bluuebunny/crossref_metadata_2025 huggingface dataset:
Spessartine Garnets in a Manganiferous Carbonate Formation from Nsuta, Ghana
Authors: Nyame Frank K. , Kase Katsuo , Yamamoto Masahiro
Published: November 2008

Abstract: Manganese carbonate ore beds and host rock manganiferous phyllites at the Nsuta mine, western Ghana, contain well developed garnet crystals. Individual crystals are idioblastic, sometimes porphyroblastic, and homogeneous, and are associated with rhodochrosite (with or without kutnahorite), quartz and muscovite. The conspicuous absence of chlorite in garnet‐rich assemblages, and of garnet in chlorite‐rich rocks, suggest chemical constraints may have been important in the formation of the two minerals. Gondite bands within carbonate ores are interpreted to have resulted from localised processes in which manganese carbonates, in environments rich in alumino‐silicate minerals, may have been completely exhausted during metamorphic reactions.
On the Occurrence of Silician Magnetites
Authors: Shimazaki Hidehiko
Published: November 2008

Abstract: About 120 specimens of magnetite from various localities are examined by an electron microprobe analyzer. Magnetites containing more than one weight percent of silica but lack of any other components than ferrous and ferric iron, called silician magnetites in the present paper, are recognized in 23 skarn, one vein and one thermally metamorphosed massive sulfide deposits. Thus it is confirmed that this mineral occurs in nature much more frequently than so far expected. Besides silician magnetites, magnetites with appreciable amounts of Al2O3, CaO, MgO and other components along with silica, are also recognized in some skarn deposits. Magnetites with such unusual compositions are found only in hydrothermal environments, and it is suggested that precipitation mechanisms seem to be responsible for their formation.

In silician magnetites, excess electric charge brought by the replacement of ferric iron in tetrahedral site by silicon, could be compensated by the replacement of ferric iron in octahedral site by ferrous iron, known as γ–Fe2SiO4 component. The natural occurrence of silician magnetites, however, gives no positive support to the existence of this component at crustal pressures. Instead a preliminary Mössbauer experiment demonstrates that one silician magnetite has a maghemite –like structure by the omission of ferrous iron from octahedral site.
Volcanic Activity, Hydrothermal Alteration and Epithermal Gold‐Silver Mineralization in the Ryuo Mine Area in the Kitami Metallogenic Province, Hokkaido, Japan
Authors: MAEDA Hiroyuki
Published: November 2008

Abstract: Characterization of Neogene magmatism in the Ryuo mine area in the Kitami metallogenic province was carried out on the basis of K‐Ar data for felsic–to–mafic terrestrial extrusive and intrusive volcanism from Late Miocene to Early Pliocene.

The Ryuo epithermal gold‐silver deposit occurs primarily in the felsic volcaniclastic rocks of the Ikutahara Formation and in Ryuo Rhyolite. The Ryuo mineralization age of 7. 7 – 8. 1 Ma coincides well with the hydrothermal alteration age (7. 7 Ma) of Ryuo Rhyolite hosting ore veins. It is concluded that the Ryuo mineralization was essentially accompanied by felsic volcanic activity during the sedimentation of the Ikutahara Formation, and was closely related both temporally and spatially to the intrusive activity of Ryuo Rhyolite.

Hydrothermal alteration related to the epithermal gold‐silver mineralization of the Ryuo deposit is primarily characterized by early regional and vein‐related alterations, and late steam‐heated alteration. Early regional alteration consists of a smectite halo (smectite+pyrite±quartz±opal–CT±mordenite°Clinoptilolite–heulandite series mineral). Early vein‐related alteration is primarily marked by potassic alteration. This alteration halo can be subdivided into a K‐feldspar halo (quartz+adular–ia+pyrite±illite±interstratified illite/smectite±smectite), an illite halo (quartz+illite + chlorite + pyrite ± interstratified illite/smec–tite±smectite) and an interstratified illite/smectite halo (quartz + interstratified illite/smectite+pyrite±smectite). Late steam‐heated alteration characterized by kaolinite or alunite locally overprints the early K‐feldspar halo.

The style of the Ryuo gold‐silver deposit is a low‐sulfidation epithermal type. The gold–silver–bearing quartz vein precipitates during boiling of ore fluid. The origin of the ore fluid might be meteoric water. The temperature and sulfur fugacity conditions during precipitation of electrum and acanthite are estimated to be 206°– 238°C and 10‐13.5 – 10‐11.6 atm, respectively.
Petrochemistry of Late Miocene to Quaternary Igneous Rocks and Metallogenesis in Southwest Hokkaido, Japan
Authors: OHTA Eijun , KAWANO Yoshinobu , NAKAGAWA Mitsuru , KAGAMI Hiroo
Published: November 2008

Abstract: Southwest Hokkaido is largely covered by Late Miocene to Quaternary igneous rocks, and has a large number of gold veins and base‐metal veins of the same age. Investigation of the silica‐normalized concentration of elements has revealed regional petrochemical zoning; large ion lithophile elements (LILE) and K2O/(Na2O+K2O) of the rocks increase toward Japan Sea, whereas total FeO, CaO, and 87Sr/86Sr decrease. Mapped concentration isoplethes of these elements are not ideally parallel to the volcanic front, but protrude to the west at Funka Bay, and to the northwest at Matsumae Peninsula. Isoplethes of 87Sr/86Sr show similar patterns and two more northwestward protrusions in the northeast (Jozankei block) of southwest Hokkaido. Contrary to the general petrochemical trend, both high– and low‐LILE volcanic rocks occur in the Jozankei block. The ore deposits are distributed in four metallogenic zones; manganese–base–metal zone on the Japan Sea side, pyrite‐limonite zone mainly along the volcanic front, gold zone in the middle, and two units of gold–base–metal zone. The northern unit of this zone is in the Jozankei block, and seems a part of the gold zone overlapped by the manganese–base–metal zone. Thus, as a rule, pyrite–limonite, gold, and base‐metal deposits accompany low–, intermediate–, and high‐LILE igneous rocks, respectively.

Individual deposits and volcanic rocks make chains oblique to the zones and the volcanic front. The majority of the ore deposits are distributed along ridges of Bouguer anomalies overlapped by the volcanic chains, which apparently control the patterns of the petrochemical isoplethes. This is typical for two volcanic chains to the north and south of Funka Bay, where the petrochemical isoplethes protrude to the west. This indicates that both the igneous activity and the mineralization have been under the control of tectonic fractures at the roots of the volcanic chains. The geological, petrochemical and metallogenic data support the idea that the chemical characteristics of the deposits are correlated mainly with the chemistry of the associated magmas, and partly with that of the host rocks.
High‐ and Low‐Temperature I‐type Granites
Authors: CHAPPELL B. W. , BRYANT C. J. , WYBORN D. , WHITE A. J. R. , WILLIAMS I. S.
Published: November 2008

Abstract: I– and S‐type granites differ in several distinctive ways, as a consequence of their derivation from contrasting source rocks. The more mafic granites, whose compositions are closest to those of the source rocks, are most readily classified as I– or S–type. As granites become more felsic, compositions of the two types converge towards those of lowest temperature silicate melts. While discrimination of the two is therefore more difficult for such felsic rocks, that in no way invalidates the twofold subdivision. If felsic granite melts undergo fractional crystallisation, the major element compositions are not affected to any significant extent, but the concentrations of trace elements can vary widely. For some trace elements, fractional crystallisation causes the trace element abundances to diverge, so the I– and S– type granites are again easily separated. Such fractionated S‐type granites can be distinguished, for example, by high P and low Th and Ce, relative to their I‐type analogues.

Our observations in the Lachlan Fold Belt show that there is no genetic basis for subdividing peraluminous granites into more mafic and felsic varieties, as has been attempted elsewhere. The subdivision of felsic peraluminous granites into I– and S‐types is more appropriate, and mafic peraluminous granites are always S–type. In a given area, associated mafic and felsic S‐type granites are likely to be closely related in origin, with the former comprising both restite‐rich magmas and cumulate rocks, and the felsic granites corresponding to melts that may have undergone fractional crystallisation after prior restite separation.

We propose a subdivision of I‐type granites into two groups, formed at high and low temperatures. The high‐temperature I–type granites formed from a magma that was completely or largely molten, and in which crystals of zircon were not initially present because the melt was undersaturated in zircon. In comparison with low‐temperature I–type granites, the compositions extend to lower SiO2 contents and the abundances of Ba, Zr and the rare earth elements initially increase with increasing SiO2 in the more mafic rocks. While the high‐temperature I–type granite magmas were produced by the partial melting of mafic source rocks, their low‐temperature analogues resulted from the partial melting of quartzofeldspathic rocks such as older tonalites. In that second case, the melt produced was felsic and the more mafic low‐temperature I–type granites have that character because of the presence of entrained and magmatically equilibrated restite.

High temperature granites are more prospective for mineralisation, both because of that higher temperature and because they have a greater capacity to undergo extended fractional crystallisation, with consequent concentration of incompatible components, including H2O.
Intrusion–Related Vein Gold Deposits: Types, Tectono‐Magmatic Settings and Difficulties of Distinction from Orogenic Gold Deposits
Authors: SILLITOE Richard H. , THOMPSON John F. H.
Published: November 2008

Abstract: A spectrum of intrusion‐related vein gold deposits is recognized. Representative examples are described of the following geochemical associations: Au‐Fe oxide–Cu, Au–Cu–Mo–Zn, Au–As–Pb–Zn–Cu, Au–Te–Pb–Zn–Cu and Au–As–Bi–Sb. The associated intrusions range from small outcropping stocks to complex batholiths.

The different vein associations are believed to reflect the compositions of related intrusions, which themselves characterize distinct tectonic settings. The Au‐Fe oxide–Cu and Au–Cu–Mo–Zn associations belong to two broad groups of deposits, Fe oxide–Cu–Au and porphyry Cu–Au, both of which are related to highly oxidized calc‐alkaline intrusions emplaced in sub–duction–related arcs. The Au–As–Pb–Zn–Cu association seems to be linked to somewhat less oxidized intrusions emplaced in a similar setting. The Au–Te–Pb–Zn–Cu association, which possesses well‐known epithermal counterparts, is also found with highly oxidized intrusions, but of alkaline composition and back‐arc location. In contrast, the Au–As–Bi–Sb association, part of a newly recognized class of intrusion‐hosted Au–Bi–W–As deposits, is related to relatively reduced intrusions, spanning the boundary between the magnetite– and ilmenite–series. Such intrusions, which may host major bulk‐mineable gold deposits, were emplaced along the landward sides of arcs, possibly during lulls in subduction, as well as in continental collision settings. Therefore, a variety of geological environments is prospective for vein and, by extrapolation, other styles of gold mineralization, not all of them fully appreciated in the past.

Several features of vein gold deposits, including imprecise relationships to individual intrusive phases, poorly developed mineral and metal zoning, apparent time gaps between intrusion and mineralization and presence of low–salinity, CO2–rich fluid inclusions, are commonly taken to indicate a non‐igneous origin and to be more typical of orogenic (mesothermal) gold deposits generated during accretionary tectonic events. However, several or all of these features apply equally to some intrusion– related vein gold deposits and, therefore, do not constitute distinguishing criteria. The currently popular assignment of most gold‐rich veins to the orogenic category requires caution, because of the geological convergence that they show with some intrusion‐related deposits. A proper distinction between intrusion‐related and orogenic gold deposits is crucial for exploration planning.
Mesozoic Granitoid Types and Metallogeny of the East China Circum‐Pacific Continental Margin
Authors: ZHU Jinchu
Published: November 2008

Abstract: This paper synthesizes the geotectonic background, genetic types and metallogenetic relations of the Mesozoic granitoids in the East China continental margin. By the Mesozoic, the Siberia Plate, North China Plate and South China Plate amalgamated together, resulting in formation of a unified Eurasia super–continent. Since the late Triassic to early Jurassic period, the territory of East China gradually became a Cordilleran style active continental margin. During the Jurassic to early Cretaceous (early to middle episodes of Yanshanian orogeny), the Paleo‐Pacific plate strongly collided with and subducted under the Eurasia continent, reactivated the consolidated East China continental margin. The granitoids of both transformation series and syntexis series were generated. Many granitoid‐related large and giant metal deposits were formed. Furthermore, the W, Sn, Be, Nb, Ta and U mineralizations are mostly associated with the transformation series; while the Fe, Cu, Mo and Au mineralizations are mostly associated with the syntexis series. The late Yanshanian orogeny (late Cretaceous) began a transition to the western Pacific style continental margin. A tensional environment resulted in development of alkaline granitoids and formation of continental red basins. The Cenozoic orogeny was characterized by a backarc spreading and rifting regime in this region.
Platinum–Group Minerals in Podiform Chromitite from the Kamuikotan Zone, Hokkaido, Northern Japan
Authors: ARAI Shoji , PRICHARD Hazel M. , MATSUMOTO Ichiro , FISHER Peter C.
Published: November 2008

Abstract: Ru–Os–Ir alloys have been found in two podiform chromitites located at the Chiroro and Bankei mines in the Sarugawa peridotite complex in the Kamuikotan zone, Hokkaido, Japan. This is the first report on the occurrence of PGM (= platinum‐group minerals) from chromitites in Japan. The Ru–Os–Ir alloys most typically form polyhedra associated with other minerals (Ni–Fe alloys and heazlewoodite) in chromian spinel. The PGM are possibly pseudomorphs after some primary PGM such as laurite and are chemically highly inhomogeneous, indicating a low‐temperature alteration origin. This is consistent with intense alteration (formation of serpentine, uvarovite and kämmererite) imposed on the Kamuikotan chromitites. High‐temperature primary PGE (platinum–group elements)–bearing sulfides were possibly recrystallized at low temperatures into a new assemblage of PGM, Ni‐Fe alloys and sulfides. Placer PGM around the peridotite complexes are chemically different from the PGM in dunite and chromitite possibly due to the, as yet, incomplete search for the rock‐hosted PGM. The PGE content in chromitites is distinctly higher in those in the Kamuikotan zone than in those in the Sangun zone of Southwest Japan, consistent with the more refractory nature (Cr# of spinel, up to 0.8) of the former than the latter (Cr# of spinel, 0.5).
Polymetallic Mineralization at the Shin‐Ohtoyo Deposit, Harukayama District, Hokkaido, Japan
Authors: IMAI Akira , MATSUEDA Hiroharu , YAMADA Ryoichi , MASUTA Kenzo
Published: November 2008

Abstract: The Shin‐Ohtoyo Cu–Au deposit is located in the Harukayama district, 20 km west of Sapporo, Hokkaido, Japan. Both acid‐type disseminated and adularia–quartz–type vein Au mineralizations have been recognized within a small distance of less than 500 m in the district.

Mineralogical characteristics of sulfide ores from the Shin‐Ohtoyo deposit have been proved to be polymetallic. Ore minerals containing Sn, V, Bi and Te are recognized. Nine ore types are recognized in terms of characteristic mineral assemblage; (1) chalcedonic quartz veinlets in silicified zone around the deposit, (2) bismuthinite, emplectite, friedrichite and tetrahedrite, (3) an unnamed Cu–Sn–Fe–Zn sulfide, colusite‐series minerals, stannoidite, emplectite and tetrahedrite, (4) bournonite, Se‐bearing galena and tetrahedrite, (5) luzonite/famatinite and Ag‐bearing tetrahedrite, (6) colusite‐series minerals, emplectite, aikinite and tetrahedrite/goldfieldite, (7) luzonite/famatinite, colusite‐series minerals, mawsonite and tetra–hedrite/goldfieldite, (8) enargite, luzonite/famatinite and tetrahedrite, and (9) colusite‐series minerals and tetrahedrite. The first occurrence of friedrichite and stibiocolusite from Japan are reported. The chemical formula of the unnamed phase corresponds to Cu6(Cu, Fe, Zn)Sn3S10.

Sulfur isotopic ratios (δ34S) of sulfides from the stockpile range from –0. 5% to +1. 9%, and those from drill cores recovered by Metal Mining Agency of Japan (MMAJ) vary from –2. 7% to +0. 8%. Sulfur isotopic ratio of barite in a cavity in the silicified tuff breccia collected from the stock pile yields +27. 1%, while that of barite collected from MMAJ core is +21. 7%. Sulfur isotopic thermometry applied for a pair of barite (+21. 7%) and associated pyrite (+1. 8%) indicates about 300°C.

High–Te tetrahedrite composition from both the chalcedonic quartz vein in the silicified zone around the Shin‐Ohtoyo deposit and the polymetallic sulfide ores from the adit of the deposit, suggests that the Au mineralization in the former is attributed to a hydrothermal system marginal to the polymetallic mineralization.
Polymetallic Mineralization at the Nakakoshi Copper Deposits, Central Hokkaido, Japan
Authors: Tsushima Norio , Matsueda Hiroharu , Ishihara Shunso
Published: November 2008

Abstract: Polymetallic mineralization at the Nakakoshi deposits, Kamikawa town, central Hokkaido, occur as fracture‐filling veins in Cretaceous slate of the Hidaka Supergroup. Ten veins have been recognized in NE‐SW and E‐W directions. Sericite in altered slate which is the host of the deposits, was dated at 31. 1 Ma, Oligocene in age.

No. 9 vein consists of massive chalcopyrite ore with various kinds of minerals such as pyrite, pyrrhotite, arsenopyrite, sphalerite, tetrahedrite, Ag‐minerals and Cu–Zn–Fe–In–Sn–S minerals, quartz and sericite. Chalcopyrite and pyrite contain sphalerite star and sphalerite with chalcopyrite emulsions. Maximum indium contents of sphalerite and the Cu–Zn–Fe–In–Sn–S minerals are 1. 8 and 16. 3 wt%, respectively. The sulfur isotopic ratios, δ34S of ore minerals, range from –12. 9 to –9. 6%. Formation temperatures of the sulfide minerals are estimated as 300–500°C, based on the paragenesis and chemical compositions of the minerals.
Plio–Pleistocene Hydrothermal Activity Related to Gold Mineralization in the Seta Area, Northeastern Hokkaido, Japan
Authors: YAHATA Masahiro , MATSUEDA Hiroharu
Published: November 2008

Abstract: Plio–Pleistocene hydrothermal activity resulted in high grade low sulfidation epithermal gold mineralization in the Seta area, the southern end of the Monbetsu‐Kamishihoro Graben of northeastern Hokkaido, Japan. Hydrothermal activity and accompanying hydrothermal eruptions began at approximately 2 Ma along NNW‐SSE trending faults, the Tohbu‐ko fault I and II. This activity resulted in two main zones of gold mineralization, the west quartz‐adularia veins(QAV) and east stock‐work zone(STZ), formed between 1. 8 and 1. 2 Ma. A smectite‐chlorite alteration zone is observed at deeper levels, while kaolinite and kaolinite‐smectite zones occur at shallower levels with an acid‐leached zone present near the surface. The kaoli‐nite and kaolinite‐smectite zones are also distributed along faults and the STZ, to depths of several hundred meters. δ34S values of pyrite and alunite from the kaolinite and silicified zones indicate alunite formed by the oxidation of sulfide, either H2S(vapor) or mineral.

Formation of the STZ and the southern part of the QAV took place during lacustrine sedimentation, while formation of the northern part of the QAV took place after eruption of andesitic lava; the latter being associated with widespread alteration formed under neutral‐pH conditions. δ18O values of quartz veins and silicified rocks indicate that the paleo‐hydrothermal waters have a large meteoric component, increasing with decreasing depth in the STZ. Acid hydrothermal waters, resulting from near surface oxidation of H2S were responsible for acid‐leaching and kaolinization of surrounding rocks. Between 1. 4 and 0. 3 Ma, the acid hot waters drained back along the STZ to depths of at least 500m, as a result of a fall in the paleo‐water table level.
Stable Isotopic Information on Calcareous Pelitic Rocks in the Tizapa Volcanogenic Massive Sulfide Deposit Area, the United Mexican States
Authors: Morozumi Haruhisa , Metsugi Hideya , Kita Yoshiyuki , Suzuki Toru
Published: November 2008

Abstract: Tizapa volcanogenic massive sulfide (VMS) deposit is hosted in greenschist facies metamorphic rocks; footwall is green schist of felsic to mafic metavolcanic rocks and hanging wall is graphite schist of metasedmentary pelitic rock. Pb‐Pb dating of ore samples indicates 103. 4Ma to 156. 3Ma for the age of mineralization (JICA/MMAJ, 1991).
Fluid Inclusion Study of Skarns in the Maruyama Deposit, the Kamioka Mine, Central Japan
Authors: TAKENO Naoto , SAWAKI Takayuki , MURAKAMI Hiroyasu , MIYAKE Kazuhiro
Published: November 2008

Abstract: Fluid inclusions in skarn minerals in the Maruyama deposit, the Kamioka mine, central Japan were studied. Homogenization temperatures (Th) of fluid inclusions in 48 skarn minerals (hedenbergite, andradite, epidote and quartz) were measured, and gas composition of fluid inclusions in 12 skarn minerals was measured with a quadrupole mass spectrometer. The maximum Th value of primary inclusions in hedenbergite is 380C with peaks around 360C. Primary inclusions in hedenbergite near contact between skarn and limestone have slightly lower Th values and their distribution has a tendency of long trail skirt toward low temperature, which indicates ceasing of skarnization coincides with temperature decrease. Fluid inclusions in andradite and quartz in the hedenbergite skarn have lower Th values, in this order, than those in hedenbergite. CH4–detected fluid inclusions are localized around the Maruyama fault. Gas composition of the fluid inclusions indicates that fluid trapped in the hedenbergite has CO2 content less than 1 mole % and is not in equilibrium with graphite.
Three–Dimensional Isotopic Characteristics of Crystalline Limestone around the Sakonishi Zn Ore Bodies in the Kamioka Mining District, Japan
Authors: MORISHITA Yuichi
Published: November 2008

Abstract: Predominant Zn‐rich ore bodies were found to a deep part of the Sakonishi area in the Kamioka mining district, Japan. The ore mineralization was recognized at 230 to 300m above sea level in the Sakonishi area. Since crystalline limestone is broadly distributed over the area, and the variation in isotopic composition is easily detected, the isotopic prospecting should be powerful in surveying of the extent of the ore bodies and the related hydrothermal system. Although isotopic anomalies have been extracted two‐dimensionally so far, three‐dimensional information is possibly more powerful.

In this paper, Zn‐rich ore bodies in the Sakonishi area are treated as hydrothermal ore deposits, and the importance of the activity of hydrothermal fluids during mineralization is emphasized. Oxygen and carbon isotopic ‘iso–surfaces’ are three‐dimensionally calculated for the Sakonishi area. The δ18O values of crystalline limestone from the surface and from the drill holes range from +8. 1 to +21. 1% and from –2. 7 to +20. 4%, respectively. The δ13C values of crystalline limestone from the surface and from the drill holes range from –1. 0 to +5. 3% and from –7. 7 to +4. 6%, respectively. The oxygen and carbon iso‐topic ratios at the mineralization level are extremely low, but there are exceptions as to carbon isotopes. The oxygen isotopic ratios of crystalline limestone may decrease by isotopic exchange reaction with a hydrothermal fluid, while the carbon isotopic ratios slightly change. Since the precipitated calcite from a hydrothermal fluid has low carbon isotopic ratio and various oxygen isotopic ratio depending on the formation temperature, the bulk sample of crystalline limestone containing the precipitated calcite has oxygen and carbon isotopic ratios of relatively low values accordingly. Thus the decrease mechanism for carbon isotopic ratio of crystalline limestone is different from that for oxygen isotopic ratio. Samples with the carbon isotopic ratio of –4 to –8% are considered to be crystallized from hydrothermal fluids.

Since the oxygen and carbon isotopic ratios of crystalline limestone at the ore mineralization level are low, the ore bodies are considered to have formed by a prominent hydrothermal activity. Thus oxygen and carbon isotopic ratios of crystalline limestone can be used as an indicator of the related hydrothermal activity. The alteration such as chloritization is intense near fractures in the Sakonishi area, showing that the hydrothermal system is controlled by a fracture system. It is assumed that the decreased isotopic ratios indicate the high degree of reactivity with hydrothermal fluids, and the depleted zone in oxygen and carbon isotopes may correspond to the conduit of the hydrothermal fluids.
Hydrothermal Alteration of Limestone and Mineral Exploration of Zn‐Pb Skarn Deposits in the Sako‐nishi Area of the Kamioka Mine, Central Japan
Authors: MURAKAMI Hiroyasu , NAKANO Takanori
Published: November 2008

Abstract: Crystalline limestone of the Sako‐nishi area in the Kamioka Zn‐Pb mine, central Japan, is depleted in 18O and 13C toward the center of mineralization due to interaction with hydrothermal fluids with a dominant meteoric water component. The relationship between isotopic composition and mineral assemblage, texture, the chemical composition of the minerals, and the bulk chemical composition in the limestone was examined. A decrease in the δ18OSMOW value correlated with: (1) increase of fine‐grained calcite which is enriched in Mn and exhibits a bright cathodoluminescence, (2) progressive hy‐drothermal alteration of clinopyroxene in the original limestone into tremolite within the weakly‐altered zone, and into chlorite and actinolite within the strongly‐altered zone, (3) dominance of hydrothermal chlorite in altered limestone having δ18O values of less than 10%. This chlorite was enriched in Fe compared to mafic minerals in the unaltered limestone. The enrichment of Fe and Mn was more conspicuous in calcite and chlorite in skarn deposits. The occurrence and chemical composition of hydrothermal minerals in the limestone, skarn, and ore indicate that the 18O–depleted zones were formed in the later stage from fluids, which were responsible for mineralization and skarnization, and for Fe and Mn enrichment.

The Al, Mn, and Fe contents, and the ratios of Mg/(Mg+Mn+Fe), Al/Mg, and Mn/Sr in the hydrochloric acid leachate of limestone varied with decreasing δ18O and δ13C values, reflecting increases in high‐Mn calcite and high‐Fe chlorite. These indexes were useful for the identification of hydrothermally altered limestone. Furthermore, the potential score weighted by each index was more effective and accurate means of detecting promising mineralization zones. An anomalous potential score due to the presence of hydrothermal minerals in the outcropping limestone occurred along the Atotsu–1GO fault. This structure indicates that the skarn deposits of the Sako‐nishi area belong to Mozumi‐type Zn–Pb skarn deposits, in which fissures and faults served as major passages for the hydrothermal fluid. High‐Mn carbonate and high‐Fe chlorite widely occur in base‐metal vein deposits and Zn‐Pb type skarn deposits. Leaching of altered rock with hydrochloric acid in addition to stable isotope composition and cathodoluminescence imaging is effective for geochemical exploration for hydrothermal deposits because it makes possible the detection of the elemental composition of hydrothermal minerals such as chlorite and carbonate and because of the rapidity and convenience of analysis.
Mineral Paragenesis, Fluid Inclusions and Sulfur Isotope Systematics of the Lepanto Far Southeast Porphyry Cu‐Au Deposit, Mankayan, Philippines
Authors: IMAI Akira
Published: November 2008

Abstract: The Lepanto Far Southeast porphyry Cu‐Au deposit is located beneath and to the southeast of the Lepanto enargite‐luzonite Cu–Au deposit in Mankayan, Benguet Province, Philippines.

The principal orebody consists of potassic alteration subjected to partial retrograde chlorite alteration that rims stock‐work of quartz‐anhydrite veinlets. Fluid inclusions found in stockwork quartz and anhydrite in the biotitized orebody center are dominated by polyphase inclusions that homogenize at temperatures of >500C. Sulfur isotopic thermometry applied to the sulfides‐anhydrite pairs suggests around 500C. The principal ore minerals associated with quartz‐anhydrite stockworks are chalcopyrite and pyrite with minor bornite and Bi–Te–bearing tennantite, with trace of native gold. Rounded pyrite grains appear fractured and corroded and are interpreted as remnants of primary intermediate solid solution + pyrite assemblage.

A breccia pipe truncates the deposit. Mineralization in the breccia pipe is brought by quartz‐anhydrite veinlets and infilling in the interstices between clasts. Chalcopyrite‐Au mineralization associated with molybdenite is recognized in the deeper zone in the breccia pipe. Fluid inclusion microthermometry on polyphase inclusions in veinlet quartz as well as sulfur isotope thermometry applied for the pair of anhydrite and sulfides suggests >450C.

Fluid inclusions in veinlet quartz and anhydrite in the fringe advanced argillic alteration are chiefly composed of coexisting liquid‐rich inclusions and gas‐rich inclusions, in addition to coexisting polyphase inclusions and gas‐rich inclusions. These inclusions exhibit a wide range of homogenization temperatures, suggesting heterogeneous entrapping in the two‐fluid unmixing region.

Sulfur isotopes of aqueous sulfide and sulfate exhibit a general trend from the smallest fractionation pairs (about 11%) in the biotitized orebody center to the largest fractionation (about 25%) pairs in the fringe advanced argillic alteration, suggesting a simple evolution of hydrothermal system. The slopes of arbitrary regression lines in δ34S versus 34S[SO4 = –H2S] diagram suggest that the abundance ratio of aqueous sulfate to sulfide in the hydrothermal fluid has been broadly constant at about 1:3 through temperature decrease. The intersection of these two regression lines at the δ34S axis indicates that the bulk δ34S is about +6%. Thus, the Lepanto FSE deposit is a further example which confirms enrichment in 34S in the hydrous intermediate to silicic magmas and associated magmatic hydrothermal deposits in the western Luzon arc.
Nickel–bearing Djerfisherite in Gehlenite‐Spurrite Skarn at Kushiro, Hiroshima Prefecture, Japan
Authors: TAKECHI Yasushi , KUSACHI Isao , NAKAMUTA Yoshihiro , KASE Katsuo
Published: November 2008

Abstract: Djerfisherite occurs intimately intergrown with troilite and pentlandite in gehlenite‐spurrite skarn at Kushiro, mainly as inclusions in gehlenite and andradite grains. The mode of occurrence indicates that the djerfisherite formed in the culminated stage of the contact metamorphic‐metasomatic process. The chemical compositions of the mineral are approximately represented by a formula of K6Na(Fe, Ni, Cu)24S26Cl with Ni up to 4. 85. It is likely that high temperature condition corresponding to the formation of gehlenite‐spurrite skarn as well as low fO2 and fS2 conditions are responsible for the formation of djerfisherite in the potassium‐rich chemical environments.
Observation of Pore Spaces and Microcracks Using a Fluorescent Technique in Some Reservoir Rocks of Oil, Gas and Geothermal Fields in the Green Tuff Region, Japan
Authors: WAJIMA Takaaki , OKUDA Shuji , CHEN Youqing , BESSHO Masahiko , NISHIYAMA Takashi
Published: November 2008

Abstract: Pore spaces and microcracks in representative oil, gas and geothermal reservoir rocks from the Green Tuff region, Japan, were examined using a fluorescent technique. This technique was developed to visualize microscopically pore spaces and microcracks filled with synthetic resin mixed with fluorescent paint under ultraviolet light. Various morphology of pore spaces and microcracks was clearly identified. Spaces in studied reservoir rocks are classified into following three types: pore spaces in matrix, pore spaces in particles, and microcracks. It is observed that valuable oil and gas reservoir rocks relatively include many pore spaces, while microcracks are important for geothermal rocks. Correlation between textural characteristics and porosity or permeability was found in the oil reservoir rocks. Effective permeability depends upon pore spaces in matrix more than upon other components such as pore spaces in particles and microcracks. Looseness in matrix caused by larger grain size of particles is strongly correlated with permeability. Pore spaces play an important role as a reservoir in oil and gas fields, but are less important in geothermal field. Instead, microcracks are important for geothermal reservoir system.
Horizontal Strain Rate in Relation to Vein Formation of the Hishikari Gold Deposits, Southern Kyushu, Japan
Authors: UTO Tadakazu , IMAI Akira , YAMATO Yu
Published: November 2008

Abstract: The Hishikari deposits comprise the Honko (Main), Yamada, and Sanjin deposits. The horizontal strain in the direction (approx. N40°W normal to the general NE‐SW strike of the Hishikari vein system was calculated, based on the measured total vein widths to the distance along three crosscuts. Veins were assumed to accompany no significant fault displacement in the calculation. Veins in the eastern and the middle parts of the Honko‐Sanjin deposits spatially occupy 3. 2% and 1. 3%, respectively, and veins in the Yamada deposit occupy 6. 7%. Significant local variation of strain is observed in some areas. Reported K‐Ar ages on adularia‐quartz veins indicate the duration of vein opening to be 2. 6 × 105 yr in the Honko‐Sanjin deposits and 5. 9 × 105 yr in the Yamada deposit. Horizontal strain rates were calculated to be 5. 0–12 × 10‐8 yr‐1through the Hishikari deposits. The calculated strain rates at the Hishikari deposits are roughly comparable to the regional horizontal strain rate in the Recent. Widespread extensional movement in southern Kyushu seems to have been able to provide sufficient strain for the formation of the Hishikari deposits, rather than contribution of local movements.
Alteration Patterns Related to Hydrothermal Gold Mineralizaition in Meta‐andesites at Dungash Area, Eastern Desert, Egypt
Authors: Helba Hossam A. , Khalil Khalil I. , Abou Nagdi M. F.
Published: November 2008

Abstract: The hydrothermal alteration patterns associating with the gold prospect hosted by metavolcanics in the Dungash area, Eastern Desert of Egypt, were investigated in order to assign their relationship to mineralization. The metavolcanics of andesitic composition are generated by regional metamorphism of greenschist facies superimposed by hydrothermal activity. Epidote and chlorite are metamorphic minerals, whereas sericite, carbonates, and chlorite are hydrothermal alteration minerals. The auriferous quartz vein is of NEE‐SWW trend and cuts mainly the andesitic metavolcanics, but sometimes extends to the neighbouring metapyroclastics and metasediments.

Quartz‐sericite, sericite, carbonate‐sericite, and chlorite‐sericite constitute four distinctive alteration zones which extend outwards from the mineralized quartz vein. The quartz‐sericite and sericite zones are characterized by high contents of SiO2, K2O, Rb, and As, the carbonate‐sericite zone is by high contents of CaO, Au, Cu, Cr, Ni, and Y, and the chlorite‐sericite zone is by high contents of MgO, Na2O, Zn, Ba, and Co. Gold and sulphide minerals are relatively more abundant in the carbonate‐sericite zone followed by the sericite one.

The geochemistry of the alteration system was investigated using volume‐composition and mass balance calculations. The volume factors obtained for the different alteration zones, mentioned above (being 1.64, 1.19, 1.17, and 1.07, respectively), indicate that replacement had taken place with a volume gain. The mass balance calculations revealed addition of SiO2, K2O, As, Cu, Rb, Ba, Ni, and Y to the system as a whole and subtraction of Fe2O3 from the system. Initial high aK+ and aH+ for the invading fluids is suggested. As the fluids migrated into wallrocks, they became more concentrated in Mg, Ca, and Na with increasing activities of CO2 and S.

The calculated loss‐gain data are in agreement with the microscopic observations. Breakdown of ferromagnesian minerals and feldspars in the quartz‐sericite, sericite, and chlorite‐sericite zones accompanied by loss in Mg, Fe, Ca, and Na under acidic conditions and low CO2/H2O ratio may obstruct the formation of carbonates and sulphides, and the precipitation of gold in these zones. The role of metamorphic fluids in the area is expected to be restricted to the liberation of Au and some associated elements from their hosts.
Acid‐sulphate Type Alteration and Mineralization in the Desmos Caldera, Manus Back‐arc Basin, Papua New Guinea
Authors: Gena Kaul , Mizuta Toshio , Ishiyama Daizo , Urabe Tetsuro
Published: November 2008

Abstract: The Onsen acid‐sulphate type of mineralization is located in the Desmos caldera, Manus back‐arc basin. Hydrothermal precipitates, fresh and altered basaltic andesite collected from the Desmos caldera were studied to determine mineralization and mobility of elements under seawater dominated condition of hydrothermal alteration.

The mineralization is characterized by three stages of advanced argillic alteration. Alteration stage I is characterized by coarse subhedral pyrophyllite with disseminated anhedral pyrite and enargite which were formed in the temperature range of 260–340°C. Alteration stage II which overprinted alteration stage I was formed in the temperature range of 270–310°C and is characterized by euhedral pyrite, quartz, natroalunite, cristobalite and mixed layer minerals of smectite and mica with 14–15 Å XRD peak. Alteration stage III is characterized by amorphous silica, native sulphur, covellite, marcasite and euhedral pyrite, which has overprinted alteration stages I and II.

Relative to the fresh basaltic andesite samples, the rims and cores of the partly altered basaltic andesite samples have very low major, minor and rare earth elements content except for SiO2 which is much higher (58–78 wt%) than SiO2 content of the fresh basaltic andesite (55 wt%). REE patterns of the partly altered basaltic andesite specimens are variably depleted in LREE and have pronounced negative Eu anomalies. Normalization of major, minor and REE content of the partly altered basaltic andesites to the fresh basaltic andesite indicates that all the elements except for SiO2 in the partly altered basaltic andesite are strongly lost (e.g. Al2O3 = ‐8.3 to ‐10.9 g/100cm3, Ba = ‐2.2 to ‐5.6 mg/100cm3, La = ‐130 to ‐200 μg/100cm3) during the alteration process. Abnormal depletion of MgO, total Fe as Fe2O3, LREE especially Eu and enrichment of SiO2 in the altered basaltic andesites from the Desmos caldera seafloor is caused by interaction of hot acidic hydrothermal fluid, which originates from a mixing of magmatic fluid and seawater.
Experimental Study Assessing the Role of Sedimentary Organic Materials to Control the Redox State of Ground Materials to Control the Redox State of Groundwater: Consumption of Dissolved Oxygen by Humic Acid
Authors: Haysahi Ken‐ichiro , Shibata Hideyuki , Yui Mikazu , Ohmoto Hiroshi
Published: November 2008

Abstract: A total of 189 runs were completed to determine the rate of dissolved oxygen consumption in water by the reaction humic acid at 25°, 45°, and 65°C. Glass vial bottles were used as reaction vessels, and humic aicd and pure water of different intitial O2 concentration was loaded with humic acid/water weight of 0.008 and 0.009. Vials were opened periodically to measure O2 concentrations. The pH of the solution fluctuated in the early stages of the experiments and gradually decreased to a constant value. Dissolved oxygen concentration decreased, for example, from initial value of 12 mg/l to 9 mg/l at 25°C, to 5 mg/l at 45°C, and to 2 mg/l at 65°C after the reaction of 500 hours. Analyses of rates suggest that the reaction is first order, and rate constants are 8.42 × 10‐9 at 25°C, 2.22 × 10‐8 at 45°C, and 1.28 × 10‐7 moles m‐2 s‐1 at 65°C.
Mineral Paragenesis of the Lepanto Copper and Gold and the Victoria Gold Deposits, Mankayan Mineral District, Philippines
Authors: CLAVERIA Rene Juna R.
Published: November 2008

Abstract: Mineral paragenesis of the alteration, ore and gangue minerals of the Lepanto epithermal copper‐gold deposit and the Victoria gold deposit, Mankayan Mineral District, Northern Luzon, Philippines, is discussed.

The principal ore minerals of the Lepanto copper‐gold deposit are enargite and luzonite, with significant presence of tennantite‐tetrahedrite, chalcopyrite, sphalerite, galena, native gold/electrum and gold‐silver tellurides. Pervasive alteration zonations are commonly observed from silicification outward to advanced argillic then to propylitic zone. The ore mineralogy of the Lepanto copper‐gold deposit suggests high fS2 in the early stages of mineralization corresponding to the deposition of the enargite‐luzonite‐pyrite assemblage. Subsequent decrease in the fS2 formed the chalcopyrite‐tennantite‐pyrite assemblage. An increase in the fS2 of the fluids with the formation of the covellite‐digenite‐telluride assemblage caused the deposition of native gold/electrum and gold‐silver tellurides.

The principal ore minerals of the Victoria gold deposit are sphalerite, galena, chalcopyrite, tetrahedrite and native gold/electrum. The alteration halos are relatively narrow and in an outward sequence from the ore, silica alteration grades to illitic‐argillic alteration, which in turn grades to propylitic alteration. The Victoria gold mineralization has undergone early stages of silica supersaturation leading to quartz deposition. Vigorous boiling increased the pH of the fluids that led to the deposition of sulfides and carbonates. The consequent decrease in H2S precipitated the gold. Gypsum and anhydrite mainly occur as overprints that cut the carbonate‐silica stages.

The crosscutting and overprinting relationships of the Victoria quartz‐gold‐base metal veins on the Lepanto copper‐gold veins manifest the late introduction of near neutral pH hydrothermal fluids.
Oxygen and Carbon Isotope Study of Calcite and Dolomite in the Disseminated Au‐Ag Telluride Bulawan Deposit, Negros Island, Philippines
Authors: MAGLAMBAYAN Victor B. , ISHIYAMA Daizo , MIZUTA Toshio , MATSUBAYA Osamu , ISHIKAWA Yohei
Published: November 2008

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.
Granitoids and Their Magnetic Susceptibility in South Korea
Authors: JIN Myung–Shik , LEE Youn Soo , ISHIHARA Shunso
Published: November 2008

Abstract: Magnetic susceptibility (MS) measurements were carried out for 1,120 samples in the Middle Proterozoic to Early Tertiary granitoids so far recognized in South Korea, and the lateral and spatial variation of their magnetic susceptibility, i.e., content of magnetite, is studied.

The Middle Proterozoic two mica granitoids related to cassiterite (Sn) deposits in northeastern part of the Sobaegsan Massif show very low MS (less than 0.3 A‐ 10‐3 SI unit), and the Permo‐Triassic tonalitic to granodioritic and monzonitic rocks which are barren in mineralization, distributed in the middle part of South Korea also show low MS (less than 1 A‐ 10‐3 SI unit).

On the contrary the Late Triassic to Jurassic granitoids (= Daebo granitoids) which were evolved from tonalite through granodiorite to granite, and are most widely distributed in South Korea, show a wide variation on MS. Particularly in the Andong, Igsan, Gimcheon and Geochang areas, the granitoids which are barren in mineralization, are characterized by high MS (more than 10 A‐ 10‐3 SI unit). The Chuncheon, Jecheon, Namyang and Geumsan plutons related to molybdenite (Mo) and/or wolframite or scheelite (W), and fluorite (F) mineralizations show a little high MS (more than 3 A‐ 10‐3 SI unit). However, more than 60% of the Daebo granitoids show low MS (less than 3 A‐ 10‐3 SI unit) and the rest show a little high MS (more than 3 A‐ 10‐3 SI unit). Heterogeneous distribution of magnetite content in the Daebo granitoids is considered to reflect heterogeneity of redox state of the source materials for these granitoids.

The Cretaceous to Early Tertiary granitoids (= Bulgugsa granitoids) in the Gyeongsang Basin had been generally evolved in the order of tonalite, diorite, granodiorite, granite and alkali‐feldspar granites, which are closely related to base metal ore deposits, and mostly show higher MS (more than 3 A‐ 10‐3 SI unit) than other granitoids mentioned above, although some exceptions are recognized in highly evolved alkali‐feldspar granites (SiO2 > 76%). In contrast, as most of the highly oxidized or evolved Cretaceous granitoids distributed in areas other than the Gyeongsang Basin show lower MS than those of the Gyeongsang Basin, and appear to be magnetite free, ilmenite‐series granites, but they might be hematite bearing magnetite‐series granitoids. Highly oxidized nature of the Bulgugsa granitoids may be due to high Fe2O3/FeO ratio of the source materials and also high level intrusion style of the granitic magma activities.

Most of the granitic rocks of the Middle Proterozoic, Permo‐Triassic and more than 60% of the Late Triassic to Jurassic (Daebo granitoids) belong to ilmenite–series, however less than 40% of the Daebo granitoids and most Cretaceous ones are magnetite–series. Thus, the granitic magma intruded in Korean Peninsula became oxidized while the intrusive ages become younger.