giant bauxite deposits of south china multistage formation linked to late paleozoic ice age lpia eustatic fluctuations abstract the lower carboniferous jiujialu formation bauxite deposits at zunyi northern guizhou are distinguished by their great thickness to 110 m and cyclic alternation of bauxite ore and bauxitic claystone layers these features are typical of the kazakhstan subtype of karst bauxite deposits although the genesis of this type of deposit is poorly understood here we undertook a petrological mineralogical and geochemical study of the zunyi deposit in drillcore zk5600 to gain insights into its formation history the zunyi profile contains seven bauxite cycles as recorded by petrological mineralogical and geochemical features indicating a multistage formation history each cycle is composed of a lower bauxitic claystone layer and an upper bauxite ore layer the bauxite ore is characterized by high al2o3 high al mineral diaspore and low sio2 content positive ce anomalies high cia values 90 and strong depletion of major elements indicate that the bauxite ore formed through intense chemical weathering and leaching in a well drained soil environment the bauxitic claystone is characterized by relatively lower al2o3 and higher sio2 and clay mineral mostly illite content this lithology exhibits both negative and positive ce anomalies moderate cia values 70 80 and enrichment of some elements e g fe k indicating formation through moderate chemical weathering in a poorly drained soil environment secular variations in chemical weathering intensity and soil drainage conditions were linked to regional hydrologic changes during the early carboniferous the zunyi area was located in a karstified coastal upland setting and its hydrologic system was affected by glacio eustatic fluctuations high groundwater table elevations during eustatic highstands led to formation of bauxitic claystone layers whereas low groundwater table elevations during eustatic lowstands led to formation of bauxite ore layers

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

231pa 230th fractionation by ocean transport biogenic particle flux and particle type 231pa and 230th are removed from the water column by a process of reversible scavenging which quickly removes 230th to the sediment 231pa is less efficiently scavenged onto particles than 230th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment this study combines particle fields dust opal caco3 poc derived from observations with the bern3d intermediate complexity ocean model and an equilibrium scavenging model for isotopes the equilibrium partition coefficient for particulate versus dissolved isotope activity is varied with particle type the model can explain many of the features of the global 231pa and 230th distribution the success of such a simple model at representing the global pattern of 231pa 230th activity ratio supports the use of this proxy in paleoceanographic studies we use the model to address the controversy concerning which particle types are dominant in fractionating 231pa 230th in the ocean the lithogenic dust flux is found to be unimportant for 231pa 230th fractionation the ocean fractionation of 231pa 230th is dominated by the distribution of the caco3 and opal flux we also confirm that opal is a weak scavenger of 230th

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

the removal rates of234th and228th from waters of the new york bight abstract the mean residence time of thorium with respect to non radioactive removal from water was determined as a function of location in three traverses of the new york bight using both 234 th 238 u and 228 th 228 ra correlates well with salinity increasing from about ten days near shore to 70 days at the shelf break it shows a much weaker correlation with suspended matter concentrations both because suspended matter varies in its scavenging efficiency and because salinity is a longer term integrator of scavenging potential s computed from 228 th 228 ra were often higher than those computed from 234 th 238 u either because of the detrital matter present as reflected in the 232 th concentrations or because the water parcels had recently arrived from environments of lower scavenging efficiency anomalous isotopic concentrations found in three adjacent samples can best be explained as the result of an episodic release of 228 ra from bottom sediments at a rate 200 times the normal one

sh propagator matrix and qs estimates from borehole and surface recorded earthquake data summary a new method is proposed for the solving of elastic and anelastic parameters of a medium between two seismometers one in a borehole and one at the surface this allows us to retrieve equivalent quality factors of the materials and at the same time gives wave velocities as well as reflection and transmission coefficients in a layered structure the study of local site effects shows that the quality factor of shallow materials can be completely masked by resonance effects and near surface amplification our method is based on the sh propagator matrix in the time domain this separates the effects of resonance and amplification in the elastic structure from those of attenuation due either to scattering or physical attenuation and we find that the elastic problem is decoupled from the anelastic one after a synthetic test we applied the method to seismic records made with a borehole surface instrument operated in the southern rhine graben valley on the french german border due to high seismic noise at the surface we were only able to resolve a one layered mean 500 m deep structure between the borehole and surface instrument an apparent qs of 40 is found between 1 and 5 hz a frequency band where classical methods failed this is in close agreement with qs at frequencies larger than 15 hz obtained from the classical method based on the slope of spectral ratios

formation of fe mn crusts within a continental margin environment abstract this study examines fe mn crusts that form on seamounts along the california continental margin ccm within the united states 200 nautical mile exclusive economic zone the study area extends from approximately 30 to 38 north latitudes and from 117 to 126 west longitudes the area of study is a tectonically active northeast pacific plate boundary region and is also part of the north pacific subtropical gyre with currents dominated by the california current system upwelling of nutrient rich water results in high primary productivity that produces a pronounced oxygen minimum zone hydrogenetic fe mn crusts forming along the ccm show distinct chemical and mineral compositions compared to open ocean crusts on average ccm crusts contain more fe relative to mn than open ocean pacific crusts the continental shelf and slope release both fe and mn under low oxygen conditions silica is also enriched relative to al compared to open ocean crusts this is due to the north pacific silica plume and enrichment of si along the path of deep water circulation resulting in si enrichment in bottom and intermediate waters of the eastern pacific the ccm fe mn crusts have a higher percentage of birnessite than open ocean crusts reflecting lower dissolved seawater oxygen that results from the intense coastal upwelling and proximity to zones of continental slope pore water anoxia carbonate fluorapatite cfa is not present and ccm crusts do not show evidence of phosphatization even in the older sections the mineralogy indicates a suboxic environment under which birnessite forms but in which ph is not high enough to facilitate cfa deposition growth rates of ccm crusts generally increase with increasing water depth likely due to deep water fe sources mobilized from reduced shelf and slope sediments many elements of economic interest including mn co ni cu w and te have slightly or significantly lower concentrations in ccm crusts relative to crusts from the pacific prime crust zone and other open ocean basins however concentrations of total rare earth elements and yttrium average only slightly lower contents and in the future may be a strategic resource for the u s

karst bauxite deposits in the zagros mountain belt iran more than 190 occurrences of bauxitic lateritic deposits were investigated in seven areas within the zagros simply folded mountain belt in southwestern of iran the bauxitic horizons are situated in eroded major nw se trending anticlines and occur in karst cavities near or at the boundary between the sarvak and ilam formations uplift in the cenomanian turanian period had exposed the sarvak limestone to karst weathering and during a period of unconformity layers of ferruginous argillaceous limestone debris developed and accumulated on its surface the ferruginous argillaceous debris was partly converted to bauxite folding and faulting in oligocene miocene time with ensuing erosion exposed the bauxitic horizons on the limbs and cores of anticlines the karst bauxite deposits are probably of authigenic origin as evidenced by their lithologic associations textural and mineralogy

radium 228 as a tracer of basin wide processes in the abyssal ocean a simple model of isopycnal mixing in a circular basin is developed in order to examine the utility of the 5 75 year half life tracer radium 228 for studying basin wide processes in the deep ocean the model shows that it is possible to resolve diffusivities of 8 107 cm2 s 1 in a basin of 3000 km diameter with profiles measured near the center and edge of the basin a least squares fit of the model to four abyssal profiles measured during geosecs in the north american basin gives an isopycnal diffusivity of 6 107 cm2 s 1

a230th profile in the atlantic ocean a230th profile dissolved particulate measured in the eastern central atlantic at 24 45 n 26 57 w displays a linear increase with depth values range between 0 2 dpm230th 104 l at the surface and 2 0 dpm230th 104 l at 4000 m this concentration is 5 times lower than total230th in the central pacific and is similar to230th measured on suspended matter in the pacific and indian ocean the lower concentration in the eastern atlantic must either reflect a higher scavenging activity at the west african margin or be a consequence of a higher particle flux through the water column yielding an average settling velocity of particulate matter of 6 2 10 3 cm s despite the lower concentration the equilibrium coefficient between dissolved and adsorbed230th is similar to the one derived for the central pacific this shows that the equilibrium model for230th scavenging from the water column derived by nozaki et al 1 and bacon and anderson 2 applies as well in the eastern atlantic

tonnage cutoff model and average grade cutoff model for a single ore deposit abstract ore reserve estimation and resource prediction are important aspects of deposit exploration and mining the cutoff has great influence on the reserve and resource calculation despite this the study on the mathematical relationships of the tonnage average grade and cutoff is still scant according to the fractal distribution of element concentrations which are obtained from analysis of channel samples of constant length along exploration or mining works the tonnage cutoff and average grade cutoff models are constructed which are applicable in both exploration and operating mine environments via these models the relationships between ore tonnage metal tonnage and cutoff are obtained in terms of the fractal model of element concentrations moreover the thickness of the mineralized zone in each exploration or mining work follows a fractal model and assuming that the thickness is a continuous variable a model for calculating the mass of the mineralized zone in a single deposit is established given the mineralized zone mass the tonnage cutoff and average grade cutoff models can be utilized to calculate ore reserve and average grade especially when the cutoff changes a fault controlled disseminated and veinlet gold deposit in jiaodong gold province china is selected as a case study the estimates of the ore reserves obtained from these models are found to be consistent with the results obtained by the traditional geometric block method

climatic and hydrologic controls on upper paleozoic bauxite deposits in south china abstract the late paleozoic era was an interval of major tectonic and climatic changes including formation of the supercontinent pangea and the 60 myr long late paleozoic ice age lpia although bauxite formation declined globally from the carboniferous to the permian in conjunction with global cooling it was an interval of widespread bauxite formation in china in south china 1 the jiujialu formation bauxite deposits in central and northern guizhou zunyi area are of early middle visean age 2 the dazhuyaun formation bauxite deposits in northern guizhou wuchuan zheng an daozheng area to southern chongqing nanchuan area and southeastern guizhou fuquan kaili area are of late pennsylvanian early permian age and 3 the heshan formation bauxite deposits in western guangxi to yunnan are of middle late permian age in north china the benxi formation bauxite deposits are of late mississippian middle pennsylvanian age the contrasting trends in bauxite metallogenesis between china and the rest of the world imply different climatic patterns in the eastern tethys high annual humidity with seasonal dryness and pangea aridification this hypothesis is further supported by differences in the chemical index of alteration or cia 80 in the eastern tethys vs 50 in western pangea and in paleotemperatures mean annual temperature or mat 20 c in the eastern tethys vs 4 c in western pangea determined from permo carboniferous siliciclastic deposits permo carboniferous bauxite deposits in south china formed in coastal plain and coastal karstic depression environments in which the position of the groundwater table was related to sea level changes during the late paleozoic high frequency eustatic fluctuations caused by waxing and waning of gondwana icesheets controlled sedimentation in these coastal depositional systems leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose and phreatic type bauxite formation the results of the present study show that during interglacial stages lateritization resulted from high pco2 high sea level and groundwater table elevations low precipitation and limited vegetation cover whereas during glacial stages bauxitization of these ferralitic weathering products was promoted by low pco2 low sea level and groundwater table elevations high precipitation and more extensive vegetation cover thus a unique combination of geographic climatic and eustatic factors accounted for widespread formation of bauxite in south china during the lpia

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

u th chronology and paleoceanographic record in a fe mn crust from the ne atlantic over the last 700 ka hydrogenetic ferromanganese crusts fe mn crusts provide a secular record of the variations of seawater composition responding to changes in ocean circulation and erosion processes in this respect the acquisition of an absolute and reliable chronology in fe mn crusts is a prerequisite here we combine four different and complementary chronometers 10 be 230 thex 230 thex 232 th 234 u 238 u in a fe mn crust dredged at 2000 m depth in the east atlantic to first establish a reliable chronology over the quaternary period then we use eds chemical analysis to look for correlation between major element chemistry and climate changes 230 thex 230 thex 232 th and be data give very consistent growth rates in particular the good match between 230 thex and 230 thex 232 th data indicates that at the location of crust 121dk 230 th and 232 th fluxes in the water column change simultaneously and suggests that the normalization of 230 thex to 232 th makes 230 thex 232 th a better chronometer our best fit model suggests that crust 121dk experi enced changes in growth rates at 122 and 312 ka and a growth with a constant 230 th initial flux this chronology returns an age of 680 ka for the uppermost 1 5 mm the 234 u 238 u depth profile however was clearly affected by diffusion of 234 u in the porous crust and can therefore not be used to derive a reliable chronology one part of the crust seems isolated from pore water diffusion and can be physically recognized as a zone of very small porosity on the basis of the 230 thex 232 th chronology major element chemistry is shown to be linked to climate change mn fe variations compare well with those in a fe mn crust from the pacific showing systematic maxima during glacial stages 2 and 4 high mn fe are tentatively interpreted to reflect expansion of the oxygen minimum zone during glacial periods resulting from higher bioproductivity in addition we note that the surface 230 th 232 th activity ratio of crust 121dk is entirely consistent with advection of deep water from the western toward the eastern atlantic basin copyright 2005 elsevier ltd

supergene alteration since the upper cretaceous on alkaline igneous and metasomatic rocks of the pocos de caldas ring complex minas gerais brazil abstract this contribution presents field evidence mineralogical observations and geochemical data of different modes of lateritic weathering which affected the alkaline magmatic rocks and their metasomatic alteration products since the upper cretaceous field relations demonstrate that ferralitic bauxitic weathering is confined to well drained hill crest and upper slope settings in the pocos de caldas area bauxite normally rests directly on parent rock stagnant drainage and reducing conditions beneath tropical peat deposits along valley floors and in lower slope situations favour sialitic saprolitic weathering the additional importance of high porosity and permeability is demonstrated by co occurring parent rocks with strongly contrasting response on weathering attack in normal nepheline syenites and phonolites nepheline breaks down first and nearly instantly upon weathering this results in high porosity giving water and atmospheric gases easy access to the more resistant minerals thus in well drained morphological positions bauxite is generated if the same original magmatic parent rocks are shielded against pervasive weathering attack by pre lateritic metasomatic alteration no comparable early permeability arises a fine grained and dense metasomatic assemblage of kaolinite illite microcline and smectite combined with the annealing of fractures and joints is able to prevent bauxite generation and saprolite is formed instead this metasomatically induced saprolite is significantly richer in illite than normal saprolite bauxite formation results in a strong depletion of mg ca na k si ni co cu zn rb ba sr y and ree sialitic saprolitic weathering leads to a generally less pronounced depletion of essentially the same elements silicon and ni are more efficiently retained than in bauxite mobile elements are mn ca na k mg co zn rb ba sr and ree cerium can be re precipitated under oxidizing local conditions closely associated positive and negative ce anomalies are due to inhomogenously concentrated precipitates in small scale spatial alternation with zones of nearly total depletion a general correlation between the type of laterite saprolite or bauxite and ce retainment or depletion does not exist host phases for most of the immobile trace elements are goethite and related plasmas in bauxites and saprolites immobility is exhibited by v pb ga nb zr th and u relict zircon is too rare to explain a seemingly retarded hree loss in saprolites

230th in the eastern north atlantic the importance of water mass ventilation in the balance of230th the230th distribution in the water column on a north south transect in the eastern north atlantic was measured using thermal ionization mass spectrometry tims water samples at three locations l1 33 n 21 6 w l2 47 4 n 19 5w and l3 54 4 n 21 1 w were filtered and the dissolved and particulate fractions were analysed for their230th and232th contents in the upper water column 2000 m at l2 suggested by our model 8 25 years is probably too rapid in comparison with previous findings based on chlorofluorocarbon data enhanced scavenging of230th would be an alternative explanation for the low concentration in neadw at l2 with the scavenging mixing model we calculated an advective export flux of230th of up to 50 of the production in the water column in the eastern north atlantic advective loss of230th has to be taken into account when using the230th flux into sediments for paleoceanographic studies in ocean basins where deep water residence time is comparable to the230th scavenging residence time

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

chemical and radiochemical investigations of surface and deep particles of the indian ocean abstract the distribution of ash the non combustible fraction of marine suspended matter and concentrations of particulate al ca fe cr ni cu sr and234th in surface waters and of210pb 230th and234th in two vertical profiles 385 4400 m of the indian ocean are reported the ash concentrations in surface waters follow the primary productivity pattern with higher abundances in samples south of 40 s and lower concentrations in the equatorial and subtropical regions opaline silica and caco3 are the dominant components of the ash in samples from 40 s and from 7 n to 39 s respectively aluminosilicates are only a minor constituent of the surface particulate matter the metal al ratios in the surface particles are significantly higher compared to their corresponding crustal ratios for all the metals analyzed in this work comparison of enrichment factors between marine aerosols plankton and surface oceanic particles seem to indicate that this high metal al ratio in surface particles most likely arises from their involvement in marine biogeochemical cycles particulate234th activity in surface waters parallels the ash abundance implying that its scavenging efficiency from surface waters depends on the particulate concentration the particulate230th and210pb concentration profiles increase monotonously with depth it is difficult to ascribe this increase to a process other than the in situ vertical scavenging of230th and210pb from the water column by settling particles the mean settling velocities of particles calculated from the particulate230th data using a one dimensional settling model is about 2 10 3 cm s the settling velocity computed from the particulate230th profiles does not appear to be compatible with the particulate210pb depth profiles one possible explanation to account for the disparity would be that230th and210pb are scavenged by different size populations of particles on the whole the geographic distribution of particulate matter their composition and settling velocities in the atlantic pacific and indian oceans are similar indicating that they are controlled by quite similar processes in the marine hydrosphere

estimating changes in seismic wave velocity from a pneumatic source in an operational mine rock mass characteristics such as applied stress pore pressure and fracture density are coupled to the seismic wave propagation velocity therefore measuring small relative changes of seismic wave velocities in operational mines has the potential for tracking changes in these important rock mass properties to this end we have conducted an experiment with the aim of measuring seismic body wave velocities in situ at williams mine hemlo canada using a pneumatic source and multiple receivers we determine that the signal to noise ratio is improved by deconvolving the source signal from the signal recorded at the remotely grouted geophones we evaluate the estimated relative changes in traveltimes and assume that these are due to changes in the body wave velocity caused by mining related activities we are able to successfully detect the source response at remote receivers in an operational mine at a distance of more than 430 m

genesis of the permian karstic pingguo bauxite deposit western guangxi china more than 0 5 billion tons of late permian bauxite overlies the karstic topography of the maokou formation of western guangxi in china here we provide new mineralogical geochemical sr nd pb isotopic and pyrite s isotope and trace element compositional data for the pingguo bauxite deposit aiming to further our understanding of the genesis of permian bauxite the pingguo bauxite contains three distinct layers a lower layer dominated by ferric clay or weathered iron ore a middle layer of cryptocrystalline and oolitic bauxite ore and an upper layer dominated by argillaceous bauxite the bauxite ore is mainly diaspore pyrite chamosite and anatase whereas the argillaceous bauxite contains diaspore kaolinite pyrophyllite pyrite and anatase two types of pyrite have been identified within the bauxite fine grained and framboidal pyrite py1 occurring in aggregates and coarse grained and euhedral pyrite py2 py1 is enriched in trace elements and is thought to have a diagenetic origin whereas py2 is deficient in trace elements and is considered to have formed by later recrystallization the s isotopic composition of pyrite 34 11 to 18 91 and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation the sr nd pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the emeishan large igneous province lip and limestones of the maokou formation microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near surface conditions

discovery of the ree minerals and its geological significance in the quyang bauxite deposit west guangxi china most of the karstic bauxite deposits in china are enriched in ree and the ree has commonly been considered to be adsorbed on the surface of clay or diaspore minerals as ion state however occurrence of ree minerals in the bauxite deposits has not been reported by far in the quyang bauxite deposit from guangxi province we find ree minerals the minerals are parisite and churchite parisite is widely distributed in the ooids and matrix inducing positive ce anomaly of the ores whereas churchite is rare and occurred in the core of ooid the compositions of the ree minerals show the eu anomaly can change gently during the weathering and the eu anomaly analyses suggest that the ree in the ores are mostly derived from the underlying carbonates the parisite is formed in an alkaline condition while churchite in an acidic situation the co existence of the two minerals in the ores suggests the permian environment for bauxite formation is complex with great change of ph value moreover parisite is inferred to be formed earlier than the churchite

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

the thorium isotope content of ocean water 232th concentrations of surface and deep pacific ocean waters are 0 01 0 02 dpm 1000 kg 60 pgm kg the230th activity is 0 03 0 13 dpm 1000 kg in surface waters and 0 3 2 7 dpm 1000 kg in deep waters chemical residence times based on in situ production from parent isotopes are about the same for230th and228th in surface waters 1 5 years but are ten times greater for230th in deep waters 10 100 years apparently there are additional sources of230th into deep waters at manop site s manganese nodule tops are enriched in th isotopes by adsorption of th from seawater and not by incorporation of th rich particulates

genesis of ree minerals in the karstic bauxite in western guangxi china and its constraints on the deposit formation conditions abstract karstic bauxites in western guangxi china comprise two subtypes permian bauxite and quaternary bauxite the quaternary bauxite originated from the breaking up rolling and accumulating of permian bauxite in karstic depressions in quaternary various types of rare earth element ree minerals were discovered during the formation of the permian and quaternary bauxites from the xinxu longhe and tianyang bauxite deposits in this study five types of ree minerals including bastnasite parisite cerianite rhabdophane and churchite were identified bastnasite and parisite are the most abundant and they are widely developed in the permian ore and also present in the quaternary ore obvious variations in bastnasite and parisite ree compositions were observed which is ascribed to distinctions in the source materials in the primary weathering profile from different areas the mode of occurrence of bastnasite and parisite suggests they were mainly precipitated under alkaline and reducing conditions during the permian bauxite forming stage and underwent intensive corrosion in the quaternary churchite was formed during the permian weathering stage under acidic condition both cerianite and rhabdophane occur in fractures within the permian bauxite ore indicating that both formed during the quaternary weathering stage it is considered that the rhabdophane enriched in ce have formed locally in the process of that the ce3 released from bastnasite rapidly entered the rhabdophane lattice before being oxidized to ce4 cerianite was mainly found in association with mn al hydroxides suggesting that the released ce3 was oxidized into ce4 and precipitated cerianite in fractures within the permian bauxite ore mass balance equations reveal a depletion in nearly all rees during the transformation from the permian to the quaternary bauxite ore mainly caused by the dissolution of bastnasite and parisite the genesis of the ree minerals together with the occurrence of other minerals indicates that intensively acidic and oxidizing conditions developed before the formation of the permian bauxite ore towards the end of the permian the conditions became reducing and alkaline favorable for the large scale bauxitization the quaternary bauxite forming stage was characterized by variable ph and eh conditions with acidic ph 4 6 and oxidizing eh 2 conditions at the surface of the exposed permian bauxite ore

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

seismic and electromagnetic controlled source interferometry in dissipative media abstract seismic interferometry deals with the generation of new seismic responses by crosscorrelating existing ones one of the main assumptions underlying most interferometry methods is that the medium is lossless we develop an interferometry by deconvolution approach which circumvents this assumption the proposed method applies not only to seismic waves but to any type of diffusion and or wave field in a dissipative medium this opens the way to applying interferometry to controlled source electromagnetic csem data interferometry by deconvolution replaces the overburden by a homogeneous half space thereby solving the shallow sea problem for csem applications we demonstrate this at the hand of numerically modeled csem data

genesis of the guangou karstic bauxite deposit in western henan china abstract the guangou bauxite deposit in western henan china is located in the north china block and to the north of the north qinling orogenic belt the orebody is hosted within the lower member of the carboniferous benxi formation which overlies unconformably upon the ordovician majiagou formation in the lower member of the benxi formation the bauxite orebody with a diaspore illite anatase mineral assemblage is sandwiched between underlying ferric clay illite hematite goethite and overlying top clay kaolinite quartz goethite according to field observations and geochemical evidence including trace and rare earth element ree compositions especially zr hf ratios the ferric clays were weathered from the underlying argillaceous limestones in the majiagou formation during this weathering process trace elements s zn ni cr v sc f ba and be are depleted li rb and b are enriched and zr hf bi ta ga nb and th are relatively immobile rees exhibit evident differentiation with enrichment of la ce pr and nd and depletion of gd tb dy ho er tm yb and lu the bauxite formed in weak reducing slightly basic water conditions according to the geneses of coexisting diaspore and anatase and it was altered during the epigenetic and second exposure periods forming kaolinite and goethite respectively interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and rees in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements for instance zircon rutile and anatase contain zr hf nb ta w and u based on geochemical evidence together with age data and chemical compositions of the detrital minerals both distant igneous rocks in the plate margin and paleozoic carbonates and precambrian rocks inside north china block provide the miscellaneous material for the bauxite ore and the top clay

correlation between mineralization intensity and fluid rock reaction in the xinli gold deposit jiaodong peninsula china constraints from petrographic and statistical approaches abstract the jiaodong peninsula the most productive gold province in china is dominated by jiaojia type gold deposits that formed at ca 120 ma the deposits are characterized by widespread alteration and mineralization resulted from fluid rock reactions in the footwall of regional faults it is known that the interrupted appearance of continuous mineralization zones and barren zones along regional faults is controlled by changes in the dip direction and dip angle of these faults which can cause local dilational sense in the continuous mineralization zone intensive fluid rock reactions occurred yet whether and how the fluid rock reaction impacted on the mineralization intensity are not well constrained in this study we selected the xinli jiaojia type gold deposit associated sanshandao cangshang fault located on the northwest margin of the jiaodong peninsula to examine in detail the distribution of orebody parameters and to observe the mineralization occurrences we applied the number size fractal model and the lacunarity method to quantify the distribution of gold concentration along drifts with the goal of clarifying the ambiguities noted above the drifts in continuous mineralization zones can be divided into stable and unstable types according to lateral changes in the dip direction and dip angle of the sanshandao cangshang fault stable and unstable drifts share several common features 1 statistical results show that changes in the dip direction and dip angle of this fault bear almost no relationship to the thickness or grade thickness of the orebody 2 mineralization along drifts is most intense at some distance from the fault plane rather than at locations immediately adjacent to the fault plane where fracturing is most extensive and according to fluid infiltration theory would be the most likely regions of intense mineralization 3 gold bearing sulfide pods and veinlets in the alteration zone commonly possess irregular and corroded boundaries that are considered to be an indicator of fluid rock reactions 4 the threshold the gold concentration that divides a segment with a lower fractal dimension in a lower concentration range from one with a higher fractal dimension in a higher concentration range and the lacunarity the parameter that evaluates the evenness of high gold concentration distribution show positive and negative relationships respectively to the thickness and grade thickness of a drift we thereby argue on the basis of these features that fluid rock reactions were an important factor responsible for the mineralization upgrade in continuous mineralization zones an increase in the threshold and a decrease in the lacunarity indicate that fluid rock reactions causing gold precipitation are more intensive and more evenly distributed throughout the footwall for better mineralization these phenomena suggest that fluid rock reactions responsible for the gold precipitation possibly own the characteristics of spatial self organization mechanism which is widely developed in various geological fluid rock reaction processes

230th232th systematics in the central pacific ocean the sources and the fates of thorium 232 th and 230 th of unfiltered and filtered sea water samples were measured along a depth profile of the central pacific ocean using isotopic dilution and thermal ionization mass spectrometry the 232 th concentration is rather constant from below 25 m down to over 2000 m 45 60 10 6 atom cm 3 and it then increases rapidly towards the bottom 119 360 10 6 atom cm 3 at 4000 m the 230 th concentration increases linearly with depth from 3 10 3 atom cm 3 at 25 m to 110 10 3 atom cm 3 at 4000 m the reproducibility of replicate analyses and the regularity of the profiles demonstrate the reliability of the procedure however some lack of reproducibility among different samples from the same depth has to be explained by natural variability or by contamination during sample collection due to the very low 232 th concentrations and relatively high 230 th concentrations the 230 th 232 th ratios can be as high as 1 6 10 3 the ratio of the amount of th on particles 0 2 m to the amount of th in solution is significantly higher for 232 th 0 37 than for 230 th 0 18 these data are interpreted in terms of a model that specifically treats particle transport assuming local equilibrium between particles and sea water the relatively high 230 th concentrations and 230 th 232 th ratios measured at 25 m are consistent with a mixed layer of about 100 m the linear increase in 230 th with depth implies that the effect of eddy diffusion is negligible for most of the water column over the th removal time scale this profile is consistent with transport of 230 th by reversible uptake on particles settling with a constant velocity the 232 th data are inconsistent with this model and they suggest that particles carrying 232 th experience 70 of mass loss between the surface and 4000 m and must follow different transport rules this difference in the transport of 230 th and 232 th demonstrates the distinctive behavior of these isotopes during particle formation and subsequent remineralization and repackaging in the water column different speciation of 230 th and 232 th may be explained by their distinctive sources in the ocean as 230 th is produced in solution and 232 th is carried by detrital material and by their respective packaging mechanisms which are not yet known

the influence of particle composition on thorium scavenging in the ne atlantic ocean pomme experiment abstract 230th 232th and 234th were analyzed in sinking particles collected by moored and drifting sediment traps in the ne atlantic ocean pomme experiment in order to constrain the phase s carrying th isotopes in the water column it reveals a contrasted behaviour between 234th and 230th 234th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters 230thxs is correlated with mn ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column the lack of correlation between 230thxs and caco3 or biogenic silica bsi indicates that caco3 and bsi are not responsible for 230th scavenging in the deep waters of this oceanic region 230th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for 230th scavenging in the deep waters or that sufficient time is required to achieve particle solution equilibration mno2 could be the prevalent 230thxs bearing phase the narrow range of kd mno2th obtained for very contrasted oceanic environments supports a global control of 230thxs scavenging by mno2 and raises the possibility that the 230th 231pa fractionation is controlled by the amount of colloidal mno2 in seawater

distribution of dissolved and particulate230th and232th in seawater from the gulf of mexico and off cape hatteras as measured by sims we present vertical and horizontal profiles of dissolved and particulate230th and232th concentrations in seawater from shelf and slope areas of the gulf of mexico and off cape hatteras in the middle atlantic bight as measured by secondary ion mass spectrometry sims and compare the partitioning of long lived230th between particles and seawater with that of short lived234th concentrations of dissolved and particulate230th and232th in surface seawater decreased from near shore to off shore in the gulf of mexico demonstrating terrestrial input to the surface waters vertical profiles indicate that lateral transport as well as surface inputs e g fluvial and aeolian and bottom sediment resuspension could be an important source of230th and232th in ocean margin regions sea water samples collected off cape hatteras contained significantly higher dissolved and particulate230th and232th concentrations than those found in the open gulf of mexico likely the distributions of230th and232th in seawater off cape hatteras are to a large extent controlled by terrestrial particles in contrast in situ production for230th and scavenging are the major processes regulating the concentrations of dissolved230th and232th in the open gulf of mexico the observed negative correlation between log kd particle solution distribution coefficient and log cp concentration of suspended particulate matter for234th and230thxs in both study areas demonstrated a particle concentration effect down to very low cp concentrations 20 g l based on the230th inventory in situ production and the small estimated surface input the overall residence time of230th in the water column at a slope station in the gulf of mexico is calculated to be about 5 yr

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

geochemistry and secular trends in the middle late permian karst bauxite deposits northwestern iran abstract this study focuses on the middle late permian bauxite deposits found within karstic depressions and sinkholes of carbonates of the ruteh and nessen formations northwestern iran data concerning five karst bauxite deposits each related to a different stratigraphic position within the bedrock were selected to address the chemical distribution and inter elemental relationships especially for critical elements factors that control bauxite formation and the parental affinity the analyzed samples mainly clayey bauxite and bauxitic clay are characterized by large compositional fluctuations involving both major and trace elements the major element composition is dominated by sio2 tio2 al2o3 and fe2o3 among the critical elements compositional fluctuations induce the occurrence of outliers for co nb ta lree and hree similar to other trace elements such as ba sr cr u and zr elemental mobility indicates that most of elements are generally depleted among the critical elements co is enriched only in several samples of the older deposits and ree are enriched in some samples of the younger deposits factor analysis suggests that due to the observed al ga covariance fairly acidic conditions were never attained during bauxitization and that detrital resistant minerals concentrated during a bauxitization stage promoting al ti accumulation furthermore the u co variance with low soluble elements nb ta and th suggests that u was mostly conservative during the formation of deposits cobalt co varies with cr and these elements accumulated during later bauxitization stages when the massive leaching of silica occurred the cia ciw and pia paleo weathering proxies indicate an upward weathering increase which suggests a trend toward more extreme weathering conditions in a wetter and warmer climate according to the permian global warming this is consistent with an upward increasing ba sr ratio and the inspection of the a cn k plot where the younger deposits fall close to the a k edge involving a clayey precursor requires a rainfall increase interestingly the upward trend toward a warmer and wetter climate was also coupled with paleo redox conditions promoting cerium oxidation as depicted by the ce ce values finally the eu anomaly and the sm nd ratio indicate that the studied bauxite deposits were mainly derived from a mafic protolith that formed in the middle late permian as a consequence of the volcanism that affected the entire iranian platform a cluster of karst bauxites however has eu eu values lower than the average standard deviation range of the mafic rocks suggesting a possible contribution of a more differentiated and less mafic protolith similarly the u th ratio at large supports the hypothesis of a mafic protolith for the middle late permian bauxite deposits although some samples show the u th values well above the average standard deviation range of the mafic rocks likely indicating that processes promoting the accumulation of resistant minerals with high u th ratios cannot be excluded this means that in this case the u th ratio does not necessarily reflect the protolith of karst bauxites and that more in general this proxy needs to be carefully interpreted when used to assess the parental affinity of residual rocks

fractal models for ore reserve estimation abstract traditional geometric and geostatistic methods for reserve estimation in a single deposit are difficult to use with skewed distribution mineralization variables including grade orebody thickness and grade thickness a common characteristic of most deposits and require complex data processing it has been shown that the skewed mineralization variables can be described by the number size model in a fractal domain based on the number size model assuming that orebody thickness and grade thickness are continuous variables the fractal model for reserve estimation fmre in a single deposit can be established in the fmre ore tonnage can be estimated given the orebody area and the fractal parameters of orebody thickness distribution and metal tonnage can be estimated based on the orebody area and the fractal parameters of grade thickness distribution the reserve estimated by the fmre can denote actual ore tonnage and metal tonnage that can be mined out of the deposit the frme was applied to the dayingezhuang gold deposit in the jiaodong gold province in china the gold reserves via the fmre and the traditional geometric block method are similar with relative errors of 3 11 in ore tonnage and 0 29 in metal tonnage compared to traditional reserve estimation the fmre is much easier in calculation process and is more reasonable in dealing with the skewed distribution however this new method fails to calculate local reserve which can be derived via any of the traditional estimation methods

equivalent medium representation of fractured rock a similarity may be found between various approaches for determining the effects of parallel fractures or aligned cracks on seismic wave propagation at wavelengths that are long compared with the scale length of the cracks fractures can be modeled using an empirical linear slip condition however natural fracture surfaces can also be simulated directly as planar distributions of small isolated areas of slip cracks model 1 or conversely as planar distributions of imperfect interfacial contacts model 2 an alternative is plane surfaces separated by thin continuous layers of viscous fluid or a soft material model 3 we present analytic expressions for the fracture compliances for these three models and using these analytic results compute the effective compliances and stiffnesses of the fractured material as a result it is possible to relate the measured compliances or stiffnesses directly to the statistics of the microstructural details of a fracture given appropriate a priori information on the fracture surfaces the results for model 1 are equivalent to a volume distribution of cracks as studied by hudson 1980 1981 for small crack density the results for model 2 are basically the same as those given by white 1983 for a packing of spheres and finally the results for model 3 are in agreement with those given by backus 1962 for combinations of two constituent layers these results can be extended to the case of nonaligned fractures and to allow for fluid flow between cracks and into a porous matrix rock finally it is shown that the ratio of the normal to shear fracture compliance is a good indicator of the properties of the fracture infill

genetic relationship between the emeishan plume and the bauxite deposits in western guangxi china constraints from u pb and lu hf isotopes of the detrital zircons in bauxite ores abstract the formation processes and alumina sources of the large and super large bauxite deposits that have developed in west guangxi in the yangtze block have been debated for a long time shrimp zircon u pb dates combined with in situ hf isotopic data of the detrital zircons from permian bauxite ores in the western guangxi province china provide new constraints on the genesis of the bauxites in west guangxi u pb dating ages of the detrital zircons cluster around 256 ma and 261 ma this is consistent with the emplacement age of the emeishan plume thus it has been determined that the detrital zircons come from magmatic rocks related to the emeishan plume and that the emeishan plume has significant control on the formation of bauxites in addition this work presents new evidence for the evolution of the emeishan plume most of the e hf t values of the zircons around 256 ma and 261 ma are negative varying widely from 1 3 to 16 1 this data indicates the melting of yangtze block basement rocks and the mixing of magmas generated both from the mantle and from the crust occurred at the periphery of the plume in the main phase of emeishan lip magmatism this study verified that the plume induced uplift exposed carbonates as well as the mafic and felsic rocks generated by the emeishan plume to long periods of intense weathering under humid tropical conditions the weathering remnants of the high alumina magmatic rocks and carbonates were deposited on or transported to the paleokarst surface and converted to bauxites

mineralogical and geochemical evolution of the bidgol bauxite deposit zagros mountain belt iran implications for ore genesis rare earth elements fractionation and parental affinity the present study focuses on the late cretaceous bidgol bauxite deposit in the zagros simply fold belt sw iran the orebody is located in the eroded major nw se trending koh e hosseyn anticline and hosted as discontinuous stratified layers and lenses within the upper member of the cenomanian turonian sarvak formation detailed mineralogical analysis reveals that diaspore hematite goethite anatase clinochlore chamosite and calcite are the major mineral components accompanied by minor amounts of detrital and ree bearing minerals such as rutile zircon and parisite the ore texture suggest that the bauxite material has an authigenic origin but in some parts it has been transported short distances from a primary in situ environment and redeposited in karstic depressions the spheroidal pisolites of the bidgol bauxite formed under conditions of low water activity favouring the formation of large diaspore cores and a single dry to wet climatic fluctuation the mass change calculations relative to the immobile element ti show that elements such as si fe mg k na and sr are leached out of the weathered system al ni zr ga cr and ba are concentrated in the residual system and hf ta co rb cs be and u are relatively immobile during the bauxitisation processes the nb th y v sc sn and ree are relatively immobile in the initial stage of bauxitisation processes in the bauxite ores but were slightly mobile at the later stage of bauxitisation geochemical data reveal progressive enrichment of the ree and intense lree hree fractionation toward the lower parts of the bauxite profile cerium behaves differently from the other rees especially lree and show positive anomalies in the upper horizons that gradually become negative in the deeper parts of the profile the distribution and fractionation of trace elements and rees during the bauxitisation process in the bidgol deposit are mainly controlled by the presence of ree bearing minerals fluctuations in soil solution ph ree ionization potential and the presence of bicarbonates or organic matter geochemical analyses confirm a protolith contribution from the bedrock argillaceous limestone and suggest that the source material for the bidgol bauxite was provided from a siliciclastic material derived from a continental margin the mid turonian uplift led to the formation of karstic topography rubbly breccia and a layer of ferruginous argillaceous debris that was affected by lateritic weathering under humid tropical climate subsequently mobile elements are removed from the profiles while al fe and ti are enriched resulting in the formation of the pristine bauxite materials when the platform subsided into the water again the pristine bauxitic materials were partly converted to bauxite during the exposure of bauxite orebodies on the limbs and crests of anticlines and subsequent eroding and accumulation in the karstic depressions during folding and faulting in oligocene miocene important factors such as intensity of the weathering drainage and floating flow may have improved the qualities of the bauxite ores

long term observation of in situ seismic velocity and attenuation 1 we conducted 1 year continuous measurements of in situ compressional wave velocity and attenuation across a distance of 12 m in a vault at the coast of miura bay japan using a piezoelectric transducer as the ultrasonic wave source we detected for the first time periodic variations in both velocity and attenuation with amplitudes of 0 3 and of 4 respectively corresponding to the diurnal and semidiurnal lunar and solar tides these variations correlate well with the in situ areal strain change due to tidal ocean loading estimated from the strain records about 100 m away from the observational site relative minimum velocity and relative maximum attenuation occur at every time of relative maximum areal strain expansion suggesting that opening closure of pores or cracks of in situ rocks is responsible for these periodic variations the velocity variation shows a remarkable 14 day periodicity corresponding to the spring and neap tides arising from a nonlinear response of the velocity change to tidal strain change such that the velocity change depends on how slowly the tidal dilatation departs from its peak value

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

chemical characteristics and evolution of the laterite profile in hazaridadar bauxite plateau madhya pradesh india a chemical study of the laterite profile developed over basalts in the hazaridadar plateau in madhya pradesh india is presented based on data obtained from intensive exploration in ascending order the profile consists of lithomarge saprolite laterite and bauxite with laterite the formation of the profile essentially involves desilication and hydration in absolute terms there is no major gain or loss in tio 2 and al 2 o 3 judging from the chemical character of the different zones the profile has been evolved by gradual in situ weathering of basic rocks under favorable conditions it is postulated that the profile has been developed in three distinct stages first formation of lithomarge by partial desilication and hydration has been followed next by the formation of a laterite horizon with a fixed composition in terms of al 2 o 3 fe 2 o 3 desilication is more or less complete in this stage finally differential leaching of al 2 o 3 and fe 2 o 3 and the downward migration of the latter have resulted in the formation of a zone of bauxite within the laterite at the top and another of laterite at the bottom the latter showing evidence of deposition of secondary fe 2 o 3 zones favoring free movement of water in the top levels of the laterite are suggested as favorable horizons for enrichment in al 2 o 3

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

thorium isotopes in the western mediterranean sea an insight into the marine particle dynamics we present a detailed view of the 230 th 232 th systematics in the western mediterranean sea in order to constrain water and particle fluxes the conclusions obtained at the regional scale are also relevant at a more global scale although they may be more difficult to establish in the open ocean 230 th and 232 th were analyzed in size fractionated seawater and marine particle samples collected in the ligurian alboran and ionian seas the 230 thxs 230 th produced by the radioactive decay of 234 u in seawater profiles at dyfamed and in the alboran sea site are not linear due to the formation of deep waters the difference of 230 thxs concentration between these two sites is related to the aging of the water masses and to different scavenging conditions the 230 th 232 th ratio is used as a tracer during mixing processes to provide information on the pathways followed by the matter in the water column at dyfamed filtered 6 0 2 wm and ultrafiltered 6 1 kda solutions have similar 230 th 232 th ratios suggesting that an equilibrium exists between truly dissolved and colloidal th the change of the th flux and of the 230 th 232 th ratio of trapped particles observed in august between 200 m and 1000 m is best explained by aggregation of filtered large particles on the trapped particles the residence time of filtered large particles with respect to aggregation on trapped particles is of the order of 8 80 days the combined budget of 230 th and 232 th inputs to the western mediterranean sea requires the dissolution of 3 5 of the th associated with all the continental particulate inputs including particles sequestered in margins suggesting that eolian inputs are not the only source of refractory elements to the mediterranean sea and may be to the whole ocean fl 2002 elsevier science b v all rights reserved

the scavenging of u 230th and 231pa during pulsed hydrothermal activity at 20 s east pacific rise abstract uranium th and pa isotopes were measured in eight box cores from two transects to the west of the east pacific rise at 10 s and 20 s sediment geochemistry al ca fe mn and water column paniculates mn suggest that highly metalliferous plumes rich in fe and mn are emanating from the rise crest at 19 s measurements of 230thxs and 231paxs indicate decreasing sediment accumulation rates from the rise flank 0 4 cm ky 1 to the tiki basin 0 23 cm ky 1 over this geographical area al is found to have a constant flux of 3 6 10 4 g cm 2 ky 1 application of an al constant flux model to ridge crest metalliferous sediment reveals two 1 000 year pulses of hydrothermal activity during the holoccne since 11 000 y bp these hydrothermal pulses are characterised by hydrothermal fe mn ratios 3 5 1 enhanced 230th and 231pa scavenging and low 230thxs 231paxs ratios 3 4 the similarity of the 230thxs and 231paxs ratio to the dissolved seawaterrauo suggests that in fracuonation of the isotopes occurs during scavenging supplementary supply of dissolved 230th and 231pa in a westwards moving water mass is suggested

transformation from permian to quaternary bauxite in southwestern south china block driven by superimposed orogeny a case study from sanhe ore deposit abstract permian karstic bauxite and its quaternary derivative in western guangxi southwestern south china block possess a total tonnage greater than 0 5 billion tons the primary late permian karstic bauxite formed in reduced environment in the background of tethyan accretionary orogenesis and as one consequence of cenozoic convergence of the indian and eurasia continents the primary orebody was uplifted eroded and re sedimented within quaternary laterite the geochemical variation and its controls during the ore transformation from permian to quaternary remain poorly understood quaternary ore blocks comprise an inner zone of fresh ore and then it gradually transited through a middle zone to a margin with extensive weathering one such bauxite block was selected and further subdivided into twenty three samples for geochemical and mineralogical analysis the inner and middle zones contain similar mineralogical compositions dominated by diaspore and amesite with minor illite anatase goethite pyrite zircon and rutile the margin is composed of diaspore with small amounts of amesite boehmite illite goethite anatase kaolinite zircon rutile and barite bauxite in all three zones is composed of mainly al si fe and ti and high contents of zr cr li f s zn v sr nb ba and ree variations in fe2 and fe3 between the three zones were observed the elements si al fe2 mg ba cr f li ni zn and ree decrease from the core of the ore block outwards corresponding to an increase in s and fe3 depletions in si al fe2 mg ba and cr were caused by the dissolution of amesite most of the al and si in amesite were lost during the weathering and minor retained to form kaolinite depletions in li ni and zn resulted from changes in the depositional environment between the late permian and quaternary dissolution of ree bearing fluorocarbonates resulted in depletions of ree and f the enrichment of fe3 and s was related to the precipitation of goethite hematite and barite in an oxidizing environment while local enrichment of ce resulted from the redox change of ce3 ce4 under the same condition this shows that the chemical composition of laterite enwrapping the bauxite also took part in quaternary bauxite transformation this study shows that the elements migrations during bauxite transformation were influenced by multiple independent factors except for the elemental attributes

fractals in petrology abstract a fractal power law distribution is the only statistical distribution applicable to a scale invariant process one of the major problems in petrology is the distribution of trace elements in the earth s crust extreme values of this distribution result in ore deposits there is accumulating observational evidence that tonnage grade statistics of ore deposits are often fractal power law rayleigh distillation and chromatographic models can explain power law fractal distributions for the extreme values of trace element concentrations an alternative fractal approach to problems in petrology is to use self affine fractals the standard approach is to take a fourier transform of a continuous signal an example would be the concentration of a mineral along a linear track if the fourier coefficients scale as a power law of the wavelength the distribution is a self affine fractal many well logs give this result multifractal analyses can also be applied to problems in petrology

uncertainties in passive seismic monitoring the use of passive seismic techniques to monitor oil field completion and production processes is on the rise stress changes induced by such reservoir activities as hydraulic fracturing water injection or fluid extraction will often result in failure of the rocks with a concurrent release of seismic energy in the form of compressional p and shear s waves passive seismic monitoring is based on recording these emitted waves and then using their arrival times to estimate the location of the failure events

natural and anthropogenic radionuclide distributions in the nansen basin artic ocean scavenging rates and circulation timescales abstract determination of the naturally occurring radionuclides 232 th 230 th 228 th and 210 pb and the anthropogenic radionuclides 241 am 239 240 pu 134 cs and 137 cs in water samples collected across the nansen basin from the barents sea slope to the gakkel ridge provides tracers with which to characterize both scavenging rates and circulation timescales in this portion of the arctic ocean large volume water samples 15001 were filtered in situ to separate particulate 0 5 m and dissolved th isotopes and 241 am thorium 230 displays increases in both particulate and dissolved activities with depth with dissolved 230 th greater and particulate 230 th lower in the deep central nansen basin than at the barents sea slope dissolved 228 th activities also are greater relative to 228 ra in the central basin residence times for th relative to removal from solution onto particles are 1 year in surface water 10 years in deep water adjacent to the barents sea slope and 20 years in the eurasian basin deep water lead 210 in the central basin deep water also has a residence time of 20 years with respect to its removal from the water column this texture of scavenging is reflected in distributions of the particle reactive anthropogenic radionuclide 241 am which shows higher activities relative to pu in the central nansen basin than at the barents sea slope distributions of 137 cs show more rapid mixing at the basin margins barents sea slope in the south gakkel ridge in the north than in the basin interior cesium 137 is mixed throughout the water column adjacent to the barents sea slope and is present in low but detectable activities in the eurasian basin deep water in the central basin at the time of sampling 1987 the surface water at all stations had been labeled with 134 cs released in the 1986 accident at the chernobyl nuclear power station in the 1 year since the introduction of chernobyl 134 cs to the nansen basin it had been mixed to depths of 800 m at the barents sea slope and to 300 m in the central basin prechernobyl inventories of 137 cs as well as 239 240 pu are 10 times those expected from global atmospheric fallout from nuclear weapons testing and are derived principally from releases from the sellafield u k nuclear fuel reprocessing facility on the irish sea based on the sources of 137 cs to the nansen basin mixing time scales are 9 18 years for the upper water column to 1500 m and 40 years for the deep water these mixing time scales combined with more rapid scavenging at the basin margin relative to the central basin produce residence times of particle reactive radionuclides in the nansen basin comparable to other open ocean areas e g north west atlantic despite the presence of permanent ice cover and long periods of low light levels that limit productivity in the arctic

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

li b rich rhaetian metabauxite tuscany italy reworking of older bauxites and igneous rocks abstract li b rich metabauxite layers occur in two outcrops of talus metabreccias intercalated between norian and liassic marbles in the alpi apuane tuscany italy field evidence petrographical geochemical and paleogeographic paleoclimatologic considerations suggest that bauxitic material was derived from a multistage reworking of late carboniferous early autunian primary deposits now completely removed the identified lithotypes are cookeite rich metabauxite cookeite bearing metabreccia chloritoid schist and chloritoid phyllite the mg content of calcite and the si content of muscovite and mineral assemblages indicate temperatures of 350 380 c pressures of f o 2 values of 10 30 to 10 24 for the alpine metamorphism in comparison with the average mesozoic bauxite of bronevoy et al 1985 the metabauxite is strongly enriched in si k ca mg li b be ni and ce it shows comparable contents of co la eu tb ta and th it is depleted in ga cr v zn mn hf u and is strongly depleted in sr f cu a metabauxite layer shows decreasing abundance of fe and ga from bottom to top with a pattern opposite to that of primary bauxite deposits inverted profile the strong enrichment of li and b is not related to evaporitic conditions since the mgo na 2 o and sr contents are too low and indicator minerals such as dravitic tourmaline albite and scapolite are missing during the permian volcanic products similar to the coeval peralkaline peraluminous rocks of corsica sardinia were widespread in tuscany b li rich minerals were produced by circulation of hot hydrothermal fluids within the permian volcanic rocks during and soon after their emplacement the erosion of such hydrothermal products supplied detrital material to the talus metabreccia

controls on seawater 231pa 230th and 232th concentrations along the flow paths of deep waters in the southwest atlantic measurements of dissolved th 230 pa 231 and th 232 were made for twelve full depth profiles along a southwest atlantic section during geotraces cruise ga02s sampling captures all the main atlantic deep water masses along their meridional flow paths and allows insight into the control on th and pa in a setting where waters are flowing in opposing directions with direct relevance to understanding the use of pa 231 th 230 as an ocean circulation proxy water column th 230 increases linearly with depth in line with expected reversible scavenging models pa 231 increases from the surface to similar to 1200 1500 m but is invariant or decreases with greater depth deviating from the behavior expected for reversible scavenging dissolved pa 231 th 230 ratios display a mid water column maximum at similar to 1000 2000 m which is broadly coincident with upper circumpolar deep water below 2000 m nuclide distributions and ratios exhibit no dependence on water mass nor any indication of progressive change within a water mass challenging the use of pa 231 th 230 as a past circulation tracer in the south atlantic calculation of horizontal transport of th 230 and pa 231 by ocean circulation indicates a net southward export out of the atlantic of 19 of the pa 231 and 3 of the th 230 produced in that ocean this removal is all from the north atlantic while in the south atlantic removal to sediment equals production simple one dimensional modeling can simulate th 230 profiles but not the mid water column maximum observed in pa 231 profiles suggesting an additional source of pa 231 perhaps lateral transport from the margin or removal at depth due to bottom scavenging near seafloor minima in concentrations indicates bottom scavenging of th 230 and 231 pa which is enhanced in the presence of nepheloid layers particularly for 231pa this additional scavenging fractionates th 230 and pa 231 and in the presence of nepheloid layers may lead to an increase in sedimentary pa 231 th 230 ratios th 232 concentrations were paired with th 230 derived residence times in the upper 250 m of the water column to test the application of th as a tracer of dust deposition maxima in th 232 indicate high dust input from the african and possibly south american continents

natural and anthropogenic radionuclide distributions in the northwest atlantic ocean we have used in situ pumps which filter large volumes of sea water through a 1 m cartridge prefilter and two mno2 coated cartridges to obtain information on dissolved and particulate radionuclide distributions in the oceans two sites in the northwest atlantic show subsurface maxima of the fallout radionuclides137cs 239 240pu and241am although the processes of scavenging onto sinking particles and release at depth may contribute to the tracer distributions comparison of predicted and measured water column inventories suggests that at least 35 50 of the pu and241am are supplied to the deep water by advection the depth distributions of the naturally occurring radionuclides232th 228th and230th reflect their sources to the oceans 232th shows high dissolved concentrations in surface waters presumably as a result of atmospheric or riverine supply activities of232th decrease with depth to values 0 01 dpm 1000 l 228th shows high activities in near surface and near bottom water due to the distribution of its parent 228ra dissolved230th produced throughout the water column from234u decay increases with depth to 3000 m values in the deep water 3000 m are nearly constant 0 6 0 7 dpm 1000 l and the distribution of this tracer and perhaps other long lived particle reactive tracers as well may be affected by the advection inferred from pu and241am data the ratio of particulate to dissolved activity for both230th and228th is 0 15 0 20 this similarity precludes the calculation of sorption rate constants using a simple model of reversible sorption equilibrium moreover in mid depths228th tends to have a higher particulate dissolved ratio than230th suggesting uptake and release of230th and228th by different processes this could occur if228th produced in surface water were incorporated into biogenic particles formed there and released as those particles dissolved or decomposed during sinking 230th produced throughout the water column may more closely approach a sorption equilibrium at all depths 230th 241am and239 240pu are partitioned onto particles in the sequence th am pu with 15 of the230th on particles compared with 7 for am and 1 for pu distribution coefficients kd are 1 3 1 6 107 for th 5 6 106 for am and 7 10 105 for pu the lower reactivity for pu is consistent with analyses of pu oxidation states which show 85 oxidized v vi pu however thekd value for pu may be an upper limit because pu like228th may be incorporated into particles in surface waters and released at depth only by destruction of the carrier phase

distribution of 230th in the labrador sea and its relation to ventilation abstract measurements of dissolved and particulate230th and232th by thermal ionization mass spectrometry were made on samples collected from the labrador sea and the denmark strait and iceland scotland overflow waters the large scale feature of low and invariant230th evident in deep waters of the labrador sea and previously observed in the deep northern atlantic can be reproduced using a reversible scavenging model that includes the effect of ventilation advective transport also must be important in the redistribution of230th in other regions of the atlantic and for other long lived tracers such as231pa 26al and10be

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

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

a multifractal analysis of mineralization characteristics of the dayingezhuang disseminated veinlet gold deposit in the jiaodong gold province of china abstract the gold concentration distributions along drifts in the dayingezhuang fault controlled disseminated veinlet gold deposit in the jiaodong gold province eastern china has been analyzed using a multifractal technique with the aim of better understanding the ore forming processes some intensely mineralized areas show small gold singularities representing compact concentration distributions which is resulted from intense stress release and development of abundant microfractures with various sizes several intensely and moderately mineralized areas are characterized by isolated distributions of lower concentrations suggesting that only relatively large microfractures locally develop resulted from less intense stress release some barely and moderately mineralized areas show isolated distributions of higher concentrations due to occurrences of only a few fractures or large microfracture most barely mineralized areas are characterized by dense concentrations distributions because the widespread development of relatively small microfractures caused by weak stress release thus making the areas unsuitable for gold deposition these characteristics reflect that variable development of the structures is responsible for different gold mineralization within the deposit the ratios between the singularity a q and its fractal dimension f a q for the different drifts vary similarly as q 0 8 or q 0 8 thus from the multifractal viewpoint it is suggested that gold enrichment processes are consistent in both mineralized and barely mineralized areas despite their differing mineral intensities

downhole receiver function a case study receiver function is defined as the spectral ratio of the radial component and the vertical component of the ground motion it is used to characterize converted waves we extend the use of the receiver function to downhole data using waves recorded in a borehole excited by an earthquake of magnitude 4 0 near san fran cisco california on 26 june 1994 the focal depth of the event was 6 6 km and the epicenter was located at a distance of 12 6 km from the borehole array six three component sensors were located at different depths in a borehole to extract a co herent response of the near surface from the incoherent earthquake waves we de convolve the waves recorded by the sensors at different depths with the waves recorded by the sensor on the surface deconvolution applied to the waves in the s time window recorded by the radial component result in an upgoing and adowngoing wave propagating with s wave velocity for the waves in the p time window re corded by the radial component deconvolution also gives an upgoing and a down going wave propagating with s wave velocity this interesting result suggests a p to s conversion at a depth below the deepest sensor to diagnose this we compute the receiverfunction forthe borehole recording of the earthquakewaves thereceiver function shows an upgoing wave with an arrival close to time t 0 for the deepest sensor the agreement of the upgoing wave in the receiver function with the travel time curve for the p to s converted wave calculated using the p and the s wave velocity profile supports the hypothesis of a pronounced p to s conversion we present a synthetic example to illustrate that the first arrival of the receiver function applied to borehole data gives the upward propagating p to s converted wave to corroborate the observation of the mode conversion we apply receiver function to a different earthquake data recorded by the same borehole array in 1998 the focal depth of the event was 6 9 km and the epicenter was located at a distance of 13 km from the borehole array the receiver function for these data also show an upgoing wave with a pulse close to time t 0 at the deepest sensor the moveout of the upgoing wave agrees with the travel time curve for the p to s converted wave hence supporting our observation of the mode conversion

the water column distributions of thorium isotopes in the western north pacific abstract four vertical profiles of 230 th and 228 th were determined using large volume water samples in the western north pacific an almost linear increase of 230 th with depth was observed for all of the profiles for which the unidirectional first order scavenging model was difficult to explain we developed a model which included a dissolved particulate transformation as well as parameters of the scavenging model application of the model to the vertical distributions of total and the geosecs particulate th isotopes 230 th and 234 th yielded the residence time of dissolved th with respect to adsorption to particles and the turnover time of particulate th to be 235 days and 57 days respectively the th isotopes appeared to be carried down the water column by fine particles with a mean settling velocity of 1 m day which continually release th into sea water as well as pick up th from the water along their journey to the bottom for 228 th a large excess over 232 th was observed throughout the water column with pronounced high concentrations in surface and bottom waters suggesting that the 228 th was derived from 228 ra diffused out of sediments the vertical distributions of 228 th seemed to be significantly influenced by lateral mixing along isopycnals

millennial scale climate changes manifest milankovitch combination tones and hallstatt solar cycles in the devonian greenhouse world sub milankovitch rhythmic features in sedimentary records have been reported from throughout geological time however their origin remains enigmatic in particular during so called greenhouse periods in earth s history to better understand such short term climatic changes we sampled two 3 m thick intervals of early devonian hemipelagic carbonate at 1 cm resolution in the pod barrandovem section czech republic greenhouse conditions prevailed during early devonian times and the chosen resolution enables the detection of millennial scale climate change as recorded by elemental abundances we used a previously published astrochronology for the section to transform the studied series from the stratigraphic into the time domain spectral analysis of the time calibrated log transformed ti records reveal obliquity and precession cycles confirming the applied astrochronology additional spectral peaks with periods of 2 3 2 7 6 8 and 10 12 k y appear in both records furthermore a 1 5 k y periodicity close to the pleistocene dansgaard oeschger oscillation is also identified but only in the record with higher accumulation rate 3 5 cm k y bi coherence spectra reveal that the 6 8 and 10 12 k y periodic components are combination tones of milankovitch cycles we infer the shorter 2 5 k y periodicity to be the result of solar forcing related to the hallstatt cycle these new observations strengthen the case for an external origin of millennial scale features