late carboniferous to permian sedimentation in inner mongolia china and tectonic relationships between north china and siberia a belt of deformed permo carboniferous sedimentary rocks in inner mongolia represents an orogenic zone between the north china and siberian blocks the belt apparently contains accretionary terranes thrust onto the margins of both blocks with scattered ophiolite blueschist suites indicating the consumption of oceanic crust at least slightly older than the age of deformation upper carboniferous to lower permian strata in central inner mongolia show both sedimentological and paleontological differences from middle and upper permian rocks in comparison with pre middle permian rocks younger permian strata 1 contain less laterally extensive limestone and more lensoidal carbonate in clastic sections 2 contain a higher percentage of coarse clastic material 3 grade upward from marine to terrestrial deposits 4 contain fauna indicating more restricted circulation particularly toward the western part of the belt and 5 contain fauna that are consistent with but do not require northward movement

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

a geochemical study of solid bitumen in an eocene epithermal deposit owen lake british columbia canada abstract the owen lake deposit british columbia canada is an epithermal polymetallic deposit related to eocene volcanic activity and igneous intrusions the deposit contains both solid and liquid hydrocarbons generated during early and late stages of ore deposition gc ms py gc rock eval electron microprobe as well as carbon isotope fluid inclusion and optical techniques have been applied and the results integrated into a deposit model incorporating fluid flow fluid source and thermal structure of the volcanic terrane most solid bitumen examined is of the albertite variety and is related to the latest stage of mineral deposition gas chromatography of saturated hydrocarbons yielded n alkanes from c15 to c33 with a maximum at n c23 steranes and diasteranes are of low abundance relative to n alkanes terpanes and hopanes regular steranes dominate over rearranged steranes hopanes dominate over tricyclic terpanes and gammacerane is a significant component aromatic compounds are very low in abundance and are represented mainly by triaromatic steroids these results together with carbon isotope values suggest a mixed marine terrestrial organic source of the bitumen with saline or hyper saline conditions prevailing during deposition or very early diagenesis of the source rock based on the geological framework of the deposit two possible sources of the solid bitumen together with the fluid path are suggested

geology and geochemistry of wall rock alteration at the carlin gold deposit nevada the carlin disseminated gold deposit occurs in an autochthonous sequence of paleozoic sedimentary rocks exposed in a structural window in the roberts mountains thrust in north central nevada the upper 175 m of the silurian roberts mountains formation hosts the majority of ore at carlin and is characterized by laminated fine grained calcareous and or dolomitic argillaceous siltstone with local coarser grained siltstones and 50 cm thick lenticular interbeds of sand and granule sized calcareous bioclastic debris or fossil hash detailed studies of drill core and exposures in the east pit of the carlin mine show that alteration and mineralization are zoned away from crosscutting fault conduits and these more permeable bioclastic beds indicating that these two features were major inflow zones for hydrothermal fluid in unoxidized rocks unaltered calcareous siltstone 1 containing quartz dolomite calcite illite k feldspar and pyrite is progressively converted to assemblages of 2 quartz dolomite calcite illite pyrite 3 quartz dolomite illite k mica pyrite 4 quartz illite k mica pyrite and 5 quartz kaolinite dickite pyrite adjacent to inflow zones where jasperoids are developed gold most consistently enriches the zone of calcite and dolomite removal 3 and 4 above though it occurs in all zones locally in high concentrations this zoned alteration was accomplished by a co 2 rich acidic fluid this acidic alteration enhanced the passage of fluids by extensive carbonate removal to form zones of higher permeability oxidation is wholly a supergene effect related to deep weathering because the oxidation is superimposed on both mineralized and altered rocks with only minor effect on the major element chemistry it has produced low temperature goethitic fe oxides rather than higher temperature hematite and is not spatially related to au distribution at the mine or on a district scale because of extensive carbonate removal leading to local volume reduction through collapse and or compaction geochemical effects are examined using ratios to relatively immobile elements such as al and ti extensive depletion of ca mg aud co 2 and introduction of si au and s have occurred potassium is depleted in the conversion of illite to dickite kaolinite in proximal silicified inflow zones and fe enriches some pyritized rock carbonate removal and silicification are two separate processes both of which are spatially associated with mineralization mineralized decarbonated rocks and barren footwall rocks commonly are not silicified and intensely silicified proximal alteration zones are generally low grade

alligator ridge district east central nevada carlin type gold mineralization at shallow depths carlin type deposits in the alligator ridge mining district are present sporadically for 40 km along the north striking mooney basin fault system but are restricted to a 250 m interval of devonian to mississippian strata their age is bracketed between silicified ca 45 ma sedimentary rocks and unaltered 36 5 to 34 ma volcanic rocks the silicification is linked to the deposits by its continuity with ore grade silicification in devonian mississippian strata and by its similar 18 o values 17 and trace element signature as sb tl hg eocene reconstruction indicates that the deposits formed at depths of 300 to 800 m in comparison to most carlin type gold deposits they have lower au ag au grades and contained au more abundant jasperoid and textural evidence for deposition of an amorphous silica precursor in jasperoid these differences most likely result from their shallow depth of formation the peak fluid temperature 230 c and large 18 o h2o value shift from the meteroric water line 20 suggest that ore fluids were derived from depths of 8 km or more a magnetotelluric survey indicates that the mooney basin fault system penetrates to mid crustal depths deep circulation of meteoric water along the mooney basin fault system may have been in response to initial uplift of the east humboldt ruby mountains metamorphic core complex convection also may have been promoted by increased heat flow associated with large magnitude extension in the core complex and regional magmatism ore fluids ascended along the fault system until they encountered impermeable devonian and mississippian shales at which point they moved laterally through permeable strata in the devonian guilmette formation devonian mississippian pilot shale mississippian joana limestone and mississippian chainman shale toward erosional windows where they ascended into eocene fluvial conglomerates and lake sediments most gold precipitated by sulfidation of host rock fe and mixing with local ground water in zones of lateral fluid flow in reactive strata such as the lower devonian mississippian pilot shale

the application of electron microscopy and microanalysis in conjunction with organic petrology to further the understanding of organic mineral association examples from mount isa and mcarthur basins australia organic petrology supported by electron microscopical and micro analytical techniques was applied to organic matter in proterozoic sediments to better understand hydrothermal processes responsible for ore grade mineralisation it was shown that organic maturation was not only closely linked to the geological history of the sediments but also highlighted heat transfer by convection as differentiated from conduction solely through sediment burial and step wise subsidence water rock ratios effect organic maturation in hydrothermal systems and erratic reflectance profiles are indicators of convective heat transfer identification and characterisation of organic materials in terms of source rock and migrated hydrocarbons was shown to be a powerful tool in reconstructing the thermal history of sediments identifying hydrothermal episodes fluid pathways and heat source in the northern australian proterozoic basins higher reflectance of organic matter towards the central parts of the mount isa basin and some of the most northerly parts point to proximity to higher heat flow at times in contrast to relatively low temperatures prevailing in the western parts of the basin next to the murphy inlier a close correlation shown between peak organic reflectance values and super sequence boundaries farther highlighted the valuable information to be gained from organic petrology by allowing the separation of processes responsible for metal dissolution and transportation from those inducing precipitation c 2001 elsevier science b v all rights reserved

hydrothermal maturation of indigenous organic matter at the alligator ridge gold deposits nevada the organic matter of the devonian mississippian pilot shale which hosts the disseminated gold mineralization at alligator ridge nevada has been investigated in an attempt to determine its source and maturation processes and to find an alteration parameter which reflects precious metal distribution more accurately than mineralogical alteration patterns the alligator ridge deposits are similar to other disseminated gold deposits in the great basin of the western united states visible alteration features consisting of quartz replacement of carbonates and oxidation of sulfides and organic matter do not provide significantly useful guides for exploration in this study the type abundance and maturity of organic matter in the pilot shale were determined using techniques standard to petroleum exploration the type and abundance of organic matter in background and mineralized samples are similar transmitted light examination of kerogen concentrates shows that most of the organic matter consists of fine amorphous algal aggregates with a minor amount of vitrinite this corresponds with type i or ii organic matter of tissot and welte 1978 which is derived from a marine source total organic carbon makes up 1 to 3 percent of most carbonaceous rocks at alligator ridge no evidence was found for hydrothermal introduction or remobilization of organic matter the maturity of organic matter as determined by pyrolysis and vitrinite reflectance is considerably higher in mineralized samples than in samples unaffected by the processes of mineralization hydrogen index values for mineralized samples are generally 40 h c approximately 0 5 compared with a background of 230 to 315 h c approximately 1 changes in vitrinite reflectance show a similar but less dramatic change mineralized samples have reflectance values of 1 to 1 3 percent background reflectance is 0 4 to 0 5 percent all reflectance values however are anomalously low due to the extremely small grain size of the vitrinite and therefore cannot be used to determine paleotemperatures spatially hydrogen index contours increase concentrically away from gold mineralization except near the lower pilot shale contact here hydrogen index isopleths are nearly concordant and parallel other alteration features the spatial pattern indicates that hydrothermal flow was dominantly along this contact and away from mineralization this study shows that the organic matter in the pilot shale is of a marine sedimentary origin the total organic carbon of mineralized and background material is similar indicating that the organic matter was not added to the pilot shale hydrothermally however hydrothermal activity has increased the organic matter maturity suggesting that maturation studies can be useful to exploration programs

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

sulfidation of organic matter associated with gold mineralization pueblo viejo dominican republic the pueblo viejo district is one of the largest producers of precious metals in the world yielding more than 11 000 kg of au annually gold mineralization at pueblo viejo is hosted in spilite and coarse elastic and finely laminated fine grained carbonaceous sedimentary rocks of the lower cretaceous los ranchos formation mineralization was accompanied by sulfidation as evidenced by i the occurrence of siderite distal to mineralization and pyrite proximal to mineralization 2 increased s fe ratios associated with au mineralization 3 the occurrence of native s in and adjacent to mineralization and 4 the presence of sulfidized organic matter organo s compounds in mineralized rocks organic matter in the carbonaceous sedimentary rocks comprises vitrinite and pyrobitumen rock eval pyrolysis data indicate that this organic matter is overmature hi 55 the organic matter is s rich up to 14 wt s in rocks where all fe has been sulfidized to pyrite x ray absorption near edge structure xanes analysis indicates that the c bonded s is thiophenic early disseminated au mineralization is postulated to have occurred in response to sulfidation of ferrous fe to form pyrite the consequent decline in the activity of h2s in the mineralizing fluid would have destabilized au bisulfide complexes and caused deposition of gold the restriction of s rich organic matter to rocks in which all fe occurs as pyrite indicates that sulfidation of organic matter postdates sulfidation of ferrous fe and therefore deposition of much of the au

absolute reconstructions of the paleozoic oceans abstract the orientation of three intraplate magmatic belts the mongolian from 130 to 280 m y south siberian from 320 to 400 m y and baltic from 365 to 400 m y belts which can be considered as hot spot tracks are used together with apparent paleomagnetic pole wander paths to reconstruct true motions of continents during paleozoic times the reconstructions obtained show that the old late precambrian pangea continued to exist in the early paleozoic with an inner arrangement of constituent continents strongly different from that of the late paleozoic pangea the continents were constantly located in the eastern hemisphere only the western hemisphere was occupied by the paleo pacific oceans four oceans existed in paleozoic times between the continents in the eastern hemisphere 1 the iapetus which originated in the late precambrian and closed before devonian times 400 m y 2 the asiatic paleo ocean which originated in the late precambrian and closed 450 m y ago 3 the uralian paleo ocean which opened around 500 m y ago and closed in the latest permian 240 230 m y 4 the paleo tethys which opened in the ordovician 480 450 m y and became the mesozoic tethys life duration of the oceans was 200 400 m y the main trend in the earth s evolution during the paleozoic was a break up of the old precambrian supercontinent and construction of the new late paleozoic pangea

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

foraminiferal coloration index as a guide to hydrothermal gradients around the porgera intrusive complex papua new guinea the porgera intrusive complex and gold deposit is hosted in friable black mudstones of cretaceous age in the deformed northern part of the papuan basin papua new guinea hydrothermal fluids associated with the pliocene intrusions created thermal gradients in the surrounding sedimentary rocks these gradients were partitioned by preexisting faults in the sedimentary rocks creating cells of fluid circulation assemblages of agglutinated foraminifera reported from north america have shown color gradients which are interpreted as being related to the thermal maturation of sedimentary rocks down drill holes this paper presents the first known application of color changes in foraminifera marine protistan microfossils to hydrothermal mineral exploration the foraminiferal assemblages of the bathyal mudstones from the porgera region contain abundant agglutinated foraminifera color changes recognized in the agglutinated foraminifera were used to map the thermal maturation of sedimentary rocks in the porgera area palynological fluorescence used in petroleum exploration to determine thermal maturation could not be used owing to the over maturation of the organicmaterials throughout the area surrounding the porgera intrusive complex the agglutinated foraminifera showed a gradation in color from white to dark gray in surface samples taken throughout the porgera area mapping of the foraminifera colors using a geographic information system gis illustrated the thermal maturation of the sedimentary rocks around the intrusive complex owing to conductive heating in addition the mapping showed patterns consistent with convective heating caused by hydrothermal fluid circulation the foraminiferal coloration showed pairing of hot and cold areas across major structures interpreted to be associated with the upflow hot and recharge cold of fluids from the surrounding host sedimentary rocks illite crystallinity and vitrinite reflectance analyses conducted on a transect of samples from across the porgera intrusive complex supported the proposed hydrothermal fluid circulation model interpreted from the foraminiferal colors paleotemperatures associated with the foraminiferal coloration index from the porgera region range from 205 to 415 c and are anomalously high in comparison to other parts of the papuan fold and thrust belt the foraminiferal coloration index fci is a guide to the thermal maturation of sedimentary rocks and provides a useful and low cost exploration tool for locating and evaluating the size of buried intrusive systems in late palaeozoic to cenozoic marine shales it is an invaluable tool for determining the size and partitioning of a hydrothermal cell associated with hydrothermal epithermal mineral deposits the fci method is also useful on a regional scale in areas where sandstones shales or limestones blanket aero magnetic and resistivity data the technique is used currently to identify drilling targets for the exploration of the porgera deposit

new paleomagnetic data from the mongol okhotsk collision zone chita region south central russia implications for paleozoic paleogeography of the mongol okhotsk ocean we present a reconnaissance paleomagnetic study of rocks from several formations of the chita region of south central russia representative location 51 n 116 e within the mongol okhotsk collision zone sections of siltstone and fine grained sandstone dated using fossils as bashkirian to moscovian epochs ussr carboniferous system middle carboniferous early permian late permian and triassic in age were sampled the resulting collection from five stratigraphic sections is a total of 319 oriented samples from 51 sites generally 5 to 10 samples per site were collected sample orientation was determined using both magnetic and sun shadow azimuths all paleomagnetic measurements were completed in the paleomagnetic laboratory at the university of pittsburgh using a 3 component 2g superconducting rock magnetometer srm in a magnetically shielded room thermal demagnetization was completed using between 12 to 20 heating steps up to temperatures of 685 c principal component analysis of the demagnetization data was successful in isolating two characteristic remanent magnetizations the lower unblocking temperature component component a fails the fold test is always of downward directed magnetic inclination and may record the present day earth s pdf magnetic field pdf i 69 4 d 351 8 component a ig 65 1 dg 356 5 95 6 2 n sites 50 the higher unblocking temperature magnetic component b was observed in the triassic bt n 3 late permian blp n 14 early permian bep n 5 and bashkirian to moscovian epochs of the late carboniferous bmc n 8 sections the b component differs significantly from component a and is recorded by sites of both downward and upward directed magnetic inclinations in the late permian and bashkirian to moscovian epoch sections component bmc and blp may represent primary remanent magnetizations the bashkirian to moscovian epochs of the late carboniferous mean paleolatitude is mc 19 9 14 8 and the late permian mean paleolatitude is lp 19 6 14 5 both are similar to that expected from reference paleomagnetic poles from the north china block but significantly different from paleolatitudes calculated using reference poles from the siberian or european plates we interpret the results of this study to suggest that the sampled sections were located near or associated with the north china block during their deposition

present trends and the future of zircon in geochronology laser ablation icpms in situ u th pb geochronology was born some two decades ago with the introduction and development of high resolution secondary ion mass spectrometry sims or shrimp sensitive high mass resolution ion microprobe compston et al 1984 williams 1998 compston 1999 davis et al this volume ireland and williams this volume this technique clearly demonstrated the existence of age heterogeneities within the single crystals of zircon and other accessory phases and therefore the need for high spatial resolution tens to hundreds of cubic micrometers geochronological data in situ dating by ion probe is capable of achieving an analytical precision that is only an order of magnitude worse than the conventional isotope dilution thermal ionization mass spectrometry id tims dating technique it has the advantage however of more readily identifying concordant portions of grains does not require chemical treatment of samples prior to the analysis is essentially nondestructive and can achieve greater sample throughputs a major obstacle to the wider use of ion probe dating has always been the high cost of instrumentation and hence relative scarcity of suitably equipped geologic laboratories laser ablation inductively coupled plasma mass spectrometry la icpms emerged in 1985 and rapidly became an important analytical tool for trace element determinations in geological samples jackson et al 1992 it was soon realized that the large variations in radiogenic pb and pb u isotopic ratios found in nature could be resolved by icpms techniques and when coupled to a laser icpms could be used as a dating tool similar to the ion probe the pioneering work of feng et al 1993 fryer et al 1993 hirata and nesbitt 1995 and jackson et al 1996 illustrated the potential usefulness of laser sampling for in situ dating by icpms particularly well however these studies and others that followed also revealed the major

hydrocarbon and ore bearing basinal fluids a possible link between gold mineralization and hydrocarbon accumulation in the youjiang basin south china the youjiang basin which flanks the southwest edge of the yangtze craton in south china contains many carlin type gold deposits and abundant paleo oil reservoirs the gold deposits and paleo oil reservoirs are restricted to the same tectonic units commonly at the basinal margins and within the intrabasinal isolated platforms and or bioherms the gold deposits are hosted by permian to triassic carbonate and siliciclastic rocks that typically contain high contents of organic carbon paragenetic relationships indicate that most of the deposits exhibit an early stage of barren quartz pyrite stage i a main stage of auriferous quartz arsenian pyrite arsenopyrite marcasite stage ii and a late stage of quartz calcite realgar orpiment native arsenic stibnite cinnabar dolomite stage iii bitumen in the gold deposits is commonly present as a migrated hydrocarbon product in mineralized host rocks particularly close to high grade ores but is absent in barren sedimentary rocks bitumen dispersed in the mineralized rocks is closely associated and or intergrown with the main stage jasperoidal quartz arsenian pyrite and arsenopyrite bitumen occurring in hydrothermal veins and veinlets is paragenetically associated with stages ii and iii mineral assemblages these observations suggest an intimate relationship between bitumen precipitation and gold mineralization in the paleo petroleum reservoirs that typically occur in permian reef limestones bitumen is most commonly observed in open spaces either alone or associated with calcite where bitumen occurs with calcite it is typically concentrated along pore vein centers as well as along the wall of pores and fractures indicating approximately coeval precipitation in the gold deposits aqueous fluid inclusions are dominant in the early stage barren quartz veins stage i with a homogenization temperature range typically of 230 c to 270 c and a salinity range of 2 6 to 7 2 wt nacl eq fluid inclusions in the main and late stage quartz and calcite are dominated by aqueous inclusions as well as hydrocarbon and co2 rich inclusions the presence of abundant hydrocarbon fluid inclusions in the gold deposits provides evidence that at least during main periods of the hydrothermal activity responsible for gold mineralization the ore fluids consisted of an aqueous solution and an immiscible hydrocarbon phase aqueous inclusions in the main stage quartz associated with gold mineralization stage ii typically have a homogenization temperature range of 200 230 c and a modal salinity around 5 3 wt nacl eq homogenization temperatures and salinities of aqueous inclusions in the late stage drusy quartz and calcite stage iii typically range from 120 c to 160 c and from 2 0 to 5 6 wt nacl eq respectively in the paleo oil reservoirs aqueous fluid inclusions with an average homogenization temperature of 80 c are dominant in early diagenetic calcite fluid inclusions in late diagenetic pore and fissure filling calcite associated with bitumen are dominated by liquid c2h6 vapor ch4 ch4 h2o and aqueous inclusions with a typical homogenization temperature range of 90 c to 180 c and a salinity range of 2 8 wt nacl eq it is suggested that the hydrocarbons may have been trapped at relatively low temperatures while the formation of gold deposits could have occurred under a wider and higher range of temperatures the timing of gold mineralization in the youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits among the limited isotopic data the rb sr date of 206 12 ma for au bearing hydrothermal sericite at jinya as well as the re os date of 193 13 ma on auriferous arsenian pyrite and 40ar 39ar date of 194 6 2 ma on vein filling sericite at lannigou may provide the most reliable age constraints on gold mineralization this age range is comparable with the estimated petroleum charging age range of 238 185 ma and the sm nd date of 182 21 ma for the pore and fissure filling calcite associated with bitumen at the shitouzhai paleo oil reservoir corresponding to the late indosinian to early yanshanian orogenies in south china the close association of carlin type gold deposits and paleo oil reservoirs the paragenetic coexistence of bitumens with ore stage minerals the presence of abundant hydrocarbons in the ore fluids and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated migrated and precipitated along with the hydrocarbons in an immiscible gold and hydrocarbon bearing basinal fluid system

organic matter and gold ore association in a hydrothermal deposit france abstract the aim of this study was to define the part played by organic matter in au ore genesis the possible associations and relations between carbonaceous matter and au were studied at various observation scales drill hole rock sample and microanalysis in an early stage au shear zone type deposit the west viges prospect creuse department france prior work had shown that in this type of deposit au mainly occurs within the structure of arsenopyrite the study of three cores from drill holes revealed a relation between the distribution of the mineralization and the presence of moderately brecciated anthracitic layers within the host volcanosedimentary tuffs chemical assays for au performed on the rock samples after destruction of the carbonaceous material by calcination showed that the au content is nearly always higher after calcination this may indicate that part of the au initially contained in the rock is trapped in the organic phase x ray diffraction spectra on carbonaceous phases isolated from some samples indicated the presence of elemental au these results indicate that like arsenopyrite organic matter is the bearer of au and retains it during conventional acid treatment of the ore

comments on petrology of the hegenshan ophiolite and its implication for the tectonic evolution of northern china by t nozaka and y liu earth planet sci lett 202 2002 89 104

evolution of the mongol okhotsk ocean as constrained by new palaeomagnetic data from the mongol okhotsk suture zone siberia summary this paper presents new data from palaeomagnetic investigations on the upper palaeozoic and mesozoic geological units from the siberian platform and the mongol okhotsk suture zone within the southern portion of the mongol okhotsk suture we collected palaeomagnetic samples from the late permian belektuy formation borzya region 50 7un 116 9ue and the middle late jurassic shadaron formation unda daya 51 5un 117 5ue we sampled the late permian alentuy formation khilok region 50 8un 107 2ue the early to middle jurassic irkutsk sedimentary basin isb 52 0un 104 0ue the late jurassic badin formation mogzon region 51 8un 112 0ue and the early cretaceous gusinoozesk formation gusinoe lake region 51 2un 106 5ue additionally in the northern region of the mongol okhotsk suture apart from the results of the isb and gusinoozersk formations which show very large ellipses of confidence and might be the present day geomagnetic field overprint our results allow us to constrain the evolution of the mongol okhotsk ocean palaeomagnetically from the late permian to the middle late jurassic they confirm that this large permian ocean closed during the jurassic ending up in the late jurassic or the beginning of the cretaceous in the eastern end of the suture zone as suspected on geological grounds however although geological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data show evidence of a still large palaeolatitude difference between the amuria and siberia blocks this is interpreted as a result of the quite fast closure of the ocean after the middle jurassic finally our new palaeomagnetic results exhibit very large tectonic rotations around local vertical axes which we interpret as probably arising both from collision processes and from a left lateral shear movement along the suture zone due to the eastward extrusion of mongolia under the effect of the collision of india into asia

the most ancient ophiolite of the central asian fold belt u pb and pb pb zircon ages for the dunzhugur complex eastern sayan siberia and geodynamic implications abstract ophiolitic rocks with a zircon age of 1020 ma occur in the dunzhugur complex of east sayan siberia and are part of a neoproterozoic to early palaeozoic segment of the central asian fold belt the most spectacular suite is exposed along the oka and bokson rivers where a complete ophiolite sequence with mantle tectonites a layered sequence composed of dunite wehrlite and pyroxenite a gabbro section a sheeted diabase dyke complex and basaltic pillow lavas are exposed petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic ultramafic crustal section and support a supra subduction zone setting in a fore arc rifting environment for its origin two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean 207pb 206pb age of 1020 10 ma evaporation of three additional fractions of three to four grains each from the same sample produced a mean 207pb 207pb age of 1019 9 0 7 ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite this is the oldest ophiolite so far dated from the central asian fold belt the southern margin of the siberian craton and the palaeo asian ocean were established at the end of the mesoproterozoic at least 1000 ma ago during the time interval 1000 570 ma one or several large ocean basins existed between baltica siberia kazakhstan tarim and northern china and these blocks are therefore unlikely to have been part of the supercontinent rodinia rifting initiation of subduction and marginal basin formation began prior to 1000 ma and continued through 570 ma the dunzhugur ophiolite of eastern sayan provides evidence for the early opening of the palaeo asian ocean not later than 1000 ma ago

petrology of the hegenshan ophiolite and its implication for the tectonic evolution of northern china abstract petrographic observations and mineralogical and geochemical analyses have revealed that the hegenshan ophiolite is of mid ocean ridge origin and has been subjected to dynamothermal metamorphism at medium p t conditions the metamorphism is characterized by a prograde change in paragenesis from the greenschist to epidote amphibolite facies with peak temperature conditions of 570 640 c at pressures of 4 10 kbar the amphiboles formed by this metamorphism show k ar ages of 110 130 ma the metamorphic conditions and k ar ages suggest that the hegenshan ophiolite is located at the suture between the siberian and north china continental blocks where the continental collision in this area took place in middle mesozoic time given the temporal and spatial distribution of the igneous activity around the da hinggan ling mountains it is suggested that the extensive yanshanian magmatism in this region resulted predominantly from a southward subduction of an oceanic plate prior to collision alternatively it may possibly have resulted from the collision itself at the final stage

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

deep burial hydrothermal alteration of the pre salt carbonate reservoirs from northern campos basin offshore brazil evidence from petrography fluid inclusions sr c and o isotopes abstract petrographic mineralogical elemental isotopic and fluid inclusion analyses were integrated to unravel the diagenetic evolution of brazilian pre salt lacustrine carbonate reservoirs of northern campos basin southeast brazilian margin detailed thin section and cathodoluminescence petrography scanning electron microscopy and electron microprobe analyses established a paragenetic evolution of diagenetic processes and products comprising extensive dolomitization silicification and dissolution a paragenesis including saddle dolomite macrocrystalline calcite mega quartz sr barite celestine fluorite dickite sphalerite galena and other metallic sulfides filling fractures and dissolution porosity and aqueous fluid inclusions with homogenization temperatures of 92 152 c and salinities between 13 and 26 wt eq nacl characterized a hydrothermal system with some analogy to carbonate hosted pb zn mississippi valley mvt and irish type deposits petroleum inclusions and solid bitumen testify atypical oil generation and migration associated with the hydrothermal flow the host pre salt spherulitic and fascicular carbonates present highly radiogenic 87sr 86sr ratios indicating strong interaction with continental crust materials hydrothermal phases show 18o values more negative than syngenetic and diagenetic carbonates the 13c values are interpreted as result of interaction between the hydrothermal fluids and the host rocks the combined data set provides clear evidence of intense hydrothermal alteration of northern campos basin pre salt reservoirs at deep burial conditions 2 km possibly related to late cretaceous or more probably paleogene magmatic activity mixed sourced fluids bearing a basinal signature fed the hydrothermal system and promoted dissolution of the host rocks the hydrothermal alterations had strong impact on the porosity permeability and heterogeneity contributing together with the associated fracturing to the excellent production performance of the pre salt reservoirs

a carbonaceous sedimentary source rock model for carlin type and orogenic gold deposits this paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for au and as in sediment hosted orogenic and carlin type gold deposits and develops a corresponding genetic model in this two stage basin scale model gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis stage 1 and concentrated to ore grades by later hydrothermal structural or magmatic processes stage 2 in reduced continental margin basin settings organic matter sedimented under anoxic to euxinic conditions immobilizes and concentrates gold arsenic and a range of trace elements particularly v ni se ag zn mo cu u present in marine bottom waters into fine grained black mudstone and siltstone of slope and basin facies during early diagenesis gold and certain other trace elements ni se te ag mo cu pge are preferentially partitioned into arsenian pyrite that grows in the muds these processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic commonly from 5 to 100 ppb au and 10 to 200 ppm as rare organic and sulfide rich metalliferous black shales may contain up to 1 to 2 ppm au and over 1 000 ppm as present as refractory gold in arsenian pyrite and nanoparticles of free gold during late diagenesis and early metamorphism stage 2 the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations and the organic matter is cooked to bitumen under higher grade metamorphism lower greenschist facies and above arsenian pyrite in carbonaceous shales is converted to pyrrhotite these processes release gold arsenic sulfur and other elements sb te cu zn mo bi tl and pb from the source rocks to become concentrated by hydrothermal processes locally to produce gold ores in structural sites such as fold hinge zones shear or breccia zones within or above the black shale sequence la icp ms analyses of diagenetic pyrite in carbonaceous sediments both associated and not associated with gold deposits suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits application of this sedimentary source rock model enables a systematic exploration approach for sediment hosted gold deposits based on the distribution composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite

first evidence of heat treatment during the early neolithic in northeastern italy the site of la vela sector vii trentino alto adige italy provides one of the few complete stratigraphic sequences ranging from the mesolithic to the middle neolithic in northwestern italy the site is located in the adige valley a way of communication between the po plan and the alps this research focuses on the early neolithic lithics ascribable to the gaban facies dated to 5000 4700 cal bc different rocks coming from local exposures have been exploited the goal of the reduction sequence was the production of blades by pressure knapping technique the technological study of the assemblage raised a particular interest for the presence of flint artifacts suggesting the usage of controlled heat treatment the presence of this technique has been tested by an experimental approach based on fourier transform infrared ft ir spectroscopy complementary microstructural and analytical characterizations with low vacuum scanning electron microscopy lvsem observations combined with energy dispersive x ray spectroscopy edxs have been performed the analyses confirm the presence of artifacts intentionally heat treated the thermal treatment achieved in order to increase the quality of the blade production is the first evidence of this technique in northeastern italy during the early neolithic

geochemistry mineralization structure and permeability of a normal fault zone casino mine alligator ridge district north central nevada abstract we examine the geochemical signature and structure of the keno fault zone to test its impact on the flow of ore mineralizing fluids and use the mined exposures to evaluate structures and processes associated with normal fault development the fault is a moderately dipping normal fault zone in siltstone and silty limestone with 55 100 m of dip slip displacement in north central nevada across strike exposures up to 180 m long 65 m of down dip exposure and 350 m of along strike exposure allow us to determine how faults fractures and fluids interact within mixed lithology carbonate dominated sedimentary rocks the fault changes character along strike from a single clay rich slip plane 10 20 mm thick at the northern exposure to numerous hydrocarbon bearing calcite filled nearly vertical slip planes in a zone 15 m wide at the southern exposure the hanging wall and footwall are intensely fractured but fracture densities do not vary markedly with distance from the fault fault slip varies from pure dip slip to nearly pure strike slip which suggests that either slip orientations may vary on faults in single slip events or stress variations over the history of the fault caused slip vector variations whole rock major minor and trace element analyses indicate that au sb and as are in general associated with the fault zone suggesting that au and silica bearing fluids migrated along the fault to replace carbonate in the footwall and adjacent hanging wall rocks subsequent fault slip was associated with barite and calcite and hydrocarbon bearing fluids deposited at the southern end of the fault no correlation exists at the meter or tens of meter scale between mineralization patterns and fracture density we suggest that the fault was a combined conduit barrier system in which the fault provides a critical connection between the fluid sources and fractures that formed before and during faulting during the waning stages of deposit formation the fault behaved as a localized conduit to hydrocarbon bearing calcite veins the results of this study show that fault zone character may change dramatically over short deposit or reservoir scale distances the presence of damage zones may not be well correlated at the fine scale with geochemically defined regions of the fault even though a gross spatial correlation may exist

thermal maturity of jurassic shales from the newark basin u s a influence of hydrothermal fluids and implications to basin modeling abstract organic geochemical investigations were conducted on a series of cores that systematically sampled the uppermost jurassic strata from the northern newark basin each sedimentary unit consists of fluvial red sandstones and siltstones with cyclic deposits of interbedded black lacustrine shales and gray deltaic siltstones in a suite of organic rich shales from the boonton towaco and feltville formations organic maturation parameters were used to determine aspects of the thermal history of the newark basin comparisons of model calculations and measured maturities support 39 ar 40 ar geochronometer studies that indicate a hydrothermal event occurred 175 ma ago an increase in the regional geothermal gradient to 7 5 c 100 m for 5 ma best conforms to the organic geochemical observations biomarker compounds in boonton and towaco strata should have been relatively unaltered by this regional event but anomalous molecular distributions in the organic rich rocks may have resulted from localized heating by hydrothermal fluids the effects of this interaction would be very subtle and may be indistinguishable from variations caused by differences in organic facies within this uncertainty sterane and hopane isomerization and steroid aromatization reactions advanced in the boonton and towaco formation strata primarily because of burial and normal geothermal heating that followed the hydrothermal event biomarker kinetic models indicate that 2400 m of boonton and post boonton strata were eroded after basinal uplift commenced 50 ma ago

thermodynamics of organic transformations in hydrothermal fluids hydrothermal fluids obtain organic compounds through diverse pathways in submarine systems organic compounds are already dissolved in seawater that is heated and transformed into hydrothermal fluids through water rock reactions microbes inhabiting hydrothermal systems produce metabolites that enter the fluids and cells can be carried into the reaction zones by circulating fluids and pyrolyzed analogous sources of organic compounds can be anticipated in continental systems with the possible addition of novel plant and soil derived organic compounds from the surface in addition hydrothermal systems possess large potentials for abiotic organic synthesis that may add a novel suite of compounds when sedimentary rocks are present ancient biogenic organic matter can be mobilized or transformed by hot fluids these transformations accompany the generation of petroleum coal and other fossil fuels suggesting that expectations for hydrothermal transformations can be built on those that occur in sedimentary basins likewise some types of ore deposition are accompanied by transformations of organic compounds and metal organic complexes may be involved in enhancing the transport of metals in ore forming and other crustal fluids with these thoughts in mind this review starts with an inventory of the types of organic compounds found in hydrothermal systems and some ways that hydrothermal organic compounds are transformed methane can be generated biotically and abiotically from organic or inorganic reactants and since it lacks a carbon carbon bond some researchers would not consider it to be an organic compound nevertheless more data exist for methane in hydrothermal fluids than for any organic compound that fits the definition methane has been quantified in continental and submarine hydrothermal fluids fumarolic gases associated with hydrothermal systems oil field brines deep fluids in sedimentary basins and igneous basement rocks fluids associated with active serpentinization and fluid inclusions in minerals from ore deposits sedimentary basins and deep crustal settings recent examples include

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

review and update of the applications of organic petrology part 2 geological and multidisciplinary applications abstract the present paper is focused on organic petrology applied to unconventional and multidisciplinary investigations and is the second part of a two part review that describes the geological applications and uses of this branch of earth sciences therefore this paper reviews the use of organic petrology in investigations of i ore genesis when organic matter occurs associated with mineralization ii the behavior of organic matter in coal fires self heating and self combustion iii environmental and anthropogenic impacts associated with the management and industrial utilization of coal iv archeology and the nature and geographical provenance of objects of organic nature such as jet amber other artifacts and coal from archeological sites and v forensic science connected with criminal behavior or disasters this second part of the review outlines the most recent research and applications of organic petrology in those fields

geology and geochemistry of three sedimentary rock hosted disseminated gold deposits in guizhou province people s republic of china abstract five sedimentary rock hosted disseminated gold deposits have been discovered since 1980 in southwestern guizhou province prc submicron sized gold is disseminated in silty carbonate and carbonaceous shale host rocks of permian and triassic age arsenic antimony mercury and thallium accompany the gold associated hydrothermal alteration resulted in decarbonatization of limestone silicification and argillization and depletion of base metals barium and many other elements organic material occurs in most host rocks and ores it was apparently devolatilized during a regional heating event that preceded hydrothermal activity and thus was not mobilized during mineralization and did not affect gold deposition the geologic setting of the guizhou deposits includes many features that are similar to those of sedimentary rock hosted deposits of the great basin western united states the heavy element suite that accompanies gold is the same but base metals are even scarcer in the guizhou deposits than they are in u s deposits the guizhou deposits discovered to date are smaller than most u s deposits and have no known spatially associated igneous rocks

hydrothermal petroleums from yellowstone national park wyoming u s a abstract in yellowstone national park oil is actively discharging with thermal waters at several widely separated thermal areas samples from two locations were studied petroleum from calcite springs occurs as vapor condensates in steam vents detailed geochemical analyses show a complex origin for the petroleum fluid deeply buried hydrothermally altered sedimentary rocks are believed to have contributed a high temperature pyrolysate consisting largely of polynuclear aromatic hydrocarbons and heterocyclic compounds shallow sedimentary rocks which are also hydrothermally altered have contributed large amounts of aromatic and polar compounds as well as minor amounts of hydrocarbons the permian phosphoria formation is suggested as a likely source rock for the bulk of the oils autochthonous pyrolysates and lipids from thermally altered surface and near surface bacterial and land plant debris have also been introduced to the vents the latter may have been introduced by downward percolating meteoric water the oil from rainbow springs is a highly paraffinic low s crude oil depleted in light hydrocarbons unlike the calcite springs samples the oil from rainbow springs is believed to have originated from a single sedimentary source rock with little or no hydrocarbon contributions from surface biota the oil contains a unique molecular marker assemblage that suggests both gymnosperm and angiosperm input and places the age of the source unit in the tertiary consideration of the local stratigraphy and water temperatures limits the probable source zone to the eocene aycross formation an intra volcanic lacustrine mudstone calculation of deep water temperatures indicates that this unit is exposed to thermal waters in an extensive near surface aquifer such conditions are consistent with the widespread surface manifestations and biomarker kinetic models consideration of the petroleum chemistry and regional hydrodynamics indicates that the yellowstone park oils did not migrate into the park from distant sources the chemical data are also inconsistent with the oils being generated and trapped prior to tertiary volcanism at both calcite springs and rainbow springs oil generation appears to be contemporaneous and is attributed to thermal alteration of relatively shallow sedimentary rocks by hydrothermal fluids

organic petrology chemical composition and reflectance of pyrobitumen from the el soldado cu deposit chile solid pyrobitumen residual petroleum is found intimately associated with sulfides in several manto type strata bound cu deposits of central chile el soldado lat 32 38 8 s long 71 06 7 w is one of the largest deposits of this type 130 mt 1 5 cu and is hosted by volcanic and subvolcanic rocks of the cretaceous lo prado fm detailed organic petrology of authigenic sulfide inclusions degassing vesicles and anisotropic pyrobitumen and graphitic carbon allowed the elucidation of a complex diagenetic history of a biodegraded reservoir in faulted volcanic and subvolcanic rocks due to the overmaturity of the host sequence biomarker techniques aliphatic and aromatic were unsuitable to investigate the composition of the pyrobitumen however microprobe and laser ablation inductively coupled plasma mass spectrometry la icpms analyses rock eval pyrolysis and 13 c nmr techniques were used to ascertain the composition of the pyrobitumen spatial variations in the maturity of the pyrobitumen were assessed using both random reflectance r o and rotational reflectance r omax and r omin the data are consistent with the following evolution for el soldado as a result of burial in the cretaceous back arc basin petroleum was generated from organic rich shales in the underlying lower lo prado fm and migrated into primary and structural porosity in the host rocks the predominantly volcanic upper lo prado fm low temperature 90 c biodegradation of petroleum developed an early assemblage stage i assemblage of pyrite sphalerite chalcopyrite geopetal structures related to pressure degassing of semisolid petroleum suggest that migration occurred while the strata were horizontal at ca 130 ma continued basinal burial led to thermal degassing increased maturation and contraction of the petroleum into pyrobitumen around 20 ma later an influx of high temperature ca 250 350 c cu rich fluids induced by regional granitoid intrusion stage ii assemblage replaced preexisting pyrite and pyrobitumen the mineralizing fluids altered the pyrobitumen physically and chemically a increasing r o to greater than ca 5 in the core of the orebodies against a background level of ca 3 b developing anisotropy nongranular fine to coarse mosaic and coarse flow mosaic within the pyrobitumen and locally graphitized the pyrobitumen developing graphitic carbon and c incorporating cl cu fe into the pyrobitumen during the development of anisotropy

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

on the formation of granulites the tectonic settings for the formation and evolution of regional granulite terranes and the lowermost continental crust can be deduced from pressure temperature time p t time paths and constrained by petrological and geophysical considerations p t conditions deduced for regional granulites require transient average geothermal gradients of greater than 35 c km 1 implying minimum heat flow in excess of 100 mwm 2 such high heat flow is probably caused by magmatic heating tectonic settings wherein such conditions are found include convergent plate margins continental rifts hot spots and at the margins of large deep seated batholiths however particular p t time paths do not allow specific tectonic settings to be distinguished at this time under different conditions both clockwise cw pmax attained before tmax and anticlockwise acw pmax attained slightly after tmax paths are possible in the same tectonic setting both cw and acw end member paths can yield nearly isobaric cooling ibc paths such cooling paths are clearly not an artefact of thermobarometry but can be constrained by solid solid and devolatilization equilibria and geophysical modelling in terms of understanding the evolution of the deep crust a potentially significant group of regional granulite terranes are those that show evidence for acw ibc paths such paths are the likely result of i episodic igneous activity resulting in intrusions within all levels of the crust ii thickening of the crust by magmatic underplating iii slow uplift as a result of the formation of a deep garnet rich crustal root and iv excavation resulting from a later tectonic event unrelated to that resulting in the formation of the granulites the later event might be triggered by the delamination of the garnet rich lowermost crust

the hulan group its role in the evolution of the central asian orogenic belt of ne china the hulan group of central jilin province northeastern ne china consists of felsic volcanic and sedimentary rocks that underwent sub greenschist to amphibolite facies metamorphism and multiple phases of deformation during formation of the central asian orogenic belt young nd model ages of 1100 ma obtained in this study do not support earlier models that the hulan group was either rifted from the north china craton to the south or from the jiamusi block to the north since both these blocks have much older nd model ages detrital zircon u pb ages from a meta sedimentary rock of the hulan group define a maximum age of deposition of 287 6 ma not early palaeozoic as previously believed rb sr mineral isochron data indicate that metamorphism of the hulan group occurred at 250 ma this conclusion is further supported by an age of 248 4 ma for the dayushan granite which intruded the hulan group these new isotopic data together with evaluation of the regional geology indicate that final oceanic closure in the chinese segment of the central asian orogenic belt took place in the late permian the hulan area is located along the solonker xra moronchangchun suture that extends from inner mongolia across to central jilin province it is this zone that marks the final ocean closure resulting in the amalgamation of the north china and siberian cratons 2007 elsevier ltd all rights reserved