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

integrated upper carnian to lower norian biochronology and implications for the upper triassic magnetic polarity time scale abstract we summarize the ammonoid conodont and halobiid biochronology of the upper carnian to lower norian based on a discussion of data in the alps sicily balkans turkey himalayas and timor with this integrated biostratigraphic scale the pizzo mondello section sicily can be recalibrated and the carnian norian boundary more precisely located there as a result the magnetostratigraphy of this section is now in good agreement with previous results from turkey although the latter series are more condensed cross correlation of available magnetostratigraphic data from marine tethyan sections allow us to construct a composite upper carnian to upper norian geomagnetic polarity time scale gpts this gpts leads us to question previously proposed magnetobiostratigraphic and chronostratigraphic correlations within the upper triassic newark non marine sedimentary sequence

upper triassic norian cephalopod limestones of the hallstatt type oman norian crinoidal brachiopod limestones and cephalopod limestones of the hallstatt type occur as blocks in a hettangian calcareous breccia of the haliw formation in the oman mountains crinoidal and brachiopod packstones up to 12 m thick prevail in the lower part of the sequence and were deposited on a substrate of norian forereef breccia the overlying cephalopod wackestones up to 4 9 m thick have a basal white bed followed by red limestones with abundant planar and scalloped corroded surfaces and local stromatolites upward red nodular wackestones and finally slumped grey wackestones follow the analysis of geopetal fabrics in orientated samples shows that bedding of these facies is in fact inclined bedding inclinations varied between 15 and 29 in addition the restored dip directions demonstrate rotation indicating deposition on a gliding block the preferred orientation of orthoconic cephalopods and imbrication of discoidal ammonoids coincide with the dip direction measured from geopetal fabrics such features generally interpreted as current induced are here interpreted as gravity induced the overall mud supported rock fabric thus indicates deposition under very low energy conditions the common mud supported texture of the rocks contrasts with evidence for current activity found in the scalloped surfaces and shell lags particularly in the crinoidal brachiopod facies and the lower stratigraphically condensed cephalopod limestones this indicates that deposition of lime mud alternated with periods of elevated current strength a comparison of the hallstatt type limestones and current influenced sediments on the northern slope of the little bahama bank suggests that condensed sequences of the hallstatt type are restricted to relatively shallow depths with strong fluctuation of contour following currents undersaturated with respect to aragonite along carbonate shelf margins facing the open ocean on steep slopes sediment bypassing may be an additional factor for stratigraphic condensation

geology geochronology and hf isotope geochemistry of the longtougang skarn and hydrothermal vein cu zn deposit north wuyi area southeastern china abstract the recently discovered longtougang skarn and hydrothermal vein cu zn deposit is located in the north wuyi area southeastern china the intrusions in the ore district comprise several small porphyritic biotite monzonite porphyritic monzonite and porphyritic granite plutons and dikes the mineralization is zoned from a lower zone of cu rich veins and cu zn skarns to an upper zone of banded zn pb mineralization in massive epidote altered rocks the deposit is associated with skarn potassic epidote greisen siliceous and carbonate alteration molybdenite from the cu rich veins yielded a re os isochron age of 153 6 3 9 ma which is consistent with u pb zircon ages of 154 0 1 3 ma for porphyritic monzonite 154 0 0 8 ma for porphyritic biotite monzonite and 152 0 0 8 ma for porphyritic granite geological observations suggest that the cu mineralization is genetically related to the porphyritic biotite monzonite and porphyritic monzonite all the zircons from intrusive rocks in the ore district are characterized by ehf t values between 13 41 and 4 38 and hf model ages tdm2 between 2054 and 1482 ma reflecting magmas derived mainly from a proterozoic crustal source molybdenite grains from the deposit have re values of 14 6 27 7 ppm indicative of a mixed mantle crust source the porphyry skarn abundant cu and hydrothermal vein type pb zn ag deposits in the north wuyi area are related to the late jurassic porphyritic granites and early cretaceous volcanism respectively the late jurassic mineralization related granites were derived from the crustal anatexis with some mantle input which was triggered by asthenospheric upwelling induced by slab tearing during oblique subduction of the paleo pacific plate beneath the south china block and the early cretaceous mineralization related granitoids mainly from crust material formed within a series of nne trending basins during margin parallel movement of the plate

geochemistry and evolution of ore forming fluids of the yueshan cu au skarn and vein type deposits anhui province south china abstract the yueshan mineral belt is geotectonically located at the centre of the changjiang deep fracture zone or depression of the lower yangtze platform two main types of ore deposits occur in the yueshan orefield cu au fe skarn deposits and cu mo au pb zn hydrothermal vein type deposits almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the yueshan dioritic intrusion in the vicinity of the zongpu and wuhen intrusions there are many cu pb zn au s vein type and a few cu fe au skarn type occurrences fluid inclusion studies show that the ore forming fluids are characterised by a cl s na k chemical association hydrothermal activity associated with the above two deposit types was related to the yueshan intrusion the fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water in comparison the hydrothermal activity related to the zongpu and wuhen intrusions was characterised by low salinity fluids chlorine and sulphur species played an important role in the transport of ore forming components hydrogen and oxygen isotope data also suggest that the ore forming fluids in the yueshan mineral belt consisted of magmatic water mixed in various proportions with meteoric water the enrichment of ore forming components in the magmatic waters resulted from fluid melt partitioning the ore fluids of magmatic origin formed large cu au deposits whereas ore fluids of mixed magmatic meteoric origin formed small to medium sized deposits the sulphur isotopic composition of the skarn and vein type deposits varies from 11 3 to 19 2 and from 4 2 to 10 0 respectively these variations do not appear to have been resulted from changes of physicochemical conditions rather due to compositional variation of sulphur at the source s and by water rock interaction complex water rock interaction between the ore bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore forming fluids hydrodynamic calculations show that magmatic ore forming fluids were channelled upwards into faults fractures and porous media with velocities of 1 4 m s 9 8 10 1 to 9 8 10 7 m s and 3 6 10 7 to 4 6 10 7 m s respectively a decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the triassic sedimentary rocks led to the deposition of the ore forming components the major species responsible for cu transport are deduced to have been cucl cucl2 cucl32 and cucloh whereas au was transported as au2 hs 2s2 au hs 2 auhs and auh3sio4 complexes cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of cu deposition gold deposition was related to decrease of ph total sulphur concentration and fo2 which resulted from fluid boiling and mixing geological and geochemical characteristics of the two deposit types in the yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 ma and represent a continuous process during the yanshanian time the cooling of the intrusions and the mineralisation event might have lasted about 6 ma the cooling rate of the magmatic intrusions was 80 to 120 c my 1 which permitted sufficient heat supply by magma to the ore forming system

shrimp zircon u pb geochronological and whole rock geochemical evidence for an early neoproterozoic sibaoan magmatic arc along the southeastern margin of the yangtze block abstract it has been generally accepted that the south china block was formed through amalgamation of the yangtze and cathaysia blocks during the proterozoic sibaoan orogenesis but the timing and kinematics of the sibao orogeny are still not well constrained we report here shrimp u pb zircon geochronological and geochemical data for the taohong and xiqiu tonalite granodiorite stocks from northeastern zhejiang southeastern margin of the yangtze block our data demonstrate that these rocks dated at 913 15 ma and 905 14 ma are typical amphibole rich calc alkaline granitoids formed in an active continental margin combined with previously reported isotopic dates for the 1 0 ga ophiolites and 0 97 ga adakitic rocks from northeastern jiangxi the timing of the sibao orogenesis is thus believed to be between 1 0 and 0 9 ga in its eastern segment it is noted that the sibao orogeny in south china is in general contemporaneous with some other early neoproterozoic 1 0 0 9 ga orogenic belts such as the eastern ghats belt of india and the rayner province in east antarctica indicating that the assembly of rodinia was not finally completed until 0 9 ga

a fluid inclusion study of the porphyry greisen tungsten molybdenum deposit at mount pleasant new brunswick canada homogenization temperatures and salinity data are presented for fluid inclusions from hydrothermal gangue minerals quartz and fluorite associated with porphyry wolframite molybdenite arsenopyrite sphaleritebismuth chalcopyrite cassiterite mineralization within the fire tower ore zone mt pleasant new brunswick the data indicate that ore mineral precipitation occurred within a temperature range of 260 to 490 c from moderate to high salinity 10 42 wt nacl equivalent aqueous fluids two stages of hydrothermal activity characterized by high 30 wt nacl equivalent salinity fluids are recognized one which occurred at relatively high temperature 350 490 c and one which took place at lower temperature 180 250 c the high salinity high temperature stage is interpreted to be the result of resurgent boiling dilution of these early fluids by convecting meteoric water resulted in low to moderate salinity fluids which dominate the inclusion population the low temperature high salinity fluid inclusions are interpreted to represent late residual fluids derived from boiling which occurred as a result of a change in the pressure regime from dominantly lithostatic to hydrostatic conditions

sedimentation fracturing and sliding on a pelagic plateau margin the middle jurassic to lower cretaceous succession of rocca busambra western sicily italy the jurassic succession of rocca busambra consists of two lithostratigraphic units a pile of peritidal limestones several hundreds of metres thick inici formation hettangian to sinemurian and a 2 to 15 m thick sequence of rosso ammonitico type pelagic limestones toarcian to lowermost berriasian an extensive interval of non deposition is evidenced by a thick fe mn oxide crust on the bounding disconformity and is recorded partially in the material contained within a complex network of neptunian dykes and sills seven lithofacies are distinguished in the rosso ammonitico these lithofacies show that the rosso ammonitico limestones differ from most analogues both in sicily and elsewhere sediments are mostly grain supported and non nodular obviously bottom currents were important during deposition of these sediments these currents were pulsating at different frequencies and induced winnowing intraclast production and early cement precipitation other rosso ammonitico lithosomes of late jurassic to earliest cretaceous age usually decimetre thick and discontinuous overlie the inici formation without any fe mn crust their anomalous stratigraphical and geometrical relationships show that they were deposited on an inclined stepped erosional surface incised in the sub horizontal inici formation this ancient escarpment is interpreted as the result of a mainly gravitational collapse of the margin of a pelagic plateau such mass wasting was probably due to the backstepping of the tectonic plateau basin margin that is not observable directly but may be inferred from circumstantial evidence this observation clearly shows that tectonic activity affected the rocca busambra sector of the west tethys continental margins a few tens of millions of years after the end of the rifting stage the anomalous rosso ammonitico sediments are the only indication of the escarpment and their occurrence in the stratigraphic record is probably more widespread than reported in the literature more accurate palaeoenvironmental and palaeogeographic reconstructions may depend on the identification of these sediments

the logtung large tonnage low grade w scheelite mo porphyry deposit south central yukon territory mineralization is related to multiple felsic intrusions since mineralization is contained in fractures 95 rather than being disseminated logtung is not a skarn deposit the principal reason is that the reaction skarn host rocks which were derived from calcareous shales interbedded with graphitic quartzites are carbonate poor and competent hence permeable mineralization formed in permeability created by hydraulic fracturing and not by replacement logtung shows a scheme of several phases 4 of mineralization related to multiple intrusions which is similar to that which is so important in for example the evolution of the climax and urad henderson mo systems the logtung deposit shows many similarities to porphyry mo deposits in the western cordillera and may be classed as a porphyry w scheelite mo deposit with a w mo ratio of 3 3 1 0 the principal reasons are that mineralization is spatially associated with porphyritic intrusive phases and that much of the mineralization occurs as typical porphyry style crackle breccias modified journal abstract

some new data on the genesis of the linghou cu pb zn polymetallic deposit based on the study of fluid inclusions and c h o s pb isotopes abstract the linghou deposit located near hangzhou city of zhejiang province eastern china is a medium sized polymetallic sulfide deposit associated with granitic intrusion this deposit is structurally and lithologically controlled and commonly characterized by ore veins or irregular ore lenses in this deposit two mineralization events were identified of which the former produced the cu au ag orebodies while the latter formed pb zn cu orebodies silicification and calc silicate skarn type phyllic and carbonate alternation are four principal types of hydrothermal alteration the early cu au ag and late pb zn cu mineralizations are characterized by quartz sericite pyrite chalcopyrite bornite au ag minerals magnetite molybdenite and calcite dolomite sphalerite pyrite chalcopyrite galena respectively calcite clusters and calcite quartz vein are formed during the late hydrothermal stage the nacl h 2 o co 2 system fluid coexisting with nacl h 2 o system fluid and showing the similar homogenization temperatures 385 c and 356 c respectively and different salinities 16 89 21 68 wt nacl eqv and 7 70 15 53 wt nacl eqv suggests that fluid immiscibility occurred during the cu au ag mineralization stage and might have given rise to the ore metal precipitation the ore forming fluid of the pb zn cu mineralization mainly belongs to the nacl h 2 o co 2 system of high temperature 401 c and mid high salinity 10 79 wt nacl eqv fluids trapped in the quartz chalcopyrite vein cu au ag ores pb zn cu ores and calcite clusters yielded 18 o h2o and d values varying from 5 54 to 13 11 and from 71 8 to 105 1 respectively indicating that magmatic fluids may have played an important role in two mineralization events the 13 c pdb values of the calcite change from 2 78 to 4 63 indicating that the co 3 2 or co 2 in the ore forming fluid of the pb zn cu mineralization was mainly sourced from the magmatic system although dissolution of minor marine carbonate may have also occurred during the ore forming processes the sulfide minerals have homogeneous lead isotopic compositions with 206 pb 204 pb ranging from 17 958 to 18 587 207 pb 204 pb ranging from 15 549 to 15 701 and 208 pb 204 pb ranging from 37 976 to 39 052 indicating that metallic elements of the linghou deposit came from a mixed source involving mantle and crustal components based on geological evidence fluid inclusions and h o c s pb isotopic data the linghou polymetallic deposit is interpreted as a high temperature skarn carbonate replacement type two types of mineralization are both related to the magmatic hydrothermal system with the cu au ag mineralization having a close relationship with granodiorite

a late paleozoic sill complex and related paleo topography in the eastern north sea analyzed using 3d seismic data abstract in this paper we utilize large igneous intrusions as a key to a detailed analysis and understanding of the late paleozoic evolution of the ringkobing fyn high an important structural element in the north west european craton the study takes advantage of high quality 3d seismic data and boreholes to map the geometry and lateral distribution of intrusive sills cross cutting the sedimentary strata at a low angle transgressive sills our analysis shows that the transgressive sills most likely sourced the vast extrusion of volcanics which covered most of the early permian northern basin and which is associated to the skagerak centered large igneous province sclip furthermore a geometrical analysis of the sills demonstrates that the magmatic source for the sills was located se of the studied area suggesting a correlation with geophysically inferred lower crust intrusions hence we are in this study able to constrain the full magmatic system from the lower crust intrusions to the surface volcanics intrusion of the sills occurred prior to an early permian faulting event which created rotated fault blocks outlining the present ringkobing fyn high the sills exposed for erosion at the crest of the footwall in turn controlled the late permian paleo topography and the distribution of the zechstein evaporites due to the fact that they are harder to erode hence we are able to demonstrate a topography controlled thickness variation of the zechstein evaporites the study furthermore emphasizes that an understanding of the deepest parts of the north sea basin is crucial when evaluating the potential for yet unrecognized hydrocarbon plays

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

triassic pelagic deposits of timor palaeogeographic and sea level implications abstract in west timor triassic deposits are found in the parautochthonous complex as well as in the allochthonous series of sonnebait a detailed biostratigraphic investigation integrating field observations and facies analysis allowed the reconstruction of a synthetic lithostratigraphic succession for the upper triassic a stratigraphic transition from carnian shales to upper norian rhaetian limestones is also shown by this study the fossil content predominantly originates from an open marine environment lithostratigraphic units a e are dated on the basis of radiolaria and palynomorphs and unit h on ammonites and conodonts the presence of pelagic bioclasts together with normal grading horizontal laminations and current ripples is indicative of a distal slope to basin environment the ammonite rich condensed limestone of unit h was deposited on a pelagic carbonate plateau exposed to storms and currents the organic facies have been used as criteria for biostratigraphy palaeoenvironmental interpretation and sequence stratigraphy the palaeontological analysis of the triassic succession of west timor is based on the investigation of radiolaria and palynomorphs in the marls and limestones of units a e and also on ammonites and conodonts in the condensed limestone of unit h units a and b are carnian cordevolian in age based on the occurrence of the palynomorph camerosporites secatus associated with lueckisporites cf singhii vallasporites ignacii patinosporites densus and partitisporites novimundanus unit c is considered as norian on the basis of a relatively high percentage of gliscopollis meyeriana and granuloperculatipollis rudis unit d contains significant palynomorphs and radiolaria the organic facies characterized by marine elements is dominated by the norian dinocysts heibergella salebrosacea and heibergella aculeata the radiolaria confirm the norian age they range from the lowermost norian to the lower upper norian unit e also contains radiolaria associated in the upper part with the well known marker of the upper norian monotis salinaria for unit e the radiolaria attest to a lower to upper norian age based on the occurrence of capnodoce and abundant capnuchosphaera the upper part is upper norian to rhaetian based on the presence of livarella valida finally the blocks of condensed limestone with ammonites and conodonts of unit h allowed the reconstruction of a synthetic stratigraphic succession of upper carnian to upper norian age our stratigraphic data lead to the suggestion that the allochthonous complex classically interpreted as a tectonic melange of the accretionary prism of the island arc of banda is a tectonically dismembered part of a triassic lithostratigraphic succession

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

metallogeny of copper and iron deposits in the eastern yangtse craton east central china abstract the eastern yangtse craton of central to eastern china is an important fe cu metallogenic province based on studies of the regional geology and tectonic evolution this metallogenic belt is controlled by faults and aulacogens in the continental plate in the early yanshan epoch jurassic the dominant west northwest and east west lithospheric faults controlled the distribution of cu mo and au mineralization whereas in the late yanshan epoch cretaceous the north northeast and northeast lithospheric faults controlled cu fe mineralization in a mineral district the distribution of ore fields is under the dual control of basement fault s and near surface fault s based on the relation of ring and lineament faults to intrusions a three level model of vertical zonation is proposed systematic petrochemical studies of mesozoic igneous rocks and mineralization identify three subseries 1 a calc alkaline intermediate to silicic subseries rich in potassium 2 a calc alkaline intermediate to felsic subseries rich in sodium and 3 a calc alkaline intermediate to mafic subseries rich in sodium genetic types of ore deposits are diverse including fe and cu skarns cu porphyries fe ore magma injections ningwu luzong fe deposits from late orthomagmatic to pegmatitic pneumato hydrothermal and to mesothermal epithermal associated with subvolcanic rocks and remobilized sedimentary fe and or cu deposits the genetic types of ore deposits form two metallogenic series 1 a sedimentary metallogenic series active mainly in the paleozoic and 2 a magmatic hydrothermal metallogenic series consisting of three subseries active predominantly in the jurassic and cretaceous with the latter being more important in this region the superposition and compounding of these two metallogenic series contribute to many styles of mineralization in this mineral province

nature and evolution of middle triassic carbonate buildups in the dolomites italy during the middle triassic an evolution from carbonate bank to buildup highly elevated in respect of the adjacent basins is observed in the alps the dolomites in the southern alps italy are here considered as an example during the anisian subtidal banks of the upper serla fm with rare peritidal cycles show only a limited biologic density and diversity with the late anisian contrin fm a gradual development of binding and framework building communities can be observed the sinking of wide areas of the contrin carbonate bank into anoxic conditions plattenkalke fm allowed the birth of isolated buildups their increased carbonate production due to a greater diversity and density of organisms was able to keep up with the rate of subsidence the latemar buildup with additional data for the slope taken from mt coldai civetta and sass da putia is used to illustrate the main character of a lower ladinian buildup the restricted platform sediments display peritidal cycles prevalent in the subtidal portion is dasycladacean packstone grainstone associated with gastropods ammonoids and blue green algae in the supratidal portion desiccation and tepee structures are present scleractinian and sphinctozoan frameworks are rare on the upper part of the slope which is bound predominantly by encrusting organisms mainly blue green algae porifers and tubiphytes the prevailing sediments on the upper part of the slope are bindstones whilst packstones and rudstones are in the lower part of the slope the latter carbonates were cemented early under submarine conditions mostly by isopachous palisade cement polyphasic internal sediments with phreatic vadose influence are present and can in the middle lower part of the slope replace most of the original sediment

comment and reply on s type granites and their probable absence in southwestern north america the problem of muscovite in granites is also raised by dickson muscovite is common in felsic s type granites as stated by chappell and white 1974 but how much is primary and how much is secondary are debatable we currently think that very little is primary above the solidus we are not arguing that muscovite whether primary or secondary garnet and andalusite are not found in s types we are arguing that these minerals may also be found in some i types dickson is quite correct in saying that replacement of cordierite by micas results from hydration which may also affect the alkali aluminum ratio of the rock however he is not necessarily correct in his assertion that water must be introduced into the system it may be magmatic water released from the magma near the solidus during cooling and crystallization more systematic goechemical and isotopic work is required on petrographically well documented granite suites before this question is resolved

geochronology and geochemistry of granitoids related to the giant dahutang tungsten deposit middle yangtze river region china implications for petrogenesis geodynamic setting and mineralization abstract porphyry and skarn deposits in the middle yangtze valley within the northern yangtze craton have a combined tungsten resource of 3 million tonnes mt and represent one of the most important tungsten regions in the world the dahutang porphyry tungsten deposit with reserves of 1 mt is one of the largest deposits uranium pb analyses for the ore related granitoids yield ages of 147 4 0 58 ma 148 3 1 9 ma for porphyritic biotite granite 144 7 0 47 ma 146 1 0 64 ma for fine grained granite and 143 0 0 76 ma 143 1 1 2 ma for granite porphyry a progressive youngling of ages that is consistent with field observations geochemical data show that the three types of granite are characterized by enrichments in rb pb and u and depletion in ba nb p and ti with asi molar al 2 o 3 cao na 2 o k 2 o 1 1 that is characteristic of a peraluminous melt the p 2 o 5 contents of the granites are 0 13 0 37 and have a positive correlation with sio 2 and they are thus s type intrusions they exhibit initial 87 sr 86 sr of 0 721 to 0 731 and e nd t of 5 06 to 7 99 for porphyritic biotite granite 0 7196 to 0 7289 and 6 29 to 6 74 for fine grained granite and 0 7153 to 0 7365 and 5 09 to 7 64 for granite porphyry chondrite normalized rare earth element ree patterns for the granites are characterized by enrichment in the light ree and a strong negative eu anomaly indicating that they were derived from the proterozoic pelitic and psammitic basement strata and experienced strong fractional crystallization of plagioclase our ca 150 140 ma age for the dahutang s type magmatism and w mineralization is identical to that of the i type magmatism related to cu au mo fe bearing porphyry and skarn deposits along the middle to lower yangtze river valley we propose that the latest jurassic to earliest cretaceous granitoids and ores formed during a tearing of the subducting izanagi slab which caused the upwelling of asthenosphere and resulting mantle crust interaction the s type granitoids and related w ore systems resulted from the re melting of the proterozoic crust whereas the i type granitic rocks and related ores are attributed to the partial melting of the subducted slab

anatomy of a modern open ocean carbonate slope northern little bahama bank the open ocean carbonate slope north of little bahama bank consists of a relatively steep 4 upper slope between water depths of 200 and 900 m and a more gentle 1 2 lower slope between depths of 900 and 1300 m the upper slope is dissected by numerous small submarine canyons 50 150 m in relief that act as a line source for the downslope transport of coarse grained carbonate debris the lower slope is devoid of any well defined canyons but does contain numerous small 1 5 m hummocks of uncertain origin and numerous larger 5 40 m patchily distributed ahermatypic coral mounds sediments along the upper slope have prograded seaward during the cenozoic as a slope front fill seismic facies of fine grained peri platform ooze surface sediments show lateral gradation of both grain size and carbonate mineralogy with the fine fraction derived largely from the adjacent shallow water platform near surface sedimentary facies along the upper slope display a gradual downslope decrease in the degree of submarine cementation from well lithified hardgrounds to patchily cemented nodular ooze to unlithified peri platform ooze controlled by lateral variations in diagenetic potential and or winnowing by bottom currents submarine cementation stabilizes the upper part of the slope allowing upbuilding of the platform margin and controls the distribution of submarine slides as well as the headward extent of submarine canyons where unlithified sediments are heavily bioturbated and are locally undergoing dolomitization upper slope sediments are also conditioned eustatically resulting in vertical cyclic sequences of diagenetically unstable aragonite and magnesian calcite rich and stable calcite rich carbonates that may explain the well bedded nature of ancient peri platform ooze sequences lower slope sediments have prograded seaward during the cenozoic as a chaotic fill seismic facies of coarse grained carbonate turbidites and debris flow deposits with subordinate amounts of peri platform ooze coarse clasts are internally derived from fine grained upper slope sediments via incipient cementation submarine sliding and the generation of sediment gravity flows gravity flows bypass the upper slope via a multitude of canyons and are deposited along the lower slope as a wedge shaped apron of debris parallel to the adjacent shelf edge consisting of a complex spatial arrangement of localized turbidites and debris flow deposits a proximal apron facies of thick mud supported debris flow deposits plus thick coarse grained ta turbidites grades seaward into a distal apron facies of thinner grain supported debris flow deposits and thinner finer grained ta b turbidites with increasing proportions of peri platform ooze both the geomorphology and sedimentary facies relationships of the carbonate apron north of little bahama bank differ significantly from the classic submarine fan model as such a carbonate apron model offers an alternative to the fan model for palaeoenvironmental analysis of ancient open ocean carbonate slope sequences

the break up of east gondwana along the northeast coast of oman evidence from the batain basin recent detailed studies on the batain nappes northeast coast of oman which represent a special part of the so called oman exotics have led to a better understanding of the neotethyan geodynamic evolution the batain exotics bear witness to volcanic activity sea level changes tectonic instability rifting and oceanization along the eastern oman margin during late palaeozoic and mesozoic times they allow definition of the batain basin as an aborted permian branch of neotethys this marine basin was created in early permian times extending southward to the east african madagascar region and was linked to the karoo rift system the presented revised classification of the batain nappes considers the batain basin to be no longer a part of the hawasina basin and the neotethyan margin proper we attribute the batain basin to a mozambique somali masirah rift system somoma this system started in early permian times creating a marine basin between arabia and india madagascar rifting in the late triassic and oceanization during late jurassic times led to the separation of east gondwana

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

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

petrogenesis geochronology and tectonic significance of granitoids in the tongshan intrusion anhui province middle lower yangtze river valley eastern china abstract the tongshan copper deposit in anhui province is a typical mid sized skarn and porphyry type deposit in the anqing guichi district along the middle lower yangtze river valley eastern china the tongshan intrusion is closely related to this mineralization the intrusion mainly comprises rocks that are quartz diorite porphyry quartz monzonite porphyry and granodiorite porphyry plagioclase in these rocks is mostly andesine an 31 0 42 9 along with minor oligoclase biotite is magnesium rich mg mg fe 0 52 0 67 and aluminum poor al 2 o 3 12 32 14 09 wt and can be classified as magnesio biotite hornblende is tio 2 poor 0 60 and is magnesio hornblende or edenite the shrimp zircon u pb age of the quartz monzonite porphyry is 145 1 1 2 ma which corresponds to the middle yanshanian period whole rock geochemical results show that the rocks are silica rich sio 2 60 23 66 23 wt and alkali rich k 2 o na 2 o 4 97 8 72 wt and low in calcium cao 2 61 5 66 wt trace element results show enrichments in large ion lithophile element e g k rb and ba and depletions in some high field strength elements e g nb ta p and ti the total rare earth element ree content of the rocks is low ree n 10 and small positive eu anomalies average eu 1 16 these mineralogical geochronological and geochemical results show that the intrusion has a mixed crust mantle source the tongshan intrusion was formed by multiple emplacements of crustally contaminated basaltic magma generated by varying degrees of partial melting of enriched lithospheric mantle and lower crust hornblende thermobarometry yielded magmatic crystallization temperatures of 652 788 c and an average crystallization pressure of 1 4 kbar which corresponds to a depth of approx 4 7 km biotite thermobarometry yielded similar temperatures and lower pressures of 735 775 c and 0 6 kbar depth 2 1 km respectively the parental magma had a high oxygen fugacity and was produced in a volcanic arc setting related to subduction of the paleo pacific plate

molybdenite re os dating zircon u pb age and geochemistry of granitoids in the yangchuling porphyry w mo deposit jiangnan tungsten ore belt china implications for petrogenesis mineralization and geodynamic setting abstract the yangchuling w mo deposit located in the jiangnan porphyry skarn jnb tungsten ore belt is the first recognized typical porphyry w mo deposit in china in the 1980 s stockworks and disseminated w mo mineralization occur in the roof pendant of a 0 3 km 2 monzogranitic porphyry stock that intruded into a granodiorite stock hosted by neoproterozoic phyllite and slate la icpms zircon u pb analyses suggest that of the monzogranitic porphyry and granodiorite were formed at 143 8 0 5 ma and 149 8 0 6 ma respectively six molybdenite samples yielded a re os weighted mean age of 146 4 1 0 ma geochemical data show that both granodiorite and monzogranitic porphyry are characterized by enrichment of large ion lithophile elements lile relative to high field strength elements hfse indicating a peraluminous nature a cnk 1 01 1 08 two granitoids are characterized by a negative slope with significant light ree heavy ree fractionation la yb n 8 38 23 20 and negative eu anomalies eu eu 0 69 0 76 the p 2 o 5 contents of the yangchuling granitoids range from 0 12 to 0 17 and exhibit a negative correlation with sio 2 reflecting that they are highly fractionated i type they have high initial 87 sr 86 sr ratios 0 7104 0 7116 low negative e nd t 5 05 to 5 67 and homogeneous e hf t between 1 39 and 2 17 indicating similar sources additionally two stage nd model ages t dm2 of 1 3 1 4 ga and two stage hf model ages t dm2 of 1 2 1 3 ga are consistent indicating that neoproterozoic crustal rocks of the shuangqiaoshan group could have contributed to form the yangchuling magmas considering the two groups of parallel late mesozoic ore belts namely the jiangnan porphyry skarn tungsten belt jnb in the south and the middle lower yangtze river porphyry skarn cu au mo fe ore belt yrb in the north the nanling granite related w sn ore belt nlb in the south the neighboring qin hang porphyry skarn cu mo hydrothermal pb zn ag ore belt qhb in the north as well as the southeastern coast porphyry skarn cu mo au ore belt scb recognized in south china in this paper we propose that the latest jurassic to earliest cretaceous granitoids and associated ores were formed during a tearing of the subducting izanagi slab this tearing of the subduction slab caused the upwelling of asthenosphere and the resulting mantle crust interaction the granitoid related w ore systems in jnb resulted from the remelting of the proterozoic crust the mafic ultramafic volcanic rocks of the shuangqiaoshan group intercalated with phyllite and slate ophiolitic melange and magmatic arc rocks mainly comprising i type granite basalt andesite rhyolite pyroclastics together with subduction related metasomatized lithospheric mantle would have provided additional mantle material in this case the partial melting of rocks of the shuangqiaoshan group can produce s i and transitional type granitoids after strong differentiation it formed tungsten bearing granitoids characterized by enrichment of high alkali silicon and volatile components in the yangchuling mine area the small monzogranitic porphyry stock has stronger fractionation volatile content and ore forming components than the older granodiorite resulting in the development of the porphyry w mo ore system

deposition and compaction of carbonate clinothems the silurian pipe creek junior complex of east central indiana many of the larger silurian mounds throughout the midwestern united states consist predominantly of thinly bedded carbonate units inclined at angles as great as 45 because these values exceed those for reasonable estimates of angles of repose two opposing end member models for their origin have been suggested the ramifications of which affect evaluation of carbonate sources and modes of deposition one implies that steeply sloping units exhibit primary inclinations are composed largely of autochthonous carbonate debris held in place by benthic organisms and or synsedimentary cement and that deposition took place in relatively deep low energy marine settings the other holds that present steep slopes are the result of differential compaction that most carbonate is allochthonous and that deposition took place in relatively shallow high energy marine environments the pipe creek junior quarry in east central indiana exposes as much as 45 m of such clinothems paleomagnetic signatures inclinations of geopetal cavity fillings and the density and geometry of vertical extension fractures which transect inclined units record 13 of postdepositional steepening restoration of inclined units to their initial slopes requires initial depositional inclinations of no more than 32 postdepositional compaction at pipe creek junior was increasingly important in finer grained downslope lithofacies grainstone units shortened 3 grainstone mudstone units shortened 30 and mudstone units shortened 58 compaction mechanisms however varied in different lithofacies dewatering resulted in 50 compaction of mudstone and 13 compaction of grainstone mudstone units pressure solution although less important than dewatering was most intense in grainstone mudstone lithofacies where shortening was at least 17 dissolution thinned mudstone and grainstone units 8 and 3 respectively data on unit rotation and unit shortening require that axes of flank bed rotation correspond approximately to the position of the present quarry rim suggesting that only minor amounts of silurian section have been removed during devonian and pleistocene erosion these relations in conjunction with data on over all complex geometry and flank bed lithologic features indicate that the pipe creek junior complex is not truly reefal in that it consists almost entirely of allochthonous biotic debris derived from horizontal wave swept bench surfaces and deposited on laterally prograding bench margin slopes at angles of repose other large midwestern silurian carbonate buildups may have formed in similar settings

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

phosphate stromatolites from condensed cephalopod limestones upper jurassic southern spain upper jurassic phosphate stromatolites of the almola sierra southern spain encrust macrofossils and hardgrounds and form oncoids included within pelagic condensed fossiliferous limestones their accretion was determined by bacterially mediated precipitation of phosphate by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera phosphorous trace elements and rare earth elements were concentrated from degraded organic matter and seawater by stromatolite building communities which mediated the formation of phosphate rich and fe al si rich organic gels under oxic conditions favouring the precipitation of amorphous mineral precursors acp and fe al si oxyhydroxides the observed ce enrichment for some stromatolites is explained by oxidative scavenging of ce4 from seawater by fe mn oxyhydroxides the bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure and later changed to carbonate fluorapatite haematite and poorly crystalline fe rich clays under postoxic conditions phosphatization of trapped carbonate particles also occurred the phosphate stromatolites formed on a sediment starved pelagic swell during periods of no carbonate sedimentation and hardground development stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis sedimentation and erosion suggesting episodic changes in the sedimentary environment although some of the parameters that controlled phosphate precipitation associated with the stromatolites local high organic productivity sediment starvation moderate depth of deposition and physicochemical conditions were similar to those found in modern and ancient phosphogenic settings the palaeogeographical framework and the intensity of sedimentary processes were different to those of the world s major phosphorite deposits