nature of the lithosphere across the variscan orogen of sw iberia dense wide angle seismic reflection data 1 two wide angle seismic transects have been acquired across the sw iberian massif they crossed three major geological zones south portuguese zone ossa morena zone and central iberian zone with their tectonic contacts and the pyrite belt being of greatest interest a total of 690 digital seismic recording instruments 650 texans and 40 reftek 3 component units from the iris passcal instrument pool were used the transects a and b are each approximately 300 km long and consist of 3 and 6 shot points respectively with an approximately 60 km shot point interval the charge sizes range from 1000 kg at the edges to 500 kg at the center these recently acquired experiments were designed to provide velocity constraints on the lithosphere and to complement the previously acquired normal incidence seismic profile iberseis both data sets are part of the sw iberia project which was developed within the europrobe program and designed to address fundamental questions about the nature and dynamics of the variscan lithosphere the acquisition parameters provide closely spaced wide angle seismic images of the lithosphere beneath sw iberia in transect a the station spacing was on average 400 m while along transect b the receiver spacing was approximately 150 m because of this close trace spacing the lateral continuity of the seismic arrivals is greatly improved frequency analysis revealed that the recorded events feature relatively low frequencies 6 25 hz after processing the shot records show high amplitude and well defined arrivals the interpreted pmp arrival located at approximately 11 s normal incidence traveltime is characterized by high amplitude and relatively low frequency 6 12 hz a well defined pn arrival appears at offsets beyond 120 km at far offsets greater than 180 km an upper mantle reflection is observed furthermore within the upper crust the shots records feature a relatively high velocity arrival located at 4 5 s normal incidence traveltime the analysis of this arrival indicates that it probably corresponds to the top of the iberian reflective body identified in the iberseis deep seismic profile the velocity models obtained by forward modeling show a complex crust especially in the middle crust the velocity models are the most detailed ones that have been produced in the area and contain a large amount of new features that are relevant to the understanding of the composition of the crust and upper mantle beneath the zone the velocity depth functions derived from the velocity models have higher middle crustal velocities than the average in other continental areas a comparison between laboratory seismic velocity measurements and the velocities of the models was carried out in order to estimate the crustal and the upper mantle composition results indicate that the high middle crust velocities correspond to rocks of a mafic composition the combined data set reveals new aspects related to the lithospheric evolution of this transpressive orogen and allows us to attempt an interpretative cross section of the upper lithosphere in sw iberia

world class ni cu pge deposits key factors in their genesis magmatic ni cu sulfide deposits form as the result of segregation and concentration of droplets of liquid sulfide from mafic or ultramafic magma and the partitioning of chalcophile elements into these from the silicate melt sulfide saturation of a magma is not enough in itself to produce an ore deposit the appropriate physical environment is required so that the sulfide liquid mixes with enough magma to become adequately enriched in chalcophile metals and then is concentrated in a restricted locality so that the resulting concentration is of ore grade the deposits of the noril sk region have developed within flat elongate bodies 15 2 0 2 km that intrude argillites evaporites and coal measures adjacent to a major trans crustal fault and immediately below the centre of a 3 5 km thick volcanic basin studies of the overlying basalts have shown that lavas forming a 500 m thick sequence within these have lost 75 of their cu and ni and more than 90 of their pge overlying basalts show a gradual recovery in their chalcophile element concentrations to reach normal values 500 m above the top of the highly depleted zone the ore bearing noril sk type intrusions correlate with those basalts above the depleted zone that contain normal levels of chalcophile elements the high proportion of sulfide 2 10 wt associated with the noril sk type intrusions the high pge content of the ores the extensive metamorphic aureole 100 400 m around the bodies and the heavy sulfur isotopic composition of the ores 8 12 34s are explicable if the ore bearing bodies are exit conduits from high level intrusions along which magma has flowed en route to extrude at surface the first magma to enter these intrusions reacted with much evaporitic sulfur at a low r value and thus gave rise to sulfides with low metal tenors successive flow of magma through the system progressively enriched the sulfides in the conduits losing progressively less of their chalcophile metals and thus accounting for the upward increase in metals in successive lava flows above the highly depleted flows the voisey s bay deposit lies partly within a 30 100 m thick sheet of troctolite interpreted as a feeder for the 1 334 ga voisey s bay intrusion and partly at the base of this intrusion where the feeder adjoins it studies of olivine compositions indicate that an early pulse of magma through the feeder and into the intrusion was ni depleted but that subsequent pulses were much less depleted trace element re os and s and o isotope data and mineralogical studies indicate that the magma pulses interacted with country gneiss probably principally in a deeper level intrusion extracting sio2 na2o k2o and possibly sulfur form the gneiss which accounts for the magma becoming sulfide saturated the jinchuan deposit of north central china occurs within a 6 km long dyke like body of peridotite the compositions of olivine within the dyke the igneous rocks themselves and the ore are all inconsistent with derivation of the body from ultramafic magma as originally supposed and indicate that the structure forms the keel of a much larger intrusion of magnesian basalt magma flow of magma into the intrusion has resulted in olivine and sulfide being retained where the keel was widening out into the intrusion the west australian komatiite related deposits occur in thermal erosional troughs which have developed due to the channelisation of magma flow and the resulting thermal erosion of underlying sediments and basalt by the hot komatiite magma the sediments are sulfide rich and may have contributed substantially to the sulfide of the ores the mineralisation in the duluth complex occurs in troctolitic intrusions along the western margin of the complex as a result of magma interacting with and extracting sulfur from the underlying graphite and sulfide bearing sediments no magma flow channels have been identified so far and the lack of magma flow subsequent to the development of sulfide immiscibility is regarded as the reason why these deposits are not of economic grade when most major ni cu sulfide deposits are compared they prove to have a number of features in common olivine rich magma proximity to a major crustal fault sulfide bearing country rocks chalcophile element depletion in related intrusive or extrusive rocks field and or geochemical evidence of interaction between the magma and the country rocks and the presence of or proximity to a magma conduit the features are thought to explain the three key requirements sulfide immiscibilty adequate mixing between sulfides and magma and localisation of the sulfides discussed and have important implications with respect to exploration

a new scenario for related iocg and ni cu mineralization the relationship with giant mid crustal mafic sills variscan iberian massif both magmatic ni cu and hydrothermal iron oxide copper gold mineralization coexist in ancient belts but their relationship remains poorly known geochronology and field geology evidence show that in sw iberia both styles of mineralization were coeval with widespread metaluminous to peraluminous variscan magmatism 350 330 ma we propose that mineralization was probably related to a hidden large layered mafic ultramafic layered complex recently inferred from geophysics that was emplaced in a mid crustal decollement zone contamination of a primitive mantle derived magma with continental crust in the layered complex led to fractional crystallization accompanied by high t low p metamorphism and the incorporation of volatiles into the melt hot hypersaline co2 ch4 bearing brines were subsequently released and focused along major thrusts and strike slip faults to produce the iocg mineralization assimilation of continental crust also led to the formation of sulphide magmas that were tectonically injected high into the crust leading to the formation of pipe like breccia hosted ni cu ore bodies all these processes took probably place as a consequence of oblique ridge and or continent continent collision

seismic imaging and modelling of the lithosphere of sw iberia abstract data from a closely spaced wide angle transect has been used to study the middle to lower crust and the moho in sw iberia a low fold wide angle stack image reveals a highly heterogeneous seismic signature at lower crustal levels changing laterally along the profile the lower crust features an irregular distribution of the reflectivity that can be explained by a heterogeneous distribution of physical properties the moho discontinuity also features a high variability in its seismic character that correlates with the different tectonic terranes in the area a 2d finite difference code was used for solving the elastic wave equation and to provide synthetic wide angle shots relatively simple layer cake model derived from conventional refraction interpretation generates the main events of the shot records however these models cannot account for the lateral variability of the seismic signature in order to obtain more realistic simulations the velocity model was modified introducing stochastic lensing at different levels within the crust the moho was modelled as a 3 km thick layered structure the resulting average velocity models include a high velocity layer at mid crustal depth a highly reflective lower crust and a relatively thin horizontal moho this heterogeneous model can be achieved by lensing within the crust a layered mafic intrusion and a strongly laminated lower crust and moho

study of weathering processes developed on old piedmont surfaces in western spain new contributions to the interpretation of the rana profiles abstract the hercynian basement of the iberian peninsula was uplifted by the alpine orogeny during the tertiary it gave rise to a set of block mountains and tectonic grabens one of which is the ciudad rodrigo basin it is located in western spain and forms a westward extension of the great tertiary duero basin the sediments filling this graben are of continental origin their ages ranging from palaeogene to quaternary morphologically the southern part of this basin forms a set of piedmont surfaces the rana surfaces appearing above the terrace system of the present rivers this paper examines the weathering processes developed over these old piedmont surfaces using micromorphological xr diffraction scanning electron microscopy sem and microporosity techniques the rana sediments are rich in quartzite pebbles and gravel within a clayey matrix once deposited these materials underwent important in situ weathering processes under somewhat hydromorphic conditions of which hydrolysis ferrolysis and xerolysis were the most important all these processes gave rise to 1 transformation of most of the clasts of shists and slates into a matrix causing the destruction of the original sedimentary structures and a relative concentration of the resistant lithologies quartzites and quartz 2 important changes in the clay fraction leading to a predominance of kaolinite in the upper levels of the profiles 3 release of elements from primary minerals fe being one of the most important and 4 redistribution of matter mainly clay and fe oxyhydroxides within the profiles the coexistence of seasonal periods with pf higher than 4 2 repeated over a long time together with poor internal and external drainage conditions are the cause of the special features displayed by rana deposits

the aguablanca ni cu pge deposit sw spainossa morena zone lat 37 57 n long 6 11 w

geophysical evidence of a mantle derived intrusion in sw iberia 1 deep seismic reflection data acquired as part of the sw iberia europrobe project across the transpressional variscan orogen sample three tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone the seismic data reveal the existence of a mid crustal reflective body 140 km long and of variable thickness up to 5 km the iberian reflective body the conductivity image provided by coincident mt soundings the amplitude characteristics of the seismics mineralization studies related to magmatic ore deposits and the surface geology suggest that the irb is a mantle derived mafic intrusion the geophysical geological and petrological data suggest that the irb is most probably an early carboniferous approximately at 350 340 ma mantle derived intrusion possibly linked to plume activity that took place in europe in the carboniferous and permian

the effect of pedological conditions on the sources and sinks of silicon in the vertic planosols in south western ethiopia as a dynamic source and sink of elements the secondary si bearing solid phases in soil partly govern transfer of elements and pollutants terrestrial plants affect silicate mineral weathering and make si readily soluble through the formation of phytoliths a biogenic form of amorphous silica which return on topsoil through litterfall besides phytoliths other readily soluble si components such as pedogenic opal volcanic glass adsorbed si onto fe oxides and poorly crystalline aluminosilicates take part in the regulation of the si balance the aim of this paper is to assess the impact of pedological conditions on the sources of dissolved si and its dynamics in a vertic planosol characterized by contrasting bleached and vertic horizons the si containing readily soluble phases were quantified by specific extractions na2co3 sialk oxalate siox dcb sidcb and cacl2 sicacl2 performed on samples of the bleached and vertic horizons moreover amorphous silica asi from the soil including phytoliths and volcanic glass was extracted by gravimetric separation in the bleached horizon phytoliths are the main si bearing readily soluble phases of the silt sized fraction while si in the sand sized fraction is largely controlled by volcanic glass and feldspars the higher sicacl2 concentration and the significant increase of si al cacl2 ratios in soil solution of the vertic horizon attest for a marked difference in terms of si dynamics

behaviour of rare earth elements during hydrothermal alteration at the buena esperanza copper silver deposit northern chile abstract a study of the ree behaviour in alteration zones of the buena esperanza subvolcanic cu ag deposit located in the coastal range of northern chile reveals that the elements are mobile in the rocks during alteration the ore forming process developed in three different stages of alteration mineralization the hydrothermal alteration of the early and middle stages affected basaltic fragments of a breccia pipe la and ce were leached from the rock fragments located at the bottom and at the middle part of the breccia pipe and partly redeposited at the top during alteration sm eu and tb were released selectively and the heavy ree behaved as relatively immobile elements sericite is the most important alteration mineral for fixing the ree during this stage the incoming fluids had low ree contents the late stage of hydrothermal alteration happened simultaneously with the intrusion of a gabbroic volcanic neck affecting mainly these subvolcanic rocks ree patterns of samples from the top and bottom of the alteration zone exhibit roughly parallel trends but are systematically enriched in ree in comparison to unaltered samples this enrichment seems to be more intensive at the top of the altered area coinciding with the enrichment of rb k and cu in these rocks epidote plays the most important role for fixing this hydrothermal input of ree during the latest stage of alteration

weathering of permian sedimentary rocks and soil clay minerals transformations under subtropical climate southern brazil parana state abstract mineral evolution in weathering zones is usually a complex process mixed layered minerals mlms can form as a result of progressive weathering advancement promoting important geochemical changes in soils in this contribution four soil profiles located in parana state southern brazil and formed from different fine grained permian sedimentary rocks one siltstone two al rich shales and one organic black shale were characterized on mineralogical and geochemical bases general physico chemical morphological characterization xrd profile modeling of clay fractions geochemical mass balance and weathering index calculations were performed to relate clay minerals transformation with the geochemical transformations in soils mlms dominate clay mineral suite in progressive compositional ranges the three soils developed from al rich shales p1 p2 and p4 are dominated by several r0 k i kaolinite illite phases and exhibit a trend of progressive kaolinization towards surface soil horizons the soil developed from mg rich organic black shale p3 however has r0 i s illite smectite as the dominant phase and a progressive dominance of smectite in i s phase prevails towards surface these results suggest the prevalence of topotactic transformations solid state reactions during the transition of one clay into another as weathering advances in the three soils where kaolinization of k i phases prevails geochemical mass balance calculations indicate massive losses of sio2 al2o3 and alkalis in addition to high values for weathering indices conversely sio2 and mgo accumulate and values for weathering indices are lower in the p3 soil profile the agreement between the pathways of clay mineral transformations and the mass balance calculations and weathering indices suggests that transformations involving mlms drive geochemical transformation in soils the nature of clay suites in turn is highly dependent on the chemical compositions of fresh rocks which determine how transformations involving clays proceed

crustal structure of the transpressional variscan orogen of sw iberia sw iberia deep seismic reflection profile iberseis 1 iberseis a 303 km long 20 s deep seismic reflection profile was acquired across the variscan belt in sw iberian peninsula the acquisition parameters were designed to obtain a high resolution crustal scale image of this orogen the seismic profile samples three major tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone which were accreted in late paleozoic times these terranes show a distinctive seismic signature as do the sutures separating them late strike slip movements through crustal wedges are apparent in the seismic image and have strongly modified the geometry of sutures the upper crust appears to be decoupled from the lower crust all along the seismic line but some deformation has been accommodated at deeper levels a sill like structure is imaged in the middle crust as a 1 2 s thick and 175 km long high amplitude conspicuous reflective band it is interpreted as a great intrusion of mafic magma in a midcrustal decollement taking into account surface geological data and the revealed crustal architecture a tectonic evolution is proposed for sw iberia which includes transpressional collision interacting during early carboniferous with a mantle plume the moho can be identified along the entire transect as subhorizontal and located at 10 to 11 s indicating a 30 35 km average crustal thickness its seismic signature changes laterally being very reflective beneath the south portuguese zone and the central iberian zone but discontinuous and diffuse below the ossa morena zone

the mount kozak magmatic complex western anatolia abstract the mount kozak igneous complex is located close to the towns of ayvalik bergama and burhaniye in the western anatolia turkey magmatic activity occurred during the late oligocene early miocene beginning with the emplacement of the kozak pluton sheet intrusive rocks formed around it coevally they are surrounded by the volcanic rocks partly contemporaneously with the emplacement of the granitic rocks during the early miocene the upper oligocene lower miocene magmatic rocks of the kozak region are represented by a high k calc alkaline suite of predominantly intermediate and acidic composition their geochemical characteristics suggest that the magmas are hybrid and were formed from a similar source representing mantle derived magmas contaminated by crustal materials the cogenetic plutonic rocks the hypabyssal rocks and the overlying volcanic associations are related to one another in space and time and appear to have been connected to a shallow level granitic intrusion in a caldera collapse setting the calc alkaline magmatic activity waned during the middle miocene when the volcanism was rejuvenated during the late miocene pliocene alkaline basalt lavas were formed as fissure eruptions

mineralogy and genesis of planosols under a semi arid climate borborema plateau ne brazil abstract planosols such as those found on the borborema plateau ne brazil form an important class of moderately weathered soils that support subsistence agriculture in underdeveloped regions of africa asia and south america despite its socioeconomic importance the genesis of this soil class has not yet been fully elucidated this study was conducted with the aim of improving knowledge about the genesis of planosols under a semi arid climate three planosol profiles on the borborema plateau in ne brazil were collected classified and described morphologically and the main physical and chemical attributes the pedogenetic forms of iron oxides and the mineralogical compositions of the sand silt and clay fractions were determined the results indicate that a parent materials richer in feldspar and biotite favor the formation of planosols with a higher clay content b the dissolution of primary minerals and the formation of clay minerals known as the argillation process are fundamental for the genesis of bt horizons c depth drainage deficiency leads to hydromorphism an associated gray color and the formation of mottles and d monosialitization and bisialitization processes kaolinite formation and the formation of 2 1 clay minerals respectively prevail in planosols located within landscape positions that have good and poor drainage respectively in addition the present study shows that planosols under a semi arid climate can have a clay fraction consisting predominantly of kaolinite and mineralogical alteration pathways similar to those described in soils under an analogous climate and geology in northwest africa this refutes classical theories that soils with 2 1 clay minerals prevail in warmer and drier regions this study thus provides greater knowledge about the attributes of planosols in dry and poor regions and can be used as a reference in studies on the sustainable use and management of such soils

genesis morphology and mineralogy of planosols developed from different parent materials in southern brazil abstract the genesis of planosols is a complex process since it can involve multiple cycles of soil formation deposition of allochthonous materials and also past climate changes furthermore this subject is still poorly studied in the humid tropics thus hindering a proper appraisal of the potentials and limitations of planosols the objective of this research was to study pedogenetic processes and properties of planosols formed from different parent materials in southern brazil four soils were sampled p1 hypereutric luvic albic planosol developed on lagoon plain sediments p2 orthoeutric luvic albic planosol on holocene alluvial deposits p3 hypereutric luvic albic planosol on granite and p4 orthoeutric luvic albic planosol on gneiss all planosols presented sandy horizons a and e with low ph

magma generation and sulfide saturation of permian mafic ultramafic intrusions from the western part of the northern tianshan in nw china implications for ni cu mineralization compared to permian magmatic ni cu sulfide deposits in the eastern part of the northern tianshan such as huangshan and huangshandong those in the western part e g baixintan and lubei are poorly documented zircon id tims u pb age data 279 7 0 2 ma of lherzolite and la icpms u pb age data 277 8 3 4 ma of a hornblende gabbro suggest the lubei intrusion was emplaced in the early permian the baixintan and lubei mafic ultramafic intrusive rocks are characterized by enrichments of large ion lithophile elements and th and u relative to the high field strength elements as well as depletion of nb and ta relative to mid ocean ridge basalt the 87sr 86sr t 0 70354 0 70713 end t 2 80 to 7 05 and ehf t 2 50 18 4 values for the intrusions indicate that they have assimilated tianshan basement rocks whereas the se s ratios 181 10 6 418 10 6 and 34scdt values 0 13 to 0 90 of the sulfides suggest that crustal sulfur has not been incorporated into the magma the decrease in pd zr with increasing th nb pm indicates that sulfide saturation accompanied crustal contamination the olivine compositions and whole rock chalcophile elements of the baixintan and lubei intrusions imply that the parental magma of the intrusive rocks in the west contains higher chalcophile elements than those in the east which suggests that the mafic ultramafic intrusions in the western part of the northern tianshan should be regarded as favorable ni cu sulfide exploration targets

sulfide silicate textures in magmatic ni cu pge sulfide ore deposits massive semi massive and sulfide matrix breccia ores abstract much of the value of magmatic ni cu pge sulfide orebodies is contained within massive or semi massive ores that show a wide variety of textural relationships to included or adjacent silicate rocks we identify five mutually gradational textural types 1 pure inclusion free massive sulfide ores 2 sulfide matrix ore breccias of sharp wall soft wall or mixed character 3 emulsion textured ores formed by frozen mixtures of molten silicate and sulfide most commonly developed as melt films at thermal erosion contacts 4 vein hosted sulfides formed at late magmatic or high temperature post emplacement deformation stage close to the brittle ductile transition in the country rocks or host igneous bodies and 5 tectonic durchbewegung breccias formed by mechanical inter shearing of less ductile silicate inclusions and more ductile solid sulfides some deposits the moran shoot at kambalda being the type example record the invasion of country rock footwall by downward or sideways percolating superheated molten sulfide liquid generating vertical sequences of pure massive sulfide emulsion textured ores and finely spaced invasive sulfide veins these are referred to as sulfide melting infiltration fronts and may provide a clue to the mechanism of formation of sulfide rich magmatic ores as whole sulfide matrix ore breccias are particularly well developed in the voisey s bay and aguablanca deposits where they developed by flooding of percolating sulfide melt through the silicate matrix of magmatic intrusion breccias displacing silicate melt the lithology of the silicate or carbonate rock inclusions determines the nature of the inclusion matrix relationships non refractory inclusions typically disaggregate along original grain boundaries to leave coherent inclusions surrounded by clouds of inclusion derived or matrix derived crystals with the low melting silicate component preferentially displaced by sulfide liquid whereas refractory inclusions retain sharp boundaries zonation of inclusions and overgrowths preserves reaction between inclusion and silicate matrix that pre dates invasion of the intrusion breccia by sulfide liquid the process of percolation of dense low viscosity sulfide liquid into pore space and fractures within partially molten or melting silicate rock is a unifying theme that links sulfide matrix ore breccias and emulsion textured ores with distinctive textures in less sulfide rich rocks such as net texture matrix ore texture leopard texture poikilitic net texture and interspinifex ore vein hosted massive sulfides may be emplaced under magmatic conditions where the excess pressure of the sulfide liquid column drives or enhances fracturing of the country rock and injection of sulfide into the cracks such veins are commonly referred to as remobilised a term which may obscure process understanding and should be reserved for cases where tectonic solid state mobilisation of sulfide can be demonstrated on textural and structural grounds the tendency of sulfide liquids to invade country rocks and potentially to drive the propagation of their own magmatic containers may be a critical feedback loop in the development of magmatic sulfide mineral systems

4 transpressional tectonics lower crust decoupling and intrusion of deep mafic sills a model for the unusual metallogenesis of sw iberia abstract sw iberia is interpreted as an accretionary magmatic belt resulting from the collision between the south portuguese zone and the autochthonous iberian terrane in variscan times 350 to 330 ma in the south portuguese zone pull apart basins were filled with a thick sequence of siliciclastic sediments and bimodal volcanic rocks that host the giant massive sulphides of the iberian pyrite belt massive sulphides precipitated in highly efficient geochemical traps where metal rich but sulphur depleted fluids of dominant basinal derivation mixed with sulphide rich modified seawater massive sulphides formed either in porous reactive volcanic rocks by sub seafloor replacement or in dark shale by replacement of mud or by exhalation within confined basins with high biogenic activity crustal thinning and magma intrusion were responsible for thermal maturation and dehydration of sedimentary rocks while magmatic fluids probably had a minor influence on the observed geochemical signatures the ossa morena zone was a coeval calc alkaline magmatic arc it was the site for unusual mineralization particularly magmatic ni cu and hydrothermal fe oxide cu au ores iocg most magmatism and mineralization took place at local extensional zones along first order strike slip faults and thrusts the source of magmas and iocg and ni cu deposits probably lay in a large mafic ultramafic layered complex intruded along a detachment at the boundary between the upper and lower crust here juvenile melts extensively interacted with low grade metamorphic rocks inducing widespread anatexis magma contamination and further exsolution of hydrothermal fluids hypersaline fluids 18 o fluid 5 4 to 12 were focused upward into thrusts and faults leading to early magnetite mineralization associated with a high temperature 500 c albite actinolite salite alteration and subsequent copper gold bearing vein mineralization at somewhat lower temperatures assimilation of sediments by magmas led in turn to the formation of immiscible sulphide and silicate melts that accumulated in the footwall of the layered igneous complex further injection of both basic and sulphide rich magmas into the upper crust led to the formation of ni cu rich breccia pipes younger 330 to 280 ma peraluminous granitoids probably reflect the slow ascent of relatively dry and viscous magmas formed by contact anatexis these granitoids have w sn and pb zn related mineralization that also shows geochemical evidence of major mantle crust interaction late epithermal hg cu sb and pb zn ag mineralization was driven by convective hydrothermal cells resulting from the high geothermal gradients that were set up in the zone by intrusion of the layered igneous complex in all cases most of the sulphur seems to have been derived from leaching of the host sedimentary rocks 34 s 7 to 20 with only limited mixing with sulphur of magmatic derivation the metallogenic characteristics of the two terranes are quite different in the ossa morena zone juvenile magmatism played a major role as the source of metals and controlled the styles of mineralization in the south portuguese zone magmas only acted as heat sources but seem to have had no major influence as sources of metals and fluids which are dominated by crustal signatures most of the magmatic and tectonic features related to the variscan subduction and collision seem to be masked by those resulting from transpressional deformation and deep mafic intrusion which led to the development of a metallogenic belt with little resemblance to other accretionary magmatic arcs

crystallographic preferred orientations and microstructure of a variscan marble mylonite in the ossa morena zone sw iberia the mylonitic marbles of the cherneca shear zone a variscan sinistral strike slip structure developed in the ossa morena zone sw iberia related to the emplacement of the santa olalla igneous complex were studied in detail different mylonites from protomylonites to ultramylonites were analyzed by electron back scattering diffraction ebsd in order to determine the crystallographic preferred orientation cpo of calcite the cpos show very good agreement with experimental torsion work giving suitable interpretations of the operative slip systems and strain quantifications thus the obtained natural cpos validate the experimental approaches a wide range of observed textures and microstructures are mainly controlled by the amount of shear strain the presence of secondary phases and the development of antithetic subsidiary shears the effect of secondary phases and the nucleation of antithetic shear bands on texture development are discussed

low sulfidation type au ag mineralization at bergama izmir turkey abstract bergama the center of bergama county is located in western turkey and includes the villages of ovacik narlica and saganci the ovacik epithermal gold silver deposit is located in the western anatolian volcanic and extensional province adjacent to the ene trending bergama graben some 100 km north of the city of izmir gold of economic grades at the ovacik deposit reserves 4 19 mt at 7 6 g t occurs in epithermal quartz veins which display low temperature epithermal textures including crustiform banding quartz pseudomorphs after bladed calcite and multiphase hydrothermal breccias alteration minerals at both ovacik and narlica are dominated by smectite mixed layer illite smectite chalcedonic quartz and adularia whereas major kaolinite and minor mixed layer smectite illite 13 4 a occur at saganci the total sulfide content at ovacik is low geochemical variations in altered wall rocks at ovacik and narlica are generally characterized by two fold enrichments in k rb cs and 25 to 93 depletions in sr ca mg na and even higher depletions 96 to 99 decrease in the quartz adularia vein zone lanthanum ce pr hf zr sm eu gd tb and ho also exhibit up to 50 depletions in the wall rock and even more so up to 90 depletion for la and nd in the vein structure wall rock enrichment in au ag as hg and sc is by factors of 60 150 88 8 and 3 respectively the ranges of ree in both the altered volcanic rocks and quartz adularia veins are wide and may reflect either significant mobilization of ree during alteration and mineralization or their dilution by the metasomatic processes from fresh volcanic rocks through montmorillonite illite adularia altered wallrock to quartz adularia veins high rb sr ratios in adularia illite altered areas are closely related to the presence of k rich alteration minerals low rb sr ratios and corresponding low k values at saganci are due to acid leaching of volcanic rocks positive correlation coefficients between au and ag pb zn cd cu and sb in epithermal quartz veins all of which are 0 51 are significant silver and sb are remarkably enriched at higher levels of the deposit no correlation occurs between au and as or ag and as the ovacik quartz in au ag bearing veins has 18o values ranging from 9 5 to 15 7 whereas d values of fluid inclusions in quartz range from 89 to 125 however the narlica quartz in au ag bearing veins returned 18o values ranging from 5 9 to 8 3 whereas the d values of fluid inclusion in quartz range from 82 to 99 18o results indicate that ore forming hydrothermal fluids at ovacik and narlica had 18oh2o values ranging from 2 9 to 3 5 average 0 24 and from 2 96 to 0 6 average 1 6 respectively they are thus 18o enriched in comparison with present day meteoric and hydrothermal meteoric waters 5 4 18o 18oh2o and d values suggest that mineralizing solutions were a mixture of meteoric and magmatic waters the 34s sulfide data at ovacik and narlica range from 2 1 to 5 3 average 1 7 and from 4 6 to 2 7 average 0 36 respectively these 34s sulfide values are consistent with a magmatic source for s

u pb age constraints on variscan magmatism and ni cu pge metallogeny in the ossa morena zone sw iberia new u pb zircon ages from the santa olalla igneous complex have been obtained which improve the knowledge of the precise timing of variscan magmatism in the ossa morena zone sw iberia this complex has a special relevance as it hosts the most important ni cu platinum group element pge mineralization in europe the aguablanca deposit u pb zircon ages have been obtained for seven samples belonging to the santa olalla igneous complex and spatially related granites with the exception of the cala granite 352 4 ma which represents an older intrusion the bulk of samples yield ages that cluster around 340 3 ma the santa olalla tonalite 341 5 3 ma the sultana hornblende tonalite 341 3 ma a mingling area at the contact between the aguablanca and santa olalla stocks 341 1 5 ma the garrote granite 339 3 ma the teuler granite 338 2 ma and dioritic dykes from the aguablanca stock 338 6 0 8 ma the bodonal cala porphyry which has also been dated 530 3 ma comprises a group of sub volcanic rhyolitic intrusions belonging to the bodonal cala volcano sedimentary complex which hosts the igneous rocks the knowledge that emplacement of the aguablanca deposit was related to episodic transtensional tectonic stages during the variscan orogeny will be fundamental in future mineral exploration in the ossa morena zone

unraveling complex 2 μm clay mineralogy from soils using x ray diffraction profile modeling on particle size sub fractions implications for soil pedogenesis and reactivity a specific methodology was developed to refine the complex clay mineralogy commonly encountered in soil environments the soil examined was a cambisol developed into a ferralitic paleosol the sample was split into four sub fractions of different particle sizes 0 05 0 05 0 1 0 1 0 2 and 0 2 2 mu m and their respective mass contributions to the overall 2 mu m clay fraction were determined for each sub fraction x ray diffraction xrd patterns were modeled using a trial and error approach based on the direct comparison of experimental and calculated profiles quantitative information derived from the fitting procedure for the different sub fractions allowed for the determination of the complex mineralogy of the 2 mu m clay fraction through the identification and quantification of eight clay phases the results show that the finest and most reactive clay fraction 0 05 pm was totally hidden in the xrd pattern of the 2 mu m fraction the fraction commonly considered in soil mineralogical analyses similarly this procedure revealed the presence of illite smectite chlorite and kaolinite illite mixed layer minerals seldom described in soil literature using classical methods the use of this methodology improved our understanding of the pedogenesis of this soil through the identification and quantification of clay phases structural properties the analysis of the evolution of structural parameters with particle size allowed for the detection of local modifications in the interlayer composition of expandable and hydroxy interlayered vermiculite layers following this approach key information can be derived to determine subtle changes in clay mineralogical composition that are related to microorganism and or plant activity

soil properties and their variations on two contiguous hillslopes in northeast brazil abstract information on spatial distribution of soil properties in a landscape is not only required for soil mapping and classification but also for soil management spatial patterns of soil properties in a landscape are the results of systematic variations in pedogenic processes controlled by environmental factors of which landscape position is important in northeast brazil lithosols ustorthents whose surface horizons are directly underlain by lithic or paralithic contacts occupy upper slope positions with steep gradient the cambisols ustropepts occupy the mid and lower slope positions in some cases non calcic brown soils planosol haplustalfs occupy lower slopes we examined the properties of two contiguous hillslopes in granitic and gneissic saprolite to determine whether there were any systematic variations among landscape positions and to interpret pedogenesis in the hillslopes particle size distribution and the ti content of sand plus silt and saprolite showed that the two hillslopes were formed on different parent materials at site 1 soil property variations along the slope measured by standard deviation from the means were attributed to variability in parent material rather than to landscape position except for solum thickness which increased systematically downslope variations in sand clay ecec and ph were not related to landscape position increasing solum thickness downslope was explained by the effect of erosion on the upper and deposition at the lower slopes silt and organic carbon contents at site 1 and feo and fed contents at site 2 significantly decreased downslope one possible explanation for this trend in addition to erosion and deposition is the effect of slash and burn agriculture on the lower slopes and the changes in redox conditions caused by periodic waterlogging

erratum to a new style of ni cu mineralization related to magmatic breccia pipes in a transpressional magmatic arc aguablanca spain the aguablanca deposit represents a new style of magmatic ni cu mineralization in discordant sulfide rich pyroxenitic breccia pipes the orebody is hosted by variscan calc alkaline diorites and gabbros which intruded during an oblique subduction collision event transpressional transtensional left lateral structures facilitated the intrusion of primitive magmas to shallow depths in the crust a two stage genetic model is proposed in the first stage a transitional deep magma chamber formed the primitive magma interacted at depth with wall rocks resulting in extensive crustal contamination concomitant sulfide magma immiscibility and settling of orthopyroxene clinopyroxene and sulfide rich cumulates to form a layered magmatic complex geochemical and mineralogical evidence including the virtual disappearance of olivine heavy 34s values 7 4 distinctive nd sr and pb signatures high au contents and the presence of spinel and graphite indicate a major interaction with the upper crust probably with pyrite rich carbonaceous slates of late proterozoic age the second stage was related with the emplacement of residual calc alkaline gabbroic to noritic melts and the development of an intrusive breccia containing fragments of the consolidated layered complex rocks and associated disseminated to massive sulfides

the alkaline porphyry associated yao an gold deposit yunnan china rare earth element and stable isotope evidence for magmatic hydrothermal ore formation the yao an vein type gold deposit is located in the ailaoshan jinshajiang alkaline intrusive belt yunnan province china and is associated both in time and space with 33 5 1 0 ma old alkaline intrusions the gold mineralization is associated with potassic wall rock alteration the ree distribution patterns of secondary k feldspar are generally similar to those of the igneous perthite but with about seven times higher total ree abundances the alteration is ascribed to a high ree magmatic fluid derived from the yao an alkaline intrusive suite the hydrothermal yao an gold deposit formed during two gold bearing stages i e a sulfide pyrite stage and a sulfide oxide stage pyrite specularite the ree abundance of early stage i pyrite is relatively high with strong enrichment in lree la yb n of 40 290 generally positive eu anomalies eu eu 0 86 1 55 and ree patterns very similar to those of secondary feldspar in contrast the later stage ii pyrite has much lower ree concentrations and lower la yb n of 5 5 11 8 eu eu of 0 49 0 76 and flat chondrite normalized spidergram patterns the stage i pyrite has 34s in the range of 2 2 to 3 2 and overlaps with regionally distributed pyrite in least altered syenite porphyry in contrast stage ii pyrite has much higher 34s values between 7 8 and 16 5 carbon isotope data for four samples from stage ii revealed 13c pdb values between 6 and 8 these stable isotope and ree data suggest that magmatic fluids of the alkaline intrusions caused both potassic alteration and stage i sulfide mineralization the system evolved from stage i to stage ii mineralization by influx of meteoric fluids with relatively heavier sulfur although calcite carbon isotope data suggest that the co2 remained dominantly of magmatic origin

hydrothermal alteration and hydrologic evolution of the golden cross epithermal au ag deposit new zealand golden cross located in the coromandel peninsula new zealand is a classic example of a volcanic rock hosted low sulfidation epithermal gold silver deposit gold and silver ore is confined to the empire vein system and shallow level stockwork the veins are hosted by miocene to early pliocene andesites and dacites of the waipupu formation and the waiharakeke dacite that are unconformably overlain by the postore whakamoehau andesite hydrothermal alteration minerals display distinct spatial and temporal zonation around veins as defined along three cross sections 1 000 m long 450 m deep located 200 m apart which transect the empire vein system along these sections replacement quartz chlorite and pyrite are ubiquitous with the abundance of quartz veinlets increasing toward major veins replacement adularia envelops the empire vein system and shallow stockwork in each section it is coextensive with and is variably replaced by illite that progressively grades upward and laterally into a zone of interstratified illite smectite that mantles the deposit replacement calcite and minor siderite formed contemporaneously with and also overprint the above minerals whereas late barren calcite veins crosscut mineralized quartz veins kaolinite pyrite veinlets together with rare very local alunite formed during late stage hydrothermal activity clay mineral zonation is well developed illite occurs at depth and close to the veins grading outward and upward into illite smectite with minor smectite occurring 600 m east of the empire vein system this overall zonation reflects paleothermal gradients of 150 c on the periphery to 220 c near the veins consistent with the observed t h range of 150 to 240 c for fluid inclusions in quartz platy calcite and late barren calcite veins final ice melting temperatures for inclusions mostly range from 0 0 to 1 4 c corresponding to apparent salinities of less than 2 4 wt percent nacl equiv ice melting temperatures combined with vapor bubble expansion on crushing indicate the presence of dissolved co 2 in some platy calcite and late stage barren calcite the co 2 content is estimated to range from 0 35 to 3 5 wt percent with the lower limit set by fluid inclusion vapor expansion during crushing and the upper limit by the absence of any observable clathrates depth estimates based on inclusions in platy calcite suggest that the shallow level stockwork zone formed about 100 m below the paleowater table under hydrostatic conditions veins and alteration minerals at golden cross formed in the shallow part 400 m of a hydrothermal system analogous to geothermal systems in the nearby taupo volcanic zone the assemblage of quartz adularia chlorite illite calcite and pyrite reflects the upflow of near neutral ph to weakly alkaline chloride waters contemporaneously steam heated co 2 rich waters formed on the margins and reacted with the wall rock to form the assemblage of calcite siderite smectite illite smectite and kaolinite eventual thermal collapse and invasion of these peripheral co 2 rich waters into the former upflow zone produced late stage barren calcite veins and an overprint of clay carbonate alteration minerals at the same time localized steam heated acid sulfate waters generated above the water table descended to form the late overprint of kaolinite pyrite and alunite

the evolution of troctolitic and high al basaltic magmas in proterozoic anorthosite plutonic suites and implications for the voisey s bay massive ni cu sulfide deposit the voisey s bay massive ni cu sulfide deposit is contained within troctolitic plagioclase olivine intrusions of the 1 34 to 1 29 ga nain plutonic suite coastal labrador canada and represents a new setting for magmatic sulfide deposits proterozoic anorthosite plutonic suites consist of vast quantities as much as 20 000 km 2 of cumulate anorthosite leucotroctolite leuconorite intrusions of troctolite and fe enriched dioritic rocks and large granitic batholiths crystallization ages span nearly 1 200 m y within the middle proterozoic 2 12 0 92 ga many proterozoic anorthosite plutonic suites were emplaced into relatively young proterozoic crust and some were intruded along archean proterozoic boundaries e g nain labrador laramie wyoming korosten ukraine nearly all of the largest plutonic suites contain significant areas thousands of km 2 of plagioclase rich cumulate rocks that are olivine bearing olivine anorthosite leucotroctolite troctolitic rocks 20 30 modal olivine occur in proterozoic anorthosite plutonic suites principally as cumulates in layered or massive intrusions e g kiglapait hettasch jonathon nain intruded into anorthositic rocks with the notable exception of the voisey s bay deposit nearly all troctolitic rocks crystallized late in the evolution of individual plutonic suites many of the troctolitic intrusions have fine grained olivine rich marginal rocks that closely represent parental magma compositions numerous fine grained olivine normative dikes with high al basaltic compositions also occur within many plutonic suites nain harp lake laramie adirondack and share compositional characteristics with the troctolitic magmas these olivine normative high al basaltic magmas record the least evolved compositions in proterozoic anorthosite plutonic suites mg 0 43 0 64 an 45 60 have high al 2o 3 15 19 wt and feo total 9 15 wt contents and typically show the least contaminated sr and nd isotope compositions in a given plutonic suite many dikes and marginal rocks have strong positive eu anomalies a feature of the melt composition that is not related to plagioclase accumulation except at laramie the least evolved troctolitic magmas appear to have about 8 wt percent mgo and corresponding ni and s concentrations between 100 to 150 ppm and 0 02 to 0 05 wt percent respectively based on closed system fractionation in the kiglapait intrusion sulfide saturation occurs late in the crystallization history of troctolitic magmas after ni concentrations have been severely depleted by protracted olivine fractionation the optimal conditions for formation of a ni cu sulfide deposit associated with a proterozoic anorthosite plutonic suite require a relatively high mgo parental magma that has not crystallized much prior olivine and an external source of s to promote early sulfide saturation probably through desulfurization reactions as hot troctolitic magmas ascend through the crust an economically important massive ni cu sulfide deposit on the scale of voisey s bay clearly requires large volumes of magma probably involving continuous replenishment of relatively ni rich unfractionated parental magma in staging chambers or mixing between magmas in conduits during ascent a model for the formation of troctolite associated massive ni cu sulfide deposits is proposed depending on the relative degrees of sulfide saturation and fractionation of the mixed magmas mixing between troctolitic magmas in a conduit or magma chamber may either poison the system stopping sulfide segregation or enhance sulfide segregation

acadian synorogenic mafic intrusions in the maine appalachians two belts of syn acadian mafic intrusions the central maine belt is progressively more altered and metamorphosed toward the southwest at the northeast end the moxie pluton represents the least altered and most important example in the belt forsterite contents of the most primitive olivines are consistent with the derivation of the earliest magma from a largely unfractionated mantle melt the coastal maine belt is spatially associated with the siluro devonian coastal volcanics the age difference however between the volcanics and plutonics suggests that they may not be directly related the important pocomoonshine gabbro appears to represent the well layered roof zone of a major fractionated body mineral compositions are similar to those in the moxie pluton and suggest a similar primary magma intrusions in both belts have complex contacts pronounced contact aureoles and were all deformed by late acadian deformation modified journal abstract

re os sm nd and pb isotopic constraints on mantle and crustal contributions to magmatic sulfide mineralization in the duluth complex abstract previous petrologic and stable isotopic studies of sulfide mineralization in the duluth complex have led to the premise that sulfide genesis is strongly linked to the interaction between mantle derived magmas and sedimentary country rocks in a rift zone environment in order to more fully evaluate the nature of this interaction and to gain an insight into the possible importance of externally derived metals in the ore forming process pb sm nd and re os isotopic studies of the babbitt cu ni deposit were initiated rock types examined include low sulfide troctolite that show very little petrologic evidence for contamination disseminated sulfide bearing troctolitic to gabbroic rocks that occur close to the basal contact with country rocks and contain metasedimentary xenoliths and massive sulfide lead isotopic values of whole rocks plagioclase mineral separates and massive sulfides show only subtle differences and are compatible with 3 to 5 contamination of a mantle derived melt with a proterozoic crustal contaminant e nd 1 1 ga values of the troctolite and gabbro samples are chondritic and only the massive sulfides show strong evidence for contamination based on sm nd isotopic values massive sulfides tend to be more sensitive indicators of contamination in the sm nd system because of late stage incorporation of a light rare earth element rich fluid into a ca po 4 apatite component of the immiscible sulfide liquid os 1 1 ga values are also strongly anomalous and range from 500 to 1200 in disseminated sulfide bearing troctolites and massive sulfides these values are also consistent with from 1 to 3 contamination by c rich and strongly radiogenic proterozoic sedimentary rocks elemental and isotopic mass balance calculations suggest that up to 50 of the pb and at least 35 of the os in the sulfide mineralization have been derived from external sources a corollary is that other metals may also be in part derived from external sources which would aid in explaining the compositional diversity of the sulfide mineralization selective assimilation of country rocks by mantle derived magmas may occur in crustal staging chambers during ascent to shallower levels or in situ as a result of devolatilization reactions and partial melting

investigation of clay mineralogy in a temperate acidic soil of a forest using x ray diffraction profile modeling beyond the his and hiv description abstract the crystal structures as well as the amount of hydroxy interlayered clay minerals resulting from the al hydroxylation process in temperate acidic soil developed in a forest were studied by modeling experimental x ray diffraction xrd patterns the

magma emplacement in transpression the santa olalla igneous complex ossa morena zone sw iberia the santa olalla igneous complex a late variscan group of intrusions located in the ossa morena zone sw iberia has been the focus of a gravity and structural study the structure outlined by the foliation map is complex showing two different structural domains one characterized by vertical and the other by horizontal magmatic foliations the vertical fabrics are restricted to the ne half of the complex which is in direct contact with a variscan sinistral strike slip fault cherneca fault whereas the horizontal fabrics are developed in the sw half of the complex which is characterized by a horizontal tabular geometry gravity modeling indicates that the deeper floor of the plutons is closely related to the ne margin and the cherneca fault an emplacement and structural evolution model for this igneous complex is proposed following these structural and gravity results 1 magma ascent was favored by releasing bends in the trace of the cherneca fault 2 when magma reached the present level it intruded to the sw with a horizontal sheet geometry generating the subhorizontal foliation domain 3 after emplacement the ne half of the complex suffered the external tectonic stress field provoked by sinistral motion along the cherneca fault subsequently generating the subvertical magmatic foliation domain

the evolution of the waiotapu geothermal system new zealand based on the chemical and isotopic composition of its fluids minerals and rocks abstract the waiotapu geothermal system is hosted by silicic rocks of the taupo volcanic zone new zealand exploration drilling in the late 1950s down to 1100 m provided physical information on the system measured temperatures show a boiling profile to 295 c with shallow inversions particularly in the north total discharge fluid samples were collected the geothermometry and measured temperatures show that fluids derive mainly from a shallow 400 m deep reservoir at about 225 c petrologic study of drillcore samples recovered from seven wells reveals an alteration assemblage of quartz and albite adularia with a variable distribution of chlorite pyrite calcite zeolites epidote pyrrhotite sphene leucoxene apatite and minor base metal sulfides white mica is a late overprint particularly well developed at shallow depths surficial alteration of kaolin cristobalite alunite and smectite clays reflect alteration by acid sulfate steam heated waters the activities of components in minerals determined from microprobe analyses and composition activity relations and fluids speciated to reservoir conditions indicate equilibrium now exists between the fluids and white mica the na k ratio of the fluid is being controlled by dissolution of albite and adularia while its h 2 h 2 s ratio is buffered by pyrite replacing pyrrhotite the fluids are now slightly undersaturated with respect to calcite the present deep fluids boil adiabatically from at least 300 c to 230 c at depths of 500 m this ascending chloride fluid is variably diluted by a steam heated water of zero chloride that lies over and occurs on the margin of the system like a discontinuous umbrella the steam heated water is relatively co2 rich 0 1 m the cooling at shallow levels by this mixing has shifted the alteration from albite adularia stability to white mica stability this shift is enhanced by the co2 rich nature of the diluent dilution of ascending chloride fluids by shallow waters is also supported by the oxygen and hydrogen isotopic composition of the mixture with the deep fluid being enriched in 18o and d from local meteoric by 7 and 10 respectively the patterns in whole rock 18o indicate that they were largely shifted in isotopic composition prior to incursion of steam heated waters possibly induced by a series of hydrothermal eruptions 900 years ago in contrast the 18o composition of late vug calcite indicates its formation is related to the initial incursion of steam heated groundwater and subsequent cooling this is supported by fluid inclusion evidence the d shift from local groundwater composition and the 13c composition of co2 determined from calcite 4 to 6 may be evidence for a magmatic input to the meteoric convection cell the shallow portion of the waiotapu geothermal system has recently evolved both chemically and physically by incursion of fluids from a steam heated carapace continued refluxing of these relatively cool hybrid fluids progressively deeper with their recycled co2 content will hasten hydrolytic leaching in contrast to a single pass of adiabatically cooling deep fluids this action accompanied by argillic alteration may eventually seal the deeper portions of the system hastening its demise there is evidence for similar events occurring in the fossil environment at epithermal depths

textural development in sulfide matrix ore breccias in the aguablanca ni cu deposit spain revealed by x ray fluorescence microscopy abstract the intrusion hosted ni cu sulfide deposit at aguablanca in south western spain contains a high proportion of ores in the form of sulfide matrix ore breccias these are polymict comprising autoliths and xenoliths in sulfide rich and or sulfide poor matrices inclusion lithologies include calc silicate skarn rocks from the adjacent marbles ultramafic and mafic cumulates and remelted and recrystallized mafic rocks containing spinifex like textures breccia textures have been investigated at mm to cm scale using desk top and synchrotron based microbeam xrf mapping which reveal a number of distinctive common features disaggregation of inclusions into adjacent sulfide along original silicate grain boundaries complex reverse and oscillatory zoning in cr content of clinopyroxene grains within sulfide and inside inclusions narrow reaction rims between country rock clasts and enclosing silicates and preferential disposition of pyroxene crystals within pyrrhotite pentlandite aggregates original mss relative to inclusion poor chalcopyrite the observed range of textures is explained by a model of percolation of molten sulfide through a pre existing silicate matrix intrusion breccia preferentially displacing a cotectic or eutectic plagioclase pyroxene melt the process is analogous to that believed to have formed interspinifex ore in komatiite hosted deposits and also to that responsible for superficially similar sulfide matrix ore breccias at voisey s bay the preserved range of textures is interpreted as being due to late stage gravity driven percolation of sulfide liquid from above into a pre existing partially molten intrusion breccia this intrusion breccia itself may have been emplaced into the neck of the aguablanca stock in the waning stages of magma flow

sequential mineral transformation from kaolinite to fe illite in two brazilian mangrove soils abstract mangrove soils have peculiar chemical and physical conditions generated by the variable water salinity cyclic tidal changes and intense biological activity that produce complex clay suites in this study the crystal chemical characteristics of clay minerals from two mangrove soils were investigated in detail to further our understanding of the processes taking place the two brazilian mangroves are from zones of contrasting climatic type and continental sediment character 1 tropical wet climate area receiving highly weathered sediments braganca para state and 2 mild semiarid climate area supplied with a mixture of highly and moderately weathered sediments acarau ceara state the investigation of the 2 0 2 m and 4 ions abundant in the interstitial water superior fe rich illite contents in acarau mangrove compared to braganca mangrove are explained by high inputs of 2 1 clays from sediment source areas inland the above clay mineral reactions shed light on the role of clays and the interaction between minerals and biotic components in mangrove soils in addition these reactions may influence the cycle of major elements in coastal ecosystem surrounding mangroves

origin and emplacement of the aguablanca magmatic ni cu pge sulfide deposit sw iberia a multidisciplinary approach a model is proposed for the origin and emplacement of the ca 341 ma aguablanca magmatic ni cu platinum group element pge sulfi de deposit sw iberia integrating petrological geochemical structural and geophysical data the aguablanca deposit occurs in an unusual geodynamic context for this ore type an active plate margin as an exotic magmatic subvertical breccia located at the northern part of the coeval gabbronorite aguablanca stock 341 1 5 ma structural and gravity data show that mineralized breccia occurs inside the inferred feeder zone for the stock adjacent to the cherneca ductile shear zone a variscan sinistral transpressional structure the orientation of the feeder zone corresponds to that expected for tensional fractures formed within the strain fi eld of the adjacent cherneca ductile shear two distinctive stages are established for the origin and emplacement of the deposit 1 initially the ore forming processes are attributed to magma emplacement in the crust assimilation of crustal s and segregation and gravitational settling of sulfi de melt a scenario similar to most plutonic ni cu sulfi de ores and 2 fi nal emplacement of the ni cu sulfi de bearing rocks by multiple melt injections controlled by successive opening events of tensional fractures related to the cherneca ductile shear zone

geochemistry of the kalatongke ni cu pge sulfide deposit nw china implications for the formation of magmatic sulfide mineralization in a postcollisional environment the kalatongke also spelt as karatungk ni cu platinum group element pge sulfide deposit containing 33 mt sulfide ore with a grade of 0 8 wt ni and 1 3 wt cu is located in the eastern junggar terrane northern xinjiang nw china the largest sulfide ore body which occupies more than 50 vol of the intrusion y1 is dominantly comprised of disseminated sulfide with a massive sulfide inner zone economic disseminated sulfides also occur at the base of the intrusions y2 and y3 the main host rock types are norite in the lower part and diorite in the upper part of each intrusion enrichment in large ion lithophile elements and depletion in heavy rare earth elements relative to mid ocean ridge basalt indicate that the mafic intrusions were produced from magmas derived from a metasomatized garnet lherzolite mantle the average grades of the disseminated ores are 0 6 wt ni and 1 1 wt cu whereas those of the massive ores are 2 wt ni and 8 wt cu the pge contents of the disseminated ores 14 69 ppb pt and 78 162 ppb pd are lower than those of the massive ores 120 505 ppb pt and 30 827 ppb pd however on the basis of 100 sulfide pge contents of the massive sulfides are lower than those of the disseminated sulfides very high cu pd ratios 4 5 104 indicate that the kalatongke sulfides segregated from pge depleted magma produced by prior sulfide saturation and separation a negative correlation between the cu pd ratio and the pd content in 100 sulfide indicates that the pge content of the sulfide is controlled by both the pge concentrations in the parental silicate magma and the ratio of the amount of silicate to sulfide magma the negative correlations between ir and pd indicate that the massive sulfides experienced fractionation

polymineralic orientation analysis of magmatic rocks using electron back scatter diffraction implications for igneous fabric origin and evolution abstract electron back scatter diffraction ebsd which provides an easy way of acquiring large numbers of individual crystallographic orientation data from different phases has been applied to the study of magmatic fabrics using this technique the crystallographic preferred orientation cpo of plagioclase biotite orthopyroxene hornblende and quartz in natural tonalites and quartzdiorites from the santa olalla igneous complex sw iberia deformed during the magmatic stage have been determined plagioclase is the coarser phase defining the main fabric in each sample whereas biotite can display either the same fabric as plagioclase or a completely different one the differences between these two phases occur because 1 smaller phases interact with the larger ones to produce more random orientations 2 under simple shear finer phases can completely rotate giving a girdle included in the xz plane 3 finer phases can more easily preserve relict fabrics while the coarser phases are completely reoriented by the last stress tensor the last phases to crystallize show weak to completely random cpos hornblende or completely random distributions quartz the study was completed with a shape preferred orientation analysis using the intercept method in order to detect weak magmatic lineations and numerical modelling simulations of theoretically equivalent simple shear situations for each sample

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

metamorphic degassing of carbonates in the contact aureole of the aguablanca cu ni pge deposit spain analysis of magmatic and sedimentary rocks of several large igneous provinces has demonstrated that the release of gas during plutonic metamorphic processes may be linked to global climate change and mass extinctions aguablanca one of the largest cu ni pge deposits in europe formed during the variscan orogeny when a mafic magma intruded limestones and shales creating a contact aureole composed of marble skarn and hornfels our petrological and geochemical investigation of the aureole provides evidence that a combination of the two processes led to the formation of the ore deposit the assimilation of terrigenous sediments supplied s to the magma while the assimilation of carbonates changed the oxygen fugacity and decreased the solubility of sulfur in the magma the metamorphic assemblages in the contact aureole are directly related to heterogeneity of the protolith and particularly to the original proportions of calcite and clay we modeled carbon dioxide degassing during contact metamorphism and showed that pure limestone is relatively unproductive because of its high reaction temperature the presence of clay however leads to the formation of calc silicates and significantly enhances co2 degassing our estimations suggest that degassing of the aguablanca contact aureole released about 74 8 mt of co2 a relatively low volume that we attribute to the composition of the host rock mainly a pure limestone a far larger volume of carbon dioxide was emitted by the contact metamorphism of dolostones in the contact aureole of panzhihua part of emeishan large igneous province sw china we propose that the level of emission of carbon dioxide depends strongly on the nature of the protolith and has to be considered when predicting environmental impact during the emplacement of large igneous provinces

3d gravity modelling of the aguablanca stock tectonic control and emplacement of a variscan gabbronorite bearing a ni cu pge ore sw iberia the aguablanca stock is a variscan mafic pluton located in the ossa morena zone southern iberian massif hosting an unusual ni cu pge mineralization associated with magmatic breccia pipes which intruded its northern part the emplacement of the aguablanca stock and the mineralized breccia pipes are related to the activity of the cherneca ductile shear zone a variscan sinistral shear zone that favoured magma ascent through the upper crust a detailed gravity study has been carried out in order to investigate the 3d geometry of the aguablanca intrusion and to get insights about the emplacement mechanism and tectonic controls of the mineralization the three dimensional gravity modelling shows that the stock has an inverted drop geometry with a feeder zone in contact with the cherneca ductile shear zone the inferred orientation of the feeder zone suggests that the emplacement probably took place along an open tensional crack formed within the strain field of the adjacent cherneca ductile shear zone the modelling of the breccia pipes hosting the ni cu pge ore shows that they are included inside the feeder zone thus their emplacement is probably controlled by successive opening events of this tensional crack

three component mixed layer illite smectite kaolinite i s k minerals in hydromorphic soils south china to understand clay mineral transformations in hydromorphic conditions in the red earth sediments in xuancheng south china clay mineralogy was investigated using x ray diffraction xrd and high resolution transmission electron microscopy hrtem the xrd results indicated that clay minerals in the hydromorphic soils were illite kaolinite smectite vermiculite and mixed layer illite smectite and illite smectite kaolinite changes of the kaolinitic reflections under the various conditions suggested that the kaolinitic phase is a mixed layer structure having kaolinite layers randomly interstratified with illite and smectite layers hrtem observation showed that 10 a illite layers interstratified with both 15 a smectite layers and 7 a kaolinite layers in clay particles confirming the occurrence of illite smectite kaolinite i s k three component mixed layer clays the lattice fringes of the i s k clays appeared corrugated and vanishing and also exhibited variable thickness along a lattice fringe which were consistent with changes from illite to smectite from smectite to kaolinite and from illite to kaolinite respectively hydromorphic conditions in the xuancheng soils led simultaneously to the direct transformation of illite to kaolinite and the transformation of illite to smectite to kaolinite in the pedogenic processes and the formation of i s k three component mixed layer clays as intermediate products of these processes

genesis of soils with an abrupt textural contrast in the united states abstract identified from the usda natural resources conservation service databases soils with an abrupt textural change atc occur in four orders alfisols mollisols ultisols aridisols 14 suborders and 31 great groups and represent nearly 1000 series in the usa more than three quarters 79 of the soils have an argillic horizon and 21 have a natric horizon an albic horizon is present in 40 of the soils more than half 58 of the soils with an atc occur in pale great groups suggesting older materials soil series with an atc occur primarily in fine 56 and clayey 14 particle size classes smectitic 49 and mixed 40 mineral classes mesic 39 and thermic 33 soil temperature classes and ustic 31 xeric 27 and aridic 21 soil moisture classes on average the texture of the eluvial and illuvial horizons varies by two classes on the soil textural triangle of the several theories accounting for the origin of soils with an atc clay illuviation from the eluvial to the illuvial horizon must be considered a major process more than halfof the soils are derived from alluvium and other stratified materials residual soils may also contain sedimentary layering which is important in the development of an atc elevenpercent of the soils have a lithologic discontinuity at the eluvial illuvial junction which may influence the development of an atc the atc in soils with an aquic soil moisture regime 13 such as the argialbolls may reflect plugging of the argillic horizon with fine clays which causes lateral subsurface flow that removes clay from the albic horizon climate may be important in the development of atc in the usa in that many of the soils are subject to extended dry periods followed by intense thunderstorms a third 34 of the soils with an atc occur in texas there are about 271 000 km2 of soils with an atc in the usa which accounts for 3 2 of the total land area

petrology and geochemistry of mafic ultramafic fragments from the aguablanca ni cu ore breccia southwest spain aguablanca southwest spain is the first economic ni cu pge deposit found in southern europe two features make it an unusual example of magmatic sulfide ore it is related to the development of an andean type continental magmatic arc and it is hosted by a subvertical magmatic breccia the structural style and the geodynamic context of the deposit contrast with most plutonic ni cu pge deposits elsewhere which occur at specific levels of layered mafic intrusions in rift environments the ni cu deposit is hosted by the aguablanca intrusion a mafic body composed of gabbronorite and minor quartz diorite gabbro and norite sulfides are concentrated in a gabbronorite matrix along a subvertical dip of 70 80 n funnel like magmatic breccia that contains barren or slightly mineralized ultramafic mafic cumulate fragments modal compositions of the fragments reflect a wide variety of rock types including peridotite hornblende rich werhlite dunite and hornblende rich harzburgite pyroxenite ortho and clinopyroxenite gabbro gabbro gabbronorite and hornblende gabbro and anorthosite the primary silicate assemblage includes olivine fo91 fo79 orthopyroxene mg no 0 85 0 73 clinopyroxene mg no 0 93 0 62 plagioclase an99 an38 amphibole mg no 0 87 0 68 and phlogopite mg no 0 89 0 64 the wide range of rock types and the fe enrichment trends in the primary ferromagnesian silicates suggest magmatic differentiation processes from the parent melts with the fragments representing different stages of cumulate formation the ore bearing breccia contains both semimassive and disseminated sulfides in the gabbronorite matrix textures vary between meso and orthocumulate and the rock forming magmatic silicates are orthopyroxene mg no 0 83 0 74 clinopyroxene mg no 0 89 0 78 plagioclase an50 an77 and intercumulus amphibole mg no 0 86 0 70 phlogopite 0 84 0 69 and minor quartz the gabbronorite in the matrix of the breccia is petrographically and chemically very similar to that of the unmineralized parts of the main aguablanca intrusion and exhibits a similar differentiation trend suggesting that the matrix of the ore bearing breccia and the unmineralized rocks belong to a same magmatic suite the local presence of mafic ultramafic fragments in the barren aguablanca intrusion supports this suggestion the presence of highly ni depleted olivine whole rock cu zr ratios below 1 and the local occurrence of disseminations of magmatic sulfides in the peridotite fragments point to sulfide segregation before and or during the formation of the peridotite cumulates mantle normalized incompatible trace element patterns of the fragments along with published sulfur isotope data are consistent with crustal contamination suggesting that addition of crustal sulfur from pyrite bearing black slates led to sulfide saturation these results support a model in which sulfides segregated and settled during the differentiation of an unexposed mafic ultramafic complex now sampled as fragments in the breccia whereas the overlying silicate magma most probably fed by successive fresh magma injections underwent fractional crystallization giving rise to this cumulate sequence the emplacement of the ore breccia took place at temperatures above the monosulfide solid solution mss solidus but below the olivine and pyroxene solidus likely owing to the explosive injection of a new pulse of magma into the chamber which mingled with the sulfide liquid and disrupted the overlying cumulate sequence as a consequence fragments reached their current position in the breccia injected along with the sulfide and the silicate melts which subsequently formed the sulfide rich gabbronorite

shear wave modeling and poisson s ratio in the variscan belt of sw iberia in 2003 two wide angle reflection refraction seismic transects were acquired in the variscan belt of sw iberia the approximately 250 and 300 km long dense trace spacing transects revealed clear s wave arrivals in the shot gathers recorded by vertical component sensors in both transects first s wave arrivals sg and moho reflections sms are the most prominent phases that can be correlated from shot to shot sg is observed up to relatively large offsets and constrains the upper and middle crust s wave velocities the sms is seen from offset 0 18 s twtt to 150 km offset where it intercepts first s wave arrivals sg the upper mantle refracted phase sn is difficult to recognize although pms smp converted phases can be identified using a 2 d ray tracing approach two s wave velocity models for the crust of sw iberia were obtained these s wave velocity models complement the previous p wave velocity models and provide us with relatively well resolved poisson s ratio crustal sections for sw iberia the resulting poisson s ratio models present differences between tectonic zones at upper and middle crustal depths thus supporting the existence of different tectonic zones prior to the variscan collision the most noteworthy feature is the high poisson s ratio value over 0 28 coincident with high p wave velocity areas over 6 8 km s at midcrustal depths in order to constrain the possible crustal composition p wave velocities and poisson s ratios have been compared with published laboratory measurements on different crustal rock types this comparison indicates that the high p wave velocity and poisson s ratios are compatible with a mixture of mafic to ultramafic rock types alternating with felsic ones this result is consistent with the existence of mafic layered bodies in the middle crust in the same way that has been suggested by previous works in this area

marcasite inversion and the petrographic determination of pyrite ancestry pyrite formed by the inversion of marcasite or by oxidative leaching of pyrrhotite can be recognized in polished sections by the following characteristics compiled from synthetic pyrite after marcasite and natural samples of pyrite after marcasite and after pyrrhotite pyrite formed by inversion from marcasite is characterized by approximately 2 modal percent pore space no by products filling the pores optical anisotropy dark green to dark red anhedral shape and polycrystalline daughter pyrite domains in two orientations relative to the marcasite parent crystal pyrite or marcasite formed by oxidative dissolution as opposed to leaching of pyrrhotite exhibits up to 32 modal percent pore space gaps between the pyrite and parent pyrrhotite pores and gaps filled with by product siderite magnetite hisingerite or other fe bearing phase optically isotropic character for pyrite development of crystal faces and random orientation relative to the parent pyrrhotite marcasite formed by oxidative leaching of fe as opposed to complete dissolution from pyrrhotite also exhibits a large amount of pore space but has preferred orientation relative to the parent pyrrhotite pyrite after marcasite may be used as an indicator of ph 5 and t ca 240 degrees c during deposition of the parent marcasite marcasite precipitated following dissolution of pyrrhotite is also indicative of those conditions during alteration marcasite formed by oxidative leaching of pyrrhotite cannot be used as evidence of those conditions however

quantitative clay mineralogy of a vertic planosol in southwestern ethiopia impact on soil formation hypotheses abstract planosols characterised by a bleached silt textured surface horizon abruptly overlying a dense clayey subsoil are a very common soil type in ethiopia the origin of the abrupt textural change is still often debated in literature one of the processes frequently put forward to explain the coarse textured material in the topsoil is ferrolysis an oxidation reduction sequence driven by bacterial decomposition of soil organic matter resulting in the destruction of open 2 1 clay minerals recent studies of representative profiles of vertic planosols in south western ethiopia indicate that these soils are composed of a weathered volcanic ash layer deposited on top of a deflated vertic subsoil which refutes the ferrolysis hypothesis to strengthen the geogenetic origin of these profiles a quantitative mineralogical analysis of the clay fraction was undertaken results of a sequential fractionation revealed a strong aggregation of clay particles in the bleached horizon while the effect of aggregation was far more limited in the vertic horizon this is believed to be related to the dispersed impregnative nature of iron oxides in the bleached horizon compared to the segregated nature of the sharp nodular concretions found in the vertic horizon the annealing xrd analysis revealed only minor changes in dehydroxylation temperatures of kaolinites and 2 1 minerals between untreated and dcb treated samples indicating that the pretreatment did not significantly alter the mineral lattices multi specimen full profile fitting of xrd patterns revealed no large quantitative differences between sub fractions of the bleached and vertic horizons although a net increase of 1 1 layers over 2 1 layers towards the top of the profile can be observed in the bleached horizon this could be interpreted as the result of neo formation of kaolinite the main mineralogical differences between the bleached and vertic horizons of the

plumbotectonic evolution of the ossa morena zone iberian peninsula tracing the influence of mantle crust interaction in ore forming processes the ossa morena zone in the variscan belt of the iberian peninsula is characterized by a complex geotec tonic evolution it hosts a neoproterozoic paleozoic sequence that records the existence of two orogenic events cadomian and variscan separated by rift and stable platform stages middle cambrian to late devonian volcanogenic and sediment hosted massive sulfides skarns magmatic ni cu deposits synmetamorphic and intragranitic and perigranitic veins and replacement bodies are related to different magmatic hydrothermal systems ranging in age from 650 ma to about 250 ma the lead isotope signatures from 26 different mineral deposits show variable ratios of 206pb 204pb 17 49 18 44 207pb 204pb 15 47 15 67 and 208pb 204pb 37 37 38 78 that have low average values 9 7 but high values 38 3 as a whole the lead isotope data define an irregular cluster that plots around the stacey and kramers 1975 growth curve but clearly marks the existence of two main ore forming events during cadomian and variscan times the most radiogenic samples are from some minor zn pb stratiform sedimentary exhalative mineralization they are interpreted as having a dominantly crustal derivation 10 1 in which most of the lead was leached from a pre cadomian continental basement with a long crustal history this basement has strong geochemical affinities with the oldest rocks of the iberian terrane however most of the ore samples investigated plot below the stacey and kramers 1975 reference curve indicating polyphase but variable mixing of lead from upper crustal and mantle lead reservoirs at the terrane scale clear mixing lines between the two end member reser voirs are evident only in the oldest volcanic rock and sedimentary rock hosted massive sulfide deposits related to the cadomian late neoproterozoic early cambrian magmatic arc in the other deposit types lead isotopes have more restricted values the crustal lead is interpreted as having been derived from ancient crust 2 1 2 5 ga and the derived shales montemolin formation that predated the cadomian orogeny the mantle derived lead may have been derived from three different sources neoproterozoic tholeiitic orthoamphibolite syn cadomian calc alkaline andesite or calc alkaline metaluminous plutonic rocks intruded during the variscan orogeny the first two sources probably controlled the lead isotope signatures of the cadomian massive sulfide deposits and the variscan synmetamorphic veins the input of primitive lead is especially significant during variscan times 350 300 ma and is interpreted as having been related to the existence of a large primitive reservoir that controlled the variscan magmatic metallogenic and hydrothermal evolution of the ossa morena zone this primitive lead is recognized in most of the magmatic hydrothermal deposits including the typically crust derived w and pb bearing perigranitic hydrothermal systems likewise associated plutonic rocks have more primitive lead isotope signatures than their counterparts in other iberian terranes the lead isotope evolution of the region is consistent with recent geophysical data that suggest that a deep large mafic sill was intruded below the ossa morena zone during variscan times this sill was a likely key factor in the different pb isotope evolution of the ossa morena zone compared with the nearby iberian terranes and the entire western mediterranean province which are char acterized by lengthy crustal histories with very little input of primitive lead the extensive mantle crust inter action probably explains the wide variety and the unusual metallogenic features of the ossa morena zone

alteration of platinum group minerals and dispersion of platinum group elements during progressive weathering of the aguablanca ni cu deposit sw spain the distribution mineralogy and mobility of the platinum group elements pge in the surface environment are poorly understood this study of the lower less altered and upper more altered gossan overlying the aguablanca ni cu pge magmatic deposit spain has shown that the platinum group minerals pgm are progressively oxidised and dispersed into iron oxides that form the gossan a combination of the characterization of pge in host pgm using a scanning electron microscope and measurement of pge at lower concentrations in host iron oxides using laser ablation inductively coupled plasma mass spectrometry la icp ms has for the first time allowed the total distribution of the pge within a gossan to be documented this study has revealed a complete in situ alteration and dispersion sequence of the pgm including 1 breakdown of both the more stable pt arsenides pt pd tellurides and the less stable bismuthotellurides 2 formation of partially oxidised pgm 3 development of a wide range of oxidised pt and pd bearing phases 4 subsequent formation of fe pge oxides and pge hydroxides 5 incorporation of pge into ferruginous supergene products and lastly 6 concentration of pge at the edges of veins and iron oxides dispersion of pd is greater than for the other pge with pd being widely distributed throughout the iron oxides this oxidising environment produced pge oxides rather than pge alloys also commonly found in the surface environment especially in placers these results provide critical evidence for the stages of mineralogical change from pge host mineralogy in magmatic ores to surface weathering producing pge oxides