proterozoic mafic ultramafic intrusions in the arunta region central australia part 2 event chronology and regional correlations abstract the arunta region in central australia records multiple proterozoic crustal processes over a 1500 million year period the timing of mafic ultramafic magmatism in this evolution is constrained by shrimp u pb dating of zircon which is a primary phase in mafic ultramafic intrusions across the region the earliest mafic magmatism was part of the 1810 1800 ma stafford event and a second episode is recognised during the 1790 1770 ma yambah event zircon overgrowths in some of these early intrusions record metamorphism during the strangways event a regionally pervasive metamorphic episode whose termination at ca 1690 ma coincided with intrusion of dolerite dykes gabbro intrusion during the ca 1640 ma liebig event is related to the geologically distinct warumpi province in the south of the region there is no record of mafic magmatism during the ca 1590 ma chewings event later systems include the ca 1130 ma alkaline ultramafic mordor complex and basaltic bodies are components of the irindina province which experienced high grade metamorphism during the palaeozoic the dating associates mafic ultramafic magmatism with each of these events which suggests that repeated extensional systems are an important aspect of the tectonic evolution the example of routinely obtaining zircon for dating from mafic and even ultramafic intrusions using an integrated approach of field and geochemical criteria to guide sampling opens the possiblility of dating mafic ultramafic intrusions elsewhere direct dating of mafic ultramafic magmatism permits its significance in proterozoic event systems to be evaluated directly free of assumed or conjectural timing correlations with the felsic plutons that are more often studied for age control

iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

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

soil landscape relationship in a chronosequence of the middle madeira river in southwestern amazon brazil abstract high temperatures and rainfall prevail in the brazilian amazon but some areas have soils with high clay mineral contents of 2 1 and there is limited information concerning their properties therefore it is important to study the soil formation and understand the environmental conditions in which they were formed this study aimed to investigate the physical chemical and mineralogical properties of the soil in relation to the environmental factors acting on a chronosequence in the late pleistocene sediments of the middle madeira river soil profiles were selected on three alluvial terraces morphological physical chemical mineralogical x ray fluorescence tem and sem characterizations were performed the soils that exhibited a clayey texture acidic reaction low values of exchangeable bases and high values of aluminum had profiles containing a considerable presence of 2 1 clay minerals especially illite vermiculite mica vermiculite hydroxyl interlayered vermiculite and pyrophyllite soil mineralogy indicated that these soils were recently weathered where the low values of sum of bases correspond to the low presence of these cations in the parent material meanwhile high values of exchangeable aluminum were derived from the pyrophyllite alteration different parent material and 2 1 clay minerals recent alteration therefore the parent material presence of amorphous silica different climate conditions in the past and current drainage restriction contribute to the slow alteration rate of 2 1 clay minerals of the soils of the humid tropical amazon environment

decapod crustaceans from the eocene la meseta formation seymour island antarctica a model for preservation of decapods thirteen species of fossil decapod crustaceans collected from 43 localities in the la meseta formation eocene seymour island antarctica have been located precisely using global positioning system techniques and accurately placed in their stratigraphic context using an allostratigraphic scheme three decapod species are congeneric with extant species known from outer shelf and slope habitats documenting an onshore offshore pattern of ecological preference functional morphological analysis of the decapods confirms the environmental interpretations based upon sedimentological studies species diversity is greatest in the lower and upper parts of the section in the acantilados and submeseta allomembers respectively however numerical abundance of specimens is greatest near the top of the coarsening upward sequence in the cucullaea i allomember this allomember and the underlying campamento allomember are overwhelmingly dominated by a single species lyreidus antarcticus the relatively high diversity of decapods in the lower and upper parts of the la meseta formation is interpreted as resulting from favourable preservational environments in delta front and nearshore environments where burial was rapid and sediment reworking was minimal in the middle part of the la meseta formation sediment reworking was probably high and fragile arthropod cuticular material was destroyed except in the case of lyreidus which is a burrower and was probably preserved within its burrow the pattern of diversity documented by the arthropods differs markedly from that of the molluscs probably because of the presence of more durable shell material in the pelecypods and gastropods the la meseta formation record of decapods may serve as an important model for arthropod preservation against which other occurrences can be tested

a continent wide study of australia s uranium potential part i gis assisted manual prospectivity analysis abstract this paper describes the approach to and outcomes of a manual analysis i e a cognitive assessment of spatial and non spatial data of the uranium potential of 90 geological regions in australia for this analysis the 14 principal uranium deposit types recognized by the international atomic energy agency were grouped in six uranium systems models i e surficial sedimentary igneous related metamorphic metasomatic unconformity related and vein related uranium systems on the basis of similar genetic processes environments of ore formation and ingredients mappable at the regional to continent scale the newly proposed uranium systems models are structured according to the mineral systems approach and focus on the critical mineralization processes that must occur for a uranium deposit to form in a particular region our manual prospectivity analysis employed this approach to assess the probability of the critical genetic processes having occurred in each geological region in this semi quantitative probabilistic evaluation technical quality and opportunity ranking schemes were used to rank each geological region based on the probability of occurrence of and potential for high quality uranium deposits and opportunity for securing prospective ground based on this assessment the geological regions with the greatest potential for discovery of potentially recoverable uranium resources are the ashburton broken hill litchfield mcarthur money shoal murphy paterson pine creek and northeast tasmania regions i e quality ranking of 10 0 the gawler and polda regions i e 9 0 and the amadeus georgetown stuart tanami regions i e 8 1 most of these regions contain known unconformity related or sandstone hosted uranium deposits although some of them are pure conceptual plays that have received relatively little attention in terms of uranium exploration maps based on the numerical output of the prospectivity analysis helped to inform area selection decisions and detailed follow up studies and focus time and resources the template developed in this study can easily be modified to suit prospectivity analyses for other metals or a similar investigation in another country as illustrated in part ii the best possible approach to a complex continent wide prospectivity analysis is to harness the strengths of both manual and automated i e sophisticated computational techniques applied to spatial data approaches as these methodologies essentially address each other s limitations

sulfur and oxygen isotopic evidence of country rock contamination in the voisey s bay ni cu co deposit labrador canada abstract the emplacement of basaltic magma into sulfide bearing country rocks provides a favorable geologic environment for magmatic sulfide ore formation related either directly to assimilation of country rock sulfur or indirectly to a depression of sulfide solubility caused by assimilation induced changes in magma composition pelitic country rocks of the proterozoic tasiuyak gneiss in the area of the voisey s bay ni cu co deposit contain sulfidic layers that may have provided sulfur to basaltic magmas during emplacement of the voisey s bay intrusion sulfur isotopic compositions of the tasiuyak gneiss range from 0 9 to 17 0 values typical for sulfides produced via bacterial sulfate reduction in an open marine environment archean gneisses in the area contain low amounts of sulfide and are less likely to have served as a source of externally derived sulfur sulfur isotopic compositions of the sulfide minerals from the voisey s bay deposit show consistent variations both spatially and with rock types disseminated and massive sulfides show a decrease in 34 s to the west with values typically between 0 and 2 in the eastern deeps ovoid and discovery hill zone and between 2 and 4 in the reid brook zone 34 s values of the mushua intrusion to the north and the normal troctolite in the eastern deeps are more positive ranging between 0 5 and 1 8 this range is taken to represent the isotopic composition of primary mantle derived sulfur in the area because the mushua intrusion and normal troctolite show the least geochemical evidence for contamination by country rocks sulfur isotopic data from the reid brook zone are consistent with up to a 50 sulfur contribution from the tasiuyak gneiss correspondingly lower proportions are indicated for the eastern portion of the deposit where country rocks are predominantly low sulfide enderbitic and quartzofeldspathic gneisses oxygen isotopic values of gneiss fragments in the basal breccia sequence and feeder breccia suggest that the assimilation process involved a greater proportion of high 18 o contaminant to the west 18 o values of the tasiuyak gneiss 5 9 to 14 0 enderbitic gneiss 6 4 to 8 7 and archean quartzofeldspathic gneiss 9 5 to 9 7 are consistent with an increased proportion of tasiuyak gneiss contaminant to the west isotopic data strongly indicate that sulfur from the tasiuyak gneiss has been involved in ore deposition at the voisey s bay deposit however sulfur and oxygen isotopic data also strongly suggest that the addition of externally derived sulfur was not the sole process responsible for mineralization and that assimilation of both proterozoic and archean country rocks played a key role in depressing sulfide solubility prior to sulfide localization via dynamic physical mechanisms

deep seismic profiling in central australia abstract deep seismic profiling undertaken in central australia comprised expanding spread reflection profiling long range refraction work and a small scale three dimensional refraction survey as well as the more usual near vertical incidence reflection profiling scismic reflection sections within the arunta block in central australia show abundant northerly dipping events that are interpreted as reflections from dipping faults many of which are evident in surface geological mapping the redbank deformed zone a major thrust feature has been imaged to depths of at least 30 km and defines a marked change in reflection character south of the redbank zone steep northerly dipping reflections are absent sub horizontal basement reflections are prevalent below the southern arunta province and amadeus basin seismic refraction profiles indicate that the crust is more than 50 km thick below both the boundary between the southern and central arunta provinces and the northern part of the amadeus basin expanding reflection spreads and a three dimensional refraction survey have added fine details to the results in regions of special geological interest and include the resolution of complicated velocity variations in the sedimentary rocks of the northern part of the amadeus basin and the measurement of anisotropy in the granulites of the central arunta province adjacent to the redbank zone

mineral systems approach applied to gis based 2d prospectivity modelling of geological regions insights from western australia abstract gis based 2d prospectivity modelling of three greenfield geological regions of western australia namely the west arunta orogen west musgrave orogen and gascoyne province was implemented for a range of deposit types including orogenic and intrusion related gold volcanic sediment hosted base metal sulfides magmatic nickel copper and magmatic platinum group element sulfides iron oxide copper gold tin tungsten igneous and metamorphic related rare earth elements surficial uranium and unconformity related uranium conceptual mineral systems models were generated to identify the targeting criteria the inputs to the models were the spatial proxies derived from 1 100 000 to 1 500 000 scale public domain data the results showed similar prospectivity patterns for all of the targeted deposit types except sediment hosted uranium and surficial uranium deposit types once a favourable geodynamic architecture is established it can sustain different mineral systems and produce diverse deposit types depending on the nature of ligands in the source regions and physical chemical environment in the trap regions through repeated reactivation in the subsequent geological history a model is proposed to explain the formation of different deposit types at different stages of tectonic evolution of a province the implication for gis based 2d prospectivity modelling at the scale of geological region is that the prospectivity model may not be deposit type specific further prospectivity modelling should be carried out sequentially at progressively finer scales regional to district to camp scale using only the targeting criteria that are relevant at the specific scale to delineate targets for specific deposit types

predictive mineral discovery in the eastern yilgarn craton western australia an example of district scale targeting of an orogenic gold mineral system abstract the eastern yilgarn craton eyc is one of the world s premier gold provinces subject to over a century of mineral exploration prolonged interest in the terrane has led to the assembly of multiple world class data sets suitable for testing district scale targeting methodologies district scale targeting is concerned with identifying a mineral camp 60 km 60 km in size within a prospective region or province 1000 km 1000 km in size exploration at the district scale necessitates the development of predictive exploration models which can be applied to large regions recent advances in the study of the geodynamic evolution and 3d architecture of the eyc together with an understanding of their interrelationship with the orogenic gold mineral system has resulted in identification of critical mineralisation processes responsible for the region s rich gold endowment here we describe and map these critical processes using them as a basis for district scale targeting we relate gold mineralisation to three temporally constrained geodynamic periods integrated with regional hydrothermal alteration unlike many targeting methodologies this methodology does not incorporate the location of known gold deposits in the analysis yet it predicted 75 of known gold mineralisation in 5 of the area the methodology allows critical mineralisation processes to be identified and mapped through time and space these critical processes are mostly generic and can be applied to other granite greenstone orogenic gold regions such as the abitibi in canada an important outcome of this work for the eyc is the identification of a number of new target areas not known currently for significant gold mineralisation in what is otherwise thought to represent a mature terrane for gold exploration

the age and significance of the ngadarunga granite in proterozoic central australia abstract the emplacement of the ngadarunga granite in the arunta region of central australia directly constrains the timing of the first high grade metamorphic tectonic and magmatic event in the arunta region and the timing of the geographically extensive unconformity that separates the earliest regional basin phase from younger overlying sedimentary successions previous dating had correlated this event with the 1880 1840 ma barramundi orogeny interpreted in far north australia linking the arunta region to the barramundi model of widespread synchronous cratonisation in the period 1880 1840 ma new data revise this granite emplacement to 1803 6 ma placing it in the younger 1810 1800 ma stafford event of the arunta region the provenance of detrital zircons in early arunta region sedimentary rocks was dominated by crystalline rocks formed in the period 1840 1880 ma thus the earliest rocks in the arunta region were deposited after ca 1840 ma in a basin marginal to 1880 1840 ma continental crust and their subsequent tectonism began with the stafford event

the importance of early crustal architecture for subsequent basin forming magmatic and fluid flow events the granites tanami orogen example abstract the paleoproterozoic granites tanami orogen gto consists of tightly folded predominantly greenschist facies rocks the orogen a component of the north australian craton includes a ca 1864 ma succession of turbiditic and pelagic sedimentary rocks interbedded with volcanic rocks and abundant dolerite sills in a back arc basin setting which is intruded by collision related ca 1800 ma granitic rocks integrated 4d interpretation of deep seismic profiles gravity and magnetic field observations associated with available surface geology and igneous isotope geochemistry suggest that the gto forms an imbricated crust developed on a partially inverted s dipping rifted archean basement the rifting took place in the paleoproterozoic around 1864 ma and was followed by e w orientated compressional deformation ca 1850 ma with the development of northerly trending isoclinal folds and associated faults orthogonal collisional tectonics followed at ca 1800 ma which is associated with s verging kilometre scale folds faults and orogenic lode gold deposits in the region recognition of the preserved early rift architecture in the gto has major implications for the subsequent evolution of the orogen the early architecture has influenced all subsequent deposition deformation magmatic and fluid events including spatial control of the ca 1864 ma rock succession to the location of intrusive bodies and fluid transfer during formation of ca 1800 ma orogenic gold mineralization

magnetotelluric constraints on subduction polarity reversing reconstruction models for proterozoic australia two dimensional lithospheric scale magnetotelluric imaging in the central australian proterozoic has constrained the large scale architecture of terrane assembly during paleoproterozoic accretion and collision the comparatively conductive north australian craton consisting of rocks between 2500 and 1730 ma in age has been imaged to extend for 150 km under the 1690 1620 ma warumpi province which forms part of a large comparatively juvenile terrane in central southern australia collision between the north australia craton and warumpi province occurred ca 1640 ma the boundary between these domains is modeled to be subvertical at crustal scale but dips south at 45 in the mantle to depths of 150 km we interpret this geometry to reflect lithospheric scale underthrusting of the north australian craton beneath the warumpi province and suggest that it provides a first order constraint on subduction polarity during collision ca 1640 ma in contrast most contemporary models for the evolution of paleoproterozoic australia propose that the north australian craton was located on the overriding plate of a long lived ca 1800 1550 ma north directed subduction system the polarity of these models is not consistent with the lithospheric scale geophysical architecture

fluid evolution in the kolar gold field evidence from fluid inclusion studies gold mineralization in the kolar schist belt of the dharwar craton occurs dominantly in the form of a sulfide poor au quartz lode the champion lode exposed in the mysore and other mines and sulfide rich auriferous lodes from the nundydroog mine fluid inclusion microthermometric experiments were conducted on primary inclusions in quartz intimately associated with au mineralization homogenization studies on aqueous biphase l v aqueous polyphase l v halite and aqueous carbonic lco2 vco2 laq inclusions from the champion lode furnish a temperature range of 120 to 420 c freezing of aqueous biphase inclusions and dissolution of halite in the aqueous polyphase inclusions provide salinity of 5 to 50 wt nacl equivalent fluid inclusion thermobarometry from the total homogenization of aqueous carbonic inclusions and from intersecting isochores of coeval pure carbonic lco2 vco2 and pure aqueous inclusions constrain the p t path of evolution of the fluid in the champion lode gold precipitation was likely to have been brought about in response to a sharp fall in pressure with attendant unmixing of liquid co2 from the parent h2o co2 fluid of possible metamorphic origin this would imply transportation of gold by some pressure sensitive complex such as the au carbonyl fluid characteristics are different in the sulfide rich auriferous lodes as indicated by the virtual absence of the co2 bearing and the halite bearing inclusions the fluid evolution path as evident from the crude positive colinearity of temperature and salinity is due to mixing of a low 200 c temperature low saline 7 wt nacl equivalent fluid with a high temperature 400 c high saline 50 wt nacl equivalent fluid the lack of co2 and association of au with sulfides indicate a different mode of gold transport as chloride or bisulfide complexing deposition of which was possibly brought about by fluid mixing

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

nickel sulfide deposits in australia characteristics resources and potential abstract australia s nickel sulfide industry has had a fluctuating history since the discovery in 1966 of massive sulfides at kambalda in the eastern goldfields of western australia periods of buoyant nickel prices and high demand speculative exploration and frenetic investment the nickel boom years have been interspersed by protracted periods of relatively depressed metal prices exploration inactivity and low discovery rates despite this unpredictable evolution the industry has had a significant impact on the world nickel scene with australia having a global resource of nickel metal from sulfide ores of 12 9 mt five world class deposits 1 mt contained ni and a production status of number three after russia and canada more than 90 of the nation s known global resources of nickel metal from sulfide sources were discovered during the relative short period of 1966 to 1973 australia s nickel sulfide deposits are associated with ultramafic and or mafic igneous rocks in three major geotectonic settings 1 archean komatiites emplaced in rift zones of granite greenstone belts 2 precambrian tholeiitic mafic ultramafic intrusions emplaced in rift zones of archean cratons and proterozoic orogens and 3 hydrothermal remobilized deposits of various ages and settings the komatiitic association is economically by far the most important accounting for more than 95 of the nation s identified nickel sulfide resources the ages of australian komatiitic and tholeiitic hosted deposits generally correlate with three major global scale nickel metallogenic events at 3000 ma 2700 ma and 1900 ma these events are interpreted to correspond to periods of juvenile crustal growth and the development of large volumes of primitive komatiitic and tholeiitic magmas caused by large scale mantle overturn and mantle plume activities there is considerable potential for the further discovery of komatiite hosted deposits in archean granite greenstone terranes including both large and smaller high grade 5 to 9 ni deposits that may be enriched in pges 2 to 5 g t especially where the host ultramafic sequences are poorly exposed analysis of the major komatiite provinces of the world reveals that fertile komatiitic sequences are generally of late archean 2700 ma or paleoproterozoic 1900 ma age have dominantly al undepleted al 2 o 3 tio 2 15 to 25 chemical affinities and often occur with sulfur bearing country rocks in dynamic high magma flux environments such as compound sheet flows with internal pathways facies kambalda type or dunitic compound sheet flow facies mt keith type most precambrian provinces in australia particularly the proterozoic orogenic belts contain an abundance of sulfur saturated tholeiitic mafic ultramafic intrusions that have not been fully investigated for their potential to host basal ni cu sulfides voisey s bay type mineralization the major exploration challenges for finding these deposits are to determine the pre deformational geometries and younging directions of the intrusions and to locate structural depressions in the basal contacts and feeder conduits under cover stratabound pge ni cu cr deposits hosted by large archean proterozoic layered mafic ultramafic intrusions munni munni panton of tholeiitic affinity have comparable global nickel resources to many komatiite deposits but low grades

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

exploration targeting for orogenic gold deposits in the granites tanami orogen mineral system analysis targeting model and prospectivity analysis abstract a major challenge for mineral exploration geologists is the development of a transparent and reproducible approach to targeting exploration efforts particularly at the regional to camp scales in terranes under difficult cover where exploration and opportunity costs are high in this study a three pronged approach is used for identifying the most prospective ground for orogenic gold deposits in the paleoproterozoic granite tanami orogen gto in western australia a key input to the analyses is the recent development of a 4d model of the gto architectural evolution that provides new insights on the spatio temporal controls over orogenic gold occurrences in the area in particular on the role of pre mineralization pre 1795 ma d gtoe d gto1 d gto2 architecture in localization of gold deposits and the spatial distribution of rock types in 3d this information is used to build up a model of orogenic gold minerals system in the area which is then integrated into the three mutually independent but complementary mineral prospectivity maps namely a concept driven manual and fuzzy analysis and a data driven automated analysis the manual analysis involved 1 generation of a process based gold mineral systems template to aid target selection 2 manual delineation of targets 3 manual estimation of the probability of occurrence of each critical mineralization process based on the available information and 4 combining the above probabilities to derive the relative probability of occurrence of orogenic gold deposits in each of the targets the knowledge based geological information system gis analysis attempts to replicate the expert knowledge used in the manual approach but queried in a more systematic format to eliminate human heuristic bias this involves representing the critical mineralization processes in the form of spatial predictor maps and systematically querying them through the use of a fuzzy logic model to integrate the predictor maps and to derive the western gto orogenic gold prospectivity map the data driven empirical gis analysis uses no expert knowledge instead it employs statistical measures to evaluate the spatial associations between known deposits and predictor maps to establish weights for each predictor layer then combines these layers into a predictive map using a weights of evidence wofe approach application of a mineral systems approach in the manual analysis and the fuzzy analysis is critical potential high value targets identified by these approaches in the western gto lie largely under cover whereas traditional manual targeting is biased to areas of outcrop or sub crop amenable to direct detection technology such as exploration geochemistry and therefore towards areas that are data rich the results show the power of combining the three approaches to prioritize areas for exploration while the manual analysis identifies and employs human intuition and can see through incomplete datasets it is difficult to filter out human bias and to systematically apply to a large region the fuzzy method is more systematic and highlights areas that the manual analysis has undervalued but lacks the intuitive power of the human mind that refines the target by seeing through incomplete datasets the empirical woe method highlights correlations with favorable host stratigraphy and highlights the control of an early set of structures potentially undervalued in the knowledge driven approaches yet is biased due to the incomplete nature of exploration datasets and lack of abundant gold deposits due to the extensive cover the results indicate that the most prospective areas for orogenic gold in western gto are located in the central part of the study area largely in areas blind to previous exploration efforts according to our study the procedure to follow should be to undertake the analyses in the following order manual prospectivity analysis followed by the conceptual fuzzy approach followed by the empirical gis based method undertaking the manual analysis first is important to prevent explorationists from being biased by the automated gis based outputs it is however emphasized that all of the prospectivity outputs from these three methods are possible and they should not be treated as treasure maps but instead as decision support aids therefore a final manual prospectivity analysis redefined by the mutual consideration of output from all of the methods is required the strategy employed in this study constitutes a new template for best practice in terrane to camp scale exploration targeting that can be applied to different terranes and deposit types particularly in terranes under cover and provides a step forward in managing uncertainty in the exploration targeting process

sm nd evidence for high grade ordovician metamorphism in the arunta block central australia sm nd ages from the harts range in the south eastern arunta inlier in central australia indicate that regional metamorphism up to granulite facies occurred in the early ordovician c 475 ma this represents a radical departure from previous tectonic models for the region and identifies a previously unrecognized intraplate event in central australia peak metamorphic assemblages 800 c and 10 5 kbar formed at around 476 14 ma and underwent approximately 4 kbar of near isothermal decompression at 475 4 ma a coarse grained unfoliated garnet clinopyroxene bearing marble inferred to have recrystallized late in the decompressional evolution gives an age of 469 7 ma two lines of evidence suggest the early ordovician tectonism occurred in an extensional setting first the timing of the high grade lower crustal deformation coincides with a period of marine sedimentation in the amadeus and georgina basins that was associated with a seaway that developed across central australia second isothermal decompression of lower crustal rocks was associated with the formation of a regional sub horizontal mid crustal foliation in the entia gneiss complex which forms the structurally lowest part of the harts range upper amphibolite facies metamorphism c 700 c 8 9 kbar occurred at 479 15 ma there is no evidence that p t conditions in the entia gneiss complex were as high as in the overlying units this implies that the extensional system was reworked during a later compressional event sm nd data from the mid amphibolite facies c 650 c and 6 kbar detachment zone that separates the irindina supracrustal assemblage and entia gneiss complex give an age of 449 10 ma this age corresponds to the timing of a change in the pattern and style of sedimentation in the amadeus and georgina basins and indicates that the change in basin dynamics was associated with mid crustal deformation it also suggests that compressional deformation culminating in the devonian to carboniferous 400 300 ma alice springs orogeny may have begun as early as c 450 ma at present the extent of early ordovician tectonism in central australia is unknown however granulite facies metamorphism and associated intense deformation imply an event of regional extent an implication of this work is that high grade lower crustal metamorphism and intense deformation occurred during the development of a broad shallow slowly subsiding intraplate basin

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

rapid dewatering of the crust deduced from ages of mesothermal gold deposits the large scale migration of fluids through the continental crust has been well documented but there is no consensus regarding the timing of fluid migration relative to orogenic episodes or rates of crustal dewatering1 here we present40ar 39ar dates for muscovites from quartz veins along a major shear zone in southeast alaska which show that the veins were emplaced in the early eocene during the late stages of orogenic deformation hydrother mal activity took place for only about 1 myr and along a distance of at least 200 km the fluids were generated by metamorphic reactions in subducted crust along the north american plate margin and were apparently trapped in the crust by the low permeabilities accompanying a convergent tectonic regime until 56 myr ago the rapid dewatering event coincided with a change in plate motion at 56 55 myr which caused a shift from convergent to partly transcurrent tectonics we suggest that this change in tectonic regime led to increased crustal permeabilities and hence the possibility of large scale fluid migration

melting reactions of gneissic inclusions with enclosing magma at voisey s bay labrador canada implications with respect to ore genesis the voisey s bay ni cu co sulfide deposit is associated with a 1 333 ga troctolitic gabbroic intrusion which transects the 1 85 ga collisional boundary between tasiuyak paragneiss of the proterozoic aged churchill province to the west and orthogneiss of the archean aged nain province to the east the intrusion comprises an upper chamber to the east the eastern deeps subchamber a lower chamber to the west the reid brook subchamber and a conduit connecting them sulfide mineralization is closely associated with a breccia which occurs close to the basal contact of the eastern deeps subchamber and within the conduit the breccia is composed of abundant tasiuyak paragneiss inclusions with a troctolitic gabbroic matrix the gneiss inclusions have reacted extensively with the enclosing magma in general the degree of reaction increases from the reid brook subchamber through the conduit to the eastern deeps subchamber in the course of this reaction garnet has been oxidized to form hercynite and magnetite with the release of sio2 to the magma cordierite has been dehydrated to form hercynite with the release of sio2 hypersthene and k feldspar have reacted together to produce hercynite with the release of sio2 and k2o plagioclase has broken down to produce corundum losing sio2 and na2o to the magma and itself becoming enriched in anorthite and the corundum has subsequently reacted with feo and mgo from magma to form hercynite the color of the hercynite changes progressively from beige in the reid brook subchamber through green within the conduit to black in the eastern deeps subchamber this color change reflects an increase in feal2o4 at the expense of the mgal2o4 in the hercynite the inclusions in the eastern deeps subchamber characteristically show a series of reaction rims ranging from labradorite through biotite to hypersthene it is seen that reaction with the gneiss inclusions results in the addition of sio2 k2o and na2o to the magma this felsification of magma has resulted in a decrease in its ability to dissolve sulfide and therefore has promoted sulfide immiscibility

hydrothermal alteration and mineralisation of the glen eden mo w sn deposit a leucogranite related hydrothermal system southern new england orogen nsw australia the glen eden mo sn w deposit in north eastern new south wales australia is an example of a leucogranite related low grade large tonnage hydrothermal system it occurs in the southern part of the new england orogen and is hosted within permian felsic volcanic rocks intruded at depth by dykes of porphyritic microleucogranite glen eden granite the deposit is hosted within a pipe like quartz rich greisen breccia body about 500 m in diameter surrounded by a greisen zone several hundred metres across zoning out into altered volcanic rocks the dominant ore minerals largely hosted as open space fillings and disseminations in quartz and quartz rich greisen are molybdenite wolframite and cassiterite they are accompanied by minor to trace amounts of muscovite fluorite topaz siderite pyrrhotite arsenopyrite chalcopyrite sphalerite bismuth bismuthinite joseite a cosalite galenobismutite beryl anatase and late stage dickite and kaolinite two types of breccia are recognised 1 greisenised volcanic rock fragments quartz muscovite cemented by hydrothermal quartz k feldspar ore minerals and 2 fragments of hydrothermal quartz cassiterite wolframite enclosed in quartz clay in both types of breccia and in stockwork veins there is evidence of early precipitation of mo sn w phases followed by bi minerals and base metal sulfides fluorite siderite

the nature of proterozoic reworking of early archaean gneisses mukalo creek area southern gascoyne province western australia abstract the gascoyne province a key segment of the early proterozoic capricorn orogen which separates the archaean pilbara and yilgarn cratons of western australia may be divided into northern central and southern zones the southern zone comprises predominantly archaean granulite facies quartzo feldspathic gneisses and passes southwards into the western gneiss terrain of the yilgarn block this area was part of the lower crust of a stabilized continental landmass at the end of the archaean development of the capricorn orogen 2 ga ago resulted in discontinuous deformation of the northern part of this landmass deformation was concentrated in ductile shear zones leaving blocks of relatively undeformed gneiss between them the shear zones trend between ene wsw and ese wnw and dip to the south at 50 60 strong down dip stretching lineations and asymmetric feldspar porphyroclasts indicate that the shear zones are reverse faults however metamorphic assemblages in early proterozoic dolerite dykes which post date the shear zones show that the area was still in the lower crust following the earliest proterozoic deformation isothermal uplift of the southern gascoyne province northern yilgarn block by 10 km or more occurred 1 7 1 5 ga ago and was accompanied by granitoid intrusion deformation within e w trending shear zones continued after uplift and was accompanied by patchy greenschist facies retrogression of both static and dynamic style on the local scale the effects of early proterozoic deformation on the early archaean gneisses are generally confined to shear zones and their immediate surroundings they comprise 1 realignment of gneissic trends from n s to e w 2 development of quartz ribbon mylonites by elongation of quartz grains into lenses and ribbons and reduction of feldspar grainsize by crystal plastic processes 3 growth of porphyroblastic and corona garnet in felsic and mafic gneisses the later proterozoic deformation occurred at lower temperatures and resulted in 1 further realignment of gneissic trends from northerly to easterly 2 reduction of quartz grainsize by crystal plastic processes and reduction of feldspar grainsize largely by brittle fracture 3 greenschist facies retrogression that the earliest deformation in the southern gascoyne province resulted in crustal shortening and was followed by significant uplift and granitoid intrusion indicates that proterozoic reworking of this area resulted from regional n s compression this favours development of the capricorn orogen in a collision zone between the pilbara and yilgarn cratons rather than in an ensialic mobile zone

tectonostratigraphy and base metal mineralization controls aravalli province western india new interpretations from geophysical data analysis analysis and synthesis of multi disciplinary geoscience information from geological literature maps and from digitallyprocessed aeromagnetic and gravity data pertinent to the aravalli province were carried out to address some hitherto unresolved questions about the tectonostratigraphy of this archaean proterozoic metallogenic province based on the magnetic anomalies several tectonic domains were identified these domains bounded by regional scale geophysical lineaments have distinct crustal lithological metamorphic and metallogenic characteristics and correlate broadly with lithostratigraphic belts identified by several earlier workers new interpretations on the tectonostratigraphy and the base metal mineralization controls in the aravalli province are as follows the hindoli sequences in the eastern parts of the province constitute an independent palaeo proterozoic tectonic domain and do not form part of the archaean basement complex the base metal bearing metasedimentary enclaves in the central parts of the province also constitute an independent palaeo proterozoic tectonic domain which is quite distinct from the surrounding basement complex rocks the base metal bearing metavolcano sedimentary sequences in the western parts of the province constitute an independent neo proterozoic tectonic domain the base metal deposits in the province are spatially associated with the regional scale lineaments and with the mafic metavolcanic rocks deduced from the aeromagnetic data the regional scale lineaments which possibly represent proterozoic crustal scale faults are plausible structural controls on the basemetal mineralization in the province the mafic metavolcanic rocks are plausible heat source controls on the sedex and or vmstype base metal mineralizations and are possible metal source controls on the vms type base metal mineralization in the province d 2005 elsevier b v all rights reserved

architecture and emplacement of the nebo babel gabbronorite hosted magmatic ni cu pge sulphide deposit west musgrave western australia the nebo babel ni cu platinum group element pge sulphide deposit in the west musgrave block western australia is the largest nickel sulphide discovery in the last 10 years the deposit is hosted within a concentrically zoned olivine free tube like chonolithic gabbronorite intrusion associated with the approximately 1 078 ma giles complex layered intrusions in the warakurna large igneous province emplaced into sulphide free amphibolite facies orthogneiss the fault offset nebo babel chonolith extends for 5 km and has a cross section of 1 0 5 km igneous mineralogy fabrics and textures are well preserved the lithostratigraphy includes variably textured leucogabbronorites vlgn that form an outer shell around mineralised gabbronorite mgn with barren gabbronorite bgn and oxide apatite gabbronorite oagn in the middle and lower parts of the chonolith mineral and whole rock geochemistry indicate that the units become progressively evolved in the order vlgn mgn bgn and oagn and that incompatible trace element concentrations increase downwards within the mgn and bgn the mineralisation which is confined to the early more primitive units vlgn and mgn occurs as massive sulphide breccias and stringers and as disseminated gabbronorite hosted sulphides the massive sulphides were emplaced late in the intrusive sequence have different pge chemistry and cu tenor to the disseminated sulphides and have undergone sulphide fractionation the distribution of disseminated sulphides which are primary magmatic in origin is related to chonolith geometry and magma flow regimes rather than to gravitational settling sulfur bearing country rocks are absent in the nebo babel deposit area and thus local crustal s addition was unlikely to have been the major mechanism in achieving sulphide immiscibility the nebo babel intrusion is part of an originally continuous magma chonolith with multiple and related magma pulses the parental magma was medium to low k tholeiite with 8 9 wt mgo the initial magma pulse vlgn the most primitive and sulphide saturated was probably emplaced along a linear weakness in the country rock after crystallisation of vlgn marginally more fractionated sulphide saturated magma was injected through the thermally insulated core of the conduit forming the mgn successive pulse s of more fractionated magma bgn were emplaced in the core of the intrusion after magma flow ceased closed system crystal fractionation produced consistent mineral and chemical fractionation trends within bgn and oagn after crystallisation the intrusion was overturned and then offset by the jameson fault resulting in the apparent reverse chemical and mineral trends in nebo babel

age of mineralization of the candelaria fe oxide cu au deposit and the origin of the chilean iron belt based on re os isotopes re os isotopes are used to determine the age of iron oxide cu au mineralization at candelaria chile and to explore possible genetic links with the batholithic intrusions in the area re os ages calculated from molybdenite are 114 2 0 6 ma and 115 2 0 6 ma and they are interpreted to represent the age of mineralization these ages are consistent with previously reported ages for biotite alteration that range from 114 to 116 ma an isochron calculated by re os ratios from hydrothermal magnetite and sulfides constrains an initial 187 os 188 os ratio of 0 36 0 10 the initial 187 os 188 os ratio for sulfide from bronce mine a small satellite of the candelaria orebody is 0 33 0 01 these values are broadly similar to the calculated initial 187 os 188 os ratio for magmatic magnetite in nearby batholithic rocks that range from 0 20 to 0 41 the relatively radiogenic initial 187 os 188 os ratio represents a mixture of mantle and crustal components in the ores and batholitic rocks the similarity in initial 187 os 188 os ratio of the ore and magmatic oxides suggest that the granitic plutons could be the source of metals in the candelaria district these data are consistent with the existence of a significant magmatic fluid component in the hydrothermal system as suggested by previously published work in order to establish a regional perspective we analyzed ore minerals from other chilean deposits of the iron oxide cu u au rare earth elements ree class magnetite from the manto verde iron oxide cu au deposit has os and re concentrations of 11 to 17 parts per trillion ppt and 4 to 6 parts per billion ppb respectively the initial 187 os 188 os ratio is approximately 0 20 and is similar to that of ore minerals from candelaria and of the early cretaceous batholithic intrusions these data indicate a similar metal source for the mineralization at manto verde and candelaria magnetite from three magnetite apatite deposits of the chilean iron belt have re concentrations between 0 8 and 3 ppb and os concentrations between 11 and 76 ppt calculated initial 187 os 188 os ratios of these magnetites range from 1 2 to 8 4 and are distinctly different from those of the iron oxide cu au deposits the cause of the comparatively high radiogenic signatures in the magnetite apatite ores is probably related to fluid interactions with i e leaching the surrounding sedimentary rocks during their genesis in contrast to the iron oxide cu au systems the os in magnetite apatite ores could be derived from sedimentary rocks this evidence suggests that predominantly basin derived nonmagmatic brines formed these magnetite apatite deposits

the geological setting of the platinoid and base metal sulfide mineralization in the platreef of the bushveld complex in drenthe north of potgietersrus on the farm drenthe the platreef consists of a complex assemblage of norites melanorites pyroxenites serpentinites and xenoliths of dolomite it is a zone of up to 250 m thick between the basal contact of the complex and the overlying main zone norites the composition of the orthopyroxene shows a rapid increase from en 60 to en 70 in the lower 30 m of the sequence and a sharp drop from en 70 to en 60 at the top of the platreef this compositional break at the upper contact is due to a change from primary bronzite in the platreef to inverted pigeonitc in the main zone high temperature metamorphic assemblages are preserved in the larger xenoliths whereas their outer margins and the smaller xenoliths contain retrograde metamorphic mineral assemblages the igneous rocks display irregularly distributed zones of alteration to bronzite bastitites and serpentinites the alteration process was probably dominated by degassing of the xenoliths the distribution and composition of the major sulfide minerals indicate a change from a sulfur rich to a metal rich environment during the crystallization of the platreef pyrite monoclinic pyrrhotite pentlandite and chalcopyrite dominate the lower part of the platreef and hexagonal pyrrhotite pentlandite and chalcopyrite or cubanite prevail in the upper portion whole rock analyses show an upward decrease in the ni cu ratio from 1 95 to 1 70 large variations occur in the distribution and grade of ni cu and platinum group elements although highest values are associated with a zone of serpentinization the ni and cu values are unreliable indicators in predicting pt and pd concentrations in zones of major metal enrichment ni and cu correlate strongly while pt and pd have more significant correlations with ni than cu although the minerals of the platinum group elements are primarily associated with chalcopyrite the pt pd ratio decreases upward in the sequence the mineralization is considered to have been caused by the breakup of dolomite xenoliths that added co 2 h sub 2 o and s to the magma thus simultaneously lowering the solubility of sulfur in the magma and adding sulfur from an external source which resulted in the precipitation of an immiscible sulfide liquid

sm nd and u pb zircon isotopic constraints on the provenance of sediments from the amadeus basin central australia evidence for ree fractionation abstract the amadeus basin of central australia is a late proterozoic to late palaeozoic ensialic depositional basin located between two proterozoic basement blocks of different nd crustal formation ages the older arunta block t dm nd 2 0 to 2 2 ga u pb zircon ages 1 5 1 9 ga to the north and the younger musgrave block t dm nd 1 7 to 1 9 ga u pb zircon ages 1 0 1 7 ga to the south initial nd isotopic compositions of the amadeus basin sediments generally fall into the region defined by the evolutionary trajectories of these two basement blocks indicating that the sediments are dominated by essentially two source components the older arunta block 147 sm 144 nd 0 114 and nd 0 20 4 and younger musgrave block 147 sm 144 nd 0 118 and nd 0 14 7 and or their equivalents stratigraphically higher sediments plot more closely to the evolutionary trajectory of the musgrave block this result together with the average provenance ages indicates the proportion of material from the musgrave block increases as the sediments become younger the sm nd isotopic data preclude a substantial involvement of archaean sources u pb zircon ion probe analyses of the late proterozoic heavitree quartzite and the late cambrian goyder formation are consistent with the sm nd isotopic constraints most of the zircons from the basal heavitree quartzite give concordant u pb zircon ages of 1500 to 1900 ma consistent with derivation from an arunta type source whilst zircons from the younger goyder sandstone give six discrete u pb zircon age groups of 511 20 615 15 960 109 1190 54 1633 24 and 1878 48 ma indicative of a dominantly musgrave type source with a minor contribution from the arunta block or reworked preexisting amadeus basin sediments the two youngest u pb zircon ages probably indicate some contribution from late proterozoic cambrian volcanics in central australia or a previously unrecognised younger local source in the basement blocks the 511 20 ma constrains the maximum depositional age of the sediment the amadeus basin sediments have a surprisingly wide range of 147sm 144nd ratios 0 077 0 136 irrespective of grain size and rock types in addition the calculated t dm nd values for samples from the same stratigraphic unit are well correlated with 147sm 144nd ratios with samples of different stratigraphic units forming sub parallel arrays these phenomena are interpreted in terms of ree fractionation and preferential sorting of preexisting ree rich phases during sedimentary recycling and deposition this process can lead to either an increase or a decrease in 147sm 144nd ratio of a sediment relative to its source and therefore an erroneous estimate of its t dm nd provenance age a theoretical model is developed which accounts for the observed correlation between t dm nd and 147sm 144nd ratios for suites of stratigraphically related sediments and allows a reliable estimate to be made of the provenance age of individual stratigraphic units assuming the average 147sm 144nd ratio of the source is known or can be estimated the provenance age for each stratigraphic unit of the amadeus basin has been calculated using this method the sm nd isotopic systematics in the amadeus basin sediments suggest that 1 1 ree fractionation during sedimentary recycling can in some cases be an important factor and needs to be considered 2 2 the provenance of the amadeus basin sediments was controlled by local source regions and cannot be used to infer large scale continental averages hence some caution must be evoked in using sm nd isotopic constraints from restricted sampling for more generalised models of crustal evolution

geochronological constraints on orogenic events in the arunta inlier a review early workers subdivided the arunta inlier central australia into three major tectonic provinces classified the principal tectonostratigraphic units into three divisions and separated the tectonomagmatic history into five discrete events ranging in age from 1800 ma to 300 ma a review of the evidence for tectonic boundaries within the arunta inlier suggests that no major structural discontinuity exists between the northern and central tectonic provinces but that the redbank thrust zone is at least in part a province boundary the tectonostratigraphic division concept also requires revision as division 3 rocks of the northern and southern arunta cannot be time equivalents division 1 rocks grade into division 2 in the northern region and division 3 of the northern region may be equivalent to division 1 in the central region rocks originally assigned to divisions are better grouped into a larger number of lithological assemblages until better stratigraphic and isotopic correlations can be made compilation of rb sr and 40ar39ar age determinations obtained before 1984 indicate an almost complete age spectrum from 1800 ma to 1000 ma but age clusters exist at 1400 ma 1100 ma and 400 300 ma which have geological significance subdivision of older ages into discrete tectonic events was not justified from this data alone but more recent u pb isotopic analysis of zircons in rocks designated to particular structural metamorphic events has revealed a complex tectonic history in the 1880 1600 ma interval the northern and central provinces underwent major tectonism between 1780 1730 ma but much of the southern province was not deformed until 1600 ma the revised tectonic history nomenclature is proposed for the arunta inlier following deposition of a widespread turbiditic unit at or before 1880 ma possibly on thinned archaean crust the northern and central provinces underwent localized tectonism magmatism at 1880 ma yuendumu tectonic event and 1820 ma stafford tectonic event prior to the widespread strangways orogeny which is subdivided into an early phase at 1780 1770 ma and late phase at 1745 1730 ma it is not clear whether the strangways orogeny is a single arunta wide event or a series of separate short lived smaller scale events although the major deformation in all areas appears to have involved w to sw directed thrusting in the southern province the major events occurred at 1680 ma argilke tectonic event and 1600 ma chewings orogeny the latter involving n directed thrusting that was penecontemporaneous with post tectonic pegmatite intrusion in the northern province suggesting linkage of both regions at this stage the younger history of the inlier is characterised by several stages of uplift and isolated thermal magmatic events major mesoproterozoic crustal exhumation anmatjira uplift phase has been interpreted from widespread 1500 1400 ma ages including regional scale closure of 40ar 39ar systems in hornblende from mafic granulite outcrop scale rb sr total rock isotopic systems in mylonitized granitoids and sm nd garnet hornblende pairs in mylonitized amphibolites a 1150 ma thermal event in the southern part of the inlier teapot magmatic event is recorded by intrusion of granite pegmatites and the alkaline mordor igneous complex and by isotopic resetting of rb sr mineral systems dolerite dyke injection at 1050 ma reflects limited extensional tectonism that may have related to formation of the amadeus basin the second major uplift event was the alice springs orogeny at 400 300 ma an unusual intracratonic thick and thin skinned thrust event that involved limited retrograde amphibolite facies but extensive greenschist facies metamorphism and restricted pegmatite intrusion

geology geodynamics and orogenic gold prospectivity modelling of the paleoproterozoic kumasi basin ghana west africa abstract this paper describes the geology and tectonics of the paleoproterozoic kumasi basin ghana west africa as applied to predictive mapping of prospectivity for orogenic gold mineral systems within the basin the main objective of the study was to identify the most prospective ground for orogenic gold deposits within the paleoproterozoic kumasi basin a knowledge driven two stage fuzzy inference system fis was used for prospectivity modelling the spatial proxies that served as input to the fis were derived based on a conceptual model of gold mineral systems in the kumasi basin as a first step key components of the mineral system were predictively modelled using a mamdani type fis the second step involved combining the individual fis outputs using a conjunction product operator to produce a continuous scale prospectivity map using a cumulative area fuzzy favourability caff curve approach this map was reclassified into a ternary prospectivity map divided into high prospectivity moderate prospectivity and low prospectivity areas respectively the spatial distribution of the known gold deposits within the study area relative to that of the prospective and non prospective areas served as a means for evaluating the capture efficiency of our model approximately 99 of the known gold deposits and occurrences fall within high and moderate prospectivity areas that occupy 31 of the total study area the high and moderate prospectivity areas illustrated by the prospectivity map are elongate features that are spatially coincident with areas of structural complexity along and reactivation during d4 of ne sw striking d2 thrust faults and subsidiary structures implying a strong structural control on gold mineralization in the kumasi basin in conclusion our fis approach to mapping gold prospectivity which was based entirely on the conceptual reasoning of expert geologists and ignored the spatial distribution of known gold deposits for prospectivity estimation effectively captured the main mineralized trends as such this study also demonstrates the effectiveness of fis in capturing the linguistic reasoning of expert knowledge by exploration geologists in spite of using a large number of variables the curse of dimensionality was precluded because no training data are required for parameter estimation

ordovician high grade metamorphism of a newly recognised late neoproterozoic terrane in the northern harts range central australia granulite facies rocks from the northernmost harts range complex arunta inlier central australia have previously been interpreted as recording a single clockwise cycle of presumed palaeoproterozoic metamorphism 800 875 c and 9 10 kbar and subsequent decompression in a kilometre scale e w striking zone of noncoaxial high grade c 700 735 c and 5 8 6 4 kbar deformation however new shrimp u pb age determinations of zircon monazite and titanite from partially melted metabasites and metapelites indicate that granulite facies metamorphism occurred not in the proterozoic but in the ordovician c 470 ma the youngest metamorphic zircon overgrowths from two metabasites probably meta volcaniclastics yield 206pb 238u ages of 478 4 ma and 471 7 ma whereas those from two metapelites yield ages of 463 5 ma and 461 4 ma monazite from the two metapelites gave ages equal within error to those from metamorphic zircon rims in the same rock 457 5 ma and 462 5 ma respectively zircon and possibly monazite ages are interpreted as dating precipitation of these minerals from crystallizing melt within leucosomes in contrast titanite from the two metabasites yield 206pb 238u ages that are much younger 411 5 ma 417 7 ma respectively than those of coexisting zircon which might indicate that the terrane cooled slowly following final melt crystallization one metabasite has a second titanite population with an age of 384 7 ma which reflects titanite growth and or recrystallization during the 400 300 ma alice springs orogeny the c 380 ma titanite age is indistinguishable from the age of magmatic zircon from a small late and weakly deformed plug of biotite granite that intruded the granulites at 387 4 ma these data suggest that the northern harts range has been subject to at least two periods of reworking 475 460 ma 400 300 ma during the palaeozoic detrital zircon from the metapelites and metabasites and inherited zircon from the granite yield similar ranges of proterozoic ages with distinct age clusters at c 1300 1000 and c 650 ma these data imply that the deposition ages of the protoliths to the harts range complex are late neoproterozoic or early palaeozoic not palaeoproterozoic as previously assumed