u pb zircon and 40 ar 39 ar geochronology of sericite from hydrothermal alteration zones new constraints for the timing of ediacaran gold mineralization in the sukhaybarat area western afif terrane saudi arabia the sukhaybarat east and red hill deposits in the northeastern part of the arabian shield are mesothermal vein type gold deposits hosted by late cryogenian ediacaran intrusive rocks of the idah suites diorite tonalite granodiorite and at sukhaybarat east also by ediacaran metasedimentary rocks gold mineralization comprises quartz arsenopyrite veins sukhaybarat east quartz carbonate pyrite veins red hill and subordinate gold base metal sulfide veins in the red hill deposit alteration is complicated due to multiple overprinting hydrothermal events and is characteristically affected by pervasive pink quartz k feldspar hematite alteration which is overprinted by potassic alteration characterized by a quartz biotite carbonate muscovite sericite rutile apatite assemblage this assemblage is associated with molybdenite veins which appear to form late in the paragenetic sequence and may represent either evolution of the ore fluid composition or a later unrelated mineralized fluids hydrothermal alteration at the sukhaybarat east deposit is dominated by quartz carbonate sericite arsenopyrite assemblages zircon from ore hosting tonalite at sukhaybarat east yields a u pb age of 629 6 ma and biotite from the same rock gives an 40ar 39ar age of 622 23 ma the 40ar 39ar age is within the uncertainty range for the u pb age of the host intrusion and is interpreted as a minimally disturbed cooling age for the tonalite in the red hill area granodiorite was emplaced at 615 5 ma whereas muscovite sericite separated from a mineralized sample of a quartz carbonate pyrite vein that was overprinted by molybdenite bearing veinlets yields an 40ar 39ar age of 597 8 ma we interpreted this age to represent the maximum age of the molybdenite mineralization and the probable minimum age of gold mineralization in the red hill deposit

mesozoic cenozoic tectonic evolution and metallogeny in myanmar evidence from zircon cassiterite u pb and molybdenite re os geochronology abstract it is well known that there are many sn w mo and cu au metal resources in myanmar however the absence of precise mineralization ages for these deposits significantly hinders to understand the close genetic relationship among metallogeny ore bearing intrusions and tectonic evolution in this study two groups of consistent molybdenite re os and zircon u pb ages indicate that the dapingba mo w deposit in northern myanmar tengchong terrane formed at early cretaceous 119 ma and 114 ma the dapingba ore bearing granitic magmas were mainly derived from melting of ancient tengchong crust on the basis of zircon hf isotopic compositions ehf t 9 3 to 2 5 moreover the first reported cassiterite u pb ages of 60 ma for the bawapin and kalonta sn w deposits in southern myanmar western sibumasu terrane suggest that the two deposits formed at paleocene whereas the precise molybdenite re os age for the shangalon porphyry cu au deposit in the west burma terrane indicates that this deposit formed at eocene 39 ma importantly combined with previous studies on tectonic evolution and magmatic petrogenesis in myanmar and southwest china a comprehensive mesozoic cenozoic tectono magmatic and metallogenic model are proposed two periods of early cretaceous 120 114 ma and late cretaceous 75 70 ma crust derived felsic melts and related mo sn w deposits from the tengchong and western sibumasu terranes likely formed in a continental arc during subduction of the meso and neo tethys oceanic lithosphere respectively subsequently paleocene eocene 60 50 ma sn w deposits and coeval ore bearing granites in the western sibumasu terrane possibly formed during roll back of the neo tethys oceanic slab after 50 ma india asia collision eocene 41 39 ma porphyry cu au west burma terrane and sn w deposits western sibumasu terrane likely formed during the neo tethys oceanic slab tear and break off in a collisional setting whereas miocene 19 14 ma high sulfidation epithermal cu deposit in the west burma terrane possibly formed in an arc setting during oblique subduction of the indian oceanic lithosphere

compositional variability in oils and formation waters from the ayoluengo and hontomin fields burgos spain implications for assessing biodegradation and reservoir compartmentalization abstract the main scope of this work is the geochemical characterization of 12 crude oils and formation waters of the ayoluengo oilfield basque cantabrian basin nw spain to delineate its reservoir compartmentalization the ayoluengo oil characteristics were also compared with data obtained from crude oil and formation water of the hontomin 2 well located 25 km to the se of ayoluengo the 13 ayoluengo and hontomin oil samples are very similar in composition bulk properties and isotopic signature indicating that these oils are genetically related however the hontomin oil is more mature and it is slightly biodegraded which suggests some differences in the reservoir environments the molecular parameters of both oils confirm a marine origin related to a liassic source rock coincident with the occurrence of lateral facies changes along the sedano sub basin on the other hand the connate waters are analogous and both classified as chloride calcium type given the complex nature of the sedimentology and structures of the reservoir gas chromatographic fingerprints of the analyzed crude oils have been used to detect minor variations in composition that are indicative of reservoir compartmentalization

wind tunnel experiments and field measurements of aeolian dust deposition on conical hills abstract the spatial pattern of short term aeolian dust deposition on and around cone shaped hills is investigated via the simulation in a wind tunnel of dust storms over a topographic scale model of a conical hill in the negev desert israel the results are tested during a full scale dust storm in the negev the wind tunnel experiments adequately predict the field pattern although some problems may arise on steep windward slopes where the accumulation threshold is more quickly exceeded on the scale model than in the field conical hills create an elongated area of low deposition dust shadow in their lee downwind from the shadow zone a local area of more than normal compared to the undisturbed surroundings deposition occurs on the lateral flanks of the hill and also on the small convex windward slope just upstream of the top and at the top itself dust deposition remains low to very low it is the lowermost concave windward slope that receives the largest amounts of dust the pattern described above refers to short term deposition only water erosion may seriously alter the final accumulation pattern since it will clean the slopes of important amounts of dust that accumulate in the wadis

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

effect of rock fragment eccentricity on eolian deposition of atmospheric dust abstract the effect of rock fragment eccentricity on the deposition of airborne dust was examined in a wind tunnel eccentricity was defined as the ratioa b wherea is the longest andb the intermediate axis of the rock fragments the effect of eccentricity on the deposition of dust on the pebbles on the deposition of dust between and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately and this for different values of pebble size pebble flattening cover density and wind speed the more pebbles are elongated the larger dust deposition on them will be this effect is more pronounced as pebbles become larger as they become less flattened and as wind speed increases but no correlation is observed with cover density it also holds that the more pebbles are elongated the less dust settles between and underneath them this effect is more pronounced as pebbles become smaller and cover density becomes larger but there is no relationship with pebble flattening whether or not there is a relationship with wind speed is unclear pebble eccentricity indirectly influences total dust deposition on a pebble field since it determines whether or not and to what extent total dust deposition will be a function of pebble size for circular pebbles total dust deposition is independent of pebble size but once pebbles become elongated total dust deposition will be smaller on pebble fields composed of small pebbles than on pebble fields composed of large pebbles it was also demonstrated that the more pebbles are elongated the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation plays a primary role in the deposition of dust on a rock fragment field since it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles highly elongated pebbles oriented parallel to the wind catch much more dust also per unit surface than circular pebbles the surface of which is largely located in a zone of very low deposition dust deposition density on highly elongated pebbles normal to the wind on the contrary is equal to dust deposition on circular pebbles it should be noted that all data in this study refer to initial dust deposition not accumulation since only wind velocities below the dust deflation threshold were tested

biochemical evolutionary significance of ordovician oils and their sources abstract geochemical data from several ordovician oils and kerogens from distinct basins in canada united states estonia and australia show some unique compositional characteristics the oils analyzed by gas chromatography and gas chromatography mass spectrometry are characterized by an odd dominance in the c9 c19 molecular weight range of normal paraffins and an odd dominated homologous series of cyclohexyl substituted normal paraffins the oils contain an unusually small amount of c20 components and pristane and phytane are conspicuous by their virtual absence the compositions of the oils and kerogens correlate closely and display characteristics that have not been observed in younger sediments the predominant organism found in the source kerogens for these unique oils is gloeocapsamorpha prisca a primitive prokaryotic organism data from the analysis of gloeocapsamorpha rich kerogens and the association of this organism with ordovician source rocks indicate a genetic relationship exists between the organism and the unusual oil chemistry the chemistry of the oils and kerogens suggests that gloeocapsamorpha was either non photosynthetic or that it fixed light using a chlorophyll that did not contain a phytyl side chain e g a bacteriochlorophyll the widespread occurrence of oils and kerogens possessing such a uniform composition appears unique to the ordovician certainly to the early paleozoic this suggests that paleocological conditions of ordovician anoxic environments were very similar and g prisca was particularly well adapted to these conditions

genesis of the xiaolonghe quartz vein type sn deposit sw china insights from cathodoluminescence textures and trace elements of quartz fluid inclusions and oxygen isotopes abstract quartz textures revealed by scanning electron microscope cathodoluminescence sem cl images suggest that quartz in the xiaolonghe sn deposit formed in at least three fluid episodes quartz q1 in the pre ore silicification zone has homogeneous texture high cl intensity and high ti content 19 53 ppm fluid inclusions hosted in q1 are vapor rich v1 type and homogenized as supercritical fluid at 570 c quartz q2 in the syn ore topaz cassiterite quartz veins has lower cl intensity and is characterized by euhedral growth zones with lower ti content 1 3 12 ppm fluid inclusions hosted in q2 topaz and cassiterite are liquid rich fluid inclusions of moderate salinity 15 wt nacl equiv l1 type which homogenized at 423 c the post ore quartz q3 closely associated with sericitization of topaz generally crosscuts q2 and has dark cl intensity and much lower ti concentration the upper limits of t p conditions of pre ore and syn ore stage are constrained by the intersection of nacl h2o fluid inclusion isochores and ti in quartz isopleths and the lower limits are based on microthermometry results of fluid inclusions combined with the 18ofluid value 8 3 of q1 it indicates that the pre ore supercritical fluid was directly exsolved from a granitic magma at t 570 600 c and p 0 70 0 77 kbars corresponding to a maximum depth of 2 8 km under lithostatic pressure the syn ore subcritical fluid 8 0 18ofluid 6 3 mixed with some meteoric water was under 423 450 c 0 32 0 45 kbars the transition from the pre ore supercritical fluid to the syn ore subcritical fluid indicates boiling condition probably at 512 c 0 62 kbars which was likely caused by hydraulic fracturing under high pressure both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in xiaolonghe sn deposit in the post ore stage the coexisting s type and v2 type fluid inclusions in q3 indicates a second fluid boiling at 269 c 0 05 kbars which was probably caused by decompression due to rapid denudation of the overlain strata the low salinity 5 5 wt nacl equiv l2 type fluid inclusions hosted in fluorite homogenized at 199 c and

some aspects of the organic geochemistry of petroleum fluids the most important influences on the compositions of petroleum fluids are in many cases the composition of a petroleum sample may allow the depositional environment of its source rock and its temperature history before and after expulsion to be determined this information assists the search for more petroleum in a region we suggest that this approach should be used more frequently to validate models of petroleum generation and migration in the second part of the paper we discuss the origin and nature of the differences in petroleum composition which are frequently found within individual petroleum reservoirs petroleum accumulations in permeable reservoirs are normally found to be inmechanical equilibrium and verticalchemical equilibrium this is manifested by constant subsurface fluid density at any given depth across the accumulation and increases in subsurface density with depth known as gravitational segregation however even in permeable reservoirs lateral differences in composition inherited from the reservoir filling process are not totally eliminated by mixing processes such as diffusion and convection thus lateral chemical equilibrium is often not achieved and lateral compositional variations are observed in present day oil and gas reservoirs these observations are justified in terms of order of magnitude estimates for the rates at which reservoirwide mixing occurs a case history is presented

the effect of surface curvature on the deposition of loess a physical model summary a physical model for the deposition of fine dusty material loess on curved surfaces is presented the model is tested in a sedimentation experiment with a symmetrical hill with length axis perpendicular to the flow direction in a wind tunnel it appears both from the model and the experiment that loess deposition will occur preferably on windward slopes and not on leeward ones in contrast to the widespread wind shadow concept below the deflation threshold loess deposition increases as wind speed increases above the deflation threshold an effective accumulation of the loess layer on the surface will occur within a well defined wind speed interval the loess layer on the surface will erode away only if wind speed has exceeded this interval for flat and dry surfaces free of roughness elements the upper limit of the interval is 7 m s free stream velocity for wet surfaces however it may be considerably higher 15 m s and more

metallogeny of tin in central thailand a genetic concept tin mineralization in central thailand is associated with granitic rocks of the thai burmese border range western group granitic intrusions east of bangkok and near the kampuchea border eastern group have no tin fractional crystallization is the fundamental petrogenetic process that controls the evolution of both groups of granites the tin bearing alkali feldspar aplogranites of the western group display an extreme degree of differentiation that has no petrological equivalent in the eastern group these aplogranites are the product of a combination of magmatic fractionation primary tin enrichment trend modified by fluid interaction the latter process is responsible for a secondary geochemical tin deficiency that is balanced by redistribution of tin in fracture systems i e tin mineralization the pattern of tin depletion in the aplogranites provides an indication of the tin potential in a given ore forming system

effect of rock fragments on eolian deposition of atmospheric dust abstract the effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel four parameters were studied pebble size pebble flattening cover density and wind speed the effect of these parameters on the deposition of dust on the pebbles on the deposition of dust bewween and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately deposition on the pebbles increased with pebble size pebble flattening and wind speed deposition between and underneath the pebbles increased with increasing wind speed and with decreasing pebble flattening but there was no consistent relationship with pebble size total dust deposition was not influenced by pebble size pebble flattening and cover density but it increased linearly with wind speed it was also demonstrated that the larger and the flatter the pebbles and the higher cover density the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rock fragment field as it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles it should be noted that all data in this study refer to dust deposition not accumulation since only wind velocities below the dust deflation threshold were used

rift basins of interior sudan petroleum exploration and discovery in early 1975 chevron overseas petroleum inc commenced what became a major petroleum exploration effort in previously unexplored interior sudan with the cooperation of the sudanese government chevron has acquired a vast amount of geological and geophysical data during the past 12 years these data include extensive aeromagnetic and gravity surveys 36 040 mi 58 000 km of seismic data and 86 wells this information has defined several large rift basins now recognized as a major part of the central african rift system the sedimentary basins of interior sudan are characterized by thick nonmarine clastic sequences of jurassic cretaceous and tertiary age over 45 000 ft 13 716 m of sediment was deposited in the deepest trough and extensive basinal areas are underlain by more than 20 000 ft 6 096 m of sedimentary rocks the depositional sequences include thick lacustrine shales and claystones floodplain claystones and lacustrine fluvial and alluvial sandstones and conglomerates those lacustrine claystones deposited in a suboxic environment provide good oil prone source rocks reservoir sandstones have been found in a wide variety of nonmarine sandstone facies the extensional tectonism that formed these basins began in the jurassic early cretaceous movement along major fault trends continued intermittently into the miocene this deformation resulted in a complex structural history that led to the formation of several deep fault bounded troughs major interbasinal highs and complex basin flanks this tectonism has created a wide variety of structures many of which have become effective hydrocarbon traps during the past eight years several important oil discoveries have been made significant accumulations have been delineated in the heglig and unity areas where estimated recoverable reserves are 250 300 million bbl of oil

oil composition variation and reservoir continuity unity field sudan abstract a suite of oils from stacked reservoirs in the unity field in sudan has been analyzed by various geochemical techniques for molecular information to elucidate the geological processes which cause variations in oil composition and their resulting oil fingerprints in different reservoir units analyses of these highly paraffinic oils indicate that the chromatographic fingerprint variations are due to differences in the abundances of saturated compounds including branched and cyclic alkanes neither aromatics nor nso compounds have any significant effect on the observed fingerprint variations this association of saturates instead of aromatics and nso compounds with the fingerprint variations precludes rock fluid interactions as a cause of the variations biomarker analyses show that variations in thermal maturity and organic facies of the source rock are responsible for the fingerprint variations thermal maturity increases with the depth of the reservoir suggesting a multiple charge process for the oils to fill these reservoirs over an extended period of time apparently the source rock generated and expelled progressively more mature oils and little mixing occurred during migration thus knowledge of oil compositional variations from one reservoir to another organic facies variation and source rock maturity combined with tectonic history may help explain charging and timing of oil emplacement

effect of rock fragment embedding on the aeolian deposition of dust on stone covered surfaces many stone covered surfaces on earth are subject to aeolian deposition of atmospheric dust this study investigates how the deposition of dust is affected when rock fragments become gradually more embedded in the ground or inversely become more concentrated on the surface experiments were executed in an aeolian dust wind tunnel with eight different types of pebbles the following parameters were measured dust deposition on the pebbles dust deposition between and underneath pebbles total dust deposition pebbles inter pebble space and the fraction of total deposition of dust caught by the pebbles alone the absolute amount of dust deposition and the dust deposition density dust deposition per unit surface were studied for each parameter the effects exerted by pebble size pebble flattening pebble elongation and wind speed were also investigated dust patterns on and around pebbles were also studied via flow visualization the absolute amount of dust settling on pebbles decreases the more that the pebbles become embedded dust deposition density on pebbles on the other hand increases with embedding the more pebbles become embedded in the soil the more efficient the process of dust deposition on pebbles becomes dust deposition between and underneath pebbles increases with pebble embedding dust deposition density between and underneath pebbles is maximum at 50 per cent embedding showing that in this area dust deposition is most efficient when pebbles are halfway embedded total deposition slightly decreases the more pebbles become embedded but total dust deposition density increases with embedding aerodynamic flow separation and diverging and converging airflow play an important role in the process of dust deposition on stone covered surfaces the more pebbles protrude above the soil the more they act as an obstacle and the more they disturb the air and dust flow creating scouring zones flow separation bubbles and shelter areas for the dust all these effects diminish as pebbles become more embedded in the soil however perturbations in dust patterns remain visible until pebbles have disappeared entirely

geochronology geochemistry and sr nd hf isotopic compositions of late cretaceous eocene granites in southern myanmar petrogenetic tectonic and metallogenic implications abstract the geochronology petrogenesis and tectonic setting of granites associated with tin tungsten mineralization in southern myanmar remain unclear this work presents whole rock geochemical sr nd isotopic and zircon u pb and hf isotopic data for felsic intrusions in the sibusima terrane zircon u pb dating indicates formation in the late cretaceous early eocene 84 48 ma and suggests that these intrusions likely represent a southward extension of the coeval magmatic belt in the tengchong terrane primarily classified as high k calc alkaline the granites show strong enrichments in large ion lithophile elements e g cs rb and k depletions in nb ta p and ti and negative ba and sr anomalies on primitive mantle normalized diagrams p2o5 cao al2o3 mgo tio2 contents and nb ta ratios decrease with increasing sio2 contents possibly consistent with evolution trends in fractionated i type granitic magmas in addition these intrusions display a wide range of negative end t 14 6 5 5 and zircon ehf t values 22 7 5 7 suggesting a dominant sibusimacrustal source with a minor mantle contribution notably the eocene and a few paleocene granites show more contribution of mantle material based on higher end t 8 5 5 5 and zircon ehf t 11 0 3 2 values large variations in zircon hf isotopic compositions within an individual eocene granitic intrusion e g 15 2 5 7 and corresponding biotite rich enclave 17 8 0 2 likely indicate magma mixing considering the spatial temporal distribution of magmatism in the west burma and sibusima terranes the studied late cretaceous eocene felsic magmas likely formed in a continental arc setting during normal subduction 100 60 ma and subsequent roll back of the neo tethyan oceanic lithosphere 60 50 ma additionally most of granites have the elevated sn with increasing rb sr ratios and decreasing tio2 contents and nb ta ratios suggesting sn enrichment is primarily controlled by magmatic fractionation meanwhile sn and li depletions in some granites deviate from the magmatic evolution trend likely as a result of fluid exsolution the exsolved sn rich fluids could have made a genetic contribution to hydrothermal sn mineralization in southern myanmar

neo tethyan magmatism and metallogeny in myanmar an andean analogue abstract plate margin tectonism magmatic and hydrothermal processes and the genesis of mineral deposits are intricately linked in myanmar two near parallel magmatic belts that together contain a significant proportion of that country s mineral wealth have contrasting metallogenic endowments the mogok mandalay mergui belt hosts crustal melt s type granites with significant tin tungsten mineralization while the wuntho popa arc comprises i type granites and granodiorites with copper gold mineralization the spatial juxtaposition of the two belts and their distinct but consistent metallogenic endowment bears strong similarities to the metallogenic belts of the south american cordillera recent u pb age dating has shown the potential for the two belts to be near contemporary from the late cretaceous to eocene here we investigate whether an andean type setting during subduction of neo tethys could explain the observed magmatism and mineralization within these two belts

hydrocarbon biomarkers from ordovician sediments and the fossil alga gloeocapsomorpha prisca zalessky 1917 numerous ordovician oils worldwide are known to show unusual and distinctive distributions of hydrocarbons which it has been suggested are derived from a unique benthonic mat forming non photosynthetic prokaryotic organism gloeocapsomorpha prisca zalessky 1917 which is the major contributor of organic matter organic matter rich sediments from the canning and amadeus basins of australia known to contain g prisca fossils and to have the characteristic predominance of odd carbon number c13 c19 n alkanes were investigated to determine other hydrocarbon distributions sediments from both basins contained abundant n alkylcyclohexanes with odd carbon number predominance c13 c19 and methyl n alkylcyclohexanes c14 c20 which in immature sediments showed an even carbon number predominance the isomer distribution of these latter compounds was determined by direct comparison with synthetic standards the sediments from both basins also contained very similar distributions of steranes and pentacyclic triterpanes and the derived kerogens had a characteristically light carbon isotope signature pyrolysis of a g prisca rich kerogen yielded a hydrocarbon mixture with a similar composition to the sediment extract except that there was a marked increase in the relative abundance of pristane phytane alkylcyclohexanes steranes and hopanes relative to n alkanes we argue on the basis of the geological geochemical and palynological data that g prisca was probably planktonic photosynthetic and very possibly eukaryotic and that the striking character of ordovician oils and sediments derive from bacterial and other diagenetic imprints superimposed on the primary signature of this organism

heterogeneity of oil composition within a reservoir as a reflection of accumulation history abstract the unaltered petroleums of a small oil field in the f r germany reveal pronounced spatial heterogeneities in bulk and molecular composition over most of the field area the oil in high porosity high permeability sand intervals bears a higher proportion of saturated hydrocarbons and has a higher maturity chemical signature as compared to oils occupying lower porosity lower permeability zones for all sands with less than about 13 porosity a regular relationship was observed between oil composition and porosity permeability with a decrease of the latter petrophysical properties increasingly lower chemical maturities and increasingly different bulk chemical compositions lower proportions of saturated hydrocarbons and higher proportions of nso compounds were recorded maximum contrasts measured for chemical maturities are e g 0 63 versus 0 82 vitrinite reflectance equivalents rc values calculated on the basis of the methylphenanthrene index according to radke and welte 1983 0 31 versus 0 84 for the ratio of triaromatic to mono plus triaromatic steroid hydrocarbons and 0 38 versus 0 47 for the 20s 20s 20r ratio of c29 5 h 14 h 17 h steranes these spatial heterogeneities in the composition of the oils are interpreted to reflect 1 i successive stages of trap filling due to episodes of increasing burial and maturation of the relevant source rocks in combination with 2 ii low rates of in reservoir mixing of these individual oil charges by convection or diffusion recognition of compositional heterogeneities within the oil column of individual fields may not only provide a basis for the reconstruction of reservoir filling history but may also have important implications for improving petroleum production

mid chain branched mono and dimethyl alkanes in hot spring cyanobacterial mats a direct biogenic source for branched alkanes in ancient sediments hot spring cyanobacterial mats from yellowstone national park u s a and the orakei korako thermal area new zealand have been found to contain suites of monomethyl alkanes compounds frequently reported in cultured and natural populations of cyanobacteria the complete range of possible structural isomers for mid chain branching for c17 c18 and c16 c18 alkanes occurs in the two mats respectively several c19 dimethyl and c20 multibranched alkanes were also observed as major hydrocarbons of the orakei korako mat the recognition of series of mid chain branched alkanes in modern cyanobacterial mats suggests that their occurrence in ancient sediments may reflect direct biogenic contributions rather than formation by diagenetic processes

sims u pb zircon geochronological and geochemical study of the sn deposits in tengchong north of the southeast asian metallogenic belt implications for the timing of mineralization and ore genesis abstract the tengchong lianghe sn polymetallic metallogenic zone is located in the northern segment of the southeast asian tectonic region it is an important part of the southeast asian giant sn metallogenic belt and contains two large sn deposits the xiaolonghe deposit in the north and the lailishan deposit in the central region the sn mineralization is closely spatiotemporally related to mesozoic and cenozoic granitic magmatic activity in the xiaolonghe and lailishan sn deposits the sn mineralization is closely related to biotite granites the sims u pb zircon dating analysis of the host biotite granites integrated with the la icp ms u pb data from cassiterite precisely constrain the formation of mineralization at xiaolonghe and lailishan sn deposits to 75 76 ma the late cretaceous and 50 51 ma the early eocene respectively major and trace element analyses show that the host granites from the xiaolonghe and lailishan deposits have high silicon contents and are rich in potassium somewhat alkali and metaluminous to weakly peraluminous and highly differentiated di 91 93 the granites belong to the ilmenite series which formed under reducing conditions zircon 18o of 6 82 7 99 and 5 54 7 30 for the granites from xiaolonghe and lailishan deposits along with the results of previous zircon hf isotope studies and regional data indicates that the xiaolonghe granitic magma mainly originated from the ancient lower crust whereas the lailishan granitic magma is mainly dominated by a crustal source with a small contribution of mantle material combined with the regional geology we propose for the first time the tectonically genetic model for the two episodes of sn mineralization present in the xiaolonghe and lailishan deposits during the amalgamation of the west burma block and the tengchong moulmein block in late cretaceous to early eocene a series of high silicic high potassium calc alkaline metaluminous to weakly peraluminous and collision related granitic magma including the crustal source for the xiaolonghe deposit and the crustal source plus a small amount of mantle material for the lailishan deposit experienced a strong differentiation during which abundant ore minerals precipitated and intruded into the country rocks along deep faults and associated fractures resulting in the development of the xiaolonghe and lailishan sn deposits

aeolian deposition of dust over hills the effect of dust grain size on the deposition pattern wind tunnel experiments were conducted to investigate the effects of topography on the grain size characteristics of aeolian dust deposits experiments were performed on three isolated hills having various size and aspect ratios the longitudinal profile of the median grain diameter was investigated for each hill the longitudinal dust deposition profile was also studied for nine grain size classes of between 10 and 104 m as were wind and dust concentration profiles in the atmosphere upwind of over and downwind of a hill the wind tunnel experiments show that the grain size characteristics of aeolian dust deposits are affected by topography most apparent is the occurrence of a zone of reduced grain size on the leeside of hills which extends from just upwind of the summit to a distance of several times the height of the hill slightly coarser than normal dust is deposited on the concave windward hill slope and in a zone downwind of the area of reduced grain size but the increase in grain size in these zones remains very small although the normalized dust deposition profile for a hill does not vary substantially as a function of grain size systematic trends are observed the most important tendencies are 1 a progressive extension in the downwind direction of a zone of decreased dust deposition on the leeside of a hill the coarser the grains the further downwind the zone of reduced deposition extends 2 a progressive increase in dust deposition immediately upwind of a hill the finer the grains the higher the deposition value upwind of a hill becomes both tendencies are explained by the difference in inertia of the grains which is controlled by grain size copyright 2005 john wiley sons ltd

biotite geochemistry deciphers magma evolution of sn bearing granite southern myanmar abstract hydrothermal sn w deposits are commonly formed by ore forming fluids that exsolved from water saturated granitic magmas however the timing of fluid exsolution and its influence on volatiles and ore forming elements still remain confused for this purpose geochemical and o h isotopic compositions of biotite from late cretaceous eocene granitic intrusions in the sibumasu terrane southern myanmar are presented mno content of biotite is a well negative correlation with the amount of biotite and whole rock la yb n ratio indicating that it could be a good index of granitic magma differentiation cl content of biotite from paleocene granite shows an increased first and subsequently decreased trend with increasing mno content 0 71 2 36 wt suggesting cl enrichment by magma evolution and depletion by late stage fluid exsolution fluid exsolution is also supported reduced li contents of biotite and o h isotopic compositions of residual magmatic water equilibrated with high mno biotite 18o 7 0 to 8 8 and d 114 to 93 5 all studied biotite grains from late cretaceous granite have low cl contents 0 01 0 11 wt decreased li with increasing mno contents and residual magmatic water like o h isotopic values 18o 6 9 and d 105 indicating that their host granitic melts had undergone fluid exsolution importantly a positive correlation between sn and mno contents in biotite suggests that magma differentiation is a dominant process for sn enrichment no depletion of sn by fluid exsolution likely caused by low salinity fluids exsolved from cl poor granitic melts which were estimated by low cl contents of biotite h isotopic compositions 18o 6 8 7 0 and d 61 9 to 90 2 with magmatic water suggesting that ore forming fluids probably exsolved from more evolved granitic melts with strong sn and f enrichment

late cretaceous granites from the giant dulong sn polymetallic ore district in yunnan province south china geochronology geochemistry mineral chemistry and nd hf isotopic compositions abstract as a world class tin tungsten province south china is well known for its extensive mesozoic granitic magmatism the dulong district located in the western cathaysia block of the south china tin tungsten province is characterized by widespread mesozoic granitoids and accompanying sn polymetallic ore deposit 30 mt of sn it is one of the most important polymetallic tin ore districts in china in this study three mineralization related granite types were identified in the dulong district including the dulong coarse grained granite dcg the dulong fine grained granite dfg and the dulong porphyritic granite dpg detailed studies are presented on zircon u pb ages major and trace elements mineral chemical and nd hf isotopic compositions of the tin bearing granites from the dulong district la icp ms u pb dating of zircon grains from these three granite bodies yields ages of 90 1 0 7 ma 89 7 0 8 ma and 86 0 0 5 ma respectively geochemically the granites are strongly peraluminous with high contents of alkalis enrichment in p li rb cs ta sn w and u depletion in ti mg co ni sr ba zr hf th and rare earth elements fractional crystallization of plagioclase and k feldspar was the principal process of magmatic differentiation that controlled rb sr ba and eu concentrations whereas rare earth elements were fractionated by accessory minerals such as apatite and monazite the geochemical data suggest that the rocks are highly fractionated s type granites the granites show bulk rock e nd t values in the range of 12 2 to 10 8 and zircon e hf t values from 15 5 to 2 5 with meso paleoproterozoic t dm c ages for both nd and hf isotopes geochemical and isotopic data suggest that these highly fractionated s type granites dcg dfg and dpg were originated from the same episode of partial melting of the protolith which have analogous components of metamorphosed pelitic rocks from the meso paleoproterozoic continental crust extreme fractional crystallization resulted in enrichment of tin in the evolved granitic magma and the reduced magmas fo 2 below nno would efficiently remove sn into a hydrothermal fluid and lead to deposition of sn rich mineral phases the association of dulong and gejiu magmatism in the western cathaysia block may be likely to mark the onset of back arc extension or intra arc rift in the region during late cretaceous the upwelling of asthenospheric mantle may have triggered partial melting of metasedimentary rocks in the overlying crust to generate the s type granitic magmas

the pemali tin deposit bangka indonesia the pemali tin deposit is located in a triassic granite pluton the magmatic evolution of which is characterized by a decrease of compatible ca mg ti p and zr in the sequence medium to coarse grained biotite granite megacrystic medium grained biotite granite two mica granite muscovite granite the tin mineralization is confined to the two mica granite and consists of disseminated cassiterite as well as greisen bordered veins the highly evolved muscovite granite is tin barren and is distinguished from the two mica granite by its low mica content and low loss on ignition values the fluid inclusions in quartz and fluorite of the two mica granite and of the greisen homogenize in the 115 410 c temperature range the salinities are in the range of 0 4 23 equiv wt nacl and the co2 concentrations are 2 mole

the closure of palaeo tethys in eastern myanmar and northern thailand new insights from zircon u pb and hf isotope data abstract two of the major granite belts of southeast asia are the main range and eastern province together these are interpreted to represent the magmatic expression of the closure of palaeo tethys during late palaeozoic to early mesozoic times recent geochronological and geochemical work has better delineated these belts within peninsular malaysia thereby providing important constraints on the timing of palaeo tethys suturing however the northern extension of this palaeo tethyan suture is less well understood here we present new ion microprobe u pb zircon age data from northern thailand and eastern myanmar measured ages of 219 and 220 ma from the kyaing tong granite imply northern extension of the main range province into eastern myanmar the tachileik granite in far eastern myanmar yields an age of 266 ma consistent with published eastern province ages and this therefore constrains the northern extension of the palaeo tethys suture in eastern myanmar we further discuss how this suture may extend northwards into yunnan a late cretaceous age 70 ma measured in thailand represents later magmatic activity and is similar to published magmatic ages from central myanmar this younger magmatism is interpreted to be related to the subduction of neo tethys prior to india asia collision further we present new laser ablation zircon hf isotope data from eastern myanmar which suggest that palaeoproterozoic crust underlies both the main range and eastern province granites our ehf model age of ca 1750 ma from sibumasu the basement underlying eastern myanmar lies within the range of other model ages reported thus far for the baoshan block north in yunnan interpreted by some to be the northern extension of sibumasu

origin of the granites and related sn and pb zn polymetallic ore deposits in the pengshan district jiangxi province south china constraints from geochronology geochemistry mineral chemistry and sr nd hf pb s isotopes the pengshan sn and pb zn polymetallic deposits are located in the south margin of the jiujiang ruichang jiurui district of the middle lower yangtze river metallogenic belt in south china four large deposits include huangjinwa zengjialong jianfengpo and zhangshiba the former three are sn dominant deposits which occur as stratiform orebodies in the contact zones of the pengshan granites and within the country rock strata whereas zhangshiba consists of stratiform pb zn orebodies within the precambrian metasedimentary strata in this study we present results on zircon u pb ages major and trace elements and mineral chemistry as well as sr nd hf isotope data of the granites pb and s isotopes of both the sn dominant and pb zn dominant deposits and u pb dating of cassiterite from the pengshan district shrimp and la icp ms zircon u pb dating shows that the pengshan granites were emplaced in the early cretaceous 129 128 ma which is in good agreement with the u pb dating 130 128 ma of cassiterite from the jianfengpo sn deposit the pengshan granites consist mainly of weakly peraluminous highly fractionated i type affinity granitic rocks detailed elemental and isotopic data suggest that the granites formed by partial melting of mesoproterozoic metamorphic basement materials with minor input of mantle derived melts the mineral chemistry of biotite demonstrates that the pengshan granitic magma had a low oxygen fugacity thereby precluding the tin dominantly partitioning into the rock forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages sulfur isotopes show a relatively heavy sulfur isotopic composition from 5 8 to 17 6 and no difference for sulfur isotopes between the sn deposits 5 8 13 4 huangjinwa zengjialong jianfengpo and the pb zn deposit mostly 7 1 13 0 except for one 17 6 zhangshiba the sulfur isotope data of pyrite from the host sedimentary rocks show relatively higher 34s values of 22 7 28 7 lead isotopes indicate that the granites have higher 206pb 204pb 207pb 204pb and 208pb 204pb ratios than the host precambrian metasedimentary rocks and the sulfide minerals from the orebodies fall in between them again there is no difference for pb isotopes between the sn deposits huangjinwa zengjialong jianfengpo and the zhangshiba pb zn deposit the coincidence in s and pb isotope compositions for sn and pb zn deposits suggests that similar sources for these mineralization possibly derived from a mixed source of the granitic magmas and the precambrian metasedimentary rocks these data therefore favor of a magmatic hydrothermal origin for both the sn and pb zn polymetallic mineralization in the pengshan district

geochronology and magmatic oxygen fugacity of the tongcun molybdenum deposit northwest zhejiang se china the tongcun mo porphyry deposit in northwest zhejiang is hosted in three porphyry units huangbaikeng songjiazhuang and tongcun from southwest to northeast u pb zircon ages of 162 3 0 ma for the huangbaikeng porphyry 159 9 3 0 ma for the songjiazhuang porphyry and 167 6 155 6 ma for the tongcun porphyry indicate that these intrusions formed during the jurassic and are most likely associated with the northwestward subduction of the izanagi plate trace element compositions of zircons from the tongcun deposit constrain the oxygen fugacity fo2 of the magma using zircon ce anomalies and ti in zircon temperatures the average magmatic fo2 for the porphyries in the tongcun deposit is fayalite magnetite quartz fmq 2 7 which is similar to the shapinggou fmq 3 2 and dabaoshan fmq 3 5 mo porphyry deposits but much higher than that of the reduced cretaceous ore barren shangjieshou porphyry fmq 1 1 around 8 km away from the tongcun deposit the distinct difference in magmatic oxygen fugacity between the jurassic and cretaceous porphyries may help to explain the absence of mo porphyry mineralization in northwest zhejiang during the cretaceous

possible late middle ordovician organic carbon isotope excursion evidence from ordovician oils and hydrocarbon source rocks mid continent and east central united states oils generated by middle ordovician rocks are found throughout the mid continent and east central regions of the united states gas chromatographic characteristics of these oils include a relatively high abundance of n alkanes with carbon numbers less than 20 a strong predominance of odd numbered n alkanes between c10 and c20 and relatively small amounts of branched and cyclic alkanes saturated and aromatic hydrocarbon fractions of 43 ordovician oils from the anadarko ardmore forest city illinois michigan salina sedgwick and williston basins and the iowa shelf demonstrate a wide range in carbon isotope composition dgr13csat 24 9 pmil to 33 9 pmil dgr13carom 24 3 pmil to 33 7 pmil saturated and aromatic hydrocarbons extracted from late middle ordovician shales 17 core samples show ranges in dgr13c similar to that of the oils the wide ranges in dgr13c for oils and rock extracts reflect a major positive excursion s 6 9 per pmil in organic matter dgr13c in late middle ordovician rocks this excursion has at least a regional significance in that it can be documented in sections 480 mi 770 km apart in south central kansas and eastern iowa the distance may be as much as 930 mi 1 500 km if the carbon isotope variations observed in michigan basin ordovician oils and in organic matter from late middle ordovician rocks in southwestern ontario are related to the same carbon isotope excursion organic matter dgr13c in core samples from south central kansas and eastern iowa is not directly related to variations in quantity or quality of organic matter or maceral compositi n the positive excursion in organic matter dgr13c is a possible result of increased organic matter productivity and or preservation the parallel shifts in organic and carbonate dgr13c in core samples from 1 e m greene well washington county iowa imply changes in the isotope composition of the ocean atmosphere carbon reservoir differences in the magnitude of the carbon isotope shifts between organic matter 8 8 pmil and carbonate 4 2 pmil in this core suggest a decrease either locally or regionally in available dissolved co2 possibly a result of high organic matter productivity and or limited circulation in the late middle ordovician seas

combined zircon molybdenite and cassiterite geochronology and cassiterite geochemistry of the kuntabin tin tungsten deposit in myanmar

branched alkanes from ancient and modern sediments isomer discrimination by gc ms with multiple reaction monitoring abstract linked scanning of a tandem sector mass spectrometer has been used to identify abundant first field free region ffr1 unimolecular fragmentations in branched and isoprenoid hydrocarbons the most intense structure specific reactions were selected to establish multiple reaction monitoring mrm parameters for gc ms analysis this methodology has been used to study the identity of co eluting and closely eluting hydrocarbon biomarkers from modern and ancient sediments anand from extant micro organisms some sediments of cambrian and proterozoic age have been found to contain suites of monomethylalkanes with all possible isomers present and with little apparent preference for the site of branching

wind tunnel experiments of aeolian dust deposition along ranges of hills wind tunnel experiments of aeolian dust deposition on topographic scale models of ranges of hills were conducted different hill sizes and hill spacings were used and comparisons with the deposition patterns over single isolated hills were made dust profiles over ranges of hills differ from the profiles over identical but isolated hills on isolated hills the sedimentation maximum on the windward hillslope is always single and located on the concave part of the slope in the case of ranges of hills the maximum is either single or double with the second peak on the convex part of the windward slope in the latter case the local sedimentation maximum on the convex leeslope which is rather unimportant on isolated hills is much more developed in multiple hill topography also dust deposition on the leeslopes is significantly higher in multiple hill topography than on isolated hills dust patterns on ranges of hills may be affected by the dust shadow created by the most upstream located hill if hills succeed each other quickly they are located within the shadow zone and are protected from important dust deposition the plume of high air dust concentration that is created by a hill largely determines the dust pattern on the next hill as a result of the supply of dust from above by the descending plume areas that are normally devoid of dust now experience significant dust deposition

quantification of the dry aeolian deposition of dust on horizontal surfaces an experimental comparison of theory and measurements eight techniques to quantify the deposition of aeolian dust on horizontal surfaces were tested in a wind tunnel the tests included three theoretical techniques and five measurement techniques the theoretical techniques investigated were the gradient technique the inferential technique without grain shape correction and the inferential technique corrected for grain shape the measuring techniques included the following surrogate surfaces a water surface a glass surface a metal surface a vertical array of metal plates and an inverted frisbee filled with glass marbles the efficiency of the techniques was investigated for the sediment as a whole all grain sizes together as well as for a large number of grain sizes extending from 1 to 104 m the surrogate surfaces showed more or less comparable catch efficiencies although the water surface nearly always caught the highest quantities of dust and the marble filled frisbee and the vertical array of metal plates the lowest quantities of dust the dust fluxes calculated by theoretical methods were markedly different from those obtained by direct measurements the fluxes calculated by the inferential technique approximated those of the direct measurements only for grain sizes between 30 and 40 m for smaller and coarser grains deviations from the measured fluxes were high the gradient method in its turn provided extremely low calculated fluxes for grains in all size classes investigated the latter technique was not considered very reliable for the dust used in the tests

lithium and boron in late orogenic granites isotopic fingerprints for the source of crustal melts abstract geochemically diverse late and post variscan granites of the erzgebirge vogtland the saxon granulite massif and thuringia germany formed by anatectic melting of palaeozoic sedimentary successions and associated mafic to felsic volcanic rocks the compositional diversity of the least evolved of these granites is largely inherited from the protoliths we present li and b isotopic data of these granites and compare them with the isotopic composition of their protoliths to investigate whether i there exist systematic differences in the li and b isotopic composition among different granite types and ii li and b isotopic compositions provide information on the granite sources complementary to information from the isotopic composition of sr nd and pb and the trace element signatures low f biotite and two mica granite types have flat upper continental crust ucc normalized trace element pattern with variable enrichments in li rb cs sn and w and depletions in sr ba and eu these signatures are least pronounced for the niederbobritzsch biotite granite which has the largest contribution of mafic material and most pronounced for the two mica granites the granites show a relatively narrow range of 7li values 3 0 to 0 5 and a broad range of 11b values 13 4 to 20 1 the 11b values are lower in rocks with distinctly higher contents of li rb cs and sn the high 11b of the niederbobritzsch granite may be explained by the melting of former altered oceanic crust in its source relative to ucc intermediate f to high f low p granites show strong depletions in sr ba eu as well as zr and hf strong enrichments in li rb and cs as well as nb sn ta and w and ree pattern with stronger enrichments for hree than for lree these granites show narrow ranges of 7li 2 0 to 1 6 and 11b values 14 7 to 9 1 reflecting the smaller variability of the li and b isotopic composition in their source lithologies the anomalously high 7li value 14 7 of one granite sample burgberg which is similar to 7li values of its wall rocks up to 14 5 may indicate late magmatic fluid rock interaction with external wall rock derived fluids because of the small compositional range of most source lithologies the li and b isotopic variation in the granites is also small indicating that the isotopic composition of li and b does not represent a particularly sensitive source tracer with the exception of source lithologies characterized by extreme 7li or 11b values

dry aeolian dust accumulation in rocky deserts a medium term field experiment based on short term wind tunnel simulations the spatial pattern of medium term a few months dry aeolian dust accumulation in rocky deserts is predicted using short term deposition and erosion experiments in a wind tunnel the predictions are tested in a field experiment set up in the northern negev desert of israel the results show that superimposing wind tunnel deposition and erosion maps usually leads to correct predictions of medium term dust accumulation the predictions are somewhat less confident near the inflection lines of windward hillslopes where small scale irregularities in the local topography make it difficult to locate the exact position of the areas of little accumulation elsewhere in the topography predictions are good and the method works satisfactorily highest accumulation occurs on concave windward slopes and to a lesser extent on slopes parallel to the wind little accumulation occurs on the convex windward slopes and in dust separation bubbles the smallest accumulation rates are observed immediately upwind of the top of pronounced hills and on leeslopes the rate of dry dust accumulation measured during the field experiment varied from 17 to 93 g m 2 a 1 depending on the topographic position of the accumulation plots for most plots it was of the order of 30 60 g m 2 a 1

magmatic hydrothermal evolution of the donggou porphyry mo deposit at the southern margin of the north china craton evidence from chemistry of biotite abstract late mesozoic granitoids are widespread in the southern margin of the north china craton ncc occurring commonly as both small porphyritic stocks and large batholiths most of the mo deposits are closely associated with small porphyritic bodies in order to determine the relationship between mo mineralization and the granitoids a systematic geochemical study of biotite from the taishanmiao batholith and the mo mineralization associated donggou porphyry was conducted trace element features of biotites indicate a differentiation trend from rocks of the taishanmiao batholith to those of the donggou porphyry as revealed by systematically decreasing k rb ratios co ba v and ti and increasing cs li ta and tl the contents of mo also increase with the degree of magmatic differentiation the compositions of biotite follow a trend towards more magnesium rich compositions and mostly plot above the nno buffer the fe3 fe2 values of biotite gradually increase from the taishanmiao batholith to the donggou porphyry indicating the progressive increasing fo2 during magmatic differentiation the halogen fugacities of magmatic fluids calculated from biotite compositions show a trend of magmatic differentiation the earlier fluids associated with the taishanmiao batholith are relatively f poor with log fhf fhcl 0 the high degree of melt fractionation and progressive increasing of oxygen fugacity is beneficial to concentrate mo in the residual melt in addition later relatively f rich fluid may be beneficial to extract mo from the melt and thus favorable for mo mineralization

air flow over a two dimensional hill studies of velocity speed up roughness effects and turbulence wind tunnel measurements have been made of the streamwise mean and turbulent velocities over a rough bell shaped two dimensional hill with height h and maximum slope 0 26 placed in a neutrally stable boundary layer of thickness 10 h and roughness length zo 0 02 h close agreement is found between the mean velocity and predictions obtained from taylor s 1977 computational model and jackson and hunt s 1975 analytical linearized model for locations at or upwind of the hill top but not in the wake examination of the models shows that the shear stresses are only important in an inner region close to the hill surface so that as suggested by jackson and hunt 1975 the perturbation to the mean flow outside this region is essentially inviscid the theory shows that over very rough surfaces such as wooded or urban terrain the height of this inner region can be of the same order as the height of the roughness elements so that in our experiments no measurements could be made in this region in a second experiment flow over a smooth hill on a rough surface was studied the additional increase of wind speed over the hill top can be estimated by assuming a linear superposition of the velocity changes produced by the changes in elevation and in surface roughness in this case rough to smooth in the lee of a hill however the change in roughness significantly alters the flow with flow separation being suppressed and here a linear superposition is not appropriate finally we consider why observed changes in turbulence structure close to the surface differ from those well above the surface calculations of these changes based on the simple theoretical arguments of equilibrium shear layers and rapidly distorted turbulent flows agree well with turbulence measurements in wind tunnels and in the field

tin carrier minerals in metaluminous granites of the western nanling range southern china constraints on processes of tin mineralization in oxidized granites abstract huashan guposhan and qitianling are three similar and representative metaluminous a type tin granites in the western nanling range china they all have a high oxidization state with magnetite as the dominant fe ti oxide this study presents an understanding of systematic mineralogy of sn bearing minerals biotite titanite magnetite and cassiterite in the three granites biotite has an annite composition and both electron microprobe and la icp ms analyses indicate trace amounts of tin in biotite approximately 100 20 ppm chloritization of biotite is accompanied by formation of sn rich rutile and cassiterite titanite has a long history of crystallization from the early magmatic stage through the late magmatic stage to the hydrothermal stage owing to its solid solution relationship with malayaite casnsio5 titanite always contains tin to various extents early magmatic titanite contains about 0 5 wt sno2 while the late magmatic titanite is markedly enriched in tin on average 14 8 and 3 4 sno2 in titanite from the qitianling and huashan granites respectively magnetite grains typically display a trellis structure with ilmenite lamellae where microinclusions of cassiterite

monocyclic alkanes in ordovician organic matter abstract the major compounds in the c 15 branched cyclic alkane fractions of two ordovician oils pine unit and midland farms oils and an immature ordovician rock guttenberg oil rock are monocyclics one series of these compounds was identified as n alkylcyclohexanes and another tentatively identified as methyl n alkylcyclohexanes the carbon number distribution of these compounds resembled those of the n alkanes found in these samples with an odd carbon number predominance it is suggested that the monocyclic alkanes in these ordovician samples may be principally derived from the cyclisation of straight chain algal fatty acids by mechanisms that involve decarboxylation however there is evidence from the m z 97 fragmentograms of these samples to indicate that methyl n alkylcyclohexanes can also be derived from fatty acids by a less preferred mechanism that does not involve decarboxylation or from other precursors in addition a sample of kerogen from the guttenberg oil rock was hydrously pyrolysed the saturated hydrocarbon products of this experiment showed very similar distributions including monocyclics to those observed in the ordovician oils this suggests that although the oils and the guttenberg oil rock come from widely differing geographical locations their precursor algal derived organic matter was very similar

petroleum geology and geochemistry of the middle proterozoic mcarthur basin northern australia iii composition of extractable hydrocarbons abstract middle proterozoic organic rich sediments from the mcarthur basin in northern australia contain abundant hydrocarbons which are derived from syngenetic kerogen and hence are representative of the organic remains of microorganisms living at that time the major classes of hydrocarbons identified were n alkanes monomethyl branched alkanes cyclohexyl alkanes and acyclic isoprenoids there were also low abundances of pentacyclic triterpanes comprising hopanes and methyl hopanes low concentrations of steranes were present in most samples but like the triterpanes they were only easily detected in the least thermally altered sediments and hence were of limited use in detailed assessments of thermal maturity the presence of steranes in sediments of this age is strong evidence for the existence of eukaryotic organisms as far back as 1690 ma although the relatively high abundances of branched alkanes indicates that most of this primitive organic matter was probably derived from prokaryotes