epithermal mineralization and ore controls of the shasta au ag deposit toodoggone district british columbia canada the shasta gold silver deposit british columbia canada is an adularia sericite type epithermal deposit in which deposition of precious metals coincided with the transition of quartz to calcite dominant gangue mineralization is associated with stockwork breccia zones in potassically altered dacitic lapilli tuffs and flows and consists of pyrite sphalerite chalcopyrite galena acanthite electrum and native silver pre and post ore veins consist solely of quartz and calcite respectively fluid inclusion microthermometry indicates that ore minerals were deposited between 280 and 225 c from a relatively dilute hydrothermal fluid 1 5 wt nacl equivalent abundant vapor rich inclusions in ore stage calcite are consistent with boiling oxygen and hydrogen isotopic data 18ofluid 1 5 to 4 1 dfluid 148 to 171 suggest that the fluid had a meteoric origin but was 18o enriched by interaction with volcanic wallrocks initial 280 c fluid ph and log f o2 conditions are estimated at 5 3 to 6 0 and 32 5 to 33 bar respectively during ore deposition the fluid became more alkaline and oxidizing ore deposition at shasta is attributed to localization of meteoric hydrothermal fluids by extensional faults mineralization was controlled by boiling in response to hydraulic brecciation calcite and base metal sulfides precipitated due to the increase in ph that accompanied boiling and the associated decrease in h2s concentration led to precipitation of gold and silver

hydrothermal evolution in the maher abad porphyry cu au deposit sw birjand eastern iran evidence from fluid inclusions abstract copper and gold mineralization in the maher abad deposit eastern iran is closely related to the multiple emplacement episodes of upper eocene granodiorite porphyries within andesitic volcaniclastic and coeval quartz monzonite stocks the magmatic hydrothermal fluids thereafter hydrofracturing provided appropriate conduits formed a stockwork of quartz and quartz sulfide veinlets within the porphyritic host rocks which were extensively altered into potassic propylitic phyllic and argillic assemblages four main vein veinlet groups have been identified a quartz k feldspar biotite anhydrite with pyrite chalcopyrite sporadic magnetite and pyrrhotite b quartz pyrite and minor chalcopyrite c chalcopyrite quartz and or minor bornite pyrite digenite and sporadic pyrrhotite and d quartz calcite and or clay minerals pyrite hematite galena the cu au mineralization is mainly associated with the early potassic biotite alteration zone in the deep central part of the madanha stock based on the phase contents at room temperature three types of fluid inclusions are recognized at maher abad 1 liquid rich two phase lv 2 vapor rich vl h and 3 halite bearing multiphase lvh homogenization experiments revealed a temperature range of 150 488 c for the studied inclusions ice melting of aqueous two phase inclusions and melting of halite in the aqueous multiphase inclusions provide salinity of 9 5 to 47 9 wt nacl equivalent fluid inclusion studies reveal that the single phase low salinity magmatic fluid exsolved from a granodioritic magma was separated into vapor and hypersaline brine 45 wt nacl eq phases the coexisting phases were trapped at temperature 460 c and lithostatic pressure of 350 bars corresponding to a depth of 1 3 km as vl h and lvh fluid inclusions respectively such magmatic derived fluids underwent phase separation episodically under lithostatic pressure conditions and formed the early copper sulfide bearing quartz veinlets intimately related to the potassic alteration zone copper iron sulfide precipitation and phase separation concomitant of boiling in this zone led to rapid depletion of the fluid in reduced sulfur as a result au hs 2 complexes are destabilized forcing most of the gold to precipitate above 400 c a positive trend of the homogenization temperature and salinity during the formation of the phyllic alteration zone is attributed to the cooling of a moderately saline fluid produced dominantly by magmatic vapor condensation and its subsequent boiling and mixing with meteoric waters at a hydrostatic pressure of 100 125 bars corresponding to a depth of 1 1 2 km the argillic alteration zone formed at temperature of 210 230 c from fluids with salinity of 16 18 nacl wt eq at a hydrostatic pressure of 80 bars and a depth of 800 m from paleo surface the fluid density is typically lower 3 than that of the potassic zone 1 g cm 3 indicating that the late trapped fluid was more dilute

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

intermediate sulfidation epithermal gold base metal deposits in tertiary subaerial volcanic rocks sahinli tespih dere lapseki western turkey abstract gold in the sahinli and tespih dere intermediate sulfidation gold base metal deposits in western turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures including plumose quartz vug infills comb and cockade textures and matrix supported milled breccias the total sulfide content of the veins in the area is variable ranging from fluid inclusions in main stage quartz at sahinli are only liquid rich with homogenization temperatures ranging from 220 to 322 c and the majority of th values between 250 and 300 c salinity ranges from 4 3 to 6 9 wt nacl equiv first ice melting temperatures tmf between 24 5 and 19 0 c indicate that the fluids were dominated by nacl h2o during mineralization the relatively higher average th at the tespih dere deposit 295 c is attributed to a relatively deeper level of exposure calculated 18o values indicate that ore forming hydrothermal fluids in the study area had 18oh2o ranging from 1 1 to 9 7 average 3 8 strongly 18o enriched compared with present day hydrothermal meteoric water in the area 18o 8 5 d values of fluid inclusions in quartz range from 58 to 93 and d values of clay minerals and alunite from 40 to 119 d values from intermediate argillic alteration average 68 in the study area are very similar to d values of the present day local geothermal system average d 54 whereas d values from advanced argillic alteration average d 33 are very different from the present day local geothermal system the 34s values in samples from the sahinli and tespih dere deposits average 2 9 for pyrite 3 3 for chalcopyrite 5 4 for sphalerite and 7 6 for galena these data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock

late eocene oligocene post collisional monzonitic intrusions from the alborz magmatic belt nw iran an example of monzonite magma generation from a metasomatized mantle source abstract a potassic magmatic association in the zagros hinterland of the tethyan orogen in iran is identified and characterized for relevant geochronologic and petrologic features new data including a combination of field relations u pb zircon geochronology and rock geochemistry come from seven plutons khankandi shaivar dagh yuseflu mizan saheb divan roudbar and abhar that form the arasbaran taroum batholith atb which forms part of the alborz magmatic belt amb of nw iran zircon shrimp ages range from 38 32 0 17 ma 38 94 0 42 ma and 37 78 0 28 ma for magma pulses of the abhar pluton at the east of the batholith to 24 51 0 27 ma and 23 55 0 47 ma for pulses of the mizan pluton at the west considering these ages and the previously published ones together emplacement of the batholith took place during late eocene and oligocene from 38 to 23 ma with an age progression from se to nw at a rate of 2 cm year the whole batholith is characterized by potassic rocks with k2o 2 wt in gabbros and diorites sio2 6 wt are normally found in rocks with intermediate silica contents of about 60 wt sio2 these intermediate silica rocks are truly monzonites and are the most abundant in each pluton with regard to trace elements the monzonitic rocks of the atb show some of the typical signatures of arc magmatism depletion in nb and ti most samples contain moderate contents of sr 500 800 ppm close to similar potassic magmas forming cenozoic complexes in central iran the relatively moderate sr y and la yb ratios suggest that atb magmas retain some adakitic signatures from the source region geochemical modeling is performed by using melt compositions and phase relations calculated with melts software combined with experimental data and trace element signatures we conclude that monzonitic and shoshonitic magmas of some plutons of the atb shaivar dagh kahnkandi and yuseflu have an adakitic signature inherited from early melts that metasomatized the peridotite mantle decompression melting at a relatively low pressure of a metasomatized mantle source is the most plausible explanation for the generation of potassic magmas of the atb the lack of adakitic signature in three plutons supports the hypothesis that trace element features are related to processes in the source the tectonic implications are straightforward first subduction is needed to cook a metasomatized mantle source by fluxing of calc alkaline melts adakitic or not from the subduction zone second lithosphere extension is needed to carry metasomatized mantle to melt and to generate the potassic magmatism that formed the arasbaran taroum batholith as well as other cenozoic potassic magmas of the alborz magmatic belt in nw iran

active geothermal systems with entrained seawater as modern analogs for transitional volcanic hosted massive sulfide and continental magmato hydrothermal mineralization the example of milos island greece the paradigm for low sulphidation ls volcanic arc associated mineralization is the active geothermal systems located along the taupo volcanic zone e g broadlands however this analogue is inapt where fluid salinities are consistently in excess of 3 5 wt nacl ls mineralization on milos aegean arc records high paleofluid salinities the d and 18o data do not exemplify 18o shifted meteoric waters typical of terrestrial geothermal systems nor is a submarine origin indicated stable isotope data show mixing between meteoric seawater and volcanic arc gases strontium isotope data are comparable to a nearby active seawater entrained geothermal system these are features seen in hydrothermal systems associated with emergent volcanoes for the milos ls mineralization high salinity fluids show it cannot be explained by a broadlands type model the absence of saliferous sequences and significant intrusive rocks preclude these as salinity sources the similarities between paleo and active systems in terms of salinity d 18o and strontium isotope systematics strongly suggest that seawater is the main source for na and cl we suggest geothermal systems containing seawater associated with emergent volcanoes are an alternative analogue for ls epithermal mineralization furthermore they bridge the gap between submarine and large scale terrestrial geothermal systems the modern analogues for vhms and epithermal mineralisation in the scheme of intrusion centered hydrothermal mineralization

prograde evolution and geothermal affinities of a major porphyry copper deposit the cerro colorado hypogene protore i region northern chile the middle eocene 51 8 0 6 ma hypogene protore underlying the supergene orebody of the cerro colorado porphyry cu mo deposit i region chile exhibits features not commonly documented in such hydrothermal systems early stage alteration of upper cretaceous plagioclase phyric andesite generated a sub horizontal blanket of pervasive extremely fine grained but texture preserving biotite 35 modal albite 40 magnetite 3 alteration 8 km 2 in area but lacking sulfide minerals at least seventy percent of the chalcopyrite pyrite stockwork mineralization was emplaced during the subsequent main stage alteration which comprises with decreasing depth quartz albite sericite chlorite clay smectite quartz sericite clay and andalusite diaspore pyrophyllite assemblages the deposit is apparently unique among documented central andean porphyry systems in the association of the highest grade copper mineralization with intermediate argillic alteration the subsequent transitional stage phyllic i e quartz sericite pyrite tourmaline alteration was associated with the emplacement of molybdenite rich breccia bodies the occurrence of undumortieri tized tourmaline veinlets cutting andalusite diaspore assemblages confirms that much of the advanced argillic alteration took place during the main stage early stage alteration was the product of nonboiling cool trapping temperature ca 380 c low salinity 8 wt nacl equiv fluids which added substantial k na mg fe 2 cl f and water to the host andesite the initial main stage fluids boiling at a paleodepth of ca 2 5 to 3 0 km were up to 160 c hotter 544 c and highly saline 52 wt nacl equiv as these fluids rose they cooled to 320 c were diluted to 37 wt nacl equiv deposited sulfides and leached k na ca mg fe 2 and cl from the host rocks yielding diverse broadly contemporaneous intermediate and advanced argillic alteration facies pressure estimates require that low density 0 3 g cm 3 and thus more acidic fluids were primarily responsible for the formation of the quartz sericite clay and shallow advanced argillic alteration subsequent phyllic alteration was similarly caused by boiling fluids which were hot 486 c and saline 47 wt at depth but cooler 334 c dilute 8 wt and vapor dominated at shallower levels even terminal stage pyrite veins formed at temperatures as high as 450 c albeit from low salinity 8 wt fluids following a major prograde thermal transition from the early to the main stage each sulfide depositing alteration episode at cerro colorado was generated by a pulse of high temperature fluid which cooled and diluted as it rose such changes in fluid characteristics temperature and alteration relationships are well documented in numerous geothermal fields where potassic alteration generally develops at ca 270 to 350 c and are likely to occur at an early stage in any hydrothermal system in which magmatic fluids exsolving at relatively high pressures ascend into the near surface environment the initial alteration at cerro colorado plausibly developed under conditions similar to those in nonexplosive geothermal systems in which hydrothermal fluids cool and disperse laterally at shallow depths extensive zones of biotite rich alteration generally barren and with a hornfelsic appearance occur in many andesite hosted porphyry copper deposits but few data are available elsewhere for mineralogical pressure temperature or metasomatic exchange relationships in such systems cerro colorado may however be representative of a subclass of porphyry copper deposits exhibiting unusually close analogies with geothermal systems

post collisional polycyclic plutonism from the zagros hinterland the shaivar dagh plutonic complex alborz belt iran the petrological and geochronological study of the cenozoic shaivar dagh composite intrusion in the alborz mountain belt nw iran reveals important clues to decipher complex relations between magmatic and tectonic processes in the central sectors of the tethyan alpine himalayan orogenic belt this pluton is formed by intrusion at different times of two main magmatic cycles the older cycle 1 is formed by calc alkaline silicic rocks which range in composition from diorites to granodiorites and biotite granites with abundant mafic microgranular enclaves the younger cycle cycle 2 is formed by k rich monzodiorite and monzonite of marked shoshonitic affinity the latter form the larger volumes of the exposed plutonic rocks in the studied complex zircon geochronology laser ablation icp ms analyses gives a concordia age of 30 8 2 1 ma for the calc alkaline rocks cycle 1 and a range from 23 3 0 5 to 25 1 0 9 ma for the shoshonitic association cycle 2 major and trace element relations strongly support distinct origins for each magmatic cycle rocks of cycle 1 have all the characteristic features of active continental margins shoshonitic rocks cycle 2 define two continuous fractionation trends one departing from a k rich basaltic composition and the other from an intermediate k rich composition a metasomatized mantle origin for the two shoshonitic series of cycle 2 is proposed on the basis of comparisons with experimental data the origin of the calc alkaline series is more controversial but it can be attributed to processes in the suprasubduction mantle wedge related to the incorporation of subducted melanges in the form of silicic cold plumes a time sequence can be established for the processes responsible of the generation of the two magmatic cycles first a calc alkaline cycle typical of active continental margins and second a k rich cycle formed by monzonites and monzodiorites this sequence precludes the younger potassic magmas as precursors of the older calc alkaline series by contrast the older calc alkaline magmas may represent the metasomatic agents that modified the mantle wedge during the last stages of subduction and cooked a fertile mantle region for late potassic magmatism after continental collision

fluid inclusion and stable isotope study of the lubin zardeh epithermal cu au deposit in zanjan province nw iran implications for ore genesis abstract the lubin zardeh deposit is located in the western alborz magmatic belt 45 km ne of zanjan iran this deposit contains polymetallic cu au pb zn mineralization which is hosted by the cenozoic volcanic intrusive rocks of mainly intermediate and acidic composition pyrite chalcopyrite galena sphalerite bornite and tennantite tetrahedrite with native gold and silver are present in the ores quartz adularia and clay minerals illite montmorillonite with minor calcite are the most abundant gangue minerals and generally occur as fine grained assemblages some are however medium and coarse grained assemblages the ore minerals show disseminated vein veinlet replacement and brecciated textures while the gangue minerals represent replacement cockade crustiform colloform comb vein veinlet and plumose textures alteration haloes along the main vein are silicic argillic illite montmorillonite sericitic and pyritic gold contents of the quartz chalcopyrite gold veins range from 0 002 to 10 ppm with an average of 0 52 ppm the average values for total reserve of 0 5 mt of lubin zardeh deposit has been determined 1 3 0 7 and 0 4 for cu pb and zn respectively most of fluid inclusions in the quartz gold sulfide veins consist of two vapor and liquid phases at room temperature the primary fluid inclusions have a low to intermediate homogenization temperature between 127 and 327 c and salinity between 4 07 and 13 98 wt nacl equivalent stable isotope and fluid inclusion studies indicate that mineralization occurred in two stages at lubin zardeh deposit i e stage i along which base metal deposited and stage ii which is associated with copper and gold mineralization the 18oquartz values from stage i and stage ii range from 9 56 to 12 77 and from 7 23 to 9 24 respectively while their 34s values of sulfide minerals range from 0 9 to 6 2 and form 6 6 to 1 9 the isotopic and microthermometric data indicate that the hydrothermal solution evolved through mixing of magmatic fluids with meteoric waters boiling of magmatic fluid and mixing with meteoric waters were the main mechanisms of ore deposition in the lubin zardeh low sulfidation epithermal deposit

garnet sm nd data from the saualpe and the koralpe eastern alps austria chronological and p t constraints on the thermal and tectonic history abstract garnets from recrystallized staurolite and kyanite bearing mica schists from the central saualpe base ment representing the host rocks of the type locality eclogites give concordant sm nd garnet whole rockisochronagesbetween88 5 1 7and90 9 0 7ma themillimetre sized mostly inclusion freegrainsshowfairlyhomogeneouselement pro les withpyropecontentsof25 27 narrowrims withanincreasein fe and mn and a decrease in mg document minor local re equilibration during cooling accordingto phengite geothermobarometry peak metamorphic conditions at 90 ma were close to 20kbar and680 c and similar to those recorded by the eclogites the garnet rims record about 575 c 7kbar forthe nal stages of metamorphism a phengitic garnet mica schist sampled at the immediate contact withthe gertrusk eclogite gave a garnet whole rock sm nd age of 94 0 2 7 ma garnet porphyroclasts separated from a pegmatite mylonite of the koralpe plattengneiss near stainzare unzoned and show spessartine contents of 15 composition and sm nd ages of close to 260 mapoint to a magmatic origin for these garnets the garnet data from the saualpe document an intense alpine metamorphism for this part of theaustroalpine basement the mica schists recrystallized during decompression and rapid exhumation atthe nal stages of and immediately following a high p event the koralpe data show that high alpinetemperatures did not reopen the sm nd isotope system implying a closure temperature in excess of c 600 c for this isotopic system in garnet key words alpine orogenesis closure temperature eastern alps high p metamorphism metamorphicand magmatic garnets p t t paths saualpe koralpe basement sm nd geochronology

origin of the mclaughlin mine sheeted vein complex metal zoning fluid inclusion and isotopic evidence the mclaughlin deposit is a large hot spring type gold deposit located in the northern coast ranges of california at the faulted lithologic contact between the coast range ophiolite and the great valley sequence the mclaughlin deposit is centered around the sheeted vein complex a large multistage vein swarm localized in a dilation zone formed by rheologic contrasts in the footwall polymictic melange the surface expression of the sheeted vein complex is a subaerial sinter terrace which merges into the sheeted vein complex metal zoning in the sheeted vein complex is highly telescoped the sinter is enriched in mercury whereas gold and silver are restricted to the upper 350 m with the proportion of gold to silver decreasing with depth gold is typically present as electrum and is associated with silver and base metal bearing sulfosalts below 350 m mineralization is dominated by small quartz veins with base metal sulfides fluid inclusion studies indicate that nacl is the main dissolved salt in concentrations averaging 2 4 wt percent nacl equiv the bulk of the salinity data can be explained by variable amounts of adiabatic boiling and mixing with steam heated ground water fluid inclusion homogenization data ranges from 121 degrees to 263 degrees c with the deepest portion of the system examined having the highest temperatures and the shallowest samples having the lowest temperatures fluid inclusion gas concentrations vary with depth below the sinter co 2 and to a lesser extent ch 4 shows a systematic increase with depth fluid pressures calculated from fluid inclusion homogenization temperatures and gas analysis are in excess of the hydrostatic pressure and approach or exceed lithostatic pressure self sealing of the system and tectonic dilation most likely resulted in catastrophic phase separation and hydrothermal eruption breccias geothermometry results based on fluid inclusion gas ratios show a reasonable correspondence with the highest fluid inclusion homogenization temperatures there is a strong trend for decreasing delta 18 o quartz values with depth due to the effect of temperature the calculated delta 18 o sub h 2 values are fairly constant at about 9 to 10 per mil oxygen and hydrogen isotope values as well as geologic relationships are consistent with those of hydrothermal fluids originating as meteoric water these evolved to increasingly high ones by interaction with great valley sequence sedimentary rocks lead isotope compositions of sulfides and potential source rocks indicate that lead and by inference other metals was derived from a crustal source the lead source may have been detritus from the sierra nevada batholith that comprises the great valley sequence or alternatively it may have been derived from a thorough mixture of radiogenic lead and nonradiogenic lead that occurred prior to mineralization

epithermal gold mineralization in an old volcanic arc the jacinto deposit camagueey district cuba the jacinto vein system in the camaguey district of central cuba is a low sulfidation adularia sericite epithermal gold deposit it is hosted by volcanic and volcaniclastic rocks of cretaceous age along the margin of the camaguey batholith jacinto is unusually old and much more closely associated with a large batholith than would be expected for an epithermal vein deposit in an island arc this study was undertaken to determine how jacinto could have been preserved for so long the jacinto system includes at least five veins that range in length up to 1 km have maximum widths of 60 m and extend to depths of at least 150 m the veins consist almost entirely of quartz with minor amounts of adularia calcite commonly bladed pyrite and gold which form at least 20 growth zones that can be divided into five main stages and can be correlated from one vein to another gold ore shoots are restricted vertically and are more continuous horizontally their present configuration suggests that the entire system has been tilted about 5 degrees to the northeast wall rock alteration is limited and consists of minor k feldspar and sericite fluid inclusions in vein quartz homogenize at temperatures of 200 degrees to 320 degrees c and freeze at temperatures characteristic of salinities of about 0 to 1 wt percent nacl equiv the presence of bladed calcite and silica pseudomorphs after bladed calcite suggests that the hydrothermal fluids boiled stable isotope analyses of quartz calcite and inclusion fluids indicate that the veins were deposited by waters with delta 18 o and delta d values that range from values just above those of magmatic water to those typical of cretaceous meteoric water 40 ar 39 ar analyses of adularia in the jacinto veins indicate an age of about 72 ma for mineralization and geologic relationships suggest that the vein system is related to la sierra rhyolite flows and domes of that approximate age la sierra rhyolite was extruded onto an erosion surface that exposed the camaguey batholith and related volcanic rocks indicating that erosion rates were relatively rapid immediately prior to formation of the deposit shortly after the deposit formed however it was tilted and then buried beneath late cretaceous to eocene sediments of the maraguan basin which are being eroded to expose the system today this fortuitous sequence of volcanism batholith emplacement rapid erosion to deep batholith levels extrusion of rhyolite and local sedimentation appears to be the result of collision between the cuban arc and the bahamas platform similar collisions between arcs and continental masses could have formed other epithermal deposits

tectonometamorphic evolution of the koralm complex eastern alps constraints from microstructures and textures of the plattengneis shear zone abstract lattice preferred orientations lpo of quartz have been investigated along a south north oriented section across the plattengneis of the koralm complex eastern alps the plattengneis forms an important shear zone within the austroalpine nappe complex of the eastern alps which has developed during the cretaceous evolution of the alpine orogen the quartz c axes form small circle distributions in the southernmost parts of the koralm complex which represent the uppermost structural level of the plattengneis further to the north two maxima between the y and z directions of the finite strain can be interpreted in terms of preferred slip on the rhomb planes these fabrics continuously grade into type i and type ii crossed girdle distributions in a northward direction a strong maximum near the y axis with the tendency to be distributed along a single girdle with three corresponding maxima of a axes near the margin of the pole figure can be observed in the central and northern parts such lpo are characteristic for both high grade metamorphic conditions and high finite strain the microstructures display that the deformation within the plattengneis shear zone was synmetamorphic a continuous increase of peak temperatures and pressure from approximately 550 c to approximately 750 c from the south to the central parts can be inferred from geothermometric calculations the temperatures then decrease to approximately 650 c from the central parts to the north the related pressures increase from 8 to 16 kbar and then decrease to 10 kbar the lpo changes that have been observed in the study area are best interpreted in terms of temperature dependence of the activation of glide systems within quartz aggregates the temperature and pressure evolution may indicate that the central parts of the koralm complex have been exhumed by larger amounts than the northern and southern parts this is also documented by the lpo evolution therefore we assume that the plattengneis shear zone formed during the exhumation of the koralm complex and is related to the exhumation of high pressure units in the footwall of this shear zone accordingly the kinematics of the plattengneis shear zone is rather extensional than thrust related the implications for the structural evolution of the eastern alps are shortly discussed

the nature and timing of ore formation in the budunhua copper deposit southern great xing an range evidence from geology fluid inclusions and u pb and re os geochronology abstract the budunhua copper deposit is located in the southern great xing an range where the stockwork ore bodies are mainly hosted in the lower permian dashizhai formation the mineralization occurs in two blocks the jinjiling and kongqueshan and both are characterized by four main stages arsenopyrite pyrite molybdenite quartz chalcopyrite pyrrhotite quartz galena sphalerite chalcopyrite quartz and calcite fluorite quartz wall rock alteration which is related to mineralization is dominated by silicification sericitization and chloritization fluid inclusion studies show that the ore forming fluids from cu stages in both blocks are broadly identical with trapping temperatures of 280 to 400 c for the kongqueshan and 300 to 420 c for the jinjiling estimated trapping pressures for the kongqueshan are 15 0 to 26 6 mpa and for the jinjiling are 14 9 to 29 4 mpa corresponding to entrapment depth of 1 5 to 2 7 km and 1 5 to 2 9 km below the paleowater table respectively zircon grains from the tonalite porphyry in the deposit yielded a weighted 206 pb 238 u mean age of 152 0 7 ma which is consistent with a molybdenite re os model age of 150 2 2 ma indicating that both the porphyry intrusion and the copper deposit are of late jurassic age our data suggest that the budunhua deposit is an atypical porphyry deposit related to a late jurassic magmatic hydrothermal system

stable isotope geochemistry of the pierina high sulfidation au ag deposit peru influence of hydrodynamics on so42 h2s sulfur isotopic exchange in magmatic steam and steam heated environments abstract the pierina high sulfidation au ag deposit formed 14 5 my ago in rhyolite ash flow tuffs that overlie porphyritic andesite and dacite lavas and are adjacent to a crosscutting and interfingering dacite flow dome complex the distribution of alteration zones indicates that fluid flow in the lavas was largely confined to structures but was dispersed laterally in the tuffs because of a high primary and alteration induced permeability the lithologically controlled hydrodynamics created unusual fluid temperature and ph conditions that led to complete so 4 2 h 2 s isotopic equilibration during the formation of some magmatic steam and steam heated alunite a phenomenon not previously recognized in similar deposits isotopic data for early magmatic hydrothermal and main stage alunite 34 s 8 5 to 31 7 18 o so 4 4 9 to 16 5 18 o oh 2 2 to 14 4 d 97 to 39 sulfides 34 s 3 0 to 4 3 sulfur 34 s 1 0 to 1 1 and clay minerals 18 o 4 3 to 12 5 d 126 to 81 are typical of high sulfidation epithermal deposits the data imply the following genetic elements for pierina alteration mineralization 1 fluid and vapor exsolution from an i type magma 2 wallrock buffering and cooling of slowing rising vapors to generate a reduced h 2 s so 4 6 highly acidic condensate that mixed with meteoric water but retained a magmatic 34 s s signature of 1 3 so 2 disproportionation to hso 4 and h 2 s between 320 and 180 c and 4 progressive neutralization of laterally migrating acid fluids to form a vuggy quartz alunite quartz clay intermediate argillic propylitic alteration zoning magmatic steam alunite has higher 34 s 8 5 to 23 2 and generally lower 18 o so 4 1 0 to 11 5 18 o oh 3 4 to 5 9 and d 93 to 77 values than predicted on the basis of data from similar occurrences these data and supporting fluid inclusion gas chemistry imply that the rate of vapor ascent for this environment was unusually slow which provided sufficient time for the uptake of groundwater and partial to complete so 4 2 h 2 s isotopic exchange the slow steam velocities were likely related to the dispersal of the steam column as it entered the tuffs and possibly to intermediate exsolution rates from magmatic brine the low d values may also partly reflect continuous degassing of the mineralizing magma similarly data for steam heated alunite 34 s 12 3 to 27 2 18 o so 4 11 7 to 13 0 18 o oh 6 6 to 9 4 d 59 to 42 are unusual and indicate a strong magmatic influence relatively high temperatures 140 to 180 c based on 18 o so 4 oh fractionations and partial to complete sulfur isotopic exchange between steam heated sulfate and h 2 s restricted lithologically controlled fluid flow in the host tuffs allowed magmatic condensate to supplant meteoric groundwater at the water table and create the high temperature low ph conditions that permitted unusually rapid so 4 2 h 2 s isotopic equilibration 50 300 days and or long sulfate residence times for this environment late void filling barite 34 s 7 4 to 29 7 18 o so 4 0 4 to 15 1 and later void filling goethite 18 o 11 8 to 0 2 document a transition from magmatic condensate to dominantly meteoric water in steam heated fluids during cooling and collapse of the hydrothermal system these steam heated fluids oxidized the top 300 m of the deposit by leaching sulfides redistributing metals and precipitating barite acanthite gold and goethite hematite gold steam heated oxidation rather than weathering was critical to forming the orebody in that it not only released encapsulated gold but likely enriched the deposit to ore grade au concentrations

constraints on the ore fluids in the chah zard breccia hosted epithermal au ag deposit iran fluid inclusions and stable isotope studies the chah zard gold silver deposit in the central part of the urumieh dokhtar magmatic arc udma of iran is a breccia hosted low to intermediate sulfidation epithermal deposit with a resource of 2 5 mt averaging 1 7 g t au and 12 7 g t ag gold and silver mineralization occurs in breccia and veins associated with a 6 2 0 2 ma volcanic complex microthermometric measurements on quartz and sphalerite hosted two phase liquid rich fluid inclusions indicate that the mineralization may have taken place between 260 and 345 c from a moderately saline hydrothermal fluid 8 4 13 7 wt nacl equiv first ice melting temperatures between 37 and 53 c indicate that the aqueous fluids contained nacl cacl2 mgcl2 fecl2 coexisting liquid rich and vapor rich fluid inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of adularia and bladed calcite in high grade ore zones and the presence of hydrothermal breccias and chalcedonic quartz are consistent with boiling calculated 18o values of water in equilibrium with quartz 3 4 to 13 1 suggest that the fluid may have had a magmatic source but was 18o depleted by mixing with meteoric water the average calculated 34sh2s values are 0 2 for pyrite 0 2 for chalcopyrite 1 0 for sphalerite and 0 2 for galena the 34sh2s values are consistent with a magmatic source for sulfur gold deposition at chah zard is inferred to have been largely caused by boiling although fluid mixing and or wall rock reactions may also have occurred after rising to a depth of between 970 and 440 m the fluid boiled causing deposition of fine grained quartz and sealing of the hydrothermal conduit episodic boiling in response to alternating silica sealing and hydraulic brecciation was responsible for ore deposition gold and silver may have precipitated due to the destabilization of hs complexes caused by the boiling off of h2s to vapor whereas the dilution and or cooling of hydrothermal fluids led to the precipitation of base metals

structural control on overprinting high sulfidation epithermal on porphyry mineralization in the chodarchay deposit northwestern iran abstract the chodarchay high sulfidation epithermal porphyry deposit is located in the tarom volcano plutonic subzone of western alborz structural zone in nw iran in addition to chodarchay the tarom subzone hosts several other epithermal deposits lithologic units in chodarchay consist of volcanic pyroclastic rocks and intrusive bodies petrographical studies have identified different rocks which host the mineralization mineralization has taken place in both volcanic pyroclastic units and intrusions detailed mineralogical and alteration data gathered from drill cores and thin sections provides support for the hypothesis that the high sulfidation epithermal mineralization is underlain by a porphyry copper system this deposit is the first reported porphyry epithermal mineralization in this subzone the main structure of the chodarchay area is a fault zone that formed parallel to the general tarom nw se direction based on remote sensing studies on a wider scale lineaments generally show ne sw trends but the chodarchay fault zone has a nw se strike and is associated with another w e trending fault zone these fault zones are correlated with argillic alteration there are two sets of reverse fault fractures with a strike slip component based on slickenlines in the field and core observations a normal sense of fault movement remains in the nw part of the structural system these new data sets indicate two main extensional and compressional mechanisms for the fault the evolution of the fault system from normal to reverse in the deposit characterizes the present day structural system of the chodarchay area plutonism and porphyry mineralization are related to the extensional stage whereas the epithermal part of the deposit is associated with the compressional stage of fault activation

kinematics of cretaceous nappe tectonics in the austroalpine basement of the koralpe region eastern austria krohe a 1987 kinematics of cretaceous nappe tectonics in the austroalpine basement of the koralpe region eastern austria tectonophysicz 136 171 196 the austroalpine basement of the koralpe area austria was affected by penetrative ductile deformation in the cretaceous three metamorphic events have been established ht lp metamorphism of unknown age a hercynian mt mp metamorphism and a cretaceous eo alpine mt mp metamorphism in the koralpe area cretaceous rb sr cooling ages of muscovite indicate temperatures of at least 500 o c during the eo alpine event the most intense deformation occurred along intracrustal shear zones plattengneis north to northeast directed thrusting is indicated by an inverted metamorphic gradient regional transposition of an older foliation s c fabrics and oblique quartz fabrics after development of high temperature mylonites low angle normal shear zones low temperature mylonites cut the uppermost parts of the austroalpine basement and indicate an extensional tectonic setting at about 85 to 90 ma s c and quartz fabrics indicate downdip movements of the hanging wall towards the northeast intracrystalline a slip in quartz caused strong preferred lattice orientation in high and low temperature mylonites during the e alpine deformation the basal a slip system is more pronounced at lower temperatures whereas a prism a system predominates at higher temperatures the overall kinematic history of the austroalpine nappe complex in the study area suggests a model in which an intracrustal south over north imbrication took place in an early stage of eo alpine collision these movements were outlasted by sinistral strike slip movement possibly due to oblique collision along irregular margins of the austroalpine and brianpnnais complexes the collision imbrication process resulted in crustal thickening isostatic uplift and thus extension of the higher parts of the crust low angle normal faulting initiated sedimentation in the intramontane c tic gosau basins of late cretaceous age

fluid inclusions and h o s pb isotope systematics of the chalukou giant porphyry mo deposit heilongjiang province china abstract the chalukou giant porphyry mo deposit located in the northern great xing an range is the largest mo deposit in the xing an mongolia orogenic belt this deposit s ore bodies are mainly hosted in an intermediate felsic complex and jurassic volcanic sedimentary rocks of which late jurassic granite porphyry quartz porphyry and fine grained granite are closely associated with the mo mineralization three types of fluid inclusions fis are present in the quartz associated with oxide and sulphide minerals i e liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis the fis in the quartz phenocrysts of the granite porphyry contain liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis the homogenization temperatures vary from 230 c to 440 c and 470 c to 510 c and their salinities vary from 0 7 to 53 7 nacl eq and 6 2 to 61 3 nacl eq respectively the fis of k feldspar quartz magnetite veins of the early stage are composed of liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis with homogenization temperatures and salinities of 320 c to 440 c and 4 2 to 52 3 nacl eq respectively the fis of quartz molybdenite veins and breccia of the middle stage are composed of liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis with homogenization temperatures and salinities of 260 c to 410 c and 0 4 to 52 3 nacl eq respectively fis of quartz fluorite galena sphalerite veins of the late stage are liquid rich two phase fis with homogenization temperatures and salinities of 170 c to 320 c and 0 5 to 11 1 nacl eq respectively the ore forming fluids of the chalukou deposit are characterised by high temperature high salinity and high oxygen fugacity belonging to an f rich h 2 o nacl co 2 system the 18 o w values vary from 4 5 to 3 2 and the d w values vary from 138 to 122 indicating that the ore forming fluids were a mixture of magmatic and meteoric water the 34 s values range from 1 9 to 3 6 with an average of 1 6 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of the metallic minerals are in the ranges of 18 269 18 501 15 524 15 567 and 38 079 38 264 respectively both the s and pb isotopic systems indicate that the ore metals and fluids came primarily from a deep seated magma source from the juvenile lower crust the mo mineralization in the chalukou deposit occurred at a depth of 0 5 to 1 3 km and multiple stages of phase separation or immiscibility of ore forming fluid was critical for the formation of the chalukou deposit

geology and genesis of the early paleozoic zhengguang intermediate sulfidation epithermal au zn deposit northeast china abstract zhengguang is a partly eroded about 500 m being eroded structurally controlled intermediate sulfidation is epithermal gold zinc deposit characterized by wide distribution of base metal sulfides fe poor sphalerite and mn calcite hosted by the late cambrian early ordovician basaltic andesitic volcanic and volcano sedimentary rocks in northeast china the deposit is located 4 and 8 km from the early ordovician tongshan including several is veins about 500 m away in the east called east tongshan and duobaoshan porphyry copper deposits respectively a 484 8 8 7 ma mswd 198 of re os isochron age on pyrite indicates that it is the most ancient intermediate sulfidation deposit that has been dated four stages of veins have been discerned at zhengguang early magnetite chalcopyrite epidote chlorite and k feldspar pyrite chalcopyrite veins stage i were associated with restricted k feldspar epidote locally with chlorite alteration and propylitic epidote chlorite calcite assemblages two primary epithermal gold stages developed at zhengguang pyrite quartz fe poor sphalerite chalcopyrite galena electrum petzite hessite tetrahedrite tennantite adularia veins stage ii and mn calcite quartz pyrite fe poor sphalerite chalcopyrite galena hessite native gold stage iii plus a late barren stage characterized by little sulfides calcite chlorite hematite quartz stage iv gold occurs chiefly as micro inclusions of electrum and petzite in pyrite and sphalerite of stages ii and iii stable isotope analyses and fluid inclusion results indicate a magmatic hydrothermal component in the ore fluids fluid inclusion data from stage i yielded the highest salinity 6 9 wt nacl and homogenization temperature average 264 c calculated oxygen isotope composition of fluid 18owater up to 4 9 equilibrated with quartz indicates a magmatic hydrothermal source during stage i a progressive addition of meteoric water component is suggested from stage i to iv of zhengguang based on the average 18owater values equilibrated with quartz and homogenization temperatures stage i 18owater 3 3 th 264 c stage ii 18owater 1 4 th 182 c stage iii 18owater 3 4 th 154 c stage iv 18owater 6 3 th 121 c our new pyrite re os dating result shows that zhengguang formed at the same time with tongshan and duobaoshan within errors comparable sulfur isotopic compositions of pyrite from zhengguang and tongshan analogous low fe content in sphalerite and similar mineral assemblage and alteration pattern between zhengguang and east tongshan is veins collectively indicate a genetic connection between zhengguang and tongshan which may derive from fluids exsolved from the same magma chamber high temperature assemblages e g k feldspr pyrite chalcopyrite at zhengguang indicate that there is potential for the discovery of porphyry copper gold mineralization below the current level of diamond drilling the confirmation of the zhengguang as an early paleozoic epithermal deposit implies a good preservation and exploration potential of ancient epithermal deposits in eastern central asian orogenic belt

the chemistry of fumarolic vapor and thermal spring discharges from the nevado del ruiz volcanic magmatic hydrothermal system colombia on the basis of three sets of gas samples taken during the three months preceding the november 13 1985 eruption of nevado del ruiz from fumaroles on the crater floor the composition of the vapors discharged following minor eruptive activity in september corresponded to that of an essentially magmatic gas during the subsequent quiet period in october the proportion of a hydrothermal component in the vapor discharge increased steadily up until the major eruption the gases were found to be exceptionally high in total sulfur and are super saturated with respect to elemental sulfur their thermodynamic equilibration temperatures range from 200 to 600 c gases and waters from fumaroles and thermal springs on the flanks of the volcano are likely to be derived from a two phase vapor brine envelope surrounding the magmatic system the chemistry of the fumarole discharges is compatible with the assumption of an eruptive mechanism involving the build up of pressure in an extensive vapor zone by gas released from an essentially stagnant already extensively degassed body of magmatic material at depth production of such a residual gas over extended periods may account for the large amount of so2 discharged from the volcano in relation to the small amount of ejected solids

low sulfidation type au ag mineralization at bergama izmir turkey abstract bergama the center of bergama county is located in western turkey and includes the villages of ovacik narlica and saganci the ovacik epithermal gold silver deposit is located in the western anatolian volcanic and extensional province adjacent to the ene trending bergama graben some 100 km north of the city of izmir gold of economic grades at the ovacik deposit reserves 4 19 mt at 7 6 g t occurs in epithermal quartz veins which display low temperature epithermal textures including crustiform banding quartz pseudomorphs after bladed calcite and multiphase hydrothermal breccias alteration minerals at both ovacik and narlica are dominated by smectite mixed layer illite smectite chalcedonic quartz and adularia whereas major kaolinite and minor mixed layer smectite illite 13 4 a occur at saganci the total sulfide content at ovacik is low geochemical variations in altered wall rocks at ovacik and narlica are generally characterized by two fold enrichments in k rb cs and 25 to 93 depletions in sr ca mg na and even higher depletions 96 to 99 decrease in the quartz adularia vein zone lanthanum ce pr hf zr sm eu gd tb and ho also exhibit up to 50 depletions in the wall rock and even more so up to 90 depletion for la and nd in the vein structure wall rock enrichment in au ag as hg and sc is by factors of 60 150 88 8 and 3 respectively the ranges of ree in both the altered volcanic rocks and quartz adularia veins are wide and may reflect either significant mobilization of ree during alteration and mineralization or their dilution by the metasomatic processes from fresh volcanic rocks through montmorillonite illite adularia altered wallrock to quartz adularia veins high rb sr ratios in adularia illite altered areas are closely related to the presence of k rich alteration minerals low rb sr ratios and corresponding low k values at saganci are due to acid leaching of volcanic rocks positive correlation coefficients between au and ag pb zn cd cu and sb in epithermal quartz veins all of which are 0 51 are significant silver and sb are remarkably enriched at higher levels of the deposit no correlation occurs between au and as or ag and as the ovacik quartz in au ag bearing veins has 18o values ranging from 9 5 to 15 7 whereas d values of fluid inclusions in quartz range from 89 to 125 however the narlica quartz in au ag bearing veins returned 18o values ranging from 5 9 to 8 3 whereas the d values of fluid inclusion in quartz range from 82 to 99 18o results indicate that ore forming hydrothermal fluids at ovacik and narlica had 18oh2o values ranging from 2 9 to 3 5 average 0 24 and from 2 96 to 0 6 average 1 6 respectively they are thus 18o enriched in comparison with present day meteoric and hydrothermal meteoric waters 5 4 18o 18oh2o and d values suggest that mineralizing solutions were a mixture of meteoric and magmatic waters the 34s sulfide data at ovacik and narlica range from 2 1 to 5 3 average 1 7 and from 4 6 to 2 7 average 0 36 respectively these 34s sulfide values are consistent with a magmatic source for s

extreme boiling model for variable salinity of the hokko low sulfidation epithermal au prospect southwestern hokkaido japan the hokko prospect is located in the minamikayabe area southwestern hokkaido japan where gold bearing quartz veins of pliocene age are exposed at the surface the alteration mineral assemblage is typical of low sulfidation epithermal systems with the quartz veins associated with adularia alteration overprinted on late miocene propylitic alteration fluid inclusion studies of the vein quartz reveal mean homogenization temperatures of approximately 220 c and the co existence of low salinity 2 wt nacl equivalent and moderate salinity 2 to 12 wt nacl equivalent fluid inclusions within the same veins the moderate salinity fluid inclusions 2 12 wt nacl equivalent typically have relatively low homogenization temperatures between 150 to 200 c the results obtained from stable isotope analysis of 18o in quartz vein material showed a gradual decrease in 18o signatures with increasing depth the majority of the samples have calculated fluid source signatures 18oh2o between 8 0 and 10 0 but there is a significant change in the composition above 185 m drill depth the shallower samples in particular show a wide range of oxygen isotope signatures that are associated with the moderate salinity fluid inclusions we interpret that low salinity inclusions within the hokko system represent the composition of the liquid phase of the fluid before boiling and that the moderate salinity inclusions are representative of the residual liquid phase after extensive non adiabatic boiling and vapor loss in an open system this mechanism resulted in the entrapment of fluids with variable salinities at the same time and in close proximity to each other this is also reflected in the 18oh2o values which become more variable and heavier where the moderate salinity inclusions occur deposition of ore minerals within the hokko vein system also occurred at this time as a result of boiling and gas loss

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

fluid rock interactions and the role of late hercynian aplite intrusion in the genesis of the castromil gold deposit northern portugal abstract castromil northern portugal is one of several important orogenic gold deposits located within the central iberian geotectonic zone of northwest iberia the deposit occurs at the margin of a variscan syn to late d3 biotite granite and is spatially associated with a small tourmaline aplite body that intrudes the granite at its contact with a secondary anticline of palaeozoic arenaceous and argillaceous metasediments of the valongo belt identification of the ore fluids and their pathways and the reconstruction of the p t x conditions during mineralisation were obtained by combining the geometric characteristics of veins and microstructures together with a detailed study of the inclusion fluids several stages of fluid percolation following contact metamorphism can be recognised at each stage the contact zone characterised by intrusive aplites related faults and fractures appears to have focused the hydrothermal flow and acted as a structural conduit for deeper sourced hydrothermal fluids the earliest fluid stage stage i is characterised by aqueous carbonic fluids dominated by co2 and ch4 that were probably generated by high temperature fluid rock interaction 400 500 c with graphitic schists interbedded with the metasediments these fluids were responsible for significant alteration greisenisation of the aplite and its host granite and the formation of silicified flat lying structures that can be traced along the strike length of the deposit at temperatures between 400 and 500 c fluid pressure ranges from 230 to 300 mpa which is equivalent to a depth of 10 1 5 km the second stage of mineralisation stage ii as ore stage is also characterised by aqueous carbonic fluids and represents the main phase of quartz arsenopyrite pyrite deposition the third stage of mineralisation stage iii au ore stage was accompanied by intense microfracturing of the preexisting quartz veins and the preferential deposition of gold along microfractures in the sulphides the introduction of gold corresponds to the percolation and mixing of two distinctive aqueous fluids of contrasting salinity at relatively low temperatures 150 275 c based on compositional and temperature data it is suggested that during the main phase of uplift shallow waters penetrated deep into the basement allowing gold to be leached from potential source rocks most probably the palaeozoic metasediments and deposited in structural and geochemical traps formed during earlier stages of the hydrothermal system the decrease in pressure during the as ore stage corresponds to a significant tectonic uplift around 5 6 km and probably marks the transition from lithostatic to hydrostatic pressure conditions furthermore if uplift had already been initiated during aplite emplacement the prevailing sub isothermal high temperature conditions provide an explanation for the presence of decrepitated aqueous carbonic inclusions in metamorphic quartz lenses and veins in the surrounding metasediments to conclude localised heat flows linked to late hercynian magmatism at deeper structural levels appears to be the main cause of fluid circulation at castromil evidence suggests that contact zones related to faulting along a secondary anticline of the valongo belt controlled both aplite intrusion and subsequent long lived hydrothermal fluid circulation the proposed genetic model differs from orogenic gold deposit models in emphasising the role of late stage aqueous fluids in the development of economic grade 10 15 g t gold ores

fluid inclusion and stable isotope constraints on ore genesis of the zajkan epithermal base metal deposit tarom hashtjin metallogenic belt nw iran in the zajkan pb zn cu au ag deposit of the tarom hashtjin metallogenic belt thmb northwest iran mineralization occurs as quartz base metal sulfide veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation four stages of ore formation are identified at zajkan 1 quartz chalcopyrite pyrite veins 2 quartz galena sphalerite chalcopyrite pyrite veins and breccias 3 quartz hematite veins and breccias and 4 barren quartz carbonate veinlets the primary metallic minerals are pyrite chalcopyrite sphalerite galena and trace amounts of hematite gangue minerals are mainly quartz sericite chlorite and calcite the main wall rock alteration is silicification and intermediate argillic and propylitic alteration the coexistence of different types of fluid inclusions lv vl and v in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping excluding the heterogeneously entrapped fluid inclusions the microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 degrees c from fluids with salinities between 1 7 and 6 4 wt nacl equiv the oxygen isotopic compositions delta o 18 water vsmow of 3 7 to 1 1 parts per thousand indicate that the ore forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore stages sulfur isotopic values of sulfide minerals vary over a narrow range from 5 0 to 0 9 parts per thousand vcdt averaging 2 2 parts per thousand vcdt suggesting that sulfur was derived from a homogeneous magmatic source the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at zajkan our data suggest that the zajkan deposit is an intermediate sulficiation style epithermal mineralization the estimated ore formation depth of zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the thmb

hydrothermal alteration and hydrologic evolution of the golden cross epithermal au ag deposit new zealand golden cross located in the coromandel peninsula new zealand is a classic example of a volcanic rock hosted low sulfidation epithermal gold silver deposit gold and silver ore is confined to the empire vein system and shallow level stockwork the veins are hosted by miocene to early pliocene andesites and dacites of the waipupu formation and the waiharakeke dacite that are unconformably overlain by the postore whakamoehau andesite hydrothermal alteration minerals display distinct spatial and temporal zonation around veins as defined along three cross sections 1 000 m long 450 m deep located 200 m apart which transect the empire vein system along these sections replacement quartz chlorite and pyrite are ubiquitous with the abundance of quartz veinlets increasing toward major veins replacement adularia envelops the empire vein system and shallow stockwork in each section it is coextensive with and is variably replaced by illite that progressively grades upward and laterally into a zone of interstratified illite smectite that mantles the deposit replacement calcite and minor siderite formed contemporaneously with and also overprint the above minerals whereas late barren calcite veins crosscut mineralized quartz veins kaolinite pyrite veinlets together with rare very local alunite formed during late stage hydrothermal activity clay mineral zonation is well developed illite occurs at depth and close to the veins grading outward and upward into illite smectite with minor smectite occurring 600 m east of the empire vein system this overall zonation reflects paleothermal gradients of 150 c on the periphery to 220 c near the veins consistent with the observed t h range of 150 to 240 c for fluid inclusions in quartz platy calcite and late barren calcite veins final ice melting temperatures for inclusions mostly range from 0 0 to 1 4 c corresponding to apparent salinities of less than 2 4 wt percent nacl equiv ice melting temperatures combined with vapor bubble expansion on crushing indicate the presence of dissolved co 2 in some platy calcite and late stage barren calcite the co 2 content is estimated to range from 0 35 to 3 5 wt percent with the lower limit set by fluid inclusion vapor expansion during crushing and the upper limit by the absence of any observable clathrates depth estimates based on inclusions in platy calcite suggest that the shallow level stockwork zone formed about 100 m below the paleowater table under hydrostatic conditions veins and alteration minerals at golden cross formed in the shallow part 400 m of a hydrothermal system analogous to geothermal systems in the nearby taupo volcanic zone the assemblage of quartz adularia chlorite illite calcite and pyrite reflects the upflow of near neutral ph to weakly alkaline chloride waters contemporaneously steam heated co 2 rich waters formed on the margins and reacted with the wall rock to form the assemblage of calcite siderite smectite illite smectite and kaolinite eventual thermal collapse and invasion of these peripheral co 2 rich waters into the former upflow zone produced late stage barren calcite veins and an overprint of clay carbonate alteration minerals at the same time localized steam heated acid sulfate waters generated above the water table descended to form the late overprint of kaolinite pyrite and alunite

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

the granite hosted gold deposit of moulin de cheni saint yrieix district massif central france petrographic structural fluid inclusion and oxygen isotope constraints the moulin de cheni orogenic gold deposit is the only granite hosted deposit of the saint yrieix district french massif central it occurs in 338 1 5 ma old peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization formation of quartz veins and gold deposition occurred in two successive stages an early mesozonal stage of quartz sulfide fe as s deposition usually devoid of gold and a late epizonal stage of base metal and gold deposition both stages postdate peak metamorphism and granite intrusion the genesis of the deposit is the result of four successive fluid events 1 percolation of aqueous carbonic metamorphic fluids under an assumed lithostatic regime of 400 450 c at a maximum depth of 13 km 2 formation of the main quartz lodes with coeval k alteration and introduction of as and s from aqueous carbonic fluids percolating along regional faults arsenopyrite and pyrite deposition was linked to the alteration of fe silicates into k feldspar and phengite at near constant iron content in the bulk granite temperature was similar to that of the preceding stage but pressure decreased to 100 50 mpa suggesting rapid uplift of the basement up to 7 5 km depth 3 the resulting extensional tectonic leads to the deposition of gold boulangerite galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process temperature and salinity decrease from 280 to 140 c and 8 1 wt eq nacl to 1 6 wt eq nacl respectively 4 sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids 1 6 wt eq nacl to 0 9 wt eq nacl under hydrostatic conditions at 200 150 c

geology geochemistry and genesis of axi a paleozoic low sulfidation type epithermal gold deposit in xinjiang china abstract axi is a low sulfidation type epithermal gold deposit hosted in paleozoic subaerial volcanic rocks in the western tianshan orogenic belt xinjiang china the resource is more than 50 t gold at an average grade of 4 4 ppm the deposit occurs in the tulasu volcanic fault basin in the paleozoic active continental margin on the northern side of the yili central tianshan plate the host rocks are andesitic volcaniclastic rocks of the paleozoic dahalajunshan formation and the orebodies occur as veins in annular faults of a paleocaldera mineralization at axi can be subdivided into five stages quartz and or chalcedony vein quartz vein quartz carbonate vein sulfide vein and carbonate vein there are two types of ore host quartz vein and altered rocks ore minerals are native gold electrum pyrite marcasite arsenopyrite hematite limonite and trace amounts of pyrargyrite polybasite naumannite cerargyrite sphalerite chalcopyrite tetrahedrite galena pyrrhotite and clausthalite gangue minerals are mainly quartz chalcedony illite calcite siderite dolomite adularia and laumontite the main wall rock alteration is silicification and phyllic alteration carbonatization and propylitization the deposit is characterized by an enrichment relative to crustal abundance of au ag as sb bi hg se te and mo depletion in base metals cu pb and zn and a low ag au ratio 0 5 3 7 three types of fluid inclusions were recognized in quartz from the major mineralization stages liquid aqueous inclusions liquid rich two phase inclusions and small amounts of vapor rich two phase inclusions microthermometric measurements indicate that the final ice melting temperatures are 0 3 to 4 4 c corresponding to salinities of 0 5 6 9 wt nacl equiv 2 2 wt nacl equiv in average the peak temperatures of ice melting varies from 0 4 to 1 9 c corresponding to salinities of 0 7 3 1 wt nacl equiv homogenization temperatures range mainly between 120 and 240 c with an average of 190 c and a maximum of 335 c the fluid density is 0 73 to 0 95 g cm 3 and thus the estimated maximum mineralization depth is about 700 m hydrogen and oxygen isotopic compositions of the ore fluids lie within a narrow range d h2o is 98 to 116 and 18 o h2o 1 8 to 0 4 3 he 4 he ranges from 0 0218 to 0 138 ra with an average of 0 044 ra indicating that he derived predominantly from crust with negligible mantle he in the ore fluids by contrast the 40 ar 36 ar ranges from 317 7 to 866 0 suggesting that crust derived radioactive 40 ar accounts for 7 0 to 66 and atmospheric 40 ar about 43 to 93 in the ore fluids hydrogen oxygen carbon sulfur and noble gas isotopes indicate that the ore forming fluids of the axi gold deposit consisted predominantly of circulating meteoric water ore forming metals may have derived mainly from the host volcaniclastic rocks of the dahalajunshan formation and basement rocks the occurrence of adularia platy calcite and quartz or sulfide aggregates as pseudomorphs after bladed calcite in ore veins and occurrence of aqueous liquid and liquid rich and vapor rich two phase inclusions indicates that boiling of the ore forming fluid have occurred leading to supersaturation of the hydrothermal solution and deposition of ore metals this is the main mineralization mechanism for quartz vein type ores in axi the ore forming fluid was buffered to a near neutral ph in a reduced environment during mineralization the preservation of this paleozoic axi deposit and its discovery required a rapid accumulation of sediments in the basin after formation of the deposit and minimal amount of erosion after late cenozoic uplift

fluid inclusion studies of the chinkuashih high sulfidation gold copper deposits in taiwan epithermal high sulfidation au cu deposits at chinkuashih in northeastern taiwan are found both within pleistocene calc alkaline volcanic rocks and the miocene sedimentary rocks the deposits consist of gold copper veins of the penshan group and breccia pipes of the tushihshan changjen group primary two phase inclusions in hydrothermal quartz and secondary two phase inclusions in hydrothermal quartz as well as igneous quartz phenocrysts probably represent fluids related to mineralization these inclusions have homogenization temperatures generally between 1908c and 2808c and salinities mostly from 0 5 5 0 wt nacl eq in the penshan group microthermometric data indicate that variable amounts of boiling mixing and cooling occurred in the hydrothermal system based on the th of inclusions trapped from boiling fluids and the co contents of the inclusions the hydrostatic pressure is estimated at 6 9 7 9 mpa in the tushihshan 2 changjen group the microthermometry of sulfur gas bearing secondary two phase fluid inclusions from hydrothermal quartz shows bimodal contents for a certain th value perhaps due to the intermittent incursion of brine at depth by phreatic or phreato magmatic explosions the presence of poly phase liquid q vaporq halite sylvite opaques fluid inclusions with high th 3078c 4848c and high salinities 30 51 wt nacl eq in one sample suggests a dense brine of probable magmatic derivation circulated in the chinkuashih system halite bearing inclusions which were homogenized by vapor disappearance coexisting with low salinity vapor rich inclusions in this sample may have been trapped in an immiscibility field at vapor pressures from 7 5 to 21 5 mpa halite bearing inclusions which were homogenized by halite dissolution after the vapor disappearance may have been trapped under even greater pressures fluid inclusion gas in samples were analyzed with a qms the results of bulk analyses indicate that these inclusions contain 99 45 99 67 mol h o 0 27 0 52 mol 2 co 0 015 0 066 mol n 0 0015 0 015 mol ch and small amounts of so in three samples these data suggest that 22 4 2 the inclusion fluids are dominantly meteoric waters that interacted with host rocks and accumulated upward fluxing magmatic volatiles the fluid inclusion data indicate that the hydrothermal fluids related to the ore deposition of the high sulfidation au cu deposits at chinkuashih are characterized by the interaction of magmatic fluids with meteoric water under epithermal conditions q 1999 elsevier science b v all rights reserved

intermediate sulfidation type base metal mineralization at aliabad khanchy tarom hashtjin metallogenic belt nw iran abstract the aliabad khanchy epithermal base metal deposit is located in the tarom hashtjin metallogenic belt thmb of northwest iran the mineralization occurs as cu bearing brecciated quartz veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation ore formation can be divided into five stages with most ore minerals such as pyrite and chalcopyrite being formed in the early stages the main wall rock alteration is silicification and chlorite argillic and propylitic alteration microthermometric measurements of fluid inclusion assemblages show that the ore forming fluids have eutectic temperatures between 30 and 52 c trapping temperatures of 150 290 c and salinities of 6 6 12 4 wt nacl equiv these data demonstrate that the ore forming fluids were medium to high temperature medium to low salinity and low density h2o nacl cacl2 fluids calculated 18o values indicate that ore forming hydrothermal fluids had 18owater ranging from 3 6 to 0 8 confirming that the ore fluid system evolved from dominantly magmatic to dominantly meteoric the calculated 34sh2s values range from 8 1 to 5 0 consistent with derivation of the sulfur from either magma or possibly from local volcanic wall rock combined the fluid inclusion and stable isotope data indicate that the aliabad khanchy deposit formed from magmatic hydrothermal fluids after rising to a depth of between 790 and 500 m the fluid boiled and subsequent hydraulic fracturing may have led to inflow and or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and or cooling the aliabad khanchy deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the mineralization at aliabad khanchy and other epithermal deposits of the thmb formed by hydrothermal activity related to shallow late eocene magmatism the altered eocene volcanic and volcaniclastic rocks especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the thmb

origin and evolution of hydrothermal fluids in the marshoun epithermal pb zn cu ag deposit tarom hashtjin metallogenic belt nw iran abstract the marshoun epithermal pb zn cu ag deposit is located in the tarom hashtjin metallogenic belt thmb northwest iran the epithermal base metal veins are mainly hosted in eocene volcanic and volcaniclastic rocks of the karaj formation and late eocene pyroxene quartz monzodiorite the mineralization process can be divided into five stages 1 quartz chalcopyrite pyrite veins and breccias 2 quartz calcite sphalerite galena chalcopyrite pyrite veins and breccias 3 barren post ore quartz veinlets 4 barren post ore calcite veinlets and 5 supergene mineral assemblages the primary metallic minerals are pyrite chalcopyrite sphalerite and galena gangue minerals are mainly quartz calcite sericite and chlorite the main wall rock alteration is silicification intermediate argillic carbonate and propylitic alteration microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 c from fluids with salinities between 3 4 and 6 3 wt nacl equiv coexisting lv vl and v inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of bladed calcite as well as plumose and colloform crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling obtained oxygen and sulfur isotope compositions 18owater 9 2 to 1 5 34sh2s 10 0 to 5 7 indicate there was a major contribution from a magmatic component to metallogenesis the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at marshoun the marshoun deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the epithermal mineralization in the thmb are related to late eocene ca 36 37 ma shallow magmatic hydrothermal activity the altered eocene volcanic subvolcanic rocks particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at thmb

evidence for fluid phase separation in high grade ore zones at the porgera gold deposit papua new guinea coexisting liquid rich and vapor rich primary fluid inclusions in quartz provide direct evidence for fluid phase separation in high grade quartz roscoelite gold veins and breccias from the porgera alkalic type gold deposit vapor rich fluid inclusions are co2 rich and sometimes contain liquid co2 at room temperature the close spatial and paragenetic relationship between these boiling assemblage fluid inclusions and gold suggests that gold was precipitated by phase separation at least locally additionally the occurrence of carbonate and sulfate minerals in high grade veins reflecting ph increase and oxidation of the boiled fluid and the appearance of hydrothermal breccias are consistent with the process of fluid phase separation liquid co2 bearing fluid inclusions are rare in near surface epithermal deposits and indicate that the porgera vein system was formed at greater depths and pressures our estimates suggest pressures between 250 and 340 bars it is suggested that alkalic type gold deposits may be distinguished from other epithermal deposit types by the more gaseous nature of the ore forming fluids in addition to their association with alkalic magmas

geochemical characteristics of igneous host rocks of lubin zardeh au cu deposit nw iran abstract the lubin zardeh au cu pb zn deposit is located in the azerbaijan western alborz zone 45 km ne of zanjan iran it is situated within the eocene oligocene volcanic plutonic belt of the tarom subzone of the alborz mountains range quartz monzonite and tuffs are the main host rock of the lubin zardeh au cu pb zn deposit granitoid rocks are predominantly high k calc alkaline with shoshonitic affinities they are i type metaluminous magnesian and are characterized by lile lree and th enrichment relative to hfse depletion in nb ta ti and weak depletion in hree and y these granitoids show some affinities with adakites e g high sr y and la yb ratios coupled with low yb and y and enrichment in lree and lile with weak eu anomalies their relatively low to moderate initial 87sr 86sr values 0 7047 0 7051 positive nd t 36 ma values 0 39 2 1 and tdm ages of 0 69 to 1 06 ga with pb isotopic ratios of initial 206pb 204pb 18 49 18 68 initial 207pb 204pb 15 58 15 61 and initial 208pb 204pb 38 33 38 77 are consistent with a phlogopite bearing amphibole rich and enriched lithospheric mantle source metasomatized by earlier subducted sediments the geochemical and isotopic compositions of the granitoids are similar to the host rocks of porphyry and epithermal deposits in the urumieh dokhtar zone

geology alteration age and origin of iron oxide apatite deposits in upper eocene quartz monzonite zanjan district nw iran iron oxide apatite deposits are present in upper eocene pyroxene quartz monzonitic rocks of the zanjan district northwestern iran mineralization occurred in five stages 1 deposition of disseminated magnetite and apatite in the host rock 2 mineralization of massive and banded magnetite ores in veins and stockwork associated with minor brecciation and calcic alteration of host rocks 3 deposition of sulfide ores together with potassic alteration 4 formation of quartz and carbonate veins and sericite chlorite epidote silica carbonate and tourmaline alteration and 5 supergene alteration and weathering u pb dating of monazite inclusions in the apatite indicates an age of 39 99 0 24 ma which is nearly coeval with the time of emplacement of the host quartz monzonite supporting the genetic connection fluid inclusions in the apatite have homogenization temperatures of about 300 c and oxygen isotopic compositions of the magnetite support precipitation from magmatic fluids late stage quartz resulted from the introduction of a cooler less saline and isotopically depleted fluid the iron oxide apatite deposits in the tarom area of the zanjan district are typical of a magmatic hydrothermal origin and are similar to the kiruna type deposits with respect to mineral assemblages fabric and structure of the iron ores occurrence of the ore bodies and wall rock alteration

geochemistry of igneous rocks associated with mineral deposits in the tarom hashtjin metallogenic province nw iran an analysis of the controls on epithermal and related porphyry style mineralization abstract cenozoic magmatism in iran is associated with many epithermal porphyry cu au ore systems which mainly occur within the alborz magmatic arc and urumieh dokhtar magmatic arc systems the tarom hashtjin metallogenic province in the nw part of iran is located in the western alborz magmatic arc and is host to numerous ls is and hs type epithermal deposits within eocene volcano plutonic rocks whole rock geochemical data indicate that volcanic rocks vary extensively and continuously from subalkaline basaltic to rhyolitic compositions granitoid rocks are characterized by subalkaline metaluminous to peraluminous i to a type magmatism geochemical and geochronological studies of the igneous rocks associated with epithermal deposits particularly the enrichment of large ion lithophile elements depletion of high field strength elements including nb ta depletion and their eocene ages are consistent with extensional back arc tectonic settings suggesting that primary source magmas were generated by partial melting of the mantle wedge garnet bearing depleted lithospheric upper mantle and were subsequently affected by both fractional crystallization and crustal assimilation during their magmatic evolution the regional magmatism likely contributed to the heat advection and composition of metal bearing hydrothermal fluids in the formation of the epithermal deposits considering strong plagioclase fractionation relative to hornblende fractionation an extensional back arc tectonic setting the lack of any skarn mineralization and a considerably shallower depth of magma generation the tarom hashtjin metallogenic province is proposed to be prospective for precious metal epithermal mineralization by contrast the urumieh dokhtar magmatic arc and ahar arasbaran zone systems are probably more eroded and thus more prospective for porphyry cu au exploration

field observations of surf zone inner shelf exchange on a rip channeled beach cross shore exchange between the surf zone and the inner shelf is investigated using lagrangian and eulerian field measurements of rip current flows on a rip channeled beach in sand city california surface drifters released on the inner shelf during weak wind conditions moved seaward due to rip current pulses and then returned shoreward in an arcing pattern reentering the surf zone over shoals the cross shore velocities of the seaward and shoreward moving drifters were approximately equal in magnitude and decreased as a function of distance offshore the drifters carried seaward by the rip current had maximum cross shore velocities as they exited the surf zone and then decelerated as they moved offshore the drifters moving shoreward accelerated as they approached the surfzone boundary with maximum cross shore velocities as they reentered the surf zone over shoals it was found that stokes drift was not solely responsible for the onshore transport across the surfzone boundary the cross shore diffusivity on the inner shelf was greatest during observations of locally contained cross shore exchange these field observations provide evidence that the cross shore exchange between the surf zone and inner shelf on a rip channeled beach is due to wave driven rip current circulations and results in surface material being contained within the nearshore region

mineral assemblages fluid evolution and genesis of polymetallic epithermal veins glojeh district nw iran abstract the glojeh district contains silver and base metal rich epithermal veins and is one of the most highly mineralized locations in the tarom hashtjin metallogenic province northwestern iran it consists of four major epithermal veins which are located in the south glojeh and north glojeh areas alteration in the glojeh district consists of propylitic sericitic and argillic assemblages as well as extensive silicification the ore bearing veins comprise three paragenetic stages 1 early cu au as sb fe bearing minerals 2 middle stage pb zn cu cd ag bearing minerals and 3 late hematite ag bi au pb mineralogy the veins are best classified as the product of an early high sulfidation hydrothermal system which was overprinted by an intermediate sulfidation system that was rich in ag and base metals hematite is locally altered to goethite in zones of as much as 40 m in width during supergene alteration and the goethite is an important exploration tool fluid inclusions from the early middle and late stages respectively have salinities and homogenizations temperatures ranging from 5 to 11 wt nacl eq and 220 c to 340 c to 1 to 8 wt nacl eq and 200 c to 290 c and finally to 0 1 to 2 wt nacl eq and 150 c to 200 c the oxygen isotope values in quartz range from 8 8 to 13 3 and most calculated fluid 18 o values are between 4 and 8 suggesting a magmatic fluid with some meteoric water contamination sulfur isotope values for chalcopyrite pyrite sphalerite and galena are mainly 7 3 to 1 3 and 0 3 to 8 4 for north glojeh and south glojeh respectively sulfur isotope data suggest a magmatic origin boiling isothermal mixing and dilution are the main mechanisms for ore deposition in the glojeh veins recent 40 ar 39 ar age measurements of 42 20 0 34 ma and 42 56 1 47 ma for the north glojeh and south glojeh veins respectively overlap with the 41 87 1 58 ma age of the goljin intrusion in the northern part of the district which we interpret as the main heat source controlling the hydrothermal systems

origin of massive calcite veins in the golden cross low sulfidation epithermal au ag deposit new zealand at golden cross andesitic lavas and volcaniclastic rocks host epithermal veins that formed in the shallow part 500 m depth of a hydrothermal system calcite is a trace mineral in precious metal bearing quartz veins and a common replacement mineral in the surrounding intensely altered host rocks late barren calcite veins crosscut the precious metal bearing quartz sulfide veins and were a significant source of dilution in the underground workings of the mine where large they also posed significant problems for ground control these veins range up to 10 m in width and contain more than 99 percent calcite predominantly as massive coarse crystals with only trace amounts of quartz pyrite and clays fluid inclusion data indicate that much of the late barren calcite formed between 160 and 220 c overlapping the temperature range of fluid inclusions from the precious metal bearing quartz sulfide veins ice melting temperatures range from 0 0 to 1 1 c slight vapor bubble expansion during crushing of a few calcite hosted fluid inclusions indicates the presence of dissolved carbon dioxide these results indicate that the hydrothermal solutions responsible for late calcite deposition were very dilute 2 nacl wt percent equiv and contained up to approximately 2 5 wt percent dissolved carbon dioxide the best interpretation of the steep t h vs t m cooling trend is carbon dioxide gas loss through phase separation combined with variable amounts of mixing the 18 o composition of calcite from the altered country rock and late veins ranges from 3 4 to 15 4 per mil with the bulk of the data corresponding to equilibrium 18 o water compositions of 2 to 6 per mil this range of compositions is 0 to 2 per mil lower than the 18 o compositions for the waters in equilibrium with quartz from precious metal bearing quartz sulfide veins the 13 c composition of calcite ranges from 3 1 to 9 0 per mil the equilibrium 13 c compositions of carbon dioxide for most of these data fall between 7 and 9 per mil electron microprobe analyses indicate that calcite contains less than 10 mole percent combined mn mg and fe replacement calcite and veinlet calcite show greater substitution by these elements compared to calcite in massive veins which is nearly pure the minor element compositions of calcite appear to be primarily controlled by solution composition and these constituents may be locally derived from the country rock using the knowledge from active geothermal systems of the taupo volcanic zone as a framework for interpretation we propose that the late massive calcite veins were deposited from downward moving co 2 rich steam heated water this water was heated and locally reached vapor saturation as it descended into the former upflow zone of the hydrothermal system during waning activity the reverse solubility of calcite accounts for the selective deposition of calcite over all other common hydrothermal phases and condensation of steam into local ground water accounts for the slightly lower 18 o water values from this we suggest that for some low sulfidation epithermal prospects the occurrence of barren calcite veins may be indicative of co 2 rich steam heated waters that formed as a result of boiling

origin and evolution of mineralizing fluids and exploration of the cerro quema au cu deposit azuero peninsula panama from a fluid inclusion and stable isotope perspective cerro quema is a high sulfidation epithermal au cu deposit with a measured indicated and inferred resource of 35 98 mt 0 77 g t au containing 893 600 oz au including 183 930 oz au equiv of cu ore it is characterized by a large hydrothermal alteration zone which is interpreted to represent the lithocap of a porphyry system the innermost zone of the lithocap is constituted by vuggy quartz with advanced argillic alteration locally developed on its margin enclosed by a well developed zone of argillic alteration grading to an external halo of propylitic alteration the mineralization occurs in the form of disseminations and microveinlets of pyrite chalcopyrite enargite tennantite and trace sphalerite crosscut by quartz barite pyrite chalcopyrite sphalerite and galena veins microthermometric analyses of two phase l v secondary fluid inclusions in igneous quartz phenocrysts in vuggy quartz and advanced argillically altered samples indicate low temperature 140 216 c and low salinity 0 5 4 8 wt nacl eq fluids with hotter and more saline fluids identified in the east half of the deposit cerro quema area stable isotope analyses s o h were performed on mineralization and alteration minerals including pyrite chalcopyrite enargite alunite barite kaolinite dickite and vuggy quartz the range of 34s of sulfides is from 4 8 to 12 7 whereas 34s of sulfates range from 14 1 to 17 4 the estimated 34s s of the hydrothermal fluid is 0 5 within the advanced argillic altered zone the 34s values of sulfides and sulfates are interpreted to reflect isotopic equilibrium at temperatures of 240 c the 18o values of vuggy quartz range from 9 0 to 17 5 and the 18o values estimated for the vuggy quartz forming fluid range from 2 3 to 3 0 indicating that it precipitated from mixing of magmatic fluids with surficial fluids the 18o of kaolinite ranges from 12 7 to 18 1 and d from 103 3 to 35 2 whereas the 18o of dickite varies between 12 7 and 16 3 and d from 44 to 30 based on 18o and d two types of kaolinite dickite can be distinguished a supergene type and a hypogene type combined the analytical data indicate that the cerro quema deposit formed from magmatic hydrothermal fluids derived from a porphyry copper like intrusion located at depth likely towards the east of the deposit the combination of stable isotope geochemistry and fluid inclusion analysis may provide useful exploration vectors for porphyry copper targets in the high sulfidation lithocap environment

timing and genesis of ore formation in the qarachilar cu mo au deposit ahar arasbaran metallogenic zone nw iran evidence from geology fluid inclusions o s isotopes and re os geochronology in the qarachilar cu mo au deposit of the ahar arasbaran metallogenic zone aamz northwest iran mineralization occurs as three quartz sulfide veins that cut granodiorite quartz monzodiorite rocks of the qaradagh batholith qdb ore formation can be divided into three stages with chalcopyrite molybdenite and gold bearing pyrite appearing mainly in the first two stages the main wall rock alteration is silicification and intermediate argillic carbonate and propylitic alteration fluid inclusion microthermometry indicates trapping of medium to high salinity 9 2 55 wt nacl equiv fluids at qarachilar fluid inclusion trapping conditions are estimated to be 190 degrees c 530 degrees c and 0 1 3 kbar the variable phase ratios as well as spatial coexisting of liquid and vapor rich two phase and halite bearing multiphase fluid inclusions homogenizing over the same temperatures are consistent with fluid boiling during ore formation obtained delta o 18 h2o values of quartz from ore stage veins are 5 7 parts per thousand to 9 7 parts per thousand signifying that the ore fluid system was predominantly magmatic water the average calculated delta s 34 h2s values are 1 1 parts per thousand for pyrite chalcopyrite and molybdenite consistent with a magmatic source for sulfur combined the fluid inclusion and stable isotope data indicate that the ore forming fluids at qarachilar were magmatic in origin and were subsequently cooled and diluted by meteoric water fluid boiling and mixing facilitated hydrothermal alteration and mineralization molybdenite re os dating shows that mineralization occurred at 42 35 0 16 ma coincident with formation of porphyry cu mo mineralization at agarak deposit and hanqasar aygedzor and dastakert prospects in the lesser caucasus however qarachilar is older than all porphyry cu mo mineralization in the aamz and urumieh dokhtar magmatic arc udma which suggests that collision between arabia and eurasia were oblique and thus diachronous our data suggest that mineralization at qarachilar is related to collisional eocene magmatic hydrothermal activity related to neo tethys subduction and shares a number of similarities with the vein type cu mo au mineralization related to cu mo porphyries

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

mineralogical and fluid inclusion studies of low sulfidation epithermal veins at osilo sardinia italy several precious metal bearing low sulfidation epithermal veins occur in the rolling topography of the osilo area northern sardinia the sa pala de sa fae and the sa pedra bianca veins were subject to intense diamond drilling exploration in the mid 1990 s the veins extend for 1 3 km dip steeply and range from 1 to 10 m in width high k calc alkaline volcanic deposits containing plagioclase phenocrysts along with lesser pyroxene amphibole magnetite olivine and sanidine form the main host rocks gold grades in drill intersections range from 50 m from the vein the assemblage albite fe chlorite illite pyrite montmorillonite calcite k feldspar prevails regionally and its formation is attributed to minor metasomatism of the country rock involving the addition of water carbon dioxide and hydrogen sulfide at distances 10 m from the vein the assemblage quartz k feldspar pyrite illite dominates forming an alteration envelope that cross cuts regional alteration quartz and k feldspar increase in abundance towards the vein quartz is the main vein mineral and it displays a range of morphologies and textures including crustiform colloform banding quartz pseudomorphs of platy calcite breccias and coarse euhedral crystals electrum and argentite which are the main gold and silver minerals deposited during the early stages of vein mineralization with rhomb shaped crystals of k feldspar adularia pyrite plus lesser marcasite arsenopyrite stibnite and sphalerite are the other sulfide phases in veins kaolinite halloysite jarosite form a late assemblage overprinting earlier hydrothermal alteration it is mostly restricted to shallow depths of a few meters except near veins most of this assemblage likely formed from weathering and oxidation of sulfides microthermometric measurements were made on quartz hosted two phase liquid vapor inclusions containing 75 liquid mean homogenization temperatures 750 measurements range from 220 to 250 c and ice melting temperatures 550 measurements range from 0 0 to 2 3 c the presence of co existing vapor rich and liquid rich inclusions with quartz pseudomorphs of platy calcite indicate that boiling conditions existed slight vapor bubble expansion of a few fluid inclusions subjected to crushing experiments indicates inclusion fluids contained variable but low concentrations of dissolved gas this study shows that gold silver mineralization formed in subvertical channels from ascending solutions at 250 c at around 300 to 450 m below the paleo water table in a typical low sulfidation epithermal environment hydrothermal solutions that produced vein mineralization and related alteration were dilute 4 1 equivalent wt nacl and 4 wt co2 near neutral ph reduced and at times boiling

eo alpine eclogitisation of permian morb type gabbros in the koralpe eastern alps austria new geochronological geochemical and petrological data new petrological geochemical and isotopic data sm nd rb sr from meta gabbros eclogites and metapelites from the southern koralpe are presented pl cpx gabbros mostly olivine free that have preserved their magmatic minerals to varying extent occur as relics within eclogites transformation of gabbro into eclogite is documented in different stages ranging from macro to microscale based on textural characteristics the eclogites are classified into four groups types 1 4 typical eclogite parageneses are grt omp zo ky qtz amp phe rut the metapelitic eclogite host rocks are composed of qtz ms bt pl grt ky p t estimates for both metabasites and metapelites range at 1 8 2 0 gpa 600 650 c sm nd mineral isochrons pl cpx for the gabbroic eclogite precursors give ages of between 247 16 and 255 9 ma their initial nd and sr isotopic compositions are clearly within the range of modern depleted mantle values minerals from type 1 metagabbroic eclogites are in clear nd isotopic disequilibrium pervasively recrystallized type 3 eclogites yield grt wr or grt omp zo amp wr ages of 97 5 101 7 and 109 8 ma the metapelitic eclogite host rocks mica schists yield nd dm depleted mantle model ages of 1 44 1 63 ga grt wr isochron ages from these rocks are 86 1 87 4 and 89 3 ma the new data further support the permian early mesozoic rifting event for this part of the austroalpine basement which is related to initial oceanization at the western end of the alpine tethys during alpine plate convergence pre alpine continental basement and oceanic crustal fragments where subducted to depths of c 60 km the most likely time span for the high pressure peak is c 100 10 ma rapid exhumation in the upper cretaceous is inferred from mineral cooling ages between 80 and 60 ma