mineralogy and geochemistry of gold bearing arsenian pyrite from the shuiyindong carlin type gold deposit guizhou china implications for gold depositional processes arsenian pyrite in the shuiyindong carlin type gold deposit in guizhou china is the major host for gold with 300 to 4 000 ppm au and 0 65 to 14 1 wt as electron miroprobe data show a negative correlation of as and s in arsenian pyrite which is consistent with the substitution of as for s in the pyrite structure the relatively homogeneous distribution of gold in arsenian pyrite and a positive correlation of as and au with au as ratios below the solubility limit of gold in arsenian pyrite suggest that invisible gold is likely present as au1 in a structurally bound au complex in arsenian pyrite geochemical modeling using the laser ablation inductively coupled plasma mass spectrometry la icp ms analysis of fluid inclusions for the major ore forming stage shows that the dominant au species were au hs 2 77 and auhs aq 0 23 gold hydroxyl and gold chloride complexes were negligible the ore fluid was undersaturated with respect to native au with a saturation index of 3 8 the predominant as species was h3aso30 aq pyrite in the shuiyindong deposit shows chemical zonation with rims richer in as and au than cores reflecting the chemical evolution of the ore bearing fluids the early ore fluids had relatively high activities of as and au to deposit unzoned and zoned arsenian pyrite that host most gold in the deposit the ore fluids then became depleted in au and as and formed as poor pyrite overgrowth rims on gold bearing arsenian pyrite arsenopyrite overgrowth aggregates on arsenian pyrite indicate a late fluid with relatively high activity of as the lack of evidence of boiling and the low iron content of fluid inclusions in quartz suggest that iron in arsenian pyrite was most likely derived from dissolution of ferroan minerals in the host rocks with sulfidation of the dissolved iron by h2s rich ore fluids being the most important mechanism of gold deposition in the shuiyindong carlin type deposit

gold oxysulphides in copper deposits of the greywacke zone austria a mineral chemical and infrared fluid inclusion study abstract native gold and unusual gold oxysulphides both associated with tetrahedrite occur in several abandoned copper deposits in the low grade palaeozoic greywacke zone in the eastern alps the ore mineralogy the mineral chemistry and fluid inclusions in tetrahedrite and quartz were studied from historic cu mines at larzenbach huttau st veit im pongau and mitterberg all salzburg province austria fluid inclusions in tetrahedrite which is non transparent in visible light were studied by infrared ir microthermometry tetrahedrite containing up 2 5 wt as is transparent for infrared light fluid inclusions within tetrahedrite occur as isolated inclusions in clusters and along trails at room temperatures these are aqueous two phase liquid l vapour v inclusions of low to moderate total salinity tm 3 to 14 c homogenisation temperatures th v l range between 85 and 200 c the composition of these tetrahedrite hosted fluid inclusions corresponds to that one type of fluid inclusion in quartz showing a similar range in salinity tm 3 to 12 c and total homogenisation temperatures th v l 71 5 to 250 c another type of higher saline aqueous two phase l v inclusions in quartz is apparently unrelated to gold mineralisation fluid inclusions within tetrahedrite coexist with small solid inclusions of chalcopyrite gold oxysulphides minor arsenopyrite and gold that is rich in gold oxysulphide microinclusions and occur along re healed microfractures within tetrahedrite these microfractures also control the replacement of as poor tetrahedrite by arseniferous up to 3 16 wt as tetrahedrite it is suggested that in addition to cooling the exchange of as for sb on tetrahedrite surfaces was one of the factors controlling precipitation of gold oxysulphides are associated with a native gold in unweathered primary ores and b remobilised cu rich gold in weathered ores gold thiosulphate and possibly thioarsenite complexes are the preferred species for the transport of gold in the low temperature

no genetic link between late cretaceous felsic dikes and carlin type au deposits in the youjiang basin southwest china abstract the youjiang basin in southwest china is distinguished by preserving a number of carlin type gold deposits tens of felsic dikes occur in this region and some are present within the ore fields a genetic link between these felsic dikes and ore formation has previously been proposed but detailed field investigation shows that the dikes crosscut the main ore body and clearly postdate gold mineralization three felsic dikes in the youjiang basin have been dated and sims zircon u pb dating results show that the liaotun and xiabaha dikes were emplaced at 97 2 1 1 ma mswd 2 9 and 95 4 2 4 ma mswd 0 56 respectively broadly consistent with a la icp ms zircon u pb age for the bama dike 99 4 0 37 ma mswd 1 4 combined with published dates of the other felsic dikes in this region it is suggested that the felsic magmatic event in the youjiang basin occurred between 100 and 95 ma although a wide range of ages for gold mineralization 275 46 ma has been reported by a variety of methods the best available ages suggest a timing between 235 and 193 direct re os dating on fe sulfides chen et al 2015 re os isochron ages for arsenopyrite from carlin like gold deposits in the yunnan guizhou guangxi golden triangle southwestern china significantly older than the emplacement age of the felsic dikes taken together we conclude that there is no genetic link between these late cretaceous felsic dikes and carlin type au mineralization in the youjiang basin

a review of te and se systematics in hydrothermal pyrite from precious metal deposits insights into ore forming processes abstract pyrite is one of the most common minerals in many precious and base metal hydrothermal ore deposits and is an important host to a range of trace elements including au and co and the semi metals as se sb te and bi as such in many hydrothermal ore deposits where pyrite is the dominant sulphide phase it can represent a major repository for these elements furthermore the concentrations and ratios of au as and co in pyrite have been used to infer key ore forming processes however the mechanisms controlling the distribution of te and se in pyrite are less well understood here we compare the te and se contents of pyrite from a global dataset of carlin type orogenic au and porphyry epithermal deposits to investigate 1 the potential of pyrite to be a major repository for these elements and 2 whether te and se provide insights into key ore forming processes pyrite from carlin type low sulphidation and alkaline igneous rock hosted epithermal systems is enriched in te and se compared to pyrite from high sulphidation epithermal and porphyry cu deposits orogenic au pyrite is characterised by intermediate te and se contents there is an upper solubility limit for te as a function of as in pyrite similar to that established for au by reich et al 2005 and this can be used to identify te present as telluride inclusions which are common in some epithermal porphyry and orogenic au deposits physicochemical fluid parameters such as ph redox and temperature as well as crystal chemistry control the incorporation and concentration of se and te in pyrite neutral to alkaline fluids have the ability to effectively mobilise and transport te fluid boiling in porphyry epithermal systems as well as wall rock sulphidation and oxidation in carlin type and orogenic au deposits can effectively precipitate te in association with pyrite and au in contrast se concentrations in pyrite apparently vary systematically in response to changes in fluid temperature irrespective of ph and f o 2 hence we propose that the se contents of pyrite may be used as a new geo thermometer for hydrothermal ore deposits furthermore the comparison of bulk ore and pyrite chemistry indicates that pyrite represents the major host for te and se in carlin type and some epithermal systems and thus pyrite can be considered to be of economic interest as a potential source for these elements

geochemistry and textures of gold bearing arsenian pyrite twin creeks nevada implications for deposition of gold in carlin type deposits this study relates morphology size texture and chemistry of arsenian pyrite in the twin creeks carlin type gold deposits to the chemical position and amount of gold that it contains arsenian pyrite is confirmed as the most important gold hosting mineral and four types of gold bearing arsenian pyrite are recognized among these four types the lowest amount of gold and arsenic 1 wt as 17 60 ppm au is contained in arsenian pyrite with relatively large grain sizes 10 30 mu m it formed at relatively high temperatures 250 degrees c and k super h super ratios adularia stable probably relatively slowly the largest amount of gold and arsenic 1 05 2 43 wt as 595 1 465 ppm au is contained in arsenian pyrite with small grain sizes up to 2 mu m that formed at low temperatures 120 degrees 200 degrees c and moderate k super h super ratios illite stable probably by relatively rapid deposition xanes exafs and sims analyses show that gold in arsenian pyrite is both structurally bound au i and in submicroscopic inclusions of free gold au highest amounts of structurally bound gold were observed in the relatively coarse grained arsenian pyrite noted above whereas most inclusions of free gold were observed in fine grained arsenian pyrite in general there is a good correlation between gold and arsenic in arsenian pyrite although au as ratios vary from one pyrite to another it is suggested that gold in arsenian pyrite was deposited by direct deposition of native gold and by adsorption of au i from hydrothermal solutions adsorption of gold by arsenian pyrite can take place from solutions that are not saturated with respect to native gold relative volumes of gold bearing pyrite from different paragenetic stages at twin creeks suggest that as much as 50 percent of the total gold in the deposit could have formed from solutions that were not saturated with respect to native gold because both au and au i are found together in arsenian pyrite it is likely that they were deposited by the same process consideration of possible depositional reactions suggests that a decrease in the activity of reduced sulfur is most likely to cause gold deposition

carlin gold deposits nevada origin in a deep zone of mixing between normally pressured and overpressured fluids gold mineralization at carlin is clearly younger than hydrocarbon maturation pre cretaceous and felsic dike intrusion cretaceous and older than deep oxidation late tertiary within the episode of gold mineralization the main gold ore mgo stage and late gold ore ego stage are distinguished paragenetically with a variety of vein and mineralization types in each mgo stage fluids contained 5 to 10 mole percent co 2 appreciable h 2 s and 3 or 1 wt percent nacl equiv at least portions of mgo stage mineralization were characterized by two phase boiling co 2 exsolution at 215 degrees or 30 degrees c and 800 or 400 bars in contrast ego stage fluids were gas poor with salinities 18 o sub h 2 o values of 5 to 9 per mil whereas ego stage fluids resembled unevolved meteoric water with delta 18 o sub h 2 o values 18 o values shifted from near whole rock values of 12 or 3 per mil to around 0 or 1 per mil as ego stage fluids flooded the system jasperoids also record a large range 9 22 in delta 18 o sub h 2 o values these data indicate the involvement of two very different fluids in ore deposition because mgo and ego stage features are closely associated spatially with each other and with au as sb hg and other ore elements both fluids are believed to have both been present during most stages of ore deposition at pressures of 80 to 85 percent lithostatic depths of 3 8 or 1 9 km are required to accommodate the 800 or 400 bars of pressure recorded in mgo stage fluid inclusions carlin therefore is not an epithermal or hot spring deposit carbon dioxide in gas rich mgo stage fluids may have originated either directly from buried intrusions or their contact aureoles or from low grade regional metamorphism at depth the water may have been originally meteoric and au may be magmatic or derived from leaching of deep metamorphic or sedimentary rocks ore deposition appears to have occurred in zones of throttling at a pressure seal between normally pressured and overpressured regimes where fluids experienced a change from near lithostatic to hydrostatic conditions such pressure seals are common in deep sedimentary basins and may be a key to highly localized gold deposition mixing of two fluids and interaction with host rocks along thin permeable bioclastic horizons are believed to have been the major factors in depositing ore

geology and isotope geochemistry c o s of the diyadin gold deposit eastern turkey a newly discovered carlin like deposit abstract diyadin mineralization is the first reported gold deposit located in a collisional tectonic environment in eastern anatolia the mineralization is related to n s and n10 20 w trending fault systems and hosted within the paleozoic metamorphic basement rocks of the anatolide toride microcontinent calc schist dolomitic marble and miocene and quaternary volcanic rocks comprise the exposed units in the mineralized area geochemical signatures alteration types and host rock characteristics of the diyadin gold deposit resemble those of carlin type deposits mineralization is constrained by alteration of overlying volcanic rocks to younger than 14 ma k ar carbon and oxygen stable isotope measurements of carbonate rocks were made on six drill holes n 81 with an additional four samples of fresh carbonate rocks from surface outcrops background carbonate rocks have 13cv pdb 1 8 and 18ov smow 27 isotopically altered host rock samples have decreased 18o down to 11 4 and variable 13c from 3 6 to 4 8 postore carbonate veins and cave fill material have distinctly different isotopic signatures particularly carbon from 13c 8 4 to 9 8 whether this post ore carbonate is simply very late in mineralization associated with the gold system or is a completely different younger system utilizing the same pathways is unclear at present within the host rock sample set there is no correlation between gold and 13c and a weak correlation between gold and 18o indicative of water rock interaction and isotopic alteration both the isotopic data and structural mapping suggest that the main upflow zone for the deposit is near the northern portion of the drill fence additional data at multiple scales are required to clarify the relationship s between fluid flow and mineralization

ion microprobe determination of sulfur isotope variations in iron sulfides from the post betze sediment hosted disseminated gold deposit nevada usa abstract secondary ion mass spectrometric analyses of ore samples from the post betze sedimenthosted disseminated gold deposit were utilized to constrain elemental distribution of au and as in iron sulfide phases most of the au was deposited very early in the paragenetic sequence although au and as are covariant in arsenian pyrite au apparently was depleted much more rapidly from the hydrothermal solutions than was as sensitive high resolution ion microprobe shrimp sulfur isotope analyses of iron sulfides from the post betze deposit vary widely from 34 s 29 to 23 and provide important information on the origin of sulfur and constraints on depositional mechanisms ore solutions had high 34s values and were most likely derived at least in part from thermochemical reduction of lower paleozoic seawater derived sulfate possibly bedded barite late stage ore fluids 34 s sulfide 12 to 29 are extremely depleted in 34s relative to main stage ore fluids 34 s sulfide 16 23 although such low 34s values can be generated hypothetically from the original ore fluids by oxidation possibly boiling the stability of pyrite is compromised introduction of and mixing with fe rich fluids is necessary to deposit pyrite having low isotopic values

the carbonate rock hosted epithermal gold deposit of agdarreh takab geothermal field nw iran hydrothermal alteration and mineralisation the disseminated gold deposit of agdarreh 24 5 t at 3 7 g t au is hosted in hydrothermally leached miocene reefal limestone in the takab geothermal field which is part of the cenozoic urumieh dokhtar volcanic arc of nw iran alteration and mineralisation are largely bedding controlled blanket like and include 1 pre ore decalcification 2 first stage silicification associated with pyrite early pyrite with 3 4 wt as late pyrite with 1 3 wt as and sphalerite 3 second stage silicification with precipitation of galena pb sb as sulphides sulphosalts tellurides and native bismuth 4 late stage cinnabar and barite in vugs 5 oxide ore stage and carbonate alteration complex mn fe rich oxyhydroxides arsenates sulphates aps minerals and rutile in residual leached rock and infill of karstic cavities gold occurs invisibly in the jasperoids and is enriched in the mn fe oxyhydroxide surface cap of the jasperoids gold mineralisation is associated with the hydrothermal metal suite of as sb hg te se tl ba zn ag cd bi and pb and is characterised by very low cu contents arsenian pyrite probably carried most of the primary invisible gold native gold occurs in association with the late stage cinnabar and the oxide ore

quantified multi scale x ray fluorescence element mapping using the maia detector array application to mineral deposit studies the maia large solid angle detector array and imaging system is capable of collecting high resolution images of up to 100 m pixels in size with dwell times of less than 0 2 ms per pixel and thus it is possible to document variation in textures associated with trace element chemistry by collecting quantified elemental maps of geological samples on the scale of entire thin sections in a short time frame 6 8 hr the analysis is nondestructive and allows variation to be recognised on a centimetre scale while also recognising zonations at the micron scale

alteration associated with gold deposition at the getchell carlin type gold deposit north central nevada wall rock alteration at the getchell underground deposit was examined to determine the effects of au bear ing fluids on host lithologies and the relationship between k bearing alteration minerals and au deposition the major minor and trace element geochemistry of highly altered and mineralized to unmineralized rocks from the getchell deposit was quantified for more than 50 samples collected along 13 transects through calcareous siltstone and carbonaceous limestone and along one transect through a rhyodacite dike each transect in sedimentary rocks was collected along a single homogeneous bed that could be followed from high grade ore to moderately altered rock or waste rock analyses were obtained for 39 elements 10 oxides and loss on ignition using multiple techniques petrographic studies were integrated with geochemistry and x ray diffraction and electron microbeam analyses to identify ore and alteration minerals and to correlate mineralogy with geochemical fluxes geochemical analyses indicate that ti al zr and th behave as immobile elements immobility isocon diagrams show that significant hg sb se te tl and cs are typically added to the wall rocks with au fe is im mobile in some transects added to wall rocks in others and removed from rhyodacite host rocks minor s and w are usually added to the rock whereas minor cu and mo are variably added or removed sio 2 appears to be either added during alteration or remain constant elements that are consistently removed during alteration include ca mn sr and sc and minor mg ba and k na was significantly removed from the rhyodacite au correlates positively with ag hg sb se si te and tl and negatively with ca mn and sc element fluxes correspond with observations of mineral abundances and show that sulfidation and decar bonitization are spatially associated with gold mineralization au hg sb tl cu and possibly te and w were incorporated in trace element rich pyrite as host rock fe was sulfidized fe was added to mineralized rocks in some transects indicating that pyritization occurred in addition to sulfidation cs is a component of galkhaite a trace mineral that is relatively common in some parts of the getchell system decarbonitization removed as much as 95 wt percent calcite from mineralized rocks in some transects and is responsible for loss of ca mn sr and sc although sio 2 as and s are significantly added to carlin type systems they do not appear as major added components in the isocon diagrams this is because the halos for these components are much larger than the areas examined by the sample transects x ray diffraction analyses identified minerals in ore and waste samples and quantified clay minerals including illite and montmorillonite kaolinite was not identified or is present in low abundances in both mineralized and unmineralized rocks montmorillonite does not correlate with gold and textures are consistent with pore filling deposition of montmorillonite following au deposition illite abundance exhibits a positive correlation with au r 2 0 80 intergrowths of illite with ore stage pyrite support a genetic relationship between the two minerals and indicate that illite formed as part of the au related hydrothermal event mineral abundances and textures suggest that illite formed by alteration of k feldspar during au deposition results show that dating of k bearing phases in sedimentary rocks other than illite would provide ages unrelated to gold deposition

age constraints on jerritt canyon and other carlin type gold deposits in the western united states relationship to mid tertiary extension and magmatism carlin type gold deposits are difficult to date and a wide range of ages has been reported for individual deposits therefore several methods were employed to constrain the age of the gold deposits in the jerritt canyon district dated igneous rocks with well documented crosscutting relationships to ore provided the most reliable constraints k ar and 40 ar 39 ar dates on igneous rocks are as follows andesite dikes 324 ma sericitic alteration in andesite dikes 118 ma basalt dikes 40 8 ma quartz monzonite dikes 39 2 ma and calc alkaline ignimbrites 43 1 to 40 1 ma of these only the andesite and basalt dikes are clearly altered and mineralized the gold deposits are therefore younger than the 40 8 ma basalt dikes the sericitic alteration in the andesite dikes is unrelated to the gold deposits a number of dating techniques did not work k ar and 40 ar 39 ar dates on mica from mineralized ordovician to devonian sedimentary rocks gave misleading results the youngest date of 149 ma from the smallest 187 os 188 os initial 0 9 3 6 but did not yield a meaningful isochron due to very low re and os concentrations and large analytical uncertainties paleomagnetic dating techniques failed because the hydrothermal fluids sulfidized nearly all of the iron in the host rocks leaving no remnant magnetism when published isotopic dates from other carlin type deposits in nevada and utah are subject to the rigorous evaluation developed for the jerritt canyon study most deposits can be shown to have formed between 42 and 30 ma k ar and 40 ar 39 ar dates on the youngest preore igneous rocks range from 41 to 32 ma whereas the oldest postore igneous rocks range from 35 to 33 ma hydrothermal adularia from the twin creeks deposit yields similar 40 ar 39 ar dates of 42 ma k ar dates on supergene alunite range from 4 to 30 ma k ar and 40 ar 39 ar dates on micas separated from sedimentary 395 43 ma and igneous 145 38 ma rocks are usually much older than the gold deposits and most are suspect because they are from incompletely reset preore micas or from mixtures of preore and ore stage mica fission track dates on zircons are also generally older than the deposits 169 35 ma and are not completely reset by mineralization apatites are likley to be reset by the hydrothermal systems and by younger thermal events and yield dates 83 22 ma that are younger than those from zircon independent support of a mid tertiary age is provided by the low delta d sub h 2 o values of hydrothermal fluids from 10 widely separated carlin type deposits 134 or 23ppm the low delta d sub h 2 o values are consistent with a mid tertiary age when the climate was cool but are inconsistent with the cretaceous and jurassic ages favored by some workers when the climate was warm the age and distribution of carlin type deposits coincides with areas that underwent extension and calc alkaline magmatism over the same time period despite this relationship the deposits lack clear spatial or genetic relationships to mid tertiary epizonal plutons rather many deposits are localized along preexisting crustal fault zones in the getchell trend structures tapped deep sourced metamorphic or magmatic fluids and subsequently variably exchanged meteoric water in the other trends and districts only variably exchanged meteoric water has been detected these relationships suggest either that all of the deposits formed from deep sourced fluids and were subsequently flooded by meteoric water or that fluids from different sources evolved to produce deposits with similar charateristics

visible gold in arsenian pyrite at the shuiyindong carlin type gold deposit guizhou china implications for the environment and processes of ore formation abstract carlin type gold deposits are best known for the scarcity of visible gold in their ores it has long been recognized that the majority of gold is invisible such that it cannot be resolved by conventional microscopy and resides in arsenian pyrite shuiyindong differs in that sub m to m sized native gold is present in arsenian pyrite veinlets and disseminations it is also the largest 55 tonnes and highest grade 7 to 18 ppm stratabound carlin type gold deposit in guizhou china and has produced 5 tonnes of gold from sulfide refractory ores extracted by underground mining methods in this study an electron microprobe analyzer empa was used to map the spatial distribution of invisible gold and sub m to m size visible gold particles in arsenian pyrite in high grade ore samples from the shuiyindong the samples studied are hosted in permian bioclastic ferroan limestone of the longtan formation and exhibit evidence of decarbonation silicification and sulfidation arsenian pyrite with detectable au 400 to 3800 ppm is disseminated in altered limestone and was deposited in two stages separated by an episode of corrosion in a veinlet the results show that there are two populations of native gold in arsenian pyrite one is comprised of sub m size gold particles 0 1 to 0 2 m that are occasionally present in the gold bearing arsenian pyrite disseminated in the host rocks this arsenian pyrite is interpreted to have been formed by sulfidation of ferroan calcite and dolomite another is comprised of coarser 1 to 6 m native gold grains present in the arsenian pyrite veinlet either on the first stage where it has been corroded or on the second stage the lack of fluid inclusion or other evidence of boiling and the low iron content of fluid inclusions in quartz suggest the veinlet formed by sulfidation of another fluid containing fe the fe bearing fluid may be a depleted ore fluid that gained fe by dissolution of ferroan limestone after h 2 s had been consumed the association of the largest visible gold grains with an episode of corrosion suggests that fluids episodically became undersaturated with arsenian pyrite while remaining saturated with gold e g ph decrease or an increase in the oxidation state this may have resulted from incursion of relatively acidic or oxidized fluids that were able to dissolve arsenian pyrite and remain saturated with gold in this case sulfidation of iron from the host rock was the most important depositional mechanism for au bearing arsenian pyrite with or without grains of native gold

investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid cretaceous vertebrate fossil localities in the winton formation queensland australia the winton formation of central queensland is recognized as a quintessential source of mid cretaceous terrestrial faunas and floras in australia however sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited the intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved winton formation in the eromanga basin including isisford lark quarry and bladensburg national park twenty three facies and six repeated facies associations were documented indicating a mosaic of marginal marine to inland alluvial depositional environments these developed synchronously with the final regression of the eromanga seaway from central australia during the late albian early turonian investigations of regional and local scale structural features and outcrop core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin significant palaeoenvironmental differences exist between the lower and upper portions of the preserved winton formation warranting informal subdivisions a lower tidally influenced fluvial deltaic member and an upper inland alluvial member this work further demonstrates that the isisford fauna is part of the lower member of the preserved winton formation whereas fossil localities around winton including lark quarry and bladensburg national park are part of the upper member of the winton formation these results permit a more meaningful framework for both regional and global comparisons of the winton flora and fauna

hydrocarbon and ore bearing basinal fluids a possible link between gold mineralization and hydrocarbon accumulation in the youjiang basin south china the youjiang basin which flanks the southwest edge of the yangtze craton in south china contains many carlin type gold deposits and abundant paleo oil reservoirs the gold deposits and paleo oil reservoirs are restricted to the same tectonic units commonly at the basinal margins and within the intrabasinal isolated platforms and or bioherms the gold deposits are hosted by permian to triassic carbonate and siliciclastic rocks that typically contain high contents of organic carbon paragenetic relationships indicate that most of the deposits exhibit an early stage of barren quartz pyrite stage i a main stage of auriferous quartz arsenian pyrite arsenopyrite marcasite stage ii and a late stage of quartz calcite realgar orpiment native arsenic stibnite cinnabar dolomite stage iii bitumen in the gold deposits is commonly present as a migrated hydrocarbon product in mineralized host rocks particularly close to high grade ores but is absent in barren sedimentary rocks bitumen dispersed in the mineralized rocks is closely associated and or intergrown with the main stage jasperoidal quartz arsenian pyrite and arsenopyrite bitumen occurring in hydrothermal veins and veinlets is paragenetically associated with stages ii and iii mineral assemblages these observations suggest an intimate relationship between bitumen precipitation and gold mineralization in the paleo petroleum reservoirs that typically occur in permian reef limestones bitumen is most commonly observed in open spaces either alone or associated with calcite where bitumen occurs with calcite it is typically concentrated along pore vein centers as well as along the wall of pores and fractures indicating approximately coeval precipitation in the gold deposits aqueous fluid inclusions are dominant in the early stage barren quartz veins stage i with a homogenization temperature range typically of 230 c to 270 c and a salinity range of 2 6 to 7 2 wt nacl eq fluid inclusions in the main and late stage quartz and calcite are dominated by aqueous inclusions as well as hydrocarbon and co2 rich inclusions the presence of abundant hydrocarbon fluid inclusions in the gold deposits provides evidence that at least during main periods of the hydrothermal activity responsible for gold mineralization the ore fluids consisted of an aqueous solution and an immiscible hydrocarbon phase aqueous inclusions in the main stage quartz associated with gold mineralization stage ii typically have a homogenization temperature range of 200 230 c and a modal salinity around 5 3 wt nacl eq homogenization temperatures and salinities of aqueous inclusions in the late stage drusy quartz and calcite stage iii typically range from 120 c to 160 c and from 2 0 to 5 6 wt nacl eq respectively in the paleo oil reservoirs aqueous fluid inclusions with an average homogenization temperature of 80 c are dominant in early diagenetic calcite fluid inclusions in late diagenetic pore and fissure filling calcite associated with bitumen are dominated by liquid c2h6 vapor ch4 ch4 h2o and aqueous inclusions with a typical homogenization temperature range of 90 c to 180 c and a salinity range of 2 8 wt nacl eq it is suggested that the hydrocarbons may have been trapped at relatively low temperatures while the formation of gold deposits could have occurred under a wider and higher range of temperatures the timing of gold mineralization in the youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits among the limited isotopic data the rb sr date of 206 12 ma for au bearing hydrothermal sericite at jinya as well as the re os date of 193 13 ma on auriferous arsenian pyrite and 40ar 39ar date of 194 6 2 ma on vein filling sericite at lannigou may provide the most reliable age constraints on gold mineralization this age range is comparable with the estimated petroleum charging age range of 238 185 ma and the sm nd date of 182 21 ma for the pore and fissure filling calcite associated with bitumen at the shitouzhai paleo oil reservoir corresponding to the late indosinian to early yanshanian orogenies in south china the close association of carlin type gold deposits and paleo oil reservoirs the paragenetic coexistence of bitumens with ore stage minerals the presence of abundant hydrocarbons in the ore fluids and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated migrated and precipitated along with the hydrocarbons in an immiscible gold and hydrocarbon bearing basinal fluid system

lead in the getchell turquoise ridge carlin type gold deposits from the perspective of potential igneous and sedimentary rock sources in northern nevada implications for fluid and metal sources lead isotope compositions of bulk mineral samples fluorite orpiment and realgar determined using conventional techniques and of ore stage arsenian pyrite using the sensitive high resolution ion microprobe shrimp in the getchell and turquoise ridge carlin type gold deposits osgood mountains require contribution from two different pb sources one pb source dominates the ore stage it has a limited pb isotope range characterized by 208pb 206pb values of 2 000 to 2 005 and 207pb 206pb valuesof 0 8031 to 0 8075 as recorded by 10 mm diameter spot shrimp analyses of ore stage arsenian pyrite these values approximately correspond to 206pb 204pb of 19 3 to 19 6 207pb 204pb of 15 65 to 15 75 and 208pb 204pb of 39 2 to 39 5 this pb source is isotopically similar to that in average neoproterozoic and cambrian clastic rocks but not to any potential magmatic sources whether those clastic rocks provided pb to the ore fluid cannot be unequivocally proven because their pb isotope compositions over the same range as in ore stage arsenian pyrite are similar to those of ordovician to devonian siliciclastic and calcareous rocks the pb source in the calcareous rocks most likely is largely detrital minerals since that detritus was derived from the same sources as the detritus in the neoproterozoic and cambrian clastic rocks the second pb source is characterized by a large range of 206pb 204pb values 18 34 with a limited range of 208pb 204pb values 38 1 39 5 indicating low but variable th u and high and variable u pb values the second pb source dominates late and postore stage minerals but is also found in preore sulfide minerals these pb isotope characteristics typify ordovician to devonian siliciclastic and calcareous rocks around the carlin trend in northeast nevada petrologically similar rocks host the getchell and turquoise ridge deposits lead from the second source was either contributed from the host sedimentary rock sequences or brought into the hydrothermal system by oxidized ground water as the system collapsed late ore and postore stage sulfide minerals pyrite orpiment and stibnite from the betze post and meikle deposits in the carlin trend and from the jerritt canyon mining district have pb isotope characteristics similar to those determined in getchell and turquoise ridge this observation suggests that the pb isotope compositions of their ore fluids may be similar to those at getchell and turquoise ridge two models can explain the pb isotope compositions of the ore stage arsenian pyrite versus the late ore or postore sulfide minerals in either model pb from the ordovician to devonian siliciclastic and calcareous rock source enters the hydrothermal system late in the ore stage but not to any extent during the main stage of ore deposition in one model ore stage pb was derived from a source with pb isotope compositions similar to those of the neoproterozoic and cambrian clastic sequence transported as part of the ore fluid and then deposited in the ore stage arsenian pyrite and fluorite the second model is based on the observation that the pb isotope characteristics of the ore stage minerals also are found in some ordovician to devonian calcareous and siliciclastic rocks hence ore stage pb could have been derived locally and simply concentrated during the ore stage critical to the second model is the removal of all high 206pb 204pb 20 material during alteration it also requires the retention of only the low 206pb 204pb component of the ordovician to devonian sedimentary rocks this critical step is possible only if the high 206pb 204pb values are contained in readily dissolvable mineral phases whereas the low 206pb 204pb values are found only in refractory minerals that released pb during a final alteration stage just prior deposition of auriferous arsenian pyrite distinguishing between pb transported with the ore fluid or inherited from the site of mineral deposition is not straightforward however it is simpler to explain the pb isotope compositions of ore stage arsenian pyrite and fluorite in two different but spatially related carlin type deposits getchell and turquoise ridge with different host rocks by input of pb with the ore fluid once the limited pb in the hydrothermal fluid was exhausted by incorporation in ore stage arsenian pyrite or other ore stage minerals pb from the second source the ordovician to devonian sedimentary rock sequences became available for incorporation in some but not all of the late stage sulfide minerals

molybdenite re os dating and la icp ms trace element study of sulfide minerals from the zijinshan high sulfidation epithermal cu au deposit fujian province china abstract the zijinshan cu au deposit located in fujian province is the largest high sulfidation epithermal hse deposit in southeastern china and is usually regarded as a major part of the porphyry cu system in the zijinshan ore field molybdenite samples collected from the cu mineralization zone yield a first weighted mean re os age of 111 31 0 70 ma which is explained as the time of dickite alunite alteration combining the newly reported muscovite 40ar 39ar and zircon u pb ages 113 ma the mineralization of zijinshan is likely to initiate before ca 110 ma this result is obviously older than the re os age of the adjacent luoboling porphyry cu mo deposit 105 ma pyrite chalcopyrite bornite digenite and covellite collected from the deep potassic middle phyllic and upper epithermal zones are used to conduct la icp ms trace element analysis the spatial zonings of mineralization and alteration and the regular variations of trace elements in sulfides at vertical direction imply a potentially complete transition from porphyry to epithermal mineralization and the deep origin of ore forming fluids mineralogical and trace element characteristics indicate that the chalcopyrite formed in both stages whereas bornite is the product of epithermal mineralization rather than a porphyry stage residue the majority of digenite and covellite has hypogene genesis pyrite and digenite in the epithermal zone are major carriers of primary au au in pyrite is te bi related and exists as solid solutions or different sized telluride and bi sulfosalt inclusions compared to as te and bi played more important roles to scavenge au and ag and achieve the primary au enrichment differently au in digenite is independently locked in digenite lattice bornite and digenite are good carriers of primary ag which mainly exists as solid solutions the high sulfidation state stage is the major period for concentrations of primary au and ag the upward increase of au in primary sulfides of hse cu zone implies that the distribution pattern of upper au enrichment and lower cu enrichment is not only caused by supergene process but is also controlled by hypogene trend based on the mineralization and alteration zonings the spatial variation of trace elements and the presented re os age the ore forming fluids of the zijinshan cu au deposit most likely originate from deep region rather than from the adjacent luoboling porphyry deposit the zijinshan and the luoboling deposits should belong to two independent hydrothermal systems

the touquoy zone deposit an example of unusual orogenic gold mineralisation in the meguma terrane nova scotia canada the touquoy zone deposit is host to disseminated gold mineralisation in metasiltstones of lower palaeozoic age from the close correlation between ore grades and the intersection of favourable stratigraphy and bounding faults it is apparent that mineralisation is controlled by both structural and lithological influences within the ore zone disseminated gold arsenopyrite pyrite and rare base metal sulphides are associated with a network of widely spaced millimetre scale quartz carbonate veinlets quasi pervasive fluid flow and prolonged interaction with the host rocks resulted in a diffuse but pronounced halo of wall rock alteration that is characterized by the breakdown of detrital feldspar and metamorphic chlorite and the development of hydrothermal carbonate phases k mica and disseminated sulphides these mineralogical changes are accompanied by enrichment in co2 k au as and s and depletion in na across the ore zone vein formation occurred at between 250 and 350 c and pressures of less than 1 2 kbar 1 kbar 100 mpa corresponding to an estimated depth of between 2 8 and 6 km mineralisation resulted from the unmixing of an overpressured low salinity co2 rich fluid in response to decreasing pressure during its ascent and penetration into permeable host rocks geological and geochemical features of mineralisation in the touquoy zone deposit are seen as convincing evidence for a close genetic association between disseminated style and lode gold mineralisation in orogenic terrains with the resulting style of mineralisation largely controlled by the overall structural geometry of the mineralising site rheological properties permeability and chemical receptiveness of the host rock and structural level of emplacement

gold mineralization associated with emeishan basaltic rocks mineralogical geochemical and isotopic evidences from the lianhuashan ore field southwestern guizhou province china abstract a number of gold deposits are newly discovered in the lianhuashan ore field southwestern guizhou province china the gold orebodies are restricted to the emeishan basaltic rocks and the interlayer fractures between the emeishan basaltic rocks and the limestone of the maokou formation three generations of pyrite py0 py1 and py2 have been recognized in these deposits based on morphology and paragenetic relationships electron microprobe emp laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses were carried out to characterize their chemical and sulfur isotopic compositions the framboidal py0 is enriched in as but depleted in most of the other trace elements it has negative 34s values of 14 5 1 9 which are typical of diagenetic pyrites resulted from bacterial reduction of marine sulfate py1 and arsenopyrite exhibit high concentrations of au and as making them the most dominant auriferous minerals they yield comparable 34s values of 2 8 2 1 consistent with the derivation of sulfur from the emeishan basaltic rocks py2 is characterized by well developed oscillatory zoned textures that are interpreted in terms of internal self organization processes it contains low concentrations of au and highly variable concentrations of as sb co and ni the py2 grains show slightly positive 34s values of 0 4 7 0 indicating that the sulfur was mainly sourced from the emeishan basaltic rocks with variable amounts of contamination from reduced marine sulfate the emeishan basaltic rocks may have provided not only ore hosting space but also au s and other associated elements for gold mineralization in the lianhuashan ore field similar gold deposits are expected to be discovered in the areas of emeishan basaltic rocks with high au backgrounds and small thicknesses

multistage pyrite in the getang sediment hosted disseminated gold deposit southwestern guizhou province china insights from textures and in situ chemical and sulfur isotopic analyses abstract getang is a representative sediment hosted disseminated gold shdg deposit in the southwestern guizhou province china the majority of gold is present as structurally bound au in pyrite with a minor amount occurring as nanoparticles au0 four generations of pyrite py0 py1 py2 and py3 were distinguished based on morphology and paragenesis electron microprobe emp laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses were conducted to determine the chemical and sulfur isotopic composition of the pyrite the pre ore diagenetic pyrite py0 has a framboidal texture and is characterized by relatively high concentrations of as co ni cu zn pb and mo it has negative 34s values of 38 4 to 4 0 indicating the derivation of sulfur by bacterial reduction of marine sulfate during sedimentation and diagenesis the early ore stage pyrite py1 coexists with arsenopyrite as subhedral anhedral grains and contains high concentrations of as ni cu and zn with large variation in co and pb content it has positive 34s values of 3 8 to 17 7 which are interpreted to be complete thermochemical reduction of marine sulfate the intermediate ore stage pyrite py2 is disseminated in the host rocks and occurs as overgrowths on py0 and py1 it is enriched in au and ag but depleted in as co ni cu and bi the late ore stage pyrite py3 occurs as acicular to columnar aggregates and is intergrown with calcite it contains high concentrations of as and low concentrations of pb mo and bi py2 and py3 display a comparable narrow range of 34s values from 1 9 to 8 4 which are interpreted to result from a magmatic source all the stable isotope data together with the gravity and magnetic evidences suggests that sulfur gold and the mineralizing fluids in the getang deposit were probably originated from deep magmatic hydrothermal systems the absence of igneous intrusions in southwestern guizhou may be attributed to the relatively shallow denudation depth in this area

a proposed new type of arsenian pyrite composition nanostructure and geological significance this report describes a new form of arsenian pyrite called as3 pyrite in which as substitutes for fe fe as s2 in contrast to the more common form of arsenian pyrite as1 pyrite in which as1 substitutes for s fe as s 2 as3 pyrite has been observed as colloformic overgrowths on as free pyrite in a hydrothermal gold deposit at yanacocha peru xps analyses of the as3 pyrite confirm that as is present largely as as3 empa analyses show that as3 pyrite incorporates up to 3 05 at of as and 0 53 at 0 1 at 0 27 at 0 22 at 0 08 at and 0 04 at of pb au cu zn ni and co respectively incorporation of as3 in the pyrite could be written like as3 y au 1 y 2 fe2 where au and vacancy help to maintain the excess charge hrtem observations reveal a sharp boundary between as free pyrite and the first overgrowth of as3 pyrite 20 40 nm thick and co linear lattice fringes indicating epitaxial growth of as3 pyrite on as free pyrite overgrowths of as3 pyrite onto as free pyrite can be divided into three groups on the basis of crystal size 8 20 nm 100 300 nm and 400 900 nm and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals the yanacocha deposit in which as3 pyrite was found formed under relatively oxidizing conditions in which the dominant form of dissolved as in the stability field of pyrite is as3 in contrast reducing conditions are typical of most environments that host as1 pyrite as3 pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments including high sulfidation epithermal deposits and shallow groundwater systems where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of as3 and toxic heavy metals in oxidizing natural systems

trace element contents and in situ sulfur isotope analyses of pyrite in the baiyun gold deposit ne china implication for the genesis of intrusion related gold deposits abstract trace elements distribution in minerals and formation mechanism of visible gold are poorly understood in intrusion related gold systems here we choose the baiyun gold deposit which is hosted within the paleoproterozoic metamorphic rocks in the liaodong peninsula ne north china craton ncc as a case study to address these issues the ore deposit geology characteristics and paragenesis are described in details in situ geochemical and sulfur isotopic compositions of pyrite and bulk pb isotopic ratios of pyrite were presented to define the genesis of pyrite that is closely associated with gold mineralization three generations of pyrite were recognized based on petrographic studies metamorphic pyrite py0 hydrothermal pyrite py1 coexisting with milky quartz and hydrothermal pyrite py2 coexisting with smoky quartz in situ laser ablation inductively coupled plasma mass spectrometer la icp ms spot analysis suggests that both py0 and py1 contain low contents of invisible gold mean 0 19 ppm and 0 17 ppm respectively however py1 is low in most other trace element contents and contains au ag cu pb bi micro inclusions in contrast py2 contains both invisible gold mean 0 50 ppm and au ag cu pb bi micro inclusions furthermore la icp ms mapping reveals the distributions of ag cu pb bi and te closely mimic that of au indicating an episode of ore forming fluid rich in au ag cu pb bi and te in situ sulfur isotope analysis of pyrite shows that py0 has significantly positive 34s values 11 74 17 33 suggesting that sulfur was derived from sedimentary sources py1 and py2 have negative 34s values 8 53 6 19 10 44 6 86 respectively indicating that sulfur was derived from oxidized magmatic fluids the magmatic fluids are concluded to be released from the early cretaceous microdiorite magmas providing most of the sulfur and ore forming metals proofs include the close spatial association of the ore bodies and the dykes as well the uniform pb isotopic ratios of py1 and the early cretaceous microdiorite lines of geological mineralogical geochemical and isotopic evidence consistently suggest that the gold mineralization in the baiyun deposit is intrusion related and was resulted from the 126 ma magmatic hydrothermal activities in the region visible gold precipitating in pyrite and fractures was from metal rich magmatic fluids rather than being remobilized from the metamorphic pyrite

evolution of a late mesozoic back arc fold and thrust belt northwestern great basin u s a abstract the luning fencemaker fold and thrust belt was active from the middle or late jurassic through the early cretaceous and involves rocks of the mesozoic marine province of the northwestern great basin rocks of the marine province were deposited in a back arc basin bound on the west by the sierran arc they are underlain by simatic crust formed either in a paleozoic marginal basin formed on the west coast of north america or in an exotic oceanic arc accreted to north america in the permo triassic deposition in the marine province was localized by the underlying simatic crust which later controlled the locus of back arc thrusting to the south in areas of the back arc region overlying continental crust mesozoic rocks are terrestrial volcanic and volcanogenic deposits rocks of this area are not disrupted by thrusts of significant magnitude until the southwestern end of the sevier thrust belt is encountered during contraction the luning fencemaker thrust belt underwent several hundred kilometers of nw se shortening which was not developed in the sierra nevada to the west the arc and back arc regions were separated by a regionally extensive left lateral fault system that was active during back arc thrusting the marine province was partially coupled with the sierra nevada during transpressional motion on the left lateral fault resulting in imbrication and emplacement of the luning fencemaker thrust belt in the continental region to the south decoupling was more complete and only minor thrusting was associated with the southerly displacement of the sierran arc farther south where the paleozoic miogeoclinal hingeline was encountered conditions apparently changed and the sevier thrust belt developed timing relations suggests that the andean type margin of the western united states had paired back arc thrust belts luning fencemaker and sevier for much of the late mesozoic the belts were separated by a region that underwent relatively minor internal shortening the intervening region probably was decoupled at depth and the thrust belts may have shared a decollement development of the luning fencemaker thrust belt and the associated left lateral fault system extended over a period of 40 50 m y and is best explained as a product of plate convergence the nw se shortening axis for the thrust belt and the inferred left slip on the strike slip fault are not compatible with the generally accepted right oblique subduction proposed for the sierran arc since the early triassic they suggest an interval of left oblique convergence for the middle to late jurassic and early cretaceous regionally developed structures indicate a return to right oblique convergence in the late early cretaceous

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

clay alteration and gold deposition in the genesis and blue star deposits eureka county nevada the genesis and blue star sedimentary rock hosted gold deposits occur within the 40 mile long carlin trend and are located in eureka county nevada the deposits are hosted within the devonian calcareous popovieh formation the siliciclastic rodeo creek unit and the siliciclastic vinini formation the host rocks have undergone contact metamorphism decalcification silicification argillization and supergene oxidation detailed characterization of the alteration patterns mineralogy modes of occurrence and associated geochemistry of clay minerals resulted in the following classifications least altered rocks found distal to the orebody consisting of both metamorphosed and unmetamorphosed host rock that has not been completely decalcified and altered rocks found proximal to the orebody that have been decalcified altered rocks are classified further into the following groups based on clay mineral content silicic 1 to 10 percent clay silicic argillic 10 to 35 percent clay and argillic 35 to 80 percent clay clay species identified are 1m illite 2m 1 illite kaolinite halloysite and dioctahedral smectite an early hydrothermal event resulted in the precipitation of euhedral kaolinite and at least one generation of silica this event occurred contemporaneously with decalcification which increased rock permeability and porosity a second clay alteration event resulted in the precipitation of hydrothermal 1m illite which replaced hydrothermal kaolinite and is associated with gold deposition silver and silica deposition is also associated with this phase of hydrothermal alteration hydrothermal alteration was followed by supergene alteration which resulted in the formation of supergene kaolinite halloysite and smectite as well as the oxidation of iron bearing minerals supergene clays are concentrated along faults dike margins and within rocks containing carbonate gold mineralization is not associated with supergene clay minerals within the genesis and blue star deposits rocks classified as silicic argillic in the popovich formation represent the most significant gold host silicic argillic rocks commonly exhibit bedding parallel alteration zones this pattern of alteration indicates that stratigraphy as well as northwest trending structures played a significant role in the migration of gold bearing fluids based on k ar age determinations of hydrothermal 1m illite associated with gold the main event of mineralization in the genesis and blue star deposits occurred between 93 and 100 ma during mid cretaceous time

processes influencing extreme as enrichment in shallow sea hydrothermal fluids of milos island greece abstract arsenic as is naturally enriched in most terrestrial and marine hydrothermal systems its discharge from shallow sea hydrothermal vents into coastal marine environments can dramatically affect the surrounding ecosystems shallow sea hydrothermal venting of acidic ph 5 hot 40 116 c and highly sulfidic up to 3 1 mm h2s fluids occurs at palaeochori and spathi bays off the southeast coast of milos island greece two distinct types of fluids both extremely as enriched were collected from the submarine vents often within a few meters of each other 1 a high cl fluid enriched in cl by up to 47 relative to seawater depleted in mg and so4 and enriched in major na ca k b sr and br and minor trace elements si li rb ce as fe mn and ba and 2 a low cl fluid depleted in cl by up to 66 relative to seawater also depleted in na mg so4 and br the maximum concentration of as reached 39 m in the high cl fluids and up to 78 m in the low cl fluids this is approximately 3000 times the concentration of as in seawater and far exceeds the concentrations typically found in mid ocean ridge mor and back arc basin bab fluids which are typically we used a combination of elemental analyses and stable and radiogenic isotope data oxygen deuterium and strontium to understand the primary controls on as enrichment those parameters all indicated that the fluids were a mixture of seawater and a hydrothermal fluid originally derived from seawater but altered by water rock interaction subcritical phase separation boiling and vapor brine segregation since as was extremely enriched in both the high cl and the low cl thermal fluids we conclude that this element readily partitions into the vapor phase in the milos hydrothermal system the original source of as is most likely the leaching of the greenschist facies metamorphic basement rocks transpierced by an abundance of secondary quartz and calcite veins rich in pyrite it is possible that these veins were deposited from as rich magmatic fluids similar to some epithermal au deposits a poorly crystalline orpiment precipitates as hydrothermal fluids mix with overlying seawater and removes much of the dissolved as prior to discharge

an xps study on the valence states of arsenic in arsenian pyrite implications for au deposition mechanism of the yang shan carlin type gold deposit western qinling belt abstract the enrichment of gold in arsenian pyrite is usually associated closely with the enrichment of arsenic in the mineral generally known as as1 pyrite fe as s 2 direct analyses of the valence state of au in pyrite are however difficult due to generally low ppm level au concentrations by means of x ray photoelectron spectroscopy xps this study obtained reliable valence states of as in pyrite from the yang shan gold deposit a giant carlin type au deposit in the western qinling orogen central china the arsenian pyrite specimens were sputtered with ar beam in the vacuum chamber of an xps to obtain pristine surfaces and to avoid as oxidation during sample preparation analyses before and after sputtering show that the as3 peak are only present on surface that was once exposed to the air in contrast the peak of as 1 was essentially unchanged during continuous sputtering the results indicated that as is the predominant state on the pristine surface of arsenian pyrite the peak of as3 previously reported for au bearing arsenian pyrite was probably due to oxidation when exposed to air during sample preparation it is unlikely that the coupled substitution of au as3 for 2fe2 takes place in the pyrite lattice the so called as3 pyrite proposed by previous studies may occur in some special oxidizing geologic settings but it is not observed in the yang shan gold deposit and is unlikely to be important in typical orogenic or carlin type gold deposits in which arsenian pyrite is a dominant au carrier combining previous studies on carlin type au deposits with our xps experimental results we suggest that the most likely state of au in the yang shan au deposit is lattice bounded au with or without nanoparticles au0

dating gold deposition in a carlin type gold deposit using rb sr methods on the mineral galkhaite significant effort has been expended in an attempt to date hydrothermal activity that generated carlin type gold deposits ctds in the great basin of nevada thus far these efforts have been only partially successful because the relationship s between the dated mineral and hydrothermal activity are equivocal in many cases galkhaite a trace component of at least four ctds in nevada contains significant amounts of rb and virtually no sr making it an ideal candidate for radiometric dating at the getchell deposit galkhaite is paragenetically late but clearly associated with gold mineralization our data place gold mineralization at getchell at 39 0 2 1 ma this is the first unequivocally gold related date produced for any of the carlin type systems galkhaite also has been reported at the carlin rodeo and betze deposits and is likely present in other ctds in nevada this mineral may provide a solution to the conundrum of dating of ctds

a 2d and 3d nanostructural study of naturally deformed pyrite assessing the links between trace element mobility and defect structures the links between deformation induced micro and nanostructures and trace element mobility in sulphide minerals have recently become a popular subject of research in the earth sciences due to its connections with metallic ore paragenesis it has been shown that plastic deformation in pyrite creates diffusion pathways in the form of low angle grain boundaries that act as traps for base and precious metals however the plastic behavior of pyrite and the physiochemical processes that concentrate these trace elements in deformation induced micro and nanostructures remain poorly understood in this study we develop strategies for 2d and 3d analysis of naturally deformed sulphides by combining electron backscatter diffraction electron channeling contrast imaging and atom probe tomography on pyrite in an attempt to better understand the underlying diffusion processes that mobilize trace elements the combined results reveal structures associated with crystal plastic deformation in the form of dislocations stacking faults and low angle grain boundaries that are decorated by as and co although our data support a dislocation impurity pair diffusion model we have evidence that multiple diffusion mechanisms may have acted simultaneously in this study we applied new data processing techniques that allow for orientation measurement of nanostructural crystal defects from atom probe tomography data dislocations within our studied sample occur along the 110 planes suggesting glide on 110

dike hosted ores of the beast deposit and the importance of eocene magmatism in gold mineralization of the carlin trend nevada a reply we appreciate the comments of g d langstaff and the opportunity to elaborate on the origin of carlin type gold deposits langstaff focuses on two of the critical issues regarding these deposits their age and spatial association with igneous rocks although his comment mentions almost every known carlin type deposit our reply focuses on deposits in major districts direct dating of hydrothermal minerals and indirect dating based on crosscutting relations with pre syn or postmineral rocks in nevada have demonstrated that major deposits in all trends are eocene emsbo et al 1996 leonardson and rahn 1996 phinisey et al 1996 groff et al 1997 hall et al 1997 2000 hofstra et al 1999 hofstra and cline 2000 johnston 2000 ressel et al 2000a b tretbar et al 2000 although many carlin type deposits are not dated we emphasize that no deposit has been demonstrated to be any other age preliminary 40ar 39ar dating of white micas from mineralized eocene dikes at meikle and griffin in the carlin trend gives eocene ages ressel et al 2000b any discussion of the origin especially spatial association of carlin type deposits with igneous rocks must emphasize the northern and central carlin trend fig 1 deposits there constitute 60 percent of the total estimated contained gold in carlin type deposits of nevada and utah hofstra and cline 2000 we interpreted the 700 km2 aeromagnetic anomaly fig 1 there to reflect an underlying composite eocene intrusion emplaced between about 40

the tuscarora au ag district eocene volcanic hosted epithermal deposits in the carlin gold region nevada the tuscarora mining district contains the oldest and the only productive eocene epithermal deposits in nevada the district is a particularly clear example of association of low sulfidation deposits with igneous activity and structure and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low sulfidation deposits moreover tuscarora deposits are of interest because they formed contemporaneously with nearby giant carlin type gold deposits the tuscarora deposits formed within the 39 9 to 39 3 ma tuscarora volcanic field along and just outside the southeastern margin of the caldera like mount blitzen volcanic center both deposit types formed at 39 3 ma contemporaneous with the only major intrusive activity in the volcanic field no deposits are known to have formed during any of the intense volcanic phases of the field intrusions were the apparent heat source and structures related to the mount blitzen center were conduits for hydrothermal circulation the ore forming fluids interacted dominantly with eocene igneous rocks the two deposit types occur in a northern silver rich zone that is characterized by relatively high ag au ratios 110 150 narrow alteration zones and quartz and carbonate veins developed mostly in intrusive dacite and in a southern gold rich zone that is typified by relatively low ag au ratios 4 14 more widespread alteration and quartz fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks the deposit types have similar fluid inclusion and pb and s isotope characteristics but different geochemical signatures quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260 and 230 c to less than 200 c fluid boiling may have contributed to precious metal deposition veins in both zones have relatively high as and sb and low bi te and w the silver zone has high ca pb mn zn cd tl and se the gold zone has high hg and mo a few samples from an area of overlap between the two zones share chemical characteristics of both deposit types the deposit types could represent a single zoned or evolving system in which hydrothermal fluids rose along structures within the silver zone preferentially deposited ag and base metals and then spread into the gold zone alternatively the deposit types could represent two distinct but temporally indistinguishable hydrothermal cells that only narrowly overlapped spatially as noted in previous studies the hydrothermal fluids that generated the tuscarora and other epithermal deposits could have evolved from carlin type fluids by boiling and mixing with meteoric water if so the tuscarora deposit may represent epithermal conditions above carlin type deposits and carlin type deposits may lie beneath the district

uncloaking invisible gold use of nanosims to evaluate gold trace elements and sulfur isotopes in pyrite from carlin type gold deposits one hundred nm resolution secondary ionizing mass spectrometry nanosims was used to determine the distribution of au cu as sb and s and stable isotopes of s 34s 32s in gold bearing pyrite from two refractory carlin type gold deposits west banshee northern carlin trend and turquoise ridge getchell trend located in northern nevada nanosims maps reveal that gold occurs in two discrete episodes in each deposit elevated gold concentrations correlate with elevated concentrations of as sb cu te and lower 34s 32s ratios compared to periods when gold was not deposited precipitation of elevated gold and trace elements at west banshee was followed by precipitation of pyrite with lower gold concentrations whereas at turquoise ridge precipitation of trace element rich pyrite was followed by precipitation of late ore stage minerals these nanosims results are consistent with formation of the deposits by the episodic incursion of gold rich fluids into hydrothermal systems otherwise dominated by gold poor fluids such gold rich fluid pulses may be related to incursions of magmatic fluid which have been shown to have high concentrations of gold arsenic and copper in porphyry and high sulfidation epithermal systems

silver rich sulfide mineralization in the northwestern termination of the western cycladic detachment system at agios ioannis kynigos hymittos mt attica greece a mineralogical geochemical and stable isotope study abstract identification of silver rich sulfide mineralization in the abandoned mines at northern hymittos mt central attica greece district has made this region important due to its structural relation to the world class lavrion mining district 25 km se of hymittos mt at agios ioannis kynigos mine veins of oxidized fe pb zn ag ore are hosted in mylonitic marbles that were predominantly affected by brittle ductile deformation associated with the west cycladic detachment system the major sulfides are galena and arsenian pyrite which develop as open space filling fractures and vugs disseminations and veinlets galena contains abundant inclusions of pb as sb cu ag sulfosalts tetrahedrite group minerals bournonite jalpaite an unusual silver rich galena ore i e from 192 to 1500 ppm ag is recorded from the present study with ag hosted mainly in ag tetrahedrite acanthite and jalpaite compositionally pyrite shows as enrichment and the highest as concentration i e up to 3 9 wt is found in the core of the oscillatory zoned pyrites values of 34s of galena are isotopically light 11 2 to 12 2 which suggests a sedimentary component to the ore fluid that is likely derived from leaching of the meta sedimentary calc mica schists wall rocks carbon and oxygen isotope compositions of ore stage carbonates show values i e 13cv pdb 8 2 to 11 7 and 18o 24 3 to 25 9 and for the non mineralized carbonates 13cv pdb 0 33 to 2 52 and 18o 20 8 to 26 1 the c and o isotopic composition of the carbonate wall rock distal to the orebody is typical of marine carbonates whereas hydrothermal carbonates brown calcite and dolomite are dominated by an external light c source the lowest 13cv pdb values are recorded from cerussite and correspond to the low temperature supergene alteration from meteoric waters the homogenized values of 18o in the mineralized carbonates indicate interaction of fluid with host carbonates under a low fluid rock ratio the pb zn ag mineralization at agios ioannis kynigos bears many similarities with the low temperature carbonate replacement style mineralization in kamariza lavrion area ore deposition in the northern hymittos detachment fault is focused in the structurally upper parts of the detachment fault where circulation of meteoric fluids is dominant in the hydrothermal system

source of iron for sulfidation and gold deposition twin creeks carlin type deposit nevada this study was undertaken to determine the source of iron in comus formation sedimentary rocks that were sulfidized during deposition of gold in the megapit area of the twin creeks carlin type deposit sedimentary rocks in and near the megapit contain ferroan dolomite largely as overgrowths on iron poor dolomite iron to form these overgrowths appears to have been released from mafic volcanic rocks that are interlayered with the sedimentary rocks these igneous rocks have undergone two stages of hydrothermal alteration the first stage involved formation of albite and iron rich chlorite possibly caused by interaction with seawater the second stage involved destruction of the iron rich chlorite by illite or sericite which released iron to form ferroan dolomite in the sedimentary rocks comparisons show that transfer of iron from the igneous rocks to the sedimentary rocks can account for the present distributions of iron in these rocks relative to basalts comus formation igneous rocks are enriched in iron and potassium these results suggest that ferroan dolomite in sedimentary rocks is not solely a product of diagenetic processes and can form when iron is released from adjacent iron bearing igneous rocks recognition of this additional mechanism for formation of ferroan dolomite expands the range of geologic settings that can be favorable for formation of gold deposits formed by sulfidation

data for distinguishing generations of quartz and a distinct gas signature of deep high grade carlin type gold mineralization using quadrupole mass spectrometry abstract carlin type gold deposits in north central nevada occur in a region that was the locus of igneous and or hydrothermal activity over time and the overprinting of silicification associated with metamorphism base metal mineralization barren jasperoid and post ore alteration hinders exploration efforts therefore the potential to distinguish unrelated generations of quartz using the results of quadrupole mass spectrometer qms gas analyses was evaluated for the getchell trend and compared to results from the goldstrike property in the carlin trend and a carlin type gold occurrence in the huijiabao trend china the results of fluid inclusion petrography qms analyses and interpretation of gas data using n 2 ar he ternary diagrams and co 2 ch 4 vs n 2 ar plots indicate that different generations of quartz in the getchell trend were deposited by hydrothermal fluids having distinct characteristics metamorphic quartz containing one phase ch 4 and halite bearing liquid water dominant vapor poor inclusions has the highest gas content 37 6 mol and highest n 2 ar values 3250 which are suggestive of an evolved magmatic fluid pre ore and quartz base metal veins contain co 2 bearing inclusions base metal veins have n 2 ar values 675 and a positive correlation between h 2 s ar vs n 2 ar that is suggestive of a magmatic fluid carlin type quartz contains liquid dominant vapor poor inclusions and is characterized by total gas contents 10 mol and n 2 ar values 300 that are suggestive of mixed crustal meteoric magmatic fluid sources post ore quartz and barren jasperoid formed from mixtures of gas poor meteoric water and crustal fluids samples of deep high grade mineralization from the goldstrike property have total gas contents up to 10 5 mol and n 2 ar values 300 fluid sources include crustal meteoric and magmatic gas data from the goldstrike property turquoise ridge deposit and metamorphic quartz of the getchell trend plot near the n 2 apex of n 2 ar he diagrams which is indicative of a magmatic fluid end member carlin type mineralization in the huijiabao trend is unique because fluids were ch 4 rich and there is a correlation between ch 4 and hydrocarbons gas analyses commonly record 2 is the dominant gas specie together the results show that fluid inclusion gases can be used to distinguish different generations of quartz in mining districts with complex origins

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

geochronological constraints on the baguamiao gold deposit west qinling orogen central china implications for ore genesis and geodynamic setting abstract the baguamiao gold deposit located in the fengxian taibai ore district is one of the largest gold deposits in the west qinling orogen central china the poor age constraints on the gold mineralization event at the baguamiao has caused strong debate on ore genesis and associated geodynamic controls we carried out sm nd and 40ar 39ar geochronological studies to determine more precise age constraints on the god deposition the gold mineralization at baguamiao deposit was developed during four hydrothermal stages that formed sequentially i nw trending ankerite quartz veins ii deformed and folded nw trending sulfide ankerite quartz veins iii joint hosted ne trending sulfide ankerite quartz veinlets and iv nw and ne trending quartz fissure veins stages ii and iii define the main gold mineralization the sm nd dating of dolomite ankerite and calcite yielded isochron ages of 209 3 4 2 ma mswd 1 80 and 208 1 3 1 ma mswd 0 50 for gold mineralization of stages and iii respectively the 40ar 39ar dating of muscovite intergrown with sulfides of stage yielded a plateau age of 209 5 1 4 ma mswd 0 30 the age data obtained from the two geochronological methods are consistent with each other within uncertainties indicating clearly the baguamiao gold deposit formed at ca 209 ma integrating deposit geology from this and previous studies geochronological data and regional tectonics we classify baguamiao as an orogenic gold deposit which was resulted from a number of fluid pulses but during a single ore forming episode in late norian rhaetian time of the late triassic the ore forming fluids and metals are suggested to have been derived from both metamorphic and magmatic processes in a post collisional regime of the west qinling orogen

timing of gold and arsenic sulfide mineral deposition at the getchell carlin type gold deposit north central nevada pregold mineralization at the getchell carlin type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a cretaceous granodiorite stock the veins contain minor pyrite and trace chalcopyrite arsenopyrite galena and sphalerite the pyrite is moderately coarse and in thin section has high relief is well polished and is fractured and locally cemented by the gold ore assemblage white micas are associated with veins near the granodiorite intrusion gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites microprobe analyses show that pregold pyrites have near stoichiometric compositions variable low arsenic is present in pyrite in samples overprinted by gold mineralization secondary ion mass spectrometry sims analyses detected trace gold in the coarse near stoichiometric pyrite in overprinted samples the pregold vein assemblage was fractured and cemented by gold ore stage mineralization the gold ore stage assemblage consists of gold and arsenic enriched pyrite and marcasite encompassed by jasperoid and drusy quartz and local late fluorite orpiment and galkhaite the consistent spatial association of jasperoid and ore pyrite reflects their near contemporaneous formation the ore pyrite occurs as either fine irregularly shaped grains or rims on earlier gold free pyrite in thin section the pyrite is visibly distinct and has a low polishing relief and a poor polish sims and electron microprobe analyses show that ore pyrites commonly contain 8 to 11 wt percent arsenic and as much as 2 400 ppm gold near the end of the ore stage fluorite orpiment and galkhaite precipitated locally in open space created by faulting or limestone dissolution late ore stage mineralization consists dominantly of open space filling realgar and calcite with minor quartz stibnite and framboidal pyrite realgar conforms to euhedral crystal faces of ore stage quartz fluorite and galkhaite calcite filled most remaining open space and conforms to euhedral crystal faces of quartz fluorite and realgar significant textural observations argue against an earlier interpretation that the gold mineralization and arsenic minerals formed as two discrete events separated by 40 m y in a few areas where calcite and realgar are in contact with ore stage quartz containing gold bearing pyrite realgar and calcite enclose gold bearing pyrite grains massive realgar and calcite distal from these contacts do not contain the gold bearing pyrite the presence of ore pyrite in realgar calcite and jasperoid requires close timing of these minerals and shows that there is no major time break separating ore stage and late ore stage mineral deposition textures indicate instead that the ore stage and late ore stage formed as part of a single evolving hydrothermal system the consistent successive overgrowth of younger minerals on perfectly preserved euhedral faces of older minerals supports the continuous evolution of the gold ore stage into the late ore stage these results are consistent with fluid inclusions that indicate that paragenetically successive minerals precipitated from an aqueous ore fluid with consistent salinity and gas contents but at declining temperatures results show that within error the 34 39 and 42 ma ages determined for fluorite and galkhaite at getchell and adularia at the nearby twin creeks mine respectively most closely approximate the timing of gold deposition at getchell

40 ar 39 ar k ar and fission track geochronology of sediment hosted disseminated gold deposits at post betze carlin trend northeastern nevada the post betze deposit of nevada is the largest sediment hosted disseminated gold deposit presently known both dimensionally and in terms of contained metal ore occurs primarily as submicron sized gold that is disseminated in altered sedimentary rocks of the lower paleozoic roberts mountains formation however significant portions of the ore are present in altered monzonite of the goldstrike stock alteration and mineralization were controlled by both structure and stratigraphy alteration began with early decarbonatization and was followed by silicification and finally argillization phyllosilicate mineral zoning grades from proximal kaolinitc to kaolinitc sericite to unaltered rock based on geochronologic studies utilizing the k ar 40 ar 39 ar and fission track techniques we suggest that the age of gold mineralization is approximately 117 ma the premineralization goldstrike stock was emplaced at about 158 ma and a postmineralization sill was emplaced at 39 ma these events place clear limits on the age of mineralization fine grained sericite that is interpreted to have formed during hydrothermal events which also generated gold ore was dated by either the k ar method or a modification of the standard 40 ar 39 ar fusion technique age determinations on several samples of fine grained sericite from altered host rocks both sedimentary and igneous yield ages near 117 ma younger dates are interpreted to be the result of either thermal disturbance of the k ar system or mixing of sericites of two ages one sample of coarser grained sericite that was stepheated gave discordant spectra fission track analyses of zircon and apatite from the postore sill clearly document the lack of significant thermal or hydrothermal activity younger than 39 ma although less definitive fission track data on zircon from preore sedimentary and igneous hosts suggest that no widespread hydrothermal activity having temperatures above about 100 degrees c has occurred since approximately 110 ma the 117 ma age is consistent with one of the major magmatic pulses recognized in the northern great basin it is also similar to within analytic uncertainty a k ar date of 109 ma from the welches canyon stock 20 km south of post betze an intrusion of similar age unexposed at present could have been the driving force for the hydrothermal system at post betze published geochronologic data though less well tied to mineralization suggest similar mid cretaceous ages for other sediment hosted disseminated gold deposits in nevada based on these ages we suggest that sediment hosted disseminated gold deposits are not necessarily products of extensional environments and in fact appear to be associated with compressional environments in nevada during cretaceous time the alignment of sediment hosted disseminated gold deposits and other features in the basin and range province of the western united states suggests that zones of long term crustal weakness may have controlled igneous intrusion and consequent hydrothermal gold mineralization although not all igneous episodes necessarily generated sediment hosted disseminated gold ore deposits the strong association between sediment hosted disseminated gold deposits the precambrian craton and these deep seated structures also suggests the possibility of a deep source for gold and other components of these systems

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

as sb bi au mineralization in the baogutu gold deposit xinjiang nw china here we report the occurrence of some uncommon mineral assemblages including paakonenite aurostibite native arsenic native antimony and native bismuth found in the baogutu gold deposit in the western junggar xinjiang nw china the mineralization could be generally subdivided into two types the gold bearing quartz vein type mineralization and disseminated mineralization in the wall rocks the sulfide minerals in gold lodes commonly include pyrite arsenopyrite marcasite and stibnite however the l7 lode in no 4 orebody and the l1 lode in no 11 orebody of the baogutu gold deposit are quite different in terms of their mineral assemblages the l7 lode contains native arsenic quartz veins in shallow levels and stibnite quartz veins at depth gold bearing minerals electrum native gold and rarely aurostibite mainly coexist with paakonenite stibnite native arsenic and native antimony the crystallization of as and sb bearing minerals was likely to have consumed h2s from the hydrothermal fluid which probably triggered the precipitation of native gold the l1 lode consists of several discontinuous sulfide dominated lensoid orebodies the massive sulfide ores that produced most of the gold resource are characterized by an intimate association between native bismuth and native gold mineralization

evaluation of radioisotope dating of carlin type deposits in the great basin western north america and implications for deposit genesis a variety of techniques have been used in attempts to date the mineralization in carlin type deposits in the great basin with highly variable results these techniques and results are reviewed in this paper along with presentation of two new dates for the rodeo deposit on the carlin trend and for the barneys canyon deposit in utah complete resetting of sericite by hydrothermal fluids of the temperature and duration of hydrothermal activity that form carlin type deposits is considered highly unlikely therefore dates from sericite are generally of questionable value unless that sericite can be shown to have formed during the same hydrothermal event during which au was deposited for the deposits that have been investigated to date sericite dates rarely if ever record the age of au mineralization however sericite ages do appear to record pre au events in some districts such events may have contributed to ground preparation and to a much lesser extent to the tenor of the ore fission track and u th he techniques provide important age constraints on mineralization in some districts but also suffer from a less than clear association with au rb sr dating of galkhaite an hg sulfosalt provides the only direct age of mineralization but galkhaite has been recognized in only a few locations and dated in only two deposits in a similar manner adularia is contemporaneous with au at twin creeks but twin creeks is the only carlin type deposit where adularia has been reported several other techniques u pb reos sm nd have been used in attempts to date the deposits but with limited success the best available ages are those from preore and postore igneous events and those from galkhaite galkhaite from getchell indicates a mineralization age of 39 ma and that from rodeo carlin trend indicates a mineralization age of 40 ma a new u th he age 34 ma for apatite at barneys canyon suggests contemporaneity with the nearby bingham porphyry cu system the most reliable data from several deposits and districts in the great basin indicate that carlin type mineralization occurred in a relatively narrow time interval between 33 and 42 ma this interval coincides with the transition from a compressional to an extensional tectonic environment in the region although similar tectonic environments have existed at different times and places in western north america no other carlin type mineralization is known to exist in the region therefore although the age and tectonic environment of these deposits is now reasonably well constrained it is clear that tectonic environment alone is insufficient to explain the genesis of carlin type deposits additional perhaps unique factors such as host rock geochemistry must have contributed to the development of these exceptional deposits

mineralogical study of sediment hosted gold deposits in the yangshan ore field western qinling orogen central china abstract the yangshan gold ore field is located in the southern subzone of the western qinling orogen mineralization is confined by the east west striking anchanghe thrust fault zone these subparallel faults constitute a branch of the regional mianlue structural zone crosscutting middle devonian carbonaceous carbonate and clastic rock sequences an ore bearing unit locally named the sanhekou formation the metasedimentary clastic and carbonate rocks containing fine grained sulfides are the main host rocks of the deposit with minor mineralization occurring as coarse grained pyrite quartz veinlets in black shale and as dissemination in some plagiogranite dykes electron microprobe empa and laser ablation inductively coupled plasma mass spectrometry la icp ms analyses show that arsenian pyrite and arsenopyrite are the major hosts for gold with tens of ppm up to weight percent levels of au and the au contents in arsenopyrite are one order of magnitude higher than those in pyrite a negative correlation of as and s in arsenian pyrite is consistent with the substitution of as for s in the mineral both arsenian pyrite and arsenopyrite in the yangshan ore field show chemical zonations with middle parts mantle enriched in as and au relative to cores and the outermost rims reflecting the chemical evolution of ore forming fluids high resolution transmission electron microscopy hrtem analysis failed to identify any nanoparticle of native gold even in the highest au parts of arsenopyrite this observation combined with the relatively homogenous distribution of au a positive correlation of as and au and au as ratios below the solubility limit of gold in arsenian pyrite and arsenopyrite suggests that invisible gold is likely present as structurally bound au 1 in sulfides although our work cannot exclude the existence of au nanoparticles in arsenian pyrite as identified in american carlin type gold deposits submicron native gold may be much more easily found in arsenian pyrite than in arsenopyrite because the later has larger capacity of enrichment of au 1 than the former due to the substitution of as for s the mechanism for nanoparticle formation is likely exsolution of native gold from metastable arsenian pyrite caused by later hydrothermal event which was recorded by the outermost as au poor overgrowths both in arsenian pyrite and arsenopyrite in the yangshan gold ore field

ore fluid properties and sources from quartz associated gold at the betze post carlin type gold deposit nevada united states quartz at the betze post deposit the largest carlin type gold system in the world was examined to better understand ore fluid properties and sources that generated carlin type gold deposits detailed petrography and paragenesis investigations distinguished textural relationships luminescence various generations of quartz and fluid inclusion populations microthermometry chemical analyses of quartz and in situ and conventional oxygen isotope analyses of quartz provided information about hydrothermal fluid conditions as well as fluid sources and ore formation processes pre syn late and post ore stages of quartz were distinguished during petrographic studies and confirmed by cathodoluminescence analyses ore stage jasperoid and late ore drusy quartz are spatially associated with au bearing pyrite both lack luminescence two generations of post ore drusy quartz overgrew ore and late ore quartz and exhibit bright and multiply zoned luminescence electron probe microanalyses determined that nonluminescing ore and late ore quartz have elevated concentrations of al in contrast to post ore luminescent quartz that contains low trace element concentrations fluid inclusion microthermometry determined that ore stage fluids had low salinities generally 5 wt nacl equiv and were trapped at 180 to 240 c the 18o values calculated for inclusion fluids and determined for quartz using in situ ion probe and conventional analyses indicate that the isotopic composition of hydrothermal fluids became 18o depleted with time from the ore stage through the late ore stage to the post ore stage the 18o composition of each stage of quartz also varies spatially across the betze post deposit and 18ovsmow values of ore late ore and post ore stage quartz became more depleted with increasing distance from the master post fault these patterns are interpreted to result from increasing dilution of the 18o enriched ore fluid by unevolved meteoric fluids over time and with increased ore fluid transport distance to the west away from the post fault the master fault that transmitted hydrothermal fluids to the deposit oxygen isotope results are consistent with a low fluid rock ratio during upward transport of the ore fluid via the post fault below the deposit some ore fluids were diverted into the jb series faults associated with the betze ore zones and the shalosky fault associated with the screamer ore zone in the western part of the deposit ore fluids were increasingly diluted by meteoric fluids with distance as ore fluids traveled away from the post fault and over time as different stages of quartz precipitated acidic 180 to 240 c ore fluids accessed the level of the deposits where they reacted with the devonian popovich formation and precipitated nonluminescing al enriched ore stage jasperoid and late ore drusy quartz along with au and trace element rich pyrite fluid rock reaction dissolution and replacement of silty carbonate host rocks may have produced al that substituted for si in non luminescing jasperoid and late ore stage quartz as the hydrothermal ore system began to cool and collapse late ore drusy quartz and realgar precipitated in open space as ore stage pyrite precipitation declined the hydrothermal system collapsed with meteoric water flooding post ore minerals including luminescent al poor post ore drusy quartz and later calcite and barite precipitated either from latest carlin related fluids neutralized by infiltration of meteoric waters or as part of a later separate hydrothermal event

geology and geochemistry of the deep star gold deposit carlin trend nevada deep star is a high grade carlin type gold deposit located in the northern part of the carlin trend the deposit averages 34 0 g t au and by year end 2000 had produced 37 8 t 1 217 000 oz gold with a remaining reserve of 16 0 t 513 698 oz gold the deposit is primarily hosted in brecciated calc silicate rocks of the devonian popovich formation with a minor amount of gold in the jurassic goldstrike diorite intrusion of the syn and postore deep star rhyolite constrains the age of the mineralization the postore rhyolite is compositionally and mineralogically similar to the synore dike and yielded an average 40ar 39ar isochron age of 38 3 ma eocene rhyolite dikes intruded active dilatant north to northeast striking faults and or fractures providing an important age constraint on the local stress regime at deep star during mineralization essentially horizontal west northwest directed eocene extension 291 is consistent with dextral normal oblique slip observed on north south striking east dipping portions of the gen post fault system and dilation and sinistral shear on dike filled northeast striking structures a right stepping releasing bend in the deep star fault at its intersection with northwest and north northwest striking subsidiary structures created a deep tapping dilatant conduit for gold bearing hydrothermal fluids five stages of hydrothermal alteration are present at deep star stages 1 and 2 are related to thermal metamorphism metasomatism and possibly retrograde alteration associated with intrusion of the goldstrike stock stage 3 consists of preore quartz carbonate alteration the carbonate minerals are zoned both laterally and vertically with dolomite as the dominant mineral closest to ore stage 3 overlaps with stage 4 quartz kaolinite alteration associated with the introduction of gold and is therefore interpreted to be part of the eocene mineralizing event gold is hosted in as rich rims on marcasite and pyrite within a kaolinite and quartz matrix postore stage 5 is dominated by calcite with lesser siderite and barite a three dimensional geochemical model of the deep star deposit and its environs reveals that carlin type systems may have a geochemical expression involving a much broader suite of elements than previously recognized elements with distribution patterns considered to be related to the mineralizing event include ag as au ba bi ca cd co cu fe hg mg mo mn ni p pb s sb se te tl u v w and zn the multielement anomaly associated with the deep star deposit is best described as a vertical plume that is 1 focused between the deep star and post faults below the deposit 2 present in the footwall of the deep star fault and the deep star post fault corridor at the level of the deposit and 3 broadly dispersed above and to the west of the deposit under the influence of northeast and northwest trending structural fabrics most closely associated with gold deposition are enrichments in as sb hg tl ag and zn within a halo of ca mg ba and sr depletion the elements fe mn co ni and p are most elevated in the immediate hanging wall of the deep star fault and above the deposit in a region where secondary carbonate veins ankerite kutnahorite and mn rich dolomite open space filling carbonate minerals siderite calcite have been observed some lateral zonation is evident at levels above the deposit with increases of pb and bi on its eastern margin and more mo u v and w west of the deposit isotopic analyses of kaolinite are interpreted to indicate that gold mineralizing fluids originated from either a magmatic or possibly a deep metamorphic source fluids range from near the magmatic water field for those near the center of the deep star orebody along a mixing path toward exchanged mid tertiary meteoric water as represented by the fluids near the eastern orebody margin

40 ar 39 ar dating and mineral paragenesis for carlin type gold deposits along the getchell trend nevada evidence for cretaceous and tertiary gold mineralization the orebodies at the getchell and twin creeks mines were studied through mineral paragenesis geologic relationships and 40 ar 39 ar dating mineral paragenetic relationships are based on observations made during the logging of 18 000 m of drill cuttings and core and crosscutting relationships recognized in the field and main pit at the getchell mine ages for igneous and mineralizing events were determined through 40 ar 39 ar incremental heating analyses of 15 samples of biotite k feldspar sericite and vein adularia a thermal history for the area was also developed using k feldspar multiple diffusion domain results and age determinations on cogenetic minerals which have different argon closure temperatures mineral paragenetic relationships and 40 ar 39 ar dating at the getchell and twin creeks deposits document that gold mineralization occurred in five stages between 95 and 42 ma stage 1 pyrrhotite quartz arsenopyrite chalcopyrite biotite gold mineralization in skarn is associated with 95 ma dacite dikes and granodiorite plugs stage 2 chalcopyrite sphalerite galena pyrite arsenopyrite or gold and silver mineralization in skarn is related to the 92 ma osgood mountains stock secondary k feldspar and sericite in stage 3 quartz pyrite kaolinite gold mineralization formed at 83 ma and are not related to 95 or 92 ma igneous activity stage 4 low grade quartz pyrite gold mineralization formed at about 75 ma in the matrix of a breccia pipe that cuts 83 ma silicic and argillic ores adularia intergrown with stibnite orpiment pyrite quartz gold or realgar mineralization yields precise 40 ar 39 ar plateau ages of 42 11 or 0 43 and 41 90 or 0 25 ma for stage 5 this study documents the temporal complexity of mineralization and igneous activity at the getchell and twin creeks deposits minor gold in skarn type mineralization stages 1 and 2 associated with 95 and 92 ma igneous intrusions preceded and was not genetically related to carlin type gold mineralization stages 3 and 5 the carlin type deposits at getchell and twin creeks therefore represent a composite orebody formed by the overprinting of 83 ma stage 3 quartz pyrite gold by 42 ma stage 5 orpiment stibnite pyrite gold mineralization

fluid mixing during late stage carlin type mineralization in the getchell and twin creeks deposits nevada abstract a stable isotope study of orpiment realgar calcite stibnite mineralization in the getchell and twin creeks deposits nevada was undertaken to determine the origin s of late stage fluids samples of orpiment have d values of 48 4 to 90 5 and 34s values of 0 3 2 2 which are indicative of a magmatic source whereas samples of realgar have d values of 129 1 to 139 7 that are indicative of meteoric water and 34s values of 4 2 4 9 similar to pre ore diagenetic pyrite the d and 13c data of calcite plot to form a mixing trend between fluids with magmatic and meteoric sources fluid mixing and wall rock interaction is supported by the distribution of data in a d and 18oh2o plot for calcite additional evidence of fluid mixing is provided by d values of 55 4 to 137 9 for stibnite these data document how a magmatic fluid produced orpiment au mineralization fluid mixing occurred during calcite deposition and barren realgar formed from a meteoric water