incision due to gravel mining modeling a case study from the gallego river spain abstract historical information on river degradation was used in a case study on the gallego river a tributary of the ebro river in northeastern spain the gallego drains about 4000 km 2 of the southern slopes of the pyrenees good channel surveys since the 1940s allowed a comparison of longitudinal bed profiles over time over this period about 1 million m 3 of gravel was mined according to the archival records the volume of alluvium lost due to incision in the same period was 2 million m 3 this imbalance is tentatively explained by a budget model based on a bedload equation and an algorithm to determine whether the effective bedload transport is controlled by the transport capacity or by the supply of sediment it appears that the incision process has changed the magnitude of the shear stresses on channel bed as the river became deeper the channel could accommodate higher discharges without overbank flooding the results obtained from a second model based on diffusion equation for the bed elevation compared well with the field data this model is based on the hypotheses of steady uniform flow regarding water and sediment conservation

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

delineating alteration footprints from field and aster swir spectra geochemistry and gamma ray spectrometry above regolith covered base metal deposits an example from abra western australia

geochemical and mineralogical characteristics of a power station feed coal eggborough england abstract chemical and mineralogical analyses are presented for a power station feed coal in the yorkshire coalfield u k the mineralogy of the whole coal consists of quartz kaolinite illite mixed layer clay chlorite pyrite and carbonates pyrite carbonates and some of the kaolinite are diagenetic in separated low density fractions of the coal both pyrite and kaolinite are concentrated relative to the detrital minerals compared with the high density fractions the detrital clay mineralogy of these low density fractions contains less chlorite and the mixed layer clay to illite ratio is higher which is consistent with a grain size control during sedimentation the major element analyses are comparable with mudrocks in the stratigraphic sequence but there is evidence of na 2 o enrichment related to connate brinnes and the fe 2 o 3 content shows significant enrichment particularly in the ashes of the low density fractions the dissolution of oxhydroxide grain coatings associated with detrital sediment in the coal and also in the adjacent strata are probable sources of the iron in the diagenetic pyrite there is evidence of iron mobility in the sedimentary sequence and introduction into the coal itself during diagenesis within the coal trace elements are also enriched on an ash basis relative to the mudrocks and their origin is also probably very similar to that of iron a noteworthy feature of the trace element enrichment is that the enrichment factors for a number of elements are comparable with those determined for marine black shales in the sequence this suggests a common origin for the elements during the diagenetic processes analysis of the coal density fractions after correcting for detrital mineralogy suggests pb cu ni zn and possibly mn are associated with pyrite and v sr ba zr and nb are either directly or indirectly associated with organic components possibly zr and nb originate from dispersed volcanic ash

metallogeny in the capricorn orogen western australia the result of multiple ore forming processes abstract the capricorn orogen includes metamorphosed tectonic units intrusive igneous rocks volcano sedimentary and sedimentary basins situated between the pilbara and yilgarn cratons these include the gascoyne complex ashburton blair bresnahan yerrida bryah padbury and earaheedy basins and edmund and collier former bangemall basins mineral deposits and occurrences in these units comprise stratabound base metals including the giant abra pb cu ba edmund basin and magellan pb earaheedy basin and numerous hydrothermal veins and precious and or base metal lodes some of the more important orogenic precious metal lodes are those of the peak hill group in the bryah padbury basins and the egerton field in the gascoyne complex the metallogeny of the capricorn orogen reflects syn to post capricorn orogenic events linked to either protracted convergence tectonics between the pilbara and yilgarn cratons or to a two stage convergence history one during the capricorn orogeny ca 1 83 ga pilbara yilgarn convergence the other during the yapungku orogeny ca 1 79 north australian west australian convergence the metallogeny of the capricorn orogen was further sustained by continental mafic magmatism at about 1 45 and 1 07 ga during which heat advection may have caused widespread hydrothermal circulation particularly in the edmund collier earaheedy basins and adjacent tectonic units an interesting but as yet unexplained aspect of the capricorn metallogeny is the regional pb ba enrichment a conceptual model that attempts to explain the billion year long history of the metallogeny in the capricorn orogen is proposed mineral exploration in the capricorn orogen is somewhat limited and not as intensive as is in the brown fields of the archaean terranes of western australia

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

mineralogy and geochemistry of mississippian and lower pennsylvanian black shales at the northern margin of the variscan mountain belt germany and belgium abstract exploration of unconventional gas resources from paleozoic formations in northwestern germany is just getting started large potential gas reservoirs are presumed to be present north of the rhenish massif where mississippian and pennsylvanian marine black shales occur this paper comprises geochemical and mineralogical data and other important aspects of potentially economic black shale formations of the carboniferous additionally the burial and thermal history was reconstructed using 1d modeling software schlumberger these 1d models were calibrated with vitrinite reflectance data from outcrops and shallow wells in general all paleozoic black shales are at present highly mature between about 1 5 and 3 vitrinite reflectance the shales of the uppermost mississippian upper alum shale chokier formation have high contents of organic carbon are tens of meters thick and can be regarded as potential gas shale targets most other mississippian and pennsylvanian black shales are relatively thin adjacent carbonates are often stained black and rich in solid bitumen indicating former oil impregnation of these reservoirs

detection of zinc deposits using terrestrial ferromanganese crusts abstract ferromanganese crusts coatings of iron oxide and manganese oxyhydr oxide minerals occur in various forms on a broad range of surface materials in the subaerial environment manganese oxyhydr oxide minerals in particular have very high adsorption capacities for heavy metals and trace elements thus in the scenario whereby metals from ore deposits are liberated and mobilized to the surface and interact with ferromanganese crusts there is potential for such crusts to adsorb anomalous concentrations of target and pathfinder elements thereby offering a potential sampling medium during geochemical exploration two case studies were undertaken at known base metal deposits the 200 m deep abra and 6 10 3 were returned from crusts proximal to the prairie wolf deposits and ratios in crusts decreased to as low as 3 with decreasing proximity to the mineralization ferromanganese crusts directly overlying mineralization at abra however yielded low zn mn ratios this is interpreted to be a function of limited vertical mobilization of metals and preferential mn scavenging in soils our results suggest deposits which lie deep below the base of weathering that are geochemically blind remain difficult to detect but the analysis of ferromanganese crusts from semi arid environments can be used to detect relatively shallow base metal mineralization

sensitivity analysis of nonequilibrium adaptation parameters for modeling mining pit migration the nonequilibrium adaptation parameters of a depth averaged two dimensional hydrodynamic and sediment transport model were examined in the study calculated results were compared to data measured in two sets of published laboratory experiments that investigated mining pit migration under well controlled boundary conditions including steady flow and uniform rectangular cross sections along the flume except in the vicinity of the experimental mining area the two sets of experiments were chosen as representatives of bed load dominated and suspended load dominated cases respectively a sensitivity analysis was conducted to estimate the influence of the nonequilibrium adaptation parameters on mining pit migration simulation calculated results indicate that appropriate selection of the adaptation parameters is critical in order to close the nonequilibrium sediment transport formulas when modeling mining pit migration

geochemistry of surface sediments from the arabian sea we report new geochemical data si al na k rb sr mn cu ni fe zn co and pb for 126 surficial sediments and base metal partition data for limited samples from the deep arabian sea and discuss the controls affecting these elemental concentrations the geochemical nature of and differences between sediments from three physiographically tectonically distinct regions have been identified the spatial resolution allows us to discern the various processes operative in the deep arabian sea during the holocene epoch r mode factor analysis on the geochemical data suggests that four dominant factors are responsible for the observed geochemical variations in the samples namely carlsberg ridge hydrothermal activity terrigenous contribution hydrogenous authigenic precipitates and biological contribution

abra a strata bound pb cu ba mineralization in the bangemall basin western australia abra is an upper proterozoic approximately 1 100 m y sediment hosted strata bound cu pb ba mineralization located some 900 km north northeast of perth in western australia it was discovered in 1981 is spatially related to coincident magnetic and gravity anomalies and is covered by 230 to 450 m of unmineralized clastic sediments drilling of eight exploration holes 5 000 m total length during 1981 to 1983 established an estimated 130 million metric tons of mineralized rocks with an average grade of 1 15 percent lead 0 25 percent copper and 2 5 percent barium the silver content is in the range of 2 to 50 ppm the gold content is usually low and is irregularly distributed with a maximum value of 6 9 ppm over 6 m of drill core abra occurs near the eastern margin of the jillawarra basin a west east trending graben structure in the central bangemall basin which covers an area of 143 000 km 2 and consists of shallow water sediments dated at 1 100 m y the host rock sequence in the lower bangemall group comprises over 500 m of intertidal clastics overlain by some 40 m of subaqueous evaporitic iron formation deposited in a fault bounded restricted basin these ferruginous laminites black zone grade upward into hematitic sabkha sediments red zone which form the top of the mineralization the hanging wall consists of more than 300 m of unmineralized coarse clastics and shallow water turbidites the major ore minerals are galena chalcopyrite barite subordinate tetrahedrite and minor pyrite most remarkable is the general paucity of zinc and the dominance of stratiform barite 40 m of drill core with more than 20 ba at the top of the mineralization relative metal abundances show a vertical zonation pattern of cu zn pb ba where cu is restricted to the discordant feeder zone pb has an intermediate position and some ba is of concordant nature within the sabkha sediments mineralization is accompanied by chloritization and albitization sulfur isotope analysis yielded delta 34 s values of 21 per mil for sulfides and 40 per mil for barite the mineralizing processes are linked to the geotectonic evolution of the bangemall and the jillawarra basins a genetic model involves mobilization of metal bearing fluids from an arkose of the basal bangemall group in response to anomalous heat flow emplacement of mineralization was crosscutting and replacive within unconsolidated diagenetic sediments ascent of the hydrothermal fluids was induced by the generation of deep seated faults in the coarse of the very first intracratonic rifting of the bangemall basin

an assessment of geochemical preparation methods prior to organic carbon concentration and carbon isotope ratio analyses of fine grained sedimentary rocks 1 this study summarizes organic carbon isotope 13c and total organic carbon toc data from a series of tests undertaken to provide an appropriate methodology for pre analysis treatment of mudstones from an upper carboniferous sedimentary succession in order to develop a consistent preparation procedure the main treatments involved removing both inorganic carbonate and hydrocarbons which might be extraneous before 13c and toc analysis the results show that decarbonating using hydrochloric acid causes significant reduction in 13c and total carbon tc of the bulk material due to the removal of inorganic carbonate these changes are most pronounced where soluble calcium carbonate rather than ca mg fe carbonate is present deoiled samples show only slightly higher mean 13c where visible bitumen was extracted from the bulk sample moreover the isotopic signatures of the extracts are closely correlated to those of their respective bulk samples suggesting that small yields of hydrocarbons were generated in situ with no isotopic fractionation in addition further 13c and tc analyses were performed on samples where mixing of oil based drilling mud with brecciated core material had been undertaken brecciated mudstone material did not display distinct isotopic signals compared to the surrounding fine grained material overall we show that the most accurate assessment of bulk organic carbon isotopes and concentration in these samples can be achieved through decarbonating the material prior to measurement via the rinse method however our results support recent findings that pre analysis acid treatments can cause variable and unpredictable errors in 13c and toc values we believe that despite these uncertainties the findings presented here can be applied to paleoenvironmental studies on organic matter contained within sedimentary rocks over a range of geological ages and compositions

reactivated basement structures affecting the sedimentary facies in a tectonically quiescent epicontinental basin an example from nw switzerland abstract the jurassic deposits in the southern part of central europe accumulated in a shallow epicontinental sea and their deposition has usually been believed to have corresponded to a phase of tectonic quiescence neither on conventional seismic records nor in outcrops obvious indications of synsedimentary tectonics were found nonetheless subtle variations in lithofacies and thickness occur above faults in the crystalline basement in fact preexisting structures became reactivated in the jurassic during major extensional phases when the tethys and the north atlantic opened this reactivation led to differential subsidence and or to rotation of fault bounded blocks but the sediments were deformed mainly flexurally as vertical movements in the basement were dissipated by triassic salt thus the depositional area was morphologically differentiated into swells and depressions in siliciclastic muddy environments swells were characterized by hardbottoms and hiatus beds depressions were filled by distal tempestites and gravity deposits in carbonate settings reefs nucleated on swells marls and muds were deposited in depressions many of them gravity deposits reactivation of faults occurred only during short episodes and was not synchronous throughout the study area and reactivation of individual faults was episodic and probably controlled by the palaeostress field and the faults orientation reactivation of deep rooted faults is also documented by hydrothermal activity which led to vein mineralization and alteration of minerals today exposed in nearby basement units the chronostratigraphic ages of the hydrothermal processes coincide with phases of enhanced subsidence during the sinemurian aalenian bajocian bathonian and oxfordian in turn facies changes of the sedimentary cover should be useful to predict basement structures when no seismic records are available

the importance of pyritic roof strata in aquatic pollutant release from abandoned mines in a major oolitic berthierine chamosite siderite iron ore field cleveland uk abstract the cleveland ironstone field ne england is a major sedimentary iron orefield in which the principal ore minerals are iron silicates berthierine chamosite and carbonates siderite the siderite in this area is known to be rich in mg and mn in solid solution with fe although this ore assemblage would not normally be expected to give rise to acid mine drainage phenomena a number of discrete ferruginous mine water discharges totalling some 6 5 million litres ml day 1 have been identified flowing from abandoned underground mine workings and old spoil heaps in the ore field some of these discharges are extremely acidic ph 3 3 with total fe reaching 1220 mg l 1 at the point of first emergence to the surface most of the discharges are so highly charged with dissolved co2 that they effervesce upon degassing one of the discharges precipitates a ferroan calcite deposit which is most unusual as a mine water discharge precipitate all the other discharges precipitate more usual ferrihydrite and goethite ochres the geochemistry of these waters supports the view that oxidation of pyrite in the roof strata initiates dissolution of siderite in the old workings releasing co2 fe and mg to solution this chain of reactions results in these waters having so2 4 as their major anion from pyrite weathering with mg as the major cation except where fe exceeds mg in concentration two of the near coastal discharges have na as the major cation and elevated cl concentrations suggesting a sea water component however so4 cl ratios suggest that sea water can account for no more than 20 of these waters most of the cleveland mine waters have significant environmental impacts ranging from ecological damage to receiving water courses to flooding problems caused by the clogging of surface sewers with mine water precipitates a range of remedial measures are proposed

the crystallographic fabric and texture of siderite in concretions implications for siderite nucleation and growth processes the crystallographic fabric of siderite in siderite concretions has been determined for upper carboniferous westphalian a non marine concretions and lower jurassic pliensbachian marine concretions compositional zoning indicates that individual siderite crystals grew over a period of changing pore water chemistry consistent with the concretions being initially a diffuse patch of cement which grew progressively the siderite crystallographic fabric was analysed using the anisotropy of magnetic susceptibility which is carried by paramagnetic siderite the siderite concretions from marine and non marine formations exhibit differences in fabric style although both display increases in the degree of preferred siderite c axis orientation towards the concretion margins the westphalian non marine siderites show a preferred orientation of siderite c axes in the bedding plane whereas the pliensbachian marine siderites have a preferred orientation of c axes perpendicular to the bedding in addition a single marine concretion shows evidence of earlier formed inclined girdle type fabrics which are intergrown with later formed vertical c axis siderite fabrics the marine and non marine fabrics are both apparently controlled by substrate processes at the site of nucleation which was probably clay mineral surfaces siderite nucleation processes on the substrate were most probably controlled by the bio chemistry of the pore waters which altered the morphology and crystallographic orientation of the forming carbonate the preferred crystallographic orientation of siderite results from the orientation of the nucleation substrate fabric changes across the concretions partially mimic the progressive compaction induced alignment of the clay substrates while the concretion grew during burial

an enhanced understanding of the basinal bowland shale in lancashire uk through microtextural and mineralogical observations abstract variability in the lower bowland shale microstructure is investigated here for the first time from the centimetre to the micrometre scale using optical and scanning electron microscopy om sem x ray diffraction xrd and total organic carbon content toc measurements a significant range of microtextures organic matter particles and fracture styles was observed in rocks of the lower bowland shale together with the underlying pendleside limestone and worston shale formations encountered the preese hall 1 borehole lancashire uk four micro texture types were identified unlaminated quartz rich mudstone interlaminated quartz and pyrite rich mudstone laminated quartz and pyrite rich mudstone and weakly interlaminated calcite rich mudstone organic matter particles are classified into four types depending on their size shape and location multi micrometre particles with and without macropores micrometre size particles in cement and between clay minerals multi micrometre layers and organic matter in large pores fractures are categorized into carbonate sealed fractures bitumen bearing fractures resin filled fractures and empty fractures we propose that during thermal maturation horizontal bitumen fractures were formed by overpressuring stress relaxation compaction and erosional offloading whereas vertical bitumen bearing resin filled and empty fractures may have been influenced by weak vertical joints generated during the previous period of veining for the majority of samples the high toc 2 wt low clay content 50 wt and the presence of a multi scale fracture network support the increasing interest in the bowland shale as a potentially exploitable oil and gas source the microtextural observations made in this study highlight preliminary evidence of fluid passage or circulation in the bowland shale sequence during burial

in situ u pb geochronology of xenotime and monazite from the abra polymetallic deposit in the capricorn orogen australia dating hydrothermal mineralization and fluid flow in a long lived crustal structure abstract the proterozoic capricorn orogen is a major tectonic zone that records the assembly and subsequent reworking of the west australian craton recent seismic transects across the orogen have identified major crustal structures some of which are spatially associated with hydrothermal mineral deposits the sedimentary rock hosted abra deposit which is the largest base metal accumulation in the capricorn orogen is localized within the crust cutting lyons river quartzite well fault zone robust radiometric dates for the timing of sediment deposition and hydrothermal mineralization are essential for understanding the geological history of this long lived orogen and the processes that formed the ore deposits in situ u pb shrimp geochronology of xenotime intergrown with magnetite hematite galena from the abra ore zone yields a weighted mean 207pb 206pb age of 1594 10 ma n 14 mswd 2 6 which is interpreted to represent a period of xenotime growth during the hydrothermal activity responsible for the mineralization an older coherent cluster within this group gives a weighted mean age of 1610 16 ma n 5 mswd 1 5 which constrains the depositional age of the lower edmund group sediments to between c 1680 ma maximum age of the basal mt augustus sandstone and c 1610 ma authigenic monazite from the ore zone gives 207pb 206pb ages of 1375 14 n 16 mswd 0 99 ma interpreted to represent a hydrothermal event postdating the main phase of mineralization monazites in samples distal to mineralization yield weighted mean 207pb 206pb ages of 1221 14 ma n 5 mswd 1 04 and 995 18 ma n 6 mswd 1 3 interpreted as records of discrete episodes of hydrothermal fluid flow our results suggest that the lyons river quartzite well fault which is one of the principal structures in the capricorn orogen has a long history of tectonic reactivation spanning more than 600 million years and involving crustal extension and sediment deposition hydrothermal mineralization and multiple episodes of fluid flow xenotime and monazite represent ideal chronometers for investigating the complex histories of hydrothermal mineralization and fluid flow in major crustal structures and helping to unravel the geological evolution of intracratonic orogens

the geochemistry of environmentally important trace elements in uk coals with special reference to the parkgate coal in the yorkshire nottinghamshire coalfield uk abstract the parkgate coal of langsettian age in the yorkshire nottinghamshire coalfield is typical of many coals in the uk in that it has a high sulphur s content detailed information on the distribution of the forms of s both laterally and vertically through the seam was known from previous investigations in the present work 38 interval samples from five measured sections of the coal were comprehensively analysed for major minor and trace elements and the significance of the relationships established using both raw and centered log transformed data the major elements are used to quantify the variations in the inorganic and organic coal components and determine the trace element associations pyrite contains nearly all of the hg as se tl and pb and is also the major source of the mo ni cd and sb the clays contain the following elements in decreasing order of association rb cs li ga u cr v sc y bi cu nb sn te and th nearly all of the rb is present in the clay fraction whereas for elements such as v cu and u a significant amount is thought to be present in the organic matter based on the k vs trace element regression equations only ge and possibly be would appear to have a dominant organic source the trace element concentrations are calculated for pyrite the clay fraction and organic matter for pyrite it is noted that concentrations agree with published data from the yorkshire nottinghamshire coalfield and also that tl concentrations median of 0 33 ppm in the pyrite are greater than either hg or cd unlike these elements tl has attracted less attention and possibly more information is needed on its anthropogenic distribution and impacts on man and the environment a seawater source is thought to be responsible for the high concentrations of s cl and the non detrital trace elements in the parkgate coal indicative of the seawater control is the th u ratio which expresses the detrital to non detrital element contributions using other elements similar ratios can be calculated which in combination offer greater interpretative value

lead isotopes in iron and manganese oxide coatings and their use as an exploration guide for concealed mineralization abstract lead isotopes from fe and mn oxides that coat stream pebbles from around the mount emmons porphyry molybdenum deposit in colorado were studied to assess the feasibility of using pb isotopes to detect concealed mineral deposits the fe mn oxide coatings were analyzed to determine their elemental concentrations using icp aes the pb isotope compositions of solutions from a selected suite of samples were measured using both thermal ionization and icp mass spectrometry to compare results determined by the two analytical methods heavy mineral concentrates from the same sites were also analyzed to compare the pb isotope compositions of the fe mn coatings with those found in panned concentrates the fe mn and 206 pb 204 pb ratios of the oxide coatings are related to the lithology of the host rocks fe mn oxide coatings on pebbles of black shale have higher fe mn values than do the coatings on either sandstone or igneous rocks the shale host rocks have a more radiogenic signature e g higher 206 pb 204 pb than the sandstone or igneous host rocks the pb isotope data from sandstone and igneous hosts can detect concealed mineralized rock on both a regional and local scale even though there are contributions from 1 metals from the main stage molybdenite ore deposit 2 metals from the phyllic alteration zone which has a more radiogenic pb isotope signature reflecting hydrothermal leaching of pb from the mancos shale 3 pb rich base metal veins with a highly variable pb isotope signature and 4 sedimentary country rocks which have a more radiogenic pb isotope signature an investigation of within stream variation shows that the pb isotope signature of the molybdenite ore zone is retained in the fe mn oxide coatings and is not camouflaged by contributions from pb rich base metal veins that crop out upstream in another traverse the pb isotope data from fe mn oxide coatings reflect a complex mixing of pb from the molybdenite ore zone and its hornfels margin pb rich base metal veins and sedimentary country rocks stream sediment anomalies detected using oxalic acid leaches can be evaluated using pb isotope analysesof selected geochemical anomalies such an evaluation procedure given regional target pb isotope signatures for concealed mineralization can greatly reduce the cost of exploration for undiscovered ore deposits concealed beneath barren overburden lead isotope measurements on aliquots of the same solutions showed that icp ms determinations are of low precision and vary non systematically when compared with the pb isotope values of the higher precision thermal ionization method these variations and lower precision of the icp ms measurements are attributed to matrix effects

the mesoproterozoic abra polymetallic sedimentary rock hosted mineral deposit edmund basin western australia abstract abra is a blind sedimentary rock hosted polymetallic fe pb zn ba cu au ag bi w deposit discovered in 1981 located within the easterly trending jillawarra rift sub basin of the mesoproterozoic edmund basin capricorn orogen western australia the edmund basin contains a 4 10 km thick succession of siltstone sandstone dolomitic siltstone and stromatolitic dolomite the age of the edmund group is between 1 66 and 1 46 ga the abra polymetallic deposit is hosted in siltstone dolostone sandstone and conglomerate of the irregully and kiangi creek formations but the mineralised zones do not extend above an erosion surface marking the change from fluvial to marine facies in the lower part of the kiangi creek formation the abra deposit is characterised by a funnel shaped brecciated zone interpreted as a feeder pipe overlain by stratiform stratabound mineralisation the stratiform stratabound mineralisation includes a red zone and an underlying black zone the red zone is characterised by banded jaspilite hematite galena pyrite quartz barite and siderite the jaspilite and hematite cause the predominant red colouration the black zone consists of veins and rhythmically banded sulphides laminated and or brecciated hematite magnetite fe rich carbonate and scheelite in both zones laminations and bands of sulphide minerals fe oxides barite and quartz commonly exhibit colloform textures the feeder pipe stringer zone merges with black zone and consists of a stockwork of fe carbonate quartz barite pyrite magnetite and chalcopyrite exhibiting fluidised and or jigsaw textures the abra mineral system is characterised by several overprinting phases of hydrothermal activity from several stages of brecciation and fluidisation barite and sulphide veining to barren low temperature chalcedonic epithermal regime veining hydrothermal alteration minerals include multi stage quartz chlorite prehnite fe rich carbonate and albite albite na metasomatism is an early alteration phase whereas fe rich carbonate is a late phase fluid inclusion studies indicate that the ore fluids had temperatures ranging from 162 to 250 c with salinities ranging from 5 8 to about 20 wt nacl in the course of our studies microthermometric and raman microprobe analyses were performed on fluid inclusions in carbonate quartz and barite grains fluid inclusions in quartz show homogenisation temperatures ranging from 150 to 170 c with calculated salinities of between 3 7 and 13 8 wt nacl the sulphur isotopic system shows 34 s values ranging from 19 4 to 26 6 for sulphides and from 37 4 to 41 9 for barite vogt and stumpfl 1987 austen 2007 sulphur isotope thermometry between sulphides and sulphide barite pairs yields values ranging from 219 to 336 c austen 2007 galena samples were analysed for pb isotope ratios which have been compared with previous pb isotopic data the new pb isotope systematics show model ages of 1650 1628 ma consistent with the formation of the host edmund basin re os dating of euhedral pyrite from the black zone yielded an age of 1255 ma this age corresponds to the 1320 1170 ma mutherbukin tectonic event in the gascoyne complex this event is manifested primarily along a wnw trending structural corridor of amphibolite facies rocks about 250 km to the northwest of the abra area it is possible that the re os age represents a younger re activation event of an earlier sedex style system with a possible age range of 1640 1590 ma a genetic model for abra is proposed based on the above data the model involves two end members ore forming stages the first is the formation of the sedex style mineral systems followed by a second multi phase stage during which there was repeated re working of the mineral system guided by seismic activity along major regional faults

evaluation of infilling and replenishment of river sand mining pits rivers are one of the main sources to supply sand and gravel for construction projects depending on river morphology and hydraulic characteristics its sediment transport capacity and mining operation method the extraction of river bed materials may affect its ecosystem through bank and bed erosion to advance the mechanisms of river pit infilling the effects of various parameters i e the distance between pits the pit plan shape the pit depth sediment size and approaching flow velocity on pit infilling volume are investigated in this research the results of this research show that infilling volume of upstream pit is insignificantly affected by the distance between the pits and it is completely refilled for different distances however the infilling volume of downstream pit decreases by increasing the distance between the pits in addition by reducing the ratio of pit length to its width pit shape extension in spanwise direction the pits can be excavated in a shorter distance from each other when this ratio decreases by 15 the infilling volume increases up to 30 subsequently as a cost effective option the pit distance can be reduced up to 50 in these conditions according to the obtained results although the sediment size has negligible effect on infilling volume in the studied range the infilling volume increases up to 20 by an increase of 8 in the approaching flow velocity increasing the ratio of pit length to its width pit shape extension in streamwise direction highlights the effectiveness of smaller depths so that the infilling volume increases up to 20 by a decrease of 20 in the pit depth in this regard it is recommended that the pit depth be restricted to 70 of the channel flow depth to have a complete pit refilling

mineral matter in coals cleat minerals and their origin in some coals from the english midlands abstract in four coal seam profiles from the cannock coalfield west midlands the cleat joint frequency is a function of lithotype greatest in vitarin and is inversely related to bed thickness the cleat minerals were studied 1 under the microscope optical and electron 2 by x ray diffraction and 3 chemically the minerals present are pyrite marcasite sphalerite galena sulphides quartz kaolinite silicates ankerite calcite carbonates and apatite this sequence has features in common with diagenetic sequences recorded in other rock types and it is concluded that the cleat minerals in coal form in response to pore fluid evolution and movement during burial diagenesis the elements are thought to originate from both the coal and the associated sediments mainly mudrocks similarities in diagenetic sequences are in part a reflection of the importance of organic maturation reactions in all the rock types in the sequence whereas differences are attributed to the dominance of these reactions in the coal itself

amber and organic matter from the late oligocene deep water deposits of the central western carpathians orava podhale basin abstract the occurrence of amber in the central carpathian paleogene basin is reported here for the first time the amber has been analyzed by means of optical microscopic methods infrared spectroscopy gas chromatography mass spectrometry and pyrolysis gas chromatography mass spectrometry to understand the amber composition origin taphonomy alteration and diagenesis organic petrographic and reflectance analyses of organic matter from amber bearing sediment was carried out to get information about paleoenvironment and maturity of sedimentary rock analyses confirmed polylabdane structure associated with class ib type of amber and its possible origin from the conifer family araucariaceae it is characterized by a high degree of maturity where both temperature and exogenic processes have participated in its conversion heterogeneity of reflectance values in the resinite suggests that amber was not redeposited from an older and more mature sedimentary unit the discrepancy between the maturity of the amber and amber bearing sedimentary rock along with abundant char and inertinite macerals indicates a probability of thermal alteration of the amber under the influence of heat from a wildfire and increased maturity occurring before its ultimate burial in a deep sea environment the assemblage of terrigenous macerals and numerous char and inertinite particles which were found in amber bearing sediment as well as in the amber crust suggest forest swamp type vegetation affected by wildfires the presence of amber and predominantly terrigenous organic matter besides mud rip up clasts derived from freshwater sediments in deep marine deposits indicates a direct connection of terrestrial environments to the deep water depositional system

biogenic mn oxide minerals coating in a subsurface granite environment abstract this paper reports the results of a study of biogenic mn oxide minerals coating in a subsurface granite environment this subterranean environment corresponds to galleries of a 16th century spring water tunnel dug throughout the granite bedrock located in porto city nw portugal several techniques xrd ftir raman icp ms tem eds fesem eds stem eds and stxm nexafs were used to assess the mechanisms involved in the formation of manganese oxides specifically birnessite and todorokite these manganese oxides presented peculiar shapes nano dimensions low degree of crystallinity and high levels of some trace elements such as p ca c al si ba and zn they were associated with large amounts of extracellular polymeric substances exuded by filamentous bacterial communities which serve as nuclei for preferential precipitation of manganese oxides on the extracellular sheaths scientific assessment revealed that biological activity played a major role in the development of these manganese oxides

tectonic setting and basin evolution of the bangemall supergroup in the northwestern capricorn orogen abstract the mesoproterozoic bangemall supergroup is the youngest depositional element within the capricorn orogen and comprises 4 to 10 km of fine grained siliciclastic and carbonate sedimentary rocks this succession is intruded by two generations of dolerite sills with ages of 1465 and 1070 ma field studies and geochronological data support a two fold subdivision of the bangemall supergroup into the c 1620 1465 ma edmund group and the c 1400 1070 ma collier group the principal syndepositional structural elements are parallel to the trend of major structures in the underlying ashburton fold belt and gascoyne complex these structures include the talga fault the faulted southwestern limb of the wanna syncline the lyons river fault and the northwest trending fault system that bounds the mangaroon and ti tree synclines the bangemall supergroup can be divided into six depositional packages defined by basal unconformities or major marine flooding surfaces packages 1 4 make up the edmund basin and consist of carbonate and siliciclastic shelf to basinal facies that are strongly controlled by synsedimentary movement along northwest trending basement faults source areas for the siliciclastic rocks were to the northwest northeast and southeast during deposition of packages 5 and 6 which form the collier basin the influence of the basement faults was less marked and the basin was filled with deltaic to deep marine siliciclastic facies that were derived from the northwest and southeast the bangemall supergroup has been frequently compared with proterozoic successions in northern australia but these successions are either too old or imprecisely dated to make meaningful correlations in addition the west and north australian cratons may not have been joined until the assembly of rodinia in the late mesoproterozoic

sedimentary corg p ratios paleocean ventilation and phanerozoic atmospheric po2 the corg p ratios of organic rich facies tocn1 exhibit considerable variation through the phanerozoic from b10 1 in the permian phosphoria formation to n1000 1 in some devonian black shales relative to the composition of phytoplankton c p 106 1 which provide the bulk of organic c and p to organic rich marine sediments the range of phanerozoic sedimentary corg p ratios largely reflects the influence of benthic redox conditions on diagenetic pathways of c and p remobilization enhanced preservationoforganiccatlowerredoxpotentials combinedwithenhancedsedimentaryretentionofremineralizedorganicpathigher redox potentials results in a strong relationship between benthic redox conditions and sedimentary corg p ratios the strong secular coherence of the phanerozoic corg p record i e limited variation within narrow time slices suggests that these ratios are controlled primarily by factors influencing benthic redox conditions on a global scale such as atmospheric po2 inversion and scaling of the phanerozoic corg p record yields a new atmospheric po2 model that has strong similarities to existing models based on elemental and isotopic mass balances yet differs in some potentially significant respects in particular the new model suggests that atmospheric po2 wasmarkedlylowerduringtheearlytomiddlepaleozoicthanpreviouslyinferred duringmostofthedevonian atmospherico2levels mayhavebeensufficientlylow b13 astopreventthesustainedcombustionofplantmaterial thisfeatureofthemodelmayaccount for ananomalous gapinthefossilcharcoalrecordduringthedevonian theredox dependentburialofpintheoceanresults inpositive and negative feedback mechanisms that tend to stabilize atmospheric oxygen concentrations on geologic timescales temporal variations in the burial of p relative to c suggest that the strength of these feedback mechanisms varied over the phanerozoic 2007 elsevier b v all rights reserved

coal measures namurian and westphalian blackband iron formations fossil bog iron ores blackband iron formations are essentially thin approximately 0 75 m thick siderite rich total iron up to 40 carbonaceous laminated mudrocks which commonly occur in grey coal bearing sequences in close proximity to coal seams they exhibit a conspicuous laminated macrotexture made up of carbonaceous and siderite rich laminae together with primary textures such as root disturbed laminae sideritized unflattened spores and preservation of plant cell detail these all point to formation of siderite soon after deposition in some cases before significant compaction their enclosing sediments clearly show that they were deposited in environments intermediate between delta top alluvial floodplains and coastal plain swamps in which small areas were subjected to periods of lacustrine deposition the presence of varved mudrocks and oil shales in the beds directly above many of the blackband iron formations and the distinctive fine lamination of the blackbands are evidence of such depositional environments the blackband iron formations are considered to have been formed in a similar way to recent bog iron ores and are therefore interpreted as fossil bog iron ores a model for their mode of formation is presented

depositional controls on mudstone lithofacies in a basinal setting implications for the delivery of sedimentary organic matter deep water mudstones from ancient epicontinental settings are significant repositories for organic matter but the detailed temporal variations of and controls on the abundance and type of organic matter om is little studied using micro petrographic and geochemical data from late mississippian mudstones of the widmerpool gulf uk the processes that delivered fine grained sediment to this basin during a glacioeustatic sea level cycle are interpreted from detailed lithofacies analysis seven primary lithofacies are identified from core which show specific and systematic variations in total organic carbon toc content and bulk carbon isotope composition of organic material 13corg during sea level highstands thin bedded carbonate bearing mudstones are the dominant facies deposited contain up to 6 6 toc average 4 6 1 3 and have mean 13corg of 28 5 0 9 during phases of lower sea level thin bedded silt bearing clay rich mudstones with up to 4 1 toc average 2 3 0 8 mean 13corg 28 2 1 0 were interbedded with more organic lean graded silt bearing mudstones and sand bearing silt rich mudstones average toc 1 7 0 6 derived from turbidity currents the latter mean 13corg 26 2 0 7 are closely linked to significant proportions of terrestrial plant material while some rare plant debris and sand bearing mudstones produced from debris flows have more than 7 0 toc and 13corg 26 0 the 13c values of wood fragments ranged from 27 1 to 24 0 and therefore the 13corg is interpreted as a function of the ratio of marine and terrestrial organic matter more negative values in the carbonate bearing and the clay rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material the data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea level stages marine om was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial om was delivered by sediment density flows variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine om organic rich mudstones preserved in these marine basins are potential hydrocarbon source rocks especially as unconventional shale gas reservoirs detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source rock potential of basinal mudstones and of fine grained organic rich sediments in general

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

palaeozoic oolitic ironstone of the french armorican massif a chemical and structural trap for orogenic base metal as sb au mineralisation during hercynian strike slip deformation in the saint aubin des ch teaux quarry armorican hercynian belt western france an epigenetic hydrothermal alteration affects an oolitic ironstone layer intercalated within the lower ordovician gres armoricain formation the hydrothermal overprint produced pervasive and massive sulphidation with stratoid pyritised lenticular bodies within the oolitic ironstone layer these sulphide lenses are spatially associated with strike slip faults and extend laterally from them after the massive sulphidation stage fe as stage 1 subsequent fracturing allowed the deposition of base metals stage 2 and pb sb au stage 3 parageneses in veins the dominant brittle structures are vertical extension veins conjugate shear veins and strike slip faults of various orders all these structures are filled with the same paragenetic sequence deformation analysis allows the identification of structures that developed incrementally via right lateral simple shear compatible with bulk strain affecting the central armorican domain each increment corresponds to a fracture set filled with specific parageneses successive hydrothermal pulses reflect clockwise rotation of the horizontal shortening direction geothermometry on chlorite and arsenopyrite shows an input of hot hydrothermal fluids maximum of 390 350 c during the main sulphide stage 1 the subsequent stages present a marked temperature drop 300 275 c lead isotopes suggest that the lead source is similar for all hydrothermal stages and corresponds to the underlying neo proterozoic basement lead isotope data relative ages of deformation and comparison with neighbouring deposits suggest that large scale fluid pulses occurred during the whole hercynian orogeny rather than pulses restricted to the late hercynian period the vicinity of the hercynian internal domain appears as a key control for deformation and fluid flow in the oolitic ironstones which acted as a chemical and structural trap for the hydrothermal fluids the epigenetic mineralisation of saint aubin des ch teaux appears to be very similar to epigenetic sulphidation described in banded iron formation hosted gold deposits

mineralogical and geochemical imprints to determine the provenance depositional history and tectonic settings of triassic turbidites in the semanggol and semantan basins peninsular malaysia abstract the present study provides systematic mineralogical inorganic geochemical and rock eval analyses of turbidite deposits of the semanggol and semantan formations to investigate their provenance depositional environment and tectonic setting as well as type origin and maturation of organic matter in black shale these deposits are extensively distributed in peninsular malaysia and are observed in the field as conglomerate pebbly sandstone thick bedded sandstone interbedded sandstone and shale laminated black shale and tuffaceous sandstone these sedimentary sequences are predominantly deep marine and occasional shallow marine deposits characterizing a deep marine fan system based on al2o3 tio2 ratios more felsic rocks for the semanggol formation and felsic intermediate rocks for the semantan formation are proposed as sources for their detrital fractions and this interpretation is also substantiated by the binary plot of zr vs ti v v ni v ni and ni co analyses indicate anoxic oxic conditions ternary diagram of immobile trace elements inferred passive margin for semanggol turbidites and an active continental margin for semantan turbidites the dissimilarity between geochemically and geologically derived tectonic settings mainly for the semanggol turbidites is because of changing tectonic setting and recycled nature of sediment sources that were deposited in diverse tectonic settings the black shale clay fractions from both formations dominantly contain illite and kaolininte with abundant traces of quartz the illite content varies from 43 to 56 and illite crystallinity index ic from 0 2 to 0 4 2 average 0 28 2 showing studied black shale fall in anchizone rock eval pyrolysis reveals type iii kerogens suggesting a terrestrial source of organic matter in black shale of both formations

management responses to pulses of bedload sediment in rivers abstract rivers can experience sudden pulses of sediment from human and natural erosion processes that can accumulate in the bed abundant studies have examined the sources and dynamics of sediment pulses and problems caused by these pulses particularly flooding avulsions and habitat simplification much less has been written about what managers can do about sediment pulses and that is the purpose of this review the first option for managers is to do nothing and this decision can be informed by many case studies and by theory on the propagation and character of sediment pulses their diffusion translation and celerity doing nothing should be informed by the secondary effects of sediment pulses on channels including widening avulsions and tributary interactions if managers decide that something needs to be done about the sediment they have four options 1 reducing the sediment supply at source 2 trapping sediment in the channel 3 accelerating sediment transport through a reach and 4 directly extracting sediment the most common of these actions is undoubtedly to reduce the supply at source but there are few examples of the consequences of this for sediment pulses there are even fewer examples of trapping accelerating and extracting sediment all of these options have great potential for managing sediment pulses however they also have the potential to trigger incision of tributaries and of the channel behind the passing sediment wave overall the literature equips managers to understand the dynamics of sediment pulses but it does not yet equip them to confidently manage these geomorphic events

the significance of hiatus beds in shallow water mudstones an example from the middle jurassic of switzerland abstract limestone beds formed in nearly carbonate free shallow water mudstones by discontinuous sedimentation and erosion are called hiatus beds anaerobic oxidation of organic matter by microbes provided excess alkalinity inducing carbonate precipitation a multiphase history of such beds is documented from the swiss jurassic by several cementation and dissolution phases four cement types occur micrite as earliest cement 13c 10 to 20o oo stellate calcite between micrite cemented parts 13c 5 to 10o oo fibrous calcite cement in dissolution cavities 13c 30o oo and blocky calcite in remaining pores 13c 5o oo except for the late blocky cement all cements contain pyrite indicating carbonate precipitation within the sulfate reduction zone after early cementation by micrite the beds moved relatively upwards into a shallower geochemical zone and some even to the seafloor because of erosion cavities formed during reburial by dissolution in the upper part of the sulfate reduction zone and in the upper part of the methanogenic zone strongly reduced sedimentation rates provided the requisite stable geochemical conditions for at least several thousands of years which permitted precipitation and dissolution of carbonate by biochemical processes and diffusion this happened on short lived swells caused by differential subsidence and rotation along listric faults when basement structures became reactivated during the extensional stress regime from opening of the tethys during the jurassic and cretaceous breakup of pangea the shelf area increased and differential subsidence on these newly formed shelves was the main factor responsible for the observed post paleozoic maximum in hiatus beds and hiatus concretions

origin and diagenetic evolution of ca mg fe carbonates in some coalfields of japan carbonate concretions lenses and bands in the pleistocene palaeogene and upper triassic coalfields of japan consist of various carbonate minerals with varied chemical compositions authigenic carbonates in freshwater sediments are siderite calcite ankerite dolomite ferroan magnesite in brackish water to marine sediments in the coal measures calcite dolomite ankerite siderite ferroan magnesite and in the overlying marine deposits calcite dolomite siderite most carbonates were formed progressively during burial within a range of depths between the sediment water interface and approximately 3 km the mineral species and the chemical composition of the carbonates are controlled primarily by the initial sedimentary facies of the host sediments and secondarily by the diagenetic evolution of pore water during burial based on the regular sequence and burial depth of precipitation of authigenic carbonates in a specific sedimentary facies three diagenetic stages of carbonates are proposed carbonates formed during stage i 2000 m are fe calcite and extremely high ca mg siderite the latter is exclusively in marine mudstones the supply of ca is partly from the alteration of silicates in the sediments at elevated burial temperatures after uplift calcite with low mg content precipitates from percolating groundwater and fills extensional cracks

electron microscope analysis of zoned dolomite rhombs in the jet rock formation lower toarcian of the whitby area u k zoned dolomite rhombs which occur in the organic rich jet rock formation toarcian of northeast england have been studied using backscattered scanning electron microscopy transmission electron microscopy and energy dispersive x ray microanalysis the rhombs which are 5 20 m in size are variable in chemical composition but many consist of a dolomite core surrounded by a zone of ferroan dolomite ankerite or ferroan calcite zoned rhombs occur in early diagenetic calcite cemented concretions and layers as well as dispersed throughout the shales distributional and textural evidence suggests that they formed mainly by primary precipitation from pore fluids within the zone of bacterial sulphate reduction the ferroan outer zones probably formed after burial below the sulphate reduction zone when insufficient h 2 s was available to react with all the fe 2 in solution

palaeontological and geochemical characteristics of silurian black shale formations from the central brittany domain of the armorican massif northwest france abstract within the armorican massif as well as throughout the major part of the gondwanan northern margin llandovery to ludlow deposits are mainly represented by black shales with subordinate sandy beds in brittany these euxinic silurian facies lie more or less conformably on late ordovician deposits however based on graptolite evidence a stratigraphical break corresponding to part or whole of the llandovery is noticed the silurian black shales of brittany are devoid of benthic fauna while pelagic or epipelagic elements are very common these euxinic lithofacies are characterized by peculiar geochemical compositions which are discussed in terms of their stratigraphical and geographical distribution significant enrichment of sr y rb cr and ni higher concentrations of v up to 5600 ppm and greater volatile contents are particularly apparent in contrast with other terrigenous deposits from brittany a model for the sedimentary environment of the silurian black shales of the armorican massif is proposed the transgression induces the individualisation of basins partially separated from the open ocean in which the water column is stratified then the stratification disappears progressively during ludlow times

the relationship between bitumens and mineralization in the south pennine orefield central england like many examples of mississippi valley type mineralization the south pennine orefield is well known for the occurrence of hydrocarbons within hydrothermal mineral veins bitumens from this area along with oils from the east midlands have been characterized using standard organic geochemical techniques and compared with potential source rocks lower namurian mudstones from the widmerpool gulf and the gainsborough and goyt troughs were rejected as possible sources for the bitumens and oils on the grounds of lack of sufficient thermal maturity and or essential biomarker correlation lower namurian mudstones with type ii kerogen from the edale gulf are proposed to offer a likely hydrocarbon source for the area with a minor more localized contribution from organic rich type ii mudstone partings within the dinantian limestones simple geochemical models consistent with recent sequence stratigraphic interpretation suggest a late carboniferous age for hydrocarbon generation where geothermal gradients were slightly higher c 50 c km 1 than the present day microthermometric analysis of fluid inclusions from fluorite and calcite allowed three fluid types to be distinguished one na ca cl bearing fluid was discerned to be dominant throughout the orefield being of low temperature uncorrected t h 70 110 c and high salinity c 20equiv wt nacl a second high salinity na ca cl fluid uncorrected t h 70 120 c c 24equiv wt nacl distinguished from the first by varying na ca contents was observed in the westernmost extremities of the orefield a third nacl bearing fluid of higher temperature t h 100 145 c and lower salinity 4 wt nacl was detected in the northernmost part of the orefield hydrocarbon bearing inclusions were not observed in any of the three fluids in this study sulphur isotopic analyses performed on a selection of sulphides sulphates and bitumens to gauge the role of organic matter in sulphate reduction reactions proved inconclusive the mineralization is thought to have occurred as several events that in the north is thought to be derived from the dewatering of the edale gulf towards the end of the carboniferous whilst other mineralization events occurred from the early permian onwards with the ore fluids having more distal sources predominantly from the east with a minor input from the west the main phases of hydrocarbon generation and mineralization appear to be unrelated

a mississippian black shale record of redox oscillation in the craven basin uk early diagenetic redox oscillation processes have been rarely recognised in the ancient rock record but potentially exert an important control on mineral authigenesis hydrocarbon prospectivity and supply of metals and or reduced s as part of associated mineral systems the upper unit of the mississippian bowland shale formation is a candidate record of diagenetic redox oscillation processes because it was deposited under a relatively high sediment accumulation rate linked to a large delta system and under dominantly anoxic and intermittently sulphidic bottom water conditions in order to characterise the syngenetic and early diagenetic processes sedimentological and geochemical data were integrated through the upper bowland shale at three sites in the craven basin lancashire uk organic matter om comprises a mixture of type ii ii s ii iii and iii om redox zones are defined by patterns of fe speciation and redox sensitive trace element enrichment and split into two groups sulphidic zones eux an iii an i and an it represent sediments deposited under conditions of at least intermittently active sulphate reduction in bottom waters non sulphidic zones ox rx ox f and ox represent sediments deposited under non sulphidic oxic to ferruginous anoxic bottom waters operation of a shelf to basin reactive fe fehr shuttle moderated by sea level fluctuation and delta proximity controlled the position and stability of redoxclines between zones of fe and sulphate reduction and methanogenesis early diagenetic redoxclines were capable of migration through the shallow sediment column relatively quickly in response to sea level fluctuation preservation of syngenetic and early diagenetic geochemical signals shows redoxclines between fe and sulphate reduction and the upper boundary of sulphate methane transition zone were positioned within decimetres i e 10 s cm of seabed falling sea level and increasing fehr supply is recognised as a switch from zones eux high sea level an iii and ultimately an i and an it low sea level zone an i defines the operation of redox oscillation between zones of fe and sulphate reduction in shallow porewaters associated with enhanced degradation of om and complete dissolution of primary carbonate preservation of om and carbonate in this system was a function of changing bottom and pore water redox processes redox oscillation operated in a siliciclastic prodeltaic environment associated with a relatively high sediment accumulation rate and high loadings of labile organic matter and metal oxides these findings are important for understanding late palaeozoic black shales in the context of hydrocarbon and mineral systems

migration of rectangular mining pit composed of uniform sediments sand and gravel mining from riverbeds is a major supply of construction materials a mining pit in a riverbed is very unstable and subject to scouring and deposition which results in migration of the pit a series of experiments was conducted to investigate the migration behavior of several rectangular pits of different sizes composed of uniform bed material it was found that the maximum scour depth decreases as sediment transport capacity increases and that the effective length varies inversely with sediment transport capacity the migration of the pit can be separated into two periods a convection period and a diffusion period the migration speed in each period is constant and increases as sediment transport capacity and effective length increase and vary inversely with the depth of the pit regression equations for the maximum scour depth effective length shape and migration speed of the pits were obtained these equations were then used to predict the size shape and speed of a migrating rectangular pit

geochemistry and mineralogy of marine and non marine namurian black shales from the tansley borehole derbyshire the namurian black shales studied have a good palaeontological control pyrite illite and organic matter are higher in the marine shales and siderite and kaolinite are higher in the non marine shales the distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity the same control could account for the observed clay mineral distribution by differential flocculation the major element geochemistry closely reflects the above mineral variation mn and zr are higher in the non marine shales due to siderite and zircon respectively co cr rb y and ba are not significantly different and a detrital source mainly clay minerals is suggested in the marine shales the elements pb cu v ni sr and zn are significantly higher using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated the present element locations are thought from correlation analysis to be pyrite and organic matter by analogy with experimental work and modern environments the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors the element enrichment cannot be related directly to seawater concentrations unlike some black shales and the accumulation rates for pb and cu are thought to be unusually high

late miocene pliocene coastal acid sulphate system in southeastern australia and implications for genetic mechanisms of iron oxide induration abstract ferricrete sediment cemented by iron oxides and hydroxides is common in subaerial weathering environments around the world formed under alternating oxidising and reducing conditions ferricretes record pedogenetic processes of translocation and concentration of iron and trace elements in the soil given their stability and high preservation potential ferricretes can provide insights to ancient soil forming and weathering processes in this study the key processes controlling ferricrete geochemistry in a neogene strandplain are identified and interpreted in the context of a coastal acid sulphate weathering system textural and geochemical variations in sediment indurated by hematite and goethite represent a record of in situ induration erosion and reworking this development took place within an environment of fluctuating ph and eh and subaerial wetting and drying cycles we distinguished depositional and post depositional processes based on the results of whole rock geochemistry hyperspectral mineralogy and major and trace element maps of petrographic thin sections the ferricretes have three morphological types flat lying indurations concentric pisoliths and rounded nodules with fragmented internal textures successive laminae of fe oxides and hydroxides in all morphological types of ferricrete have variable fe al and si abundances reflecting cyclic precipitation and groundwater chemistry changes episodic wetting and drying of near coastal sediments was superimposed on a long term trend of marine regression and local tectonic uplift from 7 ma to present this resulted in the diachronous exposure of relatively reduced shoreline sediments and concomitant acid production due to ferrolysis and the oxidation of biogenic sulphide local landform variations contributed to a wide variety of pedogenic processes and subsequent ferricrete formation acid sulphate weathering recorded by these indurated sediments is similar to conditions that are observed at present in the shallow water estuary of the lower lakes near the mouth of the murray river

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

irradiation of organic matter by uranium decay in the alum shale sweden the alum shale of sweden contains black shales with anomalously high uranium concentrations in excess of 100 ppm syngenetic or early diagenetic origin of this uranium indicates that organic matter within these shales has been irradiated by decaying uranium for approximately 500 ma radiation induced polymerization of alkanes through a free radical cross linking mechanism appears to be responsible for major alterations within the irradiated organic matter specific radiation induced alterations include generation of condensate like oils at reduced yields from hydrous pyrolysis experiments decrease in atomic h c ratios of kerogens decrease in bitumen organic carbon ratios and a relative increase in low molecular weight triaromatic steroid hydrocarbons conversely stable carbon isotopes of kerogens reflectance of vitrinite like macerais oil generation kinetics and isomerization of 20r to 20s c29 steranes were not affected by radiation the radiation dosage needed to cause the alterations observed in the alum shale has been estimated to be in excess of 105 mrads with respect to organic carbon this value is used to estimate the potential for radiation damage to thermally immature organic matter in black shales through the geological rock record high potential for radiation damage is not likely in cenozoic and mesozoic black shales but becomes more likely in lower paleozoic and precambrian black shales

high selenium in the carboniferous coal measures of northumberland north east england the carboniferous lower and middle coal measures coals of the northumberland coalfield are anomalously rich in selenium se content up to 62 ppm compared to the averages for the common uk and worldwide coals as well as posing an environmental toxicity threat se is now regarded as an important resource for alloys photovoltaic products and nanotechnologies and high se coals in north east england offer an opportunity to assess the se means of occurrence origins transport mechanisms and enrichment in coals at least two generations of pyrite host high se in the sampled coal seams microbial formed disseminated pyrite both cubic and framboidal in habit and later cleat filling pyrite identified by petrographic observations laser ablation methods and sulphur isotope compositions there is a notable se enrichment of up to 250 ppm in later formed cleat filling pyrite trace element enrichment may have been sourced and influenced by seawater distribution during diagenesis and localised dykes and deformation may have acted as an enrichment mechanism for sampled seams in the region the high se coals in northumberland may provide a potential e tech element source and should be considered and carefully managed as coal mining and production are reduced in the area the study also highlights the nature of se enrichment in pyritic coals affected by cleat formation and multiple episodes of mineralisation important as critical element demand continues to increase worldwide

hydrodynamics of mining pits in erodible bed under steady flow theoretical solutions are proposed for the hydrodynamical characteristics of mining pits in erodible beds these solutions are derived from the linear st venant equations of momentum and continuity for appropriate initial and boundary conditions pits of trapezoidal and rectangular shapes and discussed although it is indicated that pits of any regular geometric shape can be considered for solution solutions are also given for two trapezoidal and rectangular pits in the same bed theoretically solutions can be developed for any number of pits of any regular geometric shape in the same bed numerical results are plotted for one and two trapezoidal pits respectively in an erodible bed

the grootegeluk formation in the waterberg coalfield south africa facies palaeoenvironment and thermal history evidence from organic and clastic matter the grootegeluk formation of the waterberg coalfield is about 70 m thick and consists of relatively thin coal beds interbedded with numerous mudstone and carbonaceous mudstone layers maceral analyses of the coal seams and the interbedded carbonaceous mudstones show that vitrinite is the dominant maceral up to 90 vol whereas inertinite liptinite and reactive semifusinite generally occur in minor proportions the vitrinite content increases upward in the formation with a concomitant decrease in inertinite including reactive semifusinite from around 60 inertinite at the base of the formation the upward increase in the vitrinite concentration is associated with an increase in the energy of the depositional environment which is also considered to have been instrumental in the enhanced preservation of the vitrinite the repetitive nature of the coal mudstone succession the lateral persistence of cycles and the maceral and ash proportions indicate that the formation may have resulted from a combination of allogenic controls tectonism and climate and authigenic controls environments of deposition the vitrinite reflectance rmax of the grootegeluk formation mean 0 72 and palynological evidence indicate that the grootegeluk formation was subjected to maximum post depositional temperatures of about 100 c the lower portion of the grootegeluk formation is dominated by kaolinite quartz and minor amounts of apatite and the upper parts by quartz kaolinite and minor amounts of montmorillonite illite and microcline the base of the grootegeluk formation is considered to have been relatively more distal and the upper portions more proximal to the source of the sediments at the base of the grootegeluk formation a 2 m thick tonstein zone occurs which is dominated by well crystallised kaolinite organic matter 40 wt siderite calcite and minor proportions of apatite the tonstein zone has mineralogical maceral and chemical characteristics distinctive from the other mudstones calcite lenses which occur predominantly in the upper half of the grootegeluk formation are interpreted as syndepositional early diagenetic globular pyrite and spherulitic siderite occur in the coals and organic rich mudstones of the grootegeluk formation fine grained granular siderite is present predominantly in the organic poor mudstones of the grootegeluk formation and the overlying beaufort group systematic changes in the mineralogy and major element chemistry make major element whole rock chemistry an ideal stratigraphic indicator tool for the grootegeluk formation the tonstein has anomalously high concentrations of the trace elements sc v cr mn ni cu ge se br rb sr y zr nb mo ba la ce nd pb th and u and low concentrations of s co as and zn which in addition to its mineralogical character and correlation throughout the basin make the tonstein an important chronostratigraphic marker for local and intrabasinal correlation the overlying beaufort group mudstones contain no organic matter however interpretation of the mineralogical and chemical data indicates that they were deposited with organic matter which was later degraded the mineralogy of the mudstones and the concentration of trace elements suggest that the sediments were deposited in fresh rather than in marine waters

fractionation of zn isotopes in terrestrial ferromanganese crusts and implications for tracing isotopically heterogeneous metal sources abstract zinc liberated from geological sources during surface weathering is the main source of zn to the surface environment and is ultimately sequestered by sinks such as mn oxides and oxyhydroxides this behaviour has been applied to geochemical mineral exploration studies and terrestrial ferromanganese crusts have been shown to have anomalously high zn mn ratios around known zn pb ore deposits this poses the question if zn isotopic compositions of these fe mn crusts can also discriminate the underlying anomalous metal sources from the surrounding non mineralized lithologies isotopic fractionation during fractionation onto mn oxides in well studied marine fe mn crusts has shown that isotopically heavy zn is preferentially adsorbed in that environment which has a comparatively isotopically homogeneous zn reservoir however isotopic fractionation behaviour in terrestrial fe mn crusts that may have more heterogeneous zn sources is unknown here we present the first zn and pb isotope study of terrestrial fe mn crusts to test if zn isotopic compositions can be used to delineate isotopically different lithological metal sources our data from fe mn crusts that formed overlying isotopically variable lithologies hydrothermal polymetallic zn pb deposits and non mineralized archean rocks show that while adsorption of zn onto mn oxyhydroxides in terrestrial fe mn crusts generally favours isotopically heavy zn the magnitudes of isotopic fractionation varies in fe mn crusts overlying mineralized and non mineralized areas fractionation factors 66 64zncrust source up to 0 54 in crusts overlying non mineralized lithological sources with a 66zn value of 0 30 are comparable with the predicted equilibrium fractionation onto birnessite conversely magnitudes of 66 64zncrust source up to 0 37 in crusts overlying isotopically light zn pb mineralization that has a mean 66zn value of 0 15 are much lighter than non mineralized counterparts with similar zn mn ratios this difference may be explained by changes in hydrogeochemical complexation of zn with localized chloro complexes that carry isotopically light zn from the isotopically light mineralization these findings demonstrate that different lithological zn sources that are isotopically variable give rise to isotopic heterogeneity in the surface zn reservoir this can be reflected by differing fractionation patterns following adsorption onto mn oxyhydroxides in terrestrial fe mn crusts that overly different zn sources furthermore pb isotope compositions of the fe mn crusts also closely reflect that of the underlying geology this highlights that the use of zn isotopes may be a valuable means of vectoring towards anomalous metal sources such as ore deposits

the use of burial diagenetic calcite cements to determine the controls upon hydrocarbon emplacement and mineralization on a carbonate platform derbyshire england

microfabric mineralogy and early diagenetic history of the whitby mudstone formation toarcian cleveland basin u k the whitby mudstone formation in northeast england contains three shale facies normal restricted and bituminous which have previously been differentiated on the basis of sedimentary structures and faunal assemblages this paper shows that the three facies can also be differentiated by mineralogical geochemical and microtextural criteria determined using bsem edxra xrd and xrf the bituminous shale facies consists of finely laminated shales containing an early diagenetic mineral assemblage dominated by pyrite calcite and dolomite the weakly laminated restricted facies shales contain an early diagenetic assemblage dominated by pyrite the normal facies shales are very weakly laminated and contain siderite in addition to pyrite the geochemical conditions which left a dominant early diagenetic imprint on the three facies are interpreted to be carbon rich sulphidic carbon poor sulphidic and very carbon poor sulphidic respectively

regional scale metasomatism in the fortescue group volcanics hamersley basin western australia implications for hydrothermal ore systems mafic to intermediate volcanic rocks of the fortescue group form the lowermost stratigraphic unit of the 100 000 km2 hamersley basin on the southern margin of the archaean pilbara craton western australia these represent one of the oldest 2 8 2 7 ga known examples of a continental flood basalt sequence a regional burial metamorphic gradient extends across the basin from prehnite pumpellyite facies in the north to epidote actinolite greenschist facies in the south and west superimposed on this metamorphic gradient regional scale metasomatism has affected extensive areas of the fortescue group metasomatized mafic lavas are characterized by well developed assemblages dominated by pumpellyite quartz or epidote quartz associations the mineral associations of metasomatic domain types broadly match the distribution of metamorphic isograd indicator minerals with a southward and westward increase in the proportion of epidote a continuum exists between least altered rocks that preserve the regional metamorphic signature and the most intensely altered metasomatized rocks metasomatism is essentially continuous over a stratigraphic strike length of 100 km and across a strike width of 20 km regionally metasomatically altered volcanic rocks occur widely across the hamersley basin and its outliers over an area of some 450 km by 200 km metasomatic alteration is most conspicuous in the lower grade metamorphic zones because pumpellyite and epidote rich rocks are green to yellow green in outcrop whole rock geochemical data indicate that metasomatism is associated with strong depletions in alkalis na k li rb alkali earths mg sr be ba and heavy first transition series metals mn fe co ni cu zn with a significant enrichment in si calcium shows more variable mobility such geochemical trends particularly depletions in fe mn and base metals co ni cu zn together with the metasomatic mineral assemblages are comparable with those associated with the sub sea floor circulation of seawater particularly in relation to the metal depleted root zones of base metal deposits petrographic features indicate that the development of metasomatic mineral associations post dates the formation of regional metamorphic assemblages consequently it is interpreted that the hydrothermal fluid flowed through the buried pile after sufficient time to allow for the metamorphic mineral assemblages to approach equilibrium with ambient p t conditions the hydrothermal depletion in fe observed across the fortescue group mafic lavas is intriguing given the abundance of iron ore in the overlying hamersley group and a possible connection cannot be ignored furthermore the scale of fluid flow observed in the fortescue group which occurred through zones of inherent permeability such as vesicular and brecciated lava flow tops without the aid of major cross cutting structures has significant implications for the size of metasomatic systems in other mafic volcanic terranes with potential consequences for the exploration for hydrothermal mineral deposits

composition and structure of nanocrystalline fe and mn oxide cave deposits implications for trace element mobility in karst systems abstract fe and mn oxides are ubiquitous highly reactive minerals in the environment which often control the distribution and speciation of trace elements in soils and aquatic systems pautler cave in southwest illinois contains fe and mn oxide deposits with properties that differ spatially and temporally two depositional environments exist in the cave fe and mn precipitation where anoxic groundwater enters the oxic cave passage seep deposition and direct deposition from the cave stream seep waters have higher concentrations of ca2 fe2 and mn2 lower ph and lower o2 aq concentrations relative to stream waters in addition seep waters have nearly constant 18o values that are similar to the yearly average of local precipitation whereas cave stream waters have more erratic 18o values and appear to be influenced by seasonal variations of 18o in rainfall these differences suggest that the seep water source has a longer residence time in the subsurface than the cave stream water fe oxides are solely found as seep deposits whereas mn oxides are deposited both by groundwater seepage and cave streams freshly precipitated fe oxides are composed of ferrihydrite and filamentous material consistent with biomineralization structures of the microbial genera gallionella and leptothrix mn oxide minerals consist of 7 and 10 a phyllomanganates having a range of three dimensional order mn oxide samples show a greater heavy metal and trace element content compared to fe oxides and mn oxides deposited by cave streams have higher concentrations of metals than mn oxide seep deposits in addition phyllomanganate particle morphologies and crystallinity display a compositional dependence with platelet size and phyllomanganate sheet stacking order decreasing with increasing ba and trace element content and decreasing ca content these properties also appear to correlate with dissolved mn ii in the source water these observations suggest that fe and mn oxide minerals in oxic cave systems affect trace element concentrations in carbonate fed springs and illustrate a previously unrecognized limitation on the transport of inorganic nutrients and contaminants in karst aquifers

siderite concretions indicators of early diagenesis in the gammon shale cretaceous the upper cretaceous gammon shale in the northern great plains contains abundant siderite concretions that formed during the early compactional history of the fine grained marine sediments the relative depth of siderite precipitation can be estimated on the basis of textural mineralogical and isotopic evidence siderite concretions that formed at shallow depths in the sediment column contain a large volume percent carbonate 75 85 preserve uncompacted sediment textures and have oxygen isotope ratios similar to those of carbonates precipitated in equilibrium with seawater delta 18 o nearly equal e 0 to 2 per thousand pdb in contrast lower volume percent carbonate values 55 75 and relative decreases in 18 o 16 o values characterize concretions that formed longer after deposition and or at greater depths in the accumulating sediments both volume percent carbonate and delta 18 o values are strongly correlated with independently determined sediment accumulation rates concretions in rapidly deposited sediments formed at shallow depths 200 m later in the burial history the gammon served as both source rock and reservoir for accumulations of biogenic methane and like the siderite concretions the methane was generated during early diagenesis both siderite precipitation and methane accumulation require interstitial pore waters that have sufficiently high bicarbonate activities and that are depleted in dissolved sulfur and free oxygen because of chemical requirements siderite did not precipitate until after the onset of methane generation therefore if the depth of siderite formation is known the minimum depth for the onset of methane accumulation can be inferred the presence of abundant pyrite in slowly accumulated gammon sediments suggests by analogy to data from recent sediments that the depth of siderite precipitation and methane accumulation was controlled by the sedimentation rate in slowly accumulating sediments most organic matter was probably consumed by aerobic organisms and sulfate reducing anaerobic bacteria whereas in areas of more rapid deposition large quantities of organic matter were available for methane generation