experimental determination of the compositional limits of immiscibility in the system cacl2h2oco2 at high temperatures and pressures using synthetic fluid inclusions abstract using the synthetic fluid inclusion method the temperature pressure and compositional limits of fluid immiscibility in the binary system cacl 2 h 2 o have been determined at 600 and 700 c at pressures between 1 and 2 kbar the limits of the immiscible regions were determined by observation of two different inclusion types in the samples and by measurements of the depression of ice melting temperatures the region of immiscibility in this system extends to much higher pressures than that of the nacl h 2 o system with similar compositional ranges a similar study was done on the cacl 2 h 2 o co 2 system at 500 600 and 700 c at pressures of 1 1 5 2 and 3 kbar in the ternary system the presence of two different inclusion types and the measurement of clathrate melting temperatures were used to delineate the compositional regions of immiscibility the presence of co 2 extends the regions of immiscibility shown in the binary system study to much higher pressures tie lines in the two phase regions were determined by measuring the homogenization temperatures of co 2 vapor and liquid phases and the volume ratios of inclusion bubble to total inclusion in vapor rich type inclusions the locations of these tie lines indicate that the cacl 2 is heavily partitioned towards the more liquid rich phase the experimental results show that with even relatively small amounts of a divalent salt such as cacl 2 immiscibility can exist to very high temperatures and pressures from these results immiscibility should be a very common phenomenon in geologic processes ranging from sedimentary to quite high grade metamorphic environments and that it should have a very important effect on reactions between hydrothermal fluids and rocks and the resulting mineral assemblages

recent developments in element concentration and isotope ratio analysis of individual fluid inclusions by laser ablation single and multiple collector icp ms abstract laser ablation inductively coupled plasma mass spectrometry la icp ms has become a most powerful technique for the elemental analysis of individual polyphase inclusions completely enclosed in minerals be they solid or a solid liquid gas mixture at the time of measurement simultaneous accurate quantification of major to ultra trace element concentrations from li to u by well controlled ablation of the entire fluid or melt inclusion content and successful use of largely matrix independent external calibration protocols are unique features of this method this contribution reviews fluid inclusion fundamentals relevant for their bulk analysis by la icp ms and discusses key aspects of the analytical protocol emphasis is on figures of merit precision accuracy obtained from the analysis of individual inclusions and fluid inclusion assemblages and procedures and technical developments to improving data quality are elaborated a new equation for the calculation of detection limits for la icp ms analysis is presented which closely follows iupac conventions applications are reviewed with emphasis on the use of synthetic fluid inclusions in constraining metal solubility and distribution between co existing phases new data for natural bismuth fluid inclusions document the seamless transition to melt inclusion analysis by la icp ms thus highlighting the fact that the procedures presented here are generally applicable to the analysis of inclusions in complex host minerals isotope ratio analysis of individual fluid inclusions by multicollector icp ms mc icp ms is a recent development that requires fast transient signals to be accurately recorded by instrumentation designed for high precision static measurements of long lasting stable ion beams we address the general principles based on pb isotopes and review a first application to the bingham canyon porphyry cu au mo deposit a pilot study using about 50 synthetic fluid inclusions containing srm 987 sr and variable nacl ca and rb concentrations demonstrates that accurate 87 sr 86 sr isotope ratios can be obtained on an individual rb poor fluid inclusion at absolute 2 precisions of 0 0003 to 0 002 a residual trend in 87 sr 86 sr as a function of the rb sr abundance ratio in the fluid inclusions suggests that interference correction of 87 rb on mass 87 assuming identical mass bias coefficients for the two elements may be inaccurate however the offset can be accurately corrected for by regressing the data to zero 87 rb the versatility and detection power of la icp ms makes this technique the method of choice for solute abundance and isotope ratio analysis of individual fluid inclusions significant future progress can be achieved by improvements in ion production transmission and data recording efficiency and by further improving control on inclusion ablation by pulsed laser beams data quantification strategies may also have to be further refined to keep pace with instrumental progress and innovation

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

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

the partitioning behavior of silver in a vapor brine rhyolite melt assemblage abstract the partitioning of silver in a sulfur free rhyolite melt vapor brine assemblage has been quantified at 800 c pressures of 100 and 140 mpa and f o 2 nno nickel nickel oxide silver solubility 2 in rhyolite increases 5 fold from 105 21 to 675 98 g g as pressure increases from 100 to 140 mpa nernst type partition coefficients d ag i j 2 describing the mass transfer of silver at 100 mpa between vapor and melt brine and melt and vapor and brine are 32 30 1151 238 and 0 026 0 004 respectively at 140 mpa values for d ag i j 2 for vapor and melt brine and melt and vapor and brine are 32 10 413 172 and 0 06 0 03 respectively apparent equilibrium constant values 2 describing the exchange of silver and sodium between vapor and melt k ag na v m at 100 and 140 mpa are 105 68 and 14 6 the average values 2 for silver and sodium exchange between brine and melt k ag na b m at 100 and 140 mpa are 313 288 and 65 12 these data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase s is enhanced at 100 mpa relative to 140 mpa suggesting that decompression increases the silver ore generative potential of an evolving silicate magma model calculations using the new data suggest that the evolution of low density aqueous fluid i e vapor may be responsible for the the silver tonnage of many porphyry type and perhaps epithermal type ore deposits for example halter et al halter w e pettke t and heinrich c a 2002 the origin of cu au ratios in porphyry type ore deposits science 296 1842 1844 used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km3 to satisfy the copper budget at the bajo de la alumbrera copper gold silver ore deposit using their melt volume estimate with the data presented here model calculations for a 15 km3 felsic melt saturated with pyrrhotite and magnetite suggest that a low salinity magmatic vapor may scavenge on the order of 7 1012 g of silver from the melt this quantity of silver exceeds the discovered 2 109 g of ag at alumbrera calculated tonnages for numerous other deposits yield similar results the excess silver in the vapor remaining after porphyry formation is then available to precipitate at lower ptconditions in the stratigraphically higher epithermal environment these data suggest that silver and perhaps other ore metals in the porphyry epithermal continuum may be derived solely from the time integrated flux of dominantly low salinity vapor exsolved from a series of sequential magma batches

the engineer mine british columbia an example of epithermal au ag mineralization with mixed alkaline and subalkaline characteristics abstract the engineer mine epithermal precious metal deposit in british columbia canada is related to eocene sloko skukum group ssg volcanism and according to previous studies contains roscoelite in intimate association with electrum roscoelite a vanadian mica is considered characteristic of low sulfidation epithermal deposits related to alkaline magmatism this contradicts the fact that the ssg volcanics are subalkaline in order to address this ambiguity and to accurately classify the style of epithermal mineralization at the engineer mine we conducted detailed petrographic mineralogical geochronological fluid inclusion and stable isotope studies the principal ore assemblage of the engineer mine epithermal veins precipitated in response to boiling during a hydrothermal event at 49 90 ma 0 25 ma during this event electrum arsenopyrite pyrite chalcopyrite sphalerite lollingite tetrahedrite group phases allargentum acanthite hessite dyscrasite stibarsen galena and an unidentified ag rich phase were deposited in conjunction with amorphous silica platy and rhombic calcite k feldspar and vanadian illite fluid inclusion and stable isotope data suggest that the ore forming fluid was boiling at 220 c during vein mineralization and had an isotopic composition derived from local meteoric water based on these results the engineer mine is classified as an epithermal low sulfidation deposit which shares similarities with alkaline and subalkaline epithermal low sulfidation deposits this is attributed to the fact that the ssg volcanic rocks are borderline subalkaline to alkaline in character and that the sedimentary host rocks are vanadium bearing these sedimentary rocks contributed the bulk of the vanadium to the engineer mine epithermal system the presence of roscoelite at the engineer mine could not be confirmed during this study the mica referred to as roscoelite in previous publications instead is vanadian illite to our knowledge the only alkaline low sulfidation epithermal precious metal deposit that contains v mica which exclusively qualifies as true roscoelite is the porgera deposit papua new guinea

fluid inclusion evidence of basinal brines in archean basement thunder bay pb zn ba district ontario canada fluid inclusions from three quartz galena sphalerite barite calcite veins in the thunder bay district of western ontario contain liquid vapor halite and homogenize by vapor disappearance or halite dissolution at temperatures of 90 200 c cyclically frozen liquid vapor type i inclusions undergo four melting events upon gradual warming initial melting at 55 to 46 c ice disappearance at 30 2 to 25 4 c inversion of hydrohalite to halite at 8 0 to 0 7 c and halite melting at 14 0 to 56 3 c liquid vapor halite type ii inclusions behave similarly but have higher t m ice 27 2 to 21 7 c and t m halite 105 203 c scanning electron microscopy and energy dispersive analysis of fluid inclusion derived decrepitates indicate that the solutes consist of nacl cacl 2 kcl and are consistent with the low temperature phase observations in that they define two distinct populations based on cacl 2 cacl 2 nacl ratios the temperatures and compositional trends defined by the inclusion results are similar to those documented for basinal brines and from fluid inclusions in mississippi valley type ore deposits the thunder bay veins cross the basal unconformity of the middle proterozoic sibley basin and extend into archean basement granites such that the fluid inclusions results provide direct evidence that basinal waters infiltrated basement rock in western ontario the inclusion fluids and associated mineralization are thought to result either from dewatering of the sibley basin during keweenaw age rifting or from the introduction of exotic paleozoic basinal waters when the michigan basin extended over the region

synthetic h2oco2 fluid inclusions in spontaneously nucleated forsterite enstatite and diopside hosts the method and applications abstract synthetic h2o co2 fluid inclusions have been produced in forsterite diopside and enstatite hosts during the spontaneous nucleation and growth of these phases at t 800 980 c and p 6100 7800 bars via the reactions 2 trem 18h 2 o 4 diopside 3 forsterite 5si oh 4 2h 2 o 1 trem 3h 2 o 2 diopside 3 enstatite si oh 4 2h 2 o 2 the inclusions are large 10 40 m abundant and commonly of regular shape making them ideal as standards for microthermometric and spectroscopic analyses the technique provides the opportunity to study fluid inclusion trapping mechanisms and their potential effect on inclusion chemistry the fluid inclusions exhibit a small degree of compositional scatter about the ambient composition deviations between the ambient and inclusion composition increase for experiments performed in the presence of low 3 8 c thermal gradients along the capsule length this observation suggests that compositional heterogeneities may develop in the absence of fluid convection in the capsule the effect on the inclusion composition however does not exceed 3 mol in xco2 for all inclusions studied the advantages of this technique are 1 it provides a means of producing fluid inclusions of known compositions in hosts other than quartz and 2 inclusion formation is relatively slow allowing ample time for the p t x fluid conditions of the run to equilibrate the disadvantages are that the small grains produced can be difficult to work with and the host producing reactions are viable over a relatively narrow range of p t x fluid conditions

fluid overpressure along an oligocene out of sequence thrust in the shimanto belt sw japan abstract out of sequence thrusts osts exposed in ancient accretionary prisms are considered as fossil analogs of present day megasplay faults in subduction margins and can provide direct information about the conditions of deformation during thrust activity in modern as well as in ancient accretionary prisms first order megasplay faults or osts truncate or merge with faults of lesser importance called second order osts structural analysis of the makinokuchi fault a branch of an oligocene to lower miocene second order ost in the tertiary shimanto belt of central kyushu sw japan brings information about the conditions of deformation at the time of thrusting the studied exposure shows that the fault footwall and to a much lesser extent the fault hanging wall consist of quartz cemented syntectonic dilatant hydraulic breccias testifying to pore fluid pressures larger than the least principal stress component the footwall sandstones are crossed by several centimeters thick quartz veins that merge with the footwall breccias the continuity between the veins and the breccias suggest that the veins acted as conduits which likely collected fluids from the footwall side sandstones upward and toward the fault fluid inclusions indicate that the quartz cementing the breccias and that filling the feeder veins crystallized from similar fluids and under similar pressure and temperature conditions 245 285 c and 5 8 km depth these similarities suggest that the fluids responsible for syn tectonic hydraulic brecciation were collected from the footwall through the conduits the fluid inclusion trapping temperatures are close to the temperatures expected to be reached along the seismogenic zone our analysis shows that fluid overpressures can play a key role in the growth and activity of second order osts in accretionary prisms and suggests that fluids collected along second order osts or splay faults may flow upward along first order osts or megasplay faults

synthetic fluid inclusions xix experimental determination of the vapor saturated liquidus of the system h2o nacl fecl2 abstract magmatic hydrothermal fluids associated with felsic to intermediate composition magmas are generally dominated by na k cl but often the fluids also contain significant concentrations of fecl 2 previously fluid inclusions containing such fluids were interpreted using the properties of h 2 o nacl because the effect of fecl 2 on the phase equilibrium and volumetric pvtx properties of aqueous fluids was essentially unknown in this study synthetic fluid inclusion experiments have been conducted to determine the vapor saturated liquidus phase relations of the system h 2 o nacl fecl 2 microthermometric and microanalytical measurements on synthetic fluid inclusions have been combined with the limited existing data as well as with predictions based on pitzer s formalism to determine the ternary cotectic and peritectic phase boundaries and liquidus fields the liquidus is qualitatively similar to those of other ternary systems of h 2 o nacl plus divalent cation chlorides mgcl 2 and cacl 2 and has been characterized through empirical equations that represent the liquid salinity on the ice and halite liquidus surfaces the ice and halite liquidi intersect at a metastable cotectic curve which can be used to determine fluid compositions in this system if metastable behavior is observed furthermore based on the experimentally determined liquidus bulk salinities of natural fluid inclusions can be determined from the last dissolution temperatures of ice and or halite using the new empirical equations

the digital elevation model of italy for geomorphology and structural geology abstract the geomorphological setting and main geo structural features of the central southern italian peninsula have been investigated by creating and analyzing a digital elevation model dem and derived slope aspect and shaded relief images the dem has been assembled from the mean heights archive provided by the italian geological survey for the whole country the elevation data exhibit a grid mesh spacing of 7 5 latitude and 10 longitude firstly three different methods for calculating from a dem slope and aspect are discussed the four contiguous right triangles the maximum downward gradient and the bicubic spline first derivative the resulting maps have been compared with each other at regional scale and for a small area with a slope map obtained by using classical techniques the main goal of the comparison has been the choice of the best technique for the computation of the digital slope map of italy the four contiguous right triangles method yields better results both at local and at regional scale and is being used to create from the dem a slope map and a shaded relief of the whole country which will be published by the italian geological survey secondly the integrated analysis of dem derived slope digital map and shaded relief has permitted verification for the italian peninsula of the trends of already mapped fractures and faults and detection of previously unmapped structures showing morphological evidence the analysis of 1520 regional structural features has showed that the morphological setting of the studied area is strictly related to the tectonics about 90 of the mapped faults and folds are detectable on the shaded relief which proved to be the most useful byproduct of the dem for morphological analysis

the effect of fluid chemistry on quartz microcrack lifetimes abstract metamorphic porosity consists of a branching hierarchy of primary features grain boundaries secondary features 3 and 4 grain junction tubules tertiary features microcracks and higher order features fractures while some of these features are rarely open to bulk fluid flow e g boundaries higher order features are open to fluid flow for timescales which vary significantly as a function of temperature pressure and fluid and rock chemistry the kinetics of microcrack healing in quartz between 300 600 c at 200 mpa increases as a function of fluid chemistry in the following order co 2 h 2 o 2 o m nacl 2 m cacl 2 6 m nacl changes in fluid chemistry which increase quartz solubility correlate with increased rates of healing these observations suggest that local redistribution of quartz occurs by solution precipitation driven by gradients in curvature along the crack surface and is possibly rate limited by pore fluid diffusion however the effect of crack geometry is larger than the effect of fluid chemistry at elevated temperatures and pressures aqueous fluids with elevated nacl concentrations can penetrate pervasively into polycrystalline quartz along a branching hierarchy consisting of episodically open fractures connected to 3 and 4 grain junction tubule networks while pure water or h 2 o co 2 fluid can only infiltrate pervasively along episodically open fractures 1 at lower temperatures and pressures 3 and 4 grain tubule networks in polycrystalline rocks may be closed to all fluids limiting fluid infiltration to microfacture networks lifetimes of quartz microcracks in all these fluids p fluid p confining is geologically short even at temperatures as low as 200 c

heterogeneous melt and hypersaline liquid inclusions in shallow porphyry type mineralization as markers of the magmatic hydrothermal transition cerro de pasco district peru recently identified occurrences of porphyry style mineralization evidence the link of the world s second largest known epithermal base metal cerro de pasco deposit peru to a porphyry system emplaced at depth they consist of i quartz monzonite dykes and ii the south western part of the large diatreme dome complex adjacent to the main ore bodies of cerro de pasco and iii stockwork of banded quartz magnetite chalcopyrite pyrite porphyry type veinlets crosscutting trachyte porphyritic intrusion cropping out at surface in the central part of the diatreme dome complex the latter porphyry type mineralization observed at the same erosion level as the main epithermal base metal carbonate replacement ore bodies is the subject of this work geological constraints indicate a shallow emplacement level depth 1 km p 270 bar implying rather unusual low pressure and high temperature environment for the formation of porphyry style mineralization the banded porphyry type veinlets record a multiphase history of formation with two successive high temperature n600 c stages followed by a lower temperature b350 c stage more than 90 of the quartz in veinlets precipitates during the first two high temperature stages stage 1 is characterized by the entrapment in hydrothermal quartz of inclusions containing variable proportions of both silicate melt and metal rich hypersaline n90 wt nacl eq liquid hereafter referred to as heterogeneous silicate melt inclusions hsmis the latter are rarely described in porphyry type mineralization we suggest that during stage 1 the inclusions result from heterogeneous entrapment of an evolved hydrous rhyolitic melt mixed with a hypersaline fluid phase at low pressure 270 bar and high temperature n600 c the stage 2 is marked by the entrapment of metaland sulfur rich hypersaline liquid inclusions with salinity around 70 wt nacl eq originated from the adiabatic ascent of magmatic hypersaline fluids transferred fromdeeper parts of the system the lower temperature stage 3 is characterized by an important temperature drop from n600 c to b350 c as revealed bymicrothermometry of aqueous two phase liquid vapor l v inclusions quartz textures revealed by sem cl imaging allowascribing the sulfide precipitation to the low temperaturemineralization stage 3 in situ sims 18o 16o isotope analyses of quartz across the veinlets are indicative of a magmatic signature of the fluids during the first two stages while quartz from stage 3 has oxygen isotopic compositions suggestive of minor contribution of meteoric waters to a predominantly magmatic aqueous fluid 10 vol of meteoric input which probably triggered cu fe sulfide precipitation in the stockwork high metal and sulfur contents of hsmis and hypersaline liquid inclusions determined by la icp ms are interpreted to represent the fluid composition prior to the main sulfide precipitation event the similar pb zn ratio of the bulk ore extracted from the epithermal ore bodies at cerro de pasco and the hsmis and hypersaline liquid inclusions suggest a common source of the fluids associated with the different mineralization styles at cerro de pasco

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

natural hydraulic fracturing of tight gas sandstone reservoirs piceance basin colorado natural fractures form preferred pathways for basinal fluid flow and associated heat and mass transport in gas sandstone reservoirs with low matrix permeability fractures provide flow pathways between organic rich source and reservoir layers during gas charge and between matrix pores hydraulic fractures and the well bore during production while the formation of natural fractures has previously been associated with gas generation and pore fluid pressure increase through a process referred to as natural hydraulic fracturing other driving mechanisms such as stress changes by tectonic or exhumation processes remained viable alternatives to test whether these mechanisms contributed to fracture development we investigated the spatial and temporal distribution of fracture formation and its relationship to gas generation migration and charge in sandstone of the cretaceous mesaverde group across the entire production interval on a basinwide scale using fluid inclusion microthermometry of crack seal fracture cement formed concurrently with fracture opening we observed temperature trends that when compared with temperature evolution models of the formation date fracture formation between 41 and 6 ma in the northern and between 39 and 6 ma in the southern piceance basin the onset of fracture formation 20 30 m y prior to maximum burial eliminates changes in stress state associated with exhumation as a mechanism for triggering the onset of fracture formation instead calculated paleo pore fluid pressures of 40 90 mpa 5800 13 000 psi during fracture opening and the presence of methane rich inclusions in fracture cement suggest that fracture formation was aided by high pore fluid pressures during gas generation in organic rich shales and coals and associated charging of adjacent and interlayered sandstone reservoirs a 10 20 m y age progression in the onset of fracture formation from deeper to shallower horizons of the mesaverde group is consistent with gas generation and onset of fracture formation activated by burial temperature with limited upward migration of gas at this stage of reservoir evolution this age progression with depth is inconsistent with fracture formation triggered by changes in stress conditions associated with tectonic or structural processes expected to affect the entire formation synchronously our observations are thus most consistent with fracture formation by natural hydraulic fracturing in response to gas generation in interbedded source layers and reservoir charge based on widespread observations of fractures with similar structural and diagenetic attributes we consider natural hydraulic fracture formation in response to thermocatalytic gas generation to be a fundamental mode of brittle failure in otherwise structurally quiescent basins

mineralogical petrographic and fluid inclusion evidence for the link between boiling and epithermal ag au mineralization in the la luz area guanajuato mining district mexico abstract theoretical experimental and observation data provide strong evidence that boiling is the dominant depositional mechanism in many low to intermediate sulfidation epithermal precious metals deposits textural and petrographic features that are evidence for boiling in the epithermal environment include the presence of coexisting liquid rich and vapor rich fluid inclusions assemblages consisting of only vapor rich fluid inclusions colloform quartz adularia and bladed calcite we have examined 213 samples collected from surface outcrops underground workings and drill cores from the central part of the la luz vein system in the guanajuato mining district mexico in each sample the various features that are evidence of boiling have been recorded these observations have been quantified using a boiling confidence factor that provides a means of scoring and rating each sample or area relative to the likelihood that boiling occurred homogenization temperatures of liquid rich fluid inclusions within assemblages of coexisting liquid rich and vapor rich fluid inclusions have been measured to estimate the depth of trapping of the inclusions and these data have been used to estimate the depth to the 300 c isotherm along the la luz vein system fluid inclusions and mineral textural features show strong evidence of boiling in the deepest levels sampled in the la luz system this observation suggests that the bottom of the boiling zone is at some depth beneath the deepest levels explored and opens the potential for additional resources at depth

fluid inclusion constraints on the uplift history of the metamorphosed massive sulphide deposits at ducktown tennessee standard petrographic microthermometric and raman spectroscopic analyses of fluid inclusions from the metamorphosed massive sulphide deposits at ducktown tennessee indicate that fluids with a wide range of compositions in the c o h n s salt system were involved in the syn to post metamorphic history of these deposits primary fluid inclusions from peak metamorphic clinopyroxene contain low salinity h2o ch4 fluids and calcite quartz and pyrrhotite daughter crystals many of these inclusions exhibit morphologies resembling those produced in laboratory experiments in which confining pressures significantly exceed the internal pressures of the inclusions secondary inclusions in metamorphic quartz from veins pods and host matrix record a complex uplift history involving a variety of fluids in the c o h n salt system early fluids were generated by local devolatilization reactions while later fluids were derived externally isochores calculated for secondary inclusions in addition to the chronology of trapping and morphological features of primary and secondary fluid inclusions suggest an uplift path which was concave toward the temperature axis over the p t range 6 3 kbar and 550 225 c immiscible h2o ch4 n2 nacl fluids were trapped under lithostatic to hydrostatic pressure conditions at 3 0 5 kbar and 215 20 c entrapment occurred during alleghanian thrusting and the fluids may have been derived by tectonically driven expulsion of pore fluids and thermal maturation of organic material in lower plate sedimentary rocks which are thought to underlie the deposits episodic fracturing and concomitant pressure decreases in upper plate rocks which host the ore bodies would have allowed these fluids to move upward and become immiscible post alleghanian uplift appears to have been temperature convex uplift rates of 0 10 0 05 mm year 1 from middle ordovician to middle silurian late devonian and 0 07 0 12 mm year 1 from middle silurian late devonian to late permian are suggested by our uplift path and available geochronological data

structure and origin of the gold mineralization in the nacimiento block the los burros deposits central california abstract the los burros gold deposit is located within the franciscan complex of the nacimiento block california although this deposit was mined during the late 19th and early 20th centuries its origin and its relationship with the regional metamorphism and deformation are unclear in order to better understand the mode of formation of the deposit and its possible link with a post subduction thermal anomaly we performed a detailed geological and structural mapping within the los burros district coupled with a u th he thermochronological study on apatite and zircon fluid inclusion and stable isotope o and c analyses of the ore deposit provide constraints on the temperature and potential source of the fluid s responsible for the los burros gold formation our results demonstrate that the los burros au deposit formed from a metamorphic aqueous co2 ch4 fluid at temperatures of 300 c results from raman spectroscopy of carbonaceous materials confirm the presence of a thermal anomaly in the range 260 320 c near the los burros mining district as previously inferred by vitrinite reflectance techniques our structural and preliminary thermochronological analyses show that the los burros au deposit consists of a series of meter wide quartz calcite sulfide en echelon veins formed during a late transpressive event related to san andreas fault activity and the subduction of a slab window during the past 30 ma our new data suggest that the thermal anomaly recorded in the vicinity of the los burros mining district is not associated with a magmatic derived hydrothermal system such as described within the epithermal mclaughlin deposit in northern california but rather with a late transpressive deformation event that uplifted deeply buried metamorphic rocks possibly connected to a local metamorphic overprint

raman spectroscopic characterization of h2o in co2 rich fluid inclusions in granulite facies metamorphic rocks abstract water h2o has been identified during raman analyses at 150 200 c of fluid inclusions from granulites that were previously thought to contain pure co2 at room temperature h2o in a co2 rich fluid inclusion forms an optically unresolvable liquid wetting the inclusion walls during heating the h2o phase evaporates into the co2 phase to produce a homogeneous h2o co2 fluid throughout the inclusion volume and the h2o raman peak at 3640 cm 1 is clearly resolvable at elevated temperatures to test and confirm the method synthetic h2o co2 fi of known composition 87 5 mol and 95 mol co2 were also analyzed previously studied granulite samples from the adirondack mountains usa and from the kerala khondalite belt sittampundi complex and sevitturangampatti india were tested for the presence of h2o in co2 rich fluid inclusions traces of h2o were found in co2 rich fluid inclusions in quartz crystals from the adirondacks and from the kerala khondalite belt h2o was not detected in co2 rich secondary fluid inclusions in garnet from the sittampundi complex and from sevitturangampatti rather hydrogarnet was detected along the walls of inclusions in garnet as evidenced by a peak at 3661 cm 1 the hydrogarnet is interpreted to be a step daughter phase that formed by reaction of the h2o in the fluid inclusion with the garnet host during retrogression these observations confirm the presence of an h2o bearing co2 rich fluid at some time during granulite petrogenesis but do not resolve the question of whether these co2 rich fluids were trapped at peak metamorphic conditions or during retrogression or whether the fluid inclusions have reequilibrated following entrapment

geological link between fluid inclusions dilatant microcracks and paleostress field seismic investigations using three component instruments have demonstrated shear wave splitting in widely different geological and tectonic environments shear wave analysis suggests that the inferred anisotropy can best be explained if the rocks contain distributions of subparallel subvertical fluid filled microfractures which are aligned according to the current stress field the crampin extensive dilatancy anisotropy eda model geological evidence for widespread fluid activity in the earth s crust supports this hypothesis and suggests that the myriads of planes of microscopic secondary fluid inclusions which characterise most geological materials represent fossil eda cracks field studies confirm a strong spatial relationship between the orientation of fluid inclusion arrays and the paleodirections of maximum compressive stress at elevated temperatures and pressures the healing of fluid filled cracks in the crust of whatever origin is considered to be a fairly rapid process moreover the inclusions which form as a result of crack healing respond to changes in temperature pressure and stress by changing shape and or volume this indicates a high degree of fracture compliance sufficient perhaps to react to rapid changes in the current stress field and associated shear wave splitting though individual inclusions typically 20 m will have no effect on the propagation of seismic waves with wavelengths of tens to hundreds of meters the rock volume sampled by the waves will be rendered anisotropic if the overall average of the inclusions shows a preferred orientation thus fluid inclusions may constitute one of the principal types of fluid filled microcrack described by the eda hypothesis

formation of archean batholith hosted gold veins at the lac herbin deposit val d or district canada mineralogical and fluid inclusion constraints the lac herbin deposit consists of a network of mineralized parallel steep reverse faults within the synvolcanic bourlamaque granodiorite batholith at val d or in the archean abitibi greenstone belt there are two related quartz tourmaline carbonate fault fill vein sets in the faults which consist of subvertical fault fill veins associated with subhorizontal veins the paragenetic sequence is characterized by a main vein filling ore stage including quartz tourmaline carbonate and pyrite hosted gold chalcopyrite tellurides pyrrhotite and cubanite inclusions most of the gold is located in fractures in deformed pyrite and quartz in equilibrium with chalcopyrite and carbonates with local pyrrhotite sphalerite galena cobaltite pyrite or tellurides petrography and microthermometry on quartz from the main vein filling ore stage reveal the presence of three unrelated fluid inclusion types 1 gold bearing aqueous carbonic inclusions arranged in three dimensional intragranular clusters in quartz crystals responsible for the main vein filling stage 2 barren high temperature aqueous moderately saline inclusions observed in healed fractures postdating the aqueous carbonic inclusions and considered as a remobilizing agent of earlier precipitated gold in late fractures and 3 barren low temperature aqueous high saline inclusions in healed fractures similar to the crustal brines reported throughout the canadian shield and considered to be unrelated to the gold mineralization at the lac herbin deposit the aqueous carbonic inclusions are interpreted to have formed first and to represent the gold bearing fluid which were generated contemporaneous with regional greenschist facies metamorphism in contrast the high temperature aqueous fluid dissolved gold from the main vein filling ore stage transported and reprecipitated it in late fractures during a subsequent local thermal event

stress in the earth s crust the link between crustal fluids and extensive dilatancy anisotropy observations of seismic shear wave splitting birefringence along almost all raypaths in the earth9s crust have led to the recognition that the fluid filled cracks microcracks and pores known to pervade most rocks in the crust have been preferentially aligned by the prevailing stress field this phenomenon is known as extensive dilatancy anisotropy or eda and the fluid filled microstructures as eda cracks because the seismic effects can be modelled by distributions of parallel cracks the effects of these stress aligned eda cracks have been observed in many different areas and they appear ubiquitous in the upper 10 to 20 km of the crust many details of the crack geometry and the current stress field can be readily determined from records of the shear waves which have propagated through these aligned cracks in separate studies geochemists have confirmed the presence of microscopic fluid filled cavities in almost all geological material these are referred to as fluid inclusions and provide unequivocal evidence of crustal fluid circulation often along stress controlled fractures different stress episodes can be recognized in many rock samples and studies of fluid inclusions can be used to interpret the palaeo stress history of a rock where the in situ morphology of these inclusions is related to the current regional stress field this paper discusses the relationship between the fluid inclusions of the geochemical literature and eda cracks and concludes that the former may be regarded as one of the constituent inclusion types of extensive dilatancy anisotropy

synsedimentary to early diagenetic rejuvenation of barite sulfides ore deposits example of the triassic intrakarstic mineralization in the lodeve basin france the exhumed lodeve basin herault france provides a rich suite of outcrops showing diagenetic ba pb fe cu fronts trapped in karst system in cambrian dolomites during the triassic post rift exhumation of the basin the sedimentological analysis on 10 sites in the basin reveals that barites sulfides fronts formed during humid arid climate fluctuations and the emplacement of a shallow lake environment the fabric of ore deposits the microthermometry of fluid inclusions entrapped within barites and the strontium sulfur isotopic compositions of barite sulfides associations indicate two distinct groups of mineralizations type i and type ii which are contemporaneous but resulting from different processes the synsedimentary mineralization of the type i the presence of only primary single phase liquid fluid inclusions within barite crystals and the gradual increase of 34s for both barites and chalcopyrites with depth from 7 to 18 9 v cdt suggest ore precipitation close to the vadose zone under bacterial sulfate reduction bsr in a confined sulfate rich playa lake aquifer the similar 87sr 86s ratios between barites and the overlying triassic evaporites indicate that the barium and strontium derived directly from the overlying sulfate rich lake for the type ii the high homogenization temperature of fluid inclusions entrapped within barite modal th between 60 and 80 c and the association with hydrocarbon markers confirm the participation of deeper basinal brines in addition to downward percolating sulfates derived from the lake environment the high positive values of 34s for both barites and sulfides are typical of a precipitation linked to the combined action between anaerobic oxidation of methane and sulfate reduction aom sr at the sulfate methane transition zone smtz during hydrocarbon migration similar 87sr 86sr ratios between middle triassic barites and previous late permian barites confirm that the source of metals precipitated at the smtz originated from the dissolution of anterior ore deposits located in the sulfate depleted zone this study links very shallow metallogenesis processes to reworking of mvt ore deposits by the action of sulfate reducing bacteria around hydrocarbon seeps in a karstic environment

an evaluation of synthetic fluid inclusions for the purpose of trapping equilibrated coexisting immiscible fluid phases at magmatic conditions we report data that allow us to evaluate the method of trapping immiscible saline aqueous fluids i e vapor and brine in the nacl kcl hcl fecl2 auhcl2 h2o system as synthetic fluid inclusions in pre fractured quartz cores in order to quantify the concentrations of au fe k and na among coexisting three phase immiscible fluids i e haplogranite melt brine and vapor at magmatic conditions coexisting vapor and brine were trapped experimentally at 800 c and 100 110 mpa as synthetic fluid inclusions in both quartz microfractures and quenched silicate melt i e glass and also sampled indirectly using the recovered quenched aqueous fluid quartz hosted and glass hosted brine inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms and instrumental neutron activation analysis inaa respectively quenched aqueous fluid from each experiment containing a quartz core was recovered and analyzed by atomic absorption spectrophotometry aas the composition of aqueous fluids trapped as quartz hosted inclusions glass hosted inclusions and those recovered after quench yield consistent and precise data at the 2 uncertainty level for the elements of interest the overlapping au fe k and na concentrations in aqueous fluids trapped and analyzed via three entirely different instrumental techniques i e la icpms inaa and aas suggest strongly that quartz microfractures heal on a slow enough time scale to permit entrapment of fully equilibrated aqueous fluids at our experimental ptx conditions the data evince clearly that the chemical composition of fluids in quartz microfractures at the time of self healing represents equilibrium conditions hence synthetic fluid inclusions in experiments with low thermal gradients across the charge provide a reasonable estimate of fluid composition at least at the experimental conditions examined in this study

fluid inclusions and preliminary studies of hydrothermal alteration in core hole pltg 1 platanares geothermal area honduras abstract the platanares geothermal area in western honduras consists of more than 100 hot springs that issue from numerous hot spring groups along the banks or within the streambed of the quebrada de agua caliente brook of hot water evaluation of this geothermal area included drilling a 650 m deep pltg 1 drill hole which penetrated a surface mantling of stream terrace deposits about 550 m of tertiary andesitic lava flows and cretaceous to lower tertiary sedimentary rocks in the lower 90 m of the drill core fractures and cavities in the drill core are partly to completely filled by hydrothermal minerals that include quartz kaolinite mixed layer illite smectite barite fluorite chlorite calcite laumontite biotite hematite marcasite pyrite arsenopyrite stibnite and sphalerite the most common open space fillings are calcite and quartz biotite from 138 9 m depth dated at 37 41 ma by replicate 40 ar 39 ar analyses using a continuous laser system is the earliest hydrothermal mineral deposited in the pltg 1 drill core this mid tertiary age indicates that at least some of the hydrothermal alteration encountered in the pltg 1 drill core occured in the distant past and is unrelated to the present geothermal system furthermore homogenization temperatures t h and melting point temperatures t m for fluid inclusions in two of the later formed hydrothermal minerals calcite and barite suggest that the temperatures and concentration of dissolved solids of the fluids present at the time these fluid inclusions formed were very different from the present temperatures and fluid chemistry measured in the drill hole liquid rich secondary fluid inclusions in barite and caicite from drill hole pltg 1 have t h values that range from about 20 c less than the present measured temperature curve at 590 1 m depth to as much as 90 c higher than the temperature curve at 46 75 m depth many of the barite t h measurements ranging between 114 and 265 c plot above the reference surface boiling point curve for pure water assuming hydrostatic conditions however the absence of evidence for boiling in the fluid inclusions indicates that at the time the minerals formed the ground surface must have been at least 80 m higher than at present and underwent stream erosion to the current elevation near surface mixed layer illite smectite is closely associated with barite and appears to have formed at about the same temperature range about 120 to 200 c as the fluid inclusion t h values for barite fluid inclusion t h values for calcite range between about 136 and 213 c several of the calcite t h values are significantly lower than the present measured temperature curve the melting point temperatures t m of fluid inclusion ice yield calculated salinities ranging from near zero to as much as 5 4 wt nacl equivalent which suggest that much of the barite and calcite precipitated from fluids of significantly greater salinity than the present low salinity platanares hot spring water or water produced from the drill hole

fluid and melt inclusion evidence for the origin of idiomorphic quartz crystals in topaz bearing granite from the salmi batholith karelia russia abstract idiomorphic quartz crystals in topaz bearing granite from the salmi batholith contain primary inclusions of silicate melt and abundant mostly secondary aqueous fluid inclusions microthermometric measurements on melt inclusions give estimates for the granite solidus and liquidus of 640 680 c and 770 830 c respectively using published solubility models for h2o in granitic melts and the obtained solidus liquidus temperatures from melt inclusions the initial water concentration of the magma is deduced to have been approximately 3 wt and the minimum pressure about 2 kbar at this initial stage volatile undersaturation conditions of magma were assumed these results indicate that the idiomorphic quartz crystals are magmatic in origin and thus real phenocrysts during subsolidus cooling and fracturing of the granite several generations of aqueous fluid inclusions were trapped into the quartz phenocrysts the h2o inclusions have salinities and densities of 1 41 wt nacl eq and 0 53 1 18 g cm3 respectively

fluid inclusions in the system h2o nacl co2 an algorithm to determine composition density and isochore abstract fluid inclusions approximated by the system h2o nacl co2 are common in a wide variety of geologic settings requiring protocols to evaluate the composition phase equilibria density and isochoric pressure temperature relations this study presents a generic approach to determine these properties of h2o nacl co2 inclusions based on petrographic microthermometic and or raman spectroscopic data invoking mass balance and conservation of bulk molar volume constraints the generic algorithm is implemented using a combination of new correlation equations and existing equations of state the resulting computer program accepts a variety of possible input types according to the particular microthermometric properties thus according to bulk composition and density and measured data and includes tools for reconstructing phase boundaries as well as the pressure temperature trajectories of the inclusion during heating i e the isochore the program is written in visual basic for applications in microsoft excel

mineral zoning and gold occurrence in the fortuna skarn mine nambija district ecuador the fortuna oxidized gold skarn deposit is located in the northern part of the nambija gold district southern ecuador it has been subdivided into four mineralized sites covering a distance of 1 km which are named from north to south cuerpo 3 mine 1 mine 2 and southern sector massive skarn bodies occur in k na metasomatized volcanic and volcaniclastic rocks of the triassic piuntza unit they appear to result from selective replacement of volcaniclastic rocks very minor presence of bioclast relicts suggests the presence of subordinate limestone endoskarn type alteration with development of na rich plagioclase k feldspar epidote actinolite anhedral pyroxene and titanite affects a quartz diorite porphyritic intrusion which crops out below the skarn bodies in mine 2 and the southern sector endoskarn alteration in the intrusion grades into a k feldspar biotite magnetite assemblage k alteration suggesting that skarn formation is directly related to the quartz diorite porphyritic intrusion the latter being probably emplaced between 141 and 146 ma the massive skarn bodies were subdivided into a dominant brown garnet skarn a distal green pyroxene epidote skarn and two quartz rich varieties a blue green garnet skarn and light green pyroxene garnet skarn which occur as patches and small bodies within the former skarn types the proximal massive brown garnet skarn zone is centered on two 060 trending faults in mine 2 where the highest gold grades 5 10 g t were observed it grades into a distal green pyroxene epidote skarn zone to the north cuerpo 3 granditic garnet shows iron enrichment from the proximal to the distal zone diopsidic pyroxene exhibits iron and manganese enrichment from proximal to distal zones the retrograde stage is weakly developed and consists mainly of mineral phases filling centimeter wide veins vugs and interstices between garnet and pyroxene grains the main filling mineral is quartz followed by k feldspar epidote calcite and chlorite with minor sericite apatite titanite hematite pyrite chalcopyrite and gold metal and sulfur contents are low at fortuna and the highest gold grades coincide with high hematite abundance which suggests that retrograde stage and gold deposition took place under oxidizing conditions fluid inclusions from pyroxene indicate precipitation from high temperature high to moderate salinity fluids 400 to 460 c and 54 to 13 wt eq nacl which result probably from boiling of a moderately saline 8 wt eq nacl magmatic fluid later cooler 180 to 475 c and moderate to low saline fluids 1 to 20 wt eq nacl were trapped in garnet epidote and quartz and are interpreted to be responsible for gold deposition chlorite analysis indicates temperature of formation between 300 and 340 c in accordance with fluid inclusion data it appears thus that gold was transported as chloride complexes under oxidizing conditions and was deposited at temperatures around 300 c when transport of chloride complexes as gold carriers is not efficient

fluid evolution in the el sid gold deposit eastern desert egypt auriferous quartz carbonate veins in the el sid mine cut through the western margin of the fawakhir granitic intrusion and the immediate country ophiolites gold mineraliz ation is spatially and temporally associated with ene wsw fault shear zones developed late in the deformational history of the area field and microscopic studies suggest two distinct ore stages namely an early gold fe as sulphide and a late gold base metal mineralization new microthermometric and raman data suggest gold deposition as a result of a complex history of fluid immiscibly dilution of low salinity aqueous carbonic fluids in the early mineralization stage while wall rock alteration and pressure loss precipitated au from intermediate salinity aqueous ore fluids during the late stage fluid inclusion isochoric reconstructions combined with oxygen and sulphur isotope data indicate conditions of 320 20 8c and 1 3 0 2 kbar for the early gold fe as sulphide mineralization and c 200 15 and 0 6 0 9 kbar for the late gold zn pb cu sulphide stage the clockwise evolution path in pressure temperature space likely documents gold mineralization under post peak metamorphic conditions the calcu lated sulphide d 34 sh2s equilibrium values 29 04 to 4 75 may refer to a variable redox state of sulphur in the ore fluids from the early to late mineralization stages the stable isotope signature of the vein quartz and calcite suggest mixed magmatic and metamorphic fluid sources d 18 o h2o 4 9 to 7 4 unusually low d 13 c values of calcite in the late mineralization 213 9 to 214 7 may reflect input of magmatic co2 and or oxidized carbonaceous mate rial in the infiltrating fluid gold bearing quartz veins associated with variably tectonized ophiolitic and island arc rocks or adja cent to their interferences are common in the southern and central sectors of the eastern desert of egypt whereas gold occurrences confined to granitic intrusions that are in some cases associ ated with felsic subvolcanic porphyries is a com mon feature in the northern eastern desert e g moharram et al 1970 sabet bordonosov 1984 klemm et al 2001 botros 2004 based on sev eral geological and mineralogical studies a gold granitoid association in the eastern desert has been suggested by many authors e g garson

genetic relationship between silver lead zinc mineralization in the wutong deposit guangxi province and mesozoic granitic magmatism in the nanling belt southeast china more than 50 of the world s total reserves of tungsten are in china and most tungsten deposits are located in the nanling range in southeast china this study explores the potential genetic relationship between tungsten tin w sn mineralization and shallower ag pb zn deposits in the nanling range based on data from the wutong deposit guangxi province the lead oxygen carbon sulfur and strontium isotopic compositions of minerals at wutong indicate that a single crustal derived fluid was responsible for mineralization wutong likely formed at relatively low temperatures 200 300 c and low pressures as indicated by the similarity between homogenization temperatures of fluid inclusions and those estimated from s isotopic compositions of minerals the hubnerite age 92 3 104 4 ma indicates that the wutong mineralization is likely related to nearby late yanshanian cretaceous s type granites derived from proterozoic crust this mineralization event coincides with the last w sn mineralization event and the cretaceous peak of mineralization in the nanling range

the compositional limits of fluid immiscibility in the system h2onaclco2 as determined with the use of synthetic fluid inclusions in conjunction with mass spectrometry abstract the compositional limits of fluid immiscibility in the system nacl h2o co2 were investigated from 500 to 700 c at pressures of 1 2 and 3 kbar synthetic fluid inclusions formed in quartz prisms were equilibrated with high temperature high pressure fluids in hydrothermal pressure vessels the inclusions were analyzed optically by mass spectrometry and by microthermometry the fields of immiscibility were defined as a function of temperature and pressure mass spectrometry was used to validate the existence of the immiscible fluids and to determine the co 2 h 2 o ratios of the two coexisting phases microthermometry i e the measurement of the melting temperature of solid sodium chloride was used in conjunction with the results of the mass spectrometry measurements to define the tie lines within the two phase fields isochores and the location of a portion of the isopleth were determined for composition nacl8 9 h2o76 1 co215 0

fluid inclusion study of the ore quartz veins at haftcheshmeh porphyry copper mo deposit ahar arasbaran magmatic belt nw iran abstract the haftcheshmeh porphyry copper deposit in alborz arasbaran magmatic belt aamb of northwestern iran is hosted by i type granitoids of calcalkaline series of eocene to miocene age the mineralization consists of chalcopyrite molybdenite rare amounts of covellite pyrite and magnetite that are commonly found in silicified veins of the potassic sericitic alteration zones in the host quartzdiorite quartzmonzonite and granodiorite porphyries the obtained fluid inclusion data t mco 2 57 5 to 60 5 c in ore quartz veins shows enrichment in co 2 the coexistence of cu sulfide daughter crystals together with halite crystals and the co 2 bearing fluid inclusions suggest the presence of two immiscible fluids a high salinity co 2 rich magmatic fluid with high metal contents 31 1 and 48 4 wt nacl equivalent t h 169 to 500 c and a low salinity fluid 0 88 and 11 1 wt nacl equivalent t h 242 to 418 c whereas the presence of liquid and gaseous co 2 implies fluid immiscibility measured first melting temperatures of 21 to 40 c in fluid inclusions of the ore quartz veins at haftcheshmeh deposit are below the eutectic point of nacl h 2 o indicating the presence of bivalent cations including the copper salt cucl 2 4h 2 o in the ore solution the salinity of the magmatic fluids in the a type quartz veins 31 8 to 43 1 wt nacl equivalent is close to the salinities in the d type quartz veins 31 1 to 48 4 wt nacl equivalent and the homogenization temperatures of lv inclusions in the a type quartz veins 242 to 327 c are only slightly lower than in the d type quartz veins 261 to 387 c these data together with the very close homogenization temperatures of vl inclusions in the a type 302 to 418 c and the d type quartz veins 300 to 395 c suggest similar ore fluid sources for both quartz vein types the 18 o values of the ore quartz veins showing a typical magmatic fluid and suggests that the early fluid inclusions were of magmatic origin it is envisaged that co 2 degassing in the primary magma at haftcheshmeh could have led to separation of the vapor phase and destabilization of the metal transporting complexes and the ore formation

the patricia zn pb ag epithermal ore deposit an uncommon type of mineralization in northeastern chile the patricia ore deposit represents an unusual example of economic zn pb ag mineralization at the northernmost end of the late eocene oligocene metallogenic belt in chile it is hosted by volcano sedimentary units which are typically tuffaceous and andesitic breccias the ore body consists of a set of subvertical e w vein systems developed under a sinistral strike slip regime that included transtensive domains with generalized extensional structures where the ores were deposited the deposit is divided into two blocks by a set of nnw ese trending reverse faults which uplifted the eastern block and exhumed thicker and deeper parts of the deposit at least 200 m of volcano sedimentary pile hosting the mineralization has been eroded in this block by contrast the western block exposes a shallower part of the system where cherts amorphous silica and jasperoids occur three main stages of mineralization have been defined 1 pre ore stage is characterized by early quartz pyrite and arsenopyrite 2 base metal and silver stage characterized by sphalerite 6 to 15 mol fes galena chalcopyrite pyrrhotite and ag bearing minerals freibergite polybasite stephanite pyrargyrite freieslebenite and acanthite and 3 post ore stage characterized by late quartz kutnohorite and minor sulfides arsenopyrite sphalerite pyrite galena ag bearing minerals and pb sulfosalts whole ore geochemistry shows two groups of elements that are positively correlated 1 ag cd cu pb zn related to the base metal sulfides and 2 au as ge sb w related to arsenopyrite and pyrite hydrothermal alteration is pervasive in the outcropping mineralized areas including silicification and locally vuggy silica textures at depth chloritic and sericitic alteration is developed along vein selvages and is superimposed to the regional propylitic alteration fluid inclusions indicate that the base metal ores were deposited from 250 to 150 c moderate salinity fluids 1 9 wt nacl the pre ore stage is characterized by a saline fluid 6 22 wt nacl and between 210 and 250 c whereas the post ore stage has salinity of 4 8 wt and temperature from 175 to 215 c cooling was the mechanism of ore mineral precipitation in the patricia deposit although mixing of fluids could have occurred in the pre ore stage mineralogical geochemical and fluid inclusion evidence is consistent with an intermediate sulfidation is epithermal deposit type this study highlights the high potential for hidden economic mineralization at depth in the western block and for extension of the ore body both to the south and to deeper levels in the eastern block of the patricia ore deposit to a larger extent the implications of finding such polymetallic epithermal style of mineralization in the northern chile precordillera is relevant both to the regional metallogenic perspective and to the exploration potential of the region where the late eocene early oligocene metallogenic belt apparently disappears

a method to synthesize large fluid inclusions in quartz at controlled times and under unfavorable growth conditions a new synthesis technique allows large fluid inclusions to be produced at conditions under which one normally would obtain only small inclusions with the additional advantage that the timing of fluid entrapment can be controlled in the first step primary fluid inclusions are grown at p t conditions under which it is relatively easy to produce large inclusions in the second step which can be performed either during the same experiment or during a separate experiment after a desired time of pre equilibration some of the primary inclusions produced during the first step are re opened by in situ fracturing causing partial replacement of the inclusion content the sample is then left at high pressure and temperature until the cracks leading to the re opened inclusions are healed to test the method and quantify the efficiency of fluid replacement in the re opened inclusions we produced primary inclusions at 700 c 200 mpa and re opened them during a second experiment in the presence of a compositionally different fluid at 500 c 70 mpa laser ablation icp ms la icp ms analyses of eight primary and 11 refilled inclusions demonstrate that in the latter more than 97 of the original fluid was replaced by new fluid thus the refilled inclusions are representative of the surrounding fluid at the time of in situ fracturing

strain response and re equilibration of ch4 rich synthetic aqueous fluid inclusions in calcite during pressure drops abstract aqueous fluids in sedimentary basins often contain dissolved methane particularly in petroleum environments pvtx pressure volume temperature composition reconstructions performed using fluid inclusion data are largely based on the assumption that inclusions do not change from the time of trapping until the present many authors however consider that fluid inclusions can re equilibrate particularly in fragile minerals like calcite in order to understand this re equilibration phenomenon in the metamorphic domain previous experiments have been performed under high pt conditions but few have been performed at low to medium pt conditions such as those associated with sedimentary burial diagenesis and no previous studies have examined ch 4 bearing aqueous inclusions in calcite an experimental study of the preservation modification of ch 4 rich synthetic fluid inclusions in calcite during isothermal decompression was conducted an autoclave was used for accurate ptx control allowing equilibrium between liquid and vapour in the ch 4 h 2 o system ptx conditions were maintained at four stages of decreasing pressure with each stage held for 7 days to simulate an isothermal pressure drop in order of decreasing pressure the pressure temperature conditions monitored were 276 10 bar at 180 7 c 176 10 bar at 180 7 c 76 10 bar at 180 7 c and 10 3 bar at 180 15 c at the end of the experiment the calcite was recovered and analyzed by microthermometry and raman microspectroscopy for ptx reconstruction a careful procedure was adopted to limit re equilibration of inclusions during analytical procedures four types of inclusion shapes and four types of strain patterns were differentiated classification of the petrographic strain patterns was carried out these strain patterns were associated with inclusion stretching and or leakage regarding ch 4 t h and p h compared to experimental conditions factors controlling the preservation or acquisition of strain patterns included the initial shape and size of the inclusion and the pressure differential p between the confining pressure p cf and the internal pressure p i within the inclusion most fluid inclusions seemed to be trapped during the first 7 days of the experiment although few 4 of these preserved the initial pt conditions of 276 10 bar whereas 8 preserved the second and third run of pt conditions overall the majority of inclusions 88 did not reflect accurately the ptx trapping conditions a petrographic guide to the inclusions is presented here that allows strain identification for pvt reconstructions re equilibration patterns and evidence for preferential methane leakage from aqueous inclusions in calcite are important findings revealed by this study and may be useful for the reconstruction of post trapping events in investigations of natural samples and in other experiments using synthetic inclusions in calcite

conodont sr ca and δ18o record seawater changes at the frasnian famennian boundary abstract the oxygen isotopic composition 18 o p and strontium calcium sr ca p ratios have been measured in late devonian conodonts palmatolepis sp from contemporaneous sections at coumiac france and m rirt morocco the sequences encompass two anoxic horizons the lower kellwasser lkw and upper kellwasser ukw events with the top of the ukw coinciding with the mass extinction at the frasnian famennian boundary the genus palmatolepis survived the faunal crisis but exhibited plastic responses to the environmental changes which are recorded in the evolution of shape during the anoxic events the present study demonstrates that shape 18 o p and sr ca p values of conodonts are correlated in both localities excluding diagenesis as the driving process for the measured 18 o p and sr ca p values the conodonts 18 o p and sr ca p values are correlated in both localities and distributed into either a pre crisis and crisis group using the relationships between the 18 o p and sr ca p values we estimate that the variation of the seawater sr ca ratio during the frasnian famennian mass extinction was of about 20 its initial value this drastic decrease of the seawater sr ca ratio is discussed in the light of the reef demise that occurred during the faunal crisis

a mechanism for preferential h 2 o leakage from fluid inclusions in quartz based on tem observations preferential leakage of h2o from fluid inclusions containing multiple gas components has been suspected in natural metamorphic rocks and has been demonstrated experimentally for synthetic h2o co2 rich inclusions in natural quartz knowledge of the physical and chemical characteristics of the leakage mechanism which may be very complex increases the value of natural fluid inclusions to metamorphic geology it is proposed that crystal defects play a major role in nondecrepitative preferential h2o leakage through quartz and remain effective during metamorphism inclusions with either an internal overpressure or underpressure produce strain in the adjacent quartz crystal via the nucleation of many dislocations and planar defects like dauphine twin boundaries these defects allow preferential loss of h2o from h2o co2 rich inclusions at supercritical conditions the transport capacity of this leakage mechanism is enhanced by nucleation of small bubbles on defect structures the nucleation of these bubbles seems to be a recovery process in strained crystals solubility gradients of quartz in water in a crystal with internally underpressurized inclusions may result in optical visible implosion halos in a three dimensional spatial arrangement caused by the growth of small bubbles at the expense of the larger original fluid inclusion natural fluid inclusions from naxos greece are always associated with numerous interlinked dislocations these dislocations may have been produced by plastic derormation or by crystal growth related processes e g crack healing the presence of small bubbles on these dislocations indicates that a similar leakage mechanism for h2o must have occurred in these rocks

synthetic fluid inclusions in natural quartz ii application to pvt studies synthetic fluid inclusions have been used to determine volumetric properties of h2o and a 20 wt kcl solution from 300 700 c and 1 3 kb comparison of results obtained for h2o with previously published data indicates that the synthetic fluid inclusion technique provides pvt data that are within a few percent of those obtained from conventional pvt studies this technique thus provides a fast relatively simple means of determining pvt properties of many fluids of geologic interest

genesis of the wulong gold deposit northeastern north china craton constraints from fluid inclusions h o s pb isotopes and pyrite trace element concentrations abstract the wulong vein type gold deposit located along the northeastern margin of the north china craton ncc contains 80 tonnes of gold at an average grade of 5 35 g t a total of 380 auriferous quartz veins are hosted in late jurassic gneissic two mica granite and early cretaceous granodiorite a paragenetic sequence representing three hydrothermal stages has been identified 1 quartz pyrite 2 quartz polymetallic sulfide and 3 quartz calcite pyrite petrography fluid inclusion microthermometry and laser raman spectroscopy revealed three types of fluid inclusions co2 ch4 type i h2o co2 ch4 type ii and h2o nacl type iii fluid inclusion data indicate that during mineralization fluid temperatures evolved from 283 to 395 c to 219 328 c to 144 255 c and salinities varied from 0 70 to 8 95 wt to 0 18 7 86 wt to 0 18 4 96 wt nacl equivalent quartz yielded 18oh2o smow and dsmow values of 0 9 7 3 and 65 to 48 respectively indicating that the ore forming fluids were derived from magmatic water and mixed with meteoric water during the later stages of mineralization sulfides have 34scdt sulfur isotopic compositions ranging from 0 9 to 3 9 suggesting that the s was derived from a magmatic source pb isotopic compositions of sulfides 206pb 204pb 17 488 17 718 207pb 204pb 15 565 15 631 and 208pb 204pb 38 190 38 766 indicate that the pb was derived primarily from the upper crust with minor input from the mantle in situ laser ablation inductively coupled plasma mass spectrometry la icp ms trace element analyses of three generations of pyrite py1 py2 and py3 reveal that gold concentrations in py2 are higher than those in py1 and py3 which indicates that gold mineralization occurred primarily during the middle stage high co ni ratios of pyrite are consistent with a hydrothermal origin we suggest that the wulong gold deposit formed during lithospheric thinning associated with destruction of the ncc this process was triggered by subduction of the paleo pacific plate during the early cretaceous

platinum solubility and partitioning in a felsic melt vapor brine assemblage abstract the solubility and partitioning of pt in a s free vapor brine rhyolite melt pt metal assemblage has been quantified at 800 c f o 2 nno and pressures of 100 and 140 mpa vapor and brine were sampled at run conditions by trapping these phases as glass hosted fluid inclusions as the melt cooled through the glass transition temperature the vapor and brine were in equilibrium with the melt at the time of trapping and thus represent fluids which were sampled at the termination of each experimental run the microthermometrically determined salinities of vapor and brine are 2 and 63 wt nacl eq and 9 and 43 wt nacl eq at 100 and 140 mpa respectively platinum solubilities in vapor brine and glass i e quenched melt were quantified by using laser ablation inductively coupled plasma mass spectrometry la icp ms equilibrium is discussed with reference to the major and trace element concentrations of glass hosted fluid inclusions as well as the silicate melt over run times that varied from 110 to 377 h at 140 mpa and 159 to 564 h at 100 mpa platinum solubility values 1 in h2o saturated felsic melt are 0 28 0 13 g g and 0 38 0 06 g g at 140 and 100 mpa respectively platinum solubility values 1 x at 140 and 100 mpa respectively in aqueous vapor are 0 91 0 29 g g and 0 37 0 17 g g and in are brine 16 10 g g and 3 3 1 0 g g the measured solubility data were used to calculate nernst type partition coefficients for pt between vapor melt brine melt and vapor brine the partition coefficient values 1 x for vapor melt brine melt and vapor brine at 140 mpa are 2 9 1 0 67 27 and 0 13 0 05 and at 100 mpa are 1 0 0 2 6 8 2 4 and 0 15 0 05 the partitioning data were used to model the pt scavenging capacity of vapor and brine during the crystallization driven degassing i e second boiling of a felsic silicate melt over a depth range i e 3 6 km consistent with the evolution of magmatic hydrothermal ore deposits model calculations suggest that aqueous vapor and brine can scavenge sufficient quantities of pt and by analogy other platinum group elements pge to produce economically important pge rich magmatic hydrothermal ore deposits in earth s upper continental crust

fluid inclusion geochemistry of the early proterozoic pirila gold deposit in rantasalmi southeastern finland the small pirila gold deposit which is located in the southeastern part of the svecofennian complex near the archean proterozoic boundary is hosted by quartz veins and lenses occurring in mica schist the rocks of the area were metamorphosed under conditions of amphibolite facies gold is invariably associated with sulphides microthermometry of fluid inclusions in quartz indicates four types of inclusions 1 weakly saline h2o co2 4 0 eq wt nacl with small amounts of ch4 10 mole ch4 2 co2 10 mole ch4 3 ch4 and 4 h2o 25 eq wt nacl with less than 0 85 mole co2 in the vapour phase texturally these inclusion types are classified as primary h2o co2 and secondary h2o co2 and ch4 leachate analysis shows that in addition to na the aqueous fluids contain ca and fe with minor amounts of k and mg the primary h2o co2 and the secondary h2o inclusions contain sulphide and unidentified opaque grains respectively the secondary ch4 inclusions are often associated with short trails of arsenopyrite grains fluid inclusion and geological data suggest ore mineral mobilization crystallization of host quartz and deposition of sulphides controlled by the d2 and d3 structures in the presence of a h2o co2 fluid mainly during the plastic d3 deformation and during the amphibolite facies metamorphism i e 3 4 kbars 540 670 c during ductile brittle deformation probably d4 precipitation of tectonic remobilized gold from sulphides in fractures occurred in the presence of ch4 and h2o fluids at lowered temperature 440 c and pressure 2 kbars

synthetic fluid inclusions xx critical ptx properties of h2o fecl2 fluids abstract iron chloride is a common and abundant component in hydrothermal fluids in many geologic environments yet the thermodynamic and ptx properties of fecl2 bearing aqueous fluids are poorly known in this study we have used the synthetic fluid inclusion technique to characterize the ptx conditions along the critical curve of the system h2o fecl2 for a given temperature or salinity the critical pressure in the h2o fecl2 system is lower than that in the h2o nacl system in contrast the critical curves of aqueous solutions of other divalent cation chlorides such as mgcl2 and cacl2 are at higher pressure than that of nacl solutions of equivalent temperature or salinity the results of this study provide the first quantitative constraints on the ptx extent of liquid vapor immiscibility for fecl2 rich fluids owing to the low pressure along the critical curve compared to other common aqueous chloride systems immiscibility of fecl2 rich fluids appears to be limited to relatively low pressures or relatively shallow levels in the crust compared to other saline hydrothermal fluids

formation of oreshoots in mesothermal gold quartz vein deposits examples from queensland australia abstract mesothermal gold quartz vein deposits in granitoid hosted and melange sediment hosted goldfields contain oreshoots in areas of structural dilation the environment of formation is localized at depths of 2 5 km in brittle to brittle ductile shear zones which have stick slip seismic movement lithologic contacts and fissure intersections affect the shape and geometry of the oreshoots mineralizing fluids in these shear zones range between 3 and 10 wt nacl equiv with 18 o values of about 5 8 fluids are locally co 2 bearing with formation temperatures of between 220 and 350 c fluid source is either of deep magmatic or metamorphic origin and can rarely be correlated directly with nearby plutonism fluid transport is via single pass flow in high permeability conduits such as mylonites in granitoids or melange cleavage in sediments complex mixtures of mineralized quartz gouge fault rocks and altered wall rock reflect the environment of formation comb ribbon buck and breccia quartz and microscopic textures indicate different processes and stages of oreshoot formation quartz deposition is due to changes in silica solubility resulting from temperature and pressure fluctuations local pressure changes are due to reduced velocity of the fluid in dilated zones according to bernoulli s equation at restricted or dilated portions of the fissure throttling and adiabatic cooling are common and result in quartz deposition and channel choking which lead to pressure and temperature build ups and faulting the long dip lengths in many mesothermal oreshoots may also account for substantial pressure and temperature reductions in the fluid from bottom to top the venturi effect in connecting fissures may also affect quartz deposition microscopic textures indicate that multiple generations of quartz have been involved in cracking stress corrosion and dissolution due to porosity changes and dilation prior to and during faulting gouge and clay seams stabilize fault movement and may have acted as impermeable barriers and pressure seals which channelled fluid flow and if hydrated may have expelled concentrated brines when compressed by faulting hydrothermal alteration indicates early diffusive transport and chemical and ph gradients away from the oreshoots four main stages of oreshoot formation occur from the outside to the inside of oreshoots as 1 ground preparation and nucleation 2 reinjection and sheeting 3 major fault movement channeling of fluid flow local dissolution and cracking and 4 consolidation and oreshoot growth including fluid stagnation and ponding

experimental decrepitation and re equilibration of fluid inclusions in synthetic quartz abstract strong discrepancies between densities of the fluids trapped in fluid inclusions f i and p tp couples deduced from other geological considerations are common so it was decided to test experimentally the possible f i re equilibrations when bringing the host crystal in p tp conditions different from trapping conditions runs were conducted on synthetic quartz in a gas apparatus and in a griggs solid medium apparatus the following modifications of the f i were observed 1 1 drastic shape changes of the primary f i and appearance of clusters or trails of small secondary inclusions sometimes related to a crack 2 2 lowering of the fluid densities such a re equilibration is a decrepitation phenomenon first hydraulic fracturing then sealing of the cracks with appearance of secondary inclusions when using the gas apparatus the new measured densities are in very good accordance with the nominal p tp conditions when using the solid medium apparatus the new densities are surprisingly low relative to the nominal p t conditions probably due to a strongly anisotropic stress state in the apparatus

direct analysis of ore precipitating fluids combined ir microscopy and la icp ms study of fluid inclusions in opaque ore minerals laser ablation inductively coupled plasma mass spectrometry la icp ms in combination with near infrared microscopy of fluid inclusions hosted by ore minerals that are opaque to visible light can provide the composition of ore precipitating fluids we applied the two techniques to well constrained fluid inclusion assemblages hosted by pyrite enargite and quartz to trace the source and evolution of the fluids in high sulfidation epithermal veins overprinting a porphyry copper deposit at rosia poieni romania despite some analytical limitations caused by the sulfide host minerals the data demonstrate that fluids trapped in apparently cogenetic quartz and ore minerals are chemically different systematic changes in major and trace element ratios between liquid vapor vapor rich and brine fluid inclusion assemblages in the three minerals record an evolving fluid source at the porphyry to epithermal transition regarding their cs na k ratios most of epithermal quartz hosted fluid inclusion assemblages form a well defined cluster which coincides with the narrow range of the porphyry stage fluids trapped in early quartz of the porphyry stockwork veins their cu na k ratios are 10 to 100 times lower compared to the pyrite hosted inclusions and correspond to the lowest cu na k ratios recorded for the porphyry stage fluids by contrast pyrite hosted vapor rich fluid inclusions have the highest cu na k similar to the highest cu na k ratios measured in the porphyry stage fluid inclusions the results led to the conclusion that the gangue and ore minerals in the high sulfidation epithermal veins at rosia poieni formed by successive pulses of chemically distinct hydrothermal fluids that were successively exsolved from residual melt batches of a progressively crystallizing magma at greater depth these results are consistent with detailed textural observations but petrography alone could not have led to this unambiguous conclusion

high density co2 inclusions in the colorado front range a fluid density in an inclusion is commonly observed to be too low for the p t estimates for the postulated time of trapping and is generally attributed to a fluid loss during the uplift process it is more difficult to explain a fluid density which is too high in the 1700 m y front range migmatites such high densities occur in some of co2 inclusions which were deduced to have formed during the migmatization episode the peak p t estimates for migmatization in the front range are 4 6 kb and 650 700 c in sillimanite field but pressures required to form the most dense inclusions are 7 6 kb in kyanite field the high density is not likely to be a relic of a higher pressure condition earlier than the main migmatization episode for the following reasons a no kyanite or any other relic high pressure phase has been found in the precambrian front range b the high density inclusions are rare in zones with least signs of deformation and melting paleosomes and quartz inclusions within feldspar grains which instead contain relatively undisturbed early inclusions c high density inclusions with th 30 c are associated with heavily altered plagioclase caused by hydrothermal activity which was a late event in leucosome formation further there is evidence for post entrapment change s in density an intragranular trail in quartz contains co2 inclusions that exhibit almost the whole range in th 40 to 24 c as displayed by the entire population of the early co2 inclusions 66 to 30 c the density of an inclusion in the trail is not related to inclusion size but to the position of the inclusion relative to apparent micro shear zones crossing the co2 trail a change to a higher density a smaller volume could have resulted from an initially isobaric cooling path which intersects co2 isochores with increasingly higher densities additional excess pressure may have resulted from overthrusting however because high density inclusions occur selectively in the zones in which plagioclase shows alteration indicating a high a h 2 o and because there is a correlation between shear zones and high density inclusions it is postulated that local hydrolytic weakening of quartz was necessary for the decrease of inclusion volume which occurred during deformation the localized deformation may also result in an excess pressure however the introduction of a small amount of h2o into these inclusions as a possible cause of high density inclusions cannot be ruled out