Basinal Brines Research Articles

The mineralization of Daxiao carbonate-hosted Pb-Zn deposit, northeast Yunnan province, SW China: Constraints from Rb-Sr isotopic dating and H[sbnd]O[sbnd]S-Pb isotopes

The Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province located in western Yangtze Block contains more than 400 carbonate-hosted Pb-Zn deposits. Uncertain mineralization age and ore-forming material source causing debates on the genesis of these carbonate-hosted Pb-Zn deposits. To address this issue, the Daxiao Pb-Zn deposit was chosen as a case study. The orebodies of Daxiao deposit are hosted in Mesoproterozoic Heishan formation argillaceous dolomite interbedded with slate. Three main mineralization stages have been identified, including syn-sedimentary stage, hydrothermal stage and supergene stage. The ore minerals consist of galena, sphalerite, chalcopyrite, argentite, smithsonite, anglesite and cerussite in the deposit. The early hydrothermal stage sphalerite yielded a Rb-Sr isochron age of 223.5 ± 2.9 Ma, consistent with the spike of Pb-Zn mineralization in SYG metallogenic province. Quartz in hydrothermal stage yields δDSMOW values of −69.6 to −65.8 ‰ and calculated δ18OFluid values of + 3.4 – +5.6 ‰, showing an affinity of metamorphic water. While the quartz in supergene stage yields δDSMOW values of −68.3 to −65.8 ‰ and calculated δ18OFluid values of −4.1 to −1.7 ‰, indicating abundant basinal brine or meteoric water had mixed into ore-forming fluid during its evolution from hydrothermal stage to supergene stage. Sulfur isotopic composition (δ34S = +6.3 – +19.1 ‰) of different stage sulfides reveal that the ore-forming sulfur originated from sulfates within the wall rocks, and mainly reduced by Thermal-chemical reduction (TSR). Moreover, the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of early hydrothermal stage sphalerite are 18.282 – 18.312, 15.603 – 15.681and 38.287 – 38.311, respectively. Those of late hydrothermal stage galena are 18.315 – 18.491, 15.676 – 15.721 and 38.314 – 38.326, respectively. All of them plot in the overlapping area of Emeishan flood basalts, Kunyang and Huili groups and Sinian to Triassic strata, indicating that these wall rocks jointly contributed the ore-forming metals for these Pb-Zn deposits in SYG metallogenic province. Hence, a metallogenic model for Daxiao and other carbonate-hosted Pb-Zn deposit in SYG metallogenic province was proposed: In the thrustfold systems caused by the subduction of Paleo-Pacific and the closure of Jinshajiang-Ailaoshan Paleo-Tethys ocean in Late Triassic to Early Jurassic. The fluids originated from metamorphic water migrated along deep faults and extracted ore-forming materials from wall rocks (including Proterozoic basement rocks, Sinian to Triassic sedimentary wall rocks and Permian Emeishan flood basalts), and then precipitated ores in the secondary thrust faults or interlayered fractures within these thrustfold systems.

Fluid flow and water/rock interaction during the Early Triassic evolution of the western Canada sedimentary basin as revealed by carbonate diagenesis

Diagenetic evolution of sedimentary basins, which is crucial to resource exploration and development, and carbon capture, utilization, and storage (CCUS), is mainly controlled by fluid influx associated with the regional tectonic and hydrogeologic setting of these basins. Therefore, petrographic and isotope geochemical studies integrated with geodynamics of sedimentary basins, fluid flow and transport hydrodynamics are insightful tools to reconstruct the regional history of paleofluid flow and their driving mechanisms. This study investigates carbonate diagenesis in the Lower Triassic Montney Formation of the Western Canadian Sedimentary Basin (WCSB) to constrain the origin of diagenetic fluids, their major flow systems, and their association with the tectonics and hydrogeology of the WCSB. Petrographic analysis shows various generations of early-to late-stage non-ferroan to ferroan calcite (C1–C3) and dolomite (D1-D4) cement. Bulk δ13C and δ18O values of carbonate cements range from −7.1 to +0.4‰ and −9.5 to −2.8‰ (VPDB), respectively, noticeably more depleted than those estimated for Early Triassic seawater. Their 87Sr/86Sr isotope ratio, 0.7108 to 0.7128, is significantly more radiogenic than Early Triassic seawater. These isotopic values confirm the extensive interaction of the Montney Formation pore water with hot basinal brines of Precambrian metasediments and siliciclastic strata, the influx of hydrothermal fluids, and high burial temperature in the basin. The 13C-depleted signature of these cements supports the contribution of organic carbon, from the breakdown and oxidation of organic matter and hydrocarbons via microbial and thermochemical sulfate reduction processes. The results of this study suggest that Montney Formation diagenesis was influenced by evolved Montney pore water interacting with fluids sourced from metasediments of the Cordillera thrust belt and topography-driven fluids from Columbian and Laramide tectonism. This study highlights the importance of an integrated approach to better understand changes in fluid compositions during diagenesis and reconstruction of basin-scale paleofluid flow systems in sedimentary basins.

Formation of the Banxi Sb deposit in Eastern Yangtze Block: Evidence from individual fluid inclusion analyses, trace element chemistry, and He-Ar-S isotopes

The Banxi Sb deposit (>100,000 t Sb metal with a grade of 0.02%–64.5% Sb (typically 15.3%–25.9% Sb) in the Eastern Yangtze Block is hosted in Neoproterozoic low-grade metamorphic clastic rocks of the Banxi Group. The deposit is characterized by vein-type Sb-only mineralization. Analyses of individual quartz-hosted fluid inclusions obtained by LA-ICP-MS identified Na as the most abundant cation (thousands to tens of thousands of ppm) in the ore-forming fluids of the Banxi Sb deposit, together with variable contents of K, Ca, Al, As, Fe and Sb (tens to thousands of ppm). Multiple chemical criteria, including high Na+/K+ (typically 3–15) and low Mn2+/Na+ (0.003–0.2) and Sr2+/Na+ (0.001–0.01) ratios of individual fluid inclusions, suggest that the fluids responsible for quartz and stibnite precipitation in the Banxi Sb deposit were likely dominated by basinal brines within low-grade metasedimentary rocks. Moreover, the extremely low 3He/4He ratios (0.001–0.048Ra) but relatively high 3He/36Ar (0.5 × 10−5–5.8 × 10−4) and 40Ar/36Ar ratios (323–1111 with an average of 737) of fluid inclusions trapped in ore-stage quartz further support a sedimentary origin of ore-forming fluids in this deposit. The positive and homogeneous sulfur isotopic values (δ34S = 8.0–9.5‰) of stibnite and arsenopyrite are comparable to those of sulfides in Proterozoic metasedimentary rocks (δ34S = 5.6–11.5‰), indicating these metasedimentary rocks may have served as the primary source of S for the Banxi Sb deposit. Combined with geological features and new trace element chemistry data for quartz and stibnite, we envisaged a new formation model for the Banxi Sb deposit that assumes that circulation of weakly alkaline basinal brines through faults under an extensional tectonic setting during the Early Cretaceous (∼130 Ma), mobilization of Sb and S from the underlying and host metasedimentary rocks and ascent of ore- forming fluids along faults, and ultimately precipitation of Sb minerals in or around fault/fracture zones as a result of the decreasing pH of the ore-forming fluids as well as sulfidation during fluid-rock reaction.

Geological, fluid inclusion microthermometry and geochemical constraints on the ankeritic-sideritic iron deposits in the Delijan mining district, Malayer-Esfahan metallogenic belt, Iran

The Kahak, Raveh, and Khoreh stratabound sideritic-ankeritic iron deposits are located in the Malayer-Esfahan metallogenic belt (MEMB), Iran. Geological, geochemical, fluid inclusion and S isotope studies have been carried out on the Kahak, Raveh, and Khoreh deposits which are hosted by different types of Lower Cretaceous dolomite, sandstone, and tuff in the Delijan mining district (DMD). Ankerite and siderite ores display a strong lithological control and form stratabound stacked ore lenses hosted in different horizons by Kc2, Kcv, Kc3, and Km units. Economic orebodies are restricted to the hanging wall of the syn-sedimentary normal faults. Three ore types can be distinguished based on the petrographic studies: stringer zone ore facies, bedded ore facies, and massive-replacement ore facies. Ore minerals are predominantly ankerite, siderite, barite, chalcopyrite, sphalerite, galena, and pyrite. Ore mineralization in the Kahak, Raveh, and Khoreh deposits has emplaced in two stages. The fine-grained ore bands (stage 1) which are intricately interlayered with host rock beds, exhibit sedimentary textures such as lamina and bedding and indicate a syn-sedimentary origin. The coarser-grained stage 2 ores show massive and vein-veinlet textures that are considered to form by replacement during sub-seafloor fluid flow. Hydrothermal alteration minerals developed in the wall rock include dolomite, quartz, and calcite. A microthermometric study of fluid inclusions from the barite samples indicates homogenization temperatures between 162 and 210 °C. Salinities of ore-forming fluids range from 7.8 to 16.8 wt% NaCl eq. Fluid inclusion studies suggest that the ore-forming fluids were derived from basinal or formational brines. Fluid mixing (basinal brine and seawater) may have played an important role during Fe mineralization. Calculated δ34S values for the ore fluid vary between + 10.69 and + 31.98‰. Sulfur isotopic compositions suggest that the source of sulfur for barite was derived from seawater. These data show that the Kahak, Raveh, and Khoreh ankeritic-sideritic iron deposits are comparable with those of sub-seafloor carbonate-replacement SEDEX-type deposits.

Temperature and basinal fluid controls on feldspar diagenesis, Lower Cretaceous sandstones, Scotian Basin, Canada

The passive-margin Scotian Basin accumulated thick Upper Jurassic–Lower Cretaceous deltaic sandstones and shales, which were influenced by high heat flow in the mid-Cretaceous and deformed by salt tectonics. This study takes advantage of the complex thermal history and record of saline fluid flow in the basin to determine the relative importance of burial depth, temperature, salinity of basinal brines, overpressure, and sandstone permeability in controlling the dissolution of detrital feldspar and growth of authigenic K-feldspar and albite. Feldspar grains and volcanic lithic clasts from two transects, with differing thermal and salt tectonic histories, were studied by scanning electron microscope (SEM) backscattered electron images, energy-dispersive spectroscopy, SEM cathodoluminescence (CL) imaging, and hot-cathode CL microscopy. Published fluid inclusion measurements are integrated with burial history curves and timing of deformation on salt detachment surfaces to provides a new synthesis of the post-Jurassic thermal and saline fluid flow history of the basin. Surface-controlled dissolution of K-feldspar and growth of authigenic K-feldspar rims occur from 1.5 to 3.1 km. More destructive transport-controlled dissolution, down to 3.9 km, is more effective in thick-bedded permeable sandstones that acted as fluid pathways. Albitization of detrital K-feldspar and sodic plagioclase, and of feldspars in volcanic lithic clasts was facilitated by high Na+ content of formation waters migrating preferentially through such pathways at the time of silica and carbonate cementation, with strong albitization coinciding with transport-controlled dissolution of K-feldspar. Authigenic albite partially fills pores created by K-feldspar dissolution. Overpressured conditions enhance albite authigenesis, as a result of slower fluid advection. Episodic release of hot, saline, overpressured fluids in the zone of surface-controlled dissolution of K-feldspar favoured albitization but had no detectable effect on K-feldspar dissolution. Basin hydrology plays a definitive role in feldspar diagenesis, producing patterns that cannot be interpreted as a simple consequence of temperature and activity of Na+.

Stratigraphic and structural controls on the occurrence of saline springs within the Illinois Basin, U.S.

Saline springs within intracratonic basins are a common, but rarely studied phenomena. Derived primarily from the mixing of basin brines (evaporated seawater) with shallow groundwater and/or freshwater recharge, there are many saline springs within the Illinois Basin. These include free-flowing springs, bedrock seeps into otherwise freshwater aquifers, and salt licks. In this study, a total of 44 saline springs, seeps, licks and wells were sampled. The chemical compositions of the saline springs of the Illinois Basin are dominated by Na and Cl- with a combined concentration as high as 60,000 mg/L. Some of the springs are enriched in H2S supporting populations of white filamentous, sulfide-oxidizing bacteria. Because the spring water contains a component of basin brines, and because basin brines of the Illinois Basin have been well characterized by others, ion mass ratios were used to identify the geologic period of the source formation(s).In general and on a basin-wide scale, saline groundwater discharge occurred along geologic structures and from strata along the margins of the Illinois Basin, originating from every period of the basin’s geologic strata (Cambrian through Pennsylvanian). The greatest number of saline springs occurred where geologic structures intersect large streams or major aquifers. Saline springs were often found in clusters that may extend over many square kilometers. The occurrence of saline springs are a reflection of the geology, geologic structure, geologic history including continental glaciation, surface water-groundwater interactions, groundwater flow regimes, and overall groundwater chemistry within the Illinois Basin. In parts of the Illinois Basin, our data suggest that brines within strata of older geologic periods have migrated upward along geologic structures, infiltrated strata of younger geologic periods, and mixed with, and in some cases, replaced brines within those strata. The source of salinity in springs within the center of the Illinois Basin is typically brines from geologic strata that outcrops and subcrops along structures associated with the LaSalle Anticlinorium. Salt licks that occur near the southeastern boundary of the Illinois Basin in Kentucky constitute points of discharge for regional groundwater flow from the basin. The Cl/Br and K/Cl mass ratios of the salt licks in Kentucky suggest that the saline groundwater is a mixture of brines from Cambrian and Ordovician strata.

Stable Isotopes and Halogen Geochemistry of the Huayuan Carbonate‐hosted Pb‐Zn Ore District, South China: Implications for the Salt Source of Ore‐forming Fluids

AbstractThe Huayuan Pb‐Zn ore district in China, located in western Hunan Province, is a giant carbonate‐hosted Pb‐Zn ore district. The source of ore‐forming brines in this ore district remains poorly constrained. Whether the highly saline brines are derived from evaporated seawater or dissolved evaporates continues to be intensely debated. Carbonate minerals associated with Pb‐Zn mineralization have δ13CV‐PDB and δ18OV‐SMOW values ranging from −5.55‰ to +1.35‰ (mean value of −0.69‰; n = 14) and +16.28‰ to +25.05‰ (mean value of +20.22‰; n = 14), respectively. This indicates that carbonate minerals are dominantly formed from dissolved ore‐hosted carbonate rocks. The δ34S values of sulfides range from +20.2‰ to +36.8‰, with an average value of +30.0‰ (n = 27). These results suggest that sulfur is predominantly derived from the thermochemical sulfate reduction of marine sulfate. The crush‐leach analyzed solute data of fluid inclusions in sphalerite show the ore‐forming fluids have Cl/Br molar ratios range from 118 to 384, and Na/Br molar ratios from 39 to 160 (n = 8). These Cl/Br ratios of hydrothermal fluid are much lower than those of seawater (657 to 564), but are consistent with bittern brines through early halite precipitation. We propose that ore‐forming fluids are mainly derived from evaporitic basin brines, which leached base metals from the basement and/or country rocks. The brine then migrated to the basin margins through clastic rocks of basement and then precipitated sulfides by thermochemical sulfate reduction.

Two hydrothermal events associated with Au mineralization in the Youjiang Basin, southwestern China

The Youjiang Basin in southwestern China hosts remarkably large amounts of Carlin-type Au deposits. In such deposits, Au is mainly ionically bound to arsenian pyrite characterized by core and rim textures. Understanding the formation mechanism of zoned pyrite may improve our understanding of the genesis of massive Carlin-type Au deposits. This study examined the elemental content, mineral composition, and pyrite texture and chemistry of wall rock and ore from the Lannigou Au deposit, one of the largest Carlin-type Au deposits in the Youjiang Basin, to identify the genetic mechanisms of zoned pyrite.Five distinct types of pyrites, i.e., pyrite 1 (Py1), 2 (Py2), 3 (Py3), 4 (Py4), and ore pyrite (OPy), were identified in the Lannigou Au deposit. Py1, Py2, and Py3 were mainly observed in the wall rock, whereas Py4 and OPy, constituting the core and rim of zoned pyrite, respectively, were only discovered in the ore. Mineral mapping of the wall rock and ore indicated that pyrite is scarce in the wall rock (0.021 vol%). However, the amount of zoned pyrite significantly increased in the ore (1.275 vol%). Py1, Py2, and Py3, showing framboidal, nodular, and fine euhedral microcrystal textures, had high Pb, Co, Ni, Mn, Zn, and Mo contents (medians ranging from 10 to 1,000 ppm) and variable δ34S compositions ranging from −5.1 to 35.4‰, implying a sedimentary (syngenetic or diagenetic) origin. Py4 was homogeneous and contained numerous illite and quartz inclusions and fractures. In contrast, OPy showed multiple As-rich sub-bands and a lack of illite or quartz inclusions and fractures. Py4 had significantly lower Au, As, Tl, and Cu contents than OPy; however, Py4 had Pb, Co, Ni, Mn, Zn, and Mo contents similar to OPy. The range of δ34S values for Py4 and OPy were both narrow, but Py4 (7.6 to 13.3‰, with an average of 9.1‰) had lower δ34S values than OPy (9.4–14.1‰, with an average of 12.4‰). These texture and chemical features indicate that Py4 likely sedimented from a pre-ore hydrothermal fluid, but not at the early stage of the ore-forming fluid.Hydrothermal pyrite cores were also widespread and exhibited textural and chemical differences compared to Au-rich pyrite rims from other Au deposits in the Youjiang Basin. Based on the two geochronological clusters of Au deposits in the Youjiang Basin, we inferred the occurrence of at least two episodes of large-scale hydrothermal events. The two hydrothermal fluid episodes, which contributed to the zoned pyrite formation, likely originated from the mixing of initial magmatic fluid with δ34S values of ∼0 ± 5‰ and basin brine with elevated δ34S values (δ34S > 18‰). Pre-ore hydrothermal pyrite likely resulted in the rapid non-equilibrium crystallization of ore pyrite; thus, more Carlin-suite elements were captured by ore pyrite. Additionally, low-grade Au orebodies may have locally formed during the pre-ore hydrothermal event. These multiple hydrothermal events may have been crucial for the formation of massive Carlin-type Au deposits in the Youjiang Basin.

A Mississippi Valley–type Zn-Pb mineralizing system in South China constrained by in situ U-Pb dating of carbonates and barite and in situ S-Sr-Pb isotopes

AbstractThe ages of Zn-Pb deposits are exceptionally challenging to determine owing to the lack of suitable mineral chronometers and techniques. Here we present the first result for in situ LA-ICP-MS U-Pb dating of carbonates and barite from a Mississippi Valley– type (MVT) Zn-Pb deposit in South China. Hydrothermal dolomite in close textural and paragenetic association with Zn-Pb sulfides, and calcite and barite cement from the breccia ores, yield ages of 473.4 ± 2.7 Ma and 368.7 ± 3.1 Ma, respectively. Together with new in situ S-Pb-Sr isotope values, these data reveal an epigenetic Zn-Pb mineralization history, agreeing well with a model involving basinal brine accumulation and MVT Zn-Pb sulfide precipitation. Because carbonate is a common mineral in Zn-Pb deposits worldwide, and other minerals in such deposits suitable for isotope dating are generally absent, in situ U-Pb dating of gangue carbonates opens a new window for better defining the ore genesis of this globally important Zn-Pb deposit type and for tracking hydrothermal fluid flow in sedimentary basins.

Jingwenite-(Y) from the Yushui Cu deposit, South China: The first occurrence of a V-HREE-bearing silicate mineral

Abstract Jingwenite-(Y), Y2Al2V24+(SiO4)O4(OH)4, the first V-HREE-bearing silicate mineral discovered in nature, is an abundant component of a sediment-hosted stratiform Cu (SSC) deposit, Yushui, South China. The mineral occurs in bedded/massive sulfide-bearing ore and is associated with bornite, chalcopyrite, galena, xenotime-(Y), nolanite, thortveitite, roscoelite, barite, and quartz. Optically, jingwenite-(Y) is biaxial (+), with α = 1.92(4), β = 1.95(2), γ = 1.99(3) (white light), and 2V (calculated) = 83°. The dispersion is medium with r < v, and the pleochroism is with X = light brown, Y = brown, Z = dark brown. The color, streak, luster, and hardness (Mohs) are light brown, yellowish gray, vitreous, and 4½–5, respectively. Jingwenite-(Y) is monoclinic, with space group I2/a, Z = 4, and unit-cell parameters a = 9.4821(2) Å, b = 5.8781(1) Å, c = 19.3987(4) Å, β = 90.165(2)°, and V = 1081.21(4) Å3. The structure of jingwenite-(Y) has chains of edge-sharing Al(V,Fe)-O octahedra and V(Ti)-O octahedra extending along the b-axis and linked by insular Si-O tetrahedra, leaving open channels occupied by HREEs. Jingwenite-(Y) is a new nesosilicate structural type. Sm-Nd dating and Nd isotope signatures of jingwenite-(Y) reveal an epigenetic origin and suggest that HREEs and V were added to the SSC system via leaching of abundant heavy minerals in the footwall red sandstone by oxidized basinal brines. The abundance of jingwenite-(Y) at Yushui indicates that it could potentially be a valuable resource for HREE and V. Moreover, HREE and V mineralization can also occur in the same sediment-hosted Cu mineral system.

Genesis of the Baiyangping Cu–Co and Pb–Zn Mineralizations in Lanping Basin, SW China

The Oligocene to Miocene Baiyangping Cu–Co and Pb–Zn mineralization was deposited during the collision of the India and Asia continents. The mineralization is hosted in veins in faulted carbonate and clastic rocks, which act as fluid pathways. A detailed fluid-inclusion analysis and C–O–S isotopic study are reported, focusing on the origin of the mineralizing fluids and mineralizing processes. The microthermometry of fluid inclusions hosted in quartz and carbonates indicate that the fluid peak temperature for both Cu–Co and Pb–Zn mineralizations ranges from 160 to 200 °C and from 120 to 160 °C, respectively. During these metallogenic hydrothermal events, salinity evolved from 2.7 wt% NaCl equiv to 24.8 wt% NaCl equiv. The δ34S values measured on sphalerite and tennantite range from +5.2‰ to +9.5‰, which indicates that sulfur originated from a reservoir characterized by thermochemical sulfate reduction (TSR). The C–O isotopic values obtained from the carbonate samples suggest that the fluid mainly originates from basinal brines. The combination of C and S isotopic values of the Cu–Co and Pb–Zn mineralization indicate the sedimentary source of the basin. Mineralization is controlled by faults, thermochemical sulfate reduction, and the physicochemical conditions of the fluid.

Early Cambrian highly metalliferous black shale in South China: Cu and Zn isotopes and a short review of other non-traditional stable isotopes

Early Cambrian black shales on the Yangtze Platform host a regionally distributed highly metalliferous sulfide-rich carbonaceous unit which has been the subject of extensive debate. This marker unit, with a few centimeters or tens of centimeters in thickness, displays extreme enrichment in Mo and Ni (wt% range), and in a broad spectrum of other metals such as As, Au, PGE, Re, Cu, Zn, Cd, Ag, Sb, Se, Tl, and Hg, and occurs discontinuously along the western passive margin of the Yangtze Platform. It grades laterally in stratigraphically equivalent meter-thick vanadium-rich shale and tens-of-meter-thick sapropelite (combustible shale). New Cu and Zn isotope data, combined with existing Cd, Cr, Ni, Mo, Hg, and Se isotope and other chemical data, allow to attempt an integrated view on the formation of this intriguing unit of hyper-enriched metalliferous black shale. The authigenic Cu enrichment in the 1000-ppm range has produced no or little Cu isotope fractionation (0.03 ± 0.26 ‰ δ65Cu) beyond the lithogenic background. Heavy zinc and cadmium isotope enrichment in the sulfidic samples (1.11 ± 0.18 ‰ δ66Zn, 0.31 ± 0.10 ‰ δ114Cd) is controlled by sulfide fractionation and contrasts with V-rich and barren shale (0.60 ± 0.18 ‰ δ66Zn, 0.00 ± 0.14 ‰ δ114Cd). The distinctly negative Ni isotope composition of the metalliferous unit (−0.84 ± 0.05 ‰ δ60Ni) with Ni in the percent range has been interpreted as due to hydrothermal activity related to the leaching of mafic rocks and their sulfides. Sorption processes (Fe-oxyhydroxides) and redox cycling in the water column and the bottom sediment with microbial activity could be an alternative interpretation. The extreme metal enrichment can be understood as due to a process chain, from high biological productivity in the oxic photic zone to sulfate reduction in the deeper sulfidic water column and upper sediment layer. Key to the metal enrichment seems to be extremely low clastic sedimentation and advanced carbon destruction by anaerobic oxidation. Hydrothermal input of basinal brines along the rifted margin of the Yangtze Platform was likely a part of this scenario.

Fluid sources in basement-hosted unconformity–uranium ore systems: tourmaline chemistry and boron isotopes from the Patterson Lake corridor deposits, Canada

The Patterson Lake corridor is a new uranium district located on the southwestern margin of the Athabasca Basin. Known resources extend almost 1 km below the unconformity in graphite- and sulfide-bearing shear zones within highly altered metamorphic rocks. Despite different host rocks and greater depths below the unconformity, alteration assemblages (chlorite, illite, kaolinite, tourmaline and hematite), ore grades and textures are typical of unconformity-related deposits. This alteration includes at least three generations of Mg-rich tourmaline (magnesio-foitite). The boron isotopic composition of magnesio-foitite varies with generation: the earliest generation, which is only observed in shallow samples from the Triple R deposit (Tur 1), contain the heaviest isotopic signature ( δ 11 B ≈ 19–26‰), whereas subsequent generations (Tur 2 and Tur 3) yield lighter and more homogeneous isotopic signatures ( δ 11 B ≈ 17.5–19.9‰). These results are consistent with precipitation from low-temperature, NaCl- and CaCl 2 -rich brine(s) derived from an isotopically heavy boron source (e.g. evaporated seawater) that interacted with tourmaline and silicates in the basement rocks and/or fluids derived from depth (with low δ 11 B values). The lower δ 11 B values in paragenetically later magnesio-foitite reflect greater contributions of basement-derived boron over time, whereas minor compositional variations reflect local metal sources (e.g. Cr, V, Ti) and evolving fluid chemistry (decreasing Na and Ca, increasing Mg) over time. The δ 11 B and chemical variation in magnesio-foitite over time reinforce the strong interactions with basement rocks in these systems while supporting incursion of basinal brines well below the unconformity contact. Supplementary material: Complete analytical dataset including reference materials are available at https://doi.org/10.6084/m9.figshare.c.5727555 Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

Superimposed zinc and gold mineralization in the Dunde iron deposit, western Tianshan, NW China: Constraints from LA-ICP-MS fluid inclusion microanalysis

The submarine volcanogenic iron oxide (SVIO) deposits are one of the most important sources of high-grade iron ores in China. Many large- and medium-scale SVIO deposits were recently discovered in the Awulale metallogenic belt (AMB) in Western Tianshan, NW China. The Dunde deposit in the AMB is a unique iron deposit containing large-scale Zn and medium-scale Au resources. The zinc mineralization in this deposit is generally located at the margin of iron orebodies constituting composite iron-zinc orebodies. To clarify the genetic relation between iron and Zn with Au mineralization, we conducted a detailed investigation of sphalerite-hosted fluid inclusions in the Dunde deposit. The primary fluid inclusions in sphalerite are liquid-rich, with homogenization temperature in the range of 189–219 ℃, and salinity of 19.68–22.38 wt% NaCl equiv. Single fluid inclusion LA-ICP-MS analysis suggests a magmatic source for the fluid as reflected by high Rb/Na (0.001–0.016), K/Na (0.18–0.83) and low Ca/K (1.03–9.38) ratios, which are distinctly different from those of basinal brines. The Cs/(K + Na + Ca)*10000 values (6.0–13.4) of sphalerite-hosted fluid inclusions are equivalent to those in porphyry-type Cu-Mo deposit (4.7–23.8), indicating that the ore-forming fluid originated from a highly evolved granitic magma, rather than intermediate-mafic magmatism related to iron mineralization. Thus, we propose that the zinc and gold mineralization in the Dunde deposit might be products of superimposed mineralization on iron orebodies during hydrothermal alteration related to granitic intrusions.

Mineralization and Structural Controls of the AB-Bid Carbonate-Hosted Pb-Zn (±Cu) Deposit, Tabas-Posht e Badam Metallogenic Belt, Iran

The Ab-Bid deposit, located in the Tabas-Posht e Badam metallogenic belt (TPMB) in Central Iran, is the largest Pb-Zn (±Cu) deposit in the Behadad-Kuhbanan mining district. Sulfide mineralization in the Ab-Bid deposit formed in Middle Triassic carbonate rocks and contains galena and sphalerite with minor pyrite, chalcopyrite, chalcocite, and barite. Silicification and dolomitization are the main wall-rock alteration styles. Structural and textural observations indicate that the mineralization occurs as fault fills with coarse-textured, brecciated, and replacement sulfides deposited in a bookshelf structure. The Ab-Bid ore minerals precipitated from high temperature (≈180–200 °C) basinal brines within the dolomitized and silicified carbonates. The sulfur isotope values of ore sulfides suggest a predominant thermochemical sulfate reduction (TSR) process, and the sulfur source was probably Triassic-Jurassic seawater sulfate. Given the current evidence, mineralization at Ab-Bid resulted from focusing of heated, over-pressurized brines of modified basinal origin into an active fault system. The association of the sulfide mineralization with intensely altered wall rock represents a typical example of such features in the Mississippi Valley-type (MVT) metallogenic domain of the TPMB. According to the structural data, the critical ore control is a bookshelf structure having mineralized dextral strike-slip faults in the northern part of the Ab-Bid reverse fault, which seems to be part of a sinistral brittle shear zone. Structural relationships also indicate that the strata-bound, fault-controlled Ab-Bid deposit was formed after the Middle Jurassic, and its formation may be related to compressive and deformation stages of the Mid-Cimmerian in the Middle Jurassic to Laramide orogenic cycle in the Late Cretaceous-Tertiary.

LA-ICP-MS trace element geochemistry of sphalerite: Metallogenic constraints on the Qingshuitang Pb–Zn deposit in the Qinhang Ore Belt, South China

Many hydrothermal vein-type Pb–Zn deposits were discovered in the Qinhang Ore Belt (South China), but their origin remains enigmatic due to the lack of constraints on the ore-forming process and ore-fluid physicochemical conditions. The Qingshuitang (0.426 Mt @ 3.65% Zn and 1.94% Pb) is a representative Pb–Zn deposit in the central Qinhang Ore Belt, and its mineralization comprises four stages, namely quartz-pyrite-arsenopyrite (I), quartz-galena-sphalerite (II), barite-galena-sphalerite (III), and calcite-galena-sphalerite (Ⅳ). Three generations of sphalerite were identified, namely Sp1 (Stage II), Sp2 (Stage III), and Sp3 (Stage IV).The mineralization temperature at Qingshuitang, as determined by the GGIMFis sphalerite geothermometer, is 82–204 °C (Sp1), 66–104 °C (Sp2), and 72–172 °C (Sp3), consistent with their high Ga/In (avg. 3461) but low In/Ge (<3.97) and Zn/Cd (avg. 199) ratio. These suggest that the Qingshuitang ore-forming fluid was low-temperature, with its average sulfur fugacity (fS2) evolving from Sp1(10–22.6 atm) to Sp2 (10–27.1 atm) and then to Sp3 (10–23.5 atm). Moreover, the decreasing median Mn content from Sp1 (4.86 ppm) to Sp2 (1.71 ppm) indicates an elevated oxygen fugacity (fO2) of the ore-forming fluids from Stage II to III, while the increasing median Mn content to Sp3 (2.78 ppm) reveals a subsequent fO2 drop. The low Fe–Mn–In–Co contents, low Zn/Cd (avg. 199), high Ge–Cd–Ga contents, and high Cd/Fe (avg. 1.39), Cd/Mn (721–7741), Ga/In (avg. 3469) and Ge/In (avg. 605) ratios in the Qingshuitang sphalerite resemble Mississippi Valley-type (MVT) sphalerite, but are markedly different from those in magmatic-related deposits (i.e., epithermal-, skarn-, and volcanogenic massive sulfide (VMS)-type). The Qingshuitang Pb–Zn deposit has distinct epigenetic characteristics, and similar low-temperature ore-fluids to those of MVT deposits. Therefore, we suggest that the Qingshuitang is a MVT deposit, and the physicochemical shift between Stage III and IV is probably associated with basinal brine incursion into the ore-fluids.

Groundwater Methane in Northeastern Pennsylvania Attributable to Thermogenic Sources and Hydrogeomorphologic Migration Pathways.

Conflicting evidence exists as to whether or not unconventional oil and gas (UOG) development has enhanced methane transport into groundwater aquifers over the past 15 years. In this study, recent groundwater samples were collected from 90 domestic wells and 4 springs in Northeastern Pennsylvania located above the Marcellus Shale after more than a decade of UOG development. No statistically significant correlations were observed between the groundwater methane level and various UOG geospatial metrics, including proximity to UOG wells and well violations, as well as the number of UOG wells and violations within particular radii. The δ13C and methane-to-higher chain hydrocarbon signatures suggested that the elevated methane levels were not attributable to UOG development nor could they be explained by using simple biogenic-thermogenic end-member mixing models. Instead, groundwater methane levels were significantly correlated with geochemical water type and topographical location. Comparing a subset of contemporary methane measurements to their co-located pre-drilling records (n = 64 at 49 distinct locations) did not indicate systematic increases in methane concentration but did reveal several cases of elevated concentration (n = 12) across a spectrum of topographies. Multiple lines of evidence suggested that the high-concentration groundwater methane could have originated from shallow thermogenic methane that migrated upward into groundwater aquifers with Appalachian Basin brine.

Factors affecting groundwater quality used for domestic supply in Marcellus Shale region of North-Central and North-East Pennsylvania, USA

Factors affecting groundwater quality used for domestic supply within the Marcellus Shale footprint in north-central and north-east Pennsylvania are identified using a combination of spatial, statistical, and geochemical modeling. Untreated groundwater, sampled during 2011–2017 from 472 domestic wells within the study area, exhibited wide ranges in pH (4.5–9.3), total dissolved solids (TDS, 22–1960 mg/L), sodium (0.3–760 mg/L), chloride (0.3–1020 mg/L), bromide (<0.01–8.6 mg/L), and methane (<0.001–77 mg/L). The wells had depths ranging from 10 to 394 m; 69.5 percent were completed in sandstone bedrock, 19.3 percent in shale, 4.2 percent in siltstone, 4 percent in carbonate, and 3 percent in unconsolidated alluvial or glacial deposits. Groundwater quality in the Delaware River watershed, in the eastern part of the study area where Marcellus gas has not been developed, was similar to that in the Susquehanna, Allegheny, and Genesee River watersheds in the western part of the study area where natural gas production from Marcellus Shale has been ongoing since 2008. Most groundwaters were calcium/bicarbonate type with near-neutral pH; approximately 10 percent were sodium/bicarbonate and 1 percent were sodium/chloride types. Sodium-enriched waters, which were mostly from shale and siltstone aquifers, had the greatest frequency of elevated pH (>8.5) and elevated concentrations of TDS (>250 mg/L), bromide (>0.15 mg/L), methane (>7.0 mg/L), and lithium (>60 μg/L). Geochemical models indicate these characteristics could result from progressive mineral dissolution combined with cation exchange, plus mixing with locally important salinity sources, including as much as 0.7 percent Appalachian Basin brine and/or road-deicing salt. Multivariate correlation models suggest the observed variability in methane concentrations may be attributed to several environmental factors, such as geochemical evolution along groundwater flow paths, redox conditions, and/or mixing with saline groundwater or brine. Most samples having elevated methane were from shale aquifers, which were mainly in the Susquehanna River basin and had the greatest density of gas wells compared to other lithologies. Samples having elevated methane were also observed in the Delaware River watershed and other areas outside gas development. Isotopic compositions of methane for a subset of 39 samples (selected because of elevated methane) and relatively high ratios of methane to ethane in those samples indicated methane could be derived from microbial gas mixed with thermogenic gas that may have undergone degradation and/or fractionation during migration. The methods used in this study could be broadly applicable to understanding major factors affecting groundwater quality, particularly for explaining variations in ionic composition with pH and identifying sources of salinity and associated constituents (e.g. sodium, chloride, bromide, lithium, methane) that may have geogenic or anthropogenic origins.

Rare earth elements geochemistry, O and S isotopic compositions, and microthermometric data of barite from the Kuh–Ghalagheh deposit, Markazi Province, Iran

The Kuh–Ghalagheh barite deposit is located 43 km southwest of the city of Mahallat in Markazi Province, Iran. The barite mineralization occurs as a stratabound, lenticular massive orebody in siliciclastic rocks of Eocene age. Barite is accompanied by calcite, Fe- and Mn-oxides, quartz, and minor malachite. The concentration of total REEs (∑REE) is very low in barite, ranging from 0.38 to 6.26 ppm. Chondrite-normalized REE patterns show enrichment of LREE relative to HREE, and dominantly negative La, Gd, and Ce anomalies. The δ18O and δ34S isotopic values of the barite samples fall within narrow ranges of +4.0 to +5.6‰ and +26.2 to +27.8‰, respectively, which do not match those of contemporaneous seawater (Eocene). This suggests that isotopically modified seawater sulfate is the source of oxygen and sulfur in barite. Three types of aqueous, aqueous–carbonic, and carbonic fluid inclusions were found in barite, suggesting that two immiscible fluids (aqueous and carbonic) were involved in the deposition of barite. Salinity values in the aqueous fluid inclusions ranged from 1.57 to 13.40 wt% NaCl equivalent. The aqueous–carbonic inclusions have salinity values ranging from 9.43 to 16.84 wt% NaCl equivalent. The salinity ranges of the aqueous and aqueous–carbonic inclusions show that two fluids have mixed, one with moderate salinity (>15 wt% NaCl equivalent) from basinal origin and a second with low salinity (<5 wt% NaCl equivalent) from seawater. The broad homogenization temperature ranges of 130–258 °C for aqueous and 118–290 °C for aqueous–carbonic inclusions do not represent the actual temperatures of the trapped fluids, but were generated by thermal re-equilibration of the inclusions due to deep burial of barite. The available data are consistent with a cold seeps model for barite formation in the Kuh–Ghalagheh deposit. The entry of Ba-rich basinal brines into the sedimentary basin resulted in the reaction of Ba with seawater sulfate, and the deposition of barite in siliciclastic sediments.

Hydrochemical impact of a mantle plume recorded by petrology, geochemistry, and U[sbnd]Pb geochronology of a calcite vein within the Ottawa-Bonnechere graben, Ontario, Canada

Petrology, geochemistry, fluid inclusions and UPb dating of a wide (30 cm) calcite vein in Upper Ordovician (Sandbian) limestone characterize a hydrochemical microcosm of changing fluid sources and carbon pathways related to burial, then uplift during the Phanerozoic along the Ottawa-Bonnechere graben, central Canada. UPb dating of the host limestone produces an age younger than its chronostratigraphic age suggesting the impact of diagenesis, otherwise well-defined petographically. An interred calcite fragment dated as Cambrian may highlight a platform source in this part of the graben hitherto unrecognized stratigraphically. The vein was initiated with extension across a high-angle narrow (2 cm) fault gouge allowing incursion of hot (80–125 °C) basin-derived (Mg, Ca)-Cl2 brine recorded by a saddle dolomite–dedolomite–calcite succession, not isotopically datable. Microbial methanogenesis occurred in initial narrow structural recesses giving way to recycled sedimentary bicarbonate with fracture widening. The oldest datable vein calcite (122 ± 5 Ma) consists of microcrystalline geopetal cumulates of vadose meteoric origin demarcating renewed carbonate formation following a period of near-surface alteration, dissolution, and microfracturing of the prior vein calcite during uplift. Initial 207Pb/206Pb ratios are consistent with average crust (0.819 ± 0.003), and δ18O signatures identify a meteoric signature similar to the host rock. Subsequent interlayering of isopachous calcite and pyrite, with an age of 105 ± 3 Ma for the calcite, defines onset of a meteoric phreatic environment. The role of microbial sulphate reduction is characterized isotopically. Initial 207Pb/206Pb ratios scatter below the crustal average (0.84–0.76) that, along with a meteoric δ18O signature, suggest incursion of a new fluid reservoir. A subsequent Sr, Mn, Ba-bearing–magnesium calcite marks the beginning of sustained phreatic meteoric dilution for the remaining vein history. Stable (C, O) isotopes document varying temperature and bicarbonate mixtures of sedimentary and bacterial (sulphate reduction) origins associated with a meteoric fluid. This calcite has a mean age of 94 ± 2 Ma and displays the widest range of initial 207Pb/206Pb ratios, which scatter down to 0.65. Stable and radiogenic isotopic compositions suggest a meteoric setting largely influenced by a crustal fluid reservoir of long residence time and-or transport resulting in leaching of radiogenic minerals. The final vein calcite, also of meteoric origin, has an 87Sr/86Sr ratio similar to that of the initial basin brine, yet with 13C signatures that characterize a source of oxidized methane. UTh series analysis delimits an age older than 0.5 Ma. This stage of vein calcite likely arises through meteoric fracking of Ordovician source rocks during continued basin inversion. In summary, initial brine influx followed by a shallow-crustal meteoric realm document structurally focused fluid migration with and following early Mesozoic graben exhumation. The phreatic meteoric regime of Early Cretaceous age spans a ~ 20 Ma period coincident with transient magmatism arising from near passage of the Great Meteor Hotspot. Regional paleohydrology appears to have been influenced for ~10 Ma after plume passage.