the mokrsko west gold deposit bohemian massif czech republic mineralogy deposit setting and classification abstract the mokrsko west deposit is unique among european variscan gold deposits from the points of view of both the structure an approx 200 m thick complex of sheeted several mm thick densely spaced quartz veins and the economic viability gold reserves of about 100 t the deposit is hosted mainly by tonalite of the calc alkaline sazava tonalite suite ca 354 ma of the central bohemian plutonic complex mineralization is characterized by quartz dominated gangue no visible hydrothermal alteration low sulfide content high fineness native gold accompanied by maldonite aurostibite native bismuth and numerous bi te s phases five mineralogical stages are described in great detail arsenopyrite and chlorite thermometers mineral phase stabilities and published isotope and fluid inclusion data are used to reconstruct the temperature and compositional evolution of the system the role of liquid bismuth in the sequestration of gold is also discussed the deposit shares the features of both orogenic gold org and intrusion related gold irg deposits the irg model is advocated by close spatial association between the ore zone and the tonalite host intrusion by the absence scarcity of hydrothermal alteration by the au bi te as elemental association and by marked thermal gradients from the early to late mineralization stages the org model is advocated by an approx 15 10 ma gap between the intrusion of the tonalite host and the ore formation by isotope and geochemical evidence for a key role of metamorphic fluids in the mobilization and transfer of many elements species inclusive s and au the apparently ambiguous classification of the deposit can most probably be attributed to deposit formation at a depth of 9 km and to setting of the deposit at inside a large scale plutonic complex with multiple and prolonged tectonic and intrusive activity

a fluid inclusion and isotopic study of an intrusion related gold deposit irgd setting in the 380 ma south mountain batholith nova scotia canada evidence for multiple fluid reservoirs a set of sheeted quartz veins cutting 380 ma monzogranite at sandwich point nova scotia canada provide an opportunity to address issues regarding fluid reservoirs and genesis of intrusion related gold deposits the quartz veins locally with arsenopyrite 5 and elevated au bi sb cu zn occur within the reduced south mountain batholith which also has other zones of anomalous gold enrichment the host granite intruded p 3 5 kbars lower paleozoic metaturbiditic rocks of the meguma supergroup well known for orogenic vein gold mineralization relevant field observations include the following 1 the granite contains pegmatite segregations and is cut by aplitic dykes and zones 1 2 m of spaced fracture cleavage 2 sheeted veins containing coarse comb textured quartz extend into a pegmatite zone 3 arsenopyrite bearing greisens dominated by f rich muscovite occur adjacent the quartz veins and 4 vein and greisen formation is consistent with riedel shear geometry although these features suggest a magmatic origin for the vein forming fluids geochemical studies indicate a more complex origin vein quartz contains two types of aqueous fluid inclusion assemblages fia type 1 is a low salinity 3 wt equivalent nacl with minor co2 2 mol and has th 280 340 c in contrast type 2 is a high salinity 20 25 wt equivalent nacl ca rich fluid with th 160 200 c pressure corrected fluid inclusion data reflect expulsion of a magmatic fluid near the granite solidus 650 c that cooled and mixed with a lower temperature 400 c wall rock equilibrated ca rich fluid evidence for fluid unmixing an important process in some intrusion related gold deposit settings is lacking stable isotopic o d s analyses for quartz muscovite and arsenopyrite samples from vein and greisens indicate the following 1 18oqtz 11 7 to 17 8 and 18omusc 10 7 to 11 2 2 dmusc 44 to 54 and 3 34saspy 7 8 to 10 3 these data are interpreted in conjunction with fluid inclusion data to reflect contamination of a magmatic derived fluid delta 18 hbox o rm h 2 rm o 10 by an external fluid delta 18 hbox o rm h 2 rm o 15 the latter having equilibrated with the surrounding metasedimentary rocks the 34s data are inconsistent with a direct igneous source based on other studies for the host intrusion delta 18 hbox o rm h 2 rm o 5 and are instead consistent with an external reservoir for sulphur based on 34sh2s data for the surrounding metasedimentary rocks divergent fluid reservoirs are also supported by analyses of pb isotopes for pegmatitic k feldspar and vein arsenopyrite collectively the data indicate that the vein and greisen forming fluids had a complex origin and reflect both magmatic and non magmatic reservoirs thus although the geological setting suggests a magmatic origin the geochemical data indicate involvement of multiple reservoirs these results suggest multiple reservoirs for this intrusion related gold deposit setting and caution against interpreting the genesis of intrusion related gold deposit mineralization in somewhat analogous settings based on a limited geochemical data set

the krasna hora milesov and přicovy sb au ore deposits bohemian massif mineralogy fluid inclusions and stable isotope constraints on the deposit formation the krasna hora milesov and p icovy districts czech republic are the unique examples of sb au subtype orogenic gold deposits in the bohemian massif they are represented by quartz stibnite veins and massive stibnite lenses grading into low grade disseminated ores in altered host rocks gold postdates the stibnite and is often replaced by aurostibite the ore zones are hosted by hydrothermally altered dikes of lamprophyres krasna hora milesov or are associated with local strike slip faults p icovy formation of sb au deposits probably occurred shortly after the main gold bearing event 348 338 ma au only deposits in the central part of the bohemian massif fluid inclusion analyses suggest that stibnite precipitated at 250 to 130 c and gold at 200 to 130 c from low salinity aqueous fluids the main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 c early quartz arsenopyrite veins are not associated with the sb au deposition and formed from low salinity aqueous carbonic fluid at higher pressure and temperature 250 mpa 400 c the estimated oxygen isotope composition of the ore bearing fluid 4 1 smow based on post ore calcite suggests its metamorphic or mixed magmatic metamorphic origin and excludes the involvement of meteoric water rapid cooling of warm hydrothermal fluids reacting with cold host rock was probably the most important factor in the formation of both stibnite and gold

dating the onset of variscan crustal exhumation in the core of the bohemian massif new u pb single zircon ages from the high k calc alkaline granodiorites of the blatna suite central bohemian plutonic complex abstract the variscan central bohemian plutonic complex crops out between the upper crustal tepla barrandian and the high grade moldanubian units bohemian massif much of the complex is made up of calc alkaline plutonic rocks 1 the geochemically more primitive na rich 354 4 ma sazava suite which was emplaced syntectonically during regional shortening 2 the younger more evolved potassic blatna suite which records both the shortening along its nw contact and the onset of normal shearing related to exhumation of the moldanubian unit to the se new ion microprobe u pb zircon ages for the high k calc alkaline blatna suite pinpoint this major switch in the tectonic regime both blatna and kozarovice granodiorites 346 2 ma and 347 2 ma 2 were generated by melting of heterogeneous crust and were emplaced contemporaneously to form the blatna composite pluton from age spectra preserved in inherited zircons and whole rock sr nd isotope signatures the likely crustal sources for the magmas were immature greywackes rich in neoproterozoic 615 10 ma kozarovice or late cambrian early ordovician 492 4 ma blatna volcanogenic detritus an additional important petrogenetic process was variable mixing with enriched mantle derived monzonitic magmas which may also have supplied the extra heat for crustal anatexis supplementary material analytical techniques selected whole rock major and trace element geochemical analyses and u th pb data are available at http www geolsoc org uk sup18391

the dewulu reduced au cu skarn deposit in the xiahe hezuo district west qinling orogen china implications for an intrusion related gold system abstract the triassic west qinling orogen which formed by the continental collision between the south china block and north china craton following the subduction and closure of the paleo tethyan ocean hosts numerous gold deposits that have commonly considered as products of metamorphic dehydration during the oceanic subduction and subsequent continental collision however whether or not there are gold deposits that are genetically related to regional magmatism remains poorly understood here we present mineralogical compositional and geochronological data of the dewulu au cu skarn deposit in the xiahe hezuo district to understand the ore genesis and its genetic link to many coeval sediment hosted disseminated and magmatic hosted vein gold deposits in the same district which collectively reveal a possible intrusion related gold system the dewulu au cu skarn deposit in the eastern zone of the xiahe hezuo district is associated with the early triassic i type ilmenite series dewulu quartz diorite pluton that intrudes permian marine clastic and carbonate rocks ore related hydrothermal biotite separates yield a well defined 40ar 39ar plateau age of 239 9 1 4 ma 2 which agrees with a previous zircon u pb age 238 6 1 5 ma at 2 of the dewulu quartz diorite and thus demonstrates a temporal and likely genetic link between the two both prograde and retrograde skarn assemblages are well developed in the dewulu au cu deposit prograde garnet and pyroxene are compositionally dominated by grossularite and hedenbergite respectively indicating a reduced skarn system au cu mineralization is largely represented by the arsenopyrite loellingite chalcopyrite pyrrhotite bornite assemblage and is associated with retrograde skarns gold is mostly hosted in arsenopyrite loellingite and chalcopyrite and has close textural relations with native bismuth or bismuthides mineral stability relationships and fluid inclusion microthermometric data confirm that the prograde skarns formed at a low oxygen fugacity high temperature 630 c and a depth range of 2 9 to 6 5 km arsenopyrite and chlorite geothermometers indicate that the retrograde skarns and late quartz sulfide calcite assemblages formed at 550 to 345 c and

cu and mo re enrichment during ductile deformation a case study of the yuleken porphyry cu deposit eastern junggar nw china abstract porphyry cu deposits can be strongly deformed during subsequent tectonic evolution to date research pertaining to the deformation and the enrichment of mineralization in porphyry deposits has suffered from a paucity of proof here we describe the diagnostic petrologic and geochemical signatures of the yuleken porphyry cu deposit from stages of metallogenic overprinting the rocks studied in this work are from deformation metallogenic structures that have 1 a distinguished metallogenic and tectonic evolution 2 a three layer spatial deformation metallogenic structure 3 distinguishably different fluid components within protomylonite mylonite and ultramylonite zones and 4 variational geochemical characteristics of coexisting chalcopyrite and magnetite integrated sulfide and oxide mineral investigations pertaining to the mineral deformation and the trace element variation of the minerals chalcopyrite and magnetite in the yuleken porphyry cu deposit indicated that cu and mo can be enriched during ductile deformation through physical analogous geochemical characteristics of chalcopyrite from different stages and chemical migrations the elemental variation of magnetite magnetites from deformed stages have higher contents of ti v co mn and ga than those from other stages and the variation of the fluid components within the protomylonite mylonite and ultramylonite zones reveal that the migration and precipitation of cu mo and fe were influenced by oxygen fugacity fluid components and temperature variation in conclusion the arc related porphyry deposits were able to become involved in the ductile deformation zone inducing areas of cu and mo enrichment in theory units subjected to ductile deformation may have great potential for porphyry cu mo deposit formation under the influence of magmatism

temporal evolution of mineralization events in the bohemian massif inferred from the re os geochronology of molybdenite molybdenite is a common mineral accompanying sn w au and base metal mineralizations located in different geotectonic units of the bohemian massif but it is also widespread in granitoids and or related quartz veins pegmatites forming disseminated mo mineralization thirty re os ages were obtained for molybdenite samples from the bohemian massif to provide constraints on the timing and duration of mineralization event s within the framework of previously published geochronological data for the host and or associated rocks the obtained data for sn w li deposits in the erzgebirge metallogenetic province indicate the predominance of one and or multiple short time mineralization events taking place between 319 and 323 ma with the exception of the krupka deposit associated with the altenberg teplice caldera where the data may suggest prolonged activity until 315 ma the ages of the pb zn au mo h rky u rakovnika and fe cu as ob i d l mineralizations from the exocontacts of the cista pluton and krkonose jizera plutonic complex respectively provide evidence for synchronous emplacement of the ore and the associated granitic rocks in contrast the padr fe as mo mineralization postdates the age of the associated padr granite disseminated mo mineralization in cadomian and variscan granitoids and or related to quartz veins pegmatites provides re os ages that overlap with the previously published geochronological data for the host rocks suggesting coeval evolution molybdenite samples from the sazava suite granites of the central bohemian plutonic complex cbpc have resolvable younger ages than their host granites but similar to the age of spatially related au mineralization which is associated with the latest evolution of the cbpc

sulfur isotope evidence for the origin of 3 4 to 3 1 ga pyrite at the princeton gold mine barberton greenstone belt south africa abstract the princeton mine is one of several mesothermal gold deposits found in the barberton greenstone belt the host rocks of the ore bodies are carbonaceous and pyritic shales of the fig tree group 3 4 to 3 2 ga in age the methothermal gold mineralization has occurred during the latest thrusting and deformation events at 3 1 ga micro analyses of sulfur isotopes of pyrite were performed on four representative samples collected from the princeton mine the 34 s values were determined in situ on individual pyrite crystals or aggregates of fine grained pyrite by the laser microprobe method 58 analyses and also on aggregates of separated pyrite crystals by the conventional cu 2 o combustion method 11 analyses trace element concentrations of pyrite were also determined using an electron microprobe based on their grain sizes and chemical compositions the pyrite samples examined are divided into two groups 1 fine grained pyrite and 2 coarse grained pyrite the fine grained group includes disseminated pyrite and pyrite laminae concordant to sedimentary bedding their textures suggest that the fine grained pyrite was formed during sedimentation of the carbonaceous shale at 3 4 to 3 2 ga the 34 s values of the fine grained pyrite range from 0 8 to 4 4 within a micro scale area 1 mm 2 mm 29 laser microprobe analyses suggesting that the microbial reduction of seawater sulfate was responsible for the formation of fine grained pyrite this further suggests that the 3 4 to 3 2 ga ocean already contained an appreciable amount of sulfate which is in contrast to the previously popular theory that the archean ocean was h 2 s rich and pyrite in archean sedimentary rocks was formed by an inorganic process coarse grained pyrite is associated with auriferous quartz veins and often contains gold grains trace element concentrations of coarse grained pyrite such as as concentrations are different from these of fine grained pyrite the petrographic features suggest that the most coarse grained pyrite was directly precipitated from high temperature hydrothermal fluids coarse grained pyrite has homogeneous 34 s values ranging from 1 1 to 3 6 29 laser microprobe analyses suggesting that source of sulfur for the coarse grained pyrite was reduced sulfur species in hydrothermal fluids

the silidor deposit rouyn noranda district abitibi belt geology structural evolution and paleostress modeling of an au quartz vein type deposit in an archean trondhjemite late orogenic gold bearing quartz vein deposits within the rouyn noranda mining district occur mainly within archean tonalitic plutons of the blake river group southern abitibi belt the silidor deposit is a representative example of a pluton hosted lode gold deposit the silidor mine contained 2 95 million tons mt mined and estimated reserves grading 5 1 g t au 15 t au the mineralized zone is 900 m in length and has a vertical extent of 900 m an average thickness of 3 5 m and trends northwest southeast with a dip of 50 to 70 ne its alteration envelope consists of a red hematite altered trondhjemite measured 18 o values for quartz veins 7 7 10 9 and 34 s values for pyrite 6 1 to 9 4 imply oxidizing conditions during gold deposition the mineralized zone comprises vein quartz white gray and smoky varieties beige mineralized trondhjemite and green carbonate sericite fuchsite breccia which resulted from shearing and metasomatism of an early northwest southeast dioritic dike a quantitative microtectonic study 400 measurements was carried out on the powell tonalitic sill in the silidor mine area to reconstruct the deformation before during and after the mineralizing events the reduced stress tensors display large variations in 1 orientation trending successively northwest southeast northeast southwest and finally north south the silidor deposit is the result of several vein filling events which occurred during evolution from strike slip faulting to reverse faulting regimes with 1 remaining northeast southwest but with exchange of orientation of 2 and 3 such variations may reflect an oblique collision and processes of stress permutation paleostress mapping of archean terranes can be used as a targeting tool for mesothermal lode gold deposits reduced stress tensors were used for the computation of paleostress maps using a distinct element model the silidor au quartz mineralization appears on these paleostress maps in an area characterized by low mean stress throughout the deformation history of the area near the horne creek fault this study emphasizes the role of second order faulting in the location of low and high pressure zones in the archean crust and the possible role of a tectonic indentor in the location of au mineralization

the la belliere gold and antimony district french armorican massif a two stage evolution model controlled by variscan strike slip tectonic the la belliere gold district in the ligerian domain of the armorican massif is the third one of france in term of production it shows gold bearing quartz veins neighboring with a complex network of sb veins hosted in the neoproterozoic metasedimentary basement of the mauges nappe new structural data mineralogical textural and geochemical assays have been carried out to clarify the gold and sb veins relationships our results favor of two step hydrothermal event with an early deep seated gold event followed by a late shallower sb event the gold bearing quartz veins are hosted by n60 e to n90 e sinistral strike slip faults these veins exhibit a four stage paragenesis 1 early barren quartz filling 2 arsenopyrite pyrite with minor scheelite assemblage 3 gold and base metal sulfides crystallized after a ductile brittle deformation stage and 4 pyrite carbonate coeval with a late brittle stage these results support a continuous evolution model from a deep emplacement level 12 to 9 km to a shallow one 7 to 5 km with a brutal change in the p t conditions that triggered the deposition of gold stage 2 controlled by a seismic valve mechanism on the contrary sb veins correspond to open space vein types hosted in a n20 w to n20 e conjugated strike slip fault network arranged in a riedel shear model controlled by n130 140 e regional dextral strike slip shear zone associated to the south armorican shear zone system a two stage evolution is recognized the first one consists of early pyrite arsenopyrite with microcrystalline quartz followed by a late stibnite stage formed after geodic quartz deposition quartz texture argues for a shallow emplacement 5 km of veins controlled by a suction pump mechanism chronologically the gold vein opening complies with a ne sw maximum shortening direction different from the late variscan stress field responsible for the dextral armorican shear zone during late carboniferous and constrains an indirect dating thus a visean age is proposed for the formation of gold veins the overall features of gold deposits are close to those of mesozonal orogenic gold deposits in europe conversely sb bearing veins are generated by a n s shortening during the late carboniferous the sb event distinct in time from the earlier gold one might correspond to a different expression of the so called epizonal type in the orogenic gold model it is proposed that the late carboniferous or 300 event is not the unique metallogenic period for gold deposition in the french variscan domain our study highlights the role of the sinistral strike slip shearing of possible visean age in the gold metallogenesis of the ligerian domain

sphysicochemical conditions of fluid wall rock interaction at amphibolite facies conditions in two archean hydrothermal gold deposits in the mt york district pilbara craton western australia synamphibolite facies archean gold mineralization in the mt york district pilbara craton western australia is hosted in metamorphosed banded iron formation main hill breccia hill prospect amphibolites and ultramafic schists zakanaka prospect mineralization at main hill occurs in quartz breccias with sulfide matrices and in altered wall rock adjacent to quartz biotite amphibole clinopyroxene veins alteration associated with quartz veins is zoned with biotite pyrrhotite vein selvedges and a distal calcic amphibole arsenopyrite lollingite zone hydrothermal biotite and actinolite have highest mg mg fe ratios where associated with abundant sulfarsenides in the distal alteratin zone whole rock geochemical analyses and calculated metasomatic reactions indicate the addition of k al s as au ag and ni during hydrothermal alteration mineralization at zakanaka is characterized by a broad wall rock alteration halo of biotite amphibole and zoned quartz calc silicate veins proximal to ore

the variscan kasperske hory orogenic gold deposit bohemian massif czech republic kasperske hory one of the largest gold deposits in the bohemian massif is characterised by shear zone related gold bearing quartz veins at the tectonic boundary of the two metamorphic terranes of the moldanubian unit studies of the geology mineral paragenesis fluid inclusions and oxygen geothermometry have been carried out to determine the mineralisation events and alternative p t t model of this deposit the pre mineralisation stage is characterised by geochemical evidence of pegmatites 700 c and 1 1 0 45 gpa and metamorphic structures resulting from deformation dx 1 at the regional metamorphic peak 650 c and 0 5 gpa the mineralisation in dx 2 began to develop from the formation of the q1 and q2 quartz veins stage i under brittle ductile conditions with the n s extension these quartz veins were filled mainly by apatite plagioclase 1 muscovite and arsenopyrite 1 revised and reinterpreted gechronological data indicate that the earliest quartz veins can be dated at 344 ma the q3 veins were formed later under brittle to brittle ductile conditions with crystallisation of plagioclase 2 arsenopyrite 2 scheelite chlorite pyrite and calcite stage ii the corresponding fluids of stages i and ii belong to the c h o n system the p t conditions correspond to 590 520 c and to 0 44 0 25 gpa for stage i and 480 390 c and 0 2 gpa for stage ii stage iii is characterised by the precipitation of younger quartz chlorite molybdenite calcite pyrrhotite 1 galena 1 native gold bismuth and other bi te minerals the associated aqueous fluids salinity 1 5 8 wt nacl equiv follow fluid inclusion trails and were trapped at relatively low pressures and temperatures 290 180 c and 0 1 gpa stage iv is mainly dominated by carbonate and fluorite fillings of the open fractures and cracks arsenopyrite 1 and 2 and molybdenite are the main gold bearing and gold carrying ore phases at this deposit the means of microanalysis indicate the presence of both micron sized and probably submicron sized particles of gold 920 1000 in the fractures and fissures of the arsenopyrite 1 and structurally bound invisible gold in the arsenopyrite 2 crystal lattice e g gold as au i economic gold mineralisation native free gold flakes 930 1000 is linked to stage iii

magmatic stoping as an important emplacement mechanism of variscan plutons evidence from roof pendants in the central bohemian plutonic complex bohemian massif the presence of numerous roof pendants stoped blocks and discordant intrusive contacts suggests that magmatic stoping was a widespread large scale process during the final construction of the central bohemian plutonic complex bohemian massif the measured total length of the discordant contacts that cut off the regional cleavage and were presumably formed by stoping corresponds to about half of all contacts with the upper crustal host rocks in addition at least some of the straight cleavage parallel intrusive contacts may also have recorded complex intrusive histories ending with piecemeal stoping of thin cleavage bounded host rock blocks into the magma chamber based on the above we argue that the fast strain rates required for emplacement of large plutons of the central bohemian plutonic complex into brittle upper crustal host rocks over relatively short time span could not have been accommodated entirely by slow ductile flow or slip along faults instead the emplacement was largely accommodated by much faster thermal cracking and extensive stoping independent of regional tectonic deformation finally we emphasize that magmatic stoping may significantly modify the preserved structural patterns around plutons may operate as an important mechanism of final construction of upper crustal plutons and thus may contribute to vertical recycling and downward transport of crustal material within the magma plumbing systems in the crust

multiple fluid sources pathways and severe thermal gradients during formation of the jilove orogenic gold deposit bohemian massif czech republic abstract the jilove deposit in the central part of the bohemian massif represents a vein to stockwork type of orogenic type gold deposit it is hosted by neoproterozoic rocks of the jilove belt and by various magmatic dikes related to the 355 to 335 ma central bohemian plutonic complex the deposit is situated along the terrane boundary of the tepla barrandian and moldanubian units the deposit offered an exceptional opportunity to trace o c s and sr stable isotope evolution of parent fluids based on combined mineralogical and geochemical study of carbonate quartz scheelite and sulfide minerals which represent six stages of mineralization including the gold bearing event stable isotope data and mineral and isotope thermometry indicate gangue and ore mineral formation between 350 c and 18 o smow 4 2 0 5 and 13 c pdb 11 1 gold precipitation stage 5 probably started at about 300 c but the major event probably occurred at 230 30 c from a fluid with more variable isotope values 18 o smow 2 5 to 5 and 13 c pdb 9 to 13 5 the carbon speciation was characterized by predomination of dissolved co 2 h 2 co 3ap in the fluids some gold however undoubtedly precipitated from bicarbonate dominated fluids even at extreme variations in the 18 o values of carbonate minerals obtained from sampling profiles across individual veins with macroscopic gold revealed severe thermal gradients during vein formation 50 to 100 c difference of crystallization temperatures between the vein margin and core the sulfur stable isotope composition of sulfide minerals indicates the dominant role of sulfur remobilization from neoproterozoic rocks and stratiform mineralizations of the jilove belt by variscan hydrothermal fluids similarly the sr isotope composition of carbonates indicates both relatively primitive 87 sr 86 sr 0 7055 and more evolved 87 sr 86 sr 0 7090 fluid compositions probably indicating fluid exchange with the jilove belt and the central bohemian plutonic complex rocks respectively age determination of hydrothermal muscovite related to stage 2 via 40 ar 39 ar indicated an age of 339 0 1 5 ma for the quartz veins the mineralization is essentially coeval with the late intrusive phases of the central bohemian plutonic complex i e the ultrapotassic suite and with late orogenic large scale tectonic movements at the boundary between the two crustal terranes tepla barrandian and moldanubian based on evaluation of the available age data on the hydrothermal and magmatic activity within the broader area of the central bohemian plutonic complex we suggest two intervals of gold mineralization 347 to 341 ma and 340 to 337 ma the former interval overlaps with the intrusive activity of the blatna high k suite granodiorite the associated gold deposits mokrsko and petrackova hora exhibit strong affiliation to the intrusion related gold type deposit the later interval overlaps with the ultrapotassic magmatism and is associated with more or less classical orogenic gold type deposits jilove b lcice libcice deposits

bicarbonate rich fluid inclusions and hydrogen diffusion in quartz from the libcice orogenic gold deposit bohemian massif abstract unusual paleofluid composition is reported for the libcice orogenic type gold deposit located in the central bohemian plutonic complex cbpc czech republic unexpected bicarbonate rich fluids and their complex chemistry variations characterize primary fluid inclusions from the main gold bearing quartz vein a detailed microthermometry laser raman micro spectroscopy lrms and sem cathodoluminescence study was used to understand the complex chemistry and p t x history the results indicate the presence of h 2 o and h 2 o co 2 ch 4 n 2 h 2 s fluids the latter displaying variations of the co 2 ch 4 ratio in the gaseous phase from 6 8 to 0 06 variation of the ch 4 content across single grains and between different levels of the mine was recorded the presence of nahcolite h 2 up to 6 mol and ethane 0 0 2 mol in the fluids were also discovered by lrms potential models for the formation of different types of fluids present in the deposit are discussed including the genesis of hco 3 rich fluids as well as h 2 and c 2 h 6 presence in the primary fluid inclusions the potential influence of organic matter bearing sediments as well as the impact of the intrusion of cbpc re equilibration and or re speciation of fluid inclusions during the post entrapment history is considered to have the main impact on the complex paleofluid chemistry based on the thermodynamic modeling h 2 diffusion into the fluid inclusions was shown to be the main reason for the ch 4 variation on the scale of a single grain as well as across the whole vein although the exact processes of production formation of hco 3 and h 2 at the libcice deposit remain open to discussion reactions in the c o h system are considered to be a possible formation mechanism this work also contributes to our understanding of the importance of post entrapment modifications and reactions in the c o h system on interpretation deciphering the processes in orogenic type deposits

is the palea kavala bi te pb sb au district northeastern greece an intrusion related system abstract intrusion related gold systems are generally characterized by a au bi te sn w metal assemblage genetically linked to the emplacement of granitoids the palea kavala ore system greece consists of 150 minor fe mn pb zn ag fe mn au fe as au fe cu au and bi te au occurrences that occur primarily in quartz calcite sulfide veins hypogene mineralization or as supergene bodies in overlapping zones centered on the 21 22 ma granodioritic kavala pluton which intrudes metamorphic rocks of the paleozoic rhodope metamorphic core complex the pluton consists mostly of granodiorite with lesser amounts of diorite tonalite and monzodiorite which was emplaced along the regional e w trending kavala komotini fault the recently discovered 4 km long e w trending so called kavala vein is a sheeted quartz vein system of bi te pb sb au mineralization that crosscuts the kavala pluton and the schists and gneisses of the rhodope massif the kavala vein system is comprised of quartz with lesser amounts of k feldspar plagioclase and muscovite quartz sericite pyrite alteration is pervasive but minor kaolinite is also present pyrite 5 of vein volume contains inclusions of tetradymite some gold bearing bismuthinite and cosalite sulfur isotope values n 27 of pyrite from the kavala and chalkero veins as well as pyrite and galena from garizo hill fe mn pb vein range from 1 9 to 1 0 with one outlier of 4 6 and suggest a magmatic sulfur source homogenization temperatures th of type i two phase aqueous liquid vapor and type ii three phase h2o co2 rich fluid inclusions that homogenize into the liquid phase in quartz from the kavala and chalkero veins range from 216 0 to 420 0 c n 216 and 255 7 to 414 0 c n 112 respectively the th of type iii two phase aqueous liquid vapor which homogenize into the vapor phase ranges from 210 4 to 323 4 c n 28 the salinities of type i and type ii inclusions range from 15 9 to 22 6 wt nacl equiv and 5 5 to 11 2 wt nacl equiv respectively eutectic temperatures of 58 5 to 44 3 c for type i inclusions suggest the presence of appreciable cacl2 in addition to nacl clathrate melting temperatures for type ii inclusions of 56 7 c indicate that co2 is the major component of the gaseous phase however up to 6 ch4 is present in some inclusions the presence of a zoned metallogenetic district centered on bi te pb sb au mineralization within the kavala pluton the presence of both magnetite and ilmenite in the kavala pluton and the two high temperature high salinity immiscible carbonic and aqueous fluids associated with the kavala and chalkero veins are consistent with them being part of an intrusion related gold system that formed along the ilmenite magnetite buffer

the geology and mineralogy of the loulo mining district mali west africa evidence for two distinct styles of orogenic gold mineralization loulo is a world class orogenic gold mining district in the birimian terrane of western mali orebodies are located along second or higher order shears associated with the senegal mali shear zone with gold mineralization largely linked to a transtensional event the mine camp is divided into two distinct styles of gold deposit on the basis of differing geologic characteristics one group is typified by the gara deposit whereas the other by the yalea deposit both deposit styles are hosted by similar rock types calcareous graywackes and calciticdolomitic marbles gara style orebodies occur as sulfide disseminations or ankerite rich shear vein stockworks hosted in folded tourmalinized sandstones and breccias mainly within 2 km of the senegal mali shear zone these deposits are characterized by intense multi stage albitization and tourmalinization pre syn and postmineralization gold lodes are fe rich dominated by nickeloan pyrite contain cu ni co minor and trace sulfides e g chalcopyrite gersdorffite pentlandite cobaltite millerite and show consistently high levels of p ree w bearing phases apatite monazite xenotime and scheelite base metal concentrations show a marked increase in marble host rocks with the formation of nickeloan pyrite cobaltite clausthalite ores in contrast yalea style deposits are associated with quartz ankerite vein lodes and disseminated sulfide stringer zones mineralization occurs along highly altered tourmaline absent brittle ductile shears up to 8 km away from the senegal mali shear zone wall rock alteration is characterized by addition of k 2 o cao co 2 h 2 o and sio 2 with mineral assemblages consisting of chlorite sericite carbonate quartz albite ore paragenesis is enriched in as mainly as multistage growth of arsenopyrite and arsenian pyrite base metal sulfides scheelite and ree phosphates are extremely rare the diversity in the ore paragenesis is controlled by a dynamic hydrothermal system that sourced fluids and metals from different reservoirs within the region the as rich yalea style deposits have characteristics typical of birimian gold mineralization in ghana and auriferous fluids are likely derived from the dewatering of sedimentary rocks during regional metamorphism on the other hand the polymetallic fe b rich gara style orebodies show atypical features for birimian gold mineralization instead field relations and the mineralogy and geochemistry of the gara style lodes indicate a strong hydrothermal influence from surrounding intrusive stocks with possible links between gold mineralization and iron oxide skarn development in the region the data collected at loulo highlight the diverse nature of orogenic gold deposits especially in west africa this style of ore deposit can form from a variety of fluid sources both metamorphic and magmatic

a special issue devoted to abitibi ore deposits in a modern context preface the abitibi greenstone belt which is part of the larger abitibi subprovince in the superior province of the canadian shield e g card and ciesielski 1986 is the largest known archcan greenstonegranite terrane 300 km n s x 400 450 km mineral production and reserves are significant particularly in relation to volcanogenic massive sulfide deposits and structurally controlled archcan goldbearing quartz vein systems the term au quartz vein being used in the sense of lindgren 1933 e g the gold quartz veins of ontario p 662669 volcanogenie massive sulfide production and reserves to 1989 1990 total 424 million metric tons

an archean fold thrust belt in the northwestern abitibi greenstone belt structural and seismic evidence an integration of structural field data and lithoprobe seismic reflection line 28 in the northwestern abitibi greenstone belt agb reveals a crustal scale south to southwest vergent thrusting event that developed in sequence above a shallowly 15 north dipping sole thrust at a mid crustal level seismic reflector geometry above this decollement suggests a mid crust 6 20 km depth dominated by low angle thrusts with smooth trajectory ramps and culmination folds or antiformal stacks similar to the structural style of neighbouring high grade plutonic gneissic opatica and sedimentary pontiac subprovinces in contrast low to high angle east west trending thrusts at the upper crust greenstone belt level 6 9 km depth are interpreted to be listric they occur in two fault systems the chicobi and taibi that resemble imbricate fan systems the contrasting structural geometry of the upper and mid crust is interpreted as variations in level through the thrust stack and resembles paleozoic mountain

climatic effects of glacial lake agassiz in the midwestern united states during the last deglaciation stable isotope and pollen analyses of a sediment core from deep lake minnesota provide new information on the climatic effects of glacial lake agassiz in minnesota and insights into the cause of the prominent picea recurrence during the younger dryas in the southern great lakes region bulk carbonate 18o exhibited large fluctuations between 12 0 and 9 1 ka dates are in calendar years throughout this paper unless indicated otherwise probably reflecting the effects of glacial lake agassiz superimposed on climatic warming related to large scale climatic controls in particular a 3 decrease in 18o 11 2 10 2 ka interrupted the 18o enrichment of 1 from 12 0 to 11 2 ka and 3 5 from 10 2 to 9 1 ka this 18o decrease coincided with the expansion of lake agassiz we interpret this decrease as a result of decreased summer temperature and increased precipitation derived from the cold and isotopically light meltwaters of lake agassiz during this 18o decline pinus pollen continued to increase at the expense of picea pollen at deep lake as at other minnesota sites providing evidence that climatic cooling induced by lake agassiz did not cause a reversal to a picea dominated vegetation the absence of such a vegetational response implies that the prominent picea recurrence during the younger dryas in the southern great lakes region was not caused solely by climatic cooling due to increased flux of meltwater from lake agassiz into the great lakes instead the picea recurrence might have been driven primarily by the westward penetration of the younger dryas cooling

influence of structural setting on sulphur isotopes in archean orogenic gold deposits eastern goldfields province yilgarn western australia the published mean 34s values of ore related pyrites from orogenic gold deposits of the eastern goldfields province yilgarn craton lie between 4 and 4 as for orogenic gold deposits worldwide most deposits have positive means and a restricted range of 34s values but some have negative means and wider ranges of 34s values wall rock carbonation and back mixing of similar source fluids with different fluid pathways can explain some of the more negative 34s signatures however structural setting appears to be the most important factor controlling ore fluid oxidation state and hence the distribution of 34s values in gold related pyrites shear hosted deposits appear to have experienced fluid dominated processes such as phase separation whereas stockwork vein hosted or disseminated deposits formed under conditions of greater rock buffering at victory defiance in particular negative 34s values are more common in gently dipping dilational structures compared to more compressional steeply dipping structures it appears most likely that fluid pressure fluctuations during fault valve cycles establish different fluid flow regimes in structures with different orientations rapid fluid pressure fluctuations in dilational structures during seismic activity can cause partitioning of reduced gas phases from the ore fluid during extreme phase separation and hence are an effective method of ore fluid oxidation leading to large local fluctuations in oxidation state it is thus not necessary to invoke mixing with oxidised magmatic fluids to explain 34s signatures indicative of oxidation in any case available robust geochronology in the eastern goldfields province does not support the direct involvement of oxidised magmatic fluids from adjacent granitic intrusions in orogenic gold genesis thus negative mean 34s values and large variations in 34s values of ore related pyrites in world class orogenic gold deposits are interpreted to result from multiple mechanisms of gold precipitation from a single ubiquitous ore fluid in varying structural settings rather than from the involvement of oxidised ore fluids from a different source such signatures are indicative but not diagnostic of anomalously large orogenic gold systems

brittle origins for disseminated gold mineralization in mylonite gaocun gold deposit hetai goldfield guangdong proince south china gold mineralization in the hetai goldfield in south china is almost entirely confined to a series of steeply dipping ductile shear zones generated during hercynian indosinian orogenesis of sinian host rocks approximately half of the mineralization is in the form of disseminations in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in einlets and as sulfide cement to brecciated mesoscopic quartz eins heaily influenced by the presence of disseminated mineralization all publications on hetai determine a major role for ductile deformation in the introduction of gold into the deposit the brittle deformation is typically regarded as redistributing within the host structures the gold initially introduced as a result of ductile deformation mechanisms howeer textures of the sulfides associated with the gold indicate an entirely postductile deformation timing as they display none of the features attributed to ductile deformation during the eident brittle deformation phase competence contrasts at the microscopic scale allowed fracturing to focus on the quartz sericite domain boundaries of the mylonite foliation thus permitting the introduction of auriferous fluid into the mylonite to create disseminated mineralization the control exerted by preexisting structures is further reflected in the restriction of disseminated mineralization to the quartz domains presumably because the sericite domains accommodated the deformation in a more distributed fashion seeral other lines of eidence support an origin of the hetai deposit in an upper crustal regime a similar style of disseminated mineralization to that seen in the mylonite surrounds microeinlet terminations in the brecciated quartz eins as well as oerprinting pseudotachylite which is associated with cataclasite there are also large olumes of unmineralized mylonite indicating no connection between the intensity of strain and gold grade we conclude that in structurally controlled deposits the textural category of disseminated gold mineralization can be generated either under entirely ductile or entirely brittle conditions and that microtextural eidence has to be carefully analyzed to determine the mode of formation of a deposit

chronology of the kasperske hory orogenic gold deposit bohemian massif czech republic the kasperske hory deposit represents one of the economically most important hydrothermal gold deposits in the bohemian massif czech republic we present new re os age determinations for sulfides complemented by ar ar determinations on silicate minerals in order to provide temporal constraints on the deposit formation arsenopyrite and molybdenite formed during gold bearing stages i iii yielded similar re os ages between 341 and 333 ma overlapping with the ar ar cooling age of the metamorphic host rocks below 500 c continuous cooling of the ore system below 270 c during stage iii is reflected by ar ar muscovite ages spanning from 332 to 325 ma representing the long interval of formation of gold productive stage iii thus the kasperske hory gold deposit is younger than the gold deposits spatially associated with the central bohemian plutonic complex 349 339 ma belonging to the central bohemian metallogenetic zone e g mokrsko west jilove petrackova hora this may indicate a rather close relationship to the nearby moldanubian batholith while still suggesting an intimate link between mineralization and variscan orogenesis and associated magmatism

geochemical and mineralogical diagnosis on gold ores a case study from the cadillac larder lake fault zone abitibi canada abstract numerous orogenic gold deposits have been discovered within the archean abitibi greenstone belt of canada these include the francoeur wasamac astoria zulapa goldex lamaque lac herbin and beaufor deposits all of which are located within the cadillac larder lake fault zone cllfz these gold deposits are hosted by various lithologies and vary in terms of style of mineralization sulfide abundance and hydrothermal alteration these variations mean that exploration for new deposits has been difficult in this area using common exploration criteria this study presents the results of a principal component analysis pca based approach combining geochemical and mineralogical data to quickly identify different types of gold mineralization within the cllfz including assessing the use of this approach in mineral exploration the first principal components in both classification methods used during this study pce1 and pcm1 representing element geochemical and mineralogical classification respectively can efficiently discriminate between mineralization and barren altered rocks the second principal components pce2 and pcm2 can be used to constrain the host rocks altered vs barren and style of mineralization disseminated vs vein hosted respectively finally pce3 and pcm3 give more detailed information on the nature of the mineralization in an area possible reflecting variations in the composition of ore forming fluids all of the above indicates that the two pce and pcm classification methods are complementary which means that using approaches that combine these methods will provide a comprehensive understanding of the nature of studied samples and or deposits information extracted from the results of the pca undertaken during this study may be beneficial for mineral exploration in unknown districts such as glaciated areas where traditional geological fieldwork is challenging this study also defines element and mineral mineralization indices based on pce1 and pcm1 which enables evaluation of the extent and style of gold mineralization in an area this study indicates that pca based automated mineralogical and geochemical classification methods could be highly useful in exploration for gold deposits

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

mineralogy fluid inclusion and stable isotope constraints on the genesis of the roudný au ag deposit bohemian massif orogenic gold deposits with gold of low fineness are relatively rare in the bohemian massif but occur locally within the late variscan blanice graben structure in the moldanubian zone among them the roudn deposit has been the most important with total production of about 6 t of gold between 1895 and 1930 the ore is related to an irregular quartz stockwork and is represented by sulfide and electrum impregnations within the quartz gangue and the altered host rocks ore grade varies from 4 to 25 g t au the gold is present as macro and microscopic electrum fineness 658 665 and also as invisible gold in the crystal structure of early sulfides as rich pyrite and sb rich arsenopyrite three mineralization stages have been distinguished 1 the largely barren pre ore stage 2 the main ore stage with economic au ag mineralization 3 the late stage with subeconomic ag pb zn mineralization fluid inclusion and mineral thermometry indicate that the three stages were formed at about 400 to 330 350 to 250 and 250 to 70 c respectively early mineralization stages are related to complex h2o co2 ch4 n2 low salinity 3 9 wt nacl equiv fluids with isotopic signatures consistent with a metamorphic origin 18ofluid 4 7 2 9 smow most of the main ore stage minerals including the electrum precipitated from aqueous fluids 2 4 wt nacl equiv during the late mineralization stage the salinity of aqueous fluid was higher 7 9 wt nacl equiv the isotopic composition of the late fluid however also records gradually increasing proportions of meteoric water 18ofluid 2 to 1 smow elevated arsenic contents 120 210 ppm as were found in aqueous carbonic fluids by the la icp ms technique models of fluid mixing at the transition of the main to late mineralization stages are used to estimate the temperature and paleogeothermal gradient possible ages of electrum mineralization 300 to 275 ma and ag pb zn vein type mineralization 275 to 265 ma are discussed overall the roudn deposit shows striking similarities with 300 ma gold deposits of the french massif central

geology and genesis of variscan porphyry style gold mineralization petrackova hora deposit bohemian massif czech republic a large number of variscan mesothermal gold deposits are located in the central part of the bohemian massif close to the central bohemian plutonic complex the petrackova hora deposit has many features that distinguish it from other deposits in the region and suggest its mineralization is closely related to the late magmatic processes associated with the petrackova hora granodiorite the gold ores occur as sheeted arrays of quartz veins and veinlets hosted by the small petrackova hora granodiorite stock gold is found mainly as free grains of 900 fineness and is accompanied by abundant pyrrhotite and chalcopyrite and accessory pyrite arsenopyrite loellingite and molybdenite molybdenite from the petrackova hora deposit has been dated by the re os method at 344 4 2 8 ma hydrothermal alteration in the petrackova hora deposit exhibits a distinct temporal paragenesis selectively pervasive early k alteration and silicification are the oldest hydrothermal phases these were followed by early quartz veins q1 to q4 that contain most of the gold mineralization late quartz veins q5 and fracture controlled silicification are gold poor or barren barren calcite veins are the youngest hydrothermal product extensive low temperature meteoric water dominated alteration as is typical of classic porphyry deposits is absent however the lower 18o whole rock values for petrackova hora granodiorite and aplite 2 4 to 5 1 smow compared to other intrusions in the region reflect either interaction with isotopically light external fluids or magma assimilation of small volumes of hydrothermally altered country rock the 18o isotopic compositions for quartz scheelite and hornblende 7 7 to 13 4 smow and the 34s compositions for sulfide minerals 1 to 3 5 cdt from early gold rich quartz veins indicate formation at high temperatures 590 to 400 c from fluids with a magmatic isotopic signature 18ofluid of 5 7 to 7 2 fluids related to late quartz veins q5 suggest the presence of a significant component of non magmatic water 18ofluid 2 5 to 4 0 the 34s values of post q5 sulfide minerals 4 5 to 3 5 reflect at least partial derivation of late stage sulfur from a source external to the intrusions aqueous aqueous carbonic and nitrogen bearing fluid inclusions were identified in hydrothermal and igneous quartz with the aqueous inclusions being the most common in hydrothermal vein quartz the salinity of primary aqueous inclusions falls into ranges 6 to 23 and 33 to 41 equiv wt nacl in igneous quartz populations in salinity were observed between 5 to 16 35 to 40 and 62 to 70 equiv wt nacl the salt component of these fluids is best and minimally approximated by the nacl kcl cacl2 system low and high salinity aqueous carbonic inclusions are accessory in many of the analyzed samples three large successive pulses of fluids are recognized each pulse begins with a high salinity 30 equiv wt nacl magmatic fluid and evolves toward a lower salinity 5 equiv wt nacl fluid data suggest that external meteoric water s were significant for only the third fluid pulse which formed the late q5 quartz veins and the calcite veins polyphase fluid inclusions hosted by igneous quartz of the petrackova hora granodiorite indicate minimum trapping conditions of about 3 kbar and 550 c the gold rich q1 to q4 veins may have formed along a quasi isobaric cooling path at 2 5 to 1 5 kbar and 590 to 400 c this was followed by uplift and formation of late q5 quartz veins 0 5 to 1 5 kbar 300 c and post ore calcite veins 0 5 kbar 100 to 140 c the characteristics of the petrackova hora deposit suggest that it may represent a position intermediate between intrusion related gold systems e g fort knox deposit alaska and gold rich copper poor porphyry deposits e g maricunga belt in chile as such the petrackova hora deposit might be an example of the reduced gold sub type of porphyry deposit

the geology and alteration patterns of a disseminated shear zone hosted mesothermal gold deposit the francoeur 3 deposit rouyn noranda quebec the francoeur 3 gold deposit located approximately 15 km southwest of rouyn noranda quebec is one of several geologically similar archean mesothermal gold deposits occurring along the francoeur wasa shear zone a second order reverse structure possibly related to the cadillac larder lake break the principal gold mineralization which is completely hosted by the francoeur wasa shear zone is associated with disseminated pyrite and occurs in tabular zones of intense hydrothermal replacement the mineralized zones consist of a buff or gray colored very fine grained carbonate albite pyrite assemblage which occurs in very different lithologies including sheared andesite red albitite dikes and gabbro three types of hydrothermal alteration occur in the deposit in chronological order they are 1 a widespread pervasive preore carbonate hematite muscovite alteration associated with the intrusion of late kinematic albitite dikes 2 an albite pyrite alteration closely associated with the gold mineralization and 3 a postore sulfate bearing alteration the distribution of alteration assemblages and replacement textures suggests evolution of fluid rock interaction the initial hydrothermal alteration involved the hydrolysis of metamorphic silicates and oxides to form carbonate muscovite and hematite with net additions in co 2 k rb and tio 2 subsequently muscovite and hematite were replaced in the ore zones by albite and pyrite respectively resulting in k 2 o and rb depletion and large enrichments in na 2 o s w and au these two alteration types are crosscut by late gypsum and anhydrite veinlets which are associated with late brittle extensional faults and possibly mark the last product of hydrothermal activity in the francoeur wasa shear zone in this area it is proposed that gold deposition occurred as a result of changes in physicochemical conditions of ore forming fluids in response to progressive fluid rock interaction the combined effects of an increase in f sub o 2 and a sub na super or k super and reductions in both f sub h 2 s and ph controlled au solubility and very efficiently partitioned its deposition in the albite pyrite alteration facies this interpretation is consistent with preliminary sulfur isotope data which indicate that pyrite coexisting with gold is highly depleted in delta 34 s 10 5 or 0 8ppm compared with pyrite elsewhere in the shear zone as a result of reduced s oxidation the absence of an auriferous quartz carbonate vein system and the occurrence of disseminated replacement mineralization at francoeur suggest that this hydrothermal system remained relatively permeable through much of the hydrothermal process such that fluid flow operated under near constant hydraulic gradient such a fluid regime is very different from that generally proposed for the formation of mesothermal gold quartz veins in which episodic fluid pressure elevations above lithostatic pressure are thought to control fluid migration wall rock alteration and gold deposition

element migration of pyrites during ductile deformation of the yuleken porphyry cu deposit nw china abstract the strongly deformed yuleken porphyry cu deposit ypcd occurs in the kalaxiangar porphyry cu belt kpcb which occupies the central area of the central asian orogenic belt caob between the sawu er island arc and the altay terrane in northern xinjiang the ypcd is one of several typical subduction related deposits in the kpcb which has undergone syn collisional and post collisional metallogenic overprinting the ypcd is characterized by three pyrite forming stages namely a hydrothermal stage a py i a syn ductile deformation stage b py ii characterized by cu au enrichment and a fracture filling stage c py iii in this study we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite which formed during different stages in order to constrain the physicochemical conditions of the ore formation euhedral fragmented py i has low pb and high te and se concentration and ni contents are low with co ni ratios mostly between 1 and 10 average 9 00 py i is further characterized by enrichments of bi as ni cu te and se in the core relative to the rim domains anhedral round py ii has moderate co and ni contents with high co ni ratios 10 average 95 2 and average contents of 46 5 ppm pb and 5 80 ppm te py ii is further characterized by decreasing bi cu pb zn ag te mo sb and au contents from the rim to the core domains annealed py iii has the lowest co content of all pyrite types with co ni ratios mostly

geological mineralogical and geochemical characteristics of the radzimowice au as cu deposit from the kaczawa mountains western sudetes poland an example of the transition of porphyry and epithermal style the sheeted quartz sulfide veins of the radzimowice au as cu deposit in the kaczawa mountains are related to upper carboniferous post collisional potassic magmatism of the composite zelezniak porphyry intrusion multiple intrusive activity ranges from early calc alkaline to sub alkaline and alkaline rocks and is followed by multiple hydrothermal events early crustally derived dacitic magma has low mg 3 ppm au is about 1 5 geometric mean hydrothermal alteration started with sericitization pyritization and kaolinitization in vein selvages followed by alkaline hydrothermal alteration of propylitic character illitization and chloritization albitization and carbonatization the mineralization of the radzimowice deposit is considered as related to alkaline magmatism and is characterized by the superposition of low sulfidation epithermal mineralization on higher temperature and deeper seated mesothermal porphyry style

gold deposits in the xiaoqinling xiong ershan region qinling mountains central china the gold rich xiaoqinling xiong ershan region in eastern shaanxi and western henan provinces central china lies about 30 50 km inland of the southern margin of the north china craton more than 100 gold deposits and occurrences are concentrated in the xiaoqinling west xiaoshan middle and xiong ershan east areas late archean gneiss of the taihua group and middle proterozoic metavolcanic rocks of the xiong er group are the main host rocks for the deposits mesozoic granitoids ca 178 104 ma are present in most gold districts but deposits are typically hosted in the precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones deposits in the xiaoqinling and xiaoshan areas are best classified as orogenic gold deposits with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks alteration assemblages are dominated by quartz sericite pyrite and carbonate minerals the ore forming fluids were low salinity co2 rich and characterized by isotopically heavy 18o four deposits dongchuang wenyu yangzhaiyu and dahu in the xiaoqinling area each contain resources of about 1 moz au some of the gold deposits in the xiong ershan area represent more shallowly emplaced tellurium enriched orogenic systems which include resources of approximately 1 1 5 moz au at shanggong and beiling or tantou others are epithermal deposits e g qiyugou and dianfang that are hosted in volcanic breccia pipes isotopic dates for all gold deposits although often contradictory generally cluster between 172 99 ma and are coeval with emplacement of the post kinematic granitoids the gold deposits formed during a period of relaxation of far field compressional stresses clearly subsequent to the extensive paleozoic early mesozoic accretion of arc terranes and the yangtze craton onto the southern margin of the north china craton hydrothermal and magmatic events occurred locally where extension related precambrian basement uplifting took place along the craton margin fluids for the orogenic gold deposits in the xiaoqinling xiaoshan and xiong ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones alternatively for the epithermal gold deposits at shallower levels in the xiong ershan area gold transporting fluids were mainly exsolved from coeval magmas although meteoric water was also involved in these hydrothermal systems

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