Electromagnetic signals associated with stick–slip of quartz-free rocks

We recorded clear transients in the electric and magnetic fields upon sudden slip in stick–slip experiments on dry, cylindrically shaped, quartz-free rock specimens of basalt and peridotite with a 30° saw-cut (representing a fault) at confining pressures of up to 120 MPa. The amplitudes of the measured electric field signals were always higher at the electrode pair oriented parallel to the strike of the fault than at the pair oriented perpendicular. This anisotropy suggests a preferred electric polarization normal to the slip surface. The transients in the electric and magnetic fields were observed only when the fault slip occurred by stick–slip mode, not by a stable mode of the sliding, and the amplitudes of the electric field signals increased with increasing stress drop. It is suggested that the generation process of the electromagnetic signals is closely related to the characteristic behavior of the fault at the time of the initiation of slip during stick–slip events, probably with respect to the intensity of the signals. We propose that one or both of the following two processes characteristic of the fault at the time of the initiation of slip during stick–slip events are essential for the generation of detectable electromagnetic signals: rapid slip along the simulated fault and separation of the rock masses across the fault.     

满洲里-新巴尔虎右旗斑岩系列矿床石英流体包裹体液相组分的PIXE分析和地质应用

ＰＩＸＥ（质子感应Ｘ射线分析）方法是目前国际上新的流体包裹体成分分析方法。在前人工作的基础上,尝试用ＰＩＸＥ方法分析了满洲里－新巴尔虎右旗斑岩系列多金属矿床石英流体包裹体的液相多元素化学组分,其结果反映了地质矿化规律。该方法对于多金属矿床石英流体包裹体成分研究非常有用。结合其他包裹体研究,提出甲乌拉与直干布拉根矿床流体组分和成矿物理化学条件均不同,初步认为不存在同一矿化中心;还提出了查干布拉根矿床西矿段深部可能存在乌奴格吐山式斑岩型Ｃｕ矿床,应引起注意。     

Development and installation of bedload monitoring systems with submerged load cells

Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain river. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of: (1) an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, (2) two submerged load cells 0.7 m apart, (3) a pressure sensor and, (4) an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute (DPRI) of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells. Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.     

Hedonic approaches based on spatial econometrics and spatial statistics: application to evaluation of project benefits

This study discusses the theoretical foundation of the application of spatial hedonic approaches—the hedonic approach employing spatial econometrics or/and spatial statistics—to benefits evaluation. The study highlights the limitations of the spatial econometrics approach since it uses a spatial weight matrix that is not employed by the spatial statistics approach. Further, the study presents empirical analyses by applying the Spatial Autoregressive Error Model (SAEM), which is based on the spatial econometrics approach, and the Spatial Process Model (SPM), which is based on the spatial statistics approach. SPMs are conducted based on both isotropy and anisotropy and applied to different mesh sizes. The empirical analysis reveals that the estimated benefits are quite different, especially between isotropic and anisotropic SPM and between isotropic SPM and SAEM; the estimated benefits are similar for SAEM and anisotropic SPM. The study demonstrates that the mesh size does not affect the estimated amount of benefits. Finally, the study provides a confidence interval for the estimated benefits and raises an issue with regard to benefit evaluation.     

Fractionation of sulfur isotopes and selenium between coexisting sulfide minerals from the Besshi deposit,Central Shikoku,Japan

Fractionation of sulfur isotopes and selenium was measured between coexisting pyrite and chalcopyrite and between coexisting pyrrhotite and chalcopyrite from the Besshi deposit of Kieslager-type, Central Shikoku, Japan. In all the pyrite-chalcopyrite pairs studied, ³⁴S is enriched in pyrite relative to chalcopyrite, while selenium is enriched conversely in chalcopyrite relative to pyrite. The mean ³⁴S_py-cp value is +0.53±0.36 per mil, and the mean value of the distribution coefficient of selenium, D_cp-py, is 2.58±0.64. In all the pyrrhotite-chalcopyrite pairs studied, the two minerals are very close to each other both in sulfur isotope and Se/S ratios. The mean ³⁴S_po-cp value is –0.08±0.16 per mil and the mean D_cp-po value is 0.99±0.05. The results have been discussed in comparison with similar data obtained for the Hitachi deposits of Kieslager-type, Japan (Yamamoto et al. 1983).     

Oxygen and Carbon Isotope Study of Calcite and Dolomite in the Disseminated Au-Ag Telluride Bulawan Deposit, Negros Island, Philippines

Abstract: The disseminated Au‐Ag telluride Bulawan deposit, Negros island, Philippines, is hosted by dacite porphyry breccia pipes which formed in a Middle Miocene dacite porphyry stock. Electrum and Au‐Ag tellurides occur mostly as grains intergrown with or filling voids between sphalerite, pyrite, chalcopyrite, galena and tennantite. Calcite, quartz and rare dolomite are the principal gangue minerals. Four types of alteration were recognized in the deposit, namely; propylitic, K‐feldspar‐sericitic, sericitic and carbonate alteration. Carbonate alteration is correlatable to the gold deposition stage and occurs mostly along fault zones. The δ¹⁸O and δ¹³C compositions of calcite and dolomite in propylite zone and ore‐stage dacite porphyry breccia were determined. The δ¹⁸O values of calcite in propylitized andesite range from +12.2 to +14.7%, and their δ¹³C values range from ‐6.1 to ‐1.0%. The δ¹⁸O values of calcite and dolomite in sericite‐ and carbonate‐altered, mineralized dacite porphyry breccia and dacite porphyry rocks range from +15.1 to +23.1%, and the δ¹³C values of calcite and dolomite range from ‐3.9 to +0.9%. The δ¹⁸O and δ¹³C values of the hydrothermal fluids were estimated from inferred temperatures of formation on the basis of fluid inclusion microthermometry. The δ¹⁸O values of hydrothermal fluid for the propylitic alteration were calculated to be +8.5 ‐ +9.5%, assuming 375°C. On the other hand, the δ¹⁸O values of ore solutions for base metal and Au mineralization were computed to be +13.6 ‐ +14.6%, assuming 270°C. The hydrothermal fluids that formed the Bulawan deposit are dilute and ¹⁸O‐enriched fluids which reacted with ¹⁸O‐ and ¹³C‐rich wallrocks such as limestone.     

Atmospheric gravity waves identified by ground-based observations of the intensity and rotational temperature of OH airglow

Spectroscopic observations of OH airglow undertaken on May 2, 2006 at Uji, Japan reveal variations in intensity and rotational temperature related to the passage of an atmospheric gravity wave. The variations exhibit a period of approximately 1 h and magnitudes of 2–6% in intensity and 0.5–2% in rotational temperature. The vertical wavelength and intrinsic frequency of the atmospheric gravity wave were determined from the horizontal wavelength derived by an OH airglow imager, the background horizontal wind velocity obtained by the middle and upper atmosphere (MU) radar, and the dispersion relationship. The observed variations are consistent with the values calculated using the model of Liu, A.Z., Swenson, G.R. [2003. A modeling study of O₂ and OH airglow perturbations induced by atmospheric gravity waves. J. Geophys. Res. 108 (No. D4), 4151. doi:10.1029/2002JD002474].     

The timing of ultrahigh-temperature metamorphism in Southern India: U–Th–Pb electron microprobe ages from zircon and monazite in sapphirine-bearing granulites

We report here U–Pb electron microprobe ages from zircon and monazite associated with corundum- and sapphirine-bearing granulite facies rocks of Lachmanapatti, Sengal, Sakkarakkottai and Mettanganam in the Palghat–Cauvery shear zone system and Ganguvarpatti in the northern Madurai Block of southern India. Mineral assemblages and petrologic characteristics of granulite facies assemblages in all these localities indicate extreme crustal metamorphism under ultrahigh-temperature (UHT) conditions. Zircon cores from Lachmanapatti range from 3200 to 2300 Ma with a peak at 2420 Ma, while those from Mettanganam show 2300 Ma peak. Younger zircons with peak ages of 2100 and 830 Ma are displayed by the UHT granulites of Sengal and Ganguvarpatti, although detrital grains with 2000 Ma ages are also present. The Late Archaean-aged cores are mantled by variable rims of Palaeo- to Mesoproterozoic ages in most cases. Zircon cores from Ganguvarpatti range from 2279 to 749 Ma and are interpreted to reflect multiple age sources. The oldest cores are surrounded by Palaeoproterozoic and Mesoproterozoic rims, and finally mantled by Neoproterozoic overgrowths. In contrast, monazites from these localities define peak ages of between 550 and 520 Ma, with an exception of a peak at 590 Ma for the Lachmanapatti rocks. The outermost rims of monazite grains show spot ages in the range of 510–450 Ma.While the zircon populations in these rocks suggest multiple sources of Archaean and Palaeoproterozoic age, the monazite data are interpreted to date the timing of ultrahigh-temperature metamorphism in southern India as latest Neoproterozoic to Cambrian in both the Palghat–Cauvery shear zone system and the northern Madurai Block. The data illustrate the extent of Neoproterozoic/Cambrian metamorphism as India joined the Gondwana amalgam at the dawn of the Cambrian.     

Characteristics of Triassic epithermal Au mineralization at the Q prospect,Chatree mining area,Central Thailand

The Chatree deposit is located in the Loei‐Phetchabun‐Nakhon Nayok volcanic belt that extends from Laos in the north through central and eastern Thailand into Cambodia. Gold‐bearing quartz veins at the Q prospect of the Chatree deposit are hosted within polymictic andesitic breccia and volcanic sedimentary breccia. The orebodies of the Chatree deposit consist of veins, veinlets and stockwork. Gold‐bearing quartz veins are composed mainly of quartz, calcite and illite with small amounts of adularia, chlorite and sulfide minerals. The gold‐bearing quartz veins were divided into five stages based on the cross‐cutting relationship and mineral assemblage. Intense gold mineralization occurred in Stages I and IV. The mineral assemblage of Stages I and IV is characterized by quartz–calcite–illite–laumontite–adularia–chlorite–sulfide minerals and electrum. Quartz textures of Stages I and IV are also characterized by microcrystalline and flamboyant textures, respectively. Coexistence of laumontite, illite and chlorite in the gold‐bearing quartz vein of Stage IV suggests that the gold‐bearing quartz veins were formed at approximately 200°C. The flamboyant and brecciated textures of the gold‐bearing quartz vein of Stage IV suggest that gold precipitated with silica minerals from a hydrothermal solution that was supersaturated by boiling. The δ¹⁸O values of quartz in Stages I to V range from +10.4 to +11.6‰ except for the δ¹⁸O value of quartz in Stage IV (+15.0‰). The increase in δ¹⁸O values of quartz at Stage IV is explained by boiling. P_H2O is estimated to be 16 bars at 200°C. The f_CO2 value is estimated to be 1 bar based on the presence of calcite in the mineral assemblage of Stage IV. The total pressure of the hydrothermal solution is approximately 20 bars at 200°C, suggesting that the gold‐bearing quartz veins of the Q prospect formed about 200 m below the paleosurface.