tectonic setting of synorogenic gold deposits of the pacific rim abstract more than 420 million oz of gold were concentrated in circum pacific synorogenic quartz lodes mainly during two periods of continental growth one along the gondwanan margin in the palaeozoic and the other in the northern pacific basin between 170 and 50 ma these ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary rock dominant terranes the auriferous veins contain only a few percent sulphide minerals have gold silver ratios typically greater than 1 1 show a distinct association with medium grade metamorphic rocks and may be associated with large scale fault zones ore fluids are consistently of low salinity and are co2 rich in the early and middle palaeozoic in the southern pacific basin a single immense turbidite sequence was added to the eastern margin of gondwanaland deformation of these rocks in southeastern australia was accompanied by deposition of at least 80 million oz of gold in the victorian sector of the lachlan fold belt mainly during the middle and late devonian lesser devonian gold accumulations characterized the more northerly parts of the gondwanan margin within the hodgkinson broken river and thomson fold belts additional lodes were emplaced in this flyschoid sequence in devonian or earlier palaeozoic times in what is now the buller terrane westland new zealand minor post devonian growth of gondwanaland included terrane collision and formation of gold bearing veins in the permian in australia s new england fold belt and in the jurassic early cretaceous in new zealand s otago schists collision and accretion of dozens of terranes for a 100 m y long period against the western margin of north america and eastern margin of eurasia led to widespread latest jurassic to eocene gold veining in the northern pacific basin in the former location late jurassic and early cretaceous veins and related placer deposits along the western margin of the sierra nevada batholith have yielded more than 100 million oz of gold additional significant ore forming events during the development of north america s cordilleran orogen included those in the klamath mountains region california in the late jurassic and early cretaceous the klondike district yukon by the early cretaceous the nome and fairbanks districts alaska and the bridge river district british columbia in the middle cretaceous and the juneau gold belt alaska in the eocene gold bearing veins deposited during the late jurassic and early cretaceous terrane collision that formed the present day russian far east have been the source for more than 130 million oz of placer gold the abundance of gold bearing quartz carbonate veins throughout the gondwanan north american and eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata the common temporal association between gold veining and magmatism around the pacific rim reflects these thermal episodes melting of the lower thickened crust during arc formation slab rollback and extensional tectonism and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore forming processes

evolution of methane sorption capacity of coal seams as a function of burial history a case study from the campine basin ne belgium based on extensive data sets of high pressure sorption isotherms and canister desorption data from two central european coal basins campine and ruhr basins a computational scheme has been developed to calculate the maximum coal bed methane cbm sorption capacity of coal seams as a function of pressure temperature and coal rank in addition the effects of in situ moisture content and maceral composition have been tentatively implemented using this algorithm it is possible to explicitly take into account variations in sorption capacity of the coal seams in sedimentary basins over geologic time as a function of burial history and thermal evolution the procedure has been applied to model the evolution and the present day coal bed methane content of the campine basin ne belgium it is demonstrated how the present day gas content of the campine basin is controlled by the burial history of the coal layers throughout geologic time the maximum gas sorption capacity typically occurs at a depth range between 500 and 1000 m during periods of uplift and erosion 250 and 90 ma before present the uppermost coal layers have lost methane due to a reduction of gas storage capacity while their storage capacity has increased during periods of burial 300 and 180 ma ago and present additionally the present day gas content is controlled by the gas generation history coal layers which have lost storage capacity during geologic time will stay undersaturated if not replenished by late stage e g microbial gas the gas content profile of test well kb206 in the ne campine basin established from canister desorption tests can be reproduced by assuming that undersaturation of the coals is due to erosion and re burial and that no significant gas generation e g microbial gas has taken place after the time of maximal burial isotopic data d 178 13c 59 indicate the presence of a small portion of microbial gas the absolute gas contents in this well are lower than the calculated maximum present day sorption capacity this may be due to an underestimation of the effect of water content on sorption capacity or result from degassing via nearby faults enforced by fluid circulation

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

changes of the lignite seam architecture a case study from polish lignite deposits abstract the architecture of a lignite seam is not only of great cognitive importance but it is also important for the planning and exploitation of lignite therefore this paper presents the factors that had or could have an impact on the deformation of lignite seams all the currently extracted lignite seams in poland of the early and middle miocene age have been considered their development as indicated by the thickness from a few to nearly 250 m was controlled by intensive subsidence during deposition of the peat reaching a maximum of more than 700 m most cases that are theoretically possible were supported by data from boreholes and observations in existing opencast mines both surfaces bounding the lignite seam that is bottom and roof were taken into account the following factors could impact on the formation of the bottom of the lignite seam the paleotopography before the development of peat mires and syn and post depositional tectonics on the other hand the roof of the lignite seam could be deformed by such geological processes as the post depositional tectonics post depositional erosion and compaction the causes of changes in the bottom of the lignite seam deformations are relatively easy to explain in contrast the causes of the roof of the lignite seam irregularities are still poorly understood in the latter case often overlooked or underestimated is the impact of compaction with maximum sizes ranging up to 450 m in fact the compaction of peat lignite often plays a major role in the folding of the roof of the lignite seam

world class ni cu pge deposits key factors in their genesis magmatic ni cu sulfide deposits form as the result of segregation and concentration of droplets of liquid sulfide from mafic or ultramafic magma and the partitioning of chalcophile elements into these from the silicate melt sulfide saturation of a magma is not enough in itself to produce an ore deposit the appropriate physical environment is required so that the sulfide liquid mixes with enough magma to become adequately enriched in chalcophile metals and then is concentrated in a restricted locality so that the resulting concentration is of ore grade the deposits of the noril sk region have developed within flat elongate bodies 15 2 0 2 km that intrude argillites evaporites and coal measures adjacent to a major trans crustal fault and immediately below the centre of a 3 5 km thick volcanic basin studies of the overlying basalts have shown that lavas forming a 500 m thick sequence within these have lost 75 of their cu and ni and more than 90 of their pge overlying basalts show a gradual recovery in their chalcophile element concentrations to reach normal values 500 m above the top of the highly depleted zone the ore bearing noril sk type intrusions correlate with those basalts above the depleted zone that contain normal levels of chalcophile elements the high proportion of sulfide 2 10 wt associated with the noril sk type intrusions the high pge content of the ores the extensive metamorphic aureole 100 400 m around the bodies and the heavy sulfur isotopic composition of the ores 8 12 34s are explicable if the ore bearing bodies are exit conduits from high level intrusions along which magma has flowed en route to extrude at surface the first magma to enter these intrusions reacted with much evaporitic sulfur at a low r value and thus gave rise to sulfides with low metal tenors successive flow of magma through the system progressively enriched the sulfides in the conduits losing progressively less of their chalcophile metals and thus accounting for the upward increase in metals in successive lava flows above the highly depleted flows the voisey s bay deposit lies partly within a 30 100 m thick sheet of troctolite interpreted as a feeder for the 1 334 ga voisey s bay intrusion and partly at the base of this intrusion where the feeder adjoins it studies of olivine compositions indicate that an early pulse of magma through the feeder and into the intrusion was ni depleted but that subsequent pulses were much less depleted trace element re os and s and o isotope data and mineralogical studies indicate that the magma pulses interacted with country gneiss probably principally in a deeper level intrusion extracting sio2 na2o k2o and possibly sulfur form the gneiss which accounts for the magma becoming sulfide saturated the jinchuan deposit of north central china occurs within a 6 km long dyke like body of peridotite the compositions of olivine within the dyke the igneous rocks themselves and the ore are all inconsistent with derivation of the body from ultramafic magma as originally supposed and indicate that the structure forms the keel of a much larger intrusion of magnesian basalt magma flow of magma into the intrusion has resulted in olivine and sulfide being retained where the keel was widening out into the intrusion the west australian komatiite related deposits occur in thermal erosional troughs which have developed due to the channelisation of magma flow and the resulting thermal erosion of underlying sediments and basalt by the hot komatiite magma the sediments are sulfide rich and may have contributed substantially to the sulfide of the ores the mineralisation in the duluth complex occurs in troctolitic intrusions along the western margin of the complex as a result of magma interacting with and extracting sulfur from the underlying graphite and sulfide bearing sediments no magma flow channels have been identified so far and the lack of magma flow subsequent to the development of sulfide immiscibility is regarded as the reason why these deposits are not of economic grade when most major ni cu sulfide deposits are compared they prove to have a number of features in common olivine rich magma proximity to a major crustal fault sulfide bearing country rocks chalcophile element depletion in related intrusive or extrusive rocks field and or geochemical evidence of interaction between the magma and the country rocks and the presence of or proximity to a magma conduit the features are thought to explain the three key requirements sulfide immiscibilty adequate mixing between sulfides and magma and localisation of the sulfides discussed and have important implications with respect to exploration

la icp ms zircon u pb dating trace element and hf isotope geochemistry of the heyu granite batholith eastern qinling central china implications for mesozoic tectono magmatic evolution article i nfo mesozoic granitoids are widespread in the southern margin of the north china craton and of particular geo logical interests because of their indication for lithospheric evolution and close association with porphyry mo mineralization in this contribution in situ la icp ms u pb hf isotope and trace element analyses of zircon crystals have been combined to constrain the emplacement time and petrogenesis of the heyu granitic bath olith which hosts the yuchiling porphyry mo system henan province china as inferred from field investiga tions the concentrically zoned heyu batholith mainly consists of four texturally distinguishable phases and displays a pattern of monotonically decreasing u pb age from 143 0 1 6 ma for phase 1 through 138 4 1 5 ma for phase 2 through to ca 135 ma for phase 3 and to 133 6 1 3 ma for the mo mineralized yuchiling granite porphyry phase 4 the ehf t values 27 7 to 3 4 and the two stage hf model ages 1403 to 2924 ma of zircon grains together with the ages of local strata suggest that the magmas forming the heyu batholith were dominantly sourced from the crust with input of a mantle component the higher ce ce ratios of the zircon crystals in the mineralized yuchiling porphyry compared to those in the mo barren phases suggests that fluids exsolved from oxidic magmas might be more favorable for mo enrichment a regional synthesis suggests that intensive lithospheric thinning in the southern margin of the north china craton should not be earlier than 130 ma

the stratigraphic distribution of inertinite abstract the paper presents the results of an investigation into the stratigraphic distribution of inertinite in humic coals ranging from the silurian to the neogene periods this range equals the time span during which both land plants and atmospheric oxygen evolved the survey is based on a literature study of inertinite in coals covering a variety of depositional environments and climates in all continents the inertinite percentages listed in this paper have been arranged in stratigraphic order they are the mean values based on mineral free whole coal compilations maceral compositions listed in the literature for individual subsections have been averaged to represent complete coal seams beds although this might not have been always possible due to some ambiguity in the published record moreover not all of the published and unpublished information could be used because of poor sample description obscure geographic origin or insufficient stratigraphic information the results show that there have been times in the geological past e g during the late permian in which coals were particularly rich in inertinite compared with other times e g during much of the late tertiary in which many coals contained very little inertinite occasionally such primary global trends were modulated by a diffuse distribution of inertinite percentages that correspond to differences in climate depositional settings e g active orogenic margins versus tectonically inactive shelf margins and other local or regional variations although various mechanisms for the generation of inertinite have been proposed in the past the overall pattern in its stratigraphic distribution supports the notion of incomplete combustion as the main source of inertinite in coal this points to secular variations in the atmospheric oxygen content as an explanation for the global changes in the inertinite distribution while differential subsidence and climatically influenced reaction rates governed regional and local variations in inertinite percentages

geochronology and petrogenesis of gray gneisses from the taihua complex at xiong er in the southern segment of the trans north china orogen implications for tectonic transformation in the early paleoproterozoic the taihua complex in the xiong er area along the southern segment of the trans north china orogen tnco consists of gray gneisses with minor amphibolites zircon u pb dating of the gray gneisses reveals at least two episodes of early paleoproterozoic magmatism 2 30 2 32 ga and 2 07 2 19 ga each with distinct geochemical features the tieluping ttg gneisses of the early suite have very low hree ybn 0 58 4 75 and y contents 2 05 13 2 ppm with moderate to high la yb n 14 3 192 6 and sr y ratios 38 5 220 1 pronounced negative ta nb and ti anomalies but positive sr and pb anomalies the protoliths of these gneisses were most likely derived from partial melting of thickened lower crust with residual garnet and amphibole and underwent garnet amphibole fractionation plagioclase accumulation and or fractionation the tieluping ttg gneisses have variable zircon hf model ages tdm hfc 2 48 3 06 ga and whole rock end t values 4 89 4 98 and the youngest whole rock depleted mantle nd model age tdm 2 32 ga is close to the crystallization age of the ttg 2318 8 ma the protolith of the gneisses formed from a combination of pre existing continental crust and juvenile materials implying an andean type continental margin arc environment it is suggested that crustal thickening was the result of accretionary orogenesis accompanied by basaltic underplating the ganshugou potassium rich gneisses of the later suite have low na2o and high k2o and show fractionated lree and nearly flat hree patterns with strong negative ta nb and ti anomalies they are characterized by negative end t values 5 01 to 2 33 and heterogeneous zircon ehf t values 10 65 2 10 with decoupling of zircon hf model ages tdm hfc 2 64 3 23 ga and whole rock nd model ages tdm 2 55 2 81 ga the protolith of the ganshugou gneisses was a potassium rich igneous rock which was likely the result of partial melting of pre existing crustal materials at shallow depth compatible with a post collisional setting there is therefore a tectonic transformation from an accretionary orogenesis to an extensional regime as a consequence of post collisional uplift in the southern segment of the tnco in the early paleoproterozoic

contrasting origins of late mesozoic adakitic granitoids from the northwestern jiaodong peninsula east china implications for crustal thickening to delamination two suites of granitoids the late jurassic 158 3 ma linglong suite and the early cretaceous 130 126 ma guojialing suite crop out in the northwestern jiaodong peninsula eastern china the linglong suite is a monzogranite comprising alkali feldspar plagioclase quartz and fe rich biotite the guojialing suite includes at least five plutonic bodies of both granodiorite and monzo granite the rocks are composed of plagioclase alkali feldspar quartz mg rich amphibole and mg rich biotite both the linglong and guojialing suites have adakitic affinity they are enriched in lree with high la yb ratios and show positive eu anomalies the rocks are also enriched in lile and depleted in hfse with high sr y ratios the linglong granite shows very uniform sr nd isotopic compositions with initial 87 sr 86 sr ratios of 0 7119 0 7126 and e nd t values of 21 3 to 21 6 which are similar to those of the local neoarchaean basement the guojialing suite has variable initial 87 sr 86 sr ratios 0 7108 0 7120 and e nd t values 10 8 to 17 2 which are distinct both from those of the neoarchaean basement and from those of the local enriched lithospheric mantle inferred from the coeval mafic dykes in the studied area detailed petrological and geochemical data indicate that the linglong suite was derived by partial melting of neoarchaean metamorphic lower crustal rocks at depth of 50 km with a eclogite residue whereas the guojialing suite was formed by the reaction of delaminated eclogitic crust derived melt with the upwelling asthenospheric mantle the petrogenesis of these two contrasting adakitic granitoids suggests intensive lower crustal delamination during early cretaceous times following a crustal thickening process from the late stage of the early jurassic to early stage of the late jurassic with crustal thickness of 50 km respectively

melting of enriched archean subcontinental lithospheric mantle evidence from the ca 1760ma volcanic rocks of the xiong er group southern margin of the north china craton abstract the xiong er group is an important geologic unit in the southern margin of the north china craton it is dominated by the volcanic rocks dated at 1763 15 ma that have sio2 contents ranging from 52 10 wt to 73 51 wt these volcanic rocks are sub alkaline and can be classified into three subgroups basaltic andesites andesites and rhyolites they unexceptionally show enrichment of light rare earth elements lree and share similar trace element patterns depletions in nb ta sr p and ti relative to the adjacent elements are evident for all the samples the volcanic rocks are evolved with low mgo contents 0 29 5 88 wt and accordingly low mg values of 11 53 the nd isotopes are enriched and show a weak variation with nd t 7 12 to 9 63 zircon hf isotopes are also enriched with hf t 12 02 0 45 the volcanic rocks of the xiong er group are interpreted to represent fractional crystallization of a common mantle source the volcanic rocks might have been generated by high degree partial melting of a lithospheric mantle that was originally modified by the oceanic subduction in the late archean this brings a correlation with the subduction modified lithospheric mantle in an extensional setting during breakup of the columbia supercontinent in the late paleoproterozoic rather than in an arc setting the elevated sio2 contents and evolved radiogenic isotope features indicate the possible incorporation into their source of lower crustal materials that have similar nd isotopic characteristics to the subcontinental lithospheric mantle the existence of extensive xiong er volcanic rocks 60 000 km2 indicates an early large scale subduction related metasomatism in the area and probably suggest a flat subduction model for the plate margin magmatism in the late archean

hf nd isotopic evolution of the lower crust we report hf isotopic data for over 50 well studied lower crustal samples from three proterozoic and phanerozoic regions in southwest europe eastern australia and southern mexico we use these data to characterize the lu hf isotopic composition of the lower crust and in combination with existing sm nd data to constrain coupled hf nd isotopic behavior and evolution within this reservoir although most of these samples have present day parent daughter p d ratios consistent with hf nd evolution within the terrestrial hf nd array some samples have divergent p d ratios that would evolve out of the terrestrial array in 1 ga or less the present day 176hf 177hf and 143nd 144nd isotopic compositions of all samples with one lone exception plot within the terrestrial array this indicates that 1 some present day p d ratios may be a relatively recently acquired characteristic through magmatic or metamorphic processes not related to the time integrated sm nd and lu hf ratios of their sources and or 2 the lu hf and sm nd p d variations exist on a small hand size scale but not necessarily on a larger scale the lower crust from this initial data set is broadly similar to the upper crust in terms of both its present day p d values and time integrated lu hf and sm nd evolution as a result the lower crust appears to have a hf and nd isotopic composition similar to that of all other crust and mantle reservoirs so far characterized

composition and origin of coalbed gases in the lower silesian basin southwest poland abstract coalbed gases in the lower silesian coal basin lscb of poland are highly variable in both their molecular and stable isotope compositions geochemical indices and stable isotope ratios vary within the following ranges hydrocarbon chc index chc ch4 c2h6 c3h8 from 1 1 to 5825 wet gas c2 index c2 c2h6 c3h8 c4h10 c5h12 ch4 c2h6 c3h8 c4h10 c5h12 100 from 0 0 to 48 3 co2 ch4 cdmi index cdmi co2 co2 ch4 100 from 0 1 to 99 9 13c ch4 from 66 1 to 24 6 d ch4 from 266 to 117 13c c2h6 from 27 8 to 22 8 and 13c co2 from 26 6 to 16 8 isotopic studies reveal the presence of 3 genetic types of natural gases thermogenic ch4 higher gaseous hydrocarbons and co2 endogenic co2 and microbial ch4 and co2 thermogenic gases resulted from coalification processes which were probably completed by late carboniferous and early permian time endogenic co2 migrated along the deep seated faults from upper mantle and or magma chambers minor volumes of microbial ch4 and co2 occur at shallow depths close to the abandoned mine workings late stage microbial processes have commenced in the upper cretaceous and are probably active at present however depth related isotopic fractionation which has resulted from physical and physicochemical e g diffusion and adsorption desorption processes during gas migration cannot be neglected the strongest rock and gas outbursts occur only in those parts of coal deposits of the lscb which are dominated by large amounts of endogenic co2

stable isotope geochemistry of coals humic kerogens and related natural gases isotope systematics are well defined for conventional sapropelic type i ii kerogens and their associated bacterial and thermogenic natural gas products these geochemical tools are used to estimate source type maturity and depositional environment and as a correlation technique in many cases the natural gas signatures in near surface samples and drill cuttings can be used to classify or predict a deeper lying source rock or reservoir corresponding interpretative schemes for coals type iii kerogens and their associated hydrocarbons are progressing quickly the shift in attention to humic sources is driven primarily by depletion of conventional oil and gas resources and the economic and societal requirements of coal and coal bed methane carbon hydrogen and nitrogen stable isotope variations can be large between different coals and humic kerogens these differences can often be recognized in their bulk 13corg dorg and 15norg values isotope signatures of coals can be diagnostic of several factors including deposit age type geographic location maturity and generation history however these characteristic isotopic variations are substantially better defined by the c h and n isotope ratios of the separate maceral groups such as vitrinite exinite and inertinite this new application of stable isotopes at the maceral and compound levels have great potential to improve the interpretative precision over conventional whole coal or bulk techniques hydrocarbon gases including coal gases derived from coals and humic kerogens can be distinguished from type i ii sources based on their molecular rations i e c1 c2 c3 and by comparing their stable isotope compositions especially 13cch4 and dch4 the 13cc2h6 can also be valuable but ethane is generally present in small amount 1 vol and requires

petrographic characteristics of lignite gasification chars abstract the article presents the petrographic characteristics of lignite subjected to fluidized bed gasification and the residues after the process the gasifying agents were air oxygen and carbon dioxide the petrographic composition of the lignite is dominated by huminite group with 81 7 vol share the inertinite group is 3 6 vol while the liptinite group amounts to 7 0 vol the mineral matter in the tested samples is 7 7 vol the gasification temperature was in the range of 850 950 c therefore the study focused mainly on the pyrolysis of coal the dominant particles in the residues after the gasification process include inertoid 35 5 vol and crassinetwork 31 6 vol the total amount of char with different kinds of pores arising as a result of degassing tenuisphere crassisphere tenuinetwork crassinetwork and mixed porous is 52 3 vol of all components the macerals from inertinite group do not change form during the gasification process the particles with thicker walls crassinetwork and intertoids represent approximately 70 vol are dominant such char composition is related to the chemical structure of coal during gasification process the macerals from liptinite group such as resinite release carboxyl groups increased porosity and swelling a similar phenomenon is observed in the case of textinite macerals of low porosity mainly ulminite do not substantially increase their porosity and take the inertoid form mineroids represent about 8 vol of char but the mineral matter is also associated with coal particles taking into account the efficiency of gasification process it should be noted that only a small percentage

mesozoic felsic arc magmatism and continental olivine tholeiites in zhejiang province and their relationship with the tectonic activity in southeastern china abstract the mesozoic geology of zhejiang province in southeastern china is characterized by two distinct geodynamic settings separated by a major tectonic event during the late jurassic early cretaceous a continental magmatic arc developed with a westward subduction of the kula or izanagi plate under the south china block during the development of this magmatic arc microsyenite porphyries and quartz bearing porphyries were emplaced in western zhejiang about 124 ma ago these porphyritic rocks intruded felsic tuffs that rest unconformably on carboniferous and permian folded strata geochemically they are enriched in lil and light rare earth elements lree which are features of acid shoshonitic suites isotopically they are characterized by negative nd t 124 5 3 to 4 7 values and high initial 87 sr 86 sr ratios 0 7079 0 7084 later in eastern zhejiang quartz phyric ignimbrites and subordinate acid andesites were emplaced and intruded by nearly contemporaneous microsyenitic and rhyolitic domes during the cretaceous about 97 ma ago all these rocks belong to the high k calc alkaline suites they show geochemical features of volcanic arc granites emplaced in an active continental margin and are characterized by negative nd t 97 8 8 to 7 1 and high initial sr isotopic ratios 0 7081 0 7089 the negative nd t 97 values of all the cretaceous calc alkaline and shoshonitic rocks of intermediate to acid composition suggest that these rocks were probably derived from a mantle wedge source contaminated by variable amounts of old crustal components likely represented by the proterozoic basement rocks of the south china block the contemporaneous igneous rocks in vietnam as well as in the fujian and guangdong provinces china represent the lateral counterparts of the zhejiang calc alkaline plutonic and volcanic rocks in the late early cretaceous an important tectonic event occurred which provoked the ending of the inagazi or kula plate subduction and affected the continental magmatic arc this tectonic event is likely related to the collision of the china indochina margin with the west philippine block after this tectonic event in the beginning of the late cretaceous continental stretching and crustal attenuation affected the south china block leading to the development of ne sw faulted basins in which continental olivine tholeiites and minor alkaline rhyolites were erupted both characterized by low nd t 97 ratios ca 4 meanwhile continental conglomerates and sandstones were also deposited this rifting process began likely before the india asia indentation and lasted at least until the late tertiary

petrologic studies of terrestrial organic matter in carpathian flysch sediments southern poland abstract in the carpathian flysch coal is present either as exotics of carboniferous coal deposits or as autochthonous thin layers of lustrous coal this paper present the results of the studies of coal bearing rocks that are coeval with the enclosing flysch sediments these coals form lenses up to 0 15 m thick their morphology precludes an exotic origin the main petrographic component is collinite with admixtures of poorly fluorescing telinite minor components are exudatinite sporinite fusinite micrinite and sclerotinite mineral matter consists of framboidal pyrite clay minerals and quartz the random reflectance of telocollinite varies from 0 38 to 0 72 which corresponds to subbituminous and bituminous ranks correlation between chemical analysis coking properties and relfectance measurements leads to the conclusion that boundary between subbituminous and bituminous coals should be defined by the following values c 80wt volatiles 43wt calorific value 32 3 mj kg and r o 0 56 0 57 atypical properties such as upper c value 75 80wt high volatile matter contents over 43wt and low random reflectance o about 0 38 0 57 in subbituminous coals low c value about 80 82wt low reflectance 0 56 0 72 and good coking properties of the bituminous coals are attributed to quick coalification during increasing temperature as a result of tectonic stress

petrogenesis and tectonic setting of volcanic rocks in the xiaoshan and waifangshan areas along the southern margin of the north china craton constraints from bulk rock geochemistry and sr nd isotopic composition abstract as part of the xiong er volcanic belt along the southern margin of the north china craton volcanic rocks in the xiaoshan and waifangshan areas have a compositional range from the basaltic andesite andesite dacite to rhyolite which display consistent variation trends in terms of their major and trace elements and sr nd isotopic compositions the variable yb contents with nearly constant la yb and tb yb ratios of volcanic rocks in two areas suggest that the fractional crystallization may have played an important role in the differentiation from the basaltic andesite through andesite and dacite to rhyolite the volcanic rocks in these two areas are characterized by the lile and lree enrichments and negative hfse anomalies implying hydrous melting of a mantle wedge in a subduction zone variable sr nd ratios of the basaltic andesite and andesite are interpreted as a result of the fluid addition from a subducting slab non radiogenic nd isotopic compositions as well as high zr y and nb y ratios suggest that the volcanic rocks in these areas were derived from an enriched mantle source on the other hand the volcanic rocks of the basaltic andesite and andesite possess markedly higher fe ti and hfse concentrations than those of typical intra oceanic arcs implying that the mantle source from which the volcanic rocks were derived was metasomatised by siliceous melts during the archean to paleoproterozoic subduction collision in the trans north china orogen these data suggest that in the paleo mesoproterozoic the southern margin of the north china craton was most likely an andean type continental arc in which slab dehydration not only induced the melting of a pre existing metasomatised mantle source but also released lile enriched fluids into the mantle source masking the inherent hfse enriched characteristics of the volcanic rocks along the southern margin of the craton the results of this study indicate that the north china craton like many other continental components e g north america greenland baltica amazonia australia etc of the supercontinent columbia nuna also underwent a subduction related outgrowth along its southern margin during the paleo mesoproterozoic time

lignite cleat studies from the first middle polish first lusatian lignite seam in central poland abstract some miocene lignite seams are characterized by the presence of natural discontinuities so called cleats most often they are opening mode fractures consisting of two orthogonal sets face and butt both almost perpendicular to the bedding this paper determines distributions of cleat orientation spacing and aperture from the first group of the middle polish first lusatian lignite seams mpls 1 which has been exploited inter alia in the jo win iib and kazimierz n opencast mines in central poland all observations and measurements were conducted at macroscopic scale the cleats mean orientations are ne sw and nw se dipping at a high angle 75 the first set of fractures refers to the face cleats and the second one to the butt cleats the spacing of face cleats is from 10 0 to 17 2 cm averaging 12 65 cm and the spacing of butt cleats is from 9 3 to 24 3 cm averaging 13 75 cm on the other hand aperture measurements of these cleats range from 0 2 to 1 9 cm averaging 0 68 cm and from 0 1 to 1 5 cm averaging 0 42 cm respectively the obtained results clearly indicate that face cleat orientations nw se are strictly parallel to the elongation of the main tectonic structures in the study area their origin may be explained in at least two ways that is by tectonic folding the maximum principal stress 1 was horizontal or by salt diapirism the maximum principal stress 1 was vertical in both cases the intermediate principal stress 2 was parallel to the face cleat strikes namely nw se although the well developed butt cleats in the context of regional geology provide additional evidence for the creation of an orthogonal system of fractures cleats in the cover of salt structures thus the nw se direction is characteristic of both the extent of the main tectonic units in central poland and the face cleat orientation in mpls 1

characterizing thermogenic coalbed gas from polish coals of different ranks by hydrous pyrolysis abstract to provide a better characterization of origin and volume of thermogenic gas generation from coals hydrous pyrolysis experiments were conducted at 360 c for 72 h on polish coals ranging in rank from lignite 0 3 r r to semi anthracite 2 0 r r under these conditions the lignites attained a medium volatile bituminous rank 1 5 r r high volatile bituminous coals attained a low volatile bituminous rank 1 7 r r and the semi anthracite obtained an anthracite rank 4 0 r r hydrous pyrolysis of a coal irrespective of rank provides a diagnostic 13 c value for its thermogenic hydrocarbon gases this value can be used quantitatively to interpret mixing of indigenous thermogenic gas with microbial methane or exogenous thermogenic gas from other sources thermogenic methane quantities range from 20 dm 3 kg of lignite 0 3 r r to 0 35 dm 3 kg of semi anthracite 2 0 r r at a vitrinite reflectance of 1 7 r r approximately 75 of the maximum potential for a coal to generate thermogenic methane has been expended at a vitrinite reflectance of 1 7 r r more than 90 of the maximum potential for a coal to generate co 2 has been expended assuming that these quantities of generated co 2 remain associated with a sourcing coal bed as uplift or erosion provide conditions conducive for microbial methanogenesis the resulting quantities of microbial methane generated by complete co 2 reduction can exceed the quantities of thermogenic methane generated from the same coal bed by a factor of 2 5

sorption of methane on lignite from polish deposits abstract coal samples from miocene lignite deposits ortholignite ece un 2002 in belchatow adamow konin and turow poland were analyzed to determine the relationships between coal properties and gas capacity investigations presented here addressed the occurrence of methane sorbet in lignite deposits within poland s largest penetrated lignite deposits e g belchatow adamow turow and konin lignite samples collected from surface mines were detritic coal with variable contents of xylites the highest level of xylites up to 25 vol was found in carbon samples taken from the belchatow deposit samples from other mines contained no more than 10 vol xylites petrographic compositions were dominated by huminite group macerals 73 88 vol with atrinite densinite and texto ulminite a porous form of ulminite inertinite groups were less important components 4 8 vol isotherms were determined for methane sorption at 298 k with test pressure ranges below 1 2 mpa at a pressure of 1 0 mpa the largest gas capacity of approximately 1 7 dm3 stp kg was found in the sample from belchatow this result may have been attributable to differences in the porosity of the samples the porosity of the sample from belchatow was twice as high as the porosities of the other coal samples this variation in porosity resulted from the lithologic and maceral composition of the coal sample that contained substantial quantities of porous textinite and texto ulminite the thermal sorption equation was used to determine the limiting values of isosteric enthalpy of sorption which suggested weak interactions between methane and the lignite matrix the residual gas capacity of the tested samples was also determined all samples exhibited a high residual methane bearing capacity which may not only cause methane to be released from coal at a pressure of 1 bar but also may pose a gas risk during mining operations

representation of basin scale in flood peak distributions a lognormal cascade model is developed for representing basin scale in flood peak distributions the model is developed from the multiplicative cascade modeling framework developed by gupta and waymire 1990 for spatial hydrologic processes the lognormal cascade model has a simple parameterization of basin scale that can represent either simple scaling or multiscaling processes likelihood based statistical inference procedures are developed for parameter estimation and hypothesis testing for the lognormal cascade model the lognormal cascade model is used to examine scale properties of annual flood peaks from 104 stations in the central appalachian region of maryland and virginia drainage area for the basins ranges from 0 3 square miles 0 78 km2 to nearly 10 000 square miles 26 100 km2 the empirical results suggest two hypotheses concerning scaling properties of central appalachian flood peaks 1 the multiscaling hypothesis holds over the entire range of scales for this hypothesis some anomalous properties of flood peaks in small basins must be dealt with and 2 scaling properties of rainfall and the channel floodplain system impose a peak in variability of flood magnitudes for basins with drainage area between 10 and 100 square miles between 26 and 260 km2

methane and carbon dioxide adsorption diffusion experiments on coal upscaling and modeling numerical modelling of the processes of co2 storage in coal and enhanced coalbed methane ecbm production requires information on the kinetics of adsorption and desorption processes in order to address this issue the sorption kinetics of co2 and ch4 were studied on a high volatile bituminous pennsylvanian upper carboniferous coal vrr 0 68 from the upper silesian basin of poland in the dry and moisture equilibrated states the experiments were conducted on six different grain size fractions ranging from 0 063 to f3 mm at temperatures of 45 and 32 jc using a volumetric experimental setup co2 sorption was consistently faster than ch4 sorption under all experimental conditions for moist coals sorption rates of both gases were reduced by a factor of more than 2 with respect to dry coals and the sorption rate was found to be positively correlated with temperature generally adsorption rates decreased with increasing grain size for all experimental conditions based on the experimental results simple bidisperse modelling approaches are proposed for the sorption kinetics of co2 and ch4 that may be readily implemented into reservoir simulators these approaches consider the combination of two first order reactions and provide in contrast to the unipore model a perfect fit of the experimental pressure decay curves the results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process half life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated further it was shown that an upscaling of the experimental and modelling results for co2 and ch4 can be achieved by performing experiments on different grain size fractions under the same experimental conditions in addition to the sorption kinetics sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions d 2004 elsevier b v all rights reserved

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

petrogenesis of the early cretaceous intermediate and felsic intrusions at the southern margin of the north china craton implications for crust mantle interaction abstract new major and trace element whole rock sr and nd isotopes and zircon u pb ages and hf isotope data are presented for rocks from the early cretaceous tianqiaogou dioritic and taishanmiao granitic plutons at the southern margin of the north china craton ncc in order to investigate their petrogenesis and geological evolution la icp ms u pb analyses for zircons from these two plutons yield similar 206 pb 238 u ages of 122 ma and 115 125 ma respectively monzodiorites from the tianqiaogou pluton have whole rock e nd t values ranging from 6 2 to 1 3 and zircon e hf t values from 2 9 to 6 2 they are variably enriched in ra ba and sr and depleted in nb ta zr hf and ti indicating that they were derived from a depleted mantle and underwent subsequent magma differentiation and crustal contamination the taishanmiao pluton is composed of metaluminous to peraluminous highly fractionated i type granites that have high sio 2 na 2 o k 2 o rb th and u and low p ba sr ti and eu contents the granites have strong negative whole rock e nd t values 16 1 to 7 5 and zircon e hf t values 20 9 to 6 1 their nd t dm ages 1 19 to 2 01 ga and zircon hf t c dm ages 1565 to 2490 ma are much younger than the basement rocks beneath the southern margin of the ncc suggesting derivation from an ancient crustal source with minor involvement of mantle derived components therefore rocks from the tianqiaogou dioritic pluton were partial melts of the mantle source underplating of the mafic magmas initiated partial melting of the ancient continental crust resulting in the formation of the taishanmiao granitic pluton their complex petrogenesis reflects a strong crust mantle interaction process related to lithospheric thinning beneath the southern margin of the ncc in early cretaceous

sequence of late jurassic early cretaceous magmatic hydrothermal events in the xiong ershan region central china an overview with new zircon u pb geochronology data on quartz porphyries recent investigations have revealed several large au and mo deposits in the xiong ershan region central china most quartz porphyries associated with the mineralization occur as dikes and apophyses or as rubbles cemented in mineralized breccia pipes three types of quartz porphyries were sampled from the leimengou mo deposit the qiyugou au deposit and the niutougou au deposit la icp ms zircon u pb analysis was performed in zircons from two quartz porphyries the results yielded ages of 125 4 0 77 ma for leimengou mo deposit and 150 1 1 1 ma for qiyugou au deposit the magma source of leimengou quartz porphyry is similar to that of the mineralized cementing material in breccia pipes of the qiyugou au deposit whereas the magma source of qiyugou quartz porphyry is the same as that of quartz porphyries in niutougou au deposit based on the new u pb isotopic ages of granitic plutons reported in this study together with the age data in the literature we identify distinct magmatic pulses in the xiong ershan region at ca 160 150 143 133 125 and 115 ma during the late jurassic early cretaceous the ages of au and mo mineralization coincide with the thermal events at about 115 125 133 and 143 ma are considered to be co eval with granitic magmatism no mineralization ages of 150 and 160 ma thermal events have been previously reported our study demonstrates late jurassic early cretaceous multiple magmatic pulses and mineralization in the xiong ershan region

on the effects of petrographic composition on coalbed methane sorption abstract the effect of petrographic composition on the methane sorption capacity has been determined for a suite of coals and organic rich shales subbituminous and bituminous coals were separated into bright and dull lithotypes by hand picking the methane sorption capacities range between 0 5 and 23 9 cm 3 g at a pressure of 6 mpa the low volatile bituminous canmore coal and the anthracite sample have the highest capacities with the natural coke having the lowest for low rank coals there is no significant difference between bright and dull samples except for one coal with the dull sample having a greater sorption capacity than its bright equivalent for higher rank coals the bright samples have a greater methane capacity than the dull samples and the difference between sample pairs increases with rank the boghead coal samples have the highest sorption capacities in the liptinite rich coals suite and are higher than subbituminous to medium volatile bituminous samples pore size distribution indicates that methane is held as solution gas in liptinite rich coals and by physical sorption in micropores in liptinite poor coals these contrasting processes illustrate that liptinite rich samples need to be independently assessed the positive relationship between reactive inertinite content and methane sorption capacity occurs within the subbituminous to medium volatile bituminous coals because the reactive inertinite is structurally similar to vitrinite and have a higher microporosity than non reactive inertinite reactivity of inertinite should be assessed in cbm studies of dull coals to provide a better understanding of petrographic composition effects on methane capacity

the shanggong gold deposit eastern qinling orogen china isotope geochemistry and implications for ore genesis abstract the shanggong au deposit in the xiong er terrane east qinling china has resources of about 30 ton au making it one of the largest orogenic mesothermal au deposits hosted in volcanic rocks of the mesoproterozoic xiong er group three stages of hydrothermal activity are recognized early middle and late of which two early and middle were ore producing and characterized by quartz pyrite and polymetallic sulfides respectively the third and late stage is represented by a carbonate quartz assemblage hydrogen oxygen and carbon isotope systematics of the shanggong deposit from a previous work suggest that the early stage fluids were derived from magmatic and or metamorphic devolatilization of sedimentary rocks at depth this is supported by new c s and published sr and pb isotopic data presented in this paper these new data 13c values ranging from 1 5 for early stage ankerite to 2 2 for late stage ankerite negative 34s values for sulfides from the middle stage 19 2 to 6 3 suggest a contribution from organic matter and that the ore fluid evolved from deeply sourced to shallowly sourced with those of the middle stage representing a mixture of these two fluid systems the comparison of the hydrogen oxygen carbon sulfur lead strontium isotope systematics between the shanggong deposit and the main lithologies in the xiong er terrane shows that neither these nor the underlying lower crust and mantle or combinations thereof could be considered as the source of ore fluids for the shanggong au deposit a likely source was a carbonaceous carbonate sandstone shale chert sequence in the underthrusted guandaokou and luanchuan groups exposed south of the xiong er terrane ar ar and rb sr isochron ages for mineral phases of the early middle and late stages together with geological field data constrain the timing of the hydrothermal activity and au metallogenesis at 242 10 167 7 and 112 7 ma respectively this metallogenesis and associated granitic magmatism can be related to the continental collision between the yangtze and north china cratons that resulted in the formation of the qinling orogen led to the different hydrothermal systems that were responsible for the three stages that formed the shanggong au deposit over a period of about 130 myrs

dehydration melting of a basaltic composition amphibolite at 1 5 and 2 0 gpa implications for the origin of adakites this study presents the results of dehydration melting experiments on a basaltic composition amphibolite under conditions appropriate to a hot slab geotherm 1 5 and 2 0 gpa and temperatures of 850 to 1150 c dehydration melting produces an omphacitic augite and garnet bearing residue coexisting with rhyolitic to andesitic composition melts at 1 5 gpa the amphibolite melts in two stages between 800 and 1025 c the 2 0 gpa data also define two melting stages at 2 0 gpa the first stage involves nearly modal melting of the original amphibolite minerals qtz pl amp to produce melt cpx grt during the second stage the eclogite restite melts non modally 0 86 cpx 0 14 grt 1 melt the experimental results were combined with data from the literature to generate a composite p t phase diagram for basaltic composition amphibolites over the 800 to 1100 c temperature range for pressures up to 2 0 gpa comparison of the major element compositions of the experimentally produced melts with compositions of presumed slab melts adakites shows that partial melting of amphibolite at conditions appropriate to a hot slab geotherm produces melts similar to andesitic and dacitic adakites except for significant mgo and cao depletions trace element modelling of amphibolite dehydration melting using the 2 0 gpa melting reactions produces ree abundances similar to those of adakites at 10 15 wt batch melting but the models do not reproduce the high sr y ratios characteristic of adakites taken together the major and trace element results are not consistent with the derivation of adakites by dehydration melting of the subducted slab with little or no interaction with the mantle wedge or crust if adakites are partial melts of the subducted slab they must undergo significant interaction with the mantle and or crust during which they acquire a number of their distinctive characteristics

geology mineralization and geochronology of the qianhe gold deposit xiong ershan area southern north china craton the qianhe gold deposit in the xiong ershan area is located along the southern margin of the archean paleoproterozoic north china craton the deposit consists of six orebodies that are hosted in paleoproterozoic andesites to basaltic andesites and structurally controlled by roughly ew trending faults individual orebodies comprise auriferous quartz veins and disseminated au bearing pyrite within hydrothermally altered rocks on both sides of or close to the veins ore related hydrothermal alteration has produced various mixtures of k feldspar quartz sericite chlorite epidote carbonate and sulfides pyrite is the most important ore mineral associated with minor amounts of galena sphalerite and chalcopyrite other trace minerals include molybdenite arsenopyrite scheelite rutile xenotime and parisite gold occurs mostly as native gold and electrum enclosed in pyrite or along microfractures of sulfides and quartz microthermometric measurements of primary inclusions in auriferous quartz suggest that gold and associated minerals were precipitated in the range of 160 305 c from aqueous or carbonic aqueous fluids with salinities of 6 22 wt nacl equiv samples of molybdenite coexisting with au bearing pyrite have re os model ages of 134 135 ma whereas ore related hydrothermal sericite separates yield 40ar 39ar plateau ages between 127 and 124 ma the re os and 40ar 39ar ages are remarkably consistent with zircon u pb ages 134 5 1 5 and 127 2 1 4 ma 1 of the biotite monzogranite from the heyu intrusive complex and granitic dikes in and close to the qianhe gold mine indicating a close temporal and thus possibly genetic relationship between gold mineralization and granitic magmatism in the area fluid inclusion waters extracted from auriferous quartz have d values of 80 to 72 whereas the calculated 18oh2o values range from 3 1 to 3 8 the hydrogen and oxygen isotopes from this study and previous work indicate that ore fluids were likely derived from degassing of magmas with addition of minor amounts of meteoric water gold mineralization at qianhe is temporarily coincident with pervasive bimodal magmatism widespread fault basin formation and well development of metamorphic core complexes in the whole eastern north china craton that have been interpreted as reflecting reactivation of the craton in the late mesozoic after prolonged stabilization since its formation in the late paleoproterozoic it is therefore concluded that the qianhe gold deposit formed as a result of this craton reactivation event

assessment of hydrocarbon source rock potential of polish bituminous coals and carbonaceous shales abstract we analyzed 40 coal samples and 45 carbonaceous shale samples of varying thermal maturity vitrinite reflectance 0 59 to 4 28 from the upper carboniferous coal bearing strata of the upper silesian lower silesian and lublin basins poland to evaluate their potential for generation and expulsion of gaseous and liquid hydrocarbons we evaluated source rock potential based on rock eval pyrolysis yield elemental composition atomic h c and o c and solvent extraction yields of bitumen an attempt was made to relate maceral composition to these source rock parameters and to composition of the organic matter and likely biological precursors a few carbonaceous shale samples contain sufficient generation potential pyrolysis assay and elemental composition to be considered potential source rocks although the extractable hydrocarbon and bitumen yields are lower than those reported in previous studies for effective type iii source rocks most samples analysed contain insufficient capacity for generation of hydrocarbons to reach thresholds required for expulsion primary migration to occur in view of these findings it is improbable that any of the coals or carbonaceous shales at the sites sampled in our study would be capable of expelling commercial amounts of oil inasmuch as a few samples contained sufficient generation capacity to be considered potential source rocks it is possible that some locations or stratigraphic zones within the coals and shales could have favourable potential but could not be clearly delimited with the number of samples analysed in our study because of their high heteroatomic content and high amount of asphaltenes the bitumens contained in the coals are less capable of generating hydrocarbons even under optimal thermal conditions than their counterpart bitumens in the shales which have a lower heteroatomic content

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

crustal structure of china and surrounding regions from p wave traveltime tomography 1 a three dimensional 3 d p wave velocity model is developed for the crust and uppermost mantle of china and the surrounding area by applying the tomography method of zhao et al using 500 000 high quality p wave first arrivals extracted from the annual bulletin of chinese earthquakes abce this tomographic method can accommodate velocity discontinuities such as the moho in addition to smooth velocity variations the spatial resolution is 1 1 in the horizontal direction and 10 km in depth the velocity images of the upper crust correspond well with the surface geologic features such as basins and the tibetan plateau high velocity anomalies are found in the lower crust beneath the precambrian regions tarim basin ordos basin sichuan basin and western half of songliao basin the highest velocity anomaly is beneath the sichuan basin high and low velocity anomalies imaged beneath the bohai gulf are associated with the presence of a major cenozoic rift system in the lower crust beneath the south china block p wave velocities are lower in the north than in the south the indochina block shows low velocities both in the crust and in the uppermost mantle due to volcanism the pn velocities in the tibet area are higher than those in other areas largely due to thicker crust tomographic model significantly reduces the traveltime residuals tests conducted by relocating large explosions and earthquakes validate the 3 d velocity model

revelation of organic matter sources and sedimentary environment characteristics for shale gas formation by petrographic analysis of middle jurassic dameigou formation northern qaidam basin china abstract the 7th member of middle jurassic dameigou formation j2d7 in northern qaidam basin china was proposed to have good hydrocarbon generating potential in previous studies here we apply an integrated petrographic and geochemical analysis to investigate the depositional environment real thermal maturity and shale gas potential of organic matter om rich assemblage the relatively high content of c29 regular sterane 56 8 62 8 and vitrinite predominance in maceral composition suggesting plenty of higher plant input combined with the high pristane phytane ratio pr ph 2 8 8 2 and low gammacerane index 0 2 0 4 reveals oxic water column with in situ depositional condition of carbonaceous mudstone when the lower j2d7 was deposited the maceral composition of oil shale at the upper part of j2d7 is mainly amorphous om with small proportion of reworked vitrinite and inertinite consistent with a mainly algea and small amount of exogenous om input when associated with low pr ph 0 8 and high gammacerane index 4 3 the oil shale was deposited in an anoxic saline water column with mainly zooplankton om source the geochemical and petrographic result implies a transitional environment ranging from suboxic semi saline to oxic fresh water environment with varying proportion of higher plant and algae input by in situ deposition and distant transportation for the mudstone at the middle part of j2d7 by use of random reflectance ro distribution two sedimentary environment microcycles which are confirmed by maceral composition from the depth of 1983 m to 1962 m and 1954 m to 1931 9 m are differentiated within the homogenous mudstone section the variation of om input condition and alternation of depositional environment led to accumulation and deposition of various kinds of abundant om when j2d7 was deposited although the om has actually low maturity at oil window with vitrinite reflectance around 0 6 according to the petrographic results the liptinite inherited from higher plants especially suberinite is the main maceral to generate gaseous hydrocarbons at the low maturity which implies that the dameigou formation j2d7 of qaidam basin is of gas potential

distribution composition and origin of coalbed gases in excavation fields from the preloge and pesje mining areas velenje basin slovenia abstract coal gas outbursts especially co 2 present a high risk in mining of lignite in the velenje coal mine located in the velenje basin in northern slovenia a programme of monitoring geochemical parameters was set up to help understand the behaviour of the coalbed gas distribution in advance of the working face using mass spectrometric methods to study its molecular and isotopic compositions and origin coalbed gas samples from four different excavation fields g2 c and k 130 a from the north and south preloge mining area and k 5 a and k 50 c from the pesje mining area which were operational between the years 2010 and 2011 were investigated the major gas components are co 2 and methane temporal changes in the chemical and isotopic composition of free seam gases were observed within boreholes as a function of the advancement of the working face the study also revealed that at a distance of around 120 m from the working face the influence of coal exploitation by the velenje longwall mining method causes coalbed gas to migrate at a distance of 70 m the lignite structure is crushed causing desorption of fixed co 2 from the coal differences in coalbed gas composition at the longwall panels which underlie the unmined area or under previously mined areas were found a high cdmi co 2 co 2 ch 4 100 index with values up to 95 6 was typical for areas of pre mined excavation fields south preloge k 130 a and pesje area k 5 a while in excavation fields with no previous mining activity north preloge g2 c and pesje area k 50 c up to 61 9 vol of ch 4 was detected the concentration measurements and isotopic studies revealed endogenic co 2 including co 2 originating from dissolution of carbonates with 13 c co2 values ranging from 7 0 to 5 5 microbial methane and co 2 with values ranging from 70 4 to 50 and from 11 0 to 7 0 respectively higher 13 c ch4 values ranging from 50 to 19 8 could be attributed to so called secondary processes influencing the 13 c ch4 value such as migration due to lignite excavation escape of isotopically lighter methane in excavation fields g2 c and k 50 c with no premining activity higher 13 c ch4 values could also be explained by migration of methane from deeper strata the 13 c ch4 value also depended on the depth of the excavation field at shallower levels of the excavation field k 5 a a lower 13 c ch4 value was traced indicating microbial gas while at deeper levels higher 13 c ch4 values were found

late jurassic to early cretaceous magmatism in the xiong ershan gold district central china implications for gold mineralization and geodynamics the xiong ershan area is the third largest gold producing district in china the late jurassic to early cretaceous magmatism in the xiong ershan area can be divided into two episodes early 165 150 ma and late 138 113 ma laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating yields ages of 160 7 0 6 ma and 127 2 1 0 ma for the wuzhangshan and huashan monzogranites in the xiong ershan area respectively representing the two magmatic episodes the wuzhangshan monzogranites exhibit adakite like geochemical features e g high sr y ratios low yb and y contents their sr nd hf isotopic compositions are consistent with those of the amphibolites of the taihua group indicating that the wuzhangshan monzogranites were formed from partial melting of the taihua group metamorphic rocks compared to the wuzhangshan rocks the huashan monzogranites have higher mgo cr co and ni contents but lower sr y and fe 3 fe 2 all the samples from the huashan monzogranites plot in the area between the taihua group amphibolite rocks and the mantle rocks in the 87 sr 86 sr t vs e nd t and age vs e hf t diagrams suggesting that the huashan monzogranites were probably generated by mixing of mantle derived magmas and the taihua group metamorphic basement melts the gold mineralization 136 110 ma is coeval with the emplacement of the late episode magmas implying that crustal mantle mixed magma might be a better target for gold mineralization compared to the ancient metamorphic basement melt the data presented in this study further indicate that the transformation of the lithosphere from thickening to thinning in the xiong ershan area probably occurred between 160 ma and 127 ma and that the gold mineralization in this area was probably related to lithospheric thinning

evaluation of the 87rb decay constant by age comparison against the u pb system abstract the rb sr decay system is one of the most widely used geochronometers for obtaining ages and cooling rates of terrestrial magmatic metamorphic and hydrothermal events it has also been extensively applied to date extraterrestrial early solar system events the accuracy of rb sr ages however strongly depends on the accuracy of the 87 rb decay constant 87 rb we determined 87 rb relative to the decay constants of 235 u and 238 u by comparing rb sr ages of minerals with u pb ages obtained from the same intrusion comparison of u pb emplacement ages with high precision rb sr mineral ages from three rapidly cooled igneous rocks covering an age range of ca 2 5 ga yields an unweighted mean 87 rb of 1 393 0 004 10 11 yr 1 i e 0 3 corresponding to a half life of 49 76 10 9 years because this decay constant is 2 lower than the presently recommended one many previously published ages are 2 too young and the resulting geologic interpretations may need revision

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

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

combined u pb hafnium and oxygen isotope analysis of zircons from meta igneous rocks in the southern north china craton reveal multiple events in the late mesoarchean early neoarchean abstract we report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from lushan in the far south of the trans north china orogen of the north china craton that reveal the oldest rocks yet dated from the orogen a detailed investigation of the internal structures of zircons combined with targeted sims u pb and oxygen isotope analyses and icp ms hf zircon analyses has resulted in the discovery of previously unknown geological events in the north china craton magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829 18 ma to 2832 11 ma in the tonalites and from 2838 35 ma to 2845 23 ma in amphibolite hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination oxygen isotope ratios in zircons range from 5 1 to 7 3 vsmow with high 18 o results recorded only from metamorphic domains the earliest stage of metamorphic zircon growth present in all four samples analyzed in this study occurred between 2772 17 22 in the tonalites and 2776 20 and 2792 12 ma in the amphibolites a younger metamorphic event at 2638 61 in the tonalite and between 2671 13 and 2651 13 ma in the amphibolites is recognized in zircons from three of the four samples investigated this is the first time that metamorphic events at either of these times have been recorded in the north china craton importantly there is no evidence for the 1 8 ga high grade metamorphic event that is manifest in the northern and central parts of the trans north china orogen