Pb Isotopic Compositions Of Sulfides Research Articles

S–Pb isotopic geochemistry, U–Pb and Re–Os geochronology of the Huanggangliang Fe–Sn deposit, Inner Mongolia, NE China

The Huanggangliang Fe–Sn deposit is located in the eastern section of the Central Asian Orogenic Belt (CAOB) and in the southern segment of the Great Hinggan Range polymetallic belt. This deposit is the largest tin-based polymetallic ore deposit in the northern part of the North China plate. The Fe–Sn mineralization principally occurs in skarn zones, which formed in the contact areas between granite intrusions and marbles. Twenty-one δ34SV-PDB values for sulfides from the Huanggangliang Fe–Sn deposit range from −2.3 to +2.7‰, with an average of +0.38‰, and these values are interpreted to reflect a deep magmatic source of the sulfur contained within the ore minerals of the deposit. The distribution of lead isotopic compositions from sulfides in the Huanggangliang Fe–Sn deposit exhibits a generally concentrated field, indicating that those sulfides have homogeneous lead isotopes and may derive from the same metallic source. The existence of such identical Pb isotopic compositions of sulfides and host granites suggests that granitic magmatism was probably largely responsible for the Huanggangliang mineralization.Zircon LA-ICP-MS U–Pb dating from the Huanggangliang granite exhibits a tight cluster on the Concordia plot and yields a weighted mean 206Pb/238U age of 139.96±0.87Ma, which is considered to be the best estimate of the crystallization age of the Huanggangliang granite. Results obtained from the molybdenite Re–Os isotopic analysis indicate Re–Os model ages of 133.6 to 141.5Ma and a weighted mean age of 135.1±2.3Ma. The molybdenite Re–Os dating yields an isochron age of 134.9±5.2Ma and an initial 187Os/188Os ratio of −0.22±0.35. The molybdenite Re–Os isochron age is largely consistent with the zircon U–Pb age, indicating that both granite intrusion and Fe–Sn mineralization were associated with the Mesozoic magmatism in NE China.Based on ore deposit geology, isotope geochemistry and geochronology of the Huanggangliang Fe–Sn deposit and regional geodynamic evolution, the formation of this deposit is believed to be related to lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere under the intra-continental extension in NE China. The dynamic setting for the geological processes should be linked to the NNW subduction of the Izanagi plate beneath the Eurasian plate during the Mesozoic. This subduction triggered intensive magmatism and mineralization events in the Great Hinggan Range of NE China, making this district an important Cu–Mo–Sn–Fe–Ag–Pb–Zn metallogenic province.

Genesis of the Au–Bi–Cu–As, Cu–Mo ± W, and base–metal Au–Ag mineralization at the Mountain Freegold (Yukon, Canada): constraints from Ar–Ar and Re–Os geochronology and Pb and stable isotope compositions

The genesis of mineralized systems across the Mountain Freegold area, in the Dawson Range Cu–Au ± Mo Belt of the Tintina Au province was constrained using Pb and stable isotope compositions and Ar–Ar and Re–Os geochronology. Pb isotope compositions of sulfides span a wide compositional range (206Pb/204Pb, 18.669–19.861; 208Pb/204Pb, 38.400–39.238) that overlaps the compositions of the spatially associated igneous rocks, thus indicating a magmatic origin for Pb and probably the other metals. Sulfur isotopic compositions of sulfide minerals are broadly similar and their δ34S (Vienna-Canyon Diablo Troilite (V-CDT)) values range from −1.4 to 3.6 ‰ consistent with the magmatic range, with the exception of stibnite from a Au–Sb–quartz vein, which has δ34S values between −8.1 and −3.1 ‰. The δ34S values of sulfates coexisting with sulfide are between 11.2 and 14.2 ‰; whereas, those from the weathering zone range from 3.7 to 4.3 ‰, indicating supergene sulfates derived from oxidation of hypogene sulfides. The δ13C (Vienna Peedee Belemnite (VPDB)) values of carbonate range from −4.9 to 1.1 ‰ and are higher than magmatic values. The δ18O (V-SMOW) values of magmatic quartz phenocrysts and magmatic least-altered rocks vary between 6.2 and 10.1 ‰ and between 5.0 and 10.1 ‰, respectively, whereas altered magmatic rocks and hydrothermal minerals (quartz and magnetite) are relatively 18O-depleted (4.2 to 7.9 ‰ and −6.3 to 1.5 ‰, respectively). Hydrogen isotope compositions of both least-altered and altered igneous rock samples are D-depleted (from −133 to −161 ‰ Vienna-Standard Mean Ocean Water (V-SMOW)), consistent with differential magma degassing and/or post-crystallization exchange between the rocks and meteoric ground water. Zircon from a chlorite-altered dike has a U–Pb crystallization age of 108.7 ± 0.4 Ma; whereas, the same sample yielded a whole-rock Ar–Ar plateau age of 76.25 ± 0.53 Ma. Likewise, molybdenite Re–Os model ages range from 75.8 to 78.2 Ma, indicating the mineralizing events are genetically related to Late Cretaceous volcano-plutonic intrusions in the area. The molybdenite Re–Os ages difference between the nearby Nucleus (75.9 ± 0.3 to 76.2 ± 0.3 Ma) and Revenue (77.9 ± 0.3 to 78.2 ± 0.3 Ma) mineral occurrences suggests an episodic mineralized system with two pulses of hydrothermal fluids separated by at least 2 Ma. This, in combination with geological features suggest the Nucleus deposit represents the apical and younger portion of the Revenue–Nucleus magmatic-hydrothermal system and may suggest an evolution from the porphyry to the epithermal environments.

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.

Pb Isotopic Geochemistry of Carbonate-Hosted Pb-Zn Deposits, NW Guizhou Pb-Zn Metallogenic District, China

The NW Guizhou Pb-Zn metallogenic district is an important part of the Yunnan – Sichuan - Guizhou Pb-Zn metallogenic province (SYG), and also is one of the important Pb-Zn producers in China. We analyzed the Pb isotopic compositions of sulfides, hosting rocks and basement rocks, the results show that the206Pb/204Pb,207Pb/204Pb, and208Pb/204Pb ratios of sulfides range from 18.029 to 19.900, 15.357 to 17.716 and 38.004 to 40.695, respectively. The206Pb/204Pb,207Pb/204Pb and208Pb/204Pb ratios of hosting rocks and basement rocks range from 18.397 to 19.483, 15.545 to 16.700 and 38.204 to 39.140, respectively. This indicates that the compositions of Pb isotopes of sulfides are basically consistent with that of hosting rocks and basement rocks, so the metals were sourced from various strata of carbonate rocks and underlying rocks.

Geological, geochemical characteristics and isotope systematics of the Longqiao iron deposit in the Lu-Zong volcano-sedimentary basin, Middle-Lower Yangtze (Changjiang) River Valley, Eastern China

The Middle-Lower Yangtze (Changjiang) River Valley metallogenic belt is located on the northern margin of the Yangtze Craton of eastern China. Most polymetallic deposits in the Changjiang metallogenic belt are clustered in seven districts where magmatism of Mesozoic age (Yanshanian tectono-thermal event) is particularly extensive. From west to east these districts are: E-dong, Jiu-Rui, Anqing-Guichi, Lu-Zong, Tong-Ling, Ning-Wu and Ning-Zhen. World-class iron ore deposits occur in the Lu-Zong and Ning-Wu ore clusters, which are mainly located in continental fault-bound volcanic-sedimentary basins. One of these deposits is the Longqiao iron deposit, discovered in the northern part of the Lu-Zong Basin in 1985. This deposit consists of a single stratabound and stratiform orebody, hosted in sedimentary carbonate rocks of the Triassic Dongma'anshan Formation. A syenite pluton (Longqiao intrusion) is situated below the deposit. The iron ore is massive and disseminated and the ore minerals are mainly magnetite and minor pyrite. Wall rock alteration mostly consists of skarn minerals, such as diopside, garnet, potassic feldspar, quartz, chlorite, phlogopite and anhydrite. Thin sedimentary siderite beds of Triassic age occur as relict laminated ore at the top and the margin of the magnetite orebody. These sideritic laminae are part of Triassic evaporite-bearing carbonate deposits (Dongma'anshan Formation). Sulfur isotopic compositions show that the sulfur in the deposit was derived from a mixture of magmatic hydrothermal fluids and carbonate–evaporite host rocks. Similarly, the C and O isotopic compositions of limestones from the Dongma'anshan Formation indicate that these rocks interacted with magmatic hydrothermal fluids. The O isotopic compositions of the syenitic rocks and minerals from the deposit show that the hydrothermal magnetite and skarn minerals were formed from magmatic fluids. The Pb isotopic compositions of sulfides are similar to those of the Longqiao syenite. Phlogopite coexisting with magnetite in the magnetite ores yielded a plateau age of 130.5 ± 1.1 Ma (2 σ), whereas the LA-ICP MS age of the syenite intrusion is 131.1 ± 1.5 Ma, which is slightly older than the age of phlogopite. The Longqiao syenite intrusion may have crystallized from a parental alkaline magma, generated by partial melting of lithospheric mantle, during extensional tectonics. The ore fluids were probably first derived from magma at depth, later emplaced in the sedimentary rocks of the Dongma'anshan Formation, where it interacted with siderite and evaporite-bearing carbonate strata, resulting in the formation of magnetite and skarn minerals. The Longqiao iron deposit is a skarn-type stratabound and stratiform mineral system, genetically and temporally related to the Longqiao syenite intrusion. The Longqiao syenite is part of the widespread Mesozoic intracontinental magmatism (Yanshanian event) in eastern China, which has been linked to lithospheric delamination and asthenospheric upwelling.

Lead Isotopic Composition and Lead Source of the Huogeqi Cu-Pb-Zn Deposit, Inner Mongolia, China

The Huogeqi orefield located on the northern side of Mt. Langshan, Inner Mongolia occurs in the Middle Proterozoic Langshan Group metamorphic rocks, and the orebodies are stratiform. In the past twenty years, many Chinese geologists have conducted researches on the Huogeqi Cu-Pb-Zn deposit, but there has been still a controversy on its origin. Some advocate that the deposit is of sedimentary-metamorphic reworking origin, some hold that it is of sea-floor SEDEX origin, and others have a preference for magmatic superimposition origin. The crux of the controversy is that there is no common understanding about the source of ore-forming materials. In this paper, the Pb isotopic compositions of regional Achaean-Early Proterozoic basement rocks, various types of sedimentary-metamorphic rocks and volcanic rocks in the mining district, Late Proterozoic and Hercynian magmatic rocks are introduced and compared with the ore-lead composition, so as to constrain the source of the ore lead. The result indicates that (1) sulfides in the ores have homogeneous Pb isotopic compositions, showing a narrow variation range. Their 206Pb/204Pb ratios are within a range of 17.027–17.317; 207Pb/204Pb ratios, 15.451–15.786 and 208Pb/204Pb ratios, 36.747–37.669; (2) the Pb isotopic compositions of the regional Achaean-Early Proterozoic basement rocks are characteristic of the old Pb isotopic composition at the early-stage evolution of the Earth, which varies over a wider range, reflecting significant differences in Pb isotopic compositions of the ores. All this indicates that the source of ore lead has no bearing on the basement rocks; (3) the sedimentary-metamorphic rocks in the mining district are characterized by highly variable and more radiogenic Pb isotopic compositions and their Pb isotopic ratios are obviously higher than those of ores, demonstrating that ore lead did not result from metamorphic reworking of these rocks; (4) Pb isotopic compositions of Late Proterozoic diorite-gabbro and Hercynian granite are higher than those of ores. Meanwhile, the Pb isotopic compositions of sulfides in the small-sized strata-penetrating mineralized veinlets formed at later stages are completely consistent with that of sulfides in stratiform-banded ores, suggesting that these veinlets are the product of autochthonous reworking of the stratiform-banded ores during the period of metamorphism and the late magmatic superimposition-mineralization can be excluded; (5) amphibolite, whose protolith is basic volcanic rocks, has the same Pb isotopic compositions as ores, implying that ore lead was derived probably from basic volcanism. So, the source of ore-forming materials for the Huogeqi deposit is like that of the volcanic massive sulfide (VMS) deposits. However, the orebodies do not occur directly within the volcanic rocks, and instead they overlie the volcanic rocks, showing some differences from those typical VMS-type deposits.

Age and Paleotectonic Setting of Volcanogenic Massive Sulfide Deposits in the Guerrero Terrane of Central Mexico: Constraints from U-Pb Age and Pb Isotope Studies

The Guerrero terrane of central and western Mexico comprises volcanic and sedimentary strata of mainly Mesozoic age, with geochemical signatures indicating formation in juvenile back-arc to slightly more evolved arc environments. At least 60 volcanogenic massive sulfide (VMS) deposits have been discovered thus far within the Guerrero terrane. They comprise two main belts: the Coastal belt mainly comprising deposits in the Zihuataneo subterrane (including the Cuale-Bramador district), and the Central belt, which includes deposits in the Teloloapan subterrane (Campo Morado, Tlanilpa-Azulaquez, Tizapa, Rey de Plata, etc.), the Guanajuato subterrane (El Gordo, Las Gavalinas), and the Zacatecas subterrane (San Nicolas and El Salvador deposits). The age of host rocks for the VMS mineralization in the various subterranes was poorly constrained prior to this study. Eleven new U-Pb zircon ages for volcanic host rocks from the Campo Morado, Tlanilpa-Azulaquez, Leon-Guanajuato, and San Nicolas-El Salvador VMS districts, together with recently determined U-Pb ages from the Cuale area, demonstrate that VMS deposits in the Guerrero terrane range from latest Middle Jurassic to early Early Cretaceous (Callovian to Valanginian) in age. The oldest ages were obtained from the Cuale district (total age range of 157.4 ± 4.1 Ma for three units) and the youngest are from the Tlanilpa-Azulaquez district (total age range of 139.7 ± 2.5 Ma for two samples). Volcanogenic massive sulfide deposits in the Central belt resemble those of the bimodal-siliciclastic deposit type, whereas those in the Coastal belt are more similar to the bimodal-felsic type. Published geochemical and radiogenic isotope data from the various subterranes suggest that VMS deposits in the Coastal belt and most of those in the Central belt are hosted within juvenile to slightly evolved arc settings. The San Nicolas and El Salvador deposits of the Zacatecas subterrane are the only deposits that unequivocally formed in a back-arc setting. Our new U-Pb dating results, together with existing stratigraphic, geochemical, and radiogenic isotope data from throughout the Guerrero terrane, are consistent with the Guerrero terrane having developed as a west-facing continental margin arc that was built on mainly oceanic crust (and overlying Early Mesozoic siliciclastic fans shed from the east) along the western margin of nuclear Mexico. Slab rollback in the Middle Jurassic led to the development of a “Rocas Verdes-type” continental back-arc inboard of the arc, which is now preserved as the Arperos basin in the central and southern Guerrero terrane and the host rocks for the San Nicolas and El Salvador deposits farther to the north in southeastern Zacatecas State. We have determined Pb isotope compositions of sulfides from VMS deposits and several other styles of mineralization from throughout the Guerrero terrane. A compilation of these and previously published data shows that isotopic compositions from the various VMS deposits fall in a relatively confined field that overlaps the average upper crustal growth curve. This suggests that metals were mainly sourced from continentally derived sedimentary strata that are interlayered with or immediately underlie the host volcanic section and/or from the host volcanic rocks themselves (or subvolcanic intrusive equivalents) that had assimilated significant quantities of upper crustal material either at the point of origin or during subsequent ascent and eruption. Lead isotope compositions from the Francisco I Madera deposit in Zacatecas State indicate that most of the sulfides in this deposit are epigenetic rather than syngenetic in origin and are likely Tertiary in age.

The Source of Metals in the Qilinchang Zn-Pb Deposit, Northeastern Yunnan, China: Pb-Sr Isotope Constraints

Qilinchang, a Mississippi Valley-type Zn-Pb deposit, has essentially homogeneous lead isotope compositions as follows: 206Pb/204Pb = 18.432 to 18.487 (i.e., 18.460±0.15%), 207Pb/204Pb = 15.664 to15.720 (i.e., 15.697±0.18%), and 208Pb/204Pb = 38.729 to 38.874 (i.e., 38.833±0.19%). Strontium isotope compositions at the time of mineralization were relatively heterogeneous: 87Sr/86Sr = 0.7170 for pyrite, 0.7138 to 0.7180 for sphalerite, 0.7109 to 0.7143 for galena, and about 0.7158 to 0.7168 for calcite. The mineralizing metals of the Qilinchang ore deposit, Pb and Zn, have only one source rock. The Pb isotope compositions of sulfides of the deposit are essentially the same as those of the Upper Proterozoic (i.e., lower Sinian) igneous rock suite, if the preferential migration of Pb isotopes during the leaching and the in situ radiogenic Pb back correction are taken into account. The 207Pb/206Pb ratios of sulfides in the deposit are notably high (0.850–0.851), which suggests that this ore deposit contains material with very old signatures. On the basis of kinetic and thermodynamic calculations of water/rock interaction, we obtain a value of about 0.745 of source rock 87Sr/86Sr for the mineralizing metals. This value is similar to that of the lower Sinian igneous rock suite at the time of mineralization. That the lower Sinian igneous rock suite served as the source is also favored by its characteristic of leachability and its content of metals in this and other geologic bodies.

Diamond growth history from in situ measurement of Pb and S isotopic compositions of sulfide inclusions

In a continuing effort to understand crust-mantle dynamics, we have determined the S and Pb isotopic compositions of mantle sulfides encapsulated within diamonds from under the Siberian craton and compared these results to those of previously investigated African counterparts. Because diamond inclusions are isolated from exchange with surrounding mantle, they may preserve the history of diamond growth and act as direct tracers of the origins of mantle materials. Study of these inclusions may thus offer the best chance of recognizing global-scale interaction between Earth9s crust and mantle. Although δ 34 S values of the Siberian sulfides do not deviate significantly from the mantle value of 0‰ ± 3‰, Pb isotopic compositions are highly variable. Pb isotopic compositions of sulfides from peridotitic suite diamonds generally plot near the terrestrial Pb growth curve, with model ages ranging between 0 and 2 Ga, whereas sulfides from eclogitic suite diamonds have radiogenic compositions, plotting beyond the growth curve. These results, which are similar to those for sulfides in African diamonds, suggest that the sulfides from eclogitic suite diamonds were derived from a source with an unusually high U/Pb ratio and may indicate a common process (such as subduction of crystal materials into the mantle) operating beneath Africa and Siberia. The absence of extremely radiogenic Pb in sulfides from eclogite xenoliths suggests that the radiogenic material from which eclogitic suite diamonds grew was a transient feature of the mantle, associated with diamond growth. The ultimate origin of this high U/Pb signature, however, remains enigmatic. Large variations in Pb isotopic composition of sulfides from different zones in a single peridotitic suite diamond document (1) crystallization of the diamond9s core near 2.0 Ga, (2) growth of its outer zone in an environment with a high U/Pb ratio similar to the growth environment of eclogitic suite diamonds, and (3) growth of the diamond rim near the time of kimberlite emplacement.