geochemistry and stratigraphic correlations application to the investigation of geothermal and mineral resources of tuscany italy contribution to the knowledge of the ore deposits of tuscany ii abstract major element geochemistry 364 analyses is used to obtain quantitative information on the initial mineralogical composition and the depositional environment of paleozoic more or less metamorphic rocks from tuscany and elba furthermore this method can be used to improve stratigraphic correlations by comparing the chemical compositions of the metamorphic rocks and their possible non metamorphic counterparts of known stratigraphic position the stratigraphic units were divided into two sets the first includes the units of known stratigraphic or tectonic position taken as reference groups permian red porphyries carboniferous rocks buti group l s porphyritic schists porphyroids lower phyllites and metabasites from the apuan alps and elba the second set comprises the units of uncertain position metapelites and metapsammites from outcrops mines and boreholes from the boccheggiano niccioleta area calamita schists and metabasites associated with these two units micaschists gneisses and associated amphibolites the main results are 1 1 the porphyroids and porphyritic schists differ strongly from the permian red porphyries thus confirming that they belong to two different volcanic episodes 2 2 all the reference units consist of shales sandstones s s or graywackes differing by their degree of maturity increasing from the lower phyllites to the buti group and to the carboniferous formations 3 3 the carboniferous rocks the buti group and the lower phyllites have distinct chemical compositions 4 4 the boccheggiano formation l s and the calamita schists are similar and include rocks chemically equivalent to the lower phyllites the buti group and the carboniferous formations 5 5 the micaschists and gneisses derive from shales and graywackes respectively and chemically recall the lower phyllites 6 6 the metabasites from the apuan alps and from niccioleta are within plate basalts whereas the amphibolites interlayered within the micaschists and gneisses seem ocean floor basalts

neoarchean crustal growth by accretionary processes evidence from combined zircon titanite u pb isotope studies on granitoid rocks around the hutti greenstone belt eastern dharwar craton india abstract the neoarchean hutti greenstone belt hosts mesothermal gold deposits and is surrounded by granitoid rocks on all sides combined u pb dating of zircon and titanite from the granitoid rocks constrains their emplacement history and subsequent geologic evolution the golapalli and yelagatti granodiorites occurring to the north of the hutti greenstone belt were emplaced at 2569 17 ma the yelagatti granodiorite yielded a younger titanite age of 2530 6 ma which indicates that it was affected by a post crystallization thermal event that exceeded the titanite closure temperature the western granodiorites from kardikal have identical titanite and zircon ages of 2557 6 ma and 2559 19 ma respectively the eastern kavital granodiorites yielded titanite ages of 2547 6 ma and 2544 24 ma which are identical to the published u pb zircon shrimp ages these ages imply that the granitoid rocks surrounding the hutti greenstone belt were formed as discrete batholiths within a short span of ca 40 ma between 2570 ma and 2530 ma ago they were juxtaposed by horizontal tectonic forces against the supracrustal rocks that had formed in oceanic settings at the end of the archean the first phase of gold mineralization coincided with the last phase of granodiorite intrusion in the hutti area a metamorphic overprint occurred at ca 2300 ma ago that reset the rb sr isotope system in biotites and possibly caused hydrothermal activity and enrichment of au in the ore lodes the eastern dharwar craton consists of quartz monzodiorite granodiorite granite suites of rocks that are younger than the greenstone belts that are older than 2650 ma reported from earlier studies the granitoid magmatism took place between 2650 and 2510 ma ago indicating accretionary growth of the eastern dharwar craton

helium 3 anomalies and crust mantle interaction in italy abstract the distribution of primordial 3he in the crust of italy has been investigated through a survey of groundwaters hot springs exploration and production geothermal wells the mantle derived component varies from 0 to 60 and reaches a maximum at vulcano in the eolian islands 3he anomalies occur where the conductive heat flow is relatively high but the relationships between heat flow and anomaly are uncertain the distribution of 3he in the main reservoir and cap rock to the larderello geothermal system shows that the mantle derived 3he varies from 5 to 40 of total he and reaches a maximum in fluids extracted from a depth of ca 3 km within the basement bomb produced tritiogenic 3he appears to make a near negligible contribution well 107 at larderello has been monitored over a period of 17 months and the 3 he 4 he ratio r varies from 1 4 to 1 6 times the atmospheric ratio ra whilst he ne varies from 9 to 160 a model is proposed for the larderello geothermal system whereby mantle derived heat and volatiles are advected to shallow 6 8 km depths in association with melts and released into the main geothermal reservoir at larderello in a non uniform manner possibly associated with fracturing isotopic and elemental equilibrium of gaseous species c o h appears to have taken place in the basement to the main reservoir from where fluid with r ra 3 2 has been extracted

geodynamic evolution of southern costa rica related to low angle subduction of the cocos ridge constraints from thermochronology abstract the late tertiary shallow subduction of the cocos ridge under the caribbean plate controlled the evolution of the cordillera de talamanca in southeast costa rica which is a mountain range that consists mainly of granitoids formed in a volcanic arc setting fission track thermochronology using zircon and apatite as well as 40ar 39ar and rb sr age data of amphibole and biotite in granitoid rocks constrain the thermal history of the cordillera de talamanca and the age of onset of subduction of the cocos ridge shallow intrusion of granitoid melts resulted in fast and isobaric cooling a weighted mean zircon fission track age 13 analyses and rb sr biotite ages of about 10 ma suggest rapid cooling and give minimum ages for granitoid emplacement in some cases 40ar 39ar and rb sr apparent ages of amphibole and biotite are younger than the zircon fission track ages which can be attributed to partial resetting by hydrothermal alteration apatite fission track ages range from 4 8 to 1 7 ma but show no correlation with the 3090 m elevation span over which they were sampled the apatite ages seem to indicate rapid exhumation caused by tectonic and isostatic processes the combination of the apatite fission track ages with subduction parameters of the cocos plate such as subduction angle plate convergence rate and distance of the cordillera de talamanca to the trench implies that the cocos ridge entered the middle america trench between 5 5 and 3 5 ma

alpine tectonothermal evolution of the tuscan metamorphic complex in the larderello geothermal field northern apennines italy on the internal tyrrhenian side of the northern apennines high heat flow and geothermal gradient in the larderello geothermal field are evidence of a large scale thermal anomaly related to the emplacement of a large batholith of pliocene age extending from the upper to middle crust these intrusions relate to the miocene to recent northern apennines magmatism which developed as a result of crustal extension and upwelling of the asthenosphere at the base of the thinned crust in the subsurface of the larderello geothermal field medium and high grade metamorphic rocks tuscan metamorphic complex cored in several geothermal wells have previously been considered to be variscan basement new structural and petrographic data on these metamorphic rocks indicate an alpine tectonometamorphic history and provide evidence that medium to high grade mineral assemblages are related to pliocene thermal metamorphism centred on intrusions at shallow depth these data allow a new interpretation of the tuscan metamorphic complex as a tectonic wedge of the late palaeozoic triassic units and in particular highlight the considerable extent of pliocene thermal metamorphism and hydrothermal circulation as a result of convective cooling of intrusions

exhumation and doming of the thasos metamorphic core complex s rhodope greece structural and geochronological constraints abstract the thasos island metamorphic core complex s rhodope n aegean sea was generated between 26 and 13 ma progressive extensional tectonics was associated with upwarping of the deeper parts of this core complex to a narrow gneiss dome and with formation of a steep topographic high we present a combined structural microstructural and geochronological study that constrains the deformation time path of progressive extension and exhumation thasos island consists of three superimposed more or less flat lying metamorphic units with downward decreasing geochronologic ages which are separated by two systems of low angle normal detachment surfaces trending nw se the upper unit stayed in supracrustal level since 50 ma representing the upper plate during an early phase of extension not later than 26 23 ma upper levels of the core complex intermediate unit underwent pervasive mylonitization with top to the sw shear from about 21 ma onward the intermediate unit was rigid and top to the sw slip continued at least until 13 8 ma on the discrete detachment surface that separates the core complex from the upper plate yet in the 21 15 ma period deeper levels lower unit still deformed plastically and deformation successively concentrated in zones of high strain and in discrete detachment surfaces that caused decoupling of the lower from the intermediate unit these indicate downdip movements in opposite sense associated with doming of the lower unit at that stage simultaneously the intermediate unit was fragmented on high angle normal faults that sole into the dome bounding detachment surface and roof into the core complex bounding detachment surface these faults confine tilt blocks that are arranged around the lower unit gneiss dome doming of the core complex occurred simultaneously with subsidence of basins located on the upper plate

geology and geochemistry of sulfide mineralization underlying the pueblo viejo gold silver oxide deposit dominican republic the large pueblo viejo oxide gold deposit was developed by weathering of a gold quartz pyrophyllite deposit that formed during sedimentation in a small basin in the upper part of the los ranchos formation one of the oldest volcanic units in the greater antilles the basin is floored by conglomerates and agglomerates which grade upward into standstones and carbonaceous sediments that include chert with thin pyrite layers plant fossils which are common in the carbonaceous sediments indicate that the basin was near a land mass the mineralized zone is roughly funnel shaped and expands to its maximum horizontal dimensions in the carbonaceous sediments the lower part of the funnel tube contains alunite and diaspore pervasive pyrophyllite alteration makes up most of the overlying tube and upper part of the zone and locally extensive silicification makes up the top of the funnel supergene kaolinite is present in the upper part of the funnel metallic minerals consisting mostly of pyrite are found as disseminations layers and veins with base and precious metal values being highest in the veins veins are most common in the carbonaceous sediments and diminish in abundance downward into the coarser clastic units the veins contain abundant pyrite sphalerite and quartz minor barite enargite and pyrophyllite and traces of electrum argentite colusite tetrahedrite tennantite geocronite galena and tellurides containing gold silver and copper there is a strong correlation between au and zn in the upper parts of the mineralized zone and the au ag ratio which averages 1 7 decreases slightly with depth au is in electrum in the lower part of the mineralized zone and partly in tellurides in the upper part fluid inclusions indicate that fluids in the veins were very dilute boiled at least locally and reached temperatures of 130 degrees to 190 degrees c pyrophyllite stability requires minimum temperatures of about 260 degrees c for the hydrothermal system isotopic data indicate that most of the sulfur in the mineralization was derived from seawater whereas the strontium and lead came from the los ranchos formation which probably also supplied the precious metals the pueblo viejo system is similar to other gold quartz pyrophyllite deposits except that it contains no known mineable vein orebodies and instead contains numerous narrow closely spaced irregular veins that can be mined by bulk methods these veins are thought to have formed by hydraulic fracturing of the carbonaceous sediments caused by fluid pressures as the hot spring system developed the size and shape of the mineralized system at pueblo viejo resemble active hot spring systems such as wairakei new zealand and its environment of formation probably resembled that of the quaternary volcano chain which crosses lake managua in nicaragua

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

metamorphism and diachronous cooling in a contractional orogen the strandja massif nw turkey the southern part of the strandja massif northern thrace turkey comprises a basement of various gneisses micaschists and rare amphibolite and a cover of metaconglomerate and metasandstone separated from each other by a pre metamorphic unconformity metamorphic grade decreases from the epidote amphibolite facies in the south to the albite epidote amphibolite greenschist facies transition in the north estimated p t conditions are 485 530 c and 0 60 0 80 gpa in the epidote amphibolite facies domain and decrease towards the transitional domain between greenschist and epidote amphibolite facies rb sr muscovite ages range from 162 9 1 6 ma to 149 1 2 1 ma and are significantly older 279 296 ma in the northernmost part of the study area the rb sr biotite ages decrease from 153 9 1 5 ma in the south to 134 4 1 3 ma in the north these age values in conjunction with the attained temperatures suggest that the peak metamorphism occurred at around 160 ma and cooling happened diachronously and rb sr muscovite ages were not reset during the metamorphism in the northernmost part structural features such as i consistent s dipping foliation and sw to se plunging stretching lineation ii top to the n shear sense and iii n vergent ductile shear zones and brittle thrusts suggest a n vergent compressional deformation coupled with exhumation we tentatively ascribe this metamorphism and subsequent diachronous cooling to the northward propagation of a thrust slice the compressional events in the strandja massif were most probably related to the coeval n vergent subduction collision system in the southerly lying rhodope massif

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

heavy mineral analysis and clinopyroxene geochemistry applied to provenance analysis of lithic sandstones from the azuero sona complex nw panama abstract the volcaniclastic sandstones of the middle eocene to lower miocene tonosi formation were deposited within the forearc realm of an island arc system which today is part of the southern central american landbridge both heavy mineral analyses and geochemical analyses of clinopyroxenes clearly reveal differences in the composition between sediments of the lower and upper tonosi formation indicating changes within the tectonic setting as well as island arc evolution during time of deposition based on characteristic heavy mineral suites three lithogroups can be determined and assigned to the lower and upper tonosi formation respectively provenance analyses indicate that the sandstones of the tonosi formation were generally derived from an island arc setting the abundance of a mafic heavy mineral suite relative to heavy minerals derived from metamorphic and sialic intrusive rocks indicates a convergent plate boundary setting for provenance of the lower tonosi formation this result is supported by the chemistry of clinopyroxenes within the heavy mineral suite which indicates evolved basaltic magma types sourced the detrital grains within the hb ol id cpxbrown opx cpxgreen diagram most samples of the upper tonosi formation plot in the field for divergent plate boundaries the geochemical analyses also show that clinopyroxenes of the upper tonosi formation additionally exhibit affinities to within plate alkaline magma types as an integration of our results we present a provisional two stage model for the tectono sedimentary evolution of the western panamanian forearc area during the deposition of the tonosi formation

the evolution of latera caldera central italy in the light of subsurface data subsurface geothermal exploration has considerably added to our knowledge of the latera volcanic complex a syenitic body is located about 2 km below the present day surface k ar data point a 0 9 ma age the primary magma was a silica saturated trachyte undersaturated hauyne bearing products are found near the carbonatic wall rocks and have been interpreted as reaction products subsurface data from deep drilling and geophysical surveys suggest that the latera caldera resulted from three main successive collapse phases i formation of an old caldera now buried related to the eruption of ignimbrites from the syenitic magma chamber ii sinking of the eastern sector as a consequence of the formation of the nearby bolsena caldera 0 3 ma iii multistage formation of the present latera caldera 0 16 ma

the larderello geothermal field a review abstract this paper reviews published geological geophysical petrological and geochemical data together with reservoir engineering parameters of the larderello geothermal reservoir of southern tuscany italy some theories are proposed on the deep origin evolution in time and natural state of this geothermal field prior to its exploitation the interaction between the vapor dominated reservoir and surrounding aquifers is discussed analysis of hydrogeochemical data suggests that meteoric waters from shallow external aquifers contribute little to the production of steam the vapor dominated system and the cold external aquifers are separated by areas of very low permeability where physical conditions change greatly over short distances the presence and significance of liquid phases in the peripheral areas of the vapor dominated reservoir are interpreted as being due to steam condensation the latter is a consequence of a low permeability conditions in the deep buried parts of the carbonate reservoir formations in the north northwestern sector of the field and b by the mixing of ascending superheated steam from depth with cold caso4 meteoric waters circulating in unconfined shallow aquifers within the outcrops of the carbonate reservoir formations in the south southeastern parts of the field the presence of steam below these liquid dominated sectors of the reservoir seems possible the limited natural recharge of the system the constant steam production rate for geothermal power generation 3000 t h 1 since 1951 the persistence of natural thermal features and the fact that reinjection has had little effect on the characteristics of the fluid discharged seem to indicate a steady state for the larderello field the main contribution to production seems to be from superheated steam ascending from depth and the in situ evaporation of water stored in the small pores of the rocks present in larderello in a system that is much larger than the one known at present

40ar 39ar and k ar dating of k rich rocks from the roccamonfina volcano roman comagmatic region italy abstract roccamonfina is the northernmost volcano of the campanian area of the k rich roman comagmatic region of italy it erupted a huge amount of pyroclastics and lavas belonging to both the leucite basanite and leucitite series lbls and the shoshonite series ss spread over an area of about 300 km2 the above series correspond to the high k series hks and low k series lks of appleton 1972 respectively 40ar 39ar and k ar dating of samples from both series gave ages ranging from 0 656 to 0 096 ma for the ss and from 1 03 to 0 053 ma for the lbls these results indicate that the products of the two series were outpoured together at least between 0 7 and 0 1 ma ago i e during both the so called pre caldera phase and the post caldera phase of activity the latest products of the volcanism at roccamonfina were erupted just before the deposition of the grey campanian ignimbrite which erupted from vents located about 50 km to the south in the phlegrean fields near naples and has an age of about 33 000 years taking into account all the available radiometric data we conclude that roccamonfina was active between 1 5 and 0 05 ma ago in excellent agreement with the stratigraphie evidence in this same time span is concentrated the activity of all the centers of the roman region north of naples

thermochronological analysis of the dynamics of the southern alps new zealand the isotopic ages of material exposed close to the alpine fault in the southern alps new zealand vary in a consistent fashion along the orogen for the k ar system muscovite and biotite ages display two distinct spatial trends that meet in the area of fox glacier where a strong relationship is observed between k ar age and altitude excess argon is present in samples between mount kinnaird and haast pass in the southwest of the southern alps giving unrealistically old inconsistent k ar ages across this region incorporation of excess argon appears to be highly variable however and minimization of its influence on dynamical interpretations of thermochronology is possible through considering only the youngest age from a given area such treatment indicates that excess argon contamination does not play an important role in the systematic k ar age variation identified along the southern alps the observed age distribution is consistent with estimates of the modern rapid uplift and exhumation of the southern alps beginning ca 5 ma k ar mica ages older than this south of the copland valley indicate that substantial late cenozoic exhumation occurred along the southern alps prior to the development of the modern tectonic regime but at rates lower than at present total exhumation during the current phase of tectonism in the southern alps decreases from the whataroa river southward north of fox glacier the southern alps have attained a dynamical steady state such that the observed distribution of exhumation will not change significantly with further deformation and denudation under current conditions

kinematic analysis and analogue modelling of the passeier and jaufen faults implications for crustal indentation in the eastern alps crustal deformation in front of an indenter is often affected by the indenter s geometry rheology and motion path in this context the kinematics of the jaufen and passeier faults have been studied by carrying out paleostress analysis in combination with crustal scale analogue modelling to infer 1 their relationship during indentation of the adriatic plate and 2 their sensitivity in terms of fault kinematics to the geometry and motion path of adria the field study reveals mylonites along the jaufen fault which formed under lower greenschist facies conditions and is associated with top to the west northwest shear with a northern block down component in addition a brittle reactivation of the jaufen shear zone under nnw sse to nw se compressional and ene wsw tensional stress conditions was deduced from paleostress analysis the inferred shortening direction is consistent with fission track ages portraying neogene exhumation of the meran mauls basement south of the fault along the passeier fault deformation was only brittle to semi ductile and paleostress tensors record that the fault was subjected to e w extension along its northern segment varying into nw se compression and sinistral transpression along its southern segment in the performed analogue experiments a rigid triangular shaped indenter was pushed into a sand pile resulting in the formation of a passeier like fault sprouting from the indenter s tip these kinds of north trending tip faults formed in all experiments with shortening directions towards the nw n or ne consequently we argue that the formation of the passeier fault strongly corresponds to the outline of the adriatic indenter and was only little affected by the indenter s motion path due to induced strain partitioning in front of the different indenter segments the associated fault kinematics along the passeier fault including both e w extension and nnw to nw shortening however is most consistent with a northward advancing adriatic indenter

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

tectono thermal evolution of a distal rifted margin constraints from the calizzano massif prepiedmont brianconnais domain ligurian alps the thermal evolution of distal domains along rifted margins is at present poorly constrained in this study we show that a thermal pulse most likely triggered by lithospheric thinning and asthenospheric rise is recorded at upper crustal levels and may also influence the diagenetic processes in the overlying sediments thus representing a critical aspect for the evaluation of hydrocarbon systems the thermal history of a distal sector of the alpine tethys rifted margin preserved in the ligurian alps case tuberto calizzano unit is investigated with thermochronological methods and petrologic observations the studied unit is composed of a polymetamorphic basement and a sedimentary cover providing a complete section through the prerift synrift and postrift system zircon fission track analyses on basement rocks samples suggest that temperatures exceeding 240 25 c were reached before 150 160 ma upper jurassic at few kilometer depth neoformation of green biotite stable at temperatures of 350 to 450 c was synkinematic with this event the tectonic setting of the studied unit suggests that the heating cooling cycle took place during the formation of the distal rifted margin and terminated during late jurassic 150 160 ma major crustal and lithospheric thinning likely promoted high geothermal gradients 60 90 c km and triggered the circulation of hot deep seated fluids along brittle faults causing the observed thermal anomaly our results suggest that rifting can generate thermal perturbations at relatively high temperatures between 240 and 450 c at less than 3 km depth in the distal domains during major crustal thinning preceding breakup and onset of seafloor spreading

occurrence and40ar 39ar dating of a granite in thera santorini greece a granite was drilled in the prevolcanic basement of thera an island of the attico cycladic belt it intruded the blueschist facies country rocks k ar biotite ages and ar ar plateau ages on two feldspars indicate rapid cooling as all ages cluster around 9 5 ma its occurrence indicates that the thermometamorphic evolution that characterizes the attiko cycladic belt extends as far as thera

the bagni di lucca thermal waters tuscany italy an example of ca so4 waters with high na cl and low ca so4 ratios abstract the bagni di lucca thermal waters lucca province tuscany italy have been well known since the middle age for their alleged curative properties in the present work the waters have been analysed for major and trace components and for o h s and sr isotopes the 2 h and 18 o values indicate a meteoric origin of the waters and the tritium content suggests long term more than 40 years circulation at depth the 34 s values in dissolved sulphate of the warmest waters doccione paolina bernabo demidoff cova indicate interaction with triassic evaporites however the 34 s values as well as the 87 sr 86 sr ratios in the waters appear to be a little higher on average 17 6 0 4 and 0 70834 0 00006 respectively than in triassic sulphate minerals from the northern apennines 16 0 0 5 and 0 70778 0 00011 the waters are ca sulphate and characterised by high na cl 2 and low ca so 4 0 7 mole ratios high sr 12 mg l f 4 2 mg l as 80 g l cs 70 g l rb 107 g l and salinity up to 3087 mg l of total dissolved solids low alkalinity and ph in the range 6 3 7 5 assuming equilibrium of the waters with anhydrite and chalcedony the evaluated temperature and pressure are about 70 75 c and 200 300 bar considering the pressure as hydrostatic the evaluated depth of equilibration approaches that of the metamorphic basement about 3 0 3 8 km underlying the carbonate evaporite formations occurring in the area thermodynamic computations indicate that the high na cl ratio and the low ca so 4 ratio in the waters may be due to progressive dissolution of albite anhydrite dolomite and carbon dioxide accompanied by calcite precipitation the linear correlations between the major and trace components including 2 h and 18 o demonstrate that thermal springs undergo dilution by low salinity shallow waters which are recharged at low elevation

early fluid migration in a deep part of the larderello geothermal field a fluid inclusion study of the granite sill from well monteverdi 7 abstract metamorphic magmatic to hydrothermal fluids trapped in fluid inclusion planes fip were studied in a microfractured granite sill from a deep level 3483 3486 m b g l of the well monteverdi 7 larderello geothermal field this granite has recorded a complex succession of fluid migration through a dense set of healed microcracks nine generations of fluids trapped within specific microcrack networks are distinguished and include vapors and liquids of the c h o n s system aqueous liquids and brines with distinctive sets of cation chlorides licl nacl nacl cacl 2 and nacl detailed studies of the geometrical and chronological relationships between the fluid inclusion planes allow the establishment of a clear relative chronology with the c h o n s and licl fluids being earlier than the nacl cacl 2 and nacl aqueous liquids and brines in particular it can be shown that the c h o n s and licl fluids are strongly associated in space and time since the corresponding fluid inclusion planes display evidence of mutual contamination of inclusions within the planes significant changes in the physical chemical parameters occurred in the conditions of fluid trapping during the evolution of the larderello field all observed paleofluids have compositions differing from that encountered in the present day fluids and record a complex p t t x evolution from an early stage dominated by magmatic and metamorphic derived fluids towards a later stage dominated by more surficial waters at the early stage hydrothermal circulation occurred under lithostatic pressure at a depth of ca 4 5 km at temperatures as high as 450 500 c such conditions are very reminiscent of contact metamorphism and were probably created by the deep intrusive body detected by geophysical studies batini et al 1983 1985 the involved fluids are c h o n s vapors and liquids of metamorphic derivation and aqueous li bearing brines of probable magmatic derivation they are consistent with the hypothesis of the intrusive being a granite at the later stage physical conditions had evolved towards hydrostatic pressure at a depth close to the present 3 5 km one and temperatures of 400 350 c still higher than the present day ones early fluids were no longer present the observed fluids record the involvement of more surficial waters both meteoric and connate transient boiling events were probably occurring heralding the present day conditions vapor dominated geothermal system nevertheless no trapped fluids display similar composition and density with the present day geothermal fluids at larderello in old geothermal fields such as larderello it must be emphasized that the use of fluid inclusions in order to reconstruct past hydrothermal evolution is strongly dependent onto pressure estimation since significant temperature corrections may be needed in the larderello case failing to take in account the pressure effects would have led to seriously misleading conclusions

missing history 16 71 ma of the galapagos hotspot implications for the tectonic and biological evolution of the americas we present the results of volcanological geochemical and geochronological studies of volcanic rocks from malpelo island on the nazca plate 15 8 17 3 ma belonging to the gala pagos hotspot tracks and igneous complexes 20 8 71 3 ma along the pacific margin of costa rica and panama the igneous complexes consist of accreted portions of ocean island and seamount volcanoes and aseismic ridges representing the missing primarily subducted history of the gala pagos hotspot the age and geochemical data directly link the gala pagos hotspot tracks on the pacific ocean floor to the caribbean large igneous province ca 72 95 ma confirming a pacific origin for the caribbean oceanic plateau from the gala pagos hotspot we propose that emplacement of this oceanic plateau between the americas and interaction of the gala pagos hotspot tracks with the central american arc played a fundamental role in the formation of land bridges between the americas in late cretaceous paleocene and pliocene holocene time the land bridges allowed the exchange of terrestrial faunas e g dinosaurs mastodons saber tooth cats and ground sloths between the americas and served as barriers for the exchange of marine organisms between the central pacific ocean and the caribbean sea and the central atlantic ocean

helium isotopes in paleofluids and present day fluids of the larderello geothermal field constraints on the heat source 1 the he isotope composition of paleofluids entrapped in fluid inclusions of hydrothermal minerals is compared with the present day fluid composition of the larderello geothermal field almost constant values of 3he 4he m 3he 4he air r ra over time indicate that no important changes have occurred in the deep source of gases at least during the last 3 8 million years on a regional scale a correlation has been found between the r ra spatial distribution heat flow and bouguer gravity anomaly high values of r ra and heat flow and low bouguer anomaly values indicate that the larderello field is an area of preferential escape for mantle derived fluids a positive correlation has also been found between the r ra spatial distribution and a major seismic reflector named the k horizon a deep magma source refilled by periodic gas input from the mantle is the most likely source of 3he enriched fluids and the anomalously high heat flow the nearly constant value of r ra clearly indicates that input of fresh mantle material has occurred up to recent times clear evidence of mixing between mantle and crustal fluids indicates that the high r ra is the lower limit of the actual mantle value which is suggested to be similar to the subcontinental european mantle the decrease of r ra over time in the peripheral part of the larderello field indicates that important changes in the feeding fracture system and or cooling rate have occurred in these areas

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

extension uplift of rocks and cooling ages in thinned crustal provinces the larderello geothermal area inner northern apennines italy in extensional tectonic settings vertical movements of the earth s surface are largely controlled by rates of strain extensional strain rates within the larderello geothermal area located in inner parts of the northern apennines have been evaluated together with uplift rates and 40 ar 39 ar cooling ages results indicate that extensional strain rates have been relatively low 5 8 10 17 s 1 since the middle pliocene differential uplift rates are estimated to have been high c 0 2 mm year strain and uplift rates within the larderello region are consistent with the regional tectonic framework the low strain rate rapid uplifting and high heat flow within southern tuscany can be explained by an eastward dipping lithospheric shear maintained since at least middle pliocene times

geothermometry from 40ar39ar dating experiments abstract we have selected a variety of minerals from three basic intrusions within the high grade metamorphic terrane near haliburton ontario for k ar dating by application of 40 ar 39 ar incremental heating experiments we conclude that the discordant k ar mineral dates can best be explained by a slow cooling history from the stepwise heating experiments we calculated isotopic closure temperatures using dodson s theory for slow cooling and from these constructed a cooling curve this curve was then compared to independent constraints to test the overall validity of our procedures and assumptions the results are geologically reasonable insofar as 1 a the maximum calculated temperatures from hornblendes of 700 c are consistent with independent approximate metamorphic grid arguments 2 b the ar closure temperatures for biotites 350 400 c are consistent with independent evidence and 3 c minerals with older k ar dates have higher calculated closure temperatures the resultant geological cooling curve implies that a maximum temperature of 700 c was reached before 1000 ma ago and thereafter the temperature decreased via changes in uplift and cooling rates to below 200 c by 700 ma ago we have discovered that plutonic plagioclases are very sensitive indicators comparable to k felds pars of ar loss and therefore can usefully extend the range of application of the 40 ar 39 ar stepwise heating method we also describe experiments in which we have tested the effects on the ar systematics of acid leaching of plagioclases

petrography and geochemistry of fault controlled hydrothermal dolomites in the riopar area prebetic zone se spain abstract the present paper reports the first detailed petrographical and geochemical studies of hydrothermal dolomites related to mvt zn fe pb deposits in the riopar area mesozoic prebetic basin se spain constraining the nature origin and evolution of dolomitizing and ore forming fluids mapping and stratigraphic studies revealed two stratabound dolostone geobodies connected by other patchy bodies which replace carbonate units of upper jurassic to lower cretaceous ages these dolostones are associated to the w e trending san jorge fault indicating a main tectonic control for fluid flow seven different dolomite types were identified i matrix replacive planar s red i ii matrix replacive planar e red ii iii planar e sucrosic cement sud iv non planar grey saddle dolomite cement sad i pre dating zn fe pb sulfides v non planar milky to pinkish saddle dolomite cement sad ii post dating zn fe pb ores vi ore replacive planar e porphyrotopic pod and vii planar s cloudy cement ced meteoric calcite types were also recognized the different dolomite types are isotopically characterized by i depleted 18 o from 25 1 to 27 6 v smow and 13 c from 2 3 to 0 9 v pdb values compared to upper jurassic to lower cretaceous limestone signature 18 o 27 6 to 30 9 v smow 13 c 0 5 to 3 2 v pdb and ii 87 sr 86 sr ratios for the main dolomitization phases red and sud 0 70736 0 70773 close to the jurassic and cretaceous carbonate values 0 70723 0 70731 whereas more radiogenic values 0 70741 0 70830 for saddle dolomites sad related to the zn fe pb sulfide mineralization prevailed after fluid interaction with rb bearing minerals microthermometrical studies on two phase liquid and vapor fluid inclusion populations in planar and non planar dolomites and sphalerite show homogenization temperatures between 150 and 250 c these data indicate that both planar and non planar dolomite textures formed at high temperatures under hydrothermal conditions in deep burial diagenetic environments the main dolomitizing phase red i red ii and sad i shows low to moderate fluid inclusions salinity 5 14 wt eq nacl whereas the dolomitization related to ore precipitation sphalerite and sad ii spreads to higher salinity values 5 25 wt eq nacl these data may respond to a mixing between a low salinity fluid fluid a less than 5 wt eq nacl and a more saline brine fluid b more than 25 wt eq nacl at different fluid proportions

isotopic dating in metamorphic belts isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions of these temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed the central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated in order to illustrate the factors which control closure temperatures and limit their application in practice the possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined taking examples involving k ar rb sr sm nd and u pb analyses the indirect dating of metamorphism via structurally dated plutons is briefly considered and the problems of interpreting both discordant u pb zircon ages and rb sr whole rock isochrons in metamorphosed granites are discussed the value of near concordant zircon ages is emphasized the extent of isotopic equilibration during metamorphism specifically of sr isotopes in metasediments is shown not to be a simple function of metamorphic grade the flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently the concluding discussion briefly examines existing data for the dalradian and indicates the potential for further progress using both well established and novel approaches

solfataric alteration in the san juan mountains colorado oxygen isotope variations in a boiling hydrothermal environment an oxygen isotope study was made on hydrothermal quartz and altered volcanic rocks from six areas of advanced argillic alteration in the san juan volcanic field southwest colorado these include the historically productive mining districts at summitville delta 18 o quartz 13 0 15 5ppm and the national belle pipe at red mountain pass delta 18 o quartz 10 0 12 3ppm other areas studied are engineer pass delta 18 o quartz 6 4ppm delta 18 o sub whole rock 1 9 3 4ppm carson camp delta 18 o quartz 11 9 13 6ppm and calico peak near rico delta 18 o quartz 6 9 9 0ppm delta 18 o sub whole rock 4 7 6 9ppm samples were also analyzed from surface outcrops delta 18 o quartz 4 9 11 2ppm and from an 837 m cored drill hole in the red mountain quartz latite lava dome on the eastern edge of the 23 m y old lake city caldera at this locality the altered volcanic rocks delta 18 o sub whole rock 1 7 8 2ppm and the hydrothermal quartz delta 18 o quartz 1 4 11 2ppm exhibit a distinct vertical 18 o 16 o gradient of about 0 8 per mil 100 m with the highest delta 18 o values at the highest elevations these data are incorporated into a general model for solfataric alteration in these mid to late tertiary hot spring systems this involves a convecting meteoric hydrothermal fluid which at shallow depths rises along the hydrostatic boiling curve the delta 18 o variation in solfataric quartz in the uppermost 300 m of the hot spring system from 5 11ppm is mainly a function of a temperature variation from about 225 degrees to 125 degrees c along the boiling curve and to a lesser extent a result of the delta 18 o effects that accompany vapor phase separating during boiling

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

stable isotope and noble gas isotope compositions of inclusion fluids from larderello geothermal field italy constraints to fluid origin and mixing processes noble gas and n 2 compositions have been determined in paleofluids of core samples from geothermal wells in the larderello area italy the results were coupled with hydrogen and carbon isotope compositions of similar fluids from an independent batch of samples to provide constraints on the origin of the fluids the fluids trapped during early stage hydrothermal circulation are characterized by relatively high 4 0 ar 3 6 ar and n 2 ar ratios 332 4 0 ar 3 6 ar 564 and 248 n 2 ar 4197 respectively and indicate the presence of radiogenic 4 0 ar and excess n 2 when compared to air asw air saturated water the fluid inclusions related to late stage hydrothermal activity show low n 2 ar and 4 0 ar 3 6 ar ratios 309 4 0 ar 3 6 ar 354 and 47 n2 ar 66 respectively similar to present day geothermal fluids the 6d values of the inclusion fluids range from 53 to 85 indicating that the fluids were derived from mixing of water rich components probably from a shallow reservoir similar in composition to present day meteoric waters and fluids from a deeper reservoir the r r a ratios up to 3 2 of the paleofluids and present day fluids suggest a deep he contribution at larderello the 1 3 c values for co 2 trapped during early stage activity 3 8 o to 0 5 o were produced by carbonate country rock volatilisation 1 3 c values as low as 17 were measured in inclusion fluids related to late stage circulation and were likely produced by oxidation of organic matter at shallow depths

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

water rock interaction in the larderello geothermal field southern tuscany italy an 18o16o and dh isotope study abstract stable isotope and fluid inclusions investigations were carried out on metamorphic rocks belonging to the southern tuscany paleozoic basement that constitutes the main deep fluid reservoir 1000 m below ground level of the larderello geothermal field whole rock samples have 18o and d values ranging from 2 9 to 11 6 and from 65 to 76 respectively most negative 18o and d values have been obtained on rocks from highly fractured levels calculated 18o and d values for the fluids in equilibrium with the rocks are from 3 to 8 and 31 to 43 respectively temperatures of homogenization of fluid inclusions range from 245 c to 324 c and salinities from 1 0 to 12 8 wt nacl eq the combined data are consistent with mixing between a deep circulating 2500 m below ground level meteoric hydrothermal water and a deep thermal water of probable magmatic or metamorphic origin after mixing and exchange the water rock mass ratios are small typically 250 c in the deeper explored levels contrast with the much less strongly 18o shifted meteoric hydrothermal waters which circulate in the upper 1000 m or so of the system at t these new stable isotope data and other petrological geophysical and geochemical data are all consistent with the existence of two apparently separate hydrothermal systems and productive horizons at different depths bearing fluids of different physico chemical characteristics the shallow upper meteoric system may not be continuosly connected to the lower meteoric magmatic system because at least locally fluid pressures in the lower levels are higher than hydrostatic pressures

chronology of magmatism and mineralization in the kassandra mining area greece the potentials and limitations of dating hydrothermal illites abstract various geochronological methods u pb rb sr and k ar have been applied to constrain the timing of magmatism and polymetallic mineralization in the kassandra mining district northern greece these data provide the first geochronological evidence that porphyry copper mineralization proximal copper skarns and distal high temperature carbonate hosted pb zn ag au replacement ores formed contemporaneously and probably within less than 2 million years polymetallic mineralization is temporally related to the emplacement of granodioritic to quartz dioritic porphyries 24 25 ma that postdate the largest post tectonic intrusion of the area the stratoni granodiorite 27 9 1 2 ma andesite porphyry dikes which crosscut the pb zn ag au ores and associated alterations represent the last magmatic phase in the area 19 1 0 6 ma and did not contribute to metal concentration the combination of k ar rb sr and oxygen isotope studies of hydrothermal illite rich clays and careful granulometric analysis constrains the reliability of these geochronological methods and emphasizes the importance of characterizing the post formational history of the sample we identify various processes which partly disturbed the k ar and rb sr system of some clays such as retrograde alteration by heated meteoric waters superimposed supergene illitization and resetting of both isotopic systems due to a hydrothermal overprint related to the intrusion of the andesite porphyry our data however suggest that diffusive ar loss from the finest clay fractions k ar system conventional k ar ages of 200 c therefore do not give reliable formation ages the loss of ar may be used to model the cooling history of the hydrothermal system applying the concept of closure temperatures dodson 1973 40k 40arrad isochrons of natural coarser grained 0 6 m size fractions of illites from single samples even when slightly contaminated with feldspars may yield meaningful ages either of the formation or of a reheating event the rb sr dating of hydrothermal clays is sensitive to contamination by adsorbed strontium which may not be cogenetic with the clay as well as feldspars which may not have been homogenized isotopically by the illitization process

very low grade metamorphic sr isotopic resettings of magmatic rocks and minerals evidence for a late givetian strike slip division of the brabant massif belgium rb sr isochron ages recorded by the ashgillian ignimbrites from deerlijk and harelbeke and the caradocian quartz diorites from quenast and bierghes significantly post date their emplacement at quenast two mineral isochrons biotite wr plagioclase 372 13 ma k feldspar wr epidote 375 14 ma reveal that the brabantian branch of the caledonian belts was affected by a post siegenian pre tournaisian event this overprint turns out to be contemporaneous with the development of the oudenaarde bierghes fault zone which is dated to 373 11 ma and 379 13 ma on foliated rocks from bierghes deerlijk and harelbeke this c 375 ma cluster of events is interpreted as representing late givetian stresses developed along the oudenaarde bierghes fault zone for which the balance of geological data favours strike slip movements since this compressive phase of deformation is posterior to the givetian opening of the borain trough the brabant massif appears to have been affected by successive crustal extension and shortening events in the middle devonian petrological evidence demonstrates the very low grade character of the metamorphism in the metasediments on both sides of the oudenaarde bierghes fault zone from this we deduce that sr isotopic homogenization of whole rock ignimbrite and the loss of radiogenic sr from biotite and k feldspar could be operative even at temperatures below 250 c

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

new insight into the dynamic development of the southern alps new zealand from detailed thermochronological investigation of the mataketake range pegmatites

reconstruction of an early permian sublacustrine magmatic hydrothermal system mount carlton epithermal au ag cu deposit northeastern australia the mt carlton au ag cu deposit northern bowen basin northeastern australia is an uncommon example of a sublacustrine hydrothermal system containing economic high sulfidation epithermal mineralization the deposit formed in the early permian and comprises vein and hydrothermal breccia hosted au cu mineralization within a massive rhyodacite porphyry v2 open pit and stratabound ag barite mineralization within volcano lacustrine sedimentary rocks a39 open pit these orebodies are all associated with extensive advanced argillic alteration of the volcanic host rocks stable isotope data for disseminated alunite 34s 6 3 29 2 18oso4 0 1 to 9 8 18ooh 15 3 to 3 4 d 102 to 79 and pyrite 34s 8 8 to 2 7 and void filling anhydrite 34s 17 2 19 2 18oso4 1 8 5 7 suggest that early advanced argillic alteration formed within a magmatic hydrothermal system the ascending magmatic vapor 34sss 1 3 was absorbed by meteoric water 50 60 meteoric component producing an acidic ph 1 condensate that formed a silicic quartz alunite quartz dickite kaolinite zoned alteration halo with increasing distance from feeder structures the oxygen and hydrogen isotope compositions of alunite forming fluids at mt carlton are lighter than those documented at similar deposits elsewhere probably due to the high paleolatitude s60 of northeastern australia in the early permian veins of coarse grained banded plumose alunite 34s 0 4 7 0 18oso4 2 3 6 0 18ooh 10 3 to 2 9 d 106 to 93 formed within feeder structures during the final stages of advanced argillic alteration epithermal mineralization was deposited subsequently initially as fracture and fissure filling au cu rich assemblages within feeder structures at depth as the mineralizing fluids discharged into lakes they produced syngenetic ag barite ore isotope data for ore related sulfides and sulfosalts 34s 15 0 to 3 0 and barite 34s 22 3 23 8 18oso4 0 2 to 1 3 and microthermometric data for primary fluid inclusions in barite th 116 233 c 0 0 1 7 wt nacl are consistent with metal deposition at temperatures of 200 40 c for au cu mineralization in v2 pit and 150 30 c ag mineralization in a39 pit from a low salinity sulfur and metal rich magmatic hydrothermal liquid that mixed with vapor heated meteoric water the mineralizing fluids initially had a high sulfidation state producing enargite dominated ore with associated silicification of the early altered wall rock with time the fluids evolved to an intermediate sulfidation state depositing sphalerite and tennantite dominated ore mineral assemblages void filling massive dickite 18o 1 1 to 2 1 d 121 to 103 with pyrite was deposited from an increasingly diluted magmatic hydrothermal liquid 70 meteoric component exsolved from a progressively degassed magma gypsum 34s 11 4 19 2 18oso4 0 5 3 4 occurs in veins within postmineralization faults and fracture networks likely derived from early anhydrite that was dissolved by circulating meteoric water during extensional deformation this process may explain the apparent scarcity of hypogene anhydrite in lithocaps elsewhere while the mt carlton system is similar to those that form subaerial high sulfidation epithermal deposits it also shares several key characteristics with magmatic hydrothermal systems that form base and precious metal mineralization in shallow submarine volcanic arc and back arc settings the lacustrine paleosurface features documented at mt carlton may be useful as exploration indicators for concealed epithermal mineralization in similar extensional terranes elsewhere

the relationship between k ar mineral ages mica grainsizes and movement on the moine thrust zone nw highlands scotland muscovite and biotite separated from moine schists close to the moine thrust zone yield a range of k ar ages incompatible with the simple cooling regime previously proposed for the caledonides of northern scotland differences of only 1 ma between muscovite and biotite of the same grainsize contrast with differences of 12 13 ma between the 125 200 m and 250 500 m grainsize fractions this is contrary to the normally accepted dominance of mica type over grainsize effects dynamic recrystallization of the micas during early deformation associated with the moine thrust zone is thought to play a role as important as temperature in determining the k ar ages the conclusions drawn have important implications for the use of uplift and cooling rates derived from the absolute k ar closure temperatures of micas close to thrust zones although the k ar ages from micas with diameters greater than 200 m are not reproducible the data can be used to show that deformation associated with thrusting commenced between c 443 ma and c 435 ma and that the thrust zone was active until at least 422 ma ago

a fluid inclusion and stable isotope study of the moonta copper gold deposits south australia evidence for fluid immiscibility in a magmatic hydrothermal system abstract the copper gold ores of the moonta mineral field in the eastern part of the archaean mesoproterozoic gawler craton south australia are vein deposits occupying fractures and shear zones within the palaeoproterozoic moonta porphyry the veins show a spatial relationship with mesoproterozoic granites equivalents of the hiltaba suite granites that are widespread in the gawler craton the ores were deposited in four hydrothermal stages separated by episodes of fracturing the first two stages were dominated by fe oxides the third by fe sulfides and the final stage by a cu fe co au zn pb s assemblage three types of fluid inclusions are present in quartz associated with the oxide and sulfide minerals type 1 fluid inclusions are two phase vapour rich with homogenization temperatures up to 473 c and low to moderate salinity 2 to 22 wt nacl equivalent type 2 are two phase liquid rich with lower homogenization temperatures up to 269 c and low to moderate salinities 0 7 to 22 wt nacl equivalent type 3 are liquid rich solid s bearing with homogenization temperatures up to 467 c and high salinities 28 to 55 wt nacl equivalent the coexistence of types 1 and 3 suggests that these fluid inclusions resulted either from trapping of boiling fluids or represent two immiscible fluids most likely derived from a magma the fluid history reflected in fluid inclusion characteristics was complex involving variable amounts of boiling cooling and mixing in the vein system salinity homogenization temperature relationships indicate mixing of the hypersaline fluid and the vapour rich fluid with a surface derived fluid of low temperature and low to moderate salinity d h 2 o values 22 to 31 and 18 o h 2 o values 2 9 to 5 1 calculated from analyses of chlorite and 18 o h 2 o values calculated from analyses of quartz 0 6 to 8 8 on the basis of mean to maximum fluid inclusion homogenization temperatures are intermediate between magmatic water and surface derived fluids i e seawater or meteoric water the narrow range of 18 o values of quartz 10 8 to 12 7 may be explained by mixing of a magmatic fluid and either seawater or a low latitude moderately evolved meteoric water with a coupled decrease in fluid temperature and 18 o content similar ranges for 34 s values of ore sulfides 2 3 to 6 4 and disseminated sulfides in the moonta porphyry and interdigitated doora schist 1 5 to 4 6 suggest assimilation of crustal sulfur by the granitic magma or ore fluids the combined fluid inclusion and stable isotope data support previous proposals based on field and mineralogical evidence for a genetic relationship between the moonta ores and the mesoproterozoic granitoids

stable isotope evidence for magmatic fluids in the pueblo viejo epithermal acid sulfate au ag deposit dominican republic stable isotope h c o and s systematics of the pueblo viejo acid sulfate system the world s largest bulk mineable acid sulfate gold deposit were investigated to determine the importance of magmatic fluids in hydrothermal systems of this type mineralization at pueblo viejo is hosted by a maar diatreme system that cuts sedimentary rocks and spilites of the late cretaceous los ranchos formation the deposit is characterized by two stages of advanced argillic alteration stage i fluids produced deep alunite quartz and shallower kaolinitc quartz both associated with disseminated pyrite stage ii fluids overprinted stage i and produced deep pyrophyllite diaspore and an overlying silica cap an increase in temperature from stage i 250oc to stage ii 250o 300oc is indicated by mineral stabilities and sulfur isotope thermometry of coexisting sulfide sulfate pairs stage i quartz alunite kaolinite pyrite alteration and associated disseminated au ag mineralization are interpreted to

unravelling the complex interaction between mantle and crustal magmas encoded in the lavas of san vincenzo tuscany italy part ii geochemical overview and modelling abstract this work reports a geochemical overview and modelling of the lavas erupted 4 4 ma ago at san vincenzo tuscan magmatic province tmp although these lavas cover a relatively small area 10 km2 they show very large geochemical variations caused by the interaction of mantle derived and crustal anatectic magmas the lavas consist of peraluminous rhyolites 87sr 86sr i up to 0 726 hosting primarily variably sized magmatic enclaves with shoshonite latite compositions 87sr 86sr i down to 0 708 new whole rock data for a large shoshonite enclave show high concentrations of lree lile and tetravalent hfse coupled with pentavalent hfse depletions and enrichments in compatible elements such as cr and co the chondrite normalised ree pattern is strongly fractionated and characterised by a negative eu anomaly eu eu 0 79 hybridisation and afc models suggest that the shoshonite enclave is the result of 12 rhyolite contamination of a mantle derived magma akin to the potassic trachybasalt shoshonite lavas of capraia island 4 6 ma tmp following an 18 5 assimilation of late triassic metasediments 13 evaporite and 5 5 carbonate and 56 fractionation of clinopyroxene 39 plagioclase 10 and biotite 7 each rhyolite sample is characterised by mineral scale isotopic disequilibria e g 87sr 86sr i 0 711 0 726 glass inclusions with large k2o na2o variations 1 1 3 4 and a poli thermobarometric history of crustal melt production at eutectic conditions a multi parametric approach accounting for k2o na2o 1 3 2 2 87sr 86sr i 0 713 0 725 sr 104 311 ppm and rb 294 403 ppm whole rock variations allowed us to divide the anatectic a rhyolites into five groups a1 a2 1 a2 2 a2 3 a3 group a1 shows the highest 87sr 86sr i ratios and the lowest values of sr k2o na2o and rb it is related to a2 1 and a3 rhyolites by positive k2o na2o rb and k2o na2o feo correlations these three rhyolite groups crop out in the south of san vincenzo and are interpreted to derive from mixing and ascent of peraluminous magma batches locally extracted at progressively higher temperatures from the heterogeneous paleozoic metamorphic basement the a2 3 rhyolites show the highest rb concentrations up to 403 ppm and inverse sr rb and k2o feo correlations suggesting reactions involving the incongruent melting of a biotite bearing crustal source which was previously depleted in low temperature melting components such as muscovite and albite most of the a2 3 rhyolites crop out in the northern svvc area and appear spatially and geochemically related to the a2 2 rhyolites by similarly low 87sr 86sr i ratios however a2 2 rhyolites show lower rb contents 296 316 ppm and geochemical correlations e g 87sr 86sr i rb sr rb mgo feo clearly indicating hybridisation mixing with the shoshonite mantle derived magma rb 109 122 ppm finally we propose a four stage model for the magma plumbing system of san vincenzo produced by the uprising of a mantle derived magma in a normally faulted and doubled crustal basement characterised by two sections of paleozoic siliciclastic rocks separated by late triassic evaporite carbonate sequences

episodic hydrothermal alteration recorded by microscale oxygen isotope analysis of white mica in the larderello travale geothermal field italy abstract microscale oxygen isotope analysis 18o 16o of minerals can identify distinct events of fluid rock interaction this method is however still limited to a few major and accessory minerals of which most are anhydrous minerals we present the systematic study of oxygen isotope distribution in white mica by secondary ion mass spectrometry sims texturally and chemically distinct white mica populations in granitic and contact metamorphic rocks from the larderello travale geothermal field ltgf italy record stages of magmatic crystallization metamorphic hydrothermal replacement and fluid rock interaction the large range in intra and inter grain white mica 18o values between 1 and 14 reflects varying protoliths and degrees of fluid mineral interaction at variable temperatures 180 450 c present day temperatures p d t this variability reflects the large scale circulation of both 1 magmatic syn intrusive to early contact metamorphic hydrothermal fluids with high 18o values and 2 meteoric fluids with 18o values of 7 during a post intrusive late hydrothermal stage metasedimentary rocks from the upper reservoir contain distinct white mica populations occurring in close proximity m scale including detrital grains 18o 12 14 high na low mg partially altered white mica 18o 8 9 and late hydrothermal white mica 1 6 low na mid mg the late hydrothermal white mica has similar 18o values to other secondary minerals and is in equilibrium with meteoric dominated fluids with a 18o of 6 to 0 5 which circulated in the late hydrothermal stage downhole towards the lower reservoir white mica from two contact metamorphic micaschist samples shows either 1 homogeneous 18o values of ca 9 likely due to recrystallization in the contact metamorphic hydrothermal stage t ca 600 c or 2 a large spread in 18o from 2 to 12 within and across grains of variable texture and chemistry in the host rock and a cross cutting quartz white mica vein ca 300 c present day temperature hereafter p d t this contrasting 18o signature of white mica is also recorded in granite cored at up to 4 6 km depth the carboli granite contains white mica with a homogeneous magmatic 18o of 10 0 6 whereas older granite samples from radicondoli have magmatic to hydrothermal white micas that vary in 18o from 4 to 10 a pronounced intra grain 18o variability of up to 6 occurs in white mica domains with higher fe mg ti halos around inclusions of chloritized biotite as a result of interaction with dominantly meteoric fluids that infiltrated to depths of at least 4 6 km in the porto azzurro granite on elba italy altered white mica has 18o values of 2 6 down from 10 in unaltered grains the distribution of oxygen isotope ratios in white mica is thus firstly a result of pervasive versus selective fluid alteration at depth sample and grain scale secondly the actual preservation of these m scale variabilities indicates that volume diffusion is not detectable at microscale at p d t at or below 350 c where most of the heterogeneous white mica is found selective sample and grain scale fluid penetration occurs episodically and anisotropically on micro and megascale along faults fractures and cleavages producing lower 18o white mica at various times in zones of higher secondary permeability and active hydrothermal fluid circulation

airborne laser scanning of forested landslides characterization terrain model quality and visualization abstract mapping complex landslides under forested terrain requires an appropriate quality of digital terrain models dtms which preserve small diagnostic features for landslide classification such as primary and secondary scarps cracks and displacement structures flow type and rigid type optical satellite imagery aerial photographs and synthetic aperture radar images are less effective to create reliable dtms under tree coverage here we utilized a very high density airborne laser scanning als data with a point density of 140 points m 2 for generating a high quality dtm for mapping landslides in forested terrain in the barcelonnette region the southern french alps we quantitatively evaluated the preservation of morphological features and qualitatively assessed the visualization of als derived dtms we presented a filter parameterization method suitable for landslide mapping and compared it with two default filters from the hierarchical robust interpolation hri and one default filter from the progressive tin densification ptd method the results indicate that the vertical accuracy of the dtm derived from the landslide filter is about 0 04 m less accurate than that from the ptd filter however the landslide filter yields a better quality of the image for the recognition of small diagnostic features as depicted by expert image interpreters several dtm visualization techniques were compared for visual interpretation the openness map visualized in a stereoscopic model reveals more morphologically relevant features for landslide mapping than the other filter products we also analyzed the minimal point density in als data for landslide mapping and found that a point density of more than 6 points m 2 is considered suitable for a detailed analysis of morphological features this study illustrates the suitability of high density als data with an appropriate parameterization for the bare earth extraction used for landslide identification and characterization in forested terrain

rb sr and k ar ages on minerals at temperatures of 300 400 c from deep wells in the larderello geothermal field italy rb sr and k ar ages have been obtained on six biotites two muscovites and one hornblende from samples of micaschist gneiss and amphibolite of lower paleozoic to precambrian age at a depth exceeding 2 000 m in basement rocks of the larderello travale geothermal region most of the data cluster in the range 2 5 3 7 ma revealing the existence of a pliocene thermal event to which the origin of the field may be attributed the resulting duration of the larderello geothermal field is unexpectedly long in the basement levels of the two wells examined unstabilized minimum temperatures of 290 and 380 c were measured all the biotites show almost complete 40ar and 87sr retention at the measured well temperatures petrologic evidence stilpnomelane stability and experimental data activation energies and diffusion coefficients also favour a closure temperature above 400 c for rb sr and k ar in biotites in agreement with recent direct experimental determinations

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

transition from orogen perpendicular to orogen parallel exhumation and cooling during crustal indentation key constraints from 147sm 144nd and 87rb 87sr geochronology tauern window alps abstract the core of the alpine orogen in the eastern alps tauern window experienced a change from orogen normal shortening and post nappe doming to predominantly orogen parallel extension and tectonic unroofing during late oligocene to miocene northward indentation of the adriatic microplate a new 147 sm 144 nd isochron age of 25 7 0 9 ma on a garnet bearing assemblage from the lowest nappe complex forming a dome in the eastern part of the tauern window indicates that high temperatures related to post nappe barrovian type metamorphism overlapped in time with the onset of doming new 87 rb 87 sr biotite ages from this same complex combined with previously published 87 rb 87 sr white mica ages suggest that doming and exhumation began no later than 28 ma immediately in front of indenting austroalpine crustal blocks then migrated laterally to the ese during rapid exhumation and orogen parallel stretching beginning at about 23 ma rapid cooling ended at approximately 17 ma in the footwall of the katschberg normal fault which delimits the eastern margin of the tauern window a similar pattern of migrating doming orogen parallel extension and cooling is recognized in the western part of the tauern window where rapid exhumation began at about 20 ma some 2 3 ma later than in the eastern part this difference in the onset of rapid exhumation as well as the overall migration of doming from the center to the ends of the tauern window are attributed to fragmentation of the aforementioned austroalpine blocks along the leading edge of the main adriatic indenter southern alps as this indenter advanced to the north

isotope and chemical microsampling constraints on the history of an s type rhyolite san vincenzo tuscany italy fine scale heterogeneities in strontium isotope ratios 40ar 39ar ages and chemical com sition have been determined for individual mineral grains and enclaves in the rhyolites of san vincenzo italy the rhyolites are peraluminous with phenocrysts of alkali feldspar piagioclase biotite and cordierite and have previously been divided into two groups on the basis of whole rock major element chemistry group b lavas are distinguished from group a in having higher mgo and cao contents as well as containing two pyroxenes and chilled latite enclaves the group b lavas show textural evidence for d sequilib um such as resorption and sieve zones in feldspars laser fusion 40ar 39ar dating of individual alkali feldspar crystals suggests that the eruption of these rhyolites took place 4 38 0 04 ma though small amounts of excess argon are present in subhedral and cloudy crystals the groundmass in the group a sample has a higher initial r7sr 86sr 0 725 than that of the group b 0 7 13 the sr isotope compositions of chemically and texturally characterized individual grains reveal marked disequilibrium between minerals and the host glass as well as within grain zonation the feldspars and coarse grained biotites have initial 87sr 8 sr that are intermediate between those of the group a and b glasses with alkali feldspar generally having higher initial 87sr 86sr ratios than plagioclase chilled latite enclaves which are present in only the group b lavas have relatively low initial 8 sr 86sr ratios in the range 0 7082 0 7088 the mineral chemistry and isotope data indicate that restite does not form a significant portion of the crystalline assemblage and therefore cannot be the source of the strontium isotope dis equilibrium xenocrysts mixed into the rhyolite from a mafic magma were identified as clinopyroxene megacrysts clinopyroxene orthopyroxene clots orthopyroxene plagioclase clots and plagioclase with extensive sieve textures these grains all have relatively low initial 87sr 86sr ratios other grains that may be xenocrysts are cordierites with cores containing inclusions of biotite spinel and sillimanite and alkali feldspars with excess 4 ar the strontium isotope di quilib um in phenocrysts of plagioclase alkali feldspar and biotite is attributed to a changing melt chemistry that was too rapid for strontium diffusive equilibration a mode1 for the san vincenzo magma chamber is proposed in which the sr isotope evolution of the group b rhyolites is due to magma mixing of a crustal melt with latite magma containing unra diogenic strontium the variable initial strontium isotope compositions of group a phenocrysts may be due to assimilation or crystallization along the interface between mingled group a and b magmas

arc continent collision and orocline formation closing of the central american seaway closure of the central american seaway was a local tectonic event with potentially global biotic and environmental repercussions we report geochronological six u pb la icp ms zircon ages and geochemical 19 xrf and icp ms analyses data from the isthmus of panama that allow definition of a distinctive succession of plateau sequences to subduction related protoarc to arc volcaniclastic rocks intruded by late cretaceous to middle eocene intermediate plutonic rocks 67 6 1 4 ma to 41 1 0 7 ma paleomagnetic analyses 24 sites 192 cores in this same belt reveal large counterclockwise vertical axis rotations 70 9 6 7 and moderate clockwise rotations between 40 4 1 and 56 2 11 1 on either side of an east west trending fault at the apex of the isthmus rio gatun fault consistent with isthmus curvature an oligocene miocene arc crosscuts the older deformed and segmented arc sequences and shows no significant vertical axis rotation or deformation there are three main stages of deformation 1 left lateral strike slip offset of the arc 100 km and counterclockwise vertical axis rotation of western arc segments between 38 and 28 ma 2 clockwise rotation of central arc segments between 28 and 25 ma and 3 orocline tightening after 25 ma when this reconstruction is placed in a global plate tectonic framework and published exhumation data is added the central american seaway disappears at 15 ma suggesting that by the time of northern hemisphere glaciation deep water circulation had long been severed in central america

cerro quema azuero peninsula panama geology alteration mineralization and geochronology of a volcanic dome hosted high sulfidation au cu deposit cerro quema azuero peninsula southwest panama is a high sulfidation epithermal au cu deposit hosted by a dacite dome complex of the rio quema formation late campanian to maastrichtian a fore arc basin sequence mineral resource estimates indicated inferred are 30 86 mt at 0 73 g t au containing 728 000 oz au including 76 900 oz au equiv of cu ore hydrothermal alteration and mineralization are controlled by an e trending regional fault system hydrothermal alteration consists of an inner zone of vuggy quartz with locally developed advanced argillic alteration enclosed by a well developed zone of argillic alteration grading to an external halo of propylitic alteration mineralization produced disseminations and microveinlets of pyrite and minor chalcopyrite enargite and tennantite with traces of sphalerite crosscut by late stage base metal veins new 40ar 39ar data of igneous rocks combined with biostratigraphic ages of the volcanic sequence indicate a maximum age of lower eocene 55 49 ma for the cerro quema deposit it was probably triggered by the emplacement of an underlying porphyry like intrusion associated with the valle rico batholith the geologic model suggests that in the azuero peninsula high sulfidation epithermal mineralization occurs in the cretaceous paleogene fore arc this consideration should be taken into account when exploring for this deposit type in similar geologic terranes

geochronology at the namew lake ni cu orebody flin flon area manitoba canada thermal history of a metamorphic terrane intermediate composition orthogneisses of the southward extension of the flin flon greenstone belt surround the ultramafic host rock of the namew lake ni cu deposit in northern manitoba the gneiss

formation of authigenic minerals and their use as indicators of the physicochemical parameters of the fluid in the larderello travale geothermal field different authigenic mineral assemblages and mineral compositions have been found in different areas of the larderello travale geothermal field in the peripheral areas the most abundant authigenic minerals are quartz calcite chlorite and sulfides they formed in a temperature range of 150 sup 0 to 250 sup 0 c and with a p sub co2 range of 0 1 to 1 0 atm in a hotter part of the field at depths between 200 and 1 300 m where the main productive fractures are located the most important authigenic minerals are quartz chlorite calcite k feldspar and k bearing mica with which wairakite hematite anhydrite and barite are sometimes associated deposition of all these minerals occurs in a temperature range of 200 sup 0 to 300 sup 0 c under p sub co2 of about 1 atm and relatively high p sub o2 in fluids sometimes characterized by silica oversaturation below the 1 300 m depth in the hottest part of the field k feldspar chlorite epidote sulfides with minor sphene prehnite clinopyroxene and clinoamphibole are present these minerals form in a temperature range of 250 sup 0 to 350 sup 0 c under a p sub co2 of less than 1 atm and a p sub o2 ranging from 10 sup 40 to 10 sup 33 atm and reasonablymore reflect the physicochemical parameters of the geothermal fluid before exploitation evidence of an earlier hydrothermal stage characterized by higher temperatures can be seen in the occurrence of relic wollastonite and andradite less

geology geochemistry and origin of high sulfidation cu au mineralization in the nansatsu district japan the nansatsu district of southern kyushu has been the site of calc alkaline volcanism for the last 10 m y shifting eastward with time associated hydrothermal activity followed deposition of the volcanic host rocks by about 0 5 m y and was characterized by interaction of magmatic fluids with meteoric water under epithermal conditions resulting in the formation of high sulfidation cu au deposits at kasuga iwato and akeshi the orebodies consist of 95 wt percent sio 2 and result from leaching of the original andesite lava and pyroclastic flows by acid chloride sulfate waters these are inferred to have formed when magmatic vapors containing hcl and so 2 condensed into meteoric water the residual silica now quartz orebodies are best developed where the host was initially permeable the margins of the quartz bodies are abrupt with narrow 1 2 m halos representing the reaction front of acid waters isochemically dissolving the host rock the halo comprises alunite strongly zoned in na and k with p rich cores dickite and or kaolinite or pyrophyllite grading out into illite and interlayered illite smectite clays and finally propylitic alteration this pattern is characteristic of deposits of this type throughout the world for example at summitville colorado and lepanto philippines mineralization occurred after initial leaching by the vapor condensates with metals transported by a dense magmatic fluid mixing with meteoric water and the subsequent temperature decrease caused the general decrease in grade toward the margin of the quartz bodies ore grades are restricted to the quartz bodies gold is most closely associated with enargite and pyrite later minerals include covellite and then sulfur the last stage of activity was steam heated with descending waters oxidizing sulfides to goethite and locally remobilizing au into fractures this varies in degree between deposits erosion exposed the orebodies to supergene weathering continuing the sulfide oxidation and au remobilization stable isotope results indicate that hypogene alunite formed from a mixture of magmatic fluid delta 18 o 7 or 2 per thousand delta d 25 or 5 per thousand similar to nearby active volcanic discharges with local meteoric water in contrast the clays in the marginal halo have isotopic compositions indicating a delta 18 o shift of 6 to 8 per mil from local meteoric water values probably due to water rock interaction and the delta 18 o values of residual silica quartz may also be due to meteoric water domination fluid inclusion study of postmineralization quartz crystals indicates that the fluids had a salinity of about 1 wt percent nacl equiv during late quartz growth though there is evidence in one sample for higher salinity fluid having been present up to 30 wt percent nacl equiv some inclusions contain daughter minerals of halite and sulfur the t h values of over 1 000 measurements on late quartz from the ore zones indicate that the mean temperature during that stage ranged from 200 degrees c at akeshi to about 200 degrees c at iwato and 230 degrees c at kasuga the presence of vapor rich inclusions some with t hv similar to t hl indicate the presence at times of a two phase fluid in the center of the ore zones with depths of about 150 to 300 m below the paleowater table the mineralizing fluid was relatively oxidized sulfide sulfate ratio about 3 1 close to pyrite alunite coexistence under these redox conditions a ph of 3 and over a temperature range of 200 degrees to 300 degrees c aucl 2 super complexing may dominate over hau sh 2 at salinities above about 2 wt percent nacl several conditions are conducive for high sulfidation mineralization to occur 1 a crystallizing magma exsolves a fluid with lower pressure conditions favoring metal fractionation from melt to fluid 2 the exsolved fluid separates into vapor and saline liquid phases due to immiscibility with the latter being metal rich 3 the gas rich hcl and so 2 h 2 s vapor ascends to the surface with at least a portion condensed into meteoric water forming an acid fluid which leaches the host rock to create permeable zones for later mixing and 4 the dense metal bearing fluid also ascends into this leached zoned and precipitates cu sulfosalts sulfides and au upon mixing with meteoric water if the saline liquid is not released from its source adjacent to the magma due to lack of fracturing or if there is a strong hydraulic gradient caused by high relief only the vapor related stage may occur this will leave leached barren rock which is characteristic of many eroded volcanic terranes

the geysers cobb mountain magma system california part 2 timescales of pluton emplacement and implications for its thermal history abstract over 400 ion microprobe u pb isotopic ages measured for zircons extracted from 24 geothermal wells that penetrate the geysers plutonic complex gpc allow us to conclude that the entire known extent of the gpc crystallized during the early pleistocene nine samples of the microgranite porphyry that forms the shallow cupola 100 1 500 m below sea level mbsl of the gpc yield the oldest model u pb age 1 75 0 01 ma after correction for initial u series disequilibrium errors 1 twelve samples from the main intrusive phase orthopyroxene biotite granite present at depths 1 250 mbsl define a crystallization age of 1 27 0 01 ma this coincides with the age determined for a structurally and compositionally distinct body of granodiorite 1 25 0 01 ma n 5 samples that is intruded over a similar depth range two petrographically distinct varieties of orthopyroxene biotite granite yield ages of 1 46 0 03 gpc21 6000 and 1 16 0 02 ma ca5636 74f 21 three samples u pb zircon ages for dikes intruded in metagraywacke country rocks overlap with those obtained from the main body of the gpc and include the youngest material identified dike sample negu2 st1 7700 1 11 0 03 ma overall the u pb results demonstrate that the main body of the gpc 300 km3 was emplaced and crystallized within the upper crust over a short time interval 0 2 ma that overlaps with zircon crystallization ages of overlying silicic volcanic units