The Wangu shear zone hosting gold deposit is located on splay faults of the regional scale Tanlu deep fault zone that extends to the MOHO and likely through the lithosphere. Fluid inclusions in pyrite from gold bearing veins have ³He/⁴He (R/Ra) values of 3.5 to 9.8. Fluid inclusions in pyrite from barren vein have R/Ra values of 0.8, and 0.9. The projections of the analyses in ³He/⁴He vs. ⁴⁰Ar/³⁶Ar diagram can be separated obviously as two groups and display the variable degrees of mixing between mantle and crustal fluids. Fluid inclusion in quartz from auriferous veins are characterized by a higher temperature (Th = 207 to 310°C), dilute, aqueous carbonic fluids, with δD and δ¹⁸O values overlapping the magmatic fluids, whereas barren veins have low temperature (Th = 138, 145°C), more saline, aqueous fluid with relatively low, light δD and δ¹⁸O values, consistent with evolved meteoric water. Lithosphere extension accompanied with displacement of the Tanlu sinistral fault, with development of gas and oil-bearing sedimentary basins proximal to the fault. The CO₂-bearing fluids have high He contents of up to 0.1% He, ³He/⁴He = (3∼7.2)R/Ra, ⁴⁰Ar/³⁶Ar = 573∼7744, and δ¹³C_CO2 = −3.4 to −16.9‰ (Xu et al., 1995; Tao et al., 1996). During the lithosphere extension and decompressional melting of asthenosphere, noble gases and CO₂ exsolved from basalt melts, advected up to the Tanlu fault zone into splay faults where gold mineralization developed, and through sedimentary basin. There was mixing with isotopically and compositionally evolved meteoric water.

View full abstract

To elucidate the source of an air-like component in fluid inclusions of xenoliths from the subcontinental mantle, we measured N, He and Ar elemental and isotopic composition in gases released by crushing from spinel-lherzolites of the Newer Volcanics, south-eastern Australia. Gas released from fluid inclusions in olivine separates shows δ¹⁵N ranging from −6.0 ± 1.2‰ to +2.0 ± 1.7‰. The range of measured δ¹⁵N values are in contrast with a remarkably uniform ³He/⁴He ratio of 10.1 ± 0.2 × 10^-6. The lightest δ¹⁵N value of −6.0 ± 1.2‰ is consistent with the measured MORB-like ³He/⁴He ratio of 10.1 ± 0.2 × 10^-6 and suggests that gases in xenoliths of southeast Australia are derived from a well-mixed upper mantle reservoir. The heavier nitrogen isotopic signatures (from ∼0 to +2‰) and elemental ratio of argon to nitrogen could be explained by the addition of 30% to 40% of a recycled sedimentary component. Nitrogen is indeed recycled more efficiently in the mantle than helium, preserving the trace of present or past subduction. The heavy N component has been observed in xenoliths from the eastern side of the Newer Volcanic province. Sedimentary nitrogen may result from subduction along the eastern margin of Australia, during Paleozoic time. The present nitrogen results, together with the relatively low ⁴⁰Ar/³⁶Ar ratios and apparently correlated ³He and ³⁶Ar contents in those xenoliths, suggest the long-term preservation of recycled surface volatiles in the continental lithospheric mantle.

View full abstract

The Xihuashan, Dangping and Piaotang deposits in the Jiangxi Province, south China can be considered as typical high-temperature hydrothermal quartz vein-type W-Sn mineralization, that is temporally and spatially related to Mesozoic S-type granite. Microthermometric studies of fluid inclusions in various minerals from these deposits were conducted to obtain homogenization temperature and salinity data. Major organic and inorganic aqueous components of the fluid inclusions were extracted by a crush-leaching, and concentrations of short-chain carboxylate (formate, acetate, propionate, oxalate), fluoride, chloride and sulfate anions in the leachates were determined using ion chromatography. The results indicate the presence of formate and acetate as well as minor amounts of oxalate and propionate in leachates, and the dominance of formate over other carboxylates. The molar ratio of acetate to formate appears to be a potential indicator of the redox state for the ore fluid system. Oxygen and hydrogen isotopic data show that inclusion water in quartz is mainly magmatic in origin. It is postulated that the dissolved carboxylate anions in the ore fluids for the deposits probably were generated by the breakdown of kerogen in “primitive sedimentary rocks” during the formation of S-type granites. The possibility of inorganic synthesis of the carboxylate species in a C-H-O system can not be excluded.

View full abstract

The objective of this study is to clarify the effect of photooxidation on δ¹³C of benzo(a)pyrene (BaP) and benzo(e)pyrene (BeP) in the atmosphere. They are structural isomers but are known to differ significantly in terms of photooxidation rate. The results of literature reviews and measurements revealed that the concentration ratio of BaP and BeP (BaP/BeP) is almost constant independent of the fuel type and emission source (almost constant at 2.1), while δ¹³C values for the two PAHs are almost equal. On the other hand, the results of ultraviolet irradiation experiments indicated that the concentration of BaP was reduced by photooxidation while δ¹³C of the remaining BaP increased due to isotopic fractionation. In contrast, BeP was not photooxidized and there was no change in δ¹³C. These results lead to the expectation that BaP/BeP and the difference in δ¹³C between BaP and BeP (δ¹³C_BaP – δ¹³C_BeP) would decrease and increase, respectively, from the corresponding values at the time of emissions (BaP/BeP: ∼2.1; δ¹³C_BaP – δ¹³C_BeP: ∼0) with the progress of photooxidation. This anticipated relationship was close to the results observed over Matsue, which is located on the Japan Sea coast, strongly suggesting there is a change in δ¹³C of BaP due to photooxidation. In addition, the observed results revealed that BaP/BeP and δ¹³C_BaP – δ¹³C_BeP levels during the winter, when photooxidation is less likely to occur compared to the summer, were similar to the levels during the summer. This supports the hypothesis that in winter, BaP emitted in the Asian continent was photooxidized during the long-range transport process before reaching the atmosphere over Matsue.

View full abstract

Participation of metallic iron in the processes of natural diamond formation has recently been suggested based on experimental studies, as well as the observation of native iron inclusions in natural diamond. The redox conditions of diamond-producing metal-carbon melts in the Earth's mantle are therefore of interest. We calculated the values of oxygen fugacity, corresponding to the equilibrium of Fe-C and Fe-Ni-C melts with wüstite and diamond at a pressure of 60 kbar. Diamond crystallization from Fe-Ni-C-O melts at usual P-T conditions of the catalytic diamond synthesis was shown experimentally. It was also shown that iron-carbon melts are stable at the values ranging from the stability filed of iron to that of wüstite. From metal-carbon melts either iron (iron-nickel) or wüstite can crystallize along with diamond, depending on the redox conditions. The stability of the metal-carbon melts is not limited to such reducing conditions as solid metals, and such conditions could have existed in the ancient Earth's mantle.

View full abstract

The Mitsuishi district, noted for the largest Roseki production in Japan, is generally characterized by the alteration zoning from center to margin; Quartz zone → Roseki ore (Pyrophyllite, Pyrophyllite-sericite and Sericite zones) → K-feldspar-sericite zone → Albite zone. They are overlain by Weakly propylitized zone. The filling temperatures of fluid inclusions in euhedral quartz crystals indicate the hydrothermal solution was about 300–350°C for the formation of Quartz zone. The chemical composition of the hydrothermal solution was estimated from salinity of the fluid inclusions, analytical results of altered rocks and minerals (feldspars and sericite), thermochemical calculations on the K-feldspar-albite and muscoviteparagonite solid solutions and equilibria in the Na₂O-K₂O-SiO₂-Al₂O₃-H₂O-HCl system, and mobility calculation on the water-rock interaction process. It is deduced that pH dramatically increased, while K and SiO₂ concentrations decreased, and Na concentration remained relatively constant in the hydrothermal solution from center to margin of the alteration zones.

View full abstract

The Jinding Pb-Zn deposit occurs in the Tertiary red sedimentary formation of the Cenozoic continental fault depression basin at Lanping, western Yunnan. The orebodies are stratiform and stratoid in form and giant in size, with the associated Sr and Cd being of high grade. In the past thirty years the source of lead in this deposit has been a long-standing controversial problem. Some scholars considered that lead came from the upper mantle while others shed doubt on that viewpoint. However, no conclusive evidence has been obtained to support their respective viewpoints, and to find a more definite answer to the above question. We have re-examined the lead isotopic composition of the Jinding Pb-Zn deposit. The lead isotopic ratios of the striped ore are ²⁰⁶Pb/²⁰⁴Pb = 18.138–18.552, ²⁰⁷Pb/²⁰⁴Pb = 15.345–15.552, and ²⁰⁸Pb/²⁰⁴Pb = 37.803–38.443, and the lead isotopic ratios of the massive ore are ²⁰⁶Pb/²⁰⁴Pb = 18.394–18.600, ²⁰⁷Pb/²⁰⁴Pb = 15.583–15.767, and ²⁰⁸Pb/²⁰⁴Pb = 38.266–39.046. In terms of the lead isotopic composition of minerals and whole rock samples from basic-ultrabasic rocks and alkaline rockbodies in the region of western Yunnan, we have determined the lead isotopic composition of the upper mantle in this region at Meso- and Cenozoic times, as ²⁰⁶Pb/²⁰⁴Pb = 17.850–18.350, ²⁰⁷Pb/²⁰⁴Pb = 15.430–15.540, and ²⁰⁸Pb/²⁰⁴Pb = 37.800–38.410. Then in the light of the lead isotopic composition of metamorphic rocks and sedimentary rocks from Precambrian to Tertiary, which are exposed in the Lanping Basin and its adjacent areas, we have determined the lead isotopic composition of the upper crust, as ²⁰⁶Pb/²⁰⁴Pb = 18.420–19.200, ²⁰⁷Pb/²⁰⁴Pb = 15.500–16.010, and ²⁰⁸Pb/²⁰⁴Pb = 38.450–39.500, and several mineral samples from granulite and eclogite xenoliths yielded the lead isotopic information of the lower crust, as ²⁰⁶Pb/²⁰⁴Pb = 18.135–18.187, ²⁰⁷Pb/²⁰⁴Pb = 15.335–15.388 and ²⁰⁸Pb/²⁰⁴Pb = 37.836–37.899. A comparison has been made with the lead isotopic composition of the ore, and it is indicated that lead in the Jinding Pb-Zn deposit was not derived from the upper mantle, and there are two sources of lead: one is the upper crust and the other is the lower crust.

View full abstract