Carbonate-hosted Pb-Zn Research Articles

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 860Mt 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 41.1–38.1Ma, 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 65Ma and 30Ma and between 30Ma and 16Ma 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.

The Giant Navan carbonate-hosted Zn–Pb deposit: exploration and geology: 1970–2015

The Navan Orebody is a world-class carbonate-hosted Zn–Pb deposit mined by the Boliden Group. It is currently the largest Zn mine in Europe producing around 2.5 mtpa at grades of 7.0% Zn, 1.4% Pb u...

Carbonate-Hosted Nonsulfide Pb-Zn Deposits of the Quesnel Lake District, British Columbia, Canada

Carbonate-hosted Pb and Zn mineralization in the Quesnel Lake district (Flipper Creek, Dolomite Flats, Main, Gunn, and Que deposits) forms an ~8-km-long belt in metasedimentary and metavolcanic rocks of the Cariboo terrane, a displaced piece of the ancestral North American margin. The mineralization is strata-bound, dolostone hosted, and consists of Pb- and Zn-bearing sulfide and nonsulfide minerals. The supergene nonsulfides mimic the morphology of preexisting sulfides occurring as disseminations, veins, and fracture fillings, and irregular replacement zones in the Neoproterozoic to Upper Cambrian dolostones of the Cunningham Formation. The main sulfides are galena, sphalerite, and minor amounts of pyrite, which have been partially or completely transformed into nonsulfide minerals by supergene processes. The main nonsulfide minerals are smithsonite [ZnCO 3 ] and hemimorphite [Zn 4 Si 2 O 7 (OH) 2 ⋅(H 2 O)], with variable amounts of cerussite [PbCO 3 ], anglesite [PbSO 4 ], hydrozincite [Zn 5 (CO 3 ) 2 (OH) 6 ], and iron oxides. The δ 18 O VSMOW , δ 13 C VPDB , and 87 Sr/ 86 Sr values of the nonmineralized and mineralized dolostones are indistinguishable and consistent with the composition of carbonates that underwent postdepositional recrystallization and isotopic reequilibration during deep burial fluid-rock interaction. The δ 18 O VSMOW and δ 13 C VPDB values range from 17.4 to 20‰ and −0.8 to +1.4‰, respectively, and 87 Sr/ 86 Sr values are above 0.71048. Carbon and oxygen ratios of smithsonite show a limited range of values, which are slightly lower than those of the host dolostones with δ 18 O VSMOW values of 16.9 to 17.8‰ and δ 13 C VPDB values of −1.6 to −0.9‰. The carbon isotope values suggest that the host dolostones are the carbon source for smithsonite. The δ 18 O smithsonite values are lower than typical values for nonsulfides formed under warm, humid, and arid-to-hyperarid climates elsewhere in the world. The precipitation temperatures derived from the isotope data for the Quesnel Lake smithsonite vary between 9° and 33°C. This temperature range is favorable for supergene smithsonite formation. For most deposits of the Quesnel Lake district examined in this study, close spatial relationships (including textures and morphological similarities) between sulfide and nonsulfide zones, coexisting sulfide-nonsulfide assemblages, and stable oxygen and carbon isotope data suggest that the oxidation of sulfides occurred after the Laramide orogeny (

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 2.0milliontonnes (Mt) of sulfide ores at average grades of 1.64wt.% Pb, 6.64wt.% Zn and 45g/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 δ13CPDB and δ18OSMOW 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 δ13CPDB and δ18OSMOW 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. δ34SCDT 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.

The Bou Dahar Jurassic carbonate-hosted Pb–Zn–Ba deposits (Oriental High Atlas, Morocco): Fluid-inclusion and C–O–S–Pb isotope studies

The Bou Dahar Pb–Zn–Ba (±Sr) is hosted in the Lower and Middle Liassic carbonate platform in the oriental High Atlas of Morocco. The paragenetic sequence includes quartz–pyrite–melnicovite–sphalerite–galena–calcite–barite±fluorite–±celestite. Fluid-inclusion studies were conducted on sphalerite (early mineralizing stage) and barite, and celestite (late mineralizing stage). These studies reveal two end-member fluids, a hot (~143°C) and saline fluid (~23wt.% NaCl eq.) and a cooler (<50°C) and diluted fluid (~5wt.% NaCl eq.). Based on fluid-inclusion and C–O–S isotope studies, a conclusion is reached that the Bou Dahar ore deposits were formed by the mixing of two fluid — a diluted, SO2−4-rich fluid, and an 18O-enriched basinal brine that carried Pb, Zn, and Ba. The sulfur required for the precipitation of sulfides was generated by the thermochemical sulfate reduction of dissolved sulfate (SO42−) of the Mesozoic seawaters, and delivered to the site of ore deposition. The sulfur of sulfate minerals was derived directly from these dissolved SO42. The Pb isotope compositions are homogenous with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios ranging from 18.124 to 18.183, 15.630 to 15.634, and 38.325 to 38.440 respectively. This Pb isotope composition is indicative of an upper crust and orogene reservoirs as the source of lead and other metals. The emplacement of mineralization occurred during the Eocene–Miocene Alpine orogeny, and tectonic burial and compression were the driving forces behind the circulation of the orogenic-brines. These ore-forming fluids migrated, along thrusting regional E–W and NE–SW deep-seated faults, to the confined carbonate-Liassic reservoir.

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

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

Composite soil-geochemical halos delineating carbonate-hosted zinc–lead–barium mineralization in the Irankuh district, Isfahan, west-central Iran

The Irankuh district in west-central Iran hosts several largely unexposed Lower Cretaceous carbonate-hosted Zn–Pb deposits whose host rocks are overlain by soil cover. This paper documents a detailed soil-geochemical exploration program, comprising 804 residual soil samples that were treated with a microwave acid digestion and analyzed by ICP-MS for a multi-element package. The soils overlying the Zn–Pb–Ba veins and mineralized zones have geochemical contrast and element enrichments that are more than two to twenty-one times greater than the non-mineralized background soil values. The most diagnostic elements are Zn, Pb, Ag, Ba, Hg and Sb which show multi-point anomalies across the entire mineralized zone with concentration ranges of 282–10,000ppm Zn, 73–10,000ppm Pb, 2.2–71.9ppm Ag, 1500–3400ppm Ba, 0.89–36ppm Hg and 11–164ppm Sb, respectively. The newly proposed composite geochemical halos defined by Ag*Cd/Pb*Zn, Ag*As/Pb*Zn, Ca*Mg/Pb*Zn, Sb*As/Pb*Zn, Hg*Sb/Pb*Zn, Sb*Ba/Pb*Zn, Ba*Ca/Pb*Zn and Ag*As* Sb/Pb*Zn*Bi correlate well with the anomalous patterns of the individual elements. The anomalies are coincident with the main faults and fractures, in particular Gushfil and Rumarmar faults of the area. On the basis of the low contents of Cu and Fe and the variodiagram of log (Pb+Zn) versus Pb/Pb+Zn, the composition of the samples suggests epigenetic stratabound Zn–Pb–Ba mineralization of the Mississippi-Valley-Type (MVT). The mode of occurrences of the anomalies is likely controlled by structural replacement in sphalerite, galena, carbonates and barite or adsorption by iron–manganese oxides and clay minerals. Follow-up sampling of gossans in highly faulted-fractured zones may indicate more concealed Zn–Pb mineralization.

Geology, isotope geochemistry and geochronology of the Jinshachang carbonate-hosted Pb–Zn deposit, southwest China

The Jinshachang Pb–Zn deposit, an exceptionally radiogenic Pb-enriched sulfide deposit, hosted by dolostone of the Upper Sinian (Neoproterozoic) Dengying Formation and the Lower Cambrian Meishucun Formation, is located in the western Yangtze Block, about 300km northeast of Kunming city in southwest China. Ore bodies in this deposit are dominated by strata-bound type and steeply dipping vein type. Primary ores in these two types are composed of sphalerite, galena, fluorite, barite and quartz with massive, banded, veined and disseminated structures. Twenty-seven ore bodies in the Jinshachang deposit host 4.6milliontons of sulfide ores at average grades of 4.07wt.% Pb and 5.03wt.% Zn. Quartz separates from the sulfide ores have δDH2O values ranging from −137‰ to −86.2‰ with an average of −114‰ (n=7), lower than those of magmatic, metamorphic and meteoric water, suggesting a contribution of organic water. δ34SCDT values of ninety-one sulfide separates range from +1.1‰ to +13.4‰ with an average of +5.7‰, lower than those of evaporites (δ34SCDT=+15‰ to +35‰) in the Cambrian to Triassic sedimentary strata in NE Yunnan province. δ34SCDT values of eight barite separates range from +32‰ to +35‰ (average +34‰), within the range of evaporites. These data suggest that S2− in the hydrothermal fluids derived from evaporites by thermo-chemical sulfate reduction (TSR), whereas SO42− directly originated from the evaporites. Six sulfide separates have highly radiogenic 206Pb/204Pb ratios ranging from 20.74 to 21.18 (average 20.92), 207Pb/204Pb ratios ranging from 15.85 to 15.89 (average 15.87), and 208Pb/204Pb ratios ranging from 40.89 to 41.42 (average 41.16). The Pb isotopes of the sulfides plot above the upper crust Pb average evolution curve and overlap the Cambrian sedimentary rocks, but are different from the Sinian dolostone. This indicates a crustal source of Pb most likely derived from the Cambrian sedimentary rocks. The initial 87Sr/86Sr ratio of seven main stage sphalerite separates from the Jinshachang deposit is 0.713, which is higher than those of the Upper Sinian Dengying Formation dolostone (0.708–0.710), Lower Cambrian carbonates (0.708–0.710), Devonian to Lower Permian sedimentary rocks (0.707–0.711) and Middle Permian Emeishan flood basalts (0.704–0.708), and lower than those of the Proterozoic folded basement rocks (0.724–0.729), but similar to those of Lower Cambrian black shale (0.712–0.714). Therefore, the Sr isotope data of the sphalerite support the view that the Lower Cambrian sedimentary rocks, in particular the black shale, were important source of metals. The main stage sphalerite separates have an Rb–Sr isotopic age of 206.8±3.7Ma, reflecting the timing of Pb–Zn mineralization. This study suggests that the Jinshachang Pb–Zn deposit is an epigenetic, thrust fold-controlled and strata-bound deposit with fluids and metals derived from the Cambrian sedimentary strata.

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 (>100Mt 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 (23–24wt.% NaCl equivalent) basinal brine containing Na+–K+–Mg2+–Ca2+–Cl− ions and abnormally high SO42− 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 (19–20wt.% NaCl equivalent) metamorphic fluid containing Na+–K+–Mg2+–Cl––SO42− 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 SO42− quickly descended into the structural traps along the reactivated faults, causing reduction of SO42− 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.

Metallogenic Geological Conditions and Prospecting Indicators of the Carbonate-Hosted Pb-Zn Deposits in Northeastern Yunnan Province, China

Based on large scale geological mapping, geological-section, tectonic and geochemical studies on the carbonate-hosted Pb-Zn deposits in NE Yunnan, the metallogenic geological conditions are discussed, and the ore-prospecting indicators are summarized. The Pb-Zn deposits have many common features, which are mainly controlled by the thrust fault-fold structures and lithological conditions. The ore-forming mechanism of them is similar to the MVT Pb-Zn deposit. The combination of thrust fault-fold structures and altered carbonate rocks with geochemical anomalies are good indicators for prospecting.

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 270km 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 2.7milliontonnes of sulfide ores grading 0.54 to 8.94wt.% Pb and 1.09 to 26.64wt.% Zn. Calcite samples have δ13CPDB and δ18OSMOW 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 δ13CPDB vs. δ18OSMOW diagram, suggesting that carbon in the hydrothermal fluid was most likely derived from the carbonate country rocks. The δ34SCDT 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 δ34SCDT 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/86Sr200Ma 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.

Strontium isotopic geochemistry of Tianqiao Pb-Zn deposit, Southwest China

Tianqiao carbonate-hosted Pb-Zn deposit, controlled by NW-trending F37 thrust fault and NW-trending Tianqiao anticline, is located in the eastern part of Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province, southwestern Yangtze Block, southwest China. Ore bodies in this deposit are hosted in the Devonian-Carboniferous carbonate rocks, and ore minerals include sphalerite, galena and pyrite, while the gangue minerals are dominated by calcite and dolomite. Using high-precision solid thermal ionization mass spectrometry (TIMS), this paper reports the strontium isotopic compositions (0.7119 to 0.7167) of sulfide samples from the Tianqiao deposit in order to trace the origin of hydrothermal fluids. Compared with the country rocks, the calculated 87Sr/86Sr200 Ma values of sulfide range from 0.7118 to 0.7130, higher than those of the age-corrected Devonian to Permian sedimentary rocks (0.7073 to 0.7101) and the Middle Permian Emeishan flood basalts (0.7078 to 0.7039), but lower than those of the age-corrected Proterozoic basement rocks (such as the Kunyang and Huili Groups, 87Sr/86Sr200 Ma=0.7243 to 0.7288). This implies a mixed strontium source between the older basement rocks and the younger cover sequences. Together with geologic and previous isotopic evidences, we considered that the fluids’ mixing is a possible mechanism for sulfide precipitation in the Tianqiao deposit.

Mapping subsurface geological structure using TEMPEST data, McArthur Basin, Northern Territory

The airborne TEMPEST electromagnetic (EM) and magnetic survey is a proven tool for mapping geological structure for exploration. This technique was applied at the Bulman project area in the McArthur Basin to identify the geological environment of stratabound carbonate-hosted Pb-Zn mineralisation. The Late Palaeoproterozoic to Early Mesoproterozoic sedimentary fill of the McArthur Basin in the Bulman project area consists of the Dook Creek and Limmen Formations. They are intruded by Early Mesoproterozoic dolerite sills and dykes. The location of the intrusive rocks was mapped using magnetic data while their depth was estimated from EM data. To find the top of the intrusives, depth to resistive basement was mapped using Conductivity Depth Images (CDIs) generated from the TEMPEST B-field Z-component data. Additionally, a voxel model was constructed from the CDIs to show the conductivity distribution in three dimensions. The conductivity pattern indicates that the dolomite sandstone and siltstone of the Dook Creek Formation are more conductive than the overlying coarse sandstone of the Limmen Formation. A disconformable boundary between the formations is shown as a distinct interface in the EM data. There is no marked conductivity contrast between intrusives and other rocks making up the resistive basement. As a result, the picked depth to resistive basement horizon corresponds to the bottom of a surface conductive unit that is interpreted to be the base of the Cenozoic unconsolidated deposits or part of the Dook Creek Formation. In places, the base of a sub-surface conductive zone is interpreted to be the top of the intrusives. The thickness of sediments above the resistive basement is variable, reaching up to 170 metres in the central - eastern part of the study area. Additionally, a 3D geological model has been constructed to image the distribution of the interpreted geological units and the tectonic pattern.

Zinc, sulfur and lead isotopic variations in carbonate-hosted Pb–Zn sulfide deposits, southwest China

The Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province in the western Yangtze Block, southwest China, contains more than four hundred Pb–Zn deposits with more than 200milliontons of Pb–Zn ores at mean grades of 5wt.% Pb and 10wt.% Zn. These deposits are hosted in Sinian (Ediacaran) to Permian carbonate rocks and are structurally controlled by thrust fault–fold structures, and are spatially associated with the late Permian~260Ma Emeishan flood basalts. Two representative low temperature hydrothermal Pb–Zn sulfide deposits, the Tianqiao and Banbanqiao deposits in the southeastern part of the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province are selected for Zn–S–Pb isotopic analyses. Sphalerite from the Tianqiao deposit has δ66Zn values ranging from −0.26 to +0.58‰ relative to the JMC 3–0749L zinc isotope standard, whereas δ66Zn values of sphalerite from the Banbanqiao deposit range from +0.07 to +0.71‰. The zinc isotopic composition of sphalerite from both deposits increase from early to final mineralization stage. In addition, sphalerite from the center (near to bottom) part of the No. 1 ore body in the Tianqiao deposit has lower δ66Zn values (−0.01 to +0.43‰) than those (+0.11 to +0.57‰) in the periphery (near to top). Sinian to Permian sedimentary rocks and Permian Emeishan flood basalts, the potential zinc metal source rocks, have δ66Zn values range from −0.24 to +0.17‰ and from +0.32 to +0.44‰, respectively. The majority of the hydrothermal sphalerite has heavier zinc isotope than the country rocks, precluding the mixing of multiple zinc sources as the key factor controlling the spatial and temporal variations of zinc isotope. Therefore, the increased δ66Zn values from the early to late stage and from the center to top could be due to kinetic Raleigh fractionation. Sphalerite from the Tianqiao and Banbanqiao deposits has δ34S values ranging from +10.9 to +14.8‰ and from +3.9 to +9.0‰, respectively, lower than Cambrian to Permian marine sulfates (+15 to +35‰) and sulfate-bearing evaporates (+15 to +28‰) in the Devonian to Permian carbonate host rocks. Sulfur of the Pb–Zn ores from both deposits is interpreted as the result of thermal chemical sulfate reduction of evaporates in the sedimentary rocks, most likely the host rocks. Sphalerite from the Tianqiao deposit has Pb isotope similar to that of age-corrected Devonian to Permian carbonate host rocks, whereas sphalerite from the Banbanqiao deposit has Pb isotope similar to that of age-corrected underlying Precambrian basement rocks. Therefore, at least lead in the Tianqiao and Banbanqiao deposits was mainly originated from the host rocks and the underlying basements, respectively. Zn–S–Pb isotopic studies of sphalerite from both deposits indicate that sources of metals and sulfur in the hydrothermal fluid for the Tianqiao deposit are the Paleozoic carbonate host rocks, whereas for the Banbanqiao deposit the sources are the Precambrian basements and the Paleozoic carbonate host rocks, respectively.

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).

Experimental and theoretical evidence of zinc structurally bound in vermiculite from naturally metal-enriched soils

AbstractThis paper provides evidence of appreciable amounts of Zn (up to 0.52 a.p.f.u.) residing in the crystal structure of trioctahedral vermiculite; the results were obtained by a combination of experimental methods (X-ray diffraction, energy dispersive X-ray spectrometry, electron microprobe analysis and selective chemical extractions) and theoretical studies based on density functional theory (DFT). Vermiculite occurs in size fractions ranging from 10 to 40 μm of near-neutral soils naturally enriched in Zn (up to 8110 mg kg–1) due to the weathering of carbonate-hosted Zn-Pb deposits in SW Spain. Zinc was partitioned among the various pedogenic phases during soil formation, but the larger part (&gt;80%) was concentrated in the residual silicate fraction. The soil exchangeable Zn pool was found to be virtually negligible. The DFT calculations support the hypothesis that the role of vermiculite is an effective sink for geogenic Zn; this is consistent, in terms of energetic stability, with the assumption that most Zn is structurally bound in octahedral sheets rather than in the interlayer exchange sites. The findings conclusively indicate that the potential mobility of Zn should remain low under the present soil conditions.

The origin of the Maozu carbonate-hosted Pb–Zn deposit, southwest China: Constrained by C–O–S–Pb isotopic compositions and Sm–Nd isotopic age

The Maozu Pb–Zn deposit, located on the western margin of the Yangtze Block, southwest China, is a typical carbonate-hosted deposit in the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province with Pb+Zn reserves of about 2.0 million tonnes grading 4.15wt.% Pb and 7.25wt.% Zn. Its ore bodies are hosted in Sinian (635–541Ma) Dengying Formation dolostone and show stratiform, vein and irregular textures. Ores are composed of sphalerite, galena, pyrite, calcite, dolomite, quartz and fluorite with massive, banded, disseminated and veined structures. The C–O–Sm–Nd isotopic compositions of hydrothermal calcites and S–Pb isotopic compositions of sulfides were analyzed to constrain the origin of the Maozu deposit. δ13CPDB and δ18OSMOW values of hydrothermal calcites range from −3.7‰ to −2.0‰ and +13.8‰ to +17.5‰, respectively, and plot near the marine carbonate rocks field in a plot of δ13CPDB vs. δ18OSMOW, with a negative correlation. It suggests that CO2 in the hydrothermal fluids was mainly originated from marine carbonate rocks, with limited influence from sedimentary organic matter. δ34SCDT values of sulfides range from +9.9‰ to +19.2‰, similar to that of Cambrian to Triassic seawater sulfate (+15‰ to +35‰) and evaporate (+15‰ to +30‰) in the Cambrian to Triassic sedimentary strata. It suggests that reduced sulfur was derived from evaporate in sedimentary strata by thermo chemical sulfate reduction. Sulfides have low radiogenic Pb isotope compositions (206Pb/204Pb=18.129–18.375, 207Pb/204Pb=15.640–15.686 and 208Pb/204Pb=38.220–38.577) that plot in the field between upper crust and the orogenic belt evolution curve in the plot of 207Pb/204Pb vs. 206Pb/204Pb, and similar to that of age corrected Proterozoic basement rocks (Dongchuan and Kunyang Groups). This indicates that ore-forming metals were mainly derived from basement rocks. Hydrothermal calcite yields a Sm–Nd isotopic age of 196±13Ma, possibly reflecting the timing of Pb–Zn mineralization in the SYG province, younger than the Permian Emeishan mantle plume (∼260Ma). All data combined suggests that hydrothermal fluids circulated through basement rocks where they picked up metals and migrated to surface, mixed with reduced sulfur-bearing fluids and precipitated metals. Ore genesis of the Maozu deposit is different from known magmatic–hydrothermal, Sedimentary Exhalative or Mississippi Valley-types, which maybe represent a unique ore deposit type, named as the SYG-type.

Lead and sulfur isotope constraints on the genesis of the polymetallic mineralization at Oued Maden, Jebel Hallouf and Fedj Hassene carbonate-hosted Pb–Zn (As–Cu–Hg–Sb) deposits, Northern Tunisia

The Oued Maden, Jebel Hallouf and Fedj Hassene Pb–Zn (Ba–Sr–F–Fe–Hg) hydrothermal ore deposits are located in the Nappe zone of Northern Tunisia. These ore deposits occur as epigenetic veins, karst and stockwork fillings in Upper Cretaceous limestones. The ore mineralogy consists mainly of galena and sphalerite, accompanied by minor amounts of jordanite, pyrite, chalcopyrite, orpiment, realgar, and other sulfosalts. Sulfur isotope data from sphalerite and galena indicate that the reduced sulfur was derived through thermochemical and/or bacterial reduction of dissolved sulfate resulting in metal precipitation. Lead isotope ratios and corresponding calculated age models indicate that the Pb in galenas has been derived from a homogenous crustal source during Upper Miocene time.

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.

Metallogeny of Permian–Triassic carbonate-hosted Zn–Pb and F deposits of Iran: A review for future mineral exploration

There are more than 300 sediment-hosted Zn–Pb deposits and occurrences in Iran and most of them occur within carbonate rocks, including world-class deposits such as Mehdiabad, Irankuh and Angouran. To achieve a broad metallogenetic framework for carbonate-hosted (CH) Zn–Pb resources in Iran, we developed a GIS database with all reported deposits and occurrences of this affinity. From this database and the age of host rocks, two major groups of CH Zn–Pb deposits can be established and linked to different tectonic events: (a) Permian–Triassic-hosted deposits (mainly of the Mississippi Valley-type; MVT), and (b) Cretaceous-hosted deposits. The Permian–Triassic-hosted deposits are concentrated in the Central Alborz metallogenic belt, the NE margin of Sanandaj–Sirjan Zone (SSZ), and the Tabas-Posht e Badam metallogenic belt, whereas those hosted by Cretaceous carbonate rocks are distributed in the SSZ, the Yazd Block and the Central Iranian Geological and Structural (CIGS) transitional zone. In addition, the formation of numerous F-rich deposits hosted by Permian–Triassic carbonate rocks is also explained by a MVT deposit model. According to our GIS-based metallogenic maps, there is a significant correspondence between the distribution of CH Zn–Pb deposits and the main suture zones in and around the Iran Plate. Most of the orogenic Permian–Triassic-hosted MVT deposits occur along the suture zones that resulted from the collision of the Iran Plate with the Eurasia Plate when the Paleo-Tethys Ocean closed (during Upper Triassic time). The close spatial, temporal and (therefore assumed) genetic relationships between the Permian–Triassic-hosted MVT deposits and the Main-Cimmerian orogenic events reflect the development of a foreland basin during the Upper Triassic, which encompassed Zn–Pb and F mineralising processes. The modern distribution of these deposits in Iran is explained by the formation of this foreland basin, and by the subsequent (post-Upper Triassic) fragmentation of the Central Iranian Microcontinent into blocks that rotated along right-lateral strike-slip faults. This late process split the Permian–Triassic-hosted MVT province into the Tabas-Posht e Badam and the Central Alborz metallogenic belts.