distribution and dispersal of surface sediments on the continental margins of india abstract the vast area varying climate regimes diverse source terrain lithology of the mainland india generate complex weathering and erosional patterns and leads to diverse sediment distribution and dispersal on the surrounding continental margins of india thus to delineate the sources distribution and sediment dispersal pathways around india 254 sediment cores from the eastern and western continental margins of india were investigated for physical properties using non destructive whole core logging technique combined with grain size analyses the distribution of magnetic susceptibility gamma ray density and grain size traces the sources in the indian landmass which contribute sediments to the margins and demarcates their extent of influence the results from the magnetic susceptibility distribution indicate that the dominant influx of modern high susceptibility sediment into the margins of india originates from the weathering of deccan basalts and its subsequent transportation by narmada and tapti rivers in the west coast and krishna and godavari rivers in the east coast though the himalayan sources are the second largest supplier of magnetic minerals to the shelf their contribution when compared to the deccan sediments is not significant the lack of present day sedimentation in the outer shelf regions of margins of india is evident from the gamma ray density distribution and is confirmed by the discrete sample grain size analysis gamma ray density variations in the margins follow the same pattern as the grain size variations and demarcate the boundary between inner shelf modern clayey sediments and the outer shelf relict carbonate sands regional distribution maps of physical properties and grain size for both the margins of india are presented and geographical limits of each provenance are defined thus providing a comprehensive picture of sediment distribution and dispersal patterns in the area and highlights the use of magnetic susceptibility as a powerful tool in deciphering the source to sink pathways of sediments

modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

the stable isotope signature of kilometre scale fracturedominated metamorphic fluid pathways mary kathleen australia abstract large calcite veins and pods in the proterozoic corella formation of the mount isa inlier provide evidence for kilometre scale fluid transport during amphibolite facies metamorphism these 10 to 100 m scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 10 km mary kathleen fold belt despite the isotopic heterogeneity of the surrounding wallrocks the fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks the pods have 13ccalcite values of 2 to 7 and 18ocalcite values of 10 5 to 12 5 away from the pods metadolerite wallrocks have 18owhole rock values of 3 5 to 7 and unaltered banded calc silicate and marble wallrocks have 13ccalcite of 1 6 to 0 6 and 18ocalcite of 18 to 21 in the alteration zones adjacent to the pods the 18o values of both metadolerite and calc silicate rocks approach those of the pods large calcite pods hosted entirely in calc silicates show little difference in isotopic composition from pods hosted entirely in metadolerite thus 100 to 500 m scale isotopic exchange with the surrounding metadolerites and calc silicates does not explain the observation that the 18o values of the pods are intermediate between these two rock types pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc silicates these data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the corella formation at the presently exposed crustal level although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc silicates or thermal fluctuations attending deformation and metamorphism the overall l shaped trend of the data on plots of 13c vs 18o is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc silicate rocks localization of the vein systems in dilatant sites around metadolerite calc silicate boundaries indicates a strong structural control on fluid flow and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km the ultimate source for the external fluid is uncertain but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism

the candelaria punta del cobre iron oxide cu au zn ag deposits chile several iron oxide rich cu au zn ag deposits define an approximately 5 km wide and at least 20 km long belt along the eastern margin of the coastal batholith near copiapo chile this belt includes the large candelaria mine and a group of middle and small sized mines in the punta del cobre district which is located about 3 km northeast of the candelaria deposit estimated geologic resources of the belt are on the order of 700 to 800 million metric tons mt at 1 0 percent cu the ore occurs in veins breccia and stringer bodies and in replacement bodies that are roughly concordant to bedding the orebodies are hosted mainly by volcanic and volcaniclastic rocks of the punta del cobre formation and in places also occur in volcaniclastic intercalations in the lower part of the overlying early cretaceous chanarcillo group most of the larger orebodies in the belt are located where northwest trending brittle faults intersect the contact between massive volcanic and volcaniclastic rocks these northwest faults and a major northeast trending ductile shear zone control portions of the ore of the candelaria deposit chalcopyrite is the only hypogene cu mineral the cu au ore is characterized by abundant magnetite and or hematite and by locally elevated concentrations of ag zn mo and light rare earth elements the ore is hosted mainly in zones with biotite potassium feldspar calcic amphibole epidote alteration at candelaria in the punta del cobre district ore in the deeper parts of the deposits is similarly associated whereas at shallow levels it occurs in zones of biotite potassium feldspar or albite chlorite calcite alteration mineralization at candelaria punta del cobre took place under relatively oxidized conditions manifested by the formation of specular hematite in parts of the district the pseudomorphic replacement of early specular hematite by magnetite during the main iron oxide formation marks a shift toward more reduced conditions or higher temperatures the bulk of the magnetite probably formed at temperatures of about 500 to 600 c the main sulfide stage followed with formation of pyrite and chalcopyrite at temperatures of 470 to 328 c subsequent martitization of the magnetite points to a temperature decrease cooling of the hydrothermal system is also indicated by the homogenization temperatures of 236 c of saline fluid inclusions in late stage calcite oxygen isotope combined with microthermometric data suggest that magmatic fluids or nonmagmatic fluids equilibrated with magmatic silicates were dominant during the main copper mineralization relatively light oxygen isotope signatures of fluids in equilibrium with late calcite suggest mixing with a nonmagmatic fluid e g basinal brines or meteoric waters during the late stages of hydrothermal activity sulfur isotope ratios of chalcopyrite pyrite pyrrhotite and sphalerite from the bronce candelaria las pintadas santos and socavon rampa deposits range from 34scdt values of 0 7 to 3 1 per mil this narrow range of sulfur isotope ratios near 0 per mil is consistent with sulfur of magmatic origin anhydrite from the candelaria mine paragenetically overlaps with chalcopyrite fluid inclusions in this anhydrite homogenize between 340 and 470 c and it has 34scdt values between 14 5 and 17 5 per mil a sulfate sulfide value of 13 4 per mil for a sample with coexisting anhydrite and chalcopyrite is consistent with sulfide sulfate fractionation at temperatures on the order of 400 c ore lead isotope signatures are homogeneous and similar to those of least altered volcanic host rocks and nearby intrusive rocks radiometric ages including new 40ar 39ar ages for hydrothermal alteration at candelaria point to a main cu au mineralization event at candelaria punta del cobre at around 115 ma the ages indicate that ore formation was broadly coeval with batholithic granitoid intrusions and with regional uplift they further imply that the cu au zn ag deposits formed at shallow crustal levels 3 km the stable isotope data the presence of previously reported hypersaline co2 rich fluid inclusions in the main cu ore stage and saline fluid inclusions in late stage calcite the oxidized character of the first ore fluid pulses and the mineralization age coeval with nearby intrusive activity are consistent with but not unequivocally evidence of magmatic fluid contribution into the hydrothermal system

the lightning creek sill complex cloncurry district northwest queensland a source of fluids for fe oxide cu au mineralization and sodic calcic alteration the lightning creek cu au prospect is hosted by a cogenetic suite of plutonic i type granitoids the dominant rock type is a porphyritic quartz monzodiorite that is intruded by more fractionated rocks including monzogranite and alkali feldspar granite a series of flat lying sills are interpreted to be late stage differentiates based on their timing mineralogy and chemistry in parts of the prospect there is pervasive sodic calcic alteration pyroxene after amphibole albite after k feldspar and oligoclase of the plutonic rocks this alteration predates sill emplacement and is unrelated to veining or fracturing of any kind the presence of small amounts of carbonate in the altered rocks suggests that the fluids were co2 bearing quartz and feldspar separates from these altered rocks have oxygen isotope compositions similar to those from fresh quartz monzodiorite suggesting that the fluids were hot and of magmatic composition sodium and ca were added and k fe cl and cu were stripped during what is interpreted as an autometasomatic event the sills display considerable textural and mineralogical complexity and evolved from equigranular quartzofeldspathic rocks aplites with magmatic chemistry to unusual fe rich rocks albite magnetite quartz that exhibit a range of bizarre spherulitic textures some of the albite and magnetite in the sills is secondary albite forms pseudomorphs after k feldspar na fe ca alteration along sill margins and within sills at the contacts between different textural zones halos of disseminated magnetite clinopyroxene fe ca na alteration are developed adjacent to early magnetite veins fluid inclusion studies indicate that these rocks crystallized at temperatures in excess of 500 c and at pressures in excess of 1 5 kbar the range of spherulitic textures is taken to indicate crystallization under hydrous conditions with the episodic release of a fluid phase this magmatic fluid phase was dominated by h2o co2 and chlorine and underwent phase separation into a co2 rich vapor and a hypersaline brine 33 55 wt nacl equiv the hypersaline fluid was enriched in fe 10 wt and cu 1 wt pixe analysis in addition to na k and ca where this fluid was retained within fe rich portions of the sills it caused ca fe na alteration pyroxene albite magnetite growth at the expense of quartz where the fluid was expelled from the sills it produced quartz magnetite clinopyroxene albite veins broadly coeval with the early magnetite veins although rich in cu these granitoid derived magmatic fluids did not generate significant cu au mineralization perhaps because of the high temperatures involved and or a lack of reduced sulfur in the fluids or host rock however the amount of iron present is estimated from the aeromagnetic anomaly to be in excess of 2 000 million tonnes mt a later generation of calcite chlorite pyrite chalcopyrite veins contain traces of cu au mineralization fluid inclusion and stable isotope work indicate that these veins probably crystallized from cooler 200 c more dilute 15 28 wt nacl equiv fluids perhaps generated by the admixture of a meteoric component the conclusions reached in this study have implications for understanding the genesis of fe oxide cu au deposits and related sodic calcic alteration the study indicates the potential for co2 rich granitoid magmas to evolve hypersaline fe and cu rich fluids capable of causing intense magnetite veining and cu au mineralization autometasomatic sodic calcic alteration of the granitoids may be an important precursor to mineralization contributing fe k cu and cl to the magmatic fluids

kiruna type deposits their origin and relationship to intermediate subvolcanic plutons in the great bear magmatic zone northwest canada magnetite apatite actinolite rocks similar to those at kiruna sweden and the st francois mountains missouri are associated with seven epizonal plutons that intrude andesitic stratovolcanoes of a broadly folded early proterozoic continental magmatic arc located in the northwestern canadian shield the plutons mainly medium grained quartz monzonite monzodiorite diorite iugs sheets and laccoliths 5 to 25 km in diameter are spatially temporally and compositionally related to host andesitic stratovolcanoes they were emplaced at 2 to 3 km depth are compositionally heterogeneous metasomatically altered and had plagioclase as the liquidus phase in addition they have kilometer wide alteration halos comprising an inner zone of nearly complete wall rock albitization an intermediate zone of magnetite apatite actinolite veins pods breccias and wall rock replacement and an outer zone of disseminated sulfides one pluton balachey has a halo that is more or less completely outside the body but another rainy lake has a halo that is partly superimposed over it separation of iron phosphate and silicate melts by liquid immiscibility is not supported by 1 the gradual replacement of plagioclase by chessboard albite toward the roof of the rainy lake pluton 2 the chemical trends in the rainy lake intrusion 3 the mineralogical zoning low temperature mineralogy and replacement textures of the magnetite apatite actinolite and 4 the relationship of the magnetite apatite actinolite veins and bodies to the plutons however all available data are compatible with a deuteric origin it is concluded that high temperature low initial water content and shallow level emplacement by intermediate plutons are necessary for the development of kiruna type deposits

the ca 1740 1710 ma leichhardt event inversion of a continental rift and revision of the tectonic evolution of the north australian craton abstract interpretation and modelling of high resolution regional geophysical data of the central leichhardt river fault trough in the mount isa inlier are used to determine the timing of a major basin inversion event following the development of the ca 1780 1740 ma leichhardt superbasin inversion of the leichhardt superbasin formed the regional north south trending leichhardt anticline during east west shortening the limbs of the anticline are overprinted by several east west trending wedge shaped non magnetic sub basins filled with ca 1710 ma calvert and isa superbasin successions these relationships suggest inversion of the leichhardt superbasin occurred between ca 1740 and 1710 ma the event is also known to have affected the northern and eastern north australian craton the scale of the inversion suggests it was a significant event that we have defined as the leichhardt event this event requires a major tectonic driver to the east of the north australian craton possibly the accretion of a micro continental ribbon to the east of the mount isa inlier the results of this study have implication for paleogeographic reconstruction of the australian continent during the formation of nuna because eastern north australian craton faced an ocean at ca 1740 1720 ma the results also challenge the significance and intensity of crustal shortening associated with the ca 1600 1500 ma isan orogeny throughout the western mount isa inlier

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

trace element composition of iron oxides from iocg and ioa deposits relationship to hydrothermal alteration and deposit subtypes trace element compositions of magnetite and hematite from 16 well studied iron oxide copper gold iocg and iron oxide apatite ioa deposits combined with partial least squares discriminant analysis pls da were used to investigate the factors controlling the iron oxide chemistry and the links between the chemical composition of iron oxides and hydrothermal processes as divided by alteration types and iocg and ioa deposit subtypes chemical compositions of iron oxides are controlled by oxygen fugacity temperature co precipitating sulfides and host rocks iron oxides from hematite iocg deposits show relatively high nb cu mo w and sn contents and can be discriminated from those from magnetite hematite and magnetite ioa deposits magnetite iocg deposits show a compositional diversity and overlap with the three other types which may be due to the incremental development of high temperature ca fe and k fe alteration iron oxides from the high temperature ca fe alteration can be discriminated from those from high and low temperature k fe alteration by higher mg and v contents iron oxides from low temperature k fe alteration can be discriminated from those from high temperature k fe alteration by higher si ca zr w nb and mo contents iron oxides from ioa deposits can be discriminated from those from iocg deposits by higher mg ti v pb and sc contents the composition of iocg and ioa iron oxides can be discriminated from those from porphyry cu ni cu and volcanogenic massive sulfide deposits

radiogenic and stable isotope constraints on the genesis of the eloise cu au deposit cloncurry district northwest queensland new radiogenic 40ar 39ar and stable oxygen hydrogen and sulfur isotope analyses of metamorphic and metasomatic minerals constrain the age metasomatic evolution and genesis of the eloise cu au deposit 3 1 mt 5 5 cu 1 4 g t au and 16 g t ag biotite from a pre to syn d2 stage vein has an 40ar 39ar age of 1555 4 ma which is interpreted to coincide with a regional metamorphic event synchronous with d2 six later stages of alteration and mineralization are recognized all of which postdate peak metamorphism and d2 stages i to iii are volumetrically the most significant and comprise early albitization stage i quartz hornblende biotite veins and alteration stage ii and cu au mineralization stage iii stages iv v and vi are localized vein events and postdate the main cu au mineralization stage ii vein and alteration hornblendes have 40ar 39ar ages of 1530 3 ma biotite from the same stage has an 40ar 39ar age of 1521 3 ma muscovite from a postore shear zone has an 40ar 39ar age of 1514 3 ma these results provide a maximum ca 1530 ma and minimum ca 1514 ma age for the mineralizing event however the intimate relationship between stage ii mafic silicate veins and alteration and the stage iii cu au event combined with fluid inclusion results which indicate that a cooling evolving high salinity fluid was responsible for both stages suggests that the older age is likely to be closer to the age of mineralization the stage ii biotite age of ca 1521 ma is interpreted to record thermal resetting during postore ductile deformation the results suggest that micas in the cloncurry district are more susceptible to later thermal resetting than amphiboles which may have significant implications for deposits which have only been dated by micas quartz from stages ii iii and iv have 18oquartz values ranging between 10 1 and 11 9 per mil stage ii biotite has a lower 18o composition 5 6 than biotite from a pre d2vein 6 9 but both have identical d compositions 84 stage ii hornblende has lower 18o 6 8 and 7 4 and d 88 and 90 values than does stage iii actinolite 8 0 and 84 respectively the 34s values for chalcopyrite pyrrhotite and pyrite fall in a narrow range between 0 0 and 2 3 per mil a distinct trend can be recognized with 34s values becoming progressively greater from south to north thus reflecting the zoned alteration system magnetite pyrite rich in the south through to pyrrhotite rich in the north the change in mineralogy and sulfur isotope values may be due to cooling and sulfidation processes which resulted in changes in oxygen and sulfur fugacities the oxygen hydrogen and sulfur isotope data combined with high temperature and high salinity fluid inclusion data indicate a predominantly magmatic origin for the ore forming fluids the deposit is interpreted to have formed from magmatic hydrothermal fluids which were tapped by deep seated crustal structures

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

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

stable isotope evidence for magmatic fluid input during large scale na ca alteration in the cloncurry fe oxide cu au district nw queensland australia sodic calcic alteration is common in mineralized hydrothermal systems yet the relative importance of igneous vs basinal fluid sources remains controversial one of the most extensive volumes of sodic calcic rocks occurs near cloncurry nw queensland and was formed by overlapping hydrothermal systems that were active synchronously with emplacement of mid crustal batholithic granitoids c 1 55 1 50 ga altered rocks contain albite oligoclase actinolite diopside titanite and magnetite alteration was localized by a composite veins and breccias containing crystallized magma intimately intergrown with hydrothermal precipitates b intrusions that host setting a veins and breccias and c extensive breccia and vein systems linked to regional fault systems isotope analyses of actinolites in settings a and b indicate calculated 18oh2o 8 2 to 10 6 and variably depleted dh2o 130 to 54 compared with typical magmatic fluids whereas those from setting c typically indicate calculated 18oh2o 8 0 to 12 8 and dh2o 29 to 99 the lowest dh2o values are interpreted as representing residual fluids after significant 90 open system magmatic degassing overall the stable isotope field geochronological and geobarometric data suggest that these sodic calcic alteration systems were formed by the episodic incursion of magmatic fluids that underwent minor isotopic modification as a result of varying degrees of interaction with country rocks

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

using elemental and boron isotopic compositions of tourmaline to trace fluid evolutions of iocg systems the worldclass dahongshan fe cu deposit in sw china abstract the worldclass dahongshan iron oxide copper gold iocg deposit is hosted within the late paleoproterozoic dahongshan group in the kangdian region sw china the orebodies are spatially associated with sub volcanic intrusions and are structurally controlled extensive metamorphic overprinting during the neoproterozoic makes it difficult to determine the initial compositions of the ore fluids tourmaline however is a useful phase for this purpose because of its refractory nature and chemical diversity it occurs widely in the four stages of mineralization and alteration of the dahongshan deposit including pre mineralization sodic alteration stage i iron oxide mineralization stage ii sulfide mineralization stage iii and late quartz calcite veining stage iv the temporal association between tourmaline and hydrothermal alteration provides an excellent opportunity to investigate the fluid evolution tourmaline from all four stages belongs to the alkali group and ranges from dravite to schorl in composition in situ b isotope analyses of tourmaline conducted by la mc icpms yielded a total range of 11 b values from 14 7 to 5 9 and the values show significant variations among the different stages tourmaline of stage i albitization has 11 b values from 14 7 to 5 7 stage ii tourmaline from fe oxide ores shows 11 b values of 11 6 to 6 1 similar to those of stage i whereas stage iii tourmaline from cu sulfide ores displays significantly heavier isotopes with 11 b values from 4 4 to 0 6 tourmaline of stage iv represented by barren quartz calcite tourmaline veins in intensely altered wall rocks has positive 11 b values from 2 9 to 5 9 the observed variations of b isotopes cannot be produced by fractionation of the ore fluids alone mixing of b from at least two distinct sources a magmatic source and external sources with highly positive 11 b values are hence proposed on the basis of geological constraints and modal calculations the calculated oxygen isotope compositions of fluids in equilibrium with hydrothermal minerals that associated with tourmaline from stage ii stage iii and stage iv are 7 4 to 10 2 8 4 to 8 6 and 3 8 to 8 0 the decreasing trend of 18 o of fluids from stage ii to stage iv is consistent with the incursion of external basinal brines by fluid mixing our dataset thus demonstrates that ore fluids of dahongshan iocg system were initially of magmatic origin stages i and ii and were later progressively modified by mixing with external brines stages iii and iv

the effect of heterogeneous stress and strain on metamorphic fluid flow mary kathleen australia and a model for large scale fluid circulation in the proterozoic mary kathleen fold belt northern australia infiltration of large volumes of externally derived fluid occurred synchronously with regional amphibolite facies metamorphism and deformation this paper develops a model of structurally controlled fluid migration by comparing the distribution of fossil fluid pathways with the inferred stress and strain patterns during the deformation intense fluid flow was localized within strong relatively brittle meta intrusive bodies and in discrete veined brecciated and altered zones around their margins in metasediments folded in a ductile manner outside these areas fluid infiltration was negligible the direct correlation between structural styles and the magnitude of veining and metasomatism suggests control of permeability enhancement and hence fluid flow by deformation finite difference modelling of a strong body in a weaker matrix has been used to evaluate the variation of stresses during the deformation from which it is clear that stress and strain heterogeneities have systematically influenced the development and maintenance of metamorphic fluid pathways particular regions in which mean stress may be significantly lower than the average lithostatic pressures include the strain shadow zones adjacent to the strong bodies other dilatant zones around the bodies and the bodies themselves this geometry is favourable not only for localized brittle deformation under amphilobite facies conditions but also for focused fluid flow in the low mean stress regions as evidenced by the abundance of veins fluid access through these metamorphic aquifers occurred during tensile failure episodes with particularly large dilations and decimetre scale veining in areas of strain incompatibility it appears likely that fluid circulated many times through the fold belt with flow concentrated in the metamorphic aquifers a model is developed that explains both the structurally focused fluid flow and the postulated multi pass recirculation by dilatancy pumping the pump engines comprising the low mean stress zones

delineating the structural controls on the genesis of iron oxide cu au deposits through implicit modelling a case study from the e1 group cloncurry district australia iron oxide cu au iocg deposits encompass a range of ore body shapes including strata bound replacement ores and hydrothermal breccias we use the implicit method to make a detailed three dimensional geological model of a strata bound iocg in the cloncurry district the e1 group to elucidate structural controls on mineralization this model is compared with the nearby world class ernest henry breccia hosted iocg deposit cu au mineralization in the e1 group occurs as structurally controlled mainly strata bound replacement bodies hosted in metasedimentary and metavolcaniclastic rocks intercalated with barren meta andesite replacement bodies in the e1 group conform to a series of nnw plunging folds formed in regional d2 during peak metamorphism folding was followed by local d3 regional d4 shortening which formed a dextral transpressional riedel brittle to ductile system along the regional cloncurry fault zone modelling suggests that much of the cu au mineralization is controlled by synthetic r structures associated with this riedel system the deformation sequence at ernest henry is comparable but differences in host rock rheology permeability and fluid pressure may explain the variation in ore body types and total cu au resource between the two deposits the results carry implications for other districts containing these styles of iocg mineralization

reduced and oxidized au cu bi iron oxide deposits of the tennant creek inlier australia an integrated geologic and chemical model iron oxide associated au cu bi deposits of the tennant creek gold field range from magnetite pyrrhotite pyrite reduced cu rich deposits through sulfide poor magnetite rich high grade au bi intermediate f o2 deposits to hematite rich high grade au oxidized deposits discordant magnetite hematite chlorite quartz ironstone bodies that host the ore formed hydrothermally during the 1840 to 1860 ma barramundi orogeny at temperatures up to 350 to 400 c and 2 5 to 5 kbars deposition of ironstone minerals was localized by dilatency that was generated during d1 reverse shearing and folding a separate au cu bi hydrothermal stage overprinted selected ironstones during d2 at or before 1825 to 1830 ma where favorable d1 structures and fluid pathways were reactivated the extremes of the reduced to oxidized deposit spectrum represent divergent chemical conditions that cannot be reconciled by the action of a single fluid we have identified both reducing and oxidizing fluids that helped to form the au cu bi deposits at the west peko deposit which represents the reduced end member subtype constraints from oxide silicate sulfide mineral stabilities fluid inclusions and chlorite thermochemistry indicate that au cu bi ore was introduced into ironstone at 300 to 340 c by a reducing pyrrhotite stable weakly acidic sulfur rich and n2 ch4 rich aqueous fluid containing 3 to 10 wt percent nacl equiv an ore fluid source outside the relatively oxidized metasedimentary host sequence warramunga formation is implied we suggest similar ore fluids for other reduced cu and sulfide rich deposits in the district chemical mass transfer modeling of reactions between reducing fluid and ironstone incorporating estimated thermodynamic properties for aqueous bismuth complexes indicates that highly efficient gold and native bi deposition was predominantly in response to desulfidation and oxidation of the fluid chalcopyrite precipitated mainly in response to increased ph gold bismuth ore in the eldorado deposit an oxidized and hematitic end member is interpreted to have involved mixing of an oxidizing hematite stable ca na cl brine with an intermediate f o2 low to moderate salinity ore fluid as well as reaction of both fluids with ironstone furthermore the mass transfer modeling suggests that mixing of reducing and oxidizing fluids in the absence of ironstones could have resulted in high grade au deposits lacking fe oxides a subtype that has received comparatively little exploration attention in the tennant creek district

the geology of the rakkurijarvi cu au prospect norrbotten a new iron oxide copper gold deposit in northern sweden the rakkurijarvi prospect consists of a group of mineralized magnetite and lithic breccias within the ca 2 05 to 1 90 ga proterozoic supracrustal sequence of the kiruna district northern sweden potentially economic grades of cu and au largely in the form of chalcopyrite and other sulfide assemblages are hosted in brecciated magnetite and metavolcanic rocks the extent of the mineralization is currently open both downdip and along strike the deposit was discovered through an integrated geophysical and geochemical program focused on iron oxide copper gold iocg style mineralization it is hosted by brecciated greenschist facies metavolcanic rocks within and adjacent to an east northeast trending shear zone the dominant characteristics of the deposit are consistent with the iocg class and include magnetite and lithic breccias hosted in a metavolcanic sequence with matrices of albite actinolite and calcite surrounded by halos of sodic albitescapolite and potassic scapolite k feldspar biotite alteration a distinctive accessory mineral assemblage includes apatite titanite and allanite the paragenesis and textural evolution of the deposit includes early narich alteration accompanying massive magnetite alteration the na rich alteration is overprinted by potassic alteration also associated with magnetite although the paragenesis is complex and multiple generations of both sodic and potassic alteration are recognized alteration of lithic clasts to magnetite confirms a metasomatic origin as opposed to an orthomagmatic origin for the magnetite mineralization re os analyses of two separates of molybdenite intergrown with magnetite interpreted as cogenetic with the sulfide assemblage yield mineralization ages of 1853 6 and 1862 6 ma reconnaissance bulk rock chemistry of the host volcanic rocks is consistent with an intermediate volcanic protolith but much of the original character of the rocks is masked by albitization and incipient iron sodic and potassic alteration the data also indicate significant element mobility during metasomatism and in particular the addition of ti to the rock mass in biotite and as titanite the compositions of secondary minerals are consistent with alteration and mineralization caused by highly saline fluids of relatively low f activity the stable isotope characteristics of calcite with 18osmow ranging from 9 43 to 19 89 per mil and 13cpdb ranging from 11 69 to 4 88 per mil suggest that the fluids of the calcite and sulfide stage were derived from a magmatic source but had interacted extensively with local sedimentary and volcanic rocks

relationship between altered pyroxene diorite and the magnetite mineralization in the chilean iron belt with emphasis on the el algarrobo iron deposits atacama region chile north of el algarrobo one of the four main deposits of the chilean iron belt the iron mineralization magnetite etrmolite actinolite apatite is related to clinoand orthopyroxene diorite intrusions which have crystallized at shallow depth 4km under increasing oxygen fugacities the supercritical fluid phase exsolved during cooling after the consolidation of the plutons 800 900 c results in a h cl and sodic enrichment and in the sequential leaching of fe at less than 700 c then ca and mg between 600 and 500 c from minerals of the primary magmatic diorite assemblage titanomagnetite ilmenite plagioclase an70 40 augite hypersthene as a consequence of the cationic leaching the lower mobility of silica and aluminium and the enrichment in sodium residual altered dioritic rocks present a retromorphic mineral assemblage evolving down to boundary conditions of the greenchist amphibolite facies 450 c fe mg and ca are carried in cationic form associated with cl anions toward cooler rocks where they are precipitated the deposition between 550 and 450 c of magnetite followed iron mineralization paragenesis and occurred in fractured zones located both in altered diorites and contact andesites

geochronology of early to middle proterozoic fold belts in northern australia a review abstract this geochronological review integrates geologically relevant isotopic data from the several early to middle proterozoic fold belts of northern australia a number of firm chronological benchmarks largely established by means of u pb zircon studies now provide a time framework within which to better quantify the tectonostratigraphic history of many of these terranes the apparent worldwide dearth of crustal events in the earliest proterozoic between 2500 and 2000 ma was broken in northern australia with the advent of a major crust forming episode between 1880 and 1850 ma ago these rocks may have evolved from an initial mantle or lower crustal melting and fractionation process about 400 300 ma earlier that is evidenced from sm nd model ages the extent involvement and or degree of assimilation of any pre existing archaean crust is small but whether or not it is negligible or zero is not satisfactorily known the 1880 1850 ma event the barramundi orogeny is well represented in northern australia both lithologically and analytically and the rocks that pre and post date it have a similar tectonic setting over very wide areas of the continent two consistent and widespread elements of this tectonism are regional metamorphism and deformation of the first cycle of supracrustals barramundi orogeny and crystallization of i type k rich felsic magmas closely following and in some cases overlapping with deformational processes in the halls creek inlier the ages of this rapid deep crustal to supracrustal tectonic transition cannot be distinguished within the range 1860 1850 ma this major yet short lived tectonism is mirrored in other fold belts such as pine creek tennant creek and mount isa in which u pb zircon ages give slightly older constraints of 1885 1870 ma 1920 1870 ma and 1885 10 ma respectively the ensuing felsic magmatism in these latter terranes continued for a few tens of millions of years with the crystallization and emplacement of comagmatic volcanic plutonic pairs throughout in the interval 1870 1860 ma in the georgetown and arunta inliers direct evidence of this otherwise ubiquitous event if present is masked by younger high grade metamorphism in the latter however metamorphic crustal components having approximate protolith ages of this order can be inferred from their evolved isotopic signatures the geochronological and geochemical coherency of the extensive early proterozoic 1870 ma magmatism contrasts with that of post 1800 ma magmatism which is less extensive generally anorogenic commonly bimodal in character and varies in age from one terrane to another several major sedimentary basins were being filled at this time major igneous events at 1790 1740 ma 1670 ma and 1500 ma are recognized elongate sublinear volcanic and plutonic belts 1790 1740 ma old are present at mount isa in high grade granitic gneisses of the arunta inlier a few u pb zircon ages and extrapolated rb sr protolith ages are coincident at about 1760 1750 ma indicating that this event may be important in the development of the division 2 sequences of that fold belt the platformal hart dolerite and oenpelli dolerite two of the largest mafic intrusions in the world were emplaced at 1762 25 ma and 1688 13 ma younger felsic plutonism and volcanism gave rise to rapakivi type granites in the mount isa tennant creek and the granites tanami inliers at 1670 ma a time close to that of the aileron deformational metamorphic event in central australia further at 1650 ma there is growing evidence of an unexpectedly coherent hydrothermal episode that reset or disturbed many rb sr ages gave rise to pegmatites and was possibly associated with mineralization in the davenport and eastern arunta inliers discrete middle proterozoic deformational events between 1610 and 1470 ma punctuate the tectonostratigraphic history in the arunta mount isa and georgetown fold belts where they are best documented

u pb and 40ar 39ar geochronology and isotopic constraints on the genesis of copper gold bearing iron oxide deposits in the hasancelebi district eastern turkey the hasancelebi deposit in eastern turkey with proven reserves of 95 million metric tons is a copper gold bearing iron oxide deposit it is chiefly hosted by rocks that underwent widespread sodic calcic and potassic styles of alteration in the hasancelebi district pervasive na ca and k fe alteration types are overprinted by sericitization and by late alteration that occur in multiple overprinting systems the age of hydrothermal alteration and mineralization ca between 74 68 ma overlaps with the age of alkaline magmatism in the hasancelebi district crystallization and cooling of alkaline magmatism is associated with hydrothermal features that spanned the duration of the district s igneous history the 40ar 39ar and u pb geochronology of magmatism indicate that the hydrothermal system was synchronous with diabase and syenite and or microsyenite porphyry intrusions and consisted of several discrete phases of na ca and k fe alteration the oldest alteration phase 1 formed at ca 74 4 to 74 3 ma it is spatially and temporally associated with the emplacement of diabase dikes and contains scapolite and phlogopite the next younger alteration phase 2 formed at about 71 3 ma and is spatially and temporally associated with syenite porphyry and microsyenite porphyry intrusions it consists of scapolite garnet pyroxene and actinolite that are superimposed on the first alteration phase the next alteration assemblage phase 3 formed at about 68 6 ma and consists of phlogopite 2 and magnetite mineralization still later alteration phase 4 overprints phases 1 2 and 3 and consists of sericite quartz chalcopyrite hematite calcite fluorite and barite oxygen 18o and hydrogen d isotope analyses were carried out on phlogopite sericite barite calcite fluorite and quartz representing the mineral assemblage formed during phases 1 and 4 of the hydrothermal alteration the calculated 18o h2o and d h2o composition of the fluids that formed preore k fe alteration and postore alteration of phase 4 range between 15 1 to 8 5 and 124 to 85 6 per mil respectively and partially overlap the range for traditional magmatic waters oxygen and h isotope compositions from alteration minerals highlight two major points na ca and k fe alteration assemblages are likely derived from high temperature primary magmatic fluids and late sericitization is likely derived from fluids exsolved from cooling alkaline plutons during hydrothermal fracturing and consequent degassing at moderate temperatures the initial ndi values of the alteration zones range from 2 02 to 2 08 close to the calculated nd value of associated syenite porphyry at the time of alteration nd 68 64ma 1 9 nd sr isotope compositions combined with 40ar 39ar and u pb geochronology of the associated alteration suggest that the fluids were sourced from coeval diabase dikes and syenite porphyry and or microsyenite porphyry intrusions the rare earth element characteristics 40ar 39ar and u pb geochronology of alteration and fresh magmatic rocks 18o d nd and sr isotope systematics together suggest that the fluids responsible for the high to moderate temperature assemblages are largely derived from the coeval alkaline igneous rocks diabase and microsyenite porphyry dikes that intrudes the sedimentary volcanosedimentary basin

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

low latitude meteoric fluid flow along the cloncurry fault cloncurry district nw queensland australia geodynamic and metallogenic implications hydrothermal alteration within the mount isa block mib is typically largely to have ceased at the end of the isan orogeny ca 1 50 ga however late large brittle quartz rich vein systems including those of the cloncurry fault cut mesoproterozoic tectonic fabrics intrusions and products of regional na ca hydrothermal alteration associated features display affinities to iron oxide cu au ore deposits including specular hematite bearing veins and cu au u lree ba mineralization stable isotope data suggest late veins in the vicinity of the cloncurry fault eastern fold belt efb formed from fluids with 18oh2o and dh2o 250 c of 4 to 3 and 22 to 4 respectively the high dh2o moderate 18oh2o and cacl2 nacl rich character of the saline fluids indicates they were mixtures of low latitude meteoric fluids and evaporite derived basinal brines which with time became progressively dominated by meteoric water deposited barite and cooled the low latitude meteoric signature demonstrates that the fault fracture systems were active when in equatorial regions paleomagnetic data for the mib and the australian protocontinent together with structural and thermal considerations and geochronological arguments suggest the veins probably formed sometime after 1 10 ga and potentially as late as during the alice springs orogeny ca 0 34 ga the late quartz veining was unrelated to two phases of regional na ca alteration and economically significant fe oxide cu au mineralization at 1 60 1 58 and 1 53 1 50 ga

the aitik cu au ag deposit in northern sweden a product of high salinity fluids the aitik cu au ag deposit is located in northern sweden and is hosted by strongly deformed 1 9 ga svecofennian volcano sedimentary rocks the main copper mineralization which occurs as disseminations and veinlets is hosted by garnet biotite schist subeconomic mineralization in the footwall to the ore is hosted by feldspar biotite amphibole gneiss and porphyritic quartz monzodiorite the deposit has been affected by post mineralization metamorphic and igneous activity fluid inclusions in six samples of copper mineralized quartz veins record the presence of three different fluid populations the main ore was deposited from an aqueous highly saline 31 37 eq wt nacl cacl2 fluid this fluid was trapped in inclusions intimately associated with the main chalcopyrite mineralization later bornite deposition took place from a less saline 18 27 eq wt nacl cacl2 aqueous fluid a third fluid composed of almost pure co2 interacted with the copper rich system during a post ore event the aitik cu au ag deposit shares some features with both porphyry type and fe oxide cu au deposits a high calcium content of the ore fluids similar to other cu au deposits in northern scandinavia suggests a contribution to the salinity of the mainly magmatic hydrothermal fluids from evaporitic rocks in stratigraphically lower units

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

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

constraints of sr isotopic compositions of apatite and carbonates on the origin of fe and cu mineralizing fluids in the lala fe cu mo lree deposit sw china abstract numerous fe cu deposits with mineralization styles similar to iron oxide copper gold iocg deposits form the kangdian fe cu metallogenic province southwestern sw china as one of the largest deposits in the region the 1 0 ga lala fe cu deposit is hosted in a paleoproterozoic volcanic sedimentary succession named the hekou group which is alternately intruded by 1 0 ga doleritic plutons this deposit has a paragenetic sequence evolving from stage i of na alteration to stage ii of fe mineralization and finally to stage iii of cu mo ree mineralization coeval with mafic felsic intra plate magmatism in the region this study conducted in situ sr isotopic analyses on apatite and carbonate aiming to resolve the long controversial issue regarding the origin of the fe and cu mineralizing fluids in the deposit apatite of stage ii has 87sr 86sr ratios varying from 0 71380 to 0 72733 much higher than those of synchronous igneous rocks in the region 0 7074 to 0 7091 but similar to the paleoproterozoic host rocks 0 71368 to 0 71837 at 1 0 ga this similarity indicates that radiogenic sr of the fe mineralizing fluid was dominantly sourced from the host rocks apatite and calcites of stage iii have 87sr 86sr ratios 0 75758 0 79293 much higher than apatite of stage ii and the host rocks but similar to the archean basement rocks as high as 0 80 at 1 0 ga beneath the cover of the yangtze block suggesting that the highly radiogenic sr isotopic composition of the cu mineralizing fluid was mainly inherited from the old basement rocks in combination with previous c o s isotopic data indicating a magma hydrothermal origin it was suggested that the fe mineralizing fluid was exsolved from a mafic magma that generated the 1 0 ga doleritic plutons and inherited radiogenic sr from the host rocks during fluid rock interaction by contrast the cu mineralizing fluid might have been sourced from another pulse of magmatic cu mo ree and co2 rich fluid which have once interacted with archean basement rocks prior to mineralization the source of such a cu mo ree rich fluid was not well constrained in current study but was inferred to be exsolved from a hidden felsic magma we propose that intrusions of the bimodal magmas in kangdian are responsible for regional hydrothermal circulation which led to fe cu mo ree mineralization in the kangdian province

chemical and stable isotopic characteristics of syn tectonic tourmaline from the western fold belt mount isa inlier queensland australia abstract understanding hydrothermal fluid flow events related to orogenic events is important because they provide large scale redistribution of metals which may become concentrated in ore deposits in this study we determine the origin of tourmaline bearing quartz veins and pegmatites in the western fold belt of the proterozoic mount isa inlier a region which host numerous syn orogenic cu deposits this paper uses tourmaline mineral chemistry and isotopic analyses in situ b and bulk o and h isotopes to fingerprint the fluid reservoirs that contributed to the fluid budget during the isan orogeny all the tourmaline samples have schorl dravite solid solution compositions quartz tourmaline 18 o 11 0 12 6 and 7 7 9 4 v smow respectively pairs yield equilibrium formation temperatures of 305 to 575 c with the higher temperatures related to pegmatitic tourmaline tourmaline d values have a relatively narrow range from 68 to 56 v smow in most cases calculated 18 o fluid and d fluid values are compatible with primary magmatic water with a small component of metamorphic 18 o enriched formation waters however there are large variations in tourmaline 11 b values which range from 10 7 to 17 0 with the majority of values between 10 and 15 variations in 11 b tur in the pegmatites suggest that boron degassing generated relative 11 b depletion during crystallization similar 11 b tur values in quartz tourmaline veins spatially associated with the pegmatites in cordierite and sillimanite bearing metamorphic rocks west of the mount isa fault demonstrate a similar origin for b in this tourmaline in contrast quartz tourmaline veins of similar timing hosted by greenschist grade metamorphic rocks east of the mount isa fault have much higher 11 b tur values 6 2 to 10 7 which reflect the involvement of a distinct b isotopic reservoir mostly likely a near surface derived evaporitic brine thus the b isotopic data reveal important differences in fluid origin that are not reflected in the 18 o values therefore at least two isotopically distinct fluids one sourced from fractionating anatectic pegmatites and the other from external basinal brines circulated contemporaneously in separate areas during the isan orogeny there is no evidence based on the tourmaline isotopic data to suggest that these fluids mixed which demonstrates that the hydrothermal plumbing system in the western fold belt during the isan orogeny was disconnected probably due to differences in thermal structure metamorphic grade across the western fold belt during orogenesis

the evolution of a porphyry cu au deposit based on la icp ms analysis of fluid inclusions bajo de la alumbrera argentina the chemical and physical evolution of magmatic to hydrothermal processes in the porphyry cu au deposit of bajo de la alumbrera northwestern argentina has been reconstructed with a quantitative fluid inclusion study fluid inclusion petrography microthermometry and single inclusion microanalysis by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms are combined to determine the evolution of pressure temperature and ore metal concentrations including cu and au in the fluids complementary hydrogen and oxygen isotope analyses are used to further constrain the water sources in the evolving system the combined data provide a new level of insight into the mechanisms of metal sourcing and ore mineral precipitation in a porphyry style magmatic hydrothermal system based on previously reported observations of the igneous geology alteration geochemistry and veining history of the subvolcanic porphyries at alumbrera the distribution of fluid inclusion types in space and time is documented six major inclusion types are distinguished the highest temperature brine inclusions up to 750 c p 1 kbar are mainly recorded in barren quartz magnetite veins in the core of the alteration system these polyphase brine inclusions halite sylvite multiple opaque and transparent daughter crystals are interpreted as the most primitive magmatic fluid recorded at the level of the deposit they are of moderately high salinity 50 60 wt nacl equiv dominated by nacl kcl and fecl 2 and contain on average 0 33 wt percent cu and 0 55 ppm au upon cooling and decompression these saline liquids exsolve a vapor phase which is preferentially enriched in cu relative to its main salt components but probably plays a minor role in the formation of this particular deposit because of the inferred small mass fraction of vapor cooling and decompression from the highest initial p t conditions down to about 450 c causes magnetite k silicate alteration but no saturation in au or cu sulfides as recorded by continually high ore metal concentrations in the fluid inclusions coprecipitation of cu and au as chalcopyrite and native gold some early bornite occurs over a narrow range of decreasing fluid temperature with cooling from 400 to 305 c the cu concentration in the brine drops by about one order of magnitude to less than 0 07 wt percent without a proportional decrease in major salt components ore mineral precipitation extracts 85 percent of the cu and au from the fluid it is associated with potassic alteration as shown by a concomitant decrease in the k na ratio of the cooling magmatic brine and by an increase in its ba and sr concentrations elements which are probably liberated in the destruction of calcic igneous minerals the fluid chemical data demonstrate that the metal ratios in this and probably many other porphyry style ore deposits are primarily controlled by the magmatic source of the ore brines on the other hand the final hypogene ore grade of the deposit is controlled by the efficiency of ore mineral precipitation at alumbrera metal extraction is governed by the efficiency of cooling a high flux of magmatic fluid within a small rock volume dilution of residual magmatic fluids as recorded by aqueous fluid inclusions of decreasing salinities and temperatures below 295 c follows after the main stage of copper introduction and is associated with feldspar destructive phyllic alteration geometric relationships fluid analyses and stable isotope data together indicate that phyllic alteration results from postmineralization hydrothermal activity involving minor mixing between meteoric water residual brine and a waning input of magmatic vapor

hematite breccia hosted iron oxide copper gold deposits require magmatic fluid components exposed to atmospheric oxidation evidence from prominent hill gawler craton south australia

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

petrology geochronology and isotope geochemistry of the post 1820 ma granites of the mount isa inlier mechanisms for the generation of proterozoic anorogenic granites four distinct episodes of granitic intrusion occurred in the mount isa inlier at 1820 1800 ma 1760 1740 ma 1700 1670 ma and 1560 1480 ma combined these granites cover at least 4700 km2 and they contrast in composition and intrusive style with an earlier major felsic magmatic event which occurred between 1870 and 1840 ma post 1820 ma granite batholiths are of two types large major coarse grained anorogenic i type intrusives and small minor microgranites which are probably s type the i type granites are all pink to red colour and most contain fluorite rapakivi textures are common they have a high ratio of fe mg and are more enriched in tio2 zr nb y and u than the 1870 1840 ma felsic igneous rocks the post 1820 ma i types are interpreted to have formed by small degrees of partial melting of a mafic underplate the smaller microgranites are relatively k2o enriched and are sometimes muscovite bearing they are interpreted to be derived from proterozoic feldspathic metasediments the first three episodes of granite magmatism are coeval with major extensional sedimentary sequences but they are generally spatially displaced from the maximum area of surface rift development this separation is predicted by the asymmetric detachment model of continental extension the tectonic relationship of the youngest granite episode is not clearly defined the 143nd 144nd initial ratios of the post 1820 ma granites fall into two groups one having positive relatively primitive nd values of 1 8 to 3 5 the other having negative nd values ranging from 2 9 to 3 7 samples with positive nd values are interpreted as partial melts of mafic sources formed post 1870 ma whilst the group with negative nd values are derived from significantly older sources formed probably around 2300 2000 ma the sources of these granites are produced by significant underplating events that may occur during either extension or compression

hydrothermal alteration associated with magnetite mineralization in the bafq iron deposits iran abstract bafq mining district bmd is an iron mineralization province that contains more than 2 gt of iron ore located in the early cambrian volcano plutonic arc known as the kashmar kerman zone the host rocks of the fe mineralization are granitic and microgranitic rocks and their extrusive equivalents field observations and petrographic studies showed that both sodic and calcic alteration are related to iron mineralization other alteration styles including silicic chlorite epidote and sericite alteration are less important and post dated the mineralization sodic alteration is associated with the formation of chessboard albite whereas the calcic alteration is featured by a mineral assemblage of actinolite tremolite magnetite apatite available evidence suggests that the involved metasomatic fluids could be mainly of evaporitic sources with a minor contribution from magmatic fluids we suggest that mineralization formed at the end of the precambrian in pull apart basins in a magmatic back arc region associated with subduction of the proto tethys oceanic crust under central iranian plate iron ore mineralization may be related to the interaction of granite derived hydrothermal fluids and brine derived fluids sourced from the latest precambrian rizu and dezu evaporitic sequences

maramungee a proterozoic zn skarn in the cloncurry district mount isa inlier queensland australia the significant but subeconomic 1 8 mt4 4 zn maramungee deposit is 90 km south southeast of cloncurry in northwest queensland it lies in the eastern fold belt of the proterozoic mount isa inlier within rocks of the maronan supergroup that also hosts the large pb zn ag deposits at cannington and pegmont the maramungee deposit is a product of a series of processes that occurred during the metamorphic evolution of the eastern fold belt and the brittle structures that host sulfide mineralization are likely to have been active after the emplacement of the late to post tectonic granites of the williams batholith maramungee is hosted by upper amphibolite sillimanite k feldspar zone gneisses exceptionally iron rich metabasites and foliated granite mineralization was restricted to an elongate embayment in the margin of the maramungee granite pluton created by the antiformal part of a steeply inclined parasitic f 2 fold a major photolinear feature lies immediately west of the hinge in both the granite and its host rocks this structure was initiated by fabric intensification during attenuation of the adjacent fold limb mineralization was further localized by a heterogeneous altered rock package including 1 potassic rocks generally foliated with large amounts of microcline and or biotite 2 skarns partly discordant including both manganoan hedenbergite fe mn rich grossularite quartz apatite rocks and ca rich almandine or clinopyroxene bearing metabasites and 3 a range of compositionally intermediate assemblages distinguished by the coexistence of fe mn ca and k bearing metamorphic silicates graphite commonly occurs at levels of several modal percent in the altered rocks but magnetite and zincian spinel are absent the most strongly altered rocks have a chemical component derived from the metasedimentary gneisses and possibly reflect alteration of a unit which previously contained carbonates this alteration would have involved reduction producing graphite coupled with differential addition of k fe mn p and f the potassic and skarnoid rocks are distinctive components of a regional pattern of metasomatism that exploited steeply inclined d 2 structures early metasomatic fluids in equilibrium with graphite at maramungee are unlikely to have been evolved from the magnetite bearing pluton sulfides mainly sphalerite pyrrhotite and pyrite occur in veinlets and microbreccia matrices that overprint all the earlier rock types and alteration assemblages they are associated with the development of retrograde hydrous and comparatively oxidized secondary minerals including cl and fe rich amphiboles chlorite scapolite calcite albite epidote and muscovite hematite is present in the youngest alteration assemblages retrograde phase relationships suggest that sulfide deposition was induced by reduction of the infiltrating fluid initially occurred at temperatures of 450 degrees to 500 degrees c and may have continued through a significant cooling interval zn is the only economically significant metal present although pb ag cu cd and sb are commonly anomalous and there are sporadically elevated amounts of au as and mo molybdenite is associated with fluorite and enrichments of rb ba u th and light ree in the early potassic alteration with the exception of zn and cd there is little overall correlation among the chalcophile elements there is a crude zoning toward higher cu zn ratios in the southern part of the prospect and there are sporadic occurrences of cu fe sulfide mineralization that have no clear relationship to the main zn zone associated with silicification muscovite chlorite alteration and variably anomalous au ag se co ree and u

geochemistry of hydrothermal tourmaline from iocg occurrences in the great bear magmatic zone implications for fluid source s and fluid composition evolution abstract tourmaline crystallized during iron oxide and alkali calcic alteration and iocg mineralization in the great bear magmatic zone canada within the samples analyzed tourmaline occurs as small crystals in the groundmass of hydrothermal breccias southern breccia and contact lake or as large prismatic crystals in quartz ore mineralogy veins contact lake devries lake and nico the tourmaline from these localities is predominantly shorlitic in composition with minor dravitic uvitic and feruvitic components the boron isotopic composition ranges from 15 to 5 with the majority of values between 15 and 10 the lack of variation among samples supports a common fluid source across the belt for the metasomatic hydrothermal systems these results are isotopically similar to global magmatic and non marine evaporitic reservoirs and lighter than seawater and marine sedimentary rocks the 11b results support a single fluid iocg deposit model for the systems studied wherein metasomatic hydrothermal fluids derived by magmatism ascend and evolve over time through fluid rock interactions

a fluid inclusion study of the suicide ridge breccia pipe cloncurry district australia implication for breccia genesis and iocg mineralization abstract the suicide ridge barren breccia pipe 1527 4 ma is one of numerous breccia occurrences that characterize the cloncurry district australia interest in breccia systems in the cloncurry district is related to their possible link with iron oxide copper gold deposits the suicide ridge barren breccia pipe is temporally and spatially associated with a granite that outcrops at its southwestern boundary and which is ascribed to the williams and naraku magmatic event ca 1550 1500 ma the breccia is characterized by clasts of variable dimensions degree of rounding and composition that includes dominant calc silicate clasts of the corella formation that underlie rocks of the soldiers cap group that host the pipe indicating a dominant upward transport of the fragments other breccia fragments include granite bodies characterized by albite quartz mineralogy and textures typical of the magmatic hydrothermal transition these rocks are interpreted to have formed in a fractionated granite carapace during the exsolution and accumulation of volatiles associated with the cooling magma two dominant types of inclusions have been identified at the suicide ridge barren breccia pipe these include early primary and pseudosecondary carbonic fluid inclusions observed only in magmatic hydrothermal transitional textures of granite breccia clasts and secondary sodic calcic brine inclusions that occur in all the collected samples variable homogenization temperatures in the primary and pseudosecondary pure co2 fluid inclusions indicate that they were trapped under different pressure conditions pressures estimated from the primary co2 fluid inclusions suggest that they were trapped at 4 2 kbar at least 1 kbar above the inferred lithostatic pressure this likely represents the overpressuring produced by release of co2 rich volatiles during the crystallization of magma and which ultimately caused the subsequent brecciation estimated pressures for pseudosecondary co2 fluid inclusions indicate pressure entrapment conditions around 2 7 kbar similar to the lithostatic pressure and 1 5 kbar lower than pressures recorded by type ia fluid inclusions this significant drop of pressure likely represents the sudden pressure depression occurring in response to brecciation evidence from field relationships breccia characteristics mineralogy and textures of granite clasts within the pipe and fluid inclusion studies support an origin of the suicide ridge barren breccia pipe in response to overpressuring generated by the release expansion and possibly phase separation of fluids of dominant carbonic composition from a crystallizing magma beneath and adjacent to the pipe sodic calcic fluid inclusions represent a later influx of fluids in the breccia system that produced widespread albitization significantly high temperature ultrasaline multisolid fluid inclusions abundant in iocg deposits and considered to be samples of the mineralizing fluid were not observed at the suicide ridge breccia pipe their absence in the barren systems suggests that they were critical for the formation of iocg deposits

acoustic generation of underwater cavities comparing modeled and measured acoustic signals generated by seismic air gun arrays underwater vapor cavities can be generated by acoustic stimulation when the acoustic signals from several air guns are reflected from the sea surface the pressure drop at some locations is sufficient for cavity growth and subsequent collapse in this paper the generation of multiple water vapor cavities and their collapses are numerically modeled and the results are validated by comparing with field data from a seismic air gun array test in a first modeling attempt where cavity interaction is neglected a correspondence between measured and modeled data is found then this correspondence is improved by assuming that the acoustic signal generated by the other cavities changes the hydrostatic pressure surrounding each cavity this modeling can be used to estimate the amount and strength of high frequency signals generated by typical marine air gun arrays given that a calibration step is performed prior to the modeling

mineralogical and geochemical constraints on mobilization and mineralization of rare earth elements in the lala fe cu mo ree deposit sw china the lala fe cu mo ree deposit in the northern kangdian iocg metallogenic province sw china has a paragenetic sequence that includes pre ore na alteration stage i fe p mineralization stage ii and sulfide mineralization stage iii rare earth element ree minerals which are chiefly monazite parasite and bastnasite with minor xenotime are associated with sulfide mineralization these ree minerals together with biotite muscovite and calcite are accompanied with k ca carbonate alteration of stage iii where magnetite and apatite of stage ii are overprinted by minerals of stage iii the apatite grains are commonly embayed or eroded and contain abundant rounded to subrounded and needle like inclusions of monazite and minor bastnasite calcite and sulfide minerals these monazite bearing apatite grains are texturally similar to metasomatized apatite in the laboratory and can be attributed to the formation from stage ii apatite via a dissolution precipitation process during fluid infiltration the monazite bearing apatite has ree contents and la sm ratios much lower than the original stage ii apatite suggesting that rees were leached and mobilized from this stage ii apatite and that these processes were responsible for the formation of monazite inclusions within the apatite hosts the monazite inclusions have compositions similar to those of stage iii monazite suggesting that rees in stage ii apatite were mobilized by stage iii fluids consistent with occurrences of sulfide and calcite inclusions within the apatite mass balance analysis using bulk compositional data for host rocks that underwent k ca carbonate alteration indicates that rees of the hosting rocks were also mobilized and that up to 70 percent of the light rees were leached out during alteration therefore ree mobilization recorded in apatite grains and country rocks support a model in which the country rocks were important sources for rees in the lala deposit compositions of amphibole and biotite together with previously acquired fluid inclusion data demonstrate that stage iii fluids are dominated by na and cl but had higher k co2 or hco3 and co32 and hf hcl fugacity and lower salinity nacl than stage ii fluids elevated k and co2 in stage iii fluids or associated k carbonate alteration is proposed to be important for extensive ree mobilization on country rocks the rees leached from country rocks are inferred to have been transported as chloride complexes prior to being deposited as ree minerals deposition of ree minerals from stage iii fluids was likely triggered by mixing with external relatively low temperature f rich and high ph fluids and or by local interaction with carbonate host rocks we suggest that the common association of rees with cu ores in many iocg deposits is related to the unique nature of the cu mineralizing fluids

chronology of magmatism skarn formation and uranium mineralization mary kathleen queensland australia uranium mineralization is hosted in a metasedimentary sequence intruded by felsic and mafic bodies in which the zircon u pb systems are 1 730 to 1 740 m y old felsic dikes characterized by exceptionally high uranium contents crystallized at essentially the same time 1 737 or 15 m y primary rb sr systematics in these igneous rocks are profoundly disturbed u pb discordia establish age of uranium mineralization as 1 550 or 15 m y derivation of uranium protore in the host rocks prior to regional metamorphism and 1 550 m y uraninite formation was probably by ca 1 740 m y hydrothermal activity modified journal abstract

the high grade mo re merlin deposit cloncurry district australia paragenesis and geochronology of hydrothermal alteration and ore formation the merlin deposit located in the cloncurry district mt isa inlier is the world s highest grade mo re deposit although the district is renowned for iron oxide copper gold iocg type mineralization merlin and other mo rich occurrences in the district cannot be classified as iocg type deposits the merlin deposit is hosted by the kuridala group 1690 1650 ma which comprises interbedded phyllite and carbonaceous slate calcsilicate rocks and silicified metasiltstone the mount dore granite part of the williams naraku batholith ca 1540 1490 ma is locally thrust over the metasedimentary rock package an early cu pb zn sulphide stage mount dore deposit mostly overlies with only partial spatial overlap the younger mo re mineralization merlin deposit cu pb zn is mainly hosted by carbonaceous slate as infill of hydrothermal coast supported carbonate breccias the younger mo re mineralization merlin deposit occurs as molybdenite infill of hydrothermal matrix supported breccias along or near the contact between carbonaceous slate and calc silicate rocks and locally cuts the cu pb zn mineralization based on detailed petrography and radiometric age dating u pb zircon and titanite ages re os molybdenite ages we define four main stages of hydrothermal alteration stage 1 represents the earliest hydrothermal stage dated here by u pb titanite geochronology at 1551 12 ma and is characterized by na ca alteration with the formation of hematite dusted albite amphibole carbonates titanite apatite quartz magnetite epidote stage 2 is characterized by the formation of k feldspar tourmaline carbonates quartz apatite and cu pb zn mineralization with chalcopyrite sphalerite pyrite galena stage 3 is dated at 1535 6 ma re os molybdenite and consists of the main mo re event that formed intensely mineralised matrix supported breccias accompanied by k feldspar chlorite alteration stage 4 dated here at 1521 3 ma re os molybdenite is of an age similar to that of the emplacement of the mount dore granite 1517 7 ma u pb zircon and is interpreted as either a remobilization event or a later addition of mo re in veins and disseminations that extends several meters below the mo re breccias with formation of chlorite k feldspar apatite rutile the mount dore granite was thrust above the metasedimentary package at ca 1500 ma which coincided with the waning of the hydrothermal activity in the cloncurry district this event is interpreted to be manifested at the merlin deposit as minor millimeter scale mo re vein formation collectively our data indicate that the merlin and the mount dore mineralization formed via a complex and protracted hydrothermal history that includes a time period ca 1560 1540 that has previously been regarded as unprospective for ore deposit formation in the region

the proterozoic albitite hosted valhalla uranium deposit queensland australia a description of the alteration assemblage associated with uranium mineralisation in diamond drill hole v39 the valhalla uranium deposit located 40 km north of mount isa queensland australia is an albitite hosted mesoproterozoic u deposit similar to albitite hosted uranium deposits in the ukraine sweden brazil and guyana uranium mineralisation is hosted by a thick package of interbedded fine grained sandstones arkoses and gritty siltstones that are bound by metabasalts belonging to the ca 1 780 ma eastern creek volcanics in the western succession of the mount isa basin alteration associated with u mineralisation can be divided into an early main and late stage the early stage is dominated by laminated and intensely altered rock comprising albite reibeckite calcite titano magnetite brannerite the main stage of mineralisation is dominated by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite apatite uranoan zircon uraninite anatase albite reibeckite calcite and hematite the late stage of mineralisation comprises uraninite red hematite dolomite calcite chlorite quartz and pb fe cu sulfides brannerite has u pb and pb pb ages that indicate formation between 1 555 and 1 510 ma with significant pb loss evident at ca 1 200 ma coincident with the assemblage of rodinia the oldest ages of the brannerite overlap with 40ar 39ar ages of 1 533 9 ma and 1 551 7 ma from early and main stage reibeckite and are interpreted to represent the timing of formation of the deposit these ages coincide with the timing of peak metamorphism in the mount isa area during the isan orogeny lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater mount isa district reveals that mineralisation involved the removal of k ba and si and the addition of na ca u v zr p sr f and y u th ratios indicate that the ore forming fluid was oxidised whereas the crystal chemistry of apatite and reibeckite within the ore zone suggests that f and text po 3 4 were important ore transporting complexes 18o values of co existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380 c and involved a fluid having 18ofluid values between 6 5 and 8 6 reibeckite d values reveal that the ore fluid had a dfluid value between 98 and 54 the mineral assemblages associated with early and main stages of alteration plus 18ofluid and dfluid values and timing of the u mineralisation are all very similar to those associated with na ca alteration in the eastern succession of the mount isa basin where a magmatic fluid is favoured for this style of alteration however isotopic data from valhalla is also consistent with that from the nearby mount isa cu deposit where a basinal brine is proposed for the transport of metals to the deposit based on the evidence to hand the source fluids could have been derived from either or both the metasediments that underlie the eastern creek volcanics or magmatism that is manifest in the mount isa area as small pegmatite dykes that intruded during the isan orogeny

inherited zircon and titanite upb systems in an archaean syenite from southwestern australia implications for upb stability of titanite abstract inherited zircon and titanite have been identified in a syenite from the archaean of southwestern australia conventional and shrimp analyses on euhedral zoned zircon and zoned rims on complex grains define a crystallisation age of 2654 5 ma for the syenite in addition shrimp analyses on zircon cores and unzoned subhedral zircons show that zircon has a ca 3250 ma inherited component conventional u pb ages on titanite also fall between ca 3250 ma and ca 2650 ma demonstrating that inherited titanite as well as zircon is present in the syenite the syenite has been affected by regional upper amphibolite facies metamorphism at an estimated temperature of 625 650 c retention of the inherited radiogenic pb in the titanite is evidence that the closure temperature for titanite is greater than 650 c the presence of inherited titanite and zircon also demonstrates a crustal source component for the syenite and indicates it originated by partial assimilation of crustal rocks by a potassic magma at

magmatic hydrothermal albite actinolite apatite rich rocks from the cloncurry district nw queensland australia abstract albite quartz actinolite apatite rich rocks with accessory titanite form a carapace that caps a small dome like intrusion of roxmere pluton and provide evidence of the accumulation and release of magmatic fluids that may have contributed to regionally extensive na ca alteration in the proterozoic cloncurry district australia the roxmere pluton was emplaced after the peak amphibolite facies metamorphism and into psammitic metasedimentary rocks that are stratigraphically younger and overlie the calc silicate rich mary kathleen group na ca hydrothermal assemblages closely spatially related to the roxmere pluton suggest that na ca alteration in this case is inconsistent with excepted up temperature metamorphic fluid circulation models the carapace rocks comprise two variants aplite and pegmatite both of which were affected by alteration and brecciation aplitic material predominates and the carapace has a brecciated top and a distinct textural zonation from an aplite rich pegmatite poor base to a relatively aplite poor pegmatite rich top this zonation is interpreted to represent the progressive accumulation of volatile phases toward the top of the carapace which culminated in fluid overpressuring and brecciation of the granitoid stock the convoluted and ptygmatic habit of the aplitic and pegmatitic material within the carapace is similar in nature to the comb quartz unidirectional solidification textures that are developed in the roof zones of some porphyry stocks these complex textures are interpreted to have formed from a single phase of fluid saturation the roxmere pluton or a deeper equivalent has a na mg and ca rich composition and a clinopyroxene amphibole rich mineralogy that is consistent with the formation of the contained albite actinolite apatite rich phases however the source of the rocks within the carapace is equivocal given that their contact relationships are obscured the 18 o composition of minerals within the carapace has the following ranges albite 7 1 8 7 actinolite 8 0 8 5 and quartz 8 9 11 4 albite and quartz 18 o equilibria suggest that these minerals in the pegmatitic and aplitic components formed at temperatures of 510 c to 540 c the calculated 18 o composition of a fluid in equilibrium with these minerals 6 0 to 8 0 at temperatures between 450 c and 550 c is consistent with a magmatic origin these estimated temperatures and 18 o fluid composition are comparable to estimates for regional na ca alteration in contrast d analysis of actinolite 136 to 150 within the carapace demonstrates that these fluids have a significantly lower d signature compared to na ca alteration assemblages associated with regional alteration 70 to 90 the low values in the carapace could either be interpreted as being produced from meteoric fluids or from degassed magmatic fluids although a meteoric fluid model is deemed improbable as meteoric fluids in the district have a documented d composition of ca 0 0 as a consequence an open system degassed magmatic hydrothermal fluid origin is considered to be the most plausible explanation for the low isotopic signatures and is also consistent with the complex textural relationships described within the carapace

geology geochemistry fluid inclusion and genesis of the guijeh qaleh ioa type iron ore deposit north of takab district northwestern iran abstract the guijeh qaleh iron deposit located in the takab district of northwestern iran contains ca 0 3 million metric tons mt of ore at 48 wt fe the host rocks are eocene to oligocene volcano sedimentary sequences consisting of andesite trachy andesite to basaltic andesite flows intruded by granites to granodiorite intrusions the hydrothermal alterations include argillic sericitic silicified carbonate and hematitic zones silicified and hematitic alteration zones are spatially associated with the mineralization and occur proximal to ore bodies whereas sericite carbonate and argillic alteration zones are distal to main ore bodies iron mineralization occurred as several quartz hematite specularite veins 0 5 to 5 m wide and 10 to 20 m long which were formed within and along normal and strike slip fault zones the mineralogy of ore bodies consists of hematite specularite pyrite subordinate magnetite and apatite together with minor malachite after chalcopyrite with open space filling disseminated massive and breccia textures geochemical analyses of high grade ore bodies show that fe concentration is strongly correlated with mo zn mn pb sio2 mgo tio2 and p2o5 the chondrite normalized ree patterns of the altered and mineralized ore bodies displays with lree hree ratio with a negative eu anomaly and low eu eu values characteristic of the kiruna type ioa deposits fluid inclusion studies from quartz occurring with the mineralization characterized mineralizing fluids with homogenization temperatures ranging from 133 to 464 c and apparent salinities between 0 2 to 23 2 wt nacl equ interpretation of fluid inclusion data suggest that mixing of magmatic and meteoric fluids and cooling caused ore precipitation geology mineralogy ore textures geochemistry and fluid inclusion data suggest that iron mineralization in the guijeh qaleh deposit is similar to kiruna type ioa deposits the presented data show that the takab district has the potential for hosting kiruna type ioa mineralization in the northwest of iran

mid crustal fluid mixing in a proterozoic fe oxide cu au deposit ernest henry australia evidence from ar kr xe cl br and i fluid inclusions in six quartz veins associated with cu au mineralisation at the giant ernest henry iron oxide copper gold deposit 167 mt 1 1 cu 0 54 ppm au in northwest queensland have been analysed for naturally occurring and neutron produced noble gas isotopes of ar kr and xe a combination of thermal and mechanical decrepitation methods enables distinction between four types of fluid inclusion ultra high salinity 30 to 70 wt nacl eq fluid inclusions have compositions that define two end members that are variably mixed in different samples the first end member has a 40 ar 36 ar value of 29 000 a 40 are cl value of 3 10 3 and mantle like br cl and i cl values of 1 2 10 3 and 11 10 6 respectively the second end member has a much lower 40 ar 36 ar value of less than 2500 a 40 are cl value of 10 6 low br cl values of 0 4 10 3 and i cl values of 1 2 10 6 all ratios are molar carbon dioxide and later lower salinity liquid vapour fluid inclusions have similar 40 ar 36 ar values of less than 2500 in all samples these data are compatible with genetic models in which cu au mineralisation formed at a depth of 6 10 km from circulation of magmatic fluids derived from regionally abundant a type granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust the largest source of co2 was probably carbonate rich lithologies in the midcrust later lower salinity fluids with a surficial origin diluted the mineralising brines and are preserved in the latest secondary fluid inclusions these data provide insight on the composition of crustal fluids during the proterozoic furthermore the magmatic fluid endmember derived from melts generated by re melting lower crustal paleoproterozoic igneous rocks with a mantle source preserves mantle like br cl and i cl these geochemical characteristics are interpreted to provide insight on i recycling at subduction zones and the composition of seawater in the paleoproterozoic 2007 elsevier b v all rights reserved

alteration facies linkages among iron oxide copper gold iron oxide apatite and affiliated deposits in the great bear magmatic zone northwest territories canada high temperature metasomatism driven by ascent of voluminous saline fluid columns in the upper crust plays a major role in the genesis of iron oxide alkali alteration ore systems but fundamental questions remain on genetic linkages among iron oxide copper gold iocg iron oxide apatite ioa albitite hosted uranium and skarn deposits that they produce excellent surface exposures of such systems in the great bear magmatic zone of northernwestern canada record the depth to paleosurface prograde evolution of iron oxide alkali alteration facies and mineralization across the belt albitite corridors that are tens of kilometers in length record the earliest reactions between highly saline fluids and host rocks along fault zones and subvolcanic intrusions pervasive albitization partitioned metals from the host rocks into the ascending fluid column leaving behind structurally weakened corridors of porous albitite these corridors were cut replaced and overprinted by amphibole and magnetite bearing calcic iron alteration assemblages in extreme cases the discharge of calcium iron and specialized metals formed iron oxide apatite deposits vanadium rare earth elements while recharging the outgoing fluids in sodium potassium and base and precious metals as temperatures declined and fluid chemistry evolved through fluid rock reactions the formation of potassic iron alteration assemblages breccias and sulfides resulted in magnetite and hematite group iocg mineralization within carbonate units skarns formed prior to are replaced by and evolved to calcic iron alteration facies skarns can locally host base metal mineralization tectonically uplifted albitite breccias replaced by potassic iron alteration assemblages became a preferential host for uranium mineralization the results of this study also illustrate that permutations and cyclical build up of alteration products can arise from a combination of faulting differential uplift and renewed magmatism framed within an alteration facies deposit model alteration zones and mineral occurrences play a pivotal role in predicting the mineral potential of iron oxide and alkali altered systems at district to deposit scales

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

arc related sodic hydrothermal alteration in the western united states sodium rich hydrothermal alteration is widely developed in permian to jurassic arc igneous rocks of the western united states but it is rare in younger rocks na rich alteration reflects a paleogeographic control on development two varieties naca and na can be defined by mineralogic and compositional changes both are common in permian to jurassic arc plutonic and volcanic rocks and are accompanied by fe and cu zn mineralization geologic relations and mineralogic stable isotopic and fluid inclusion data indicate that the fluids responsible for sodium rich alteration were isotopically heavy moderately to highly saline fluids of marine formation and or meteoric origin with or without a magmatic component the transition away from widespread na ca rich alteration in the late mesozoic corresponds to and is consistent with the change from an early mesozoic marine and or arid rifted arc setting to a fully emergent continental arc environment in the cretaceous

mineralogical and chemical evolution of the ernest henry fe oxide cu au ore system cloncurry district northwest queensland australia the ernest henry cu au deposit was formed within a zoned post peak metamorphic hydrothermal system that overprinted metamorphosed dacite andesite and diorite ca 1740 1660 ma the ernest henry hydrothermal system was formed by two cycles of sodic and potassic alteration where biotite magnetite alteration produced in the first cycle formed ca 1514 24 ma whereas paragenetically later na ca veining formed ca 1529 11 8 ma these new u pbtitanite age dates support textural evidence for incursion of hydrothermal fluids after the metamorphic peak and overlap with earlier estimates for the timing of cu au mineralization ca 1540 1500 ma a distal to proximal potassic alteration zone correlates with a large up to 1 5 km k fe mn ba enriched alteration zone that overprints earlier sodic alteration mass balance analysis indicates that k fe mn ba alteration largely produced during pre ore biotite and magnetite rich alteration is associated with k rb cl ba fe mn and as enrichment and na ca and sr depletion the aforementioned chemical exchange almost precisely counterbalances the mass changes associated with regional na ca alteration this initial transition from sodic to potassic alteration may have been formed during the evolution of a single fluid that evolved via alkali exchange during progressive fluid rock interaction cu au ore dominated by co precipitated magnetite minor specular hematite and chalcopyrite as breccia matrix forms a pipe like body at the core of a proximal alteration zone dominated by k feldspar alteration both the core and k feldspar alteration overprint na ca alteration and biotite magnetite k fe alteration ore was associated with the concentration of a diverse range of elements e g cu au fe mo u sb w sn bi ag f ree k s as co ba and ca mineralization also involved the deposition of significant barite k ba feldspar calcite fluorite and complexly zoned pyrite the complexly zoned pyrite and variable k ba feldspar versus barite associations are interpreted to indicate fluctuating sulphur and or barium supply together with the alteration zonation geochemistry and overprinting criteria these data are interpreted to indicate that cu au mineralization occurred as a result of fluid mixing during dilation and brecciation in the location of the most intense initial potassic alteration a link between early alteration na ca and k fe and the later k feldspathization and the cu au ore is possible however the ore related enrichments in particular elements especially ba mn as mo ag u sb and bi are so extreme compared with earlier alteration that another fluid possibly magmatic in origin contributed the diverse element suite geochemically independently of the earlier stages structural focussing of successive stages produced the distinctive alteration zoning providing a basis both for exploration for similar deposits and for an understanding of ore genesis

alteration mineralization and fluid evolution at the eloise cu au deposit cloncurry district northwest queensland australia the eloise deposit 3 1 million metric tons mt 5 5 cu 1 4 g t au and 16 g t ag is hosted by proterozoic rocks of the soldiers cap group in the eastern fold belt of the mount isa inlier the deposit is characterized by very high grade chalcopyrite pyrrhotite rich mineralization hosted by mafic silicate alteration alteration and mineralization lie within and adjacent to a major shear zone the main metasomatism comprised three stages early pervasive albite alteration stage i was overprinted by stage ii hornblende biotite quartz veins and alteration stage iii chalcopyrite pyrrhotite magnetite pyrite calcite quartz chlorite and actinolite replaced and brecciated the earlier mafic silicates the lodes occupy a narrow portion of a zoned mineralized system that is at least 2 km in length magnetite pyrite rich mineralization occurs in the south with chalcopyrite pyrrhotite rich mineralization in the central lode zone and pyrrhotite rich mineralization in the north the system has a distinct chemistry with enriched cu au ag co ni and zn fluid inclusions in pre syn and late to postmineralization veins indicate an evolving fluid history primary inclusions and associated hornblende biotite assemblages in premineralization veins indicate a high temperature fluid 450 degrees 600 degrees c and salinity estimates suggest it was an ultrasaline brine 32 68 wt total salts fluid inclusions in stage iii quartz in mineralized veins display a wide range of homogenization temperatures approximately 100 degrees 500 degrees c and gangue assemblages actinolite chlorite muscovite suggest mineralization was a cooler event 200 degrees 450 degrees c inclusions associated with the mineralization have a lower salinity 30 47 wt total salts than do premineralization inclusions and variable fluid inclusion types occur within the same clusters which may reflect fluid mixing the ultrasaline nature of the fluids and preliminary sulfur isotope results 0 4 2 0ppm suggest the ore fluid was predominantly magmatic metals were carried as chlorocomplexes and h 2 s was the dominant sulfur species important factors in ore deposition were a decrease in temperature and salinity and sulfidation of fe silicates eloise is interpreted to be a structurally controlled distal magmatic hydrothermal vein deposit

mineral chemistry of ore and hydrothermal alteration at the sossego iron oxide copper gold deposit carajas mineral province brazil abstract the sossego iron oxide copper gold deposit in the carajas mineral province comprises two major orebodies sequeirinho and sossego sodic alteration albite hematite and sodic calcic alteration zones represented by albite ferro edenite hastingsite up to 3 8 wt cl actinolite magnesiohornblende magnetite titanite epidote and calcite are predominant at sequeirinho magnetite bodies with envelopes of apatite rich actinolitite were formed with the sodic calcic event at high temperatures 500 c at 1 4 kbar in the sossego orebody potassic alteration with orthoclase and cl rich biotite up to 3 1 wt and chloritization are the main alteration types mineralized breccias in both orebodies have coarse grained zoned actinolite ferro actinolite cl apatite and magnetite within the matrix sulfides occur in equilibrium with a paragenetically late calcite quartz chlorite epidote allanite assemblage the al iv contents of the chlorite indicate crystallization at temperatures below 300 c chalcopyrite occurs associated with pyrite up to 2 3 wt co and 0 2 wt ni native gold up to 14 9 wt ag siegenite millerite vaesite pd melonite and hessite dilution and cooling of the hot metalliferous fluid 500 c by mixing with meteoric fluids may have been the main mechanisms responsible for the deposition of metals transported as metal chloride complexes in both orebodies of the sossego deposit

causes for large scale metal zonation around mineralized plutons fluid inclusion la icp ms evidence from the mole granite australia detailed reconstruction of the fluid evolution in several ore deposits associated with the sn w and base metal mineralized mole granite shows that multiple factors contributed to the zonal metal distribution around this intrusion information about the mechanism of ore formation was obtained from field relationships detailed petrographic studies and laser ablation inductively coupled plasma mass spectrometry la icp ms microanalysis of single fluid inclusions premineralization fluid inclusions in sn deposits are characterized by high sn w ratios whereas early fluid inclusions from w deposits contain higher w concentrations and comparatively low sn w ratios this indicates that the metal ratio in these deposits already was predefined by the composition of the magmatic input fluid however in both types of deposits the input fluid actually contained much higher concentrations of base metals pb zn cu etc than sn and w demonstrating that metal precipitation was highly selective the metal zonation around the mole granite therefore reflects both a compositional variation of the source fluid as well as sequential metal precipitation from it an additional process contributing to metal fractionation occurred by phase separation of the hydrothermal fluid into saline brine and low density vapor whereby cu b li as s ag la preferentially partitioned into the vapor phase analyses on six assemblages of unambiguously coexisting vapor and brine inclusions allowed direct determination of vapor brine distribution coefficients for 24 elements

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

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

the noble gas systematics of late orogenic h2o co2 fluids mt isa australia abstract the noble gases he ne ar kr and xe are powerful geochemical tracers because they have distinctive isotopic compositions in the atmosphere crust and mantle this study illustrates how noble gases can be used to trace fluid origins in high temperature metamorphic and mineralising environments and at the same time provides new information on the composition of noble gases in deeper parts of the crust than have been sampled previously we report data for h2o and co2 fluid inclusions trapped at greenschist to amphibolite facies metamorphic conditions associated with three different styles of mineralisation and alteration in the proterozoic mt isa inlier of australia sulphide fluid inclusions are dominated by crustal 4he however co variations in fluid inclusion 20ne 22ne 21ne 22ne 40ar 36ar and 136xe 130xe indicate noble gases were derived from three or more reservoirs in most cases the fluid inclusions elemental noble gas ratios e g ne xe are close to the ranges expected in sedimentary and crystalline rocks however the elemental ratios have been modified in some of the samples providing evidence for independent pulses of co2 and interaction of co2 with high salinity aqueous fluids compositional variation is attributed to mixing of i magmatic fluids or deeply sourced metamorphic fluids characterised by basement derived noble gases with 20ne 22ne 8 4 21ne 22ne 0 4 40ar 36ar 40 000 and 136xe 130xe 8 ii basinal metamorphic fluids with a narrow range of compositions including near atmospheric values and iii noble gases derived from the meta sedimentary host rocks with 20ne 22ne 8 9 8 21ne 22ne these data provide the strongest geochemical evidence available for the involvement of fluids from two distinct geochemical reservoirs in mt isa s largest ore deposits in addition the data show how noble gases in fluid inclusions can provide information on fluid origins the composition of the crust s major lithologies fluid rock interactions and fluid fluid mixing or immiscibility processes

structural and lithological controls on iron oxide copper gold deposits of the southern selwyn mount dore corridor eastern fold belt queensland australia the eastern fold belt of the proterozoic mount isa inlier has undergone numerous episodes of deformation hydrothermal alteration and iron oxide copper gold mineralization the structural and lithological controls on the location and geometry of five iron oxide copper gold deposits starra mount elliott swan mount dore and lady ella in the selwyn mount dore corridor were studied through geologic mapping core logging structural analysis and examination of 3 d grade distribution all the deposits in this area occur in close proximity to the selwyn shear a long lived regional structure which developed at the contact between carbonate rich and siliciclastic dominated rock packages this fault and a series of subparallel structures have been the focus of multiple reactivation events and have controlled the distribution of alteration and mineralization which occurred in this area at 1595 1570 1530 1515 1500 and 1485 ma ironstone hosted mineralization at starra developed in a preexisting zone of sodic and iron oxide alteration along the n striking starra shear kinematic indicators along the starra shear reveal that it has been reused numerous times early d2 thrusting post d2 sinistral shearing and pre d4 syn d3 dextral brittle faulting were all associated with sodic sodic calcic and iron oxide alteration either the post d2 or pre d4 strike slip faulting events can explain the steeply plunging nature of the orebodies at starra however the dextral pre d4 event produces dilational structures in ironstones and is associated with regionally important sodic and iron oxide alteration along ne to ene trending faults which intersect the starra shear close to the main orebodies we consider this the more likely main mineralizing event at starra both strike slip faulting events correspond with a change from e w oriented compression during the main phase of the isan orogeny to transpression that may have been driven by crustal overthickening during orogenesis at mount elliott and swan mineralization is associated with post d4 dextral and reverse movement across a sinistral fault jog along the nnw striking mount elliott fault during transpression mineralization alteration and veins at these deposits clearly overprint all ductile structural features overall the orebody geometry is controlled by the orientation of the mount elliott fault but high grade ore shoots are controlled by breccia formation in elongate pods which are parallel to preexisting f2 fold axes in contrast gently plunging grade shells at the slightly younger mount dore and lady ella deposits formed in response to renewed e w compression and reverse displacement along n to ne striking fault segments of the mount elliott fault and newly formed subparallel faults examination of the structural setting of mount dore and lady ella also demonstrates that strain partitioning between mechanically heterogeneous rock sequences metasedimentary rocks metabasalts granite and strongly silicified rock types exerted strong controls on the location of later mineralized systems the important episodes of iron oxide copper gold mineralization in the eastern fold belt between 1595 and 1485 ma appear to be associated temporally with compressive or transpressive structural regimes these events developed in response to far field tectonic stresses that evolved in response to the collision of laurentia with the proto australian continent during the isan orogeny late in the orogenic history the emplacement of voluminous a type batholiths associated with hot spot plume activity likely generated localized transient shortening events which are also associated with iron oxide copper gold mineralization this unique geodynamic evolution was responsible for the large scale metal enrichment and remobilization into suitable chemical and structural traps over significant time periods in the eastern fold belt iron oxide copper gold district

noble gas and halogen constraints on regionally extensive mid crustal na ca metasomatism the proterozoic eastern mount isa block australia fluid inclusions in late isan quartz veins associated with regional na ca alteration albitisation in the mary kathleen fold belt and the cloncurry district of the eastern mt isa block have been analysed for naturally occurring and neutron produced isotopes of ar kr and xe the noble gases have been extracted using a thermal decrepitation procedure that enables partial deconvolution of the different fluid inclusion types including variably saline aqueous liquid carbon dioxide and mixed aqueous carbonic varieties the variably saline 5 65 wt aqueous fluid inclusions dominate and have 40ar 36ar values of less than 2700 in most of the samples from across the region these fluid inclusions have extremely variable molar br cl values of 0 3 4 10 3 and i cl values of 0 2 35 10 6 and the fluids are interpreted to represent sedimentary formation waters derived from the upper crust that have dissolved variable quantities of halite or scapolite to achieve their ultra high salinity fluid inclusions in a sample from the snake creek anticline in the cloncurry district have the highest 40ar 36ar value of 25 000 demonstrating a deep magmatic or metamorphic fluid origin in this case a magmatic origin is favoured because this fluid is very similar to a fluid involved in iron oxide copper gold iocg mineralization at ernest henry that was also interpreted to have a magmatic origin and because the aqueous fluid inclusions have br cl of 1 2 10 3 and i cl of 10 10 6 that are similar to mantle derived igneous rocks carbon dioxide fluid inclusions dominate samples from the knobby quarry in the mary kathleen fold belt and have a maximum 40ar 36ar value of 6000 7000 these fluid inclusions are estimated to have a 36ar concentration of 1 4 ppb that is similar to the range determined for aqueous fluid inclusions in all the other samples in addition aqueous and carbonic fluid inclusions in all the samples have similar 129xe 36ar plus 84kr 36ar values that are unfractionated and close to the air air saturated water asw range these data are interpreted to indicate an independent and dominantly metamorphic origin for co2 and the presence of mixed aqueous carbonic fluid inclusions are attributed to fluid mixing and or mingling rather than fluid unmixing however the data do not preclude the presence of a minor magmatic co2 component in the samples from the knobby quarry fluid inclusions in most of the samples from the mary kathleen fold belt have higher br cl and i cl values higher 36ar concentrations and lower maximum 40ar 36ar values than fluid inclusions in samples from the cloncurry district this suggests na ca alteration in these different parts of the eastern mt isa block occurred independently however fluid inclusions associated with na ca alteration in the cloncurry district have a very similar composition to fluid inclusions in iocg mineralization stage quartz veins from ernest henry these data are therefore compatible with a genetic relationship between regional na ca alteration and iocg mineralization in the cloncurry district in both cases the ultra saline hydrothermal fluids had a dominant origin from sedimentary formation water but are interpreted to contain a magmatic component sourced from the late isan williams naraku batholiths which may have driven fluid convection

geochemistry and origin of proterozoic skarns at the mount elliott cu au co ni deposit cloncurry district nw queensland australia diopside rich skarn hosted copper gold ore derived primarily from carbonaceous metapelites at mount elliott forms a distinctive member of the spectrum of cu au fe oxide deposit styles in the cloncurry district of the paleoproterozoic to mesoproterozoic mount isa block the mine sequence is a package of carbonaceous metapelites and metagreywackes containing amphibolites derived from tholeiitic basic rocks a 40ar 39ar age spectrum with an extensive plateau like segment at 1 510 3 ma from an actinolite associated with sulfides is taken to represent the age of mineralization and is identical within error to the ages of most of the nearby batholithic granitoids the mine sequence is locally intruded by 1 to 10 m thick late to post tectonic trachyandesite dykes which were emplaced during the hydrothermal activity that created the orebodies and have affinities with the regional high potassium eureka supersuite granitoids stable isotope data are consistent with dominantly magmatic fluids during mineralization and the regionally distinctive skarn ca mg and cu au ni co te se low pb zn ag sb chalcophile element associations may reflect a primitive magmatic fluid source and or leaching of these elements from country rocks mount elliott is an unusual skarn deposit characterized by pronounced early albitization k fe mg depletion of the host rocks succeeded by predominantly open space deposition of sodic diopside actinolite scapolite andradite magnetite sulfides apatite allanite tourmaline calcite the ca fe mg na rich manganese poor chemistry was imposed from the fluid phase in the absence of carbonate rich protoliths immobile trace element ti zr nb geochemistry shows that mount elliott skarns formed in both metasedimentary and mafic metavolcanic host rocks but the former are the main hosts of ore in upper and lower ore zones that represent most of the resource banded skarns derived from a distinct calc silicate marble package at the nearby swan prospect have higher nb tio2 and zr tio2 ratios than the mount elliott metasediment derived skarns consistent with different provenance of the detrital components in the two sequences medium to coarse grained massive skarn and skarn breccia in the mount elliott lower ore zone formed in pelites and the trachyandesite dykes are the only intrusive rocks that could be genetically related to the mineralization in the immediate vicinity of the orebodies

discrete element modelling applied to mineral prospectivity analysis in the eastern mount isa inlier numerical modelling using a discrete element technique is employed here to examine the response of a fracture system in the eastern mount isa inlier to an applied stress regime model scale parameters and boundary conditions were varied to test which combinations of geometry and material properties produce the best correspondence between the known mineral deposit distribution and zones of anomalous model stress modelled areas of combined low minimum principal stress 3 and low mean stress m show the best correlation with deposits but these areas do not clearly correspond to specific fault orientations or configurations rather the models produce complex zoning of stress anomalies in response to the partitioning of stress across complex fault blocks and the interaction between more competent granitoid bodies less competent meta sedimentary rocks and the fault and rock boundary complexities adding fluid to the models and identifying an optimum orientation of the stress field with 1 in an ese direction produces the highest degree of visual correspondence with the known mineral deposit distribution and the previous empirical prospectivity analysis and also identifies several potentially prospective areas that may not have been previously tested by explorers the models are consistent with mineralisation occurring or being remobilised from earlier concentrations during a major phase of regional fluid flow facilitated by a complex fault array late during the evolution of the isan orogeny and synchronous with the waning stages of the emplacement of the williams batholith

geophysical signature of the nico au co bi cu deposit and its iron oxide alkali alteration system northwest territories canada models of the three dimensional physical property variation of the nico au co bi cu deposit northwest territories and the southern breccia albitite hosted uranium occurrences and their iron oxide alkali alteration envelopes were derived from inversion of high resolution aeromagnetic gravity and magnetotelluric mt data at deposit to regional scales in turn integration of the geophysical results with physical property measurements and geologic observations leads to a new understanding of the geometry of the deposit adjacent mineralized and altered zones and potential cogenetic links within the host metasomatic system nico which is a variant of the magnetite group iron oxide copper gold iocg class of deposit is spatially associated with a discrete zone of lower electrical resistivity occurring within a broader ne dipping zone of higher density the high density zone overlaps a ne dipping zone of higher magnetic susceptibility and is truncated to the southwest by a nw striking geophysical discontinuity interpreted as a major fault zone this inferred fault divides the magnetite altered metasedimentary rocks hosting the nico deposit from the albite altered rocks within the southern breccia corridor to the southwest that host the uranium mineralization having been active during development of the metasomatic system this fault influenced the formation of these distinct but complementary deposit types

iron mobility during synmetamorphic alteration in the selwyn range area nw queensland implications for the origin of ironstone hosted au cu deposits the proterozoic metamorphic rocks of the selwyn range area in western queensland contain a variety of styles of au cu deposit including some e g selwyn mine and osborne prospect that are spatially associated with magnetite rich ironstones the area is characterized by extensive alkali chloride metasomatism that occurred during the later stages of regional metamorphism existing experimental data indicate that hot saline fluids will dissolve and transport iron as they move through temperature pressure gradients in the vicinity of the amphibolite greenschist facies transition and predict that circulation cells will move iron and concentrate it in relatively cool dilute and or oxidized parts of such systems new geological mapping coupled with geochemical data from the amphibolite facies zone of the selwyn range area suggest such processes occurred on a large scale and that large masses of fe were mobilized particularly in association with na metasomatism of biotite bearing metasediments and high fe tholeiitic dolerites field and textural features of ironstones and other fe rich lithologies demonstrate that some of them at least formed by replacement of other rocks during metamorphism and deformation mineralization localized within such iron stones must itself be epigenetic

evaluation of cover sequence geochemical exploration sample media through assessment of element migration processes abstract cover sequence materials of the bulldog shale and underlying cadna owie formation within the eromanga basin south australia that overlie the prominent hill iron oxide copper gold iocg deposit are evaluated for their potential to host a geochemical expression of the underlying mineral system and thereby as geochemical exploration sampling media the bulldog shale is clay rich and has elevated concentrations of trace elements however its major and trace element cu mo ni pb u zn and ree chemical characteristics are significantly influenced by intense surface weathering to a depth of 50 m from the landsurface the cadna owie formation is sand dominated with lesser clay rich horizons and has elevated concentrations of multiple trace elements cu u mo ni and ree a positive correlation between trace and al2o3 suggests these elements are concentrated within clay rich horizons a comparison with background element concentrations within the cadna owie formation in the broader eromanga basin however shows introduction of additional elements via upward element migration from the underlying mineralised basement rocks and or downward element migration from the bulldog shale once weathering influences and natural background concentrations are accounted for elevated cu concentrations in the bulldog shale and trace elements in the cadna owie formation appear to be spatially associated with the prominent hill deposit and surrounding prospects and can then be useful sampling media for mineral exploration in the prominent hill region

sodic calcic alteration in fe oxide cu au districts an origin via unmixing of magmatic h 2 o co 2 nacl cacl 2 kcl fluids iron oxide cu au deposits particularly those formed in deeper level plutonic environments are commonly characterized by regional scale sodic calcic alteration which typically formed pre or syn cu au mineralization the sodic calcic assemblages include albite scapolite pyroxene actinolite apatite titanite epidote and calcite the consistent presence of coexisting hypersaline aqueous and co2 rich fluids in minerals from sodic calcic alteration and associated fe oxide cu au deposits is the result of unmixing of h2o co2 nacl cacl2 kcl magmatic fluids experimental evidence indicates that the na na k ratio of fluids in equilibrium with two alkali feldspars in co3 2 bearing parent fluids would be significantly higher than in unmixed chloride bearing aqueous fluids therefore fluid unmixing caused by decreases in temperature and or pressure will result in albitization of wall rocks as is observed in most deeper level fe oxide cu au deposits this alteration style may be succeeded by k feldspathization with decreasing temperature because of the increase in equilibrium na na k in chloride bearing fluids buffered by alkali feldspars

the oued belif hematite rich breccia a miocene iron oxide cu au u ree deposit in the nefza mining district tunisia the upper miocene oued belif ring shaped breccia is located in the nefza mining district of northern tunisia within the internal zone of the collisional alpine maghrebide belt it encloses chaotic triassic material evaporites altered siltites and pelites within an extrusive diapiric structure reactivated in a late miocene nappe emplacement episode this deep rooted structure drove the hydrothermal activity that caused the brecciation of the oued belif breccia and the emplacement of two generations of shallow felsic magmatism which most notably include a serravallian granodiorite stock and a tortonian rhyodacite dome the inverted cone shaped matrix supported oued belif breccia comprises clasts of triassic material and others deriving from the regional substrate as well as a very small amount of volcanic related material that suggests a possible phreatomagmatic origin fine grained low ti si al rich hematite 20 vol is the main matrix mineral along with rare earth element ree minerals bastnaesite parisite and subordinate monazite and u minerals uraninite the oued belif breccia is not an economic cu au deposit although it does possess a distinct geochemical anomaly in mafic cu co au elements with local cu enrichment at depth from drill core material as well as in felsic bi w sn u elements a multiphase alteration episode k fe mg metasomatism responsible for the formation of k feldspar fe phlogopite fe muscovite and tourmaline with fluorite and barite predates the fe light ree lree u mineralization the major brecciation event occurred slightly after this alteration and is coeval with the main iron oxide lree u mineralization event and the emplacement of the oued belif rhyodacite intrusion hydrothermal mineralizing fluids were hot 540 c saline and f co 2 rich brines possibly with a mixed basinal salt related and magmatic alkaline related origin except for its lack of economic cu and au content the oued belif breccia shares most typical attributes of the hematite group of iron oxide copper gold iocg deposits one may therefore classify it either as an iron oxide associated alkali altered porter 2010 or as an iron oxide uranium skirrow 2010 mineral system k ar dating of k feldspar sets the oued belif breccia formation at 9 2 0 25 ma which could make it the youngest presently known representative of the iron oxide associated alkali altered iocg class of deposits from a geodynamic viewpoint the oued belif structure fits within a still active collisional belt even though the oued belif breccia was formed in a postcollisional stage in this respect oued belif differs from most other iocg deposits especially from older proterozoic ones it nevertheless shares two essential characteristics considered necessary to yield iocg deposits skirrow 2010 namely a metasomatized subcontinental lithospheric mantle and a lithospheric delamination process identifying the oued belif breccia as a member of the iron oxide associated alkali altered iocg family opens new frontiers within the study of iocg deposits within the geodynamic environment of collisional belts future research in this area should focus particularly on the circum mediterranean segment of the alpine belt 2013 society of economic geologists inc

re os and pb pb geochronology of the archean salobo iron oxide copper gold deposit carajas mineral province northern brazil rhenium osmium ages were determined for two molybdenite samples and a pb pb age was derived from bornite chalcopyrite magnetite at the salobo iron oxide copper gold deposit to determine the timing of mineralization and its relation to the nearby old salobo granite rhenium osmium dating of molybdenite spatially associated with copper sulfide minerals yields ages with weighted means of 2576 8 and 2562 8 ma removing the error multiplier introduced by the decay constant uncertainty appropriate for comparing ages from the same isotopic system these data convincingly argue for two temporally separated pulses of molybdenite deposition at 2576 1 1 4 ma n 2 and 2561 7 3 1 ma n 3 the 2576 8 ma age coincides with a previously published u pb age of 2573 2 ma for the old salobo granite suggesting that main stage ore formation may have been contemporaneous with granite magmatism the slightly younger 2562 ma age most likely represents new molybdenite precipitation associated with the development or reactivation of local shear zones lead lead stepwise leaching of copper sulfide minerals yields a less precise isochron age of 2579 71 ma and supports an archean age for the salobo ores this is the first documentation of an archean iron oxide copper gold deposit and the re os and pb pb geochronology herein support 2580 2550 ma estimates for basement reactivation and regional granite magmatism associated with the development of brittle ductile shear zones