an energy dispersive miniprobe multielement analyzer emma for direct analysis of trace elements and chemical age dating of single mineral grains abstract an energy dispersive miniprobe multielement analyzer emma was designed and constructed for the analysis of trace elements as cr cu fe ga ge hf mn ni pb rb se sr th y u zn in small individual mineral grains such as apatite garnet monazite sphene zircon and other accessory minerals the instrument is sensitive ppm for most elements rapid 3 6 min per analysis non destructive and essentially no sample preparation is required with respect to single zircon grains as small as 50 m with mass as low as a few g for example the detection limits for u th and pb are on the order of 10 ppm 5 10 times better than the electron microprobe here the emma is used to illustrate the variation in hf and y concentrations in single zircon grains from pegmatites granites basalts carbonatites and kimberlites also the instrument is used for chemical age dating u th total pb of 1 single zircon grains from the berdyshevsky intrusive complex ukraine and 2 single monazite grains from a small placer deposit within the transition zone between the saxothuringikum and moldanubikum bavaria germany the average age of the single zircon grains from berdyshevsky granite determined using emma 2 19 0 17 ga 1 is consistent with the u pb zircon intrusion age of this complex 2 14 0 07 ga and monazite data ranging from 1 95 to 2 48 ga with respect to the pegmatite from this complex the average age of 1 93 0 09 ga found with emma is geologically consistent with zircon and monazite ages ranging from 1 90 to 2 29 ga regarding the monazite grains from the placer the age dates obtained using emma 328 28 ma are comparable to the isotopic ages conventional u pb and pb pb step leaching which yielded ages of 312 3 and 324 12 ma respectively

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

origin of ore forming brines in sediment hosted zn pb deposits of the basque cantabrian basin northern spain fluid inclusion data microthermometry and na k li cl br chemistry from mississippi valley type zn pb deposits in the basque cantabrian basin north iberian peninsula indicate that fluid mixing occurred during mineralization cl br ratios of the ore forming brines suggest that the high salinity was primarily acquired by evaporation of seawater only in deposits near salt domes orduna and murgia diapirs do the ore forming brines have halogen signatures indicative of halite dissolution mixing of fluids frequently cannot be detected using only microthermometry or halogen data although microthermometric data can indicate mixing where one of the end members is fresh water or a highly diluted fluid combining the two allows both the recognition of mixing and an estimation of the relative proportion of the different fluids involved the effects of mixing on the salinity and halogen ratios of the resulting mixture have been calculated using four types of fluids 1 seawater 2 evaporated seawater before the onset of halite precipitation 3 seawater evaporated past the point of halite precipitation and 4 a halite saturated brine at 25oc derived from halite dissolution the calculated cl br na br mixing curves have been compared to data from the zn pb deposits of the basque cantabrian basin and show that mixing between a residual brine and a halite dissolution brine can account for the deposits in the western biscay district txomin matienzo barambio most of the ore forming brines from the studied deposits around the orduna and murgia salt domes altube monteleon jugo originated by halite dissolution although there is also significant contribution 20 50 wt from a highly evaporated brine

proto tethyan remnants in northwest iran geochemistry of the gneisses and metapelitic rocks abstract the iran continental crust was metamorphosed intruded by granitoid magmas folded and faulted during the late precambrian by the pan african orogeny the basement complex in the takab complex northwest iran consists of gneisses amphibolites pelitic schists meta ultramafic and calc silicate rocks geochemically the protoliths of the takab gneisses are slightly peraluminous and medium to high potassic with calc alkaline affinity these gneisses may have been emplaced in volcanic arc tectonic setting furthermore the metapelitic protolith is shale deposited in an active continental margin setting all these characteristics and presence of paleo suture zone and ophiolitic rocks i e serpentines meta mafic and meta ultramafic rocks around the high grade metamorphic rocks suggest that a continental margin magmatic arc andean type formed the takab precambrian basement the basement complexes are extensively overprinted by the pan african orogeny and younger igneous events this supports the inference that early cambrian orogenesis in the takab complex region of northwest iran marks one of the fundamental lithospheric boundaries within gondwana which belonged to a greater late neoproterozoic early paleozoic orogenic system that was active along the proto tethyan margin of the gondwana supercontinent extending at least from its arabian margin to the himalayan margin of the indian subcontinent

nondestructive chemical dating of young monazite using xrf 1 design of a mini probe age data for samples from the central alps and comparison to u pb tims data the analytical capabilities of an improved mini xrf instrument for trace element analysis are explored to obtain u th pb ages for single monazite grains as small as 50 m the detection limits for u th and pb with counting times of 10 min are 10 ppm counts collected for 40 min are sufficient to date single monazite grains as young as 15 ma the precision of the age data depends essentially on the counting statistics of the main x ray peak npb l 1 2 used to analyze for lead the age uncertainty is proportional to the age of the grain the total contents of th and u and the squared integration time the reliability of the chemical dating method is tested using monazite separates from amphibolite facies metamorphic monazite samples from the central alps for which the chemical ages are compared to mass spectrometric u pb tims ages we show that populations of analyses obtained using the new instrument on single grains as young as 25 30 ma agree within error with the tims data for monazite separates with complex age patterns such as polymetamorphic samples yielding discordant isotopic ages the statistical analysis of chemical age data obtained from populations of 26 50 grains is advantageous in that it may provide additional insight into the reasons for the discordancy chemical th u pb dating of monazite by the xrf method offers considerably improved accuracy and precision compared with chemical dating by electron microprobe which typically becomes impractical for samples less than 100 200 ma in age conversely the minimum grain size required for the new instrument 50 m is well above the spatial resolution of the electron microprobe 2 m a companion paper scherrer et al this volume describes further developments towards microanalysis by xrf with improved spatial resolution

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

preservation of chemical residue melt equilibria in natural anatexite the effects of deformation and rapid cooling a combined petrologic textural and chemical approach is used to interpret the relationship between chemical exchange and deformation during partial melting of a granodioritic gneiss in the contact aureole of the bergell pluton central alps in contrast to most regional metamorphic anatexites chemical equilibrium between residue and segregated melt was attained and preserved by several elements as shown by their present distribution equilibrium involved both the major and the trace elements hosted in the rock forming minerals and the light rare earth elements lree hosted primarily in allanite equilibrium with respect to lrees was achieved because allanite had a reactive behaviour during water present melting in contrast to the refractive behaviour of xenotime which mostly controls the distribution of the hree s the attainment and preservation of equilibrium between leucosome and residue requires peculiar boundary conditions we propose that the achievement of equilibrium between melt and residue was promoted by deformation operating via a mechanism of melt present granular flow i e dissolution accommodated grain boundary sliding active during partial melting microstructural observations indicate that melt present granular flow was the dominating deformation mechanism in these anatexites the preservation of residue melt equilibrium is inferred to result from rapid cooling under contact metamorphic conditions and from the lack of deformation below the solidus

origin of secondary potash deposits a case from miocene evaporites of nw central iran abstract in early miocene times an extensive carbonate shelf developed in central iran and during several cycles of sea level fluctuations evaporite bearing carbonate sequences of the qom formation were deposited however in the early middle miocene development of restricted marine conditions led to a facies change from shelf carbonates of the qom formation to the evaporite series of the m 1 member of the overlying lower red formation this member is a facies mosaic of lagoonal and salina evaporites mainly halite beds admixed with wadi siliciclastics the purpose of this study which focuses on two salt mines in the northwestern portion of central iran in the zanjan province was to reveal the origin sedimentary environment and diagenesis of these potash bearing evaporite sequences petrographic examination revealed the following mineral assemblage halite gypsum anhydrite and carnallite as primary precipitates and langbeinite and aphthitalite as secondary metamorphic potash salts in the iljaq mine distorted halite beds are dominated by burial and deformational textures and a great deal of secondary potash salts in the qarah aghaje mine however the bedded halite shows pristine primary textures and is devoid of the secondary potash salts high bromine content of most evaporite minerals suggests their marine origin and confirms the absence of the extensive meteoric alterations and subsequent bromine depletions potash salts are mainly secondary and resulted from diagenetic replacements of distorted halite beds during thermal and dynamic metamorphism in a burial setting

opaline and al si phytoliths from a tropical mire system of west malaysia abundance habit elemental composition preservation and significance abundant and unique opaline and al si phytoliths and opaline bioliths have been discovered in holocene peat deposits of tropical tasek bera in peninsular malaysia these are secreted mainly by plants higher plants and algae and incorporated in the sediment cycle during the rapid biomass turnover many wetland plants have entire skeletons secreted the study shows that differing plant parts of same species as well as same parts of differing plant species incorporate different amounts of elements whilst deciduous trees of the swamp forest have phytoliths enriched in al most phytoliths of palms sedges and grasses of the littoral swamp are composed of opaline silica incorporation of al and many other elements into relatively stable phytoliths is the result of high evapotranspiration rate and ample plant available elements and can serve to detoxify the soil solution because of the abundance of such opaline and al si structures spongillid and algal remains in acid peat accumulating environments tropical peatlands represent repositories of si and al which together with variable amounts of other elements could provide the prime material for silicate neoformation during later diagenetic processes neoformation of minerals from bioliths would explain the scarcity of biogenic remains in carboniferous and tertiary coal deposits furthermore incorporation of major elements in phytoliths may limit the rate of leaching of these elements in an environment where biomass turnover is rapid thus reducing the loss of nutrients and other plant essential elements most nutrients of tropical peats are recycled by plants within the top 150 cm and an upward migration of plant essential elements such as mg ca or p but also of si and al occurs during peat accumulation such elemental cycling strongly influences the geochemical composition of the peats during mire evolution utilizing al for normalization of major and minor elements of tropical peats for paleoclimatic and paleodepositional analyses may thus result in incorrect interpretations

sediment hosted disseminated gold mineralisation at zarshuran nw iran mineralisation at the zarshuran nw iran occurs on the flank of an inlier of precambrian rocks hosted in black silty calcareous and carbonaceous shale with interbedded dolomite and limestone varying in thickness from 5 to 60 m and extending along strike for approximately 5 6 km two major steeply dipping sets of faults with distinct trends occur in the zarshuran 1 northwest 310 325 and 2 southwest 255 265 the main arsenic mineralisation occurs at the intersection of these faults the mineral assemblage includes micron to angstrom size gold orpiment realgar stibnite getchellite cinnabar thallium minerals barite au as bearing pyrite base metal sulphides and sulphosalts hydrothermal alteration features are developed in black shale and limestone around the mineralisation types of alteration include 1 decalcification 2 silicification 3 argillisation 4 dolomitisation 5 oxidation and acid leaching and 6 supergene alteration the early stage of mineralisation involved removal of carbonates from the host rocks followed by quartz precipitation the main stage includes massive silicification associated with argillic alteration in the late stage veining became more dominant and the main arsenic ore was deposited along fault cross cuts and gouge these characteristics are typical of carlin type sediment hosted disseminated gold deposits the early stage of mineralisation contains only two phase aqueous fluid inclusions the main stage has two groups of three phase co2 bearing inclusions with minor ch4 n2 associated with high temperature two phase aqueous inclusions during the late stage fluids exhibit a wide range in composition salinity and temperature and ch4 becomes the dominant carbonic fluid with minor co2 associated with a variety of two phase aqueous fluid inclusions the characteristics of fluids at the zarshuran imply the presence of at least two separate fluids during mineralisation the intersections of coexisting carbonic and aqueous inclusion isochores together with stratigraphic and mineral stability evidence indicate that mineralisation occurred at 945 445 bar and 243 59 c implying a depth for mineralisation of at least 3 8 1 8 km assuming a lithostatic pressure gradient fluid density fluctuations and the inferred depth of formation suggest that the mineralisation occurred at the transition between overpressured and normally pressured regimes geochronologic studies utilising k ar and ar ar techniques on hydrothermal argillic alteration whole rock and separated clay size fractions and on volcanic rocks indicates that mineralisation at zarshuran formed at 14 2 0 4 ma and was contemporaneous with nearby miocene volcanic activity 13 7 2 9 ma it is proposed that mineralisation was the result of the infiltration of hydrothermal fluids containing a magmatic gas component and that it was localised in the zarshuran unit because of the redox boundary that it provided and or because it lay between an overpressured region at depth and a zone of circulating hydrostatically pressured fluids above

br cl na systematics in illinois basin fluids constraints on fluid origin and evolution the authors present here bromide chloride and sodium data for fluids from reservoirs of ordovician through pennsylvania age in the illinois basic which suggest that remnant marine fluids contribute significantly to fluid cl budgets cl br and nabr ratios for ordovician through devonian formation fluids are relatively uniform and near those for seawater despite greater than a factor of ten range in cl concentration in contrast fluids from mississippian and pennsylvanian reservoirs separated from older reservoirs by the new albany shale group have more variable fluid cl br and na br ratios most of which are significantly greater then those of seawater the 1 1 stoichiometry of cl and na increases for mississippian and pennsylvanian formation fluids is consistent with halite dissolution nevertheless br systematics and mass balance considerations indicate that he overall cl budget of illinois basin formation fluids appears to be more significantly influenced by the contribution from subaerially evaporated seawater than by halite dissolution

new improved equations for and sio2 geothermometers by outlier detection and rejection abstract we present new improved equations for three still widely used na k na li and sio 2 geothermometers obtained by statistical treatment of the data and application of outlier detection and rejection as well as theory of error propagation and compare them with those by fournier and others new equations are also developed for estimating errors associated with the use of these new geothermometric equations and comparing them with the performance of the original equations the errors in the use of the new na k equation for temperatures ranging from 80 to 350 c vary from about 19 to 34 which is lower than the corresponding errors 24 43 for the original fournier equation similarly for temperatures ranging from about 50 to 320 c our new equation for na li geothermometer for cl 2 2 geothermometer we have proposed a linear equation for the temperature range of 210 to 310 c sio 2 295 ppm which shows considerably smaller total propagated errors 2 3 than for the original equation 5 29

high precision 207pb206pb zircon geochronology using a small ion microprobe abstract a small geometry ion microprobe cameca ims 4f has been successfully used for the routine measurement of 207 pb 206 pb ratios in individual zircons with a spatial resolution of 20 m in spite of the lower sensitivity of the small ion microprobe resulting from operating at high mass resolution m m 4600 in order to resolve isobaric molecular interferences we can discern archean components whose ages differ by 50 ma a single measurement requires 90 min of data acquisition thus a comprehensive study of a zircon population can be accomplished in a few days three sets of precambrian zircons analyzed earlier by other techniques yielded ages which are within 2 of their true values as our first unknown we analyzed zircons from a sample of orthogneiss collected from the aravalli craton of northwestern india for this sample we obtained a minimum age of 3281 3 ma 1 which we believe closely approximates the time of crystallization of the gneiss s igneous protolith

numerical simulation and a geochemical model of supergene carbonate hosted non sulphide zinc deposits abstract the proposed metallogenetic model presented in this paper is based on observations from the iranian non sulphide zinc deposits mehdi abad iran kuh and kuh e surmeh the emplacement of non sulphide ore can be generally subdivided into an oxidation stage followed by a post oxidation stage the formation of carbonate hosted non sulphide zinc deposits is primarily controlled by three factors climate protore composition and geology lithology and structure of the wall rocks the climate controls the oxidation and metal transport predominantly through the amount of meteoric water and the availability of oxygen which indirectly is controlled through the thickness of the soil cover and biogenic oxygen consumption favourable conditions for oxidation are an arid climate with minimal biogenic activity within the soil as a consequence oxygen can reach the sulphides easily resulting in higher metal concentrations of the supergene aqueous solutions dry climates are associated with a low water table preventing descending zn bearing fluids from contact with the aquifer and thus from dilution dispersion and removal of metals commonly non sulphide zinc deposits consist of two types of ore red zinc ore rich in zn 20 fe 7 pb as and white zinc ore typically with very high zinc grades up to 40 but low concentrations of iron 4 2 ions during the oxidation stage leads to the precipitation of highly insoluble anglesite which results in low pb 2 concentration within the fluid most of the zinc up to 80 at ph 6 or 97 at ph 5 leaves the oxidation zone and precipitates as zinc carbonates in adjacent parts of the carbonate host rock the neutralisation processes of the sulphuric acid with the carbonates of the host rock during the oxidation stage lead to the formation of co 2 g consequently the co 2 partial pressure p co2 g increases drastically and forms a co 2 g halo around the active oxidation zone thus most of the zinc precipitates as smithsonite which is stable and occurs exclusively in a high p co2 g environment the p co2 g decreases during the post oxidation stage and reaches the level of atmospheric p co2 g under these conditions hydrozincite becomes stable and starts to replace smithsonite most of the stage i smithsonite becomes corroded and is altered to stage ii hydrozincite the post oxidation stage is also associated with the successive formation of local zinc hydro silicates depending on the availability of sio 2 within the solution generally arid climates provide the best conditions for the preservation of non sulphide deposits the limited availability of meteoric water and deep to very deep water tables protect the non sulphide ore from subsequent dissolution

combined high precision chronometry and geochemical tracing using accessory minerals applied to the central alpine bergell intrusion central europe abstract the behaviour of nd u th and pb isotopes in granitic rocks is usually controlled by accessory minerals in this study an approach is adopted which uses the initial 143 nd 144 nd as a geochemical tracer together with high precision u th pb geochronology for accessory phases and their respective whole rock this combination of techniques is applied to zircon allanite sphene apatite and thorite from both a tonalite and a granodiorite from the tertiary alpine bergell intrusion inherited isotopic signatures have been identified in bulk zircon fractions by inverse discordance in the u pb system in the case of the granodiorite the initial nd in the zircon is 1 77 units lower than the bulk rock this result indicates that nd isotopes in zircon may serve as a useful tool for tracing crustal precursors in silicic rocks all other accessories yield an initial nd equal to their respective whole rock and u th pb ages equal to or lower than the respective intrusion ages this indicates either the absence of inherited cores or that such cores have exchanged their nd and pb in the case of apatite also sr by diffusion where available experimental mineral melt equilibria and diffusion models are consistent with this behaviour u pb geochronology of carefully selected core free zircons yields a precise intrusion age of 31 88 0 09 ma for the tonalite in contrast granodioritic zircons are partially reset due to radiation damage caused by high u concentrations however an alternative means of dating young intrusions is to use 232th 208pb ages of allanite in the case of allanite the presence of a large excess of 206pb derived from 230th indicates that no total pb loss has occurred since crystallization and the nd isotopes indicate the absence of inheritance using both the allanite age and a 238u 206pb age for sphene an intrusion age of 30 13 0 17 ma is indicated for the granodiorite taken together with an allanite th pb age for the tonalite these results strongly support the high closure temperatures for the allanites studied here 700 800 c at high post magmatic cooling rates all other accessory mineral ages are reset to values similar to hornblende 39ar 40ar ages and reflect the effect of post magmatic cooling superimposed on post metamorphic cooling

mineral chemistry and phase relations of co ni arsenides and sulfarsenides from the baycheh bagh deposit zanjan province iran abstract the polymetallic hydrothermal veins of baycheh bagh deposit in nw iran occur in quartz carbonate veins which are hosted by oligocene to miocene volcanic mainly andesite and volcaniclastic agglomerate tuff rocks unconformably overlying metamorphic basement rocks three transitional paragentic stages of hypogene mineralization have been identified stage 1 includes base metal cu zn pb sulfides and gold and is succeeded by co ni fe as minerals and bismuth stage 2 and cu bi sulfides sulfosalts stage 3 stage 2 ni co fe mineralization is complex and is subdivided into three substages starting with sulfarsenides arsenopyrite alloclasite i ii followed by native bismuth triarsenides skutterudite i ii iii and diarsenides rammelsbergite safflorite and terminated by sulfarsenides gersdorffite cobaltite solid solution alloclacite iii skutterudite and alloclasite are present in several generations and preserve delicate growth zoning reflecting a multi stage episodic growth the sulfarsenides and arsenides reveal significant substitution of ni co fe as well as as and s reflecting compositional changes of the ore forming fluid e g activities of metals as s as well as changes in ph and oxidation state the mineral assemblages and comparison with similar as dominated vein type ni co mineralization elsewhere collectively referred to as five element veins suggest that the complex arsenide sulfarsenide assemblages formed at temperatures below 300 c baycheh bagh can be regarded as a member of this heterogeneous group of bi co ni as deposits a peculiarity of hydrothermal vein type mineralization at baycheh bagh is that initial epithermal cu au zn pb mineralization evolved into bi co ni as mineralization with time

nakhlak carbonate hosted pb ag deposit isfahan province iran a geological mineralogical geochemical fluid inclusion and sulfur isotope study abstract the upper cretaceous nakhlak epigenetic vein type pb ag deposit is located 55 km northeast of the town of anarak in isfahan province iran the deposit contains 7 mt of galena barite ore with an average grade of 8 33 pb 0 38 zn and 72 ppm ag the ore mineralization occurs as stratabound epigenetic steeply dipping east west trending veins in faulted or fracture controlled upper cretaceous sadar carbonates galena and barite are the primary minerals minor sphalerite tennantite tetrahedrite pyrite and chalcopyrite occur as inclusions in galena cerussite with minor amounts of anglesite and plattnerite formed in the oxidized supergene zone the ore and ore related minerals were deposited in the hydrothermally dolomitized carbonate host rock containing saddle shaped dolomite geochemically the dolomitized carbonate host rocks are enriched in mgo fe 2 o 3 mno pb zn and ba but depleted in cao the galena concentrate contains high values of ag 932 ppm sb 342 ppm cu 422 ppm as 91 ppm and zn 296 ppm the presence of these trace elements indicates a low temperature type of galena mineralization this interpretation is corroborated by fluid inclusions containing 12 98 wt nacl equivalent salinity the inclusions homogenize at the low temperature of about 152 1 c the similarity between 34 s v cdt values in nakhlak barite and permian triassic 34 s marine sulfate values indicates that the nakhlak sulfur was probably provided from evaporates of permian triassic age the 34 s v cdt values of galena and barite samples occupy the ranges of 1 04 to 8 62 and 10 95 to 13 71 respectively and are similar to mississippi valley type mvt deposits the low temperature basinal fluids evaporate originated sulfur and fault or fracture controlled galena rich veins in the nakhlak deposit resemble the type of geological features documented in pb rich mvt deposits

hypogene zn carbonate ores in the angouran deposit nw iran the world class angouran nonsulfide zn pb deposit is one of the major zn producers in iran with resources estimated at about 18 mt at 28 zn mainly in the form of the zn carbonate smithsonite this study aims to characterize these carbonate ores by means of their mineralogy and geochemistry which has also been extended to the host rocks of mineralization and other local carbonate rock types including the prominent travertines in the angouran district as well as to the local spring waters petrographical chemical and stable isotope o h c sr data indicate that the genesis of the zn carbonate ores at angouran is fairly distinct from that of other classical nonsulfide zn deposits that formed entirely by supergene processes mineralization occurred during two successive stages with the zinc being derived from a preexisting sulfide ore body a first main stage of zn carbonates stage i carbonate ore is associated with both preexisting and subordinate newly formed sulfides whereas a second stage is characterized by supergene carbonates zn and minor pb coexisting with oxides and hydroxides stage ii carbonate ore the coprecipitation of smithsonite with galena pyrite and arsenopyrite as well as the absence of fe and mn oxides hydroxides and of any discernible oxidation or dissolution of the sphalerite rich primary sulfide ore shows that the fluids responsible for the main stage i carbonate ores were relatively reduced and close to neutral to slightly basic ph with high fco2 smithsonite 18ovsmow values from stage i carbonate ore range from 18 3 to 23 6 while those of stage ii carbonate ore show a much smaller range between 24 3 and 24 9 the 13c values are fairly constant in smithsonite of stage i carbonate ore 3 2 6 0 but show a considerable spread towards lower 13cvpdb values 4 6 to 11 2 in stage ii carbonate ore this suggests a hypogene formation of stage i carbonate ore at angouran from low temperature hydrothermal fluids probably mobilized during the waning stages of tertiary quaternary volcanic activity in an environment characterized by abundant travertine systems throughout the whole region conversely stage ii carbonate ore is unambiguously related to supergene weathering as evidenced by the absence of sulfides the presence of fe mn oxides and arsenates and by high 18o values found in smithsonite ii the variable but still relatively heavy carbon isotope values of supergene smithsonite ii suggests only a very minor contribution by organic soil carbon as is generally the case in supergene nonsulfide deposits

nondestructive chemical dating of young monazite using xrf 2 context sensitive microanalysis and comparison with th pb laser ablation mass spectrometric data a newly developed xrf microprobe at the institute of mineralogy and petrology university of bern switzerland has been applied for precise chemical th u pb dating of individual monazite grains separated from pb free polished petrographic thin sections the nondestructive nature of the xrf measurement permitted a comparative study of dating methods by sequentially applying chemical dating by electron microprobe analysis empa chemical dating by xrf microprobe analysis and isotopic 208pb 232th dating by laser ablation plasma ionisation multi collector mass spectrometry la pimms analysis as an example the 2 precision achieved with the xrf microprobe for well characterised reference material monazite fc 1 tims age 54 3 1 ma xrf age 55 3 2 6 ma doubly polished to 30 m in thickness is below 5 after 90 min integration time 50 kv 30 ma at a spatial resolution of 90 m at 38 m spatial resolution the uncertainty is 35 for the same integration time the sample characteristics are 200 300 ppm of pb xrf 3 8 5 1 wt of th empa and 0 4 1 4 wt u empa combined with an electron microprobe and conventional optical microscopy the xrf microprobe is thus a competitive low cost and nondestructive alternative to more costly isotopic methods the xrf microprobe is easy to use and maintain

eocene gold ore formation at muteh sanandaj sirjan tectonic zone western iran a result of late stage extension and exhumation of metamorphic basement rocks within the zagros orogen a multidisciplinary study including field geology microstructure analysis 40ar 39ar dating and fluid inclusion microthermometry and raman spectrometry has been carried out on the muteh gold deposit located in a greenschist to amphibolite facies metamorphic rock complex of the sanandaj sirjan tectonic zone zagros orogen iran the muteh gold deposit has been previously interpreted as genetically related to precambrian granitic intrusions as an exhalative hot spring deposit related to paleozoic rhyolitic acidic tuffs and to local metamorphic processes host rocks of the gold deposit are predominantly schist and gneiss and subsidiary amphibolite and quartzite and are intruded by leucogranites in the vicinity of the gold deposit the metamorphic and granitic rocks display a subhorizontal mylonitic foliation containing a northeast oriented stretching lineation field investigations in one of the producing open pits show that the gold orebodies are controlled by northwest oriented normal faults and joints dipping to the northeast and the southwest and crosscutting the ductile fabric of the host rocks both the ductile fabric of the host rocks and the gold ore controlling brittle structures are interpreted to have formed within a single continuous extensional event which started with ductile deformation and gradually changed into brittle deformation hydrothermal alteration associated with ore formation consists of quartz muscovite pyrite dolomite ankerite and albite which crosscuts the ductile fabric and overprints the metamorphic minerals of the host rocks pyrite is the dominant opaque mineral and is the major phase associated with gold chalcopyrite marcasite bismuth galena sphalerite and pyrrhotite are subsidiary to rare phases 40ar 39ar incremental heating and in situ laser ablation age data reveal a coherent sequence of cooling and hydrothermal events in the metamorphic complex hosting the muteh gold deposit muscovite samples from the alteration zone and from one quartz vein from the orebodies yield 40ar 39ar ages between 55 7 and 38 5 ma and show that gold mineralization is the youngest among the different dated events this eocene age is consistent with the young structural setting of the gold orebodies revealing an emplacement along northwestoriented normal faults which can be correlated with tertiary extensional tectonic events reported by previous field investigations the data also indicate that gold ore formation is coeval with magmatism in the adjacent tertiary urumieh dokhtar magmatic belt and with intrusive activity within the sanandaj sirjan zone with a 40ar 39ar age of 54 ma near muteh according to our study the remaining 40ar 39ar data reveal a cretaceous to early tertiary metamorphic magmatic and deformation history of the complex hosting the muteh gold deposit the fluid inclusion study showed that distinct fluids were present during the regional geologic evolution predating ore formation and later eocene gold ore formation early regional fluids consist of an h2o co2 nacl fluid with subsidiary n2 and ch4 that underwent local unmixing the salinities of the liquid rich inclusions resulting from unmixing range between 2 2 and 17 5 wt percent nacl equiv and those of the co2 rich vaporrich inclusions range between 2 8 and 7 2 wt percent nacl equiv the high salinity of the regional liquid rich fluids is attributed to metamorphism of evaporite bearing sedimentary rocks magmatic intrusions retrograde hydration reactions metamorphism of impure marbles and migmatization the fluid inclusions spatially associated with the gold veins postdating regional metamorphism and ductile deformation of the host rocks contain a low salinity aqueous fluid with a dilute low density co2 component and maximum salinities between 2 6 and 5 8 wt percent nacl equiv gold deposition at muteh occurred during or after late stages of eocene brittle extension as a result of exhumation of the host metamorphic complex possibly during magmatic activity in the sanandaj sirjam zone it is most likely linked to the introduction of a distinct low salinity low co2 content aqueous fluid during crustal extension these fluids are younger than and therefore unrelated to the highly saline and co2 rich regional metamorphic magmatic fluids our results refute previous models advocating precambrian to paleozoic ages of the muteh gold deposit

versatile monazite resolving geological records and solving challenges in materials science monazite is ubiquitous in the geological realm overstreet 1967 its compositional and isotopic response to changes in intensive and extensive rock parameters has made it an increasingly important component of integrated pressure temperature deformation composition time p t d x t studies particularly in complex poly metamorphic terranes janots et al 2012 kelly et al 2012 langille et al 2012 the utility of monazite also includes its role in understanding igneous sedimentary and hydrothermal systems dumond et al 2008 mahan et al 2010 aleinikoff et al 2012 and more recently as a means for examining repositories of radioactive waste oelkers and montel 2008 since the broader potential applications of monazite as a geochronometer were described by parrish 1990 several significant developments have since occurred that allow for the routine compositional and isotopic analysis of monazite by a variety of techniques these include technological advances in electron probe microanalysis epma suzuki and adachi 1991 montel et al 1996 pyle

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

holocene environmental change in eastern spain reconstructed through the multiproxy study of a pedo sedimentary sequence from les alcusses valencia spain abstract we present a multiproxy characterization of a complex polycyclic soil sequence from les alcusses moixent valencia se spain the area has abundant settlements dating from early neolithic to roman times the sequence comprises six main units dating back to 8 7 8 5 ka cal bp we integrated mineralogy inorganic ph grain size elemental composition and organic chemistry pyrolysis gas chromatography mass spectrometry pyrolysis gc ms micro charcoal pollen and non pollen palynomorph npp data all data is contextualized within a framework of archaeological information and radiocarbon dating with the aim of deciphering the holocene environmental changes we infer a shift from wetter and warmer in the early mid holocene to drier and cooler climatic conditions with increased fire occurrence in the mid late holocene particularly after 5 3 ka cal bp although the pollen record indicates a rapid forest retreat and expansion of grasslands for the neolithic period local proxies molecular soil om indicators and npp point to the presence of pine forest in the studied location well after the regional decline started the same proxies suggest a sharp forest decline after about 7 0 ka cal bp strong soil erosion likely linked both to climatic instability and the intensification of human exploitation resulted in a hiatus from the late neolithic to the roman period a certain climate amelioration wetter conditions and land abandonment or at least lower human pressure are suggested for the late roman period early middle ages direct evidence of changes in soil properties due to agriculture was not detected in the sequence except for the upper soil unit studied which reflects intense agricultural management with the possible use of agrochemicals

marble hosted sulfide ores in the angouran zn pb ag deposit nw iran interaction of sedimentary brines with a metamorphic core complex the angouran zn pb ag deposit zanjan province nw iran is located within the central sanandaj sirjan zone of the zagros orogenic belt the deposit has proven and estimated resources of 4 7 mt of sulfide ore at 27 7 zn 2 4 pb and 110 g t ag and 14 6 mt of oxidized carbonate ores at 22 zn and 4 6 pb it is hosted by a metamorphic core complex that is unconformably overlain by a neogene volcanic and evaporite bearing marine to continental sedimentary sequence the sulfide orebody precursor to the significant nonsulfide ores is located at the crest of an open anticline at the contact between neoproterozoic to cambrian footwall micaschists and hanging wall marbles 40ar 39ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid mid miocene exhumation of the metamorphic basement 20 ma and yield an upper age constraint for mineralization the fine grained sulfide ore is massive replacive often brecciated clearly postmetamorphic and dominated by fe poor sphalerite with minor galena pyrite anhydrite quartz muscovite dolomite and rare calcite sphalerite contains na ca cl brine inclusions 23 25 mass total dissolved solids with homogenization temperatures of 180 70 c fluid inclusion chemistry na k li ca mg cl br ore geochemistry s and pb isotope data suggest that the angouran sulfide ore formed by the interaction of modified strongly evaporated miocene seawater and the lithotypes of an exhumed metamorphic core complex minor contributions of metals from miocene igneous rocks cannot be excluded mineralization occurred in a collisional intra arc setting with high heat flow probably during the transition from an extensional to a compressional regime the angouran deposit may represent a new type of low temperature carbonate hosted zn pb ore that is distinct from mississippi valley type and sedimentary exhalative deposits

chlorine isotopes in fluid inclusions determination of the origins of salinity in magmatic fluids abstract thermal ionisation mass spectrometry tims of the cs 2 cl ion has been used to determine the 37 cl value of paleofluids trapped in fluid inclusions modifications to the existing published method have lowered the precision by a factor of 2 0 09 1 thereby allowing real differences to be measured with greater certainty the method has been applied to determine 37 cl of two sets of magmatic fluids trapped in fluid inclusions samples were studied from the capitan pluton in new mexico and the sw england batholith both of which have high temperature fluids whose d and 18 o signatures are distinctly magmatic relative to standard mean ocean chloride smoc the 37 cl values of the capitan samples cluster around 0 whereas those from sw england cluster around 1 8 the br cl ratios of the capitan fluid inclusions are low indicative of halite dissolution and are comparable to local high salinity waters derived from leaching permian evaporites the br cl ratios of the sw england fluid inclusions are much higher and within the range of values normally considered to be magmatic we conclude that the 37 cl value of the capitan magmatic fluids confirms the evidence from br cl ratios that cl was derived from an evaporite source whereas the 37 cl value of the sw england fluids appears to be more representative of a deep magmatic source

timing of post tectonic cadomian magmatism on guernsey channel islands evidence from 40ar 39ar mineral ages the channel island of guernsey exposes pre and post tectonic calc alkaline plutonic rocks attributed to late precambrian cadomian subduction activity 40 ar 39 ar mineral cooling ages presented here clarify the age and time span of post tectonic intrusions amphibole from the bon repos meladiorite yields an isotope correlation age of 605 3 4 6 ma indicating emplacement during late stages of the tectonothermal event recorded within its host rocks igneous hornblendes from the northern igneous complex record consistent isotope correlation ages st peter port gabbro 570 2 1 1 ma bordeaux diorite complex 569 0 1 1 and 565 3 2 2 ma and a comagmatic enclave within cobo granite 570 2 1 5 ma hornblende and biotite from contact metamorphosed host rocks adjacent to the cobo granite yield isotope correlation ages of 569 6 1 1 and 563 8 3 3 ma respectively these ages together with field data demonstrate that the various members of the northern igneous complex were emplaced contemporaneously at c 570 ma significantly earlier than a c 500 ma rb sr whole rock isochron age previously reported for the cobo granite the 40 ar 39 ar ages indicate that post tectonic magmatism on guernsey was broadly coeval with post metamorphic cooling around the baie de st brieuc on the adjacent french mainland and occurred c 30 ma prior to peak cadomian deformation and metamorphism in the st malo area

genesis of sediment hosted zn pb ba deposits in the irankuh district esfahan area west central iran the results of isotopic studies on carbonates and sulfur bearing minerals of the irankuh deposit occurring in lower cretaceous carbonate strata provide information concerning the nature of the fluids responsible for zn pb ba mineralization and associated dolomitization an epigenetic model for the irankuh deposits is supported by their discordant nature emplacement along the irankuh fault progressive depletion in stable carbon isotope ratios of the host dolostones as mineralization is approached and isotopic characteristics of the ore stage dolomites and barites the host rock dolostones show extensive depletion in 18 o delta 18 o 4 9 to 12 7ppm due to diagenetic modification and or recrystallization at increased temperatures based on isotopic and fluid inclusion data the ore stage dolomites in the deposits are interpreted as having formed from warm approximately 100 degrees c saline 87 sr enriched fluids similar to oil field brines the overlap in delta 18 o values and 87 sr 86 sr ratios between host dolostones and sucrosic and saddle dolomites implies that these rocks have been isotopically modified and precipitated by similar fluids the delta 34 s values of metal sulfides range from 3 6 to 9 6 per mil whereas barite values ranging from 14 3 to 18 9 per mil fall within the range of cretaceous age sulfate values it is inferred that seawater sulfate acted as the source of the sulfides and barite mineralization the reduced sulfur was generated by partial reduction of seawater sulfate by organic matter under hydrothermal conditions the presence of a hydrocarbon i e traces of bitumen and saddle and fracture filling dolomite with low delta 13 c values ranging to 6 4ppm in conjunction with the temperature of ore deposition provides evidence for thermochemical sulfate reduction carbonates and barites show 87 sr 86 sr ratios enriched in 87 sr which is atypical of derivation from normal seawater the enrichment of 87 sr is explained by extensive interaction of fluids with the underlying siliciclastic rock evolving toward more radiogenic compositions the release of the overpressurized fluids appears to have been due to dehydration reactions and regional tectonism the metal bearing fluids responsible for mineralization migrated along the major irankuh fault and mixed with sulfate bearing fluids at the ore depositional site hydrologic considerations demonstrate that the proposed model is feasible

shrimp u pb zircon geochronology of the late archaean ruinnaesset syenite skjoldungen alkaline province southeast greenland abstract a sample of the ruinnaesset syenite of the southeast greenland skjoldungen alkaline province contains a homogeneous population of zircons up to 1 mm diameter that are devoid of new overgrowths and old inherited cores u pb isotopic analyses of these zircons form a single population with weighted mean 207 pb 206 pb and 206 pb 238 u ages of 2699 4 ma and 2690 20 ma 2 respectively these dates are interpreted as giving the time of crystallisation of the syenite

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

single mineral pbpb dating a new stepwise leaching procedure applied to ca bearing silicates enables the selective recovery of radiogenic and common pb from a mineral and thus makes single phase pbpb dating possible this permits independent dating of rock forming minerals within a paragenetic sequence and the direct combination of age data with petrological results furthermore the stepwise leaching technique has the advantage over multi phase pbpb dating in that it does not require initial pb isotope equilibrium among the phases but may be used to test it the presence of microscopic solid inclusions which complicate dating of single phases if they are not in equilibrium with the host can be traced via the behaviour of the 208pb 204pb ratio through the various leaching steps this constitutes a major advantage over conventional bulk phase pbpb dating in addition the precision of an isochron age can be improved relative to that of the bulk mineral approach since the 207pb 204pb and 206pb 204pb data spread is significantly enhanced therefore the technique may both be used to date younger phases and or minerals with less favourable u pb ratios and to extend the applicability of self consistent p t t modelling

grain coarsening in contact metamorphic carbonates effects of second phase particles fluid flow and thermal perturbations under contact metamorphic conditions carbonate rocks in the direct vicinity of the adamello pluton reflect a temperature induced grain coarsening despite this large scale trend a considerable grain size scatter occurs on the outcrop scale indicating local influence of second order effects such as thermal perturbations fluid flow and second phase particles second phase particles whose sizes range from nano to the micron scale induce the most pronounced data scatter resulting in grain sizes too small by up to a factor of 10 compared with theoretical grain growth in a pure system such values are restricted to relatively impure samples consisting of up to 10 vol micron scale second phase particles or to samples containing a large number of nano scale particles the obtained data set suggests that the second phases induce a temperature controlled reduction on calcite grain growth the mean calcite grain size can therefore be expressed in the form d 1 4 c2 eq rt dp fp m where c2 is a constant q is an activation energy t the temperature and m the exponent of the ratio dp fp i e of the average size of the second phases divided by their volume fraction however more data are needed to obtain reliable values for c2 and q besides variations in the average grain size the presence of second phase particles generates crystal size distribution csd shapes characterized by lognormal distributions which differ from the gaussian type distributions of the pure samples in contrast fluid enhanced grain growth does not change the shape of the csds but due to enhanced transport properties the average grain sizes increase by a factor of 2 and the variance of the distribution increases stable d18o and d13c isotope ratios in fluid affected zones only deviate slightly from the host rock values suggesting low fluid rock ratios grain growth modelling indicates that the fluid induced grain size variations can develop within several ka as inferred from a combination of thermal and grain growth modelling dykes with widths of up to 1 m have only a restricted influence on grain size deviations smaller than a factor of 1 1 to summarize considerable grain size variations of up to one order of magnitude can locally result from second order effects such effects require special attention when comparing experimentally derived grain growth kinetics with field studies

two tiered magmatic hydrothermal and skarn origin of magnetite from gol gohar iron ore deposit of se iran in situ la icp ms analyses abstract genesis of magnetite from gol gohar iron deposit ggid of southeastern iran is studied with reference to elemental composition more than 1 2 billion tonnes of magnetite ore at 58 total fe is hosted by greenschist to amphibolite facies metapelites and magnesian marbles the ggid occurs in the mainly metamorphic terrain of sanandaj sirjan geological province with continental margin tectonic setting the magnetite bearing ore is divided into two distinct types of massive and banded the latter hosted mainly by magnesian marbles both subtypes of the ore bodies are associated with mineral assemblages consisting of calcite dolomite forsterite tremolite actinolite talc serpentine and chlorite the ore minerals in both subtypes are magnetite hematite with minor amounts of pyrite pyrrhotite and chalcopyrite concentrations of temperature dependent elements ti al and ga in the two subtypes would suggest that temperature of formation was higher for the massive magnetite with ti 626 ppm al 69 ppm and ga 56 ppm on average and relatively lower for the banded magnetite with ti 60 ppm al 62 ppm and ga 4 ppm on average the multi element diagrams for massive magnetite show patterns closer to those of magmatic hydrothermel iron deposits kiruna type whereas patterns of the banded magnetite match better with those of skarn deposits particularly the magnesian skarns average concentrations of v 1000 ppm and cr 4 ppm of the massive subtype fall within the range of those of kiruna type deposits and the in average lower concentrations of v 10 ppm and cr 1 ppm of the banded magnetite match the values of skarn deposits the average v content of the massive magnetite 1342 ppm is consistent with the global range of magmatic hydrothermal magnetite up to 3880 ppm but different from global values of purely magmatic magnetites up to 6600 ppm the banded magnetites contain 0 21 25 ppm v which is only consistent with the lowest values of hydrothermal magnetites we contend that the massive magnetite was formed by magmatic hydrothermal processes i e kiruna type and the banded magnetites were generated via metasomatic reactions between iron rich residual magmatic fluids and the magnesian carbonate host rocks i e skarn type

long lived eocene miocene stationary magmatism in nw iran along a transform plate boundary abstract the eocene miocene mianeh hashtroud igneous district in nw iran is part of the turkish caucasus iranian collision zone a key region to decipher the assembly and differentiation of gondwana derived terranes along the alpine himalayan convergence zone major inherited tectonic structures control in space and time the mesozoic cenozoic transition from oceanic subduction to continental collision in the region the geology of the study area is dominated by a polyphase long lived magmatic activity spanning from 45 to 6 ma the igneous products are subalkaline to alkaline with intermediate to acid compositions and a high k calcalkaline to shoshonitic affinity evidence of crustal contamination is attested by inherited zircons in the oldest eocene oligocene samples with ages spanning from neo archean to paleocene the sr nd isotopic compositions of the eocene oligocene samples plot close to the bulk silicate earth estimate whereas the miocene samples document stronger crustal contamination the lack of correlation between nd sr isotopes and sio2 supports a scenario of magma differentiation of different magma batches rather than crustal contamination major oxide and sr nd isotopic variation lead us to suggest that magmatism is the consequence of re melting of earlier underplated mesozoic tertiary magmatic products controlled by amphibole dominated fractionation processes regional scale correlations show long lived cenozoic magmatism in nw iran and caucasus region where the main porphyry and epithermal deposits occur we propose that the cenozoic collisional magmatism and the associated mineralisation at the junction between nw iran and caucasus was controlled by the activity of a major lithosphere scale inherited boundary transverse to the convergence zone in such a geodynamic setting the along strike segmentation of the lithosphere slab generated asthenospheric melts their upwelling into the metasomatised supra subduction mantle wedge and the potential activation of different mantle and crustal sources with consequent mineral endowment in the region

recognition of the regional lineaments of iran using geospatial data and their implications for exploration of metallic ore deposits abstract the relationship between major structural lineaments and locations of ore deposits in iran has been investigated using geospatial data in the course of lineament extraction satellite images aeromagnetic data digital elevation model dem and structural maps were processed and the lineaments and large scale faults were identified the extracted lineaments based on subjective assessment from each dataset were imported into gis software and the lineament map of iran was prepared by data integration the analysis for selecting significant lineament was mainly based on fault correlated lineament and lineament with field map fractures which was sets as benchmarks for compiling a final output map four major regional lineament trends of n s e w nw se and ne sw were identified in the data of all images which are corresponded to the structural zones and the major fault systems of iran the mineral deposits active and abandoned and mineral indications database compiled are based on the published maps papers reports and the ore deposits data files of geological survey of iran integrating the output of these two datasets by gis software resulted in the combined map of lineaments and gold copper lead zinc and iron deposits of iran the number and distance of ore deposits toward the lineaments were processed by the counting and cumulative methods in the gis software s approximately over 90 of the ore deposits of iran are located in the central part of the lineaments 15 km on each side which are concordant with a definition of large lineament about 50 of these mineral deposits are closer than 5 km to the lineaments there are significant correlations between lineament density and intersections with ore deposits occurrences the observed associations at this scale are informative in establishing exploration strategy and decreasing exploration risks for detailed work on ore deposit scale

u pb zircon and sm nd geochronology of mafic and ultramafic rocks from the central part of the tauern window eastern alps geochronological and geochemical analyses were carried out in order to identify the pre variscan basement of the tauern window eastern alps maficultramafic rocks from the central part of the tauern window have been studied by ree analysis and u pb and sm nd isotopic analyses on whole rock zircons garnets and sphene u pb and sm nd zircon dating define both magmatic pan african and cambro ordovician events from 650 ma to 486 ma within the alpine fold belt this indicates a time span of 150 ma for magmatic activities in the tauern window of the eastern alps the ages of 657 ma u pb zircon and 644 sm nd zireon obtained from an amphibolite are the oldest dates of the eastern alps they may be related to the pan african orogeny and imply an early cycle of magmatic intrusion before major activity started at around 500 ma sm nd whole rock analyses of the precambrian rocks do not define an isochron reflecting heterogenities within the mantle source the initial end values 1 2 to 4 7 are very low implying an enrichment of the magma source the second main phase of magmatic activity 539 486 ma is characterized by the emplacement of mafic ultramafic rock sequences as no ophiolitic relies are observed in these domains the early paleozoic magmatism was likely associated with extensional tectonics obtained ages of 301 3 and 314 4 3 ma point to a variscan metamorphism the first combined u pb zircon sm nd zircon data for an amphibolite from the basal amphibolite formation baf favoured the sm nd zircon isochron age as a magmatic age whereas the low initial end value point to an enriched magma source as well as to heterogenities within the magma source the obtained ages suggest that parts of the pre variscan basement within the alpine fold belt were formed during the pan africa cycle the detection of pre variscan ages within the alpine basement must reffect a complex history involving significant pre variscan activity

zircon u pb ages and hf o isotopic composition of migmatites from the zanjan takab complex nw iran constraints on partial melting of metasediments abstract we study migmatites and other metamorphic rocks in the zanjan takab region of nw iran and use these results to report the first evidence of oligocene core complex formation in iran four samples of migmatites associated with paragneisses including leucosomes and associated para amphibolite melanosomes were selected for u pb dating and hf o isotopic analysis zircon cores interpreted as originally detrital zircons have variable ages that peak at ca 100 110 ma but their sedimentation age indicated by the youngest 206 pb 238 u ages is ca 35 40 ma new zircons associated with incipient melting occur as overgrowths around zircon cores and or as newly grown grains morphologies and internal structures suggest that rim growth and formation of new zircons were associated with partial melting all four samples contain zircons with rims that yield 206 pb 238 u ages of 28 25 ma indicating that partial melting occurred in late oligocene time 18 o values for zircon rims vary between 8 2 and 12 3 significantly higher than expected for mantle inputs 18 o 6 and consistent with equilibrium with surface materials zircon rims yield ehf t between 2 2 and 12 4 and two stage hf model ages of 448 562 ma indicating that the region is underlain by cadomian caledonian crust according to the hf o isotopic values the main mechanism forming zircon rims was dissolution of pre existing detrital zircons with reprecipitation of new zircon shortly thereafter oligocene ages indicate that partial melting accompanied core complex formation in the zanjan takab region extension melting and core complex formation in south central iran are eocene in age but younger ages of oligocene miocene in nw iran and turkey indicate that extension was distributed throughout the region during cenozoic time

archean and proterozoic mineralization and tectonics at the renco mine northern marginal zone limpopo belt zimbabwe gold mineralization at the renco mine occurs within the northern marginal zone of the limpopo belt along east northeast trending structures that formed in the late arehean 2 6 ga pb pb step leach age on syntectonic garnet under granulite facies the mineralization is hosted by a massive enderbite which intruded at 2 57 ga u pb zircon age north northeast trending pyroxenite dikes were intruded around 2 4 ga pb pb step leach age of garnet and pyroxene probably associated with the intrusion of the great dyke and satellites the northern marginal zone had been exhumed to crustal levels corresponding to greenschist facies by this time the major gold bearing pyrrhotite chalcopyrite or bismuth mineralization occurred under greenschist facies conditions 400 degrees c this occurred at approximately 2 0 ga as deduced from cooling of biotite associated with mineralization 1 88 ga rb sr age this ca 2 0 ga age of the mineralization implies a link with the important early proterozoic tectono thermal event in the limpopo belt during which shearing occurred under greenschist facies conditions in the triangle shear zone the reneo deposit is not as formerly suggested a high grade mineralization although there is some evidence for a precursory high grade phase of mineralization in the late archean its genesis is quite distinct from most of the greenstone associated deposits of the zimbabwe craton which are known or inferred to be late archean in age

dating a variscan pressure temperature loop with staurolite staurolite with a complex internal metamorphic and structural relationship occurs in metapelite from the silvretta thrust sheet eastern alps stepwise leaching of a core and rim fraction of a single staurolite crystal resulted in a total pb pb isochron of 308 28 ma the variscan metamorphism has been confirmed by a further single bulk staurolite pb pb age of 298 42 ma which is in accordance with u pb ages of 306 8 ma and 304 6 ma respectively obtained from combined u pb leaching of the same crystals direct dating of the staurolite in reaction isograd was therefore successful our results date the prograde part of a variscan counterclockwise pressure temperature path in the silvretta thrust sheet proximity with white mica rb sr and k ar cooling ages suggests that the whole variscan episode was fast and took place within a few million years

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

pb isotopic compositions of some zn pb deposits and occurrences from urumieh dokhtar and sanandaj sirjan zones in iran abstract this study reports pb isotope ratios of galena pbs sampled from some zn pb deposits and occurrences n 18 within two major structural provinces of iran the sanandaj sirjan zone ssz and urumieh dokhtar zone udz regardless of the nature of the host rock and ore type the pb isotopic data plot in distinct isotopic fields according to their geographic situation which suggest that the structural terranes had an important control on the lead isotope compositions the zn pb deposits in the udz record distinctly higher 206pb 204pb and 208pb 204pb ratios compared to those within the ssz both zones however have radiogenic 207pb 204pb ratios 15 55 suggesting a dominant input of pb from crustal sources in thorogenic 208pb 204pb vs 206pb 204pb and uranogenic 207pb 204pb vs 206pb 204pb plots the pb isotope data define two linear arrays which may be attributed to mixing between mantle like end members and at least two distinct crustal sources characterized by high u pb and th u ratios in plumbotectonic discrimination diagrams the samples plot proximal to the orogenic curve which again supports interaction between crustal and mantle reservoirs however both neo tethys subduction and in particular mesozoic and tertiary orogenic activities seem to have played important roles in remobilizing pb and forming zn pb deposits in ssz and udz respectively the similarity of pb isotopic compositions between udz deposits and those for previously reported eocene volcanics demonstrates that long lived and widespread hydrothermal activity promoted remobilization of lead from the crust the latter occurred subsequent to neo tethys lithosphere subduction in the tertiary and continued subsequent the collision of the iranian and arabian plates in the miocene

age dating of individual grains of uraninite in rocks from electron microprobe analyses it is shown that an electron microprobe analysis of the u th and pb content of a single uraninite uo2 grain may be used to calculate the age of formation of that grain this is known as a chemical age examples are shown for a range of natural samples with a wide range of ages comparison with ages derived from isotopic measurements shows the results to be valid approximate formulae which have been proposed for the calculation of the chemical age are not sufficiently reliable especially where the th content is high and for older ages a method for calculating the age by iteration is presented this uses the full and exact formula and is shown to produce a reliable age for the uraninite compared to isotopic measurements the method is particularly useful for samples where the minerals and mineral textures record information on more than one event two examples of samples recording information on dual ages are discussed to show how these ages can be related to events in the formation of the host rocks in one example an alluvial heavy mineral concentrate is shown to contain uraninites from two distinct sources with significantly different ages in the other example two phases of u mineralisation are distinguished in the same rock sample one phase relates to the genesis of the sediments from which the rock was formed the second phase records remobilisation of the u during later tectonic movement

whole grain evaporation for 207 pb 206 pb age investigations on single zircons using a double filament thermal ion source a technique has been developed and tested to analyse 207pb 206pb apparent ages by thermal evaporation of radiogenic lead directly from untreated whole zircon grains 0 3 mm the evaporation analyses are performed in the double filament arrangement of a thermal ion mass spectrometer thims the method is a powerful tool to distinguish between different lead components occurring in the same grain because differing activation energies of the competing lead components cause their sequential evaporation from the zircons the evaporation of test samples results in 207pb 206pb apparent ages in good agreement with u pb ages known from literature single zircons from a granite of the marble mountains california yield an age of crystallization of 1 410 30 ma ceylon zircons from heavy mineral bearing gravels yield 560 40 ma as age of crystallization of the pegmatitic gravel sources individuals from a heterogeneous zircon population of a diatexite from the southern schwarzwald sw germany indicate metamorphic zircon formation around 500 ma and the existence of middle proterozoic relics 1 95 0 05 ga

jabali a zn pb ag carbonate hosted deposit associated with late jurassic rifting in yemen the jabali deposit 3 8 mt at 16 zn 2 pb and 132 g t ag is hosted by dolomitized platform carbonates of kimmeridgian age at the southwestern edge of the oil producing wadi al jawf rift basin in northern yemen paleogeographical reconstructions demonstrate that tensional synsedimentary tectonic activity from the late jurassic to early cretaceous was responsible for the thick accumulation of argillaceous and evaporitic sediments in the subsident rift basin the unstable margin of which was the site of rapid facies changes local disconformities and periods of emergence as well as of dolomitization along the wnw and nnw striking boundary fault system in the jabali area the upper part of the jurassic sequence underwent two stages of dolomitization before emergence and deep karstic erosion solution cavities and depressions in the eroded surface were filled by dolomite sand and black pyritic mudstone prior to a last marine transgression of limited extent subsequent ore deposition and associated late dolomitization sealed the network of solution cavities impregnating the dolomite sands and the host dolomites sphalerite i and wurtzite followed by silver bearing zoned sphalerite ii associated with galena crystallized from a cyclic influx of low temperature 75 100 c saline solutions lead isotope geochemistry indicates that the lead zinc and silver probably originated from an early proterozoic basement the dissolved metals were likely derived from the basal aquifer detrital material of basement origin of the evaporite bearing sequence filling the wadi al jawf trough migrating metalliferous brines from the basin to the uplifted jabali area where ore deposition was favoured by a reducing environment were probably channelled by the boundary fault system during the last stages of synsedimentary tectonic activity

petrogenesis and tectonic evolution of metaluminous sub alkaline granitoids from the takab complex nw iran the takab complex is composed of a variety of metamorphic rocks including amphibolites metapelites mafic granulites migmatites and meta ultramafics which are intruded by the granitoid the granitoid magmatic activity occurred in relation to the subduction of the neo tethys oceanic crust beneath the iranian crust during tertiary times the granitoids are mainly granodiorite quartz monzodiorite monzonite and quartz diorite chemically the magmatic rocks are characterized by asi 1 04 ai 0 87 and high contents of cao up to 14 5 wt which are consistent with the i type magmatic series low feot feot mgo values 0 75 as well as low nb y and k2o contents of the investigated rocks resemble the calc alkaline series low sio2 k2o na2o and al2o3 accompanied by high cao and feo contents indicate melting of metabasites as an appropriate source for the intrusions negative ti and nb anomalies verify a metaluminous crustal origin for the protoliths of the investigated igneous rocks these are comparable with compositions of the associated mafic migmatites in the takab metamorphic complex which originated from the partial melting of amphibolites therefore crustal melting and a collision related origin for the takab calc alkaline intrusions are proposed here on the basis of mineralogy and geochemical characteristics the p t evolution during magmatic crystallization and subsolidus cooling stages is determined by the study of mineral chemistry of the granodiorite and the quartz diorite magmatic crystallization pressure and temperature for the quartz diorite and the granodiorite are estimated to be p 7 8 2 5 kbar t 760 75 c and p 5 1 kbar t 700 c respectively subsolidus conditions are consistent with temperatures of 620 c and 600 c and pressures of 5 kbar and 3 5 kbar for the quartz diorite and the granodiorite respectively

late neoproterozoic ordovician and carboniferous events recorded in monazites from southern central madagascar abstract the evolution of the basement of southern madagascar north and south of the ranotsara shear zone was investigated using u th pb electron probe monazite age dating in combination with petrographic constraints several monazite grains show a stepwise progression of younger ages towards the rim indicating partial and complete resetting during tectonic metamorphic and or fluid events the oldest ages ranging from 630 2400 ma occur relatively rare in relic cores a first clear age population is dated at 550 560 ma most ages fall in two populations at 420 460 and 490 500 ma which in some samples overlap in error we interprete these ages as dating low pressure and high temperature metamorphism we have also clear evidence for carboniferous 300 310 ma monazite overgrowth rims which can not directly be related to macroscopic structures or metamorphic parageneses in combination with literature data we propose that the observed monazite age populations are related to gondwana amalgamation and subsequent rifting events during the break up of gondwana our study confirms that only the electron or ion microprobe yields sufficient spatial resolution to date individual shells of multiple zoned monazites in the polymetamorphic basement of madagascar

emarat carbonate hosted zn pb deposit markazi province iran a geological mineralogical and isotopic s pb study abstract the emarat deposit with a total proved reserve of 10 mt ore grading 6 zn and 2 26 pb is one of the largest zn pb deposits in the malayer esfahan belt the mineralization is stratabound and restricted to early cretaceous limestones and dolomites the ore consists mainly of sphalerite and galena with small amounts of pyrite chalcopyrite calcite quartz and dolomite textural evidence shows that the ore has replaced the host rocks and thus is epigenetic sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from cretaceous seawater through thermochemical sulfate reduction sulfur isotope compositions of four apparently coprecipitated sphalerite galena pairs suggest their precipitation was under equilibrium conditions the sulfur isotopic fractionation observed for the sphalerite galena pairs corresponds to formation temperatures between 77 c and 168 c which agree with homogenization temperatures of fluid inclusions lead isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high 238 u 204 pb and 232 th 204 pb ratios ages derived from the pb isotope model give meaningless ages ranging from early carboniferous to future it is probable that the pb isotope model ages that point to an earlier origin than the early cretaceous host rocks are derived from older reservoirs in the underlying carboniferous or jurassic units either from the host rocks or from earlier formed ore deposits within these units this research and other available data show that the emarat zn pb deposit has many important features of mississippi valley type mvt lead zinc deposits and thus we argue that it is an mvt type ore deposit

geology and geochemistry of the reocin zinc lead deposit basque cantabrian basin northern spain the reocin zn pb deposit 30 km southwest of santander spain occurs within lower cretaceous dolomitized urgonian limestones on the southern flank of the santillana syncline the reocin deposit is one of the largest known strata bound carbonate hosted zinc lead deposits in europe the total metal endowment of the deposit including past production and remaining reserves is 62 mt of ore grading 8 7 percent zn and 1 0 percent pb the epigenetic mineralization consists of sphalerite and galena with lesser marcasite and trace pyrite with dolomite as gangue microprobe analyses of different generations of dolomite revealed nonstoichiometric compositions with various amounts of iron up to 14 mol of feco3 replacement of host dolomite open space filling of fractures and cementation of breccias derived from dissolution collapse are the principal types of ore occurrence detailed cross section mapping indicates a stratigraphic and structural control on the deposit a stratiform morphology is present in the western part of the orebody capa sur whereas mineralization in the eastern part is highly discordant but strata bound barrendera stratigraphic studies demonstrate that synsedimentary tectonic activity related to the rifting of the north atlantic bay of biscay was responsible for variation in sedimentation presence of unconformities including paleokarsts local platform emergence and dolomitization along the n60 fault trend in the reocin area two stages of dolomitization are recognized the first stage is a pervasive dolomitization of the limestone country rocks that was controlled by faulting and locally affected the upper part of the aptian and the complete albian sequence the second dolomitization event occurred after erosion and was controlled by karstic cavities this later dolomitization was accompanied by ore deposition and locally filling of dolomite sands and clastic sediments in karstic cavities the circulation of hydrothermal fluids responsible for sulfide deposition and the infilling of karst cavities were broadly contemporaneous indicating a post albian age vitrinite reflectance data are consistent with previously measured fluid inclusion temperatures and indicate temperatures of ore deposition that were less than 100 c carbon and oxygen isotopic data from samples of regional limestone host rock dolostone and ore stage dolomite suggest an early hydrothermal alteration of limestone to dolostone this initial dolomitization was followed by a second period of dolomite formation produced by the mixing of basinal metal rich fluids with local modified seawater both dolomitization events occurred under similar conditions from fluids exhibiting characteristics of basinal brines the 34s values of sulfides are between 1 8 and 8 5 per mil which is consistent with thermochemical sulfate reduction involving organic matter as the main source of reduced sulfur galena lead isotope compositions are among the most radiogenic values reported for zn pb occurrences in europe and they are distinct from values reported for galena from other basque cantabrian deposits this suggests that a significant part of the lead was scavenged from the local underlying asturian sediments the stratigraphic and structural setting timing of epigenetic mineralization mineralogy and isotopic geochemistry of sulfide and gangue minerals of the reocin deposit are consistent with the features of most of mississippi valley type ore deposits