mobilization of gold as a polymetallic melt during pelite anatexis at the challenger deposit south australia a metamorphosed archean gold deposit the challenger gold deposit in south australia is hosted by pelitic migmatites that underwent peak metamorphism at 7 5 1 5 kbars and at least 800 c nd model ages suggest a protolith age of 2900 ma zircon u pb and garnet sm nd dating indicates that peak metamorphism occurred at 2440 ma and that garnet was present during this event at this time in situ vapor absent melting affected the pelitic host rock indicating that peak metamorphism occurred without introduction of a foreign fluid or melt thus evidence indicating the presence of ore minerals during peak metamorphism implies a prepeak mineralization event this evidence includes the occurrence of invisible gold in lollingite but not in adjacent arsenopyrite and the presence of spherical gold sulfide inclusions in peak metamorphic garnet and other silicates textures developed between pyrrhotite lollingite arsenopyrite and gold the lack of silicate alteration minerals supports this conclusion experimental evidence is presented to support our interpretation that a gold rich polymetallic melt was mobilized into leucosomes synchronously with silicate melt during peak metamorphism visible gold is restricted to migmatitic leucosomes and to a lesser extent melanosomes large inclusions of gold with coexisting arsenopyrite pyrrhotite and bismuth are hosted within peak metamorphic silicate minerals and at grain boundaries trails of micrometric spherical inclusions of predominantly gold and bismuth propagate along annealed fractures from these larger inclusions we show that these gold sulfide inclusions represent the crystallized products of an immiscible polymetallic melt metamorphism of the challenger deposit resulted in partial melting of the pelitic host rock and formation of this gold rich melt these two melts were synchronously redistributed to accumulate as leucosomes during development of a stromatic migmatite formation of a polymetallic melt thereby enabled extensive mobilization of gold producing leucosomes enriched in gold this occurred because the immiscible metallic melt was physically entrained rather than chemically dissolved within the silicate melt gold rich shoots at challenger parallel the plunge of ptygmatically folded leucosomes that are shown to be parasitic to a larger scale fold geometry which appears to be structurally related to the ore shoots it is interpreted that concurrent migration of polymetallic and silicate melt allowed concentration of gold into a series of dilational structures which developed within the larger scale fold geometry challenger represents a new deposit type other deposits around the world such as renco and griffins find are hosted in granulite facies rocks but challenger is the first reported example of leucosome hosted gold in migmatites

gold bearing mesothermal veins from the gubong mine cheongyang gold district republic of korea fluid inclusion and stable isotope studies the gubong deposit consists of five massive gold bearing mesothermal quartz veins that fill fractures oriented northeast and northwest along fault shear zones over an area of 14 km2 in precambrian metasedimentary rocks of the gyeonggi massif the veins are divided into three groups based on their orientation and location they have a ribbon texture that is interpreted to result from repeated hydraulic fracturing events mineral deposition was associated with hydrothermal fluid overpressuring within and below the active fault shear zones the vein mineralogy and paragenesis of the veins allow two separate discrete mineralization episodes to be recognized separated by a major faulting event the ore minerals are contained within quartz and calcite associated with fracturing and healing of veins that occurred during both mineralization episodes wall rock alteration minerals during stage i the main ore stage include sericite chlorite and minor pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena and argentite electrum also was deposited during stage ii mineralization in the one group of veins along with pyrite sphalerite chalcopyrite and galena but the second stage of deposition in other veins was barren petrographic examination of textural relationships among sulfides fluid inclusions microfracturing and quartz shows chronological and genetic relationships between gold deposition and fluid entrapment systematic studies of fluid inclusions in stage i vein indicate two contrasting events a relatively high temperature 203 432 c and pressure 943 2 098 bars event related to early sulfide deposition and associated with h2o co2 ch4 nacl n2 fluids less than about 13 4 wt nacl and a lower temperature 202 399 c and pressure 670 850 bars late sulfide depositional event involving h2o nacl fluids 3 9 17 3 wt nacl the h2o nacl fluid involved in ore related stage ii mineralization had a salinity of 0 4 to 4 2 wt percent nacl and a homogenization temperature of 201 to 378 c the calculated sulfur isotope compositions of hydrothermal fluids from the stage i veins 34sh2s 3 5 10 5 indicate that ore sulfur was derived mainly from a magmatic source but also in part from sulfur contained in the host rocks the calculated and measured oxygen and hydrogen isotope compositions of the ore forming fluids stage i 18oh2o 1 1 9 0 d 92 to 21 stage ii 18oh2o 0 1 to 0 3 d 95 to 93 indicate that the fluids were derived from magmatic and or deep seated metasedimentary rocks stage i and evolved by mixing with local meteoric water stage ii by limited water rock exchange and by degassing during mineralization in uplift zones the h2o nacl fluids involved in the stage i development of these veins represent fluids that evolved either through unmixing of h2o co2 ch4 nacl n2 fluids following a decrease in fluid pressure or through mixing with deeply circulating meteoric waters possibly as a result of uplift and or unloading during mineralization the h2o nacl fluid involved in stage ii was derived from meteoric water early deposition of gold in stage i was caused by a decrease in sulfur fugacity h2s loss that accompanied the immiscible separation of carbonic vapor from h2o co2 ch4 nacl n2 fluids gold in late stage i and stage ii veins was precipitated from h2o nacl fluids by cooling and by dilution caused by mixing with meteoric water

the pampe gold deposit ghana constraints on sulfide evolution during gold mineralization abstract the ashanti belt a world renowned gold producing region in southwest ghana has received renewed attention in recent years most studies however focused on the major deposits situated along the ashanti shear zone and in the adjacent tarkwa basin to the east neglecting smaller yet important occurrences such as the pampe deposit which occurs few kilometers to the west of this shear zone on the akropong trend nevertheless investigating such simpler smaller scale mineralizing systems is attractive in that this can help shedding light on the processes that control gold deposition at the regional scale at pampe gold endowment has been estimated at approximately half a million ounces with an average gold grade of 2 8 g t the mineralization is related to two sets of quartz veins a first set v 1 which has a ne trend and is sub parallel to the main foliation s 1 and a second set v 2 which crosscuts this foliation the v 2 veins have a nnw sse trend with local conjugate geometries indicating that they formed during nnw sse shortening which regionally is linked to major orogenic gold deposition gold mineralization is systematically associated with sulfides which occur disseminated in the vein walls and in the surrounding host rocks the ore sulfide paragenesis consists of 1 a first generation of pyrite which is associated with v 1 veins 2 a second generation of sulfides consisting of an intergrowth of arsenopyrite and pyrite that crystallized contemporaneously with the formation of the second vein set 3 a late phase of pyrite growth which occurs as overgrowths on phase 2 sulfides and formed during the waning stages of v 2 emplacement invisible sub microscopic gold was detected in all sulfide generations by la icp ms the analytical profiles for the au signal are mimicked by those for pb cu as ag te and bi invisible gold is thus interpreted to have precipitated within sulfides in the form of nanoparticles colloidal gold alloys conversely visible native gold grains were recognized exclusively in association with arsenopyrite from late v 2 veins either as inclusions or more commonly at the boundary with other sulfides as well as in micro fractures that crosscut the sulfides gold precipitation was likely induced by sulfidation of the wall rock during fluid rock interaction the pampe deposit exemplifies the mineralization processes that took place at larger scale in neighboring world class deposits such as obuasi bogoso and prestea

gold rich mesothermal vein deposits of the republic of korea geochemical studies of the jungwon gold area gold vein deposits of the jungwon area are among the first documented examples of mesothermal gold deposition in the republic of korea the deposits are composed of massive quartz veins up to 1 0 m wide which occupy fault planes in precambrian gneiss k ar dating of alteration sericite 146 156 m y indicates a late jurassic age for ore mineralization similar to that of a nearby granodiorite the veins are gold rich and sulfide poor with ore shoots up to 200 m in horizontal and vertical extent ore grades average 10 2 g ton gold with an average gold silver production ratio of 6 1 fluid inclusion data indicate that gold was deposited between 375 degrees and 290 degrees c from relatively dilute fluids asymp 4 equiv wt nacl containing asymp 15 to 25 mole percent co 2 evidence of fluid unmixing co 2 effervescence indicates pressures of 1 200 to 1 500 bars gold deposition was likely a result of decrease of sulfur activity caused by sulfide deposition and or h 2 s loss accompanying fluid unmixing measured and calculated compositions of ore fluids in the jungwon area delta 18 o 5 0 to 7 7ppm delta d 78 to 113ppm indicate that gold was deposited from a highly evolved meteoric water that underwent extreme 18 o enrichment and moderate d enrichment mineralogy and ore fluid chemistry of the jungwon area deposits are similar to those of mesothermal gold vein deposits of the canadian cordillera canadian archcan greenstone belts and the mother lode district of california the diversity of host rocks in these deposits indicates that host rock petrology is not a controlling factor in the formation of mesothermal gold vein deposits these observations together with our geochemical studies of korean deposits may validate a more general application of meteoric water models for the formation of mesothermal gold vein deposits

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

gold mineralization in as rich mesothermal gold ores of the bogosu prestea mining district of the ashanti gold belt ghana remobilization of invisible gold the bogosu prestea mining district of southwestern ghana is a 33 km section of the early proterozoic ashanti gold belt greenschist facies carbonaceous and carbonate bearing turbidites and greywackes and mafic dikes host numerous economic mesothermal gold deposits structurally higher ores in the bogosu concession have brittle deformation and consist of disseminated sulphide lodes in tectonically disrupted sedimentary rocks and carbonate altered mafic dikes most gold occurs as micrometre size particles in arsenian pyrite and as invisible gold in arsenian pyrite and arsenopyrite the structurally deeper ores of the adjoining prestea concession are associated with brittle ductile deformation and consist of extensive crack seal quartz veins and graphitic shear zones only minor amounts of invisible gold were detected in these deeper lodes gold occurs dominantly as abundant microscopic and larger particles in sulphide arsenide minerals and in gangue the gold distribution patterns revealed by sims microprobe analysis and ion maps emp and colour staining suggest that most of the primary gold in the bogosu prestea system precipitated in solid solution with sulphide arsenide minerals however post depositional concentration and redistribution occurred in increasing degree with 1 increase in metamorphic hydrothermal gradients in the gold system depth 2 decrease in the refractory properties of the host mineral and 3 increase in the amount of post depositional host mineral recrystallization and deformation gold evolved from primary solid solution within sulphide arsenide minerals to colloidal and micrometre size particles concentrated in voids fractures and internal grain boundaries and finally to microscopic and larger particles at sulphide arsenide grain margins and in the gangue assemblage the general conclusions presented here are applicable to as rich gold deposits of all ages worldwide the presence of gold in late fractures is insufficient evidence for late stage introduction of gold in mesothermal gold systems

unraveling the western churchill province paleoproterozoic gold metallotect constraints from re os arsenopyrite and u pb xenotime geochronology and la icp ms arsenopyrite trace element chemistry at the bif hosted meliadine gold district nunavut canada the gold endowment of the western churchill province is conventionally attributed to reworking and attendant metamorphism during the trans hudson orogeny 1 9 1 8 ga the meliadine gold district is regarded as a type example of this inferred paleoproterozoic gold metallotect and also represents one of canada s largest emerging orogenic greenstone and banded iron formation bif hosted gold districts 2 8 moz contained au in reserves and total resource of 5 8 moz au the largest gold deposits are cospatial with the pyke fault and associated quartz ankerite veining which cuts neoarchean ca 2 66 ga plutonic and supracrustal rocks comprising the rankin inlet greenstone belt meliadine gold occurs as inclusions within idioblastic arsenopyrite crystals at sulfide crystal boundaries and or as sulfide fracture fills in hydrothermally altered sulfidized and veined bif clusters of gold bi mo telluride chalcopyrite and galena inclusions characterize high grade ore zones and are spatially associated with sieve textured arsenopyrite domains these microtextural relationships suggest that incipient sulfide recrystallization liberated gold which along with other precious and base metals was redistributed during late fluid assisted and deformation metamorphic driven remobilization late precious and base metal enrichment is also demonstrated by in situ laser ablation inductively coupled plasma mass spectrometry la icp ms arsenopyrite mapping hydrothermal xenotime crystals occur with gold in low strain microtextural sites and yield u pb ages at ca 1 86 ga suggesting that remobilization was concomitant with trans hudson orogenesis new re os arsenopyrite model ages range from 2 3 to 1 8 ga and document a hitherto unrecognized pre 1 86 ga hydrothermal activity the range of re os model ages tends to support partial open system behavior and or mixing of disparate arsenopyrite generations that are evident from microtextural observations and in situ la icp ms element mapping replicate analyses of the two most rhenium rich arsenopyrite samples yield reproducible re os model ages at ca 2 27 and 1 90 ga these rhenium rich samples are also gold poor and likely yield ages that predate gold remobilization and subsequent enrichment along arsenopyrite crystal boundaries and fractures we suggest that pre 1 86 ga hydrothermal activity was likely critical to the gold endowment of the district but is obscured by reworking during the later stages of the trans hudson orogeny at 1 86 ga if correct these new ages imply that the paleoproterozoic gold metallotect which is recorded across the western churchill province in fact comprises multiple temporally distinct gold events differentiating between disparate paleoproterozoic gold events represents a critical step for effective mineral exploration in the western churchill province and at other reworked archean terranes

reply to comment by a revil and n linde on streaming potential dependence on water content in fontainebleau sand revil and linde recently commented our paper concerning streaming potential sp measurements in unsaturated sand during drainage experiments this comment suggests that the approach used to infer sp coefficients was inappropriate for unsaturated conditions and therefore yielded wrong conclusions and unphysical results regarding the behaviour of the relative sp coefficient this reply argues that even if in allegre et al we neglected some secondary electrokinetic sources the resulting conclusions are still representative of the behaviour of the true sp coefficient and that the remarks of revil linde arose from a misunderstanding of the drainage experiment conditions we also find support for our results from a comparison between our observations and previous experimental studies

a multidisciplinary study of invisible gold in arsenopyrite from four mesothermal gold deposits in siberia russian federation characterization of gold in four siberian mesothermal gold deposits was done through a multidisciplinary investigation including ore microscopy inaa sims epma and 197 au moessbauer spectroscopy the deposits are olympiada and veduga in the enisei mountain range and nezhdaninskoye and sentachan in the verkhoyansk kolyma area in which vein and disseminated orebodies are hosted by sedimentary sequences metamorphosed to amphibolite olympiada and greenschist facies ore minerals include arsenopyrite and pyrrhotite or pyrite as major constituents with minor scheelite and sphalerite chalcopyrite and native gold as minor constituents with or aurostibite galena gudmundite tetrahedrite stibnite and berthierite some of the gold mineralization is metallurgically refractory in all four deposits largely due to the presence of invisible gold in arsenopyrite and to a lesser extent in pyrite several generations of arsenopyrite are recognized in the auriferous zones of the veduga nezhdaninskoye and sentachan deposits textural observations indicate late deposition of native gold with respect to arsenopyrite no evidence was found of arsenopyrite recrystallization and the crystallization of native gold is considered to result from an evolution of fluids rather than redeposition of gold wide variations in the gold contents of arsenopyrite occur within deposits within samples and within individual grains inna analyses of individual arsenopyrite grains 30 70 mu m in size show that the gold concentration ranges from 197 au moessbauer spectra of arsenopyrite concentrates from the veduga nezhdaninskoye and sentachan deposits exhibit mainly a component with isomer shifts between 3 3 and 3 6 mm s which is interpreted as strong evidence of the presence of chemically bound gold in the arsenopyrite crystal structure the spectra of samples from the veduga deposit also contain minor amounts of native gold for which negative isomer shifts near 1 2 mm s are expected metallic gold dominates in the 197 au moessbauer spectra of samples from the olympiada deposit but varying amounts of chemically bound gold are also visible in the spectra some attributed to aurostibite it is concluded that the ores from these deposits are refractory partly because the gold occurs in arsenopyrite as chemically bound gold as well as submicroscopic metallic particles probably as small as 2 nm this study also shows that au bearing arsenopyrite is usually depleted in as with respect to its stoichiometric composition but correlation of au enrichment to fe deficiency was not found it is inferred from 197 au moessbauer spectroscopy that substitution of fe super 3 for au super 3 is most likely the temporal change in different modes of gold occurrence i e as native gold or invisibly in sulfides in the mineralized zones and veins is interpreted to result from an evolution of fluids rather than to be a recrystallization phenomenon dissemination of au bearing sulfides within the altered halos infers that a pervasive fluid rock interaction was an effective mechanism for deposition of minerals and gold absorption of gold complexes onto sulfide surfaces is also suggested to have played an important role in the deposition of native gold during the latest episodes in the formation of the deposits

la icp ms trace element analysis of arsenopyrite from the samgwang gold deposit south korea and its genetic implications abstract the samgwang deposit previously classified as an orogenic gold deposit consists of several structurally controlled auriferous quartz veins hosted by metasedimentary rocks of the precambrian gyeonggi massif south korea the gold at samgwang occurs as electrum commonly associated with arsenopyrite laser ablation inductively coupled plasma mass spectrometry la icp ms coupled with ore microscopy was conducted on au and trace elements distributed in arsenopyrite grains contained in quartz vein and wall rock samples resulting profiles for au co ni and sb were relatively flat and showed little variability indicating that the elements were relatively homogeneously distributed and exchanged via substitution in arsenopyrite while variability and noisy depth profiles inferred that pb was present as tiny inclusions or discrete particles furthermore measured gold concentrations were typically higher in arsenopyrite grains from laminated quartz veins avg 2 07 ppm than in grains from massive quartz veins avg 0 26 ppm and wall rock samples avg 0 33 ppm in the case of wall rock and massive quartz vein samples arsenopyrite grains of euhedral shape illustrate an element distribution pattern whereby au concentrations tend to decrease towards the rims of the analyzed grains in contrast the rims of arsenopyrite grains in laminated quartz vein samples recorded much higher au concentrations of up to 20 1 ppm with increasing pb bi and ag particularly within domains of fractured or recrystallized arsenopyrite grains the newly acquired la icp ms data along with textural evidence may be interpreted in terms of the release and remobilization of invisible gold that was originally locked up in the arsenopyrite this release is linked to late deformation and hydrothermal event during which the remobilized invisible gold was redeposited as electrum in addition there is evidence for the introduction of additional gold and other precious and base metals by the late stage hydrothermal fluids based on the above and in contrast to previous genetic models we propose a more complex metallogenic concept for samgwang in which the economically important gold enrichment process was genetically related to intrusive activity during the waning stages of jurassic to early cretaceous daebo orogenesis

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

paragenesis and composition of ore minerals in the randalls bif hosted gold deposits yilgarn craton western australia implications for the timing of deposit formation and constraints on gold sources the randalls district comprises three individual gold deposits cock eyed bob maxwells and santa craze hosted in the same unit of banded iron formation bif in the southern eastern goldfields superterrane yilgarn craton western australia the iron formation is a silicate oxide facies unit with overprinting sulfides and has undergone metamorphism upper greenschist facies and deformation two generations of folds the gold deposits are hosted in two structural locations hinge zones of anticlinal folds e g santa craze and maxwells and overturned steeply dipping limbs of anticlinal folds e g cock eyed bob gold dominantly occurs as inclusions of native gold and or electrum within or around pyrrhotite magnetite and arsenopyrite the earliest mineral assemblage preserved in the banded iron formation at randalls is banded magnetite quartz magnetite in all forms has elevated mg al ti v mn cr zn and w but very low ni compared to other bifs globally pyrrhotite the most abundant sulfide is restricted to ore zones and occurs as laminae blebs and veinlets all of which have replaced magnetite some pyrrhotite in the hydrothermally altered bifs especially in near surface samples has been re sulfidized to pyrite trace elements associated with pyrrhotite include co ni ag sb and pb large coarse grained arsenopyrite overgrows the pyrrhotite defined foliation it is enriched in co ni sb and te but contains very little invisible gold 0 01 ppm au unlike arsenopyrite in many orogenic au systems globally commonly 0 1 ppm au petrographic studies of several mineralized bifs from randalls reveal that pyrrhotite and arsenopyrite are associated with fe ca amphibole which grew during contact metamorphism caused by granite plutons this spatial sulfide amphibole relationship indicates that gold mineralization likely occurred during granite intrusion consistent with prior studies on randalls the trace element characteristics of the sulfides show that they were not inherited from replaced magnetite further these characteristics suggest that the fluid from which sulfides crystallized was not indigenous to the bifs and that this s rich fluid either contained s in abundance originally or interacted with a lithology lithologies that were rich in s before reaching the bifs black shale containing diagenetic nodular pyrite occurs in the upper black flag group which unconformably underlies the belches supersequence at depth 3 km the trace element composition of nodular pyrite from this unit fits well with the trace element characteristics of the bif pyrrhotite and arsenopyrite and the nodular pyrite contains an average of 0 5 ppm au however the nodular pyrites have an average 34s value of 5 6 n 13 which contrasts markedly with the 34s average of pyrrhotite pyrite and arsenopyrite in mineralized bifs 0 8 n 17 thus a definitive source of gold arsenic silver and tellurium in the randalls system remains elusive although we would contend that the upper black flag group should be considered as a possible metal and s source in areas of the yilgarn where it forms a thick substrate to ore camps

la icp ms trace element analysis of pyrite from the chang an gold deposit sanjiang region china implication for ore forming process abstract the chang an gold deposit yunnan province is one of five large gold deposits in the ailaoshan gold belt that is the most important ore belt of the sanjiang tethyan metallogenic domain geochemical study of pyrite in the deposit was conducted using laser ablation inductively coupled plasma mass spectroscopy three types of hydrothermal pyrite were identified in the ores and wall rocks i e the coarse euhedral crystals in syenite py1 the coarse grains disseminated in altered sandstones or sandstone ores py2 and the fine grained euhedral pyrite in sandstone ores py3 their trace elements exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes the cores of py1 were formed by magmatic fluids and have the lowest concentrations of au as cu and zn the cores of py2 were formed by metamorphic fluids and have relatively high au ag ni pb and cu concentrations the py3 grains and the growth rims of py1 and py2 show consistently high contents of au as pb and co suggesting that all of them were rapidly deposited from a mixing fluid system that was probably composed of fluids of metamorphic and magmatic origins this interpretation is supported by the observation that the high grade ores generally contain lots of py2 and py3 hence we consider that the deposit was formed during india asia collision slightly postdate the 33 35 ma tectono magmatism

arsenopyrite pyrite association in an orogenic gold ore tracing mineralization history from textures and trace elements laser ablation inductively coupled plasma mass spectrometry la icp ms spot analysis and element mapping coupled with high resolution focused ion beam scanning electron microscopy fib sem imaging has been performed on au hosting sulfides from a proterozoic orogenic gold deposit tanami gold province north central australia gold distribution patterns in the arsenopyrite pyrite assemblage which probably crystallized toward the end of the au forming event suggest a process of initial scavenging of au into arsenopyrite and subsequent remobilization of that au following brittle fracture gold expelled from the sulfide lattice during the remobilization event is reconcentrated around the margins of the same arsenopyrite grains and within swarms of crosscutting microfractures the distribution of pb bi and ag closely mimic au indicating that these elements were also reconcentrated preservation of oscillatory zonation patterns for co ni sb se and te in arsenopyrite imply however that no significant degree of sulfide recrystallization took place residual concentrations of invisible gold in grain centers are 5 ppm in arsenopyrite and 1 ppm in coexisting pyrite the presence of submicron sized pores is suggestive of a fluid driven process rather than solid state diffusion micron scale 2 10 m remobilized gold is accompanied by fine particles 200 nm 2 m and nanoparticles 200 nm of gold the extensive variation of au concentrations within single arsenopyrite grains underlines the significance of textures when using trace element data to understand how gold ores evolved

bimodal distribution of gold in pyrite and arsenopyrite examples from the archean boorara and bardoc shear systems yilgarn craton western australia this study investigates the microstructures geochemistry and hydrothermal evolution of gold bearing pyrite and arsenopyrite from six orogenic gold deposits in the archean eastern goldfields province western australia scanning electron microscope sem electron microprobe emp and laser ablation inductively coupled plasma mass spectroscopy la icp ms analyses show that the gold bearing minerals possess a number of similar textural features including the occurrence of invisible gold within initial phases of growth and later stage visible gold associated with alteration rims the alteration rims are characterized by a higher than average atomic mass mainly owing to arsenic enrichment and are preferentially located along fractures and grain boundaries in the pyrite and arsenopyrite these observations suggest that visible gold formation is associated with hydrothermal alteration of preexisting pyrite and arsenopyrite textural observations and la icp ms data suggest that some invisible gold was remobilized from early formed pyrite and arsenopyrite to form visible gold during development of these alteration rims gold may also have been added by hydrothermal fluids during a later stage of mineralization in situ geochemistry and phase relationships of alteration rims are used to further constrain the hydrothermal process responsible for formation of alteration rims and visible gold in fractures based on sulfide stability relations our data indicate that development of arsenopyrite alteration rims associated with late stage visible gold formation was related to an increase in temperature maximum increase from 310 to 415 c and up to of sic orders of magnitude increase in sulfur fugacity whereas changes in oxygen fugacity were less important la icp ms analyses show that the relative and absolute variations in selected trace element au ag sb bi ba te pb co and mo concentrations can also be used to distinguish between unaltered and altered pyrite and arsenopyrite in general trace elements within pyrite and arsenopyrite have a relatively uniform distribution whereas later stage alteration rims have more variable trace element distributions although the observed textures are typical of prograde metamorphic coronae we suggest that they are the consequence of variations in fluid conditions and chemistry and that mineralization occurred in response to syn and or postpeak metamorphic fluid infiltration

trace and minor elements in sphalerite from base metal deposits in south china a la icpms study laser ablation icp mass spectroscopy has been used to investigate the geochemistry of sphalerite in a range of nine zn pb deposits in south china the deposits which are of different ages and belong to different metallogenic provinces have been assigned to the following genetic types skarn hetaoping luziyuan syngenetic massive sulphide dabaoshan laochang and bainiuchang and mississippi valley type huize mengxing niujiaotang based on the features of the ore even though their origin is heavily debated based on other criteria the giant jinding deposit is considered separately sphalerite from each genetic class of deposit shows a distinct chemical signature sphalerite from the skarn deposits is characterised by elevated lattice bound concentrations of co and mn the distal character of these skarn systems is reflected by the low in content of sphalerite the three syngenetic massive sulphide deposits feature sphalerite strongly enriched in in sn and ga whereas the deposits of mvt type are typically enriched in ge cd tl and as these divergent characters are reflected in absolute element abundances as well as in element ratios time resolved depth profiles for sphalerite from the chinese deposits confirm the presence of elements such as co in ge ga and cd in solid solution but the dataset expands the understanding of sphalerite mineral chemistry by also indicating that other elements whose ability to enter the crystal structure of sphalerite has been previously debated ag sn tl sb may also be in solid solution sphalerite is a refractory mineral and trace element analysis of sphalerite shows promise as a tracer of ore genesis even in overprinted ores systematic work on larger sample suites may help define the geochemical signature of different metallogenic epochs in regions as geologically complex as south china and help resolve the mechanism by which many of the debated ore deposits were formed

mineralogical siting and distribution of gold in quartz veins and sulfide ores of the ashanti mine and other deposits in the ashanti belt of ghana genetic implications the ashanti belt of ghana constitutes a gold province which has produced a total of about 1500 t of gold historically gold mineralization is found in steep nne ssw to ne sw trending shear zones predominantly transecting metasediments of the palaeoproterozoic birimian supergroup 2 2 2 1 ga disseminated in ca 2 1 ga granitoids in paleo conglomerates of the tarkwaian group 2135 ma and in recent placers the distribution of gold its chemistry paragenesis and mineralogical siting in the mesothermal ores of the major mines in the ashanti belt namely konongo ashanti bogosu and prestea mine are the subject of this study at the localities studied gold is present in two main types of ores 1 quartz veins with free milling gold the gold is relatively silver rich true fineness values from 730 to 954 and is accompanied by a distinct suite of cu pb sb sulfides 2 sulfide ores consisting of arsenopyrite pyrite and rarer pyrrhotite and marcasite with refractory gold the ores have apparent fineness values larger than 910 arsenopyrite and locally at bogosu pyrite were identified as the hosts of submicroscopic gold mean concentrations of gold in arsenopyrite in various samples from the different mines obtained by secondary ion mass spectrometry sims range from 67 to 314 ppm au gold concentration mapping in individual arsenopyrite crystals from the different deposits revealed similar patterns of gold distribution the grains possess a gold poor core and elevated gold contents are present along distinct crystal growth zones towards their rims the outermost crystal layer is usually gold poor the well preserved distribution patterns also indicate that remobilization of gold from the sulfides played an insignificant role in the ores of the ashanti belt multiple quartz veining and growth zoning of the sulfides are interpreted as manifestations of multiple episodes of fluid infiltration fluid flow and mineral deposition the bimodal occurrence of gold in spatially closely associated quartz vein and sulfide ores indicates a genetic link between these ore types a model implying a grossly coeval formation of the ores from mesothermal fluids is proposed

trace element characteristics of different pyrite types in mesoarchaean to palaeoproterozoic placer deposits a comparative in situ la icp ms trace element study on pyrite from three different variably auriferous archaean to palaeoproterozoic palaeoplacer deposits in the ouro fino syncline quadrilatero ferrifero brazil the elliot lake area north of lake huron se canada and several deposits within the witwatersrand basin south africa revealed systematic differences between morphologically different pyrite types and between the various palaeoplacer deposits especially the ni and au concentrations as well as co ni and mo ni ratios were found to be systematically different in detrital compact detrital porous and post sedimentary hydrothermal pyrite grains from different source areas high co ni ratios and low au concentrations are typical of post sedimentary pyrite which is hydrothermal in origin in contrast relatively low co ni ratios and high au contents characterise detrital porous banded and concentric pyrite grains au 1 ppm which are syn sedimentary in origin in the elliot lake area and the witwatersrand basin detrital compact rounded pyrite is characterised by high co ni ratios which is in agreement with derivation from a hydrothermal source low au concentrations in this pyrite type support the contention of the gold and the pyrite in these deposits coming from different source rocks in contrast derivation from an originally diagenetic pyrite is suggested for the detrital compact pyrite in the ouro fino syncline because of low to intermediate co ni ratios high au contents may indicate a genetic relationship between pyrite and gold there systematic differences exist between the three areas with respect to au ni co mo and cu distributions in detrital pyrite which reflects differences in the provenance a predominantly mafic ultramafic source is indicated for the ouro fino a felsic source for the elliot lake and a mixed felsic mafic provenance for the witwatersrand pyrite populations independently of pyrite type the higher au endowment of the studied witwatersrand and ouro fino conglomerates are also reflected by an overall higher au concentration in the respective pyrite grains compared to the relatively au poor samples from elliot lake in general a strong positive correlation between au and pb levels in the various pyrite grains is noted analogous to pb which is well known for not being easily accommodated in the pyrite crystal lattice but occurring as discrete pbs phases au is considered to be present mainly in the form of discrete au phases in minute pores and interstices of the pyrite grains rather than within the pyrite lattice

phanerozoic high pressure eclogite and intermediate pressure granulite facies metamorphism in the gyeonggi massif south korea implications for the eastward extension of the dabie sulu continental collision zone abstract petrological analysis zircon trace element analysis and shrimp zircon u pb dating of retrogressed eclogite and garnet granulite from bibong hongseong area sw gyeonggi massif south korea provide compelling evidence for triassic 231 4 3 3 ma high pressure hp eclogite facies m1 metamorphisms at a peak pressure temperature p t of ca 16 5 20 0 kb and 775 850 c this was followed by isothermal decompression itd with a sharp decrease in pressure from 20 to 10 kb and a slight temperature rise from eclogite facies m1 to granulite facies m2 followed by uplift and cooling granitic orthogneiss surrounding the baekdong garnet granulite and the ophiolite related ultramafic lenticular body near bibong records evidence for a later silurian 418 8 ma intermediate high pressure ihp granulite facies metamorphism and a prograde p t path with peak p t conditions of ca 13 5 kb and 800 c k ar ages of biotite from garnet granulites amphibolites and granitic orthogneisses in and around the bibong metabasite lenticular body are 208 219 ma recording cooling to about 310 c after the early triassic metamorphic peak neoproterozoic zircon cores in the retrogressed eclogite and granitic orthogneiss provide evidence that the protoliths of these rocks were 800 and 900 ma old respectively similar to the ages of tectonic episodes in the central orogenic belt of china this and the evidence for triassic hp uhp metamorphism in both china and korea is consistent with a regional tectonic link within northeast asia from the time of rodinia amalgamation to triassic continent continent collision between the north and south china blocks and with an eastward extension of the dabie sulu suture zone into the hongseong area of south korea

application of arsenopyrite geothermometry and sphalerite geobarometry to the taebaek pb zn ag deposit at yeonhwa i mine republic of korea the taebaek pb zn ag deposit of the yeonhwa i mine republic of korea occurs in a broadly folded and reverse faulted terrain of paleozoic sedimentary rocks the taebaeksan basin the orebodies consist of several thin tabular orebodies of hydrothermal replacement type where they are hosted by carbonate rocks the pb zn ag mineralization can be divided into four distinct stages based upon the mode of occurrence of ore minerals ore textural relationships and their composition based on temperatures inferred from arsenopyrite compositions by means of electron microprobe and fluid inclusions the estimated temperatures for the stages i ii iii and iv reach 330 to 350 c 270 to 340 c 230 to 250 c and 220 c respectively the sulphur activity atm of ore formation at the taebaek deposit was estimated for each stage as 10 11 to 10 11 5 10 9 5 to 10 13 10 13 5 to 10 15 and 10 15 respectively even though application of sphalerite geobarometry is problematic because of the absence of good mineral assemblages sphalerite coexisting with pyrite but not with pyrrhotite was used to estimate the minimum mineralization pressure about 1 kbar

invisible gold in arsenian pyrite and arsenopyrite from a multistage archaean gold deposit sunrise dam eastern goldfields province western australia the sunrise dam gold mine 11 1 moz au is the largest deposit in the archaean laverton greenstone belt eastern goldfields province yilgarn craton western australia the deposit is characterized by multiple events of fluid flow leading to repeated alteration and mineralization next to a major crustal scale structure the au content of arsenian pyrite and arsenopyrite from four mineralizing stages d1 d3 d4a and d4b and from different structural and lithostratigraphic environments was measured using in situ laser ablation inductively coupled plasma mass spectrometry pyrite contains up to 3 067 ppm au n 224 whereas arsenopyrite contains up to 5 767 ppm n 19 gold in arsenopyrite d4a stage was coprecipitated and remained as invisible gold nanoparticles and or lattice bound during subsequent deformation events in contrast gold in pyrite is present not only as invisible gold but also as micrometer size inclusions of native gold electrum and au ag tellurides pristine d1 and d3 arsenian pyrite contains relatively low au concentrations 26 ppm the highest au concentrations occur in d4a arsenian rich pyrite that has recrystallized from d3 pyrite textures show that this recrystallization proceeded via a coupled dissolution reprecipitation process and this process may have contributed to upgrading au grades during d4a in contrast au in d4b pyrite shows grain scale redistribution of invisible gold resulting in the formation of micrometer scale inclusions of au minerals the speciation of au at sunrise dam and the exceptional size of the deposit at province scale result from multiple fluid flow and multiple au precipitating mechanisms within a single plumbing system

gold upgrading in metamorphosed massive sulfide ore deposits direct evidence from laser ablation inductively coupled plasma mass spectrometry analysis of invisible gold the metamorphosed boliden volcanic hosted massive sulfide vhms ore deposit northern sweden is characterized by an abundance of massive arsenopyrite ore and unusually high gold enrichments up to 300 600 g t in crosscutting veins and fracture zones the ore textures observed record progressive recrystallization and porphyroblast growth during meta morphism we conducted a systematic laser ablation inductively coupled plasma mass spectrom etry la icp ms study on the gold distribution in fine grained massive arseno pyrite and pyrite ore partially recrystallized arsenopyrite ore and both arsenopyrite and pyrite porphyroblasts found in gold rich veins the gold concentrations in massive arseno pyrite are highest 30 50 ppm on average and systematically decrease to 0 2 7 ppm with increasing degree of recrystallization by contrast gold concentrations in pyrite ore are much lower and do not exceed 0 2 ppm the la icp ms data coupled with textural data provide the first direct conclusive evidence that gold is progressively liberated from massive sulfide ores during metamorphism and reprecipitated in veins and other low strain sites we suggest that such upgrading is the principal mechanism responsible for significant gold enrichment observed in many metamorphosed vhms deposits worldwide

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

pyrite and pyrrhotite textures and composition in sediments laminated quartz veins and reefs at bendigo gold mine australia insights for ore genesis the various types textures and compositional zoning of pyrite in the gold bearing saddle reefs quartz veins and surrounding sedimentary rocks provide new information on the potential source and timing of gold and arsenic and related fluid processes responsible for mineralization at bendigo nodular diagenetic pyrite in the black shale tops to sandstone turbidites is enriched in invisible gold and arsenic with mean values of 0 61 ppm au 1 300 ppm as and au ag 1 based on la icpms analyses other elements enriched in the diagenetic pyrite within the organic rich shales are mn zn mo cu v ba ag cd tl co ni bi pb and te in contrast euhedral and growth zoned hydrothermal pyrite in the turbidites and bedding parallel laminated quartz veins contains lower contents of most trace elements but has higher contents of invisible au and as especially on the outermost rim of the pyrite the gold rich pyrite rims generally become thicker a few to hundreds of microns in proximity to the gold bearing saddle reefs pyrite in the reef commonly has the highest levels of invisible au and as and the lowest levels of other trace elements it is characterized by au ag 1 and au pb 0 01 in the deepest stratigraphic levels below known productive gold reefs diagenetic pyrite in the most carbonaceous shales has been replaced by pyrrhotite during metamorphism la icpms analyses reveal that the disseminated pyrrhotite contains similar levels of ni and co to the diagenetic pyrite but is strongly depleted in as and au the spatial relationships between organic rich shales folded bedding parallel laminated quartz veins and gold arsenic bearing saddle reefs combined with the consistent trends in the trace element composition of pyrite hosted by these three geological elements is interpreted to indicate that the black shales were an initial source of au and as and the laminated quartz veins acted as the initial pathways for hydrothermal fluid flow carrying au and as from the source shales to the saddle reefs maximum gold and arsenic input into the reefs principally as free gold plus arsenopyrite occurred late during deformation toward the end of the hydrothermal cycle and is expressed by the au as rich rims to hydrothermal pyrite in the sedimentary host rocks laminated quartz veins and reefs this corresponds with final fold lockup and the development of through going fault arrays linking adjacent anticlines the source of au and as for this final and most economically important fluid flow event is considered to be from carbonaceous shales deeper in the basin where original gold bearing diagenetic arsenian pyrite reacts with organic matter and is converted to pyrrhotite with release of au as and s to the metamorphic fluid

crustal evolution of the gyeonggi massif south korea nd isotopic evidence and implications for continental growths of east asia abstract we investigated the sm nd isotopic characteristics of the gyeonggi massif korea in order to delineate its crustal growth history nd isotopic depleted mantle model ages t dm obtained from 32 new measurements of basement and supracrustal samples and from the literature suggest that the gyeonggi massif is as old as middle archean 3 0 ga and was primarily extracted from the mantle during the late archean 2 9 2 5 ga in addition minor crustal formation occurred during the early proterozoic ca 1 9 1 8 ga late archean early proterozoic crustal growth of the gyeonggi massif is comparable with that of the sino korean or yangtze craton the t dm distribution pattern alone is not sufficient to determine the crustal affinity of the gyeonggi massif with either of the chinese cratons however late proterozoic crustal evolution of the gyeonggi massif appears to favor its tectonic correlation with the yangtze craton

mineralogical fluid inclusion and stable isotope constraints on mechanisms of ore deposition at the samgwang mine republic of korea a mesothermal vein hosted gold silver deposit the samgwang mine is located in the cheongyang gold district cheonan metallogenic province of the republic of korea it consists of eight massive gold bearing quartz veins that filled ne and nw striking fractures along fault zones in precambrian granitic gneiss of the gyeonggi massif their mineralogy and paragenesis allow two separate vein forming episodes to be recognized temporally separated by a major faulting event the ore minerals occur in quartz and calcite of stage i associated with fracturing and healing of veins hydrothermal wall rock alteration minerals of stage i include fe rich chlorite fe fe mg ratios 0 74 0 81 muscovite illite k feldspar and minor arsenopyrite pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena argentite pyrargyrite and argentian tetrahedrite only calcite was deposited during stage ii fluid inclusions in quartz contain three main types of c o h fluids co2 rich co2 h2o and aqueous inclusions quartz veins related to early sulfides in stage i were deposited from h2o nacl co2 fluids 1 500 5 000 bar average 3 200 with thtotal values of 200 c to 383 c and salinities less than about 7 wt nacl equiv late sulfide deposition was related to h2o nacl fluids 140 1 300 bar average 700 with thtotal values of 110 c to 385 c and salinities less than about 11 wt nacl equiv these fluids either evolved through immiscibility of h2o nacl co2 fluids as a result of a decrease in fluid pressure or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization or both measured and calculated sulfur isotope compositions 34sh2s 1 5 to 4 8 of hydrothermal fluids from the stage i quartz veins indicate that ore sulfur was derived mainly from a magmatic source the calculated and measured oxygen and hydrogen isotope compositions 18oh2o 5 9 to 10 9 d 102 to 87 of the ore forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water rock exchange and by partly degassing in uplift zones during mineralization while most features of the samgwang mine are consistent with classification as an orogenic gold deposit isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the jurassic to cretaceous daebo orogeny

la icp ms trace element analysis of pyrite from the xiaoqinling gold district china implications for ore genesis abstract the xiaoqinling district the second largest gold producing district in china is located on the southern margin of the north china craton it consists of three ore belts namely the northern ore belt the middle ore belt and the southern ore belt pyrite from the dahu gold deposit in the northern ore belt and wenyu and yinxin gold deposits in the southern ore belt were investigated using a combination of ore microscopy and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms a range of trace elements was analyzed including au te ag pb bi cu co ni zn mo hg as and si the results show that there are no systematic differences between the trace element compositions of pyrite in the three deposits from different ore belts in general au concentrations in pyrite are low from 2 rich ore fluids spatial association with large scale compressional structures of the qinling orogen 18 o and d data suggestive of mixing between metamorphic and meteoric waters 34 s and pb isotopic data that point to a mixed crustal mantle source all point to typical orogenic type gold deposits high ni concentrations up to 8425 ppm of pyrite possibly linked to deep seated mafic ultramafic metamorphic rocks provide further evidence on the orogenic gold deposit affinity but against the model of a granitic derivation of the mineralizing fluid as previously suggested by some workers generally low au concentration in pyrite is also consistent with those from worldwide orogenic gold deposits therefore the gold mineralization in the xiaoqinling district is described as orogenic type and is probably related to indosinian collision between the north china craton and the yangtze craton

a new concept on tectonic correlation between korea china and japan histories from the late proterozoic to cretaceous abstract the dabie sulu collision belt in china extends to the hongseong odesan belt in korea while the okcheon metamorphic belt in korea is considered as an extension of the nanhua rift within the south china block the hongseong odesan belt divides korea s gyeonggi massif into northern and southern portions the southern gyeonggi massif and the yeongnam massif are correlated with china s yangtze and cathaysia blocks respectively while the northern gyeonggi massif is part of the southern margin of the north china block the southern and northern gyeonggi massifs rifted from the rodinia supercontinent during the neoproterozoic to form the borders of the south china and north china blocks respectively subduction commenced along the southern and eastern borders of the north china block in the ordovician and continued until a triassic collision between the north china and south china blocks while subduction was occurring on the margin of the north china block high p t metamorphic belts and accretionary complexes developed along the inner zone of southwest japan from the ordovician to the permian during the subduction the hida belt in japan grew as a continental margin or continental arc collision between the north and south china blocks began in korea during the permian 290 260 ma and propagated westwards until the late triassic 230 210 ma creating the sinistral tanlu fault in china and the dextral fault in the hida and hida marginal belt in japan phanerozoic subduction and collision along the southern and western borders of the north china block led to formation of the qinling dabie sulu hongseong hida yanji belt

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

large scale present day plate boundary deformations in the eastern hemisphere determined from vlbi data implications for plate tectonics and indian ocean growth the dynamics of the planet earth are manifestations of diverse plate tectonic processes which have been occurring since the archean period of the earth s evolution and continue to deform the plate boundaries very long baseline interferometry vlbi is an efficient space geodetic method that enables precise measurement of plate motion and associated deformations we analyze here vlbi measurements made during a period of approximately three decades at five locations on the eastern hemisphere of the globe which are geographically distributed over five continents plates around the indian ocean computed rate of change of baseline length show the deformation pattern and its rate at the boundaries between the major tectonic plates constituting the eastern hemisphere of the earth the african nubian and antarctic plates are moving apart at 13 5 mm year which is mostly attributed to spreading of the south west indian ridge similarly spreading of 59 0 mm year is observed for the south east indian ridge that separates the antarctic and australian plates shortening at the rate of 3 9 mm year is estimated across the subduction boundary between africa nubia and eurasia similar convergence is evident between the australian and sunda blocks of the eurasian plate the associated deformation of 54 8 mm year seems to be chiefly accommodated along the banda arc system where the australian plate is subducting under the sunda block vlbi sites within the eurasian plate wettzell in germany and seshan on the south china block are moving apart at 3 6 mm year this relative motion between locations on the same plate is interpreted as a result of the deformation process along a large strike slip fault which is identified as the western boundary of the south china block expansion of the indian ocean at 91 5 m2 year is also estimated from the rate of deformation estimated within the five baselines studied here from the hurst exponent values which are indicators of the future trend of time series data we predict deceleration of the various tectonic processes occurring at present

granitoid associated orogenic intrusion related and porphyry style metal deposits in the archean yilgarn craton western australia abstract the yilgarn craton hosts three types of archean granitoid associated metallogenic systems orogenic gold intrusion related and porphyry systems these systems may occur in the same terrane and share many broad characteristics including spatial coincidence with granitoids gangue silicate mineralogy metal associations and local structural controls features of archean orogenic gold systems spatially associated with granitoids include i a broad range of granitoid host compositions ii gold mineralization is mostly late with respect to yilgarn wide granitoid emplacement peak metamorphism and deformation iii orebodies are structurally controlled and iv gold deposition occurs over a large range of temperatures pressures and crustal depths 2 to 15 km from a co 2 rich low to moderate salinity reduced ore fluid that was derived from a metamorphic and or distal magmatic fluid source these systems do not display deposit scale vertical or lateral zonation of metals away from granitoid contacts host granitoid age composition or oxidation state are not important in controlling gold mineralization processes whereas structural setting and fluid flux are paramount archean intrusion related au mo w and mo au systems in the yilgarn craton are commonly small 2 bearing moderate to high salinity fluid during ore deposition archean porphyry cu mo au cu mo and cu au systems are spatially and temporally associated with volumetrically small pervasively altered felsic plutons and dikes surrounded by altered and mineralized supracrustal countryrock lateral zonation of metals away from porphyry centers commonly includes a decrease in cu au and ag au ratios with distance from the source pluton microthermometry studies on fluid inclusions in gold bearing veins suggest that early ore fluids were high temperature and high salinity and that mineralization occurred at 2 o 3 feo are demonstrated in phanerozoic terranes but are presently ill defined in the yilgarn craton crustal depth estimation is important in defining areas likely to have preserve shallow forming archean porphyry systems