heavy metal adsorption by ferromanganese coatings on stream alluvium natural controls and implications for exploration abstract the adsorption of cu and zn by natural ferromanganese coatings on stream pebbles collected from varied geologic environments was studied utilizing aqueous solutions of cu and zn special emphasis was given to determining the effect on adsorption of several natural variables including metal concentration ph and ionic strength conditions covered the range known to occur in streams the potential of stream turbulence coating age and periodic drying of coatings to alter adsorption characteristics was also investigated composition of the coatings studied varied considerably but their adsorption characteristics were remarkably similar adsorption increased with metal concentration but was not significantly affected by solution aeration simulating increased stream turbulence increased ionic strength air drying for one year or coating age these results suggest that coatings represent a uniform sampling medium perhaps subject to less variation in metal adsorption behavior than fine grained stream alluvium

mesozoic cenozoic tectonic evolution and metallogeny in myanmar evidence from zircon cassiterite u pb and molybdenite re os geochronology abstract it is well known that there are many sn w mo and cu au metal resources in myanmar however the absence of precise mineralization ages for these deposits significantly hinders to understand the close genetic relationship among metallogeny ore bearing intrusions and tectonic evolution in this study two groups of consistent molybdenite re os and zircon u pb ages indicate that the dapingba mo w deposit in northern myanmar tengchong terrane formed at early cretaceous 119 ma and 114 ma the dapingba ore bearing granitic magmas were mainly derived from melting of ancient tengchong crust on the basis of zircon hf isotopic compositions ehf t 9 3 to 2 5 moreover the first reported cassiterite u pb ages of 60 ma for the bawapin and kalonta sn w deposits in southern myanmar western sibumasu terrane suggest that the two deposits formed at paleocene whereas the precise molybdenite re os age for the shangalon porphyry cu au deposit in the west burma terrane indicates that this deposit formed at eocene 39 ma importantly combined with previous studies on tectonic evolution and magmatic petrogenesis in myanmar and southwest china a comprehensive mesozoic cenozoic tectono magmatic and metallogenic model are proposed two periods of early cretaceous 120 114 ma and late cretaceous 75 70 ma crust derived felsic melts and related mo sn w deposits from the tengchong and western sibumasu terranes likely formed in a continental arc during subduction of the meso and neo tethys oceanic lithosphere respectively subsequently paleocene eocene 60 50 ma sn w deposits and coeval ore bearing granites in the western sibumasu terrane possibly formed during roll back of the neo tethys oceanic slab after 50 ma india asia collision eocene 41 39 ma porphyry cu au west burma terrane and sn w deposits western sibumasu terrane likely formed during the neo tethys oceanic slab tear and break off in a collisional setting whereas miocene 19 14 ma high sulfidation epithermal cu deposit in the west burma terrane possibly formed in an arc setting during oblique subduction of the indian oceanic lithosphere

absolute timing of sulfide and gold mineralization a comparison of re os molybdenite and ar ar mica methods from the tintina gold belt alaska new re os molybdenite dates from two lode gold deposits of the tintina gold belt alaska provide direct timing constraints for sulfide and gold mineralization at fort knox the re os molybdenite date is identical to the u pb zircon age for the host intrusion supporting an intrusive related origin for the deposit however 40ar 39ar dates from hydrothermal and igneous mica are considerably younger at the pogo deposit re os molybdenite dates are also much older than 40ar 39ar dates from hydrothermal mica but dissimilar to the age of local granites these age relationships indicate that the re os molybdenite method records the timing of sulfide and gold mineralization whereas much younger 40ar 39ar dates are affected by post ore thermal events slow cooling and or systemic analytical effects the results of this study complement a growing body of evidence to indicate that the re os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems

vertical distribution of trace elements in laterite soil suriname abstract the vertical distribution of 20 elements in a 12 5 m thick laterite profile from suriname south america has been investigated using neutron activation analysis atomic absorption spectrometry and x ray fluorescence the mineralogical composition was quantitatively determined from calculations based on results from x ray diffraction thermal gravimetric methods and from the data obtained for major elements using x ray fluorescence the most characteristic change observed in the mineralogy with depth is the increase in kaolinite relative to gibbsite a considerable fractionation with depth is found for different trace elements the enrichment of the lanthanoids la and ce at 3 4 m below surface and of sm and eu at 10 12 5 m depth demonstrates that the distribution of elements despite the similarity in chemical properties is seriously affected by weathering processes the laterite soil samples were also separated in al and fe rich fractions using naoh these separation experiments demonstrated that the trace elements are mainly associated with the fe rich red mud fraction of the laterite soil

in situ u pb sr nd and hf isotopic analysis of eudialyte by la mc icp ms abstract eudialytes are a group of complex na ca zirconosilicate minerals that generally occur in peralkaline agpaitic syenites given that eudialytes are easily altered and commonly contain inclusions of earlier crystallized minerals in situ laser ablation is considered as the most suitable method to determine their u pb ages and sr nd and hf isotopic compositions electron microprobe and la icp ms analysis of eudialytes from nepheline syenites from ilimaussaq greenland khibiny and lovozero russia saima china tamazeght morocco kipawa and mont saint hilaire canada pocos de caldas brazil and langesund fjord norway indicate that this mineral typically has high contents of u pb nb ta zr hf and rare earth elements ree analysis of an in house standard eudialyte by both solution and laser ablation methods demonstrates that precise and accurate u pb ages can be obtained from eudialyte after correction for the common pb content the high sr nd and hf contents in eudialyte coupled with the generally low rb sr and lu hf ratios also permit the precise determination of in situ sr nd and hf isotopic ratios by la mc icp ms methods however some eudialytes with rb sr ratio of 0 02 and yb sr 0 1 and lu hf 0 08 or yb hf 0 4 0 5 cannot be used for in situ sr and hf isotopic measurement eudialyte is the only mineral investigated to date for which it is possible to determine simultaneously u pb ages and sr nd and hf isotopic compositions

petrogenesis of the lijiagou spodumene pegmatites in songpan garze fold belt west sichuan china evidence from geochemistry zircon cassiterite and coltan u pb geochronology and hf isotopic compositions abstract spodumene and other pegmatites in the lijiagou area are located in the central songpan garze fold belt sgfb west sichuan these pegmatites are hosted within the giant songpan garze polymetallic belt a lack of precise geochronological constraints on the magmatic crystallization of the pegmatite suite and nearby plutonic granitoids has precluded definitive statements on genetic links between spodumene ore formation and the magmatic suite systematic zircon cassiterite and coltan u pb dating hf isotope and whole rock geochemical analysis were undertaken two mica granite and muscovite albite granite have s type granite affinities and chemical compositions suggesting a post orogenic setting and the albite spodumene pegmatites belong to the lct li cs ta group of pegmatites zircon la mc icp ms u pb dating of the two mica granite muscovite albite granite albite pegmatite and albite spodumene pegmatite give crystallization ages of 219 2 2 3 ma mswd 0 55 217 2 8 ma mswd 0 47 202 8 4 9 ma mswd 3 9 and 200 1 4 6 ma mswd 3 1 respectively zircons from the same units yield ehf t values of 39 17 to 6 81 22 73 to 2 83 11 17 to 8 14 and 4 92 to 2 4 respectively consistent with mixed crustal sources for the pegmatite and granite magmas cassiterite from albite spodumene pegmatite yields a concordia intercept age of 211 4 3 3 ma mswd 2 9 while coltan yields a weighted mean age of 211 1 1 0 ma mswd 0 97 the u pb zircon ages of the two mica granite and muscovite albite granite are interpreted as ages of magmatic crystallization metamictization of zircon in both albite and albite spodumene pegmatites makes their u pb zircon ages liable to inaccuracy due to pb loss the coltan u pb age is regarded as an accurate measure of the magmatic crystallization age of the albite spodumene pegmatite given the differences in magmatic ages and ehf t ranges between albite spodumene pegmatite and both the two mica granite and the muscovite albite granite the albite spodumene pegmatites probably represent anatectic melts and not fractionation products of either of the granitic magmas u pb coltan and u pb cassiterite dating are more likely to provide accurate crystallization ages of albite spodumene pegmatites than u pb zircon ages

the mineralogical distribution of pathfinder elements in gossans derived from dolomitic shale hosted pb zn deposits northwest queensland australia abstract the gossans formed on pb zn mineralization in northwest queensland contain potential pathfinder and indicator elements such as ag ba cl cu pb sr and zn in variable amounts studies of the secondary minerals in these gossans reveal that mineralogy strongly influences elemental abundances in the whole rock an understanding of the distribution of the pathfinder elements within the secondary minerals should therefore aid assessment of the economic potential of a gossan for example because of the ready incorporation of pb and the more mobile cu and zn in alunite jarosite minerals the absence of pb in these minerals can be considered to reflect barren fe sulfides at depth pb and ba form simple sulfates which incorporate minor amounts of zn and cu significant zn and ag may occur in cerussite but other elements are incorporated only in minor amounts secondary carbonates indicate more alkaline conditions at the time of formation than do secondary sulfates cl occurs in trace amounts in many secondary minerals but only forms simple chlorides with ag and na late in the development of a gossan hemimorphite forms under alkaline conditions and does not preferentially incorporate other base metals of the secondary non oxide minerals only the alunite jarosite minerals are both good hosts to pathfinder elements and relatively abundant in outcrop thus although the fe oxides are quantitatively the most important hosts to pathfinder elements a significant proportion of such elements may be stabilized by alunite jarosite minerals

silurian s type granite related w mo mineralization in the nanling range south china a case study of the pingtan w mo deposit abstract the pingtan deposit in southwestern hunan province is a newly discovered large sized w mo deposit this deposit is situated in the northwestern part of the miao ershan granite batholith western nanling range the tungsten mineralization is mainly hosted in biotite monzogranite and the alteration related to mineralization is controlled by a ne trending fault zone in this paper we present new molybdenite re os and zircon u pb ages zircon lu hf isotope and ree geochemical data aiming to constrain the w mo mineralization age and ore hosting granite petrogenesis in the pingtan w mo deposit molybdenite re os dating of eight ore samples yielded a weighted average model age of 427 0 5 4 ma mswd 0 24 the la icp ms zircon u pb analysis of two biotite monzogranite yielded 206pb 238u ages of 430 8 2 4 ma and 431 0 1 8 ma respectively suggesting that the w mo mineralization is spatial temporally associated with the biotite monzogranite the ore related granites have high contents of sio2 and k2o belong to weakly to strongly peraluminous a cnk 1 00 1 30 and geochemically classified as s type affinity molybdenite re contents 2 262 7 297 g g zircon ehf t 10 34 5 87 and 176hf 177hf 0 282241 0 282376 values of the biotite monzogranite suggest that the ore forming materials are predominantly derived from the crust this is the first identification of tungsten mineralization related to silurian s type granites caledonian granites in the miao ershan granite intrusion indicating caledonian is an important mineralization period of w in the western part of nanling range south china

tourmaline in a sub cambrian palaeosol on the proterozoic lewisian rocks of nw scotland tourmaline not hitherto recorded in lewisian rocks of sutherland nor reported as a secondary mineral in precambrian palaeosols occurs in a late proterozoic sub cambrian palaeosol in nw scotland from field and petrological criteria the tourmaline is secondary and peculiarly associated with the alteration profile hence it formed either during weathering or later in the profile s history a minor constituent of the palaeoregolith immediately below the unconformity the tourmaline mostly occurs as sub millimetre radiating acicular aggregates and is schorl in composition black tourmaline quartz veinlets cross cut the profile stable isotope and fluid inclusion data suggest that the tourmaline formed from surface derived fluids at c 110oc it is concluded that boron was adsorbed onto precursor illitic clays of the soil profile during the cambrian marine transgression thus the tourmaline formed subsequently after burial under the sedimentary pile probably during the caledonian orogeny when temperatures were high enough to allow its formation at suitable sites of nucleation e g adjacent to biotite its peculiarity as a palaeosol phase is due to the combination of a marine transgression over an exposed permeable illitic soil and underlying regolith followed by increase in temperature suffcient to allow the tourmaline to form

conflicting sm nd whole rock and u pb zircon ages for archean lavas from newton township abitibi belt ontario abstract archean komatiitic and tholeiitic lavas from newton township ontario have a sufficient range of sm nd ratios to define a well constrained line on the normal 143 nd 144 nd vs 147 sm 144 nd isochron plot the data give an isochron age of 2826 64ma and an initial e nd of 2 65 0 26 however u pb analysis of zircons from a dacitic volcaniclastic that underlies the komatiite tholeiite suite give an age of 2697 1 1ma there is strong evident that the zircon age is the eruption age suggesting that the older sm nd age is incorrect and probably results from mixing between isotopically distinct mantle sources at the time of eruption the sources had e nd values from about 4 2 to 1 6 indicating that the archean mantle in this area was markedly heterogeneous and not uniformly depleted

in situ la mc icp ms and id tims u pb geochronology of cassiterite in the giant furong tin deposit hunan province south china new constraints on the timing of tin polymetallic mineralization abstract the furong deposit located in southern hunan province china is a newly discovered giant tin deposit spatially associated with the a type qitianling granite the petrogenetic link between the giant furong tin deposit and the qitianling granite batholith remains controversial because of the lack of precise dating for the tin polymetallic mineralization here we report for the first time in situ u pb data on cassiterite obtained by la mc icp ms and the results are compared to id tims data the in situ la mc icp ms analyses of the cassiterites provide a reliable age constraint for tin polymetallic mineralization in the furong deposit yielding an isochron age of 159 9 1 9 ma at 95 confidence level mswd 18 which is indistinguishable from the id tims 206 pb 238 u weighted mean age of 158 2 0 4 ma the in situ u pb ages corroborate the ar ar dates published for the furong tin deposit which indicate that the mineralization is coeval with the emplacement of the qitianling granite batholith these results provide further evidence of a close temporal link between the pluton s emplacement and tin mineralization in the furong area the data obtained clearly demonstrate that in situ la mc icp ms u pb dating of cassiterite is a robust geochronometer for direct dating of tin polymetallic mineralization

mineralogical evidence for magmatic and hydrothermal processes in the qitianling oxidized tin bearing granite hunan south china emp and mc la icpms investigations of three types of titanite abstract the qitianling granite which is located in hunan province southern china is a metaluminous sn granite that crystallized at relatively oxidized conditions between the ni nio nno and fe 2 o 3 fe 3 o 4 mh buffers titanite sphene catisio 5 is a common tin carrier mineral in the qitianling granite based on electron microprobe emp and multi collector mc laser ablation la icpms investigations we describe three types of titanite with various textures and sno 2 contents which probably formed during the magmatic and hydrothermal processes responsible for the granite crystallization and later evolution the form of type i titanite ranges from subhedral to euhedral coarse grained crystals and typically exhibits an envelope like shape and sector zoning it is characterized by a high fe 2 o 3 content on average 2 44 wt and low sno 2 0 43 wt which indicates crystallization during an early magmatic stage its formation temperature is estimated to have been 721 to 780 c from emp and la icpms using the zr in titanite geothermometer type ii titanite occurs as both discrete grains and symplectitic intergrowths and typically fills interstices between other minerals it contains up to 26 wt sno 2 which suggests a late magmatic origin chondrite normalized ree patterns for type ii titanite reveal a lanthanide tetrad effect that was linked to differentiation of the granite magma type iii titanite is restricted to cleavage cracks in chlorite and is rich in al 2 o 3 it is obviously the secondary product of biotite alteration at a temperature that is estimated to be lower than 400 c during the hydrothermal stage this hydrothermal activity also impacted the primary titanites type i titanite experienced alteration to different degrees via coupled dissolution reprecipitation which gave rise to the formation of secondary minerals including cassiterite micro grains some grains of the type ii titanite reacted with fluids along the grain boundary which led to the gradual leaching of sn based on information from these types of titanite and their sn behavior we discuss the progressive enrichment of sn during and after granite crystallization under a high oxidation state as well as the predominant role of fluids in the leaching concentration and transportation of sn during hydrothermal processes which favors vein type sn mineralization

zircon u pb and hf o isotopes trace the architecture of polymetallic deposits a case study of the jurassic ore forming porphyries in the qin hang metallogenic belt china abstract the qin hang intra continental porphyry skarn cu polymetallic belt qhmb is among the economically important metallogenic belts in south china the significant differences in the size and metal assemblage of the jurassic magmatic hydrothermal ore deposits in this belt remain as an enigma here we employ zircon u pb and hf o isotopes of the tongshanling and baoshan cu pb zn deposits in the central part of the qhmb to investigate the contrasting metallogenic architecture our sims zircon u pb data indicate that the tongshanling and baoshan granodiorite formed at 160 ma these rocks show high mg values and negative zircon e hf t and high 18 o values suggesting that the magmas of the granodiorite porphyries were mainly generated through the anatexis of older crustal components triggered by the input of mantle derived magma the minor content of amphibole phenocrysts low sr y ratios negative eu anomaly and low zircon ce 4 ce 3 ratios indicate that the porphyries are relatively less oxidized with less water content compared with the ore bearing porphyries in the dexing and yuanzhuding porphyry cu deposits in the northern and southern part of the qhmb suggesting that high magmatic water content and oxidation state are important prerequisites for the formation of large size porphyry skarn copper deposits in the qhmb the positive correlation between zircon e hf t values with the cu reserves as well as zircon 18 o values with the cu cu pb zn ratios of the deposits indicate that the magmatic sources exerted a first order control on the volume and metal assemblage of deposits in the qhmb the hf and nd isotope contour maps indicate that the central part of the qhmb has high potential for pb zn dominated magmatic hydrothermal deposits whereas the northern and southern part of the qhmb are prospective for large cu deposits our results have important implications in formulating regional exploration strategies for jurassic porphyry skarn cu pb zn deposits in the qin hang belt

elemental partitioning into mn and fe oxides derived from dolomitic shale hosted pbzn deposits northwest queensland australia abstract exploration for dolomitic shale hosted base metal mineralization in northwest queensland is largely dependent upon geochemical evaluation of ironstones fe oxides because of their abundance in the weathered zone often quantitatively account for most of the base metal content of an ironstone mn oxides are less well developed but provide particularly good hosts for ba zn and pb and hence assume importance where present the mn fe coatings found in stream coatings vigorously scavenge and concentrate solution transported base metals and hence have to be very carefully evaluated when used during exploration however the present survey of base metal contents in gossans and ironstones in northwest queensland has shown that the ba cu p pb ni s and zn contents of the mn and fe oxides can be used to accurately indicate their parent material only ce and co are possibly preferentially incorporated into mn oxides but neither element is a pathfinder for pb zn mineralization development of the mn oxides chalcophanite todorokite lithiophorite and the cryptomelane group incorporating k ca mg ba co zn and pb reflects acid conditions during sulfide oxidation when an ironstone consistently contains mn oxides with greater than 1 pb or 10 zn it can be regarded as derived from pb or zn rich mineralization as ba is often associated with sulfides and facilitates the incorporation of pb into cryptomelane ba without accompanying base metals in a mn oxide implies derivation from base metal barren pyrite and or pyrrhotite cu pb zn al phosphate sulfate and arsenate are all incorporated into fe oxides however only pb which is more strongly partitioned into hematite and al and phosphate which are preferentially incorporated into goethite show clear partitioning between the fe oxide phases the preferential incorporation of phosphate rather than sulfate into an fe oxide makes areas showing higher sulfate contents particularly good targets knowledge of the nature of the distributions of pathfinder elements helps understanding of the associations seen in whole rock analyses and leads to rational application of geochemical data during exploration

precambrian paleosols in canada although at least 38 precambrian paleosols have been reported in canada few have received the attention afforded most other geological phenomena the most intensively studied of these are widely distributed early proterozoic paleosols associated with the sub huronian and matonabbee new name unconformities criteria that have been most useful in identifying precambrian paleosols in canada include macrostructures ascending protolith disruption saprolith and corestones micromorphology sepic texture and peds mineralogical changes dissolution transformation geochemical signatures ascending depletion of some elements characteristic weathering indices and distinctive colour contrast diagenetic mechanical and geochemical overprinting of the paleosols evident in many canadian examples includes paleosol compaction veins cutting pedogenic features and widespread alkali and alkaline earth element metasomatism metamorphism and deformation also tend to mask pedogenic features as attested by th

precise zircon u pb and molybdenite re os dating of the shuikoushan granodiorite related pb zn mineralization southern hunan south china abstract the shuikoushan ore district located in southern hunan province south china contains pb zn au mineralization hosted in the devonian to triassic strata and mesozoic granodiorite intrusions ore minerals are mainly pyrite sphalerite galena and minor molybdenite molybdenite usually intergrown with pyrite formed during pb zn hydrothermal mineralization in order to determine the precise age of pb zn mineralization and further understand the relationship between magma emplacement and hydrothermal mineralization in the ore district molybdenite re os dating and zircon sims u pb dating were undertaken the zircon u pb dating reveals that the granodiorite intrusion was emplaced at 158 8 1 8 ma mswd 0 40 re os isotopic age of seven molybdenite samples yields model ages ranging from 157 5 2 5 ma to 161 0 2 4 ma and gives a well defined 187re 187os isochron age of 157 8 1 4 ma 2 mswd 1 3 indicating the timing of pb zn mineralization in the shuikoushan ore district at about 158 ma this date coincides well with the zircon sims u pb age of the granodiorite revealing a genetic association between the pb zn mineralization and the granitic magmatism combined with geochronological data published for other pb zn cu deposits in southern hunan it can be concluded that the granodiorite related pb zn mineralization throughout southern hunan mainly occurred at 160 156 ma rather than 180 170 ma or 170 160 ma as considered previously the pb zn mineralization and major w sn mineralization in southern hunan are coeval and may be related to the same geological event

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

regolith landform processes and geochemical exploration for base metal deposits in regolith dominated terrains of the mt isa region northwest queensland australia abstract the regolith in the mt isa region of queensland consists of a variety of saprolites and duricrusts developed on proterozoic basement rocks and fresh to weathered mesozoic tertiary and quaternary cover all of which has impeded base metals exploration this paper presents an overview of some of the regolith geochemical work conducted in the mt isa region as part of an industry supported three year crc leme amira project a complex weathering and landscape history has produced a landscape of a continuously exposed and exhumed basement rocks that have undergone varying intensities of weathering and partial stripping b weathered and locally eroded mesozoic cover sequences and c areas with younger transported cover concealing basement and mesozoic cover various regolith sample media have been evaluated at a number of prospects and deposits which represent different regolith landform terrains and landscape history geochemical dispersion processes and models are presented and false anomalies explained where ferruginous duricrust or ferruginous nodular gravel are preserved on weathered bedrock on an eroded plateau they exhibit large 500 m multi element as pb sb dispersion haloes and are useful sampling media dispersion haloes in truncated profiles on weathered bedrock covered with colluvium are restricted are limited to tens of metres from subcrop of the source and contrast to the extensive anomalies in ferruginous duricrust and nodules geochemical exploration in covered areas depends on the possible presence of dispersion through the sediments or leakage along faults or fractures but may be complicated by high metal backgrounds in the sediments themselves some of the most prominent anomalies occur in ferruginous materials and soils representing emergent residual terrain developed on mesozoic sediments these are largely due to weathering of sulfide mineralization that continued during submergence in a marine environment with hydromorphic dispersion into the sediments as they accumulated multi element cu as zn sb au anomalies occur in basal sediments and at the unconformity due to a combination of clastic and hydromorphic dispersion and represent a useful sample target metal rich horizons in weathered sediments higher in the sequence can also be targeted particularly by specifically sampling ferruginous units and fragments however these are less certainly related to mineralization zinc and cu concentrated in fe and mn oxides at redox fronts may be derived by leaching from the sediments with concentration in the sesquioxides and be unrelated to any proximal basement mineralization in all these regolith dominated terrains a clear understanding of local geomorphology regolith framework topography of unconformities and the origins of ferruginous materials is essential to sample medium selection and data interpretation

paleoclimate deduced from some early jurassic basalt derived paleosols from northern israel abstract earthy red layers intercalated amid basalt flows from an early jurassic 2500 m thick volcanic sequence in northern israel were examined mineralogically micromorphologically and chemically distinct pedological features such as wavy illuviation argillans and iron oxide nodules observed by micromorphological examinations identified the clayrich layers as basalt derived paleosols the clay by comparison with the mineralogy and micromorphology of modern basalt derived vertisols a moderately wet mediterranean type climate with pronounced seasonality was inferred for the formation time of the paleosols a similar lower jurassic paleoclimate had previously been inferred from a paleosol in the negev

mineralogy and composition of concentric layers within a manganese nodule from the north pacific ocean abstract the minor element composition of concentric layers within a single ferromanganese nodule from the eastern north pacific exhibits strong correlations with fe and mn contents but appears to be independent of pronounced mineralogic variations on the basis of these correlations the elemental composition of individual layers apparently is controlled by the relative contribution of two sources seawater and interstitial water of associated sediment in contrast the mineralogy of the nodule consisting of birnessite in the outer few layers and todorokite in the inner layers is considered to be a function of nodule diagenesis

the relationship between ductile shear zone and mineralization in the jiufeng sn deposit northern guangxi south china evidence from structural analysis and cassiterite u pb dating abstract the jiufeng sn deposit is located in the outer contact zone southwest of the neoproterozoic motianling granitic pluton in northern guangxi south china the deposit is characterized by a nne striking 30 200 m wide ductile shear zone named the jiufeng ductile shear zone majority of the sn orebodies including four large ones are hosted by the shear zone field and microstructural observations electron backscatter diffraction measurements and magnetic fabric analyses show that the shear zone is characterized by sinistral thrust shearing the shear zone has also slightly modified the sn orebodies quartz in the shear zone exhibits core mantle structure and undulose extinction quartz has experienced significant sub grain rotation and grain boundary migration recrystallization lattice preferred orientation analysis reveals primarily basal rhomb and prism slips cassiterite grains in the shear zone however demonstrate brittle deformation therefore the deformation temperature during the ductile shearing is estimated lower than 650 c and below u pb closure temperature of cassiterite as such the u pb isotopic composition of the cassiterite was not disturbed by the shearing and the u pb age of the cassiterite could be used for the age of the sn mineralization la icp ms u pb dating of cassiterite grains selected from a cassiterite bearing tourmalinite sample performed in this study yielded a tera wasserburg u pb lower intercept age of 832 3 5 3 ma this age is consistent within error with that of the neighboring neoproterozoic motianling granitic pluton which suggests a close genetic relationship between the sn mineralization and the granitic magmatism studies show that the jiufeng ductile shear zone was produced by a widespread caledonian or kwangsian tectonic event in south china indicating that the shearing was much later than the sn mineralization and has no generic relationship to the sn deposit

a precise u pb age on cassiterite from the xianghualing tin polymetallic deposit hunan south china we report the first precise u pb isotope data on cassiterite from the large xianghualing tin polymetallic deposit in the central nanling district south china the results show that four separates from sample xf 51 have a relatively narrow range of 206pb 238u apparent ages varying from 152 to 157 ma and the three 206pb 238u apparent ages yield a weighted average value of 156 4 ma mswd 0 32 separates from two other cassiterite samples do not have sufficient radiogenic pb to generate a reliable 206pb 238u age seven separates from the above three cassiterite samples define a well constrained 238u 206pb isochron corresponding to an age of 157 6 ma mswd 34 a comparison of the u pb cassiterite ages with published ar ar dates on muscovite from this deposit and k ar age data on biotite from the pluton genetically related to the tin mineralization in this area demonstrates that the u pb isotope system of cassiterite is a potential geochronometer combined with the ar ar dates of muscovite from this deposit we can constrain the absolute age of tin polymetallic mineralization in xianghualing at 154 157 ma the dates obtained in this study consistent with the published geochronological results from other important deposits in this region reveal that the large scale tungsten tin mineralization in the central nanling region was predominantly emplaced during 150 161 ma

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

saprolite formation beneath coastal plain sediments near washington d c crystalline rocks buried beneath atlantic coastal plain sediments in the washington d c area commonly have weathering profiles that resemble exposed saprolite of the piedmont cuts along the washington metropolitan area transit authority wmata route in northern virginia show a bedrock weathering profile beneath cretaceous and younger sediments three lines of evidence indicate that this buried weathering profile saprolite has formed in the subsurface and is post miocene in age the thickness of the profile ranging from 2 to 15 m is thinner beneath clays and thicker beneath sands apparently a function of the permeability of the overlying material the buried profile shows no evidence of soil formation at its upper surface and therefore no evidence of ever having been sub aerially exposed consolidation tests on the cohesive clayey silts in the samples of the weathering profile indicate mechanical equilibrium with the present overburden whereas consolidation tests on superjacent cretaceous clays indicate over consolidation resulting from a thicker pre upper miocene overburden the post miocene age for the subsurface saprolite profile shows that not all saprolite beneath cretaceous sediment is pre cretaceous in age these observations have important implications for the interpretation of age of the exposed piedmont saprolite

re os ages for the shameika porphyry mo deposit and the lipovy log rare metal pegmatite central urals russia the ages for pegmatite rare metal and beryl emerald deposits as well as porphyry mo deposits in the hercynian uralide orogen are not well known five molybdenite samples from the lipovy log pegmatite ta nb mo deposit and 11 molybdenite samples from the shameika porphyry mo deposit were selected for re os dating both mineral occurrences are spatial temporally associated with the adui composite granite pluton a well known rare metal related granite intrusion a re os isochron age of 262 0 7 3 ma was obtained for the lipovy log pegmatite ta nb mo deposit the shameika porphyry mo deposit associated with the malyshevo leucogranitic stock and surrounding hornfels provided isochron ages of 273 5 and 282 6 ma for two groups of molybdenite within stock and within hornfels all of these re os ages are consistent with presumed hercynian ages for the granite intrusions formed in a post collisional setting within the uralide orogen

properties and genesis of a soil and the underlying gibbsite bearing saprolite cape breton island canada brownish yellow saprolite derived from granite gneiss is exposed beneath 1 2 m of reddish brown till along a roadcut in the cape breton highlands the strongly acid soil is similar to other podzolic soils of the region except for the presence of gibbsite in the silt and clay fractions in the saprolite feldspar and biotite have weathered to poorly crystalline kaolinite gibbsite and a minor component of iron oxide the poorly crystalline kaolinite does not occur in the overlying till the evidence presented is consistent with the view that the area was covered either by cold based or by stagnant warm based glaciers that eroded the pre quaternary surface only slightly and deposited a thin discontinuous veneer of till derived mainly from local bedrock and saprolite weathering products from the saprolite are probably incorporated commonly in tills of the area during the formation of soils in these tills the poorly crystalline kaolinite and most of the gibbsite are either transformed to other minerals

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

distribution of ree in the eastern belt supergroup montana u s a implications for stratigraphic correlations and basin evolution abstract shales of the mid proterozoic newland formation belt basin contain a geochemical marker horizon that is characterized by the appearance of negative eu anomalies in shale ree patterns ree pattern changes appear to be related to changes in weathering intensity and tectonic activity in the hinterland stratigraphic and sedimentologic considerations suggest that this ree marker horizon defines an approximate time line within the sequence comparison of ree patterns of the newland formation and the coarse clastic lahood formation that was deposited to the south shows that the lower portions of the newland formation were deposited prior to lahood sedimentation such a correlation implies that early belt sediments may have covered a much larger area than delineated by the outline of the present day belt basin and that contrary to earlier views of basin evolution the half graben configuration of the eastern belt basin was established at some later point of basin history

the relationships between rock derived lead and iron in natural waters abstract the relationships between fe and pb released to the hydrocycle via rock weathering is examined in terms of field observations and laboratory experiments rock soil and unpolluted water samples from granodiorite basalt and carbonate terrains were analyzed for their pb fe and other element ca mg na k si al mn concentrations samples of granodiorite soil developed on the granodiorite basalt and dolomite rocks as well as biotite and feldspar minerals were also used for laboratory leaching experiments fe pb ratios found in granodiorite basalt and insoluble residue of carbonate bedrocks are preserved within an order of magnitude in surface and shallow groundwater reservoirs draining these rocks with the exception of carbonate rocks leachates of these rocks have fe pb ratios similar to that of the bedrock laboratory experiments suggest that pb is adsorbed and coprecipitates with fe rich particles even in the presence of higher concentrations of competing ions e g mg2 complexation of pb by ethylenediaminetetraacetate edta however substantially decreases the amount of pb bound to surface sites ligand competition based on our results we suggest that in early phases of the weathering cycle pb both coprecipitates and is adsorbed on surfaces of fe rich particles because of complementary transport mechanisms and comparable rates of release from common source rock and soil minerals the molar ratio of fe to natural rock derived pb in the particulate load of rivers in many cases it includes particles which pass through 0 45 m pore size filters is similar to that of the upper continental crustal rock approximately 6500 this ratio can vary in watersheds which drain rocks with different fe pb ratios than the average upper continental crust in rivers loaded with dissolved natural organic matter or in rivers polluted with pb or with anthropogenic chelators secondary pollution effect

u pb dating of perovskite by la icp ms an example from the oka carbonatite quebec canada abstract the potential for u pb dating of the mineral perovskite using laser ablation inductively coupled plasma mass spectrometry la icp ms has been evaluated perovskite can have relatively elevated u and th contents making it a potentially useful geochronometer kimberlite lamprophyre and carbonatite intrusions are prone to alteration and typically contain abundant xenocrysts thus standard techniques for dating the magmatic emplacement of these rocks becomes highly problematic perovskite however is commonly present as a primary magmatic mineral in these rocks and has been used to constrain the timing of kimberlite and lamprophyre emplacement the main limitations to the production of accurate la icp ms u pb ages for perovskite are the lack of suitable standards coupled with the large common pb correction required 204 hg can produce large isobaric interference on the non radiogenic 204 pb isotope and methods based on 208 pb 206 pb and u th ratios are hampered by the enhanced th content present in most perovskite crystals after careful calibration using zircon reference materials common pb corrected 206 pb 238 u ages can be determined on each individual la icp ms analysis by using the measured 207 pb 206 pb ratio which is dominated by the common pb proportion in phanerozoic rocks this method assumes that the perovskite crystals analyzed are cogenetic and have the same initial pb ratios the la icp ms method has been applied to data collected on two large single perovskite crystals from the oka carbonatite complex quebec canada the weighted mean 206 pb 238 u age of 131 7 ma n 25 mswd 0 42 is consistent with published geochronology data from the region and suggests that la icp ms dating of perovskite could be a useful low cost alternative to compliment existing techniques

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

sediment and basalt hosted regoliths in the huronian supergroup role of parent lithology in middle precambrian weathering profiles weathering profiles developed side by side on sandstone and a mafic dike provide an unusual opportunity to examine the role of parent rock bulk composition in the chemical evolution of middle precambrian regoliths because the profiles are adjacent to one another differences in topography can be eliminated in accounting for differences in the chemical evolution of the two profiles both profiles show upward increases in al ti k and rb and decreases in mg ca and na in addition the mafic regolith increases upward in zr and nb and decreases in zn and ni total fe decreases upward in both profiles but the sandstone profile retains significantly more of its initial fe than does the mafic dike this difference in fe loss is consistent with weathering in a low oxygen atmosphere of rock types with very different initial fe contents and therefore different atmospheric requirements for complete oxidation of the fe present the fe in the sandstone was mostly oxidized and retained within the profile whereas

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

granite related tin metallogenic events and key controlling factors in peninsular malaysia southeast asia new insights from cassiterite u pb dating and zircon geochemistry

premetamorphic lateritisation in proterozoic metabasites of rogaland sw norway heterogeneous layers of granulite facies metamorphic basites of the proterozoic supracrustal faurefjell formation in rogaland s w norway display an extreme chemical variation within a single layer the bulk chemical composition gradually changes from approximately basaltic in basic granulites to alumina iron rich in granofelses component ratios and composition volume relations indicate open system chemical reactions mainly involving the extraction of silica apparent enrichment in fe ti p al zr ni co zn y nb hf and ree and variations in resulting metamorphic mineral assemblages are related to premetamorphic progressive lateritisation of a basaltic protolith the weathering generated a continuous chemical suite from sio2 48 wt fe2o3 10 wt and al2o3 19 wt in the basic granulites to 14 wt 40 wt and 25 wt in the fe al granofelses metasomatism during diagenesis and during very high grade metamorphism 1200 900 ma further perturbed the concentrations of relatively mobile elements ca mg k rb sr ba na and li in the laterites without affecting the transition metal ratios in particular the ree did not fractionate differentially during the supracrustal and metasomatic alteration

chemistry and mineralogy of precambrian paleosols at the base of the dominion and pongola groups transvaal south africa abstract we have studied alteration zones found between sedimentary rocks of the lowest proterozoic dominion and archean pongola groups and underlying granitic rocks transvaal south africa the alteration zones have a transitional lower boundary primary igneous minerals are gradually destroyed upward toward the contact with overlying sedimentary rocks ca mg na p and mn are progressively lost upwards in the zone the chemical and mineralogical variations and available stratigraphic evidence are all consistent with the interpretation that these zones are paleosols formed by precambrian weathering 2 8 3 0 ga ago after formation the paleosols underwent metasomatism and metamorphism sericite now present in the paleosols was probably formed by low temperature potassium metasomatism of original clays andalusite in the pre pongola paleosol was probably formed by metamorphism of original clays in impermeable zones which prevented groundwater flow and potassium metasomatism the dominion paleosol was investigated at three localities the effects of weathering were similar at the three sites except for the behavior of iron one site lost about 20 of iron whereas the other sites lost 75 and 80 of initial iron content the differences in iron loss may be due to variation in soil ventilation and diffusion of atmospheric gases as a function of grain size and topography variations in iron loss may be used to place some constraints on the composition of the precambrian atmosphere given constraints imposed by dominion paleosols overlying uraniferous conglomerates requirements for chemical weathering and the greenhouse effect and possible presence of non diffusing photochemical oxidants the partial pressures of oxygen and carbon dioxide gases probably are in the ranges po1 0 02 to 0 5 pal present atmospheric level and pco2 5 to 30 pal

lithogeochemical patterns around pb zn mineralizations in dinantian carbonate rocks of eastern belgium the lithogeochemical distribution patterns of mg sr na zn pb fe mn k corg organic matter and ir insoluble residue in the dinantian limestones and dolomites from the eastern part of belgium have been studied dinant and verviers synclinorium comparison of geochemical data of non mineralized strata revealed higher background values in the strata of the verviers synclinorium where pb zn mineralizations occur in this area a relation may exist with the metallogenetic district herve vesdre theux district proposed by dejonghe 1985b however the higher background values also could relate to the more restricted sedimentation conditions in the verviers synclinorium as opposed to the more open marine conditions in the dinant synclinorium the influence of mineralization on the geochemistry of limestones is limited and unpredictable in dolomites however the effect can be important in these rocks the lithogeochemical distribution of zn pb and mn can be subdivided into three populations i e a regional background a local high background and a halo population the higher trace element concentrations in the halo population is caused by the existence of disseminated sulfide minerals sphalerite galena and pyrite and zn bearing goethite mainly pseudomorphs after pyrite and mn oxides the sulfides relate to the ore emplacement in the local high background only the zn bearing oxides occur their presence and thus the development of the local high background relates to weathering processes

petrography and geochemistry of a 2000 2200 ma old hematitic paleo alteration profile on ongeluk basalt of the transvaal supergroup griqualand west south africa abstract a 4 m thick paleo alteration profile thought to represent one of the oldest known ferruginized hematitic paleoweathering zones is described from a depth of 720 m in a drill core on the farm drakenstein 263 some 20 km northwest of hotazel in griqualand west south africa the paleo alteration profile is developed on 2240 57 ma ongeluk basalt along the angular unconformity that separates transvaal strata from 2070 95 ma basal red beds of the olifantshoek group basaltic ongeluk lava was subjected to greenschist facies metamorphism represented by a mineral assemblage of fe pumpellyite chlorite albite and quartz before paleosol development the subsequent paleo alteration is characterized by concentration of fe2o3 in the form of hematite iron rich chlorite and abundant sericite the abundance of sericite results in a large excess of k2o relative to the amount of al2o3 that could have been derived from weathering of the parent basalt the origin of the excess potassium is problematical and could have been derived from basin water groundwater or metamorphic fluids field relationships favour introduction from basin water during deposition of overlying olifantshoek red beds elements such as sodium calcium and magnesium were leached from the alteration profile whereas ree became concentrated within it the most interesting aspect of the ree distribution is the preferred concentration of the lighter lanthanides la and nd in the middle part of the alteration profile relative to heavy ree and the development of a marked negative ce anomaly in the paleo weathered material hydrothermal vein alteration took place after deposition of the overlying olifantshoek red beds

a new occurrence of merensky reef on the flanks of the zaaikloof dome northeastern bushveld complex relationship between diapirism and magma replenishment exploration for platinum group elements has resulted in the discovery of an occurrence of merensky reef in the eastern limb of the bushveld complex south africa the new discovery was made on the dwarsrand property in the poorly known boundary area between the intensively explored western and central sectors of the eastern limb this boundary area is largely composed of domes and basins that may in part be aligned along a regional lineament the wonderkop fault transvaal supergroup metasediments in the core parts of the domes form prominent hills whereas the bushveld complex in the intervening basins is restricted to areas of poor outcrop the formation of domes is attributed to diapirism triggered by gravitational loading and heating of the transvaal supergroup in response to intrusion of the bushveld complex merensky reef was located beneath cover rocks in an area where the critical and main zones are uplifted and attenuated against the southern flank of the zaaikloof dome drill holes although collared in upper zone intersected the critical and main zones at relatively shallow depths as a result of the uplift the critical and main zones including the merensky reef are steeply dipping the base of the upper zone forms an intrusive unconformity and the layering in this zone has a much shallower dip economically significant grades were obtained on the dwarsrand property but exploration was terminated because of poor strike continuity the new findings suggest that uplift and attenuation of the bushveld complex on the flanks of domes in the northeastern part of the complex are both more extensive and more severe than previously realized a complex history of intrusion and uplift is implied some domes even penetrate into the overlying bushveld granite the occurrence of markedly angular unconformities may be contrasted with the layercake sequences typically associated with the bushveld complex diapirism in response to crustal loading and heating by ultramafic sequences occurred in the early stages of magma emplacement episodic intrusion and uplift are consistent with multiple replenishment models in which each of the many dozens of cycles that comprise the critical and main zones corresponds to a new magma pulse with the oldest layers being dragged to higher structural levels in response to the uplift periodic reactivation of doming is indicated by the lowermost layers within the critical and main zones abutting against the southern flank of the zaaikloof dome at progressively higher levels the transgressive nature of the upper zone and bushveld granite relative to the critical and main zones may indicate that the upper zone formed by new intrusions of magma rather than the generally accepted model of differentiation within the chamber the discovery of hidden merensky reef at relatively shallow depths beneath transgressive upper zone and granite could provide the impetus for further exploration possibilities within the bushveld complex particularly on the flanks of regionally extensive domal structures

a vertic paleosol at the archean proterozoic contact from the singhbhum orissa craton eastern india abstract we report on an inferred paleoproterozoic soil horizon from the singhbhum orissa craton near keonjhargarh orissa eastern india which preserves vertic vertisol like features the 2 10 m thick white shale consists of quartz muscovite pyrophyllite interpreted as a paleosol overlies 3 32 ga granite and is covered by pre 2 0 ga sandstones kolhan group deposited in marginal marine environments the paleosol passes downwards through a partly altered granite saprolith zone to fresh granite abundant pedogenic slickensides ped structures gilgai topography reddish stain on ped surfaces and sepic plasmic microfabric in the paleosol were probably related to shrink and swell processes driven by marked seasonal precipitation in a well drained landscape an observed decrease of alkali elements and an increase of silica alumina and cia values from granite to paleosol together with relatively constant ti al ratios suggest in situ weathering of granite protolith however a paleo vertisol necessitates a mafic parent rock either directly igneous or reworked through alluvium the c 2 25 ga malangtoli jagannathpur basaltic rocks are relatively widespread and close to the inferred paleosol occurrences and provide a logical solution geochemistry of the highly depleted paleosol in contrast particularly when applying the isochon method strongly supports a granitic parent the apparent conundrum can possibly be solved through repeated alluvial reworking of both granitic and mafic detritus and accumulation of weathered material with varying proportions of these two components yet enough smectitic clays 30 to form a paleo vertisol this pre 2 0 ga weathering event in the singhbhum craton is consistent with a global scenario of paleoproterozoic weathering which followed an extended global glaciation and thus has the potential to contribute to understanding of pre 2 0 ga amalgamation of regional and global cratonic blocks

autochthonous development of superior province greenstone belts abstract models for superior province greenstone belt development have changed over the last 30 years from ensimatic generally autochthonous models to suspect allochthonous terrane models based on the plate tectonic paradigm models intermediate between these end members such as autochthonous terrane models have not been prominent within the superior province there is a secular variation from early ca 3 ga platformal assemblages with overlying rift related komatiite tholeiite units representing breakup of ca 3 ga continental fragments to late ca 2 7 ga pull apart basins autochthonous terranes should demonstrate some sort of logical order such as that described above whereas allochthonous terranes will be largely oceanic in character and should be essentially random in their occurrence rather than exhibiting secular order in the face of this situation this paper reviews evidence from throughout the superior province that suggests many but not all greenstone assemblages developed autochthonously or parautochthonously the earliest greenstone assemblages in the superior province are generally quartzite and carbonate bearing platform sequences in the north caribou terrane and the marmion terrane deposited unconformably upon granitoid or greenstone basement the evidence for autochthonous parautochthonous development includes the presence of unconformities between keewatin type greenstone units such as 1 basal unconformities between ca 3 ga granitoid or volcanic basement and slightly younger platformal assemblages 2 between ca 2 9 ga platformal assemblages and younger platformal and andean arc assemblages stratigraphic patterns such as adjacent greenstone belt assemblages representing sharply differing geodynamic settings with some indication of palinspastic order or progression in the northern central and southern superior province are considered suggestive of orderly autochthonous progression from platforms through rifting of continental fragments and late assembly during the kenoran orogeny petrogenetic data indicating involvement of older granitoid crust in genesis of greenstone assemblages of a variety of ages throughout the superior province suggests the presence of older basement implying autochthonous or parautochthonous development of many assemblages younger greenstone assemblages in the abitibi wawa subprovince and the north caribou terrane contain xenocrystic zircons similar in age to stratigraphically underlying greenstone assemblages this pattern has been interpreted to represent autochthonous greenstone development the current above enumerated evidence for autochthonous development of greenstone assemblages is generally indirect few actual unconformities between keewatin type greenstone assemblages have been recognized in the superior province to aid in future recognition of unconformities in keewatin type greenstone assemblages examples of unconformities of varying degrees of subtlety in archean sequences are reviewed archean unconformities ranging from sharp angular discordances in the northern superior province to subtle stratigraphic patterns to weathering related geochemical mobilization along inter formational contacts are described these styles of unconformity in archean sequences suggest previously unrecognized major disconformities and unconformities may well exist between keewatin type assemblages in the superior province generally and the abitibi wawa subprovince specifically the most important disconformity suggested in the abitibi wawa subprovince is between the ca 2726 ma deloro and the ca 2708 ma tisdale assemblages the presence of unconformities and disconformities coupled with the indirect lines of evidence cited above suggest an autochthonous origin for many superior province greenstone belts this autochthonous origin involves either autochthonous or parautochthonous evolution of assemblages at least in part in place that is development of ca 3 ga platform sequences in selected locales followed by in place evolution of a succession of plume oceanic and arc assemblages culminating in late pull apart basin sequences implications of the autochthonous model for greenstone belts of the superior province particularly the abitibi wawa subprovince include the future ability to recognize unconformity bounded sequences potentially improving regional scale correlation

precise and accurate in situ pb pb dating of apatite monazite and sphene by laser ablation multiple collector icp ms to evaluate in situ pb dating by laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icp ms we analysed apatite sphene and monazite from paleoproterozoic metamorphic rocks from west greenland pb isotope ratios were also determined in the national institute of standards and technology nist 610 glass standard and were corrected for mass fractionation by reference to the measured thallium isotope ratio the nist 610 glass was used to monitor pb isotope mass fractionation in the low tl pb accessory minerals replicate analyses of the glass 1 to 2 min yielded ratios with an external reproducibility comparable to conventional analyses of standard reference material 981 by thermal ionisation mass spectrometry tims mineral grains were generally analysed with a 100 m laser beam although some monazite crystals were analysed at smaller spot sizes 10 and 25 m the common pb isotope ratios required for age calculations were either measured on coexisting plagioclase by la mc icp ms or could be ignored as individual crystals exhibit sufficient pb isotopic heterogeneity to perform isochron calculations on replicate analyses of single crystals mean mineral ages with the 204pb ion beam measured in the multiplier were as follows apatite 1715 23 m y sphene 1789 11 m y and monazite 1783 to 1888 m y with relative uncertainties on individual monazite ages of 0 2 but highly reproducible age determinations on single monazite crystals 1 isochron ages calculated from several mineral analyses without assumption of common pb also yield precise age determinations apatite and monazite pb ages determined by in situ pb isotope analysis are identical to those determined by conventional tims analysis of bulk mineral separates and the analytical uncertainties of these short laser analyses with no prior mechanical or chemical separation are comparable to those obtained by tims detailed examination of the sphene in situ age data does however show a small discrepancy between the la mc icp ms and tims ages 1 younger high resolution mass scans of the sphene during ablation clearly showed several small and as yet unidentified isobaric interferences that overlap with the 207pb peak at the resolution conditions for measurement of isotope ratios these might account for the age discrepancy between the la mc icp ms and tims sphene ages la mc icp ms is a rapid accurate and precise method for in situ determination of pb isotope ratios that can be used for geochronological studies in a manner similar to an ion microprobe albeit currently at a somewhat degraded spatial resolution further modifications to the la mc icp ms system such as improved sensitivity ion transmission and la methodology may lead to this type of instrument becoming the method of choice for many types of in situ pb isotope dating

geochemistry of late archaean metagreywackes from the western dharwar craton south india implications for provenance and nature of the late archaean crust abstract late archaean metagreywackes of the ranibennur formation dharwar supergroup in the dharwar shimoga schist belt of the western dharwar craton wdc are texturally and mineralogically immature of the quartz intermediate type the sio 2 content in them ranges from 60 58 to 65 26 wt chemical index of weathering ciw values varies between 50 and 65 4 indicating a low degree of chemical alteration of the provenance rocks a high degree of correlation between k 2 o and al 2 o 3 r 0 73 and low rb sr ratios also suggest a low degree of alteration of provenance rocks abundances of transition group elements cr 118 221 n 89 154 v 89 192 and sc 11 16 ppm as well zr 132 191 ppm suggest a mixed mafic felsic provenance for the metagreywackes low hree and y content and low tb yb ratios 0 23 0 41 suggest the presence of tonalite as an important component in the provenance areas values of eu eu 0 78 and th sc 0 55 suggest that the granodioritic upper crust had evolved prior to serving as the provenance mixing calculations suggest 50 55 vol tonalite 20 25 vol granite 18 20 vol basalt and 5 vol komatiite composition for the provenance geochemical characteristics of the ranibennur metagreywackes suggest that sedimentary basin formed in the vicinity of a magmatic arc in a continental island arc setting and the detritus were shed from the arc rock

mineralogy and geochemical dispersion in lateritic soil profiles of northern nigeria abstract six lateritic soil profiles overlying metasedimentary and crystalline basement rocks of northern nigeria have been investigated in order to study the mineralogical and geochemical relationships between bedrock and weathering products a total of 96 samples have been collected including 26 from exposed quarry and road cut faces and 70 from auger holes to a depth of 8 m two selective leaching methods cold extraction with 0 1 m hci and hot extraction with aqua regia have been applied to the m fraction and up to sixteen elements determined by aas conclusions are based largely on the auger hole samples where element distributions have not been modified by subaerial exposure quartz is the dominant mineral in the upper part of the soil profile while kaolinite increases strongly with depth at the base of some profiles mica is also abundant elements are distributed through the soil profile according to their association with clays iron oxides and to a lesser extent carbonates while intercalations of lateritic crusts obscure general trends with depth dispersion and accumulation processes appear to be similar within each profile in spite of the intensive weathering and secondary accumulation processes characteristic of the savanna belt the lateritic soils within surface sampling depth appear to retain a geochemical imprint of the underlying bedrock criteria and potential problems in the application of soil geochemistry to bedrock mapping are discussed

an archean quartz arenite andesite association in the eastern baltic shield russia implications for assemblage types and shield history abstract shallow water sedimentary units are generally considered scarce in archean greenstone belts we describe an unusual quartz arenite subaerial andesite association within the archean hisovaara greenstone belt a fragment of the parandovo tikshozero belt within the karelian craton of the baltic shield the hisovaara greenstone belt consists of several lithotectonic assemblages 1 a komatiite tholeiite assemblage 2803 ma based on ages of cross cutting dikes 2 an andesite quartz arenite assemblage cut by similar dikes 3 an assemblage of coarse volcaniclastic rocks and 4 an upper mafic assemblage of tholeiitic basalts with minor pyroxene komatiite volcanic rocks the andesite quartz arenite assemblage 100 to ca 750 m thick has basal amygdaloidal fragmental andesites overlain by massive andesites then amygdaloidal and plagioclase phyric andesites unconformably overlying the andesite is a unit of quartz rich sandstones 6 40 m thick dominated by quartz arenite extending several km along strike at the north end the quartz arenite succession consists of basal andesite overlain by quartz arenite exhibiting hummocky cross stratification followed by aluminous coarse metasediments and sulfidic argillite and an unconformably overlying tholeiite komatiite unit at the south end the succession is basal andesite regolith cross bedded quartz arenite weathered andesites a second quartz arenite argillite and then subaerial rhyolite ree and hfse geochemistry has been obtained on the rocks of the andesite quartz arenite assemblage the quartz arenites contain low abundances and chondrite normalized patterns vary from relatively fractionated to flat with most of the variation related to grain size with pebbly units having higher abundance and more fractionated patterns combined major and trace element geochemistry indicates that a sodic felsic source with some admixture of mafic material will explain the geochemistry of the quartz arenites the andesites display moderately fractionated spidergrams with negative anomalies at ti ta and nb typical of arc volcanism the andesite quartz arenite assemblage represents accumulation of shallow water quartz rich sediments in a setting typical of the later stages of arc volcanism in which the volcanic edifice is subaerial at the southern end of the assemblage however at the north end our evidence is interpreted as indicating subaerial andesitic volcanism subsidence to a shallow marine basin which then deepens and rifts therefore the hisovaara andesite quartz arenite assemblage provides a linkage in archean greenstones between assemblages representing continental volcanism and a platform to rift setting the presence of an erosional interval in 2 8 ga greenstones suggests possible pre 2 7 ga orogeny in the baltic shield the pre 2 7 ga quartzrich sedimentation is similar in age to platformal assemblages in the pre 2 7 ga north caribou terrane of the superior province canada

cassiterite potential for direct dating of mineral deposits and a precise age for the bushveld complex granites u pb and pb isotopic measurements of cassiterite from the 200 ma tin deposits of belitung indonesia and 2100 ma zaaiplaats deposit in south africa demonstrate that cassiterite can be used to directly date mineral deposits rather than associated minerals such as zircon and rutile a precise u pb age of 2099 3 ma has been determined for cassiterites hosted in granites from the bushveld complex on conventional 207 pb 204 pb 206 pb 204 pb plots the data for the indonesian deposits give an age apparently older than that obtained from u pb plots perhaps indicative of inheritance of pb from an older source

mineralization and fluid inclusion study of the shizhuyuan w sn bi mo f skarn deposit hunan province china the shizhuyuan deposit china is a world class w sn bi mo f skarn deposit hosted by devonian limestone in the thermal aureole of the qianlishan granite complex the qianlishan complex comprises five separate intrusions including fine grained porphyritic biotite granite 182 187 ma granite 1 medium grained biotite k feldspar granite 158 163 ma granite 2 fine grained biotite and k feldspar granite granite 3 granitic porphyry 144 146 ma granite 4 and diabase 142 ma the upper part of the granite complex is characterized by extensive greisen alteration skarn zones distributed around the intrusions are mainly calcic consisting of garnet garnet pyroxene vesuvianite garnet and wollastonite vesuvianite progressively outward from the intrusion following the primary skarn formation some of the skarn zones underwent retrograde alteration the high garnet pyroxene ratio and the diopside rich and andradite rich compositions of the pyroxene and garnet indicate that the skarn belongs to the oxidized type mineralization consists of sn be veinlet ore type i in marble and porphyry massive w bi mo sn skarn ore type ii stockwork w sn bi mo f ore type iii and w sn mo bi greisen ore type iv mainly associated with granite 2 emplacement of granite 2 was accompanied by late intense fracturing characterized by stockwork mineralization type iii which was superimposed on massive skarn and greisen zones the stockwork ore consists mainly of greisen and skarn veins and veinlets with scheelite wolframite molybdenite cassiterite bismuthinite and fluorite the sm nd method has been used to analyze the sm nd concentration and data for pyroxene and garnet in the massive skarn type ii ore associated with granite 2 yields an isochron age of 157 ma this age corresponds closely to the age of granite 2 fluid inclusion studies of four types of ore samples reveal four types of inclusions aqueous two phase inclusions h2o co2 inclusions gas rich inclusions and daughter mineral bearing inclusions containing halite or calcite homogenization temperatures of fluid inclusions in skarn minerals range from 350 to 535 c the homogenization temperatures of fluid inclusions in greisen and stockwork are lower than that in skarn and range from 200 to 360 c the fluid inclusion data indicate that there are two types of fluids associated with the massive skarn and greisen having salinities from 26 to 41 wt percent nacl equiv and from 1 to 21 wt percent nacl equiv respectively the high salinity inclusions are daughter mineral bearing whereas the low salinity inclusions are dominantly aqueous with a few gas rich inclusions the results suggest the evolution of the ore forming fluids either by immiscibility or by mixing between a high temperature high salinity magmatic water and a low temperature low salinity fluid such as meteoric water consistent with previously published isotopic studies the shizhuyuan deposit is a multi element skarn highly enriched in w sn bi mo and f this is interpreted to reflect multiple sources and stages of mineralization which in turn may account for the large size of the shizhuyuan deposit

direct evidence of late archean to early proterozoic anoxic atmosphere from a product of 2 5 ga old weathering because precambrian paleosols ancient soils formed by weathering are usually subjected to later alteration the evidence gleaned from chemical studies has provided inconclusive evidence on the atmospheric o2 evolution in a 2 6 2 45 ga paleosol developed on archean granite near pronto mine canada we found that ce rich rhabdophane formed directly during weathering replaced primary apatite and has survived for about 2 5 ga because of its low solubility and high resistance to heat our data show that la ce and nd behaved similarly in both rocks and rhabdophane i e most ce existed as ce3 in the weathering solution unlike the younger weathering profiles where ce3 oxidizes and forms cerianite ceo2 the presence of rhabdophane with ce3 throughout the pronto paleosol provides compelling evidence of an anoxic atmosphere 2 6 2 45 ga ago because apatite is a common accessory mineral in granitic rocks ce content of the replaced rhabdophane can be a useful indicator for tracing o2 evolution in the precambrian

precise molybdenite re os and mica ar ar dating of the mesozoic yaogangxian tungsten deposit central nanling district south china the yaogangxian deposit in the central nanling region south china consists of vein type ore bodies hosted in cambrian to jurassic strata and mesozoic granitic intrusions wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz feldspar phlogopite and muscovite we have carried out molybdenite re os and phlogopite and muscovite 40ar 39ar dating to better understand the timing and genesis of mineralization re os dating of eight molybdenite samples yielded model ages ranging from 152 0 3 5 to 161 1 4 5 ma with an average of 156 0 ma the re os analyses give a well defined 187re 187os isochron with an age of 154 9 2 6 ma mswd 2 4 hydrothermal phlogopite and muscovite display extremely flat 40ar 39ar age spectra phlogopite yields a 40ar 39ar plateau age of 153 0 1 1 ma whereas muscovite yields a plateau age of 155 1 1 1 ma both 40ar 39ar ages are in good agreement with the re os ages placing the timing of tungsten mineralization at about 154 ma this age is consistent with the field relationships our new data when combined with published geochronological results from other major deposits in this region suggest that large scale w sn mineralization occurred throughout the central nanling region in the late jurassic

rare earth element enriched cobaltiferous wads bungonia eastern australia wad occurs as a cement to fluvial sediments which unconformably overlie a complex palaeozoic basement comprising flysch type greywacke limestone shale tuff and granodiorite the eocene fluvial sediments are variably cemented by fe oxides mn oxides and silica the area underwent 0 5 0 75 km uplift throughout the tertiary and was intenseely lateritised in the late miocene the mn rich cement comprises cobaltian todorokite lithiophorite birnessite in sandstones which contain up to 12 mno and enrichments in co max 1 8 total ree max 0 5 ce max 0 2 nd max 0 1 ni max 0 3 cu max 0 2 and li max 0 1 the total ree content ce content and nasc normalized la lu ratio are positively correlated with the mno fe2o3 ratio enrichment of ree especially lree and other elements derives from miocene lateritisation and resultant mobilization of elements from basalt fe co ni cu ree shale ree limestone mn and granite li these warm acid fluids were focussed in eocene fluvial channels which acted as aquifers and redox barriers by the oxidative precipitation of fe and mn oxide cements further oxidation of ce and adsorption of ree co etc by todorokite have resulted in the extraordinary enrichment of ree in wad cemented fluvial sandstones

profiles of elemental concentrations in precambrian paleosols on basaltic and granitic parent materials abstract profiles of elemental concentrations are interpreted for four precambrian paleosols two developed on basalt and two on granodiorite all four paleosols appear to be the erosional remnants of originally thick soil saprolite regoliths the granitic paleosols are in south africa where they underlie the 2 9 3 0 ga pongola supergroup and the 2 8 2 9 ga dominion reef conglomerate one of the basaltic paleosols also occurs in south africa where it caps the ventersdorp basalt and underlies the 2 3 ga black reef quartzite the other basaltic paleosol underlies sandstone of the 2 7 ga timiskaming group in the abitibi belt of the canadian shield all four paleosols exhibit pronounced upward loss of sodium but no consistent loss of the heavier alkali elements rubidium and cesium iron decreases upward above iron rich basaltic parent rocks but there is no consistent loss of iron above iron poor granitic parents the rare earth elements are less fractionated than during intensive modern weathering uranium locally has been fractionated from thorium possibly due to oxidative dissolution during precambrian weathering

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

laser ablation icp ms titanite u th pb dating of hydrothermal ore deposits a case study of the tonglushan cu fe au skarn deposit se hubei province china abstract titanite from the tonglushan cu fe au skarn deposit daye district eastern china has been successfully dated by laser ablation inductively coupled plasma mass spectrometry la icp ms hydrothermal titanite from both skarn ores and calcite veins cutting the ore bodies are characterized by having much lower ree and th u and lu hf ratios compared to their magmatic equivalents from the ore related yangxin quartz diorite intrusion and a late stage albitite dike titanite from the yangxin quartz diorite and an albitite dike which intrudes both the quartz diorite intrusion and ore bodies yield weighted mean 206pb 238u ages of 136 0 1 5 ma and 120 6 2 3 ma 2 respectively in agreement within analytical uncertainty to their 208pb 232th ages in situ analysis of epidote enclosed hydrothermal titanite in thin sections of a skarn ore sample yields a mean 206pb 238u age of 135 9 1 3 ma and 208pb 232th age of 138 2 4 5 ma whereas titanite in calcite from a calcite dominated vein cross cutting the skarn ore body has consistent 206pb 238u and 208pb 232th ages of ca 121 ma the data thus reveal two independent hydrothermal events the earlier event was responsible for the known cu fe au skarn mineralization at tonglushan and throughout the daye district and was caused by coeval magmatism that has resulted in the emplacement of the yangxin quartz diorite the later event previously unrecognized was associated with a second magmatic pulse as represented by the albitite dikes and provides potential for discovering new mineral deposits at tonglushan and possibly over the daye district this study represents the first direct dating of skarn deposits using titanite u th pb geochronometer and signifies the utilization of titanite for precise dating of hydrothermal ore formation

distribution and mobilization of sn in silicate minerals from the mesozoic shizhuyuan w dominated polymetallic deposit south china abstract although mobilization and concentration of elements in super large deposits have become hot topics in recent years studies of the mobilization of metals between minerals using in situ analyses are rare the shizhuyuan w dominated polymetallic deposit in south china is one of the largest non ferrous metal deposits in the world and contains large metal reserves of sn w bi and rare earth elements using laser ablation inductively couple plasma mass spectrometry la icp ms we analyzed trace elements in major silicate minerals and magnetite from granites and skarns of the shizhuyuan deposit tin concentrations of muscovitized biotite range from 196 to 558 ppm muscovite from 57 7 to 332 ppm chloritized biotite from 1 62 to 527 ppm k feldspar from 4 16 to 6 97 ppm kaolinized k feldspar from 1 15 to 9 38 ppm plagioclase from 1 87 to 5 09 ppm sericitic plagioclase from 2 53 to 28 7 ppm kaolinized plagioclase from 0 99 to 17 7 ppm epidote from 1199 to 3382 ppm garnet from 797 to 2860 ppm chloritized garnet from 72 5 to 2548 ppm chlorite from 19 6 to 159 ppm and magnetite from 23 7 to 872 ppm thus sn is mainly hosted in biotite muscovitized biotite garnet and epidote sn occurs as an isomorphous substitution and is predominantly associated with fe3 for fe3 poor minerals sn can isomorphously substitute al in the form of simple cation due to similar radius at the octahedral site such as in k feldspar and kaolinized k feldspar however sn cannot substitute al in the si o tetrahedrons therefore sn and al correlate different in different silicate minerals alteration of biotite to muscovite and chlorite can release a large amount of sn to the magmatic hydrothermal fluids which may be already enriched in sn during the formation of skarn deposits sn f complexes can be converted to cassiterite sno2 to free up f by hydrolysis a significant amount of sn enters the lattices of garnet and epidote therefore release of sn during alteration of garnet to chlorite in a retrograde stage of alteration may have contributed to the mineralization

petrogenesis of jurassic tungsten bearing granites in the nanling range south china evidence from whole rock geochemistry and zircon u pb and hf o isotopes abstract the nanling range nlr is the largest tungsten metallogenic province in china and perhaps in the world the tungsten mineralization is believed to be related to jurassic granitic magmatism however the petrogenesis of these granites and their relation to the tungsten mineralization are still debated whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for w bearing granitic intrusions from the southern jiangxi province in the nlr in order to constrain their magmatic sources and petrogenesis the nlr granites include biotite granites two mica granites and garnet muscovite granites sims and la icpms u pb dating of zircons and monazites give emplacement ages of 161 154 ma for these rocks the granites are metaluminous to strongly peraluminous with high sio 2 72 3 wt and high k 2 o 3 7 wt petrographic and geochemical features show that they are highly fractionated i type granites the biotite granites are enriched in light rare earth elements lrees relative to heavy rees have weakly negative eu anomalies and are depleted in nb ba p and ti in contrast the two mica and garnet bearing muscovite granites have tetrad type ree patterns with strongly negative eu anomalies and are extremely depleted in ba nb sr p and ti magmatic garnets are mainly almandine and spessartine and have low mn cores and high mn rims their y hree contents are high and generally decrease from core 1 2 wt to rim average 4955 ppm all of these granites are characterized by variable whole rock initial 87 sr 86 sr 0 7053 0 8000 e nd t 12 6 to 9 4 and e hf t 12 3 to 8 5 as well as variable zircon e hf t and 18 o with values of 16 3 to 7 4 and 7 6 to 10 0 respectively they contain abundant zircon xenocrysts and xenoliths of micaceous schist all of these features are consistent with a process of crystal fractionation of crustally derived magmas coupled with strong assimilation of sedimentary rocks the assimilation of meta sedimentary materials increased the concentrations of tungsten alumina and manganese in the magmas whereas high degrees of crystal fractionation further enriched them in the evolved granitic rocks the w enriched magmatic fluids formed the tungsten bearing quartz veins revealing the genetic relationship between tungsten mineralization and emplacement of garnet bearing two mica or muscovite granites in the nlr

rare earth element zonation in pacific ferromanganese nodules abstract the lower surfaces of ferromanganese nodules from the north equatorial pacific ocean which are enriched in mn cu and ni and the upper surfaces which are enriched in fe p and co have been analyzed for la ce nd sm eu gd dy er and yb the ree contents are lower and the ce anomaly is smaller in the lower surfaces than in the upper surfaces the magnitude of the ce anomaly increases with decreasing mn fe ratio indicative of a seawater origin the zonal distribution of the other ree supports the conclusion derived previously from inter nodule and nodule sediment relationships that diagenetic fixation of rare earths in sediments affects their enrichment by nodular iron oxyhydroxides

topographic control on precambrian weathering in the elliot lake uranium district canada the voluminous uraniferous conglomerate beds at elliot lake canada lie directly above or within several metres of a palaeosol that developed on archaean granite and greenstone metabasalt this lower proterozoic paleosol provides evidence for the environment in which the uraniferous conglomerate accumulated previous investigators have interpreted a few analyses of the palaeosol to indicate palaeoweathering under an atmosphere devoid of free oxygen however we have independently analysed in detail three oxidized palaeosols that formed contemporaneously with reduced palaeosols the degree of oxidation correlates well with palaeoelevation

geology of precambrian paleosols at the base of the huronian supergroup elliot lake ontario canada abstract detailed examination of two new profiles through the denison series paleosol and one new profile through a pronto series paleosol in the elliot lake area lend fresh insight into atmospheric and hydrogeologic environmental conditions of precambrian earth these are reassessed with reference to the results of previous studies as true indigenous paleosols of polygenetic character virtually all of the criteria grandstaff et al 1986 for identification of paleosols are met the paleosols bear strong mineralogical and chemical similarities despite derivation from different parent materials and sampling at locations distant from each other there has evidently been a common reaction to weathering processes peculiar to the early proterozoic diagenetic and metamorphic events mask to a considerable extent the role played by environmental and hydrologic conditions in the development of the paleosols in the denison greenstone derived paleosol clay formed from amphibole feldspar and chlorite is altered to sericite increased quartz content is due to residual concentration and to secondary development in granodiorite derived paleosol quartz and sericite are generally more abundant quartz is relatively concentrated toward the top of the profile the paleosols are thus primarily sericite quartz and chlorite assemblages rutile and leucoxene are accessory minerals profiles of elemental chemistry show the most drastic changes in concentration at the base in transition to bedrock magnesia and lime are leached from all profiles as in modern soils although in common with most precambrian paleosols potash accumulated total fe is strongly depleted from the profiles except just above the bedrock contact with granodiorite a condition attributed to mobilization of fe from the paleosol to a position directly over relatively impermeable parent rock use of holland s method of establishing oxygenation from paleosols indicates that in terms of fe content parent material of granodiorite derived paleosol should produce a reduced fe paleosol the oxygen demand of this rock was greater than granite owing to an abundant ferromagnesian content two fossil eluvial horizons marked by high chlorite and a dramatic decrease in sericite content are recognized in the denison paleosol their existence shows that although initial stages of weathering may have occurred under water saturated conditions conditions were probably more arid than supposed by previous workers particularly during the later stages of development of the paleosol although fe enriched the eluvial horizons are drastically depleted in potash al and th removal of al 2 o 3 negates normalization of chemical analyses of paleosols to al 2 o 3 for purposes of constant volume calculations th associated with sericite in the profiles increases at the contact with the overlying matinenda formation in association with rutile and leucoxene owing to interaction with diagenetic u bearing fluids from overlying sediments rutile and leucoxene originate from parent rocks and are a late stage form of mineralization these titaniferous phases indirectly contributed to the local dominance of brannerite type orc through diagenetic processes of mineralization involving the pronto reaction paleotopographic greenstone highs are related to local anomalously high concentrations of heavy minerals in the brannerite rich orc this involves hydraulic deposition of heavy minerals in the lee of crescent shaped greenstone highs with subsequent diagenetic upgrading granodiorite derived paleosol contains 5 10 times more au than the denison paleosol and is modestly enriched above background a slight decrease in au content upward evident in all profiles is an artefact of erosion of the top of the paleosols

the distribution of fe mn ni cr and co between the acid soluble and fe oxides and hydroxides and matrix fractions of the gercus red beds of northeast iraq abstract twenty samples of the gercus middle eocene red marl and carbonate of northeast iraq have been analysed for their mn cr ni co and fe content in the hcl soluble and free fe oxide and hydroxide phases the greater bulk of hcl soluble mn is associated with carbonate minerals only trace amounts up to 120 ppm of mn are associated with free fe oxides and hydroxides hcl soluble cr ni and co varies between 12 and 67 68 and 529 and 14 and 41 ppm respectively these constitute 4 5 26 and 36 9 respectively of their total content in the samples good positive correlation was found between free fe oxides and hydroxides and the associated cr ni co and mn content cr ni and co was found to be enriched in the free fe oxides and hydroxides relative to their total content in the main matrix enrichment factors are in the order co 5 0 ni 3 5 cr 2 4 this together with the similar partition order of these elements in the hcl soluble phase is in agreement with the relative mobility of these elements during the weathering transportation and deposition regime of the sediments

rb sr geochronology of chalcopyrite from the chehugou porphyry mo cu deposit northeast china and geochemical constraints on the origin of hosting granites the chehugou porphyry mo cu deposit is located ca 300 km north of beijing in the boundary zone between the archean north china craton and the neoproterozoic mesozoic central asian orogenic belt using hydrothermal chalcopyrite from this deposit we are able to show for the first time that the rb sr isotope system in massive nonfractured chalcopyrite grains can provide reliable age constraints for mo cu deposits we analyzed two chalcopyrite samples from slightly different petrogenetic environments showing contrasting texture and deformation history five 2 to 5 mg fragments of a single nonfractured chalcopyrite grain containing spatially isolated inclusions of k mica k feldspar and quartz yielded an rb sr isochron age of 256 7 ma 2 including uncertainty for this sample the dense chalcopyrite matrix apparently inhibited diffusion of rb and sr after chalcopyrite crystallization and the age should therefore reflect the time of crystallization of chalcopyrite from the mo cu mineralizing fluids the evidence for mo cu mineralization during the late permian requires a revision of the previous notion that the chehugou deposit was formed during the yanshanian orogeny lasting from 200 to 60 ma fragments of a second chalcopyrite sample that in contrast to the first had experienced deformation as indicated by intragranular fractures and alignment of k mica and k feldspar inclusions along these fractures this sample yielded a clearly younger rb sr isochron age of 207 15 ma 2 this age obviously reflects an isotopically open system due to fluid movement and or prolonged diffusion of rb and sr along the fractures single biotite crystals from an associated monzogranite yielded an rb sr isochron age of 250 ma which is interpreted as a lower age limit for the mo cu mineralization and the time when the granite cooled below 400 to 300 c considering the field evidence for a broadly contemporaneous origin of the mo cu mineralization and the hosting granitoids we suggest that the granitoids are not much older than ca 260 ma the mo cu hosting granitoids range in composition from monzogranite to highly evolved syenogranite with high la yb and sr y ratios initial end values of ca 21 to 23 nd crustal residence times of the sources 1 9 to 2 7 ga indicate melting of the predominantly archean north china craton and a subordinate juvenile mantlederived component much older u depleted lower crustal sources for the granitoids are supported by high initial 208pb 204pb ratios lithospheric delamination and underplating of hot mantle derived material may have facilitated crustal melting in a late orogenic to postcollision

re os isochron ages for arsenopyrite from carlin like gold deposits in the yunnan guizhou guangxi golden triangle southwestern china abstract the yunnan guizhou guangxi golden triangle is considered to be one of the regions hosting carlin like gold deposits in china gold deposits in this region can be grouped into lode type that are controlled by faults and layer like type controlled by stratigraphy arsenopyrite is one of the major gold bearing minerals in these deposits rhenium os isotopic dating of arsenopyrite from the lode type lannigou and jinya and the layer like type shuiyindong gold deposits yields isochron ages of 204 19 ma 206 22 ma and 235 33 ma respectively the data suggest that the carlin like gold deposits formed in late triassic to early jurassic which is clearly earlier than the ca 100 80 ma acid to ultra basic magmatism in this part of southwestern china the ages are consistent with ore formation during a period of post collisional lateral transpression which is similar to that of the carlin like gold deposits in western qinling of china but quite different from carlin type gold deposits in nevada u s a

he pb and s isotopic constraints on the relationship between the a type qitianling granite and the furong tin deposit hunan province china abstract the furong tin deposit located in southern hunan province china is a large newly discovered deposit with an estimated sn reserve of about 700 000 tons the deposit is spatially and temporally associated with the a type qitianling granite the 3he 4he ratios of fluid inclusions trapped in sulfides from the deposit range from 0 13 to 2 95 ra indicating a mixed crust mantle source similar to that of the qitianling granite complex lead isotopes in feldspars of the granite mostly in the range of 206pb 204pb 18 547 19 180 207pb 204pb 15 598 15 825 208pb 204pb 37 912 39 068 and in sulfide minerals 206pb 204pb 18 467 18 836 207pb 204pb 15 503 15 772 208pb 204pb 38 607 39 099 are essentially the same indicating that the lead in both was derived mainly from the upper crust with a small mantle component the sulfur isotopic values of the ore minerals vary widely ranging from 26 1 to 10 4 but are mainly within the range of 0 2 to 10 4 implying that the s in the hydrothermal fluids was derived mainly from magmatic fluids with minor contributions from the mantle sedimentary rocks and biogenic material the he pb and s isotopes all confirm that the ore forming fluids of the furong deposit were magmatic in origin derived from the melts that produced the qitianling a type granite the tin mineralization occurs within or along the margins of the qitianling granite complex and the timing of the mineralization coincides with the intrusive age of the granite the available data suggest that the emplacement of the granites and the mineralization was related to mantle upwelling and extension of the lithosphere in south china during the mesozoic

metalliferous manganese oxide mineralization associated with the boleo cu co zn district mexico apart from its large reserves of cu co zn mineralization contained within stratiform ore beds or mantos the boleo district of central baja mexico also contains significant concentrations of mn oxides typically 2 3 wt mn interspersed with hydrothermal sulfides and both hydrothermal and weathering related metal oxide minerals within the mantos mn oxides occur as concentric nodules disk shaped concretions laminae granules or aggregates veins dendrites and various replacements the oxides are composed of varying amounts of hollandite cryptomelane todorkite romanechite pyrolusite and x ray amorphous mn oxide chemically the manto oxides are unique owing to their extraordinarily high abundances of co cu pb and zn typically 2 5 wt but up to 23 wt existing mineralogical and geochemical classifications are ambiguous regarding the genetic classification of mn oxides within the mantos a new mno 2 fe 2 o 3 t mgo diagram is proposed in order to discriminate among highly metalliferous mn oxides based on the new classification scheme manto mn oxides record a complex interaction between hydrothermal and diagenetic processes to better understand the mechanism of oxide deposition radiogenic isotopes sr and pb and ree geochemistry were used to delineate fluid and metal sources isotopic and ree constraints indicate that the boleo mn oxides are largely hydrothermal in origin however they show varying degrees of modification resulting from diagenetic processes hydrothermal mn oxides are syngenetic synsedimentary to syndiagenetic in origin and were precipitated in association with sulfides reflecting localized variations in redox conditions within the manto sequence due to the downward infiltration of metal bearing brines apart from morphological and stratigraphic evidence e g occurrence of nodular crusts along the upper contact of the manto a syngenetic origin is supported by a single k ar date of 7 0 0 2 ma which is within the estimated age range for deposition of boleo formation clastic sediments interaction between brine and seawater or brine and pore fluid as it infiltrates the sedimentary pile produced hydrothermal precipitates with certain hydrogenetic attributes i e positive ce anomaly lree enrichment on the other hand oxides with hydrogenetic and with mixed hydrothermal hydrogenetic affinities represent diagenetic alteration and remobilization of earlier formed hydrothermal oxides by meteoric fluids by far the greatest degree of remobilization occurred in response to compactional dewatering of the manto where the dewatering pore waters enriched the uppermost manto strata in mn fe zn co and to lesser degrees cu later diagenetic modifications coincided with the development of a supergene overprint which typifies boleo formation strata at elevations above the present day water table

archaean metasedimentary rocks from the northwestern pontiac subprovince of the canadian shield chemical characterization weathering and modelling of the source areas abstract the northwestern pontiac subprovince is dominated by a monotonous greywacke sequence metamorphosed and deformed during the late archaean kenoran orogeny limited chemical weathering of the source rocks is suggested by 1 low values of the chemical index of alteration 2 no preferential leaching of ca sr and ba 3 well defined correlations among mgo k2o and al2o3 and 4 small variations of cr ni the source was dominantly felsic as indicated by high th sc average 0 39 la co 1 06 zr cr 0 7 zr y 11 2 and sio2 mgo 19 4 the composition of these metasedimentary rocks can be modelled by mixing of three end member components 1 tonalites trondhjemites 65 in order to explain the sio2 al2o3 th u zr sr and ba abundances na k ratios strong depletion in hree and hfse relative to lree and lile low th y and k2o and fractionated la yb 19 4 2 komatiites 5 in order to explain the high cr 220 ppm and ni 66 ppm contents and 3 tholeiitic basalts 30 accounting for the observed tio2 0 62 wt v 144 ppm and sc 17 ppm concentrations the source region may be considered as a deeply eroded greenstone belt intruded by abundant tonalite trondhjemite plutons possibly now located to the south and east in the grenville province or possibly to the north underlying the dominantly volcanic abitibi subprovince