Characteristics of the Cibaliung Gold Deposit: Miocene Low-Sulfidation-Type Epithermal Gold Deposit in Western Java, Indonesia     

Agung Harijoko    Yukiko Ohbuchi    Yoshinobu Motomura    Akira Imai  Koichiro Watanabe 《Resource Geology》2007,57(2):114-123

Middle Miocene (11.18–10.65 Ma) low sulfidation‐type epithermal gold mineralization occurred in the Cibaliung area, southwestern part of Java Island, Indonesia. It is hosted by andesitic to basaltic andesitic lavas of the Middle Miocene Honje Formation (11.4 Ma) and is covered by Pliocene Cibaliung tuff (4.9 Ma). The exploration estimates mineral resource of approximately 1.3 million tonnes at 10.42 g/t gold and 60.7 g/t silver at a 3 g/t Au cut‐off. This equates to approximately 435,000 ounces of gold and 2.54 million ounces of silver. That resource resulted from two ore shoots: Cibitung and Cikoneng. Studies on ore mineralogy, hydrothermal alteration, geology, fluid inclusion, stable isotopes and age dating were conducted in order to characterize the deposit and to understand a possible mechanism of preservation of the deposit. The ore mineral assemblage of the deposit consists of electrum, naumannite, Ag‐Se‐Te sulfide minerals, chalcopyrite, pyrite, sphalerite and galena. Those ore minerals occur in quartz veins showing colloform–crustiform texture. They are enveloped by mixed layer clay illite/smectite zone, which grades into smectite zone outward. The temperature of mineralization revealed by fluid inclusion study on quartz in the veins ranges from 170 and 220°C at shallow and deep level, respectively. The temperature range is in agreement with the temperature deduced from the hydrothermal alteration mineral assemblage including mixed layered illite/smectite and laumontite. The mineralizing fluid is dilute, with a salinity <1 wt% NaCl equivalent and has stable isotopes of oxygen and hydrogen composition indicating a meteoric water origin. Although the deposit is old enough that it would have been eroded in a tropical island arc setting, the coverage by younger volcanic deposits such as the Citeluk tuff and the Cibaliung tuff most probably prevented this erosion.  相似文献   

沙丘人工差不嘎蒿植被建立后的微气候变化     

李胜功  赵哈林  何宗颖  常学礼  原芳信 《中国沙漠》1997,17(2):133-137

运用文比热量平衡法和空气动力学梯度法初步分析了人工固定沙丘过程中的微气象变化。研究结果表明,随着流沙的固定,反射率减小;净辐射占太阳辐射的比例增大;热收支中,潜热通量所占的份额增多;近地表风速及其垂直切变减小。  相似文献   

Analysis of long‐term water balance in the source area of the Yellow River basin     

Yoshinobu Sato  Xieyao Ma  Jianqing Xu  Masayuki Matsuoka  Hongxing Zheng  Changming Liu  Yoshihiro Fukushima 《水文研究》2008,22(11):1618-1629

To analyse the long‐term water balance of the Yellow River basin, a new hydrological model was developed and applied to the source area of the basin. The analysis involved 41 years (1960–2000) of daily observation data from 16 meteorological stations. The model is composed of the following three sub‐models: a heat balance model, a runoff formation model and a river‐routing network model. To understand the heat and water balances more precisely, the original model was modified as follows. First, the land surface was classified into five types (bare, grassland, forest, irrigation area and water surface) using a high‐resolution land‐use map. Potential evaporation was then calculated using land‐surface temperatures estimated by the heat balance model. The maximum evapotranspiration of each land surface was calculated from potential evaporation using functions of the leaf area index (LAI). Finally, actual evapotranspiration was estimated by regulating the maximum evapotranspiration using functions of soil moisture content. The river discharge estimated by the model agreed well with the observed data in most years. However, relatively large errors, which may have been caused by the overestimation of surface flow, appeared in some summer periods. The rapid decrease of river discharge in recent years in the source area of the Yellow River basin depended primarily on the decrease in precipitation. Furthermore, the results suggested that the long‐term water balance in the source area of the Yellow River basin is influenced by land‐use changes. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Characteristics of Gold Mineralization at the Ciurug Vein, Pongkor Gold-Silver Deposit, West Java, Indonesia     

Syafrizal    Akira Imai    Yoshinobu Motomura  Koichiro Watanabe 《Resource Geology》2005,55(3):225-238

Abstract. The Pongkor Gold‐Silver Mine, Bogor district, West Java, is approximately 80 km southwest of Jakarta. The gold and silver mineralization in the area is present in a deposit consisting of an epithermal vein‐system named individually as the Pasir Jawa, Gudang Handak, Ciguha, Pamoyanan, Kubang Cicau, and Ciurug veins. In the area studied, rocks of basaltic‐andesitic composition are dominated by volcanic breccia and lapilli tuff, with andesite lava and siltstone present locally. The hydrothermal alteration minerals in the Ciurug area are typical of those formed from acid to near‐neutral pH thermal waters, where the acid alteration is distributed from the surface to shallow depth, while the near‐neutral pH alteration becomes dominant at depths. The Ciurug vein shows four main mineralization stages where each discrete stage is characterized by a specific facies; these are, from early to late: carbonate‐quartz, manganese carbonate‐quartz, banded‐massive quartz and gray sulfide‐quartz facies. The major metallic minerals are pyrite, sphalerite, chalcopyrite and galena; they occur in almost each mineralization stage. Bornite was observed only in the southern part of the Ciurug vein at a depth of 515 m, and the occurrence of this mineral is reported here for the first time. Electrum and silver sulfides (mostly acanthite) are minor, whereas silver sulfosalts, stromeyerite and mckinstryite, and covellite are in trace amounts. The silver sulfosalts have compositional ranges of pearceite, antimon‐pearceite and polybasite. Most of the electrum occurs coexisting with other sulfide minerals, as inclusions in pyrite grains, with very little as inclusions in chalcopyrite or sphalerite. Gold grades within the Ciurug vein vary from 1.2 to hundreds of ppm, where the highest gold grade occurs in the latest mineralization stage in a thin sulfide band in vein quartz. Fluid inclusion microthermometry of calcite and quartz indicates deposition throughout the mineralized veins in the range from 170 to 230d?C and from low salinity fluids (predominantly lower than 0.2 wt% NaCl equiv.). Fluid inclusions occur with features of boiling.  相似文献   

Gold-bearing Quartz Veins and Hydrothermal Alteration of the Paleozoic Epithermal System in the Francis Creek Area, North Queensland, Australia     

Agung Harijoko    Koichiro Watanabe    Yoshinobu Motomura  Eiji Izawa 《Resource Geology》2002,52(4):353-358

Abstract. The Francis Creek area located at the Sybil graben in North Queensland, Australia, has some features of epithermal gold mineralization such as gold-bearing quartz vein and silica body hosted in rhyodacitic rocks of the Late Carboniferous Hells Gate Formation. In order to understand the nature of the paleo-hydrothermal activity in this area and to aid exploration for an economic gold deposit in this area, we carried out hydrothermal alteration mapping surrounding the veins and silica body, over an area of about 7 times 5 km².
We defined two alteration zones and inferred the center of hydrothermal activity. Fluid inclusion shows the boiling feature, and the microthermometry analysis resulted in the trapping temperature of 240°C and low salinity. This temperature is consistent with the formation temperature of clay mineral in the host rocks. On the basis of whole-rock composition, the silica body was identified as silicified rocks. Precious metal minerals such as electrum and acanthite coexist with sulfide minerals. Iodagylite was identified as a product of weathering. The sulfide minerals imply that the low-sulfidation epithermal gold mineralization occurred in the Francis Creek area.  相似文献   

Tsunami ascending in rivers as an undular bore     

Yoshinobu Tsuji  Takashi Yanuma  Isao Murata  Chizuru Fujiwara 《Natural Hazards》1991,4(2-3):257-266

At time of the 1983 Japan Sea tsunami, waves in the form of a bore ascended many rivers. In some cases, bores had the form of one initial wave with a train of smaller waves, and in other cases, such a wave train did not appear and only a step with a flat water surface behind was observed. In the present study, it is clarified that both undular-type and nonundular-type bores can be recognized as solutions of the KdV-Burger's equation which was introduced by Johnson in 1972. Numerically obtained analytical solutions and results of laboratory experiments are compared.  相似文献   

Damage to coastal villages due to the 1992 Flores Island earthquake tsunami     

Yoshinobu Tsuji  Hideo Matsutomi  Fumihiko Imamura  Minoru Takeo  Yoshiaki Kawata  Masafumi Matsuyama  Tomoyuki Takahashi  Sunarjo  Prih Harjadi 《Pure and Applied Geophysics》1995,144(3-4):481-524

A field survey of the 1992 Flores Island earthquake tsunami was conducted during December 29, 1992 to January 5, 1993 along the north coast of the eastern part of Flores Island. We visited over 40 villages, measured tsunami heights, and interviewed the inhabitants. It was clarified that the first wave attacked the coast within five minutes at most of the surveyed villages. The crust was uplifted west of the Cape of Batumanuk, and subsided east of it. In the residential area of Wuring, which is located on a sand spit with ground height of 2 meters, most wooden houses built on stilts collapsed and 87 people were killed even though the tsunami height reached only 3.2 meters. In the two villages on Babi Island, the tsunami swept away all wooden houses and killed 263 of 1,093 inhabitants. Tsunami height at Riang-Kroko village on the northeastern end of Flores Island reached 26.2 meters and 137 of the 406 inhabitants were killed by the tsumani. Evidence of landslides was detected at a few points on the coast of Hading Bay, and the huge tsunami was probably formed by earthquake-induced landslides. The relationship between tsunami height and mortality was checked for seven villages. The efficiencies of trees arranged in front of coastal villages, and coral reefs in dissipating the tsunami energy are discussed.  相似文献   

Frequency-wavenumber spectra of equatorial waves detected from satellite altimeter data     

Yoshinobu Wakata 《Journal of Oceanography》2007,63(3):483-490

The sea surface height anomaly in the Pacific equatorial area was separated into equatorial modes using satellite altimeter data. The power-spectral density (PSD) was obtained for the east-west wavenumber and frequency for each separated mode. The PSD distribution was compared with the theoretical dispersion curve for the equatorial modes derived by Matsuno (1966). The first Rossby modes have a high-density distribution that is slightly lower than the theoretical dispersion curve, but the Kelvin mode and the higher Rossby modes have high-density distribution that almost matches each dispersion curve. Results of analyses of satellite observational data show that wave motion near the equator mainly shows characteristics of equatorial waves, especially for a intraseasonal time scale.  相似文献   

Variability of the Sea Surface Salinity (SSS) in the Western Tropical Pacific: On the Ability of an OGCM to Simulate the SSS, and on the Sampling of an Operating Merchant Ship SSS Network     

Mansour Ioualalen  Yoshinobu Wakata  Yoshikazu Kawahara  Yves Gouriou  David Varillon 《Journal of Oceanography》2003,59(1):105-111

The sea surface salinity (SSS) derived from a network developed at Institut de Recherche pour le Développement (IRD/Nouméa) has been analyzed during the period 1995–1998 in the tropical western Pacific. The measurements were made with thermosalinographs installed on merchant ships selected for their regularity and routes. The western tropical Pacific was sampled mainly along three regular routes across the equator leading to an average of a one month frequency. We analyze here how such a network can be efficient in monitoring the SSS at time scales longer than one month. For this purpose we have used results derived from the Princeton Ocean Model (POM) which is forced by the surface flux of National Centers for Environmental Prediction (NCEP) reanalysis data. The interannual variability of the simulated SSS exhibits very similar features to (sub-sampled) observations despite its being weakly damped to a climatology in order to avoid biases. Even smaller time scale phenomena can be simulated, like the erosion/reconstruction of the region composed of low density waters lying within the Pacific warm pool. The agreement between the observational data and the simulations indicate that the network sampling is sufficient to monitor the SSS variability of the western tropical Pacific from three-month to interannual time scales. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Kelvin Waves Excited by Intraseasonal Wind Forcing     

Yoshinobu Wakata 《Journal of Oceanography》2001,57(6):693-707

The Kelvin wave excited by an intraseasonal wind forcing with a 40-day period over the western Pacific Ocean was simulated using an ocean general circulation model, and was investigated by the use of spectral analysis. The amplitude of the temperature has two peaks north and south of the equator at the depth of the thermocline, and the amplitude of zonal velocity also has two peaks on the equator above and below the thermocline. The phase shows the upward propagation of the wave. It was queried why this wave, which appears to be transient rather than modelike, is formed quickly and always propagates with a phase velocity of about 3 m/s. The vertical one-dimensional forcing problem was studied, where the external forcing of up and down motions moving eastward is imposed at the surface. The growth time is estimated from the resonant solution. The first mode can resonate quickly, but the second cannot. The response in the infinitely deep ocean was also studied to focus on the transiency, where the reflection from the bottom is inhibited. The wave response to the forcing with a speed of about 3 m/s has a large amplitude, i.e. quasi-resonance occurs. In this case, the thermocline plays the role of a reflector, and the upper ocean between the sea surface and the thermocline behaves as a duct. Here, the small resonant cavity explains why the wave is formed so quickly, and the special value of the wave velocity is interpreted as a resonance condition in the duct. The wave corresponding to the second baroclinic mode could not be excited easily by the short-lived forcing at the surface, since this mode is mainly structured under the thermocline. It was found that the wave damps in consequence of leaking energy downward, and the damping rate depends on the period of the wave. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献