bluuebunny/crossref_metadata_2025 huggingface dataset:
Gold Mineralization and Occurrence of Sinter in the Hoshino Area, Fukuoka Prefecture, Japan
Authors: Belhadi Ahmed , Nakanishi Tetsuya , Watanabe Koichiro , Izawa Eiji
Published: November 2008

Abstract. Several epithermal gold deposits occur in the Hoshino area, which is located in the western end of the late Cenozoic Hohi volcanic zone, north‐central Kyushu, Japan. The area is characterized by intermediate to felsic extrusive rocks of Pliocene age. In the Hoshino area, the shallow manifestation of the hydrothermal activity is exposed on the surface. Several outcrops of sinter are still preserved on the top of hydro thermally altered volcanic rocks, and high‐grade gold‐bearing quartz veins occur on the surface at lower levels. The hydrothermal alteration resulted into well‐developed alteration zones. The zonal alteration pattern, primarily of near‐neutral pH type, is characterized by the outer smectite zone of a lower temperature, and the inner mixed layer minerals zone of a higher temperature. Quartz vein‐related or fracture‐controlled alteration, is represented by the occurrence of interstratified illite/smectite and K‐feldspar, suggesting a potassium‐enriched alteration.

The mineralization in the Hoshino area is recognized on the surface by the occurrence of gold‐bearing quartz veins distributed mainly in the mixed layer minerals zone. The fracture system related to the gold mineralization is mainly characterized by NW‐SE trend. The alteration pattern and the mineralogical composition of the veins suggest that the mineralizing fluids had near‐neutral pH and the mineralization is of low‐sulfidation‐type. Fluid inclusion data and textures observed in quartz veins indicate that gold precipitated during boiling. The chemical composition of quartz veins shows that high‐grade gold‐bearing quartz veins are characterized by higher content of Al2O3, K2O and Rb.

Several outcrops of silica‐sinters are distributed on the top of the mixed layer minerals zone. Although their structures are not very well preserved, because of later silicification, the Hoshino sinters still show characteristic textures identical to those observed in modern sinters, such as the presence of plant fossil incorporated into the sinters, the strongly developed depositional laminations and the columnar structures perpendicular to the depositional surfaces. Quartz is the only silica mineral constituting the Hoshino sinters presently. The conversion of amorphous silica into quartz was probably governed by higher temperatures resulting from later hydrothermal activity. This later hydrothermal activity is reflected by the intense silicification affecting mainly the lower parts of the sinters and also by the presence of quartz veins cutting the sinters. The distribution of sinters in the Hoshino area is very significant. The presence beneath the sinters of concealed high‐grade gold‐bearing quartz veins should be highly considered and exploration work is strongly suggested.
Mineral Paragenesis and Fluid Inclusions of Some Pluton‐hosted Vein‐type Copper Deposits in the Coastal Cordillera, Northern Chile
Authors: Trista Dania , Kojima Shoji
Published: November 2008

Abstract. Formation conditions of some vein‐type copper deposits of the Tocopilla district (Deseada, San Jose, Santa Rosa) and the Gatico district (Yohanita, Toldo‐Velarde, Argentina) in the Coastal Cordillera of northern Chile were inferred from mineral paragenesis and fluid inclusion data, and were compared with those of neighboring stratiform copper deposits. The vein‐type copper deposits are hosted in Late Jurassic dioritic to quartz‐dioritic plutons intruding extensively an andesite‐dominant volcanic pile of the Jurassic La Negra Formation. Primary mineralization is characterized by chalcopyrite + magnetite + pyrite + bornite, and supergene alteration of these minerals produced anilite, covellite, atacamite and chrysocolla. The hypogene mineral assemblage indicates relatively high sulfur fugacity and weakly oxidized conditions, distinct from the stratiform copper deposits formed under low sulfur fugacity and moderately oxidized conditions. Furthermore, the fluid inclusion data of the vein‐type deposits indicate high temperature (401–560d̀C) and high salinity (39–68 wt% NaCl equiv.) ranges in contrast to the stratiform deposits, suggesting that this type of deposits formed by magma‐associated hypersaline ore fluids.
Paleoceanography and Heavy Metal Enrichment of Mudstones in the Green Tuff Region, Northeastern Japan
Authors: Komuro Kosei , Kajiwara Yoshimichi
Published: November 2008

Abstract. A series of mudstones corresponding to N.8 to N.17 of Blow from the Uyashinai Mudstone Member, the Onnagawa Formation and the Funakawa Formation in the Taiheizan area of the central Green Tuff region, northeast Japan, was examined by chemical analysis. According to conventional chemical systematics, the mudstones are analyzed in terms of detrital, biogenic‐A (siliceous), biogenic‐B (calcareous) and hydrogenous components. The relative contribution of the biogenic‐A (siliceous) component increases in upward succession in the Uyashinai and Onnagawa mudstones, whereas the contribution of the biogenic‐B (calcareous) component is restricted to the lower Uyashinai mudstones. The contribution of hydrogenous components Zn, Pb, Cu and Ba tends to increase during the Nishikurosawa stage, and decreases near the Nishikurosawa/Onnagawa boundary (Pb and Ba) or in the Onnagawa stage (Zn and Cu). The observed enrichment of heavy metals in the Uyashinai mudstones is attributed to the onset of vigorous upwelling of deep water with higher nutrient and metal content associated with a contemporaneous change in global deep‐water circulation.
Near‐infrared and Visible Light Microthermometry of Fluid Inclusions in Sphalerite from a Possible Southeast Extension of the Toyoha Polymetallic Deposit, Japan
Authors: Shimizu Toru , Aoki Masahiro , Kabashima Taro
Published: November 2008

Abstract. Near‐infrared (NIR) and visible light microthermometry was applied to the fluid inclusions in sphalerite from a possible southeast extension of the Toyoha polymetallic deposit. Sphalerite occurs as euhedral‐subhedral crystals or collo‐form aggregates with a variety of color, which contain a well‐developed growth banding. Combined with morphological observations, fluid inclusions in dark‐colored sphalerite were examined using a near‐infrared light microscopic technique, whereas those in light‐colored sphalerite and quartz were examined by a conventional visible light microscopy.

Salinities of fluid inclusions in dark‐colored sphalerite have a wide variation (1.0–10.3 wt % NaCl equiv.) compared to that in light‐colored sphalerite and quartz (0.0–3.4 wt % NaCl equiv.). These variations suggest that the conventional microthermometric data from light‐colored sphalerite and quartz were inadequate to interpret the ore formation process. Dark‐colored colloform sphalerite and a dark core of subhedral sphalerite formed from high‐salinity fluids (6.5–10.3 wt % NaCl equiv.) under highly supersaturated conditions with respect to sphalerite.

The NIR and visible light microthermometry of fluid inclusions in sphalerite combined with its morphological observations is an invaluable method to infer the formation conditions of sphalerite. The NIR and visible light microthermometry is useful to reveal how the nature of ore fluids changed with time.
Geochemical Features of Vein Anhydrite from the Kakkonda Geothermal System, Northeast Japan
Authors: Sasaki Munetake , Fujimoto Koichiro , Tsukamoto Hitoshi , Sawaki Takayuki , Sasada Masakatsu , Kurosawa Masanori , Yagi Masahiko , Muramatsu Yoichi , Kato Osamu , Komatsu Ryo , Kasai Kaichiro , Doi Nobuo
Published: November 2008

Abstract. Cathodoluminescence (CL) color, rare earth element (REE) content, sulfur and oxygen isotopes and fluid inclusions of anhydrite, which frequently filled in hydrothermal veins in the Kakkonda geothermal system, were investigated to elucidate the spatial, temporal and genetical evolution of fluids in the deep reservoir. The anhydrite samples studied are classified into four types based on CL colors and REE contents: type‐N (no color), type‐G (green color), type‐T (tan color) and type‐S (tan color with a high REE content). In the shallow reservoir, only type‐N anhydrite is observed. In the deep reservoir, type‐G anhydrite occurs in vertical veins whereas type‐T and ‐N in lateral veins. Type‐S anhydrite occurs in the heat‐source Kakkonda Granite. The CL textures revealed that type‐G anhydrite deposited earlier than type‐T in the deep reservoir, implying that fracture system was changed from predominantly vertical to lateral.

Studies of fluid inclusions and δ34S and δ18O values of the samples indicate that type‐N anhydrite deposited from diluted fluids derived from meteoric water, whereas type‐G, ‐T and ‐S anhydrites deposited from magmatic brines derived from the Kakkonda Granite with the exception of some of type‐G with recrystallization texture and no primary fluid inclusion, which deposited from fossil seawater preserved in the sedimentary rocks. Type‐G, ‐T and ‐S anhydrites exhibit remarkably different chondrite‐normalized REE patterns with a positive Eu anomaly, with a convex shape (peak at Sm or Eu) and with a negative Eu anomaly, respectively. The difference in the patterns might result from the different extent of hydrothermal alteration of the reservoir rocks and contribution of the magmatic fluids.
Mineralogical and Genetical Aspects of the Doyashiki Kuroko Deposits, Hokuroku Basin, Japan
Authors: Kitazono Satoshi , Ueno Hirotomo
Published: November 2008

Abstract. A detail investigation of ore and gangue minerals was performed on the Doyashiki Kuroko deposits, Hokuroku basin, Japan for the first time. Main ore minerals are sphalerite, galena, pyrite, chalcopyrite, tetrahedrite‐tennantite and digen‐ite. Small amounts of enargite, wittichenite, electrum, covellite, bornite, marcasite and hematite are also observed. Quartz, barite and gypsum are common gangue minerals. Homogenization temperatures and salinities of fluid inclusions in quartz, sphalerite and barite range from 190 to 240d̀C and 3.0 to 5.5 wt% NaCl equivalent, respectively. The FeS contents of sphalerite and Ag contents of electrum were 0.12 to 0.18 mol %, 39.0 to 39.6 atom %, respectively. The chemical composition of digenite as a primary mineral shows high sulfur contents.

These data indicate that ore fluid responsible for digenite and associated ore minerals was characterized by a range of high sulfur fugacity with a moderate formation temperature. This is concordant with the mineral assemblage of bornite‐pyrite and chalcopyrite, which shows high sulfur fugacity conditions. It seems that the mineralization closely associated with acidic volcanism has occurred around 13 Ma of Middle Miocene on the seafloor at the depth of about 1500 m.
Experiments on the Element Distribution between the Granodiorite JG‐1a and 2M NaCl Hydrothermal Solution at Temperatures of 300 to 800°C and a Pressure of 1 kb
Authors: Uchida Etsuo , Haitani Takuro , Suetsugu Takayuki , Kashima Takahiro , Tsutsui Ken
Published: November 2008

Abstract. The distribution of Na, K, Ca, Mg, Mn and Fe between the granodiorite JG‐la, one of the geochemical standard rocks, and 2M NaCl aqueous solution was experimentally determined at temperatures of 300 to 800d̀C and a pressure of 1 kb using standard cold seal‐type pressure vessels. The solid run products melted partially at 800d̀C. Only K shows a significantly different behavior from the experiments using the basalt JB‐la (Uchida and Tsutsui, 2000) due to the presence of ortho‐clase in the JG‐la. The transition elements tend to be preferably partitioned into the aqueous chloride solutions with increasing temperature. At 800d̀C and 1 kb, the Fe concentration of the aqueous chloride solutions reached up to 5,000 ppm, and the Mn concentration up to 350 ppm. The distribution coefficient, KD, i = Ci, sol/Ci, rock, is in the order of Na>K>Mn>Ca> Fe>Mg at 300d̀C, but changed in the order of Mn>N>K>Fe>Ca>Mg at 800d̀C. The distribution coefficients of the divalent cations for the JG‐la are higher than those for the JB‐1a. The distribution coefficient of the transition elements, Fe and Mn, increases significantly with increasing temperature. The thermodynamic analysis for aqueous speciation revealed that this is attributable to the formation of the tri‐chloro complexes of the transition elements at higher temperatures.
Mineralization Characteristics and Structural Controls of Hydrothermal Deposits in the Gyeongsang Basin, South Korea
Authors: Koh Sang‐Mo , Ryoo Chung‐Ryul , Song Min‐Sub
Published: November 2008

Abstract. Hydrothermal deposits in the Gyeongsang Basin show the genetic relationship with igneous activity from Late Cretaceous to Early Tertiary in the spatial and temporal viewpoints. Many hydrothermal Au‐Ag‐Cu‐Pb‐Zn and clay deposits are dominantly distributed within the Gyeongsang Basin. The Gyeongsang Basin is divided into seven metallogenic provinces by spatial distribution. The age ranges of igneous activity and mineralization are 140∼40 Ma and 100∼40 Ma, respectively, and the most dominant age ranges of the both activities are from 90 Ma (Coniacian) to 50 Ma (Eocene). The age consistency between igneous activity and mineralization suggests that this age range is the climactic period of the hydrothermal activity of the Gyeongsang Basin. The metallogenic epochs in the Gyeongsang Basin are divided into three epochs of 100∼80 Ma (western part of the Gyeongsang Basin), 80∼60 Ma (central part of the Gyeongsang Basin), and 60∼40 Ma (eastern part of the Gyeongsang Basin). The mineralization and igneous activity tend to become young eastward in the Gyeongsang Basin.

NNW‐SSE mineralized veins from 100 to 80 Ma in the western part of the Gyeongsang Basin are interpreted as the control of the parallel tensional fissures caused by NNW‐SSE compressional stress. NW‐SE mineralized veins from 80 to 60 Ma in the central part of the Gyeongsang Basin seem to have been formed under the same stress as that of the Gaeum and Yangsan Fault Systems. Namely, NW‐SE tensional stress is associated with a conjugate set of fracturing of the WNW‐ESE Gaeum Fault System and NNE‐SSW Yangsan Fault System. Also NE‐SW mineralized veins from 60 to 40 Ma in the eastern part of the Gyeongsang Basin seem to be controlled by the NE‐SW fractures. The fractures are related with NE‐SW compressional stress and are developed as secondary fractures within the dextral strike slip Yangsan Fault System.
Fluorite Deposits at Voznesenka in the Khanka Massif, Russia: Geology and Age of Mineralization
Authors: Sato Kohei , Suzuki Kazuhiro , Nedachi Munetomo , Terashima Shigeru , Ryazantseva Margarita D. , Vrublevsky Anatoly A. , Khanchuk Alexander I.
Published: November 2008

Abstract. A huge fluorite deposit at Voznesenka in the Khanka massif, Far East Russia is concluded to have formed at ca. 450 Ma in Late Ordovician time based on the K‐Ar ages for Li‐micas in the fluorite ore and greisenized leucogranite within the deposit. This conclusion is inconsistent with the current view of Devonian mineralization that stemmed from widely scattered whole‐rock Rb‐Sr isotope data for the heterogeneous leucogranite stocks influenced by strong alteration. The Voznesenka and neighboring fluorite deposits may have formed in Cambrian limestone in relation to the intrusion of the Li‐F‐rich felsic magma which has a similar chemistry to representative Li‐F‐rich felsic rocks including topaz granite and ongonite or topaz rhyolite; these rocks may be classified as a specific group of highly fractionated felsic magmas.

Biotite granite plutons exposed in the Voznesenka district are divided in age into two groups based on the CHIME age data for zircon, monazite and xenotime: Ordovician and Permian. The Ordovician plutons seem to be coeval to the fluorite deposits and are characterized by F‐rich chemistry, reduced nature and association of tin mineralization with the deposition of fluorite and tourmaline. The biotite granite magmas of initially enhanced F contents could have been highly fractionated to form Li‐F‐rich leucogranite cupolas that provided fluorite deposits within the host limestone. Future prospecting for similar fluorite deposits is to be focused on areas of intersection between Ordovician Li‐F‐rich granite and Cambrian carbonate sequences.

The Permian granite of southeastern margin of the Grodekovo batholith is characterized by lesser F content, oxidized nature and the lack of tin and fluorite mineralization in contrast to the Ordovician granite. The result of Permian age does not support the current view of Silurian age for the batholith and requires overall chronological reinvestigation in connection with the tectonic history of the Khanka massif because the Grodekovo is a representative of Paleozoic batholiths in Primorie.
40Ar‐39Ar Spectra of Alunite from Phreatic Craters in the Muine Volcano, Hokkaido, Japan
Authors: Watanabe Yasushi
Published: November 2008

Abstract. 40Ar‐39Ar analyses of two alunite samples from phreatic craters in the Pliocene Muine volcano in southwest Hokkaido, Japan, were carried out. The alunite with 17.4 permil δ34SV_CDT value in hydrothermal breccia from the Nagaoyama crater and that with 14.3 permil δ34SV_CDT value in silicified andesite from the Konuma crater give total fusion ages of 1.40 ± 0.04 Ma (la uncertainty) and 1.24 ± 0.08 Ma, respectively. However, the spectra of these samples indicate they have been effected by thermal overprinting and/or the existence of excess argon. These preliminary 40Ar‐39A analyses suggest that the alunite underwent multiple hydrothermal activity by magmatic gas and vapor subsequent to the main hydrothermal activity.
Carbonatitic Volcanic Genesis of Hetaoqing Fe‐Cu Deposit in Central Yunnan, China
Authors: Zhang Yongbei , Sun Shihua , Xu Chengyan , Wang Hao , Zhao Chongsun , Zhu Zhihua
Published: November 2008

Abstract. The Kunyang rift on western margin of Yangtze Platform is a continental rift, and also a rare Precambrian Fe‐Cu mineralization zone in China. The Wuding‐Lufeng mineralization area in the middle section of the rift is an important part of the zone, and an elliptic‐shaped volcanic collapsed basin, controlled by a ring fracture system with carbonatitic volcanic rocks mainly occurring along the northwestern edge of the basin. The Hetaoqing Fe‐Cu ore deposit at the western side of the basin is hosted in carbonatitic volcanic rocks and pyroclastic sedimentary rocks. The original ore bodies occur as layers, bands and lenses conformable to the host carbonatitic rocks. The ores usually appear as massive, impregnated and granular in carbonatitic rocks, and as brecciform and sandy in pyroclastic sedimentary rocks. Ore‐forming minerals are magnetite, hematite, chalcopy‐rite, bornite, pyrite, carrollite, molybdenite, cobaltite and skinnerite, and secondary minerals limonite, chalcocite, azurite, malachite and tenorite. Gangue minerals are calcite, dolomite, ankerite, common hornblende, arfvedsonite, augite, aegirine‐augite, albite, phlogopite, biotite, chlorite and apatite. Evidences of mineral chemistry, trace elements and isotopic ratios of ores, as well as geological features, suggest that the original ores are igneous in origin. Chemical features of magnetites in the deposit belong to carbonatite type, and are similar to those from the Bayan Obo carbonatites. The ores are rich in iron, titanium, rare earth elements, niobium, tantalum, gold, silver, phosphor and sulfur. These features indicate that the Fe‐Cu deposit associated with volcanic activity in the Wuding‐Lufeng basin is alkali‐carbonatite volcanic type.
Geochemical Characteristics of Granitoids of the Erdenet Porphyry Copper Deposit, Mongolia
Authors: Morozumi Haruhisa
Published: November 2008

Abstract. The Erdenet porphyry copper deposit is one of the major mineral deposits in Mongolia. The geochemical data of granitoids acquired for the Erdenet and its surrounding areas are re‐examined. The granitoids of the Erdenet deposit with hypogene type mineralization show the lowest TiO2 content. Although Ti was possibly lost through the pyritization, it is also possible that the hypogene type mineralization occurred accompanied with the most differentiated granitoids. The variation of the element contents related to the mineralization of the Erdenet deposit shows the decrease of MgO and CaO contents, rather constant K2O content, rather constant to decrease of Na2O content, with respect to the Cu contents. The rather constant Na2O in the mineralized zone is owing to the residual albite against the sericitic alteration. The granitoids of the Erdenet area show an increase of Na2O content and a decrease of K2O content with an increase of SiO2 content. This trend makes clear contrast to granitoids in the surrounding areas. The granitoids of the Erdenet area might have the adakitic nature based on the Sr and Y contents.
Preface
Authors: Matsumoto Ryo
Published: November 2008

Editorial Board for the Special Issue on “Gas Hydrate in Nankai Trough, Japan”

Takashi Uchida (JAPEX Research Center, Japan Petroleum Exploration Co., Ltd.), Amane Waseda (JAPEX Research Center, Japan Petroleum Exploration Co., Ltd.), Naotatsu Shikazono (Department of Applied Chemistry, Keio University), Yutaka Aoki (JGI Inc.) and Yoshihiro Tsuji (Technology Research Center, Japan Oil,

Gas and Metals National Corporation)
BSRs and Associated Reflections as an Indicator of Gas Hydrate and Free Gas Accumulation: An Example of Accretionary Prism and Forearc Basin System along the Nankai Trough, off Central Japan
Authors: Baba Kei , Yamada Yasuhiro
Published: November 2008

Abstract. Multi‐channel seismic data obtained from the Nankai accretionary prism and forearc basin system has been studied to elucidate the migration and accumulation process of gas to the BGHS and examine the distribution pattern of BSRs and characteristic reflections associated with them.

BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins (33,000 km2) and 90 % of them have migration and recycling origins. The widest distribution of the BSRs can be seen at the prism. A correlation between the BSR distributions and prism size shows that the BSRs tend to be more well‐developed in a prism of large size. This suggests that a large prism may produce much amount of gas‐bearing fluids that migrate to the BGHS and form the BSRs (tectonic control), hi the forearc basins, the BSRs are identified at topographic highs, anticlines and basin margins (structural control).

The upward migration of gas‐bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low‐permeable mud facies (time control).

Those results imply that structural, tectonic, sedimentary and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area.
Lithology, Biostratigraphy, and Magneto stratigraphy of Gas Hydrate‐Bearing Sediments in the Eastern Nankai Trough
Authors: Hiroki Yoshihisa , Watanabe Kazue , Matsumoto Ryo
Published: November 2008

Abstract: Stratigraphic controls on the formation and distribution of gas hydrates were examined for sediments from a BH‐1 well drilled in the landward slope of the Nankai Trough, approximately 60 km off Omaezaki, Japan. Three lithologic units were recognized in the 250 m‐thick sequence of sediments: Unit 1 (0–70 mbsf) consists of calcareous silt and clay with thin volcanic ash layers, Unit 2 (70–150 mbsf) consists of calcareous silt and clay with volcanic ash and thin sand layers, and Unit 3 (150–250 mbsf) consists of weakly consolidated calcareous silt and clay with thick and frequent sand layers. Soupy structures and gas bubbles in the sediments indicate the presence of two hydrate zones between 40 and 130 mbsf and below 195 mbsf. Nannofossil biostratigraphy and magnetostratigraphy indicate that the sequence recovered at the BH‐1 well is mostly continuous and represents sediments deposited from 0 to 1.5 Ma. Calculation of the sedimentation rate reveals a condensed section between 65 and 90 mbsf. The inferred distribution of gas hydrates in the BH‐1 well appears to be strongly controlled by the stratigraphy and lithology of the sediments. Thick, gently inclined sand layers in Unit 3 provide a conduit for the migration of gases from deeper regions, and are considered responsible for the formation of the hydrate zone below 195 mbsf. At shallower levels, thin, gently inclined sand layers are also considered to allow for the migration of gases, leading to the formation of the upper hydrate zone between 40 and 130 mbsf. The overlying sub‐horizontal silt and clay of the condensed section, truncating the underlying gently inclined sand and silt/clay layers, may provide an effective trap for gases supplied through the sand layers, further contributing to hydrate formation in the upper hydrate zone.
Occurrence of Free‐Gas Associated with Methane‐Hydrate‐Bearing Formations in the MITI Nankai Trough Wells, Offshore Tokai, Japan
Authors: Takayama Tokujiro , Nishi Masatoshi , Yamamoto Hiroaki , Sanada Yoshinori , Matsuda Shigemi , Uchida Takashi
Published: November 2008

Abstract. The MITI Nankai Trough wells were drilled for exploration of methane‐hydrate‐bearing sediments in association with seismic inferred bottom simulating reflectors (BSRs). In this project, log data showed low velocity compressional‐wave (P‐wave) layers below methane‐hydrate‐bearing formations. Dipole shear sonic acoustic tools (DSI) could not acquire accurate compres‐sional velocity in this zone, thus it was not possible to accurately correlate between logging, VSP and surface seismic profiles.

Small amount of gas was presumed to cause the problem in obtaining the low velocity P‐wave data. VSP interval velocity data was used to assess the DSI inferred low‐velocity layer, which showed lower values than the velocity of the drilling muds. Synthetic seismogram was created by VSP‐compensated velocity to compare against corridor stack of VSP. As a result, the depths above and below the methane‐hydrate‐bearing interval were correlated with synthetic seismograms and reflectivity events on the VSP profiles. By using this correlation technique, distribution of methane‐hydrate‐bearing formations and free‐gas‐bearing formations can be determined.
Application of AVO Analysis to Seismic Data for Detection of Gas below Methane Hydrate Stability Zone in Nankai Trough Area
Authors: Hato Masami , Inamori Takao , Bahar Alfian , Matsuoka Toshifumi
Published: November 2008

Abstract. For the purpose of development of methane hydrate, occurring in the deep marine subsurface, as a resource, the most important issue is to understand the methane hydrate system (generation, migration and accumulation) as well as to delineate the methane hydrate reservoir properties. We have applied the Amplitude Versus Offset (AVO) analysis to the seismic data acquired in the Nankai Trough, offshore Japan, in order to confirm the occurrence of gas just below the methane hydrate‐bearing zone, assuming that gas will show a so‐called Class‐3 AVO response. Knowledge of the amount and occurrence of gas in the sediment below methane hydrate‐bearing zone is one of the keys to understand the methane hydrate system.

We have utilized the qualitative analysis of AVO methodology to delineate how gas is located below the BSR, which is thought to be the reflection event from the interface between the methane hydrate‐bearing zone and the underlying gas‐bearing zone. In the region of MITI Nankai Trough Well PSW‐3, we observe two BSRs separated by 25 ms. After AVO modeling using well data, we applied AVO attribute analysis and attribute crossplot analysis to the seismic data. Finally we applied an offset‐amplitude analysis to CMP gather data at specific locations to confirm the results of AVO attribute analysis. The AVO analysis shows that there is very little gas located in the underlying sediment below methane hydrate‐bearing zone. This result supports the fact that we could not obtain any clear evidence of gas occurrence just below the methane hydrate‐bearing zone in the Nankai Trough well drilling.
High Resolution, Deep‐Tow Seismic Survey to Investigate the Methane Hydrate Stability Zone in the Nankai Trough
Authors: Ward Peter , Asakawa Eiichi , Shimizu Shoshiro
Published: November 2008

Abstract. A high frequency deep‐tow seismic survey was carried out in the Nankai Trough area in 1996. The objective of the survey was to obtain high resolution seismic sections and velocity profiles of the methane hydrate zone, inferred from the strong BSR events seen on conventional seismic data in the area. A special feature of the survey is that both the source and the streamer cable are towed close to the seabed. This special acquisition geometry requires special data processing to handle the varying source and receiver depths. A CMP floating datum processing sequence was designed which led to high quality sections of the shallow geology. A key step in the processing was devising a residual statics technique to compensate for errors in the measured depths.

The processing sequence was applied to a number of lines, totaling 200 km. The final data quality was highly variable. Some lines produced high quality sections and others, much poorer sections with few interpretable events. Conventional seismic data in the area also shows variation in the data quality so part of the reason is a variation in the sub‐sea geology, but the deep‐tow data is much more sensitive to change in conditions than conventional data. With the current acquired data and processing sequence the deep‐tow system offers most advantages when 1) the water depth is around 1 km or greater, 2) the seabed and underlying geology is not too complex, and 3) the acquisition proceeds smoothly with regular shotpoints, slowly varying depths, and with accurate positioning.
Application of a Simulation Model for the Formation of Methane Hydrate to the Nankai Trough and the Blake Ridge: Natural Examples of Two End‐member Cases
Authors: Baba Kei , Katoh Arata
Published: November 2008

Abstract. Simulation experiments with a one‐dimensional static model for formation of methane hydrate are used to demonstrate models of hydrate occurrence and its generation mechanism for two end‐member cases. The simulation results compare well with experimental data for two natural examples (the Nankai Trough and the Blake Ridge).

At the MITI Nankai Trough wells, the hydrate occurrence is characterized by strongly hydrated sediments developing just above the BGHS. Such occurrence can be reproduced well by simulation in which the end‐member case of upward advective fluid flow from below the BGHS is set. The strongly hydrated sediments is formed by oversaturated solution with free gas which directly enters the BGHS by the upward advective fluid flow. The recycling of dissociated methane of preexisting hydrate also contributes to the increase of hydrate saturation.

At the Site 997 in the Blake Ridge area, the hydrate occurrence is characterized by thick zone with poorly hydrated sediments and no hydrate zone developing above the hydrate zone. Such occurrence can be reproduced well by simulation in which the end‐member case of in‐situ biogenic production of methane in the sediment of methane hydrate zone is set. The distribution pattern of hydrate saturation is basically controlled by that of TOC. However, the hydrate concentration near the bottom of the hydrate zone is increased by the effect of recycling of dissociated methane of pre‐existing hydrate. No hydrate zone expresses the geologic time needed until the local concentration of methane exceeds the solubility by gradual accumulation of in‐situ biogenic methane with burial.
Oxygen Isotopic Characteristics of Granitic Intrusions Related to Haobugao Zn‐Pb‐Cu‐Sn Skarn Deposit, East Inner Mongolia, China
Authors: Wang Jingbin , Wang Lijuan , Wang Yuwang , Li Tiejun , Shimazaki Hidehiko
Published: November 2008

Abstract. Granitic rocks related to the formation of Haobugao Zn‐Pb‐Cu‐Sn skarn deposit, Inner Mongolia, China, show unusual low whole‐rock δ18O values down to ‐8.8 % (V‐SMOW), whereas separated quartz crystals from those rocks give positive δ18O values of+4.1 to +9.9 %. Chemical analyses and microscopic observation of those granitic rocks confirm that they suffered hydrothermal alteration. Some skarn specimens and quartz from the Haobugao deposit also show negative δ18O values. The isotopic evidence indicates that intensive meteoric water circulation occurred at the time of granitic intrusion, and caused the pervasive hydrothermal alteration of granitic rocks and the precipitation of skarn deposit in this area.
Petrographic Discrimination of Low‐ and High‐Temperature I‐type Granites
Authors: White Allan J. R. , Chappell Bruce W.
Published: November 2008

Abstract. The existence of two groups of I‐type granites, those formed at relatively low‐ and high‐temperatures, has been established using differences in zircon saturation and patterns of bulk compositional variation between those two groups. Granites of these two groups also show some distinctive petrographic differences. The clearest petrographic distinction between the low‐ and high‐temperature granites is seen in the crystals of plagioclase. In all but the most felsic low‐temperature granites these crystals are always complex and commonly have corroded cores, which may be as calcic as An80. Core compositions are fairly uniform in composition compared with the outer parts, which display normal and oscillatory zones of varying widths. In the high‐temperature granites the crystals of plagioclase are generally better‐shaped with a uniform composition and lack the prominent corroded cores of the low‐temperature granites. These differences are due to the fact that homogenization of plagioclase proceeds very slowly at low magmatic temperatures.
Gold Deposits in Beishan Mountain, Northwestern China
Authors: Jiang Si‐Hong , Nie Feng‐Jun , Lie Yan
Published: November 2008

Abstract. The Beishan Mountain spans three provinces ‐ Gansu, Xinjiang and Inner Mongolia, having an area of 120,000 km2 Tectonically, it transverses three different tectonic units, i.e. Siberia, Kazakhstan and Tarim plates, and is composed of nine ter‐rains with widely exposed Precambrian and Paleozoic strata, complex structures, intensive magmatic activities and widespread ore deposits. It is not only a main part of Tianshan‐Yinshan‐Great Hinggan metallogenic belt in China, but also a key to under‐stand the evolution of central‐Asian orogenic system.

At present, more than 100 gold deposits and prospects have been discovered, explored and mined, among which Nanjinshan, Mazhuangshan, Liushashan, Jinwozi, Zhaobishan and Xiaoxigong are the most important ones. Based on the host rocks and the geological features, all these gold occurrences can be subdivided into three groups (or types): (1) hosted by Carboniferous or Permian volcanic or subvolcanic rocks; (2) hosted by or related to plutonic intrusions; and (3) hosted by Precambrian metamorphic rocks. The first group includes the Mazhuangshan gold deposit, which occurs in Hercynian quartz por‐phyry and rhyolite porphyry as gold‐bearing quartz veins. The second group is composed of the Liushashan, Nanjinshan Zhaobishan and Jinwozi gold deposits. Gold mineralization at these four deposits occurs within Hercynian granitoids intrusion: or late Paleozoic sedimentary rocks as quartz veins, veinlets and altered rocks. The Xiaoxigong gold deposit belongs to the third group, and is hosted by Precambrian schist, amphibolite and migmatite as quartz veins and altered rocks.

Isotopic age dating data, geological and geochemical evidence suggest that most of the groups 1 and 2 gold deposits were generated during the emplacement of the Hercynian or partly Indosinian intrusions. These intrusions may provide both heat and metals for groups 1 and 2 deposits. In contrast, although the formation is closely related to the Hercynian magma‐tism, the ore‐forming materials of the group 3 deposits may not only come from the intrusions, but also from the Precambrian metamorphic rocks.
Magma Mingling/mixing vs. Magmatic Fractionation: Geneses of the Shirakawa Mo‐mineralized Granitoids, Central Japan
Authors: Ishihara Shunso , Tani Kenichiro
Published: November 2008

Abstract. Leucocratic biotite granites are main components in the Hatogaya pluton and the Hirase stock in the Shirakawa region of central Japan. Molybdenite‐quartz vein mineralizations are widespread in and around the Hatogaya pluton and the Hirase stock, in which the largest is vein swarm of the Hirase mine. Mafic enclaves occur abundantly with granitic to granodi‐oritic matrix in the northern part of the Hatogaya pluton, while they are rare in the Hirase granitic stock. The enclaves with generally round shape have mostly diabasic to fine plutonic textures under the microscope, and show interfingering and lobate contacts with the felsic matrix. The enclaves are quartz monzodiorite in composition containing SiO>2 mostly around 60 %. They have felsic blebs, thus are considered a mingled magma of basaltic compositions originated in depth and a felsic magma generated from the Hida metamorphic‐plutonic complexes or their basement.

The mingled magma further mixed with and reacted with the felsic magma with SiO2 70 %, and then formed granodiorite‐granite of the high Na group (Na2O higher than 4.25 %). Thus, compositional variation of the northern part of the Hatogaya pluton was caused by the magma mingling. The mingling happened to be deeper level produced homogeneous granodiorite of the Mihoro pluton. Biotite granite of the low Na group (less than 4.25 %) could have originated in a granitic magma generated also from the Hida metamorphic‐plutonic complexes or their basement. Most of the granites, occurring in the southern part of the Hatogaya pluton and Hirase stock, show high Rb/Sr ratio, strong Eu negative anomalies and flat REE patterns, and are thus considered as fractionated products of the SiO2 70 % original magma. The strong concentration of molybdenum in the Hirase stock can be explained by high degree of magmatic fractionation which produced MoS2‐rich residual melts, suitable fractures developed at the latest Cretaceous time, and preservation of the mineralized fractures at the present level of erosion.
Kuroko and Hydrocarbon Deposits from Northern Honshu, Japan: A Possible Common Hydrothermal/Magmatic Origin?
Authors: Glasby Geoffrey P. , Yamanaka Toshiro , Yamamoto Junji , Sato Hiroshi , Notsu Kenji
Published: November 2008

Abstract. Northern Honshu is the most important area for mineral and oil resources in Japan. Many kuroko deposits and oil and gas fields are distributed in two belts along the northeast Japan arc, the kuroko metal‐belt on the Pacific side and the oil‐belt on the Sea of Japan side. The kuroko deposits are located mainly in the Green Tuff strata which formed as a result of submarine vol‐canism during the late Miocene and Pliocene. Most of the source rocks of the oil and gas deposits formed at the same time as the kuroko deposits and some of them are located in reservoirs of hydrothermally‐altered volcanic rocks in the Green Tuff region. There is general agreement that the kuroko deposits formed as a result of submarine hydrothermal and magmatic activity whereas almost all petroleum geologists and geochemists consider that hydrocarbon deposits were generated independently of such activity. Since the discovery of hydrothermally‐generated petroleum in the Guaymas Basin, Gulf of California, however, it is clear that petroleum can be formed almost instantaneously in terrestrial and submarine hydrothermal areas. The paleo‐northeastern Sea of Japan is therefore considered to be a potential area for hydrothermal petroleum generation because thick organic‐rich sediments overlie an active submarine volcanic area. Several lines of geological and geochemical evidence suggest the possibility of hydrothermally‐enhanced maturation of organic matter and the contribution of magmatic activity to the formation of these deposits. Although most of the oil and gas in northern Honshu has been generated conventionally as a consequence of the high geothermal gradients there, it appears that some of the oil and gas fields may have formed as a result of extensive hydrothermal and magmatic activity during the late Miocene to Pliocene. Because of the much steeper angle of the faults in the vicinity of the Hokuroku basin than in the Akita basin, the magmatic contribution to the kuroko mineralization would have been far greater than to the oil and gas deposits of the Niigata and Akita basins. We therefore propose a strong relationship between metal and oil and gas generation in northern Honshu based on the structure and tectonics of the northern Honshu arc‐backarc system.
Polymetallic Mineralization at the Suttsu Vein‐type Deposit, Southwestern Hokkaido, Japan
Authors: Ono Shuji , Hirai Koji , Matsueda Hiroharu , Kabashima Taro
Published: November 2008

Abstract. The Suttsu polymetallic vein‐type deposit, hosted by tuff, tuff breccia and shale of the Miocene Kunnui Formation and propylitized hornblende‐augite andesite, is located in southwestern Hokkaido, Japan. It has been exploited and explored for Cu, Pb, Zn and Ag until 1962.

In this study, we examined K‐Ar ages, ore mineralogical characteristics and fluid inclusions to obtain new data for the deposit.

The K‐Ar ages on sericite indicate that the polymetallic mineralization occurred in Late Miocene (8.1–5.7 Ma). The polymetallic banded ore from the Ohkubo vein is characterized by an abundance of Au, Ag, Sn, Bi, in, Se and Te. These metals are mainly ascribed to electrum (30.3–37.8 atom% Ag), Se‐bearing pavonite (8.5–9.5 wt% Se), gustavite‐lillianite solid solution, Se‐bearing bismuthinite (5.0–5.3 wt% Se), kawazulite, cassiterite, Sn‐bearing chalcopyrite (3.3–4.2 wt% Sn), In‐bearing stannite, stannite‐chalcopyrite solid solution, and In‐ and Sn‐bearing sphalerite (2.6–8.4 wt% In and 1.8–4.3 wt% Sn), occurring in narrow bands of the ore. The In‐ and Sn‐bearing sphalerite likely forms a sphalerite‐roquesite‐stannite solid solution with the contents of roquesite and stannite being about 2–9 and 2‐A mole%, respectively. Temperatures and salinities (in wt% NaCl equiv.) of the ore fluids are estimated to be 180d̀‐250d̀C and 3–4 wt%, respectively. The Sn‐bearing chalcopyrite therefore probably precipitated metastably. The geologic and mineralogical features suggest that pre‐Tertiary basement rocks rich in organic material underlie the Miocene Kunnui Formation nearby the deposit and that they contributed to local and temporary reduction of magnetite‐series magmas favorable for the early stage tin‐polymetallic mineralization.
Laumontization and Secondary Pores of Sandstones in the Paleogene and Upper Cretaceous Coal Measures, off Northeast Honshu, Japan
Authors: Yanagimoto Yutaka , Iijima Azuma
Published: November 2008

Abstract. Sandstones with high reservoir quality occur in the Paleogene and Upper Cretaceous coal measures off Sanriku and Sohma in the Pacific coast of northeast Honshu. The sandstone porosity was generally produced by the dissolution of calcite cement and clastic grains such as feldspar and glassy volcanics. The most probable cause of dissolution is the organic acids generated from the maturation of coal and coaly matter in the deeply subsiding source area prior to thermogenic hydrocarbon generation. The pore fluid including organic acids dissolved calcite and clastic silicates to form a small amount of laumontite and kaolinite at around 60d̀C. The acidic and not neutralized pore fluid was responsible for the formation of kaoli‐nite. On the other hand, laumontite was formed when the acidic pore fluid was neutralized and then made alkaline after the reaction with minerals such as plagioclase, glassy volcanics and calcite cement. Therefore, laumontite and kaolinite generally occur separately. Laumontite is 0.6–4.6 % by volume, whereas kaolinite is 0.6–9.8 % and the sandstone porosity remains from 10 to 22 %. This type of laumontization after the secondary pore formation might not give a severe damage to the reservoir property of the Paleogene and Upper Cretaceous coal measures in the Pacific coast of northeast Honshu and indicates further exploration possibility.
Magmatic Fluid Inclusions from the Zaldivar Deposit, Northern Chile: The Role of Early Metal‐bearing Fluids in a Porphyry Copper System
Authors: Campos Eduardo A. , Touret Jacques L. R. , Nikogosian Igor
Published: November 2008

Abstract. The occurrence of a distinct type of multi‐solid, highly‐saline fluid inclusions, hosted in igneous quartz phe‐nocrysts from the Llamo porphyry, in the Zaldivar porphyry copper deposit of northern Chile is documented. Total homoge‐nization of the multi‐solid type inclusions occurs at magmatic temperatures (over 750d̀C), well above the typical temperatures of hydro thermal fluids (less than 600d̀C) usually recorded in porphyry copper systems. The analysis of this type of fluid inclusions, using a combination of non‐destructive microthermometry, Raman and PIXE techniques and the identification of daughter minerals by SEM method, indicates that the trapped fluid was a dense, complex chloride brine in which Cl, Na, K, Fe, Cu, and Mn are dominant. The high chlorine and metal contents indicate that the metals were separated from the crystallizing magma as homogeneous aqueous chloride‐rich solutions that represent the primary magmatic fluids exsolved at high temperatures and depth during the crystallization of the parental intrusive.

The multi‐solid type inclusion illustrates the mechanism by which ore components are sequestered from the crystallizing parental magma and concentrated in the exsolved magmatic aqueous fluids. These fluids are significant with respect to the origin of porphyry copper deposits, as they are responsible for the first enrichment of metals and represent the precursors of metal‐bearing hydrothermal fluids in a porphyry copper system.
Factors Controlling the Hydrothermal Sulphur Ore Deposition in Keciborlu Mine Area (SW Turkey)
Authors: Ozguner Abdullah Mete
Published: November 2008

Abstract. Replacement‐type subsurface sulphur ores of Keciborlu are situated in fault controlled and metasomatically altered fragmental ophiolite media between alkaline Pliocene volcanics of Isparta and Afyon regions, SW Turkey. Subsurface volcanic sulphur‐mineralising fluids and gases were brought up along the sulphur‐hosting oblique slip fault zone into the oxidising meteoric water‐saturated media and the sulphur‐ore bodies were developed at more porous, cross‐fault locations.

Chemically the sulphotaric alteration of the parent rock and sulphur ore formation is characterised by outward volcanic gas and sulphuric acid leaching and oxidation to sulphur from the crushed porous centres. Consequently, concentric pyritiferous, opaline and argillaceous zones developed adjacent to the sulphur ores. The inner alteration zones progressed and widened toward the outer zones through time and the central sulphur ore developed during a single, continuous phase of mineralisation in the water saturation zone such that the alteration zones do not cross each other.