relationships for non darcy flow in rockfill this paper describes a synthesis of various studies on non darcy flow in rockfill material based on pipe theory and taylor s 1948 definition for mean hydraulics radius in rockfill material theoretical relationships between friction coefficient and reynolds number and relationships between hydraulic gradient and bulk seepage velocity have been obtained the new relationships between hydraulic gradient and bulk velocity are then compared to the various formulas for rockfill available in the literature by computer simulation

measurements and analyses of velocity profiles and frazil ice crystal rise velocities during periods of frazil ice formation in rivers the vertical concentration distribution of frazil ice crystals in a stream during the form ation and gro lth of frazil ice was discussed in a prel imi nary way by gosi nk and osterkamp 1981 thi s paper extends and completes the analysis of buoyant rise velocities of frazil ice crystals and applies the results to an interpretation of measured veloc ity profiles in rivers during frazil ice events additional experimental data are also presented two tillle scales are defined the buoyant time scale tb whi ch represents the time requi red for a frazil crystal to rise huoyantly from the river bottom to the water surface and the diffusive time scale to which represents the time required for a frazil crystal to be transported by turbulence through the derth it is shown that the ratio of the time scales tb td defines the nature of the layering processes in particular if tb to l i11 be layered conversely if tb to l turbulent mixing will proceed faster than buoyant 1 ifti ng and the fl ow ii 11 be well mixed this ratio for frazil particles of di arneter 2 illfll or more corresponds to rul e of thumb velocity criteria developed in non ay and canada to di sti ngui sh 1 ayered frazil i ce l later fl o i frol l we11mixed flow the development of this theory depends in large part upon the deterr lination of tb which depends upon the rise velocity of frazil ice crystals a force ba lance node 1 was developed for the ri se velocity of a frazil crystal field observations during frazil ice formation in goldstream creek and in the chatanika river north of fairbanks are reported including a series of measure ents of the rise velocities of frazil ice crystals typical particle size of frazil ice was about 2 n with a rise velocity of about 10 0 mm s l the agreement of measured rise velo cities with the theoretical model is good considering uncertainties in the drag coefficient and in the deterlllination of frazil crystal sizes under field conditions velocity profiles in the chatanika river and in sol dstream creek duri ng frazil formati on suggest that the time scale ratio may serve as a transition criter ioi1 betvlee l layered frazil ice water flow and we11iilixed flo l this ratio was calculated with the rise velocity of frazil ice crystals arbitrarily chosen to be 0 01 m s i i ntrooucti on observations of ice formation in northern rivers during the freeze up period show that three ice flol regimes are common sheet ice floating frazil ice and a well mixed flow frazil ice crystals and water in the last case if the velocity of the river is sufficiently high open water conditions may persist throughout the winter designers of hydraulic structures such as canals water transportation facilities hydroelectric power structures water intake structures etc may require information on which flow regime to expect under a given set of flow conditions and on the trans ition from an ice cover to open water flow thus there is substantial interest in developing criteria which can be used to predict the conditions that lead to each of these three flovl regimes and the presence or absence of an ice cover it could be argued that the criteria for the transition from floating frazil ice to a well mixed flow should be the same as the criteria for the form ation of an ice cover the reason for this is that if the frazil crystals remain mixed with the flow then they cannot accumulate on the surface to form an ice cover however it is clear that other hydrological aspects of rivers enter into criteria on the pres ence or absence of an ice cover these include the sinuosity channel and slope variability bed rough ness and also the mechani cs of fraz il crystal floc pan and floe interactions osterkamp and gosink in press and changes of these parameters during the growth of an ice cover for many locations rule of thumb flow velocities have been determined which define the transitions from well mixed flow to floating frazil ice and the formation of a coherent ice cover for example in norway wllere rivers are often wide shallow with steep slopes and underlain with rocks or boulders the water surface is usually covered with moving frazil slush if the water velocity is 0 5 and 1 2 m s l carstens 1971 on the saint lawrence waterway in canada layered frazil ice flow may be expected at river velocities 0 8 and 1 0 m s i

frazil ice formation in an ice shelf water plume 1 we present a model for the growth of frazil ice crystals and their accumulation as marine ice at the base of antarctic ice shelves the model describes the flow of buoyant water upward along the ice shelf base and includes the differential growth of a range of crystal sizes frazil ice formation starts when the rising plume becomes supercooled initially the majority of crystals have a radius of similar to0 3 mm and concentrations are below 0 1 g l depending on the ice shelf slope which controls the plume speed frazil crystals increase in size and number typically crystals up to 1 0 mm in radius are kept in suspension and concentrations reach a maximum of 0 4 g l the frazil ice in suspension decreases the plume density and thus increases the plume speed larger crystals precipitate upward onto the ice shelf base first with smaller crystals following as the plume slows down in this way marine ice is formed at rates of up to 4 m yr in some places consistent with areas of observed basal accumulation on filchner ronne ice shelf the plume continues below the ice shelf as long as it is buoyant if the plume reaches the ice front its rapid rise produces high supercooling and the ice crystals attain a radius of several millimeters before reaching the surface similar ice crystals have been trawled at depth north of antarctic ice shelves but otherwise no observations exist to verify these first predictions of ice crystal sizes and volumes

water temperature measurements in turbulent streams during periods of frazil ice formation field measurements of water temperatures in two turbulent streams in interior alaska have been made during periods of frazil ice production the measured equilibrium temperature of the water te 0 005 c agrees with the value calculated from the electrical conductivity of the water average cooling rates of the streams during the summer to fall stream cooling period were on the order of several tenths of a degree per day with average surface heat losses of 5 to 18 w m 2 just prior to a frazil ice event the water cooling rates were 1 to 3 mk min 1 with surface heat losses of 47 to 140 w m 2 super cooling at the water surface of a stream prior to and during frazil ice production does not exceed o 2 c as shown by measurements of air water tempera ture profiles and by radiometer measurements water supercooling at the time of frazil ice nucleation was 10 mk these measurements show that frazil ice nuclei in streams must be other ice particles cold organic materials cold soil particles or a combin ation of these that may be introduced into the stream by mass exchange processes at the air water interface the maximum observed supercooling was 6tm 40 mk two measured values for the residual supercooling were 3 and 9 mk frazil growth rates calculated from the observed values of supercooling show that unless the period of residual supercooling is very long most of the frazil ice production during one night of super cooling occurred in the transient thermal period from the time of nucleation to the time that the water became residually supercooled i ntroducti on frazil ice formation in northern rivers causes many problems which are fascinating from scientific and engineering points of view and are of immediate economic importance frazil ice can cause flooding block water supply intakes reduce or halt power generation in hydroelectric facilities interfere with ship and barge transportation and damage or restrict the use of hydraulic structures and facil ities development of rational design methods for alleviating or avoiding these problems is still hindered by deficiencies in the present state of understanding of frazil ice formation a knowledge of the water temperature in turbulent streams during periods of frazil ice formation can be used to increase our understanding of heat losses supercooling nucleation and growth of frazil ice and other processes and parameters associated with its formation however very few in situ measurements of water temperature during periods of frazil ice production have been reported this situation is surprising in view of the fact that frazil ice appears to be the dominant form of ice occurring in turbulent streams in alaska as well as in other northern regions figure 1 illustrates an idealized thermal history of a turbulent stream during periods of frazil ice production these ideal curves are observed in laboratory experiments when heat loss from the water surface is constant carstens 1966 michel 1967 however the variability of heat loss from natural streams leads to more uneven curves osterkamp 1978 and the magnitudes of the various parameters that define the curves are different for curves obtained under laboratory conditions compared to those obtained in streams figure 1 illustrates the fact that the equilibrium temperature of the water te at time te is usually depressed because of the presence of dissolved substances in the water in principle frazil i ce nucl eati on can occur at any time t after the water temperature has been reduced to te nucle ation occurs at time tn and temperature tn the minimum stream temperature tm occurs at time tm at any time t te the magnitude of the supercooling of the water is

frazil dynamics and precipitation in a water column with depth dependent supercooling when seawater becomes supercooled collections of small ice crystals known as frazil ice form and grow a model of frazil ice dynamics is presented that deals explicitly with the buoyant settling of frazil crystals onto an overlying surface this yields further insight into transport associated with the ice pump mechanism whereby ice is melted at depth and transferred to a shallower location as a result of the pressure variation of seawater s freezing temperature the model is applied to a vertical cross section through an ice shelf water plume beneath filchner ronne ice shelf antarctica and helps to elucidate the depth variation in its properties for the first time as well as predicting the precipitation rate of frazil crystals the model predicts that frazil ice should be preferentially located in a narrow layer near the ice shelf base as a result of the maximum supercooling there and an influx of crystals rising under their own buoyancy the deposition of these crystals onto the ice shelf is governed by the balance between crystal rising and turbulent transfer of frazil away from the shelf which is investigated in some detail

frazil ice entrainment of sediment large tank laboratory experiments laboratory experiments that simulate natural ice formation processes and sediment entrainment in shallow water are presented a 10 30 cm s 1 current was forced with impellers in a 20 m long 1 m deep indoor tank turbulence in the flow maintained a suspension of sediments at concentrations of 10 20 mg l 1 at 0 5 m depth low air temperatures 15 c and 5 m s 1 winds resulted in total upward heat fluxes in the range 140 260 w m 2 the cooling produced frazil ice crystals up to 2 cm in diameter with concentrations up to 4 5 g l 1 at 0 5 m depth considerable temporal variability with time scales of 1 min was documented a close to constant portion of the smaller frazil crystals remained in suspension after some hours the larger crystals which made up most of the ice volume accumulated as slush at the surface current measurements were used to calculate the turbulent dissipation rate and estimates of vertical diffusion were derived after 5 8 hours sediment concentrations in the surface slush were normally close to those of the water after 24 hours however they were 2 4 times higher data indicate that sediment entrainment depends on high heat fluxes and correspondingly high frazil ice production rates as well as sufficiently strong turbulence waves do not seem to increase sediment entrainment significantly

a model of marine ice formation within antarctic ice shelf rifts large rifts that open in antarctic ice shelves are known to be filled by snow accumulations ice shelf fragments and sea ice this work demonstrates how these rifts may also be filled from below through their interaction with ocean water by marine ice the model presented here quantifies both the rate of marine ice accumulation at the top of the rift which results from melt driven convection at its sides and the impact of this process on waters occupying the confined environment of the rift the results show that such a system could fill the rift with tens of meters of marine ice in the process the temperature and salinity of the ambient water in the rift evolve through two distinct phases the first is characterized by rapid change that takes the properties of the ambient water to near equilibrium values followed by a second phase of much slower change the melting rate at the lower part of the walls of the rift emerges as the principal factor influencing many aspects of model behavior testing the model against field observations from an antarctic rift showed it to be robust and successful in reproducing the main observed features including the presence of a thick layer of supercooled ocean water inside the rift

placed rock as protection against erosion by flow down steep slopes the additional resistance to erosion due to flows down steep slopes that can be achieved by placing rock instead of dumping randomly has been quantified during a large scale flume investigation testing was undertaken for slopes of 0 2 0 3 and 0 4 with two layers of armor overlying a filter consistent with conventional rock protection designs two sizes of sandstone with mean diameters of 76 and 109 mm and basalt with a mean diameter of 94 mm were tested placing rock to achieve maximum bulk density mass per unit in situ volume increased failure flow flow at exposure of the filter by 30 of that achieved with the same type of randomly dumped material but the total armor mass per unit surface area increased by 35 a damage approach to steep erosion protection that is similar to that used for coastal breakwater design is presented an improved method of partition between the aerated flow over as well as flow through both random and placed rock has also been quantified better characterization of aer

br cl geochemistry of hydrothermal brines associated with proterozoic metasediment hosted copper mineralization at mount isa northern australia abstract instrumental neutron activation analyses inaa of small bulk samples of vein quartz are used to estimate the br cl ratio of saline fluid inclusions associated with late metamorphic copper mineralization in quartz dolomite breccias at mount isa the results are compared with similar data from veins associated with district scale metasomatism in potential copper source rocks near mount isa and with quartz samples from other locations in northern australia which may have trapped fluids approaching the br cl composition of paleoproterozoic halite evaporites br cl ratios in some of the evaporite related samples are similar to present day seawater 0 0035 while others range up to 0 015 all samples from the mount isa copper ores fluids with total salinities mostly between 10 and 25 wt nacl eq have consistently high br cl ratios between 0 008 and 0 018 on average 3 5 times higher than modern seawater fluids associated with district scale alteration of metabasalts up to 30 km away from the deposit have high br cl ratios identical to those of the ore fluids this indicates a common source of the salts and supports a tentative correlation between mine and district scale alteration events and may ultimately help to trace potential fluid flow paths to or from the site of ore deposition the observed fluid compositions are contrary to the low br cl ratios that would be expected from a simple model of ascending fluids derived by prograde metamorphism of salt bearing paleoproterozoic metasediments mass balance calculations based on mine and district scale alteration suggest that the high br cl fluids may have originated above the present level of erosion as basin brines which infiltrated the terrain during the waning stages of regional metamorphism they may have formed in an inferred evaporitic cover sequence of mesoproterozoic age as residual bitterns or by diagenesis and partial dissolution of halite similar to modern br enriched basin brines secular variation in oceanic br cl preferential chlorine removal from evaporite derived metamorphic fluids by fluid rock interaction or an unusually br rich magma source beneath the deposit could provide alternative explanations for the high br cl ratios of the mount isa brines but are considered to be less likely processes in light of the available geologic data

the composition of hypersaline iron rich granitic fluids based on laser icp and synchrotron xrf microprobe analysis of individual fluid inclusions in topaz mole granite eastern australia abstract high temperature 550 c hypersaline 50 wt salts fluid inclusions representative of the earliest hydrothermal fluids associated with the sn w cu pb zn mineralised mole granite of eastern australia are well developed in topaz from the fielders hill locality methods based on inductively coupled plasma emission spectroscopy following laser ablation and on synchrotron x ray fluorescence microanalysis are described and applied to the semiquantitative point analysis of these inclusions crushleach analysis provides further information as well as highlighting the importance of point methods when several generations of inclusions are present the laser icp results confirm the dominance of fe k and na in these early high temperature fluids the mean fe k na atomic ratios 0 95 0 79 1 00 are entirely in agreement with published experimental data on the composition of chloride brines in equilibrium with synthetic granite at magmatic temperatures and support the view that these fluids are direct products from a cooling granite magma a number of trace and minor elements have also been detected in the inclusions these include ca mg li b be ba sr and several of the ore metals order of magnitude estimates of the ore metal contents of these fluids based on combined xrf microprobe and laser icp analysis are in the percent range for fe mn and zn in the range from several hundred to several thousand ppm in the case of sn cu and pb and less than 600 ppm for mo and w these results have important implications for ore genesis in granitic environments and point to the very high ore carrying potential of high temperature hypersaline chloride rich brines exsolved from cooling granite magmas

geochemistry of hypersaline fluid inclusions from the starra fe oxide au cu deposit cloncurry district queensland studies of liquid vapor multisolid l v ns and liquid vapor halite fluid inclusions suggest that at least three fundamentally different brines were involved in the genesis of the proterozoic ironstone hosted starra au cu deposit element concentrations determined from proton induced x ray emission pixe analysis of groups of l v ns inclusions from the early barren magnetite ironstone stage 400 550 c and the younger mineralization stage 220 360 c covary over concentration ranges greater than the deduced analytical errors the l v ns inclusions in the two stages are very different with higher ratios of fe and k to ca mn cu zn sr ba and pb in the ironstone stage quite distinct pseudosecondary nacl cacl h o inclusions are abundant in mineralization stage quartz calcite and anhydrite high concentrations of cu ca 1 000 ppm are present in some l v ns inclusions of both stages and the data suggest that large amounts of cu mn zn as ba and pb passed through the starra system as it evolved cl br ratios in the inclusions are mostly less than 0 002 and clearly different from those of ore fluids of the giant sedimentary hosted copper orebody at mount isa this could reflect a major magmatic contribution to the salinity at starra that is consistent with the preferred origin of the water in published stable isotope studies ba concentrations of at least several wt percent in some mineralization stage l v ns inclusions are associated with oxidized sulfur bearing mineral parageneses given the low solubility of barite this suggests that a s2 f o2 relationships varied during mineralization

extension of an ice shelf water plume model beneath sea ice with application in mcmurdo sound antarctica a one dimensional frazil laden plume model predicts the properties of ice shelf water isw as it evolves beneath sea ice beyond the ice shelf edge an idealized background ocean circulation which moves parallel to the plume imitates forcings other than the plume s own buoyancy the size distribution and concentration of the plume s suspended frazil ice crystals are affected by the background circulation velocity the root mean square tidal velocity the drag coefficient and the efficiency of secondary nucleation consequently these variables are the key physical controls on the survival of supercooled water with distance from the ice shelf which is predicted using several realistic parameter choices starting at 65 m thick the in situ supercooled layer thins to 11 5 and 4 3 m at distances of 50 and 100 km respectively we apply the extended model in mcmurdo sound antarctica along the expected path of the coldest water three late winter oceanographic stations along this path in conjunction with historical data provide initial conditions and evaluation of the simulations near the ice shelf in the western sound the water column consisted entirely of isw and the subice platelet layer thickness exceeded 5 m with platelet crystals dominating the sea ice structure suggesting that isw persisted throughout winter presuming a constant isw flux the model predicts that the plume increases thermodynamic growth of sea ice by approximately 0 1 m yr 1 5 of the average growth rate even as far as 100 km beyond the ice shelf edge

the composition of a primary granite derived ore fluid from s w england determined by fluid inclusion analysis abstract electrolyte concentrations in aqueous fluid inclusions in quartz from a high temperature hydrothermal rock have been measured for 15 elements by an improved crush leach procedure the primary hydrothermal fluid was dominated by nacl and has been shown by previous studies to have been about 3 m with respect to cl on this basis the molar concentrations include fe 0 21 mn 0 06 and zn 0 02 and the fluid is interpreted as parental to some of the s w england ore bodies

the marcona magnetite deposit ica south central peru a product of hydrous iron oxide rich melts marcona the preeminent andean magnetite deposit 1 9 gt 55 4 fe and 0 12 cu is located in the iron oxide copper gold iocg subprovince of littoral south central peru fe oxide and cu zn pb sulfide mineralization was controlled by northeast striking faults transecting a middle jurassic aalenian to oxfordian andesitic shallow marine arc and a succession of contiguous plate boundary parallel late jurassic to mid cretaceous volcanosedimentary basins at marcona hydrothermal activity was initiated in the earliest middle jurassic 161 177 ma by high temperature mg fe metasomatism represented by cummingtonite and phlogopite magnetite assemblages subsequently during the terminal eruptions 156 162 ma of the arc widespread albite marialite alteration na cl metasomatism was followed by the emplacement of an en echelon swarm of massive magnetite ore bodies with subordinate overprinted magnetite sulfide assemblages hosted largely by paleozoic metasilici clastics the magnetite orebodies exhibit abrupt smoothly curving contacts dike like to tubular apophyses and intricate amoeboid interfingering with dacite porphyry intrusions there is no convincing megascopic or microscopic evidence for large scale fe metasomatism associated with the main sulfide poor mineralization the largest 400 mt minas 2 3 4 orebody is interpreted as a bimodal magnetite dacite intrusion comprising commingled immiscible melts generated through the dissolution of metasedimentary quartz in parental andesitic magma oxygen and sulfur stable isotope geothermometry indicates that the evolution at ca 159 ma from magnetite biotite calcic amphibole phlogopite fluorapatite to magnetite phlogopite calcic amphi bole pyrrhotite pyrite assemblages coincided with quenching from above 800 c to below 450 c and the concomitant exsolution of dilute aqueous brines subsequently chalcopyrite pyrite calcite pyrrhotite sphalerite galena assemblages in part metasomatic were deposited from lower temperature 360 c brines the cu poor marcona kiruna type magnetite and cu rich iocg deposits in the district therefore although spatially contiguous represent contrasting ore deposit types the former are interpreted as the product of fe oxide melt coexisting with dacite magma within an andesitic arc which failed during the closure of a back arc basin the weak associated magmatic hydrothermal cu sulfide mineralization at marcona was generated through melt vesiculation and contrasts with the considerably higher grade cu and ag rich orebodies of the major cu rich iocg deposits in the central andes e g la candelaria punta del cobre mantoverde raul condestable and mina justa which were the products of cool oxidized hydrothermal fluids plausibly expelled from the adjacent basins during tectonic inversion

chemistry origin and evolution of mineralized granites in the lachlan fold belt australia the metallogeny of i and s type granites granites crop out over 20 percent of the total exposed area of the lachlan fold belt and comprise subequal proportions of i and s types despite the volume of granite present economic mineralization is sporadic major sn mineralization is related to s and i type granites that are both reduced and have undergone extended feldspar dominated crystal fractionation mo showings are common but as for cu large deposits are absent scheelite skarn mineralization is represented by the major king island deposits however granite related w mineralization of a similar scale is not found elsewhere within the belt the i type granites of the belt represent the products of partial melting of older tonalitic granodioritic source rocks in the deep crust which were themselves ultimately derived through fusion of mantle materials m types this evolution is also mirrored in the nature of related mineralization which changes from cu dominated at the chemically primitive end of this series through to lithophile dominated in the more evolved i types most of the lachlan fold belt i types have not undergone significant crystal fractionation and are neither strongly oxidized nor reduced two prominent mineralized i type suites the boggy plain supersuite of the central lachlan fold belt and the grassy suite of king island are anomalously mineralized relative to other lachlan i types both are chemically distinct from other i types in the belt by being enriched in the incompatible elements and ni and cr mafic s types are universally restite rich and unmineralized s type magmas are in general more evolved chemically than 1 types are all relatively reduced and when highly fractionated are related to sn or w mineralization the ore element ratios sn w cu mo etc of granite related mineralization in the lachlan fold belt is a straightforward function of the relative oxidation state and degree of fractionation within the associated granite

a comparison of mineral deposits at the gecko and white devil deposits implications for ore genesis in the tennant creek district northern territory australia detailed geologic metal zonation paragenetic fluid inclusion and stable isotope studies have been undertaken of the cu rich gecko k44 and the au rich white devil deeps zone orebodies in the proterozoic tennant creek district of the northern territory australia despite differences in the grade and mineral abundances in the ores three paragenetic stages are present in both deposits 1 an early synkinematic oxide stage at which time the ironstones formed 2 a syn to postkinematic sulfide stage at which time cu au and bi were introduced and 3 a late minor carbonate stage with minor pb and zn the oxide stage involved precipitation of magnetite hematite quartz and chlorite this stage was subsequently foliated the sulfide stage involved the precipitation of gold chalcopyrite bi minerals chlorite and quartz and the hematization of magnetite the carbonate stage involved precipitation of carbonate talc galena and sphalerite and the alteration of chalcopyrite to bornite and covellite fluid inclusion studies indicate that oxide stage minerals formed from low temperature 250 degrees c high salinity 15 20 wt nacl equiv fluids whereas the sulfide stage formed from high temperature 350 degrees c high salinity 20 wt nacl equiv fluids that show evidence of phase separation sulfur isotope studies indicate that lower delta 34 s values occur in au rich pods whereas higher delta 34 s values occur in cu rich halos metal zonation studies indicate that in the white devil deeps zone orebody a basal au rich zone is surrounded by a bi rich shell this zonation is broadly similar to zonation at the juno deposit au bi cu pyrite large 1975 owing to its very low grades the distribution of cu in the white devil deeps orebody is erratic conversely the gecko k44 orebody is only weakly zoned with au enrichment at the top of the orebody in the sulfide tongue mineral deposition occurred in well zoned au rich e g juno and white devil and weakly zoned chalcopyrite hematite rich e g gecko deposits owing to the reduction of highly oxidized sulfide stage fluids through hematization of magnetite in ironstones the fluids evolved through the hematite field in f sub o 2 ph space to the hematite pyrite join and then followed the hematite pyrite join toward the hematite pyrite magnetite triple point this fluid evolution caused early gold precipitation in the hematite field but chalcopyrite precipitated only along the hematite pyrite join which accounts for metal zonation in well zoned au rich deposits in chalcopyrite hematite rich deposits fluid evolution was restricted to the hematite pyrite join and minor gold precipitated with chalcopyrite the k44 sulfide tongue is inferred to be a small zoned au rich system adjacent to the main k44 orebody differences in metal abundance and zonation can be interpreted in terms of varying proportions of highly oxidized magmatic hydrothermal fluids relative to more reduced connate basinal fluids introduced into the ore forming systems a large component resulted in well zoned au rich deposits an intermediate component resulted in chalcopyrite hematite rich au poor deposits and a small component resulted in unzoned chalcopyrite rich pyrrhotite bearing deposits with intermediate au grades e g peko

modeling the effects of frazil ice crystals on the dynamics and thermodynamics of ice shelf water plumes the seawater that comes into contact with the base of a floating ice shelf is modified as a result of the phase changes that occur melting is prevalent in the deepest parts of the subice cavity and this drives a buoyant flow of ice shelf water isw along the sloping ice shelf base the ascent of the isw toward the surface of the ocean causes supercooling because the freezing point rises with the falling pressure and this induces a change from melting to freezing assuming that seed crystals exist the isw now fulfills the condition for the rapid growth of disc shaped frazil ice crystals which may subsequently settle upward out of suspension under the action of gravity a simple numerical model of these processes has been developed based on the theory of inclined plumes the isw is treated as a turbulent particle laden gravity current ascending a reactive boundary and containing a suspended crystal load which evolves in response to the supercooling of the water and the inverted sedimentation of the crystals the frazil ice has two important effects on the behavior of the isw plume because the generation of crystals through out the plume provides such a large area over which phase changes can occur the conversion of supercooling into ice happens much more readily than is possible through turbulent transfer of heat and mass at the ice shelf base a suspended crystal load reduces the bulk density of the isw so that a growing suspension causes the plume to accelerate while deposition of crystals onto the ice shelf effects a deceleration there are positive feedbacks in that an acceleration of the plume induces more rapid crystal growth while a deceleration allows suspended crystals to settle out more easily

geochemistry of post 1540 ma granites in the cloncurry district northwest queensland proterozoic fe oxide cu au co mineralization in the cloncuriy district is spatially and temporally related to intrusion of voluminous postpeak metamorphic granites that form most of the williams and naraku batholiths detailed mapping and geochemical study of these granites in the southern part of the district have identified two groups of intrusions that are referred to here as the cloncurry supersuite and eureka supersuite the cloncurry supersuite is composed mainly of monzogranite and syenogranite which consist of quartz plagioclase alkali feldspar hornblende biotite with accessory magnetite titanite apatite and zircon the timing of intrusion of the wiley igneous complex is interpreted to be pre or syn d 3 based on overprinting relationships while hornblende geobarometry suggests an emplacement depth of approximately 14 km the granites are subalkaline high k metaluminous rocks and range from 59 to 74 wt percent sio 2 increasing sio 2 is accompanied by increasing k 2 o rb and th and decreasing mgo fe 2 o 3 feo tio 2 cao p 2 o 5 sr eu zr cu zn ni v and sc this is consistent with fractionation of observed phases including plagioclase amphibole biotite magnetite titanite and apatite the eureka supersuite ranges from diorite to syenogranite in composition more mafic varieties contain pyroxene and hornblende while more felsic varieties contain biotite as the only ferromagnesian silicate sodiccalcic alteration events are closely linked in space and time to intrusion of eureka supersuite magmas the timing of intrusion is interpreted to be pre and post d 3 based on overprinting relationships between different plutons and mylonitic fabrics hornblende geobarometry suggests an emplacement depth of approximately 10 km for the mount angelay igneous complex eureka supersuite granites in the mount angelay igneous complex range from 51 to 76 wt percent sio 2 the granites are alkaline and k 2 o rich leading to their classification as a shoshonite series with increasing sio 2 content tio 2 al 2 o 3 fe 2 o 3 t mno mgo cao p 2 o 5 sr eu cu zn ni v and sc decrease indicating fractionation of observed minerals including apatite magnetite pyroxene hornblende plagioclase and biotite some samples are characterized by very high abundances of k 2 o p 2 o 5 sr ba and light rare earth elements lree compared to other eureka supersuite samples this may reflect their derivation from a source that was variably enriched in incompatible elements compared with many other shoshonitic rocks high k eureka supersuite samples are strongly depleted in sr and to a lesser extent eu and enriched in y and heavy rare earth elements hree this suggests that garnet was not a stable phase in the source region that the source contained plagioclase as a stable phase and or the granites evolved by extensive plagioclase fractionation partial melting in the lower crust to generate post 1540 ma granites was most likely caused by intrusion of basic magma into the crust eureka supersuite magmas were probably derived from partial melting of variably incompatible element enriched gabbroic rocks while cloncurry supersuite magmas were most likely derived from partial melting of more felsic material of dioritic to tonalitic composition

modification of a palaeoproterozoic porphyry like system integration of structural geochemical petrographic and fluid inclusion data from the aitik cu au ag deposit northern sweden the aitik cu au ag deposit in the gallivare area in northern sweden is sweden s largest sulphide mine with an annual production of 35 mt of ore and the biggest open pit operation in northern europ

stable isotope evidence for the origin of the mesoproterozoic starra au cu deposit cloncurry district northwest queensland new stable isotope data are consistent with a metasomatic origin for the controversial mesoproterozoic ironstone hosted au cu deposit at starra in the cloncurry district of northwest queensland this supports textural and mineralogical evidence that the ore bearing ironstones formed after the peak of metamorphism and were strongly controlled by brittle ductile deformation three dominant paragenetic stages are recognized these are 1 early widespread na ca metasomatism quartz albite scapolite actinolite 2 localized k fe metasomatism biotite magnetite hematite quartz pyrite and 3 mineralization quartz anhydrite barite hematite calcite gold pyrite chalcopyrite bornite chalcocite chlorite muscovite crosscutting anhydrite veins associated with carbonate or hematite are rare in the upper parts of the system but more common at depths greater than 700 m stage 3 minerals demonstrate that the ore fluid was highly oxidized a restricted range of fe oxide delta 18 o implies isotopically similar fluids were responsible for the magnetite ironstones and later hematite alteration associated with gold and sulfides between 0 2 to 3 3ppm except for one magnetite at 5 4ppm sulfur isotope compositions suggest that pyrite 0 2 to 3 9ppm chalcopyrite 5 8 to 0 7 and 14 6ppm bornite 4 7ppm chalcocite 0 1ppm and anhydrite 1 1 2 4ppm all formed from the same sulfur source anhydrite delta 34 s falls within the sulfide range suggesting that the sulfate inherited its delta 34 s through hydrolytic processes similar to those of some porphyry environments delta 13 c of ore stage carbonates range from 7 3 to 2 2 per mil temperatures based on stage 2 quartz magnetite pairs imply 400 degrees to 500 degrees c for ironstone formation and stage 3 calcite hematite pairs indicate 180 degrees to 330 degrees c for mineralization stage 2 fluid inclusions have homogenization temperatures between 345 degrees and 615 degrees c and salinities of 34 to 52 wt percent nacl equiv stage 3 fluid inclusions homogenized between 225 degrees and 360 degrees c and have salinities of 30 to 42 wt percent nacl equiv calculated delta 18 o fluid compositions for magnetite quartz and hematite calcite average 7 8 per mil and 9 5 per mil respectively fluid compositions for stages 2 and 3 fall within the range for a magmatic or metamorphic fluid however combined stable isotope and fluid inclusion data and thermodynamic considerations suggest a magmatic metasomatic origin for both the magnetite ironstones and the highly oxidized mineral assemblage associated with high grade gold deposition

a framework of overprinting orogens based on interpretation of the mount isa deep seismic transect a deep seismic reflection transect and coincident refraction study reveal the crustal structure developed during mesoproterozoic orogenesis preserved in the mount isa inlier of northwest queensland australia geologic interpretation of the reflection data indicates a two stage evolution for east west shortening the first stage involved west directed folding and thrusting above a decollement in the eastern part of the terrane this decollement system was the forehand of an orogenic system rooted east of the present day inlier the second stage is characterized by a network of basement cutting reverse and strike slip faults that dissected the decollement this overprinting system was linked to crustal thickening within the mount isa terrane the refraction profile indicates the crust beneath the inlier is currently approximately 55 km thick rocks with transitional velocities 7 km s in the lower 15 km are interpreted as mafic underplate formed during the pre orogenic rift history of the inlier the refraction profile also reveals two west dipping high velocity layers within the crust evaluating the origin of these layers in light of the kinematics of crustal thickening suggests they are portions of the underplated material thrust to midcrustal levels during the second stage of shortening the overprinting orogenic scenario has implications for the geodynamic evolution of the inlier that should have a direct bearing on mineralizing systems localized by reverse faults developed during the second stage of shortening this basement cutting stage established a linked fault network able to tap deeper crustal circulation during the intrusion of late to postorogenic granitoids

frazil deposition under growing sea ice 1 platelet ice may be an important component of antarctic landfast sea ice typically it is found at depth in first year landfast sea ice cover near ice shelves to explain why platelet ice is not commonly observed at shallower depths we consider a new mechanism our hypothesis is that platelet ice eventually appears due to the sudden deposition of frazil ice against the fast ice ocean interface providing randomly oriented nucleation sites for crystal growth brine rejected in plumes from landfast ice generates stirring sufficient to prevent frazil ice from attaching to the interface forcing some of it to remain in suspension until ice growth rate and brine rejection slow to the point that frazil can stick we calculate a brine plume velocity and match this to frazil rise velocity we consider both laminar and turbulent environments we find that brine plume velocities are generally powerful enough to prevent a significant range of frazil sizes from sticking in the case of laminar flow and that in the turbulent case there may be a critical ice thickness at which most remaining circulating frazil suddenly settles

modeling ice ocean interaction in ice shelf crevasses ocean freezing within ice shelf basal crevasses could potentially act as a stabilizing influence on ice shelves however ice ocean interaction and ocean dynamics within these crevasses are as yet poorly understood to this end an idealized 2 d model of an ice shelf basal crevasse has been developed using fluidity a finite element ocean model using an unstructured mesh a simple model of frazil ice formation and deposition has been incorporated into fluidity to better represent the freezing process model results show two different flow regimes dependent on the amount of freezing in the crevasse one driven by freezing at the top of the crevasse and the other by the ingress of meltwater from outside the crevasse in the first freezing at the top of the crevasse leads to the formation of an unstable overturning circulation due to the rejection of dense salty water in the second a buoyant layer is formed along the sides and roof of the crevasse stratifying the water column frazil ice precipitation is found to be the dominant freezing process at the top of the basal crevasse in the freeze driven case with direct freezing being dominant in the melt driven case in both cases melting occurs lower down on the walls of the crevasse due to the strong overturning circulation the freezing in ice shelf crevasses and rifts is found to be highly dependent upon ocean temperature providing a stabilizing influence on ice shelves underlain by cold waters that is not present elsewhere

high salinity fluids the result of retrograde metamorphism in thrust zones abstract highly saline fluid inclusions in vein quartz from caledonian thrust zones of northern norway are associated with late orogenic retrograde metamorphic reactions several retrograde reactions have been observed in pelitic lithologies and all involve the rehydration of earlier higher grade metamorphic assemblages the most common products of these reactions are chlorite and sericite which have formed at the expense of garnet kyanite staurolite and hornblende chlorite geothermometry suggests temperatures between 330 and 370 c for the formation of the retrograde chlorite a range of total fluid salinities has been determined by microthermometry between 27 and 50 wt these high fluid salinities result from relatively rapid rehydration reactions during limited infiltration of the thrust zones by aqueous fluids crush leach analyses show the fluids to be multi component fluids whose electrolyte contents are na and cl dominated but with appreciable contents of ca k fe and sr geochemical modelling of the fluid compositions suggests that the concentrations of the major elements in solution were buffered by the retrograde rehydration reactions the source of the infiltrating fluids which caused the retrogression is not identifiable from their major element chemistry surface derived meteoric sea or sedimentary formation waters fluids may have utilised pre existing thrust zones as fluid pathways and are considered to have been important in the retrogression in the structurally higher parts of the caledonian allochthon at deeper levels however metamorphic fluids produced by devolatilisation reactions in underthrust units may have migrated upwards into the thrust zones and resulted in the retrogression of the hangingwalls of overlying higher grade nappes

estimation of flow through and over armored slopes models developed for the transient routing of intense rainfall on small armored slopes depend on expressions for flow resistance below and above the surface of the armored layer a series of 52 experiments are conducted in two flumes to collect data on the basic relationships of flow resistance crushed rock of 26 155 mm median diameter is placed on embankments with slopes ranging from 0 01 to 0 2 and subjected to steady flow in the flumes flow through the rock layer is found to be approximately proportional to the rock layer porosity the square root of the slope and the mean diameter of the rock and weakly proportional to the stage the portion of flow through the filter layer generally cannot be neglected flow resistance decreases and conveyance greatly increases when the stage exceeds the depth of the rock layer a model for flow both beneath and above the rock surface on an armored slope is synthesized from formulas developed for flow in rubble dams and darcy weisbach formulas developed for flow

the effects of rotation and ice shelf topography on frazil laden ice shelf water plumes a model of the dynamics and thermodynamics of a plume of meltwater at the base of an ice shelf is presented such ice shelf water plumes may become supercooled and deposit marine ice if they rise because of the pressure decrease in the in situ freezing temperature so the model incorporates both melting and freezing at the ice shelf base and a multiple size class model of frazil ice dynamics and deposition the plume is considered in two horizontal dimensions so the influence of coriolis forces is incorporated for the first time it is found that rotation is extremely influential with simulated plumes flowing in near geostrophy because of the low friction at a smooth ice shelf base as a result an ice shelf water plume will only rise and become supercooled and thus deposit marine ice if it is constrained to flow upslope by topography this result agrees with the observed distribution of marine ice under filchner ronne ice shelf antarctica in addition it is found that the model only produces reasonable marine ice formation rates when an accurate ice shelf draft is used implying that the characteristics of real ice shelf water plumes can only be captured using models with both rotation and a realistic topography

riprap design for overtopping flow near prototype flume studies were conducted in which riprap protected embankments were subjected to overtopping flows embankment slopes of 1 2 8 10 and 20 were covered with riprap layers with median stone sizes of 1 2 4 5 and or 6 in each riprap layer was tested by slowly increasing the discharge to failure riprap design criteria for overtopping flows were developed for estimating incipient stone movement and riprap layer failure as a function of the unit discharge stone shape median stone size and embankment slope incipient stone movement occurred at approximately 74 of the riprap layer failure unit discharge it was determined that rounded shape stone should be oversized approximately 40 to provide comparable protection of an angular shape stone flow channelization was observed to occur at approximately 88 of the unit discharge at failure a flow concentration factor of approximately 1 to 3 was introduced for sizing stone

a model for entrainment of sediment into sea ice by aggregation between frazil ice crystals and sediment grains avertical numerical model has been developed that simulates tank experiments of sediment entrainment into sea ice physical processes considered were turbulent vertical diffusion of heat salt sediment frazil ice and their aggregates differential growth of frazil ice crystals secondary nucleation of crystals and aggregation between sediment and ice the model approximated the real size distribution of frazil ice and sediment using five classes of each frazil crystals 25 m to 1 5 cm were modelled as discs with a constant thickness of their diameter each class had a constant rise velocity based on the density of ice and drag forces sediment grains 1 600 m were modelled as constant density spheres with corresponding sinking velocities the vertical diffusion was set constant for experiments based on calculated turbulent rms velocities and dissipation rates from current data the balance between the rise sinking velocities and the constant vertical diffusion is an important feature of the model the efficiency of the modeled entrainment process was estimated through a an aggregation factor values for a are in the range but average values are often close to 0 01 entrainment increases with increasing sediment concentration and turbulence of the water and heat flux to the air

origin of hydrothermal fluids at olympic dam preliminary results from fluid inclusions and stable isotopes fluid inclusions and stable isotope data provide evidence of the temperature composition and sources of hydrothermal fluids associated with formation of the fe rich breccias that host cu u au ag ore at olympic dam early magnetite associated with pyrite and siderite precipitated from fluids of high delta 18 o content approx 10ppm at temperatures near 400 degrees c and magnetite in k feldspar apatite veins at the nearby acropolis deposit probably formed from similar fluids in contrast hematite associated with ore bearing breccias formed at lower temperatures 200 degrees 400 degrees c from fluids of lower delta 18 o content 9ppm fluid inclusion homogenization temperatures in quartz fragments within hematite breccias overlap with and are lower than those indicated by isotope geothermometry two phase liquid plus vapor inclusions mainly homogenize at temperatures between 130 degrees and 280 degrees c with a mode at 170 degrees to 190 degrees c quartz fragments within rare laminated barite clasts display a larger range of homogenization temperatures from 110 degrees to 420 degrees c and may have preserved evidence of early high temperature hydrothermal events measurement of freezing point depressions in fluid inclusions provides evidence of widely varying salinities and complex solute chemistry indicated salinities vary from a minimum of 7 3 wt percent nacl equiv 1 3 m to a maximum of 23 7 wt percent nacl equiv 4 2 m in two phase fluid inclusions and up to 42 wt percent nacl equiv in halite saturated three phase inclusions all the fluid inclusions studied displayed evidence of additional solutes in addition to nacl all required a high degree of supercooling to induce freezing and displayed initial ice melting at temperatures below 23 degrees c and many formed distinctive brown granular ice in addition several inclusions also formed co 2 clathrates and other metastable solids qualitative assessment of these characteristics indicates fluids carrying multiple solutes probably including nacl kcl cacl 2 fecl 2 caf and co 2 these preliminary results suggest that at least two sources of fluids of contrasting temperature composition and oxygen isotope characteristics were involved in the formation of olympic dam early magnetite was deposited from hydrothermal fluids of deep seated possibly magmatic origin but magnetite bearing rocks are not significant hosts for copper uranium mineralization later hematite associated with ore bearing breccias was deposited by fluids of significantly lower temperature and lower delta 18 o values the geologic setting of the deposit a fault bounded depression at or near the palcosurface implies that waters of surficial origin seawater closed basin water or ground water may have been involved in the later stages of hydrothermal activity that formed the hematite breccias although our preliminary isotopic data do not require such waters they are consistent with this conclusion

numerical model of frazil ice and suspended sediment concentrations and formation of sediment laden ice in the kara sea a one dimensional vertical numerical model of currents mixing frazil ice concentration and suspended sediment concentration has been developed and applied in the shallow southeastern kara sea the objective of the calculations is to determine whether conditions suitable for turbid ice formation can occur during times of rapid cooling and wind and wave induced sediment resuspension although the model uses a simplistic approach to ice particles and neglects ice sediment interactions the results for low stratification shallow 20 m freeze up conditions indicate that the coconcentrations of frazil ice and suspended sediment in the water column are similar to observed concentrations of sediment in turbid ice this suggests that wave induced sediment resuspension is a viable mechanism for turbid ice formation and enrichment mechanisms proposed to explain the high concentrations of sediment in turbid ice relative to sediment concentrations in underlying water may not be necessary in energetic conditions however salinity stratification found near the ob and yenisey rivers damps mixing between ice laden surface water and sediment laden bottom water and probably limits incorporation of resuspended sediment into turbid ice until prolonged or repeated wind events mix away the stratification sensitivity analyses indicate that shallow 20 m unstratified waters with fine bottom sediment settling speeds of 1 mm s 1 or less and long open water fetches 25 km are ideal conditions for resuspension

evolution of the starra and selwyn high strain zones eastern fold belt mount isa inlier implications for au cu mineralization the starra magnetite ironstone hosted au cu deposit in the eastern fold belt mt isa inlier is localized by the development of the starra high strain zone the associated eastern barren hematite rich ironstones occur in the adjacent selwyn high strain zone integrated macro meso and microstructural analysis of rocks from both of these high strain zones and the surrounding country rocks reveals that they have undergone the same sequence of successive shallow and steeply oriented deformation events all of these rocks preserve evidence for four main ductile deformation events d 1 to d 4 d 1 d 2 and d 4 equate with regional d 1 d 2 and d 3 respectively as observed by workers in the mount isa region followed by two weaker events d 5 d 6 which exhibit both ductile and brittle character d 1 produced a shallowly dipping layer parallel foliation d 2 is the most pervasive event and produced upright tight to isoclinal f 2 folds with an intense steeply southeast dipping axial plane foliation s 2 trending northeast southwest d 3 rotated initially upright f 2 folds onto their western limb by top to the west shear and formed crenulations with shallowly dipping east west striking axial planes the fourth deformation event d 4 produced a steeply east dipping foliation s 4 which is similar in orientation to s 2 consequently differentiation of s 2 from s 4 is difficult except where s 2 was rotated by d 3 s 4 when observed is generally developed as a broad crenulation cleavage microstructural analysis of 115 spatially oriented thin sections from the vicinity of the starra orebodies demonstrates that the dominant fabric is a strongly differentiated composite s sub 2 4 foliation rather than simply s 2 as had been thought previously the starra and selwyn high strain zones resulted from a significant increase in strain during d 4 and preserve a predominant shear sense of west side up the western mineralized and eastern unmineralized ironstones resulted from intense iron metasomatism and were emplaced as en echelon north northeast striking lenses late syn post d 4 the rocks between the high strain zones young consistently eastward hence duplication of the ironstones by folding is precluded au cu mineralization within the starra orebodies was emplaced during and after iron metasomatism late syn to post d 4

the role of langmuir circulation in suspension freezing in november 2004 we used an acoustic doppler velocimeter adv to measure the three components of velocity in langmuir circulation lc cells when frazil was forming in a lake lc circulation was indicated by windrows of slush ice on the water surface we also collected samples of lake water ice interstitial water and ice to determine their sediment concentrations the adv record showed rotating currents in the cross wind vertical plane indicative of lc downward directed velocities were large enough to entrain frazil into the water column for 27 of the 97 min observation time at the adv location sediment concentrations in the ice and interstitial water samples were greater than concentrations in water column samples collected in upwelling zones of lc cells we conclude that suspension freezing was forming particle laden ice as frazil trapped below lc convergence zones grew in downwelled supercooled water the rotating roll vortices of langmuir circulation play an important role in forming sediment laden ice

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

design of rock protection to prevent erosion by water flows down steep slopes conventional stability analysis methods for determining rock armor size to protect steep tan 0 1 embankments from erosion due to downslope flow do not predict the correct dependency of armor size on the slope consequently such methods become very conservative discharge factor of safety 8 at high slopes we review published large scale measurements recorded in the literature and show that adequate representation of flow aeration is important as proposed by hartung and scheuerlein in 1970 however the assembled measurements show that the hartung and scheuerlein design method is not conservative the aerated flow equations of hartung and scheuerlein when combined with a correctly formulated stability equation yield good collapse of the available large scale data and a conservative design method

a metasomatic origin for the iron oxide au cu starra orebodies eastern fold belt mount isa inlier the starra ironstone hosted au cu deposit in northwest queensland australia displays evidence of a polyphase history of late post metamorphic structurally controlled metasomatism the mineralisation is hosted within several massive ironstone units which occur at a lithological contact of metamorphosed sandstone and siltstone sequences and foliated chlorite biotite magnetite schists the ironstones strike north south and occur as discontinuous lenses that cross cut the host rocks in places magnetite ironstone textures are generally massive in appearance but relict deformed breccia and foliation textures are locally preserved sulphide ore textures are more brittle and consist of fine pervasive brecciation of the ironstones and host rocks petrological and textural observations support a hydrothermal origin for both ironstone and mineralisation three dominant post peak metamorphic paragenetic stages of alteration and mineralisation are recognised 1 early widespread na ca metasomatism consisting of albite quartz actinolite scapolite 2 localised k fe metasomatism consisting of biotite magnetite hematite quartz pyrite and 3 the mineralising stage consisting of anhydrite calcite hematisation of magnetite pyrite chalcopyrite gold and extreme chloritisation of biotite the na dominant alteration occurs throughout the eastern fold belt and for at least 50 km to the east and 150 km to the north of starra the ironstones were products of localised fe metasomatism associated with shearing and brecciation of previously na metasomatised host rocks gold and copper mineralisation resulted from the interaction of magnetite a late oxidising fluid and an increase in ph this produced variable hematisation of magnetite and caused the solubility of chloride complexed gold to decrease dramatically high gold copper ratios can be explained in terms of the solubility differences of gold and copper in the thermochemical conditions that existed at starra

hostrocks to the stratabound iron formation hosted starra gold copper deposit australia this paper documents the timing geochemistry and possible origin of sodium enrichment associated with proterozoic iron formation hosted copper gold ore lenses at the starra deposit australia the ore lenses are immediately underlain by variably sheared albitemagnetite hematite pyrite bearing rocks and overlain by mainly unaltered less sheared meta sediments evidence indicating that albite was abundant prior to deformation and also prior to the main hydrothermal addition of fe s cu and au includes 1 regional albite development at this stratigraphic level 2 alteration of albite by ore related sericite and 3 inclusion of unfoliated inclusions of albite and hematite in ore related pyrite nevertheless albite also developed around dolerites and within hangingwall shears during metamorphism and deformation least altered albite footwall rocks have sio2 67 31 73 13 wt al2o3 9 89 12 51 wt total alkali elements 6 40 9 43 wt and hfs elements e g zr 179 275 ppm ti zr 7 6 14 1 comparable with felsic volcanics but have high relative na2o contents 5 08 5 81 wt and variable to high na2o k2o ratios 0 05 68 37 an episode of alkali alteration by high na fluids prior to the ore related alteration is postulated to account for sodic compositions after chemical consideration of the alternatives 1 arkosic sediments 2 trondhjemitic volcaniclastics and 3 na metasomatism of staveley formation sediments during the most intense ore alteration isocon analysis indicates a density increase of 23 compared to the least altered albitised hostrocks cu fe au sn w zn k ba and rb were enriched during the mineralising process whereas mn ca si nb and zr were lost and al ti and y were not changed and were used to define the isocon the loss of some high field strength elements during this alteration indicates that igneous rock classification diagrams based on immobile element ratios should be used with caution for albitemuscovite magnetite pyrite assemblages associated with iron formation hosted copper gold deposits zircon was partially soluble whereas titanium oxides were probably stable in the saline high temperature 260 380 c acid ph 3 9 6 0 fluids envisaged for ore related alteration

proterozoic iron oxide cu u au ree deposits further evidence of hydrothermal origins the emmie bluff fe oxide deposit south australia is unequivocally of hydrothermal origin and exhibits overprinting relations visible at both the meso and microscopic scale that strongly support a model involving two temporally distinct fluids as previously proposed for the enormous olympic dam deposit the evidence indicates that the first stage of magnetite rich ore formation was associated with high temperature fluids from a major mid proterozoic felsic intrusive event this was followed by infiltration of lower temperature fluids that produced the hematite rich mineralization from authors

a model for vertical frazil distribution a model is presented for the evolution of frazil over depth and with time in a turbulent flow the net upward migration due to buoyancy of the frazil is opposed by intermittent mixing induced by large energy containing eddies a surface renewal model is used to describe the effects of large eddy mixing parameters that represent an entire water body are obtained by averaging those of discrete water columns using a probability density function these parameters include the concentration profile the surface age and the surface layer thickness a dimensionless surface renewal frequency characterizes the frazil distribution at equilibrium the rate of heat loss from the water surface the surface renewal frequency and the critical surface layer thickness determine whether the frazil will evolve toward a well mixed equilibrium state or a layered state the model provides a physical basis for understanding the transition between these states consistent with existing empirical criteria and field data

on the conditional frazil ice instability in seawater abstractit has been suggested that the presence of frazil ice can lead to a conditional instability in seawater any frazil forming in the water column reduces the bulk density of a parcel of frazil seawater mixture causing it to rise as a result of the pressure decrease in the freezing point this causes more frazil to form causing the parcel to accelerate and so on this study uses linear stability analysis and a nonhydrostatic ocean model to study this instability the authors find that frazil ice growth caused by the rising of supercooled water is indeed able to generate a buoyancy driven instability even in a gravitationally stable water column the frazil ice mechanism can still generate convection the instability does not operate in the presence of strong density stratification high thermal driving warm water a small initial perturbation high background mixing or the prevalence of large frazil ice crystals in an unstable water column the instability is not necessarily expressed in fra

lagrangian modelling of frazil ice in the ocean a new modelling framework using lagrangian particle tracking has been developed to assess dynamic and thermodynamic effects of underwater frazil ice this frazil ice model treats a lagrangian particle as a bulk cluster of many frazil crystals and calculates the thermodynamic growth of each particle and the corresponding budget of latent heat and fresh water the effective density and viscosity of sea water depend on the mass fraction of underwater frazil ice and hence affect ocean convection an idealized experiment using our model successfully reproduces the formation of underwater frazil ice and its transition to grease ice at the surface because underwater frazil ice does not reduce the atmosphere ocean heat exchange surface heat flux and net sea ice production in the experiment with frazil ice are relatively high compared with the experiment where surface cooling directly leads to columnar growth of a solid ice cover which effectively insulates the heat flux these results suggest that large scale sea ice models which do not take account of the effects of frazil ice might underestimate atmosphere ocean heat exchange particularly at times of active new ice formation

the sources and evolution of mineralising fluids in iron oxide copper gold systems norrbotten sweden constraints from br cl ratios and stable cl isotopes of fluid inclusion leachates we have analysed the halogen concentrations and chlorine stable isotope composition of fluid inclusion leachates from three spatially associated fe oxide cu au mineralising systems in norrbotten sweden fluid inclusions in late stage veins in fe oxide apatite deposits contain saline brines and have a wide range of br cl molar ratios from 0 2 to 1 1 10 3 and 37cl values from 3 1 to 1 0 leachates from saline fluid inclusions from the greenstone and porphyry hosted cu au prospects have br cl ratios that range from 0 2 to 0 5 10 3 and 37cl values from 5 6 to 1 3 finally the cu au deposits hosted by the nautanen deformation zone ndz have br cl molar ratios from 0 4 to 1 1 10 3 and 37cl values that range from 2 4 to 0 5 although the bulk of the data fall within 0 0 5 the br cl ratios of leachates are consistent with the derivation of salinity from magmatic sources or from the dissolution of halite most of the isotopic data from the fe oxide apatite and greenstone deposits are consistent with a mantle derived source of the chlorine with the exception of the four samples with the most negative values the origin of the low 37cl values in these samples is unknown but we suggest that there may have been some modification of the cl isotope signature due to fractionation between the mineralising fluids and cl rich silicate assemblages found in the alteration haloes around the deposits if such a process has occurred then a modified crustal source of the chlorine for all the samples cannot be ruled out although the amount of fractionation necessary to generate the low 37cl values would be significantly larger the source of cl in the ndz deposits has a crustal signature which suggests the cl in this system may be derived from meta evaporites or from input from crustal melts such as granitic pegmatites of the lina suite