Huang Sijing

Saddle-Dolomite-Bearing Fracture Fillings and Records of Hot Brine Activity in the Jialingjiang Formation, Libixia Section, Hechuan Area of Chongqing City

Most vein minerals deposited in fractures of the Jialingjiang Formation from Libixia section, Hechan area include a large amount of saddle dolomite and accompanying celestite, calcite and fluorite. This study analyzed the nature, source, evolution of the fluids by plane-light petrography, fluid-inclusion methods, cathodoluminescence images, and stable isotopic compositions. The homogenization temperatures of two-phase aqueous fluid inclusions in dolomite range between 100 and 270°C. Combined with the δ18O data, it is suggested that the fluid responsible for the precipitation of fracture fillings have δ18O values between 10‰ and 18‰ (relative to SMOW). The saddle dolomite and the accompanying minerals were the result of activity of dense brines at elevated temperatures. Moreover, analysis shows that the fluid was derived from a mixture of marine-derived brine and deeper circulating flow. This fluid was enriched in Sr during diagenesis and formed celestite in fracture and for regional mineralization. Dissolution of saddle dolomite was attributed to the cooling of Mg/Ca-decreased fluids, which may relate to a leaching of gypsum to celestite in surrounding carbonates.

Global correlation for strontium isotope curve in the Late Cretaceous of Tibet and dating marine sediments

Abstract87Sr/86Sr ratios of marine carbonate samples collected from a sedimentary section of the Late Cretaceous in the south of Tibet were measured. Based on the absence of cathodo-luminescence and a very low Mn/Sr ratio (average 0.06) of the samples, it is thought that they contain information on the original seawater strontium isotope composition. The strontium isotope evolution curve of the Late Cretaceous in Tibet we established here, is consistent with other coeval curves from Europe, North America and Antarctica, supports the notion that the strontium isotope composition of seawater is governed by global events, which provides a new approach for the inter-continental and inter-basinal correlations of Late Cretaceous in the area and is a complementarity for biostratigraphy. In addition, we attempt to determine the age of the boundaries for Campanian/Santonian and Maastrichtian/Campanian by87Sr/86Sr ratios for Gamba section in southern Tibet. The two boundaries are located in the thickness of 217 m (83.5 Ma) and 291 m (71.3 Ma), respectively.

Geochemical characteristics of deep-seated potassium-rich brine in the Middle Triassic Leikoupo Formation, Sichuan, China

Brine extremely rich in potassium, boron and bromine has been discovered from the Middle Triassic Leikoupo Formation at a depth of 4300 m in Sichuan Province. It contains ∼50 g/L of K+, >92 g/L of Na+, >12 g/L of B2O3, >2.36 g/L of Br− and ∼0.030 g/L of I+. The solid precipitates during evaporation at 25°C include KB5O8·4H2O, K2B4O7·3H2O, MgCl2·6H2O and KMgCl3·6H2O. The brine ranges from 2.2‰ to 2.8‰ (SMOW) in δ18O, − 38‰ – − 53‰ (SMOW) in δD, 15.6‰ in δ34S, and 13.5‰–15.1‰ in δ11B. These data, particularly the isotopic composition of boron, indicate that the brine has a composite derivation from marine and nonmarine brines and dissolved marine evaporites in the Triassic system.