Geological and geochemical constraints on the Cheshmeh-Frezi volcanogenic stratiform manganese deposit,southwest Sabzevar basin,Iran

The Cheshmeh-Frezi Mn deposit belongs to the southwest Sabzevar basin to the north of the Central Iranian microcontinent. This basin, which hosts abundant mineral deposits including Mn exhalative and Besshi-type Cu-Zn volcanogenic massive sulfide deposits, followed an evolution closely related to the subduction of the Neo-Tethys oceanic crust beneath the Central Iranian microcontinent. Two major sedimentary sequences are recorded within this basin: (I) the Lower Late Cretaceous volcano-sedimentary sequence (LLCVSS) and (II) the Upper Late Cretaceous sedimentary dominated sequence (ULCSS). The Cheshmeh-Frezi Mn deposit is hosted within red tuff with interbeds of green tuffaceous sandstone of the LLCVSS. Mineralization occurs as stratiform blanket-like and tabular orebodies. Psilomelane, pyrolusite and braunite are the main minerals of the ore, which display a variety of textures. Such as layered, laminated, disseminated, massive, replacement or open space fillings. The footwall and hanging-wall volcanic rocks are predominantly andesite and trachyandesite rocks. Footwall and hangingwall volcanic rocks at Cheshmeh-Frezi are enriched in light rare earth elements (LREEs) compared to chondrite, have steep REE patterns, and generally show Ta and Nb depletions relative to chondrite which are characteristic of back-arc environments. The significant geochemical characteristics of ore such as high Mn content (12.41–33.14 wt%; average 19.41 wt%), low concentration of Fe (0.64–2.27 wt%; average 1.63 wt%), high Ba (49.7–9901 ppm, average 2728.67 ppm), LREE > HREE, and negative Ce and Eu anomalies reveal a primary distal hydrothermal-exhalative source for mineralization. Cheshmeh-Frezi deposit, in comparison with different types of volcanogenic manganese deposits shows broad similarities with the Cuban-type Mn deposits such as tectonic, host and associated rock types, geometry, textures, structures, mineralogy and lithogeochemistry.     

The Xitieshan volcanic sediment-hosted massive sulfide deposit,North Qaidam,China: Geology,structural deformation and geochronology

The Xitieshan deposit (~ 64 Mt at 4.86% Zn, 4.16% Pb, 58 g/t Ag, and 0.68 g/t Au) is hosted by the Middle to Late Ordovician Tanjianshan Group of the North Qaidam tectonic metallogenic belt, NW China. This belt is characterized by island arc volcanic, ultra-high pressure (UHP) metamorphic and ophiolitic rocks. The Tanjianshan Group constitutes a succession of metamorphosed bimodal volcanic and sedimentary rocks, which are interpreted to have formed on the margin of a back-arc ocean basin between the Qaidam block and the Qilian block.Four stratigraphic units are identified within the Ordovician Tanjianshan Group. From northeast to southwest they are: 1) unit a, or the lower volcanic-sedimentary rocks, comprising bimodal volcanic rocks (unit a-1) and sedimentary rocks (unit a-2) ranging from carbonates to black carbonaceous schist; 2) unit b, or intermediate-mafic volcaniclastic rocks, characterized by intermediate to mafic volcaniclastic rocks intercalated with lamellar carbonaceous schist and minor marble lenses; 3) unit c, a purplish red sandy conglomerate that unconformably overlies unit b, representing the product of the foreland basin sedimentation during the Early Silurian; 4) unit d, or mafic volcanic rocks, from base to up, comprising the lower mafic volcaniclastic rocks (unit d-1), middle clastic sedimentary rocks (unit d-2), upper mafic volcaniclastic rocks (unit d-3), and uppermost mafic volcanic rocks (unit d-4). Unit a-2 hosts most of the massive sulfides whereas unit b contains subordinate amounts.The massive stratiform lenses constitute most of the Xitieshan deposit with significant amount of semi-massive and irregularly-shaped sulfides and minor amounts in stringer veins. Pyrite, galena and sphalerite are the dominant sulfide minerals, with subordinate pyrrhotite and chalcopyrite. Quartz is a dominant gangue mineral. Sericite, quartz, chlorite, and carbonate alteration of host rocks accompanies the mineralization.U-Pb zircon geochronology yields three ages of 454 Ma, 452 Ma and 451 Ma for the footwall felsic volcanic rocks in unit a-1, sedimentary host rocks in unit a-2 and hanging-wall unit b, respectively. The Xitieshan deposit is considered to be coeval with the sedimentation of unit a-2 and unit b of the Tanjianshan Group. The Xitieshan deposit has been intensely deformed during two phases (main ductile shear and minor ductile-brittle deformation). The main ductile shear deformation controls the general strike of the ore zones, whereas minor deformation controls the internal geometry of the ore bodies. ⁴⁰Ar-³⁹Ar age of muscovite from mylonitized granitic gneisses in the ductile shear zone is ~ 399 Ma, which is interpreted to date the Xitieshan ductile shear zone, suggesting that Early Devonian metamorphism and deformation post-dated the Tanjianshan Group.The Xitieshan deposit has many features similar to that of the Bathurst district of Canada, the Iberian Pyrite Belt of Spain, the Wolverine volcanogenic massive sulfide deposit in Canada. Based on its tectonic setting, host-rock types, local geologic setting, metal grades, geochronology, temperatures and salinities of mineralizing fluid and source of sulfur, the Xitieshan deposit has features similar to sedimentary exhalative (SEDEX) and VMS deposits and is similar to volcanic and sediment-hosted massive sulfide (VSHMS) deposits.     

The trinity pattern of Au deposits with porphyry,quartz–sulfide vein and structurally-controlled alteration rocks in Ciemas,West Java,Indonesia

The Ciemas gold mining area is located in the Sunda arc volcanic rock belt, West Java, Indonesia. Ore bodies are associated with Miocene andesite, dacite and quartz diorite porphyrite. To constrain ore genesis and mineralization significance, a detailed study was recently conducted examining these deposits, which included detailed field observation, petrographic study, petrochemistry, sulfur isotope analyses, zircon U–Pb dating, and fluid inclusion analysis. The results include the following findings. 1) Ore types have been identified as porphyry, a quartz–sulfide vein, and structure-controlled alteration rocks. 2) In host rocks, zircon LA–ICP-MS U–Pb dating of quartz diorite porphyrite, amphibole tuff breccia and andesite yield ages of 17.1 ± 0.4 Ma, 17.1 ± 0.4 Ma and 17.5 ± 0.3 Ma, respectively. 3) Fluid inclusions in the quartz from ore are given priority to liquid and gas–liquid phases, and their components are of the NaCl–H₂O system with homogenization temperatures of 240–320 °C, salinities of 14–17%, densities of 0.85–0.95 g/cm³, and fluid pressure values between 4.1 and 46.8 MPa, corresponding to metallogenic depths from 150 to 1730 m. Fluid characteristics are identified as similar to those of high sulfur epithermal deposits. 4) The sulfur isotopic compositions are notably uniform, the δ³⁴S values of wall rocks range from 3.71 to 3.85‰, and the δ³⁴S values of ores vary from 4.90‰ to 6.55‰. The sulfur isotopic composition of ores is similar to that of the wall rocks, indicating a mixed origin of mantle with a sedimentary basement. 5) The trace element patterns of different ore types are similar, which indicates that they originate from the same source. Au deposits primarily occurred during the late magmatic activity. Finally, we have set up the regional metallogenic model, confirming that this gold deposit in the Sunda arc volcanic rock belt belongs to a metallogenic system from porphyry to epithermal type.     

Chadormalu Kiruna-type magnetite-apatite deposit,Bafq district,Iran: Insights into hydrothermal alteration and petrogenesis from geochemical,fluid inclusion,and sulfur isotope data

The Chadormalu is one of the largest known iron deposits in the Bafq metallogenic province in the Kashmar-Kerman belt, Central Iran. The deposit is hosted in Precambrian-Cambrian igneous rocks, represented by rhyolite, rhyodacite, granite, diorite, and diabasic dikes, as well as metamorphic rocks consisting of various schists. The host rocks experienced Na (albite), calcic (actinolite), and potassic (K-feldspar and biotite) hydrothermal alteration associated with the formation of magnetite–(apatite) bodies, which are characteristic of iron oxide copper-gold (IOCG) and iron oxide-apatite (IOA) systems. Iron ores, occurring as massive-type and vein-type bodies, consist of three main generations of magnetite, including primary, secondary, and recrystallized, which are chemically different. Apatite occurs as scattered irregular veinlets in various parts of the main massive ore-body, as well as apatite-magnetite veins and disseminated apatite grains in marginal parts of the deposit and in the immediate wall rocks. Minor pyrite occurs as a late phase in the iron ores. Chemical composition of magnetite is representative of an IOA or Kiruna-type deposit, which is consistent with other evidence.Whole rock geochemical data from various host rocks confirm the occurrence of Na, Ca, and K alteration consistent with the formation of albite, actinolite, and K-feldspar, respectively. The geochemical investigation also includes the nature of calc-alkaline igneous rocks, and helps elaborating on the spatial and temporal association, and possible contribution of mafic to felsic magmas to the evolution of ore-bearing hydrothermal fluids.Fluid inclusion studies on apatites from massive- and vein-type ores show a range of homogenization temperatures from 266 to 580 °C and 208–406 °C, and salinities from 0.5 to 10.7 wt.% and 0.3–24.4 wt.% NaCl equiv., respectively. The fluid inclusion data suggest the involvement of evolving fluids, from low salinity-high temperature, to high salinity-low temperature, in the formation of the massive- and vein-type ores, respectively. The δ³⁴S values obtained for pyrite from various parts of the deposit range between +8.9 and +14.4‰ for massive ore and +18.7 to +21.5‰ for vein-type ore. A possible source of sulfur for the ³⁴S-enriched pyrite would be originated from late Precambrian-early Cambrian marine sulfate, or fluids equilibrated with evaporitic sulfates.Field observations, ore mineral and alteration assemblages, coupled with lithogeochemical, fluid inclusion, and sulfur isotopic data suggest that an evolving fluid from magmatic dominated to surficial brine-rich fluid has contributed to the formation of the Chadormalu deposit. In the first stages of mineralization, magmatic derived fluids had a dominant role in the formation of the massive-type ores, whereas a later brine with higher δ³⁴S contributed to the formation of the vein-type ores.     

Metallogeny of the Shilu Fe–Co–Cu deposit,Hainan Island,South China: Constraints from fluid inclusions and stable isotopes

The Shilu deposit is a world-class Fe–Co–Cu orebody located in the Changjiang area of the western part of Hainan Island, South China. The distribution of Fe, Co, and Cu orebodies is controlled by strata of the No. 6 Formation in the Shilu Group and the Beiyi synclinorium. Based on a petrological study of the host rocks and their alteration assemblages, and textural and structural features of the ores, four mineralization stages have been identified: (1) the sedimentary ore-forming period; (2) the metamorphic ore-forming period; (3) the hydrothermal mineralization comprising the skarn and quartz–sulfide stage; and (4) the supergene period. The fluid inclusions in sedimentary quartz and/or chert indicate low temperatures (ca. 160 °C) and low salinities from 0.7 to 3.1 wt.% NaCl_eq, which corresponds to densities of 0.77 to 0.93 g/cm³. CO₂-bearing or carbonic inclusions have been interpreted to result from regional metamorphism. Homogenization temperatures of fluid inclusions for the skarn stage have a wide range from 148 °C to 497 °C and the salinities of the fluid inclusions range from 1.2 to 22.3 wt.% NaCl_eq, which corresponds to densities from 0.56 to 0.94 g/cm³. Fluid inclusions of the quartz–sulfide stage yield homogenization temperatures of 151–356 °C and salinities from 0.9 to 8.1 wt.% NaCl_eq, which equates to fluid densities from 0.63 to 0.96 g/cm³.Sulfur isotopic compositions indicate that sulfur of the sedimentary anhydrite and Co-bearing pyrite, and the quartz–sulfide stage, was derived from seawater sulfate and thermochemical sulfate reduction of dissolved anhydrite at temperatures of 200 °C and 300 °C, respectively. H and O isotopic compositions of the skarn and quartz–sulfide stage demonstrate that the ore-forming fluids were largely derived from magmatic water, with minor inputs from metamorphic or meteoric water. The Shilu iron ore deposit has an exhalative sedimentary origin, but has been overprinted by regional deformation and metamorphism. The Shilu Co–Cu deposit has a hydrothermal origin and is temporally and genetically associated with Indosinian granitoid rocks.     

Geological and geochemical characteristics and formation mechanisms of the Zhaishang Carlin-like type gold deposit,western Qinling Mountains,China

Located in the western part of the Min–Li metallogenic belt within the western Qinling Mountains, the Zhaishang gold deposit is a giant Carlin-like disseminated gold deposit discovered recently. The ore deposit is present both in rocks of low grade metamorphic Middle Devonian and Lower Permian clastic formation, which is composed of quartz sandstone, siltstone, calcareous slate and argillaceous limestone. Gold mineralization is strictly controlled by a fault zone. Minerals in ores are quite complex and consist of sulfides, sulfosalt, oxides, sulfate, carbonate, tungstate, telluride, native metals, and polymetallic alloys. The diversity of mineral in the ores and the existence of microscopic visible native gold constitute the outstanding features of the gold deposit.We believe that the mineral source of the ore deposit has a close connection with the host rocks, because all samples show the light of the REE distribution patterns. The S, C, Pb, H and O isotopic compositions show that the ore-forming elements were mainly derived from the country rocks, the underlying rocks, and partially deep sources. Data obtained suggest that the ore-forming fluids were derived predominantly from an active meteoric groundwater system. Mineralization and related alteration have features of a low water/rock ratio. Ore-forming temperatures are estimated to have been in the range from 120 to 240 °C. The dissolution of ferruginous limestone in the host rocks and the sulfidation of the dissolved iron by H₂S introduced by ore fluids constituted not only the most important depositional mechanisms for the existence of microscopic visible gold grains but also favorable conditions for gold enrichment in the Zhaishang gold deposit.     

Geology,geochemistry and ore genesis of the Wenyu gold deposit,Xiaoqinling gold field,Qinling Orogen,southern margin of North China Craton

The Wenyu giant gold deposit is hosted in the Precambrian Taihua Supergroup metamorphic rocks within the Xiaoqinling terrane (Qinling Orogen), on the southern margin of the North China Craton. The mineralization can be divided into three stages: quartz–pyrite veins early, quartz–sulfide veins middle (main), and carbonate–quartz veinlets late, with gold being mainly introduced in main stage. Quartz formed in two earlier stages contains three compositional types of fluid inclusions, i.e. pure CO₂, CO₂–H₂O and NaCl–H₂O, but the late-stage minerals only contain the NaCl–H₂O inclusions. The inclusions in quartz formed in the early, main and late stages yield total homogenization temperatures of 262–417 °C, 236–407 °C and 114–239 °C, respectively, with salinities no higher than 13 wt.% NaCl equiv. Trapping pressures estimated from CO₂–H₂O inclusions are 139–399 MPa and 111–316 MPa in the early and main stages, corresponding to mineralization depths of 14 km and 11 km, respectively. Fluid boiling and mixing caused rapid precipitation of sulfides and native Au. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO₂-rich to CO₂-poor in composition, and from metamorphic to meteoric, as indicated by decreasing δ¹⁸O_water values from early to late. The carbon, sulfur and lead isotope compositions suggest the hostrocks within the Taihua Supergroup to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, fluid inclusion and C–H–O–S–Pb isotope geochemistry, we conclude that the Wenyu gold deposit was an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic–Early Cretaceous continental collision between the North China and Yangtze Cratons.     

Genesis of the Zinkgruvan stratiform Zn-Pb-Ag deposit and associated dolomite-hosted Cu ore,Bergslagen, Sweden

Zinkgruvan, a major stratiform Zn-Pb-Ag deposit in the Paleoproterozoic Bergslagen region, south-central Sweden, was overprinted by polyphase ductile deformation and high-grade metamorphism (including partial melting of the host succession) during the 1.9–1.8 Ga Svecokarelian orogeny. This complex history of post-ore modification has made classification of the deposit difficult. General consensus exists on a syngenetic-exhalative origin, yet the deposit has been variably classified as a volcanogenic massive sulfide (VMS) deposit, a sediment-hosted Zn (SEDEX) deposit, and a Broken Hill-type (BHT) deposit. Since 2010, stratabound, cobaltiferous and nickeliferous Cu ore, comprising schlieren and impregnations of Cu, Co and Ni sulfide minerals in dolomitic marble, is mined from the stratigraphic footwall to the stratiform Zn-Pb-Ag ore. This ore type has not been fully integrated into any of the existing genetic models. Based on a combination of 1) widespread hematite-staining and oxidizing conditions (Fe₂O₃ > FeO) in the stratigraphic footwall, 2) presence of graphite and reducing conditions (Fe₂O₃ < FeO) in the ore horizon and hangingwall and 3) intense K-feldspar alteration and lack of feldspar-destructive alteration in the stratigraphic footwall, we suggest that both the stratiform Zn-Pb-Ag and the dolomite-hosted Cu ore can be attributed to the ascent and discharge of an oxidized, saline brine at near neutral pH. Interaction of this brine with organic matter below the seafloor, especially within limestone, formed stratabound, disseminated Cu ore, and exhalation of the brine into a reduced environment on the sea floor produced a brine pool from which the regionally extensive (>5 km) Zn-Pb-Ag ore was precipitated.Both ore types are characterized by significant spread in δ³⁴S, with the sulfur in the Cu ore and associate marble-hosted Zn mineralization on average being somewhat heavier (δ³⁴S = −4.7 to +10.5‰, average 3.9‰) than that in the stratiform Zn-Pb-Ag ore (δ³⁴S = −6 to +17‰, average 2.0‰). The ranges in δ³⁴S are significantly larger than those observed in syn-volcanic massive sulfide deposits in Bergslagen, for which simple magmatic/volcanic sulfur sources have been invoked. Mixing of magmatic-volcanic sulfur leached from underlying volcanic rocks and sulfur sourced from abiotic or bacterial sulfate reduction in a mixing zone at the seafloor could explain the range observed at Zinkgruvan.A distinct discontinuity in the stratigraphy, at which key stratigraphic units stop abruptly, is interpreted as a syn-sedimentary fault. Metal zonation in the stratiform ore (decreasing Zn/Pb from distal to proximal) and the spatial distribution of Cu mineralization in underlying dolomitic marble suggest that this fault was a major feeder to the mineralization. Our interpretation of ore-forming fluid composition and a dominant redox trap rather than a pH and/or temperature trap differs from most VMS models, with Selwyn-type SEDEX models, and most BHT models. Zinkgruvan has similarities to both McArthur-type SEDEX deposits and sediment-hosted Cu deposits in terms of the inferred ore fluid chemistry, yet the basinal setting has more similarities to BHT and felsic-bimodal VMS districts. We speculate that besides an oxidized footwall stratigraphy, regionally extensive banded iron formations and limestone horizons in the Bergslagen stratigraphy may have aided in buffering ore-forming brines to oxidized, near-neutral conditions. In terms of fluid chemistry, Zinkgruvan could comprise one of the oldest known manifestations of Zn and Cu ore-forming systems involving oxidized near-neutral brines following oxygenation of the Earth’s atmosphere.     

A combined fluid inclusion and S–Pb isotope study of the Neoproterozoic Pingshui volcanogenic massive sulfide Cu–Zn deposit,Southeast China

The Pingshui Cu–Zn deposit is located in the Jiangshan–Shaoxing fault zone, which marks the Neoproterozoic suture zone between the Yangtze block and Cathaysia block in South China. It contains 0.45 million tons of proven ore reserves with grades of 1.03 wt.% Cu and 1.83 wt.% Zn. This deposit is composed of stratiform, massive sulfide ore bodies, which contain more than 60 vol.% sulfide minerals. These ore bodies are hosted in altered mafic and felsic rocks (spilites and keratophyres) of the bimodal volcanic suite that makes up the Neoproterozoic Pingshui Formation. Metallic minerals include pyrite, chalcopyrite, sphalerite, tennantite, tetrahedrite and magnetite, with minor galena. Gangue minerals are quartz, sericite, chlorite, calcite, gypsum, barite and jasper. Three distinct mineralogical zones are recognized in these massive sulfide ore bodies: a distal zone composed of sphalerite + pyrite + barite (zone I); an intermediate zone characterized by a pyrite + sphalerite + chalcopyrite assemblages (zone II); and a proximal zone containing chalcopyrite + pyrite + magnetite (zone III). A thin, layer of exhalative jaspilite overlies the sulfide ore bodies except in the proximal zone. The volcanic rocks of the Pingshui Formation are all highly altered spilites and keratophyres, but their trace element geochemistry suggests that they were generated by partial melting of the depleted mantle in an island arc setting. Homogenization temperatures of the primary fluid inclusions in quartz from massive sulfide ores are between 217 and 328 °C, and their salinities range from 3.2 to 5.7 wt.% NaCl equivalent. Raman spectroscopy of the fluid inclusions showed that water is the dominant component, with no other volatile components. Fluid inclusion data suggest that the ore-forming fluids were derived from circulating seawater. The δ³⁴S values of pyrite from the massive sulfide ores range from − 3.6‰ to + 3.4‰, indicating that the sulfur was primarily leached from the arc volcanic rocks of the Pingshui Formation. Both pyrite from the massive sulfide ores and plagioclase from the spilites have similar lead isotope compositions, implying that the lead was also derived from the Pingshui Formation. The low lead contents of the massive sulfide ores and the geochemistry of their host rocks are similar to many VMS Cu–Zn deposits in Canada (e.g., Noranda) and thus can be classified as belonging to the bimodal-mafic subtype. The presence of magnetite and the absence of jaspilite and barite at the − 505 m level in the Pingshui deposit suggest that this level is most likely the central zone of the original lateral massive sulfide ore bodies. If this interpretation is correct, the deep part of the Pingshui Cu–Zn deposit may have significant exploration potential.     

Fluid types and their genetic meaning for the BIF-hosted iron ores,Krivoy Rog,Ukraine

This paper contributes to the understanding of the genesis of epigenetic, hypogene BIF-hosted iron deposits situated in the eastern part of Ukrainian Shield. It presents new data from the Krivoy Rog iron mining district (Skelevatske–Magnetitove deposit, Frunze underground mine and Balka Severnaya Krasnaya outcrop) and focuses on the investigation of ore genesis through application of fluid inclusion petrography, microthermometry, Raman spectroscopy and baro-acoustic decrepitation of fluid inclusions. The study investigates inclusions preserved in quartz and magnetite associated with the low-grade iron ores (31–37% Fe) and iron-rich quartzites (38–45% Fe) of the Saksaganskaya Suite, as well as magnetite from the locally named high-grade iron ores (52–56% Fe). These high-grade ores resulted from alteration of iron quartzites in the Saksaganskiy thrust footwall (Saksaganskiy tectonic block) and were a precursor to supergene martite, high-grade ores (60–70% Fe). Based on the new data two stages of iron ore formation (metamorphic and metasomatic) are proposed.The metamorphic stage, resulting in formation of quartz veins within the low-grade iron ore and iron-rich quartzites, involved fluids of four different compositions: CO₂-rich, H₂O, H₂O–CO₂(± N₂–CH₄)–NaCl(± NaHCO₃) and H₂O–CO₂(± N₂–CH₄)–NaCl. The salinities of these fluids were relatively low (up to 7 mass% NaCl equiv.) as these fluids were derived from dehydration and decarbonation of the BIF rocks, however the origin of the nahcolite (NaHCO₃) remains unresolved. The minimum P–T conditions for the formation of these veins, inferred from microthermometry are T_min = 219–246 °C and P_min = 130–158 MPa. The baro-acoustic decrepitation analyses of magnetite bands indicated that the low-grade iron ore from the Skelevatske–Magnetitove deposit was metamorphosed at T = ~ 530 °C.The metasomatic stage post-dated and partially overlapped the metamorphic stage and led to the upgrade of iron quartzites to the high-grade iron ores. The genesis of these ores, which are located in the Saksaganskiy tectonic block (Saksaganskiy ore field), and the factors controlling iron ore-forming processes are highly controversial. According to the study of quartz-hosted fluid inclusions from the thrust zone the metasomatic stage involved at least three different episodes of the fluid flow, simultaneous with thrusting and deformation. During the 1^st episode three types of fluids were introduced: CO₂–CH₄–N₂(± C), CO₂(± N₂–CH₄) and low salinity H₂O–N₂–CH₄–NaCl (6.38–7.1 mass% NaCl equiv.). The 2^nd episode included expulsion of the aqueous fluids H₂O–N₂–CH₄–NaCl(± CO₂, ± C) of moderate salinities (15.22–16.76 mass% NaCl equiv.), whereas the 3^rd event involved high salinity fluids H₂O–NaCl(± C) (20–35 mass% NaCl equiv.). The fluids most probably interacted with country rocks (e.g. schists) supplying them with CH₄ and N₂. The high salinity fluids were most likely either magmatic–hydrothermal fluids derived from the Saksaganskiy igneous body or heated basinal brines, and they may have caused pervasive leaching of Fe from metavolcanic and/or the BIF rocks. The baro-acoustic decrepitation analyses of magnetite comprising the high-grade iron ore showed formation T = ~ 430–500 °C. The fluid inclusion data suggest that the upgrade to high-grade Fe ores might be a result of the Krivoy Rog BIF alteration by multiple flows of structurally controlled, metamorphic and magmatic–hydrothermal fluids or heated basinal brines.     

In situ Pb and bulk Sr isotope analysis of the Yinchanggou Pb-Zn deposit in Sichuan Province (SW China): Constraints on the origin and evolution of hydrothermal fluids

The Yinchanggou Pb-Zn deposit, located in southwestern Sichuan Province, western Yangtze Block, is stratigraphically controlled by late Ediacaran Dengying Formation and contains >0.3 Mt of metal reserves with 11 wt% Pb + Zn. A principal feature is that this deposit is structurally controlled by normal faults, whereas other typical deposits nearby (e.g. Maozu) are controlled by reverse faults. The origin of the Yinchanggou deposit is still controversial. Ore genetic models, based on conventional whole-rock isotope tracers, favor either sedimentary basin brine, magmatic water or metamorphic fluid sources. Here we use in situ Pb and bulk Sr isotope features of sulfide minerals to constrain the origin and evolution of hydrothermal fluids. The Pb isotope compositions of galena determined by femtosecond LA-MC-ICPMS are as follows: ²⁰⁶Pb/²⁰⁴Pb = 18.17–18.24, ²⁰⁷Pb/²⁰⁴Pb = 15.69–15.71, ²⁰⁸Pb/²⁰⁴Pb = 38.51–38.63. These in situ Pb isotope data overlap with bulk-chemistry Pb isotope compositions of sulfide minerals (²⁰⁶Pb/²⁰⁴Pb = 18.11–18.40, ²⁰⁷Pb/²⁰⁴Pb = 15.66–15.76, ²⁰⁸Pb/²⁰⁴Pb = 38.25–38.88), and both sets of data plotting above the Pb evolution curve of average upper continental crust. Such Pb isotope signatures suggest an upper crustal source of Pb. In addition, the coarse-grained galena in massive ore collected from the deep part has higher ²⁰⁶Pb/²⁰⁴Pb ratios (18.18–18.24) than the fine-grained galena in stockwork ore sampled from the shallow part (²⁰⁶Pb/²⁰⁴Pb = 18.17–18.19), whereas the latter has higher ²⁰⁸Pb/²⁰⁴Pb ratios (38.59–38.63) than the former (²⁰⁸Pb/²⁰⁴Pb = 38.51–38.59). However, both types of galena have the same ²⁰⁷Pb/²⁰⁴Pb ratios (15.69–15.71). This implies two independent Pb sources, and the metal Pb derived from the basement metamorphic rocks was dominant during the early phase of ore formation in the deep part, whereas the ore-hosting sedimentary rocks supplied the majority of metal Pb at the late phase in the shallow part. In addition, sphalerite separated from different levels has initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7101 to 0.7130, which are higher than the ore formation age-corrected ⁸⁷Sr/⁸⁶Sr ratios of country sedimentary rocks (⁸⁷Sr/⁸⁶Sr_200 Ma = 0.7083–0.7096), but are significantly lower than those of the ore formation age-corrected basement rocks (⁸⁷Sr/⁸⁶Sr_200 Ma = 0.7243–0.7288). Again, such Sr isotope signatures suggest that the above two Pb sources were involved in ore formation. Hence, the gradually mixing process of mineralizing elements and associated fluids plays a key role in the precipitation of sulfide minerals at the Yinchanggou ore district. Integrating all the evidence, we interpret the Yinchanggou deposit as a strata-bound, normal fault-controlled epigenetic deposit that formed during the late Indosinian. We also propose that the massive ore is formed earlier than the stockwork ore, and the temporal-spatial variations of Pb and Sr isotopes suggest a certain potential of ore prospecting in the deep mining area.     

The nappe-hosted Hoshbulak MVT Zn–Pb deposit,Xinjiang, China: A review of the geological,elemental and stable isotopic constraints

The Hoshbulak Zn–Pb deposit is located in South Tianshan, Xinjiang, China. The Zn–Pb orebody is tabular and stratoid in form and it is hosted in calcareous rocks of the Upper Devonian Tan'gaitaer Formation which were thrust over the Carboniferous system. The ores are mineralogically simple and composed mainly of sphalerite, galena, pyrite, calcite, dolomite and exhibit massive, banded, veinlets, colloidal, metasomatic, eutectic, concentric ring and microbial-like fabrics. The Co/Ni ratios of pyrite in the ores range from 0.46 to 0.90 by electron microprobe, which suggested that the Hoshbulak Zn–Pb mineralization was formed in a sedimentary environment. The REE patterns of the hydrothermal calcite coincide well with those of recrystallized micritic limestones, suggesting that the Hoshbulak Pb–Zn mineralization was closely genetically related to limestones of the Tan'gaitaer Formation. The C-, H- and O-isotopic compositions of hydrothermal calcite and dolomite in the ores yield δ¹³C(VPDB) values ranging from − 1.9‰ to + 2.6‰ (mean 0.79‰), δ¹⁸O(VSMOW) values from 22.41‰ to 24.67‰ (mean 23.04‰) and δD values from − 77‰ to − 102‰ for fluid inclusions. It is suggested that the ore-forming fluids, including CO₂, were derived from the calcareous strata of the Tan'gaitaer Formation in association with hydrocarbon brines. The δ³⁴S(VCDT) ranges from − 22.3‰ to − 8.5‰ for early ore-stage sulfides and from 5.9‰ to 24.2‰ with a cluster between 14.4‰ and 24.2‰ for the sulfides (pyrite, sphalerite, galena) in the main ore-stage. The ore sulfur may have been derived from evaporite rocks by thermochemical sulfate reduction (TSR) as the predominant mechanism for H₂S generation. The Pb-isotopic compositions of the sulfide minerals from the Hoshbulak ores yield ²⁰⁶Pb/²⁰⁴Pb ratios from 17.847 to 18.173, ²⁰⁷Pb/²⁰⁴Pb ratios from 15.586 to 15.873 and ²⁰⁸Pb/²⁰⁴Pb ratios from 37.997 to 38.905, which indicate that the metals were sourced mainly from the Tan'gaitaer Formation. We conclude that the genesis of the Hoshbulak Mississippi Valley-type deposit was closely related to thrust faulting in the South Tianshan orogen of China.     

Fluid metasomatic genesis of stratiform skarn in the Suoerkuduke Cu-Mo deposit,East Junggar,NW China

Stratiform skarns associated with ore deposits are widespread in the north of East Junggar, particularly in the Suoerkuduke Cu-Mo deposit. The Suoerkuduke stratiform and stratoid skarns are hosted by Devonian intermediate-mafic volcanic and pyroclastic rocks, mainly andesite, andesitic porphyry and tuffaceous sandstone, without carbonate or calcareous rocks. The skarns consist of dominant andradite-grossular, epidote, diopside-hedenbergite and minor actinolite, quartz, magnetite and metallic sulfides. The garnet and epidote composition, especially Fe^3 + and Al contents, is largely a function of the bulk composition and physicochemical environment (particularly fO₂) during crystallization. Such mineralogy indicates a relatively oxidizing environment and medium acidity of solution during skarnization.The Suoerkuduke skarns are distinct from typical contact metasomatic skarn in wall rock, as no carbonate or calcareous rocks were found, and differ in the distribution patterns of skarn zonation in that gradually weakened skarn zones are not quite symmetrically distributed on both sides of the alteration center (a garnet skarn). Abundant remnants of andesite, andesitic porphyry and tuffaceous sandstone in the weakened skarn zone indicate that the protolith of the skarn is andesite, andesitic porphyry and tuffaceous sandstone. Magmatic water, meteoric and seawater are involved in skarn alteration. Moyite and granitic porphyry are not coeval with skarn, and their emplacement resulted in the hornfelization of wall rock instead of skarnization, and themselves keep away from skarn alteration. Therefore, there was probably a huge batholith supplying magmatic fluid for skarn formation. Mass balance estimates suggest that hydrothermal fluid must contribute a portion of Ca and Fe to ensure sufficient supply for skarn formation in the absence of local carbonate and calcareous rocks. In conclusion, the stratiform skarns in the Suoerkuduke are products of intermediate-mafic volcanic and pyroclastic rocks metasomatised by hydrothermal fluid that probably leached calcareous wall rock during ascent.     

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 (− 96 m level: + 4.4‰ to + 6.6‰, n = 13) than sulfides within the shallow part of the deposit (20 m 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.     

A review of the geological characteristics and mineralization history of iron deposits in the Altay orogenic belt of the Xinjiang,Northwest China

In this review, we describe the geological characteristics and metallogenic–tectonic origin of Fe deposits in the Altay orogenic belt within the Xinjiang region of northwestern China. The Fe deposits are found mainly within three regions (ordered from northwest to southeast): the Ashele, Kelan, and Maizi basins. The principal host rocks for the Fe deposits of the Altay orogenic belt are the Early Devonian Kangbutiebao Formation, the Middle to Late Devonian Altay Formation, with minor occurrences of Lower Carboniferous and Early Paleozoic metamorphosed volcano-sedimentary rocks. The principal mineral-forming element groups of the deposits are Fe, Fe–Cu, Fe–Mn, Fe–P, Fe–Pb–Zn, Fe–Au, and Fe–V–Ti. The Fe deposits are associated with distinct formations, such as volcanic rocks, skarn deposits, pegmatites, granite-related hydrothermal vein mineralization, and mafic pluton-related V–Ti-magnetite deposits. The Fe deposits are most commonly associated with volcanic rocks in the upper Kangbutiebao Formation, in the volcano-sedimentary Kelan Basin, and in skarn deposits at several localities, including the lower Kangbutiebao Formation in the volcano-sedimentary Maizi Basin, and the Altay Formation at Jiaerbasidao–Kekebulake region. Homogenization temperatures of fluid inclusions in the prograde, retrograde and sulfide stages of the skarn type deposit are mainly medium- to high-temperature (cluster between 200 and 500 °C), medium-temperature (cluster between 200 and 340 °C) and low- to medium temperature (cluster between 160 and 300 °C), respectively. Ore fluids in the sedimentation period in the volcano-sedimentary type deposit are characterized by low- to medium temperature (with a peak around 190 °C), low to moderate salinity (3.23 to 22.71 wt.% NaCl equiv). Ore fluids in the pegmatite type deposit are characterized by low- to medium temperature (with a peak at 240 °C), low salinity (with a peak around 9 wt.% NaCl equiv). An analysis of the isotopic data for Fe deposits from the Altay orogenic belt indicates that the sulfur was derived from several sources, including volcanic rocks and granite, as well as bacterial reduction of sulfate from seawater. The present results indicate that different deposit types were derived from various sources. The REE geochemistry of rocks and ores from the Fe deposits in the Altay orogenic belt suggests that the ore-forming materials were derived from mafic volcanic rocks. Based on isotopic age data, the timing of the mineralization can be divided into four broad intervals: Early Devonian (410–384 Ma), Middle Devonian (377 Ma), Early Permian (287–274 Ma), and Early Triassic (c. 244 Ma). The ore-forming processes of the Fe deposits are closely related to volcanic activity and the emplacement of intermediate and felsic intrusions. We conclude that Fe deposits within the Altay orogenic belt developed in a range of tectonic settings, including continental arc, post-collisional extensional settings, and intracontinental settings.     

The Guelb Moghrein Cu–Au deposit: Neoarchaean hydrothermal sulfide mineralization in carbonate-facies iron formation

The Guelb Moghrein copper–gold deposit in the Islamic Republic of Mauritania reopened in 2006 and has produced copper concentrate and gold since then. The deposit is hosted in Neoarchaean–Palaeoproterozoic Fe–Mg carbonate-dominated metamorphic rocks interpreted as carbonate-facies iron formation. It forms tabular orebodies controlled by shear zones in the hanging wall and footwall of this meta-iron formation. Copper and gold are hosted in a complex sulfide ore in tectonic breccia replacing Fe–Mg carbonate and magnetite. Hydrothermal monazite dates the mineralization at 2492 ± 9 Ma. Two types of aqueous fluid inclusions suggest fluid mixing at 0.75–1.80 kbar and ~ 410 °C as the mineralization and precipitation mechanism, which is temporally coincident with regional retrograde metamorphism at 410 ± 30 °C (garnet-biotite). Distal alteration zones are enriched in K, Rb and Cu, whereas orebodies are depleted in K, Rb, Sr and Ba. The copper–gold mineralization at Guelb Moghrein formed during retrograde shearing in metamorphic rocks and contemporaneous hydrothermal alteration. The stable isotope signature of alteration and ore minerals suggest an external crustal fluid source. Fluids were focused in the reactive and competent meta-iron formation. Potassium alteration, magnetite and copper–gold mineralization suggest an IOCG mineral system akin similar deposits in Australia and Brazil.     

Geology and genesis of Kafang Cu–Sn deposit,Gejiu district,SW China

Kafang is one of the main ore deposits in the world-class Gejiu polymetallic tin district, SW China. There are three main mineralization types in the Kafang deposit, i.e., skarn Cu–Sn ores, stratiform Cu ores hosted by basalt and stratiform Cu–Sn ores hosted by carbonate. The skarn mainly consists of garnet and pyroxene, and retrograde altered rocks. These retrograde altered rocks are superimposed on the skarn and are composed of actinolite, chlorite, epidote and phlogopite. Major ore minerals are chalcopyrite, pyrrhotite, cassiterite, pyrite and scheelite. Sulfur and Pb isotopic components hint that the sources of different types of mineralization are distinctive, and indicate that the skarn ore mainly originated from granitic magma, whereas the basalt-hosted Cu ores mainly derived from basalt. Microthermometry results of fluid inclusions display a gradual change during the ore-forming process. The homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages. The salinities and freezing temperatures exhibit similar evolutionary tendencies with the T _{homogenization}, while the densities of the different types keep constant, the majority being less than 1. Oxygen and hydrogen isotopic values (δ¹⁸O and δD) of the hydrothermal fluids fall within ranges of 3.1 to 7.7‰ with an average of 6.15‰, calculated at the corresponding homogenization temperature, and − 73 and − 98‰ with an average of − 86.5‰, respectively. Microthermometry data and H–O isotopes indicate that the ore-forming fluid of the Kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage. Molybdenite Re–Os age of the skarn type mineralization is 83.4 ± 2.1 Ma, and the stratiform ores hosted by basalt is 84.2 ± 7.3 Ma, which are consistent with the LA-ICP-MS zircon age of the Xinshan granite intrusion (83.1 ± 0.4 Ma). The evidence listed above reflects the fact that different ore styles in the Kafang deposit belong to the same mineralization system.     

Metallogeny of the Northern Norrbotten Ore Province,northern Fennoscandian Shield with emphasis on IOCG and apatite-iron ore deposits

The Northern Norrbotten Ore Province in northernmost Sweden includes the type localities for Kiruna-type apatite iron deposits and has been the focus for intense exploration and research related to Fe oxide-Cu-Au mineralisation during the last decades. Several different types of Fe-oxide and Cu-Au ± Fe oxide mineralisation occur in the region and include: stratiform Cu ± Zn ± Pb ± Fe oxide type, iron formations (including BIF's), Kiruna-type apatite iron ore, and epigenetic Cu ± Au ± Fe oxide type which may be further subdivided into different styles of mineralisation, some of them with typical IOCG (Iron Oxide-Copper-Gold) characteristics. Generally, the formation of Fe oxide ± Cu ± Au mineralisation is directly or indirectly dated between ~ 2.1 and 1.75 Ga, thus spanning about 350 m.y. of geological evolution.The current paper will present in more detail the characteristics of certain key deposits, and aims to put the global concepts of Fe-oxide Cu-Au mineralisations into a regional context. The focus will be on iron deposits and various types of deposits containing Fe-oxides and Cu-sulphides in different proportions which generally have some characteristics in common with the IOCG style. In particular, ore fluid characteristics (magmatic versus non-magmatic) and new geochronological data are used to link the ore-forming processes with the overall crustal evolution to generate a metallogenetic model.Rift bounded shallow marine basins developed at ~ 2.1–2.0 Ga following a long period of extensional tectonics within the Greenstone-dominated, 2.5–2.0 Ga Karelian craton. The ~ 1.9–1.8 Ga Svecofennian Orogen is characterised by subduction and accretion from the southwest. An initial emplacement of calc-alkaline magmas into ~ 1.9 Ga continental arcs led to the formation of the Haparanda Suite and the Porphyrite Group volcanic rocks. Following this early stage of magmatic activity, and separated from it by the earliest deformation and metamorphism, more alkali-rich magmas of the Perthite Monzonite Suite and the Kiirunavaara Group volcanic rocks were formed at ~ 1.88 Ga. Subsequently, partial melting of the middle crust produced large volumes of ~ 1.85 and 1.8 Ga S-type granites in conjunction with subduction related A −/I-type magmatism and associated deformation and metamorphism.In our metallogenetic model the ore formation is considered to relate to the geological evolution as follows. Iron formations and a few stratiform sulphide deposits were deposited in relation to exhalative processes in rift bounded marine basins. The iron formations may be sub-divided into BIF- (banded iron formations) and Mg-rich types, and at several locations these types grade into each other. There is no direct age evidence to constrain the deposition of iron formations, but stable isotope data and stratigraphic correlations suggest a formation within the 2.1–2.0 Ga age range. The major Kiruna-type ores formed from an iron-rich magma (generally with a hydrothermal over-print) and are restricted to areas occupied by volcanic rocks of the Kiirunavaara Group. It is suggested here that 1.89–1.88 Ga tholeiitic magmas underwent magma liquid immiscibility reactions during fractionation and interaction with crustal rocks, including metaevaporites, generating more felsic magmatic rocks and Kiruna-type iron deposits. A second generation of this ore type, with a minor economic importance, appears to have been formed about 100 Ma later. The epigenetic Cu-Au ± Fe oxide mineralisation formed during two stages of the Svecofennian evolution in association with magmatic and metamorphic events and crustal-scale shear zones. During the first stage of mineralisation, from 1.89–1.88 Ga, intrusion-related (porphyry-style) mineralisation and Cu-Au deposits of IOCG affinity formed from magmatic-hydrothermal systems, whereas vein-style and shear zone deposits largely formed at c. 1.78 Ga.The large range of different Fe oxide and Cu-Au ± Fe oxide deposits in Northern Norrbotten is associated with various alteration systems, involving e.g. scapolite, albite, K feldspar, biotite, carbonates, tourmaline and sericite. However, among the apatite iron ores and the epigenetic Cu-Au ± Fe oxide deposits the character of mineralisation, type of ore- and alteration minerals and metal associations are partly controlled by stratigraphic position (i.e. depth of emplacement). Highly saline, NaCl + CaCl₂ dominated fluids, commonly also including a CO₂-rich population, appear to be a common characteristic feature irrespective of type and age of deposits. Thus, fluids with similar characteristics appear to have been active during quite different stages of the geological evolution. Ore fluids related to epigenetic Cu-Au ± Fe oxides display a trend with decreasing salinity, which probably was caused by mixing with meteoric water. Tentatively, this can be linked to different CuAu ore paragenesis, including an initial (magnetite)-pyrite-chalcopyrite stage, a main chalcopyrite stage, and a late bornite stage.Based on the anion composition and the Br/Cl ratio of ore related fluids bittern brines and metaevaporites (including scapolite) seem to be important sources to the high salinity hydrothermal systems generating most of the deposits in Norrbotten. Depending on local conditions and position in the crust these fluids generated a variety of Cu-Au deposits. These include typical IOCG-deposits (Fe-oxides and Cu-Au are part of the same process), IOCG of iron stone type (pre-existing Fe-oxide deposit with later addition of Cu-Au), IOCG of reduced type (lacking Fe-oxides due to local reducing conditions) and vein-style Cu-Au deposits. From a strict genetic point of view, IOCG deposits that formed from fluids of a mainly magmatic origin should be considered to be a different type than those deposits associated with mainly non-magmatic fluids. The former tend to overlap with porphyry systems, whereas those of a mainly non-magmatic origin overlap with sediment hosted Cu-deposits with respect to their origin and character of the ore fluids.     

Fluid inclusion,rare earth element geochemistry,and isotopic characteristics of the eastern ore zone of the Baiyangping polymetallic Ore district,northwestern Yunnan Province,China

The Baiyangping Cu–Ag polymetallic ore district is located in the northern part of the Lanping–Simao foreland fold belt, which lies between the Jinshajiang–Ailaoshan and Lancangjiang faults in western Yunnan Province, China. The source of ore-forming fluids and materials within the eastern ore zone were investigated using fluid inclusion, rare earth element (REE), and isotopic (C, O, and S) analyses undertaken on sulfides, gangue minerals, wall rocks, and ores formed during the hydrothermal stage of mineralization. These analyses indicate: (1) The presence of five types of fluid inclusion, which contain various combinations of liquid (l) and vapor (v) phases at room temperature: (a) H₂O (l), (b) H₂O (l) + H₂O (v), (c) H₂O (v), (d) C_mH_n (v), and (e) H₂O (l) + CO₂ (l), sometimes with CO₂ (v). These inclusions have salinities of 1.4–19.9 wt.% NaCl equivalents, with two modes at approximately 5–10 and 16–21 wt.% NaCl equivalent, and homogenization temperatures between 101 °C and 295 °C. Five components were identified in fluid inclusions using Raman microspectrometry: H₂O, dolomite, calcite, CH₄, and N₂. (2) Calcite, dolomitized limestone, and dolomite contain total REE concentrations of 3.10–38.93 ppm, whereas wall rocks and ores contain REE concentrations of 1.21–196 ppm. Dolomitized limestone, dolomite, wall rock, and ore samples have similar chondrite-normalized REE patterns, with ores in the Huachangshan, Xiaquwu, and Dongzhiyan ore blocks having large negative δCe and δEu anomalies, which may be indicative of a change in redox conditions during fluid ascent, migration, and/or cooling. (3) δ³⁴S values for sphalerite, galena, pyrite, and tetrahedrite sulfide samples range from −7.3‰ to 2.1‰, a wide range that indicates multiple sulfur sources. The basin contains numerous sources of S, and deriving S from a mixture of these sources could have yielded these near-zero values, either by mixing of S from different sources, or by changes in the geological conditions of seawater sulfate reduction to sulfur. (4) The C–O isotopic analyses yield δ¹³C values from ca. zero to −10‰, and a wider range of δ¹⁸O values from ca. +6 to +24‰, suggestive of mixing between mantle-derived magma and marine carbonate sources during the evolution of ore-forming fluids, although potential contributions from organic carbon and basinal brine sources should also be considered. These data indicate that ore-forming fluids were derived from a mixture of organism, basinal brine, and mantle-derived magma sources, and as such, the eastern ore zone of the Baiyangping polymetallic ore deposit should be classified as a “Lanping-type” ore deposit.     

Tracing the ore-formation history of the shear-zone-controlled Huogeqi Cu–Pb–Zn deposit in Inner Mongolia,northern China,using H,O, S,and Fe isotopes

The original ore-fluid of the Huogeqi Cu–Pb–Zn deposit in Inner Mongolia, northern China, was enriched in heavy oxygen isotopes with δ¹⁸O values ranging from 9.9 to 11.4 per mil, which is characteristic of the metamorphic devolatilization of pelitic rocks. The δD values determined by direct measurement of syn-ore hydrothermal tremolite range from − 116 to − 82 per mil, lying between the domains of typical metamorphic fluid and meteoric water, which is in equilibrium with organic matter. Oxygen and hydrogen isotope ratios indicate that the ore-fluid was derived from deep-sourced metamorphic fluid and interacted with organic-rich shale during fluid migration, which is consistent with the fluid evolution history revealed by a previous fluid inclusion study. Sulfides in the deposit are characteristically enriched in heavy S isotopes, with an average δ³⁴S value of 13.4 ± 6.2 per mil (1σ, n = 103). The S-isotope ratios are identical to stratabound sulfides generated through the non-bacterial reduction of Neoproterozoic marine sulfate (with δ³⁴S values of ~ 17 per mil). Previous studies on lead isotopes of sulfides revealed that the ore-forming metals (Cu, Pb, and Zn) at the Huogeqi deposit were also remobilized from a stratabound source. This source was syngenetically elevated in its Cu-, Pb-, and Zn-sulfide content as a result of submarine hydrothermal activities forming sulfide-rich layers within a rift tectonic setting. The Fe isotope ratios for sulfides are consistent with those of an intercalated iron-formation within the ore-hosting rocks, suggesting that the Fe in the sulfides was derived from local host rocks during sulfide precipitation and the Fe-rich rocks are favorable lithological units for high-grade mineralization. The heterogeneous sources of ore-fluid, S, ore-forming metals, and Fe are explained by a multistage genetic model, which is supported by the geological characteristic of the deposit. The enriched sulfides were subsequently remobilized and enriched by metamorphic devolatilization during the Permian and Triassic periods. The metamorphic ore-fluid ascended along a shear zone and interacted with organic-rich shale. Sulfides eventually precipitated within the shear zone at a shallower crustal level, especially where the shear zone intersected Fe-rich host rocks. This multistage genetic model has implications for mineral exploration. Greenschist to amphibolite facies terranes containing thick Neoproterozoic rift sequences are ideal regions for potential Cu–Pb–Zn mineralization. In particular, intercalated volcanic rocks within the rift sequences are indicative of high heat-flow and are ideal for the development of submarine hydrothermal systems. The primary structures hosting mineralization and ore shoots in the Huogeqi area are jogs in the shear zones. In addition, Fe-rich lithological units, such as iron-formations, are ideal hosts for high-grade ore.