magmatism in the iberian pyrite belt petrological constraints on a metallogenic model igneous formations associated with massive sulphide deposits in the iberian pyrite belt ipb are essentially composed of basic lavas and dolerites and dacitic to rhyolitic volcanites intermediate lavas are subordinate the basic rocks show variable geochemical characteristics lavas and dolerites comparable to recent within plate alkaline basalts seem restricted to the western and southern parts of the ipb whereas basic rocks comparable to continental tholeiites or arc related basalts occur across the whole belt the felsic rocks are classified as calc alkaline and belong to the low al2o3 and high yb type at given sio2 al2o3 and tio2 contents they show variable zr nb and hree contents heavy rare earth element fractionation decreases from the dacites to the rhyolites gd yb n 1 whereas the negative eu anomaly becomes more pronounced the characteristics of the rhyolites are typical of sulphide fertile volcanic packages trace element modelling suggests that the felsic rocks evolved from a dacitic parent magma through fractional crystallization of hornblende and plagioclase partial melting of an amphibolite protolith which appears as the most probable model for the origin of this dacitic magma requires a high t p gradient in the crust the occurrence of alkaline basalts and continental tholeiites is consistent with formation of the ipb in a tensional tectonic setting however the associated island arc tholeiites suggest a location in a domain of plate convergence emplacement in a fore arc basin over a recently accreted crustal segment is envisaged as a possible hypothesis to account for the geological and petrological constraints a high geothermal gradient and eruption in a submarine tensional basin could have been two key ingredients for the development of massive sulphide deposits within the ipb

stratigraphy of the tectonically imbricated lithological succession of the neves corvo mine area iberian pyrite belt portugal biostratigraphic research based on palynomorphs and ammonoids of the tectonically imbricated lithological succession of the neves corvo mine in the portuguese part of the iberian pyrite belt has yielded ages for all formerly recognised lithostratigraphic units these can be assembled in three main lithological sequences 1 detrital sandy shale substrate phyllite quartzite formation of late famennian age 2 volcano sedimentary complex divided into a lower and an upper suite in which one basic three dolerite sills and four felsic volcanic units and a mineralised package of massive sulphides are identified with ages which range from the late famennian to the late visean 3 flysch succession mertola formation composed of shale and greywacke dated as late visean to early serpukhovian precise biostratigraphic dating of the sedimentrary host rocks of massive sulphide mineralisation constrains the age of the latter to the late strunian 354 8 354 0 ma three stratigraphic hiatuses corresponding to early middle strunian tournaisian and early visean respectively and a south westward progressive unconformity were also recognised sequences 1 and 2 are related to extensional episodes while sequence 3 marks the beginning of compressive tectonic inversion which gave rise to south westward flysch progradation in close relation to a foreland basin development our results lead to the reinterpretation of the tectonic structure of the neves corvo mine with implications for the interpretation of the regional basin dynamics and metal exploration

the aguablanca cu ni ore deposit extremadura spain a case of synorogenic orthomagmatic mineralization age and isotope composition of magmas sr nd and ore s abstract the aguablanca cu ni orthomagmatic ore deposit is hosted by mafic and ultramafic rocks of the aguablanca stock which is part of the larger high k calc alkaline santa olalla plutonic complex this intrusive complex ca 338 ma in age is located in the ossa morena zone omz of the iberian variscan belt mineralization consists mainly of pyrrhotite pentlandite and chalcopyrite resulting from the crystallization of an immiscible sulphide rich liquid isotope work on the host igneous rocks sr nd and the ore s suggests that contamination with an upper crustal component took place at some depth before final emplacement of the plutons end338 6 to 7 5 sr 338 0 7082 to 0 7100 34s sulphides near 7 4 assimilation fractional crystallization afc processes are invoked to explain early cumulates and immiscible sulphide magma formation intrusion took place at the beginning of the type a oblique subduction of the south portuguese zone under the ossa morena zone and was probably driven by transpressive structures strike slip faults the mineralization is thus synorogenic aguablanca is probably the first case referred to in the literature of a magmatic cu ni ore deposit hosted by calc alkaline igneous rocks

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

balanced sections and the propagation of decollement a jura perspective 1 the propagation of thrusting is an important problem in tectonics that is usually approached by forward kinematical modeling of balanced sections although modeling techniques are similar in most foreland fold thrust belts it turns out that in the jura there are modeling problems that require modifications of widely used techniques in particular attention is called to the role of model constraints that complement the set of observational constraints in order to fully define the model in the eastern jura such model constraints may be inferred from the regional geology which shows a peculiar noncoaxial relation between thrusts and subsequent folds this relation implies changes in the direction of translation and the mode of deformation in the course of the propagation of decollement these changes are conjectured to be the result of a change in partial decoupling between the thin skinned fold thrust system nappe and the obliquely subducted foreland as a particularly instructive case in point a cross section through the weissenstein range is discussed a two step forward kinematical model is proposed that uses both local observational constraints as well as model constraints inferred from regional data as a first step a fault bend fold is generated in the hanging wall of a thrust of 1500 m shortening as a second step this structure is transferred by flexural slip into the actual fold observed at the surface this requires an additional 1600 m of shortening and leads to folding of the original thrust thereafter the footwall is deformed so as to respect the constraint that this deformation must fit into the space defined by the folded thrust as the upper boundary and the decollement surface as the lower boundary and that in addition should be confined to the area immediately below the fold in modeling the footwall deformation a mix of balancing methods is used fault propagation folds for the competent intervals of the stratigraphic column and area balancing for the incompetent ones further propagation of decollement into the foreland is made possible by the folding process which is dominated by a sort of kinking and which is the main contribution to structural elevation and hence to producing a sort of critical taper of the moving thin skinned wedge

variscan accretionary complex of northwest iberia terrane correlation and succession of tectonothermal events the allochthonous terranes of northwest iberia can be correlated with specific paleogeographic realms of the continental masses and intervening oceans involved in the variscan collision assuming that the existing ophiolites represent the suture formed by the closure of the rheic ocean the units in the footwall to the suture correspond to the outer edge of the gondwana continental margin and the units in the hanging wall are interpreted as fragments of the conjugate margin represented by the meguma terrane this correlation establishes a precise link between circum atlantic terranes and makes it possible to draw a relatively simple scenario of the successive tectonothermal events recorded following the amalgamation of avalon to laurentia the remaining outboard terranes underwent a progressive accretion to this continent that ended with the collision between laurentia and gondwana

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

granite petrogenesis in the gander zone ne newfoundland mixing of melts from multiple sources and the role of lithospheric delamination silurian to devonian granites within the gander zone of the appalachian central mobile belt in northeastern newfoundland formed adjacent to the former gondwanan continental margin following terminal closure of the iapetus ocean comparison of geochemical and isotopic characteristics of the granites with their host migmatites and metasediments amphibolite and orthogneiss constrain their potential source nd and sr isotopic compositions indicate that no single source or binary mixing product could have produced the granites instead we show that they result from multicomponent mixing involving a contribution from unexposed crystalline basement mantle or underplate and variable contamination by supracrustal host rocks the timing and composition of granite magmatism do not exhibit collisional orogenic subduction related or continental rifting characteristics hence we relate magmatism to lithospheric melting following delamination of an orogenic keel this process provides the influx of mantle derived magma into fertile crust and hence promotes lower crustal melting and primary magma mixing

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

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

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

composite synvolcanic intrusions associated with precambrian vms related hydrothermal systems large subvolcanic intrusions are recognized within most precambrian vms camps of these 80 are quartz diorite tonalite trondhjemite composite intrusions the vms camps spatially associated with composite intrusions account for 90 of the aggregate sulfide tonnage of all the precambrian intrusion related vms camps these low alumina low k and high na composite intrusions contain early phases of quartz diorite and tonalite followed by more voluminous trondhjemite they have a high proportion of high silica 74 sio2 trondhjemite which is compositionally similar to the vms hosting rhyolites within the volcanic host rock successions the quartz diorite and possibly tonalite phases follow tholeiitic fractionation trends whereas the trondhjemites fall within the composition field for primitive crustal melts these transitional m i type primitive intrusive suites are associated with extensional regimes within oceanic arc environments subvolcanic composite intrusions related to the archean sturgeon lake and noranda and paleoproterozoic snow lake vms camps range in volume from 300 to 1 000 km3 three have a sill morphology with strike lengths between 15 and 22 km and an average thickness between 1 500 and 2 000 m the fourth has a gross stock like shape the vms deposits are principally restricted to the volcanic strata above the strike length of the intrusions as are areally extensive thin exhalite units the composite intrusions contain numerous internal phases which are commonly clustered within certain parts of the composite intrusion these clusters underlie eruptive centers surrounded by areas of hydrothermal alteration and which contain most of the vms deposits early quartz diorite and tonalite phases appear to have intruded in rapid succession evidence includes gradational contacts magma mixing and disequilibrium textures they appear to have been emplaced as sill dike swarms these early phases are present as pendants and xenoliths within later trondhjemite phases the trondhjemite phases contain numerous internal contacts indicating emplacement as composite sills common structural features of the composite intrusions include early xenolith phases abundant small comagmatic dikes fractures and veins and in places columnar jointing internal phases may differ greatly in texture from fine to coarse grained aphyric and granophyric through seriate to porphyritic mineralogical and isotopic evidence indicates that early phases of each composite intrusion are affected by pervasive to fracture controlled high temperature 350 450 c alteration reflecting seawater rock interaction trondhjemite phases contain hydrothermal magmatic alteration assemblages within miarolitic cavities hydrothermal breccias and veins this hydrothermal magmatic alteration may in part be inherited from previously altered wall rocks two of the four intrusions are host to cu mo rich intrusive breccias and porphyry type mineralization which formed as much as 14 ma after the main subvolcanic magmatic activity the recognition of these precambrian subvolcanic composite intrusions is important for greenfields vms exploration as they define the location of thermal corridors within extensional oceanic arc regimes which have the greatest potential for significant vms mineralization the vms mineralization may occur for 2 000 m above the intrusions in some cases vms mineralization has been truncated or enveloped by late trondhjemite phases of the composite intrusions evidence that much of the trondhjemitic magmatism postdates the principal vms activity is a critical factor when developing heat and fluid flow models for these subseafloor magmatic hydrothermal systems

ore genesis age of the tharsis mining district iberian pyrite belt a palynological approach massive sulphide deposits of the tharsis mining district iberian pyrite belt are included in a black shaly series that is stratigraphically conformable with the underlying phyllite quartzite group well preserved palynomorph assemblages have been obtained from this shaly series the miospore assemblages are assigned to the ln biozone indicating a latest devonian age this is consistent with the re os age of 348 6 12 3 ma from both massive sulphides and stockwork mineralization palynological and isotopic results from elsewhere in the pyrite belt are similar suggesting that mineralization was synchronous throughout the region

is the ancestral yellowstone hotspot responsible for the tertiary carlin mineralization in the great basin of nevada we propose a genetic relationship between the 43 34 ma magmatism extensional tectonics and gold mineralization event centered in the great basin of nevada and the development of the ancestral yellowstone hotspot the model is compatible with cenozoic regional tectonics and provides a plausible explanation of the spatial coincidence of the eocene oligocene magmatic events and the carlin type gold deposits these features are centered in the battle mountain region of the great basin coincident with the inferred ca 40 30 ma position of the yellowstone hotspot the yellowstone hotspot is probably a plume that ascended from the core mantle boundary a region thought to be anomalously rich in gold and in the moderately siderophile elements associated with gold deposits as the hotspot was progressively overridden by the north american plate after ca 60 ma a magmatically quiescent period related to subhorizontal subduction gave way to the generation of ca 43 34 ma voluminous intracrustal melts and metamorphic devolatization as the hotspot broke though the subducted farallon plate coeval crustal extension and convective circulation of hydrothermal fluids in the upper crust facilitated the exploitation of the structural and lithologic traps that characterize the classic carlin type deposits

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

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

multiple sources for ore forming fluids in the neves corvo vhms deposit of the iberian pyrite belt portugal strontium neodymium and lead isotope evidence lead rb sr and sm nd isotopes have been used to constrain the sources and the timing of mineralisation at the neves corvo vhms deposit of the iberian pyrite belt ipb sulfide and cassiterite rich ores together with a mineralised felsic volcanic rock yield a rb sr errorchron age of 347 25 ma with an initial 87sr 86sr 0 71031 65 the rb sr results agree with palynological age constraints for ore formation at neves corvo and are indistinguishable from several other mineralisation ages indicating that major orebodies in the ipb formed coevally at 350 ma in contrast wide variations in initial 143nd 144nd indicate limited rare earth element redistribution during ore deposition initial end 350 ma values range from 0 2 to 9 7 for copper ores 8 9 to 9 4 for copper tin ores and 6 9 cassiterite to 9 5 for tin ores implying that neither the ipb volcanic host rocks end 350 ma 2 1 87sr 86sr0 0 70664 nor contemporaneous seawater 87sr 86sr0 0 708 could have been the exclusive sources for the neves corvo ores distinct mixing arrays in the end 350 ma sm nd and 206pb 204pb 207pb 204pb diagrams demonstrate that sulfide and tin ore deposition involved ore forming solutions from different sources whereas sulfide ore compositional variations are consistent with significant incorporation of typical ibp volcanic seawater derived hydrothermal components the highly radiogenic lead and exclusively low end values preserved in tin ores require a predominant derivation from external sources this could be either a magmatic source which must have been different from the typical ipb felsic magmas or a metamorphic fluid deeply circulated through older basement rocks

age constraints to the relationships between magmatism metamorphism and tectonism in the aracena metamorphic belt southern spain the aracena metamorphic belt amb southwest iberian peninsula is characterized by the following geological elements a a high temperature low pressure ht lp metamorphic belt a few kilometres wide and more than 200 km long b a linear belt of oceanic amphibolites with a low pressure inverted metamorphic gradient c crustal scale ductile shear zones and d mafic noritic intrusions of high mg andesite boninite composition the relationships between these elements led to the proposal of a model of ridge subduction for this sector of the hercynian belt of europe this interpretation is supported by the age relationships displayed between the main rock units considered representative of the main tectonic and petrological processes responsible for the geological elements mentioned previously the results of a geochronological study ar ar rb sr and sm nd clearly support a late paleozoic tectonic evolution at an active continental margin the time evolution of the metamorphism in the oceanic domain ranging from 342 6 0 6 ma in the west to 328 4 1 2 ma in the east over a distance of 70 km along the metamorphic belt support a tectonic model of triple junction migration responsible for the creation at depth of a slab free window with decisive consequences for the thermal evolution of the region the origin of the linear metamorphic belt of ht lp regime may be explained by the migration along a continental margin of a punctual thermal anomaly induced by the creation of a triple junction at the continental margin

hydrothermal precipitates associated with bimodal volcanism in the central bransfield strait antarctica polymetallic sulfide sulfate mineralization enriched in pb ag as sb hg occurs in the bransfield strait a late tertiary quaternary marginal basin close to the antarctic peninsula the mineralization is associated with bimodal volcanism and pelagic and volcaniclastic sediment in rifted continental crust hydrothermal precipitates have been recovered from two shallow 1 050 1 000 m water depth submarine volcanoes hook ridge and three sisters in the central bransfield strait mineralization at hook ridge consists of polymetallic sulfides massive barite and pyrite and marcasite crusts in semilithified pelagic and volcaniclastic sediment native sulfur commonly infills void space and cements the volcaniclastic sediment the polymetallic sulfides are dominated by sphalerite with minor galena enargite tetrahedrite tennantite pyrite chalcopyrite and traces of orpiment cemented by barite and opal a the presence of enargite at hook ridge the abundance of native sulfur and the low fe content of sphalerite indicate a high sulfur activity of the hydrothermal fluids responsible for mineralization the sulfur isotopic composition of hook ridge precipitates documents the complexity of the sulfur sources in this hydrothermal system with variable influence of biological activity and possibly magmatic contributions homogenization temperatures and salinities of fluid inclusions in barite and opal a suggest that boiling may have affected the hydrothermal fluids during their ascent the discovery of massive barite silica precipitates at another shallow marine volcano three sisters volcano attests to the potential for hydrothermal mineralization at other volcanic edifices in the area the characteristics of the mineralization in the bransfield strait with rifting of continental crust the presence of bimodal volcanism including highly evolved felsic volcanic rocks the association with sediments and the pb ag as sb hg enrichment are similar to the setting of massive sulfide deposits in the okinawa trough and distinct from those of sediment dominated hydrothermal systems such as escanaba trough middle valley and guaymas basin the geological setting of the bransfield strait is also broadly similar to that of some of the largest volcanogenic massive sulfide deposits in the ancient record such as the iberian pyrite belt

chert in the iberian pyrite belt since lenses of chert are common within the volcano sedimentary succession hosting the massive sulphide deposits of the iberian pyrite belt spain and portugal we examined numerous chert occurrences both petrographically and geochemically to test their possible value for massive sulphide exploration the chert is found at two main lithostratigraphic levels upper and lower that are also interpreted as massive sulphide bearing in both cases the chert is located at the top of acidic volcanic sequences or in the associated sediments we have not been able to observe the relationships between massive sulphides and chert but some of the large orebodies of the province lousal la zarza tharsis planes san antonio body of rio tinto neves are described as being locally capped by chert facies four main types are recognized among the chert and associated facies 1 red hematitic chert magnetite 2 radiolarian and or sedimentary textured conglomeratic chert with hematite and or mn oxides 3 pale sulphidic chert 4 rhodonite and or mn carbonate magnetite facies in the spanish part of the province the radiolarian chert is confined to the upper level the distribution of the other types appears to be haphazard the hydrothermal origin of the south iberian chert is shown by its high fe mn and low co ni cu contents the presence of small positive ce anomalies indicates a shallow marine environment shelf or epicontinental sea which is consistent with the volcanological and sedimentological data the chert was emplaced below the sea floor through chemical precipitation and or through alteration and replacement of the country rock residual traces of which are ghost phenocrysts and high al ti and rare earth contents macro and microscopic relationships indicate that the oxide facies hematite magnetite formed first probably providing a protective insulating cover against the marine environment and enabling an evolution towards sulphide facies a phase of mn carbonate and silicate quartz chlorite sulphides appears to be even later it was not possible through discrimination to isolate a chert that could be considered as representing a lateral marker of massive sulphides moreover both field observations and geochemical data seem to indicate a relative independence of this siliceous sulphide hydrothermal activity from the hydrothermal activity giving rise to the massive sulphides such is also indicated by the lead isotopic signature of the chert which is appreciably more radiogenic than that of the massive sulphides the lead enrichment in the sulphidic chert facies indicates the participation of a different source sediments sea water from that of the massive sulphides the hypothesis of an independent hydrothermal chert event can thus be envisaged wherein the chert reflects submarine low temperature hydrothermal activity that is most apparent during a break within the volcano sedimentary succession and which may locally have competed with the high temperature hydrothermal activity giving rise to the massive sulphides the interest of the chert thus rests in its palaeodynamic significance as a marker of periods of volcanic quiescence and in its possible role as a protective insulating cap favourable to the deposition of massive sulphides

the nain churchill boundary and the nain plutonic suite a regional perspective on the geologic setting of the voisey s bay ni cu co deposit northern labrador is the site of two major lithotectonic elements of eastern canadian shield geology first it encompasses a paleoproterozoic continental suture zone archean rocks of the nain province tectonically juxtaposed against paleoproterozoic and reworked archean rocks of the churchill province the nain churchill suture evolved between 1860 and 1740 ma impressing upon the archean and paleoproterozoic rocks a regional metamorphic and tectonic signature referred to as the torngat orogen an important component of the torngat orogen is the tasiuyak gneiss a paleoproterozoic metasedimentary unit that occupies most of the eastern margin of the churchill province second northern labrador is the site of a world renowned terrane of mesoproterozoic anorogenic igneous rocks the nain plutonic suite that sits astride the suture and acts as a stitching batholith between the nain and churchill provinces the nain plutonic suite comprising amalgamated granitic anorthositic dioritic and troctolitic intrusions largely obscures the suture for nearly half of its total length the suite evolved between 1350 and 1290 ma and is interpreted as a product of magmatism associated with limited intracontinental rifting of the conjoined nain churchill crust above a mantle plume the voisey s bay ni cu co deposit serendipitously discovered in 1993 resides within one of the oldest troctolitic intrusions of the nain plutonic suite a 1334 ma intrusion that transgresses a contact between archean and paleoproterozoic gneisses genetic controls on the setting of mineralization have been built upon the nain churchill boundary as a zone of weakness that was exploited by mantle magmas and have implicated the tasiuyak gneiss as a crustal sulfur source although the archean paleoproterozoic junction at voisey s bay is presently interpreted as representing the nain churchill boundary in reality the provincial affinity of the archean gneisses is equivocal this uncertainty dictates caution in assigning the nain churchill boundary as the convenient transcrustal conduit that allowed the voisey s bay mafic intrusions rapid transit from their mantle staging area modeling the sulfide deposit as being solely a result of sulfur saturation of mafic magma by proximal paleoproterozoic tasiuyak paragneisses is also questionable because other genetic processes may have been responsible for example desilication of gneiss is strongly indicated by aluminous refractory minerals in vestiges of fused tasiuyak gneiss the spatial distribution of the mineralized rock at voisey s bay apparently within the subchamber plumbing system feeding a larger intrusion and within remnants of the larger intrusion itself may serve as a paradigm for similar deposits in the nain area but the preerosional comparative morphology of that larger intrusion relative to the better preserved ones may never be known a thorough understanding of the setting and genesis of the voisey s bay deposit will better facilitate establishing exploration targets in other parts of the nain region in labrador as a whole and in other geologically similar regions of the world

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

postvolcanic paleozoic of the iberian pyrite belt an example of basin morphologic control on sediment distribution in a turbidite basin abstract the iberian pyrite belt south portuguese zone hercynian chain an important metallogenic province has a volcanic sedimentary origin overlying this volcanic succession is a thick sedimentary unit the culm group which represents postvolcanic paleozoic sediments of the iberian pyrite belt it consists of three stratigraphic units the basal shaly formation bsf the culm facies turbiditic formation cftf and the shallow platform sandy unit spsu the bsf is represented by finegrained sediments of volcanic to nonvolcanic origin that mark the end of volcanism in the region the reworking of volcanic products in a shallow marine basin and the beginning of autochthonous sedimentation of pelagic clay it constitutes a depositional sequence sensu mitchum et al 1977 the d stribution facies and facies associations of the turbidites of the cftf are related to the configuration of the basin which controlled the mechanisms of deposition and distribution of the detritus from different source areas the spsu represents sediments eroded from the volcanic upland and redistributed over the shelf detailed study of these three units and their relationships provides the means to define the geometry and evolution of the postvolcanic carboniferous basin of the iberian pyrite belt the basin was roughly subdivided by the paymogo and the puebla de guzman paleoridges together with the allochthonous ossa morena zone north of the study area they formed three topographic barriers that delineated two interconnected subbasins sedimentation in the postvolcanic basin of the iberian pyrite belt can be related to a model of oscillating sea level synorogenic characteristics of the culm group sediments support a tectonic origin for the sea level oscillations particularly since the sediments had already been affected by the first pulses of the hercynian orogeny

lead isotope systematics of the giant massive sulphide deposits in the iberian pyrite belt lead isotope analyses were performed on 26 polymetallic massive sulphide deposits of the iberian pyrite belt as well as on overlying gossans and associated volcanic rocks all the massive sulphide deposits except for neves corvo and nearly all the volcanic rocks show very similar isotopic compositions grouped around 18 183 206pb 204pb 15 622 207pb 204pb and 38 191 208pb 204pb indicating that most of the ore deposit lead was derived from the same continental crust environment as the associated volcanic rocks the isotopic compositions are representative of the average south iberian crust during the devonian to early carboniferous dinantian and their constancy implies a homogenization of the mineralizing fluids before the deposition of the massive sulphides from hydrothermal fluids circulating through interconnected regional fracture systems this isotopic constancy is incompatible with multiple small independent hydrothermal cells of the east pacific rise type and fits much better with a model of hydrothermal convections driven by magmatic floor heating neves corvo is the only south iberian massive sulphide deposit to have a heterogeneous isotopic composition with in particular a highly radiogenic stanniferous ore 206pb 204pb of the cassiterite is 18 40 a model of lead mixing with three components is proposed to explain these variations 1 one derived from the devonian to early carboniferous dinantian continental crust that generated all the other massive ores 2 an eohercynian stanniferous mineralization partly remobilized during the formation of the massive sulphides but independent of them and 3 a precambrian continental crust component the juxtaposition of three different sources places neves corvo in a specific paleogeographic situation that could also explain its mineralogical specificity the geodynamic context that best explains all the obtained isotopic results is one of an accretionary prism the fact that lead isotope signatures of the gossans are almost identical to those of the underlying massive sulphides means that this technique could be a useful exploration tool for the iberian pyrite belt

volatile lines of descent in submarine plutonic environments insights from stable isotope and fluid inclusion analyses microthermometric and isotopic analyses of fluid inclusions in primitive olivine gabbros oxide gabbros and evolved granitic material recovered from ocean drilling program hole 735b at the southwest indian ridge provide new insights into the evolution of c o h nacl fluids in the plutonic foundation of the oceanic crust the variably altered and deformed plutonic rocks span a crustal section of over 1500 m and record a remarkably complex magma hydrothermal history magmatic fluids within this suite followed two chemically distinct paths during cooling through the subsolidus regime the first path included formation of co21ch41h2o1c fluids with up to 43 mole ch 4 the second path produced hypersaline brines that contain up to 50 nacl equivalent salinities subsequent to devolatilization respeciation of magmatic co2 attendant graphite precipitation and cooling from 800 c to 500 c promoted formation of ch 4 enriched fluids these fluids are characterized by average d 13 c ch4 values of 227 1 6 4 3 n5 45 with associated d 13 c co2 compositions ranging from 224 9 to 21 9 n539 and average dd values of exsolved vapor of 241 6 12 n523 in pods veins and lenses of highly fractionated residual material hypersaline brines formed during condensation and by direct exsolution in the absence of a conjugate vapor phase entrapped co21ch41h2o rich fluids within many oxide bearing rocks and felsic zones are significantly depleted in 13 c with d 13 c co2 values down to about 225 and contain co 2 concentrations higher than those predicted by equilibrium devolatilization models we hypothesize that lower effective pressures in high temperature shear zones promoted infiltration of highly fractionated melts and compositionally evolved volatiles into focused zones of deformation significantly weakening the rock strength in felsic rich zones volatile build up may have driven hydraulic fracturing of gabbroic wall rocks resulting in the formation of magmatic breccias comparison of isotopic compositions of fluids in plutonic rocks from 735b the mark area of the mid atlantic ridge and the mid cayman rise indicate 1 that the carbon isotope composition of the lower oceanic crust may be far more heterogeneous than previously believed and 2 that carbon bearing species in the oceanic crust and their distribution at depth are highly variable copyright 2001 elsevier science ltd

critical stress localization of flow associated with deformation of well fractured rock masses with implications for mineral deposits fluid flow and deformation of fractured rock masses is investigated using numerical models based on distinct element methods udec which couple mechanical and hydraulic behaviour a series of numerical experiments is presented in which diffuse flow through fracture networks changes to highly localized flow at a critical stress state slip on parts of the fracture network causes the opening up of some fractures often at fracture intersections thus a change in the stress state results in a sudden localization of deformation and fluid flow a series of plots of hydraulic conductivity v differential stress are presented for some natural fracture networks to demonstrate the influence of fracture network geometry and in situ stress on the critical phase boundary between diffuse and localized flow the onset of localized deformation and fluid flow is a critical point phenomenon resulting in fractal properties fractal and multifractal techniques are used to characterize heterogeneity of the flow in order to generalize the results of the modelling of discrete systems to a continuum based description of the flow the significance of the models and their implications for crustal behaviour are discussed in relation to hydrothermal mineralization and natural vein systems

electromagnetic imaging of variscan crustal structures in sw iberia the role of interconnected graphite abstract the western part of the iberian peninsula iberian massif is the best exposed fragment of the variscan orogen in europe its southern half was generated by an oblique collision between three continental terranes belonging to the margins of laurassia avalonia the south portuguese zone spz and gondwana the ossa morena zone omz and the central iberian zone ciz the boundaries between them are considered to be suture zones a 200 km long magnetotelluric profile across the three variscan terranes was done in a nne direction approximately perpendicular to the main tectonic features the results of two dimensional inversion of the mt dataset reveal high conductivity zones coinciding with the transitions spz omz and omz ciz these conductive bodies related to the sutures at depth were interpreted as graphite enrichments along shear planes formed due to the overall transpressive regime a high conductivity layer extending along the whole omz was found at a depth of 15 25 km the top of which spatially correlates with a broad reflector detected by a recently acquired deep seismic reflection profile the high conductivity was interpreted as caused by the precambrian serie negra graphite rich rocks carbon and oxygen x ray mapping with electron microprobe on polished sections of serie negra samples from omz revealed the presence of interconnected graphite which supports the hypothesis that graphite is determinant for the high conductivity two graphite types which help to record the geological evolution were identified graphite accumulations in the schistosity surfaces produced by folding and metamorphism and metallic films of graphite developed along late faults the conductive layer shows blobs of higher conductivity suggesting macro anisotropy additional mylonitisation and shearing produced by thrusting at depth can be the origin of these zones of enhanced conductivity given that the detachment level is located within the serie negra several high resistivity features were found in the upper crust related to devonian and carboniferous successions and probably to some unexposed plutons in the spz and the palaeozoic series of omz plus some granitic intrusions in the ciz a high resistivity zone extending to the whole crust is correlated with extensive late variscan granite intrusions

petrographic and geochemical evolution of pervasively altered bushveld granites at the zaaiplaats tin mine tin with associated tungsten and rare earth element mineralization at the zaaiplaats mine is hosted by alkali feldspar granites of the lebowa granite suite which intrude granophyric granites of the rashoop granophyre suite from the upper contact downward the alkali feldspar granites include a marginal pegmatite stockscheider the fine grained lease granite and the coarse grained bobbejaankop granite the major mineralization styles consist of subhorizontal tabular zones low grade orebodies containing disseminated cassiterite in the lease granite a zone of disseminated cassiterite mineralization zdm in the bobbejaankop granite approximately 50 m below the lease granite and a series of shallowly plunging and branching pipe orebodies which occur in both granite types and which show a close spatial relationship to zones of disseminated mineralization the granites contain miarolitic cavities generally less than 5 mm in diameter which range from more than 10 vol percent in the upper facies of the lease granite to less than 1 vol percent in the deeper part of the bobbejaankop granite miarolitic cavities are filled or partially filled by hydrothermal minerals including quartz albite chlorite sericite fluorite hematite and calcite the zones of disseminated mineralization contain high abundances of miarolitic cavities and appear to reflect zones of hydrothermal fluid accumulation during crystallization in addition to the small cavities within the disseminated cassiterite mineralization zone the bobbejaankop granite contains a series of large cavities to approx 1 m and patches of strongly miarolitic granite additional infill phases in mineralized zones include cassiterite scheelite synchisite arsenopyrite chalcopyrite galena and other sulfide phases pervasive alteration of the granites is expressed mainly by the replacement of primary biotite by chlorite sericite and hematite by ordering of alkali feldspar maximum microcline low albite and by substantial replacement of alkali feldspar by chlorite sericite hematite and other hydrothermal phases in the bobbejaankop granite below the disseminated cassiterite mineralization zone amounts of al 2 o 3 k 2 o na 2 o ba rb nb ta and u increase with increasing elevation whereas sio 2 and ti decrease this is compatible with upward crystallization in an evolving f rich magma but it may partly reflect upward transport of alkalies and incompatible elements via a fluid phase the zdm is a zone of enrichment in sio 2 ba cu pb zn and sn whereas it is depleted in al 2 o 3 k 2 o na 2 o rb ta and u compared to the underlying granite the increasing importance of sericite as an infilling and replacement mineral as the alpha pipe is approached suggests that part of the alteration and cavity filling in the lease granite occurred at the same time as alteration and mineral precipitation in the alpha pipe this increasing importance of sericitic alteration is reflected in the geochemical data by increasing co 2 rb and cs contents and decreasing na 2 o f and ba contents with proximity to the pipe the distribution of disseminated and pipe style mineralization at zaaiplaats reflects a combination of processes including 1 early separation of an h 2 o nacl co 2 fluid enriched in boron to produce pipelike conduits by collection and upward flow beneath crystallization fronts supplemented by later dissolution of granite 2 accumulation of fluorine rich fluids evolved at a more advanced stage of crystallization beneath downward advancing crystallization fronts to produce strongly miarolitic zones of the lease granite containing disseminated cassiterite low grade orebodies 3 accumulation of fluorine rich hydrothermal fluids possibly between upward and downward advancing crystallization fronts to produce the disseminated cassiterite mineralization zone and 4 pervasive alteration of the granites accompanied by filling of miarolitic cavities and pipes the lack of significant hydraulic or tectonic fracturing during crystallization of the granites at zaaiplaats was probably the most crucial factor in the development of these unusual styles of mineralization

a special issue devoted to porphyry copper deposits of northern chile chile is known worldwide as the site of one of the largest copper concentrations on earth a total resource including production of about 400 million tons mt of fine copper has been identified in 50 porphyry copper deposits and numerous prospects fig 1 considering 10 mt of contained fine copper as a minimum tonnage to classify a porphyry copper deposit as a giant ore deposit the chilean cordillera contains nine of the 16 giant porphyries along the circum pacific belt among them are the three largest of all el teniente rio blanco los bronces and chuquicamata fig 1 all containing resources plus production of more than 50 mt of fine copper currently chile annually produces about 4 6 mt of fine copper that represents about 37 percent of the world production this enormous geologic potential has triggered numerous international mining companies to concentrate their exploration efforts in the central andes with emphasis in chile during the past 25 years exploration expenditures have surpassed a figure on the order of us 2 billion as a result a total of 76 copper and gold discoveries have been made 24 of which are already in production cabello 2000 among them the most relevant discoveries are the porphyries at la escondida escondida norte zaldivar rosario and ujina in the collahuasi mining district quebrada blanca lomas bayas and in the last 5 years spence and gaby sur the presence of such a significant number and large size of copper porphyries intrigued several generations of researchers during the twentieth century the ongoing exploration efforts have enhanced the interest in understanding the andean geological evolution and metallogenesis the geological processes that are common factors in controlling the emplacement of these orebodies have been the subject of research by numerous individuals in chile and elsewhere the support of mining companies has been

the filon norte orebody tharsis iberian pyrite belt a proximal low temperature shale hosted massive sulphide in a thin skinned tectonic belt the filon norte orebody tharsis iberian pyrite belt is one of the largest pyrite rich massive sulphide deposits of the world the present structure of the mineralization consists of an internally complex low angle north dipping thrust system of variscan age there are three major tectonic units separated by thick fault zones each unit with its own lithologic and hydrothermal features they are internally organized in a hinterland dipping duplex sequence with high angle horses of competent rocks igneous and detritic rocks and massive sulphides bounded by phyllonites the mineralization is within the lower unit and is composed of several stacked sheets of massive sulphides and shales hosting a stockwork zone with no obvious zonation the intermediate unit is made up of pervasively ankeritized shales and basalts spilites here hydrothermal breccias are abundant the upper unit is the less hydrothermally altered one and consists of silicified dacites and a diabase sill the tectonic reconstruction suggests that the sequence is inverted and the altered igneous rocks were originally below the orebody carbon oxygen and sulphur isotopes in the massive sulphides and hydrothermal rocks as well as the mineral assemblage and the paragenetic succession suggest that the sulphide precipitation in the sea floor took place at a low temperature 150 c without indication at least in the exposed section of a high temperature copper rich event sporadic deep subsea floor boiling is probably responsible for the formation of hydrothermal breccias and the wide extension of the stockwork its co au enrichment is interpreted as being related with the superposition of some critical factors such as the relationship with black shales the low temperature of formation and the boiling of hydrothermal fluids the present configuration and thickness of the orebody is due to the tectonic stacking of a thin and extensive blanket 2 4 km2 of massive sulphides with low aspect ratio they were formed by poorly focused venting of hot modified seawater equilibrated with underlying rocks into the seafloor massive sulphide precipitation took place by hydrothermal fluid quenching bacteriogenic activity and particle settling in an unusual restricted euxinic and shallow basin brine pool with a low detritic input but with important hydrothermal activity related to synsedimentary extensional faulting resedimentation of sulphides seems to be of major importance and responsible for the observed well mixed proximal and distal facies the tectonic deformation is largely heterogeneous and has been mostly channelled along the phyllonitic tectonized shales deformation bands thus sedimentary and diagenetic textures are relatively well preserved outside the deformation bands in the massive sulphides superimposed variscan recrystallization is not very important and only some early textures are replaced by metamorphic tectonic ones the stockwork is much more deformed than the massive sulphides the deformation has a critical effect on the present morphology of the orebody and the distribution of the ore minerals this deposit is a typical example of the sheet like shale hosted anoxic low temperature and zn rich massive sulphides developed in a ensialic extensional basin

zn pb cu massive sulfide deposits brine pool types occur in collisional orogens black smoker types occur in backarc and or arc basins volcanic hosted massive sulfide deposits of zn pb cu type were derived either from seawater dominated buoyant fluids that built mounds on the seafloor e g the ores of the hokuroku basin japan or from saline fluids that reversed buoyancy on mixing with seawater and filled basins on the seafloor e g several ores of the iberian pyrite belt and the mount read province in tasmania the hokuroku ores formed above subduction zones during protracted periods of regional extension but both the iberian pyrite belt and the mount read province formed under extensional stress during continent continent iberia or arc continent mount read collision and orogenesis in the iberian pyrite belt oblique convergence resulted in transcurrent faulting and this may also be the case for the mount read province transcurrent faulting may have allowed easy vertical access for the ore related magmas some of which were sourced in the asthenosphere as well as the blueschist and eclogitic facies emplaced in adjacent terrains and possibly also saline fluids exsolved from the magmas

discrete particle model of aeolian sand transport comparison of 2d and 2 5d simulations abstract a discrete particle model is applied to describe aeolian sand transport in this model the inter particle collisions and the fluid particle coupling interactions are considered the fluid turbulence is treated with a mixing length theory and the motion of each particle is directly tracked the 2 5d model includes the 2d flow for gas and the 3d motion for sand particles the differences between 2d and 2 5d simulations are compared the results show that the 2 5d simulation can produce the non uniform distribution of particle in the spanwise direction in the 2d simulation the particle motion is limited only to a vertical plane so the number density or concentration of particle in the 2d simulation is artificially increased the particle concentration in the 2 5d simulation is less than that in the 2d simulation both the mean horizontal velocity of particles and the wind velocity in the 2 5d simulation are more than those obtained in the 2d simulation the decay rate of sand mass flux with increasing height in the 2 5d simulation is larger than that in the 2d simulation in the saltation layer the particle shear stress in the 2 5d simulation is less than that in the 2d simulation while the fluid shear stress in the 2 5d simulation is larger than that in the 2d simulation the 2 5d model can consider the particle motion in all the three coordinate directions and improve the simulated results of the 2d model and thus acquire better results

a deep seismic reflection profile over a caledonian granite in central england in 1980 a short deep reflection profile undertaken jointly by the university of leicester and the institute of geological sciences crossed a buried caledonian granite to the south west of melton mowbray in leicestershire little structure is seen in the section between the top of the granite at 0 25 s two way time stwt and a zone of very strong sub horizontal reflections at 6 s twt a further reflection zone is identified at 7 2s twt below which there are a series of strong but impersistent reflections to the full reording time of 12 s twt the data indicate that the granite must be relatively homogeneous and underlain by several marked sub horizontal boundaries at mid to lower crustal levels this suggests that during emplacement either the granite must have had little effect on the lower crust sampled by the profile or the lower crust was mobile enough to have developed layering since the granite was emplaced during the caledonian orogeny