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

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

nano mineralogy and geochemistry of high grade diasporic karst type bauxite from parnassos ghiona mines greece abstract in the present work a combination of various techniques is utilized for the study of nano mineralogy and geochemistry of high grade karst type bauxite al rich and fe depleted samples al2o3 ca 80 wt from the parnassos ghiona mines located in greece initial characterization using pxrd and electron microscopy in microscale and mesoscale sem eds including stem mode proved the presence of fe cr ti containing diaspore anatase and minor rutile the study by means of 57fe mossbauer spectroscopy in correlation with magnetic susceptibility measurements and complemented with synchrotron based spectroscopies at the microscale sr micro xrf and micro xanes exafs indicated that fe3 in contrast to 6 cr3 is not exclusively a component of the diaspore structure while cr3 substitutes al3 in octahedral sites of diaspore 6 cr3 6 al3 the electron microscopy in nanoscale tem eds eels revealed that fe exists in the form of peculiar fe3 bearing nanominerals most likely maghemite type phases between 25 and 45 nm in size in addition to the fe3 ions substituting al3 in the diaspore structure moreover it was proven that tio2 polymorph mineral nanoparticles particularly rounded anatase mesocrystals and nanocrystals and individual needle shaped rutiles are dispersed into the diaspore matrix thus diaspore in the studied bauxite concerns in fact a distinct fe3 cr3 alooh low t authigenic phase demonstrated for the first time in literature on the other hand the observed tio2 mineral nanoparticles formed together with diaspore during diagenesis and fe nanominerals formed during epigenesis were hitherto unknown not only for the allochthonous karst type bauxite deposits of greece but also for the overall bauxite deposits worldwide

trace and rare earth elements constraints on the sources of the yunfeng paleo karstic bauxite deposit in the xiuwen qingzhen area guizhou china abstract a number of carboniferous paleo karstic bauxite deposits occur in the xiuwen qingzhen area central guizhou province which constitute an important part of the central guizhou southern chongqing bauxite belt in southwestern china these deposits consist of lenticular and stratiform orebodies hosted in the lower carboniferous jiujialu formation which lies unconformably above carbonate rocks mainly dolomite of the middle and upper cambrian loushanguan group shilengshui formation and lower cambrian qingxudong formation although it is generally agreed that the bauxite resulted from weathering of cambrian rocks below the unconformity it remains unclear whether the carbonates alone can provide sufficient material for the formation of the deposits in this study we examined the mineralogy and major trace and rare earth elements geochemistry of bauxite and bauxitic clays from the yunfeng deposit in the xiuwen qingzhen area and compared them to previously published data of a paleo weathering profile consisting of loushanguan dolomite underlying the sub carboniferous unconformity and the black rock sequence of the lower cambrian niutitang formation in order to evaluate the sources of the bauxite the bauxite ores are composed of diaspore as the main ore mineral along with small amounts of pyrite arsenopyrite galena stibnite xenotime and uranium bearing minerals and are characterized by high contents of uranium and phosphorus chondrite normalized ree patterns and various bivariant diagrams commonly used to study the provenance of bauxite including eu eu vs tio2 al2o3 eu eu vs sm nd tio2 vs al2o3 tio2 th th vs ta th vs nb and nb vs ta suggest that the loushanguan dolomite and the niutitang black rock sequence are both potential source rocks however a comparison in u and th contents between the paleo weathering profile of the loushanguan dolomite and the bauxite samples suggests that the dolomite alone cannot provide the materials for the bauxite ores instead the black rock sequence may have contributed most of the ore forming materials which are mainly transported from source regions where the niutitang formation was exposed weathered and eroded therefore the yunfeng bauxite deposit is of mixed autochthonous and allochthonous origin

metabauxite horizons containing remobilized origin gem diaspore and related mineralization milas mugla province sw turkey abstract remobilized origin gem diaspore and related minerals occur as infill within structurally controlled voids that developed in the upper of two distinct karst unconformity type metabauxite diasporite horizons in the ilbir mountains area of the milas mugla province sw turkey colour change diaspore trademarked as zultanite and associated mineral specimens greenish muscovite chloritoid donbassite specular hematite ilmenite goethite and younger calcite occur in fracture zones veins and open structures that cross cut the metabauxite horizons the mineralized fracture zones do not extend into the enclosing marbles probably because of the ductility contrast between the brittle bauxite and relatively plastic carbonate beds thick white to light gray and dark gray limestone beds were deposited in the ilbir mountains area during the cretaceous 146 65 ma and contain two stratigraphically distinct karst fill bauxite horizons al fe si and ti rich solutions that infiltrated the karstified limestone probably originated from altered schist and gneiss that surround the basin the limestone beds 2000 m thick were subjected to burial metamorphism forming marble subsequently the marble block was folded during nappe emplacement toward the ssw as part of late alpine contractional deformation during the paleogene 65 23 8 ma the upper bauxite horizons within the folded block were cross cut by fracture zones because of their relatively brittle rheology at this time increased pressure and temperature in the bauxite horizons resulted in remobilization of the primary constituents of the bauxite within an aqueous complex resulting in the crystallization of coarse grained assemblages in the cross cutting structures ultimately erosion and mineral exploration revealed the steeply dipping bauxite outcrops and mine workings evident today this paper focuses on the mine geology of surface outcrops of diasporic bauxite the upper bauxite horizon within underground mine galleries at elevations of 600 632 637 642 652 657 and 702 m and in open pits at sites in the kucukcamlik and buyukcamlik hills milas mugla province sw turkey

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

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

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

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

experimental tests of middle palaeolithic spear points using a calibrated crossbow abstract controlled experiments using a calibrated crossbow to thrust stone tipped spears into animal carcasses reveal a relationship between levallois point morphology and their performance as spear points a comparative study of morphometric variation of levallois points from levantine mousterian contexts supports the hypothesis that the demand for stone spear points was an important factor in levallois point production

palaeosols in early himalayan foreland basin sequences demonstrate latitudinal shift related long term climatic change the palaeogene sedimentary record in the himalayan foreland basin contains palaeosols that are interpreted as reflecting changes in climate through time with the passage of the indian plate from the equator to 30 n latitude to understand spatial and temporal variation in the occurrence of diagnostic palaeosol types 12 exposed stratigraphic sections were investigated and studied in detail using petrographic and geochemical techniques including scanning electron microscopy and x ray mineralogy oxisol bauxite is a karst bauxite that occurs in crudely bedded and laminated forms it contains gibbsite goethite and kaolinite and shows chemical index of alteration values close to 100 demonstrating intense weathering no gradual change in the concentrations of trace and rare earth elements is recorded however their behaviour suggests that the oxisol was produced by weathering of basalt under a warm and humid climate histosol coal found stratigraphically higher than oxisols contains woody structures dominated by vitrinite maceral the histosol is interpreted as having originated from an undisturbed peat developed in a swamp of high tree density under wet tropical climatic conditions up section calcrete profiles of stages 3 and 4 containing rhizoliths pellets filamentous calcite and microcodium have developed by pedogenic processes large negative stable carbon 8 5 to 11 2 and oxygen isotope values 8 5 to 12 6 suggest that the studied calcretes formed under the influence of meteoric water and soil organic matter in dry sub tropical climatic conditions the formation of oxisol in a warm and humid climate was possible in the equatorial region when part of the indian subcontinent was close to the equator the coal developed under a humid climate when the northern tip of the indian subcontinent reached the intertropical convergence zone while the pedogenic calcrete formed once the sub tropical climatic zone was reached hence it is suggested that these palaeosols formed in different climatic zones during northward drift of the indian plate and that the drift brought them to their present positions between 30 n and 35 n within the sub tropical climatic zone

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

quantifying lithic curation an experimental test of dibble and pelcin s original flake tool mass predictor this paper describes an experimental test of a method proposed by dibble pelcin 1995 for reconstructing the original flake mass from striking platform dimensions the results of this test indicate that while there is a correlation between flake mass and flake attributes for hard hammer lithic production systems using the specific variables identified by dibble pelcin exterior platform angle and platform thickness consistently underestimates original flake mass the reasons for this discrepancy and possible future research directions to resolve it are explored

combined tectonic and paleogeographic controls on the genesis of bauxite in the early carboniferous to permian central yangtze island abstract two bauxite horizons with a total reserve of 1 29 bt occur in the lower carboniferous and lower permian in the central south china block different from other intracontinental bauxites in china which are genetically linked to the orogenesis along the continental margin these bauxites were generated in the absence of marginal orogenesis the genesis of these bauxites were studied based on tectonic paleogeographic and paleoclimatic controls the orebody in huofengchong hfc region is hosted within the lower carboniferous which overlies upon the cambrian dolomite unconformably the orebody in the regions of yanfengba yfb and baiyantou byt occurs in lower permian which overlies upon the silurian shale or devonian dolomite unconformably the mineral assemblages in the carboniferous hfc bauxite consist of diaspore illite anatase and in permian yfb and byt bauxite the minerals are diaspore anatase illite clinochlore and kaolinite the data from the u pb isotope measurements of detrital zircons from these bauxites provide two main ages 1 a maximum u pb age peak of ca 800 ma from the carboniferous hfc and 2 a maximum age peak of ca 1100 ma for the permian byt and yfb the ca 800 ma detrital zircons from the carboniferous bauxite are dominating in the paleozoic sedimentary units which likely derive from the erosion of the mid to neo proterozoic felsic volcanic and intrusive rocks panxi hannan arc occurring in the western margin of the south china block by contrast the zircons with ages of ca 1100 ma are prevalent in the paleozoic sediments from the center of the block the above results indicate that the lower carboniferous and lower permian bauxites are sourced from the sedimentary rocks in the western and central parts of the south china block respectively despite the difference in the provenance these two episodes of deposits were both deposited in a tidal flat restricted platform attached to an ew trending yangtze island occupies the western to central parts of the south china block this indicates that the shift from a marginal to central uplift within the paleo island from early carboniferous to early permian has induced the transition in the provenance of the source material in addition the weathered materials from the two provenances both accumulated in the coastal region receiving further bauxitization the bauxitization was boosted by the persistent preferable tepid and humid paleoclimate defined by the equatorial position of south china block and the drop of global temperature during the metallogenic period

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

chronological and behavioral contexts of the earliest middle stone age in the gademotta formation main ethiopian rift there is a general consensus that our species emerged first in africa currently the best known skeletal evidence for the earliest anatomically modern homo sapiens amhs derives from sites in the rift valley in ethiopia however archaeological evidence from cave sites in southern and northern africa largely dominates discussions on behaviors that characterize the dawn of modern humans later middle pleistocene open air sites in east africa present unparalleled geochronological control and thus a better chance to study hominin behavior here we present results of a multidisciplinary investigation of the archaeology and geochronology of one of the oldest known middle stone age msa occupations from the gademotta formation fm in the main ethiopian rift renewed excavation lithic analysis fracture mechanics and tephrochronological investigations at gademotta provide a better understanding of the chronological and behavioral contexts during the critical period immediately preceding the origin of our species

gem quality transparent diaspore zultanite in bauxite deposits of the ilbir mountains menderes massif sw turkey several m thick karst unconformity type metabauxite horizons in the ilbir mountains of sw turkey host open space mineralization of gem quality diaspore trademarked as zultanite associated with muscovite hematite ilmenite chloritoid and younger calcite the hydrothermal metamorphogenic mineralization occurs in fracture zones veins and open structures that crosscut the metabauxite horizons but does not extend into the marble host rocks the white to dark gray marble sequence over 2 000 m in thickness is of cretaceous depositional age and was affected by alpine paleogene tectonometamorphism which caused the hydrothermal remobilization of primary bauxite components into crosscutting structures

the application and misapplication of mass analysis in lithic debitage studies the technique of debitage mass analysis based upon size grades of debitage populations is shown to be prone to errors when making interpretations about the kind of tool produced or the kind of lithic reduction technology used significant sources of error may originate from differences in individual flintknapping styles and techniques raw material size and shape variants and mixing of debitage from more than one reduction episode these sources of error render debitage mass analysis ineffective for determining the kind of stone tool reduction activities practiced at excavated sites mass analysis may be effective for determining artifact reduction sequences if it is used on debitage from a single reduction episode or part of a reduction episode however it is shown that mass analysis when used for assessing reduction sequence information must also control for the effects of raw material variability assemblage mixing and flintknapping styles

source and path of magma for volcanoes in the subduction zone of northeastern japan the assumption that the source of magma for volcanoes in subduction zones is located in the mantle immediately above the top of the subducting slab at approximately 100 km depth and straight beneath the volcanoes is incorrect in northeastern japan the combination of evidence from velocity tomography in the mantle wedge above the slab and mapping of earthquake size distribution within it strongly points to a source of fluids at the top of the slab at 140 to 150 km depth from where material rises along an inclined path to the volcanoes

the technology of stone age colonization an empirical regional scale examination of clovis unifacial stone tool reduction allometry and edge angle from the north american lower great lakes region abstract there is now broad consensus that the appearance of clovis in northeastern north america great lakes new england represents a colonization pulse into recently deglaciated landscapes due to the increased resource uncertainty that comes with colonizing unfamiliar landscapes it was hypothesized that the majority tool component of clovis assemblages unifacial stone tools should have been knapped on tool blanks possessing the design properties of longevity and functional flexibility to facilitate exploration mobility and guard against the absence of toolstone sources in the new landscape these properties are optimized by large flat flakes possessing large surface area relative to flake thickness since discarded and at times exhausted unifacial stone tools do not preserve the original dimensions of the blank upon which they were created necessary items for a true test of blank morphology selection this study presents a set of predictions for inferring whether clovis unifacial stone tool blanks were selected for the properties of longevity and functional flexibility based on evidence that clovis people actually capitalized on those properties due to the nature of clovis unifacial stone tools tool size was of necessity used as a proxy for tool reduction on the grounds that smaller tools are more likely to have been resharpened than larger tools at least in the case of unifacial flake tools the results showed that less resharpened tools possessed flatter less spherical shapes than the more resharpened tools which possessed more globular spherical shapes suggesting clovis foragers exploited the retouch potential afforded by the larger flatter blanks edge angles showed no relationship with tool reduction suggesting that clovis foragers exploited the functional flexibility afforded by flatter blanks by adjusting the edge angle to be either higher or lower as needed these results are consistent with the notion that human colonizers who did not know the abundance or location of stone outcrops prior to settling an unfamiliar territory not only geared up before leaving a stone source but geared up as efficiently as possible by carefully selecting the blanks they chose to carry broader implications for such careful unifacial stone tool blank selection are discussed

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

content and mode of occurrences of rare earth elements in the zagrad karstic bauxite deposit niksic area montenegro abstract three vertical sections through the zagrad deposit of jurassic karst bauxite in central montenegro have provided knowledge of the vertical distribution of major and some selected trace elements including rare earth elements ree variations in the mineralogy particularly those hosting ree have been studied this has revealed the presence of authigenic mineral phases such as xenotime mottramite and monazite best proved using raman microprobe analysis as well as residual phases such as zircon titanite and monazite the mobility of the elements during bauxitization processes has been studied to show that the ree minerals ensure progressive concentration of these elements during removal of major elements through weathering the similarity of normalized ree in the bauxite to the typical post archean australian shales paas and upper continental crust ucc profile and the preserved eu anomaly are evidence that the bauxite was not derived from carbonates and represents alteration of shale marly limestone and volcanogenic or proximal igneous sourced detritus that accumulated in the original karst landform mass change during bauxitization using ti as index element and compared to paas composition revealed almost 100 depletion of si and weak enrichment in al deeper parts of the deposit with authigenic minerals exhibit very strong enrichment in all ree the bauxite ores have high ree contents 693 5 6953 4 ppm especially lree contents 582 8 4882 9 ppm while hree contents 106 6 2070 5 ppm are much lower

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

deep structure of the northeastern japan arc and its relationship to seismic and volcanic activity evidence for possible deep seated magmatic activity beneath northeastern japan can be obtained from seismic observations tomographic inversions of p wave velocity data show low velocity zones distributed in the crust and upper mantle beneath active volcanoes in or around these zones anomalously low frequency micro earthquakes perhaps caused by magmatic activity are found at depths of 25 40 km distinct s wave reflectors corresponding to the upper surfaces of magma bodies are found at depths of 10 18 km large crustal earthquakes also occur around the low velocity zones these observations reveal the distribution of magma reservoirs at depths and elucidate its relation with shallow seismicity beneath volcanic arcs

estimating original flake mass from 3d scans of platform area this study confirms the increased capacity to predict flake mass that arises from more accurately measuring surface area in three dimensions using a digital scanner we also reveal the existence of significantly different relationships between platform area and flake mass for flakes with different platform types and ventral and dorsal morphologies these different relationships between platform surface area and mass have not been previously identified and reveal the complexity of platform mass relationships using multivariate regression of 3d platform surface area and external platform angle we improve the accuracy of predictions of original flake mass we propose a method for studying reduction intensity on retouched flakes based on comparing predictions of the initial mass of the flake with measurements of the mass following retouching to estimate the amount of mass removed through retouching we name this approach the initial terminal mass comparison or itmc our experiments demonstrate that the capacity of the 3d platform scans to predict flake mass and by implication the capacity of the itmc to estimate mass loss rivals or exceeds the capacity demonstrated for existing reduction measures

geological geochemical and mineralogical characteristics of ree bearing las mercedes bauxite deposit dominican republic abstract bauxite deposits traditionally the main source of aluminum have been recently targeted for their remarkable contents in rare earth elements ree with ree lanthanoids sc y concentrations systematically higher than 1400 ppm av 1530 ppm the las mercedes karstic bauxites in the dominican republic rank as one of the ree richest deposits of its style the bauxitic ore in the las mercedes deposit is mostly unlithified and has a homogeneous massive lithostructure with only local cross stratification and graded bedding the dominant arenaceous and round grained texture is composed of bauxite particles and subordinate ooids pisoids and carbonate clasts mineralogically the bauxite ore is composed mostly of gibbsite and lesser amounts of kaolinite hematite boehmite anatase goethite chromian spinel and zircon identified ree minerals include cerianite and monazite ce whose composition accounts for the steady enrichment in light relative to medium and heavy ree of the studied bauxites considering the paleo geomorphology of the study area we propose that bauxites in the las mercedes deposit are the product of the erosion and deposition of lithified bauxites located at higher elevations in the bahoruco ranges based on the available data we suggest a mixed lithological source for the bauxite deposits at the district scale bedrock carbonates and an igneous source of likely mafic composition

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting

geochemical and mineralogical features of karst bauxite deposits from the alborz zone northern iran implications for conditions of formation behavior of trace and rare earth elements and parental affinity abstract the present study focuses on three outcrops of upper permian to lower jurassic karst bauxite deposits in the alborz zone north of iran the deposits occur as sharp semi continuous lenses within the upper permian ruteh formation gheshlagh and the upper triassic elika formation siahrudbar and separdeh carbonate rocks textural characteristics such as pelitomorphic matrix local ooidic pisoidic fluidal and clastic textures indicate authigenic allothigenic origins mineralogically kaolinite boehmite goethite and hematite in the gheshlagh diaspore hematite and kaolinite in the siahrudbar and kaolinite hematite goethite diaspore siderite and chamosite in the separdeh deposits are the main phases the distribution patterns of major elements normalized to the upper continental crust ucc depict enrichments of al fe and ti in all three deposits the three deposits are variably enriched in transition trace elements cr ni co v u th and high field strength elements ga hf zr nb y relative to ucc the studied bauxites have average concentrations of rare earth elements ree la lu between 305 97 and 373 69 ppm geochemical data reveal progressive enrichment of ree and an intense lree hree n fractionation toward the lower parts of the profile in the separdeh deposit due to the alkaline conditions of the carbonate bedrock and irregular distribution patterns at the gheshlagh and siahrudbar deposits due to water level and ph fluctuations the positive ce anomalies at separdeh and siahrudbar suggest oxidizing conditions in the upper parts of the profiles at gheshlagh the negative to nil ce anomalies reflect low intensity of oxidation based on previous geochemical analysis data the upper permian basalts in the gheshlagh and the upper triassic basalts in the separdeh and siahrudbar areas were the most likely source materials the local uplift of the permian upper triassic series led to the formation of karstic topography filled with materials derived from weathering of the basaltic rocks under humid tropical paleoclimate the initial weathering converted the source rocks to kaolinitic soils characterized by the enrichment of al fe and ti then they were transferred to the karstic depressions and sinkholes and underwent in situ leaching and desilicification bringing about a relatively higher ore grade the overall field and petrographic evidence demonstrate that these deposits were formed in shallow and swampy environments in the eastern part of the alborz zone at siahrudbar and gheshlagh better drainage conditions have enhanced the quality of ores