Distribution by Scientific Domains
Distribution within Earth and Environmental Science

Kinds of Deposits

  • alluvial deposit
  • amyloid deposit
  • avalanche deposit
  • bank deposit
  • beach deposit
  • calcific deposit
  • calcium deposit
  • cave deposit
  • clay deposit
  • copper deposit
  • cu deposit
  • fan deposit
  • fat deposit
  • fibrillar deposit
  • flood deposit
  • flow deposit
  • fluvial deposit
  • glacial deposit
  • gold deposit
  • hemosiderin deposit
  • immune deposit
  • iron deposit
  • lacustrine deposit
  • lake deposit
  • linear deposit
  • loess deposit
  • magnetite deposit
  • marine deposit
  • metal deposit
  • metastatic deposit
  • mineral deposit
  • ore deposit
  • peat deposit
  • plaque deposit
  • polymetallic deposit
  • porphyry copper deposit
  • protein deposit
  • quaternary deposit
  • sedimentary deposit
  • slope deposit
  • soil deposit
  • sulfide deposit
  • terrestrial deposit
  • tin deposit
  • vein deposit

  • Terms modified by Deposits

  • deposit feeder
  • deposit insurance

  • Selected Abstracts


    C. Fischer
    The fluvial-aeolian Rotliegend succession exposed in a quarry near Magdeburg (Flechtinger Höhenzug, Northern Germany) is an analogue for deeply-buried gas-bearing Rotliegend sandstones in the Southern Permian Basin. The spatial configuration of bounding surfaces within this succession was reconstructed with reference to twelve profiles with 926 sample points. Generally sub-horizontal interdune migration surfaces were surveyed, and the areal extent of small-scale superimposition surfaces and the thicknesses of intervening strata were measured. Based on these observations and also on the extent of different lithofacies types and on corresponding porosity and permeability data, a 3D lithofacies model (including bounding surface configurations) incorporating porosity and radial permeability was created using PETRELTÔ software. In the quarry, aeolian sandstones approximately 12 m thick (,, 5-11 vol. %, ,radial, 0.01-10mD) are separated into a number of tabular bed sets by sub-horizontal interdune migration surfaces. The surfaces are often associated with thin pelitic intervals with low permeabilities which originate from deflation and sheet flow events. Aeolian deposits consist mainly of two lithotypes: low-angle cross-bedded, and steeply cross-bedded medium-grained sandstones. Superimposition surfaces occur at the base of the low-angle cross-bedded sandstone bodies. The highest porosities and permeabilities occur within the steeply cross-bedded sandstones, reflecting intense eodiagenetic calcite and quartz cementation with subsequent calcite dissolution. The low-angle cross-bedded sandstones may act as flow baffles. This outcrop-derived, high resolution model may contribute to a better understanding of the subsurface architecture and reservoir properties of aeolian-fluvial successions. Taking into consideration the centimetre- to metre-scaled inhomogeneities observed at outcrop, lithotype modelling with reference to the occurrence of bounding surfaces may help to predict how similar reservoir rocks are partitioned. [source]


    S. F. Khafizov
    This paper discusses specific facies associated with Cretaceous deep-water slumps and sandstone intrusions in the West Siberian Basin. The slumps were formed during sea-level falls when storms caused sediment masses to be discharged into deep-water areas where they imposed a significant load on the underlying semi-consolidated black shales, deforming and partially destroying them. Multiple slump / avalanche events are observed at the boundary between the Lower Cretaceous (Neocomian) and Upper Jurassic (Tithonian) sequences and form potential targets for oil exploration. High-resolution sequence stratigraphic analyses show that both slump and distal fans are genetically related to lower slope/basin floor sediments and were deposited during regressions and subsequent lowstands. Two key depositional environments are recognized: the proximal parts of fans, where the most prospective potential reservoirs are found; and the more distal parts of slumps, which are principally composed of deformed shale clasts in a silt-mudstone matrix. A third facies ("slump head") is only observed on seismic profiles and is probably related to horizontally displaced "shingled" semi-consolidated black shales. [source]


    H. Mohseni
    The Pabdeh Formation is part of a thick carbonate-siliciclastic succession in the Zagros Basin of SW Iran which includes carbonate reservoirs of Cretaceous and Cenozoic ages. From field observations and petrographic and facies analysis of exposures in the type section of the Pabdeh Formation, four lithofacies were recognized. These are from oldest to youngest: (i) a mottled, bioturbated bioclastic wackestone/mudstone facies; (ii) a wackestone/packstone facies with horizontal burrows on bedding planes; (iii) a thin-bedded bioclastic wackestone/mudstone facies alternating with thin bioclastic-oolitic-intraclastic intervals; and (iv) a bioclastic foraminiferal / algal / peloidal packstone facies. These observations indicate that facies evolved upwards from deep outer-ramp deposits to inner-ramp deposits within a shoal complex, suggesting progradation of the ramp depositional system. Storm events significantly influenced the ramp system. Storm-generated surges transported sediments from nearshore to the deeper outer-ramp environment where they were deposited as shell-lags, composed mostly of bioclastic packstones, rich in pelagic microfauna with sharp, undulatory erosional basal contacts. The packstones rest on outer ramp mudstones deposited below storm base level. Sedimentary structures in the Pabdeh Formation are those typical of storm deposits, such as hummocky cross-stratification, ripple cross-lamination, ripple marks, escape burrows on the tops of the beds, couplets of fine- and coarse-grained laminae and mixed fauna, as well as intraclasts derived from underlying facies. These distinctive sequences are interpreted to have been generated by waning storm-generated currents. The dominance of fine-grained sediments (medium to fine sand); the lack of large- scale hummocky cross-stratification; the minor amounts of intraclasts derived from underlying facies; the paucity of amalgamated tempestite beds; and the finely-laminated (mm to cm scale) couplets of coarse and fine lamina all suggest a distal tempestite facies. Palaeogeographic reconstruction of the Zagros Basin during the Eocene indicates that the study area was situated in tropical, storm-dominated palaeolatitudes. [source]


    Article first published online: 11 MAR 200
    Siciliano G.1, D'Avino C.1, Panichi V.2, Azzarà A.3, Del Corona A.1, Pollina L.3, Murri L.1 1Department of Neuroscience, 2Department of Internal Medicine and 3Department of Oncology,University of Pisa-Italy Amyloidosis is a systemic disease with a wide organic involvement. Amyloidotic polyneuropathies may be genetic in their origin or present in association with a number of chronic inflammatory dysimmune disorders. We report on three patients affected by predominantly sensitive polyneuropathy, monoclonal gammopathy and amyloidosis. Patient 1. Woman, 72 years old, with a one year history of painful paraesthesias, ataxic gait and demyelinating predominantly sensitive polyneuropathy at 4 limbs also with involvement of sympathetic fibres. Blood protein electrophoresis showed a monoclonal gammopahty (IgG-k) with normal bone marrow biopsy and positivity for amyloid at fat biopsy. The patient has been treated with melphalan 0.2 mg/Kg/day+prednisone 100 mg/day for 7 days each month for 6 months with good efficacy and only a transient reduction in platelet and white blood cells count. Patient 2. Man, 60 years old, new diagnosis of diabetes with a 9 month history of painful paraesthesias and hyposthenia, a demyelinating sensory-motor polyneuropathy at 4 limbs. The patient presented an IgG-, monoclonal gammopathy with normal bone marrow biopsy, fat biopsy but not sural nerve biopsy positive for amyloid. The patient underwent melphalan+prednisone therapy, with insulinic control of glycemia. He presented a clear-cut improvement in sensitive-motor symptomatology. Patient 3. Man, 72 years old, with a 15 year history of ulcerous rectocolites. Since 1998 started complaining of paraesthesias and disaesthesias at four limbs associated with gait disturbances. The patient presented an IgG-, monoclonal gammopathy with normal bone marrow aspiration and elevated serum Interleukin-6 levels, fat biopsy positive for amyloid, and high anti-MAG antibodies titer (1:100000). Because of RCU, melphalan therapy was excluded and the patient is at the moment under fludarabine (25 mg/m2/day) ev for 5 days each 6 weeks for 6 bouts. [source]


    G21; F36 Foreign currency deposits (FCD) are prevalent in many low-income developing countries, but their impact on bank lending has rarely been examined. An examination of cross-country data indicates that a higher proportion of FCD in total deposits is associated with more private credit only in inflationary circumstances. FCD can lead to a decline in private credit below a certain threshold level of inflation. Given that FCD exhibit persistence, deregulating them in low-income countries could cause more harm than good to financial intermediary development in the long term. [source]


    ARCHAEOMETRY, Issue 5 2010
    J. M. PARÉS
    We use a combination of rock magnetism (anisotropy of magnetic susceptibility, AMS) and magnetic polarity to characterize cave deposits and as a proxy for sedimentary fabric. In three localities at the Atapuerca archaeological site (Galeria, Gran Dolina and Sala de los Cíclopes), magnetic foliation (Kmax/Kint) is always greater than lineation (Kint/Kmin), consistent with a primary, depositional, sedimentary fabric. Our results, although preliminary, reveal a higher degree of anisotropy in autochtonous deposits compared to allochthonous deposits, possibly indicative of a higher hydrodynamic regime in the former. At two localities the magnetic lineation (Kmax) defines a cluster, which is thought to be antipodal to the palaeocurrent direction. Hence we are able to retrieve palaeoflow directions in deposits that otherwise lack any other sedimentary structure. We conclude that AMS is a powerful tool for determining the hydrodynamic character of depositional environments in cave sediments at the Atapuerca archaeological site. A better understanding of the depositional environment and how sedimentation occurred allows reconstruction of the karst evolution and ultimately a better definition of human interaction with the environment. [source]

    Deposit for the Future: Remnant vegetation management through community cost-sharing

    Martin Driver
    First page of article [source]

    Morphology and Roughness of Silver Deposit Formed by Cementation at Various Temperatures in Pure Sulfuric Acid

    Abstract The morphology and surface roughness of silver (Ag) deposit formed on metallic copper (Cu) by cementation conducted in a 0.5M H2SO4 solution was investigated at various temperatures above 25°. The influence of the presence or absence of oxygen (O2) on Ag morphology was studied at an initial Ag+ concentration of 20,mg/dm3. An analysis of distribution diagrams of the surface height calculated from scanning-electron-microscope (SEM) top-view images was performed. The cementation reaction results in a non-homogeneous Ag deposit formed on the surface independently of the presence or absence of O2 in solution. The Ag deposit covers Cu mainly with a uniform and compact layer with separated germs of predendrites, but also a huge ,fern-leaf-shaped' and ,lycopodium-twigs-shaped' dendrites appear occasionally on the surface. The presence of O2 in the system and temperature do not affect significantly the morphology of Ag dendrite as well as a deposit formed on the smooth part of the surface. The roughness of surface with Ag cement varies with temperature only under aerobic conditions where the enhanced Cu corrosion increases the size of anodic sites. The results obtained from the surface-height-distribution diagrams constructed for anaerobic conditions showed that the reaction between Cu+ and Ag+ does not start in the bulk of the solution even at the highest studied temperature. [source]

    K,Ar ages of the Ohmine Granitic Rocks, south-west Japan

    ISLAND ARC, Issue 4 2003
    Tomoaki Sumii
    Abstract The Ohmine Granitic Rocks are a series of granitic rocks that are distributed in a chain stretching along the central axis of the Kii Peninsula. Their precise ages have not been determined, although precise ages have been reported for other geological units of the early to middle Miocene distributed over the peninsula. In this study, biotite K,Ar ages were obtained for the six major granitic plutons of the Ohmine Granitic Rocks: Dorogawa, Shirakura, Kose, Asahi, Tenguyama and Shiratani. Most are aged from 14.8 to 14.6 Ma. Although one pluton is older (15.4 ± 0.2 Ma) and two are younger (14.0 ± 0.2 Ma and 13.4 ± 0.1 Ma), these ages are excluded from the discussion of the mutual correlation among the plutons because some ambiguities exist in their ages. The age of the southernmost unit, the Katago,Mukuro Dykes, was not determined because of its intense alteration, but stratigraphic constraints suggest that it is younger than 16.1 Ma. The majority of the Ohmine Granitic Rocks concentrate within a narrow age window of approximately 14.8,14.6 Ma, although their geochemical/petrographical characteristics suggest that they were generated by multiple magma batches. The results of this study also reveal the simultaneous occurrence of the major activities of the Ohmine Granitic Rocks and the gigantic felsic igneous activities in the Kii Peninsula, such as the Kumano Acidic Rocks and the Muro Pyroclastic Flow Deposit. [source]

    Ag-rich Tetrahedrite in the El Zancudo Deposit, Colombia: Occurrence, Chemical Compositions and Genetic Temperatures

    RESOURCE GEOLOGY, Issue 3 2010
    Alba Nury Gallego Hernández
    Abstract Chemical compositions of tetrahedrite,Ag-rich tetrahedrite,freibergite solid solutions (Ag-rich tetrahedritess) and homogenization temperatures of fluid inclusions in quartz and carbonates of seventeen samples from nine veins in the El Zancudo deposit, Antioquia, Colombia, were investigated to reveal the origin of silver in Ag-rich tetrahedritess, to derive their crystallization temperatures and to examine the relationship between chemical compositions of Ag-rich tetrahedritess and their crystallization temperatures. The ores consist of arsenopyrite, pyrite, sphalerite, Ag-rich tetrahedritess, galena, boulangerite, andorite, owyheeite, diaphorite, jamesonite, miargyrite, bournonite, chalcopyrite, and electrum. Ag-rich tetrahedritess forms about 10 volume % of the total ores and is one of the most common and widely distributed sulfosalts in this deposit. Ag-rich tetrahedritess is rich in Ag (1.13 to 31.02 wt%) and Sb (22.93 to 29.82 wt%), and poor in As (0.06 to 2.43 wt%), consistent with the reported incompatibilities of Ag and As in Ag-rich tetrahedritess. The Zn/(Zn + Fe)-, Ag/(Ag + Cu)- and Sb/(Sb + As + Bi)-atomic ratios exhibit some variations among the veins. Ag-rich tetrahedritess with higher Ag/(Ag + Cu) ratios coexist with diaphorite, whereas those with lower ratios are not associated with this sulfosalt. Ag-rich tetrahedritess in the assemblages of Ag-rich tetrahedritess+ sphalerite and of Ag-rich tetrahedritess+ bournonite + galena shows no Zn , Fe and Cu , Ag variations between core and rim, respectively, negating the possibility of solid state reaction during cooling. Ag-rich tetrahedritess is thus regarded as primary phase. Homogenization temperatures of primary fluid inclusions in quartz and carbonates co-existing with Ag-rich tetrahedritess define the mineralization temperatures of 134 to 263°C. Independent crystallization temperatures of Ag-rich tetrahedrite estimated based on Zn/(Zn + Fe) and Ag/(Ag + Cu) ratios of the Ag-rich tetrahedritess associated with silver minerals such as miargyrite, andorite and diaphorite using Sack's thermochemical database lie in a range between 170 and ,250°C. Both results are thus in good agreement. [source]

    Ag-Cu-Pb-Bi-S Minerals Newly Discovered from the Ohori Base Metal Deposit, Yamagata Prefecture, NE Japan: Implications for Bi-metallogenesis in the Green-Tuff Region

    RESOURCE GEOLOGY, Issue 1 2010
    Yu Yokoro
    Abstract The Ohori deposit, one of the base metal deposits in the Green-Tuff region, NE Japan, is composed of two types of mineralization; a skarn-type (Kaninomata orebody) made by the replacement of the Miocene calcareous layer, and a vein-type (Nakanomata orebody). While the ore mineral assemblage of the deposit (chalcopyrite, pyrite, sphalerite and galena) has been known for being rather simple, some Pb-Bi-S minerals have been discovered for the first time in the present study. The minerals mainly occur in the chalcopyrite-rich ores of both orebodies. They essentially belong to the Pb-Bi-S system and contain Cu and Ag in minor amounts, which correspond to the lillianite,gustavite solid solution series (phases Z and X), cosalite, neyite, felbertalite, krupkaite and Bi-bearing galena. The chalcopyrite-rich (Bi-bearing) ores from both orebodies are richer in chalcopyrite, pyrite and chlorite, and have higher homogenization temperatures (>300°C) of fluid inclusions, and higher FeS contents in sphalerite compared to the Bi-free ores. In the Green-Tuff region, Bi-minerals have been reported from many base metal deposits. Most of these Bi-bearing ore deposits are referred to as xenothermal-type deposits, and are characterized by the following common features; composite mineralization of high- and low-temperatures in the shallower environments, and close relationships with the Tertiary granitic rocks. The whole mineralization at the Ohori deposit also has a similar xenothermal character because of the coexistence of high-temperature chalcopyrite-rich ores with Pb-Bi-S minerals, which were formed by the influence of the Tertiary granitic rocks at a shallow depth. [source]

    REE, Mn, Fe, Mg and C, O Isotopic Geochemistry of Calcites from Furong Tin Deposit, South China: Evidence for the Genesis of the Hydrothermal Ore-forming Fluids

    RESOURCE GEOLOGY, Issue 1 2010
    Yan Shuang
    Abstract The Furong tin deposit in the central Nanling region, South China, consists of three main types of mineralization ores, i.e. skarn-, altered granite- and greisen-type ores, hosted in Carboniferous and Permian strata and Mesozoic granitic intrusions. Calcite is the dominant gangue mineral intergrown with ore bodies in the orefield. We have carried out REE, Mn, Fe, and Mg geochemical and C, and O isotopic studies on calcites to constrain the source and evolution of the ore-forming fluids. The calcites from the Furong deposit exhibit middle negative Eu anomaly (Eu/Eu*= 0.311,0.921), except for one which has an Eu/Eu* of 1.10, with the total REE content of 5.49,133 ppm. The results show that the calcites are characterized by two types of REE distribution patterns: a LREE-enriched pattern and a flat REE pattern. The LREE-enriched pattern of calcites accompanying greisen-type ore and skarn-type ore are similar to those of Qitianling granite. The REE, Mn, Fe, and Mg abundances of calcites exhibit a decreasing tendency from granite rock mass to wall rock, i.e. these abundances of calcites associated with altered granite-type and greisen-type ores are higher than those associated with skarn-type ores. The calcites from primary ores in the Furong deposit show large variation in carbon and oxygen isotopic compositions. The ,13C and ,18O of calcites are ,0.4 to ,12.7, and 2.8 to 16.4,, respectively, and mainly fall within the range between mantle or magmatic carbon and marine carbonate. The calcites from greisen and altered granite ores in the Furong deposit display a negative correlation in the diagram of ,13C versus ,18O, probably owing to the CO2 -degassing of the ore-forming fluids. From the intrusion to wall-rock, the calcites display an increasing tendency with respect to ,13C values. This implies that the carbon isotopic compositions of the ore-bearing fluids have progressively changed from domination by magmatic carbon to sedimentary carbonate carbon. In combination with other geological and geochemical data, we suggest that the ore-forming fluids represent magmatic origin. We believe that the fluids exsolved from fractionation of the granitic magma, accompanying magmatism of the Qitianling granite complex, were involved in the mineralization of the Furong tin polymetallic deposit. [source]

    Mineralogy, Lithogeochemistry and Elemental Mass Balance of the Hydrothermal Alteration Associated with the Gold-rich Batu Hijau Porphyry Copper Deposit, Sumbawa Island, Indonesia

    RESOURCE GEOLOGY, Issue 3 2009
    Arifudin Idrus
    Abstract This paper discusses the mineralogy, whole-rock geochemistry and elemental mass balance of the hydrothermal alteration zones within the Batu Hijau porphyry copper-gold deposit, Sumbawa Island, Indonesia. The hydrothermal alteration and mineralisation developed in four stages, namely (i) the early stage consisting of a central copper-gold-bearing biotite (potassic), proximal actinolite (inner propylitic) and the distal chlorite-epidote (outer propylitic) zones; (ii) the transitional stage represented by the chlorite-sericite (intermediate argillic) zone; (iii) the late stages distinguished into the sericite-paragonite (argillic) and pyrophyllite-andalusite (advanced argillic) zones; and (iv) the very late stage typified by the illite-sericite zone. In general, major elements (particularly Ca, Mg, Na and K) and some minor and rare earth elements decrease from the least altered rocks towards the late alteration zones as a consequence of the breakdown of Ca-bearing hornblende, biotite and plagioclase. Chemical discrimination by means of millicationic R1 -R2 diagram indicates that R1 [4Si , 11(Na + K) , 2(Fe + Ti)] increases while R2[6Ca + 2Mg + Al] decreases with increasing alteration intensity, from least-altered, through early, transitional, to late alteration zones. Rare earth elements-chondrite (C1) normalised patterns also exhibit the depletion of the elements through the subsequent alteration zones. These results are consistent with the elemental mass balance calculation using the isocon method which shows that the degree of mass and volume depletion systematically increases during alteration. A decrease of the elements as well as mass and volume from early, through transitional to late alteration stages may imply a general decrease of the element activities in hydrothermal fluids during the formation of the alteration zones. [source]

    Variations in Chemical Composition of Clay Minerals and Magnetic Susceptibility of Hydrothermally Altered Rocks in the Hishikari Epithermal Gold Deposit, SW Kyushu, Japan

    RESOURCE GEOLOGY, Issue 1 2008
    Hiroyasu Murakami
    Abstract Hydrothermal alteration, involving chiefly chlorite and illite, is extensively distributed within host rocks of the Pleistocene Hishikari Lower Andesites (HLA) and the Cretaceous Shimanto Supergroup (SSG) in the underground mining area of the Hishikari epithermal gold deposit, Kagoshima, Japan. Approximately 60% of the mineable auriferous quartz-adularia veins in the Honko vein system occur in sedimentary rocks of the SSG, whereas all the veins of the Yamada vein system occur in volcanic rocks of the HLA. Variations in the abundance and chemical composition of hydrothermal minerals and magnetic susceptibility of the hydrothermally altered rocks of the HLA and SSG were analyzed. In volcanic rocks of the HLA, hydrothermal minerals such as quartz, chlorite, adularia, illite, and pyrite replaced primary minerals. The amount of hydrothermal minerals in the volcanic rocks including chlorite, adularia, illite, and pyrite as well as the altered and/or replaced pyroxenes and plagioclase phenocrysts increases toward the veins in the Honko vein system. The vein-centered variation in mineral assemblage is pronounced within up to 25 m from the veins in the peripheral area of the Honko vein system, whereas it is not as apparent in the Yamada vein system. The hydrothermal minerals in sandstone of the SSG occur mainly as seams less than a few millimeters thick and are sporadically observed in halos along the veins and/or the seams. The alteration halos in sandstone of the SSG are restricted to within 1 m of the veins. In the peripheral area of the Honko vein system, chlorite in volcanic rocks is characterized by increasing in Al in its tetrahedral layer and the Fe/Fe + Mg ratio toward the veins, while illite in volcanic rocks has relatively low K and a restricted range of Fe/Fe + Mg ratios. Temperature estimates derived from chlorite geothermometry rise toward the veins within the volcanic rocks. The magnetic susceptibility of tuff breccia of the HLA varies from 21 to less than 0.01 × 10,3 SI within a span of 40 m from the veins and has significant variation relative to that of andesite (27,0.06 × 10,3 SI). The variation peripheral to the Honko vein system correlates with an increase in the abundance of hematite pseudomorphs after magnetite, the percentage of adularia and chlorite with high Fe/Fe + Mg ratios, and the degree of plagioclase alteration with decreasing distance to the veins. In contrast, sedimentary rocks of the SSG maintain a consistent magnetic susceptibility across the alteration zone, within a narrow range from 0.3 to 0.2 × 10,3 SI. Magnetic susceptibility of volcanic rocks of the HLA, especially tuff breccia, could serve as an effective exploration tool for identifying altered volcanic rocks. [source]

    Epithermal Gold-Silver Mineralization of the Asachinskoe Deposit in South Kamchatka, Russia

    RESOURCE GEOLOGY, Issue 4 2007
    Ryohei Takahashi
    Abstract The Asachinskoe epithermal Au-Ag deposit is a representative low-sulfidation type of deposit in Kamchatka, Russia. In the Asachinskoe deposit there are approximately 40 mineralized veins mainly hosted by dacite,andesite stock intrusions of Miocene,Pliocene age. The veins are emplaced in tensional cracks with a north orientation. Wall-rock alteration at the bonanza level (170,200 m a.s.l.) consists of the mineral assemblage of quartz, pyrite, albite, illite and trace amounts of smectite. Mineralized veins are well banded with quartz, adularia and minor illite. Mineralization stages in the main zone are divided into stages I,IV. Stage I is relatively barren quartz,adularia association formed at 4.7 ± 0.2 Ma (K-Ar age). Stage II consists of abundant illite, Cu-bearing cryptomelane and other manganese oxides and hydroxides, electrum, argentite, quartz, adularia and minor rhodochrosite and calcite. Stage III, the main stage of gold mineralization (4.5,4.4 ± 0.1,3.1 ± 0.1 Ma, K-Ar age), consists of a large amount of electrum, naumannite and Se-bearing polybasite with quartz,adularia association. Stage IV is characterized by hydrothermal breccia, where electrum, tetrahedrite and secondary covellite occur with quartz, adularia and illite. The concentration of Au+Ag in ores has a positive correlation with the content of K2O + Al2O3, which is controlled by the presence of adularia and minor illite, and both Hg and Au also have positive correlations with the light rare-earth elements. Fluid inclusion studies indicate a salinity of 1.0,2.6 wt% NaCl equivalent for the whole deposit, and ore-forming temperatures are estimated as approximately 160,190°C in stage III of the present 218 m a.s.l. and 170,180°C in stage IV of 200 m a.s.l. The depth of ore formation is estimated to be 90,400 m from the paleo-water table for stage IV of 200 m a.s.l., if a hydrostatic condition is assumed. An increase of salinity (>CNaCl, 0.2 wt%) and decrease of temperature (>T , 30°C) within a 115-m vertical interval for the ascending hydrothermal solution is calculated, which is interpreted as due to steam loss during fluid boiling. Ranges of selenium and sulfur fugacities are estimated to be logfSe2 = ,17 to ,14.5 and logfS2 = ,15 to ,12 for the ore-forming solution that was responsible for Au-Ag-Se precipitation in stage III of 200 m a.s.l. Separation of Se from S-Se complex in the solution and its partition into selenides could be due to a relatively oxidizing condition. The precipitation of Au-Ag-Se was caused by boiling in stage III, and the precipitation of Au-Ag-Cu was caused by sudden decompression and boiling in stage IV. [source]

    Geology, Wall-rock Alteration and Vein Paragenesis of the Bilimoia Gold Deposit, Kainantu Metallogenic Region, Papua New Guinea

    RESOURCE GEOLOGY, Issue 3 2007
    Joseph Onglo Espi
    Abstract The Bilimoia deposit (2.23 Mt, 24 g/t Au), located in the eastern Central Mobile Belt of mainland Papua New Guinea, is composed of fault-hosted, NW,NNW-trending Irumafimpa,Kora and Judd,Upper Kora Au-quartz veins hosted by Middle,Late Triassic basement that was metamorphosed to medium-grade greenschist facies between Middle,Late Triassic and Early,Middle Jurassic. Mineralizing fluids were introduced during crustal thickening, rapid uplift, change of plate motions from oblique to orthogonal compression, active faulting and S3 and S4 events in an S1,S4 deformation sequence. The Bilimoia deposit is spatially and temporally related to I-type, early intermediate to felsic and late mafic intrusions emplaced in Late Miocene (9,7 Ma). Hydrothermal alteration and associated mineralization is divided into 10 main paragenetic stages: (1) chlorite,epidote-selvaged quartz,calcite,specularite vein; (2) local quartz,illite,pyrite alteration; (3) quartz,sericite,mariposite,fuchsite,pyrite wall-rock alteration that delimits the bounding shears; (4) finely banded, colloform-, crustiform- and cockade-textured and drusy quartz ± early wolframite ± late adularia; (5) hematite; (6) pyrite; (7) quartz ± amethyst-base metal sulfides; (8) quartz,chalcopyrite,bornite,Sn and Cu sulfides,Au tellurides and Te ± Bi ± Ag ± Cu ± Pb phases; (9) Fe ± Mn carbonates; and (10) supergene overprint. Fluid inclusions in stage 4 are characterized by low salinity (0.9,5.4 wt% NaCl equivalent), aqueous,carbonic fluids with total homogenization temperatures ranging from 210 to 330°C. Some of the inclusions that homogenized between 285 and 330°C host coexisting liquid- and vapor-rich (including carbonic) phases, suggesting phase separation. Fluid inclusions in quartz intergrown with wolframite have low salinity (0.9,1.2 wt% NaCl equivalent), aqueous,carbonic fluids at 240,260°C, defining the latter's depositional conditions. The ore fluids were derived from oxidized magmatic source initially contaminated by reduced basement rocks. Wall-rock alteration and involvement of circulating meteoric waters were dominant during the first three stages and early part of stage 4. Stage 5 hematite was deposited as a result of stage 4 phase separation or entrainment of oxygenated groundwater. Gold is associated with Te- and Bi-bearing minerals and mostly precipitated as gold-tellurides during stage 8. Gold deposition occurred below 350°C due to a change in the sulfidation and oxidation state of the fluids, depressurization and decreasing temperature and activities of sulfur and tellurium. Bisulfides are considered to be the main Au-transporting complexes. The Bilimoia deposit has affinities that are similar to many gold systems termed epizonal orogenic and intrusion-related. The current data allow us to classify the Bilimoia deposit as a fault-controlled, metamorphic-hosted, intrusion-related mesothermal to low sulfidation epithermal quartz,Au,Te,Bi vein system. [source]

    Orogenic Gold Mineralization in the Qolqoleh Deposit, Northwestern Iran

    RESOURCE GEOLOGY, Issue 3 2007
    Farhang Aliyari
    Abstract The Qolqoleh gold deposit is located in the northwestern part of the Sanandai-Sirjan Zone, northwest of Iran. Gold mineralization in the Qolqoleh deposit is almost entirely confined to a series of steeply dipping ductile,brittle shear zones generated during Late Cretaceous,Tertiary continental collision between the Afro-Arabian and the Iranian microcontinent. The host rocks are Mesozoic volcano-sedimentary sequences consisting of felsic to mafic metavolcanics, which are metamorphosed to greenschist facies, sericite and chlorite schists. The gold orebodies were found within strong ductile deformation to late brittle deformation. Ore-controlling structure is NE,SW-trending oblique thrust with vergence toward south ductile,brittle shear zone. The highly strained host rocks show a combination of mylonitic and cataclastic microstructures, including crystal,plastic deformation and grain size reduction by recrystalization of quartz and mica. The gold orebodies are composed of Au-bearing highly deformed and altered mylonitic host rocks and cross-cutting Au- and sulfide-bearing quartz veins. Approximately half of the mineralization is in the form of dissemination in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in quartz,sulfide microfractures, microveins and veins. Only low volumes of gold concentration was introduced during ductile deformation, whereas, during the evident brittle deformation phase, competence contrasts allowed fracturing to focus on the quartz,sericite domain boundaries of the mylonitic foliation, thus permitting the introduction of auriferous fluid to create disseminated and cross-cutting Au-quartz veins. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification and sulfidation zone (major ore body); sericite and carbonate alteration zone; and sericite,chlorite alteration zone that may be taken to imply wall-rock interaction with near neutral fluids (pH 5,6). Silicified and sulfide alteration zone is observed in the inner parts of alteration zones. High gold grades belong to silicified highly deformed mylonitic and ultramylonitic domains and silicified sulfide-bearing microveins. Based on paragenetic relationships, three main stages of mineralization are recognized in the Qolqoleh gold deposit. Stage I encompasses deposition of large volumes of milky quartz and pyrite. Stage II includes gray and buck quartz, pyrite and minor calcite, sphalerite, subordinate chalcopyrite and gold ores. Stage III consists of comb quartz and calcite, magnetite, sphalerite, chalcopyrite, arsenopyrite, pyrrhotite and gold ores. Studies on regional geology, ore geology and ore-forming stages have proved that the Qolqoleh deposit was formed in the compression,extension stage during the Late Cretaceous,Tertiary continental collision in a ductile,brittle shear zone, and is characterized by orogenic gold deposits. [source]

    Chemical Composition of Rock-Forming Minerals in Copper,Gold-Bearing Tonalite Porphyries at the Batu Hijau Deposit, Sumbawa Island, Indonesia: Implications for Crystallization Conditions and Fluorine,Chlorine Fugacity

    RESOURCE GEOLOGY, Issue 2 2007
    Arifudin Idrus
    Abstract Copper,gold mineralization at the world-class Batu Hijau porphyry deposit, Sumbawa Island, Indonesia, is closely related to the emplacement of multiple stages of tonalite porphyries. Petrographic examination indicates that at least two texturally distinct types of tonalite porphyries are currently recognized in the deposit, which are designated as "intermediate tonalite" and "young tonalite". They are mineralogically identical, consisting of phenocrysts of plagioclase, hornblende, quartz, biotite and magnetite ± ilmenite, which are set in a medium-coarse grained groundmass of plagioclase and quartz. The chemical composition of the rock-forming minerals, including plagioclase, hornblende, biotite, magnetite and ilmenite in the tonalite porphyries was systematically analyzed by electron microprobe. The chemical data of these minerals were used to constrain the crystallization conditions and fluorine,chlorine fugacity of the corresponding tonalitic magma during its emplacement and crystallization. The crystallization conditions, including temperature (T), pressure (P) and oxygen fugacity (fO2), were calculated by applying the hornblende,plagioclase and magnetite,ilmenite thermometers and the Al-in-hornblende barometer. The thermobarometric data indicate that the tonalite porphyries were emplaced at 764 ± 22°C and 1.5 ± 0.3 × 105 kPa. If the pressure is assumed to be lithostatic, it is interpreted that the rim of hornblende and plagioclase phenocrysts crystallized at depths of approximately 5.5 km. As estimated from magnetite,ilmenite thermometry, the subsolidus conditions of the tonalite intrusion occurred at temperatures of 540,590°C and log fO2 ranging from ,20 to ,15 (between Ni-NiO and hematite,magnetite buffers). This occurred at relatively high fO2 (oxidizing) condition. The fluorine,chlorine fugacity in the magma during crystallization was determined on the basis of the chemical composition of magmatic biotite. The calculation indicates that the fluorine,chlorine fugacity, represented by log (fH2O)/(fHF) and (fH2O)/(fHCl) in the corresponding tonalitic magma range from 4.31 to 4.63 and 3.62 to 3.79, respectively. The chlorine fugacity (HCl) to water (H2O) is relatively higher than the fluorine fugacity (HF to water), reflecting a high activity of chlorine in the tonalitic magma during crystallization. The relatively higher activity of chlorine (rather than fluorine) may indicate the significant role of chloride complexes (CuCl2, and AuCl2,) in transporting and precipitating copper and gold at the Batu Hijau deposit. [source]

    Sulfur Isotope Geochemistry of the Supergiant Xikuangshan Sb Deposit, Central Hunan, China: Constraints on Sources of Ore Constituents

    RESOURCE GEOLOGY, Issue 4 2006
    Dong-sheng Yang
    Abstract. The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of ,34S values (+5 , +8 %) for both early and late main-stage stibnite; a single early-stage stibnite exhibits ,34S value (+7.5 %) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 %). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in ,34S values for early main-stage stibnite (+3.5 to +16.3 %, av. +7.5 %) compared to that for late main-stage stibnite (+5.3 to +8.1 %, av. +6.2 %) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with ,34Spyrite values at ca. +11 , +24 % and -7.0 ,-11 %. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids. [source]

    Genetic Environment of the Intrusion-related Yuryang Au-Te Deposit in the Cheonan Metallogenic Province, Korea

    RESOURCE GEOLOGY, Issue 2 2006
    Sang Joon Pak
    Abstract. The Yuryang gold deposit, comprising a Te-bearing Au-Ag vein mineralization, is located in the Cheonan area of the Republic of Korea. The deposit is hosted in Precambrian gneiss and closely related to pegmatite. The mineralized veins display massive quartz textures, with weak alteration adjacent to the veins. The ore mineralization is simple, with a low Ag/Au ratio of 1.5:1, due to the paucity of Ag-phases. Ore mineralization took place in two different mineral assemblages with paragenetic time; early Fe-sulfide mineralization and late Fe-sulfide and Au-Te mineralization. The early Fe-sulfide mineralization (pyrite + sphalerite) occurred typically along the vein margins, and the subsequent Au-Te mineralization is characterized by fracture fillings of galena, sphalerite, pyrrhotite, Te-bearing minerals (petzite, altaite, hessite and Bi-Te mineral) and electrum. Fluid inclusions characteristically contain CO2 and can be classified into four types (Ia, Ib, IIa and IIb) according to the phase behavior. The pressure corrected temperatures (,500d,C) indicate that the deposit was formed at a distinctively high temperature from fluids with moderate to low salinity (<12 wt% equiv. NaCl) and CH4 (1,22 mole %). The sphalerite geo-barometry yield an estimated pressure about 3.5 ,2.1 kbar. The dominant ore-deposition mechanisms were CO2 effervescence and concomitant H2S volatilization, which triggered sulfidation and gold mineralization. The measured and calculated isotopic compositions of fluids (,18OH2O = 10.3 to 12.4 %o; ,DH2O = -52 to -77 %o) may indicate that the gold deposition originated from S-type magmatic waters. The physicochemical conditions observed in the Yuryang gold deposit indicate that the Jurassic gold deposits in the Cheonan area, including the Yuryang gold deposit are compatible with deposition of the intrusion-related Au-Te veins from deeply sourced fluids generated by the late Jurassic Daebo magmatism. [source]

    Magmatic Fluid Inclusions from the Zaldivar Deposit, Northern Chile: The Role of Early Metal-bearing Fluids in a Porphyry Copper System

    RESOURCE GEOLOGY, Issue 1 2006
    Eduardo A. Campos
    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 750d,C), well above the typical temperatures of hydro thermal fluids (less than 600d,C) 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. [source]

    Rare Earth, Major and Trace Elements in the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

    RESOURCE GEOLOGY, Issue 4 2005
    Yasuhiro Kato
    Abstract. Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today. [source]

    Evolution of Hydrothermal System at the Dizon Porphyry Cu-Au Deposit, Zambales, Philippines

    RESOURCE GEOLOGY, Issue 2 2005
    Akira Imai
    Abstract. Evolution of hydrothermal system from initial porphyry Cu mineralization to overlapping epithermal system at the Dizon porphyry Cu-Au deposit in western central Luzon, Zambales, Philippines, is documented in terms of mineral paragen-esis, fluid inclusion petrography and microthermometry, and sulfur isotope systematics. The paragenetic stages throughout the deposit are summarized as follows; 1) stockwork amethystic quartz veinlets associated with chalcopyrite, bornite, magnetite and Au enveloped by chlorite alteration overprinting biotite alteration, 2) stockwork quartz veinlets with chalcopyrite and pyrite associated with Au and chalcopyrite and pyrite stringers in sericite alteration, 3) stringer quartz veinlets associated with molybdenite in sericite alteration, and 4) WNW-trending quartz veins associated with sphalerite and galena at deeper part, while enargite and stibnite at shallower levels associated with advanced argillic alteration. Chalcopyrite and bornite associated with magnetite in quartz veinlet stockwork (stage 1) have precipitated initially as intermediate solid solution (iss) and bornite solid solution (bnss), respectively. Fluid inclusions in the stockwork veinlet quartz consist of gas-rich inclusions and polyphase inclusions. Halite in polyphase inclusions dissolves at temperatures ranging from 360d,C to >500d,C but liquid (brine) and gas (vapor) do not homogenize at <500d,C. The maximum pressure and minimum temperature during the deposition of iss and bnss with stockwork quartz veinlets are estimated to be 460 bars and 500d,C. Fluid inclusions in veinlet stockwork quartz enveloped in sericite alteration (stage 2) consist mainly of gas-rich inclusions and polyphase inclusions. In addition to the possible presence of saturated NaCl crystals at the time of entrapment of fluid inclusions that exhibit the liquid-vapor homogenization temperatures lower than the halite dissolution temperatures in some samples, wide range of temperatures of halite dissolution and liquid-vapor homogenization of polyphase inclusions from 230d,C to >500d,C and from 270d,C to >500d,C, respectively, suggests heterogeneous entrapment of gaseous vapor and hypersaline brine. The minimum pressure and temperature are estimated to be about 25 bars and 245d,C. Fluid inclusions in veinlet quartz associated with molybdenite (stage 3) are dominated by gas-rich inclusions accompanied with minor liquid-rich inclusions that homogenize at temperatures between 350d,C and 490d,C. Fluid inclusions in vuggy veinlet quartz associated with stibnite (stage 4) consist mainly of gas-rich inclusions with subordinate polyphase inclusions that do not homogenize below 500d,C. Fluid inclusions in veinlet quartz associated with galena and sphalerite (stage 4) are composed of liquid-rich two-phase inclusions, and they homogenize into liquid phase at temperatures ranging widely from 190d,C to 300d,C (suggesting boiling) and the salinity ranges from 1.0 wt% to 3.4 wt% NaCl equivalent. A pressure of about 15 bars is estimated for the dilute aqueous solution of 190d,C from which veinlet quartz associated with galena and sphalerite precipitated. In addition to a change in temperature-pressure regime from lithostatic pressure during the deposition of iss and bnss with stockwork quartz veinlets to hydrostatic pressure during fracture-controlled quartz veinlet associated with galena and sphalerite, a decrease in pressure is supposed to have occurred due to unroofing or removal of the overlying piles during the temperature decrease in the evolution of hydrothermal system. The majority of the sulfur isotopic composition of sulfides ranges from ±0 % to +5 %. Sulfur originated from an iso-topically uniform and homogeneous source, and the mineralization occurred in a single hydrothermal system. [source]

    Invisible Gold from the Hishikari Epithermal Gold Deposit, Japan: Implication for Gold Distribution and Deposition

    RESOURCE GEOLOGY, Issue 2 2005
    Nobutaka Shimada
    Abstract. The presence of invisible gold was confirmed in arsenian pyrite from the Hishikari epithermal gold deposit, Kagoshima, Japan, by means of EPMA and SIMS analyses. The relative concentration of invisible gold may be positively correlated with As contents (0.01 to 10.37 wt%) of fine-grained arsenian pyrite which commonly occurs in the auriferous quartz veins. Although arsenian pyrite occurs widely in any mineralization stage with electrum and other sulfide, sulfosalts, selenide or telluride minerals, arsenian pyrites having higher As contents accompanied by invisible gold occur dominantly in the middle stage of fine-adularia-quartz and in the late stage of coarse-quartz rather than in the early stage of columnar-adularia. [source]

    Carbonatitic Volcanic Genesis of Hetaoqing Fe-Cu Deposit in Central Yunnan, China

    RESOURCE GEOLOGY, Issue 4 2003
    Yongbei Zhang
    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. [source]

    Tectonic Controls on the Formation of the Liwu Cu-rich Sulfide Deposit in the Jianglang Dome, S W China

    RESOURCE GEOLOGY, Issue 2 2003
    Dan-Ping Yan
    Abstract. The Liwu Cu-rich sulfide deposit occurs within the Jianglang dome in the eastern margin of the Tibetan plateau. The dome consists of a core, a middle slab and a cover sequence. The main deposit is hosted in the core with minor ore bodies in the middle slab. The protolith of the core consists of clastic sedimentary rocks with inter-layered volcanic rocks. All of the ore bodies are substantially controlled by an extensional detachment fault system. The ore bodies within the core are distributed along the S2 foliation in the hinge of recumbent fold (D2), whereas ore bodies with en echelon arrangement are controlled by the mylonitic foliation of the lower detachment fault. Ore bodies within the middle slab are oriented with their axes parallel to the mylonitic foliation. Pyrite and pyrrhotite from the ores contain Co ranging from 37 to 1985 ppm, Ni from 2.5 to 28.1 ppm, and Co/Ni ratios from 5 to 71. These sulfides have ,34S values ranging from 1.5 to 7.5 % whereas quartz separates have ,18O values of 11.9 and 14.3 % and inclusion fluid in quartz has ,D value of-88.1 %. These features suggest that the deposit was of hydrothermal origin. Two ore-forming stages are recognized in the evolution of the Jianglang dome. (1) A low-temperature ore-forming process, during the tectonic transport of the upper plate above the lower detachment, and the initial phase of the footwall updom-ing at 192,177 Ma. (2) A medium-temperature ore-forming stage, related to the final structural development of the initial detachment at 131,81Ma. Within the core, the ore bodies of the first stage were uplifted to, or near, the brittle/ductile horizon where the ore-forming metals were re-concentrated and enriched. A denudation stage in which a compressional tectonic event produced eastward thrusting overprinted the previous structures, and finally denuded the deposit. The Liwu Cu-rich sulfide deposit was formed during a regional extensional tectonic event and is defined as a tectono-strata-bound hydrothermal ore deposit. [source]

    Hydrothermal Alteration and Cu-Au Mineralization at Nena High Sulfidation-type Deposit, Frieda River, Papua New Guinea

    RESOURCE GEOLOGY, Issue 4 2002
    Joseph Onglo Espi
    Abstract. The Nena Cu-Au deposit, located in the Frieda River mineral district of northwestern mainland Papua New Guinea, is a composite structurally-lithologically controlled high sulfidation (HS) system. Its hydrothermal alteration and Cu-Au mineralization are presented in this paper. Initially propylitized andesitic volcanics veined by epithermal quartz were pervasively superimposed by zoned HS alteration. The zonation grades from vuggy silica core to sulfur-rich, pyritic silica-alunite halo followed by pyrophyllite-dickite-kaolinite interval and finally to thin illite-smectite margin, suggesting progressive decrease in temperature and increase in pH. This zonation is enveloped by chlorite-epidote-calcite-gypsum alteration. The acid altered rocks were then invaded by multiple phases of pyrite, subsequently crosscut by quartz, vein alunite and barite. Then sequential deposition of bladed covellite, enargite, luzonite and stibioluzonite occurred from the NW to the SE portions of the deposit, forming a zonation suggestive of progressive decrease in temperature, sulfur fugacity and sulfidation stage. Most ore mineralization occurs in the vuggy silica core. Gold mineralization commenced from the transition of enargite to luzonite and continued throughout the stibioluzonite stage. Associated with gold deposition are Au-rich pyrite, tennantite-tetrahedrite, chalcopyrite-bornite, native tellurium, electrum, calaverite, bismuthinite and galena. Native sulfur occupied the remaining cavities and represents the waning stage of the hydrothermal system. Fluid inclusions studies distinguished magmatic (>300,350d,C, 9,15 wt% NaCl equiv.) and meteoric (<150,200d,C, 1,2 wt% NaCl equiv.) fluids (Holzberger et al., 1996). Temperatures and salinities of fluid inclusions from barite associated with Cu sulfides show a general decrease from NW (330d,C, 9,15 wt% NaCl equiv.) to SE (172d,C, 10 wt% NaCl equiv.) parts of the deposit, indicating gradual entrainment of ground water (Hitchman and Espi, 1997). Interaction of magmatic fluids with meteoric water accompanied by changes in temperature, salinity, acidity and oxidation state of the resultant fluids is interpreted to have been the main cause of metal precipitation. Finally, supergene processes generated Au zone with an underlying chalcocite-covellite-digenite blanket over the primary sulfides at depth. Gold occurs as lattice constituent in scorodite, limonite-goethite and jarosite. Chalcocite is more abundant and widespread than other Cu sulfides. Acidic fluids deposited powdery alunite and kaolinite, vein alunite and amorphous silica. Weakly secondary biotite-quartz altered porphyry located below the known HS Cu-Au deposit contains chalcopyrite-bornite and is overprinted by quartz-alunite-pyro-phyllite-pyrite assemblage. This feature indicates close temporal, spatial and genetic relation between the two deposit types. [source]

    Mass Transfer, Oxygen Isotopic Variation and Gold Precipitation in Epithermal System: A Case Study of the Hishikari Deposit, Southern Kyushu, Japan

    RESOURCE GEOLOGY, Issue 3 2002
    Naotatsu SHIKAZONO
    Abstract: Transportation of various kinds of elements occurred in wall rocks (Quaternary andesites) during the hydrothermal alteration accompanied by the Hishikari epithermal gold mineralization. For example, K2O and MgO contents of wall rocks decrease away from the gold-quartz veins, while (CaO+Na2O) content increases, and SiO2 content is variable near the veins. Hydrothermal alteration zoning and bulk compositional variations in wall rocks suggest that the mixing of hydrothermal solution and acidic groundwater took place an important role as the cause for the hydrothermal alteration and bulk compositional variations. The relationship between dissolved silica concentration and temperature of hydrothermal solution mixed with groundwater is obtained based on precipitation kinetics-fluid flow,mixing model, and the computed results are compared with the distribution of SiO2 minerals (quartz and cristobalite) in the hydrothermal alteration zones. This comparison suggests that the most reasonable flow rate of fluids migrating through hydrothermal alteration zones, and A/M (A: surface area of rocks interacting with fluid, M: mass of fluid) are estimated to be ca. 10 -4.2 m/sec, and ca. 0.10 m2/kg, respectively. The mixing of two fluids (hydrothermal solution and acidic groundwater) can also explain ,18O zoning in the altered country rocks, hydrothermal alteration zoning from K-feldspar through K-mica to kaolinite from the center (veins) to margin, and deposition of gold. [source]

    Dashuigou Tellurium Deposit in Sichuan Province, China: S, C, O, and H Isotope Data and Their Implications on Hydrothermal Mineralization

    RESOURCE GEOLOGY, Issue 1 2002
    Jingwen MAO
    Abstract: Dashuigou, a unique tellurium-dominated deposit over the world, is located in the western margin of the Yangtze cra-ton in southwestern China. It is characterized by high-grade tellurium accompanied by bismuth, gold, silver, and sulfur, and occurs in the area of less than one km2. The mineralization is divided into three stages, i.e. (1) tellurium-bearing pyrrhotite,pyrite stage, (2) tetradymite stage, and (3) auriferous quartz veins stage. Tellurium mineralization coexisting with bismuth, silver, selenium, and gold predominantly develops in the stage 2, while the stage 1 is enriched only in sulfur and iron, and the stage 3 is very weakly mineralized with gold. The ,34S values of sulfides in the ore of the deposit vary in a narrow range of ,3.1 - +2.8 per mil with ,3.1 - +2.8 per mil for the stage 1 and ,0.5 - +2.1 for the stage 2, showing the isotopic characteristics of mantle derived sulfur. The ,13C values of vein dolomites vary from ,5.3 to ,7.2 per mil, with ,5.3 - ,6.6 per mil for the stage 1 and ,5.3 - ,7.2 per mil for the stage 2, which are significantly different from those of surrounding Triassic marble with ,13C values of ,0.3 - +2.8 per mil, and show characteristics of mantle derived carbon. The ,18O values of vein dolomites range from +10.2 to +13.1 per mil, which are higher than those of carbonatite, but lower than those of the marble. Their corresponding ,18Owater values are +0.6 - +3.9 per mil, with +2.7 - +3.8 per mil for the stage 1 and +0.6 - +3.9 per mil for the stage 2. The data implies that these vein carbonates were formed by the mixing fluids of magmatic or mantle source with meteoric or formation water. The ,18O values of ore-forming fluids responsible for the formation of vein quartz are estimated to be +3.2 to +6.8, the ,D values of inclusion fluids of the quartz are measured to be ,54 to ,82 per mil. All those stable isotopic data suggest the involvement of the fluids from mantle and/or mantle-derived magmas through fault system in the forming process of the Dashuigou tellurium deposit. [source]

    Mineralogy, Geochemistry, and Age Constraints on the Beni Bou Ifrour Skarn Type Magnetite Deposit, Northeastern Morocco

    RESOURCE GEOLOGY, Issue 1 2002
    Mohammed EL RHAZI
    Abstract: The Beni Bou Ifrour deposit of northeastern Morocco is a skarn type magnetite deposit. K-Ar age determination suggests that the mineralization occurred at 7.040.47 Ma. The spatial relationship between skarn and dikes of microgran-odiorite derived from the batholith of Wiksane Granodiorite, and the similarity of age (8.020.22 Ma), confirms that the Wiksane Granodiorite is the igneous rock most probably related to mineralization. The skarn is distributed asymmetrically in the limestone, and magnetite ore was developed just below the calc-silicate skarn as two parallel beds separated by 100 m of barren limestone and schist. The mineralization can be divided into three stages. The early stage is characterized by the formation of calc-silicate minerals, mainly clinopyroxene (80,70 % diopside) and garnet (early almost pure andradite to the late 60 % andradite). The main stage is characterized by the formation of a large amount of magnetite. Epidote and quartz formed simultaneously with magnetite. Fluid temperatures exceeded 500 C during the early to main stages. Fluid with very high salinity (50,75 wt% NaCl equiv.) was responsible for the formation of the magnetite ore. The oxygen isotope composition, together with the fluid inclusion data, suggests that magmatic fluid was significant for the formation of calc-silicate skarn minerals and magnetite. Low temperature (-230C) and low salinity (-10 % NaCl equiv.) hydrothermal fluids dominated by meteoric water were responsible for the late stage quartz and calcite formation. [source]