timing and origin of multi stage magmatism and related w mo pb zn fe cu mineralization in the huangshaping deposit south china an integrated zircon study abstract the huangshaping deposit south china is closely related to hypabyssal granites e g quartz porphyry granophyre and granite porphyry developing massive skarn type w mo fe polymetallic mineralization skarn type pb zn cu mineralization and vein type pb zn cu mineralization to better constrain the geochronology fluid composition magma source metallogenic affinity and source of ore forming materials in the huangshaping deposit morphological textural in situ geochronological compositional and lu hf isotopic studies on zircons hosted in granitoids skarns ores and wall rocks have been carried out overall five types of zircons are identified low u magmatic abbreviated as lumz high u magmatic humz hydrothermally altered metamict haz inherited and detrital types round shaped inherited and detrital zircons with low trace element compositions are rarely captured in the granite porphyry and largely hosted in sulfide skarn ores and wall rocks the humz are mainly observed in the granophyre and are easily distinguished from lumz by their much higher u th and y contents black cl images and stronger eu anomalies in addition the crystallization time of humz was later than that of lumz the haz uniquely exists in granite porphyry and genetic related skarns with cracked and porous textures and strong enrichment of many trace elements these zircons were originally humz that have undergone rapid partial metamictization and subsequent fluid zircon interaction this study demonstrates that the granophyre is a two stage intrusion with ages of 179 0 3 ma and 163 0 7 ma whereas the granite porphyry yields younger ages of 157 0 5 ma the discovery of triassic inherited zircons in the latter leads us to propose the presence of a concealed triassic pluton 220 ma the zircon populations of w mo fe mineralized garnet skarns are mainly composed of 160 and 180 ma magmatic zircons whereas magnetite skarn ores contain both magmatic zircons 50 and inherited zircons 50 in contrast inherited zircons are the dominant zircon population of the skarn pb zn ores this may indicate that the granite porphyry the foremost one and granophyre mostly contributed to the skarn type w mo fe mineralization whereas the carboniferous and devonian carbonate strata significantly contributed to the skarn type pb zn cu mineralization fluids separated from the granite porphyry that modified the zircons are likely the principal ore forming fluids which are enriched in f u th y ree nb ta hf ca p ti pb w mo and fe zircon hf isotopes suggest that these magmas at least the granophyre and granite porphyry were generated by reworking of mesoproterozoic crustal rocks without significant input of mantle materials this study highlights the use of different types and generations of zircons from variable rock types to reveal fluid compositions and mineralization potentials in complex metallogenic systems

holocene evolution of phra thong s beach ridge plain thailand chronology processes and driving factors abstract beach ridge plains are a common morphological element of coastal areas all over the world while morphological depressions of beach ridge plains swales may function as archives for deposits of extreme wave events the ridges are not only used as an indicator for coastal evolution but also to reconstruct the processes that are responsible for their formation in this study the morphological sedimentary and chronological structure of the beach ridge plain on phra thong island was used as an archive for the temporally and spatially complex pattern of shoreline changes during the holocene the presence of three spatio temporal ridge plain units separated by episodes of shoreline erosion and characterised by varying directions and rates of shoreline progradation reveals six distinct phases of island evolution within the last 6000 years unit i was deposited during phase 1 5500 4000 years ago with high progradation rates of 2 1 2 5 m year subsequent to a short episode of erosion during phase 2 4000 3800 years ago fast shoreline progradation at a rate of 2 7 m year unit iia occurred once again in phase 3 3800 3300 years ago after 3300 years ago the sedimentation rate decreased to less than 1 m year resulting in the formation of unit iib during phase 4 3300 1500 years ago in phase 5 between 1500 and 800 years ago ridge plain formation was once more interrupted by significant shoreline erosion finally over most of the last 800 years during phase 6 slow shoreline progradation led to the formation of unit iii this evolution is best explained by the interaction of long term sea level change wave climate episodic events tsunamis and storms and local sediment supply however the linkage of successive ridge and swale formation changing progradation rates and switch over between phases of erosion and deposition with its trigger mechanisms remains speculative since i the processes involved vary locally and are poorly understood for phra thong island and ii even our comparably large dataset cannot reconstruct the complex spatial and temporal pattern of shoreline evolution without significant uncertainties this implies that interpretations of ridge plains based on small datasets might be too generalised to capture the real complexity of the system and as a consequence might lead to incorrect conclusions about palaeoenvironmental conditions

evidence for a transgressive barrier within a regressive strandplain system implications for complex coastal response to environmental change clastic depositional strandplain systems have the potential to record changes in the primary drivers of coastal evolution climate sea level and the frequency of major meteorological and oceanographic events this study seeks to use one such record from a southern brazilian strandplain to highlight the potentially complex nature of coastal sedimentological response to small changes in these drivers following a 2 to 4 m highstand at ca 5 8 ka in southern brazil falling sea level reworked shelf sediment onshore forcing coastal progradation smoothing the irregular coastline and forming the 5 km wide pinheira strandplain composed of ca 500 successive beach and dune ridges sediment cores grab samples and 11 km of ground penetrating radar profiles reveal that the strandplain sequence is composed of well sorted fine to very fine quartz sand since the mid holocene highstand the shoreline prograded at a rate of ca 1 to 2 m yr 1 through the deposition of a 4 to 6 m thick shoreface unit a 1 to 3 m thick foreshore unit containing ubiquitous ridge and runnel facies and an uppermost beach and foredune unit however the discovery of a linear 100 m wide barrier ridge with associated washover units a 3 to 4 m deep lagoon and 250 m wide tidal inlet within the strandplain sequence reveals a period of shoreline transgression at 3 3 to 2 8 ka during the otherwise regressive developmental history of the plain the protected nature of pinheira largely buffered it from changes in precipitation patterns wave energy and fluvial sediment supply during the time of its formation however multiple lines of evidence indicate that a change in the rate of relative sea level fall probably due to either steric or ice volume effects may have affected this coastline thus whereas these other potential drivers cannot be fully discounted this study provides insights into the complexity of decadal scale to millennial scale coastal response to likely variability in sea level change rates

intra shoreface erosion in response to rapid sea level fall depositional record of a tectonically uplifted strand plain pacific coast of japan this study documents lowering of the surf zone i e the upper shoreface leading to intra shoreface erosion following two rapid relative sea level falls along a tectonically uplifted coast during the holocene and the characteristics of the resultant prograding shoreface deposits these findings are based on high resolution analysis and radiocarbon dating of three new drill cores obtained from the kujukuri strand plain pacific coast of eastern japan combined with previously published borehole data and information on modern shoreline profile adjustments a shallowing upward sandy succession composed of lower and upper shoreface facies foreshore and backshore facies was recognized in the drill cores two rapid falls in relative sea level at 2ae 3t o 2ae6 and 1ae 8t o 2ae0 ka are recorded by downstepping of the base of the foreshore facies and farther seawards by the lowering of an erosional boundary between the upper and lower shoreface facies superimposed bed profiles of an adjacent modern beach define an envelope the base of which reflects shore normal migration of longshore bars and troughs the base of the envelope represents an erosional surface that divides the surface mobile layer above from preserved deposits beneath the surface is concave upwards and steeper than the mean beach profile and exhibits a flat platform approximately at the lower limit of the upper shoreface equating to the storm surf zone the seaward transition of this surface rather than the mean equilibrium profile controls the metre scale to decimetre scale internal structure of the kujukuri shoreface deposits depositional models for sea level fall based on an exponential equilibrium profile do not adequately account for the presence and migration of longshore bars and troughs

mesozoic crustal growth in mainland southeast asia zircon u pb and hf isotopic evidence from the late cretaceous luyingtang granitic pluton in the northernmost se asian granite province sw china abstract the changning menglian suture in the sanjiang region of sw china the chiang rai line in thailand and the bentong raub suture in peninsular malaysia are marked by remnants of the paleo tethys oceanic lithosphere in mainland southeast asia we present u pb ages and hf isotopic compositions of zircon from luyingtang granites east of the changning menglian suture with the aim of identifying their sources and petrogenesis which are significant for understanding the crustal evolution of the mainland southeast asia the luyingtang granitic pluton is located in the northernmost se asian granite province sw china new zircon u pb ages indicate that the granites were emplaced in the late cretaceous in accordance with the regional scale inland magmatic event in mainland southeast asia petrographically the samples range from granodiorite biotite granite two mica granite to pegmatite the biotite granite two mica granite and pegmatite have low contents of tio2 al2o3 feo mgo cao and p2o5 but high values of sio2 and k2o compared to the granodiorite the granodiorite biotite granite and two mica granite invariably show enrichment in light rare earth elements lree the biotite granite and two mica granite show negative eu anomalies but the granodiorite displays weak eu anomaly the pegmatites show a clear tetrad effect and contain pronounced negative eu anomalies all the rocks demonstrate characteristic negative nb ta sr and ti anomalies and a positive pb anomaly when plotted on spidergrams most of the granites are characterized by positive ehf t values 0 3 8 and fairly young tdm2 ages 612 1094 ma suggesting they contain a significant proportion of juvenile component hf isotopic modelling shows that the luyingtang granites are likely to have been produced by partial melting of mixed sources which were probably of basalts in proportions of 50 70 and precambrian continental crust the emplacement of granites with such a large proportion of mantle derived component indicates crustal growth in mainland southeast asia during mesozoic in contrast one of the two mica granite samples displays negative ehf t values 7 6 to 3 and older tdm2 ages 1305 1599 ma which suggest a more crustal affinity the arc continent collision during the cretaceous may have induced foundering of an over thickened lithospheric mantle keel beneath the paleo tethys orogenic belt and then resulted to localized upwelling of asthenosphere mantle and basaltic underplating the parental magmas of the hinterland i type granites formed by melting of a mixed source containing both precambrian crust and mantle derived basalt followed by extensive magmatic differentiation

precise zircon shrimp u pb and quartz vein rb sr dating of mesozoic taoxikeng tungsten polymetallic deposit in southern jiangxi the taoxikeng tungsten deposit in central nanling region of south china consists of vein type ore bodies hosted in cambrian to jurassic strata and is closely related to mesozoic granitic intrusions wolframite is the dominant ore mineral intergrown with such gangue minerals as quartz feldspar phlogopite and muscovite the authors conducted zircon shrimp and quartz rb sr dating for the purpose of better understanding the timing and genesis of the mineralization zircon shrimp dating of two granite samples yielded ages of 158 7 3 9 ma and 157 6 3 5 ma rb sr analyses gave a well defined 87rb 86sr isochron with ages of 154 4 ma 157 3 ma and 161 4 ma compared with known molybdenite re os dating 154 ma it is found that the granite and the mineralization were formed at the same time these new data combined with available geochronological data from other major deposits in nanling region suggest that large scale w sn mo bi nb ta pb zn mineralization took place throughout central and eastern nanling region at 160 150 ma suggesting a geodynamic setting of crustal extension during the middle late jurassic transformation of tectonic regimes

u pb dating of serpentinization hydrothermal zircon from a metasomatic rodingite shell sudetic ophiolite sw poland abundant zircon grains were found within a metasomatic chlorite corrensite trioctahedral regularly interstratified chlorite smectite shell that surrounds rodingite from the jordanow gogolow jg serpentinite massif sudetic ophiolite bohemian massif the zircon grains bear two types of primary fluid inclusions containing either liquid co2 or aqueous solutions the inclusions were used to assign the p t conditions of the zircon formation 270 300 c ca 1 kbar using the crossed isochore method abraded single zircon grains give a u pb age of 400 4 3 ma which is interpreted as the age of zircon crystallization this zircon formed during rodingitization i e a metasomatic process directly connected with the serpentinization and thus provides the opportunity of direct dating of the early serpentinization process the zircon age from the jordanow gogolow massif is consistent with the crystallization age of metagabbro protoliths from the sudetic ophiolite as determined by oliver et al j geol soc lond 150 1993 355 a ce anomaly combined with the mineralogical record of greenschist facies metamorphism of the mafic rocks from sudetic ophiolite suggests that the sm nd whole rock isotopic data of pin et al lithos 21 1988 195 353 21 ma possibly characterize the age of later metamorphic event

genesis of the xianghualing sn pb zn deposit south china a multi method zircon study abstract the xianghualing sn pb zn deposit is situated near the center of the world class nanling w sn ore belt associated with the highly evolved laiziling granite of jurassic age previous studies focused mainly on geochemical and geochronological features of the mineralization related granite whereas research on the source evolution and geochronology of the ore forming fluids has been limited we carried out precise u pb dating trace element and hf isotopic analyses on magmatic and hydrothermally altered zircons from the skarn stage and sulfide stage ores in the xianghualing deposit zircon u pb dating results from the two ore forming stages show distinct geochronological populations the skarn stage ores contain mainly magmatic and hydrothermally altered zircons in three age clusters 150 ma 220 ma and 420 ma whereas the sulfide stage ores are characterized by abundant old detrital zircons ranging from 497 to 3409 ma with a peak at 800 1000 ma this pattern may indicate that magmatic hydrothermal events in the silurian and triassic were precursors to the main sn mineralization event in the jurassic when circulation of evolved fluids through older sedimentary rocks led to pb zn mineralization the jurassic zircons exhibit high trace element contents e g hf p y nb ta th u and low ti contents eu anomalies nb ta and th u ratios which imply that the laiziling magma experienced significant plagioclase biotite and muscovite fractional crystallization and that it interacted extensively with post emplacement f rich hydrothermal fluids the positive ce anomalies of these zircons ce ce 1 0 226 indicate that the magmatic hydrothermal fluids that led to the jurassic sn mineralization event were reducing the less negative ehf t values of triassic zircons 18 7 to 2 6 compared to the silurian zircons 14 6 to 2 3 suggest more limited interaction between the mantle and the magma source region the jurassic magmatic zircons in the skarns exhibit even more negative ehf t values 30 7 to 6 7 along with tdmc model ages ranging from 1627 to 3134 ma indicating that the jurassic magma was derived from partial melting of old continental crustal basement based on the combined study of zircons in the skarns and sulfide ores we propose a three stage ore genetic model for the xianghualing sn pb zn deposit

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

holocene sea level change on the southeast coast of australia a review a revised holocene sea level curve for the southeast coast of new south wales australia is presented based on a review of previously published geochronological results for fossil molluscs organi

quantifying rates of coastal progradation from sediment volume using gpr and osl the holocene fill of guichen bay south east south australia guichen bay on the south east coast of south australia faces west towards the prevailing westerly winds of the southern ocean the bay is backed by a 4 km wide holocene beach ridge plain with more than 100 beach ridges the morphology of the guichen bay strandplain complex shows changes in the width length height and orientation of beach ridges a combination of geomorphological interpretation shallow geophysics and existing geochronology is used to interpret the holocene fill of guichen bay six sets of beach ridges are identified from the interpretation of orthorectified aerial photographs the ridge sets are distinguished on the basis of beach ridge orientation and continuity a 2 25 km ground penetrating radar gpr profile across the beach ridges reveals the sedimentary structures and stratigraphic units the beach ridges visible in the surface topography are a succession of stabilized foredunes that overlie progradational foreshore and upper shoreface sediments the beach progrades show multiple truncation surfaces interpreted as storm events the gpr profile shows that there are many more erosion surfaces in the subsurface than beach ridges on the surface the width and dip of preserved beach progrades imaged by gpr shows that the shoreface has steepened from around 2 9 to around 7 5 the changes in beach slope are attributed to increasing wave energy associated with beach progradation into deeper water as guichen bay was infilled at the same time the thickness of the preserved beach progrades increases slightly as the beach prograded into deeper water using the surface area of the ridge sets measured from the orthophotography and the average thickness of upper shoreface foreshore and coastal dune sands interpreted from the gpr profile the volume of holocene sediments within three of the six sets of beach ridge accretion has been calculated combining optically stimulated luminescence osl ages and volume calculations rates of sediment accumulation for ridge sets 3 4 and 5 have been estimated linear rates of beach ridge progradation appear to decrease in the mid holocene however the rates of sediment accumulation calculated from beach volumes have remained remarkably consistent through the mid to late holocene this suggests that sediment supply to the beach has been constant and that the decrease in the rate of progradation is due to increasing accommodation space as the beach progrades into deeper water changes in beach ridge morphology and orientation reflect environmental factors such as changes in wave climate and wind regime

experimental investigation of h2o and cl solubilities in f enriched silicate liquids implications for volatile saturation of topaz rhyolite magmas to interpret the degassing of f bearing felsic magmas the solubilities of h2o nacl and kcl in topaz rhyolite liquids have been investigated experimentally at 2000 500 and 1 bar and 700 to 975 c chloride solubility in these liquids increases with decreasing h2o activity increasing pressure increasing f content of the liquid from 0 2 to 1 2 wt f and increasing the molar ratio of al na ca mg si small quantities of cl exert a strong influence on the exsolution of magmatic volatile phases mvps from f bearing topaz rhyolite melts at shallow crustal pressures water and chloride bearing volatile phases such as vapor brine or fluid exsolve from f enriched silicate liquids containing as little as 1 wt h2o and 0 2 to 0 6 wt cl at 2000 bar compared with 5 to 6 wt h2o required for volatile phase exsolution in chloride free liquids the maximum solubility of cl in h2o poor silicate liquids at 500 and 2000 bar is not related to the maximum solubility of h2o in chloride poor liquids by simple linear and negative relationships there are strong positive deviations from ideality in the activities of each volatile in both the silicate liquid and the mvp s plots of h2o versus cl in rhyolite liquids for experiments conducted at 500 bar and 910 930 c show a distinct 90 break in slope pattern that is indicative of coexisting vapor and brine under closed system conditions the presence of two mvps buffers the h2o and cl concentrations of the silicate liquids comparison of these experimentally determined volatile solubilities with the pre eruptive h2o and cl concentrations of five north american topaz and tin rhyolite melts determined from melt inclusion compositions provides evidence for the exsolution of mvps from felsic magmas one of these the cerro el lobo magma appears to have exsolved alkali chloride bearing vapor plus brine or a single supercritical fluid phase prior to entrapment of the melt inclusions and prior to eruption

last glacial coastal dunes in eastern australia and implications for landscape stability during the last glacial maximum abstract the last glacial maximum or lgm 25 000 15 000 yr b p has been recognized in australia as a period of increased dryness coolness continentality and windiness compared to earlier and later period enhanced aeolian activity during the lgm occurred in arid and semi arid regions of western central and eastern australia the east coast has been considered to have been better watered and vegetated however at a number of sites from tasmania to north queensland there is evidence for extensive aeolian instability of coastal sand deposits dating by radiocarbon and thermoluminiscence techniques has supported morphologic and stratigraphic evidence of dune formation during the lgm under the influence of westerly offshore winds in the southern sector of the east coast i e south of 31 s latitude and southeast winds to the north it is now apparent that vegetation cover on sandy surfaces was quite patchy during the lgm sand surface instability under conditions of strong west or southeast winds promoted linear and or parabolic dune development this suggests greater concentration of forests in more discrete protected sites along the eastern escarpment than was previously considered by palaeoecologists more widespread drier and cooler climatic conditions operated even in coastal regions on expanded continental shelves at this time stabilization of areas of active dunes became more likely as sea levels rose reduced windiness occurred and precipitation increased as sea surface temperatures began to rise in the holocene

a tentative discussion on differences between large scale tungsten and tin mineralizations in south china both tungsten and tin are the most prevailing mineral resources in china large scale tungsten and tin mineralizations took place mostly in south china especially in the nanling mountains and the neighboring areas the two elements are very closely related to and accompanied with each other and always occur together in most ore deposits however differences do exist between tungsten and tin mineralizations in many aspects spatial distribution shows that the eastern sector of the nanling mountains is characterized by strong and dense w mineralization while sn mineralization becomes stronger westwards china s two largest sn ore deposits are distributed in the western margin of the south china fold system although both tungsten and tin mineralizations have the same highest ore forming epoch of 160 150 ma the tin mineralization is spanned from the late xuefeng period 800 ma to late yanshanian movement 80 ma the late yanshanian movement is in fact another highlight of tin mineralization the tin bearing granite and tin mineralization show much closer relationship with the participation of mantle derived materials than tungsten mineralization therefore the large scale tin mineralization took place either near the so called shi hang zone where long term deep faulting was activated and a type granites were emplaced or during the late yanshanian period when the south china continent was in a strong tensional geodynamic environment the principal factors responsible for these differences may include the diversity of geochemical properties between the two elements and the differences in tectonic backgrounds stratigraphic characteristics and magmatic activities between the eastern part and the western part of south china

formation of extremely f rich hydrous melt fractions and hydrothermal fluids during differentiation of highly evolved tin granite magmas a melt fluid inclusion study quartz crystals from topaz zinnwaldite albite granites from zinnwald erzgebirge germany contain in addition to primary and secondary fluid inclusions fis abundant crystalline silicate melt inclusions mis with diameters up to 200 m these mis represent various stages of evolution of a highly evolved melt system that finally gave rise to granite related sn w mineralization the combination of special experimental techniques with confocal laser raman microprobe spectroscopy and empa permits precise measurement of elevated contents of h2o f and b in re homogenized mis the contents of h2o and f were observed to increase from 3 to 30 and 1 9 to 6 4 wt respectively during magma differentiation however there is a second mi group very rich in h2o with values up to 55 wt h2o and an f concentration of approximately 3 wt ongoing enrichment of volatiles h2o f b and cl and of cs and rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus is suggested to reflect elemental abundances in natural magmas and not boundary layer melts partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements particularly sn the coexistence of two types of mis with primary fis indicates fluid saturation early in the history of magma crystallization connected with a continuous sequestration of sn f and b the results of this study provide additional evidence for the extraordinary importance of the interplay of h2o f and b in the enrichment of sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid

radiation effects in zircon the widespread distribution of zircon in the continental crust its tendency to concentrate trace elements particularly lanthanides and actinides its use in age dating and its resistance to chemical and physical degradation have made zircon the most important accessory mineral in geologic studies because zircon is highly refractory it also has important industrial applications including its use as a lining material in high temperature furnaces however during the past decade zircon has also been proposed for advanced technology applications such as a durable material for the immobilization of plutonium or when modified by ion beam irradiation as an optic waveguide material in all of these applications the change in properties as a function of increasing radiation dose is of critical importance in this chapter we summarize the state of knowledge on the radiation damage accumulation process in zircon

geological characteristics and re_os dating of molybdenites in hehuaping tin polymetallic deposit southern hunan province the hehuaping tin polymetallic deposit a large tin ore field newly discovered in southern hunan consists of skarn and cassiterite sulfide ores at present the controlled reserves amount to about 110 700 tons of tin 10 000 tons of bismuth 50 000 tons of lead and 10 000 tons of zinc with the advance of the exploration work four ore bodies have been explored which are located in the southeast portion of wangxianling indosinian gra nite pluton and hosted in granite granite porphyry and devonian limestone and sandstone respectively re os dating of molybdenites yields model ages between 223 3 2 9 and 225 2 2 7 ma and an isochron age of 224 0 1 9 ma for the skarn ore related to wangxianling granite indicating that w sn mineralization in southern hunan also took place in indosinian period the zircon shrimp u pb dating of the late granite porphyry is 142 3 ma the granite porphyry has been partly mineralized and altered and contains tin ore bodies all this implies that there existed late mineralization of yanshanian period in hehuaping area the early mineralization is supposed to correspond to underplating of the basic magma

refined insight into 40ar 39ar progressive crushing technique from k cl ar correlations in fluid inclusions abstract hydrothermal fluid activity associated with geological processes can now be dated by 40ar 39ar progressive crushing of minerals thanks to recent advances in high precision mass spectrometry however methods of data analysis and interpretation for these high resolution measurements still need to be refined in this study we report further insights into using k cl ar diagrams as tools for interpreting ages of secondary and primary fluids from 40ar 39ar stepwise crushing experiments three paragenetic mineral pairs of muscovite and wolframites from a southern china tungsten deposit were investigated using the 40ar 39ar technique through laser incremental heating and progressive crushing of single minerals incremental heating analyses of muscovites yielded flat age spectra defining plateau ages of 156 153 ma progressive crushing experiments of wolframites yielded anomalously old apparent ages due to excess 40ar however the apparent ages decline quickly after the initial steps and stabilize to form age plateaus of 156 153 ma without excess 40ar the plateau age steps interpreted as ages of gases derived from primary fluid inclusions pfis yield well defined isochrons with ages ranging from 157 to 153 ma and initial 40ar 36ar values that are indistinguishable from the modern atmospheric value digitally created 2d and 3d diagrams of k cl ar correlations can easily reveal distribution trends and correlation planes from the crushing steps interpretations of these diagrams further reveal the ages of secondary fluid inclusions sfis 87 to 83 ma and primary fluid inclusions pfis 159 to 150 ma raw data from sfis degassed during the initial crushing steps form scatters on inverse isochron plots however 2d and 3d k cl ar diagrams yield sfi ages that agree with 40ar 39ar ages of k feldspar veins cutting the tungsten ore bodies

internal structures and dating of complex zircons from meissen massif monzonites saxony abstract u pb zircon ages were determined for accessory zircons from two monzonites from the meissen massif northern bohemian massif germany by shrimp ion microprobe bse and cl imaging revealed that the monzonite zircons showing oscillatory growth zoning often contain inherited cores raman microprobe measurements showed that zoned rims u 277 1426 ppm th 144 910 ppm are slightly disordered to moderately metamict whereas cores have a wide spectrum of structural states from well crystallized to highly metamict the radionuclide u th content of cores varies from a few hundred to more than 20 000 ppm shrimp ion probe measurements on zoned rims interpreted as zircon growth during crystallization of the monzonite magma gave concordant carboniferous 206 pb 238 u ages of 326 6 ma monzonite from leuben and 330 5 ma monzonite from heidenschanze 95 confidence respectively these ages are consistent with recently published 40 ar 39 ar ages of 329 1 2 8 to 330 4 2 8 ma 2 on amphiboles from the same rocks in contrast shrimp measurements on cores range from slightly discordant proterozoic relic ages in low u and th cores to highly discordant data in the most metamict cores previously obtained 207 pb 206 pb ages single zircon evaporation technique in the range 340 16 to 357 16 ma 1 are probably mixed ages between magmatic and inherited zircon components the u pb ages of the monzonite zircons postdate the upper devonian lower carboniferous subduction and collision events in the area by about 20 ma due to their shoshonitic chemical signature which is typical of rocks from destructive plate boundary settings the meissen massif monzonites might be interpreted as originating during these 350 ma events and the earlier 207 pb 206 pb ages appeared to confirm this interpretation however both the 40 ar 39 ar ages and our current results show that only the enrichment of the lithospheric mantle source but not the monzonite intrusion itself was directly related to these events the monzonite intrusion itself took place 330 ma ago in the framework of strike slip tectonics in the elbe valley zone widely occurring zircon cores are indicative of crustal contamination of the magma causing considerable modification of chemical signatures trace element content of the monzonites

zircon records multiple magmatic hydrothermal processes at the giant shizhuyuan w sn mo bi polymetallic deposit south china abstract the supergiant shizhuyuan w sn mo bi polymetallic deposit is located in the nanling range and is intimately related to the qianlishan granite complex intruded during the late jurassic period the complex consists of three intrusive phases porphyritic biotite granite pbg equigranular biotite granite ebg and porphyritic granite dyke in this work the distinct geochemical features of magmatic and hydrothermally altered zircons from the qianlishan complex are used to reveal the magmatic hydrothermal evolution of the deposit whole rock geochemistry and mineralogy show that ebg samples have experienced stronger fractional crystallization than pbg samples zircon u pb dating constrains the intrusive episodes at 155 153 ma and 152 ma for the pbg and ebg respectively and subsequent hydrothermal events revealed by hydrothermal zircon ages at 154 153 ma and 152 150 ma hydrothermally altered zircon and paragenetic mineral inclusions from ebg samples show textures and compositional properties suggesting they were intensely altered by a zirconium saturated aqueous fluid type 1 enriched in most trace and metallogenic elements e g zr rees hf p u th nb ta ti pb al fe mg ca mn w and sn and volatiles f cl li co2 and h2o this fluid was relatively lower in temperature pressure and oxygen fugacity average ce4 ce3 11 2 type 2 fluid represented by hydrothermally altered zircons found in pbg was depleted in trace elements and had a relatively higher temperature and pressure and low fo2 ce4 ce3 2 12 29 16 type 3 fluid as evidenced by fluid altered zircons from the greisenized granite was likely a further evolved product of the type 2 fluid given its moderate cargo of most trace elements but also with exceedingly low ce4 ce3 values 2 9 33 45 the type 3 fluids might be precursors of w sn mineralizing fluids whereas the type 1 fluids were likely to represent mature ore forming fluids which were activated during the late skarn stage but before the retrograde mineralization stage compared with the fo2 of pbg and ebg magmas calculated by non altered magmatic zircons average ce4 ce3 31 47 and 49 21 it seems that the hydrothermal fluids generated by them became more reduced during the further evolution a progressive process can thus be divided pbg type 2 type 3 ebg type 1 with the gradual accumulation of ore forming materials the enrichment of most elements in hydrothermal zircons further indicates a substitution of y rees p hf u th ti nb ta ca k fe and mn for zr4 and si4 in the zircon lattice most fluid altered zircons exhibit a similar 176hf 177hf distribution range 11 to 6 but evidently elevated 176lu 177hf and 176yb 177hf ratios with magmatic ones this indicates that three types of hydrothermal fluids were magmatic derived whereas lu and yb were highly mobile during the hydrothermal event based on the results a magmatic hydrothermal evolution model is presented for shizhuyuan zircons this research highlights the use of zircon as a powerful tool in revealing the complex magmatic hydrothermal processes and perhaps mineralization potential in highly evolved granite associated mineralization systems

archaean hydrothermal zircon in the abitibi greenstone belt constraints on the timing of gold mineralisation abstract hydrothermal zircons have been found in archaean mesothermal au veins and altered wallrock selvages at val d or in the abitibi greenstone belt of canada the zircons are paragenetically associated with vein quartz tourmaline mica carbonate scheelite pyrite and gold zirconium mobility and the consequent occurrence of hydrothermal zircon may be associated with the intense tourmalinisation characteristic of archaean gold deposits in this district the shrimp ion microprobe has been used to analyse hydrothermal zircons from four separate mines spatially associated with the bourlamaque batholith and has yielded ages constraining formation of the au bearing vein systems to within 20 ma of emplacement of the pluton the ion microprobe data reveal multiple stages of hydrothermal zircon growth in the vein systems contemporaneous with the regional metamorphic peak and late kinematic activity along regional structures younger including proterozoic ages previously obtained for the veins using other minerals and isotopic schemes must reflect either alteration or renewed mineral growth during much later reactivation of fluids along the same structures up to 400 ma after initial formation of the veins

hydrothermal zircon and baddeleyite in val d or archean mesothermal gold deposits characteristics compositions and fluid inclusion properties with implications fortiming of primary gold mineralization zircon and baddeleyite occur within quartz tourmaline veins at four gold deposits in the val d or district of the archean abitibi southern volcanic zone host rocks have experienced intense metasomatic enrichment of zr hf y and rare earth elements the zircons contain primary inclusions of quartz tourmaline pyrite albite k mica scheelite and gold and gold occurs in primary fluid inclusions in zircons magmatic zircons in host rocks do not have this suite of inclusions consequently a wall rock inheritance model for the vein zircons is implausible compositionally the zircons feature pronounced interzone and intergrain variations of hf y yb th and u and sporadic anomalous ce contents of 1100 ppm distinct from magmatic counterparts two principal types of primary fluid inclusion occur in the vein zircons type 1 h2o co2 inclusions have low salinities variable quantities of co2 and homogenization temperatures of 260 380 c and type 2 co2 rich inclusions contain minor h2o and ch4 the vei

formation of phosphorus rich olivine in dar al gani 978 carbonaceous chondrite through fluid assisted metamorphism phosphorus rich olivine p 2 o 5 1 wt is a mineral that has been reported only in a few terrestrial and extraterrestrial occurrences previous investigations suggest that p rich olivine mainly forms through rapid crystallization from high temperature p rich melts here we report a new occurrence of p rich olivine in an ungrouped carbonaceous chondrite dar al gani dag 978 the p rich olivine in dag 978 occurs as lath shaped grains surrounding low ca pyroxene and olivine grains the lath shaped olivine shows a large variation in p 2 o 5 0 5 5 wt the p rich olivine grains occur in a chondrule fragment and is closely associated with chlorapatite merrillite feni metal and troilite tiny cr rich hercynite is present as inclusions within the p rich olivine the lath shaped texture and the association with cr rich hercynite indicates that the p rich olivine in dag 978 formed by replacing low ca pyroxene precursor by a p rich fluid during a thermal event rather than by crystallization from a high temperature melt the large variation of p 2 o 5 within olivine grains on micrometer scale indicates a disequilibrium formation process of the p rich olivine the occurrence of p rich olivine in dag 978 reveals a new formation mechanism of p rich olivine

accretionary tectonics of back arc oceanic basins in the south tianshan insights from structural geochronological and geochemical studies of the wuwamen ophiolite melange

the mobility of zirconium and other immobile elements during hydrothermal alteration abstract development of zircon and other zr phases in hydrothermal deposits indicates that zr can be highly mobile in these systems mobility is most common in but not restricted to f rich hydrothermal systems related to alkalic f rich igneous suites these suites can range from peralkaline through metaluminous to peraluminous a few examples are neither alkalic nor f rich three locations in the trans pecos magmatic province texas u s a demonstrate this hydrothermal zr mobility all three igneous systems are alkalic and f rich but vary in alkali al ratios peralkaline rhyolites and trachytes in the christmas mountains contain as much as 2100 ppm zr mostly in aegirine or arfvedsonite zircon is rare or absent fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38 000 ppm zr occurring as small disseminated zircons the deposits also are enriched in a variety of incompatible elements including be rare earth elements ree y nb mo hf pb th and u the sierra blanca intrusions a series of mildly peraluminous f rich rhyolite laccoliths contain as much as 1000 ppm zr mostly as zircon hydrothermal zircon occurs as overgrowths on magmatic grains as veinlets connected to overgrowths and in fluorspar replacement bodies in adjacent limestone the highest zr concentrations in fluorspar are 200 ppm metaluminous quartz monzonite from the infiernito caldera contains 400 600 ppm zr mostly as zircon euhedral zircon in quartz fluorite veins in the quartz monzonite indicates mobility of zr zirconium concentrations in the veins are unknown but the paucity of zircon suggests little zr enrichment relative to the host zircon and more rarely zirconolite occur in skarn in the ertsberg district of irian jaya indonesia unlike in texas related igneous rocks are metaluminous and the hydrothermal system was f poor worldwide hydrothermal zircon other zr phases and ti and al bearing phases occur in skarn epithermal precious metal veins volcanogenic massive sulfide deposits and mylonites we propose that differences in zr mineralogy of igneous source rocks is an important factor in determining the availability of zr to hydrothermal fluids although zr concentrations in the sierra blanca and christmas mountains rhyolites are similar zr enrichment in fluorspar was much greater in the christmas mountains we suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release zr but that zircon was only moderately attacked therefore far more zr was available for transport and subsequent deposition in the christmas mountains than at sierra blanca availability of other trace elements probably is also governed by their mineral host although zr mobility is most common in f rich hydrothermal systems related to alkalic and f rich igneous systems mobility at ertsberg may have been promoted by sulfate complexing

the zircon bearing chromitites of the phlogopite peridotite of finero ivrea zone southern alps evidence and geochronology of a metasomatized mantle slab the phlogopite peridotite unit of the finero complex is a restitic largest in the alps the chromite is magnesian and locally harzburgite that records two metasomatic events the first event is contains inclusions of fe ni cu sulphide and platinum related to the intrusion of basaltic magma which reacted with the group element minerals ferrario garuti 1990 pyroxene of the host harzburgite to produce chromitite pods with dunite chromitite forms well defined bodies with modal chrohaloes it also produced secondary clinopyroxene and amphibole in mite concentrations as high as 75 the occurrences the harzburgite and enriched harzburgite in na and the light rare were described by roggiani 1948 friedenreich 1956 earth elements the second metasomatic event is related to the later forbes et al 1978 and saager et al 1982 intrusion of clinopyroxenitic dykes during this event water rich the petrology of the finero complex is poorly unvapour penetrated the harzburgite along fractures and reacted with derstood one reason is that the phlogopite peridotite it to form phlogopite thus enriching the rock in k chromitites host which makes up the core of the complex exhibits anzircons that yield an age for the first metasomatic event of 207 9 omalous petrographic and geochemical characteristics 1 7 1 3 ma during which time extensional tectonics prevailed in indicative of metasomatism and of a multistage evolution the southern alps coltorti siena 1984 cumming et al 1987 voshage et al 1987 hartmann wedepohl 1993 lu et al 1997a 1997b one aim of this study is to unravel the sequence of events that affected the phlogopite peridotite

a precise u pb age on cassiterite from the xianghualing tin polymetallic deposit hunan south china we report the first precise u pb isotope data on cassiterite from the large xianghualing tin polymetallic deposit in the central nanling district south china the results show that four separates from sample xf 51 have a relatively narrow range of 206pb 238u apparent ages varying from 152 to 157 ma and the three 206pb 238u apparent ages yield a weighted average value of 156 4 ma mswd 0 32 separates from two other cassiterite samples do not have sufficient radiogenic pb to generate a reliable 206pb 238u age seven separates from the above three cassiterite samples define a well constrained 238u 206pb isochron corresponding to an age of 157 6 ma mswd 34 a comparison of the u pb cassiterite ages with published ar ar dates on muscovite from this deposit and k ar age data on biotite from the pluton genetically related to the tin mineralization in this area demonstrates that the u pb isotope system of cassiterite is a potential geochronometer combined with the ar ar dates of muscovite from this deposit we can constrain the absolute age of tin polymetallic mineralization in xianghualing at 154 157 ma the dates obtained in this study consistent with the published geochronological results from other important deposits in this region reveal that the large scale tungsten tin mineralization in the central nanling region was predominantly emplaced during 150 161 ma

evidence for storm dominated early progradation of castle neck barrier massachusetts usa abstract washovers dune scarps and flattened beach profiles with concentrations of coarse grained sediment or heavy minerals are the diagnostic geological signatures of large storms on barriers today it is clear that storms are a major force driving transgressive barriers onshore but what is not as well understood is the role these powerful erosive events play in the evolution of prograding barriers application of ground penetrating radar gpr and a combination of coring techniques have significantly improved our ability to image barrier architecture results of these studies reveal a more complex evolution than previously recognized it is now possible to precisely locate and map storm deposits within prograded barrier lithosomes a comprehensive study of northern castle neck massachusetts was performed using 15 km of gpr surveys a 120 m long seismic line 11 cores and several radiocarbon dates storm related layers are the most prominent horizons contained in the barrier stratigraphy the geometry and sedimentology of these layers closely resembles those of a present day post storm beach twenty closely spaced curvilinear heavy mineral layers imaged in the landward portion of the barrier suggest that the castle neck barrier was heavily influenced by storms during its initial phase of progradation beginning 4000 years bp approximately 1800 years bp two intense storms impacted the coast depositing two extensive coarse grained units these layers mimic the flat lying sand and gravel deposits that occur in front of a nearby eroding till outcrop following major storms the great number of storm deposits in the early history of castle neck is related to either a period of greater storm activity and or a slow rate of barrier progradation the occurrence and preservation of these earlier storm layers are likely a product of the exposure of nearby drumlins resulting in greater availability of iron oxide and ferromagnesian sands the supply of heavy mineral sands has gradually diminished as the barrier prograded and the proximal drumlin source was buried by beach and dune sands

granite pegmatite connection and mineralization age of the giant renli tanb deposit in south china constraints from u th pb geochronology of coltan monazite and zircon abstract the recently discovered renli ta nb deposit in northeastern hunan province is the largest known pegmatite ta nb deposit in south china previous research has shown that biotite monzogranite is locally spatially associated with the pegmatites and could be the parental granite of the nb ta mineralization in this study we determine that muscovite monzogranite also has a close spatial relationship with the nb ta pegmatites we present new u th pb ages for coltan monazite and zircon that constrain the timing of nb ta mineralization and related magmatism laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of coltan from the nb ta pegmatite yielded a weighted mean 206pb 238u age of 140 2 2 3 ma zircon grains from the biotite monzogranite and muscovite monzogranite yielded weighted mean 206pb 238u ages of 154 1 2 5 ma and 141 0 2 4 ma respectively and monazite grains from the muscovite monzogranite yielded a weighted mean th pb age of 140 7 2 2 ma rare earth element contents of the coltan suggest that the nb ta mineralization is related to highly evolved granite the muscovite monzogranite shows highly evolved features with higher contents of sio2 and al2o3 and lower contents of fe2o3t k2o tio2 cao mgo and p2o5 than the biotite monzogranite the obtained ages and the close spatial relationship between the pegmatite type mineralization and the muscovite monzogranite together with the major and trace element compositions indicate that the nb ta mineralization is genetically related to the early cretaceous muscovite monzogranite rather than the late jurassic biotite monzogranite muscovite monzogranite that formed during the early cretaceous should be considered a target for nb ta exploration in south china

towards more robust chronologies of coastal progradation optically stimulated luminescence ages for the coastal plain at moruya south eastern australia accurate chronologies are fundamental for detailed analysis of palaeoenvironmental conditions archaeological reconstructions and investigations of holocene coastal morphological changes chronolog

holocene palaeoecology and formation of the shoalhaven river deltaic estuarine plains southeast australia the shoalhaven river is one of the largest rivers on the south coast of new south wales and the deltaic estuarine plains associated with its mouth represent a mature stage of infill of a barrier estuary the stratigraphy of sediments from more than 60 drillholes from the plains indicates that the area has infilled during the mid holocene as a result of input of marine sands associated with a sand barrier on the high energy coast and fluvial mud and sands from the shoalhaven river molluscan assemblages indicate that marine influence was initially widespread throughout the eastern and southern parts of the embayment and that most of the plains infilled under estuarine conditions prominent levees across the plains surface are interpreted to be part of a birdsfoot delta distributary complex and individual floodbasins accreted progressively as they were encapsulated by distributary extension these former tidal environments mean that there are extensive potential acid sulphate soil conditions beneath the

petrological and geochemical evolution of the kymi stock a topaz granite cupola within the wiborg rapakivi batholith finland abstract the 6 3 km kymi monzogranite stock represents the apical part of an epizonal late stage pluton that was emplaced within the 1 65 to 1 63 ga wiborg rapakivi batholith the stock has a well developed zonal structure from the rim to the center stockscheider pegmatite equigranular topaz granite porphyritic topaz granite the contact between the two granites is usually gradational within a few centimeters but local inclusions of the porphyritic granite in the equigranular granite indicate that the latter solidified later hydrothermal greisen and quartz veins some of which contain genthelvite beryl wolframite cassiterite and sulfides cut the granites of the stock and the surrounding country rocks the equigranular granite contains 1 to 4 vol topaz and its biotite is lithian siderophyllite the porphyritic granite has 0 to 3 vol topaz and the mica is siderophyllite the equigranular granite is geochemically highly evolved with elevated li rb ga ta and f and very low ba sr ti and zr the ree patterns show deep negative eu anomalies and tetrad effects indicating extreme magmatic fractionation and aqueous fluid rock interaction the zonal structure of the stock is interpreted as a result of differentiation within the magma chamber internal convection in the crystallizing magma chamber and upward flow of residual melt as a boundary layer along sloping contacts resulted in accumulation of a layer of highly evolved volatile rich magma in the apical part of the chamber crystallization of this apical magma produced the stockscheider pegmatite and the equigranular granite the underlying crystal mush solidified as the porphyritic granite much of the crystallization took place from volatile saturated melt and episodic voluminous degassing expelled fluids into opened fractures where they or their derivatives reacted with country rocks and caused alteration and mineralization

direct dating of tin tungsten mineralization of the piaotang tungsten deposit south china by 40ar 39ar progressive crushing abstract dating ore minerals is the most direct method to determine the mineralization age of a deposit but only a few ore minerals can be directly dated by traditional isotopic geochronometers the aim of this study is to investigate the possibility of direct dating of the ore minerals cassiterite and wolframite from the piaotang tungsten deposit using the 40ar 39ar stepwise crushing technique comparing the age to coexisting k rich muscovite dated by 40ar 39ar laser stepwise heating the cassiterite wolframite and muscovite samples were separated from four pieces of ore hand specimens the 40ar 39ar isochron ages of cassiterite and wolframite are concordant with ages of their coexisting muscovite indicating that cassiterite and wolframite are suitable ore minerals for directly dating the ore forming event by 40ar 39ar stepwise crushing

the interrelation and distinction between flood tidal delta and washover deposits in a transgressive barrier island abstract the distinction and interrelation between flood tidal delta and washover deposits is described by comparing back barrier sands associated with an active and a relict tidal inlet system on the south shore of long island guidelines for comparison include three dimensional morphology sedimentary structures sediment texture and facies sequences the active modern flood tidal delta is covered by reversing small scale ripples represented by bidirectional small scale cross bedding in the subsurface large scale flood oriented cross beds are associated with non reversing sand waves on the flood ramp the relict flood tidal delta is represented by medium to fine grained sands characterized by small scale cross bedding or massive bedding relict flood tidal delta deposits are overlain by distinct washover deposits separated by thin units of salt marsh peat dominant washover structures are parallel laminations well preserved roots are commonly found in washover sands but are largely absent in flood tidal delta sands facies sequences of the relict inlet system indicate that flood tidal delta deposits extend the width of the barrier island overwashing serves to infill abandoned channels of the delta and contributes to vertical buildup

influence of climate fluctuations and changes in catchment land use on late holocene and modern beach ridge sedimentation on a tropical macrotidal coast keppel bay queensland australia abstract beach ridges at keppel bay central queensland australia preserve a record of sediment accumulation from the historical period back to middle holocene times the ridges comprise fine well sorted feldspar rich quartz sand that was eroded from the fitzroy river catchment deposited in keppel bay during floods of the fitzroy river and reworked onshore into beach and foredune deposits by the prevailing currents waves and wind these floods have an average recurrence interval of at least 7 yr and are induced by the passage of cyclones onshore into the large fitzroy catchment the youngest series of beach ridges sit sub parallel to the modern beach and comprise six accretional units each unit formed by a set of ridges and delineated by prominent swales optically stimulated luminescence osl ages of beach ridges in these units indicate they were deposited in periods of rapid progradation approximately 1500 1000 450 and 230 yr bp when there was an enhanced supply of sediment to the beach from the fitzroy river via keppel bay estimates of the mass of sediment stored in the beach ridge strandplain show that it represents a significant sediment store potentially trapping the equivalent of 79 of the estimated long term 100 yr average annual bedload of the fitzroy river that is deposited in keppel bay there has been a reduction in the rate of sediment accumulation in the strandplain since around 1000 yr bp which is consistent with other coastal records in eastern australia of a relatively wetter phase of climate in the late holocene compared to the present the youngest beach ridges osl ages

hydrogen oxygen and sulfur isotope geochemical characteristics of taoxikeng tungsten deposit in chongyi county southern jiangxi province the taoxikeng tungsten deposit in chongyi county of southern jiangxi province is mainly a quartz vein type polymetallic tungsten deposit based on hydrogen oxygen and sulfur isotopic characteristics this paper studied the origin and evolution of the ore forming fluid the results show that d values of fluids from fluid inclusions in quartz vary from 77 to 45 18o values of quartz from the ore change from 7 3 to 12 2 18oh2o values range from 3 1 to 1 2 34s values of pyrite from the ore range from 0 1 to 2 1 34s values of chalcopyrite from the ore range from 1 3 to 2 3 and 34s values of arsenopyrite from the ore range from 1 4 to 1 8 hydrogen and oxygen isotopic composition of the fluid inclusions in quartz of the major ore forming stage indicates that the water was derived mainly from mixed me teoric and magmatic water whereas sulfur isotopes in ore forming fluid were derived mainly from the magma

zircon indicators of fluid sources and ore genesis in a multi stage hydrothermal system the dongping au deposit in north china abstract the syenite hosted dongping gold deposit represents the largest gold deposit on the northern margin of the north china craton here we present new u pb age trace element concentration and hf isotope data from magmatic and hydrothermal zircons to better constrain the timing and genesis of gold mineralization geochronological data combined with field and petrologic results document two mineralization events the earlier event in the mid devonian 380 ma was associated with the intrusion of the shuiquangou syenite whereas the later event in the early cretaceous 140 ma was related to the emplacement of the shangshuiquan granite devonian hydrothermal zircons extracted from gray auriferous quartz veins were formed via metasomatic alteration of magmatic zircons derived from the syenite by an oxidizing f rich fluid in contrast cretaceous hydrothermal zircons hosted in the altered shangshuiquan granite and milky gold rich quartz ores were precipitated directly from a high temperature zr saturated aqueous fluid that was contaminated by basement materials possessing a substantially different hf isotopic composition from the contemporaneous magmatic zircons we propose that the devonian au mineralization event at dongping involved a magmatic fluid and auto metasomatism during crystallization of the shuiquangou syenite complex whereas the cretaceous au mineralization event involved a fluid exsolved from the shangshuiquan alkaline pluton results from this study highlight the potential utility of zircons as indicators of fluid sources and ore genesis in a multi stage hydrothermal system

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

zircon upb and hornblende 40ar39ar ages for the dufek layered mafic intrusion antarctica implications for the age of the ferrar large igneous province abstract new high precision zircon u pb ages for the dufek intrusion establish the crystallization age for the only layered mafic intrusion sensu stricto known in the ferrar igneous province antarctica one of the largest igneous provinces in the world three concordant zircon fractions from the capping lexington granophyre yield an age of 183 9 0 3 ma 2 which we interpret as the crystallization age for the dufek intrusion concordant zircon fractions from a silicic dike crosscutting the upper layered gabbroic sequence yield a slightly younger crystallization age of 182 7 0 4 ma 2 for both samples agreement within errors between the two u pb and 207 pb 206 pb ages for three fractions each with a unique set of physical and chemical characteristics demonstrates that inheritance of older zircon components from the country rocks was imperceptible it also suggests that assimilation or anatexis of the lower paleozoic country rocks was not the dominant mechanism in the formation of the granophyre these new u pb dates agree within analytical errors with recent zircon and baddeleyite u pb ages for dolerite sills in both the ferrar and karoo igneous provinces which demonstrates the vastness of the rift axis along which simultaneous magmatic activity occurred contemporaneity between the dufek intrusion and other ferrar group rocks supports the possibility that this pluton acted as a conduit for magmas of the widely distributed ferrar sills and flows hornblende 40 ar 39 ar ages for the lexington granophyre 175 2 ma barely overlap with those for a silicic dike 179 2 ma in the layered gabbro section just below the granophyre the younger of the two hornblende ages may be explained by degassing of inclusions or by protracted hydrothermal alteration preventing the ar ar geochronometer form becoming a closed system in the higher level granophyre until after it had done so in the more deeply positioned silicic dike the 179 2 ma age of the dufek silicic dike is interpreted to represent cooling through the ar retention temperature for hornblende of about 500 c combining this cooling age with the u pb crystallization age of 182 7 0 4 ma yields a cooling rate for the dike of approximately 100 c m y inasmuch as this rate is not rapid it can be inferred that the bulk of the dufek intrusion was still fairly hot when the dated silicic dike was emplaced

transgressive and regressive stratigraphies of coastal sand barriers in southeast australia abstract in recent years attempts have been made in southeast australia to document the stratigraphic characteristics of coastal sand barriers two basic arrangements of facies are distinguished those associated with transgressive depositional sequences and those associated with regressive sequences transgressive sequences either are formed during the postglacial marine transgression or are related to receding or transgressive barriers at present sea level in the former case complex interfingering of nearshore washover and lagoonal facies are evident in many areas these facies underlie those associated with regressive sequences which have formed since sea level has reached its present position ca 6000 6500 yrs ago examples of regressive sequences associated with both prograded and stationary barrier types occur in southeast australia here the thickness of nearshore facies in particular is commonly greater than equivalent units beneath barriers on coasts of lower energy and for less steep inner shelf gradients in the northern hemisphere the interplay of various factors within embayments has led to the development of several barrier types such as prograded stationary receded and episodic dune with some sedimentary characteristics in common with similar types recognized in other parts of the world e g texas delaware the netherlands barriers formed as a result of migrating spits and tidal inlets are not common in southeast australia

post glacial sea level changes around the australian margin a review abstract it has been known since rhodes fairbridge s first attempt to establish a global pattern of holocene sea level change by combining evidence from western australia and from sites in the northern hemisphere that the details of sea level history since the last glacial maximum vary considerably across the globe the australian region is relatively stable tectonically and is situated in the far field of former ice sheets it therefore preserves important records of post glacial sea levels that are less complicated by neotectonics or glacio isostatic adjustments accordingly the relative sea level record of this region is dominantly one of glacio eustatic ice equivalent sea level changes the broader australasian region has provided critical information on the nature of post glacial sea level including the termination of the last glacial maximum when sea level was approximately 125 m lower than present around 21 000 19 000 years bp and insights into meltwater pulse 1a between 14 600 and 14 300 cal yr bp although most parts of the australian continent reveals a high degree of tectonic stability research conducted since the 1970s has shown that the timing and elevation of a holocene highstand varies systematically around its margin this is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice melt including a process known as ocean siphoning i e glacio hydro isostatic adjustment processes several seminal studies in the early 1980s produced important data sets from the australasian region that have provided a solid foundation for more recent palaeo sea level research this review revisits these key studies emphasising their continuing influence on quaternary research and incorporates relatively recent investigations to interpret the nature of post glacial sea level change around australia these include a synthesis of research from the northern territory queensland new south wales south australia and western australia a focus of these more recent studies has been the re examination of 1 the accuracy and reliability of different proxy sea level indicators 2 the rate and nature of post glacial sea level rise 3 the evidence for timing elevation and duration of mid holocene highstands and 4 the notion of mid to late holocene sea level oscillations and their basis based on this synthesis of previous research it is clear that estimates of past sea surface elevation are a function of eustatic factors as well as morphodynamics of individual sites the wide variety of proxy sea level indicators used their wide geographical range and their indicative meaning some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level the inter comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years these issues need to be thoroughly understood before proxy sea level indicators can be incorporated into credible reconstructions of relative sea level change at individual locations many of the issues which challenged sea level researchers in the latter part of the twentieth century remain contentious today divergent opinions remain about 1 exactly when sea level attained present levels following the most recent post glacial marine transgression pmt 2 the elevation that sea level reached during the holocene sea level highstand 3 whether sea level fell smoothly from a metre or more above its present level following the pmt 4 whether sea level remained at these highstand levels for a considerable period before falling to its present position or 5 whether it underwent a series of moderate oscillations during the holocene highstand

textural features and chemical evolution in tantalum oxides magmatic versus hydrothermal origins for ta mineralization in the tanco lower pegmatite manitoba canada tantalum a key element in the electronics industry is produced mainly from rare element granitic pegmatites although their internal structure mineralogy and petrogenesis have been extensively investigated the processes that control tantalum mineralization remain poorly understood in particular the role of fluids in the crystallization of tantalum ore one of the major problems arises from the difficulty in distinguishing primary magmatic from secondary hydrothermal textures in such complex rocks in the tanco pegmatite manitoba canada tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite eight different families of tantalum oxides occur in various associations and compositions the tanco lower pegmatite is an isolated body beneath the main pegmatite body that contains abundant tantalum associated with mica alteration tantalum mineralization in the tanco lower pegmatite occurs as three different styles facies 1 is hosted by the wall zone and hosts primary magmatic ta oxides with simple textures progressive and oscillatory zoning facies 2 is hosted by the lower and upper intermediate zones where most mineralization occurs with dendritic amblygonite facies 3 is hosted by the central zone which is affected by mica alteration in this latter facies the oxides show particularly complex textures evident from x ray mapping by combining information obtained from textural observations and chemical analyses we are able to determine the paragenesis for each ta oxide bearing mineral assemblage and hence to evaluate the relative contributions of magmatic versus hydrothermal processes in complex associations we observe relics of primary ta phases that are replaced or overgrown by secondary ta phases we propose the paragenetic sequence columbite group minerals microlite early primary magmatic columbite wodginite group minerals microlite late primary magmatic wodginite group minerals microlite secondary magmatic ferrotapiolite secondary magmatic in addition chemical variations were identified in the columbite and wodginite group minerals both at the crystal scale and at the pegmatite scale columbite and wodginite group minerals show the typical ta ta ta nb and mn mn mn fe atomic ratios increase from earlier to later zones at the crystal scale the increase in ta and mn with fractionation in the columbite group is explained by the higher solubility of the ta end member relative to the nb end member and the crystallization of other minerals that shift the melt composition toward mn enrichment the fractionation trend in the wodginite group shows fe enrichment which is consistent with experimental results that show a higher solubility of the fe end member relative to the mn end member in columbite group minerals considering the available experimental data as well as the intimate association of ta oxides with zircon observed in this study we conclude that tantalum mineralization is a product of direct crystallization from the melt rather than hydrothermal in origin fluids are attributed an indirect role only as they could have brought minor elements fe mn or ca into the melt which resulted in the crystallization of secondary ta phases textural evidence shows that the late secondary phases were formed at the same time as mica alteration we suggest that mica alteration was due to a late melt rather than a hydrothermal fluid that reacted with the blocky k feldspar of the central zone during the alteration event tantalum was remobilized from primary phases and incorporated in new secondary ta oxide species

reos dating of molybdenites from ore deposits in japan implication for the closure temperature of the reos system for molybdenite and the cooling history of molybdenum ore deposits abstract rhenium and osmium abundances were determined on molybdenites from eighteen ore deposits in japan fifteen vein type a skarn type a greisen type and a pegmatite type deposit re os ages obtained for molybdenites from northeastern central and southwestern japan are 100 130 ma 50 75 ma and ca 10 ma respectively reflecting the ages of regional igneous activities in individual areas for vein type ore deposits re os ages for molybdenites agree with rb sr whole rock ages of host granitoids while they are 3 12 ma older than k ar mineral ages of the host rocks on the other hand re os ages of molybdenites from skarn pegmatite and greisen type ore deposits agree with k ar ages of the host rocks the comparison of re os ages for molybdenites with rb sr and k ar ages of host rocks in vein type deposits suggests that re os closure temperature for vein molybdenite is close to whole rock rb sr closure temperature for host granitic rocks i e roughly estimated to be around 500 c and higher than k ar closure temperature for host granodiorites i e 230 370 c if the thermal history of vein molybdenites is essentially equivalent to that of host rocks one possible explanation for age discrepancies of 3 12 ma between re os ages for molybdenites and k ar ages for the wall rocks observed in vein type molybdenum deposits is that later thermal events after formation of molybdenum ores may reset k ar ages hydrothermal alteration might have occurred in such a temperature condition as to disturb k ar mineral systems in wall rocks and made them younger but not the re os system in molybdenite the other explanation might be that the age discrepancies correspond to a cooling interval from ca 500 to 300 c of host granitoid on the other hand the agreement of re os ages of molybdenites and k ar ages of host rocks in skarn pegmatite and greisen type deposits in this study indicates no later disturbance for k ar system in the wall rock or the rapid cooling of the ore and wall rocks after the formation of molybdenite deposits

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

zircons reveal multi stage genesis of the xiangdong dengfuxian tungsten deposit south china abstract as a typical tungsten deposit of the xitian ore field nanling range south china the xiangdong deposit is a quartz vein type w deposit related to a triassic jurassic granitic complex with total ore reserves of 7 mt wo3 30 kt in this study zircon cl and bse imaging la mc icp ms u pb dating trace element and hf isotopic analyses were carried out on the fluid altered granites and related w ores in the xiangdong deposits aiming to reveal the genesis of the deposit zircon u pb dating yielded three age clusters pre triassic 250 ma n 19 triassic 227 214 ma or 220 ma n 111 and jurassic 159 149 ma or 150 ma n 27 zircon morphology and geochemistry suggest that triassic granites and jurassic quartz veins experienced stronger influences from high temperature hydrothermal fluids than other geological bodies in the deposit high contents of p y pb and u are found in triassic granite zircons whereas high concentrations of nb and ta occur in jurassic quartz vein zircons indicating different hydrothermal fluid systems during the triassic and jurassic the triassic and jurassic zircons yield high y ho ratios up to 35 representing fractionated non chondritic compositions which are indicative of a late stage residual melt that co existed with f rich fluids decreases in zircon ce ce and eu eu ratios from the triassic to the jurassic suggest a decline in fo2 that is likely to have facilitated large scale jurassic w mineralization high 176yb 177hf and 176lu 177hf ratios in the hydrothermally altered jurassic zircons indicate intense fluid exsolution from the source magma whereas the more variable 176hf 177hf ratios and hf model ages of the triassic zircons suggest multiple fluid sources and more complex alteration processes a new ore genesis model is proposed for the xiangdong w deposit initial enrichment of ore materials during the late triassic followed by large scale tungsten precipitation during the late jurassic the triassic granite provided the initial w source whereas granite derived fluids successively formed magma differentiated ore veins and infilling metasomatic ore veins during the jurassic

the world class nanling metallogenic belt jiangxi china w and sn deposition at 160 ma followed by 30 m y of hydrothermal metal redistribution abstract the w sn maoping deposit and related w sn deposits from the world class nanling range in southeast china formed at ca 160 ma and experienced several phases of metal addition and metal redistribution between 160 and 130 ma isotopic dating of ore mineral wolframite of maoping demonstrates that w was deposited first during a hydrothermal event at ca 160 ma successive fluid episodes at ca 156 ma mo and sn rich fluid and 152 ma ree rich fluid resulted in the formation of ree and fe cu zn sulfide minerals a last fluid event occurring at ca 130 ma was responsible for the deposition of zr ree nb ta minerals that are attributed to magmatic fluids derived from unexposed magmatic bodies the three episodes of fluid circulation post dating w deposition resulted in partial to complete resetting of the isotopic systems mica wolframite xenotime which are conventionally used for dating such deposits we show that w and sn mineralization in the nanling range formed during a unique fluid event at ca 160 ma later fluid episodes redistributed the previously deposited metals and sequentially introduced additional metals including mo sn fe cu zn and zr ree nb ta direct dating of paragenetically well constrained minerals is therefore critical for determining the age and the duration of mineralizing processes and for characterizing the fluid evolution of magmatic hydrothermal systems as exemplified in the nanling range

isotopic and paleomagnetic constraints on the mesozoic tectonic evolution of south china in order to better constrain the paleogeographic evolution of south china we measured sm nd and rb sr isotopic compositions for 23 mesozoic granites that crop out throughout the area tightly grouped neodymium depleted mantle model ages 1 4 0 3 ga suggest the region is underlain by relatively homogeneous proterozoic crust and fail to define crustal provinces neither the isotopic nor geologic data suggest that a mesozoic suture exists however granites possessing anomalously high sm 8 ppm and nd 45 ppm concentrations relatively high initial epsilon neodymium 4 to 8 and high but variable initial 87sr 86sr 0 759 to 0 713 form a northeast trending zone that coincides with two prominent mesozoic basins southeast of the zone lie the majority of mesozoic intrusives and upper triassic to lower cretaceous extensional basins found in south china mesozoic paleomagnetic poles are well clustered northwest of the zone pre cretaceous poles southeast of it are discordant with respect to those from the northwest the only recognized tectonostratigraphic terrane in south china lies southeast of the zone the terrane is bordered by a northeast trending sinistral fault that was active in the mesozoic other faults in south china have similar attitudes ages and sense of shear together the observations suggest that the mesozoic tectonic regime in south china consisted of strike slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults the zone defined by the granites enriched in nd and sm demarcates displaced terranes to the southeast from relatively stable land to the northwest

geochronological and mineralogical constraints on mineralization of the hetai goldfield in guangdong province south china abstract the hetai goldfield located in the southern segment of the qinzhou bay hangzhou bay juncture orogenic belt qhjb is the largest concentration of gold deposits in guangdong province south china the gold mineralization is hosted within the late neoproterozoic to early paleozoic yunkai group and strictly confined to mylonite ductile shear zones the nature of the structural control of mineralization in particular the role of ductile versus brittle deformation and their ages which remain unclear despite numerous previous studies are examined in this paper through an integrated study of geochronology and mineralogy lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism but the majority of the ores are associated with brittle deformation features in combination with macroscopic and microscopy observations on shear fabrics la icp ms u pb dating on zircons of hydrothermal origin from mylonites suggests that the hetai goldfield was subjected to two shearing events an early sinistral ductile shearing at ca 240 ma and a late dextral ductile brittle shearing at ca 204 ma indosinian these ages are ca 90 30 ma older than the previously published gold mineralizing ages of ca 175 152 ma yanshanian suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation this inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite ca 350 290 c chlorite ca 260 230 c and sphalerite ca 230 170 c intergrown with native gold which are considerably lower than that for the ductile deformation 500 300 c or higher based on these data we propose that the gold mineralization in the hetai goldfield predominantly occurred during the yanshanian event and only minor gold mineralization and associated sulfidation took place during the earlier indosinian ductile deformation

internal structure of a barrier beach as revealed by ground penetrating radar gpr chesil beach uk abstract chesil beach dorset is one of the most famous coastal landforms on the british coast the gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as the fleet the beach links the isle of portland in the east to the mainland in the west despite its iconic status there is little available information on its internal geometry and evolutionary history here we present a three fold model for the evolution of chesil beach based on a series of nine ground penetrating radar gpr traverses located at three sites along its length at abbotsbury langton herring and at ferry bridge the gpr traverses reveal a remarkably consistent picture of the internal structure of this barrier beach the first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr bp the second evolutionary phase involves the bulking out of the beach during continued sea level rise but in the presence of abundant gravel supplied by down drift erosion of periglacial slope deposits this episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole the final phase in the evolution of chesil beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance but during a still stand or slight fall in relative sea level this phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the south coast of britain and dated to between 1 2 and 2 4 k yr bp subsequently the barrier appears to have become largely inactive except for the reworking of sediment on the beach face during storm events the case study not only refines the evolutionary picture of chesil beach but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system in addition it also illustrates the potential of gpr in resolving the evolutionary history of gravel rich coastal landforms such as chesil beach

genesis of the giant shizhuyuan w sn mo bi pb zn polymetallic deposit south china constraints from zircon geochronology and geochemistry in skarns abstract the giant shizhuyuan w sn mo bi pb zn polymetallic skarn type deposit which lies in the world famous nanling w sn metallogenic belt has a close affinity with the qianlishan granite complex previous studies focused on the qianlishan granitoids rather than relevant skarns where the evolutionary processes of skarn forming fluids mineralized fluids and sources of metals are debated this study carried out systematic epma and la icpms zircon u pb dating major and trace element and lu hf isotopic analyses for three types of skarns ore free greisen stockwork and sulfide bearing skarns at shizhuyuan the whole skarn zircons were classified into six age clusters 125 187 ma 235 ma 345 509 ma 677 772 ma 811 921 ma and 1000 ma and three genetic types detrital magmatic and hydrothermally altered among them the majority of the skarn zircons are of detrital origin 345 to 2225 ma peaking at 410 ma 710 ma and 905 ma and showing a wide range of th u ratios 0 05 7 09 they share similar characteristics of zircons hosted by devonian strata in south china suggesting the inheritance from wall rock the magmatic zircons in skarns can be further subdivided into two clusters triassic 235 ma and jurassic 150 ma which are derived from the corresponding granite ore free skarn contains only detrital zircons that have experienced the weakest alteration indicating the minor participation of granitic fluid the greisen stockwork skarn consists of both detrital zircons and jurassic magmatic hydrothermal zircons implying that granitic and stratigraphic materials may both contribute greatly to the w sn polymetallic mineralization sulfide bearing skarn includes abundant detrital zircon a few of triassic zircons but no jurassic zircons indicating that the latest sulfide mineralization was dominated by sediments rather than granitic rocks the two mineralized skarn zircons display elevated concentrations of most trace elements e g u ree ti y p nb and ta coupled with decreased si and zr which reflects strong fluid rock reaction the lowest ratios of ce ce 1 22 89 78 mean 24 13 in greisen stockwork skarn zircons reveal the most reducing environment for the main w sn mineralizing event jurassic zircons are homogeneous in 176hf 177hf 0 282352 0 282454 and ehf t 11 58 to 7 27 in well accord with local granitic rocks triassic zircons have variable ehf t 9 5 to 1 6 values suggesting more mantle input of precursor pluton before the jurassic main mineralization event based on the zircon geochronology in skarns we speculate that concealed triassic magmatism exists in the deep shizhuyuan area consequently a three stage ore forming model was established for the giant shizhuyuan deposit this study further illustrates that zircon can be used as an important indicator for ore genesis in complex metallogenic systems

trace elements u pb ages and hf isotopes of zircons from mesozoic granites in the western nanling range south china implications for petrogenesis and w sn mineralization abstract the e w trending nanling range located in the southern part of the south china block scb is characterized by widespread intra continental mesozoic granitoids and accompanying w sn polymetallic ore deposits detailed studies are presented on trace elements u pb ages and lu hf isotopes in zircons from the mesozoic a2 type like granitoids including the qianlishan qitianling xianghualing huashan guposhan niumiao tong an jinziling and jinjiling plutons from the western nanling range la icp ms u pb analyses of zircon indicate that these granites intruded mainly from ca 160 150 ma two types of zircon magmatic and late magmatic hydrothermal with similar ages can be distinguished based on their zircon trace element compositions the late magmatic hydrothermal zircons have high contents of metallogenic elements e g w and sn and may be closely related with the ore deposits the ehf t values of zircons from the mesozoic granitoids are mildly negative to positive indicating the reworking of both old and young crustal components the significant involvement of mesozoic juvenile mantle derived materials in the source can be excluded because of the rare occurrences of mafic rocks with radiogenic isotopic signatures in the area the average crustal residence age patterns of the mesozoic granites in the western nanling range are similar to those of the neoproterozoic magmatic rocks in the eastern part of the jiangnan orogen which may represent the neoproterozoic collisional belt between the yangtze and cathaysia blocks considering the specific isotopic and metallogenic features of the mesozoic granitoids in the study area we propose that the western nanling range may represent a western extension of neoproterozoic arc continent collisional belt in south china the mesozoic granitoids of this area may have been generated mainly by reworking of deeply buried neoproterozoic arc related volcanic sedimentary materials due to thermal perturbations triggered by the subduction of the paleo pacific plate in mesozoic time

precise molybdenite re os and mica ar ar dating of the mesozoic yaogangxian tungsten deposit central nanling district south china the yaogangxian deposit in the central nanling region south china consists of vein type ore bodies hosted in cambrian to jurassic strata and mesozoic granitic intrusions wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz feldspar phlogopite and muscovite we have carried out molybdenite re os and phlogopite and muscovite 40ar 39ar dating to better understand the timing and genesis of mineralization re os dating of eight molybdenite samples yielded model ages ranging from 152 0 3 5 to 161 1 4 5 ma with an average of 156 0 ma the re os analyses give a well defined 187re 187os isochron with an age of 154 9 2 6 ma mswd 2 4 hydrothermal phlogopite and muscovite display extremely flat 40ar 39ar age spectra phlogopite yields a 40ar 39ar plateau age of 153 0 1 1 ma whereas muscovite yields a plateau age of 155 1 1 1 ma both 40ar 39ar ages are in good agreement with the re os ages placing the timing of tungsten mineralization at about 154 ma this age is consistent with the field relationships our new data when combined with published geochronological results from other major deposits in this region suggest that large scale w sn mineralization occurred throughout the central nanling region in the late jurassic

assessing inheritance of zircon and monazite in granitic rocks from the monashee complex canadian cordillera zircon and monazite from granitic sheets and dikes in the monashee complex canadian cordillera were investigated to determine whether igneous crystallization occurred at 1 9g a or 50 ma with 1 9 ga inherited zircon and monazite four of the five samples are weakly deformed to undeformed despite occurring in a gneiss dome at the structurally deepest exposed level of the orogen that elsewhere was strongly deformed and partly melted at 50 ma based on u th pb ages from zircon and monazite field relationships and mineral composition and zoning we conclude that the granitic rocks crystallized at 1 9 ga and were metamorphosed at 50 ma all dated zircon is 1 9 ga except for 2 3 2 0g a inherited cores and 1 9 ga monazite makes up 490 of the population in four samples the remainder of the monazite is 50 ma and all monazite in one sample is 50 ma composition and zoning of 1 9 ga zircon and monazite are uniform within samples yet differ between samples indicating growth from 1 9 ga magmas that are unique to each sample this relationship is unlikely if the grains are inherited because the host rocks are heterogeneous 2 3 2 1 ga gneisses the 1 9 ga zircon and monazite have zoning that is consistent with growth from magmas whereas the 50 ma monazite has variable composition and zoning that suggest growth from diverse metamorphic fluids the results demonstrate that part of the monashee complex was last strongly deformed and partly melted at 1 9 ga and thus largely escaped cordilleran tectonism

causes for large scale metal zonation around mineralized plutons fluid inclusion la icp ms evidence from the mole granite australia detailed reconstruction of the fluid evolution in several ore deposits associated with the sn w and base metal mineralized mole granite shows that multiple factors contributed to the zonal metal distribution around this intrusion information about the mechanism of ore formation was obtained from field relationships detailed petrographic studies and laser ablation inductively coupled plasma mass spectrometry la icp ms microanalysis of single fluid inclusions premineralization fluid inclusions in sn deposits are characterized by high sn w ratios whereas early fluid inclusions from w deposits contain higher w concentrations and comparatively low sn w ratios this indicates that the metal ratio in these deposits already was predefined by the composition of the magmatic input fluid however in both types of deposits the input fluid actually contained much higher concentrations of base metals pb zn cu etc than sn and w demonstrating that metal precipitation was highly selective the metal zonation around the mole granite therefore reflects both a compositional variation of the source fluid as well as sequential metal precipitation from it an additional process contributing to metal fractionation occurred by phase separation of the hydrothermal fluid into saline brine and low density vapor whereby cu b li as s ag la preferentially partitioned into the vapor phase analyses on six assemblages of unambiguously coexisting vapor and brine inclusions allowed direct determination of vapor brine distribution coefficients for 24 elements

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

zircons from syros cyclades greece recrystallization and mobilization of zircon during high pressure metamorphism zircons were studied from high pressure low temperature metamorphosed meta igneous lithologies from syros these rocks carry several zircon generations related to each other by dissolution reprecipitation processes one generation is pristine zircon that shows growth zoning relatively elevated contents of trivalent cations and high th u ratios the other end member is a skeletal zircon generation with negligible trivalent cation contents and low th u ratios 0 1 texturally between these two there is a range of zircon crystals with complex inclusion populations of y hree th phases and fluid inclusions showing variable progress of replacement recrystallization both end members yield distinct sensitive high resolution ion microprobe shrimp u pb ages the pristine generation has an age of 80 2 1 6ma from a metagabbro and 76 4 2 1ma from a meta plagiogranite dyke the skeletal low th u zircon generation yields an age of 52 4 0 8ma the older late cretaceous zircons are interpreted to date emplacement of the magmatic protoliths in a small segment of oceanic crust the younger eocene age however dates a zircon recrystallization event which possibly coincides with high solubility and mobility of high field strength elements in a high pressure aqueous fluid phase intergrowth relations between zircon and peak metamorphic garnet and excellent agreement of the u pb ages with white mica ar ar ages for the same samples support the conclusion that eocene is the true age of high pressure metamorphism on syros

assessment of the ore forming process of the gejiu tin district south china abstract the gejiu tin district of southern china is the largest tin polymetallic ore district in the world even though the mining operation has lasted more than 2000 years in this area the metallogenic mechanism of this gigantic tin mineralization is still controversial based on petrographic geochemical and zirconological information from this study we present a particular model of the magma evolution and tin mineralization for the gejiu tin district the ore forming processes involved both a batholithic biotite monzogranite bmg emplaced at 94 ma and a satellitic muscovite alkali feldspar granite mag emplaced at 72 ma the bmg and the mag were produced from a long lived magma chamber by two stages of magmatic activity during intracontinental orogeny in the youjiang block the hiatus between the two magmatic stages indicates that the deep seated magma chamber persisted during the dominant phase of the orogeny progressive fractional crystallization of the magma caused the extreme enrichment of incompatible elements which include ore forming components such as tin aqueous fluids and other volatiles in the residual magma when the regional tectonic environment evolved into the extensional regime at 72 ma the highly fractionated residual magma ascended and once emplaced it formed the highly evolved mag with a mean zircon crystallization age of 71 8 1 2 ma the mag is temporally and spatially associated with cassiterite bearing quartz vein cqv with a mean zircon crystallization age of 72 6 1 6 ma this metallogenic model of the bmg mag cqv association is generally applicable to other granite related metallic deposits in south china southeast asia and elsewhere australia bolivia brazil usa etc the recognition of this bmg mag cqv association in regional geological survey may facilitate the future exploration for this type of deposit

the muscovite granites parental rocks to the nanling range tungsten mineralization in south china abstract muscovite granites mgs in the nanling range south china occur as satellite intrusions within or surrounding batholitic biotite monzogranites bms the mgs are massive and fine grained with a porphyritic texture and contain quartz k feldspar and albite in nearly equal portions the accessory minerals in the mgs include alumina rich minerals e g mn and fe rich garnet andalusite topaz and tourmaline anatase rutile wolframite cassiterite xenotime chalcopyrite molybdenite and volatile rich minerals e g microlite topaz tourmaline fluorite and calcite compared with the bms the mgs are geochemically enriched in major elements of si k and na and incompatible trace elements of rb cs y u nb ta w sn pb bi li and be and depleted in major elements of fe mg ca ti and p and compatible trace elements of ba sr co ni cr cd v as well as zr and hf the chondrite normalized ree patterns of the mgs are flat with large negative eu anomalies the mineralogical and geochemical features of the mgs indicate that they crystallized from highly fractionated granitic magmas zircons separated from the mg samples which were collected from six different tungsten deposits show characters of hydrothermal origin according to their morphologies chemical compositions and inclusions in situ u pb dating of the zircons yields a weighted mean 206pb 238u age of 133 4 1 0 ma this age is similar to the mean age of the zircons from wolframite bearing quartz veins wqvs in the nanling range 133 7 1 3 ma reported from our previous study zircon hf isotopes also reveal that the mgs and the wqvs are homologous these mineralogical geochemical and zirconological features indicate that the mgs are the parental rocks of the tungsten deposits in the nanling range this study provides a new guidance for the exploration of magmatic hydrothermal tungsten deposits

petrogenesis of jurassic tungsten bearing granites in the nanling range south china evidence from whole rock geochemistry and zircon u pb and hf o isotopes abstract the nanling range nlr is the largest tungsten metallogenic province in china and perhaps in the world the tungsten mineralization is believed to be related to jurassic granitic magmatism however the petrogenesis of these granites and their relation to the tungsten mineralization are still debated whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for w bearing granitic intrusions from the southern jiangxi province in the nlr in order to constrain their magmatic sources and petrogenesis the nlr granites include biotite granites two mica granites and garnet muscovite granites sims and la icpms u pb dating of zircons and monazites give emplacement ages of 161 154 ma for these rocks the granites are metaluminous to strongly peraluminous with high sio 2 72 3 wt and high k 2 o 3 7 wt petrographic and geochemical features show that they are highly fractionated i type granites the biotite granites are enriched in light rare earth elements lrees relative to heavy rees have weakly negative eu anomalies and are depleted in nb ba p and ti in contrast the two mica and garnet bearing muscovite granites have tetrad type ree patterns with strongly negative eu anomalies and are extremely depleted in ba nb sr p and ti magmatic garnets are mainly almandine and spessartine and have low mn cores and high mn rims their y hree contents are high and generally decrease from core 1 2 wt to rim average 4955 ppm all of these granites are characterized by variable whole rock initial 87 sr 86 sr 0 7053 0 8000 e nd t 12 6 to 9 4 and e hf t 12 3 to 8 5 as well as variable zircon e hf t and 18 o with values of 16 3 to 7 4 and 7 6 to 10 0 respectively they contain abundant zircon xenocrysts and xenoliths of micaceous schist all of these features are consistent with a process of crystal fractionation of crustally derived magmas coupled with strong assimilation of sedimentary rocks the assimilation of meta sedimentary materials increased the concentrations of tungsten alumina and manganese in the magmas whereas high degrees of crystal fractionation further enriched them in the evolved granitic rocks the w enriched magmatic fluids formed the tungsten bearing quartz veins revealing the genetic relationship between tungsten mineralization and emplacement of garnet bearing two mica or muscovite granites in the nlr

structural control of tertiary au ag bearing breccias in an extensional environment nelson area southern nevada usa gold silver mineralization in the nelson area of southern nevada was controlled by structures associated with intrusion of an east west oriented pluton flatlying breccias formed during intrusion have allowed passive flooding of highly permeable zones and deposition of mineralized quartz and calcite steep fractures were formed in the pluton and immediate country rock during cooling and later reactivated by north south extension these fractures have channelled fluids and some have been the sites of hydrothermal eruptions which produced further brecciation and deposition of mineralized quartzcalcite veins the mineralizing fluid was water which was boiling at or near 100 c the calcite deposited by this water has 13c 5 4 to 7 1 and 18o 5 8 to 11 3 and the water was probably meteoric in origin mineralization had an epithermal style with strong local structural control rather than deep sourced regional detachment related hydrothermal origin

a possible linkage between highly fractionated granitoids and associated w mineralization in the mesozoic yaogangxian granitic intrusion nanling region south china abstract the yaogangxian ygx w deposit in the central nanling w province south china is one of the largest w deposits worldwide both vein type wolframite and skarn type scheelite orebodies were exposed in ygx these scheelite and wolframite mineralization are spatially associated with the ygx granitic intrusion the exposed intrusion contains two main intrusive phases lower zone coarse grained two mica granite and upper zone fine grained muscovite granite an integrated study of whole rock geochemistry la icp ms zircon u pb geochronology and zircon hf isotopic geochemistry of the ygx granitic intrusion was undertaken to constrain its magmatic source and petrogenesis cassiterite la icp ms u pb dating was also undertaken to constrain the connection between the intrusion and hydrothermal w mineralization zircon u pb dating yielded weighted mean ages of 161 3 and 157 2 ma for the two mica and muscovite granites respectively cassiterite crystals from wolframite quartz veins display growth zonation under cathodoluminescence and have a weighted mean zircon u pb age of 158 2 ma the formation of the muscovite granite and related w mineralization in the ygx deposit was thus initiated during the early yanshanian the ygx granites display typical metaluminous to strongly peraluminous characteristics with high sio2 73 5 79 1 wt and k2o 3 0 5 0 wt contents they are enriched in heavy rare earth elements rees comparative to light rees notably they exhibited strong negative eu anomalies and are depleted in sr ba p and ti in addition muscovite granites in ygx are more significantly enriched in heavy rees relative to light rees than two mica granites indicating that the former experienced higher degree fractionation than the latter zircon grains of the ygx granitoids have strongly negative ehf t 15 to 10 3 with two stage hf model ages of 2 15 1 86 ga indicating a magma source of reworked ancient crustal material without obvious involvement of juvenile materials the results of petrology and geochemistry indicate that the ygx granitic intrusion is a highly fractionated s type granite emplaced during widespread 160 150 ma granitic magmatism in the nanling region further evolution to late stage for multiphase ygx granitic intrusion is needed to enrich ore forming elements after magmatic emplacement it is suggested that the extensional environment of continental lithosphere caused by the northwest subduction of the paleo pacific plate may play an key role in the genesis of ygx s type granite w rich proterozoic basement rocks and fractional crystallization may provide material for the formation of the granite related tungsten mineralization

an absolute chronology for the raised beach and associated deposits at sewerby east yorkshire england the raised beach sediments revealed in the cliffs at sewerby east yorkshire are widely regarded as ipswichian in age previously reported evidence for this dating is reviewed and new results from a range of luminescence dating techniques applied to the blown sand deposit overlying the raised beach are reported these provide the first absolute date for the sewerby site of 120 84 11 82 ka which places the blown sand at the boundary between oxygen isotope stages ois 5e and 5d as the underlying raised beach is little older than the blown sand it probably formed during ois stage 5e as suggested by the faunal evidence

hydrothermal zircon geochronology age constraint on nanling range tungsten mineralization southeast china abstract the nanling range southeast china is well known for its wolframite bearing quartz vein wqv tungsten deposit this study focuses on the geochemistry and geochronology of zircons from the wqv and challenges the current view of the tungsten mineralization in the nanling range the features of the wqv zircons include 1 pale brown murky brown or orange red color and translucence under microscope 2 110 101 type crystal form 3 weak cathodoluminescence 4 enrichment of hf ranging from 1 97 to 7 83 wt hfo2 u ranging from 0 02 to 3 97 wt uo2 th ranging from 0 to 0 65 wt tho2 and p ranging from 0 to 1 82 wt p2o5 and 5 presence of solid hydrothermal and ore minerals and fluid inclusions these features indicate that the wqv zircons crystallized from hydrothermal fluids during tungsten mineralization the in situ la icpms u pb results of the wqv zircons from five different tungsten deposits in the nanling range yield similar ages ranging from 134 4 1 9 ma to 132 9 1 5 ma approximately 20 million years younger than proposed tungsten ore ages 155 5 ma several mineralization characteristics and field observations also cast doubt on the current model nanling range tungsten ore is the result of orthomagmatic processes the zircon characterization method provided in this study could be applied to tungsten metallogenic research in other parts of the world

reply to the discussion by dillenburg et al on evidence for a transgressive barrier within a regressive strandplain system implications for complex response to environmental change

understanding geologic processes with xenotime composition chronology and a protocol for electron probe microanalysis abstract xenotime ypo 4 is iso structural with zircon group minerals and lies at one end of a compositional solid solution with monazite as with monazite and zircon naturally occurring xenotime may accommodate significant concentrations of rare earth elements as well as th and u making it an important repository for these valuable geochemical marker elements and a potential geochronometer xenotime grows in sediments during diagenesis in low to granulite grade metamorphic rocks in migmatites and is common in peraluminous igneous rocks xenotime can be a complement or indeed an alternative to monazite and or zircon in geochemical and geochronological studies to maximise the petrographic potential of xenotime a complete understanding of its composition and relationship to rock forming assemblages is essential electron beam techniques provide micron scale resolution of compositional and textural variation and yield precise dates for individual micro volumes in multi domain grains methods for collecting trace element data by electron probe microanalysis differ from those routinely employed to collect major element concentrations careful characterisation of background curvature and background interferences around the th u and pb peaks is required to avoid large overlap correction for y l 2 3 on pb m analysis of pb is made on the m peak a broad array of geochemical and geochronological applications can take advantage of the links between xenotime composition and texture and the evolution of silicate mineral assemblages in a diversity of environments one example of metasomatised xenotime from a pegmatite in sw norway demonstrates a practical application to dating geologic processes as well as the potential limitations that arise in compositionally heterogeneous xenotime

discussion evidence for a transgressive barrier within a regressive strandplain system implications for complex response to environmental change by hein et al 2013 sedimentology 60 469 502

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

magmatic to hydrothermal crystallization in the w sn mineralized mole granite nsw australia part i crystallization of zircon and ree phosphates over three million years a geochemical and u pb geochronological study abstract zircon monazite and xenotime crystallized over a temperature interval of several hundred degrees at the magmatic to hydrothermal transition of the sn and w mineralized mole granite magmatic zircon and monazite thought to have crystallized from hydrous silicate melt were dated by conventional u pb techniques at an age of 247 6 0 4 and 247 7 0 5 ma respectively xenotime occurring in hydrothermal quartz is found to be significantly younger at 246 2 0 5 ma and is interpreted to represent hydrothermal growth from associated fluid inclusions it is concluded that it precipitated from a hydrothermal brine 600 c which is below the accepted closure temperature for u pb in this mineral these data are compatible with a two stage crystallization process precipitation of zircon and monazite as magmatic liquidus phases in deep crustal magma followed by complete crystallization and intimately associated sn w mineralization after intrusion of the shallow sill like body of the mole granite later hydrothermal formation of monazite in a biotite fluorite topaz reaction rim around a mineralized vein was dated at 244 4 1 4 ma which distinctly postdates the mole granite and is possibly related to a younger hidden intrusion and its hydrothermal fluid system obtaining precise age data for magmatic and hydrothermal minerals of the mole granite is hampered by uncertainties introduced by different corrections required for multiple highly radiogenic minerals crystallising from evolved hydrous granites including 230 th disequilibrium due to th u fractionation during monazite and possibly xenotime crystallization variable th u ratios of the fluids from which xenotime was precipitating elevated contents of common lead and post crystallization lead loss in zircon enhanced by the fluid saturated environment the data imply that monazite can also survive as a liquidus phase in protracted magmatic systems over periods of 10 6 years the outlined model is in agreement with prominent chemical core rim variation of the zircon