the nature and origin of gold deposits of the tarcoola goldfield and implications for the central gawler gold province south australia the tarcoola goldfield in central south australia is hosted by the paleoproterozoic paxton granite and tarcoola formation metasedimentary rocks both of these units are intruded by narrow dikes of the lady jane diorite which is considered to be part of the gawler range hiltaba volcano plutonic event crosscutting relationships and 40ar 39ar dating of alteration sericite and primary hornblende have demonstrated that veining alteration and mineralization occurred synchronously with intrusion of the diorite dikes at 1580 ma mineralization at the perseverance deposit in the tarcoola goldfield is hosted by quartz veins in both granite and the lower parts of the tarcoola formation alteration intensity and mineralization are related to fracture density very high gold grades up to 270 ppm are recorded in carbonaceous siltstones of the tarcoola formation primary fluid inclusions from mineralized quartz veins at perseverance are dominated by two phase aqueous inclusions and three phase h2o co2 l co2 v ch4 inclusions both inclusion types have salinities of 10 wt percent nacl equiv with evidence of other salts being present both types homogenize between 150 and 340 c they occur together in single quartz grains which suggests the coexistence of aqueous and carbonic fluids at the perseverance deposit the maximum depth of fluid inclusion formation is estimated as 10 km processes resulting from pressure fluctuations during brittle fracturing causing phase separation are suggested to be the dominant gold precipitation mechanism although definitive fluid inclusion evidence for either phase separation or fluid mixing is lacking wall rock sulfidation may have also contributed to gold deposition pb isotope compositions of galena from gold bearing mineralized veins at perseverance are similar to k feldspar and whole rock samples of the paxton granite this is consistent with a common source of pb and possibly other ore components for both the granite and galena but not all potential reservoirs were tested variably altered and gold mineralized samples that had paxton granite precursors show a loss of nd and a trend from end 1580ma values of about 6 2 in slightly altered samples toward more positive end values of about 3 3 in high grade gold samples of the local lithologic units the lady jane diorite has end 1580ma values of about 0 1 and is the most probable source of the more primitive nd isotope components in mineralized samples mineralization in the tarcoola goldfield has similarities to both orogenic and intrusion related gold styles the demonstrated coeval timing of diorite dikes and mineralization at tarcoola together with the nd isotope constraints on metal sources and the presence of similar mafic dikes in several other known gold prospects in the central gawler gold province suggests that the diorite was an essential part of the gold mineralization event throughout this province

crystal chemistry of titanite from the roxby downs granite south australia insights into petrogenesis subsolidus evolution and hydrothermal alteration titanite textures and chemistry have been investigated from the roxby downs granite host to the olympic dam cu u au ag deposit south australia three textural subtypes of titanite are documented primary magmatic cores and rims deuteric and hydrothermal low t recrystallisation magmatic cores are defined by enrichment in lree 3 wt nb up to 1 wt and zr relative to rims which typically contain 1 wt lree and nb as well as greater concentrations of al ca fe and f deuteric titanite occurs as overgrowths on pre existing titanite and other magmatic accessory minerals magnetite and ilmenite and is depleted in hfse compared to magmatic rims showing geochemical trends consistent with substitution of ca2 ti4 ree3 al fe 3 hydrothermal titanite forms as a low temperature hydrothermal overprint on primary titanite as well as an alteration product of chloritised phlogopite applying zr in titanite geothermometry three temperature ranges are obtained for titanite crystallisation magmatic cores 765 to 780 c rims 705 to 740 c and deuteric 680 to 690 c titanite breakdown is a ubiquitous feature of the roxby downs granite and occurs through interaction with co2 and f rich fluids forming pseudomorphs characterised by the presence of ree fluorocarbonates which are subsequently overprinted by ree phosphates with increased proximity to the olympic dam breccia complex this change is related to interaction with fluids containing appreciable po42 liberated from local dissolution of fluorapatite such observations are consistent with and linked to later retrograde stages in the formation of the olympic dam deposit

electromagnetic induction studies recent developments in electromagnetic induction studies of the lithosphere and the asthenosphere are reviewed attention is given to geoelectrical studies of active tectonic areas in terms of the major zones of crustal extension the basin and range province along western regions of north america and the rio grande rift studies have also been performed of tectonic activity around iceland the salton trough and cerro prieto and the subduction zones of the cascade mountains volcanic belt where magnetotelluric and geomagnetic variation studies have been done geomagnetic variations experiments have been reported in the central appalachians and submarine electromagnetic studies along the juan de fuca ridge controlled source electromagnetic and dc resistivity investigations have been carried out in nevada hawaii and in the adirondacks mountains laboratory examinations on the conductivity of representative materials over a broad range of temperature pressure and chemistry are described

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

40ar 39ar thermochronology of the southern gawler craton australia implications for mesoproterozoic and neoproterozoic tectonics of east gondwana and rodinia 40ar 39ar thermochronology of the southern gawler craton australia reveals a protracted history of slow cooling with local crustal heating rapid cooling and fault reactivation between 1700 and 700 ma hornblendes from most of the southern part of the craton including the kalinjala mylonite zone yield ages 1580 1610 ma with younger more discordant samples showing evidence of retrogression these results indicate that the region cooled below 500 c 100 m y after the kimban orogeny and coincident with the gawler range hiltaba suite magmatism to the north perhaps associated with postorogenic extension biotite and k feldspar data indicate that regional cooling after this time was more gradual with a few exceptions locally in the southeastern eyre peninsula rapid cooling at 1425 ma is indicated by nearly concordant hornblende and biotite ages and may record a phase of regional extension other exceptions include areas of lower grade archean rocks that cooled to 350 c by 1700 1640 ma greenschist facies reactivation of shear zones occurred at 1100 ma during the musgravian orogeny on the basis of biotite single grain data and retrogressed amphiboles k feldspar age spectra record cooling at 700 800 ma following regional intrusion of the gairdner dike swarm and or denudation during rifting along the pacific margin of east gondwana and breakup of rodinia tectonothermal events revealed by these results previous geochronological and geological studies and available paleomagnetic data are comparable to other cratons and mobile belts in australia east gondwana and laurentia providing evidence that southeastern australia and north america were adjacent during much of proterozoic time

a geomagnetic scattering theory for evaluation of earth structure summary structural features of the earth s lower crust and upper mantle can be mapped by the analysis of temporal geomagnetic fluctuations using the electromagnetic scattering theory developed in this paper decomposing geomagnetic field fluctuations at the earth s surface into an excitation part and a scattered part forms the basis of a power series development the vertical field component is interpreted as a scattering of the excitation field the horizontal gradient and geomagnetic depth sounding methods are special cases of the theory developed the horizontal gradient sounding method has a tensorial aspect which has not been recognized before it should be included to obtain correct penetration depth parameter evaluations from field data

geomagnetic induction soundings over the michigan basin abstract geomagnetic variation sounding and magnetotelluric results from six sites on an east west long period profile across the michigan basin are presented a strongly conductive zone on the western flank of the presumed underlying keweenawan rift system in the precambrian basement is shown to exist near cadillac michigan this zone is perhaps similar in character to the flambeau anomaly exposed at the surface in wisconsin also on the flank of the keweenawan rift whose conductivity resides in iron formations and in massive and disseminated graphite and sulphides no clear expression of the michigan basin itself or of the presumed keweenawan rift in the basement is seen in the results the limited magnetotelluric sounding results correspond to a surface conducting layer over a resistive deeper crust over a rise in conductivity at mantle depths they show several hundred seimens of crustal conductance in excess of that provided by the phanerozoic sediments of the basin but do not determine whether the excess crustal conductivity is associated with the underlying keweenawan clastics and volcanics or whether some of that conductivity is in a deeper crustal layer like that found under the adirondack dome by connerney et al

first results of the moses experiment sea sediment conductivity and thickness determination bute inlet british columbia by magnetometric offshore electrical sounding a static electrical method has been developed to determine the electrical resistivity of crustal rock beneath the sea the transmitter is a vertical long wire bipole extending from the sea surface to the sea floor a commutated current generated on the ship is fed to two large electrodes one near the sea surface the other at the end of a long insulated wire the return path for the current is through the sea and the subjacent crust the receiver is a self contained remote microprocessor controlled magnetometer which is deployed from the ship to the sea floor and subsequently recovered the data are measurements of the azimuthal component of the magnetic field as a function of transmitter receiver horizontal separation the acronym moses has been coined for the method the choice of the name moses is appropriate because the system geometry is carefully arranged to remove many of the adverse effects of the relatively conductive sea water in particular accurate estimates of sea floor resistivity ar

apatite at olympic dam south australia a petrogenetic tool abstract the 10 000 million tonne olympic dam cu au u ag deposit eastern gawler craton south australia is one of the largest orebodies in the world the deposit is hosted within the olympic dam breccia complex placed at the centre of and resulting from multiple brecciation and fe metasomatism of the roxby downs granite rdg the latter is part of a larger batholith emplaced at 1 6 ga apatite petrography and chemistry were studied in non mineralised rdg and coeval granitoids and dolerites as well as in mineralised rdg from deep 2 km and distal 2 7 km to ne locations in both latter cases although the mineralisation corresponds to the same early chalcopyrite pyrite magnetite hematite stage identified in the outer and deeper zones of the deposit itself the character of granite alteration differs sericite chlorite alteration with all feldspar replaced in the deep location and red stained k feldspar on top of prevailing albitization in the distal location close to end member fluorapatite is a key accessory mineral in all igneous rocks and a common product of early hydrothermal alteration within mineralised granite variations in habit morphology and textures correlate with chemical trends expressed as evolving cl f ratios and concentrations of ree y hereafter rey sr mn s si and na magmatic apatite is unzoned in the dolerite but features core to rey enriched rim zonation in the granitoids increases in cl and sr contents correlate with rock basicity calculation of cl in the vapour phase relative to melt at the apatite saturation temperature for zoned apatite in the rdg shows higher values for grains with inclusion rich cores associated with mafic enclaves concordant with assimilation of exotic material during magma crystallisation hydrothermal alteration of magmatic apatite is most varied in the dolerite where interaction with fluids is expressed as subtle changes in cl versus f and rey enrichment and most importantly s enrichment in grains adjacent to crosscutting carbonate sulphide bearing veins highly acidic fluids which not only corroded apatite but also quartz led to recycling of rey via subsequent crystallisation of discrete rey bearing species notably monazite hydrothermal apatite often occurs as interstitial aggregates and displays a wider range of textures indicating variability in local growth conditions and or sustained interaction with evolving hydrothermal fluids apatite from the deep mineralisation is richer in cl whereas increases in rey and s correlate with higher si in both deep and distal cases the co correlation between na and s in apatite from distal mineralisation ties apatite crystallisation to replacement of albite by sericite chlorite the textural and chemical variation of apatite relative to magmatic to hydrothermal transition suggests that the mineral represents a petrogenetic tool to gain insights into mineralising processes at olympic dam apatite evolution clearly played a key contributing role in the elevated rey concentrations seen at olympic dam the marked differences in apatite chemistry between mineralised and non mineralised lithologies show promise for potential application as a tool in mineral exploration in which apatite chemistry represents a means for outlining spatial position within an alteration envelope or identifying if a particular alteration system is barren or fertile with respect to cu au mineralisation

linking olympic dam and the cariewerloo basin was a sedimentary basin involved in formation of the world s largest uranium deposit the supergiant olympic dam cu u au ag deposit is hosted by the olympic dam breccia complex within a ca 1 59 ga granite the breccia complex is largely granite derived but also includes volcanic clasts and domains of bedded clastic facies recently discovered quartz rich sandstone has a provenance that included paleoproterozoic and archean units represented by zircon populations centered at ca 2 4 ga and ca 1 7 ga the texture detrital and cement mineralogy and distribution of detrital zircon ages in the quartz rich sandstone closely match those in sandstone of the pandurra formation deposited in the regionally extensive intracratonic cariewerloo basin ca 1 44 ga the age of authigenic apatite 1 44 0 02 ga in the brecciated quartz rich sandstone is equivalent to the minimum depositional age of the pandurra formation we conclude that the quartz rich sandstone is a remnant of the pandurra formation that the pandurra formation originally extended across the olympic dam breccia complex and that it was incorporated by tectonic activity at least 150 myr after initial formation of the breccia complex furthermore we speculate that oxidized u bearing fluids from the overlying cariewerloo basin may have interacted with the olympic dam u resource consistent with mounting evidence for substantial post 1 59 ga remobilization and probable addition of u

geochemical and grain size evidence for the provenance of loess deposits in the central shandong mountains region northern china abstract widespread loess deposits in the central shandong mountains yield valuable paleoclimatic records for this currently semi humid monsoonal region of northern china the grain size distribution and major element composition for bulk samples and two grain size fractions

an andosol cambisol toposequence on granite in the austrian bohemian massif in europe non allophanic andosols are linked with hercynian basic and metabasic rocks in smoothed highlands with a cool and humid climate we describe an andosol cambisol toposequence derived from variscan coarse grained granite in northern austria bohemian massif where andosols have formed on plateaus and cambisols on steep slopes the climate is continental cool and humid mean annual temperature and rainfall 5 4 degreesc and 914 mm with a 100 day mean annual period of snow cover the forest is dominated by beech and spruce trees both soils are rich in organic matter and strongly acidic but the andosol is more strongly weathered than the cambisol below the 15 cm thick litter in the andosol the 38 cm thick ab bw solum is dark reddish brown to strong brown has a large c content 9 0 4 4 and meets all the requirements of an andic horizon in these horizons oxalate extractable iron content 1 62 8 fe o represents 76 84 of free iron and is much larger than al o 0 8 1 5 both biotite and plagioclase are sources of fe and al the fort nation of non allophanic andosol from granite was likely due to the combination of the following factors cool and humid climate large accumulation of organic matter high infiltration rate intense water percolation during spring thawing and significant content of weatherable minerals as such conditions are not rare in european highlands andic soils are probably more widespread in europe than is currently thought c 2003 elsevier b v all rights reserved

occurrence of sombric like subsurface a horizons in some andic soils of the nilgiri hills southern india and their palaeoecological significance this paper deals with four pedons three fulvudands and one andic haplorthox located at high elevations 2000 2400 m a s l in the nilgiri hills on an old laterized surface of south india and characterized by thick 50 100 cm epipedons whose colour tends to darken with depth in two of them the colour contrast between the top and the bottom a horizons was so well expressed that they were morphologically very similar to the african oxisols reported to have sombric subsurface horizons soil organic matter som of the different selected a horizons was characterized by its mean residence time mrt and its delta 13 c value whereas their humic acids has were examined by techniques that made it possible to determine their chemical composition and their chromatic properties it was found that the darker colour of the subsurface a horizons of these soils was related to three joined characteristics a som delta 13 c signature indicating a c4 type vegetation i e a grassland type origin the presence of humic acids belonging to the a type i e melanic category of kumada kurnada k 1987 chemistry of soil organic matter developments in soil science elsevier tokyo and large mean residence time values in contrast the top a horizons had a more recent som mainly inherited from a c3 type vegetation and humic acids has that were less condensed than the a type has it was also found that where the presence of sombric like subsurface a horizons was the most evident the vegetation change recorded by the soils i e the change from a grassland type vegetation towards a c3 type vegetation was expressed on the thickest part of their epipedon these observations led us to propose that the occurrence of sombric like subsurface a horizons resulted from the following sequence of events i an exceptionally thick accumulation of organic matter deriving from grassland followed by ii its progressive replacement by less dark organic matter derived from a c3 type vegetation this proposal was found to be in reasonable agreement with the history of the vegetation changes experienced by the nilgiri hills since the end of the pleistocene on the other hand it is also very similar to one of the hypotheses proposed by van wambeke van wambeke a 1992 soils of the tropics properties and appraisal mcgraw hill new york to explain the frequent occurrence of sombric horizons in the oxisols and ultisols of the high altitude areas of central africa c 2003 elsevier science b v all rights reserved

an intrusion related origin for cu au mineralization in iron oxide copper gold iocg provinces major cu au deposits of iron oxide copper gold iocg style are temporally associated with oxidized potassic granitoids similar to those linked to major porphyry cu au deposits stable and radiogenic isotope evidence indicates fluids and ore components were likely sourced from the intrusions iocg deposits form over a range of crustal levels because co2 rich fluids separate from the magmas at higher pressures than in co2 poor systems thereby promoting partitioning of h2o cl and metals to the fluid phase at deep levels the magma fluid system cannot generate sufficient mechanical energy to fracture the host rocks as in porphyry systems and the iocg deposits therefore form in a variety of fault related structural traps where the magmatic fluids may mix with other fluids to promote ore formation at shallow levels the iocg deposits form breccia and fracture hosted mineralization styles similar to the hydrothermal intrusive breccias and sulphide vein systems that characterize many porphyry cu au deposits the fluids associated with iocg deposits are typically h2o co2 salt fluids that evolve by unmixing of the carbonic phase and by mixing with fluids from other sources in contrast fluids in porphyry systems typically evolve by boiling of moderate salinity fluid to produce high salinity brine and a vapor phase commonly with input of externally derived fluids these different fluid compositions and mechanisms of evolution lead to different alteration types and parageneses in porphyry and iocg deposits porphyry cu au deposits typically evolve through potassic sericitic and intermediate and or advanced argillic stages while iocg deposits typically evolve through sodic calcic potassic and carbonate rich stages and at deeper levels generally lack sericitic and argillic alteration the common association of porphyry and iocg cu au deposits with potassic oxidized intermediate to felsic granitoids together with their contrasting fluid compositions alteration styles and parageneses suggest that they should be considered as part of the broad family of intrusion related systems but that they are typically not directly related to each other

occurrence and origin of soils with andic properties in calabria southern italy abstract andic like soils along with andosols have previously been reported in non volcanic ecosystems of the coastal and mountainous areas of the calabria region southern italy but little is known about their properties soil formation processes and volcanic source areas chemical mineralogical microscopic sub microscopic and magnetic analyses were carried out on 8 soils which were selected from the major calabrian geological sectors in order to assess relationships between parent material and bedrock soil chemical properties revealed an occurrence of andic or vitric properties in the studied soils as a whole and the optical microscopy enabled to identify volcanic glass micro pumices and soil isotropic matrix clearly indicating volcanic inputs three groups of soils identified on the basis of the degree of andic properties showed rather homogeneous also in terms of chemical properties clay mineralogy and land use as well as with regard to micromorphology and magnetic susceptibility part of the intra group similarities was a consequence of similar distances between sites and volcanic source area as suggested by the correlations found between ferrihydrite content andic i e of ammonium oxalate extractable al 0 5 fe and phosphate retention and magnetic properties vs distances from several sicilian districts the elemental composition obtained by sem eds analyses of soil glass fragments supported these findings and related the origin of most of the studied soils to the high potassium calc alkaline magmatism of the southernmost eolian islands mainly lipari and vulcano except for soils from the marine terraces of northern calabria pra and the aspromonte massif del which were both linked albeit uncertainly to campanian volcanism soil magnetic properties were significantly 0 79 correlated to the andic properties so confirming the high performance of magnetic susceptibility as low cost proxy for the identification of volcanic constituents

induction models of southern india and the effect of off shore geology abstract simple numerical tests based on thin sheet modelling are used to define the conductors most probably responsible for current channelling in the region including southern india a combination of crustal conductors located in the indo ceylon graben and underneath the comorin ridge best reproduces the observations at periods of 50 100 min in so far as channelling is concerned daytime variations do not help to define the location of conductors any better than night time data and may thus be ignored

characteristics origin and significance of mesoproterozoic bedded clastic facies at the olympic dam cu u au ag deposit south australia mesoproterozoic bedded clastic facies occur in the olympic dam breccia complex which hosts the olympic dam cu u au ag deposit south australia contacts of the bedded clastic facies with breccia of the olympic dam breccia complex are faulted and or brecciated fragments of the bedded clastic facies occur in the breccia complex the bedded clastic facies comprise five main facies associations four of which are organised into mappable units these associations have distinct textures and components and have not been mixed major sources of detritus were felsic and mafic volcanic units and granitoids of the 1590 ma gawler silicic large igneous province archean and paleoproterozoic zircons in well sorted quartz rich sandstone indicate that older gawler craton basement successions also contributed sediment to the bedded clastic facies accumulation of the bedded clastic facies was at least partly contemporaneous with rhyolitic explosive eruptions from vent s probably tens of km away because bubble wall shards are present in tuffaceous mudstone facies deformation of the bedded clastic facies prior to final lithification produced folds that have diverse shapes and sizes and that lack cleavage the folds have a reasonably consistent gentle plunge to the northeast these soft sediment folds could be related to slumping on a northeast striking paleoslope that dipped either to the northwest or southeast the depocenter in which these facies accumulated may have been bounded by a combination of northeast striking and northwest striking faults because the bedded clastic facies occur at the top of the olympic dam breccia complex and contributed clasts to it the fault controlled sedimentary basin was in place when the breccia complex and the olympic dam ore deposit formed

magnetic and chemical parameters of andic soils and their relation to selected pedogenesis factors in the case of andic soils developed on volcanic rocks permanently humid conditions are essential for andosolisation processes although volcanic rocks are usually rich in highly magnetic iron oxides knowledge about these minerals in andic soils with respect to the soil development is missing the aim of this contribution is to investigate the relationship between magnetic and basic chemical properties of soils developed on volcanic basement and parameters related to the pedogenesis factors the studied sites are located on basaltic lava flows in the eastern part of the french massif central investigated pedons with alu andic sil andic and vitric properties were pedologically described and analysed by a set of magnetic and soil chemical methods magnetic parameters include low field volume specific and mass specific magnetic susceptibility frequency dependent magnetic susceptibility remanent properties including s ratio and coercivities chemical parameters included the phh2o soil organic matter total cation exchange capacity base saturation and content of fe and al extracted in dithionite citrate acid ammonium oxalate and pyrophosphate solutions micro morphology of andosols and parent material was observed by scanning electron microscopy completed with energy dispersive spectrometry the pedogenesis factors are represented by parent rock age annual precipitation and soil thickness our findings suggest that 1 precipitation is the most important pedogenesis factor with a strong relationship to the relative magnetic grain size concentration of ferrimagnetic minerals aluminium dissolved in pyrophosphate and acid ammonium oxalate and content of organic matter 2 parent material age shows a well pronounced relationship with magnetic grain size parameters represented by the frequency dependent susceptibility and ratio of saturation remanent to saturation induced magnetisation mrs ms selective dissolution parameters and phh2o 3 thickness of soil profile shows a link to mrs ms phh2o and content of organic matter

sources of mineralising fluids for the olympic dam deposit south australia smnd isotopic constraints abstract the olympic dam cu u au ag deposit south australia is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system the deposit is characterised by extreme enrichments of ree which are a product of the ore forming process therefore making the sm nd isotopic system an ideal tool for clarifying the complex relationships between the different ore and breccia types pyrite chalcopyrite and bornite chalcocite rich hematitic ores share an initial end signature of 2 5 which suggests that these ore types are cogenetic these ores together with sulphide poor hematitic breccias yield a 14 point sm nd isochron age of 1572 99 ma the host roxby downs granite has an initial nd of 5 and therefore cannot alone have been the source of the mineralising fluids for the hematitic ores in contrast to hematitic rocks volumetrically minor magnetite rich assemblages have the same initial nd signature as the host granite suggesting that they are cogenetic assuming that both hematite and magnetite were precipitated from solution their contrasting isotopic signatures require that ore deposition involved two distinct fluids the isotopic data do not allow the distinction between a model involving concurrent activity of such fluids in a mixing regime and a model involving temporally separate overprinting of magnetite by hematite cu sulphides the ore signature of nd 2 5 cannot have been derived solely from pre existing crustal rocks of the gawler craton it must have involved a contribution from a mantle derived source rock or magma the most likely source of this nd component are the mantle derived rocks produced during the gawler range volcanics event e g altered alkaline mafic ultramafic dykes within the deposit which have initial isotopic signatures as high as nd 4 assuming end member compositions equivalent to these dykes and the roxby downs granite the ore signature implies that 30 of the nd in the ores was derived from the mafic ultramafic source if nd was leached from source rocks rather than derived from magmatic volatiles the inferred rock fractions contributing ree to the deposit are 13 mafic ultramafic rocks and 87 roxby downs granite or its volcanic equivalent massbalance calculations indicate that 13 rock fraction of mafic ultramafics can account for 50 of the cu contained in the deposit the involvement of mafic ultramafic rocks is therefore inferred to have been crucial to the genesis of the cu enriched ores at olympic dam

contribution at satellite altitude of electromagnetically induced anomalies arising from a three dimensional heterogeneously conducting earth using sq as an inducing source field summary the induced magnetic signature at satellite altitude associated with crustal and mantle electrical heterogeneities is examined using five different earth models the three dimensional induction problem is solved in these models using the solar quiet daily variation as an inducing source field every model has an upper shell representing the land ocean electrical conductivity distribution the different models have either a homogeneous mantle or a heterogeneous mantle containing either subduction zones a ridge system or conductive blocks electromagnetic anomalies presented in the form of geographical maps are calculated for wavelengths related to spherical harmonics of degrees in the ranges 1 12 and 13 27 respectively magnetic anomalies are calculated at an altitude of 400 km and for three different local times 6 12 and 18 h

uraninite from the olympic dam iocg u ag deposit linking textural and compositional variation to temporal evolution the olympic dam iocg u ag deposit south australia the world s largest known uranium u resource contains three main u minerals uraninite coffinite and brannerite four main classes of uraninite have been identified uraninite occurring as single grains is characterized by high pb and ree y rey but based on textures can be classified into three of these classes typically present in the same sample primary uraninite class 1 is smallest 10 50 m displays a cubic euhedral habit and both oscillatory and sectorial zoning zoned uraninite class 2 is coarser sub euhedral and combines different styles of zonation in the same grain cobweb uraninite class 3 is coarser still up to several hundred micrometers has variable hexagonal octagonal morphologies varying degrees of rounding and features rhythmic intergrowths with sulfide minerals in contrast the highest grade u in the deposit is found as micrometer sized grains to aphanitic varieties of uraninite that form larger aggregates up to millimeter and vein fillings massive class 4 and have lower pb and rey but higher ca nanoscale characterization of primary and cobweb uraninite shows these have defect free fluorite structure both contain lattice bound pb rey which for primary uraninite is concentrated within zones and for cobweb uraninite is within high pb rey domains micro fractured low pb rey domains sometimes with different crystal orientation to the high pb rey domains in the same cobweb grain contain nanoscale inclusions of galena cu fe sulfides and rey minerals the observed pb zonation and presence of inclusions indicates solid state trace element mobility during the healing of radiogenic damage and subsequent inclusion nucleation recrystallization during formula 1 driven percolation of cu bearing fluid tetravalent lattice bound radiogenic pb is proposed based on analogous evidence for u bearing zircon calculating the crystal chemical formula to uo2 stoichiometry the sum of cations m is 1 for most classes but the presence of mono di and trivalent elements rey ca etc drive stoichiometry toward hypostoichiometric m o2 x in the absence of measured o and constraints of hypostoichiometric fluorite structure charge balance calculations showing o deficit in the range 0 15 0 36 apfu is compensated by assumption of mixed u oxidation states crystal structural formulas show up to 0 20 apfu pb and 0 25 apfu rey in classes 1 3 while for class 4 these are an order of magnitude less low pb and rey subcategories of classes 2 and 3 are similar to massive uraninite with 0 2 apfu ca other elements si na mn as nb etc show two distinct geochemical trends 1 across classes 1 3 and 2 class 4 whereby low pb rey sub populations of classes 2 and 3 are part of trend 2 for certain elements plots of alteration factor cao sio2 fe2o3 vs pb u suggest two uraninite generations early high pb rey classes 1 3 and late massive class 4 there is evidence of pb loss from diffusion leaching and or recrystallization for classes 2 3 low pb rey domains micro analytical data and petrographic observations reported here including nanoscale characterization of individual uraninite grains support the hypothesis for at least two main uraninite mineralizing events at olympic dam and multiple stages of u dissolution and reprecipitation early crystalline uraninite is only sparsely preserved with the majority of uraninite represented by the massive aphanitic products of post 1590 ma dissolution reprecipitation and possibly addition of uranium into the system coupled dissolution reprecipitation reactions are suggested for early uraninite evolution across classes 1 to 3 the calculated oxidation state u6 u4 u6 of the early and late populations point to different conditions at the time of formation charge compensation for rey rich early fluids rather than auto oxidation of uraninite late uraninites may have formed hydrothermally at lower temperatures t 250 c 1 embed mml math 1 gif

soil formation in kettle holes from high altitudes in central apennines italy abstract kettle holes are relatively common features of glaciated landscapes and have been widely reported in the literature the work reported here documents the presence of kettle holes at high altitude and low latitude in the central apennines italy and describes the geomorphic and pedogenic processes that originated the soils infilling these depressions the areas selected for this study were located on three of the main massifs of the central apennines italy gran sasso majella and sibillini the kettle holes on these massifs formed at the end of the wurm glaciation appear smaller and shallower than those reported from elsewhere in the northern hemisphere are roughly circular in form and do not contain bogs or lakes in each area the dimensions of 40 kettle holes were measured and three kettle holes were excavated to examine the soils developed inside them the size of the kettle holes was highest in the sibillini massif where the glaciers reached altitudes as low as 1700 m in the very narrow low lying valleys it is hypothesised that at lower elevations the glacier receded more rapidly generating larger blocks of ice and consequently larger kettle holes once formed the kettle hole depressions were very effective as sediment traps and acted as sink for materials washed in from the surrounding slopes or from more distant wind blown sources in the kettle holes from gran sasso and majella massifs small fragments of woody charcoal were found the material filling the kettle holes accumulated inside them in the form of layers soils formed inside the kettle holes showed horizons whose thickness and properties appeared mostly inherited from the amassed layers the only pedogenic process common to the kettle holes of the three massifs was the incorporation of organic matter that as expected from the rather cold climatic conditions was subjected to slow dynamics in the kettle holes of the majella massif the horizons developed from layers rich of materials of volcanic origin and the formation of short range order minerals occurred we conclude that the soils inside the kettle holes are a repository of geomorphic pedogenic and in reference to the source of the charcoal paleo environmental information

a sedimentary overlap assemblage links australia to northwestern laurentia at 1 6 ga abstract the columbia nuna supercontinent existed from approximately 1 9 ga to 1 3 ga laurentia was part of columbia and the western edge of laurentia current coordinates was likely proximal to a large landmass during parts of this interval here we present detrital zircon ages of a paleoproterozoic sedimentary succession in northern yukon canada that bear on the evolution of columbia the sedimentary succession is preserved as clasts within 1 60 ga hydrothermal megabreccias analyses of detrital zircon reveal abundant 1 78 1 68 ga zircon with evolved hf isotope values 16 1

an objective real time data adaptive technique for efficient model resolution improvement in magnetotelluric studies a scheme is described whereby the error associated with the least well resolved model eigenparameter in a magnetotelluric survey is reduced by focusing data collection on a specific range of frequencies the scheme also gives a quantitative estimate of the statistical error associated with the least well resolved model parameter and thus provides an objective criterion to the operator regarding when to cease data collection at that location the scheme is based on a linearization of the relationship between variations in the model parameters and the changes thereby introduced to the computed response function the matrix of partial derivatives describing this linearization is factored orthogonally by a singular value decomposition the scheme is illustrated by applying it to a synthetic data set also the algorithm has been coded in basic on an hp9845 and employed in the field an example is given of its field operation in a sedimentary basin environment

uranium bearing hematite from the olympic dam cu u au deposit south australia a geochemical tracer and reconnaissance pb pb geochronometer abstract uranium bearing hematite containing up to several wt u also containing al mo w and radiogenic pb is described from olympic dam south australia these elements are present in grains that display both oscillatory zonation and porous structures laser ablation inductively coupled mass spectrometry la icp ms element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238u and 206pb and are distinct from those of w and mo the crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope focused ion beam technique satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long range superstructure ordering that is inferred to assist metal incorporation via the substitution 2fe3 me6 vacancy where me u w mo the suitability of u bearing hematite for pb pb geochronology as a first pass was tested on both zoned and porous hematite grains via la icp ms using the gj 1 zircon as the primary external standard only pb pb ages were considered and resulted in 207pb 206pb ages of 1590 8 ma and 1577 5 ma for oscillatory and sector zoned hematite from two samples although reconnaissance in nature these ages potentially support the supposition that mineralization is coeval with emplacement of the gawler range volcanics and associated hiltaba intrusive suite the geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron bearing ores

late quaternary tephra derived paleosols in central italy s carbonate apennine range stratigraphical and paleoclimatological implications abstract detailed stratigraphical pedological and geochronological 14c dating research was carried out on numerous sections located in the carbonate apennine range of central italy two paleosols late pleistocene pedomarker a and holocene pedomarker b in age were recognized as having developed from air fall pyroclastic material given their special properties and widespread distribution both soils represent valuable markers in the late quaternary stratigraphy of central italy information about the climatic conditions that have influenced their pedogenesis through time has been obtained pedomarker a formed under temperate wet conditions related to the last interstadial fluctuations of the pleniglacial its development ceased after ca 30 ka because of the onset of last glacial maximum dry cold conditions pedomarker b formed at the beginning of the holocene under udic and perudic soil moisture regimes its development ceased in some localities because of a change towards a drier climate after ca 4 5 ka petrographic and geochemical characteristics of the parent materials are discussed and correlations with the campanian ignimbrite pedomarker a and neapolitan yellow tuff pedomarker b both related to activity in the phlegrean fields are proposed

volcanic soil formation in calabria southern italy the cecita lake geosol in the late quaternary geomorphological evolution of the sila uplands abstract this paper focuses on the main morphological physical chemical and mineralogical features of an andic like soil widely outcropping in the sila upland plateau of calabria southern italy and its potential role in tephrostratigraphy a multidisciplinary and multiscale approach allowed identification of this soil as a masked distal archive of volcanic products developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis the study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence limited extent or poor preservation of primary eruptive products the soil has an andisol like appearance despite laboratory data that do not match the entire suite of diagnostic criteria for the andisol taxonomic order geomorphological stratigraphic and pedologic results coupled with tephrostratigraphic and radiometric data concur to suggest a late pleistocene to holocene age of the andisol like soil in particular the rhyolitic chemical composition of small sized glass fragments identified by sem eds analyses indicates soil genesis contributed by volcanic ash probably sourced from aeolian arc explosive activity spanning the last 30 ka accordingly the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties in turn related to the neoformation of clay minerals from the weathering of volcanic glass are consistent with a climatic shift from a seasonally contrasted to a constantly humid pedoenvironment this change can be ascribed to the lateglacial or early middle holocene to late holocene transition calibrated ams 14 c dates performed on charcoal fragments sampled from three representative soil profiles provide late holocene ages 3136 19 343 16 and 92 24 yr bp in accord with archaeological finds on the basis of the consistent stratigraphic position lateral continuity and wide extent the soil can be considered a good pedostratigraphic marker in the sila highlands and is informally defined as the cecita lake geosol it supplies valuable time constraints for the underlying occasionally overlying deposits and or soils moreover it allows regional scale morphostratigraphic correlations and detailed reconstruction of late pleistocene holocene geomorphic events in calabria a very suitable region for distal tephra deposition in the central mediterranean peri volcanic area the effects of high energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals

the hidden nature of parent material in soils of italian mountain ecosystems abstract soils with andic features are known to be very important as regards both ecosystem fertility and susceptibility to land degradation in recent years there has been an increasing number of finds of these soils in non volcanic mountain ecosystems nvme in different parts of the world under different environmental settings in italian nvme there has been extensive investigation proving that these soils have a much wider distribution than previously thought but despite these important findings very little is known about their genesis or properties against this background our investigation aims to question the nature of parent material in andic soils in italian nvme we consider this question fundamental for proper understanding of such soils we address the question of the parent material by highlighting similarities dissimilarities between soils and their underlying bedrocks and ascertaining whether soils developed as a result of in situ weathering or because of eolian inputs the study was conducted on 41 soil profiles distributed throughout italian nvme performing an integrated analysis of i grain size distribution gsd by laser granulometry ii end member modelling of obtained gsd iii soil bedrock differences in magnetic susceptibility and iv soil bedrock differences based on the geochemistry of 38 elements the final results from these investigations show that the investigated soils are mainly derived from eolian sediments and that weathering of the underlying bedrock plays a minor role two main types of eolian parent materials seem to coexist in different proportions according to the soil type eolian sediments with a similar composition of the underlying bedrock termed autochthonous loess and eolian sediments of volcanic type pyroclasts autochthonous loess represents the main component of the parent material in the following studied soils aluandic andosols cambisols phaeozems and podzol 67 63 44 and 73 respectively all these soils exhibit low to moderate andic features volcanic type eolian sediments constitute about 90 of the parent material in most andic soils that are silandic andosols but occur in different proportions in most of the investigated soils the nature of soil parent materials surprisingly follows a clear trend with latitude with autochthonous loess characterizing most parent materials in northern italy whilst volcanic sediments form most parent materials in the south in accordance with their latitude other soils exhibit an intermediate behaviour

electrical resistivity structure of the senegal basin as determined from magnetotelluric and differential geomagnetic soundings summary the methods of magnetotelluric mt and differential geomagnetic soundings dgs have been applied to study the electromagnetic response of the structure of the senegal sedimentary basin the measurements at 10 sites were carried out along a profile running perpendicularly across a zone of north south flexures and faults over the period range 10 1000 s variation of periods up to 10000 s were obtained at two sites the anomalous geomagnetic variation field across the major fault zone is characterized by an increase in the magnetic eastward component two dimensional modelling of the apparent resistivities and phases reveals a highly anomalous upper crustal structure involving a low resistivity zone in the central part of the basin less than 30 am to satisfy the additional long period data at two sites a deep conductor is also required at a depth below 300 km with a resistivity less than 10 am the crustal discontinuity located 200 km off the coast is possibly related to the opening of the atlantic ocean the difficulty in resolving the question of the nature of the crust in this region results in part from the limitations of the methods used at present for this determination

origin of the supergiant olympic dam cu u au ag deposit south australia was a sedimentary basin involved the supergiant olympic dam cu u au ag ore deposit of south australia occurs in a tectonic hydrothermal breccia complex that is surrounded by mesoproterozoic granite the breccia is composed mainly of granite clasts and minor amounts of mesoproterozoic volcanic clasts very thick 350 m sections of bedded sedimentary facies that occur in the breccia complex include laminated to very thin planar mudstone beds thin to medium internally graded sandstone beds and thick conglomerate beds the bedded sedimentary facies extend continuously across a 1 5 km 0 9 km area and are not limited to small separate maar craters as previously thought detrital chromite and volcanic quartz in the bedded sedimentary facies cannot be matched with local sources and imply that the provenance extended beyond the area of olympic dam the lateral continuity provenance characteristics great thickness below wave base lithofacies and intracontinental setting suggest that the bedded sedimentary facies are remnants of a sedimentary basin that was present at olympic dam prior to formation of the breccia complex we conclude that the olympic dam hydrothermal system operated beneath and partly within an active sedimentary basin was not confined to maar craters and did not vent this new view of the setting raises the possibility that sedimentary processes were involved in ore genesis

observing geomagnetic induction in magnetic satellite measurements and associated implications for mantle conductivity 1 currents induced in earth by temporal variations in the external magnetic field have long been used to probe mantle electrical conductivity but almost exclusively from sparsely distributed land observatories satellite borne magnetometers such as flown on magsat orsted and champ offer the prospect of improved spatial coverage the approach we have taken is to isolate induction by harmonic dst disturbance storm time excitation of the magnetospheric ring current in satellite magnetic measurements this is done by removing the magnetic contributions of the main core magnetic field the crustal magnetic field and ionospheric fields cause of the daily variation using sabaka et al s 2000 2002 cmp3 comprehensive model the dst signal is then clearly evident in the midlatitude satellite passes lower than 50 degrees geomagnetic latitude at higher latitudes auroral and field aligned currents contaminate the data we fit the internal and external components of the dst signal for each equatorial pass exploiting the fact that the geometry for the internal and external components is different for the azimuthal and radial vector components the resulting timeseries of internal and external field variations shows that the dst signals for the dawn passes are half those of the dusk passes the sum of equatorial external and internal components of the field averaged over dawn and dusk passes provides an excellent estimate for the dst index and may in fact be superior when used as a proxy for the purposes of removing induced and magnetospheric fields from satellite magnetic data we call this estimate satellite dst cross spectral analysis of the internal and external timeseries shows both greater power and higher coherence in the dusk data we processed the transfer function between internal and external dusk timeseries to provide globally averaged frequency dependent impedances that agree well with independently derived estimates we estimate earth s radial electrical conductivity structure from these impedances using standard regularized inversion techniques a near surface conductor is required of thickness less than 10 km with a conductivity thickness product almost exactly that of an average earth ocean inversions suggest that an increase in conductivity at 440 km depth predicted by recent laboratory measurements on high pressure phases of olivine is not favored by the data although as in previous studies the 670 km discontinuity between the upper and lower mantle is associated with a two orders of magnitude jump in conductivity a new feature in our inversions is a further increase in lower mantle conductivity at a depth of 1300 km a global map of the internal induced component of the magnetic field provides a qualitative estimate of three dimensional 3 d variations in earth electrical conductivity demonstrating graphically that the satellite data are responsive to lateral variations in electrical conductivity caused by the continents and oceans

the electrical resistivity of canada s lithosphere and correlation with other parameters contributions from lithoprobe and other programmes over the last 30 years through lithoprobe and other programmes modern high quality magnetotelluric mt measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across canada in all provinces and territories except nova scotia some regions are well covered particularly alberta southern british columbia and western ontario whereas others remain poorly covered such as quebec and large swaths of nunavut prior publications from individual studies have added significantly to the wealth of canada s geoscience knowledge and have demonstrated that mt can contribute significantly to understanding of the tectonic processes that have shaped canada however to date no continent scale maps of lithospheric electrical parameters have been constructed from the extensive mt database herein we review the contributions made by the mt components of lithoprobe and present new continental scale maps of various electrical parameters at crustal and upper mantle

new constraints on the timing of host rock emplacement hydrothermal alteration and iron oxide apatite mineralization in the kiruna district norrbotten sweden high spatial resolution zircon u pb geochronological data obtained directly on the kiirunavaara iron oxide apatite ioa deposit related orebodies and host rocks provide new constraints on the timing of mineralization in these deposits these data raise new arguments in the debate of a magmatic versus hydrothermal metasomatic genesis of these major 2 500 mt 30 70 wt fe paleoproterozoic deposits the main orebody at kiirunavaara contains ti poor magnetite and minor 0 05 5 wt p apatite located between a trachyandesite footwall and a rhyodacite hanging wall which also hosts smaller orebodies nukutus rektorn and tuolluvaara the pervasive na and k metasomatism in the host rock is documented by whole rock geochemical data and cathodoluminescence cl microscopy zircon u pb data for the metavolcanic rocks in the footwall and hanging wall cluster between 1884 4 and 1880 3 ma in the footwall a syenite aplite system yields ages of 1880 7 and 1881 4 ma a granite pluton exposed underground has an age of 1874 4 ma zircons in two ore samples never directly dated before this study yield ages of 1877 4 and 1874 7 ma brecciation at the contacts between the ore and host rocks the tight age at ca 1880 ma for most volcanic and plutonic rocks in the footwall and hanging wall and the marginally younger age for ore at ca 1877 to 74 ma matching the age of the spatially related granite pluton suggest a magmatic hydrothermal emplacement model for the kiruna area ioa ores

cu au mineralisation in the curnamona province south australia a hybrid stratiform genetic model for mesoproterozoic iocg systems in australia abstract the proterozoic curnamona province lies between two of the most endowed cu bearing mineral belts on the australian continent the gawler craton which hosts the giant olympic dam iron oxide copper gold iocg system and the mount isa inlier which hosts the giant mount isa cu system and iocg belt of the eastern succession this study focuses on cu au deposits within the proterozoic rocks of the benagerie ridge magnetic complex in the central curnamona province the benagerie ridge is buried beneath neoproterozoic and phanerozoic cover sequences we use drillcore and geophysical data to determine the structural architecture and structural controls of cu au mineralisation in the benagerie ridge the portia and north portia deposits are the most significant cu au mineral deposits in the benagerie ridge and lie adjacent to an extensive regional redox boundary that separates lower magnetic units from upper non magnetic units the redox boundary is extensive throughout the curnamona province and is linked with mineralisation in the region significant chalcopyrite bornite and molybdenite occur along bedding parallel layers and shear structures these factors support a strong lithological control on cu au mineralisation at all scales deformation in the benagerie ridge involved the development of a d1 layer parallel foliation s1 which is overprinted by d2 recumbent folds and d3 upright folds the deformation history is associated with the c 1610 1580 ma olarian orogeny overprinting of d2 structures during d3 has resulted in a type 2 interference pattern which we have successfully mapped using aeromagnetic data several later phases of post olarian faults overprint f2 and f3 fold interference patterns and have resulted in the remobilisation of some of the cu au mineralisation we propose that the stratiform cu au mineralisation occurred prior to the onset of the olarian orogeny mineralisation is preserved within the thickened hinge zone of a similar type f2 fold proximal to the hinge of an overprinting f3 fold which we propose has enhanced mineralisation within the north portia deposit consequently the identification of the redox boundary within f2 folds elsewhere in the curnamona province particularly when located proximal to f3 fold hinges which place the mineralised zones into structurally favourable locations provide good targets for future mineral exploration

prominent hill a hematite dominated iron oxide copper gold system the discovery of iron oxide copper gold iocg mineralization at prominent hill in the mount woods inlier south australia by minotaur resources ltd in november 2001 was based on an empirical exploration model that focused specifically on the hematite end member of the iocg ore deposit model type copper and gold bearing hematite rich breccias formed by repetitive hydrothermal brecciation milling and explosive venting within a volcanic setting high pressure spalling chemical corrosion of breccia clasts and compositional layering within the breccias are distinctive features iron oxide sericite silica alteration is pervasive within and marginal to the main breccias and is surrounded by a wider zone of less intense alteration iron copper gold barium fluorine uranium cerium and lanthanum are strongly correlated and associated with a relatively low temperature hydrothermal system mineralization was synchronous with volcanism and sedimentation within a narrow east west trending graben that developed at 1585 ma

joint inversion of geophysical data summary by jointly inverting several different kinds of geophysical measurements at a site we avoid some of the ambiguity inherent in the individual methods we show how this can be done for the combination of dc resistivity and magnetotelluric measurements on a layered medium by considering a simple 3 layer model the combination resolves the resistivity of the thin resistive second layer even though neither of the two methods can do so alone the method is then applied to field data from a shallow sedimentary basin a blind zone occurs beneath a thick near surface conductive shale by a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data but additional dc data at larger spacing would yield no improvement

interpretation of a ca 1600 1580 ma metamorphic core complex in the northern gawler craton australia abstract the mount woods domain in the gawler craton south australia records a complex tectonic evolution spanning the palaeoproterozoic and mesoproterozoic the regional structural architecture is interpreted to represent a partially preserved metamorphic core complex that developed during the 1600 1580 ma hiltaba event making this one of the oldest known core complexes on earth the lower plate is preserved in the central mount woods domain which comprises the mount woods metamorphics these rocks yield a detrital zircon maximum depositional age of 1860 ma and were polydeformed and metamorphosed to upper amphibolite to granulite facies during the 1740 1690 ma kimban orogeny the upper plate comprises a younger succession the skylark metasediments deposited at 1750 ma within the upper plate sedimentary and volcanic successions of the gawler range volcanics were deposited into half graben that evolved during brittle normal faulting the skylark shear zone represents the basal detachment fault separating the upper and lower plate of the core complex the geometry of normal faults in the upper plate is consistent with ne sw extension both the upper and lower plates are intruded by 1795 1575 ma hiltaba suite granitic and mafic plutons the core complex was extensively modified during the 1570 1540 ma kararan orogeny exhumation of the western and eastern mount woods domain is indicated by new 40ar 39ar biotite cooling ages that show that rock packages in the central mount woods domain cooled past 300 c 50 c at 1560 ma which was 20 million years before equivalent cooling in the western and eastern mount woods domain exhumation was associated with activity along major syn kararan orogeny faults

age constraints on the hydrothermal history of the prominent hill iron oxide copper gold deposit south australia the mesoproterozoic prominent hill iron oxide copper gold deposit lies on the fault bound southern edge of the mt woods domain gawler craton south australia chalcocite bornite chalcopyrite ores occur in a hematitic breccia complex that has similarities to the olympic dam deposit but were emplaced in a shallow water clastic carbonate package overlying a thick andesite dacite pile the sequence has been overturned against the major steep east west hangingwall fault beyond which lies the clastic to potentially evaporitic blue duck metasediments immediately north of the deposit these metasediments have been intruded by dacite porphyry and granitoid and metasomatised to form magnetite calc silicate skarn pyrite chalcopyrite the hematitic breccia complex is strongly sericitised and silicified has a large sericite chlorite halo and was intruded by dykes during and after sericitisation this paper evaluates the age of sericite formation in the mineralised breccias and provides constraints on the timing of granitoid intrusion and skarn formation in the terrain adjoining the mineralisation the breccia complex contains fragments of granitoid and porphyry that are found here to be part of the gawler range volcanics hiltaba suite magmatic event at 1600 1570 ma this indicates that some breccia formation post dated granitoid intrusion monazite and apatite in fe p ree albite metasomatised granitoid paragenetically linked with magnetite skarn formation north of the hangingwall fault grew soon after granitoid intrusion although the apatite experienced u pb lree loss during later fluid mineral interaction this accounts for its calculated age of 1544 39 ma to the south of the fault within the breccia 40ar 39ar ages yield a minimum age of sericitisation cu fe ree of dykes and volcanics of 1575 ma firmly placing prominent hill ore formation as part of the gawler range volcanics hiltaba suite magmatic event within the olympic cu au province of the gawler craton

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

an integrated approach to studying the genesis of andic soils in italian non volcanic mountain ecosystems abstract over recent decades andic soils have been increasingly found in non volcanic mountain ecosystems nvme in many parts of the world in italy this type of soil has proved to be greatly affected by aeolian deposits and to be widely distributed geographically however there are still many open questions especially regarding the genesis of these soils this paper focuses on five representative pedons taken from nvme soil forming processes and relationships between soil and underlying bedrock were investigated by using an integrated approach including geochemical magnetic mineralogical micromorphological and particle size distribution psd analysis the 5 pedons showed andic character and similar morphology and micromorphology e g silt illuviation pedorelicts as well as large differences in terms of soil reaction and clay mineralogy the analysis of the vertical distribution of c al and fe extracted in pyrophosphate along with related geochemical indices e g c p al p enabled us to indicate andosolization as the main process of soil formation and to exclude podzolization with respect to the soil bedrock relationship 2 soils showed great similarity to the underlying bedrock along with a clear aeolian particle size distribution footprint whereas in the remaining 3 soils there was a clear soil bedrock discontinuity and an evident volcanic fingerprint some of the soil bedrock differences related to the geographical settings and latitude

granulometrical mineralogical and geochemical characterization of loess deposits in the tajo basin abstract loess research has the merit of enabling reconstructions of pleistocene sedimentation dynamics in many parts of the world however there is still very few information regarding the occurrence of loess deposits in the mediterranean area even though such records may provide a unique opportunity to investigate landscape evolution for a period for which terrestrial archives are very rare in this region this paper presents the first results of investigations on a loess sequence in the middle tajo valley in central spain findings from detailed granulometrical mineralogical geochemical and grain morphological analyses help to give a first overview on character and composition of these deposits very high levels of carbonates 60 but also of gypsum both to large extents of primary origin indicate the incorporation of material derived from marls and limestone furthermore we found evidence that allows deduction of possible loess proveniences more precisely dolomite contents of up to 20 indicate that the iberian range might have been an important source area of loess sediments the fact that these uplands are located to the east seems to be opposed to the common assumption of prevailing west winds for glacial periods the studied sequence paraiso profile is one of seven sections that have been investigated as part of a programme to reconstruct upper pleistocene landscape dynamics in central spain in this context the detailed characterisation of sediment properties is crucial for discussing loess proveniences and sedimentary environments

electromagnetic evidence for lateral inhomogeneities within the earth s upper mantle abstract the composition of the upper mantle is of great significance to our understanding of plate tectonics and global evolution information about the physical properties of the earth at upper mantle depths including lateral variations in electrical conductivity can be deduced from measurements of the electric and magnetic fields at the earth s surface electromagnetic methods appear to give poorer resolution than do some other methods for example seismics but as they are sensitive to quite different properties of a medium they provide a different and complementary class of information the basic theory of electromagnetic sounding methods is briefly reviewed below and evidence regarding lateral conductivity inhomogeneities in the earth s upper mantle is examined while lateral electrical conductivity inhomogeneities appear to be the rule rather than the exception the interpretation of electromagnetic data still presents difficulties and the results from many regions are not as yet unambiguous where the data are of sufficient resolution a rapid increase in electrical conductivity can usually be identified within the upper mantle the depth to this highly conductive zone is different in different tectonic environments but is broadly consistent between analogous but widely separated tectonic environments a comparatively shallow conducting region is found beneath the ocean lithosphere the depth of this region is dependent on lithospheric age many of the more shallow conducting regions in both continental and oceanic environments are associated with high heat flow values and seismic low velocity zones these highly conducting regions may be zones of partial melt

timing of iron oxide cu au u hydrothermal activity and nd isotope constraints on metal sources in the gawler craton south australia the eastern gawler craton hosts australia s premier uranium bearing iron oxide copper gold iocg belt the 500 km long olympic cu au u province in addition to the olympic dam cu u au and prominent hill cu au deposits numerous barren and weakly mineralized iocg prospects are present in the province new geochronological data for hydrothermal minerals combined with constraints from host rock ages demonstrate that alteration and associated iocg mineralization formed between 1570 and 1600 ma in three districts of the province this iocg hydrothermal activity temporally overlaps with magmatism of the hiltaba suite and gawler range volcanics titanites in paragenetically early magnetite bearing alteration in the olympic dam and prominent hill districts yield u pb ion probe ages of 1576 5 and 1567 10 ma respectively molybdenite in veins crosscutting magnetite biotite and albitic alteration in the moonta wallaroo district have re os ages of 1574 6 and 1599 6 ma respectively these represent minimum ages of the iocg alteration assemblages in this district a muscovite 40ar 39ar age of 1575 11 ma provides a minimum age of paragenetically later hematitic alteration in the olympic dam district neodymium isotope compositions were determined for 44 whole rock samples from barren and weakly mineralized cu au prospects and host rocks in the olympic dam and prominent hill districts the new geochronological framework enables comparison of the nd isotope data across two iocg districts at the time of formation of the olympic dam deposit ca 1590 ma magnetite rich weakly cu mineralized alteration from five prospects yields a relatively narrow range end 1590 values of 5 8 to 4 1 both hematite and magnetite rich alteration yield generally similar end 1590 values that match values from fresh and weakly altered paleoproterozoic metasedimentary and metagranitic rocks 6 6 to 3 5 as well as from most felsic hiltaba suite intrusions and gawler range volcanics in the eastern gawler craton ca 6 to 4 these data are consistent with crustal sources for ree and by implication for associated copper in the barren and weakly mineralized prospects mineralization and alteration in these minor iocg systems can be geochemically discriminated from the giant olympic dam deposit where greater inputs of mantle derived ree and other ore components are evident 2007 society of economic geologists inc

re os dating of molybdenite within hematite breccias from the vulcan cu au prospect olympic cu au province south australia the vulcan prospect is a newly discovered cu au prospect located within the eastern gawler craton south australia the prospect is entirely subsurface and defined by a geophysical anomaly intersected by diamond drilling eight drill holes have all intersected hematite rich alteration and cu au mineralization within a variety of breccia types ranging from those composed entirely of hydrothermal hematite sericite chlorite to those dominated by altered rock in which clasts of protolith rock are preserved the highest grade zones of mineralization at vulcan occur within hematite dominant breccias molybdenite within hematite rich brecciated granite samples has been dated via the re os method and yields a crystallization age of 1586 8 ma including decay constant uncertainties shrimp zircon u pb analyses show that a sample of hematite sericite chlorite altered and brecciated granite was emplaced at 1743 7 ma the new data from vulcan confirm that hematite breccia related cu au mineralization formed during a widespread alteration and mineralization event between ca 1600 and 1570 ma broadly coeval with the voluminous felsic large igneous province of the gawler range volcanics hiltaba suite and are consistent with most interpretations of the geology of the olympic cu au province

sedimentary thickness variations and deformation intensity during basin inversion in the flinders ranges south australia abstract the central and northern parts of the adelaide fold belt in the flinders ranges south australia consist of a sequence of neo proterozoic cambrian sediments overlying a meso proterozoic basement complex both of which were mildly deformed in an intracratonic setting during the 500 ma delamerian orogeny the fold belt lies within a prominent heat flow anomaly average heat flows of 90 mwm 2 reflecting extraordinary enrichments in heat producing elements in the meso proterozoic basement suggesting that anomalous thermal regimes may have been significant in localising delamerian deformation however spatial variations in deformation intensity correlate more closely with variations in the thickness of the sedimentary sequence than with observed variations in heat flow suggesting that the thickness of the sedimentary blanket plays a crucial role in localising delamerian deformation during basin inversion we use simple numerical models of lithospheric strength to investigate the potential role of sedimentary thickness variations on the distribution and style of deformation focussing on the impact of a variable thickness sediment pile deposited above a radioactive basement we show that for thermal parameters appropriate to the flinders ranges moho temperatures may vary by 25 30 c for every additional kilometre of sediment for a brace goetze lithospheric rheology controlled by a combination of temperature dependent creep processes and frictional sliding the observed variations in thickness of the sedimentary pile are sufficient to cause dramatic reductions in the vertically integrated strength of the lithosphere by many orders of magnitude thereby providing a plausible explanation for observed correlation between sediment thickness and deformation intensity during basin inversion

the electrical structure of the slave craton the slave craton in northwestern canada a relatively small archean craton 600400 km is ideal as a natural laboratory for investigating the formation and evolution of mesoarchean and neoarchean sub continental lithospheric mantle sclm excellent outcrop and the discovery of economic diamondiferous kimberlite pipes in the centre of the craton during the early 1990s have led to an unparalleled amount of geoscientific information becoming available over the last 5 years deep probing electromagnetic surveys were conducted on the slave using the natural source magnetotelluric mt technique as part of a variety of programs to study the craton and determine its regional scale electrical structure two of the four types of surveys involved novel mt data acquisition one through frozen lakes along ice roads during winter and the second using ocean bottom mt instrumentation deployed from float planes the primary initial objective of the mt surveys was to determine the geometry of the topography of the lithosphere asthenosphere boundary lab across the slave craton however the mt responses revealed completely serendipitously a remarkable anomaly in electrical conductivity in the sclm of the central slave craton this central slave mantle conductor csmc anomaly is modelled as a localized region of low resistivity 10 15 v m beginning at depths of f80 120 km and striking ne sw where precisely located it is spatially coincident with the eocene aged kimberlite field in the central part of the craton the so called corridor of hope and also with a geochemically defined ultra depleted harzburgitic layer interpreted as oceanic or arc related lithosphere emplaced during early tectonism the csmc lies wholly within the ne sw

sulphide formation from granulite facies s rich scapolite breakdown scapolite in granulite facies terranes provides a reservoir for volatile components such as sulfur and carbon in rocks that are otherwise considered dry formed at lower crustal conditions the high s endmember of scapolite silvialite is a major host of sulfur in granulites compositional and textural changes involving scapolite reveal that s rich scapolite becomes unstable during hydration and deformation at amphibolite facies conditions either scapolite changes composition whereby so42 is exchanged for co32 or cl in its structure or scapolite is replaced by amphibole and or epidote sulfur that is released from silvialite is deposited as sulfides within the original silvialite grain boundaries and can remain relatively immobile in undeformed anorthosites however increased sulfide mobility is evident in areas of increased deformation and hydration reactions involving s bearing scapolite not only have important implications for sulfide deposition and the s cycle but may also influence conductivity variation in the lower crust this article is protected by copyright all rights reserved

on the interpretation of the distinctive pattern of geomagnetic induction observed in northwest india the geomagnetic variation data from the 1979 indian array experiment have been reanalyzed and reexamined using the hypothetical event analysis technique the contour map of the z h ratio replicates distinctive anomaly in northwest india previously delineated in maps of the fourier coefficients the anomaly reveals the presence of a significant conductor under the ganga basin the contour map has been used to derive a response profile perpendicular to the strike of the anomaly for comparison with 2 d numerical models an excellent fit was found for a conductor at a depth of 32 km with a width of 110 km and a conductivity contrast of 1000 this result places the conductor deep within the lithosphere in the absence of supporting data the origin of the conductor is difficult to resolve however it is thought to be related to pressure released partial melting caused by fracturing of the indian crust during the collision of india with asia

magnetovariational sounding of the earth using observatory and magsat satellite data abstract deep magnetovariational soundings have been carried out using data from the geomagnetic observatory net and the magsat satellite complex apparent resistivities have been estimated from satellite data by two independent methods the joint results have been interpreted assuming spherical symmetry of the earth s layers the global estimation of the electrical structure of the earth s mantle has confirmed the existence of a layer with high conductance at a depth of approximately 600 700 km the nature and possible causes of this layer are discussed

first evidence for the presence of andisols in the dry hot environment of the arabian shield abstract saudi arabia has many volcanoes and extensive basaltic lava fields known as harrats located along the western part of the arabian shield sub parallel to the red sea the soils developed on these volcanic materials have not yet been investigated forty representative soil profiles were selected from six harrats and their morphological and physicochemical properties as well as their mineralogical compositions were characterized using standard chemical xrd sem and tem techniques the main objective of this study was to determine if the soils developed from basaltic rocks in the harrats of the arabian shield are andisols the results revealed that all representative profiles had volcanic glass content that ranged from 15 to 40 p retention capacity 35 and acid oxalate extractable a1o 1 2 feo that ranged from 0 44 to 2 20 the crystalline clay minerals were dominated by smectite kaolin kaolinite halloysite and mica illite whereas chlorite hydroxy interlayered vermiculite ch hiv palygorskite ca zeolites and pseudo chlorite were present as minor components small amounts of allophane imogolite and ferrihydrite made up the poorly crystalline clay minerals all representative profiles satisfied the criteria for andic soil properties and were classified as torrands due to the presence of an aridic soil moisture regime in the area paleoclimatic conditions that existed in the arabian peninsula over the last few thousand years are consistent with the formation of andic and or vitric soil properties because of this andisols developed from pyroclastic parent materials and are now present in dry hot conditions the presence of andisols in the study area was demonstrated and was mainly attributed to the influence of pleistocene paleoclimatic conditions

fluid evolution and origins of iron oxide cu au prospects in the olympic dam district gawler craton south australia geologic observations suggest two stages of hydrothermal activity at a number of presently subeconomic iron oxide copper gold systems in the olympic dam district eastern gawler craton they contain high and moderate to low temperature fe oxide rich hydrothermal alteration the mineral assemblages include magnetite calc silicate alkali feldspar fe cu sulfides and hematite sericite chlorite carbonate fe cu sulfides u ree minerals in all documented prospects the minerals of the hematitic assemblages replace the minerals of the magnetite rich assemblages the bulk of the subeconomic cu au mineralization is associated with the hematitic alteration assemblages microanalysis by proton ion probe pixe of hypersaline fluid inclusions in magnetite rich assemblages however demonstrates that significant amounts of copper 500 ppm were transported by the early stage high temperature 400 c fluids responsible for the magnetite rich alteration these brine inclusions contain multiple solid phases liquid vapor multiple solids including chalcopyrite in some cases in comparison inclusions of the hematitic stage are relatively simple liquid vapor types with homogenization temperatures of 200 to 300 c and containing 1 to 8 wt percent nacl equiv the br cl ratios of the magnetite forming fluids measured by pixe lie beyond the range of typical magmatic and or mantle values allowing for the possibility that the fluids originated as brines from a sedimentary basin or the crystalline basement sulfur isotope compositions of chalcopyrite and pyrite demonstrate that sulfur in both alteration assemblages was derived either from cooling magmas and or crystalline igneous rocks carried by relatively oxidized fluids so42 h2s 34ssulfides from 5 to 2 or from crustal sedimentary rocks 34ssulfides from 5 to 10 oxygen and hydrogen isotope compositions of waters calculated for minerals of the magnetite rich assemblage have 18o values of 7 7 to 12 8 per mil and d values of 15 to 21 per mil the only available 18o and dfluid values for the hematitic assemblage are 4 7 and 9 per mil respectively the isotopic compositions of both fluids coupled with the available literature data can be explained in terms of fluid reequilibration with felsic gawler range volcanics or other felsic igneous rocks in the region and with metasedimentary rocks of the wallaroo group at low water to rock ratios prior to their arrival at the mineralization sites the lack of significant copper mineralization associated with magnetite forming fluids that carried copper suggests that there was no effective mechanism of saturation of copper minerals or the quantity of these fluids was not sufficient to produce appreciable copper mineralization association of the copper gold mineralization with the hematitic alteration in the subeconomic prospects can be explained by a two stage model in which preexisting hydrothermal magnetite with minor associated copper gold mineralization was flushed by late stage oxidized brines that had extensively reacted with sedimentary or metamorphic rocks the reduction of these brines driven by conversion of magnetite to hematite resulted in precipitation of copper and gold the oxidized brines may have contributed additional copper and gold to the system in addition to upgrading preexisting subeconomic cu au mineralization when compared to published models for the olympic dam deposit the new data for fluids in subeconomic fe oxide cu au prospects of the olympic dam district indicate the diversity of origins of iron oxide copper gold systems even within the same geologic region

mapping iron oxide cu au iocg mineral potential in australia using a knowledge driven mineral systems based approach abstract iron oxide copper gold iocg deposits are consequences of lithospheric to deposit scale earth processes and form where there was a coincidence of ore forming processes in space and time building on previous conceptualisations we view a mineral system as an ore forming geological system in which four components are required to have operated efficiently and coincidentally namely 1 available sources of ore metals i e copper gold uranium rare earth elements and hydrothermal fluids 2 energy sources to drive fluids in the ore forming system 3 active crustal and mantle lithospheric architecture representing hydrothermal fluid and or magma flow pathways and 4 physico chemical gradients along which ore metals were deposited to form ore bodies this holistic multi scale mineral systems framework has been used to develop a practical knowledge based yet data rich prospectivity mapping method applicable at regional to continental scales for hydrothermal and orthomagmatic ore forming systems we demonstrate how the mineral system components can be translated into mappable criteria and show how maps of mineral potential are generated by integrating diverse and rich input data sets the method enables prediction of mineral potential not only in brownfields areas but also in greenfields and covered terranes with no previously known mineralisation here we report the application of this methodology in regional scale mapping of the potential for iocg deposits in australia using examples from five studies over the last decade in northern queensland eastern south australia and southern and central eastern northern territory uncertainties in the results arising from assignment of weightings to input data layers were investigated by the application of monte carlo type probabilistic simulations the results of 500 iterations using randomly assigned weightings overall support the deterministic results but also show that modelled prospectivity is controlled mainly by variations in intrinsic values of the input geoscientific data sets e g highs and lows of gravity values rather than by the weightings the results of the knowledge driven data rich analyses of iocg potential have been validated against known iocg deposits not used directly in the analysis we find in all five studies queensland south australia and northern territory a good spatial correspondence with few exceptions statistical analysis of prospectivity mapping results from the tennant creek mt isa study area demonstrate that 15 of 16 iocg deposits occur in the highest modelled prospectivity areas within 4 2 of the study area representing an area reduction of 95 8 moreover several new discoveries of cu au mineralisation have been made within areas previously highlighted as highly prospective this success and validation support the utility of geoscience australia s approach as a decision support tool to assist exploration companies and governments in craton to regional scale area selection for discovery of iocg and other mineral systems

surface and subsurface facies architecture of a small hydroexplosive rhyolitic centre in the mesoproterozoic gawler range volcanics south australia abstract at menninnie dam south australia a drilling program has revealed a complete section through the subsurface feeder system and erupted products of a small hydroexplosive rhyolitic centre within the mesoproterozoic gawler range volcanics porphyritic rhyolite intruded near vertical faults in the palaeoproterozoic basement and at less than a few hundred metres depth interacted with fault hosted hot groundwater hydrofracturing of the wall rock occurred in advance of and at the margins of the rhyolitic intrusions the rhyolitic intrusions have peperitic margins and grade into discordant lithic rich pb facies the advancing fragmentation front intersected the palaeosurface triggering phreatic eruptions that deposited a poorly sorted lithic rich explosion breccia rhyolite then rose to the surface through the intrusive breccias and shallow seated magma water interaction occurred in the conduit within 800 m from the inferred source the products include muddy sandstone and pumice breccia at the end of the eruption rhyolitic lava was extruded in the form of a small dome the presence of contemporaneous pb zn ag mineralisation in the wall rocks suggests that an active hydrothermal system may have been involved in the formation of the menninnie dam hydroexplosive volcanic centre

lithology and hydrothermal alteration control the distribution of copper grade in the prominent hill iron oxide copper gold deposit gawler craton south australia the prominent hill iron oxide copper gold iocg deposit located in the gawler craton of south australia contains ca 278 million metric tons mt of ore at 0 98 cu 0 75 g t au and 2 5 g t ag in contrast to the predominantly granite hosted olympic dam iocg deposit prominent hill is mainly within unmetamorphosed sedimentary rocks comprising coarse clastic to laminated argillaceous lithologies with some volcaniclastic components and variable carbonate including local massive dolomite essentially unmetamorphosed sedimentary rocks and structurally underlying mafic to intermediate composition lavas inferred to be members of the lower gawler range volcanics host the economically mineralized hematite breccias the volcanic sedimentary package was downfaulted and tilted along a major east west fault north of which similar but regionally low grade metamorphosed rocks were affected by subeconomic skarn mineralization and on a more regional scale of the mount woods domain intruded by granitic and gabbroic bodies hydrothermal alteration and mineralization at prominent hill involved pervasive and texturally destructive replacement of formerly calcareous dolomitic and siliciclastic breccia components hydrothermal alteration minerals comprise hematite magnetite siderite ankerite quartz sericite chlorite kaolinite fluorapatite fluorite barite ree u minerals including monazite uraninite and coffinite together with cu sulfides including chalcopyrite bornite and chalcocite in the highest grade ore brecciation and replacement caused mechanical mixing as well as chemical alteration of primary lithologies such that sedimentary contacts became obscured mass balance calculations identify al ti si and zr as least mobile components during hematite chlorite sericite to weak hematite quartz alteration because zr was not regularly assayed in drill cores we use concentration ratios of ti al and si from the deposit scale assay database to delineate the distribution of lithochemical units prior to hydrothermal alteration and cu mineralization the resulting lithochemical model based on one horizontal and five vertical cross sections is used as a basis for mapping alteration patterns calculated from molar fe si fe si al k na and k al ratios these chemical patterns in conjunction with mineral stoichiometry indicate that the spatial distribution of hematite chlorite variably phengitic sericite and or illite kaolinite quartz bearing alteration is superimposed on the pattern of interpreted lithologic contacts the alteration patterns confirm visual logging results showing that hematite enrichment correlates only partially with the distribution of cu grades of 0 25 wt a subvertical body of complete replacement by hematite and quartz with consistent but subeconomic gold enrichment forms a cu barren core in the central and eastern parts of the deposit zones of increasing k al and k na ratios extend upward and westward from this cu barren core transgressively overprinting lithologic contacts the degree of hematite quartz replacement can be measured by a hematite quartz alteration index here termed the hmsi value fe si fe si al which inversely correlates with the normal probability for cu grade areas of highest cu grade 1 wt spatially correlate with irregular zones having intermediate molar alteration indices 0 34 k al 0 40 20 k na 36 and hmsi 0 98 hematite breccias and cu ore deposition developed after tilting of the host sequence into its present steep orientation as indicated by geopetal structures within the breccia matrix thus the economic mineralization occurred late in the deformational history of the region and after extrusion of the lower gawler range volcanics the formation of the prominent hill orebodies occurred during or after upthrusting of deeper seated rocks containing subeconomic cu in skarns north of the fault faulting as well as ore formation may be related to orogenic processes in the central and northern part of the mount woods domain iron oxide introduction was decoupled from and at least partly preceded hydrothermal deposition of high grade cu geochemical and petrographic data indicate that economic cu mineralization occurred together with mildly acidic hematite chlorite sericite siderite alteration of originally carbonate illite and feldspar bearing sedimentary rocks the presence of copper enrichment with an intermediate degree of cation leaching from the host rocks indicates that ph neutralization of initially highly acidic metal transporting fluids was an essential factor causing cu sulfide deposition distinct ranges in na k al ratios and low hmsi values offer potential as exploration indicators pointing toward higher ore grades these results from prominent hill are consistent with recently published mineralogical studies at the giant olympic dam deposit indicating similar ore depositional controls despite lithologically different host rocks

early deep magnetite fluorapatite mineralization at the olympic dam cu u au ag deposit south australia the olympic dam iron oxide copper gold iocg uranium silver deposit south australia is hosted in the large olympic dam breccia complex within the 1 59 ga roxby downs granite this breccia complex formed through multiple stages of hydrothermal activity and texturally destructive brecciation that affected the granite the deepest diamond drill hole to date rd2773 end at 2 329 m intersected weakly altered in situbrecciated granite 370 2 329 m and a quartz phyric felsic unit 2 010 2 265 m these two rock units host coarse grained hydrothermal minerals from 2 150 m to the end of the drill hole the main minerals in this assemblage are magnetite hematite pyrite fluorapatite and quartz with minor disseminated chalcopyrite sericite chlorite rare earth element ree fluorcarbonates monazite uraninite thorite galena sphalerite anhydrite schorl rutile and pyrrhotite the assemblage is cut by abundant multiphase veinlets and calcite fluorite barite veins a zircon u pb age for the felsic unit 1591 11 ma implies that this unit is broadly coeval with the granite whereas u pb ages for hydrothermal uraninite 1593 5 5 1 ma fluorapatite 1583 3 6 5 ma and hematite 1592 15 ma indicate that deposition of the u ree rich hydrothermal magnetite fluorapatite pyrite quartz assemblage and replacement of magnetite by hematite occurred soon after emplacement of the granitic host rocks sm nd dating of ubiquitous calcite veins suggests formation at 1 54 ga the deep 1 59 ga magnetite fluorapatite pyrite quartz assemblage at olympic dam resembles those characteristic of iron oxide apatite deposits and many other sensu stricto iocg deposits this study confirms that the 1 59 ga event involved significant and widespread iocg mineralization in the olympic cu au province

cobalt nickel copper arsenide sulfarsenide and sulfide mineralization in the bou azzer window anti atlas morocco one century of multi disciplinary and geological investigations mineral exploration and mining

precise geochronological constraints on the origin setting and incorporation of ca 1 59 ga surficial facies into the olympic dam breccia complex south australia the olympic dam breccia complex host to the olympic dam cu u au ag deposit is derived largely from granite roxby downs granite but includes clasts and domains derived from surficial facies felsic volcanic rocks and bedded clastic facies new highprecision ca tims geochronology is used to constrain the ages of the granite the volcanic rocks and bedded clastic facies the felsic volcanic rocks 1594 73 ma 0 30 ma are slightly older than the granite 1593 87 ma 0 21 ma these ages together with the absence of any older country rock in the breccia complex suggest the felsic volcanic rocks that were originally present at olympic dam were intruded by the granite the deposition of the bedded clastic facies tuffaceous mudstone has been constrained to 1590 97 0 58 ma indicating the presence of a basin around 3 myr after emplacement of the granite and felsic volcanic rocks extrusive correlatives of maficultramafic dykes intruding the breccia complex are proposed as a local source of detrital cr spinel in the bedded clastic facies the granitoid dominated provenance of some of the bedded clastic facies implies that ca 1590 ma granitoids were exposed when the bedded clastic facies were accumulating the absence of 1740 ma detrital zircons indicates the provenance did not extend beyond granitoids of the burgoyne batholith in the vicinity of olympic dam an initial stratigraphic sequence is proposed for the bcf involving a transition in provenance from volcanic dominated to granitoid dominated faults are proposed to have been responsible for the segmentation and incorporation of the bedded clastic facies into the olympic dam breccia complex the formation of the olympic dam breccia complex and olympic dam hydrothermal system post dated the emplacement of the roxby downs granite at 1593 87 0 21 ma the bedded clastic facies 1590 97 0 58 ma have been altered and mineralised

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

uranium and sm isotope studies of the supergiant olympic dam cu au u ag deposit south australia the olympic dam cu u au ag deposit in the archean proterozoic gawler craton south australia is a type example of the iron oxide copper gold iocg spectrum of deposits and one of the largest cu u au resources known mineralization is hosted in a lithologically and texturally diverse hematite rich breccia complex developed within a granite of the 1 59 ga gawler silicic province emerging evidence indicates that both the breccia complex and its metal content developed over 1000 ma responding to major tectonic events e g at 1300 1100 825 and 500 ma however metal sources and exact mechanism s of ore formation remain poorly known new high precision 238u 235u data for a set of 40 whole rock samples representing all major lithological facies of the breccia complex show a narrow range 238ucrm112a 0 56 to 0 04 at the scale of sampling there is no correlation of 238u with lithology degree of alteration or u mineralogy although ores with u 5 wt have subtly higher 238u values 0 20 to 0 00 than the majority of samples 0 7 wt u 0 56 to 0 23 the new u isotope data are consistent with published data for uraninites from olympic dam and with published results from high temperature u deposits they overlap completely with the range of 238u values in granitoids including the host granite 0 18 to 0 32 and with estimates of the upper continental crust in general this similarity suggests that olympic dam 238u values reflects the crustal sources of u which probably include felsic volcanic rocks and granitoids the isotopic homogeneity suggests depositional mechanisms that involve minimal isotopic fractionation of u alternatively primary fractionation signatures may have been erased during the long history of the u mineralization high grade u ores may record isotopic neutron capture effects related to fissionogenic neutrons high precision sm isotope data for five high u 5 wt u u sm 500 olympic dam ores define a neutron capture line with correlated depletions in 149sm up to 2e units and excesses in 150sm up to 4e units but fission fragment contributions to sm are below detection these observations provide evidence for small scale neutron capture effects with calculated neutron fluences of 1015 to 1016 n cm 2 similar to those observed in several proterozoic and phanerozoic u deposits the apparent lack of fission fragment contributions in olympic dam high grade ores can be explained with an age of u deposition or re deposition that is substantially younger than the initial 1 59 ga age of the oldest iocg style mineralization the results presented here thus i suggest uranium sources in common likely igneous upper crustal lithologies ii support geochronological evidence for gradual addition of u in several stages over 1000 ma at elevated temperatures of mineralization and iii do not show the high 238u signatures expected from low temperature reworking of older low 238u ores

the electrical conductivity of the upper mantle as estimated from satellite magnetic field data the electrical conductivity of the upper mantle is estimated from low latitude magnetic field variations magnetic storms caused by large fluctuations in the equatorial ring current the data base is derived from magnetic field magnitude data measured by satellites ogo 2 4 and 6 which offer better global coverage than land based observatories the procedure of analysis consist of 1 separation of the disturbance field into internal and external parts relative to the surface of the earth 2 estimation of an electromagnetic response function q omega which relates the internally generated magnetic field variations to the external variations due to the ring current and 3 interpretation of the estimated response function using theoretical response functions for assumed conductivity profiles special consideration is given to possible oceanic and ionospheric effects best estimates of the geomagnetic response function q omega for 0 2 to 2 0 cpd indicate an upper mantle conductivity of the order of 10 sup 2 s m this conductivity is reasonable especially when laboratory measurements of conductivity versus temperature for olivine are considered

cooling and exhumation history of the northeastern gawler craton south australia abstract we present biotite 40ar 39ar ages and from the palaeo to mesoproterozoic mount woods inlier in the northeastern gawler craton south australia in combination with garnet biotite fe mg exchange modelling using the thermal history program these data are used to constrain a post peak metamorphic p t path cooling rates and a temperature time path for the inlier consistently well defined plateaus at 1 53 ga of biotite 40ar 39ar age spectra indicate that the rocks cooled through 300 c at this time cooling rates within the inlier are 3 9 c ma from peak high temperature low pressure metamorphism at 1 59 ga to 1 53 ga cooling rates subsequently decreased to 4 c ma cooling is suggested to be a function of cessation of voluminous magmatism and mantle heat input in conjunction with exhumation initiated along the southwestern margin of the inlier ca 1 592 1 582 ga the temperature time path of the inlier has a concave shape the peak metamorphic and ensuing cooling history of the mount woods inlier are akin to the nearby curnamona province coober pedy ridge and mabel creek ridge within the south australian craton deformation during high grade metamorphism within these terranes was accommodated at mid crustal levels and large scale exhumation did not occur until the terranes cooled and were able to be exhumed as coherent rigid blocks along discrete shear zones and faults

rejuvenation vs recycling of archean crust in the gawler craton south australia evidence from u pb and hf isotopes in detrital zircon abstract zircon grains from modern and ancient drainages of the gawler craton south australia have been analysed to define the relative contributions of juvenile sources and recycled crust to magmatic activity as a function of time and to constrain the role of mantle inputs during the proterozoic rejuvenation of the archean gawler craton the integration of hf isotope data with u pb age spectra shows that the crustal evolution was dominated by long periods of crustal reworking and that crust generated in the paleoarchean 3 2 3 5 ga was largely reworked during proterozoic time four periods of juvenile mantle input can be recognised at ca 2540 ma 1853 ma 1595 ma and 1169 ma the 1169 ma event is not previously recognised in the gawler craton but the absence of other important age peaks argues against the transport of these zircons from the musgrave block only minor proportions of the magmatic zircons with paleoproterozoic to mesoproterozoic ages have strongly juvenile signatures e hf 4 indicating that crustal reworking was the dominant process with relatively minor mantle input comparison of the crustal evolution with that of nearby australian terranes suggests that although the gawler craton shows some similarities with the mount isa block and the georgetown inlier in neoarchean paleoproterozoic time it evolved independently between ca 1800 and 1550 ma

transvaporite model of ore genesis and an exploration strategy for new giant ore deposits abstract in the current work we stand for the revival of the transvaporite ore genesis model which was introduced by hungarian academician e szadeczky kardoss more than half a century ago but has now fallen out of favor and superseded by the orthomagmatic model our arguments in support of the transvaporite model are based on the contemporary overpressure theory developed for mesozoic cenozoic petroleum basins we propose a new variant of the transvaporization model whereby the formation of giant ore deposits occurs in the areas where former petroleum rich basins are intersected by large igneous provinces lips at such sites structural magmatic activity leads to hydrocarbon deposits being destroyed and many new ore deposits being created beneath a new regional volcanic fluid seal built by rapidly accumulating up to 3 4 km in 1 ma lava flows in such conditions a zone of significant overpressure that is 1 4 1 8 times higher than hydrostatic pressure develops subsequently under the influence of compressive mechanism of mass transfer gas saturated brines of sedimentary rocks migrate toward intruding melts and then mix with them as a result unusual rocks transvaporites are formed and giant ore deposits created here we review six supergiant ore deposits of various types and ages with different associations of metals and host rocks including the norilsk district in russia cu ni co pt pd el teniente los bronces district in chile cu mo almaden deposit in spain hg ermakovskoe deposit in russia be pebble copper deposit in southern alaska cu mo au and olympic dam deposit in southern australia u cu au ree noting that all listed metals in each and every deposit do reach giant reserves in all these deposits transvaporization appears to play the key role in ore genesis given the 1 short duration of the main ore genesis stage a significant practical implication of the transvaporite model is that it should modify future strategies for ore deposits exploration instead of pursuing just any deposit exploration efforts should focus specifically on giant ore deposits concentrating search efforts at the sites where former petroleum basins have been intersected by lips basin analysis of enriched oil and gas provinces is already being conducted in detail by seismic transects involving two dimensional cross sections and areal surveys followed by three dimensional mapping of productive reservoirs the same strategy should be applied to ore bearing regions but at better precision and accuracy given the smaller velocity contrast in seismic wave propagation in ore rocks compared with oil and gas bearing sedimentary rocks important advances in the ore geology of lips such as geological mapping and gravity and magnetic surveys have already produced significant new data these studies can be divided into two types which first involve a general description of the lip and are then followed by an investigation of major intrusions likely to be directly linked to ore genesis a combination of these investigations into hydrocarbon basins and lips will lay the foundation for transvaporite exploration which will be the key criterion for the successful search for new giant ore deposits

sulfate sorption in nonvolcanic andisols and andic soils from galicia nw spain soils with andic soil properties generally retain large amounts of so42 a feature related to their elevated contents of short range ordered minerals and or insoluble al humus compounds the objective of this study was to investigate the relationships between so42 sorption and contents of al and fe compounds in soils from galicia nw spain with andic soil properties nineteen soils derived from gabbros amphibolites basic granulites biotitic schists and amphibolitic phyllites were sampled sulfate sorption was studied by adding a 0 4 mm so42 solution initially acidified to ph 3 0 to soils aluminum humus complexes were abundant in surface horizons oxalate and pyrophosphate extractable al alo and alp respectively decreased with depth whereas there was an increase in the naoh extractable al aln minus alo fraction associated with an increase in poorly crystalline forms of both gibbsite and 1 1 phyllosilicates iron was mostly present as crystalline oxyhydroxides the abundance of variable charge materials and the acidity of these soils ph h2o 5 7 explain the high so42 sorption detected sulfate sorption was positively correlated at p 0 01 with aln alo and alp in surface horizons and with aln alo fe extractable with dithionite citrate fed and oxalate feo in subsurface horizons the correlation between so42 sorption and alo decreased sharply when data from all horizons were pooled blockage of reactive surfaces by organic compounds in surface horizons and the different al compounds found in both types of horizons may explain the differences between them in the relationships between the al fe fractions and so42 sorption the results emphasize the high so42 retention capacity of both surface and subsurface horizons of nonvolcanic andisols and andic soils from galicia

constraining models of the tectonic setting of the giant olympic dam iron oxide copper gold deposit south australia using deep seismic reflection data abstract in the gawler craton the completeness of cover concealing the crystalline basement in the region of the giant olympic dam cu au deposit has impeded any sufficient understanding of the crustal architecture and tectonic setting of its iocg mineral system to circumvent this problem deep seismic reflection data were recently acquired from 250 line km of two intersecting traverses centered on the olympic dam deposit the data were recorded to 18 s twt 55 km the crust consists of neoproterozoic cover in places more than 5 km thick over crystalline basement with the moho at depths of 13 14 s twt 40 42 km the olympic dam deposit lies on the boundary between two distinct pieces of crust one interpreted as the archean paleoproterozoic core to the craton the other as a meso neoproterozoic mobile belt the host to the deposit a member of the 1590 ma hiltaba suite of granites is situated above a zone of reduced impedance contrast in the lower crust which we interpret to be source region for its 1000 c magma the crystalline basement is dominated by thrusts this contrasts with widely held models for the tectonic setting of olympic dam which predict extension associated with heat from the mantle producing the high temperatures required to generate the hiltaba suite granites implicated in mineralization we use the seismic data to test four hypotheses for this heat source mantle underplating a mantle plume lithospheric extension and radioactive heating in the lower crust we reject the first three hypotheses the data cannot be used to reject or confirm the fourth hypothesis

evolution of uranium fractionation processes through time driving the secular variation of uranium deposit types uranium deposit types have evolved considerably from the archean to the present the major global drivers were 1 change of geotectonic conditions during the late archean 2 strong increase of atmospheric oxygen from 2 4 to 2 2 ga and 3 development of land plants during the silurian other significant variations of uranium deposit types are related to unique conjunctions of conditions such as those during phosphate sedimentation in the cretaceous earth s uranium fractionation mechanisms evolved through four major periods the first from 4 55 and 3 2 ga corresponds to formation of a thin essentially mafic crust in which the most fractionated trondheimite tonalite granodiorite ttg rocks attained uranium concentrations of at most a few parts per million moreover the uranium being essentially hosted in refractory accessory minerals and free oxygen being absent no uranium deposit could be expected to have formed during this period the second period from about 3 1 to 2 2 ga is characterized by several widespread pulses of highly fractionated potassic granite strongly enriched in u th and k late in this period peraluminous granite was selectively enriched in u and to a lesser extent k these were the first granite and pegmatite magmas able to crystallize high temperature uraninite the erosion of these granitic suites liberated thorium rich uraninite which would then be concentrated in placer deposits along with pyrite and other heavy minerals e g zircon monazite fe ti oxides within huge continental basins e g witwatersrand south africa and bind river canada the lack of free oxygen at that time prevented oxidation of the uraninite which formed the oldest economic uranium deposit types on earth but only during this period the third period from 2 2 to 0 45 ga records increased oxygen to nearly the present atmospheric level tetravalent uranium from uraninite was oxidized to hexavalent uranium forming highly soluble uranyl ions in water uranium was extensively trapped in reduced epicontinental sedimentary successions along with huge quantities of organic matter and phosphates accumulated as a consequence of biological proliferation especially during the late paleoproterozoic a series of uranium deposits formed through redox processes the first of these developed at a formational redox boundary at about 2 0 ga in the oklo area of gabon all known economically significant uranium deposits related to na metasomatism are about 1 8 ga in age the high grade large tonnage unconformity related deposits also formed essentially during the late paleoproterozoic to early mesoproterozoic the last period 0 45 ga present coincided with the colonization of continents by plants the detrital accumulation of plants within continental siliciclastic strata represented intraformational reduced traps for another family of uranium deposits that developed essentially only during this period basal roll front tabular and tectonolithologic types however the increased recognition of hydrocarbon and hydrogen sulfide migration from oil or gas reservoirs during diagenesis suggests potential for sandstone hosted uranium deposits to be found within permeable sandstone older than the silurian large uranium deposits related to high level hydrothermal fluid circulation and those related to evapotranspiration calcretes are only known during this last period of time probably because of their formation in near surface environments with low preservation potential

the icelandic rofabard soil erosion features soil erosion and desertification are severe problems in iceland erosion processes are numerous and more than one can occur at each site resulting in many erosional forms erosion forms and an erosion severity scale are the basis for a recent national survey of erosion in iceland one of the most distinctive erosion forms in iceland is an erosion escarpment termed rofabard in icelandic rofabards are formed in thick but non cohesive andosols that overlie more cohesive materials such as glacial till or lava the relatively loose andosols beneath the root mat are undermined creating escarpments or rofabards the rofabards retreat as a unit with a fully vegetated and rich ecosystem on top but leaving barren desert in their place rofabards are common within a 20 000 km2 area the agricultural research institute and soil conservation service erosion database suggests that erosion associated with rofabards has denuded 15 000 30 000 km2 of land that was previously fully vegetated and had fertile andosols but is now mostly desert erosion rates associated with rofabards are reported as the loss of vegetated land with andosol mantle measured as hectares per square kilometre per year this measure of erosion has more meaning for icelandic landscapes than the traditional tonnes per hectare per year estimated losses of andosol cover in rofabard areas for the whole country are currently about 230 ha a 1 this rate is about 10 times lower than the rate needed to cause estimated losses of andosol mantle in rofabard areas since settlement 1125 years ago during peak years of soil erosion losses were probably several thousand hectares per year but the erosion rates slowed down as extensive andosol areas have become barren deserts copyright 2000 john wiley sons ltd

opening the magmatic hydrothermal window high precision u pb geochronology of the mesoproterozoic olympic dam cu u au ag deposit south australia

multidisciplinary characterization of the middle holocene eolian deposits of the elsa river basin central italy abstract in temperate regions eolian deposits of different natures are often pedogenically altered and mixed with underlying sediments the research reported in this paper identifies for the first time the presence of eolian deposits in soils of central tuscany and investigates the characteristics and origin five relict polycyclic paleosol profiles were studied p1 was situated in a natural dust trap a doline on top of an isolated limestone hill p2 and p3 were both situated on a limestone plateau and p4 and p5 on a mid and foot slope on schist the profiles were sampled for routine analyses iron forms heavy minerals major and trace elements and pollen spores and non pollen palynomorphs undisturbed samples were taken for micromorphological and sem analyses nine soil horizons were sampled for osl dating eolian deposits were dominant or abundant in the first layers of p1 p2 and p3 osl age determinations of soil horizons deriving from eolian parent material were middle holocene chemical and heavy mineral analyses indicated different possible sources including bare slopes alluvial fans and wide channels coming from the nearby streams that drain the middle tuscany ridge and the mounts of chianti marginal contribution of volcanic ashes was only found in p1 the research demonstrated that wind soil erosion accompanied water erosion and colluvial deposition during the middle holocene in the elsa river basin pollen spectra in particular indicated that soil degradation occurred in an environment showing signs of incipient desertification resulting from an increase of aridity in a land already strongly influenced by humans although central italy is currently considered to be only marginally affected by wind soil erosion a climate change which would imply increased arid conditions could trigger a new cycle of slope denudation wind erosion and loess deposition

tectonic framework and evolution of the gawler craton southern australia the gawler craton is the major crustal province in the southern australian proterozoic and is pivotal in models seeking to describe the evolution of proterozoic australia the craton is host to the olympic dam iron oxide cu au u ree deposit as well as a number of other iron oxide copper gold iocg au and iron ore deposits the evolution of the gawler craton is dominated by two major phases of tectonic activity late archean and late paleoproterozoic early mesoproterozoic in total spanning ca 1 billion years the late archean 2560 2500 ma basin development was coeval with arclike felsic magmatism and mafic ultramafic magmas including komatiites collisional deformation between 2480 and 2420 ma led to ca 400 m y of tectonic quiescence conceivably within an early paleoproterozoic continental interior the second major phase of tectonic activity was in the middle to late paleoproterozoic and early mesoproterozoic 2000 1450 ma paleoproterozoic tectonism was initially dominated by rift related events which produced a series of basins over the interval ca 1900 to 1730 ma some of which contain significant iron ore reserves transient contractional deformation at ca 1850 ma led to batholith scale granitic magmatism in part derived from melting of the late archean basement major basin development was finally terminated by the 1730 to 1690 ma kimban orogeny the effects of which are widespread and include the formation of crustal scale shear systems granitic magmatism and low to high grade metamorphism the kimban orogeny was followed by a renewed period of extension between ca 1680 and 1640 ma leading to local magmatism and sedimentation which appears in part to have been coeval with the high grade ca 1650 ma ooldean event in the western gawler craton at ca 1620 to 1615 ma the generation of the arc related st peter suite in the southern gawler craton implies that craton components were located at an active plate margin the arc environment was superseded by a transition to a continental interior regime which coincided with the voluminous gawler range volcanics 1595 1590 ma and hiltaba suite granitoids 1595 1575 ma the hiltaba suite is dominated by high t fractionated felsic rocks with coeval mafic magmatism confirming a mantle involvement emplacement of the hiltaba suite coincided with the major mineralizing interval in the gawler craton regionally two distinct mineral systems have been recognized the olympic iocg province in the eastern part of the craton and the gold dominated systems within the central gawler gold province the spatial distribution of iocg versus au dominated mineral systems appears to reflect regional variations in crustal composition and hiltaba suite petrogeneses hiltaba aged granites in the olympic iocg province are isotopically more evolved richer in u and th and oxidized compared to similar aged granites in the au dominated province modern day heat flow in the iocg province is significantly higher 90 10 mwm 2 compared to the au dominated province 54 5 mwm 2 suggesting there are important lithospheric compositional differences between the two metallogenic provinces which may reflect an older phase of craton assembly widespread northwest southeast contractional deformation coeval with the emplacement of the hiltaba suite is expressed by the formation and or reactivation of shear zones ranging up to crustal scale within this regime northwest trending structures such as those in the vicinity of the olympic dam deposit are likely to have accommodated dilation associated with strike slip movements intersection between these structures and northeast trending contractional faults may have formed suitable structural traps for 1590 to 1580 ma mineralization the timing of syn hiltaba deformation overlaps with transpression and medium to high grade metamorphism associated with the ca 1570 to 1540 ma kararan orogeny which dominates the geophysical architecture of the central northern part of the craton the youngest phase of deformation in the craton is expressed by reactivation of shear zones between ca 1470 and 1450 ma and regional cooling

u pb geochronological constraints on the genesis of the olympic dam cu u au ag deposit south australia the olympic dam cu u au ag deposit is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system which occurs entirely within and clearly postdates the roxby downs granite the u pb zircon age of the roxby downs granite is well constrained at 1588 or 4 ma field evidence indicates that brecciation hydrothermal alteration and cu u au ag ree mineralization in the olympic dam breccia complex were penecontemporaneous but this is inconsistent with differing ages from previous u pb and rb sr isotopic data on pitchblende and sericite new shrimp u pb zircon data for three olympic dam breccia complex igneous rock units confirm that cu u au ag ree mineralization was contemporaneous with brecciation and alteration and directly followed cooling of the roxby downs granite by as little as several 8 million years two of the dated olympic dam breccia complex rock units are interpreted as autobrecciated felsic dikes one crosscuts laminated hematite quartz sandstones and the other crosscuts cu u mineralized hematite rich breccias zircons from these dikes yielded ages of 1592 or 8 and 1584 or 20 ma respectively the third unit dated is a disrupted ash fall tuff horizon from within a diatreme which crosscuts hematite quartz breccias near the center of the deposit the northern extremities of this diatreme also crosscut hematitic breccias containing a substantial cu u ore zone zircons from this tuff horizon have an age of 1597 or 8 ma the tuff and associated subaerial or subaqueous volcaniclastics were unconsolidated or only weakly lithified at the time of their incorporation into the diatreme so the age of the tuff also reflects the age of diatreme activity these new isotopic data indicate that the olympic dam breccia complex has an age of approximately 1590 ma and therefore imply that brecciation closely followed emplacement and cooling of the roxby downs granite because these breccias contain sulfide fragments and polyminerallic ore fragments exhibit penecontemporaneous sulfide oxide textural relationships and show a close association between cu or u or ag or ree mineralization and fe rich breccias we argue that the metals of economic interest were introduced

feldspar evolution in the roxby downs granite host to fe oxide cu au u mineralisation at olympic dam south australia abstract the textural relationships and geochemistry of feldspars from least altered to sericite hematite altered and mineralised 1 595 ga roxby downs granite rdg at olympic dam south australia were examined the sample suite is representative of rdg both distal 5 km and proximal 27 34 is recognised along with a more abundant less calcic plagioclase an 12 20 both displaying rapakivi and anti rapakivi textures with alkali feldspar alkali feldspars or 55 ab 43 an 2 record post magmatic evolution from cryptoperthite to patch perthite subsequent patch perthite is overprinted by highly porous near end member albite and k feldspar while plagioclase undergoes replacement by albite sericite ba rich k feldspar in sericite hematite altered and mineralised rdg along the margin of the odbc sericite replaces all plagioclase whereas red stained fe rich k feldspar persists sulphide uranium rare earth element mineralisation is observed in association with hydrothermal feldspars and increases in abundance with proximity to the orebody petrographic observations and whole rock geochemistry illustrate the transformation of plagioclase and alkali feldspar from igneous to hydrothermal processes and indicate that hydrothermal albite and k feldspar formed within the rdg without the need for an external source of alkalis feldspar geothermometry indicates a minimum crystallisation temperature of 765 c at 2 2 kbar for alkali feldspar pressure estimate obtained using plagioclase amphibole geobarometry followed by a range of lower temperature transformations late stage magma mixing contamination is postulated from supportive temperature and pressure estimates along with feldspar and mafic mineral relationships