the niujiaotang cd rich zinc deposit duyun guizhou province southwest china ore genesis and mechanisms of cadmium concentration the niujiaotang zinc deposit in southeastern guizhou china is a mississippi valley type zn deposit within early cambrian carbonate rocks sphalerite is enriched in cadmium average 1 4 wt cd which occurs mostly as isomorphous impurities in the sphalerite lattice discrete cadmium minerals greenockite and otavite are rare and are found almost exclusively in the oxidation zone of the deposit probably formed as secondary minerals during weathering leaching processes geochemical data show that the sulfides are enriched in heavy sulfur with 34s ranging from 10 0 to 32 8 mean 22 5 the consistent pb isotopic compositions in different sulfide minerals are similar to that of cambrian strata the ore lead probably came from u and th rich upper crustal rocks such as the lower cambrian wuxun formation the ore fluid is of low temperature 101 c to 142 c type with a na ca mg cl dominant composition and is interpreted as oil field brine the data indicate that the metals were mainly derived from the early cambrian strata qingxudong and wuxun formations whereas sulfur is sourced from sulfate in cambrian strata or oil field brines of the majiang petroleum paleoreservoir the genetic model for the deposit invokes an early cambrian shallow sea environment on the yangtze platform zinc and cd in seawater were concentrated in abundant algae via unknown biological mechanisms resulting in large amounts of zn and cd rich algal ooliths during the ordovician concurrent with destruction of the majiang petroleum paleoreservoir oil field brines migrated from the center of the basin to the margin leaching metals from the cambrian strata in the niujiaotang area preexisting zn and cd particularly in the qingxudong and wuxun formation were further mobilized by hot brines rising along the zaolou fault system forming stratiform and generally conformable zn cd orebodies in reactive carbonate lithologies

cierco pb zn ag vein deposits isotopic and fluid inclusion evidence for formation during the mesozoic extension in the pyrenees of spain the cierco pb zn ag vein deposits located in the central pyrenees of spain crosscut paleozoic metasedimentary rocks and are in close proximity to hercynian granodiorite dikes and plutons galena and sphalerite in the deposits have average delta 34 s values of 4 3 and 0 8 per mil cdt respectively coexisting mineral pairs give an isotopic equilibration temperature range of 89 degrees to 163 degrees c which overlaps with the 112 degrees to 198 degrees c range obtained from primary fluid inclusions coexisting quartz has a delta 18 o value of 19 or 1 per mil vsmow the fluid which deposited these minerals is inferred to have had delta 18 o sub h 2 o and delta 34 s sub h 2 s values of 5 or 1 and 1 or 1 per mil respectively chemical and microthermometric analyses of fluid inclusions in quartz and sphalerite indicate salinities of 3 to 29 wt percent nacl equiv with na super and ca super 2 as the dominant cations in solution the br cl and i cl ratios differ from those characteristic of magmatic waters and pristine seawater but show some similarity to those observed in deep ground waters in crystalline terranes basinal brines and evaporated seawater barite which postdates the sulfides spans isotopic ranges of 13 to 21 per mil 10 to 15 per mil and 0 7109 to 0 7123 for delta 34 s delta 18 o and 87 sr 86 sr respectively the three parameters are correlated providing strong evidence that the barites are products of fluid mixing we propose that the cierco deposits formed along an extensional fault system at the margin of a marine basin during the breakup of pangea at some time between the early triassic and early cretaceous sulfide deposition corresponded to an upwelling of hydrothermal fluid from the paleozoic basement and was limited by the amount of metals carried by the fluid barite deposition corresponded to the waning of upward flow and the collapse of sulfate rich surface waters onto the retreating hydrothermal plume calcite precipitated late in the paragenesis as meteoric or marine waters descended into the fault system possibly during a regression in the overlying basin there are other deposits resembling cierco elsewhere in the iberian peninsula taken as a group they are evidence that hydrothermal circulation systems were widespread during mesozoic extension differences among the deposits can be related to the fact that h 2 s and other solutes had local and variable sources

textural control on gold distribution in as free pyrite from the dongping huangtuliang and hougou gold deposits north china craton hebei province china article i nfo pyrite from the dongping huangtuliang and hougou gold deposits hebei province china was investigated using a combination of ore microscopy including back scattered imaging and in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms a range of elements including au te ag pb bi cu co ni and as was analyzed with the aim to constrain the textural controls and influence of superimposed deformation on the distribution of invisible gold in as free pyrite thedatasetshowsexcellentcorrespondence betweenmeasuredhighgoldvaluesandthreekeytexturalcriteria i areasofclusteredtellurideinclusions especiallyindongping ii microshearingandfracturing brecciation dongping and huangtuliang and iii pyrite recrystallization huangtuliang invisible gold is only at trace levels in the hougou and gold bearing telluride minerals are not observed this is considered to result from larger scale remobilization of gold during advanced brecciation and recrystallization of pyrite pyrite grains containing clustered inclusions have by far the highest gold concentrations up to 1 wt with consistent values of thousands of ppm au interpretation of textures and la icp ms data infers that in these areas the distribution of telluride inclusions extends pervasively from micron to nanoscale i e as fields of nanoparticles local employment of coupled dissolution reprecipitation reaction between pyrite and fluids driving the k metasomatic alteration dated at 150 ma is invoked to explain such patterns syn deformational grain scale mobilization of gold and other elements took place leading to a portion of the gold being recrystallized within fractures and microshears the deformational event leads to gold enrichment in the huangtuliang pyrite where brittle fracturing brecciation has been followed by a resorption and recrystallization in the latter case foam textured pyrites again without as can contain up to hundreds of ppm gold theinterpreted sequenceof pyritepost depositional eventsis inaccordancewith the protracted magmaticevolution of the area starting with variscan alkaline intrusions 390 ma and reactivated during the yanshanian orogeny 150 ma thestudyshows i thatas freepyritecanreadilycontainsignificantamountsofinvisiblegold bothasnanoparticles

formation and deformation of pyrite and implications for gold mineralization in the el callao district venezuela the el callao mining district is the most important gold producing region in venezuela it is hosted in the paleoproterozoic guasipati el callao greenstone belt which forms part of the guayana craton the venezuelan extension of the guiana shield of south america it consists of volcanic and volcanosedimentary sequences that were affected by several deformation events particularly localized shear zones the colombia mine the largest active mine in the district produces 4 tonnes t 128 600 oz of gold annually with reserves estimated at 740 t 24 moz and grades of up to 60 g t gold mineralization is concentrated within a vein network in the colombia corridor a shear fracture hosted mesh of interconnected quartz ankerite albite veins enclosing fragments of altered metabasaltic host rocks gold occurs mostly in the metabasaltic fragments and is spatially associated with pyrite in which it occurs as invisible gold micron sized native gold inclusions and filling fractures based on optical and scanning electron microscopy backscattered electron observations two types of pyrite are recognized a simple zoned pyrite and a less common oscillatory zoned pyrite both types consist of a mineral inclusion rich core and a clearer rim however in oscillatory zoned pyrite the latter is composed of complex rhythmic overgrowths of alternating as rich and as poor bands laser ablation inductively coupled plasma mass spectrometry la icp ms analysis and elemental mapping reveal the presence of invisible gold in all generations of pyrite the highest concentrations 5 23 ppm au are found in oscillatory zoned pyrite rims which correlate with the highest as concentrations 16 000 23 000 ppm in as poor bands au up to 1 5 ppm and as 300 6 000 ppm concentrations decrease by about an order of magnitude copper bi te sb pb and ag always occur with invisible gold particularly in pyrite cores suggesting that at least part of the gold occurs in sulfosalt nanoparticles of these metals and metalloids visible native gold grains occur as small inclusions throughout core and rim of both pyrite types as well as in fractures within it in both occurrences chalcopyrite sphalerite tellurobismuthite ankerite albite and chlorite accompany native gold and gold fineness ranges between 900 and 930 at an early stage of vein mesh formation pyrite formed in the metabasaltic fragments at the expense of ankerite which in turn resulted from alteration of fe ti oxides gold together with other chalcophile elements was incorporated within the structure of pyrite most likely by destabilization of metal sulfide complexes during ankerite replacement subsequent cyclic reactivations of the shear zone caused development of pressure shadows around pyrite generating local and repeated decreases in pressure which triggered local boiling of the hydrothermal fluid as evidenced by the presence of primary fluid inclusions containing immiscible liquid rich and vapor rich aqueous carbonic fluids this process was responsible for a number of physical chemical changes in the liquid all of which contributed to the formation of the as and au rich overgrowths in pyrite 1 removal of h 2 o into the vapor phase inducing saturation of dissolved metals in the remaining liquid 2 an increase in ph due to partition of h 2 s and co 2 into the vapor thus decreasing the solubility of sulfide minerals and 3 an adiabatic decrease in temperature lowering the solubility of as and au in the liquid waning of this process restored precipitation of as poor pyrite until the onset of a new cycle because pressure drops are more significant adjacent to open spaces oscillatory zoned pyrite probably crystallized near newly formed veins whereas simple zoned pyrite formed away from them previously formed pyrite underwent fracturing during reactivation of the deformation especially through the brittle deformation events that postdated shearing resulting in local pulverization of pyrite this newly created porosity facilitated fluid circulation and remobilization of structurally bound gold as well as of other chalcophile elements ag cu bi te pb and sb which reprecipitated together with pyrite in the form of native gold sulfides and tellurides either as small inclusions or as larger grains within fractures this remobilization process facilitates the exceptionally high gold tenor found in the deposit where the colombia corridor is intersected by the santa maria fault

geology petrography and mineral chemistry of the vazante non sulfide and ambrosia and fagundes sulfide rich carbonate hosted zn pb deposits minas gerais brazil the vazante paracatu region represents the most important zn district known in brazil and includes the vazante hypogene non sulfide zn deposit composed mainly of willemite zn2sio4 and sphalerite rich carbonate hosted zn pb deposits fagundes is a stratabound deposit characterized by strong silicification dolomitization and a fe rich carbonate alteration halo the main ore is represented by rhythmically banded colloform and zoned pyrite sphalerite and galena related to wall rock dissolution and sulfide infilling which probably occurs late during the burial diagenesis later veins and breccia ore types reflect epigenetic mobilization related to brittle ductile structures the ambrosia mineralization is mainly fault controlled and related to brecciated dolomite which is tectonically imbricated with black shales and slates typical features include host rock recrystallization minor silicification baroque dolomite and ankerite formation pyrite marcasite sphalerite and minor galena occur in brecciated comb veins and veinlets which overprint stylolites and tectonic fractures suggesting an epigenetic origin for the ore the vazante deposit differs from all other deposits of the district due to the presence of willemitic ore which is composed of willemite dolomite siderite quartz hematite zn rich chlorite barite franklinite and zincite the willemitic ore occurs tectonically imbricate to small sulfide ore bodies which comprises sphalerite and galena metabasites and hydrothermalized dolomites within the vazante shear zone the relationships between willemite formation and the development of mylonitic structures suggest that willemitic mineralization and deformation are synchronous episodes closely related to the vazante shear zone low zn cd ratios in sphalerite from vazante 64 to 98 and fagundes colloform 96 to 244 and zoned sphalerite 89 to 305 could reflect the regional role of mineralizing fluids with similar low zn cd ratios and low contents of reduced sulfur sred high ge up to 2200 ppm and the low fe cu mn and ag contents in late diagenetic fagundes sphalerite might suggest that this metal bearing fluid could be derived from the underlying basin fill which comprise clastic sediments and organic matter rich pelitic sequences systematic relationships among sphalerite composition and paragenetic evolution of the fagundes and ambrosia deposits suggest that progressive fluid mixing processes were important for the genesis of the sulfide rich deposits in the district these mixing processes possibly involved the hot metal bearing fluid with low contents of reduced sulfur and moderate temperature highly saline fluids which could represent an important sulfur supply the predominance of the highly saline brines in later epigenetic mineralization episodes might be related to episodic migration of hydrothermal fluids mainly derived from reduced shale sequences during the brasiliano compressive events the small variation in chemical and sulfur isotopic composition of the vazante sphalerite could imply that the high temperature metal bearing fluid with low zn cd ratios could represent a minor reservoir of reduced sulfur which permitted only subordinate sphalerite precipitation in the vazante deposit the lack of reduced shale sequences above the vazante deposit could represent a limiting factor for h2s supply additionally overall mixture between this hot sulfur deficient metal bearing fluid and meteoric fluids channeled to the vazante shear zone favor the high fo2 s2 conditions responsible for the stability of the vazante willemitic assemblage

geology mineralogy and stable isotope geochemistry of the kabwe carbonate hosted pb zn deposit central zambia abstract the carbonate hosted kabwe pb zn deposit central zambia has produced at least 2 6 mt of zn and pb metal as well as minor amounts of v cd ag and cu the deposit consists of four main epigenetic pipe like orebodies structurally controlled along ne sw faults sphalerite galena pyrite minor chalcopyrite and accessory ge sulphides of briartite and renierite constitute the primary ore mineral assemblage cores of massive sulphide orebodies are surrounded by oxide zones of silicate ore willemite and mineralized jasperoid that consists largely of quartz willemite cerussite smithsonite goethite and hematite as well as numerous other secondary minerals including vanadates phosphates and carbonates of zn pb v and cu galena sphalerite and pyrite from the pb zn rich massive orebodies have homogeneous negative sulphur isotope ratios with mean 34 s cdt permil values of 17 75 0 28 1 16 54 0 0 27 and 15 82 0 25 respectively the zn rich and pb poor no 2 orebody shows slightly heavier ratios of 11 70 0 5 34 s for sphalerite and of 11 91 0 71 34 s for pyrite the negative sulphur isotope ratios are considered to be typical of sedimentary sulphides produced through bacterial reduction of seawater sulphate and suggest a sedimentary source for the sulphur carbon and oxygen isotope ratios of the host dolomite have mean 13 c pdb and 18 o smow values of 2 89 and 27 68 respectively which are typical of marine carbonates the oxygen isotope ratios of dolomite correlate negatively to the sio 2 content introduced during silicification of the host dolomite the depletion in 18 o in dolomite indicates high temperature fluid rock interaction involving a silica and 18 o rich hydrothermal solution two types of secondary fluid inclusions in dolomite both of which are thought to be related to ore deposition indicate temperatures of ore deposition in the range of 257 to 385 and 98 to 178 c respectively the high temperature fluid inclusions contain liquid vapour solid phases and have salinities of 15 to 31 eq wt nacl whereas the low temperature inclusions consist of liquid vapour with a salinity of 11 5 eq wt nacl fluid transport may have been caused by tectonic movements associated with the early stages of the pan african lufilian orogeny whereas ore deposition within favourable structures occurred due to changes in pressure temperature and ph in the ore solution during metasomatic replacement of the host dolomite the termination of the kabwe orebodies at the mine club fault zone and observed deformation textures of the ore sulphides as well as analysis of joint structures in the host dolomite indicate that ore emplacement occurred prior to the latest deformation phase of the neoproterozoic lufilian orogeny

microstructural evolution and trace element mobility in witwatersrand pyrite microstructural analysis of pyrite from a single sample of witwatersrand conglomerate indicates a complex deformation history involving components of both plastic and brittle deformation internal deformation associated with dislocation creep is heterogeneously developed within grains shows no systematic relationship to bulk rock strain or the location of grain boundaries and is interpreted to represent an episode of pyrite deformation that predates the incorporation of detrital pyrite grains into the central rand conglomerates in contrast brittle deformation manifest by grain fragmentation that transects dislocation related microstructures is spatially related to grain contacts and is interpreted to represent post depositional deformation of the central rand conglomerates analysis of the low angle boundaries associated with the early dislocation creep phase of deformation indicates the operation of 100 slip systems however some orientation boundaries have geometrical characteristics that are not consistent with simple 100 deformation these boundaries may represent the combination of multiple slip systems or the operation of the previously unrecognized 120 slip system these boundaries are associated with order of magnitude enrichments in as ni and co that indicate a deformation control on the remobilization of trace elements within pyrite and a potential slip system control on the effectiveness of fast diffusion pathways the results confirm the importance of grain scale elemental remobilization within pyrite prior to their incorporation into the witwatersrand gold bearing conglomerates since the relationship between gold and pyrite is intimately related to the trace element geochemistry of pyrite the results have implications for the application of minor element geochemistry to ore deposit formation suggest a reason for heterogeneous conductivity and localized gold precipitation in natural pyrite and provide a framework for improving mineral processing

noble gas isotopic systematics of fe ti v oxide ore related mafic ultramafic layered intrusions in the panxi area china the role of recycled oceanic crust in their petrogenesis olivine and clinopyroxene grains have been separated from four large fe ti v oxide ore bearing intrusions panzhihua hongge baima and taihe in the panxi area emeishan large igneous province southwest china for he and ar isotope studies the samples examined revealed extremely low 3 he 4 he ratios 0 078 4 34 ra with the mean value 0 78 ra for gases extracted by stepwise heating this feature combined with low 40 ar 36 ar ratios can be interpreted as due to addition of subduction related fluids and melts that had been stored in the lithospheric mantle for long periods considering the regional geologic history such addition can be attributed to the paleo subduction that occurred along the western margin of the yangtze block during the neoproterozoic the subducted oceanic crust beneath the panxi area underwent eclogite facies metamorphism and subsequent exhumation the infiltration of subduction related melts and fluids into the lithospheric mantle led to enriched isotopic signatures from that of the slightly depleted asthenopheric mantle which has been suggested by the sr nd and pb isotopic data of the emeishan basalts and picrites in addition considerable amounts of eclogitic melts produced by partial melting of eclogite facies oceanic crust extensively contaminated the lithospheric mantle during the late permian partial melting of an upwelling mantle plume that contained an eclogite or pyroxenite component generated the parental fe rich magma that supplied the ore bearing intrusions the combination of these factors may have been the crucial reason that many world class fe ti v oxides deposits are clustered in the panxi area

rapid cycling of subducted sediments into the samoan mantle plume harzburgite xenoliths from the samoan hotspot carry extraordinarily enriched sr nd pb isotopic ratios previously attributed to metasomatism by a carbonatitic fluid derived from recycled sediments i describe here the gas composition and microthermometric properties of fluid inclusions that have trapped this unusual agent the inclusions are dominantly pure co 2 and were apparently formed at the base of the crust they have high 3he 4he ratios 12 times the atmospheric ratio inconsistent with the radiogenic values expected for recycled sediments furthermore inclusion c 3he ratios of 3 10 9 are indistinguishable from typical mantle values and are far lower than those in sediments 10 11 these striking observations imply that little of the helium and carbon in the metasomatic fluid was derived from the recycled source required by the sr nd pb isotopes the metasomatic fluid is probably a product of mixing within the samoan hot spot of a volatile rich high 3he 4he plume melt and recycled sediments the retention of high 3he 3he ratios in such a mixture requires very rapid cycling of the sedimentary component through the mantle probably 10 7 yr rather than the billions of years often envisaged this time scale indicates involvement of material recently returned to the mantle at the nearby tonga trench and pelagic sediments near the trench have approximately the requisite geochemical signature the unique isotopic characteristics of the samoan plume likely arise from its unusual tectonic setting at the northern terminus of subduction in the tonga trench

geological features and origin of the huize carbonate hosted zn pb ag district yunnan south china abstract the huize zn pb ag district in the sichuan yunnan guizhou zn pb ag metallogenic region contains significant high grade zn pb ag deposits the total metal reserve of zn and pb exceeds 5 mt the district has the following geological characteristics 1 high ore grade zn pb 25 wt 2 enrichment in ag and a range of other trace elements ge in ga cd and tl with galena sphalerite and pyrite being the major carriers of ag ge cd and tl 3 ore distribution controlled by both structural and lithological features 4 simple and limited wall rock alteration 5 mineral zonation within the orebodies and 6 the presence of evaporite layers in the ore hosting wall rocks of the early carboniferous baizuo formation and the underlying basement fluid inclusion and isotope geochemical data indicate that the ore fluid has homogenisation temperatures of 165 220 c and salinities of 6 6 12 wt nacl equiv and that the ore forming fluids and metals were predominantly derived from the kunyang group basement rocks and the evaporite bearing rocks of the cover strata ores were deposited along favourable specific ore controlling structures the new laboratory and field studies indicate that the huize zn pb ag district is not a carbonate replacement deposit containing massive sulphides but rather the deposits can be designated as deformed carbonate hosted mvt type deposits detailed study of the deposits has provided new clues to the localisation of concealed orebodies in the huize zn pb ag district and of the potential for similar carbonate hosted sulphide deposits elsewhere in ne yunnan province as well as the sichuan yunnan guizhou zn pb ag metallogenic region

did the giant broken hill australia zn pb ag deposit melt abstract recent published research has proposed that some metamorphosed massive sulfide deposits including the broken hill deposit australia have partially melted here we discuss the evidence for and against this process the broken hill deposit is located in the curnamona craton within a rift in an apparent upward coarsening sequence of clastic metasediments into which paleoproterozoic mafic and felsic melts intruded the deposit was metamorphosed to granulite facies conditions 750 800 c and 5 6 kbar and was subjected to at least five periods of deformation at peak p t conditions a melt phase was produced in silicate rocks especially granitoids and psammopelites and in ore characterized by the systems cu as s ag pb s ag sb as s cu sb pb s sb as s cu sb s and fe as s however the proportion of minerals in these s bearing systems is insignificant 2 feo mno cao al 2 o 3 p 2 o 5 co 2 zns pbs fes feass feas 2 which is the most relevant system to broken hill ores p t conditions were never high enough to produce a melt phase in this system authors arguing for sulfide rock melting suggest that mn rich lithologies garnetite and quartz garnetite which are intimately associated with the pb rich ores at the broken hill deposit were produced by a reaction between mn rich sphalerite and aluminous wall rocks however to produce such rocks would require mn contents of sphalerite compositions that are unrealistically high and yet to be found in nature moreover the implication of the melt model is that wherever mn rich quartz garnetite and garnetite are found sphalerite should be located next to them this is clearly not the case the presence of polyphase sulfide inclusions within garnet in garnetite has also been considered by some in the literature to be sulfide melt inclusions with the implication that the enclosing garnet was a product of melting however we consider these sulfides to be products of hydrothermal processes during retrograde metamorphism it is impossible to form garnetite and quartz garnetite in rocks within the curnamona craton that formed at upper greenschist lower amphibolite facies conditions by partial melting p t conditions were too low we consider that the fe and mn component of garnetite and quartz garnetite are products of exhalation and inhalation at or near the sea floor and that these rocks are meta exhalites or meta inhalites some garnet rich rocks also formed by metasomatic processes throughout the protracted metamorphic history that affected the curnamona craton

hydrothermal alteration and mineralization in the neves corvo volcanic hosted massive sulfide deposit portugal ii oxygen hydrogen and carbon isotopes the oxygen hydrogen and carbon isotope compositions of hydrothermally altered rocks and minerals from massive and stockwork ores of the neves corvo volcanic hosted massive sulfide deposit have been used to infer its thermal history and the origins of the hydrothermal fluids quartz and cassiterite separated from the stringer and massive cassiterite ores of the corvo orebody tin corridor have 18o values of 12 5 to 13 6 and 1 4 to 0 4 per mil respectively quartz cassiterite oxygen isotope fractionation indicates temperatures of 174 to 207 c avg 191 c for precipitation of this mineral pair the calculated oxygen isotope composition of the fluid 18oh2o 0 4 to 0 7 avg 0 1 suggests that cassiterite precipitation resulted from extensive mixing of a tin bearing fluid with seawater at sea floor hydrothermal vents the whole rock oxygen isotope composition of the hydrothermally altered felsic volcanic rocks hosting the sulfide stockwork of the corvo orebody varies from the central stockwork chloritic alteration zone i 18o 8 7 9 6 to the peripheral zones sericitic and paragonitic alteration zones iia 18o 11 6 13 1 and iib 18o 11 0 14 1 the 18o values of quartz also increase from alteration zone i avg 13 9 to alteration zone iia avg 14 4 to alteration zone iib avg 15 0 quartz from the hanging wall jasper unit yielded higher 18o values of 15 5 to 17 9 per mil chlorite from alteration zone i has 18o values of 6 1 to 8 4 per mil avg 7 4 sericite has 18o and d values that vary slightly from 18o 9 3 to 10 1 per mil avg 9 9 and d 59 to 47 per mil avg 53 in alteration zone i to 18o 9 8 to 11 4 per mil avg 10 5 and d 50 per mil in alteration zone iia to 18o 9 4 to 11 7 per mil avg 10 6 and d 61 to 36 per mil avg 45 in alteration zone iib siderite associated with waning hydrothermal activity has low 13c values 11 1 to 5 8 suggesting the incorporation of oxidized organic carbon from the footwall sequence and or the addition of magmatic carbon in alteration zone i quartz chlorite fractionation indicates temperatures of 249 to 402 c avg 335 c and 18oh2o values of 6 1 to 10 2 per mil avg 8 3 quartz sericite pairs gave isotopic equilibrium temperatures of 250 to 289 c avg 269 c and 18oh2o values of 5 8 to 7 0 per mil avg 6 4 in alteration zone iia and 170 to 318 c avg 223 c and 18oh2o 1 4 to 8 3 per mil avg 4 5 in alteration zone iib the oxygen isotope data show that in the core of the feeder system alteration zone i the temperature and the 18oh2o values were very high the d values calculated for the ore fluids d 37 to 11 are also significantly lower than seawater outward from the central stockwork alteration zones iia and iib the ore fluid was depleted in 18o and the temperatures were lower the oxygen hydrogen and carbon isotope signatures of the neves corvo ore fluids are best explained by incorporation of magmatic and or metamorphic fluids into a seawater dominated hydrothermal system magmatic fluids in particular were a likely source for the tin and much of the copper in the neves corvo ores

arrens zn pb ba devonian deposit pyrenees france an exhalative sedimentary type deposit similar to meggen the perrefitte anticlinorium district in the paleozoic province of the pyrenees contains abundant mineral occurrences prospects and old mines in the upper volcano sedimentary layer of the ordovician and devonian sediments which have been metamorphosed in the greenschist to amphibolite facies although of different lithologic environments the mineralization shows as everywhere in the pyrenees many common characteristics however the arrens deposit outcropping over 5 km on both limbs of a syncline displays specific characteristics abundant barite with lateral zn pb ba zoning exceptionally thick subreef footwall limestone overlain by black siltstone abundant ba silicate in particular celsianite locally cymrite and siliceous sedimentary hydrothermal gangue due to deformation such as tight folds and flow cleavage the paleogeography of the arrens geological environment could not be precisely reconstructed however the deposit is very likely located in an unstable shelf zone lithology underwent many changes close to the synsedimentary faults including at arrens a limestone shelf facies and some small basins of black siltstone at the bottom of which mineralization occurs as all the mineralization of the pyrenees paleozoic the deposit is of the exhalative or hydrothermal sedimentary type and bears some analogies with other exhalative deposits throughout the world the word exhalative is etymologically related to gases although hydrothermal is a more exact word as it pertains to hot water exhalative will be used in this paper being of most current usage

geochemical and mineralogical distribution of germanium in the khusib springs cu zn pb ag sulfide deposit otavi mountain land namibia abstract the khusib springs deposit in the otavi mountain land namibia is a small though high grade carbonate hosted cu zn pb ag as sb ge deposit of the tsumeb type containing approximately 300 000 t of ore grading 10 cu 1 8 pb and 584 ppm ag a lens shaped sulfide orebody up to 10 m thick and elongated parallel to bedding replaces limestone locally brecciated of the lower tsumeb subgroup damara supergroup in the northern limb of a large ne trending synclinal structure a prominent zone of dolomite alteration surrounds the orebody in a drill core through the orebody the uppermost 2 m are enriched in zn up to 5 and ag up to 3350 ppm but lower in ge 26 v 2 as ge 6 s 32 forming small usually geochemical and mineralogical features of sulfide ores from khusib springs resemble some sulfide ores of the pipe shaped polymetallic ge rich tsumeb deposit similar to the latter ore formation probably occurred during d 2 deformation and metamorphism and involved highly saline hot brines up to 370 c chetty d frimmel h e 2000 the role of evaporites in the genesis of base metal sulfide mineralization in the northern platform of the pan african damara belt namibia geochemical and fluid inclusion evidence from carbonate wall rock alteration mineralium deposita 35 364 376 carrying sulfur derived from evaporite sequences a polyphase mineralization involving three successive stages is proposed early sphalerite pyrite chalcopyrite bornite mineralization is replaced by tennantite enargite galena and ge bearing colusite a late stage mineralization overprints parts of the orebody at lower temperatures leading to precipitation of schalenblende cu and ag rich digenite tetrahedrite and pearceite polybasite the occurrence of small but high grade ge rich cu zn pb ag deposits in the lower tsumeb subgroup has important consequences on the mineral potential of the area because prospecting for cu rich ores has been traditionally performed in the uppermost tsumeb subgroup only in relation to paleokarst structures

germanium geochemistry and mineralogy abstract germanium is enriched in the following geologic environments 1 1 iron meteorites and terrestrial iron nickel 2 2 sulfide ore deposits particularly those hosted by sedimentary rocks 3 3 iron oxide deposits 4 4 oxidized zones of ge bearing sulfide deposits 5 5 pegmatites greisens and skarns and 6 6 coal and lignitized wood in silicate melts ge is highly siderophile in the presence of native iron nickel otherwise it is highly lithophile among silicate minerals ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz in deposits formed from hydrothermal solutions ge tends to be enriched mostly in either sulfides or in fluorine bearing phases it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites greisens and skarns in sulfide deposits that formed from solutions having low to moderate sulfur activity ge is concentrated in sphalerite in amounts up to 3000 ppm sulfide deposits that formed from solutions having higher sulfur activity allowed ge to either form its own sulfides particularly with cu or to substitute for as sn or other metals in sulfosalts the ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids or is due to the incorporation of ge from the country rocks particularly from those containing organic material germanium bonds to lignin derivative organic compounds that are found in peat and lignite accounting for its common concentration in coals and related organic material germanium is precipitated from water together with iron hydroxide accounting for its concentration in some sedimentary and supergene iron oxide deposits it also is able to substitute for fe in magnetite in a variety of geologic environments in the oxidized zone of ge bearing sulfide deposits ge is concentrated in oxides hydroxides and hydroxy sulfates sometimes forming its own minerals it is particularly enriched in some iron and manganese bearing oxides and hydroxides including goethite up to 5300 ppm and hematite up to 7000 ppm

evidence for subduction related components in the subcontinental mantle from low 3he 4he and 40ar 36ar ratio in mantle xenoliths from far eastern russia abstract by applying both vacuum crushing and stepwise heating methods for the extraction of the noble gases we have discovered 3he 4he ratios much lower than the atmospheric ratio 0 3 ra ra is the atmospheric 3he 4he ratio of 1 4 10 6 and relatively low 40ar 36ar ratios spectroscopic and petrographic observations confirm that there are at least two compositionally distinct fluids in these xenoliths liquid co2 inclusions and melt inclusions with shrinkage bubbles based on the crushing experiments it is inferred that the inclusions of liquid co2 have a 3he 4he ratio similar to that of morb and the component with the low 3he 4he ratio is derived from the shrinkage bubbles in the melt inclusions for the present samples the 40ar 36ar ratios obtained by crushing were less than 1000 suggesting incorporation of atmospheric components in the source materials since low 40ar 36ar ratios were observed irrespective of the occurrence of the liquid co2 inclusions the atmospheric component exists in the melt inclusions ne and xe isotopes are also consistent with incorporation of atmospheric components since the far eastern russia area was located at a subduction zone in the jurassic early cretaceous period it is most likely that the melt inclusions displaying atmospheric noble gas characteristics together with low 3he 4he ratios have been derived from the jurassic cretaceous subducted slab although we cannot exclude the possibility that low 3he 4he ratios are due to the existence of minor u bearing minerals in the lithospheric continental mantle caused by metasomatism we have no petrographical evidence for such minerals in this area on the other hand 3he 4he ratios observed in the liquid co2 inclusions which are similar to the morb like value might reflect the general character of the upper mantle the far eastern russian mantle may therefore be a morb like source that has been partly infiltrated by subduction related fluids

relationship between microstructures and grain scale trace element distribution in komatiite hosted magmatic sulphide ores komatiite hosted nickel sulphides from the yilgarn craton australia consist of two main sulphide phases pyrrhotite fe7s8 and pentlandite fe ni 9s8 two minor sulphide phases chalcopyrite cufes2 and pyrite fes2 and trace arsenides samples of massive sulphides from three deposits with diverse deformation and metamorphic histories the silver swan perseverance and flying fox deposits have been studied by electron backscatter diffraction and laser ablation inductively coupled plasma mass spectrometry and nano scale secondary ion mass spectrometry these ore bodies were selected to investigate the relationship between microstructures and mineral trace element chemistry in three dominant sulphide species in each deposit in all three samples pyrrhotite preserves a strong evidence of crystal plasticity relative to both pentlandite and pyrite the trace element composition of pyrrhotite shows significant variation in specific elements pb bi and ag this variation correlates spatially with intragrain pyrrhotite microstructures such as low angle and twin boundaries minor signatures of crystal plasticity in pyrite and pentlandite occur in the form of rare low angle boundaries pentlandite and mild lattice misorientation pyrite trace element compositions of pentlandite and pyrite show no correlation with microstructures variations in pyrrhotite are interpreted as a result of intragrain diffusion during the syn and post deformation history of the deposit intragrain diffusion can occur either due to bulk diffusion dislocation impurity pair diffusion or by pipe diffusion i e along fast diffusion pathways at high and low angle and twin boundaries this contribution examines three different diffusion models and suggests that dislocation impurity pair diffusion and pipe diffusion are the most likely processes behind increased trace element concentration along the microstructures in pyrrhotite the same phenomenon is observed in samples from three different deposits that experienced widely different metamorphic conditions implying that the final disposition of these elements reflects a post peak metamorphic stage of the geological history of all three deposits

trace and minor elements in sphalerite from base metal deposits in south china a la icpms study laser ablation icp mass spectroscopy has been used to investigate the geochemistry of sphalerite in a range of nine zn pb deposits in south china the deposits which are of different ages and belong to different metallogenic provinces have been assigned to the following genetic types skarn hetaoping luziyuan syngenetic massive sulphide dabaoshan laochang and bainiuchang and mississippi valley type huize mengxing niujiaotang based on the features of the ore even though their origin is heavily debated based on other criteria the giant jinding deposit is considered separately sphalerite from each genetic class of deposit shows a distinct chemical signature sphalerite from the skarn deposits is characterised by elevated lattice bound concentrations of co and mn the distal character of these skarn systems is reflected by the low in content of sphalerite the three syngenetic massive sulphide deposits feature sphalerite strongly enriched in in sn and ga whereas the deposits of mvt type are typically enriched in ge cd tl and as these divergent characters are reflected in absolute element abundances as well as in element ratios time resolved depth profiles for sphalerite from the chinese deposits confirm the presence of elements such as co in ge ga and cd in solid solution but the dataset expands the understanding of sphalerite mineral chemistry by also indicating that other elements whose ability to enter the crystal structure of sphalerite has been previously debated ag sn tl sb may also be in solid solution sphalerite is a refractory mineral and trace element analysis of sphalerite shows promise as a tracer of ore genesis even in overprinted ores systematic work on larger sample suites may help define the geochemical signature of different metallogenic epochs in regions as geologically complex as south china and help resolve the mechanism by which many of the debated ore deposits were formed

behavior of critical metals in metamorphosed pb zn ore deposits example from the pyrenean axial zone rare metals ge ga in cd are key resources for the development of green technologies and are commonly found as trace elements in base metal mineral deposits many of these deposits are in orogenic belts and the impact of recrystallization on rare metal content and distribution in sphalerite needs to be evaluated based on laser ablation inductively coupled plasma mass spectrometry la icp ms analyses and micro imaging techniques such as laser induced breakdown spectroscopy libs and electron backscattered diffraction ebsd we investigate the minor and trace element composition related to sphalerite texture for three types of mineralization from the pyrenean axial zone paz vein mineralization type 2b appears significantly enriched in ge and ga compared to disseminated and stratabound mineralizations type 1 and type 2a respectively in vein mineralization the partial recrystallization induced by deformation led to the remobilization of ge ga and cu from the sphalerite crystal lattice into accessory minerals we propose that the association of intragranular diffusion and fluid rock reaction were likely responsible for the formation of patchy oscillatory zoning in sphalerite and the crystallization of ge rich accessory minerals chemical and textural heterogeneity is common in sphalerite from various world class deposits and a full understanding of these heterogeneities is now crucial to assess the rare metal potential and associated extraction processes of deformed base metal ores

on the geological availability of germanium based on a detailed statistical analysis of chemical data published in the scientific literature estimates were made of the minimum amounts of recoverable ge contained within sulphidic zinc ores and coals given current processing technologies it is expected that at least 119 kt 7 kt in zinc ores and 112 kt in coal of recoverable germanium exist within proven reserves at present stage of knowledge at grades in excess of 100 ppm in sphalerite and 200 ppm in coal while at least 440 kt 50 kt in zinc ores and 390 kt in coal should become recoverable in the future being associated to coal reserves at 8 200 ppm ge and zinc resources containing in excess of 100 ppm ge in sphalerite mississippi valley type mvt deposits are expected to be the most important hosts of germanium rich sphalerite while both brown and hard coals are expected to be equally important as hosts of germanium the approach taken in this publication shows that reliable minimum estimates for the availability of by product metals lacking suitable reserve resource data may be attained by using robust statistical methods and geochemical data published in the scientific literature

thickness of a submarine lava flow determined from near bottom magnetic field mapping by autonomous underwater vehicle magnetic field surveys obtained near the seafloor can map the boundaries of recent volcanic eruptions and can provide thickness estimates of these lava flow units independent of bathymetry differencing methods magnetic thickness estimation requires knowledge of the intensity of magnetization of the new lava and surrounding terrain but this can be satisfactorily obtained by representative sampling of the various volcanic units while bathymetry differencing requires pre existing data to assess the thickness of new lava eruptions magnetic surveys can be obtained after an eruption has occurred in this study near bottom magnetic surveys were obtained using an autonomous underwater vehicle auv which operates without a tether or human intervention auv technology offers rapid deployment and an efficient surveying approach for remotely mapping recent lava eruption sites on the seafloor

trace elements of indium bearing sphalerite from tin polymetallic deposits in bolivia china and japan a femto second la icpms study abstract indium bearing tin polymetallic base metal deposits in japan toyoha ashio and akenobe china dulong and dachang and bolivia potosi huari huari bolivar and porco were studied using femto second laser ablation icpms fsla icpms and epma analyses for major and minor elements in sphalerite paying special attention to in concentrations sphalerite is a principal mineral in these tin polymetallic deposits and a broad range of in concentration is measured in the ores there are distinct differences in mode of occurrence of the sphalerite and the distribution of in the highest in concentration up to 18 wt occur as a zn in mineral within black sphalerite zones in an oscillatory zoned sphalerite from the huari huari deposits additionally jamesonite from the huari huari deposit also contains anomalous in values ranging from several hundreds to thousands g g sphalerite from the toyoha and the other bolivian deposits are characterized by oscillatory and chemical zoning whereas those from akenobe and the chinese deposits are represented by homogeneous distribution of in the 1000in zn values of sphalerite are in good agreement with those of the ore grade for each of the selected tin polymetallic deposits indicating that sphalerite is the principal host of in the in bearing sphalerite principally involves the combined coupled substitutions 2zn2 cu in3 3zn2 cu ag sn4 and 3zn2 2cu sn4 the first of these is apparent in sphalerite from huari huari and bolivar whereas the second is prominent in sphalerite from toyoha ashio potosi porco and dachang akenobe and dulong sphalerite features the dominant coupled substitution of 2zn2 cu or ag in3 owing to their poor sn content occasionally sub micron inclusions of minerals such as stannite and pb sb bearing sulfides can occur in sphalerite contributing to high cu sn and high ag contents respectively the observed correlations of each element in the in cu ag sn bearing sphalerite can be proposed as a fundamental reason for the indium enrichment related to sulfur rich oxidized magmatism in addition the ag content in sphalerite is considered a possible indicator of formation depth which ranges from plutonic to subvolcanic environments

flow mechanisms in sulphide minerals abstract the sulphide minerals as a group display a diverse range in strength and mechanical behaviour in crustal environments deforming by a range of different flow mechanisms which can lead to the development of characteristic microfabrics the dependence of creep rate on imposed parameters such as stress difference temperature grainsize effective confining pressure and the activities of various components varies for each type of flow mechanism for particular phases changes in the dominant operative flow mechanism may occur in response to changes in the imposed environmental variables at high applied stress differences low effective confining pressures and low temperatures brittle failure and cataclastic flow are significant deformation mechanisms in some sulphide minerals at elevated confining pressures brittle failure can be suppressed and low temperature plasticity processes involving dislocation glide and or deformation twinning may operate with decreasing applied stress difference and at elevated temperatures even though strain may be accommodated largely by dislocation glide deformation may be rate controlled by recovery processes and dynamic recrystallization may be significant in influencing microfabric development the operation of dislocation glide processes leads to the development of crystallographic preferred orientations at very low applied stress difference various grainsize dependent atomic transfer deformation mechanisms may be important in many fluid present low to medium grade metamorphic environments solution precipitation creep processes are active in the deformation of some sulphide phases in fluid absent situations grain boundary diffusion creep may be significant at higher temperatures where intragranular diffusion is relatively rapid lattice diffusion creep processes are expected to be a major deformation mechanism in fine grained sulphide assemblages at elevated temperatures grain boundary sliding may be an important deformation mechanism

primary and tectonic features of the currawong zn cu pb au massive sulfide deposit benambra victoria implications for ore genesis the late silurian currawong zn cu pb au massive sulfide deposit is located in the northeastern highlands of victoria southeastern australia the currawong deposit forms two strata bound concordant massive sulfide lenses which have been dissected by late subvertical faulting each massive sulfide lens possesses a concordant stringer system in the footwall to the massive sulfides which presumably represent major hydrothermal fluid pathways to the mineralization host rocks are comprised of subaqueous rhyodacitic to andesitic breccias and coherent volcanic rocks and equivalent temporally and spatially epiclastic rocks that are contained in and interfinger with a monotonous succession of turbidites the geometry and distribution of ore types in the currawong deposit are characteristic of both sheet and layered type deposits as described in australia mineralization is divided into six types pb zn pyrite zn massive pyrite pyrite magnetite footwall stringer and overprinting veins and breccias related to local remobilization of base metal sulfides during deformation three generations of deformation are recognized in the host stratigraphy these can be correlated to deformation textures observed within the ore based on consistent structural geometries unequivocal evidence that mineralization predates the earliest deformation the internal stratigraphy of the deposit is erratic with ore facies changing laterally over tens of meters however a general vertical zonation of ore types exists within both lenses from hanging wall to footwall the zonation is exemplified by pb zn ore pyrite zn ore intermixed pyrite zn and massive pyrite ores and pb zn and pyrite zn ore associated with sporadic occurrences of hydrothermally altered volcanic rocks this zonation can be repeated up to three times in lens 1 forming a cyclic distribution pyrite magnetite ore occurs at the base of the deposit located immediately above footwall stringer mineralization metal zonation

gold upgrading in metamorphosed massive sulfide ore deposits direct evidence from laser ablation inductively coupled plasma mass spectrometry analysis of invisible gold the metamorphosed boliden volcanic hosted massive sulfide vhms ore deposit northern sweden is characterized by an abundance of massive arsenopyrite ore and unusually high gold enrichments up to 300 600 g t in crosscutting veins and fracture zones the ore textures observed record progressive recrystallization and porphyroblast growth during meta morphism we conducted a systematic laser ablation inductively coupled plasma mass spectrom etry la icp ms study on the gold distribution in fine grained massive arseno pyrite and pyrite ore partially recrystallized arsenopyrite ore and both arsenopyrite and pyrite porphyroblasts found in gold rich veins the gold concentrations in massive arseno pyrite are highest 30 50 ppm on average and systematically decrease to 0 2 7 ppm with increasing degree of recrystallization by contrast gold concentrations in pyrite ore are much lower and do not exceed 0 2 ppm the la icp ms data coupled with textural data provide the first direct conclusive evidence that gold is progressively liberated from massive sulfide ores during metamorphism and reprecipitated in veins and other low strain sites we suggest that such upgrading is the principal mechanism responsible for significant gold enrichment observed in many metamorphosed vhms deposits worldwide

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

the legacy of crystal plastic deformation in olivine high diffusivity pathways during serpentinization crystal plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow although crystal plastic deformation and serpentinization are spatio temporally decoupled we identified compositional readjustments expressed on the micrometric level as a striped fe enriched bar x text fe 0 24 0 02 zones 0 12 0 02 bulk or fe depleted bar x text fe 0 10 0 01 zones 0 13 0 01 bulk zoning in partly serpentinized olivine grains from two upper mantle sections in norway focused ion beam sample preparation combined with transmission electron microscopy tem and aberration corrected scanning tem enabling atomic level resolved electron energy loss spectroscopic line profiling reveals that every zone is immediately associated with a subgrain boundary we infer that the zonings are a result of the environmental fe2 mg 1 exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium this is facilitated by enhanced solid state diffusion along subgrain boundaries in a system which otherwise re equilibrates via dissolution reprecipitation fe enrichment or depletion is controlled by the silica activity imposed on the system by the local olivine orthopyroxene mass ratio temperature and the effect of magnetite stability the fe mg exchange coefficients k text d text atg text ol between both types of zoning and antigorite display coalescence toward exchange equilibrium with both types of zoning mn is enriched and ni depleted compared with the unaffected bulk composition nanometer sized heterogeneously distributed antigorite precipitates along olivine subgrain boundaries suggest that water was able to ingress along them crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries

zinc germanium ores of the tres marias mine chihuahua mexico the tres marias carbonate hosted zn ge deposit in chihuahua mexico contains sphalerite with the highest average ge 960 ppm and willemite with the highest reported ge contents of mississippi valley type mvt deposits worldwide this has prompted current exploration efforts to focus on the deposit as a high grade source of germanium the sulfide rich ore type 125 000 t at 20 zn and 250 g t ge contains fe rich botryoidal sphalerite type i associated with solid hydrocarbons this type exhibits distinctive intimately intergrown lamellar texture of high fe sphalerite average 9 9 wt fe and 800 ppm ge and a somewhat less fe rich sphalerite phase average 5 5 wt fe and 470 ppm ge reddish brown banded sphalerite type ii average 5 7 wt fe and 1 320 ppm ge is subordinately followed by galena and pyrite the sulfide poor oxidized zinc ore up to 50 wt zn 250 to 300 ppm ge is a fine grained often friable alteration product of the sulfide ore and associated limestone and breccia host while some areas are dominated by carbonates and sulfates others are enriched in silicates such as hemimorphite and willemite the gangue assemblage includes goethite hematite and amorphous silica or quartz minor wulfenite greenockite cinnabar and descloizite also occur willemite occurs as interstitial replacement of sphalerite and fracture fillings in the oxidized ore and can be unusually rich in pb up to 2 0 wt and ge up to 4 000 ppm oscillatory zonation reflects trace element incorporation into willemite from the oxidation of primary ge bearing sphalerite and galena by siliceous aqueous fluids the tres marias deposit has hybrid characteristics consisting of a primary low temperature mvt ge rich zn pb sulfide ore body overprinted by ge rich hemimorphite willemite and fe oxide mineralization

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

polymetamorphism and ductile deformation of staurolite cordierite schist of the bossost dome indication for variscan extension in the axial zone of the central pyrenees the bossost dome is an e w trending elongated structural and metamorphic dome developed in cambro ordovician metasedimentary rocks in the variscan axial zone of the central pyrenees a steep fault separates a northern half dome cored by massif granite from an e w trending doubly plunging antiform with granitic sills and dykes in the core to the south the main foliation is a flat lying s 1 2 schistosity that grades into a steeper dipping slaty cleavage at the dome margins three major deformational and two metamorphic phases can be differentiated s 1 2 schistosity is an axial planar cleavage to w vergent recumbent folding that probably occurred in mid westphalian time peak regional metamorphism m 1 is characterized by static growth of staurolite and garnet following thermal relaxation of the previously thickened crust strong non coaxial deformation recording uniform top to the se extension during d 2 a is preserved in staurolite garnet schists in a 1 5 km thick shallowly se dipping zone in the southeastern dome a 500 m thick contact aureole m 2 was imprinted on the regionally metamorphosed rocks following the intrusion the bossost granite during d 2 b more coaxial deformation prevailed during synkinematic growth of m 2 phases in the inner part of the contact aureole around the northern part of the dome where it obliterated d 2 a fabrics progressive non coaxial deformation continued in the southeastern antiform and is recorded by late synkinematic growth of cordierite successive overprinting of the m 1 staurolite garnet assemblage by andalusite and cordierite of m 2 is preserved in the southern part the assemblage muscovite cordierite staurolite biotite is considered metastable given the low mn and zn contents of staurolite and cordierite and interpreted as the result of prograde metamorphism during decompression p t conditions during m 2 were approximately 3 kbar and 600 c pervasive crenulations and mesoscopic to regional southerly verging folds are the result of d 3 nne ssw compression post dating ductile deformation and contact metamorphism polymetamorphic assemblages of the bossost dome preserve a regionally confined zone of ese directed extensional shearing within an overall n s compressional setting exact timing of extensional shearing is not known but can be constrained by recumbent folding during the mid westphalian and granitic intrusions which confine it to late carboniferous time c 305 ma crustal scale flat lying extensional shear zones with similar orientation and time frame are observed in the hospitalet massif of the eastern axial zone this suggests that crustal extension though probably restricted by regional strain partitioning over orthogneiss or intruding granitic bodies within an overall compressive setting was not uncommon in late carboniferous time in the axial zone of the pyrenees

timing of granite emplacement crustal flow and gneiss dome formation in the variscan segment of the pyrenees the variscan segment of the pyrenees is well suited to study the timing of crustal scale deformations as crustal flow and gneiss dome formation this has been constrained from a synthesis of available structural and geochronological data of intrusive rocks as well as new zircon u pb age determinations via laser ablation inductively coupled plasma mass spectrometry la icp ms after a stage of moderate thickening by fold thrust belt development in the upper crust between 323 and 308 ma the variscan segment of the pyrenees experienced crustal flow at c 306 ma and then gneiss dome formation at c 304 ma localization of the deformation along reverse dextral shear zones occurred at c 300 ma the variscan segment of the pyrenees recorded a high temperature regime which allowed crustal flow of the middle crust but with limited amounts of heat which induced rapid cooling the development of this enigmatic orogenic segment of the variscan belt is closely contemporaneous with the formation of the cantabrian orocline and could correspond to a lithospheric scale shear zone that accommodated buckling of the orocline late variscan lithospheric delamination and asthenospheric upwelling associated with buckling in the core of the cantabrian orocline could explain the short period high temperature regime in the variscan segment of the pyrenees

sediment hosted zn pb cu deposits in the central african copperbelt abstract stratabound epigenetic sulphide zn pb cu ore deposits of the central african copperbelt in the democratic republic of congo and zambia are mostly hosted in deformed shallow marine platform carbonates and associated sedimentary rocks of the neoproterozoic katanga supergroup economic orebodies that also contain variable amounts of minor cd co ge ag re as mo ga and v occur mainly as irregular pipe like bodies associated with collapse breccias and faults as well as lenticular bodies subparallel to bedding kipushi and kabwe in the democratic republic of the congo and zambia respectively are the major examples of carbonate hosted zn pb cu mined deposits with important by products of ge cd ag and v in the lufilian arc a major metallogenic province famous for its world class sediment hosted stratiform cu co deposits the carbonate hosted deposits range in age from neoproterozoic to early palaeozoic 680 to 450 ma the formation of the relatively older neoproterozoic deposits is probably related to early collision events during the lufilian orogeny whereas the younger palaeozoic deposits may be related to post collisional processes of ore formation fluid inclusion and stable isotope data indicate that hydrothermal metal bearing fluids evolved from formation brines during basin evolution and later tectonogenesis ore fluid migration occurred mainly along major thrust zones and other structural discontinuities such as karsts breccias and faults within the katangan cover rocks resulting in ore deposition within favourable structures and reactive carbonates of the katangan supergroup