geochemistry of cassiterite and wolframite from tin and tungsten quartz veins in portugal cassiterite and wolframite compositions from snnw and wnsn bearing quartz veins in northern and central portugal are compared to provide evidence on fluid compositions in snnw bearing quartz veins euhedral cassiterite shows sequences of alternating parallel darker and lighter zones the darker zones are pleochroic oscillatory zoned exhibit exsolutions of columbite and ixiolite and are richer in nb ta and fe than the lighter zones which consist of nearly pure sno2 cassiterite from wnsn bearing quartz veins is usually zoned with homogeneous and slightly pleochroic darker zones which are chemically similar to lighter zones bothzoneshaveinclusionsofrutileandrareilmenite thedarkerzonesofcassiteritefrom theformer veins arericherin nb taandfe contents and poorer in ti than the darker and lighter zones of cassiterite from the latter veins this is attributed to differences in the composition of magmatic hydrothermal fluids wolframite compositions from snnw and wnsn bearing quartz veins do not show any significant distinction because they precipitate from relatively similar magmatic hydrothermal fluids in some deposits most wolframite crystals are homogeneous but others are heterogeneous inner patches rich in a hubnerite component rarely occur in crystals from the filharoso and panasqueira deposits zoned crystals showing an increase in fe and a decrease in mn from core to rim were found in the vale das gatas deposit complex oscillatoryzonedcrystals occur inthe carris deposit later wolframite contains inclusions ofscheelite partially replaces itand is richer in fe and poorer in mn than earlier wolframite wolframite from snnw bearing quartz veins in the argozelo deposit and wnsn bearing quartz veins from vale das gatas and panasqueira deposits has significant nb content this does not depend on the fe and mn content of the wolframite but w content is negatively correlated with nb content only very rare single crystals of wolframite show an increase in w and a decrease in nb from core to rim snnw bearing quartz veins contain wolframite poorer in nb than the darkerzones of cassiterite which exsolved columbite andixiolite inwnsn bearing quartz veins from panasqueira and vale das gatas the wolframite has a higher nb content than the cassiterite which contains rutile inclusions enriched in nb because cassiterite and wolframite are derived from two distinct magmatic hydrothermal fluids of different age the fluid responsible for wolframite precipitationwillhaveasimilarcompositiontothatresultingfromtheevolutionofthefluidresponsibleforcassiteriteprecipitationinthe

metallogenesis at the carris w mo sn deposit geres portugal constraints from fluid inclusions mineral geochemistry re os and he ar isotopes abstract the carris orebody consists of two partially exploited w mo sn quartz veins formed during successive shear stages and multipulse fluid fillings they cut the variscan post d3 geres i type granite the most important ore minerals are wolframite scheelite molybdenite and cassiterite there are two generations of wolframite the earlier generation of wolframite is rare and has the highest wo4mn content 91 mol and the most common wolframite contains 26 57 mol wo4mn re os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 1 2 ma and 280 3 1 2 ma respectively which are in very good agreement with the previous id tims u pb zircon age for the carris granite 280 5 ma 3he 4he ratio of pyrite ranging between 0 73 and 2 71 ra 1 ra 1 39 10 6 and high 3he 36ar 0 8 5 10 3 indicate a mixture of a crustal radiogenic helium fluid with a mantle derived fluid the fluid inclusion studies on quartz intergrown with wolframite and scheelite beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit the first was a low to medium salinity aqueous carbonic fluid co2 between 4 and 14 mol with less than 1 95 mol n2 which was only found in quartz associated with wolframite the other was a low salinity aqueous fluid found in all the four minerals the homogenization temperatures indicate minimum entrapment temperatures of 226 310 c average 280 c for the h2o co2 n2 nacl fluid and average temperatures of 266 c for scheelite and 242 c 190 c and 160 c for the last generations of beryl fluorite and quartz respectively it was estimated that wolframite was deposited 7 km depth assuming a lithostatic pressure probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event precipitation of scheelite and sulphides took place later at the same depth but under a hydrostatic or suprahydrostatic pressure regime and probably caused by mixing between the magmatic hydrothermal fluid and meteoric waters that deeply penetrated the basement during post variscan decompression

lead isotope and pb pb model age determinations of ores from central europe and their metallogenetic interpretation the paper presents lead isotope data from 211 samples from phanerozoic lead bearing ore occurrences in central europe particularly from the southern part of the former german democratic republic the data are interpreted in terms of amov s dynamic model of continuous lead isotope evolution the relationships between thoro genic and urano genic model ages and the source of lead in different regional units are discussed we observed differences in lead isotope evolution in the hercynian internides and externides within the moldanubian and saxothuringian zones we distinguish five main lead bearing ore associations 1 cambrian stratiform base metal hermsdorf waldsassen 206pb 204pb 17 50 17 70 2 devonian vein type sb bearing metamorphogene neumuhle hartmannsdorf 17 80 18 00 3 upper carboniferous permian polymetallic including tin vein type kutna hora freiberg altenberg 18 00 18 20 4 triassic jurassic pb ba vein type st ibro halsbrucke 18 20 18 60 5 cenozoic polymetallic vein type riftogene roztoky banska stiavnica 18 80 19 10 pb isotope characteristics from ores of the montagne noire and the brioude massiac district correspond to this subdivision ore associations from the rheno hercynian zone display higher 207pb 204pb ratios which can be explained by more evolved and less metamorphosed source rocks mineralizations of the eastern harz strasberg neudorf belong to the permian association those from the western harz clausthal bad grund to the triassic jurassic because of pb isotope agreement the stratabound rammelsberg and the vein bound ramsbeck i mineralization are presumed to be isogenetic pb isotope identity of distinct mineralizations in the basement zone halsbrucke bad grund and in the triassic sediments gorny slask mechernich bleiglanzbanke suggests a strong genetic coherence pb isotope conformity between the upper carboniferous permian triassic ore associations and hercynian postkinematic granitoids and lamprophyric rocks also favours a close relationship pb isotope and other data indicate crustal sources as the age of the ore associations decreases crustal influences generally increase apart from the roztoky mineralization

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

ore deposits of the french massif central insight into the metallogenesis of the variscan collision belt the french massif central fmc represents the whole west european variscan wev belt in terms of both the geodynamic evolution and the metallic content thus a study of the metallogenic evolution of the fmc may elucidate the conditions that allow the mineralisation of a collision belt since recent collision belts e g the himalayas or the alps show that mineralisation does not necessarily result from the collision process the palaeozoic history of the fmc is divided into three geodynamic stages unevenly involved from the metallogenic view point the eo variscan stage cambrian to silurian was not important the meso variscan stage devonian early carboniferous was of limited importance and most of the mineralisations formed during the neo variscan stage late carboniferous early permian in addition some more mineralisation was produced during the mesozoic because of the thermal reactivation linked with the alpine orogenies

water in granite and pegmatite forming melts article i nfo in this paper we have compiled water concentration data obtained from melt inclusion in minerals mostly quartz and topaz from granites and pegmatites a small number of data come from analysis of natural glasses about 4600 melt inclusions are from granites and about 2100 melt inclusions are from pegmatites another 4159 values are from melt inclusions and glasses of rocks with more than 66 g g sio2 are added belonging to a recent compilation the total of 10 859 melt inclusions provides a statistically significant basis from which to derive some conclusions generally the water concentration in granite melt inclusion is b10 g g with three maxima at 4 0 1 3 5 9 1 2 and 8 1 1 1 g g water for pegmatites a larger range of water contents was found from 2 to more than 50 g g water with two distinct maxima at 10 5 8 1 and 26 2 14 3 g g we show that the great spread and the generally high water content of the pegmatite forming melts as sampled by melt inclusions are the result of melt melt immiscibility pro cesses connected with the formation of conjugate melt fraction with contrasting physical and chemical char acteristics which have also a major influence on the element partitioning between such fractions in this paper we also discuss viscosity as an important transport property of natural silicate melts and we show that due to high primary water concentration in the pegmatite forming melts their viscosity is very low over a wide range of temperatures in the case of water rich peralkaline melt fractions the viscosity can decrease still further together these suggest that liquidus undercooling as the major cause of pegmatite textures is redundant furthermore we demonstrate that the effect of boron carbonates and bicarbonates on pegmatite melts these two last mostly ignored in the past have a large influence on the melt structure and they enable pegmatite formation in the absence of the usual discussed fluxing elements such as f and p

geochemistry of white micas from portuguese tin and tungsten deposits abstract magmatic muscovite of hercynian s type granite muscovite of greisenized granite muscovite of selvages at quartz vein schist contacts and muscovite within the vein of the portuguese w sn deposit from panasqueira are distinguished mainly by trace element contents and there is a tendency for log f h 2 o f hf to increase in this sequence several correlations were found between major elements of these muscovites and of muscovites of hypothermal quartz veins of the sn deposit from montezinho the sn w deposit from argozelo and the w deposit from borralha northern portugal f content of muscovite depends on unit cell parameter b si mg fe2 fe3 alvi and oh sn content of muscovite seems to depend on its celadonite content and is carried by fluorine sn correlates positively with mg fe2 fe3 and f in muscovites from each deposit but a positive correlation between sn and cs was found in hydrothermal muscovites from all deposits the contents of both elements may be guides of sn and w mineralizations w is generally less abundant than sn in muscovite and was probably transported by water as tungstic acid or wo2 4 the muscovite of quartz veins from different deposits can be distinguished by major and trace element contents the muscovites of w quartz veins crystallized at greater log f h 2 o f hf than the muscovite of sn sn w and w sn quartz veins muscovite is also abundant in schists bordering quartz veins and has more distinct major and trace element contents than those of white mica of regional metamorphism and of hydrothermal muscovite of selvages along the vein schist contact it also crystallized at different log f h 2 o f hf

a sm 1bnd isotopic study of heterogeneous granulites from the archean kasai lomami gabbro norite and charnockite complex zaire africa abstract sm 1bnd model ages t dm of acid granulites from the kasai complex agree with previous rb 1bsr and u 1bpb ages of 2 8 ga for the early and main stage of granulite facies metamorphism these sm 1bnd results give an upper limit of 3 1 ga for the age of the protoliths of the charno enderbites and metapelitic gneisses which represent the majority of the acid rocks of the complex a sm 1bnd study whole rock and internal isochrons and t dm ages of the associated basic granulites meta gabbro norite massif and metadolerite dykes crosscutting the acid granulites demonstrates that the second stage of granulite metamorphism corresponding to regional deformation of all the rocks is nearly coeval with the emplacement of the basic rocks at 2 4 ga

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

horizontal sedimentation differences in a eutrophic swiss lake settling fluxes measured by means of sediment traps were 887 g dry wt m 2 yr i 113 g poc m 2 yr i and 2 6 g pp m 2 yr i in 1982 1983 at a central station in eutrophic lake hallwil switzerland nearshore settling rates were higher by a factor of 1 4 3 4 since particulate organic carbon poc particulate phosphorus pp and biomass concentration in the lake water showed vertical rather than horizontal differences this result was attributed to permanent bottom sediment resuspension and redeposition in the littoral zone horizontal sediment transport sediment focusing and sediment resuspension in the profundal zone in winter when wind and turbulence are increased accounted for only about 20 of the sedimentation rates because 70 80 of the total sedimentation for the year occurred during summer such processes are of minor importance in lake hallwil although a nepheloid layer with increased poc and pp concentrations 5 8 m above the bottom was present it is stressed that the mechanisms of sediment transport must be known to permit interpretation of trap results and to understand lake metabolism

pressure fluctuations phase separation and gold precipitation during seismic fracture propagation gold mineralization at croagh patrick western ireland occurs in quartz veins associated with three synchronous oblique tensile shear systems the veins evolved by progressive thickening of isolated en echelon lensoid tensile fractures that show a power law relation between their length and thickness a change in power law exponent marks the linking of the en echelon arrays by large oblique tensile veins fluid inclusion data show that gold was deposited due to unmixing of an h 2 o co 2 nacl fluid at 320 240 c and 160 30 mpa primarily due to decreases in fluid pressure evidence for phase separation is only observed in the large linking veins and is abundant close to intersections of the vein arrays these sites are where high gold grades occur the distribution of gold is believed to reflect both spatial and temporal variations in fluid pressure fluctuation during seismic fracture propagation controlled by the vein growth mechanism and zones of maximum dilation

infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the xihuashan tungsten deposit jiangxi province china the xihuashan tungsten deposit jiangxi province china is a world class vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions there are two major sets of subparallel ore bearing quartz veins the ore mineral assemblage includes wolframite and molybdenite with minor amounts of arsenopyrite chalcopyrite and pyrite there are only two phase aqueous rich inclusions in wolframite but at least three major types of inclusions in quartz two or three phase co2 rich inclusions two phase pure co2 inclusions and two phase aqueous inclusions indicating boiling fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities 239 380 c 3 8 13 7 wt nacl equiv compared with those in quartz 177 329 c 0 9 8 1 wt nacl equiv these distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process enthalpy salinity plot shows a linear relationship implying mixing of different sources of fluids although boiling occurred during vein type mineralization it seems negligible for wolframite deposition mixing is the dominant mechanism of wolframite precipitation in xihuashan 34s values of the sulfides range from 1 6 to 0 1 indicative of a magmatic source of sulfur 18o values of wolframite are relatively homogeneous ranging from 4 8 to 6 3 oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite

effects of calculation procedure and sampling site on trap method estimates of sediment resuspension in a shallow lake resuspension estimates given by two different trap methods in a shallow lake were compared the sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored the methods were label method in which resuspension is estimated by determining the organic fraction of surface sediment suspended seston and trapped material and spim spm method where the relationship between settling particulate inorganic matter spim and total settling particulate matter spm is used during the whole 111 day study period according to the label method at a sheltered station 1949 g m 2 dry weight of sediment was resuspended whereas spim spm gave an estimate of 1815 g m 2 the difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods sensitivity analysis showed that of the two methods the label method was more sensitive to variations in the organic content of trapped material at a wind exposed station the total amounts of resuspended matter given by the label method and by the spim spm method were 4966 g m 2 and 4971 g m 2 respectively due to wind effects escape of trapped material took place which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods of the two methods the spim spm method seems thus more suitable for lakes where bacterial activity is high if cyanobacterial blooms take place the label method is probably more reliable providing that the exposure time of sediment traps is kept adequately short

fluid regime and ore formation in the tungsten yttrium deposits of kyzyltau mongolian altai evidence for fluid variability in tungsten tin ore systems abstract the kyzyltau ore field is located in the northern part of the mongolian altai mountains w y be mo mineralization occurs in veins and stockworks in granites felsic volcanics basaltic flows and conglomerates the main ore minerals in the veins are wolframite fluorite beryl and minor molybdenite inclusions in hydrothermal quartz fluorite and beryl from veins as well as in magmatic quartz in vein hosting granites of the ulaan uul buraat uul and tsunkheg deposits were investigated using microthermometry and laser raman spectroscopy pseudosecondary primary inclusions in the kyzyltau ore veins are predominantly liquid rich aqueous inclusions containing variable amounts of co 2 as the main gas component and showing n 2 ch 4 ratios 1 secondary inclusions contain no or only trace concentrations of gases as indicated by clathrate melting the t h values of pseudosecondary primary inclusions in veins are between 180 and 433 c fluid inclusion data indicate that phase separation processes leading to fluid immiscibility occurred in vuggy quartz ii and green fluorite ii in the ulaan uul and buraat uul ore veins phase separation pressures of 100 350 bars were estimated fluorite i from the kyzyltau ore field shows a strong enrichment of hree and a strong negative eu anomaly common for rare metal bearing ore systems fluorite ii from buraat uul and tsunkheg is characterized by a change in the incorporation of rare earth elements ree with decreasing hree contents and a decreasing eu anomaly the ree distribution patterns in fluorite ii from ulaan uul remained unchanged compared with fluorite i despite a strong increase in the total ree content a review of the literature shows that from high temperature fe rich k dominated brines cassiterite ores can precipitate in quartz veins together with fe chlorite and fe tourmaline bolivian type if phase separation of a gas rich low salinity and fe rich fluid occurs cassiterite wolframite ores may be deposited cornwall devon type the deposits of kyzyltau are characterized by low fe alteration assemblages a predominance of sodium over potassium high contents of ree and y and a lack of extended tin mineralization despite the tin potential of the ore systems fluid inclusion data as well as geochemical and geological indications suggest formation of the tungsten deposits near the tops of li f rich sub volcanic intrusions we interpret the ph of the mineralizing fluid to be the main factor controlling wolframite precipitation in the kyzyltau ore field fluid wall rock interactions a lowering of the temperature and unmixing processes in the ore fluid generated contributions to neutralization and buffering of the acid co 2 bearing fluid into a ph range where tungstates were precipitated it can be inferred that formation of tungsten ores without precipitation of extended tin mineralization is possible in deposits characterized by high potential tin and tungsten according to this inference tin mineralization may be found in a more favourable setting in the vicinity of the kyzyltau deposits

geological and shrimp ii u pb constraints on the age and origin of the breves cu au w bi sn deposit carajas brazil the breves deposit in the carajas copper gold belt brazil a member of the cu au w bi sn group of deposits contains about 50 mt of 1 22 cu 0 75 g t au 2 4 g t ag 1 200 g t w 70 g t sn 175 g t mo and 75 g t bi it is hosted by sandstones and siltstones of the aguas claras formation minimum age of 2 681 5 ma in the roof zone of a complex highly altered granite intrusion the mineralisation is disseminated in a greisenized zone resulting from alteration of probable monzogranites and syenogranites the ore bearing greisen contains abundant xenomorphic quartz in association with fe chlorite and muscovite the gangue assemblage also includes fluorite tourmaline and minor amounts of monazite xenotime chlorapatite thorite zircon calcite siderite and bastnaesite copper mineralisation is dominated by chalcopyrite associated with pyrite arsenopyrite pyrrhotite and molybdenite gold particles in equilibrium with native bismuth are common as inclusions in chalcopyrite the greisen contains sub economic concentrations of tungsten and niobium that are related to the presence of ferberite qitianlingite and nb rutile shrimp ii zircon dating of the host granites gives 207pb 206pb ages of 1 878 8 and 1 880 9 ma for two phases and a combined age of 1 879 6 ma shrimp ii dating of monazite and xenotime grains in late to post mineralisation veins gives a combined 207pb 206pb age of 1 872 7 ma indistinguishable from the ages of the granites this provides a genetic connection between the breves deposit and the ca 1 88 ga a type granite magmatism that typifies the carajas belt as part of a much larger intracratonic magmatic province that extends over much of the amazonian craton the recognition of this association has exploration implications not only for the geophysical signature of the granite roof zones but also for likely geochemical dispersion around the deposits of this type

evolution and paragenetic context of low δd hydrothermal fluids from the panasqueira w sn deposit portugal new evidence from microthermometric stable isotope noble gas and halogen analyses of primary fluid inclusions abstract the evolution paragenetic context and origin of remarkably low d hydrothermal fluids from the hercynian panasqueira w sn cu ag deposit have been investigated through a combined microthermometric stable isotope halogen and noble gas fluid inclusion study large variations in d between 60 and 134 have been observed in primary fluid inclusions from growth zones in a quartz crystal pa66 paragenetically constrained to the main sulfide stage mss of ore formation the same fluids exhibited relatively constant fluid inclusion homogenisation temperatures 254 to 260 c salinities 7 4 to 8 7 wt nacl equivalent and calculated fluid 18o 3 8 to 4 4 all the fluids exhibited 40ar excesses mean molar br cl and i cl ratios varied from 2 3 10 3 4 2 10 3 and 8 10 4 10 10 4 respectively with the more br rich fluids being associated with the more deuterium depleted fluids the low palaeolatitude of panasqueira throughout the main stages of ore formation and the overwhelming predominance of meteoric fluids in the main late and post ore mineralising fluids with d of 40 to 65 lends little support for any models involving low d palaeometeoric water the limited range of 40ar cl ratios 1 1 10 5 1 6 10 5 also precludes boiling during the mss or mixing of meteoric water with highly fractionated deuterium depleted magmatic waters as viable mechanisms for producing the low d fluids the high br cl and i cl of the mss fluids indicate significant fluid interactions with organic rich sediments or metasediments in particular regionally abundant carboniferous coals or coaly sediments that are inferred to be depleted in deuterium by around 85 compared to palaeometeoric water the large range of d observed in the mss fluids may be explained by isotopic exchange of palaeometeoric water with these coals at varying water rock wt wt ratios between 0 02 and 0 002 with fluid oxygen isotopic compositions controlled by exchange with the beira schists such a model is consistent with the requirements that any satisfactory model must take into account viz i the relative constancy of temperature salinity 40ar and fluid 18o during excursions to low d ii the high i cl and br cl ratios observed and iii the coincidence of these low d fluids with the onset of precipitation of polymetallic sulfides and phosphates under reducing conditions the model indicates that meta sedimentary sources of ore forming components became increasingly important during the evolution of the panasqueira sn w deposit and accounts in part for the observed progression from oxide dominated to base metal sulfide dominated parageneses

antimony quartz and antimony gold quartz veins from northern portugal abstract antimony and pb sb quartz veins from the braganca district portugal are mainly hosted by silurian phyllites antimony au quartz veins from the durico beira region are mainly hosted by a cambrian schist metagraywacke complex as well as ordovician phyllites and quartzites the deposits were mostly exploited in the late 19th century mineralogical characteristics and chemical compositions of individual ore minerals are similar in the two areas first and second generations of arsenopyrite precipitated at 390 and 300 c respectively berthierite and stibnite are the most abundant sb bearing minerals and precipitated between 225 and 128 c native antimony at

the dominant processes of sediment distribution and focusing in a small eutrophic monomictic lake there is evidence for 10 mechanisms of sediment distribution in small lakes the sediment accumulation rates measured from a common horizon in cores from 64 sites on esthwaite water u k were used to determine the relative importance of these mechanisms on the distribution of sediment in the lake river inflows generally produced localized effects but there were indications of periodic turbidity flows to the deepest point of the lake from the major inflow active sediment focusing processes were the dominant distribution mechanisms a major resuspension of sediment at autumn overturn probably being the most important the remaining variance was much greater than observed in similar work elsewhere suggesting that redistribution of sediment by direct and indirect wave action may be taking placeall over the lakebcd during isothermal periods the relative contributions of the different processes were corroborated by analysis of previously published sediment trap data

pressure fluctuation during uplift of the northern apennines italy a fluid inclusions study abstract p t conditions existing after the main syn collision tectonic phase in the western part of the northern apenninic chain italy e g in the tuscan nappe outcropping in the la spezia area were estimated on the basis of a detailed microstructural structural petrographic and fluid inclusion study of quartz of syn tectonic d2 veins developed in the tertiary flysch at the top of the tuscan nappe macigno formation three main fluid events have been distinguished as follows during retrograde metamorphism d1 to d2 phase fluids in equilibrium with turbidites from the tuscan nappe were h2o ch4 mixtures issued from water organic matter interactions in temperatures conditions that may have reached at least 260 c or more 280 c depending on the considered depth estimates and maximum pressures around 210 250 mpa evidence of strong fluid pressure fluctuation between lithostatic and hydrostatic within the metamorphic formations up to 100 150 mpa possibly linked to fault valve activity at the beginning of the uplift triggered phase separation of the water methane fluids and production of methane rich and water rich fluids fluctuations in pressure during these events played a crucial role in quartz crystallization especially in extensional fissures formed perpendicular to the d2 folds axial foliation changes in the fluid regime and sources with time are evidenced by the input of brines which mix to distinct degrees and are trapped in healing microfissures during retrograde fluid evolution such mixing processes are an indication of the connection between separate fluid reservoirs with different temperature conditions consequently mass and heat transfer have to be taken into account as the downward percolation of cooler fluids probably accelerated the rate of cooling of the exhumed formations these processes are certainly common to most orogenic terrains and can be quantitatively studied through p v t x reconstruction using fluid inclusion data on the drainage zones where the mixing processes occurred this work confirms that fluid inclusion studies can provide accurate quantitative estimates of fluid pressure variations during the evolution of orogenic terrains and could therefore constitute a useful tool in tectonic interpretations at the light of the models developed for pressure variations in the upper crust

extreme alkali bicarbonate and carbonate rich fluid inclusions in granite pegmatite from the precambrian ronne granite bornholm island denmark our study of fluid and melt inclusions in quartz and feldspar from granite pegmatite from the precambrian ronne granite bornholm island denmark revealed extremely alkali bicarbonate and carbonate rich inclusions the solid phases daughter crystals are mainly nahcolite nahco3 zabuyelite li2co3 and in rare cases potash k2co3 in addition to the volatile phases co2 and aqueous carbonate bicarbonate solution rare melt inclusions contain nahcolite dawsonite naal co3 oh 2 and muscovite in addition to fluid and melt inclusions there are primary co2 rich vapor inclusions which mostly contain small nahcolite crystals the identification of potash as a naturally occurring mineral would appear to be the first recorded instance from the appearance of high concentrations of these carbonates and bicarbonates we suggest that the mineral forming media were water and alkali carbonate rich silicate melts or highly concentrated fluids the coexistence of silicate melt inclusions with carbonate rich fluid and nahcolite rich vapor inclusions indicates a melt melt vapor equilibrium during the crystallization of the pegmatite these results are supported by the results of hydrothermal diamond anvil cell experiments in the pseudoternary system h2o nahco3 sio2 additionally we show that boundary layer effects were insignificant in the bornholm pegmatites and are not required for the origin of primary textures in compositionally simple pegmatites at least