intersector element partitioning in tourmaline a potentially powerful single crystal thermometer hourglass sector zoning and related polar overgrowths are common features of metamorphic tourmaline developing as a result of variations in element preference on the different growth surfaces for sector zoned crystals three domains are present for each growth zone c c and a with compositional differences most distinct for ca and ti and among c and c sectors intersector differences vary commonly showing decreasing fractionation from core to rim attributed to increasing metamorphic grade here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers based on c c and c a partitioning of ca and ti these thermometers are applicable over a range of temperatures and bulk rock compositions intersector partitioning is not affected by re equilibration and records and preserves complete t histories of individual tourmaline grains from prograde to peak and on to retrograde growth information on element mobility is preserved by tourmaline composition because intersector partitioning is independent of element concentration these factors make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment and tourmaline s refractory nature preserves these signatures even into the sedimentary record

composition morphology and stratigraphy of noachian crust around the isidis basin definitive exposures of pristine ancient crust on mars are rare and the finding that much of the ancient noachian terrain on mars exhibits evidence of phyllosilicate alteration adds further complexity we have analyzed high resolution data from the mars reconnaissance orbiter in the well exposed noachian crust surrounding the isidis basin we focus on data from the compact reconnaissance imaging spectrometer for mars as well as imaging data sets from high resolution imagine science experiment and context imager these data show the lowermost unit of noachian crust in this region is a complex brecciated unit of diverse compositions breccia blocks consisting of unaltered mafic rocks together with rocks showing signatures of fe mg phyllosilicates are commonly observed in regions of good exposure layered or banded phyllosilicate bearing breccia rocks are observed suggestive of pre isidis sedimentary deposits in places the phyllosilicate bearing material appears as a matrix surrounding mafic blocks and the mafic rocks show evidence of complex folded relationships possibly formed in the turbulent flow during emplacement of basin scale ejecta these materials likely include both pre isidis basement rocks as well as the brecciated products of the isidis basin forming event at 3 9 ga a banded olivine unit capped by a mafic unit covers a large topographic and geographic range from northwest of nili fossae to the southern edge of the isidis basin this olivine mafic cap combination superimposes the phyllosilicate bearing basement rocks and distinctly conforms to the underlying basement topography this may be due to draping of the topography by a fluid or tectonic deformation of a previously flatter lying morphology we interpret the draping superposed olivine mafic cap combination to be impact melt from the isidis basin forming event while some distinct post isidis alteration is evident carbonate kaolinite and serpentine the persistence of olivine from the time of isidis basin suggests that large scale aqueous alteration processes had ceased by the time this unit was emplaced

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

stability limits of hydrous minerals in sediment and mid ocean ridge basalt compositions implications for water transport in subduction zones phase relationships in hydrated natural sediment and mid ocean ridge basalt morb compositions were investigated experimentally from 6 to 15 gpa and 700 c to 1400 c in order to determine the stability of hydrous phases in subducting slabs and to constrain reactions resulting in the release of water from subduction zones to the mantle phengite and hydrous aluminum silicates topaz oh and phase egg are stable in the sediment composition at depths greater than 150 km and constitute h2o reservoirs similarly lawsonite is an h2o reservoir in morb composition at depths greater than 150 km according to mass balance calculations based on experimental run products the weight proportions of phengite and h2o at 6 gpa in the sediment are about 50 and 2 respectively at pressures from 8 to 12 gpa topaz oh al2sio4 oh 2 appears as the hydrous mineral and the sediment retains about 0 5 0 7 wt h2o at higher pressures phase egg alsio3 oh appears as the hydrous phase with a large stability field the h2o content in the sediment is about 0 5 wt at pressures greater than 12 gpa in natural morb compositions lawsonite is the hydrous phase at pressures lower than 10 gpa about 1 wt h2o in the morb composition is retained by lawsonite at 6 gpa and 800 c above 6 gpa a lawsonite out reaction is controlled by compositional changes of garnet and clinopyroxene if the oceanic crust descends with an overlying sediment layer water can be carried down into the transition zone by the sediment the amount of transported water is controlled by the chemical compositions of the subducting sediments water in the morb layer can be stored to 300 km in lawsonite for a cold subduction zone geotherm water release at depths greater than 200 km through progressive lawsonite breakdown can hydrate the overlying mantle causing the generation of a peridotite region including hydrous phases chondrodite clinohumite phase a and phase e if this hydrous peridotite is dragged down by the descending oceanic crust water can be transported into the transition zone by the subduction process the amount of transported water is controlled by the thermal state of the slab and the chemical composition of morb

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

serpentinization of the martian crust during noachian abstract this paper proposes a model of serpentinization of the southern martian crust that may explain the topographic dichotomy the absence of an associated free air gravity anomaly and the presence of strong magnetic anomalies in the southern hemisphere the thermodynamical conditions for serpentinization were likely met in the lithosphere during the noachian period this process may have decreased the density in the southern crust and created the topographic dichotomy different reactions of serpentinization that can form magnetite have been considered assuming an intense magnetic field core dynamo we obtain chemical remanent magnetizations that are in the order of the estimates deduced from martian magnetic anomaly studies the pertinence and the implications of our model concerning the early thermal evolution of mars are discussed with emphasis on the intensity of the paleo magnetic field

age of the camaguey gold silver district cuba tectonic evolution and preservation of epithermal mineralization in volcanic arcs epithermal precious metal deposits commonly form in middle to late cenozoic volcanic arcs several kilometers above the level at which batholiths are emplaced this relationship has led to the guideline that epithermal deposits should not be sought in volcanic arcs where batholiths are widely exposed the camaguey district in central cuba violates this tenet and provides important insights into arc forming processes that create and expose epithermal deposits the camaguey district hosts the jacinto and florencia low sulfidation vein deposits and the deseada and golden hill high sulfidation prospects all of which are within a few kilometers of the large camaguey batholith some of the deposits such as jacinto lie immediately below a local paleosurface that exposes the batholith and probably formed when rhyolite domes were emplaced onto this surface a second group of deposits such as the deseada high sulfidation system is hosted by volcanic rocks that overlie the camaguey batholith and stand above the paleosurface new ar ar age measurements indicate that jacinto type deposits and prospects cooled through ar ar closure temperatures for adularia and muscovite at about 71 ma and are slightly younger than the widespread granodiorite facies of the camaguey batholith in contrast deseada type deposits and mineralized zones cooled through roughly similar closure temperatures for sericite illite and alunite at about 80 ma which is older than the age of the immediately underlying camaguey batholith these ages are best explained if the camaguey batholith and surrounding volcanic rocks underwent rapid uplift probably by tectonic unroofing to form the paleosurface below which jacinto type deposits formed and if the older deseada type deposits were thrust into place over this surface this tectonic unroofing probably took place in an extensional regime generated during oblique convergence of cuba with yucatan as the greater antilles arc moved north into the caribbean region during late cretaceous time thrusting probably accompanied late stages of this convergence and or later collision with the bahamas bank in eocene time all of the epithermal deposits were covered by late cretaceous eocene sedimentary rocks that have been removed only recently by erosion thus accounting for the preservation of these unusually old epithermal deposits extensional events causing tectonic unroofing are probably common in arcs that undergo oblique convergence and could be an important agent for formation of epithermal deposits in other parts of the world preservation of these deposits might be aided by deposition and later erosion of sedimentary cover related to later collisions

boron cycling by subducted lithosphere insights from diamondiferous tourmaline from the kokchetav ultrahigh pressure metamorphic belt abstract subduction of lithosphere involving surficial materials into the deep mantle is fundamental to the chemical evolution of the earth however the chemical evolution of the lithosphere during subduction to depth remains equivocal in order to identify materials subjected to geological processes near the surface and at depths in subduction zones we examined b and li isotopes behavior in a unique diamondiferous k rich tourmaline k tourmaline from the kokchetav ultrahigh pressure metamorphic belt the k tourmaline which includes microdiamonds in its core is enriched in 11b relative to 10b 11b 1 2 to 7 7 and 7li relative to 6li 7li 1 1 to 3 1 it is suggested that the k tourmaline crystallized at high pressure in the diamond stability field from a silicate melt generated at high pressure and temperature conditions of the kokchetav peak metamorphism the heavy isotope signature of this k tourmaline differs from that of ordinary na tourmalines in crustal rocks enriched in the light b isotope 11b 16 6 to 2 3 which experienced isotope fractionation through metamorphic dehydration reactions a possible source of the heavy b isotope signature is serpentine in the subducted lithospheric mantle serpentinization of the lithospheric mantle with enrichment of heavy b isotope can be produced by normal faulting at trench outer rise or trench slope regions followed by penetration of seawater into the lithospheric mantle serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy b isotope signature which was acquired during the serpentinization prior to subduction the fluids could ascend and cause partial melting of the overlying crustal layer and the resultant silicate melt could inherit the heavy b isotope signature the subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle

genesis of epithermal au ag mineralization of the koryu mine hokkaido japan koryu is an epithermal gold silver quartz vein deposit in southwestern hokkaido japan the deposit occurs in an east west shear zone within miocene black mudstone the deposit consists of eight major veins with a general east west strike the three major veins show variable internal structure and texture in both vertical and horizontal directions k ar ages for adularia from veins 1 and 3 are 0 8 to 1 2 ma indicating a pleistocene age of mineralization based on crosscutting relationships and mineral parageneses the veins appear to have formed during two mineralization epochs the earlier event is further divided into three stages e i ii iii whereas seven stages can be distinguished in the later event l i ii iii iv v vi vii the wide veins consist of multiple mineralization stages most gold silver mineralization is associated with the l iii stage the earlier mineralization stages are characterized by manganocalcite johannsenite and small amounts of ore minerals whereas the later stages are characterized by large amounts of ore minerals gangue minerals associated with later ore consist of interstratified chlorite smectite and microcrystalline quartz alternately banded with adularia and comb texture quartz gold silver bearing minerals include electrum aeanthite aguilarite polybasite pearceite pyrargyrite proustite jalpaite mckinstryite hessite an ag te se s mineral and tetrahedrite the presence of vapor dominated fluid inclusions in several stages suggests that boiling occurred intermittently throughout ore deposition the formation temperatures of the earlier mineralization epoch 263 degrees 283 degrees c were slightly higher than those of the later mineralization epoch 246 degrees 260 degrees c except for stages e iii b 223 degrees c and l vii 206 degrees c salinities range from 0 5 to 6 0 wt percent nacl equiv although co 2 concentrations up to 1 4 wt percent in some later stages account for a portion of the apparent salinity these data indicate that maximum p total of the ore fluid was 31 to 68 bars equivalent to 430 to 850 m below the paleowater table quartz morphology combined with fluid inclusion studies suggests that boiling of the fluid occurred repeatedly leading to silica supersaturated conditions with respect to quartz and resulting in the formation of the various silica textures recrystallization of silica to quartz occurred throughout vein formation the stable isotope data combined with parageneses quartz textures and fluid inclusion studies suggest the following model for the koryu gold silver deposits the veins show two distinct mineralization epochs an earlier and a later one which were responsible for type 1 and 2 hydrothermal fluids respectively both types are dominantly meteoric water in origin the early fluid is characterized by relatively heavy delta 18 o values 5 3 to 4 7ppm and a temperature of or 260 degrees c the later fluid is characterized by relatively low delta 18 o values 9 3 to 6 0ppm and a temperature of or 250 degrees c type 1 fluids may have circulated deeply and leached ca and mn which were precipitated as manganocalcite and johannsenite during the earlier mineralization epoch type 2 fluids mixed with shallower water ascended through new conduits and apparently carried large amounts of gold and silver although the source of the metals cannot be determined at present when the hydrothermal fluids ascended at discrete time intervals to the boiling zone 850 m during the later epoch gold and silver were precipitated at 250 degrees c

factors in the preservation of coesite the importance of fluid infiltration the survival of coesite in ultrahigh pressure uhp rocks is most commonly attributed to rapid exhumation continuous cooling during uplift and inclusion in strong phases that can sustain a high internal over pressure during decompression exceptions to all of these criteria exist perhaps less attention has been paid to the role of fluid infiltration in the preservation of coesite we used infrared spectroscopy to measure water contents of coesite and coesite pseudomorphs in a variety of uhp rocks in all cases oh concentrations in coesite are below the detection limit of 100 ppm h2o the silica phases surrounding coesite however show varying amounts of h2o this is most spectacularly observed in pyrope quartzites from the dora maira massif that contain at least three phases of silica replacing coesite also distinguished by varying color of cathodoluminescence cl palisade textured quartz 100 ppm h2o red violet cl mosaic quartz which is actually chalcedony up to 0 4 wt h2o yellow brown cl and a rare highly hydrated silica phase interpreted to be opal 7 wt h2o dark blue cl very similar signatures are observed in a grospydite xenolith from the roberts victor kimberlite the quartz replacing coesite in other uhp samples studied contains on the order of 500 ppm h2o or less and most measurements are under the detection limit of our technique we infer that palisade quartz forms under dry or nearly dry conditions and at high temperatures during dilation of the host phase the formation of hydrous silica phases such as chalcedony and opal however must take place at much lower temperatures after cracking of the host phase which allows external fluids to infiltrate delay of fluid infiltration to low temperatures where kinetics are slow even in the presence of water is the most critical factor in the preservation of coesite

fluid inclusion from drill hole dw 5 hohi geothermal area japan evidence of boiling and procedure for estimating co2 content abstract fluid inclusion studies have been used to derive a model for fluid evolution in the hohi geothermal area japan six types of fluid inclusions are found in quartz obtained from the drill core of dw 5 hole they are i primary liquid rich with evidence of boiling ii primary liquid rich without evidence of boiling iii primary vapor rich assumed to have been formed by boiling iv secondary liquid rich with evidence of boiling v secondary liquid rich without evidence of boiling vi secondary vapor rich assumed to have been formed by boiling homogenization temperatures t h range between 196 and 347 c and the final melting point of ice t m between 0 2 and 4 3 c the co 2 content was estimated semiquantitatively to be between 0 and 0 39 wt based on the bubble behavior on crushing nacl equivalent solid solute salinity of fluid inclusions was determined as being between 0 and 6 8 wt after minor correction for co 2 content fluid inclusions in quartz provide a record of geothermal activity of early boiling and later cooling the co 2 contents and homogenization temperatures of fluid inclusions with evidence of boiling generally increase with depth these changes and nacl equivalent solid solute salinity of the fluid can be explained by an adiabatic boiling model for a co 2 bearing low salinity fluid some high salinity inclusions without co 2 are presumed to have formed by a local boiling process due to a temperature increase or a pressure decrease the liquid rich primary and secondary inclusions without evidence of boiling formed during the cooling process the salinity and co 2 content of these inclusions are lower than those in the boiling fluid at the early stage probably as a result of admixture with groundwater

diversity of potassium bearing tourmalines in diamondiferous kokchetav uhp metamorphic rocks a geochemical recorder from peak to retrograde metamorphic stages abstract chemical variations and inclusion mineralogy of tourmaline in diamond bearing ultrahigh pressure uhp gneisses and related siliceous rocks from the kokchetav massif kazakhstan are extensively investigated in conjunction with a review of previously discovered k bearing tourmaline with microdiamond inclusions tourmalines in these kokchetav uhp rocks have a wide compositional range dravite potassium oxy dravite schorl uvite feruvite foitite and some of their oxy variants with potassium content ranging from 0 to 0 576 atoms per formula unit apfu based on y z t cations 15 or 0 2 76 wt k 2 o and decreasing from core to rim the variation in potassium is spatially related to the inclusion mineralogy and is attributed to changes in metamorphic grade four stages of tourmaline growth in the kokchetav uhp rocks are recognized based on the potassium contents and occurrences in order of decreasing p and t 1 k dominant tourmaline k na ca and x vacancy with microdiamond and high si ti phengite inclusions and without quartz inclusions 2 k rich tourmaline k 0 2 0 05 apfu with graphite phengite kyanite and quartz inclusions 3 k poor tourmaline k 0 05 0 01 apfu with matrix quartz and biotite and 4 k free anhedral or overgrown tourmaline associated with low p t minerals such as amphibole or chlorite several lines of evidence also suggest that k dominant tourmaline crystallized in the diamond stability field tourmalines in the kokchetav uhp rocks recorded multi stage growth history from peak uhp conditions through a granulite facies overprint event including partial melting and ultimately to the latest retrograde metamorphism during exhumation

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

saline fluid inclusions in sphalerite from the broadlands ohaaki geothermal system a coincidental trapping of fluids being boiled toward dryness report of a fluid inclusion study of sphalerites from the broadlands ohaaki geothermal system the findings indicate that brine filled fluid inclusions do exist in sphalerite from one location but that their origin is a consequence of local boiling toward dryness rather than introduction of a deep brine

alteration minerals fluids and gases on early mars predictions from 1 d flow geochemical modeling of mineral assemblages in meteorite alh 84001 clay minerals although ubiquitous on the ancient terrains of mars have not been observed in martian meteorite allan hills alh 84001 which is an orthopyroxenite sample of the early martian crust with a secondary carbonate assemblage we used a low temperature 20 c one dimensional 1 d transport thermochemical model to investigate the possible aqueous alteration processes that produced the carbonate assemblage of alh 84001 while avoiding the coprecipitation of clay minerals we found that the carbonate in alh 84001 could have been produced in a process whereby a low temperature 20 c fluid initially equilibrated with the early martian atmosphere moved through surficial clay mineral and silica rich layers percolated through the parent rock of the meteorite and precipitated carbonates thereby decreasing the partial pressure of co 2 as it evaporated this finding requires that before encountering the unweathered orthopyroxenite host of alh 84001 the fluid permeated rock that became weathered during the process we were able to predict the composition of the clay minerals formed during weathering which included the dioctahedral smectite nontronite kaolinite and chlorite all of which have been previously detected on mars we also calculated host rock replacement in local equilibrium conditions by the hydrated silicate talc which is typically considered to be a higher temperature hydrothermal phase on earth but may have been a common constituent in the formation of martian soils through pervasive aqueous alteration finally goethite and magnetite were also found to precipitate in the secondary alteration assemblage the latter associated with the generation of h 2 apparently despite the limited water rock interaction that must have led to the formation of the carbonates 3 9 ga ago in the vicinity of the alh 84001 source rocks clay formation would have been widespread

retention of an atmosphere on early mars the presence of valley networks and indications of high erosion rates in ancient terrains on mars suggest that mars was warm and wet during heavy bombardment various processes that could occur on early mars were integrated into a self consistent model to determine what circumstances might lead to warm temperatures during and at the end of heavy bombardment included were weathering and burial of co2 as carbonates impact erosion sputtering and recycling of co2 back into the atmosphere by burial and heating the models suggest that despite losses from the atmosphere by weathering and impact erosion mars could retain a 0 5 to 1 bar atmosphere at the end of heavy bombardment partly because weathering temporarily sequesters co2 in the ground and protects it from impact erosion while the impact rate is declining and impact erosion is becoming less effective because of the low output of the early sun surface temperatures can be above freezing only for a very efficient greenhouse such as that suggested by forget and pierrehumbert 1997 with weak greenhouse models temperatures are below freezing throughout heavy bombardment and such a large amount of co2 is left in the atmosphere at the end of heavy bombardment that it is difficult to eliminate subsequently to arrive at the present surface inventory with strong greenhouse models temperatures are well above freezing during heavy bombardment and drop to close to freezing at the end of heavy bombardment at which time the atmosphere contains 0 5 to 1 bar of co2 this can be largely eliminated subsequently by sputtering and low temperature weathering such a model is consistent with the change in erosion rate and the declining rate of valley formation at the end of heavy bombardment conditions that favor warm temperatures at the end of heavy bombardment are an efficient greenhouse low weathering rates low impact erosion rates and a smaller fraction of heat lost by conduction as opposed to transport of lava to the surface

tourmaline breakdown in a pelitic system implications for boron cycling through subduction zones pressure temperature conditions of tourmaline breakdown in a metapelite were determined by high pressure experiments at 700 900 c and 4 6 gpa these experiments produced an eclogite facies assemblage of garnet clinopyroxene phengite coesite kyanite and rare rutile the modal proportions of tourmaline clearly decreased between 4 5 and 5 gpa at 700 c between 4 and 4 5 gpa at 800 c and between 800 and 850 c at 4 gpa with tourmaline that survived the higher temperature conditions appearing corroded and thus metastable decreases in the modal abundance of tourmaline are accompanied by decreasing modal abundance of coesite and increasing that of clinopyroxene garnet and kyanite the boron content of phengite increases significantly these changes suggest that with increasing pressure and temperature tourmaline reacts with coesite to produce clinopyroxene garnet kyanite and boron bearing phengite and fluid our results suggest that 1 tourmaline breakdown occurs at lower pressures and temperatures in sio2 saturated systems than in sio2 undersaturated systems 2 in even cold subduction zones subducting sediments should release boron rich fluids by tourmaline breakdown before reaching depths of 150 km and 3 even after tourmaline breakdown a significant amount of boron partitioned into phengite could be stored in deeply subducted sediments

geochemical fluid inclusion and o h s isotope studies of the milajerd au polymetallic prospect central iran implications for ore genesis abstract the milajerd pb zn au polymetallic prospect in naein qom magmatic zone is a favorable target for exploration geological and geochemical characteristics such as setting alteration assemblages fluid inclusion microthermometry and stable isotopes are consistent with the milajerd pb zn au polymetallic prospect being a typical low sulfidation ls epithermal deposits the au polymetallic mineralization occurs mainly as structurally controlled veins and brecciated dikes hosted by calc alkaline volcanic rocks mineralization at the milajerd prospect is controlled by an annular fault system the sulfide mineralogy of the deposit includes sphalerite galena pyrite arsenopyrite and marcasite the principal gangue minerals are quartz calcite sericite and adularia the alteration assemblages include quartz pyrite quartz sericite pyrite and chlorite calcite epidote fluid inclusions in quartz sulfide veins have homogenization temperatures th of 158 255 c and salinities of 4 7 7 7 wt nacl equiv whereas those in barren quartz carbonate veins yield th values of 135 176 c and salinities of 1 1 4 3 wt nacl equiv the h and o isotopic composition dwater 120 to 92 inferred 18owater 6 2 to 3 5 of fluid inclusions in quartz veins imply that cooling a mixed magmatic and meteoric waters was the main mechanisms of ore deposition at milajerd deposit the 34s values of ore sulfides are mostly close to zero avg 0 1 indicating a magmatic source of sulfur which could have emanated directly from magmatic activity or have been leached from the surrounding volcanic rocks

evolution of an au ag producing hydrothermal system the tayoltita mine durango mexico hydrothermal fluid circulation in the tayoltita geothermal system evolved from pervasive to fracture controlled flow the early pervasive circulation produced the widespread propylitic alteration around the mine in the lower levels of the system this pervasive propylitization is dominated by chlorite whereas in the upper levels epidote and albite are also major components of the alteration fluid temperatures associated with this stage ranged from 360 degrees c in the lower level of the mine based on the alteration assemblage oligoclase actinolite chlorite sphene to 2 0 wt nacl equiv in the earlier quartz associated with ore the higher salinity inclusions also present in the early isolated quartz veinlets are believed to represent early mixing of a saline magmatic fluid component

multiple zircon growth during fast exhumation of diamondiferous deeply subducted continental crust kokchetav massif kazakhstan diamondiferous rocks from the kokchetav massif kazakhstan represent deeply subducted continental crust in order to constrain the age of ultra high pressure uhp metamorphism and subsequent retrogression during exhumation zircons from diamondiferous gneisses and metacarbonates have been investigated by a combined petrological and isotopic study four different zircon domains were distinguished on the basis of transmitted light microscopy cathodoluminescence trace element contents and mineral inclusions mineral inclusions and trace element characteristics of the zircon domains permit us to relate zircon growth to metamorphic conditions domain 1 consists of rounded cores and lacks evidence of uhp metamorphism domain 2 contains diamond coesite omphacite and titanian phengite inclusions providing evidence that it formed at uhp metamorphic conditions p 43 kbar t 950 c domain 3 is characterised by low pressure mineral inclusions such as garnet biotite and plagioclase which are common minerals in the granulite facies overprint of the gneisses p 10 kbar t 800 c this multi stage zircon growth during cooling and exhumation of the diamondiferous rocks can be best explained by zircon growth from zr saturated partial melts present in the gneisses domain 4 forms idiomorphic overgrowths and the rare earth element pattern indicates that it formed without coexisting garnet most probably at amphibolite facies conditions p 5 kbar t 600 c the metamorphic zircon domains were dated by shrimp ion microprobe and yielded ages of 527 5 528 8 and 526 5 ma for domains 2 3 and 4 respectively these indistinguishable ages provide evidence for a fast exhumation beyond the resolution of shrimp dating the mean age of all zircons formed between uhp metamorphic conditions and granulite facies metamorphism is 528 3 ma indicating that decompression took place in less than 6 ma hence the deeply subducted continental crust was exhumed from mantle depth to the base of the crust at rates higher than 1 8 cm year we propose a two stage exhumation model to explain the obtained p t t path fast exhumation on top of the subducted slab from depth 140 to 35 km was driven by buoyancy and facilitated by the presence of partial melts a period of near isobaric cooling was followed by a second decompression event probably related to extension in a late stage of continental collision

hydrothermal alteration and veins at the epithermal au ag deposits and prospects of the waitekauri area hauraki goldfield new zealand the waitekauri area of the hauraki goldfield new zealand contains several adularia sericite epithermal au ag deposits and prospects from west to east the area contains the sovereign jubilee scimitar scotia teutonic and jasper creek deposits and prospects which are hosted by andesitic and dacitic flows breccias and localized pyroclastic and air fall deposits drill core reveals spatial and temporal zonation of alteration and vein minerals along a 3 km long composite cross section through the area most host rocks are intensely altered with 100 percent of the igneous minerals replaced by hydrothermal minerals although the alteration intensity becomes more variable and weaker toward the east alteration minerals include quartz adularia albite chlorite pyrite illite interstratified illite smectite smectite calcite hematite and minor epidote many of these minerals have zoned distributions adularia is widespread at sovereign but is restricted to shallow levels at both scotia and jasper creek albite occurs in a discrete zone below adularia at scotia and minor epidote is restricted to sovereign and jubilee illite occurs throughout sovereign and jubilee and at the western margin of scotia and scimitar where it grades eastward into interstratified illite smectite and smectite at teutonic and jasper creek veins are typically less than 10 cm wide but have diverse mineralogy with zoned distributions quartz veins dominate at sovereign and jubilee whereas calcite veins are more abundant at scotia scimitar and jasper creek laumontite occurs at scotia and locally at scimitar whereas veins of clinoptilolite and mordenite calcite occur at jasper creek and stilbite veins occur at teutonic fluid inclusions in quartz and calcite homogenized between 132 and 310 c and trapped a dilute solution with an apparent salinity of less than 2 6 wt percent nacl equiv homogenization temperatures are highest at sovereign avg 241 c jubilee avg 239 c and scimitar avg 236 c lower at scotia avg 204 c and lowest at teutonic avg 168 c and jasper creek avg 162 c estimated positions of the paleowater table above sovereign jubilee scimitar scotia jasper creekg and teutonic relative to present elevations was at least 690 750 575 450 225 and 150 m above sea level respectively the deposits and prospects therefore span a 600 m vertical interval individual deposits and prospects have undergoen at least 35 to more than 455 m of erosion with the greatest erosion to the west alteration intensity alteration and vein mineral distributions and fluid inclusion microthermometry are interpreted to indicate that sovereign and jubilee formed at relatively high temperatures whereas teutonic and jasper creek formed at relatively cooler temperatures several hydrologic reconstructions are possible including 1 a single hydrothermal system with an inclined water table and significant lateral outflow to the east or 2 a single low relief hydrothermal system with a flat lying water table that has subsequently been displaced by postmineral faults or tilted approximately 10 to the east regardless of the preferred reconstruction the sovereign and jubilee deposits appear to have formed in the main zone of fluid upflow whereas the teutonic and jasper creek prospects appear to have formed toward the margin moreover the greatest erosion has occurred at the jubilee and sovereign deposits 300 400 m and these may represent the roots of a more extensive vein network that has largely been eroded

hydrothermal fluids in epithermal and porphyry au deposits in the central slovakia volcanic field the neogene central slovakia volcanic field in the carpathian arc contains various au deposits hosted by central zones of large andesite stratovolcanoes fluids involved in mineralization have been studied at three different types of deposit mostly by fluid inclusion and stable isotope techniques the rozalia mine in the stiavnica stratovolcano hosts intermediate sulphidation style au ag epithermal mineralization in subhorizontal veins related to hydrothermal activity during an early stage of caldera collapse associated fluids of low salinity underwent extensive boiling at 280 330 c on transition from suprahydrostatic towards hydrodynamic conditions at shallow depths c 550 m from fluids of mixed magmatic and meteoric origin the kremnica ore field hosts a large system of low sulphidation style au ag veins contemporaneous with rhyolite magmatism and situated on resurgent horst faults fluids were of low salinity predominantly of meteoric origin and showed gradual decrease in temperature along the system c 270 140 c related to a decrease in erosion level from c 500 to c 50 m the biely vrch au porphyry deposit in the javorie stratovolcano is associated with quartz stockwork in diorite porphyry intrusion the major type of ore bearing fluid was high temperature magmatic vapour 720 380 c accompanied by fe rich salt melt gold precipitated in a high temperature but low pressure subvolcanic environment

the ti saturation surface for low to medium pressure metapelitic biotites implications for geothermometry and ti substitution mechanisms the ti content of biotite can serve as a geothermometer for graphitic peraluminous metapelites that contain ilmenite or rutile and have equilibrated at roughly 4 6 kbar the relationship between ti content temperature and mg mg fe value was calibrated empirically using an extensive natural biotite data set 529 samples from western maine and south central massachusetts in combination with the petrogenetic grid of spear et al 1999 the calculated ti saturation surface is curved such that for a given mg mg fe value ti concentration increases as a function of temperature in a nonlinear fashion and for a given temperature ti concentrations decrease with an increase in mg mg fe the fit to the ti saturation surface can be reformulated as the geothermometric expression t ln ti a c x mg 3 b 0 333 in which t is temperature in degrees celsius ti is the number of atoms per formula unit apfu normalized on the basis of 22 o atoms x mg is mg mg fe a 2 3594 b 4 6482 10 9 and c 1 7283 the calibration range for this expression is x mg 0 275 1 000 ti 0 04 0 60 apfu and t 480 800 c precision of the ti in biotite geothermometer is estimated to be 24 c at the lower temperature range and improves to 12 c at higher temperatures application of the ti in biotite geothermometer to ilmenite or rutile bearing graphitic peraluminous metapelites equilibrated at 3 6 kbar is generally consistent with independent temperature determinations but with some deviations that represent local reequilibration consequently the ti systematics in biotite can also serve as the basis of a very sensitive indicator of chemical equilibrium or lack thereof application of the geothermometer to metapelites not containing the requisite mineral assemblages can lead to minor to significant errors in estimated temperatures biotite ti substitution mechanisms are controlled by several factors based on the biotite calibration data set magnesian biotites x mg 0 65 incorporate ti in accordance with the exchange vector tial2r 1si 2 where r is the sum of the divalent cations mg fe mn this substitution mechanism is primarily a response to misfit of the octahedral and tetrahedral layers in magnesian biotites intermediate biotites x mg 0 65 particularly at higher temperatures exhibit enhanced ti concentrations most consistent with the ti deprotonation tio2r 1 oh 2 exchange vector dominance of ti deprotonation substitution is largely a function of reduction of h2o activity at higher metamorphic grades supplementary biotite data from metaluminous amphibolites and mafic granulites metamorphosed isothermally with variable h2o activities reveal that low al biotite incorporates significantly higher concentrations of ti relative to peraluminous biotite as a result of a combination of the exchange vectors tio2r 1 oh 2 and rsial 2 substituting in roughly an 8 1 ratio

hydrothermal formation of clay carbonate alteration assemblages in the nili fossae region of mars abstract the compact reconnaissance imaging spectrometer for mars crism has returned observations of the nili fossae region indicating the presence of mg carbonate in small

geochemistry and stable isotope composition of altered rocks at the golden cross epithermal au ag deposit new zealand golden cross is a late miocene volcanic hosted epithermal au ag deposit associated with quartz calcite adularia illite assemblages located in the coromandel peninsula new zealand gold and ag bearing quartz veins occur in intensely altered flows and lesser pyroclastic volcanic rocks of andesitic and dacitic composition the primary control of whole rock geochemistry at golden cross as at other volcanic hosted epithermal deposits associated with quartz calcite adularia illite assemblages is the destruction of igneous plagioclase by hydrothermal alteration and k metasomatism from hydrothermal fluids quantitative mass change calculations indicate that irrespective of the rock type andesite versus dacite hydrothermally altered rocks are enriched in k rb as and sb around the empire vein system and stockwork in contrast na and sr are strongly depleted around the veins with fe locally depleted silicon ca mg and ba are variably enriched and depleted with si enriched immediately adjacent to the veins and ca only locally enriched the enrichment and depletion trends for these elements are directly related to the degree of alteration and the alteration mineralogy intensely altered rocks show addition of k and rb coupled with loss of na and sr which reflect the replacement of plagioclase by adularia and or illite calcium depletion also reflects the destruction of plagioclase although ca loss is locally offset by the formation of hydrothermal calcite progressively higher na and sr away from the veins reflect greater preservation of plagioclase and the transition into less altered rocks on the margins potassium rb na and sr all define anomalies that extend 200 to 350 m east of the veins and are more widespread than as and sb which are anomalous within 150 to 200 m of the veins the geochemical zonation patterns identified at golden cross are very similar to those at other epithermal deposits associated with quartz calcite adularia illite assemblages potassium na rb sr and ca enrichment and depletion patterns provide insight into the intensity and type of alteration thereby complementing traditional analyses of au ag and other pathfinder elements such as as and sb that are used to explore for epithermal au ag deposits potassium na rb sr and ca enrichment and depletion patterns at golden cross are larger than halos defined by precious metals and other trace element pathfinders thereby providing a larger target area for exploration potassium metasomatism is particularly important because the empire vein system occurs in altered rocks that are significantly enriched in k potassium metasomatism can be evaluated by raw k 2 o data or more effectively by k mass changes molar element ratios of 2ca na k al versus k al wt k 2 o 100 ppm sr rb sr ratios and k numbers k 2ca k na molar whole rock oxygen isotope patterns at golden cross are similar to those described at other epithermal deposits associated with quartz calcite adularia illite assemblages however the area defined by low 18 o values is smaller than the area that can be defined by field mapping of alteration minerals or whole rock major and trace element geochemistry

identification of carbonate rich outcrops on mars by the spirit rover decades of speculation about a warmer wetter mars climate in the planet s first billion years postulate a denser co2 rich atmosphere than at present such an atmosphere should have led to the formation of outcrops rich in carbonate minerals for which evidence has been sparse using the mars exploration rover spirit we have now identified outcrops rich in magnesium iron carbonate 16 to 34 weight percent in the columbia hills of gusev crater its composition approximates the average composition of the carbonate globules in martian meteorite alh 84001 the gusev carbonate probably precipitated from carbonate bearing solutions under hydrothermal conditions at near neutral ph in association with volcanic activity during the noachian era

reproducing hydrogeochemical conditions triggering the formation of carbonate and phyllosilicate alteration mineral assemblages on mars nili fossae region 1 the cooccurrence of mg fe ca carbonate and stratigraphically lower phyllosilicate bearing rock units identified in the nili fossae region on mars may reveal a co2 driven aqueous alteration process on ancient mars we reproduce hydrogeochemical conditions for concurrent carbonate and phyllosilicate formation in rock columns by using hydrogeochemical one dimensional transport modeling which is based on chemical equilibrium thermodynamics our models assume the isochemical low temperature equilibration of ultramafic rocks with pure water at varying atmospheric co2 partial pressure water to rock ratio temperature and rock composition equilibration among 1 mineral assemblages of olivine rich rocks 18 28 wt mgo 2 pure water water to rock ratio 500 50 mol mol 1 3 co2 transferred from the atmosphere co2 partial pressure lower than 2 bars and higher than 0 01 bar at 278 k and 4 100 000 years of diffusive mass transport create hydrogeochemical conditions enabling the concurrent formation of mg rich mg fe ca solid solution carbonate and stratigraphically lower phyllosilicate rich alteration assemblages in rock columns the modeled composition of alteration mineral assemblages their depth distribution and carbonate composition are similar to the observations from the nili fossae region higher equilibration temperature 373 k results in the formation of ca dominated ca mg carbonate instead of mg rich mg fe ca carbonate and in an inverse stratification with phyllosilicate rich units overlying carbonate rich units modeling results suggest that rocks in the nili fossae region hosting the carbonate and phyllosilicate mineral assemblage have been exposed to a groundwater alteration process driven by atmospheric co2 partial pressures ranging between 2 bars and 0 01 bar at low temperature 278 k

geologic setting and genesis of the mule canyon low sulfidation epithermal gold silver deposit north central nevada the mule canyon mine exploited shallow low sulfidation epithermal au ag deposits that lie near the west side of the northern nevada rift in northern lander county nevada mule canyon consists of six small deposits that contained premining reserves of about 8 2 mt at an average grade of 3 81 g au tonne it is an uncommon mafic end member of low sulfidation au ag deposits associated with tholeiitic bimodal basalt rhyolite magmatism the ore is hosted by a basalt andesite eruptive center that formed between about 16 4 to 15 8 ma during early mafic eruptions related to regionally extensive bimodal magmatism hydrothermal alteration and au ag ores formed at about 15 6 ma and were tightly controlled by north northwest to north striking high angle fault and breccia zones developed during rifting emplacement of mafic dikes and eruption of mafic lava flows hydrothermal alteration assemblages are zoned outward from fluid conduits in the sequence silica adularia adularia smectite smectite intermediate argillic and smectite carbonate propylitic all alteration types contain abundant pyrite and or marcasite arsenopyrite field relations indicate that silica adularia alteration is superimposed on argillic and propylitic alteration little or no steam heated acid sulfate alteration is present probably the result of a near surface water table during hydrothermal alteration and ore deposition two distinct ore types are present at mule canyon early replacement and later open space filling replacement ores consist of disseminated and vesicle filling pyrite marcasite and arsenopyrite in argillically altered or weakly silicified rocks ore minerals consist of au bearing arsenopyrite and arsenian pyrite overgrowths on earlier formed pyrite and marcasite open space filling ores include narrow stockwork quartz adularia veins banded and crustiform opaline and chalcedonic silica adularia veins silica adularia cemented breccias and sparse carbonate pyrite and or marcasite veins ore minerals consist mostly of electrum and ag sulfide and selenide minerals with minor to major amounts of pyrite marcasite and arsenopyrite and local stibnite both types of ores have similar geochemical signatures characterized by high au ag as sb and se contents locally high hg mo tl and w contents and low cu pb and zn contents stable isotope data indicate that ore fluids consisted dominantly of meteoric water that evolved by deep circulation through paleozoic sedimentary rocks at low water rock ratios about 1 and high temperatures 200 c calculated isotopic compositions of ore fluids are 18oh2o 3 to 7 per mil dh2o 107 to 124 per mil 13cco2 0 to 6 per mil and 34sh2s 3 to 8 per mil the ore fluids obtained much of their h2s and co2 and probably scavenged ore metals and trace elements from the paleozoic sedimentary rocks some h2s and co2 may have been derived from degassing miocene magmas mule canyon formed at shallow depths probably about 100 m below the paleosurface ore fluids were dilute nearly neutral in ph reduced h2s rich and co2 bearing peak temperatures in ore zones reached 230 to 265 c at nearly lithostatic pressures when some crystalline quartz adularia precipitated but most ore formed at temperatures 200 c at near hydrostatic pressures and was accompanied by precipitation of opaline and chalcedonic silica adularia calcite and dolomite deposition of gold in as rich overgrowths on pyrite and or marcasite in disseminated ores occurred owing to decreasing h2s in the ore fluids resulting from sulfidation reactions later electrum and ag selenide precipitation in open spaces occurred owing to boiling loss of h2s to the vapor phase and cooling mule canyon is similar to most other low sulfidation au ag deposits associated with miocene tholeiitic bimodal basalt rhyolite magmatism in the great basin such as sleeper midas and buckhorn major differences at mule canyon are the high fe sulfide contents of some ores and altered wall rocks the paucity of silicification and the presence of only narrow and discontinuous gold bearing siliceous veins these differences primarily are due to the mafic composition of the host rocks mule canyon differs from low sulfidation deposits associated with subduction related calc alkaline porphyry intrusions such as the comstock lode in that a much smaller proportion of water salts and metals was derived from crystallizing magmas

sensitivity analysis of prospectivity modeling to evidence maps enhancing success of targeting for epithermal gold takab district nw iran abstract the takab metallogenic province in the northwestern iran hosts a number of gold resources including carline like and epithermal type mineralization these occurrences are hosted by tectonized country rocks of precambrian basement metamorphic rocks and tertiary volcanic and sedimentary units which are intruded by the intrusion of probable age of eocene and the sub volcanic domes of miocene age plausible mineralized zones in this high potential area can be delimited based on mineral prospectivity maps during the regional exploration surveys however the success of mineral prospectivity mapping mpm is always plagued by different types of uncertainties stochastic and systemic the main aim of this study is to reduce those uncertainties resulting from a the imprecise incorrect selection of targeting criteria b adverse effects of using inefficient or least efficient evidence maps and c employing an integration methodology which suffers from user interference in this regard the first case was modulated through the precise identification and selection of controls on mineralization as well as ore forming processes the second case was declined by the sensitivity analysis of input geochemical geological and structural parameters to mpm using the area under the receiver operating characteristics roc curve and the third case was controlled by incorporation of genetic algorithm ga and artificial neural networks here mlp ann as a suitable data driven mpm method through sensitivity analysis and using mlp ga ann and mlp ann algorithms various prospectivity models were generated and compared the results of prediction rate curves demonstrated that the exclusion of poor evidence maps and that employing a self adapted data driven approach e g mlp ga ann can significantly reduce the systematic uncertainty in mapping of mineral prospectivity accordingly the superior model was then selected for delineating efficient exploration targets

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

hydrothermal breccias and veins at the kelian gold mine kalimantan indonesia genesis of a large epithermal gold deposit mineralized hydrothermal breccias and veins formed during and after the waning stages of maar diatreme related volcanic activity at kelian kalimantan indonesia subsurface phreatic explosions occurred around the margins of the diatreme breccia complex focusing high temperature fluid flow and generating several large mineralized hydrothermal breccia bodies tectonic phreatomagmatic and hydraulic processes also contributed to hydrothermal brecciation explosive phreatic brecciation was followed by in situ hydraulic brecciation and then by minor veining as the system returned to steady state geothermal conditions brecciation and mineralization mostly occurred 400 to 700 m below the paleowater table the kelian deposit contained more than 240 t au prior to mining precious metals occur with sulfide minerals as disseminations in sheeted and conjugate veins and as breccia cement there is a progression from pyrite dominated stage 1 to base metal sulfide dominated stages 2 and 3 to sulfosalt dominated hydrothermal breccias and veins stage 4 in terms of gangue minerals the system evolved from illite quartz to adularia and or quartz and or illite dominated and then carbonate dominated boiling produced abundant bladed carbonate during stages 3 and 4 overall carbonate and base metal sulfide minerals are abundant whereas quartz is comparatively minor free gold is most abundant in stages 3 and 4 but also occurs in stages 1 and 2 native gold occurs principally as inclusions in pyrite sphalerite galena arsenopyrite quartz bladed carbonate and sulfosalts hydrothermal alteration assemblages are zoned about contacts faults breccias and veins and consist of secondary quartz illite pyrite chlorite and various carbonate minerals kelian preserves evidence of a magmatic component to the mineralizing fluids fluid inclusion analyses revealed the presence of saline fluid inclusions in particular from stage 3 isothermal mixing of low salinity 0 to 2 wt nacl equiv with moderate salinity fluids 10 to 25 wt nacl equiv rather than boiling resulted in the range of salinity and homogenization temperatures of fluid inclusions in sphalerite carbonate and quartz deposited during stage 3 salinities of 4 to 6 wt percent nacl equiv for inclusions in adularia and quartz from stages 2 and 4 and in rhodochrosite and proustite pyrargyrite from stage 4 may also reflect a component of mixing of low salinity water with a moderately saline fluid sulfur isotope values from kelian sulfides 34s 1 4 to 5 5 per mil are consistent with a magmatic sulfur source both boiling and fluid mixing contributed to high grade au mineralization at kelian rapid formation hundreds of years or less is inferred for the individual hydrothermal breccia bodies 2008 society of economic geologists inc

epithermal au ag and related deposits of the hauraki goldfield coromandel volcanic zone new zealand epithermal au ag vein deposits of the hauraki goldfield in the coromandel volcanic zone new zealand produced 320 000 kg au and 1 5 million kg ag between 1862 and 2006 from a total land area of approximately 2 900 km2 approximately 69 percent of the production was from the world class martha deposit at waihi some 97 percent of total past gold production was from deposits hosted in miocene andesite and dacite of the coromandel group although this unit represents only 61 percent of the rocks exposed in the goldfield the deposits consist of quartz calcite vein systems 0 5 to 4 5 km long within alteration zones up to 20 km2 in size they were mined over vertical intervals of 170 to 330 m but up to 575 m at martha and 700 m at karangahake electrum and acanthite are the main ore minerals although pyrite sphalerite galena chalcopyrite sulfosalt minerals and te and se bearing minerals are present in some deposits stibnite and cinnabar occur locally as late minerals and some deposits are overprinted by late massive calcite fluid inclusion ice melting temperature tm measurements indicate that fluids associated with base metal and precious metal deposition had apparent salinities of between 0 5 and 2 wt percent nacl equiv with a maximum of 6 1 wt percent nacl equiv when fitted to hydrostatic boiling point with depth curves the homogenization temperature th data define paleodepths spanning a vertical interval from near the water table to a depth of approximately 1 300 m the presence of vapor rich fluid inclusions and occurrences of lattice textures and vein adularia indicate that periods of boiling coincided with deposition of some epithermal ores sulfur and carbon isotope values of vein minerals are consistent with a magmatic origin for sulfur and carbon oxygen isotope values of vein quartz and calcite are consistent with derivation from evolved meteoric water with possibly a small magmatic water component in some samples the epithermal deposits can be broadly subdivided into northern southern and eastern groups based on their host rocks age variability of vein strike au ag ratios occurrence or relative abundance of key minerals such as adularia calcite and arsenopyrite the grain size of vein quartz and differences in vein textures early ca 14 10 ma steeply dipping planar veins occur in the oldest andesite and dacite in the northern portion of the goldfield but some of these are bonanza grade veins that contained significant gold resources larger veins typically with well developed crustiform textures formed in andesite and dacite in the southern gold field at 7 to 6 ma and these contributed most of the au and ag that has been recovered from the goldfield in contrast rhyolite in the eastern goldfield hosts smaller less well developed veins plus stockworks that have produced the least amount of au and ag epithermal mineral deposits in the hauraki goldfield evolved through time reflecting changes in volcanic activity and more speculatively tectonic and structural history and setting

structural evolution of the golden cross epithermal au ag deposit new zealand golden cross located in the hauraki goldfield of new zealand is a classic example of a fault fracture hosted epithermal vein system gold silver mineralization was mined in two areas the open pit stock work veins and the underground empire vein system which are collectively referred to as the empire zone open pit stockwork veins are either parallel or subperpendicular to northeast striking moderately southeast dipping bedding bedding perpendicular veins are mostly pure extensional structures whereas bedding parallel veins open in an extensional regime with a minor component of shear vein frequency across strike is typically 15 m and most veins are 0 01 to 0 2 m thick the underground empire vein system consists of the steeply west dipping empire vein and a complex array of footwall veins the 2 to 10 m thick empire vein strikes northeast dips steeply 65 85 northwest has a mineralized strike length of about 500 m and a vertical extent of 250 m it is localized in a deflection of the empire fault where the dip of the fault decreases the footwall veins are low angle gently west dipping veins up to 100 m long hosted in extensional shear and pure extension fractures they splay off the empire vein at an average angle of 30 up to seven vein types record the multiple fault fracture openings that provided highly permeable pathways for hydrothermal fluids in the empire zone the empire zone was initially characterized by a pervasive network of thin barren sulfide veins followed by two to five stages of electrum bearing quartz veins the most voluminous of these stages were quartz adularia veins with well developed colloform and crustiform bands and breccia textures the final stage was massive coarsely crystalline calcite veins similarities in vein type orientation and crosscutting relationships between the empire vein system and stockwork veins suggest that they formed under similar stress regimes and that mineralization in the two areas overlapped in time at least in part host rocks at golden cross dip 50 to the southeast if the vein system and bedding are rotated so that bedding is restored to horizontal the empire fault and empire vein reflect a steeply southeast dipping normal fault after rotation the former footwall veins form a network of subvertical veins in the hanging wall of the empire fault they form an en echelonlike array similar to horse tail extensional fracture networks that commonly develop in normal faults in the near surface therefore we infer that before tilting empire zone fractures and veins formed in an extensional regime with 1 subvertical 2 subhorizontal oriented northeast south west and 3 subhorizontal oriented northwest southeast consistent with the interpreted rift tectonics of the coromandel volcanic zone during the late miocene time of mineralization

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

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

the waihi epithermal gold silver base metal sulfide quartz vein system new zealand temperature and salinity controls on electrum and sulfide deposition the large andesite hosted quartz vein system at waihi contains a major epithermal au ag deposit total production of 6 4 moz au and 39 9 moz ag ag au 6 2 it is notable for a large vertical extent up to 575 m of economic au ag ore a pervasive adularia quartz illite chlorite pyrite alteration zone bounds the larger quartz veins and is associated with veinlets of quartz calcite pyrite adularia illite this zone is enveloped by an illite quartz adularia chlorite calcite pyrite alteration zone which grades out through a transition zone characterized by interlayered illite smectite into a smectite chlorite calcite alteration zone in the least altered andesites the formation of the adularia quartz chlorite calcite pyrite and some illite in these alteration assemblages was associated with an initial stage of vein filling by platy calcite and quartz this was followed by a main stage of quartz and sulfide vein filling with crustiform quartz at deeper levels and colloform quartz plus minor adularia at shallow levels deposition of main stage quartz and sulfides was accompanied by illite overprinting adularia in the wall rock and filling fractures in the quartz calcite pyrite adularia veinlets sulfide bearing bands associated with the main stage quartz show a zonation with decreasing depth from a coarse grained sphalerite galena pyrite chlorite assemblage at deep levels to a finer grained sphalerite galena pyrite chalcopyrite acanthite electrum assemblage at medium to shallow levels fluid inclusion studies indicate that the main stage quartz was deposited from fluids which ranged in temperature and composition from up to 295 c and 1 7 wt percent nacl equiv at depth to 190 c and 0 2 wt percent nacl equiv at shallow levels these are true salinities because the fluids extracted from the fluid inclusions have low co 2 contents 0 05 0 24 wt quartz within electrum poor zn pb fe sulfide bands was deposited at higher temperatures 295 242 c and salinities than quartz in electrum bearing zn pb fe cu ag sulfide bands 260 190 c temperature versus depth profiles for fluid inclusions with evidence of boiling indicate that the paleowater table was located about 160 m above the present erosion level during deposition of the main stage quartz minor amethyst as the final stage of vein filling was locally preceded by inesite and was not associated with sulfides and electrum amethyst was deposited at 253 to 170 c from fluids containing up to 4 5 wt percent nacl equiv these higher salinities are attributed to concentration of salts in the residual liquid by localized open system boiling chloride depth chloride enthalpy and 18 o water enthalpy plots indicate mixing of deep fluids up to 1 7 wt nacl for the main stage quartz with very low salinity steam heated ground water oxygen isotope 18 o values for vein quartz and amethyst range from 6 1 to 11 6 per mil and for vein calcite from 2 29 to 9 4 per mil calculated 18 o water values define a trend from 2 9 per mil at shallow levels to 0 6 per mil at depth extrapolation of the dilution trend on a 18 o water enthalpy plot indicates that the deep fluid 18 o water 0 6 was mixed with heated 160 180 c ground water of local meteoric water composition 5 5 dilution of a deep chloride fluid 1 2 wt nacl equiv carrying zinc and lead as chloride complexes with steam heated ground water is inferred to have been responsible for deposition of the electrum poor zn pb fe sulfide assemblage from 300 to 240 c at a paleodepth below about 500 m deposition of this assemblage may also have been promoted by decrease of sulfur in solution through loss of h 2 s gas by boiling during episodic fracturing the decrease in salinity following dilution favored the transport of gold silver and copper as hydrosulfide complexes and led to the deposition of the electrum bearing zn pb fe cu ag sulfide assemblage over a temperature range of 260 to less than 190 c at paleodepths of 500 to less than 250 m in this assemblage the decrease of sulfur in solution as a result of deposition of the associated chalcopyrite pyrite and galena is a likely mechanism for electrum deposition

olivine carbonate mineralogy of the jezero crater region a well preserved ancient delta deposit in combination with ample exposures of carbonate outcrops makes jezero crater in nili fossae a compelling astrobiological site we use compact reconnaissance imaging spectrometer for mars crism observations to characterize the surface mineralogy of the crater and surrounding watershed previous studies have documented the occurrence of olivine and carbonates in the nili fossae region we focus on correlations between these two well studied lithologies in the jezero crater watershed we map the position and shape of the olivine 1 m absorption band and find that carbonates are found in association with olivine which displays a 1 m band shifted to long wavelengths we then use thermal emission imaging spectrometer themis coverage of nili fossae and perform tests to investigate whether the long wavelength shifted redshifted olivine signature is correlated with high thermal inertia outcrops we find that there is no consistent correlation between thermal inertia and the unique olivine signature we discuss a range of formation scenarios for the olivine and carbonate associations including the possibility that these lithologies are products of serpentinization reactions on early mars these lithologies provide an opportunity for deepening our understanding of early mars and given their antiquity may provide a framework to study the timing of valley networks and the thermal history of the martian crust and interior from the early noachian to today

ancient groundwater flow in the valles marineris on mars inferred from fault trace ridges long linear ridges in the valles marineris region of mars most likely represent fault zones that have been cemented by water deposited minerals this implies that water in the martian crust could have traversed long distances via faults and fractures

coesite inclusions and prograde compositional zonation of garnet in whiteschist of the hp uhpm kokchetav massif kazakhstan a record of progressive uhp metamorphism coarse grained whiteschist containing the assemblage garnet kyanite phengite talc quartz coesite is an abundant constituent of the ultrahigh pressure metamorphic uhpm belt in the kulet region of the kokchetav massif of kazakhstan garnet displays prograde compositional zonation with decreasing spessartine and increasing pyrope components from core to rim cores were recrystallized at t 380 c inner to 580 c outer at p 10 kbar garnet ilmenite geothermometry margarite quartz stability and mantles at t 720 760 c and ph20 34 36 kbar coesite graphite stability phengite geobarometer kfmash system reaction equilibria textural evidence indicates that rims grew during decompression and cooling within the qtz stability field silica inclusions quartz and or coesite of various textural types within garnets display a systematic zonal distribution cores contain abundant inclusions of euhedral quartz type 1 inclusions inner mantle regions contain inclusions of polycrystalline quartz pseudomorphs after coesite type 2 with minute dusty micro inclusions of chlorite and more rarely talc and kyanite in their cores intense radial and concentric fractures are well developed in the garnet intermediate mantle regions contain bimineralic inclusions with coesite cores and palisade quartz rims type 3 which are also surrounded by radial fractures subhedral inclusions of pure coesite without quartz overgrowths or radial fractures type 4 occur in the outer part of the mantle garnet rims are silica inclusion free type 1 inclusions in garnet cores represent the low p low t precursor stage to uhpm recrystallization and attest to the persistence of low p assemblages in the coesite stability field coesites in inclusion types 2 3 and 4 are interpreted to have sequentially crystallized by net transfer reaction kyanite talc garnet coesite h2o and were sequestered within the garnet with progressively decreasing amounts of intragranular aqueous fluid during the retrograde evolution of the rock all three inclusion types diverged from the host garnet p t path at the coesite quartz equilibrium and followed a trajectory parallel to the equilibrium boundary resulting in inclusion overpressure coesite in type 2 inclusions suffered rapid intragranular h2o catalysed transformation to quartz and ruptured the host garnet at about 600 c when inclusion p 27 kbar garnet host p 9 kbar instantaneous decompression to the host garnet p t path passed through the kyanite talc chlorite quartz reaction equilibrium resulting in the dusty micro assemblage in inclusion cores type 3 inclusions suffered a lower volumetric proportion transformation to quartz at the coesite quartz equilibrium and finally underwent rupture and decompression when t 400 c facilitating coesite preservation type 4 coesite inclusions are interpreted to have suffered minimal transformation to quartz and proceeded to surface temperature conditions along or near the coesite quartz equilibrium boundary

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

a comparison of the evolution of diamondiferous quartz rich rocks from the saxonian erzgebirge and the kokchetav massif are so called diamondiferous gneisses magmatic rocks abstract the petrography and chemical composition of minerals of quartz rich diamondiferous rocks from the kokchetav massif especially the zonation of garnet were studied and compared with diamondiferous quartzofeldspathic rocks from the saxonian erzgebirge many compositional and textural features were found to be similar for instance microdiamonds are enclosed systematically in a specific intermediate growth zone of garnet in these rocks on the basis of experimental data a magmatic scenario was constructed to check if the quartz rich diamondiferous rocks are of magmatic origin by this the p t paths derived here for the kokchetav rocks and the textural observations it is concluded that the minerals of the diamondiferous rocks have crystallized from silicate melts these melts originated by anatexis of deeply submerged metasediments erzgebirge at t as high as 1200 c kokchetav massif at 50 100 c lower t and ascended from at least 200 km depth relics of the pre anatectic evolution are still present for instance as garnet cores after ascent and emplacement of the magma in deep portions of thickened continental crust kokchetav massif 45 50 km close to 800 c erzgebirge 55 60 km at 30 50 c lower t considerable quantities of white and or dark micas formed by peritectic reactions from melt for instance garnets could be resorbed at this stage and biotite grew instead after the magmatic stage retrogression took place much stronger in the kokchetav massif this was accompanied by deformation transforming broadly the magmatic texture of quartz rich diamondiferous rocks from the kokchetav massif to a gneissic texture

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

on the occurrence and boron isotopic composition of tourmaline in ultra high pressure metamorphic rocks abstract the extensive p t stability and the high chemical variability of tourmaline tur together with its common occurrence in metasediments proves its high potential for petrological and isotope geochemical studies on fluid rock interaction in subduction and collision related rocks this paper reviews the occurrence major element chemistry and boron isotopic composition of tur in high and ultrahigh pressure metamorphic uhpm rocks in addition it presents a new discovery of coesite bearing tur schorl from the erzgebirge germany as well as tur dravite related to the retrograde history of coesite and diamond bearing rocks from the erzgebirge and the kokchetav massif kazakhstan the scarce data on worldwide occurrences of u hpm tur reveal a high occupation of the crystallographic x site dominated by na and the possible presence of excess b with little further distinctiveness in its major element composition when compared with tur from medium grade rocks high k 2 o contents in tur are probably not related to uhp growth or equilibration the b isotopic composition of u hpm tur ranges in 11 b from 16 to 1 with many samples in or below the range of continental crust in contrast tur formed during retrograde fluid influx typically shows high 11 b values up to 28 suggesting heavy b fluids infiltrating the exhuming u hpm units coesite inclusions in tur characterized by raman spectroscopy are regarded as the best indicator for its uhp stability supplementary material analytical methods tourmaline compositions and boron isotope values are available at http www geolsoc org uk sup18354

metamorphic evolution of diamond bearing and associated rocks from the kokchetav massif northern kazakhstan representative diamond bearing gneisses and dolomitic marble eclogite and ti clinohumite bearing garnet peridotite from unit i at kumdy kol and whiteschist from unit ii at kulet eastern kokchetav massif northern kazakhstan were studied diamond bearing gneisses contain variable assemblages including grt bt qtz pl kfs zo chl tur cal and minor ap rt and zrn abundant inclusions of diamond graphite chlorite or calcite phengite clinopyroxene k feldspar biotite rutile titanite calcite and zircon occur in garnet diamond bearing dolomitic marbles consist of dol di grt phl inclusions of diamond dolomite graphite biotite and clinopyroxene were identified in garnet whiteschists carry the assemblage ky tlc grt rt garnet shows compositional zoning and contains abundant inclusions of talc kyanite and rutile with minor phlogopite chlorite margarite and zoisite inclusions and zoning patterns of garnet delineate the prograde p t path inclusions of quartz pseudomorphs after coesite were identified in garnet from both eclogite and gneiss other ultrahigh pressure uhp indicators include na bearing garnet up to 0 14 wt na2o with omphacitic cpx in eclogite occurrence of high k diopside up to 1 56 wt k2o and phlogopite in diamond bearing dolomitic marble and cr bearing kyanite in whiteschist these uhp rocks exhibit at least three stages of metamorphic recrystallization the fe mg partitioning between clinopyroxene and garnet yields a peak temperature of 800 1000 c at p 40 kbar for diamond bearing rocks and about 740 780 c at 28 35 kbar for eclogite whiteschist and ti bearing garnet peridotite the formation of symplectitic plagioclase amphibole after clinopyroxene and replacement of garnet by biotite amphibole or plagioclase mark retrograde amphibolite facies recrystallization at 650 680 c and pressure less than about 10 kbar the exsolution of calcite from dolomite and development of matrix chlorite and actinolite imply an even lower grade greenschist facies overprint at c 420 c and 2 3 kbar a clockwise p t path suggests that supracrustal sediments together with basaltic and ultramafic lenses apparently were subjected to uhp subduction zone metamorphism within the diamond stability field tectonic mixing may have occurred prior to uhp metamorphism at mantle depths during subsequent exhumation and juxtaposition of many other tectonic units intense deformation chaotically mixed and mylonitized these lithotectonic assemblages

hydrothermal alteration stable isotopes and fluid inclusions of the golden cross epithermal gold silver deposit waihi new zealand the golden cross epithermal gold silver deposit is located 120 km north of presently active geothermal systems of the taupo volcanic zone in the waihi district coromandel peninsula new zealand gold and silver of economic grades 1 20 g metric ton equiv gold over 7 million metric tons occur in zones dominated by quartz reefs veins and silicified hydrothermal breccias with adularia common in these zones the highest precious metal concentrations occur in an inferred fluid up flow zone gold and silver are thought to have precipitated from cooling hydrothermal fluid largely of meteoric origin in direct response to hydraulic fracturing and subsequent boiling alteration minerals are dominated by clay quartz adularia calcite and pyrite hydrothermal clays show a distinct zonation with the sequence smectite interstratified illitesmectite illite and chlorite corresponding to a regional increase in temperature with depth kaolinite overprints the above mineral assemblage to at least 400 m below the present ground surface quartz and adularia appear to be good indicators of high permeability in the past whereas bladed calcite indicates local boiling fluid permeability was enhanced by repeated hydraulic fracturing alkali chloride fluids with near neutral ph were responsible for the dominant alteration described above whereas the downward percolation of a near surface acid sulfate fluid as hydrothermal activity waned precipitated kaolinite or hematite or jarosite fluid inclusion studies reveal that in main stage quartz type i liquid rich inclusions with an average t h of 200 degrees c and t sub m ice of 0 5 degrees to 1 6 degrees c are dominant type i inclusions within late precipitated calcite show a t h decrease from 210 degrees to 150 degrees c from the center to the periphery of a large calcite body early type ia liquid rich inclusions within quartz have a t h 350 degrees c and t sub m ice values of 7 degrees to 10 2 degrees c type ii vapor rich and type iii two liquid vapor rich inclusions within quartz with a t h 270 degrees c have t sub m ice values typically from 25 4 degrees to 29 7 degrees c type iii inclusions have not previously been described from epithermal deposits in new zealand and possibly contain organic liquid s oxygen isotopes of hydrothermal quartz exhibit distinct horizontal and vertical gradients in an east west cross section through the deposit the delta 18 o smow values from 7 0 to 11 7 per mil are inferred to represent a gradient in permeability variable water rock ratios with higher fluid flowthrough in the west of the cross section where precious metals are concentrated calcite delta 18 o smow values of 5 2 to 7 8 per mil combined with fluid inclusion homgenization temperatures are consistent with a model whereby calcite was precipitated late and over a relatively short period of time calculated values of delta 18 o smow of water for main stage quartz and late phase calcite indicate a meteoric source of 5 to 6 per mil for the hydrothermal water values for delta 34 s cdt from hydrothermal pyrite of 1 4 to 4 8 per mil reflect in part late acid sulfate fluid alteration assemblages inferred fluid compositions temperature apparent salinity and water isotopic compositions of the golden cross epithermal gold silver deposit are analogous to those for some active geothermal systems of the taupo volcanic zone golden cross may thus have been a part of a much larger geothermal system not unlike those of the zone today

alteration mineralogy of home plate and columbia hills formation conditions in context to impact volcanism and fluvial activity the mars exploration rover spirit investigated the igneous and alteration mineralogy and chemistry of home plate and its surrounding deposits here we focus on using thermochemical modeling to understand the secondary alteration mineralogy at the home plate outcrop and surrounding columbia hills region in gusev crater at high temperatures 300 c magnetite occurs at very high w r ratios but the alteration assemblage is dominated by chlorite and serpentine over most of the w r range quartz epidote and typical high t phases such as feldspar pyroxene and garnet occur at low w r at epithermal temperatures 150 c hematite occurs at very high w r a range of phyllosilicates including kaolinite nontronite chlorite and serpentine are precipitated at specific w r amphibole with garnet feldspar and pyroxene occur at low w r if the co2 content of the system is high the assemblage is dominated by carbonate with increasing amounts of an sio2 phase kaolinite carpholite and chlorite with lower w r at temperatures of hydrous weathering 13 c the oxide phase is goethite silicates are chlorite nontronite and talc plus an sio2 phase in the presence of co2 the mineral assemblage at high w r remains the same and only at low w r i e with increasing salinity carbonate precipitates the geochemical gradients observed at home plate are attributed to short lived initially high 300 c temperature but fast cooling events which are in agreement with our models and our interpretation of a multistage alteration scenario of home plate and gusev in general alteration at various temperatures and during different geological processes within gusev crater has two effects both of which increase the habitability of the local environment precipitation of hydrous sheet silicates and formation of a brine which might contain elements essential for life in diluted easily accessible form

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

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

the evolution of the waiotapu geothermal system new zealand based on the chemical and isotopic composition of its fluids minerals and rocks abstract the waiotapu geothermal system is hosted by silicic rocks of the taupo volcanic zone new zealand exploration drilling in the late 1950s down to 1100 m provided physical information on the system measured temperatures show a boiling profile to 295 c with shallow inversions particularly in the north total discharge fluid samples were collected the geothermometry and measured temperatures show that fluids derive mainly from a shallow 400 m deep reservoir at about 225 c petrologic study of drillcore samples recovered from seven wells reveals an alteration assemblage of quartz and albite adularia with a variable distribution of chlorite pyrite calcite zeolites epidote pyrrhotite sphene leucoxene apatite and minor base metal sulfides white mica is a late overprint particularly well developed at shallow depths surficial alteration of kaolin cristobalite alunite and smectite clays reflect alteration by acid sulfate steam heated waters the activities of components in minerals determined from microprobe analyses and composition activity relations and fluids speciated to reservoir conditions indicate equilibrium now exists between the fluids and white mica the na k ratio of the fluid is being controlled by dissolution of albite and adularia while its h 2 h 2 s ratio is buffered by pyrite replacing pyrrhotite the fluids are now slightly undersaturated with respect to calcite the present deep fluids boil adiabatically from at least 300 c to 230 c at depths of 500 m this ascending chloride fluid is variably diluted by a steam heated water of zero chloride that lies over and occurs on the margin of the system like a discontinuous umbrella the steam heated water is relatively co2 rich 0 1 m the cooling at shallow levels by this mixing has shifted the alteration from albite adularia stability to white mica stability this shift is enhanced by the co2 rich nature of the diluent dilution of ascending chloride fluids by shallow waters is also supported by the oxygen and hydrogen isotopic composition of the mixture with the deep fluid being enriched in 18o and d from local meteoric by 7 and 10 respectively the patterns in whole rock 18o indicate that they were largely shifted in isotopic composition prior to incursion of steam heated waters possibly induced by a series of hydrothermal eruptions 900 years ago in contrast the 18o composition of late vug calcite indicates its formation is related to the initial incursion of steam heated groundwater and subsequent cooling this is supported by fluid inclusion evidence the d shift from local groundwater composition and the 13c composition of co2 determined from calcite 4 to 6 may be evidence for a magmatic input to the meteoric convection cell the shallow portion of the waiotapu geothermal system has recently evolved both chemically and physically by incursion of fluids from a steam heated carapace continued refluxing of these relatively cool hybrid fluids progressively deeper with their recycled co2 content will hasten hydrolytic leaching in contrast to a single pass of adiabatically cooling deep fluids this action accompanied by argillic alteration may eventually seal the deeper portions of the system hastening its demise there is evidence for similar events occurring in the fossil environment at epithermal depths

have olivine will gas serpentinization and the abiogenic production of methane on mars 1 spatial variability of methane ch4 on mars suggests the presence of localized subsurface sources here we show that olivine hydration in the martian regolith and crust may be a major ch4 source which contributed significantly to the warming of early mars methane production is kinetically and thermodynamically favored during low t aqueous alteration of olivine rich rocks sustained release of ch4 on present day mars may come through the breakdown of ancient ch4 hydrates and from springs driven by geothermal heat

whole rock geochemical techniques for evaluating hydrothermal alteration mass changes and compositional gradients associated with epithermal au ag mineralization volcanic rocks hosting quartz calcite adularia illite epithermal deposits undergo elemental mass changes associated with k metasomatism k h metasomatism and h metasomatism that are developed progressively upward and outward from the site of mineralization as hydrothermal fluid ascends boils and cools resultant hydrothermal mineral zonation shows increasingly k rich mineral assemblages with proximity to deposits thus patterns of k enrichment provide a vector toward those deposits we describe whole rock geochemical techniques for identifying these patterns and for evaluating attendant hydrothermal mineral zonation whole rock geochemical anomalies are evaluated by calculating mass changes associated with hydrothermal alteration using a modified version of gresens 1967 equation to compare the composition of altered rocks to fresh rock equivalents hydrothermally altered rocks most affected by k metasomatism will be characterized by the largest k gains and generally na and ca losses mass changes associated with k metasomatism are also evaluated graphically using plots of molar 2ca na k al versus molar k al since molar values are used to construct the plot compositions of altered rocks can be compared to the compositions of primary and secondary k na ca and al bearing minerals that are located in the same compositional space allowing identification of important hydrothermal minerals e g adularia illite smectite and alteration processes that are reflected in trends from fresh rock compositions toward the compositions of hydrothermal minerals the intensity of k metasomatism encompassing both k gains and na and ca losses can be represented by the slope of the line between an altered rock composition and the origin i e the molar k 2ca na k value determinations of mass changes in altered rocks surrounding selected epithermal deposits demonstrate the predominance of k metasomatism proximal to and commonly increasing in intensity toward mineralized veins comparisons of k mass changes to trace element concentrations indicate that the area affected by k metasomatism is more extensive 100s to 1 000s of meters than that containing anomalous concentrations of precious metals base metals and pathfinder elements 10s to 100s of meters therefore whole rock geochemical techniques potentially extend the area over which geochemical targeting may be effective data from this study show that intensity of k metasomatism molar k 2ca na k values and concentrations of precious metals and pathfinder elements increase toward ore and are greatest proximal to ore so that pathfinder element and whole rock geochemical anomalies are complementary

carbon sequestration on mars on earth carbon sequestration in geologic units plays an important role in the carbon cycle scrubbing co 2 from the atmosphere for long term storage while carbonate is identified in low abundances within the dust and soils of mars at 1 wt in select meteorites and in limited outcrops no massive carbonate rock reservoir on mars has been identified to date here we investigate the largest exposed carbonate bearing rock unit the nili fossae plains combining spectral thermophysical and morphological analyses to evaluate the timing and carbon sequestration potential of rocks on mars we find that the olivine enriched 20 25 basalts have been altered by low temperature in situ carbonation processes to at most 20 fe mg carbonate thus limiting carbon sequestration in the nili fossae region to 0 25 12 mbar of co 2 during the late noachian early hesperian before or concurrent with valley network formation while this is large compared to modern day co 2 reservoirs the lack of additional comparably sized post late noachian carbonate bearing deposits on mars indicates ineffective carbon sequestration in rock units over the past 3 7 b y this implies a thin atmosphere 500 mbar during valley network formation extensive post noachian atmospheric loss to space or diffuse deep sequestration by a yet to be understood process in stark contrast to earth s biologically mediated crust atmosphere carbon reservoir ratio of 10 4 10 5 mars ratio is a mere 10 10 3 even if buried pre noachian crust holds multiple bars

regional 18o depletion of neoproterozoic igneous rocks from avalonia cape breton island and southern new brunswick canada neoproterozoic igneous rocks of the avalonian mira terrane cape breton island and caledonia terrane southern new brunswick have experienced regional 18 o depletion the majority of these rocks have 18 o wr values between 1 and 6 markedly different from igneous rocks of the inboard ganderian terranes which have normal high 18 o wr values of 7 to 12 the 18 o depletion of these avalonian terranes resulted from pervasive hydrothermal alteration all of the igneous rocks contain classic propylitic alteration assemblages of turbid feldspar chlorite epidote sericite and calcite and host multiple generations of veins containing the same phases the 18 o values of the rock forming minerals show strong disequilibrium with qtz fs ranging from 2 5 to 11 0 and kfs plg from 0 5 to 1 0 such values are indicative of post magmatic hydrothermal alteration the hydrothermal alteration occurred at ca 560 550 ma during initial transcurrent rifting of avalonia at the gondwanan margin the development of rift wrench basins with associated bimodal volcanism allowed large volumes of hydrothermal fluids to penetrate and circulate within mira and caledonia terrane crust before its submergence in the early cambrian ca 540 530 ma the hydrothermal fluids were predominantly meteoric although the presence of a significant seawater component cannot be ruled out the almost ubiquitous 18 o depletion exhibited by the neoproterozoic rocks in these avalonian terranes is absent in the associated ganderian terranes suggesting that avalonia remained separate from ganderia until at least the cambrian ordovician this 18 o depletion provides an additional geochemical tool for identification of avalonian crust in other areas of the appalachians and europe

reproducing early martian atmospheric carbon dioxide partial pressure by modeling the formation of mg fe ca carbonate identified in the comanche rock outcrops on mars 1 the well defined composition of the comanche rock s carbonate magnesite0 62siderite0 25calcite0 11rhodochrosite0 02 and its host rock s composition dominated by mg rich olivine enable us to reproduce the atmospheric co2partial pressure that may have triggered the formation of these carbonates hydrogeochemical one dimensional transport modeling reveals that similar aqueous rock alteration conditions including co2partial pressure may have led to the formation of mg fe ca carbonate identified in the comanche rock outcrops gusev crater and also in the ultramafic rocks exposed in the nili fossae region hydrogeochemical conditions enabling the formation of mg rich solid solution carbonate result from equilibrium species distributions involving 1 ultramafic rocks ca 32 wt olivine fo0 72fa0 28 2 pure water and 3 co2partial pressures of ca 0 5 to 2 0 bar at water to rock ratios of ca 500 molh2o mol 1rock and ca 5 c 278 k our modeled carbonate composition magnesite0 64siderite0 28calcite0 08 matches the measured composition of carbonates preserved in the comanche rocks considerably different carbonate compositions are achieved at 1 higher temperature 85 c 2 water to rock ratios considerably higher and lower than 500 mol mol 1 and 3 co2partial pressures differing from 1 0 bar in the model set up the comanche rocks hosting the carbonate may have been subjected to long lasting 104 to 105 years aqueous alteration processes triggered by atmospheric co2partial pressures of ca 1 0 bar at low temperature their outcrop may represent a fragment of the upper layers of an altered olivine rich rock column which is characterized by newly formed mg fe ca solid solution carbonate and phyllosilicate rich alteration assemblages within deeper unexposed units

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

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

evidence for extensive olivine rich bedrock on mars color infrared observations of an area around the nili fossae acquired by the mars odyssey thermal emission imaging system have been used to map the regional distribution and geologic context of olivine rich materials that first were identified from mars global surveyor thermal emission spectrometer data spectral thermal geomorphic and topographic data demonstrate that the majority of olivine rich material is in the form of inplace layered rock covering an area roughly four times larger than previously recognized some high olivine concentrations are associated with spatially small areas dominated by sediments we favor olivine rich basalts as the origin of the observed olivine enrichment although several hypotheses are viable

hydrothermal hydration of martian crust illustration via geochemical model calculations if hydrothermal systems existed on mars hydration of crustal rocks may have had the potential to affect the water budget of the planet we have conducted geochemical model calculations to investigate the relative roles of host rock composition temperature water to rock ratio and initial fluid oxygen fugacity on the mineralogy of hydrothermal alteration assemblages as well as the effectiveness of alteration to store water in the crust as hydrous minerals in order to place calculations for mars in perspective models of hydrothermal alteration of three genetically related icelandic volcanics a basalt andesite and rhyolite are presented together with results for compositions based on snc meteorite samples shergotty and chassigny temperatures from 150 c to 250 c water to rock ratios from 0 1 to 1000 and two initial fluid oxygen fugacities are considered in the models model results for water to rock ratios less than 10 are emphasized because they are likely to be more applicable to mars in accord with studies of low grade alteration of terrestrial rocks we find that the major controls on hydrous mineral production are host rock composition and temperature over the range of conditions considered the alteration of shergotty shows the greatest potential for storing water as hydrous minerals and the alteration of icelandic rhyolite has the lowest potential

high pressure behaviour of selected boron minerals and the question of boron distribution between fluids and rocks abstract experimental results in the simplest possible systems up to generally 20 50 kbar in a few cases 100 kbar bearing on the pt stability limits of 17 end member borosilicates and borates are summarized except for the sillimanite structure type minerals grandidierite and werdingite which break down near 10 kbar the following phases are stable up to much higher pressures and no influence of boron coordination with oxygen three or fourfold can be recognized alkali free dravite b nepheline boromuscovite danburite dravite dumortierite jeremejevite oh kotoite magnesiodumortierite prismatine pseudosinhalite reedmergnerite szaibelyite sinhalite suanite the framework borosilicates reedmergnerite and danburite remain more stable towards higher pressures than their al analogues albite and anorthite respectively kornerupine stability decreases with decreasing boron content in the mineral from about 37 kbar for near end member prismatine to 12 kbar for the boron free end member with a maximum thermal stability of 1050 c at 30 kbar boron rich kornerupine prismatine is the thermally most stable borosilicate at high pressures thus all the above 15 phases can in principle occur as minerals of ultrahigh pressure metamorphic rocks boron initially enriched in crustal rocks may be subducted to depths exceeding 100 km in al rich systems b 2 o 3 generally behaves as an inert component and enters refractory minerals so that such rocks may act as sinks for boron even in the presence of h 2 o in other systems rich sio 2 na 2 o mgo however boron is more volatile and may fractionate into hydrous fluids that may cause metasomatism elsewhere altogether the behaviour of boron in natural petrogenetic systems is strongly dependent on the local chemical environment

two populations of carbonate in alh84001 geochemical evidence for discrimination and genesis we present major and trace element oxygen isotope textural and structural data for carbonates and related phases in the snc meteorite alh84001 these data document the existence of at least two distinct carbonate populations one composed of finely zoned chemically and isotopically heterogeneous concretions of magnesio siderite with distinct white magnesite rims and a second composed of relatively homogeneous isotopically and compositionally simple domains of ankeritic carbonate and intimately intergrown glass and fine grained pyroxene we suggest on the basis of textural evidence and geochemical systematics that the first population consists of low temperature aqueous precipitates and the second is produced by shock melting of the first values of 18 o and sr ca ratios are correlated with one another in magnesio siderite concretions the trend formed by these data is consistent with the predicted relationship for inorganic precipitation of carbonate from a solution of constant composition between temperatures of 190 c for concretion cores to 20 c for magnesite rich concretion rims given the assumptions inherent in this temperature estimate the aqueous fluid parental to carbonate concretions is constrained to have a 18 o of 5 vsmow significantly mass fractionated compared with expected juvenile martian volatiles and minor element abundances broadly similar to terrestrial seawater

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

geophysical characteristics of adularia sericite epithermal gold silver deposits in the waihi waitekauri region new zealand aeromagnetic airborne radiometric and surface gravity data from the adularia sericite epithermal province of the hauraki goldfield have delineated distinct anomalies associated with pervasive hydrothermal alteration and gold silver mineralization aeromagnetic derivative images particularly the analytic signal define the boundaries of several magnetic quiet zones that result from magnetite destruction in the volcanic host rocks six discrete zones each of 10 km2 areal extent are evident and are comparable in size to modern day geothermal systems in the taupo volcanic zone an extensive 20 km2 zone in the waitekauri valley is likely to be the result of multiple overlapping systems for which there are also analogues in the taupo volcanic zone that form single large scale alteration zones up to 100 km2 low pass filtering of the analytic signal data reveals still wider zones of relatively low magnetic intensity interpreted as areas of hydrothermally altered rock extending below younger unaltered cover many of these magnetic quiet zones are aligned along a north northeast south southwest structural corridor indicating that regional scale structures may have controlled the location of these geophysical features radiometric data delineate local high potassium anomalies that reflect up to 12 100 g potassium enrichment in the core of alteration zones in the form of adularia and illite a broad k th anomaly correlates with the extent of the magnetic quiet zones and indicates widespread potassium enrichment in the waitekauri maratoto area gravity data in the waihi district define a unique double peaked 50 gravity unit positive residual anomaly that correlates closely with the extent of the magnetic quiet zone and the locations of the waihi and favona deposits preliminary modeling indicates that the anomaly source body beneath the near surface low density altered andesite has a volume of up to 11 km3 and a minimum density of 2 900 kg m 3 the nature of this source body is enigmatic possible causes include a dense intrusion uplifted anomalously dense basement dense sulfide mineralization or some combination of these in addition the correlation of each of the two gravity peaks with a north northeast trending fault may indicate some structural focusing process active at the deposit scale this integration of geophysical data provides an outstanding case study of the district to regional scale geophysical characteristics of a classic epithermal province and demonstrates the strengths of geophysical surveys in the exploration for epithermal mineral deposits

experimental constraints on phase relations in subducted continental crust synthesis piston cylinder experiments were carried out in the range 2 0 4 5 gpa and 680 1 050 c to investigate phase relations in subducted continental crust a model composition kcmash has been used because all major ultrahigh pressure uhp minerals of the whole range of rock types typical for continental crust can be reproduced within this system the combination of experimental results with phase petrologic constraints permits construction of a uhp petrogenetic grid the phase relations demonstrate that the most important uhp paragenesis consists of coesite kyanite phengite clinopyroxene and garnet in subducted continental crust below 700 c talc is stable instead of garnet as most of these minerals are also stable at much lower pressure and temperature conditions it is thus not easy to recognize uhp metamorphism in subducted crust a general feature however is the absence of feldspars at h2o saturated conditions plagioclase is never stable at uhp conditions but k feldspar can occur in h2o undersaturated rocks mineral compositions in the experiments are fully buffered by coexisting phases the si content of phengite and biotite increase with increasing pressure at 4 0 gpa 780 c biotite contains 3 28 si per formula unit which is most probably caused by solid solution of biotite with talc above 800 c the caal2sio6 component in clinopyroxene buffered with kyanite coesite and a mg phase increases with increasing temperature providing a tool to distinguish between cold and hot eclogites up to 10 ca eskolaite ca0 5 0 5alsi2o6 in clinopyroxene has been found at the highest temperature and pressure investigated 900 c 4 5 gpa garnet buffered with coesite kyanite and clinopyroxene displays an increase of grossular component with increasing pressure for a given temperature although the investigated system represents a simplification with respect to natural rocks it helps to constrain general features of subducted continental crust the observed phase relations and phase compositions demonstrate that at pressures 3 0 gpa and temperatures 800 c continental crust can retain significant amounts of h2o 1 wt whereas k free mafic or ultramafic rocks are dry at these conditions uhp parageneses are only preserved if the whole exhumation path is situated within the stability field of phengite i e if there is cooling during exhumation or if the whole exhumation occurred at t 700 c in contrast break down of phengite and concomitant partial melting in terranes that show isothermal decompression may lead to a complete recrystallization of the subducted crust during exhumation the density of uhp rocks can be estimated on the basis of the established phase relations pelitic rocks are likely to have a density close to mantle rocks 3 3 g cm3 because of significant amounts of dense garnet and kyanite whereas granitic rocks are less dense 3 0 g cm3 hence subducted average continental crust is most probably buoyant with respect to mantle rocks and tends to get exhumed as soon as it is detached from the down going slab electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00410 001 0336 3

implications for early hydrothermal environments on mars through the spectral evidence for carbonation and chloritization reactions in the nili fossae region 1 previous identification of serpentine and magnesium carbonate in the eastern nili fossae region of mars indicates hydrothermal alteration of an olivine rich protolith here we characterize fe mg phyllosilicates associated with these units and present spectral evidence for the presence of a talc component distinguishable from saponite locations with magnesium carbonate are exclusively associated with talc related phyllosilicates in the westernmost portions of the nili fossae region where a mafic protolith dominates fe mg phyllosilicates display spectral evidence for a wide degree of chloritization we propose that noachian fe mg smectites were uniformly buried by hesperian lava flows that initiated hydrothermal alteration in the eastern nili fossae region the chloritization of smectites may have produced silica rich fluids necessary for the serpentinization of olivine temperature and depth constraints indicated by their distribution also suggest a hydrothermal system was present the subsequent carbonation of serpentine and or olivine in eastern nili fossae while requiring an additional co2 source provides an explanation for the limited occurrence of serpentine and the colocation of carbonate and talc bearing material throughout this area the consequence of the hypothesized carbonation reaction and the presence of serpentine provides geochemical constraints for the proportion of co2 present in the fluids that interacted with the protolith if this carbonation reaction was a widespread phenomenon it may have been an important process in the ancient martian carbon cycle and could have provided a sink for co2 in the past

jurassic lake t oo dichi a large alkaline saline lake morrison formation eastern colorado plateau a large alkaline saline lake lake t9oo9dichi9 occupied the entire eastern part of the colorado plateau region during deposition of the brushy basin member of the upper jurassic morrison formation the lake extended from near the site of albuquerque new mexico to near the site of grand junction colorado and occupied a region that encompassed the san juan and ancestral paradox basins making it the largest ancient alkaline saline lake known the lake was typically shallow and frequently evaporated to dryness although the water table was probably never far beneath the surface intermittent streams carried detritus from source areas to the west and southwest far out into the lake basin a reflection of a low depositional gradient and the ephemeral nature of the lake prevailing westerly winds carried silicic volcanic ash to the lake basin from an arc region to the west and southwest a lateral hydrogeochemical gradient characterized by increasing salinity and alkalinity from the margin of the lake to the center developed in pore waters of the lacustrine sediments and resulted in alteration of the ash to a variety of authigenic minerals that define concentric zones within the lake basin the basinward progression of diagenetic mineral zones is smectite clinoptilolite analcime potassium feldspar albite a concomitant lateral zonation of mixed layer illite smectite developed from highly smectitic in the outermost zones to highly illitic in the central zone authigenic albite and illitic mixed layer clay minerals previously thought to require elevated temperatures for formation crystallized during early diagenesis at syndepositional temperatures in the lacus trine sediments of lake t9oo9dichi9 this study presents evidence for a syndepositional origin for both of these minerals these findings have important implications in terms of limiting the use of these minerals as geothermometers recognition of alkaline saline lake deposits in the morrison formation significantly alters interpretations of depositional environments of this formation and it also has important implications for paleoclimatic interpretation late jurassic climate was apparently much more and than had previously been thought in fact sedimentologic evidence suggests that the lake basin was typically dry for extended periods and enjoyed only brief wet intervals this conclusion has important consequences for environmental interpretation of the habitat that was favorable for large herbivorous dinosaurs which thrived in the late jurassic

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

discovery of olivine in the nili fossae region of mars we have detected a 30 000 square kilometer area rich in olivine in the nili fossae region of mars nili fossae has been interpreted as a complex of grabens and fractures related to the formation of the isidis impact basin we propose that post impact faulting of this area has exposed subsurface layers rich in olivine linear mixture analysis of thermal emission spectrometer spectra shows surface exposures of 30 olivine where the composition of the olivine ranges from fo30 to fo70

the geothermobarometric potential of tourmaline based on experimental and natural data the geothermobarometric potential of tourmaline has been assessed by investigating element exchange among tourmaline and coexisting minerals in metamorphosed pelites and graywackes and in experimental exchange between tourmaline and biotite in the natural samples a temperature dependence of tourmaline mg fe exchange with biotite staurolite garnet chlorite and muscovite and ca na exchange with plagioclase is observed equilibrium calculations for the complete mineral assemblage show that tourmaline is in compositional equilibrium with all coexisting phases which would allow for an internally consistent set of thermometers among all these phases to be defined however a prohibitively large spread is present in the k d vs t relations this is not caused by analytical effects compositional zoning or disequilibrium among the minerals the experimental results show that it is the result of inter site partitioning of elements over the y and z octahedral sites of tourmaline variations in the element distribution over these sites their relative participation in the exchange and differences in the temperature dependence of exchange with each site strongly affects the k d vs t relation observed with the slope actually changing sign depending on the elements residing at each site non ideal interactions among the elements at each site will also affect this and furthermore link every exchange to the bulk tourmaline composition and hence the element mobility in the rock the promising potential of tourmaline geothermobarometry can therefore not be fulfilled until effects of inter site partitioning and non ideal interactions are known

using a mineral lifetime diagram to evaluate the persistence of olivine on mars we present a diagram that shows the effect of ph temperature grain size composition hydrodynamics and the laboratory field discrepancy on the lifetime of olivine grains in weathering environments because the persistence of olivine grains on mars can be used to constrain the duration of liquid water we can use this diagram to predict a range of possible maximum contact times for olivine grains with liquid water before they dissolve away completely depending upon the physicochemical conditions this contact time could range between a few thousand and several million years

the favona epithermal gold silver deposit waihi new zealand the favona deposit is a new epithermal vein discovery 595 000 oz au 2 367 500 oz ag resource located less than 2 km east of the world class martha deposit 6 7 million oz au 42 1 million oz moz ag in the hauraki goldfield of new zealand the concealed favona vein is hosted in late miocene andesitic lava flows and occurs to the east of the nearby historically mined silverton amaranth mascotte and union veins hydrothermal alteration is characterized by a variety of alteration minerals that display distinct zonation along four subsurface cross sections 800 m long 450 m deep that transect the favona cowshed and amaranth veins hydrothermal quartz and pyrite are ubiquitous adularia is widespread and envelopes veins it locally coexists with hydrothermal albite adjacent to the amaranth vein at depth both adularia and albite are variably replaced by illite which together with broadly coextensive chlorite are generally restricted to the foot wall of the favona and cowshed veins although both minerals appear locally at depth in the hanging wall interstratified illite smectite containing 10 to 70 percent smectite and rare discrete smectite are mostly confined to the hanging wall of the favona and cowshed veins late stage kaolinite cristobalite and rare alunite locally overprint the above minerals at shallow levels whereas late stage overprinting calcite occurs at depth near the amaranth cowshed and southern portion of the favona veins aeromagnetic data show that the favona and martha deposits both fit within a broad zone of hydrothermally induced demagnetization that is approximately 3 7 3 0 km alteration is broadly similar at each deposit although albite and calcite are more abundant at martha fluid inclusion data indicate that both the favona and martha deposits formed at similar levels with veins developed over extensive vertical intervals exceeding 400 and 600 m respectively based on these data we propose that the veins comprising the favona and martha deposits formed at similar shallow levels 1 km in a single paleogeothermal system it is unclear if the martha and favona veins systems formed within a single upflow zone a migrating upflow or within two separate upflow zones regardless widespread alteration surrounding the veins includes quartz adularia albite chlorite illite plus pyrite and reflects formation from alkali chloride waters that contained moderate concentrations of aqueous co2 focused and episodic boiling of these chloride waters along extensive open conduits resulted in the formation of gold and silver bearing colloform and crustiform banded quartz veins steam heated waters formed above and on the margins of the paleogeothermal system and during the eventual thermal collapse resulted in overprinting by kaolinite cristobalite and alunite from descending steam heated acid sulfate waters and late calcite from localized steam heated co2 rich waters the discovery of the favona deposit next to the large martha deposit highlights the importance of determining the physical limits of hydrothermal alteration in a system in order to identify the limits of paleogeothermal activity and define the area that may be explored for veins the veins at favona martha and golden cross empire vein combined with a resource at karangahake collectively total more than 3 5 moz au and should encourage the exploration of known epithermal deposits throughout the hauraki goldfield for additional resources

mineralogy of the volcanic influenced great northern coal seam in the sydney basin australia abstract the mineralogy of the individual coal plies and intra seam claystone bands in the great northern seam of the sydney basin has been evaluated using optical and scanning electron microscopy and quantitative x ray diffraction techniques the uppermost two claystone bands are tonsteins consisting mainly of well ordered kaolinite with graupen to vermicular textures idiomorphic crystals of k feldspar within these tonsteins may represent members of the anorthoclase sanidine series or a sodic sanidine and indicate an acid to intermediate volcanic ash input in contrast the lowermost parting was largely derived from epiclastic sediment admixed with minor volcanic material such as high temperature quartz and a different type of k feldspar component the mineral fraction of the coals especially in the middle and upper parts of the seam is dominated by authigenic kaolinite with a very low abundance of quartz apart from the tonsteins authigenic processes therefore appear to be the dominant mechanism of mineral matter formation authigenic k feldspar also occurs in the lower few metres of the seam with a variety of modes of occurrence including cell and cleat infillings cross cutting veins and thin laminae parallel to the organic matter and detrital clay bands a late syngenetic low temperature hydrothermal fluid injection process is suggested for formation of the feldspar veins the origin of the fluid is uncertain but is most likely associated with contemporaneous volcanic activity

orbital evidence for more widespread carbonate bearing rocks on mars carbonates are key minerals for understanding ancient martian environments because they are indicators of potentially habitable neutral to alkaline water and may be an important reservoir for paleoatmospheric co 2 previous remote sensing studies have identified mostly mg rich carbonates both in martian dust and in a late noachian rock unit circumferential to the isidis basin here we report evidence for older fe and or ca rich carbonates exposed from the subsurface by impact craters and troughs these carbonates are found in and around the huygens basin northwest of hellas in western noachis terra between the argyre basin and valles marineris and in other isolated locations spread widely across the planet in all cases they cooccur with or near phyllosilicates and in huygens basin specifically they occupy layered rocks exhumed from up to 5 km depth we discuss factors that might explain their observed regional distribution arguments for why carbonates may be even more widespread in noachian materials than presently appreciated and what could be gained by targeting these carbonates for further study with future orbital or landed missions to mars

fluids during diagenesis and sulfate vein formation in sediments at gale crater mars we model the fluids involved in the alteration processes recorded in the sheepbed member mudstones of yellowknife bay ykb gale crater mars as revealed by the mars science laboratory curiosity rover investigations we compare the gale crater waters with fluids modeled for shergottites nakhlites and the ancient meteorite alh 84001 as well as rocks analyzed by the mars exploration rovers and with terrestrial ground and surface waters the aqueous solution present during sediment alteration associated with phyllosilicate formation at gale was high in na k and si had low mg fe and al concentrations relative to terrestrial groundwaters such as the deccan traps and other modeled mars fluids and had near neutral to alkaline ph ca and s species were present in the 10 3 to 10 2 concentration range a fluid local to gale crater strata produced the alteration products observed by curiosity and subsequent evaporation of this groundwater type fluid formed impure sulfate and silica rich deposits veins or horizons in a second separate stage of alteration partial dissolution of this sulfate rich layer in yellowknife bay or beyond led to the pure sulfate veins observed in ykb this scenario is analogous to similar processes identified at a terrestrial site in triassic sediments with gypsum veins of the mercia mudstone group in watchet bay uk

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

coesite exsolution from supersilicic titanite in uhp marble from the kokchetav massif northern kazakhstan coesite exsolved from supersilicic titanite was discovered in an impure calcite marble at kumdy kol in the kokchetav uhp ultrahigh pressure metamorphic terrane northern kazakhstan this impure marble consists mainly of calcite k feldspar diopside and symplectites of diopside zoisite with minor amount of titanite phengite and garnet no diamond was found in the marble coesite and quartz which have needle or platy shapes measuring about 20 60 m in length occur as major exsolved phases in the cores and mantles of titanite crystals with minor calcite and apatite the strongest raman band for the coesite needles and plates was confirmed at about 524 cm 1 with a weak band at about 271 cm 1 to estimate the initial composition of the titanite before coesite exsolution exsolved phases were reintegrated by measuring their area fractions on digital images the highest excess si in titanite was thus determined to be 0 145 atoms per formula unit apfu this composition requires a pressure higher than 6 gpa on the basis of phase relations in the system catisio5 casi2o5 this pressure is consistent with other evidence of high pressure in the same marble such as 1 4 1 8 wt k2o and over 1000 ppm h2o in diopside supersilicic titanite and coesite exsolution also indicate that sio2 exsolution occurred in the coesite stability field during exhumation of the uhp metamorphic unit