pb isotope fingerprinting of mesothermal gold deposits from central victoria australia implications for ore genesis new pb isotope data from three major mesothermal lode gold deposits ballarat west tarnagulla maldon in central victoria support a model whereby the metals derived from a large reservoir with a long residence time in the crust below the palaeozoic lachlan fold belt the pb isotopic ratios of least radiogenic samples from these deposits are in close agreement with published pb signatures for turbidite hosted gold deposits and for devonian granites elsewhere in the lachlan fold belt despite their spatial distribution and variations in the geological setting the pb signatures point to the extraction and transport of metals from a crustal source area by long lasting large scale hydrothermal systems resulting in the prominent homogenisation of pb isotopic ratios the enduring interaction between large hydrothermal systems and an extensive crustal source reservoir were a vital pre requisite in the formation of the victorian gold province in this regard the prospectivity of victoria is analogous to world class ore provinces elsewhere such as the archaean yilgarn block in western australia

criteria for determining initial lead isotopic compositions of pyrite in archaean lode gold deposits a case study at victory kambalda western australia abstract the initial pb isotopic compositions of ore associated sulphides are important in isotopic tracer studies studies of archaean lode gold deposits from western australia indicate that the pb isotopic data distribution for ore associated galenas and pyrites is commonly linear and determination of the initial pb ratio relies on selecting the least radiogenic composition this detailed pb isotopic study of sulphides from the 32 ore zone which transects a variety of rocks in the victory mine mineralisation dated at 2627 ma has resolved the origin of the pb isotopic heterogeneities which yield linear arrays it has led to the development of criteria for sample selection which more efficiently and effectively target pyrite samples which best preserve the initial pb ratio of the sulphide and hence the ore fluid the most important controls on the displacement of the measured pb ratio of pyrite from the initial pb ratio are in order of importance 1 pb content of pyrite 2 pyrite abundance 3 proximity of pyrite to ore fluid channelway i e vein and 4 host rock the host rock is important because the th u and pb contents and presence of minor u th bearing phases influence the amount and nature of any post formation pb represented in the pyrite data the first three parameters control the magnitude of that influence a high pb content high pyrite abundance and setting in a vein or at a vein margin produce a pb isotopic composition which is more likely to be dominated or buffered by fluid pb i e more accurately reflects the initial pb isotopic ratio conversely pyrite with a low pb content low abundance and siting distal from veining is likely to be more susceptible to post formation modification by contributions from the host rock resulting in a more radiogenic pb isotopic composition

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

zircon u pb dating and sr nd pb hf isotopes of the ore associated porphyry at the giant donggebi mo deposit eastern tianshan nw china abstract the giant donggebi porphyry mo deposit is located in the jueluotage metallogenic belt of eastern tianshan xinjiang northwest china mo mineralization mainly occurs as numerous veinlets in the altered sandstone wall rocks with the development of potassic phyllic argillic and propylitic alteration assemblages outward from a buried porphyritic granite stock zircon crystals from the buried porphyritic granite yield a weighted average 206 pb 238 u age of 236 2 2 ma mswd 1 2 1 n 17 slightly older than the molybdenite re os isotope ages of 231 234 ma suggesting that the donggebi porphyry mo deposit was formed in the triassic post collisional tectonism subsequent to termination of the paleo asia ocean the samples from porphyritic granite show high contents of sio 2 k 2 o and al 2 o 3 low contents of tio 2 mgo and cao and peraluminous high k calc alkaline to shoshonite affinity with obvious lree enrichment and negative eu anomalies they have high initial 87 sr 86 sr ratios of 0 70618 to 0 70821 e nd t values of 0 60 to 1 62 and t dm2 nd ages of 0 88 to 0 96 ga their 206 pb 204 pb t 207 pb 204 pb t and 208 pb 204 pb t values are 17 122 18 577 15 493 15 574 and 37 887 38 006 respectively zircons from the porphyritic granite yield ehf t values of 1 58 to 4 82 and t dm2 hf ages of 0 96 1 36 ga these geochemical and isotopic data imply that the donggebi porphyritic granite originated mainly from partial melting of lower continental crust derived from a depleted mantle the donggebi mo deposit is unique based upon the crustal source for the causative porphyry the distal position of mineralization and the previously revealed co 2 rich ore forming fluids and thus belongs to the collisional or dabie type porphyry deposits as exemplified by the qiane chong and yaochong deposits in dabie shan the donggou deposit in qinling orogen china

sims u pb dating of vein hosted hydrothermal rutile and carbon isotope of fluids in the wulong lode gold deposit ne china linking gold mineralization with craton destruction abstract wulong is the largest lode gold deposit in the liaodong peninsula northeastern north china craton ncc gold mineralization mainly occurs in the quartz sulfide veins which are hosted in jurassic monzogranite and early cretaceous diorite dikes here rutile grains are firstly identified in the auriferous quartz pyrite vein the vein hosted rutiles have textural associations with quartz chlorite pyrite and bi sulfosalts and host fluid inclusions indicating that they are unequivocally of hydrothermal origin and co precipitate with gold the rutile grains are characterized by high w and v concentrations and u shaped rare earth elements pattern with the greatest depletion in mree due to excess zr incorporation during fast rutile crystal growth process from the f rich ore forming fluids zr in rutile thermometers provide unrealistic crystallization temperatures 550 c which are much higher than the previous homogenization temperatures data of fluid inclusions yu et al 2018 all these geochemical signatures also support that rutiles formed from the hydrothermal fluids the 13c values of co2 gases in low salinity aqueous carbonic fluid inclusions from the mineralized quartz range from 9 6 to 1 7 average 5 7 indicating mantle magmatic sources for the ore forming fluids sims u pb dating yields a more precise and robust age of 122 3 1 1 ma n 23 mswd 0 82 for the gold mineralization at wulong this new date is roughly coeval with the ore hosted diorite dikes and the sanguliu granitic pluton most in 125 120 ma such close temporal association provides additional weights of evidence for a magmatic affinity to the gold formation regionally the rutile u pb age indicates that the gold mineralization occurs in an extensional tectonic regime caused by the thinning and destruction of the lithosphere beneath the ncc meanwhile the timing of gold mineralization is the same as the peak age of ncc destruction therefore we propose that the wulong deposit has a genetic link with this craton destruction this is similar to numerous other early cretaceous gold deposits across the ncc such as those in the xiaoqinling and jiaodong districts our study indicates that rutile is a robust u pb chronometer for the lode gold deposit but may be not a good geothermometer in the case of f rich hydrothermal fluid system

the source of lead in the osen sandstone lead deposit on the baltic shield norway the sandstone hosted lead deposits on the baltic shield occur in marine late precambrian to early cambrian sedimentary rocks a ground water model in which the basement is postulated as the metal source has been proposed for these deposits to test this model the osen deposit was selected because it lies directly on a homogeneous granite basement on the basis of u th pb whole rock isotopic analyses for three samples of unweathered basement granite trysil granite a basement age of 1 598 m y was established the lead isotopic compositions of four out of five specimens of galena from the osen deposit plot between isochrons calculated for the granite at 500 m y and 540 m y this is strong support for the hypothesis that the lead source was basement granite and suggests that mineralization took place soon after sedimentation a basement source for the lead is further substantiated by the regional pattern of lead isotopic compositions of sandstone lead deposits which reflects the character of adjacent basement terranes

geological fluid inclusion h o s pb isotope and ar ar geochronology constraints on the genesis of the nancha gold deposit southern jilin province northeast china abstract the nancha gold deposit located in the central part of southern jilin province in the northeastern portion of the north china craton contains orebodies hosted in a proterozoic metamorphosed volcanic sedimentary sequence the distribution of the orebodies is controlled by nne trending brittle ductile shear zones and faults the gold orebodies consist of auriferous quartz veins and auriferous altered rocks mineralization can be divided into three stages 1 quartz pyrite 2 quartz gold polymetallic sulfide and 3 quartz carbonate with gold being introduced mainly in the second stage three types of fluid inclusions were identified in the vein mineral assemblages based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type and pure co 2 pc type crystals in the early quartz pyrite stage veins mainly contain c type primary fluid inclusions and rare pc type inclusions the fluid inclusions in these veins completely homogenize at temperatures of 273 432 c and show low salinities of 0 63 7 78 wt nacl equiv in the middle quartz gold polymetallic sulfide stage all three types of fluid inclusions were observed these fluid inclusions homogenize at temperatures of 132 to 255 c and show salinities of 0 83 11 72 wt nacl equiv in contrast crystals in the late quartz carbonate stage contain only w type fluid inclusions that show homogenization temperatures of 132 255 c and salinities of 0 35 7 86 wt nacl equiv these data indicate that the metallogenic system evolved from a co 2 rich metamorphogenic fluid to a co 2 poor fluid due to inputs of meteoric waters fluid boiling and mixing caused the rapid precipitation of sulfides and gold trapping pressures estimated from boiling c type fluid inclusions were 152 367 mpa in the ore forming stage this suggests an alternating lithostatic hydrostatic fluid system controlled by a fault valve activity at a depth of 13 8 15 2 km one hydrothermal sericite sample from an auriferous quartz vein yielded an 40 ar 39 ar isotopic plateau age of 170 1 1 9 ma indicating that mineralization occurred in the middle jurassic and was unrelated to the volcanics and intrusions in the mineralized area the characteristics of h o s pb isotopes and fluid inclusions suggest that the ore forming fluids were of metamorphic origin with the s originating from proterozoic crustal components and the pb originating from a mixture of ore forming metamorphogenic fluids and host rocks the results combined with existing data on the regional geology ore geology fluid inclusions h o s pb isotope geochemistry age of mineralization and tectonic setting indicate that the nancha gold deposit was an orogenic type system that formed in a middle jurassic accretionary orogenic regime following subduction of the paleo pacific plate beneath the eurasian continent

structure mineralogy and pb isotopic composition of the as au ag deposit rotgulden eastern alps austria significance for formation of epigenetic ore deposits within metamorphic domes the abandoned as au ag mining district rotgulden is located within the eastern tauern window of the eastern alps and was reinvestigated in order to evaluate ore deposition during alpine late orogenic tectonic processes four major ore types have been recognized 1 quartz sulfide veins within variscan basement rocks 2 deformed metamorphic massive ores within fold hinge zones saddle reefs of permian to mesozoic cover sequences 3 ores in tension gashes of the cover sequence and 4 irregular replacement ore bodies in marbles of the cover sequence ore deposition was intimately related to late orogenic exhumation by stretching of footwall sequences within the tauern metamorphic core complex during late oligocene and neogene hydrothermal systems developed and metals from apparently distinct sources were deposited under decreasing temperature conditions lead is distinctly radiogenic and resembles the lead in au quartz veins of the mesozoic cover sequence of the hohe tauern

lead isotope variations across terrane boundaries of the tien shan and chinese altay the altaid orogen was formed by aggregation of paleozoic subduction accretion complexes and precambrian basement blocks between the late proterozoic and the early mesozoic because the altaids are the site of abundant granitic plutonism and host some of the largest gold deposits in the world understanding their formation has important implications on the comprehension of phanerozoic crustal growth and metallogeny in this study we present the first extensive lead isotope data on magmatic and metasedimentary rocks as well as ore deposits of the southern part of the altaids including the tien shan tianshan and southern altay altai orogenic belts our results show that each terrane investigated within the tien shan and southern altay is characterized by a distinct pb isotope signature and that there is a sw ne pb isotope gradient suggesting a progressive transition from a continental crust environment in the west the kyzylkum and kokshaal segments of the southern tien shan to an almost 100 juvenile morb type mantle derived crust environment in the east altay the pb isotope signatures of the studied ore deposits follow closely those of magmatic and metasedimentary rocks of the host terranes thus supporting the validity of lead isotopes to discriminate terranes whereas this apparently suggests that no unique reservoir has been responsible for the huge gold concentration in this region masking of a preferential pb poor au bearing reservoir by mixing with pb rich crustal reservoirs during the mineralizing events cannot be excluded

microthermometric laser raman spectroscopic and volatile ion chromatographic analysis of hydrothermal fluids in the paleozoic muruntau au bearing quartz vein ore field uzbekistan fluid inclusions in quartz and scheelite from flat steeply dipping central and stockwork type quartz veins within the muruntau au bearing quartz vein ore field have been investigated in a reconnaissance study using fluid inclusion mapping microthermometry laser raman spectroscopy and integrated gas and ion chromatography for bulk volatile and cation anion analysis muruntau central veins are dominated by inferred early co2 bearing fluid inclusions in contrast flat quartz veins contain considerable numbers of low density pure aqueous inclusions on deformation and recrystallization related microstructures fluid phase separation is indicated for samples from the muruntau central ore veins by fluid inclusion observational work as well as by microthermometry and bulk fluid geochemistry co2 ch4 co2 n2 and co2 c2 and c3 hydrocarbon ratios salinity data however in flat veins and all samples from the myutenbai deposit no evidence for fluid immiscibility could be found quartz microstructural results and fluid inclusion data suggest formation of the low grade mineralized flat veins before the main stage of hydrothermal activity and considerable variation in the geochemical conditions during fluid evolution in the muruntau and myutenbai deposits mixing of fluids from different sources in variable proportions may be inferred from halide geochemistry furthermore fluid inclusion br cl ratios differ significantly for samples from different vein types fluid phase separation is suggested as a mechanism for the precipitation of au from the hydrothermal fluid in the muruntau high grade au mineralized central veins

lead isotope evidence for a hercynian origin of the salsigne gold deposit southern massif central france the salsigne gold deposit contains a complex association of sulphide layers gold rich disseminations quartz bearing veins and flat reefs which are hosted by folded and slightly metamorphosed paleozoic sediments on both sides of a major thrust zone it is demonstrated that these various au as ore types have similar lead isotope compositions 206pb 204pb 18 22 18 56 which are characteristic of hercynian ore deposits in the southern massif central the lower cambrian to devonian host rocks and associated pb zn ba occurrences display distinctly less radiogenic corrected isotopic signatures 206pb 204pb 17 83 17 98 which are characteristic of cambrian lead in the montagne noire concerning the controversial origin of the salsigne gold mineralization these results disagree with the former syngenetic hypothesis and support a new model of hercynian syntectonic gold concentration

geochemistry and evolution of ore forming fluids of the yueshan cu au skarn and vein type deposits anhui province south china abstract the yueshan mineral belt is geotectonically located at the centre of the changjiang deep fracture zone or depression of the lower yangtze platform two main types of ore deposits occur in the yueshan orefield cu au fe skarn deposits and cu mo au pb zn hydrothermal vein type deposits almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the yueshan dioritic intrusion in the vicinity of the zongpu and wuhen intrusions there are many cu pb zn au s vein type and a few cu fe au skarn type occurrences fluid inclusion studies show that the ore forming fluids are characterised by a cl s na k chemical association hydrothermal activity associated with the above two deposit types was related to the yueshan intrusion the fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water in comparison the hydrothermal activity related to the zongpu and wuhen intrusions was characterised by low salinity fluids chlorine and sulphur species played an important role in the transport of ore forming components hydrogen and oxygen isotope data also suggest that the ore forming fluids in the yueshan mineral belt consisted of magmatic water mixed in various proportions with meteoric water the enrichment of ore forming components in the magmatic waters resulted from fluid melt partitioning the ore fluids of magmatic origin formed large cu au deposits whereas ore fluids of mixed magmatic meteoric origin formed small to medium sized deposits the sulphur isotopic composition of the skarn and vein type deposits varies from 11 3 to 19 2 and from 4 2 to 10 0 respectively these variations do not appear to have been resulted from changes of physicochemical conditions rather due to compositional variation of sulphur at the source s and by water rock interaction complex water rock interaction between the ore bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore forming fluids hydrodynamic calculations show that magmatic ore forming fluids were channelled upwards into faults fractures and porous media with velocities of 1 4 m s 9 8 10 1 to 9 8 10 7 m s and 3 6 10 7 to 4 6 10 7 m s respectively a decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the triassic sedimentary rocks led to the deposition of the ore forming components the major species responsible for cu transport are deduced to have been cucl cucl2 cucl32 and cucloh whereas au was transported as au2 hs 2s2 au hs 2 auhs and auh3sio4 complexes cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of cu deposition gold deposition was related to decrease of ph total sulphur concentration and fo2 which resulted from fluid boiling and mixing geological and geochemical characteristics of the two deposit types in the yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 ma and represent a continuous process during the yanshanian time the cooling of the intrusions and the mineralisation event might have lasted about 6 ma the cooling rate of the magmatic intrusions was 80 to 120 c my 1 which permitted sufficient heat supply by magma to the ore forming system

constraints of fluid inclusions and in situ s pb isotopic compositions on the origin of the north kostobe sediment hosted gold deposit eastern kazakhstan abstract the north kostobe gold deposit in the kalba gold province eastern kazakhstan is tectonically located in the chara shear zone of the western altaids the chara shear zone separates the kazakhstan microcontinent and siberia craton which collided in the late carboniferous in the north kostobe deposit au mineralization is distributed along an e w striking shear zone linked to the nw se trending regional faults and is mainly concentrated in quartz sulfide carbonate veins or in disseminated sulfides hosted in carbonaceous metasedimentary rocks sulfide minerals are mainly pyrite and arsenopyrite and were formed in three generations the first generation is dominated by pyrite py1 occurring as microcrystal aggregates followed by the second generation including euhedral arsenopyrite and compact pyrite py2 locally overgrowing early py1 grains as rims third generation of pyrite py3 is present in barren micro fractures crosscutting early mineralized rocks native gold is present in cracks of brecciated arsenopyrite grains and as inclusions in py2 investigations on fluid inclusions in auriferous quartz veins indicate that the ore related fluids are co 2 bearing with homogenization temperatures of 288 c and low salinity 1 42 to 8 03 wt nacl equiv the fluids have calculated 18 o and d values ranging from 9 96 to 11 86 and from 75 to 97 1 respectively suggesting that they were most likely metamorphic in origin the first and second generations of ore sulfides have similar 34 s values 6 to 2 6 which possibly indicating a common sulfur source as the hosting sedimentary rocks in contrast py3 grains have a huge range of 34 s values 40 to 54 5 indicating a biogenic source for the sulfur on the other hand in situ pb isotopic compositions of different generations of sulfides show a similarly mixed lead source possibly involved orogen mantle and lower crust pb reservoirs we propose that the gold bearing fluids of the north kostobe gold deposit were most likely derived from gold rich pyritic carbonaceous sedimentary rocks through dehydration during the metamorphism that was related to the collision between the kazakhstan microcontinent and siberia craton in the late carboniferous it is thus concluded that the north kostobe gold deposit shares many characteristics with typical orogenic gold deposits in terms of tectonic settings mineralization styles fluid compositions and source of fluids and gold our new findings thus have important implications for regional exploration in the kalba gold province

fluid inclusion geochemistry and 40ar 39ar geochronology constraints on the genesis of the jianchaling au deposit china abstract the giant jianchaling gold deposit is located in the shaanxi province china the mineralization is hosted by wnw trending faults in the mianxian lueyang yangpingguan mly area the mineralization can be divided into three stages based on mineralogical assemblages and crosscutting relationships of mineralized quartz veins these stages from early to late are characterized by the mineral assemblage of 1 quartz coarse grained pyrite pyrrhotite pentlandite dolomite 2 quartz pyrite gold sphalerite galena carbonate arsenopyrite fuchsite and 3 dolomite calcite quartz fine grained pyrite realgar orpiment three types of fluid inclusions have been recognized in this study based on petrographic and microthermometric measurements including pure co 2 and or ch 4 pc type nacl h 2 o w type and nacl co 2 h 2 o c type fluid inclusions these fluid inclusion types are present in quartz from the stage 1 and 2 assemblages whereas the stage 3 quartz only contains w type fluid inclusions the stage 2 assemblage is associated with the mineralization at the jianchaling deposit fluid inclusions of stage 1 quartz homogenize mainly between 250 and 360 c with salinities up to 15 6 wt nacl equiv whereas the stage 3 dolomite with homogenization temperatures of 160 220 c and salinities of 1 1 7 4 wt nacl equiv this indicates that the ore fluid system evolved from co 2 rich probably metamorphic hydrothermal to co 2 poor meteoric fluid all three types of fluid inclusions can be observed in the stage 2 quartz suggesting that this heterogeneous association was trapped from a boiling fluid system these inclusions homogenized at temperatures of 200 250 c and salinities of 1 2 12 4 wt nacl equiv the estimated trapping pressures of the fluid inclusions are between 117 and 354 mpa in stage 1 suggesting an alternating lithostatic hydrostatic fluid system which was controlled by a fault valve at the depth of 12 km two fuchsite samples collected from the stage 2 polymetallic quartz veins yielded well defined 40 ar 39 ar isotopic plateau ages of 197 2 and 194 2 ma and 39 ar 36 ar 40 ar 36 ar normal isochrones of 198 2 and 199 2 ma this indicates that the mineralization at jianchaling is early jurassic ca 198 ma in age we propose that jianchaling is an orogenic gold deposit and formed during continental collision related to the northward subduction of the mian lue oceanic plate during the early jurassic we also conclude that the beginning of the continental collision between the yangtze and the north china cratons took place around 200 ma

the hydrothermal fluid of archaean lode gold deposits at different metamorphic grades compositional constraints from ore and wallrock alteration assemblages a low salinity mixed aqueous carbonic fluid is common to all archaean lode gold deposits throughout the range of mineralising conditions from sub greenschist to lower granulite facies temperatures alteration assemblages and fluid inclusion data give constraints on the fluid composition fluid xco2 is 0 1 0 3 in typical greenschist facies mesothermal deposits at higher temperatures the assemblages are consistent with formation from a fluid of similar composition but slightly higher or lower xco2 cannot be ruled out and fluid inclusion data indicate that ch4 may be an important component in ore fluids at these temperatures fluid ph is neutral or weakly alkaline at all conditions a range of relative oxidation states of four orders of magnitude fo2 is indicated at any temperature with deposits more oxidising relative to qfm at lower temperature sulphur contents of the fluids vary from 10 to 10 3 5m s with a trend towards lower sulphur contents at lower temperatures the relative concentrations of major cations in solution are similar at all conditions with na k ca although ca may be less abundant at low temperatures the broad similarities in ore fluid composition at all temperatures give support to crustal continuum models in which archaean lode gold mineralisation involved either a single fluid moving through the middle and upper crust or derivation of ore fluids by similar processes at different crustal levels many of the compositional differences between high and lowtemperature ore fluids may be attributed to evolution of deep sourced hydrothermal solutions as they rise along structurally controlled conduits the constancy of major ore fluid component concentration e g co2 cl k suggests fluid buffering and high fluid rock ratios along fluid pathways fluid buffered conditions can also explain the ore fluid fo2 temperature relations with equilibria between oxidised and reduced aqueous carbon or sulphur species controlling the oxidation state in contrast the concentrations of components present in lesser abundance in archaean gold ore fluids e g s ca h were probably controlled either by saturation of one or more mineral phases brought on by decreasing temperature or were rock buffered through fluid rock reactions extrapolation to high temperatures of the k na and ca contents of the gold bearing fluids indicates that their composition is consistent with derivation from or final equilibration with rocks of intermediate granitic composition thus giving support to isotopic and geological arguments for ore fluid source regions external to the greenstone belts the fluid oxidation states are characteristic of a wide range of potential source rocks including mantle derived igneous rocks calc alkaline granitoids and magmas and seaflooraltered metabasalts strongly oxidised magmatic sources or unusually oxidising source processes e g co2 streaming during granulitisation of the lower crust are therefore not required in the genesis of arch an lode gold deposits

geochronology isotopic chemistry and gold mineralization of the black slate hosted haoyaoerhudong gold deposit northern north china craton abstract the haoyaoerhudong gold deposit is the largest gold deposit in the north margin of the north china craton gold province and contains over 7 moz of gold at an average grade of 0 62 g t the deposit is hosted in the carbonaceous and pyritic slate phyllite and schist and is controlled by a tight syncline and shear zones the high grade orebodies contains abundant pyrite veins and pyrite quartz veins three stages of pyrite have been identified including the diagenetic disseminated pyrite pyrite veins caused by peak matamorphism and pyrite quartz veins forming during post peak metamorphism native gold has been observed in pyrite veins and pyrite quartz veins the 40ar 39ar plateau age of a biotite separate from a tails of boudinaged pyrite quartz veins is 260 1 2 9 ma combined with previously published 40ar 39ar mica age data and low closure temperature of mica these results suggest that pyrite veins and pyrite quartz veins were formed during the peak to post peak metamorphism during 285 260 ma respectively the lower limit of the formation age of sedimentary disseminated pyrites has constrained to 1670 1560 ma by the intruded mafic ultramafic dikes disseminated pyrite separates have 34s values ranging from 39 40 to 17 85 206pb 204pb of 19 144 21 892 207pb 204pb of 15 681 15 864 and 208pb 204pb of 37 502 38 925 suggesting they were formed from seawater sulfate and has experienced strong sulfur isotopic fractionation in contrast hydrothermal pyrites from pyrite veins and pyrite quartz veins have 34s values ranging from 6 8 to 16 47 206pb 204pb of 18 566 18 922 207pb 204pb of 15 645 15 684 and 208pb 204pb of 38 924 38 983 which may reflect dissolution reprecipitation of disseminated sulfides from the pre existing organic rich sediments the mineral paragenetic geometric and cross cutting relationships of pyrite veins and pyrite quartz veins at haoyaoerhudong suggest that gold was most likely introduced into pyrite accompanying sedimentation of the organic rich shales and then became enriched during diagenesis subsequently the hydrothermal fluids following metamorphism and shear zone activity make dissolution of the gold in the diagenetic pyrite and precipitated in the intersection of shear zone and tight syncline

late permian triassic metallogeny in the chinese altay orogen constraints from mica 40ar 39ar dating on ore deposits abstract the central asian orogenic belt caob constitutes the largest phanerozoic accretionary orogen on earth it extends over 5000 km and hosting numerous metal deposits the chinese altay orogen an important element of the caob hosts abundant devonian ca 410 370 ma deposits the 40 ar 39 ar dating of seven mica separates from the representative samples syngenetic with orogenic type mineralization is summarized to record a poorly studied permian to triassic metallogenic episode in the chinese altay orogen the kelan and maizi basins in the chinese altay orogen which likely represent an arc accretionary complex contain a series of polymetallic lode deposits hosted in low grade metamorphic volcano sedimentary rocks two muscovite and five biotite separates were obtained from the ore forming veins paragenetically associated with au bearing polymetallic sulfides in the keketale pb zn wulasigou cu tiemurt pb zn dadonggou pb zn and sarekuobu au deposits these separates yielded 40 ar 39 ar plateau ages ranging from 260 ma to 205 ma integration of these results with other published geological and geochronological data indicates that the au cu pb zn mineralization post dated the final caob assembly with fluid movement and mineralization possibly driven by regional metamorphism and deformation it is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the caob results into the formation of the deposits

hydrothermal alteration fluid inclusions and stable isotope characteristics of the shaquanzi fe cu deposit eastern tianshan implications for deposit type and metallogenesis abstract the shaquanzi fe cu deposit is an important fe cu deposit in the yamansu fe mineralization belt eastern tianshan five stage stage i to v hydrothermal alteration mineralization have been recognized the early skarn stage i and late skarn stage ii stages are featured by extensive garnet and amphibole alteration respectively magnetite mineralization stage stage iii is associated with pervasive k fe ca alteration forming magnetite mushketovite k feldspar epidote magnetite pyrite and quartz chalcopyrite mineralization stage stage iv has an ore mineral assemblage of chalcopyrite bornite acicular hematite and sphalerite accompanied with broad epidote chlorite calcite alteration the late veins stage stage v occurs mainly as epidote calcite veins crosscutting the host rocks and earlier stage minerals stage i hydrothermal fluids have high temperatures 600 c medium high salinities with magmatic 18ofluid 6 to 11 7 stage iii ore forming fluids are medium high temperature ca 470 570 c with medium salinity stage iii minerals were formed under dfluid 45 7 to 24 3 18ofluid 5 8 to 9 1 and 34sfluid 1 7 to 4 7 indicative of magmatic fluids mixed with minor seawater in contrast stage iv fluids have low temperatures ca 160 c medium low salinities and are ca rich with isotopic compositions reflecting basinal brine mixed with meteoric water 13cfluid 6 6 to 2 3 18ofluid 3 3 to 2 8 and 34sfluid 24 8 the shaquanzi diorite zircon u pb age 298 5 ma is broadly coeval with previous re os ages of the shaquanzi magnetite and pyrite 303 12 ma and 295 7 ma respectively indicating that the shaquanzi fe cu metallogeny may have been genetically linked to the regional magmatic hydrothermal activities led by the yamansu arc backarc basin inversion features of hydrothermal alterations mineral assemblages ore forming fluids and tectonic setting all suggest that the shaquanzi fe cu deposit is an iocg like deposit similar to those in the cenozoic central andes

lead and sulfur isotope studies of the wulashan quartz k feldspar and quartz vein gold deposit southwestern inner mongolia people s republic of china the newly discovered wulashan gold deposit in southwestern inner mongolia people9s republic of china is hosted by archean metamorphosed volcano sedimentary sequences of the wulashan group and surrounded by a number of late paleozoic granitoid dikes and a batholith the gold mineralization occurs in quartz k feldspar and quartz veins related to these intrusions sulfur isotope analyses of 21 sulfide mineral galena and pyrite samples from the gold bearing quartz k feldspar and quartz veins hornblende plagioclase gneiss sillimanite biotite gneiss and granitoid intrusions in the wulashan district suggest that the sulfur of the ore bearing fluids was mainly derived from a mixing of sources from late paleozoic granitoid intrusions and archean metamorphosed volcano sedimentary rocks lead isotope data for amphibolite one of the major host rocks of these gold bearing veins define a correlation line with a slope of 0 1641 or 0 0003 2sigma which corresponds to an age of 9 498 or 76 ma 2sigma this lead isotope line also overlaps with the late paleozoic granite line of the dahuabei granitoid batholith defined by five k feldspar samples lead isotope data of 13 galena and pyrite samples from the gold bearing quartz k feldspar and quartz veins plot in between data for the amphibolite and dahuabei granitoid batholith samples and constitute a mixing line plots of all these lead isotope data 206 pb 204 pb vs 207 pb 204 pb and 206 pb 204 pb vs 208 pb 204 pb display a linear trend with k feldspar of the dahuabei granitoid batholith at the most radiogenic end and amphibolite of the wulashan group at the least radiogenic end this trend is probably a result of the mixing of mantle derived lead with lead from a radiogenic granitoid source the results of lead isotope studies indicate that protoliths of the amphibolite and the dahuabei granitoid batholith have identical or similar initial lead isotope compositions but that they may possess quite different mu values the amphibolite was derived from mantle related mafic igneous rocks erupted or intruded at 2498 ma whereas the dahuabei granitoid batholith was probably derived by selective remelting of previously formed volcano sedimentary rocks during a late paleozoic variscan tectonic event the lead and sulfur of the gold bearing quartz k feldspar and quartz veins were derived from multiple sources including archean amphibolite and the late paleozoic granitoid batholith

lead isotope systematics and pyrite trace element geochemistry of two granitoid associated mesothermal gold deposits in the southeastern lachlan fold belt

a fluid inclusion study of the hetai goldfield in the qinzhou bay hangzhou bay metallogenic belt south china abstract the hetai goldfield is located in the southern section of the qinzhou bay hangzhou bay metallogenic belt qhmb south china gold mineralization is controlled by ne trending ductile shear zones gold grade is higher at the shear zone centers and decreases sharply away from the shear zones regardless of the host rock type fluid inclusions fis preserved in the auriferous quartz veins have been analyzed to constrain their genesis three types of gold mineralization related fis including moderate salinity aqueous a type low salinity h 2 o co 2 b type and co 2 dominated c type have been newly identified the measured homogenization temperatures t h range from 130 c to 310 c with two peaks of about 245 c and 170 c the calculated pressures of fis range from 50 mpa to 170 mpa immiscibility and co 2 effervescence of fluids may have played an important role in gold precipitation during the ascent of the ore forming fluids the hetai goldfield is a typical example of orogenic gold deposits originating from auriferous metamorphic fluids

syndeposition and epigenetic modification of the strata bound pb zn cu deposits associated with carbonate rocks in western kunlun xinjiang china abstract lead zinc copper pb zn cu deposits in the western kunlun orogen of china are mostly distributed along the keziletao kusilafu fault zones in the palaeozoic clastic carbonate rocks which formed in a late palaeozoic subsidence belt at the south west margin of the tarim platform geological and geochemical studies were conducted on these deposits including detailed field observation petrographic study and geochemical and isotopic analyses of sulfur lead strontium rhenium osmium and argon isotopes as well as fluid inclusion geochemistry the characteristics of the deposits include 1 except for the tiekelike pb cu deposit associated with mid devonian rocks all of the other deposits were developed in the lower layers of the early carboniferous strata these strata mostly comprise sedimentary dolomitic limestone sandy limestone black limestone and calcareous shale 2 the ore bodies are stratiform and host veins the stratiform ores are coeval with host rocks yielding ore forming ages of 331 337 ma while the vein ore bodies are mostly massive deposits formed at 206 235 ma the isotopic compositions of the sulfur and lead reveal that the ore forming elements originated from various sources 3 the mineralization in cements of brecciated ore is a veinlet type while in the breccias it is a disseminated type the stratoid disseminated and framboidal structures of the ore reveal the synsedimentary ore formation however the veins mesh veins and massive structures indicate late stage hydrothermal mineralization 4 the principal metallic minerals include sphalerite galena and pyrite while the secondary oxide minerals include variable distributions of cerussite anglesite and limonite the gangue minerals include dolomite calcite quartz sericite and gypsum with minor chert and barite 5 the original host rocks likely experienced dolomitization calcitization and minor silicification the ore deposits underwent hydrothermal alterations sub greenschist facies metamorphism and brecciation the ore deposits may have initially formed via syndeposition in a subsidence belt along the southwest margin of the late paleozoic tarim platform these deposits were further modified during later hydrothermal alteration and orogenesis during the triassic period

isotope geochemistry of the tieluping silver lead deposit henan china a case study of orogenic silver dominated deposits and related tectonic setting the tieluping silver deposit which is sited along ne trending faults within the high grade metamorphic basement of the xiong er terrane in the qinling orogenic belt is part of an important recently discovered mesozoic orogenic type ag pb belt ore formation includes three stages an early barren quartz pyrite stage e an intermediate polymetallic sulfide ore stage m and a late barren carbonate stage l carbon sulfur and lead isotope systematics indicate that the e stage fluids are deeply sourced the l stage fluids are shallow sourced meteoric water whereas the m stage fluids are a mix of deep sourced and shallow sourced fluids sulfur and lead isotope data show that the ore forming fluids must have originated from a source with elevated radiogenic lead and low 34s values that differs significantly from exposed geologic units in the xiong er terrane the lower crust and the mantle this supports the view that the carbonate shale chert sequences of the guandaokou and luanchuan groups south of the machaoying fault might be the favorable sources although little is known about their isotopic compositions a tectonic model that combines collisional orogeny metallogeny and hydrothermal fluid flow is proposed to explain the formation of the tieluping silver deposit during the mesozoic collision between the north china craton and south china block early mid triassic indosinian orogeny crustal slabs containing the carbonate shale chert sequences of the guandaokou and luanchuan groups locally rich in organic matter carbonaceous shale were thrust northwards beneath the xiong er terrane along the machaoying fault metamorphic devolatilisation of this underthrust slab probably provided the ore forming fluids to develop the ag pb ore belt which includes the tieluping silver deposit fluids and magmas were emplaced during extensional stages related to the jurassic cretaceous yanshanian orogeny

age and source constraints for the giant muruntau gold deposit uzbekistan from coupled re os he isotopes in arsenopyrite the muruntau gold deposit uzbekistan is one of the largest gold deposits known worldwide but its origin remains controversial we used re os arsenopyrite geochronology to precisely determine the age of main stage gold mineralization at muruntau to be 287 5 1 7 ma which overlaps the emplacement of proximal post tectonic granitoid magmatism additionally we suggest that arsenopyrite growth may have occurred over an interval of at least 2 m y os initial ratios derived from arsenopyrite were coupled with he isotopic data from fluid inclusions within arsenopyrite to constrain the source of ore metals and fluids muruntau arsenopyrite yields relatively unradiogenic initial os 0 37 0 27 and elevated 3he 4he ratios 0 23 0 33 r a relative to purely crustal os he reservoirs these data suggest the presence of a mantle derived component in the ore system that was probably introduced during the generation of the granitoid magmas these new timing and source constraints provide important new insight into the generation of this giant gold deposit and they necessitate reexamination of genetic models for muruntau and potentially other giant orogenic gold deposits worldwide

structure and origin of the gold mineralization in the nacimiento block the los burros deposits central california abstract the los burros gold deposit is located within the franciscan complex of the nacimiento block california although this deposit was mined during the late 19th and early 20th centuries its origin and its relationship with the regional metamorphism and deformation are unclear in order to better understand the mode of formation of the deposit and its possible link with a post subduction thermal anomaly we performed a detailed geological and structural mapping within the los burros district coupled with a u th he thermochronological study on apatite and zircon fluid inclusion and stable isotope o and c analyses of the ore deposit provide constraints on the temperature and potential source of the fluid s responsible for the los burros gold formation our results demonstrate that the los burros au deposit formed from a metamorphic aqueous co2 ch4 fluid at temperatures of 300 c results from raman spectroscopy of carbonaceous materials confirm the presence of a thermal anomaly in the range 260 320 c near the los burros mining district as previously inferred by vitrinite reflectance techniques our structural and preliminary thermochronological analyses show that the los burros au deposit consists of a series of meter wide quartz calcite sulfide en echelon veins formed during a late transpressive event related to san andreas fault activity and the subduction of a slab window during the past 30 ma our new data suggest that the thermal anomaly recorded in the vicinity of the los burros mining district is not associated with a magmatic derived hydrothermal system such as described within the epithermal mclaughlin deposit in northern california but rather with a late transpressive deformation event that uplifted deeply buried metamorphic rocks possibly connected to a local metamorphic overprint

geological and geochemical characteristics of the sawaya erdun gold deposit southwestern chinese tianshan the sawaya erdun gold deposit in the western segment of the south tianshan xinjiang china is a large low grade orogenic gold deposit an abundance of index fossils in the ore hosting strata including brachiopoda corals and schwagerina show that the fossil age of the country rocks ranges from late carboniferous to early permian whole rock rb sr and sm nd isochron ages ranging from 292 43 0 38 to 304 7 11 6 ma are concordant with a late carboniferous age gold mineralization is strictly controlled by a fault zone ore minerals are dominated by sulfides with gold inhomogeneously distributed within them gangue minerals are quartz siderite or calcite data suggest that the ore forming fluid was derived predominantly from an active meteoric groundwater system ore forming temperatures are estimated to have been within the range 110 to 220 c new 40 ar 39 ar isotope age determinations of auriferous quartz are in excellent agreement with rb sr ages obtained from fluid inclusions in quartz they suggest gold mineralization at 206 to 213 ma late indosinian such an age is consistent with the age of formation given for other gold deposits in the region such as bulong and dashankou combined with k ar geochronological data and observed geological features it is concluded that the indosinian metallogentic epoch represents a previously unrecognized major period of gold metallogeny in the southwestern chinese tianshan in some ways the sawaya erdun gold deposit can be compared with the muruntau gold deposit in uzbekistan with respect to geological setting host lithology mineralization style mineral assemblages geochemical association and metallogenic processes involved despite this the sawaya erdun gold deposit possesses a number of characteristics typical of only low temperature metallogenesis 2007 elsevier b v all rights reserved

metallogeny during continental outgrowth in the columbia supercontinent isotopic characterization of the zhaiwa mo cu system in the north china craton abstract the eastern qinling molybdenum belt eqmb in central china represents the largest mo province in the world located at the southern margin of the north china craton this mo province is largely associated with mesozoic granitoids here we report re os isochron age of 1761 33 ma 2 mswd 2 9 from molybdenite in the recently discovered zhaiwa porphyry mo cu system within the eqmb this age coincides with the peak eruption period 1 78 1 75 ga of the xiong er group volcanic rocks which unconformably overlie the taihua supergroup and are interpreted to have developed on a continental arc the re concentrations 1 to 43 ppm of the zhaiwa molybdenites are similar to those of typical porphyry cu mo au systems developed on continental arcs the 34 s values of the zhaiwa ores 2 7 7 3 average 5 2 suggest that the sulfur was mainly sourced from a magmatic system the sulfides from the ores yield sr i average of 0 70533 similar to that of the xiong er group 0 70547 albeit higher than that of the kuanping group 0 70334 and lower than the taihua supergroup 0 70763 suggesting a mixed source the average e nd 1 76 ga of the sulfides from the ores 0 9 falls between the averages of the taihua supergroup ca 6 8 and the kuanping group ca 7 4 the pb isotope ratios of the ores are similar to but slightly higher than those of the taihua supergroup reflecting preferential leaching of radiogenic pb from the taihua supergroup by magmatic fluids integrated data and interpretations constrain the zhaiwa mo cu deposit to be a porphyry mineral system developed within a ca 1 76 ga continental arc related to oceanic plate subduction beneath the southern margin of the north china craton a correlation between tectonic settings and metallogenic types clearly indicate that the xiong er group was formed in a volcanic arc confirming paleo mesoproterozoic continental outgrowth along the margins of the columbia supercontinent the isotopic characterization of the zhaiwa deposit provides new insights into the enigma of the widespread distribution of large and super large mo deposits of eqmb along the southern margin of the north china craton

isotopic geochemistry of the sawayaerdun orogenic type gold deposit tianshan northwest china implications for ore genesis and mineral exploration the sawayaerdun gold deposit is hosted by carbonaceous metasediments and is considered to be the largest muruntau type gold deposit in the chinese tianshan metallogenic belt gold mineralization at sawayaerdun occurs in quartz veins associated with three major hydrothermal events an early barren quartz vein stage middle stage mineralized quartz veins with pyrite and late carbonate quartz veins the isotopic compositions of quartz and sulfides from the sawayaerdun gold deposit show some variation but are generally comparable to those of other orogenic type gold deposits fluids trapped in early stage quartz have a 18o range of 13 6 to 15 4 d of 48 to 75 13c of 0 5 to 4 2 and 30si of 0 2 to 0 in contrast isotopic compositions of fluids trapped in middle stage quartz have 18o values of 6 7 to 14 7 d of 56 to 110 13c of 0 4 to 10 1 and 30si of 0 3 to 0 diagenetic and hydrothermal pyrite have similar sulfur 1 8 to 0 9 and pb isotopic values that are associated with host rock compositions the early stage 18o and 13c rich fluids are probably derived from metamorphic decarbonation of the sedimentary host rock at depth leading to the precipitation of early barren quartz veins in the middle stage a decrease in the regional pressure and temperature regime could have resulted in the incorporation of external fluids into the ore forming system these external fluids with isotopic signatures similar to that of the host rock and generally rich in 34s and radiogenic pb mixed with original ore forming fluids to generate extensive metal precipitation late stage fluids trapped by calcite veins show isotopic compositions similar to meteoric water indicating the cessation of hydrothermal fluid circulation at sawayaerdun occurred at this time the metallogenetic model illustrated by stable and pb isotopes is also consistent with fluid inclusion studies in sawayaerdun the development of mineralization at sawayaerdun is strongly linked to fluid mixing as witnessed by the isotopic signatures of fluids from identified ore bearing zones the isotopic compositions of other anomalous zones at sawayaerdun are similar to those of the mineralized zones suggesting a high potential for further exploration 2012 elsevier b v

electron microprobe analyses of ore minerals and h o s isotope geochemistry of the yuerya gold deposit eastern hebei china implications for ore genesis and mineralization abstract the yuerya gold deposit in eastern hebei province china is located on the eastern margin of the north china craton and is hosted by mesozoic yanshanian granitoid rocks and adjacent mesoproterozoic gaoyuzhuang formation carbonates the auriferous quartz veins in this deposit are dominated by pyrite with subordinate sphalerite chalcopyrite and galena in a quartz dominated gangue that also contains calcite dolomite barite apatite and fluorite gold is present as native gold and electrum which are generally present as micron size infillings in microfissures within pyrite and less commonly as tiny inclusions within pyrite quartz and tellurobismuthite the pyrite in this deposit has high co ni ratios and contains elevated concentrations of both of these elements suggesting that the yuerya gold deposit has a magmato hydrothermal origin and that the ore forming fluids that formed the deposit leached trace elements such as co ni as and au during passage through archean metamorphic rocks mesoproterozoic carbonates and the yanshanian yuerya granitoid pyrite in the study area has s se ratios and s isotopic compositions that suggest that the sulfur and by inference the gold within the deposit was sourced from magmato hydrothermal fluids that were probably originally derived from archean metamorphic rocks and yanshanian granitoids tellurobismuthite in the study area is closely intergrown with gold and was the single telluride phase identified during this study the fineness of gold associated with tellurobismuthite is greater than the fineness of gold associated with pyrite although the fine particle size of the gold surrounded by tellurobismuthite means that the recovery of this gold is difficult in turn meaning that the tellurobismuthite has little significance to the economics of the yuerya gold deposit only trace amounts of sulfides are associated with the tellurobismuthite within the yuerya gold deposit suggesting that this mineral was deposited under conditions of low fs2 and or high fte2 in addition the presence of tellurides within the yuerya gold deposit reflects a genetic relationship between the deposit and magmatism quartz from mineralized veins in the study area has 18o values of 11 2 12 9 and the fluids that formed these veins have d values of 78 3 to 72 1 the 34s values of pyrite within the deposit are rather restricted 2 3 3 5 these data combined with the trace element geochemistry of sulfides within the deposit suggest that the formation of the yuerya gold deposit was closely related to both archean metamorphic rocks and the yanshanian yuerya granitoid

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

stable isotope o h s c and n systematics of quartz vein systems in the turbidite hosted central and north deborah gold deposits of the bendigo gold field central victoria australia constraints on the origin of ore forming fluids the central and north deborah gold deposits are located in one of 15 mining centers of the bendigo gold field central victoria australia a major world class gold province developed in a turbidite terrane gold mineralization occurs primarily within domes and reverse fault systems in multiply deformed lower ordovician metaturbidites deformation and thrusting occurred between 450 and 420 ma coevally with regional metamorphism at zeolite to greenschist facies in the central and north deborah deposits six stages of quartz veining each with characteristic geometry and mineral paragenesis developed sequentially stages 1 2 and 4 are gold bearing whereas stages 3 5 and 6 are barren gold related quartz veins were deposited at temperatures of 350 25 c based on oxygen isotope geothermometry of silicate phases quartz muscovite and sulfur isotope compositions of coexisting sulfide mineral pairs sphalerite galena this result is consistent with temperatures inferred from fluid inclusions the 18o values of gold bearing vein quartz and coexisting hydrothermal muscovite are uniform within and between the six vein stages ranging from 15 9 to 17 2 per mil and 11 6 to 12 8 per mil respectively the d values of hydrothermal muscovites are also uniform at 68 to 55 per mil ore fluids have calculated 18o values of 8 to 11 per mil and d values of 37 to 17 per mil pyrite of synsedimentary diagenetic origin in slate and sandstone displays sulfur isotope compositions of 23 5 to 8 0 per mil and 0 1 to 11 9 per mil respectively sulfides from gold bearing quartz veins have a range of 7 4 to 8 1 per mil median ca 2 5 the relatively uniform vein pyrites indicate a large uniform sulfur source most likely from desulfidation reactions of sulfide minerals interaction of the ore forming fluid with depleted sulfides at the site of deposition may have shifted the sulfur isotope signatures of source sulfides to more negative values carbon isotope compositions of carbonates range from 5 1 to 9 0 per mil median ca 6 5 nitrogen concentrations and nitrogen isotope compositions of hydrothermal muscovite from quartz veins are 652 to 895 ppm and 2 84 to 4 49 per mil respectively collectively the data define a band in n content vegh rsus 15n coordinate space from higher n and lower 15n in the phanerozoic metasedimenary hosted central and north deborah gold deposits to lower n and higher 15n in predominantly meta igneous hosted neoarchean gold provinces collectively the h o s c and n isotope compositions of ore related hydrothermal minerals indicate that the dilute aqueous carbonic and n bearing ore forming fluids were generated from metamorphic dehydration reactions at deeper crustal levels and were variably influenced by exchange with wall rocks during transport to the site of deposition this genetic model for the central and north deborah gold deposits is consistent with other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes in contrast these data are not consistent with either mantle derived fluids or magmatic fluids nor do they support a deeply circulated meteoric surface water model for vein formation

the genesis of the ores and granitic rocks at the hongshi au deposit in eastern tianshan china constraints from zircon u pb geochronology geochemistry and isotope systematics abstract the hongshi gold deposit is located in the southwestern margin of the kanggur huangshan ductile shear zone in eastern tianshan northwest china the gold ore bodies are predominantly hosted in the volcanogenic metasedimentary rocks of the lower carboniferous gandun formation and the carboniferous syenogranite and alkali feldspar granite the syenogranite and the alkali feldspar granite yield shrimp zircon u pb ages of 337 6 4 5 ma 2 mswd 1 3 and 334 0 3 7 ma 2 mswd 1 1 respectively indicating that the hongshi gold deposit is younger than 334 ma the granitoids belong to shoshonitic series and are relatively enriched in large ion lithophile elements rb k ba and pb and depleted in high field strength elements nb ta p and ti moreover these granitoids have high sio 2 al 2 o 3 and k 2 o contents low na 2 o mgo and tio 2 contents low nb ta ratios and slightly positive eu anomalies the e hf t values of the zircons from a syenogranite sample vary from 1 5 to 8 8 with an average of 5 6 the e hf t values of the zircons from an alkali feldspar granite sample vary from 5 0 and 10 1 with an average of 7 9 the 34 s values of 10 sulfide samples ranged from 11 5 to 4 2 with peaks in the range of 1 to 4 the above mentioned data suggest that the hongshi granitoids were derived from the melting of juvenile lower crust mixed with mantle components formed by the southward subduction of the paleo tianshan ocean plate beneath the aqishan yamansu island arc during the early carboniferous the hongshi gold deposit was formed by post collisional tectonism during the permian the granitoids most likely acted as impermeable barriers that prevented the leakage and runoff of ore bearing fluids thus the granitoids probably played an important role in controlling gold mineralization

paleoproterozoic positive δ13ccarb excursion in the northeastern sino korean craton evidence of the lomagundi event abstract the 2 33 2 06 ga positive 13 c carb excursion associated with environmental change and the breakup of the kenorland or superia supercontinent is called the lomagundi or jatulian event or great oxidation event and has been reported in many early precambrian cratons but not yet in the sino korean craton the guanmenshan formation of the liaohe group occurs in the northeastern part of the sino korean craton 13 c carb and 18 o values in 42 samples from this formation range from 3 5 5 9 v pdb and 15 4 24 8 v smow respectively showing a clear positive 13 c carb excursion that characterizes the lomagundi event thirty five of the 42 samples with less hydrothermal alteration have higher 13 c carb and 18 o carb values than the other 7 samples obviously affected by fluid flow confirming that it was fluid flow that reduced the 13 c carb and 18 o carb values this positive 13 c carb excursion places deposition of the guanmenshan formation within the age range of 2 33 2 06 ga

geology geochemistry and ore genesis of the wenyu gold deposit xiaoqinling gold field qinling orogen southern margin of north china craton abstract the wenyu giant gold deposit is hosted in the precambrian taihua supergroup metamorphic rocks within the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided into three stages quartz pyrite veins early quartz sulfide veins middle main and carbonate quartz veinlets late with gold being mainly introduced in main stage quartz formed in two earlier stages contains three compositional types of fluid inclusions i e pure co2 co2 h2o and nacl h2o but the late stage minerals only contain the nacl h2o inclusions the inclusions in quartz formed in the early main and late stages yield total homogenization temperatures of 262 417 c 236 407 c and 114 239 c respectively with salinities no higher than 13 wt nacl equiv trapping pressures estimated from co2 h2o inclusions are 139 399 mpa and 111 316 mpa in the early and main stages corresponding to mineralization depths of 14 km and 11 km respectively fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co2 rich to co2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18owater values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology fluid inclusion and c h o s pb isotope geochemistry we conclude that the wenyu gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

geological characteristics tectonic setting and preliminary interpretations of the jilau gold quartz vein deposit tajikistan the southern tien shan metallogenic province of central asia hosts a number of important gold resources including the jilau gold quartz vein system in western tajikistan these deposits were formed at the late stages of continent continent collision in association with subduction related magmatism metamorphism and continental margin deformation attributed to the central asian hercynian orogeny jilau is hosted by a hercynian syntectonic granitoid intrusive that was emplaced into bituminous dolomite country rocks economic mineralisation is associated with a dilational jog within a high angle oblique dextral reverse slip shear zone that was undergoing brittle ductile deformation the orebody takes the form of shear zone subparallel quartz veins and lenses that emanate from a steeply plunging ore shoot of veins and stringers within a silicified and sulphidised granodiorite core it is thought to have formed by a dynamic process in which fluid flow was governed by a fault valve mechanism numerous cycles of fluid pressure build up fault failure jog dilation fluid flow phase separation of low salinity h2o co2 ch4 n2 fluids and sealing took place gold appears together with scheelite and bismuth minerals predominantly as inclusions in arsenopyrite in quartz veins and altered wall rock and is mainly associated with quartz containing fluid inclusions enriched in ch4 the correlation between high gold grades and high ch4 concentrations suggests that components of the mineralising fluids were derived from or passed through the reducing carbonaceous rocks in the contact aureole of the intrusive the occurrence of au and w in an adjacent hercynian skarn deposit and in the jilau orebody infers that the ore metals in both these systems were ultimately derived from a magmatic source

infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the woxi orogenic au sb w deposit western hunan south china abstract the woxi au sb w deposit hosted by the neoproterozoic low grade metamorphic clastic rocks is located in a brittle ductile shear zone within the xuefengshan range south china orebodies are predominantly banded quartz veins which are strictly controlled by bedding faults and display significant vertical extents up to 2 km without obvious vertical metal zoning fluid inclusions hosted in quartz scheelite and stibnite from quartz scheelite and quartz sulfide gold veins have been studied using conventional and infrared microscopy respectively four types of fluid inclusions were identified based on petrography including type i two phase liquid rich aqueous inclusions type ii two or three phase co 2 rich inclusions type iii two phase vapour rich aqueous inclusions and type iv single phase aqueous inclusions the fluid inclusions in ore minerals scheelite and stibnite and their coexisting quartz largely share similar characteristics in terms of their types homogenization temperatures and salinities this is consistent with the fact that these ore minerals are always intergrown with quartz microthermometric and laser raman data indicate a low to moderate temperature 140 240 c low salinity 2 rich n 2 bearing aqueous ore forming fluid such fluid is further identified as a deeply non magmatic crustal fluid rather than a mantle source fluid by the significantly low 3 he 4 he ratios 0 002 0 281 ra and a small amount of meteoric water or host rock buffered fluid could be involved w ore precipitation was probably associated with mixing between a deeply originated crustal fluid and host rock buffered fluid based on the fluid inclusion features in scheelite and quartz i however au and sb ore deposition probably resulted from boiling which was caused by the marked pressure drop geological features such as banded structure and crack sealing structure also indicate that fluid pressure fluctuation induced by fault valve mechanism occurred during ore precipitation these characteristics of the ore forming fluids in the woxi deposit are in good agreement with the definition of orogenic gold deposits and the woxi au sb w deposit is probably an atypical orogenic gold deposit for its unique ore forming element association

fluid inclusion geochemistry and ar ar geochronology of the cenozoic bangbu orogenic gold deposit southern tibet china abstract located along the southern part of the yarlung zangbo suture zone in southern tibet bangbu is one of the largest gold deposits in tibet auriferous sulfide bearing quartz veins are controlled by second or third order brittle fractures associated with the regional qusong cuogu zhemulang brittle ductile shear zone fluid inclusion studies show that the auriferous quartz contains aqueous inclusions two phase and three phase co2 bearing inclusions and pure gaseous hydrocarbon inclusions the co2 bearing inclusions have salinities of 2 2 9 5 nacleq and homogenization temperatures th of 167 336 c the d 18o and 13c compositions of the bangbu ore forming fluids are 105 5 to 44 4 4 7 to 9 0 and 5 1 to 2 2 respectively indicating that the ore forming fluid is mainly of metamorphic origin with also a mantle derived contribution the 3he 4he ratio of the ore forming fluids is 0 174 to 1 010 ra and 40ar 36ar ranges from 311 9 to 1724 9 calculations indicate that the percentage of mantle derived he in fluid inclusions from bangbu is 2 7 16 7 these geochemical features are similar to those of most orogenic gold deposits dating by 40ar 39ar of hydrothermal sericite collected from auriferous quartz veins at bangbu yielded a plateau age of 44 8 1 0 ma with normal and inverse isochronal ages of 43 6 3 2 ma and 44 3 ma respectively this indicates that the gold mineralization was contemporaneous with the main collisional stage between india and eurasia along the yarlung zangbo suture which resulted in the development of near vertical lithospheric shear zones a deep metamorphic fluid was channeled upward along the shear zone mixing with a mantle fluid the mixed fluids migrated into the brittle structures along the shear zone and precipitated gold sulfides and quartz because of declining temperature and pressure or fluid immiscibility the bangbu is a large scale cenozoic syn collisional orogenic gold deposit

graptolite biostratigraphy of the lower silurian llandovery shelf deposits of the western iberian cordillera spain eight lower silurian graptolite biozones triangulatus convolutus linnaei turriculatus cris pus griestoniensis tullbergi and spiralis and three subzones runcinatus gemmatus palmeus and hispani cus have been recognized in the sierra menera nevera and tremedal massifs in the castilian branch of the iberian cordillera western iberian cordillera early silurian rhuddanian low diversity normalograp tid faunas are also present and these together with the rich graptolite faunas of the aeronian triangulatus and convolutus biozones come from black shaly intercalations within the quartzose sandstones of the upper part of the los puertos quartzite telychian graptolite biozones have been recognized in the succeeding black shale sequence of the badenas formation diachroneity of the transition from sandstones to black shales is dated by graptolites it ranges from about the base to at least the top of the linnaei biozone we sug gest that the lower silurian black shales of the western iberian cordillera were deposited in a shallow shelf environment not much deeper than that of presumably storm influenced sandstones of the los puertos quartzite

the identification of the guqiong orogenic ag au polymetallic deposit in southern tibet evidences from mineralogy geochronology and fluid evolution abstract guqiong is an ag au polymetallic deposit located in the eastern part of the au sb ore belt along the indus yarlung zangbo suture in the north himalaya in this study we have identified three major alteration mineralization stages for guqiong based on the mineral assemblages and their paragenetic relationships namely the i pre ore alteration forming mainly ore barren thick quartz veins and vuggy quartz ii main ore stage that comprises quartz veins with sulfide mineralization including ag au bearing minerals in this stage sericite occurs closely associated with sulfides iii the post ore stage characterized by the formation of calcite and quartz with trace sulfides fluid inclusion assemblage fia microthermometry was conducted on barren and mineralized quartz and sphalerite three types of inclusions are identified based on their petrographic features and laser raman spectra i e the pure carbonic pc aqueous carbonic three phase c1 and two phase c2 and aqueous w types the fias in stage i ore barren quartz are mainly pc type and c1 type which are characterized by being high temperatures 260 to 300 c low salinities 0 8 to 3 5 wt nacl eqv and with abundant co2 sphalerite of main ore stage contains mainly w type with limited c2 type of low temperatures 158 to 180 c and medium salinities 5 6 to 6 7 wt nacl eqv meanwhile the fia in mineralized quartz is featured by the general coexistence of c2 type and w type with local pc type and c1 type inclusions the fluid system may have been a mixture of the two aforementioned fluids in barren quartz and sphalerite as indicated by two significantly different fias c type and w type with contrasting homogenization temperatures 260 to 290 c and 180 to 220 c respectively but comparable salinities 0 2 to 8 2 and 0 2 to 8 1 wt nacl eqv respectively the fluid d 18o and 13c values of the main ore stage quartz are 172 to 114 8 8 to 13 1 and 13 4 to 7 7 respectively the negative 13c values are interpreted as devolatilization products of biogenic carbon with a metamorphic origin while the d and 18o values likely reflect meteoric water involvement into metamorphic fluids we propose that fluid mixing had occurred and caused sulfide precipitation at the main ore stage additionally the estimated fluid trapping depth of 5 to 6 km obtained using 3 d phase diagram is consistent with the formation depth of many orogenic type deposits worldwide 40ar 39ar dating on sericite yielded a well defined plateau age of 42 03 0 42 ma with normal and inverse isochron ages of 42 8 1 6 ma and 42 9 1 9 ma respectively these ages bracket the ag au mineralization at guqiong place it in the main stage india asia collision and further support its orogenic type origin

a ductile to brittle shear zone hosted cu mineralization geological geochronological geochemical and fluid inclusion studies of the lingyun cu deposit southern tianshan nw china abstract the lingyun cu deposit is located at the northern margin of the south tianshan accretionary complex nw china in the lingyun mine area the rocks are cut by a nw trending yanxingshan ductile to brittle shear zone all orebodies are hosted in crystal tuff the sulfide mineralization in the lingyun cu deposit can be divided into early e and late l paragenetic stages the e stage is characteristic of fault controlled sulfide assemblages chalcopyrite bornite chalcocite quartz veins in the foliation fabric of the crystal tuff with albite sericite epidote biotite assemblages in the l stage the assemblages of ankerite chalcopyrite bornite chalcocite are present in veinlets that cut the e stage assemblages the sulfide assemblages in the lingyun deposit are characterized by striations in the metamorphosed crystal tuff ribbon like silicate minerals in the crystal tuff share common deformation features with the sulfide assemblages the host rock of the lingyun cu deposit yields a concordia age of ca 405 ma indicating that the aerbishibulake formation formed during southward subduction of the south tianshan ocean beneath the tarim block moreover crystal tuff samples show well developed negative sr anomaly and positive rb th u nd and p anomalies which are common in arc related volcanic rocks the ca 297 ma re os isochron age yielded by sulfides is much younger than the host rock which implies that the lingyun cu deposit is a typical epigenetic deposit both similar ree fractionated patterns between sulfide ores and crystal tuff and the high initial 187 os 188 os ratio 18 54 0 67 indicate significant crustal materials input the 40 ar 39 ar plateau age of ca 292 ma from the ribbon like sericite in crystal tuff is coeval with the mineralization occurrence in the lingyun cu deposit by contrast diorite dikes that crosscut the crystal tuff formed at ca 221 ma which is much younger than the sulfide mineralization thus the mineralization in the lingyun deposit is likely to have been generated by shear zone activity rather than the intrusion of diorite dikes three types of fluid inclusions have been identified in the lingyun cu deposit aqueous w type mixed aqueous carbonic m type and pure carbonic c type inclusions these three types of fluid inclusions are all found in the e stage quartz whereas only the w type fluid inclusions have been observed in l stage ankerite fluid inclusions from the e stage commonly contain co 2 and h 2 o locally with n 2 with low salinity which are common in orogenic deposits by contrast l stage fluid inclusions show low co 2 concentrations and salinity indicating a significant inflow of meteoric water given the regional geology ore geology coeval ore forming and deformation and fluid inclusion features the lingyun cu deposit may be associated with the orogenic class of mineral systems

isotope geochemistry of the sarekuobu metavolcanic hosted gold deposit in the chinese altay nw china implications for the fluid and metal sources the late triassic sarekuobu lode gold au deposit reserves 8 00 u 202f t au at 3 68 u 202f g t is situated in the kelan volcanic basin of the chinese altay orogen nw china gold mineralization is hosted in the deformed metavolcanic sequences of the devonian kangbutiebao formation multi isotope analyses were conducted to constrain the ore forming fluid and metal sources of the sarekuobu deposit the measured dv smow values of the fluid inclusions from the mineralized quartz stages ii and iii are of 132 9 to 78 5 the measured 18ov smow values of the quartz range from 11 to 13 6 the corresponding calculated 18oh2o values for the ore fluids 4 2 6 9 which are consistent with those of typical orogenic au deposits worldwide and fall between the metamorphic water and meteoric water fields in the 18oh2o vs dv smow diagram this implies that the ore forming fluids were mainly derived from metamorphic devolatilization with some meteoric water input calcite in the late mineralization stage iii veinlets contains 13cv pdb of 5 2 to 1 2 and 18oov pdb of 20 4 to 19 9 similar to the carbonates limestone and marble of the kangbutiebao formation and plots near the marine continental carbonate field s in the 13cv pdb vs 18oov pdb diagram this suggests that the carbon in the late stage hydrothermal fluids was originated from marine terrestrial carbonates with organic sediment decarboxylation input the 34s values for the au hosting sulfides 1 8 8 2 overlap with the volcanic wall rocks of the kangbutiebao formation 4 7 18 7 which suggests that the sulfur was most likely wall rock derived the sarekuobu sulfides contain 206pb 204pb 207pb 204pb and 208pb 204pb values of 18 071 18 874 15 520 15 669 and 37 860 38 961 respectively the sulfide sr and nd isotopes are featured by their narrow compositional ranges and crustal affinities i e 87sr 86sr i u 202f u 202f 0 70959 0 72216 and calculated end t 3 20000 to 1 86000 all the pb sr and nd isotope compositions of the sarekuobu ore sulfides are similar to those of the kangbutiebao formation wall rocks indicating that the metals were mainly wall rock derived the structurally controlled nature the wall rock metamorphism and alteration styles e g silicic chlorite epidote and carbonate and the abundance of co2 rich and low salinity fluid inclusions of the sarekuobu deposit are similar to typical orogenic au deposits we therefore propose that the sarekuobu au deposit is a typical metavolcanic hosted orogenic au deposit and was likely formed in a triassic collisional related setting

geology geochronology and sulphur isotope geochemistry of the black schist hosted haoyaoerhudong gold deposit of inner mongolia china implications for ore genesis abstract the haoyaoerhudong gold deposit is located in the urad middle banner area of inner mongolia in china and is hosted by black schist of the bilute formation in the mesoproterozoic bayan obo group the gold mineralization is within a 4500 m long and 100 m wide zone associated with sulphide quartz veins following the schistosity and crosscutting fractures in the host rocks locally as disseminated sulphide in altered black schist the sulphide mineral assemblage is pyrrhotite pyrite arsenopyrite chalcopyrite sphalerite and is associated with a weak hydrothermal alteration characterized by a silica halo with variable amounts of biotite sericite and carbonate the bilute formation was intruded by multi stage dykes these include metamorphosed porphyritic diorite that pre dates mineralization unmetamorphosed amphibole olivine gabbro that pre dates mineralization and tourmaline bearing pegmatite that post dates mineralization in order to constrain the timing of the gold mineralization and host rocks zircons from the porphyritic diorite amphibole olivine gabbro and tourmaline bearing pegmatite were extracted for u pb dating gold bearing pyrite samples were analysed for 34 s to help determine the possible source of s in the mineral zones a weighted mean 206 pb 238 u age date of 288 3 ma mswd 2 4 was obtained for the porphyritic diorite a weighted mean 206 pb 238 u age date of 282 1 ma mswd 0 58 was obtained from the amphibole olivine gabbro and a weighted mean 206 pb 238 u age date of 182 1 ma mswd 1 04 was obtained from the tourmaline bearing pegmatite these dates constrain the timing of gold mineralization to between 282 1 and 182 1 ma and are consistent with the hydrothermal alteration ages of ca 267 246 ma reported from the literature these new zircon dates indicate that the regional metamorphism of the bayan obo group ceased by the time the haoyaoerhudong gold mineralization was deposited and the genesis of mineralization is not related to the regional metamorphic event the gold bearing pyrites gave positive 34 s v cdt values between 6 8 and 13 4 and are different from the 34 s widely distributed values for the typical black rocks indicating that the sulphur is not derived from the black bilute formation but sourced from some other relatively uniform reservoir widespread contemporaneous granitic magmatism is developed in the haoyaoerhudong area and we suggest that the sulphur forming the gold bearing sulphides is probably sourced from a carbonate contaminated granitic magma reservoir the new zircon dates for the dykes and the 34 s data for gold bearing sulphides indicate that the gold mineralization did not form from metamorphosed black schist in the bayan obo group but is associated with magmatic hydrothermal activity

the carbon isotopic composition and nitrogen content of lithospheric and asthenospheric diamonds from the jagersfontein and koffiefontein kimberlite south africa asthenospheric diamonds from the jagersfontein kimberlite south africa have a 13c range from 8 9 to 24 4 vs pdb deep diamonds from the nearby koffiefontein mine have 13c values between 2 9 and 6 1 at these two locations asthenospheric diamonds are more frequently nitrogen type ii than type i if they are type i the nitrogen content is low and its state of aggregation is high diamonds from the jagersfontein kimberlite have a bimodal 13c distribution on the basis of the carbon isotopic composition of the hosts and their mineral inclusion composition one can suggest that as many as six distinct diamond source regions were sampled by the kimberlite in the mantle beneath jagersfontein the relative abundance of low 13c diamonds may be higher in the asthenosphere than in the lithosphere in the koffiefontein sample suite asthenospheric and lithospheric diamonds are indistinguishable in 13c the differences in the nature of the relationships between isotope and inclusion chemistry demonstrated by deep diamonds from two diatremes which are very closely associated in space and time indicate a high degree of complexity in mantle carbon geochemistry even within the asthenosphere

genesis of the dadonggou pb zn deposit in kelan basin altay nw china constraints from zircon u pb and biotite 40ar 39ar geochronological data abstract the genesis of polymetallic deposits in southern altay nw china has been disputed between a syngenetic seafloor hydrothermal process and an epigenetic orogenic type mineralization the dadonggou pb zn deposit occurs as nw trending veins in the devonian kangbutiebao formation volcanic sedimentary sequence in the kelan basin southern altay a set of integrated zircon u pb and biotite 40ar 39ar geochronological data were applied to constrain the forming ages of the ores and their country rocks three samples of host volcanic rocks yielded weighted mean 206pb 238u ages of 397 1 4 5 ma 391 7 3 6 ma and 391 1 4 2 ma respectively indicating that the kangbutiebao formation was deposited in a devonian back arc basin two biotite samples separated from the pb zn containing quartz veins yielded 40ar 39ar plateau ages of 205 9 2 1 ma and 204 3 2 2 ma respectively which represent the age of the pb zn mineralization that is attributed to the closure of the kelan back arc basin and the late triassic orogeny combining the available geological and geochronological data this contribution outlines the successive evolution from the development of a devonian back arc basin to the late triassic post subduction orogeny and proposes that the dadonggou pb zn deposit is an epigenetic orogenic type deposit placed in the late triassic orogeny

rb sr geochronology of single gold bearing pyrite grains from the katbasu gold deposit in the south tianshan china and its geological significance abstract the newly discovered katbasu gold deposit in the south tianshan region has a gold reserve of 76 t at an average grade of 3 84 g t it is the first large gold deposit in the central segment of the south tianshan gold mineralization is hosted within granite and is associated with potassic phyllic and chloritic alteration gold bearing pyrite occurs as disseminations in the host rock and as quartz sulfide veins cross cutting the potassic and phyllic alteration assemblage rubidium rb strontium sr analyses on sericite within five individual pyrite grains from a phyllic alteration sample yield an isochron age of 322 5 6 8 ma mswd 3 2 the host granite has a sims u pb zircon age of 351 4 1 1 ma mswd 0 13 the rb sr isochron age represents the mineralizing age of the katbasu gold deposit which significantly postdates the ore hosting granite but is consistent with the age of regional porphyry type mineralization at 320 ma in the south tianshan discovery of the katbasu gold deposits indicates huge potential for gold exploration in the central segment of the south tianshan as it is geologically similar to the western and eastern segments of the south tianshan which both host many world class gold deposits

paleozoic early mesozoic gold deposits of the xinjiang autonomous region northwestern china the late paleozoic early mesozoic tectonic evolution of xinjiang autonomous region northwestern china provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major eastern asia cratonic blocks these sutures are now represented by the altay shan tian shan and kunlun shan ranges with the former two separated by the junggar basin and the latter two by the immense tarim basin in northernmost xinjiang final growth of the altaid orogen southward from the angara craton is now recorded in the remote mid to late paleozoic altay shan accreted early to middle devonian oceanic rock sequences contain typically small precious metal bearing fe cu zn vms deposits e g ashele orogenic gold deposits are widespread along the major irtysh e g duyolanasayi saidi taerde kabenbulake akexike shaerbulake and tuergen hongshanzui e g hongshanzui fault systems as well as in structurally displaced terrane slivers of the western junggar e g hatu and eastern junggar areas geological and geochronological constraints indicate a generally late carboniferous to early permian episode of gold deposition which was coeval with the final stages of altaid magmatism and large scale right lateral translation along older terrane bounding faults the tian shan an exceptionally gold rich mountain range to the west in the central asian republics is only beginning to be recognized for its gold potential in xinjiang in this easternmost part to the range northerly and southerly directed subduction accretion of early to mid paleozoic and mid to late paleozoic oceanic terranes respectively to the precambrian yili block central tian shan was associated with 400 to 250 ma arc magmatism and carboniferous through early permian gold forming hydrothermal events the more significant resulting deposits in the terranes of the southern tian shan include the sawayaerdun orogenic deposit along the kyrgyzstan border and the epithermal and replacement deposits of the kanggurtag belt to the east in the chol tagh range gold deposits of approximately the same age in the yili block include the axi hot springs epithermal deposit near the kazakhstan border and a series of small orogenic gold deposits south of urumqi e g wangfeng gold rich porphyry copper deposits e g tuwu define important new exploration targets in the northern tian shan of xinjiang the northern foothills of the kunlun shan of southern xinjiang host scattered small placer gold deposits sources for the gold have not been identified but are hypothesized to be orogenic gold veins beneath the icefields to the south they are predicted to have formed in the tianshuihai terrane during its early mesozoic accretion to the amalgamated tarim qaidam kunlun cratonic block

the giant muruntau gold deposit geologic geochronologic and fluid inclusion constraints on ore genesis we reinterpret the regional geologic setting of the giant muruntau gold deposit and report new 40 ar 39 ar isotope age determinations and a laser raman microprobe analysis of fluid inclusions new 40 ar 39 ar isotope age determinations of hydrothermal sericite selvages to gold stage quartz veins are in excellent agreement with older rb sr dates on auriferous quartz veins they suggest triassic sericite formation at 245 and 220 ma some 30 m y later than subjacent felsic intrusions as defined by rb sr data these dates call into question the role of magmatic fluid metal and heat input indeed the rb sr pluton ages may be a reflection of hydrothermal activity rather than cooling from magmatic conditions the muruntau deposit is situated adjacent to a major rift which has been periodically active from the devonian to the tertiary and has accumulated a substantial thickness of chemical volcaniclastic and clastic sediments including red beds and evaporites we infer that the muruntau deposit is so large because of the presence of a major source of reduced sulfur in these nearby evaporitic sediments via thermochemical sulfate reduction some support for the role of reduced sulfur is provided by the presence of detectable h2s in fluid inclusions from late stage auriferous quartz veins reduced sulfur rich fluids could have been focused into the depositional site along major northeast trending structures which have influenced rift basin architecture as recently as the jurassic oxidation could therefore be an important ore precipitating mechanism a change from early ch4 to later syngold co2dominant fluid inclusions may be an indication of this process

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

origin of the wunugetushan porphyry cu mo deposit inner mongolia ne china constraints from geology geochronology geochemistry and isotopic compositions abstract the wunugetushan porphyry cu mo deposit is located in the southeastern margin of the mongol okhotsk orogenic belt and in the northwestern segment of the great xing an range ne china the orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith the shrimp zircon u pb dating of the granitic porphyry dyke yielded ages of 201 4 3 1 ma 2 mswd 1 5 these results indicate that the magmatism in the wunugetushan area might have occurred at ca 201 ma in the early jurassic and that the mineralization age ca 181 ma of this deposit is later than the age of intrusive granitic porphyry in the area geochemically the wunugetushan granitoids belong to high k calc alkaline and shoshonitic series enriched in k rb nd and pb and depleted in sr nb ti and p with negative eu anomalies in situ hf isotopic analyses of zircons using la mc icp ms indicate that the ehf t values for zircons from a granitic porphyry sample vary from 2 4 to 11 8 and that the corresponding crustal model ages tdmc vary from 483 to 1088 ma the least altered monzogranitic porphyry granitic porphyry and biotite granite yielded relatively uniform end t values from 1 0 to 0 6 and low 87sr 86sr i ratios ranging from 0 704387 to 0 708385 the geochemical and sr nd hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust the 34s values of sulfides show a narrow range 0 76 to 3 20 similar to those of magmatic sulfur further implying a lower crust origin based on the results of this study and the regional geodynamic evolution it is proposed that the formation of the wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the mongol okhotsk oceanic plate beneath the erguna massif during the early jurassic and that the monzogranitic porphyry intrusions in wunugetushan area probably provided important ore metals responsible for the large scale cu mo mineralization

geology geochronology and s pb os geochemistry of the alastuo gold deposit west tianshan nw china the alastuo gold deposit located in the narati region of the chinese west tianshan is a newly discovered gold deposit within the world class tianshan gold belt the gold mineralization is hosted by an early carboniferous granodiorite intrusion and controlled structurally by subsidiary faults of the transcrustal north narati fault the deposit consists of auriferous alteration assemblages and minor vein ores field relations and petrographic data suggest four stages of mineralization with gold precipitated coevally with quartz chlorite epidote pyrite and galena during the second and third stages that are characterized by tectonic transformation from ductile shearing to brittle deformation the temperature range of gold precipitation is estimated to be 280 330 c using chlorite geothermometry ten auriferous pyrite samples yielded a well defined re os isochron age of 325 3 ma and two sericite samples yielded plateau like 40ar 39ar ages of 321 7 3 0 ma and 321 2 2 8 ma these consistent ages suggest that the gold mineralization in the narati region was emplaced in a transitional regime from subduction to continental collision between the tarim block and middle tianshan terrane 325 310 ma rather than during the post collisional stage as in most part of the tianshan gold belt gold bearing pyrite has an initial osi value of 0 7 0 1 and lead isotopes ratios of 17 897 to 18 723 for 206pb 204pb 15 474 to 15 643 for 207pb 204pb and 37 522 to 38 299 for 208pb 204pb while samples of pyrite galena and sphalerite have 34sv cdt of 1 9 to 7 8 the isotope data suggest that the sulfur and metals are most likely derived from mixed mantle and crustal sources including metamorphic devolatilization of subducted oceanic slab and overlying sedimentary rocks the mineralization styles structural controls metal and sulfur sources and the timing of gold mineralization with respect to the orogenic event all suggest that the alastuo gold deposit represents an orogenic type deposit this newly recognized carboniferous orogenic gold mineralization event calls for a re evaluation of the gold metallogeny in the middle tianshan

fluid inclusion and stable isotope study of the shagou ag pb zn deposit luoning henan province china implications for the genesis of an orogenic lode ag pb zn system abstract the shagou deposit located in the eastern qinling orogenic belt central china and hosted by the taihua supergroup is a large sized ag pb zn deposit and has proven reserves of 1 54 million tons of ore with grades of 767 g t ag 13 24 pb and 4 31 zn the ore forming fluids have been previously interpreted as products of direct exsolution of a crystallizing magma or sudden decompression of the fluid exsolved from magma defining the shagou deposit as an intrusion related system in this study the shagou deposit has been identified as an orogenic type mineralization system the hydrothermal ore forming process can be divided into the early quartz pyrite middle quartz polymetallic sulfides and late quartz carbonate stages four types of fluid inclusions in quartz can be distinguished between pc c w and pw types the early and middle stage quartz contains the pc c and w type fluid inclusions while only w and pw type fluid inclusions can be observed in the late stage quartz in the early stage the w type fluid inclusions homogenized at 173 369 c concentrating at 200 240 c with salinities ranging from 5 4 to 8 3 wt nacl equiv but in the middle stage the c and w type fluid inclusions homogenized at 112 313 c concentrating at 180 220 c with salinities ranging from 0 7 to 13 6 wt nacl equiv in the late stage the w type fluid inclusions homogenized at 108 253 c concentrating at 160 200 c with salinities ranging from 2 1 to 8 1 wt nacl equiv the fluids may have experienced a boiling process or fluid mixing in the middle stage the estimated trapping pressures of fluid inclusions in the middle stage ranged from 33 to 211 mpa corresponding to a mineralization depth from 3 3 to 7 7 km for the early stage fluids the calculated 18 o h 2 o and d h 2 o values are 7 5 9 1 96 2 to 110 5 respectively for the middle stage fluids these two values are 1 5 5 3 75 6 to 110 7 but change to 1 0 and 87 for the late stage suggesting an evolution from metamorphic to meteoric in origin in general the shagou ag pb zn deposit is similar in many respects to typical orogenic type mineralization systems

the relationship between gold mineralization exhumation of metamorphic core complex and magma cooling formation of the anjiayingzi au deposit northern north china craton abstract the anjiayingzi gold deposit is hosted by the jiguanzi quartz monzonite in the footwall of the kalaqin metamorphic core complex mcc at chifeng in the northern part of the north china craton ncc an earlier ca 135 125 ma top to the ne ductile brittle shear and a later ca 121 ma top to the nw and se brittle detachment normal faulting are recognized around the kalaqin mcc the jiguanzi quartz monzonite intruded the footwall of the kalaqin mcc at ca 133 1 ma with crystallization temperatures of 640 691 c pressures of 167 271 mpa and an average depth of 8 6 km gold veins in the anjiayingzi gold deposit are hosted by the monzonite and controlled by the ne trending brittle ductile and brittle fault zones these ore bearing faults are products of a regional sinistral shearing event coinciding with the earlier top to the ne ductile brittle shear at the kalaqin mcc the ore of the anjiayingzi deposit is characterised by its low au ag ratio 2 o co 2 nacl fluid system with salinities of 1 3 15 6 wt nacl equiv trapping pressures of ore fluids were 50 110 mpa corresponding to an average depth of 2 5 km under a lithostatic load and 7 5 km under a hydrostatic load fluid mixing and immiscibility are potential causes for the rapid precipitation of sulphides carrying au the stable isotope d 80 3 to 96 5 and 18 o h 2 o 3 7 to 5 5 of the ore fluids the consistent pb isotope compositions between the ore bearing sulphides and k feldspar from the jiguanzi quartz monzonite and a 2 billion year time gap between the gold mineralization and metamorphism of the basement all indicate that the mineralizing fluids and metals are derived from a concealed intrusion near the major eastern louzidian fault in the kalaqin mcc this proposal is supported by the presence of mafic magmatic enclaves and rhyolite dykes in the jiguanzi quartz monzonite and higher average th total 322 c and 34 s 2 4 of eastern veins than those of western veins with a th total of 287 c and 34 s value of 0 3 the ca 133 126 ma gold mineralization at anjiayingzi was formed during rapid cooling of ca 133 126 ma jiguanzi quartz monzonite at a cooling rate of 42 71 c ma and fast exhumation and cooling of the kalaqin mcc between ca 135 and 121 ma at a cooling rate of 30 c ma this process was accompanied by fluid immiscibility and mixing within the structural transition from ductile brittle to brittle deformation with resultant fluid pressure fluctuations between the supra hydrostatic and hydrostatic regimes

isotope and fluid inclusion geochemistry and genesis of the qiangma gold deposit xiaoqinling gold field qinling orogen china abstract the qiangma gold deposit is hosted in the 1 9 ga taihua supergroup metamorphic rocks in the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided as follows quartz pyrite veins early quartz polymetallic sulfide veinlets middle and carbonate quartz veinlets late stages with gold being mainly introduced in the middle stage three types of fluid inclusions were identified based on petrography and laser raman spectroscopy i e pure carbonic carbonic aqueous co 2 h 2 o and aqueous inclusions the early stage quartz contains pure carbonic and co 2 h 2 o inclusions with salinities up to 12 7 wt nacl equiv bulk densities of 0 67 to 0 86 g cm 3 and homogenization temperatures of 280 365 c the early stage is related to h 2 o co 2 n 2 ch 4 fluids with isotopic signatures consistent with a metamorphic origin 18 o water 3 1 to 5 2 d 37 to 73 the middle stage quartz contains all three types of fluid inclusions of which the co 2 h 2 o and aqueous inclusions yield homogenization temperatures of 249 346 c and 230 345 c respectively the co 2 h 2 o inclusions have salinities up to 10 9 wt nacl equiv and bulk densities of 0 70 to 0 98 g cm 3 with vapor bubbles composed of co 2 and n 2 the isotopic ratios 18 o water 2 2 to 3 6 d 47 to 79 suggest that the middle stage fluids were mixed by metamorphic and meteoric fluids in the late stage quartz only the aqueous inclusions are observed which have low salinities 0 9 9 9 wt nacl equiv and low homogenization temperatures 145 223 c the isotopic composition 18 o water 1 9 to 0 5 d 55 to 66 indicates the late stage fluids were mainly meteoric water trapping pressures estimated from co 2 h 2 o inclusions are 100 285 mpa for the middle stage suggesting that gold mineralization mainly occurred at depths of 10 km fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co 2 rich to co 2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18 o water values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology and fluid inclusion and c h o s pb isotope geochemistry we conclude that the qiangma gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

albian cenomanian a type granite related ag pb zn veins in the central yidun terrane sw china constraints from the xiasai deposit the xiasai lianlong metallogenic belt in the central yidun terrane china hosts several sn ag and sn ag pb zn deposits which are spatially associated with cretaceous granites the xiasai ag pb zn deposit about 0 27 mt pb zn 1028 t ag and 20 000 t sn is the largest deposit in the belt and is related to a monzogranite intrusion the deposit consists of sulfides in hydrothermal veins resulting from three successive mineralization stages i iii a rb sr isochron of sphalerite samples yielded an age of 99 3 ma and zircon u pb laser ablation inductively coupled plasma mass spectrometry la icp ms dating of the xiasai monzogranite gave ages between 102 1 and 101 1 ma the xiasai monzogranite has a weakly peraluminous a type granite composition with high sio2 alkali and feot contents and low cao mgo and tio2 contents it is marked by enrichments in rb th and u with depletions in ba nb sr p and ti relative to the primitive mantle the ree patterns show a negative slope due to lree enrichment with negative eu anomalies eu eu 0 1 0 3 the xiasai monzogranite with variable ehf t values 2 7 to 0 6 and meso to neoproterozoic two stages hf model ages tdm2 925 1095 ma was probably derived from mixing of melts derived from partial melting of the paleoproterozoic crustal basement and the early cretaceous mantle in an extensional tectonic setting hydrothermal fluids are characterized by high temperatures 423 481 c and salinities 14 9 19 0 wt nacl for sn mineralization stage i moderate temperatures 285 386 c and salinities 3 5 8 0 wt nacl for the cu zn mineralization substage ii 2 and low temperatures 158 242 c and salinities 3 4 5 7 wt nacl for the ag pb mineralization substage ii 3 the h o isotopes indicate that the hydrothermal fluid likely has a magmatic component that mixed over time with infiltrating meteoric water and organic matter during fluid rock interactions the 34s values of sphalerite range from 9 7 to 3 1 and those from galena from 10 5 to 4 9 the estimated 34s value of the hydrothermal fluid is 8 5 using the sulfur isotopic fractionation of sphalerite galena pairs that are interpreted to be in equilibrium sulfides from substages ii 2 and ii 3 have relatively homogeneous pb isotopic compositions which are similar with those of k feldspars from the xiasai monzogranite geochronological and isotope data support a magmatic hydrothermal origin for the xiasai ag pb zn deposit

a fluid inclusion study of au bearing quartz vein systems in the central and north deborah deposits of the bendigo gold field central victoria australia the central and north deborah gold deposits with a production of about 7 tons au are located in one of 15 domes in the bendigo gold field central victoria australia an important mesothermal lode gold province the gold bearing quartz vein systems are hosted predominantly by reverse faults in lower ordovician turbidites which underwent lower greenschist facies metamorphism in the central and north deborah mines there are six stages of quartz veins that developed in the following sequence 1 laminated veins with a metal association of au as sb pb zn ni 2 spurs au 3 massive barren veins main dilation stage 4 brecciated veins with au as 5 quartz ankerite veinlets and 6 late pure quartz or calcite veinlets of the three mineralized vein stages 1 2 and 4 only the first one predated or was coeval with the main deformation event whereas stages 2 and 4 postdated the main deformation the vein structures indicate that vein development was controlled by repeated fluctuations of fluid pressure inducing hydraulic fracturing fluid inclusions in vein quartz contain c o h fluids of variable compositions three main types of fluid inclusions are recognized at room temperature type i two phase primary ch4 v h2o l fluid inclusions type ii two or three phase primary pseudosecondary co2 v or l ch4 v or l h2o l fluid inclusions including iia ch4 co2 h2o and iib co2 h2o fluid inclusions and type iii h2o v h2o l fluid inclusions type iii fluid inclusions are further divided into three groups iiia primary pseudosecondary vapor rich iiib primary pseudosecondary liquid rich and iiic secondary liquid rich data from fluid inclusion distribution microthermometry and raman spectroscopy indicate that fluids associated with au mineralized quartz veins stages 1 2 and 4 have moderate salinity ranging from 0 to 12 wt percent nacl equiv modeled salinities around 7 8 wt nacl equiv these veins formatted at temperatures from 325 to 375 c and pressures of 200 to 300 mpa with emplacement depths of about 8 to 12 km fluids associated with barren quartz veins stages 3 5 and 6 have a low salinity of about 0 to 3 wt percent nacl equiv modeled salinities about 2 3 wt nacl equiv and lower temperatures there is evidence of fluid immiscibility in all vein stages and mixing between fluids of the same souce but differing fo2 may also have influenced gold deposition cox et al 1995 hydrothermal ore forming fluids responsible for gold mineralization are in the ch2 co2 h2o nacl system whereas those of massive barren veins stage 3 and veinlets stages 5 and 6 are in the co2 h2o nacl and h2o nacl systems respectively the carbonic phases of type i and ii fluid inclusions range from pure ch4 through mixed ch4 and co2 to pure co2 gold ore forming fluids were weakly acidic with f o2 estimated to have been 10 25 to 10 37 bars and generally above the co2 ch4 and below the so2 h2s buffer boundaries throughout gold mineralization the relatively reduced mineralizing fluids are similar to those of other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes

formation of the baiyun gold deposit liaodong gold province ne china constraints from zircon u pb age fluid inclusion and c h o pb he isotopes abstract the baiyun gold deposit is located in the liaodong peninsula in ne china the gold orebodies are hosted in the paleoproterozoic liaohe group metamorphic rocks the alteration mineralization can be divided into three stages i quartz pyrite k feldspar veins ii quartz polymetallic sulfide veins iii quartz carbonate veins new la icp ms zircon u pb dating suggests all the ore related porphyries including monzonite porphyry 224 2 1 3 ma quartz porphyry 221 4 1 2 ma and diorite porphyry 221 8 1 2 ma were emplaced in the late triassic four types of fluid inclusions fis are identified in the ore related quartz i e liquid rich two phase vapor rich two phase co2 bearing and pure co2 fis the ore forming fluids were likely characterized by medium temperature low salinity low density co2 rich and belong to the h2o nacl co2 n2 c4h6 system we propose that fluid phase separation likely caused rapid precipitation of the ore minerals the c h o pb isotope data indicate that the ore forming fluids may have had multiple sources including magmatic metamorphic and meteoric fluids the ore forming materials may have mainly derived from metamorphic rocks of the proterozoic gaixian formation and minor from the triassic intermediate felsic rocks the he ar isotope data indicate that the ore forming fluids were mainly crust derived we conclude that the baiyun gold deposit is an orogenic type system formed during the late triassic north china yangtze continent continent collision

evolution of ore forming fluids in the sawayaerdun gold deposit in the southwestern chinese tianshan metallogenic belt northwest china the sawayaerdun gold deposit was discovered in the early 1990s and is the largest orogenic gold deposit in the chinese tianshan gold mineralization occurs in quartz veins which are hosted in carbonaceous metasediments and controlled by faults and fractures three major hydrothermal events can be identified at sawayaerdun an early barren quartz vein stage middle stage quartz veins with pyrite and gold mineralization and late carbonate quartz veins fluid inclusion studies of quartz pyrite and carbonate formed during the major hydrothermal stagesshow distinct changes in fluid temperature composition and redox conditions occurred during fluid evolution three types of fluid inclusions have been identified at sawayaerdun h2o nacl l v h2o nacl co2 l v and co2 l v fluids trapped in early barren quartz have high temperatures 280 420 c low salinities 3 wt nacl equiv high cl and are co2 rich middle stage quartz contains fluids with lower temperatures 210 310 c and variable salinities 0 8 17 5 wt nacl equiv they are commonly s rich co2 containing and relatively reduced compared with early stage fluids in contrast hydrothermal pyrite hosted in middle stage quartz veins trapped fluids formed over a narrower temperature range 220 270 c more oxidized high co2 ch4 ratio and have higher ca k and mg than fluids in quartz late stage carbonate is dominated by fluids with low temperatures 200 c and low contents of cl s and k fluid immiscibility probably commenced at the onset of mineralization along with middle stage quartz formation resulting in the generation of coexisting fluid inclusions with distinguishable vapor liquid ratios and salinities the compositional difference between fluids trapped in pyrite and quartz indicate fluid mixing may have occurred during the mineralization stage the oxidized fluids probably a mixture of meteoric water and fluids generated during water host rock interaction emerged into the ore forming system to generate extensive metals precipitation the fluid immiscibility and fluid mixing are most likely caused by pressure decrease during late paleozoic uplift and erosion in the chinese southern tianshan area comparison of fluids between four major mineralization zones at sawayaerdun indicate that zone ii is similar to the most important zone iv and the order of similarity is probably zone ii xi i which could be applied to the future mineral exploration in this area

ore genesis of the weibao lead zinc district eastern kunlun orogen china constrains from ore geology fluid inclusion and isotope geochemistry the weibao lead zinc district composed by two deposits named the east weibao deposit and the west weibao deposit respectively is located in the qimantagh area eastern kunlun orogen although both controlled by skarn alternation and experienced similar mineralization processes the east weibao deposit is dominated by massive ores while the west weibao deposit is characterized by banded ores the ore forming processes of both the deposits can be divided into four stages including prograde skarn stage retrograde skarn stage sulfide stage and carbonate stage three types of fluid inclusions i e pure co2 fluid inclusion pc type co2 bearing fluid inclusion c type and aqueous types w type have been identified in quartz calcite and sphalerite from different stages noteworthily only sulfide stage of the east weibao deposit contains carbonic fluid inclusions whereas only aqueous fluid inclusions were observed in sulfide stage of the west weibao deposit the co2 rich and aqueous type fluid inclusions in sulfide stage of the east weibao deposit were homogenized at temperatures between 263 and 424 c concentrating at 360 400 c with salinities ranging between 3 2 and 13 6 wt nacl eqv the w type fluid inclusions in sulfide stage of the west weibao deposit were homogenized at temperatures between 228 and 381 c concentrating at 280 340 c with salinities between 1 6 and 9 0 wt nacl eqv and the aqueous type fluid inclusions in carbonate stage in both deposits were homogenized at temperatures between 115 and 336 c concentrating at 200 240 c with salinities between 0 2 and 5 9 wt nacl eqv the ore forming fluid in sulfide stage at the east weibao deposit yielded calculated updelta 18 text o text h 2 text o and 18d values of 4 2 to 5 6 and 88 to 83 respectively the results are 8 8 to 10 8 99 to 92 for the sulfide stage at the west weibao deposit and 1 0 to 0 2 50 to 45 for carbonate stages in both deposits the lead isotopic ratios of sulfide samples from the weibao lead zinc district range between 18 259 and 18 336 for 206pb 204pb 15 580 and 15 659 for 207pb 204pb and 38 007 and 38 253 for 208pb 204pb respectively and the corresponding sulfur isotopic values range between 2 2 and 3 6 the fluid inclusion and isotope studies on the two deposits in the weibao lead zinc district suggest that they both have magmatic origin but mineralized by different mechanisms mineralization at the east weibao deposit may be caused by fluid immiscibility and mixing while at the west weibao deposit mineralization may result from water rock reactions between magmatic fluid and impure carbonate wall rocks combined with geological observation we conclude that the weibao lead zinc district as a united magmatic hydrothermal fluid system associated with the triassic magmatism that widely distributes in the qimantagh area

the determination of progressive deformation histories from antitaxial syntectonic crystal fibres abstract antitaxial syntectonic crystal fibres are modelled here as mechanically passive features the fibres representing displacement paths forming within a homogeneously deforming material evidence that many fibres develop in this way is widespread asymptotic curvature thinning of fibres and strained old fibres a measuring technique is proposed by which the complete deformation history excluding translation may be determined the method involves the iterative unstraining of two complete fibres whose development began and ended simultaneously a source of error is introduced by assuming that each of the two fibres developed at constant proportional rates although synthetic examples suggest this error to be minimal it is suggested that the kinematics of non passive fibres are unobtainable since the rheologies and boundary conditions of the material involved are relatively unknown and cannot be determined from geometry alone analysis of natural fibres found within the ordovician slates in new jersey u s a indicates that volume losses of up to 50 may occur during the formation of some slates general constraints concerning the geometrical analysis of syntectonic crystal fibres are briefly discussed and it is concluded that deformation histories must be interpreted with some modicum of caution

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

the first precambrian gold deposit in north xinjiang nw china geochronology metallogenic character and ore genesis of the dajingou gold deposit abstract the dajingou gold deposit is one of the typical gold deposits in the quruqtagh metamorphic terrane north of the tarim craton the deposit mainly comprises gold bearing quartz veins hosted in precambrian metamorphic rocks and structurally controlled by the subsidiary faults and ductile shear zone to determine the age of gold mineralization in the dajingou deposit a single sericite 40ar 39ar age of 829 4 4 8 ma mswd 0 57 and hydrothermal zircon weighted average u pb ages 812 15 ma mswd 3 2 from auriferous quartz veins were obtained in this study indicating that mineralization occurred in the mid neoproterozoic ca 0 83 ga corresponding to regional metamorphism of the tarim craton termed the tarim orogeny the dajingou deposit is the first precambrian gold deposit identified in north xinjiang nw china the 18o and d of quartz ranges from 14 7 to 15 9 and 104 to 75 respectively the calculated 18oh2o of the fluids ranges from 0 9 to 5 0 this suggests that the ore forming fluids in the dajingou gold deposit were derived from dehydration of metamorphic rocks during regional metamorphism with a subsequent input of meteoric water based on its similarities with typical orogenic gold deposits the dajingou deposit is proposed to be an orogenic gold deposit formed during the mid neoproterozoic tarim orogeny in the tarim craton

an isotopic c o sr study of vein gold deposits in the meguma terrane nova scotia implication for source reservoirs vein quartz carbonate and tourmaline from 19 meguma gold deposits in the meguma terrane of nova scotia have been analyzed for stable delta 18 o delta 13 c and radiogenic 87 sr 86 sr isotopes in order to assess the nature and origin of the vein forming fluids as with other mesothermal gold provinces the meguma gold deposits are well suited to such a study because carbonate is the next most abundant phase after quartz in these mesothermal lode gold deposits all vein types have been sampled for quartz and carbonate and in addition all compositional and textural varieties of carbonate have been sampled vein quartz is of uniform isotopic composition with most 18 o values between 10 2 to 17 6 per mil avg ca 14 per mil except for one deposit west gore sb au where values go to 19 4 per mil there is no systematic variation for quartz within a deposit or position within the meguma group stratigraphy vein carbonate 18 o values range from 11 8 to 27 5 per mil with most in the 13 to 16 per mil range the relatively 18 o enriched carbonates reflect exchange with low temperature fluids based on analyses of quartz carbonate pairs that indicate disequilibrium fractionation delta sub quartz carbonate or 0 this is best illustrated by the strong negative correlation between delta 18 o carbonate and delta sub quartz carbonate the 18 o water is estimated at 10 or 3 per mil for a temperature of vein formation of 350 degrees to 400 degrees c and using the appropriate mineral water fractionation equations whereas delta 18 o water values partly overlap the field for magmatic fluids the values are wholly consistent with a metamorphic fluid and it is considered unlikely that a primary magmatic fluid signature has been substantially modified due to wall rock influences given that mesothermal gold systems are sites of high fluid rock ratios vein carbonate has delta 13 c values of 13 1 to 25 9 per mil but a slight negative correlation between delta 13 c carbonate and delta sub quartz carbonate suggests that the primary values lie in the range 20 to 25 per mil thus the delta 13 c values indicate a reduced biogenic source for the carbon oxidation of the reduced carbon as indicated by co 2 in fluid inclusions may have occurred via hydrolysis of graphite or dissolution of carbonate minerals both of which occur in the wall rock lithologies of the meguma group the latter of which has the appropriate isotopic composition the initial 87 sr 86 sr of the vein fluid estimated from the analyses of 52 vein carbonates 17 deposits and four tourmalines three deposits ranges from 0 70118 to 0 72284 and within deposits considerable variation is observed there is insufficient data to quantify the extent of the low temperature overprint which has modified the c and o isotope data although it is likely that some influence is present nevertheless the data cannot be reconciled by a source confined exclusively to the meguma group which suggests therefore involvement of another reservoir s the isotopic heterogeneity can be explained by variable amounts of contamination of a primary fluid with radiogenic sr derived from meguma group lithologies by interaction along the fluid path or at the site of vein formation concomitant with wall rock alteration as discussed above a dominantly magmatic source is not considered feasible this fluid source is suggested to be within the structural basement to the meguma group and the liscomb gneisses are the favored source based on the combined results of the sr isotope data presented herein and previously published pb isotope data collectively the data indicate that a primary fluid of metamorphic origin has had its isotopic signature variably modified due to interaction with different reservoirs the most affected isotopic systems are c and s based on earlier work on delta 34 s values which are abundant as graphite carbonate and sulfides in the meguma wall rock respectively the range in 87 sr 86 sr values of the fluid also reflects contamination but this was quite variable the uniform delta 18 o water value for the fluid indicates that this was the least affected isotopic system except for the later exchange of carbonate at low temperatures

lead isotope composition of caledonian sulfide bearing veins in sweden linear trend in the 207 pb 204 pb vs 206 pb 204 pb diagram extending from a normal caledonian lead composition 206 pb 204 pb nearly equal 17 9 to highly radiogenic values 206 pb 204 pb nearly equal 26 0 early proterozoic svecokarelian basement as source of the radiogenic component selective leaching of different minerals in the svecokarelian rocks and mixing with various proportions of nonradiogenic caledonian magmatic lead modified journal abstract

metallogenesis of the hengjiangchong gold deposit in jiangnan orogen south china abstract the hengjiangchong gold deposit is located in northeastern hunan of the central jiangnan orogen south china distribution of auriferous sulfide calcite quartz vein type orebodies are controlled by nw wnw trending ductile shear zones and hosted in the lengjiaxi group gp low grade metamorphic sequences and the hengjiangchong granite ore minerals include mainly pyrite arsenopyrite pyrrhotite chalcopyrite sphalerite galena and native gold whilst the major alteration styles include silicic sericite carbonate and chlorite alteration mineralization can be divided into three stages quartz calcite pyrite arsenopyrite mineralization stage 1 quartz calcite polymetallic sulfide mineralization stage 2 and quartz calcite ore barren alteration stage 3 two types of fluid inclusion fi are present in the auriferous sulfide calcite quartz ore veins co2 bearing c and h2o rich w type petrographic and microthermometric analyses of the fis yielded homogenization temperatures for stage 1 2 and 3 to be 254 377 191 339 and 134 223 c respectively with corresponding salinities of 2 22 10 37 2 23 9 98 and 1 56 4 94 wt naclequiv pressures of stage 1 and 2 mineralization are estimated to be 280 370 and 170 300 mpa respectively 18o and d values are determined to be 9 8 10 1 and 70 2 to 68 7 stage 1 7 4 8 1 and 72 4 to 71 2 stage 2 and 2 7 to 2 9 and 79 1 to 73 0 stage 3 respectively these results indicate that the primary ore forming fluids were derived from a metamorphic source for the auriferous sulfides their 34s values are of 15 4 to 7 5 whilst their 208pb 204pb 207pb 204pb and 206pb 204pb values are of 38 663 44 861 15 637 15 769 and 18 301 20 936 respectively both the stable and radiogenic isotopic data indicate that ore forming fluids and metals were derived from a deeper and higher metamorphic grade source e g underlying metamorphosed rocks fluid immiscibility and fluid rock interactions were likely critical for the gold ore precipitation the hengjiangchong deposit exhibits many features of orogenic gold deposits such as the structural control on orebody distribution alteration and mineralization styles and fi microthermometric and h o s pb isotopic features therefore the hengjiangchong is best classified as an orogenic gold deposit

ore genesis of axi post collisional epithermal gold deposit western tianshan nw china constraints from u pb dating hf isotopes and pyrite in situ sulfur isotopes abstract the axi gold deposit has long been regarded as a typical paleozoic low sulfidation epithermal deposit located in the western tianshan in the central asian orogenic belt caob sims zircon u pb dating of the ore bearing andesite and dacite yielded concordia ages of 350 8 2 7 ma and 351 3 3 1 ma respectively in situ sims hydrothermal rutile u pb dating yielded two 207pb corrected ages as 306 1 16 9 ma and 303 8 14 6 ma respectively these ages are considerably younger than the zircon sims u pb ages of ore bearing volcanic rocks which precludes a genetic link between the epithermal gold mineralization and the subduction related late devonian early carboniferous magmatism in the western tianshan instead the gold mineralization is interpreted to be genetically related to a buried 300 ma pluton that formed in a post collisional environment combined with previously published zircon hf isotopic compositions of 300 ma felsic intrusive rocks from western tianshan the results show that 300 ma felsic rocks have higher zircon ehf t values than those from 351 ma felsic rocks in the axi deposit these elevated ehf t values suggest that mantle material inputs of 300 ma axi epithermal deposit in a post collisional environment pyrite the most common sulfide in the axi ores displays heterogeneous textures and has a large variation of as contents and sulfur isotopes suggesting complex ore forming processes in the axi deposit this study highlights the importance of in situ isotopes of hydrothermal minerals to decode the ore forming histories of epithermal systems

geology c h o s pb isotope systematics and geochronology of the yindongpo gold deposit tongbai mountains central china implication for ore genesis abstract the yindongpo gold deposit is located in the weishancheng au ag dominated polymetallic ore belt in tongbai mountains central china the ore bodies are stratabound within carbonaceous quartz sericite schists of the neoproterozoic waitoushan group the ore forming process can be divided into three stages represented by early barren quartz veins middle polymetallic sulfide veinlets and late quartz carbonate stockworks with most ore minerals such as pyrite galena native gold and electrum being formed in the middle stage the average 18owater values changed from 9 7 in the early stage through 4 9 in the middle stage to 5 9 in the late stage with the d values ranging between 65 and 84 the 13cco2 values of ore fluids are between 3 7 and 6 7 with an average of 1 1 the h o c isotope systematics indicate that the ore fluids forming the yindongpo gold deposit were probably initially sourced from a process of metamorphic devolatilization and with time gradually mixed with meteoric water the 34s values range from 0 3 to 5 2 with peaks ranging from 1 to 4 fourteen sulfide samples yield 206pb 204pb values of 16 990 17 216 207pb 204pb of 15 419 15 612 and208pb 204pb of 38 251 38 861 both s and pb isotope ratios are similar to those of the main lithologies of the waitoushan group but differ from other lithologic units and granitic batholiths in the tongbai area which suggest that the ore metals and fluids originated from the waitoushan group the available k ar and 40ar 39ar ages indicate that the ore forming process mainly took place in the period of 176 140 ma during the transition from collisional compression to extension and after the closure of the oceanic seaway in the qinling orogen the yindongpo gold deposit is interpreted as a stratabound orogenic style gold system formed during the transition phase from collisional compression to extension the ore metals in the waitoushan group were extracted transported and then accumulated in the carbonaceous sericite schist layer the carbonaceous sericite schist layer especially at the junction of collapsed anticline axis and fault structures became the most favorable locus for the ore bodies

dating the xiaobaishitou skarn w mo deposit eastern tianshan nw china constraints from zircon u pb muscovite 40ar 39ar and molybdenite re os system abstract the xiaobaishitou deposit 36 264 tonnes 0 78 wt wo3 in the eastern tianshan orogenic belt is a medium sized skarn deposit characterized by w mo ore bodies that developed along contacts between triassic biotite granite and mesoproterozoic carbonaceous rocks scheelite and molybdenite are the dominant metallic minerals in this deposit and mostly precipitated during the retrograde stage and or quartz sulfide stage respectively laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms zircon u pb dating of the mineralization related biotite granites from underground openings and outcrops yields ages of 247 9 1 7 ma 1 n 22 mswd 0 69 and 252 2 3 0 ma 1 n 12 mswd 1 60 implying they were emplaced in the early triassic a muscovite 40ar 39ar weighted plateau age of 247 6 2 3 ma 2 mswd 2 03 and molybdenite re os model ages ranging from 235 8 5 7 ma to 249 6 3 6 ma weighted mean age 251 1 1 6 ma 2 mswd 0 70 are interpreted as the time of the hydrothermal activity mineralization the excellent agreement among the u pb 40ar 39ar and re os chronometers confirms that the xiaobaishitou deposit formed in the early triassic the re contents of the molybdenites range from 18 477 to 130 447 ng g suggesting that the ore forming materials were derived from continental crust together with the involvement of abundant mantle components as one of the representative triassic deposit in eastern tianshan the xiaobaishitou provides important chronological evidence for metallogenic regularity in the eastern tianshan and the central asian orogenic belt the new ages reported here confirm that the xiaobaishitou deposit represents one of the magmatic hydrothermal mineralization events that occurred in the eastern tianshan orogenic belt in lithospheric extension during the triassic it is suggested that mantle material played a role in producing the triassic mineralization and associated magmatism

mid ludfordian coeval carbon isotope natural gamma ray and magnetic susceptibility excursions in the mielnik ig 1 borehole eastern poland dustiness as a possible link between global climate and the silurian carbon isotope record abstract the graptolite bearing upper silurian succession of the mielnik ig 1 borehole eastern poland represents a periplatform setting on a neritic carbonate platform located on the palaeocontinent of baltica and records widely recorded positive mid ludfordian carbon isotope excursion cie the initial increase of 13 c values occurs in the uppermost part of the neocucullograptus kozlowskii zone whereas pronounced increase and maximal values 6 74 are noted in the n kozlowskii pseudomonoclimacis latilobus interzone pristiograptus dubius bloom interval the thickness time relation in the section indicates that the main initial shift in carbon isotope ratio of 2 7 occurred over a very short time estimated to be around 4000 years and is coeval with a rapid initiation of deposition of rock forming silt sized detrital dolomite and quartz the cie decline is interpreted as steeper than in inner shelf sections and is coincident with a flooding event in the ps latilobus slovinograptus balticus zone whereas the end of the excursion is coeval with the next flooding surface marked by the ps latilobus uncinatograptus acer graptolite assemblage combined sgr spectral gamma ray facies and faunal records during the cie suggest prolonged sea level lowstand conditions the abundant detrital material dolomite siltstone facies occurring exclusively in the cie interval is noted in microfacies as well as in the geophysics record as pronounced negative excursions in total natural gamma ray and magnetic susceptibility both resulting from dilution by diamagnetic and low radioactivity minerals the perfectly sorted vertically equally sized silt material contains unique constant and low diversified grain assemblage euhedral dolomite quartz minute ooids suggesting its provenance exclusively from the shallower and or emerged parts of the carbonate platform interior the spot findings of graptolites and nautiloids along with delicate parallel lamination of sediments indicates relatively deep environment with absence of traction processes these features along with the lack of dolomite detritus in accompanying redeposited carbonates suggest its derivation by wind with regard to the earlier noted presence of aeolian detritus in the middle ludfordian we suggest dustiness as a plausible driving force of the cie in the hypothesis proposed bioavailable fe bearing dust inflow in concert with antiestuarine circulation on shelfs caused nutrient n p ratio disturbances resulting in methanogenesis in surface layer of the seas the surface layer methanogenesis should resulting in bathymetric gradient of isotope fractionation what is consistent with the cie record coincidence of sea level lowstand low latitude aridity and gustiness of the global climate are in accordance with the hypothetical short lived glaciation in mid ludfordian time