Structural and diagenetic origin of breccias in the carbonate-hosted Polaris Zn–Pb deposit,Nunavut, Canada

The Polaris deposit, located on Little Cornwallis Island in the Canadian Arctic, was a Mississippi Valley-type Zn–Pb deposit hosted by brecciated carbonate rocks of the Upper Ordovician Thumb Mountain Formation. Mapping indicates that strike-slip faults on the east side of the Polaris deposit were active during the last stage of the Late Devonian Ellesmerian Orogeny. Polaris is on a jog in the north-oriented, Early Devonian Boothia fault system and was the site of localized extension during south-directed Late Devonian Ellesmerian compression. This structural setting elsewhere in the district may be prospective for Zn–Pb mineralisation.Ore fluids rising in the Late Devonian interacted with the host rock causing dissolution, brecciation and collapse. Carbonate beds are thinned, indicating widespread removal of carbonate material. Five breccia types (crackle, pseudo, cobble, mega and collapse) are present in the vicinity of the deposit. Crackle breccia is preserved around the periphery of the deposit and is indicative of structural dilation or the early stages of mineralisation. Dolomite and pseudobreccias are also preserved around, and extend beyond, the periphery of the deposit. These are considered an early stage of alteration directly related to the mineralising fluids and could act as a vector to the centre of the mineralising system where collapse, mega and cobble breccias occur intimately with massive mineralisation.     

Physico-chemical controls on ore deposition in the Arapucandere Pb–Zn–Cu-precious metal deposit,Biga Peninsula,NW Turkey

Arapucandere is one of a number of similar Cu–Zn–Pb ± Au–Ag epithermal deposits in the Biga Peninsula, which are mineralogically and tectonically similar. Fluid inclusions have very low salinities between 1.7 and 0 wt.% NaCl and a wide range of temperatures from ~ 360 to 160 °C. There was extensive boiling and “flashing” of the hydrothermal fluids which initiated mineral deposition. The range of temperatures is consistent with emplacement of the veins at ~ 700 m depth, with the pressure decreasing from near lithostatic to near hydrostatic and a decrease in temperature to ~ 250 °C due to adiabatic expansion of the fluids. There is evidence of a limited amount of boiling, but the temperature and pressure decrease was close to the liquid–vapour curve. Flashing of the fluids was caused by sudden drops to sub-hydrostatic pressures and even lower temperatures. Mineralization was caused by these pressure related temperature decreases as there is no evidence of cooling and dilution of the ore-fluids. δ³⁴S values of sulphides indicate a magmatic source but the more negative than usual values also suggest boiling affected isotopes. δD and δ¹⁸O of the fluids indicate a mixing between meteoric waters and magmatic fluids, with the large range of δD due to boiling. LA-ICP-MS analyses of fluid inclusions reveal high Cu–Zn–Pb concentrations in the fluids, despite their low salinity, transported as chloride complexes. Exceptional pressure and temperature decrease causing the fluids to “flash” was likely to have been in response to earthquakes.     

Geology and chronology of the Zhaofayong carbonate-hosted Pb–Zn ore cluster: Implication for regional Pb–Zn metallogenesis in the Sanjiang belt,Tibet

Mississippi Valley type (MVT) Pb–Zn deposits can occur in orogenic thrust belts. However, the relationship between MVT ore-forming processes and thrusting is unclear. The 1500-km-long Sanjiang Metallogenic Belt in Tibetan Plateau is an important thrust-controlled MVT ore province with 860 Mt at 0.76–2.3% Pb, 0.3–6.1% Zn. The Zhaofayong MVT ore cluster in the Changdu area is a typical sample. The orebodies in this ore cluster are hosted in limestone, controlled by secondary faults to regional thrusts and forming along these faults. Two Pb–Zn mineralization stages in this cluster are recognized. Stage I is characterized by coarse and euhedral galena + sphalerite + calcite + fluorite + barite and Stage II by fine grained sphalerite + galena + pyrite + calcite. Sm–Nd isotopic dating of calcite forming in Stage I yields isochron ages of 41.1–38.1 Ma, suggesting the mineralization formed during extension following the first regional compression in the Changdu area. The connection between Stage I mineralization and the regional thrusting in the Changdu area can extend to the whole Sanjiang belt. Two stages of regional Pb–Zn mineralization are recognized between 65 Ma and 30 Ma and between 30 Ma and 16 Ma in the belt. The two Pb–Zn mineralization stages are consistent with those regional episodic thrusting activities and both of them immediately occurred after the episodic thrusting. An interpretation of the regional Pb–Zn mineralization is that regional compression forced the movement of hydrothermal fluids along regional thrust-nappe detachment faults and subsequent post-thrust extension caused the migration of hydrothermal fluids to the ore forming locations. The two mineralization stages in the Sanjiang Belt indicate complex processes related to India–Eurasia collision and the gradually younger mineralization ages from southeast to northwest indicate the collision follows the same direction.     

Geological and isotopic constraints on the origin of the Anle carbonate-hosted Zn–Pb deposit in northwestern Yunnan Province,SW China

The Anle Zn–Pb deposit, hosted by Upper Cambrian dolostone, is located in the southern Songpan–Ganzi Block in southwest China. In this deposit, ore bodies occur as stratiform lenses and consist of galena, sphalerite and pyrite as ore minerals, and quartz, dolomite and calcite as gangue minerals. The mineralization shows mainly vein, banded and brecciated structures. Four ore bodies have been found in the Anle deposit, with a combined 2.0 million tonnes (Mt) of sulfide ores at average grades of 1.64 wt.% Pb, 6.64 wt.% Zn and 45 g/t Ag. Brown, brownish-yellow and yellow sphalerite samples have δ⁶⁶Zn values ranging from + 0.08 to + 0.10‰ (average + 0.09‰, n = 3), + 0.12 to + 0.38‰ (average + 0.24‰, n = 8) and + 0.40 to + 0.50‰ (average + 0.46‰, n = 3), respectively. We interpret the progressively heavier Zn isotopes from brown to yellow sphalerite as being led by kinetic Raleigh fractional crystallization. Calcite samples have δ¹³C_PDB and δ¹⁸O_SMOW values ranging from − 4.8 to − 0.2‰ (average − 1.7‰, n = 7) and + 17.9 to + 21.4‰ (average + 19.6‰, n = 7), respectively. Whole-rock δ¹³C_PDB and δ¹⁸O_SMOW values of the Cambrian ore-hosting dolostone range from + 0.1 to + 1.1‰ (average + 0.6‰, n = 3) and + 23.2 to + 24.1‰ (average + 23.6‰, n = 3), respectively. This suggests that carbon in the ore-forming fluids was provided by the host dolostone through carbonate dissolution. δ³⁴S_CDT values of sulfide samples range between − 1.3‰ and + 17.8‰ with an average value of + 6.3‰ (n = 25), lower than evaporites (such as barite + 19.8‰) in the overlaying Lower Ordovician sedimentary strata. The data suggest that sulfur in the hydrothermal fluids were derived from evaporites by thermo-chemical sulfate reduction (TSR). ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios for sulfide minerals range from 17.63 to 17.86, 15.58 to 15.69 and 37.62 to 37.95, respectively. The data are similar to those of the age-corrected Cambrian ore-hosting dolostone (²⁰⁶Pb/²⁰⁴Pb = 17.70–17.98, ²⁰⁷Pb/²⁰⁴Pb = 15.58–15.65 and ²⁰⁸Pb/²⁰⁴Pb = 37.67–38.06), but lower than those of age-corrected Ordovician sandstone and slate (²⁰⁶Pb/²⁰⁴Pb = 18.54–19.58, ²⁰⁷Pb/²⁰⁴Pb = 15.73–15.81 and ²⁰⁸Pb/²⁰⁴Pb = 38.44–39.60). This indicates that ore Pb was most likely to be derived from the Cambrian ore-hosting dolostone. Therefore, our new geological and isotopic evidence suggests that the Anle Zn–Pb deposit is best classified to be an epigenetic carbonate-hosted Mississippi Valley-type (MVT) deposit.     

Geological and C–O–S–Pb–Sr isotopic constraints on the origin of the Qingshan carbonate-hosted Pb–Zn deposit,Southwest China

Located in the western Yangtze Block, the Qingshan Pb–Zn deposit, part of the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province, contains 0.3 million tonnes of 9.86 wt.% Pb and 22.27 wt.% Zn. Ore bodies are hosted in Carboniferous and Permian carbonate rocks, structurally controlled by the Weining–Shuicheng anticline and its intraformational faults. Ores composed of sphalerite, galena, pyrite, dolomite, and calcite occur as massive, brecciated, veinlets, and disseminations in dolomitic limestones.

The C–O isotope compositions of hydrothermal calcite and S–Pb–Sr isotope compositions of Qingshan sulphide minerals were analysed in order to trace the sources of reduced sulphur and metals for the Pb–Zn deposit. δ¹³C_PDB and δ¹⁸O_SMOW values of calcite range from –5.0‰ to –3.4‰ and +18.9‰ to +19.6‰, respectively, and fall in the field between mantle and marine carbonate rocks. They display a negative correlation, suggesting that CO₂ in the hydrothermal fluid had a mixed origin of mantle, marine carbonate rocks, and sedimentary organic matter. δ³⁴S values of sulphide minerals range from +10.7‰ to +19.6‰, similar to Devonian-to-Permian seawater sulphate (+20‰ to +35‰) and evaporite rocks (+23‰ to +28‰) in Carboniferous-to-Permian strata, suggesting that the reduced sulphur in hydrothermal fluids was derived from host-strata evaporites. Ores and sulphide minerals have homogeneous and low radiogenic Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.561 to 18.768, ²⁰⁷Pb/²⁰⁴Pb = 15.701 to 15.920, and ²⁰⁸Pb/²⁰⁴Pb = 38.831 to 39.641) that plot in the upper crust Pb evolution curve, and are similar to those of Devonian-to-Permian carbonate rocks. Pb isotope compositions suggest derivation of Pb metal from the host rocks. ⁸⁷Sr/⁸⁶Sr ratios of sphalerite range from 0.7107 to 0.7136 and (⁸⁷Sr/⁸⁶Sr)_200Ma ratios range from 0.7099 to 0.7126, higher than Sinian-to-Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than Proterozoic basement rocks. This indicates that the ore strontium has a mixture source of the older basement rocks and the younger cover sequence. C–O–S–Pb–Sr isotope compositions of the Qingshan Pb–Zn deposit indicate a mixed origin of the ore-forming fluids and metals.     

Two pulses of mineralization and genesis of the Zhaxikang Sb–Pb–Zn–Ag deposit in southern Tibet: Constraints from Fe–Zn isotopes

Zhaxikang is one large Sb–Pb–Zn–Ag deposit located in the North Himalaya of southern Tibet. To date, the genesis of this deposit still remains controversial. Here, we present new pyrite Fe and sphalerite Zn isotopic data for the first three stages of mineralization, Fe–Zn isotopic data for Mn–Fe carbonate that formed during the first two stages of mineralization, and Zn isotopic data for the slate wall rocks of the Jurassic Ridang Formation to discuss the genesis of the Zhaxikang deposit. The overall δ⁵⁶Fe and δ⁶⁶Zn values range from −0.80‰ to 0.43‰ and from −0.03‰ to 0.38‰, respectively. The δ⁵⁶Fe values of Mn–Fe carbonates are lighter than those of associated pyrite in six mineral pairs, indicating that the iron carbonates are preferentially enriched in light Fe isotopes relative to pyrite. The sphalerite has lighter δ⁶⁶Zn values than associated Mn–Fe carbonates in three mineral pairs.The δ⁵⁶Fe values of pyrite that formed during the first three stages of mineralization gradually increase from stage 1 (−0.33‰ to −0.09‰) through stage 2 (−0.30‰ to 0.19‰) to stage 3 (0.16‰–0.43‰). In comparison, the sphalerite that formed during these stages has δ⁶⁶Zn values that gradually decrease from stage 1 (0.16‰–0.35‰) through stage 2 (0.09‰–0.23‰) to stage 3 (−0.03‰ to 0.22‰). These data, in conjunction with the observations of hand specimens and thin sections, suggest that the deposit was overprinted by a second pulse of mineralization. This overprint would account for these Fe–Zn isotopic variations as well as the kinetic Rayleigh fractionation that occurred during mineralization. The temporally increasing δ⁵⁶Fe and decreasing δ⁶⁶Zn values recorded in the deposit are also coincident with an increase in alteration, again supporting the existence of two pulses of mineralization. The δ⁵⁶Fe values of the first pulse of ore-forming fluid were calculated using theoretical equations, yielding values of −0.54‰ to −0.34‰ that overlap with those of submarine hydrothermal solutions (−1‰ to 0‰). However, the δ⁵⁶Fe values of the stage 3 pyrite are heavier than those of typical submarine hydrothermal solutions, which suggests that the second pulse of mineralization was probably derived from a magmatic hydrothermal fluid. In addition, the second pulse of ore-forming fluid has brought some Fe and taken away parts of Zn, which results the lighter δ⁶⁶Zn values of sphalerite and heavier δ⁵⁶Fe values of pyrite from the second pulse of mineralization. Overall, the Zhaxikang deposit records two pulses of mineralization, and the overprint by the second pulse of mineralization causes the lighter δ⁶⁶Zn values and heavier δ⁵⁶Fe values of modified samples.     

Geology,isotope geochemistry and ore genesis of the Shanshulin carbonate-hosted Pb–Zn deposit,southwest China

The Shanshulin Pb–Zn deposit occurs in Upper Carboniferous Huanglong Formation dolomitic limestone and dolostone, and is located in the western Yangtze Block, about 270 km west of Guiyang city in southwest China. Ore bodies occur along high angle thrust faults affiliated to the Weishui regional fault zone and within the northwestern part of the Guanyinshan anticline. Sulfide ores are composed of sphalerite, pyrite, and galena that are accompanied by calcite and subordinate dolomite. Twenty-two ore bodies have been found in the Shanshulin deposit area, with a combined 2.7 million tonnes of sulfide ores grading 0.54 to 8.94 wt.% Pb and 1.09 to 26.64 wt.% Zn. Calcite samples have δ¹³C_PDB and δ¹⁸O_SMOW values ranging from − 3.1 to + 2.5‰ and + 18.8 to + 26.5‰, respectively. These values are higher than mantle and sedimentary organic matter, but are similar to marine carbonate rocks in a δ¹³C_PDB vs. δ¹⁸O_SMOW diagram, suggesting that carbon in the hydrothermal fluid was most likely derived from the carbonate country rocks. The δ³⁴S_CDT values of sphalerite and galena samples range from + 18.9 to + 20.3‰ and + 15.6 to + 17.1‰, respectively. These values suggest that evaporites are the most probable source of sulfur. The δ³⁴S_CDT values of symbiotic sphalerite–galena mineral pairs indicate that deposition of sulfides took place under chemical equilibrium conditions. Calculated temperatures of S isotope thermodynamic equilibrium fractionation based on sphalerite–galena mineral pairs range from 135 to 292 °C, consistent with previous fluid inclusion studies. Temperatures above 100 °C preclude derivation of sulfur through bacterial sulfate reduction (BSR) and suggest that reduced sulfur in the hydrothermal fluid was most likely supplied through thermo-chemical sulfate reduction (TSR). Twelve sphalerite samples have δ⁶⁶Zn values ranging from 0.00 to + 0.55‰ (mean + 0.25‰) relative to the JMC 3-0749L zinc isotope standard. Stages I to III sphalerite samples have δ⁶⁶Zn values ranging from 0.00 to + 0.07‰, + 0.12 to + 0.23‰, and + 0.29 to + 0.55‰, respectively, showing the relatively heavier Zn isotopic compositions in later versus earlier sphalerite. The variations of Zn isotope values are likely due to kinetic Raleigh fractional crystallization. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of the sulfide samples fall in the range of 18.362 to 18.573, 15.505 to 15.769 and 38.302 to 39.223, respectively. The Pb isotopic ratios of the studied deposit plot in the field that covers the upper crust, orogenic belt and mantle Pb evolution curves and overlaps with the age-corrected Proterozoic folded basement rocks, Devonian to Lower Permian sedimentary rocks and Middle Permian Emeishan flood basalts in a ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagram. This observation points to the derivation of Pb metal from mixed sources. Sphalerite samples have ⁸⁷Sr/⁸⁶Sr_200 Ma ratios ranging from 0.7107 to 0.7115 similar to the age-corrected Devonian to Lower Permian sedimentary rocks (0.7073 to 0.7111), higher than the age-corrected Middle Permian basalts (0.7039 to 0.7078), and lower than the age-corrected Proterozoic folded basement (0.7243 to 0.7288). Therefore, the Sr isotope data support a mixed source. Studies on the geology and isotope geochemistry suggest that the Shanshulin deposit is a carbonate-hosted, thrust fault-controlled, strata-bound, epigenetic, high grade deposit formed by fluids and metals of mixed origin.     

Dolomite textures in the Upper Cretaceous carbonate-hosted Pb–Zn deposits,Zakho, Northern Iraq

In the northeast of Zakho City, Northern Iraq, the host rocks of Pb–Zn deposits are composed predominantly of dolomites with subordinate dolomitic limestone intervals. This study is focused on the dolomites of the Bekhme Formation (Upper Campanian) carbonate-hosted Pb–Zn deposits. The amount of dolomites, however, increases toward the mineralized zone. Dolomites are dominated by replacement dolomite with minor dolomite cements. Petrography study allowed identification of six different dolomite textures. These are (1) fine crystalline, planar-s (subhedral) dolomite, RD1; (2) medium to coarse crystalline, planar-e (euhedral) to planar-s (subhedral) dolomites, RD2; (3) medium crystalline, planar-s (subhedral) to nonplanar-a (anhedral) dolomites, RD3; (4) coarse crystalline, planar-s (subhedral) to nonplanar-a (anhedral) dolomites, RD4; (5) planar (subhedral) void-filling dolomite cements, CD1; and (6) nonplanar (saddle) void-filling dolomite, CD2. The RD1, RD2, RD3, and RD4 dolomite textures are replacive in origin and are volumetrically the most important types, whereas CD1 and CD2 dolomites with sparry calcite are commonly cements that fill the open spaces. Although the dolomites of the Bekhme Formation are not macroscopically observed in the field, their different types are easily distinguished by petrographic examination and scanning electron microscopy. It was observed that the dolomites of the Bekhme Formation are formed in two different diagenetic stages: the early diagenetic from mixing zone fluids at the tidal–subtidal (reef) environments and the late diagenetic from basinal brines which partially mixed with hydrothermal fluids at the shallow-deep burial depths. The latter occurs often with sphalerite, galena, and pyrite within mineralized zone. These dolomite types are associated base-metal mineralization (Mississippi Valley type).     

Constraints of C–O–S–Pb isotope compositions and Rb–Sr isotopic age on the origin of the Tianqiao carbonate-hosted Pb–Zn deposit,SW China

The Tianqiao Pb–Zn deposit in the western Yangtze Block, southwest China, is part of the Sichuan–Yunnan–Guizhou (SYG) Pb–Zn metallogenic province. Ore bodies are hosted in Devonian and Carboniferous carbonate rocks, structurally controlled by a thrust fault and anticline, and carried about 0.38 million tons Pb and Zn metals grading > 15% Pb + Zn. Both massive and disseminated Pb–Zn ores occur either as veinlets or disseminations in dolomitic rocks. They are composed of ore minerals, pyrite, sphalerite and galena, and gangue minerals, calcite and dolomite. δ³⁴S values of sulfide minerals range from + 8.4 to + 14.4‰ and display a decreasing trend from pyrite, sphalerite to galena (δ³⁴S_pyrite > δ³⁴S_sphalerite > δ³⁴S_galena). We interpret that reduced sulfur derived from sedimentary sulfate (gypsum and barite) of the host Devonian to Carboniferous carbonate rocks by thermal–chemical sulfate reduction (TSR). δ¹³C_PDB and δ¹⁸O_SMOW values of hydrothermal calcite range from –5.3 to –3.4‰ and + 14.9 to + 19.6‰, respectively, and fall in the field between mantle and marine carbonate rocks. They display a negative correlation, suggesting that CO₂ in the hydrothermal fluid was a mixture origin of mantle, marine carbonate rocks and sedimentary organic matter. Sulfide minerals have homogeneous and low radiogenic Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.378 to 18.601, ²⁰⁷Pb/²⁰⁴Pb = 15.519 to 15.811 and ²⁰⁸Pb/²⁰⁴Pb = 38.666 to 39.571) that are plotted in the upper crust Pb evolution curve and overlap with that of Devonian to Carboniferous carbonate rocks and Proterozoic basement rocks in the SYG province. Pb isotope compositions suggest derivation of Pb metal from mixed sources. Sulfide minerals have ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7125 to 0.7167, higher than Sinian to Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than basement rocks. Again, Sr isotope compositions are supportive of a mixture origin of Sr. They have an Rb–Sr isotopic age of 191.9 ± 6.9Ma, possibly reflecting the timing of Pb–Zn mineralization. C–O–S–Pb–Sr isotope compositions of the Tianqiao Pb–Zn deposit indicate a mixed origin of ore-forming fluids, which have Pb–Sr isotope homogenized before the mineralization. The Permian flood basalts acted as an impermeable layer for the Pb–Zn mineralization hosted in the Devonian–Carboniferous carbonate rocks.     

Zircon U–Pb and pyrite Re–Os age constraints on pyrite mineralization in the Yinjiagou deposit,China

We report new zircon U–Pb and pyrite Re–Os geochronological studies of the Yinjiagou poly-metallic deposit, sited along the southern margin of the North China Craton (SMNCC). In this deposit, pyrite, the most important economic mineral, is intergrown/associated with Mo, Cu, Au, Pb, Zn, and Ag. Prior to our new work, the age of chalcopyrite–pyrite mineralization was known only from its spatial relationship with molybdenite mineralization and with intrusions of known ages. The U–Pb and Re–Os isotope systems provide an excellent means of dating the mineralization itself and additionally place constraints on the ore genesis and metal source. Zircons separated from the quartz–chalcopyrite–pyrite veins include both detrital and magmatic groups. The magmatic zircons confine the maximum age of chalcopyrite–pyrite mineralization to 142.0 ± 1.5 Ma. The Re–Os results yield an age of 141.1 ± 1.1 Ma, which represents the age of the chalcopyrite–pyrite mineralization quite well. The common Os contents are notably low (0.5–20.1 ppt) in all samples. In contrast, the Re contents vary considerably (3.0–199.2 ppb), most likely depending on intensive boiling, which resulted in an increase of Re within the pyrite. This study demonstrates that the main chalcopyrite–pyrite mineralization occurred late in the magmatic history and was linked to a deeper intrusion involving dominant mantle-derived materials. This mineralization event might be related to the Early Cretaceous lithospheric destruction and thinning of the SMNCC.     

Fluid origin of fluorite-rich carbonate-hosted Pb–Zn mineralization of the Himalayan–Zagros collisional orogenic system: A case study of the Mohailaheng deposit,Tibetan Plateau,China

A significant belt of carbonate-hosted Pb–Zn mineralization occurs in the Himalayan–Zagros collisional orogenic system. Three differing types of these Pb–Zn deposits within this belt have been identified based on variations in gangue mineral assemblages, leading to the classification of carbonate-, quartz- and fluorite-rich classes of Pb–Zn deposits. The third Pb–Zn mineralization (fluorite-rich) type is common in this orogenic system, but little research has been undertaken on it. Here, we focus on the Mohailaheng deposit, a large-sized fluorite-rich carbonate-hosted Pb–Zn deposit (> 100 Mt Pb + Zn ores with average grade of 2.18%–4.23%); the deposit is located in the Sanjiang Cenozoic thrust-fold belt, an important part of the Himalayan–Zagros collisional orogenic system and an area that formed during the early Tertiary India–Eurasia collision. The main orebodies in this deposit are stratabound and are hosted by Carboniferous limestones that are located along secondary faults associated with a regional thrust fault. The main assemblage is a sphalerite + galena + pyrite sulfide assemblage associated with a calcite + fluorite + barite + quartz + dolomite gangue assemblage. Detailed field and experimental work indicates that the deposit formed during three distinct phases of hydrothermal activity. Studies on fluid inclusion and stable isotopes of gangue minerals indicate that two dominant distinct fluids involving the deposit formation. They include (1) a low-temperature (130–140 °C), high-salinity (23–24 wt.% NaCl equivalent) basinal brine containing Na⁺–K⁺–Mg^2 +–Ca^2 +–Cl⁻ ions and abnormally high SO₄^2 − concentrations, which probably derived from Tertiary basins in the regional district, and (2) a low- to moderate-temperature (170–180 °C) and moderate- to high-salinity (19–20 wt.% NaCl equivalent) metamorphic fluid containing Na⁺–K⁺–Mg^2 +–Cl^––SO₄^2 − ions and abnormally high F⁻ and organic matter concentrations, that probably formed during regional metamorphism. Some evaporated seawaters and meteoric fluids were also identified in mixtures with these two dominant fluids. The Pb–Zn mineralization at Mohailaheng formed during three distinct stages, consistent with the regional tectonic history. The first stage involved the formation of favorable lithological and structural traps at Mohailaheng during regional thrusting, leading to the migration of compressed metamorphic waters at depth along a detachment zone, sequestering metals from sediments within the region. Basinal brines at the surface also began to infiltrate down along the secondary faults, dissolving gypsum from the underlying sediments. The second stage was associated with the cessation of thrusting and the onset of strike-slip movements along these thrust faults. Metamorphic fluids containing high concentrations of halogen ions, organic gases, and metals ascended into the structural traps at Mohailaheng along the reactivated thrust faults, causing fluorite, calcite, and some sulfide precipitation. Then, basinal brines rich in SO₄^2 − quickly descended into the structural traps along the reactivated faults, causing reduction of SO₄^2 − by organic matter, and producing significant amounts of H₂S. The reduced sulfur then reacted with the metals in the fluids, causing significant sulfide precipitation. The third stage was associated with metal-depleted fluids, which only resulted in the precipitation of calcite from the diluted basinal brines. Combining these findings with research results on other fluorite-rich carbonate-hosted Pb–Zn deposits in the Himalayan–Zagros orogenic system suggests that this type of carbonate-hosted Pb–Zn deposits can also be classified as Mississippi Valley-type (MVT) deposits, and that the origin of the fluorite in these deposits may be related to multiple hydrothermal fluids involved in the mineralization evolution.     

The Nadun Cu–Au mineralization,central Tibet: Root of a high sulfidation epithermal deposit

A new high sulfidation epithermal Cu–Au occurrence (Nadun) has been discovered adjacent to the Cretaceous Duolong porphyry Cu–Au deposit within the Bangong–Nujiang metallogenic belt, central Tibet. The Nadun Cu–Au mineralization is hosted in a tectonic–hydrothermal breccia with advanced argillic alteration, which occurs above sandstone, associated with quartz–pyrite veins. The granodiorite porphyry with strong argillic alteration yields a zircon U–Pb age of 119.1 ± 1.3 Ma, whereas the weakly argillic granodiorite porphyry intruded into the breccia has a younger age of 116.1 ± 1.3 Ma. This indicates that Cu–Au epithermal mineralization likely occurred between ~ 116 Ma and ~ 119 Ma, consistent with the duration of magmatic–hydrothermal activity at Duolong (~ 115–118 Ma), and providing evidence that Nadun and Duolong were formed during the same event. Moreover, the Nadun and Duolong porphyries have similar Hf isotopic compositions (εHf(t) values ranging from − 8.8 to 8.1; mean = 5.0 ± 1.1, n = 32), likely indicating that the deposits are comagmatic. In addition, boiling assemblages in vapor-rich inclusions coexisting with brines occur in early stage quartz–pyrite veins, and likely record phase separation at a temperature of > 550–300 °C and pressure of 700–110 bars. Most liquid-rich fluid inclusions formed at the breccia stage show similar salinity (1.7–19.3 wt.% NaCl equiv) to vapor-rich inclusions from the underlying quartz–pyrite veins, likely indicating vapor contraction during cooling at elevated presssure. This suggests that quartz–pyrite veins may act as conduits for ore-forming fluid traveling from the porphyry to the epithermal hydrothermal system. O and H isotopic compositions (δ¹⁸O_fluid = 0.42–9.71‰ and δD = − 102 to − 66‰) suggest that ore-forming fluids are dominantly from a magmatic source with a minor addition of meteoric water at a later stage. The S and Fe isotope compositions of sulfides (δ³⁴S = − 5.9 to 0.5‰ and δ⁵⁷Fe = − 2.15 to 0.17‰) decrease from the quartz–pyrite vein to breccia ore, indicating that ore-forming fluids gradually become SO₄²-enriched and relatively oxidized. This body of evidence suggests that the Nadun Cu–Au mineralization may represent the root of a high sulfidation epithermal deposit.     

The Chaqupacha Mississippi Valley-type Pb–Zn deposit,central Tibet: Ore formation in a fold and thrust belt of the India–Asia continental collision zone

The newly discovered Chaqupacha Mississippi Valley-type (MVT) Pb–Zn deposit in central Tibet has been found to be helpful for understanding MVT ore formation relative to tectonic evolution of a foreland fold and thrust belt. The deposit lies in the Tuotuohe area of the western Fenghuo Shan-Nangqian fold and thrust belt of the India–Asia continental collision zone. It contains NNW-striking and folded Late Permian strata including an upper clastic unit and an underlying limestone unit. The strata overlie late Oligocene clastic rocks through a south-dipping reverse fault that is associated with regional northward thrusting during the Paleogene. The Late Permian and late Oligocene strata are unconformably overlain by flat-lying early Miocene marl and mudstone of the Wudaoliang Formation. Lead and zinc ores are mainly hosted by pre-ore dissolution and collapse breccias in the Late Permian limestone. The style of mineralization is epigenetic, as shown by replacement of the pre-ore dissolution breccia matrix and open-space-fill by galena, sphalerite, calcite, and minor barite and pyrite. δ³⁴S values of the main sulfide galena range from − 27.5‰ to + 12.6‰. These features, together with the lack of magmatic activity during the mineralization, suggest that Chaqupacha is an MVT deposit. Subordinate mineralization is also present in the early Miocene Wudaoliang Formation marl and the paleokarst breccia which contains matrix compositionally equivalent to strata of the Wudaoliang Formation. The mineralization shares similar mineral associations and textures with the pre-ore dissolution breccia-hosted mineralization. Thus, the Pb and Zn mineralization in the entire deposit probably resulted from the same mineralizing event, which is younger than the youngest ore-hosting rocks (i.e., the early Miocene Wudaoliang Formation). Considering that thrusting in the Tuotuohe area had ceased prior to deposition of the Wudaoliang Formation host rocks, the mineralization at Chaqupacha post-dated the regional deformation. The Chaqupacha deposit thus provides a good example of MVT mineralization in a foreland fold and thrust belt that post-dates regional thrusting.     

Ore genesis of the Tianbaoshan carbonate-hosted Pb–Zn deposit,Southwest China: geologic and isotopic (C–H–O–S–Pb) evidence

The Tianbaoshan Pb–Zn deposit, part of the Sichuan–Yunnan–Guizhou (SYG) Pb–Zn metallogenic province, is located in the western Yangtze Block and contains 2.6 million tonnes of 10–15 wt.% Pb + Zn metals. Ore bodies occur as vein or tubular types and are hosted in Sinian (late Proterozoic) carbonate rocks and are structurally controlled by the SN-trending Anninghe tectonic belt and NW-trending concealed fractures. The deposits are simple in mineralogy, with sphalerite, galena, pyrite, chalcopyrite, arsenopyrite, freibergite, and pyrargyrite as ore minerals and dolomite, calcite, and quartz as gangue minerals. These phases occur as massive, brecciated, veinlet, and dissemination in dolostone of the upper Sinian Dengying Formation. Hydrogen and oxygen isotope compositions of hydrothermal fluids range from –47.6 to –51.2‰ and –1.7 to +3.7‰, respectively. These data suggest that H₂O in hydrothermal fluids had a mixed origin of metamorphic and meteoric waters. Carbon and oxygen isotope compositions range from –6.5 to –4.9‰ and +19.3 to +20.2‰, respectively. These compositions plot in the field between mantle and marine carbonate rocks with a negative correlation, suggesting that CO₂ in the ore-forming fluids had multiple sources, including the Permian Emeishan flood basalts, Sinian-to-Permian marine carbonate rocks, and organic matters in Cambrian-to-Permian sedimentary rocks. Sulphur isotope compositions range from –0.4 to +9.6‰, significantly lower than Cambrian-to-Permian seawater sulphate (+15 to +35‰) and sulphate (+15 to +28‰) from evaporates in Cambrian-to-Permian strata, implicating that the S was derived from host-strata evaporates by thermal–chemical sulphate reduction. ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios range from 18.110 to 18.596, 15.514 to 15.878, and 38.032 to 39.221, respectively, which plot in field of the upper crust Pb evolution curve, unlike those of Proterozoic basement rocks, Sinian dolostone, Devonian-to-Permian carbonate rocks, and the Permian Emeishan flood basalts, implying complex derivation of Pb metal in the ore-forming fluids. Geological and isotopic studies of the Tianbaoshan Pb–Zn deposit reveal that constituents in the hydrothermal fluids were derived from multiple sources and that fluid mixing was a possible metallogenic mechanism. The studied deposit is not distal magmatic–hydrothermal, sedimentary exhalative (SEDEX), or Mississippi Valley (MVT) types, rather, it represents a unique ore deposit type, named in this article the SYG type.     

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.     

Research on the growth orientation of pyrite grains in the colloform textures in Baiyunpu Pb–Zn polymetallic deposit,Hunan, China

Mineralogy and Petrology - A large number of colloform-textured pyrites were found in Baiyunpu Pb–Zn ore bodies in Xinshao County, Hunan, China. This study investigates the growth orientation...     

The Hakkari nonsulfide Zn–Pb deposit in the context of other nonsulfide Zn–Pb deposits in the Tethyan Metallogenic Belt of Turkey

The Hakkari nonsulfide zinc deposit is situated close to the southeastern border of Turkey. Here both sulfide and nonsulfide Zn ≫ Pb ores are hosted in carbonate rocks of the Jurassic Cudi Group with features typical of carbonate-hosted supergene nonsulfide zinc mineralization. The regional strike extent of the mineralized district is at least 60 km. The age of the supergene deposit has not been determined, but it is probable that the main weathering happened during Upper Tertiary, possibly between Upper Miocene and Lower Pliocene. The Hakkari mineralization can be compared to other carbonate-hosted Zn–Pb deposits in Turkey, and an interpretation made of its geological setting. The zinc mineral association at Hakkari typically comprises smithsonite and hemimorphite, which apparently replace both sulfide minerals and carbonate host rock. Two generations of smithsonite are present: the first is relatively massive, the second occurs as concretions in cavities as a final filling of remnant porosity. Some zinc is also hosted within Fe–Mn-(hydr)oxides. Lead is present in cerussite, but also as partially oxidized galena. Lead can also occur in Mn-(hydr)oxides (max 30% PbO). The features of the supergene mineralization suggest that the Hakkari deposit belongs both to the “direct replacement” and the “wall-rock replacement” types of nonsulfide ores. Mineralization varies in style from tabular bodies of variable thickness (< 0.5 to 13 m) to cross-cutting breccia zones and disseminated ore minerals in pore spaces and fracture planes. At Hakkari a As–Sb–Tl(≫ Hg) geochemical association has been detected, which may point to primary sulfide mineralization, quite different from typical MVT.