metallogenesis of the siding pb zn deposit in guangxi south china rb sr dating and c o s pb isotopic constraints abstract the siding pb zn deposit is located in the transition zone between the yangtze craton and the cathaysian block on the southwestern margin of the jiangnan orogenic belt and is a representative example of the pb zn deposits found in northern guangxi south china in this study sphalerite rb sr dating and c o s pb isotope analyses were used to investigate the mineralization age and source of the ore forming minerals in the siding pb zn deposit the 13cpdb and 18osmow values of the gangue mineral calcites were determined to be between 5 0 and 1 1 average 2 6 and between 13 2 and 18 4 average 16 4 respectively these values are roughly consistent with those of the carbonate minerals in the ore hosting strata namely 1 63 to 0 83 average 0 34 and 19 0 22 0 average 20 9 respectively indicating a mainly sedimentary origin of the ore forming fluids the 34s values of the ore minerals were determined to be 17 1 to 5 1 average 2 6 while they were 8 6 to 5 1 average 0 8 for sphalerite 7 8 to 2 7 average 1 6 for galena and 17 1 to 2 3 average 7 3 for pyrite the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of the sulfides pyrite galena and sphalerite were determined to be 18 12 18 76 average 18 50 15 66 15 97 average 15 80 and 38 36 39 71 average 38 96 respectively which are consistent with those of limestone in the region 206pb 204pb 17 65 18 77 207pb 204pb 15 60 15 91 and 208pb 204pb 37 82 39 59 pb and s isotope analyses showed that the ore forming materials originated from the crust as also substantiated by the 87sr 86sr i ratios 0 710806 0 713740 of the sphalerite the isochron age determined by rb sr dating was 360 5 0 ma indicating the formation of the siding deposit in the late devonian hercynian period this mineralization age substantially differs from those determined for the dachang tongshanling huangshaping and shuikoushan pb zn deposits on the southern margins of the jiangnan orogenic belt but is comparable with those of the adjacent daliangzi bokouchang and dadongla pb zn deposits in northeastern guizhou we therefore propose that the formation of the siding pb zn deposit is related to a basin scale fluid flow induced by late devonian extensional rifting in south china in response to the tectonic evolution of the southwestern yangtze craton

petrochronology and tims thermal ionization mass spectrometers or tims were developed by the pioneers of mass spectrometry in the mid 20th century and have since been workhorses for generating isotopic data for a wide range of elements later developed mass spectrometric techniques have many advantages over tims including higher spatial resolution with in situ techniques such as secondary ion mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icpms and greater versatility in terms the elements that can be easily and well measured the reason tims persists as an important method for geochronology is that for some key parent daughter systems e g u pb sm nd it can produce isotopic data and resultant dates with 10 100 times higher precision and more quantifiable accuracy than in situ techniques even when sample sizes are very small such as those that might result from single crystals or even small portions of zoned crystals for many questions in the geosciences the highest achievable precision and accuracy are required to resolve the timescales of processes and or correlate events globally as an example modern tims u pb geochronology is capable of producing dates with precision and accuracy better than 0 1 of the age for single crystals with only a few picograms pg of pb therefore it is possible to constrain the durations of single zircon crystal growth in magmatic systems over tens to hundreds of kyr in mesozoic and younger rocks if these dates and rates can be connected with other igneous processes such as magma transfer emplacement and crystallization then it becomes possible to calibrate thermal and mass budgets in magmatic systems and evaluate competing models for pluton assembly and subvolcanic magma storage as another example sm nd geochronology of garnet permits dates with precision better than 1 million years for garnets of any age including multiple concentric growth zones in single crystals such

ages of sediment hosted himalayan pb zn cu ag polymetallic deposits in the lanping basin china re os geochronology of molybdenite and sm nd dating of calcite abstract the lanping basin is a significant pb zn cu ag mineralization belt of the sanjiang tethyan metallogenic province in china over 100 thrust controlled sediment hosted himalayan base metal deposits have been discovered in this basin including the largest sandstone hosted pb zn deposit in the world jinding and several cu ag co deposits baiyangping baiyangchang and jinman these deposits with total reserves of over 16 0 mt pb zn 0 6 mt cu and 7000 t ag are mainly hosted in meso cenozoic mottled clastic rocks and strictly controlled by two cenozoic thrust systems developed in the western and eastern segments of the lanping basin to define the metallogenic history of the study area we dated nine calcite samples associated with copper sulfides from the jinman cu deposit by the sm nd method and five molybdenite samples from the liancheng cu mo deposit by the re os method the calcite sm nd age for the jinman deposit 58 5 ma and the molybdenite re os age for the liancheng deposit 48 2 ma together with previously published chronological data demonstrate 1 the cu ag mineralization in the western lanping basin mainly occurred in three episodes i e 56 54 51 48 and 31 29 ma corresponding to the main and late collisional stages of the indo asian orogeny and 2 the pb zn ag cu mineralization in the eastern lanping basin lacked precise and direct dating however the apatite fission track ages of several representative deposits 21 4 ma to 32 5 ma may offer some constraints on the mineralization age

gold mineralization in the mazowe area harare bindura shamva greenstone belt zimbabwe ii genetic relationships deduced from mineralogical fluid inclusion and stable isotope studies and the sm nd isotopic composition of scheelites in the mazowe area some 40 km nw of harare in zimbabwe gold mineralization is hosted in a variety of lithologies of the archean harare bindura shamva greenstone belt in structures related to the late archean regional d2 3 event conspicuous mineralzogical differences exist between the mines the mainly granodiorite hosted workings at mazowe mine are on pyrite rich reefs mines of the bernheim group have metabasalt host rocks and are characterized by arsenopyrite rich ores and stori s golden shaft and alice mine both in metabasalts work sulfide poor quartz veins in contrast to the mineralogical diversity near identical fluid inventories were found at the different mines both h2o co2 ch4 fluids of low salinity and highly saline fluids are present and are regarded to indicate fluid mixing during the formation of the deposits notably these fluid compositions in the mazowe gold field markedly contrast to ore fluids typical of archean mesothermal gold deposits on other cratons stable isotope compositions of quartz from the various deposits 18o 10 8 to 13 2 smow calcite 18o 9 5 to 11 9 smow and 13c 3 2 to 8 0 pdb inclusion water d 28 to 40 smow and sulfides 34s 1 3 to 3 2 cdt are uniform within the range typical for archean lode gold deposits worldwide the fluid and stable isotope compositions support the statement that the mineralization in the mazowe gold field formed from relatively reduced fluids with a metamorphic signature during a single event of gold mineralization microthermometric data further indicate that the deposits formed in the pt range of 1 65 2 3 kbar and 250 380 c ages obtained by using the sm nd and rb sr isotope systems on scheelites are 2604 84 ma for the mineralization at stori s golden shaft mine and 2 40 0 20 ga for mazowe mine the archean age at stori s is regarded as close to the true age of gold mineralization in the area whereas the proterozoic age at mazowe mine probably reflects later resetting

texture and geochemistry of multi stage hydrothermal scheelite in the tongshankou porphyry skarn cu mo w deposit eastern china implications for ore forming process and fluid metasomatism

geochronological constraints on the genesis of high grade iron ore in the gongchangling bifs from the anshan benxi area north china craton abstract the gongchangling iron deposit located in the northeast of the north china craton is hosted in late neoarchean algoma type bifs it is famous for the major production of high grade iron ore in the gongchangling no 2 mining area in china with regard to the genesis of high grade iron ore more and more evidences indicate that it was related with hydrothermal enrichment of bifs however the hydrothermal nature was argued for meteoric metamorphic or migmatitic fluid in this study the trace element compositions of garnet from the altered wall rock of high grade iron ore obtained by la icp ms show compositional zoning indicating it is a metamorphic origin these garnets yield a sm nd isochron age of 1888 77 ma interpreted as the time of metamorphism in this area la icp ms u pb dating of zircon from the upper migmatite zone shows that the migmatitic granite was formed at 2478 36 ma since the ree patterns of garnet suggest that it was formed in the nearly neutral fluid rather than the acid meteoric fluid in the paleoproterozoic hence combined the ages of metamorphism and migmatization with high grade iron ore of 1840 7 or 1860 7 ma obtained by previous studies it indicates that the genesis of the high grade iron ore derived from the enrichment of bifs by metamorphic hydrothermal fluid

a shear zone related greenstone belt hosted gold mineralization in the archean of west greenland a petrographic and combined pb pb and rb sr geochronological study abstract widespread gold showings have been found in an archean greenstone belt on storo in godthabsfjord west greenland the storo greenstone belt sgb comprises metasedimentary and metavolcanic rocks with minor magnetite rich bands gold mineralization is hosted by amphibolites mica schists and garnetite rocks gold occurs in various mineral associations but its presence in lollingite arsenopyrite pyrrhotite parageneses is prevalent to a lesser extent native gold occurs within seriticized plagioclase in sheeted quartz veins and as inclusions in garnet based on petrographic observations and comparison with similar ore mineral textures from other deposits we propose the following model for the deposition of the gold bearing lollingite arsenopyrite pyrrhotite assemblage on storo in the first stage arsenopyrite likely formed with gold in solid solution in the second stage gold bearing arsenopyrite was replaced by lollingite and pyrrhotite this took place during regional prograde metamorphism gold accumulated within lollingite as discrete grains during subsequent retrograde metamorphic conditions lollingite and pyrrhotite reacted and formed arsenopyrite and gold was subsequently exsolved and preferably deposited as discrete grains or films along arsenopyrite lollingite grain boundaries during a later event a garnet overgrowth partly affected the gold bearing lollingite arsenopyrite pyrrhotite assemblage the isotopic composition of pb released from these garnets by pb stepwise leaching experiments pbsl and the bulk pb isotopic compositions of arsenopyrite and pyrrhotite indicate a common source of pb in the fluid from which first the sulfides and subsequently garnet were formed bulk pb analyses and pbsl experiments of arsenopyrite and pbsl experiments of garnet yield ages of 2863 24 ma 2 mswd 0 2 for arsenopyrite and 2748 62 ma 2 mswd 220 for garnet the 2863 24 ma age is thus a minimum age for the mineralization rb sr isotopic analyses of cogenetic biotite from within strongly mineralized zones reveal middle proterozoic ca 1 65 ga mineral ages well in accordance with a regional reheating event known to have affected the area and are thus interpreted as cooling ages thereof this regional reheating event has apparently not affected the pb pb isotopic system of arsenopyrite implying that the blocking temperature of the u pb system in arsenopyrite is likely to be above 300 c the late archean ages for arsenopyrite and garnet are consistent with the regional amphibolite facies metamorphism related to major terrane assemblies in the study area occurring at that time the ore textures preserved today are interpreted as those formed under this regional metamorphic event

upb zircon and rutile chronology of archean greenstone formation and gold mineralization in the val d or region quebec abstract u pb geochronology provides an absolute time framework for the evolution of the sigma gold deposit and surrounding rocks at val d or southern abitibi subprovince the bourlamaque batholith the largest pluton in the area gives a 2699 8 1 0 ma u pb zircon age this pluton cuts the val d or formation which hosts the mineralization a u pb zircon age of 2704 9 1 1 ma on a felsic volcanic rock the colombiere rhyolite 13 km east of the mine dates that formation the gold bearing quartz vein system at sigma is hosted by andesites and two generations of porphyry intrusions all metamorphosed to the greenschist facies the oldest porphyry porphyritic diorite shows the same deformation as the volcanic rocks and has a 2703 7 2 5 ma u pb zircon age the porphyritic diorite and volcanic rocks are cut by feldspar porphyry dykes which post date regional folding and have a 2694 0 2 2 ma u pb zircon age regional greenschist metamorphism has been dated directly with a u pb date of 2684 7 ma on rutile in the colombiere rhyolite the mineralization and hydrothermal alteration in the mine are superimposed on the metamorphic minerals hydrothermal rutile from an alteration halo around the veins in andesite has a 2599 9 ma u pb age textural evidence clearly indicates that the wall rock alteration and vein filling are contemporaneous and hence the vein system and gold mineralization appear to have developed at least 80 m y after the formation and metamorphism of host greenstones

recent developments in dating ancient crustal fluid flow several isotopic techniques have recently been developed or substantially improved allowing the accurate determination of the timing of fluid related processes these include k ar rb sr and sm nd dating of diagenetic minerals in clastic rocks u pb dating of carbonates sm nd dating of fluorite and uraninite re os and rb sr dating of sulfides 40ar 39ar and rb sr dating of fluid inclusions and u pb dating of ilmenite magnetite sphene and rutile while many of these techniques require further evaluation some have already resulted in new constraints on a variety of crustal fluid flow models

in situ 87sr 86sr of scheelite and calcite reveals proximal and distal fluid rockinteraction during orogenic w au mineralization otago schist new zealand

origins of nd sr pb isotopic variations in single scheelite grains from archaean gold deposits western australia accessory gangue scheelite cawo4 from the archaean mt charlotte lode au deposit can be divided into two types with different rare earth element ree signatures in some scheelite grains specific ree signatures are reflected by different cathodoluminescence colours which can be used to map their often complex oscillatory intergrowths domains with specific ree contents from two grains were sampled for sm nd rb sr and pb isotopic analyses using a micro drilling technique type i scheelite is strongly enriched in middle ree mree and eu anomalies are either absent or slightly positive four fragments collected from type i regions of two crystals have initial 87sr 86sr and end values ranging from 0 70141 to 0 70163 and 2 5 to 3 5 respectively and pb isotope ratios reflecting the composition of greenstone sequence this may indicate that nd and pb have their source either locally or regionally in the greenstones basic greenstone lithologies have 87sr 86sr 0 7015 and the radiogenic sr signatures indicate that part of the sr originated from felsic lithologies located either within or beneath the host greenstone pile alternatively the sr signature may have evolved from preferential leaching of a rb rich mineral during hydrothermal alteration of the greenstone the ree patterns of type ii scheelite are either flat or mree depleted and have strong positive eu anomalies three fragments collected from type ii regions of the same two crystals have initial 87sr 86sr ratios and end values between 0 70130 and 0 70146 and 1 1 to 2 6 respectively and pb isotope signatures that are once again similar to that of the greenstone this implies that 87sr 86sr ratios in type ii fluids were closer to those of the host dolerite 0 7008 0 7013 due to more extensive fluid interaction with the dolerite a positive correlation between na and ree suggests that ree3 are accommodated by the coupled substitution ree3 na 2 ca2 into both type i and type ii scheelite this is consistent with a fractional crystallisation model to explain the change in ree patterns from type i to type ii but not with a model involving different coupled substitutions and fluids from different origins we propose that the complex ree and isotopic signatures of scheelite at mt charlotte are related to small m to medium km scale processes involving mixing between fresh batches of hydrothermal fluid with fluids that had already been involved in extensive wall rock alteration the very high end values measured in some scheelites have been previously used to link gold mineralisation with komatiites containing unusually high sm nd ratios however tiny 20 m grains of secondary hydroxyl bastnasite were found within micro fractures of one scheelite grain containing an extremely high end signature the hydroxyl bastnasite probably formed during recent ree redistribution within the scheelite as a result of meteoric fluid circulation the scale of this cryptic low temperature alteration is sufficient to explain the anomalously high endi values observed in scheelite from western australia

rb sr sm nd and pb isotope systematics of pyrite implications for the age and genesis of lode gold deposits lode gold deposits commonly consist of pyrite and lesser amounts of lead and zinc sulfides accompanied by quartz and calcite their exact origin remains controversial mainly because of the scarcity of reliable geochronological data here we present direct rb sr dating of pyrite from a lode gold deposit and propose the method as a useful geochronological technique for gold mineralization for which age data are poor a positive correlation between present day 87 sr 86 sr and 87 rb 86 sr ratios of pyrite fes 2 subsamples from the linglong gold mine of china corresponds to an age of 122 123 ma which dates the age of gold mineralization the sr nd and pb isotopic compositions of pyrites and the associated rocks suggest that the hydrothermal fluids responsible for the pyrite and gold mineralization were probably derived from a mixed source i e degassing of mafic magmas and meteoric water that had leached the country rocks

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

diverse metal sources of archaean gold deposits evidence from in situ lead isotope analysis of individual grains of galena and altaite in the ross and kirkland lake deposits abitibi greenstone belt canada lead isotope compositions for individual grains of galena and altaite pbte were determined in situ using a secondary ion mass spectrometer sims galena was collected from the ross deposit and altaite from the kirkland lake kl deposits in the southern abitibi greenstone belt superior province of canada the samples from kl are more radiogenic than those from the ross deposit isotopic compositions vary significantly between different grains in each deposit and form broad linear arrays in 207pb 204pb 206pb 204pb and 208pb 204pb 206pb 204pb diagrams the linear arrays of pb isotope data are attributed to mixing of pb from different sources at least two sources are required for individual deposits one with low u pb and th pb ratios and the other with high ratios lead minerals occurring with au are less radiogenic than those that are not obviously associated with au suggesting that au was supplied from low u pb sources such as sulphides or older ultramafic mafic rocks while most data are consistent with the derivation from local rocks highly radiogenic pb with relatively low 207pb 206pb ratios recorded at kl require post archaean mineralization or derivation of the pb from an unusual crustal source with low the latter interpretation is favored because of the lack of textural evidence and because it is difficult to dissolve and precipitate altaite at low temperatures the presence of a pb reservoir with low is also inferred from the data of archaean banded iron formations and volcanogenic massive sulphide deposits different isotopic patterns of the two deposits suggest different sources of metals in the two deposits while this conclusion does not reject the derivation of fluids from the lower crust or mantle the data are not in accord with conceptual models invoking a common source reservoir for metals the study suggests that fluids which may have a common origin leached metals and other constituents from the upper crustal rocks during their ascent the proposed model different origins for different constituents explains much of the conflicting evidence presented by archaean au deposits including provinciality of mineralogy and relatively uniform fluid inclusion and c isotope data from many au deposits

magmatic hydrothermal fluids at the sedimentary rock hosted intrusion related telfer gold copper deposit paterson orogen western australia pressure temperature composition constraints on the ore forming fluids the neoproterozoic telfer deposit one of australia s largest gold copper deposits is located in the paterson orogen several highly differentiated calc alkaline to alkali calcic peraluminous granites intruded the metasedimentary rocks near 5 20 km telfer contemporaneously with structurally controlled gold copper mineralization fluid inclusion assemblages with different fluid inclusion types were identified in samples from a range of different vein types these inclusion types range from three phase aqueous laq vaq shalite high salinity 50 wt nacl equiv high temperature 460 c inclusions to two phase aqueous or two phase aqueous carbonic low to moderate salinity 2 22 wt nacl equiv moderate to high temperature 480 c fluid inclusions fluid inclusion trapping mechanisms and interpreted precipitation mechanisms for gold and copper include 1 adiabatic cooling between 450 and 200 c in all veins and 2 locally fluid phase separation at about 300 c the trapping pressure of fluid inclusion assemblages trapped during phase immiscibility was calculated to be approximately 1 5 kbar for fluid inclusion assemblages that lack evidence for phase immiscibility a pressure at the temperature of final homogenization of up to 3 kbar was calculated this high pressure value is interpreted to be related to local fluid overpressure as a consequence of fault zone movement in faults and fractures that localized gold at telfer phase immiscibility and gold precipitation were induced during sharp pressure decrease accompanying fault zone movement in situ laser inductively coupled plasma mass spectrometry icp ms analyses of fluid inclusions revealed high trace element contents in all fluid inclusion assemblages manganese fe ratios of 0 24 is observed given the high temperatures and salinities of up to 480 c and 42 wt nacl equiv au and cu were likely transported as chloride complexes this interpretation is supported by the observation that the highest base metal contents occur in the highest salinity fluid inclusion potassium ca ratios of 1 in most assemblages the high homogenization temperatures 480 c in many fluid inclusion assemblages and the high trace element contents e g fe mg k na in most of the fluid inclusion assemblages are compatible with involvement of a magmatic hydrothermal fluid during gold copper mineralization this fluid was probably derived from the coeval granites in the telfer area and thus telfer is interpreted to be a distal intrusion related metasedimentary rock hosted gold copper deposit type

weathering fluxes of arsenic from a small catchment in slovak republic inputs of as to a small catchment due to chemical weathering of bedrock mechanical weathering of bedrock and atmospheric precipitation were 71 53 23 98 and 0 02 g ha 1 year 1 respectively the output fluxes of as due to mechanical erosion of soil biological uptake stream discharge and groundwater flow were 6 32 4 77 0 37 and 0 02 g ha 1 year 1 respectively the results indicate that arsenic accumulates in soil and regolith with a very high rate this is attributed to the selective weathering and erosion with respect to arsenic and fixation of arsenic in the secondary solids produced by weathering the output fluxes of as in stream and groundwater in vydrica catchment in slovak republic 0 39 g ha 1 year 1 based on muscovite biotite granites and granodiorites were much lower compared to catchments in a gold district in the czech republic these results may be ascribed to the low levels of arsenic pollution measured in vydrica catchment the arsenic fluxes were estimated by calculation of mechanical and chemical weathering rates of the bedrocks in vydrica catchment from mass balance data on sodium and silica the justification of the steady state of na and si is that neither of the elements is appreciably accumulated in plants and in exchangeable pool of ions in soil

rb sr dating of sphalerite and s pb isotopic studies of the xinxing crypto explosive breccia pb zn ag deposit in the southeastern segment of the lesser xing an zhangguangcai metallogenic belt ne china abstract the xinxing pb zn ag deposit is located in the southeastern segment of the lesser xing an zhangguangcai metallogenic belt ne china it is a small scale deposit pb zn

scheelite geochemistry in porphyry skarn w mo systems a case study from the gaojiabang deposit east china abstract scheelite cawo4 a hydrothermal mineral commonly displaying enrichment in mo up to 16 and or rare earth elements ree is the main economic mineral in the gaojiabang porphyry skarn type w mo deposit east china based on microscopic observations and in situ la icp ms and la mc icp ms analysis three groups of scheelite each with different geochemical characteristics can be recognized this evidence provides a good basis for considering the behavior of some trace elements in scheelite and how they may constrain ore genesis in porphyry skarn systems p group scheelite occurs inside the porphyry rocks in the form of vein hosted or disseminated scheelite these have the lowest 87sr 86sr i values 0 7089 0 7108 lowest mo concentration mean 213 ppm n 51 lree hree ratios of 16 33 84 91 and highest ree concentration 191 405 ppm with downwards sloping ree fractionation trends s group scheelite occurs in skarns coexists with skarn minerals garnet diopside epidote etc and has the highest 87sr 86sr i values 0 7103 0 7113 highest mo concentration mean 1 323 ppm n 29 highest lree hree ratio 62 6 164 and lowest ree concentrations 68 5 112 ppm also with strongly downwards sloping ree fractionation trends h group scheelite occurs within veins hosted by hornfels and displays moderate 87sr 86sr i 0 70104 0 70122 mo mean 806 ppm n 17 lree hree ratio 16 32 42 55 and ree concentration 98 3 167 6 ppm during hydrothermal precipitation of scheelite changing redox state plays a major role in controlling mo behavior both the precipitation of early skarn minerals and changing redox states of ore forming fluids likely result in an increase in mo and corresponding decrease of hree in scheelite particularly in s group scheelite the sr isotope study indicates that crustal materials provided the main source for w mo bearing ore forming fluids furthermore both fluid mixing and fluid rock interaction played an important role in the evolution of ore forming fluids formation water or groundwater was likely involved in ore formation a geochemical model is described combining data for the different types of scheelite and the behavior of mo rees and sr isotopes to constrain the evolution of ore forming fluids and constrain ore genesis in the porphyry skarn system at gaojiabang this study contributes to the fingerprinting of ore deposits using scheelite geochemistry

scheelite elemental and isotopic signatures implications for the genesis of skarn type w mo deposits in the chizhou area anhui province eastern china scheelite is well developed in hydrothermal deposits providing a window into genetic processes and facilitating comparative studies however few studies have focused on characterizing scheelite in skarn type w mo deposits the primary ore mineral in the jitoushan and baizhangyan skarn type w mo deposits anhui province eastern china scheelite was analyzed for major trace and rare earth element ree abundance and for sr nd isotopes the analysis revealed two unique geochemical characteristics that distinguish the scheelite from skarn type w mo deposits to that from vein type au w and porphyry type w mo deposits higher mo content with a negative correlation between moo 3 and wo 3 and a strong hree depletion skarn type scheelite mainly inherited ree signatures from ore forming fluids and the early precipitation of skarn minerals e g garnet diopside and amphibole has most likely resulted in the observed strong hree depletion in scheelite and the decoupling of lrees and hrees of the numerous substitution mechanisms suggested by previous workers 3ca 2 2ree 3 ca where ca is a ca site vacancy is preferred for the substitution of ree 3 for ca 2 and in this study particularly given the low salinity of ore fluids as the scheelite eu anomalies were inherited from ore forming fluids with variable redox conditions and ph the complex deu mo correlation indicates that mo increasingly entered the scheelite under oxidizing conditions and reached a maxim at deu values of 0 8 to 1 in contrast under reducing conditions mo contents in scheelite decrease gradually and mo is precipitated as molybdenite as a result of the change in dominant valence state unlike the sr nd isotope compositions of scheelite from vein type au w and w sb au deposits the scheelite from skarn type w mo deposits has low 143 nd 144 nd t most 87 sr 86 sr t values most between 0 708 and 0 715 the end t values of the scheelite varied from 16 to 12 3 in the baizhangyan deposit and from 9 5 to 9 1 in the jitoushan deposit indicating that the ore forming materials in the two w mo deposits were mainly derived from crustal sources

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

hydrothermal apatite sims th pb dating constraints on the timing of low temperature hydrothermal au deposits in nibao sw china abstract precise geochronology is a crucial tool for understanding the genesis of low temperature hydrothermal mineral deposits but datable minerals are not always available e g mineralization within sedimentary rocks such as carlin type or carlin like au deposits here we demonstrate that hydrothermal apatite associated with au from the large nibao deposit in the yunnan guizhou guangxi region of south china can be dated to yield the age of au mineralization nibao is a carlin like deposit hosted in a permian carbonate bearing pyroclastic breccia the auriferous minerals are predominantly zoned pyrite containing as cu and au rich rims euhedral and subhedral apatite forms a mosaic texture and is intergrown with hydrothermal quartz sericite and zoned auriferous pyrite indicating that the apatite is of hydrothermal origin and was coeval with au mineralization unlike sedimentary and igneous apatite hydrothermal apatite is relatively depleted in lrees enriched in mrees and slightly depleted in eu hydrothermal apatite also has high th u ratios negligible u concentrations and very low concentrations of common pb this makes the apatite a potential candidate for th pb dating our sims th pb analyses yield a weighted mean 232th 208pb age of 141 3 ma n 23 mswd 2 2 for apatite coeval with auriferous pyrite and this is the best estimate of the timing of au mineralization hydrothermal apatite is also present in similar deposits in the golden triangle of south china therefore th pb dating of hydrothermal apatite potentially allows for the accurate dating of low temperature hydrothermal deposits in china and worldwide

nd sr pb isotopic constraints on metal and fluid sources in w sb au mineralization at woxi and liaojiaping western hunan china this paper presents nd sr pb isotope data on scheelite inclusion fluids and residues of gangue quartz and sulfides from the w sb au ore deposits at woxi and liaojiaping ljp in the xuefeng uplift belt xub western hunan china sm and nd concentrations in scheelite from woxi are much lower than in scheelite from ljp and can be distinguished by their high 147sm 144nd ratios of 1 25 from the much lower ratios around 0 26 in scheelites from the ljp end values compared to values at 200 ma which is the average timing of granitoid emplacement during the indosinian yanshanian periods in the xub are around 10 for the ljp and compare well with the range of 5 to 11 defined by the granitoids whereas they are around 27 for scheelite from woxi this might indicate that rees in the mineralizing fluids at ljp originated from granitoids that are concentrated along the southern border of the xub whereas in the case of woxi the original fluids might have been masked by rees released during intense high temperature wall rock alteration of unexposed precambrian basement rocks at depth sr isotopes of scheelite from these two deposits show similar relations to host nearby rocks in that 87sr 86sr t 200 ma ratios of 0 721 for ljp scheelite agree with values ranging between 0 718 0 726 for granitoids whereas these ratios are much higher i e 0 745 for scheelite from woxi and correspond to the 87sr 86sr t 200 ma ratio range of 0 743 0 749 for precambrian host slates crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two point fluid residue tie lines in rb sr isochron diagrams however sr released from fluid inclusions generally reveals lower initial 87sr 86sr ratios than the respective residues and shows affinities to 87sr 86sr t 200 ma values of indosinian yanshanian granitoids both at woxi and ljp pb stepwise leaching of scheelite and sulfides did not result in sufficient spreads in pb isotope diagrams and therefore no information regarding exact mineralization ages in the two deposits could be deduced overall ore pb isotopes reveal upper crustal signatures and are compatible with pb isotope signatures of the predominant precambrian slates in the woxi area steep trajectories through late stage quartz sulfide mineralization in pb isotope diagrams may hint at mixing scenarios involving pb from the host rocks and a component with lower 207pb 204pb and 208pb 204pb ratios relative to 206pb 204pb ratios which cannot be linked to any known reservoir in the xub mining district sr isotopes of four out of seven residual sulfide samples from woxi plot along a paleomixing line at an age of 199 8 ma supporting a mixing scenario for the fluids indicated by the pb isotopes and pointing to a possible genetic relationship with the emplacement of indosinian yanshanian granitoids the budgets of rees rb sr and pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but after sealing of the major pathways the mineralizing fluids tend to have better preserved their original signatures these attest a genetic relationship between the metallogeny in the xub w sb au province and the emplacement of indosinian yanshanian granitoids during mesozoic intracontinental tectonic uplift and thrusting

in situ sr isotopic measurement of scheelite using fs la mc icpms abstract scheelite is one of the main ore minerals in tungsten deposits and sr isotopic compositions of scheelite can be used to examine the petrogenesis of igneous rocks and fluid metasomatism in mineralization processes both thermal ionization mass spectrometer tims and femsecond laser ablation multi collector inductively coupled plasma mass spectrometer fs la mc icp ms have been applied to analyze sr isotopic compositions in scheelite here we describe a la mc icp ms technique which can obtain in situ accurate high precision 87sr 86sr ratios from 20 to 50 m scheelite in line mode without requiring time consuming mineral separation and pre chemical procedures we found that ca dimers and ca argides do not detectably affect the obtained 87sr 86sr ratios and the adopted protocol overcomes interferences from kr rb er2 and yb2 the results of three mpi ding reference glasses kl2 g ml3b g and sths6 80 g are consistent with the recommended values here we show that the values of 87sr 86sr are relatively homogeneous for two scheelites from quartz veins and are comparable to the values determined by a traditional solution method hence these two scheelite samples have the potential to be reference materials for sr isotopic determination by la mc icp ms to illustrate the utility of the technique sr isotopes of scheelites from three different types of tungsten deposits of south china are documented the 87sr 86sr of scheelite from granite related veinlet disseminated and porphyry tungsten deposits varies systematically showing a positive correlation between sr content and 87sr 86sr ratios these micrometer scale inhomogeneities could be explained by mixing of two components reflecting intense fluid metasomatism during mineralization processes high 87sr 86sr ratios were obtained for the scheelite samples from a quartz vein type tungsten deposit indicating that the late stage ore forming fluid was mainly derived from the surrounding strata these examples show that in situ sr isotopic measurement of scheelite is a powerful tool to decipher the degree of fluid rock interaction in ore forming processes

sm nd dating and ree composition of scheelite for the honghuaerji scheelite deposit inner mongolia northeast china abstract sm nd analyses of seven scheelite samples from scheelite quartz veins in the honghuaerji scheelite deposit produce a well defined linear array on an isochron diagram with a mean square weighted deviation mswd of 0 87 corresponding to an age of 178 4 2 9 ma with end t 1 50 this age is interpreted to represent the age of scheelite mineralization the scheelite sm nd age is in good agreement with u pb ages obtained from a mineralization related granite 179 4 178 6 ma indicating that there is no apparent age gap between granite crystallization and ore formation rare earth element ree abundances in the scheelite were determined by in situ laser ablation inductively coupled plasma mass spectrometry la icp ms and the scheelite samples contain elevated ree concentrations with total ree y contents in the range of 3339 to 6321 ppm the chondrite normalized ree distribution patterns of all scheelites are middle ree mree enriched with strong negative eu anomalies eu eu 0 09 0 23 the ree characteristics of the honghuaerji scheelite suggest that ree 3 substituted into the ca site along with na and nb dominated by na whereas eu is predominantly present as eu 2 in the scheelite and may have crystallized from relatively reduced fluids all sulfur isotope data 34 s for sulfide separates range from 2 0 to 3 8 with an average of 3 2 measured 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios vary from 18 243 to 18 451 15 494 to 15 574 and 37 933 to 38 340 respectively on the basis of common sr nd pb hf isotopic characteristics between the scheelite and the host granite and the positive initial nd isotope ratios 1 46 1 52 low 87 sr 86 sr ratios 0 704983 0 705297 in the scheelites it is inferred that the hydrothermal fluids responsible for tungsten mineralization at honghuaerji were of magmatic origin with a mantle derived signature based on the regional geology tectonic evolution and geochemical evidence the honghuaerji granite is thought to have been derived from the partial melting of thickened lower crust produced during post collisional orogenic events associated with the closure of the mongol okhotsk ocean

cassiterite la mc icp ms u pb and muscovite 40 ar 39 ar dating of tin deposits in the tengchong lianghe tin district nw yunnan china the tengchong lianghe tin district in northwestern yunnan china is an important tin mineralization area in the sanjiang tethyan metallogenic domain there are three n s trending granite belts in the tengchong lianghe area with emplacement ages ranging from early cretaceous to late cretaceous and early cenozoic tin mineralization is spatially associated with these granitic rocks however the petrogenetic link between the tin deposits and the host granites is not clear because of the lack of age data for the tin mineralization we investigate the possibility of direct dating of cassiterite from three typical tin deposits in the tengchong lianghe tin district using laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms in situ la mc icp ms dating of seven cassiterite samples from the lailishan lls 1 and lls 2 xiaolonghe xlh wds dsp and hjs and tieyaoshan tys tin deposits yielded well defined 206pb 207pb 238u 207pb isochron ages to assess the accuracy of the in situ u pb dating of cassiterite 40ar 39ar dating of coexisting muscovite in samples lls 1 dsp and tys was also performed the cassiterite in situ u pb ages 47 4 2 0 71 9 2 3 and 119 3 1 7 ma respectively are in excellent agreement with the coexisting muscovite 40ar 39ar ages 48 4 0 3 71 9 1 4 and 122 4 0 7 ma respectively the u pb ages of cassiterite combined with the 40ar 39ar ages of muscovite indicate that there are three tin mineralization events in this district the lailishan tin deposit at 47 4 2 0 to 52 2 7 ma the xiaolonghe tin deposit at 71 6 2 4 to 3 9 2 0 ma and the tieyaoshan tin deposit at 119 3 1 7 to 122 5 0 7 ma these ages are highly consistent with the zircon u pb ages of the host granites it is su ggested that the cretaceous tin mineralization might have taken place in a subduction environment while the early tertiary tin metallogenesis was in a postcollisional geodynamic setting

ore genesis and fluid evolution of the qiaomaishan cu w deposit in the middle lower yangtze river metallogenic belt evidence from in situ analyses of apatite and scheelite abstract the newly exploited qiaomaishan skarn type cu w deposit located in the xuancheng ore cluster district in the middle lower yangtze river metallogenic belt mlyrb is one of the few tungsten polymetallic deposits in this region this study conducted a series of in situ analyses of elements and isotopes for apatite scheelites and sulfides aiming to provide new insights into the source hydrothermal ore forming processes fluid evolution history and genesis of this deposit and important knowledge to investigate regional tungsten mineralization events in the mlyrb apatite geochemistry shows that the early magma source of the ore related rocks in qiaomaishan obviously displayed adakitic affinity with high oxygen fugacity and featured fluorine rich fluids originating from a w rich mixed source the tungsten mineralization is dominated by scheelite in the qiaomaishan deposit based on microscopic observations and in situ analysis two types of scheelite with different geochemical characteristics were recognized two types of scheelite in the qiaomaishan have controlled by different mechanism of ree substitutions scheelite i occurs in the sulfide stage and displays high na and ree concentrations downwards sloping ree fractionation trends with negative eu anomalies and 87sr 86sr ratios 0 70945 0 71033 similar to those of ore related granodiorite porphyry however scheelite ii shows relatively low ree concentrations high na contents mree rich patterns with positive eu anomalies and high 87sr 86sr ratios 0 71477 0 72352 distinct eu anomalies and sr concentrations of the two types of scheelite and s isotopes of sulfides indicate that the early stage fluids were inherited from the primary granodioritic magmatic hydrothermal fluids however the late stage fluids were modified by intense fluid rock interactions and inputs from the host gypsum bearing carbonates collectively the f and w rich sources intense fluid rock interactions and changes in oxidation reduction conditions favoured tungsten mineralization which resulted in the formation of the qiaomaishan tungsten deposit

samarium neodymium isotope systematics of hydrothermal calcites from the xikuangshan antimony deposit hunan china the potential of calcite as a geochronometer abstract the xikuangshan antimony mine located at central hunan china is the largest antimony deposit in the world hydrothermal calcites from the xikuangshan mine display relatively large variations in ree abundance and sm nd ratios and are characterized by mree and hree enriched and lree depleted patterns sm nd isotopic compositions of syn sulfide calcites fall on well defined lines in the isochron plot calcites from early and late stage mineralization form two distinct isochrons corresponding to 155 5 1 1 and 124 1 3 7 ma respectively the isochron ages suggest that sb mineralization took place during the late jurassic early cretaceous period in the xikuangshan district consistent with previous geological observations and with independent isotope data samarium neodymium dating of calcites shows potential for determining ages of hydrothermal mineralization

characteristics and genesis of kanggur gold deposit in the eastern tianshan mountains nw china evidence from geology isotope distribution and chronology abstract the kanggur gold deposit lies in east tianshan mountains eastern section of central asia orogenic belt the gold mineralization occurs on the northern margin of the aqishan yamansu island arc in the tarim plate it is mainly hosted in lower carboniferous volcanic rocks and controlled by syn tectonic intrusions and the ductile shear zone the host rock is a calc alkaline volcanic rock series consisting of andesite dacite tuff and subvolcanic rocks the gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation ore controlling structure is ew trending normal brittle ductile shear zone the gold ore bodies are composed of au bearing altered rocks and a few au bearing sulfide quartz veins the mineralization shows vertical zonation in which au was enriched in the upper orebodies au pb zn were enriched in the middle and au cu were enriched in the lower orebodies according to mineral assemblages and alteration intensity hydrothermal alteration could be divided into three zones silicification chloritization pyritization and magnetization zone major ore body pyrite phyllic rock and or sericite alteration zone and sericite chlorite alteration zone five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins the 34 s values of sulfide in the ores range from 0 9 to 3 3 similar to those of the volcanic and subvolcanic rocks 3 21 1 3 indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur the lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks the initial 87 sr 86 sr ratios of the ores vary between 0 7077 and 0 7106 similar to those of the host rocks 0 7079 0 7125 according to the sr s and pb isotopic data it is indicated that the ore forming materials were derived from the surrounding volcanic rocks and feature deep source the 18 o values of the ore fluids vary from 3 83 to 1 77 and the d values from 46 to 66 the 18 o vs d and 18 o vs 87 sr 86 sr diagrams indicate that ore fluids were derived from dynamic metamorphic water magmatic water and meteoric water the ore forming ages of kanggur gold deposit are determined by rb sr and sm nd isochron methods the results show that the main ore forming stages of kanggur gold deposit are 290 282 ma secondary mineralization stages are 275 254 ma studies on regional geology ore geology isotope geochemistry and ore forming ages have proved that the kanggur gold deposit was formed in the compression extension transition stage during the latest paleozoic continental collision and is characterized by orogenic gold deposits

the molybdenite re os isotope chronology in situ scheelite and wolframite trace elements and sr isotope characteristics of the chuankou tungsten ore field south china abstract the chuankou tungsten ore field situated in the central area of the qing hang ancient suture zone in south china is characterized by predominantly quartz vein type tungsten mineralization that formed near the contact between the chuankou granite and slightly metamorphosed silt bearing sericite slate based on field work cathodoluminescence molybdenite re os dating and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms analysis the chuankou tungsten ore was formed at 230 6 2 9 ma to 229 4 2 6 ma in a typical indosinian metallogenic event in addition three distinct generations of scheelite and two types of wolframite can be clearly distinguished type 1 wolframite has a semiautomorphic grain or brecciated vein structure with a high heavy rare earth element hree content and an obvious negative eu anomaly type 2 wolframite grains are strongly altered as residual pseudomorphic structures by ore forming fluids and have relatively low ree contents sch 1 scheelite is present in the interior of the type 2 wolframite grains the sch 1 scheelite grains have an elevated ree content and low 87sr 86sr ratios with a strongly negative eu anomaly which suggests an inheritance signal of the host rocks comparatively sch 2 and the altered sch 1 scheelite have characteristic extremely low ree contents and remarkably strong positive eu anomalies these scheelites also have increased 87sr 86sr ratios and low 88sr signals sch 3 is idiomorphic with perfect oscillating zoning the ree content of sch 3 which typically has the lowest 87sr 86sr ratios is higher than those in sch 1 and sch 2 and the extremely high 88sr signals indicate a distinct thermal fluid event that was directly derived from the host rock the correlations between the ree and nb of scheelite imply a type b substitution of sch 1 and sch 2 but a type c substitution for sch 3 the correlation of eun and eun shows an eu3 substitution process for stages sch 1 and sch 2 and an eu2 substitution process for stage sch 3 thus we confirm that ore bearing hydrothermal rocks must undergo early stage metasomatism and filling middle stage fluid mixing between wall rocks and magmatic hydrothermal activity and refilling of late stage magmatic hydrothermal activity during the metallogenic process during the indosinian period the mineralization stages of polymetallic deposits in the indosinian were composed of stage 1 240 to 220 ma and stage 2 220 to 200 ma the chuankou tungsten ore field can be considered as the typical representation of the stage 1 metallogenic event in south china this ore field is derived from remelting of the ancient basement and was reduced by regional extension under the dominant compression regime in the south china block

dating scheelite stages a strontium neodymium lead approach from the felhertal tungsten deposit central alps austria abstract new sm nd rb sr and pb pb isotope data of scheelites and their host rocks from the felbertal scheelite deposit central tauern window eastern alps austria are presented the oldest stage 1 scheelites are rarely preserved they plot together with recrystallized stage 2 scheelite porphyroblasts on a sm nd isochron of 581 105 ma this sm nd age is regarded as the time of the primary tungsten mineralization our interpretation is enhanced by a within error limits similar age of 517 114 ma derived from a 207pb 206pb scheelite isochron and a date of 517 130 ma obtained from two co genetic relics a clinopyroxene and a tschermakitic amphibole within a metapyroxenite the stage 2 scheelite blastesis was possibly triggered by an still unassured ordovician caledonian metamorphism and further promoted by a carboniferous granitoid intrusion and a variscan metamorphism without an isotopic reset both yellowish fluorescent mo bearing stage 1 and stage 2 scheelites were formed under oxidizing alkaline conditions which obviously did not promote ree fractionation and did not disturb the original sm nd isotopic system this evidently was not the case during younger remobilizations in late variscan and alpine metamorphic times when stage 3 319 34 ma and stage 4 29 17 ma scheelites formed both stages consist of bluish fluorescent mopoor to mo free scheelites that reveal significant ree depletion and fractionation probably due to repeated corrosion and re precipitation under more reducing neutral to slightly acidic conditions the source and mechanism of deposition of the primary tungsten mineralization are deduced from five facts 1 the radiogenic strontium isotopic data of stage 1 scheelites 87 sr 86 sr 0 726 0 730 occurring together with normal crustal neodymium isotopic compositions echurt 1 3 8 to 7 3 2 unusually high u concentrations up to 74 ppm in stage 1 scheelites 3 a sudden 87sr increase between the formation of magmatic clinopyroxene 87sr 86srt 0 707 considered to have precipitated within a magma chamber and of ubiquitous tschermakitic hornblende 87 sr 86 sr t 0 736 interpreted as subsolidus mineralization during infiltration of a hydrous fluid 4 an extraordinary enrichment of cesium a lesser but still significant enrichment of rubidium and lithium and normal arc like contents of potassium in the mafites 5 the lead isotopic compositions of the scheelites and their host rocks the latter indicate a mantle signature overprinted by a crustal component at an active continental margin we suggest that a midlevel crustal position in an active continental margin setting is the most probable site for the primary tungsten source tungsten bearing ascending fluids from dehydrated granulites with mica breakdown reactions established a convective fluid system supported by gabbroic and co eval granitoid intrusions we assume that a rock mass of some 103 km3 may have undergone granulite facies reactions with fluid formation to provide the total tungsten content of 200 000 tons in the felbertal deposit this would imply that the tungsten content in the released fluid has been some 100 ppm

vadose zone lag time and potential 21st century climate change effects on spatially distributed groundwater recharge in the semi arid nebraska sand hills summary deep drainage of water below plant root zones potential groundwater recharge will become groundwater recharge gr after a delay or lag time in which soil moisture traverses the vadose zone before reaching the water table depending on the thickness of the vadose zone the magnitude of deep drainage and soil hydraulic properties lag times will vary broadly exceeding decades to centuries in semi arid and arid environments yet studies of future climate change impacts to gr have typically avoided focusing on impacts beyond 100 years and often neglect to consider lag effects caused by the vadose zone we investigate the effects of vadose zone lag time and potential 21st century climate change on the spatial distribution and timing of gr throughout the semi arid nebraska sand hills nsh region 50 000 km2 we propose a simple and rapid quantitative approach for assessment of the groundwater system response time to changes in climate understanding of such effects is needed for groundwater modeling analysis of climate change impacts on groundwater and the effective management and sustainability of future water resources lag time estimates are made using the pressure based vertical velocity of soil moisture changes equivalent to a kinematic wave approximation of richards equation the underlying assumptions unit hydraulic gradient and relatively slow changes in climate are supported by observations in the high plains aquifer region encompassing the nsh the analysis relies on four sources of input data including spatially distributed high resolution 1 1 km gr rates as the difference in 2000 2009 mean precipitation and evapotranspiration estimated using a novel modis based approach thickness of the vadose zone based on 30 m digital elevation models of the land surface and water table elevations statistically downscaled estimates of future 2010 2099 potential gr rates from two hydroclimate model projections wrcp cmip3 with opposing gr trends and estimates of hydraulic conductivity and vertical velocity of the vadose zone pressure changes using the van genuchten mualem equation we found that vadose zone lag times with a mean gr rate of 78 mm yr for 2000 2009 have an estimated spatial mean of 5 28 yrs vertical velocity of 5 68 m yr end of century lag times with mean potential gr rates of 128 and 61 mm yr for 2090 2099 have estimated spatial means of 3 78 and 6 55 yrs vertical velocities of 8 13 and 4 69 m yr for wet and dry scenarios respectively findings suggest that the highly conductive materials primarily sand deposits and high potential gr rates in the nsh lead to relatively quick drainage of vadose zone water on the order of several years less than a decade for the entire 21st century however considerable spatial variations of lag times exist due to gradients in potential gr rates and the highly variable vadose zone thickness in the nsh

constraints of in situ zircon and cassiterite u pb molybdenite re os and muscovite 40ar 39ar ages on multiple generations of granitic magmatism and related w sn mineralization in the wangxianling area nanling range south china abstract the nanling range in south china hosts numerous w sn rare metal deposits associated with several cycles of polygenetic granitic intrusions in the wangxianling area of the middle nanling range igneous intrusions include the wangxianling and hehuaping granite plutons and more than 20 granite porphyry dykes the wangxianling pluton has a central phase of medium grained tourmaline two mica granite and a marginal phase of medium grained tourmaline muscovite granite the pluton hosts several tungsten deposits including shuiyuanshan and yejiwo mineralization type is dominantly scheelite greisen with subordinate scheelite skarn and wolframite quartz veins the hehuaping pluton composed of coarse grained biotite granite and granite porphyry dykes to the east of the wangxianling pluton have an associated hehuaping tin deposit with tin skarn and subordinate porphyry and greisen mineralization in situ zircon and cassiterite u pb dating molybdenite re os and muscovite 40ar 39ar dating techniques are used to refine the age spectra of granitic rocks and w sn mineralization in the wangxianling area granites of the wangxianling pluton have zircon u pb ages of 224 ma tungsten bearing quartz veins from both the shuiyuanshan and yejiwo tungsten deposits have an average molybdenite re os isochron age of 224 ma and muscovite of scheelite greisen from the shuiyuanshan tungsten deposit yields a 40ar 39ar plateau age of 214 ma the two mineralization ages are consistent with the zircon u pb age of the wangxianling pluton indicating a close association between pluton emplacement and w mineralization in the late triassic both the hehuaping pluton and granite porphyry dykes have zircon u pb ages of 156 ma in situ la icp ms u pb dating of cassiterite in both the tin skarn and tin greisen yields an average age of 156 ma showing that the sn mineralization occurred at a similar time to the late jurassic granitic magmatism thus two mineralization events are identified in the wangxianling area and include an earlier w dominant mineralization event and a later sn dominant mineralization event the earlier event is related both spatially and temporally to intrusion of the late triassic s type wangxianling granite pluton whereas the later mineralization is associated both spatially and temporally with intrusion of the late jurassic hehuaping a2 type granite pluton and a2 type granite porphyry dykes

sm nd and rb sr isotope systematics of scheelites possible implications for the age and genesis of vein hosted gold deposits a positive correlation between present day sup 143 nd sup 144 nd and sup 147 sm sup 144 nd ratios from scheelite samples from the hollinger mcintyre coniaurum gold deposit of ontario canada corresponds to an age of 2403 plus minus 47 ma and may date the age of gold mineralization initial isotope ratios of scheelites suggest that the fluid responsible for the scheelite and gold mineralization was probably of mantle origin and that it subsequently interacted with continental crust

inhomogeneous distribution of ree in scheelite and dynamics of archaean hydrothermal systems mt charlotte and drysdale gold deposits western australia scheelite is a widespread accessory mineral in hydrothermal gold deposits and its rare earth element ree patterns and nd and sr isotopic compositions can be used to constrain the path and origin of the mineralising fluids and the age of the hydrothermal activity micro analyses by laser ablation high resolution inductively coupled mass spectroscopy and cathodoluminescence imaging reveal a very inhomogeneous distribution of the ree in single scheelite grains from the mt charlotte and drysdale archaean gold deposits in western australia two end member ree patterns are distinguished type i is middle ree mree enriched with no or minor positive eu anomaly whereas type ii is flat or mree depleted with a strong positive eu anomaly the chemical inhomogeneity of these scheelites is related to oscillatory zoning involving type i and type ii patterns with zone widths varying from below 1 to 200 m intra sectorial growth discontinuities syn crystallisation brittle deformation and variations in the relative growth velocities of crystallographically equivalent faces suggest a complex crystallisation history under dynamic hydraulic conditions the co existence of mree enriched and mree depleted patterns within single scheelite crystals can be explained by the precipitation of a mineral which strongly partitions mree relative to light and heavy ree scheelite itself has such characteristics as does fluorapatite which is locally abundant and has ree contents similar to that of scheelite in this context the systematic increase of the eu anomaly between type i and type ii patterns is produced by the difference between the partition coefficients of eu2 and eu3 and not by fluid mixing or redox reactions consequently the high positive eu anomaly typical of scheelite from gold ores may not necessarily be inherited from the hydrothermal fluid but may reflect processes occurring during ore deposition this case study demonstrates that in hydrothermal systems characterised by low ree concentrations in the fluid and by the precipitation of a ree rich mineral which strongly fractionates the ree the ree patterns of such a mineral will be highly sensitive to the dynamics of the hydrothermal system

40ar 39ar age constraints on the thermal history of the archean abitibi greenstone belt and the pontiac subprovince implications for terrane collision differential uplift and overprinting of gold deposits 40ar 39ar mineral age spectra of granitic and metamorphic rocks in conjunction with existing conventional zircon geochronology indicate that at least two major late archean thermal events affected tectonic blocks of the abitibi southern volcanic zone svz and the juxtaposed pontiac subprovince the earlier thermal activity 2690 2670 ma was accompanied by the intrusion of voluminous syntectonic plutons and caused low pressure greenschist facies metamorphism in the svz and intermediate pressure metamorphism in the pontiac subprovince the second thermal event 2660 2630 ma was coeval with the emplacement of syncollisional s type garnet muscovite granites in the pontiac subprovince and the higher grade lacorne block of the abitibi svz and reset the k ar systems in preexisting rocks magmatic amphibole from the syntectonic round lake batholith 2695 ma u pb zircon age of the abitibi svz has a slightly disturbed ar release spectrum with an upper plateau age of 2669 6 ma signifying that the low gra

hydrothermal alteration associated with mesozoic granite hosted gold mineralization at the sanshandao deposit jiaodong gold province china abstract the sanshandao gold deposit reserves of more than 200 t au and average grade of 3 96 g t located at northwestern edge of the jiaodong peninsula eastern north china craton is one of the largest gold deposits in the jiaodong gold province in this deposit disseminated and stockwork style ores are hosted in mesozoic granitoids mineralization and alteration are largely controlled by the regional sanshandao cangshang fault host granitic rocks for the deposit display a complex paragenetic sequence of alteration and mineralization activities of the sanshandao cangshang fault created structurally controlled permeability allowing for infiltration of hydrothermal fluids leading to diffusive k feldspar alteration on the two fault planes later large scale diffusive sericitization symmetrically developed across the main fault and partially overprinted the earlier k feldspar alteration following the sericitization relatively small scale silicification occurred but now it is only retained in the hanging wall of the main fault subsequently the fault gouge formed as a barrier layer which is impermeable for later fluids to move upward after that strong pyrite sericite quartz alteration occurred only in the footwall of the main fault and was accompanied by gold precipitation the last stage carbonation and quartz carbonate veins marked the waning of gold related hydrothermal activity mass balance calculations indicate complex behaviors of different types of elements during fluid rock interaction most major elements were affected by intensive mineral replacement reactions as expected the fluid mobile elements lile and lree generally show moderate to high mobility it is notable that even the commonly assumed fluid immobile elements such as hree and hfse tend to be changed to various degrees in addition y ho zr hf and nb ta fractionations are observed in altered domains studies on alteration assemblages and fluid inclusions suggest that the ore forming fluids were characterized by low salinity 8 4 wt nacl equiv moderate temperature 300 400 c weakly acidic ph 3 5 and relatively reducing log fo2 28 characteristics in this type of fluids gold was most likely transported as au hs 2 complex with alteration going on log ak ah of fluids generally decreased due to significant formation of secondary k bearing minerals in addition there might be a decrease of fo2 from pre gold alteration stage to the main gold mineralization stage and decrease of fo2 was probably one of the factors controlling gold precipitation the sr and nd isotopic compositions of hydrothermal minerals combined with previous h o and he ar isotopic studies indicate that the hydrothermal fluids were mainly derived from crustal sources e g degassing of felsic magmas and meteoric water but with involvement of mantle derived components the gold mineralization event just coincided with reactivation of the north china craton as marked by asthenosphere upwelling voluminous igneous rocks and high crustal heat flow which may have provided sufficient heat energy and fluid input required for the formation of the gold deposits

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

ore genesis of the zhuxi supergiant w cu skarn polymetallic deposit south china evidence from scheelite geochemistry abstract scheelite is the main ore mineral in skarn type tungsten deposits which can be used to track the ore forming processes and sources the zhuxi w cu deposit 3 44 mt wo3 at 0 54 and 0 10 mt cu at 0 57 located in the northern part of the jiangnan orogen is one of the largest tungsten deposits in the world skarn and orebodies occur mainly within the contact zone between the mesozoic highly fractionated intrusions and carboniferous carbonate sediments huanglong and chuanshan formations our data reveal that the rees of scheelite are mainly controlled by the substitution mechanism 3ca2 2ree3 ca scheelites from the zhuxi deposit show negative eu anomalies in the prograde skarn stage but positive eu anomalies in the retrograde skarn stage in the chondrite normalized ree patterns variation of eu anomalies recorded the ore forming processes the negative eu anomalies were inherited from the mesozoic granites and the positive ones formed under more reduced redox conditions the decrease of mo concentrations along with increase of eu and ce of scheelite from prograde to retrograde skarn stage support a temporal decrease in oxygen fugacity of the mineralization fluids the scheelites from the zhuxi deposit are characterized by low end t values 10 1 to 7 0 and high initial 87sr 86sr ratios 0 71231 0 72371 which are different from the scheelites hosted in vein type au w deposits contributed mainly by mantle the nd sr isotopes of scheelites are consistent with the results of the three mesozoic granites indicating their genetic relationship however the scheelites show variable nb ta compositions which straddle between the values of mesozoic granites and the country rock of shuangqiaoshan group meta sedimentary rocks indicating the shuangqiaoshan group also has contributed to mineralization this is different from a commonly accepted model that the ore forming fluids and metals were exsolved exclusively from the granite plutons

calcite sm nd isochron age of the shuiyindong carlin type gold deposit guizhou china abstract shuiyindong is one of the largest and highest grade stratabound carlin type gold deposits in china it is hosted in permian bioclastic limestone near the axis of an anticline hydrothermal calcite is common on the periphery of central zones of ferroan carbonate dissolution that provided the main source of iron that was sulfidized during gold deposition these calcite veins contain relatively high concentrations of rare earth elements with mree enriched patterns and yield sm nd isochron ages of 134 3 ma to 136 3 ma with significant different initial end values of 12 9 and 2 0 respectively these ages are interpreted to record age of decarbonation and gold deposition during the late stages of yanshanian orogeny the initial nd isotopic compositions of the calcites suggest that nd was primarily derived from the permian longtang formation that hosts all ore bodies at the deposit this study shows that sm nd isotopic compositions of hydrothermal calcites can be used to constrain the age and source of nd in carlin type gold deposits

u pb garnet and titanite age for the bristol township lamprophyre suite western abitibi subprovince canada a u pb age of 2687 3 ma has been determined for a garnetite dike using melanite garnet and titanite mineral separates this is the first primary igneous u pb age reported using garnet the garne

the role of fluids during formation and evolution of the southern superior province lithosphere an overview models for fluid flow and hydrothermal alteration for the abitibi greenstone belt are reviewed in the light of lithoprobe results in the region in the abitibi greenstone belt eruption of volcanic sequences over 2750 2700 ma was accompanied by pervasive low temperature hydrothermal alteration at high water rock ratios giving systematic 18o enrichment archean ambient ocean water bottom temperatures were likely ca 30 c and 18o 0 1 chert iron formations precipitated from low temperature hydrothermal discharge base metal massive sulphide deposits formed at or near the seafloor from focussed discharge of high temperature 300 400 c fluids in convective cells sited above subvolcanic intrusions the ore fluids were evolved seawater that had undergone compositional and isotopic evolution by high temperature low water rock exchange with the volcanic pile to nacl 3 7 wt or cacl2 nacl up to 30 wt brines of 18o 0 8 these volcanic associated hydrothermal deposits are associated with greenst

meso and neoarchean banded iron formations and genesis of high grade magnetite ores in the anshan benxi area north china craton a reply