regional geologic setting of epithermal gold deposits chile epithermal gold deposits in chile are cretaceous to cenozoic in age the ores and the volcanic rocks with which they are associated were generated at a noncollisional ocean continent convergent plate margin they are related to long slightly sinuous north northeast trending magmatic belts roughly parallel to the pacific coast most of the deposits are associated with eroded volcanic centers and subvolcanic porphyries north south variations in the nature extent and timing of magmatism control the succession of mineralization events in the late cretaceous vein districts e g el bronce and hydrothermal alteration zones were formed in central chile paleocene eocene volcanic rocks constitute a large diffuse volcanic field in the antofagasta region 21 degrees 26 degrees s which contains epithermal precious metal and porphyry copper deposits associated with coeval extrusive rocks e g faride san cristobal guanaco and cachinal de la sierra in the late eocene early oligocene volcanism diminished and finally ceased in northern chile probably as a consequence of highly oblique plate convergence oligocene magmatism was restricted to emplacement of porphyries carrying copper deposits along transtensional zones within a strike slip fault system one of these deposits potrerillos hosted by sedimentary rocks developed epithermal gold mineralization in its cupola el hueso the late oligocene to mid miocene magmatic province of north central chile 26 degrees 31 degrees s coincides approximately with the modern nonvolcanic fiat slab segment of the chilean andes and hosts the largest number of known epithermal developments deposits such as el indio tambo nevada la pepa lobo marte and la coipa are hosted by oligocene miocene volcanics the deposits are associated with large zones of argillic and advanced argillic alteration in some places related to shallow level stocks and flow domes a younger event of alteration mineralization is recognized in the eroded cores of middle miocene composite volcanoes which cap some of the older altered areas e g refugio la laguna the main alteration event began at 23 ma continued after a major deformation event initiated at 18 to 16 ma and ended at 11 to 8 ma the precious metal deposits and mineralized zones of the oligo miocene province were exposed by erosion after the cessation or eastward shift of volcanism in the late miocene which was probably due to shallowing of the subduction zone between 26 degrees 30 and 33 degrees s late miocene to holocene magmatism in chile is present in two segments beneath which the dip of the benioff zone remains steep north of 27 degrees s central volcanic zone cvz and south of 33 degrees s southern volcanic zone svz the central is characterized by widespread neogene hydrothermal alteration zones and native sulfur deposits associated with composite volcanoes calderas subvolcanic intrusions and active geothermal fields which are superimposed on the oligocene miocene volcanic belt these features are believed to represent a very shallowly eroded epithermal environment in this setting the late miocene choquelimpie deposit is located in the exposed core of a volcano

metallogeny of the handagai skarn fe cu deposit northern great xing an range ne china constraints on fluid inclusions and skarn genesis abstract the newly discovered handagai skarn fe cu deposit is located in the northern great xing an range of ne china and is hosted by the ordovician luohe formation the orebodies that form the deposit are generally concordant with the bedding within these sediments and are spatially related to areas of skarn development the fe cu mineralization in this area records four stages of paragenesis namely prograde skarn retrograde skarn quartz sulfide and quartz carbonate stages the handagai deposit is a calcic skarn that is dominated by an andradite diopside epidote actinolite assemblage the mineralogy and geochemistry of the skarn indicate that it formed from a hydrothermal fluid that altered the carbonate units in this area to a garnet and42 95grs4 53 and pyroxene di71 78hd22 29jo0 2 bearing skarn the epidote within the skarn has an epidote end member composition with the chlorite in the skarn dominantly fe rich indicating that these minerals formed in an fe rich environment the petrographic microthermometric and raman spectroscopic analysis of fluid inclusions within garnet epidote actinolite quartz and calcite precipitated at different stages of formation of the handagai deposit indicate that mineralization related fluid inclusions are either liquid rich two phase h2o nacl type i gas rich two phase h2o nacl type ii three phase liquid vapor solid h2o nacl type iii or co2 h2o nacl inclusions type iv the early stages of mineralization are associated with all four types of inclusion whereas the later stages of mineralization are only associated with type i and ii inclusions inclusion homogenization temperatures vary between the four stages of mineralization 370 c 530 c and 600 c 210 c 290 c 190 c 270 c and 150 c 230 c from early to late respectively with salinities also varying between the earlier and later stages of mineralization 11 18 and 45 7 15 6 9 and 3 7 wt nacl equivalent equiv respectively the majority of the inclusions within the handagai deposit have homogenization temperatures and salinities of 200 c 350 c and 4 14 wt nacl equiv respectively indicating that this is a medium high temperature and medium low salinity type deposit the fluid inclusions were trapped at pressures of 11 to 72 mpa corresponding to depths of 0 4 to 2 9 km the geology mineralogy geochemistry and fluid inclusions microthermometry indicate that the handagai deposit formed as a result of contact infiltration metasomatism with the deposition of ore minerals resulting from a combination of factors that include boiling as a result of reduced pressure cooling and fluid mixing

re os and pb pb geochronology of the archean salobo iron oxide copper gold deposit carajas mineral province northern brazil rhenium osmium ages were determined for two molybdenite samples and a pb pb age was derived from bornite chalcopyrite magnetite at the salobo iron oxide copper gold deposit to determine the timing of mineralization and its relation to the nearby old salobo granite rhenium osmium dating of molybdenite spatially associated with copper sulfide minerals yields ages with weighted means of 2576 8 and 2562 8 ma removing the error multiplier introduced by the decay constant uncertainty appropriate for comparing ages from the same isotopic system these data convincingly argue for two temporally separated pulses of molybdenite deposition at 2576 1 1 4 ma n 2 and 2561 7 3 1 ma n 3 the 2576 8 ma age coincides with a previously published u pb age of 2573 2 ma for the old salobo granite suggesting that main stage ore formation may have been contemporaneous with granite magmatism the slightly younger 2562 ma age most likely represents new molybdenite precipitation associated with the development or reactivation of local shear zones lead lead stepwise leaching of copper sulfide minerals yields a less precise isochron age of 2579 71 ma and supports an archean age for the salobo ores this is the first documentation of an archean iron oxide copper gold deposit and the re os and pb pb geochronology herein support 2580 2550 ma estimates for basement reactivation and regional granite magmatism associated with the development of brittle ductile shear zones

absolute timing of sulfide and gold mineralization a comparison of re os molybdenite and ar ar mica methods from the tintina gold belt alaska new re os molybdenite dates from two lode gold deposits of the tintina gold belt alaska provide direct timing constraints for sulfide and gold mineralization at fort knox the re os molybdenite date is identical to the u pb zircon age for the host intrusion supporting an intrusive related origin for the deposit however 40ar 39ar dates from hydrothermal and igneous mica are considerably younger at the pogo deposit re os molybdenite dates are also much older than 40ar 39ar dates from hydrothermal mica but dissimilar to the age of local granites these age relationships indicate that the re os molybdenite method records the timing of sulfide and gold mineralization whereas much younger 40ar 39ar dates are affected by post ore thermal events slow cooling and or systemic analytical effects the results of this study complement a growing body of evidence to indicate that the re os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems

re os ages for the erdenet and tsagaan suvarga porphyry cu mo deposits mongolia and tectonic implications the erdenet and tsagaan suvarga deposits are the two largest known porphyry cu mo deposits in mongolia replicate re os analyses of molybdenite from these deposits yield ages of 240 7 0 8 and 240 4 0 8 ma for erdenet and 370 1 1 2 and 370 6 1 2 ma for tsagaan suvarga 2 errors the re os age of erdenet is significantly older and that of tsagaan suvarga is slightly older than published 40ar 39ar ages for sericite associated with mineralization in these deposits 207 4 5 0 and 364 9 7 0 ma respectively these re os results suggest that in the hydrothermal environment 40ar 39ar ages may be partly to significantly reset whereas re os ages record and maintain the age of primary mineralization events these re os ages indicate that porphyry mineralization at erdenet and tsagaan suvarga are related to porphyritic intrusions representing the youngest event during regional magmatism in northern and southern mongolia respectively the re os age of erdenet marks the final stage of arc magmatism in northern mongolia followed by late permian collision between the mongolian north china and siberian blocks the re os age of tsagaan suvarga indicates that devonian arc magmatism in southern mongolia was active at the present latitude of 44 n at least until 370 ma

anatomy structural evolution and slip rate of a plate boundary thrust the alpine fault at gaunt creek westland new zealand minimum slip rates calculated for plate vector parallel slickenside trends in cataclasite on the sole of the alpine fault at gaunt creek westland new zealand range from 18 to 24 mm yr between half and two thirds of the total relative motion between the pacific and australian plates is being accommodated by movement on a single structure the alpine fault during the past 14 ka the leading edge of the alpine fault has changed from a moderately southeast dipping oblique reverse fault to a shallowly dipping thrust the hanging wall pacific plate is composed of a gradational sequence from basal gouge through pseudotachylite bearing cataclasite to progressively more coherent schist derived mylonite which has been faulted against subhorizontally bedded fluvio glacial gravel in the footwall australian plate during uplift the hanging wall sequence has been internally sheared and imbricated producing duplex structures and retrogressively veined and altered by pervasive hydrothermal fluid flow erosion of the exhumed fault zone produced angular cataclasite and mylonite derived talus fan breccias building a west dipping apron beneath the fault scarp wood fragments from near the base off the talus breccias have been 14 c dated at 12 650 90 yr b p progressive tectonic shortening resulted in 180 m of overthrusting of a schist derived nappe across an irregular talus fan surface composed of its own erosional debris the structural history of the alpine fault at gaunt creek illustrates the importance of the interaction between fault induced topography and erosion and the control these processes exert on the continued tectonic geometric and geomorphic evolution of the fault zone

regional setting and geochronology of the late cretaceous banatitic magmatic and metallogenetic belt the 1 500 km long banatitic magmatic and metallogenetic belt bmmb of romania serbia and bulgaria is a complex calc alkaline magmatic arc of late cretaceous age it hosts a variety of magmatic hydro thermal cu au mo zn pb and fe deposits including europe s only world class porphyry copper deposits regional metallogeny can be linked to subduction of the vardar ocean during the late cretaceous as part of the closure of the neotethys ocean that had separated europe and africa in the mesozoic porphyry cu au mo and intimately associated epithermal massive sul phides dominate in the central segments of the belt in southernmost banat romania serbia and north west bulgaria these districts are the economically most im portant today including major active cu au mines at moldova noua in romania majdanpek veliki krivelj and bor in serbia and elatsite assarel and chelopech in bulgaria more numerous and mostly mined in the past are fe cu and zn pb skarns which occur mainly at the two ends of the belt in eastern bulgaria and in romania this paper summarises some of the deposit characteristics within the geodynamic framework of terminal vardar subduction heterogeneous terranes of the belt including the apuseni mountains at the western end are aligned parallel to the vardar front following continental collision of the dacia and tisza blocks all available geochronological data numerous k ar and some u pb and re os ages are compiled and are complemented by a new high precision re os date for the dognecea skarn deposit south west romania 76 6 0 3 ma these data indicate that magmatism extended over at least 25 million years from about 90 to 65 ma in each segment of the belt within apuseni mountains and banat where magma emplacement was related to syn collisional extension in the orogenic belt of carpathians ore formation seems to be restricted in time and maybe constrained by a shared tectonic event

magmatic hydrothermal activity in the shuteen area south mongolia the shuteen area is located in the gurvansaikhan island arc terrane of south mongolia it contains a large domain of intensely developed silicic and advanced argillic alteration that has strongly affected the adakitic volcanoplutonic shuteen complex the local occurrence of low grade copper mineralization within porphyritic intrusive rocks is indicative of porphyry style mineralization hydrothermal quartz veins host gold mineralization locally the results of scanning electron microscope cathodoluminescence imaging and fluid inclusion microthermometry indicate that the veins and altered rocks at shuteen were produced by multiple hydrothermal events the occurrence of co2 inclusions in quartz from granitoids and the 34s values obtained for sulfide and sulfate within the hydrothermal breccias provide evidence of the involvement of magmatically derived fluids in the early stages of the shuteen magmatic hydrothermal system inferred to be sourced from a porphyry style intrusive center late stage fluids produced abundant barren quartz veins and clay alteration assemblages the weak mineralization and widespread alteration in the shuteen complex are typical of lithocaps found in high level porphyry copper gold molybdenum and high sulfidation epithermal districts the presentday erosion level at shuteen is relatively shallow implying that economic porphyry style mineralization may exist at depth within or beneath the shuteen lithocap

new 40 ar 39 ar age data and implications for porphyry copper deposits of mongolia porphyry copper deposits and related rocks of mongolia have not been generally well dated a few papers report radiometric ages but do not provide raw data or references and most papers that discuss ore deposits report the age at the period level only as part of a larger study examining several deposits and prospects in mongolia we present new 40 ar 39 ar data for three localities porphyry copper deposits and host rocks at erdenet and bayan uul 250 km northwest and 180 km southwest of ulaan baatar respectively yield early jurassic 207 4 or 2 5 ma and late triassic 220 223 ma ages samples from tsagaan suvarga in southern mongolia yield a devonian 364 9 or 3 5 ma age from the ore zone and a carboniferous 313 0 or 2 9 ma age from a porphyry dike that crosscuts the hydrothermal alteration these ages help constrain the timing of metallogenic and tectonic events the devonian and carboniferous ages record part of the development of magmatic arcs in southern mongolia and the late triassic ages may be evidence for the closing of the mongol okhotsk ocean

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

exhumation and preservation of porphyry cu au deposits at oyu tolgoi south gobi region mongolia field relationships and u pb data zircon are used to constrain the timing of tectonomagmatic events that occurred shortly after the formation of late devonian 372 ma porphyry cu au deposits at oyu tolgoi mongolia in the two northernmost of the several discrete porphyry centers hugo dummett deposits upper devonian rocks positioned stratigraphically above copper gold mineralization preserve a record of uplift exhumation and subsequent burial shortly after mineralization strongly altered and mineralized quartz monzodiorite and volcanic rocks at hugo dummett are overlain by an unmineralized dacite sequence 369 2 ma the basal breccia and conglomerate of the dacite sequence contain mineralized porphyry clasts derived from erosion of the porphyry deposits two zircon grains recovered from one of these mineralized porphyry clasts yielded chemical abrasion thermal ionization mass spectrometry ca tims 206 pb 238 u dates of 374 0 1 9 and 371 4 1 6 ma which are consistent with previously published ages for mineralized intrusions this implies that oyu tolgoi or other nearby porphyry deposits were exhumed shortly after the main mineralization event weakly mineralized granodiorite dikes intruded the postmineralization dacite sequence as well as devonian sedimentary and volcaniclastic rocks that structurally overlie the dacite a weighted mean 206 pb 238 u age of 370 6 0 5 ma for this rock is based on the three youngest grains analyzed by the ca tims technique mswd 1 14 burial of the cu au deposits at oyu tolgoi soon after their exhumation was critical to their preservation exhumation and subsequent burial occurred at 371 ma during a short time frame within the overlapping u pb zircon ages for the quartz monzodiorite mineralized porphyry clast unmineralized dacite sequence and granodiorite unit

fault zone architecture of the san jacinto fault zone in horse canyon southern california a model for focused post seismic fluid flow and heat transfer in the shallow crust abstract we report results of a new study of the architecture of the san jacinto fault zone in horse canyon california where stream incision has exposed a nearly continuous outcrop of the fault zone at 0 4 km depth the fault zone at this location consists of a fault core transition zone damage zone and tonalitic wall rocks we collected and analyzed samples for their bulk and grain density geochemical data clay mineralogy and textural and modal mineralogy progressive deformation within the fault zone is characterized by mode i cracking subsequent shearing of already fractured rock and cataclastic flow grain comminution advances towards the strongly indurated cataclasite fault core damage progression towards the core is accompanied by a decrease in bulk and grain density and an increase in porosity and dilational volumetric strain palygorskite and mixed layer illite smectite clay minerals are present in the damage and transition zones and are the result of hydrolysis reactions the estimated percentage of illite in illite smectite increases towards the fault core where the illite smectite to illite conversion is complete suggesting elevated temperatures that may have reached 150 c chemical alteration and elemental mass changes are observed throughout the fault zone and are most pronounced in the fault core we conclude that the observed chemical and mineralogical changes can only be produced by the interaction of fractured wall rocks and chemically active fluids that are mobilized through the fault zone by thermo pressurization during and after seismic events based on the high element mobility and absence of illite smectite in the fault core we expect that the greatest water rock ratios occur within the fault core these results indicate that hot pore fluids circulate upwards through the fractured fault core and into the surrounding damage zone though difficult to constrain we speculate that the site studied during this investigation may represent the top of a narrow ephemeral hydrothermal circulation cell that dissipates heat generated from rupture events at deeper levels 4 km

re os and u pb geochronology of the clear creek dublin gulch and mactung deposits tombstone gold belt yukon canada absolute timing relationships between plutonism and mineralization new re os molybdenite and u pb zircon dates from deposits of the tombstone gold belt provide direct timing constraints for sulphide mineralization and crystallization of spatially associated plutons at clear creek re os molybdenite dates 93 6 0 3 to 92 4 0 4 ma are in excellent agreement with the host intrusion u pb zircon age 92 3 0 3 ma consequently we propose the nominally younger existing 40 ar 39 ar hydrothermal mica ages 91 7 0 4 and 90 0 0 3 ma for clear creek are a result of slow cooling at dublin gulch the re os molybdenite date 93 2 0 3 ma for a late stage vein is nominally younger than the host intrusion u pb zircon age 94 0 0 3 ma in agreement with the deposits paragenesis the u pb zircon date 92 1 0 2 ma for the mactung pluton which lies adjacent to the w skarn has a younger age than the re os molybdenite dates 97 5 0 5 ma fluid inclusion geochemical data for ore fluid indicate a magmatic origin for the w skarn however the u pb and re os age data suggest that the exposed mactung stock is not the source of ore fluid for the w skarn and that the progenitor pluton for ore fluid is unknown the robust age constraints obtained for mineralization and magmatism in this study are in accord with the hypothesis that these deposits are intrusion related ore systems the results are also in agreement with previous studies demonstrating that the re os molybdenite chronometer can provide accurate and precise dates for the timing of metallic mineralization with rigorous sampling protocol

microstructural observations on natural syntectonic fibrous veins implications for the growth process abstract syntectonic antitaxial and ataxial fibrous veins were investigated using sem microprobe cathodoluminescence cl and optical microscopy in antitaxial calcite veins fibres and surrounding selvage grew simultaneously with similar growth rates of crystallographically differently oriented grains new material precipitated at the vein margin in antitaxial and bi mineralic ataxial microstructures bridges of country rock material formed during vein growth in an initial en echelon vein system in our antitaxial and bi mineralic ataxial samples the spacing of solid inclusions does not reflect individual crack seal openings

geochronology and geochemistry of the max porphyry mo deposit and its relationship to pb zn ag mineralization kootenay arc southeastern british columbia canada the max porphyry mo deposit is located at the northern end of the kootenay arc in southeastern british columbia canada molybdenum mineralization is genetically related to the variably altered trout lake granodiorite stock which has lithogeochemical affinities to the low fluorine calc alkaline granodiorite hosted porphyry mo deposit type three molybdenite samples from early and late mo bearing veins yield re os dates that overlap within analytical error with a weighted average age of 80 3 0 2 ma these dates are in close agreement with two 206pb 238u weighted average zircon ages for phases of the trout lake stock at 80 3 1 6 and 79 2 1 0 ma indicating that crystallization of the stock and hydrothermal molybdenite formation were coeval and likely cogenetic 40ar 39ar plateau ages for primary biotite in igneous dikes secondary biotite in early potassic alteration and muscovite in late phyllic alteration range from 80 to 76 ma the younger 40ar 39ar plateau ages may reflect unusually slow cooling of the magmatic hydrothermal system or a late thermal disturbance pb zn ag vein deposits are common throughout the kootenay arc and several such veins are located within and proximal to the max porphyry mo deposit the presence of rare molybdenite associated with sphalerite and argentiferous galena in some of these pb zn ag veins suggests that they represent a late stage event related to the max magmatic hydrothermal system fluid inclusions in quartz from mo and pb zn ag veins are similar and can be divided into two compositional groups type 1 aqueous liquid rich fluid inclusions and type 2 aqueous carbonic liquid rich fluid inclusions pressure corrected 1 4 1 7 kbar trapping temperatures of typical type 1 inclusions from mo bearing veins range from 430 to 460 c and for pb zn ag veins from 335 to 365 c the ranges of salinity 0 12 wt nacl equiv in fluid inclusions from both vein types are almost identical and type 2 inclusions from both vein types contain similar amounts of co2 avg xco2 0 08 with traces of ch4 the similarity of chemistry in the two vein types suggests a genetic link between porphyry mo mineralization and adjacent pb zn ag deposits however muscovite from the alteration halo around a pb zn ag vein within the max deposit yielded a 40ar 39ar plateau age of 72 2 0 5 ma this date is significantly younger than the 80 ma age of porphyry magmatism and mo mineralization suggesting either that this event is in fact unrelated to porphyry mo mineralization at 80 ma or that the k ar isotope system has been disturbed by a later thermal event

frictional strength rate dependence and healing in dfdp 1 borehole samples from the alpine fault new zealand abstract the alpine fault in southern new zealand is a major plate boundary fault zone that according to various lines of evidence may be nearing the end of its seismic cycle and approaching earthquake failure in order to better characterize this fault and obtain a better understanding of its seismic potential two pilot boreholes have been completed as part of a larger drilling project samples representative of the major lithologic subdivisions of the fault zone at shallow 100 m depths were recovered and investigated in laboratory friction experiments we show here that materials from within and very near the principal slip zone psz tend to exhibit velocity strengthening frictional behavior and restrengthen heal rapidly compared to samples of the wall rock recovered near the psz fluid saturation causes the psz to be noticeably weaker than the surrounding cataclasites 0 45 and eliminates the velocity weakening behavior in these cataclasites that is observed in dry tests our results indicate that the psz has the ability to regain its strength in a manner required for repeated rupture but its ability to nucleate a seismic event is limited by its velocity strengthening nature we suggest that seismogenic behavior at depth would require alteration of the psz material to become velocity weakening or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the psz coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the alpine fault and may be facilitated by the slightly weaker psz material and or high rates of healing in the psz which support fault locking and eventual stress drops

a review of the geological characteristics and geodynamic setting of late paleozoic porphyry copper deposits in the junggar region xinjiang uygur autonomous region northwest china abstract in this review we describe the geological characteristics of porphyry copper deposits in junggar region xinjiang and place these into their metallogenic tectonic context these porphyry copper deposits are mainly found in four metallogenic belts 1 a late silurian to early devonian cu mo metallogenic belt in the qiongheba area 2 the late devonian kalaxiange er cu metallogenic belt 3 the early carboniferous xilekuduke suoerkuduke porphyry skarn cu mo metallogenic belt and 4 the late carboniferous baogutu porphyry cu metallogenic belt the ages of mineralization can be divided into three broad intervals

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

frictional properties of exhumed fault gouges in dfdp 1 cores alpine fault new zealand principal slip zone gouges recovered during the deep fault drilling project dfdp 1 alpine fault new zealand were deformed in triaxial friction experiments at temperatures t of up to 350 c effective normal stresses n of up to 156 mpa and velocities between 0 01 and 3 m s chlorite white mica bearing dfdp 1a blue gouge 90 62 m sample depth is frictionally strong friction coefficient 0 61 0 76 across all experimental conditions tested t 70 350 c n 31 2 156 mpa it undergoes a transition from positive to negative rate dependence as t increases past 210 c the friction coefficient of smectite bearing dfdp 1b brown gouge 128 42 m sample depth increases from 0 49 to 0 74 with increasing temperature and pressure t 70 210 c n 31 2 93 6 mpa the positive to negative rate dependence transition occurs as t increases past 140 c these measurements indicate that in the absence of elevated pore fluid pressures dfdp 1 gouges are frictionally strong under conditions representative of the seismogenic crust

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

geochronological framework of the early paleozoic bainaimiao cu mo au deposit ne china and its tectonic implications abstract the bainaimiao cu mo au deposit of ne china is an important ore deposit in the middle section of the northern margin of the north china craton the early paleozoic bainaimiao group is the main ore hosting rock the mineralization at the deposit shows features of porphyry alteration and late stage orogenesis and transformation zircon la icp ms u pb age data indicate that the ages of the third and fifth formations of the bainaimiao group are 492 7 2 9 ma mswd 0 53 and 488 9 3 1 ma mswd 0 92 respectively the age of quartz diorite that intrudes the bainaimiao group is 459 3 6 4 ma mswd 2 20 molybdenite samples from massive cu mo bearing ores and quartz veins in the southern ore belt yield a re os isochron age of 438 2 2 7 ma mswd 0 16 which is consistent with the re os isochron age of molybdenite in the northern ore belt implying that the two ore belts belong to the same mineralization system muscovite from a post magmatic cu mo bearing quartz calcite vein yields an ar ar isochron age of 422 5 3 9 ma mswd 0 64 with an initial 40ar 36ar ratio of 286 21 the well defined plateau age of the muscovite is 422 4 2 6 ma mswd 0 05 which represents the time of the post magmatic orogenic transformation event based on our new age data and previous findings we propose that the bainaimiao cu mo au deposit formed in an active continental margin setting and experienced four stages of ore mineralization 1 a late cambrian middle ordovician volcanic sedimentary stage 2 a late ordovician porphyry mineralization stage 3 a late silurian regional metamorphism stage and 4 an orogenic transformation stage subhedral and euhedral paleoproterozoic 2402 1810 ma inherited zircons indicate that the bainaimiao group has a tectonic affinity with the north china craton the central asian orogenic belt which is closely related to the complex closure of the paleo asian ocean is favorable for prospecting for paleozoic porphyry cu mo or cu au mineralization and associated epithermal au deposits

zircon ages and geochemical compositions of the manlay ophiolite and coeval island arc implications for the tectonic evolution of south mongolia abstract numerous small dismembered ophiolite fragments occur in south mongolia but they are very poorly studied the lack of age data and geochemical analysis hampers our understanding of the paleozoic tectonic evolution of the region we conducted detailed studies on the manlay ophiolitic complex and huree volcanic rocks south of the main mongolian lineament mml to provide some constraints on these rocks the manlay ophiolite consists of dunite harzburgite pyroxenite gabbro plagiogranite basalt and chert locally with chromite mineralization in dunite the gabbro and plagiogranite yielded shrimp zircon weighted mean 206 pb 238 u ages of 509 5 ma and 482 4 ma respectively the basalt and dolerite samples of this complex show enrichment in lree and lile and negative nb ta and ti anomalies and the chrome spinel from the chromitite lens in the dunite is characterized by high cr and low tio 2 contents these features suggest a supra subduction zone ssz origin for the ophiolitic complex the huree volcanic rocks ranging from basalt to dacite display enrichment in lree and lile weak eu anomalies and distinctly negative nb ta and ti anomalies consistent with those of typical magmas in a subduction environment an andesite sample from this arc yielded a shrimp 206 pb 238 u zircon age of 487 5 ma which is the oldest reliable age for an island arc in south mongolia recognition of an early paleozoic ophiolitic complex and a coeval island arc indicates that south mongolia underwent a period of active volcanism during late cambrian to ordovician additionally the tuff overlying the ophiolitic complex and a granite intruding the ophiolite have shrimp zircon u pb ages of 391 5 ma and 304 4 ma respectively combining the available data we propose that the early paleozoic subduction accretionary complexes likely constitute the basement of the late paleozoic arc formations and correlate with the lake zone in western mongolia

granites of the southern mongolia carboniferous arc new geochronological and geochemical constraints the crust in southern mongolia is part of the central asian orogenic belt a vast accretionary orogen that records the opening and closure of the palaeo asian ocean in the late proterozoic to palaeozoic the crustal evolution of the region is revealed in basement inliers that also contain intrusion related porphyry ore bodies that are important mineral exploration targets the saykhandulaan inlier in southeast mongolia is a devonian carboniferous segment of island arc crust which is dominantly composed of extrusive and sedimentary lithologies but which also contains the oyut ulaan i type quartz monzonite intrusion a u pb zircon age for the oyut ulaan monzonite indicates emplacement at 330 0 0 5 ma to the east of the saykhandulaan inlier intrusive complexes dominate the neighbouring mandakh inlier new ages are presented for four of these plutons the bronze fox granodiorite 333 6 0 6 ma the narin hudag monzonite 333 2 0 6 ma the shuteen quartz monzonite 325 5 1 0 ma and the north mandakh granite 292 3 0 5 the intrusive bodies of the saykhandulaan and mandakh inliers have two distinct geochronological and geochemical associations 1 mid carboniferous i type monzonites that constitute the most easterly intrusive expression of the southern mongolia carboniferous arc and 2 early permian a type and peralkaline granites that represent a post orogenic phase of voluminous granite emplacement both groups are significantly younger than the nearby oyu tolgoi and tsagaan suvarga cu porphyry ore bodies which have previously been dated as early and late devonian respectively the new data presented here provide constraints on the timing of the transition from island arc magmatism to post collisional extension related magmatism in the region and possible controls on fertile and infertile granitoid intrusions with respect to cu au mineralisation

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

a 2 5 ga porphyry cu mo au deposit at malanjkhand central india implications for late archean continental assembly abstract eight re os ages from six molybdenite samples representative of the cu mo au mineralization at the giant malanjkhand deposit in madhya pradesh were obtained using id ntims these data provide a clear late archean early paleoproterozoic age for this deposit and by implication for its calc alkaline granitoid host among other diverse models the origin of malanjkhand has been debated as orogenic lode style associated with development of a quartz reef in a shear zone or as porphyry style associated with a pink granitoid intrusion that is conspicuously present in the vicinity of the brittle ductile deformed quartz reef previous models included middle proterozoic ages for the cu mo au mineralization based on poorly constrained rb sr and k ar data direct dating of molybdenite shows that stringer mineralization in the quartz reef and disseminated and vein mineralization in the granite were contemporaneous at 2490 8 ma 2489 5 1 4 ma based on regression without uncertainty in the 187re decay constant mswd 0 5 n 5 additional molybdenite from the quartz reef dated at 2475 and 2450 ma represents at least two pulses of reworking that we suggest configured the elongate and arcuate quartz reef into its present position we suggest that the quartz reef is a high silica stockwork cap embedded in its primary potassic alteration halo and subsequently tilted so that it lies convex to the east with deeper levels exposed to the north petrographic evidence coupled with high re concentrations for molybdenites 400 650 ppm support this scenario and suggest that malanjkhand is a subduction related stockwork porphyry style cu mo au deposit involving mantle malanjkhand geology shares little affinity with three surrounding and tectonically juxtaposed terranes we suggest that the malanjkhand cu mo au deposit and the surrounding batholith containing multiple cu mo au prospects may be the vestiges of a microplate captured along the north margin of the nearly amalgamated southern indian craton at 2 5 ga as the southern craton began to converge with the northern indian craton or other protocontinents now embedded or consumed within the central indian tectonic zone citz this scenario could imply an early paleoproterozoic age for the earliest development of the citz at least in the region of the central indian shear suture cis whose marked ene trend imprints the northwestern part of the malanjkhand batholith and the cu mo au deposit based on a compilation of 2 5 ga events in both the southern and northern indian cratons we suggest that some units in the citz linked an extensive and continuous late archean early paleoproterozoic orogenic belt that may extend to the moyar bavali bhavani attur palghat and cauvery shear zones in southern india and include inboard units of the eastern ghats and the aravalli delhi orogenic belts robust geochronology that can be tied to the early history within these orogenic belts is scarce and extensive reworking during grenvillian and pan african time creates a pervasive overprint at some localities this late archean early paleoproterozoic belt preserves sutures within a coalesced late archean continent that included east antarctica napier and vestfold hills complexes at 2 5 ga

crustal evolution of the saykhandulaan inlier mongolia implications for palaeozoic arc magmatism polyphase deformation and terrane accretion in the southeast gobi mineral belt abstract the saykhandulaan inlier in south east mongolia lies within the central asian orogenic belt caob and records a complex history of palaeozoic tectonism and magmatism associated with terrane accretion on the northern margin of the palaeo asian ocean the inlier spans the boundary between the gobi altai back arc basin terrane in the north and the mandalovoo and gurvansayhan island arc terranes in the south which are notable for their many mineralised intrusions including the oyu tolgoi gold rich copper porphyry deposit results from cross strike transects within the saykhandulaan inlier reveal that it can be subdivided into five parallel east west striking litho tectonic domains 1 the northern slate belt comprising devonian greenschist grade pelites and psammites with deep marine to coastal siliciclastic protoliths 2 the saykhandulaan valley lineament zone svlz a tectonised zone of faulted and lithologically altered volcanic rocks 3 the high strain belt consisting of tightly folded and flattened metamorphosed clastic sedimentary rocks 4 the molasse succession consisting of relatively undeformed coarse conglomerates and sandstones and 5 the oyut ulaan volcanic group a nearly 5 km thick folded carboniferous volcanic succession that hosts the mid carboniferous oyut ulaan mineralised granite the northern slate belt metasedimentary rocks record a northerly cratonic provenance whereas all rocks to the south of the svlz have arc affinities the svlz is thus interpreted to be the boundary between the gobi altai and mandalovoo terranes two major deformation events are documented 1 back arc basin closure and inversion involving regional scale folding and greenschist grade metamorphism in the northern slate and high strain belts 2 contraction associated with mandalovoo terrane accretion and final closure of the palaeo asian ocean to the south following terrane accretion and cessation of subduction crustal extension and strike slip faulting further modified the crustal architecture of the inlier the results presented here provide a useful framework for understanding the crustal evolution of adjacent regions within the southeast gobi mineral belt

the south siberia central mongolia transect abstract studies of geological and geophysical data on the south siberia central mongolia geoscience transect which runs approximately along 100 e show that the asian continent was formed in the phanerozoic by accretion of terranes most of which were microcontinents with precambrian basement suture zones separating the terranes are deformed and deeply eroded magmatic arcs of different widths likewise classified as specific terranes in these sutures magmatic arc rocks are locally associated with fore and back arc basin series most of the oceanic crust has been subducted the observed ophiolite belts are as a rule attributed to the base of oceanic island arcs the fragment of the asian continent traversed by the transect was formed through early middle and late paleozoic stages of accretion

geochronological constraints on pre syn and postmineralization events at the world class cleo gold deposit eastern goldfields province western australia recent geological and geochronological studies have led to a reevaluation of whether or not the majority of the lode gold deposits of the yilgarn craton formed nearly synchronously during an archean craton wide hydrothermal event as previously proposed the majority of reliable data indicate that gold mineralization took place at ca 2640 to 2625 ma however recent work in the far north of the eastern goldfields province provides structural evidence for instances of earlier gold mineralization and geochronological data for interpreted postore rocks that are considerably older than 2640 ma the documentation of xenotime and monazite in association with ore minerals at the cleo deposit provides a valuable means of determining the absolute age of gold mineralization at the cleo deposit high grade western lodes veins crosscut the sunrise shear zone at a high angle with only centimeter scale offset given that the stratigraphic sequence indicates at least several hundred meters offset across the shear zone the minimal offset of the western lodes veins indicates that gold mineralization was late in the history of movement in the shear zone the absolute ages of pre syn and postmineralization elements in the mine stratigraphic succession have been determined using a variety of geochronological techniques fuchsite micas formed in the sunrise shear zone yield an 40ar 39ar isochron age of 2667 19 ma rhyodacite porphyry dikes postdate the formation of the shear zone but predate the main phase of gold mineralization dike intrusion is constrained to 2674 3 ma by shrimp ii u pb analysis of zircons from these dikes rhenium os analysis of molybdenite from quartz chalcopyrite molybdenite veins that crosscut the porphyry dikes gives an age of formation at 2663 11 ma consistent with their relationship to the porphyry dikes both the dikes and these veins are crosscut by gold bearing western lodes veins mutually crosscutting relationships with ore minerals indicate that microscopic xenotime and monazite grains were deposited during ore formation in the western lodes ore zones shrimp ii u pb analyses of xenotime and monazite grains indicate that western lodes mineralization took place at 2654 8 ma at least 9 m y after the intrusion of the porphyry dikes 95 confidence evidence for substantial temporal separation between intrusive activity and gold mineralization is recorded by other researchers for other deposits associated with granitic intrusions in the leonora laverton area phlogopitic micas from a lamprophyre that crosscuts the whole succession including the sunrise shear zone yield an ar ar plateau age of 2080 4 ma this study constrains the timing of multiple events at cleo including the main phase of gold mineralization during a relatively short span of time however in the context of the larger debate about the existence of a dominant 2640 to 2625 ma period of gold mineralization and the extent of a proposed widespread pre 2660 ma mineralization event in the yilgarn craton the data from cleo are equivocal the 2654 8 ma age for mineralization being significantly older than 2640 ma but not significantly pre 2660 ma even if the maximum possible age is accepted

re os and 40ar 39ar ages of porphyry molybdenum deposits in the east greenland volcanic rifted margin precise re os dating of molybdenite from the malmbjerg and flammefjeld rift related porphyry molybdenum deposits indicates that they are among the youngest magmatic events 25 8 0 1 and 39 7 0 2 ma in their respective areas of the east greenland rifted continental margin an 40 ar 39 ar age for biotite from the malmbjerg granite stock 25 7 0 3 ma demonstrates that molybdenite mineralization is essentially concurrent with granite emplacement further the identical ages obtained by argon and re os geochronology suggest that for the youngest events in a region re os and argon based methods produce similar age results whereas this is generally not the case for older ore forming events that have been thermally overprinted in the latter case disturbance of argon systematics produces ages younger than those determined by re os both deposits postdate continental breakup and the associated flood volcanism episode at 56 to 54 ma we suggest that the malmbjerg and flammefjeld molybdenum deposits formed during later periods of lithospheric uplift which at least in the case of malmbjerg may have been related to plate tectonic reorganization of the northeast atlantic ocean basin this uplift may have caused decompression mantle melting and renewed generation of mafic magma that led to crustal anatexis and the establishment of major hydrothermal systems the suggestion that molybdenum mineralization occurred at times of late uplift of a volcanic rifted margin may be useful in prospecting

160 ma of magmatic hydrothermal and metamorphic activity in the gallivare area re os dating of molybdenite and u pb dating of titanite from the aitik cu au ag deposit northern sweden host rocks to the aitik cu au ag deposit in northern sweden are strongly altered and deformed early proterozoic mica amphibole schists and gneisses the deposit is characterised by numerous mineralisation styles vein and alteration types four samples were selected for re os molybdenite dating and 12 samples for u pb titanite dating in order to elucidate the magmatic hydrothermal and metamorphic history following primary ore deposition in the aitik cu au ag deposit samples represent dyke vein and alteration assemblages from the ore zone hanging wall and footwall to the deposit re os dating of molybdenite from deformed barite and quartz veins yielded ages of 1 876 10 ma and 1 848 8 ma respectively a deformed pegmatite dyke yielded a re os age of 1 848 6 ma and an undeformed pegmatite dyke an age of 1 728 7 ma u pb dating of titanite from a diversity of alteration mineral associations defines a range in ages between 1 750 and 1 805 ma with a peak at ca 1 780 ma the ages obtained together with previous data bracket a 160 ma 1 890 1 730 ma time span encompassing several generations of magmatism prograde to peak metamorphism and post peak cooling events resulting in the redistribution and addition of metals to the deposit this multi stage evolution of the aitik ore body suggests that the deposit was affected by several thermal events that ultimately produced a complex ore body the re os and u pb ages correlate well with published regional re os and u pb age clusters which have been tied to major magmatic hydrothermal and metamorphic events primary ore deposition at ca 1 890 ma in connection with intrusion of haparanda granitoids was followed by at least four subsequent episodes of metamorphism and magmatism early metamorphism at 1 888 1 872 ma overlapping with haparanda 1 890 1 880 ma and perthite monzonite 1 880 1 870 ma magmatism clearly affected the aitik area as well as late metamorphism and lina magmatism at 1 810 1 774 ma and tib1 magmatism at 1 800 ma the 1 848 ma re os ages obtained from molybdenite in a quartz vein and pegmatite dyke suggests that the 1 850 ma magmatism recorded in parts of northern norrbotten also affected the aitik area

u pb and re os geochronology of the bainaimiao cu mo au deposit on the northern margin of the north china craton central asia orogenic belt implications for ore genesis and geodynamic setting abstract the bainaimiao cu mo au deposit located at the northern margin of the north china craton ncc in central inner mongolia is a large cu dominant deposit orebodies are hosted in strongly deformed and metamorphosed granodiorite porphyry intrusions or in ew trending shear zones in greenschist and sericite felsic schist of the bainaimiao group mineralization can be divided into early middle and late stages characterized by quartz pyrite polymetallic quartz sulfides and carbonate quartz respectively hydrothermal activity led to pervasive silicification k feldspar biotite and chlorite epidote carbonate alteration eight samples from cu mo bearing quartz veins and massive sulfide ores in greenschist were collected from the viii orebody in the north ore belt and molybdenite separates were selected for re os analyses the concentrations of re and 187 os range from 216 6 to 1051 ppm and 2302 to 4913 ppb respectively all samples give re os model ages between 441 2 and 445 9 ma and yielded an isochron age of 445 0 3 4 ma mswd 0 26 with an initial 187 os of 4 17 ppb a granodiorite porphyry sample for shrimp u pb dating was collected from the underground of the xiii orebody of the north ore belt spots from 14 zircon grains have 206 pb 238 u values between 426 2 and 462 9 ma and form a tight cluster on concordia yielding a weighted mean 206 pb 238 u age of 445 6 ma this is considered to be the best estimate of crystallization age of the granodiorite porphyry the re os isochron age of the molybdenite is consistent with the shrimp u pb age of the granodiorite porphyry which indicates that the deposit is a porphyry system of paleozoic age according to geodynamic setting and geological history of the northern margin of the ncc the deposit was probably related to magmatic activity of the middle paleozoic ondor sum subduction accretion complex bainaimiao arc during the devonian the bainaimiao arc was accreted to the northern margin of the ncc collision between the bainaimiao arc and ncc led to regional metamorphism of the ore hosting terrane and ore metals were remobilized in this process gold mineralization was probably overprinted onto the earlier cu mo mineralization

gold deposits of the northern margin of the north china craton multiple late paleozoic mesozoic mineralizing events the northern margin of the north china craton is well endowed with lode gold deposits hosting a resource of approximately 900 tonnes t of gold the 1 500 km long region is characterized by east trending blocks of metamorphosed archean and proterozoic strata that were episodically uplifted during variscan indosinian and yanshanian deformational and magmatic events at least 12 gold deposits from the daqinshan yan liao includes the zhangjiakou yanshan and chifeng gold districts and changbaishan gold provinces contain resources of 20 100 t au each most deposits are hosted in uplifted blocks of precambrian metamorphic rocks although felsic paleozoic and mesozoic plutons are typically proximal and host 30 of the deposits the lodes are characterized by sulfide poor quartz veins in brittle structures with low base metal values and high au ag ratios although phyllic alteration is most common intensive alkali feldspar metasomatism characterizes the wulashan dongping and zhongshangou deposits but is apparently coeval with variscan alkalic magmatism only at wulashan stepwise 40ar 39ar geochronology on 16 samples from gangue and alteration phases combined with unpublished shrimp u pb dates on associated granitoids suggest that gold mineralizing events occurred during variscan indosinian and yanshanian orogenies at circa 350 250 200 180 150 and 129 ma however widespread permo triassic 250 ma and early jurassic 180 ma thermal events caused variable resetting of most of the white mica and k feldspar argon spectra as well as previously reported k ar determinations compiled and new stable isotope and fluid inclusion data show that most 18o values for ore stage veins range from 8 to 14 indicating a fluid in equilibrium with the precambrian metamorphic basement rocks d values from fluid inclusions range widely from 64 to 154 which is indicative of a local meteoric component in some veins and highly variable 34s data 7 to 17 even within individual deposits indicate various local country rock sources for sulfur fluid inclusions from all districts show variable homogenization temperatures between 240 and 400 c and are consistently characterized by low salinity h2o co2 ch4 n2 solutions although the data are largely consistent with that from orogenic gold veins intrusion related veins and epithermal veins are also recognized the multiple episodes of mineralization are coincident with episodic tectonic reactivations and associated magmatism along the northern margin of the north china craton electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0239 2

diffusion in carbonates fluorite sulfide minerals and diamond this chapter focuses on diffusion in non silicate minerals that do not fall under any of the other chapter categories this includes minerals that are not oxides fluorite sulfide minerals diamond and those like the carbonates that are not among the oxide minerals discussed in chapter 17 of this volume van orman and crispin 2010 although there are numerous minerals in these categories limited diffusion data exist for many of them so the primary phases that will be considered are carbonates fluorite diamond and sulfide minerals carbonate minerals are major constituents of sediments and many sedimentary rocks fractionation of o and c isotopes between carbonate rocks and fluids can provide insight into paleoclimates and sedimentary histories the behavior of the isotopes of major elements in calcite and aragonite has become of increasing interest due to the important role of co2 and carbonate dissolution precipitation in the oceans and the connections to global climate e g arita and wada 1990 chacko et al 1991 dickson 1991 beck et al 1992 cole 1992 graham et al 1998 cole and chakraborty 2001 ca mg diffusion rates affect the process of dolomitization hardie 1987 fisler and cygan 1999 and characterization of diffusion of these species is important for refinements in application of the calcite dolomite geothermometer e g essene 1982 farver and yund 1996 and better understanding of deformation mechanisms for example calcium isotopic fractionation between seawater and calcite and aragonite has been observed in marine samples zhu and macdougall 1998 de la rocha and depaolo 2000 schmitt et al 2003 with possible applications as a thermometer ca isotopic fractionation also occurs in biologic systems as in the growth of foraminifera skulan et al 1997 zhu and macdougall 1998 diffusion of major elemental species plays an important rate limiting

late and mid cretaceous mineralization in the northern canadian cordillera constraints from re os molybdenite dates new re os molybdenite dates are presented from three deposits casino cash and mt nansen in the dawson range yukon northern canadian cordillera the re os molybdenite dates provide constraints on the timing of sulfide mineralzation and together with 40 ar 39 ar and k ar mineral dates yield estimates for the longevity of the porphyry hydrothermal system at the casino deposit re os molybdenite dates associated with the potassic 75 05 0 28 74 69 0 28 ma alteration are nominally older to overlapping with re os molybdenite dates 74 4 0 28 ma n 2 with phyllic alteration and suggest that it is likely that potassic and phyllic mineralization alteration was contemporaneous the re os molybdenite dates are significantly older than hydrothermal k feldspar 40 ar 39 ar and k ar biotite dates 72 ma which most likely reflect the cessation of the porphyry hydrothermal system the molybdenite age data combined with silicate hydrothermal mineral dates suggest a porphyry hydrothermal system longevity of 4 16 to 1 94 casino 8 66 to 6 44 cash and 2 47 to 1 48 ma mt nansen these longevity estimates for porphyry hydrothermal systems are greater than previously proposed 50 c km may control the disparate re os molybdenite and 40 ar 39 ar k feldspar dates of the porphyry systems of this study the contrasting re os and 40 ar 39 ar dates clearly show the re os isotope system in molybdenite is resistant to prolonged 1 ma interaction with a high temperature 400 500 c hydrothermal fluid and that the re os isotope systematics in molybdenite unambiguously record directly the timing of sulfide mineralization this ability to directly date sulfide mineralization has identified mid pattison idaho creek 102 104 ma and late cretaceous zappa koffee 74 5 ma mineralization which is hosted by the mid cretaceous 104 102 ma casino plutonic suite the late cretaceous date is very similar to that for molybdenite mineralization at casino and we suggest that the zappa koffee mineralization is an area of late cretaceous porphyry mineralization for which the host pluton has not yet been discovered

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

origin of small scale segmentation and transpressional thrusting along the alpine fault new zealand the alpine fault is the major structural feature of the australian pacific plate boundary in the south island of new zealand geologic evidence suggests that half to three quarters of the plate boundary displacement is accommodated by movement on the fault detailed investigation of the central section of the alpine fault has revealed that it consists of oblique thrust sections striking 020 050 that are linked by subvertical right lateral faults striking between 065 and 090 the segmentation is on a scale of 1 10 km similarly oriented right lateral faults are abundant southeast of the alpine fault and are consistent with stresses induced in an elastic layer by an oblique slip ductile fault zone below propagation of the fault to the surface is predicted to result in an en echelon arrangement of strike slip and thrust segments it is suggested that the spatial distribution of segments is affected by the existence of deeply incised valleys in the hanging wall that disturb the stress field to depths of 1 4 km the segmentation is near surface and does not appear to act as a barrier to the propagation of large earthquakes

chemical and physical characteristics of pulverized tejon lookout granite adjacent to the san andreas and garlock faults implications for earthquake physics we present new detailed analyses of samples of pulverized tejon lookout granite collected from sections adjacent to the san andreas and garlock faults in southern california the tejon lookout granite is pulverized in all exposures within about 100 m from both faults chemical analyses indicate no or little weathering in the collected samples although xrd analysis shows the presence of smectite illite and minor kaolinite in the clay size fraction weathering products may dominate in the less than 1 micron fraction the average grain size in all samples of pulverized tejon lookout granite ranges between 26 and 208 microns silt to fine sand with the particle size distribution in part a function of proximity to the primary slip zone the san andreas fault samples that we studied are generally finer grained than those collected from adjacent to the garlock fault the particle size distribution for each studied sample from both faults follows a pseudo power law with a continuously changing exponent which suggests that pulverization is not simply a consequence of direct shear the average particle size that we determined for our samples is considerably coarser than reported in previous investigations which we attribute to possible measurement errors in the prior work our data and observations suggest that dynamic fracturing in the wall rock of the san andreas and garlock faults only accounts for about 1 or less of the earthquake energy budget

age and evolution of late mesozoic metamorphic core complexes in southern siberia and northern mongolia numerous cretaceous metamorphic core complexes mccs extend from transbaikalia in russia to northern mongolia within the central asian orogenic belt we investigated the buteel and zagan mccs in detail shear sense indicators in mylonitized rocks show footwall to the nw tectonic transport single zircon dating of footwall rocks in the buteel mcc establishes the emplacement of granitoid orthogneiss precursors at 240 211 ma a felsic metavolcanic rock at 265 0 1 2 ma a syenite at 265 5 1 2 ma and a metarhyolite of the pre granitoid basement at 553 6 2 9 ma a peralkaline granite intruding orthogneisses of the zagan mcc has a new u pb zircon age of 151 6 0 7 ma 40 ar 39 ar ages of 133 5 1 8 ma of hornblende from amphibolite and 122 6 1 8 ma of biotite from mylonitized gabbro dolerite of the buteel mcc are interpreted as cooling ages representing the time of deformation in the footwall geological data suggest that the mccs in transbaikalia and northern mongolia formed as a result of extension in a crust that had previously been thickened by abundant calc alkaline magmatism in an andean type setting on the border of the closing mongol okhotsk ocean by widespread collisional to post collisional thrusting and by extensive alkaline peralkaline magmatism

laser probe 40 ar 39 ar ages of early and late stage alteration assemblages rosario porphyry copper molybdenum deposit collahuasi district i region chile sensibly identical laser probe 40 ar 39 ar dates of 32 9 or 0 5 2sigma and 32 9 or 0 6 ma are determined for respectively early stage hydrothermal biotite and late stage hydrothermal muscovite from the giant rosario porphyry copper deposit in the collahuasi district of northern chile the age determinations were carried out on ca 1 cm 2 1 to 0 5 mm thick wafers of altered rock or on smaller chips broken therefrom obviating the requirement for mineral separation and permitting direct petrographic control of the analytical procedure the age data although not unambiguous imply that this extremely large hydrothermal center was emplaced over a short interval hydrothermal activity in this central andean transect migrated eastward over a period of ca 3 to 4 m y from copaquire through quebrada blanca to rosario the intensity of mineralization increasing with time rosario chuquicamata and la escondida the largest of the west fissure domeyko fault system array were apparently emplaced coevally in the terminal stage of the late eocene early oligocene metallogenic episode

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

an re os date for molybdenite bearing quartz vein mineralization within the kangerlussuaq alkaline complex east greenland implications for the timing of regional metallogenesis the kangerlussuaq alkaline complex east greenland is one of the largest alkaline complexes in the world it is known to host a number of occurrences of base and precious metal mineralization including the flammefjeld porphyry mo deposits and a suite of epithermal style base and precious metal veins in an area around the sondre syenitgletscher here we describe and date a previously unknown occurrence of molybdenite pyrite scheelite bearing quartz veins associated with alkali basalt dikes that intrude the main syenites of the complex the veins appear to be cogenetic with the dikes which crosscut and brecciate granodiorites of the cirque 1320 complex sulfur isotope signatures of molybdenite and pyrite in the veins give a tight range with mean 34 s of 2 2 0 7 consistent with a magmatic s source related to the intrusion of the dikes molybdenite from the veins gave an re os age of 52 74 0 26 ma some 13 m y older than molybdenite at the flammefjeld porphyry deposit thus distinguishing this metallogenic episode as a distinct event temporally unrelated to the known mo mineralization at flammefjeld significantly in terms of the timing of regional metallogenesis and magmatism our date suggests that the age of the kangerlussuaq alkaline complex itself may be slightly older than the 50 ma currently accepted based on 40 ar 39 ar dating from biotites in the main syenites given the common discrepancy in ore systems of 40 ar 39 ar which produce slightly younger dates than those by re os and u pb we suggest the actual age of the kangerlussuaq alkaline complex may be closer to 53 to 52 ma

timing and duration of high temperature gold mineralization and spatially associated granitoid magmatism at chalice yilgarn craton western australia the chalice gold deposit in the eastern goldfields province yilgarn craton western australia is located in a middle to upper amphibolite facies metamorphic domain and is hosted by a mafic ultramafic rock sequence that has been locally intruded by four generations of monzogranite dikes two stages of gold mineralization identified on the basis of crosscutting relationships formed under broadly synpeak to postpeak metamorphic conditions main stage gold mineralization 95 of the resource comprises foliation parallel quartz albite diopside titanite garnet gold veins and wall rock replacement both within locally developed asymmetric folds in mafic amphibolite second stage gold mineralization 5 of the resource is temporally associated with a second generation monzogranite dike that crosscuts the folds and hence is younger than the main event it is represented by disseminated gold in the dike as well as by foliation discordant quartz gold quartz diopside gold actinolite gold and molybdenite tellurobismuthite gold veins gold is in textural equilibrium with the hydrothermal alteration assemblages in both mineralization stages and also with primary igneous phases quartz and feldspar in the monzogranite dike in the second stage ore magmatic zircons and titanite from second and fourth generation monzogranite dikes and a monzogranite stock as well as hydrothermal titanite and molybdenite in equilibrium with gold from hydrothermal alteration assemblages allow dating of the important magmatic and hydrothermal events using the u pb and re os isotope systems two gold events are identified main stage mineralization is coincident with asymmetric fold development at 2644 8 ma shrimp u pb on titanite and second stage mineralization 2621 10 ma re os on molybdenite is coeval within the error of the isotopic ages with the intrusion of the gold mineralized second generation monzogranite dike 2626 9 ma shrimp u pb on zircon ages of hydrothermal titanite in monzogranite dikes 2631 10 ma 2624 7 ma 2623 5 ma and 2619 6 ma shrimp u pb ages indicate contemporaneous hydrothermal alteration gold mineralization and evolving magmatism during the second stage event a fourth generation flat lying pegmatite which truncates all mine rock units constrains the minimum age of mine scale gold bearing alteration and magmatism to 2622 13 ma the geologically constrained geochronologic data suggest that the chalice gold deposit is a product of two independent gold events separated by up to 20 m y within an extended period of granitoid magmatism also extending over 20 m y it demonstrates for the first time in the extensively gold mineralized yilgarn craton a clear interdependence and interplay between ongoing granitoid magmatism deformation hydrothermal alteration and gold mineralization in amphibolite hosted deposits however although integrated field and geochemical research establish a clear chronology of events the controversy of contribution from magmatic and or metamorphic fluids for the ore remains unresolved because these events are broadly coeval within the resolution of the isotopic techniques

hydraulic and acoustic properties of the active alpine fault new zealand laboratory measurements on dfdp 1 drill core abstract we report on laboratory measurements of permeability and elastic wavespeed for a suite of samples obtained by drilling across the active alpine fault on the south island of new zealand as part of the first phase of the deep fault drilling project dfdp 1 we find that clay rich cataclasite and principal slip zone psz samples exhibit low permeabilities 10 18 m 2 and that the permeability of hanging wall cataclasites increases from c 10 18 m 2 to 10 15 m 2 with distance from the fault additionally the psz exhibits a markedly lower p wave velocity and young s modulus relative to the wall rocks our laboratory data are in good agreement with in situ wireline logging measurements and are consistent with the identification of an alteration zone surrounding the psz defined by observations of core samples the properties of this zone and the low permeability of the psz likely govern transient hydrologic processes during earthquake slip including thermal pressurization and dilatancy strengthening

evolution of strength recovery and permeability during fluid rock reaction in experimental fault zones abstract physical and chemical fluid rock interactions are implicated in controlling earthquake nucleation and recurrence in particular interseismic compaction sealing and healing of fractured fault rocks can lead to strength recovery and stabilisation of fault zones in contrast these same processes can also assist increases in pore fluid pressures and consequent destabilisation of faults here we present high temperature hydrothermal experiments designed to assess the evolution of strength of fault zones in previously intact rock and also characterise the associated changes to porosity and permeability cores of fontainebleau sandstone were initially loaded to failure in a high pressure gas medium apparatus the failed specimens were then hydrothermally reacted at 927 c for variable duration under isostatic conditions and subsequently re fractured to determine the interseismic strength recovery in the most extreme case hydrothermally induced gouge compaction cementation and crack healing resulted in 75 strength recovery after reaction for 6 h isostatic hydrothermal treatment also resulted in dramatic reduction in porosity and permeability strength of the fault zone following hydrothermal reaction appears to be closely correlated to porosity consistent with previous studies on brittle failure of porous aggregates the experimental results show how hydrothermal reactions in fault zones may lead to two competing time dependent effects fault strengthening due to increased cohesion in the fault zone and fault weakening arising from elevated pore pressures within a well cemented low permeability gouge layer

contrasting ore styles and their role in understanding the evolution of the altaids abstract the altaids is a paleozoic orogenic collage in central asia it occupies 10 of the eurasian continent and it is one of the richest concentrations of mineral deposits in the world comparable to those of the circum pacific and tethyan orogenic belts in particular it contains many types of hydrothermal ore deposits that are sensitive to the nature and origin of their host terranes including porphyry copper gold molybdenum volcanogenic massive sulfide copper lead zinc and orogenic gold deposits which are all diagnostic of convergent continental margins extensional arc related submarine basins and transpressional terrane boundaries within the altaids porphyry copper deposits are mostly concentrated within the kazakhstan and tuva mongolia micro continents where they formed almost continuously from the early ordovician to permian only a few are cambrian and triassic and most are late carboniferous most volcanogenic massive sulfide ore deposits are distributed along the south urals and rudny altai in the western altaids where they formed in a short time window from the early to middle devonian important orogenic gold deposits formed along regional strike slip faults between craton island arc or micro continent boundaries from the neoproterozoic to permian mostly in the early permian in limited key areas volcanogenic massive sulfide deposits formed upon much older 100 ma basement rocks than those of coeval porphyry deposits indicating that the altaids could not have developed from a single arc furthermore the porphyry deposits outline the distribution of several continental fragments the combined area of which is far less than that of the altaids which suggests that extensive new juvenile material has been added into island arc systems which may have been accreted to surrounding continental margins these metallogenic distributions in localized areas were a result of the mechanisms of crustal growth within the overall tectonic evolution of the altaids and they are consistent with the interpretation that the altaids is a multiple subduction accretion collage

progressive strain localization in a major strike slip fault exhumed from midseismogenic depths structural observations from the salzach ennstal mariazell puchberg fault system austria 1 analysis of a strike slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high strain fault core we focus on the ennstal segment of the 400 km long salzach ennstal mariazell puchberg semp strike slip fault system in the eastern alps which accommodated 60 km of left lateral displacement during oligo miocene time macroscopic and microscopic observations reveal a zoned fault featuring a high strain core at least 10 m wide within a fault zone that is at least 150 m wide grain size distribution analysis shows how the ennstal segment of the semp evolved our data reveal a 10 m wide high strain fault core characterized by a power law relationship of grain sizes d2 2 0 bordered by a 54 m wide transition zone where the largest and smallest grains are characterized by two power law relationships d2 2 0 and 1 6 respectively this zone is in turn bordered by a region with grain sizes that show a single low strain power law relationship of d2 1 6 we interpret these relationships to be the result of concentrated shear overprinting an initial low strain power law grain size distribution before strain localized to the core this is consistent with the theory that faults mature by smoothing geometrical complexities forming a highly localized high strain fault core the data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure

late triassic sinistral shear in the east gobi fault zone mongolia abstract tectonic studies of the east gobi fault zone in southeastern mongolia reveal multiple distinct intracontinental deformation events postdating late paleozoic arc accretion and continental amalgamation metamorphic tectonites of the tsagan subarga and tavan har blocks previously mapped as precambrian basement comprise a sinistral shear zone dominated by steeply dipping northeast striking foliations field observations and petrographic analyses indicate that the protoliths of the metamorphic tectonites are paleozoic arc volcanic and sedimentary sequences 40ar 39ar step heating analyses of minerals from pre syn and late to post kinematic lithologies bracket the timing of ductile sinistral shear as late triassic the main phase of distributed deformation associated with cooling through amphibolite upper greenschist facies conditions occurred ca 225 ma and shear zone activity waned ca 210 ma cooling rates inferred from the 40ar 39ar data are on the order of 40 20 c myr 1 apparent differences for the two basement blocks may reflect subsequent differential uplift during late jurassic cretaceous rifting relatively rapid late triassic cooling suggests a transtensional component to the deformation and is coincident with core complex formation in northern china late triassic intraplate deformation in southeastern mongolia is likely the result of far field forces associated with collision between mongolian arcs and the siberian craton i e closure of the mongol okhotsk ocean and or collisions associated with closure of the paleotethys the ductile shear zone has been documented over 250 km along strike and has been modified by subsequent brittle deformation events in the mesozoic and cenozoic

regional mineral mapping of island arc terranes in southeastern mongolia using multi spectral remote sensing data abstract over the last few decades many porphyry cu deposits have been discovered in southeastern se mongolia in particular the gurvansayhan and mandalovoo island arc terranes have high potential for ore deposits regional mineral mapping of these terranes using data from the landsat enhanced thematic mapper plus etm and the advanced spaceborne thermal emission and reflection radiometer aster have provided new geological information on the metallogenic province revealing potential mineral deposits for future explorations iron oxides hydroxides with high etm band 1 3 ratio values occur extensively in quaternary deposits located at the boundary between the gurvansayhan and mandalovoo island arcs terranes and basins the high average band ratios 1 35 registered for the porphyry cu and au deposits and their occurrences are associated with iron oxidation which originates from the erosion and weathering of ore zones regional mapping of the island arc terranes using the aster shortwave infrared swir logical operators showed circular or semicircular alteration patterns which usually cluster along faults the mineral assemblages mapped by the aster swir analysis in five major porphyry cu districts can be divided into two types the first type includes argillic phyllic and propylitic mineral assemblages as exemplified by the shuteen ikh shankhai and oyu tolgoi deposits the second type of assemblage includes phyllic and propylitic mineral assemblages as exemplified by the kharmagtai and tsagaan suvarga deposits within the deposits of the first type quartz was also mapped using the aster thermal infrared tir mineral index the difference between the two types may be related to the presence of a lithocap the results of a field survey including spectral reflectance measurements in the ikh shankhai porphyry cu district showed a good correlation with the image analysis results

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

late cretaceous granitic magmatism and sn mineralization in the giant yinyan porphyry tin deposit south china constraints from zircon and cassiterite u pb and molybdenite re os geochronology the yinyan porphyry tin deposit in western guangdong is spatially associated with quartz porphyry and granite porphyry la icp ms zircon u pb dating defined an emplacement age of 78 5 0 4 ma for the quartz porphyry and 79 2 0 9 ma for the granite porphyry la icp ms cassiterite u pb dating yielded tera wasserburg lower intercept ages of 78 5 0 6 78 6 1 2 and 78 2 0 7 ma for cassiterite from a cassiterite sulfide vein cassiterite sulfide ore and a cassiterite topaz quartz stringer respectively re os dating of molybdenite from seven different veins yielded an isochron age of 77 0 0 5 ma all these new age data are indistinguishable within analytical uncertainty and therefore indicate a genetic relationship between the sn mineralization and the porphyry magmatism in the yinyan deposit the ree tetrad effect and very low nb ta and zr hf ratios indicate that the quartz porphyry and the granite porphyry are highly evolved the u pb dated cassiterite is enriched in fe w and u and in high field strength elements hfses such as zr hf nb and ta the high fe nb and ta contents may be responsible for the dark luminescence of cassiterite in cl images the zr hf ratio of cassiterite may potentially be used to distinguish the mineralization type cassiterite from pegmatites has lower zr hf ratios 5 6 in comparison with granite greisen related 9 30 cassiterite cassiterite from the early hydrothermal stage typically contains higher amounts of ti nb ta zr and hf than that from the late hydrothermal stage in combination with published geochronological data of other sn w deposits in the western guangdong province two sn w metallogenic events at ca 85 and 77 80 ma have been identified these two metallogenic events are part of a larger scale 75 100 ma sn w mineralization event in south china which we suggest was probably related to the subduction of the neo tethyan oceanic plate

late archean cu au mo mineralization at gameleira and serra verde carajas mineral province brazil constraints from re os molybdenite ages new re os molybdenite ages provide constraints on the timing of late archean cu au mo mineralization in the northern carajas mineral province molybdenite from the gameleira iron oxide cu au mo deposit yielded an age of 2 614 14 ma this age overlaps within its analytical error with re os ages of molybdenite from the serra verde cu au mo vein deposit 2 609 13 ma and from the nearby small garimpo fernando gold mining operation 2 592 13 and 2 602 13 ma which is probably related to the latter the geochronological data imply that the hydrothermal cu au mo mineralization in these three deposits was epigenetic and coincides with a regional tectonic regime changing from dextral transtension and clastic sedimentation at 2 7 2 6 ga to sinistral transpression and inversion at 2 6 ga previously reported stable isotope and microthermometric data are compatible with a magmatic affiliation of the cu au mo ores at gameleira and serra verde a genetic relationship of mineralization may therefore exist with 2 56 2 76 ga archean alkaline granitoids or with 2 6 2 7 calc alkaline to tholeiitic volcanic arc type magmatism

petrography geochemistry and geochronology of the host porphyries and associated alteration at the tuwu cu deposit nw china a case for increased depositional efficiency by reaction with mafic hostrock tuwu is the largest porphyry copper deposit discovered in the eastern tianshan mountains xinjiang china a newly recognized volcanic complex in the early carboniferous qi eshan group at tuwu consists of basalt andesite and diorite porphyry the plagiogranite porphyry was emplaced into this complex at 332 8 2 5 ma u pb zircon sims determination whole rock element geochemistry shows that the volcanic complex and plagiogranite porphyry formed in the same island arc although the complex was derived by partial melting of the mantle wedge and the plagiogranite porphyry by partial melting of a subducting slab the diorite and the plagiogranite porphyries have both been subjected to intense hydrothermal alteration and associated mineralization but the productive porphyry is the plagiogranite porphyry three alteration and mineralization stages including pre syn and post ore stages have been recognized the pre ore stage formed a barren propylitic alteration which is widespread in the volcanic complex the syn ore stage is divided into three sub stages stage 1 is characterized by potassic alteration with chalcopyrite bornite chalcocite stage 2 is marked by chlorite sericite albite alteration with chalcopyrite pyrite bornite stage 3 is represented by phyllic alteration with chalcopyrite pyrite molybdenite the post ore stage produced a barren argillic alteration limited to the diorite porphyry a specific feature of the tuwu deposit is that the productive porphyry was emplaced into a very mafic package and reaction of the resulting fluids with the ferrous iron rich hostrocks was a likely reason that tuwu is the largest porphyry in the district

geochronology of the porphyry copper deposits and related mineralization of mexico k ar dating demonstrates that all but eight of 41 dated porphyry copper and related ore deposits of mexico were emplaced during the laramide episode of maximum plate convergence one older deposit is related to the jurassic volcanic arc of western north america one is pre laramide cretaceous four are oligocene in age and two late cenozoic deposits are within the modern trans mexican chiapenecan volcanic arc thirty three of the deposits lie within a long narrow belt that continues into arizona and new mexico and widens from 100 km to over 300 km in the region of maximum extension in the southern basin and range province eighty five percent of the deposits were emplaced during the eastward transgression of the cordilleran volcanic arc in middle cretaceous through eocene time the occurrence of the porphyry copper deposits of mexico appears to be independent of the terrane intruded and the copper content of the wall rocks where the wall rocks predate the volcanic arc which is syngenetic with the porphy

dating the giant zhuxi w cu deposit taqian fuchun ore belt in south china using molybdenite re os and muscovite ar ar system abstract the recently discovered zhuxi w cu ore deposit is located within the taqian fuchun ore belt in the southeastern edge of the yangtze block south china its inferred tungsten resources based on new exploration data are more than 280 mt by 2016 at least three paragenetic stages of skarn formation and ore deposition have been recognized prograde skarn stage retrograde stage and hydrothermal sulfide stage secondly greisenization marmorization and hornfels formation are also observed scheelite and chalcopyrite are the dominant metal minerals in the zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding carboniferous carbonate sediments huanglong and chuanshan formations and the neoproterozoic slate and phyllites the scheelite was mostly precipitated during the retrograde stage whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage a muscovite 40ar 39ar plateau age of about 150 ma is interpreted as the time of tungsten mineralization and molybdenite re os model ages ranging from 145 9 2 0 ma to 148 7 2 2 ma for the subsequent hydrothermal sulfide stage of activity as the time of the copper mineralization our new molybdenite re os and muscovite 40ar 39ar dating results along with previous zircon u pb age data indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 myr from 150 6 1 5 to 145 9 1 ma and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite the new ages reported here confirm that the zhuxi tungsten deposit represents one of the mesozoic magmatic hydrothermal mineralization events that took place in south china in a setting of lithospheric extension during the late jurassic 160 150 ma it is suggested that mantle material played a role in producing the zhuxi w cu mineralization and associated magmatism

assessment of the 187re decay constant by cross calibration of re os molybdenite and u pb zircon chronometers in magmatic ore systems the past decade has seen renewed interest in 187re 187os geochronology using a variety of matrices including sulfide minerals shales and meteorites the most widely used value of the 187re decay constant 187re is 1 666 0 005 10 11 a 1 0 31 which is based on cross calibration of re os and pb pb chronometers for certain meteorites smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 however other recent studies have yielded alternate values of 187re based upon either direct counting experiments or analysis of meteorites here we provide an independent assessment of 187re using methodology sample materials and preparation of os standard solutions different from those of smoliar et al 1996 combining re os age data for molybdenite formed in magmatic ore deposits with the u pb zircon age of the magmatic rocks a refined 187re value is determined by averaging 11 individual cross calibration experiments spanning ca 2700 ma of earth history using the u decay constants of jaffey jaffey a h flynn k f glendenin l e bentley w c and essling a m 1971 precision measurement of half lives and specific activities of 235u and 238u phys rev 4 1889 1906 a value for 187re of 1 6668 0 0034 10 11 a 1 is determined using the 238u value of jaffey et al 1971 and 235u value of schoene schoene b crowley j l condon d j schmitz m d and bowring s a 2006 reassessing the uranium decay constants for geochronology using id tims u pb data geochim cosmochim acta 70 426 445 a value for 187re of 1 6689 0 0031 10 11 a 1 is determined these values are nominally higher ca 0 1 and ca 0 2 than the value determined by smoliar et al smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 but within calculated uncertainty further refinement of 187re by cross calibrating the molybdenite and u pb zircon chronometers should be possible by utilizing high precision single grain chemical abrasion zircon u pb analyses

prehistoric dates of the most recent alpine fault earthquakes new zealand we use four methods to investigate the earthquake history over the past 600 yr of the central alpine fault new zealand trenches across the active fault trace at five locations identify two ruptures on the fault in the past 450 yr three other indirect indicators episodes of landsliding and aggradation dated either via 14 c or from forest establishment on the resulting surfaces and tree ring growth anomalies provide further evidence for these two earthquakes and a greater resolution in estimates of their timing and extent the most recent earthquake occurred in a d 1717 and the rupture extended over a section of fault between milford and the haupiri river a distance of 375 km about 1630 another earthquake occurred on the fault and this extended between at least the paringa and ahaura rivers 250 km regional episodes of landsliding and forest establishment provide evidence for a third earthquake at about 1460 over the same section of fault the pattern of earthquake recurrence is not regular but averages 200 yr and varies from 100 yr to at least 280 yr which is the lapsed time since the most recent rupture

geology and geochronology of the xilamulun molybdenum metallogenic belt in eastern inner mongolia china the xilamulun molybdenum metallogenic belt located in eastern inner mongolia china has great economic potential as a major producer of molybdenum four major types of mo deposits have been recognized in the xilamulun molybdenum metallogenic belt porphyry quartz vein volcanic hosted and greisen these mesozoic mo deposits are closely related to si and k rich intrusives and are usually hosted by granite plutons or located at the endo or exo contact zones of the granite porphyry shrimp zircon u pb dating gives the emplacement ages of the intrusions related to mo mineralization as 245 1 4 4 152 4 1 6 and 139 1 2 3 ma re os analysis of five molybdenite samples from the chehugou porphyry mo deposit yields an isochron age of 245 5 ma 2 indicating that the mineralization age of the porphyry mo deposit is about 245 ma re os analyses of six molybdenite samples from the nianzigou quartz vein type mo deposit yield an isochron age of 154 3 3 6 ma 2 constraining the mineralization age of the quartz vein mo deposit to 154 ma our results suggest that the mo mineralization in the xilamulun belt formed during at least three stages i e the triassic late jurassic and early cretaceous and is coeval with the granitic magmatism the corresponding geodynamic background covers the syncollision between the north china and siberian plates during the early to middle triassic a compression setting related to the subduction of the paleo pacific plate during the jurassic and lithospheric thinning during the early cretaceous in eastern china

characteristics and 40ar 39ar geochronology of the erdenet cu mo deposit mongolia the early to middle triassic erdenet porphyry cu mo deposit in northern mongolia developed in a continent continent arc collision zone within the central asian orogenic belt the porphyry system is related to multiple intrusions of crystal crowded biotite granodiorite porphyry which formed a composite stock about 900 m in diameter with multiple porphyritic microgranodiorite dikes wall rocks are late permian to early triassic medium grained granodiorite with similar whole rock geochemistry mineralogy and composition to the granodiorite porphyry whole rock analysis of the granodiorite porphyry and wall rocks shows that these rocks cannot be discriminated but both have depleted middle heavy rare earth elements and y typical of fertile porphyry magmatic suites at the current pit level 1 250 m elev early porphyry style quartz veins a and b type are locally infilled by pyrite chalcopyrite with subordinate bornite but most of the chalcopyrite occurs in d veins that constitute more than 50 of the cu grade 0 5 wt cu the 0 3 wt cu shell resembles a molar tooth enveloping the granodiorite porphyry with deeper roots extending down the wal rock contacts molybdenite occurs in monomineralic veins and in finely laminated to massive quartz molybdenite veins the most important alteration is quartz muscovite which occurs as relatively coarse 100 500 m alteration selvages 1 5 cm that envelop d veins the d veins cut illite kaolinite smectite or intermediate argillic alteration intermediate argillic alteration together with abundant pink anhydrite commonly hydrated to gypsum extends from at least 1 300 to 900 m elevation in the deepest drill holes and has overprinted early potassic alteration or relatively unaltered red granodiorite meter wide zones of kaolinite cut the anhydrite gypsum at all levels there is an abrupt transition outward from the intermediate argillic alteration to chlorite epidote propylitic alteration at 50 to 200 m from the granodiorite porphyry contact although d veins and chalcopyrite extend outward to the propylitic zone the erdenet porphyry system was overprinted by advanced argillic alteration which outcrops 2 km northwest of the pit and forms a lithocap that extends over 10 2 5 km it is characterized by residual quartz andalusite na ca and k alunite diaspore pyrophyllite zunyite topaz dickite and kaolinite the upper part of the porphyry cu mo deposit removed by mining comprised a bornite chalcocite enriched zone up to 300 m thick with an average grade of 0 7 wt cu and up to 5 wt cu locally based on hypogene bornite chalcocite mineral textures and high sulfidation state mineralogy the enriched zone is inferred to be of hypogene origin but modified by supergene processes consequently it may be related to formation of the lithocap previous re os dates of 240 4 and 240 7 0 8 ma for molybdenite in quartz veins are comparable to new 40 ar 39 ar dates of 239 7 1 6 and 240 2 ma for muscovite that envelops d veins one 40 ar 39 ar date on k alunite from the lithocap of 223 5 1 9 ma suggests that it may be about 16 m y younger than erdenet but this result needs to be verified by further dating

characteristics of the late devonian tsagaan suvarga cu mo deposit southern mongolia the late devonian tsagaan suvarga deposit 255 mt at 0 55 cu 0 02 mo is located on the nw margin of the tsagaan suvarga complex tsc which extends ene over 15 10 km and comprises mainly medium grained equigranular hornblende biotite quartz monzonite and monzodiorite distinct mineralized intrusions are inferred from distribution of cu mo mineralization but are not clearly discernible the tsagaan suvarga complex is a window within carboniferous volcanic and sedimentary rocks and wall rocks to the tsc are not known or exposed in the nearby district whole rock analyses and sr nd isotopes 87sr 86sr0 0 7027 to 0 7038 n 12 and end0 4 26 to 2 77 n 12 show that the granitoids are subduction related i type high k calc alkaline to shoshonitic series and derived from a mantle source they exhibit fractionated light rare earth elements without depleted eu and depleted middle heavy rare earth elements and y typical of oxidized fertile porphyry magmatic suites early porphyry style quartz veins include a and b type molybdenite occurs in monomineralic veins 1 5 mm or a veins copper mineralization occurs mainly as chalcopyrite and subordinate bornite disseminated and associated with quartz muscovite veins pyrite vol content is less than chalcopyrite and bornite combined deep oxidation to about 50 m depth has formed zones of malachite and covellite in late fractures the most important alteration is actinolite biotite chlorite magnetite replacing hornblende and primary biotite quartz k feldspar alteration is minor late albite replaces primary k feldspar and enhances sodic rims on plagioclase crystals quartz muscovite or sericitic alteration overprints actinolite biotite and porphyry type quartz veins field observations and petrographic studies suggest that the bulk of the chalcopyrite bornite mineralization at the tsagaan suvarga formed together with coarse muscovite alteration

geodynamics and metallogeny of the central eurasian porphyry and related epithermal mineral systems a review abstract major porphyry cu au and cu mo deposits are distributed across almost 5000 km across central eurasia from the urals mountains in russia in the west to inner mongolia in north eastern china these deposits were formed during multiple magmatic episodes from the ordovician to the jurassic they are associated with magmatic arcs within the extensive subduction accretion complex of the altaid and transbaikal mongolian orogenic collages that developed from the late neoproterozoic through the palaeozoic to the jurassic intracratonic extension the arcs formed predominantly on the palaeo tethys ocean margin of the proto asian continent but also within two back arc basins the development of the collages commenced when slivers of an older proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the palaeo tethys ocean margin of the combined eastern europe and siberian cratons subduction of the palaeo tethys ocean beneath the karakum and altai tarim microcontinents and the associated back arc basin produced the overlapping late neoproterozoic to early palaeozoic tuva mongol and kipchak magmatic arcs contemporaneous intra oceanic subduction within the back arc basin from the late ordovician produced the parallel urals zharma magmatic arc and separated the main khanty mansi back arc basin from the inboard sakmara marginal sea by the late devonian the tuva mongol and kipchak arcs had amalgamated to form the kazakh mongol arc by the mid palaeozoic the two principal cratonic elements the siberian and eastern european cratons had begun to rotate relative to each other drawing in the two sets of parallel arcs to form the kazakh orocline between the two cratons during the late devonian to early carboniferous the palaeo pacific ocean began subducting below the siberian craton to form the sayan transbaikal arc which expanded by the permian to become the selanga gobi khanka arc by the middle to late permian as the kazakh orocline continued to develop both the sakmara and khanty mansi back arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes during the permian and triassic the north china craton approached and docked with the continent closing the mongol okhotsk sea an embayment on the palaeo pacific margin to form the mongolian orocline subduction and arc building activity on the palaeo pacific ocean margin continued to the mid mesozoic as the indosinian and yanshanian orogens significant porphyry cu au mo and au cu deposits were formed during the ordovician in the kipchak arc e g bozshakol cu au in kazakhstan and taldy bulak porphyry cu au in kyrgyzstan silurian to devonian in the kazakh mongol arc e g nurkazgan cu au in kazakhstan and taldy bulak levoberezhny au in kyrgyzstan devonian in the urals zharma arc e g yubileinoe au cu in russia devonian in the kazakh mongol arc e g oyu tolgoi cu au and tsagaan suvarga cu au in mongolia carboniferous in the kazakh mongol arc e g kharmagtai au cu in mongolia tuwu yandong cu au in xinjiang china koksai cu au kounrad cu au and the aktogai group of cu au deposits in kazakhstan carboniferous in the valerianov beltau kurama arc e g kal makyr dalnee cu au in uzbekistan benqala cu au in kazakhstan late carboniferous to permian in the selanga gobi khanka arc e g duobaoshan cu au in inner mongolia china triassic in the selanga gobi khanka arc and jurassic in the selanga gobi khanka arc e g wunugetushan cu mo and jiguanshan mo in inner mongolia china in addition to the tectonic geologic and metallogenic setting and distribution of porphyry cu au mo mineralisation within central eurasia the setting geology alteration and mineralisation at each of the deposits listed above is described and summarised in table 1

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

role of fluids in the metamorphism of the alpine fault zone new zealand models of fluid rock interaction in and adjacent to the alpine fault in the hokitika area south island new zealand were investigated using hydrogen and other stable isotope studies together with field and petrographic observations all analysed samples from the study area have similar whole rock d values dwr 56 to 30 average 45 n 20 irrespective of rock type degree of chloritization location along the fault or across strike distance from the fault in the garnet zone the green chlorite rich fault rocks which probably formed from australian plate precursors record nearly isothermal fluid rock interaction with a schist derived metamorphic fluid at high temperatures near 450 500 c d of water in equilibrium with the green fault rocks dh2o green 18 d of water in equilibrium with the greyschists and greyschist derived mylonites dh2o grey 19 at 500 c dh2o green 17 dh2o grey 14 at 450 c there is no indication of an influx of a meteoric or mantle derived fluid in the alpine fault zone in the study area the alpine fault zone at the surface shows little evidence of late stage retrogression or veining which might be attributed to down temperature fluid flow it is probable that prograde metamorphism in the root zone of the southern alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the alpine fault up to the surface owing to the combined effects of the fault the disturbed isotherms under the southern alps and the brittle ductile transition such fluids could mix with meteoric fluids to deposit quartz rich possibly gold bearing veins in the region c 5 10 km back from the fault trace these results and interpretations are consistent with interpretations of magnetotelluric data obtained in the south island geophysical transects sight programme

semi brittle deformation within the alpine fault zone new zealand abstract this paper reports the results of an attempt to identify the deformation micromechanisms in the brittle ductile transition zone of the alpine fault new zealand characterization of sequentially developed microstructures was carried out using optical microscopy hvem and stem analysis it was found that the transition zone corresponds to a broad zone of retrogression produced initially by microcracking and fluid infiltration the non catastropic nature of the fracturing indicates that fluid enhanced sub critical cracking is a significant crustal deformation mechanism after the initial phase of retrogression both ductile and brittle processes coexist and cyclically alternate in response to stress cycling the relative importance of macroscopic brittle processes may decrease with time as more ductile minerals especially phyllosilicates develop during continued retrogression

u pb 39ar 40ar geochronology of the metamorphosed volcanic rocks of the bainaimiao group in central inner mongolia and its implications for ore genesis and geodynamic setting abstract the greenschist facies volcano sedimentary sequence of the bainaimiao group in central inner mongolia hosts the bainaimiao cu mo au deposit and the bainaimiao lode gold deposit but the ore classification and genetic process of the bainaimiao cu mo au deposit is still disputed in this study we have selected the interbedded metamorphosed volcanic rocks of the bainaimiao group for la icp ms zircon u pb analysis 17 analyses form a tight cluster on the concordia and yield a weighted mean 206 pb 238 u age of 465 1 ma 95 confidence level mswd 0 95 n 17 which represents the best estimate of the crystallization age of the volcanic rocks of the bainaimiao group biotite from the greenschist of the bainaimiao group yielded a well defined plateau with an age of 429 2 4 1 ma the inverse isochron age is 429 1 4 2 ma with an elevated 40 ar 36 ar i ratio of 299 9 22 7 which represents the time of regional greenschist facies metamorphism previous studies showed that the re os isochron age of the molybdenite from the bainaimiao cu mo au deposit is 445 0 3 4 ma and the mineralized granodiorite porphyry yielded a weighted mean 206 pb 238 u age of 445 6 ma these data indicate that the bainaimiao volcanic rocks were formed at about 465 ma and the porphyry cu mo au mineralization took place at about 445 ma volcanic rock emplacement is 20 ma older than the cu mo au mineralization indicates it is a porphyry deposit rather than vms deposit the dynamic setting for the porphyry mineralization is the paleo asian oceanic plate subduction along the northern margin of the north china craton in early paleozoic subsequently the collision between the bainaimiao arc and the north china craton led to regional metamorphism and deformation at about 430 ma and the old porphyry system may have been overprinted during this metamorphic process

zircon u pb geochronology geochemistry and sr nd hf isotopes of granitoids in the yulekenhalasu copper ore district northern junggar china petrogenesis and tectonic implications abstract the yulekenhalasu porphyry copper deposit is located in the kalaxiange er metallogenic belt in northern junggar china we present the results from zircon u pb geochronology and geochemical and sr nd hf isotope analyses of the granitoids associated with the ore deposits with a view to constrain their petrogenesis and tectonic setting the granitoids consist of quartz diorite diorite porphyry porphyritic monzonite and quartz porphyry emplaced at 382 379 375 374 and 348 ma respectively which span late devonian to early carboniferous ages the ore bearing intrusion is mainly diorite porphyry with subordinate porphyritic monzonite the late devonian intrusions are characterized by sio2 contents of 54 5 64 79 wt na2o contents of 3 82 8 24 wt enrichment in na light rare earth elements lrees and large ion lithophile elements they also display relative depletion in y ba p nb ta and ti and weak negative eu anomalies eu 0 6 0 87 the early carboniferous quartz porphyry is characterized by high sio2 content 72 26 73 35 wt enrichment in lrees k and sr and relative depletion in y 10 82 12 52 ppm and yb 1 06 1 15 ppm the late devonian and early carboniferous granitoids are characterized by positive end t values 5 2 10 1 one sample at 1 9 positive ehf t values 7 46 18 45 low 87sr 86sr i values 0 70363 0 70476 and young crustal residence ages these data indicate that the sources of the granitoids were mainly mantle derived juvenile rocks geochemical and nd sr hf isotopic data demonstrate that the late devonian granitoids formed in an oceanic island arc and they were formed from different sources among which the mineralized diorite porphyry might have originated from a mixed slab derived and mantle wedge melt source the early carboniferous quartz porphyry was likely emplaced in a mature island arc environment and was probably derived from juvenile crust

the oyut ulaan volcanic group stratigraphy magmatic evolution and timing of carboniferous arc development in se mongolia abstract the palaeozoic mesozoic tectonic evolution of central asia including the vast terrane collage that makes up mongolia has been a topic of considerable debate the oyut ulaan volcanic group is a sequence of volcanic and sedimentary rocks in se mongolia that forms the southern part of the devonian permian saykhandulaan inlier fieldwork traverses and mapping have established four distinct formations in the oyut ulaan volcanic group that record the nature of arc activity in part of the central asian orogenic belt during the carboniferous physical volcanological and sedimentological characteristics of the four formations suggest three clear eruptive styles 1 periodic andesite volcanism in an actively eroding arc setting that also contained large rivers and swamps 2 highly effusive plateau andesite volcanism 3 explosive rhyolitic effusion geochemical analyses of volcanic lithologies suggest that the group represents subduction related mature continental arc volcanism geochemical results document an evolving magma system to which surface processes of the volcano sedimentary model may be linked magma pulses and replenishments are identified from variations in chemostratigraphy newly obtained zircon ages from the volcanic succession fix its emplacement eruption at 323 0 0 7 ma mid carboniferous or late mississippian a granite cobble from the lower part of the oyut ulaan volcanic group gives a u pb zircon age of 338 9 0 4 ma indicating that arc plutons were emplaced 10 ma prior to the oyut ulaan volcanism and were eroded soon after our work provides timing constraints for final accretion and continental assembly in se mongolia and also sheds light on the petrological development of a magmatic arc system within an evolving accretionary orogen

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment

the structure of an exhumed intraplate seismogenic fault in crystalline basement abstract the 600 m thick gole larghe fault zone glfz is hosted in jointed crystalline basement and exposed across glacier polished outcrops in the italian alps ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes solidified frictional melts formed at 9 11 km depth and ambient temperatures of 250 300 c previous work focused on the southern part of the fault zone here we quantitatively document fault zone structure across the full width of the glfz and surrounding tonalite host rocks by using a combination of structural line transects and image analysis of samples collected across fault strike these new datasets indicate that the glfz has a broadly symmetric across strike damage structure and contains distinct southern central and northern zones distinguished by large variations in fracture density distribution of pseudotachylytes volume of fault rock materials and microfracture sealing characteristics the c 100 m wide central zone is bound by two thick 2 m and laterally continuous 1 km protocataclastic to ultracataclastic horizons within and immediately surrounding the central zone fracture density is relatively high due to cataclastic fault fracture networks that reworked earlier formed pseudotachylytes the fault fracture networks were associated with pervasive microcracking and fluid rock interaction resulting in the development of a c 200 m thick alteration zone delimited by lobate fluid infiltration fronts in the c 250 m thick southern and northern zones fracture densities are much lower and pseudotachylytes systematically overprint cataclastic faults that exploited pre existing magmatic cooling joints analysis of the structure of the glfz suggests that it shares certain characteristics with the seismogenic source responsible for the 2002 au sable forks intraplate earthquake sequence in the northeastern usa including seismicity distributed across a fault zone 500 1000 m thick and large 100 mpa static stress drops associated with frictional melting

the upper crustal structure of the qiangtang basin revealed by seismic reflection data abstract the qiangtang basin located in central tibet is a thick and widely developed jurassic marine sedimentary stratum and it is the largest marine basin on the chinese mainland without a breakthrough in oil or gas exploration various forms of crustal movement related to the convergence between the eurasian and indian plates in the cenozoic have played significant roles in the formation and preservation of the oil and gas resources of the qiangtang basin to determine the shallow crustal structure of the qiangtang basin and forecast its prospects for oil and gas extraction we reprocessed the seismic reflection data 0 6 s twt from 11 reflection sections acquired at different times by different groups and connected them to form a 350 km shallow seismic reflection profile across the qiangtang basin this profile provides reliable data on the north to south changes of the basement and the upper crustal structures of the qiangtang basin we speculated that the reflective events at 3 4 s twt in the qiangtang basin represent the paleozoic basement which runs shallow beneath the central anticline the location of the proterozoic basement was determined from the discontinuous reflection events at approximately 4 5 s twt the data indicate that the basements of the qiangtang basin are deeper in the south and shallower in the north the shallow crustal deformations approximately 0 3 s twt are quite different between the north and south qiangtang basin in the north qiangtang basin there are strong fold deformations alternating between uplifts and depressions while the deformations are relatively flat in the south qiangtang basin continuous arc reflections interpreted as paleozoic strata were found beneath the central anticline of the qiangtang block a half graben on the north side of the central anticline represents a possible location for oil and gas resources

the geology and re os geochronology of the palaeoproterozoic vaikijaur cu au mo porphyry style deposit in the jokkmokk granitoid northern sweden the vaikijaur cu au mo deposit is located in the ca 1 88 ga calc alkaline jokkmokk granitoid near the archaean proterozoic palaeoboundary within the fennoscandian shield of northern sweden the skellefte vms district lies immediately to the south and the northern norrbotten fe oxide cu au deposits to the north the vaikijaur deposit occupies an area of 2 3 km within the jokkmokk granitoid and includes stockwork quartz sulphide veinlets and disseminated chalcopyrite pyrite gold molybdenite magnetite and pyrrhotite porphyritic mafic dykes were emplaced along fractures in a ring dyke pattern the jokkmokk granitoid dykes and the mineralized area are foliated indicating that mineralization predated the main regional deformation the mineralized area is characterized by strong potassic alteration phyllic and propylitic alteration zones are also present a pyrite rich inner core is surrounded by a concentric zone with pyrite chalcopyrite and gold molybdenite is distributed irregularly throughout the chalcopyrite zone geophysical data indicate a strongly conductive central zone in the mineralized area bordered by conductive and high magnetic zones five high precision re os age determinations for three molybdenite occurrences from outcrop and drill core samples constrain the age of porphyry style cu au mo mineralization to between 1889 10 and 1868 6 ma a younger molybdenite is associated with a much later metamorphic event at about 1750 ma these data suggest that primary porphyry style mineralization was associated with calc alkaline magmatism within the archaean proterozoic boundary zone at ca 1 89 1 87 ga