molybdenite re os and muscovite 40 ar 39 ar dating of quartz vein type w sn polymetallic deposits in northern guangdong south china northern guangdong is an important part of nanling tungsten tin metallogenic belt south china the tungsten mineralization in this area consists of mainly quartz wolframite vein type mineralization with w sn polymetallic deposits mostly distributed at the outer contact zone between concealed late jurassic granitic stocks and cambrian ordovician low metamorphosed sandstones and shales molybdenite re os and muscovite 40ar 39ar isotopic dating of three typical tungsten vein type deposits yaoling meiziwo and jubankeng in northern guangdong show that two episodes of late jurassic w sn polymetallic mineralization occurred in this area an early episode during the late jurassic 158 159 ma represented by the yaoling hongling and meiziwo tungsten deposits and a younger event during the early cretaceous 138 ma represented by the jubankeng deposit analysis of available radiometric ages of several w sn deposits in the nanling region indicate that these deposits formed at several intervals during the mesozoic at 90 100 134 140 144 162 and 210 235 ma and that large scale w sn mineralization in this region occurred mainly between 150 and 160 ma

geology and molybdenite re os age of the dahutang granite related veinlets disseminated tungsten ore field in the jiangxin province china this is a brief research report about the recently discovered and currently being explored dahutang tungsten deposit or ore field in northwestern jiangxi south central china the deposit is located south of the middle lower yangtze river valley cu au mo fe porphyry skarn belt yrb the mineralization is genetically associated with cretaceous porphyritic biotite granite and fine grained biotite granite and is mainly hosted within a neoproterozoic biotite granodiorite batholith the dahutang ore field comprises veinlets disseminated 95 of the total reserve breccia 4 and wolframite scheelite quartz vein 1 ore styles the mineralization and alteration are close to the pegmatite shell between the cretaceous porphyritic biotite granite and neoproterozoic biotite granodiorite and the three styles of ore bodies mentioned above are related to zoned hydrothermal alteration that includes greisenization k feldspar alteration silicification carbonatization chloritization and fluoritization arranged in time early to late and space bottom to top five samples of molybdenite from the three types of ores have been collected for re os dating the results show re os model ages ranging from 138 4 ma to 143 8 ma with an isochron age of 139 18 0 97 ma mswd 2 9 the quite low re content in molybdenite falls between 0 5 ppm and 7 8 ppm that is indicative of the upper crustal source this is quite different from molybdenites in the yrb cu au mo fe porphyry skarn deposits that contain between 53 ppm and 1169 ppm re indicating a mantle source the dahutang tungsten system is sub parallel with the yrb porphyry skarn cu au mo fe system both are situated in the north margin of the yangtze craton and have a close spatial temporal relationship this possibly indicates a comparable tectonic setting but different metal sources both systems are related to subduction of the paleo pacific plate beneath the eurasian continent in early cretaceous the cu au mo fe porphyry skarn ores are believed genetically related to granitoids derived from the subducting slab whereas the porphyry w deposits are associated with s type granitoids produced by remelting of the upper crust by heat from upwelling asthenoshere

mantle derived noble gases in ore forming fluids of the granite related yaogangxian tungsten deposit southeastern china more than 90 of the tungsten resources of china are in the nanling region of south china and the yaogangxian vein deposit is the largest tungsten deposit in this region the tungsten deposits have ages of 150 160 ma and are spatially temporally and genetically related to granites which were previously believed to be produced by crustal anatexis this paper provides he and ar isotope data of fluid inclusions in pyrite and arsenopyrite from the yaogangxian w veins 3he 4he ratios range from 0 41 to 3 03 ra where ra is the 3he 4he ratio of air 1 39 10 6 and 40ar 36ar ratios from 328 to 1 191 moreover there are excellent correlations between he and ar isotopic compositions the results suggest that the ore forming fluids are a mixture between a crustal fluid containing atmospheric ar and crustal 4he and a fluid containing mantle components it is likely that the former is a low temperature meteoric fluid and the later is a fluid exsolved from the w associated granitic magma which formed by crustal melting induced by intrusion of a mantle derived magma

comparison of pelagic and nepheloid layer marine snow implications for carbon cycling abstract marine snow from upper and mid water i e pelagic depths on the california margin is texturally and compositionally different from that traveling in the nepheloid layer transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts e g diatom frustules foram tests organic matter and microbes these components are entrained as discrete particles or small aggregates 10 m in diameter in a loose network of exocellular muco polysaccharide material clays are infrequent but when present are constituents of comparatively compact organic rich microaggregates microbes are abundant and appear to decrease in number with increasing water depth in contrast marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles clay flocs and relatively dense clay organic rich microaggregates in an exocellular organic matrix bioclasts and microorganisms occur only rarely the prevalence of clay organic rich aggregates in the nepheloid layer suggests that prior to final deposition and burial marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter samples examined were collected offshore of northern and central california

direct dating of hydrothermal w mineralization u pb age for hubnerite mnwo4 sweet home mine colorado abstract we have investigated the potential of hubnerite for u pb dating hubnerite forms typically at medium to low temperatures in a wide range of pneumatolytic hydrothermal mineral deposits particularly porphyry molybdenum and sn specialized granites hubnerite from the sweet home mine alma colorado formed in a pb rich u poor environment but still developed relatively radiogenic pb isotopic compositions the low pb common contents in hubnerite 0 075 to 0 155 ppm demonstrate that pb is efficiently excluded from the crystal lattice in contrast u may substitute for mn the u pb data of hubnerite scatter most of the scatter originates from samples with 206 pb 204 pb values below 50 where pb blank contributes up to 30 to pb total using the least radiogenic galena pb samples with 206 pb 204 pb values above 70 have overlapping 206 pb 238 u and 207 pb 235 u values and yield a 206 pb 238 u age of 25 7 0 3 ma 2 late stage apatite from the sweet home mine yields a 206 pb 204 pb 238 u 204 pb isochron corresponding to an age of 24 8 0 5 ma 2 a comparison of the u pb hubnerite ages with literature 40 ar 39 ar ages on earlier sericite and the u pb age on later apatite suggests that i hubnerite yields accurate u pb ages and ii the evolution of the sweet home mineralization from greisen type mineralization to medium temperature hydrothermal vein mineralization took place in a few hundred thousand years at most aqueous low n 2 bearing and aqueous inclusions in the dated hubnerite have homogenization temperatures between 325 and 356 c and moderate salinity up to 6 7 wt nacl equiv thus hubnerite represents one of the rare examples of a mineral that can be dated accurately and carries petrological information

an intercalibration study of the fish canyon sanidine and biotite 40ar 39ar standards and some comments on the age of the fish canyon tuff the age of the fish canyon tuff fct has been the subject of intense study due to its potential significance as a geochronological test to establish age concordance between the k ar and u pb isotopic systems minerals from the fct notably sanidine and biotite are in widespread use as 40ar 39ar fluence monitors standards and have been employed as both primary and intercalibrated standards in attempting to constrain the true age of fct the distinction between primary vs intercalibrated ages is important as only the primary age determinations are valid an investigation of both fish canyon sanidine fcs and fish canyon biotite fct 3 was undertaken to assess the chemical and isotopic homogeneity of the minerals on a grain to grain scale electron microprobe results show that fcs is chemically homogeneous verifying previous studies although there are some very small zones of minor k depletion fct 3 biotite commonly contains numerous and small mineral inclusions 40ar 39ar experiments further show that fcs is remarkably homogeneous confirming previous observations whereas fct 3 shows much greater isotopic variability due to contamination from the mineral inclusions by setting the age of fcs equal to 27 98 0 15 ma 2 as intercalibrated to the u pb system by villeneuve et al 2000 the resultant intercalibration factor between fcs and fct 3 is 1 005 0 017 yielding an age of 28 13 0 47 ma 2 for fct 3 although the significant intragrain chemical and isotopic variability precludes its use as an effective 40ar 39ar fluence monitor the true age of the fct is problematic a survey of all primary ages for fct shows that mean k ar ages for plagioclase hornblende biotite and sanidine are consistently younger than mean u pb ages from titanite and zircon in conjunction with recently published petrological results which indicate that the fct contains material from multiple crystallization events this significant discrepancy between the k ar and u pb data sets demonstrates that the fish canyon tuff cannot serve as a golden standard between the k ar and u pb systems

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

subsurface fractures and their relationship to stress history in east texas basin sandstone abstract subsurface fractures were sampled with more than 400 m of core from the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 600 m thick that was deposited in the gradually subsiding gulf coast basin depth to the top of the formation in east texas now ranges between 1800 and 2900 m fractures in sandstone exhibit features that are due to intermittent fracturing and sealing crack seal which suggest that the fractures are the result of episodes of fluid pressure in excess of hydrostatic correlation of the vein mineral precipitation sequence with the diagenetic history and the results of previous 18 o studies of quartz cement indicates that fractures propagated at depths of between 900 and 1500 m during the migration of quartz precipitating fluids fracture permeability provides a mechanism for the passage of large fluid volumes recorded by the precipitation of extensive quartz cement in the formation fractures stopped propagating before maximum burial depth was achieved during approximately 1500 m of subsequent burial fractures either remained partly open or were sealed by postkinematic ankerite and clay minerals

in situ u pb geochronology of xenotime and monazite from the abra polymetallic deposit in the capricorn orogen australia dating hydrothermal mineralization and fluid flow in a long lived crustal structure abstract the proterozoic capricorn orogen is a major tectonic zone that records the assembly and subsequent reworking of the west australian craton recent seismic transects across the orogen have identified major crustal structures some of which are spatially associated with hydrothermal mineral deposits the sedimentary rock hosted abra deposit which is the largest base metal accumulation in the capricorn orogen is localized within the crust cutting lyons river quartzite well fault zone robust radiometric dates for the timing of sediment deposition and hydrothermal mineralization are essential for understanding the geological history of this long lived orogen and the processes that formed the ore deposits in situ u pb shrimp geochronology of xenotime intergrown with magnetite hematite galena from the abra ore zone yields a weighted mean 207pb 206pb age of 1594 10 ma n 14 mswd 2 6 which is interpreted to represent a period of xenotime growth during the hydrothermal activity responsible for the mineralization an older coherent cluster within this group gives a weighted mean age of 1610 16 ma n 5 mswd 1 5 which constrains the depositional age of the lower edmund group sediments to between c 1680 ma maximum age of the basal mt augustus sandstone and c 1610 ma authigenic monazite from the ore zone gives 207pb 206pb ages of 1375 14 n 16 mswd 0 99 ma interpreted to represent a hydrothermal event postdating the main phase of mineralization monazites in samples distal to mineralization yield weighted mean 207pb 206pb ages of 1221 14 ma n 5 mswd 1 04 and 995 18 ma n 6 mswd 1 3 interpreted as records of discrete episodes of hydrothermal fluid flow our results suggest that the lyons river quartzite well fault which is one of the principal structures in the capricorn orogen has a long history of tectonic reactivation spanning more than 600 million years and involving crustal extension and sediment deposition hydrothermal mineralization and multiple episodes of fluid flow xenotime and monazite represent ideal chronometers for investigating the complex histories of hydrothermal mineralization and fluid flow in major crustal structures and helping to unravel the geological evolution of intracratonic orogens

potential field evidence for a volcanic rifted margin along the texas gulf coast potential fi eld data along the texas portion of the gulf of mexico indicate a large amplitude coast parallel magnetic maximum and a smaller bouguer gravity high models constrained by seismic refraction data indicate that these maxima manifest a deeply buried volcanic rifted passive margin or other magnetic high in the outer transitional crust buried 12 15 km the source is 220 km wide similar to the voring plateau in norway and the u s east coast this margin which formed during the opening of the gulf of mexico differs in origin from the transform boundary of the northeast mexico margin tehuantepec transform and we infer a jurassic triple junction related to the borderland rift system which is traceable as far as southeast california

are open fractures necessarily aligned with maximum horizontal stress abstract fluid flow in fractured rock is an increasingly central issue in recovering water and hydrocarbon supplies and geothermal energy in predicting flow of pollutants underground in engineering structures and in understanding large scale crustal behaviour conventional wisdom assumes that fluids prefer to flow along fractures oriented parallel or nearly parallel to modern day maximum horizontal compressive stress or s hmax the reasoning is that these fractures have the lowest normal stresses across them and therefore provide the least resistance to flow for example this view governs how geophysicists design and interpret seismic experiments to probe fracture fluid pathways in the deep subsurface contrary to these widely held views here we use core stress measurement and fluid flow data to show that s hmax does not necessarily coincide with the direction of open natural fractures in the subsurface 3 km depth consequently in situ stress direction cannot be considered to predict or control the direction of maximum permeability in rock where effective stress is compressive and fractures are expected to be closed chemical alteration dictates location of open conduits either preserving or destroying fracture flow pathways no matter their orientation

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

types and distribution of silver ore deposits in china silver is generally recovered as a by and co product along with au pb zn cu sb bi hg sn and w from polymetallic and gold mines in china chinese silver deposits can be classified into five principal types according to host rocks these types and their host rocks are 1 marine volcanic sedimentary rocks hosting la massive sulfide pb zn cu ag ores and 1b stratiform ag au ores 2 continental volcanic sedimentary rocks containing 2a various polymetallic silver veins and or stockworks and 2b ag au veins in pyroclastic rocks 3 rocks affected by metasomatic processes including 3a complex sn polymetallic ag ores 3b pb zn cu ag skarns 3c associated w ag quartz veins and or skarns and 3d ag au zones and veins in altered carbonate rocks 4 metamorphic intrusive rocks principally ag au veins in sheared and brecciated metamorphic rocks and 5 sedimentary rocks including 5a stratiform pb zn ag ores in carbonate rocks 5b ag v mantos in black shales and 5c cu ag layers in red sandstones a sixth grouping includes gossans the tectonic settings geological features and temporal and spatial distribution of these different types of silver occurrences indicate that silver mineralization reflects to a great extent the evolution of tectonic environments in china throughout geological time type 1 is generally developed in association with several fold belts from the caledonian to yanshanian orogens while types 2 3 and 4 correlate with rejuvenation of the eastern china continent during the mesozoic period the three subgroups of type 5 are recognized in different stages and various sedimentry and diagenetic environments during the development of paraplatforms and fold belts type 6 results from recent weathering of existing sulfide ores or protores

mesozoic large scale magmatism and mineralization in south china preface abstract south china is famous for its polymetallic deposits with more than 50 of the world s w and sb reserves and 20 of the sn reserves as well as abundant cu mo pb zn au ag ta nb hree and u this special issue reports recent progress on the tectonic evolution magmatism and ore deposits of south china which leads to a more comprehensive understanding of the mesozoic large scale magmatism and mineralization events 1 south china has been located in backarc settings during multiple subductions since the paleozoic which may have contributed to pre enrichments of the ore forming materials 2 the pacific plate subduction was a principle factor that controlled the late mesozoic large scale magmatism and mineralization in south china through flat subduction ridge subduction slab tearing and slab rollbacks

origin of the atypical puy les vignes w breccia pipe massif central france constrained by trace element and boron isotopic composition of tourmaline abstract the puy les vignes w deposit is an atypical wolframite bearing hydrothermal breccia pipe hosted in migmatitic biotite sillimanite gneisses in the northwestern french massif central the deposit is characterized by volumetrically important tourmaline alteration allowing to investigate the fluid evolution of the ore forming hydrothermal system four generations of hydrothermal tourmaline tur 1 tur 4 formed during pre syn and post mineralization stages were identified based on detailed petrographic observations and were analyzed in situ for their chemical and boron isotopic compositions at the grain scale tourmaline commonly shows oscillatory zoning and dissolution textures resulting from a multi stage crystallization in a fluid dominated system the different generations of hydrothermal tourmaline have dravite schorl compositions and show similar major and trace element contents falling into the field of metamorphic rocks high concentrations of v cr sr and low concentrations of li sn in tourmaline suggest a metamorphic dominated origin of these elements the boron isotopic compositions of tourmaline range between 13 3 and 7 8 and cannot unambiguously distinguish between a magmatic and a metamorphic fluid origin our data indicate that the chemical and boron isotopic composition of tourmaline was dominantly controlled by high temperature fluid rock interactions between the metamorphic basement and boron rich reduced and low salinity hydrothermal fluids based on these results we propose a fluid evolution scenario for the puy les vignes ore forming hydrothermal system release of magmatic hydrothermal fluids from an unexposed peraluminous leucogranite at ca 324 ma is proposed as the main mechanism responsible for early greisenization and formation of disseminated tur 1 this episode was followed by massive tourmalinization and hydraulic brecciation of the overlying gneisses producing a tourmaline rich tur 2 crackle breccia by interactions with boron rich hydrothermal fluids fluid assisted reopening and collapse of the former tourmalinite at ca 318 ma yielded a matrix supported quartz tourmaline breccia pipe and formation of wolframite bearing quartz veins accompanied by deposition of tur 3 finally post ore hydraulic fracturing at ca 300 ma led to formation of tourmaline rich microbreccias tur 4 possibly from metamorphic fluids

paleozoic continent ocean transition in the ouachita mountains imaged from passcal wide angle seismic reflection refraction data a wide angle reflection reflection experiment sponsored by the program for array seismic studies of the continental lithosphere passcal was conducted in the ouachita mountains area of southwestern arkansas and northwestern louisiana this experimental employed 400 state of the art seismic recorders and overlapped the southern one third of the cocorp consortium for continental reflection profiling deep seismic reflection profile in the area a wide variety of data processing and interpretation techniques was employed to derive an earth model from these data the model depicts a preserved early paleozoic continental margin buried beneath allochthonous paleozoic strata and younger sedimentary rocks the southern part of the model indicates the presence of oceanic or highly extended continental crust overlain by about 15 km of mostly paleozoic sedimentary rock these results are consistent with little if any shortening of crystalline continental crust during the ouachita orogeny

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

temporal consistency between granite evolution and tungsten mineralization in huamei ao southern jiangxi province china evidence from precise zircon u pb molybdenite re os and muscovite 40ar 39ar isotope geochronology abstract the large huamei ao tungsten deposit with total wo 3 reserves of 67 400 tons at an average grade of 1 334 wo 3 is located in the convergent zone of the eastern nanling e w trending tectono magmatic belt and the western wuyishan nne ssw trending tectono magmatic belt in southern jiangxi province china the tungsten mineralization in this deposit is mainly found in quartz wolframite veins with most orebodies distributed at the outer contact zone between concealed late jurassic granitic stocks and sinian weakly metamorphosed sandstones and phyllites zircons collected from medium to fine grained biotite granite in a diamond drill hole at a sea level of ca 10 m yield a crystallization age of 159 9 1 2 ma through laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms u pb dating molybdenite and muscovite that were both separated from quartz wolframite veins yield a re os isochron age of 158 5 3 3 ma and an 40 ar 39 ar weighted plateau age of 157 9 1 1 ma respectively these dates obtained via three independent geochronological techniques constrain the ore forming age of the huamei ao deposit and link the genesis of the ore and the underlying granite analyses of available high precision zircon u pb molybdenite re os and muscovite 40 ar 39 ar radiometric ages of major w sn deposits in southern jiangxi province indicate that there is no significant time interval between w sn mineralization and its intimately associated parent granite emplacement interval of 0 6 ma these deposits formed over three intervals during the mesozoic 240 210 170 150 and 130 90 ma with large scale w sn mineralization occurring mainly between 160 and 150 ma the majority of w sn deposits in this region are located in southern jiangxi and southern hunan provinces

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

succession of permian and mesozoic metasomatic events in the eastern pyrenees with emphasis on the trimouns talc chlorite deposit recent studies proposing pre orogenic mantle exhumation models have helped renew the interest of the geosciences community in the pyrenees which should be now interpreted as a hyper extended passive margin before the convergence between iberia and eurasia occurred unresolved questions of the pyrenean geology as well as the understanding of the formation of hyper extended passive margins are how the crust was thinned and when where and how the crustal breakoff occurred the study of the variscan and pre variscan pyrenean basement is thus critical to document and understand this cretaceous crustal thinning in order to specify the timing of mesozoic metasomatism and the associated deformation in the pre mesozoic basement of the pyrenees we carried out a u th pb laser ablation icp ms study on a large panel of ree and titanium rich minerals titanite and rutile from talc chlorite ores from the eastern pyrenees with a special emphasis on the trimouns deposit the world s largest talc quarry our results suggest that the trimouns talc formation was restricted to the upper aptian cenomanian time while the talc and chlorite formation in the eastern pyrenees occurred during several distinct permian jurassic and cretaceous episodes these results give strong constraints on the tectonic setting of the pyrenean domain during the transition between the variscan and alpine orogenic cycles and particularly on when and how the upper crust was thinned before the crustal breakoff and the final mantle exhumation

detailed paragenesis and li mica compositions as recorders of the magmatic hydrothermal evolution of the maoping w sn deposit jiangxi china abstract li micas have been used as indicators of the evolution of granites however hydrothermal li micas are less documented world class w sn deposits associated with early yanshanian granites south jiangxi china show magmatic and hydrothermal li micas which could help unravelling the magmatic hydrothermal evolution of rare metal deposits six types of li micas have been identified in the vein system of the maoping w sn deposit through detailed petrography and epma and la icp ms analyses by chronological order i late magmatic li micas in feldspar veins associated with late crystallization of a peraluminous melt ii hydrothermal fe li micas fe li mica veins and selvages iii hydrothermal fe li micas in w sn veins iv fe li micas in later banded quartz veins v li muscovite in the final stages and finally vi micas associated with alteration at each stage based on oscillatory variations and trends in major elements composition the chemical variations in li micas from the successive stages and in hydrothermal micas that crystallized in the veins are interpreted to reflect mixing between at least three fluids of possible magmatic meteoric and metamorphic origins the crystallization of zircons and ree minerals combined with variations of major and trace element concentrations in the li micas notably an enrichment of rare metals w sn ta nb in the li micas implies emplacement of a hidden peralkaline ree rich magma during the crystallization of the banded quartz veins a source which was different to the pre existing peraluminous granites the possible involvement of both peraluminous and peralkaline intrusives suggests the existence of polyphase magmatic hydrothermal systems in the maoping deposit during the yanshanian event 190 80 ma

an infrared microthermometric study of fluid inclusions in coexisting quartz and wolframite from late mesozoic tungsten deposits in the gannan metallogenic belt south china abstract numerous wolframite quartz vein type tungsten deposits are present in the gannan metallogenic belt south china including the piaotang and dangping deposits in the chong you yu ore cluster the dajishan deposit in the jiulianshan ore cluster and the pangushan deposit in the yushan ore cluster the ores generally consist of quartz and wolframite with variable amounts of base metal sulfides wolframite and quartz are intergrown but the genetic relationships between them are still ambiguous quartz contains two phase aqueous inclusions type i and two or three phase co 2 bearing inclusions type ii but wolframite only contains two phase aqueous inclusions type iw the homogenization temperatures for primary inclusions in wolframite are generally 40 to 100 c higher than those in quartz in a single deposit moreover there are variable amounts of co 2 in inclusions in quartz but no co 2 rich inclusions are identified in coexisting wolframite type i fluid inclusions in quartz from the piaotang deposit show that fluid mixing is predominant in the formation of quartz veins whereas fluid inclusions from the dangping deposit suggest that simple cooling is the primary factor quartz from the dajishan and pangushan deposits contains both type i and coexisting type ii inclusions indicating a process of fluid immiscibility the homogenization temperatures of two phase aqueous inclusions type iw in wolframite from all of these deposits show a clearly decreasing trend with constant salinities implying a simple cooling process hence simple cooling fluid mixing and fluid immiscibility take place in quartz but only simple cooling happens in wolframite our results show that the gangue and ore minerals from the late mesozoic tungsten deposits in the gannan metallogenic belt have different homogenization temperatures volatile compositions and fluid processes the gangue minerals do not provide reasonable estimates of the depositional conditions of the ore minerals even though they are intimately intergrown

geologic analysis of the upper jurassic haynesville shale in east texas and west louisiana the upper jurassic haynesville shale is currently regarded as one of the most prolific emerging shale gas plays in the continental united states it has estimated play resources of several hundred trillion cubic feet and per well reserves estimated as much as 7 5 bcf the reservoir spans more than 16 counties along the boundary of eastern texas and western louisiana although this basin has a long history of exploration and analysis of its mesozoic section a comprehensive subsurface study characterizing the haynesville shale has not been conducted this article is the first to address the structural setting stratigraphy depositional environment and facies fracturing and production challenges of the haynesville shale gas play basement structures and salt movement influenced carbonate and siliciclastic sedimentation associated with the opening of the gulf of mexico the haynesville shale is an organic and carbonate rich mudrock that was deposited in a deep partly euxinic and anoxic basin during the kimmeridgian to the early tithonian related to a second order transgression that deposited organic rich black shales worldwide the haynesville basin was surrounded by carbonate shelves of the smackover and haynesville lime louark sequence in the north and west several rivers supplied sand and mud from the northwest north and northeast into the basin haynesville mudrocks contain a spectrum of facies ranging from bioturbated calcareous mudstone laminated calcareous mudstone and silty peloidal siliceous mudstone to unlaminated siliceous organic rich mudstone framboidal to colloidal pyrite is variably present in the form of concretions laminae and individual framboids and replaces calcite cement and mollusk shells haynesville reservoirs are characterized by overpressuring porosity averaging 8 to 12 sw of 20 to 30 nanodarcy permeabilities reservoir thickness of 200 to 300 ft 70 to100 m and initial production of as much as 30 mmcf day reservoir depth ranges from 9000 to 14 000 ft 3000 to 4700 m and lateral drilling distances are 3000 to 5000 ft 1000 to 1700 m typical haynesville wells exhibit a steeper decline curve 80 in the first year than other shale gas plays which is attributed to a very high overpressure

elemental dispersion and stable isotope fractionation during reactive fluid flow and fluid immiscibility in the bufa del diente aureole ne mexico evidence from radiographies and li b sr nd and pb isotope systematics the 31 6 0 3 ma old bufa del diente alkali syenite ne mexico intruded a sequence of cretaceous limestones with intercalated sub horizontal chert layers the cherts acted as aquifers that facilitated transport of brines and pegmatitic melts within the shallow level 1 kbar contact metamorphic aureole fluid driven reactions between chert and marble wallrock and the influx of late melts and various fluids gave rise to distinct chemical and isotopic signatures within the aquifer and across the zones of infiltration and fluid driven reaction aqueous brines of magmatic origin produced thick wollastonite mantles around the chert layers wollastonite formation occurred at the expense of limestone and chert and generated co2 this co2 induced fluid unmixing into an aqueous brine and a low density co2 rich fluid which was lost to the overlying marble where it oxidized organic matter and caused 13c and 18o shifts in a zone some 5 10 cm wide after wollastonite formation the chert aquifers were locally intruded by pegmatite veins carrying alkali feldspar quartz aegirine augite eudialyte zircon and apatite aqueous fluids that exsolved during crystallization of the pegmatite veins escaped along late cross fractures and migrated along the inner and outer borders of the wollastonite margins chemical dispersion patterns of u al na k p s fe and ree across the chert to marble boundary and its metasomatic rims are shown by autoradiography and neutron induced radiography scavenging of cations at mineralogical contacts and cation transport into the marbles occurred only on the mm to cm scale isotopic data for pb and sr across a simple metachert marble boundary and for pb sr nd b and li across a metachert pegmatite marble sequence demonstrate the following 1 the pb and sr isotopic signature of early fluids was buffered by the carbonate wallrock only late fluids shielded from wallrock interaction by a wollastonite mantle variably preserved a memory of their initial magmatic signature 2 since the nd isotope signature of marble and chert is bound to calcite and clay minerals systematic shifts to unradiogenic nd in marble reflect loss of carbonate bound nd as the wollastonite margin is approached nd in the wollastonite margin is dominated by nd originally bound to clay minerals the later emplacement of the pegmatite which carried the nd isotope signature of its alkali syenite source had little effect on the nd isotopic composition of the wollastonite rim 3 although the li and b isotopic compositions reflect the alkali syenite source they are also affected by isotopic fractionation and partitioning between melt fluid and solids

geological characteristics and metallogenic epoch of pangushan w bi te ore deposit in yudu county jiangxi province the pangushan tungsten ore deposit is a large size wolframite quartz vein type w bi te ore deposit in the exocontact zone of the buried rock body within the eastern part of the nanling metallogenic belt the authors collected molybdenite samples from the w bearing quartz veins of different geological modes of occurrence re os isotopic dating yielded isochron ages of molybdenite 157 75 0 76 ma mswd 0 99 and 158 8 5 7 ma mswd 1 7 the ages indicate that these two mineralized veins belong to the same product and were formed in the same period i e early yanshanian the study also provides useful evidence that the ore deposit is the product of nanling ew trending tectonic magmatic belt

40 ma of hydrothermal w mineralization during the variscan orogenic evolution of the french massif central revealed by u pb dating of wolframite we present u pb thermal ionization mass spectrometer tims ages of wolframite from several granite related hydrothermal w sn deposits in the french massif central fmc located in the internal zone of the variscan belt the studied wolframite samples are characterized by variable u and pb contents typically 10 ppm and show significant variations in their radiogenic pb isotopic compositions the obtained u pb ages define three distinct geochronological groups related to three contrasting geodynamic settings i visean to namurian mineralization 333 327 ma coeval with syn orogenic compression and emplacement of large peraluminous leucogranites ca 335 325 ma ii namurian to westphalian mineralization 317 315 ma synchronous with the onset of late orogenic extension and emplacement of syn tectonic granites ca 315 310 ma and iii stephanian to permian mineralization 298 274 ma formed during post orogenic extension contemporaneous with the permian volcanism in the entire variscan belt the youngest ages 276 274 ma likely reflect the reopening of the u pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration e g ferberitization our results demonstrate that w sn mineralization in the fmc formed during at least three distinct hydrothermal events in different tectono metamorphic settings over a time range of 40 ma

le gisement de tungstene de xihuashan sud jiangxi chine relations granites alterations deuteriques hydrothermales mineralisations le gisement de tungstene de xihuashan sud jiangxi chine est situe sur la bordure d un stock granitique forme de 4 unites intrusives chronologiquement infa sup5 inf2b sup5 inf2c sup5 inf2e sup5 le gite est encaisse dans inf2a sup5 et in2b sup5 don le contact est jalonne par un stockscheider et par la presence sporadique d un facies granitique a grain fin inf2b sup5 les zones d episyenites feldspathiques localisees principalement dans inf2b sup5 correspondent a des zones d alterations du granite elles caracterisent l activite des fluides en relai d actions mecaniques prealables un drainage de liquides residuels sous controle structural le gisement filonien de xihuashan district minier de dayu est du type quartz a wolframite dominante et il est principalement developpe dans inf2b sup5 la densite du systeme filonien et l importance de la mineralisation dans inf2b sup5 s explique par l effet de carapace joue par inf2a sup5 inf2b sup5 et le stockscheider le gite comprend 615 filons a teneur economique teneur moyenne 1 08 en wo3 caracterises par quatre stades de mineralisations un zoning vertical inverse est generalement observe

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

multiple fluids involved in granite related w sn deposits from the world class jiangxi province china abstract this paper aims at providing new insights into w sn ore forming processes within one of the largest granitic provinces in the world nanling range south china which was emplaced during the jurassic cretaceous period the origin composition and pressure temperature conditions of fluids involved in the w sn ore forming processes have been investigated by microthermometry raman spectroscopy la icpms hydrogen isotope analyses of fluid inclusions and oxygen isotope analyses of minerals from the maoping and piaotang w sn deposits for each deposit pre quartz syn wolframite and cassiterite and post ore quartz topaz and fluorite minerals were studied in both deposits the vast majority of fluid inclusions are aqueous with salinities between 0 0 and 12 6 wt equiv nacl and homogenization temperatures between 136 and 349 c a minor proportion 5 of inclusions observed in the ore stage quartz from maoping have aquo carbonic compositions for both deposits four compositional groups are defined early quartz fluid inclusions are characterized by salinities between 0 4 and 9 0 wt equiv nacl trapping temperatures between 150 and 350 c and pressures between 20 and 150 mpa la icpms analyses of these fluid inclusions reveal a wide range of na k and li concentrations as well as relatively low metal contents w at piaotang fluid inclusions in wolframite as well as in post ore quartz and fluorite have salinities of 5 6 to 12 6 wt eq nacl trapping temperatures between 150 and 400 c and pressures of 20 to 150 mpa la icpms analyses of these fluid inclusions reveal similar compositions to early quartz fluid inclusions values of 18o in wolframite and quartz crystals range from 0 8 to 5 2 vsmow while the d values of fluid inclusions range from 66 to 62 vsmow collectively the data suggest the involvement of four aqueous fluid end members mixed episodically in the mineralization process a a low salinity low temperature metal poor low 18o low d fluid derived from meteoric water b a high salinity high temperature metal poor high 18o low d fluid derived from a differentiated peraluminous granitic magma c a high salinity high temperature metal rich lower d magmatic fluid derived from a more differentiated peraluminous granitic magma and d a high salinity high temperature metal rich high 18o low d magmatic fluid this study shows that multiple fluids with distinct magmatic and meteoric origins were involved in the formation of these w sn deposits and that the dilution of metal bearing magmatic fluids by meteoric fluids was probably the main driver for ore deposition the common fluid history of the two deposits studied as well as similarities with other deposits in the jiangxi province points toward common ore forming processes at the regional scale

thermal evolution of the north central gulf coast the subsidence history of the north louisiana salt basin determined from well data indicates that the region underwent extension during rifting and has since passively subsided due to conductive cooling of the lithosphere timing of the rifting event is consistent with opening of the gulf of mexico during late triassic to early jurassic time crustal extension by a factor of 1 5 to 2 was computed from tectonic subsidence curves however data from the early subsidence history are insufficient to distinguish between uniform and nonuniform extension of the lithosphere the magnitude of extension is in good agreement with total sediment and crustal thicknesses from seismic refraction data in the adjacent central mississippi salt basin the temperature distribution within the sediments is calculated using a simple heat conduction model temperature and subsidence effects of thermal insulation by overlying sediments are included the computed temperature distribution is in good agreement with bottom hole temperatures measured in deep wells temperature histories predicted for selected stratigraphic horizons within the north louisiana salt basin suggest that thermal conditions have been favorable for hydrocarbon generation in the older stata results from a two dimensional heat conduction model suggest that a probable cause for the early formation of the adjacent uplifts is lateral heat conduction from the basin rapid extension of the lithosphere underneath areas with horizontal dimensions of 50 100 km produces extremely rapid early subsidence due to lateral heat conduction the moderate subsidence rate observed in the north louisiana salt basin during the jurassic and early cretaceous suggests slow extension over a long period of time

geological setting mineralogy and genesis of tungsten mineralization in dayu district jiangxi people s republic of china an outline the city of dayu is the center of the most important tungsten district of prc valuable quantities of sn mo bi nb ta ree cu pb zn ag be and li are also recovered at the xihuashan and dangping mines hundreds of the typical jiangxi wolframite quarz veins located at the top and marginal parts of a jurassic biotite granite intrusion are mined at piaotang the mined ore bodies consist of a stockwork type of mineralization which cuts the roof rocks cambrian metasediments phyllite quartz sandstone hornfels of the biotite granite around the mineralizations the country rocks display extensive alteration namely k feldspar alteration and greisenization in granite tourmalinization muscovitization silicification pyrophillitization in the metasediments the main mineralogy and parageneses of the veins and veinlets can be summarized as follows i stage oxide wolframite cassiterite molybdenite quartz k feldspar beryl fluorite topaz the best represented ii stage sulphide chalcopyrite galena sphalerite pyrite pyrrhotite bismuthinite cassiterite wolframite quartz well represented at piaotang iii stage carbonate pyrite scheelite chlorite sericite fluorite quartz calcite the fracture controlled mineralizations of dayu appear to be the product of a continous multistage process related to the late phases of the jurassic yenshanian magmatism

genesis of the yuanlingzhai porphyry molybdenum deposit jiangxi province south china constraints from petrochemistry and geochronology abstract the newly discovered yuanlingzhai porphyry molybdenum mo deposit in southern jiangxi province belongs to the group of mo only deposits in the nanling region the mineralization developed at contact zones between the yuanlingzhai granite porphyry and neoproterozoic metamorphic rocks of the xunwu formation precise la mc icpms zircon u pb dating of the yuanlingzhai porphyry as well as the adjacent western keshubei and eastern keshubei granites yielded ages of 165 49 0 59 ma 159 68 0 43 ma and 185 13 0 52 195 14 0 63 ma respectively molybdenite re os isochron ages of the ores are 160 1 162 7 1 1 ma which is consistent with the age of large scale w sn deposits in south china the yuanlingzhai porphyry is characterized by high k2o p2o5 and a cnk 1 33 1 59 and low cao and na2o the rock shows relatively enriched lree without significant eu anomalies eu eu 0 80 0 90 geochemical and mineralogical characteristics indicate that the ore hosting porphyry is a typical s type granite generated from the partial melting of crustal material with only minor mantle contribution both harker and evolutionary discrimination diagrams indicate that the yuanlangzhai and western keshubei granites are not products of co magmatic evolution the keshubei granites and xunwu formation were not significant sources for the components in the porphyry mineralization but the yuanlangzhai granite may have supplied some ore forming material however the main ore forming material was carried by fluids from deep sources as demonstrated by fluid inclusion and stable isotope data from the molybdenum deposit the mo porphyry deposit formed in an extensional setting and was possibly associated with jurassic subduction of the izanagi plate

primary migration by oil generation microfracturing in low permeability source rocks application to the austin chalk texas fracturing of low permeability source rocks is induced by pore pressure changes caused by the conversion of organic matter to less dense fluids oil and gas these fractures increase the permeability and provide pathways for hydrocarbon migration an equation for the pressure change is derived using four major assumptions 1 the permeability of the source rock is negligibly small 0 01 d 10 20 m2 so that the pore pressure buildup by the conversion is much faster than its dissipation by pore fluid flow 2 the stress state is isotropic so that horizontal and vertical stresses are equal the source rock fails when the pore pressure equals the overburden pressure 3 the properties of the rock organic matter and fluids remain constant during oil generation this assumption is valid when the change in depth i e pressure and temperature is small 4 only two reaction rates are required for the conversions a low temperature reaction rate for the kerogen oil conversion e approx 24 kcal mol a approx 1014 m y and a high temperature reaction rate for oil gas conversion e approx 52 kcal mol a approx 5 5 1026 m y the equations for generation rate and pressure change are applied to the austin source rock by adjusting the several variables to fit geochemical data core saturations and observed levels of oil and gas production this application demonstrates that the equations are easily applied in calculating depths of primary migration for low permeability source rocks

shrimp u pb ages of diagenetic and hydrothermal xenotime from the archaean witwatersrand supergroup of south africa shrimp dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition thus xenotime dating has significant economic application to precambrian sediment hosted ore deposits such as witwatersrand au u for which there are no precise depositional ages the growth history of xenotime in the witwatersrand supergroup is texturally complex with several phases evident the oldest authigenic xenotime 207pb 206pb age obtained in sandstone underlying the vaal reef is 2764 5 myr 1 and most likely represents a mixture of diagenetic and hydrothermal growth nevertheless this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition other xenotime data record a spread of ages that correspond to numerous post diagenetic thermotectonic events including a ventersdorp event at 2720 ma up to the 2020 ma vredefort event

lithospheric structure of the south central united states recent seismic data in the ouachita mountains area and the gulf of mexico make it possible to construct a lithospheric scale cross section transect from the midcontinent region to the gulf the authors constructed a transect in the form of a gravity model but it incorporates all available seismic drill hole and geologic data as constraints the thrust sheets of the ouachita orogenic belt appear as a thin veneer covering the southern part of the arkoma basin and the preserved paleozoic continental margin mesozoic rifting is evident in three areas 1 southern arkansas and northern louisiana where extension was minor 2 the vicinity of the texas louisiana coastline where modification of the lithosphere and subsidence were considerable and 3 the deep gulf of mexico where rifting was successful a significant variation in the average density of the mantle which could delineate the north american craton as a lithospheric feature was detected near the paleozoic continental margin

ouachita trough part of a cambrian failed rift system pre flysch cambrian mississippian strata of the ouachita mountains of arkansas and oklahoma include two main sandstone lithofacies 1 a craton derived lithofacies made up largely of mature medium to coarse grained quartzose and carbonate detritus and in some units sediment eroded from exposed basement rocks and 2 an orogen derived facies made up mainly of fine grained quartzose sedimentary and metasedimentary debris and possibly in lower units a volcaniclastic component paleocurrent and distribution patterns indicate that detritus of facies i in the benton uplift was derived from north and detritus of facies ii throughout the ouachitas was derived from south and east of the depositional basin overall sedimentological results suggest that the ouachita trough was a relatively narrow two sided basin throughout most and probably all of its existence and never formed the southern margin of the north american craton regional comparisons suggest that it was one of several basins including the southern oklahoma aulacogen reelfoot rift illinois basin and rome trough that formed as a cambrian failed rift system 150 to 250 m y after initial rifting along the appalachian margin of the north american craton

infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the xihuashan tungsten deposit jiangxi province china the xihuashan tungsten deposit jiangxi province china is a world class vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions there are two major sets of subparallel ore bearing quartz veins the ore mineral assemblage includes wolframite and molybdenite with minor amounts of arsenopyrite chalcopyrite and pyrite there are only two phase aqueous rich inclusions in wolframite but at least three major types of inclusions in quartz two or three phase co2 rich inclusions two phase pure co2 inclusions and two phase aqueous inclusions indicating boiling fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities 239 380 c 3 8 13 7 wt nacl equiv compared with those in quartz 177 329 c 0 9 8 1 wt nacl equiv these distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process enthalpy salinity plot shows a linear relationship implying mixing of different sources of fluids although boiling occurred during vein type mineralization it seems negligible for wolframite deposition mixing is the dominant mechanism of wolframite precipitation in xihuashan 34s values of the sulfides range from 1 6 to 0 1 indicative of a magmatic source of sulfur 18o values of wolframite are relatively homogeneous ranging from 4 8 to 6 3 oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite

diagenetic origin of quartz silt in mudstones and implications for silica cycling mudstone the most abundant sedimentary rock type1 composed primarily of clay or silt sized particles contains most of the quartz found in sedimentary rocks2 these quartz grains which are chemically and mechanically resistant and therefore preserve their characteristics well have long been considered to be derived from the continental crust1 here we analyse quartz silt from black shales in the eastern usa dating back to the late devonian period about 370 million years ago using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe our results indicate that up to 100 of the quartz silt in our samples does not originate from the continental crust instead it appears to have precipitated early in diagenesis in algal cysts and other pore spaces3 with silica derived from the dissolution of opaline skeletons of planktonic organisms such as radiolaria and diatoms transformation of early diatoms into in situ quartz silt might explain the time gap between the earliest fossil occurrences of diatoms about 120 myr ago4 and molecular evidence for a much earlier appearance between 266 or even 500 myr ago5 6 moreover if many other mudstone successions show similarly high proportions of in situ precipitated rather than detrital quartz silt the sedimentary record in mudstones may have been misinterpreted in the past with consequences for our estimates of palaeoproductivity as well as our perceptions of the dynamics and magnitude of global biogeochemical cycling of silica

tracing metal sources in peribatholitic hydrothermal w deposits based on the chemical composition of wolframite the example of the variscan french massif central abstract we present a complete dataset for major minor and trace elements in wolframite fe mn wo4 based on the example of several peribatholitic hydrothermal w deposits located in the variscan french massif central fmc the wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation inductively coupled plasma mass spectrometry most samples are fe dominated wolframites and are characterized by variable fe fe mn values for the studied deposits from 0 36 to 0 86 without significant alteration features wolframites present intracrystalline variations for concentrations of several minor and trace elements principally for nb ta and sn which reflect growth zoning the minor and trace element compositions of the different wolframite samples show at first order similar enrichments in ta nb sn zn and in as well as depletions in lree li th ti zr hf pb v co and mg compared to the upper continental crust second order compositional variations are observed between the studied deposits which can be separated in four main regional geochemical groups this work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid the regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid i e variable metal sources therefore this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals the comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal w deposits from the fmc whereas metasedimentary rocks have a limited to no influence on the metal budget

mississippian barnett formation fort worth basin texas bulk geochemical inferences and mo toc constraints on the severity of hydrographic restriction abstract chemostratigraphic evidence from the barnett formation texas usa elucidates the restricted nature of the depositional environment in the fort worth basin during the early progression of the late paleozoic ouachita orogeny in accord with recent lithostratigraphic and petrographic studies stratigraphic bulk geochemical analyses reveal that the environment of deposition was anoxic to euxinic sediment starved with relatively high rates of organic matter accumulation using an environmental proxy developed from the sediment geochemistry of modern anoxic silled basins the stratigraphic concentrations of total organic carbon toc and molybdenum mo in the barnett formation reveal a high degree of subpycnoclinal water mass restriction and an extended timescale of deep water renewal of at least 8 103 years and potentially as long as 2 104 years an integrated assessment of elemental concentrations the degree of pyritization and toc s fe relationships reveals that severe fe limitation controlled pyrite formation and the large excess of sulfide in the overlying water column mineralogical and elemental constraints suggest that following sulfate reduction less easily bio extractable fe iii was bio reduced under methanogenic conditions consequently liberating fe ii which was subsequently incorporated into pore water formed dolomite i e organogenic dolomite the preserved mo toc toc s fe and fe bearing mineral relationships collectively indicate that the protracted turnover rate and persistent sediment starvation resulted in a biologically inhospitable environment that limited the microbial consumption rate of organic carbon

basement cover sequences within the uhp unit of the dabie shan field data define two lithologically distinct basement cover sequences within the ultrahigh pressure metamorphic uhpm unit of the dabie shan eastern china one of the cover units the changpu unit comprises calc arenitic metasediments in stratigraphic contact with a basement consisting of gneisses of the yangtze craton the second cover unit the ganghe unit consists of felsic intermediate metavolcanics and clastic metasediments basement exposure of the ganghe unit is not known fold axes in the ganghe unit are oblique to those of the changpu unit which are parallel to those of the yangtze gneisses preservation of primary textures in some volcanic rocks and tectonic separation from the yangtze gneisses by a greenschist facies mylonite support an interpretation of the ganghe unit as a low strain domain protolith associations in the ganghe and changpu units are compatible with deposition in a rift setting and along a passive continental margin respectively a u pb single zircon age of 761 33 ma for volcanoclastic rocks of the ganghe unit demonstrates a neoproterozoic deposition age concordant with inferred rifting at that time eclogite facies parageneses in the gneisses and both cover units along with p t data demonstrate regional uhpm in the dabie shan

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

genetic relationship between silver lead zinc mineralization in the wutong deposit guangxi province and mesozoic granitic magmatism in the nanling belt southeast china more than 50 of the world s total reserves of tungsten are in china and most tungsten deposits are located in the nanling range in southeast china this study explores the potential genetic relationship between tungsten tin w sn mineralization and shallower ag pb zn deposits in the nanling range based on data from the wutong deposit guangxi province the lead oxygen carbon sulfur and strontium isotopic compositions of minerals at wutong indicate that a single crustal derived fluid was responsible for mineralization wutong likely formed at relatively low temperatures 200 300 c and low pressures as indicated by the similarity between homogenization temperatures of fluid inclusions and those estimated from s isotopic compositions of minerals the hubnerite age 92 3 104 4 ma indicates that the wutong mineralization is likely related to nearby late yanshanian cretaceous s type granites derived from proterozoic crust this mineralization event coincides with the last w sn mineralization event and the cretaceous peak of mineralization in the nanling range

a shallow layer model for heavy gas dispersion from natural sources application and hazard assessment at caldara di manziana italy several nonvolcanic sources in central italy emit a large amount of carbon dioxide co2 under stable atmospheric conditions and or in the presence of topographic depressions the concentration of co2 which has a molecular mass greater than that of air can reach high values that are lethal to humans or animals several episodes of this phenomenon were recorded in central italy and elsewhere in order to validate a model for the dispersion of a heavy gas and to assess the consequent hazard we applied and tested the code twodee 2 an improved version of the established twodee model which is based on a shallow layer approach that uses depth averaged variables to describe the flow behavior of dense gas over complex topography we present results for a vented co2 release at caldara di manziana in central italy we find that the model gives reliable results when the input quantity can be properly defined moreover we show that the model can be a useful tool for gas hazard assessment by evaluating where and when lethal concentrations for humans and animals are reached

an early cretaceous w sn deposit and its implications in southeast coastal metallogenic belt constraints from u pb re os ar ar geochronology at the feie shan w sn deposit se china the feie shan w sn deposit is in eastern guangdong province which is a newly explored deposit in the southeastern coastal metallogenic belt in order to constrain the age of mineralization in the feie shan w sn deposit we collected molybdenites and hydrothermal biotite of the feie shan w sn deposit for dating the tungsten mineralization is spatially associated with the biotite monzonitic granite porphyry la mc icp ms zircon u pb dating of the biotite monzonitic granite porphyry yielded a weighted mean pb u age of 139 2 1 7 ma which was interpreted as the emplacement age of the biotite monzonitic granite porphyry the re os model ages ranged from 137 3 2 0 ma to 146 1 2 1 ma with a weighted mean age of 140 6 1 9 ma and ar ar isotopic analyses of hydrothermal biotite yield a plateau ar ar age of 135 1 0 8 ma these dates obtained via three independent geochronological techniques constrained the ore forming age of the feie shan deposit and linked the genesis of the ore to the underlying biotite monzonitic granite porphyry combined with previous studies it is suggested that there is a period at 144 132 ma for w sn mineralization in the southeastern coastal metallogenic belt the feie shan w sn deposit belongs to the 144 132 ma metallogenic events in the scmb in a geodynamic setting of lithospheric extension

highly fractionated jurassic i type granites and related tungsten mineralization in the shirenzhang deposit northern guangdong south china evidence from cassiterite and zircon u pb ages geochemistry and sr nd pb hf isotopes abstract the shirenzhang tungsten deposit is a classic wolframite quartz vein type deposit located in northern guangdong province eastern segment of the nanling w sn polymetallic belt the ore veins controlled by the nw striking fault system are mainly hosted in the ordovician metasedimentary rocks and can also be found with less amount in the cupola of the concealed granitic stock displaying a typical five floor vertical zonation proposed by the chinese geologists the concealed granitic stock mainly comprises two intrusive facies the porphyritic biotite granite g1 in the outer zone and the medium to fine grained monzogranite g2 in the inner zone in this paper we report new cassiterite u pb ages and pb isotopes of sulfides for the shirenzhang tungsten deposit combined with new zircon u pb ages and hf isotopes elemental geochemistry and sr nd pb isotopes of the concealed granitic rocks with aims to elucidate the origin of the ore related granites and the link between the tungsten mineralization and granitic magmatism la icp ms zircon u pb dating gives the weighted mean ages of 164 2 ma for g1 and 162 4 ma for g2 respectively cassiterite from the wolframite bearing quartz vein and the drusy quartz vein yield the weighted mean ages of 164 2 ma and 160 2 ma respectively these ages suggest that both the granitic intrusion and related w sn mineralization in the shirenzhang deposit were initiated during the late jurassic ca 160 ma the shirenzhang granitic rocks are weakly peraluminous highly fractionated i type granites detailed elemental and isotopic data demonstrate that the granitic rocks were derived from partial melting of the paleoproterozoic basement rocks at a relatively shallow depth of 30 km triggered by underplating of basaltic magma and underwent extensive fractional crystallization of hornblende biotite feldspar and monazite and or allanite a continental arc setting induced by northwesterly subduction of the paleo pacific plate is suggested for the genesis of the shirenzhang i type granites the comparable pb isotopic compositions of feldspar and sulfides imply that the lead in the ore veins was of magmatic origin integrating the spatial temporal relationship between the ore veins and the concealed granitic rocks with the pb isotopes from the sulfides and granites we suggest that the tungsten mineralization is genetically linked with the concealed granitic rocks in the shirenzhang deposit fractional crystallization and melt fluid interaction may play an important role on the formation of the granite related tungsten mineralization

upper jurassic reef play east texas basin an updated overview part 1 background and outboard trend this paper is the first part of a two part update on geologic and geophysical characterization of gas productive upper jurassic carbonate buildups in the cotton valley limestone of the east texas basin continued exploration in this play has yielded important new information on the nature timing and genesis of the relevant buildup features this information is crucial to an understanding of existing and future productive trends in the play recent drilling and discovery have resulted in the identification of two major fairways 1 an older outboard or downdip trend existing along the distally steepened portions of the ramp at present day depths of 16 000 17 000 ft 4880 5185 m and 2 a younger inboard or updip trend located along the salt deformed portion of the late jurassic ramp system and lying at depths of 14 100 15 300 ft 4300 4666 m this paper focuses on the outboard trend with discussion of the inboard trend reserved for part 2 both articles present core thin section and other sample data as well as seismic information that together offer the most comprehensive overview of these buildups yet available

review of late jurassic depositional systems and potential hydrocarbon plays northern gulf of mexico basin abstract post salt upper jurassic siliciclastic and carbonate rocks in the east texas north louisiana mississippi region record the early post rift evolution of the interior zone rift basins of the northern gulf of mexico basin four major river systems were fixed in space but variable in supply rate they carried sand and mud in from the northwest ancestral red river the north ancestral ouachita river the northeast ancestral mississippi river and the east ancestral alabama river shoal water carbonate deposits formed when siliciclastic inputs were low and shallow water high energy conditions prevailed usually in association with basement highs salt swells and abandoned deltaic shelf margins smackover shoal water carbonates formed within an extensive carbonate ramp from south central arkansas to central texas and were influenced by initial salt movement subsequent haynesville age gilmer carbonate shoals in texas rimmed rift related high blocks as well as highs formed by early salt movement siliciclastic sedimentation progressively dominated east of shreveport and submarine fans developed in association with a lowstand episode during early cotton valley time a major southeastward advance of the ancestral red river delta formed the taylor and bossier sand series while to the east lower terryville shoreline sands began to prograde southward in front of an expanding lagoon during late cotton valley time continued clastic sedimentation formed wave dominated deltas in texas and upper terryville strike fed sandstones in north louisiana at the close of cotton valley deposition in the earliest cretaceous regional transgression allowed knowles carbonates to colonize the abandoned shelf edge and form a thick shelf edge reef complex on its seaward slope the significant calvin lowstand wedge of sandstones was deposited offshore of this edge in louisiana during a subsequent major sea level fall and was then covered by winn carbonates deposited during the subsequent sea level rise high potential exploration plays remain in upper jurassic strata smackover and buckner gilmer shoals have produced over 10 trillion cubic feet of gas tcfg and 750 million barrels of oil mmbo in east texas and north louisiana but large segments of the complex atolls along the sabine uplift have not been defined complex shoals may rim old rift related highs such as the sabine and wiggins highs the gilmer cotton valley lime pinnacle reefs of the robertson leon trend may develop in one form or another over a broad swath of east central texas into westernmost louisiana haynesville age submarine fans may extend eastward into mississippi updip cotton valley is an established 10 tcf tight gas sandstone play in texas and louisiana but its basinward extensions have high untapped potential significant high quality upper cotton valley production similar to the north louisiana blanket sands may still be found in central mississippi the earliest cretaceous knowles calvin winn margin is poorly tested calvin like sandstones of the lowstand wedge should occur in east central texas and in southwestern mississippi

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

zircon u pb molybdenite re os and muscovite ar ar isotopic dating of the xitian w sn polymetallic deposit eastern hunan province south china and its geological significance the xitian tungsten tin w sn polymetallic deposit located in eastern hunan province south china is a recently explored region containing one of the largest w sn deposits in the nanling w sn metallogenic province the mineral zones in this deposit comprise skarn greisen structurally altered rock and quartz vein types the deposit is mainly hosted by devonian dolomitic limestone at the contact with the xitian granite complex the xitian granite complex consists of indosinian late triassic 230 215 ma and yanshanian late jurassic early cretaceous 165 141 ma granites zircons from two samples of the xitian granite dated using laser ablation inductively coupled mass spectrometer la icpms u pb analysis yielded two ages of 225 6 1 3 ma and 151 8 1 4 ma representing the emplacement ages of two episodic intrusions of the xitian granite complex molybdenites separated from ore bearing quartz veins yielded a re os isochron age of 149 7 0 9 ma in excellent agreement with a weighted mean age of 150 3 0 5 ma two samples of muscovites from ore bearing greisens yielded 40ar 39ar plateau ages of 149 5 1 5 ma and 149 4 1 5 ma respectively these isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon u pb age of 151 8 1 4 ma of the yanshanian granite in the xitian area indicating that the w sn mineralization is genetically related to the late jurassic magmatism the xitian deposit is a good example of the early yanshanian regional w sn ore forming event 160 150 ma in the nanling region the relatively high re contents 8 7 to 44 0 ppm average of 30 5 ppm in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore forming fluids and melts based upon previous geochemical studies of early yanshanian granite and regional geology we argue that the xitian w sn polymetallic deposit can be attributed to back arc lithosphere extension in the region which was probably triggered by the break off of the flat slab of the palae pacific plate beneath the lithosphere

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

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

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

prolonged history of episodic fluid flow in giant hematite ore bodies evidence from in situ u pb geochronology of hydrothermal xenotime abstract absolute ages for hydrothermal mineralization and fluid flow are critical for understanding the geological processes that concentrate metals in the earth s crust yet many ore deposits remain undated because suitable mineral chronometers have not been found the origin of giant hematite ore deposits which are hosted in precambrian banded iron formations bifs remains contentious several models have been formulated based on different sources and timing for the mineralizing fluids supergene metamorphic syn orogenic late orogenic extensional collapse and syn extensional precise geochronology of the ore offers a means of discriminating between these models in this study two u pb chronometers xenotime and monazite have been identified in high grade hematite ore bodies from the mount tom price mine in the hamersley province northwestern australia both phosphate minerals occur as inclusions within the hematite ore and as coarser crystals intergrown with martite hematite pseudomorph after magnetite and microplaty hematite indicating that the xenotime and monazite precipitated during mineralization in situ u pb dating by ion microprobe indicates that both phosphate minerals grew during multiple discrete events our results suggest that ore genesis may have commenced as early as 2 15 ga with subsequent hydrothermal remobilization and or mineralization at 2 05 ga 1 84 ga 1 67 ga 1 59 ga 1 54 ga 1 48 ga and 0 85 ga the location of the ore bodies along ancient fault systems and the coincidence of at least some of the u pb phosphate dates with episodes of tectonothermal activity in the adjacent proterozoic capricorn orogen implies that fluids were channelled through major structures in the southern pilbara craton during discrete phases of tectonic compression and extension our results show that the hematite ore bodies formed at sites of repeated focussed hydrothermal fluid flow in contrast to the aforementioned models our results imply that iron ore formation was probably a long lived multi stage process spanning more than one billion years

improving recovery from mature oil fields producing from carbonate reservoirs upper jurassic smackover formation womack hill field eastern gulf coast u s a reservoir characterization modeling and simulation were undertaken to improve production from womack hill field eastern gulf coast united states this field produces oil from upper jurassic smackover carbonate shoal reservoirs these reservoirs occur in vertically stacked heterogeneous depositional and porosity cycles the cycles consist of lime mudstone and wackestone at the base and ooid grainstone at the top porosity has been enhanced through dissolution and dolomitization porosity is chiefly interparticle solution enlarged interparticle grain moldic intercrystalline dolomite and vuggy pores dolostone pore systems and flow units have the highest reservoir potential petroleum trapping mechanisms include a fault trap footwall uplift with closure to the south against a major west southeast trending normal fault in the western area a footwall uplift trap associated with a possible southwest northeast trending normal fault in the south central area and a salt cored anticline with four way dip closure in the eastern area potential barriers to flow are present as a result of petrophysical differences among and within the cycles as well as the presence of normal faulting reservoir performance analysis and simulation indicate that the unitized western area has less than 1 mmstb of oil remaining to be recovered and that the eastern area has 2 3 mmstb of oil to be recovered a field scale reservoir management strategy that includes the drilling of infill wells in the eastern area of the field and perforating existing wells in stratigraphically higher porosity zones in the unitized western area is recommended for sustaining production from the womack hill field

combined zircon and cassiterite u pb dating of the piaotang granite related tungsten tin deposit southern jiangxi tungsten district china abstract the large low grade piaotang w sn deposit in the southern jiangxi tungsten district of the eastern nanling range south china is related to a hidden granite pluton of jurassic age the magmatic hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets stringers five floor zonation model most mineralization is in quartz veins with wolframite cassiterite the hidden granite pluton in underground exposures comprises three intrusive units i e biotite granite two mica granite and muscovite granite the latter unit is spatially associated with the w sn deposit combined la mc icp ms u pb dating of igneous zircon and la icp ms u pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization zircon from the three granite units has a weighted average 206pb 238u age of 159 8 0 3 ma 2 mswd 0 3 the cathodoluminescence cl textures indicate that some of the cassiterite crystals from the wolframite cassiterite quartz vein system have growth zonations i e zone i in the core and zone ii in the rim dating on cassiterite zone ii yields a weighted average 206pb 238u age of 159 5 1 5 ma 2 mswd 0 4 i e the magmatic and hydrothermal systems are synchronous this confirms the classical model of granite related tin tungsten mineralization and is against the view of a broader time gap of 6 myr between granite magmatism and w sn mineralization which has been previously proposed for the southern jiangxi tungsten district the elevated trace element concentrations of zr u nb ta w and ti suggest that cassiterite zone ii formed in a high temperature quartz vein system related to the piaotang granite pluton

multi stage crust mantle interaction in se china temporal thermal and compositional constraints from the mesozoic felsic volcanic rocks in eastern guangdong fujian provinces abstract the mesozoic geology of southeastern se china was characterized by emplacement of voluminous felsic magmas we present zircon u pb hf isotopic compositions and whole rock major and trace elemental compositions of a series of felsic volcanic rocks from the eastern guangdong and fujian provinces the volcanic rocks have been divided into three formations the douling nanyuan and shimaoshan fms zircon u pb dating defines three eruption cycles 168 145 ma for the douling fm 143 130 ma for the nanyuan fm and 104 95 ma for the shimaoshan fm in situ hf isotope analyses on dated zircon yield an ehf t range of 13 8 to 6 9 and a tdm hf range from 1400 to 486 ma with a peak at ca 930 ma the majority of the mesozoic felsic lavas have more radiogenic hf than that of metamorphic basement rocks and related igneous rocks requiring the involvement of a juvenile component in their origin the mesozoic felsic magmas are predominantly dacites and rhyolites with only minor basalt and andesite and show relatively homogeneous hf isotopic compositions of zircon in single sample combined these data indicated that neither differentiation of a mantle derived magma nor mixing of magmas from different sources was a dominant petrogenetic process both the ehf t of zircon and the magma temperature increase from the douling and nanyuan fms to the shimaoshan fm all these facts imply an increasing contribution of contemporaneous underplated hot and dry mantle derived magmas as both a heat source inducing crustal melting and as a source of material melt that variably mixed with the local crustal melts the felsic crustal melt component was generated at amphibolite facies conditions with a residual assemblage of plagioclase hornblende garnet zircon our results suggest a progressive role of crust mantle interaction in generating the episodic felsic volcanic eruption during the mesozoic

origin of arches in the northwestern gulf of mexico basin the san marcos and sabine arches are prominent north to northwest trending basement uplifts in the northwestern gulf of mexico basin that may be late mesozoic to cenozoic foreland or intraplate folds rather than domes over plutons or buoyant basement blocks these arches are subparallel to and contemporaneous with orogenic episodes in the northwest trending fold thrust belt of mexico arch movement was also contemporaneous with rapid convergence between the north american and pacific plates arch development in the gulf as a result of tectonic compression is plausible in view of increasing recognition of wide zones of foreland and intraplate deformation in continents current tectonic models of the development of the gulf inaccurately predict gradual decelerating subsidence when these arches were most active

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

multiple mesozoic mineralization events in south china an introduction to the thematic issue mesozoic mineral deposits in south china include world class deposits of w sn and sb and those that provide the major sources of ta cu hg as tl pb zn au and ag for the entire country these deposits can be classified into polymetallic hydrothermal systems closely related to felsic intrusive rocks sn w mo granites cu porphyries polymetallic and fe skarns and polymetallic vein deposits and low temperature hydrothermal systems with no direct connection to igneous activities mvt deposits epithermal au and sb deposits recent studies have shown that they formed in the triassic indosinian jurassic cretaceous early yanshanian and cretaceous late yanshanian stages indosinian deposits include major mvt pb zn ag deposits and granite related w sn deposits early yanshanian deposits are low temperature sb au and high temperature w sn and cu porphyry types many late yanshanian deposits are low temperature au as sb hg and u deposits and also include high temperature w sn polymetallic deposits the formation of these deposits is linked with a specific tectonothermal evolution and igneous activities this special issue brings together some of the latest information in eight papers that deal with the origins and tectonic environments of mineral deposits formed in these stages we anticipate that this issue will stimulate more interests in these ore deposits in south china

genetic types mineralization styles and geodynamic settings of mesozoic tungsten deposits in south china abstract south china hosts the most abundant and largest tungsten w deposits in the world being a famous w metallogenic region located at the eastern part of the south china block which was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic these w deposits were mainly formed during the mesozoic the w mineralization is dominanted by greisen quartz vein skarn and porphyry types all of which are genetically related to the evolution of highly fractionated granitoids four episodes of w mineralization are recognized 1 late triassic 230 210 ma in the central and western parts of south china 2 middle jurassic ca 170 ma to early cretaceous ca 140 ma in the interior of south china with the mineralization being concentrated in southern jiangxi province between 165 and 150 ma 3 early cretaceous 136 120 ma with deposits across south china and 4 late cretaceous 100 80 ma mainly in the southwestern parts of south china these four periods of mineralization are closely related to the closure of paleo tethys and subduction of the paleo pacific plate in the late triassic these two events caused local extensional environments facilitating emplacement of the peraluminous granitoids and formation of the w deposits in the middle jurassic break off of the subducting oceanic plate resulted in emplacement of highly fractionated granites in the nanling region later anticlockwise rotation of the paleo pacific plate created widespread s type granitoids and associated middle jurassic to early cretaceous w mineralization in the interior of south china since 136 ma rollback of the subducting pacific plate resulted in weak w mineralization across south china finally a change of direction in the retreating plate from se to ese resulted in intensive mineralization of the southwestern part of south china

direct dating of hydrothermal tungsten mineralization using in situ wolframite u pb chronology by laser ablation icp ms abstract the wolframite series may contain relatively high u and low common pb contents and thus has been used for direct u pb dating of hydrothermal w mineralization in this paper we present in situ laser ablation inductively coupled plasma mass spectrometry la icpms analysis of u pb isotopes and trace elements of wolframite crystals from the giant yaogangxian and piaotang w deposits in the extensive nanling metallogenic belt south china the objective of this work is to directly constrain the timing of hydrothermal w mineralization in these two deposits wolframite crystals from both deposits show textural evidence for two generations early wolframite wol 1 has higher fe and lower mn contents relative to those in the late wolframite wol 2 uranium is correlated positively with nb5 tetravalent ti sn zr hf and trivalent sc v y rees cations in all wolframite samples suggesting that the incorporation of u into wolframite is controlled by the coupled substitution mechanisms the early and late wolframite domains from the yaogangxian deposit yielded u pb ages of 159 1 2 0 ma 2 mswd 0 7 and 153 7 0 7 ma 2 mswd 0 5 respectively similarly two wolframite generations from the piaotang deposits yielded u pb ages of 159 5 1 3 ma 2 mswd 0 3 and 152 1 0 9 ma 2 mswd 0 5 the obtained u pb ages confirm two successive episodes of hydrothermal w mineralization at 159 ma and 153 ma in the yaogangxian and piaotang deposits this study demonstrates the potential of u pb dating of wolframite by la icpms and highlights its importance for directly dating hydrothermal ore forming processes

re os isotopic chronology of molybdenites from hongling tungsten deposit of guangdong province and its geological significance located in the middle part of reshui composite pluton the hongling tungsten deposit is a medium size tungsten ploymetallic deposit tungsten mineralizations in this deposit include quartz vein wolframite type and altered granitic scheelite type rhenium and osmium isotopic dating of 8 molybdenite samples from the hongling quartz vein type tungsten deposit has yielded a precise isochron age of 159 1 1 5 ma and a weighted average model age of 158 8 0 88 ma the intercept of isochron is 0 010 0 041 suggesting that there is no measurable normal os in these molybdenite samples statistics of precise ore forming ages of wsn deposits from eastern and central nanling region show that ore forming ages are concentrated mostly in the range of 150 160 ma corresponding to the main periods of large scale granitic emplacement in this region the results obtained by the authors show that there is no distinct age gap between tungsten mineralization and granite intrusion in nanling region