Stratiform Sulfide Deposits Research Articles

Using Hg isotopes and trace elements to constrain the origin of the Ordovician Xiangquan Tl deposit, South China

Sediment-hosted stratiform sulfide (SHSS) deposits commonly contain large amounts of strategic metals, such as Tl, Hg, Cd, Ge and Ga, however, sources of these metals remain debate. Here we present new elemental and Hg isotopic data to constrain the metal sources for the Xiangquan Tl deposit (South China), a unique SHSS deposit with 250 t Tl at an average grade of 928 ppm. Stratiform pyrite orebodies are hosted in the Ordovician marine sedimentary succession of mostly limestone with minor mudstone. Pyrite, the dominant ore mineral, is rich in Hg (up to 1360 ppm). Bulk ores and pyrite separates from this deposit have significant variations of δ202Hg (−5.48 to −0.65 ‰) and Δ199Hg (−0.01 to 0.36 ‰). The Δ199Hg values are mostly positive, similar to those of seawater and marine sediments. Ore petrography, trace element enrichment coefficients, rare earth element patterns, Re-Os ages (478 ± 33 Ma) and S isotope compositions of pyrite indicate that Hg and other metals were derived from hydrothermal fluids venting at the seafloor. We suggest that the ore-forming fluids of the Xiangquan deposit were predominantly originated from large-scale circulation of evolved seawater, which leached Hg and Tl from the marine country rocks. These metal-rich fluids migrated upward, vented to the seafloor, and mixed with anoxic H2S-rich seawater to precipitate Hg- and Tl-rich pyrite. Our study highlights that the combined application of Hg isotopes and trace elements could be used to trace the sources of metals in hydrothermal ore deposits such as SHSS deposits.

Constraints of Fe-S-C stable isotopes on hydrothermal and microbial activities during formation of sediment-hosted stratiform sulfide deposits

Microbial and hydrothermal venting activities on the seafloor are important for the formation of sediment-hosted stratiform sulfide (SHSS) deposits. Fe isotopic compositions are sensitive to both microbial and hydrothermal activities and may be used to investigate the formation of these deposits. However, to the best of our knowledge, no Fe isotopic studies have been conducted on SHSS deposits. In the Devonian Dajiangping SHSS-type pyrite deposit (389 Ma), South China, laminated pyrite ores were precipitated from exhalative hydrothermal fluids, whereas black shales were deposited during intervals with no exhalation. Pyrite grains from black shales mostly display positive δ56Fe-py (0.01–0.73‰), higher than marine sediments (ca. 0‰), due to pyrite deriving Fe from basinal shuttled Fe(III) (hydr-)oxides and slowly crystallizing in pores of sediments with equilibrium fractionation, except for negative δ56Fe-py (−0.17‰ to −0.24‰) of two samples caused by mixing of Fe from underlain laminated ores. The positive δ34S-py (3.50–24.5‰) of black shales reflect that sulfur of pyrite originated from quantitative reduction of sulfate in closed pores of sediments. In contrast, pyrite grains of laminated ores have negative δ56Fe-py (−0.60‰ to −0.21‰), which were not only inherited from the negative δ56Fe of hydrothermal fluids but also caused by kinetic fractionation during rapid precipitation of a pyrite precursor (FeS) in hydrothermal plumes. These ores have negative δ34S-py (−28.7‰ to −1.82‰), because H2S for pyrite mineralization was produced by bacterial sulfate reduction (BSR) in a sulfate-rich seawater column or shallow sediments.The δ56Fe-py values of laminated ores co-vary positively with δ34S-py and δ13C-carbonate along the ore stratigraphy, with δ13C-carbonate values ranging from −12.0‰ to −2.50‰. However, they correlate negatively with aluminum-normalized total organic carbon (TOC/Al2O3). Organic carbon is thus considered to enhance the production of H2S by BSR activities, increase pyrite precipitation rates and promote the expression of kinetic fractionation of Fe isotopes. Intriguingly, in the ore units with vigorous hydrothermal venting activities, δ56Fe-py, δ34S-py and δ13C-carbonate values display a consistently increasing trend. Such results suggest that venting hydrothermal fluids significantly inhibited the H2S production of BSR, which then reduced the pyrite crystallization rate and decreased the kinetic fractionation of Fe isotopes. Our study reveals that the formation of SHSS deposits relies on H2S from microbial activities and metals from hydrothermal exhalation on the seafloor, but that vigorous exhalation can inhibit microbial activities and thus sulfide precipitation rates. The integrated use of Fe, S, and C isotopes can effectively elucidate these dynamic interactions between hydrothermal venting and microbial activities during the formation of SHSS deposits.

Origin of Tin Mineralization in the Sullivan Pb-Zn-Ag Deposit, British Columbia: Constraints from Textures, Geochemistry, and LA-ICP-MS U-Pb Geochronology of Cassiterite

Abstract Textural, geochronological, and geochemical data are presented here for cassiterite from the giant (149.7 million tonnes [Mt]) Mesoproterozoic Sullivan Pb-Zn-Ag deposit, which has been subjected to several tectonothermal events. These data provide constraints on the age and origin of the tin concentrations and new insights into related base metal mineralization. Sullivan is rare among sediment-hosted, stratiform Pb-Zn-Ag deposits in having high tin contents in ore (up to 2.5 wt %; avg 310 ppm Sn). Cassiterite occurs in all facies of this deformed and metamorphosed deposit, including (1) high-grade veins with arsenopyrite and pyrrhotite, (2) bedded Pb-Zn-Ag ores, (3) massive pyrrhotite, (4) footwall and hanging-wall tourmalinites, and (5) other altered wall rocks. New in situ U-Pb dates for Sullivan cassiterite obtained by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) are modeled by a multicomponent-based algorithm that yields three age peaks: 1475 ± 4 Ma (51% of the data), 1366 ± 10 Ma (25%), and 1074 ± 7 Ma (24%). These dates are attributed, respectively, to primary tin mineralization at ca. 1475 Ma, the East Kootenay orogeny at ca. 1370 to 1300 Ma, and the Grenvillian orogeny at ca. 1100 to 980 Ma. Based on the presence and local abundance of cassiterite in all ore and ore-related rocks at Sullivan, the U-Pb date of 1475 ± 4 Ma reported here represents the first direct age for ore mineralization in the deposit. Occurrence of texturally discordant rims on Sullivan cassiterite grains having U-Pb dates coeval with the East Kootenay and Grenvillian orogenies suggests that these young dates reflect dissolution-reprecipitation processes associated with channelized metamorphic fluid flow. LA-ICP-MS U-Pb dates obtained on low-U (<10 ppm) cassiterite also indicate that U-Pb dates for cassiterite from other metamorphosed deposits should be viewed with caution and not assumed to record an age of primary tin mineralization. Aqueous transport conditions for tin are evaluated to gain insights into the cassiterite mineralization at Sullivan. Based on fO2-pH topology of aqueous tin species at 250°C, tin transport was dominated by an SnCl3− complex at fO2 of about –40 and pH of <4.0, conditions that were constrained, respectively, by widespread occurrence of pyrrhotite in deep footwall siliciclastic metasedimentary rocks of the host Aldridge Formation and by release of CO2 from shallow mafic sills and resulting formation of carbonic acid in condensed brine. The low fO2 value also reflects inferred production of CH4 from heating of organic matter in the sediments during emplacement of these sills. Based on a fluid pH restriction of <4.0 and a requirement for sparse or no K-feldspar in the source, the tin likely derives from previously altered Lower Aldridge strata. This model relies on the early diagenetic dissolution of K-feldspar from these sediments by basinal brines, followed by interaction with a later, more acidic hydrothermal fluid generated during the emplacement of large mafic sills in the shallow subsurface that leached tin from accessory minerals such as titanite in siliciclastic sediments of the Lower Aldridge Formation. Mass balance calculations suggest that derivation of the tin from this sedimentary source (avg 2.0 ppm Sn) required ~40 km3 and a cylinder diameter of 3.2 km (height 5.0 km) in order to supply the 0.1 Mt of tin contained in the deposit. The presence of mafic sills in the footwall of several other tin-bearing, sediment-hosted, stratiform Pb-Zn-Ag deposits and in modern, tin-rich, sediment-hosted sulfide deposits in the northeast Pacific Ocean suggests that siliciclastic marine basins that contain mafic sills—with or without stratiform sulfide deposits—should be evaluated for possible tin mineralization.

On the genesis of stratiform sulphide deposits in sedimentary environments with discussion

On the genesis of stratiform sulphide deposits in sedimentary environments with discussion

Stable Isotope Geochemistry of the Carboniferous Zn-Pb-Cu Sediment-Hosted Sulfide Deposits, Northeastern Spain

Carboniferous sedimentary rocks in the southwestern Catalonian Coastal Ranges contain stratiform (Zn, Pb, Cu) sulfide deposits. Stable isotope compositions of sulfur, oxygen, and hydrogen were studied in five localities in order to establish the source of hydrothermal fluids and the influence of metamorphism on these deposits. Sulfur isotopes were analyzed in pyrrhotite, pyrite, sphalerite, chalcopyrite, and galena. The δ34S(CDT) values lie mostly between -1.0 and +7.0‰ (average +4.4‰). Except for pyrrhotite-pyrite pairs, all the sulfide minerals show isotopic disequilibrium. δ34S values suggest that sulfur was derived by thermochemical reduction of seawater sulfate in a deep-circulating convective system. Fluid inclusions were studied in quartz crystals from the sediment-hosted stratiform occurrences. They are two-phase (L-V), with salinity between 1.1 and 18.0 wt% NaCl eq., and homogenization temperatures mainly in the range of 220-260°C. Oxygen and hydrogen isotopes were analyzed in chlorite crystals from four ore-bearing beds. δD(V-SMOW) values in chlorite range from -63 to -33‰, whereas δ18O values lie between +2.7 and +6.8‰. δ18O(V-SMOW) values in quartz range between +8.4 and +10.7‰. Most of the calculated oxygen and hydrogen isotope compositions of ore-forming fluids plot close to the isotopic composition of seawater. Therefore, the ore-forming fluid must have been mainly seawater that interacted with sedimentary rocks during convective circulation within a basin. This process took place in a subsiding Carboniferous basin divided into sedimentary highs and depressions by synsedimentary normal faults, which acted as permeable areas that favored fluid circulation.

Potential for stratiform massive sulphide mineralisation in south-west England

This study provides an assessment of the potential for stratiform massive sulphide mineralisation in two parts of south-west England, the Central Area between Bodmin Moor and Dartmoor, and North Devon. The Central Area was selected on the basis of its tectonic, stratigraphical and lithological similarities with the Iberian Pyrite Belt (IPB) where numerous volcanogenic massive sulphide (VMS) deposits occur. North Devon is considered prospective on account of its similarities to the Harz Massif in Germany that hosts the major polymetallic sedimentary exhalative (Sedex) deposit at Rammelsberg. More than 60 stratiform mineral occurrences are known in the two areas and previous exploration, including extensive drainage geochemical surveys, geophysical surveying and drilling, has revealed stratiform mineralisation at some localities, including at Egloskerry, near Bodmin Moor, where up to 10% Pb over 4·5 m was recorded. In North Devon, stratiform mineralisation has been recorded from a borehole at Honeymead Farm, and further evidence of potential is provided by a distinct aeromagnetic anomaly parallel to the regional strike over the upland areas of Exmoor.The potential for the occurrence of stratiform sulphide deposits in North Devon and the Central Area has been assessed by GIS-based prospectivity analysis software, Arc-Spatial Data Modeller (Arc-SDM), using knowledge-driven and data-driven modelling techniques. This analysis used both new and legacy multivariate datasets including geophysics (aeromagnetic and gravity), geochemical data, mineral occurrences, and digital 1:50 000 geological linework. This has confirmed known occurrences as well as identifying new targets for stratiform mineralisation. Zones of high prospectivity in the Central Area occur along the northern edges of Bodmin Moor and Dartmoor, in the intervening ground underlain by Lower Carboniferous strata, and in the Lower Carboniferous strata on the eastern side of Dartmoor. In North Devon, prospective areas were identified at a number of localities in the Upper Devonian and Lower Carboniferous strata, with the highest potential occurring along strike from Combe Martin near Honeymead Farm.

Geochemical evidences of sedimentary-exhalative origin of the shale-hosted PGE–Ag–Au–Zn–Cu occurrences of the Prades Mountains (Catalonia, Spain): trace-element abundances and Sm–Nd isotopes

The Llandoverian black shales of the Prades Mountains, SW Catalonian Coastal Ranges, contain several metamorphosed stratiform sulfide deposits. The mineralized interval, up to 30 m in thickness, consists of interbedded sulfide-rich (mostly pyrrhotite) shales, feldspar-rich layers and apatite beds. The ore contains Zn, Cu, Pb, Au, Ag and PGE. Whole-rock trace-element analyses were performed by ICP-MS, and the results were normalized to NASC reference standard. The REE patterns show enrichment in Eu (La) and a strong depletion in Ce. This distribution is compatible with REE mostly inherited from seawater, but a significant hydrothermal component is inferred for Eu. Profiles of redox-sensitive trace elements show great V, Cr, Ni, Co, Mo and U enrichments with respect to NASC standard. Part of this enrichment could derive from a direct precipitation from seawater, favoured by the euxinic conditions of the Silurian basin. Nevertheless, V (up to 5444 ppm) and Cr (up to 640 ppm) contents would require additional sources. These elements could be scavenged from seawater by exhalative particles in a hydrothermal derived plume that finally accumulated on the seafloor. In contrast, high Ni, Co and Mo values could be of hydrothermal origin. Sm–Nd isotopic analyses of feldspar-rich layers yielded an isochron age of 437±57 Ma (Llandoverian). These results, as well as the fine-grained textures, the lack of evidences of replacement and the pre-deformational and pre-metamorphic character support the syngenetic origin of the mineralization. Trace-element geochemistry and Sm–Nd isotopes are consistent with a submarine-exhalative origin of the mineralization processes, and suggest that the feldspar-rich levels are metaexhalites.

The Upper Permian Sedimentary Facies and Its Role in the Dajing Cu‐Sn Deposit, Linxi County, Inner Mongolia, China

Abstract: Exhaustive investigations were launched for confirming the upper Permian host rocks of the Dajing Cu‐Sn Deposit, probing into the possibility that Dajing is a Sedex type deposit during cosedimentation, complementing the deficiency of previous researches and going further into substantiating the role of the upper Permian strata in the control of ore distribution. After more than two years work, we reclassified the sedimentary facies in the Dajing area and its periphery as shallow fresh water lake and delta. Indicative sedimentary structures, such as ripple marks, rain marks, and mud cracks combined with contemporary fossils, were revealed. Having measured the flow directions, performed chemical comparison, and analyzed various sediments from sourceland in the Dajing area by XRF, we consequently redivided the strata into four sedimentary members, among which P2l1 and P2l2 were concluded as significant ore‐hosted strata. The upper Permian basin was a lateral rift basin. The water and sediments in the basin are much deeper and thicker in the north than those in the south.The indicators of special sedimentary facies, such as gravity flow, brine pool and synchronogenic stratiform structure of the ore cannot be found in the Dajing area. There was no growth fault, assemblage of sulfide and sulfate, and no zonation as well.On the basis of study in this area, taking into account the paleosedimentary environment as capriciously flowing shallow lake, which approximated the state of oxidation, we figured that the paleogeography made it prohibitively difficult to form stratiform sulfide deposits which are prone to form in deoxidized environment. It can be ruled out the possibility that the Dajing deposit is a syngenetic deposit during sedimentation.

The Xinqiao Cu–S–Fe–Au deposit in the Tongling mineral district, China: synorogenic remobilization of a stratiform sulfide deposit

The Cu–S–Fe–Au deposit at Xinqiao is located in the Tongling mineral district, Anhui Province, People's Republic of China. It is a large-scale polymetallic deposit with drilling indicated reserves of 0.5 million tonnes of Cu averaging 0.71%, 75.5 million tonnes of S averaging 29.3% and 24.9 million tonnes of Fe averaging 46%, as well as 11.2 tonnes of Au averaging at 4.7 g/tonne plus 248.4 tonnes of Ag averaging at 248.4 g/tonne. There are two major mineralization types in the Xinqiao deposit: one is the economically significant stratiform orebody hosted in the Lower Carboniferous Gaolishan siltstone (C 1g) and overlying Middle Carboniferous Huanglong limestone (C 2h), while the other is the less important skarn-type mineralization restricted to the contact between the Yanshanian diorite (110–168 Ma) and the Lower Permian Qixia marble (P 1q). The ore in the Xinqiao deposit is dominated by massive pyrite with minor amount of chalcopyrite, magnetite, pyrrhotite, galena, sphalerite, quartz and dolomite. Four stages of deformation have been recognized to affect the sedimentary rocks in the Xinqiao area. The first two (D 1 and D 2) produced mainly NE–SW and NNE–SSW trending open folds, whereas D 3 is characterized by normal faults striking NNE–SSW and D 4 is dominated by post-mineralization strike-slip faults segmenting the orebody. The structural information obtained by this study not only revealed the transgressive nature of the stratiform orebody, but also identified a strong structural control on the formation of the deposit. It is concluded that the Xinqiao polymetallic deposit was formed through remobilization of a Carboniferous sulfide source bed by hydrothermal solutions related to late Yanshanian plutonism (110 Ma), during which D 3 normal faulting played an important role in localization of the mineralization. Such a two-stage ore-forming model is consistent with the most recent genetic interpretations of the deposit.

Some evidence for the base-metal potential of the Pretoria Group: stratigraphic targets, tectonic setting and REE patterns

The Timeball Hill and Silverton Formations of the 2.1–2.3 Ga Pretoria Group have regional lithological associations which are thought to have been favourable for the genesis of stratiform sulphide deposits. The observed association of carboniferous and pyritic black shales, tuffaceous material, stromatolitic carbonates and inferred turbidity current deposits is common in stratiform sulphide deposits of the sedimentary exhalative group. Massive sulphides in the Silverton Formation are compatible with a syngenetic brine discharge, probably related to deep fracture systems. The basal shales of the Timeball Hill Formation are significantly enriched in base-metals and Ba. Interlayered tuff beds at this stratigraphic level have PGE-contents of up to 1 g/t. The REE-geochemistry of Pretoria Group sedimentary rocks supports hydrothermal activity as an important factor in both stratigraphic units.

Pb and Sr Isotopic Study of Mineralization at Mahd Adh Dhahab and Nuqrah, Arabian Shield

Lead extracted from 5 samples of galena from the Au-Agbase metal vein deposit of Mahd adh Dhahab shows a tightly clustered isotopic composition with an average two-stage Pb-Pb model age of 685 Ma. Vse of the Tatsumoto group of constants yields an average age of 766 Ma. A minimum age of769::!: 5 had previously been established by V-Pb dating of zircon separated from the Ramram granite intruding the Mahd Group, which hosts the mineralization. The obtained Pb-Pb dates are, however, older than a Rb-Sr isochron date of 645 ::!: 19 Ma obtained on a porphyritic rhyolite plug which also intrudes the Mahd Group. This relationship ascertains the noninvolvement of the rhyolite in the ore formation. With the exception of the Mahd adh Dhahab deposit, all dated vein-type deposits in the Shield have Pb-Pb dates that range between 550 and 450 Ma. Lead extracted from 3 samples of the stratiform massive sulfide deposit of An Nuqrah prospect also has a uniform isotopic composition similar to that of Mahd adh Dhahab. It yields an average Pb-Pb model date of 685 Ma, with a possibility of being too young by 30-50 Ma. A Rb/Sr isochron age on Asfar granite batholith emplaced into Hulayfah Group rocks hosting the mineralization also gave a 685 Ma date. The deformation effects of the batholith on the ore minerals implies that the granite intrusion occurred shortly after the deposition of the Hulayfah Group volcanosedimentary rocks, and their contemporaneous massive sulfides. Common lead ages obtained are similar to ages obtained previously on other massive sulfide deposits of the Arabian Shield. Application of the plumbotectonics model indicates evolution of mineralization in both areas within an island arc environment. However, the similarity of Pb isotope compositions between An-Nuqrah and Mahd adh Dhahab does suggest that the source regions of lead in the two areas have remarkably similar isotopic composition.

Tourmalinization and garnet compositions at Nora-Viker, Bergslagen, south-central Sweden: Prospecting tools for stratiform Zn-Pb sulphide deposits

Tourmalinization and garnet compositions at Nora-Viker, Bergslagen, south-central Sweden: Prospecting tools for stratiform Zn-Pb sulphide deposits

Alteration of Late Middle Proterozoic Volcanics and its Relation to Stratabound Copper-Silver-Gold Mineralization Along the Margin of the Kalahari Craton in Swa/Namibia and Botswana

Summary Metavolcanic and metasedimentary rocks of late Middle Proterozoic age are preserved in basins along the northern margin of the Kalahari Craton. Three broad stratigraphic divisions are recognized: a lower acid extrusive unit, a basic extrusive/red bed unit and a shallow marine unit. The basalts of the basic extrusive/red bed unit are interpreted to be continental within-plate basalts. Copper mineralization occurs as native copper in amygdaloidal altered basalt, and as sediment-hosted, stratiform sulphide deposits at the base of the shallow marine unit. The rocks have been strongly altered during regional metamorphism which reached temperatures up to 350°C. Massive domains were metamorphosed to oligoclase-chlorite-epidote-haematite rocks. In permeable zones such as flow top breccias, amygdaloidal zones, and regions of secondary, tectonically induced fracturing, the basalts have been altered to epidote-quartz-chlorite-haematite-muscovite rocks. During this epidote alteration copper, zinc and cobalt were leached from the basalts, thus providing a possible metal source for the sediment-hosted deposits. A model for multiphase ore genesis is presented in which basalt alteration is the main metal source for epigenetic mineralization.

DEPÓSITOS DE SULFETOS SINSEDIMENTARES: UM PROCESSO EXALATIVO DE SALMOURAS CONATAS METALÍFERAS

Several stratiform sulphide deposits disseminated in argillaceous lithology rich in organic material, show primary structural features which suggest their formation at the time of deposition of host rock. The distribution of these deposits seems to be more noticeable in rift type basins or in structured sedimentary basins in a tectonic environment with geothermal gradient higher than normal, at least during the mineralization period. The unlink of the mineralization mechanism to direct volcanic events and the close relationship between these processes with geothermically anomalous zones of the basin, are widely discussed. The formation of these deposita require the coincidence of exhalative events of connate metalliferous brines at the bottom of a euxinic sapropelic basin in active process of biogenic generation of H 2 S. Finally, the main parameters which determine mineralogie zoning (frequently present in this type of deposit) are postulated, and are discussed the mechanisms which regulate the distribution and grades of metal sulphides in black shales.

Correlation of massive sulfide deposits in the Appalachian-Caledonian orogen on the basis of paleotectonic setting

Over 70 major (>1 million metric tons) strata-bound and stratiform sulfide deposits of late Proterozoic and early Paleozoic age in the fragmented Appalachian-Caledonian orogen are correlated on the basis of their paleotectonic setting. The latter is defined in terms of two parameters, the plate tectonic paleosetting and the paleogeographic location relative to various cratonic margins. Attention is focused on geochemical data from mafic volcanic and high-level intrusive rocks associated with massive sulfide deposits, as well as on structural settings and regional tectonostratigraphic correlations. Host-rock data for over 20 key deposits or groups of deposits are discussed.Massive sulfides formed in intraplate (ensialic) as well as ocean-floor and convergent plate boundary settings are recognized in the orogen. The intraplate (ensialic) setting involves environments marginal to the Laurentian and Baltoscandian cratons; it includes both sedimentary and volcanic host-rock sequences and is interpreted as an incipient divergent plate boundary. The ocean-floor setting includes massive sulfides in ophiolites formed either at a major ocean spreading axis or within back- or interarc basins, as well as deposits hosted by sequences of mafic volcanics, graphitic phyllite, and chert possibly formed in an off-axis (intraplate) situation; deposits in this setting are restricted to the northern Appalachians and the Norwegian Caledonides. The convergent plate boundary setting includes massive sulfides hosted by subduction-related volcanics, and by postarc and post-early collision volcano-sedimentary sequences. Both ensimatic and ensialic subarc crustal environments are represented, the latter recognized outboard (northwest) of the Avalonian platform in the Appalachians and its equivalent in the United Kingdom-Ireland Caledonides. The majority of massive sulfide deposits in the orogen formed within a convergent plate boundary setting.Assessment of the host-rock data in connection with the correlation theme has revealed: (1) the presence of both regional and sulfide-localized alterations in volcanic host rocks and the occurrence of sulfide-localized alteration in several of the sediment-hosted deposits; (2) evidence for an extensional tectonic regime either during or immediately after deposition of many of the massive sulfide deposits, including some of those formed in a convergent plate boundary setting (rifted-arc, postarc, and post-early collision sequences); (3) the likelihood that massive sulfides were deposited during a single cycle of ocean basin opening and closure, although possible reservations to this model are raised by volcanic-hosted deposits in the southern Appalachians; and (4) possible target areas for future mineral exploration.

Phyllosilicates and associated minerals in some Paleozoic stratiform sulfide deposits of southeastern Australia

The Pb-Zn ores of eight of the nine deposits are characterized by one or the other of the phyllosilicate assemblages chlorite + talc + phlogopite-biotite or chlorite + muscovite. The other contains chlorite + phlogopitic trioctahedral mica but no talc. Phyllosilicate mineral chemistry is highly systematic and is related to ore type and ore stratigraphy. In all cases chemical equilibrium between the phyllosilicates has been approached on a small scale. Equilibria were established substantially at the sedimentary-early diagenetic stage. The phyllosilicates were deposited as chemical precipitates in the hydrothermal aprons at the time of sea-floor exhalative activity. Subsequent metamorphism has done little more than perfect crystal structures and coarsen grain size.--Modified journal abstract.

Sulphur isotope studies of the Mt Molloy, Dianne and O.K. stratiform sulphide deposits, Hodgkinson Province, North Queensland, Australia

Stratiform sulphide deposits which have been metamorphosed to lower greenschist facies occur within the Paleozoic strata of the Hodgkinson Province, northeast Queensland. Massive cupreous pyrite is ubiquitous and Mt Molloy and Dianne also have layered chalcopyrite-rich and sphalerite-rich lenses. Sulphide δ34S values for the mineralisation show a narrow spread, around 0‰2030; at the Dianne and O.K. deposits, but a wider spread and an average several per mil higher at the Mt Molloy area. The minerals can not be used for geothermometry due to isotopic disequilibrium. However, metamorphic effects on the isotopic compositions appear not to have been significant. A decrease in temperature and contact of the ore fluid with sea water probably caused the precipitation of the ore minerals. A magmatic ore fluid with δ34SΣS around 0‰2030; predominated at the Dianne and OK deposits whereas the fluid at Mt Molloy mixed with sea water to acquire a higher δ34SΣS value.

鉱石面からみた三波川帯・田老帯・グリーンタフ地域の層準規制型硫化物鉱床

The stratabound-type sulfide deposits in Japan are divided into two types; the Besshi-type deposit and the Kuroko-type deposit, on the basis of their geological and mineralogical aspects and isotopic characteristics. The “Kuroko” deposit is a polymetallic sulfide-sulfate deposit genetically related to submarine calc-alkaline acid volcanic activity of Neogene Tertiary. All of the Kuroko deposits occur in the so-called Green Tuff region. The nature of deposits changes downward from the stratiform deposit to the disseminated and/or the stockwork deposits. Meanwhile, the Kuroko deposit can be generally divided into the following four zones according to the mineral assemblage of ores; Quartz-hematite zone, Kuroko (black ore) zone, Oko (yellow ore) zone, and Keiko (siliceous ore) zone in stratigraphically descending order. The main hypogene minerals constituting the sulfide ore are pyrite, chalcopyrite, sphalerite, galena, minerals of tetrahedrite group, marcasite, bornite in decreasing order with quartz and barite as gangue minerals. Gypsum-anhydrite ores are well developed in the Kuroko deposit closely associated with sulfide ores. Besshi-type deposit, that is to say, the bedded cupriferous iron-sulfide deposit, is well known in the Sambagawa metamorphic belt, and the deposits of allied type occur in the non-metamorphic Palaeozoic terrains and in the Shimanto belt. Besshi-type deposit is usually associated with submarine basic volcanic materials, and are modified by later metamorphism and deformation. The ore minerals consist chiefly of pyrite, chalcopyrite, sphalerite and of less amount of bornite. A negligible amount of galena is one of the most significant features of ore. Magnetite or hematite layers occassionally interbedded in the cupriferous pyrite layers, are worthy of notice of the connection with the fugacities of S2 and O2 during ore deposition. Taro deposit, Kuroko-type deposit of the early Cretaceous age, occurs in the Taro belt of northeast Japan, being genetically related to submarine calcalkaline acid volcanic activity. The sulfide minerals consist chiefly of pyrite, chalcopyrite, sphalerite, and galena. Barite is rather less in amount than that in the Neogene Kuroko deposit. Small lenticular masses consisting of gypsum and calcite is poorly deleloped below the stratiform sulfide deposit. The ore deposit is comparatively monotonous in mineral assemblages, and variety of minerals is far less than that in the Kuroko deposit. However, alabandite occurring in the hanging wall side is noteworthy for studing the physico-chemical condition of ore deposition. In this paper, all of the minerals from the above-mentioned deposits are listed up, and some of them are described about their chemical compositions, and also mineral assemblages, in order to offer useful information on the investigation of physico-chemical environments of ore formation. Moreover, the texture and structure of ores from the deposits are briefly summarized.

Applications of computer modeling to the study of the genesis of stratiform sulfide deposits

Stratiform sulfide deposits are considered to have formed at or near the discharge vents of submarine hydrothermal systems. Such deposits constitute an important source of zinc, lead, copper, silver, and gold. They are often divided on the basis of the dominant host-rock lithology into volcanogenic and sediment-hosted types. In terms of their economic base metal contents, volcanogenic deposits contain either Cu and Zn or Zn, Pb, and Cu, whereas sediment-hosted deposits usually contain predominantly Zn and Pb.

Structure control of stratiform sulfide deposits, with a new example from Sulitjelma; reply

Structure control of stratiform sulfide deposits, with a new example from Sulitjelma; reply