three examples illustrating the analysis of organic matter associated with uranium ores abstract sedimentary uranium ore deposits provide interesting case histories for studies in organic geochemistry conversely organic geochemical data often contribute to the understanding of uranium ore forming processes recent improvements in analytical techniques have also facilitated sophisticated investigations of organic matter related to the deposits three examples of organic geochemical studies are discussed 1 1 barren and highly mineralized bitumens from saskatchewan deposits canada display very different isotopic composition but quite similar gross geochemical characteristics nmr and py gc analyses distinguish between these two types of bitumens on the basis of the amount and length of alkyl substituents on aromatic rings 2 2 organic matter from the precambrian witwatersrand deposits south africa display micro textured variations which have been investigated by micro raman spectroscopy spectral characteristics vary with respect to the uranium content and petrographic characteristics 3 3 the maximum age of uranium mineralization in the breccia pipes in arizona u s a has been determined by modelling the maturation of the source rocks responsible for the genesis of hydrocarbons closely associated with the uranium mineralization these examples illustrate how sophisticated studies are useful and necessary to acknowledge the complexity of organics associated to uranium ore deposits

a calculation of ionospheric currents due to semidiurnal antisymmetric tides the fully developed equivalent circuit method is used to calculate the ionospheric electric current flow due to the 2 3 and 2 5 tidal modes the 2 5 mode currents are of negligibly small amplitude the 2 3 current pattern has meridional currents in the same direction at a given local time in both north and south hemispheres there is also sometimes a minimum in the zonal current around 10 degree dip latitude and the equatorial electrojet pattern may be different in different longitude zones these features may be possible explanations of 1 the meridional current pattern observed at saint santin 2 current flows on abnormal quiet days aqds 3 the reverse equatorial electrojet 4 the seasonal phase anomaly in the lunar geomagnetic tide and 5 the invasion of one hemisphere s current pattern by that from the opposite hemisphere the recent detection of antisymmetric semidiurnal winds just below the dynamo region further demonstrates the importance of these modes

sulphur isotope abundances in aphebian clastic rocks implications for the coeval atmosphere the evolution of the atmosphere has been of interest to many scientists because it relates to the history of the ocean the sedimentary cycle the geochemical cycle of volatile elements and the development of life it also has a key role in the genesis of iron formations and gold and uranium deposits although it is generally accepted that the primitive atmosphere was reducing a debatable aspect is when and how the oxygen content increased a rise of atmospheric oxygen pressure about 2 000 myr bp is suggested by the appearance of redbeds and the banded iron formations1 2 on the other hand high atmospheric oxygen in very early precambrian time as a result of photodissociation of water has been proposed3 this is supported by occurrences in precambrian rocks of sulphates4 5 volatile elements6 detrital minerals5 7 and palaeosols8 which are similar to those found in younger rocks because the change of sulphur valency is often accompanied by isotopic fractionation sulphur isotope abundances in minerals have been used to infer the environment at the time of their formation it occurred to us that additional sulphur isotope analyses of pyrite from continental sedimentary rocks might provide evidence relative to the question of oxygen development in the atmosphere accordingly a major study of sulphur isotope abundances in pyrite from fluviatile sedimentary rocks in the elliot lake area canada and for comparison data from occurrences in northwest territories canada witwatersrand south africa and jacobina brazil are now reported and implications respecting the coeval atmosphere discussed

oxygen in the precambrian atmosphere an evaluation of the geological evidence geological evidence often presented in favor of an early anoxic atmosphere is both contentious and ambiguous the features that should be present in the geologic record had there been such an atmosphere seem to be missing many of the features advanced in support of an anoxic model can be ascribed to diagenetic alterations and most diagenetic environments are reducing recent biological and interplanetary studies seem to favor an early oxidized atmosphere rich in co 2 and possibly containing free molecular oxygen the existence of early red beds sea and groundwater sulphate oxidized terrestrial and sea floor weathering crusts and the distribution of ferric iron in sedimentary rocks are geological observations and inferences compatible with the biological and planetary predictions it is suggested that from the time of the earliest dated rocks at 3 7 b y ago earth had an oxygenic atmosphere

gold and sulphide minerals in tertiary quartz pebble conglomerate gold placers southland new zealand abstract auriferous quartz pebble conglomerates qpc formed during tertiary sedimentary recycling in the waimumu district southland new zealand these sediments contain fine grained gold of detrital origin with abundant surface textures and gold forms associated with authigenic gold remobilisation most authigenic gold contains no detectable silver and occurs as overgrowths on detrital au ag and au ag hg alloys that contain up to 13 wt ag and 9 wt hg fine grained au ag and au ag hg alloys are compositionally heterogeneous exhibiting both well defined silver depleted and silver enriched rims rare coarse au ag alloy is intergrown with quartz and is homogenous discrete grains of authigenic porous sheet like gold occur in carbonaceous mudstone within a qpc sequence some qpc contain abundant sulphide minerals some of these sulphides pyrite and arsenopyrite are of long distance detrital origin presumably from the otago schist whereas the bulk of the sulphide suite is marcasite of variably transported diagenetic origin derived from the erosion of qpc and underlying tertiary sediments there has also been authigenic deposition of sulphide minerals in the qpc themselves these diagenetic sulphides include framboidal and anhedral marcasite and framboidal and euhedral pyrite sulphur isotope data for the sulphide minerals range from 45 to 18 relative to vcdt sulphur isotope data for euhedral detrital pyrite and arsenopyrite range from 9 to 1 and are most likely derived from the otago schist to the north both framboidal and anhedral marcasite have lower values both the gold and diagenetic sulphides from the belle brook qpc are compositionally similar to gold and sulphides from archaean qpc porous sheet like authigenic gold is morphologically similar to gold associated with carbonaceous material in the witwatersrand in addition southland marcasite textures resemble the rounded and banded pyrite in witwatersrand qpc placers there is abundant evidence from these tertiary qpc in southern new zealand for sedimentary transport of sulphide minerals and post depositional sulphide mineralisation in the surficial environment despite an oxygen rich atmosphere these young deposits thus provide an example of authigenic gold and sulphide textures formed during diagenesis in unmetamorphosed placers many of these textures are similar to those commonly ascribed to metamorphic processes in archaean auriferous qpc

spherical harmonic analysis of geomagnetic tides 1964 1965 the mathematical forms chosen for analyses of s q and l by seventeen different authors are reviewed on the basis of the review and on consideration of the ionospheric dynamo theory and the hough function structure of wind velocities in the upper atmosphere a mathematical model is chosen that includes two more terms than the recent analysis by malin 1973 hourly mean values from 130 magnetic observatories for the i q s ys international quiet solar years 1964 and 1965 were prepared in machine readable form and analysed the solar and lunar transient magnetic variations were evaluated together with the lunar elliptic magnetic tide and the seasonal change at one and two cycles per year for all magnetic tides spherical harmonic analyses were made of the phase law tides and the smaller partial tides altogether 94 different spherical harmonic analyses were completed for a total of ten different magnetic tides two of the ten tides are the solar and lunar magnetic tides usually denoted s and l respectively the results are tabulated in a form that distinguishes between eastward and westward moving terms which is suitable for the evaluation of phase angle differences and amplitude ratios between internal and external parts malin s ocean dynamo calculation has been applied to the lunar and lunar elliptic magnetic tides the spherical harmonic coefficients are compared in some detail with those of malin 1973 for years of high sunspot activity the magnetic tidal potential associated with a given atmospheric tidal mode is derived theoretically and used to obtain an estimate of the hough function components of the solar and lunar semi diurnal atmospheric tides at ionospheric levels from the corresponding magnetic tidal potential

the deposition of elemental gold from gold i thiosulfate complexes mediated by sulfate reducing bacterial conditions the role of sulfate reducing bacteria in the precipitation of elemental gold through a geologic stratum was investigated using column experiments the mixed culture dominated by sulfate reducing bacteria was isolated from the driefontein consolidated gold mine witwatersrand basin republic of south africa bacterially mediated gold precipitation from the gold i thiosulfate complex was more efficient than the corresponding abiotic experiments in the bacterial systems sulfate reducing bacteria i e desulfovibrio sp deposited gold inside the cells as spherical nanoparticles over time these nanoparticles of gold were released from the cells and deposited at cell surfaces and in the bulk solutions ultimately these nanoparticles of gold contributed to the formation of micrometer scale octahedral gold crystals occasional framboidlike structures 1 5 m diam and millimeter scale gold foils typically surrounding the silicate grains spherical gold particles 1 m diam were precipitated in the abiotic experiments and the formation of octahedral gold framboidlike structures and gold foils were not observed in these experiments the reduction and enrichment of elemental gold by sulfate reducing bacteria occurred without the concomitant death of the bacteria suggesting that in natural systems this process could go on over geologic time scales as long as nutrients and gold i thiosulfate were provided to the system

a diurnal modulation of the lunar tide in the upper atmosphere analysis of geomagnetic data from several stations in the equatorial region shows that the amplitude of the lunar semimonthly tide frequently does not have the expected symmetry about noon in its diurnal variation there is a distinct tendency for larger amplitudes in the morning at many stations this effect is largest in equinoctial months though there are regional differences analysis of data from different years confirms its presence the interaction between solar and lunar tides in the middle atmosphere may be responsible for the observed modulation

the timescale and mechanism of granulite formation at kurunegala sri lanka incipient charnockite formation at kurunegala in sri lanka is characterized by the growth of orthopyroxene at the expense of amphibole and biotite in an originally homogeneous gneiss mineral equilibria in the charnockite assemblage record pressure temperature p t conditions of 738 60 c and 6 9 1 2 kbar at 17 0 1 2 log fo2 and ah2o 0 18 0 16 wholerock trace element and isotopic measurements show that charnockite formation was accompanied by a systematic depletion of sm rb pb u sr nd with a fractionation of rb sr sm nd and th u ratios and crystallization of the charnockite assemblage at 535 5 ma major element fe mg ca and sm nd equilibration between minerals occurred at 524 9 ma whereas pb and rb sr underwent continued exchange to 501 5 ma and 486 1 ma respectively trace element data for both amphibolite and charnockite minerals show that depletion on a whole rock scale can be accounted for either by changes in mineral modes or trace element abundances within the immediate area of dehydration the fractionation of sm nd on a whole rock scale is controlled by the breakdown of amphibole without the growth of a major new host phase for sm in the charnockite rubidium and sr are dependent on the relative behaviour of biotite plagioclase and alkali feldspar modelling of dehydration melting involving the breakdown of amphibole biotite and alkali feldspar reproduces the observed sm nd and rb sr fractionation and indicates the loss of small melt fractions on a cm scale from the charnockite these observations suggest that partial melting is the most plausible means of effecting both the dehydration and depletion that accompanies charnockite formation

principal components of quiet time temporal variability of equatorial and low latitude geomagnetic fields diurnal variations of the horizontal component of the geomagnetic field h on international quiet days of 1999 2012 measured hourly at two stations in the same longitude zone in the northern hemisphere near and away from the dip equator have been subjected to principal component analysis this technique is also applied to the difference heej of h at these two stations which is attributed to the equatorial electrojet eej the first three principal components pc1 pc2 and pc3 account for 91 96 of the variances in the data maximum contribution to the quiet day variations in h around its peak in the morning hours at both the stations and in the eej comes from the day to day variation of the amplitude of pc1 patterns of day to day variations of pc1 amplitudes for the equatorial station and the eej are essentially semiannual modulated by solar euv flux superimposed on a longer time scale solar euv flux dependent trend contributions from pc2 and to a lesser extent from pc3 are seen to be responsible for the absence of semi annual variations in h in the afternoon hours at the equatorial station distribution of amplitudes of pc2 and pc3 for heej for weak electrojet days shows seasonal features in accordance with greater occurrence of afternoon morning counter electrojet during june december solstice during the extended solar minimum pc3 amplitudes for h at the equatorial station and for the eej display annual variation possible sources for these seasonal features in the variations of equatorial h are discussed

mineralogical characterization and origin of uranium mineralization in witwatersrand like metaconglomerate of the moeda formation quadrilatero ferrifero brazil abstract the moeda formation is the basal unit of the minas supergroup in the quadrilatero ferrifero brazil and has quartz pebble metaconglomerate that hosts au u mineralization commonly assumed to be detrital in origin the au u mineralization occurs immediately above an unconformity with the underlying archean rio das velhas greenstone sequence in this work we focus on the moeda metaconglomerate in its u bearing portions in the gandarela syncline the southern sector near the syncline axis and the western limb near the palmital gold deposit the metaconglomerate has mica seams that host zircon xenotime rutile nodules of organic matter and sulfide minerals the sulfide assemblage includes four generations of pyrite along with fe ni cu co zn pb mo sulfides a sb as sulfosalt assemblage of gersdorffite stibnite and ullmannite is late in relation to pyrite and other sulfides gold is argentiferous with minor hg uranium minerals include uraninite coffinite brannerite and uranyl arsenates an early generation of uraninite and brannerite occurs as inclusions in organic matter nodules mainly in the southern sector a late generation of uraninite formed due to a low temperature hydrothermal overprint coffinite and late stage brannerite are products of hydrothermal alteration of zircon and rutile respectively uranyl arsenates have ni as the prevalent cation they formed as replacement of arsenic minerals such as gersdorffite by oxidized fluids containing u microstructural data and mineral chemistry favor a hydrothermal hypothesis analogous to an unconformity related setting rather than a detrital placer deposit model for the occurrence of u in the moeda metaconglomerate

lunar and solar tidal variabilities in mesospheric winds and eej strength over tirunelveli 8 7 n 77 8 e during the 2009 major stratospheric warming 1 mesospheric wind observations by the medium frequency radar and geomagnetic field observations at tirunelveli 8 7 n 77 8 e 1 75 n dip angle are used to study the relative importance of solar and lunar influences in the variabilities of mesospheric tides and equatorial electrojet eej strength during the unprecedented major stratospheric sudden warming ssw of 2009 it is observed that the afternoon reversal in the eej popularly known as counter electrojet occurs consecutively for several days during the ssw event when there is an enhancement of solar semidiurnal tide in both zonal wind at 90 km and eej strength over tirunelveli although the amplitude of lunar tides also shows enhancement it is much less than that of solar the diurnal tidal amplitude in zonal wind and eej strength also shows large enhancement just before the onset of ssw however solar semidiurnal tide dominates diurnal tide during the ssw the diurnal tidal phase in zonal wind shifts to a few hours earlier during the ssw the lunar semidiurnal tidal phase shifts to later hours in both zonal wind and eej strength the main observation of the present study is that the large semidiurnal tide observed during the ssw 2009 is mostly solar driven and only partly lunar driven although tidal planetary wave interaction also may play a vital role although a similar behavior is noticed during the ssw 2006 also the large lunar semidiurnal tide observed in the eej strength without having large lunar semidiurnal tide in the underlying mesospheric winds needs further investigation

characteristics and origin of coarse gold in late pleistocene sediments of the cariboo placer mining district british columbia canada the cariboo placer mining district 1000 km2 sited in the interior plateau of central british columbia canada is the premier placer gold mining district of the province gold is recovered from three late pleistocene sedimentary facies postglacial fluvial gravels 25 ka this study reports the morphology size roundness sphericity of 1636 gold grains ranging in size from 0 25 to 17 mm recovered from 19 placer mines older gravels contain the smallest gold grains mean grani size 1 53 mm grains of intermediate size occur in till 2 23 mm and the coarsest gold occurs in postglacial gravels 2 34 mm with a mean of 1 93 mm for the mining district as a whole the most common grain shapes are sub rounded discoidal 14 73 of the grain population sub angular discoidal 10 88 and sub rounded sub discoidal 9 59 the most angular grains occur in postglacial gravels in situ growth of coarse angular grains is indicated by a composite grain structure consisting of aggregates of gold particles welded together by high grade ag 2 filamentous gold in situ coarsening may be reliant on organic complexing agents produced below a dense forest cover an evolutionary sequence of grain form from angular aggregates to rounded pumpkin seed grains is suggested rounded grains commonly show a crystalline structure which may result from the cold hammering of gold during transport fracturing along crystal boundaries is common gold grains may undergo cycles of coarsening rounding diagenesis and breakup in response to repeated recycling through pleistocene sedimentary environments

mesospheric planetary wave signatures in the equatorial electrojet 1 using five years 1994 1998 of simultaneous and collocated measurements of horizontal winds associated with mesosphere and lower thermosphere mlt region and geomagnetic field measurements in the indian geomagnetic dip equatorial region an extensive experimental study has been made on the influences of mesospheric planetary waves on the equatorial electrojet eej the winds are measured using medium frequency mf radar 1 98 mhz located at tirunelveli the eej strength is determined by measuring the geomagnetic field strength at both the geomagnetic dip and off dip equatorial stations trivandrum and alibag india by noting the simultaneous time evolution of spectral signal morlet wavelet analysis in both the eej strength and mesospheric winds at 88 km it is found that mesospheric planetary waves with periodicities of 2 25 days often do propagate up to the ionospheric dynamo region and have their influences on eej strength sometimes only one of the parameters shows strong spectral signal in this periodicity range it is also observed that often the diurnal oscillation in eej strength and mesospheric winds exhibits coherent variations in amplitude when the signature of mesospheric planetary scale oscillations is found in the eej strength also it is found that variations in high energy solar radiations f10 7 is used as a proxy can influence the eej strength at planetary timescales this leads to an interesting question what actually causes the vertical coupling between ionosphere and atmosphere through upward propagating planetary waves to be operative only during some and not all of the episodes

thucholite in mesoproterozoic shales from northern north china occurrence and indication for thermal maturity abstract thucholites have mostly been observed in the intergranular pores of sandstones and conglomerates in this study investigation of thucholites in mesoproterozoic shales has been undertaken to explain the origin and maturation of the organic matter an optical microscope and a scanning electron microscope equipped with an oxford x ray energy dispersive spectrometer sem xds were used to study the thucholite in the hongshuizhuang formation 1 4 ga from the yanshan basin of northern north china the rare and scattered thucholites are present in the shales and do not occur in the dolomites argillaceous dolomites the thucholite contains an apparent radioactive mineral particle as the core the inner rim around the radioactive mineral core generally shows higher reflectance and non fluorescence whereas the outer rim displays low reflectance and strong fluorescence these contrasting observations indicate higher polymerization in the inner rim relative to the outer rim the mineral grains in the thucholites are mostly monazite and less commonly zircon the radioactive mineral grains of granodiorite provenance fell into algal mats at the sediment water interface through seawater transportation followed by polymerization of organic matter by ionizing radiation from the radioactive mineral matter through geological time this process of formation of thucholites in shales is different from that in sandstones and conglomerates the outer rim of the thucholites shows strong fluorescence indicating that the thermal maturity of these 1 4 ga old sediments is still in the oil window consistent with the low equivalent vitrinite reflectance values 0 82 0 88 calculated from protobitumen reflectance the reflectance of the outer rim is close to the average of protobitumen reflectance of the whole sample suggesting that radioactive heat has limited effect on the thermal maturity of the organic matter

variability of the equatorial electrojet its relations to the sq current system and semidiurnal tides average diurnal and seasonal variations of the horizontal geomagnetic element delta h are examined the semiannual variation in equatorial electrojet strength is found to disappear in afternoon hours this may be related to changes in the latitude of the sq current system focus during the day this in turn may be caused by a superposed semidiurnal tide and may also explain delta h variations at stations near the focus

possible microbial pathways in the formation of precambrian ore deposits extant micro organisms and their products interact with heavy metals in a variety of ways consideration of these activities provides a background against which possible influences of microbes on the mobilization accumulation and deposition of heavy metals in modern and ancient environments may be examined several different interactions between micro organisms and their products and heavy metals are described experiments on the uptake and metabolism of gold uranium iron and other heavy metals are reported several examples from recent studies and younger fossil deposits are reported and discussed concerning their applicability to precambrian conditions

alternative model for the derivation of gold in the witwatersrand supergroup present models of the derivation of the gold in the witwatersrand conglomerates of south africa as detrital grains directly from primary deposits in a source area consisting mainly of archaean schist belts meets with a volume problem witwatersrand deposits have yielded about 923 kg km 2 au compared to about 65 kg km 2 au in the richest known schist belts differences in the extent of mining activities cannot account for these differences in yield gold fineness grain size and morphology of the gold particles are also difficult to reconcile with a purely detrital derivation data on the mobility of gold in the hydrosphere and in the weathering cycle are used to erect a model which predicts that most of the gold in the witwatersrand conglomerates was derived from a source area in trace amounts in a 9dissolved9 form and precipitated at or close to the edge of the depositional basin possibly under organic influences subsequent sedimentary reworking and metamorphic diagenetic remobilization led to the formation of the complex association of minerals observed now in the conglomerates

origin and distribution of gold in the huronian supergroup canada the case for witwatersrand type paleoplacers abstract field observations and experimental results show that gold is mobile under a wide range of natural conditions in the surficial environment however the extent to which and the form s in which gold was mobile in ancient placers remains speculative rather more convincing is the extent to which diagenetic and metamorphic processes have been active in redistributing the gold huronian paleoplacer gold deposits span a critical transition in earth history namely the oxyatmoversion evidence for which exists in the upper gowganda formation dated at 2 288 ga prior to this transition deposition of gold occurred under reducing atmospheric conditions with transportation of the more finely divided material possibly as organic protected colloids as has been suggested for the witwatersrand following the oxyatmoversion gold deposition will have been subject to secondary enrichment like many phanerozoic placer gold occurrences for this reason and on purely sedimentological grounds upper huronian strata ought to have as much potential for hosting economic deposits of gold as the basal units a total of 121 au and au u occurrences including several past and presently producing mines from the huronian supergroup are examined these are classified according to whether mineralization is in or adjacent to diabase dikes 11 cases in quartz quartz carbonate veins 85 cases stratiform 25 cases of the non diabase hosted occurrences 41 3 occur in the cobalt group 15 7 in the quirke lake group 24 9 in the hough lake group and 9 in the elliott lake group frequency of occurrence can be related to transgressive sedimentary cycles with deposits concentrated in the matinenda mississagi and gowganda formations which immediately overlie the archean huronian unconformity most of the deposits occur in the gowganda formation although none of these is stratiform in terms of au content there is a large overlap in class intervals of stratiform vein deposits vein deposits are in general richer than stratiform by a factor of 10 selected stratiform deposits in the matinenda mississagi and serpent formations are examined in light of available geological and geochemical data in these deposits anomalous gold values in dominantly quartzitic metasediments are accompanied by fine grained pyrite and other heavy minerals including uranium which occurs in most but not all cases metamorphic grade ranges from upper greenschist to lower amphibolite facies a few of the stratiform occurrences are accompanied by accumulations of carbonaceous material an association reminiscent of the witwatersrand goldfields results of electron microprobe study indicate that much of the gold in the huronian metasediments occurs as low level concentrations in pyrite of morphologically different types in arsenopyrite chalcopyrite and in pyrrhotite variously altered to marcasite it is clear that huronian paleoplacer gold deposits exist but only in conditions much modified by diagenetic and metamorphic processes

uranium bearing stratiform organic matter in paleoplacers of the lower huronian supergroup elliot lake blind river region canada the elliot lake blind river ontario paleoplacer deposits in the basal matineda formation lowermost member of the 2 25 2 45 ga old huronian supergroup contain organic matter chemically consistent with kerogen this substance is also referred to as thucholite uranium ores and some gold occur here and these minerals may be in close association with the kerogen two uraniferous and auriferous stratiform kerogens obtained from the denison mines limited s denison mine and rio algom limited s stanleigh mine have been analyzed by combined high vacuum pyrolysis gas chromatography mass spectrometry and by neutron activation the reflectances of these samples have also been determined related samples containing dispersed kerogen have been examined by backscattered scanning electron microscopy the polymer like matrix of the two stratiform kerogens consists of aromatic alkyl aromatic hydrocarbon and sulphur moieties and contains 20 and 32 uranium with gold abundances in the parts per billion range

day to day changes in the latitudes of the foci of the sq current system and their relation to equatorial electrojet strength 1 the latitudes of the foci of the sq current systems over australia and japan are determined on a daily basis during the period from december 1989 to june 1990 the availability of a dense network of observatories in australia during that time enabled a better determination in that region latitudinal movements of the foci are compared with the strength of the equatorial electrojet and generally an increase in electrojet strength is accompanied with a poleward movement of the focus especially in japan some examples are noted where the foci in the two hemispheres move poleward or equatorward together from one day to the next but this relationship was not found to be statistically significant it is hard to disentangle effects due to other current systems such as sqp from changes related to atmospheric tides if some of the observed effects are due to tides then the 2 3 and 2 4 semidiurnal modes are more likely contributors than the 2 2 mode

characterization of insoluble organic matter from the lower proterozoic huronian supergroup elliot lake ontario abstract elliot lake organic matter falls into two main groups 1 stratiform kerogens with reflectance from 2 63 to 7 31 ro max exhibit a high level of aromaticity and low atomic h c ratios 0 41 0 60 2 less aromatic disseminated globules most resembling solid bitumen are of lower maturity with ro max from 0 72 to 1 32 and atomic h c ratios 0 71 0 81 stratiform kerogens originated from cyanobacteria have 13c values from 15 to 25 one exception with 13c 31 8 may have originated from methanogenic source biota thus two genetically distinct populations of kerogen are tentatively recognized in elliot lake metasediments globular bitumens remobilized by hydrous pyrolysis from kerogen exhibit 13c values ranging from 25 tp 33 0 the overall isotopic bimodality among elliot lake organic material is explained by analogy to petroleum generation from particulate kerogen that matured under conditions of catagenesis to metagenesis and was subjected to radiation over a long time barium u th au pt pd and ree contents of elliot lake stratiform kerogen greatly exceed of average black shales except for as pt pd and au all metals ti v cr mn fe co ni zn se rb sr ag sb cs ba hf ta w hg th and u are more concentrated in stratiform kerogens than in the derivative bitumen this signals a significant role for a low temperature transfer of noble metals to migrating bitumen

the geochemistry of witwatersrand type gold deposits and the possible influence of ancient prokaryotic communities on gold dissolution and precipitation abstract compared to the prokaryote dominated lower proterozoic there are few environments now left on earth where prokaryotes are dominant by about 2 5 ga chemical conditions affecting the solution and precipitation of minerals were much influenced by microbial communities results of recent experiments show that modern living prokaryotes are capable of actively precipitating or flocculating gold this process goes far towards explaining the phenomenal extent to which gold is enriched in kerogenous marker seams on the witwatersrand neutron activation analyses confirm that gold is likewise anomalously enriched in kerogenous material present in the lower huronian metasediments of ontario long known as thucholite it appears from pyrolysis and x ray studies of a sample from a stratiform occurrence that it is a kerogen remarkably similar to kerogen from the vaal reef south africa a prokaryote precursor has been postulated for the vaal reef kerogen and the same may well be true of at least some of the stratiform occurrences of kerogen in the huronian simplifying solutions to the metallogeny of witwatersrand type gold that do not take into account the diverse types of gold in the deposits are unrealistic precipitated gold associated with kerogen is only one of four main types of witwatesrand gold but it may be the major one our proposed model to account for this gold involves the weathering of gold from archean source rock under anaerobic conditions and probably in the presence of s cycling microbial communities transported as a solution or colloid the gold was stabilized by humic acids or s cycle intermediates and was deposited onto braided alluvial plains there in the presence of extensive prokaryote microbial mats now preserved as kerogen gold was precipitated in forms characteristic of biologically induced biomineralization

ground magnetic effects of the equatorial electrojet simulated by the tie gcm driven by timed satellite data quiet time daily variations of the geomagnetic field near the magnetic equator due to the equatorial electrojet are simulated using the national center for atmospheric research ncar thermosphere ionosphere electro dynamics general circulation model tie gcm and compared to those observed by ground based magnetometers simulations are run both with and without tidal forcing at the height of the model lower boundary 97 km when the lower boundary forcing is off the wind that generates an electro motive force in the model is primarily the vertically non propagating diurnal tide which is excited in the thermosphere due to daytime solar ultra violet heating the lower boundary tidal forcing adds the effect of upward propagating tides which are excited in the lower atmosphere and propagate vertically to the thermosphere the main objective of this study is to evaluate the relative importance of these thermospherically generated tides and upward propagating tides in the generation of the equatorial electrojet fairly good agreement is obtained between model and observations when the model is forced by realistic lower boundary tides based on temperature and wind measurements from the thermosphere ionosphere mesosphere energetics and dynamics timed satellite as determined by wu et al 2012 the simulation results show that the effect of upward propagating tides increases the range of the geomagnetic daily variation in the magnetic northward component at the magnetic equator approximately by 100 it is also shown that the well known semiannual change in the daily variation is mostly due to upward propagating tides especially the migrating semidiurnal tide these results indicate that upward propagating tides play a substantial role in producing the equatorial electrojet and its seasonal variability

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes