epithermal gold mineralisation in the active aegean volcanic arc the profitis ilias deposit milos island greece the profitis ilias gold deposit located on the western part of milos island greece is the first epithermal gold deposit discovered in the pliocene pleistocene aegean volcanic arc estimated ore reserves are 5 million tonnes grading 4 4 g tonne au and 43 g tonne ag the deposit is closely associated with a horst and graben structure and occurs in a series of steep interconnected crustiform banded quartz veins up to 3 m wide extending to depths of at least 300 m the mineralisation occurs in three stages and is hosted by 3 5 2 5 ma old silicified and sericitised rhyolitic lapilli tuffs and ignimbrites it consists of pyrite galena chalcopyrite electrum and native gold additionally adularia occurs with quartz mainly in veins homogenisation temperatures of primary liquid rich inclusions vary from 145 to 399 c for the ore stage and 112 to 263 c for the post ore stage salinities range between 0 1 and 11 4 wt nacl equiv and 0 93 to 8 5 wt nacl equiv for the ore stage and the post ore stage respectively rare vapour rich inclusions in ore stage quartz homogenise between 368 and 399 c and estimates of eutectic melting 25 to 38 c indicate the presence of ca and mg in the ore fluids sample elevation versus fluid inclusion th salinity relationships show 1 a high salinity trend where moderate temperature 300 250 c and moderate salinity brines 3 wt nacl equiv trend to high salinity up to 15 wt nacl equiv fluids with lower 25 50 c homogenisation temperatures and 2 a high th trend where moderate salinity and moderate temperature brines 200 250 c 3 wt nacl equiv develop into low salinity 350 c fluids these trends are best explained by extreme boiling and vapourisation phenomena between 200 and 250 c the 430 450 m asl metres above sea level level marks the transition between a lower liquid dominated segment of the system where only the steep high salinity trend is seen and an upper vapour dominated segment where the high th trend or a combination of both are seen there is a close spatial association between mineable gold grades and the upper segment of the system depth to boiling curves suggest that the paleo surface was 200 m above the present summit of profitis ilias comparison of the mineralisation and fluid geochemistry at profitis ilias with that of the nearby modern geothermal system indicates that the processes of metal mineralisation have probably been continuous since the late pliocene

the development of volcanic hosted massive sulfide and barite gold orebodies on wetar island indonesia wetar island is composed of neogene volcanic rocks and minor oceanic sediments and forms part of the inner banda arc the island preserves precious metal rich volcanogenic massive sulfide and barite deposits which produced approximately 17 metric tonnes of gold the polymetallic massive sulfides are dominantly pyrite locally arsenian with minor chalcopyrite which are cut by late fractures infilled with covellite chalcocite tennantite tetrahedrite enargite bornite and fe poor sphalerite barite orebodies are developed on the flanks and locally overly the massive sulfides these orebodies comprise friable barite and minor sulfides cemented by a series of complex arsenates oxides hydroxides and sulfate with gold present as 10 m free grains linear and pipe like structures comprising barite and iron oxides beneath the barite deposits are interpreted as feeder structures to the barite mineralization hydrothermal alteration around the orebodies is zoned and dominated by illite kaolinite smectite assemblages however local alunite and pyrophyllite are indicative of late acidic oxidizing hydrothermal fluids proximal to mineralization altered footwall volcanic rocks give an illite k ar age of 4 7 0 16 ma and a 40ar 39ar age of 4 93 0 21 ma fluid inclusion data suggest that hydrothermal fluid temperatures were around 250 270 c showed no evidence of boiling with a mean salinity of 3 2 wt equivalent nacl the 34s composition of sulfides ranges between 3 3 and 11 7 and suggests a significant contribution of sulfur from the underlying volcanic edifice the 34s barite data vary between 22 4 and 31 0 close to miocene seawater sulfate whole rock 87sr 86sr analyses of unaltered volcanic rocks 0 70748 0 71106 reflect contributions from subducted continental material in their source region the 87sr 86sr barite data 0 7076 0 7088 indicate a dominant miocene seawater component to the hydrothermal system the mineral deposits formed on the flanks of a volcanic edifice at depths of 2 km spectacular sulfide mounds showing talus textures are localized onto faults which provided the main pathways for high temperature hydrothermal fluids and the development of associated stockworks the orebodies were covered and preserved by post mineralization chert gypsum globigerina bearing limestone lahars subaqueous debris flows and pyroclastics rocks

volcanology and petrology of volcanic products from the island of milos and neighbouring islets abstract new geochronological and volcanological data from volcanics of the island group of milos south aegean active volcanic arc allow four main cycles of volcanic activity to be distinguished ranging in age between 3 5 and 0 1 m y b p the oldest volcanic activity consists almost totally of pyroclastics and submarine products followed by subaerial ones the eruptive centers migrated in time and concentrated during the most recent volcanic phase in the central part of milos and on the island of antimilos the oldest products are dominated by andesites and dacites while the most recent ones mainly consist of rhyolites the volcanic evolution and the geochemical characters of the erupted products suggest that the feeding system of the oldest volcanism was located in the deep continental crust where contamination and fractional crystallization jointly occurred the younger cycle of volcanic activity was fed from small and relatively shallow magma chambers where contamination processes played a minor role these magma bodies are considered to responsible for the shallow thermal anomaly giving rise to the high enthalpy field on milos

simple two dimensional model of propagation of magma filled cracks abstract the direction of propagation of magma filled cracks was theoretically examined for a two dimensional model the analytical result indicates that magma filled cracks which have magmatic pressures larger than a critical value propagate in parallel with the maximum principal direction of far field stress this may give one of theoretical grounds to the dike method by which the regional stress field is estimated

the geochemistry of carbonate replacement pb zn ag mineralization in the lavrion district attica greece fluid inclusion stable isotope and rare earth element studies strata bound carbonate replacement pb zn ag deposits in the lavrion district greece are spatially related to a late miocene granodiorite intrusion 7 10 ma and various sills and dikes of mafic to felsic composition the plaka granodiorite contains porphyry molybdenum mineralization and is locally associated with a ca fe skarn carbonate replacement deposits occur predominantly in marbles upper and lower marble of the basal unit kaesariani schists and along a major detachment fault that separates the basal unit from the upper unit orebodies are mainly strata bound carbonate replacement although sulfides also occur in veins the mineralogy of carbonate replacement deposits is dominated by base metal sulfides and sulfosalts of ag bi sn sb as and pb particularly at plaka and kamariza carbonates are intergrown with earlier formed sulfides and sulfosalts but are more abundant late in the paragenetic sequence with fluorite and barite fluid inclusion studies of sphalerite fluorite calcite and quartz in carbonate replacement deposits suggest that they were deposited from 132 to 365 c from co2 poor low to high salinity fluids 1 20 wt nacl equiv carbon and oxygen isotope compositions of calcite 13c 15 6 to 1 5 and 18o 9 2 to 17 3 intergrown with sulfides reflect variable exchange of the ore bearing fluid with the upper and lower marbles and proximity to the plaka granodiorite post archean australian shale paas normalized rare earth and yttrium patterns of the upper and lower marbles and calcite intergrown with sulfides show positive eu and negative ce anomalies as well as y ho ratios between 40 and 80 normalized rare earth and yttrium patterns of fluorite also have positive eu and negative ce anomalies such anomalies for both the carbonates and fluorite reflect the high ph or high f o2 conditions of the late stage hydrothermal fluids and the likely derivation of calcium from marine carbonates precursors of the upper and lower marbles the range of sulfur isotope compositions for sulfides 34s 4 9 to 5 3 with one outlier of 9 4 in carbonate replacement and vein deposits is due likely to a magmatic sulfur source with a contribution of reduced seawater sulfate sulfur isotope compositions of barite from carbonate replacement range from 34s 17 2 to 23 7 per mil and reflect miocene seawater sulfate values if a magmatic source of sulfur is assumed along with an average temperature of 250 c for the ore forming fluids as based on fluid inclusion studies sulfides in carbonate replacement deposits were deposited at values of log f o2 41 to 36 and a ph 5 8 to 9 1 however the range of sulfur isotope values does not rule out the possibility that sulfur in sulfides could have been produced by the reduction of seawater sulfate with no contribution from a magmatic source the carbonate replacement deposits resemble manto type sulfide deposits in mexico central colorado south korea nevada and northern greece

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

hydrothermalism in the mediterranean sea abstract hydrothermalism in the mediterranean sea results from the collision of the african and european plates with the subduction of the oceanic part of the african plate below europe high heat flows in the resulting volcanic arcs and back arc extensional areas have set up hydrothermal convection systems most of the known hydrothermal sites are in shallow coastal waters

the geochemistry of fluids from an active shallow submarine hydrothermal system milos island hellenic volcanic arc abstract geothermal activity in the aegean island of milos greece associated with island arc volcanism is abundant both on and off shore hydrothermal fluids venting from several sites mainly shallow submarine up to 10 m but also just above seawater level in one locality were sampled over four summer field seasons some of the discharging fluids are associated with the formation of hydrothermal edifices overall the main characteristics of the hydrothermal fluids are low ph and variable chlorinity the lowest recorded ph was 1 7 and chlorinity ranged from 0 1 to 2 5 times that of seawater the highest fluid temperatures recorded on site were 115 c two main types of fluids were identified low chlorinity fluids containing low concentrations of alkalis potassium lithium sodium and calcium and high concentrations of silica and sulphate and high chlorinity fluids containing high concentrations of alkalis and calcium and lower concentrations of silica and sulphate the type locality of the high chlorinity fluids is shallow submarine in palaeochori near the east end of the south coast of the island whereas the type locality of the low chlorinity fluids is a cave to the west of palaeochori the two fluid types are therefore often referred to as submarine and cave fluids respectively both fluid types had low magnesium and high metal concentrations but were otherwise consistently different from each other the low chlorinity fluids had the highest cobalt nickel aluminium iron and chromium up to 1 6 m 3 6 m 1586 m 936 m and 3 0 m respectively and the high chlorinity fluids had the highest zinc cadmium manganese and lead up to 4 1 m 1 0 m 230 m and 32 m respectively geochemical modelling suggests that metals in the former are likely to have been transported as sulphate species or free ions and in the latter as chloride species or free ions isotopic values for both water types range between d 12 to 33 and 18 o 1 2 to 4 6 the range of fluid compositions and isotopic contents indicates a complex history of evolution for the system both types of fluids appear to be derived from seawater and thus are likely to represent end members of a single fluid phase that underwent phase separation at depth

submarine gold mineralization near lihir island new ireland fore arc papua new guinea gold rich siliceous veins with disseminated polymetallic sulfides and pyritic stockwork mineralization have been recovered from the top of conical seamount a shallow 1 050 m water depth submarine volcano located about 10 km south of lihir island papua new guinea grab samples from the summit of conical seamount contain the highest concentration of gold yet reported from the modern sea floor max 230 ppm au avg 26 ppm n 40 the gold occurs in sulfide rich veins of black amorphous silica hosted by intensely altered high k calc alkaline basalts sulfides in the veins consist of sphalerite galena pyrite chalcopyrite marcasite and a variety of cu pb as sb sulfosalts the gold occurs as native gold and electrum in the amorphous silica and as inclusions in the sulfides the highest gold concentrations are associated with high ag as sb and hg zoned alteration adjacent to the veins consists of illite smectite amorphous silica k feldspar secondary plagioclase minor chlorite and trace carbonate the association of gold with illite smectite amorphous silica and k feldspar indicates deposition from near neutral ph hydrothermal fluids however the auriferous polymetallic sulfide veins and the associated alteration are overprinted on stockwork pyrite mineralization that is associated with earlier acid alteration containing alunite aluminum phosphate sulfates kaolinite and other clay minerals the platy habit of the alunite in this assemblage the presence of alumium posphate sulfate minerals and the sulfur isotope ratios of the crystalline pyrite 8 6 to 0 2 34 s n 28 and alunite 7 5 and 6 4 34 s are consistent with a contribution of magmatic volatiles in the earliest stages of the hydrothermal system framboidal pyrite within and at the margins of the mineralized zone has 34 s values suggesting involvement of biogenic activity 11 6 to 13 9 34 s the gold rich veins at conical seamount are distinct from sea floor massive sulfide deposits and represent a new style of mineralization on the modern sea floor the mineralogy alteration geochemistry and texture of the veins resemble those of some subaerial epithermal gold deposits and indicate that features long considered to define a subaerial setting can also form in a submarine environment the proximity of conical seamount to the giant ladolam epithermal gold deposit on nearby lihir island also raises the possibility that both subaerial and submarine gold mineralization in the region may be related to the same district scale magmatic events

i type plutonism in a continental back arc setting miocene granitoids and monzonites from the central aegean sea greece miocene extension in the aegean sea was accompanied by the intrusion of granitoid and monzonitic magmas at upper crustal levels with increasing distance from the trench the metaluminous to slightly peraluminous i type intrusives show a systematic regional variation in their compositions medium to high k granodiorites in the wsw high k low silica granites in the central region and high k high silica granites monzonites monzogranites and composite lamprophyric monzonitic dikes in the ene the granodioritic and low silica granitic plutons comprise similar ranges of sio2 63 5 71 6 wt and initial nd sr and o isotopic values end i 7 0 to 9 8 87sr 86sr i 0 7092 0 7115 18o 9 7 11 5 but display significant differences in their chemical compositions compared with the granodiorites the low silica granites have higher abundances of large ion lithophile light rare earth and some high field strength elements initial isotopic signatures of the high silica granites in the ene end i 9 0 to 9 6 87sr 86sr i 0 7128 0 7144 18o 10 8 12 0 are slightly more crust like than those of the low silica granites in chemical variation diagrams samples from the high silica granites continue the trends defined by those from the low silica granites it is suggested that all granitoid magmas originated by dehydration melting of metaluminous older crustal sources most probably metagreywackes u pb systematics of zircon populations in conjunction with zr sio2 systematics and zircon saturation temperatures suggest a high proportion of restitic or assimilated crustal material in these magmas monzonitic to monzogranitic rocks show chemical and isotopic characteristics end i 0 8 to 3 6 87sr 86sr i 0 7059 0 7071 18o 9 4 10 6 that are significantly different from those of the granitoids a small portion of an older crustal component in these magmas is indicated by u pb systematics of zircon populations lamprophyric dikes display chemical and isotopic signatures end i 0 5 87sr 86sr i 0 7044 18o 8 9 that are compatible with an origin from either a mantle source previously enriched by slab derived hydrous fluids melts as suggested by negative nb ta anomalies or a new k rich basaltic underplate abundant composite dikes indicate the coexistence of and mingling mixing between lamprophyric melts and monzonitic magmas

bismuth and cobalt minerals as indicators of stringer zones to massive sulphide deposits iberian pyrite belt the stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the iberian pyrite belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides these are fairly rare cobalt sulphoarsenides cobaltite alloclasite galucodot that were formed at the beginning of the massive sulphide genesis and fairly common bismuth sulphides bismuthinite hammarite wittichenite cosalite kobellite joseite etc including species rare at world scale nuffieldite giessenite jaskolskiite that were deposited from last stage high temperature 300 c copper bearing fluids containing bi te se the last stage fluids precipitated chalcopyrite containing cu bi te se sulphosalts at the base of the sulphide mound to form a high cupriferous zone their interaction with the massive sulphides is reflected by the formation of an exchange zone a few metres thick showing chalcopyrite disease textures at the base of the mound this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals gold is undoubtedly in part if not totally related to this last phase the bismuth concentrations being equivalent in the massive sulphides and the stringers the presence of bismuth minerals in the stringer zones results from high temperature conditions combined with a rarity of galena which impedes absorption of available bi the distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone with a deep low as2 zone containing native bismuth and tellurides and a shallow higher as2 zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides these results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature and provide mineralogical criteria for the proximity of copper rich zones they enrich the very complex mineralogy of the iberian pyrite belt

the role of granites in volcanic hosted massive sulphide ore forming systems an assessment of magmatic hydrothermal contributions assessment of geological geochemical and isotopic data indicates that a significant subgroup of volcanic hosted massive sulphide vhms deposits has a major or dominant magmatic hydrothermal source of ore fluids and metals this group which is typically characterised by high cu and au grades includes deposits such as those in the neoarchean doyon bousquet laronde and cambrian mount lyell districts these deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones in many of these deposits 34ssulphide is low with a major population below 3 34ssulphate differs from coexisting seawater and 34ssulphate sulphide 20 30 these characteristics are interpreted as the consequence of disproportionation of magmatic so2 as magmatic hydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic hydrothermal contribution other characteristics that we consider diagnostic of significant magmatic hydrothermal input into vhms ore fluids include uniformly high 3 times modern seawater values salinities or very 18o enriched 18o 5 ore fluids we do not consider other criteria e g variable salinity moderately high 18ofluid 2 5 34ssulphide near 0 metal assemblages or a spatial association with porphyry cu or other clearly magmatic hydrothermal deposits that have been used previously to advocate significant magmatic hydrothermal contributions to be diagnostic as they can be produced by non magmatic processes known to occur in vhms mineral systems however in general a small magmatic hydrothermal contribution cannot be excluded in most vhms systems considered conclusive data that imply minimal magmatic hydrothermal contributions are only available in the paleoarchean panorama district where coeval seawater dominated and magmatic hydrothermal systems appear to have been physically separated this district which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages is typical of many vhms deposits around the world suggesting that for garden variety vhms deposits a significant magmatic hydrothermal contribution is not required other than deposits associated with advanced argillic alteration assemblages the only deposit for which we ascribe a major magmatic hydrothermal contribution is the devonian neves corvo deposit this deposit differs from other deposits in the iberian pyrite belt and around the world in being extremely sn rich with the sn closely associated with cu and in having formed from high 18o rich fluids 18ofluid 8 5 we consider these characteristics particularly the last as diagnostic of a significant magmatic hydrothermal contribution our analysis indicates that two subgroups of vhms deposits have a major magmatic hydrothermal contribution cu au rich deposits with aluminous alteration assemblages and reduced very sn rich deposits in which sn was introduced in a high temperature ore assemblage comparison with normal vhms deposits suggests that these subgroups of vhms deposits may form in specialised tectonic environments the cu au rich deposits appear to form adjacent to magmatic arcs an environment conducive to the generation of hydrous oxidised melts by melting metasomatised mantle in the wedge above the subducting slab this contrasts with the back arc setting of normal vhms deposits in which relatively dry granites in this contribution we use the term granite sensu latto formed by decompression melting drive seawater dominated hydrothermal circulation the tectonic setting of highly sn rich vhms deposits such as neves corvo is less clear however thick continental crust below the ore hosting basin may be critical as it is in other sn deposits

hydrothermal gases offshore milos island greece hydrothermal fluids emerge from the seafloor of paleohori bay on milos the gases in these fluids contain mostly co2 but ch4 concentrations up to 2 are present the stable carbon isotopic composition of the co2 near 0 indicates an inorganic carbon source dissociation of underlying marine carbonates the carbon and hydrogen isotopes of most ch4 samples are enriched in the heavy species delta 13c 9 4 to 17 8 per mille sign delta d 102 to 189 per mille sign which is believed to be characteristic for an abiogenic production of ch4 by co2 reduction fischer tropsch reactions depletions in the deuterium content of three ch4 samples to 377 are probably caused by unknown subsurface rock alteration processes secondary hydrogen isotope exchange processes between methane hydrogen and water are most likely responsible for calculated unrealistic methane formation temperatures we show that excess helium slightly enriched in 3he is present in the hydrothermal fluids emerging the seafloor of paleohori bay when the isotopic ratio of the excess component is calculated a 3he 4heexcess of 3 6 10 6 is obtained this indicates that the excess component consists of about one third of mantle helium and two thirds of radiogenic helium we infer that the mantle derived component has been strongly diluted by radiogenic helium during the ascent of the fluids to the surface

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

sulfur isotope evidence for magmatic contributions to submarine and subaerial gold mineralization conical seamount and the ladolam gold deposit papua new guinea conical seamount is a submarine alkali basalt volcano situated 10 km south of lihir island in the tabar feni island chain papua new guinea polymetallic zn pb ag au as sb veins pyritic stockwork and hydrothermally altered rocks discovered on the summit of conical seamount represent a unique example of submarine gold mineralization with mineralogical chemical and textural characteristics common to some subaerial epithermal systems the giant ladolam epithermal gold deposit 42 moz au is situated in the crater of an alkali stratovolcano on lihir island portions of the epithermal mineralization and alteration assemblages at ladolam are similar to those observed on conical seamount conical seamount has the lightest hydrothermal i e nondiagenetic sulfide d34s values 17 5 to 6 1 measured to date from modern sea floor hydrothermal systems a previous model for the conical seamount hydrothermal system suggested a contribution of magmatic volatiles in the earliest stages of mineralization stage 1 followed by a combination of sulfur leached from the underlying volcanic rocks and reduced seawater sulfate during the main base and precious metal precipitating event stage 2 new sulfur isotope data allow a reinterpretation of this model that suggests a greater input of magmatic volatiles plus boiling throughout both stage 1 and 2 mineralization sulfides from the ladolam gold deposit have a range of sulfur isotope values 12 9 to 3 6 similar to that of conical seamount these sulfur isotope data have previously been interpreted as the result of magmatic volatiles escaping from a crystallizing magma and mixing with dilute meteoric ground water anhydrite associated with the gold mineralization has two populations of d34s values 8 14 and 20 22 which indicate the interaction of magmatic volatiles with seawater that has previously been discounted the range of sulfide and sulfate d34s values at ladolam is reinterpreted to be due to a complex interaction of magmatic hydrothermal fluids meteoric ground water and seawater native sulfur in thermal areas in luise caldera and pyrite in offshore hydrothermal vents in luise harbor have similar d34s values to the ladolam epithermal mineralization indicating that fluids similar to the young ladolam ore forming event are still reaching the floor of luise caldera sulfur isotope data from conical seamount and the ladolam deposit suggest that magmatic volatiles have contributed a significant amount of sulfur to both these gold rich hydrothermal systems

trace metal content of the pueblo viejo precious metal deposits and their relation to other high sulfidation epithermal systems we provide here information on the distribu tion of copper zinc lead gold silver barium arsenic antimony mercury selenium and tellurium in the moore and monte negro high sulfidation epithermal deposits in the pueblo viejo district dominican republic moore and monte negro are funnel shaped zones of advanced argillic alteration and precious metal mineralization which extend to depths of about 350 m below the present surface the uppermost part of the moore deposit has been removed by erosion whereas the monte negro deposit is covered by rocks containing low but still anomalous gold grades at moore con centrations of all elements except copper increase up ward through the deposit at monte negro all elements except barium and zinc show a similar upward increase in concentration to a point near the top of the deposit from which they decrease upward this difference re flects the fact that the top of the moore deposit has been removed by erosion because the deposits are funnel shaped and average metal concentrations increase by almost an order of magnitude upward most of the metals are concentrated in the upper parts of the deposits the upward increase in concentration of most metals is gradual and similar in magnitude to the pro grade temperature dependence in solubilities of many metal complexes suggesting that the metals were deposited by cooling by contrast concentrations of mercury and to a lesser extent tellurium increase more abruptly in the upper part of the deposits this change probably reflects boiling of the hydrothermal solutions and partitioning of mercury and tellurium into a rising vapor phase and it suggests that host rocks overlying the deposits will be anomalous in mercury and tellurium comparison to the broadlands new zealand hydro thermal system supports these inferred depositional processes it shows that the behavior of arsenic and antimony at broadlands was different from that at pueblo viejo possibly because the elements were com plexed differently in the two ore fluids comparison of trace element abundances at pueblo viejo to other high sulfidation epithermal systems shows differences in base metal arsenic and mercury abundances which may be related to the depths at which the deposits formed the results of this study highlight the application and need for quantitative trace element data from epithermal deposits

acidic and sulfate rich hydrothermal fluids from the manus back arc basin papua new guinea hot 88 120 c and acidic ph 2 1 hydrothermal fluids rich in sulfate were discovered venting in the desmos caldera depth 1926 m eastern manus back arc basin bismarck sea surrounded by papua new guinea the abundant sulfate 32 8 m m higher than the seawater value of 28 m m with elemental sulfur deposition around the vents and remarkably low d h 2 o and 34 s h 2 s values 8 1 and 5 6 respectively are suggestive of the incorporation of a magmatic fluid and the disproportionation of the exsolved so 2 from a magma body the desmos fluid may be similar in origin to the acidic sulfate chloride hot springs associated with subaerial volcanic activity in contrast to the typical hydrothermal end member mg concentration of 0 the desmos fluids are rich in mg 46 52 m m probably because of mg dissolution by acid attack upon magnesium silicate minerals

mn ba hg mineralization at shallow submarine hydrothermal vents in bahia concepcion baja california sur mexico coastal submarine hydrothermal venting occurs on the west shore of the fault bounded bay of bahia concepcion along a stretch of about 700 m of rocky shoreline diffuse hydrothermal seepage of water and continuous gas bubbling mainly co2 and n2 take place through the sediment covered seafloor at shallow depth 5 to 15 m in addition at about 500 m se a cluster of hot springs occurs within the intertidal zone the temperature and ph of the hydrothermal fluids varies from 72 to 87 c and 5 95 to 6 02 in the submarine diffuse venting area and reaches 62 c and ph of 6 68 in the intertidal hot springs mn ba hg mineralization is presently forming as a result of the hydrothermal venting at the intertidal hot springs moss like crusts of manganese oxides and structureless detrital aggregates cemented by opal a barite and calcite occur around the main discharge conduits these aggregates are overlaid by silica carbonate fine layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders manganese crusts are made up of barium rich x ray amorphous todorokite like and romanechite phases and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment in the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter thick iron oxyhydroxide coatings on volcanic cobbles and boulders these coatings are composed of poorly crystallized six line ferrihydrite accompanied by minor cinnabar and fine grained colloform pyrite textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition the vent precipitates display a significant enrichment of hg as and sb arsenic is probably adsorbed onto mn and fe oxide substrates the nasc north american shale composite normalized ree patterns of the vent precipitates show a pronounced positive eu anomaly that is probably inherited from the hydrothermal fluid

shallow submarine epithermal pb zn cu au ag te mineralization on western milos island aegean volcanic arc greece mineralogical geological and geochemical constraints abstract milos island contains several epithermal deposits e g profitis ilias chondro vouno pb zn ag au te cu triades galana agathia kondaros pb zn ag bi w mo cu au and katsimoutis kondaros vani pb zn ag mn of late pliocene to early pleistocene age these deposits are hosted in calc alkaline volcanic rocks emplaced as a result of three successive magma pulses in an emergent volcanic edifice submarine rhyolitic to rhyodacitic cryptodomes at ca 2 7 ma profitis ilias chondro vouno submarine to subaerial andesite to dacite domes at ca 2 2 to 1 5 ma triades galana kondaros katsimouti vani hydrothermal alteration of the volcanic rocks includes advanced argillic both hypogene and steam heated argillic phyllic adularia sericite and propylitic types in the northern sector triades galana agathia kondaros initial magma degassing derived from andesitic dacitic intrusives along ne sw to e w trending faults resulted in the development of pre ore hypogene advanced argillic alteration dickite alunite diaspore pyrophyllite halite and pyrite in a submarine environment mineralogical data indicate common features among the profitis ilias chondro vouno kondaros katsimoutis vani and triades galana mineralized centers all of which are characterized by the presence of galena fe poor sphalerite and chalcopyrite as well as abundant barite adularia sericite and to a lesser extent calcite which are typical of intermediate sulfidation epithermal type deposits locally at triades galana and kondaros agathia high sulfidation conditions prevailed as suggested by the presence of coexisting enargite and covellite the high silver and gold content of the western milos deposits is derived from ag bearing sulfosalts polybasite pearceite pyrargyrite freibergite and tellurides gold at profitis ilias both as native gold and silver gold tellurides is present in base metal precipitates within multicomponent blebs which recrystallized to form hessite petzite altaite coloradoite and native gold mineralogical evidence e g microchimney structures copper sulfides widespread occurrence of barite aragonite suggests that precious metal mineralization in western milos mineralization formed in a submarine setting we present information on the surface distribution of au ag cu pb zn as sb hg mo bi w and cd at western milos gold is enriched at profitis ilias chondro vouno deposits and to a lesser extent at triades galana arsenic is absent from the southern sector but shows elevated concentrations together with molybdenum bismuth and tungsten at the northern sector triades galana vani deposits the differences in precious and base metal abundances may be related to the depths at which the deposits are exposed and or different sources of magma the metal signatures of the triades galana and agathia kondaros katsimouti vani mo bi w as hg ag au occurrences compared to profitis ilias te au ag reflect different sources of magma dacite rhyodacite for profitis ilias andesite dacite for triades galana and dacite for kondaros katsimoutis the enrichment of te mo w and bi in the deposits is a strong indication of a direct magmatic contribution of these metals at western milos precious and base metal vein mineralization was deposited during episodic injection of magmatic volatiles and dilution of the hydrothermal fluids by seawater the mineralization represents seafloor sub seafloor precipitation of sulfides that formed in stockwork zones base and precious metal mineralization formed from intermediate to high sulfidation state fluids and mostly under boiling conditions as indicated by the widespread occurrence of adularia associated with metallic mineralization we speculate that the widespread occurrence of boiling and the shallow depth of the precious and base metal emplacement prevented the formation of seafloor massive sulfides

formation and decay of a modern massive sulfide deposit in the indian ocean in december 1993 the first massive sulfides were recovered from the indian ocean floor north of the rodrigues triple junction the polymetallic deposit is situated in the fourth central indian ridge segment close to the rift axis it is hydrothermally no longer active the deposit appears to be typical of mid ocean ridge massive sulfide occurrences but is in a phase of disintegration and about to be buried by sediment the chimney structures were formed by multiple hydrothermal events and are now degraded by mass wasting showing various stages of weathering later stage low temperature hydrothermal mineralization processes led to copper and gold enrichment here we report on the geological setting mineral zonation different sulfide types and stages of formation of the sonne sulfide field which is part of a larger mineralized zone

do fluid inclusions preserve δ18o values of hydrothermal fluids in epithermal systems over geological time evidence from paleo and modern geothermal systems milos island aegean sea stable isotope compositions of quartz d 18 oquartz and fluid inclusion waters d 18 ofi and ddfi were analysed from profitis ilias a low sulphidation epithermal gold mineralisation deposit on milos island greece to establish if d 18 ofi preserve a record of paleogeothermal processes previous studies show that mineralisation at profitis ilias resulted from extreme boiling and vaporisation with a zone located at approximately 430 m above sea level asl representing the transition between liquid and vapor dominated systems miner depos 36 2001 32 the deposit is also closely associated with an active geothermal system whose waters have a well characterised stable isotope geochemistry pflumio c boulegue j liakopoulos a briqueu l 1991 source transport and deposition of metals balkema rotterdam the samples were collected over an elevation interval of 440 m 210 650 m asl to give information on the liquid and vapor dominated sections of the paleosystem the data show systematic variations with sample elevation samples from the highest elevations ca 650 m asl have the lightest d 18 ofi 7 3x and ddfi 68 0x whilst the deepest ca 210 m asl are isotopically heavier d 18 ofi 0 3x ddfi 19 0x relative changes in d 18 ofi closely parallel those in ddfi d 18 oquartz shows an opposite trend from the lightest values 13 9x at the lowest elevations to the heaviest 15 1x at the highest elevations d 18 ofi shows correlations with other parameters for example variable fluid inclusion homogenisation temperatures in the vapor dominated part of the system correlate with a rapid shift in ddfi 33 3xto 50 5x and d 18 ofi 4 1xto 6 2x gold contents also increase in the same zone up to 50 ppm au comparable correlations in d 18 oquartz or d 18 ocalculated estimated geothermal fluid from fluid inclusion homogenisation data are absent d 18 ocalculated are always 5 10xheavier than d 18 ofi comparison with the present day geothermal field shows that ddfi and d 18 ofi are similar isotope data for the modern system and fluid inclusion waters fall on linear trends subparalleling the meteoric water line and project towards seawater values numerical modelling favours kinetically controlled fractionation to explain differences in d 18 ocalculated and d 18 ofluid rather than diffusive posttrapping reequilibration the evidence suggests that in low temperature epithermal systems d 18 ofi may represent

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

facies architecture and late pliocene pleistocene evolution of a felsic volcanic island milos greece the volcanic island of milos greece comprises an upper pliocene pleistocene thick up to 700 m compositionally and texturally diverse succession of calc alkaline volcanic and sedimentary rocks that record a transition from a relatively shallow but dominantly below wave base submarine setting to a subaerial one the volcanic activity began at 2 66 0 07 ma and has been more or less continuous since then subaerial emergence probably occurred at 1 44 0 08 ma in response to a combination of volcanic constructional processes and fault controlled volcano tectonic uplift the architecture of the dominantly felsic intermediate volcanic succession reflects contrasts in eruption style proximity to source depositional environment and emplacement processes the juxtaposition of submarine and subaerial facies indicates that for part of the volcanic history below wave base to above wave base and shoaling to subaerial depositional environments coexisted in most areas the volcanic facies architecture comprises interfingering proximal near vent medial and distal facies associations related to five main volcano types 1 submarine felsic cryptodome pumice cone volcanoes 2 submarine dacitic and andesitic lava domes 3 submarine to subaerial scoria cones 4 submarine to subaerial dacitic and andesitic lava domes and 5 subaerial lava pumice cone volcanoes the volcanic facies are interbedded with a sedimentary facies association comprising sandstone and or fossiliferous mudstone mainly derived from erosion of pre existing volcanic deposits the main facies associations are interpreted to have conformable disconformable and interfingering contacts and there are no mappable angular unconformities or disconformities within the volcanic succession

crustal scale geometry and kinematics of late orogenic extension in the central aegean cyclades and ewia island abstract the aegean continental domain is known to be the site of widespread back arc extension since at least the middle miocene overprinting structures related to the mesozoic cenozoic hellenic orogeny features attributed to early thrusting include the overall ductile deformation within two broad belts that have suffered hp lt metamorphism across the aegean this study summarizes the results of a structural study in the central aegean area cyclades and evvia island examining in particular the relationship between ductile and brittle deformation on a regional scale extension appears to be responsible for most of the ductile deformation within hp rock units that have experienced penetrative greenschist facies and higher grade metamorphic overprinting on each island studied progressive extensional deformation has occurred through the development of a major normal sense detachment zone down to depths of about 18 25 km the geometry of the extensional system on the scale of the central aegean is described taking into account the characteristic features of the regional scale ductile strain field at least two probably three subparallel major north dipping detachment zones are identified trending nw se in the northwestern cyclades and e w in the southeastern cyclades both with initial dips estimated at around 30 45 the present geometry of the extensional system implies that these detachment zones and related metamorphic core complexes interfere with each other two main evolutionary models are considered which can account for such a kinematic link between parallel detachment zones structural data favour the sequential development of synthetic major detachments zones in a direction opposite to the sense of dip of the detachments early oligocene lower miocene detachment type extension in the area studied is related to a late orogenic post thickening back arc setting

copper ore grade hydrothermal mineralization discovered in a seamount in the tyrrhenian sea mediterranean is the mineralization related to porphyry coppers or to base metal lodes abstract a luzonite and tennantite tetrahedrite bearing massive sulfide mineralization was discovered when sampling the crater of the palinuro seamount located within a probable island arc or marginal basin tectonic setting the mineralization is made up of indurated sulfide crusts interpreted to have been deposited by a seawater sediment interface and mixed with ooze of organic and volcanic origin a preliminary investigation of the economic minerals showed besides luzonite and tennantite tetrahedrite native rare copper all associated with pyrite predominantly and baryte native silver bismuthinite and stibnite were also found a dust like white precipitate was observed by submersible close to the mineralized zone but no structures or edifices resembling black smokers have yet been identified massive pyrite deposits associated with such uncommon mineral assemblages are found in the high level volcanic parts of porphyry copper systems or associated with base metal lodes the massive sulfide discovery is suggested to have a volcanogenic exhalative origin and a genetic relationship with porphyry coppers or base metal sulfide lodes

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

copper isotope systematics of the lucky strike rainbow and logatchev sea floor hydrothermal fields on the mid atlantic ridge in this paper we present the copper isotope signatures of black smoker sulfides massive sulfides and their alteration products and provide new insights into mineralization processes and applications of copper isotope geochemistry to sea floor hydrothermal systems on the mid atlantic ridge the hydrothermal systems studied include the lucky strike field at 37 17 n on a basaltic substrate and the rainbow and logatchev fields situated on ultramafic rock copper isotope variation in the hydrothermal precipitates was examined in conjunction with s isotopes and se and co concentrations the comparison between 65cu and se contents shows that subsurface precipitation of cu rich sulfides does not control significantly the 65cu values of the hydrothermal chimneys it appears that the major cause of copper isotope fractionation in hydrothermal systems up to 3 is the sea floor oxidation of primary copper sulfides enrichment in the heavy copper isotope can be explained by processes occurring at the sea floor such as hydrothermal reworking of previously altered sulfides by high temperature fluid massive sulfides characterized by negative 65cu values have undergone extensive recrystallization in these mineralogical assemblages isotopically heavy copper typical of altered sulfides has been leached and redeposited in the external zones or incorporated in hydrothermal fluids copper isotopes are therefore a promising tool for the study of supergene processes and the recycling of previously oxidized sulfides as well as a means of characterizing the degree of hydrothermal reworking of large sulfide deposits further studies of copper isotope fractionation under controlled laboratory experimental conditions are required to identify copper isotope fractionation during sulfide alteration in particular the possible biological mediation of copper isotope fractionation during sulfide oxidation may be an important direction for further studies

submarine hydrothermal activity and gold rich mineralization at brothers volcano kermadec arc new zealand brothers volcano of the kermadec intraoceanic arc is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world it has two distinct vent fields known as the nw caldera and cone sites whose geology permeability vent fluid compositions mineralogy and ore forming conditions are in stark contrast to each other the nw caldera site strikes for 600 m in a sw ne direction with chimneys occurring over a 145 m depth interval between 1 690 and 1 545 m at least 100 dead and active sulfide chimney spires occur in this field and are typically 2 3 m in height with some reaching 6 7 m their ages at time of sampling fall broadly into three groups 4 23 and 35 years old the chimneys typically occur near the base of individual fault controlled benches on the caldera wall striking in lines orthogonal to the slopes rarer are massive sulfide crusts 2 3 m thick two main types of chimney predominate cu rich up to 28 5 wt cu and more commonly zn rich up to 43 8 wt zn geochemical results show that mo bi co se sn and au up to 91 ppm are correlated with the cu mineralization whereas cd hg sb ag and as are associated with the dominant zn rich mineralization the cone site comprises the upper cone site atop the summit of the recent main dacite cone and the lower cone site that straddles the summit of an older smaller more degraded dacite cone on the ne flank of the main cone huge volumes of diffuse venting are seen at the lower cone site in contrast to venting at both the upper cone and nw caldera sites individual vents are marked by low relief 0 5 m mounds comprising predominately native sulfur with bacterial mats vent fluids of the nw caldera field are focused hot 300 c acidic ph 2 8 metal rich and gas poor calculated end member fluids from nw caldera vents indicate that phase separation has occurred with cl values ranging from 93 to 137 of seawater values by contrast vent fluids at the cone site are diffuse noticeably cooler 122 c more acidic ph 1 9 metal poor and gas rich higher than seawater values of so4 and mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water rock interactions iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from fe rich brines evidence for magmatic contributions to the hydrothermal system at brothers includes high concentrations of dissolved co2 e g 206 mm kg at the cone site high co2 3he negative d and 18oh2o for vent fluids negative 34s for sulfides to 4 6 sulfur to 10 2 and 15n2 to 3 5 vent fluid ph values to 1 9 and mineral assemblages common to high sulfidation systems changing physicochemical conditions at the brothers hydrothermal system and especially the cone site occur over periods of months to hundreds of years as shown by interlayered cu au and zn rich zones in chimneys variable fluid and isotopic compositions similar shifts in 3he 4he values for both cone and nw caldera sites and overprinting of magmatic mineral assemblages by water rock dominated assemblages metals especially cu and possibly au may be entering the hydrothermal system via the dissolution of metal rich glasses they are then transported rapidly up into the system via magmatic volatiles utilizing vertical 2 5 km long narrow 300 m diameter pipes consistent with evidence of vent fluids forming at relatively shallow depths the nw caldera and cone sites are considered to represent stages along a continuum between water rock and magmatic hydrothermal dominated end members

variation in noble gas isotopic composition of gas samples from the aegean arc greece abstract in contrast to most other arcs with oceanic plate subduction the aegean arc is characterized by continent continent subduction noble gas abundances and isotopic compositions of 45 gas samples have been determined from 6 volcanoes along the arc 2 islands in the back arc region and 7 sites in the surrounding areas the 3he 4he ratios of the samples ranged from 0 027ra to 6 2ra ra denotes the atmospheric 3he 4he ratio of 1 4 10 6 demonstrating that even the maximum 3he 4he ratio in the region is significantly lower than the maximum ratios of most oceanic subduction systems which are equal to the morb value of 8 1 ra regional variations in the 3he 4he ratio were observed both along and across the arc the maximum 3he 4he ratio was obtained from nisyros volcano located in the eastern end of the arc and the ratio decreased westward possibly reflecting the difference in potential degree of crustal assimilation or the present magmatic activity in each volcano across the volcanic arc the 3he 4he ratio decreased with an increasing distance from the arc front reaching a low ratio of 0 063ra in macedonia which suggested a major contribution of radiogenic helium derived from the continental crust at nisyros a temporal increase in 3he 4he ratio due to ascending subsurface magma was observed after the seismic crisis of 1995 1998 and mantle neon was possibly detected the maximum 3he 4he ratio 6 2ra in the aegean region which is significantly lower than the morb value is not probably due to crustal assimilation at shallow depth or addition of slab derived helium to morb like mantle wedge but inherent characteristics of the subcontinental lithospheric mantle sclm beneath the aegean arc

the precipitation of aragonite from shallow water hydrothermal fluids in a coral reef tutum bay ambitle island papua new guinea the fringing reef in tutum bay on the west side of ambitle island papua new guinea is the only presently known coral reef exposed to the extensive discharge of a hot mineralized hydrothermal fluid there aragonite and ferrihydrite a hydrous ferric oxide are the prominent hydrothermal precipitates aragonite forms two distinct crystal habits a euhedral pseudohexagonal crystals up to 2 cm long and b micro crystals similar in appearance to feather dendrite aragonite encrusts dead coral fragments volcaniclastic boulders and pebbles and fills secondary fracture and remaining primary intergranular porosity within volcaniclastic arenite the hydrothermal aragonite has a distinctively different isotopic composition when compared to normal shallow water marine inorganic and organic carbonate that precipitated from seawater this difference arises from precipitation at high temperature from a mixture of seawater and hydrothermal fluid that has lower 87 sr 86 sr and d 18 o values than seawater based on a 87 sr 86 sr mixing model aragonite precipitated from a hydrothermal fluid seawater mixture of approximately 9 1 precipitation from the hydrothermal solution is mainly caused by co2 degassing but mixing between hydrothermal fluid and seawater may have enhanced precipitation due to an increase in ph the d 13 c of tutum bay hydrothermal aragonite ranges from 1 9xto 2 2x vpdb this range of values is in good agreement with experimental data j phys chem 72 1968 800 geochim cosmochim acta 61 1997 3461 indicating that c 13 equilibirum has been reached during its formation values for d 18 o range from 14 2xto 14 7xand calculated isotopic equilibrium temperatures are approximately 20 jc lower than directly measured vent fluids and those temperatures obtained from fluid inclusion experiments and the 87 sr 86 sr mixing model this indicates that either oxygen isotope equilibrium was not attained or that the calcite water fractionation factor for oxygen isotopes is not applicable for the precipitation of tutum bay hydrothermal aragonite trace element concentrations except for the rees y and sr are low the ree patterns of aragonite are similar to those of tutum bay vent water indicating the hydrothermal origin of the aragonite rare earth element concentrations are higher in the coarse than in the fine grained aragonite which might be caused by a change in precipitation rate and seawater mixing d 2004 elsevier b v all rights reserved

two cells phase separation in shallow submarine hydrothermal system at milos island greece boron isotopic evidence 1 three types of hydrothermal vent fluids herein referred to as cave submarine brine and seawater like were recovered from a shallow submerged system at milos in the aegean sea greece for detailed chemical and isotopic analyses the cave fluids discharge through rock fissures near sea level and have low ph chlorinity and b concentrations relative to seawater the submarine brine fluids are characterized by high cl and contain 10 times seawater b concentrations a scenario involving a two cells circulation is proposed one occurs at 1 2 km and another at shallower depth the deeper saline reservoir has experienced subcritical phase separation partitioning 0 42 mm b in vapor and 6 8 mm in brine with no detectable isotopic fractionation the reaction temperature in the saline reservoir is 313 c calculated from the na k ca geothermometry the vapors rise directly to form the cave vents whereas the saline fluids transport in different pathways and are influenced by seawater mixing to form the variable submarine brine fluids the seawater like fluids circulate at shallower depths where calculated temperature is 248 c and show slightly diluted b 0 36 0 41 mm and seawater 11b these fluids probably resulted from heating of down flow seawater and may have experienced groundwater discharge and partial mg removal this study represents the first two cells circulation occurring at milos and emphasizes the important role of phase separation in shallow submarine hydrothermal system

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

tsunami taxonomy and detection from recent mediterranean tide gauge data abstract sea level records collected in digital form with high sampling rate by recently upgraded tide gauges located along the mediterranean coasts are subjected to a posteriori investigation to examine and characterize occurrence of sea level oscillations in the tsunami period range induced by both underwater or coastal earthquakes and by meteorological events after performing a rigorous quality control procedure on the raw sea level time series a wavelet based analysis is applied to 2 h high pass filtered data to identify oscillations generated by earthquakes and a few events are modeled aiming to verify travel time and expected spectral shape seismic tsunami oscillations that are not reported in published catalogues are identified in the sea level records of the period 2010 2014 just after three different earthquake events a method is proposed to detect occurrence of tsunami like oscillations of meteorological origin from the available tidal records based on the distribution of the detided level process over spectral bandwidth parameter and mean period the developed methodology is also the first presented which allows to distinguish sea wave induced harbor seiches from fluctuations of meteorological origin associated with passage of atmospheric disturbances meteotsunamis in sea level time series the results of the analyses show that during the considered period in the mediterranean sea tsunamis of seismic origin are rare and weak meteotsunamis on the contrary are relatively frequent and in critical areas may reach intensities exceeding astronomical tide the availability of the recently acquired high frequency records and the presented approach allow to extend the list of recorded tsunami events of both seismic and meteorological origin the identified event sets may be used for improved hazard analyses and risk assessments along the mediterranean coasts

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

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

precious metal vein systems in the national district humboldt county nevada the national district 20 miles 33 km southeast of mcdermitt nevada produced 200 000 ounces of gold and 750 000 ounces of silver during the period 1906 1941 precious metal quartz sulfide silicate veins near the townsite of national and on buckskin mountain occur within a 3 000 ft thick 910 m sequence of miocene volcanic and intrusive rocks which vary in composition from basalt to rhyolite veins formed about 15 6 million years ago and associated rhyolites are approximately 18 to 15 m y old the volcanic pile at national is highly faulted and deposits are localized within orthogonal fault sets that coincide with major upper crustal structures in the northern great basin intrusive rhyolite and eruptive centers spatially related to veins at national partly define the goosey lake depression a shallow basin situated on the western edge of the owyhee volcanic plateau wall rock in the district is progressively hydrolyzed and sulfidized to assemblages dominated by chlorite calcite illite montmorillonite quartz pyrite and kaolinite quartz pyrite as veins are approached alteration assemblages exposed by exploration on buckskin mountain include the paleosurface at buckskin planar open space filled veins disperse upward into structurally unconfined flat lying zones of kaolinite quartz quartz alunite and chalcedonic silica sinter quartz altered rhyolite the latter being the paleosurface assemblage metallic minerals in four nested and coalescing vein stages include cinnabar stibnite electrum silver sulfosalts and selenides and base metal sulfides vein silicates are quartz kaolinite illite and at depth muscovite the spatial distribution of hydrothermal sulfides and silicates throughout buckskin mountain is strongly influenced by physical properties of premineralization volcanic rocks porous and permeable rhyolite tuff capping buckskin mountain is pervasively hydrolyzed to laterally extensive silica alunite and kaolinite bearing assemblages which lack tabular zones of open space filling underlying dense and brittle rhyolite flows confine hydrothermal assemblages to a relatively few planar fractures flanked by parallel selvedges of progressively altered wall rock at buckskin mountain two distinct but synchronous thermal events are documented by fluid inclusion studies the earlier event involved temperatures ranging from approximately 295 degrees to 250 degrees c and culminated in rupture of overlying rhyolite producing an inverted conical mass of bilithic breccia fluids associated with the second postbrecciation event boiled at 100 degrees to 255 degrees c from the paleosurface to depths exceeding 2 000 ft 606 m near surface hydrothermal assemblages were deposited from low salinity 1 2 wt nacl solutions containing 2 weight percent dissolved gases precious metal precipitation occurred at a temperature of about 250 degrees c and a pressure of about 40 bars largely from boiling solution periodic restrictions to convective heat loss resulting from silica deposition and episodic fluid circulation cause observed temperature and pressure data to deviate somewhat from an ideal hydrostatic model the vertical temperature gradient is consistent with a water saturated melt of granitic composition about 10 000 ft 3 030 m below the paleosurface during mineralization close spacing of isotherms below 200 degrees c reflects paleosurface proximity cooling by conduction and steam loss as well as accelerated convective cooling of fluid circulating through permeable rhyolite tuff integration of hydrothermal assemblages thermal measurements fluid mineral equilibria and active hot springs data suggests that as temperatures in buckskin mountain decreased from 250 degrees c at depth to 100 degrees c at the surface ph increased from approximately 3 7 to near neutral sigma s increased from 10 super 4 5 m to approximately 10 super 2 6 m and f sub o 2 decreased from 10 super 39 to 10 super 48 the distribution of alteration assemblages precious metal minerals stibnite and cinnabar was apparently controlled by boiling a sulfldation gradient temperature decreases and near surface hydrology