first evidence of high pressure metamorphism in the cover series of the southern menderes massif tectonic and metamorphic implications for the evolution of sw turkey abstract the menderes massif occupies a large part of western turkey it is tectonically overlain by nappes of the izmir ankara suture zone including the bornova flysch zone on its northern flank the afyon zone on its eastern border and the lycian nappes on its southern flank the discovery of magnesiocarpholite kyanite assemblages in the mesozoic cover sequence of the southern menderes massif leads to the very first consideration that a major high pressure hp metamorphic event affected the massif during its alpine evolution estimations of minimum pressure temperature conditions about 10 12 kbar and 440 c suggest a minimum burial of 30 km for the metasedimentary rocks of the menderes massif similar to that for the eocene dilek blueschists which belong to the cycladic complex this finding of high pressure rocks within the menderes cover series as well as the recent description of low grade high pressure parageneses in the basal thrust sheets of the overlying lycian nappe complex has strong implications for the tectono metamorphic evolution of these units the characteristics of this high pressure metamorphism and the deformation features observed in the southern menderes massif allow consideration of a fast burial during alpine subduction and nappe stacking three high pressure units were piled up during the eocene collision of the sakarya continent and the tauride menderes block the lowermost unit consists of the imbricated core and cover of the menderes massif the intermediate unit is the cycladic blueschist complex dilek and samos regions and the uppermost unit is made of the lycian nappes the retrogression of high pressure parageneses from the menderes massif follows an isothermal decompression path and the associated deformation is characterized by a severe stretching oriented n s to ne sw during the high pressure event and its exhumation we propose a tectono metamorphic model in three main stages 1 the southward translation of the high pressure lycian nappes and the burial of the menderes and cycladic metasediments to a depth of at least 30 km to allow their eocene high pressure metamorphism 2 a northward continuum of deformation responsible for top to the north fabrics associated with the main menderes metamorphism peak paleocene eocene and its progressive cooling late eocene north verging folding thrusting imbrication of core and cover series and n s to ne sw intense stretching associated with the menderes high pressure metamorphism and its exhumation these top to the north to top to the northeast movements are probably related to the northward backthrusting of the lycian nappes reactivating the contact between the menderes massif and the lycian nappes as a top to the ne shear zone that allowed exhumation of the lycian high pressure rocks 3 oligo miocene n s extension during which the final exhumation of the metamorphic rocks along kilometre scale low angle detachments occurred

geochemical and geochronological evidence for early triassic calc alkaline magmatism in the menderes massif western turkey pan african basement rocks and a paleozoic cover series which were intruded by the protoliths of leucocratic orthogneisses have been recognized in the menderes massif located in the western part of the alpine orogenic belt of turkey this geochemical and geochronological study focuses on the evolution of the menderes massif at the end of paleozoic time geochemical data suggest that the crustally derived leucocratic orthogneisses have chemical composition typical of calc alkaline and s type granite zircon grains which are euhedral with typical igneous morphologies were dated by the 207pb 206pb evaporation method single zircon dating of three samples yielded mean 207pb 206pb ages of 246 5 241 5 and 235 6 ma these ages are interpreted as the time of protolith emplacement in triassic geological and geochronological data suggest that leucocratic granites were emplaced in a period following a metamorphic event related to the closure of the paleo tethys the leucocratic granites were metamorphosed during the alpine orogenesis and transformed into orthogneisses the similar triassic magmatic event at 233 2 ma was also occurred using single zircon evaporation method from granitic gneisses which rest upon the migmatites with tectonic contacts in naxos cycladic complex this indicates that the menderes massif and cycladic complex had a common pre early triassic magmatic evolution

the evolution of the southern menderes massif in sw turkey as revealed by zircon dating this geochronological study concentrates on the evolution of the southern part of the menderes massif a metamorphic core complex in w turkey by dating single zircons with the pb pb evaporation and the u pb methods we have analysed zircons from granitic augen gneisses of the core as well as from quartzites of the metasedimentary envelope zircons from the granitic core gneisses are euhedral with typical igneous morphologies the single zircon ages of these gneisses indicate a time span for magmatic activity from 520 to 570 ma with a major event at about 550 ma some gneisses contain older zircons of c 660 ma which are interpreted as inherited grains zircons from the quartzites are detrital as indicated by their rounded shapes and pitted surfaces their ages vary from 526 to 2094 ma these data partially coincide with the ages of the gneisses but also indicate an older source region for the sediments neither a tertiary origin nor metamorphic overgrowth is documented in the pb ages of the zircons the results suggest that the southern part of the menderes massif developed during a major magmatic episode in latest proterozoic times thus suggesting a relation with other pan african regions in n africa

mobilization of gold as a polymetallic melt during pelite anatexis at the challenger deposit south australia a metamorphosed archean gold deposit the challenger gold deposit in south australia is hosted by pelitic migmatites that underwent peak metamorphism at 7 5 1 5 kbars and at least 800 c nd model ages suggest a protolith age of 2900 ma zircon u pb and garnet sm nd dating indicates that peak metamorphism occurred at 2440 ma and that garnet was present during this event at this time in situ vapor absent melting affected the pelitic host rock indicating that peak metamorphism occurred without introduction of a foreign fluid or melt thus evidence indicating the presence of ore minerals during peak metamorphism implies a prepeak mineralization event this evidence includes the occurrence of invisible gold in lollingite but not in adjacent arsenopyrite and the presence of spherical gold sulfide inclusions in peak metamorphic garnet and other silicates textures developed between pyrrhotite lollingite arsenopyrite and gold the lack of silicate alteration minerals supports this conclusion experimental evidence is presented to support our interpretation that a gold rich polymetallic melt was mobilized into leucosomes synchronously with silicate melt during peak metamorphism visible gold is restricted to migmatitic leucosomes and to a lesser extent melanosomes large inclusions of gold with coexisting arsenopyrite pyrrhotite and bismuth are hosted within peak metamorphic silicate minerals and at grain boundaries trails of micrometric spherical inclusions of predominantly gold and bismuth propagate along annealed fractures from these larger inclusions we show that these gold sulfide inclusions represent the crystallized products of an immiscible polymetallic melt metamorphism of the challenger deposit resulted in partial melting of the pelitic host rock and formation of this gold rich melt these two melts were synchronously redistributed to accumulate as leucosomes during development of a stromatic migmatite formation of a polymetallic melt thereby enabled extensive mobilization of gold producing leucosomes enriched in gold this occurred because the immiscible metallic melt was physically entrained rather than chemically dissolved within the silicate melt gold rich shoots at challenger parallel the plunge of ptygmatically folded leucosomes that are shown to be parasitic to a larger scale fold geometry which appears to be structurally related to the ore shoots it is interpreted that concurrent migration of polymetallic and silicate melt allowed concentration of gold into a series of dilational structures which developed within the larger scale fold geometry challenger represents a new deposit type other deposits around the world such as renco and griffins find are hosted in granulite facies rocks but challenger is the first reported example of leucosome hosted gold in migmatites

re os age of the pueblo viejo epithermal deposit dominican republic re os analyses of pyrite from the pueblo viejo high sulfidation epithermal deposit both monte negro and moore ore zones yield an isochron age of 111 9 3 7 ma and initial 187 os 188 os ratio of 0 22 0 18 mean square of weighted deviates 84 n 21 isochrons grouped by pyrite setting layered versus vein or locations yield ages within uncertainty of the overall isochron and with each other and as such do not yield temporally distinguishable ages sphalerite vein samples as well as shale source rocks show evidence of open system behavior and loss of re and therefore are not included in the above regression these results confirm that the pueblo viejo deposit is early cretaceous in age and coeval with the volcanic los ranchos formation which hosts the deposit recent paleontological age assignments for the hatillo formation which overlies the los ranchos formation show that it is only slightly younger opening the possibility that mineralization in the hatillo formation could also be related to late stages of los ranchos magmatism whether these revised los ranchos hatillo relations provide sufficient cover to account for the paragenetically late formation of pyrophyllite at pueblo viejo remains unclear recognition that pueblo viejo is coeval with the los ranchos formation shows that large scale high sulfidation epithermal mineralization can form from basal island arc tholeiitic magmatism a review of available experimental data confirms that these magmas can generate hydrothermal solutions of the necessary composition favorability of the los ranchos formation might have been enhanced by its bimodal composition these results suggest that exploration for epithermal precious metal deposits should include basal island arc tholeiite terranes

eclogites within the menderes massif western turkey metagabbros in the core series of the menderes massif for some time considered as post orogenic miocene intrusives revealed a strong poly metamorphic history the metagabbro bodies exhibit a pronounced zonation within their cores igneous minerals are still preserved coronitic textures are interpreted as results of a high temperature possibly granulitic overprint the outer parts of the metagabbro bodies mostly consist of strongly to completely retrograded garnet amphibolites but occasionally contain relics of eclogites petrologic investigations confirmed a high pressure overprint and allowed preliminary p t estimates 650 c 1 3 gpa the intensity of the hp metamorphism seems to rise from south to north within the menderes basement thus pointing to a northward subduction as the cause the age of the high pressure event still awaits clarification however its very existence reanimates the question how close the relationship between menderes and the cyclades evolution might have been

exhumation driven devolatilization as a fluid source for orogenic gold mineralization at the damang deposit ghana gold mineralization at the damang deposit is unique among currently known orogenic gold deposits in ghana comprising gold hosted within metasediments of the tarkwaian system and contained in a subhorizontal extensional quartz vein array that formed during regional compression the damang region has an extended paragenesis involving numerous structural metamorphic igneous and metasomatic events orogenic gold mineralization occurred late in the geologic paragenesis at damang postdating regional metamorphism and an earlier episode of hydrothermal alteration locally termed pink hematite alteration associated with the intrusion of mafic sills and dikes this earlier pink hematite alteration event involves extensive silicification that changed the rheology of the altered rocks and promoted later fracturing following peak regional metamorphism at around 2005 ma the damang region underwent a short period of rapid exhumation as constrained through numerical thermal modeling of existing pressure temperature time data this exhumation triggered the generation of a subhorizontal fracture array that was fed by fluids released through decompression driven metamorphic devolatilization the interaction between these fluids and the host rock resulted in precipitation of gold in association with sulfide carbonate potassic alteration halos around quartz veins such postpeak metamorphic exhumation driven devolatilization is unlikely to be a singular occurrence and represents a potentially important source of fluid for orogenic gold deposits elsewhere in ghana west africa and globally

miocene nne directed extensional unroofing in the menderes massif southwestern turkey structural investigations in the central part of the menderes massif odemio kiraz submas sif reveal the presence of a large scale low angle extensional shear zone with a top to the n ne shear sense regional ductile deformation was accompanied by the intrusion of two syntectonic granodiorites that have been dated with the 40 ar 39 ar method one hornblende isochron age of 19 5 1 4 ma and two biotite plateau ages of 13 1 0 2 and 12 2 0 4 ma respectively constrain that extension was already active in the early miocene successive tectonic denudation of the odemio kiraz submassif resulted in the formation of a n dipping detachment fault in which ductile fabrics were severely reworked by cataclasis under decreasing temperature syntectonic neogene sediments currently exposed along the southern margin of the gediz graben were deposited in the hanging wall of the extensional fault system and were tectonically emplaced onto the cataclasites during progressive exhumation minor rotation c 15 caused southward tilting of the sediments ongoing nne directed extension created a steep normal fault that truncates the detachment fault and constitutes the southern boundary fault of the gediz graben

east asian gold deciphering the anomaly of phanerozoic gold in precambrian cratons early cretaceous orogenic gold deposits in eastern asia are globally unique in that large phanerozoic lode gold deposits occur in archean paleoproterozoic cratons in the northern pacific region ca 125 ma orogenic gold deposits in the north china yangzte and siberian craton margins as well as in young terranes in california may ultimately relate to the giant cretaceous mantle plume in the southern pacific basin and the relatively rapid tectonic consequences along both continental margins from resulting pacific plate reconfigurations in eastern asia such consequences include reactivation of and fluid flow along major fault systems with fluid focusing into simultaneously forming isolated core complexes of uncertain genesis deposition of gold ores in previously devolatilized high grade precambrian metamorphic rocks requires an exotic source of ore fluid most likely subducted mesozoic oceanic crust and or overlying sediment an implication is that phanerozoic metamorphic core complexes in other destabilized craton margins could host large gold resources

metallogenesis at the carris w mo sn deposit geres portugal constraints from fluid inclusions mineral geochemistry re os and he ar isotopes abstract the carris orebody consists of two partially exploited w mo sn quartz veins formed during successive shear stages and multipulse fluid fillings they cut the variscan post d3 geres i type granite the most important ore minerals are wolframite scheelite molybdenite and cassiterite there are two generations of wolframite the earlier generation of wolframite is rare and has the highest wo4mn content 91 mol and the most common wolframite contains 26 57 mol wo4mn re os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 1 2 ma and 280 3 1 2 ma respectively which are in very good agreement with the previous id tims u pb zircon age for the carris granite 280 5 ma 3he 4he ratio of pyrite ranging between 0 73 and 2 71 ra 1 ra 1 39 10 6 and high 3he 36ar 0 8 5 10 3 indicate a mixture of a crustal radiogenic helium fluid with a mantle derived fluid the fluid inclusion studies on quartz intergrown with wolframite and scheelite beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit the first was a low to medium salinity aqueous carbonic fluid co2 between 4 and 14 mol with less than 1 95 mol n2 which was only found in quartz associated with wolframite the other was a low salinity aqueous fluid found in all the four minerals the homogenization temperatures indicate minimum entrapment temperatures of 226 310 c average 280 c for the h2o co2 n2 nacl fluid and average temperatures of 266 c for scheelite and 242 c 190 c and 160 c for the last generations of beryl fluorite and quartz respectively it was estimated that wolframite was deposited 7 km depth assuming a lithostatic pressure probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event precipitation of scheelite and sulphides took place later at the same depth but under a hydrostatic or suprahydrostatic pressure regime and probably caused by mixing between the magmatic hydrothermal fluid and meteoric waters that deeply penetrated the basement during post variscan decompression

geochemistry and textures of gold bearing arsenian pyrite twin creeks nevada implications for deposition of gold in carlin type deposits this study relates morphology size texture and chemistry of arsenian pyrite in the twin creeks carlin type gold deposits to the chemical position and amount of gold that it contains arsenian pyrite is confirmed as the most important gold hosting mineral and four types of gold bearing arsenian pyrite are recognized among these four types the lowest amount of gold and arsenic 1 wt as 17 60 ppm au is contained in arsenian pyrite with relatively large grain sizes 10 30 mu m it formed at relatively high temperatures 250 degrees c and k super h super ratios adularia stable probably relatively slowly the largest amount of gold and arsenic 1 05 2 43 wt as 595 1 465 ppm au is contained in arsenian pyrite with small grain sizes up to 2 mu m that formed at low temperatures 120 degrees 200 degrees c and moderate k super h super ratios illite stable probably by relatively rapid deposition xanes exafs and sims analyses show that gold in arsenian pyrite is both structurally bound au i and in submicroscopic inclusions of free gold au highest amounts of structurally bound gold were observed in the relatively coarse grained arsenian pyrite noted above whereas most inclusions of free gold were observed in fine grained arsenian pyrite in general there is a good correlation between gold and arsenic in arsenian pyrite although au as ratios vary from one pyrite to another it is suggested that gold in arsenian pyrite was deposited by direct deposition of native gold and by adsorption of au i from hydrothermal solutions adsorption of gold by arsenian pyrite can take place from solutions that are not saturated with respect to native gold relative volumes of gold bearing pyrite from different paragenetic stages at twin creeks suggest that as much as 50 percent of the total gold in the deposit could have formed from solutions that were not saturated with respect to native gold because both au and au i are found together in arsenian pyrite it is likely that they were deposited by the same process consideration of possible depositional reactions suggests that a decrease in the activity of reduced sulfur is most likely to cause gold deposition

a short duration of chondrule formation in the solar nebula evidence from 26al in semarkona ferromagnesian chondrules abstract the 26 al 26 mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite semarkona ll3 0 were studied using a secondary ion mass spectrometer their glass or plagioclase portions contain excesses of 26 mg and in two chondrules the 26 mg excesses are well correlated with 27 al 24 mg which demonstrates the in situ decay of 26 al the initial 26 al 27 al ratios in these chondrules obtained from the slope of isochrons show a narrow range of between 6 10 6 and 9 10 6 indicating their short formation duration of less than 1 my if the solar nebula was initially homogeneous in al isotopes the chondrule formation ages are 2 my younger than those of cais our results based on the study of the least metamorphosed uoc are consistent with the previous studies on al rich chondrules that the chondrule formation started at least 2 my after cais alternatively the older records before 2 my were erased by chondrule recycling process it further suggests that the young apparent ages 3 to 5 my after cais for chondrules in type 3 4 uocs are due to the disturbance of the 26 al 26 mg system possibly during parent body metamorphism the result is not consistent with the extended nebular time scale of 5 my and the chondrule formation by planetary processes the ni isotopic analysis of the feo rich olivines in a type ii chondrule in semarkona did not show any detectable excess 60 ni in spite of their high fe ni ratios the upper limit of the initial 60 fe 56 fe ratio of the solar system was estimated to be 3 4 10 7 which is consistent with the previous estimate 0 2 1 9 10 7 from eucrites this result confirms that the 60 ni excess previously observed from cais was not due to the decay of the short lived nuclide 60 fe but a ni isotopic anomaly of nucleosynthetic origin

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

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

la icpms and epma studies of pyrite arsenopyrite and loellingite from the bhukia jagpura gold prospect southern rajasthan india implications for ore genesis and gold remobilization abstract the bhukia jagpura gold prospect is hosted by a paleoproterozoic metasedimentary rock sequence that constitutes the lowermost part of the aravalli supergroup lying in close proximity to the basement cover contact a combined ore petrographic la icpms and epma studies of iron sulfides and sulfarsenides from the prospect has revealed four varieties of pyrite and two varieties of arsenopyrite with different trace element compositions the data indicates a sedimentary diagenetic origin for the earliest pyrites py i and ii which are devoid of any gold in contrast to hydrothermal py iii and iv with a minor but significant content of invisible gold 0 3 1 6 ppm associated loellingite 35 51 ppm and arsenopyrite aspy i 0 28 10 ppm contain the maximum concentration of invisible gold while it is substantially lower in aspy ii 0 06 1 5 ppm the compositions of the gold bearing pyrites low ni co ratios arsenopyrites and loellingite rich in co and the presence of au bi te mineral phases within arsenopyrite support a magmatic hydrothermal model for the origin of gold sulfide mineralization which appears to have taken place during the peak of regional metamorphism or at an earlier stage the different stages of deformation and metamorphism released and remobilized gold in invisible and discrete forms from the sulfarsenides during prograde metamorphism of aspy i gold was partially incorporated and relatively enriched within the structure of loellingite later during retrograde metamorphism gold was exsolved as visible grains at the interface of loellingite and aspy ii and or within loellingite

deep fluid circulation in fault zones massive fluid circulation in retrogressive ductile shear zones is a well established but poorly understood phenomenon in some cases surface derived fluids which must initially have been at hydrostatic pressures can be shown to have entered shear zones in which fluids would normally be expected to be at lithostatic pressure in these circumstances thermal convection is an unlikely driving force for fluid movement underthrusting of a surficial fluid reservoir beneath shear zones is a viable mechanism in some cases but not for metasomatic shear zones in the pyrenees where insufficient underthrusting has occurred seismic pumping provides an alternative mechanism to explain the paradox of fluid access into ductile shear zones a kinematic analysis of a hypothetical fault zone shows that stress and dilatancy cycles will be out of phase above and below the frictional quasiplastic transition if this effect is sufficiently large hydraulic gradients may force fluid downward across the transition immediately after earthquake rupture through highly permeable microcrack networks between earthquake cycles plastic creep in mylonites will overprint microcrack networks increase fluid pressure and promote slow upward movement of fluid at low permeability for smaller shear zones such as those in the pyrenees seismic pumping could occur down a shallow decollement with subsequent upward fluid flow through shear zones in the hanging wall of the decollement

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

geology of the bozdag area central menderes massif sw turkey pan african basement and alpine deformation the menderes massif consists of a precambrian core series that preserves evidence for a polymetamorphic history and a paleozoic mesozoic cover series that experienced only the alpine tectonometamorphic evolution structural petrographic and geochronologic investigations in the central menderes massif demonstrate that a part of the metamorphic and structural evolution of the precambrian basement is older than the undeformed 551 1 4 ma old birgi metagranite and b inferred alpine fabrics overprinting the cover series largely have the same attitudes as the old structures in the much older core series the inferred alpine fabrics include both contractional and extensional structures contraction under greenschist to amphibolite facies conditions resulted in the imbrication of the core and cover series and generated an inverted metamorphic sequence by north directed thrusting during alpine extension most of the south dipping thrust faults were reactivated as extensional shear zones under decreasing greenschist facies conditions

mineral deposits of turkey in relation to tethyan metallogeny implications for future mineral exploration the tethyan metallogeny of turkey shaped by the interplay between subduction collision postcollision and rifting processes is mainly associated with late cretaceous to cenozoic volcanoplutonic and ophiolitic rocks a wide spectrum of ore deposits is represented from those occurring in island arcs to those associated with continental settings though turkey has been one of the leading producers of chromite the country is an emerging producer of precious and base metals this assessment of the metallogeny of turkey is based on a comprehensive gis database compilation that contains known mineral deposits and prospects with relevant descriptive data the data set contains information on major deposit types of economic importance such as porphyry skarn epithermal including both high and low sulfidation polymetallic volcanic associated massive sulfide vms deposits including both kuroko and cyprus types podiform chromite lateritic nickel carbonate hosted lead zinc with nonsulfide zinc including sedimentary exhalative sedex and mississippi valley type mvt karstic and lateritic bauxite orogenic gold including both mesothermal and listwanite hosted types and placer deposits well known deposit types that are less well represented in the database include sediment hosted cu carlin type gold iron oxide copper gold iocg and detachment fault related gold systems exploration programs in the last two decades have started to reveal the true mineral potential of the country turkey is an underexplored country by today s standards with a large prospective area with a wide spectrum of mineral deposits reflecting the diverse geological environments that are present turkey is the least well explored portion of the tethyan belt which hosts au and cu endowments comparable with the andes and the southwest pacific metallogenic belts

stratigraphic structural and geochemical features of the ne sw trending neogene volcano sedimentary basins in western anatolia implications for associations of supra detachment and transtensional strike slip basin formation in extensional tectonic setting western anatolia has been the focus of many geological studies of the classical extensional tectonics in the region the ne sw trending neogene volcano sedimentary basins that characterize western anatolia are mainly located on the northern part of the menderes massif a progressively exhumed mid crustal metamorphic unit that has undergone neogene extensional tectonics in the area the ne sw trending basins are the bigadic gordes demirci selendi emet gure and u ak basins although many studies have been carried out in these basins the stratigraphic and tectonic evolution of the ne sw trending volcano sedimentary basins remains controversial and hence different evolutionary models have been proposed by various authors recent studies concluded that there was a close relation in both space and time between the basin formation and the progressive exhumation of the menderes massif in this study we present new stratigraphic geochemical and tectonic observations from the gordes demirci and emet basins and couple them with data from the other ne sw trending basins to produce a tectono stratigraphic evolutionary model for the area gordes basin was opened by strike to oblique slip movements on the basin bounding faults as a result of dextral transtension such that the transtensional gordes basin formed where extension is oblique to the margin that bounded the basin the demirci selendi emet and gure basins have similar stratigraphic and tectonic features and began to develop as supra detachment extensional basins on an early miocene corrugated detachment fault the simav detachment fault sdf in these basins deposition of a middle miocene volcano sedimentary succession was controlled by ne sw trending strike to oblique slip faults which developed as accommodation faults in the hanging wall of a second detachment fault located further south the gediz detachment fault gdf these data suggest that the menderes massif was exhumed through basin formation in the upper plate that arose from successive detachment faulting accommodated by kinematically linked dextral strike to oblique slip motion to the west strike slip faulting is linked to a previously described crustal scale zone of weakness on which the gordes basin was formed the zmir bal kesir transfer zone the ne sw trending basins were also deformed by ne sw trending dextral and nw se trending sinistral strike slip faulting under pure shear during the late miocene and by e w trending dip slip normal faulting in the pliocene quaternary the data indicate that the region has been extended in a not vert similarn s direction since at least the early miocene and that this extension occurred episodically in several phases

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

oxygen isotope and 26al 26mg systematics of aluminum rich chondrules from unequilibrated enstatite chondrites correlated in situ analyses of the oxygen and magnesium isotopic compositions of aluminum rich chondrules from unequilibrated enstatite chondrites were obtained using an ion microprobe among eleven aluminum rich chondrules and two plagioclase fragments measured for 26al 26mg systematics only one aluminum rich chondrule contains excess 26mg from the in situ decay of 26al the inferred initial ratio 26al 27al o 6 8 2 4 x 10 6 is consistent with ratios observed in chondrules from carbonaceous chondrites and unequilibrated ordinary chondrites the oxygen isotopic compositions of five aluminum rich chondrules and one plagioclase fragment define a line of slope 0 6 0 1 on a three oxygen isotope diagram overlapping the field defined by ferromagnesian chondrules in enstatite chondrites but extending to more 16o rich compositions with a range in 18o of about 12 based on their oxygen isotopic compositions aluminum rich chondrules in unequilibrated enstatite chondrites are probably genetically related to ferromagnesian chondrules and are not simple mixtures of materials from ferromagnesian chondrules and calcium aluminum rich inclusions cais relative to their counterparts from unequilibrated ordinary chondrites aluminum rich chondrules from unequilibrated enstatite chondrites show a narrower oxygen isotopic range and much less resolvable excess 26mg from the in situ decay of 26al probably resulting from higher degrees of equilibration and isotopic exchange during post crystallization metamorphism however the presence of 26al bearing chondrules within the primitive ordinary carbonaceous and now enstatite chondrites suggests that 26al was at least approximately homogeneously distributed across the chondrite forming region

helium and argon isotope geochemistry of alkaline intrusion associated gold and copper deposits along the red river jinshajiang fault belt sw china abstract the red river jinshajiang strike slip fault zone on the eastern margin of the tibetan plateau was originally produced by the india eurasia collision 60 70 myr ago numerous post collisional mantle derived alkaline igneous rocks with ages of 40 30 ma have been intruded along this fault zone in recent years several copper and gold deposits associated with the alkaline intrusions of this region were discovered such as the yao an and beiya gold deposits and the yulong and machangqing copper deposits studied in this paper the mineralised intrusions are felsic with sio 2 ranging from 61 4 to 67 7 wt k 2 o na 2 o from 8 1 to 11 5 wt and k 2 o na 2 o 1 the deposits are located at both the exo and endo contact zones of the intrusions the mineral deposits are of hydrothermal origin with the ore forming temperatures mainly in the range 150 450 c this paper presents he and ar isotope analyses of these four deposits the concentrations of 4 he trapped in fluid inclusions of pyrites from the ores are 0 7 54 1 10 6 cm 3 stp g 1 and those of 40 ar are 0 6 7 3 10 6 cm 3 stp g 1 3 he 4 he ratios are 0 3 2 5 ra ra represents the 3 he 4 he ratio of air 1 39 10 6 40 ar 36 ar ratios are 316 1736 and 3 he 36 ar ratios are 0 2 11 2 10 3 generally the 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios for the gold deposits are higher than those for the copper deposits we suggest that the ore forming fluids of both gold and copper deposits were differentiated from the mantle derived alkaline magmas but were diluted by modified air saturated water masw that experienced intensive interaction with crustal rocks however the magmatic fluids responsible for the gold deposits were less extensively diluted by masw resulting in higher 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios than the copper deposits

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

osmium sulphur and helium isotopic results from the giant neoproterozoic epithermal imiter silver deposit morocco evidence for a mantle source the giant epithermal ag hg deposit of imiter anti atlas morocco was investigated to study the transfer of chalcophile elements from the mantle to superficial crustal levels the origin of metals and ligands sulphides was deduced from s fluid inclusions he and re os data obtained on sulphide phases and gangue minerals sulphur isotope analyses show the existence of two distinct isotopic reservoirs one found in pyrite from the surrounding black shale country rocks 34scdt 38 and the other in pyrites associated with a synchronous rhyolitic dome 34scdt 7 to 2 the 34scdt values of the silver mineralization event range from 28 to 2 and are interpreted as resulting from preferential degassing of so2 in ascending fluids as well as mixing between the magmatic isotopic reservoir and a country rock reservoir helium isotope analyses of sulphides and gangue minerals yield similar results with 3he 4he ratios ranging from 0 76 to 2 64ra these data and the absence of 20ne in the analyzed fluid inclusions suggest a mantle origin for the fluids associated with the epithermal silver event os isotopic ratios have been measured for the first time in ag and ag sulphosalts these data and those obtained on other sulphide phases directly associated with the ag mineralization show measured 187os 188os ratios of 0 142 0 197 indicating a dominantly mantle source for the associated os assuming that os and ag are derived from the same source the black shale country rock provided less than 10 of the silver metal stock this study highlights the conditions required to transfer 8000 metric tons of ag and other elements such as hg co ni pb zn from the mantle i e i an efficient vector such as the sulphide ligand ii a major and sudden break in the geodynamic environment similar to the one which occurred near the precambrian cambrian transition to provide pathways from the mantle wedge and the lithospheric base to the surface and iii a strongly extensional tectonic setting to provide traps for the concentration of metals in ore deposits

fluid immiscibility and gold deposition in the xincheng deposit jiaodong peninsula china a fluid inclusion study abstract the xincheng gold deposit located in west jiaodong peninsula in southeast north china craton is a representative mesothermal lode deposit hosted in late mesozoic granitoids in jiaodong gold mineralization occurs as disseminated and stockwork style ores within the hydrothermal breccias and cataclastic zones controlled by the jiaojia fault whereas echelon tensile auriferous veins hosted in the ne and nne trending subsidiary faults cutting the granitoids occur subordinately according to crosscutting relationships and mineral paragenesis four paragenetic stages were identified which are pyrite quartz sericite stage 1 quartz pyrite stage 2 quartz polysulfide stage 3 and quartz carbonate stage 4 gold was deposited during the quartz pyrite and quartz polysulfide stages on the basis of microthermometry and raman spectroscopy on fluid inclusions contained within the quartz veins from stages 2 and 3 three types of fluid inclusions were recognized 1 type 1 h 2 o co 2 inclusions that show high temperatures ca 260 c low salinities 2 4 8 9 wt equiv nacl and variable xco 2 0 03 to 0 20 2 type 2 aqueous inclusions with medium temperatures ca 220 c and low to moderate salinities 3 1 13 3 wt equiv nacl 3 type 3 pure co 2 inclusions with a carbonic phase density of 0 712 0 03 g cm 3 types 1 and 2 inclusions appear in the same growth phase of the quartz grains from the breccias and tensile auriferous veins these coexisting inclusions are likely formed by fluid immiscibility due to unmixing from a single homogeneous h 2 o co 2 parent fluid at trapping p t conditions of 221 to 304 c average 261 19 c and 780 to 2080 bar the fluid immiscibility is interpreted to be initiated by fluid pressure decrease at ca 300 c the ore fluid p t x conditions of the xincheng gold deposit are the same as those for mesothermal deposits gold was most probably transported as a au hs 2 complex at xincheng fluid immiscibility over the temperature interval of 221 304 c resulted in significant h 2 s loss from the hydrothermal solution thereby reducing au hs 2 solubility with concomitant deposition of gold the mineralizing process of the granitoid hosted xincheng lode gold deposit is likely related to the fluid immiscibility

the akato tagh bend along the altyn tagh fault nw tibet 1 cenozoic structure smoothing by vertical axis rotation and the effect of topographic stresses on borderland faulting

mineralogy and geochemistry of sulfosalts from baia sprie ore deposit romania new bismuth minerals occurrence abstract the baia sprie epithermal ore deposit is one of the best known deposits in romania and europe it consists mainly of a vein system with two major veins 1 principal vein and 2 southern vein along fractures that delimitate an andesitic block and a subvolcanic intrusion the principal vein is one of the longest hydrothermal veins in europe with more than 5 km in length a thickness that varies between 0 5 and 22 m and it extends vertically on more than 800 m samples belonging to different levels of principal vein have been analyzed using electron microprobe a new occurrence of bismuth minerals was identified within the deeper part of the deposit bismuthinite lillianite gustavite disordered intergrowths of lillianite homologues heyrovskyite and cosalite the presence of bi sulfosalts suggests temperature of 350 c while the as content in arsenopyrite indicates formation temperatures between 320 and 360 c the oscillatory zoning bands of pyrite and tetrahedrite tennantite members indicate an increased sb and as concentration in hydrothermal solutions the zoning textures suggest a high s and low as concentration in the early fluids followed by multiple pulses of as rich solutions in the late fluids the high content of as in pyrite and the presence of bismuth minerals at baia sprie deposit can represent indicators for significant au concentrations within the lower level of the mineralization from the type locality baia sprie new analytical data for semseyite were presented and for the first time a new occurrence of geocronite jordanite series was identified in the intermediate and upper part of the deposit

link between gold provinces low salinity high temperature 200 degrees c reducing fluids are poorly represented in ore forming processes yet appear to account for 90 percent of the primary gold mined to date such fluids have been implicated in the formation of many archcan greenstone witwatersrand slate belt and epithermal gold deposits these low salinity auriferous fluids occur in variable time space lithological sequence and tectonic settings and are most easily explained by metamorphic devolatilization of mafic and or graywacke successions metamorphism of chlorite calcite albite quartz assemblages e g mafic or graywacke at the greenschist amphibolite facies boundary occurs around 480 degrees or 20 degrees c for 3 5 kbars and produces large volumes of low salinity h 2 o co 2 fluid similar in composition to those recorded in many gold deposits widespread pyrite in the above assemblage typically leads to elevated levels of dissolved sulfur such conditions are ideal for gold transport as a molecular au s complex and can lead to deposits rich in gold relative to silver and base metals deposition of gold occurs in the temperature range of 250 degrees to 400 degrees c and can be facilitated by lower temperature lower sulfur activity and changes in oxygen activity lower sulfur activity is most readily achieved by fluid interaction with fe rich host rocks with the formation of pyrite or pyrrhotite whereas lower oxygen activity is readily achieved by interaction with carbonaceous metasediments low salinity fluids produced by metamorphic devolatilization provide a common theme embracing the formation of many archcan greenstone slate belt witwatersrand and potentially epithermal gold deposits it involves the common features of high geothermal gradient low salinity fluid high au ag high au base metals and broad synchroneity with metamorphism it also accounts for the considerable variability in hosting structures detailed timing relations host rocks alteration assemblages and geologic age of different deposits interestingly the similarities are explained by deeper processes the differences by processes at or near the depositional sites

some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration porphyry copper gold skarn copper gold sediment hosted carlin style gold breccia pipe low sulphidation epithermal gold pluton related mesothermal or orogenic gold vein and volcanogenic massive sulphide deposits associated with alkaline rocks are commonly broadly similar to those hosted by their calc alkaline counterparts in contrast porphyry molybdenum gold deposits are confined to alkaline igneous centres alkaline suites are notably deficient in high sulphidation epithermal gold deposits and even in the advanced argillic lithocaps which host them this is surprising given that the required oxidised sulphur species are seemingly more abundant than in calc alkaline igneous centres highly efficient buffering of acidic fluid by metasomatised alkaline rocks may offer a viable explanation all types of intrusion related zinc deposits also appear to be poorly developed in alkaline provinces the characteristics of several gold and copper deposits associated with alkaline rocks including the giant porgera cripple creek ladolam olympic dam and phalaborwa examples are judged to diverge appreciably from their most closely related deposit types rendering them arguably unique most of these aberrant mineralisation styles may be due to variations in magmatic fluid compositional and liberation characteristics consequent upon the extreme diversity of ore related alkaline magmas most types of gold and copper deposits developed in calc alkaline provinces also constitute exploration targets in and around alkaline igneous centres although porphyry copper gold and low sulphidation epithermal gold deposits are considered to possess the greatest potential perhaps of even greater interest however is the possibility of encountering unconventional giant gold and copper deposits which lack closely analogous examples if already defined aberrant deposits are truly unique then exploration designed specifically to detect additional examples is pointless furthermore exploration for new unique deposits is difficult because their defining geological parameters are unknown alkaline rocks within or behind calc alkaline arcs at convergent plate boundaries probably offer the greatest exploration potential although anorogenic intracontinental extensional settings should not be ignored

tectonic significance of mafic volcanic rocks in a mesozoic sequence of the menderes massif west turkey the mesozoic platform sequence of the menderes massif consists of thick succession of detrital and carbonate rocks in this sequence there are mafic metavolcanic rocks at two different levels the first level of mafic metavolcanic intercalations is in the late triassic detrital rich series located in the caltasi formation which is the lowermost unit of the mesozoic platform the second level of the mafic metavolcanic rocks is located in the late cretaceous paleocene selcuk formation laying on top of the platform sequence the caltasi formation which is composed of mica schists thinly bedded cherts calc schist and mafic volcanic intercalations unconformably overlie the bayindir formation which consists of mica schists phyllites and white quartzites of palaeozoic or probably older age the mafic volcanic rocks in the caltasi formation are alkaline basalts with within plate characteristics and are formed during an intraplate extension the caltasi formation is conformably overlain by the kayaalti formation represented by calc schists dolomitic marbles and rudist and emery bearing massive marbles in ascending order the selcuk formation overlies the kayaalti formation and consists of a mica schist matrix with allochthonous blocks of mafic volcanic rocks metaperidotites metagabbros and massive marbles the mafic volcanic rocks in the selcuk formation are tholeiitic basalts and are petrologically similar to mid oceanic basalts the geological and geochemical characteristics of the mafic metavolcanic rocks in the caltasi formation indicate that during the late triassic the menderes platform was segmented probably by the opening of a branch of the neotethyan ocean between the late triassic and the late cretaceous the menderes carbonate platform was built up during the latest cretaceous early paleocene a slab of oceanic crust obducted on this platform and provided slices of mafic metavolcanic rocks into the selcuk formation

craton scale distribution of archean greenstone gold deposits predictive capacity of the metamorphic model genetic models should not only attempt to explain features of archean gold mineralization on the scale of mines or districts but should also explain its marked spatial and temporal heterogeneity in greenstone belts the application of genetic models developed with such a philosophy can have predictive capacity in gold exploration the metamorphic model one of a number of current genetic models for archean gold deposits involves generation of auriferous h 2 o co 2 fluids by devolatilization of the stratigraphically lowermost greenstones during metamorphism and broadly synchronous synkinematic granitoid intrusion crustal scale fault shear systems are required to induce channeled fluid flow and to focus ore fluids toward suitable host rocks and structural sites declining temperature below the amphibolite greenschist transition combined with sulfidation of fe rich host rocks is a particularly efficient au depositing mechanism the model suggests that the major controlling factors in declining order of importance are 1 high temperature low pressure generally low strain metamorphic regimes 2 crustal scale fault systems 3 unaltered fe rich rocks tholeiites banded iron formation at a suitable stratigraphic metamorphic level and 4 abundant au enriched komatiites and s rich sediments in source regions the low pressure metamorphic conditions combined with the occurrence of elongate high strain zones in most if not all generally low strain greenstone belts may explain the ubiquitous occurrence of gold deposits in archean terranes all four favorable parameters appear to act in concert to produce the largest gold deposits and most abundant gold mineralization in 2 7 or 0 1 b y old rift phase greenstone belts interpreted to have formed under conditions of high crustal extension and extensive crustal thinning i e with predicted high geothermal gradients high fault density limited synvolcanic alteration and abundant komatiites and sulfidic sediment horizons more widespread commonly older platform phase greenstone belts which formed under conditions of lesser crustal extension and thinning are less mineralized as predicted by the metamorphic model the ability of the model to explain the regional distribution of known archean gold deposits lends credence to its predictive capacity for example 1 greenstone belts in any one craton can be broadly ranked in order of likely relative gold potential 2 the likelihood of discovery of large deposits in poorly exposed or poorly explored belts of known type can be estimated 3 areas with the highest potential can be defined in rift phase greenstone belts by the coincidence of critical parameters such as specific host rock sequences and metamorphic facies 4 prospective structural sites for gold mineralization can be postulated in platform phase greenstone belts affected by diapiric tectonics and 5 the possible spacing of large deposits can be estimated further the potential use of the model in exploration emphasizes serious gaps in our knowledge of parameters crucial to understanding greenstone belt metallogeny including alteration patterns metamorphic p t paths and regional scale structural regimes

timing of tectonic events in the menderes massif western turkey implications for tectonic evolution and evidence for pan african basement in turkey the menderes massif forms the western of the two large metamorphic culminations within the turkish alpide orogen it has three major lithologic units with a gneissic core at the base and a schist and a marble envelope overlying it successively although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the massif we present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the massif to constrain the timing of major tectonic events that shaped the massif since the late proterozoic pt3 in the southern part of the massif sensu stricto three episodes of deformation and metamorphism are distinguished whereas in its northern part there are four the first episode occurred at 500 10 ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis in the central part of the massif the 470 9 ma old now highly deformed tonalitic and granitic intrusions mark the end of this episode on a cambrian reconstruction of continents around the eastern mediterranean the menderes massif forms the southern end of the pan african orogenic collage of northeastern africa and arabia the area of earliest palaeozoic deformation in the menderes may connect with the northwest african orogenic collage along the strike via the bozburun and saricicek diabases arkoses and schists in the center of the karacahisar dome interpreted herein as fragments of a pan african suture the earliest palaeozoic deformations to affect the rocks were probably related to the last pan african collisions and associated postcollisional convergence the southern part of the massif was undeformed from early ordovician to the early later eocene whereas the northern part was deformed metamorphosed and intruded possibly during the late triassic related to the closure of the karakaya marginal basin of palaeo tethys the next major event affecting the whole of the massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts and only greenschist grade in the outermost envelope this metamorphism here called the main menderes metamorphism mmm is biostratigraphically constrained between early eocene and early oligocene time rb sr isotopic data show a spread of ages between 60 ma and 25 ma with the greatest number of determinations around 35 5 ma this number is in excellent agreement with the stratigraphic evidence and shows that mmm took place during latest eocene time or at the transition from eocene to oligocene time along the northern border of the massif deformation and metamorphism had already taken place during the late cretaceous in a high pressure low temperature hp lt metamorphic belt northernmost part of menderes massif sensu lato which was then covered by palaeocene molasse the evolution of the hp lt belt was probably related to the obduction of the bozkir ophiolites from the izmir ankara branch of the neo tethys ocean and preceded terminal collision in the evolution of the massif the mmm was a product of the latest palaeocene collision across neo tethys and the consequent internal imbrication of the menderes taurus block that resulted in the burial of the menderes massif area beneath the lycian nappe complex a low grade metamorphic event dated at 10 to 5 ma is interpreted to be related to the extensional deformation in the aegean and western turkey which has been dated stratigraphically to have begun during the tortonian 11 5 ma

hibonite bearing microspherules a new type of refractory inclusions with large isotopic anomalies reported are petrographic descriptions major and trace element chemistry and mg ca and ti isotopic compositions of a new class of refractory inclusions that consist of spherules composed of hibonite and a silicate glass the distinctive features of these inclusions are excesses in 48ca and 50ti in both glass and hibonite and 26mg depletions relative to terrestrial isotopic compositions three spherules have been examined and analyzed one from the lance co3 meteorite and two from the murchison cm2 meteorite lance 3413 1 31 la3413 1 31 and murchison 7 228 mur7 228 have euhedral to subhedral hibonite crystals enclosed within glass murchison 7 753 mur7 753 has a rounded hibonite core with several small inclusions of perovskite a small fragment of glass is attached to the hibonite and an fe silicate rim is imperfectly preserved around the grain la3413 1 31 has a group ii ree pattern mur7 228 a refractory pattern with depletions in the relatively volatile elements sr ba nb v and eu and mur7 753 a pattern characterized by the prior removal of an ultrarefractory component and overall fractionation of all rees the partitioning of the lrees between hibonite and glass in mur7 228 is consistent with equilibrium hibonite liquid partition coefficients previously determined la3413 1 31 shows much less partitioning while mur7 753 shows no evidence for partitioning and preserves an unequilibrated refractory component highly enriched in gd all spherules have initial magnesium depleted in 26mg by around 3 relative to terrestrial mg but only mur7 228 shows evidence for in situ decay of 26al with an initial 26al27al of 1 7 0 7 10 5 both hibonite and glass in all three spherules show excesses of 48ca and 50ti ranging up to 40 and 20 respectively relative to terrestrial ca and ti spherules such as these are rare and the only other occurrence is in the unique chondrite alh85085 the hibonite in the spherules shows similarities to isotopically anomalous hibonite crystal fragments placs but it is unlikely that the spherules formed by remelting of placs the precursors include isotopically anomalous ca ti carriers but also isotopically normal refractory components that probably formed as condensates the spherules formed by melting of these precursors under disequilibrium conditions and rapid cooling after hibonite crystallization these inclusions must have formed early prior to the dilution of isotopic anomalies by mixing processes and in an area characterized by excesses of 48ca and 50ti depletions of 26mg and lack of 26al

pan african high pressure metamorphism in the precambrian basement of the menderes massif western anatolia turkey the menderes massif is made up of pan african basement and a paleozoic to early tertiary cover sequence imbricated by late alpine deformation the precambrian basement comprises primarily medium to high grade schists paragneisses migmatites orthogneisses metagranites charnockites and metagabbros high pressure relics in the pan african basement are divided into two groups eclogites and eclogitic metagabbros the mineral assemblage in the eclogites is omphacite jd 44 garnet clinozoisite rutile the eclogites occur as pods and boudinaged layers in the basement schists and paragneisses inclusions found in the cores of the garnets indicate a medium pressure protolith the eclogitic metagabbros are closely related to precambrian gabbroic stocks the igneous texture and relic magmatic phases are preserved in these high pressure rocks which are characterized by the mineral assemblage omphacite jd 25 garnet rutile kyanite the p t conditions of the pan african high pressure metamorphism in the eclogites are estimated to be 644 c with a minimum pressure of approximately 15 kbar the eclogites are partly to completely retrograded to garnet amphibolites by a barrovian type overprint which developed under isothermal decompression conditions for this post eclogitic event the p t estimates are 7 kbar and 623 c the eclogite relics provide strong support for a correlation of the menderes massif with the bitlis massif in terms of common pan african high pressure evolution

fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising fluids the naturally occurring noble gas isotopes 40ar 36ar 84kr and 129xe and halogens cl br i have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits pcd bingham canyon utah and silverbell ray mission pinto valley and globe miami in arizona in addition analyses of 3he 4he have been obtained from sulphide minerals hosted by the quartz veins at silverbell ray pinto valley and globe miami the majority of pcd fluids studied have br cl and i cl ratios that overlap those of fluids included in mantle diamond suggesting that the salinity had a juvenile origin the high i cl 121 10 6 mole m in samples from the propylitic zone of silverbell is attributed to the presence of sedimentary formation water 3he 4he ratios have r ra values in the range 0 3 to 1 72 and provide evidence for the involvement of a crustal component in addition to mantle volatiles 40ar 36ar ratios vary from meteoric values of 317 in the propylitic zone of bingham canyon and 323 in the skarn alteration of mission up to 3225 in the potassic zone of pinto valley fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end member comprising meteoric water and air and a high salinity end member consisting of a mixed mantle and crustal fluid the 40ar cl ratio of fluid inclusions at pinto valley 10 4 m is similar to values obtained previously for mantle fluids the 40ar cl value is two orders of magnitude lower at bingham canyon where a depleted 36ar concentration 0 2 10 6 cm3 g below that of air saturated water asw and a range of highly fractionated noble gas compositions f84kr 13 and f129xe 160 indicate that boiling and pulsed fluid flow have occurred

preservation of permian allanite within an alpine eclogite facies shear zone at mt mucrone italy mechanical and chemical behavior of allanite during mylonitization this study addresses the mechanical and chemical behavior of allanite during shear zone formation under high pressure metamorphism understanding physico chemical processes related to the retention or resetting of pb isotopes in allanite during geological processes is essential for robust petrochronology dating of allanite in meta granodiorite showing variable amounts of strain from an undeformed protolith to mylonite at monte mucrone sesia zone nw italy gave surprising results based on structural and petrographic observations the shear zones at mt mucrone are alpine yet allanite located within an eclogite facies mylonite yielded permian ages 208pb 232th average age 287 7 ma these mm sized allanite grains are rimmed by an aggregate of coarse grained garnet phengite thought to derive from former epidote these aggregates were immersed in a weak matrix that experienced granular flow and they were thus chemically and mechanically shielded during alpine mylonitization in undeformed samples 8a and 8b two populations of epidote group minerals were found allanite forms either coronas around permian monazite or individual grains with patchy zoning both types yield permian ages 208pb 232th age 291 5 ma on the other hand grains of ree rich clinozoisite of cretaceous age are found in undeformed rocks these grains appear as small fragments with embayed surface outlines and minute satellites or rims around permian allanite these re crystallized grains are sr rich and show mosaic zoning these results indicate that allanite crystals retained their chemical and isotopic characteristics and thus their permian age as a result of strong strain partitioning between the epidote group porphyroclasts and the eclogite facies matrix in hp mylonites the observed partial mobilization of pb isotopes which lead to the cretaceous aged rims or grains in undeformed samples was facilitated by re crystallization of allanite and not by mere pb diffusion alone under the hp conditions

constraints of mineralogical characterization of gold ore implication for genesis controls and evolution of gold from kundarkocha gold deposit eastern india abstract gold mineralization in kundarkocha gold deposit occurs in the eastern indian craton that is hosted by sheared quartz carbonate sulfide veins emplaced within the graphitic schist carbonaceous phyllite and talc chlorite serpentine schist belongs to gorumahisani badampahar schist belt of iron ore group gold mineralization exhibits both lithological and structural controls in the study area albeit the stratigraphic control is more ubiquitously observed detailed mineralogical characterization coupled with electron probe microanalysis of the sulfide phases reveal the occurrences of gold in three distinct forms i as lattice bound form within sulfides especially enriched in arsenopyrite loellingite pyrite pyrrhotite and chalcopyrite in decreasing order of abundance ii as micro inclusions or nano scale gold inclusions within pyrite and arsenopyrite especially along the growth zones and micro fractures as substrates and iii as free milling nugget gold grains either along the grain boundaries of sulfides or within the host rocks three generations of pyrite py i py ii and py iii and arsenopyrite asp i asp ii asp iii have been identified based on textural morphological characteristics and mineral chemistry the lattice bound gold content in pyrite and arsenopyrite varies from 600 to 2700 ppm and 900 to 3600 ppm respectively and increase in concentration of such refractory gold is seen in the order of chalcopyrite pyrrhotite pyrite loellingite arsenopyrite the evolutionary stages of different forms of gold include remobilization of the lattice bound grains in pyrite and arsenopyrite py i and asp i and re concentration along the zoned pyrite and arsenopyrite py ii and asp ii and ultimately as native gold nuggets surrounding the sulfides as well as within the main mineralized zone lattice bound gold distribution could have resulted due to metamorphic devolatilization reactions which are further aided by the influx of hydrothermal fluids these reactions along with additional input of hydrothermal fluid paved the way for expulsion of lattice bound gold from sulfides to concentrate as nuggets main lode within shear fractures channelizing the fluid flow thermometry results of the arsenopyrite pyrite pyrrhotite assemblage yielded a temperature range from 375 to 390 c which is the ideal condition for gold precipitation native silver gersdorffite and arsenian ullmannite are being reported for the first time from this deposit indicating the complexity and wide variety of mineral phases associated with gold implying magmatic hydrothermal input of the source fluid

helium isotope composition of fluid inclusions hosted in massive sulfides from modern submarine hydrothermal systems noble gas compositions of fluid inclusions hosted in sulfides from two modern submarine hydrothermal sites of contrasting tectonic settings have been analyzed the jade field central okinawa trough japan is located in an active intracontinental back arc basin whereas the so 134 field is related to the central spreading ridge of the north fiji basin which represents an active highly mature intra ocean back arc system previous conventional studies of fluid inclusions have revealed compelling evidence for subcritical phase separation of the hydrothermal fluids at both sites elemental abundances of ne ar kr and xe in fluid inclusions in all studied samples of chalcopyrite and sphalerite from both hydrothermal sites indicate that the heavier noble gases are derived from ambient seawater in contrast helium concentrations are 1 to 2 orders of magnitude higher than expected for equilibrium solution in seawater indicating that helium is predominantly derived from a magmatic source beneath the hydrothermal systems the 3 he 4 he ratios in sphalerite hosted fluid inclusions from the jade field and the so 134 field are similar to those reported from related vent fluids and show that fluid inclusions reliably record the helium isotope ratio of the original hydrothermal fluid however in the north fiji basin earlier black smoker activity and the formation of fe rich kies type sulfides seems to have been related to a more morb like volcanism whereas the younger recent white smoker hydrothermal activity in the north fiji basin can be attributed to a hot spot magmatism in the study area

mineralogical siting and distribution of gold in quartz veins and sulfide ores of the ashanti mine and other deposits in the ashanti belt of ghana genetic implications the ashanti belt of ghana constitutes a gold province which has produced a total of about 1500 t of gold historically gold mineralization is found in steep nne ssw to ne sw trending shear zones predominantly transecting metasediments of the palaeoproterozoic birimian supergroup 2 2 2 1 ga disseminated in ca 2 1 ga granitoids in paleo conglomerates of the tarkwaian group 2135 ma and in recent placers the distribution of gold its chemistry paragenesis and mineralogical siting in the mesothermal ores of the major mines in the ashanti belt namely konongo ashanti bogosu and prestea mine are the subject of this study at the localities studied gold is present in two main types of ores 1 quartz veins with free milling gold the gold is relatively silver rich true fineness values from 730 to 954 and is accompanied by a distinct suite of cu pb sb sulfides 2 sulfide ores consisting of arsenopyrite pyrite and rarer pyrrhotite and marcasite with refractory gold the ores have apparent fineness values larger than 910 arsenopyrite and locally at bogosu pyrite were identified as the hosts of submicroscopic gold mean concentrations of gold in arsenopyrite in various samples from the different mines obtained by secondary ion mass spectrometry sims range from 67 to 314 ppm au gold concentration mapping in individual arsenopyrite crystals from the different deposits revealed similar patterns of gold distribution the grains possess a gold poor core and elevated gold contents are present along distinct crystal growth zones towards their rims the outermost crystal layer is usually gold poor the well preserved distribution patterns also indicate that remobilization of gold from the sulfides played an insignificant role in the ores of the ashanti belt multiple quartz veining and growth zoning of the sulfides are interpreted as manifestations of multiple episodes of fluid infiltration fluid flow and mineral deposition the bimodal occurrence of gold in spatially closely associated quartz vein and sulfide ores indicates a genetic link between these ore types a model implying a grossly coeval formation of the ores from mesothermal fluids is proposed

intrusion age of pan african augen gneisses in the southern menderes massif and the age of cooling after alpine ductile extensional deformation

age and source of the kure odemis arsenopyrite gold mineralization menderes massif turkey determined by re os he isotopes abstract the menderes massif mm is considered to be one of the principal regions hosting vein type quartz arsenopyrite orogenic gold deposits and occurrences in turkey gold mineralizations in the mm can be grouped into i schistosity conformable e trending veins and ii shear controlled nw trending veins arsenopyrite is one of the major gold bearing minerals in these deposits or occurrences rhenium osmium isotopic dating of two types of arsenopyrite from the schistosity conformable and vein type kure odemis gold deposit has yielded two groups of model ages maximum ages at 557 574 ma and 246 250 ma respectively the data suggested that the quartz arsenopyrite gold deposit formed in the neoproterozoic and early triassic with the former and the latter corresponding to pan african compressional orogenesis and palotethys rifting respectively fluid inclusions in kure arsenopyrite have 3he 4he ratios of 0 08 0 09 ra ra 1 39x10 6 the 3he 4he ratio of air being within the range of middle to upper crustal values a minor helium contribution of mantle fluids to the kure gold deposit is possible because the 4he concentrations in arsenopyrite are enriched 170 to 9520 times relative to argon and typical atmospheric values indicating that contribution of atmospheric he to the mineralizing fluids is negligible and 0 08 0 09 ra is slightly above typical crustal 3he 4he ratios arsenopyrite yields relatively non radiogenic initial os isotopic compositions also indicating possiblecontribution from mantle fluids carbonic fluid inclusion type 2 h2o co2 nacl ch4 in quartz of nw trending veins at kure are gas liquid hydrate crystal rich and their homogenization temperatures th range from 244 to 387 c salinity values range from 0 2 to 5 7 wt nacl equiv the homogenization temperatures th of aqueous fluid inclusions type 1 h2o nacl in quartz from nw trending veins at kure vary between 237 and 358 c whereas salinity values range from 1 7 to 7 7 wt nacl equiv quantitative epma spot analyses on arsenopyrite minerals have shown that as concentrations in ew trending and nw trending veins range from 32 5 to 33 8 and 32 3 33 8 respectively based on a phase diagram for the fe as s system along with the arsenopyrite geothermometer the ranges of temperature and corresponding logf s2 at which arsenopyrite is in equilibrium with pyrite are between 380 and 480 c and 7 4 and 4 3 for apy 1 respectively these values are between 390 and 475 c and 7 0 and 4 5 for apy 2 respectively

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

gold in turkey a missing link in tethyan metallogeny abstract the gold metallogeny of turkey constitutes a sector of the tethyan eurasian metallogenic belt temb within the alpine himalayan orogenic system that formed from jurassic cretaceous to the present this orogenic system produced many different types of deposits related to subduction collision post collision and rifting processes gold deposits as well as other mineral deposits of turkey are mainly concentrated in late mesozoic and tertiary rocks evaluation of the gold metallogeny of turkey is based on a gis database compilation of known gold deposits and prospects currently available data show that turkey has a gold endowment including reserves and resources of approximately 31 5 m oz 979 tonnes in 51 deposits 21 of which contain more than 0 2 m oz gold the other 30 deposits contain a total of approximately 1 m oz 31 tonnes gold resources two recent discoveries kisladag and copler currently contain total resources of 17 6 m oz au 549 tonnes more than 50 of the total turkish gold endowment turkey possesses a wide spectrum of gold deposits related to mesozoic and cenozoic volcanoplutonic arcs however porphyry gold copper epithermal gold including both high and low sulfidation styles and gold rich volcanic associated massive sulfide including both kuroko and cyprus types are the most economically important to date orogenic gold including listwanite hosted placer gold and skarn hosted gold are relatively less important or abundant deposit types other potential gold systems for exploration include carlin type gold detachment fault related gold iron oxide copper gold and gold in carbonate replacement and manganese deposits

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

tellurium magmatic fluids and orogenic gold an early magmatic fluid pulse at cononish gold deposit scotland significant tellurium enrichment occurs in many orogenic gold deposits but the factors causing this are little understood some authors suggest this demands a magmatic input whereas others suggest it need not fractionation of te from se and s could offer insight into source pathway processes of auriferous fluids the metasedimentary hosted cononish vein gold deposit scotland is unusually te rich compared to many orogenic gold deposits with te au 2 4 whereas most orogenic deposits have te au 1 here ag in au ag alloy increases from 10 to 90 wt through the paragenesis correlating with decreasing hessite ag2te abundance this suggests the au ag alloy composition was controlled by the fluid te activity and that this decreased through time this is coupled to an increase in pyrite 34s from 2 0 to 11 4 through the paragenesis thus the deposit formed from a primary fluid with a low 34s and high te au ag that evolved to a high 34s low te pb cu bearing fluid the high 34s of the later fluid suggests it can only be sourced from specific nearby metamorphosed sedex horizons the early fluid that deposited most of the gold could be sourced from other metasedimentary units in the stratigraphy or be magmatic in origin we argue that two observations taken together suggest it is most likely that this fluid was magmatic the age of the mineralisation is identical to the last stage of crystallization of nearby granite batholiths and the fluid has a s isotope signature consistent with a magmatic source gold deposits in orogenic belts are almost certainly polygenetic and this study demonstrates evidence for te rich orogenic deposits having a significant magmatic component

revision of leptite gneisses in the menderes massif a supracrustal metasedimentary origin the pan african basement of the menderes massif comprises a regular lithological succession that reaches a thickness of 8 km the oldest units of which are in ascending order so called leptite gneisses a quartzite sequence transition zone and mica schists new findings suggest that the protoliths for the leptite gneisses proposed to be of volcanic origin in previous studies were predominantly clastic sediments of litharenitic composition geochemical data indicate that the protoliths for the leptite gneisses were of cratonic provenance because they have undergone pan african polymetamorphism and are intruded by approximately 550 ma gneisses of granitic origin it is believed that the time of deposition of their protoliths was late proterozoic relict parageneses indicate that the pan african metamorphism reached granulite facies conditions in the leptite gneisses supracrustal sedimentary origin of these rocks require that these rocks formerly termed leptite and or leptite gneiss should be renamed sillimanite garnet gneiss and or paragneiss

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

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

ore forming fluids in archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec canada archean gold bearing quartz veins at the sigma mine occur in deformed metavolcanics intruded by two generations of preore porphyries the veins were emplaced during a late compressional tectonic event and they consist primarily of quartz tourmaline carbonates pyrite and scheelite vein minerals have been deformed and are also cut by abundant healed fractures outlined by fluid inclusions in the veins gold typically occurs in late fractures and in recrystallized quartz microthermometric sem eda leachate analysis and gas chromatographic techniques were used to study fluid inclusions in quartz most fluid inclusions at sigma occur in late fractures and are secondary the fluid inclusions are commonly found in fractures parallel to or less commonly within gold bearing fractures and are genetically related to the gold three types of fluid inclusions are identified 1 high salinity na ca cl aqueous inclusions 25 34 wt salt with small amounts of co 2 some containing halite calcite and nahcolite as daughter minerals 2 co 2 rich inclusions containing small amounts of h 2 o and ch 4 and 3 low salinity h 2 o co 2 inclusions 10 equiv wt nacl with co 2 contents which are variable but commonly in the range of 15 to 30 mole percent co 2 leachate analyses show that in addition to na and ca the aqueous fluids contain minor amounts of k fe mg and li homogenization temperatures of h 2 o co 2 inclusions with constant phase ratios range from 285 degrees to 395 degrees c those of aqueous inclusions range from 60 degrees to 295 degrees c the aqueous and co 2 rich inclusions are interpreted to have trapped two coexisting fluids resulting from the unmixing of a homogeneous h 2 o co 2 parent fluid itself occasionally trapped in late fractures the ore bearing fluid is interpreted to be a low salinity 10 equiv wt nacl fluid containing 15 to 30 mole percent co 2 at minimum temperatures in the range of 285 degrees to 395 degrees c the relatively low homogenization temperatures of aqueous inclusions are interpreted to be the result of co 2 effervescence from a co 2 saturated aqueous fluid due to pressure fluctuations at the time of entrapment it is also proposed that the onset of gold deposition is related to the onset of fluid unmixing

supra pan african unconformity between core and cover series of the menderes massif turkey and its geological implications abstract well preserved primary contact relationships between a late proterozoic metasedimentary and the metagranitic core and palaeozoic cover series of the menderes massif have been recognized in the eastern part of the cine submassif on a regional scale metaconglomerates occur as laterally discontinuous channel fill bodies close the base of the metaquartzarenite directly above the basement the pebbles in the metaconglomerates consist mainly of different types of tourmaline rich leucocratic granitoids tourmalinite and schist in a sandy matrix petrographic features geochemical compositions and zircon radiometric ages 549 6 3 7 552 3 3 1 ma of the diagnostic clasts of the metaconglomerates e g leucocratic granitoids and tourmalinites show excellent agreement with their in situ equivalents 549 0 5 4 ma occurring in the pan african basement as stocks and veins the correlation between clasts in the metaconglomerates and granitoids of the basement suggests that the primary contact between the basement and cover series is a regional unconformity supra pan african unconformity representing deep erosion of the pan african basement followed by the deposition of the cover series hence the usage of core cover terminology in the menderes massif is valid consequently these new data preclude the views that the granitic precursors of the leucocratic orthogneisses are tertiary intrusions

stratigraphic and metamorphic inversions in the central menderes massif a new structural model the menderes massif is a large area of dominantly tertiary metamorphic rocks in western turkey it is bordered in the west by the cycladic metamorphic complex with eocene high pressure low temperature hp lt metamorphism in the central menderes the aydin mountains are made up of a thrust stack of eocene age at the base of the thrust stack greenschist facies paleozoic metasediments of the menderes massif form an inverted stratigraphic sequence the barrovian type metamorphism is also inverted with garnet bearing metapelites lying over the lower grade biotite bearing metapelites the p t conditions in the garnet zone are estimated as 530 c and 8 kbar this schist sequence of the central menderes massif is interpreted as the inverted lower limb of a major southward closing recumbent fold with the southern menderes massif representing a section from the near hinge of this fold the paleozoic metamorphic rocks of the central menderes massif are tectonically overlain by gneiss klippen possibly originating from the sheared and southward translated core of the menderes fold lying also tectonically over the paleozoic metamorphic rocks is a major thrust sheet belonging to the cycladic metamorphic complex it consists of garnet micaschist mesozoic marble serpentinite and amphibolitised eclogite although it has a highly sheared internal structure it probably represents an initially coherent sequence that has undergone hp lt metamorphism during the eocene the aydin mountains are dominated by contractional structures with subordinate extensional structures

structural and metamorphic evolution of the northern part of the menderes massif new data from the derbent area and their implication for the tectonics of the massif the menderes massif represents the western part of the metamorphic axis of the alpide orogen of anatolia asia minor a restricted area in its poorly known northern part around the village of derbent was studied to shed some light on its geological evolution and to compare it with that of the southern part of the massif in the derbent area three lithologic groups are recognized on the basis of their lithology and structural position namely the gneiss and the schist complexes and the marbles petrographic mineralogic and structural data indicate that the schist complex and the overlying marbles have undergone at least three phases of deformation and metamorphism the first phase probably reflects the closure of the karakaya marginal basin located to the north of the present menderes massif during the late triassic the traces of the first phase have been largely obliterated by the second phase which led to amphibolite facies metamorphism a pronounced flat lying foliation and a nne ssw trending

fluid inclusion geochemistry of high grade vein hosted gold ore at the pamour mine porcupine camp ontario this study was undertaken to characterize fluid inclusions associated with high grade vein hosted gold at the pamour mine in the porcupine camp of ontario and to compare them with fluid inclusions in quartz veins associated with wall rock hosted gold which is much more common the pamour mine contains two principal types of orebodies metasediment hosted fracture zones and larger metavolcanic or metasediment hosted quartz carbonate veins gold in the veins is distributed erratically attains very high grades locally and increases in grade at higher levels zoned alteration around the veins is dominated by addition of k 2 o co 2 as s and cao and depletion of na 2 o k 2 o co 2 and s are concentrated in the hanging wall and the intensity of co 2 and h super metasomatism increases upward in the mine roughly parallel to the trend seen in gold values gold was introduced along with sphalerite galena calcite chlorite and chalcopyrite late in the paragenetic history after brittle deformation of earlier vein hosted quartz tourmaline feldspar and pyrite sphalerite that is directly associated with high grade gold contains two types of primary inclusions a co 2 ch 4 fluid 20 45 mole ch 4 and an h 2 o rich liquid with a carbonaceous phase co 2 ch 4 as well as muscovite and graphite daughter minerals aqueous phase salinity estimates range from 2 to 9 equiv wt percent nacl and sem analyses of evaporitic residues of thermally decrepitated inclusions contain nacl and cacl 2 with lesser amounts of kcl mgcl 2 s zn and fe these two inclusion types appear to represent immiscible fluids trapped along the solvus in the h 2 o co 2 ch 4 salt system at temperatures of 325 degrees or 25 degrees c and pressures of 1 to 2 kbars these fluids are similar to those observed in vein quartz at the mcintyre and hollinger deposits where most gold is hosted by wall rocks except that co 2 immiscibility appears to have been more widespread at pamour the separation of immiscible fluids of the type identified in this study would increase the f sub o 2 and ph of the residual fluid owing to the partitioning of h 2 s ch 4 and co 2 into the carbonaceous phase the net effect of these changes would be to decrease the solubility of bisulfide complexed gold suggesting that co 2 immiscibility is an important contributor to gold deposition within veins where wall rock interaction is limited it is not clear whether all vein hosted gold formed from such unmixing or only the higher grade ore shoots

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

al mg systematics of hibonite bearing ca al rich inclusions from ningqiang hibonite bearing ca al rich inclusions cais usually occur in cm and ch chondrites and possess petrographic and isotopic characteristics distinctive from other typical cais despite their highly refractory nature most hibonite bearing cais have little or no 26mg excess the decay product of 26al but do show wide variations of ca and ti isotopic anomalies a few spinel hibonite spherules preserve evidence of live 26al with an inferred 26al 27al close to the canonical value the bimodal distribution of 26al abundances in hibonite bearing cais has inspired several interpretations regarding the origin of short lived nuclides and the evolution of the solar nebula herein we show that hibonite bearing cais from ningqiang an ungrouped carbonaceous chondrite also provide evidence for a bimodal distribution of 26al two hibonite aggregates and two hibonite pyroxene spherules show no 26mg excesses corresponding to inferred 26al 27al 8 x 10 6 two hibonite melilite spherules are indistinguishable from each other in terms of chemistry and mineralogy but have different mg isotopic compositions hibonite and melilite in one of them display positive 26mg excesses up to 25 parts per thousand that are correlated with al mg with an inferred 26al 27al of 5 5 0 6 x 10 5 the other one contains normal mg isotopes with an inferred 26al 27al 3 4 x 10 6 hibonite in a hibonite spinel fragment displays large 26mg excesses up to 38 parts per thousand that correlate with al mg with an inferred 26al 27al of 4 5 0 8 x 10 5 prolonged formation duration and thermal alteration of hibonite bearing cais seem to be inconsistent with petrological and isotopic observations of ningqiang our results support the theory of formation of 26al free poor hibonite bearing cais prior to the injection of 26al into the solar nebula from a nearby stellar source

pressure fluctuation during uplift of the northern apennines italy a fluid inclusions study abstract p t conditions existing after the main syn collision tectonic phase in the western part of the northern apenninic chain italy e g in the tuscan nappe outcropping in the la spezia area were estimated on the basis of a detailed microstructural structural petrographic and fluid inclusion study of quartz of syn tectonic d2 veins developed in the tertiary flysch at the top of the tuscan nappe macigno formation three main fluid events have been distinguished as follows during retrograde metamorphism d1 to d2 phase fluids in equilibrium with turbidites from the tuscan nappe were h2o ch4 mixtures issued from water organic matter interactions in temperatures conditions that may have reached at least 260 c or more 280 c depending on the considered depth estimates and maximum pressures around 210 250 mpa evidence of strong fluid pressure fluctuation between lithostatic and hydrostatic within the metamorphic formations up to 100 150 mpa possibly linked to fault valve activity at the beginning of the uplift triggered phase separation of the water methane fluids and production of methane rich and water rich fluids fluctuations in pressure during these events played a crucial role in quartz crystallization especially in extensional fissures formed perpendicular to the d2 folds axial foliation changes in the fluid regime and sources with time are evidenced by the input of brines which mix to distinct degrees and are trapped in healing microfissures during retrograde fluid evolution such mixing processes are an indication of the connection between separate fluid reservoirs with different temperature conditions consequently mass and heat transfer have to be taken into account as the downward percolation of cooler fluids probably accelerated the rate of cooling of the exhumed formations these processes are certainly common to most orogenic terrains and can be quantitatively studied through p v t x reconstruction using fluid inclusion data on the drainage zones where the mixing processes occurred this work confirms that fluid inclusion studies can provide accurate quantitative estimates of fluid pressure variations during the evolution of orogenic terrains and could therefore constitute a useful tool in tectonic interpretations at the light of the models developed for pressure variations in the upper crust

early triassic potassic volcanism in the afyon zone of the anatolides turkey implications for the rifting of the neo tethys afyon zone which was derived from the anatolide tauride platform during closure of the neo tethys is made up of pre mesozoic basement and unconformably overlying triassic early tertiary cover series the afyon zone contains widespread metavolcanic rocks which are dominated by rhyolite dacite and trachyandesite they form a distinct volcanic succession which is separated from the underlying silurian lower carboniferous metacarbonates and meta siliciclastics by a regional unconformity trachyandesitic metavolcanics are made up of massive lava flows pyroclastics and epiclastics less frequently domes and dikes which were developed on a deeply eroded subaerial landmass u pb and pb pb zircon geochronology yielded lower triassic 250 ma ages which are interpreted as extrusion age of trachyandesitic volcanics based on the stratigraphic geochronological and geochemical data we suggest that these lower triassic magmatic rocks represent an extensional tectonic setting on the northern active margin of the gondwana which led to the development of the northern branch of the neo tethys

magma interaction processes in syn extensional granitoids the tertiary menderes metamorphic core complex western turkey abstract western turkey which forms the eastern part of the aegean region was subjected to continental extension that led to formation of metamorphic core complexes and associated syn extensional granitoids this study deals with petrogenesis of the syn extensional early miocene alacamdag ag and middle miocene salihli sg granitoids and associated mafic microgranular enclaves mme in order to better understand the time progressive evolution of the mantle sources beneath the extended continental crust in western turkey ag and sg granitoids consist of undeformed and ductility deformed granitoids together with abundant mmes they are calc alkaline to high k calc alkaline rocks that are metaluminous to slightly peraluminous mg of ag host rocks is slightly lower than that of sg host rocks ag host rocks have higher na 2 o ba rb rb la and lower al 2 o 3 cao mgo tio 2 zr y values than those of the sg host rocks ag and sg host rocks differ from those of mmes with their lower al 2 o 3 cao mgo fe 2 o 3 tio 2 sr v mg and higher sio 2 values mmes are intermediate corresponding to monzonite monzodiorite in ag and diorite in sg compositions and are more mafic with respect to their host rocks in the primitive mantle pm normalized trace element patterns host rock and mme samples have similar trace element patterns all of these rocks are enriched in large ion lithophile elements liles cs rb ba th k and sr and strongly depleted high field strength elements hfses ta nb p ti compared to the primitive mantle the isotope ratios of the syn extensional ag and sg rocks display increasing radiogenic strontium and decreasing radiogenic neodymium isotopic values for the ag and sg host rocks and mme samples are 87 sr 86 sr ag host 0 708835 0 710206 and e nd t ag host 5 36 to 7 36 87 sr 86 sr ag mme 0 709107 0 709801 and e nd t ag mme 5 36 to 7 36 87 sr 86 sr ag mme 0 709107 0 709801 and e nd t ag mme 5 55 to 6 51 87 sr 86 sr sg host 0 712200 0 712408 and e nd t sg host 8 03 to 8 61 87 sr 86 sr sg mme 0 712028 0 712351 and e nd t sg mme 7 57 to 8 48 syn extensional granitoids in western turkey were mainly affected by crustal contamination fractional crystallization and magma mixing mingling mm processes magma mixing mingling partial mixing appear to have larger affects on the compositional range of the magmas than those generated by partial melting crustal contamination and fractional crystallization mafic and felsic magmas forming syn extensional granitoids have also undergone metasomatism chemical equilibrium and diffusional exchange processes during cooling syn extensional granitoids have been derived from a hybrid magma that originated from mixing of coeval lower crustal derived felsic magma and lithospheric mantle derived mafic magmas during extensional processes

the origin and evolution of the menderes massif w turkey a rubidium strontium and oxygen isotope study the menderes massif located in the alpine orogen of western turkey has three litho structural units a basal gneiss core a schist mantle covering the gneiss core and an overlying marble mantle this study reports isotopic data from samples of metasediments and migmatites from the southern type a and of tonalitic to granitic metaigneous rocks from the northern menderes massif type b type a rocks define a rb sr whole rock isochron age of 502 10 ma and an initial87sr 86sr ratio of 0 71174 73 this is interpreted as the age of migmatization type b rocks give a rb sr whole rock isochron age of 471 9 ma with an initial87sr 86sr ratio of 0 70684 25 which we interpret as the intrusion age k white micas from rock type a give an average rb sr mineral age of 56 1 ma which can be interpreted as the formation age of the alpine mineral paragenesis k white micas from rock type b give rb sr mixed ages of 120 230 ma between alpine and pan african orogenies biotites from both rock types yield an average rb sr age of 37 1 ma which is interpreted as an alpine cooling age the oxygen isotope ratios of type a rocks range from 10 4 to 14 6 and of type b from 8 9 to 11 8 the oxygen and strontium isotopic compositions together clearly distinguish rocks of types a and b compositions of type a rocks suggest a crustal origin type b rocks have compositions transitional between those of crustal and mantle derived materials

factors in the formation of the giant kalgoorlie gold deposit abstract kalgoorlie golden mile plus mt charlotte accounts for more than half the gold won from the 2000 deposits that comprise the widespread gold mineralization of the archaean yilgarn block of western australia it is also one of the largest gold deposits globally 1800 t au production and reserves an analysis of the various stages of formation of the kalgoorlie deposits from source through solution of gold in hydrothermal fluids and their infiltration along channelways through to gold precipitation at depositional sites reveals several features that make kalgoorlie favourably disposed as a site for a major gold deposit however none alone account for its anomalously large size it is concluded that the giant kalgoorlie gold deposit owes its size and unique position in western australian gold production history to favourable host rock chemical composition favourable host rock thickness and mechanical properties and to the favourable geometry of its host units and hosting greenstone belt at favourable pt conditions within the greenschist facies collectively these factors together with proximity to the regional scale boulder lefroy fault allowed highly focussed fluid flow on both a deposit and district scale in this regard it is significant that the structural setting of gold mineralization and the greenstone architecture at the largest canadian archaean deposit timmins are remarkably similar to kalgoorlie orebody size distribution histograms for both the yilgarn block and the abitibi belt canada are highly skewed with extremely few giant deposits but numerous deposits of 10 tonnes gold existing this topology can be accounted for in terms of system efficiency the probability of all six factors in the ore forming system being optimized high heat flow large fluid reservoir proximity to major structure efficient fluid focussing and large and compositionally favourable host lithology is extremely small in contrast the probability of two processes coupling to give low efficiency is very large resulting in numerous small deposits kalgoorlie appears to have formed by the same basic processes that formed the plethora of smaller yilgarn gold deposits however it represents a mineralized domain in which there was a conjunction of a number of favourable parameters both on a regional and deposit scale that produced high system efficiency and allowed the effective fluid focussing and gold deposition that formed this giant deposit

origin of ore fluids in the muruntau gold system constraints from noble gas carbon isotope and halogen data abstract hydrothermal vein minerals directly associated with native gold mineralization in the muruntau vein system uzbekistan have been studied for noble gas carbon isotope and halogen chemistry of the trapped ore related fluids helium trapped in early arsenopyrite 1 which has preserved the original fluid signature better than associated scheelite and quartz indicates a small input from a mantle source 5 of total he however the overwhelming majority of the he in the fluid 95 is from crustal sources the noble gases ne kr and xe in the sample fluids are dominated by gases of atmospheric origin the carbon isotope 13 c 2 1 to 5 3 and halogen characteristics of the fluids log br cl 2 64 to 3 23 lend further support for the activity of juvenile fluids during the main ore stage the high proportion of crustal components in the ore forming fluids may be explained by intense fluid rock interaction and is also supported by previous nd and sr isotope studies the involvement of a juvenile fluid component during the main stage of hydrothermal activity at muruntau 275 ma can be linked to the emplacement of lamprophyric dikes at muruntau due to apparently overlapping ages for high temperature alteration related ore vein formation and intrusion of the dikes the input of mantle derived fluids possibly related to the hercynian collisional event in the western tien shan stimulated intense fluid rock interaction in the crust in this context the mantle derived fluid should be considered as one possible carrier of metals significant amounts of external meteoric fluids circulating in fracture systems are interpreted to have modified the noble gas signature of fluid in quartz mostly during late low temperature fluid circulation

the hemlo gold deposit ontario an example of melting and mobilization of a precious metal sulfosalt assemblage during amphibolite facies metamorphism and deformation the timing of mineralization at the hemlo gold deposit has long been a controversial issue we present arguments that use partial melting of the ore assemblage to explain the mechanism of ore mobilization and resolve problems with the model of premetamorphic mineralization the results have implications for mine exploitation and exploration strategies we show that the ore mineral assemblage underwent partial melting during middle amphibolite facies metamorphism 600 650 c 6 7 kbars primarily through breakdown of stibnite and arsenopyrite in a high s2 environment concurrent deformation led to segregation of the resulting sb and as rich sulfosalt melt interaction between this melt and a range of unmelted sulfides led to further melting and incorporation of other elements into the melt the gold bearing melt was mobilized from compressional high strain sites into dilational domains such as boudin necks and extensional fractures developed in competent lithologies ore minerals that did not melt significantly pyrite molybdenite pyrrhotite and sphalerite were not extensively mobilized and largely remained within high strain compressional domains this segregation of melt from residue thus resulted in the observed heterogeneous distribution of ore minerals within the deposit crystallization of the sulfosalt melt produced a diverse suite of ore minerals dominated by stibnite and realgar and containing an array of rare sulfosalts native elements intermetallic compounds and tellurides some sulfosalt melt persisted to low temperature 300 c allowing continued small scale localized mobilization during late deformation although gold occurs at moderate concentrations within the compressional high strain domains it is particularly concentrated in the dilational domains a consequence of its mobilization within a sulfosalt melt our model of partial melting of the ore mineral assemblage with consequent mobilization explains how ore minerals that are unstable even at greenschist facies conditions came to be hosted in structures that formed at or near the peak of amphibolite facies metamorphism

grain boundary migration microstructures in a naturally deformed quartzite abstract in this study several grain scale microstructures are presented that are thought to demonstrate the migration direction of once mobile grain boundaries in a naturally deformed quartzite an analysis is presented of the sense of migration of the boundaries and the characteristics of the patterns of relative grain growth and shrinkage grain boundary migration seems to be correlated with the relative crystallographic orientations of neighbouring grains for the quartz quartz grain boundaries and the pattern of preferred grain growth is roughly symmetrical about the mica foliation plane

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

bivergent extension in orogenic belts the menderes massif southwestern turkey the central menderes massif is characterized by an overall dome shaped foliation pattern and a north northeast trending stretching lineation the asymmetry of shear bands and quartz c axis fabrics on either side of the structural dome demonstrate a top to thenorth northeastshearsenseinthenorthernpartandatoptothesouth southwestshear sense in the southern part of the submassif i e a bivergent downdip movement this suggests a symmetric collapse of the alpine menderes orogenic belt along two extensional shearzones conjugateshearbandsandsymmetricquartzc axisfabricsintheeast trendingtransitionzonedemonstrateacoaxialdeformationbetweenthetwoextensiondomains bivergent extension in the menderes massif is in contrast to asymmetric extension in the aegeansea here thestill activehellenicsubductionzoneevolvedfromanadvancingplate boundary associated with crustal thickening into a retreating plate boundary in oligocene miocene time southward rollback of the subducting plate during continuous northward subduction allowed asymmetric top to the north northeast extension in the back arc region during the exhumation of the cycladic core complexes in western turkey the arrival of the thick continental crust of the menderes massif halted subduction and probably caused the symmetric collapse of the massif because the high potential energy of the thickened crust was no longer supported by subduction

multistage exhumation of the menderes massif western anatolia turkey structural analyses along selected transects across the menderes massif and incorporation of existing data have resulted in a synthetic cross section across southwestern turkey the tectonic interpretation has been combined with 40ar 39ar laser probe experiments on two syn kinematic white mica populations which respectively predate and overprint documented early miocene deformational fabrics our results indicate that the regional extension had initiated by eocene oligocene times a 36 2 ma 40ar 39ar age derived from white mica which formed during a regionally observed northward directed tectonic transport suggests that the extension was contemporaneous with the tectonic emplacement of mid crustal continental basement alternatively the age may relate to the regional cooling of the basement sequence and thus postdates the tectonic emplacement in the latter scenario the analysis fails to solve the present ambiguity on the pan african or alpine affinity of the northward directed transport further exhumation of basement rocks is characterized by a dominant displacement along the north dipping gediz detachment at the northern margin of the massif which developed under ductile conditions in the early miocene by partial exploitation of older zones of weakness which originated from an earlier phase of basement emplacement youngest semi ductile activity along the gediz detachment has been recorded as having a 7 1 ma 40ar 39ar age derived from syn kinematic white mica in the top of the detachment following the initiation of the ductile gediz detachment an antithetic semibrittle and south dipping buyuk menderes detachment had developed in the center of the massif which together with the gediz detachment accommodated further doming of the central part of the menderes massif and controlled the architecture of the surrounding supradetachment basins