regional variations in fluid formation and metal sources in mvt mineralization in the pennine orefield uk implications from rare earth element and yttrium distribution sr nd isotopes and fluid inclusion compositions of hydrothermal vein fluorites abstract the pennine orefield is one of the most important ore fields for pb zn ba f mineralization in great britain it is subdivided into the northern pennine orefield npo consisting of the alston and askrigg blocks and the southern pennine orefield spo the alston block is underlain by the early devonian weardale granite and the askrigg block by the coeval wensleydale granite the potential relationship between the batholiths and the mineralization is a matter of debate we here studied the rare earth elements and y rey geochemistry sr nd isotopes and fluid inclusion fi compositions of fluorites from the two structural blocks in the npo and found that the fluorite mineralization in these blocks differ substantially the rey in askrigg fluorites show features that are characteristic for leaching of adjacent lower carboniferous limestones in contrast alston fluorites have significantly higher rey concentrations lack reysn limestone signatures and show a decoupling of redox sensitive eu from its trivalent rey neighbours neodymium isotopes indicate a similar crustal source of rey in both blocks but higher rey concentrations and lower y ho ratios suggest lower carboniferous shales as potential rey source in the alston block the fluids that precipitated the alston fluorites experienced temperatures 250 c prior to mineral formation as evidenced by eu geothermometry fluorite formation however occurred at much lower temperatures as suggested by homogenization temperatures in fi that fall within ranges of 105 159 c in alston and 99 160 c in askrigg fluorites mineralization of the mississippi valley type usually lack association with igneous activity we show that some of the fluids responsible for the npo mineralization were influenced by magmatic sources the rey systematics in alston fluorites may be linked to an interaction of the permian age whin sill dolerite with the basement granite which heated fluids and focussed fluid flow into the overlying sedimentary rocks in the askrigg block where such a dolerite intrusion was not described fluorites lack any positive eusn anomalies indicating that these fluids had never been subjected to temperatures exceeding 200 250 c

influence of the antarctic circumpolar wave upon new zealand temperature and precipitation during autumn winter abstract autumn winter temperature and precipitation records at 34 stations over new zealand from 1982 to 1995 are found by empirical orthogonal function eof analysis to fluctuate together with 3 6 yr quasi periodicity similar to that associated with the antarctic circumpolar wave acw which propagates slowly eastward past new zealand in its global traverse around the southern ocean by allowing these eof time sequences to represent new zealand temperature and precipitation indices both the positive temperature index related to warm sea surface temperature sst anomalies around new zealand and the positive precipitation index related to warm cool sst anomalies north and east south and west of new zealand are found these warm cool sst anomalies are associated with poleward equatorward meridional surface wind msw anomalies the same as observed in association with the acw when warm cool sst and poleward equatorward msw anomalies are located north south of new zealand then anomalous

major trace and rare earth element ree geochemistry of different colored fluorites in the bobrynets region ukraine abstract the bobrynets fluorite mineralization in the exo contact zone of krivograd novoukrainian granite intrusion is found in the southern part of the kirovograd cherkassy fault zone between the novoukrainian anticlinoria and the ingulo ingulets synclinoria the fluorite mineralization appears as vein and disseminat as well as in the form of a cement in the tectonic breccia among the metasomatically altered granites fluorite mineralization is observed for 5 km along this fault zone down to a depth of 300 m with the thickness of the individual mineralized zones ranging from a few meters to 75 m with average fluorite contents ranging from 1 2 to 28 the estimated reserve of bobrynets fluorites is approximately 1 56 million tonnes fluid inclusion data in the studied fluorites indicate that the study area has two types of fluorites high temperature fluorites 240 280 c and low temperature fluorites 100 150 c the total rare earth element ree contents of the fluorites range from 62 4 ppm to 527 9 ppm with a mean of 218 ppm the mean ree concentrations of different colored massive fluorites range from 80 2 ppm for yellow fluorites to 258 ppm for green fluorites 97 4 ppm for violet fluorites and 526 5 ppm for granite samples the mean y concentrations of the studied fluorites are 86 2 ppm for violet fluorites 104 5 ppm for yellow fluorites 242 5 ppm for green fluorites and 39 9 ppm for granite samples the chondrite normalized ree patterns of the bobrynets fluorites exhibit trends similar to each other and show a decrease from light rees lree to heavy rees hrees all fluorites in the study area have positive ce anomalies between 1 06 and 1 16 with mean of 1 12 negative eu anomalies with a range of 0 35 to 0 58 mean 0 46 and positive y anomalies between 1 38 and 2 67 with mean of 2 12 the y ho values change from 48 3 to 92 2 with mean of 71 1 the tb ca and tb la ratios of the bobrynets fluorites are between 0 00000249 and 0 0000404 and between 0 098 and 0 30 respectively and these ratios also indicate a formation from fractionated ore bearing fluids at an early stage of mineralization mainly a hydrothermal and less pegmatitic stage the tb yb n la yb n ratios are low because these fluorites are not lree rich when compared to other fluorite deposits the la yb n eu eu n values also indicate low negative eu anomalies and low lree enrichments for the bobrynets fluorites the sc eu vs sr diagram and sc vs ree diagram show that the bobrynets fluorites have low sr contents and high sc eu values and that they cover the same areas as the rift deposits of new mexico and the skarn fluorite deposits of akdagmadeni the 208pb 204pb isotope values of fluorites vary between 53 5 and 62 6 and the 206pb 204pb isotope values of fluorites vary between 23 3 and 26 8 the 208pb 204pb vs 206pb 204pb ratios indicate that fluorites originated from upper crust materials all these findings indicate that ree contents of the bobrynets fluorites have different physicochemical parameters such as decrease in temperature or increases in o2 and ph high oxygen fugacity in the source of the hydrothermal fluids and low sr and high sc values similar to rift and skarn deposits

thermomechanical interactions between crustal magma chambers in complex tectonic environments insights from eastern turkey abstract crustal segments such as those in eastern turkey which host magma chambers volcanoes and fault zones experience complex stresses generated through interactions between regional tectonic loading magmatic pressure and geothermal dynamics here we model these competing loading mechanisms and examine their effects on generating stresses in a complex crustal segment which has been subjected to orogenesis and hosted voluminous magma discharge this simulated region hosts several volcanoes thermal fields and has experienced complex tectonic deformation which manifests as crustal faults we present a suite of purely thermal models to show the temperature distribution within the crust assuming an arrangement of crustal magma chambers and a realistic geothermal gradient we also present a suite of linear elastic mechanical models to investigate the effect of magma pressure and regional tectonic loading in the absence of temperature variations using different arrangements of magma chambers and faults finally we present coupled linear elastic thermomechanical models that highlight the influence of temperature on the distribution of both crustal stresses and deformation using the same complex geometries results show that thermal stresses generate two competing consequences 1 they increase the level of shear stress around the magma chambers potentially leading to fault nucleation or reactivation and 2 they partially act to suppress the level of tensile stress originally generated both by magma pressure and tectonic loading this implies that for any magmatic recharge event which increases the internal magma chamber pressure the contribution of temperature increase in the surrounding host rocks must also be taken into account when considering the distribution magnitude and type of stresses around magma chambers in such crustal environments

sm nd dating of fluorite from the worldclass montroc fluorite deposit southern massif central france a three point sm nd isotope isochron on fluorite from the very large montroc fluorite vein deposit southern massif central france defines an age of 111 13 ma initial end of 8 6 and initial 87sr 86sr of 0 71245 suggest an upper crustal source of the hydrothermal system in agreement with earlier work on fluid inclusions which indicated a basinal brine origin the mid cretaceous age of 111 ma suggests the albian aptian transition as the most likely period for large scale fluid circulation during a regional extensional tectonic event related to the opening of the north atlantic ocean

the origin of the calcites from pb zn veins in the harz mountains federal republic of germany abstract studies of the ree distribution in calcites from hydrothermal banded pb zn mineralizations as well as in calcites from pelitic and psammitic unmetamorphosed rocks and magmatites of the harz mountains revealed that the calcite of the banded ores crystallized from hybrid magmatic metamorphic solutions these were rather rich in ree3 fe3 and probably zn2 and pb2 ion concentrations the absence of any negative eu anomalies points to oxidizing conditions the sulphides have crystallized from a different solution it is suggested that the necessary hs rich solutions stem from near surface hydrothermal convection cells set up by nearby granitic intrusions the alternating deposition of calcite and sulphide banded ores may be explained by assuming that farther away from the intrusions the hs rich solutions were intermittedly admixed with the hybrid fluids this caused a decrease in temperature an interruption of calcite deposition and sulphide mineralization near the intrusion continuous mixing of these two fluids became more common and consequently banded ores are rather rare

tracing element sources of hydrothermal mineral deposits ree and y distribution and sr nd pb isotopes in fluorite from mvt deposits in the pennine orefield england fluorite from mississippi valley type mvt deposits in the south pennine orefield england displays significantly different distributions of rare earths and yttrium rey compared to fluorite from similar mvt deposits in the north pennine orefield samples from the south pennine orefield display negative ce and positive gd and y anomalies but lack any eu anomaly indicating that the rey were mobilized from relatively pure marine sedimentary carbonates in marked contrast fluorite from the north pennine orefield lacks any ce and gd anomalies but shows a pronounced positive eu anomaly suggesting that the rey were provided by different source rock s that the mineralizing hydrothermal fluid had experienced higher temperatures prior to fluorite precipitation and that it was derived from deeper crustal levels in the north compared to the south the isotopic composition of sr in blue john fluorite from the south pennine orefield suggests that sr was mobilized from lower carboniferous tournaisian limestones whereas pb isotopes suggest that in contrast to rey and sr pb was derived from aluminosilicate rocks neither nd nor sr or pb isotopes can be used to radiometrically date the formation of blue john fluorite all isotope systems studied indicate that the limestone host rock of this fluorite mineralization did not contribute to the trace element budget of the hydrothermal fluid our results show that different solutes in a natural water hydrothermal fluid groundwater etc may be derived from different sources and that the study of a small set of elements or isotope ratios may not provide full insight into the genesis or history of a mineralization or a hydrothermal fluid our data provide evidence for the uncoupling of sr nd and pb during fluid rock interaction and fluid migration and show that the use of plots such as 87sr 86sr vs end to learn about mixing relationships as is commonly done in igneous geochemistry is unreliable when applied to natural waters and their precipitates

effects of water sediment interaction and irrigation practices on iodine enrichment in shallow groundwater abstract high iodine concentrations in groundwater have caused serious health problems to the local residents in the datong basin northern china to determine the impact of water sediment interaction and irrigation practices on iodine mobilization in aquifers isotope 2 h 18 o and 87 sr 86 sr and hydrogeochemical studies were conducted the results show that groundwater iodine concentrations vary from 14 4 to 2180 g l and high iodine groundwater 150 g l mainly occurs in the central area of the datong basin sediment iodine content is between 87 sr 86 sr values and groundwater chemistry suggest that aluminosilicate hydrolysis is the dominant process controlling hydrochemical evolution along groundwater flowpath and the degradation of toc iodine rich sediment mediated by microbes potentially triggers the iodine release from the sediment into groundwater in the discharge area the vertical stratification of groundwater 18 o and 2 h isotope reflects the occurrence of a vertical mixing process driven by periodic surface irrigation the vertical mixing could change the redox potential of shallow groundwater from sub reducing to oxidizing condition thereby affecting the iodine mobilization in shallow groundwater it is postulated that the extra introduction of organic matter and o 2 no 3 so 4 could accelerate the microbial activity due to the supplement of high ranking electron acceptors and promote the iodine release from the sediment into shallow groundwater

ree systematics in hydrothermal fluorite abstract ree patterns of fluorite from 63 post variscan hydrothermal veins of the schwarzwald area germany can be divided into two major groups type a fluorite shows roof shaped paas normalized patterns with enriched mree the turning point of the curvature is at ho or er position all patterns of type a show a distinct positive eu anomaly type b fluorite shows roof shaped patterns with enriched mree and strongly depleted hree and a characteristic steep slope between nd and sm the turning point of the curvature is at gd to dy all patterns of type b show negative or no eu anomalies laser ablation icp ms traverses through single grains combined with cathodoluminescence imagery revealed either i identical ree patterns and total ree concentrations from core to rim ii identical ree patterns but concentration gradients or iii variable ree patterns and concentration gradients from core to rim these features are explained by different degrees of supersaturation or different fluid fluorite ratios during crystallization and by complexly controlled precipitation processes under closed system conditions petrographically late fluorites from several deposits show the characteristics of new fluid batches rather than the expected remobilization features lree enrichment close to the crystal faces in some grains may result from the copreciptiation of a submicrometer sized lree enriched phase or from lree clustering in late cool fluids by comparison with literature data on natural waters from gneissic and granitic aquifers and of leachates of granites and gneisses we show that the hydrothermal vein fluorite preserves the characteristic source related ree feature of the hydrothermal fluid that migrated through either gneissic type a or granitic type b host rocks the immediate host rocks of the veins however are not the source rocks of the ree which indicates large scale fluid convection in the basement gneiss related type a fluorite shows tb ca tb la trends of primary hydrothermal crystallization whereas granite related type b fluorite indicates remobilization of possibly pegmatitic or variscan fluorite

mesozoic fluorite veins in ne spain record regional base metal rich brine circulation through basin and basement during extensional events abstract basinal brines are commonly involved in the formation of hydrothermal base metal ore deposits in sedimentary basins although in many instances the source of metals is often thought to be the underlying basement rocks the evidence of brine infiltration through the basement is sometimes directly found in vein systems in fracture zones crosscutting the basement that is the case of the fluorite barite base metal veins found throughout the hercynian basement of europe north africa and the appalachians a geochemical study of brines trapped in these veins can reveal their origin and evolution but also their mineralizing potential and coupled with the timing of fluid circulation can give clues to elucidate the role of these or similar brines in the genesis of base metal mineralizations together with their possible links to tectonic events the sm nd dating of fluorite samples from one of these veins in ne spain the rigros fluorite vein has yielded an age of 137 25 ma 2 mswd 0 40 the vein formation took place during the late jurassic early cretaceous rifting event in the western european basins which is related to the opening of the atlantic inclusion fluids in samples from rigros and another vein system from the same region the berta fluorite vein have been studied with microthermometry crush leach and la icp ms the brines trapped in the two studied vein systems are na ca cl k mg brines with homogenization temperatures 120 c and salinities up to 25 equiv mass nacl the source of this salinity is related to evaporated seawater at least in the halite precipitation field and to the leaching of mesozoic halite and gypsum sequences by seawater and or meteoric water the basinal brines later evolved through water rock interaction with the crystalline basement resulting in some sodium loss and potassium calcium strontium the latter inferred from isotope data and barium enrichment the analyzed brines have concentrations of zn between 3 and 790 ppm of pb between 3 and 995 ppm and of fe between 27 and 2639 ppm which are similar to those reported in comparable hydrothermal veins and mississippi valley type deposits but higher than in most present day sedimentary brines despite the fact they were able to transport large amounts of metals no significant precipitation of sulfides occurred in the veins and consequently the mineralizing potential of these brines was still preserved after fluorite vein formation

direct dating of mississippi valley type mineralization use of sm nd in fluorite suggested that the technique may be applicable to mississippi valley type deposits in the present study an sm nd age and ree contents in fluorite from the illinois kentucky fluorite district are used to constrain the timing and genesis of mississippi valley type ore deposition

succession of permian and mesozoic metasomatic events in the eastern pyrenees with emphasis on the trimouns talc chlorite deposit recent studies proposing pre orogenic mantle exhumation models have helped renew the interest of the geosciences community in the pyrenees which should be now interpreted as a hyper extended passive margin before the convergence between iberia and eurasia occurred unresolved questions of the pyrenean geology as well as the understanding of the formation of hyper extended passive margins are how the crust was thinned and when where and how the crustal breakoff occurred the study of the variscan and pre variscan pyrenean basement is thus critical to document and understand this cretaceous crustal thinning in order to specify the timing of mesozoic metasomatism and the associated deformation in the pre mesozoic basement of the pyrenees we carried out a u th pb laser ablation icp ms study on a large panel of ree and titanium rich minerals titanite and rutile from talc chlorite ores from the eastern pyrenees with a special emphasis on the trimouns deposit the world s largest talc quarry our results suggest that the trimouns talc formation was restricted to the upper aptian cenomanian time while the talc and chlorite formation in the eastern pyrenees occurred during several distinct permian jurassic and cretaceous episodes these results give strong constraints on the tectonic setting of the pyrenean domain during the transition between the variscan and alpine orogenic cycles and particularly on when and how the upper crust was thinned before the crustal breakoff and the final mantle exhumation

geochemistry and geochronology of the banxi sb deposit implications for fluid origin and the evolution of sb mineralization in central western hunan south china abstract central western hunan in south china hosts the largest antimony belt in the world with two types of sb deposits identified sb au woxi type and sb only xikuangshan type banxi is the most representative deposit in the region with vein type sb mineralization hosted in neoproterozoic clastic rocks stibnite developing in ores and arsenopyrite mainly occurring in altered country rocks trace element contents including rare earth elements ree and isotopic ratios s pb sr nd he and ar in stibnite and or arsenopyrite were analyzed to determine the timing of ore formation and to elucidate fluid origin and evolution processes most sulfides have high ree contents 45 103 ppm moderate fractionation between lree and hree lree hree 6 38 11 56 and slightly negative eu anomalies eu eu 0 53 0 72 the 34 s values are 3 88 5 81 for stibnite and 9 25 11 82 for arsenopyrite the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios range from 18 617 to 18 635 15 695 to 15 739 and 38 965 to 38 981 for stibnite and from 18 594 to 18 609 from 15 587 to 15 698 and from 38 893 to 38 926 for arsenopyrite the 87 rb 86 sr and 87 sr 86 sr ratios are 0 3016 3 538 and 0 711463 0 717591 respectively for stibnite and 0 2251 2 214 and 0 711244 0 711565 respectively for arsenopyrite the 147 sm 144 nd and 143 nd 144 nd ratios are 0 1174 0 9816 and 0 511942 0 512768 for stibnite with end t values t 130 ma ranging from 12 4 to 6 6 and two stage model ages t 2dm ranging from 1457 to 1932 ma the 40 ar 36 ar and r ra ratios where ra is the atmospheric 3 he 4 he ratio of 1 4 10 6 are 409 545 and 0 0088 0 0348 respectively for stibnite the rb sr and sm nd isotopic analyses of the sulfides yield isochron ages of 129 4 2 4 ma 2 mswd 1 3 and 130 4 1 9 ma 2 mswd 1 6 respectively the combined trace element and isotopic data set indicates that the ore forming fluids were a mixture of dominantly deep basement derived solute rich parent water and a small amount of dilute heated meteoric water the decreases in ree 34 s 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb 87 rb 86 sr 87 sr 86 sr 147 sm 144 nd and 143 nd 144 nd and increases in 40 ar 36 ar and 4 he contents in the stibnite from the earlier quartz stibnite mineralization stage stage ii through to the later stibnite mineralization stage stage iii indicate that the influx of meteoric water increased during sb mineralization the deep sourced relatively high temperature rock reacted fluid mixed with increasing amounts of more oxidized low temperature meteoric fluids causing the precipitation of arsenopyrite and stibnite sequentially at the banxi deposit a two period genetic model has been proposed for the world class sb mineralization in the central western hunan region the woxi type sb au deposits were derived from orogenic fluids generated from folding and shearing during the caledonian and indosinian orogeny whereas the xikuangshan type sb deposits were formed by mixing heated basement derived hydrothermal fluid circulating during the flare up of magmatism in south china with lower temperature meteoric water

origin and age of rift related fluorite and manganese deposits from the san rafael massif argentina abstract the san rafael massif is characterized by widespread fluorite and manganese epithermal ore deposits whose origin has been under debate to the present isotopic sm nd and k ar and geochemical trace elements and ree data of fluorite and manganese ore allowed to establish the age and genesis of the deposits and to propose a regional genetic model the fluorite deposits were formed during the upper triassic lower jurassic as a result of the triassic rifting that launched a hydrothermal activity at regional scale the hydrothermal fluids had low t and high fo2 with fluorine probably derived from a mantle source and ree scavenged from the volcanics of the gondwanan choiyoi magmatic cycle upper section the manganese deposits were formed by oxidizing hydrothermal fluids that collected mn from deep sources and also leached ree from the upper section of the choiyoi magmatic cycle during two mineralization episodes one episode was linked to the rift tectonic setting that remained active up to the upper cretaceous and the other was related to an early miocene back arc extensional geodynamic setting both manganese and fluorite deposits were formed in extensional tectonic settings within an epithermal environment near the surface and can be ascribed to the general model of detachment related deposits

inclusions of sedimentary brines in post variscan mineralizations in the federal republic of germany a study by neutron activation analysis abstract the post variscan vein mineralizations in the federal republic of germany are characterized by highly saline fluid inclusions t e t mice 26 to 20 c t h 1 ca 22 000 60 000 mg kg 1 cl 85 000 200 000 mg kg 1 and br 550 2 600 mg kg 1 composition and salinity of the inclusion solutions are similar to brines in deep sedimentary basins it is assumed that formation waters of the na ca cl type migrated out of permo triassic sediment troughs into culmination zones of the variscan orogen where they were heated and caused mineralizations through cooling and mixing with sulfate bicarbonate waters when reascending

300 million years of episodic hydrothermal activity stable isotope evidence from hydrothermal rocks of the eastern iberian central system the eastern iberian central system has abundant ore showings hosted by a wide variety of hydrothermal rocks they include sn w fe and zn w calcic and magnesian skarns shear zone and episyenite hosted cu zn sn w orebodies cu w sn greisens and w sn base metal and fluorite barite veins systematic dating and fluid inclusion studies show that they can be grouped into several hydrothermal episodes related with the waning variscan orogeny the first event was at about 295 ma followed by younger pulses associated with early alpine rifting and extension and dated near 277 150 and 100 to 20 ma respectively events ii iv the 18o d and 34s studies of hydrothermal rocks have elucidated the hydrological evolution of these systems the event i fluids are of mixed origin they are metamorphic fluids h2o co2 ch4 nacl 18o 4 7 to 9 3 d ab 34 related to w sn veins and modified meteoric waters in the deep magnesian sn w skarns h2o nacl 4 5 6 4 wt nacl eq 18o 7 3 7 8 d 77 to 74 and epizonal shallow calcic zn w and fe skarns h2o nacl 14 wt nacl eq from evaporites hosted in the post variscan sequence the d values are very similar to most of those recorded by kelly and rye in panasqueira and confirm that the upper paleozoic meteoric waters in central iberia had very negative d values 52 whereas those of early mesozoic age ranged between 65 and 36

strontium and sulphur isotope geochemistry of low temperature barite fluorite veins of the catalonian coastal ranges ne spain a fluid mixing model and age constraints sulphur and strontium isotope analyses from the low temperature barite fluorite veins of the catalonian coastal ranges ne spain reveal the nature and source of the ore forming fluids and constrain the ages of the mineralizations sulphur isotope values in the barite 34s 15 to 20 are similar to those of sulphates in nearly triassic jurassic evaporites 34s 11 to 19 87sr86sr isotopic composition ratios of barites and fluorites are 0 7094 0 7167 the variation of 87sr86sr within individual veins suggests that the sr had two different sources granites rocks in the hercynian basement and seawater or evaporites of triassic early jurassic age vein formation is modelled as a two component mixing process in which the s and sr isotopic composition of the end members change with time the observed difference in mean s and sr isotopic compositions among the veins is interpreted to reflect differences in mineralization age ore deposition occurred between 225 and 195 ma triassic to early jurassic in all cases except the berta mine which may be as young as miocene

the age and origin of the barite fluorite pbzn veins of the sierra del guadarrama spanish central system spain a radiogenic nd sr and stable isotope study fluorite and barite rich veins sulphides of the sierra del guadarrama spanish central system are usually hosted by hercynian granitoids zoned fluorites from one of these veins have a sm nd age of 145 18 ma this age is similar to the k ar ages obtained in other hydrothermal rocks of the spanish central system 156 152 ma and confirms the existence of an important hydrothermal event during the late jurassic probably related to extensional fracturing accompanying the opening of the north atlantic ocean the 87sr 86sr ratio found in fluorite and barite 0 7154 0 7207 is in most cases lower than that found in the host granitoids 0 7194 and 0 7209 suggesting more than one source of strontium this in turn supports previous models that involve mixing of two fluids during mineralization an ascending hot 300 c and low salinity fluid and a shallow cooler 100 c and more saline brine the ascending fluid probably reacted to a variable extent with the host granitoids and the most likely source for the shallow fluid derived from a marine evaporitic environment with a low 87sr 86sr ratio 0 7069 in the late jurassic the calculated end composition of the fluorites 8 8 to 7 6 as well as the 147sm 144nd variation found in this mineral 0 153 0 405 do not conflict with the mixing model although they can be largely explained by interaction of the ascending fluid with the host granitoids sulphur isotopic compositions of sulphides range between 3 4 and 0 8 and those of barites from 15 5 to 15 8 the near 34s value of the sulphides suggests that their sulphur was derived from the hydrothermal leaching of the granitoids by the ascending fluid the 34s value of barite is consistent with upper jurassic marine sulphate as the source of sulphate in the shallow fluid the absence of equilibrium between reduced and oxidized sulphur species can be easily interpreted as a consequence of the short residence time of the mixed fluid in the open fractures at temperatures between 250 and loo c although no pre cretaceous sediments are found on this part of the iberian hercynian basement the data presented here support the existence of a shallow platform joining central spain with the iberian or the subbetic realm in late jurassic times

geochronological isotopic and mineral geochemical constraints on the genesis of the diyanqinamu mo deposit inner mongolia china abstract the diyanqinamu mo deposit located in central inner mongolia in china is a newly discovered mo deposit due to the lack of detailed deposit scale studies the metallogenesis of the deposit has been a matter of debate in this study petrography zircon u pb geochronology sr nd and pb isotopes and apatite mineral geochemistry have been used to constrain the genesis of the diyanqinamu mo deposit petrographic evidence indicates that the granites in the diyanqinamu deposit have experienced fluid exsolution as demonstrated by the corroded quartz in the porphyritic granites skeletal quartz in the aplitic granites and the unidirectional solidification texture ust in the apex of the aplitic granites sr and nd isotopic data of the purple fluorite from the fluorite molybdenite veins showing the 87sr 86sr i 0 7046 0 7052 avg 0 7048 and end t values 2 4 3 8 avg 3 3 are similar to those of the porphyritic and aplitic granites this similarity implies that the mo ore forming fluids may have been derived from the granitic magmas the hypothesis is further supported by the fluorine content 3 79 5 48 wt avg 4 53 wt in apatite from the porphyritic granites and the widely distributed fluorite in the hydrothermal alteration mineral assemblages which indicate that the porphyritic granites contain high f content and the hydrothermal fluids are also f rich petrographic observation also shows that magnetite occurs commonly in the hydrothermal mineral assemblages indicating that the hydrothermal fluids are characterized by high oxygen fugacity fo2 it is important to note that the intruding granites are essentially barren and the mo is mainly hosted in the andesite and volcaniclastic rocks in comparison pb isotopic compositions of molybdenite are similar to those of both the andesite and k feldspar from the porphyritic granites which suggests that both the intruding granites and ore hosting andesite have contributed to the ore forming materials this hypothesis is further supported by the abnormally high mo for the andesite our new evidence suggests that the diyanqinamu mo deposit may have formed in a post collisional extensional environment ore forming materials may have been derived mainly from the granites and minimally from the host rocks the ore fluids are characterized by high fo2 and being f rich and the trigger for the mo mineralization has been attributed to the reduction of fo2 and or temperature for the ore fluids

variability in fluid sources in the fluorite deposits from asturias n spain further evidences from ree radiogenic sr sm nd and stable s c o isotope data fluorite deposits in asturias iberian peninsula n spain are hosted in permo triassic and paleozoic rocks the three main districts of berbes la collada and villabona preferentially occur along the margins of a mesozoic basin and comprise veins and stratabound mineralization composed of fluorite barite calcite dolomite quartz and sulphides although the geological framework is similar and fluorite dominates in all deposits variability in sources and processes has led to each area having its own distinctive characteristics sr isotope data of fluorite calcite and barite 87sr 86sr 0 7080 to 0 7105 are compatible with a mixing between seawater and an evolved groundwater that interacted with basement rocks sm nd ratios in fluorites from villabona district provide an isochron age of 185 28 ma late triassic late jurassic consistent with other hydrothermal events in the iberian peninsula and europe the total ree content of fluorite increases from berbes to villabona by an order of magnitude 0 4 to 9 3 the la lu ratio in fluorites decreases from a mean value of 0 36 in berbes 0 17 in la collada to 0 09 in villabona indicating a strong fractionation between lree and hree calculated 18o of fluids ranges from 0 3 to 7 4 during barite precipitation from 0 8 to 4 during quartz formation and around 3 during carbonate deposition the 34s of barite 17 to 56 is explained by sulphate reduction processes either thermochemically or bacterially mediated in a system closed with respect to sulphate the 34s of sulphide 0 6 to 32 is compatible with these processes although bacterial processes must have dominated at villabona organic matter was an important source of c in the fluids especially in villabona 13c 14 8 to 2 5 in calcites and from 7 9 to 2 2 in dolomites differences in host rock and position within the basin and the lithology of the basement seem to have exerted a strong control on the chemistry of mineralizing fluids providing each district with distinctive characteristics