a continental drift flipbook abstract forty six miniature plate tectonic reconstructions are presented that can be assembled into a flipbook that illustrates the movement of the continents since the late precambrian 750 m yr ago six principal lines of evidence have been used to reconstruct the past positions of the continents 1 linear magnetic anomalies produced by sea floor spreading 2 paleomagnetism 3 hotspot tracks and large igneous provinces 4 the tectonic fabric of the ocean floor mapped by satellite altimetry 5 lithologic indicators of climate e g coals salt deposits tillites and 6 the geologic record of plate tectonic history i discuss the probable uncertainties associated with the plate tectonic reconstructions and give an estimate of the uncertainty in the positions of the continents back through time

the sediment hosted stratiform copper ore system sediment hosted stratiform copper deposits comprise disseminated to veinlet cu and cu fe sulfides in siliciclastic or dolomitic sedimentary rocks sediment hosted stratiform copper deposits are extremely common though economically significant deposits are rare they account for approximately 23 percent of the world s cu production and known reserves in addition to being significant sources of co and ag three sedimentary basins the paleoproterozoic kodaro udokan in siberia the neoproterozoic katangan in central africa and the permian basin of central europe contain supergiant 24 million metric tons mt contained cu deposits sediment hosted stratiform copper deposits are the products of evolving basin scale fluid flow systems that include source s of metal and s source s of metal and s transporting fluids the transport paths of these fluids a thermal and or hydraulic pump to collect and drive the fluids and the chemical and physical processes which result in precipitation of the sulfides metal sources are undoubtedly red bed sedimentary rocks containing fe oxyhydroxides capable of weakly binding metals sulfur may be derived from marine or lacustrine evaporites reduced seawater or hydrogen sulfide bearing petroleum metals appear to have been transported at low to moderate temperatures in moderately to highly saline aqueous fluids with the temperature of the fluid largely dependent on the time of fluid migration in the basin s burial history these basinal fluids were focused to potential metal precipitation sites by thinning of the red bed sequence at basin margins by faults by differentially permeable sedimentary units by paleotopography within the basin or along the margins of salt diapirs fluid movement produced widespread basin scale alteration that has commonly been overlooked but can form an important exploration guide sulfide precipitation occurred due to reduction typically caused by reaction with carbonaceous rocks or petroleum the amount of sulfides present at any deposit may be either metals or sulfide limited or could have been controlled by the amount of available reductant e g petroleum while understanding of sediment hosted stratiform copper ore genesis at the deposit scale is relatively robust there are still significant questions in regards its position in terms of basin evolution a wide variety of basin architectures and processes can lead to the formation of sediment hosted stratiform copper deposits despite general agreement that sulfides postdate sedimentation the absolute age of mineralization in many deposits has been difficult to document and the available evidence suggests that deposits can form throughout a basin s evolution from early diagenesis of ore host sediments to basin inversion and metamorphism supergiant and giant deposits formed in basins which underwent prolonged periods of fluid flow and in which unique conditions allowed for the accumulation of large amounts of metal bearing fluid sufficient reduced s and large amounts of reductants

wave induced sediment transport and sandbar migration onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood here a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach in both the observations and the model the location of the maximum acceleration induced transport moves shoreward with the sandbar resulting in feedback between waves and morphology that drives the bar shoreward until conditions change a model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45 day period

origin of the copper cobalt deposits of the zambian copperbelt an epigenetic view from nchanga the zambian copperbelt is arguably the most significantly mineralized neoproterozoic basin on earth preserving a truly spectacular scale of mineralization in excess of 1 109 t of ore at 2 7 copper has been extracted to date and there are also major cobalt accumulations the origin of these deposits has been hotly debated for more than six decades yet the driving forces that generated this system are poorly understood in particular the relationships between tectonics paleo fluid circulation and ore deposition we present new field and isotopic data for the nchanga deposits in which the bulk of the mineralization is hosted by shale capped feldspathic arenites and arkoses that have undergone recrystallization and hydrothermal alteration within a host rock package controlled by low angle thrust faults by using in situ laser combustion we show for the first time that the range of 34s for copper cobalt ore sulfides 1 to 18 cannot have the same source as diagenetic pyrite 1 to 17 we suggest a new epigenetic model for the formation of these spectacular nchanga orebodies that involves the introduction of metal and sulfate bearing hydrothermal fluids into quartzofeldspathic units during basin inversion with sulfide derived from thermochemical reduction of the sulfate near the site of deposition

extreme 13ccarb enrichment in ca 2 0 ga magnesite stromatolite dolomite red beds association in a global context a case for the world wide signal enhanced by a local environment abstract the palaeoproterozoic positive excursion of 13 c carb is now considered as three positive shifts of 13 c carb separated by returns to 0 which all occurred between 2 40 and 2 06 ma this isotopic event is unique in terms of both duration 300 ma and 13 c enrichment up to 18 the mechanism responsible for one of the most significant carbon isotopic shifts in earth history remains highly debatable to date 13 c of 10 to 15 cannot be balanced by organic carbon burial forg as there is no geological evidence for an enhanced corg accumulation prior to or synchronous with the excursion instead termination of these excursions is followed by formation of a vast reservoir of 13 c depleted organic material 45 at shunga and by one of the earliest known oil generation episodes at 2 0 ga none of the three positive excursions of 13 c carb is followed by a negative isotopic shift significantly below 0 as has always been observed in younger isotopic events reflecting an overturn of a major marine carbon reservoirs this may indicate that forg was constant implying that the mechanism involved in the production of corg was different onset of intensive methane cycling resulting in c change is another possibility the majority of sampled 13 c carb rich localities represents shallow water stromatolitic dolostones red beds and evaporites formed in restricted intracratonic basins and may not reflect global 13 c carb values closely spaced drill core samples n 73 of stromatolitic dolostones from the 1980 27 ma tulomozerskaya formation in the onega palaeobasin russian karelia have been analysed for 13 c carb and 18 o carb in order to demonstrate that different processes were involved in the formation of 13 c carb rich carbonates the 800 m thick magnesite stromatolite dolomite red beds succession formed in a complex combination of environments on the karelian craton peritidal shallow marine low energy protected bights barred basins evaporative ephemeral ponds coastal sabkhas and playa lakes the carbonate rocks exhibit extreme 13 c enrichment with 13 c values ranging from 5 7 to 17 2 vs v pdb mean 9 9 2 3 and 18 o from 18 6 to 26 0 vs v smow mean 22 0 1 6 the tulomozerskaya isotopic excursion is characteristic of the global 2 4 2 06 ga positive shifts of carbonate 13 c 12 c although it reveals the greatest enrichment in 13 c known from this interval an external basin s is considered to have provided an enhanced corg burial and global seawater enrichment in 13 c the global background value for the isotopic shift at tulomozero time ca 2 0 ga is roughly estimated at around 5 an explosion of stromatolite forming microbial communities in shallow water basins evaporative and partly restricted environments high bioproductivity enhanced uptake of 12 c and pene contemporaneous recycling of organic material in cyanobacterial mats with the production and consequent loss of co2 and ch4 are believed to be additional local factors which may have enhanced 13 c from 5 up to 17 such factors should be taken into account when interpreting carbon isotopic data and attempting to discriminate between the local enrichment in 13 c and globally enhanced 13 c values we propose that many previously reported 13 c values from other localities where environmental interpretations are not available or have not been taken into account may not represent the global 13 c values

the mesoproterozoic copperwood sedimentary rock hosted stratiform copper deposit upper peninsula michigan copperwood is located in gogebic county upper peninsula michigan within the porcupine mountains copper district it was discovered in 1956 and in 2008 orvana minerals corp began exploration and development work with production projected in the near future stratiform copper mineralization is hosted by gray to black shales and siltstones of the basal nonesuch formation copper mineralization is overlain by laminated gray siltstones of the nonesuch formation and is underlain by red bed sandstones conglomerates and minor siltstones of the copper harbor formation these rocks are part of a thick section of clastic sedimentary rocks that comprise the upper fill of the mesoproterozoic 1 1 1 0 ga midcontinent rift the copper deposit is a tabular body that averages 2 5 m thick lacks significant basal undulations and dips 8 to 12 northward on the southwest limb of the western syncline an open fold with a shallow plunge to the northwest chalcocite is the only cu bearing mineral in the orebody and occurs as concentrations along stratigraphic laminations and as disseminated grains within the orebody there is no mineral or metal zoning cu ag and s are strongly enriched zn is very slightly enriched and pb and co lack enrichment gangue minerals in the orebody are quartz clinochore muscovite illite plagioclase k feldspar calcite and hematite which are consistent with temperatures of less than 130 c only one significant fault a shallow nw dipping reverse fault with displacement of up to 7 m has disturbed the section the mineralized zone at copperwood is stratigraphically equivalent to that at the white pine mine but copperwood lacks the structural complexity and the hydrothermal overprint manifested by the native cu mineralization at white pine reported canadian national instrument 43 101 compliant measured indicated and inferred resources are 33 million metric tonnes mt of 1 60 cu and 4 1 ppm ag for total contained cu of about 1 165 billion lb and 4 32 moz of ag the characteristics of copperwood are consistent with those of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits the proposed genetic model is chalcocite replacement of pyrite in unlithified sediments during diagenesis as a result of emanating upward focused compaction driven cu bearing saline basinal waters with cu leached from the underlying red bed paleoquifer the simplicity of the mineralizing event and the undeformed nature of the deposit distinguish copperwood from most other examples of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits throughout the world

karelian shungite an indication of 2 0 ga old metamorphosed oil shale and generation of petroleum geology lithology and geochemistry abstract the ca 2 0 ga old 600 m thick upper zaonezhskaya formation near lake onega nw russia contains unusually high concentrations of corg up to 98 averaging around 25 the formation contains an estimated 25 1010 tonnes of organic carbon accumulated within an area of 9000 km2 organic material is represented by shungite which forms a black dense amorphous or nanocrystalline mass consisting of c with traces of n o s and h autochthonous shungite occurs as disseminated organic material 0 1 50 corg which when mixed with migrated bitumen now pyrobitumen appears as coal like seams and lenses of semilustrous and semimat layer shungite rocks oil shales 50 75 corg the migrated bitumen originally petroleum represented by the lustrous vein and layer shungite conformably fills interbedding spaces or cross cutting joints and usually contains 80 98 corg the shungite bearing rocks of the upper zaonezhskaya formation represent one of the most richest accumulations of organic material reported from the palaeoproterozoic and one of the geologically earliest stages of petroleum generation the sediments of the zaonezhskaya formation were initially deposited in brackish water in a non euxinic lagoonal environment the high c s ratio 8 1000 with a zero intercept on the c s cross plot indicates that deposition occurred in sulphur poor water intensive synchronous volcanism may have contributed to both the enhanced delivery of nutrients and elevated sedimentation rate and eventually to the high degree of preservation of organic material the integrated data suggest that the organic material has a biogenic origin most likely algal or bacterial the organic material suffered complex catagenetic and metamorphic alteration which is reflected in 1 the four modal distribution of corg content with maxima at 5 30 65 and 95 2 highly variable 13 c org 45 to 17 3 bimodal distribution of 13 c org with maxima at 28 and 39 and 4 low h c ratios 0 005 0 2 abundant diagenetic carbonates associated with shungite rocks 13 c carb 5 to 26 and the presence of pyrite 34 s 22 to 31 reflects substantial loss of organic matter via bacterial reduction of sulphate during diagenesis the shungite rocks are characterised by a further substantial loss 50 of biologically produced organic material in the course of thermal maturation and by a depletion in 12 c 10 the isotopic composition of carbonate concretions does not indicate the involvement of fermentative diagenesis conservative estimates give 13corg of 34 as the best value of the initial biomass lustrous vein and layer shungite containing more than 80 corg are considered to be allochthonous migrated bitumen originally petroleum the semilustrous and semimat layer shungite rocks containing 55 75 corg represent oil shales with both migrated bitumen originally petroleum and autochthonous kerogen residues the oil source rocks were apparently hosted in the zaonezhskaya formation the generated oil has migrated both vertically and laterally with the highest concentration in cupola structures the locality at shunga represents the most significant volume of trapped petroleum from the study area

upper proterozoic supracrustal rocks of north america a brief review abstract well preserved successions of supracrustal rocks of upper proterozoic age are present around the margins of north america but are rare in the continental interior the thickest and most complete assemblage is present in the cordilleran region particularly in the central and northern parts in these regions a three fold subdivision of the supracrustals is possible the oldest assemblage sequence a is older than 1 2 ga the middle assemblage sequence b is between ca 1 2 ga and 0 8 ga and sequence c is between ca 0 8 ga and 0 57 ga the base of the cambrian here upper proterozoic is used as roughly equivalent to sequences b and c sequence a is only briefly considered detailed lithostratigraphic correlation is possible between the rocks of sequences a and b and generally thinner counterparts in the canadian arctic on the northern margins of the canadian shield sequence c is not represented by sedimentary rocks on the northern edge of the continent the break between sequences a and b the racklan orogeny is not recognised in the southern part of the cordillera but there is evidence of widespread mafic igneous activity at about the same time ca 1 2 ga ago upper proterozoic rocks are poorly represented in the continental interior the keweenawan succession provides an exception it rocks fill an intracratonic rift possibly related to early movements during the grenville orogeny the upper proterozoic history of the eastern part of north america is much simpler in that it comprises a single supracrustal assemblage corresponding to sequence c and the upper part of sequence b all formed after the grenville orogeny thus the different tectonic histories of the eastern and western margins of north america resulted in development of different sedimentary accumulations with the exception of the racklan orogeny which affected the northern part of the cordillera the upper proterozoic assemblages of both the eastern and western margins of the north american continent reflect sedimentary accumulation and subsidence that culminated in the opening of phanerozoic oceans

magmato hydrothermal space a new metric for geochemical characterisation of metallic ore deposits abstract magmato hydrothermal space is a new mathematical construct where 24 ore and pathfinder elements are used to quantify ore element signatures quantification allows relationships between ore deposit samples to be mapped the broad scale view of magmato hydrothermal space reveals three important trends 1 zn pb sediment hosted mineralisation to igneous associated cu au mineralisation 2 cu au mineralisation to au only mineralisation and 3 ultramafic associated magmatic ni cu pge mineralisation through cu au mineralisation to granitoid associated mo w and sn mineralisation the view provided by magmato hydrothermal space reveals that there is a spectrum of ore element signatures that mirrors the spectrum of ore deposit classes described in the literature geochemical variations within individual ore deposit classes are examined for orogenic au vhms epithermal and sediment hosted cu samples sub groups within each of these classes are compared on element enrichment diagrams and described in the context of magmato hydrothermal space orogenic au samples are divided into two sub groups of as sb rich mineralisation and four sub groups of relatively as sb poor mineralisation the as sb poor sub groups include a te cu ag rich sub group that overlaps with the porphyry cu class and a te w bi mo rich class dominated by granitoid hosted deposits the vhms class ranges from a cu rich sub group that overlaps with porphyry cu and iocg classes through a cu zn sub group to two zn cu sub groups one of which overlaps with the shms class the epithermal class is divided into zn rich cu rich and base metal poor sub groups

late paleoproterozoic sedimentary rock hosted stratiform copper deposits in south china their possible link to the supercontinent cycle giant sedimentary rock hosted stratiform copper ssc deposits commonly occur in rift environments tem porally coincident with the breakup of the rodinia and pangea supercontinents however whether or not such deposits have also formed during the breakup of the paleo proterozoic columbia supercontinent is not well known a group of dolostone hosted cu deposits in late paleoproter ozoic rift related sedimentary sequences of the dongchuan group south china form one of the largest ssc districts in the world being one of the largest ssc deposits in the region the yinmin deposit has stratiform cu orebodies intruded by dolerite dykes one dyke has a sims zircon u pb age of 1 701 28 ma slightly younger than the ore hosting strata with a zircon u pb age of 1 742 13 ma for a tuff unit six chalcopyrite and bornite separates from strat iform orebodies contain highly radiogenic os and extremely low common os and yield a weighted mean re os model age of 1 666 82 ma and a 187 os 187 re errorchron age of 1 585 100 ma the present zircon u pb and sulfide re os ages thus constrain the timing of the mineralization at 1 700 ma the yinmin deposit and by inference other ssc deposits in the region arguably represent a large scale ssc mineralization event during the late paleoproterozoic the formation of these deposits was coeval with the initial breakup fragmentation of the columbia supercontinent this study highlights the temporal and likely genetic links between large sized ssc deposits and the supercontinent cycle

sea level sediments and the composition of seawater the composition of seawater changed significantly during the course of the phanerozoic in concert with long term changes in sea level which were largely the result of changes in the volume of mid ocean ridges these reflect changes in the rate of seafloor spreading and determine the rate of seawater cycling through mid ocean ridges spencer and hardie 1990 and hardie 1996 proposed that the changes in the cycling rate of seawater through mid ocean ridges have been responsible for the changes in the composition of seawater during the phanerozoic this explanation cannot account for the major changes in the composition of seawater during the cenozoic which was a time of nearly constant seafloor spreading rate however changes in the rate of deposition of shallow water carbonates and their penecontemporaneous dolomitization can explain the cenozoic changes in seawater composition this indicates that sedimentologic parameters have played a major role in the chemical evolution of seawater the more rapid cycling of seawater through mors during the mesozoic can explain semiquantitatively the fairly minor differences between the composition of seawater in the eocene and in the jurassic changes in the composition of seawater during the paleozoic were probably determined both by changes in the rate of dolomite and gypsum anhydrite deposition and by changes in the rate of seawater cycling through mid ocean ridges if the causes of these compositional changes are the same as those during the cenozoic and mesozoic then sedimentologic factors have been significantly more important than the rate of cycling of seawater through mors in shaping the chemical evolution of seawater during the phanerozoic

carbonate deposition climate stability and neoproterozoic ice ages the evolutionary success of planktic calcifiers during the phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate ion concentration the saturation dependent preservation of carbonate in sea floor sediments before this buffering was primarily accomplished by adjustment of shallow water carbonate deposition to balance oceanic inputs from weathering on land neoproterozoic ice ages of near global extent and multimillion year duration and the formation of distinctive sedimentary cap carbonates can thus be understood in terms of the greater sensitivity of the precambrian carbon cycle to the loss of shallow water environments and co 2 climate feedback on ice sheet growth

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

geology and geochemistry of the sediment hosted cheshmeh konan redbed type copper deposit nw iran the several hundred m thick miocene upper red formation in northwestern iran hosts stratiform and fault controlled copper mineralization copper enrichment in the percent range occurs in dm thick carbonaceous sandstone and shale units within the clastic redbed sequence and consists of fine grained disseminated copper sulfides chalcopyrite bornite chalcocite and supergene alteration minerals covellite malachite and azurite the copper mineralization formed after calcite cementation of the primary rock permeability copper sulfides occur mainly as replacement of diagenetic pyrite which in turn replaced organic matter electron microprobe analysis on bornite chalcocite and covellite identifies elevated silver contents in these minerals up to 0 12 0 72 and 1 21 wt respectively whereas chalcopyrite and pyrite have only trace amounts of silver 0 26 and 0 06 wt respectively microthermometric data on fluid inclusions in authigenic quartz and calcite indicate that the cu mineralization is related to a diagenetic fluid of moderate to low temperature th 96 160 c but high salinity 25 38 wt cacl2 equiv the range of 34s in pyrite is 41 9 to 16 4 average 31 4 where framboidal pyrite shows the most negative values between 41 9 and 31 8 and fine grained pyrite has relatively heavier 34s values 29 2 to 16 4 consistent with a bacteriogenic derivation of the sulfur the cu sulfides chalcopyrite bornite and chalcocite show slightly heavier values from 14 6 to 9 0 and their sulfur sources may be both the precursor pyrite s and the bacterial reduction of sulfate bearing basinal brines carbonates related to the ore stage show isotopically light values of 13cv pdb from 8 2 to 5 1 and 18ov pdb from 10 3 to 7 2 indicating a mixed source of oxidation of organic carbon ca 20 and hco3 from seawater porewater ca 0 the copper mineralization is mainly controlled by organic matter content and paleopermeability intragranular space to large fracture patterns enhanced by feldspar and calcite dissolution the cheshmeh konan deposit can be classified as a redbed type sediment hosted stratiform copper ssc deposit

modeling north american freshwater runoff through the last glacial cycle the northern hemisphere ice sheets decayed rapidly during deglacial phases of the ice age cycle producing meltwater fluxes that may have been of sufficient magnitude to perturb oceanic circulation the continental record of ice sheet history is more obscured during the growth and advance of the last great ice sheets ca 120 000 20 000 yr b p but ice cores tell of high amplitude millennial scale climate fluctuations that prevailed throughout this period these climatic excursions would have provoked significant fluctuation of ice sheet margins and runoff variability whenever ice sheets extended to mid latitudes giving a complex pattern of freshwater delivery to the oceans a model of continental surface hydrology is coupled with an ice dynamics model simulating the last glacial cycle in north america meltwater discharged from ice sheets is either channeled down continental drainage pathways or stored temporarily in large systems of proglacial lakes that border the retreating ice sheet margin the coupled treatment provides quantitative estimates of the spatial and temporal patterns of freshwater flux to the continental margins results imply an intensified surface hydrological environment when ice sheets are present despite a net decrease in precipitation during glacial periods diminished continental evaporation and high levels of meltwater production combine to give mid latitude runoff values that are highly variable through the glacial cycle but are two to three times in excess of modern river fluxes drainage to the north atlantic via the st lawrence hudson and mississippi river catchments averages 0 356 sv for the period 60 000 10 000 yr b p compared to 0 122 sv for the past 10 000 yr high amplitude meltwater pulses to the gulf of mexico north atlantic and north pacific occur throughout the glacial period with ice sheet geometry controlling intricate patterns of freshwater routing variability runoff from north america is staged in the final deglaciation with a stepped sequence of pulses through the mississippi st lawrence arctic and hudson strait drainages

evidence for low temperature alteration of sulfides in the kupferschiefer copper deposits of southwestern poland minerals of the cu fe s system from the lubin and rudna mines in the polish kupferschiefer display textures and compositional trends consistent with copper depletion the compositions optical properties textures and distribution of cu s minerals indicate progressive alteration from chalcocite to covellite in the sequence chalcocite djurleite anilite geerite spionkopite yarrowite covellite bornite compositions plot on the cu fe s phase diagram along a line between ideal bornite cu 5 fes 4 and idaite cu 3 fes 4 the range in bornite compositions extends from ideal bornite to cu sub 3 5 fes 4 copper poor bornites within the composition range cu sub 4 5 fes 4 to cu sub 3 5 fes 4 texturally appear to have partially decomposed to covellite and chalcopyrite both of these mineralogical trends have been previously reported from zones of supergene alteration in other copper deposits where they result from copper leaching grains observed to be of uniform anilite composition indicate that the alteration occurred at low temperatures probably less than 40 degrees c in the lubin mine samples the most copper depleted minerals yarrowite covellite copper poor bornite and chalcopyrite occur in association with veins of gypsum anhydrite and atacamite this association probably results from the interaction of saline mine waters with the sulfides in the rudna mine samples copper leaching is confined to distinct impermeable horizons most notably at the top of the weissliegendes and in the kupferschiefer at the contact between the cu and pb zones on both horizons the mineralogical change passing upward corresponds to increasing copper depletion considering the impermeability of the horizons and the low temperature of anilite formation the horizon specific copper depletion probably occurred during early diagenesis

a modified law of the wall applied to oceanic bottom boundary layers 1 near the bottom the velocity profile in the bottom boundary layer over the continental shelf exhibits a characteristic law of the wall that is consistent with local estimates of friction velocity from near bottom turbulence measurements farther from the bottom the velocity profile exhibits a deviation from the law of the wall here the velocity gradient continues to decrease with height but at a rate greater than that predicted by the law of thewall with the local friction velocity we argue that the shape of the velocity profile is made consistent with the local friction velocity by the introduction of a new length scale that near the boundary asymptotes to a value that varies linearly from the bottom farther from the boundary this length scale is consistent with the suppression of velocity fluctuations either by stratification in the upper part of the boundary layer or by proximity to the free surface the resultant modified law of the wall provides a good representation of velocity profiles observed over the continental shelf when a local estimate of the friction velocity from coincident turbulence observations is used the modified law ofthe wall is then tested on two very different sets of observations from a shallow tidal channel and from the bottom of the mediterranean outflow plume in both cases it is argued that the observed velocity profile is consistent with the modified law of the wall implicit in the modified law of the wall is a new scaling for turbulent kinetic energy dissipation rate this new scaling diverges from the law of the wall prediction above 0 2d where d is the thickness of the bottom boundary layer and agrees with observed profiles to 0 6d

reos and s isotopic constraints on the origins of two mineralization events at the tangdan sedimentary rock hosted stratiform cu deposit sw china abstract the tangdan stratiform cu deposit in the kangdian region of south china is hosted in sedimentary rocks of the late paleoproterozoic to early mesoproterozoic dongchuan group orebodies mainly occur in dolostone and black shale above a thick sequence of hematitic sandstone and siltstone mineralization consists mainly of bedding parallel stratiform ores with minor amounts of discordant vein type ores both stratiform and vein type ores are composed of bornite and chalcopyrite with minor chalcocite and digenite associated with gangue minerals including ankerite dolomite calcite and quartz cu sulfides from vein type ores contain 122 293 ppb re much higher than those of stratiform ores 0 6 14 ppb re they have highly radiogenic os with re os model ages ranging from 1413 to 1457 ma and a weighted mean re os model age of 1432 19 ma 2 mswd 0 30 which is within uncertainty in agreement with isochron ages of 1401 30 ma 2 mswd 0 67 and 1397 71 ma 2 mswd 0 22 using 187 re 188 os versus 187 os 188 os and 187 re versus 187 os regression respectively in contrast sulfides from stratiform ores did not yield meaningful model ages due to the extremely low concentrations of re and radiogenic os however early studies have shown that the stratiform ores were likely formed at 1700 ma during the diagenesis of the host strata sulfides from the vein type ores have 34 s values ranging from 15 to 8 significantly lower than those of stratiform ores 3 to 10 suggesting that organic matter may have been involved in the formation of the vein type ores contrasting re os and s isotopes suggest that the two types of ores at the tangdan deposit were likely formed from different ore forming fluids we propose that stratiform ores were precipitated from basinal fluids during the early evolution of the rift basin whereas the vein type ores were formed due to a much younger thermal event during which hydrothermal fluids interacted with overlying black shale to account for the high re and negative 34 s values this study demonstrates that re os isotopes of sulfides can be used to study the origin of hydrothermal system

a model for calcium magnesium and sulfate in seawater over phanerozoic time a theoretical model has been constructed for calculating the concentrations of dissolved calcium magnesium and sulfate in seawater over the past 550 million years phanerozoic time it is demonstrated that the weathering of ca carbonates and silicates by carbonic acid can be generally ignored in the modeling a previous model of the carbon cycle is used to guide input to the oceans of mg from carbonate and silicate weathering by h 2 co 3 similarly a previous model of the sulfur cycle is used to guide input fluxes to the ocean by calcium sulfate weathering and the weathering of ca and mg carbonates and silicates by sulfuric acid the sulfuric acid is derived from the oxidation of pyrite during weathering plus the oxidation of sulfur gases derived from the metamorphic volcanic decomposition of pyrite and caso 4 calcium is removed from seawater as sedimentary carbonates and sulfates so 4 is removed as sedimentary pyrite and caso 4 and mg is removed by exchange for ca via basalt seawater reaction and or dolomitization plus minor burial in sediments with pyrite as anoxic dolomite by adjusting starting conditions modeling results can be found that agree well with results of studies of salt fluid inclusions for variations of ca and so 4 this is especially true of the timing when ca was more abundant in seawater than so 4 and vice versa general agreement was also found with fluid inclusion results for changes in the mg ca ratio thereby distinguishing calcite seas from aragonite seas because of this overall agreement the modeling offers a new perspective on why oceanic ca mg and so 4 have varied over phanerozoic time

cyclonic spirals in tidally accelerating bottom boundary layers in the zhujiang pearl river estuary abstracta velocity spiral in the tidally accelerating bottom boundary layer bbl was defined as a directional shear of the prevailing flow with the elevation and the tidal phase however so far there is no information on the spiral for the oscillatory bbl flows or a valid explanation for its origin life history and persistence to investigate this rotating current in the tidally accelerating bbl flow the authors performed instrumented tripod observations in the tidally energetic zhujiang pearl river estuary the tidal bbl flows may fall into three distinct regimes i the quasi steady phase in the peak tide ii the accelerating decelerating phase at the slack tide and iii the transition between i and ii when a cyclonic spiral occurs only in the early late ebb the subcritical spiral defined by a froude number of the oscillatory bbl flow may be analytically examined by unsteady linearized turbulent bbl equations the spiral is formed under the momentum balance between local acceleration

low latitude glaciation in the palaeoproterozoic era one of the most fundamental enigmas of the earth s palaeoclimate concerns the temporal and spatial distributions of precambrian glaciations through four billion years of precambrian history unequivocally glacial deposits have been found only in the palaeoproterozoic and neoproterozoic record nonetheless some of these deposits are closely associated with tropical rather than just polar palaeolatitudinal indicators such as carbonate rocks red beds and evaporites these observations are quantitatively supported by palaeomagnetic results indicating a 5 latitude for neoproterozoic glaciogenic rocks in australia similarly reliable palaeolatitudes for the older palaeoproterozoic glaciogenic rocks have not yet been obtained as such deposits commonly suffer from poor preservation and secondary magnetic overprinting the archaean palaeoproterozoic transvaal supergroup on the kaapvaal craton in south africa is however exceptionally well preserved and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes within this supergroup the 2 2 billion year old ongeluk lavas are a regionally extensive largely undeformed and unmetamorphosed extrusive volcanic succession which conformably overlies glaciogenic deposits the makganyene diamictite here we report a palaeomagnetic estimate of 11 5 depositional latitude for the lavas and hence for the underlying contemporaneous glacial rocks the palaeoclimate enigma is thus deepened a largely ice free precambrian world was apparently punctuated by two long ice ages both yielding glacial deposits well within tropical latitudes

formation of sedimentary rock hosted stratiform copper deposits through earth history sedimentary rock hosted stratiform copper deposits form by movement of oxidized copper bearing fluids across a reduction front that results in the precipitation of copper sulfides large scale production of such oxidized fluids as well as the formation of mobile hydrocarbons oil has probably been common since the formation of the first red beds in the paleoproterozoic and deposits of this type occur in rocks from the paleoproterozoic to the tertiary however supergiant deposits are currently recognized in only three basins the paleoproterozoic kodaro udokan basin of siberia the neoproterozoic katangan basin of south central africa and the permian zechstein basin of northern europe the paucity of data regarding the udokan deposit makes understanding this system difficult in terms of earth history events both the neoproterozoic and the permian were times of supercontinent breakup with major landmasses at low latitudes this global tectonic framework favored the formation of failed rifts that subsequently became significant intracratonic basins with basal synrift red bed sequences overlain by marine and or lacustrine sediments and in some basins located at low latitudes by thick evaporitic strata the intracratonic setting of these basins allowed the development of a hydrologically closed basinal architecture in which highly oxidized and saline moderate temperature basinal brines were produced that were capable of supplying reduction controlled sulfide precipitation over very long time periods tens to hundreds of millions of years the length of time available for the mineralizing process may be the key factor necessary to form supergiant deposits however examination of the absolute ages for the kupferschiefer zechstein basin and katangan deposits allows speculation that other factors may also have been important both the neoproterozoic and permian were times of major glacial events glaciation may also be conducive for the formation of supergiant sediment hosted stratiform copper deposits glacial periods correspond to magnesium and sulfate rich oceans that could have been responsible for additional sulfur in basinal brines developed during evaporite formation and would then be available during the long mineralization process

genesis of copper lead mineralization in the regionally zoned agnigundala sulfide belt cuddapah basin andhra pradesh india shallow marine sandstone shale carbonate sedimentary rocks of the paleoproterozoic northern cuddapah basin host copper nallakonda deposit copper lead dhukonda deposit and lead mineralization bandalamottu deposit which together constitute the agnigundala sulfide belt the cu sulfide mineralization in sandstone is both stratabound and disseminated and pb sulfide mineralization occurs as stratabound fracture filling veins and or replacement veins within dolomite systematic mineralogical and sulfur carbon and oxygen isotope studies of the three deposits indicate a common ore fluid that deposited copper at nallakonda copper lead at dhukonda and lead at bandalamottu under progressive cooling during migration through sediments the ore fluid was of low temperature 200 c and oxidized thermochemical reduction of basinal water sulfate produced sulfide for ore deposition it is envisaged that basal red bed and evaporite bearing rift related continental to shallow marine sediments might have acted as the source for the metals rift related faults developed during sedimentation in the basin might have punctured the ore fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration the ore bearing horizons have participated in deformations during basin inversion without any recognizable remobilization

genesis of kupferschiefer cu ag deposits by convective flow of rotliegendes brines during triassic rifting extensive and rich cu ag sulfide mineralization occurs in poland across the contact between the upper permian zechstein restricted marine sequence and the lower permian rotliegende continental volcanic and clastic sequence geologic evidence suggests that the mineralization was formed during late diagenesis when metalliferous brines migrated through the rotliegende leaching metals from the volcanic detritus and up the flanks of basement highs possibly along fracture porosity to the pyritic kupferschiefer and zechstein limestone above thick evaporites in the lower zechstein preclude a vertical flow through model but metal zoning attitudes suggest that the brines overturned where the rotliegende pinched out against the highs and moved laterally along the base of the zechstein toward the basin centers presumably to sink back down into the rotliegende completing a convection cell a middle triassic paleomagnetic age for the metal zoning and kimmerian attitudes of dilatant sulfide veinlets indicate that the mineralizing event coincided with continental rifting associated with the opening of the tethys ocean slow unicellular convection may be commonplace in sandstone basins where small lateral temperature gradients delta t exist but greater velocities are necessary to form large orebodies an anomalous tensional and thermal event such as rifting can increase velocities by increasing permeability slope angle or delta t the paleothermal structure of southwestern poland was determined by modeling the conductive heat flow in 14 one dimensional geologic sections which described the evolution of the basin architecture for 10 m y in the early triassic rifting was simulated by increasing the lower boundary condition from 500 degrees to 1 000 degrees c at 25 km this thermal pulse produced a surprisingly high delta t of 25 degrees c across the lubin ore district solely from differences in thermal conductivities between the basement high 4 2 w m degrees c the sandstone 2 5 w m degrees c and the shale basin center 1 25 w m degrees c unicellular convection patterns would be induced by the lateral boundary conditions of warm basement highs and cold shale centers and by the greater horizontal permeability these cells were 15 to 20 km long 400 m high and subhorizontal a slope angle of 2 degrees and a permeability of 1 d produces a convection velocity of 13 cm yr which with a copper solubility of 1 000 mg kg in 20 to 30 percent ca na cl brines in equilibrium with hematite can form the lubin deposit in less than 6 m y using a fracture permeability of 2 d and a solubility of 300 mg kg the time needed is less than 10 m y the konrad mine can be formed in similar time periods without the continuous recycling of the brine inherent in convective flow 20 times or more the metal solubilities needed to form the lubin deposits by a flow through model would be unreasonably high natural gases likely migrated along with the metalliferous brines and helped convection by creating secondary porosity and increasing the buoyancy of the fluids because the fluids are recirculated and not expelled convection provides a way in which secondary migration of methane and petroleum can occur effectively in solution as well as in separate phases

regional aeromagnetic and stratigraphic correlations of the kalahari copperbelt in namibia and botswana abstract the late mesoproterozoic to neoproterozoic kalahari copperbelt kcb in namibia and botswana is widely covered by kalahari sand which precludes direct correlations between known stratabound sediment hosted cu ag districts we use a combination of review of literature data and newly processed and interpreted high resolution aeromagnetic maps in both countries to provide a new correlative cross border interpretation lithostratigraphic control on the aeromagnetic response allows detailed indirect mapping of the kalahari copperbelt lithotectonic domains below the sand cover this enabled us to redefine the width and lateral extent of the kcb as two continuous magnetic domains the rehoboth and ghanzi chobe domains extending from central namibia to northern botswana and helped in resolving problems of stratigraphic correlations across the international border the rehoboth magnetic domain in the western part of the kcb in namibia records continental arc magmatism at 1200 ma during orogenic events along the northwestern edge of the kalahari craton this was followed at 1110 1090 ma by widespread magmatism identified within the entire kcb and related to the 1112 1106 ma umkondo large igneous province the basal parts of the tsumis group in namibia and ghanzi group in botswana were deposited in shallow water environments after a period of erosion and peneplanation subsequently and prior to the sturtian glaciation the host rocks of the cu ag deposits formed by the deposition of chemically reduced shales and siltstones that formed in deeper water and overlie chemically oxidised shallow water sandstones this regional interface which is both a permeability barrier and redox boundary played a critical role in the formation of the stratabound sediment hosted cu ag deposits of the kalahari copperbelt and the interface with its strong magnetic contrast can be followed through the entire ghanzi chobe magnetic domain of the copperbelt the whole kcb was affected by the damara orogeny during early cambrian times which resulted in the formation of a ne sw trending 250 km wide fold and thrust belt

contrasts between estuarine and river systems in near bed turbulent flows in the zhujiang pearl river estuary china a bottom mounted instrumental tripod was deployed in the tidally energetic zhujiang pearl river estuary to examine the contrasting properties of the bottom boundary layer bbl flows between estuarine and tide affected river systems three aspects of the bbl flows were investigated to understand the mechanism of the turbulence responses to the large scale ambient forcing the flow structures profile anisotropy and spectra shearing strains and stresses and the balance of turbulent kinetic energy tke single log law profiles and turbulence anisotropy predominated in the two systems but the non log regime and stronger anisotropy occurred more frequently at the slack tide in the estuary the adv based turbulence intensities and shearing strains both exceeded their low frequency counterparts frictional velocities and mean shears derived from the logarithmic law on the contrary the adv based reynolds stresses were smaller than the log profile derived bottom stresses so the hypothesis of a constant stress layer cannot be well satisfied especially in the river the bandwidth of the inertial subrange in the river was of one decade larger than in the estuary the balance between shear production and viscous dissipation was better achieved in the straight river this first order balance was significantly broken in the estuary and in the meandering river by non shear production dissipation due to wave induced fluctuations or salinity sediment stratification all these disparities between two systems in turbulence properties are essentially controlled by the anisotropy induced by the large scale processes such as secondary currents density stratification in conclusion the acceleration of unsteady flows determines the profile structure of the bbl flow and turbulence anisotropy results in the invalidation of the phenomenological relations such as the constant stress hypothesis and the first order tke balance

geology of the enterprise hydrothermal nickel deposit north western province zambia the enterprise nickel deposit 40 mt of 1 07 ni is located on the eastern edge of the kabompo dome in the north western province of zambia the deposit area contains basement schists overlain by neoproterozoic metasedimentary rocks nickel sulfides are hosted within a sequence of quartz carbonate and carbon rich metasedimentary rocks that interfinger with and overlie siliciclastic metasedimentary rocks the host rocks contain significant kyanite talc and magnesian chlorite silicification and magnesian metasomatism occurred prior to or concurrent with a regional metamorphic event 590 500 ma mineralization resulted in the precipitation of nickel and iron nickel sulfides in veins and as semimassive replacements of the host rocks nickel sulfides precipitated in two main stages a millerite vaesite pyrite assemblage that formed disseminations and semimassive replacements in vuggy textured rocks and a later millerite bravoite molybdenite assemblage in quartz kyanite veins and local semimassive replacements the deposit contains minor copper and trace amounts of cobalt and platinum group elements pges a discrete zone of copper sulfides underlies a portion of the nickel sulfide zone re os geochronology on molybdenite yields a 540 6 1 8 ma age for mineralization at enterprise the approximate age of metamorphism sulfur isotope results indicate that the sulfur at enterprise was derived largely from neoproterozoic marine sulfate by thermochemical sulfate reduction significant volumes of mafic igneous rocks are not present in the immediate area of the enterprise deposit no evidence of prealteration concentrations of nickel exists within the sedimentary rock sequence at the deposit the alteration and mineralization style of the enterprise deposit is similar to the much less metamorphosed nickel bearing shinkolobwe uranium deposit in the democratic republic of congo drc though the enterprise deposit does not contain significant uranium the sediment hosted nickel rich deposits of central african copperbelt exemplified by enterprise appear to represent a new style of hydrothermal nickel mineralization

age of native copper mineralization keweenaw peninsula michigan amygdaloidal flood basalts and conglomerates are the host for substantial deposits of native copper within the portage lake volcanics in the keweenaw peninsula of michigan a wide variety of gangue minerals are associated with the regional hydrothermal alteration mineralization event application of the rb sr method to amygdule filling microcline calcite epidote and chlorite suggests an age of mineralization between 1 060 and 1 047 m y or asymp 20 m y these results are supported by a fission track age on epidote of 1 044 or 169 m y the age of native copper mineralization determined in this study is consistent with geologic evidence which suggests that mineralization postdated the deposition of most or all of the overlying freda sandstone variable initial 87 sr 86 sr ratios between the low rb sr phases suggest mixing of isotopically distinct sources of sr during the generation and equilibration of the hydrothermal solutions

hypersaline fluids generated by high grade metamorphism of evaporites fluid inclusion study of uranium occurrences in the western zambian copperbelt in the pan african lufilian belt western zambian copperbelt uranium mineralizations preferentially scattered in kyanite talc micaschists metamorphosed evaporitic sediments or concentrated along transposed quartz veins provide an opportunity to 1 understand the time space relationship between the ore minerals and the deformation of the host rocks 2 identify the different fluid events associated with specific stages of quartz deformation and 3 characterize the ore fluid geochemistry in terms of fluid origin and fluid rock interactions in the u occurrences studied in lolwa and mitukuluku domes region western zambian copperbelt two mineralizing stages are described the first generation of ore fluids 53 59 wt cacl2 13 15 wt nacl n2 h2 in the gas phase of fluid inclusions circulated during the high temperature quartz recrystallization at 500 700 c this temperature is in agreement with the p t conditions recorded during the crustal thickening related to continental collision at ca 530 ma la icpms analyses show the presence of uranium within this fluid with a concentration mode around 20 ppm the second generation of ore fluid 21 32 wt nacl 19 21 wt cacl2 co2 co in the gas phase of fluid inclusions percolated at lower temperature conditions at the brittle ductile transition between 200 and 300 c this temperature could be related to the exhumation of the high grade metamorphic rocks at ca 500 ma the formation of h2 and co is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions finally a late fluid 14 16 wt naclequiv circulated in the brittle domain but seems unrelated to u re mobilization event

age of the zambian copperbelt the sediment hosted stratiform cu co deposits and prospects of the central african copperbelt are characterized by two intimately associated mineralization styles disseminated sulfides and sulfide bearing quartz carbonate veins and veinlets it has been widely accepted that the disseminated mineralization was introduced during sediment diagenesis in a rift setting and possibly in multiple events spanning several hundred million years in contrast the veinlet hosted mineralization is commonly thought to have been derived either by remobilization of the disseminated sulfides during the lufilian collisional orogeny or introduced at broadly the same time s as the disseminated sulfides during diagenesis and subsequent orogeny the results of 15 re os molybdenite age determinations from cu co deposits and prospects across the zambian part of the central african copperbelt suggest that both the disseminated and veinlet mineralization styles were indeed generated together but in a 50 myr cambrian window 540 490 ma during the later stages of the lufilian collisional orogeny the molybdenite ages for the disseminated stratiform mineralization at two localities do not support the notion of syndiagenetic cu introduction the molybdenite ages also show that individual deposits formed over minimum time intervals of 10 24 myr

near bottom turbulence measurements in a partially mixed estuary turbulent energy balance velocity structure and along channel momentum balance abstract a set of moored bottom mounted and shipboard measurements obtained in a straight section of the lower hudson estuary during late summer and early fall of 1995 determine velocity density and along channel pressure gradient throughout the 15 m water column as well as providing direct eddy correlation estimates of reynolds stress and indirect inertial range estimates of dissipation within 3 m of the bottom the analysis focuses on testing 1 a simplified turbulent kinetic energy equation in which production balances dissipation 2 the prandtl karman law of the wall which is a relationship between bottom stress and near bottom velocity gradient and 3 a simplified depth integrated along channel momentum balance involving local acceleration pressure gradient and bottom stress estimates of production and dissipation agree well throughout the entire record the relationship between bottom stress and velocity gradient is consistent with the law of the wall within approximately 1 m of the sea

late paleoproterozoic to early mesoproterozoic tangdan sedimentary rock hosted strata bound copper deposit yunnan province southwest china sedimentary rock hosted strata bound copper deposits are widespread in the kangdian region of the central yunnan and southern sichuan provinces southwest china the deposits occur within weakly metamorphosed rocks of the late paleoproterozoic to early mesoproterozoic dongchuan group and are spatially associated with discordant breccia bodies that are interpreted as having formed from salt diapirs the tangdan deposit the largest in the region consists of stratiform and discordant orebodies predominantly hosted in dolostones immediately above hematitic sandstones and siltstones and in black shales above the dolostones host rocks for the deposit display a complex paragenetic sequence of alteration and mineralization early sodic alteration resulted in the growth of both albite and ferroan dolomite later potassic alteration resulted in the precipitation of potassium feldspar and locally biotite in argillaceous layers sulfide mineralization was temporally and spatially associated with silicification that postdated both sodic and potassic alteration textures suggest that silicification may have preferentially affected evaporite minerals in the dolostones copper sulfides form bedding parallel disseminations veinlets and to a lesser extent stockworks copper sulfides are dominated by chalcopyrite with lesser bornite and chalcocite hypogene chalcopyrite and bornite from the tangdan deposit have 34s values that range from 12 7 to 9 3 and cluster between 3 to 5 the values suggest derivation from mesoproterozoic marine sulfates the dolostone host rocks have relatively homogeneous c and o isotope values ranging from 0 2 to 1 3 13cv pdb and from 19 1 to 22 4 18ov snow carbonate minerals in quartz sulfide veins display both a trend toward lighter oxygen isotope values and a trend to significantly lighter carbon isotope values the light carbon isotope values suggest involvement of organic carbon in the mineralizing process alteration and mineralization at tangdan probably occurred via interaction of oxidized saline brines derived from the underlying red bed sequence with partially to wholly lithified dolostones sulfide precipitation was likely due to both redox reactions and mineralizing fluid ph changes resulting from dolomite and sulfate dissolution the styles of alteration and mineralization at the tangdan deposit are similar to those observed in the central african copperbelt particularly the dolostone hosted orebodies in the mines series of the democratic republic of congo

the diagenetic origin of stratiform copper mineralization coates lake redstone copper belt n w t canada extensive stratiform copper mineralization occurs in three upper proterozoic embayments along a 250 km long arcuate belt in the mackenzie mountains supergroup northwest territories canada mineralization is found in transgressive strata between the continental red beds of the redstone river formation and shallow restricted marine carbonates of the overlying coppercap formation a mafic volcanic succession lying stratigraphically beneath the red beds possibly provided copper bearing detritus to the red beds the coates lake deposit the object of this study contains cupriferous sulfides principally chalcocite bornite and chalcopyrite hosted by microbial laminated limestones and dolostones these carbonates are intercalated with red siltstones to form as many as seven red bed carbonate couplets within the 110 m thick transition zone regional and local studies indicate that the host sediments were deposited in a peritidal setting associated with a sabkha environment paragenetic studies reveal a consistent order of precipitation for gangue and ore forming minerals these minerals can be related to the diagenetic evolution of the host sediments their presence at the coates lake deposit may be divided chronologically into four syngenetic to early diagenetic stages syndiagenesis precipitation of gypsum anhydrite after gypsum dolomitization diagenesis 1 deposition of calcite with partial replacement of anhydrite preore pyrite authigenic silica with partial replacement of anhydrite and calcite and authigenic feldspar diagenesis 2 precipitation of copper bearing sulfides in the presence of reduced sulfur sulfate reducing bacteria and organic matter and partial replacement of preore pyrite anhydrite calcite and quartz and diagenesis 3 neomorphism of calcite mineralization identified with the second stage of diagenesis would have preceded the marked reduction in permeability associated with the formation of neomorphic calcite

neoproterozoic allochthonous salt tectonics during the lufilian orogeny in the katangan copperbelt central africa the neoproterozoic katangan rocks in the copperbelt of shaba democratic republic of the congo and zambia contain the world s largest concentration of stratiform copper cobalt ores we propose that during the lufilian orogeny the katangan basin was radically transformed first by extrusion of allochthonous evaporites then by orogenic shortening salt tectonics plausibly explains spectacular breccias underlying 25 000 km2 and containing gigaclasts up to 10 km long the brecciated shaban roan supergroup the lowermost katangan unit forms regional detachments and diapirs the former existence of roan evaporites is indicated by sabkha facies crystals and pseudomorphs of gypsum and anhydrite stratigraphic gaps underlain by collapse breccias chloride inclusions in ores hydrothermally propylitized ore hosts and saline springs salt tectonics began during deposition of the roan supergroup between 1050 and 950 ma in mid roan time small walls and extrusions of evaporite gigabreccia began to be emplaced in early kundelungu time 940 850 ma evaporitic diapirs enlarged lufilian deformation began between 850 and 650 ma by laterally squeezing diapirs to form salt welds then a large sheet of commingled roan evaporite and carbonate dominated sediments and ores was extruded northward by 65 km extrusion was fast enough to blanket a uniform preorogenic footwall unit without overriding any synorogenic deposits continued shortening then emplaced large thrust sheets lubricated by the preexisting salt sediment extrusive sheet restoration suggests that the lufilian foreland in this area shortened from 193 km to 85 km the depositional northern edge of the evaporite basin controlled the shape of the outer lufilian arc we infer three original salt provinces the large scale salt tectonics inferred here has implications for ore genesis and may yet be recognized in other precambrian basins

the world s by product and critical metal resources part iii a global assessment of indium abstract indium has considerable technological and economic value to society due to its use in solar panels and liquid crystal displays for computers television and mobile devices yet without reliable estimates of known and potentially exploitable indium resources our ability to sustainably manage the supply of this critical metal is limited here we present the results of a rigorous deposit by deposit assessment of the global resources of indium using a new methodology developed for the assessment of critical metals outlined in part ii of this study werner et al 2017 we establish that at least 356 kt of indium are present within 1512 known mineral deposits of varying deposit types including vms skarn epithermal and sediment hosted pb zn deposits a total of 101 of these deposits have reported indium contents some 76 kt of contained in with the remaining 1411 deposits having mineralogical associations that indicate they are indium bearing yielding 280 kt of contained indium an additional 219 deposits contain known indium enrichments but have unquantifiable contents indicating that our global resource figure of 356 kt of contained indium is therefore most certainly a minimum a limited number of case studies also indicates that a further minimum of 24 kt indium is present in mine wastes a total that is undoubtedly smaller than reality given the minimal reporting of mine waste indium concentrations and the extensive volume of historical mine wastes these quantities are sufficient to meet demand for indium this century assuming current and projected levels of consumption however given indium s classification as a critical metal its supply still remains a concern and hence we have also discussed the economic viability and spatial distribution of the indium resources identified during this study to further our understanding of the geopolitical scarcity of this critical metal our results suggest that the global indium supply chain is fairly adaptable primarily as the spatial distribution of indium resources deviates significantly from the current supply chains for this metal our study provides a stronger basis for future studies of indium criticality provenance supply chain dynamics and stocks and flows in the fields of economic geology and industrial ecology

earth s middle age this research was funded through natural environment research council grant ne j021822 1 and the apc was paid through the rcuk oa block grant

pb isotope constraints on the age of sulfide ore deposition and u pb age of late uraninite veining at the musoshi stratiform copper deposit central africa copper belt zaire the musoshi copper deposit is a typical ore shale type deposit located centrally in the zaire zambian copper belt cu fe sulfides are disseminated in a 20 m thick laminated black siltstone unit the ore shale which occurs above a thick approximately 1 km sequence of oxidized arkosic sediments of the roan group at the base of the katangan sedimentary basin uraninite occurs in veins which cut the ore shale and extend from major hydrothermal alteration zones in the footwall rutile accompanying this veining was dated by richards et al 1988 at 514 or 2 m y 2sigma in the present study nine analyses of five uraninite samples give a u pb age of 514 or 3 m y 2sigma in exact agreement with the rutile age information concerning the age and source of the copper mineralization at musoshi has been sought by study of pb isotopes in the cu fe sulfides and other minerals leach residue analyses of most ore samples show poor correlations on 207 pb 204 pb vs 206 pb 204 pb diagrams and scatter in a band these samples typically display mature recrystallized textures and may contain thin concordant sulfide veinlets with coarse secondary biotite quartz and carbonate however analyses of three samples from near the center of the ore shale which show less evidence for recrystallization and contain no veinlets form a wellcorrelated line mswd 2 54 15 analyses corresponding to a two stage model age of 645 or 15 m y 2sigma data from the other samples scatter below this line on the pb pb diagram and toward the secondary isochron obtained from the hydrothermal rutiles similar phenomena are observed on a 208 pb 204 pb vs 206 pb 204 pb diagram where addition of u to the disturbed samples is clearly demonstrated we conclude that the samples record disturbance of pb isotopes in a simple two stage system by the late uranium depositing hydrothermal event at 514 m y the significance of the 645 m y fractionation event is not clear however at least two interpretations may be given that the event reflects primary cu fe sulfide ore deposition or that pb isotopes were homogenized at this time in a preexisting orebody by some process which also introduced u and th into the deposit we are not able at present to distinguish between these two alternatives but whichever is correct it is clear that copper ore deposition occurred at or before 645 m y and is thus unrelated to the later 514 m y hydrothermal event a high integrated u pb source ratio mu 10 2 obtained from the 645 m y sulfide isochron suggests an evolved crustal source for pb in the orebody and rules out a significant contribution from mafic igneous rocks if cu and pb are assumed to share a common source these results do not support derivation of the metals from mantle derived materials at musoshi this u pb ratio contrasts strongly with a value of mu 9 7 calculated from the rutile analyses for the late hydrothermal overprint and further confirms that this later event was not involved in the formation of the copper deposit other than in coarsening and locally concentrating the ore the high temperature 397 degrees or 5 degrees c fluids associated with this event were probably derived from deep levels in the crust and appear to have been expelled during a late pulse of activity at the close of the lufilian orogeny

estimating bottom stress in tidal boundary layer from acoustic doppler velocimeter data bed stresses in the bottom boundary layer of the york river estuary virginia were estimated from three dimensional near bottom velocities measured by acoustic doppler velocimeters advs and also by a profiling array of electromagnetic current meters by assuming the measurements were made in a constant stress layer four methods of stress estimation were evaluated using advs direct covariance cov measurement turbulent kinetic energy inertial dissipation utilizing the kolmogorov spectrum and log profile the four methods yielded similar estimates of frictional velocity u based on adv output from both 14 cm and 44 cm above bed all eight estimates of average u were consistent with the overall mean of 1 10 cm s to within the 95 confidence interval for individual burst estimates the cov method worked slightly better nearer the bed possibly because of the sensitivity of cov to the upper limit of the constant stress layer the inertial dissipation method performed marginally well at 14 cm above bed likely because of sediment induced stratification and insufficient separation of turbulent production and dissipation scales the log profile method was the most variable and appeared most sensitive to stratification and to the thickness of the constant stress layer the turbulent kinetic energy method was the most consistent at both heights and appears most promising for further development results encourage future use of the adv in estuarine environments but also favor the simultaneous use of several methods to estimate bottom stress

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

organic geochemistry and mineralogy i characterisation of organic matter associated with metal deposits abstract as geochemical appraisals of mineral regions of commercial prospectivity evolve the organic matter associated with metal rich ores has attracted greater attention petroleum basin and modern seafloor hydrothermal vent studies have suggested that organic matter can have a significant influence on the behaviour of mineralising fluids there have been many isolated reports of certain organic compositional or morphological e g pyrobitumen features showing an apparent relationships with hydrothermal fluids or minerals raising expectations that organic based parameters might be useful to mineral exploration however the understanding of organic inorganic relationships in earth systems is far from complete for example the detailed mechanics of the interaction of organics with hydrothermal fluids over geological time remain largely undefined organic geochemistry studies have traditionally involved the measurement and interpretation of the hydrocarbon composition of sedimentary rocks here we review the types of aliphatic hydrocarbons aromatic hydrocarbons and metalloporphyrins often detected from organic geochemical investigations in mineral rich regions such molecular data can be particularly diagnostic of biochemical sources and the palaeo environments at the time mineral associated organic matter was deposited sub surface trends of hydrocarbon alteration may also reflect major biogeochemical processes such as thermal maturity and biodegradation organic geochemistry data can also occasionally provide information about the nature e g origin composition temperatures and migration pathways of hydrothermal fluids and can make a contribution to holistic ore genesis models the well preserved organic matter associated with the economic here s your chance pb zn ag mine paleoproterozoic barney creek formation mcarthur basin australia and the transition metal rich early permian kupferschiefer formation germany poland have attracted significant attention a more detailed summary of the organic character of these deposits is provided to highlight the contribution organic geochemistry can make to understanding mineralisation processes most organic geochemical studies of highly mineralised regions however have not adequately addressed the significance of organic matter to mineralisation a slightly different analytical focus than traditionally used for exploration appraisal of petroleum hydrocarbons may be required to properly evaluate the significance of organic species to the mobilisation transport and deposition of ore metals the characterisation and subsequent thermodynamic modeling of organic substances and complexes within metalliferous hydrothermal systems will contribute to a better understanding of the nature and role of organic inorganic fluids or other affiliated organics in ore systems

latent thermal effects from porcupine volcanics calderas underlying the white pine presque isle stratiform copper mineralization northern michigan economic stratiform copper mineralization in the fine grained carbonaceous basal nonesuch formation of the 50 km wide white pine presque isle mining district northern michigan has long been explained by the essentially vertical infiltration of cupriferous brine across the full width of basal nonesuch strata from the underlying copper harbor conglomerate aquifer followed by copper precipitation mainly by reactions with in situ iron sulfide based on that model why do lesser amounts of total copper measured in vertical sections occur in coarser grained presumably more permeable basal nonesuch strata situated laterally to the east and west of the mining district the answer may lie in increased infiltration rates for copper harbor hosted ore forming brine warmed locally by latent volcanic heat from a resurgent caldera or calderas located within the large porcupine volcanics dome underlying the mine district not only would caldera heat have warmed the brine and lowered its density but more importantly it would have produced a remarkable decrease in the brine viscosity an increase in temperature from 15 to 100 c could have increased the brine infiltration rate by more than four times in very early diagenetic time when the sediments were poorly compacted and highly porous because progressive compaction would have opposed the temperature effect a very early diagenetic timing is suggested for main stage copper mineralization over the porcupine volcanics caldera textural evidence has also long supported an early mineralization event at the rift basin scale the exceptionally rapid upward flux of warmed brine into fine grained nonesuch over the caldera would have required equivalent volumes of replacement brine which would in turn have required a lateral convergence of brine within the footwall copper harbor conglomerate aquifer toward the white pine presque isle district this lateral focus of brine toward the warm caldera area would have created a more efficient basin scale ore forming system than that resulting from a linear hydrogeologic flow most concepts described here deserve further evaluation through quantitative hydrogeologic modeling thermal effects on ore brine viscosities and densities developed here for the sediment hosted stratiform copper mineralization of the white pine presque isle district could be considered in genetic models for other deposits and deposit types the effects are especially strong for solutions warmed from low temperatures e g 20 c or lower to 100 c and could also be important to ore fluid flow for ores involving much higher hydrothermal temperatures if solutions with initially low temperatures played a role in their genesis

sandbars in motion nearshore surf zones are turbulent places yet despite the apparently chaotic nature of the sea surface in these areas sandbars often show complex patterns with an intricate structure in their perspective stive and reniers discuss recent efforts to understand how these patterns form they highlight the report by hoefel and elgar who consider a new transport mechanism based on flow acceleration within the waves this mechanism should help to improve the predictability of sandbar structures

metal sources and mineralizing fluids characteristics and evolution of the khoemacau sediment hosted cu ag deposits in the ghanzi chobe belt portion of the kalahari copper belt abstract khoemac a u mining kcm cu ag deposits in the ghanzi chobe belt gbc portion of the kalahari cu belt are hosted in the neoproterozoic sedimentary succession of the ghanzi group these deposits are characterized by two styles of mineralization including disseminated and structurally controlled mineralization a detailed study that combined whole rocks and sulfides pb isotope characteristics carbonate rare earth element ree analysis and fluid inclusion examination was carried out in order to constrain the source s of cu amd ag characterize the mineralizing fluids and then unravel the processes that converged and led to the genesis of the khoemac a u sediment hosted cu ag deposits the pb isotope compositions of both the sulfides and whole rocks overlap and display a heterogeneous character whereas sulfides yielded 206pb 204pb t of 17 204 67 717 207pb 204pb t ranging from 15 576 to 19 025 and 208pb 204pb t between 37 026 and 45 911 whole rocks are characterized by 206pb 204pb 0 16 284 20 897 207pb 204pb 0 15 273 15 869 and 208pb 204pb 0 36 128 42 537 previous studies regarded the underlying basalts of the kgwebe formation as the main metal source however our results rule out the possibility of the rhyolites of the kgwebe formation as the source of the metals on the other hand clastic rocks of the ngwako pan formation red beds that underlie the mineralized unit and their precursor felsic basement rocks are likely the main cu ag source rocks for the kcm deposits with a possible minor contribution from the dolerite of the kgwebe formation furthermore the carbonates from the kcm cu ag deposits are characterized by significant variation in their ree contents 26 4 328 5 ppm and extreme diversity in ree patterns these results indicate that both the metals of interest cu and ag and fluids were sourced from multiple sources and multi stage hydrothermal activities were involved in the genesis of the kcm cu ag deposits the negative eu anomalies 0 28 0 88 of hydrothermal calcite associated with cu ag mineralization are also consistent with the involvement of reduced hot at temperatures above 200 c hydrothermal mineralizing fluids these fluids are characterized by a wide range of salinities 4 0 23 5 wt nacl cacl2 equiv and homogenization temperatures th ca 94 396 c thus suggesting that the fluids involved in the mineralization processes of the kcm cu ag deposits are both basinal brines possibly mixed with seawater and meteoric water as well as metamorphic fluids the bimodal distribution vapor rich and liquid rich of fluid inclusions at room temperature is attributed to the boiling of fluids during entrapment meanwhile the occurrence of both high temperature high salinity and low temperature moderate salinity fluids as well as fluid inclusions characterized by a wide range of salinities but similar th reflects fluid mixing a decrease of th in the fluid inclusions but with very similar salinities also indicates a simple cooling process during the evolution of the ore forming fluids

fluid rock interactions in a geothermal rotliegend permo carboniferous reservoir north german basin abstract comprehensive data on the chemical composition of reservoir rocks and geothermal brines from the geothermal well doublet gro schonebeck north german basin drilled into a rotliegend sedimentary and permo carboniferous volcanic rock reservoir were sampled over the past years they were characterized with respect to their major and minor elemental composition including various isotope ratios the study considered the impact of drilling and reservoir operations on fluid composition and aimed at determining fluid rock interactions to gain information on fluid origin and hydraulic pathways the highly saline fluids up to 265 g l tds show 18 o and d of water 2 7 5 6 and 3 1 15 respectively as well as 34 s of sulfate 3 6 5 and 87 sr 86 sr ratios 0 715 0 716 that resemble rotliegend brines from an area located around 200 km in the west the altmark halogen ratios indicated that brines developed predominantly by evaporation of meteoric water primary brine together with halite dissolution brine secondary brine indication for mixing with zechstein brine or with younger meteoric water was not found no geochemical distinction was possible between fluids deriving from different rock formations dacites or sedimentary rocks respectively this is due to the evolution of the sediments from the effusive rocks resulting in a similar mineralogical and chemical composition and due to a hydraulic connectivity between the two types of rock this connection existed probably already before reservoir stimulation as indicated by a set of faults identified in the area that could connect the rotliegend formation with both the volcanic rocks and the lower units of the zechstein additional geochemical indication for a hydraulic connectivity is given by 1 the very high heavy metal contents mainly cu and pb in fluids and scaling that derive from the volcanic rocks and were that were also found in increased amounts up at the zechstein border kupferschiefer formation 2 the 87 sr 86 sr isotope ratios of fluid samples correspond to the ratios determined for the sedimentary rocks indicating that initially the fluids developed in the sedimentary rocks and circulated later when faults structures were created by tectonic events into the volcanic rocks

sediment trapping of turbidity maxima in the changjiang estuary abstract sediment trapping in the turbidity maxima tm is highly variable in different estuaries or at different times in the same estuary how related processes influence the tm behavior and its structure has not yet been completely clear here we present moored and shipboard observations in the 2008 flood and dry seasons in the lower reaches of the changjiang estuary where the deepwater navigation channel was still under construction the excavation of the pristine mouth bar has caused the saline wedge to move upstream resulting in new tm zones the magnitude and extent of the tm are strongly seasonal under the influence of distinct sediment processes the tm appears as a high concentration undercurrent in the flood season whereas they occur as a low concentration sediment cloud over the water column in the dry season the hyperpycnal flow can be formed by flocculation settling and the sediment cloud can be caused primarily by resuspension the sediment trapping in the tm occurs more often during accelerating and decelerating ebb tides when the bed stress is small but the flow is highly accelerating and decelerating sediment resuspension and deposition at these tidal reversals can be induced by the growing and decaying flow spirals respectively therefore the diversity of the tm may be associated with density stratification accelerating flows flocculation or generally the interaction between stratified flows and cohesive sediments

formation of sulfide calcite veinlets in the kupferschiefer cu ag deposits in poland by natural hydrofracturing during basin subsidence calcite and copper iron sulfide veinlets in the kupferschiefer ore deposits in southwestern poland display many characteristics of antitaxial veinlets including trails of wall rock shards from wall to wall cross cutting relationships demonstrate a change from sulfate to sulfide chemical stability and an evolution of stress orientation during ore formation bedding plane sulfate veinlets and later bedding plane sulfide veinlets are superseded by vertical sulfide veinlets suggesting tectonic extension during ore formation thin bedding plane calcite sulfide veinlets record a return to pre ore stress conditions after ore formation ceased the vertical veinlets are thin and lens shaped typically 1 3 mm thick 30 35 cm high and 50 70 cm long with orientations similar to kimmerian age triassic jurassic directions sulfide replacement lenses cut across and are cut by vertical veinlets suggesting contemporaneous formation after lithification a mid triassic paleomagnetic age and cross cutting alpine

genesis of the spar lake strata bound copper silver deposit montana part i controls inherited from sedimentation and preore diagenesis mineable zones of the spar lake deposit occur where argentiferous copper sulfides and native silver formed cements and replaced certain earlier cements and clasts in the gently dipping middle quartzite beds of the upper member of the revett formation middle proterozoic belt supergroup the copper sulfides and native silver are part of a large zoned system of authigenic ore and gangue minerals at spar lake mineral zone boundaries of ore and gangue phases cross all five stratigraphic units of the upper member deduced depositional environments for the host sedimentary rocks include beach and near shore slope environments for the lower quartzite beds and subtidal channels for the middle quartzite beds the deposit must be epigenetic because mineral zone boundaries cross every facies in the sequence of beach and nearshore slope sediments mineral zonation has been mapped and seven major associations each named for its most abundant sulfide and or most characteristic gangue cement are recognized zones that appear to be developed on a regional scale include in spatial order pyrite calcite chalcopyrite ankerite and the lavender hematitic zone minor concentrations of base and precious metals occur along boundaries between the hematite and chalcopyrite ankerite zones and between the chalcopyrite ankerite and pyrite calcite zones however at the major concentrations of metals in the revett formation including the spar lake deposit additional mineral zones are developed between the chalcopyrite ankerite and pyrite calcite regional zones mineral zones at the deposit are from northwest to southeast pyrite calcite galena calcite chalcopyrite calcite bornite calcite chalcocite chlorite and chalcopyrite ankerite gangue minerals including carbonates fe ti oxides chlorite barite authigenic feldspars and apatite are zonally distributed with boundaries parallel to the sulfide mineral zone boundaries bornite calcite and chalcocite chlorite zones form ore grades in certain but not all quartzite intervals as observed at unmetamorphosed deposits where sulfide mineral zonation is similar some pyrite calcite zone minerals were probably replaced by galena calcite zone minerals which were probably succeeded in sequence by minerals of the chalcopyrite calcite bornite calcite and chalcocite chlorite zones this inferred paragenesis suggests that the chalcocite chlorite zone is more proximal to the source of ore solutions than the galena calcite or pyrite calcite zones the subeconomic chalcopyrite ankerite zone found farthest to the southeast at the spar lake deposit was apparently even more proximal to the source than ore ore deposition took place during diagenesis from solutions that migrated upward and laterally through the sediments from a southeasterly source the distributions of mineral zones and ore grades were controlled by two factors one inherited from sedimentation and the other from preore diagenesis all mineral zones spread out within coarser grained portions of quartzite units suggesting that lateral migration of ore solutions was controlled by primary permeability of the sediments however high grades of copper and silver are found only in certain of the coarser grained beds the distributions of higher grades suggest that ore mineral abundances reflect the abundances of preore diagenetic phases which were involved in the ore precipitation reactions preore reactant phases were evidently more abundant in sandstones deposited in subtidal channels the ore grade middle quartzite beds than in sandstones deposited in beach and nearshore slope environments the lower quartzite beds the identity of the reactant phases and the processes that resulted in their concentration at the site of later ore deposition remain unknown although a preore sulfide and hydrocarbon bearing pore fluid appears to be the best hypothesis as to the identity of the reactants

world class base and precious metal deposits a quantitative analysis over 62 percent of the 193 000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits about 55 percent of the 1 740 000 metric tons of silver found is in four countries and 45 percent is in four types of deposits fifty six percent of the 1 52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total over 50 percent of both the 713 000 000 metric tons of zinc and 349 000 000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits all discovered gold would fit in a cube with a height of 22 m silver in a 55 m cube copper in a 550 m cube zinc in a 460 m cube and lead in a 310 m cube at least 74 percent of gold silver zinc and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits lower grade deposits contain less total metal than higher grade deposits tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal s total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits world class deposits defined as the upper 10 percent of deposits in terms of contained metal account for over 86 percent of all gold 79 percent of silver 84 percent of copper 71 percent of zinc and 73 percent of lead these giant deposits contain at least 100 metric tons 3 2 moz gold 2 400 metric tons 77 moz silver 2 million metric tons copper 1 7 million metric tons zinc or 1 million metric tons lead mineral deposits occur rarely in the earth s crust and large ones are especially uncommon this analysis shows that only the unusually large deposits can significantly affect supply

movable bed roughness in unsteady oscillatory flow a model to predict the roughness in unsteady oscillatory flows over movable noncohesive beds is presented the roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds the model partitions the roughness into two distinct contributions these two contributions are due to the form drag around individual bed forms and to the near bed sediment transport the form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress the ripples are predicted as a function of the local skin friction and a semiempirical expression is derived using standard law of the wall arguments which gives the ripple or form roughness as a function of the boundary geometry the ripple roughness is found to be proportional to the product of the ripple steepness and height favorable comparison of the form drag model with the results of bagnold s 1946 fixed ripple study is found the value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from carstens et al s 1969 experiments this value is found to be 7 or 8 grain diameters an expression is derived for the roughness associated with the maximum thickness of a near bottom sediment transporting layer consistent with owen s 1964 roughness hypothesis for saltation of uniform grains in air at large values of the boundary shear stress relative to the critical value for initial sediment motion the derived expression is similar to the results of smith and mclean s 1977 unidirectional flow approach modified for oscillatory flow the total roughness model is found to compare favorably with carstens et al s 1969 data in contrast to smith and mclean s 1977 steady flow findings the results here show that when ripples are present they account for a significant portion of the boundary roughness

linkage of crustal deformation between the archaean basement and the proterozoic cover in the perapohja area northern fennoscandia abstract reconstructed variations in stratigraphic thicknesses combined with mapped variations in fold and thrust belt structural styles and patterns of the entire palaeoproterozoic perapohja belt in northern finland show that both the deposition of the 2 4 1 9 ga supracrustal rocks and the structural evolution during the subsequent svecofennian orogeny 1 9 1 8 ga have been tightly controlled by i the palaeo topography of the archaean 2 5 ga basement and ii the reactivation of archaean basement faults during the multiple stages of rifting and deposition of the supracrustals as well as during subsequent basin inversion and fold and thrust belt development folds and thrusts in the supracrustal sequence are found to be largely detached from the underlying basement along the petajaskoski detachment zone pdz that formed within a mechanically weak stratigraphic unit in the basal part of the perapohja belt stratigraphy the pattern of contractional structures is complex but developed during one phase of simple progressive south vergent thrusting two styles of basement cover linkage are recognised the hard linked style is best illustrated by the reverse sihtuuna fault currently defining the northern margin of the e w to ene wsw trending basement horsts and the overlying anticlines and juxtaposing the stratigraphically lowermost perapohja belt rocks with higher up stratigraphy indicating the fault is inherited after a pre existing basement structure based on the distribution and thickness variation of the palaeoproterozoic supracrustal units the faults bounding the basement horst were active as extensional faults during deposition the soft linked style relationship is evident as abrupt terminations of thrust related elongate domes and localisation of the compressional overprint into the nw se trending central graben understanding the basement architecture and basement cover linkages is highly significant because the majority of the known mineralizations of the belt are located along or close to the basement faults

secular variations in precambrian seawater chemistry and the timing of precambrian aragonite seas and calcite seas an extension of the seawater secular variation model that successfully predicted the observed timing of phanerozoic mgso 4 vs kcl marine evaporites and aragonite seas vs calcite seas has been applied to the prediction of the secular variations in the major ion chemistry of seawater and aragonite seas vs calcite seas during the precambrian testing of the predictions was based on those precambrian seafloor carbonate precipitates that have been interpreted by others to have formed originally as aragonite of 16 examples of precambrian seafloor aragonite 14 fall within the 6 periods of aragonite seas predicted for the late archean proterozoic by the model 1 falls on the transition between an aragonite sea and calcite sea and 1 falls in a period of calcite seas this strong correlation supports the following predictions of the model 1 precambrian seawater was a saline nacl water with ca hco 3 since at least the late archean 2 the major ion compositions of precambrian seawater chemistry and their secular variations are in the same ranges as those of phanerozoic seawater 3 the mg ca mole ratio in seawater has controlled the types of caco 3 polymorphs that have precipitated from earth9s oceans throughout the phanerozoic and most if not all of the precambrian

pyrite re os geochronology of the sareke sediment hosted cu deposit xinjiang nw china abstract the sareke cu deposit in the western tarim region xinjiang nw china is hosted in continental sedimentary rocks of the upper jurassic kuzigongsu formation and lower cretaceous kezilesu group stratabound orebodies occur mainly in conglomerate and minor in siltstone both stratabound major and vein type minor ores are composed of chalcocite chalcopyrite bornite and pyrite with minor sphalerite and galena which show a zonation pattern of chalcocite chalcopyrite sphalerite galena pyrite from north to south of sareke carbonation is the most important hydrothermal alteration at sareke and dolomite together with calcite are the dominant gangue minerals six pyrite samples which coexist closely with copper sulfides are re os dated and yielded a re os isochron age of 115 8 4 7 ma and a weighted mean age of 114 3 1 8 ma which constrain the sareke cu mineralization to the late early cretaceous this age is synchronous with the tectonic inversion event and the basaltic magma activities of the tuyon basin which could been sources of dynamics and thermodynamics during the ore forming process this is the first unambiguous evidence for an appreciable copper concentration of mesozoic age and based on this evidence additional mesozoic sediment hosted stratabound copper mineralization event may have occurred elsewhere within basins along the talas fergana fault