stable isotopes and fluid inclusion constraints on the fluid evolution in the bacaba and castanha iron oxide copper gold deposits carajas mineral province brazil abstract the evolution of the bacaba and castanha iron oxide copper gold deposits located in the carajas mineral province brazil is discussed based on petrography scanning electron microscopy stable isotopes and fluid inclusion analyses the castanha deposit is mainly hosted by ca 2 75 ga subvolcanic and volcanic rhyodacitic rocks and gabbros early sodic albite scapolite alteration was followed by high temperature calcic iron actinolite magnetite potassic biotite and minor chlorite and sericite alteration calcite ree carbonate and epidote represent a late and proximal alteration to ore bodies ore breccias with durchbewegung structure comprise chalcopyrite pyrrhotite pyrite cobaltpentlandite sphalerite marcasite and are notable due to their nickel zinc enrichment the bacaba deposit is hosted by the ca 3 00 ga bacaba tonalite 2 85 ga serra dourada granite and gabbro bodies early ca 2 70 ga alteration at bacaba includes sodic albite scapolite iron magnetite and potassic iron k feldspar magnetite biotite associations well developed late chlorite albite sericite calcite hematite musketovite alteration formed during a paleoproterozoic overprinting ca 2 06 ga the bacaba ore is composed of i chalcopyrite magnetite bornite and ii chalcopyrite pyrite hematite musketovite related to early potassic iron and late alteration respectively the castanha deposit was formed from magmatic fluid 18oh2o 9 5 0 5 to 5 2 1 0 at 500 to 400 c and sulfur 34s 0 1 3 sources with a limited contribution of externally derived fluids during its evolution ore precipitation progressed under considerably low fs2 and fo2 conditions at relatively high temperatures 370 50 c fluid inclusion analyses indicate greater proximity of the castanha deposit to the source of a hot overpressured magmatic fluid suggesting its formation in a high temperature hydrothermal center fluid rock interaction coupled with increasing ph might have been the critical factors in destabilizing the metal chloride complex in the castanha deposit the bacaba deposit evolved from a fluid mixing between hot 450 c hypersaline cacl2 nacl bearing magmatic brine 30 mass equivalent and a less saline colder and 18o depleted and d enriched fluid e g seawater or low latitude meteoric water mixing resulted in an oxidizing environment dilution salinities between 35 and 4 mass equivalent and temperature drop 160 190 c triggering the ore precipitation at bacaba the slightly higher 34s values 1 3 5 4 may reflect an additional contribution of externally derived sulfur through the thermochemical reduction of oxidized sulfur species in the southern copper belt the regional spatial distribution of the sulfur isotope compositions shows the highest 34ssulfide values close to the paleoproterozoic sossego orebody and the alvo 118 deposit this might suggest significant involvement of externally derived components e g diluted fluids and sulfur during late stages of a protracted hydrothermal evolution in the carajas iocg deposits

geotectonic signature and hydrothermal alteration of metabasalts under and overlying the giant serra norte iron deposits carajas mineral province abstract archean metabasalts enclose the serra norte iron deposits in the carajas mineral province brazil they experienced seafloor hydrothermal alteration regional metamorphism under low greenschist facies conditions and hematite associated hydrothermal alteration characterizing i least altered ii chlorite and iii hematite chlorite basalts in the n4 and n5 deposits their petrographic and geochemical changes were caused by both chlorite and hematite hydrothermal alteration nevertheless part of the original igneous textures and some of their primary minerals plagioclase and clinopyroxene are commonly preserved geochemical investigation of the least altered basalt indicates a calc alkaline affinity trace element behavior e g nb and th is consistent with an arc related setting and continental crustal contamination where hydrothermal alteration affects basalts the most distal intermediate and proximal alteration zones are distinguished based on the amount of chlorite hematite less magnetite chlorite composition in i ii and iii marks these three mafic lithotypes with variations in the fet fe mg ratios that clearly reflect buffered through unbuffered conditions mineralogical and textural features such as ruptured amygdales indicate fluid interaction with hydrothermal minerals forming veins and breccias caused by hydraulic fracturing both chlorite and hematite chlorite basalts experienced renewed isotopic equilibrium due to hydrothermal alteration showing a decrease in 18o 7 4 to 1 9 in comparison to the least altered basalt reflecting an increase in fluid rock ratio on most discrimination diagrams and morb normalized spidergram the investigated rocks are comparable to a volcanic arc environment associated with subduction zone these and other evidence such as a a seafloor associated volcanogenic sequence b arc type sedimentation of the grao para group indicated by hyaloclastic tufts breccias and volcaniclastic rocks c jaspilites in the serra norte and d a large subduction signature expressed by enrichment in th all suggest that the grao para basalts overflowed on the continental crust in a back arc environment with the primary magma having experienced significant upper crustal contamination the arc association evolution and the variability of lithological sedimentological igneous volcanic structural metamorphic and other evolutionary aspects of the itacaiunas supergoup is suggestive of a greenstone belt type setting an arc associated evolution and the variability of lithological sedimentological igneous volcanic structural metamorphic and other aspects of the itacaiunas supergoup supports a greenstone belt type setting

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

temporal evolution of the giant salobo iocg deposit carajas province brazil constraints from paragenesis of hydrothermal alteration and u pb geochronology the giant salobo copper gold deposit is located in the carajas province amazon craton detailed drill core description petrographical studies and u pb shrimp iie and la icp ms geochronology unravel its evolution regarding the host rocks hydrothermal alteration and mineralization within the cinzento shear zone the deposit is hosted by orthogneisses of the mesoarchean xingu complex 2950 25 and 2857 6 7 ma and of the neoarchean igarape gelado suite 2763 4 4 ma which are crosscut by the old salobo granite remnants of the igarape salobo metavolcanic sedimentary sequence are represented by a quartz mylonite with detrital zircon populations ca 3 1 3 0 2 95 2 86 and 2 74 ga high temperature calcic sodic hydrothermal alteration hastingsite actinolite was followed by silicification iron enrichment almandine grunerite magnetite tourmaline formation potassic alteration with biotite copper gold ore formation and later fe rich hydrated silicate alteration myrmekitic bornite chalcocite and magnetite comprise the bulk of copper gold ore all these alteration assemblages have been overprinted by post ore hematite bearing potassic and propylitic alteration which is also recognized in the old salobo granite in the central zone of the deposit the mylonitized igarape gelado suite rocks yield an age of 2701 30 ma zircon ages of 2547 5 3 and 2535 8 4 ma were obtained for the old salobo granite and for the high grade copper ore respectively a u pb la icp ms monazite age 2452 14 ma from the copper gold ore indicates hydrothermal activity and overprinting in the siderian therefore a protracted tectono thermal event due to the reactivation of the cinzento shear zone is proposed for the evolution of the salobo deposit

geology and shrimp u pb geochronology of the igarape bahia deposit carajas copper gold belt brazil an archean 2 57 ga example of iron oxide cu au u ree mineralization a striking feature of the carajas region brazil is the clustering of a variety of different types of cu au deposits the most abundant in the belt are the 200 million metric tons mt of fe oxide cu au u ree deposits which despite the variety of host rocks and different orebody morphologies share a number of diagnostic features including 1 intense fe metasomatism leading to the formation of grunerite fayalite and or fe oxides magnetite and or hematite 2 intense carbonate alteration mainly siderite 3 sulfur poor ore mineralogy chalcopyrite and bornite 4 quartz deficient gangue 5 extreme low ree enrichment and 6 enrichment in u and co the igarape bahia deposit is perhaps the best documented fe oxide cu au u ree deposit of the belt containing about 219 mt at 1 4 percent cu and 0 86 g t au the cu au ore consists of steeply dipping breccia bodies that are hosted by hydrothermally altered metavolcano sedimentary rocks shrimp ii zircon dating of the host metavolcanic rocks gives a 207pb 206pb age of 2748 34 ma this suggests a correlation between the igarape bahia volcano sedimentary sequence and the grao para volcanic rocks which have published ages of ca 2 75 ga shrimp dating of monazite from the matrix of ore bearing magnetite breccias gives a 207pb 206pb age of 2575 12 ma confirming the epigenetic nature of the mineralization and placing it 175 m y after accumulation of the host volcano sedimentary sequence the 2575 12 ma shrimp age of hydrothermal monazite from the igarape bahia mineralization is indistinguishable from published conventional 207pb 206pb ages for zircons from the archean a type granites of the carajas belt indicating that mineralization processes at igarape bahia were temporally related to these a type archean granites the wide range of highly radiogenic 87sr 86sr ratios 0 714 0 755 of carbonates from the igarape bahia deposit suggests multiple crustal sources consistent with a magmatic hydrothermal origin shrimp dating of zircon xenocrysts recovered from crosscutting diabase dikes indicates a maximum 207pb 206pb age of 2670 ma consistent with field evidence and the age of host rocks but does not unequivocably constrain the age of the ores the styles of hydrothermal alteration mineralogy and geochemistry of the igarape bahia ore as well as published fluid inclusion and stable isotope data support its classification as a member of the world class olympic dam type fe oxide cu au u ree group of deposits as previously argued by several authors the shrimp age of 2575 12 ma for hydrothermal monazite indicates that igarape bahia is an archean example of this deposit group

the anatomy of shallow crustal transpressional structures insights from the archaean carajas fault zone amazon brazil abstract the carajas fault zone cfz is the most prominent structure in the e w trending carajas strike slip system casss an ancient upper crustal fault network of probable late archaean age that cuts across the precambrian amazonian craton in brazil the subvertical faults reactivated pre existing high grade basement shear zone fabrics itacaiunas shear zone and display a complex long lived history of movement 1 ga dominated by oblique and strike slip displacements a postulated early regional phase of dextral movement downfaulted units of low grade to unmetamorphosed basement rocks into dilational bends and offsets in the casss subsequent sinistral transpression ca 2 6 ga led to faulting and folding during partial inversion of the cover rocks in these dilational sites with much of the associated deformation focused in the immediate vicinity

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

reactivation of archaean strike slip fault systems amazon region brazil the itacaiunas belt on the southeastern margin of the amazonian craton comprises two e w trending archaean fault zones carajas and cinzento strike slip systems developed sub parallel to a broad zone of earlier ductile shearing older basement rocks display a pervasive e w trending mylonitic fabric formed at high temperatures during sinistral transpression c 2 8 ga a sequence of younger archaean cover rocks was deformed under low greenschist facies conditions during a second phase of sinistral transpression associated with retrogression and reworking of basement fabrics all these rocks are overlain unconformably by very low grade to unmetamorphosed volcanic and sedimentary rocks of late archaean early proterozoic age the carajas and cinzento strike slip fault systems formed during subsequent regional dextral transtension c 2 6 2 7 ga which down faulted cover sequence rocks into dilational fault jogs later sinistral transpression c 1 9 ga partially inverted these dilation zones producing oblique compressional faults and folds evident mainly in cover rocks renewed fracturing regional emplacement of granitic plutons and swarms of dykes c 1 8 ga were followed by fault controlled deposition of immature sandstones and conglomerates phanerozoic activity is limited although some faults display evidence of minor neotectonic activity the waning influence of the basement architecture and decreasing intensity of later reactivations is consistent with lithosphere scale weakening with a finite life span

mineralogy geochemistry and petrology of neoarchean ferroan to magnesian granites of carajas province amazonian craton the origin of hydrated granites associated with charnockites abstract 2 75 to 2 73 ga old granitic intrusions associated with coeval charnockitic rocks were emplaced in the northern domains of the carajas province the vila jussara suite was recognized recently and its geologic mineralogical and geochemical characteristics are presented in this paper and compared with the data available in the literature on the estrela complex serra do rabo and igarape gelado granites and planalto suite monzogranites and syenogranites are dominant in most units but in the igarape gelado granite and vila jussara suite granodiorites and tonalites are also relatively abundant the main mafic phases in all these granitoids are amphibole potassian hastingsite with subordinate magnesiohastingsite 0 95 fe fe mg 0 47 and biotite 0 88 fe fe mg 0 52 with rare occurrence of clinopyroxene relict crystals magmatic epidote of pistacite component from 26 to 31 occurs only in the vila jussara suite the rocks of estrela serra do rabo and planalto units contain only ilmenite generally with coronas of titanite or ilmenite associated with magnetite and are essentially reduced ferroan granites whole rock feot feot mgo 0 89 that evolved at low f o 2 fmq 0 5 the igarape gelado granite needs additional studies but it is formed apparently by reduced ferroan and oxidized ferroan granites the vila jussara suite is also composed of reduced ferroan granites that are similar to those of the other granite units however it has additionally oxidized ferroan and magnesian granitoids which contain magnetite ilmenite as the main fe ti oxide phase and evolved respectively at moderate f o 2 nno 0 5 and at comparatively higher f o 2 nno to nno 1 the magmas of these granites were formed at temperatures 900 c and derived from a heterogeneous dominantly reduced and tholeiitic granulitic crust locally varying to oxidized and calc alkaline in composition plagioclase orthopyroxene clinopyroxene and fe ti oxides were the main phases in the melt residues and the liquids were enriched in ba zr y and ree except for eu but not in sr compared to their sources the magmas should have relatively high water content 4 wt the magmatic evolution was strongly influenced by partial melting processes the different varieties of the vila jussara suite are not linked by fractional crystallization and derived from distinct magmas the neoarchean granites of the carajas province were emplaced in a collisional tectonic setting they are syntectonic granites that were deformed and sometimes intensely recrystallized during their emplacement and subsequent subsolidus cooling the magmas were generated in the crust at pressures of 800 to 1000 mpa and emplaced at pressures of 200 to 500 mpa the studied granitoids are similar geochemically to the ferroan and magnesian groups of charnockites the magnesian variety of the vila jussara suite is similar to the pyroxene free granitoids of the neoarchean matok pluton of the collisional limpopo belt the neoarchean granites of carajas are hydrated granites emplaced at comparatively higher crustal levels when compared with the matok pluton

40 ar 39 ar dating of archean iron oxide cu au and paleoproterozoic granite related cu au deposits in the carajas mineral province brazil implications for genetic models 40ar 39ar dating of biotite from iocg and granite related cu au deposits in the carajas mineral province provides evidence for the timing of mineralization and constraints on genetic models of ore formation ages of biotite from greisen and quartz rich vein and breccia deposits alvo 118 1885 4 ma breves 1886 5 ma estrela 1896 7 ma and gameleira 1908 7 ma demonstrate the close temporal relationship between cu au mineralization and subjacent a type granites mineralization is hosted within granite cupolas breves or in vein breccia systems emanating from the cupolas estrela and gameleira consistent with a genetic relationship of mineralization to the b li f rich granites plateau and minimum ages of biotite from iocg deposits including igarape bahia cristalino corta goela and gt34 range from 2537 6 ma to 2193 4 ma the 40ar 39ar age of biotite from igarape bahia 2537 6 ma is similar to a previous shrimp 207pb 206pb age for monazite of 2575 12 ma when the uncertainties in the respective analyses and standards are taken into account the age spectrum for biotite from cristalino shows increasing ages for successive steps consistent with post crystallization ar loss and the age of 2388 5 ma for the last three steps is considered a minimum age for cu au mineralization the age of biotite from the gt34 prospect 2512 7 ma coincides with a previously identified period of basement reactivation and may indicate the formation of cu au mineralization at this time or resetting of biotite from an older mineralization event at this time at corta goela within the canaa shear zone the biotite age of 2193 4 ma lies between the ages of iocg 2 57 2 76 ga and granite related cu au 1 88 ga deposits elsewhere in the carajas district but is similar to previously reported 40ar 39ar ages for amphibole from sossego possibly indicating that mineralization at both sossego and corta goela was affected by a thermal event at this time the paleoproterozoic cu au deposits are commonly hosted within neoarchean iocg alteration systems and the common occurrence of potassic alteration especially biotite in both types of deposits means that special care is required in interpreting the paragenesis of alteration in both types of deposits the paleoproterozoic cu au deposits are reduced and sulfur and quartz rich deposits lacking in major amounts of iron oxides and are therefore unlike iocg deposits instead they share many characteristics in common with widespread paleoproterozoic sn w deposits in the amazon craton including close spatial and temporal relationships with reduced a type b li f granites and the occurrence of greisen and quartz rich vein breccia systems within and above granite cupolas the occurrence of sericitic alteration in the paleoproterozoic cu au deposits is not evidence for an upward transition to sericitic alteration in iocg deposits in the carajas mineral province

role of magma pressure tectonic stress and crystallization progress in the emplacement of syntectonic granites the a type estrela granite complex carajas mineral province brazil the archaean syntectonic a type estrela granite complex carajas mineral province brazil consists of three plutons emplaced in a greenstone sequence under low pressure conditions 180 p 310 mpa it is composed mainly of annite ferropargasite hedenbergite and ilmenite bearing monzogranites the contact aureole is affected by a subvertical penetrative schistosity conformable with the limits of the plutons meso to microstructures and mineral reactions in the granites indicate that deformation occurred in a continuum from above solidus to low t subsolidus conditions two distinct planar structures are observed i a concentrical primary foliation s0 corresponding to rhythmic isomodal phase layering associated with a faint grain shape fabric it is horizontal in the centre and vertical towards the edges of the plutons and ii a steep to subvertical foliation s1 associated with the deformation of s0 and accompanied with emplacement of synplutonic dykes and veins of leucocratic granites and pegmatites emplacement differentiation and consolidation of the estrela granite complex are considered to result from a continuous evolution under decreasing temperatures in a single stage strained crust transpression with two main periods 1 the first period is controlled by body forces and it corresponds to inflation with magma ponding as long as the rheology is melt dominated magma pressure is the critical parameter and almost no strain is recorded with decreasing t magmas crystallize and differentiate leading to a concentrical magmatic phase layering the growing magmatic bodies are mechanically decoupled from the country rocks and their evolution depends on internal magma chamber processes 2 for higher amount of crystallization residual melt fraction f 0 5 the role of magma pressure becomes insignificant establishment of a continuous crystal framework leads to the coupling of plutons with their surroundings and deformation in response to tectonic stress most of the strain is recorded during this period which starts from the rigid percolation threshold and extends to subsolidus low grade conditions this leads to deformation of the partially crystallized volume and redistribution of fluid enriched differentiated melts the amount of crystallization through the rheological thresholds appears as the critical parameter determining the transition from magma controlled processes inflation and differentiation of the magma chamber with development of a phase layering to tectonic controlled processes deformation of the phase layering and redistribution of residual melts this accounts for the fact that syntectonic plutons commonly display intermingled boudinaged layers with distinct modal compositions and in some cases well preserved rhythmic layering

slip distributions on active normal faults measured from lidar and field mapping of geomorphic offsets an example from l aquila italy and implications for modelling seismic moment release surface slip distributions for an active normal fault in central italy have been measured using terrestrial laser scanning tls in order to assess the impact of changes in fault orientation and kinematics when modelling subsurface slip distributions that control seismic moment release the southeastern segment of the surface trace of the campo felice active normal fault near the city of l aquila was mapped and surveyed using techniques from structural geology and using tls to define the vertical and horizontal offsets of geomorphic slopes since the last glacial maximum 15 3 ka the fault geometry and kinematics measured from 43 sites and throw heave measurements from geomorphic offsets seen on 250 scarp profiles were analysed using a modification of the kostrov equations to calculate the magnitudes and directions of horizontal principal strain rates the map trace of the studied fault is linear except where a prominent bend has formed to link across a former left stepping relay zone the dip of the fault and slip direction are constant across the bend throw rates since 15 3 ka decrease linearly from the fault centre to the tip except in the location of the prominent bend where higher throw rates are recorded vertical coseismic offsets for two palaeo earthquake ruptures seen as fresh strips of rock at the base of the bedrock scarp also increase within the prominent bend the principal strain rate calculated by combining strike dip slip direction and post 15 3 ka throw rate decreases linearly from the fault centre towards the tip the strain rate does not increase across the prominent fault bend the above shows that changes in fault strike whilst having no effect on the principal horizontal strain rate can produce local maxima in throw rates during single earthquakes that persist over the timescale of multiple earthquakes 15 3 ka detailed geomorphological and structural characterisation of active faults is therefore a critical requirement in order to properly define fault activity for the purpose of accurate seismic hazard assessment we discuss the implications of modelling subsurface slip distributions for earthquake ruptures through inversion of gps insar and strong motion data using planar fault approximations referring to recent examples on the nearby paganica fault that ruptured in the mw 6 3 2009 l aquila earthquake

u pb geochronology of archean magmatism and basement reactivation in the carajas area amazon shield brazil abstract the archean carajas subprovince is a metallogenic district bif bauxite cu ni mn au located in the easternmost amazonian craton in brazil the main conclusions from a u pb study of the itacaiunas supergroup and a locality in the xingu complex are the following the xingu basement complex the oldest unit underwent migmatization at 2859 2 ma and also grew new zircon at 2851 4 ma the luanga mafic intrusion is 2763 6 ma old and coeval with the 2759 2 ma felsic volcanics of the grao para group amphibolites from the salobo group contain 2851 ma zircons were metamorphosed 2761 3 ma and intruded by granitic veins ca 2758 ma at the time of grao para magmatism and also grew new zircon at 2732 2742 ma the data indicate that the salobo group is part of the xingu complex and not of the itacaiunas supergroup as heretofore believed the pojuca group possibly coeval with the salobo group was metamorphosed at 2732 3 ma a late archean reactivation event of regional extent is marked by titanite growth at 2581 5 ma in the mirim area intrusion of the old salobo granite at 2573 2 ma new zircon growth in salobo group amphibolites at 2555 4 3 ma and monazite growth in a metamorphosed iron formation at 2551 2 ma in addition k metasomatism associated with shear zones formed titanite in salobo group amphibolites at 2497 5 ma and new titanite at 2519 5 ma in the xingu complex events in the 2581 2497 ma interval are probably associated with the latest activity of a wnw ese sinistral shear system which could also be responsible for the establishment of a transtensional basin filled by the volcano sedimentary sequence of the grao para bahia and rio fresco groups finally undeformed proterozoic granitoid intrusions were dated at 1883 2 ma cigano 1883 5 2 ma musa 1880 2 ma carajas and 1874 2 ma pojuca

transpression and the build up of the cordillera the example of the bucaramanga fault eastern cordillera colombia widespread wrench tectonics have been described along the northern andes the bucaramanga fault described as sinistral strike slip bounds the high santander massif we combine structural and thermochronological data from the central southern portion of the fault to investigate the vertical displacement the structural survey data show old phases of activity preserved in the host rocks along the fault trace with the superimposition of different generations of slickenlines and both strike slip and dip slip kinematics indicators new and previous thermochronological data show that differential exhumation of the fault walls has been ongoing for the last 50 ma the hanging wall the santander massif records in the central portion decreasing exhumation rates from the early miocene to the mid to late miocene and in the southern portion constant rates from the late oligocene to the pliocene combining such observations the thermochronological offset resulting from the relative motion of the two fault walls is comparable with the observed drop in elevation across the fault suggesting that the present topography of the santander massif is related to vertical movement along the bucaramanga fault we infer that the fault has a significant neogene reverse component consistent with the present day horizontal global positioning system vector data long term exhumation rates and the structural assemblage supplementary material the supplementary materials contain methodological information on the thermochronological procedures a compilation of the previously published data used in this study and the structural geology dataset https doi org 10 6084 m9 figshare c 4620140

the neoarchean gt 34 ni deposit carajas mineral province brazil an atypical iocg related ni sulfide mineralization abstract the gt 34 deposit located 12 km to the sw of the sossego copper gold mine in the carajas province northern brazil represents an unusual ni sulfide mineralization the deposit occurs along a ne sw trending sub vertical shear zone marked by progressive mg alkalic alteration zones predominantly hosted in granitic and locally in granodioritic to tonalitic orthogneisses initial alteration zones result in unique scapolite orthopyroxene assemblage which is partially preserved within pervasive hornblende chlorapatite plagioclase replacement zones nickel mineralization occurs mainly as matrix supported breccias characterized by a pentlandite pyrrhotite rich matrix and rounded fragments chiefly of hornblende and chlorapatite irregular stockworks and net textured veins containing chalcopyrite pentlandite are less common phlogopite talc actinolite alteration and late stage veinlets crosscut the previous alteration zones and the mineralization the phlogopite talc actinolite alteration occurs as irregular veins and chalcopyrite pyrrhotite magnetite are commonly observed where such alteration intersects the ni mineralization late stage veinlets are represented by k feldspar epidote chlorite calcite and quartz albite chlorite calcite epidote veins both containing minor amounts of millerite pyrite and f oh apatite high resolution sims u pb zircon geochronology obtained for the gt 34 deposit revealed an age of 2828 4 ma for zircon grains inherited from the host orthogneisses the timing of the mineralization altered zircon grains from the scapolite orthopyroxene and phlogopite talc actinolite alteration zones is attributed to an age interval between 2751 and 2720 ma although poorly constrained the geochronological data corroborate a neoarchean age for the gt 34 ni mineralization similar to that of other iocg deposits in the carajas province and coeval with the bimodal magmatism in the area the atypical orthopyroxene marialite mineral chemistry support a metasomatic crystallization at high temperatures 700 c low ah2o

intraplate deformation in central australia the link between subsidence and fault reactivation abstract central australia has experienced two intraplate orogenic events involving significant north south shortening the late neoproterozoic to early cambrian petermann orogeny and the devonian to carboniferous alice springs orogeny in each event pre existing structures inherited from mesoproterozoic terrain amalgamation were reactivated and basement rocks exhumed from beneath thick sedimentary successions accumulated in the centralian superbasin the pattern of fault reactivation during these events shows a striking similarity to the pattern of subsidence in the overlying basin immediately prior to the petermann orogeny the centralian superbasin was thickest in the vicinity of the musgrave block the region in which deformation was subsequently localised at the same time crustal scale faults elsewhere in central australia that were covered by a relatively thin sheet of sediment remained inactive despite being favourably oriented to accommodate the north south shortening between the petermann and alice springs orogenies subsidence patterns shifted such that fault systems in the arunta block and also those in the southern musgrave block were buried by significant thicknesses of sediment whereas the major structures that were exhumed during the petermann orogeny were not significantly buried during the alice springs orogeny reactivation once again occurred along the most deeply buried faults even in the instances where those faults had remained inactive during the earlier petermann orogeny importantly the major petermann aged structures that were not buried during renewed subsidence remained inactive during the alice springs orogeny the record of reactivation implies that the presence of pre existing crustal scale faults alone was insufficient to localise deformation rather fault reactivation appears to have required a priming process that modulated the strength of the lithosphere on a regional scale the correspondence between the distribution of basement fault reactivation and subsidence patterns during both the petermann and alice springs orogenies implies a link between relatively thick sedimentation and long term lithospheric weakening we show that this link is compatible with the thermal effects of a thick sedimentary blanket in the context of central australia the mechanical impact of basin formation is likely to be enhanced by the presence of regionally elevated heat production in the proterozoic basement

inversion and propagation of the late paleozoic porjianghaizi fault north ordos basin china controls on sedimentation and gas accumulations abstract in contrast to typical intracratonic basins the ordos basin comprises marginal deformation belts and complex fault systems this study uses 3d seismic data tied to sonic and stratigraphic data from exploration wells to document the geographic extend of the porjianghaizi fault and its control on sedimentation and gas accumulation in the northern ordos basin our results show that the geometry of large porjianghaizi fault is controlled by five small fault segments the growth history of the porjianghaizi fault composes four stages 1 an initiation stage late carboniferous to early permian 2 a reactivation stage during the late triassic 3 an inversion stage during the middle jurassic and 4 an interaction and linkage stage during the late jurassic detailed studies show that the porjianghaizi fault had significant control on sedimentation and gas accumulation during the initiation stage late carboniferous to early permian five fault segments and associated relay ramps controlled the sedimentation in the study area the relay ramps formed transport pathways in which sediment extended from north basin margin to the basin center in contrast sedimentation along the fault was more localized based on shale gouge ratios sgr and formation water salinity the fault sealing capacity of the porjianghaizi fault is characterised by horizontal segmentation which means the fault composes laterally sealed areas and laterally connected areas along the fault strike as a corollary we propose that gas resources were mainly generated from the south where there are thick source rocks migrating vertically through interbedded open fractures first and then laterally through the junction zone of fault relay ramps it eventually accumulated in structural traps found in the northern areas understanding the evolution of the porjianghaizi fault is important for predicting the distribution of sedimentary facies in upper carboniferous and lower permian units as well as understanding the migration and distribution of gas resources in the north ordos basin these results can further help in hydrocarbon exploration in the north ordos basin

geological and shrimp ii u pb constraints on the age and origin of the breves cu au w bi sn deposit carajas brazil the breves deposit in the carajas copper gold belt brazil a member of the cu au w bi sn group of deposits contains about 50 mt of 1 22 cu 0 75 g t au 2 4 g t ag 1 200 g t w 70 g t sn 175 g t mo and 75 g t bi it is hosted by sandstones and siltstones of the aguas claras formation minimum age of 2 681 5 ma in the roof zone of a complex highly altered granite intrusion the mineralisation is disseminated in a greisenized zone resulting from alteration of probable monzogranites and syenogranites the ore bearing greisen contains abundant xenomorphic quartz in association with fe chlorite and muscovite the gangue assemblage also includes fluorite tourmaline and minor amounts of monazite xenotime chlorapatite thorite zircon calcite siderite and bastnaesite copper mineralisation is dominated by chalcopyrite associated with pyrite arsenopyrite pyrrhotite and molybdenite gold particles in equilibrium with native bismuth are common as inclusions in chalcopyrite the greisen contains sub economic concentrations of tungsten and niobium that are related to the presence of ferberite qitianlingite and nb rutile shrimp ii zircon dating of the host granites gives 207pb 206pb ages of 1 878 8 and 1 880 9 ma for two phases and a combined age of 1 879 6 ma shrimp ii dating of monazite and xenotime grains in late to post mineralisation veins gives a combined 207pb 206pb age of 1 872 7 ma indistinguishable from the ages of the granites this provides a genetic connection between the breves deposit and the ca 1 88 ga a type granite magmatism that typifies the carajas belt as part of a much larger intracratonic magmatic province that extends over much of the amazonian craton the recognition of this association has exploration implications not only for the geophysical signature of the granite roof zones but also for likely geochemical dispersion around the deposits of this type

spatial analysis of mineral deposit distribution a review of methods and implications for structural controls on iron oxide copper gold mineralization in carajas brazil abstract mineral deposits are formed by interaction of various geological processes and conditioned by controls that favor their formation and preservation the understanding of mineralization controls is critical for mineral exploration because it allows focusing exploration on regions where these controls are concentrated the analysis of the spatial distribution of mineral deposits particularly on a regional scale can provide information relevant to the understanding of regional scale processes involved during their formation here we present a review of fry and fractal methods for spatial analysis of mineral deposit distribution and an application using the iron oxide copper gold iocg deposits of the carajas mineral province brazil results show that different iocg mineralization structural controls acted in scales of 40 km the iocg deposits cluster at scales of

stratigraphy and geochronological constraints of the serra sul formation carajas basin amazonian craton brazil abstract the carajas basin amazonian craton hosts extensive neoarchean to paleoproterozoic sedimentary archives which are still poorly constrained regarding their depositional settings ages and type of basin in which they have been deposited in this study we performed detailed sedimentological investigations and u pb dating of detrital zircon in four drill cores intercepting the recently defined serra sul formation our data show that this formation corresponds to various shallow to deep subaqueous environments shallow water environments are characterized by local occurrences of microbially mediated structures while deep water environments are characterized by polymictic conglomerates resulting from the mixing of materials of different origins during downslope debris flow both sedimentary facies and common occurrence of syn sedimentary deformations attest for recurrent slope instabilities geochronological investigations allow to define a maximum depositional age of 2684 10 ma that is several tens million years younger than other neoarchean sedimentary units of the carajas basin major peaks in age distribution indicate that the serra sul formation derives from local sources that constitute the basement of the carajas basin the infilling of the carajas basin by local sources together with sedimentary facies and depositional environments attesting for slope instabilities suggest that the serra sul formation was deposited during an active extensional tectonic phase such neoarchean to early paleoproterozoic tectonic setting compares with those documented in many other cratons worldwide and suggests that it could correspond to the break up of one of the first documented supercontinent

timing of multiple hydrothermal events in the iron oxide copper gold deposits of the southern copper belt carajas province brazil the southern copper belt carajas province brazil hosts several iron oxide copper gold iocg deposits including sossego cristalino alvo 118 bacuri bacaba castanha and visconde mapping and u pb sensitive high resolution ion microprobe shrimp iie zircon geochronology allowed the characterization of the host rocks situated within regional wnw ese shear zones they encompass mesoarchean 3 08 2 85 ga ttg orthogneiss granites and remains of greenstone belts neoarchean ca 2 74 ga granite shallow emplaced porphyries and granophyric granite coeval with gabbro and paleoproterozoic 1 88 ga porphyry dykes extensive hydrothermal zones include albite scapolite biotite scapolite tourmaline magnetite alteration and proximal potassium feldspar chlorite epidote and chalcopyrite formation u pb laser ablation multicollector inductively coupled mass spectrometry la mc icp ms analysis of ore related monazite and re os ntims analysis of molybdenite suggest multiple neoarchean 2 76 and 2 72 2 68 ga and paleoproterozoic 2 06 ga hydrothermal events at the bacaba and bacuri deposits these results combined with available geochronological data from the literature indicate recurrence of hydrothermal systems in the southern copper belt including 1 90 1 88 ga ore formation in the sossego curral ore bodies and the alvo 118 deposit although early hydrothermal evolution at 2 76 ga points to fluid migration coeval with the carajas basin formation the main episode of iocg genesis 2 72 2 68 ga is related to basin inversion coupled with neoarchean ca 2 7 ga felsic magmatism the data suggest that the iocg deposits in the southern copper belt and those in the northern copper belt 2 57 ga salobo and igarape bahia alemao deposits do not share a common metallogenic evolution therefore the association of all iocg deposits of the carajas province with a single extensive hydrothermal system is precluded

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

from the roots to the roof an integrated model for the neoarchean carajas iocg system brazil abstract the carajas mineral province located in northern brazil comprises the oldest iron oxide copper gold mineralizing system on earth and is one of the world s most significant cluster of large tonnage iocg deposits based on a critical assessment of the literature a new integrated model for the carajas neoarchean iocg deposits the model considers the hydrothermal alteration footprint and the rock textures the geometry of the mineralization and the ore assemblage and the isotopic and geochronological signature the majority of the deposits form in the hypozonal domain pervasive and well developed sodic magnesian and calcic iron hydrothermal alteration halos form through magmatic derived hydrothermal fluids the occurrence of hydrothermal orthopyroxene marialite in the ni rich gt 34 and salobo deposits extend further the p t boundaries to temperatures of up to 700 c and 5 kbars thus co is proposedrresponding to the root zone of the system epizonal deposits conversely are characterized by low temperature potassic biotite phlogopite propylitic and chloritic hydrolytic hydrothermal assemblages towards shallower crustal levels although a mantle contribution to the hydrothermal fluids is recognized the o b stable isotopic signature reveals the participation of surface derived basinal brines in the ore forming process the occurrence of polymetallic ooids in the alemao orebody igarape bahia deposit hosting identical hydrothermal alteration mineralogy to the chalcopyrite breccias of other iocg deposits in the carajas mineral province suggests that the mineralizing fluids may have reached the paleo surface of the carajas basin in the neoarchean representing the roof of the iocg system conversely the ore mineralogy is consistent throughout the vertical scheme magnetite is the only iron oxide formed and precipitate from iron rich hydrothermal alteration accompanying the calcic alteration similarly chalcopyrite represents the cu sulfide there is no transition to more oxidized assemblages towards shallower zones supporting that the overall system was relatively reduced since more oxidizing phases hematite bornite are not observed as part of the neoarchean iocg system thus the neoarchean carajas iocg system represents a crustal scale continuum of a vertical paleo hydrothermal system formed coevally to the voluminous bimodal magmatism and the formation of the world class banded iron formation hosted iron ore

intracratonic strike slip partitioned transpression and the formation and exhumation of eclogite facies rocks an example from the musgrave block central australia mountain belts developed in an intracratonic setting during the neoproterozoic in the center of australia mesoproterozoic granulite and amphibolite facies gneisses of the musgrave block were overprinted during the petermann orogeny 550 ma with zones of high strain concentrated along broadly east west trending shear zones these zones formed under eclogite facies t 650 c and p 12 kbars to greenschist facies conditions and may form part of a strike slip related crustal scale flower type structure granulite facies gneisses preserve ages older than 700 ma suggesting that these rocks did not experience temperatures greater than 350 c at 550 ma for these rocks not to have been thermally equilibrated to temperatures of 350 c at a depth of 12 kbars requires either an extraordinarily low geothermal gradient 9 c km 1 or if the geothermal gradient was more typical 20 c km 1 then transport to that depth and subsequent exhumation occurring in a short time interval 40 myr

structural controls and metallogenic model of polyphase uranium mineralization in the kiggavik area nunavut canada the kiggavik area is located on the eastern boundary of the paleo to mesoproterozoic thelon basin nunavut canada and hosts uranium mineralization in archean basement rocks the major fault fracture network in the kiggavik area is mainly oriented ene wsw and ne sw consisting of polyphased fault zones initiated during the thelon and trans hudsonian orogenies ca 1900 1800 ma these faults were subsequently mineralized in four stages referred to as u0 u1 u2 and u3 the first event u0 is inferred to be of magmatic origin and is related to microbrecciation and weak clay alteration under a wsw ene 1 u0 is a ca 1830 event which predates intense quartz brecciation qb and veining at ca 1750 ma qb is associated with emplacement of the kivalliq igneous suite and caused pervasive silicification of former fault zones which in turn controlled subsequent fracture development and behaved as barriers for later u mineralizing fluids u1 to u3 u1 u2 and u3 postdate deposition of the thelon basin u1 and u2 occurred under a regional strike slip stress regime with the direction of 1 evolving from wnw ese u1 to ne sw ene wsw u2 both formed at 1500 1330 ma and are related to circulation of thelon derived uranium bearing basinal brines a post u2 but pre mackenzie dykes ca 1270 ma extensional transtensional stress regime with 3 oriented ne sw caused normal dextral offset of the orebodies by reactivating nnw sse and e w trending faults this fracturing event triggered circulation of hot 300 c probably acidic fluids that dissolved quartz and caused illitization and bleaching of the host rocks finally u3 records remobilization of the previous mineralization along redox fronts through percolation of low temperature meteoric fluids during two main tectonic events at ca 550 and 350 ma this study provides evidences for the presence of a primary pre thelon basin uranium stock within the kiggavik prospects and a strong structural control on mineralization in the kiggavik area our study also shows a nearly similar evolution of uranium mineralization in this area compared to the world class uranium district of the athabasca basin saskatchewan canada

history and evolution of mesolithic landscapes in the haut quercy lot france new charcoal data from archaeological contexts charred wood analyses have been performed on three mesolithic sites located on the causse de gramat a karstic plateau in southwestern france lot department les fieux les escabasses and le cuzoul de gramat the sites yielded occupations dating from the early to the late mesolithic 9th to the 6th millennia cal bc in the absence of palynological data charcoal analysis allowed us to characterise the woody environment exploited by mesolithic hunter gatherers our results point at the minor place of softwoods in the landscape and the local importance of rosaceae prunoideae marking an original type of pre forest vegetation in order to retrace the local vegetation dynamics these results are synthesized and discussed thanks to a correspondence analysis which includes previous anthracological data from azilian and middle mesolithic levels of two other sites of the causse the homogeneity of the results speaks in favour of the stability of the local environment and confirms the specific vegetation feat

neoarchean and paleoproterozoic iron oxide copper gold events at the sossego deposit carajas province brazil re os and u pb geochronological evidence the sossego iron oxide copper gold iocg deposit is situated within the wnw ese trending canaa shear zone in the southern copper belt carajas province brazil the sossego deposit consists of two major groups of orebodies sequeirinho pista baiano and sossego curral the sequeirinho pista baiano orebodies are characterized by deep emplaced magnetite apatite and albite actinolite rich zones whereas the sossego curral orebodies have predominant potassic and chlorite alteration typical of shallow crustal levels u pb shrimp iie and la icpms geochronology on host rocks reveals mesoarchean 3 08 ga xingu complex ca 2 99 ga sequeirinho granite and 2 97 ga pista felsic metavolcanic rock and bimodal neoarchean ca 2 74 ga sossego granophyric granite curral granite and gabbronorite units dating of hydrothermal monazite u pb la mc icpms and molybdenite re os ntims of the sequeirinho pista orebodies rendered ages of ca 2 71 to 2 68 ga while ore related monazite of the sossego curral orebodies yielded ages of ca 1 90 to 1 88 ga the neoarchean iocg forming events reflect coupling of ductile sinistral transpression with nne directed oblique shortening and neoarchean magmatism ca 2 7 ga the shallow emplaced paleoproterozoic system formed after progressive exhumation of the deep emplaced neoarchean iocg deposits coincides in age with the emplacement of 1 88 ga a type granites the latter may have caused regional circulation of magmatic and externally derived fluids along crustal discontinuities favoring copper gold ore deposition as well as metallogenic diversity in the carajas province e g sn w au pd pt deposits

critical assessment of geochronological data from the carajas mineral province brazil implications for metallogeny and tectonic evolution abstract the carajas domain in the amazonian craton brazil displays remarkable metallogenetic diversity containing iron oxide copper gold iocg cu au mn fe ni co pge cr and au pge mineral systems it consists of mesoarchean 2 83 3 08 ga basement granitoids and gneisses overlain by the ca 2 73 2 76 ga rift related meta volcanosedimentary units of the neoarchean carajas basin coeval ca 2 76 mafic ultramafic complexes host nickel cobalt laterite vermelho puma onca and magmatic pge cr luanga deposits unconformably overlying this is the aguas claras formation a package of fluvial to shallow marine sedimentary rocks of controversial but probable archean age based on 2 6 2 7 ga cross cutting mafic dikes this hosts manganese deposits azul small polymetallic cu au deposits breves and the serra pelada au pt pd deposit iocg deposits are located along wnw regional shear zones hosted within the itacaiunas supergroup mesoarchean basement and bimodal 2 76 2 73 ga neoarchean granitoids and gabbro geochronology supports the existence of multiple superimposed and episodic hydrothermal and mineral systems multiple mineralization ages are common within single deposits and establishing the age of primary mineralization as opposed to overprinting hydrothermal events is challenging copper mineralization formed as early as ca 2 76 ga coeval with basin formation while structurally controlled iocg deposits formed or were substantially modified during multiple hydrothermal episodes ca 2 72 2 68 ga 2 6 2 45 ga and 1 88 ga for the northern iocg deposits e g salobo and igarape bahia alemao a temporal overlap between 2 57 ga mineralization and the 2 57 ga alkaline old salobo granite is commonly used to infer a genetic link yet this geochronology s reliability is debatable younger ages exist for the old salobo granite 2 55 2 53 ga zircons are metamict and older mineralization ages have been reported suggesting a more complex history the occurrence of ages ca 2 60 2 45 ga is spatially restricted to the north and coincides with an important yet poorly understood tectono thermal event involving reactivation of the northern cinzento shear zone and amphibolite facies metamorphism whether iocg deposits formed during this tectonic event or represent substantially modified or metamorphosed older mineralization or both is contentious older mineralization ca 2 71 ga at the igarape cinzento iocg deposit in the north is coeval with the southern iocg deposits formed ca 2 72 2 68 ga sequeirinho bacaba and bacuri this does not convincingly overlap with the intrusion of widespread 2 76 2 73 ga syntectonic granitoids so a genetic link with magmatic fluids is speculative and basinal brines may play a role due to controversy regarding the timing of compression and basin closure the tectonic setting is debated mineralization either formed during rifting or synchronous with basin inversion but the latter is more supported by geochronology and ore textures in the south paleoproterozoic ca 1 88 ga iocgs the sossego curral orebodies of the sossego deposit and alvo 118 or alternatively overprinting cu au systems formed coeval with craton wide a type 1 88 ga granite magmatism this magmatic hydrothermal system is responsible for a large part of the metallogenetic diversity of carajas domain small generally

late cretaceous bonanza style metal enrichment in the serra pelada au pd pt deposit para brazil a 40 ar 39 ar age of 75 6 ma 2 was obtained for aggregates of mn ba oxide intergrown with palladiferous gold and pd pt minerals representative of near surface bonanza au pd pt mineralization that triggered the gold rush to serra pelada in northern brazil the mineralization occurs in goethite rich tectonic breccia and records recurrent fault displacement in the still active cinzento strike slip fault system the goethite rich tectonic breccia is truncated by the bonanza style au pd pt mn ba enrichment with which tabular hematite is spatially associated on a micrometric scale the tabular hematite is coarsely crystalline 5 m in grain size and lines cavity walls in the goethite rich breccia the presence of coarsely crystalline tabular hematite constrains the metalliferous overprint to temperatures in excess of about 100 c we suggest that the bonanza mineralization is a late cretaceous epithermal like fault breccia system that overprinted paleoproterozoic intrusion related au pd pt mineralization preserved at depth

trace element and multi isotope geochemistry of late archean black shales in the carajas iron ore district brazil abstract the 250 300 m thick carajas formation in the carajas mineral province northern brazil consists of banded iron formation including giant high grade iron ore deposits and minor black shale overlying a thick pile 2 3 km of about 2 75 ga old metabasalt carbonaceous shale with pyrite and locally pyrrhotite rich patches from drillcore of the serra sul exploration project has up to 29 ppm mo iron speciation analysis indicates essentially ferruginous and for some samples likely euxinic depositional conditions positive 34 s isotope ratios of tris are between 0 3 to 10 7 with heavy data restricted to pyrrhotite free samples the data suggest microbial sulfate reduction under at least partially sulfate limiting conditions with later overprint by migrating solutions the black shale is affected by pronounced low temperature potassium metasomatism k 2 o na 2 o 100 up to 10 wt k 2 o as adularia related to diagenetic processes at 98 95 mo for continental input t dm of 2 8 3 1 ga according to nd isotope data and 0 9 98 95 mo for a hydrogenous component black shale samples from the bottom of the bif sequence have heavy mo isotope composition of up to 1 8 98 95 mo the significant mo isotope fractionation is either the result of an early and transient whiff of oxygen at 2 7 ga or the result of hydrothermal fluid overprint

iron and sulphur isotopes from the carajas mining province para brazil implications for the oxidation of the ocean and the atmosphere across the archaean proterozoic transition abstract mineralogical analyses and major and trace element geochemistry combined with iron and sulfur isotopes were applied to banded iron formations bifs and pyrite bearing sandstones from the carajas mineral province brazil the bifs belong to the 2 7 ga old grao para group and show a rather simple mineralogy hematite and quartz or cryptocrystalline silica their ree y patterns suggest deposition under marine sub oxic conditions fe isotopes show highly positive values 57 fe irmm 14 2 06 0 34 in average which can be explained by the partial oxidation of fe 2 aq in the surface ocean subsequent to the upwelling of deep anoxic seawater the resulting iron oxy hydroxides likely formed in the shallow photic zone as a seasonal process and acquired highly positive iron isotope signature values consistent with a rayleigh distillation model the pyrite bearing sandstones belong to the aguas claras formation of palaeoproterozoic younger age and were cored at the base of the giant azul manganese deposit diagenetic pyrite is characterized by positive 57 fe irmm 14 1 02 0 2 and 34 s vctd 11 97 0 12 average values that are different from values of modern marine biogenic pyrite results likely indicate that dissolved sulfate was the limiting factor controlling biogenic pyrite formation at that time near zero 33 s values 0 013 0 003 indicate minimal mass independent sulfur isotope fractionation mif s consistent with the 2 1 ga age previously obtained from the aguas claras pyrites this result suggests deposition at a time when the oxygen partial pressure in the atmosphere was already high enough 10 5 to 10 2 pal or present atmospheric level to hinder mif s by photochemical reactions incidentally this also confirms that the giant mn deposit of carajas is in the same age range 2 1 0 2 ga as other mn ores in gabon and south africa pointing to the importance of mn precipitation in paleoproterozoic times

the fractal nature of structural controls on ore formation the case of the iron oxide copper gold deposits in the carajas mineral province brazilian amazon the formation of ore minerals in hydrothermal deposits is the result of a complex interplay between physical and chemical processes that are conditioned by the geologic environment in which they occur in the last decades research has increasingly indicated that many of these processes display different forms of scale invariance i e they show fractal geometry this suggests that behind the apparent disorder and irregularity of the geometry of mineral deposits at different scales an underlying regular pattern is present if properly understood this regular geometrical pattern could be useful in a variety of theoretical and applied fields a great portion of this scale invariance is given by the structural framework during mineralization because structures are a dominant factor controlling fluid flow here we assess the geometry of iron oxide copper gold iocg mineralization in the world renowned carajas mineral province focusing on one of the largest and most economically important orebodies the sossego deposit the geometry of mineralization is evaluated at the microscale ore minerals in thin sections local scale orebodies in mine maps and regional scale deposit distribution on regional maps we show that the spatial distribution and shape of ore minerals at the microscale is largely nonrandom presents fractal geometry and displays defined trends in spatial distribution and anisotropy additionally the geometric trends observed at the microscale mimic those of the local scale geometry of orebodies as well as the regional scale distribution of mineralization the main property controlling the observed scale invariance is permeability which is intrinsically associated with structures at multiple scales these results contribute to further understanding the fractal nature of processes controlling mineral deposit formation and revealing new multiscale approaches to investigate structural controls on ore deposition