chloritisation along the thanewasna shear zone western bastar craton central india its genetic linkage to cu au mineralisation abstract the cu au mineralisation of thanewasna bastar craton central india is hosted in quartz chlorite veins traversing granitoid rocks mineralisation and associated alteration are controlled by a nw se trending brittle ductile shear zone large scale alkali magmatism in the form of k rich granite emplacement is found in the vicinity of the shear zone the emplacement of this granite 1587 14 ma along the northern shoulder of the godavari rift produced a high geothermal gradient resulting in intense chloritisation and mineralisation field and petrographic studies show that the chlorite formed in two possible modes viz a replacement of ferromagnesian minerals of the host rock and or b precipitated directly from hydrothermal solutions mineral chemistry epma coupled with sem and xrd studies reveals that chamosite with minor clinochlore varieties of chlorite is commonly associated with cu and au mineralisation chlorite shows variation in fe fe mg ratios from 0 54 to 0 60 0 55 to 0 64 and 0 49 to 0 55 and al iv from 1 88 to 2 40 1 91 to 2 50 and 1 80 to 1 94 apfu respectively at the surface and in the sub surface mineralisation and host rock empirical and thermodynamic geothermometers have been used to determine the temperature of chlorite formation based on chemical composition six empirical methods based on al iv al vi and fe fe mg ratio showed a temperature range of 187 c to 381 c temperatures of chlorite formation have also been determined by the thermodynamic solid solution method the thermodynamic equations of three intra crystalline equilibria at 2 kbar pressure show that temperature ranges from 215 to 454 c for low si contents 2 8 apfu the thermodynamic method of vidal et al 2001 and 2005 was not so compatible for an estimation of temperature of hydrothermal fe rich chlorites associated with cu au mineralisation at the thanewasna copper deposit tcd the temperature of chlorite formation increases from the host rock mean 201 c to proximal mineralisation zone mean 234 c to distal k na alteration zone mean 251 c integrating field and laboratory results suggested that tcd chlorite is part of a structurally controlled high sulphidation epithermal system this characterization would help in the regional exploration for base and precious metals and the results are applicable for the entire western bastar craton wbc of central india and similar deposit elsewhere

early cretaceous syn rotational extension in the organya basin new constraints on the palinspastic position of iberia during its rotation article i nfo in this study we interpret the paleo stress pattern in the organya basin southern pyrenees northern spain as inferred from the anisotropy of magnetic susceptibility ams of 39 sites distributed over the entire basin combined with information from other cretaceous iberian basins such analysis adds to constrain kinematic reconstructions of the cretaceous rotation of iberia allied with the opening of the bay of biscay and the northward propagation of the north atlantic the organya basin is an inverted cretaceous basin in the hanging wall of the boixols thrust the lithologies are mainly weakly deformed pelagic and hemi pelagic limestones and marls which recorded the aptian 35 counterclockwise rotation of iberia three types of ams fabrics could be distinguished all representing typical intermediate and tectonic fabrics ew magnetic lineations dominate in the eastern part of the basin and are related to crustal shortening during the pyrenean orogeny this interpretation is consistent with structural cross sections across the basin showing more intense shortening in the east in the central part of the basin approximately ns oriented magnetic lineations are observed interpreted as the original extensional direction during basin foundering so in line with results from previous studies ams can still unveil the original extensional direction in an inverted sedimentary basin something which may be difficult to reconstruct from geological data alone the original extension direction in the organya basin is perpendicular to the boixols thrust bounding the basin to the south correction for the aptian rotation of iberia leads us to infer a ne sw oriented extension direction at the onset of the rotation of iberia this extension direction is inconsistent with current plate kinematic reconstructions of the cretaceous rotation and motion of iberia we therefore suggest that during the opening of the bay of biscay and related iberian rotation iberia was in a much more westerly position than assumed in current models and that the rotation of iberia was followed by dominantly eastward translation with respect to southern france prior to n s convergence and shortening in the pyrenees since the latest cretaceous

dating crystalline groundmass separates of altered cretaceous seamount basalts by the 40ar 39ar incremental heating technique abstract alteration of submarine basalts compromises geochronology using conventional k ar and 40 ar 39 ar techniques to help overcome these problems we re evaluated the potential of groundmass dating techniques incremental heating on acid leached groundmass samples following an overnight bakeout at 200 c and using high resolution heating schedules eliminated most of the low temperature alteration effects in the submarine basalts studied more than 75 of the groundmass analyses n 32 display accurate age plateaus consisting of 30 70 of the total amount of 39 ar k released more than 50 of the analyses have plateau ages concordant with their total fusion ages implying minor or proportional loss of radiogenic 40 ar and 39 ar k overall we could show a high degree of coherence between ages of groundmass separates and comagmatic phenocrysts this suggests that the dating of aphyric basalts which previously has proven problematic can be accomplished with increasing confidence as well adding these rock types to the list of datable submarine basalts significantly enhances our ability to understand the eruptive history of linear submarine volcanic chains

tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

contributions from mafic alkaline magmas to the bingham porphyry cu au mo deposit utah usa the bingham porphyry cu au mo deposit utah may only be world class because of substantial contributions of sulfur and metals from mafic alkaline magma to an otherwise unremarkable calc alkaline system volcanic mafic alkaline rocks in the district are enriched in cr ni and ba as well as cu au platinum group elements pge and s the bulk of the volcanic section that is co magmatic with ore related porphyries is dacitic to trachytic in composition but has inherited the geochemical signature of high cr ni and ba from magma mixing with the mafic alkaline rocks the volcanic section that most closely correlates in time with ore related porphyries is very heterogeneous containing clasts of scoriaceous latite latitic and minette and flows of melanephelinite shoshonite and olivine latite in addition to volumetrically dominant dacite trachyte bingham ore related porphyries show ample evidence of prior mixing with mafic alkaline magmas intrusive porphyries that have not been previously well studied have several chemical and mineralogical indications of magma mixing these mixed lithologies include the hybrid quartz monzonite porphyry biotite porphyry and minette dikes even some of the more silicic latite and monzonite porphyries retain high cr and ba contents indicative of mixing and contain trace amounts of sapphire 1 mm the heterogeneous block and ash flow deposits also contain sapphire and are permissively correlated with the intrusions based on chemical mineralogical and isotopic data magma mixing calculations suggest about 10 of the monzonitic latitic ore related magma may have been derived from mafic alkaline magma similar to the melanephelinite if the original s content of the mafic magma was about 2 000 4 000 ppm comparable with similar magmas then the mafic magma may have been responsible for contributing more than half of the s and a significant portion of the cu au and pge in the bingham deposit

porphyry and epithermal deposits in greece an overview new discoveries and mineralogical constraints on their genesis abstract greece hosts a variety of magmatic hydrothermal ore deposits prospects with porphyry and epithermal styles playing a major role in its total gold endowment these deposit types are mainly clustered in two areas the rhodope and attico cycladic massifs and formed from about 33 ma to the pleistocene as a result of back arc extension in the aegean sea metamorphic core complex formation and contemporaneous post subduction and arc magmatism in the serbo macedonian massif porphyry cu au deposits include skouries fisoka tsikara vathi and gerakario causative intrusives are oligocene to miocene granodiorites to monzonites gold and pge mineralization is associated with potassic alteration of the intrusives in the eastern rhodope massif and the ne aegean islands porphyry prospects occur at pagoni rachi konos hill myli melitena west thrace fakos sardes and kaspakas limnos island and stypsi lesvos island mineralization is associated with oligocene to miocene subvolcanics of calc alkaline to shoshonitic affinity feature of these prospects which they share in common with several porphyry au only systems is their shallow depth of emplacement the presence of potassic sodic calcic and or phyllic alteration a strong epithermal overprint their low cu content an extreme re enrichment the multistage introduction of au the presence of banded quartz veinlets and the local presence of tourmaline new discoveries of porphyry style mineralization at king arthur st philippos and aisymi increases the gold potential in west thrace high intermediate sulfidation epithermal au ag polymetallic deposits prospects overprint and or occur laterally from porphyry style mineralization where they are spatially associated with lithocaps of advanced argillic alteration high intermediate sulfidation au ag epithermal mineralization at perama hill mavrokoryfi and pefka in west thrace and at pterounda mesotopos and megala therma on lesvos island is controlled by steeply dipping extensional faults within volcanic rocks without any obvious genetic relationship to spatially related porphyry style mineralization polymetallic epithermal deposits and prospects contain critical and energy critical metals e g te se bi sb in ge and ga which may be considered as by products in the attico cycladic area porphyry mo w mineralization occurs as sheeted quartz veins and stockworks cutting a potassic to sericitic altered miocene granodiorite stock in the lavrion district bonanza grade au and or ag rich veins with epithermal affinities crosscut metamorphic rocks at lavrion and on syros tinos antiparos and anafi islands milos island is characterized by shallow submarine volcanic hosted is hs epithermal au ag te and base metal deposits antimony as ag au deposits prospects on chios samos and kos islands in the eastern aegean sea indicate the potential for carlin style mineralization in greece several factors played a role to the metal endowment of the aegean porphyry epithermal systems magma fertility in the source regions depth of emplacement of causative intrusives relative contribution of mantle versus crustal material redox state of subduction related magmas and physico chemical fluid conditions at the site of ore deposition

migration of widespread long lived volcanism across the galapagos volcanic province evidence for a broad hotspot melting anomaly abstract the well studied galapagos archipelago is a small part of the much larger galapagos volcanic province gvp consisting of the cocos carnegie coiba and malpelo aseismic ridges and related seamount provinces although these aseismic ridges and seamounts dominate the morphology of the region little is known about their origin due to a lack of direct age and geochemical information in order to establish how well the gvp fits with the predictions of the standard fixed hotspot and mantle plume hypotheses we conducted a first reconnaissance dredge grab sampling of submerged regions of the gvp we present here 40ar 39ar ages for many of these new basement samples and evaluate their implications for the various models put forward to explain the origin of the gvp correlating new and published sample site ages with distance from the western side of the galapagos islands show that volcanism has not progressed in narrow time progressive lines of seamounts and ridges as predicted by the conventional fixed hotspot and mantle plume hypothesis rather volcanism apparently migrated time progressively across the gvp in broad regions of long lived and possibly concurrent volcanism we propose that the most viable explanation for these observations is that the gvp is the product of cocos and nazca plate motions across a broad hotspot melt anomaly the complex spreading history of the cocos nazca spreading centre likely controlled the relative distribution of gvp volcanism between the cocos and nazca plates while creating lithosphere of variable age thickness across the region while the notion of a broad galapagos hotspot melting anomaly linked to a complex regional tectonic history requires significant testing it nevertheless highlights the need to test alternative mantle upwelling shapes and sizes compared to the widely accepted notion of a narrow continuous long lived galapagos mantle plume conduit defined by the size and location of a galapagos island

the transition from porphyry to epithermal style gold mineralization at ladolam lihir island papua new guinea a reconnaissance study the exceptionally large gold resource at ladolam 1 300 metric tons of gold lihir island resulted from the transition of an early stage low grade porphyry gold system to a low sulfidation epithermal gold event this transition was probably triggered by rapid decompression during the partial slope failure of luise stratovolcano and accompanied by the ingress of seawater the original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite magnetite altered monzodiorite with disseminated pyrite chalcopyrite and poorly developed pyrite quartz stockwork veins the breccias are overprinted by biotite magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite the breccias are cut by late stage epithermal quartz chalcedony illite adularia pyrite veins and associated illite adularia alteration that locally contain bonanza gold grades of up to 120 g t isotope data suggest a magmatic source of sulfur in the gold bearing fluids at ladolam electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0230 y

central city colorado the upper part of an alkaline porphyry molybdenum system the distribution of molybdenite fluorite rhodochrosite enargite and telluride minerals together with anomalous quantities of cu pb zn and mo in rocks and variations in stable isotope ratios define a complex zoned hydrothermal system in the central city mining district the molybdenite mineralization is centered on a laramide quartz bostonite or alkali rhyolite breccia pipe that occurs at the intersection of the dory hill fault and the idaho springs ralston shear zone stream sediment geochemistry suggests that significant amounts of w may be present in the system uranium base and precious metal mineralization of a similar age but with a distribution different from the molybdenite mineralization is also present and is considered to be a part of the same hydrothermal system fluid inclusion data for the molybdenite and precious and base metal mineralization indicate that fluid inclusions associated with early molybdenite veins are of two types co 2 rich and rare halite bearing with respective homogenization temperatures of 340 degrees to 420 degrees c and 240 degrees to 340 degrees c inclusions associated with precious metal bearing pyrite and base metal veins are aqueous two phase types with homogenization temperatures in the range of 220 degrees to 380 degrees c those from late molybdenite veins are aqueous two phase inclusions with homogenization temperatures of 200 degrees to 280 degrees c salinities as equiv wt nacl are between 34 to 42 for halite bearing inclusions and 2 to 12 for all other types no evidence of boiling has been found trapping pressures of co 2 rich inclusions are 0 46 to 0 75 kb which suggest an emplacement depth of about 2 km for the molybdenite mineralization respective quartz delta 18 o and fluid inclusion delta d values are 1 early molybdenite veins 9 3 to 14 3 per mil and 87 to 66 per mil 2 precious metal bearing pyrite and base metal veins 8 4 to 15 9 per mil and 90 to 47 per mil and 3 late molybdenite veins 10 1 to 15 4 per mil and 77 to 69 per mil with associated fluorite having fluid inclusion delta d values of 70 to 57 per mil a late telluride vein has a quartz delta 18 o value of 11 2 per mil and fluid inclusion delta d value of 86 per mil these data suggest that all except the telluride ore fluids contained large proportions of a d rich magmatic fluid the distribution of fluid inclusion delta d values defines two distinct anomalies each zoned with delta d enrichment occuring inward toward centers which correspond to the areas of known molybdenite occurrences and precious and base metal mineralization likewise delta d values for sericites developed during early hydrothermal activity increase inward toward the quartz bostonite pipe various intrusive breccias and molybdenite mineralization in the district there is no indication at central city of negative delta 18 o anomalies in the precambrian country rock within or peripheral to the centers of mineralization suggesting that ore fluids were thus essentially confined to discrete fractures it is concluded that molybdenite and other mineralization in this classic gold mining district may be related and may represent the upper part of an alkaline porphyry molybdenum system

the relationship between epithermal and porphyry hydrothermal systems within the tavua caldera fiji the shoshonitic tavua caldera in viti levu fiji defines the volcanic center of the tavua volcano the caldera occurs at the intersection of the northeast trending viti levu lineament and a northwest trending lineament locally manifested by the nasivi shear zone fault related subsidence which contributed to the evolution of the tavua caldera the central inner caldera and the structural preparation for mineralization occurred on these two regional fault systems and local concentric normal faults a continuum of mineralization and alteration styles is evident along the nasivi shear zone caused by a northwesterly evolution and migration of intrusion and hydrothermal activity porphyry style subeconomic copper gold mineralization and associated alteration occurred at depth in the nasivi shear zone at the center of the caldera approximately contemporaneously with the development of the inner caldera acid sulfate style epithermal alteration and minor gold mineralization immediately postdated and were superimposed on this porphyry style alteration farther northwest along the nasivi shear zone transitional ac d sulfate to adularia sericite epithermal alteration and minor gold mineralization occur variation in hydrothermal style is considered to reflect an increasing distance from magmatic source combined with an increasing proportion of meteoric water mixing with the hydrothermal fluid northwest of this system at the intersection of the nasivi shear zone and the viti levu lineament the 4 4 m oz adularia sericite style epithermal emperor gold mine occurs high level epithermal mineralization and alteration occur 4 km northeast of the emperor gold mine in an area which has a demonstrable present day hydraulic connection with the mine variations in fluid inclusion homogenization temperatures from the mine indicate that fluids entered the structurally prepared mine area via the nasivi shear zone emperor epithermal mineralization postdated magmatism by approximately 0 4 ma stable isotope data the presence of albitic alteration beneath mineralization and high salinities within the mine indicate that the emperor northern prospects hydrothermal system is related to an intrusion into the nasivi shear zone beneath the mine this is consistent with a demonstrable northwesterly migration of intrusions with time along the nasivi shear zone albitic phyllic and propylitic assemblages comprise the main porphyry style alteration types in the caldera center calculated temperatures of formation of chlorite in these assemblages indicate that these three alteration facies formed in the temperature range 270 degrees to 340 degrees c in good agreement with available fluid inclusion data and the stability ranges of the mineral assemblages kubler indices of illite likewise imply that these assemblages formed at relatively high temperature epithermal lode alteration mineralization at emperor is shown by fluid inclusion data to have formed around 200 degrees c kubler indices of illite confirm that this alteration formed at significantly lower temperatures than did porphyry alteration and that chlorites in the emperor mine have calculated temperatures of formation mostly below 200 degrees c high level epithermal alteration occurring northeast of emperor is inferred to have formed at even lower temperatures

the permian mafic dyke swarm of the panticosa pluton pyrenean axial zone spain simultaneous emplacement with the late variscan extension the panticosa dyke swarm was emplaced into the late carboniferous 301 7 ma panticosa pluton it consists of diabase and lamprophyre dykes according to their composition two lithotypes are differentiated i an early system of calc alkaline affinity and n s average trend and ii a late system of alkaline affinity and e w average trend the fracture pattern distribution with respect to both dyke systems suggests that all dykes occupied pre existing fractures the magnetic fabric analysis and petrological data indicate that the emplacement model differed for each dyke system for the calc alkaline dykes magma flow and tectonic stress conditions influenced emplacement the emplacement of alkaline dykes on the other hand was mainly controlled by tectonic stress the combined interpretation of structural and magnetic fabric data suggests an emplacement history for all late variscan dykes during a constant regional n s trending extension this study emphasizes the role of pure extension in the late variscan evolution of the pyrenean axial zone

high precision pb isotope measurements reveal magma recharge as a mechanism for ore deposit formation examples from lihir island and conical seamount papua new guinea abstract lihir island part of the tabar lihir tanga feni island chain in the sw pacific hosts the giant ladolam gold deposit polymetallic gold mineralization also was discovered offshore at conical seamount in 1998 during rv sonne cruise so 133 the seamount and the island are composed mainly of trachybasalts and basaltic trachyandesites although some monzonites are found on lihir sr isotopic analyses of mineralized samples from the island and the seamount suggest that most of the sr is derived from the local alkaline lavas elevated 87sr 86sr ratios in some of the samples suggest that during the waning stages of the hydrothermal system part of the sr was contributed either from seawater or the thick sequence of marine sediments underlying the island high precision pb isotopic analyses conducted with mc icp ms show that the ores and volcanic rocks share similar pb isotopic compositions suggesting that the pb in the mineralized zones was ultimately derived from local magmatic sources the pb isotopic data however reveal small but significant differences between the mineralized zones and the associated host lavas mineralized samples from lihir have slightly less radiogenic lead isotopic ratios than their host lavas these lead isotopic compositions are similar however to some of the fresh lavas recovered from conical seamount and to a monzonite intrusion underlying the ladolam deposit lead isotopic ratios in mineralized samples from conical seamount are slightly more radiogenic than their host lavas and similar to those of fresh lavas recovered from nearby tubaf and edison seamounts petrographic observations and microprobe elemental analyses reveal a complex magmatic history for the magma chamber inferred beneath conical seamount based on zoning patterns in the conical seamount clinopyroxenes it appears that a sub seamount magma chamber was recharged with a mafic magma similar to the most primitive volatile rich and xenolith bearing lavas recovered from tubaf and edison seamounts rapid cooling of this mafic magma accompanied by exsolution of metal bearing fluids in the relatively shallow magma chamber is proposed as the mechanism that ultimately led to the formation of the gold mineralization similarity of the lead isotopic ratios between the ores and the mafic magmas in the area indicate that the ore metals were primarily derived from the recharging magma not by hydrothermal leaching of the host lavas suggesting that ore deposit genesis can be related to a single volatile rich magmatic pulse within otherwise barren polyphased volcano magmatic complex

active formation of chaos terrain over shallow subsurface water on europa the galileo spacecraft revealed a number of chaos regions on jupiter s moon europa where the surface terrain appears to have been disrupted from below in many places the surface contains sharp edged blocks or rafts of ice that have at some point been flipped or rotated some characteristics of these regions have been hard to explain such as the fact that the archetypal conamara chaos stands above its surroundings and contains matrix domes schmidt et al apply lessons learned from analogous processes within earth s subglacial volcanoes and ice shelves to an analysis of archival data that suggests chaos terrain forms above liquid water lenses that are perched only 3 kilometres deep within the ice shell the data suggest that ice water interactions and freeze out give rise to the varied morphology of chaos terrains implying that more water is involved than has been previously appreciated for instance the sunken topography of thera macula a large chaos area may indicate that europa is actively resurfacing over a lens comparable in volume to north america s great lakes europa the innermost icy satellite of jupiter has a tortured young surface1 2 3 4 and sustains a liquid water ocean1 2 3 4 5 6 below an ice shell of highly debated thickness1 2 3 4 5 7 8 9 10 quasi circular areas of ice disruption called chaos terrains are unique to europa and both their formation and the ice shell thickness depend on europa s thermal state1 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 no model so far has been able to explain why features such as conamara chaos stand above surrounding terrain and contain matrix domes10 18 melt through of a thin few kilometre shell3 7 8 is thermodynamically improbable and cannot raise the ice10 18 the buoyancy of material rising as either plumes of warm pure ice called diapirs1 9 10 11 12 13 14 15 or convective cells16 17 in a thick 10 kilometres shell is insufficient to produce the observed chaos heights and no single plume can create matrix domes10 18 here we report an analysis of archival data from europa guided by processes observed within earth s subglacial volcanoes and ice shelves the data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 kilometres our results suggest that ice water interactions and freeze out give rise to the diverse morphologies and topography of chaos terrains the sunken topography of thera macula indicates that europa is actively resurfacing over a lens comparable in volume to the great lakes in north america

tectonothermal evolution of the northeastern margin of iberia since the break up of pangea to present revealed by low temperature fission track and u th he thermochronology a case history of the catalan coastal ranges abstract the catalan coastal ranges ccr form part of the northeastern iberian mediterranean margin this margin typifies the transition zone between the thickened crust of the pyrenees and ebro basin 32 to 40 km and the extremely thinned continental crust of the offshore valencia trough 8 km despite intensive geological research in recent decades the issue of the unsolved thermochronological history has hardly been addressed for the catalan margin this study provides for the first time a continuous low temperature thermochronological dataset covering the period from late paleozoic to present day more than 100 analyses have been performed in an area less than 200 km long by 50 km wide zircon and apatite fission track zft and aft results of the hercynian basement yield cooling ages between 254 41 104 16 ma and 223 27 16 3 ma respectively apatite u th he ages range between 58 3 and 2 0 0 2 ma these thermochronological data provide evidence for a very active geothermal past revealing above all an important thermal period coeval with the triassic early jurassic break up of pangea hereby we discuss and suggest various mechanisms responsible for the elevated crustal temperatures detected this new dataset also provides new constraints on the allocation of areas where exhumation uplift occurred synchronous with some tectonic phases the widespread presence of hydrothermal mineralizations and the present day overmaturity state of the mesozoic sediments with regard to oil potential in the ccr despite the local scale of the catalan margin the very detailed study here presented sheds some light on the geological implications of results from other more regional thermochronological studies on the iberian microplate studies that yield similar mesozoic thermochronological record for areas that also experienced extensional fracturing and subsidence during the break up of pangea

helium and argon isotope geochemistry of alkaline intrusion associated gold and copper deposits along the red river jinshajiang fault belt sw china abstract the red river jinshajiang strike slip fault zone on the eastern margin of the tibetan plateau was originally produced by the india eurasia collision 60 70 myr ago numerous post collisional mantle derived alkaline igneous rocks with ages of 40 30 ma have been intruded along this fault zone in recent years several copper and gold deposits associated with the alkaline intrusions of this region were discovered such as the yao an and beiya gold deposits and the yulong and machangqing copper deposits studied in this paper the mineralised intrusions are felsic with sio 2 ranging from 61 4 to 67 7 wt k 2 o na 2 o from 8 1 to 11 5 wt and k 2 o na 2 o 1 the deposits are located at both the exo and endo contact zones of the intrusions the mineral deposits are of hydrothermal origin with the ore forming temperatures mainly in the range 150 450 c this paper presents he and ar isotope analyses of these four deposits the concentrations of 4 he trapped in fluid inclusions of pyrites from the ores are 0 7 54 1 10 6 cm 3 stp g 1 and those of 40 ar are 0 6 7 3 10 6 cm 3 stp g 1 3 he 4 he ratios are 0 3 2 5 ra ra represents the 3 he 4 he ratio of air 1 39 10 6 40 ar 36 ar ratios are 316 1736 and 3 he 36 ar ratios are 0 2 11 2 10 3 generally the 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios for the gold deposits are higher than those for the copper deposits we suggest that the ore forming fluids of both gold and copper deposits were differentiated from the mantle derived alkaline magmas but were diluted by modified air saturated water masw that experienced intensive interaction with crustal rocks however the magmatic fluids responsible for the gold deposits were less extensively diluted by masw resulting in higher 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios than the copper deposits

a transtensional basin model for the organya basin central southern pyrenees based on magnetic fabric and brittle structures summary the purpose of this paper is to explain the kinematics of the inverted extensional organy basin centralsouthernpyrenees duringitsextensionalevolution thestudyoftheanisotropy of magnetic susceptibility ams and the study of brittle mesostructures are the instruments used to decipher the extensional kinematics separation of magnetic subfabrics analyses of ams at low temperature and anisotropy of the anhysteretic remanence aarm has been also done to properly interpret the obtained magnetic fabric data the combination of all magnetic fabric and brittle mesostructures analyses has provided new information to clarify thestructuralevolutionofthebasin whichsupportanewtectonicmodelfortheaptian albian basinal stage 20 sites for the magnetic fabric analysis were sampled in aptian lower albian marls the ams ellipsoids obtained at room temperature show their kmin axes perpendicular to bedding and kmax axes oriented nw se in 70 per cent of the samples n s in 15 per cent and ne sw in 15 per cent analyses of ams at low temperature show a better clustering of the axes of the magnetic ellipsoid pointing out that phyllosilicates constitute the carriers of the ams whereas the analyses of the aarm confirm the scattering of the ferromagnetic grains these results suggest that the obtained ams in the organy a basin was acquired during or shortly after deposition of the aptian lower albian marls without any subsequent overprint the direction of the magnetic lineation obtained from the ams at room and low temperatures agrees with the orientation of the stress axes obtained from the analysis of brittle mesostructures mainly faults and calcite filled tension gashes indicating its tectonic origin we interpret the orientation of the magnetic ellipsoids related to the transtensional movements linked to the formation of the organy a basin during the aptian albian interval which are consistent with the eastward displacement and rotation of iberia with respect to europe analysis oftensiongashesalsoindicatesamainnw seextensiondirection whereaspalaeostressanalysis of striated faults shows a more n s trending 3 the transtensional model proposed from magnetic fabric and brittle mesostructures for the organy a basin during the aptian albian is consistent with the creation of a strongly subsiding area south of the axial zone during the cretaceous and implies that rotation and separation of iberia respect to europe took place simultaneously

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

regional scale cretaceous albitization in the pyrenees evidence from in situ u th pb dating of monazite titanite and zircon abstract albitization is a common metasomatic process active in various geodynamic contexts in the northern pyrenees there are several occurrences of albitites but until now only one occurrence has been dated 117 ma ar ar dating this paper presents new u th pb ages for several albitite occurrences throughout the pyrenees to test whether they are contemporaneous and if so to specify the regional extent of the albitization event ages obtained from large euhedral titanite and monazite grains from distinct albitites are 110 8 and 98 2 ma respectively the zircon u th pb isotopic system did not record this cretaceous metasomatic event even when grains were selected in metasomatically zr enriched rocks or in hydrothermal structures millimetre sized veins cross cutting granitoids we argue that the total time span of 20 ma recorded by albitites corresponds to a long lived hydrothermal system that was active during the rotation of iberia around europe along the north pyrenean fault because albitization and talc mineralization have the same spatial and temporal distribution in the pyrenees we argue that these two metasomatic phenomena are two independent records of this single regional scale long lived hydrothermal system

new lithostratigraphy for the cantabrian mountains a common tectono stratigraphic evolution for the onset of the alpine cycle in the w pyrenean realm n spain abstract the pyrenean cantabrian orogen arose through the collision of the iberian and eurasian plates mostly in cenozoic times this orogen comprises two main mountain ranges the pyrenees to the east and the cantabrian mountains to the west to date the early alpine tectono sedimentary phases preserved in the cantabrian mountains of permian and triassic age have been considered independently from the same phases in neighbouring basins of sw europe and even from the eastern part of the same orogeny the pyrenean orogeny in consequence the beginning of the alpine cycle in the cantabrian mountains has been interpreted within a specific geodynamic context far from the general evolutionary phases of the western peri tethys basins through detailed field work including geological mapping sedimentology lithostratigraphy and petrology of volcanic rocks and new palaeontological data here we define several new lithostratigraphical formations and five new tectono sedimentary cycles ts i v for the initial phases of evolution of the mesozoic basque cantabrian basin interrupted by periods of tectonic stability to complete this information we include data from an onshore borehole villabona mine and two offshore boreholes constrained by 2d reflection seismic profiles acquired in the north iberian continental platform the main tectono sedimentary cycles related to the deposition of five major identified lithostratigraphic units can be described as follows ts i late gzelian early asselian relating to the late variscan deformation and preserved in a single outcrop in all the cantabrian mountains san tirso formation this formation is constituted by medium distal alluvial fan deposits in which humid intervals predominate forming some thin coal beds ts ii asselian sakmarian a post variscan extensional phase with associated calc alkaline magmatism represented by profuse volcanic and volcanosedimentary intercalations in the early permian sedimentary basins acebal formation and small plutons in surrounding areas ts iii kungurian or reactivation of the post variscan extension leading to alluvial and lacustrine carbonate sedimentation in arid climate conditions which do not change during the rest of the permian and triassic periods sotres formation a generalized karstification in the basin represents the end of permian deposition followed by an interruption in sedimentation longer than 30 myr the permian tectono sedimentary cycles ts ii and ts iii are contemporary with variscan belt collapse and the basins are controlled by extensional reactivation of ne sw and e w variscan structures and nw se late variscan structures ts iv late anisian middle carnian renewed sedimentation in more extensive basins precursors of the great mesozoic basque cantabrian basin this cycle is represented by fluvial deposits cicera formation or buntsandstein facies which are interrupted by the first mesozoic marine ingression rueda formation or muschelkalk facies ts v norian rhaetian or shallow marine carbonate deposits transicion formation related to increasingly compartmentalized sub basins controlled by normal faults this final ts is broadly connected with different basins of the western peri tethys domain the identification of units ts i v in the cantabrian mountains along with the volcanic character of ts ii all indicate the development of a common post variscan to early alpine tectono sedimentary evolution for the whole pyrenean cantabrian realm

extensional salt tectonics in a contractional orogen a newly identified tectonic event in the spanish pyrenees a new coniacian early santonian extensional salt tectonics event has been identified in the cotiella thrust sheet of the central spanish pyrenees we present a new interpretation of the cotiella thrust system and describe exceptional outcrop examples of postrift gravity driven extensional growth faults the thrust sheet contains three kilometer scale extensional faults with as much as 5 5 km of coniacian lower santonian growth strata in their hanging walls these postrift listric growth faults detached on the prerift triassic evaporites on the uplifted and eroded southern flanks of early cretaceous rift basins early alpine late santonian maastrichtian contractional deformation reactivated and reversed the displacement on both the early cretaceous rift faults and some of the postrift salt detachment faults hanging walls of the listric growth faults deformed into major antiforms but the original extensional geometries are well preserved continued alpine shortening incorporated these reactivated extensional fault systems into the thin skinned thrust sheets of the southern pyrenees these postrift extensional structures account for significant thickness variations in the postrift succession and for along strike changes in the styles of the thrust structures the late cretaceous extensional salt tectonics is interpreted to result from gravity induced northward sliding on the early cretaceous rift margin toward the axis of the rift basin the listric growth faults are similar to those found on the gulf of mexico margin in the southern north sea and the south atlantic margins

post late paleozoic tectonism in the southern catalan coastal ranges ne spain assessed by apatite fission track analysis abstract we report the first apatite fission track thermochronologic data for 17 samples from the southern catalan coastal ranges of ne spain thermal histories of carboniferous metasediments late hercynian intrusions and lower triassic buntsandstein sediments from three tectonic blocks miramar prades and priorat are derived and interpreted within the geodynamic framework and tectonic evolution of the region the apatite fission track ages range from 198 24 to 38 5 ma and mean fission track lengths are all

extreme crustal thinning in the bay of biscay and the western pyrenees from observations to modeling recent observations and models of continental rifting in magma poor environments have led to the concept of multiphase stages of lithospheric extension in these concepts it is shown that extreme crustal thinning of the crust predates exhumation of lower crustal and subcontinental mantle rocks during final rifting the bay of biscay is a v shaped ocean basin that opened in aptian albian time in front of this propagating ocean several rift basins formed that show evidence for extreme crustal thinning and locally also mantle exhumation the parentis arzacq mauleon and cantabrian basins in this paper we propose based on geological and geophysical observations and using numerical modeling a model that can explain the extreme crustal thinning observed in the arzacq mauleon and parentis basins our results show that rifting in the bay of biscay was initiated by distributed oblique stretching latest jurassic to early aptian before it underwent an more orthogonal asymmetric thinning and exhumation phase from late aptian to albian time these last two stages of deformation are similar to those observed in orthogonal rift systems we show that thinning is accomplished by the formation of a semibrittle shear zone that allows for the transfer of middle to lower crustal material from the side of the rift collocated with the hanging wall to the side of the rift collocated with the footwall of the detachment system the main difference with an orthogonal rift system appears to be generated by the formation of flower structures during the distributed oblique phase and the capacity of localizing the deformation in the subsequent stages these oblique slip faults form very steep normal faults that induce the development of strongly localized compartmentalized and asymmetric rift basins in the case of the parentis and arzacq mauleon basins these strike slip faults separate upper plate sag basins to the north from lower plate sag basins to the south while the northern sag basins do not show any evidence for exhumation the southern ones are more complex and floored by detachment faults as indicated by the occurrence of syntectonic and posttectonic sediments onlapping directly onto exhumed lower crustal and mantle rocks

alkalic intrusive rocks associated with the mount kare gold deposit papua new guinea comparison with the porgera intrusive complex the mount kare gold deposit is located 18 km southwest of the giant porgera gold mine proven and probable reserves of 51 5 million metric tons at 0 23 oz au t in the highlands of papua new guinea both deposits are spatially associated with late miocene alkalic intrusive complexes emplaced in mesozoic tertiary shelf sedimentary sequences near the edge of the australasian plate close geologic similarities between the two deposits including the presence of quartz roscoelite au veins and breccias have spurred recent exploration efforts at mount kare the mount kare and porgera intrusive complexes consist of hypabyssal suites of comagmatic volatile rich mafic intrusions containing clinopyroxene olivine plagioclase hornblende chromian spinel and apatite in melagabbros and mafic porphyries with plagioclase hornblende clinopyroxene titanian magnetite and apatite in more evolved rocks listed in decreasing order of abundance analcite occurs as an alteration phase of the groundmass and fills miarolitic cavities in evolved leucogabbros at mount kare but has not been observed in the porgera intrusive complex least altered igneous rocks from both suites are nepheline normative and are characterized by high volatile alumina large ion lithophile and high field strength element contents they display light rare earth element enrichments la yb cn 9 28 at mount kare 14 20 at porgera but relatively low concentrations of k and ti on mantle normalized diagrams the rocks are mostly sodic na 2 o 2 or k 2 o according to the total alkali silica classification scheme nd sr and pb isotope compositions and k ar ages of hornblende and biotite from the two suites are virtually indistinguishable epsilon nd 6 7 87 sr 86 sr asymp 0 7036 208 pb 204 pb asymp 38 5 207 pb 204 pb asymp 15 55 206 pb 204 pb asymp 18 65 k ar age of mount kare intrusive complex 6 0 or 0 1 ma 2gma porgera intrusive complex 6 0 or 0 3 ma 2gma these combined characteristics indicate a dominantly alkalic intraplate affinity for the parental magma at both locations although a weak subduction zone signature is also suggested by the relatively high volatile and alumina and low ti abundances it is proposed that magmatic activity was related to changes in geodynamic configuration occurring immediately prior to early pliocene collision between the australasian plate and an island arc system minor differences such as divergent trajectories of pb isotope crustal contamination arrays the occurrence of analcite only at mount kare and the widespread presence of excess 40 ar in igneous amphiboles only at porgera indicate that although related the mount kare and porgera intrusive complexes developed independently of one another disseminated auriferous pyrite from the mount kare au deposit is associated with phyllic alteration of intrusive and sedimentary rocks a single k ar analysis of illitc from altered rock records an age of 5 5 or 0 1 ma 2sigma which falls in the middle of the range of illite and roscoelite ages from the porgera au deposit 5 1 6 1 ma this result combined with slightly older ages of igneous activity suggests a close temporal and genetic association between magmatism and mineralization at both locations in addition the narrow range of pb isotope compositions of galenas from veins at mount kare is identical with that from porgera suggesting that similar ore forming processes were involved at the two locations recognition of closely similar igneous lithologies and ore types at mount kare and porgera supports theories of a genetic relationship between volatile rich mafic alkalic magmatism and meso to epithermal au mineralization as previously proposed at porgera it is suggested that both of these deposits belong to the alkalic epithermal group to which cripple creek colorado emperor fiji and ladolam lihir island papua new guinea also belong igneous centers with these characteristics and located in complex convergent tectonic settings should be considered as prospective targets for precious metal exploration

some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration porphyry copper gold skarn copper gold sediment hosted carlin style gold breccia pipe low sulphidation epithermal gold pluton related mesothermal or orogenic gold vein and volcanogenic massive sulphide deposits associated with alkaline rocks are commonly broadly similar to those hosted by their calc alkaline counterparts in contrast porphyry molybdenum gold deposits are confined to alkaline igneous centres alkaline suites are notably deficient in high sulphidation epithermal gold deposits and even in the advanced argillic lithocaps which host them this is surprising given that the required oxidised sulphur species are seemingly more abundant than in calc alkaline igneous centres highly efficient buffering of acidic fluid by metasomatised alkaline rocks may offer a viable explanation all types of intrusion related zinc deposits also appear to be poorly developed in alkaline provinces the characteristics of several gold and copper deposits associated with alkaline rocks including the giant porgera cripple creek ladolam olympic dam and phalaborwa examples are judged to diverge appreciably from their most closely related deposit types rendering them arguably unique most of these aberrant mineralisation styles may be due to variations in magmatic fluid compositional and liberation characteristics consequent upon the extreme diversity of ore related alkaline magmas most types of gold and copper deposits developed in calc alkaline provinces also constitute exploration targets in and around alkaline igneous centres although porphyry copper gold and low sulphidation epithermal gold deposits are considered to possess the greatest potential perhaps of even greater interest however is the possibility of encountering unconventional giant gold and copper deposits which lack closely analogous examples if already defined aberrant deposits are truly unique then exploration designed specifically to detect additional examples is pointless furthermore exploration for new unique deposits is difficult because their defining geological parameters are unknown alkaline rocks within or behind calc alkaline arcs at convergent plate boundaries probably offer the greatest exploration potential although anorogenic intracontinental extensional settings should not be ignored

age of the cretaceous alkaline magmatism in northeast iberia implications for the alpine cycle in the pyrenees cretaceous magmatism in northeast iberia is related to the opening of the bay of biscay and counterclockwise rotation of iberia with respect to europe and predates the collision between iberia and europe that resulted in the formation of the pyrenees to better constrain the age of this magmatism we have undertaken a ar ar study on samples from the pyrenees and the catalonian coastal ranges in the basque cantabrian basin and the north pyrenean basins we have obtained albian ages ca 102 ma in the northern catalonian coastal ranges we have obtained campanian ages ca 79 ma we integrate our data with a review of previously published ages and discuss our results in terms of their geodynamic significance the cretaceous magmatism in the pyrenees is albian santonian mostly occurring between 105 to 85 ma and was emplaced in a tectonically unclear context after the opening of the bay of biscay and rotation of iberia the magmatism in the catalonian coastal ranges is well constrained to ca 79 ma and could mark the onset of alpine shortening in the pyrenean realm in northeasternmost iberia finally we describe a late triassic ca 232 ma early jurassic ca 180 ma phase of magmatism in the central pyrenees previously considered to be cretaceous that widens temporally and geographically the extent of the rift related alkaline magmatism in southwestern europe at that time key points new ar ar data update the age of the cretaceous magmatism in ne iberia magmatism in the pyrenees postdates the rotation of iberia magmatism in the catalonian coastal ranges could mark the onset of alpine shortening

the cretaceous peri atlantic alkaline pulse paap deep mantle plume origin or shallow lithospheric break up abstract although the early jurassic initial phases of atlantic rifting were marked by the tholeiitic basalt flows and dikes of the central atlantic magmatic province camp the cretaceous era was characterised by widespread alkaline igneous activity on widely separated peri atlantic continental margins nearly half the peri atlantic alkaline rocks dated between 250 to 50 ma fall within the 125 80 ma range this period of intense alkaline activity during the mid cretaceous formed the peri atlantic alkaline pulse paap the mechanisms for the opening of the atlantic ocean as well as for the camp and later paap magmatic events have been attributed either to deep mantle plumes or to a combination of tensional forces lithospheric rifting and structural controls we describe the paap event for the first time and test the plume and structural models the paap displays evidence of strong structural control and appears to be related to reactivation of pre existing lithospheric structures throughout the peri atlantic zone early stages of continental separation and abrupt changes in plate motion were the most likely mechanisms for the reactivation of favourably oriented pre existing structures mid cretaceous pulses in alkaline magmatic activity were closely associated with major atlantic tectonic events the opening of the south atlantic the change in intensity and direction of both seafloor spreading and plate motion and the consequent fluctuation in intra plate stresses were responsible for two spikes in peri atlantic alkaline magmatism at 125 ma and 85 80 ma the general lack of evidence for a deep hotspot associated with the peri atlantic zone seems incompatible with a mantle plume origin on the other hand the spatial distribution of the paap along passive continental margins suggests an ideal setting for the development of edge driven convection we propose that the periodic reactivation of deep seated pre existing zones of weakness during the major stages of atlantic tectonic evolution combined with coeval asthenospheric upwelling due to edge driven convection and continental insulation flow enhanced the ascent of alkaline magmas this mechanism of shallow small scale upwelling during periodic structural reactivation provides a more likely explanation for the paap than the commonly proposed deep mantle plume scenario

40ar 39ar geochronology of neogene phreatomagmatic volcanism in the western pannonian basin hungary abstract neogene alkaline basaltic volcanic fields in the western pannonian basin hungary including the bakony balaton highland and the little hungarian plain volcanic fields are the erosional remnants of clusters of small volume possibly monogenetic volcanoes moderately to strongly eroded maars tuff rings scoria cones and associated lava flows span an age range of ca 6 myr as previously determined by the k ar method high resolution 40 ar 39 ar plateau ages on 18 samples have been obtained to determine the age range for the western pannonian basin neogene intracontinental volcanic province the new 40 ar 39 ar age determinations confirm the previously obtained k ar ages in the sense that no systematic biases were found between the two data sets however our study also serves to illustrate the inherent advantages of the 40 ar 39 ar technique greater analytical precision and internal tests for reliability of the obtained results provide more stringent constraints on reconstructions of the magmatic evolution of the volcanic field periods of increased activity with multiple eruptions occurred at ca 7 95 ma 4 10 ma 3 80 ma and 3 00 ma these new results more precisely date remnants of lava lakes or flows that define geomorphological marker horizons for which the age is significant for interpreting the erosion history of the landscape the results also demonstrate that during short periods of more intense activity not only were new centers formed but pre existing centers were rejuvenated

pyrenean orogeny and plate kinematics 1 the evolution of the pyrenees a mountain range between iberia and eurasia has remained the subject of many debates between geologists and geophysicists for a long time by combining the identification of seafloor spreading anomalies a33o to m0 in the bay of biscay with those in the north atlantic we have derived a position of a mean pole of rotation for the entire opening of the bay of biscay four hundred kilometers of shortening took place between the iberian and eurasian plates in the pyrenean domain during the opening of the bay of biscay from chrons m0 to a33o time 118 to 80 ma the deep seismic etude continentale et oceanique par reflexion et refraction sismique ecors profile shot across the pyrenees and teleseismic data show the presence of two distinct slabs which dip to the north the southern slab is linked to the subduction of the neo tethys ocean which was created from late jurassic to early aptian simultaneously elongated back arc basins formed along the future pyrenean domain this slab was active from at least 118 ma early aptian to 100 ma late albian the northern slab active since 85 ma is linked to the subduction of the lower continental crust located south of the pyrenean domain in the upper crust normal faults as well as the north pyrenean fault became reverse faults and former back arc basins were inverted giving rise to the uplift of the pyrenees as a double asymmetrical wedge

mesozoic evolution of the upper mantle beneath the eastern pyrenees evidence from xenoliths in triassic and cretaceous alkaline volcanics of the eastern corbieres france abstract upper mantle material can be sampled from two distinctive suites in the north pyrenean zone npz of the pyrenees these occur either as ultramafic tectonic slices in the central and western part of the npz or as discrete xenoliths in alkaline magmas in its eastern part know as the corbieres in the eastern part of the pnz two ultramafic xenolith suites have been found the first suite is enclosed within triassic basalts and the second suite is enclosed within cretaceous monchiquites both suites essentially comprise spinel peridotites showing varying degrees of depletion but each clearly distinguishable by texture and mineral chemistry the triassic suite of ultramafic xenoliths is characterized by coarse texture and homogeneous composition of mineral constituents this records equilibrium temperature of around 950 c before inclusion in the host basalt they represent fragments of an upper mantle type normally occurring beneath continental rift systems the cretaceous suite of ultramafic xenoliths display porphyroclastic textures which grade locally to ultramylonites the pyroxene porphyroclasts are compositionally zoned titanian pargasite is ubiquitous and equilibrium temperatures of around 750 800 c are indicated they appear to be similar to peridotites occurring in ultramafic tectonic massifs in the npz and with a common texture mineralogy and thermal history this indicates therefore that shear deformation and alkaline magmatism experienced during the middle cretaceous affected the upper mantle along the entire length of the npz this can then be related to the regional transcurrent movements that were produced by sinistral strike slip of iberia with respect to the rest of europe

carbonate platform growth influenced by contemporaneous basaltic intrusion albian of larrano spain carbonate platform growth in active tectonic settings may be strongly influenced by the structural evolution of the basin including volcanic activity in this paper the sedimentary tectonic evolution of the duranguesado carbonate platform larrano in northern spain is described and an evolutionary depositional model is presented the albian duranguesado carbonate platform deposits are dominated by rudist and coral limestones with small intervening argillaceous limestone filled troughs 10 30 m deep the platform succession is divided into two parts the lower platform deposits were intruded by volcanics and tilted before the deposition of the upper platform succession a volcanic vent plug filling an upward flaring pipe occurs in the lower carbonate platform succession the timing of intrusion is well constrained to the early albian tectonic extension and active deep seated strike slip faults induced magma ascent at a fault intersection sedimentological analysis of these areas indicates that before volcanic intrusion they acted as weakened zones of extension and were slightly more subsident basinal areas these sites contain anomalous accumulations of siliceous sponge spicule deposits linked to the release of hydrothermal fluids on the sea floor after the phase of intrusion tilting and erosion of the platform and its associated volcanic products occurred as the intrusion cooled the platform downwarped leading to the formation of an overlying perched capping basin bordered by carbonate platforms over the volcanic plug carbonate mounds grew on local palaeohighs the presence of strike slip and magma emplacement in the duranguesado platform is related to movements between the iberian and european lithospheric plates which were accommodated by rotation and lateral movement of the crust along wrench faults

cretaceous slab break off in the pyrenees iberian plate kinematics in paleomagnetic and mantle reference frames the pyrenees at the iberia europe collision zone contain sediments showing albian cenomanian high temperature metamorphism and coeval alkaline magmatic rocks stemming from different views on jurassic cretaceous iberian microplate kinematics two schools of thought exist on the trigger of this thermal pulse one invoking hyperextension of the iberian and eurasian margins the other suggesting slab break off competing scenarios for mesozoic iberian motion compatible with pyrenean geology comprise 1 transtensional eastward motion of iberia versus eurasia or 2 strike slip motion followed by orthogonal extension both favoring hyperextension related heating and 3 scissor style opening of the bay of biscay coupled with subduction in the pyrenean realm favoring the slab break off hypothesis we test these kinematic scenarios for iberia against a newly compiled paleomagnetic dataset and conclude that the scissor type scenario is the only one consistent with a well defined 35 counterclockwise rotation of iberia during the early aptian we proceed to show that when taking absolute plate motions into account aptian oceanic subduction in the pyrenees followed by late aptian early albian slab break off should leave a slab remnant in the present day mid mantle below nw africa mantle tomography shows the reggane anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500 km depth below southern algeria mantle tomography is therefore consistent with the scissor type opening of the bay of biscay coupled with subduction in the pyrenean realm slab break off may thus explain high temperature metamorphism and alkaline magmatism during the albian cenomanian in the pyrenees whereas hyperextension that exhumed pyrenean mantle bodies occurred much earlier in the jurassic

mineralogy and sulfur isotope geochemistry of polymetallic porphyry epithermal mineralization peripheral to the golden sunlight gold mine montana abstract the golden sunlight mine located 50 km east of the famous butte porphyry lode deposit is the largest gold mine in montana and has produced over 3 6 m oz of gold in its 36 year history most of this gold has come from the mineral hill breccia pipe mhbp a west plunging cylindrical body of brecciated latite porphyry and siliciclastic sedimentary rocks of the mesoproterozoic belt supergroup this paper focuses on four areas of mineralization outside the mhbp termed the apex bonanza north pit and 102 sunlight zones the apex and 102 sunlight areas consist of auriferous pyrite rich veins cutting precambrian sediments and the cambrian flathead quartzite whereas the bonanza and north pit areas are polymetallic mo cu ag au prospects hosted in latite porphyry and belt sediments recent dating 40ar 39ar of igneous biotite shows the porphyry at bonanza was emplaced at 78 1 ma which is several m y younger than the porphyry associated with the mhbp 81 9 1 9 ma zircon u pb and several m y older than the main phase of the boulder batholith that hosts the butte deposit overall the ore and gangue mineral assemblages in the peripheral deposits are similar to those described previously for the mhbp deposit pyrite locally as rich is abundant in all settings with varying amounts of galena sphalerite chalcopyrite bornite molybdenite at bonanza tetrahedrite tennantite and traces of pearceite tetradymite aikinite calaverite petzite goldfieldite buckhornite gold and electrum gangue minerals include quartz carbonates fe dolomite siderite magnesite barite anhydrite adularia and alumino phosphate sulfate aps minerals spectral analysis indicates that some of the adularia is ammonium rich i e buddingtonite values of 34s for sulfide minerals from the peripheral deposits overlap with values obtained by previous workers from the mhbp the bulk of the analyses including all samples from the porphyry hosted bonanza deposit have 34s values between 12 and 4 with a tail to heavier values 5 it is postulated that most of the lighter s was introduced into the district by late cretaceous magmatic hydrothermal fluids whereas the heavier s is attributed to sedimentary pyrite in the precambrian greyson and lahood formations a weak negative correlation exists between gold grade and the 34s of associated pyrite all samples in this study that contain 0 1 oz ton au have 34s reduced s

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

delineating mineralized phases based on lithogeochemical data using multifractal model in touzlar epithermal au ag cu deposit nw iran the aim of this study is to delineate and separate mineralization phases based on surface lithogeochemical au ag as and cu data using the concentration area c a fractal method in the touzlar epithermal au ag cu deposit nw iran four mineralization phases delineated by multifractal modeling for these elements are correlated with the findings of mineralization phases from geological studies the extreme phase of au mineralization is higher than 3 38 ppm which is correlated with the main sulfidation phase whereas ag extreme phase higher than 52 48 ppm is associated with silicic veins and veinlets the resulting multifractal modeling illustrates that au and ag have two different mineralization trends in this area extreme higher than 398 1 ppm and high mineralization phases of cu from the c a method correlate with hydrothermal breccias and main sulfidation stage in the deposit respectively different stages of au mineralization have relationships with as enrichment especially in high and extreme higher than 7 9 phases the obtained results were compared with fault distribution patterns showing a positive correlation between mineralization phases and the faults present in the deposit moreover mineralization phases of these elements demonstrate a good correlation with silicification and silicic veins and veinlets

gold mineralization in the northern margin of the north china craton influence of alkaline magmatism and regional tectonic during middle paleozoic mesozoic abstract the northern margin of north china craton nncc has undergone multiple tectonic and magmatic episodes associated with numerous gold mineralization during devonian to cretaceous the origin of gold mineralization is a subject of debate in the nncc but there is a consensus on a metamorphic hydrothermal origin and a magmatic hydrothermal origin for this study we focused on four gold districts including the daqingshan zhangjiakou west liaoning and changbaishan from west to east we specifically constrain the link between the hadamengou dongping jinchanggouliang erdaogou and haigou gold deposits and their magmatic episodes the dahuabei and haigou granites and dongping syenite rocks have an alkaline affinity in contrast the xitaizi jinchanggouliang and xiaoxigou granites as well as the duimiangou quartz monzonites are calc alkaline with high alkaline rocks they are predominantly metaluminous and high fractionated i type granites except the xiaoxigou granite which is a type granites with peraluminous nature this indicates a variable mixing between depleted mantle derived mafic magma and ancient crust derived magma the magmatic events overlap the gold mineralization episodes in the nncc we have identified four magmatic episodes during middle paleozoic to mesozoic at 400 320 ma 245 221 ma 199 161 ma and 143 125 ma on the other hand gold mineralization was emplaced from carboniferous to cretaceous 390 110 ma with a peak in the middle jurassic 170 160 ma the available sulfur oxygen and carbon isotopic data from the studied nncc gold deposits suggest that the ore forming fluids were derived from a mixture of magmatic fluids and meteoric waters that flow in the wall rocks except for the hadamengou and jinchanggouliang gold deposits both late deposits present a multi source involving organic matter and other regional crustal rocks as shown by their positive 34s values 0 6 18 5 the intrusive rocks and sulfides in the nncc display similar lead isotope data suggesting that the lead isotopes might have similar origin the gold forming materials resulting from the mixing of these fluids are the product of several alkaline magmatism activities in this region hence this study has proved that gold mineralization is spatially and temporally related to the alkaline magmatism in the nncc the dominant tectonic events in the nncc are marked by post collisional or anorogenic geodynamical setting which is characterized by high alkaline features and andean type arc related to subduction geodynamical setting and characterized by calc alkaline features of the studied rocks both tectonic events are controlled by 1 the collision between the ncc and the bainaimiao arc 2 the subduction of the paleo asian ocean plate beneath the ncc 3 the collision between the siberian craton and the ncc and 4 the subduction of the western paleo pacific beneath the ncc these tectonic regimes are expressed by a transitional regime changing from compression to extension at western and an extensional regime at western and eastern parts of the nncc respectively

structure and organization of submarine basaltic flows sheet flow transformation into pillow lavas in shallow submarine environments distal pillows occur associated with a sheet flow and megapillows in the menakoz outcrops of the basque cantabrian basin n spain basaltic volcanic rocks are interbedded with turonian sediments and depict typical features of shallow submarine emissions an exceptional basaltic flow displays four types of morphology 1 sheet lava with columnar jointing 2 welded columnar breccia 3 megapillows and 4 pillow lavas with sparse megapillows the field data from menakoz combined with experimental and field data from the literature for similar volcanic facies can be integrated into a new propagation model for the transition from sheet flows to pillow lavas in underwater environments at near vent high emission rates lava flows develop a thin crust immediately after its emplacement and break at the front under the magma pressure allowing for the massive propagation of lava as a sheet flow increased cooling promotes thickening of the lava outer crust far from the vent while continuous supply of fresh magma increases the pressure onto the thick crust until its rupture the lava emitted in small volumes from the flow front promotes the formation of megapillows and pillow lavas that are later on covered by the advancing sheet flow the lava flow freezes progressively toward more distal parts gradually increasing its viscosity until it stops the crust temporarily holds the residual melt pressure increasing the volume of the flow distal section by inflation finally the internal magma pressure breaks the crust and liberates lava at moderate to low flow rates producing pillows while lava drainage inside the inflated sheet flow produces lava tunnels and gravitational collapse of the roofs by hydrostatic pressure to form breccias nurtured by columnar lava fragments

formation of the trimouns talc chlorite deposit pyrenees from persistent hydrothermal activity between 112 and 97 ma for many economically important deposits precise duration and age of hydrothermal ore formation are poorly known we tackle these questions for the large trimouns talc chlorite deposit by u pb analyses of xenotime and monazite which crystallized within cm size geodes in the hanging wall dolostones formation of geodes and ree minerals occurred in relation to 300 350 c 0 2 0 3 gpa metasomatism along a host shear zone sixteen xenotime fragments broken off from four single euhedral grains define an age range from 112 to 97 myr and a monazite age of 99 myr some ages of individual fragments are grain specific whereas others show the same range of dates given the analytical uncertainties on individual fragments about 1 myr the absence of inherited components and the fact that no thermal event has affected these crystals after their formation these ages are interpreted to record continuous crystallization between 112 and 97 ma this means that the trimouns deposit was produced by hydrothermal activity lasting for at least 16 million years occurring along a shear zone through which fluids continuously or episodically circulated to allow ion transport from the country gneisses to the deposit locality persistent deformation and high heat flow related to the transtensional regime that opened the bay of biscay seems to be the most likely tectonic scenario to explain this activity

gold in turkey a missing link in tethyan metallogeny abstract the gold metallogeny of turkey constitutes a sector of the tethyan eurasian metallogenic belt temb within the alpine himalayan orogenic system that formed from jurassic cretaceous to the present this orogenic system produced many different types of deposits related to subduction collision post collision and rifting processes gold deposits as well as other mineral deposits of turkey are mainly concentrated in late mesozoic and tertiary rocks evaluation of the gold metallogeny of turkey is based on a gis database compilation of known gold deposits and prospects currently available data show that turkey has a gold endowment including reserves and resources of approximately 31 5 m oz 979 tonnes in 51 deposits 21 of which contain more than 0 2 m oz gold the other 30 deposits contain a total of approximately 1 m oz 31 tonnes gold resources two recent discoveries kisladag and copler currently contain total resources of 17 6 m oz au 549 tonnes more than 50 of the total turkish gold endowment turkey possesses a wide spectrum of gold deposits related to mesozoic and cenozoic volcanoplutonic arcs however porphyry gold copper epithermal gold including both high and low sulfidation styles and gold rich volcanic associated massive sulfide including both kuroko and cyprus types are the most economically important to date orogenic gold including listwanite hosted placer gold and skarn hosted gold are relatively less important or abundant deposit types other potential gold systems for exploration include carlin type gold detachment fault related gold iron oxide copper gold and gold in carbonate replacement and manganese deposits

the rotation of iberia during the aptian and the opening of the bay of biscay abstract the cretaceous rotation of the iberian plate in a geodynamical active setting between africa and europe is contemporaneous with the opening of the northern atlantic ocean and provides fundamental temporal and kinematical constraints on the evolution of the bay of biscay and the pyrenees here we report new paleomagnetic data from 50 sites 1109 drilled cores from marine sediments of the cretaceous organya basin in the southern pyrenees to constrain the timing and magnitude of the rotation of iberia berriasian to barremian directions in exclusively limestone lithology are remagnetised in agreement with previous organya basin studies the aptian to cenomanian marls and limestones in the organya basin however provide primary magnetisations asserted by rock magnetic experiments and positive fold tests our results constrain the rotation of iberia to be finished just before the albian paleomagnetic data cannot well constrain the onset of the rotation but sea floor anomaly studies restrict the onset of the rotation to anomaly m0 or the barremian aptian boundary this implies that the entire rotation of iberia happened in one single phase and is confined to the aptian this is in contrast to earlier studies that suggested a two phase rotation of iberia but we argue that the large errors in published ages are not in disagreement with our results in summary we constrain the 35 rotation of iberia to the aptian period which implies a rotation rate of 2 7 5 1 myr depending on the controversial duration of the aptian

the geology and geochemistry of jinchangyu gold deposit north china craton implications for metallogenesis and geodynamic setting abstract the jinchangyu au deposits contained an original resource of 50 t of gold and is located close to the northeastern margin of the north china craton ncc the orebodies are controlled by structures in the amphibolite units of the archaean zunhua group mineralization is generally associated with albite and hematite which is indicative of na al si fe alteration the most common styles of mineralization are subdivided based on the cross cutting relationships of mineral assemblages as follows i quartz albite hematite ii quartz albite polymetallic sulfides with gold and molybdenite iii quartz pyrite and iv quartz carbonate quartz samples from the second stage ii and third stage iii assemblages contain two phase fluid inclusion types these are i co2 h2o fluid inclusions and ii daughter mineral bearing inclusions which have homogenization temperatures of 270 350 c for assemblage stage ii and 180 240 c for stage iii and salinities of 13 wt nacl equiv a few s type fluid inclusions suggesting salinities of 27 6 28 3 wt nacl equiv the s isotope composition of pyrite and molybdenite from stage ii 34s 4 4 to 1 9 indicates that the mineralizing fluid originated predominantly from a magmatic source the h o isotope signatures from stage ii indicate a magmatic dominated source for the mineralizing fluid with some addition of meteoric fluids previously published pb and c isotope data indicate that ore and magma in the eastern part of the hebei province of china interacted with precambrian country rocks and so the fluids moved from the lower crust to shallower level during mineralization the red quartz albite hematite veins from jinchangyu were generated under strongly oxidizing alkaline conditions that were favorable for the incorporation of gold into the fluid and the crystallization of albite during the early stage of gold deposition seven molybdenite samples from jinchangyu yield re os model ages of ca 233 to 219 ma with a weighted mean age of 225 4 ma and an isochron age of 223 5 ma this indicates that at least some of the gold associated with molybdenite is late triassic in age and could be associated with buried intrusions that are part of the late triassic dushan granites in the eastern portion of the ncc this mineralization was formed after the closure of the paleo asian ocean these results indicate that the intrusion related jinchangyu deposit is the far field structural product of the collision of the ncc with the siberian craton to the north along the northern margin of the ncc

ijolite versus carbonatite as sources of fenitization ijolite carbonatite complexes are ubiquitously surrounded of an aureole of metasomatically altered rocks the process of alteration is termed fenitization and is generally caused by peralkaline fluids emanating from cooling alkaline i e ijolite and carbonatite magmas ijolites and carbonatites normally occur together and attempts to determine the source of the fenitizing fluids may therefore lead to controversial if not erroneous conclusions mineralogical and chemical data of fenites from oldoinyo lengai tanzania fen norway and alno sweden are reviewed in the present paper in order to reveal the main factors controlling the fenitization around ijolite and carbonatite despite the overall alkaline nature of the process variables such as xco2 of the fluid activity gradients of sio2 al2o3 and cao feo mgo ratio fo2 and temperature gradients may differ producing distinctive patterns of fenitization around the two magmatic sources the ijolitic type fluid has low xco2 high activities of alkalies sio2 and al2o3 and low activity of cao the fo2 evolves along the hm mt buffer conditions and the temperature falls gradually with distance from the magmatic source the carbonatitic type fluid has high xco2 high activities of alkalies and cao and low activities of sio2 and al2o3 temperatures and fo2 are initially high but decrease sharply with distance from the source moreover the co2 rich fluid may complex and transport the ree

mantle exhumation crustal denudation and gravity tectonics during cretaceous rifting in the pyrenean realm sw europe insights from the geological setting of the lherzolite bodies 1 the pyrenean peridotites lherzolites form numerous small bodies of subcontinental mantle a few meters to 3 km across exposed within the narrow north pyrenean zone npz of mesozoic sediments paralleling the north pyrenean fault recent studies have shown that mantle exhumation occurred along the future npz during the formation of the albian cenomanian pyrenean basins in relation with detachment tectonics this paper reviews the geological setting of the pyrenean lherzolite bodies and reports new detailed field data from key outcrops in the bearn region only two types of geological settings have to be distinguished among the pyrenean ultramafic bodies in the first type sedimented type or s type the lherzolites occur as clasts of various sizes ranging from millimetric grains to hectometric olistoliths within monogenic or polymictic debris flow deposits of cretaceous age reworking mesozoic sediments in dominant proportions as observed around the lherz body in the second type tectonic type or t type the mantle rocks form hectometric to kilometric slices associated with crustal tectonic lenses both crustal and mantle tectonic lenses are in turn systematically associated with large volumes of strongly deformed triassic rocks and have fault contacts with units of deformed jurassic and lower cretaceous sediments belonging to the cover of the npz these deformed mesozoic formations are not older that the aptian early albian they are unconformably overlain by the albian cenomanian flysch formations and have experienced high temperature low pressure mid cretaceous metamorphism at variable grades such a tectonic setting characterizes most of the lherzolite bodies exposed in the western pyrenees these geological data first provide evidence of detachment tectonics leading to manle exhumation and second emphasize the role of gravity sliding of the mesozoic cover in the preorogenic evolution of the pyrenean realm in the light of such evidence a simple model of basin development can be inferred involving extreme thinning of the crust and mantle uprising along a major detachment fault we demonstrate coeval development of a crust mantle detachment fault and generalized gravitational sliding of the mesozoic cover along low angle faults involving triassic salt deposits as a tectonic sole this model accounts for the basic characteristics of the precollisional rift evolution in the pyrenean realm

evidence for a genetic link between gold silver telluride and porphyry molybdenum mineralization at the golden sunlight deposit whitehall montana fluid inclusion and stable isotope studies the golden sunlight gold silver telluride deposit hosted primarily within the mineral hill breccia pipe is spatially related to a high level late cretaceous multiphase alkaline to subalkaline porphyry system latite porphyries quartz monzodiorite and lamprophyres base metal veins and manganese rhodochrosite mineralization occur up to 2 km from the mineral hill breccia pipe and form part of a regional mineral zonation pattern genetically related to a low grade porphyry molybdenum system alteration associated with this system consists of a proximal zone pervasive in style disseminations and veinlets that is core to the alkaline igneous rocks and a distal zone that is vein controlled proximal alteration is composed of an early barren zone of quartz hematite pyrite and barite as well as a pervasive zone composed of quartz sericite k feldspar base metal sulfides tellurides molybdenite and native gold distal alteration is characterized by the same mineralogy as the precious and base metal zone of the proximal zone except that it is vein controlled and does not contain molybdenite a base metal and rhodochrosite zone occurs farthest from the center of the porphyry system k feldspar alteration occurs as selvages to quartz molybdenite mineralization and as a pervasive replacement of clasts in the mineral hill breccia pipe early whereas quartz sericite alteration is dominantly associated with auriferous veins and the breccia pipe late molybdenite occurs in high veinlet density quartz veins at the margins and deeper portions of the breccia pipe in clasts in prebreccia pipe quartz pyrite k feldspar veinlets as fine grained disseminations in breccia fragments and as rims to fragments of xenolithic latite previously four periods of hypogene mineralization in the breccia pipe were identified stages i and iv constitute asymp 99 percent of the mineralization native gold calavertite and bi tellurides sulfosalts occur in stage i whereas au ag tellurides developed in stage iii minor amounts of base metals are present in stage ii whereas barite dolomite magnesite trace kaolinite and sericite develop in stage iv proterozoic rocks of the lahood formation and the informally named bull mountain group host the breccia pipe and contain strata bound sulfides sulfosalts up to 50 pyrite with minor to trace amounts of chalcopyrite tennantite pyrrhotite sphalerite galena and molybdenite fluid inclusion homogenization temperatures of primary and pseudosecondary aqueous liquid vapor inclusions constant liquid to vapor ratios in quartz pyrite molybdenite veins range from 131 8 degrees to 398 2 degrees c primary and pseudosecondary inclusions with highly variable liquid vapor ratios that coexist with rare three phase co 2 h 2 o and multiphase inclusions one or more solid phases in addition to liquid and vapor also occur in quartz pyrite k feldspar molybdenite veins and indicate periods of intermittent boiling homogenization temperatures for fluid inclusions in stage i auriferous pyrite veins range from 145 degrees to 345 degrees c with salinities of asymp 1 to 10 wt percent nacl equiv values of delta 34 s for sulfides in the mineral hill breccia pipe quartz pyrite k feldspar molybdenite veins proterozoic sedimentary rocks and distal base metal veins range from 12 2 to 3 1 per mil 8 1 to 0 8 per mil 0 7 to 6 1 per mil and 8 9 to 9 5 per mil respectively and suggest a mixed magmatic sedimentary sulfur source calculated delta 18 o values for water in equilibrium with late stage sericite at 170 degrees c vary from 0 7 to 2 8 per mil whereas delta d water values range from 67 to 8 per mil geologic paragenetic fluid inclusion and stable isotope studies are consistent with an early magmatic fluid associated with quartz pyrite k feldspar molybdenite veins that subsequently mixed with meteoric water during stages i to iv breccia pipe hosted and auriferous pyrite vein formation ore forming components e g au ag te cu bi mo and much of the s were most likely derived from the late cretaceous intrusive system with possible contributions from the proterozoic host rocks

resources of gold in phanerozoic epithermal deposits we have estimated earth s endowment of gold in phanerozoic epithermal deposits using a tectonic diffusion model which simulates the emplacement of deposits at a shallow crustal depth and their subsequent vertical tectonic migration in the crust the calculation was calibrated by least squares comparison of a calculated age frequency distribution to the age frequency distribution for 448 epithermal deposits of phanerozoic age results indicate that 17 percent of the epithermal deposits that formed through phanerozoic time remain in the crust today whereas 83 percent have been removed by erosion assuming a similar age distribution for all 1 181 epithermal deposits in our compilation indicates that 307 000 deposits formed throughout phanerozoic time that 63 000 of these remain in the crust and that 244 000 have been eroded grade and tonnage data of gold in 757 epithermal deposits in the compilation have an arithmetic average of 34 7 t and yield an estimate of 2 2 106 t of gold for epithermal deposits remaining in the crust using the model based vertical distribution of deposits remaining in the crust we estimate that epithermal deposits in the upper kilometer of the united states contain 2 9 104 t of gold adjusting for areas of outcropping volcanic rocks in each continent increases our estimate to 4 0 104 t these estimates are similar to the 1 7 104 t gold resource estimated by the u s geological survey using completely different methods several comparisons based on these results provide insights into the efficiency of processes that form epithermal deposits and the outlook for sustainability for instance all of the epithermal deposits that formed through phanerozoic time represent only about 0 03 percent of the gold in the crust only about 0 007 percent of crustal gold remains in epithermal deposits the rest has been eroded and recycled this is consistent with comparisons based on the flux of gold in the taupo volcanic zone which indicate that epithermal deposits trap only 0 1 to 0 2 percent of the gold that moves through convergent margin hydrothermal systems epithermal gold deposits that remain in the crust can supply current production from them for 1 400 to 5 000 years depending on success of exploration and depth of mining finally we are consuming gold from epithermal deposits about 17 000 times faster than earth is replenishing the supply

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

diatreme forming volcanism in a deep water faulted basin margin lower cretaceous outcrops from the basque cantabrian basin western pyrenees abstract deep water diatremes and related eruption products are rare and they have been mainly interpreted from seismic based data we present lithofacies and geochemistry analysis of two lower cretaceous albian deep water diatremes and associated extra diatreme volcaniclastic deposits at a well exposed outcrop of the northern margin of the basque cantabrian basin north iberia the studied diatremes are located along a n s trending albian fault and present sub circular to elongate sections inward dipping steep walls and smooth to very irregular contacts with the host rocks they are filled by un bedded mixed breccias constituted by juvenile and lithic sedimentary igneous and metamorphic clasts their textural and structural characteristics indicate that they represent lower diatreme and root zones of the volcanic system mapping geochemical and petrologic data from diatreme fills support their genetic relationship with the extra diatreme volcaniclastic beds which would be generated by the eruption of an incipiently vesicular trachytic magma studied diatremes result from multiple explosions that lasted over an estimated period of 65 k y during the late albian h varicosum ammonite zone pro parte and reached up to a maximum subsurface depth of ca 370 m whereas extra diatreme volcaniclastic beds were formed by eruption fed gravity driven flows on the deep water 200 500 m paleoseabed petrological features suggest that these diatremes and related extra diatreme deposits resulted mainly from phreatomagmatic explosions in addition organic geochemistry data indicate that the thermal effect of the trachytic melts on the sedimentary host caused the conversion of the abundant organic matter to methane and co 2 gases which could also contribute significantly to the overpressure necessary for the explosive fragmentation of the magma and the host rocks considering the inferred confining pressures ca 8 11 mpa and the possible participation of unvesiculated or degassed melts our results stress the importance of active hydraulic structures e g faults and the supplementary driving forces e g thermogenic gases in the formation of deep water marine diatremes

testing iberian kinematics at jurassic cretaceous times 1 paleogeographic reconstructions of iberia at the mesozoic are still a matter of debate the incompatibility between kinematic models and paleomagnetic data older than 120 ma is a major problem for which no cause has yet been determined here we use a new method to investigate the origin of this misfit we solve the inverse problem of finding the euler poles that fit paleomagnetic poles with the global apparent polar wander path gapwp and then test their implications on iberian reconstructions we show that iberian poles from the early cretaceous mean poles for 123 and 130 ma are incompatible with the gapwp bringing into question their validity contrarily late jurassic data mean pole at 151 ma are compatible with the gapwp and thus can be considered reliable based on these results we propose a new magnetic reconstruction of iberia and surrounding plates at 150 ma m22 anomaly this work provides new constraints for the kinematic evolution of iberia during jurassic cretaceous however the development of a detailed and consensual model for the kinematic evolution of iberia is dependent on the acquisition of new high quality paleomagnetic data and a reevaluation of seafloor magnetic anomalies

intraplate mafic magmatism degasification and deposition of mercury the giant almaden mercury deposit spain revisited abstract the giant almaden mercury deposit spain is hosted by the lower silurian criadero quartzite in turn this ore bearing rock unit is cross cut by the so called frailesca unit a diatreme body of basaltic composition the geochemical characteristics of the silurian to devonian almaden district volcanic units indicate that these rocks originated from an enriched evolving mantle source that ultimately yielded basanites nephelinites to rhyolites through olivine basalts pyroxene basalts trachybasalts trachytes very scarce rhyolites and quartz diabases the silurian intraplate alkaline volcanism developed in submarine conditions which triggered widespread hydrothermal activity resulting in hg ore formation and pervasive alteration to carbonates the 18 o 13 c and 34 s isotopic signatures for carbonates and pyrite suggest different sources for carbon and sulfur including magmatic and organic for the former and magmatic and sea water for the latter the most important and efficient natural source of mercury on earth is by far the volcanic activity which liberates mercury via quiescent degassing and catastrophic plinian events when eruptions can overwhelm the atmospheric budget of hg thus we suggest that co 2 degasification and coeval distillation of mercury from the volcanic rocks fed the huge hydrothermal system that led to massive deposition of mercury at almaden build up of hg 0 gas in magmatic chambers during waning rifting in the late ordovician followed by renewed volcanism in the early silurian would have resulted in massive degasification of the accumulated mercury part of this mercury went into the criadero quartzite leading to formation of the huge almaden deposit and others e g el entredicho along the same stratigraphic level progressive depletion of the deep seated magmatic hg stock would have resulted in a drastic reduction in ore deposit size after the lower silurian when smaller deposits formed e g las cuevas

the late cretaceous alkaline igneous province in the iberian peninsula and its tectonic significance abstract the iberian province consists of the following the three subvolcanic syenitic major intrusive complexes of monchique sines and sintra in w and sw portugal together with their basanitic lamprophyric minor intrusive suites basanitic volcanic complexes around lisbon at least some of a widespread suite of basanitic to theralitic minor intrusives in west central portugal about 80 small basanitic lamprophyric to nepheline syenitic intrusions scattered through the pyrenees ne spain the french corbieres and off the coast of nw spain and the ormonde seamount of the gorringe bank off the sw coast of portugal most of these occurrences have been dated isotopically or from field evidence as late cretaceous geological and petrological details of the various occurrences are compiled and reviewed primary basanitic magmas were probably parental to the entire province and generated syenitic magmas by differentiation processes oversaturated rocks were produced by alkali loss and perhaps also by crustal involvement the iberian province is related to the opening of the n atlantic specifically that of the bay of biscay

magnetic evidence for slow seafloor spreading during the formation of the newfoundland and iberian margins there is considerable debate concerning the nature and origin of the thin crust within the ocean continent transition oct zones of many passive non volcanic continental margins located between thinned continental and true oceanic crust this crust is usually found to be underlain by upper mantle material of 7 2 7 4 km s velocity at shallow depths 1 2 km it has been proposed that such crustal material could have originated either by exhumation of upper mantle material during rifting of continents or by slow seafloor spreading one of the examples of occurrence of such a crust are the conjugate margins of newfoundland and iberia here we present an interpretation of magnetic data from these regions to show that their oct zones are underlain by crustal material formed by slow seafloor spreading 6 7 mm yr soon after iberia separated from the grand banks of newfoundland in the late jurassic similarities in the magnetic anomalies and velocity distributions from these regions with those from the sohm abyssal plain a region lying immediately south of the newfoundland basin and formed by seafloor spreading at a similar rate of spreading give further support to such an interpretation the idea that these regions were formed by unroofing of upper mantle during rifting of iberia from newfoundland may be likely but the presence of weak magnetic anomalies in these regions which bear all the characteristics of seafloor spreading anomalies makes it difficult to ignore the possibility that these regions could be underlain by oceanic crust formed during slow seafloor spreading the similarities in velocity structure and the presence of small amplitude magnetic anomalies both across this pair of conjugate margins of the north atlantic and that of the labrador sea suggest that this oct velocity structure may be the norm rather than the exception across those passive non volcanic margins where the initial seafloor spreading was slow furthermore the existence of similar velocity distributions along a few active spreading centers raises the possibility of formation of similar crust across slow spreading ridges fl 2000 elsevier science b v all rights reserved

porphyry cu au mineralization in the mirkuh ali mirza magmatic complex nw iran abstract the mirkuh ali mirza cu au porphyry system in east azerbaijan province is located on the western part of the cenozoic alborz azerbaijan volcanic belt the belt is also an important cu mo au metallogenic province in northwestern iran the exposed rocks in the study area consist of a volcaniclastic sequence subvolcanic rocks and intermediate to mafic lava flows of neogene age the volcanic rocks show a typical subduction related magmatic arc geological and geochemical signature with low concentration of nb ta and ti mineralization is hosted by neogene dacitic tuff and porphyritic dacite situated at the intersections of northeast and northwest faults field observations alteration zonation geochemical haloes and isotopic data of the mirkuh ali mirza magmatic complex show similarities with typical convergent margin cu au porphyry type deposits the following features confirm the classic model for cu au porphyry systems a close spatial association with high k calcalkaline to shoshonitic rock related to post collision extensional setting b low grade cu 0 57 c stockworks as well as disseminated sulfides c zonality of the alteration patterns from intense phyllic at the center to outward weak phyllic argillic and propylitic d the presence of a pyritic halo e accompanied by sheeted veins and low sulfidation epithermal gold f mineralization spatially associated with intersection of structures g genetically related to diorite porphyry stocks at depth h geochemical zonation of cu au ag bi cu mo bi au pb zn as au mo pb zn as ag sb mn ba pb zn hg hg from center to outwards i the range of sulfur isotopic values is approximately zero interpreted to have magmatic source and similar to other subduction related porphyry cu deposits

high resolution la icp ms trace element mapping of igneous minerals in search of magma histories we report experiments on optimisation of la icp ms mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals the experimental design was refined with maps on clinopyroxene and amphibole macrocrysts mainly antecrysts from a porphyritic lamprophyre in ne spain as well as on a high precision metal wire grid in terms of spatial resolution we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0 4 and 0 7 mu m of material depending on ablation parameters maps were produced with square laser beam spots of 12 and 24 mu m it was found that complexities can be resolved in the sample even though they are smaller than the beam diameter e g 7 10 mu m discontinuities using 12 mu m laser beam resolution in x and y was found to be identical probably reflecting the fast washout of the two volume ablation cell and the short total dwell time of the analyte menu selected due to the excellent stage reproducibility and the limited ablation depth it is feasible to re ablate the identical map area many times employing different instrument parameters or analyte menus on the magmatic crystals la icp ms maps define very sharp compositional zoning in trace elements highlighting complex crystallisation histories where normal magmatic fractionation is not the only process events of mafic recharge are easily recognised as zones enriched in compatible metals such as cr ni or sc further trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data these include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones therefore la icp ms mapping opens a new window of opportunity for analysis of magmatic histories the wide combination of instrumental parameters such as laser beam size scan speed and repetition rate make it possible to carry out experiments at different levels of detail we recommend a two step approach to mapping the initial step involves rapid maps to gain an overview of potential complexities in the sample this enhances representativeness of the analysed materials as a large number of crystals and trace elements can be tested in little time subsequently detailed maps can be carried out on areas of interest an additional functionality is to create 1d profiles from 2d maps the potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond c 2015 elsevier b v all rights reserved