multiscale organisation of organic matter associated with gold and uranium minerals in the witwatersrand basin south africa abstract organic matter from the northern part of the early proterozoic witwatersrand basin carbon leader reef was investigated using optical om and transmission electron tem microscopes completed by xrd analysis the multiscale organization texture microtexture structure of the organic matter was observed in order to gain information about the processes which affected organic material after its deposition in sediments in the micrometre scale optical microscope the shape and size of the reflectance indicating surface ris of the organic matter were determined the organic matter reveals a prevailing biaxial symmetry the size of ris is generally dependent on uranium and increases with increasing uranium concentration furthermore it appears that more than one ris is present within the scale of a single sample each with a different symmetry and size the presence of domains differing in organisation of the aromatic framework was confirmed by tem observation in the df mode the aromatic skeleton of organic matter is composed of short often crumpled mostly isolated non stacked polyaromatic layers whose fringe length corresponds to 3 16 aromatic rings the data indicate reorganization of the polyaromatic organic matter structure under stress in high pressure and relatively low temperature conditions the organic matter was in a solid state within the rocks before the pressure event

metamorphism of the witwatersrand gold fields conditions during peak metamorphism pelitic assemblages from all major witwatersrand gold fields record metamorphic conditions of the greenschist facies with minimal regional grade changes over at least 200 km strike length diagnostic metamorphic assemblages are less common in the volumetrically dominant quartzites the actively exploited auriferous conglomerates and some of the regionally persistent metapelitic horizons bulk rock composition has been a major control on assemblage development key metapelitic assemblages include pyrophyllite chloritoid chlorite and muscovite in each gold field with less common metamorphic biotite accessory minerals are pyrite tourmaline rutile and zircon the abundance of chloritoid and pyrophyllite in thin shaly units together with their minor but widespread distribution in quartzites and conglomerates indicate that metamorphic temperatures reached 350 c 50 c in all the gold fields pressures are less well constrained 1 2 kbar being inferred outside the gold fields higher grades are indicated by andalusite and kyanite near granitoid domes and later intrusions the temperatures during peak metamorphism and the abundance of pyrite provide ideal conditions to re mobilize gold and may explain its secondary textural features

hydrothermal alteration in the witwatersrand goldfields abstract alteration is recorded throughout much of the 3 km thick upper witwatersrand succession in south africa and extends for 300 km around the basin and 50 km into the basin the evidence for this alteration comes from petrography mineralogy geochemistry rock fabrics and stratigraphy the alteration conceived as a giant halo enveloping each major goldfield requires a major hydrothermal event focused on the auriferous upper wits central rand group the scale and nature of the alteration and its relationship to gold distribution on various scales strongly support a hydrothermal model for gold deposition such a model can account for the 50 000 t of gold mined from the witwatersrand goldfields the model works within the context of the major advances in understanding of the geological framework of the witwatersrand basin including the recognition of the importance of post burial processes it is highly significant that the age of witwatersrand sedimentation is much older than 2700 my and thus the host rocks for gold were deposited at least 100 my before the major global archean greenstone gold event the shale units from 40 major mines covering the seven goldfields are examined to establish the nature and distribution of the alteration and to make the connection between the fluid infiltration that caused the alteration and the introduction of gold into the witwatersrand basin in the hydrothermal model described here an auriferous low salinity fluid is produced at about 500 c during the metamorphism of mafic material that was below and adjacent to the witwatersrand basin large shear zones in the footwall of goldfields are the inferred fluid pathways into the upper wits succession and then unconformities smaller shear zones veins and the reef packages guide local fluid flow in this model gold precipitation occurs in response to the reaction of the fluid with carbon and iron bearing rocks that are abundant in the reef packages immediately overlying unconformity surfaces gold precipitation occurred at about 350 c and 10 km depth with the implication of a high geothermal gradient approaching 35 c per km the alteration of the shales but lack of abundant gold in them is predicted from the paucity of appropriate rocks or minerals in the shale units to precipitate gold but fluid infiltration still changed their composition fundamentally the source of the witwatersrand gold its present distribution and the alteration are explained within this hydrothermal model with similarities to the models invoked for other major gold provinces it is worth noting that quartz pebble conglomerate is a poor term for this gold type and has almost certainly limited exploration opportunities globally

widespread fluid infiltration during metamorphism of the witwatersrand goldfields generation of chloritoid and pyrophyllite chloritoid and pyrophyllite occur together in all major goldfields of the witwatersrand basin and are widespread in virtually all rock types of the upper witwatersrand supergroup including metaconglomeratic reefs and altered mafic rocks both minerals are particularly characteristic of the pelitic horizons intimately associated with reef packages but they are also developed locally in the regionally persistent metapelites that have basin wide extent pyrophyllite is particularly common in foliated zones adjacent to quartz veins and near unconformably overlying auriferous conglomerates the wide distribution of chloritoid and pyrophyllite in metapelites of the witwatersrand basin is attributed to alteration of chlorite rich shales rather than to unusual premetamorphic starting materials this alteration event involved the redistribution of many elements with up to 40 volume loss mainly due to removal of silica removal of most of the mg and some fe accounts for the stabilization of chloritoid and pyrophyllite relatively immobile elements included al ti nb cr v p la and ce whereas si fe mn zn co ni cu mg and ca were lost and k rb and ba were introduced by an infiltrating fluid the alteration event is inferred to have been within the chloritoid and pyrophyllite stability field and thus syn metamorphic as bulk chemical changes in metapelites are from chlorite directly towards chloritoid and then pyrophyllite rather than to lower grade minerals such as kaolinite muscovite chlorite chloritoid and muscovite chloritoid pyrophyllite assemblages are attributed to fluid buffering along appropriate curves as their production by metamorphism of lower grade mineral mixes is considered unlikely based on the present bulk rock compositional data a metamorphic timing for the alteration accounts for the correlation of strongly foliated areas with greater degrees of inferred alteration the transitions from chlorite to chloritoid to pyrophyllite define zones of increasing alteration widespread infiltration as part of peak metamorphism is suggested by the distribution of chloritoid and pyrophyllite quartz veining and textures fluid rock ratios calculated from a silica budget in one metapelitic horizon exceed 100 1 over many square kilometres these values need not imply multi pass fluid flow as much of the silica migration may be redistribution on a scale of a few metres from source rocks into veins although infiltration during metamorphism may have affected much of the upper witwatersrand succession channelized fluid flow within reef packages along faults and unconformities and in certain metaconglomerates and metapelites is inferred

the origin of no3 and n2 in deep subsurface fracture water of south africa abstract deep 0 8 km depth fracture water with residence time estimates on the order of several ma from the witwatersrand basin south africa contains up to 40 m of no3 up to 50 mm n2 90 times air saturation at surface and 1 to 400 m nh3 nh4 to determine whether the oxidized n species were introduced by mining activity by recharge of paleometeoric water or by subsurface geochemical processes we undertook n and o isotopic analyses of n species from fracture water mining water pore water fluid inclusion leachate and whole rock cores the no2 no3 and nh3 nh4 concentrations of the pore water and fluid inclusion leachate recovered from the low porosity quartzite shale and metavolcanic units were 104 times that of the fracture water the 15n no3 and 18o no3 of the pore water and fluid inclusion leachate however overlapped that of the fracture water with the 15n no3 ranging from 2 to 7 and the 18o no3 ranging from 20 to 50 the 15n no3 of the mining water ranged from 0 to 16 and its 18o no3 from 0 to 14 making the mining water no3 isotopically distinct from that of the fracture pore and fluid inclusion water the 15n n2 of the fracture water and the 15n n from the cores ranged from 5 to 10 and overlapped the 15n no3 the 15n nh4 of the fracture water and pore water nh3 nh4 ranged from 15 to 4 although the no3 concentrations in the pore water and fluid inclusions were high mass balance calculations indicate that no3 accounts for 10 of the total rock n whereas nh3 nh4 trapped in fluid inclusions or nh4 present in phyllosilicates account for 90 of the total n based on these findings the fluid inclusion no3 appears to be the source of the pore water and fracture water no3 rather than paleometeoric recharge or mining contamination irradiation experiments indicate that radiolytic oxidation of nh3 to no3 can explain the fluid inclusion no3 concentrations and perhaps its isotopic composition but only if the no3 did not attain isotopic equilibrium with the hydrothermal fluid 2 billion years ago the 15n n 15n n2 and 15n nh4 suggest that the reduction of n2 to nh4 also must have occurred in the witwatersrand basin in order to explain the abundance of nh4 throughout the strata although the depleted no3 concentrations in the fracture water relative to the pore water are consistent with microbial no3 reduction further analyses will be required to determine the relative importance of biological processes in the subsurface n cycle and whether a complete subsurface n cycle exists

stratigraphic control of chemistry and mineralogy in metamorphosed witwatersrand quartzites within metamorphosed quartzites of the witwatersrand supergroup bulk chemistry is the major control on the distribution of metamorphic mineral phases and on their chemistry bulk chemistry is in turn controlled by stratigraphic position pyrophyllite distribution varies directly with whereas feldspar distribution varies inversely with bulk al chloritoid distribution is more complex and varies with both bulk al and bulk fe mg despite the overprint of low grade metamorphism and possibly of other alteration processes both detrital and metamorphic phyllosilicates can be recognized and characterized al in metamorphic white mica and metamorphic chlorite varies with bulk al whereas the composition of detrital white mica is unrelated to bulk chemistry similarly mg in metamorphic chlorite varies with bulk mg bulk chemical variation particularly in al mg and na and thus metamorphic mineral chemistry is controlled by stratigraphic position both within individual stratigraphie units and in the strat

metamorphism of the witwatersrand gold fields a review abstract there is widespread evidence for greenschist facies metamorphism in different rock types within all the witwatersrand gold mines the silicate mineral assemblages suggest near uniform peak metamorphic conditions equivalent to the chlorite zone in all the major witwatersrand gold fields assemblages of coexisting pyrophyllite chloritoid have been recorded in most of the gold mines and the critical assemblage of pyrophyllite chloritoid muscovite chlorite quartz tourmaline rutile pyrite is found in most gold fields kaolinite paragonite biotite pyrrhotite and arsenopyrite have more local distribution pelites shales quartzites meta conglomerates metabasalts and some dykes record these metamorphic assemblages albeit in different mineral proportions and pyrophyllite and chloritoid are recorded from many gold producing reefs andalusite kyanite garnet and or cordierite bearing assemblages indicate higher metamorphic grades in three discrete areas along the nw margin of the witwatersrand basin to the ne of the evander gold field and around the collar of the vredefort dome concentric metamorphic facies around the vredefort dome culminate in granulite facies assemblages near the centre it is important to note that there are no definitive published data constraining the temporal relationships between the granulites and amphibolites of the vredefort dome greenschist facies assemblages in the vredefort collar rocks thermal metamorphism related to intrusion of the bushveld complex and the regional greenschist facies metamorphism documented in the gold fields metamorphic conditions of 350 50 c and up to 3 kbars are inferred for the gold fields with temperatures increasing to around 700 c in granulites of the vredefort dome other geothermometric methods including illite crystallinity fluid inclusions carbon elemental ratios and vitrinite reflectance are compatible with the above estimates but are each associated with considerable temperature uncertainties fluids in equilibrium with pyrophyllite muscovite quartz pyrite paragonite are inferred during metamorphism suggesting slightly acid conditions and elevated sulphur activities regional greenschist facies metamorphism documented in the witwatersrand gold mines was accompanied by widespread deformation large fluxes of aqueous fluid and considerable element mobility the low intermediate pressure of this metamorphic terrain and the lack of large scale tectonic thickening favours underplating by mafic magmas as the likely cause of the metamorphic pattern no model for gold genesis in the witwatersrand basin is complete without accommodating post burial processes including metamorphism deformation and alteration any placer gold would be overprinted by these processes and any epigenetic gold could potentially be introduced during these periods of thermal and fluid activity it is also important to note at least two quite unusual features of the witwatersrand metamorphic assemblages the virtual absence of feldspar from the 3 km thick central rand group over 300 km and the narrow range of metamorphic grade inferred for the gold mines over this same distance

sudoite in the archaean witwatersrand basin sudoite with almost ideal composition of mg2al4si3o10 oh 8 has been found in the khaki shale of the witwatersrand basin south africa the sudoite occurs in aggregates of elongate bundles alternating with muscovite and rarely pyrophyllite in an assemblage of sudoite pyrophyllite muscovite quartz rutile pyrite the stability of sudoite is attributed to a particularly mg rich bulk rock composition elevated sulphur activity and metamorphic conditions just above the kaolinite to pyrophyllite transition nearby low variance chlorite chloritoid and pyrophyllite bearing assemblages represent differing bulk rock compositions at potentially very similar metamorphic conditions as the first find of sudoite in the archaean this occurrence in the witwatersrand basin extends the metamorphic setting and age in which sudoite is found to well beyond phanerozoic belts of crustal thickening

the origin of the gold and uranium ores of the black reef formation transvaal supergroup south africa abstract the black reef formation is a laterally extensive sedimentary succession at the base of the transvaal supergroup the quartz pebble conglomerates host erratic concentrations of gold and uranium however in areas that are located spatially above the gold and uranium bearing reefs of the witwatersrand supergroup the concentrations can reach ore grade although the depositional environment was similar to that of the witwatersrand supergroup the processes that lead to the high gold and uranium concentrations in the black reef were quite different the black reef experienced intense post depositional hydrothermal alteration by circulating aqueous and hydrocarbon fluids oils that deposited large volumes of native gold uranium minerals and pyrobitumen the gold which is filamentous is concentrated along as ni rich surfaces of pyrite and with uraninite in pyrobitumen in both environments the gold is interpreted to be the product of chemically triggered precipitation from hydrothermal fluid s the uraninite occurs either as precipitates in pyrobitumen or is invisible in the pyrite occurring as nanoparticles in this mineral this indicates that conditions were sufficiently oxidizing for the hydrothermal transport of uranium and contrasts with the case for the witwatersrand reefs where much of the uranium is detrital luminescent radiation damage associated with vein quartz and pyrobitumen as well as the diffuse distribution pattern of uranium in the pyrobitumen may indicate that some uranium was transported by liquid hydrocarbons pyrite in the black reef sedimentary detrital and hydrothermal pyrite is highly enriched in gold uranium and other redox sensitive trace elements provenance analyses using the trace element compositions of the pyrite show that it was not the result of erosional reworking of the underlying witwatersrand reefs however the close spatial association of high gold and uranium concentrations in the black reef with ore bearing witwatersrand reefs suggests strongly that gold and uranium whether in pyrite or occurring as native gold and uraninite were hydrothermally recycled uranium may have been recycled by hydrocarbon fluids from the witwatersrand reefs

gold mineralization within the witwatersrand basin south africa evidence for a modified placer origin and the role of the vredefort impact event the chemical composition of gold within the archaean metasedimentary rocks of the witwatersrand supergroup displays significant heterogeneity at the micro meso and regional scales a detailed electron microbeam analytical and petrological study of the main auriferous horizons in the central rand group throughout the witwatersrand basin indicates that gold has been remobilized late in the paragenetic sequence over distances of less than centimetres contemporaneous chlorite formation was strongly rock buffered gold mobilization occurred under fluid poor conditions at temperatures that did not exceed 350 c widespread circulation of mineralizing fluids within the central rand group is not supported by the gold and chlorite chemical data brittle deformation that affects most of the paragenetic sequence of the central rand group late in its post depositional history is followed by sequences of mineral growth and dissolution that appear throughout the central rand group and have consistent textural relationships with gold the consistent location within the paragenetic sequence the wide regional and stratigraphic extent of the brittle deformation together with mineral chemical and petrological data suggest that the vredefort impact event 2 02 ga was the cause of this late deformation and that post impact fluid poor metamorphism resulted in crystallization of a significant proportion of the gold on and within mineral grains that were deformed during this event

evidence for major mass transfer and volume strain during regional metamorphism of pelites systematic examination of published sedimentary and metamorphosed pelite analyses has revealed evidence of significant mass transfer and volume strain during regional metamorphism statistical analysis of the data shows that barrovian zone metamorphism of pelitic schist generally causes increases in the whole rock concentrations of the low solubility elements ti and all the observed increases in ti and al contents as functions of metamorphic grade are almost certainly due to residual enrichment caused by the removal of other more soluble species application of mass balance principles to the petite compositional trends indicates that the average pelite may lose as much as 30 of its mass and volume during progressive metamorphism from subgreenschist to amphibolite facies conditions the bulk of the lost mass is silica not volatiles in addition other elements particularly ca na and k appear to be highly mobile in deep crustal metamorphism contrary to conventional interpretations it is concluded that the regional metamorphism of pelites is not an isochemical process

diagenetic alteration of a mesozoic fluvial gold placer deposit southern new zealand abstract gold paleoplacers become progressively more affected by diagenetic processes with age and burial mesozoic paleoplacer deposits in southern new zealand display intermediate stages of diagenetic transformation compared to little affected late cenozoic paleoplacers and strongly affected paleozoic and precambrian paleoplacers the mesozoic cretaceous diagenesis resulted in near pervasive alteration cementation and lithification of the paleoplacer lithic clasts and matrix have been extensively altered to illite ferrous iron bearing smectite vermiculite and kaolinite and the cement consists mainly of clays and calcite diagenetic pyrite marcasite vivianite and mn oxide also contributed to cementation alteration occurred under near surface

geochemistry of fluid inclusions from the mcintyre hollinger gold deposit timmins ontario canada type 1 h 2 o co 2 type 2 h 2 o co 2 type 3 ch 4 co 2 h 2 o and type 4 ch 4 fluid inclusions type 1 type 3 and some type 2 inclusions are primary or pseudosecondary in origin whereas type 4 and most type 2 inclusions are secondary the primary or pseudosecondary type 1 and 2 inclusions homogenized at temperatures of 220 degrees to 385 degrees c secondary type 2 inclusions homogenized at 160 degrees to 215 degrees c crushing tests confirm the presence of co 2 in samples with type 1 and 2 inclusions visually estimated x co2 values in type 1 inclusions range from 3 to 24 mole percent with bulk molar volumes of 19 to 28 cm 3 mole mineralizing fluids were at equilibrium with graphite at temperatures of 380 degrees to 480 degrees c and pressures of 1 to 3 kb calculated oxygen fugacities lie near the quartz fayalite magnetite buffer the mineralizing fluids differ compositionally from fluids in other types of ore deposits but resemble fluids derived from metamorphic rocks and deep level felsic intrusions modified journal abstract

evidence for submarine weathering from metamorphosed weathering profiles on basaltic rocks tananao metamorphic complex taiwan the metamorphosed paleo weathering horizon s developed on basaltic rocks in the tananao metamorphic complex forms distinct al fe rich rocks and occurs as two parallel belts demonstrating its potential as a stratigraphic correlation unit in this structurally complicated metamorphic terrain these al fe rich rocks have been metamorphosed under amphibolite greenschist facies conditions leading to the formation of garnet chloritoid rocks chloritoid rich rocks the chemical changes along three profiles from metabasite to garnet chloritoid rock show prominent k rb cs and ba enrichment yet also a large depletion of other elements if it is assumed that ti zr nb ta and hf remained relatively immobile the ree s however behaved non coherently these chemical characteristics are attributed to pre metamorphic processes and are shown to be similar to those observed with submarine weathering of basaltic rocks in contrast the chloritoid rich rocks reveal distinct k rb cs and ba depletion it is suggested that this resulted from subaerial weathering processes k enrichment is not an uncommon feature in paleozoic precambrian paleosols the present case study demonstrates that submarine weathering should be considered as a probable cause

hydrothermally altered peraluminous archaean granites as a provenance model for witwatersrand sediments hydrothermal alteration of peraluminous granitic rocks occurring at varkenskraal northwest of the witwatersrand basin consists of two major styles the first style pervasive in nature is represented by two stages i a propylitic alteration and ii a disseminated sericitization both alteration stages were accompanied by a deposition of disseminated sulphides the second style is represented by a vein related alteration in four stages including potassium feldspar minor carbonate and minor sulphide mineralization nodules of uraniferous carbonaceous matter and small amounts of particulate gold could possibly be associated with either one or both styles hydrothermally altered rocks of similar nature have been observed in a number of other localities close to the witwatersrand basin their abundance large volumes and low grade disseminated pyrite gold mineralization indicate that rocks of this type could have been the provenance of the witwatersrand gold bearing sediments

evidence for an intrabasinal source and multiple concentration processes in the formation of the carbon leader reef witwatersrand supergroup south africa laser ablation inductively coupled plasma mass spectrometer la icp ms trace element maps of pyrite and gold from the carbon leader reef in the witwatersrand basin provide new evidence that a significant proportion of the pyrite and gold was intrabasinal derived from the west rand group or equivalent shales stratigraphically below this reef rounded detrital pyrite grains in the carbon leader reef vary from compact to porous to sooty with similar textures and composition to diagenetic pyrites reported from sedimentary rocks in the west rand group detrital porous and sooty pyrites contain 0 4 to 11 3 ppm solid solution gold sulfur isotope 34s values from 17 to 16 and high levels of as and te plus a wide range of other trace elements in decreasing order ni co sb cr cu u pb bi mo zn and ag the sooty pyrite is the most au te and mo rich and is intergrown with alumino silicates and organic matter the detrital pyrite textures s isotopes and geochemistry resemble diagenetic pyrite developed under suboxic to anoxic bottom water conditions the laicp ms maps also show that the detrital pyrite grains have euhedral hydrothermal pyrite overgrowths containing micro inclusions of gold brannerite and ni as sulfides the pyrite overgrowths are also enriched in solid solution gold tellurium and other trace elements including in decreasing order as co ni cr cu mn pb bi and ag fractured and brecciated pyrite associated with brittle bedding parallel fracture zones in the carbon leader reef are also enriched in these elements due to alteration of pyrite surrounding the fractures laser icp ms pb isotope determinations on the cores of detrital pyrite indicate an age between 2750 and 2950 ma with hydrothermal overgrowths originating between 2100 and 2020 ma incorporating highly radiogenic pb this study demonstrates that both of the two competing theories for the origin of the witwatersrand gold reefs are likely to be correct we suggest that the hydrothermal event was widespread kilometer scale and involved basinal fluids that scavenged gold tellurium arsenic and trace elements co ni cr cu mn pb bi ag from gold bearing sedimentary units in the central rand group 2013 society of economic geologists inc

hydrothermal gold mineralization in the witwatersrand basin the origin of the gold mineralization in the witwaterstrand basin of south africa the largest known gold province has been controversial for decades with arguments favouring detrital1 2 placer modified placer3 4 and hydrothermal5 6 origins here we present the results of an extensive geological study of witwatersrand rocks which show that the gold and associated uranium mineralization is hydrothermal in origin and postdates a regional high temperature alteration event alteration processes identified on a small scale can be mapped out regionally as roughly strata bound zones of acid metasomatism extending far into the basin the fluid flow responsible for this alteration was concentrated in small scale structures localized along lithological boundaries we find that the gold precipitated as a consequence of interactions of the fluid with shale derived hydrocarbons present within the basin

petrographic evidence for emplacement of carbon into witwatersrand conglomerates under high fluid pressure abstract much gold in the witwatersrand conglomerates is directly associated with seams of carbon that are generally parallel with bedding some seams locally crosscut bedding and form anastomosing fracture patterns showing that emplacement of liquid hydrocarbons in those seams was postdepositional and infilled fractures that are generally parallel to bedding seams that are not observed to crosscut bedding are nonetheless petrographically identical and are believed to have a common postdepositional origin carbon also occurs along sets of bedding parallel microfractures through individual quartz pebbles in mineralized conglomerates planes of fluid inclusions parallel to the microfractures in pebbles show further evidence for the importance of bedding parallel fluid flow the occurrence of carbon seams on sedimentary discontinuity surfaces may reflect preferential emplacement of carbon along planes of weakness brittle extensional fracturing in pebbles indicates high fluid pressures which may relate to hydrocarbon generation bedding parallel minealization by quartz clays metamorphic chlorite pyrophyllite and gold which reflect a complex multistage paragenesis indicate repeated reactivation of bedding plane permeability previous arguments against a hydrocarbon origin for the carbon seams have been based upon the low intergranular permeability of the rocks however the present study shows that this condition actually caused focusing of hydrocarbon fluid flow along discontinuity surfaces and facies boundaries interaction with uranium could have caused fixation of fluid hydrocarbon by radiolytic polymerization the columnar nature of carbon in many of the seams interpreted by others as a biogenic structure could instead reflect polymer swelling normal to bedding in the direction of least confining stress

rare earth element mobility in alteration pipes below massive cuzn sulfide deposits abstract a convincing demonstration of trace element mobility should satisfy two criteria 1 the range of trace element concentrations in the rock before and after alteration must be known with confidence and 2 the absolute abundances and the ratios of the mobile trace elements should vary between altered and unaltered rocks these criteria have been applied to the host felsic volcanics and alteration pipes associated with several canadian massive cu zn sulfide deposits although there is no evidence of rare earth element ree mobility in the pervasive low grade alteration envelopes adjacent to the deposits the light and middle ree lree and mree plus y have been systematically mobilized relative to the heavy ree hree and other trace elements in the alteration pipes beneath the ore zones there is evidence of minor lree and mree depletion in the most altered rocks at the south bay mine uchi lake and of significant lree depletion in the alteration pipe beneath the mattabi mine sturgeon lake however the strongest mobility is found at the kidd creek mine where the lree were leached from the rocks in the footwall stringer zone and redeposited in a metasomatic chlorite zone directly beneath the massive ore horizon and the mree and y were preferentially lost from the system producing distinctive chondrite normalized ree patterns with tb yb n ratios less than unity eu2 was found to be more mobile than the trivalent ree especially at kidd creek where there is a marked increase in the magnitude of the eu anomaly in the most altered samples high field strength elements such as u th hf and zr have not decoupled and apparently remained relatively immobile during all but the most intense alteration i e kidd creek preliminary data suggest that the degree of ree mobility increases with the size of the deposit thus ree mobility is a potentially useful method of distinguishing between small and large massive sulfide deposits at an early stage in exploration however this hypothesis requires further testing

discussion of assessing overconsolidation ratios in soil with piezocone referencing soil index properties by steven r saye alan j lutenegger jorge santos and bryan p kumm

ab initio investigation of high pressure phase relation and elasticity in the naalsi2o6 system 1 subducted crusts contain aluminous phases with incompatible elements such as sodium in order to understand the fate of subducted crusts and how they recycle within the earth it is important to investigate high pressure stability and elastic properties of host phases here we have studied naalsi2o6 jadeite a naalsio4 calcium ferrite cf type phase and sio2 stishovite by means of a first principles computation method jadeite was found to dissociate into an assemblage of the cf type phase and stishovite at about 18 gpa associated with remarkable increases of compressional wave 18 7 shear wave 26 4 bulk sound 13 3 velocities and density 15 1 proximity of this transition condition to the 660 km discontinuity in the mantle transition zone suggests that seismically observed splitting of the reflection could be related to this phase transition implying subduction of crustal materials down to the mantle transition zone