the iberian type of volcano sedimentary massive sulphide deposits the iberian pyrite belt located in the sw iberian peninsula contains many paleozoic giant and supergiant massive sulphide deposits including the largest individual massive sulphide bodies on earth total ore reserves exceed 1500 mt distributed in eight supergiant deposits 100 mt and a number of other smaller deposits commonly with associated stockwork mineralizations and footwall alteration haloes massive sulphide bodies largely consist of pyrite with subordinated sphalerite galena and chalcopyrite and many other minor phases although substantial differences occur between individual deposits both in mineral abundance and spatial distribution these deposits are considered to be volcanogenic roughly similar to volcanic hosted massive sulphides vhms however our major conclusion is that the iberian type of massive sulphides must be considered as a vhms sub type transitional to shms

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

a case study of the internal structures of gossans and weathering processes in the iberian pyrite belt using magnetic fabrics and paleomagnetic dating in the rio tinto district of the iberian pryrite belt of south spain the weathering of massive sulfide bodies form iron caps i e true gossans and their subsequent alteration and re sedimentation has resulted in iron terraces i e displaced gossans to study the stucture and evolution of both types of gossans magnetic investigations have been carried out with two foci 1 the characterisation and spatial distribution of magnetic fabrics in different mineralised settings including massive sulfides gossans and terraces and 2 paleomagnetic dating hematite has been identified as the suceptibility carrier in all sites and magnetic fabric investigation of four gossans reveals a vertical variation from top to bottom with 1 a horizontal foliation refered to as mature fabric in the uppermost part of the primary gossans 2 highly inclined or vertical foliation interpreted as immature fabric between the uppermost and lowermost parts and 3 a vertical foliation interpreted to be inherited from hercynian deformation in the lowermost part of the profiles in terraces a horizontal foliation dominates and is interpreted to be a sedimentary fabric rock magnetic studies of gossan samples have identified goethite as the magnetic remanence carrier for the low temperature component showing either a single direction close to the present earth field pef direction or random directions maghemite hematite and occasionally magnetite are the remanence carriers for the stable high temperature component that is characterized by non pef directions with both normal and reversed magnetic polarities no reliable conclusion can be yet be drawn on the timing of terrace magnetization due to the small number of samples in gossans the polarity is reversed in the upper part and normal in the lower part this vertical distribution with a negative reversal test suggests remanence formation during two distinct periods remanence in the upper parts of the gossans is older than in the lower parts indicating that the alteration proceeded from top to bottom of the profiles in the upper part the older age and the horizontal mature fabric is interpreted to be a high maturation stage of massive sulfides alteration in the lower part the age is younger and the inherited imature vertical hercynian fabric indicates a weak maturation stage these two distinct periods may reflect changes of paleoclimate erosion and or tectonic motion

high pressure metamorphism in the early variscan subduction complex of the sw iberian massif abstract several units exposed in the boundary area of the ossa morena zone omz and the south portuguese zone spz preserve petrographic and thermobarometric evidence for an early metamorphic episode m1 developed under a high p low to intermediate t gradient related to early variscan subduction in the sw iberian massif in the omz these are the cubito moura unit p min 9 2 kbar and t 395 45 c blueschists from its basal melange p min 12 4 kbar and t 310 11 c and the underlying fuenteheridos group p 10 9 0 4 kbar and t 449 31 c the equivalent units in the spz are the la minilla formation p 8 7 0 4 kbar and t 388 16 c and the lawsonite pseudomorphs bearing pulo do lobo formation all these units formed part of an approximately ne verging orogenic wedge present coordinates developed by the accretion of subducted slabs of the outermost margin of gondwana and other elements of the rheic ocean realm from at least the middle devonian to the lowermost tournaisian high pressure rocks were subsequently emplaced on more internal zones of the omz that only experienced a younger high t low to intermediate p metamorphism m2 this high t event was coeval with magmatic activity from the uppermost devonian to the middle mississippian probably as a consequence of transtensional lithospheric thinning and or delamination of the lower crust and mantle lithosphere of the gondwana margin pre late devonian synorogenic sedimentation in forearc and back arc basins of the subduction complex evolved to a late devonian middle mississippian foreland basin system in early collisional stages finally a new middle late mississippian fold and thrust belt with opposite sw vergence and new foreland basins developed during late collisional stages

illite and hydrocarbon exploration illite is a general term for the dioctahedral mica like clay mineral common in sedimentary rocks especially shales illite is of interest to the petroleum industry because it can provide a k ar isotope date that constrains the timing of basin heating events it is critical to establish that hydrocarbon formation and migration occurred after the formation of the trap anticline etc that is to hold the oil illite also may precipitate in the pores of sandstone reservoirs impeding fluid flow illite in shales is a mixture of detrital mica and its weathering products with diagenetic illite formed by reaction with pore fluids during burial k ar ages are apparent ages of mixtures of detrital and diagenetic end members and what we need are the ages of the end members themselves this paper describes a methodology based on mineralogy and crystallography for interpreting the k ar ages from illites in sedimentary rocks and for estimating the ages of the end members

facies architecture and palaeoenvironmental constraints of subaqueous felsic volcanism in the iberian pyrite belt the paymogo volcano sedimentary alignment abstract the paymogo volcano sedimentary alignment pvsa is an essentially igneous sequence associated with vhms deposits of the iberian pyrite belt unlike other areas of this iberian mining district where mafic igneous rocks are abundant in the pvsa these are essentially felsic two facies associations have been distinguished based on petrographic and chemical features a lower dacite facies association and an upper rhyolite facies association the main ore horizons appear related to volcanic breccias of the rhyolite facies association a detailed petrographic study of these breccias suggests they are resedimented hyaloclastite deposits the analysis of volcanic facies indicates that the volcanism developed at water depths deeper than 500 m consistent with the minimum depth at which vhms deposits can form we conclude that detailed volcanological studies provide effective constraints to palaeoenvironmental interpretations which are relevant in assessing regional stratigraphy and area selection for vhms exploration

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

origin and distribution of tonsteins in late permian coal seams of southwestern china abstract we have surveyed the areal and stratigraphic distribution of tonsteins in late permian coalfields of southwestern china over an area of several hundred thousand square kilometers we studied the relationship between tonstein distribution and sedimentary environment based on mineralogical and petrographic data we have concluded that these tonsteins originated as air fall volcanic ashes following accumulation in the peat swamps in situ alteration of the vitric and lithic components took place under acidic conditions leading to the formation of kaolinite based on petrologic mineralogic and chemical analytical data we have determined that the application of mineralogic and geochemical criteria for tonsteins may be useful in correlating coal beds predicting coal qualities and reconstructing related sedimentary paleoenvironmental conditions

chemostratigraphy k ar ages and illitization of silurian k bentonites from the central belt of the southern uplands down longford terrane british isles the central belt of the southern uplands terrane in both scotland and ireland is a faulted and imbricated sequence of caradoc to llandovery shales and llandovery turbidites with numerous interbedded k bentonites the bentonites are composed dominantly of r3 ordered mixedlayer illite smectite i s containing 90 95 illite and represent the product of illitization during low grade metamorphism k ar age determination on the m size fraction gave a range from 379 10 to 406 10 ma the fixed k is thought to have originated in the precursor ash and was remobilized during the transformation of smectite to i s k ar ages record a retrograde thermal event that post dates wenlock prehnite pumpellyite facies metamorphism and is contemporaneous with cooling and uplift during the end silurian early devonian collision of laurentia with the east avalonian terrane differences in rb and other trace elements between the k bentonite beds are due in part to differences in original ash composition and can be used to group the beds within biostratigraphically defined boundaries the chemical identification of groups of k bentonite beds offers additional criteria for their stratigraphical correlation on a regional scale

mineralogy and geochemistry of the subcrenatum marine band and associated coal bearing sediments langsett south yorkshire a detailed description is given of the stratotype marking the namurian westphalian boundary in the carboniferous major element analyses are presented for twelve representative samples including in upward sequence underclay coal nonmarine shale and marine shale the clay mineralogy is described based on powder and smear mounts of whole rock samples and clay sized fractions subjected to standard treatments and cation saturations ascending the sequence there is a decrease in the proportion of kaolinite and increases both in the ratio of discrete illite to mixed layer illite smectite and in their sum chlorite and vermiculite are absent in the underclay but appear higher in the sequence the upward changes are attributed to progressive flooding associated with a eustatic rise in sea level leading to reworking of mature soils in the flood plain environment with time this source decreased in importance compared with the detrital clay input from the primary source area the underclay in the section has undergone extensive alteration indicative of long subaerial exposure possibly due to eustatic fall in sea level

tectonic style and structural analysis of the puebla de guzman antiform iberian pyrite belt south portuguese zone sw spain

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

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

characteristics of zircons from volcanic ash derived tonsteins in late permian coal fields of eastern yunnan china abstract kaolinitic tonsteins of altered synsedimentary volcanic ash fall origin are well developed in the late permian coal bearing formations of eastern yunnan province because of their unique origin wide lateral extent relatively constant thickness and sharp contacts with enclosing strata great importance has been attached to these isochronous petrographic markers in order to compare tonsteins with co existing non cineritic claystones and characterize the individuality of tonsteins from different horizons for coal bed correlation a semi quantitative method was developed that is based on statistical analyses of the concentration and morphology of zircons and their spatial distribution patterns this zircon based analytical method also serves as a means for reconstructing volcanic ash fall dispersal patterns the results demonstrate that zircons from claystones of two different origins i e tonstein and non cineritic claystone differ greatly in their relative abundances crystal morphologies and spatial distribution patterns tonsteins from the same area but from different horizons are characterized by their own unique statistical patterns in terms of zircon concentration values and morphologic parameters crystal length width and the ratio of these values thus facilitating stratigraphic correlation zircons from the same tonstein horizon also show continuous variation in these statistical patterns as a function of areal distribution making it possible to identify the main path and direction in which the volcanic source materials were transported by prevailing winds

supergene enrichment of precious metals by natural amalgamation in the las cruces weathering profile iberian pyrite belt sw spain abstract natural au ag hg alloys occur in the las cruces ore deposit in the eastern part of the iberian pyrite belt they are mainly concentrated in the lower part of the gossan profile including a sheared black shale level where the gossan makes contact with a barren pyrite zone within the supergene cu rich mineralization drill core analyses show a heterogeneous distribution of au ag and hg within the weathering profile with mean values of 5 1 ppm 155 ppm and 52 ppm respectively in general the absolute tenures increase towards the bottom of the weathered profile mineralogical studies conducted on samples from the active mine workings indicate that hg and precious metals occur mainly as au ag hg alloys these associations constitute the best potential resource for precious metals at the las cruces deposit this paper describes how this unusual precious metal enrichment is produced along the weathering profile by supergene processes combining paragenetic information mineral chemistry and the data pertaining to the solubilities of au ag and hg in a weathering profile we suggest a two stage genetic model for the formation of the las cruces au ag hg mineralization 1 release of au ag and hg from the massive sulfide deposit by weathering processes during the gossan formation at ph 0 9 v conditions au ag and hg are mobilized downward through the weathering profile as chloride complexes and fixed as elemental au halides oxides and sulfates and 2 remobilization of hg ag and au in the gossan after the deposit was buried beneath the neogene carbonate rich sedimentary cover the buffering capacity of the percolating fluids due to their interaction with the carbonate rich sedimentary pile leads to significant mineralogical and geochemical changes at near neutral conditions ph 6 7 eh 0 v hg ag and au are newly remobilized as thiosulfate sulfate and hydroxide complexes and newly fixed by sorption during ferric hydroxide formation and as sulfates several cycles of dissolution precipitation of au ag and hg near the redox front occur by oscillations in the water table and changes in the ph eh conditions the interaction of downward migrating fluids with high reductant lithologies black shales and massive sulfides seems to be responsible for the reduction of different complexes and for the precipitation of cinnabar ag sulfides and sulfosalts as well as the precipitation of au ag hg amalgams

geochemistry and u pb dating of felsic volcanic rocks in the riotinto nerva unit iberian pyrite belt spain crustal thinning progressive crustal melting and massive sulphide genesis abstract we present new geochemical sm nd and u pb data on the felsic volcanic rocks containing the world class volcanic hosted massive sulphide deposits in the riotinto nerva unit iberian pyrite belt spain three new u pb ages from older plagioclase quartz phyric dacites and plagioclase phyric rhyolites to youngest plagioclase quartz phyric rhyolites indicate a time span for felsic volcanism ranging from 351 5 0 4 to 345 7 0 6 ma the youngest felsic rocks exhibit lower e nd as well as contrasting ti sr zr hf and eu eu values we interpret that in the riotinto nerva unit crustal melting successively affected shallower more evolved horizons in the crust progressive crustal melting is consistent with current interpretations of the iberian pyrite belt in terms of a late devonian early carboniferous transtensional setting coupled with underplating by basic magma we suggest that low e nd evolved crustal magmatism could be used as a proxy in studies of the genesis of these and possibly other phanerozoic massive sulphide deposits supplementary material details of the analytical methods and whole rock data for basalts are available at http www geolsoc org uk sup18452

comment on a new geodynamic interpretation for the south portuguese zone sw iberia and the iberian pyrite belt genesis by j onezime et al

type of volcanoes hosting the massive sulfide deposits of the iberian pyrite belt the volcanic sedimentary complex vsc of the iberian pyrite belt ipb in southern portugal and spain comprises an upper devonian to lower carboniferous submarine succession with a variety of felsic volcanic lithofacies the architecture of the felsic volcanic centres includes felsic lavas domes pyroclastic units intrusions and minor mafic units that define lava cryptodome pumice cone volcanoes the diversity of volcanic lithofacies recognized in different areas of the ipb mainly reflects variations in proximity to source but also differences in the eruption style the ipb volcanoes are intrabasinal range in length from 2 km to 8 km and their thickest sections vary from 400 m to 800 m these volcanoes are dominated by felsic lavas domes that occur at several stratigraphic positions within the volcanic centre however the pyroclastic units are also abundant and are spatially related to the lavas domes the intrusions are minor and define cryptodomes and partly extrusive cryptodomes the hydrothermal systems that formed the neves corvo and lousal massive sulfide ore deposits are associated with effusive units of felsic volcanic centres at neves corvo the massive sulfide orebodies are associated to rhyolitic lavas that overlie relatively thick fiamme rich pyroclastic unit in several other locations within the belt pyroclastic units contain sulfide clasts that may have been derived from yet to be discovered coeval massive sulfide deposits at or below the sea floor which enhances the exploration potential of these pyroclastic units and demonstrates the need for volcanic facies analysis in exploration

the monterey event in the mediterranean a record from shelf sediments of malta oligo miocene carbonate platform and shelf sediments outcropping on the maltese islands provide an excellent archive of the paleoceanography of the central mediterranean a sequence of shallow water limestones than shelf limestones and marls followed again by shallow water limestones reflects drowning of a carbonate platform the establishment of a shelf environment and in the late miocene renewed progradation and aggradation of shallow water carbonates the sequence recording the deepening of the maltese platform contains several phosphorite hardgrounds and phosphorite pebble beds these phosphorites were dated with strontium isotopes major episodes of phosphogenesis occurred between 25 and 16 ma and they are coeval with those phosphorite events reported from florida and north carolina a miocene carbon isotope and oxygen isotope stratigraphy was established on planktic and benthic foraminifera and on bulk samples a major carbon isotope excursion with an amplitude of up to l between 18 and 12 5 ma can be correlated with the globally recognized monterey carbon isotope excursion this is the first record of this event both in shallow water sediments and in the mediterranean the carbon isotope excursion precedes an oxygen isotope excursion which also was recognized in deep sea records major episodes of phosphogenesis and platform drowning preceded the carbon isotope excursion by up to millions of years

geological constraints on the paleozoic tectonic evolution of tectonostratigraphic terranes in the iberian massif abstract the presence of oceanic paleozoic sequences in the iberian variscan fold belt is used to identify and separate suspected exotic terranes from a reference iberian autochthon terrane which constitutes the greater part of it in this paper the relevant data characterizing the pre accretionary evolution of the paleozoic iberian terranes are presented as well as the available evidence concerning the accretionary process itself emphasis is placed on the analysis of the sedimentary igneous and structural expression of the major events which affected the iberian terranes before during and after their amalgamation the main conclusions of such an analysis may be summarized as follows 1 a recognition of rift and passive margin stages in all the iberian massif terranes during the early paleozoic 2 b late paleozoic accretion of the exotic terranes to the iberian autochthon via a long and complex process variscan orogeny which involved initial subduction underneath the latter and eventual obduction followed by oblique collision of a promontory the iberian autochthon northwestern margin with a northwestern continental block this latter process could account for the large scale crustal imbrication shown by the northern branch of the orogen coeval with predominant strike slip faulting in the southern branch as well as with the formation of the typical arcuate shape of this orogenic belt major present uncertainties relate to the palinspastic provenance of continental suspect terranes and their correlation with similar units in other circum atlantic paleozoic orogens a discussion and speculations on this subject are dealt with in the final section of this paper

volcanic architecture in the odiel river area and the volcanic environment in the riotinto nerva unit iberian pyrite belt spain abstract in order to assess the volcanic architecture of the vsc in the iberian pyrite belt spain a study of the volcanic and sedimentary lithofacies has been undertaken on a section up to 1000 m thick in the odiel river considered to be also representative of other areas of the riotinto nerva unit among other mineral deposits this unit includes the world class volcanic hosted massive sulfide deposits of the riotinto mining district several conclusions have been obtained a a complex thick volcanic succession as well as mafic and felsic sills and thin sedimentary intervals predated the genesis of the sulfide deposits which did not form in a dominantly sedimentary environment b two successive felsic volcanic sequences can be distinguished showing textural and chemical variations from bottom to top c mafic lithofacies decrease upwards in the sequence and d volcanic structures eruption style and internal organization suggest a deep subaqueous depositional environment which agrees with the depositional setting for massive sulfide deposits

geochemical and nd isotopic signature of felsic volcanic rocks as a proxy of volcanic hosted massive sulphide deposits in the iberian pyrite belt sw spain the paymogo volcano sedimentary alignment abstract the iberian pyrite belt ipb located in the south portuguese zone of the iberian massif spain is a world class vhms province containing numerous huge mineral deposits hosted by bimodal volcanic sequences the province can be subdivided in several domains which differ from each other both in the nature and relative abundance of their volcanic sequences and in the distribution of associated vhms deposits in spite of its geological and economic interest information available for the northern part of the province is still relatively scarce we present a new dataset of geochemical and nd isotopic analyses on the paymogo volcano sedimentary alignment pvsa an area that is considered to be representative of this northern segment of the ipb volcanic sequences in the pvsa contain very scarce mafic rocks in contrast felsic rocks are abundant and have been classified in two groups i the paymogo rhyolitic sequence hosting most of the vhms deposits and ii a dacitic sequence although approximately coeval these groups of felsic rocks clearly differ in geochemical features and nd signature in view of these differences it is suggested that felsic rocks were produced from different mid crustal domains during a major event of partial melting related to a regional late devonian early carboniferous transtensional event it is further suggested that some volcanic rocks previously described as andesites are better interpreted as dacites the age 347 3 0 8 ma geochemical features zr

mineralogical evolution of the las cruces gossan cap iberian pyrite belt from subaerial to underground conditions abstract the las cruces vms deposit is located at the eastern corner of the iberian pyrite belt sw spain and is overlain by the neogene quaternary sediments of the guadalquivir foreland basin the deposit is currently exploited from an open pit by cobre las cruces s a being the supergene cu enriched zone the present mined resource the las cruces orebody is composed of a polymetallic massive sulfide orebody a cu rich stockwork and an overlying supergene profile that includes a cu rich secondary ore initial reserves of 17 6 mt 6 2 cu and a gossan cap initial reserves of 3 6 mt 3 3 pb 2 5 g t au and 56 3 g t ag the mineralogy of the las cruces weathering profile has been studied in this work textural relationships mineral chemistry deposition order of the minerals and genesis of the las cruces gossan are described and discussed in detail a complex mineral assemblage composed by the following minerals has been determined carbonates such as siderite calcite and cerussite fe sulfides including pyrite marcasite greigite and pyrrhotite pb sb sulfides and sulfosalts like galena stibnite fuloppite plagionite boulangerite plumosite and the jordanite geocronite series ag hg sb sulfides and sulfosalts including miargyrite pyrargyrite sternbergite acanthite freibergite cinnabar ag au hg amalgams and bi pb bi sulfides and sulfosalts such as bismuthinite galenobismutite others unidentified bi pb sulfosalts native bi and unidentified fe pb sb sulfosalts remains of the former oxidized assemblage appear as relicts comprised of hematite and goethite combining paragenetic information textures and mineral chemistry it has been possible to derive a sequence of events for the las cruces gossan generation and subsequent evolution in that sense the small amount of fe oxyhydroxides and their relict textures replaced by carbonates and sulfides suggest that the gossan was generated under changing physico chemical conditions it is proposed that the las cruces current gossan represents the modified residue of a former gossan mineralization where prolonged weathering led to dissolution and leaching out of highly mobile elements and oxidation of the primary sulfides later the gossan was subject to seawater gossan interaction and then buried beneath a carbonated rich cover the basinal fluids gossan interaction and the equilibration of fluids with the carbonated sediments brought to the carbonatization and sulfidation of the gossan and thus to the generation of fe carbonates and pb sb sulfides the las cruces mineral system likely represents a new category within the weathering class of ore deposits

the massive sulphide event in the iberian pyrite belt confirmatory evidence from the sotiel coronada mine well preserved miospore and organic walled microphytoplankton assemblages have been recovered from the black shaly series hosting the massive sulphide deposits of sotiel coronada mine iberian pyrite belt the productive samples yielded miospore assemblages representing the uppermost famennian retispora lepidophyta verrucosisporites nitidus ln miospore biozone of western europe this palynological evidence has important implications for the local geology constraining the commencement of the volcanic activity and corroborating the previously defined local tectonic style moreover at regional scale the new data permit correlation of the black shaly series which hosts the mineralization in all the sulphide deposits hitherto dated in the region reinforcing the hypothesis of an anoxic event occurring in the iberian pyrite belt in the latest devonian times

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

isotope geochemistry tracks the maturation of submarine massive sulfide mounds iberian pyrite belt the massive sulfide deposits of the southern iberian pyrite belt ipb occur as shale hosted exhalative mounds or shallow sub seafloor replacive bodies that formed at the devonian carboniferous boundary in anoxic bottoms the geochemistry of the mineralization and the host shale from some of the major deposits including a detailed 50 m thick section through the migollas orebody shows a marked textural and vertical zonation that is also reflected in the chemical textural and isotopic variations of pyrite and carbonates pyrite evolves from primary framboids and colloform aggregates to late euhedral crystals which accompanies a redistribution of the contained base metals and grain coarsening sims analyses depict an extreme variability of 34s values from 42 3 to 4 4 with a gradual increase that is related to the textural maturation there is also a systematic rise in the 87sr 86sr ratios 0 70846 to 0 71354 13c 12 2 to 5 2 and 18o values 14 1 to 27 8 of the associated carbonates which evolve from early dolomite to late siderite this evolution evidences the maturation of the exhalative mineralization during mixing between two fluids modified seawater enriched in biogenically derived reduced sulfur and upflowing hydrothermal fluids early sulfides precipitated in the seawater mound interface towards the core of the mounds there was an increasing influence of deep fluids that modified the early mineral textures and the isotopic signatures this evolution is similar to that observed in modern submarine hydrothermal systems and confirms the importance of mound refining in the evolution of fossil exhalative mounds and the formation of economic ores

tuffaceous deposition in the newcastle coal measures challenging existing concepts of peat formation in the sydney basin new south wales australia abstract the late permian newcastle coal measures of the northern sydney basin australia contain numerous volcanic ash deposits occurring as both interseam tuffs and intraseam tonsteins these tuffaceous units have been used to correlate seams of the newcastle coal measures with the stratigraphically equivalent wollombi coal measures in the adjacent hunter coalfield such correlations across the width of the northern sydney basin are based not on only tuffaceous markers but also on chemical and maceral profiles within individual coal plies and carbonaceous shales these correlations imply a lateral continuity of the peat forming environment previously unrecognised in the sydney basin and have led directly to the discovery of a new open cut coal resource in the hunter coalfield the uniform distribution of tonsteins and coal plies also challenges many existing concepts of peat formation it is proposed that the peat surface was predominantly below the water table and the term lowered mire is proposed to describe this environment a subaqueous peat surface would protect thin volcanic ash deposits from subsequent redistribution by rainfall and surface runoff and is consistent with a lack of tree preservation within the intraseam tonsteins it is envisaged that trees were generally restricted to the peat margins and to specific horizons where the peat surface was exposed by a fall in the water table long distance correlations of tonsteins also contradict models of coal formation incorporating lateral peat migration where time constant horizons such as tonsteins should transgress the coal seam profile over large distances

the origin of tonsteins an overview and links with seatearths fireclays and fragmental clay rocks abstract tonsteins are volcanic ash falls in coal bearing sequences that have altered to kaolinite only in the last twenty years or so has the volcanic origin become firmly established the evidence for the volcanic origin encompasses bed form including lateral extent structures textures volcanogenic mineralogy and geochemistry the lines of evidence are reviewed from a historical perspective tonsteins came to prominence over a hundred years ago because of their stratigraphic value tonsteins continue to be of value in coalfield exploration but their stratigraphic value has been enhanced in recent years with the ability to determine radiometric ages with a high level of accuracy the geochemistry not only provides good evidence for the volcanic origin but also enables tectomagmatic deductions to be made for areas external to the coal basin in addition some tonsteins are the indicators for the discovering of rare metal ore deposits nb rees and ga there is also the potential to use the geochemistry to identify specific tonsteins essentially a chemostratigraphic approach tonsteins are seen as one class of bentonites others include k bentonites metatonsteins and possibly illitic bentonites tonsteins have been linked to seatearths fireclays and fragmental clay rocks although all such rocks contain kaolinite the origins differ the seatearths contain rootlets and were subjected to pedogenic activity alteration of the silicate minerals is limited under conditions of a high water table and in the presence of organic matter reducing conditions prevailed leading to gleization on the other hand the fireclays show extensive alteration to kaolinite there is a link with the major marine bands and this has implications in terms of sequence stratigraphy the fragmental clayrocks have also been linked to soil forming processes but in this case possibly the reworked soil was the product of an open system containing free alumina minerals that reacted with silica in solution during diagenesis

mineralogy of the volcanic influenced great northern coal seam in the sydney basin australia abstract the mineralogy of the individual coal plies and intra seam claystone bands in the great northern seam of the sydney basin has been evaluated using optical and scanning electron microscopy and quantitative x ray diffraction techniques the uppermost two claystone bands are tonsteins consisting mainly of well ordered kaolinite with graupen to vermicular textures idiomorphic crystals of k feldspar within these tonsteins may represent members of the anorthoclase sanidine series or a sodic sanidine and indicate an acid to intermediate volcanic ash input in contrast the lowermost parting was largely derived from epiclastic sediment admixed with minor volcanic material such as high temperature quartz and a different type of k feldspar component the mineral fraction of the coals especially in the middle and upper parts of the seam is dominated by authigenic kaolinite with a very low abundance of quartz apart from the tonsteins authigenic processes therefore appear to be the dominant mechanism of mineral matter formation authigenic k feldspar also occurs in the lower few metres of the seam with a variety of modes of occurrence including cell and cleat infillings cross cutting veins and thin laminae parallel to the organic matter and detrital clay bands a late syngenetic low temperature hydrothermal fluid injection process is suggested for formation of the feldspar veins the origin of the fluid is uncertain but is most likely associated with contemporaneous volcanic activity

the high grade las cruces copper deposit spain a product of secondary enrichment in an evolving basin the las cruces deposit iberian pyrite belt includes a large high grade cementation zone capped by unusual rocks that contain carbonates galena iron sulphides and quartz between the late cretaceous and tortonian the volcanogenic massive sulphides were exhumed and affected by subaerial oxidation that formed paired cementation and gossan zones onset of alpine extension produced accelerated growth of the cementation zone along extensional faults leading to formation of the high grade copper ore at ca 11 ma later replacement of the overlying gossan by sulphide and carbonate rich rocks beneath sealing marl sediments is thought to have involved microbial processes occurring between the messinian ca 7 2 ma and today isotope data show that the cementation zone formed by the mixing of descending acidic waters derived from oxidation of the massive sulphides with upwelling geothermal waters flowing at temperatures above 100 c the c o and sr isotope values of the mineralization 87sr 86sr 0 7101 0 7104 and of the local groundwater 0 7102 0 7104 reflect equilibration with basement rocks and indicate that influence on the ore forming process by marl equilibrated water 0 7091 0 7093 or miocene seawater 0 7086 0 7092 was negligible the high sulphur isotope values of the sulphides in the biogenic zone most 19 to 24 are well above those of the primary sulphides 34s ca 6 8 to 10 3 and likely reflect formation of the biogenic sulphides by reduction of aqueous sulphate in the groundwaters sulphur isotope values of the cementation zone 34s ca 2 4 to 21 7 are also consistent with some contribution of sulphur from the biogenic reduction of aqueous sulphate