genesis of autochthonous and allochthonous apulian karst bauxites southern italy climate constraints abstract the apulian carbonate platform acp in southern italy has experienced several episodes of subaerial exposure which were in some cases associated with the formation of karst bauxite deposits the acp contains both autochthonous canyon like bauxite and allochthonous salento type bauxite with the latter having been derived from a weathered and eroded pristine bauxite deposit the remnants of this pristine bauxite are preserved as transported pebbles embedded in a clayey matrix the autochthonous bauxite and the pebbles of the allochthonous bauxite have the same texture of sub spheroidal components ooids dispersed in a fine grained matrix the fractal dimension of ooids from both deposits is very similar and corresponds to the growth of aggregates under a diffusion controlled process the ooids of the autochthonous bauxite have a different composition to those in the pebbles of the allochthonous bauxite because they formed under different climatic conditions during the turonian autochthonous bauxite ooids formed in alternating wet tropical conditions promoting al hematite formation and drier conditions favouring boehmite stability in the allochthonous pebbles ooids formed mainly in a dry climate promoting the formation of large boehmite cores the ooids matrix ratio and the geometrical features of the ooids reflect these climate differences the differences in composition and age post turonian of the salento type bauxite bedrock suggest that the pristine bauxite that produced the salento type pebbles was different in composition to and younger in age than the canyon like bauxite the latter probably formed during a middle campanian emersion event evidenced by large karstic cavities which is correlated with the subaerial exposure of karst recorded on the adriatic island of brac

geological geochemical and mineralogical characteristics of the mandan and deh now bauxite deposits zagros fold belt iran the mandan and deh now bauxite deposits are located 40 km northeast of the dehdasht city in the zagros simply fold belt these deposits occur in eroded major nw se trending anticlines and occupy karst cavities near or at the boundary between the sarvak and ilam formations local uplifts at the end of the cenomanian and the mid turonian caused erosion and karstification of the sarvak formation these unconformities in the upper cretaceous favoured the formation and enrichment of bauxite deposits in the zagros fold belt the bauxite sequence in the mandan deposit consists of white gray black pisolitic red and yellow bauxites this sequence was repeated in the deh now area but without gray and black bauxites the present mineralogical studies of the sarvak formation and the mandan and deh now bauxite deposits indicate oxidizing to reducing conditions during the upper cretaceous in the zagros fold belt which had a significant effect on the compositions of the bauxites at least two phases of bauxitization can be distinguished in the study area i an oxidizing phase represented by boehmite diaspore hematite and kaolinite and ii a reducing phase represented by pyrite and chlorite geochemical data show that trace elements like zr hf nb ta th and u were enriched during bauxitization the bauxite deposits and carbonate rocks show similar ree patterns namely they are enriched in rees although the lrees are more enriched than the hrees mass change calculations demonstrate that mg mn ca k and p2o5 were leached out of the weathered system whereas al fe and si become concentrated in the residual system this study indicates that the mandan and deh now deposits are karst type bauxites formed by karstification and weathering of the sarvak formation

mineralogical characteristics of the karstic bauxite deposits in the xiuwen ore belt central guizhou province southwest china abstract the karstic bauxite deposits in the xiuwen ore belt of central guizhou province are hosted by the lower carboniferous jiujialu formation and show parallel unconformity with the overlying and underlying strata the ore bearing rock series that exhibits a typical coal bauxite iron structure is divided into three segments from the bottom upward namely an iron layer a bauxite layer and a coal layer based on the textural features and iron abundances the bauxite ores occurring in the middle segments are divided into three types of ores clastic compact and high iron the bauxite ores primarily comprise diaspore boehmite kaolinite illite and hematite with minor zircon pyrite rutile and feldspar the existence of rutile within diaspore lumps which were inherited from laterization suggests that diaspore was transformed from gibbsite and that karstic bauxite was transformed from laterite bauxite the results of x ray diffraction xrd scanning electron microscopy sem and electron probe x ray microanalyses epma suggest that diaspore and boehmite differ with regard to appearance and element abundance diaspore 2 10 m displays short prismatic or platy shapes and contains low sio2 abundances ranges from 0 2 to 0 51 wt whereas boehmite 0 2 5 m exhibits granular or irregular shapes and contains high contents of sio2 that vary between 2 71 and 10 4 wt the fe cu pb zn ba sulfide and sulfate mineral assemblages associated with cryptocrystalline kaolinites are discovered in the xiaoshanba deposit from the xiuwen ore belt mineralogical and geochemical studies reveal that the genesis of these assemblages is controlled by the decomposition processes of organic matter and the activities of microorganisms within the ore bearing rock series geochemical data suggest that elements rich in high organic cryptocrystalline kaolinite are produced from the adsorption effect of organic matter whereas the low concentration of these elements in pure kaolinite can be attributed to the scavenging effect during kaolinite crystallization in addition coexisting organic matter cryptocrystalline kaolinite and sulfide and sulfate minerals see sample xsb 14 indicate that the forming environment of the bauxite was hot humid tropical or subtropical climates

ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

petrography and detrital zircon study of late carboniferous sequences in the southwestern north china craton implications for the regional tectonic evolution and bauxite genesis abstract the north china craton ncc has been flanked by the north qilian and north qinling arc accretionary belts to the south and southwest since 400 ma the part of the ncc to the east of the alax terrane e ncc experienced a long sedimentary hiatus and tectonic quiescence between the middle ordovician and the late carboniferous the northern margin of the e ncc was reactivated and uplifted with contemporaneous volcanism during the late carboniferous an event that partly induced the transformation of the e ncc from an erosional platform to a continental sedimentary basin however the factors controlling this transformation are still not fully understood a series of sedimentary rocks overlying ordovician carbonates in the southwestern e ncc contains a lower iron oxide layer and an upper phyllosilicate layer detrital zircons from different parts of the profile from the base to the top of the two layers have similar u pb ages these zircons have a minimum age of ca 300 ma and a prominent peak at ca 450 ma with subordinate peaks at ca 1000 and 2500 ma the near identical minimum age for the two layers suggests they were semi simultaneously deposited in the late carboniferous after the long hiatus in sedimentation detrital zircons with ages of 450 ma have initial hf isotopic compositions that vary from large negative to elevated positive these data together with the trace element compositions of these zircons indicate that these minerals formed in a continental arc environment samples from the upper sedimentary layer contain mica group minerals that are weakly buckled and fractured and have weathered to form clay minerals including chlorite and illite this suggests that the protolith of this sedimentary layer was dominated by mica schist or mica bearing granitoid that most likely located near the adjoined part between the north qilian and north qinling arc accretionary belts detrital zircons with the youngest ages ca 300 ma were considered to derive from the northern marginal region of the e ncc an area characterized by contemporaneous volcanism the co existence of the 450 and 300 ma groups of detrital zircons also suggests that the northern and southern marginal regions of the e ncc underwent almost simultaneous late carboniferous tectonic uplift and denudation a tectonic change that led to the formation of the sedimentary basins within the e ncc late carboniferous phyllosilicate layers within the profile are likely to be the equivalent of economically important diaspore and clay dominated bauxites within the e ncc suggesting that the diaspore in these bauxites was derived from mica group minerals by resolution precipitation processes

geology and petrography of the masatdagi diasporic bauxites alanya antalya turkey abstract there are more than fifteen bauxite outcrops in the study area located in the southern part of the central taurides the bauxites are developed in the upper permian cebireis formation carbonate rocks interbedded with schist and lower triassic asmaca formation limestone dolomite quartzite and schist the bauxite outcrops are observed as parts of two or three independent bauxite blocks that were broken apart by faulting and an erosional surface based on outcrop appearances four ore types can be defined black earthy clayey and fe and mn bearing bauxites oolitic textures are common in all ore types except the earthy ones bauxites are represented by a mixture of diaspore and clay in varying proportions diaspore boehmite gibbsite corundum hematite goethite amorphous iron hydroxide magnetite chamosite pyrite marcasite psilomelane rutile kaolinite illite muscovite hydro muscovite chlorite chloritoid rectorite ephesite albite microcline quartz k mg al silicate hydrated k al silicate and dolomite are present in the ore paragenesis bauxites which are observed at or near the contact between the cebireis and asmaca formations are thought to be fillings of cavities within and or on late triassic early cretaceous carbonate rocks

genesis of the dogankuzu and mortas bauxite deposits taurides turkey separation of al fe and mn and implications for passive margin metallogeny the taurides region of turkey is host to a number of important bauxite al rich laterite and mn deposits the most important bauxite deposits dog ankuzu and mortas are karst related unconformity type deposits in upper cretaceous limestone the bottom contact of the bauxite ore is undulatory and bauxite fills depressions and sinkholes in the footwall limestone whereas its top surface is concordant with the hanging wall limestone the thickness of the bauxite varies from 1 to 40 m and consists of bohmite hematite pyrite marcasite anatase diaspore gypsum kaolinite and smectite the strata bound sulfide and sulfate bearing low grade lower part of the bauxite ore bed contains pyrite pseudomorphs after hematite and is deep red in outcrop owing to supergene oxidation the lower part of the bauxite body contains local intercalations of calcareous conglomerate that formed in fault controlled depressions and sinkholes bauxite ore is overlain by fine grained fe sulfidebearing and calcareous claystone and argillaceous limestone which are in turn overlain by massive compact limestone of santonian age that 50 m thick limestone is in turn overlain by well bedded bioclastic limestone of campanian or maastrichtian age rich with rudist fossils fracture fillings in the bauxite orebody are up to 1 m thick and consist of bluish gray green pyrite and marcasite 20 with bohmite diaspore and anatase these sulfide veins crosscut and offset the strata bound sulfide zones sulfur for the sulfides was derived from the bacterial reduction of seawater sulfate and fe was derived from alteration of oxides in the bauxite iron sulfides do not occur within either the immediately underlying or overlying limestone the platform limestone and shale that host the bauxite deposits formed at a passive margin of the tethys ocean extensive vegetation developed on land as the result of a humid climate thereby creating thick and acidic soils and enhancing the transport of large amounts of organic matter to the ocean alteration of the organic matter provided co2 that contributed to formation of a relatively 12 c rich marine footwall limestone relative sea level fall resulted from strike slip faulting associated with closure of the ocean and local uplift of the passive margin that uplift resulted in karstification and bauxite formation in topographic lows as repre

importance of hydrogeological conditions during formation of the karstic bauxite deposits central guizhou province southwest china a case study at lindai deposit abstract karstic bauxite deposits are widespread in central guizhou province sw china and high grade ores are frequently sandwiched with overlying coal and underlying iron rich layers and form a special coal bauxite iron structure the lindai deposit which is one of the most representative karstic bauxite deposits in central guizhou province was selected as a case study based on textural features and iron abundances bauxite ores in the lindai deposit are divided into three types of ores i e clastic compact and high iron the bauxite ores primarily comprise diaspore boehmite kaolinite illite and hematite with minor quartz smectite pyrite zircon rutile anatase and feldspar the al 2 o 3 53 76 8 wt is the main chemical contents of the bauxite ore samples in the lindai district followed by sio 2 fe 2 o 3 tio 2 cao mgo s and p etc our geological data on the lindai deposit indicated that the ore bearing rock series and its underlying stratum have similar rare earth elements distribution pattern and similar y ho zr hf and eu eu values additionally all ore bearing rock samples are rich in mgo range from 0 16 wt to 0 68 wt and the plots of the dolomites and laterites lie almost on or close to the weathering line fit by the al bearing rocks in zr vs hf and nb vs ta diagrams suggesting that the underlying middle cambrian shilengshui formation dolomite is the parent rock of bauxite resources in the lindai district simulated weathering experiments on the modern laterite from the shilengshui formation dolomite in the lindai bauxite deposit show that hydrogeological conditions are important for karstic bauxite formation si is most likely to migrate its migration rate is several magnitudes higher than those of al and fe under natural conditions the reducing inorganic acid condition is the most conducive to al enrichment and si removal fe does not migrate easily in groundwater al enrichment and fe removal can occur only in acidic and reducing conditions with the presence of organic matter the geological and experimental studies show that coal bauxite iron structure in lindai deposit is formed under certain hydrogeological conditions i e since lateritic bauxite or al rich laterite deposited upon the semi closed karst depressions si can be continuously removed out under neutral acidic groundwater conditions the coal carbonaceous rock overlying the bauxitic materials were easily oxidized to produce acidic h 2 s h 2 so 4 etc and reductant groundwater with organic materials that percolated downward resulting in enrichment of al in underlying bauxite it also reduced fe 3 to its easily migrating form fe 2 moving downward to near the basal carbonate culminated in precipitating of ferruginous fes 2 feco 3 etc strata of the coal bauxite iron structure thus the bauxitic materials experienced al enrichment and si and fe removal under above certain hydrogeological conditions forming the high quality bauxite

constraints on pennsylvanian glacioeustatic sea level changes using oxygen isotopes of conodont apatite conodonts from u s midcontinent cyclothems were studied for oxygen isotopes in order to constrain pennsylvanian glacioeustatic sea level fluctuations pennsylvanian deposits of the midcontinent united states are composed of cyclic alternations of thin transgressive limestones offshore gray to black phosphatic shales and thick regressive limestones a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds glacioeustatic sea level fluctuations are considered the primary cause for the formation of these cyclothems oxygen isotope analyses of conodont apatite from the black 20 1 0 5 vienna standard mean ocean water vsmow and gray shale units 20 5 0 5 vsmow show lowest average 18 o values whereas conodont elements from the regressive 21 0 0 3 vsmow and transgressive limestone units 21 1 0 6 vsmow are enriched in 18 o the maximum change in 18 o of conodonts from the black shale and carbonate units from individual cyclothems is 1 7 the 1 7 c difference in 18 o compares relatively well to pleistocene interglacial glacial changes in 18 o of equatorial surface dwelling foraminifers and suggests that pennsylvanian glacioeustatic sea level changes may have been of comparable amplitude however since the pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record pennsylvanian glacioeustatic sea level changes were probably larger than the 120 m fluctuations recorded for the pleistocene glaciations

bottom trawling contribution to the spatio temporal variability of sediment fluxes on the continental shelf of the bay of biscay france abstract based on experiments a trawling induced erosion dynamics was included in a 3d realistic and pre validated hydro sedimentary model so as to assess its contribution to the overall regional sediment dynamics in the specific case of the bay of biscay continental shelf the effect of trawling was investigated throughout a 5 year period in terms of horizontal vertical fluxes and changes in seabed mud content and compared to the natural variability of sediment fluxes at different spatio temporal scales trawling is shown in the model to significantly contribute to sediment re suspension and changes in the seabed at the scale of the shelf the contribution of trawling to re suspension is 80 during the high fishing season at many locations on the outer shelf and over the grande vasiere area a large and intensively trawled muddy zone located in the middle of the shelf the contribution of trawling is significantly weaker in winter and at annual scale particularly over zones with muddy sand facies between 1 and 1 but remains high and reaches 20 of the annual erosion over muddy areas e g northern part of the grande vasiere this significant trawling induced erosion dynamics results in high sediment fluxes which increase natural poleward dynamics from a few percent up to 40 and contributes to the natural offshore export of sediment on the outer shelf e g 35 of mud fluxes along the 130 m isobath it is noteworthy that trawling induced fluxes are larger in winter although the corresponding re suspension is lower than in summer this is due to stronger near bottom flows occurring at this period largely influenced by energetic wind conditions in contrast on the inner shelf trawling induced sediment fluxes are rather oriented towards the coast finally simulation results reveal a trawling signature on changes in the seabed a significant decrease between 10 and 50 in mud content is simulated over trawling hotspots especially over the internal part of the grande vasiere and on mud patches located in front of the gironde estuary conversely trawling causes or intensifies mud deposition on both sides of these preferentially trawled areas

quantitative mineralogical characterization of karst bauxite deposits in the southern apennines italy the southern italian karst bauxite deposits occur at a late cretaceous hiatus on a bahamian type carbonate platform succession cropping out in the southern apennines and are mainly located in the abruzzi mountains in apulia gargano peninsula and murge area and in campania the bauxites of southern italy are presently uneconomic but can be considered as a model analogue for economic karst bauxite ores the texture of the bauxite deposits is mainly oolitic to pisolitic but can also be arenitic conglomeratic suggesting reworking of evolved lateritic soils the minerals boehmite and hematite are more abundant in the ooids whereas kaolinite is found at high levels in the groundmass and titanium oxides are also present furthermore small amounts of rare earth elements have been detected in most of the bauxite occurrences scanning electron microscopy with energy dispersive spectrometry sem eds and geochemical analyses on several of the deposits confirmed the diagenetic texture of the bauxite and provided an estimate of the mineralogy of the different components and their chemical composition the mineralogical and petrographic characteristics of bauxite are crucial for the bayer process and can influence its economic evaluation both the particle size distribution in the ore and the presence of reactive silica phases associated with ti and fe oxides can reduce the efficiency of processing quantitative analyses combining different methods x ray diffraction xrd rietveld quantitative phase analysis qpa and qemscan have been carried out on a limited number of samples from two of the bauxite districts of the campania region the matese mountains and the caserta province qemscan analysis allowed a more rapid quantification of mineralogy including trace detrital phases and assessment of the individual textural characteristics of the bauxite lithotypes showing a detailed image of the distribution of economic and noneconomic minerals and their intergrowths this methodology can augment or replace other time consuming quantitative phase analyses for mineralogical studies of bauxites provided that the species identification protocol sip database has been carefully validated by preliminary use of xrd and sem eds both xrd qpa and qemscan analytical techniques can be complementary for bauxite ore evaluation and a very powerful tool for exploitation and mineral processing

effect of degradation on seismic response of israeli continental slope constitutive models of soil behavior under cyclic loading that incorporate masing rules are often used to perform seismic site response analyses these analyses often ignore the effect of cyclic degradation of stiffness and strength on the seismic response of horizontal soft clay strata the authors recently proposed a normalized form of the shear stress strain relationship for undrained cyclic simple shear of soft clay cyclic degradation is considered via a single fatigue parameter the mean effective stress used in normalization of stresses and strains cyclic degradation of the small strain shear modulus though is neglected the normalized model is combined with an effective stress model for simple shear loading and boundary conditions developed within the framework of bounding surface kinematic and isotropic hardening plasticity to produce a model that is suitable for site response analysis this paper demonstrates the use of this model in one dimensional propagation analysis to compare the expected response in a soft clay profile to that response that would be estimated without accounting for cyclic degradation by neglecting cyclic degradation underestimation of velocities and accelerations developed in the profile are apparent

trace element content of karst bauxites and their parent rocks in the mediterranean belt this work deals with a concise but comprehensive study of trace element distribution in the bauxite deposits of mediterranean belt although the alloctonous and mainly detritic characters of several karst bauxite deposits are well established their parent rock has remained largely enigmatic evidence is available that some chemical elements notably zr cr and ga are largely immobile during the weathering and diagenesis and study of such trace elements in karst bauxites permits to make an approach to the lithological nature of their parent rocks it is shown by reference to analyses of bauxites from mediterranean areas that all the deposits studied are aligned from a cr rich pole related to ultramafics to another pole rich in ga and zr contents and in genetical relation with acidic parent rocks the results obtained by this way have been controlled by application of trace element accumulation coefficient which permits to distinguish four principal zones of bauxite derived from the parent rock of different lithological characters fig 3

numerical modeling of bottom trawling induced sediment transport and accumulation in la fonera submarine canyon northwestern mediterranean sea bottom trawling leads to recurrent sediment resuspension events over fishing grounds recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons which subsequently impacts deep sea ecosystems present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed the present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in la fonera submarine canyon northwestern mediterranean sea thus contributing to an improved assessment of trawling impacts based on mooring data within a canyon gully we use an inverse model to retrieve the unknown time series of resuspension due to trawling over the fishing grounds this resuspension is later used as forcing for the direct problem we simulate trawling induced flows through the canyon and provide a 3d visualization of potential trawling impacts on sediment dynamics including the identification of the propagation patterns of sediments resuspended by trawling flows coming from shallower fishing grounds are funneled through canyon flank gullies towards the canyon axis with part of the resuspended sediment reaching the continental rise out of the canyon across the open continental slope trawling induced sediment flows promote sediment accumulation beyond the canyon mouth given the wide geographical distribution of bottom trawling our results have far reaching implications that go much beyond la fonera submarine canyon our study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins

the coal bauxite iron structure in the ore bearing rock series as a prospecting indicator for southeastern guizhou bauxite mines bauxite deposits in southeastern guizhou occur in the lower permian liangshan formation the rock series bearing the sedimentary bauxite exhibit a typical coal bauxite iron structure in which the lower part consists of bauxitic shale intercalated with siderite concretions the middle part consists of bauxitic rock intercalated with multilayer lenticular or earthy bauxite and the upper part consists of carbonaceous shales and sandstones intercalated with coal seams the paralic coastal and paludal depositional environments at one time had a stable tectonic setting by studying the elemental geochemistry of the ore bearing rock series it can be seen that the common presence of the coal bauxite iron structure has resulted from 1 the extensive desilication and iron depletion during the formation of the sedimentary bauxite due to the varying physical and chemical environment and 2 the sufficient supply of organic matter by the external environment such geological anomalies that resulted from the physical and chemical changes during the formation of the layered structure in the ore bearing rock series can serve as a mineralization indicator in prospecting for new deposits

the impact of shrimp trawling and associated sediment resuspension in mud dominated shallow estuaries abstract to address the relative importance of shrimp trawling on seabed resuspension and bottom characteristics in shallow estuaries a series of disturbance and monitoring experiments were conducted at a bay bottom mud site 2 5 m depth in galveston bay texas in july 1998 and may 1999 based on pre and post trawl sediment profiles of 7be pore water dissolved oxygen and sulfide concentration and bulk sediment properties it was estimated that the trawl rig including the net trawl doors and tickler chain excavate the seabed to a maximum depth of approximately 1 5 cm with most areas displaying considerably less disturbance water column profile data in the turbid plume left by the trawl in these underconsolidated muds 85 90 porosity

mass change calculations in altered rock series a technique is presented whereby precursors of altered rocks in a fractionated rock series can be identified and changes in chemical components mass and volume accurately calculated the procedure utilizes elements with high degrees of immobility in hydrothermal and associated interactive water rock systems igneous rock series and sedimentary and metamorphic rocks with primary continuity of chemical composition are amenable to this treatment in the procedure for igneous rocks best fit fractionation lines are established for an immobile igneous compatible incompatible element pair the latter element functioning as the fractionation monitor alteration paths are linear and pass through the origin intersections of the fractionation and alteration lines yield the immobile element concentrations in the precursors to the altered rocks mobile components are determined from fractionation lines and monitor values total mass changes are proportional to the displacement of altered samples from the fractionation line masses of other elements in an altered sample reconstructed values are recalculated to the concentration of the monitor element in the precursor chemical changes are the differences between the calculated precursor compositions and the reconstructed altered rock compositions errors are mainly a function of the positioning of the fractionation lines

earthquake induced deformations of soft clay slopes an existing one dimensional non linear degrading stress strain soil model for horizontal sites is extended to mildly sloping sites and a practical procedure to analyze the earthquake induced deformation of mildly sloping soft clayey sites is presented the proposed soil mode assumes a unique relationship between the degradation index and residual strain and appears to provide satisfactory results when compared to laboratory tests results an example analysis of a hypothetical mildly sloping site using the computer program dcharms is shown to illustrate the application of the procedure the proposed procedure is similar to the stress path method as applied to the earthquake deformation analysis of an embankment the procedure however assumes the decoupling of the cyclic part and the residual part of the response and incorporates omly the cyclic part of the response in the actual response calculations

geochemical and mineralogical characteristics of bauxites darling range western australia abstract the lateritic bauxites of the darling range western australia vary greatly in chemical and mineralogical properties and it shown that this is due partly to the parent materiald ranging from granatic to doleritic rocks gibbsite is the dominant form of al in the friable and duricrust zones goethite is the major fe oxide mineral and is highly al substituted 16 33 mole whereas hematite shows lower al substitution 3 11 mole halloysite and kaolinite are mostly responsible for the reactive silica content of these bauxites maghemite 0 10 and secondary microcrystalline corundum 0 3 5 occur only in duricrust and their abundances are very highly correlated indicating a common origin and they may have been formed during forest fires the abundances of several elements are highly correlated due to the association of these elements within specific minerals such as ti mn and v in residual ilmenite grains the mineralogical and chemical properties of the darling range bauxite deposits are compared with those of other large bauxite deposits in australia and overseas these properties are also related to problems in processing bauxite using the bayer process darling range deposits differ from other australian and many other of the world deposits in that they are low grade 34 5 al2o3 and high in silica 21 sio2 and fe 21 fe2o3 the provision of detailed information on the mineral and chemical constituents of these bauxites has enabled refinery operators to improve the efficiency of the bayer process

geochemistry of the apulian karst bauxites southern italy chemical fractionation and parental affinities article i nfo this study focuses on a late cretaceous karst bauxite deposit in the murge area of the apulia district southern italy the first analysis of the vertical distributions of a wide range of elements including rees and selected trace elements throughout the deposit was shown in order to identify the processes determining element frac tionation during the evolution of the bauxite the studied karst bauxite deposit exhibits an ooidal texture is mineralogically homogeneous and contains higher abundances of boehmite than of hematite kaolinite and anatase the major element composition of the bauxite is dominated by elevated concentrations of sio2 t io2 a l2o3 a nd fe2o3 and analyses of element mo bility within the bauxite indicate that all elements except for nb and ni and to a lesser extent cr are depleted relative to the immobile element ti r mode factor analysis revealed a number of key findings i some low solubility elements e g zr th ti v ga were concentrated in detrital zircon and monazite zr th in anatase ti v and possibly in boehmite and hematite ga during the later stages of bauxitisation ii fe and cr were concentrated during wet conditions whereas al and co accumulated during dry conditions iii distributions of the light rees lrees and the heavy rees hrees are controlled by the same processes suggesting that little lree hree fractionation occurred during bauxite formation and iv the behaviour of cerium is different from that of the other rees and highly variable cerium anomalies are observed across the deposit with three characteristic ce ce maxima with values ofn2 parisite was the only authigenic cerium mineral detected during this study thus we propose a three step model to explain the distribution of ce cerianite is dissolved by cerium reduction is transported by downward moving meteoric water per descensum and finally parisite is precipi tated this cycle was repeated several times in the apulian karst bauxite in response to eh decreases under alka line conditions promoted by fluctuations in the groundwater level finally we used the value of the eu anomaly todiscuss theparental affinity or protolith of thebauxite the value of the eu anomaly min eu eu 0 76 max eu eu 0 89 indicates that the bauxite was not derived from carbonates but rather that the majority of the bauxite was influenced by intermediate to mafic magmatic sources eu eu vs sm nd diagram suggests that the parental material for the bauxite was derived from a combination of a distant magmatic source and clastic material derived from a continental margin northern africa to the south

the geometry and anatomy of the los pijiguaos bauxite deposit venezuela abstract the los pijiguaos bauxite mine in the western part of the state of bolivar venezuela represents the only currently exploited bauxite deposit in the country since mining commenced in 1987 total crude bauxite production has amounted to more than 43 million tonnes mt with a present annual production close to 5 mt proven and probable reserves are around 570 mt at an economic cut off grade of about 44 wt alumina al 2 o 3 and a total silica sio 2 content of less than 20 wt the orebody has an irregular dismembered geometry as a result of strong and prolonged fluvial erosion during and after uplift of the region the isolated minable blocks are located on plateau remnants separated by deep valleys as a result only half of the entire lease area is accessible for mining los pijiguaos represents a typical laterite bauxite deposit that formed on a flat topped plateau from weathering of the underlying mid proterozoic rapakivi type parguaza granite the complete laterite profile is characterized by a vertical zonation comprising a concretionary zone the bauxite horizon and a mottled zone the saprolite horizon on granitic bed rock the economic bauxite zone attains an average thickness of 7 6 m on a mine scale best ore grades and greatest thickness of the ore horizon are at topographic highs laterally grade distribution is also not isotropic but follows distinct wnw sse trends the spatial control on the mineralization is a result of the westerly inclination of the planation surface and the formation of major nw striking fault systems in the region gibbsite is the most abundant mineral in the economic grade bauxite horizon the occurrence of minor nordstrandite is also restricted to that zone kaolinite is not present in the bauxite zone but in the lower saprolite zone kaolinite can be more than 5 wt an inverse correlation exists between gibbsite and quartz abundance ratios for the two minerals decrease from around 45 in the bauxite horizon to around 2 in the lower saprolite zone hematite is commonly more abundant than goethite in the bauxite horizon however the goethite hematite ratio is greater than 1 anatase occurs as an accessory phase mainly in the bauxite horizon mass balance considerations demonstrate that bauxitization resulted in progressive desilication hydration and al 2 o 3 and fe 2 o 3 concentration in the residual weathering blanket silica as well as alkali and alkaline earth metals were almost completely leached mass and volume losses in the order of 61 and 77 respectively attest to severe mineralogical textural and chemical changes from an economic point of view the los pijiguaos bauxite represents a high quality almost pure gibbsitic ore that allows processing to alumina by the low temperature bayer process around 140 c in terms of material consumption 2 3 tonnes of dry bauxite are used for every tonne of alumina produced the accompanying mass of red mud amounts to 550 kg per tonne alumina the relatively high abundance of hematite in the bauxite has a positive effect on the red mud settling rate and thus favors a high extraction yield of the alumina plant los pijiguaos is based on a huge reserve that will provide bauxite for more than 100 years at the current rate of mining the entire region may contain as much as 6 billion tonnes of probable bauxite resources

ce anomalies in the textural components of upper cretaceous karst bauxites from the apulian carbonate platform southern italy the chemical and mineralogical composition of upper cretaceous apulian karst bauxites southern italy and their textural components i e ooids and matrix has been studied the bulk samples are composed of boehmite hematite anatase and kaolinite the samples collected along a vertical profile show a downward enrichment for the elements rb sr ba ni and cr a similar distribution is observed in deposits bauxitized in situ at the expense of matrix like material collected in the karst zone the ooids consist mainly of hematite with minor boehmite and anatase whereas in the matrix boehmite prevails on hematite kaolinite and anatase in the void fillings in the matrix there is a ca fluorocarbonate having a ce ce of 5 8 the ooids with the exception of ce are enriched in ree and show a higher la yb ch ratio relative to the matrix the matrix exhibits a large positive ce anomaly whereas the ooids have negative ce anomaly the ce fractionation between the textural components can be explained assuming 1 ce oxidation and cerianite precipitation in the uppermost part of the deposits 2 scavenging of ree from ce depleted percolating solutions by the iron oxide inducing both ree enrichment and ce negative anomalies in ooids 3 remobilization of cerium as fluoride complex as a consequence of more acidic conditions in the uppermost part of the deposit and precipitation of ce3 as fluorocarbonate mineral toward the carbonate bedrock barrier at alkaline ph alternatively the cerium remobilization possibly as a carbonate fluoride complex could be due to an eh decrease favoured by a rise of the groundwater level

mineralogical characteristics of the superlarge quaternary bauxite deposits in jingxi and debao counties western guangxi china abstract in recent decades more than 0 5 billion tons of ores scattered in the quaternary laterite in western guangxi china have been explored the ores were derived from a bauxite horizon in permian via physical break up and re sediment process utilizing various test methods i e xrd dta tg dtg sem eds and epma the mineralogical characteristics of the quaternary bauxite ores in jingxi and debao counties were investigated xrd was used together with tg dtg to obtain relatively accurate ore mineral abundance diaspore is the major phase whereas hematite kaolinite anatase chamosite gibbsite goethite illite and rutile are minor diaspore is characterized by a small particle size low degrees of crystallinity and complex chemical composition both gibbsite and goethite have a varied particle size and goethite crystals contain high al substitution and si it is clarified that diaspore chamosite and anatase were formed in a mildly reduced and alkaline depositional environment in permian while gibbsite hematite goethite and part kaolinite were precipitated from al 3 si 4 and fe 3 enriched solutions within an quaternary oxidized environment the ions al 3 si 4 and fe 3 are mostly released from chamosite in its dissolution process the different physicochemical conditions between the permian depositional and the quaternary weathering periods resulted in a complex mineral assemblage in the quaternary bauxite

argillite debris converted to bauxite during karst weathering evidence from immobile element geochemistry at the olmedo deposit sardinia the olmedo bauxite deposit occurs in the nurra district of northwest sardinia it forms a stratiform horizon in cretaceous limestone and marl uplift in mid cretaceous had exposed recently deposited limestone to karst weathering and a layer of argillaceous debris accumulated on its surface and was partly converted to bauxite intermediate products were desiccated marl bauxitic argillite and argillaceous bauxite subsidence followed and the bauxite was preserved by the deposition of late cretaceous limestone and other sediments uplift in oligocene miocene time with ensuing erosion exposed the bauxite horizon to its present configuration concentrations of normative minerals illustrate chemical processes and the build up of al in the bauxite horizon plots of chemical data and correlation coefficients show that al ti zr nb th cr and v were immobile during the bauxitization process mass changes point to large net removal of si mg and k from the system although some of this material and slightly mobile al were reprecipitated in the underlying argillite and altered marl immobile element ratios trace the source of the bauxite to the underlying argillaceous limestone al in the bauxite was accumulated from the degradation of 25 to 50 m of the argillaceous limestone

contribution to the geochemistry of the rare earth elements in the karst bauxite deposits of yugoslavia and greece abstract distribution of the rare earth elements ree including la lu y along vertical profiles is presented for four well studied karst bauxite deposits from yugoslavia and greece for one deposit from jamaica la and y contents are given all deposits a downward enrichment of the ree culminating at the base where authigenic ree minerals have been formed this ree pattern is characteristic for karst bauxites formed in situ through the bauxitization of argillaceous material collected in karstic depressions in this way the highest enrichment of the ree in the sedimentary cycle has been achieved both light ree lree and heavy ree hree were mobile during the bauxitization process and were concentrated at the alkaline barrier of the carbonate footwall in four out of five studied deposits the ratios lre hree and la y in bauxites decrease downwards showing an enrichment of the hree relative to lree a further fractionation of the ree took place in the formation of authigenic ree minerals which exhibit a very high enrichment of lree relative to hree in spite of this these minerals and bauxites in four studied deposits have a general similarity of the ree distribution patterns which indicate a close genetic relationship

geochemical distribution and removal of as fe mn and al in a surface water system affected by acid mine drainage at a coalfield in southwestern china the chemical characteristics formation and natural attenuation of pollutants in the coal acid mine drainage amd at xingren coalfield southwest china are discussed in this paper based on the results of a geochemical investigation as well as geological and hydrogeological background information the chemical composition of the amd is controlled by the dissolution of sulfide minerals in the coal seam the initial composition of the groundwater and the water rock interaction the amd is characterized by high sulfate concentrations high levels of dissolved metals fe al mn etc and low ph values ca2 and so42 are the dominant cation and anion in the amd respectively while ca2 and hco3 are present at significant levels in background water and surface water after the drainage leaves the mine site the ph and alkalinity increase asymptotically with the distance along the flow path while concentrations of sulfate ferrous iron aluminum and manganese are typically controlled by the deposition of secondary minerals low concentrations of as and other pollutants in the surface waters of the xingren coalfield could be due to relatively low quantities being released from coal seams to adsorption and coprecipitation on secondary minerals in stream sediments and to dilution by unpolluted surface recharge although as is not the most serious water quality problem in the xingren region at present it is still a potential environmental problem

strong motion seismology strong motion seismology is concerned with earthquake ground motion in the amplitude range that poses the threat of human injury or property damage because the occurrence of strong motion cannot be predicted in advance and because the time between significant events at any one place may range from tens to thousands of years strong motion data is recorded on triggered instruments that typically must be maintained in readiness for years between periods of significant recording as a consequence the strong motion data set is sparse because of the engineering need for estimates of future ground motion the scope of the field of strong motion seismology encompasses seismic source theory and any other aspect of seismology that can provide insights helpful in making the best possible estimates given the limited data this relationship with the rest of seismology is a reciprocal one in that strong motion data gives perhaps the best information available on earthquake source processes

a distant magmatic source for cretaceous karst bauxites of southern apennines italy revealed through shrimp zircon age dating karst bauxites occur at a late cretaceous hiatus on a bahamiantype platform in southern apennines italy in contrast to the well defined stratigraphic context their origin remains controversial detrital zircon grains preserve textures and th u ratios consistent with crystallization from a melt occasionally around older cores u pb isotopic data collected using shrimp ii record several age populations the youngest 90 ma falls into the age interval of bauxite formation as defined by stratigraphic criteria the zircons must therefore be derived from a contemporary cretaceous volcanic source the older zircons may be interpreted as xenocrysts associated with the cretaceous magmas or derived from different sources because the bauxite occurs on a isolated carbonate platform the grains must come from far away sources most probably transported by wind the age palaeogeography and inferred cretaceous wind pattern are consistent with a prevailing origin from the dinaric and carpatho balkan orogenic belts with its cretaceous bimodal volcanism

orebody vertical structure and implications for ore forming processes in the xinxu bauxite deposit western guangxi china abstract the xinxu bauxite orebodies which are contained in quaternary depressions overlying strata of permian to devonian age were formed through the break up oxidation and re sedimentation of a pre existing permian bauxite horizon with progressive karsitification the underlying strata of the quaternary orebodies were eroded out downwards in sequence gradually transiting from permian to devonian thus an older underlying stratum generally infers a higher degree of weathering a total of 47 exploration wells sampled each meter were chosen from several orebodies to evaluate the vertical distribution of four major components al 2 o 3 fe 2 o 3 sio 2 and loss on ignition in the ores the vertical evenness is quantified via a box gliding multifractal model the small width of the multifractal spectrum suggests that the vertical ore quality is even overall indicating an intertwining break up and mixing up processes during evolution of the quaternary orebody although the four components show complex spatial distributions topographic elevation displays a positive relationship with the mean fe 2 o 3 content and a negative correlation with the vertical unevenness of al 2 o 3 and fe 2 o 3 in the wells this is taken to reflect the more uniform oxidizing environment in the higher depressions which facilitates a homogeneous and greater increase of fe 2 o 3 content throughout the orebody in contrast the redox conditions in lower depressions are less oxidizing and varied in space inducing great variation in degree of fe 2 o 3 increase in the ores this study also demonstrates that in the xinxu deposit the ore forming redox environment has more impact on the ore quality than the degree of weathering as the contents show irregular vertical changes in the lower depressions it follows that it is the ancient redox environment rather than the modern conditions which affect the orebody vertical structure this clarifies the fact that the vertical structure of the orebody is jointly constrained by the physical melange accumulation of ores and the differences between the ancient redox environments in the higher and lower locations these factors should be the primary factors affecting the vertical structure of karst bauxite deposits

late cretaceous coal overlying karstic bauxite deposits in the parnassus ghiona unit central greece coal characteristics and depositional environment abstract the pera lakkos coal located on top of bauxite deposits in the ghiona mining district central greece is the only known mesozoic late cretaceous coal in the country it was derived from herbaceous plants and algae growing in mildly brackish mires that formed behind a barrier system during a regression of the sea on a karstified limestone partly filled in with bauxitic detritus petrological mineralogical and geochemical data point to the predominance of reducing conditions and intense organic matter degradation in the palaeomires o c vs h c and oi vs hi plots based on elemental analysis and rock eval data characterize kerogen types i ii this reflects the relatively high liptinite content of the coal besides kerogen composition o c vs h c plot for the pera lakkos coals is in accordance with a catagenesis stage of maturation in contrast with vitrinite reflectance and t max from rock eval pyrolysis which indicate the onset of oil window maturation stage suppression of vitrinite reflectance should be considered and the high liptinite content corroborates this hypothesis despite some favourable aspects for petroleum generation presented by the pera lakkos coal its maximum thickness up to 50 cm points to a restricted potential for petroleum generation coal oxidation took place either during the late stage of peat formation due to wave action accompanying the subsequent marine transgression or epigenetically after the emergence of the whole sequence due to percolation of drainage waters both options are also supported by the ree shale normalized profiles which demonstrate an upwards depletion in the coal layer oxidation also affected pyrite included in the coal this led to the formation of acidic sulfate rich solutions which percolated downwards resulting in bleaching of the upper part of the underlying bauxite

mineralogical and geochemical studies of boron rich bauxite ore deposits in the songqi region sw henan china the songqi region sw henan is an important bauxite province in china the bauxite ore deposits occur unconformably on the top of middle ordovician argillaceous carbonates the bauxite ores from the songqi region are characterized by unusually high boron contents in this paper we report the mineralogical and chemical compositions of selected bauxite ores from the region these new data together with existing geochemical data of soils in the region are used to evaluate the origin of boron enrichment in the bauxite ores the compositional characteristics of tourmaline in the bauxite ores suggests that this mineral was likely derived from a meta sedimentary protolith mass balance calculation reveals that tourmaline only accounts for a small portion of boron in the bauxite ores the majority of boron in the ores must occur in other forms possibly by ion absorption on the surfaces of diaspore and clay minerals in the songqi region the precambrian meta sedimentary rocks are known to contain abundant tourmalines whereas the cambrian ordovician argillaceous carbonates and the upper proterozoic shales are all enriched in boron in free ion state we suggest that these rocks provided tourmaline and boron ion to the bauxite deposits in the region most known bauxite deposits in the songqi region occur at the margins of boron rich soil domains suggesting that boron in soils is a potential exploration indicator for unknown bauxite deposits in this region