Stratiform Orebodies Research Articles

Age and Tectonic Setting of Mesothermal Magmatic Hydrothermal Vein‐Type Pb–Zn–(Ag) Mineralization in the Xiaohongshilazi Deposit, Central Jilin Province, Northeast China

AbstractThe Xiaohongshilazi deposit located in central Jilin Province, Northeast China, is a newly discovered and medium‐scale Pb–Zn–(Ag) deposit with ore reserves of 34,968 t Pb, 100,150 t Zn, and 158 t Ag. Two‐stage mineralization has been identified in this deposit. Stratiform volcanic‐associated massive sulfide (VMS) Pb–Zn mineralization interbedding with the marine volcanic rocks of the Late Carboniferous–Early Permian Daheshen Formation was controlled by the premineralization E–W‐trending faults. Vein‐type Pb–Zn–(Ag) mineralization occurs within or parallel to the granodiorite and diorite porphyries controlled by the major‐mineralization N–S‐trending faults that cut the stratiform mineralization and volcanic rocks. To constrain the age of vein‐type Pb–Zn–(Ag) mineralization and determine the relationship between mineralization and magmatism, we conducted LA–ICP–MS U–Pb dating on zircon from the ore‐bearing granodiorite and diorite porphyries and Rb–Sr dating on metal sulfide. Granodiorite and diorite porphyries yield zircon U–Pb weighted‐mean 206Pb/238U ages of 203.6 ± 1.8 Ma (Mean Standard Weighted Deviation [MSWD] = 1.8) and 225.6 ± 5.1 Ma (MSWD = 2.3), respectively. Sulfides from four vein‐type ore samples yield a Rb–Sr isochron age of 195 ± 17 Ma (MSWD = 4.0). These results indicate a temporal relationship between the granodiorite porphyry and vein‐type Pb–Zn–(Ag) mineralization. The granodiorite associated with vein‐type mineralization has high SiO2 (68.99–70.49 wt.%) and Na2O (3.9–4.2 wt.%; Na2O/K2O = 1.07–1.10) concentrations, and A/CNK values of 0.95–1.04; consequently, the intrusion is classified as a high‐K, calc‐alkaline, metaluminous I‐type granite. The granodiorite porphyry is enriched in large‐ion lithophile elements (e.g. Rb, Th, U, and K) and light REE and is depleted in high‐field‐strength elements (e.g. Nb, Ta, P, and Ti) and heavy REE, indicating that it represents a subduction‐related rock that formed at an active continental margin. Furthermore, the granodiorite porphyry has Mg# values of 31–34, indicating a lower crustal source. Based on petrological and geochemical features, we infer that the ore‐bearing granodiorite porphyry was derived from the partial melting of the lower crust. In summary, mineralization characteristics, cross‐cutting relationships, geochronological data, and regional tectonic evolution indicate that the region was the site of VMS Pb–Zn mineralization that produced stratiform orebodies within the Late Carboniferous–Early Permian marine volcanic rocks of the Daheshen Formation, followed by mesothermal magmatic hydrothermal vein‐type Pb–Zn–(Ag) mineralization associated with granodiorite porphyry induced by the initial subduction of the Paleo‐Pacific Plate beneath the Eurasia Plate during the Late Triassic–Early Jurassic.

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 vein‐type 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 vein‐type 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 VMS‐type 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.

Genesis of the Dachang Sn-polymetallic and Baoshan Cu ore deposits, and formation of a Cretaceous Sn-Cu ore belt from southwest China to western Myanmar

Large scale Cretaceous magmatism and SnCu mineralization occurred in an E-W-trending ore belt from southwest China to western Myanmar. We investigated the genesis of the world-class Dachang Sn-polymetallic and newly discovered Baoshan Cu deposit in Guangxi Province, southwest China, and the tectonic setting of this belt. The Dachang ore field contains a giant vein ore body (No. 100) and stratiform ore bodies (No. 91 and 92). The cassiterite U-Pb age (92.5 ± 4.4 Ma) of the No. 100 ore body is similar to the zircon U-Pb age of the Longxianggai biotite granite (90.8 ± 1.0 Ma), suggesting the vein ore body was related to Cretaceous magmatism. The fluid inclusions in the No. 92 ore body are similar to those in the No. 100 ore body, and contain CO2-H2O, liquid-rich and halite-bearing fluid inclusions, with homogenization temperatures of 300–410 °C. These data further suggest that mineralization was related to Cretaceous magmatism. The mineralization in the Baoshan Cu deposit occurs as veins in the Baoshan porphyry and adjacent country rocks. The Baoshan porphyry yielded a zircon U-Pb age of 90.6 ± 1.3 Ma, EuN/Eu* = 0.05, CeN/Ce* = 12.2 and εHf(t) = −11.39 to −7.37. These data indicate that the porphyry magma was reduced and crustally derived. Low Sr/Y ratios (<0.1) and large negative Eu anomalies (EuN/Eu* = 0.03–0.06), along with rare earth element tetrad effects further imply the porphyry magma was highly fractionated. The Baoshan porphyry was genetically associated with Cu mineralization, but is distinct from the typical Cu-mineralizing porphyry magmas.This Cretaceous Sn-Cu ore belt was likely related to subduction and roll-back of the Neo-Tethys Plate rather than northwestward subduction of the Paleo-Pacific Plate.

Ore-Forming Fluids Characteristics and Metallogenesis of the Anjing Hitam Pb-Zn Deposit in Northern Sumatra, Indonesia

The Anjing Hitam Pb-Zn deposit in northern Sumatra (Indonesia) is one of the largest Pb-Zn deposits in the region. The stratiform orebodies are mainly hosted in the middle member of the Carboniferous-Permian Kluet Formation of the Tapanuli Group. Mineral paragenesis and crosscutting relationships suggest a two-stage Pb-Zn mineralization: (I) sedimentary and (II) hydrothermal mineralization. Ore-related calcite from both stages I and II contains mainly liquid- and gas-liquid two-phase-type fluid inclusions (FI). For stage I ore-forming fluids, FI homogenization temperatures (Th) are 105 to 199 °C, and the salinities are 9.6 wt.% to 16.6 wt.% NaCleqiv, reflecting low temperature and medium-low salinity; whereas in stage II, the Th (206 to 267 °C) and salinity (19.0 wt.% to 22.5 wt.% NaCleqiv) are considerably higher. Fluid inclusion and C-O isotope characteristics suggest that the stage I ore-forming fluids were mainly derived from a mixture of seawater and magmatic fluids (probably from deep-lying plutons), whereas the stage II ore-forming fluids were likely magmatic-derived with wall rock input. We propose that the Anjing Hitam deposit was a Carboniferous exhalative sedimentary (SEDEX) deposit overprinted by the Pleistocene vein-style magmatic-hydrothermal mineralization.

Alteration and mineralization zoning, ore textures and ore-forming process of Yongping copper deposit, Jiangxi Province

Yongping copper deposit, associated with S-W-Pb-Zn mineralization, is located at the southern margin of the Jiangshan-Shaoxing suture and between the Yanshanian granite belt and the Hercynian-Indosinian depression in the northern Wuyi Mountains. Late Paleozoic stratigraphy, Yanshanian granite, and copper ore body is controlled by thrust napper structure, as the basement rocks of the Zhoutan Group thrusting on the Late Paleozoic strata, Early Yanshanian biotite granite-granodiorite, quartz porphyry, and granite porphyry intruding along weak planes of thrust, and stratiform ore bodies occurring within the skarnized Carboniferous Yejiawan Formation. The ore body occurred in garnet skarn, phyllitic shale and skarnized marble. This study deciphers the ore-forming episodes and metallogenic process of the deposit based on mineralization-alteration zonation and textures of the ores. Exploration and mining working faces indicate that the mineralization and alteration of the deposit is granite-centered. If taking one side into consideration, i. e., from the granite to the limestone wall rock, following zonation can be delineated : (1) skarn minerals vary from garnet, via diopside, to wollastonite ; (2) the garnet varies in color from red, via brown, to green; (3) economic mineralization mainly occurring as banded and stock veins in the brown garnet skarn zone, leading to the ore grade increasing firstly and then decreasing. Metal mineral association of banded and stock veins in skarns, metasandstone-shales, and large sulfide-quartz veins ( up to 10m wide) is identical, consisting mainly of pyrite, scheelite, galena, sphalerite and chalcopyrite, indicating that different types of ores in the Yongping copper deposit are products of the same hydrothermal mineralization system in diverse wall rocks and ore-controlling structures. According to mineral assemblages and ore textures, six metallogenic stages can be divided for the deposit, which are garnet, mag-hematite, scheelite, iron-copper sulfide, lead-zinc sulfide, and carbonate stages, respectively. Skarn zonation formed during garnet stage, and massive pyrrhotite-grunerite formed at late period of this stage; magnetite, hematite composed mag-hematite stage; scheelite stage dominate tungsten mineralization, occurring as quartz-scheelite stock and disseminated wolframite. Iron-copper sulfide stage is the main period of copper mineralization; lead-zinc and carbonate stage likely marks the late and end of the primary mineralization, respectively.

Genesis of the Dongguashan skarn Cu-(Au) deposit in Tongling, Eastern China: Evidence from fluid inclusions and H-O-S-Pb isotopes

The Dongguashan copper-(gold) deposit is located in the Eastern Tongling ore district of the Middle-Lower Yangtze River Valley Metallogenic Belt (MLYRB), Eastern China. The Cu-(Au) mineralization is associated with the Qingshanjiao quartz monzodiorite and consists of various types including stratiform, porphyry, vein-like and skarn. There are three deposit models, including: 1) stratabound skarn-type; 2) exhalative sedimentary (SEDEX)-hydrothermal superimposition-type; and 3) exhalative sedimentary (SEDEX) type. The ore-forming processes can be divided into the prograde skarn alteration (Stage I), retrograde alteration (Stage II) and quartz-carbonate alteration (Stage III). Four types of fluid inclusions (FIs) are recognized at Dongguashan: Vapor-rich two-phase aqueous (Type I), liquid-rich two-phase aqueous (Type II), daughter-mineral-bearing three-phase (homogenized to liquid by the disappearance of vapor phase; Type III), and daughter-mineral-bearing three-phase (homogenized to liquid by the disappearance of daughter minerals; Type IV). All four types of FIs are present in Stage II. Stage I does not contain Type IV FIs, and only Type II FIs are found in Stage III. For Stage I, Type I, II and III FIs homogenized at 379–548 °C, 319–522 °C and 450–512 °C, respectively, with salinities of 10.1–19.6, 5.9–19.4 and 36.7–43.3 wt% NaCl equivalent. For Stage II, Type I, II, III and IV FIs homogenized at 286–378 °C, 235–372 °C, 265–349 °C and 324–350 °C, respectively, with salinities of 1.4–17.0, 4.3–16.1, 34.7–40.6 and 34.4–41.0 wt% NaCl equivalent. The Type I to III FIs in Stage I and II have similar homogenization temperatures but different salinities, which indicates the occurrence of fluid immiscibility. Hydrogen-oxygen isotopes of the quartz (δD = −84.0 to −71.5‰, δ18OH2O = +4.51 to +8.97‰) and calcite (δD = −70.7 to −60.95‰, δ18OH2O = +4.41 to +4.91‰) suggest that the ore-forming fluids were principally magmatic-derived. δ34S values of the stratiform orebodies (+4.1 to +5.3‰), vein-like orebodies (+4.2 to +5.7‰), skarn orebodies (+4.9‰), porphyry orebodies (+5.1 to +5.7‰) and the Qingshanjiao pluton (−2.2 to +5.2‰) are different from those of the wall rocks (−29.5 to −4.6‰), suggesting that wall rocks were unlikely to be a major sulfur source. Lead isotopes of the sulfides from the different orebody types are similar to those of the plagioclase from the Mesozoic intermediate-felsic rocks in the MLYRB, suggesting that they have had similar Pb source. Sulfur and lead isotopes suggest that the ore-forming materials were derived from a deep-seated magmatic source. The ore-forming fluid immiscibility during Stage I and II may have altered the physicochemical conditions of the hydrothermal fluid system, leading to the Cu-(Au) sulfide precipitation. Based on the ore geological and alteration/mineralization features, mineral assemblages, ore-forming material source and fluid evolution, we consider that Dongguashan is best classified as a porphyry–skarn Cu-(Au) deposit.

The carbonate-hosted MVT Morro Agudo Zn-Pb deposit, central Brazil

Morro Agudo is the largest known Mississippi-Valley Type deposit (MVT) in Brazil with original estimated reserves of 18.3 Mt @ 5.08% Zn and 1.75% Pb of which 3.92 Mt@ 4% Zn and 1.45% Pb remained in 2017. In spite of having been mined for more than 30 years, a comprehensive study of Morro Agudo metallogenic features was still lacking in the international literature. This deposit is hosted within the 250 km long Vazante Sequence, a N-S-trending Mesoproterozoic-Neoproterozoic carbonate-dominant sedimentary sequence thrusted over Neoproterozoic rocks during the Brasiliano Orogeny. Sulfide bodies in Morro Agudo are restricted to the Morro do Calcário Formation as a 1300 m long ore envelope averaging 9 m thick, comprising stacked up stratabound orebodies that thin out down dip and are limited to the NE by the Main Fault. Five orebodies are described: (a) Breccia-hosted orebody “GHI”, (b) Sphalerite-rich doloarenite orebody “JK”, (c) Galena-rich doloarenite orebody “L”; (d) Lower replaced stratiform orebody “M”; (e) Upper replaced stratiform orebody “N”. Comparison of these orebodies reveals mineral zonation patterns and variations in Zn-Pb grade consistent with sulfide textural relationships. These relationships indicate five mineralization styles that provide spatial and timing constraints for Morro Agudo; (a) Stratiform sulfides, (b) Massive Ore, (c) Laminated Ore, (d) Breccia-hosted Ore, (e) Late stage fracture-filling Ore. Carbon and oxygen stable isotope data for each mineralization style shows a pattern of mixing of signatures of mineralizing fluids and barren host rocks and supports our interpretation that these mineralization styles occurred in more than one stage of ore formation. The ore was later offset by a set of strike slip normal faults associated with compression related to the Brasiliano Orogeny, of which the Main Fault (Falha Principal) is the most important because it limits the deposit to the NE. Previous interpretation of upper orebodies as part of a SEDEX system is revisited in the present work. In our model, data used to support a syngenetic origin for Morro Agudo, such as synsedimentary structures, Pb isotopes in sulfides and fluid inclusion data indicate a younger, barren generation of sulfides deposited long before Zn-Pb mineralization, during sedimentation of the Morro do Calcário Formation in the Mesoproterozoic. These early sulfides were preserved in cherts and as massive pyrite beds that were later overprinted by sphalerite and galena. Overprinting thus mixed Meso and Neoproterozoic Pb isotopic sources and led to a long standing argument over whether the Morro Agudo ores were syngenetic or epigenetic. This interpretation is also in agreement with the current classification of the Vazante Sequence as containing imbricated Neoproterozoic and Mesoproterozoic sedimentary rocks. Based on our work of sulfide textural relationships, stable isotopes, whole-rock geochemistry and previously published data, we argue that Morro Agudo ores formed by at least two stages of percolation of mildly hot hydrothermal fluid in the Neoproterozoic. The primary reason for sulfide precipitation is interpreted to be mixing of mildly-hot, metal-bearing basinal brines and seawater/connate waters.

Late Paleozoic SEDEX deposits in South China formed in a carbonate platform at the northern margin of Gondwana

SEDEX sulfide deposits hosted in black shale and carbonate are common in the South China Block. The Dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales. Sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 Ma. Pyrite from the orebodies has a Re-Os isochron age of 389 ± 62 Ma, indicative of formation of the hosting strata and syngenetic pyrite ores in the mid-late Devonian. The hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part. The ore-hosting black shales have high TOC (total organic carbon), Mo, As, Pb, Zn and Cd, indicating an anoxic-euxinic deep basin origin. The high redox proxies, V/(V + Ni) > 0.6 and V/Cr > 1, and the positive correlations of TOC with Mo and V in black shales are also consistent with an anoxic depositional environment. The Dajiangping deposit is located close to the NE-trending Wuchuan-Sihui fault, which was active during the Devonian. The mid-late Devonian mineralization age and the anoxic-euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault-bounded basin that developed in a carbonate platform of the South China Block. The regional distribution of many Devonian, stratiform, carbonaceous sediment-hosted sulfide deposits along the NE-trending fault-bounded basins in South China, similar to the Dajiangping deposit, indicates that these deposits formed at a basin developed in the passive margin setting of the South China Block during the Devonian. This environment was caused by the break-up and northward migration of the South China Block from Gandwana.

Dating Ore Deposit Using Garnet U–Pb Geochronology: Example from the Xinqiao Cu–S–Fe–Au Deposit, Eastern China

The large Xinqiao Cu–S–Fe–Au deposit in the Tongling ore district, Eastern China, is characterized by a large-scale stratiform orebody, in which garnet is widely distributed as the main gangue mineral associated with mineralization. Xinqiao garnet can be divided into early (Grt1) and late (Grt2) generations based on extensive back-scattered electron (BSE) imaging observations. Laser ablation (LA)-ICP-MS trace element and U–Pb isotope composition analyses indicate that uranium occurs homogeneously within the Xinqiao garnet, and Grt1 and Grt2 have weighted average 207Pb-corrected 206Pb/238U ages of 137.0 ± 7.8 Ma (Mean standard weighted deviation (MSWD) = 4.9) and 129.6 ± 7.1 Ma (MSWD = 1.6), respectively, similar to the zircon U–Pb age (139.6 ± 1.5 Ma) of the Jitou intrusion. These garnet U–Pb ages, combined with the low MnO content and various Y/Ho ratios, suggest that the Xinqiao garnet is likely to have a magmatic hydrothermal replacement origin associated with the Jitou stock. Based on previous studies of the Xinqiao deposit, we infer that the Xinqiao stratiform orebody may have formed from the Early Cretaceous magmatic hydrothermal fluids associated with the Jitou stock, and may have been generated by the Early Cretaceous tectono-thermal event in Eastern China.

Jurassic magmatism and metallogeny in the eastern Qin-Hang Metallogenic Belt, SE China: An example from the Yongping Cu deposit

The large Yongping Cu deposit is situated in the eastern Qin-Hang Metallogenic Belt (SE China) and close to the Jiang-Shao suture zone. Igneous rocks at Yongping occur as granitoids, including the porphyritic biotite granite stock of Shizitou and quartz porphyry and granite porphyry dykes, which recorded the Jurassic – Cretaceous magmatic evolution and tectonic setting at Yongping.This integrated study comprises whole-rock analysis, U–Pb zircon dating and Hf isotope analyses of the Yongping granitoids in order to better understand the genesis of the Yongping Cu deposit. The Yongping granitoids show typical I-type affinity with P2O5 decreasing with fractionation, and yielded ages of 160.2 ± 1.6 Ma (the porphyritic biotite granite), 158.7 ± 1.5 Ma (the quartz porphyry) and 152.7 ± 1.7 Ma (the granite porphyry), indicating their formation in the Late Jurassic. The Nb/Ta, Mg#, εHf(t) and TDM2 of porphyritic biotite granite, quartz porphyry and granite porphyry suggests that they are the partial melting product of Precambrian metamorphosed crustal basement with contribution of mantle material and that the porphyritic biotite granite and the granite porphyry contain more mantle-derived material than the quartz porphyry. In addition to the close temporal and spatial relationship between the Shizitou stock and the Yongping stratiform orebody, the magma of the porphyritic biotite granite has higher oxygen fugacity (avg. zircon Ce4+ / Ce3+ = 303) and is more hydrous also indicate quite a good potential for Cu mineralization, in contrast to the late quartz and granite porphyries. Overall, the Yongping stratiform mineralization may have been a skarn-type mineralization associated with the porphyritic biotite granite stock of Shizitou. The Shizitou stock as well as the quartz porphyry and granite porphyry dykes are products of the lithospheric extension and asthenospheric upwelling related to the Paleo-Pacific plate subduction.

Fingerprinting the Hydrothermal Fluid Characteristics from LA-ICP-MS Trace Element Geochemistry of Garnet in the Yongping Cu Deposit, SE China

The large Yongping Cu deposit is situated in the eastern Qin-Hang Metallogenic Belt, Southeast China and on the southern side of the Yangtze—Cathaysia suture zone, and is characterized by large stratiform orebodies. Garnet represents the main non-metallic mineral at Yongping, and shows variations in color from dark red to green to light brown with distance from the Shizitou porphyritic biotite granite stock. An in situ elemental analysis using EPMA and LA-ICP-MS and fluid inclusions microthermometric measurement on the Yongping garnet were conducted to constrain the hydrothermal and physicochemical mineralization conditions and the ore origin. The Yongping garnet ranges from nearly pure to impure andradite, is characterized by low concentrations of MnO (0.11–0.71 wt %) with a wide range of Y/Ho (2.1–494.9) and does not exhibit any melting inclusions or fluid-melt inclusions, indicating that they are likely to be resulted from hydrothermal replacements. The Yongping garnet is rich in LREEs, Cs, Th, U and Pb; relatively depleted in HREEs, Rb, Sr and Ba; but exhibits distinct Eu anomalies (δEu of the dark red, green and light brown garnet range 2.12–20.54, 0.74–1.70 and 0.52–0.85, respectively) with the homogenization temperatures and salinities of the fluid inclusions principally ranging from 387–477 °C and 7.8–16.0 wt % NaCl equivalent, respectively. The distinct trace elements and microthermometric characteristics reveal that the garnet was formed in a physicochemical conditions of medium-high temperature, 44–64 MPa pressures, mildly acidic pH levels, and unstable oxygen fugacity, and indicate that they were primarily formed by infiltration metasomatism, quite fitting with the scenario that the preferential entrance of magmatic-hydrothermal fluids derived from the Shizitou stock into the relatively low-pressure fracture zones between the limestone and quartz sandstone in the Yejiawan Formation, and further led to the formation of the Yongping stratiform mineralization.

Trace and rare earth elements constraints on the sources of the Yunfeng paleo-karstic bauxite deposit in the Xiuwen-Qingzhen area, Guizhou, China

A number of Carboniferous paleo-karstic bauxite deposits occur in the Xiuwen-Qingzhen area, central Guizhou Province, which constitute an important part of the central Guizhou-Southern Chongqing bauxite belt in southwestern China. These deposits consist of lenticular and stratiform orebodies hosted in the Lower Carboniferous Jiujialu Formation, which lies unconformably above carbonate rocks (mainly dolomite) of the Middle and Upper Cambrian Loushanguan Group, Shilengshui Formation and Lower Cambrian Qingxudong Formation. Although it is generally agreed that the bauxite resulted from weathering of Cambrian rocks below the unconformity, it remains unclear whether the carbonates alone can provide sufficient material for the formation of the deposits. In this study, we examined the mineralogy and major, trace and rare earth elements geochemistry of bauxite and bauxitic clays from the Yunfeng deposit in the Xiuwen-Qingzhen area and compared them to previously published data of a paleo-weathering profile consisting of Loushanguan dolomite underlying the sub-Carboniferous unconformity and the “Black Rock Sequence” of the Lower Cambrian Niutitang Formation, in order to evaluate the sources of the bauxite. The bauxite ores are composed of diaspore as the main ore mineral, along with small amounts of pyrite, arsenopyrite, galena, stibnite, xenotime and uranium-bearing minerals, and are characterized by high contents of uranium and phosphorus. Chondrite-normalized REE patterns and various bivariant diagrams commonly used to study the provenance of bauxite including Eu/Eu∗ vs TiO2/Al2O3, Eu/Eu∗ vs Sm/Nd, TiO2 vs Al2O3, TiO2/Th, Th vs Ta, Th vs Nb and Nb vs Ta suggest that the Loushanguan dolomite and the Niutitang “Black Rock Sequence” are both potential source rocks. However, a comparison in U and Th contents between the paleo-weathering profile of the Loushanguan dolomite and the bauxite samples suggests that the dolomite alone cannot provide the materials for the bauxite ores. Instead, the “Black Rock Sequence” may have contributed most of the ore-forming materials, which are mainly transported from source regions where the Niutitang Formation was exposed, weathered and eroded. Therefore, the Yunfeng bauxite deposit is of mixed autochthonous and allochthonous origin.

LA-ICP-MS trace element geochemistry of garnets: Constraints on hydrothermal fluid evolution and genesis of the Xinqiao Cu–S–Fe–Au deposit, eastern China

The Xinqiao Cu–S–Fe–Au deposit in the Tongling ore district, an important part of the Middle-Lower Yangtze River Valley metallogenic belt in eastern China, is located along the northern margin of the Yangtze Block. The deposit consists of two major mineralization types: stratiform and skarn (the genesis of the former is disputed). The more important stratiform orebody (90% of the total Cu, S and Fe reserves) has abundant garnet as the main gangue mineral, similar to the skarn orebody hosted in the intrusive contact.Garnets from the Xinqiao stratiform orebody range from pure andradite (And100) to And50Gro46, and can be divided into the early (Grt1) and late (Grt2) generation. Both generations contain low MnO (0.19–0.89%), wide range of Y/Ho (39.0–40.7 for Grt1, 29.8–67.9 for Grt2), and do not contain melt or fluid-melt inclusions, indicative of a magmatic-hydrothermal replacement origin. Grt1 and the Grt2 cores are grandite, whilst the Grt2 rims are mainly andradite with some grandite zones. Grandite is enriched in heavy rare earth elements (HREEs), and displays low ΣLREE/ΣHREE, LaN/YbN and U concentrations with negative Eu anomalies, whereas andradite is HREE-depleted, and displays high ΣLREE/ΣHREE, LaN/YbN ratios and U concentrations with positive Eu anomalies. The distinct trace element features suggest that the hydrothermal fluids for Grt1 and the Grt2 cores were of nearly neutral (pH), relatively oxidized and HREE-enriched, whereas those for the Grt2 rims had experienced episodic inflections between a mildly acidic, relatively reduced and HREE-depleted fluid and a nearly neutral, relatively oxidized and HREE-enriched fluid. Meanwhile, they also reveal that Grt1 and the Grt2 cores may have formed by diffusive metasomatism in a closed system, whereas the Grt2 rims may have formed by infiltration metasomatism in an open fracture system, possibly related to the unconformity that hosts the Xinqiao stratiform orebody. We propose that the Xinqiao stratiform orebody may have formed from Early Cretaceous magmatic-hydrothermal fluids associated with the Jitou stock, similar to the skarn-type orebodies in the district.

Genesis of the Xinqiao Cu–S–Fe–Au deposit in the Middle-Lower Yangtze River Valley metallogenic belt, Eastern China: Constraints from U–Pb–Hf, Rb–Sr, S, and Pb isotopes

The Xinqiao Cu–S–Fe–Au deposit in the Tongling ore district, one of important part of Middle-Lower Yangtze River Valley metallogenic belt in Eastern China, is located along the northern margin of the Yangtze craton. It consists of two major types of mineralization: a more economically significant stratiform orebody with pyrite-bearing quartz veins in its footwall, and the less economically important skarn-type orebodies.An integrated study of zircon U–Pb–Hf and trace elements analysis for the quartz diorite in Xinqiao Jitou stock, Rb–Sr isotope analysis for quartz fluid inclusions from the footwall stockwork mineralization, as well as a systematic S–Pb isotope analysis of sulfides was carried out, all based on detailed field investigations. U–Pb zircon dating of Jitou stock yielded an age of 139.6±1.5Ma (MSWD=0.80), close to the Rb–Sr isotope isochron age (138.0±2.3Ma, MSWD=5.40, an initial 87Sr/86Sr value of 0.71138±0.00014) of quartz fluid inclusions from the footwall stockwork mineralization. The εHf(t) values of zircon grains vary from −15.3 to −8.5 with TDM2 ranging from 2151 to 1729Ma, suggesting that the magma for Jitou stock was probably dominant in crustal-derived magmas with minor mantle material inputs, based on the previous studies on Sr isotope compositions, Nb/Ta ratios and Mg#. The ΔFMQ values (−4.44 to 7.77, average 4.36) suggest that the Jitou stock was derived from the highly oxidized magma and favorable for the Cu mineralization. The systematic S–Pb isotope data and the initial 87Sr/86Sr values demonstrate that the stratiform orebody and the footwall stockwork mineralization were likely to be genetically linked to magmatic-hydrothermal events of Yanshanian (Jurassic – Cretaceous) age, as confirmed by closeness of ages of mineralization and magmatism. Therefore, it is interpreted that the Xinqiao stratiform mineralization may have resulted from Yanshanian magmatic hydrothermal fluids associated with the Jitou stock, as may be the case also for the skarn-type mineralization hosted in the contact between the Yanshanian Jitou stock and the Lower Permian Qixia Formation limestone, based on the basis of ore deposit geology. Generally, the Xinqiao Cu–S–Fe–Au mineralization may have been generated by the Yanshanian tectono-thermal event in Eastern China.

Genesis of the Kaladawan Fe–Mo ore field in Altyn, Xinjiang, China: Constraints from mineralogy and geochemistry

The Kaladawan Fe–Mo ore field in Altyn (Xinjiang Province, NW China) contains six Fe (–Mo) deposits, with total proven reserves of 60Mt Fe and 10,000t Mo. Tabular, lensoidal and stratiform orebodies occur in the Cambrian foliated marble, phyllite, carbonaceous slate, chlorite–sericite schist and quartz–sericite schist along the exocontact zone of the Kaladawan granite. Skarns are extensively developed and dominated by garnet, pyroxene, epidote, tremolite and actinolite, with minor chlorite, zoisite, quartz and calcite. Ore minerals are mainly magnetite and molybdenite. Five alteration and mineralization stages (I–V) were identified: the prograde (I) and retrograde (II) skarns are characterized by assemblages of garnet–pyroxene and epidote–tremolite–actinolite, respectively, intruded and replaced by mineral assemblages of magnetite–epidote–zoisite (III), quartz–sulfides (IV) and calcite–chlorite (V) in younging order. The Kaladawan garnet contains more andradite (61.2–94.4mol%) than grossularite (37.5–5.0mol%). Pyroxene is Mg-rich and Fe-poor, with an endmember range of 55.4–94.7mol% diopside and 42.5–4.7mol% hedenbergite. Amphibole comprises mainly tremolite and actinolite. The Kaladawan skarn mineral contents resemble typical skarn Fe and Mo deposits. In-situ LA-ICP-MS magnetite trace element analysis had identified unusually high Mg, Mo and Cr concentrations. The high Mo and the absence of molybdenite inclusions in magnetite suggest that the hydrothermal fluids may have been Mo-rich. The magnetite also contains similar (Ti+V) and (Al+Mn) values with typical skarn Fe deposits. Therefore, the Kaladawan Fe–Mo mineralization is best attributed to be skarn-type, and related to the Kaladawan granite intrusion.

In-situ LA-ICP-MS trace elements analysis of scheelites from the giant Beiya gold–polymetallic deposit in Yunnan Province, Southwest China and its metallogenic implications

The Beiya gold–polymetallic deposit, located in the middle of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt, is the largest skarn gold deposit in China. Scheelite is a typical hydrothermal mineral which can serve as mineralization process tracer and is significant for the hydrothermal deposit study. In this paper, we present in-situ LA-ICP-MS scheelite geochemical data from the different parts of the skarn mineralization in the Beiya deposit. The data indicate that the Beiya scheelite has high Mo (average: 38,943ppm) and high LREE/HREE (average: 29.6), resembling typical skarn-type scheelite. The mechanism of REE substitution of Ca in the Beiya scheelite was probably 3Ca2+=2REE3++□Ca, which implies that the scheelite inherited its REE composition from magma-derived ore-forming fluids. The scheelite from near the marble shows negative Eu anomaly (average δEu: 0.45), indicating an oxidizing condition, whereas that from near the porphyry shows positive Eu anomaly (average δEu: 3.58), indicating a reducing environment. Scheelite from the sandstone-hosted stratiform orebody shows slight and variable Eu anomalies (δEu: 0.66–1.47), indicating possible fluctuating physicochemical conditions. Our data demonstrate an increasing oxygen fugacity (fO2) trend from the ore-related intrusion to the surrounding carbonates at Beiya. The Rb/Sr, Nb/Ta and Zr/Hf ratios of the Beiya scheelite suggest an addition of mantle-derived components to the ore-forming materials of the Beiya deposit.

Origin of the granites and related Sn and Pb-Zn polymetallic ore deposits in the Pengshan district, Jiangxi Province, South China: constraints from geochronology, geochemistry, mineral chemistry, and Sr-Nd-Hf-Pb-S isotopes

The Pengshan Sn and Pb-Zn polymetallic deposits are located in the south margin of the Jiujiang-Ruichang (Jiurui) district of the Middle-Lower Yangtze River Metallogenic Belt in South China. Four large deposits include Huangjinwa, Zengjialong, Jianfengpo, and Zhangshiba, the former three are Sn-dominant deposits which occur as stratiform orebodies in the contact zones of the Pengshan granites and within the country rock strata, whereas Zhangshiba consists of stratiform Pb-Zn orebodies within the Precambrian metasedimentary strata. In this study, we present results on zircon U-Pb ages, major and trace elements, and mineral chemistry as well as Sr-Nd-Hf isotope data of the granites, Pb and S isotopes of both the Sn-dominant and Pb-Zn dominant deposits, and U-Pb dating of cassiterite from the Pengshan district. SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the Pengshan granites were emplaced in the Early Cretaceous (129–128 Ma), which is in good agreement with the U-Pb dating (130–128 Ma) of cassiterite from the Jianfengpo Sn deposit. The Pengshan granites consist mainly of weakly peraluminous highly fractionated I-type affinity granitic rocks. Detailed elemental and isotopic data suggest that the granites formed by partial melting of Mesoproterozoic metamorphic basement materials with minor input of mantle-derived melts. The mineral chemistry of biotite demonstrates that the Pengshan granitic magma had a low oxygen fugacity, thereby precluding the tin dominantly partitioning into the rock-forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages. Sulfur isotopes show a relatively heavy sulfur isotopic composition from 5.8 to 17.6 ‰, and no difference for sulfur isotopes between the Sn deposits (5.8–13.4 ‰, Huangjinwa, Zengjialong, Jianfengpo) and the Pb-Zn deposit (mostly 7.1–13.0 ‰, except for one 17.6 ‰, Zhangshiba). The sulfur isotope data of pyrite from the host sedimentary rocks show relatively higher δ34S values of 22.7–28.7 ‰. Lead isotopes indicate that the granites have higher 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios than the host Precambrian metasedimentary rocks, and the sulfide minerals from the orebodies fall in between them. Again, there is no difference for Pb isotopes between the Sn deposits (Huangjinwa, Zengjialong, Jianfengpo) and the Zhangshiba Pb-Zn deposit. The coincidence in S and Pb isotope compositions for Sn and Pb-Zn deposits suggests that similar sources for these mineralization, possibly derived from a mixed source of the granitic magmas and the Precambrian metasedimentary rocks. These data therefore favor of a magmatic-hydrothermal origin for both the Sn and Pb-Zn polymetallic mineralization in the Pengshan district.

S, Pb, and Sr isotope geochemistry and genesis of Pb–Zn mineralization in the Huangshaping polymetallic ore deposit of southern Hunan Province, China

The Huangshaping Pb–Zn–W–Mo polymetallic deposit, located in southern Hunan Province, China, is one of the largest deposits in the region and is unique for its metals combination of Pb–Zn–W–Mo and the occurrence of significant reserves of all these metals. The deposit contains disseminated scheelite and molybdenite within a skarn zone located between Jurassic granitoids and Carboniferous sedimentary carbonate, and sulfide ores located within distal carbonate-hosted stratiform orebodies. The metals and fluids that formed the W–Mo mineralization were derived from granitoids, as indicated by their close spatial and temporal relationships. However, the source of the Pb–Zn mineralization in this deposit remains controversial.Here, we present new sulfur, lead, and strontium isotope data of sulfide minerals (pyrrhotite, sphalerite, galena, and pyrite) from the Pb–Zn mineralization within the deposit, and these data are compared with those of granitoids and sedimentary carbonate in the Huangshaping deposit, thereby providing insights into the genesis of the Pb–Zn mineralization. These data indicate that the sulfide ores from deep levels in the Huangshaping deposit have lower and more consistent δ34S values (−96m level: +4.4‰ to +6.6‰, n=13) than sulfides within the shallow part of the deposit (20m level: +8.3‰ to +16.3‰, n=19). The δ34S values of deep sulfides are compositionally similar to those of magmatic sulfur within southern Hunan Province, whereas the shallower sulfides most likely contain reduced sulfur derived from evaporite sediments. The sulfide ores in the Huangshaping deposit have initial 87Sr/86Sr ratios (0.707662–0.709846) that lie between the values of granitoids (0.709654–0.718271) and sedimentary carbonate (0.707484–0.708034) in the Huangshaping deposit, but the ratios decreased with time, indicating that the ore-forming fluids were a combination of magmatic and formation-derived fluids, with the influence of the latter increasing over time. The lead isotopic compositions of sulfide ores do not correlate with sulfide type and define a linear trend in a 207Pb/204Pb vs. 206Pb/204Pb diagram that is distinct from the composition of the disseminated pyrite within sedimentary carbonates and granitoids in the Huangshaping deposit, but is similar to the lead isotopic composition of sulfides within coeval skarn Pb–Zn deposits in southern Hunan Province. In addition, the sulfide ores have old signatures with relative high 207Pb/206Pb ratios, suggesting that the underlying Paleoproterozoic basement within southern Hunan Province may be the source of metals within the Huangshaping deposit.The isotope geochemistry of sulfide ores in the Huangshaping deposit shows a remarkable mixed source of sulfur and ore-forming fluids, and the metals were derived from the basement. These features are not found in representative skarn-type Pb–Zn mineralization located elsewhere. The ore-forming elements (S, Pb, and Zn) from the granitoids made an insignificant contribution to sulfide precipitation in this deposit. However, the emplacement of granitoids did provide large amounts of heat and fluids to the hydrothermal system in this area and extracted metals from the basement rocks, indicating that the Jurassic magmatism associated with the Huangshaping deposit was crucial to the Pb–Zn mineralization.

Ore geology and fluid evolution of the giant Caixiashan carbonate-hosted Zn–Pb deposit in the Eastern Tianshan, NW China

The Caixiashan giant carbonate-hosted Zn–Pb deposit (~131Mt@ 3.95% Zn+Pb) formed by replacement of dolomitized marble, with stratiform massive and breccia bodies is located near the base of the Proterozoic Kawabulake Group limestone and marble. It is one of the largest carbonated-hosted massive sulfides Zn–Pb ore deposits in Northwest China to have been discovered in recent years.Abundant pyrite occurs in dolomitized marble, along fractures in dolomitized clasts in the host rocks and filling cracks in the host rock. Locally, colloform or framboidal pyrites are observed in the early period and sometimes replaced by the later sphalerite. The sulfide assemblage of the main ore stage is characterized by massive or disseminated sphalerite and galena, with less pyrite than the earlier stage, and minor pyrrhotite. Galena occurs as small veins cutting the early-formed sphalerite. Dolomite and calcite are the main gangue minerals that co-precipitated with these sulfides. Tremolite and quartz alteration commonly overprints the orebodies. According to the crosscutting relationships and the different mineral associations within the host rocks and ore bodies, three stages are recognized at Caixiashan, i.e., syn-sedimentary pyrite (stage I), pyrite alteration, sphalerite–carbonate and galena–pyrite–carbonate (stage II-1, stage II-2 and stage II-3, respectively) and magmatic/metamorphic reworking (stage III).Calcite and quartz crystals are important host minerals among the three hypogene stages (stages I–III, although quartz mainly occurred in stage III). Stage I contains only aqueous inclusions (W-type), which were homogenized from 110 to 236°C (main range of 138–198°C and average at 168°C; main range=average±σ) and the salinities are from 0.5 to 16.5 (main range of 5.1–15.1 with average of 10.1) wt.% NaCl eqv. In the pyrite alteration of stage II-1 the W-type fluid inclusions homogenized from 175 to 260°C (main range of 210–260 with average of 235) and the salinities range from 8.5 to 22.4 (main range of 16.7–20.1 with average of 18.4) wt.% NaCl eqv. In the main Zn–Pb mineralization stage (stage II-2–3), four types of fluid inclusions were identified an aqueous phase (W-type), a pure carbon phase (PC-type), a carbon phase containing (C-type) and mineral bearing inclusions (S-type). The W-type fluid inclusions of stage II-2–3 homogenized at 210 to 370°C (main range of 253–323 and average at 270) and the salinities range from 5.9 to 23.1 (main range of 13.3–20.3 with average at 16.8) wt.% NaCl eqv.; C-type homogenized at 237°C to 371°C and the salinities range from 6.4–19.7wt.% NaCl eqv.; S-type fluid inclusions homogenized at 211 to 350°C and daughter minerals melted between 340 and 374°C during heating, indicating a salinity range of 42 to 44wt.% NaCl eqv. PC-type fluid inclusions with homogenization temperatures of CO2 phase show large variation from 7.4°C to 21.2°C. Laser Raman analyses show that CH4, CO2 and SO42− coexist in the main mineralization stage fluids. The magmatic/metamorphic reworking stage only contains W-type fluid inclusions which yield homogenized between 220 and 360°C (main range of 251–325 and average at 288), with salinities ranging from 1.7 to 23.0 (main range of 14.3–20.0 and average at 18.8) wt.% NaCl eqv.The textural features, mineral assemblages and fluid geochemistry suggest that the Zn–Pb ores were formed through hydrothermal convection of hot marine waters along the faults and fractures resulting in metal (Zn, Pb and Fe) enriched stratiform orebodies. Subsequent rapid precipitation of sulfides was triggered by sulfate (SO42−) thermal reduction with the CH4 preserved in sedimentary rocks and early stage I pyrite bodies. This process occurred at moderate temperatures (ca. 270°C). Higher-temperature magmatic hydrothermal alteration overprinted the orebodies, but only provided a minor contribution to the mineralization.

Metallogenic model for the Laochang Pb–Zn–Ag–Cu volcanogenic massive sulfide deposit related to a Paleo-Tethys OIB-like volcanic center, SW China

The Laochang Pb–Zn–Ag–Cu volcanogenic massive sulfide (VMS) deposit, located within the Changning–Menglian Paleotethyan suture, SW China, is an economically significant deposit with explored reserves of 866,000 metric tons (t) Pb at 4.5%, 336,000t Zn at 3.3%, 1700t Ag at 155g/t, 116,000t Cu at 0.5–0.9%, 2.84Mt pyrite and accompany 0.8t Au. The deposit comprises three ore clusters (No. I, II and III), each of which comprises dozens of vertically stacked lenticular and stratiform orebodies. Ore clusters I and II within the Early Carboniferous volcano-sedimentary sequence erupted around 320Ma comprise most of the reserves. The Early Carboniferous sequences, situating beside the Laochang caldera, are mainly composed of basaltic to andesitic lavas and volcaniclastic rocks, and divided into three major volcanic cycles. The massive sulfides mostly accumulated in the waning time of the second and third cycles. The orebodies (e.g., orebodies I1+2 and II1) display stockwork and disseminated sulfide ores in the lower part and the semi-horizontal massive sulfide lenses and laminated carbonaceous-sulfidic chert with delicate exhalative-sedimentary textures in the upper part, and they also show vertical metal zonation transiting from Fe–Cu, Cu–Zn–Pb to Pb–Zn–Ag. The underlying rock of the semi-horizontal orebodies has pervasively sericite–pyrite–quartz alteration; comparatively, the overlying is little altered. Ores are dominantly composed of sulfides, lacking sulfate and Fe-oxides, suggesting a very low SO42− concentration in the hydrothermal solution.The host andesitic tuff and basalt show pattern of fractionated rare earth elements (REE) and the enrichment in large ion lithophile elements (LILE; e.g., Rb, Th, U and light REE) and most high field strength elements (HFSE; e.g., Nb, Ta, Hf and Zr). These features are similar to those of oceanic island basalt. The higher REE fractionation and the greater enrichment of LILE (includes light REE) in the andesitic tuffs compared to those in the basalts comply with a fractionational crystallization process in a shallow magma chamber. The δ34S‰ (CDT) of the sulfides ranges from −2.1 to 3.5‰ with an average of 0.2‰. The limited variation of δ34S‰ near zero implies that the sulfur was derived via leaching of the footwall volcanic rocks and/or degassing directly from a magma chamber. Lead isotopic compositions of sulfides also have a small range. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.486–18.684, 15.668–15.712 and 38.725–39.024, respectively, indicating an extremely radiogenic feature similar to the host volcanic rocks. Previous fluid inclusion investigations revealed that ore fluid had high salinity, high temperature and the H–O–C isotopic compositions close to the primary magmatic hydrothermal. Our S–Pb isotopic analysis together with the fluid inclusion study, are supportive to the magmatic degassing genesis for this deposit. The vertical zonation of metal species, occurrence of laminated carbonaceous-sulfidic chert and lack of alteration in the hanging wall imply that the orebodies were formed via seafloor sulfide precipitation instead of sub-seafloor replacement. The occurrence of black shale intercalated with sulfide lenses and the carbonaceous-sulfidic chert caps, especially the absence of sulfate and other oxidized facies in the ores indicate a compelling local anoxic environment for mineral precipitation. This anoxic environment was caused by the venting of magmatic fluids characterized by high temperature, high salinity, metal-charged (Fe, Cu, Pb, Zn and Ag) and H2S-rich. The repetitive activity of magma degassing in the waning stage of volcanic eruption corresponded to the stacked structure of massive sulfide lenses within the top layer in a volcanic cyclothem. The enormous base metal enrichment and highly radiogenic lead isotopes at Laochang are explained to reflect the incorporation of a recycled upper continental crust component into the mantle source for the ore-bearing volcanic rocks during the evolution of Tethyan ocean.