the rare earth element ree mineralisation potential of highly fractionated rhyolites a potential low grade bulk tonnage source of critical metals abstract the rare earth elements ree have become crucial for modern industry technology and medicine with the increase in demand for these elements over the past few years currently being met by relatively few well known mineral deposits this lack of a secure supply of the ree has led to increased research into potential alternative sources of these in demand elements the primary fractionation processes involved in the petrogenesis of highly fractionated high silica rhyolites can cause the magmas that form these units to become preferentially enriched in the ree especially in the more valuable heavy ree hree although this is dependent on the mineral assemblages fractionated by the system in question a factor that is in turn a function of the source and tectonic setting of a given magmatic event the mineralogy of the ree is also important with volatile exsolution and vapour phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the ree and other elements into concentrations and more importantly potentially acid leachable and therefore processable minerals that may be economically viable to extract this combined with the fact these rhyolites are often enriched in other critical and or economically important metals e g y nb ta be li f sn rb th and u means that these volcanic units should be considered as potential sources of these critical metals in addition the large volume nature of these rhyolites combined with the fact they frequently crop out at the earth s surface makes them ideally suited for more economical bulk open pit extraction this suggests that these high silica ree enriched rhyolites should be considered potential ree analogues of bulk tonnage low grade porphyry cu deposits warranting further investigation to determine whether these rhyolites are a viable new source of the ree especially the hree and are potential targets for future mineral exploration

characterization of high molecular weight organic matter in marls of the salt iv formation of the mulhouse basin high molecular weight organic matter of six marl samples of the mulhouse basin has been characterized the kerogen asphaltene and polar fractions were analysed by flash pyrolysis gc ms in addition sulphur rich geomacromolecules present in the polar fractions were also desulphurized with raney ni and the released hydrocarbons were characterized by gc ms the kerogen and asphaltene pyrolysates are dominated by linear and isoprenoid alkanes and alkenes most likely derived from aliphatic biopolymers of algae algaenans and contain moderate to low amounts of alkylated thiophenes marls deposited under hypersaline conditions contain more organically bound sulphur and less isoprenoid algaenans in their kerogen asphaltene fractions than marls deposited under less saline conditions high contributions of terrestrial organic matter are not revealed by abundant alkyl phenols in the pyrolysates desulphurization of sulphur rich geomacromolecules present in the polar fractions yields hydrocarbons with distributions different from those of the free saturated hydrocarbons but the amounts released are low relative to the hydrocarbons present as such

an analytical solution for circular tunnels excavated in rock masses exhibiting viscous elastic plastic behavior abstract investigating time dependent behavior of tunnels driven in rocks has been the topic of interest for many years the majority of researches were conducted with the assumption that the behavior of the surrounding rock masses is viscoelastic in this paper an analytical solution is proposed for circular tunnels under hydrostatic stress field whose surrounding rock mass is isotropic homogenous obeying viscous elastic plastic constitutive model it is assumed that the rate of excavation is infinitely large therefore the solution is proposed for unlined tunnels when the advance of tunnel face is halted or after lining installation when the tunnel face is far from the studied section the results were compared with those predicted by finite difference numerical model which exhibited a good agreement for both lined and unlined tunnels except for large times where numerical model results slightly exceed the values predicted by the proposed solutions for lined tunnels

hydrocarbon biomarkers of different lithofacies of the salt iv formation of the mulhouse basin france forty nine samples from an 11 m section of the salt iv formation of the tertiary mulhouse basin alsace france covering six different lithotypes marl nodular lenticular laminated and massive anhydrite halite were analysed for hydrocarbon biomarkers the hydrocarbon biomarker assemblages are dominated by acyclic isoprenoids especially phytane 0 13 pr ph 0 52 n alkanes with specific distribution patterns and steranes large differences in their distributions indicate significant changes in the palaeoenvironment the largest changes observed are those in the desmethyl and methylsterane distributions and are probably linked to an occasional reconnection of the evaporite basin with the sea leading to an input of dinoflagellate algae 3 methylsteranes are present in all samples studied and their carbon number distribution mimics that of the 5 desmethylsteranes in line with previous suggestions that they are diagenetic products of sterols with a sugar unit at c 3 biosynthesized from dietary sterols the increase in relative abundance of the 3 methylsteranes during periods of marine incursions suggests that these precursors are biosynthesized by marine organisms variations in biomarker composition between the different lithofacies are minor probably because the organic matter is mainly associated with the marl and all lithotypes contain a marl component detailed subsampling of two marl layers and subsequent analysis indicated that the changes on a small time scale are minor to those on a larger time scale

allanite and other ree rich epidote group minerals epidote group minerals rich in rare earth elements ree in particular allanite are common accessory phases in igneous metamorphic metasomatic and sedimentary rocks small amounts of ree are present in most epidote group minerals but in allanite and the related minerals dissakisite ferriallanite dollaseite khristovite and androsite the ree are essential structural constituents an important characteristic of ree rich epidote group minerals is that their octahedrally coordinated m sites contain major amounts of divalent cations this paper summarizes literature data for these minerals and discusses their chemistry occurrence phase relations and petrologic and geologic significance the chapter emphasizes allanite because it is the most common and best studied of the ree rich epidote group minerals epidote group minerals contain isolated silicon tetrahedra and corner sharing groups of two tetrahedra and are thus assigned to the disilicate or sorosilicate structural family for a detailed description of the structure see franz and liebscher 2004 the epidote group structural formula is a2m3 sio4 si2o7 o f oh or in a simplified form a2m3si3o11 o f oh in which a ca sr pb2 mn2 th ree3 and u and m al fe3 fe2 mn3 mn2 mg cr3 and v3 deer et al 1986 there are two structurally different a sites a 1 and a 2 with different coordination numbers and there are three different m sites m 1 m 2 and m 3 which are all octahedrally coordinated ueda 1955 dollase 1971 in epidote group minerals trivalent ree are accommodated in the a sites which in endmember epidote both contain ca the incorporation of ree3 is commonly charge balanced by a divalent cation fe2 mn2 mg substituted for a trivalent one in the m sites table 1

geochemical alteration of pyrochlore group minerals pyrochlore subgroup primary alteration of uranpyrochlore from granitic pegmatites is characterized by the substitutions adyd acayo anayf acayo and anayoi i acayo alteration occurred at 450 650 c and 2 4 kbar with fluid phase compositions characterized by relatively low ana high aeah and high ph in contrast primary alteration of pyrochlore from nepheline syenites and carbonatites follows a different tre nd represented by the substitutions anayf adydand acayo adyd in carbonatites primary alteration of pyrochlore probably took place during and after replacement of diopside forsterite calcite by tremolite dolomite t ankerite at 300 550 c and 0 2 kbar under conditions of relatively low ahf low ana low aeah low ph and elevated activities of fe and sr microscopic observations suggest that some altered pyrochlor1es are transitional between primary and secondary alteration alteration paths for these specimens scatter around the trend anayf adyd alteration probably occurred at 200 350 c in the presence of a fluid phase similar in composition to the fluid present during primary alteration but with elevated activities of ba and rees mineral reactions in the system na ca fe nb o h indicate that replacement of pyrochlore by fersmite and columbite occurred at similar conditions with fluid conpositions having relatively low ana moderate aeah and moderate to high afeh secondary alteration 150 c is charactlerizedby the substitutions anayf adyd acayo adyd and acaxo adxdtogether with moderate to extreme hydration 10 15 wt h20 or 2 3 molecules per formula unit minor variations in the amounts of mg ai k mn fe sr ba and rees are commonly observed as a result of secondary alteration major cation exchange for k sr and ba is a feature of samples from laterite horizons overlying carbonatites in most cases u th and b site cations remain relatively constant radiogenic pb is typically lost via long te rm diffusion but in some grains of uranpyrochlore 25 90 of the pb is lost as a result of alteration

pyrochlores from the lueshe carbonatite complex democratic republic of congo a geochemical record of different alteration stages abstract magmatic pyrochlores from the lueshe syenite carbonatite complex from the northeastern part of democratic republic of congo ex zaire are characterized by ta nb ratios in an increasing order from pyroxenite calcite carbonatite sovite silicate xenoliths nodules to syenite substitutions involving nb ta ti and ree have been precisely described hydrothermal alteration of lueshe pyrochlore involves the substitution of na f va vy and ca o va vy va a site vacancy and vy y site vacancy in calcite carbonatite hydrothermal alteration of pyrochlore took place during and after the precipitation of ancylite ce strontianite celestite baryte and fayalite according to a fluid composition of relatively low ph a na a ca 2 and a hf and high a sr 2 and a lree 3 the supergene alteration is characterized by complete leaching of na ca and f and partial incorporation of k ba sr and ce resulting in the formation of kali bario strontio and ceriopyrochlore respectively the na poor pyrochlore may be an intermediate variety corresponding to an alteration stage between the hydrothermal and weathered pyrochlores the ir spectroscopic study has indicated that the weathered pyrochlore is a hydrated variety containing two bands of oh vibration modes at 3413 and 1630 cm 1 during hydrothermal and supergene alterations the cations at b site remain relatively constant the variable chemical compositions of the pyrochlores from the lueshe complex represent geochemical memories of the different alteration conditions including the variation in the oxidation reduction environment

polar constituents of organic matter rich marls from evaporitic series of the mulhouse basin abstract a suite of marl samples from the evaporitic series of the mulhouse basin france lower oligocene was studied for its biomarker content in particular its polar constituents novel series of 3 carboxyalkyl steranes and 15 oxo triaromatic ketones were identified by synthesis the 3 carboxyalkyl steranes probably originate from highly polar precursors yet unreported in living organisms our data suggest that micro algae could be the major source of these compounds which seem to be indicators of high algal input rather than characteristic of evaporitic environments the 15 oxo triaromatic ketones could be oxidation products of triaromatic steroid hydrocarbons formed during diagenesis although their formation during work up procedure could not be excluded

reappraisal of anoxia and organic richness with emphasis on cretaceous of north atlantic accumulation of anoxic sediments in the north atlantic during barremian through turonian time early to middle cretaceous was controlled mainly by local conditions although global climatic and oceanographic factors played a supporting role evidence does not support the popular hypothesis developed over the past few years of global or oceanwide anoxia data which contradict this hypothesis are based on 1 a reevaluation of criteria for identifying sediments that accumulated in anoxic water 2 a critical reappraisal of reported worldwide occurrences of anoxic sediments of these ages and 3 an examination of the spatial and temporal distribution of anoxic sediments in the north atlantic and elsewhere a model is proposed in which the earliest anoxic sediments of cretaceous age in the north atlantic were deposited in deep restricted basins by middle cenomanian time about 97 m y ago sluggish circulation had led to a gradual expansion of the oxygen minimum layer permitting deposition of anoxic sediment in nonbasinal settings as well expansion of the oxygen minimum layer caused the calcite compensation depth to rise promoting oxidation of organic carbon and causing contraction of the oxygen minimum layer development of anoxia was thus self damping anoxia effectively disappeared by early senonian time 88 m y ago when improved circulation created oceans more like those of the present some evidence indicates that enhanced biologic productivity and upwelling may have been local factors in fostering anoxia but the early and middle cretaceous were generally not highly productive times

organic matter of the mulhouse basin france a synthesis the lower oligocene evaporite sequence of the mulhouse basin france contains organic matter rich marl deposits these marls display an overall cyclic variation of sedimentation rate organic carbon content hydrogen index and selected molecular parameters over a 30 m thick stratigraphic interval the integration of all sedimentological and geochemical parameters has allowed the reconstruction and characterization of the paleoenvironment of deposition the marls were deposited in a perennial lake that was at times connected to the sea two organic facies end members could be assigned to a lake stage with a marine connection and a lake stage that received dominantly continental water input the overall stratigraphic variation in the organic matter content is interpreted to reflect the adaptation of the oligocene flora to the changing paleoclimate and environmental conditions

the aqueous geochemistry of the rare earth elements and yttrium 4 monazite solubility and ree mobility in exhalative massive sulfide depositing environments abstract although there is considerable evidence that rare earth elements ree and particularly the light ree lree have been mobile in the alteration zones below many massive sulfide deposits there is some disagreement over the cause of this mobility most researchers have argued or implied that the ree were mobilized by analogues of modern seafloor hydrothermal vent fluids however the few measurements that have been made of the ree concentrations of these modern fluids suggest that their ability to mobilize ree is negligible in order to shed further light on this problem we have carried out calculations of monazite solubility monazite is thought to be the principal host for the lree in a model vent fluid at temperatures from 200 to 300 c these calculations show that at 300 c the model fluid will contain 0 08 ppb ce 0 07 ppb la and 0 03 ppb nd at 200 c the concentrations increase to 0 54 ppb 0 37 ppb and 0 15 ppb respectively a decrease in ph of one unit at 300 c also increases ree solubility significantly 7 4 ppb ce 5 7 ppb la and 1 1 ppb nd these solubilities are similar to the concentrations of ree measured in seafloor hydrothermal vent fluids however they are considerably lower than required to account for the scale of ree mobility in alteration zones associated with massive sulfide deposits if the mass ratio of typical hydrothermal vent fluid to rock reached 1000 concentrations of ree in the altered rock the predicted to be in the range

evolution of montviel alkaline carbonatite complex by coupled fractional crystallization fluid mixing and metasomatism part ii trace element and sm nd isotope geochemistry of metasomatic rocks implications for ree nb mineralization abstract magmatic volatiles are critically important in the petrogenesis of igneous rocks but their inherent transience hampers the identification of their role in magmatic and metasomatic processes for example while the role of magmatic volatiles in porphyry copper systems is relatively well understood the behavior of volatiles and metasomatic fluids in mantle and crustal magmatic hydrothermal systems remains a work in progress alkaline carbonatite complexes usually originate from the mantle and typically host ree deposits which are thought to be almost always of a hydrothermal origin the question thus arises as to the origin of the ree and fluids and if the alkaline and carbonatite magmas are accompanied by fluids from the mantle up and through the crust this study presents the results of whole rock trace elements and sm nd isotopes analyses of clinopyroxenites melteigites ijolites melanosyenites leucosyenites granites silicocarbonatites magnesiocarbonatites calciocarbonatites ferrocarbonatites and polygenic breccias from the 1894 ma paleoproterozoic alkaline carbonatite complex of montviel abitibi canada the metasomatic rocks range in ree concentrations from 100 ppm to 3 54 wt and show e nd values ranging from 6 8 to 7 2 based on these results it is demonstrated that volatile saturated magmas at montviel were injected through 4 distinct mantle pulses which evolved by fractional crystallization mixing of depleted mantle and crustal fluids and metasomatism

seasonal succession and microlamina formation in a meromictic lake displaying varved sediments in a small meromictic lake near toronto canada a mass mortality of photosynthetic bacteria followed the ventilation of the chemocline during fall autumn and resulted in 3 8 g m 2 day 1 of organic matter being deposited as a dark layer in sediment traps which were suspended in the permanently anaerobic zone this mass mortality of photosynthetic bacteria occurred in late autumn following the annual thermal destratification of the lake s mixolimnion wind mixing during this period of homeothermy resulted in the introduction of low levels of dissolved oxygen into the lake s chemocline the ensuing mass mortality of photosynthetic bacteria resulted in the release of elemental sulphur as the sulphur rich bacteria decomposed and sank to the bottom of the lake the ferrous ions in the water below a depth of 15 m in crawford lake reacted with this sulphur to form black ferrous sulphides and pyrite which formed a dark microlamina on the lake floor each dark microlamina was overlain by a light coloured calcite rich layer which was deposited each spring and summer during the 3 yr period of this study the mechanism of microlamina formation elucidated here has been based on the examination of bi weekly sediment trap information this approach has permitted an explanation of the mechanisms by which specific events such as calcite precipitation and phytoplankton seasonal succession are transcribed into the sediment record

analytical solution for determining the plastic zones around twin circular tunnels excavated at great depth abstract many existing planar elastoplastic analyses have been limited to the case of only one tunnel excavated in rock mass the mohr coulomb failure criterion which is widely used in rock engineering is considered in this paper to propose an analytical method for determining the plastic zones around twin circular tunnels of equal size excavated at great depth the premise is that the plastic zone around each tunnel can completely enclose the tunnel edge and the two plastic zones are not connected the unknown elastic zone on the physical plane is mapped onto an annular region on the image plane using the conformal transformation in the complex variable method which transforms the problem of determining the elastoplastic interfaces into solving the mapping function coefficients on the basis of the stress continuity conditions along the two elastoplastic interfaces the nonlinear equations about the mapping function coefficients are established and then solved effectively by the differential evolution algorithm in which the coefficients are considered as design variables the presented solution is verified by numerical solution the influence of tunnel spacing cohesion internal friction angle and in situ stresses on plastic zones are analyzed

the chemical and hydrological evolution of the mulhouse potash basin france are marine ancient evaporites always representative of synchronous seawater chemistry abstract brine reaction processes were the most important factors controlling the major ion mg ca na k so 4 and cl evolution of brines in the oligocene mulhouse basin france evaporite basin the combined analysis of fluid inclusions in primary textures by cryo sem eds with sulfate 34 s 18 o and 87 sr 86 sr isotope ratios reveals hydrothermal inputs and recycling of permian evaporites particularly during advanced stages of evaporation in the salt iv member the lower part of the salt iv evolved from an originally marine input the basin was disconnected from direct marine inputs and a series of sub basins formed in an active rift setting where tectonic variations influenced sub basin interconnections and chemical signatures of input waters sulfate 34 s shows oligocene marine like signatures at the base of the member however enriched sulfate 18 o reveals the importance of synchronous re oxidation processes as evaporation progressed other non marine and or marine modified inputs from neighbouring basins became more important this is demonstrated by increases in k concentrations in brine inclusions and br in halite sulfate isotopes trends and 87 sr 86 sr ratios the recycling of previously precipitated evaporites of permian age was increasingly important with evaporation this supports the connection of the mulhouse basin to basins situated north of mulhouse the brine evolution eventually reached sylvite precipitation the chemical signature of the resulting brines is not compatible with global seawater chemistry changes the fast rate of intra and inter basin brine variations as well as the existence of contemporaneous brines with different chemical signatures supports our interpretation the existence of diverse non marine inputs and associated internal chemical changes to the brine preclude the use of trapped brine inclusions in reconstructing oligocene seawater chemistry without previously identifying all inputs the general hydrological evolution of the mulhouse basin is explained as a restricted sub basin with a first marine stage this gradually changed to a 40 marine source at the beginning of evaporite precipitation with the rest of inputs non marine the general proportion of solutes did not change greatly over evaporite precipitation however as the basin restriction increased the originally marine inputs changed to continental or marine modified inputs from neighbouring basins north of mulhouse basin

the elasto plastic response of underground excavations in rock masses that satisfy the hoek brown failure criterion abstract this paper is intended to illustrate the relationship between the hoek brown parameters describing the strength of rock masses and the mechanical response of underground openings a formulation of the elasto plastic behavior of rock in terms of the hoek brown criterion is presented the analysis assumes that the joint system present in the rock mass has no preferred orientation so that the medium can be considered to behave as an isotropic continuum it is shown that appropriate scaling of the hoek brown parameters leads to considerable simplification in defining the elasto plastic response of the rock mass the classical case in which the excavation process is treated as a uniform reduction of internal pressure in symmetrically loaded cylindrical and spherical cavities is considered closed form expressions are given for the extent of plastic behavior and the related stress and displacement fields a dimensionless graphical representation of these solutions is provided that allows accurate estimates of the response of excavations in hoek brown materials to be made quickly and easily examples are given to illustrate the use of the graphs illustrative applications of the derived closed form solutions are also described the construction of ground reaction curves for the design of cylindrical tunnels according to the convergence confinement method and a case study of stability analysis of spherical cavities produced by underground nuclear explosions in french polynesian atolls are discussed

hydrothermal rare earth mineralisation in carbonatites of the tundulu complex malawi processes at the fluid rock interface the tundulu carbonatite complex in southeastern malawi was intruded during the late jurassic to early cretaceous over three episodes during the first and second episodes the major rock types were calcite carbonatites ankerite carbonatites and apatite carbonatites these rocks experienced hydrothermal alteration at the close of the second episode during which quartz baryte veins containing a significant level of rare earth fluorocarbonates were deposited veins in calcite carbonatites contain abundant synchysite la ce nd ca co3 2 f with subordinate amounts of parisite la ce nd 2ca co3 3f2 and bastnaesite la ce nd co3f crystallising in the order synchysite parisite bastnaesite some of the parisite is retrograde in origin having formed as an alteration product from synchysite only synchysite has been identified in veins hosted by apatite carbonatites however bastnaesite predominates the hydrothermal assemblage in ankerite carbonatites parisite and synchysite have been found only as a fibrous fringe between wallrock ankerite and bastnaesite the crystallisation sequence seen in calcite carbonatites represents a progressive depletion of both ca2 and co2 3 in the fluids from which this mineral suite precipitated with ca2 and co2 3 poor phases precipitating last clearly the predominance of bastnaesite in veins hosted by ankerite carbonatites suggests insufficient ca2 and co2 3 in the fluids for the ubiquitous precipitation of synchysite and parisite these observations are consistent with a model in which hydrothermal fluids reacted with the various wallrocks which then released different amounts of ca2 and co2 3 that subsequently reacted with rees in the fluid to form the various fluorocarbonates as such the tundulu carbonatites provide a natural laboratory in which compositional phase relationships of rare earth fluorocarbonates can be related to variations in the activities of ca2 and co2 3 within the ln co3 f caco3 f2 co3 1 system

a molecular stratigraphic approach to palaeoenvironmental assessment and the recognition of changes in source inputs in marls of the mulhouse basin alsace france principal components analysis pca has been used to investigate changes in concentrations of the components of the hydrocarbon fractions extracted from 71 marl samples selected to cover two total organic carbon toc maxima in the lower part of the salt iv formation a lower oligocene evaporitic sequence from the mulhouse basin france the analysis indicates that the fractions can be ascribed as lying between two end member distributions the changes in these distributions are gradual suggesting that they resulted from fairly gradual changes in the depositional palaeoenvironment these changes are related to increased algal productivity associated with the evolution of a restricted lacustrine environment through to one with a greater marine influence systematic variations in the concentrations of selected components relative to the toc profile point to a repeated sequential evolution in the biological assemblage during deposition of the sequence

exact and approximate solutions for displacements around circular openings in elastic brittle plastic hoek brown rock abstract a simple exact solution is presented for the elastic brittle plastic plane strain analysis of displacements around circular openings in an isotropic hoek brown rock subjected to a hydrostatic in situ stress the integration involved in the solution is carried out by using a standard mathematical software results produced by using the present exact method are found to be identical to those obtained by using a recently published closed form but complicated solution based on a transformation technique an extremely simple but approximate closed form solution was earlier derived by making a simplifying assumption for the evaluation of the elastic part of the total strain in the plastic zone several example cases are analyzed to show that the simplifying assumption made in the derivation of the simple closed form solution has an insignificant effect on the results for displacements for practical problems the innovative approximation technique may be used to obtain simple solutions of a wide variety of complex plasticity problems in rock mechanics

ree and their relevance to the development of the kupferschiefer copper deposit in poland abstract over one hundred samples representing mainly clayey organic and carbonate rich shales kupferschiefer but also other members of different ore sections including hangingwall dolomites z1 werra and footwall weissliegend sandstone lower permian have been collected in different mines of the lubin glogow mining district mainly near the contact transitional zone between the copper mineralized zone and secondarily oxidized rote faule rf zone in general the polish kupferschiefer shales are enriched in mree in comparison to nasc in a typical copper rich ore section the ree amounts and patterns depend on lithologies being generally similar in shales and dolomite ree vary among sandstones shales and dolomites average 73 143 and 85 ppm respectively probably reflecting mainly their clay contents sandstones have strongly convex ree patterns with positive eu and negative gd anomalies and depletion in lree and enrichment in mree relative to hree the ree patterns of shale and dolomite are similar to one another and rather flat with strong negative eu anomalies and a small positive gd anomaly in the case of shales the ree patterns of shales from the mineralized cu zone are generally convex mree enriched and have negative eu anomalies however in a section with cu zn and pb shales the ree pattern of pb bearing shales shows a positive eu anomaly in contrast to other shales and overlying dolomite more oxidizing conditions of deposition can be assumed for pb shales no significant differences between ree distributions in transitional and oxidized zones have been observed their ree patterns are more convex and are much higher av 247 ppm than those in the mineralized zone and they do not show eu anomalies the strongly convex pattern may suggest either enrichment in mree or relative depletion in lree due to localized precipitation of light ree minerals both in shales and in the uppermost part of the sandstones two unique sections one cu rich and one cu lean partly oxidized comprising three shale beds interbedded with dolomites have been compared generally ree contents are similar in these two sections also similar are changes in contents of ree between beds in both sections which decrease significantly upwards from 157 171 ppm to 54 60 ppm the ree patterns of the lowermost beds directly overlying sandstones are ramp like with lree enrichments the upper beds have concave ree patterns comparison between sections shows generally stronger negative eu and positive gd anomalies in the highly mineralized section there is a highly significant positive relationship between cu and ree contents in cu rich shales and slightly less significant negative relationship for their concentration in oxidized and transitional shales there is a moderate significant positive correlation between p 2 o 5 and ree contents in cu rich shales the observed differences in ree contents cannot be provenance dependent but have been caused by diagenetic processes possibly related to mineralization and oxidation processes europium anomalies generally reflecting different eh conditions in the deposit can be eliminated by the prolonged oxidation strong enrichment of the rf zones in ree may result from their desorption from large volumes of oxidizing including mineralizing solutions which probably emerged from the underlying molasse lithologies into the rote faule areas higher contents of ree in the lowermost shales suggest upward movement of solutions from the underlying sandstones also far away from the rf areas

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

molecular characterization of organic matter in sediments from the keg river formation elk point group western canada sedimentary basin abstract distributions of free and sulfur bound biomarkers in organic rich sediments from the lower and upper keg river formation elk point group western canada reveal deposition of these sediments under reducing conditions in agreement with the geological data the predominance of aryl isoprenoids of chlorobiaceae origin indicates that photic zone anoxia occurred during time of deposition a series of novel aryl isoprenoids with a carboxylic acid function was identified by gc ms and the structure of the predominant 3 methyl 5 2 3 6 trimethylphenyl pentanoate was proven by synthesis of an authentic standard the occurrence of these acids gives evidence that oxidative breakdown at least partially accounts for the diagenetic fate of aromatic carotenoids li etnh 2 desulfurization of two kerogen concentrates yielded only low amounts of sulfur bound hydrocarbons and suggests that either sulfur sequestration was not a predominant process or more probably that a major part of the hydrocarbons initially sulfurized were released upon maturation giving further evidence that poly sulfide bonds are cleaved at relatively low levels of thermal stress

influence of plastic shear strain and confinement dependent rock dilation on rock failure and displacement near an excavation boundary abstract excavation induced rock failure and displacement near an underground opening boundary is closely associated with rock mass dilation a better understanding of rock mass dilation around the excavation helps us to predict or anticipate displacements and extent and shape of the failed zone and subsequently assist design of proper ground support systems a calibrated cohesion weakening and frictional strengthening cwfs model with a constant dilation angle can capture the stress induced brittle failure shape in hard rocks however the use of a constant dilation angle in either cwfs mohr coulomb perfectly elasto plastic or mohr coulomb strain softening models cannot simulate the displacement distribution near the excavation reasonably in the present study numerical simulations are performed to study excavation induced displacement around tunnels located in different rock mass types i e coarse grained hard rock medium grained hard rock fine medium grained soft rock and fine grained soft rock using a mobilized dilation angle model that depends on both confining stress and plastic shear strain it is illustrated from a few examples that displacement distributions obtained from the dilation angle model are more reasonable when compared with the general trend measured underground

agpaitic nepheline syenites a potential source of rare elements abstract the agpaitic nepheline syenites may with regard to their elevated contents of a number of rare elements be compared with the complex granite pegmatites both rock types form highly evolved magmas under closed system conditions which prevent volatiles from escaping agpaitic rocks are peralkaline nepheline syenites characterized by the presence of complex rare element minerals such as eudialyte and mosandrite instead of the simple minerals such as zircon and ilmenite uranium deposits have been found in agpaitic rocks in brazil pocos de caldas china saima and greenland ilimaussaq nb and apetite deposits in russia lovozero and khibina the type locality of agpaitic rocks the ilimaussaq complex in south greenland is characterized by elevated contents of elements such as zr ree y be li nb u th and f not only in pegmatites late veins and contact fenites but also in some of the rocks especially lujavrite and kakortokite the most important rare element containing minerals are eudialyte zr ree y nb steenstrupine u th ree rinkite nb ree y u pyrochlore and perovskite nb ta li mica li chkalovite be and villiaumite f occurrences of eudialyte rich kakortokite and lujavrite are presently being explored in the ilimaussaq complex as sources of zr ree y and nb

carbonatite associated with ultramafic diatremes in the avon volcanic district missouri usa field petrographic and geochemical constraints abstract here we report field petrographic and geochemical analyses of the southeast missouri avon volcanic district intrusive rocks and present the first combined textural and geochemical evidence for the presence of a primary magmatic carbonatite phase among ultramafic dikes pipes and diatremes of olivine melilitite alnoite and calciocarbonatite the 13 c vpdb values measured for primary calciocarbonatite as well as carbonates in olivine melilitite and alnoite rocks range from 3 8 to 8 2 which are within the typical range of mantle values and are distinct from values of the carbonate country rocks 0 0 to 1 3 the carbonate oxygen isotope compositions for the intrusive lithologies are in the range of 21 5 to 26 2 vsmow consistent with post emplacement low temperature hydrothermal alteration or kinetic fractionation effects associated with decompression and devolatilization metasomatized country rock and breccia contaminated igneous lithologies have carbonate 13 c vpdb values gradational between primary carbonatite values and country rock values unaltered sedimentary dolomite breccia and mafic spheroids entrained by calciocarbonatite and the lack of microstratigraphic crystal growth typical of carbonate replacement also exclude the possibility of hydrothermal replacement as the cause of the magmatic textured carbonates rare earth element ree patterns for the alnoite olivine melilitite and carbonatite are similar to each other with strong light ree enrichment and heavy ree depletion relative to morb these patterns are distinct from those of country rock rhyolite and sedimentary carbonate these data suggest that rocks of the avon volcanic district represent a single ultramafic carbonatite intrusive complex possibly derived from a single mantle source

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

convergence of circular tunnels in elastoplastic rock masses with non linear failure criteria and non associated flow laws abstract this work provides new findings on the theory of non associated plasticity applied to the study of convergence in tunnels it focuses on elasto plastic rock masses with linear and non linear strength criteria and associated and non associated flow laws it seeks to obtain the characteristic rock mass curve based on the convergence confinement method the results that are obtained are compared to other calculation procedures detailed mathematical expressions are proposed for implementation in a computer spreadsheet

palaeoclimate controlled accumulation of organic matter in oligocene evaporite sediments of the mulhouse basin abstract marl beds of a 30 m thick interval of the oligocene evaporites of the mulhouse basin display a cyclic variation in their organic carbon content that is related to changes in sedimentation rate the construction of a time scale suggests a duration of 58 000 30 yr for the interval studied calculated accumulation rates for organic matter of aquatic origin are used to assess the fluctuation of palaeoproductivity of the system the observed variation of the accumulation rates of terrigenous organic matter throughout the studied interval is most likely linked to variations in palaeoclimate

shallow water evaporitic environments and their source rock potential in the major evaporitic environments on the world s surface today most organic matter accumulates in shallow subaqueous to seasonally subaerially exposed algal mat sediments given the present depositional setting and the most likely flushing by oxidizing water it is unlikely this organic matter could be preserved to form source rocks however if we place such evaporite deposition into a geologic context then there are times in the past when source rocks could have formed in shallow water settings such settings were characterized by hydrological conditions which allowed the retention of hypersaline anoxic pore waters to depths where the organic material was buried deeply enough to generate hydrocarbons when deep basin shallow water evaporite successions were laid down in basins such as the mediterranean in the late miocene the michigan basin in the silurian and other large saline giants then conditions were right for the formation of source rocks within shallow water and salt flat evaporitic environments the evaporites in these saline giants were deposited under conditions of relatively shallow water 50 m the basin never appears to have dried out but water levels changed quickly nearly equal 10 000 years from shallow to deep continual water saturation coupled with saline pore fluids prevented the inflow of fresh oxidizing groundwater into the basin center of shallow water organic rich evaporites immature hydrocarbons derived from such rocks today drip from the 5 5 m y evaporites of sicily in active salt and sulfur mines organic rich sediments could also be preserved to generate hydrocarbons in rapidly subsiding rift basins in such basins rapid burial has prevented the entrance of fresher oxygenated waters and the associated degradation and destruction of the organic matter the early continental riff stage generates the source rocks the ephemeral streams wadis and dune fields generate the reservoirs and the subsequent evaporite stage seals the reservoir

the mulhouse basin evidence from porphyrin distributions for water column anoxia during deposition of marls abstract marls from the evaporitic mulhouse basin oligocene alsace france contain alkyl porphyrins dominated by nickel complexed species the presence in high relative abundance of a range of components with carbon numbers up to c 37 indicates that anaerobic photosynthetic bacteria made a significant contribution to the photosynthetic community in the palaeoenvironment and in turn that anoxic conditions extended into the photic zone of a stratified water column further evidence is given by the assignment by hplc coinjection with a standard of a c 34 component with the same carbon skeleton as one of the bacteriochlorophylls d of such bacteria significant differences in the nickel and vanadyl porphyrin distributions in one of the samples examined appear to result from changes in the depositional environment which are recorded with a stratigraphic resolution below that sampled or indicate derivation of these two porphyrin pools from different parts of the water column

na fe ca alteration and lree th nb mineralization in marble andgranitoids of sierra de sumampa santiago del estero argentina the jasimampa area in the sierra de sumampa de santiago del estero argentina contains light rare earth element lree th nb mineralization associated with several stages of carbonates and widespread fenitization of marble granite 496 2 9 ma and alkaline and siliceous igneous comendite dikes u pb zircon age of 390 ma derived from fractionation of oceanic island basalts this is the third discovery of lree mineralization in argentina and marks a new alkaline intracontinental magmatic event of devonian age albite ab 97 99 aegirine ae 70 92 ja 1 11 q 6 19 hematite mg arfvedsonite fluorine rich apatite and late ca fe mn carbonates monazite pyrochlore overprint and crosscut granite and comendite outcrops in a 15 km 2 area locally the na rich assemblage is pervasive and results in total destruction of host rocks na fe metasomatism near granite and comendite produced aegirine ae 86 91 ja 1 8 q 6 11 mg arfvedsonite and minor albite ab 98 99 in adjacent marble with multiple stages of late ca mn mg fe carbonates associated with iron and manganese oxides hematite and traces of sulfides sphalerite pyrite galena monazite ce is the main lree bearing mineral and occurs with minor ferrocolumbite pyrochlore strontiopyrochlore and apatite associated with a second generation of fine grained hematite barite and celestine structural controls on na fe ca alteration and lree mineralization in granitoid and marble protoliths include brittle ductile shear zones brittle fracture systems and a series of monolithologic and heterolithologic breccias with hydrothermal aegirine carbonate and chalcedony matrices that occur at granite marble comendite contacts fragments of multiple breccia types within breccias indicate multiple episodes of brecciation alteration and mineralization the fluid responsible for early fenitization of granite and comendite was aqueous carbonic with co 2 of relatively high density between 0 85 and 0 95 g cm 3 salinity near 9 wt percent nacl equiv and minimum temperatures in the range of 250 to 280 c pervasively altered comendite and granite have high total ree content 1 750 ppm and 2 126 ppm respectively mainly lree early banded and mottled aegirine arfvedsonite replacements of marble have high absolute ree abundance 2 513 4 663 ppm compared to the least altered marble 476 ppm subsequent hydrothermal stages with carbonates hematite pyrolusite monazite and subordinate celestine and barite caused alteration of marble that was accompanied by an increase in absolute ree abundance up to 15 45 wt percent and high sr 10 5 wt th 4 390 ppm and ba 1 8 wt alteration and mineralization at jasimampa are the result of late stage carbonatitic magma fractionation and fluid exsolution this is indicated by the strongly alkaline character of early alteration the composition of the hydrothermal carbonates apatite and lree sr and ba rich minerals the chondrite normalized ree patterns showing strong lree enrichment without an eu anomaly and the replacement of marble by assemblages with very high ba th lree and sr and strong k zr and ti depletions the alteration style and mineralization at jasimampa are similar to the giant fe lree nb deposit bayan obo and other hydrothermal lree deposits hosted in carbonatites of china

geochemical study of laterites of the jamnagar district gujarat india implications on parent rock mineralogy and tectonics abstract the laterite deposits occur in a linear stretch along the northern arabian sea coast in the jamnagar and porbandar districts of gujarat state india these deposits are characterised by presence of gibbsite kaoline calcite quartz anatase natroalunite goethite and hematite and relicts of mafic minerals and plagioclase on the basis of petro mineralogy and geochemistry these deposits are grouped as aluminous laterites fe2o3 1 45 3 84 av 3 13 al2o3 39 31 57 24 av 45 80 and laterites fe2o3 9 84 32 21 av 25 13 al2o3 34 74 49 59 av 41 27 the major trace and ree characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic andesitic composition and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation the correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements the jamnagar laterite deposits occur as capping over the deccan trap basaltic lava flows and pyroclasic deposits lateritisation prevailed during palaeocene age when india was separated from the seychelles and passing over the equator during this time climate morphology and drainage conditions were favourable for lateritisation that result in the formation of jamnagar and other laterite deposits within the deccan province flood basaltic provinces of deccan columbia north australia and hawaii appear good location for hosting laterite deposits due to their wide areal extent small geological time span and uniform chemical composition however comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate morphology and drainage are equally important factors for facilitating lateritisation

lacustrine varve formation through time abstract studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes if the bottom waters of a lake are partly or totally anoxic the seasonally deposited materials are preserved as annual groupings of laminae varves common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin precipitated carbonate minerals diatom frustules iron rich and manganese rich flocs autochthonous organic detritus and autochthonous and allochthonous materials resuspended from the bottom the style of varving has changed over geologic time reflecting changes in biologic evolution and types of materials available precipitated iron rich laminations were common in the middle precambrian graded sets of clastic organic laminations persisted through the precambrian prior to the evolution of bioturbating benthic organisms glaciolacustrine varves appear to have retained their distinctive character through time carbonate rich varves occurred sporadically in the precambrian and phanerozoic with the exception of diatoms major components of modern lacustrine varves were present through the paleozoic and mesozoic and yet varves are rare in strata of these ages and may have accumulated in marine to brackish water environments diatoms were introduced into lacustrine systems in early tertiary time and are common components of varves from then on diatom laminae combined with a greater chance for geologic preservation of younger lake deposits have increased the number of geologically young occurrences of varved sediments however seasonal associations of modern varve components and the processes they represent are present in ancient deposits and provide clues to the interpretation of ancient environments

analytical solution for a circular opening in an elastic brittle plastic rock abstract this paper deals with the analytical solutions for the prediction of displacements around a circular opening in an elastic brittle plastic rock mass compatible with a linear mohr coulomb or a nonlinear hoek brown yield criterion three different cases of definitions for elastic strains in the plastic region used in the existing solutions are mentioned the closed form analytical solutions for the displacement in the plastic region are derived on a theoretically consistent way for all the cases by employing a non associated flow rule the results of the dimensionless displacements are compared using the data of the soft and hard rocks to investigate the effect of different definitions for elastic strains with the dilation angle