re os dating of pyrite confirms an early diagenetic onset and extended duration of mineralization in the irish zn pb ore field the irish midlands region contains one of the world s largest hydrothermal zn pb ore districts but uncertainty exists in the timing of mineralization relative to host rock ages consequently genetic models for ore formation are poorly constrained and remain controversial here we use re os geochronology to show that ore stage pyrite from the lisheen deposit formed at 346 6 3 0 ma shortly after host rock deposition pyrite from the silvermines deposit returns an age of 334 0 6 1 ma indicating that at least some mineralization occurred during later burial these age determinations show that the much younger paleomagnetic ages reported for the irish zn pb deposits reflect remagnetization during the variscan orogeny a process that we suggest affects paleomagnetic dating more widely the re os ages overlap with the ages of lower carboniferous volcanic rocks in the midlands which are the product of magmatism that has been invoked as the driving force for hydrothermal activity the relatively low initial os ratios for both lisheen 0 253 0 045 and silvermines 0 453 0 006 are compatible with derivation of os from these magmas or from the caledonian basement that underlies the ore deposits

the impact of hydrothermal mineral replacement reactions on the formation and alteration of carbonate hosted polymetallic sulfide deposits a case study of the artemis prospect queensland australia abstract hydrothermal sulfidation of carbonate rocks and the reverse replacement of sulfides by carbonates are important processes responsible for the formation and subsequent alteration of ore deposits these processes have been recognized in the case study of the artemis zn cu au prospect which is located in the cloncurry district within the eastern succession of the mount isa inlier nw queensland australia the high grade polymetallic mineralization displays a complex association of massive sulfides and carbonates hosted in a vertical marble lens adjacent to garnet bearing schist staurolite muscovite schist and quartzo feldspathic psammite petrographic analyses of drill core specimen by optical and electron microscopy micro x ray florescence elemental maps electron probe microanalyses cathodoluminescence and bulk geochemistry suggested three major stages of mineralization i pre ore stage marble calcite 0 ii ore stage involving sulfidation of the marble and precipitation of calcite 1 and spherical sulfide inclusions in the first episode and the formation of calcite 2 and massive sulfide in the second episode and iii post ore stage involving replacement of sulfides by calcite 3 and garnet mineral replacement reactions are dominant processes in rocks of ore stage and post ore stage the ore stage involved the dissolution of coarse and pristine calcite 0 ca0 95mn0 3fe0 2co3 and the precipitation of sulfides and calcite 1 ca0 96mn0 3fe0 1co3 and calcite 2 ca0 96mn0 3fe0 1co3 the sulfide assemblage consists of pyrrhotite sphalerite chalcopyrite galena arsenopyrite cobaltite costibite bi cubanite ag sulfides and au in decreasing order of abundance in episode 1 calcite 1 contains spherical sulfide inclusions while in episode 2 calcite 2 envelopes calcite 1 the replacement of co rich arsenopyrite fe0 75co0 26as1 13s0 83 by relatively co poor arsenopyrite fe0 86co0 15as0 99s0 99 via a coupled dissolution precipitation reaction occurred in episode 2 based on arsenopyrite geothermometry the temperatures for the first and second episode are 650 50 and 450 70 c respectively micro xrf elemental maps of the garnet bearing schist adjacent to the sulfidized marble revealed the sulfidation front where pre ore garnet and amphibole were replaced by pyrrhotite chalcopyrite au biotite and muscovite in the post ore stage calcite 2 was partially replaced by siderite and calcite 3 ca0 94mn0 4fe0 2mg0 1co3 which shows sectoral and oscillatory zoning galena was replaced by calcite 3 as documented by embayed lobate grain boundaries between these minerals and pyrrhotite fe 1 x s x 0 091 0 119 was pervasively replaced by garnet mn1 2fe1 2ca0 6 al2si3o12 the microscale investigations of the mineralization processes in the artemis orebody document the impact of hydrothermal mineral replacement reactions on metal sequestration mineral replacement reactions facilitate the formation of ore deposits and subsequent alteration processes which may lead to the loss of economic value of the deposit

genesis of the dongguashan skarn cu au deposit in tongling eastern china evidence from fluid inclusions and h o s pb isotopes abstract the dongguashan copper gold deposit is located in the eastern tongling ore district of the middle lower yangtze river valley metallogenic belt mlyrb eastern china the cu au mineralization is associated with the qingshanjiao quartz monzodiorite and consists of various types including stratiform porphyry vein like and skarn there are three deposit models including 1 stratabound skarn type 2 exhalative sedimentary sedex hydrothermal superimposition type and 3 exhalative sedimentary sedex type the ore forming processes can be divided into the prograde skarn alteration stage i retrograde alteration stage ii and quartz carbonate alteration stage iii four types of fluid inclusions fis are recognized at dongguashan vapor rich two phase aqueous type i liquid rich two phase aqueous type ii daughter mineral bearing three phase homogenized to liquid by the disappearance of vapor phase type iii and daughter mineral bearing three phase homogenized to liquid by the disappearance of daughter minerals type iv all four types of fis are present in stage ii stage i does not contain type iv fis and only type ii fis are found in stage iii for stage i type i ii and iii fis homogenized at 379 548 c 319 522 c and 450 512 c respectively with salinities of 10 1 19 6 5 9 19 4 and 36 7 43 3 wt nacl equivalent for stage ii type i ii iii and iv fis homogenized at 286 378 c 235 372 c 265 349 c and 324 350 c respectively with salinities of 1 4 17 0 4 3 16 1 34 7 40 6 and 34 4 41 0 wt nacl equivalent the type i to iii fis in stage i and ii have similar homogenization temperatures but different salinities which indicates the occurrence of fluid immiscibility hydrogen oxygen isotopes of the quartz d 84 0 to 71 5 18oh2o 4 51 to 8 97 and calcite d 70 7 to 60 95 18oh2o 4 41 to 4 91 suggest that the ore forming fluids were principally magmatic derived 34s values of the stratiform orebodies 4 1 to 5 3 vein like orebodies 4 2 to 5 7 skarn orebodies 4 9 porphyry orebodies 5 1 to 5 7 and the qingshanjiao pluton 2 2 to 5 2 are different from those of the wall rocks 29 5 to 4 6 suggesting that wall rocks were unlikely to be a major sulfur source lead isotopes of the sulfides from the different orebody types are similar to those of the plagioclase from the mesozoic intermediate felsic rocks in the mlyrb suggesting that they have had similar pb source sulfur and lead isotopes suggest that the ore forming materials were derived from a deep seated magmatic source the ore forming fluid immiscibility during stage i and ii may have altered the physicochemical conditions of the hydrothermal fluid system leading to the cu au sulfide precipitation based on the ore geological and alteration mineralization features mineral assemblages ore forming material source and fluid evolution we consider that dongguashan is best classified as a porphyry skarn cu au deposit

850 790 ma bimodal volcanic and intrusive rocks in northern zhejiang south china a major episode of continental rift magmatism during the breakup of rodinia abstract shrimp u pb zircon ages and geochemical and nd isotopic data are reported for mid neoproterozoic igneous rocks in northern zhejiang province south china the shenwu dolerite dykes the daolinshan granite diabase complex and the shangshu bimodal basalt rhyolite volcanic rocks were dated at 849 7 ma 794 9 ma and 792 5 ma respectively all the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements resembling intraplate basaltic rocks in continental rifts the 850 ma shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca 1 1 0 9 ga sibao orogeny but seem to predate the neoproterozoic rifting our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the yangtze block until ca 800 ma the intensive 790 ma bimodal volcanic and plutonic rocks part of a major phase of mid neoproterozoic rifting are concurrent with the widespread mid neoproterozoic intraplate magmatism throughout south china they are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent rodinia

geochemistry of pyrite from stratabound massive sulfide deposits tongling region china implication for their genesis abstract stratabound massive sulfide deposits are widely distributed along middle lower yangtze river metallogenic belt in eastern china there has much debate as to whether these deposits were associated with late mesozoic igneous or carboniferous sedimentary exhalative sedex three type pyrites i e colloform py1 fine grained py2 and medium to coarse grained py3 from xinqiao and taoyuan stratabound massive sulfide deposits in tongling region were investigated using electron probe microanalysis epma in situ laser ablation inductively coupled plasma mass spectrometry la icp ms and sulfur isotopic analysis the analytic data indicate that the three type pyrites have high s and as and relatively consistent au contents the au ag bi sb and pb elements are mainly of lattice bound appearance in the xinqiao and taoyuan pyrites low au mainly 1 se tl mainly 1 and 34scdt 4 0 to 5 9 values of the studied xinqiao and taoyuan pyrites imply a magmatic hydrothermal origin high bi 1 ppm and mo contents and low co ni ratios

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

the xinqiao cu s fe au deposit in the tongling mineral district china synorogenic remobilization of a stratiform sulfide deposit abstract the cu s fe au deposit at xinqiao is located in the tongling mineral district anhui province people s republic of china it is a large scale polymetallic deposit with drilling indicated reserves of 0 5 million tonnes of cu averaging 0 71 75 5 million tonnes of s averaging 29 3 and 24 9 million tonnes of fe averaging 46 as well as 11 2 tonnes of au averaging at 4 7 g tonne plus 248 4 tonnes of ag averaging at 248 4 g tonne there are two major mineralization types in the xinqiao deposit one is the economically significant stratiform orebody hosted in the lower carboniferous gaolishan siltstone c1g and overlying middle carboniferous huanglong limestone c2h while the other is the less important skarn type mineralization restricted to the contact between the yanshanian diorite 110 168 ma and the lower permian qixia marble p1q the ore in the xinqiao deposit is dominated by massive pyrite with minor amount of chalcopyrite magnetite pyrrhotite galena sphalerite quartz and dolomite four stages of deformation have been recognized to affect the sedimentary rocks in the xinqiao area the first two d1 and d2 produced mainly ne sw and nne ssw trending open folds whereas d3 is characterized by normal faults striking nne ssw and d4 is dominated by post mineralization strike slip faults segmenting the orebody the structural information obtained by this study not only revealed the transgressive nature of the stratiform orebody but also identified a strong structural control on the formation of the deposit it is concluded that the xinqiao polymetallic deposit was formed through remobilization of a carboniferous sulfide source bed by hydrothermal solutions related to late yanshanian plutonism 110 ma during which d3 normal faulting played an important role in localization of the mineralization such a two stage ore forming model is consistent with the most recent genetic interpretations of the deposit

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

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

microfabrics in situ trace element and sulfur isotope compositions of pyrite from the jinjiwo copper deposit in chengmenshan orefield northern yangtze block syngenetic stratabound mineralization and hydrothermal remobilization abstract the jinjiwo copper deposit is located in the jiurui ore district of the middle lower yangtze metallogenic belt the deposit has stratiform orebodies hosted by late carboniferous carbonate units pyrite is the dominant metallic mineral in the ores here we report on an integrated study on the microfabrics raman spectroscopy in situ la mc icp ms trace element and sulfur isotope of pyrite with a view to understand the geochemical variation genesis of copper mineralization and ore forming process textural observations suggested four types of pyrite corresponding to three metallogenic episodes syngenetic sedimentation pyi metamorphism or deformation pyii and skarn hydrothermal mineralization including the late skarn stage pyiii and hydrothermal stage pyiv raman spectra of pyrite reveal subtle differences in band position and widths fwhm and display the increasing formation temperature of from pyi through pyiv and pyiii to pyii colloform and laminated pyrite pyi share similarities in behavior of pairs of elements and have low co ni ratios and the former contains the highest concentrations of bi cu pb zn ag au mn that suggest rapid precipitation from highly saturated fluids pyii shows high co ni and as concentrations and co ni ratios of 0 03 to 6 19 pyiii and pyiv have greatly varying co ni ratios of 1 07 to 29 and typically low au concentrations suggesting a hydrothermal source pyiii is rich in co and se but is depleted in as cu pb zn ag and au in comparison with pyiv there are two kinds of sulfur one is that 34s values are near zero suggesting that the pyrite sulfur in the ores was derived from a mixed source in deep crust and the other is that 34s values are less than 39 1 indicating the sedimentary pyrite sulfur was originated from bacterial sulfate reduction the combined textural and compositional data of pyrite suggest that the formation of the jinjiwo copper deposit might have recorded the submarine exhalation sedimentation and the mesozoic tectonic transition deformation and hydrothermal overprint

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

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

caledonian early paleozoic veins overprinted by yanshanian late mesozoic gold mineralization in the jiangnan orogen a case study on gold deposits in northeastern hunan south china abstract the jiangnan orogen situated between the yangtze and cathaysia blocks in south china is an important gold polymetallic metallogenic belt in china like many gold deposits hosted in precambrian rocks in eastern china the timing of gold mineralization in the jiangnan orogen mostly hosted by neoproterozoic rocks has been controversial a number of previous geochronological studies have suggested that mineralization ages range from neoproterozoic to cretaceous with caledonian early paleozoic and yanshanian jurassic cretaceous being considered most important as caledonian is the most important period of regional metamorphism and yanshanian is the most important period of granitic magmatism the timing of mineralization is closely related to the genetic nature orogenic versus post orogenic of the gold mineralization this paper addresses these problems by studying the ages and characteristics of ore forming fluids of two major gold deposits wangu and huangjindong in the central part of the jiangnan orogen in northeastern hunan muscovite ar ar dating suggests that the bulk of the quartz veins in the wangu and huangjindong deposits were formed at ca 399 397 ma i e during the caledonian orogeny whereas gold mineralization and associated veining took place at ca 142 130 ma i e during the yanshanian orogeny fluid inclusions in the barren caledonian veins are characterized by the h2o nacl co2 system homogenization temperatures of 266 276 c and salinities of 5 5 4 wt nacl equivalent similar to those found in many orogenic type gold deposits whereas the fluid inclusions in the gold bearing yanshanian veins with abundant sulfides overprinting the barren veins have a h2o nacl composition system homogenization temperatures of 169 to 256 c and salinities from 8 7 to 15 2 wt nacl equivalent it is proposed that both the caledonian and yanshanian veining events are controlled by the same fracture systems with the former being formed in a relatively deep orogenic deformation metamorphic environment and the latter in a relatively shallow extensional environment accompanied by extensive granitic magmatism reactivation of the caledonian structures during the yanshanian orogeny together with availability of sulfur and gold possibly associated with granitic intrusions played a key role in the formation of the gold deposits in northeastern hunan and possibly elsewhere in the jiangnan orogen

crustal structure and fault geometry of the 2010 haiti earthquake from temporary seismometer deployments haiti has been the locus of a number of large and damaging historical earthquakes the recent 12 january 2010 mw 7 0 earthquake affected cities that were largely unprepared which resulted in tremendous losses it was initially assumed that the earthquake ruptured the enriquillo plantain garden fault epgf a major active structure in southern haiti known from geodetic measurements and its geomorphic expression to be capable of producing m 7 or larger earthquakes global positioning systems gps and interferometric synthetic aperture radar insar data however showed that the event ruptured a previously unmapped fault the leog ne fault a north dipping oblique transpressional fault located immediately north of the epgf following the earthquake several groups installed temporary seismic stations to record aftershocks including ocean bottom seismometers on either side of the epgf we use data from the complete set of stations deployed after the event on land and offshore to relocate all aftershocks from 10 february to 24 june 2010 determine a 1d regional crustal velocity model and calculate focal mechanisms the aftershock locations from the combined dataset clearly delineate the leog ne fault with a geometry close to that inferred from geodetic data its strike and dip closely agree with the global centroid moment tensor solution of the mainshock but with a steeper dip than inferred from previous finite fault inversions the aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone which could indicate triggered seismicity on the offshore trois baies reverse fault we use first motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks

incursion of meteoric water triggers molybdenite precipitation in porphyry mo deposits a case study of the chalukou giant mo deposit there has been a long term debate about the timing of the incursion of meteoric water into porphyry systems and whether it plays an important role in ore precipitation to evaluate the role of meteoric water in the mineralization in porphyry mo deposits typical hydrothermal veins of different stages from the chalukou giant porphyry mo deposit are selected for combined scanning electron microscope cathodoluminescence sem cl fluid inclusion microthermometry and high resolution secondary ion mass spectroscopy sims oxygen isotope analyses multiple generations of quartz are identified in almost all of the veins the barren quartz veins and quartz magnetite veins of the early mo mineralization stage are dominated by granular cl bright quartz emq1 which usually shows dissolution and re deposition textures and are overprinted by cl dark quartz emq2 filled healed fractures the molybdenite precipitation in the quartz molybdenite veins of the main mo mineralization stage is synchronous with small volumes 85 of cl bright quartz mmq1 similar to the quartz molybdenite veins the precipitation of pyrite in the quartz pyrite veins during the transitional stage and sphalerite in the quartz sphalerite pyrite veins during the zn pb mineralization stage are also directly associated with cl dark quartz tsq2 zpq2 the sims oxygen isotopic values of emq1 and mmq1 fall into the range of 5 42 9 79 o with calculated equilibrium fluid compositions of 2 07 6 45 0 indicating a magma dominated fluid composition whereas mmq2 tsq2 and zpq2 have very low oxygen isotopic values from 4 68 to 4 29 parts per thousand with corresponding fluid compositions of 13 64 to 5 94 parts per thousand implying that the fluid formed by the mixing of magmatic water and a large proportion of meteoric water the contrasting sem cl features and oxygen isotopic compositions of the two generations of quartz in the quartz molybdenite veins demonstrate that the incursion of meteoric water into the hydrothermal system occurred earlier than the molybdenite precipitation based on these results and the crosscutting relationships and spatial distribution of the veins we reconstructed the quartz evolutionary sequence during the vein development process after the early precipitation of barren quartz the reduction in fluid pressure from lithostatic to hydrostatic conditions allowed the incursion of convecting cool meteoric water into the relatively hot hydrothermal system and the temperature of the evolved mo rich fluid decreased rapidly from 500 degrees c to 400 degrees c leading to concentrated molybdenite precipitation with small volumes of quartz fluid cooling resulting from the incursion of meteoric water may have played a greater role in the metal precipitation in the chalukou mo deposit than wallrock interactions and fluid boiling moreover this process may have also occurred in other porphyry mo deposits

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

experimental constraints on rhyolite melts and the late bishop tuff magma body thermodynamic models are vital tools to evaluate magma crystallization and storage conditions before their results can be used independently however they must be verified with controlled experimental data here we use a set of hydrothermal experiments on the late erupted bishop tuff lbt magma to evaluate the rhyolite melts thermodynamic model a modified calibration of the original melts model optimized for crystallization of silicic magmas experimental results that are well captured by rhyolite melts include a relatively narrow temperature range separating the crystallization of the first felsic mineral and the onset of the ternary minimum quartz plus two feldspars and extensive crystallization over a narrow temperature range once the ternary minimum is reached the model overestimates temperatures by 40 c a known limitation of rhyolite melts at pressures below 110 mpa model and experiments differ in the first felsic phase suggesting that caution should be exercised when applying the model to very low pressures our results indicate that for quartz sanidine plagioclase magnetite and ilmenite to crystallize in equilibrium from lbt magma magma must have been stored at 740 c even when a substantial amount of co2 occurs in the coexisting fluid such temperatures are in conflict with the hotter temperatures retrieved from magnetite ilmenite compositions 785 c for the sample used in the experiments consistent with other recent studies we suggest that the fe ti oxide phases in the late bishop tuff magma body are not in equilibrium with the other minerals and thus the retrieved temperature and oxygen fugacity do not reflect pre eruptive storage conditions

an early cretaceous carbonate replacement origin for the xinqiao stratabound massive sulfide deposit middle lower yangtze metallogenic belt china stratabound massive sulfide deposits are widespread along the middle lower yangtze metallogenic belt mlymb and serve as an important copper producer in china two contrasting genetic models have been proposed interpreting the stratabound massive sulfide deposits as a carboniferous sedex protore overprinted by cretaceous magmatic hydrothermal system or an early cretaceous carbonate replacement deposit these two contrasting models have been applied to the xinqiao stratabound cu au sulfide deposit which is dominated by massive sulfide ores hosted in marine carbonates of the carboniferous chuanshan and huanglong formations with minor cu au skarn ores localized in the contact zone between the cretaceous diorite jitou stock and the carboniferous carbonate rocks new sims zircon u pb dating suggests that the jitou stock formed at 138 5 1 1 ma 2 mswd 0 6 pyrite re os dating yields an imprecise date of 142 47 ma 2 mswd 7 8 the geochronological data thus constrain the mineralization of the xinqiao deposit at early cretaceous fluid inclusions in prograde skarn diopside have homogenization temperatures of 450 600 c and calculated salinities of 13 58 wt nacl equiv quartz from the stratabound ores and pyrite quartz vein networks beneath the stratabound ores have homogenization temperatures of 290 360 and 200 300 c with calculated salinities of 5 12 and 2 10 wt nacl equiv respectively quartz from the skarn ores and veins beneath the stratabound ores have 18o values of 12 32 0 55 2 sd n 22 and 15 57 1 92 2 sd n 60 respectively corresponding to calculated 18o values of 6 22 1 59 2 and 6 81 2 76 2 for the equilibrated ore forming fluids the fluid inclusion and oxygen isotope data thus support a magmatic hydrothermal origin rather than a sedex system for the stratabound ores with the hydrothermal fluids most likely being derived from the jitou stock or associated concealed intrusion results from this study have broad implications for the genesis and exploration of other stratabound massive sulfide deposits along the mlymb

the lower changjiang yangzi yangtze river metallogenic belt east central china intrusion and wall rock hosted cu fe au mo zn pb ag deposits abstract the lower valley of changjiang from wuhan of the hubei province in the west to zhenjiang of the jiangsu province in the east contains more than 200 polymetallic cu fe au mo zn pb ag deposits and is one of the most important metallogenic belts in china this metallogenic belt situated at the northern margin of the yangzi craton and bordered by the dabieshan ultrahigh pressure metamorphic belt to the north consists mainly of cambrian triassic marine clastic sedimentary rocks and carbonate and evaporite rocks which overlay a precambrian basement and are intruded by yanshanian 205 to 64 ma granitoid intrusions and subvolcanic complexes repeated tectonism from late proterozoic to triassic resulted in extensively developed networks of faults and folds involving the cambrian triassic sedimentary strata and the precambrian basement the yanshanian granitoid intrusions and subvolcanic complexes in the lower changjiang metallogenic belt are characterized by whole rock 18 o of 8 to 10 initial 87 sr 86 sr of 0 704 to 0 708 and ndt from 10 to 17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials also the yanshanian granitoids exhibit eastward younging and increase in alkalinity i e from older calc alkaline in the west to younger subalkaline alkaline in the east which are related to oblique collision between the yangzi and sino korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes most polymetallic deposits in the lower changjiang metallogenic belt are clustered in seven districts where the yanshanian magmatism is particularly extensive from west to east edong jiurui anqing guichi luzhong tongling ningwu and ningzhen mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits orebodies in yanshanian granitoid intrusions skarn orebodies at the contact zones between the yanshanian intrusions and late paleozoic early mesozoic sedimentary rocks and stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata the most important host sedimentary strata are the middle carboniferous huanglong formation lower permian and lower middle triassic carbonate and evaporite rocks the intrusion hosted and skarn orebodies exhibit well developed zonation in alteration assemblages metal contents and isotopic compositions within individual deposits and apparently formed from hydrothermal activities related to the yanshanian magmatism the stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano sedimentary exhalative processes in shallow marine environments however extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization on the basis of geological relationships and isotope geochemical characteristics we propose a carbonate hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies this model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the yanshanian intrusions with carbonate and evaporite wall rocks mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion hosted orebodies the stratabound massive sulfide deposits of the lower changjiang metallogenic belt share many features with the well studied high temperature carbonate hosted replacement deposits of northern mexico and western united states particularly with respect to association with small shallow granitoid complexes structural and stratigraphic controls on mineralization alteration assemblages geometry of orebodies metal association metal zonation and isotopic systematics

gis based mineral prospectivity mapping using machine learning methods a case study from tongling ore district eastern china abstract predictive modelling of mineral prospectivity using gis is a valid and progressively more accepted tool for delineating reproducible mineral exploration targets in this study machine learning methods including support vector machine svm artificial neural networks ann and random forest rf were employed to conduct gis based mineral prospectivity mapping of the tongling ore district eastern china the mineral systems approach was used to translate our understanding of the skarn cu mineral system into mappable exploration criteria resulting in 12 predictor maps that represent source transport physical trap and chemical deposition processes critical for ore formation predictive svm ann and rf models were trained by way of predictor maps and corroborated using a 10 fold cross validation the overall performance of the resulting predictive models was assessed in both training and test datasets using a confusion matrix set of statistical measurements receiver operating characteristic curve and success rate curve the assessment results indicate that the three machine learning models presented in this study achieved satisfactory performance levels characterized by high predictive accuracy in addition all models exhibited well interpretability that provided consistent ranking information about the relative importance of the evidential features contributing to the final predictions in comparison the rf model outperformed the svm and ann models having achieved greater consistency with respect to variations in the model parameters and better predictive accuracy importantly the rf model exhibited the highest predictive efficiency capturing most of the known deposits within the smallest prospective tracts the above results suggest that the rf model is the most appropriate model for cu potential mapping in the tongling ore district and therefore was used to generate a prospectivity map containing very high high moderate and low potential areas in support of follow up exploration the prospective areas delineated in this map occupy 13 97 of the study area and capture 80 95 of the known deposits the fact that two newly discovered deposits occur within the prospective areas predicted by the prospectivity model indicates that the model is robust and effective regarding exploration target generation

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

skarn manto and breccia pipe formation in sedimentary rocks of the cananea mining district sonora mexico skarns mantos and breccia pipes occur at cananea in a 2 by 4 km horst of paleozoic carbonate rock and minor quartzite surface mapping and core logging reveal a sequence of events beginning with early metamorphism that converted impure carbonate lithologies to iron poor garnet pyroxene or idocrase hornfels subsequent metasomatism formed garnet py roxene skarn along the pre cretaceous elisa fault contact between carbonate rock and mesozoic volcanic rock skarn is zoned from an andradite rich center through a zone containing both andraditic garnet and salitic pyroxene to a mineralogic sequence near the marble front which is largely a function of the sedimentary protolith chert nodules are rimmed by wollastonite dolomite is converted to massive phlogopite magnetite skarn calc silicate hornfels is over printed by veins of skarn garnet and relatively pure marble is replaced by coarse blades of iron and manganese rich pyroxene multiple generations of garnet and pyroxene can be distinguished by subtle variations in color and texture age classification on the basis of crosscutting vein and overgrowth relationships indicates that late pyroxenes are more iron and manganese rich than the early generations garnets show a less regular iron enrichment with time the spatial distribution of the different garnet and pyroxene generations is irregular garnet and pyroxene in late veins have iron rich compositions both near the skarn center and near the marble front pyrite and minor chalcopyrite are the only sulfides associated with this stage of metasomatism following the main stages of garnet and pyroxene formation veins and orbicular patches of amphibole or quartz or calcite occur replacing pyroxene and in some cases garnet most of the amphibole is actinolitic in composition and is associated with pyrite and minor amounts of chalcopyrite about 20 percent of the amphibole is subcalcic and is associated with or replaced by massive calcite the alteration of prograde skarn to amphibole or quartz or calcite can be best explained by a general temperature decline the destruction of skarn by alteration related to brecciation and breccia pipe formation and the replacement of previously unaltered carbonate rocks by stratiform blankets mantos of iron oxides and sulfides resulted in some of the highest grade orebodies breccia pipe and manto formation appears to have been largely contemporaneous with emplacement and subsequent sericitic alteration of a series of quartz monzonite porphyry stocks where breccia pipes crosscut skarn garnet pyroxene and amphibole are converted to mixtures of calcite quartz chlorite hematite siderite and sulfides where breccia pipes or porphyries crosscut previously unaltered carbonate rock mixtures of magnetite sulfides chlorite siderite calcite quartz and serpentine form massive mantos veinlets of chlorite and magnetite or pyrite or serpentine extend tens of meters beyond the zones of massive replacement there is a rough vertical and lateral zonation of sulfide minerals with respect to the democrata breccia pipe from chalcopyrite or bornite or pyrite in the core and at depth to sphalerite pyrite chalcopyrite to pyrite sphalerite galena distal to the center of mineralization mineral stability relations suggest that brecciation and mineralization took place at lower temperatures 275 degrees 25 degrees c and possibly under lower x sub co 2 conditions than the earlier skarn formation the high zn cu ratios in skarn the zonation of most hypogene mineralization relative to the breccia pipes which crosscut skarn and the lack of skarn spatially associated with the quartz monzonite porphyry stocks which intrude carbonate rock all suggest that unlike skarn in most porphyry copper districts skarn at cananea is not related to the quartz monzonite porphyry stocks that are mined elsewhere in the district for disseminated supergene enriched sulfide mineralization rather the skarn may be related to a deeper magmatic system which has not yet been encountered in subsurface exposures

genesis of gold and antimony deposits in the youjiang metallogenic province sw china evidence from in situ oxygen isotopic and trace element compositions of quartz abstract abundant carlin type gold deposits and vein type antimony deposits were discovered in the youjiang basin of sw china constituting the youjiang metallogenic province ymp although they had been widely studied by geologists the genesis of these deposits remains debatable while both intrusion linked and non intrusion linked models have been proposed in this paper new data of in situ trace elements la icp ms and oxygen isotope sims analysis of hydrothermal quartz from the yata carlin type gold deposit and the qinglong vein type antimony deposit in the province were provided to better understand the origin of ore forming fluids as well as the genetic mechanism of au and sb mineralization four quartz generations were identified from the yata yti to ytiv and the qinglong qli to qliv deposits in the yata deposit the fluid inclusions in quartz have varied homogenization temperatures from 140 260 and salinities of 2 4 7 4 wt nacleq while in the qinglong deposit the temperatures and salinities ranged from 140 200 and 0 2 7 2 wt nacleq respectively both of the temperatures and salinities tend to decrease from early to late generations in the two deposits 18o values of initial fluids in the yata yti 7 70 10 56 and the qinglong qli 4 66 8 75 deposits are similar and suggest that they were mainly from magmatic or metamorphic fluids the covariability of oxygen isotope and al concentrations indicate that interaction between fluids and wall rocks is a significant factor in determining the compositions of fluids in au mineralization and the meteoric water is a key proxy in sb mineralization respectively from these observations we proposed that the carlin type au deposit and vein type sb deposit in ymp were sourced from an analogous ore fluid different lithologies of wall rocks and the dilution of meteoric water controlled the compositional evolution of fluids which might be the main reason for the diversity of au and sb mineralization

tracing water rock interaction in carbonate replacement deposits a sims pyrite s pb isotope perspective from the chinese xinqiao system abstract deciphering the sources of metals is a prerequisite to establishing genetic models of ore formation and is of importance for developing exploration models for most magmatic hydrothermal deposits non magmatic sourced components e g fluids sulfur and metals are suggested to have minor or negligible contributions on the other hand there is substantial evidence to indicate that external ore forming components could be crucial for the mineralization of some magmatic hydrothermal deposits here we conduct a detailed pyrite sulfur and lead isotope study on the xinqiao stratabound deposit south china with the aim of constraining the contributions of ore forming components from sedimentary rocks and existing mineralization through water rock interaction traditionally the source of mineralization at xinqiao is debated for example a cretaceous magmatic hydrothermal origin was proposed as the sole source of metals in sharp contrast a carboniferous sedimentary sulfide layer as proto ore which was enriched later by the cretaceous magmatic hydrothermal fluids is required in a remobilization model crystallized pyrite grains from the stratabound orebody py1 have a 34s value of 4 09 1 42 2 sd which is similar to that of pyrite grains from the garnet bearing skarn ore py3 colloform pyrite ore which is composed of fine grained 500 nm cubic pyrite grains py2a has a 34s value of 0 20 1 14 the sulfur isotope composition of pyrite grains from the sandstone hosted quartz pyrite veins is bimodal with 34s values of 3 28 6 46 py4a and 11 87 5 43 py4b the pb isotope compositions 206 204pb 18 5 207 204pb 15 5 of py1 py4a and py4b are broadly the same as that of k feldspar from the cretaceous jitou diorite while py2a are more radiogenic 206 204pb 21 5 207 204pb 18 our pyrite s and pb isotope data show no support for the presence of a carboniferous sedimentary sulfide layer as proto ore but instead suggest that leaching sulfur and metals from permian shales and an unexposed mineralization through water rock interaction is a vital mechanism for the mineralization at xinqiao in line with previous studies contributions from the late permian shales are complementary for the stratabound orebody and recycling existing mo au rich mineralization is key for the formation of sandstone hosted gold rich pyrite quartz veins the existing mineralization is not exposed yet and should be considered in future mineral exploration limited sulfur isotope fractionation between py1 py2 and py3 0 4 further indicates a relatively reducing condition during their formation while significant lower sulfur isotope composition 34s 12 of py4 could imply an oxidizing condition during its formation our study highlights that detailed in situ sulfur and lead isotope analyses under robust geological and petrographic frameworks can tightly constrain the source of ore forming components yield insights into oxygen fugacity during ore formation and offer clues for future mineral exploration

oxygen isotope geochemistry of the sullivan massive sulfide deposit kimberley british columbia hydrothermal evolution of the deposit potential applications of isotopic analyses to exploration for stratabound stratiform pb zn ag deposits the deposit is hosted by the proterozoic aldridge formation the delta 18 o results for samples from the aldridge range from 10 0 to 13 1 per mil with an average of 11 4 or 1 0 per mil oxygen isotope results from the tourmaline alteration zone located in the footwall of the western proximal ores range from 10 7 to 13 1 per mil with an average of 11 9 or 0 8 per mil the similarity between values for the tourmalinite and the aldridge formation suggests that the fluids which produced the tourmalinite alteration did not significantly alter the primary 18 o 16 o of the host sedimentary units isotopic values for samples from the albite chlorite alteration zone located in the hanging wall of the proximal ores range from 6 1 to 7 7 per mil such values indicate that there is a distinct difference in the isotopic composition of the albite chlorite zone relative to unaltered country rocks the following sequence is proposed the first hydrothermal stage consisted of the migration of low temperature 100 degrees c boron rich fluids up permeable zones causing the development of the tourmalinite alteration zone subsequent to this event hotter approximately 150 degrees c pb zn fe bearing fluids rose through the same zone at sullivan and deposited sulfides on the sea floor the final hydrothermal event was the alteration of the tourmalinite ore and hanging wall sedimentary units to produce the albite chlorite alteration assemblage the fluids which produced the albite chlorite assemblage were most likely more saline than normal seawater and had a temperature of 250 degrees c or more modified journal abstract

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

hydrothermal biogenic and seawater components in metalliferous black shales of the brooks range alaska synsedimentary metal enrichment in a carbonate ramp setting trace element and os isotope data for lisburne group metalliferous black shales of middle mississippian early chesterian age in the brooks range of northern alaska suggest that metals were sourced chiefly from local seawater including biogenic detritus but also from externally derived hydrothermal fluids these black shales are interbedded with phosphorites and limestones in sequences 3 to 35 m thick deposition occurred mainly on a carbonate ramp during intermittent upwelling under varying redox conditions from suboxic to anoxic to sulfidic deposition of the black shales at 335 ma was broadly contemporaneous with sulfide mineralization in the red dog and drenchwater zn pb ag deposits which formed in a distal marginal basin relative to the composition of average black shale the metalliferous black shales n 29 display large average enrichment factors 10 for zn 10 1 cd 11 0 and ag 20 1 small enrichments 2 10 are shown by v cr ni cu mo pd pt u se y and all rare earth elements except ce nd and sm a detailed stratigraphic profile over 23 m in the skimo creek area central brooks range indicates that samples from at and near the top of the section which accumulated during a period of major upwelling and is broadly correlative with the stratigraphic levels of the red dog and drenchwater zn pb ag deposits have the highest zn toc total organic carbon cu toc and tl toc ratios for calculated marine fractions no detrital component of these three metals average authigenic detrital free contents of mo v u ni cu cd pb ge re se as sb tl pd and au show enrichment factors of 4 3 103 to 1 2 106 relative to modern seawater such moderate enrichments which are common in other metalliferous black shales suggest wholly marine sources seawater and biogenic material for these metals given similar trends for enrichment factors in organic rich sediments of modern upwelling zones on the namibian peruvian and chilean shelves the largest enrichment factors for zn and ag are much higher 1 4 107 and 2 9 107 respectively consistent with an appreciable hydrothermal component other metals such as cu pb and tl that are concentrated in several black shale samples and are locally abundant in the red dog and drenchwater zn pb ag deposits may have a partly hydrothermal origin but this cannot be fully established with the available data enrichments in cr up to 7 8 106 are attributed to marine and not hydrothermal processes the presence in some samples of large enrichments in eu up to 6 1 107 relative to modern seawater and of small positive eu anomalies eu eu up to 1 12 are considered unrelated to hydrothermal activity instead being linked to early diagenetic processes within sulfidic pore fluids initial os isotope ratios 187os 188os calculated for a paleontologically based depositional age of 335 ma reveal moderately unradiogenic values of 0 24 to 0 88 for four samples of metalliferous black shale a proxy for the ratio of coeval early chesterian seawater is provided by initial 187os 188os 335 ma ratios of four unaltered black shales of the coeval kuna formation that average 1 08 nearly identical to the initial ratio of 1 06 for modern seawater evaluation of possible sources of unradiogenic os in the metalliferous black shales suggests that the most likely source was mafic igneous rocks that were leached by externally derived hydrothermal fluids this unradiogenic os is interpreted to have been leached by deeply circulating hydrothermal fluids in the kuna basin followed by venting of the fluids into overlying seawater we propose that metal bearing hydrothermal fluids that formed zn pb ag deposits such as red dog or drenchwater vented into seawater in a marginal basin were carried by upwelling currents onto the margins of a shallow water carbonate platform and were then deposited in organic rich muds together with seawater and biogenically derived components by syngenetic sedimentary processes metal concentration in the black shales was promoted by high biologic productivity sorption onto organic matter diffusion across redox boundaries a low sedimentation rate and availability of h2s in bottom waters and pore fluids

crude oil and alternate energy production forecasts for the twenty first century the end of the hydrocarbon era predictions of production rates and ultimate recovery of crude oil are needed for intelligent planning and timely action to ensure the continuous flow of energy required by the world s increasing population and expanding economies crude oil will be able to supply increasing demand until peak world production is reached the energy gap caused by declining conventional oil production must then be filled by expanding production of coal natural gas unconventional oil from tar sands heavy oil and oil shales nuclear and hydroelectric power and renewable energy sources solar wind and geothermal declining oil production forecasts are based on current estimated ultimate recoverable conventional crude oil resources of 329 billion barrels for the united states and close to 3 trillion barrels for the world peak world crude oil production is forecast to occur in 2020 at 90 million barrels per day conventional crude oil production in the united states is forecast to terminate by about 2090 and world production will be close to exhaustion by 2100

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

oxygen isotope composition and temperature of fluids involved in deposition of proterozoic sedex deposits sudbury basin ontario sedex cu pb zn deposits in the sudbury basin were deposited on the sea floor from fluids in which 18o 1 and at temperatures around 170 c distal mn bearing sediments were deposited in seawate

interactions between deformation and fluids in the frontal thrust region of the nantroseize transect offshore the kii peninsula japan results from iodp expedition 316 sites c0006 and c0007 integrated ocean drilling program iodp expedition 316 sites c0006 and c0007 examined the deformation front of the nankai accretionary prism offshore the kii peninsula japan in the drilling area the frontal thrust shows unusual behavior as compared to other regions of the nankai trough drilling results integrated with observations from seismic reflection profiles suggest that the frontal thrust has been active since 0 78 0 436 ma and accommodated 13 to 34 of the estimated plate convergence during that time the remainder has likely been distributed among out of sequence thrusts further landward and or accommodated through diffuse shortening unlike results of previous drilling on the nankai margin porosity data provide no indication of undercompaction beneath thrust faults furthermore pore water geochemistry data lack clear indicators of fluid flow from depth these differences may be related to coarser material with higher permeability or more complex patterns of faulting that could potentially provide more avenues for fluid escape in turn fluid pressures may affect deformation well drained sand rich material under the frontal thrust could have increased fault strength and helped to maintain a large taper angle near the toe recent resumption of normal frontal imbrication is inferred from seismic reflection data associated decollement propagation into weaker sediments at depth may help explain evidence for recent slope failures within the frontal thrust region this evidence consists of seafloor bathymetry normal faults documented in cores and low porosities in near surface sediments that suggest removal of overlying material overall results provide insight into the complex interactions between incoming materials deformation and fluids in the frontal thrust region

multisourced metals enriched by magmatic hydrothermal fluids in stratabound deposits of the middle lower yangtze river metallogenic belt china stratabound deposits within late carboniferous carbonate units in the middle lower yangtze river metallogenic belt are important copper producers in china hitherto the genesis of these deposits has been debated due to poor constraints regarding the timing and source of the mineralization proposed models include a late carboniferous seafloor exhalative formation sedex or an early cretaceous magmatic hydrothermal origin these models imply different metal sources basinal vs magmatic fluid respectively and would require different exploration strategies new pyrite re os and trace element results from the representative xinqiao cu s fe au deposit favor a cretaceous ca 138 ma magmatic hydrothermal genesis over a sedex origin the distinct initial 187os 188os compositions osi of different pyrite types colloform osi 1 35 and euhedral grains osi 0 79 coupled with the pyrite trace element abundance indicate that the os and by inference other metals e g cu ag au was sourced from a cretaceous magmatic hydrothermal system osi 0 74 and late permian metalliferous black shales osi 7 56 3 76 in addition the genesis of au bearing stockwork pyrite veins hosted by the carboniferous sandstone is best explained by the leaching of existing mineralization e g porphyry au mo by early cretaceous magmatic hydrothermal fluids this is implied by the lack of common os high re abundances 0 1 3 7 ppm and highly variable re os model ages 379 and 173 ma which are positively correlated with re and total abundances of co ni ag au tl and ba this study highlights the importance of recycling of multisourced metals sedimentary and existing mineralization in the formation of intrusion related stratabound deposits furthermore it demonstrates the importance of integrating information regarding the source and timing of mineralization within a well defined geological framework which can yield information about the ore forming processes and help to guide mineral exploration

the deliberate search for the stratigraphic trap an introduction this special publication draws upon contributions to a similarly titled conference the deliberate search for the stratigraphic trap where are we now held at the geological society in london during 2004 observations in this introductory paper have been drawn from the authors experience talks given at the conference and papers within this volume specifically it is noted that by analogy to basins which are perceived to be mature for structural traps stratigraphic traps can have substantial remaining potential additionally current exploration for stratigraphic traps seems rather restricted to areas where seismic data allow the direct assessment of fluid fill and reservoir development it is argued that the industry is probably not doing enough to learn from established stratigraphic traps to guide future exploration for such traps looking forward it is suggested that the industry faces two key challenges firstly the use of all available data to assess fluid type and reservoir presence in areas of unfavourable rock physics and secondly the development of sufficiently sophisticated predictive models of stratigraphic trap development

late mesozoic magmatism of the jiurui mineralization district in the middle lower yangtze river metallogenic belt eastern china precise u pb ages and geodynamic implications abstract the middle lower yangtze river metallogenic belt mlyrmb extending from daye in hubei province in the west to zhenjiang in jiangsu province in the east hosts a number of large polymetallic cu au mo fe zn pb and ag deposits and constitutes one of the most important metallogenic belts in china the cu au mo deposits in the jiurui district are an important component of the mlyrmb in this study we carried out precise and detailed zircon u pb dating for all types of magmatic rocks from the wushan ore deposit in the jiurui district three samples of cu au mo related porphyries from different ore belts at wushan were analyzed and yielded zircon u pb ages of 148 0 1 0 ma 145 4 0 9 ma and 147 3 0 9 ma respectively a series of dykes were emplaced immediately following the cu au mo related porphyries at wushan a dark colored basic dyke which intruded into the granodiorite porphyry at wujia gold deposit near wushan was dated at 144 5 1 2 ma two lamprophyre dykes taken from the north ore belt at wushan underground mining stops were dated at 143 6 0 9 ma and 144 3 0 9 ma respectively a late stage dyke which was also taken from the wushan north ore belt yielded an age of 142 6 1 0 ma and might represent the end of magmatism in the wushan ore deposit these new geochronological data demonstrate that the time range of magmatism in the wushan ore deposit is approximately between 148 ma and 143 ma showing that the magmatic activity at wushan was rapid and intensive the ages of cu au mo related porphyries from other areas in the jiurui district such as the dongleiwan yangjishan and chengmenba ore deposits were also measured and yielded zircon u pb ages of 141 5 1 7 ma 143 4 1 4 ma and 146 6 1 0 ma respectively combined with those previously reported zircon u pb age results from the jiurui district the present age data set demonstrates that extensive magmatism in the jiurui district was coeval and intensive marked by a magmatic activity in the age range of 148 to 138 ma and peaked between 148 ma and 142 ma according to the statistics of all those precise zircon u pb ages the cu au mo related porphyries in the edong and tongling districts in the mlyrmb show similar ages and they have a slightly younger peak age and a longer duration than that of the jiurui district the geographic shape of the mlyrmb in the cretaceous shows an arcuate structure the jiurui district is located at the transitional point of the arcuate structure and the edong and tongling districts are situated on both sides of the arcuate structure considering that the jiurui district has a slightly older peak age and a shorter duration of magmatic activity than that in the edong and tongling districts it seems that the arcuate structure of the mlyrmb played an important role in the formation of these cu au mo related porphyries consequently we suggest that the genesis of the late mesozoic magmatic rocks along the mlyrmb may have been due to a tectonic activity developed from southeast to northwest which probably has a close relationship with the subduction of the paleo pacific plate beneath the eurasian plate in mesozoic times