the yanque prospect peru from polymetallic zn pb mineralization to a nonsulfide deposit the yanque nonsulfide pb zn deposit inferred resources 12 5 mt 3 7 pb and 3 5 zn is located in the andahuaylas yauri ore province cuzco southern peru the deposit occurs within a base metal mineralized district centered on the medium sized dolores porphyry copper a thorough geological mineralogical and geochemical study has carried out in order to define the relationships between the dolores cu porphyry ore and the yanque zn pb polymetallic mineralization and the characteristics of the economic nonsulfide concentrations both sedimentary and igneous rocks constitute the backbone of the yanque dolores area the sedimentary lithologies belong to the soraya mara and ferrobamba fms upper jurassic middle cretaceous the yanque orebody is hosted by the mara fm which prevailingly consists of a siliciclastic sedimentary breccia the original sulfide mineralization consisted of galena pyrite and sphalerite the host rock has been affected by a strong hydrothermal alteration characterized by prevailing sericite illite as in the typical porphyry related phyllic argillic alteration stage and by minor kaolinite dolomite and quartz minor element geochemistry characterized by sb as mn ag and locally also by cu points to magmatic hydrothermal related mineralizing fluids the pb isotopic compositions from dolores and yanque sulfides are similar and are typical of the tertiary magmatically derived ores in this part of peru the hydrothermally altered rocks at yanque have the same pb isotopic compositions as the sulfides thus confirming the hypothesis that the yanque primary zn pb mineralization may have been produced by hydrothermal circulation related to the emplacement of the dolores cu porphyry as it is the case of other porphyry cu systems associated with polymetallic mineralization elsewhere however no simple genetic model for the mineralization involving just one fluid circulation episode is able to explain the data the yanque economic nonsulfide ore association consists of sauconite hemimorphite smithsonite and cerussite which result from the weathering and alteration of the original sulfide mineralization zinc is allocated mainly in sauconite zn smectite rather than in carbonates a factor strictly related to the prevailing siliciclastic character of the host rock distinctive features of the yanque orebody are the comparable ore grades for both pb and zn 3 5 zn and 3 7 pb and the inverse supergene chemical zoning in fact contrary to other supergene ores of this type zinc prevails in the top zone of the yanque deposit whereas lead content increases with depth considering the different mobility of the two metals in solution it may be assumed that most of the primary zinc that was the source for the yanque nonsulfides was originally located far from the position occupied by the galena mineralization whose remnants have been observed on site zinc sulfides may have been originally contained in the eroded rock volumes that surrounded the actual deposit the zinc rich solutions have possibly migrated through the siliciclastic mara fm and precipitated the nonsulfide minerals by porosity filling and replacement processes in this sense the yanque secondary zn pb deposit could be considered as a special type of exotic mineralization

granite ascent and emplacement during contractional deformation in convergent orogens based on a case study in the central maine belt of west central maine u s a it is proposed that crustal scale shear zone systems provide an eaective focussing mechanism for transfer of granite melt through the crust in convergent orogens during contractional deformation flow of melt in crustal materials at depths below the brittle plastic transition is coupled with plastic deformation of these materials the flow is driven by pressure gradients generated by buoyancy forces and tectonic stresses within the oblique reverse central maine belt shear zone system stromatic migmatite and concordant to weakly discordant irregular granite sheets occur in zones of higher strain which suggests percolative flow of melt to form the migmatite leuco somes and viscous flow of melt channelized in sheet like bodies possibly along fractures cyclic fluctuations of melt pressure may cause instantaneous changes in the eaective permeability of the flow network if self propa gating melt filled tensile and or dilatant shear fractures are produced due to melt enhanced embrittlement in homogeneous migmatite and schlieric granite occur in zones of lower strain which suggests migration of partially molten material through these zones en masse by granular flow and channelized flow of melt carrying entrained residue founded on the central maine belt case study we develop a model of melt extraction and ascent using the driving forces stress conditions and crustal rheologies in convergent especially transpressive orogens ascent of melt becomes inhibited with decreasing depth as the solidus is approached for intermedi ate a h2o muscovite dehydration melting the water saturated solidus occurs between 400 and 200 mpa near the brittle plastic transition during high t low p metamorphism where the balance of forces favors sub horizontal fracture propagation emplacement of melt may be accommodated by ductile flow and or stoping of wall rock and inflation may be accommodated by lifting of the roof at shallower crustal levels and or sink ing of the pluton floor the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduits although these plutons may have locally discordant relations with country rock structures when viewed at the crustal scale granite ascent and emplacement in convergent orogens are syn tec tonic processes 1998 elsevier science ltd all rights reserved

textural and stable isotopic evidence for the genesis of the tynagh base metal deposit ireland at the tynagh mine county galway four major stages of mineralization can be recognized that span the diagenetic and postlithification history of the host waulsortian limestones 1 growth of colloform and granular pyrite clots during the early diagenesis of the micritic host 2 rapid geopetal precipitation of microcrystalline sphalerite galena barite and dolomite within a dilatant fracture system that developed as a consequence of the forceful injection of metalliferous fluids into the coherent waulsortian carbonate mudbanks adjacent to the tynagh fault 3 veining and replacement of the host and previously precipitated phases by tennantite chalcopyrite bornite arsenopyrite medium to coarsely crystalline galena and coarse sparry barite and 4 finally precipitation of calcite within veinlets and cavities and dolomitization of large bodies of previously unmineralized waulsortian limestones sulfur isotope ratios indicate that contemporaneous lower carboniferous seawater acted as the source of sulfate for precipitation of barite delta 34 s 21 1 to 17 4ppm stage 1 delta 34 s 3 1 to 15 5ppm and stage 2 delta 34 s 4 1 to 26 0ppm sulfides were precipitated by reduced sulfur generated during open system bacterial reduction of this sea water sulfate source isotopically heavier delta 34 s or 0ppm reduced sulfur of deep seated origin was introduced from the fault zone during stage 3 this mixed with bacteriogenic sulfur migrating into the waulsortian bank limestones to precipitate stage 3 sulfides and sulfosalts delta 34 s 11 1 to 23 0ppm mineralized limestones delta 13 c 2 1 to 4 0ppm delta 18 o 17 6 to 27 1ppm ore stage carbonates delta 13 c 2 8 to 3 4ppm delta 18 o 17 1 to 26 9ppm and postore carbonates delta 13 c 4 0 to 2 6ppm delta 18 o 15 9 to 25 8ppm are depleted in the heavier isotopes of carbon and oxygen with respect to unmineralized limestones delta 13 c 3 1 to 4 1ppm delta 18 o 22 2 to 28 1ppm the depletion in 13 c is attributed to the mixing of host derived carbon with bacterially oxidized carbon and during stage 4 deep seated carbon the 18 o depletion of the mineralized host is a consequence of isotopic exchange with the ore fluids an oxygen isotope fractionation temperature of 200 degrees c and a delta 18 o smow value of 10 5 per mil for the coexisting water is obtained from a single stage 3 quartz albite pair collected from the fault zone if these values are accepted the delta 18 o values of stage 3 carbonates can only be interpreted in terms of mixing of this isotopically heavy water introduced from the fault with isotopically lighter water already present or migrating into the bank limestones

the calamine nonsulfide zn pb deposits of belgium petrographical mineralogical and geochemical characterization abstract the belgian nonsulfide zn deposits represent the historical basis for the zinc mining and smelting industry in europe the zinc ores were called calamines and consist of a mixture of zn carbonates smithsonite hydrozincite and zn silicates hemimorphite willemite and zn clays with a variable content of pb minerals the calamines are considered to be oxidation products of primary sulfide ores the most important was the la calamine orebody more than 600 000 tons of zn metal that was continuously exploited for several centuries nonsulfide ores were also exploited at schmalgraf engis dickenbusch fossey rocheux oneux welkenraedt and in other smaller deposits all no longer accessible for study where the calamines extended from the surface to an average depth of 40 to 50 m the primary zn pb sulfide mineralization consists of post variscan hydrothermal veins and replacement bodies mostly occurring in the dinantian visean limestones the sulfides intersect the paleozoic rocks and are truncated and unconformably covered by late cretaceous sediments santonian aachen fm the same setting has been observed for the nonsulfide ores suggesting an early to mid cretaceous weathering consistent with other geological and geochronological data on paleoweathering in europe the extensive occurrence of willemite that appears to be the first deposited nonsulfide mineral is a striking particularity of the belgian calamines most fluid inclusions in willemite 80 and all inclusions in smithsonite are monophase aqueous ice melting temperatures suggest salinities between 0 and 5 wt nacl equiv homogenization temperatures of rare two phase inclusions liquid vapor in willemite display a large variation between 80 and 190 an interval matching the temperature ranges of other willemite ores throughout the world so far considered of hydrothermal origin the stable isotope variation of belgian smithsonites and cerussites is very similar to the range measured in other supergene nonsulfide deposits similar to those of sw sardinia belgian smithsonites exhibit a limited range of 18o values from 27 1 to 30 6 averaging 28 4 0 8 v smow this limited range points to a relatively uniform isotope composition of the oxidizing waters and constant temperatures of smithsonite crystallization carbon isotope values even from the same mine show a considerable range from 11 6 to 1 6 this extensive range indicates at least two carbon sources 13c depleted carbon derived from the organic matter in the soils and 13c enriched carbon originating from marine carbonate host rocks cerussites have oxygen isotope values ranging from 16 8 to 19 3 averaging 17 8 1 0 and carbon isotope values of 18 4 to 14 7 the metallic deposits of eastern belgium have undergone a polyphase history which started with a possibly jurassic sulfide mineralization followed by oxidation under high silica activities and consequently by supergene weathering owing to structure and mineralogical association we do not consider the high homogenization temperatures as reliable minimum temperature estimates of willemite formation however it is possible that the willemite concentrations could have been derived from low temperature localized hydrothermal processes caused by deeply reaching oxidizing fluids smithsonite and hemimorphite often developed at the expenses of willemite have all the characteristics of supergene oxidation products

on diagenesis dolomitisation and mineralisation in the irish zn pb orefield marine calcite cementation and lithification of carboniferous carbonate sediments hosting zn pb mineralisation in the irish orefield occurred at or near the seafloor a relatively early fine grained grey replacive dolomite preferentially developed in micrite is widely developed in the waulsortian limestone formation the main host to mineralisation and is pervasive in the southeastern midlands in proximity to the leinster massif this dolomite formed after the first four main stages of calcite cementation but probably also developed within tens of metres of the seafloor as evidenced by incorporation of clasts of dolomite in intraformational sedimentary breccias later coarse grained white dolomite preferentially replaced coarser components of the waulsortian limestone and infilled residual vuggy porosity whilst some of this coarse dolomite may be related to the fine replacive dolomite event a common spatial association with fault zones coupled with primary fluid inclusion data suggest that a significant proportion of this phase precipitated during the onset of fault controlled subsidence and widespread hydrothermal circulation within the irish midlands area fluids up to 250 c and 10 15 wt nacl equivalent sourced from a lower palaeozoic basement equilibrated fluid reservoir infiltrated the carbonate sequence via faults and fractures the more localised development of dolomite cemented breccias white matrix breccias that are frequently associated spatially with mineralisation was a consequence of the increased focusing of these hydrothermal fluids ore formation was broadly synchronous with development of the white dolomite breccias but only happened where mixing occurred between the hydrothermal ore fluids and localised near surface reservoirs of low temperature h2s rich brine in the waulsortian this process led to the precipitation of a distinctive black dolomite that forms a broad halo to massive sulphides although ore stage sulphides postdate significant diagenesis of the host rocks and often display epigenetic textures the fact that much of the cementation occurred soon after carbonate deposition means that mineralisation does not have to have formed after significant burial in fact the occurrence of clasts of hydrothermal dolomite and sulphides in intraformational debris flow breccias is only consistent with mineralising processes occurring in the near seafloor environment relatively soon after host rock deposition the regional development of a distinctive pink dolomite associated with faults and fractures was a post ore event and is considered to mark a regional brine migration linked to the onset of the variscan orogeny the development of this new tectonic and flow regime may have been responsible for the cessation of economic mineralisation in ireland

nature and origin of the nonsulfide zinc deposits in the sierra mojada district coahuila mexico constraints from regional geology petrography and isotope analyses the sierra mojada district comprises multiple types of near surface mineral concentrations ranging from polymetallic sulfide zones nonsulfide zn nsz deposits and a silver rich pb carbonate deposit hosted by lower cretaceous carbonate strata hypogene concentrations of fe zn pb cu ag sulfides and sulfosalts are locally preserved and are associated with hydrothermal dolomite and silica alteration mineralogy and sulfur isotope data suggest primary zn pb ag mineralization from circa 200 c hydrothermal fluids the nsz deposits dominantly consist of smithsonite and hemimorphite associated with local mn fe oxides the red zinc zone consists of strata bound zones dominantly of hemimorphite that fills pores in residual and resedimented fe oxides the white zinc zone shows local dissolution features including internal sediments interbanded with and cemented by smithsonite similar pb isotopic compositions of smithsonite hemimorphite and cerussite to sierra mojada galena document that the nsz deposits originated from polymetallic carbonate replacement sulfide deposits with flow of metal bearing groundwater being controlled by local topography and structural features in this extensional terrane oxygen isotope values for sierra mojada smithsonite are relatively constant 18ovsmow 20 9 to 23 3 but are unusually low compared to other supergene smithsonites using 18ovsmow 8 of modern groundwater at nearby cuatrocienegas smithsonite formational temperatures are calculated to have been between 26 to 35 c smithsonite precipitation was favored by near neutral conditions typical of carbonate terranes whereas hemimorphite precipitated by reaction with wallrock silica and locally or episodically more acidic conditions resulting from sulfide oxidation transition to and stabilization of the modern desert climate over the past 9000 years from the late pleistocene wetter cooler climate of northern mexico resulted in episodic drawdown of the water table and termination of local supergene metal mobilization

coexisting goethite and gibbsite from a high paleolatitude 55 n late paleocene laterite concentration and 13c 12c ratios of occluded co2 and associated organic matter abstract a late paleocene 60 ma bp lateritic soil from northern ireland the antrim paleosol herein referred to as nire contains coexisting goethite gibbsite phyllosilicate and hematite the fe iii oxides exhibit pisolitic and liesegang type morphologies that are mutually exclusive in hand specimens x ray diffraction xrd measurements of al substituted for fe in goethite indicate two populations 1 low al liesegang type goethites 0 mol al and 2 high al pisolitic goethites 9 to 24 mol al selective dissolution and incremental vacuum dehydration decarbonation were used to determine the concentration and 13c values of co2 occluded in the respective structures of the goethites and gibbsites in this complex mixture of nire lateritic minerals the fe co3 oh component in the high al goethites appears to retain a proxy carbon isotopic record of vadose zone co2 in the ancient soil the 13c values of co2 occluded in coexisting goethites and gibbsites indicate that these minerals did not form in equilibrium with the same environmental co2 the measured mole fractions x of fe co3 oh in the high al goethites range from 0 0059 0 0005 to 0 0077 0 0006 and correspond to soil co2 concentrations of 28 000 to 37 000 ppmv the average values of x and 13c for the four high al goethites are 0 0067 0 0007 and 20 1 0 5 respectively the 13c value of the organic matter undergoing oxidation in this midlatitude 55 n late paleocene soil appears to have been 28 2 taken together these data indicate an atmospheric co2 concentration of 2400 ppmv 1200 ppmv at 60 ma bp the inferred high concentration of atmospheric co2 would have been coincident with the warm global climate of the late paleocene and is consistent with the idea that co2 plays an important role in climate variation

mineralogical and geochemical characterization of the riopar non sulfide zn fe pb deposits prebetic zone se spain abstract the present paper reports the first detailed petrological and geochemical study of non sulfide zn fe pb deposits in the riopar area prebetic zone of the mesozoic betic basin se spain constraining the origin and evolution of ore forming fluids in riopar both sulfide and non sulfide zn fe pb calamine ores are hosted in hydrothermally dolomitized lower cretaceous limestones the hypogene sulfides comprise sphalerite marcasite and minor galena calamine ores consist of zn carbonates smithsonite and scarce hydrozincite associated with abundant fe hydr oxides goethite and hematite and minor pb carbonates cerussite three smithsonite types have been recognized i sm i consists of brown anhedral microcrystalline aggregates as encrustations replacing sphalerite ii sm ii refers to brownish subhedral aggregates of rugged appearance related with fe oxi hydroxides in the surface crystals which replace extensively sphalerite and iii sm iii smithsonite appears as coarse grayish botryoidal aggregates in microkarstic cavities and porosity hydrozincite is scarce and appears as milky white botryoidal encrustations in cavities replacing smithsonite also two types of cerussite have been identified i cer i cerussite consists of fine crystals replacing galena along cleavage planes and crystal surfaces and ii cer ii conforms fine botryoidal crystals found infill porosity calcite and thin gypsum encrustations were also recognized the field and petrographic observations of the riopar non sulfide zn fe pb revealed two successive stages of supergene ore formation under meteoric fluid processes i gossan and red calamine formation in the uppermost parts of the ore with deposition of fe hydr oxides and zn and pb carbonates sm i sm ii and cer i occurring as direct replacements of zn pb sulfides and ii gray calamine ore formation with deposition of sm iii cer ii and hydrozincite infilling microkarst cavities and porosity the stable isotope variation of riopar smithsonite is very similar to those obtained in other calamine ore deposits around the world their c o isotope data 18 o 27 8 to 29 6 v smow 13 c 6 3 to 0 4 v pdb puts constrains on i the oxidizing fluid type which was of meteoric origin with temperatures of 12 to 19 c suggesting a supergene weathering process for the calamine ore formation under a temperate climate and ii the carbon source that resulted from mixing between two co 2 components derived from the dissolution of host dolomite 13 c enriched source and vegetation decomposition 13 c depleted component

a global assessment of zn isotope fractionation in secondary zn minerals from sulfide and non sulfide ore deposits and model for fractionation control abstract we investigated extent and direction of zn isotope fractionation in secondary zinc minerals formed during low temperature hydrothermal and or supergene oxidation of primary sulfide deposits zinc isotope data have been obtained from non sulfide zinc mineral separates willemite zn2sio4 smithsonite znco3 hemimorphite zn4 si2o7 oh 2 h2o hydrozincite zn5 co3 2 oh 6 and sauconite na0 3zn3 si al 4o10 oh 2 4h2o collected from several zn deposits in ireland belgium poland namibia peru yemen and zambia the data are compared with zn isotope compositions measured on zn sulfides collected in the same areas and or derived from the existing literature to establish the controls of direction and likely extent of any fractionations we find that willemite has the greatest compositional variability with measured 66znjcm lyon values ranging from 0 42 to 1 39 spanning the entire range of terrestrial variation in zn isotopes recorded to date overall significant fractionations in positive and negative directions are recorded relative to the precursor phase primary sphalerite or an earlier secondary phase with primary sphalerite falling in a relatively narrow range of isotopic values approximately 0 1 to 0 4 most of the data observed on willemite hemimorphite and hydrozincite can be explained with a model of isotopic fractionation in which partial dissolution of primary sphalerite is followed by precipitation of an initial secondary phase that preferentially incorporates heavy zn isotopes smithsonite instead preferentially incorporates light zn isotopes this reflects the variation in the zn x bond strengths of these secondary phases with respect to the original sulfides we also observed that isotope compositions do not depend only on the difference between the fractionation factors of the involved phases but also on the amount of the secondary mineral precipitated after dissolution of primary sulfide and that the greatest fractionations occur when only small amounts of secondary mineral are precipitated progressive precipitation from migrating fluids that form phases enriched in heavy zinc isotopes would lead to a gradual decrease in the 66zn values of such phases and the fluids involved in time and space strong negative isotopic shifts are almost only observed for late crystallizing phases such as those in vugs these are interpreted to reflect precipitation from residual isotopically light fluids that are the inevitable highly fractionated product of the above described process where a more complete replacement of primary sulfide has occurred such as in the high grade core of non sulfide zinc orebodies there is limited net isotopic fractionation because dissolved primary zinc is nearly quantitatively reprecipitated locally in addition in only one case yanque peru we observed that the fringes of non sulfide zinc deposit were characterized by isotopically fractionated compositions with highly negative values implying extensive precipitation earlier or elsewhere of isotopically heavy secondary phases the higher grade ore zones where complete breakdown of primary sulfides and quantitative reprecipitation of zinc have occurred show instead less fractionated compositions

experimental deformation of partially molten westerly granite under fluid absent conditions with implications for the extraction of granitic magmas the mechanical behavior of partially molten westerly granite was investigated in the temperature range 800 1100 c 250 mpa confining pressure by means of constant strain rate creep and stress relaxation tests the only water in the samples came from the breakdown of hydrous phases biotite minor chlorite and muscovite and alteration products of feldspars thus the amount of melt was controlled by the test temperature and ranged from 3 at 800 c to 50 at 1100 c over that temperature range strength decreased from 500 mpa to less than 1 mpa and a preliminary constitutive flow law for the partially molten rock was obtained to allow extrapolation to low strain rates the comparative viscosity of the melt alone was estimated at 950 and 1000 c from the distance it could be made to penetrate into a porous sand under a known pressure gradient under all conditions deformation of the matrix of solid grains was by brittle fracture only samples containing up to 10 vol melt failed with the formation of a shear fault zone at higher melt fractions melt filled pores collapsed by shear enhanced compaction squeezing the melt into axial cracks above 40 vol melt unfractured solid grains were carried about passively in the flowing liquid there was no evidence of a rheologically critical melt percentage in this system by analogy with the uniaxial compaction of water saturated soils a simple model is erected to describe a two stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress shear enhanced compaction is inferred to drive melt into a network of melt filled veins whereupon porous flow through the high permeability vein network allows rapid drainage of melt to higher crustal levels

strain partitioning during partial melting and crystallizing felsic magmas abstract the rheology of partly molten felsic systems changes dramatically during the onset of melting and through crystallization solid to liquid and liquid to solid transitions are not rheologically identical contradicting the concept of a unique rheological critical melt percentage we use four thresholds separating the successive stages according to the melt fraction for the melting transition 1 the liquid percolation threshold connects the melt pockets at about 8 of melt thus allowing local magma displacement at the metric scale and 2 for greater melt percentages 20 25 a melt escape threshold corresponds to the onset of transport over large distances of the melt and part of the residual solid phase leading ultimately to granitic bodies for the solidification transition 3 the first formation of a rigid framework of crystals which can accumulate stress although the melt can still flow corresponds to the rigid percolation threshold 55 solids and 4 the system becomes totally locked at about 72 75 solid which corresponds to the particle locking threshold the present paper focuses on strain partitioning induced by the coexistence of two contrasting rheological phases between these thresholds on a variety of scales non coaxial deformation is preferentially accommodated by the lower viscosity melt which increases the vorticity in the melt phase and reinforces asymmetries in the flow pattern strain partitioning also increases the scale length of the weakest phase during melting and magma ascent whereas strain partitioning decreases the scale length during crystallizing strain partitioning also affects the migration of melt by raising the particle locking threshold and lowering the melt escape threshold for three dimensional deformations such as transpression the direction of melt segregation e g horizontal may differ from the direction of melt migration e g vertical

a cold supergene zinc deposit in alaska the reef ridge case the reef ridge deposit is a typical supergene nonsulfide zinc mineralization located in the yukon koyukuk region of west central alaska usa it is hosted in sedimentary rocks of the farewell terrane a continental fragment sandwiched between the siberian and laurentian cratons during the early paleozoic the mineralization occurs in lower middle devonian shallow water dolomite of a paleozoic carbonate platform succession belonging to the nixon fork tectonic unit the mineralization consists of oxidized minerals associated with minor remaining sulfides pyrite marcasite and sphalerite in the oxidation zone smithsonite is the predominant mineral mixed with fe hydr oxides goethite and hematite a complete petrographic and mineralogical study was performed samples were analyzed by x ray diffraction inductively coupled plasma mass spectrometry and emission spectrometry energy dispersive scanning electron microscopy and qemscan quantitative evaluation of minerals by scanning electron microscopy the most abundant mineral in the nonsulfide ore is smithsonite similar to other nonsulfide zn deposits worldwide the first generation of smithsonite has replaced both primary sphalerite and the host carbonates a second smithsonite generation precipitated as cement in vugs cavities and fractures minor zinc amounts also occur in the fe hydr oxides and zinc traces have been identified in clay minerals the carbon and oxygen isotope values of smithsonite at reef ridge vary from 0 7 to 2 1 relative to vienna peedee belemnite vpdb and 19 1 to 21 9 relative to vienna standard mean ocean water vsmow the 13 c values are similar to those of the host rock suggesting that the predominant carbon source for smithsonite was the host carbonates with only a limited contribution from organic carbon the oxygen isotope ratios of reef ridge smithsonite are more depleted in 18 o compared to supergene nonsulfides from other parts of the world formed under warm humid temperate or semiarid climates the oxygen isotope fractionation between water and smithsonite which relates the 18 o value of the mineralizing solution the formation temperature of smithsonite and its 18 o composition indicates that the 18 o composition of reef ridge smithsonite is related to very low formation temperatures 10 c and strong depletion in 18 o of the precipitating waters the 18 o smithsonite composition the strong 18 o depletion and the relationship of the formation of the reef ridge nonsulfide deposit with the development of the sleetmute upland surface which started in the late tertiary and continues to the present indicate that the formation of the reef ridge nonsulfide deposit is probably related to cold humid weathering episodes during a period comprised between late tertiary and holocene the traditional interpretation on the genesis of zn nonsulfide deposits in warm humid temperate or semiarid conditions should be questioned where other climate zones are indicated

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

stable isotopes of nonsulphide zn pb ores in britain and ireland fluid characteristics and palaeoclimatic variability stable isotope c o analysis was applied to smithsonites and cerussites from zn pb nonsulphide ores from britain and ireland to determine the nature of the fluids responsible for the precipitation of secondary carbonates and any relationship with palaeoclimatic conditions the carbon isotope compositions of the irish smithsonites show a major contribution of organic carbon whereas those of both zn and pb carbonates in the uk deposits indicate contribution of organic carbon and host rock carbonates 18ovsmow values for cerussite from both areas are about 13 lower than those of smithsonites uk smithsonite 18ovsmow values are more variable than those for cerussites and the irish smithsonites have unusually high values isoscape maps indicate that 18o values for both carbonates are higher in the west and decrease toward the east this trend correlates with a general decrease in the oxygen isotope compositions of rainwater moving eastward and suggests that oxidation of sulphides occurred at temperatures of about 15 20 c under climatic conditions warmer than today supplementary material a comprehensive overview of the investigated sites detailed data for the samples and sem images are available at https doi org 10 6084 m9 figshare c 4579535

mineralogical and geochemical characterization of nonsulfide zn pb mineralization at silvermines and galmoy irish midlands abstract the nonsulfide zinc lead mineralization in the irish midlands represents an example of surface oxidation of primary sulfide mineralization redeposition and preservation under glacial till in this preliminary study we report on the mineralogy and chemical composition of the nonsulfide zinc mineralization at silvermines and galmoy deposits at silvermines the analyses were carried out on samples from two drill cores drillholes 302 3 and 303 3 located in knockanroe townland at the periphery of the main orebody at galmoy the nonsulfides were sampled from the g orebody between 77 and 93 m below the surface in an area where oxidation is very strong at both sites the dominant mineral composition of oxidized ores is relatively simple with smithsonite hemimorphite at silvermines and smithsonite at galmoy primary sulfides and secondary carbonates silicates are generally associated at both localities whole rock chemical analysis sem and optical studies have revealed evidence for open space filling and replacement of both primary sulfides and carboniferous dolomite host rock by nonsulfide minerals smithsonite at silvermines shows an evolution of different forms from early encrustations and botryoidal aggregates to late rice grain shaped crystals and a systematic decrease of fe content with time in the paragenetic sequence early smithsonite replacing dolomite host rocks can be fe and mn rich this evolution points to slightly more reducing conditions during deposition of the early zn carbonates compared to late smithsonites which coexist with mn and fe oxy hydroxides a complex association of at least three different often intergrown types of smithsonite aggregates were observed at galmoy where replacement of sulfides and vug infilling are predominant early globular or crustiform pb and ca rich smithsonite is followed by tiny rounded fe poor to one dimensional fe rich clusters of smithsonite and again by late rice grain shaped smithsonite hemimorphite is virtually absent thin encrustations of sulfates such as gypsum boyleite rozenite copiapite and jarosite often coat both sulfide and nonsulfide minerals and testify to recent and or ongoing alteration the lack of rhombohedral smithsonite which characterizes the upper phreatic zone in sardinia and in belgium indicates the relative immaturity of the weathering profiles in ireland the absence of a well developed karstic network and in consequence the uneconomic character of nonsulfide concentrations

variscan dextral transpression in the french pyrenees new data from the pic des trois seigneurs granodiorite and its country rocks abstract new structural data from both the trois seigneurs granodiorite and its country rock lead to new conclusions about the variscan tectonic history of this part of the pyrenees sedimentary rocks of the massif that increase in metamorphic grade from north to south are imprinted by a single major deformation responsible for both the tight upright e w trending folds with vertical to steeply n dipping foliations and the gently w plunging stretching lineations syntectonic emplacement of the pic des trois seigneurs granodiorite is demonstrated by the parallelism between structures of the pluton as determined by magnetic fabric measurements and the foliations and lineations imprinted in the country rocks large deformation of the granodiorite magma during emplacement is indicated by strong anisotropy and ubiquitous magmatic microstructures the high thermal gradients of regional metamorphism which is also syntectonic are attributed to a large thermal aureole provided by deep seated magma reservoirs shear sense criteria in xz thin sections of the metasedimentary country rocks indicate a dextral sense of the non coaxial component of strain throughout the massif and regardless of metamorphic grade the overall structure of the massif is concluded to have derived from a major shearing event that is equated with the d 2 main phase observed in the entire variscan pyrenees as the e w oriented stretch and dextral shear cannot be separated from compressive structures generally considered to be characteristic of d 2 this phase is concluded as representing regional transpression

displacement and strain patterns from naturally occurring shear zone terminations abstract strain distribution patterns are described from several naturally occurring ductile shear zone terminations and a two fold classification is suggested type i termination patterns show a symmetrical decrease in strain area and intensity and are associated with very low shear strain values in the main shear zone the more common type ii termination patterns show a symmetrical increase in strain area with decrease in strain intensity some brittle ductile examples of type ii terminations contain secondary shears that resemble splay faults all the available evidence suggests that the deformation near the terminations of these shear zones is not plane strain nor do the observed strain patterns readily fit the existing theoretical models

dolomitization of the waulsortian limestone lower carboniferous in the irish midlands the waulsortian limestone lower carboniferous of the southern irish midlands is dolomitized pervasively over a much larger region than previous studies have documented this study indicates a complex multistage multiple fluid history for regional dolomitization partially and completely dolomitized sections of waulsortian limestones are characterized by finely crystalline 0 01 0 3 mm planar dolomite planar replacive dolomite is commonly followed by coarse 0 5 mm nonplanar replacive dolomite and pervasive void filling saddle dolomite cement is frequently associated with zn pb mineralization planar dolomite has average 18o and 13c values pdb of 4 8 and 3 9 respectively these are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the waulsortian 18o 2 2 13c 3 7 mean c and o isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement 7 0 and 3 3 7 4 and 2 4 respectively fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation the petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin possibly in equilibrium with modified carboniferous sea water where the waulsortian was exposed to hydrothermal fluids 70 280 c planar dolomite underwent a neomorphic recrystallization to a coarser crystalline planar and nonplanar dolomite characterized by lower 18o values void filling dolomite cement is isotopically similar to nonplanar replacive dolomite and reflects a similar origin from hydrothermal fluids this history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the irish midlands and provides a framework upon which to test competing models of regional vs localized fluid flow

sigmoidal structures featuring dextral shear during emplacement of the hercynian granite complex of cauterets panticosa pyrenees abstract the three plutons of the cauterets panticosa granite complex are studied by the anisotropy of magnetic susceptibility ams technique as expected from the dominantly paramagnetic nature of the rocks the magnetic susceptibility zonation accurately compares with the lithological zonation detailed examination of the linear and planar structural patterns of the plutons allows the difficult problem of their formation mechanisms to be explored the sigmoidal pattern of the linear structures only results from regional tectonics and points unequivocally to a dextral shear component for the responsible tectonic event the concentric planar structures while also affected by regional tectonics retain some imprint of magma emplacement the microstructures observed in the granitoids point to a continuous deformation from the magmatic state to the high temperature solid state in the country rocks structures and kinematic criteria underline the transpressive character of the d2 hercynian event of the pyrenees which resulted in a partitioning between zones where either compression or dextral strike slip were dominant all these data constrain a new model of d2 syn tectonic emplacement for the plutons of the cauterets panticosa complex and remarkably illustrate structural features resulting from a transpressive regime

structural and paleotopographic controls of lead zinc mineralization in the silvermines orebodies republic of ireland occurrence in lower carboniferous and devonian strata in northern tipperary the deposits comprise lower discordant zones deposited epigenetically along the channelways of the ascending ore solutions and upper late tournaisian stratiform syngenetic syndiagenetic zones of sedimentary exhalative origin mineralization occurs in a variety of sediments whose composition reflects the nature of the exhaled fluids and the variable physiochemical conditions in their depositional sites as a result of periodic tectonism on the fault zone these mineralized sediments were subjected to varying degrees of brecciation in a very unstable depositional environment the stratiform deposits of silvermines are synsedimentary products of the exhalation of mineralizing fluids from northwest trending feeder zones on to a late tournaisian sea floor of highly irregular paleotopography modified journal abstract

microgranitic enclave shapes and magmatic strain histories constraints from drop deformation theory microgranitic mafic enclaves are common components of plutonic bodies and may represent the result of mingling of mafic and felsic magmas these enclaves are often ellipsoidal or elongate in shape in order to constrain the conditions under which such enclaves were generated and deformed by their host pluton we apply drop deformation theory to model their distortion our model takes into account the change in viscosity of both the host and enclave with temperature composition and the amount of suspended solids in enclave host systems and it assumes that simple shear flow predominates in the plutonic system we focus on the deformational history of enclaves over the time period in which they remain liquid and are either more or less viscous than their granitic host we find that the most stable enclaves with respect to being broken up by their entraining flow are generally the most mafic enclaves those with silica contents near those of the host granite are highly unstable this is in reasonable accord with field observations of the abundance of enclaves of different chemistry most deformation of microgranitic enclaves is likely to occur at relatively high temperatures probably between 950 c and 1050 c and therefore the enclaves record magmatic strain of the host over only a limited temperature time range in the host s cooling history furthermore the observation of apparent deformation of these enclaves in a liquid regime coupled with our calculated dependences of enclave deformation on flow velocity implies that magmatic flow velocities are likely to be below 10 m yr in enclave bearing plutonic systems

stoped blocks in plutons paleo plumb bobs viscometers or chronometers abstract stoped blocks potentially provide information about paleohorizontal during emplacement of plutons and about the timing of and viscosities and kinematics during magmatic fabric formation in the mount stuart batholith washington we have examined magmatic fabrics patterns around stoped blocks in tonalite located near the pluton roof and completed 1 1 scale three dimensional mapping of fabric patterns around stoped blocks in diorite located 1000 m below the roof in both settings no structural record of magma ascent early emplacement or settling of the blocks is preserved instead fabric formation largely post dates the settling and trapping of stoped blocks two dimensional finite difference thermal modeling and calculations of sinking rates support short

timing of mineralization at the navan zn pb deposit a post arundian age for irish mineralization navan is the largest of the irish zn pb deposits and contains some of the most important evidence for the inferred early timing of mineralization in ireland clasts of ore above a middle carboniferous erosion surface we have examined diagenetic fabrics within the main ore pale beds and the overlying erosion surface boulder conglomerate in order to determine the timing of mineralization this diagenetic analysis and particularly the presence of premineralization dolomite in the boulder conglomerate has revealed that all of the mineralization postdates the erosion surface and therefore must be post arundian 345 ma in age furthermore the navan mineralization must be entirely epigenetic in origin i e similar to mississippi valley type deposits and is likely to be holkerian 343 ma in age or younger this conclusion disagrees with the previous model of at least partially syngenetic mineralization and has important implications for the age of other deposits in ireland and the nature of irish type deposits in general

micro and nano characterization of zn clays in nonsulfide supergene ores of southern peru zn clays are associated with several supergene nonsulfide ore deposits worldwide where they are either the prevailing economic minerals or minor components of the weathering derived mineral assemblage a tem hrtem study on zn clays from nonsulfide ore deposits of accha and yanque peru was carried out to properly determine the chemistry and complex texture of these clays not fully defined in other previous works on these but also on other similar deposits the zn clays occurring at accha and yanque are constituted by a mixture of sauconite and zn bearing beidellite the chemical composition of sauconite varies in a range of values without any chemical gap around the average composition ca 0 15 k 0 05 zn 2 1 mg 0 2 al 0 4 fe 0 15 mn 0 02 si 3 5 al 0 5 o 10 oh 2 nh 2 o beidellites present an average composition close to stoichiometry with the addition of zn ca 0 05 k 0 15 al 1 6 zn 0 25 mg 0 1 fe 0 15 si 3 6 al 0 4 o 10 oh 2 nh 2 o the chemical composition of both sauconite and beidellite is consistent through the samples with sauconite affected by a wider variation in composition than beidellite the textures of zn bearing smectites clearly indicate that a part of these clays grew on precursory mica like phyllosilicates whereas another part was derived from a direct precipitation from solutions the occurrence of a paragenesis with trioctahedral and dioctahedral smectites demonstrates that as observed in other environments also in a zn bearing system both smectite types are stable as proved for other analogous trioctahedral dioctahedral smectite systems e g saponite beidellite also in the sauconite beidellite system a chemical compositional gap exists within the series the texture indicating a direct precipitation from solutions does not exclude that a smectite amount could be genetically related to hydrothermal fluids even if several other characteristics e g the paragenetical association with fe hydroxides typical of gossans confirm the supergene origin for the bulk of the deposit

the calamines and the others the great family of supergene nonsulfide zinc ores abstract nonsulfides is a term which comprises a series of oxidized zn pb ore minerals it has also been used to define a special deposit type mainly considered as derived from the weathering of zn pb sulfide concentrations however nonsulfide zinc deposits have been distinguished between supergene and hypogene according to their mineralogy geological characteristics and genetic setting the supergene deposits formed by weathering and oxidation at ambient temperatures whereas the hypogene ones are considered hydrothermal or associated with metamorphic processes on primary sulfide ores in this review paper a comparison between a number of several nonsulfide deposits has been carried out typical calamines peculiar calamines and others the whole group comprises deposits of typical supergene origin mixed supergene hypogene mineralizations and oxidized concentrations characterized by different metals only locally associated with zinc the zn pb nonsulfide concentrations hosted in carbonate rocks which are mainly attributed to wall rock replacement and direct replacement supergene processes are the typical calamines liege district belgium iglesias district italy silesia cracow district poland peculiar calamine deposits are those mineralizations that have been generally considered as supergene but which are instead genetically related at least partly to hypogene processes e g angouran iran jabali yemen though mineralogically and texturally similar to supergene nonsulfide deposits the others are prevailingly supergene nonsulfide zinc deposits not hosted in carbonate rocks skorpion namibia yanque peru or characterized by other metals as main commodities like lead magellan australia silver sierra mojada mexico wonawinta australia or vanadium otavi mountainland namibia minerals of current economic importance in most calamine deposits are smithsonite hydrozincite and cerussite this mineralogical association is generally simple but when the calamines are dolomite hosted one of the consequences of the wall rock replacement process is the generation of a series of economically useless zn and mg bearing mixed carbonate phases secondary deposits hosted in silicatic sedimentary or volcanic rocks mainly contain hemimorphite and or sauconite lead ag and v rich nonsulfide ores are characterized by a more complex mineralogical association mixed pb carbonates pb sulfates pb phosphates pb arsenates various ag sulfosalts and zn pb cu vanadates carbon and oxygen stable isotope studies allow distinguishing between supergene and hypogene nonsulfide deposits evaluating the effects of oxidative heating and even gaining indirect paleoclimatic information the oxygen isotope variation of the individual carbonate minerals within a deposit is relatively small indicating constant formation temperatures and a single meteoric fluid source carbon isotope values are highly variable thus suggesting several isotopically distinct carbon sources periods of paleoclimatic switch overs from seasonally humid arid to hyperarid have been considered as the most favorable conditions for the formation and preservation of supergene nonsulfide deposits however while several recent nonsulfide deposits throughout the world are positioned between 15 and 45 n latitude thus pointing to a warm and humid weathering climate others have been deposited in sub arctic regions the economic value of the nonsulfide zn pb ag v ores is highly variable because more than in the case of metallic sulfide deposits it resides not only on the geological setting but also on their mineralogy that can directly influence processing and metallurgy

role of melt during deformation in the deep crust deformation in the deep crust is strongly influenced by the presence of melt injected melt or magma weakens the crust because strain will tend to localize where melt is present the amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate for plutons that intrude into rocks which are near the solidus temperature of the melt crystallization times can be quite long 1myr partial melting of deep crustal rocks can lead to melt enhanced embrittlement this occurs because the volume change for most melting reactions is positive therefore when the rate of melt production outpaces the rate at which melt can leave the system the melt pressure increases eventually the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the central gneiss belt canada this suggests that melt enhanced embrittlement occurred in these rocks an expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived assuming that migmatite has a small tensile strength differential stresses are 20 mpa in migmatitic rocks at the time melt enhanced embrittlement occurs the occurrence of melt enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting furthermore repeated episodes of melt enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains

melt enhanced deformation a major tectonic process convergent tectonics between continental crustal blocks result in deep burial and anatexis of supracrustal rocks anatectic and or mantle derived melts combine to form a melt weakened zone in the thickened lower crust the accumulation of melt eventually leads to crustal failure along melt lubricated shear zones rapid 1 mm yr vertical component movements of large crustal blocks result we refer to these crustal displacements as tectonic surges the melt lubricated shears are characterized by the close association of sheared country rocks with foliated or massive igneous sills and plutons rocks that formed at different crustal levels are juxtaposed across these shear zones one result of surges with large lateral component of movement is metamorphic inversion with high pressure and high temperature metamorphic rocks structurally over lower pressure and temperature assemblages large and rapid vertical surges may displace crust containing abundant melt and may result in high t p including granulite facies metamorphism and preservation of metamorphic textures caused by rapid decompression

response of the selle river to climatic modifications during the lateglacial and early holocene somme basin northern france abstract research on lateglacial sequences from the selle valley leads to an overview of its evolution in relation to climatic variations between the end of the weichselian upper pleniglacial and the beginning of the holocene the first major modification of the fluvial morphology is dated at the upper pleniglacial lateglacial transition 13 000 14 c yr bp at that time the response to climatic improvement and environmental modifications is marked by downcutting and evolution from a braided river to a transitional river pattern bolling infilling in the newly created channels after a short cold phase recorded in a thin calcareous bed at the top of the bolling peat attributed to the older dryas dr ii the allerod is characterized by the deposition of organic overbank silts within a large single channel meandering system in lower slope environments this period is also marked by slow rates of colluvial accumulation and by the development of upbuilding soils allerod soil on the other hand the end of the lateglacial is characterised by the infilling of the whole valley by fine calcareous overbank silts during the younger dryas cold phase overflow of a large single channel and lateral input of chalk mud a second major downcutting phase occurs at the beginning of the holocene at around 10 000 bp in parallel with another rapid climatic improvement and the renewed spread of vegetation from a general point of view the evolution of fluvial environments in the selle valley is comparable with many other river valleys in nw europe showing that fluvial systems react very quickly to climatic variations of short duration 1000 to 100 years finally in the upper selle river incision events occur clearly before the main modifications of the vegetal cover they are most likely linked to a rapid shift in the balance between water discharge and sediment supply caused by climate modifications shift to more temperate and oceanic conditions and the resulting environmental changes cessation in aeolian sedimentation strong reduction of slope processes permafrost disappearance and soil development

geochemical evolution of a palaeolaterite the interbasaltic formation northern ireland abstract the interbasaltic laterites of northern ireland were formed during a period of relative volcanic inactivity by extensive chemical weathering of tertiary basalts they reach a maximum thickness of 30 m and once provided a major source of iron and aluminium ore an extensive database comprising major minor and trace elements has been compiled for 240 samples in order to study the effects of weathering in terms of the changes in whole rock chemistry and mineralogy from basalt through to iron rich crust percolating waters caused degradation of the parent basalt mineralogy and precipitation of neoformed phases principally through incongruent dissolution processes primary olivine plagioclase feldspar and augite were successively broken down and replaced by a mineral assemblage consisting of hematite gibbsite goethite anatase meta halloysite and kaolinite changes in mineralogy facilitated concomitant changes in element concentrations mass balance calculations indicate that all elements were depleted in the iron crust enrichment of al loi cr cu and v occurred in the laterite horizon while enrichment of al loi ba ce cr cu ni and rb occurred in the lithomarge notably yttrium was found to be mobile indicating that weathered basalts should not be used in discrimination of original tectonic environments the severe leaching conditions evidenced by yttrium depletion local aluminium redistribution and iron crust formation are indicative of weathering under a humid sub tropical monsoon climate

development of high thermal gradients by coeval transpression and magmatism during the variscan orogeny insights from the cap de creus eastern pyrenees abstract the cap de creus massif in the eastern pyrenees is a fragment of the variscan mid crust geological mapping and meso and micro scale analysis of the relationships between fold structures metamorphic mineral assemblages and fabrics affecting igneous bodies suggest the interaction of three processes deformation metamorphism and magmatism low pressure prograde metamorphism grades laterally from greenschist to amphibolite facies over a distance of 5 km zones of intense metamorphism coincide with transpressional deformation and with the intrusion of small sheets of diorite and granitoid sillimanite schists and small migmatite pods are distributed around the small intrusions of basic intermediate composition the inferred maximum thermal gradient is 80 c km this thermal pattern is similar to patterns observed in other variscan massifs in the pyrenees where high metamorphic gradients are interpreted in different ways in the ne cap de creus the type and distribution of prograde metamorphism was caused or at least enhanced by the intrusion of diorites and granitoids alternatively deformation developed at prograde conditions and synchronously with magmatism displays a highly heterogeneous distribution producing a sub vertical zone of high strain that coincides with domains of highest grade metamorphism and igneous activity this zone of high strain developed in a broad transpressive regime could have favoured the injection of magmatic sheets from deep to mid crustal levels progressive folding from prograde to retrograde metamorphic conditions might account for the narrowing of metamorphic zones

constraints on the origins of fluids forming irish zn pb ba deposits evidence from the composition of fluid inclusions the numerous zn pb deposits in the irish midlands together with the quantity and grade of the ore make this a world class base metal province despite significant exploration and research there is still disagreement on the origin of the mineralizing fluids in this study we have measured the composition of fluid inclusions using a crush leach technique these data constrain the possible sources of the fluids both during and after mineralization chloride and br concentrations indicate that the main ore fluid at tynagh and silvermines was seawater that had evaporated until the salinity was between 12 and 18 wt percent however na k and li data show that water rock interactions have resulted in the depletion of na and the enrichment of k and li relative to the concentrations expected for evaporated seawater the fluids that produced postore dolomitization were also derived from seawater that had evaporated to higher salinities and had precipitated halite the concentrations of na k and li are what would be expected for seawater at this degree of evaporation and show that these fluids did not interact with the same lithologies as the ore fluids the major change to their fluid composition was exchange of mg for ca during dolomitization we suggest that the ore fluids could only have reached their high salinity by evaporation of seawater on the extensive shallow water shelf regions that existed over much of the irish midlands

use of microgranitoid enclaves as solid state strain markers in deformed granitic rock an evaluation microgranitoid enclaves are common in many plutons and are potentially valuable as solid state strain markers in tectonically deformed granitoids we consider the parameters necessary to assess enclaves as two dimensional strain markers these include i their primary shapes ii differences in rheology between enclave and host granitoid iii the magmatic shape fabric ellipse of enclave populations iv the maximum fluctuation of enclave long axes developed during magmatic processes v the angle between the magmatic shape fabric ellipse and tectonic strain ellipse at the onset of tectonic deformation and vi the type of strain path undergone by the markers enclave populations show characteristic magmatic distributions as shown by plots of the magmatic shape fabric ellipse vs enclave axial fluctuation from several plutons in the sierra nevada california and in the adamello massif italy the plots of tectonically undeformed and deformed enclaves show nearly complete overlap creating substantial uncertainties in separating magmatic strain from tectonic strain if only the final enclave axial ratio is considered enclave host strength differences have been modeled using published mineral deformation data and theoretical approaches to simulate deformation of aggregates results indicate very similar flow properties of enclaves and felsic host between 500 and 800 c and possibly at lower temperatures as well provided that biotite bearing enclave and host compositions are present two dimensional strain modeling of the enclave populations indicates that values of the total shape fabric ellipse as determined from field measurements can be close to the true tectonic strain under some circumstances but most commonly the former substantially over or underestimates the latter if the parameters i v are assessed at each strain site however and each measured surface subsequently modeled using those parameters over and underestimates of solid state strain can be greatly reduced or eliminated and reasonable values for two dimensional tectonic strain of the granitoid and its enclaves can be obtained

thrust sequences in the eastern spanish pyrenees detailed mapping of the south pyrenean zone in the eastern spanish pyrenees shows that a great number of alpine thrusts affect the basement and the cover the geometry of the thrust structures and their propagation sequence can be interpreted from balanced sections the folding dies out downwards from the higher thrust sheets to the lower ones and demonstrates a piggy back thrusting sequence these thrusts form a duplex the sole thrust of this duplex is the vallfogona thrust the roof thrust is rooted somewhere within the axial zone the thrusts climb southwards from the axial zone basement up into tertiary cover sediments these thrusts have been folded so that they now dip to the south and form the southern side of the axial zone antiformal stack locally smaller antiformal stacks developed and produced strong folds in the higher thrust sheets the south pyrenean zone studied is equivalent to the gavarnie nappe and the connection between them below the detached south pyrenean central unit may be the nogueres zone

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

syntectonic emplacement of the maladeta granite pyrenees deduced from relationships between hercynian deformation and contact metamorphism the relationships between hercynian deformation and contact metamorphism in the aureole of the aneto unit a constituent pluton of the maladeta granite complex spanish pyrenees provide new data relevant to the controversy between the syn and post tectonic models of emplacement for the pyrenean granites the deformation in the aneto aureole is related to two superimposed hercynian episodes the first was a top to the sw thrusting which induced sw verging recumbent folds the second which was essentially compressive in the aneto area is represented by e w trending subvertical cleavage and folds with subhorizontal axes this second episode can be assigned to the d2 main hercynian tectonic event of the pyrenees the contact metamorphic assemblages grew during the d2 event and were deformed by it close to the contact the conclusion that the pluton was emplaced during d2 is strengthened by the structural and kinematic similarities between the magmatic deformation in the southern rim of the pluton and the d2 deformation in the country rocks this syntectonic timing is supported by new geochronological data that conflict with an existing rb sr post tectonic permian whole rock age for the maladeta granite more generally in accordance with some very recent structural and u pb zircon studies our results contradict the geodynamical models of the pyrenees which relate the granite intrusions to a late extensional event

world class base and precious metal deposits a quantitative analysis over 62 percent of the 193 000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits about 55 percent of the 1 740 000 metric tons of silver found is in four countries and 45 percent is in four types of deposits fifty six percent of the 1 52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total over 50 percent of both the 713 000 000 metric tons of zinc and 349 000 000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits all discovered gold would fit in a cube with a height of 22 m silver in a 55 m cube copper in a 550 m cube zinc in a 460 m cube and lead in a 310 m cube at least 74 percent of gold silver zinc and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits lower grade deposits contain less total metal than higher grade deposits tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal s total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits world class deposits defined as the upper 10 percent of deposits in terms of contained metal account for over 86 percent of all gold 79 percent of silver 84 percent of copper 71 percent of zinc and 73 percent of lead these giant deposits contain at least 100 metric tons 3 2 moz gold 2 400 metric tons 77 moz silver 2 million metric tons copper 1 7 million metric tons zinc or 1 million metric tons lead mineral deposits occur rarely in the earth s crust and large ones are especially uncommon this analysis shows that only the unusually large deposits can significantly affect supply

zooming on northern cap de creus shear zones abstract the northern cap de creus shear belt provides fine examples of shear zones developed at different scales in rocks bearing pre existing penetrative foliations the shear zones developed under retrograde metamorphic conditions and they are preferentially located in crystalline schists lower grade metasedimentary rocks accommodated deformation by folding the shear zones are linked in an anastomosing framework with self similar properties they are interpreted to have formed as the result of a progressive wrench dominated deformation affecting anisotropic rocks a progressive non coaxial deformation regime is considered responsible for the development of the complex kinematic pattern wherein shear zones with opposite senses of shear may come to lie in close parallelism in such a framework individual shear zones are characterised by marked strain gradients not only across the shear zone but also along it these features together with the geometrical analysis of shear zone marginal domains indicate that these structures developed with a component of shortening across the shear zones the shear zones are interpreted to have nucleated as buckling instabilities that gradually evolved to become shear zones approaching the simple shear model microstructural and quartz c axis fabric analyses indicate that shear zone formation is associated with strong strain partitioning on all scales

deformation of mylonites in palm canyon california based on xenolith geometry abstract an analysis of xenoliths in granodiorite and mylonites of the peninsular ranges batholith in southern california documents large deformation with von mises equivalent strains ranging from 1 to 4 from the geometry of xenoliths in mylonites it is concluded that much of the deformation occurred by flattening if deformation had been homogeneous the 800 m thick mylonite sequence would have extended originally over more than 10 km contrary to xenoliths associated with ballooning diapirs these in santa rosa mylonites show much larger strains and are elongated in the lineation direction it is proposed that the overall deformation pattern is consistent with a top to the west shear displacement but most of the strain in the santa rosa mylonites was produced in flattening during emplacement of the partially solidified batholith the large deformation may have produced folds that have coalesced with the foliation to accommodate the strain