major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

comparison of granite related uranium deposits in the beaverlodge district canada and south china a common control of mineralization by coupled shallow and deep seated geologic processes in an extensional setting abstract many uranium deposits are related to granitic rocks but the mineralization ages are much younger thus excluding a direct magmatic hydrothermal link between the mineralization and the granites two such examples are the proterozoic vein type uranium deposits in the beaverlodge district in canada and the mesozoic granite related uranium deposits in south china both areas have been extensively studied but the critical factors that control the mineralization remain unclear the uranium mineralization in the beaverlodge district occurs in quartz carbonate albite veins and breccias developed within and near major deformation zones and are mainly hosted by ca 2 33 1 90 ga granitic rocks and ca 2 33 ga murmac bay group amphibolite these rocks are unconformably overlain by the martin lake basin which was formed during a period of regional extension in the later stage of the trans hudson orogeny and is filled with red beds a ca 1820 ma mafic magmatic event is manifested as volcanic rocks occurring within the martin lake basin and as dikes crosscutting the basement rocks and lower martin group strata uraninite u pb and pb pb ages range from ca 2290 ma to the granite related uranium mineralization in south china occurs mainly as quartz carbonate fluorite veins and as disseminations in the host rocks adjacent to fracture zones the deposits are hosted by or occur adjacent to granitic rocks and are spatially close to cretaceous tertiary red bed basins that were formed in a basin and range like tectonic setting related to roll back of the pacific plate these red bed basins contain intervals of bimodal volcanic rocks and are crosscut by coeval mafic dikes uraninite u pb ages dominantly range from 100 to 50 ma which is much younger than the host granites 145 ma and broadly contemporaneous with development of the red bed basins and mafic magmatism comparison of the two study areas reveals striking similarities in geologic attributes related to uranium mineralization specifically the development of large volumes of granitic rocks that are relatively enriched in uranium and the development of red bed basins with accompanying coeval mafic magmatism in extensional tectonic settings it is proposed that oxidizing basinal fluids from the red bed basins circulated into the underlying fertile granitic rocks along high permeability structural zones acquired uranium in the path through fluid rock interaction and precipitated the uranium where they encountered reducing agents elevated geothermal gradients associated with the mantle derived magmatism greatly enhanced the mineralization by facilitating the uranium extraction and transport processes thus it is the coupling of shallow red bed basin and oxidizing basinal fluid development and deep seated mantle derived magmatism and related thermal activity processes together with the pre enrichment of uranium in basement rocks particularly granitic rocks and pre existing deformation zones that controlled the formation of the granite related uranium deposits in both beaverlodge and south china and perhaps elsewhere in the world with similar geologic setting

fluid compositions and p t conditions of vein type uranium mineralization in the beaverlodge uranium district northern saskatchewan canada the beaverlodge district in northern saskatchewan is known for vein type uranium mineralization most of the uranium deposits are spatially related to major structures and hosted by ca 3 2 1 9 ga granitic rocks and albitite derived from them and by ca 2 33 ga murmac bay group amphibolite all of which are unconformably overlain locally by deformed but unmetamorphosed redbeds of the ca 1 82 ga martin group and by the flat lying ca 1 75 1 5 ga athabasca group the uranium mineralization is mainly hosted in fault rocks breccias and carbonate quartz albite veins referred to as breccia style and vein style mineralization respectively with the latter being the focus of this study most of the mineralized veins occur in the basement rocks although some crosscut the martin group this study examines the field petrographic fluid inclusion and c o isotope characteristics of mineralized and non mineralized veins from 19 deposits occurrences as well as from the martin group with an aim to better understand the mineralizing environment and processes the coexistence of liquid dominated l v vapour dominated v l and vapour only v fluid inclusions within individual fluid inclusion assemblages fias in the veins suggests fluid immiscibility and heterogeneous trapping the l v inclusions with the lowest homogenization temperatures th within individual fias are interpreted to represent homogeneous trapping of the liquid phase which yield th values from 78 to 330 c mainly 100 to 250 c and salinities from 0 2 to 30 8 wt nacl equivalent mass spectrometric analysis of bulk fluid inclusions shows that the volatiles are dominated by h2o average 97 2 mol with minor amounts of co2 ch4 h2 o2 n2 ar and he fluid pressures were estimated to be 200 bars based on the inference of fluid immiscibility fluid temperatures of 100 to 250 c and low concentrations of non aqueous volatiles 3 mol the 18ovpdb and 13cvpdb of carbonate minerals associated with mineralization range from 20 5 to 8 9 and 10 1 to 0 9 respectively the 18ovsmow values of the parent fluids calculated using the th values range from 9 6 to 17 0 with the majority from 0 to 5 0 o isotopes of paired equilibrium quartz and calcite analyzed by secondary ion mass spectrometry sims yield temperatures from 161 to 248 c which are consistent with the fluid inclusion data the new fluid inclusion and stable isotope data are inconsistent with a metamorphic or magmatic hydrothermal model as proposed in some previous studies for breccia style and vein style mineralization but rather support a model in which the vein type uranium mineralization took place at relatively low temperature 100 to 250 c and shallow 2 km conditions with fluid pressure fluctuating between hydrostatic and sub hydrostatic regimes possibly related to episodic faulting the mineralizing fluids were mainly sourced from the martin lake basin and uraninite was precipitated as a result of mixing between this basin derived fluid and fluids carrying reducing agents fe2 ch4 derived from the basement although fluid rock reactions and fluid immiscibility may have also played a role

collisional snowbird tectonic zone resurrected growth of laurentia during the 1 9 ga accretionary phase of the hudsonian orogeny the 2800 km long snowbird tectonic zone is one of the most controversial tectonic features of the canadian shield metamorphic and in situ geochronologic data reported here reveal that a 1 9 ga medium to high pressure belt extends along most of this tectonic zone in contrast to recent interpretations a collisional origin is indicated by the length of this metamorphic belt tectonic thickening documented in parts of it geological contrasts across it and subduction type microdiamonds within it this collisional event marks a pre 1 865 ga phase of the hudsonian orogeny involving microcontinent accretion that was fundamental to the growth of laurentia

high salinity fluid inclusions in the yinshan polymetallic deposit from the le de metallogenic belt in jiangxi province china their origin and implications for ore genesis a fluid inclusion investigation of the polymetallic mineralization at yinshan from the le de metallogenic belt in jiangxi province of china has been carried out using petrographic and microthermometric techniques the data obtained here indicate that three major types of fluids were involved during the formation of the deposit they are type i vapor rich type ii liquid rich and type iii halite bearing inclusions within the h2o nacl system the high salinity fluids represented by type iii inclusions being unusual to the distal part of an intrusion centered ore forming system such as yinshan have been interpreted as the product of direct exsolution of a crystallizing magma rather than a result of fluid immiscibility from a low salinity fluid evidence used to support such an interpretation includes the mode of homogenization of type iii inclusions exclusively via halite dissolution spatial separation of type i and type iii inclusions on microscopic scale the consistent phase ratios within the inclusions concerned and considerable deviation in homogenization temperature for both type i and type iii inclusions trapping conditions for type i inclusions were estimated to be around 440 degrees c and 260 bars while type iii inclusions were constrained to be trapped at least above 900 bars and 500 degrees c the formation temperatures for type ii inclusions range from 270 to 390 degrees c if a lithostatic pressure of 260 bars is assumed pressure fluctuation determined by this fluid inclusion study coupled with decreases in salinity and temperature as result of the potential fluid mixing are supposed to have played an important role in triggering the precipitation of ore minerals from the hydrothermal solution c 2006 elsevier b v all rights reserved

precise sm nd and u pb isotopic dating of the supergiant shizhuyuan polymetallic deposit and its host granite se china the supergiant shizhuyuan w sn bi mo deposit is hosted by the qianlishan granite a small highly fractionated granitic pluton 10 km 2 with multiple phases of intrusions within the early yanshanian granitoid province of se china strong alteration of skarn and greisen that formed in the contact zone between the first and second phases of granite intrusions and devonian limestone is responsible for the polymetallic mineralizations shrimp u pb zircon analysis indicates that the two early phases of the qianlishan granite formed contemporaneously at 152 2 ma metasomatic minerals garnet fluorite and wolframite separated from the skarn and greisen yield a sm nd isochron age of 149 2 ma that is interpreted as the formation age of the shizhuyuan deposit therefore the mineralization of the supergiant shizhuyuan polymetallic deposit formed contemporaneously with or very shortly after the intrusion of the small highly fractionated qianlishan granite

salt as a fluid driver and basement as a metal source for stratiform sediment hosted copper deposits the source of copper for stratiform sediment hosted copper deposits is considered to be redbed clastics situated stratigraphically below the deposits however for one of the principal copper provinces in the world the zambian copperbelt there is insufficient thickness of redbeds to constitute a viable source numerical modeling demonstrates that high salinity sedimentary brines generated beneath a halite seal will develop convective hydrothermal plumes that penetrate through the redbeds deep into the crystalline basement despite its low permeability and regardless of the availability of cross stratal conduits this greatly expands the volume of the potential metal source for this style of ore deposit

magma sources and tectonic setting of central andean andesites 25 5 28 s related to crustal thickening forearc subduction erosion and delamination

petrography and genetic history of coffinite and uraninite from the liueryiqi granite hosted uranium deposit se china abstract coffinite and uraninite banded aggregates from the liueryiqi granite hosted uranium deposit se china form a unique bull s eye texture these aggregates consist of concentric bands of uraninite and coffinite that range in thickness from 1 to 10 m electron microprobe analyses indicate that coffinite and uraninite contain ca and al impurities altered uraninite feldspar quartz or pyrite grains form the center of these aggregates other minerals associated with the bull s eye aggregates are marcasite sphalerite galena chalcopyrite bornite clausthalite microcrystalline quartz fluorite and calcite the aggregates occur within highly altered and brecciated zones of a two mica leucogranite the mineral assemblage associated with these aggregates is consistent with low temperature fluids 125 to 200 c ph 6 0 to 8 5 eh 0 640 to 0 704 v and dissolved silica contents of 10 3 5 to 10 2 7 mol l 19 to 120 ppm as sio 2 at depth co 2 concentrations of mineralizing fluids percolating through the breccia and fractured zones of the altered host granites likely ranged from 3 5 to 2 6 mol at temperatures between 126 and 178 c and a lithostatic pressure of 500 to 800 bars uranium was likely transported as a uranyl dicarbonate ion which is the dominant dissolved uranium carbonate species in the ph range 6 0 to 8 5 periodic changes in dissolved silica content in the mineralizing fluids resulted in the formation of the coffinite uraninite intergrowth banded aggregates the precipitating mechanism resulting in the precipitation of the reduced uranium phases was likely the oxidation of reduced s 2 and se 2 which were supplied by the mineralizing fluids and were in equilibrium with uranyl ions

timing of destruction of the north china craton abstract the north china craton ncc is the typical example of destruction of an ancient craton however the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction which is the key to understanding the destruction processes based on temporal and spatial distributions of the igneous rocks and their sources and tectonic settings it is recognized that six stages of tectono magmatism occurred in the ncc during the phanerozoic i e carboniferous to early permian late permian to middle triassic late triassic jurassic early cretaceous and cenozoic among them cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern ncc the first four stages of magmatism and tectonism related to the southward subduction of the paleo asian plate and the assembly of sino korean and yangtze cratons are locally distributed in limited parts of the ncc reflecting a multiple stage modification of the ncc from the late carboniferous to jurassic however the intensive development of early cretaceous magmatism extensional deformation and associated gold mineralization with significant continental crustal growth indicate that the eastern ncc was destroyed during this time period this destruction was the result of paleo pacific subduction beneath the eastern asian continent with lithospheric removal and or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere

geochemical isotopic and single crystal 40ar 39ar age constraints on the evolution of the cerro galan ignimbrites the giant ignimbrites that erupted from the cerro galan caldera complex in the southern puna of the high andean plateau are considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened crust and mantle lithosphere over a steepening subduction zone major and trace element analyses of cerro galan ignimbrites 68 71 sio2 that include 75 new analyses can be interpreted as reflecting evolution at three crustal levels afc modeling and new fractionation corrected 18o values from quartz 7 63 8 85 are consistent with the ignimbrite magmas being near 50 50 mixtures of enriched mantle 87sr 86sr 0 7055 and crustal melts 87sr 86sr near 0 715 0 735 processes at lower crustal levels are predicated on steep heavy ree patterns sm yb 4 7 high sr contents 250 ppm and very low nb ta 9 5 ratios which are attributed to amphibolite partial melts mixing with fractionating mantle basalts to produce hybrid melts that rise leaving a gravitationally unstable garnet bearing residue processes at mid crustal levels create large negative eu anomalies eu eu 0 45 0 70 and variable trace element enrichment in a crystallizing mush zone with a temperature near 800 850 c the mush zone is repeatedly recharged from depth and partially evacuated into upper crustal magma chambers at times of regional contraction crystallinity differences in the ignimbrites are attributed to biotite zoned plagioclase and other antecrysts entering higher level chambers where variable amounts of near eutectic crystallization occurs at temperatures as low as 680 c just preceding eruption 40ar 39ar single crystal sanidine weighted mean plateau and isochron ages combined with trace element patterns show that the galan ignimbrite erupted in more than one batch including a 2 13 ma intracaldera flow and outflows to the west and north at near 2 09 and 2 06 ma episodic delamination of gravitationally unstable lower crust and mantle lithosphere and injection of basaltic magmas whose changing chemistry reflects their evolution over a steepening subduction zone could trigger the eruptions of the cerro galan ignimbrites

gold and silver metallogeny of the south china fold belt a consequence of multiple mineralizing events abstract the south china fold belt is part of the south china block that is interpreted to be the result of multiple tectonic and magmatic events that formed a collage of accreted proterozoic and phanerozoic terranes the jurassic to early cretaceous yanshanian period 180 90 ma a time of major tectono thermal events that affected much of eastern and southeastern china is of great metallogenic importance in the fold belt this period is linked to subduction of the pacific plate beneath the eurasian continent and is manifested by voluminous volcano plutonic activity of predominantly calc alkaline affinity the distribution of gold and silver deposits in the south china fold belt indicates the presence of two distinct metallogenic provinces a region of basement uplifts which are controlled by shear zones and form neoproterozoic inliers of metamorphosed iron rich rock types defines the first province in this province orogenic lodes and volcanic related epithermal deposits represent the more significant precious metal mineralization the second province is essentially confined to a belt of yanshanian felsic intermediate volcanic and subvolcanic rocks that extends along most of the southeastern china coast in an area known as the coastal volcanic belt deposits in the coastal volcanic belt are silver and or copper rich volcanic hosted and epithermal in character the precious metal metallogeny of the south china fold belt is interpreted to have developed in at least three stages one as a result of collision events during the caledonian orogeny ca 400 ma the second during the indosinian orogeny ca 200 ma and the third during or soon after the formation of the yanshanian magmatic belt yanshanian orogeny 180 90 ma the latter was responsible for a hydrothermal event that affected large sections of the belt and its proterozoic substrate this may have resulted in the redistribution and enrichment of precious metals from preexisting orogenic gold lodes in neoproterozoic basement rocks which are now exposed as windows in zones of tectonic uplift the yanshanian hydrothermal activity was particularly widespread in the coastal volcanic belt and resulted in the formation of both low and high sulfidation epithermal gold and silver and locally copper and other base metal mineralization it is suggested that the coastal volcanic belt has greater potential for world class epithermal and porphyry deposits than previously realised

the south china block indochina collision where when and how this study uses new field observations and existing studies to shed new light on the origin and significance of two nw se striking orogens in nw and ne vietnam we conclude that the architecture of each belt is a stack of ne directed nappes formed either under deep ductile synmetamorphic conditions or under shallow depth in the sw and ne parts respectively the song ma zone and song chay ophiolitic melange represent two ophiolitic sutures however the late permian song da and babu mafic rocks are not ophiolites but intraplate basalts related to the emeishan plume a late triassic unconformity the 225 205 ma postorogenic plutonism and the 250 230 ma syntectonic metamorphism support an early to middle triassic age for these tectonic events both nw and ne belts are due to sw directed subduction with arc magmatism ocean closure and continental collision though two contemporary s dipping subduction zones might explain the structural evolution of the two belts a single convergent system offset by the tertiary red river fault is preferred as this s directed subduction better accounts for the late permian intraplate magmatism this scenario is discussed in the general geodynamic framework of se asia

post taltson sedimentary and intrusive history of the southern rae province along the northern margin of the athabasca basin western canadian shield abstract the southern rae province of the western canadian shield underwent extensive reworking during paleoproterozoic time widespread granitic plutonism and poorly defined metamorphism resulting from the ca 2 5 to 2 3 ga arrowsmith orogen was followed by more intense thermotectonic overprints attributed to the 1 99 1 92 ga taltson orogen in the west and ca 1 91 1 90 ga tectonic activity associated with the snowbird tectonic zone in the east the thluicho lake group is a fining upwards conglomerate arkose argillite succession deposited in an intermontane setting towards the end of the taltson orogen following deposition the thluicho lake group underwent two phases of regional folding and greenschist facies metamorphism marking the latest taltson and snowbird overprints respectively prior to the emplacement of extensive 1 82 ga mafic dykes these depositional constraints support correlation of the thluicho lake group with the lithologically similar nonacho group in the northwest territories whereas petrological similarities and coeval emplacement ages indicate that the mafic dykes represent a southeastward extension of the sparrow dykes mafic volcanic rocks geochemically linked to the dykes are intercalated within the martin group a continental redbed succession deposited in trans tensional basin settings indicating that deposition was ongoing at 1 82 ga similarities in age lithological association and depositional setting suggest that the martin group is broadly correlative with the baker lake group of the lower dubawnt supergroup in nunavut widespread lamprophyre dykes of the type that fed minette volcanic rocks of the christopher island formation in the baker lake group are also spatially associated with the martin group the broadly coeval hudson granites which extend over much of the same ground as the lamprophyres in nunavut also appear to have analogs in the southern rae province the formation of widespread trans tensional basins together with extensive dyke emplacement implies a period of intense brittle to brittle ductile deformation throughout the western churchill province at about 1 83 1 82 ga this deformation is attributed to a broadly east west stress regime imposed by accretion of the nahanni fort simpson terrane to the west combined with terminal collision in the trans hudson orogen to the east

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

early paleoproterozoic supracrustal assemblages of the rae domain nunavut canada intracratonic basin development during supercontinent break up and assembly abstract the basal paleoproterozoic supracrustal succession of the churchill province in northern canada comprises sedimentary basins overlying the archean rae and hearne domains the rae domain supracrustal succession e g amer ketyet river chantrey and montresor groups comprises four lithotectonic assemblages which include in ascending stratigraphic position 1 shallow marine fluvial quartzarenite with mainly neoarchean detrital zircons of local provenance 2 shallow marine quartzarenite with mainly local provenance that locally includes carbonates mafic volcanic flows 3 abrupt but conformable transition to basinal dark shales and overlying platformal carbonates that pass upward into siltstones and sandstones that record gradual emergence of the platform sandstones within this assemblage display a substantially different detrital zircon provenance signature dominated by early paleoproterozoic zircons with grains as young as 1 95 ga 4 unconformably to conformably overlying immature marine sandstones including turbidites with a significant component of 2 0 1 9 ga detritus probably derived from a combination of local and distal sources the thickness and relative compositional maturity of the basal lithotectonic assemblage 1 records a protracted period of enhanced weathering on a slowly subsiding but stable supercontinent e g kenorland this was followed by mafic volcanism and marine transgression consistent with partial rifting of the rae domain and crustal extension attending supercontinent break up lithotectonic assemblage 2 strata of lithotectonic assemblage 3 record basin flooding and deepening followed by platformal sedimentation along the margins of extended continental blocks assemblage 4 is interpreted to represent deposition in foreland basins during early amalgamation of laurentia part of nuna at ca 1 9 ga the stratigraphy and detrital zircon geochronology of the hurwitz group which overlies the hearne domain is broadly similar to the supracrustal sequence of the rae domain but differs through the presence of basal diamictites and lack of 2 5 ga detritus a major local source in the rae our data suggest that the rae and hearne domains were assembled together by max 1 91 ga i e max age of deposition of the uppermost hurwitz and amer groups the paleoproterozoic stratigraphic assemblage framework for the churchill province compares well with that of other cratons derived from break up of kenorland and ultimately amalgamated in nuna examples from laurentia include supracrustal rocks that overlie the southern margin of the superior province southern province e g huron supergroup animikie group marquette range supergroup whitewater group and mistassini otish group the paleoproterozoic assemblages of the southern and churchill provinces exhibit first order stratigraphic similarities that indicate a shared history of stable continental sedimentation followed by rifting basin opening and basin closure

mesozoic magmatism and granitic dome in the wugongshan massif jiangxi province and their genetical relationship to the tectonic events in southeast china abstract in se china a mesozoic granitic dome coeval to extensional tectonics is exposed in the wugongshan massif its center is occupied by mesozoic granitoids and granitic gneisses and the e w trending late paleozoic mesozoic pingxiang and anfu basins are located along its northern and southern sides respectively in this paper the petrological geochemical major incompatible and rare earth elements and isotopic characteristics of the granitoids and granitic gneisses of this dome allow us to constrain their geodynamic evolution the wugongshan mesozoic k feldspar enriched granitoids consist of six granitic bodies and lie within a paleozoic metamorphic basement the caledonian shanzhuang granodiorite containing some dioritic enclaves occurs in the study area and is a calc alkaline type granodiorite characterised by lower sio2 and composed of andesine biotite quartz hornblende magnetite and sphene the mesozoic granitoids either indosinian plutons or yanshanian bodies show a geochemical affinity of peraluminous s type granite having higher sio2 k2o contents al k na 2ca enriched in rb th and depleted in eu they also exhibit lree enriched patterns and marked negative eu anomalies the yanshanian plutons also contain characteristic minerals such as sillimanite garnet and monazite the wugongshan mesozoic granitoids have higher isr values 0 70981 0 72885 and lower end t 10 6 to 14 7 an average of 12 6 than those of the early paleozoic shanzhuang granodiorite the mesozoic granitoids were likely derived from ancient sedimentary rocks by partial melting the wugongshan mesozoic granitoids contain three petrological zones that is an early cretaceous massive granitic zone in the core zone i a foliated granitic zone zone ii and a triassic granitic gneissic zone in the outer rim zone iii the petrological and geochemical features of massive granitoids zone i are similar to those of foliated granites zone ii and of granitic gneisses zone iii in this mesozoic dome moreover geometric and kinematic features within the ductile parts units 2 and 3 are also similar to those within the brittle part unit 1 of the dome all these features show that the geologic evolution of the wugongshan doming is a continuous process lasting from triassic to early cretaceous time published 40ar 39ar and k ar ages in the wugongshan mesozoic granitic rocks fall into two major age fields corresponding to two geodynamic events of intracontinental deformation and magmatic activity the first tectonothermal event dated at 226 259 ma on the granitic gneisses in the outer rim of dome can be linked to indosinian collision between the south china plate and the north china plate during triassic time the second event took place during the early yanshanian dated at 180 120 ma on the granites of the core of dome and are responsible for final doming of the wugongshan plutons this event may be related to a westward subduction of the paleo pacific oceanic plate under the se china continent during late jurassic early cretaceous time

in situ sims uraninite u pb dating and genesis of the xianshi granite hosted uranium deposit south china abstract the southeastern part of the nanling metallogenic province china is host to numerous granite hosted vein type hydrothermal uranium deposits the geology and geochemistry of these deposits have been extensively studied however accurate and precise ages for the uranium mineralization are scarce because the uranium minerals in these deposits are usually fine grained and may have formed in several stages therefore the ages previously obtained by the bulk dating techniques are possibly a mixed age the xianshi uranium deposit located in the southeastern part of the guidong granite complex is a major uranium deposit in south china the uranium mineralization from this deposit is mainly fine grained uraninite in quartz or calcite veins which are spatially associated with the cretaceous mantle derived mafic dykes micro raman spectroscopy and x ray diffraction analyses indicate that the dominant uranium mineral occurs as a rare form of uraninite u 3 o 7 three distinct generations of uranium minerals have been identified based on petrographic and field relations stage 1 uraninite has the lowest uo 2 and highest pbo contents whereas stage 3 uraninite has the highest uo 2 and lowest pbo contents uraninite from the xianshi deposit was dated using an in situ sims u pb dating technique the results show three distinct age groups 135 4 ma 113 2 ma and 104 2 ma which are in excellent agreement with the ages of three episodes of mantle derived mafic dykes therefore the xianshi uranium deposit has experienced at least three hydrothermal events that are responsible for the deposition of uranium ores which are genetically related to the emplacement of three sets of mafic dykes

the origin of the tongkeng changpo tin deposit dachang metal district guangxi china clues from fluid inclusions and he isotope systematics tongkeng changpo is the largest tin deposit within the giant dachang polymetallic tin ore field in guangxi southern china which is part of a large skarn system associated with cretaceous granitoids the tongkeng changpo mineralization consists of veins and stockworks in the upper levels and replacement stratiform orebodies mantos at lower levels based on textural relationships three major mineralizing stages can be recognized stage i with cassiterite sulphides stannite tourmaline and quartz stage ii with cassiterite sulphides sulphosalts quartz and calcite and stage iii with calcite as the main phase the study of fluid inclusions has shown that there are two main fluid types co2 and nacl h2o homogenization temperatures are 270 to 365 c 210 to 240 c and 140 to 190 c for stages i ii and iii respectively salinities range from 1 to 7 wt nacl equiv in the early ore stage and 3 to 10 wt nacl equiv in the late stages laser raman spectroscopy indicates that the inclusion fluids in stages i and ii were of carbono aqueous composition with minor amounts of ch4 and h2s whereas those in stage iii were aqueous helium isotopic analyses of inclusion fluids indicate that the 3he 4he ratios in the ore veins are in between 1 2 to 2 9 ra ra 1 4 10 6 modern atmospheric ratio and range from 1 6 to 2 5 ra in the stratiform orebodies this range of 3he 4he ratios is significantly higher than that of crustal fluids 0 01 0 05 ra the similar characteristics of fluid inclusions and their he isotopic composition as well as age constraints indicate that the ore veins and stratiform orebodies of the tongkeng changpo deposit formed from the same hydrothermal system likely related to granite intrusions of the mesozoic yanshanian tectono thermal event in addition the high r ra ratios indicate a mantle contribution in the ore fluids

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

mechanism of mineralization in the changjiang uranium ore field south china evidence from fluid inclusions hydrothermal alteration and h o isotopes abstract the changjiang uranium ore field which contains 10 000 tonnes of recoverable u with a grade of 0 1 0 5 is hosted by triassic two mica and jurassic biotite granites and is one of the most important uranium ore fields in south china the minerals associated with alteration and mineralization can be divided into two stages namely syn ore and post ore the syn ore minerals are primarily quartz pitchblende hematite hydromica chlorite fluorite and pyrite the post ore minerals include quartz calcite fluorite pyrite and hematite the fluid inclusions of the early syn ore stage characteristically contain o 2 and those of the late syn ore and post ore stage contain h 2 and ch 4 the fluid inclusions in quartz of the syn ore stage include h 2 o h 2 o co 2 and co 2 types and they occur in clusters or along trails homogenization temperatures t h for the h 2 o co 2 and two phase h 2 o inclusions range from 106 c to 350 c and cluster in two distinct groups for each type salinities are lower than 10 wt nacl equiv the ore forming fluids underwent co 2 effervescence or phase separation at 250 c under a pressure of 1000 1100 bar the u th values of the altered granites are lowest close to the ore increase outwards but subsequently decrease close to unaltered granites from the unaltered granites to the ore the lowest fe 2 o 3 feo values become lower and the highest values higher the ree patterns of the altered granites and the ores are similar to each other the u contents of the ores show a positive correlation with total ree contents but a negative correlation with lree hree ratios indicating the pitchblende is ree bearing and selectively hree rich the eu values of the ore show a positive correlation with u contents indicating the early syn ore fluids were oxidizing the ce values show a negative correlation indicating the later mineralization environment became reducing the water rock interactions of the early syn ore stage resulted in oxidization of altered granites and reduction of the ore forming fluids and it was this reduction that led to the uranium mineralization during alteration in the early syn ore stage the oxidizing fluids leached uranium from granites close to faults and fe 2 o 3 feo ratios increased in the alteration zones the late syn ore and post ore alteration decreased the fe 2 o 3 feo ratios in the alteration zones the 18 o w smow values of the ore forming fluids range from 1 8 to 5 4 and the d w smow values range from 104 4 to 51 6 suggesting meteoric water the meteoric water underwent at least two stages of water rock interaction the first caused the fluids to become uranium bearing and the second stage which was primarily associated with ore bearing faults led to uranium deposition as pitchblende accompanied by co 2 effervescence

he pb and s isotopic constraints on the relationship between the a type qitianling granite and the furong tin deposit hunan province china abstract the furong tin deposit located in southern hunan province china is a large newly discovered deposit with an estimated sn reserve of about 700 000 tons the deposit is spatially and temporally associated with the a type qitianling granite the 3he 4he ratios of fluid inclusions trapped in sulfides from the deposit range from 0 13 to 2 95 ra indicating a mixed crust mantle source similar to that of the qitianling granite complex lead isotopes in feldspars of the granite mostly in the range of 206pb 204pb 18 547 19 180 207pb 204pb 15 598 15 825 208pb 204pb 37 912 39 068 and in sulfide minerals 206pb 204pb 18 467 18 836 207pb 204pb 15 503 15 772 208pb 204pb 38 607 39 099 are essentially the same indicating that the lead in both was derived mainly from the upper crust with a small mantle component the sulfur isotopic values of the ore minerals vary widely ranging from 26 1 to 10 4 but are mainly within the range of 0 2 to 10 4 implying that the s in the hydrothermal fluids was derived mainly from magmatic fluids with minor contributions from the mantle sedimentary rocks and biogenic material the he pb and s isotopes all confirm that the ore forming fluids of the furong deposit were magmatic in origin derived from the melts that produced the qitianling a type granite the tin mineralization occurs within or along the margins of the qitianling granite complex and the timing of the mineralization coincides with the intrusive age of the granite the available data suggest that the emplacement of the granites and the mineralization was related to mantle upwelling and extension of the lithosphere in south china during the mesozoic

controls on deposition of the st peter sandstone middle late ordovician michigan basin the st peter sandstone middle late ordovician of the michigan basin represents an approximately 10 m y interval of clastic deposition in an otherwise carbonate dominated ordovician succession this interval up to 320 m thick also coincides with a change in basin configuration from the nearly circular depocenter of the underlying shakopee formation to an east west elongate trough situated west to saginaw bay interpretation of well logs and core from throughout the basin indicates that the clastics are composed of 20 25 sequences upper shoreface to tidal flat environments the sequences are interbedded with heavily bioturbated shaly lower shoreface sandstones 1 14 m thick and in the central and southeastern parts of the basin with carbonate shales stromatolites and oolitic grain stones 2 39 m thick the eastern and southeastern margins of the basin contain the thickest carbonate accumulations hydrocarbons fields are located over structural highs formed by reactivation of basement structures detailed comparison of well logs within field shows that sedimentary cycles thin over the structures as a result of the local reduction in the formation of accommodation space by syndepositional movements on the faults the presence of thick carbonates along the southeastern margin of the basin is a result of the combination of distance form the clasticmore source and the episodic formation of accommodation space by syndepositional normal faulting along the basin margin less

geology and vein tin mineralization in the dadoushan deposit gejiu district sw china vein type tin mineralization in the dadoushan deposit laochang ore field gejiu district sw china is predominantly hosted in triassic carbonate rocks gejiu formation over cupolas of the unexposed laochang equi granular granite intrusion the most common vein mineral is tourmaline accompanied by skarn minerals garnet di opside epidote phlogopite and beryl the main ore mineral is cassiterite accompanied by minor chalcopyrite pyrrho tite and pyrite as well as scheelite the tin ore grade varies with depth with the highest grades 1 2 sn prevalent in the lower part of the vein zone muscovite 40 ar 39 ar dating yielded a plateau age of 82 7 0 7 ma which defines the age of the vein type mineralization measured sulfur isotope compositions 34 s0 4 1 to 3 9 of the sulfides arseno pyrite chalcopyrite pyrite and pyrrhotite indicate that the sulfur in veins is mainly derived from a magmatic source the sulfur isotope values of the ores are consistent with those from the underlying granite laochang equigranular granite 3 7 to 0 1 but are different from the carbonate wall rocks of the gejiu formation 7 1 to 11 1 the calculated and measured oxygen and hydrogen isotope com positions of the ore forming fluids 18 oh2o0 2 4 to 5 5 d0 86 to 77 suggest an initially magmatic fluid which gradually evolved towards meteoric water dur ing tin mineralization

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

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

mantle derived gaseous components in ore forming fluids of the xiangshan uranium deposit jiangxi province china evidence from he ar and c isotopes abstract the xiangshan u deposit the largest hydrothermal u deposit in china is hosted in late jurassic felsic volcanic rocks although the u mineralization post dates the volcanics by at least 20 ma the mineralization coincides with intrusion of local mantle derived mafic dykes formed during cretaceous crustal extension in south china ore forming fluids are rich in co 2 and u in the fluid is thought to have been dissolved in the form of uo 2 co 3 2 2 and uo 2 co 3 3 4 complexes this paper provides he and ar isotope data of fluid inclusions in pyrites and c isotope data of calcites associated with u mineralization pitchblende in the xiangshan u deposit he isotopic compositions range between 0 1 and 2 0ra where ra is the 3 he 4 he ratio of air 1 39 10 6 and correlates with 40 ar 36 ar although there is potential for significant 3 he production via 6 li n 3 h 3 he reactions in a u deposit due to abundant neutrons nucleogenic production cannot account for either the 3 he concentration in these fluids nor the correlations between he and ar isotopic compositions it is more likely that the high 3 he 4 he ratios represent trapped mantle derived gases a mantle origin for the volatiles of xiangshan is consistent with the 13 c values of calcites which vary from 3 5 to 7 7 overlapping the range of mantle co 2 the he ar and co 2 characteristics of the ore forming fluids responsible for the deposit are consistent with mixing between 3 he and co 2 rich mantle derived fluids and co 2 poor meteoric fluids these fluids were likely produced during cretaceous extension and dyke intrusion which permitted mantle derived co 2 to migrate upward and remobilize u from the acid volcanic source rocks resulting in the formation of the u deposit subsequent decay of u within the fluid inclusions has reduced the 3 he 4 he ratio and variations in u 3 he result in the range in 3 he 4 he observed with u 3 he ratios in the range 5 17 10 3 likely corresponding to u concentrations in the fluids

formation time of hongshan topaz bearing granite and its metallogenic potential prognosis in order to determine the formation age of the hongshan topaz bearing granite and make metallogenic potential prognosis the authors carried out lam icpms zircon u pb dating and detailed geochemical comparison geochemical analyses of fifteen samples show that the hongshan granite is characterized by high f contents and highly evolved geochemical features it contains abundant metallogenic elements such as sn 15 3 54 0 10 6 w 3 04 14 9 10 6 nb 22 5 36 7 10 6 ta 3 37 7 31 10 6 u 6 30 10 6 and th 12 1 36 4 10 6 geochemical comparison with other ore bearing granites in the world indicates that related mineralization especially sn and u mineralization may exists in the hongshan granite intrusive geochemical mapping shows that some geochemical parameters such as sn w ree zr th and rb exhibit a rough spatial zonation with the most evolved samples located in the southeastern part of the pluton suggesting that the most probable target area of rare metal deposits may be in the southeastern area i e between 116 8 e 116 10 e and 25 29 n 25 32 n lam icpms zircon u pb dating results indicate that the hongshan granite was formed at 226 ma therefore it is different from most topaz bearing granitoids in south china in the formation age mode of occurrence and mineralization the nanling range basement metamorphic rocks contain abundant w sn nb and ta and hence serve as the most important ore forming element source of the hongshan granite

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

structural petrological and u pb shrimp geochronological study of the western beaverlodge domain implications for crustal architecture multi stage orogenesis and the extent of the taltson orogen in the sw rae craton canadian shield abstract the beaverlodge domain is a polydeformed precambrian terrane in the southwestern rae craton whose rocks variably record the effects of archean tectonism and four major paleoproterozoic tectonic events the 2 5 2 3 ga arrowsmith orogeny the 1 99 1 93 ga taltson orogeny the ca 1 90 ga snowbird orogeny and the ca 1 87 1 80 ga hudsonian orogeny structural metamorphic analysis and in situ u pb shrimp zircon and monazite geochronology reported herein demonstrate that this domain consists of two main structural levels variably exposed due to complex interference folding a lower level comprising mainly high grade archean ca 3 0 and 2 7 2 6 ga metaplutonic and metasedimentary gneisses and a higher level comprising mainly ca 2 33 to 1 2 that led to development of the composite ese trending s 0 s 1 s 2 transposition foliation followed by more open folding d 3 the absence of taltson age plutonic rocks except for low volume crustal melts suggests that this cycle was driven by crustal thickening consistent with a clockwise p t t path derived for one sample the high degree of strain along the contact between archean rocks and the murmac bay group along with local structural discordance indicates some degree of translation of cover rocks over basement during this stage pelitic rocks at higher structural levels low to medium grade zone underwent prograde metamorphism to middle amphibolite facies whereas rocks at deeper structural levels high grade zone attained upper amphibolite facies conditions monazite data bracket prograde metamorphism and related garnet growth between 1939 6 ma and 1934 5 ma the second stage dated most precisely at 1906 7 ma involved refolding of d 1 to d 3 structures about ne trending axes f 4 and coeval dextral shearing and is correlated with snowbird orogenesis rocks of the low to medium grade zone were held at roughly the same crustal level whereas rocks in the high grade zone were uplifted via dextral oblique displacement along domain bounding shear zones instigating decompression garnet to cordierite reactions this study demonstrates that after

distinctive features of late palaeozoic massive sulphide deposits in south china abstract more than 20 sediment hosted massive sulphide deposits occur in late palaeozoic basins in south china these deposits are accompanied by a certain amount of volcanic rocks in the host sequence and are economically important for their cu pb zn au and ag reserves the deposits and their host strata were commonly intruded by mesozoic granitoids remobilisation of sedimentary ores and magmatic hydrothermal overprinting processes resulted in the coexistence of massive sulphides with vein skarn and porphyry type orebodies in the same region or within a single deposit the ore containing basins occur in different tectonic settings the lower yangtze basin occurs on a passive continental margin where the deposits are high in cu and au with minor pb and zn and recoverable ag co and mo the ores have a lower concentration of radiogenic lead and 34s values close to zero fluid inclusions are highly saline and na rich fluids and metals of the lower yangtze region are interpreted to have been derived essentially from deep sources including the precambrian basement by contrast basins of the nanling region formed in an intracontinental setting developed on a folded caledonian basement these deposits are higher in pb zn sn and w as well as cu with recoverable ag sb hg u bi tl and mo the ores are characterised by a higher concentration of radiogenic lead and a wide variation of 34s composition fluid inclusions have lower salinities and higher k na ratios fluids are considered to have been sourced substantially from seawater by convection metals for the nanling deposits were essentially derived from the caledonian basement by leaching the contrast in ore composition between these two regions appears to have been controlled by differences in basement composition of the ore forming basins

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

new depositional age constraints for the murmac bay group of the southern rae craton canada abstract the murmac bay group is one of several early supracrustal successions that were deposited on the southern rae craton churchill province western canadian shield and subsequently affected by paleoproterozoic tectono metamorphism where best understood the succession comprises basal quartzite and or psammite with intercalated dolostone patchy iron formation mafic volcanic flows and overlying psammopelite pelite previous attempts to date the murmac bay group have resulted in both archean and paleoproterozoic estimates re interpretation of critical field relationships together with acquisition of new geochronological data have greatly improved estimates for its age of deposition which in turn yield new constraints on the tectonic evolution of the region circa 2 33 2 32 ga detrital zircon from three of four dated samples including a rare basal conglomerate establishes a maximum age for the initiation of deposition a 2322 5 ma quartz feldspar porphyry dyke intruding mafic volcanic rocks near the base of the succession indicates that deposition of the murmac bay group was initiated ca 2 33 ga coeval with the earliest members of a 2 33 2 29 ga granitic suite these post collisional granites were emplaced following a 2 37 ga thermal culmination attributed to the arrowsmith orogeny deposition of the murmac bay group continued until at least 2 17 ga the youngest detrital zircon age analyzed from the upper part of the succession deposition was over by ca 1 93 ga when the murmac bay group underwent regional metamorphism and was intruded by the donaldson lake pluton for which a revised ca 1 93 ga crystallization age has been obtained according to our new age constraints the upper murmac bay group may be temporally correlative with the waugh lake group exposed about 100 km to the west northwest at the eastern margin of the taltson magmatic zone and with rocks of the rutledge river basin located 150 km to the northwest a stronger case can be made for lithostratigraphic correlation of the murmac bay group with the lower three of four assemblages in the amer and ketyet river groups 750 km to the northeast the abundance of ca 2 17 ga detrital zircon in the murmac bay group together with the presence of 2 2 2 07 ga detritus in the amer and ketyet river groups rutledge river basin and in younger sedimentary successions in the region are thought to record an early accretionary event on the western margin of the rae craton

silurian mo mineralization at baishiding molybdenum deposit in northern guangxi constraints from zircon shrimp u pb and molybdenite re os ages the baishiding molybdenum deposit is located in northern guangxi and its ore bodies occur mainly as quartz molybdenite veins in guiling biotite monzogranite and epimetamorphic neritic facies clastic rocks in nanhua system ore minerals are composed of molybdenite pyrite chalcopyrite and scheelite the mo grade ranges from 0 1 to 0 3 with an average of 0 12 with the distance from the quartz vein the monzogranite has been altered into k feldspar sericite and chlorite in succession molybdenite is precipitated in the quartz vein mostly occurring along the boundary between the monzogranite and the quartz vein or assuming disseminations in monzogranite scheelite is also intergrown with molybdenite in the quartz vein six molybdenite re os ages from six samples indicate that mineralization took place in silurian zircon shrimp u pb dating of guling biotite monzogranite shows that the granite was emplaced at 424 4 5 6 ma whereas the zircon from the enclave has an age of 428 4 ma these data suggest that the baishiding molybdenum deposit was formed in silurian implying that mo mineralization did occur in silurian in south china

geology geochemistry and age of the hukeng tungsten deposit southern china abstract the hukeng tungsten deposit located in the wugongshan area in central part of jiangxi province south china is a large scale quartz vein wolframite deposit it is hosted in the hukeng granitic intrusion based on the mineral assemblage and crosscutting relationship of the veins three mineralization stages are identified including 1 quartz wolframite stage 2 quartz fluorite wolframite stage and 3 quartz pyrite sphalerite wolframite stage the homogenization temperatures of fluid inclusions in vein quartz vary from 220 to 320 c and the salinities are from 0 to 10 wt nacl equiv corresponding densities range from 0 7 to 1 g cm 3 these features indicated that the ore forming fluids in the hukeng tungsten deposit have medium temperature low density and low salinity the 18 osmow values of quartz range from 10 8 to 14 4 with corresponding 18 o fluid values of 3 7 to 7 7 and d values of fluid inclusions of between 70 and 55 the combined isotopic data indicate that the ore forming fluids of the hukeng tungsten deposit were mainly derived from magmatic water with some minor input from meteoric water we have carried out molybdenite re os and muscovite 40 ar 39 ar dating to constrain the timing of mineralization re os dating of six molybdenite samples yielded model ages ranging from 149 1 2 0 to 150 7 3 7 ma with an average of 150 0 ma the re os analyses give a well defined 187 re 187 os isochron with an age of 150 2 2 2 ma mswd 0 60 hydrothermal muscovite yields a plateau 40 ar 39 ar age of 147 2 1 4 ma 40 ar 39 ar age is in good agreement with the re os age these ages show that the timing of tungsten mineralization occurred at about 150 ma our new data when combined with published geochronological results from the other major deposits in this region suggest that widespread w mineralization occurred in the late jurassic throughout south china

shrimp u pb zircon ar ar muscovite and re os molybdenite isotopic dating of the taoxikeng tungsten deposit south china block abstract the taoxikeng tungsten deposit is located in the jiangxi province in the southern part of china and is one of the largest wolframite quartz vein type tungsten deposits in the country the deposit is situated in sinian neoproterozoic to permian strata at the contact with the buried taoxikeng granite sensitive high mass resolution ion microprobe shrimp zircon u pb analysis of the granite has yielded dates of 158 7 3 9 and 157 6 3 5 ma which are interpreted as the emplacement age of the granite molybdenite separated from ore bearing quartz veins yields a re os isochron age of 154 4 3 8 ma and muscovite separated from greisen between the granite and country rocks yields 40ar 39ar plateau ages of 153 4 1 3 and 152 7 1 5 ma these dates obtained from three independent geochronological techniques constrain the ore forming age of the taoxikeng deposit and link the ore genesis to that of the underlying granite the taoxikeng deposit is an example of a jurassic regional scale tungsten tin ore forming event between 160 and 150 ma in the nanling region of the south china block the deposit s strikingly low rhenium contents 4 9 to 13 0 10 3 g g in molybdenite suggests that the ore was derived from a crustal source this conclusion is consistent with previously published constraints from s d and o stable isotopes sr nd systematics and petrogenetic interpretations of spatially related granites

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

alkaline syenites in eastern cathaysia south china link to permian triassic transtension two alkaline syenite plutons the tieshan and yangfang plutons have recently been recognized within ne trending fault zones in eastern cathaysia south china the rocks are very enriched in k2o 6 28 9 39 wt rare earth elements ree particularly light ree and large ion lithophile elements but are relatively low in high field strength elements isotopically they are characterized by high initial 87sr 86sr 0 7093 to 0 7123 and low nd t values 5 64 to 10 63 the geochemical data suggest that the alkaline syenites most likely formed via fractional crystallization of enriched mantle derived magmas sensitive high resolution ion microprobe zircon u pb dating indicates that these two intrusions have late permian 254 4 ma and early triassic 242 4 ma crystallization ages respectively our data suggest that a tectonic regime dominated by transtension probably existed from at least the latest permian into the triassic and was responsible for the formation of the tieshan and yangfang alkaline syenites when combined with previous paleomagnetic structural and sedimentology data we suggest that the transtension along the ne trending strike slip fault zones was related to oblique subduction of the pacific plate underneath south china

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

the archean murmac bay group evidence for a giant archean rift in the rae province canada abstract the lower amphibolite to granulite facies archean murmac bay group of the southwestern rae province canada formed during continental extension rifting of an underlying granitoid basement complex that includes the 3060 40 ma lodge bay granite and the 2999 7 ma cornwall bay granite the contact between the murmac bay group and the basement complex is an unconformity that is locally marked by polymictic conglomerate overlying the conglomerate is basal quartzite of the murmac bay group that contains a laterally extensive 10 km intraformational oligomictic quartzite pebble conglomerate that may have formed by uplift during rifting distinctive medium to coarse grained gabbro dykes and sills that cut both the basement complex and the basal quartzite are interpreted as feeders to stratigraphically overlying tholeiitic basalt flows that have geochemical signatures consistent with formation in a continental rift setting the quartzite basalt contact exhibits rare stratigraphic interlayering and is a horizon along which oxide and silicate facies iron formation dolostone and pelite locally occur ultramafic rocks with komatiitic compositions also intrude these lower stratigraphic units the upper murmac bay group is dominated by pelitic to psammitic rocks that may represent deepening of the sedimentary basin during continued extension ancient approximately 3 62 and 3 7 ga grains dominate the detrital zircon population of the murmac bay group sediments but deposition occurred after approximately 2 77 ga the youngest detrital zircon in our study the age of the murmac bay group is thus constrained as younger than approximately 2 77 ga and older than the crosscutting 2631 12 ma dead man and donaldson lake granites the gross lithological and stratigraphic make up of the murmac bay group closely resembles that of the prince albert woodburn lake and mary river groups of the northern rae province all three of which have been interpreted as approximately 2 7 ga continental rift successions we propose that the murmac bay group is correlative with these successions if correct the total length of this neoarchean rift is at least 2000 km extending from baffin island to northwestern saskatchewan canada the supracrustal rocks of the rift record the break up of a large paleo to early neoarchean continent nunavutia which experienced magmatic events at approximately 3 0 3 62 and 3 7 ga

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

u pb dating of uranium deposits in collapse breccia pipes of the grand canyon region two major periods of uranium mineralization are indicated by u pb isotope dating of uranium ores from collapse breeeia pipes in the grand canyon region northern arizona the hack 2 and 3 kanab north and ez 1 and 2 orebodies apparently formed in the interval of 200 or 20 ma similar to ages inferred for strata bound late triassic hosted uranium deposits in southern utah and northern arizona samples from the grand canyon and pine nut pipes however indicate a distinctly older age of about 260 ma the pigeon orphan and arizona 1 deposits were apparently mineralized before 220 186 and 169 ma respectively but no useful upper age limits can be inferred there is no evidence in the u pb isotope data for uranium mineralization related to laramide tectonism mid tertiary volcanism or late tertiary uplift the clustering in ages for a variety of uranium deposits at about or slightly younger than the age of the lower part of the chinle formation late triassic suggests that uranium in these deposits may have been derived by leaching from volcanic ash in the chinle and mobilized by ground water movement resulting from changing hydrologic gradients caused by regional uplift to the southwest pb isotope ratios of galenas in mineralized pipes are more radiogenic than those of sulfides from either uranium poor pipes or occurrences away from pipes this isotopic contrast suggests that fluids which passed through the pipes had interacted with the proterozoic basement possibly through the vertical fractures which influenced the location and evolution of the pipes themselves regardless of the source of the common pb in the uranium bearing pipes the generally distinct pb isotope composition of their galenas compared to those of barren pipes and nonpipe sulfides in the region may provide a useful exploration guide

hydraulic seals and their origin evidence from the stable isotope geochemistry of dolomites in the middle ordovician st peter sandstone michigan basin regionally extensive overpressured natural gas pools within the st peter sandstone middle ordovician of the michigan basin are bounded by rock types that include 3 7 m thick zones of low permeability low porosity carbonates or diagenetically banded quartz sandstones replacive dolomite from an approximately 5 m thick carbonate interval in the east central portion of the michigan basin has very low dgr13c values that systematically decrease from approximately 5 pmil at the top to 10 pmil pdb at the base dgr18o values for the replacive dolomite also decrease systematically with depth from approximately 27 to 23 pmil smow these data suggest an upward decrease in isotope exchange between the replacive dolomitization fluid and the precursor rock i e the system was rock dominated at the top of the carbonate interval which implies upward cross formational movement of the dolomitizing fluid fluid rock interaction modeling suggests that the dolomitizing fluid had a total dissolved carbon tdc content of approximately 4000 ppm and a dgr13c value of 27 pmil which indicates that the carbon was primarily derived from organic diagenesis sr isotope and major element data suggest that this dolomitizing fluid had a modified seawater origin carbonate intervals in the st peter sandstone contain dolomite cement in quartz sandstone laminations and fractures that have dgr13c values that closely mimic the large dgr13c variations of the adjacent replacive dolomite with depth this correlation indicates that the replacive dolomite controlled the dgr13c value of the carbon dissolved in the parent fluids of the later dolomite cement moreover these data suggest that the parent fluids of the dolomite cement were not confined to a common fracture network but flowed pervasively through the carbonate intervals the dgr13c values of dolomite cement in diagenetically banded quartz sandstone intervals from three locations in the central portion of the michigan basin range from 9 to 4 mil and are relatively invariant at a particular locality therefore the tdc of the dolomitizing fluid in the central michigan basin is interpreted to have contained only about 20 30 organic carbon the fact that all dolomites analyzed in the st peter sandstone have much lower dgr13c values than carbonates in adjacent formations indicates that dolomitization and the formation of hydraulic seals were related to organic matter diagenesis

zircon la icp ms u pb ages of granitoid rocks and molybdenite re os age of shedong w mo deposit in cangwu county of guangxi and its geological significance located in southern margin of dayaoshan uplift the shedong tungsten and molybdenum deposit in cangwu county of guangxi is a porphyry skarn quartz vein type ore deposit related to granitoids zircon la icp ms u pb dating of granitoids yielded the isochron age of granite porphyry 91 05 0 31 ma and that of granodiorite 435 8 1 3 ma in sheshan multiple stock as well as the isochron age of granodiorite porphyry 432 0 1 7 ma in pingtoubei ore blocks re os isochron age of molybdenite hosted in quartz veins related to granodiorite porphyry veins is 437 8 3 4 ma these high precision dating data suggest that tungsten and molybdenum mineralization was formed in early silurian related closely to granodiorite porphyry this new evidence provides constrains on the time of the caledonian orogeny and magmatic activity in southern china and indicates the probable existence of an intense w mo cu au mineralization during caledonian period in dayaoshan uplift

topaz albite granites and rare metal mineralization in the limu district guangxi province southeast china the topaz albite granites of the limu district are ultra acidic peraluminous li f na rich and sn ta nb mineralized a distinct vertical zonation is developed in the granite stocks there is an upward systematic transition from leucocratic microcline albite granite through albite microcline granite topaz albite granite pegmatite stockscheider and layered pegmatite aplite dikes to k feldspar quartz veins and lepidolite fluorite stringers in the country rocks snow ball textures homogeneous distribution of rock forming and accessory minerals disseminated mineralization and melt inclusions in quartz topaz and albite are typical features indicative of their crystallization from the late stage li f na rich and sn ta nb bearing residual granitic melts at a higher intrusion level a comparison with rare metal bearing pegmatite ongonite topaz rhyolite and obsidian glass from other regions shows the worldwide existence of these specialized residual melts their emplacement and crystallization in a variety of geological environments result in the formation of a series of chemically similar rocks with different petrographic textures and mineral associations the topaz albite granites and associated mineralization in the limu district provide a good example of highly evolved magmatic fractionation in the f rich granite system and fluid melt partitioning behavior of rare metal elements during magmatic hydrothermal evolution

geology of the sandaowanzi telluride gold deposit of the northern great xing an range ne china geochronology and tectonic controls abstract the sandaowanzi gold telluride deposit is a new discovery with dominance in gold tellurides in northeastern china the deposit is hosted in quartz veins intruding sub alkaline volcanic rocks there are two types of gold telluride ores in the sandaowanzi ore deposit i e the vein ores and the disseminated ores calaverite krennerite sylvanite petzite empressite hessite and stuetzite are the dominant au ag bearing minerals either in vein ores or in disseminated ores minor amount of other tellurides e g coloradoite altaite and sulfides e g pyrite sphalerite galena chalcopyrite and chalcocite mostly occur in the disseminated ores the gold bearing quartz veins crosscut volcanic host rocks which are dated at 135 3 124 7 ma by la icp ms u pb zircon method the latter unconformably overly a monzogranite dated as 181 6 ma diabase dikes dated at 116 6 ma intrude the gold bearing quartz veins the age data thereby bracket the timing of gold mineralization between 125 3 and 116 6 ma these geochronologic data are consistent with field relations regional comparison reveals that the widespread volcanism in the great xing an range is a product of the subduction of the izanagi plate beneath the eurasian plate gold telluride mineralization was contemporaneous with regional extension and magmatism as the subducting izanagi plate rolled back

uranium metallogenesis in south china and its relationship to crustal extension during the cretaceous to tertiary south china is rich in vein type hydrothermal uranium deposits hosted in granitic volcanic and carbonaceous and siliceous pelitic sedimentary rocks the uranium deposits are spatially associated with extensional structures and or mantle derived mafic dikes both the uranium deposits and mafic dikes are cretaceous to tertiary in age temporally coincident with the crustal extension carbon isotope analyses of calcite deposited in the main stage mineralization in the veins from 12 representative uranium deposits yield 13c values of ore forming fluids mainly from 4 to 8 per mil which are permissive of a mantle origin for the co2 in the ore forming fluids a mantle origin is consistent with the association of the deposits with mafic dikes and the 3he 4he ratios of ore forming fluids e g 0 10 2 02 ra for the volcanic hosted xiangshan uranium deposit isotopic compositions of h and o demonstrate that water in the ore forming fluids is predominantly meteoric in origin ore forming temperatures ranged approximately from 150 to 250 c uranium rich crustal rocks in south china may have been the sources for the uranium crustal extension and associated mafic magmatism are considered to have heated the rocks and allowed co2 possibly from mantle sources to migrate upward and to mix with co2 poor meteoric water the co2 rich hydrothermal fluids mobilized uranium from the source rocks and then the uranium was deposited in various host rocks to form the uranium deposits

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

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

fluid origin and structural enhancement during mineralization of the jinshan orogenic gold deposit south china the jinshan orogenic gold deposit is a world class deposit hosted by a ductile shear zone caused by a transpressional terrane collision during neoproterozoic time ore bodies at the deposit include laminated quartz veins and disseminated pyrite bearing mylonite most quartz veins in the shear zone with and without gold mineralization were boudinaged during progressive shear deformation with three generations of boudinage structures produced at different stages of progressive deformation observations of ore controlling structures at various scales indicate syn deformational mineralization fluid inclusions from pyrite intergrown with auriferous quartz have 3he 4he ratios of 0 15 0 24 ra and 40ar 36ar ratios 575 3 060 18ofluid values calculated from quartz are 5 5 8 4 and d values of fluid inclusions contained in quartz range between 61 and 75 the 13c values of ankerite range from 5 0 to 4 2 and ankerite 18o values from 4 4 to 8 0 the noble gas and stable isotope data suggest a predominant crustal source of ore fluids with less than 5 mantle component data also show that in situ fluids were generated locally by pervasive pressure solution and that widespread dissolution seams acted as pathways of fluid flow migration and precipitation the in situ fluids and fluids derived from deeper levels of the crust were focused by deformation and deformation structures at various scales through solution dissolution creep crack seal slip and cyclic fault valve mechanisms during progressively localized deformation and gold mineralization

mineralization and fluid inclusion study of the shizhuyuan w sn bi mo f skarn deposit hunan province china the shizhuyuan deposit china is a world class w sn bi mo f skarn deposit hosted by devonian limestone in the thermal aureole of the qianlishan granite complex the qianlishan complex comprises five separate intrusions including fine grained porphyritic biotite granite 182 187 ma granite 1 medium grained biotite k feldspar granite 158 163 ma granite 2 fine grained biotite and k feldspar granite granite 3 granitic porphyry 144 146 ma granite 4 and diabase 142 ma the upper part of the granite complex is characterized by extensive greisen alteration skarn zones distributed around the intrusions are mainly calcic consisting of garnet garnet pyroxene vesuvianite garnet and wollastonite vesuvianite progressively outward from the intrusion following the primary skarn formation some of the skarn zones underwent retrograde alteration the high garnet pyroxene ratio and the diopside rich and andradite rich compositions of the pyroxene and garnet indicate that the skarn belongs to the oxidized type mineralization consists of sn be veinlet ore type i in marble and porphyry massive w bi mo sn skarn ore type ii stockwork w sn bi mo f ore type iii and w sn mo bi greisen ore type iv mainly associated with granite 2 emplacement of granite 2 was accompanied by late intense fracturing characterized by stockwork mineralization type iii which was superimposed on massive skarn and greisen zones the stockwork ore consists mainly of greisen and skarn veins and veinlets with scheelite wolframite molybdenite cassiterite bismuthinite and fluorite the sm nd method has been used to analyze the sm nd concentration and data for pyroxene and garnet in the massive skarn type ii ore associated with granite 2 yields an isochron age of 157 ma this age corresponds closely to the age of granite 2 fluid inclusion studies of four types of ore samples reveal four types of inclusions aqueous two phase inclusions h2o co2 inclusions gas rich inclusions and daughter mineral bearing inclusions containing halite or calcite homogenization temperatures of fluid inclusions in skarn minerals range from 350 to 535 c the homogenization temperatures of fluid inclusions in greisen and stockwork are lower than that in skarn and range from 200 to 360 c the fluid inclusion data indicate that there are two types of fluids associated with the massive skarn and greisen having salinities from 26 to 41 wt percent nacl equiv and from 1 to 21 wt percent nacl equiv respectively the high salinity inclusions are daughter mineral bearing whereas the low salinity inclusions are dominantly aqueous with a few gas rich inclusions the results suggest the evolution of the ore forming fluids either by immiscibility or by mixing between a high temperature high salinity magmatic water and a low temperature low salinity fluid such as meteoric water consistent with previously published isotopic studies the shizhuyuan deposit is a multi element skarn highly enriched in w sn bi mo and f this is interpreted to reflect multiple sources and stages of mineralization which in turn may account for the large size of the shizhuyuan deposit

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

key factors controlling volcanic related uranium mineralization in the xiangshan basin jiangxi province south china a review abstract the xiangshan basin hosts the largest volcanic related uranium deposits in china despite several decades of extensive research the key factors controlling volcanic related uranium mineralization in the xiangshan basin remain unclear in this paper we present a review of previous studies and highlight the critical features that are closely related to the uranium mineralization in the xiangshan basin with focus on the geological feathers host rocks ore controlling structures alterations mineralization fluid inclusions and geochronological and geochemical data of the uranium deposits based on these reviews a comprehensive genetic model is proposed to better explain the uranium mineralization mechanism the uranium mineralization at xiangshan is mainly hosted in felsic volcanic and sub volcanic rocks and spatially close to the cretaceous tertiary redbeds the mineralization mainly took place from 125 to 70 ma which is much younger than the ages of host volcanic rocks 135 ma and broadly contemporaneous with the development of the redbed basins and mafic magmatism the uranium mineralization occurs mainly as veins controlled by brittle structures such as fractures faults and volcanic structures the extensional reactivation of preexisting structures and development of new fractures created permeability for the circulation of the ore forming fluids and provided spaces for uranium precipitation the ore forming fluids are characterized by basinal brines with a meteoric water origin possibly mixed with mantle derived fluids the uranium was mostly contributed by the host volcanic and sub volcanic rocks the precipitation of uranium is related to redox reactions with reductants such as fe2 h2s and ch4 as well as other mechanisms related to change of physical and chemical conditions due to fluid boiling the comprehensive review of the geological characteristics related to uranium mineralization reveals that the key factors controlling the uranium mineralization in the xiangshan volcanic basin are related to the coupling of shallow development of oxidizing fluids in the redbeds and brittle structures in the volcanic rocks and deep seated thermal activities related to mafic magmatism geological processes it is proposed that meteoric water infiltrated into the high permeability redbed basins and evolved to oxidizing basinal fluids the oxidizing fluids further circulated into the volcanic basin along brittle structures and extracted uranium from the volcanic rocks the heat provided by mafic magmatic activities accompanying upward flowing deep source hot fluids promoted the uranium extraction and transportation

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

u pb and re os geochronology and geodynamic setting of the dabaoshan polymetallic deposit northern guangdong province south china abstract the dabaoshan polymetallic deposit in northern guangdong province contains iron copper lead zinc molybdenum tungsten and sulfur mineral resources porphyry type mo w and skarn type mo w mineralization occurs along the internal and external contact zones of the granodioritic porphyry respectively la icp ms u pb dating of zircons from two granodioritic porphyry samples yielded a weighted mean 206 pb 238 u age of 175 8 1 5 ma mswd 0 037 and 175 0 1 7 ma mswd 0 41 they can be pooled together to yield a combined weighted age of 175 4 1 6 ma mswd 0 26 which is interpreted as the emplacement age of the granodioritic porphyry re os dating of three molybdenite samples from porphyry and skarn ores yielded consistent model ages of 163 2 2 3 ma to 165 2 2 4 ma with a weighted mean of 163 9 1 3 ma mswd 0 81 which is the age of mo w mineralization these ages are consistent with the molybdenite re os model age 164 7 3 ma measured by mao et al 2004a for the stratiform cu pb zn orebody and they can yield a weighted mean of 164 0 2 5 ma mswd 0 16 this implies that mo w and cu pb zn mineralization in the dabaoshan polymetallic deposit are the products of one mineralization event the mineralization in the deposit coincides closely with that of mo polymetallic mineralization 164 149 ma elsewhere in the nanling region comprising an important polymetallic metallogenic belt of south china and corresponds to the second episode of mesozoic metallogenesis in south china combined with previous studies we suggest that the dabaoshan polymetallic deposit is related to post collisional lithosphere extension in the nanling region of south china geological data and pb isotopic evolution diagrams together with stable isotopic data of fluid inclusions 18 o 3 75 7 0 d 50 7 to 56 1 and ore sulfides 34 s 2 3 suggest a genetic relationship between the dabaoshan polymetallic deposit the granodioritic porphyry and the dacitic porphyry these data combined with the re content 64 7 to 102 4 ppm of molybdenite indicate that the ore forming components were derived from mixed crustal and mantle sources

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

direct evidence for the source of uranium in the baiyanghe deposit from accessory mineral alteration in the yangzhuang granite porphyry xinjiang province northwest china

cretaceous tectonic evolution of south china a preliminary synthesis abstract the cretaceous tectonic evolution of south china is characterized by widespread extensional basin and dome generation voluminous magma intrusion eruption and associated polymetallic mineralization all of which are of world wide interests that have stimulated the attention of geologists for more than half a century due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of south china many controversies regarding the nature and origin of these features remain this paper attempts to make a review by synthesizing existing structural petrological geochronological and geochemical data of the cretaceous structures and magmas which guides us to propose a three stage tectono thermal evolutionary history of south china during the cretaceous period the earliest cretaceous 145 137 ma tectonic stage was characterized by syn orogenic shortening deformation and metamorphism under a nw se compressional setting which generated voluminous porphyry cu au ore bearing adakitic rocks in the lower yangtze river belt and gneissic granites in the coastal area its geodynamic origin was interpreted as combined effects of the pacific izanagi ridge subduction beneath the lower yangtze river belt and the pacific subduction beneath the cathaysia block this syn orogenic shortening stage was followed by a post orogenic stage 136 86 ma comprising two episodes of alternate extensional and shortening events the extension 136 118 ma in the earlier episode was dominated by a nw se extensional regime it led to significant taphrogenesis manifested by large scale extensional basins and voluminous magma intrusion eruption this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted pacific slab the subsequent nw se transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins this transpression lasted from 117 ma to 108 ma and its driving mechanism was attributed to the collision between the eastern asian margin and the west philippine block the extension 107 86 ma in the later episode was dominated by a wnw ese extensional regime which led to a second phase of basin subsidence and produced numerous a and i type granites and bimodal volcanoes the tectonic regime then changed at ca 85 ma to wnw ese oriented transpression causing inversion of the late cretaceous rift basins and cessation of extension related magmatism the change of stress field from wnw ese extension to wnw ese transpression was related to the variations of the subducted slab dynamics i e the transition from either the ese ward retreat to wnw ward subduction of the pacific slab or the alternate stress during slab break off during the latest cretaceous a drastic change of regional tectonic stress orientation from wnw ese to n s occurred in south china the third stage predominated by n s extension was developed which caused a new phase of regional crustal subsidence along the youngest e w trending extensional structures

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

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

geology and genesis of kafang cu sn deposit gejiu district sw china kafang is one of the main ore deposits in the world class gejiu polymetallic tin district sw china there are three main mineralization types in the kafang deposit i e skarn cu sn ores stratiform cu ores hosted by basalt and stratiform cu sn ores hosted by carbonate the skarn mainly consists of garnet and pyroxene and retrograde altered rocks these retrograde altered rocks are superimposed on the skarn and are composed of actinolite chlorite epidote and phlogopite major ore minerals are chalcopyrite pyrrhotite cassiterite pyrite and scheelite sulfur and pb isotopic components hint that the sources of different types of mineralization are distinctive and indicate that the skarn ore mainly originated from granitic magma whereas the basalt hosted cu ores mainly derived from basalt microthermometry results of fluid inclusions display a gradual change during the ore forming process the homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages the salinities and freezing temperatures exhibit similar evolutionary tendencies with the t homogenizaion while the densities of the different types keep constant the majority being less than 1 oxygen and hydrogen isotopic values o and d of the hydrothermal fluids fall within ranges of 3 1 to 7 7 with an average of 6 15 calculated at the corresponding homogenization temperature and 73 and 98 with an average of 86 5 respectively microthermometry data and h o isotopes indicate that the ore forming fluid of the kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage molybdenite re os age of the skarn type mineralization is 83 4 2 1 ma and the stratiform ores hosted by basalt is 84 2 7 3 ma which are consistent with the la icp ms zircon age of the xinshan granite intrusion 83 1 0 4 ma the evidence listed above reflects the fact that different ore styles in the kafang deposit belong to the same mineralization system

the arrowsmith orogeny geochronological and thermobarometric constraints on its extent and tectonic setting in the rae craton with implications for pre nuna supercontinent reconstruction abstract geochronological and thermobarometric data for two widely spaced and previously unstudied areas of the rae craton canada provide important temporal and spatial links between previously investigated areas in the northern and southern rae craton that had been interpreted to have been reworked during the ca 2 5 2 3 ga arrowsmith orogeny on southern boothia peninsula upper amphibolite to granulite facies metamorphism dated by in situ shrimp u pb analysis of monazite occurred at ca 2 64 2 60 2 54 2 50 2 49 2 44 and 2 37 2 34 ga with retrograde monazite growth at 2 27 ga shrimp u pb ages of zircon in two metasedimentary rocks provide a further indication of metamorphism at ca 2 54 and 2 50 ga which also corresponds to the age determined for a k feldspar augen granite textural relationships indicate that the regional foliation formed between ca 2 54 ga and 2 50 2 49 ga peak metamorphic conditions of 700 c and 5 6 kbar are interpreted to have been reached during the 2 37 2 34 ga event in the mccann mcarthur lake region of the southwestern rae craton upper amphibolite to granulite facies metamorphism is dated by in situ shrimp monazite ages of ca 2 53 2 47 and 2 37 2 28 ga textural relationships indicate deformation initiated by ca 2 37 ga and terminated by ca 2 30 ga metamorphic conditions of 5 kbar and 700 735 c were quenched at ca 2 3 ga following peak conditions of 7 kbar and 800 c the evidence for regional deformation at 2 54 2 49 ga on southern boothia peninsula supports an andean type accretionary margin setting for the arrowsmith orogeny a collisional event may have terminated high grade metamorphism in the northern region by ca 2 34 ga while metamorphism associated with continental arc magmatism continued in the south until at least ca 2 28 ga these combined data demonstrate the continuity and broad extent of the arrowsmith orogen along the western flank of the rae craton extending 1500 km from northern saskatchewan to northern baffin island the broad extent of this globally rare orogenic event provides an important piercing point for supercontinent reconstructions which are discussed in a companion paper the inferred convergent tectonic activity between ca 2 54 and 2 28 ga is interpreted to have occurred on the flank of a growing supercontinent a setting that could account for an apparent slowdown but not shutdown in global tectonics

high resolution sequence stratigraphic analysis of the st peter sandstone and glenwood formation middle ordovician michigan basin u s a the middle ordovician st peter sandstone and glenwood formation ancell group represent a significant target for gas exploration at the base of the tippecanoe sequence in the michigan basin core and well log data show that the st peter glenwood interval contains numerous carbonate units that provide the basis for both regional correlation and subdivision of the section into at least 20 high frequency sequences the temporal resolution afforded by these sequences allows a detailed analysis of sediment partitioning as the basin evolved the spatial distribution of the basal sequences illustrates the pronounced east to west onlap of the wisconsin arch an abrupt increase in sequence thickness upsection indicates that a major episode of basin centered subsidence began during middle st peter deposition and continued through the deposition of the glenwood formation the upper sequences show a significant beveling of the glenwood formation and the top of the st peter sandstone in the north south and southeast areas of the basin prior to deposition of the overlying black river carbonates although eustatic sea level changes were undoubtedly operating at several scales the facies distribution of this mixed clastic carbonate system also documents significant changes of local and regional tectonics

porphyry cu au mo epithermal ag pb zn distal hydrothermal au deposits in the dexing area jiangxi province east china a linked ore system abstract based on previous studies and detailed field investigations of the dexing porphyry copper deposit the yinshan ag pb zn deposit and the jinshan shear zone hosted gold deposit in the dele jurassic volcanic basin in the northeastern jiangxi province east china we propose that the three deposits share spatial temporal and genetic relationships and belong to the same metallogenic system dexing is a typical porphyry cu au mo deposit in which both ore forming fluid and metals are derived from the granite porphyry the yinshan deposit consists of a porphyry copper ore located in the cupola of a quartz porphyry stock in the lower part and ag pb zn ore veins in the upper part the hydrothermal fluids were mainly derived from the magma in the early stages of the mineralizing event and became mixed with meteoric waters in the late stages its ore metals are magma derived both the jinshan base metal veins and the hamashi dongjie and naikeng quartz vein type gold deposit are hosted by brittle ductile structures which are distal in relation to the porphyry intrusions and were formed by mixed magmatic fluids and meteoric water whereas the gold was mainly leached from the country rocks mesoproterozoic shuangqiaoshan group phyllite and schist the deposits show a distinct spatial arrangement from porphyry cu to epithermal ag pb zn and distal au we suggest a porphyry epithermal distal vein ore system model for this group of genetically related mineral deposits they were formed in a back arc setting in a middle jurassic active continental margin with magmas derived from the subducted slab

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

yanshanian late mesozoic ore deposits in china an introduction to the special issue abstract the late jurassic cretaceous yanshanian orogeny or yenshan movement one of the most important tectonothermal events is first recognized in china especially eastern china this late mesozoic orogeny which was initiated most likely by a mesozoic tectonic switch strongly reworked or destructed the older continental lithospheres or cratonic keels that are manifested by alternating compressive and extensional deformation voluminous igneous rocks and a variety of characteristic magmatic hydrothermal mineral systems despite its first discovery and definition in yenshan yinshan area of north china craton the yanshanian orogeny probably is of global tectonic magmatic and metallogenic significance however there have been hot debates on the precise starting time accurate duration or time interval detailed processes and evolution linked to deep lithospheres tectonic nature and geodynamic mechanism s of the yanshanian orogeny which inevitably have hindered the understanding of the genesis mineralizing processes and geodynamic mechanism of the late mesozoic magmatic hydrothermal mineral systems this special issue captures some of the latest research results on the yanshanian ore deposits that are involved into a few main mesozoic metallogenic belts or provinces from northeast to southwest china including 1 the jiaodong peninsula metallogenic province in the north china craton 2 the middle lower yangtze river valley metallogenic belt in the central eastern china 3 the jiangnan and 4 the nanling metallogenic belts in the south china block 5 the southeastern china coast metallogenic belt and 6 the sanjiang metallogenic belt in southwest china through a multidisciplinary study this special issue re investigated and re evaluated the relationship between the late mesozoic magmatic hydrothermal mineral systems and the yanshanian tectonothermal events in the studied metallogenic belts or provinces a few important contributions to the topic in this special issue yanshanian metallogeny are summarized as followings 1 a new ore deposit type i e the intracontinental reactivation type has been suggested to interpret the genesis of those au polymetallic deposits that are hosted within older metamorphic rocks and related to the late mesozoic basin and range extensional settings 2 late mesozoic re activation of the preexisting structures by the yanshanian tectono thermal event s might be an important mechanism controlling the yanshanian large scale mineralization 3 a type granites formed by partial melting of the mesoproterozoic crust but with inputs from mantle derived melt are also favorable for sn mineralization in addition to s type and i type granites as previously recognized 4 calculated oxygen fugacities o 2 of granitic magmas based on chemical compositions of primary biotite have been confirmed to be effective proxy for distinguishing cu au mo w sn pb zn mineralized granites from barren granites 5 a significant epoch of w sn magmatic hydrothermal ore system at ca 145 135 ma has been identified in the southeastern china coast metallogenic belt and 6 in addition to traditional structural geology mineralogy petrology geochemistry and geochronology new analytical techniques e g cu isotopes and data treatment method e g bi dimensional empirical mode decomposition can be used to provide more constraints for deep exploration

gold deposits in the xiaoqinling xiong ershan region qinling mountains central china the gold rich xiaoqinling xiong ershan region in eastern shaanxi and western henan provinces central china lies about 30 50 km inland of the southern margin of the north china craton more than 100 gold deposits and occurrences are concentrated in the xiaoqinling west xiaoshan middle and xiong ershan east areas late archean gneiss of the taihua group and middle proterozoic metavolcanic rocks of the xiong er group are the main host rocks for the deposits mesozoic granitoids ca 178 104 ma are present in most gold districts but deposits are typically hosted in the precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones deposits in the xiaoqinling and xiaoshan areas are best classified as orogenic gold deposits with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks alteration assemblages are dominated by quartz sericite pyrite and carbonate minerals the ore forming fluids were low salinity co2 rich and characterized by isotopically heavy 18o four deposits dongchuang wenyu yangzhaiyu and dahu in the xiaoqinling area each contain resources of about 1 moz au some of the gold deposits in the xiong ershan area represent more shallowly emplaced tellurium enriched orogenic systems which include resources of approximately 1 1 5 moz au at shanggong and beiling or tantou others are epithermal deposits e g qiyugou and dianfang that are hosted in volcanic breccia pipes isotopic dates for all gold deposits although often contradictory generally cluster between 172 99 ma and are coeval with emplacement of the post kinematic granitoids the gold deposits formed during a period of relaxation of far field compressional stresses clearly subsequent to the extensive paleozoic early mesozoic accretion of arc terranes and the yangtze craton onto the southern margin of the north china craton hydrothermal and magmatic events occurred locally where extension related precambrian basement uplifting took place along the craton margin fluids for the orogenic gold deposits in the xiaoqinling xiaoshan and xiong ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones alternatively for the epithermal gold deposits at shallower levels in the xiong ershan area gold transporting fluids were mainly exsolved from coeval magmas although meteoric water was also involved in these hydrothermal systems

trace element and sr nd isotope geochemistry of fluorite from the xiangshan uranium deposit southeast china the trace element and sr nd isotope geochemistry of fluorite have been investigated in the xiangshan volcanic rock hosted uranium deposit in southeast china detailed sr nd isotope data of the hydrothermal fluorite closely associated with the uranium mineralization suggest that ore forming fluids were a combination of mantle derived fluid and fluids equilibrated with basement metamorphic rocks this model is consistent with previously published h o isotope data and is incompatible with meteoric water as the only ore forming fluid trace element geochemical profiles across the uranium orebody can be interpreted to reflect reaction between the host rocks and a mantle derived fluid containing high u and th with low th u ratios the mantle derived fluid is considered to have been u f and carbonate rich mixing with shallowly circulated meteoric water within the fractures of the host volcanic rocks caused dilution and cooling of the ore forming fluid and subsequent precipitation of fluorite and uranium ore