calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

40ar 39ar and oxygen isotope studies of polymetamorphism from tinos island cycladic blueschist belt greece petrological oxygen isotope and 40ar 39ar studies were used to constrain the tertiary metamorphic evolution of the lower tectonic unit of the cyclades on tinos polyphase high pressure metamorphism reached pressures in excess of 15 kbar based on measurements of the si content in potassic white mica temperatures of 450 500 c at the thermal peak of high pressure metamorphism were estimated from critical metamorphic assemblages the validity of which is confirmed by a quartz magnetite oxygen isotope temperature of 470 c some 40ar 39ar spectra of white mica give plateau ages of 44 40 ma that are considered to represent dynamic recrystallization under peak or slightly post peak high pressure metamorphic conditions early stages in the prograde high pressure evolution may be documented by older apparent ages in the high temperature steps of some spectra eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation oxygen isotope thermometry of four quartz magnetite pairs from greenschist samples gives temperatures of 440 470 c which cannot be distinguished from those deduced for the high pressure event the exhumation and overprint is documented by decreasing ages of 32 28 ma in some greenschists and late stage blueschist rocks and ages of 30 20 ma in the lower temperature steps of the ar release patterns of blueschist micas almost flat parts of ar ar release spectra of some greenschist micas gave ages of 23 21 ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a 18o enriched fluid rather the compositions indicate that fluid to rock ratios were very low the isotopic compositions being primarily controlled by those of the protolith rocks we assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid a quartz magnetite sample from a contact metamorphic skarn taken near the miocene monzogranite of tinos gave an oxygen isotope temperature of 555 c and calculated water composition of 9 1 the value of 18o obtained from this water is consistent with a primary magmatic fluid but is lower than that of fluids associated with the greenschist overprint which indicates that the latter event cannot be directly related to the monozogranite intrusion

isotopic dating of pre alpidic rocks from the island of ios cyclades greece the lower tectonic unit of ios provides evidence of an at least four stage metamorphic and intrusive history which well might be generalized for large parts of the internal pelagonian

the nature and genesis of gold silver tellurium mineralization in the metaliferi mountains of western romania precious metal au ag and base metal pb zn deposits in the metaliferi mountains of western romania occur in steeply clipping quartz ca mn carbonate veins which are hosted by miocene andesitic stocks and lava flows and surrounding sedimentary rocks the deposits consist predominantly of sulfides pyrite chalcopyrite sphalerite galena sulfosalts of as and sb and a diverse range of au ag tellurides the igneous host rocks have undergone mild pervasive propylitic alteration whereas immediately adjacent to the veins the wall rock alteration assemblages consist of quartz sericite k feldspar calcite and pyrite fluid inclusion stable isotope and thermodynamic data suggest that the majority of the mineralization and hydrothermal alteration in these deposits was caused by loci salinity 0 5 wt nacl equiv medium temperature 200 degrees 300 degrees c near neutral ph 5 6 fluids which underwent occasional boiling the fluid inclusion and stable isotope data support a model in which a metal bearing magmatic fluid was exsolved from a crystallizing calc alkaline melt and ascended to higher levels in the crust undergoing some isotopic exchange with surrounding sedimentary rocks but limited mixing with ground waters although the deposits in this part of the romanian carpathians exhibit many of the geologic characteristics of classic low sulfidation volcanic hosted au ag epithermal deposits they seem to have formed from essentially magmatic waters and there is little evidence for the incorporation of meteoric fluids into the hydrothermal system

spectral evolution of nearshore wave energy during a sea breeze cycle abstractfrom in situ measurements taken over several sea breeze cycles off a beach in southwest sw australia the evolution of the one dimensional spectrum of wave energy is observed to have a distinctive spectral shape during the land breeze phase of the cycle lower rates of dissipation of wave energy are seen at high frequencies compared to midrange frequencies above the remnant wind sea peak a simulation of waves was performed using the simulating waves nearshore swan model and produced the same spectral evolution by generating longshore modes as seen in the observations the performance of whitecapping schemes available in swan was assessed and the alves banner scheme was found to best simulate the observed growth and decay of the wave spectra during the onshore phase of the sea breeze cycle local wave growth is duration limited and during the offshore land breeze phase wave growth is fetch limited from an examination of the modeled two dimensional spectra it is found that quadruplet in

internal structure and emplacement of the papoose flat pluton an integrated structural petrographic and magnetic susceptibility study the papoose flat pluton of eastern california is commonly cited in the geologic literature as a classic example of a forcibly emplaced pluton although the relative importance attributed to magmatic versus tectonic processes in controlling the structural evolution of the pluton has been controversial reexamination of this late cretaceous 83 ma pluton using a combination of new structural petrographic microstructural and anisotropy of magnetic susceptibility ams data on the pluton wall rock system has shown that the pluton is an inclined and internally zoned tabular structure assembled by forcible intrusion of successive pulses of magma at a crustal depth of 12 15 km initial pluton formation involved magma ascent in a vertical west northwest striking feeder dike which was arrested at a stratigraphically controlled mechanical discontinuity in the overlying cambrian metasedimentary rocks leading to formation of a southwest dipping sill subsequent sill inflation accompanied by horizontal infilling from the feeder dike at the base of the sill resulted in deformation and vertical translation of previously emplaced magma pulses and local raising of the sill roof facilitated by thermal weakening as the wall rock temperatures progressively rose during emplacement of successive magma pulses cooling from the roof of the pluton downward resulted in cessation of vertical inflation on the west side of the pluton and promoted lateral expansion toward the northeast and floor depression below the eastern part of the pluton we have been unable to document any regional scale structures e g of equivalence to similar age synplutonic strike slip shear zones in the sierra nevada batholith to the west that may have controlled emplacement of the papoose flat pluton however this fact does not preclude the likelihood that the country rocks were subjected to a regional deviatoric stress field at this time indeed tectonic overpressuring was probably essential for producing sufficiently high magma pressures for laccolith formation at this midcrustal level simple thermal modeling using microstructural and thermobarometric data indicates that the total duration of emplacement of the pluton did not exceed 30 000 yr this rapid emplacement rate may explain why the pluton appears to be anorogenic even though it was emplaced during a period of regional scale deformation

geometry of eclogite facies structural features implications for production and exhumation of ultrahigh pressure and high pressure rocks western gneiss region norway 1 well preserved eclogite facies structural features in metamorphosed gabbro and diorite gneiss in baltica crust formed at a minimum depth of 60 70 km during the scandian orogeny allow direct inferences to be made regarding the geometry of folds kinematics and original structural orientations related to production and exhumation of high pressure rocks folds associated with eclogite facies fabrics are isoclinal to tubular with axes parallel to the trend of a stretching lineation strain estimates and l s or l s fabrics indicate that these structures were formed in a constrictional strain field locally they are well preserved in eclogite facies mylonite zones at least 40 m thick that cut proterozoic gabbro and adjacent gneiss where steeply dipping they show a north side up shear sense across a younger northeast trending shallowly plunging amphibolite facies anticlinorium formed in a constrictional noncoaxial strain field where original structural facing direction can be inferred small circle rotation of the eclogite facies lineation about the anticline axis indicates that the relative motion vector of baltica with respect to overlying imbricated crust and laurentia was oriented 320 in a present day reference frame this result is identical to the orientation of the relative motion vector estimated from paleomagnetic plate reconstructions and consistent with late silurian to early devonian oblique sinistral convergence between baltica and laurentia results of this study indicate that coherent baltica crust at 60 70 km depth experienced subvertical and horizontal shortening while extending toward the foreland during tops southeast thrusting parallel to plate motion high pressure rocks were progressively imbricated and stacked along eclogite facies mylonite zones with the deforming zone separating coherent baltica crust from imbricated basement above the constrictional strains under eclogite facies conditions are interpreted to have resulted from stretching associated with sinking of the cool dense mantle lithosphere

mineralogical and geochemical studies of the emperor gold telluride deposit fiji the emperor gold telluride deposit consists of a system of quartz filled fractures lying on the margin of a caldera in the mba volcanics of miocene age in the north of viti levu fiji the veins filled fractures that developed mainly in precaldera basalts the veins are both pre and postfaulting contain vugs and show evidence of repeated opening they are dominantly quartz with minor pyrite tellurides gold sphalerite arsenopyrite chalcopyrite tetrahedrite galena dolomite calcite and mica part v rich flanking wall rocks show inner k feldspar mica quartz alteration and outer chlorite carbonate alteration crustification and replacement textures allow establishment of a generalized paragenetic sequence dominated by five stages of quartz two of ore minerals without quartz and late carbonate pyrite was among the first and the last of the minerals to precipitate and is the most common sulfide within each ore mineral stage there are small scale cycles of sulfide deposition indicating widely fluctuating fluid conditions the first of the two ore mineral stages is dominated by calaverite krennerite sylvanite and native tellurium the second by petzite hessite and native gold indicating a decline in tellurium activity with time a third of the emperor gold is thought to be in solid solution in pyrite and arsenopyrite fluid inclusions in quartz indicate that the early stages formed at temperatures ranging from 300 degrees to 250 degrees c and later stages from 250 degrees to 160 degrees c the presence of coexisting vapor and liquid vapor inclusions in much of the vein system indicates that the solutions were boiling leachate analyses and freezing point depressions of fluid inclusions yield an average fluid composition of m sub na super 0 32 m sub k super 0 25 m sub mg super 2 0 005 m sub cl super 1 0 and i ionic strength 1 0 the five quartz stages except possibly the first appear to have crystallized in isothermal conditions during periods of shallow sealing of the hydrothermal system and low mass fluid flux no homogenization data are available for the ore mineral stages but a similar temperature range to that in adjacent quartz is assumed together with high mass flux to inhibit quartz precipitation initial fluid conditions in the first ore stage assuming equilibrium at 250 degrees c are ph 5 5 m sub sigma s 10 super 3 and m sub sigma c 10 super 2 to 10 super 3 a sub o 2 10 super 40 a sub te sub 2 sub g 10 super 7 8 and a sub h sub 2 sub g 10 super 0 4 sulfide telluride and gold precipitation probably resulted largely from boiling and cooling along the boiling point depth curve changes in the fluid as a direct result of boiling include loss of h 2 h 2 s co 2 and h 2 te with loss of h 2 s the main cause of gold deposition assuming only partial equilibrium in the fluid indicates a more reduced fluid with a higher tellurium content carbon isotope ratios of carbonates and sulfur isotope ratios of sulfides indicate a dominantly sedimentary source for carbon and sulfur believed to be carbonate bearing sediments the vatukoro formation underlying the host basalts mba volcanics the delta 18 o and delta d analyses indicate that the ore fluid was mainly composed of magmatic water and seawater with a possible meteoric component the seawater was probably resident in the vatukoro formation prior to cauldron formation carbon in late carbonate coating quartz may be of magmatic origin mineralization occurs largely outside the cauldron walls and may have preceded the final stages of cauldron development

hydrothermal alteration ore fluid characteristics and gold depositional processes along a trondhjemite komatiite contact at tarmoola western australia tarmoola is a structurally controlled archean orogenic gold deposit hosted in greenschist facies metamorphosed komatiite and trondhjemite in the leonora district of the eastern goldfields province yilgarn craton high grade 1 g t au orebodies are located in komatiite wall rock adjacent to the eastern and northeastern margins of the asymmetrical north south striking tarmoola trondhjemite intrusion gold bearing veins postdate trondhjemite emplacement ca 2700 ma quartz diorite dikes ca 2667 ma and regional greenschist facies metamorphism textures and crosscutting relationships in gold bearing veins indicate two stages of hydrothermal fluid infiltration associated with a single gold related hydrothermal event a volumetrically dominant but gold poor stage i fluid and a gold rich stage ii fluid gold bearing veins contain stage i milky quartz and pyrite that are overprinted by stage ii quartz ankerite muscovite chalcopyrite sphalerite galena gold tellurides albite chlorite fuchsite epidote scheelite stage i hydrothermal alteration assemblages are different in trondhjemite and komatiite due to contrasting reactions between a common ore fluid and disparate wall rock chemistry stage ii fluid wall rock interaction was minor compared to stage i and is indicated by the overprinting of stage i mineral assemblages by stage ii microveins wall rock alteration proximal to veins in trondhjemite is characterized by replacement of igneous plagioclase amphibole biotite and metamorphic chlorite by hydrothermal quartz muscovite ankerite calcite pyrite chalcopyrite sphalerite galena tellurides and gold whereas in proximal alteration in komatiite metamorphic chlorite and talc are replaced by ankerite quartz muscovite albite chlorite fuchsite pyrite chalcopyrite sphalerite galena tellurides and gold the stage ii fluid was enriched in h2o co2 si ca k na s au ag cu pb w bi as mo zn and te based on fluid inclusion studies and stage ii mineral equilibria gold deposited from a homogeneous neutral to slightly alkaline ph 5 1 5 5 reduced low salinity 5 5 wt nacl equiv fluid that had a bulk composition of 78 mole percent h2o and 21 mole percent co2 and trace amounts of ch4 c2h6 h2 ar h2s and he gold deposition occurred at 300 50 c and 0 5 to 3 0 kbars assuming lithostatic fluid pressures gold precipitated at a 2 to 10 km depth stage ii gray quartz 18ofluid values range from 5 9 to 7 5 per mil whereas dfluid values calculated from the dehydration of muscovite grains and measured directly from bulk fluid inclusion analyses of stage ii gray quartz have ranges of 9 to 35 and 27 to 28 per mil respectively hydrothermal ore fluids were transported from greater crustal depths to the site of gold deposition during the district scale d3 event by shallowly w dipping reverse brittle ductile shear zones in supracrustal rock and along the steeply east dipping trondhjemite contact associated subhorizontal east west shortening caused the reactivation of the eastern trondhjemite margin and subparallel foliation which facilitated the transport of hydrothermal fluids and the generation of gold bearing veins and hydrothermal alteration zones in komatiite east west striking fractures in trondhjemite aided the lateral migration of ore fluids away from trondhjemite margins and the formation of east west striking gold bearing veins and broad alteration zones gold was most likely transported in the stage ii fluid as bisulfide complexes the sulfidation of trondhjemite and komatiite wall rock by the stage ii fluid caused the destabilization of au bisulfide complexes and gold deposition potassium ca and co2 metasomatism of komatiite wall rock may have enhanced gold deposition via the acidification of the stage ii fluid the physicochemical characteristics of the tarmoola ore fluid and relative timing of gold mineralization are consistent with the yilgarn wide 2650 to 2630 ma gold event the host rock chemistry vein and proximal wall rock alteration mineral assemblages and fluid temperature and pressures during gold deposition are also similar to that of earlier ca 2755 ma gold deposits in the leonora district

miocene high pressure metamorphism in the cyclades and crete aegean sea greece evidence for large magnitude displacement on the cretan detachment the cyclades in the backarc region of the present hellenic subduction zone are known for widespread late cretaceous to eocene high pressure metamorphism in the cycladic blueschist unit we report 40 ar 39 ar and rb sr phengite ages of 24 21 ma for high pressure metamorphism 8 10 kbar 350 400 c in the lowest tectonic unit in the cyclades the basal unit which structurally underlies the cycladic blueschist unit the basal unit is correlated with the tripolitza unit of the external hellenides in the forearc region of the hellenic subduction zone the tripolitza unit is unmetamorphosed on crete where it is separated from the underlying high pressure 8 10 kbar 300 400 c plattenkalk and phyllite quartzite units by the extensional cretan detachment the age for high pressure metamorphism in the latter units is similar to our age for the basal unit in the cyclades because pressure temperature conditions in the plattenkalk and phyllite quartzite units on crete and the basal unit in the cyclades are also similar they must have been in close proximity in the early miocene hellenic subduction zone a palinspastic reconstruction suggests a subsequent displacement of 100 km on the cretan detachment this is one of the greatest displacement magnitudes ever reported from detachment faults because of this large offset the cretan detachment was an efficient agent for exhuming high pressure rocks

geochemical studies of the tongyoung gold silver deposits republic of korea evidence of meteoric water dominance in a te bearing epithermal system epithermal gold silver vein mineralization of the tongyoung mine was deposited in five stages i to v of quartz rhodochrosite calcite sulfide veins 0 3 7 0 m thick which fill fault planes in cretaceous volcanic rocks of the gyeongsang basin k ar dating of alteration sericite 72 9 or 1 2 ma indicates a late cretaceous age for ore mineralization stages i and ii are au ag bearing whereas stages iii iv and v are barren ore grades average 12 g metric ton gold with a gold silver ratio of 1 11 stage ii is composed of five rhythmically banded substages which show a progressive change in ore mineralogy with increasing paragenetic time electrum 68 wt au electrum 65 wt au argentitc electrum 50 wt au ag tellurides ag tellurides native silver the shift in mineralogy reflects decreases in temperature and fugacity of sulfur with a concomitant increase in fugacity of tellurium fluid inclusion data indicate a history of progressive cooling and dilution of ore forming fluids during stages i and ii higher temperature and salinity fluids 260 degrees c 6 equiv wt nacl mixed with cooler less saline waters resulting in most ore deposition from fluids of intermediate temperature and composition 190 degrees 230 degrees c 2 5 4 5 equiv wt nacl continued cooling and dilution coupled with decreasing fugacity of sulfur resulted in deposition of ag te mineralization and ultimately in barren stage iii and iv quartz and stage v calcite stable isotope compositions of mineralizing fluids from tongyoung delta d 44 to 61ppm delta 18 o 6 8 to 9 4ppm are similar to modern meteoric and thermal spring waters in the area and indicate meteoric water dominance during all stages of the au ag te mineralizing system comparison of tongyoung to other au ag te deposits indicates that its complex sequence of mineralization is a natural consequence of repeated inundation of a hydrothermal system by progressively cooler meteoric waters

p t conditions of quartz calcite boudins and vein formation within a low angle detachment fault in tinos island aegean sea a fluid inclusion study fluid inclusions were investigated in successive generations of quartz calcite boudins and veins in the vicinity of and within the low angle detachment fault of early miocene age exposed on tinos island cyclades greece abundant boudins veins tension gashes and mineral segregations were formed during various stages of ductile and brittle shear along the detachment indicating fluid flow at various crustal levels assisted motion and slip along the detachment three generations of fluid inclusions were identified 1 syn deformation aqueous inclusions 2 local late deformation h2o co2 inclusions 3 post slip deformation partly decrepitated aqueous and h2o co2 inclusions the conditions of inclusion trapping correspond to the greenschist facies at temperatures between 300 and 450 c and pressures in the range of 1 5 4 0 kb a gradient of pressure of about 0 5 kb from the fault zone to the rocks of upper and lower plates is suggested the results indicate that the syn deformation fluid was nacl kcl sulfate dominated with a salinity of about 5 wt nacl equiv downward infiltration of meteoric water is a suitable source for this fluid during the late stage of fault activity in the brittle field fluid was of h2o co2 composition very rapid exhumation of the entire section unrelated to motion on the investigated fault is marked by numerous decrepitation clusters of the fluid inclusions

evolution of hydrothermal regime along a crustal shear zone tinos island greece 1 structural cathodoluminescence and sims 18o analyses of quartz calcite veins are combined to constrain the evolution in space and time of fluid infiltration in an exhuming detachment shear zone tinos island cyclades greece careful description of vein arrays shows that the plumbing system evolved into an interconnected network just beneath the ductile to brittle transition microtextures of quartz and calcite infilling veins display deformed relics and newly precipitated grains high resolution 18o mapping in relics yields a steady quartz calcite fractionation of 2 at 400 c whereas fractionation increases in neograins from 2 to 5 in 190 m toward the fault or a 150 c temperature fall cooling is associated with a shift of fluid stable isotope signature from 15 to 0 beneath the detachment results are interpreted as advective removal of heat by massive infiltration of surface derived fluids over depths of 10 15 km fluid penetration was promoted by the coalescence of late ductile early brittle veins as the exhuming footwall crossed the ductile brittle transition only small amounts of fluids penetrated the ductile crust beneath the transitional rheology

transpression and transtension within different structural levels in the central aegean region in the central aegean region shortening structures within the miocene molasse arc known since long ago nevertheless recently most authors have recognized extensional structures within middle to upper miocene granitoids proposing a basin and range type model for the late cenozoic evolution of the area to resolve this problem structural mapping and mesoscopic analysis of 900 faults sampled from 12 islands have been carried out late orogenic uplift of the central aegean region is the result of a continuous convergence and indentation of the pelagonian plate by the apulian plate that took place throughout the miocene formation of core complexes can be associated with a large oblique upthrusts b steeply dipping strike slip faults and c low angle normal faults the latter are produced by low multidirectional extension which has affected small crustal regions as adjacent areas underwent transpression in the late stages of collision the overthickened crust began to collapse due to transtension which was replaced by extension caused by the roll back of the hellenic subduction zone in the lower pliocene time this extensional regime has lasted until the present day

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

hydrothermal eruption mechanisms and hot spring gold deposits episodes of gold mineralization in the shallow hot spring environment are related in time to hydrothermal eruption events and in space to the resulting vent breccias and peripheral stockwork zones it is proposed that large but short lived overpressures in a geothermal reservoir probably triggered by sudden magmatic heat fluxes induce hydraulic fracturing which then evolves into hydrothermal eruptions if driven through to the surface the maximum available energy in hot shallow reservoirs appears easily sufficient to drive such eruptions particularly if co 2 rich fluids are involved in mineralized systems gold bearing fluids are subsequently channeled into the outflow conduit where they flood the permeable vent breccia and peripheral stockwork gold is lifted into this hot spring environment above a boiling level that is elevated by high flow rates to within several hundred meters of the surface and is precipitated with abundant quartz pyrite and adularia along with a distinctive and steeply zoned trace element suite these sequential events probably occur as a continuum which if repeated cyclically in a single vent zone can result in ore grade mineralization

uplift and exhumation of high pressure metamorphic terrains the example of the cycladic blueschist belt aegean sea the cycladic blueschists emerged from a depth of more than 50 km during the tertiary these rocks are now covered only by a thin fraction of the synmetamorphic overburden upper plate remnants of the upper plate include low p crystalline rocks and sediments which have been juxtaposed onto the lower plate blueschists in several stages since the early miocene the low angle contacts operated as normal faults which removed the overburden from above the cycladic blueschists detailed investigations on tinos island indicate that the fractured blocks of the upper plate lying above a low angle normal fault did not rotate this shows that the faults initiated as rather gently dipping fractures similar structures were also reported from other blueschist terrains kinematic analysis of such flat lying faults implies that the synmetamorphic overburden should be mostly located several hundred kilometers away from the present exposure of the blueschists considering that the cycladic blueschist belt exposes successively shallower units in the west and that rocks of the upper plate have an anatolian nature we suggest that these blueschists were dragged from beneath turkey we recognize that the blueschist unit has undergone further thrusting in the final stage of the exhumation as have its counterparts elsewhere in the hellenides the emergence of the blueschists in the tertiary was concomitant with continental collision and thrusting in the hellenides the operation of low angle normal faults with large extensional displacements occurred within this context of collision tectonics this extension occurred parallel to the strike of the convergent orogen

petrologic and stable isotope study of the gold bearing breccia pipe at the golden sunlight deposit montana the golden sunlight a gold silver deposit in the whitehall mining district jefferson county montana is centered on a silica cemented breccia pipe with fragments of both belt supergroup sedimentary rocks and a latite porphyry native gold and gold tellurides occur finely disseminated within gangue minerals that have filled open spaces in the breccia pipe alteration in and around approximately 0 8 km radius the pipe is principally quartz sericite within the pipe breccia fragments are also characterized by a highly silicified outer rind openspace filling is divided into four periods as follows according to the presence of the following minerals i quartz and pyrite with minor hematite chalcopyrite bornitc and gold minerals ii chalcopyrite with lesser amounts of galena sphalerite and martasite iii additional gold silver tellurides and tennantite and iv barite quartz and sericite with minor carbonates and pyrite isotopic study shows delta 34 s values of sulfides between 12 2 and 3 1 per mil whereas barite values range from 1 2 to 5 9 per mil oxygen isotope values of whole rock breccia samples range from 6 5 to 13 8 per mil quartz from 10 5 to 14 3 per mil sericite from 9 7 to 15 5 per mil and unaltered country rock from 12 3 to 16 6 per mil fluid inclusion homogenization studies indicate a temperature of deposition for period i mineralization of approximately 200 degrees c the coexistence of sylvanitc and petzite in period iii suggests a temperature less than 170 degrees c values of delta 18 o sub h 2 o computed from quartz and temperature data and sericite delta 18 o values range from 2 4 to 4 0 per mil hydrogen isotope values of fluid inclusions in period i quartz and water in equilibrium with late sericite fall betweem 56 and 33 per mil fluid inclusion freezing study of one sample of period i quartz suggests a fluid salinity of 1 equiv wt percent nacl isotopic and geologic evidence is consistent with tbrmation of a breccia pipe caused by exsolution of a vapor from a crystallizing magma oxygen and hydrogen isotope data suggest that extensive isotopic exchange between a magmatic fluid and igneous rocks occurred prior to open space filling initial brecciation was accompanied by an isoenthalpic temperature decrease which coupled with conductive cooling led to the precipitation of large amounts of silica textural features indicate that brecciation and fracturing followed by fluid infiltration occurred episodically sulfur isotope data is also consistent with derivation of sulfur from a magmatic source characterized by a delta 34 s sub sigma s value between 0 and 5 per mil evidence from mineral assemblages and sulfur isotopes suggests that gold was most likely transported as a chloride complex and was deposited due to a ph increase accompanied by decreases in f sub o 2 and possibly temperature

oxygen isotope fractionation in quartz albite anorthite and calcite laboratory measurements of equilibrium oxygen isotope fractionation in quartz albite anorthite and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600 c and above exchange in these systems is as rapid as exchange between silicates and water fractionation factors can be summarized in the following equations qc 0 38 106t 2 abc 0 57 106t 2 anc 1 59 106t 2 from which the silicate pair fractionations are readily obtained these results are compared with published theoretical estimates as well as data derived from hydrothermal experiments some significant differences are found in particular it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data the new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems

epithermal gold mineralization acupan baguio district philippines geology mineralization alteration and the thermochemical environment of ore deposition a large gold rich adularia sericite style epithermal vein system formed at 0 65 ma at acupan baguio district philippines during a period of high k magmatism low salinity asymp 0 5 wt nacl equiv gassy up to 0 41 m co 2 meteoric fluids with temperatures of up to 300 degrees c or more were focused into a series of steeply dipping interconnected faults and joints in the virac granodiorite balatoc diatreme lucbuban gabbro and zig zag formation prolonged and varied geothermal activity resulted in the formation of a series of composite banded epithermal veins with an average width of 1 m that extend to depths of at least 1 km relative to the present day surface the epithermal event was characteried by periods of hydrothermal brecciation interspersed with more quiescent periods when delicate to coarsely banded vein material was precipitated five distinct mineral assemblages have been defined in the epithermal veins type a characterized by fine grained chalcedony type b fine grained gray quartz type c coarse grained white quartz type d coarse grained calcite and type e coarse grained anhydrite electrum and au ag tellurides have been recognized in type b c and d bands interaction of ascending chloride brines with the wall rocks over the lifetime of the system produced intense symmetrical meterwide halos of altered rock characterized by sericitic silicic and sericite chlorite mineral assemblages that grade out to a weak diffuse widespread propylitically altered zone minor adularia alteration is restricted to the deeper mine levels sulfide oxide silicate carbonate phase relationships in the acupan vein system constrain the mineralizing fluids to values of log f sub o 2 between 28 and 33 log f sub h 2 between 1 5 and 3 7 and log log f sub h 2 s between 0 6 and 1 8 at 300 degrees c abundant quartz k mica pyrite alteration and vein mineralization are consistent with silica saturated reduced weakly acidic to weakly alkaline fluid compositions boiling caused the fluids to evolve to more alkaline conditions leading to the sporadic precipitation of adularia in the veins and altered wall rocks dissolved co 2 concentrations were sufficiently high up to 0 41 m to stabilize calcite at the expense of calc silicate minerals mg super 2 concentrations were low in the mineralizing fluids but increased during dissolution of primary hornblende and biotite in the country rocks resulting in the development of a sericitechlorite alteration assemblage in the deep mine levels h 2 s and h 2 co 3 were the predominant sulfur and carbon bearing species and the low salinity gassy nature of the fluids favored gold and silver transport as bisulfide complexes h 2 te and hte super were the predominant aqueous tellurium species entrainment of minor amounts of magmatic volatiles during type c and d mineralization is responsible for te enrichment in the dominantly meteoric fluids and log f sub te 2 ranged between 7 8 and 8 6 at 300 degrees c during periods of hessite deposition magmatic contributions also account for the co sub 2 super and h 2 s rich nature of the fluids and for magmatic helium isotope signatures

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

the genesis of epithermal au ag te mineralization panormos bay tinos island cyclades greece the panormos bay au ag te vein system tinos island greece which is hosted in mesozoic marbles comprises 30 subparallel steeply dipping quartz veins that extend for at least 500 m in places gold telluride mineralization occurs in hydraulic breccias and alteration halos which are the products of co 2 effervescence of the ore fluid and wall rock interaction respectively seventy ore and gangue minerals have been identified zones of chlorite talc and muscovite albite tourmaline alteration up to 50 cm wide are associated with precious metal bearing milky and clear quartz veins the au ag te mineralization is developed in stage v of eight hydrothermal stages stage v consists of three substages early middle and late that are characterized by ag cu and au bearing tellurides respectively hessite sylvanite altaite native tellurium stutzite cuprian cervelleite and an unnamed cu bearing precious metal sulfotelluride ag au cu 9 te 2 s 3 characterize the early substage whereas melonite rickardite vulcanite weissite and native tellurium are present in the middle substage the late substage contains rickardite kostovite krennerite petzite and calaverite unexploited au ag te mineralization at panormos bay is though to be genetically related to a fluorine and boron bearing per aluminous leucogranite tinos leucogranite a combination of fluid inclusion microthermometry and sylvanite geothermometry suggests that the hydrothermal mineralization was deposited under hydrostatic pressures at a minimum depth of 1 km from moderate temperature 155 320 c low to moderate salinity 0 2 13 2 wt nacl equiv effervescing co 2 bearing fluids that contained appreciable amounts of cacl 2 and mgcl 2 calculated isotope compositions of 18 o 3 3 to 5 1 per mil and d of 73 to 62 per mil for waters in equilibrium with muscovite quartz and talc are consistent with the ore fluids being derived from the tinos leucogranite 18 o 4 2 and d 71 and their subsequent mixing with a more dilute low temperature miocenic meteoric hydrothermal fluid calculated 13 c fluid 2 0 to 0 3 and 34 s h 2 s 10 5 to 0 8 compositions of the ore fluids indicate an igneous source of carbon and sulfur which were highly exchanged with a metasedimentary source physicochemical conditions of the ore fluids were t 300 to 200 c ph 4 6 to 6 5 f s 2 10 10 9 to 10 15 f o 2 10 31 5 to 10 41 f te 2 10 7 7 to 10 10 7 f co 2 10 0 2 to 10 0 8 and f h 2 s 10 1 7 to 10 1 8

age resetting of hanging wall rocks above a low angle detachment fault tinos island aegean sea the central aegean region has been affected by extensional tectonics since at least the oligo miocene on tinos island cyclades greece a low angle normal fault places low grade metamorphic rocks the upper unit above high pressure rocks the cycladic blueschist unit k ar and 40ar 39ar ages were obtained by us on white micas amphiboles and whole rock samples separated from various metamorphic rocks representing different structural levels of the hanging wall the hanging wall upper unit is commonly thought to have resided at shallow crustal levels since late cretaceous times but our geochronological data supported by previously published rb sr dating brocker m franz l 1998 rb sr isotope studies on tinos island cyclades greece additional time constraints for metamorphism extent of infiltration controlled overprinting and deformational activity geol mag 135 3 369 382 indicate severe age resetting of the base of the hanging wall during tertiary times amphiboles from the top of the hanging wall section yielded late cretaceous ages which correlate well with other cretaceous upper unit rocks in the cyclades their preservation implies that tertiary age resetting was mainly confined to the lower part of the upper unit while upper parts retained older ages the base of the hanging wall section where age resetting and ductile deformation are most pronounced is taken to represent a part of a thick extensional shear zone that operated in low greenschist facies conditions during tertiary time the results of one dimensional thermal modeling suggest that warm footwall rocks emerging from great depth subsequently to hp lt metamorphism may have supplied the heat required for the metamorphism and ductile deformation at the base of the hanging wall the model also indicates that only minor cooling of the footwall during decompression is allowed if the footwall is to warm up the hanging wall this is a priori consistent with the isothermal decompression path of footwall blueschists and eclogites deduced from previous petrological studies on tinos