low temperature in S3. The evolution of the physicochemical condition may be induced by penetration of multipulse ore-forming fluids and the transition of the ore-forming mechanism from fluid-rock interaction in S1 and early S2 to phase separation in late S2 and S3, as suggested by textural and LA-ICP-MS analyses. This study highlighted that coupled dissolution-reprecipitation reactions might facilitate the association of the Au-Sb-W elemental that successively mineralized and co-enriched in the Woxi deposit. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Woxi deposit is an orogenic Au-Sb-W deposit. • U-Pb dating on apatite and wolframite yielded a robust gold mineralization age of ca. 141 Ma. • Pyrite in situ S-Pb isotopic signatures suggest the ore-forming metals and fluids mainly derived from a metasomatized lithospheric mantle. • This study provides a new example of orogenic gold deposit that was controlled by translithospheric processes in a back-arc environment far from the plate subduction zone. The majority of gold mineralization in the Jiangnan Orogenic Belt (JOB) of South China share similarities with the orogenic type, but the nature of mineralization remains controversial, especially in terms of intracrustal versus subcrustal origin of ore fluids and metals and their relationships with the subduction of the Paleo-Pacific plate. This paper reports results of in situ analyses of minerals closely related to gold mineralization, including U-Pb ages of apatite and wolframite, and S-Pb isotopes of pyrite, from the Woxi Au-Sb-W deposit in the western Jiangnan Orogen, and use them to address the above problems. The Woxi deposit, which consists of several auriferous quartz lodes hosted by ductile–brittle shear zones in the Neoproterozoic slate. The hydrothermal mineralization and alteration processes are divided into four stages. Early-ore stage (S1) is characterized by disseminated, euhedral, porous, coarse auriferous pyrite (Py1) with minor amounts of arsenopyrite, siderite, and rutile in the bleached slate. Main-ore stage (S2) is characterized by subhedral to euhedral, auriferous pyrite (Py2) with compositional zoning, with small amounts of wolframite and apatite in quartz veinlets. Late-ore stage (S3) is represented by scheelite and stibnite with minor amounts of native gold and anhedral, dendritic auriferous pyrite (Py3) in quartz veinlets. Post-ore stage (S4) features a quartz-calcite-barite-chlorite mineral assemblage that occurs as veinlets or in pressure shadows of Py1. Apatite and wolframite associated with Py2 yield a consistent U-Pb age of ca. 141 Ma, which is corresponded to a time when the Paleo-Pacific plate started to roll back, and a Basin-and-Range style tectonic regime began to developing in South China. The different stages of pyrite have variable S isotopes, with the δ34S CDT values (mainly between −6‰ and +1 ‰) largely overlapping with those of the metasomatized mantle (−5‰ ∼ + 5 ‰), and Pb isotope ratios between crustal and mantle values. Taking these results together, we proposed that the Woxi deposit and many other gold deposits in the JOB formed from subcrustal processes involving the metasomatized upper mantle above the subduction zone. Given the extended distance from JOB to the Paleo-Pacific plate boundary, the metasomatized mantle underneath the JOB is likely initially formed during the plate subduction leading to the formation of the JOB during the Neoproterozoic, which is further fertilized by upwelling asthenosphere due to rollback of the Paleo-Pacific plate in the Mesozoic. [ABSTRACT FROM AUTHOR]

• The Aqishan deposit is a distal skarn Zn-Pb mineralization system. • Re-Os dating of pyrite and zircon U-Pb dating of granodiorite porphyry are consistent at ca. 306 Ma. • Ore-forming materials are mainly derived from magmatic source, some sulfur is sourced from country rocks. • There is significant potential for skarn Zn-Pb mineralization associated with Late Paleozoic magmatism in the Eastern Tianshan. The Aqishan deposit, located in the Eastern Tianshan, Xinjiang, China, is a newly discovered large-scale Zn-Pb deposit with a proven reserve of 1.94 Mt Pb and Zn metal at an average grade of 1.05%. The Zn-Pb orebodies are tabular and lentoid in shape, developed within skarnized carbonates and calcareous volcanoclastic rocks of the Yamansu Formation. The skarn mineral assemblages are characterized by abundant garnet, epidote, chlorite, actinolite, calcite and quartz, with minor amounts of pyroxene. Metallic minerals, comprising sphalerite, galena, chalcopyrite, pyrite, pyrrhotite and arsenopyrite, mainly occur as disseminations and irregular patches within the skarn. Re-Os dating of five syn-ore stage pyrite samples yielded an isochron age of 301 ± 13 Ma, which is in agreement with the 306 ± 2.8 Ma age obtained from the granodiorite porphyry occurring at southeast part of the Aqishan Zn-Pb deposit. The ε Hf (t) values of zircon from the granodiorite porphyry vary from + 9.62 to + 14.69, suggesting a juvenile crust source. The δ 34 S V-CDT values of 22 sulfide samples range from −11.6‰ to −2.76‰, with an average of −5.08‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 9 sulfide samples range from 18.102 to 18.336, 15.539 to 15.655, and 37.929 to 38.479, respectively, which are similar to the Carboniferous grantoids of the Aqishan area and partly overlap with the volcanoclastic rocks of the Yamansu Formation. Based on these data, we propose that the Aqishan deposit formed from magmatic-hydrothermal fluids that emanated from the granodiorite porphyry. Much of the metals were derived from the magmatic intrusions with minor contributions from the volcanoclastic rocks, whereas the sulfur may have been mainly extracted from the country rocks with slight contributions from a magmatic source. The close genetic relationships between the Carboniferous magmatism and skarn type Zn-Pb mineralization in the Aqishan area as well as other deposits in the region suggests a great potential of finding more analogous deposits in the Eastern Tianshan, where carbonates or calcareous volcanoclastic rocks and plutons that related to the subduction of the Northern Tianshan Oceanic slab beneath the Yili-Central Tianshan Terrane during Late Paleozoic are well-developed. [ABSTRACT FROM AUTHOR]

• The Zn-Pb mineralization age of the Caixiashan deposit is 337.2 ± 5.7 Ma. • Reduced sulfur of multiple sources may involve a possible input of magmatic sulfur. • Ore metals are mainly sourced from wall rocks and Carboniferous felsic intrusions. • It is a distal high-temperature carbonate replacement deposit related to intrusions. The Caixiashan Zn-Pb deposit is the largest carbonate-hosted Zn-Pb deposit in Eastern Tianshan, NW China. The deposit comprises the No. Ⅰ, Ⅱ, III and IV ore zones with a proven reserve of 131 Mt ore at 3.95% Pb + Zn. The orebodies generally occur as irregular lenses and pods in altered carbonate rocks of the Mesoproterozoic Kawabulake Group near faults. The mineralization is characterized by massive, disseminated and vein/veinlet sulfides including pyrite, pyrrhotite, sphalerite and galena with minor arsenopyrite and chalcopyrite, as well as sulfosalt minerals of Ag, As, Sb and Pb. The mineralization is associated with tremolite, chlorite, silica and carbonate alterations. Rb-Sr isotopic dating of sphalerite and pyrrhotite yields an isochron age of 337.2 ± 5.7 Ma, which is interpreted as the mineralization age. Zircon U-Pb dating reveals that stocks of diorite, quartz diorite, K-feldspar granite and monzonitic granite that occur in the deposit area were emplaced at 348.2 ± 3.7 Ma, 351.9 ± 3.5 Ma, 333.6 ± 3.6 Ma and 330.0 ± 3.6 Ma, respectively. These age data suggest that the mineralization is coeval with Carboniferous granitic magmatism. The δ34S V-CDT values of sulfides (excluding the syn-sedimentary pyrite) range from −2.42‰ to 19.1‰, suggesting that the reduced sulfur was mainly derived from thermal sulfate reduction (TSR) of seawater-derived sulfates in the marine sedimentary basement rocks and minor contribution by replacement of syn-sedimentary pyrite, as well as a possible input of magmatic sulfur. The Pb isotopic compositions of sulfides, with 206Pb/204Pb ranging from 17.074 to 17.361, 207Pb/204Pb from 15.422 to 15.614, and 208Pb/204Pb from 36.685 to 37.303, partly overlap with those of basement rocks of the Mesoproterozoic Kawabulake Group and the Carboniferous intrusions, suggesting that the ore metals were derived from both the basement and Carboniferous magmatism. On the basis of the spatio-temporal relations between hydrothermal alterations/mineralization and Carboniferous magmatism, we conclude that the Caixiashan Zn-Pb deposit is a high-temperature carbonate replacement deposit related to concealed granitic intrusions, which were formed in an arc environment related to the subduction of the South Tianshan Ocean plate beneath the Central Tianshan massif during the Carboniferous time. The results of this study indicate that there is a great potential of finding more large-scale Zn-Pb deposits similar to Caixiashan in Eastern Tianshan. [ABSTRACT FROM AUTHOR]