petrogenesis and tectonic setting of late precambrian ensimatic volcanic rocks central eastern desert of egypt abstract early stages in the geologic evolution of the central eastern desert of egypt ced reflect an intense episode of ensimatic volcanic activity similar to modern magmatism of the ocean floors and island arcs this paper reports results from studies of the petrology and petrogenesis and interprets the significance of these late precambrian volcanic rocks a three fold stratigraphy is preserved in the basement of the ced a basal section of oceanic crust includes ultramafics gabbros and pillowed basalts these older metavolcanics omv are conformably succeeded by dominantly volcanogenic metasediments which are in turn succeeded by a dominantly andesitic calc alkaline sequence of younger metavolcanics ymv the omv and ymv are largely restricted to the ced in egypt but analogous terranes are found in northern arabia 40 400 ppm and ni 30 260 ppm they are poor in k 2 o 0 05 0 92 rb 0 3 5 0 ppm and ba 11 89 ppm on ti zr cr v ni p discriminant diagrams the omv plot in the field of modern abyssal tholeiites high k rb 450 1800 and light ree depletions support this inference although k ba 25 45 is lower than modern mid ocean ridge basalts morb the sum of omv geochemical characteristics requires that these magmas were derived by the fractional fusion of the mantle it is suggested that the omv were generated by 20 25 fractional melting of previously depleted mantle at depths of less than 60 km relatively little fractionation accompanied ascent to the surface where the omv were erupted in a primitive crustal environment either a small oceanic rift or a back arc basin metamorphism of the ymv resulted in little elemental redistribution these andesites have sub alkaline clinopyroxenes and major element geochemical characteristics indistinguishable from modern calc alkaline andesites ymv andesites in the central and western ced have k rb 400 600 k ba 20 40 and are light ree enriched and heavy ree depleted high concentrations of cr 50 150 ppm and ni 20 100 ppm and low initial 87 sr 86 sr ratios 0 7028 0 7030 indicate that these magmas were generated by melting in the mantle modelling studies and consideration of experimental data indicate that these andesites were formed by 2 10 fractional fusion of hydrous undepleted garnet therzolite at depths of 65 km or more in the mantle the data show that an intense episode of instability convection and widespread melting occurred in the mantle beneath afro arabia at the end of the precambrian

syndeformational fluid trapping in quartz determining the pressure temperature conditions of deformation from fluid inclusions and the formation of pure co2fluid inclusions during grain boundary migration observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids our results imply that pure co2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation recrystallization process rather than representing a primary metamorphic fluid where the temperature of deformation can be deduced by other means the densities of fluid inclusions trapped during recrystallization which we call recrystallization primary fluid inclusions can be used to constrain the ambient pressure during deformation using these constraints the data imply that the post metamorphic hercynian exhumation in sardinia brought rocks at 300 c to within 3km of the surface this conclusion is similar to that described for the rapidly uplifted southern alps in new zealand

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

fluid evolution and chemical controls in the fazenda maria preta fmp gold deposit rio itapicuru greenstone belt bahia brazil the fazenda maria preta fmp gold deposit is confined to two regional scale sinistral oblique brittle ductile shear zones which are located in a greenschist facies metamorphosed volcano sedimentary sequence in the northern sector of the lower proterozic rio itapicuru greenstone belt ne brazil alteration is pervasive throughout the shear zones and characterized by carbonatization and sericitization of intermediate volcanic volcaniclastic and sub volcanic rocks the orebodies are mainly shear veins hosted by or directly associated with highly deformed carbonaceous volcaniclastic rocks breccia and stockwork systems or disseminations in felsic and mafic sub volcanic bodies native gold appears as free grains finely disseminated in the quartz veins or closely related to arsenopyrite pyrite pyrrhotite sphalerite and fe chlorite in the carbonaceous wallrocks fluid inclusion studies by microthermometry and laser raman microspectroscopy revealed that the vein quartz is largely dominated by primary pseudosecondary and rarely secondary populations of co2 ch4 n2 inclusions type i whereas primary groups of low salinity 6 wt eq nacl h2o co2 ch4 n2 inclusions type ii comprise the dominant inclusion type in only a few veins the thco2 l v l data indicated a variation in the co2 density of 1 05 to 0 60 g cm3 for the type i inclusions and conversely a narrower range of 0 76 0 73 g cm3 for the type ii inclusions the broader variation of the co2 density for the co2 rich fluid could have been the result of trapping of the vein fluid under a variable pressure regime or by its re equilibration during continuous deformation within the shear zone domains and reduction of the overburden pressure during uplift the co2 rich fluid inclusions provide no evidence that they have been the result of h2o loss either during infiltration e g hydration reactions or after trapping of an original h2o co2 fluid accordingly the co2 ch4 n2 and the h2o co2 ch4 n2 fluids are considered as representatives of two distinct fluid regimes which were active during the gold mineralizing events within the shear zones both types of ore fluids are interpreted as part of a deep metamorphic magmatic hydrothermal system in which i a co2 rich fluid probably originated in the mantle was transported to and released in higher structural levels mainly by tonalitic granodioritic and alkaline magmas whereas ii a h2o co2 fluid generated by devolatilization reactions during the regional metamorphism was either directly channeled into favorable structural sites i e metamorphic fluid or absorbed and later exsolved by the crystallization of felsic magmas i e magmatic fluid sensu lato in this context gold deposition occurred between 320 c and 420 c and 2 1 to 4 4 kb and calculated values of fo2 between 10 26 5 and 10 32 4 bar reveal the relatively reducing nature of the mineralizing fluids the ore paragenesis constrains fs2 to the range of 10 10 1 10 6 5 bar for these fluids under such conditions the gold was transported mainly as bisulfide complexes by the h2o co2 fluid but in the case of the co2 rich fluid the role of thiocomplexes or some other types of ligands is obscured by the lack of high temperature experimental data deposition of the metal occurred in response to redox changes which accompanied fluid carbon interaction particularly a decrease in fo2 and fs2 of the fluid on a microscopic scale phisisorption and chemisorption processes at the fluid iron sulfide interface may have further enhanced the deposition of the gold particularly on the surfaces of precipitating pyrite and arsenopyrite

origin and evolution of the um egat and dungash orogenic gold deposits egyptian eastern desert evidence from fluid inclusions in quartz shear zone related mesothermal gold deposits of um egat and dungash in the egyptian eastern desert are hosted by greenschist facies metavolcanic and or metasedimentary rocks of pan african age both deposits comprise boudinaged quartz veins that show evidence of incipient recrystallization and are similar in alteration style structural control and mineralogy the ore mineralogy includes pyrite arsenopyrite pyrrhotite chalcopyrite galena gold occurs both in the veins usually included in arsenopyrite pyrite or pyrrhotite next to fragments of altered country rocks or disseminated in the alteration haloes arsenic in arsenopyrite and aliv in chlorite geothermometers indicate that wall rock alteration and ore mineral precipitation occurred at temperatures between 400 and 250 c fluid inclusions in vein quartz occur in clusters or along trails three types of fluid inclusions were identified based on petrography and laser micro raman spectroscopy 1 two phase carbonic inclusions with co2 ch4 n2 h2o 2 two phase aqueous inclusions and 3 three phase aqueous carbonic inclusions with ch4 final melting of ice tmf for most inclusions occurs at temperatures between 4 and 0 c indicating a low salinity 300 c but cluster into two distinct groups for each type of inclusion inclusions from the same trail or cluster are commonly characterized by different degrees of fill or different th values field petrographic and microthermometric data suggest that low salinity aqueous carbonic fluids interacted with graphite bearing metasedimentary rocks to form ch4 at t 400 c and p 3 kbars these reduced fluids leached gold as they circulated through the metavolcanic rocks carrying it in the form of bisulfide complexes interaction of these aqueous carbonic fluids with the country rocks caused hydrothermal alteration and precipitated gold bearing sulfides in the alteration zones a drop of pressure during the migration of these fluids to shallower depths along the shear zones led to phase separation at t 300 c and p 2 3 kbars quartz crystallizing over a range of lower temperatures and pressures trapped carbonic and aqueous fluids as separate inclusions in clusters along pseudosecondary and secondary trails postdepositional deformation caused decrepitation of some inclusions and the stretching and leakage of others increasing th to 250 c deformation also remobilized the gold depositing it as globules of higher fineness in secondary sites

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

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

fluid chemical evolution as a factor in controlling the distribution of gold at the archean golden crown lode gold deposit murchison province western australia the golden crown lode gold deposit is one of a number of northwest southeast to north south trending quartz veins hosted by a steeply dipping 500 m thick differentiated dolerite sill the great fingall sill and adjacent graphitic shale in the day dawn district of the murchison province in the archean yilgarn craton western australia quartz veins of the golden crown deposit are shear zone hosted crosscut the dominant host rock stratigraphy at a high angle and are laminated partly boudinaged and generally bifurcate at their extremities veins are dominated by dark gray or milky white quartz with subordinate calcite and ankerite and in order of abundance arsenopyrite pyrrhotite pyrite galena chalcopyrite and minor sphalerite the vein sulfides coexist with native gold and are most abundant at vein margins textural evidence indicates that precipitation of the majority of these minerals overlapped and that most phases can be considered to have been in equilibrium during vein genesis mineral chemistry fluid inclusions alteration and ore assemblages show that there are significant systematic gradients in intensive variables within the golden crown deposit these are recorded over the approximately 450 m of vertical exposure of the vein system and over up to 30 m into the wall rocks based on proximal alteration assemblages and zoning patterns zoned wall rock alteration haloes are divisible into four sequences three of which are closely related to gold mineralization specific alteration sequences occur within different parts of the vein system biotite alteration predominates in the deeper portions whereas muscovite alteration characterizes the upper and southern portions of the system higher grade gold zones within the golden crown deposit are limited to the northern end of the system in the deeper portion of the veins and expand along strike to the south in the upper portions fluid inclusions interpreted to be trapped during gold mineralization are low salinity 10 wt nacl equiv h2o co2 ch4 inclusions with variable carbonic to aqueous contents that are interpreted to be due to fluid immiscibility inferred methane concentrations in the carbonic phase vary significantly from 19 7 mole percent in the vicinity of the shale contact to 5 2 mole percent in the shallower southern end of the deposit carbon and oxygen isotope compositions of carbonates 13ccalcite 10 5 to 1 9 13cankerite 5 3 to 4 1 18ocalcite 7 0 18 3 and 18oankerite 7 7 9 2 and oxygen isotope compositions of vein quartz 18oquartz 10 2 12 5 are well within the range of known archean orogenic lode gold deposits combining the results of all geothermometers and geobarometers a temperature of 300 to 400 c and pressure of 2 5 0 5 kbars are determined with temperature variations over the exposed quartz vein of less than 40 c the as content at of arsenopyrite and au ag ratios of native gold show significant compositional variation which appears to be controlled by parameters such as a h2s aq and f o2 not temperature gradients on the basis of the variations in fluid composition determined in the reefs the two major processes responsible for high grade gold mineralization are interpreted to have been phase separation in the deeper portions of the ore forming system approximately below 400 m level and above these levels mixing between two modified ore fluids one reduced fluid that had reacted with graphitic shale and a relatively oxidized fluid that had partly equilibrated with dolerite

synmetamorphic carbon mobility and graphite enrichment in metaturbidites as a precursor to orogenic gold mineralisation otago schist new zealand the macraes orogenic gold deposit is hosted by a graphitic micaceous schist containing auriferous porphyroblastic sulphides the host rock resembles zones of unmineralised micaceous graphitic pyritic schists derived from argillaceous protoliths that occur locally in background pelitic otago schist metasediments this study was aimed at determining the relationship between these similar rock types and whether the relationship had implications for ore formation argillites in the protolith turbidites of the otago schist metamorphic belt contain minor amounts of detrital organic matter 50 million years of evolution of the metamorphic belt from development of sheared argillite in the jurassic to postmetamorphic ductile extension in the cretaceous introduced graphite is structurally controlled and occurs with metamorphic muscovite and chlorite as veins and slicken sided shears with some veins having 50 noncarbonate carbon graphitic foliation seams in low grade micaceous schist and metamorphic quartz veins contain equant graphite porphyroblasts up to 2 mm across that are composed of crystallographically homogeneous graphite crystals graphite reflectance is anisotropic and ranges from 1 to 8 green light texturally similar porphyroblastic pyrite has grown in micaceous schist up to 10 wt s metamorphic quartz veins and associated muscovite rich shears these pyritic schists are weakly enriched in arsenic up to 60 ppm the low grade metamorphic mobility and concentration of graphite in micaceous schists is interpreted to be a precursor process that structurally and geochemically prepared parts of the otago schist belt for later more restricted gold mineralisation economic amounts of gold and associated arsenic were subsequently introduced to carbonaceous sulphidic schists in the macraes gold deposit by a separate metamorphic fluid derived from high grade metaturbidites fluid flow at all stages in these processes occurred at metamorphic rates mm year and fluids were broadly in equilibrium with the rocks through which they were passing

cyclic sedimentation in the shallow marine upper permian kennedy group carnarvon basin western australia abstract the upper permian kennedy group of the carnarvon basin western australia was deposited while the merlinleigh sub basin was undergoing thermal subsidence and the global climate was warming from the carboniferous permian glaciation to the mesozoic greenhouse conditions the kennedy group comprises siliciclastic sedimentary rocks dominated by sandstones in the lower part with coarsening up cycles from mudstones to very coarse sandstones and granule conglomerates in the upper part cycles were observed and logged in the field and although many types of cycles were found three main motifs describe most of the cycles cycle motifs are defined based on the dominance of the various facies mooka motif cycles are dominated by fine grained and bioturbated facies interpreted as deposition during relative sea level highstand with only thin laminated or cross bedded sandstones interpreted as deposited during relative sea level fall binthalya motif cycles are dominated by laminated and cross bedded sandstones and coolkilya motif cycles consist of alternating laminated and bioturbated beds a hierarchy of cycles was observed in the field and this correlated well with spectral analysis of logged parameters spectral analysis of section log data and data sets corrected for the effects of compaction and sedimentation rates detected regular cyclicity geochronology of the kennedy group is not well enough constrained to allow the cycle periods in time to be calculated but ratios of the different scale cycle thicknesses correlate well with ratios of the milankovitch orbital cycles that have been calculated for the permian the presence of regular cyclicity and even bed thicknesses across large distances are not consistent with tectonic or autocyclic models of cycle formation the cycles are more likely to have been caused by fluctuating eustatic sea levels perhaps enhanced by changing amounts or seasonality of precipitation both sea levels and climatic fluctuations would ultimately be controlled by the milankovitch orbital cycles

mechanism of mineralization in the changjiang uranium ore field south china evidence from fluid inclusions hydrothermal alteration and h o isotopes abstract the changjiang uranium ore field which contains 10 000 tonnes of recoverable u with a grade of 0 1 0 5 is hosted by triassic two mica and jurassic biotite granites and is one of the most important uranium ore fields in south china the minerals associated with alteration and mineralization can be divided into two stages namely syn ore and post ore the syn ore minerals are primarily quartz pitchblende hematite hydromica chlorite fluorite and pyrite the post ore minerals include quartz calcite fluorite pyrite and hematite the fluid inclusions of the early syn ore stage characteristically contain o 2 and those of the late syn ore and post ore stage contain h 2 and ch 4 the fluid inclusions in quartz of the syn ore stage include h 2 o h 2 o co 2 and co 2 types and they occur in clusters or along trails homogenization temperatures t h for the h 2 o co 2 and two phase h 2 o inclusions range from 106 c to 350 c and cluster in two distinct groups for each type salinities are lower than 10 wt nacl equiv the ore forming fluids underwent co 2 effervescence or phase separation at 250 c under a pressure of 1000 1100 bar the u th values of the altered granites are lowest close to the ore increase outwards but subsequently decrease close to unaltered granites from the unaltered granites to the ore the lowest fe 2 o 3 feo values become lower and the highest values higher the ree patterns of the altered granites and the ores are similar to each other the u contents of the ores show a positive correlation with total ree contents but a negative correlation with lree hree ratios indicating the pitchblende is ree bearing and selectively hree rich the eu values of the ore show a positive correlation with u contents indicating the early syn ore fluids were oxidizing the ce values show a negative correlation indicating the later mineralization environment became reducing the water rock interactions of the early syn ore stage resulted in oxidization of altered granites and reduction of the ore forming fluids and it was this reduction that led to the uranium mineralization during alteration in the early syn ore stage the oxidizing fluids leached uranium from granites close to faults and fe 2 o 3 feo ratios increased in the alteration zones the late syn ore and post ore alteration decreased the fe 2 o 3 feo ratios in the alteration zones the 18 o w smow values of the ore forming fluids range from 1 8 to 5 4 and the d w smow values range from 104 4 to 51 6 suggesting meteoric water the meteoric water underwent at least two stages of water rock interaction the first caused the fluids to become uranium bearing and the second stage which was primarily associated with ore bearing faults led to uranium deposition as pitchblende accompanied by co 2 effervescence

post entrapment modification of fluid inclusions due to overpressure evidence from natural samples effects of post entrapment fluid inclusion modification are examined with reference to retrogression related quartz veins from the caledonian ose thrust northern norway the inclusions occur in secondary trails and contain high density hypersaline aqueous fluids on morphological characteristics they are subdivided into type a elongate ellipsoidal and or irregular inclusions and type b more equant regular and or negative crystal form with reference to previous research on post entrapment modification of inclusions in quartz it is proposed that type a inclusions experienced little or no post entrapment modification whereas type b inclusions show features characteristic of post entrapment permanent inelastic stretching and or leakage this produces increased homogenization temperatures th associated with increased inclusion volume and lowering of density whilst maintaining constant salinity the similarity of data for degree of fill and salinity between type a and type b inclusions indicates that type b inclusions have primarily modified by stretch rather than leakage however the spread towards slightly larger volume of vapour in type b inclusions suggests that some leakage has also occurred because stretched and or partially leaked inclusions have increased th isochore projections significantly underestimate trapping pressure pt relative to unmodified inclusions therefore recognition of post entrapment inclusion modification due to overpressure is crucial to avoid misinterpretation of data but has considerable potential for constraining the detail of p t trajectories of individual rocks on this basis rocks from the ose thrust zone north norway are shown to have experienced rapid uplift on a clockwise p t t path during the final stages of caledonian scandian orogenesis

slope failure in underconsolidated soft soils during the development of a port in tianjin china part 1 field investigation this paper presents the field investigation of a major landslide that occurred in a newly dredged slope for port development in the city of tianjin northern china the dredged slope comprised underconsolidated soft clay of recent marine and river delta deposits the landslide consisted of a number of individual slides that occurred sequentially and extended retrogressively and laterally into reclaimed land it lasted for about 1 h occupying a plan area that is about 200 m long and 150 m wide in the reclaimed land the failed soil mass was estimated to have a volume of between 700 000 and 800 000 m3 part of the failed soil mass slipped into a newly dredged open space in the sea the distance of the debris travel into the berth was about 80 m the debris surface had a gentle slope of about 3 0 the angle from the dredged slope crest to the far edge of the debris was about 6 8 a common rupture surface was found underneath the debris and above the in situ marine mud it controlled the inland extension o

nitrogen isotope systematics of mesothermal lode gold deposits metamorphic granitic meteoric water or mantle origin archean gold bearing quartz vein systems constitute one of the most important classes of precious metal deposits however their origin remains controversial mantle granitoid meteoric water and metamorphic related models do not resolve this controversy new n and nitrogen isotope data on hydrothermal muscovite from six gold camps from the late archean superior province of canada and biotite from nine au mineralized locations from the norseman wiluna greenstone belt western australia are reported the majority of muscovites and biotites have n contents of 20 190 ppm and 15 n of 10 20 and 10 70 ppm and 10 24 respectively the 15 n of the mantle is 5 and of granitoids is 0 10 both with generally low n contents organic n is 0 10 meteoric water is 1 9 9 4 and metamorphic rocks are 3 18 increasing with higher grade accordingly the data appear to rule out a mantle hypothesis granitoid related magmatic processes or meteoric water for the deposits but are consistent with ore fluids derived by metamorphic dehydration reactions

hydrothermal transport and depositional processes in archean lode gold systems a review abstract compelling evidence now exists for the formation of archean lode gold deposits over a substantial range in metamorphic conditions and crustal depth the commonality of ore fluid isotopic and geochemical characteristics the extreme fluid rock ratios within actual ore zones and the observed depth continuity within individual orebodies all suggest that these deposits formed within vertically extensive crustal scale hydrothermal systems calculations based on new thermodynamic data and estimated ore fluid conditions suggest that gold would have been transported as au hs 2 over most of this range gold transport in the ore fluids that formed some diopside and diopside k feldspar class deposits t 550 c would have been as aucl2 whereas the au hs complex may have been significant in some of the lower temperature 270 c less alkaline ore fluids the high solubility of gold in lode gold ore fluids at amphibolite facies conditions 10 s to 1000 s ppb suggests that fluids may have been undersaturated in gold within their source regions promoting the ore fluid s capacity to retain gold in solution over the large transport distances involved ore depositional mechanisms were also likely to vary between crustal levels fluid rock interactions and wallrock sulphidation in particular appear to be the most important type of precipitation mechanism however with decreasing depth of formation the scope of other depositional mechanisms notably phase separation and fluid mixing becomes greater

fourth canadian geotechnical colloquium strength and slope stability in canadian soft clay deposits it is generally admitted that the long term stability of clay slopes should be analysed in terms of effective stresses which necessitates the knowledge of the pore pressure conditions and of the relationship between the shear strength and the effective stresses this paper deals with the determination of shear strength for stability analysis of clay slopes in eastern canada first the various concepts pertinent to slope stability in soft clay are examined and a certain justification of the use of the post peak or large strain strength is demonstrated in a second part 14 case records of natural slopes or permanent excavation slopes are presented and analysed in terms of the post peak strength finally values of post peak strength determined in the laboratory for more than 30 sites are presented and it is attempted to derive correlations by which the shear strength parameters could be readily approximated from other properties such as the apparent preconsolidation pressure or the vane strength

a new classification of the gold deposits of egypt abstract gold deposits and occurrences located in the nubian shield have been known in egypt since predynastic times despite the fact that these deposits were long under exploitation and investigated many times they are still insufficiently classified in harmony with the crustal evolution models suggested for the evolution of the nubian shield several plate tectonic models were proposed for the development of the nubian shield and the present classification relies heavily on the model that implies collision of arc inferred continent through subduction and obduction of oceanic lithosphere a three fold classification of gold deposits of egypt is offered here in harmony with this evolutionary model these are stratabound deposits and non stratabound deposits hosted in igneous and metamorphic rocks as well as placer gold deposits the stratabound deposits are hosted in island arc volcanic and volcaniclastic rocks of comparable composition formed in ensimatic island arcs they are thought to have formed by exhalative hydrothermal processes during the waning phases of sub marine volcanic activity stratabound deposits are sub divided into three main types gold bearing algoma type banded iron formation gold bearing tuffaceous sediments and gold bearing volcanogenic massive sulphide deposits non stratabound deposits occur in a wide range of igneous and metamorphic rocks they were formed during orogenic and post cratonization periods by mineralizing fluids of different sources non stratabound deposits are divided into vein type mineralization which constituted the main target for gold in egypt since pharaonic times and disseminated type mineralization hosted in hydrothermally altered rocks alteration zones which are taken recently into consideration as a new target for gold in egypt placer gold deposits are divided into modern placers and lithified placers the former are sub divided into alluvial placers and beach placers conglomerates occurring on or near ancient eroded surfaces represent lithified placers

orogenic gold formation in an evolving decompressing hydrothermal system genesis of the samut gold deposit eastern desert egypt abstract samut is a vein type gold mineralization in the eastern desert of egypt which shares many geologic features with other orogenic deposits in this region the deposit has a long history of mining activity dating back to ancient times but so far has received little attention from the standpoint of geologic study here we present new field petrographic microthermometric and microanalytical data from the samut gold deposit to evaluate its genesis and fluid evolution vein quartz at samut shows abundant evidence of precipitation coinciding with early phases of ductile deformation that show transitions to increasing brittle fracturing and fragmentation through time in some samples brecciation of the vein quartz is intense and shows evidence of repeated episodes of fragmentation this brittle style of deformation culminates with latest stage brittle opening and loss of confining pressure resulting in open space filling textures backscattered electron images and electron microprobe analysis reveal three varieties of pyrite in the mineralized quartz veins py i py ii and py iii laser ablation icpms analysis of pyrites from mineralized quartz veins reveals that the earlier py i is low in arsenic and gold whereas py ii and py iii are enriched in both elements anhedral py ii is particularly gold rich and gives way to blocky euhedral py iii that is rich in arsenic but not as rich in gold compared to py ii fluid inclusions in the least brittle deformed vein quartz indicate that the veins formed at minimum temperatures of 300 c early in the hydrothermal system the calculated fluid pressures at homogenization of the aqueous carbonic inclusions furnish a wide range throughout the paragenesis perhaps on the order of 1 to 3 kbar the 34s values of pyrites imply sulfur isotopic composition of the mineralizing fluid on the order of 0 6 to 4 9 overlapping with the broad range of 34s values calculated for ore fluids in orogenic gold deposits worldwide together these results support a general model in which gold and sulfide deposition was coinciding with an ongoing syn deformational vein formation and tending towards the late stages of vein growth prior to loss of confinement free milling gold appears to be mostly related to the later stages of brittle fracturing and re sealing of the veins during repeated fluid release as the background fluid pressure evolved from earlier dominantly lithostatic to later fully hydrostatic conditions

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

estimating the excavation disturbed zone in the permanent shiplock slopes of the three gorges project china abstract the stability and deformation of the permanent shiplock slopes are among the key issues in the design and construction of the three gorges project the permanent shiplock slopes formed by deeply and steeply cutting into weathered and fresh granites are 1607 m in length and 50 170 m in height the disturbed zone in the permanent cut slopes induced by excavation is therefore one of the most important aspects in slope stability and deformation evaluation a comprehensive investigation including non linear finite element analysis in situ testing instrumentation and monitoring back analysis and rock mass quality rating has been carried out for the identification and evaluation of the excavation disturbed zone in the permanent cut slopes the results of the investigation confirmed the existence of such an excavation disturbed zone in the permanent cut slopes this zone is characterized by a considerable weakening in the mechanical properties of the rock mass from the cut surface to the deeper region of the permanent cut slopes the excavation disturbed zone can be further divided into a damaged zone an affected zone and a slightly affected zone according to the extent of weakening in the rock mass the damaged zone and the affected zone have thicknesses of 5 10 m and 10 20 m respectively the exact pattern of the excavation disturbed zone is variable in different parts of the permanent cut slopes and are generally similar to that of the plastic zones estimated by using the non linear finite element analysis the present investigation has provided both factual data and insights for the stability and deformation evaluation of the permanent shiplock slopes the approach and methodology developed in the paper can be used to assess similar excavation disturbed zones in other large cut slopes

the bronzewing lode gold deposit western australia p t x evidence for fluid immiscibility caused by cyclic decompression in gold bearing quartz veins abstract the bronzewing lode gold deposit is located in the yandal greenstone belt in the yilgarn craton of western australia gold mineralization is hosted in tholeiitic basalt that is metamorphosed to greenschist facies individual ore bodies are controlled by a complex gold bearing quartz vein system that comprises shear and extension veins formed during a progressive d2 deformation event gold is localized in quartz along fractures and deformed grain boundaries and is interpreted to have formed late in the formation of the veins detailed petrography and microthermometry on primary pseudosecondary and secondary fluid inclusions trapped in gold bearing shear and extension veins revealed five types of fluid inclusions 1 co2 ch4 h2o nacl inclusions of variable salinity 0 1 to 17 5 eq wt nacl containing between 10 and 99 mol co2 and molar volumes that range from 22 to 76 cm3 2 h2o nacl inclusions of variable salinity 0 4 to 22 1 eq wt nacl 3 co2 ch4 inclusions with up to 58 mol ch4 and molar volumes between 54 and 73 cm3 4 ch4 h2o inclusions with ch4 ranging from 80 to 90 mol and 5 ch4 inclusions with low molar volumes of 19 to 23 cm3 types 1 2 and 3 constitute a fluid inclusion assemblage that occurs consistently in primary pseudosecondary and secondary trails and clusters within the gold bearing quartz vein system these co existing fluids are interpreted to have formed by fluid immiscibility of a low salinity homogeneous parent fluid at about 300 c and 1500 bars locally type 2 fluid inclusions exhibit total homogenization temperatures that are on average 100 c less than the co genetically trapped type 1 aqueous carbonic inclusions this discrepancy is interpreted to have involved co2 effervescence in response to fluid pressure fluctuations types 4 and 5 fluid inclusions are rare and are only present locally in secondary trails and clusters in extension veins significant pressure fluctuations but relatively constant homogenization temperatures for types 1 2 and 3 fluid inclusions suggest that cyclic decompression of the hydrothermal fluids due to seismic activity along the shear zones that host the gold bearing veins triggered fluid immiscibility the process of fluid immiscibility and subsequent lowering of gold solubility is interpreted to be the most efficient precipitation mechanism for gold in the d2 shear zone hosted vein system at bronzewing

ore forming processes of the daqiao epizonal orogenic gold deposit west qinling orogen china constraints from textures trace elements and sulfur isotopes of pyrite and marcasite and raman spectroscopy of carbonaceous material

hydrothermal fluid evolution within the cadillac tectonic zone abitibi greenstone belt canada relationship to auriferous fluids in adjacent second and third order shear zones the cadillac tectonic zone in the abitibi greenstone belt canada is spatially associated with world class gold deposits that are hosted in second and third order faults five types of hydrothermal quartz veins with distinct structural timing are distinguished in the cadillac tectonic zone in the val d or camp and are related to d 2 steep reverse faulting and d 3 oblique transcurrent movement fluid inclusions in gold bearing and barren hydrothermal quartz veins in the transcrustal cadillac tectonic zone record the progressive evolution of the hydrothermal fluids within the cadillac tectonic zone oldest h 2 o co 2 ch 4 nacl fluid inclusions which predate gold mineralization are superseded by gold associated dominantly carbonic co 2 ch 4 h 2 o nacl fluid inclusions on the basis of variable phase ratios and similar total homogenization temperatures in contemporaneous fluid inclusions trails the oldest h 2 o co 2 ch 4 nacl fluids are interpreted to have undergone phase separation the ch 4 content increases from the older x ch 4 0 03 0 24 to the younger x ch 4 0 15 0 71 fluid inclusions and the salinity is low to moderate in the older fluid inclusions mean 1 7 2 6 2 wt nacl equiv and increases in the younger fluid inclusions mean 1 16 2 6 0 wt nacl equiv trails of late stage co 2 ch 4 n 2 h 2 o and ch 4 c 2 h 6 c 3 h 8 fluid inclusions crosscut earlier carbonic aqueous fluid inclusion trails in all veins the texturally latest fluid inclusions occur in trails that crosscut earlier fluid inclusion trails and quartz deformation bands and are composed of h 2 o nacl cacl 2 postentrapment modifications are considered unlikely for most fluid inclusions in the cadillac tectonic zone the hydrothermal fluids in the cadillac tectonic zone were compared with those in second and third order fault zones in the world class sigma deposit to evaluate whether the two fluid systems are of similar derivation carbonic aqueous fluids that deposited quartz in veins and some gold in the cadillac tectonic zone are distinct from those that are hosted in structures of similar timing at sigma cadillac fluids have higher co 2 content and marginally higher salinity 0 6 15 3 wt nacl equiv and 1 10 wt nacl equiv in the cadillac tectonic zone and at sigma respectively but contain similar amounts of ch 4 the high salinity aqueous inclusions at sigma which are interpreted to represent the unmixed h 2 o rich end member of a combined co 2 ch 4 h 2 o nacl fluid are absent in the cadillac tectonic zone veins of d 3 timing which contain a high ch 4 component in the cadillac tectonic zone to 70 mole have not been documented at sigma the magnitude of the hydrothermal quartz vein field and the homogeneity of quartz vein mineralogy and textures in the val d or camp strongly suggest that the fluids that precipitated auriferous quartz veins in second and third order shear zones were not locally derived it is suggested that ore bearing fluids ascended along the cadillac tectonic zone and infiltrated the second and third order fault network an unknown amount of metamorphic h 2 o from the greenstone belt probably mixed with these fluids differences in the fluid composition in the cadillac tectonic zone and those in second and third order shear zones are explained by phase separation with preferential vapor loss into the upper portions of the cadillac tectonic zone and by in situ phase separation without vapor loss during ore deposition at sigma methane enrichment in the late fluids in the cadillac tectonic zone was most likely controlled by an increased fluid interaction with reduced carbon in sedimentary rocks but increasing mantle outgassing and cooling of an f o 2 buffered ascending fluid may also have contributed to the ch 4 budget the youngest aqueous brines in the cadillac tectonic zone are similar to fluids in late fracture fillings and to canadian shield basement brines

raman characterization of carbonaceous material in the macraes orogenic gold deposit and metasedimentary host rocks new zealand abstract raman spectroscopic and petrographic analyses were performed on samples collected from zones distal and proximal to the macraes gold deposit in the otago schist of new zealand to characterize the features and possible origins of carbonaceous material cm and to assess the potential role of cm in the formation of gold deposits cm is a common component in meta sedimentary orogenic gold deposits and it has been proposed that cm contributes to gold mineralization processes but the details of the mechanisms responsible are not fully understood documentation of the origins of the otago schist cm will improve our understanding of the role of cm in gold deposits this work has identified four types of cm of varying thermal maturity and origins from prehnite pumpellyite grade to lower greenschist grade samples in prehnite pumpellyite and pumpellyite actinolite grade rocks low maturity cm 1 coexists with framboidal pyrite indicating an in situ sedimentary origin with a potential association with the source of gold low crystallinity cm 2 is also found in low grade samples and is likely to have been deposited from fluids unrelated to gold mobilization cm 3 is the highest maturity cm recognized cm 3 is found in samples from the highest metamorphic grades studied lower greenschist facies where bands of cm 3 cross cut the foliation cm 3 is therefore thought to have been transported by fluids though possibly only at short length scales cm 4 is less mature than cm 3 and is found in mineralized rocks in association with sulfide minerals and gold cm 4 is likely to have a depositional origin but its precise role with respect to gold mineralization has not been identified

fluid inclusion and noble gas studies of the dongping gold deposit hebei province china a mantle connection for mineralization the dongping gold deposit 100 t au occurs about 200 km inboard of the northern margin of the north china craton the deposit is mainly hosted by syenite of a middle paleozoic alkalic intrusive complex that was emplaced into late archean basement rocks both groups of rocks are intruded by late jurassic to early cretaceous crustal melt granite dikes and stocks some within a few kilometers of the deposit the gold ores were deposited during this latter magmatic period at about 150 ma a time that was characterized by widespread regional north south compression that formed the east west trending yanshan deformational belt the ores include both the telluride mineral bearing low sulfide quartz veins and the highly k feldspar altered syenite with most of the resource concentrated in two orebodies 1 and 70 fluid inclusion microthermometry indicates heterogeneous trapping of low salinity e g 5 7 wt nacl equiv fluids that varied from a few to 60 mole percent nonaqueous volatile species laser raman spectroscopy confirms that the vapor phase in these inclusions is dominated by co2 but may be comprised of as much as 9 mole percent h2s and 20 mole percent n2 methane concentrations in the vapor phase are consistently 1 mole percent the variable phase ratios are consistent with fluid immiscibility during ore formation fluid inclusion trapping conditions are estimated to be 250 to 375 c and 0 6 to 1 0 kbar helium isotope studies of fluid inclusions in ore stage pyrites indicate 3he 4he ratios of 2 1 to 5 2 ra ra 1 4 10 6 for air for orebody 1 and 0 3 to 0 8 ra for orebody 70 the former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1 the lower values for orebody 70 which is characterized by a more disseminated style of gold mineralization are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks which may have contributed additional 4he to the fluids a mantle source for at least some of the components of the gold forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool archean lithosphere beneath the craton during this time the dongping deposit is located along the 100 km wide north south gravity lineament which marks the western border of the thinned crust as both regional metamorphism of mesoproterozoic and younger cover rocks and widespread granite magmatism also occurred at ca 150 ma it is unclear as to whether one or both of these also contributed fluid and or metals to the hydrothermal system importantly these new data suggest that economically significant gold deposits of similar mineral style and fluid composition which are scattered along the margins of the craton may all be products of a fluid originally partly sourced within the mantle

on the timing relationship between fluid production and metamorphism in metamorphic piles some implications for the origin of post metamorphic gold mineralisation abstract the relative timing of metamorphism at different crustal levels is quantified for a range of metamorphic environments associated with convergent deformation we characterise different metamorphic environments by making simple assumptions about the nature of heat input and the nature of heat withdrawal from the terrane if internal heat production is the major heating agent during crustal thickening then deep crustal levels reach their metamorphic temperature peak later than shallow levels in terranes heated from below such relationships apply only if erosion commenced early in the thermal history or if erosion rates are fast quantitative knowledge of these relations can be used together with simple assumptions about prograde fluid release to predict the likely timing of fluid passage through rocks higher in the column in terranes with deep later characteristics the evidence for fluid penetration may be preserved in the form of mineralised quartz veins or late stage alteration within our simple parameterisation of crustal heat sources we can use the grade of a metamorphic rock together with field evidence on the timing of metamorphism igneous intrusion and deformation in order to constrain the time scale of the underlying thermal perturbation and erosion process for a given terrane we demonstrate that time intervals up to several tens of million years may separate metamorphism and fluid emplacement in model evolutions that are scaled to describe greenschist facies metamorphic terranes that formed at low pressure such timing relationships are in fact recorded in many greenschist facies metamorphic terranes that host late stage mesothermal gold deposits we suggest therefore that there is no conflict between the observation that the emplacement of many gold deposits occurred demonstrably after peak metamorphism of their host rocks and the interpretation that metamorphic fluids are responsible for the mineralisation

thermomechanical evolution of a ductile duplex the thermomechanical evolution of a midcrustal ductile duplex in central australia has been reconstructed through space and time using 40ar 39ar thermochronology flow stress estimates cross sectional restoration of dislocation creep microstructures and microstructural and structural analysis a critical aspect of this analysis is the identification of populations of white micas in quartzite mylonites that have neocrystallized below their closure temperature and which record the time when ductile deformation ceased in dating these micas the mylonitic microstructures have effectively been dated the time temperature history of the duplex has been constrained through multidomain thermal modeling of k feldspar 40ar 39ar data the modeling demonstrates that a temperature gradient existed across the duplex during its formation the concept of microstructural continuity during ductile deformation has great potential for elucidating the kinematic evolution of ductile duplexes mapping of the deformation mechanisms and recrystallized grain sizes of quartzites deformed under greenschist facies conditions has been used to evaluate tectonic offsets that occurred after microstructural freezing this analysis shows that the duplex formed as a forward propagating thrust system accommodating 60 km of convergence between the upper and lower plates of the megathrust with a significant fraction of the displacement occurring after microstructural freezing finally using the data as input to published flow laws for quartz aggregates provides a strain rate history for the duplex although uncertainties are clearly large the timing of highest estimated strain rates during duplex evolution does indeed correlate with the highest rates of convergence between the upper and lower plates of the megathrust system according to regional cooling history studies and with coeval sedimentation in adjoining molasse basins

gold in egypt does the future get worse or better abstract within the eastern desert of egypt there are more than a hundred vein type gold deposits and occurrences gold was mined in the dynastic and roman periods of the egyptian history and most of the attention was focused entirely on the near surface high grade parts of these veins currently besides the more problematic sulfide rich quartz veins which generally occur in the lower levels of the worked out auriferous quartz veins some targets including wall rock alteration listwaenite dumps and tailings of ancient mines by product gold hosted in volcanogenic massive sulfide deposits and gold bearing algoma type bif as well as alluvial gold constitute the new targets for gold in the eastern desert of egypt in most of these targets gold displays a bimodal distribution occurring both as free milling gold and in the form of sub microscopic or invisible gold in refractory sulfides and sulfoarsenides such as pyrite chalcopyrite arsenopyrite gersdorffite and pentlandite minerals characterizing gold in an ore is important in extraction metallurgy free milling gold can be efficiently recovered by crushing grinding and cyanidation without additional processing in refractory ores on the other hand conventional milling can liberate the sulfides from the gangue allowing a low content of concentrate to be produced by a process such as flotation however direct leaching of the concentrate results in poor gold extractions as the cyanide lixiviant is unable to contact the gold locked within the refractory host oxidative pretreatment is required for such ores and the methods available for oxidation are roasting calcination pressure oxidation and bacterial oxidation all oxidize the refractory minerals in the ore to render the gold amenable to cyanidation while such oxidative methods are capable of achieving reasonable recoveries they increase the capital and operating costs an alternative applicable to the liberation of gold from the refractory host is to continue the grinding process to reduce the particle size of the host mineral thereby exposing a part of the gold surface for contact with the cyanide solution a benefit of this technique is that the environmental aspects of the oxidation reaction products are avoided however the ultra fine grinding also adds more operating costs metallurgical studies carried out on some gold deposits dumps and tailings of ancient gold mines in egypt proved that these ores are amenable to percolation leaching concentration of kcn varies between 0 5 and 1 g l for the 10 mm grain size and consequently heap leaching is a successful technique as the results of these laboratory scale column tests show in most of these studies a marked improvement in the percent of gold recovery was gained when the crushed ore is agglomerated by the addition of water lime and or cement particularly in ores containing significant quantities of clay minerals and clay forming minerals e g sericite and muscovite and by addition of kerosene which passivates the adsorption surfaces on the graphite placer gold is recovered by gravity methods utilizing the large difference in specific gravity between gold and commonly associated minerals such as quartz and feldspar the equipments range from a simple pan to more complex devices used in gold recovery plants and dredges modern studies in egypt point to the presence of different targets of gold diverse in their gold content mode of occurrence of gold and the metallurgical treatments required for extracting gold with the advance of modern techniques such as electron microprobe analyses empa laser ablation microprobe inductively coupled plasma mass spectroscopy lam icp ms gold ores in egypt should be re characterized precisely to know the specifications of these ores and consequently predict the metallurgical regime required and with the high world gold price it has become necessary to take into consideration the presence of refractory gold ores as one of these targets in egypt generally speaking laboratory experiments conducted on gold processing in egypt are encouraging to some extent however the gold extraction rates of the free milling ores with conventional cyanidation and refractory ores with direct and pretreatment techniques can be improved by modifying the conditions of extraction to be consistent with the results obtained from the re characterization stage otherwise any target for gold and whatsoever the mode of occurrence of gold in this target i e free milling and or refractory could be recovered directly by heap leaching technique and we should accept less than ideal gold recovery for any target when weighed against the capital expenditure required for processes such as roasting and the continuous grinding processes which might improve recoveries by only a small percentage

slope failure in underconsolidated soft soils during the development of a port in tianjin china part 2 analytical study this paper presents the analytical study of a major landslide that occurred in a newly dredged slope during port development in the city of tianjin northern china the slope comprised mainly underconsolidated and submerged soft soils the landslide consisted of a number of individual slides that occurred sequentially and extended retrogres sively and laterally into the reclaimed land the paper proposes a slope stability assessment methodology for the exam ination of such slope failures with retrogressive and lateral extension into reclaimed land both the total and the effective stress approaches are adopted in the slope stability assessment eight different sets of soil shear strength pa rameters are used in the assessment they were determined by using different methods in the laboratory and in the field or by back analysis the assessment results indicate that the total stress approach together with undrained vane strength values gives the best result in the stability assessment of the original dredged slope and the subsequent failed slopes the paper further examines the factors that might have caused or triggered the occurrence of the landslide backfilling of a thick general soil layer and a sand cushion for vacuum preloading of the hydraulic fill in the re claimed land might have rendered the entire slope marginally stable lowering of the tidal level might also have had an effect in triggering the landslide the engineering approach and results presented in this study could be useful in the design and construction of dredged slopes in underconsolidated soft soils

molybdenite re os age h o c s pb isotopes and fluid inclusion study of the caosiyao porphyry mo deposit in inner mongolia china abstract the giant caosiyao porphyry mo deposit located in the northern margin of the north china craton is a newly discovered mo deposit in the yan liao molybdenum belt orebodies of the deposit are mainly hosted in metamorphic rocks of the mesoarchean jining group with a small amount of orebodies in the late jurassic syenogranite porphyry the ore forming process of the deposit can be divided into three stages an early quartz molybdenite magnetite pyrite stage a middle quartz molybdenite pyrite pyrrhotite chalcopyrite stage and a late quartz carbonate pyrite fluorite pyrrhotite stage molybdenite re os dating indicates that the caosiyao deposit formed at ca 150 ma four types of fluid inclusions fis have been distinguished in quartz phenocryst and various quartz veins including liquid rich gas rich h2o co2 and daughter mineral bearing inclusions the fis in the quartz phenocrysts of the syenogranite porphyry contain liquid rich gas rich h2o co2 and daughter mineral bearing types their homogenization temperatures and salinities vary from 385 c to 550 c and 6 5 wt to 65 0 wt nacl eqv respectively the fis in the quartz of the early stage are also mainly liquid rich gas rich h2o co2 and daughter mineral bearing types their homogenization temperatures and salinities vary from 243 c to 401 c and 6 0 wt to 39 8 wt nacl eqv respectively the fis in the quartz of the middle stage are mainly liquid rich h2o co2 and daughter mineral bearing types their homogenization temperatures and salinities vary from 208 c to 336 c and 1 2 wt to 34 1 wt nacl eqv respectively the fis in the quartz of the late stage are only liquid rich type their homogenization temperatures and salinities vary from 124 c to 196 c and 3 9 wt to 13 2 wt nacl eqv respectively the ore forming fluids of the caosiyao deposit are characterized by moderate high temperature and great fluctuating salinity belonging to an h2o nacl kcl mgcl2 co2 ch4 system the 18oh2o and dh2o values of the early and middle stages vary from 3 5 to 7 4 and 96 to 77 respectively the 18oh2o and dh2o values of the late stage vary from 2 9 to 0 6 and 112 to 77 respectively indicating that the ore forming fluids of the early and middle stages mainly consist of magmatic water and that the fluid in late stage is a mixture of magmatic and meteoric water the 13c values vary from 16 5 to 8 8 for the early and middle stages and 11 4 to 5 3 for the late stage suggesting that the carbon of the early and middle stages consists of a mixture of organic and magmatic sources and that the carbon in the late stage was mainly from a magmatic source the 34s values range from 4 0 to 6 1 with an average of 4 8 the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of the metallic minerals are in the ranges of 15 962 17 832 15 200 15 511 and 35 918 37 927 respectively both s and pb isotopic systems indicate that the ore forming metals came primarily from mesozoic intermediate felsic magma the multi stage boiling or immiscibility of the ore forming fluids was the dominant mechanism for the deposition of ore forming materials

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

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

distinguishing barren and auriferous veins in the sigma mine val d or quebec the sigma mine is an archean lode gold deposit located in the abitibi greenstone belt quebec barren quartz veins occur subparallel to auriferous veins within the mine and also occur north of the