geochemistry and depositional environment of the gold mineralized proterozoic koolpin formation pine creek inlier northern australia a comparison with modern shale sequences abstract the paleo to mesoproterozoic koolpin formation is a lithologically distinct sequence in the sedimentary pile of the pine creek inlier in northern australia this succession hosts several gold deposits such as the cosmo howley gold mine matthai et al 1995a part of the koolpin formation has been referred to as iron formation and interpreted as an exhalative deep water sediment by analogy with the homestake gold deposit south dakota a syn sedimentary origin of the gold enrichment has been proposed for cosmo howley this paper presents a detailed investigation of the sedimentology petrography and geochemistry of the koolpin formation at and in the vicinity of cosmo howley it is shown that the sequence consists mainly of metamorphosed shales with narrow intercalations of formerly carbonate bearing mudstones in which chert concretions formed during periods of subaerial weathering in the hanging wall the sequence grades into carbonaceous slates which formerly contained diagenetic dolomite depositional structures indicate that the older part of the koolpin formation at cosmo howley formed in a low energy inter to supra tidal environment dominated by detrital input of terrestrial provenance the younger carbonaceous slates seem to reflect a transition to shallow marine conditions the chemical character of the metasediments and their ree signatures are comparable to modern day analogs despite potassium enrichment and ca na depletion which is inferred to be a consequence of fluid flow during mineralization and contact metamorphism iron formations as defined by james 1954 are not present at cosmo howley iron enrichment to present values 27 wt total fe is shown to have occurred from a weakly diagenetically enriched protolith due to silica loss during nodule formation volatile loss during metamorphism and epigenetic sulfide precipitation during retrograde alteration no gold enrichment can be demonstrated for the protolith similar conclusions may be reached for the iron rich metasediments which host gold mineralisation at homestake south dakota

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

element and isotope geochemical investigations of the kupferschiefer in the vicinity of rote faule indicating copper mineralization sangerhausen basin g d r abstract based upon extensive data on the elemental and isotopic compositions of kupferschiefer of the sangerhausen basin and according to results of trace element and structural investigations of bitumen extracts trends of lateral and vertical distribution of various elements and genetic assertions are presented irregular positions of f v se au and u in the correlation diagram peculiarities of the lateral distribution of these elements abnormally high elemental concentrations in the rocks and in the bituminous extracts as well as alterations discovered in the composition of hydrocarbon groups and their structures support the idea of an influx of oxidizing metalrich waters moving through the rote faule from the rotliegendes basin into the kupferschiefer sediment isotope geochemical investigations carbon nitrogen and oxygen of organic carbonate and silicate fractions were carried out in order to characterize more precisely the conditions of sedimentation and the regime of diagenesis the contrary 13 c curves of pb zn facies and rote faule facies and the 13 c enrichment in the organic matter of rote faule can be explained by different redox conditions during sedimentation and or diagenesis furthermore the decreasing 18 o values of carbonates of the rote faule also suggest an influx of meteoric waters the results oppose a final syngenetic to early diagenetic fixation of the metal contents in kupferschiefer areas in the vicinity of rote faule the established model of influx of metalliferous fluids which arose from the rotliegendes is of local interest for element input and element redistribution

measurement of u pb ages of uraninite and davidite by laser ablation hr icp ms laser ablation high resolution inductively coupled plasma mass spectrometry la hr icp ms is a rapid accurate and inexpensive technique for making in situ u pb isotopic measurements of uraninite and davidite the advantages of this method include 1 mineral separation and chemical digestion are not required 2 measurements on complex samples are feasible because significant isobaric interferences can be resolved and 3 accurate u pb and 207pb 206pb dates on 10 25 m spots can be obtained rapidly the la hr icp ms method is applied to u oxide minerals from four deposits and prospects from northern australia and the new dates are compared to previously published conventional thermal ionization mass spectroscopy tims dates and to known ages of geologically important events these comparisons permit us to assess elemental fractionation of u and pb for uraninite and davidite of the new method relative to zircon as well as its geochronological accuracy and precision u pb apparent ages measured previously agree well with our measurements for el sherena palette and mt isa additionally the upper intercept 207pb 206pb dates for adelaide river 701 190 ma 1 and palette 841 94 ma 1 uraninite measured here are similar to those previously obtained for palette 730 ma nabarlek 920 ma and koongarra 870 ma and the upper intercept date for el sherena uraninite 1573 160 ma is within error of that previously determined for ranger 1550 15 and 1472 40 ma such apparent age agreement for uraninite and similarly for davidite indicates that u and pb fractionations are within error of that for zircon whereas the inherent imprecision of our dates and their associated mswd values greater than 2 5 probably indicate that multiple resetting events affected our samples analytically these results demonstrate that the la hr icp ms technique provides excellent spatial resolution while also removing argide phosphide sulfide and halide interferences that can otherwise lead to erroneous data when using quadrupole icp ms geologically the individual 207pb 206pb and upper intercept u pb dates of uraninite from adelaide river and palette are ca 800 ma possibly reflecting recrystallization of uraninite during the break up of rodinia

diagenesis of the aphebian mistassini regolith quebec canada abstract a well developed regolith is preserved beneath early proterozoic aphebian rocks of the otish and mistassini groups in central quebec canada the regolith is covered by fluviatile clastic rocks otish group in the north and by a thick sequence of stromatolitic and sandy dolomite mistassini group in the south where preserved beneath clastic rocks the regolith exhibits the structures and textures of its crystalline parent rocks tonalite gneiss and amphibolite despite the alteration of feldspars to clay minerals and the partial oxidation of biotite a later event recrystallized the clay minerals to muscovite while conserving the original outline of the feldspars beneath the dolomite the regolith was largely replaced by dolomite but retains many original textures dolomite replaced first the clay minerals then quartz and unaltered feldspars and finally biotite repeated crustifications of dolomite with intervals of chert and minor anthraxolite surround unaltered blocks of crystalline rock within the regolith profile and similar complex veins fill many master joints these veins are identical in composition to vug fillings throughout the overlying carbonate formations clasts of partly dolomitized regolith included in non dolomitic sands filling channels and scours dug deep into the profile suggest that dolomitization commenced very early possibly related to a sabkha environment developed during the transgression

metal organic associations in sediments i comparison of unpolluted recent and ancient sediments and sediments affected by anthropogenic pollution abstract the concentrations of 19 trace elements were determined by plasma emission spectrometry in organic fractions organic solvent extractables soluble humics protokerogen and kerogen concentrates separated from various recent and ancient sediments mangrove sediments algal mats oil shales phosphorites as well as sediments polluted by industrial metal emissions rhine river port pirie smelter effluent often the organic constituents were found to be enriched in trace elements especially b v mn co ni cu zn as mo ag cd sb hg and pb up to more than three orders of magnitude compared to the bulk sediments indicating the importancesof organic substances with respect to transport and fixation of trace elements within sediments the formation of metal organic associations was found to reflect the environment of deposition marine to terrestrial as well as diagenetic transformations recent to ancient against an unpolluted natural background increasing metal pollution led to increasing metal potake by organic substances especially for b cr fe co cu zn as cd and pb

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

iridium sulfur isotopes and rare earth elements in the cretaceous tertiary boundary clay at stevns klint denmark microbial activity and redox controlled precipitation have been of major importance in the process of metal accumulation in the strongly ir enriched cretaceous tertiary k t boundary clay the fish clay at stevns klint in denmark two important findings support this view 1 1 kerogen recovered by leaching the fish clay in hcl and hf shows an ir concentration of 1100 ppb this represents about 50 of the ir present in the bulk sample fish clay strong organometallic complexes is the most probable carrier phase for this fraction of ir kerogen separated from the k t boundary clay at caravaca spain similarly exhibits enhanced ir concentrations 2 2 sulfur isotope analyses of metal rich pyrite spherules which occur in extreme abundance about 10 by weight in the basal fish clay give a 34s value of 32 this very low value shows that sulfide formation by anaerobic bacteria was intensive in the fish clay during early diagenesis since the pyrite spherules are major carriers of elements such as ni co as sb and zn microbial activity may have played an important role for concentrating these elements in the fish clay large amounts of rare earth elements have precipitated from sea water on fish scales analyses reveal that compared with sea water the fish clay is only about four times less enriched in sea water derived lanthanides than in ir this shows that a sea water origin is plausible for elements that are strongly enriched in the clay but whose origin cannot be accounted for by a lithogenic precursor

basin evolution and unconformity related uranium mineralization the camie river u prospect paleoproterozoic otish basin quebec the paleoproterozoic otish basin quebec hosts several uranium prospects that until recently remained underexplored and poorly understood in this study the camie river u prospect which shows similar charac teristics to high grade unconformity related u deposits is the focus of an integrated basin analysis in the western otish basin conglomerate and sandstone of the indicator formation which were deposited in at least six depositional sequences were affected by insignificant early diagenetic compaction and cementation this allowed the for mation of regional peak diagenetic aquifers which became muscovite altered due to interaction with fluids having 18 o and 2h values similar to those of seawater influenced basinal brines at 250 c u mineralization at camie river occurred at 1721 20 ma based on a 207 pb 206 pb date obtained by laser ablation of uraninite which coincides with a phase of the otish gabbro intrusion that has been dated at ca 1730 ma the intrusive event promoted circulation of u bearing basinal brines triggering u mineralization at several locations in the western otish basin interaction of basinal brines with the otish gabbro produced coarse grained chlorite tourmaline and phengitic muscovite which decreased the fluid conducting capabilities of diagenetic aquifers and resulted in fault zone and fracture dominated fluid flow subsequent fluid alteration events produced limited u remobilization sulfides sudoite and siderite between ca 1670 and 1410 ma based on mineral paragenesis and 40 ar 39 ar dates of muscovite metamorphic fluids having high 18 o values and temperatures around 300 c accompanied 1 2 to 1 0 ga grenville orogene sis and subgreenschist grade metamorphism in the otish basin but were present at low water rock ratios at camie river and therefore produced little alteration post grenville uplift of the otish basin likely produced late low temperature alteration minerals that have been influenced by recent meteoric water suggesting that the fault zones and fractures the minerals occupy remain as preferential fluid flow pathways to the present day radiogenic pb and the characteristic trace elements mo w nb have also preferentially dispersed from the mineralization along fault zones fractures and depositional sequence boundaries and can be used to explore for camie river style u mineralization

an empirical oxygen and hydrogen isotope geothermometer for quartz tourmaline and tourmaline water abstract oxygen isotope equilibration temperatures of coexisting quartz muscovite illite chlorite and biotite from a variety of geologic environments have been used in conjunction with the 18o and d values of associated tourmaline to formulate empirical quartz tourmaline and tourmaline water isotope fractionation factors over temperatures from 200 to 600 c the fractionation factors determined using this method are as follows 1 1 1000 in quartz tourmaline 1 0 0 17 10 6 t 2 0 39 0 44 oxygen 2 2 1000 in tourmaline water 27 2 4 4 10 6 t 2 28 1 9 8 hydrogen 350 600 c the isotopic properties of tourmaline are nearly identical to those of muscovite and illite despite the significant differences in their crystal structures similarities in the oxygen and hydrogen isotope systematics of tourmalines and micas imply that the dominant controls on the isotopic properties of these minerals are the vibrational energies of the al si o and si o bonds however the bo3 groups in the tourmalines may have some effect on oxygen isotopic properties as there are minor differences between the 18o values of coexisting tourmalines and micas d values of coexisting tourmalines and micas are generally concordant to within 10 chemical compositions indicate that varying fe mg ratios in the tourmalines appear to have only a minor control on their d values there is a discontinuity in the 1000 in tourmaline water values for hydrogen at temperatures between 200 c and 300 c suggesting that the hydroxl groups in tourmaline are affected by hydrogen bonding and changes in the properties of water near its critical point as are some other hydrous minerals

the tectonic significance of some basic dyke swarms in the canadian superior province with special reference to the geochemistry and paleomagnetism of the mistassini swarm quebec canada the mistassini dykes extend northwest from the mistassini embayment and comprise both tholeiitic and komatiitic suites they are probably 2000 ma old and yield two major paleomagnetic components one of these with a pole at 131 w 13 s is thought to be an overprint related to the elsonian disturbance 1400 1500 ma ago a very steeply down and reversed component may be primary and has a pole at 080 w 50 n these spacial chemical and age relationships between the mistassini molson marathon and payne river dyke swarms and the aphebian supracrustal fold belts on the perimeter of the superior province suggest a genetic relationship between the dyke swarms and the fold belts the supracrustal belts are evidence of the opening and closing of oceans and the dyke swarms are evidence of early stage failed arms related to these openings more rarely for example the payne river dykes early stage dyke swarms are developed and preserved parallel to the edges of newly developed spreading plate boundaries

organic geochemical studies of the muthurajawela peat deposit of sri lanka abstract organic constituents present in the muthurajawela peat deposit of sri lanka have been investigated here we report the variations with depth of sitosterol and sitostane stigmastane which were found to be major constituents of extracts and hence were selected to study the process of diagenesis these two compounds were present in anomalous concentrations in the middle horizon of the depth profile considering the stratigraphy and sterol concentrations it can be concluded that the middle horizon resulted from a sudden terrestrial input which could have been due to a pleistocene or quaternary environmental change

organic matter and gold ore association in a hydrothermal deposit france abstract the aim of this study was to define the part played by organic matter in au ore genesis the possible associations and relations between carbonaceous matter and au were studied at various observation scales drill hole rock sample and microanalysis in an early stage au shear zone type deposit the west viges prospect creuse department france prior work had shown that in this type of deposit au mainly occurs within the structure of arsenopyrite the study of three cores from drill holes revealed a relation between the distribution of the mineralization and the presence of moderately brecciated anthracitic layers within the host volcanosedimentary tuffs chemical assays for au performed on the rock samples after destruction of the carbonaceous material by calcination showed that the au content is nearly always higher after calcination this may indicate that part of the au initially contained in the rock is trapped in the organic phase x ray diffraction spectra on carbonaceous phases isolated from some samples indicated the presence of elemental au these results indicate that like arsenopyrite organic matter is the bearer of au and retains it during conventional acid treatment of the ore

formation and evolution of the centennial unconformity related uranium deposit in the south central athabasca basin canada the centennial u deposit is situated in the south central athabasca basin canada and straddles the unconformity between early paleoproterozoic to archean metasedimentary and metavolcanic rocks and granitoids and the clastic sediments of the paleoproterozoic athabasca group although it has most characteristics of an unconformity related uranium deposit the centennial deposit is atypical in that it is not directly associated with an electromagnetic conductor there is a paucity of graphite in the basement or with a major reverse fault zone it is distal from a major fluid conduit ca 300 to 400 m from the dufferin lake fault has low ni cu co zn and pb contents and contains an unusually large amount up to 5 of secondary uranyl minerals additionally a network of diabase dikes and sills is observed at centennial seemingly intruding the main u mineralization of massive uraninite based on the relatively sharp contacts between the diabase dike and the high grade u mineralization the pre u alteration assemblage at centennial includes kaolinite illite and sudoite which have been formed by fluids with isotopic and chemical compositions that are comparable with those from other sandstone hosted unconformity type u deposits in the athabasca basin pre u illite related fluids have 18o of ca 3 and d of ca 40 whereas pre u chlorite related fluids have 18o between 1 7 and 4 3 and d between 18 and 1 laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of the various u phases indicates that initial mineralization represented by disseminated uraninite found directly to the north northeast of the centennial deposit occurred at ca 1 6 ga the main u mineralization represented by massive and strongly altered uraninite followed at an unknown time a minor 5 unaltered uraninite formed from the local remobilization of the main massive uraninite at ca 380 ma the main uranyl mineral uranophane formed last at ca 2 ma the recurrence of local u remobilization might have been facilitated by the persisting high permeability of the sandstones in the area due to the nearby dufferin lake fault and to the emplacement of the diabase dikes the usefulness of pb isotopes for exploration is demonstrated at the centennial deposit with strongly radiogenic pb isotope signatures close to the deposit and a common pb signature observed at a distance of a few km from the deposit

gold and platinum in shales with evidence against extraterrestrial sources of metals abstract few black shales contain concentrations of precious metals higher than average continental crust i e 5 ppb au yet au and pt alloys have been reported from the kupferschiefer in poland moreover thin sulfide beds in certain chinese and canadian shales contain several hundred ppb au pd and pt and average 4 mo and 2 5 ni in an association that is difficult to explain volcanic and non volcanic exhalations hydrothermal epigenesis involving either igneous or sedex fluids biogenic processes and low temperature secondary enrichment are among the possible factors involved in deriving ni pge and au for black shales and sulfide beds in black shales extraterrestrial sources have been invoked in some cases e g the cambrian of china however available data on abundances of pge indicate relatively low values for ir

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

the geochemistry of au and pt in peat and algal mats a case study from sri lanka abstract the geochemistry of au and pt in the muthurajawela peat deposit the largest in sri lanka has been studied together with the au and pt contents of algal mats from the tidal flats of mannar nw of sri lanka both peat and algal mats are enriched in au and pt the source material presumably being a laterite known to contain large amounts of au and pt au appears to be enriched in the clay and fe and mn in the colloid phase whereas pt does not correlate with any particular element in the tidal flat environment of the algal mats au shows a greater tendency to migrate seawards whereas pt is enriched in the clastic rich landward side as well as in the seaward algal mats possibly being mobilized as the chloride complex

geochemistry of uraniferous bitumen in the southwest athabasca basin saskatchewan canada the sediment hosted unconformity type southwest athabasca uranium mineralization in northern saskatchewan canada contains uraniferous bitumen as observed elsewhere in the athabasca basin uraninite is present either as micron sized grains dispersed in bitumen uraniferous bitumen or as larger grains situated in the pore space between bitumen globules the spatial and textural relationships between uraninite and bitumen suggest that they were co precipitated la icp ms u pb dating of uraniferous bitumen yielded an age of 1575 53 ma similar to that of other unconformity type uranium mineralization in the athabasca basin indicating that the bitumen was formed early in the history of the basin nitrogen carbon and sulfur isotope analyses of uraniferous bitumen indicate that its source material was probably kerogen produced by cyanobacteria in a clastic environment

formation of the enigmatic matoush uranium deposit in the paleoprotozoic otish basin quebec canada the matoush uranium deposit is situated in the paleoproterozoic otish basin northern quebec canada and is hosted by the indicator formation sandstones its sheet like ore bodies are closely associated with the steeply dipping matoush fracture which hosts mafic dykes and minor quartz feldspar tourmaline pegmatites regional diagenesis involving oxidizing basinal fluids 2h 15 18o 8 produced mostly illite and possibly leached u from accessory phases in the indicator formation sandstones the bimodal matoush dyke intruded the indicator formation along the matoush fracture and the related metasomatism produced cr rich dravite and muscovite in both the dyke and the proximal sandstones uraninite formed when u6 in the basinal brine was reduced to u4 in contact with the mafic dyke and by fe2 in cr dravite and cr muscovite and precipitated together with eskolaite and hematite because of its unique characteristics the matoush deposit cannot be easily classified within the generally accepted classification of uranium deposits two of its main characteristics unusual reduction mechanism structural control do not correspond to the sandstone hosted group of deposits unconformity type tabular roll front in spite of uranium being derived from the otish group sandstones

iridium and other platinum group elements as geochemical markers in sedimentary environments iridium anomalies are commonly used as indicators of extraterrestrial processes which caused global extinctions however platinum group element pge anomalies may result from several different processes both syn and postdepositional acting separately or jointly the sources and processes of enrichment involved are extraterrestrial asteroid comet cosmic dust impact ejecta volcanogenic pge rich condensates precipitation from seawater low sedimentation rate anoxic conditions microbial concentration dissolution reprecipitation exhalative hydrothermal leaching transport and precipitation at a redox boundary geochemical characteristics of pge and accompanying elements in sediments can be used to identify the contributions of some specific sources and processes 1 extraterrestrial chondritic ru ir and os ir ratios low 187os 186os ratio high ir compared to pt pd and au 2 volcanogenic high iridium and se as sb and in contents 3 exhalative hydrothermal high au pd and pt relatively low ir contents 4 precipitation from seawater high pt and low pd contents also high cd and ag contents under anoxic conditions and 5 reduction from intermediate and low temperature solutions high pge and cu or mo u ni contents

critical geochemical and mineralogical factors for the formation of unconformity related uranium deposits comparison between barren and mineralized systems in the athabasca basin canada the spring point barren alteration system and the maurice bay subeconomic uranium deposit situated on the northwest rim of the athabasca basin northern saskatchewan are hosted by the sandstones and conglomerates of the fair point formation of the athabasca group macroscopic observations indicate two different styles of alteration for the two systems chlorite dominated partly reduced alteration at spring point and illite dominated strongly oxidized alteration at maurice bay the paragenetic sequences developed for each area are similar but the crystal chemistry of the alteration minerals differs markedly indicating that the alteration fluids at spring point were richer in mg and ca than at maurice bay this is consistent with a predominantly basement origin for the former stable isotope analyses of clay alteration minerals indicate that in particular the chlorite related fluids from spring point have a basement signature 18 o 3 5 and d 13 whereas chlorite from maurice bay is more consistent with a mixture of basement and basinal fluids 18 o 5 2 and d 28 the absence of uranium transporting basinal fluids at the critical time when reducing basement fluids were producing chlorite alteration is likely the single most important cause for the lack of uranium mineralization at spring point

the sandstone hosted beverley uranium deposit lake frome basin south australia mineralogy geochemistry and a time constrained model for its genesis the sandstone hosted beverley uranium deposit is located in terrestrial sediments in the lake frome basin in the north flinders ranges south australia the deposit is 13 km from the u rich mesoproterozoic basement of the mount painter inlier which is being uplifted 100 to 200 m above the basin by neotectonic activity that probably initiated in the early pliocene the mineralization was deposited mainly in organic matter poor miocene lacustrine sands and partly in the underlying reductive strata comprising organic matter rich clays and silts the bulk of the mineralization consists of coffinite and or uraninite nodules growing around co rich pyrite with an s isotope composition 34 s 1 0 0 3 suggestive of an early diagenetic lacustrine origin in contrast authigenic sulfides in the bulk of the sediments have a negative s isotope signature 34 s ranges from 26 2 to 35 5 indicative of an origin via bacterially mediated sulfate reduction minor amounts of zn bearing native copper and native lead also support the presence of specific reducing microenvironments in the ore zone small amounts of carnotite are associated with the coffinite ore and also occur beneath a paleosoil horizon overlying the uranium deposit provenance studies suggest that the host miocene sediments were derived from the reworking of early cretaceous glacial or glaciolacustrine sediments ultimately derived from paleozoic terranes in eastern australia in contrast the overlying pliocene strata were in part derived from the mesoproterozoic basement inlier mass balance and geochemical data confirm that granites of the mount painter domain were the ultimate source of u and ree at beverley u pb dating of coffinite and carnotite suggest that the u mineralization is pliocene 6 7 3 4 ma the suitability of the beverley deposit for efficient mining via in situ leaching and hence its economic value are determined by the nature of the hosting sand unit which provides the permeability and low reactivity required for high fluid flow and low chemical consumption these favorable sedimentologic and geometrical features result from a complex conjunction of factors including deposition in lacustrine shore environment reworking of angular sands of glacial origin deep pliocene weathering and proximity to an active fault exposing extremely u rich rocks