hydrothermal dolomitization of jurassic cretaceous limestones in the southern alps italy relation to tectonics and volcanism dolomitization has affected up to 750m of the jurassic and cretaceous pelagic carbonate sequence of the southern continental margin of the alpine tethys the sequence crops out in the southern alps of italy monti lessini late paleocene to miocene extrusion of basaltic tuffs breccias and lavas was contemporaneous with the dolomitization was was associated with extensive tectonism in an ancient back arc basin more than 200 samples were analyzed by x ray diffraction cathodoluminescence scanning electron microscopy stable isotope ratios carbon oxygen strontium and clay mineralogy the dolomite contains 40 to 50 mgco sub 3 in thin sections the crystal size distribution is unimodal about 100 mu m possibly indicating a single nucleation for the main crystallization phase the delta sup 13 c of the dolomite is not appreciably different from the undolomitized pelagic limestone 1 0 per thousand to 2 0 per thousand peedee belemnite pdb the delta sup 18 o variation 5 0 per thousand to 13 0 per thousand pdb is due to temperature variation in the system the sup 87 sr sup 86 sr ratio in the dolomite 0 70839 0 70867 is consistent with the ratio in late oligocene miocene marine water clay minerals in limestone and dolomite differ in the presence of neoformed mg chlorite indicating a maximum temperature of about 150c for dolomitization the dolomite is suggested more to have a hydrothermal origin the heat flow associated with the volcanism allowed marine water to penetrate the system and circulate in convective cells through the tectonic breccias locally dolomitizing the limestone less

new fossil evidence and diet analysis of gigantopithecus blacki and its distribution and extinction in south china the present paper reports the recently discovered fossil teeth of early pleistocene gigantopithecus blacki and associated mammalian fauna from baeryan cave bijie county in guizhou province and also reviews briefly the known fossil sites of gigantopithecus in south china of pleistocene in early pleistocene gigantopithecus had a wider distribution but withdrew southward in middle pleistocene to a limited area mainly in south china and it disappeared in the late pleistocene according to the present fossil records diet and habitat analysis from carbon isotope evidence is used to investigate the reasons for the extinction of gigantopithecus which fed on a pure c3 diet and lived in a forest habitat it was clearly different from early hominins in south and east africa such as australopithecus africanus paranthropus robustus and paranthropus boisei which had c4 diets the extinction of gigantopithecus was also related to the great changes of climate and environment of the pleistocene especially the last one million years during which homo became more and more prosperous and exerted great pressure on g blacki

40ar 39ar constraints on a temporal link between gold mineralization magmatism and continental margin transtension in the jiaodong gold province eastern china abstract the jiaodong gold province is the largest gold repository in china both mineralization and granitoid hosts are spatially related to the crustal scale tan lu strike slip fault system which developed along the mesozoic continental margin in eastern china a series of 40ar 39ar laser incremental heating analyses of hydrothermal sericite muscovite from three major gold deposits jiaojia xincheng and wangershan and igneous biotite from the granodiorite hosts were performed to establish a possible temporal link between gold mineralization magmatism and movement along the tan lu fault zone magmatic biotite crystals yield well defined and concordant plateau ages between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewco

origin of lode gold deposits of the juneau gold belt southeastern alaska mesothermal gold bearing quartz veins along the juneau gold belt formed in the early tertiary from h 2 o co 2 n 2 h 2 s ch 4 rich low salinity fluids at temperatures of 200 to 325 c and pressures in excess of 1 1 5 kbar isotopically heavy ore forming fluids with 18 o values between 8 and 12 and d values of 20 to 30 indicate a deep seated fluid source the data are compatible with a model of ore fluid generation via metamorphic devolatilization within material subducted below the southern alaska continental margin prograde metamorphic fluids infiltrated up zones of mechanically enhanced permeability associated with the coast range megalineament and formed the gold bearing veins within brittle units at higher retrograding crustal levels deposition of gold was accomplished by several mechanisms including boiling fluid wall rock reactions and decreases in pressure and temperature of the hydrothermal fluids

zircon u pb geochronology and hf isotopes of major lithologies from the jiaodong terrane implications for the crustal evolution of the eastern block of the north china craton abstract as an important component of the western shandong complex in the eastern block of the north china craton the yishui terrane consists of neoarchean high grade supracrustal rocks granitoid gneisses and charnockites la icp ms zircon u pb dating and hf isotopic analyses on these lithologies have been carried out and the results provide new insights into the neoarchean crustal evolution of the eastern block of the north china craton new zircon dating results reveal that the magmatic precursors of the supracrustal metapelites and granitoid gneisses were generated at 2 54 2 53 ga and 2 57 2 55 ga respectively and the charnockites were emplaced contemporaneously around 2 56 2 53 ga single metamorphic zircon grains and overgrowth rims from these rocks document consistent metamorphic ages at 2 50 ga suggesting that the yishui terrane experienced a high grade metamorphic event at the end of the neoarchean detrital zircons from pelitic gneisses yield 207pb 206pb ages of 2 89 2 65 ga with a major age peak at 2 53 ga and a subordinate age peak at 2 70 ga implying that the sedimentary protoliths of the pelitic gneisses may have been sourced from 2 53 ga rocks in the yishui terrane and 2 70 ga rocks in the adjacent luxi granite greenstone terrane hf isotopic compositions show that the neoarchean magmatic zircons have positive ehf t values ranging from 1 4 to 7 8 and depleted mantle model ages of 2 92 2 60 ga with a prominent peak at 2 8 2 7 ga suggesting that the neoarchean crust was derived mainly from juvenile sources and partly from the recycling of old continental crust in the yishui area combined with previous data from the adjacent luxi granite greenstone terrane and other complexes in the eastern block it is concluded that the neoarchean was an important period of crust accretion in the eastern block of the north china craton

nature age and tectonic setting of granitoid hosted orogenic gold deposits of the jiaodong peninsula eastern north china craton china the jiaodong gold province along the southeastern margin of the north china craton has combined production and resources of 900 tonnes of gold more than 95 of the gold in this province is hosted in mesozoic granitoids which intruded late archean metamorphic basement rocks episodically at ca 160 150 and 130 126 ma the deposits of the jiaodong peninsula form one of the largest provinces of granitoid hosted lode gold deposits in the world the jiaodong gold deposits occur as massive auriferous quartz veins hosted in subsidiary second or third order faults and as disseminated and stockwork style mineralization hosted in alteration zones along major regional scale faults mineralization took place during brittle reactivation d3 of pre existing d2 ductile shear zones wall rock alteration is dominated by k feldspar and sericite with also sulfide minerals and extensive silicification closest to the orebodies the alteration was accompanied by the introduction of volatiles fe mg k rb ag as au bi and sb enrichment of base metals in the gold lodes is generally low although locally significant gold deposition took place at temperatures of 250 to 350 c for most gold deposits and the ore fluids are co2 bearing and have calculated salinities of 6 13 wt nacl equiv deposits from the zhao ye xixia and muping rushan belts have similar if not identical structural controls alteration patterns ore mineral assemblages and stable isotope signatures lead isotope data indicate that the ore stage leads were buffered by their host rocks the granitoid hosted gold deposits in the zhao ye belt are most radiogenic the greenstone hosted deposits in the xixia belt is the least radiogenic and the granitoid hosted deposits in the muping rushan belt have intermediate compositions gold mineralization in the zhao ye xixia and muping rushan belts in the jiaodong gold province appears to be broadly contemporaneously at ca 130 120 ma as constrained by shrimp u pb zircon dating on host rocks and a post gold dike as well as by ar ar rb sr and k ar dating of hydrothermal alteration minerals and ores this early cretaceous age is about 100 million years younger than the peak of ultra high pressure metamorphism in the qinling dabie sulu orogen between the north china and yangtze cratons and about 500 km south of the gold province however it overlaps with the extension and exhumation stage of the collisional orogeny and the subduction of the pacific plate beneath the eurasian continental crust whereas the majority of the jiaodong gold deposits occur on the margin of the north china craton some also occur in the suture zone between the two cratons they are significantly landward relative to the subduction zone of the pacific plate compared with typical orogenic lode gold deposits globally lode gold deposits of ca 130 120 ma occurred on both sides of the tan lu fault zone available data favor a temporal link of gold mineralization with pacific plate subduction

flash vaporization during earthquakes evidenced by gold deposits fluids flowing through cavities in earth s crust can deposit gold thermo mechanical modelling of a fluid filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously

palynological analysis of the late early pleistocene sediments from queque cave in guangxi south china abstract palynomorphs extracted from the sediments in queque cave of the late early pleistocene in chongzuo guangxi zhuang autonomous region were investigated to reconstruct the paleoenvironment in the study area while the sediments are pollen poor they are sufficiently productive to carry out a paleoenvironmental analysis the source vegetation reflected by the palynomorphs from the unfossiliferous layer was temperate to warm temperate deciduous and evergreen broadleaved forest while it was warm temperate to subtropical deciduous and evergreen broadleaved forest from the mammalian horizons climatic parameters obtained using the coexistence approach indicate that the unfossiliferous layer mat 11 3 15 4 c map 601 1 1076 1 mm was cooler and drier than that from the mammal bearing layers mat 12 6 18 6 c map 784 7 1523 1 mm

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

the early pleistocene gigantopithecus sinomastodon fauna from juyuan karst cave in boyue mountain guangxi south china abstract as one of the most important quaternary mammalian faunas in southern china the gigantopithecus sinomastodon fauna has received much attention the large primate fossil teeth newly collected from juyuan karst cave in boyue mountain guangxi zhuang autonomous region of southern china can be identified as gigantopithecus blacki the morphology and size of these g blacki teeth differ from those of the middle pleistocene gigantopithecus teeth which hold evidently larger dental dimensions and more complex crenulations from hejiang cave also in guangxi and tham khuyen cave in vietnam however the g blacki teeth from juyuan cave are relatively similar to those from early pleistocene mohui cave and liucheng gigantopithecus cave both in guangxi which suggests that the three cave sites have similar age the juyuan fauna associated with gigantopithecus blacki consisting of 45 mammalian species such as sinomastodon yangziensis ailuropoda wulingshanensis stegodon huananensis and rhinoceros fusuiensis is a typical early pleistocene gigantopithecus sinomastodon fauna of southern china the juyuan fauna is mostly similar to mohui fauna also implying their contemporaneity paleomagnetic analyses demonstrate that the fossil bearing sediments in juyuan cave are dominated by normal polarity combining the faunal analysis and magnetostratigraphic evidence the juyuan sediments can be best correlated with the olduvai normal subchron giving an estimated age of 1 8 ma

geochronology of ailuropoda stegodon fauna and gigantopithecus in guangxi province southern china abstract pleistocene faunas from south china are difficult to subdivide based on the long temporal ranges of many taxa and a reduced number of genera in comparison to faunas from temperate north china in south china the ailuropoda stegodon fauna is a very general one and includes a relatively stable suite of genera that apparently persisted for long periods of time these attributes have made constraining its time range difficult application of electron spin resonance esr dating of tooth enamel constrains the ages well where uranium uptake was minor where uranium uptake into teeth was significant an approach combining esr and 230th 234u isotopic analysis also yields excellent ages previous estimates of early middle and late pleistocene time ranges previously determined by biostratigraphic seriation for the ailuropoda stegodon fauna are confirmed in all cases but are made more precise with our approach including specific time ranges for certain archaic taxa absolute dating also yields an extended time range for gigantopithecus blacki of 1200 to 310 ka

implications of pyrite geochemistry for gold mineralisation and remobilisation in the jiaodong gold district northeast china abstract the jiaodong gold district of eastern china the largest gold producing district in china is located on the eastern margin of the north china craton it consists of three mineralisation belts the western zhao ye belt the middle qixia belt and the eastern muping rushan muru belt over 85 of mineralisation is hosted in the zhao ye belt which is bordered by the mantle tapping tan lu fault zone pyrite crystals from three deposits in the zhao ye belt and three deposits in the muru belt were studied using a combination of optical petrography bulk pyrite geochemistry and in situ laser ablation icp ms results show that although mineralisation is broadly similar between the two belts there are significant differences in ore and gangue mineral textures pyrite geochemistry and style of gold mineralisation texturally pyrite grains from the zhao ye belt are generally cubic and do not exhibit zoning in contrast muru pyrite grains are more often pyritohedral commonly exhibit well defined concentric zoning and display textures in ore and gangue minerals indicative of open space growth bulk pyrite geochemistry suggests a distinct enrichment in pb bi au ag and te in the zhao ye belt whereas the muru belt pyrite is significantly enriched in as cu and co in situ pyrite geochemistry indicates that au and as are variably correlated in the zhao ye belt typically only exhibiting correlation at low au concentrations most gold occurs as visible electrum along pyrite fractures and grain boundaries with a minor generation of invisible gold formed through as facilitated uptake into pyrite in the muru belt au and as have a strong correlation and there is limited occurrence of gold particles indicating that most gold in the muru belt is invisible gold contained in the crystal structure of as rich pyrite the differences in style of gold mineralisation between the belts indicates an inherent difference in timing of gold introduction in the zhao ye belt the visible electrum accounting for most of the gold endowment is formed post pyrite whereas the invisible gold in the zhao ye and muru belts is formed syn pyrite the heterogeneity in gold distribution in the jiaodong district is attributed to melting of metallogenically fertile archean crust at the base of the well endowed zhao ye belt and the lack of a similarly fertile source region beneath the muru belt

the relations between mean rock stress and fluid flow in the crust with reference to vein and lode style gold deposits abstract fluid movement in the crust at the typical depths of formation of vein and lode style gold deposits will be dominated by upward flow focussing of upward flow into discrete channelways as required to form gold deposits is due to lateral gradients in fluid pressure fluid channelways should have lower fluid pressures than surrounding rock if lateral gradients are induced by variations in permeability this is however at variance with inferences from quartz vein structures of high relative fluid pressures during the formation of gold deposits focussing into zones of low mean rock stress will in contrast be associated with high relative fluid pressures in the zone of focussed fluid flow variations in mean rock stress are a direct consequence of a regional deviatoric stress acting on an inhomogeneous rock sequence analysis of stress fields shows a wide variety of potential sites of low mean stress dependent on the geometry of rock units and on patterns of faults fractures or shear zones a model of fluid focussing in the crust due to variations in mean stress is thus consistent with the large variety of structural setting of vein and lode gold deposits observed in nature use of the model through the technology of stress mapping has the potential to generate viable exploration targets

shrimp u pb dating trace elements and the lu hf isotope system of coesite bearing zircon from amphibolite in the sw sulu uhp terrane eastern china abstract in this study we link mineral inclusion data trace element analyses u pb age and hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi stage metamorphic evolution of amphibolites from the sulu ultrahigh pressure uhp terrane eastern china zircon grains separated from amphibolites from the ccsd mh drill hole g12 and niushan outcrop g13 were subdivided into two main types based on cathodoluminescence cl and laser raman spectroscopy big dusty zircons with inherited cores and uhp metamorphic rims and small clear zircons weakly zoned grey white luminescent inherited cores preserve mineral inclusions of cpx pl ap qtz indicative of a mafic igneous protolith dark grey luminescent overgrowth rims contain the coesite eclogite facies mineral inclusion assemblage coe grt omp phe ap and formed at t 732 839 c and p 3 0 4 0 gpa in contrast white luminescent small clear zircons preserve mineral inclusions formed during retrograde hp quartz eclogite to lp amphibolite facies metamorphism t 612 698 c and p 0 70 1 05 gpa inherited zircons from both samples yield shrimp 206 pb 238 u ages of 695 520 ma with an upper intercept age of 800 31 ma the uhp rims yield consistent triassic ages around 236 225 and 239 225 ma for g12 and g13 with weighted means of 229 3 and 231 3 ma respectively small clear zircons from both samples give 206 pb 238 u ages around 219 210 ma with a weighted mean of 214 3 ma interpreted as the age of retrograde quartz eclogite facies metamorphism matrix amphibole from both samples indicate ar ar ages of 209 0 7 and 207 0 7 ma respectively probably dating late amphibolite facies retrogression the data suggest subduction of neoproterozoic mafic igneous rocks to uhp conditions in middle triassic 230 ma times and subsequent exhumation to an early hp 214 ma and a late lp stage 208 ma over a period of 16 and 6 myr respectively thus early exhumation from a mantle depth of 120 100 km to about 60 km occurred at an average rate of 0 3 cm y while subsequent exhumation to a middle crustal level took place at approximately 0 54 cm y these exhumation rates are considerably slower than those obtained for uhp rocks in the dora maira and kokchetav massifs 2 3 cm y based on similar p t estimates and trace element and hf isotope compositions sulu amphibolites can be identified as retrograde uhp eclogites the ehf 800 of 8 implies a significant input from the depleted mantle to the sulu dabie terrane during the middle neoproterozoic overgrown rims are characterized by a distinct trace element composition with low lu hf and th u and significantly higher 176 hf 177 hf ratios than inherited cores consistent with formation during after garnet re crystallization and fractionation of the lu hf system during uhp metamorphism the combined dataset suggests homogenization of the 176 hf 177 hf ratio within the metamorphic mineral assemblage and during protolith formation observed variations are explained by mixing of material from both domains during laser ablation e g due to partial recrystallization of inherited cores

u series and esr u series dating of the stegodon ailuropoda fauna at black cave guangxi southern china with implications for the timing of the extinction of gigantopithecus blacki abstract gigantopithecus blacki was once a common primate during early pleistocene distributed throughout southern china but then it gradually declined with time and finally became extinct probably during middle pleistocene black cave in guangxi the zhuang nationality autonomous region was the first site yielding g blacki teeth in situ in 1956 it also produced numerous mammalian fossils belonging to the typical middle pleistocene stegodon ailuropoda fauna from sediments overlying the g blacki level the present study carried out coupled esr u series dating study of five bovidae teeth from this palaeontological layer and obtained a weighted mean age of 383 20 ka for this stegodon ailuropoda fauna this age estimate on fossil teeth is constrained by two 230 th u ages of 404 24 ka and 382 9 ka obtained on speleothems formed below and above the level of the stegodon ailuropoda fauna the black cave stegodon ailuropoda fauna can be therefore correlated with mis 11 and the remains of g blacki should be older than 400 ka

petrochemical evidence on the probable origin of ferriferous metasediments in western bushmanland the mineralized proterozoic metasediments of bushmanland are characterized by the presence of ferriferous rocks this includes banded and unbanded iron formations and various types of gossans these units are not laterally extensive and occur in different stratigraphic levels the prevalent minerals in the ferriferous rocks are hematite magnetite quartz garnet muscovite biotite and sillimanite but less common occurrences of graphite alunite plumbojarosite gahnite and dufrenite have been noted the chemical variation wt is extensive total fe2o3 1 3 93 5 sio2 4 93 al2o3 0 2 14 0 cao 0 02 20 7 mno 0 0 14 3 mgo 0 0 5 7 tio2 0 0 4 4 na2o 0 0 2 0 k2o 0 0 1 5 and p2o5 0 1 7 0 the preliminary nature of the data set precludes however firm conclusions regarding stratigraphic control of the chemical composition the trace element contents ppm extend over several orders of magnitude zn 0 7 000 ba 0 5 200 cu 0 1 400 pb 0 1 070 and ni 6 540 collectively the data indicate that most of the ferriferous rocks represent highly metamorphosed sediments

climate influenced cave deposition and human occupation during the pleistocene in zhiren cave southwest china abstract a large number of hominin fossil bearing caves in south china have yielded evidence for the occupation of early modern humans during the middle to late pleistocene however the geology of these caves and the paleoenvironmental context of human occupation remain poorly documented and understood in this study we obtained new ages yielded by mc icpms uranium series dating of speleothems from zhiren cave guangxi where a partial early modern human mandible and 2 m have been recovered the ages demonstrate that cave infilling of zhiren cave began at 1 ma much earlier than the date previously suggested our dating results also suggest that fossils of anatomically modern human were deposited in zhiren cave during marine isotope stage mis 6 between 190 and 130 ka representing the oldest known anatomically modern human remains in east asia the cave s sedimentary processes and the paleoenvironmental changes were reconstructed based on detailed analyses of lithostratigraphy grain size pollen assemblages and the chemical weathering intensity of the sediments inside zhiren cave the results show that major climatic changes in the middle pleistocene led to the accelerated incision of local streams and the erosion of cave sediments by controlling the regional hydrological response during the early to middle pleistocene after 300 ka increased climatic contrasts between glacial and interglacial periods dominated the accumulation of sediments and the occupation of mammals and early modern humans in zhiren cave gradually desiccating climatic conditions and reduced forest cover during the penultimate glacial period mis 6 may have define a temporal window for the human occupation of zhiren cave providing ideal environmental conditions however floodwater incursion and or dense vegetation cover corresponding to a much warmer and wetter climate in the subsequent last interglacial mis 5 may have discouraged humans from further occupying zhiren cave

cretaceous cenozoic tectonic history of the jiaojia fault and gold mineralization in the jiaodong peninsula china constraints from zircon u pb illite k ar and apatite fission track thermochronometry the jiaojia fault jjf in the jiaodong area of eastern china is an important nne trending structure that is subsidiary to the regional tancheng lujiang tan lu fault zone and hosts 1200 t of gold reserves contained in disseminated and stockwork ore dominantly in the footwall of the fault we present new zircon u pb apatite fission track and illite k ar data along the jjf and have delineated its tectonic history focusing on its formation and reactivation zircon u pb dating shows that the shangzhuang granite is a composite body with ages between 132 1 and 127 1 ma illite k ar ages for the fault s gouge range from 83 2 to 68 2 ma and the measured apatite fission track ages for ores are between 55 and 21 ma previous zircon u pb geochronology and structural studies suggest that the jjf was originally activated in the jurassic during 160 150 ma as a sinistral fault the jjf was a normal fault in the early cretaceous due to nw se orientated tension and ne sw compression which lasted from 135 to 120 ma this was followed by sinistral strike slip faulting due to nw se compression and ne sw tension during 120 110 ma and it changed to normal displacement at ca 110 ma our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca 55 ma previous age data of ca 130 110 ma for gold mineralization along the jjf coincides with the early cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike slip faulting of the jjf in early cretaceous which is interpreted to be due to changing direction of the subducting pacific plate

geology and timing of mineralization at the cangshang gold deposit north western jiaodong peninsula china the cangshang gold deposit of the north western jiaodong peninsula contains reserves of greater than 50 tonnes t and is developed by the largest open pit gold mine in china this deposit is a jiaojia style i e disseminated and veinlet deposit it is controlled by the san cang fault zone which trends 040 and dips 40 75 se at the mine site the main no 1 orebody lies between a hanging wall of precambrian metamorphic rocks mainly amphibolite of the fenzishan group and a footwall composed of the mesozoic linglong granitoid the ore zone is mainly composed of pyritized sericitized and silicified granitoid which has undergone variable degrees of cataclasis shrimp u pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530 17 ma and underwent metamorphism at 1852 37 ma the footwall granodiorite has been dated at 166 4 ma whereas zircons from the ore zone yield a younger age of 154 5 ma cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons therefore are all interpreted to be representative of magmatic crystallization dating of sericite by 40ar 39ar has been used to directly determine the timing of formation of the cangshang deposit providing the first time absolute age on formation of the jiaojia style gold deposits the well defined age of 121 3 0 2 ma provides the precise timing of gold mineralization at the cangshang deposit this age is consistent with those of linglong style vein type gold mineralization also from the north western jiaodong peninsula at between 126 and 120 ma therefore our work indicates that both styles of gold deposits in the jiaodong peninsula were formed during the same mineralization event

new 400 320 ka gigantopithecus blacki remains from hejiang cave chongzuo city guangxi south china abstract gigantopithecus blacki is a typical member of the stegodon ailuropoda faunal complex sensu lato that inhabited southern china or more broadly mainland southeast asia during the early and middle pleistocene current evidence indicates that the giant ape became extinct during the middle pleistocene recently new remains of g blacki and associated mammalian fossils have been unearthed from a karst cave site hejiang cave in chongzuo city guangxi south china the age of the gigantopithecus bearing depositional unit is estimated to be 400 320 ka using 230th 234u disequilibrium u series dating of flowstone samples bracketing the deposits these finds document the latest occurrence of gigantopithecus and provide potential insights regarding its extinction comparisons of dental dimensions between the hejiang g blacki remains more than four hundred isolated teeth from early pleistocene localities and over ninety isolated teeth from local drugstores show that the hejiang teeth are slightly larger in their buccolingual dimensions in addition the crowns of the three unerupted upper premolars differ from those of all of the other gigantopithecus material in having more complex crenulations the differences in dental dimensions and morphology are possibly reflective of dietary responses to environmental changes that eventually led to the extinction of gigantopithecus

the intraplate character of supercontinent tectonics abstract for several decades geoscientists have recognised intraplate tectonic activity far from plate margins both from modern and ancient examples this apparent disconnect with the drivers of plate tectonics does not necessarily imply unconnected processes but rather an uncertainty in understanding exactly how these systems operate are the driving forces derived locally or do they propagate from plate margins how do these forces interact with a complex tectonic inheritance to generate the observed tectonism furthermore what novel approaches have been applied to understand these processes here we review the general literature and the contents of this special issue to develop some partial answers to these questions key observations include the critical importance of local lithospheric heterogeneities as a control on the mode of orogenesis and also the role of locally derived forces from mantle upwelling or from depositing thick piles of magmatic or sedimentary rocks these processes happen within the overarching tectonic setting provided by far field plate margins which show intimate links in both time and observed processes with many intraplate regions these insights would not be possible without a growing arsenal of geological geophysical and numerical methods that can be applied to intraplate regions and this is reflected in the varied approaches within the issue we envisage that this special issue will provide a stimulus for further progress in understanding intraplate tectonics

tectonics and distribution of gold deposits in china an overview gold exploration in china has expanded rapidly during the last two decades since a modern approach to economic development has become a national priority china currently produces 180 tonnes t of gold annually which is still significantly less than south africa usa and australia however china is now recognized as possessing significant gold resources in a wide range of mineral deposit types present estimates of gold resources in china exceed 4 500 t which comprise 60 in gold only deposits more than 25 in base metal rich skarn porphyry and vein deposits and more than 10 in placer accumulations the major gold provinces in china formed during the main episodes of phanerozoic tectonism such tectonism involved interaction of china s three major precambrian cratons north china tarim and yangtze or south china when combined with cathaysia block with the angara or siberian kazakhstan kyrgyzstan and indian cratons resulting collisions included deformation of accreted oceanic sequences between the cratonic blocks the most important ore forming orogenies were 1 the late paleozoic variscan 405 270 ma which led to amalgamation of the angara north china and yangtze cratons 2 the indosinian 270 208 ma which led to the collision of north china and south china cratons 3 the yanshanian 208 90 ma which was largely influenced by the subduction of the izanagi pacific plates beneath eastern china and 4 the himalayan 90 ma indentation of the indian continent into eurasia no important precambrian gold systems are recognized in china mainly because of reworking of exposed precambrian rocks by these younger orogenies but there are a few caledonian 600 405 ma gold bearing systems in northern xinjiang most of china s orogenic epithermal and carlin like gold deposits are in the reworked margins of major cratonic blocks and in metasedimentary rock dominated fold belts adjacent to these margins accordingly the major gold provinces are present along the northern southeastern and southern margins of the north china craton along the southwestern and northwestern margins of the yangtze craton in the tianshan and altayshan orogenic belts in northern xinjiang and throughout the southeastern china fold belt gold placer deposits derived from these primary deposits are concentrated in the northernmost part of northeastern china and along the northwestern margin of the yangtze craton the major provinces with significant gold in porphyry related copper systems and base metal skarns are present in the yangtze river area along the northeastern and southeastern margin of the yangtze craton in the fold belt in southwestern china and scattered through northern china three quarters of the chinese gold only deposits occur within the north china craton margins half are located in the uplifted precambrian metamorphic rocks and most of the remainder are hosted in the phanerozoic granitoids that intruded the reworked precambrian terranes the abundance of granite hosted gold contrasts the north china craton with other precambrian cratons such as those in western australia central canada and zimbabwe where gold is mainly hosted in the archean greenstone belts this difference may be explained by the multiple episodes of phanerozoic tectonism along the north china craton margins resulting from the collision of the angara north china and south china cratons and from subduction of the izanagi pacific oceanic plates underneath the eastern china continent

juvenile vs recycled crust in ne china zircon u pb geochronology hf isotope and an integrated model for mesozoic gold mineralization in the jiaodong peninsula abstract the continental crust of the north china craton ncc is a major reservoir of mineral resources with imprints of secular changes in tectonics and metallogeny the jiaodong peninsula located in the eastern margin of the north china craton ncc is currently one of the largest gold producers over the globe and preserves the records of multiple magmatic and metamorphic events here we characterize the timing and tectonics of the major mesozoic magmatism and the associated gold metallogeny in this region through a comprehensive u pb geochronological and hf isotope investigation of zircons in a suite of granitoids mafic magmatic enclaves melanocratic dikes and melted basement rocks the linglong granite hosting one of the major gold deposits in jiaodong shows emplacement ages between 150 and 160 ma and the dominantly negative e hf t values 34 0 to 23 8 of zircons from this intrusion suggest magma derivation from recycled components in the archean basement the guojialing granodiorite and its mafic magmatic enclaves show similar ages between 123 and 127 ma with negative e hf t values 19 3 to 16 8 corresponding to crustal magma source the melanocratic dikes belonging to pre and syn mineralization stages with u pb age range of 126 to 166 ma display large variation in their zircon e hf t values 25 7 and 2 3 suggesting the involvement of both recycled crustal and juvenile mantle components zircons in the melted basement rocks with ages in the range of ca 127 132 ma also display both positive and negative e hf t values 44 6 and 9 8 indicating a mixture of recycled ancient crust and juvenile magmas our study shows that although the peak of gold metallogeny coincided with the tectonics associated with pacific plate subduction which mobilized and concentrated the ores the source materials of gold mineralization and magmatism had multiple origins including from the precambrian basement rocks mesozoic granitoids and mantle derived mafic magmas with extensive mixing of crustal lithosphere mantle and asthenospheric components a combination of delamination mantle upwelling subduction related metasomatic enrichment and recycling of ancient components facilitated the gold metallogeny in this region our study provides a typical case of juvenile and recycled components in the formation and evolution of continental crust and associated mineral resources

qingyuan high grade granite greenstone terrain in the eastern north china craton root of a neoarchaean arc abstract the qingyuan high grade granite greenstone terrain is one of the first recognized granite greenstone terrains in the eastern north china craton similar to other archaean terrains its tectonic environment is debated was it an intra continental rift or a modern analogy of arc occurrence and petrogenesis of major igneous series the ultramafic mafic and felsic volcanic rocks 2510 ma and the plutons of the quartz diorite 2570 2510 ma ttg 2570 2510 ma and quartz monzodiorite 2510 2490 ma series in xinbin area are investigated the mafic intrusives and volcanic rocks have high mgo content 5 4 7 5 wt and mg number 48 61 they show slightly depleted to flat trace element patterns the ultramafic rocks serpentinite could be genetically related to the mafic rocks the meta dacite rhyolite is adakitic with enriched light and middle rees and liles but significantly depleted hfses the quartz diorite has high mg number 60 64 moderately enriched light and middle rees and liles the ttg shows distinct light but moderate middle ree enrichment prominent nb ta depletion but zr hf enrichment zr sm 100 the quartz monzodiorite has moderate light and middle ree enrichment significant nb ta depletion and negative eu sr anomalies the ttg has more depleted sr nd isotopes endt 2 6 87sr 86srt 0 700 than all the others endt 0 2 87sr 86srt 0 701 703 their petrogenesis can be explained by an archaean style subduction defined as a mantle wedge absent flat hot subduction with significant vertical tectonism in the overriding slab the ultramafic mafic rocks were originated from primitive mantle the meta dacite rhyolite was originated from the eclogite facies overriding crust the quartz diorite was a mixture of melts from mantle and the overriding crust the ttg was from the subducting slab under amphibolite to amphibole bearing eclogite facies and the quartz monzodiorite was from the subducting slab after the derivation of the ttg the qingyuan terrain represents remnants of the root of a neoarchaean arc its anticlockwise p t path recorded the initiation of the arc to its cession and exhumation cratonization at 2480 ma

paleoenvironmental background of the early pleistocene gigantopithecus fauna in bubing basin south china thanks to the presence of the enigmatic gigantopithecus fossils vertebrate paleontologists have spent much time analyzing the pleistocene faunas of southern china although research has been conducted in the region for more than one half century the vast majority of this research has focused on the direct analysis of the associated vertebrate fossils particularly for taxonomic identification purposes in order to develop a firmer understanding of the paleoenvironment in which these various taxa lived there is still a relative paucity of data derived from other lines of evidence besides taxonomic identifications here we contribute to these paleoenvironmental reconstructions of southern china by presenting the results of clay mineral composition and geochemical analyses of the deposits from the early pleistocene mohui cave bubing basin guangxi in general the mohui cave clay mineral samples are dominated by kaolinite which indicates a warm and humid climate the relatively high content of smectite in unit ii implies a relatively long dry season within the overall context of the warm and humid environment based on the chemical index of alteration cia the estimated land surface temperature during the early pleistocene 27 c was much higher than today 21 9 c our results are consistent with previous environmental reconstructions based on vertebrate paleontological and isotopic studies of the gigantopithecus fauna in southern china that the environment during the early pleistocene was warmer and more humid than today

the jiaodong type gold deposits characteristics origin and prospecting abstract the jiaodong type comprises a unique class of gold mineralisation which includes the linglong type quartz vein hosted and the jiaojia type fracture disseminated style deposits although the type area is in the jiaodong peninsula in ne china where some of the world s richest gold reserves occur we identify similar occurrences in other parts of china and elsewhere in the world under this category the ore fluids migrated upwards forming quartz vein type of gold ore linglong type wherever the ore controlling fractures are at high angles fluid infiltration into the surrounding wall rocks and generation of the jiaojia type disseminated style deposits resulted where the ore bearing fluids encountered low angle fractures on a regional scale the jiaodong type gold mineralisation occurs along the margins of reactivated cratons within the interior of cratons along paleosuture zones or along the junctions of micro blocks and is distinctly different from the classic orogenic gold in terms of their tectonic setting ore characteristics and genetic history unlike skarn and porphyry type of deposits the jiaodong type gold deposits do not always show close spatial relationship with magmatic intrusives and some of the deposits occur distal to plutons 10 km in this paper we evaluate the salient geological geochronological geochemical and isotopic features of the jiaodong type gold deposits and propose some general guidelines for gold prospecting based on case studies we predict that the gold lodes in the jiaodong type mineralised zones might extent vertically up to 3000 m with only minor mineralogical and geochemical variations

an integrated mineral system model for the gold deposits of the giant jiaodong province eastern china abstract the giant jiaodong gold province with more than 5000 t of proven gold resources is unique in that its mesozoic gold deposits are hosted in a precambrian basement block there has long been debate on the source of gold the mechanism for its extreme enrichment and a holistic genetic model for these spectacular deposits in order to improve understanding of these factors a mineral system model is proposed for the jiaodong gold deposits for the first time it is based on a detailed review of the architecture and composition of the underlying mantle lithosphere the geodynamic setting at the time of gold mineralization the geological and geochemical features of the deposits themselves and mechanisms of their preservation regional geodynamic reconstructions combined with the nature of mesozoic magmatic systems show that late mesozoic breakoff of the subduction slab and rollback of the paleo pacific plate caused asthenosphere upwelling and lithosphere extension and thinning robust geochronological studies demonstrate that the jiaodong gold deposits formed at ca 120 ma during a change of subduction direction of the paleo pacific plate and the synchronous transition of tectonic regime from regional compression to transpression or transtension prior to peak extension caused by thinning of the lithosphere geophysical exploration data and hf nd isotope mapping of the jiaodong peninsula reveal a relatively simple ancient crustal structure cut by near vertical shear or fault zones including the lithosphere scale tan lu and wulian yantai faults that provided the first order architecture for emplacement of mantle magmas and sub crustal fluids in terms of fertility the significant older pre mineralization crustal metamorphism combined with sulfur lead and strontium isotope ratios indicate a dominant sub crustal source for the ore components for the jiaodong gold deposits consistent with evidence for volatile and gold fertilized metasomatized mantle lithosphere beneath the north china block helium ar and c o isotope ratios implicate mantle sources of ore fluids with contamination by crustal components en route to crustal depositional sites in terms of crustal architecture combined geophysical structural mineralogical fluid inclusion and geochemical studies show that the deeply sourced ore fluids and metals advected upwards through lithosphere scale faults to deposit gold via sulfidation and phase separation in crustal scale nne ne trending fault systems at mid to upper crustal levels preservation of disseminated to stockwork style deposits and auriferous quartz pyrite vein deposits was enhanced by deep crustal formation combined with limited uplift and exhumation of the province the jiaodong gold deposits although commonly hosted in granite intrusions clearly post date them on the basis of robust and reliable geochronology the spatial but non temporal relationships of gold deposits with granites their strong structural control and their other characteristics clearly place them in the orogenic gold group it is suggested because of their uniqueness that they be termed jiaodong type orogenic gold deposits

timing and structure of the 8 2 kyr b p event inferred from δ18o records of stalagmites from china oman and brazil oxygen isotope records of stalagmites from china and oman reveal a weak summer monsoon event with a double plunging structure that started 8 21 0 02 kyr b p an identical but antiphased pattern is also evident in two stalagmite records from eastern brazil indicating that the south american summer monsoon was intensifi ed during the 8 2 kyr b p event these records demonstrate that the event was of global extent and synchronous within dating errors of 50 years in comparison with recent model simulations it is plausible that the 8 2 kyr b p event can be tied in changes of the atlantic meridional overturning circulation triggered by a glacial lake draining event this in turn affected north atlantic climate and latitudinal position of the intertropical convergence zone resulting in the observed low latitude monsoonal precipitation patterns

dated co occurrence of homo erectus and gigantopithecus from tham khuyen cave vietnam abstract tham khuyen cave lang son province northern vietnam is one of the more significant sites to yield fossil vertebrates in east asia during the mid 1960s excavation in a suite of deposits produced important hominoid dental remains of middle pleistocene age we undertake more rigorous analyses of these sediments to understand the fluvial dynamics of pleistocene cave infilling as they determine how skeletal elements accumulate within tham khuyen and other east asian sites uranium thorium series analysis of speleothems brackets the pleistocene chronology for breaching infilling and exhuming the regional paleokarst clast analysis indicates sedimentary constituents including hominoid teeth and cranial fragments accumulated from very short distances and under low fluvial energy electron spin resonance analysis of vertebrate tooth enamel and sediments shows that the main fossil bearing suite s1 s3 was deposited about 475 thousand years ago among the hominoid teeth excavated from s1 s3 some represent homo erectus and gigantopithecus blacki criteria are defined to differentiate these teeth from more numerous pongo pygmaeus elements the dated co occurrence of homo erectus and gigantopithecus blacki at tham khuyen helps to establish the long co existence of these two species throughout east asia during the early and middle pleistocene

early pleistocene large mammal fauna associated with gigantopithecus at mohui cave bubing basin south china the mohui fauna associated with gigantopithecus blacki has been recovered from the pleistocene karst cave deposit in bubing basin guangxi south china the large mammalian assemblage derives from 28 species 15 of which have no historic descendants occurrence of some ancient species implies that this fauna is early early pleistocene such as hystrix magna sinomastodon yangziensis stegodon huananensis ailuropoda microta pachycrocuta licenti tapirus sanyuanensis hespertherium sp and dorcabune liuchengense comparisons to already dated early pleistocene faunas in south china combined with preliminary paleomagnetic electron spin resonance esr and u series analysis of this cave indicate mammalian fauna age around 1 7 ma comparisons to five faunal assemblages in the same basin show species level differences in ailuropoda stegodon hystrix tapirus and sus implying the large mammal fauna has passed through a slow process of evolution during the quaternary in east asia

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

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

mantle fluids in the karakoram fault helium isotope evidence abstract the karakoram fault kkf is the 1000 km long strike slip fault separating the western himalaya from the tibetan plateau from geologic and geodetic data the kkf is argued either to be a lithospheric scale fault with hundreds of km of offset at several cm a or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper crustal localization of distributed deformation at depth here we show 3he 4he ratios in geothermal springs along a 500 km segment of the kkf are 3 100 times the normal ratio in continental crust providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle mantle enrichment is absent along the indus yarlung suture zone isz just 35 km southwest of the kkf suggesting that the mantle fluids flow only within the kkf within the last few ma the kkf must have accessed tectonically active tibetan mantle northeast of the mantle suture which we therefore locate vertically beneath the kkf very close to the surface trace of the isz hence in southwestern tibet indian crust may not now be underthrusting substantially north of the isz even though miocene underthrusting may have placed indian crust north of the isz in the lower half of the tibetan plateau crust this is in significant contrast to central and eastern tibet where underthrust indian material not only forms the lower half of the tibetan crust but is also currently underthrusting for 200 km north of the isz our new constraint on kkf penetration to the mantle allows an improved description of the continuously evolving karakoram fault as a tectonically significant yet perhaps geologically ephemeral lithospheric structure

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr