characteristic straight chain lipid ratios as a quick method to assess past forest paramo transitions in the ecuadorian andes to assist sustainable reforestation efforts in the andes in northern ecuador the position of the natural upper forest line ufl has to be assessed to this end new vegetation reconstruction techniques to complement traditional reconstruction methods such as pollen analysis are being developed one such technique is the biomarker ratio approach that uses changes in characteristic ratios of extractable lipids such as n alkanes and n alcohols for a quick assessment at high spatial resolution of abrupt past vegetation changes in the present study we assessed the applicability of this approach as indicator of past vegetation shifts from forest to paramo or vice versa in northern ecuador we looked at the n alkane and n alcohol signals of two soil monoliths one taken in a forest patch located 100 m above the current ufl and the other at the same altitude in the surrounding paramo the monoliths were sampled to a depth corresponding to at least 1500 cal yr bc links were sought between biomarker ratio signals in soil organic matter som and those found in plants from the vicinity during previous research based on the outcome an attempt was made at determining whether the forest patch had been part of the continuous forest further down slope during the last 3500 cal years results show that specific ratios of extractable straight chain lipids can be used to get a quick indication of whether an area was forested or not in the past in som the n alkane relationship c29 c31 1 combined with the n alcohol relationship c22 c24 1 was found to be characteristic for dominant forest vegetation while the opposite relationships were indicative for past paramo vegetation the n alkane relationship could be explained very well by the lipid ratios of the current forest and paramo vegetation in the area while agreeing well with the n alkane signal the n alcohol signal was less robust probably partially due to degradation of wax esters in the soil contrary to expectations we conclude that the investigated forest patch was never part of the continuous forest in the vicinity in the past 3500 cal years instead our biomarker ratio approach suggests that the forest patch soil was once covered by paramo vegetation overall this study shows that the biomarker ratio approach in volcanic ash soils can serve as a quick method for an assessment of abrupt vegetation changes such as associated with past ufl shifts at a high spatial resolution and at the location where the shift occurred as such it is highly complementary to traditional proxies such as pollen analysis

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

rare earth element geochemistry of the metamorphosed volcanogenic massive sulfide deposits of the manitouwadge mining camp superior province canada a potential exploration tool trace and rare earth element bee geochemistry indicates that rocks in the manitouwadge mining camp were derived from three major lithological units mafic volcanic rocks acid volcanic tuffs and dacites the geco willroy willecho and big nama creek cu zn ag deposits are contained within the 2720 ma acid volcanic tuffs our study suggests that the thickness of the felsic volcanic unit acid tuffs and volcaniclastics may be significantly underestimated in the area medium to high grade metamorphism upper amphibolite lower granulite gave rise to specific alteration assemblages which crystallized during several episodes of deformation and plutonism because major element geochemistry of the rocks was modified during ore forming processes and later by several episodes of metamorphism and tectonism the present alteration minerals merely reflect the cumulative effect s of these episodes and are often misleading in the identification of the protoliths thus due to extensive alteration the protoliths of various lithological units can be positively identified only from trace and rare earth element geochemistry extensive up to 97 light ree depletion was observed in the felsic volcanic rocks around the geco willroy and willecho deposits the positive correlation between bee mobility and mineralization suggests that ree geochemistry can be successfully used in the exploration for volcanogenic massive sulfide deposits around the manitouwadge mining camp the absence of a well defined discordant alteration pipe at geco and localized enrichment in fe al or k at the willroy willecho big nama creek and geco deposits implies that they may be highly metamorphosed equivalents of mattabi type deposits where the original iron rich carbonates have recrystallized to calc silicate or amphibole rich assemblages during regional metamorphism localized enrichment in fe al and k in the felsic tuffs could be used to identify possible alteration pipes or semicomformable alteration zones associated with mineralization

modeling of water rock interaction in the mackenzie basin competition between sulfuric and carbonic acids the chemical weathering of continental surfaces depends on many factors including lithology climate tectonics erosion soil or vegetation and also on the availability of acidity in the weathering zone in addition to atmospheric soil co2 sulfide oxidation may represent a significant source of protons for weathering reactions as shown previously for the rivers draining the mackenzie basin canada here a numerical model describing continental weathering reactions based on laboratory kinetic laws is coupled to a dynamic global vegetation model the b witch model in order to estimate the impact of sulfide oxidation on chemical weathering and associated atmospheric co2 consumption fluxes throughout the mackenzie river basin the model is first calibrated with available field data for the various sub basin of the mackenzie watershed and then a simulation is performed removing the contribution of sulfuric acid to the weathering system the main outcomes of the present study are that 1 the dissolved silica export is controlled by secondary minerals reactivity in soils and the calcium and magnesium fluxes are driven by the dissolution of calcite and dolomite 2 the atmospheric co2 consumption by weathering processes in the mackenzie river is limited accounting for only 24 of the total bicarbonate flux to the ocean confirming a previous study and suggesting that weathering processes in the mackenzie watershed acts as a source of carbon to the atmosphere at the geological timescale and 3 the presence of sulfide minerals within a river basin decreases the apparent net consumption of atmospheric co2 through chemical weathering we show that the actual production of sulfuric acid in the weathering zone of the mackenzie basin reduces the net atmospheric co2 consumption by about two compared to what the atmospheric co2 consumption should be in the absence of sulfide minerals sulfuric acid driven chemical weathering has thus to be considered at both short and long timescales when looking at the link between chemical weathering and the global carbon cycle

timing of gold mineralization in the hutti gold deposit dharwar craton south india the hutti orogenic gold deposit in the eastern dharwar craton of south india is located in a cuspate greenstone belt which is tectonically juxtaposed against tonalite trondhjemite granodiorite ttg basement on its western margin the host rocks to gold mineralization are mafic and felsic volcanic rocks metamorphosed to the amphibolite facies mineralization is confined to nine broadly parallel quartz reefs within north south to north northwest south southeast trending shear zones that dip approximately 70 w six of these 2 to 10 m thick boudinaged veins have been mined to a depth of over 810 m free gold occurs in the veins and alteration haloes and is spatially and temporally associated with quartz and disseminated pyrite and arsenopyrite which in turn are closely associated with hydrothermal monazite and xenotime in the biotite plagioclase wall rock alteration around veins gold is considered to have been deposited during d 2 to d 3 deformation broadly coincident with the emplacement of syntectonic granitoids the history of volcanism granitic magmatism and gold mineralization is defined by u pb geochronology of magmatic zircons and hydrothermal monazite and xenotime the felsic volcanic host rocks have a u pb zircon age of 2587 7 ma about 40 m y older than the age of gold mineralization at 2547 10 ma determined from hydrothermal monazite the syntectonic kavital granitoid has a u pb zircon age of 2545 7 ma which overlaps with the timing of gold deposition and is consistent with structural interpretations the ramagiri and kolar gold deposits elsewhere in the dharwar craton are considered to have a similar structural timing and the hutti geochronology suggests that gold mineralization occurred throughout the dharwar craton some 80 to 120 m y later than the major peak of late archean world class orogenic gold mineralization in most other archean cratons

discrete mineralization events at the hongtuling au mo vein deposit in the xiaoqinling district southern north china craton evidence from monazite u pb and molybdenite re os dating abstract the xiaoqinling district the second largest gold producer in china is situated on the southern margin of the north china craton and immediately to the north of the qinling orogen the timing and genesis of the gold deposits have been hotly debated because the area has undergone multiple tectono magmatic events since the stabilization of the north china craton in the early paleoproterozoic whether they are genetically related to the triassic orogeny that formed the qinling orogen or associated with the early cretaceous tectonic reactivation of the craton remains controversial here we present monazite u pb and molybdenite re os dating results from the hongtuling vein deposit in the eastern part of the xiaoqinling district to provide new insights into the age and tectonic setting of gold mineralization the hongtuling deposit consists of gold veins at the top and minor molybdenum veins at the bottom with molybdenum veins being locally crosscut by gold veins molybdenum veins mainly consist of calcite quartz k feldspar molybdenite and pyrite with minor amounts of galena and a variety of accessory minerals gold veins are dominated by quartz and pyrite with minor to trace amounts of chalcopyrite galena sphalerite and sericite monazite grains are well developed both in molybdenum and gold veins and are intergrown with molybdenite and pyrite respectively monazites from gold vein contain lower rees contents more prominent negative eu anomalies and higher th u ratios than those from molybdenum vein the textural and geochemical evidence indicates that monazites from both veins precipitated from contrasting ore forming fluids laser ablation icp ms u pb dating of monazite from the molybdenum vein yields a 206pb 238u age of 203 5 8 1 ma mswd 0 23 2 which is statistically indistinguishable from the molybdenite re os age of 204 ma in contrast monazite from the gold vein has a significantly younger 206pb 238u age of 130 4 5 3 ma mswd 0 99 2 results presented here combined with independent studies suggest that the molybdenum and gold veins of the hongtuling deposit and by inference the other deposits in the district formed in two discrete mineralization events in the late triassic and early cretaceous the molybdenum mineralization is most likely related to the post collisional magmatism associated with the qinling orogeny whereas gold mineralization occurred in an extensional setting associated with the decratonization of the north china craton

in situ synchrotron radiation xrf study of ree phosphate dissolution in aqueous fluids to 800 c abstract the temporal evolution of the concentrations of la ce pr nd sm gd y pb th and u in the fluid during dissolution of synthetic lapo 4 monazite natural monazite and xenotime in aqueous hcl nacl solutions was studied in situ at temperatures from 25 to 800 c and pressures to about 2 gpa using hydrothermal diamond anvil cells and synchrotron radiation xrf analyses constant within error la concentrations in the fluid were attained in less than 50 min at temperatures 300 c and in less than 90 min at 200 c at 100 c the time required to reach a constant la concentration varied with the hcl molality from less than 3 h at 5 1 m hcl to 11 h at 1 m hcl the experiments indicate a significantly lower mobility of y gd and th compared to that of the lree particularly la over a large range of crustal p t conditions if controlled by interaction of monazite with acidic and chloridic fluids the corresponding change in the ree pattern is in close agreement with literature reports on natural monazites which underwent greisenization or sericitization the th pb ratio in the fluid increased with temperature and hcl concentration but was far below the th pb ratio in the monazite even at 600 c and 2 gpa the experimental results imply that monazites leached in acidic and chloridic fluids are characterized by a strong enrichment of th relative to the lree and pb

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

timing and genesis of cu au mineralization in the khetri copper belt northwestern india constraints from in situ u pb ages and sm nd isotopes of monazite ce the khetri copper belt kcb in northwestern india contains several economically important hydrothermal cu au deposits orebodies in these deposits are locally rich in monazite ce in this study in situ u pb ages and sm nd isotopic compositions of monazite ce are used to constrain the timing of mineralization and to better understand the genesis of the cu au deposits monazite ce crystals were identified in the madhan kudhan and kolihan deposits in the kcb most monazite ce crystals in the two deposits show close textural associations with hydrothermal minerals biotite chlorite and sulfide and have low contents of tho2 mostly 2 wt indicating a hydrothermal origin the hydrothermal monazite ce crystals have u pb ages of 833 5 to 840 6 ma which are interpreted to represent the timing of the mineralization in the kcb another set of monazite ce crystals in the kolihan deposit has relatively high contents of tho2 4 72 wt on average and commonly shows concentric zonation with respect to th they have a weighted average 207pb 206pb age of 1362 29 ma which may record a pre ore metamorphic event in the kcb hydrothermal monazite ce crystals from the madhan kudhan deposit have end t 835 ma values ranging from 4 3 to 16 8 9 6 on average indicating that isotopically heterogeneous materials were in the metal sources or along the flow paths of hydrothermal fluids the ages of cu au deposits in the kcb fall within the age range of the regional ca na metasomatism 830 to 850 ma combining this temporal association with relevant geochemical and isotopic data we propose that circulation of hydrothermal fluids caused widespread ca na metasomatism mobilized certain ore metals and thus facilitated the formation of cu au deposits

element behaviour during interaction of magma and fluid a case study of chamuhan granite and implications on the genesis of w mo mineralisation abstract the chamuhan granite is located in the eastern part of the central asian orogen where it crops out as an elongated ne trending composite monzogranite the pluton consists of two phases with a fine grained monzogranite g2 at depth in sharp contact with a medium grained monzogranite g1 above the medium grained monzogranite can be subdivided into g1a and g1b based on the degree of metasomatism affecting it with the g1b being more altered tungsten molybdenum mineralisation is hosted by quartz fluorite veins or forms disseminated sulfides in g1a indicating a genetic association between the monzogranite and ore magmatic zircons from g1a yield a weighted mean age of 144 2 ma and hydrothermal zircons from g1a yield a weighted mean age of 143 1 ma indicating that the hydrothermal zircons are very close in age to the medium grained monzogranite monazite grains yield u pb isotope ages of 138 3 ma for g1a 137 1 ma for g1b and 139 2 ma for the fine grained monzogranite g2 phase these dates are the same within analytical error and are coeval with the molybdenite re os weighted mean age of 140 2 ma indicating that the monazite and molybdenite were deposited during hydrothermal alteration the chamuhan granite is geochemically a metaluminous to slightly peraluminous high k calc alkaline granite and is especially characterised by its ree tetrad pattern and a huge eu depletion that are accompanied by a non charge and radius controlled charac trace element behaviour this and the o isotopic data from the granite phases are indicative of a highly differentiated magma that interacted strongly with a co existing fluid emanating from the magma during the late stage of its crystallisation the interaction between the magma and related hydrothermal fluid resulted in the enrichment of w mo nb ta th u hf rb y all the studied granitic rocks have homogeneous initial isotope values with positive end t values of 0 1 3 and tdm2 dates between 924 and 691 ma this is consistent with granites derived from a pre existing juvenile crust derived from a depleted mantle during the neoproterozoic the molybdenite in the chamuhan w mo deposit has a narrow 34svcdt range of 0 1 1 6 characteristic of a magmatic origin and the pb isotopic compositions with 206pb 204pb ratios between 18 298 and 18 882 207pb 204pb ratios between 15 494 and 15 538 and 208pb 204pb ratios between 38 046 and 38 206 are similar to the calculated initial pb isotopic ratios of the chamuhan granite we thus suggest that there is an intimate relationship between the chamuhan granite and mineralisation and that the mineralising process is related to a post collisional extensional event following the formation of an over thickened continental crust and during closure of the mongol okhotsk and paleo pacific oceanic plates

a shear hosted au cu bi metallogenic event at 1660 ma in the tennant creek goldfield northern australia defined by in situ monazite u pb th dating abstract high grade au cu and bi ores in the tennant creek goldfield have been mined from hydrothermal magnetite and or hematite rich ironstone bodies less well known is a style of au cu bi mineralisation hosted by quartz vein systems within shear zones outside ironstones we report ion probe shrimp u pb th ages of 1659 13 ma and 1659 15 ma for hydrothermal monazite associated with this mineralisation style at the orlando east au cu bi deposit and navigator 6 au prospect respectively the dated monazite at orlando east is intergrown with cu and bi sulfides and au in quartz chlorite veins within a shear zone at navigator 6 the monazite occurs both in late stage chalcopyrite bearing quartz hematite veins and within earlier formed sheared chloritic breccia that also contains anomalous au although the full significance of the 1660 ma monazite ages has yet to be determined the results indicate the introduction of au cu and bi in quartz vein systems at 1660 ma or remobilisation of earlier 1850 ma main stage au cu bi from mineralised ironstones and into quartz veins 10 s 100 s of metres from the initial mineralisation in either case hydrothermal fluids capable of transporting significant concentrations of ore metals were present in the tennant creek goldfield at 1660 ma synchronous with deformation a key implication is that rock sequences up to 200 million years younger than the ironstone hosted au cu bi deposits may now be considered prospective for a second stage of au cu bi mineralisation the results also validate non ironstone shear hosted deposits in the tennant creek region as an alternative exploration target to the well known high grade but low tonnage tennant creek ironstone hosted deposits

timing of skarn gold deposition in the giant beiya polymetallic gold deposit southwest china constraints from in situ monazite sims u th pb geochronology abstract robust dating of hydrothermal deposits is critical to understand ore genesis which depends on judicious selection of mineralization related chronometers especially for complex polymetallic mineral systems the beiya deposit in southwest china is a world class polymetallic gold system 11 9 moz au at a grade of 2 52 g t and the main mineralization is considered as skarn type however available dating results for the gold mineralization give a wide range of ages which in some cases could be inaccurate due to the use of non matrix matched external isotope standards or an equivocal relationship between gold and the dated minerals in this contribution hydrothermal monazite coexisting with gold bearing ore minerals magnetite pyrite and chalcopyrite from high grade massive magnetite sulfide gold ores at beiya was dated in situ using secondary ion mass spectrometry sims the u th pb analyses of hydrothermal monazite yielded a 208pb 232th age of 36 0 0 5 ma 2 mswd 2 0 n 27 which is considered a robust age for the beiya skarn gold mineralization our study supports a genetic link between the skarn gold mineralization and the post collisional quartz monzonite magmatism at beiya based on a new zircon u pb age of 37 2 0 4 ma compared with the previously reported molybdenite re os and sphalerite rb sr isochron ages our monazite u th pb result suggests that the gold deposition was broadly coeval with the formation of molybdenite but probably prior to the local pb zn ag mineralization at beiya

sims u pb dating of vein hosted hydrothermal rutile and carbon isotope of fluids in the wulong lode gold deposit ne china linking gold mineralization with craton destruction abstract wulong is the largest lode gold deposit in the liaodong peninsula northeastern north china craton ncc gold mineralization mainly occurs in the quartz sulfide veins which are hosted in jurassic monzogranite and early cretaceous diorite dikes here rutile grains are firstly identified in the auriferous quartz pyrite vein the vein hosted rutiles have textural associations with quartz chlorite pyrite and bi sulfosalts and host fluid inclusions indicating that they are unequivocally of hydrothermal origin and co precipitate with gold the rutile grains are characterized by high w and v concentrations and u shaped rare earth elements pattern with the greatest depletion in mree due to excess zr incorporation during fast rutile crystal growth process from the f rich ore forming fluids zr in rutile thermometers provide unrealistic crystallization temperatures 550 c which are much higher than the previous homogenization temperatures data of fluid inclusions yu et al 2018 all these geochemical signatures also support that rutiles formed from the hydrothermal fluids the 13c values of co2 gases in low salinity aqueous carbonic fluid inclusions from the mineralized quartz range from 9 6 to 1 7 average 5 7 indicating mantle magmatic sources for the ore forming fluids sims u pb dating yields a more precise and robust age of 122 3 1 1 ma n 23 mswd 0 82 for the gold mineralization at wulong this new date is roughly coeval with the ore hosted diorite dikes and the sanguliu granitic pluton most in 125 120 ma such close temporal association provides additional weights of evidence for a magmatic affinity to the gold formation regionally the rutile u pb age indicates that the gold mineralization occurs in an extensional tectonic regime caused by the thinning and destruction of the lithosphere beneath the ncc meanwhile the timing of gold mineralization is the same as the peak age of ncc destruction therefore we propose that the wulong deposit has a genetic link with this craton destruction this is similar to numerous other early cretaceous gold deposits across the ncc such as those in the xiaoqinling and jiaodong districts our study indicates that rutile is a robust u pb chronometer for the lode gold deposit but may be not a good geothermometer in the case of f rich hydrothermal fluid system

u pb shrimp geochronology of th poor hydrothermal monazite an example from the llallagua tin porphyry deposit bolivia in situ u pb shrimp analysis of hydrothermal monazite virtually free of th and poor in u 0 2 ppm th 40 103 ppm u from the world class llallagua tin porphyry deposit in bolivia defines a mineralization age of 23 4 2 2 ma mswd 0 48 confirming earlier k ar sericite alteration age data these ages are however in contrast with a weighted mean single crystal 207pb 206pb evaporation age of 39 3 6 0 ma and a related pb pb inverse isochron age of 42 4 4 0 ma mswd 0 66 on zircon from a post porphyry dike as well as with an earlier single crystal sm nd apatite isochron age our data points to a significant time gap between emplacement of the ore hosting porphyry intrusion magmatism and its hydrothermal overprint tin mineralization suggesting long lived magmatic hydrothermal activity in this part of the andean back arc crust the decoupling of porphyry magmatism and hydrothermal activity may explain the unusual occurrence of relatively little fractionated felsic rocks together with extensive tin mineralization our study demonstrates the usefulness of the application of the u pb shrimp method to direct age determination of ore mineralization using th poor hydrothermal monazite even when dealing with geological young events the common assumption of synchronous magmatism and hydrothermal ore formation in porphyry systems may not always be warranted

geochronology and geochemistry of multiple generations of monazite from the wepawaug schist connecticut usa implications for monazite stability in metamorphic rocks u pb isotope analyses rare earth and trace element analyses and petrographic observations are presented for monazites from the wepawaug schist in southern connecticut usa two samples of kyanite zone schist were collected less than a meter apart each sample contains a different variety of monazite with distinct morphology chemistry and pb isotopic composition one sample preserves a largely amphibolite facies mineralogy including kyanite staurolite garnet biotite and chlorite with little textural evidence of later shearing monazites from this sample are xenoblastic with about 1 wt tho2 0 3 wt cao and a more lree enriched pattern than monazites from the second sample these xenoblastic monazites preserve textural evidence of a retrograde reaction to apatite which involves chlorite indicating that these monazites became unstable during retrograde chloritization of biotite these monazites give strongly discordant u pb ages which fit a chord with an upper intercept age of 411 18 ma interpreted as the minimum growth age of these xenoblastic monazites perhaps during amphibolite facies metamorphism the second sample contains s c banding evidence of dynamic recrystallization and abundant retrograde chlorite this sample contains idioblastic monazites with about 3 wt tho2 0 8 wt cao and with less fractionated ree patterns these monazites give close to concordant u pb ages with a mean 207pb 206pb age of 388 2 ma this age is interpreted as probably representing the time of monazite growth during retrogression of the sample from an amphibolite to greenschist facies mineralogy

monazite chemical composition some implications for monazite geochronology an investigation of the chemical composition of monazite from a number of localities has been carried out samples used include monazites from metamorphic rocks granitic rocks and a hydrothermal ore deposit the ree distribution pattern of monazite varies greatly in accordance with its geological environment a remarkable feature of the monazites studied is that their chondrite normalised ree distribution patterns are mostly uniform between grains within the same sample but differ significantly from sample to sample this characteristic apparently indicates that there is an important effect on the ree distribution of monazite exerted by the host rock or source material from which monazite crystallised another important feature shown by the monazites studied is that monazites in rocks containing garnet as a major mineral show extreme depletion of hree whereas monazites in rocks without garnet or monazite that formed after the garnet breakdown contain significantly higher amounts of y and hree this suggests that the phase assemblage especially garnet plays an important role in the ree distribution of monazites in these rocks the value of ree distribution in monazite is exemplified with regard to the origin of monazite in the lewisian metamorphic rocks which is a fundamental issue in monazite geochronology

elevated equilibrium geotherm in stable continental shield evidence from integrated structural hydrological and electromagnetic studies on nonvolcanic hot springs in the eastern ghats belt india

uranium and gold deposits in the pine creek orogen north australian craton a link at 1 8 ga abstract the pine creek orogen pco in the north australian craton nac hosts world class unconformity related u deposits and numerous orogenic or intrusion related au deposits whose timing and genesis are the subject of ongoing controversy this study reports new geochronology results for an unconformity related u deposit ranger 1 number 3 orebody to constrain the timing of processes leading to alteration development and u mineralisation within a regional geological and metallogenic context it also examines why some u deposits in the eastern pco contain elevated au concentrations unlike their unconformity related u counterparts in canada and elsewhere key results are as follows i the ranger 1 deposit and the pco au deposits share several characteristics of hydrothermal mineralogy including chlorite white mica monazite xenotime bearing alteration assemblages some sulfides pyrite chalcopyrite silica quartz veining or silicification and au ii the primary host structure at the ranger 1 deposit is a shear zone which was reactivated at low grade metamorphic conditions as during formation of many of the syn tectonic au deposits in the pco iii ion probe u pb dating of low th monazite in an assemblage of hydrothermal white mica and fe rich chlorite from an outer alteration zone at the ranger 1 no 3 orebody yielded an age of 1800 9 ma this age is 60 million years earlier than the oldest previously reported age of unconformity related u mineralisation in the pco and is within error of several u pb ages reported for monazite and xenotime associated with au mineralisation in the pco iv iron rich chlorite intimately associated with the dated monazite is similar compositionally and texturally to chlorites in alteration zones at other u deposits in the pco two scenarios for the formation of the ranger 1 deposit are consistent with the available evidence we prefer a two stage model where an fe chlorite white mica monazite hydrothermal alteration assemblage with probable gold was introduced replacing medium grade metamorphic assemblages within a reactivated shear zone at ca 1800 ma contemporaneous with the formation of some au deposits within the pco subsequently u ore was formed within this environment at 1740 ma and or later via the reaction of oxidised u and mg bearing basin derived fluids with chemical reductants in the basement the new u pb geochronology result for monazite points to an important hydrothermal event at the site of the ranger 1 deposit during regional tectonothermal activity of the shoobridge event at 1 8 ga in the pco and suggests that this pre ore alteration and tectonism was a key factor in localising later unconformity related u mineralisation the pre ore alteration at 1800 ma at the ranger 1 deposit therefore provides a link between the genesis of the unconformity related u deposits and the orogenic or intrusion related au deposits that formed in the pco during the shoobridge event at the broader scale the newly identified 1800 ma hydrothermal activity at the ranger 1 deposit may be part of a craton wide metallogenic and tectonothermal event at 1 8 ga that includes au mineralisation in the pco and in the granites tanami orogen as proposed in other studies

in situ oxygen isotope analysis of monazite as a monitor of fluid infiltration during contact metamorphism birch creek pluton aureole white mountains eastern california monazite from the hydrothermal aureole of the cretaceous two mica birch creek plu ton in the white mountains of eastern california records the infiltration of magmatic fluids into the metasedimentary early cambrian deep spring formation monazite in the birch creek pluton displays concentric euhedral magmatic zoning 18 o 8 7 0 2 and th pb magmatic ages of 78 0 0 7 ma the middle deep spring formation 0 5 km east of the contact underwent moderate to low temperature alteration by f rich mag matic fluids monazite displays patchy zoning but has similar 18 o values 8 7 0 4 and th pb ages 78 3 1 6 ma to monazite in the birch creek pluton in contrast monazite from the upper deep spring formation 0 6 km west of the contact and outside the mapped hydrothermal zone shows concentric zoning 18 o 5 2 0 3 and partially reset detrital ages from 583 to 1069 ma deep spring formation monazite within the hydrothermal alteration zone dissolved and reprecipitated during magmatic fluid infiltra tion whereas monazite outside the zone was unaffected in contrast deep spring zircon within the hydrothermal alteration zone preserved its magmatic zoning and cambrian precambrian u pb ages zircon can reliably date events prior to hydrothermal activity whereas monazite being more susceptible to alteration by fluids is useful for mapping the extent and timing of fluid infiltration events

sulphate incorporation in monazite lattice and dating the cycle of sulphur in metamorphic belts microgeochemical data and transmission electron microscope tem imaging of s rich monazite crystals demonstrate that s has been incorporated in the lattice of monazite as a clino anhydrite component via the following exchange ca2 s6 ree3 p5 and that it is now partly exsolved in nanoclusters 5 10 nm of caso4 the sample an osumilite bearing ultra high temperature granulite from rogaland norway is characterized by complexly patchy zoned monazite crystals three chemical domains are distinguished as 1 a sulphate rich core 0 45 0 72 wt so2 th incorporated as cheralite component 2 secondary sulphate bearing domains so2 0 05 wt partly clouded with solid inclusions and 3 late s free y rich domains 0 8 2 5 wt y2o3 th accommodated as the huttonite component these three domains yield distinct isotopic u pb ages of 1034 6 1005 7 and 935 7 ma respectively uranium th pb epma dating independently confirms these ages this study illustrates that it is possible to discriminate different generations of monazite based on their s contents from the petrological context we propose that sulphate rich monazite reflects high temperature fe sulphide breakdown under oxidizing conditions coeval with biotite dehydration melting monazite may therefore reveal the presence of s in anatectic melts from high grade terrains at a specific point in time and date s mobilization from a reduced to an oxidized state this property can be used to investigate the mineralization potential of a given geological event within a larger orogenic framework

regional scale cretaceous albitization in the pyrenees evidence from in situ u th pb dating of monazite titanite and zircon abstract albitization is a common metasomatic process active in various geodynamic contexts in the northern pyrenees there are several occurrences of albitites but until now only one occurrence has been dated 117 ma ar ar dating this paper presents new u th pb ages for several albitite occurrences throughout the pyrenees to test whether they are contemporaneous and if so to specify the regional extent of the albitization event ages obtained from large euhedral titanite and monazite grains from distinct albitites are 110 8 and 98 2 ma respectively the zircon u th pb isotopic system did not record this cretaceous metasomatic event even when grains were selected in metasomatically zr enriched rocks or in hydrothermal structures millimetre sized veins cross cutting granitoids we argue that the total time span of 20 ma recorded by albitites corresponds to a long lived hydrothermal system that was active during the rotation of iberia around europe along the north pyrenean fault because albitization and talc mineralization have the same spatial and temporal distribution in the pyrenees we argue that these two metasomatic phenomena are two independent records of this single regional scale long lived hydrothermal system

provenance implications of th u pb electron microprobe ages from detrital monazite in the carboniferous upper silesia coal basin poland abstract this paper reports the results of chime chemical th u pb isochron method dating of detrital monazites from carboniferous sandstones in the upper silesia coal basin uscb a total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence age distributions were identified in detrital monazites from the uscb sequence and correlated with specific dated domains in potential source areas most monazites in all samples yielded ca 300 320 ma variscan ages however eo variscan caledonian and cadomian ages were also obtained the predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic bohemian massif bm which suggests that various crystalline lithologies in the bm were the dominant sources of uscb sediments

the 127 ma gold mineralization in the wulong deposit liaodong peninsula china constraints from molybdenite re os monazite u th pb and zircon u pb geochronology abstract the wulong deposit is a large tonnage deposit 80 t of au characterized by quartz vein style of gold mineralization in the liaodong peninsula china the auriferous quartz veins are mainly hosted by late jurassic gneissic two mica granite 165 157 ma and early cretaceous granodiorite 129 ma and are structurally controlled by nne and nw trending faults previous attempts to date the gold mineralization yielded ambiguous results 135 112 ma here we report the first in situ and direct age constraint for gold mineralization at wulong five molybdenite samples from mo bearing quartz pyrite veins yielded an isochron age of 127 6 2 3 ma in situ sims u th pb dating of hydrothermal monazite that coexists with gold bearing pyrite and quartz yielded a 208pb 232th age of 126 7 3 2 ma these robust ages together with new age data of the wulong host intrusion and post ore dike allow for a better interpretation of the ore genesis of the wulong deposit relative to a well constrained sequence of regional geological events zircon u pb dating of the wulong host intrusion gneissic two mica granite representing the oldest magmatic event at wulong gave a weighted mean age of 159 3 1 4 ma that is interpreted to be the magma emplacement age subsequent magmatic events are recorded by the early cretaceous dikes with zircon u pb ages between 127 and 113 ma a post ore diorite porphyry dike that crosscuts the early cretaceous dikes has a u pb zircon age of 121 5 1 5 ma all the lines of geochronology evidence suggest a distinct genetic link between the gold mineralization and the early cretaceous magmatism in the wulong orefield this episode of magmatism and mineralization corresponds to the lithospheric thinning within the northeastern north china craton which is triggered by the subduction of the paleo pacific plate

cyclic terpenoids of contemporary resinous plant detritus and of fossil woods ambers and coals abstract cyclic terpenoids present in the solvent extractable material of fossil woods ambers and brown coals have been analyzed the sample series chosen consisted of wood remains preserved in holocene to jurassic sediments and a set of of ambers from the philippines copalite israel canada and dominican republic the brown coals selected were from the fortuna garsdorf mine and miocene formations on fiji the fossil wood extracts contained dominant diterpenoid or sesquiterpenoid skeletons and aromatized species were present at high concentrations with a major amount of two ring aromatic compounds tricyclic diterpenoids were the predominant compounds in the ambers aromatized derivatives were the major components consisting of one or two aromatic ring species with the abietane and occasionally pimarane skeletons the saturated structures were comprised primarily of the abietane and pimarane skeletons having from three to five carbon c1 c2 etc substituents kaurane and phyllocladane isomers were present in only minor amounts bicyclic sesquiterpenoids as saturated and partial or fully aromatized forms were also common in these samples but only traces of sesterterpenoids and triterpenoid derivatives were found the brown coal extracts were composed of major amounts of one and two ring aromatized terpenoids with a greater proportion of triterpenoid derivatives than in the case of the woods and ambers this was especially noticeable for the german coal where the triterpenoids were predominant open c ring aromatized structures were also present in this coal steroid compounds were not detectable but some hopanes were found as minor components in the german brown coal an overview of the skeletal structure classes identified in each sample as well as the general mass spectrometric characteristics of the unknown compounds are included in the present paper it can be concluded from these structural distributions that aromatization is the main process for the transformation of terrestrial cyclic terpenoids during diagenesis constituting a general pathway for all terpenoids

characteristics and origin of the oak dam east breccia hosted iron oxide cu u au deposit olympic dam region gawler craton south australia oak dam east is a large 560 mt of 41 56 wt fe cu au u bearing massive fe oxide deposit in the northeastern gawler craton south australia it is one of several unmined deposits in the same province as the giant olympic dam deposit and it lies beneath more than 500 m of younger cover rocks the oak dam east breccia complex formed in a near surface environment and was characterized by an early history of skarnlike albite calc silicate magnetite formation from hypersaline 400 500 c fluids large scale brecciation was an early feature and the resulting complex was progressively filled in and replaced by 1 hematite and goethite hematite stage i 2 magnetite apatite quartz actinolite magnetite stage 3 hematite goethite quartz chalcedony pyrite chlorite monazite hematite stage ii and 4 chalcopyrite pitchblende illite hydromus covite florencite carrolite cu u au mineralization stage hematite stage ii assemblages are volumetrically most abundant and were formed from fluids of 1 to10 wt percent nacl equiv that were boiling at 170 to 190 c and had 18o values more negative than 3 7 to 1 7 per mil interpreted as meteoric water the upper 200 m of the breccia complex contains spectacular colloform hematite void fillings interpreted to have replaced hydrothermal goethite the cu u mineralized zones resemble olympic dam ore in terms of geometries being grossly subhorizontal 10 to 70 m thick and crosscutting with respect to the host breccias the mineralization is zoned vertically from pyrite 34s 6 to 0 at depth to shallower chalcopyrite 34s 14 to 7 high grade pitchblende occurs centrally within the chalcopyrite zone e g 10 m of 0 46 cu and 3 700 ppm u3o8 straddling a boundary between k mica illite alteration and underlying fe mg chlorite alteration the deposit is assigned to the 1570 to 1595 ma iron oxide cu au u event in the eastern gawler craton on the basis of its similarity to other cu au u deposits in the province an la icpms pb isotope age for monazite in hematite stage ii was calculated to be 1455 20 ma and possibly as young as 1370 54 ma to explain all isotopic data this is an age of isotopic resetting our preferred model is that cu u mineralization developed within a stratified hydrothermal brine complex analogous to the salton sea geothermal system copper fe and s in the deep brine was sourced from an evolving deep reservoir with local compositional controls on sulfur isotopes including cooling boiling and replacement of previous pyrite chalcopyrite u veins and disseminations formed as a result of mixing with overlying steam heated u rich saline ground water mixing induced cooling and dilution only occurred episodically following hydrofracturing events that ephemerally linked the brine layers within the substantially cemented upper complex by contrast high grade uo2 formation occurred as deep upflow waned via reaction of the upper brine with hematite stage ii fe mg chlorite along an interface that descended with time this resulted in an increase of u grades through time caused by leaching and reprecipitation

highly differentiated fluorine rich alkaline granitic magma linked to rare metal mineralization a case study from the boziguo er rare metal granitic pluton in south tianshan terrane xinjiang nw china abstract rare metal bearing alkaline granites have attracted extensive interests because of their economic significance the early permian 290 ma boziguo er alkaline granitic pluton exposed in the middle segment of the south tianshan terrane xinjiang nw china contain nb ta zr th u and ree bearing accessory minerals and host a large scale rare metal deposit the unalterated alkaline granites are mainly composed of alkali feldspars 40 vol orthoclase microcline and 30 vol albite quartz 20 vol arfvedsonite 5 vol and biotite 5 vol with accessory minerals at least including zircon monazite pyrochlore fe ti oxides xenotime bastnasite and astrophyllite the existence of two types of alkaline feldspars which respectively show nearly pure ab and or end member compositions suggest that the boziguo er pluton can be classified as subsolvus granites rare metal elements in the pluton are mainly contained by pyrochlore nb ta zircon zr hf th u and hree and monazite lrees grains mineral chemistry suggests that the pyrochlore and monazite are of primary igneous mineral based on morphology internal texture and mineral chemistry four types of zircons have been identified type i zircon may have crystallized from volatile undersaturated early stage magmas while type iia zircon crystallized from volatile fluorine saturated magmas the type iib and type iii zircons could have grown in an lree depleted silicate melt after the crystallization of the lree rich minerals e g monazite or an early aqueous fluid during the transition from a magmatic to hydrothermal system the type iv zircons can be regarded as low temperature hydrothermal ones a semiquantitative calculation based on mineral compositions of biotites yields 0 51 2 14 wt for f contents in granitic melts the high contents of fluorine in the hydrous minerals suggest a fluorine enriched characteristic for melt which would not only prolong the duration of the magmatic differentiation but can also enhance the solubility of ore forming elements in magma the magmatic differentiation was mainly dominated by fractional crystallization of alkali feldspar and amphibole extensive rare metal mineralization in the pluton likely occurred within a limited temperature interval and was related to the crystallization of a highly evolved intergranular melt at the latest magmatic stage

zonation of monazite in metamorphic rocks and its implications for high temperature thermochronology a case study from the lewisian terrain abstract monazite is a valuable chronometer for many geological processes and a proper interpretation for the age derived from monazite requires an adequate understanding of the behaviour of this phase and its chemical and isotopic systems during geological processes this contribution reports the results of a detailed study on chemical and isotopic zonation of monazite in lewisian granulites which is of general significance for monazite geochronology in high grade metamorphic rocks detailed investigations on two lewisian granulite samples using sem epma and sims have revealed that lewisian monazites frequently show petrographic chemical and age zonation the petrographical zonation which reflects the chemical compositional variation can be characterised as follows on the basis of the bse images 1 concentric zoning 2 patchy zoning and 3 intergrowth like zoning the chondrite normalised ree distribution patterns are remarkably similar between different zones of single monazite grains this rules out the possibility that any portion of a zoned monazite in these two samples is detrital in origin some possible mechanisms are proposed for the formation of monazite zonation these include 1 intergrowth of monazite crystals with different composition 2 episodic growth or regrowth of monazite in response to the change of environment conditions during thermal event s which may involve recrystallisation or replacement of the original crystals in short the diversity of zoning patterns in monazites observed in this study cannot be explained assuming a single mechanism accordingly interpretation of the chemical and age information from any zoned monazite requires an adequate understanding of its formation mechanism line scans of th u pb la ce nd sm ca and si across monazite zones have been performed on two monazite grains which experienced granulite facies metamorphism the very sharp boundaries in these line scans indicate that the diffusive transport of these elements in monazite is low even at the temperature of granulite facies metamorphism the effective closure of monazite grains may also depend upon other factors such as the armouring effects of the host phase and recrystallisation of the mineral itself thus great care needs to be taken for geological application of the closure temperature concept

4d history of the nimbus vhms ore deposit in the yilgarn craton western australia abstract due to its unique mineralogy in the archaean yilgarn craton the origin of the high grade nimbus ag zn au deposit has been contentious for a number of years recent interpretations of the deposit as a shallow water and low temperature volcanic hosted massive sulphide vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit were based on detailed studies of its volcanology mineralogy hydrothermal alteration assemblages geochemistry multiple s isotopes and trace element content of sulphide however this model has been questioned in favour of a late epithermal fault hosted system effective greenfields exploration for similar deposits elsewhere requires a robust deposit model and well understood timing of ore formation we present a comprehensive multi disciplinary study to further constrain the processes involved in the evolution of nimbus and generate a 4d evolutionary model of the system host rock dacite formation is well constrained by shrimp u pb zircon geochronology to c 2703 ma re os ages for the first sulphide phase gives an imprecise maximum age to the ore formation of 2682 110 ma high precision pb isotope variations in ore stage and late galenas track changes in the sulphides over time complemented by new geochronology the pb isotope data indicates that the polymetallic ore precipitation happened at the same time as the volcanism with the second generation indicating minor local remobilisation of pb in late quartz carbonate veins at c 2630 ma 40ar 39ar dating of sericite altered plagioclase from foliated dacite and u pb shrimp dating of syn to post deformation monazites have yielded ages of 2630 ma the late event at c 2630 ma is most likely related to widespread late low ca granite emplacement across the eastern goldfields this study provides arguments that suggest that nimbus is a syn volcanic deposit the ore timing is consistent with the model of replacement type vhms deposit with the age of the main mineralisation similar to the age of the dacitic host rocks at 2703 ma the late event modifies the pre existing ore and overprints the previous ore related alteration ages from the altered plagioclase high precision double spiked pb isotope constraints from late quartz carbonate veins provides an opportunity to vector to hidden deposits

geochronological constraints on pre syn and postmineralization events at the world class cleo gold deposit eastern goldfields province western australia recent geological and geochronological studies have led to a reevaluation of whether or not the majority of the lode gold deposits of the yilgarn craton formed nearly synchronously during an archean craton wide hydrothermal event as previously proposed the majority of reliable data indicate that gold mineralization took place at ca 2640 to 2625 ma however recent work in the far north of the eastern goldfields province provides structural evidence for instances of earlier gold mineralization and geochronological data for interpreted postore rocks that are considerably older than 2640 ma the documentation of xenotime and monazite in association with ore minerals at the cleo deposit provides a valuable means of determining the absolute age of gold mineralization at the cleo deposit high grade western lodes veins crosscut the sunrise shear zone at a high angle with only centimeter scale offset given that the stratigraphic sequence indicates at least several hundred meters offset across the shear zone the minimal offset of the western lodes veins indicates that gold mineralization was late in the history of movement in the shear zone the absolute ages of pre syn and postmineralization elements in the mine stratigraphic succession have been determined using a variety of geochronological techniques fuchsite micas formed in the sunrise shear zone yield an 40ar 39ar isochron age of 2667 19 ma rhyodacite porphyry dikes postdate the formation of the shear zone but predate the main phase of gold mineralization dike intrusion is constrained to 2674 3 ma by shrimp ii u pb analysis of zircons from these dikes rhenium os analysis of molybdenite from quartz chalcopyrite molybdenite veins that crosscut the porphyry dikes gives an age of formation at 2663 11 ma consistent with their relationship to the porphyry dikes both the dikes and these veins are crosscut by gold bearing western lodes veins mutually crosscutting relationships with ore minerals indicate that microscopic xenotime and monazite grains were deposited during ore formation in the western lodes ore zones shrimp ii u pb analyses of xenotime and monazite grains indicate that western lodes mineralization took place at 2654 8 ma at least 9 m y after the intrusion of the porphyry dikes 95 confidence evidence for substantial temporal separation between intrusive activity and gold mineralization is recorded by other researchers for other deposits associated with granitic intrusions in the leonora laverton area phlogopitic micas from a lamprophyre that crosscuts the whole succession including the sunrise shear zone yield an ar ar plateau age of 2080 4 ma this study constrains the timing of multiple events at cleo including the main phase of gold mineralization during a relatively short span of time however in the context of the larger debate about the existence of a dominant 2640 to 2625 ma period of gold mineralization and the extent of a proposed widespread pre 2660 ma mineralization event in the yilgarn craton the data from cleo are equivocal the 2654 8 ma age for mineralization being significantly older than 2640 ma but not significantly pre 2660 ma even if the maximum possible age is accepted

significance of in situ sims chronometry of zoned monazite from the lewisian granulites northwest scotland abstract in situ studies of lewisian metamorphic monazites show them to be strongly zones in th content th u ratio and 207 pb 206 pb age traverses across compositional zones of individual monazites by sims and empa show that there are no resolvable shifts between 232 th 238 u and 208 pb 206 pb ratios and between th and pb contents in any of the profiles obtained furthermore the difference in 208 pb 232 th ages between two zones of monazites in the same thin section is indistinguishable from the difference in 207 pb 206 pb ages determined by sims these observations together with simple models suggest that transport of pb relative to th and u did not occur significantly during younger e g the laxfordian events in the lewisian and the ages preserved in these zoned monazites are close to concordant moreover monazites having different compositions yield indistinguishable 207 pb 206 pb ages which suggests that the closure temperature of the u pb system in these monazites is not significantly dependent upon their composition consequently the pattern of age distribution observed in the monazites is taken to reflect the metamorphic history of the lewisian the results are consistent with the recent interpretations of the lewisian thermal history which suggest two high grade metamorphic events separated by 200 ma

triassic mineralization with cretaceous overprint in the dahu au mo deposit xiaoqinling gold province constraints from shrimp monazite u th pb geochronology abstract the xiaoqinling terrane in central china is the second largest gold producing area in china previous application of age constraints has yielded ages for the gold mineralization ranging from paleoproterozoic through triassic indosinian to jurassic and cretaceous yanshanian shrimp u th pb dating of hydrothermal monazite in a mo mineralized quartz vein from the dahu au mo deposit in the northern xiaoqinling terrane identifies two mineralization episodes hydrothermal monazite intergrown with molybdenite yields an initial precipitation age of 216 5 ma which is identical to but more precise than the molybdenite re os isochron age of 218 41 ma a younger generation of monazite is distinguished by data falling on a mixing array it is inferred that the younger monazite was formed at the expense of the older ones during the yanshanian probably during a single event that occurred at 125 ma combining these results with available geochronological data and geological evidence we conclude that molybdenum mineralization accompanied by monazite deposition took place in the indosinian followed by a yanshanian tectono hydrothermal event that resulted in large scale gold mineralization in the xiaoqinling terrane our observation demonstrates that monazite is sensitive to hydrothermal overprint and thus is useful for dating fluid infiltration event

u pb geochronology of monazite in precambrian tuffs reveals depositional and metamorphic histories abstract uranium lead geochronology of zircon in felsic tuffs plays a key role in the development of chronostratigraphic frameworks for sedimentary successions this is particularly true for precambrian basins where biostratigraphy is of limited use for age determination or stratigraphic correlation although zircon is widely used to date tuffs it can yield null results due to the presence of xenocrystic populations or isotopic resetting other potential u pb chronometers such as monazite which also crystallize from felsic magmas are largely unreported from felsic tuff layers consequently there has been a lack of studies to evaluate the potential of monazite for u pb isotope geochronology of tuffs we present results of in situ u pb ion microprobe dating of monazite that co exists with zircon in felsic tuffs from two precambrian basins the earaheedy basin frere formation in western australia and the bushveld basin lephala formation in southern africa we show that 207pb 206pb ages from monazite in felsic tuffs from the frere formation 1891 9 ma and the lephala formation 2307 9 ma are identical to zircon ages from the respective tuffs also monazite in the bushveld tuff preserves additional information including a chronological fingerprint of the volcanic source 2 4 2 5 ga xenocrysts and the timing of low grade metamorphism 2 16 ga overgrowths the ca 2 16 ga low grade metamorphism identified in the bushveld basin is reminiscent of that widely recorded in the pilbara craton western australian lending support to arguments for a connection between the kaapvaal and pilbara cratons igneous and low grade metamorphic monazites are readily distinguished based on texture and chemistry our study demonstrates that monazite can be used to accurately date felsic tuffs offering a powerful tool for constraining depositional and metamorphic histories of precambrian sedimentary basins

time constraints on magmatism mineralisation and metamorphism at the falun base metal sulphide deposit sweden using u pb geochronology on zircon and monazite abstract u th pb zircon and monazite ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the palaeoproterozoic falun base metal sulphide deposit in the bergslagen lithotectonic unit fennoscandian shield sweden and thereby the timing of mineralisation hydrothermal alteration and mineralisation at falun are constrained to a short interval of several million years between a 207pb 206pb weighted average age of 1894 3 ma for a rhyolitic sub volcanic rock in the felsic volcanic to sub volcanic host rock suite and a 207pb 206pb weighted average age of 1891 3 ma for a post sulphide porphyritic dacite dyke magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 3 1894 2 ma and 1893 3 ma the felsic sub volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity and burial of the supracrustal rocks two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the falun deposit yield 207pb 206pb weighted average ages of 1831 8 ma and 1822 5 ma respectively these ages fall well within the temporal range of a younger 1 84 1 81 ga m2 metamorphic episode during the 2 0 1 8 ga svecokarelian orogeny with the older episode m1 inside the bergslagen lithotectonic unit at around 1 86 ga this shows the major influence of the m2 event in the north western part of this unit leading to a complete resetting of the u th pb isotope system in monazite

long lived lree mobility in the cratonic rift and foredeep to foreland sedimentary cover at the western margin of the karelia province abstract the western margin of the karelia province of the fennoscandian shield consists of archean crust covered by remnants of paleoproterozoic c 2 5 1 9 ga metasedimentary rocks the study area in the eastern part of the margin shows 2 3 2 1 ga cratonic sedimentation followed by 2 1 2 05 ga rift sedimentation and c 1 91 1 92 ga foredeep to foreland sedimentation related to continent arc continent collision extreme lree mobility loss up 95 of la is recorded by many samples from these units monazite bastnasite and in some cases allanite have been the prealteration lree host phases in the lree depleted samples monazite was altered to th silicates with variable loss of the lree the remaining part of which was incorporated in th poor monazite the depositional age of the sedimentary units was studied by dating la mc icpms detrital zircon grains and the age of lree mobility by dating monazite and xenotime and by whole rock sm nd modeling the maximum deposition age of the foredeep to foreland basin is 1 91 1 92 ga based on detrital zircon data and the minimum age of the main foliation in the study area is 1 87 1 86 ga based on the younger age limit of late to post tectonic xenotime and the ages of few probable metamorphic zircons coeval bastnasite with xenotime in a lree enriched sample suggests that this was also one important stage of lree mobility monazite crystallizations have occurred 1 76 1 78 ga ago while the rb sr whole rock data suggest that the closure of this isotope system took place 1732 21 ma ago the sm nd modeling gives ages at 0 4 1 0 ga for lree depletion the sm nd age of 412 27 ma can be considered as the age of the latest major lree depletion event we propose that alkali bearing oxidizing fluids started to form in the cratonic sequences due to diagenetic reactions maybe as early as 2 3 2 1 ga alkalinity of fluids was later increased by interaction with alkaline 2 05 ga source materials before and during the c 1 91 1 92 ga foredeep to foreland basin stage basin inversion and metamorphic crystallization occurred at 1 91 1 87 ga episodes of fluid migration at 1 78 1 73 ga and afterwards were focused along fracture zones and in microfracture networks the 0 4 ga stage is the most prominent of the

u pb monazite ages of the kabanga mafic ultramafic intrusions and contact aureoles central africa geochronological and tectonic implications mafic ultramafic rocks of the kabanga musongati alignment in the east african nickel belt occur as bushveld type layered intrusions emplaced in metasedimentary sequences the age of the mafic ultramafic intrusions remains poorly constrained though they are regarded to be part of ca 1375 ma bimodal magmatism dominated by voluminous s type granites in this study we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole the monazite shows contrasting crystal morphology chemical composition and u pb ages monazite that formed by contact metamorphism in response to emplacement of mafic ultramafic melts is characterized by extremely high th and u and yielded a weighted mean 207pb 206pb age of 1402 9 ma which is in agreement with dates from the igneous monazite and zircon the ages indicate that the intrusion of ultramafic melts was substantially earlier by 25 m y 95 confidence than the prevailing s type granites calling for a reappraisal of the previously suggested model of coeval bimodal magmatism monazite in the metapelitic rocks also records two younger growth events at ca 1375 ma and ca 990 ma coeval with metamorphism during emplacement of s type granites and tin bearing granites respectively in conjunction with available geologic evidence we propose that the kabanga musongati mafic ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to nuna breakup which culminated during the ca 1375 ma kibaran event manifested as extensive intracrustal melting in the adjoining karagwe ankole belt producing voluminous s type granites the grenvillian aged ca 990 ma tin bearing granite and related sn mineralization appear to be the far field record of tectonothermal events associated with collision along the irumide belt during rodinia assembly since monazite is a ubiquitous trace phase in pelitic sedimentary rocks in contact aureoles of mafic ultramafic intrusions and in regional metamorphic belts our study highlights the potential of using metamorphic monazite to determine ages of mafic ultramafic intrusions and to reconstruct postemplacement metamorphic history of the host terranes georef subject absolute age africa east africa gabbros igneous rocks intrusions mesoproterozoic metamorphic rocks metamorphism metasedimentary rocks monazite neoproterozoic nesosilicates norite orthosilicates phosphates plutonic rocks precambrian proterozoic silicates tanzania u pb ultramafics upper precambrian zircon zircon group

timing of porphyry cu mo and base metal zn pb ag cu mineralisation in a magmatic hydrothermal system morococha district peru the morococha district in central peru is characterised by economically important cordilleran polymetallic zn pb ag cu vein and replacement bodies and the large toromocho porphyry cu mo deposit in its centre u pb re os and 40ar 39ar geochronology data for various porphyry related hydrothermal mineralisation styles record a 3 5 ma multi stage history of magmatic hydrothermal activity in the district in the late miocene three individual magmatic hydrothermal centres were active the codiciada toromocho and ticlio centres each separated in time and space the codiciada centre is the oldest magmatic hydrothermal system in the district and consists of a composite porphyry stock associated with anhydrous skarn and quartz molybdenite veins the hydrothermal events are recorded by a titanite u pb age at 9 3 0 2 ma and a molybdenite re os age at 9 26 0 03 ma these ages are indistinguishable from zircon u pb ages for porphyry intrusions of the composite stock and indicate a time span of 0 2 ma for magmatic hydrothermal activity the small ticlio magmatic hydrothermal centre in the west of the district has a maximum duration of 0 3 ma ranging from porphyry emplacement to porphyry mineralisation at 8 04 0 14 ma 40ar 39ar muscovite cooling age the toromocho magmatic hydrothermal centre has a minimum of five recorded porphyry intrusions that span a total of 1 3 ma and is responsible for the formation of the giant toromocho cu mo deposit at least two hydrothermal pulses are identified post dating a first pulse of molybdenite mineralisation wide spread hydrous skarn covers an area of over 6 km2 and is recorded by five 40ar 39ar cooling ages at 7 2 6 8 ma these ages mark the end of the slowly cooling and long lived toromocho magmatic hydrothermal centre soon after last magmatic activity at 7 26 0 02 ma district wide 50 km2 cordilleran base metal vein and replacement bodies post date the youngest recorded porphyry mineralisation event at toromocho by more than 0 5 ma polymetallic veins 5 78 0 10 and 5 72 0 18 ma 40ar 39ar ages and the manto italia polymetallic replacement bodies 6 23 0 12 and 6 0 0 2 ma 40ar 39ar ages are interpreted to have been formed by a single hydrothermal pulse hydrothermal activity ceased after the formation of the base metal vein and replacement bodies overlapping monazite u pb 8 26 0 18 ma and muscovite 40ar 39ar ages 8 1 0 5 ma from the early base metal stage of one cordilleran vein sample in the sulfurosa area provide evidence that a discrete hydrothermal pulse was responsible for polymetallic vein formation 2 6 ma prior to the district wide polymetallic veins these ages pre date those of toromocho porphyry cu mo formation and show that zn pb ag cu mineralisation formed during several discrete magmatic hydrothermal pulses in the same district

geochemical and isotopic study of metasomatic apatite implications for gold mineralization in xindigou northern china abstract the 0 7 moz xindigou gold deposit lies on the north margin of north china craton the orebodies are controlled by nww trending shear zones and hosted by an archean metavolcanosedimentary sequence these host schist amphibolite and marble rocks were intruded by late paleozoic granites and mafic dikes two independent magmatic hydrothermal assemblages were identified based on petrographic evidence a pre ore magmatic hydrothermal magnetite apatite pyrite zircon assemblage and an ore related potassium feldspar muscovite sulfide minor monazite assemblage apatite that has undergone later alteration shows significant intracrystalline spatial variability with respect to the concentrations of rare earth elements rees si and sr scanning electron microscope backscattered images and statistical interrogation of the compositional data acquired by la icp ms indicate that apatite grains in the pre ore magnetite apatite assemblage are homogeneous and enriched in rees and si ap1 where sulfide related alteration of mineralization stage was overlapped these apatite grains display a distinctive texture of homogeneous cores and turbid rims this dissolution reprecipitation process preferentially transported elements from the original apatite rees and si gradually decrease from the core ap1 to the altered rim ap2 ap3 whereas sr increases localized leaching of rees especially lrees from apatite was followed by precipitation of secondary monazite grains in the metasomatic apatite rims and the muscovite sulfide quartz phosphate sequence in situ sr isotope analyses of the apatite show the 87sr 86sr ratios varying from the lowest value 0 707874 in unaltered ap1 to the highest 0 714160 in altered ap3 zircon grains from migmatite display a peak metamorphic age at 2512 9 ma whereas zircons from the early magnetite apatite association formed near 1776 12 ma and late hydrothermal monazite yields a th pb age of 301 0 1 7 ma these geochronology results show that the mineralization occurred during the late paleozoic orogenesis long after neoarchean regional metamorphism and late paleoproterozoic rift related magmatism the typical hydrothermal features of orogenic gold deposit could be inferred from the fluorapatite the elemental patterns of fluorapatite grains indicate that a carbon and sr enriched acid slightly oxidized and low salinity hydrothermal system was responsible for apatite metasomatism and gold mineralization strontium isotopes further reveal that the fluid related to gold deposition was derived from mafic lower crust with extensive radiogenic sr accumulation during fluid rock interaction this study demonstrates the potential application of apatite in exploration for orogenic gold deposits and its use in tracking hydrothermal ree re mobilization during metasomatism

age constraints on the hydrothermal history of the prominent hill iron oxide copper gold deposit south australia the mesoproterozoic prominent hill iron oxide copper gold deposit lies on the fault bound southern edge of the mt woods domain gawler craton south australia chalcocite bornite chalcopyrite ores occur in a hematitic breccia complex that has similarities to the olympic dam deposit but were emplaced in a shallow water clastic carbonate package overlying a thick andesite dacite pile the sequence has been overturned against the major steep east west hangingwall fault beyond which lies the clastic to potentially evaporitic blue duck metasediments immediately north of the deposit these metasediments have been intruded by dacite porphyry and granitoid and metasomatised to form magnetite calc silicate skarn pyrite chalcopyrite the hematitic breccia complex is strongly sericitised and silicified has a large sericite chlorite halo and was intruded by dykes during and after sericitisation this paper evaluates the age of sericite formation in the mineralised breccias and provides constraints on the timing of granitoid intrusion and skarn formation in the terrain adjoining the mineralisation the breccia complex contains fragments of granitoid and porphyry that are found here to be part of the gawler range volcanics hiltaba suite magmatic event at 1600 1570 ma this indicates that some breccia formation post dated granitoid intrusion monazite and apatite in fe p ree albite metasomatised granitoid paragenetically linked with magnetite skarn formation north of the hangingwall fault grew soon after granitoid intrusion although the apatite experienced u pb lree loss during later fluid mineral interaction this accounts for its calculated age of 1544 39 ma to the south of the fault within the breccia 40ar 39ar ages yield a minimum age of sericitisation cu fe ree of dykes and volcanics of 1575 ma firmly placing prominent hill ore formation as part of the gawler range volcanics hiltaba suite magmatic event within the olympic cu au province of the gawler craton

precise ages for lode gold mineralization in the xiaoqinling gold field southern margin of the north china craton new constraints from in situ u pb dating of hydrothermal monazite and rutile

geochemical evolution and timing of uranium mineralization in the khetri copper belt western india abstract the khetri copper belt kcb located in the northwestern part of the aravalli delhi fold belt western india is famous for cu mineralization and known for au ag co fe ree u p occurrences the present study conducted in and around the madan kudan kolihan chandmari cu deposits of the kcb integrates the mode of occurrence mineralogical association textural relation and chemistry of hydrothermal minerals and in situ chemical dating of uraninite we propose that the u mineralization represented by type 1 to type 6 uraninites has evolved through six successive stages u mineralization type 1 uraninite of uncertain origin u mineralization type 2 uraninite during fe mg alteration u mineralization type 3 uraninite during ca na alteration cu fe co ree u mineralization type 4 uraninite during na ca k alteration u mineralization type 5 uraninite during chloritization fe mg alteration cu co ree u mineralization type 6 uraninite during k fe mg alteration the chemical ages of uraninite suggest that the hydrothermal mineralization associated with type 2 to type 5 uraninites formed during a hitherto unknown older event compared to the previously reported age of the mineralization in the kcb i e 850 ma which initiated during the second phase of metamorphism of 1 40 1 30 ga m2 and terminated well before the third phase of metamorphism of 985 920 ma m3 the k fe mg alteration and the associated mineralization most likely is time equivalent of the known alteration mineralization event of 850 ga the chlorite and biotite thermometry in tandem with u th ratios of uraninite suggest that uraninites crystallized at high temperature 390 c in all the hydrothermal stages the common presence of magnetite and ilmenite the occasional presence of graphite and the fe3 fe3 fe2 ratios of the co genetic gangue minerals such as amphibole biotite and chlorite suggest reduced environment below the haematite magnetite buffer during the crystallization of uraninite in all the hydrothermal stages based on the composition of gangue minerals apatite amphibole biotite chlorite and scapolite in alteration assemblages veins and physicochemical characters of the fluids we discuss the possibility of transportation of u as u4 chloride and fluoride complexes the high temperature and reduced nature of the fluids high th contents and low u th ratios of most of the uraninites similar age of mineralization type 2 to type 5 uraninite and m2 metamorphism and the absence of concomitant magmatic activity collectively suggest that hydrothermal mineralization related to type 2 to type 5 uraninites took place from metamorphic fluids we report for the first time a unique uraninite graphite association in the kcb which can be best explained by their co precipitation from a hydrothermal fluid during the earliest fe mg alteration

a textural and geochemical guide to the identification of hydrothermal monazite criteria for selection of samples for dating epigenetic hydrothermal ore deposits hydrothermal monazite is one of the most reliable geochronometers for u pb dating of epigenetic or hydrothermal ore deposits because its blocking temperature at ca 700 c is higher than that of most metamorphic conditions although igneous monazite is routinely used for age dating igneous rocks only a few ore deposits have been dated by hydrothermal monazite this is due to the similar morphology of hydrothermal and igneous monazite which prevents the reliable distinction of hydrothermal monazite in particular we demonstrate that hydrothermal monazite can be distinguished from igneous monazite by its unique geochemical signature its local abundance and to common association with hydrothermal mineral assemblages our data and the data of others reported in the literature suggest that the low tho 2 content of hydrothermal monazite 0 1 wt is distinct from that of igneous monazite 3 to 5 wt and may be used to determine their genesis

mineralogical and geochemical constraints on mobilization and mineralization of rare earth elements in the lala fe cu mo ree deposit sw china the lala fe cu mo ree deposit in the northern kangdian iocg metallogenic province sw china has a paragenetic sequence that includes pre ore na alteration stage i fe p mineralization stage ii and sulfide mineralization stage iii rare earth element ree minerals which are chiefly monazite parasite and bastnasite with minor xenotime are associated with sulfide mineralization these ree minerals together with biotite muscovite and calcite are accompanied with k ca carbonate alteration of stage iii where magnetite and apatite of stage ii are overprinted by minerals of stage iii the apatite grains are commonly embayed or eroded and contain abundant rounded to subrounded and needle like inclusions of monazite and minor bastnasite calcite and sulfide minerals these monazite bearing apatite grains are texturally similar to metasomatized apatite in the laboratory and can be attributed to the formation from stage ii apatite via a dissolution precipitation process during fluid infiltration the monazite bearing apatite has ree contents and la sm ratios much lower than the original stage ii apatite suggesting that rees were leached and mobilized from this stage ii apatite and that these processes were responsible for the formation of monazite inclusions within the apatite hosts the monazite inclusions have compositions similar to those of stage iii monazite suggesting that rees in stage ii apatite were mobilized by stage iii fluids consistent with occurrences of sulfide and calcite inclusions within the apatite mass balance analysis using bulk compositional data for host rocks that underwent k ca carbonate alteration indicates that rees of the hosting rocks were also mobilized and that up to 70 percent of the light rees were leached out during alteration therefore ree mobilization recorded in apatite grains and country rocks support a model in which the country rocks were important sources for rees in the lala deposit compositions of amphibole and biotite together with previously acquired fluid inclusion data demonstrate that stage iii fluids are dominated by na and cl but had higher k co2 or hco3 and co32 and hf hcl fugacity and lower salinity nacl than stage ii fluids elevated k and co2 in stage iii fluids or associated k carbonate alteration is proposed to be important for extensive ree mobilization on country rocks the rees leached from country rocks are inferred to have been transported as chloride complexes prior to being deposited as ree minerals deposition of ree minerals from stage iii fluids was likely triggered by mixing with external relatively low temperature f rich and high ph fluids and or by local interaction with carbonate host rocks we suggest that the common association of rees with cu ores in many iocg deposits is related to the unique nature of the cu mineralizing fluids

timing of magmatic crystallization and sn w mo greisen vein formation within the mount douglas granite new brunswick canada u pb geochronology was applied to a combination of magmatic and hydrothermal minerals to help constrain the timing of emplacement of three units in the mount douglas granite mdg and reveal their

ion microprobe u pb dating of hydrothermal xenotime from an episyenite evidence for rift related reactivation abstract hydrothermally intergrown xenotime monazite from an episyenite in the bohus granite southwest sweden has been analyzed in situ by ion microprobe although the analysed xenotime crystals are extremely small sometimes less than the ion beam diameter 17 m they retain relatively undisturbed u pb systems which yielded a 206 pb 238 u age of 252 8 ma the evolution of this episyenite involved an initial stage of quartz dissolution accompanied by albitization followed by a second stage of vug infilling and replacement of igneous fe ti phases the obtained age shows that the second alteration stage during which xenotime was precipitated was coeval with the thermal anomaly associated with permo carboniferous crustal thinning and the development of the nearby oslo rift moreover the development of the permeable episyenite structure must be ascribed to a preceding high temperature event most likely the post magmatic cooling of the host granite at 920 ma this study shows that u pb dating of young xenotimes may address geochronological problems though further work is required to characterize possible matrix effects which presently limit the accuracy of the method

point counting pores and illuvial clay in thin section abstract six soil thin sections containing various amounts of illuvial clay previously estimated by ten operators were point counted four times by an additional experienced operator the results indicate that a count of 6000 points over a section area of 25 25 mm is sufficient to quantify satisfactorily the pore space of the section replicated results for illuvial clay however differed widely for some sections these differences are attributed both to difficulties in recognising illuvial clay and to orientation and variability of soil components variability of results for illuvial clay in this study was less than that reported for ten operators but nonetheless it is evident that for most sections the amount of illuvial clay cannot be estimated precisely by a single count of 6000 points suggestions are made for improving the reliability of estimates of illuvial clay in soil thin sections and an improved basis for reporting results is proposed

micromorphological and chemical investigation of late viking age grave fills at hofstaðir iceland grave fills from seven human burials from a late viking age early medieval cemetery at hofsta ir m vatnssveit iceland were examined by soil micromorphology and organic chemical analysis detailed analysis of the weathering of the mineral constituents of the grave fills demonstrates a relationship between the extent of weathering of volcanic silicates within the fills and the presence of buried human remains gas chromatography mass spectrometry gc ms of extracts from the fills and controls of two graves revealed organic signatures dominated by plant derived organic matter with no evidence of degradation products of the body tissues transformation of n alkanes into n alkan 2 ones provides evidence for microbial activity within the fills gc ms analysis of the organic extract from under one of the skulls and pyrolysis gas chromatography of wood fragments found in that grave provide compelling evidence for the former presence of a conifer wood coffin the use of this non native wood in the burial provides evidence for either the import of foreign lumber or the utilisation of driftwood most likely originating from russia siberia

u pb dating of minerals in alteration halos of superior province massive sulfide deposits syngenesis versus metamorphism u pb geochronology of igneous zircon from rhyolitic host rocks to the archean kidd creek geco and winston lake massive sulfide deposits in the superior province of ontario shows that volcanism which accompanied mineralization occupied a narrow time span 2717 2 ma 2720 2 ma and 2723 2 ma respectively precise ages of hydrothermal monazite allanite and rutile from alteration zones surrounding the above deposits indicate that these minerals crystallized 40 70 million years after volcanism monazite from kidd creek mine is 2659 3 ma old in agreement with spatially associated 2664 25 ma old rutile monazite from a biotite schist at geoco mine gives a similar age of 2661 1 ma however monazite from a sericite schist which hosts the ore at geco mine is 2675 2 ma old abraded large monazite grains from three units in the winston lake deposit are coeval with biotite crystallization and record an age of 2677 2 ma approximately the same as monazite in the sericite schist at geco data points from allanite fractions from both the winston lake and geco deposits fall on a pb pb isochron that gives an age of 2672 5 ma rutile from winston lake gives a younger age of 2651 6 2 ma and may date retrograde alteration of biotite to chlorite the ca 2676 ma age of monazite from winston lake and in the sericite schist at geco mine probably dates a regional metamorphic event that affected most of the southern superior province the ca 2660 ma old monazite in the biotite schist at geco mine and in the chlorite sericite alteration at kidd creek may date later k metasomatism caused by metamorphically derived fluids that were focussed along old fault structures such fluids were also responsible for local sulfide remobilization monazite and rutile are spatially associated with chlorite and sericite alterations at kidd creek their young ages indicate that these originally syngenetic mineral assemblages may have been significantly affected by regional metamorphism formation of monazite at all three deposits studied was a result of significant ree remobilization during metamorphism the discrete character of syn metamorphic hydrothermal activity in different units of the same deposit as well as its synchroneity among different widely separated deposits requires a mechanism for episodic injection of heat and fluid into the crust on a regional scale these activities are broadly coeval with and probably related to plutonism within adjacent metasedimentary subprovinces and middle to lower crustal metamorphism in the superior province

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

mass transport and fractionation during monazite alteration by anisotropic replacement abstract the present experimental study investigates the causes of anisotropic replacement and its impact on the element mass transfer during monazite alteration by combining in situ characterization of solid and fluid products starting material of standard manangotry monazite was placed at 200 mpa with 18 o doped fluids at temperature t between 300 and 600 c for durations between 14 and 114 days in some cases with hematite magnetite buffer and in presence of pre fractured quartz crystals for all experiments with naoh at t 400 c monazite products show a replacement rim altered domain but with complex microstructures that are best explained by nanoscale observations at 400 c and 500 c replacement propagates anisotropically through the unaltered domain due to preferentially oriented dissolution and or fracturing at the reaction interface the altered domain corresponds to nanochannels of secondary monazite mnz2 intruding primary monazite mnz1 with nanopores filled by amorphous si rich inclusions at the reaction front interface at 600 c the altered domain increases in volume and becomes homogeneous and non porous due to textural and chemical reequilibration however nanoscale observations reveal an anisotropic propagation associated with dislocations and preservation of mnz1 relics within the apparently homogeneous altered domain textural equilibration leads to transient pores inclusions which preferentially move toward the reaction front in all experimental products the abundant porosity attests to significant mass transfer during monazite replacement nanomixture within altered domains hampers accurate determination of mnz2 composition and is assumed to be responsible for the pb measured in the rim due to mnz1 contribution however composition measurements indicate that mnz2 contains higher light rare earth elements lree higher th u ratio but lower y th u pb and ca contents compared to mnz1 elements released in the fluid by monazite replacement are mobilized from the reaction front toward the grain boundary and then redistributed between secondary th silicates and phosphates si rich gel like material and aqueous fluids at t 500 c analyses of inclusions trapped in replaced quartz confirm an efficient ree solubility in the alkaline solutions the si rich gel like inclusions contain high amounts of ree e g 950 4600 ppm ce th 4480 6170 ppm and u 30 110 ppm while aqueous fluid inclusions have high concentrations of ree and th around 100 s of ppm compared to common natural brines there is a fractionation of th and u during mnz1 replacement th u 70 with low th u ratios in the aqueous fluid 7 23 compared to the secondary solid products up to 150 independently of the initial presence of hematite magnetite buffer this accounts for a fractionation within the isotopic th pb and u pb ages within the altered domain in natural samples observed microscopically the complex anisotropic geometry of the replacement can lead to a nanomixture within apparently homogeneous altered domains with partial resetting of the u th pb geochronometer and to misleading interpretations of secondary inclusions within apparently unaltered domain

in situ th pb dating of monazite in fibrous veins direct dating of veins and deformation in the shallow upper crust of the mexican orogen abstract few methods exist for directly dating orogenic events in the upper crust here we report in situ dates from 10 m diameter monazite grown in quartz calcite fibrous veins which precipitated at very low grade metamorphic conditions about 250 c in volcaniclastic and calcareous rocks of the early cretaceous trancas fm in the zimapan basin central mexico our integrated study includes regional and local structural and kinematic analysis of vein and folds detailed textural and mineralogical characterization of vein bearing minerals and texturally controlled th pb geochronologic analysis of monazite by la mc icpms we find that monazite in the veins preferentially crystallized at the interface between vein forming calcite and quartz fibers as well as at the vein host rock interface monazite ages range from 154 to 68 ma with the youngest sub population yielding a weighted mean age of 76 8 0 8 ma coincident with the age of basin wide folding as earlier constrained by ar ar illite dating the oldest monazite ages coincide with the timing of deposition of the volcaniclastic host rock given that veins are ubiquitous in shallow crustal rocks this approach to dating of veins with enclosed monazite has great potential to improve the constraints on temporal resolution of fluid rock interaction during of deformation

tectonic transition from a compressional to extensional metallogenic environment at 120 ma revealed in the hushan gold deposit jiaodong north china craton abstract the world class giant gold province 4000 t in the jiaodong peninsula has attracted global attention and extensive studies for decades however most of the works have been focused on the western zhaoyuan laizhou and eastern muping rushan gold metallogenic belt leaving the middle penglai qixia belt largely unexplored the hushan gold deposit in the penglai qixia belt shows a unique two stage gold mineralization i e an early stage pyrite sericite quartz altered rock type mineralization and a late stage pyrite pyrrhotite vein type mineralization hydrothermal monazite coexisting with au bearing pyrite is observed in the early stage mineralization the widespread circular zoned metasomatic relict structures indicate that monazite was formed by the strong interaction between ca p ree rich fluids and feldspars plagioclase and k feldspar therefore obtained in situ u pb age of 120 0 3 1 ma for the pure monazite without mineral inclusions such as feldspars can represent the timing of the early stage gold mineralization the in situ monazite e nd t t 120 ma values vary from 20 6 to 18 4 well corresponding to nd isotopes of the late jurassic linglong granite it is inferred that the ree rich components in the ore forming fluids were extracted during the process of primary mineralizing fluids passing through the lower linglong granite body and that the nd isotopic compositions were altered due to the strong fluid rock interaction in this regard linglong granite contributes some ore forming materials to the mineralizing fluids during fluid rock interaction the early stage altered rock type gold mineralization indicates a compressional closed ore forming system whereas the late stage pyrite pyrrhotite vein type mineralization and the occurrences of fracture geode and hole in the ore samples reflect an extensional open ore forming system the presence of barite and magnetite in the late stage mineralization also suggests an increase of oxidation state during the process furthermore pyrites in the late stage generally have lower 34 s values 5 69 6 98 av 6 47 than pyrites in the early stage 34 s values 7 06 7 85 av 7 42 which can also be well explained by the increase of oxidation state therefore the hushan gold deposit uniquely records a metallogenic environmental transition from compressional reduced to extensional oxidized at 120 ma in addition the mineralizing fluids with higher oxidation state in the late stage is supposed to superimpose on the early stage mineralization dissolve and rework previously crystalized pyrite to form the high grade gold mineralization unlike the gold deposits in the western and eastern belts the hushan gold deposit temporally preserves two types of mineralization in one single deposit as a response to regional stress field transition

mineralogical and geochemical study of the rare earth element mineralization at gakara burundi abstract the rare earth element ree mineralization of gakara burundi has first been discovered in 1936 and has periodically been the subject of geological studies at times when the exploitation of bastnasite ce and monazite ce was economically interesting this study focuses on the establishment of a mineral paragenesis for gakara with special attention to the ree bearing phases to understand the formation history of the deposit the paragenesis can be subdivided into 3 stages primary ore deposition brecciation stage and supergene alteration evidence for fenitization processes i e pinkish red cathodoluminescence of k feldpar brecciation stage and the strong enrichment of light rees in bastnasite and monazite substantiate the hypothesis of a structurally controlled hydrothermal mineralization with a strong carbonatitic affinity this likely confirms the association of the gakara ree deposit with the neoproterozoic alignment of alkaline complexes and carbonatites along the present day western rift it suggests a direct link with a currently unidentified carbonatitic body at depth possibly derived from a predominantly metasomatized lithospheric mantle

versatile monazite resolving geological records and solving challenges in materials science generalizations about monazite implications for geochronologic studies with the advent of techniques that preclude mineral separation ages from specific compositional domains in monazite ce la th po 4 have provided a wealth of information regarding the timing of the geologic evolution of numerous regions however confusion can arise when single grains show large differences in age that fail to correlate to chemistry or location within the monazite generalizations that lead to incorrect age interpretations include that monazite zoning in y th and or the rare earth elements ree always identify 1 distinct tectonic events 2 environment of crystallization and 3 provenance of detrital grains increasing th contents in monazite do not always reflect 1 increasing grade in metamorphic grains 2 changes in silicate melt composition in igneous grains 3 make the mineral more susceptible to alteration nor 4 control the mineral s uptake of ree metamorphic monazites from himalayan garnet bearing rocks with coexisting allanite show no relationship between th content and ree instead chondrite normalized ree patterns of the allanite mirror those of the monazite indicating the variations are related to the reactant that formed the mineral generalizations about pb behavior in monazite remain problematic incorporation of pb into monazite has thus far been precluded by experimental studies yet common pb has been measured in many studies of natural monazite a clear understanding about controls of monazite composition and the role of the chemical and or pressure temperature p t environment of the rocks in which it forms is required to correctly interpret the meaning of the mineral s age s

earthworm activity and archaeological stratigraphy a review of products and processes the activity of earthworms has long been understood to have significant effects on archaeological stratigraphy but many of the details have not been fully grasped by stratigraphers or by the specialists who advise them although worms are widely known to cause the burial of finds due to surface casting some of their other activities are less commonly recorded amongst these their active burial of stones and seeds their building of cairns and their production of calcium carbonate granules have mostly not been studied in any detail and have been little exploited from an interpretative point of view this paper reviews the existing knowledge as well as presenting some recent research carried out into various aspects of worm actions and their relationship to taphonomy

repeated syn and post orogenic gold mineralization events between 1 92 and 1 76 ga along the kiistala shear zone in the central lapland greenstone belt northern finland abstract the central lapland greenstone belt clgb is well endowed with orogenic gold deposits along major shear zones and structural lineaments in the northern part of the belt the kiistala shear zone kisz hosts the suurikuusikko gold deposit kittila mine currently the largest gold producer in europe the iso kuotko deposit is located 10 km to the north of suurikuusikko along the same shear zone gold mineralization at iso kuotko formed in two major stages an early stage refractory gold mineralization with auriferous arsenopyrite with similarities to the ore at suurikuusikko and a late main stage mineralization with free gold in carbonate quartz veins with abundant pyrrhotite native bismuth and other sulphide minerals this latter ore is absent at suurikuusikko based on u pb dating as well as re os and pb isotope systematics of rock forming and hydrothermal minerals we evaluate the relationships between tectonic evolution and formation of gold deposits throughout the late palaeoproterozoic in the northern part of the clgb results from in situ u pb dating of zircon and petrographically well constrained hydrothermal monazite and xenotime by la icpms and model age calculations using re os isotopic data for arsenopyrite and in situ pb isotope data for galena from the iso kuotko deposit provide evidence for multiple episodes of hydrothermal activity along the kisz data suggest coincident felsic magmatism and structurally controlled fluid flow events during wrench fault dominated n s shearing associated with early micro continent accretion ushering in the svecofennian orogeny this includes the formation of refractory gold ores at suurikuusikko 1916 19 ma and iso kuotko 1868 15 ma subordinate barren veining took place at 1830 ma during transient extension between the accretion and final collision stage xenotime in late stage veins with visible gold at iso kuotko yield u pb ages between 1761 9 and 1770 7 ma this time interval is concurrent with widespread granitoid emplacement at the close of the svecofennian orogeny disturbance of the re os system in the early auriferous arsenopyrite can be connected to the late stage mineralizing processes pb isotope data suggest a mixed mantle and lower crust origin for fluids in the post orogenic hydrothermal system in situ u pb dating in polished thin sections in tandem with electron microprobe analyses of mineral compositions and detailed textural observations highlights the utility of xenotime and monazite as robust geochronometers capable of recording repeated hydrothermal events in paleoproterozoic orogenic systems results provide precise temporal constraints for orogenic gold mineralization and vital information to refine the tectonic evolution of the central lapland greenstone belt

genesis of gray monazites evidence from the paleozoic of belgium systematic mineralogical investigations carried out on panned stream concentrates from the northwestern part of the cambro ordovician stavelot massif belgium led to the discovery of nodular gray monazites these were later identified in situ in black slates associated with conglomeratic levels containing phosphatic material microscopic investigation shows that gray monazites are authigenic and predate cleavage to test the hypothesis of a sedimentary origin for rare earth elements samples of shales phosphatic conglomerates and monazite concentrates were submitted to sequential inductively coupled plasma analysis results show that the rare earth element pattern in gray monazites is a reflection of the abundance of these elements in the host rock this suggests a model invoking desorption of the rare earth elements from their clayey support and differential precipitation of rare earth phosphates in the sediment initiated by p mobility during diagenesis the genetic model for gray monazite mineralization assumes three essential and complementary phenomena 1 sedimentation of clays in a reducing marine environment 2 a phosphate anomaly in the same lithological sequence and 3 evolution to low grade epizonal metamorphic conditions these nonrestrictive genetic conditions clearly suggest that gray monazites have been generally overlooked and must be much more widespread than believed the economic interest of gray monazite lies in potential stream or beach placers their low th content and comparatively high eu content are interesting features in the scope of ore beneficiation