Search Results (7)

The Zhueryu Au deposit is one of the important quartz-vein type Au deposits. It is located at the western margin of the Jidong gold belt in China and characterized by ore bodies hosted in structural fractures within the Zhueryu syenite. The H, O, and S isotopes as well as the Rb–Sr isotope age of fluid inclusions from the quartz-polymetallic sulfide ore bodies (main stage) and the zircon U–Pb isotope age from the syenite were analyzed so as to discuss the source of ore-forming fluids and constrain the Au’s mineralization age. The textural characteristics of the fluid inclusions indicate that the fluid inclusions in the quartz (QzII) are from the same stage, with no evidence of secondary fluid inclusions from the later stage. Fluid inclusion microthermometry performed on the quartz (QzII) reveals a predominance of vapor–liquid two-phase inclusions, with homogenization temperatures ranging from 177 °C to 337 °C (average: 260 °C), characteristic of a medium-low temperature hydrothermal system. Furthermore, H, O, and S isotope analyses of the ore-forming fluids yielded δD, δ¹⁸O, and δ³⁴S values ranging from +12.8‰ to +14.8‰, +9.15‰ to +9.51‰, and −8.395‰ to -1.918‰ (average: −5.826‰), respectively. These isotopic signatures, particularly the distinctly positive δD values, strongly suggest that the Zhueryu ore-forming fluids were primarily derived from metamorphic sources, contrasting with the magmatic-hydrothermal fluids implicated in the formation of many other Au deposits within the Jidong belt. The LA–ICP–MS zircon U–Pb dating yielded a concordia age of 242 ± 2 Ma (MSWD = 0.17), indicating a Middle Triassic crystallization age for the Zhueryu syenite. In contrast, the Rb–Sr dating of primary fluid inclusions hosted within quartz (QzII) yielded an isochron age of 181 ± 12 Ma (MSWD = 2.5), placing the Au mineralization event firmly within the Early Jurassic. This demonstrates that the Au mineralization is significantly younger than the host syenite, representing a distinct mineralization event. These results might have certain significance for studying the dynamics of Au mineralization in the Jidong gold belt. Full article

The Kangjiawan Pb-Zn deposit, situated within the Shuikoushan polymetallic ore field in Changning, Hunan Province, China, is a large-scale Pb-Zn deposit unearthed in 1976. Based on detailed geological field investigations, this study presents the results of the Rb-Sr isotopic dating, electron probe microanalyses (EPMAs), and LA-ICP-MS analyses of the Kangjiawan Pb-Zn deposit in order to determine the ore-forming age and the occurrence of trace elements in sphalerite and thereby constrain the genesis of the deposit. The Rb-Sr dating of quartz-hosted fluid inclusions yielded an Rb-Sr isochron age of 150 ± 4 Ma, with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.71101 ± 0.00008 (MSWD = 1.1), suggesting that the Pb-Zn mineralization of the Kangjiawan deposit took place during the Late Jurassic, coeval with the magmatic activities within the ore field. EPMA and LA-ICP-MS analyses showed that Fe, Mn, and Cd were primarily incorporated into the sphalerite lattice through isomorphous substitution. Specifically, Fe and Mn substituted for Zn, whereas Cd replaced both Fe and Zn. Other elements such as Cu, Sb, and Sn occurred within the sphalerite lattice through mineral micro-inclusions or isomorphic substitution. EPMAs and LA-ICP-MS results showed that the FeS contents in sphalerite were less than 14.33%, with corresponding ore-forming temperatures below 259 °C. The LA-ICP-MS results showed that sphalerites from the Kangjiawan Pb-Zn deposit had relatively high Ga/In ratios ranging from 0.01 to 144, providing further support for medium-to-low-temperature mineralization. The trace element compositions of sphalerites from the Kangjiawan Pb-Zn deposit exhibit skarn-type characteristics, suggesting a potential association with contemporary magmatic activities within the Shuikoushan ore field. During the Late Jurassic, extensive granitic magmatic activities occurred in the study area. At the late stage of magma crystallization, hydrothermal fluid containing Pb and Zn precipitated at medium-to-low temperatures and generated the Kangjiawan Pb-Zn deposit. Full article

The Mississippi Valley-type (MVT) Pb-Zn deposits and hydrocarbon reservoirs coexist around the margin of the eastern Sichuan basin. This study examined the fluid inclusions, Sr isotope and systematic Rb-Sr, Sm-Nd geochronology for the distinct ore and gangue minerals of four orebodies from two MVT Pb-Zn deposits in the margin of the eastern Sichuan basin, combined with the existing research foundation of oil and gas accumulation and evolution, which was designed to understand the internal relationship between oil and gas accumulation and the involvement of organic matter in metal mineralization. High-density methane, moderate temperature, and salinity inclusions were discovered in the studied MVT Pb-Zn deposits, combined with relatively higher ⁸⁷Sr/⁸⁶Sr ratios (0.71088~0.714749), indicating that the ore-forming fluids were derived largely from the hydrocarbon associated basinal brines. Rb-Sr isochron of paragenetic sphalerites and pyrites and Sm-Nd isochron of paragenetic fluorites and calcite from the studied MVT Pb-Zn deposits define isochron ages of 144.5 Ma~138.5 Ma, and 147.6 Ma, respectively, indicating that the Late Jurassic to Early Cretaceous Yanshanian orogeny was an important metallogenic event in the margin of the eastern Sichuan basin. The close temporal and spatial relationship between the MVT mineralization and hydrocarbon accumulation and destruction in the strong structural deformation area of the margin of the eastern Sichuan basin allows us to propose a possible model in which the Yanshanian compressional tectonics drove a large-scale flow of metal- and sulfate- bearing basinal fluids passed under or through methane-bearing carbonate reservoirs, resulting in the MVT mineralization and hydrocarbon accumulation and destruction. Full article

Prominent veins of late Carboniferous barite, associated with fluorite and calcite, outcrop close to older granite plutons along an intracontinental shear zone that was active throughout the Carboniferous in southeastern Canada. Some barite is stratigraphically constrained to younger than 315 Ma and final mineralization is constrained by a published Rb–Sr isochron of 300 ± 6 Ma. Barite occurrences in the Carboniferous basins of central Nova Scotia, 50 km to the south, are synchronous with or post-date ankerite-siderite-magnetite-pyrolusite and Pb-Zn mineralization, which was facilitated by fluid interaction with thick evaporites. This study aims to determine controls on the distribution of barite in the shear zone, from field relationships, vein petrography and isotope geochemistry of minerals. The isotope chemistry of shear zone barite is similar to that occurring in Pb-Zn-Mn-Ba mineralization to the south, suggesting a common origin. Veins of barite, associated with fluorite, represent the youngest and regionally coolest phase of a 70 Ma history of Carboniferous mineralized veins along the Minas Fault Zone. Their prominence close to granite plutons reflects brittle deformation of the deeply-rooted granites in a complexly deforming fault zone, but the origin of abundant F remains uncertain. Full article

A combined ultrasonic treatment, with de-ionized H₂O, dilute HAc or dilute HCl, of three Mid-Miocene glauconite samples was applied to K–Ar date the different separates in order to compare the results with those obtained by the Rb–Sr method using the same three samples and that were analyzed strictly in the same way. Two aliquots yield opposite elemental and K–Ar trends, which suggests different initial mineral compositions for the various pellets. The K–Ar data of two untreated and leached L7 and L8 aliquots are almost within analytical uncertainty from 17.3 ± 0.6 Ma to 19.6 ± 0.7 Ma (2σ), while those of the third L10 sample are slightly higher at 22.1 ± 1.2 Ma (2σ). Comparatively, the earlier published Rb–Sr ages of the three untreated samples and of the leached aliquots gave similar data for the L7 aliquots by an isochron at 18.1 ± 3.1 (2σ) Ma and for the sample L8 by an isochron with an age of 19.6 ± 1.8 (2σ) Ma, while the untreated L10 aliquot yields a very high Rb–Sr date of 42.1 ± 1.6 (2σ) Ma. This untreated L10 glauconite fraction contains blödite, a Sr-rich carbonate that impacted the two isotopic systems differently. Generally, dilute HCl or HAc acids dissolve carbonates, sulfates, sulfites and oxides, while they do not affect the clay-type crystals such as glauconites. These soluble minerals can be identified indirectly, as here, by X-ray diffraction and the amounts of leached Na₂O, CaO and Fe₂O₃ contents. Together with the leaching of some metallic trace elements, those of NaO confirm the leaching of metals and of blödite that are both hosted by the glauconite pellets. The occurrence of this Sr-enriched mineral explains the age differences of the non-treated aliquots and suggests a systematic leaching of any glauconite separate before isotope determination and, possibly, a comparison of the Rb–Sr and K–Ar results. Ultrasonic shaking appears appropriate for physical disaggregation of any contaminating grains that may remain hosted within the pellets, even after a preliminary H₂O wash, which may dissolve and remove the soluble minerals but not the H₂O-insoluble silicates. The K–Ar study completed here as a complement to a previous Rb–Sr study highlights, again, the importance of the preparation step in isotopic studies of glauconite-type and, by extension, of any clay material, as all occurring minerals can interfere in the final age determinations and, therefore, differently in the mineral assemblages. All those not in isotopic equilibrium need to be removed before analysis, including the soluble Sr or alkali-enriched ones. Full article

The northern flank of the North China Craton (NCC) hosts a linear zone of gold, molybdenum, silver, lead, and zinc polymetallic ore deposits. Among these, the Yingfang Pb-Zn-Ag deposit is located in the central part of the Yanshan–Liaoxi metallogenic belt (YLMB) which extends for approximately 1000 km and forms part of the major mineralized zone. In this study, we characterize the mineralization and trace the ore genesis based on new sulfur and lead isotopic geochemistry and evaluate the timing of mineralization from Rb-Sr isotope dating of sulfides. The pyrite δ³⁴S values range from +3.2‰ to +5.8‰ with a mean at +4.07‰, close to the values of mantle and meteorite sulfur. The ²⁰⁶Pb/²⁰⁴Pb values range from 16.833 to 18.956, ²⁰⁷Pb/²⁰⁴Pb from 15.374 to 15.522, and ²⁰⁸Pb/²⁰⁴Pb from 37.448 to 37.928. Five samples of sulfide, from the Yingfang deposit, yield a Rb-Sr isochron age of 135.7 ± 4.1 Ma. This age is close to the age of the adjacent Niujuan Ag-Au deposit and the associated Er’daogou granite, suggesting a close relationship between magmatism and metallogeny in this region. The S and Pb isotopes of the regional silver polymetallic deposits show similar sources of ore-forming materials. According to a compilation of the available age data on the Mesozoic ore deposits in the northern flank of the NCC, we divide the mineralization into the following four periods: 240–205 Ma, 190–160 Ma, 155–135 Ma, and 135–100 Ma. Mesozoic magmatism and mineralization in the Yingfang deposit mainly took place at 245 Ma and 145–135 Ma. We correlate the Pb-Zn-Ag mineralization to metallogeny associated with large-scale inhomogeneous lithosphere thinning beneath the NCC. Full article

Direct dating of petroleum systems by hydrocarbon or associated authigenic minerals is crucial for petroleum system analysis and hydrocarbon exploration. The precipitation of authigenic pyrite in petroliferous basins is commonly genetically associated with hydrocarbon generation, migration, accumulation, or destruction. Pyrite rubidium-strontium (Rb-Sr) isotope dilution thermal ionization mass spectrometry (ID-TIMS) is a well-developed technique, and its successful application for high-temperature ore systems suggests that this dating method has the potential to directly date key processes in the low-temperature petroleum systems. Rb-Sr data for pyrites in two Ordovician carbonate rock specimens collected from ~4952 m in the YD-2 well in the Yudong region, northern Tarim Basin (NW China), yield two identical isochron ages within analytical uncertainties: 206 ± 13 (2σ) and 224 ± 28 Ma (2σ). SEM investigations demonstrate that Rb and Sr atoms mainly reside in the crystal lattice of the pyrites due to the absence of fluid and mineral inclusions. The rigorous Rb-Sr isochron relations documented in the samples indicate that such residency can result in sufficient Rb/Sr fractionation and initial Sr isotopic homogenization for geochronology. In addition, the closure temperature (227–320 °C) for the Rb-Sr isotope system in pyrite is higher than the precipitation temperature for pyrite in petroleum-related environments (below 200 °C), suggesting that the Rb-Sr age of pyrite was not overprinted by post-precipitation alteration. Integrating the lead-strontium-sulfur isotopes of the pyrites with burial history analysis, the ages are interpreted as the timing of alteration of the paleo-oil pool by a hydrothermally-triggered thermochemical sulfate reduction process. This study, for the first time, demonstrates that Rb-Sr pyrite geochronology, combined with radiogenic and stable isotopic analyses, can be a useful tool to evaluate the temporal evolution of oil pools. This approach bears great potential for dating of petroleum systems anywhere else in the world. Full article