did the massive magnetite lava flows of el laco chile form by magmatic or hydrothermal processes new constraints from magnetite composition by la icp ms the el laco magnetite deposits consist of more than 98 magnetite but show field textures remarkably similar to mafic lava flows therefore it has long been suggested that they represent a rare example of an effusive fe oxide liquid field and petrographic evidence however suggest that the magnetite deposits represent replacement of andesite flows and that the textures are pseudomorphs we determined the trace element content of magnetite by laser ablation inductively coupled plasma mass spectrometry la icp ms from various settings at el laco and compared them with magnetite from both igneous and hydrothermal environments this new technique allows us to place constraints on the conditions under which magnetite in these supposed magnetite lava flows formed the trace element content of magnetite from the massive magnetite samples is different to any known magmatic magnetite including primary magnetite phenocrysts from the unaltered andesite host rocks at el laco instead the el laco magnetite is most similar in composition to hydrothermal magnetite from high temperature environments 500 c such as iron oxide copper gold iocg and porphyry cu deposits the magnetite trace elements from massive magnetite are characterised by 1 depletion in elements considered relatively immobile in hydrothermal fluids e g ti al cr zr hf and sc 2 enrichment in elements that are highly incompatible with magmatic magnetite rare earth elements ree si ca na and p and normally present in very low abundance in magmatic magnetite 3 high ni cr ratios which are typical of magnetite from hydrothermal environments and 4 oscillatory zoning of si ca mg ree and most high field strength elements and zoning truncations indicating dissolution similar to that formed in hydrothermal fe skarn deposits in addition secondary magnetite in altered brecciated host rock forming disseminations and veins has the same composition as magnetite from the massive lenses euhedral magnetite lining both open spaced veins in the brecciated host rock and along the walls of large hollow chimneys in the massive magnetite lenses also displays oscillatory zoning and most likely formed by fluctuating composition and or physio chemical conditions of the fluid thus the chemical fingerprint of magnetite from the supposed el laco magnetite lava flows supports the hydrothermal model of metasomatic replacement of andesite lava flows by dissolution and precipitation of magnetite from high temperature fluids rather than a magmatic origin from an effusive fe oxide liquid

regional geologic and petrologic framework for iron oxide apatite rare earth element and iron oxide copper gold deposits of the mesoproterozoic st francois mountains terrane southeast missouri usa this paper provides an overview on the genesis of mesoproterozoic igneous rocks and associated iron oxide apatite ioa rare earth element iron oxide copper gold iocg and iron rich sedimentary deposits in the st francois mountains terrane of southeast missouri usa the st francois mountains terrane lies along the southeastern margin of laurentia as part of the eastern granite rhyolite province the province formed during two major pulses of igneous activity 1 an older early mesoproterozoic ca 1 50 1 44 ga episode of volcanism and granite plutonism and 2 a younger middle mesoproterozoic ca 1 33 1 30 ga episode of bimodal gabbro and granite plutonism the volcanic rocks are predominantly high silica rhyolite pyroclastic flows volcanogenic breccias and associated volcanogenic sediments with lesser amounts of basaltic to andesitic volcanic and associated subvolcanic intrusive rocks the iron oxide deposits are all hosted in the early mesoproterozoic volcanic and volcaniclastic sequences previous studies have characterized the st francois mountains terrane as a classic a type within plate granitic terrane however our new whole rock geochemical data indicate that the felsic volcanic rocks are effusive derivatives from multicomponent source types having compositional similarities to a type within plate granites as well as to s and i type granites generated in an arc setting in addition the volcanic hosted ioa and iocg deposits occur within bimodal volcanic sequences some of which have volcanic arc geochemical affinities suggesting an extensional tectonic setting during volcanism prior to emplacement of the ore forming systems the missouri iron orebodies are magmatic related hydrothermal deposits that when considered in aggregate display a vertical zonation from high temperature magmatic hydrothermal ioa deposits emplaced at moderate depths 1 2 km to magnetite dominant ioa veins and iocg deposits emplaced at shallow subvolcanic depths the shallowest parts of these systems include near surface iron oxide only replacement deposits surficial epithermal sediment hosted replacement deposits synsedimentary ironstone deposits and mn rich exhalite deposits alteration associated with the ioa and iocg mineralizing systems of the host volcanic rocks dominantly produced potassic with lesser amounts of calcic and sodic rich mineral assemblages no deposits are known to be hosted in granite implying that the mineralizing systems were operative during a relatively short postvolcanic period yet prior to intrusion of the granitoids companion studies in this special issue on mineral chemistry stable isotopes and iron isotopes suggest that the magnetite within the ioa deposits formed from high temperature fluids of magmatic or magmatic hydrothermal origin however the data do not discriminate between a magmatic hydrothermal source fluid exsolved from an fe rich immiscible liquid or an fe rich silicate magma mineral chemical fluid inclusion and stable isotope data from these new studies record the effects of metasomatic fluids that interacted with crustal reservoirs such as volcanic rocks or seawater

upgrading iron ore deposits by melt loss during granulite facies metamorphism abstract forward modelling of fe rich phyllite is used to evaluate the effects of partial melting and melt loss on the concentration of iron in the residual rock package leading to enrichment in fe oxide minerals magnetite and hematite the effect of melt loss during prograde metamorphism to peak conditions of 850 c was modelled using a series of calculated pressure temperature p t phase diagrams pseudosections the results show that metapelitic rocks with lower iron content are more fertile produce more melt and therefore show a more significant increase up to 35 in the fe oxide content in the residual melt depleted rock package rocks with primary fe rich compositions are less fertile lose less melt and therefore do not experience the same relative increase in the amount of fe oxides in the residuum the results of the modelling have implications for the formation of economic grade iron ore deposits in metamorphic terranes fe rich compositions that represent primary ore horizons prior to metamorphism may not experience significant enrichment however those horizons with lower primary iron contents may be significantly upgraded as a result of melt loss thereby improving the overall grade of the ore system the application of the modelling to the highly metamorphosed palaeoproterozoic warramboo magnetite hematite deposit in the southern gawler craton suggests that melt loss during granulite facies metamorphism led to upgrading of sub economic units within the low grade price metasediments to form the economically viable granulite facies warramboo ore system the results of this study suggest that high temperature metamorphic terranes offer attractive exploration targets for magnetite dominated iron ore deposits

chadormalu kiruna type magnetite apatite deposit bafq district iran insights into hydrothermal alteration and petrogenesis from geochemical fluid inclusion and sulfur isotope data abstract the chadormalu is one of the largest known iron deposits in the bafq metallogenic province in the kashmar kerman belt central iran the deposit is hosted in precambrian cambrian igneous rocks represented by rhyolite rhyodacite granite diorite and diabasic dikes as well as metamorphic rocks consisting of various schists the host rocks experienced na albite calcic actinolite and potassic k feldspar and biotite hydrothermal alteration associated with the formation of magnetite apatite bodies which are characteristic of iron oxide copper gold iocg and iron oxide apatite ioa systems iron ores occurring as massive type and vein type bodies consist of three main generations of magnetite including primary secondary and recrystallized which are chemically different apatite occurs as scattered irregular veinlets in various parts of the main massive ore body as well as apatite magnetite veins and disseminated apatite grains in marginal parts of the deposit and in the immediate wall rocks minor pyrite occurs as a late phase in the iron ores chemical composition of magnetite is representative of an ioa or kiruna type deposit which is consistent with other evidence whole rock geochemical data from various host rocks confirm the occurrence of na ca and k alteration consistent with the formation of albite actinolite and k feldspar respectively the geochemical investigation also includes the nature of calc alkaline igneous rocks and helps elaborating on the spatial and temporal association and possible contribution of mafic to felsic magmas to the evolution of ore bearing hydrothermal fluids fluid inclusion studies on apatites from massive and vein type ores show a range of homogenization temperatures from 266 to 580 c and 208 406 c and salinities from 0 5 to 10 7 wt and 0 3 24 4 wt nacl equiv respectively the fluid inclusion data suggest the involvement of evolving fluids from low salinity high temperature to high salinity low temperature in the formation of the massive and vein type ores respectively the 34s values obtained for pyrite from various parts of the deposit range between 8 9 and 14 4 for massive ore and 18 7 to 21 5 for vein type ore a possible source of sulfur for the 34s enriched pyrite would be originated from late precambrian early cambrian marine sulfate or fluids equilibrated with evaporitic sulfates field observations ore mineral and alteration assemblages coupled with lithogeochemical fluid inclusion and sulfur isotopic data suggest that an evolving fluid from magmatic dominated to surficial brine rich fluid has contributed to the formation of the chadormalu deposit in the first stages of mineralization magmatic derived fluids had a dominant role in the formation of the massive type ores whereas a later brine with higher 34s contributed to the formation of the vein type ores

mineralogy chemistry and fluid aided evolution of the pea ridge fe oxide y ree deposit southeast missouri usa the kiruna type pea ridge iron oxide apatite ioa deposit is hosted by a sequence of 1 47 ga rhyolite tuffs of the st francois mountains southeast missouri usa it consists of a series of altered zones composed mainly of amphibole magnetite hematite and quartz together with the presence of several rare earth element y ree rich breccia pipes in many cases the fluorapatite within these zones is rich in inclusions of monazite iron oxide and quartz inclusions plus minor xenotime monazite and minor xenotime are also found intergrown as inclusions in the fluorapatite as well as in surrounding recrystallized magnetite and hematite in the magnetite ore monazite and xenotime typically occur as inclusions within both oxides monazite ce and xenotime y are both relatively poor 2 wt in tho2 and uo2 no significant compositional differences exist in the y ree chemistry between monazite and xenotime inclusions in fluorapatite compared to grains intergrown with magnetite and hematite suggesting that these two ree rich minerals are cogenetic monazite xenotime geothermometry and geochronology of monazite inclusions in fluorapatite provide evidence that formation remobilization of the y ree phosphates took place at ca 50 to 400 c approximately 5 to 10 m y after emplacement of the main iron oxide phosphate orebody evidence from field relationships and fluid inclusion chemistry together with the massive recrystallization and remobilization of fluorapatite monazite xenotime and iron oxides at pea ridge suggest a subvolcanic origin coupled with a strong metasomatic reworking of the ioa deposit

kiruna type deposits their origin and relationship to intermediate subvolcanic plutons in the great bear magmatic zone northwest canada magnetite apatite actinolite rocks similar to those at kiruna sweden and the st francois mountains missouri are associated with seven epizonal plutons that intrude andesitic stratovolcanoes of a broadly folded early proterozoic continental magmatic arc located in the northwestern canadian shield the plutons mainly medium grained quartz monzonite monzodiorite diorite iugs sheets and laccoliths 5 to 25 km in diameter are spatially temporally and compositionally related to host andesitic stratovolcanoes they were emplaced at 2 to 3 km depth are compositionally heterogeneous metasomatically altered and had plagioclase as the liquidus phase in addition they have kilometer wide alteration halos comprising an inner zone of nearly complete wall rock albitization an intermediate zone of magnetite apatite actinolite veins pods breccias and wall rock replacement and an outer zone of disseminated sulfides one pluton balachey has a halo that is more or less completely outside the body but another rainy lake has a halo that is partly superimposed over it separation of iron phosphate and silicate melts by liquid immiscibility is not supported by 1 the gradual replacement of plagioclase by chessboard albite toward the roof of the rainy lake pluton 2 the chemical trends in the rainy lake intrusion 3 the mineralogical zoning low temperature mineralogy and replacement textures of the magnetite apatite actinolite and 4 the relationship of the magnetite apatite actinolite veins and bodies to the plutons however all available data are compatible with a deuteric origin it is concluded that high temperature low initial water content and shallow level emplacement by intermediate plutons are necessary for the development of kiruna type deposits

trace elements in magnetite from massive iron oxide apatite deposits indicate a combined formation by igneous and magmatic hydrothermal processes iron oxide apatite ioa deposits are an important source of iron and other elements e g ree p u ag and co vital to modern society however their formation including the namesake kiruna type ioa deposit sweden remains controversial working hypotheses include a purely magmatic origin involving separation of an fe p rich volatile rich oxide melt from a si rich silicate melt and precipitation of magnetite from an aqueous ore fluid which is either of magmatic hydrothermal or non magmatic surface or metamorphic origin in this study we focus on the geochemistry of magnetite from the cretaceous kiruna type los colorados ioa deposit 350 mt fe located in the northern chilean iron belt los colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in ioa deposits laser ablation inductively coupled plasma mass spectroscopy la icp ms transects and electron probe micro analyzer epma wavelength dispersive x ray wdx spectrometry mapping demonstrate distinct chemical zoning in magnetite grains wherein cores are enriched in ti al mn and mg the concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt whereas magnetite rims show a pronounced depletion in these elements consistent with magnetite grown from an fe rich magmatic hydrothermal aqueous fluid further magnetite grains contain polycrystalline inclusions that re homogenize at magmatic temperatures 850 c smaller inclusions 500 ppm concentrations

magnetite compositions from the baba ali iron deposit in the sanandaj sirjan zone western iran implications for ore genesis abstract the economically significant baba ali iron ore deposit is located in the sanandaj sirjan zone western iran is associated with diorite the mineralization trends in a ene wsw direction with thickness that varies from 30 m up to 50 m and a length of about 250 m the main mineral assemblages are massive magnetite epidote actinolite tourmaline quartz calcite and pyrite using different magnetite compositional discrimination diagrams the low concentrations of ti 0 11 wt al 0 06 wt cr 19 62 ppm and co 20 26 and high ni cr ratios 6 34 are consistent with a hydrothermal origin similar to typical skarn mineralization the different elemental compositions of various magnetite generations might be due to an ore forming fluid that initially a high t magmatic hydrothermal character then evolved to a lower temperture meteoric water dominated system it seems that fe bearing saline fluids infiltrated the carbonate host rocks causing high temperature acid metalliferous fluids to become neutralized during reaction with carbonates causing a decrease in iron solubility and saturating as a magnetite with increasing ph and decreasing the temperature the close spatial and temporal association of the mineralization with the fracture systems suggests that a pressure decrease also had a significant impact on the iron solubility triggering ore precipitation and replacement at relatively low temperatures 300 c under reducing conditions

iron rich fragments in the yamansu iron deposit xinjiang nw china constraints on metallogenesis abstract volcanic rock hosted iron deposits are among the important iron ores in china however the nature of primary magma and petrogenesis associated with these iron ores remains controversial here we report iron rich fragments irf from the yamansu iron deposit in eastern tianshan mountains nw china which occurs in association with volcanic breccia submarine volcanic breccia and ignimbrite the irf is composed of five types including oligoclase iron oxide type oio oligoclase albite iron oxide type oaio albite iron oxide type aio albite k feldspar iron oxide type akio and k feldspar iron oxide type kio these fragments display typical volcanic fabric features such as porphyritic texture hyalopilitic texture of the groundmass and vesicles filled by minerals to form amygdales the feldspar phenocrysts of irf are dominantly albite the groundmass of irf consists of magnetite and feldspar the magnetite is distributed in between the feldspar laths and together display hyalopilitic texture which could be observed only in volcanic rocks the vesicles are filled with magnetite feldspar chlorite and calcite from the margin to the interior the irf has high si al fe ca ti na and k contents and low mg content the average total fe is 26 wt the magnetite is mostly titanium vanadium magnetite with the tio2 content ranging up to 4 86 wt and v2o3 content up to 3 20 wt the irf probably came from iron rich melts and represent the products of the fenner magma evolution the basaltic magma evolved into the fe na rich residual melts by crystallization under low oxygen fugacity condition in a closed magma chamber after intruding into the shallow crust the fe na rich residual melts were emplaced in hypabyssal environments or erupted generating the orebodies or providing the material source for the generation of the high grade iron ores which were subsequently enriched by the late stage hydrothermal fluids

geochemistry of magnetite from the giant paleoproterozoic dahongshan fe cu deposit sw china constraints on nature of ore forming fluids and depositional setting abstract the dahongshan fe cu ore deposit hosted in the paleoproterozoic meta volcanic and meta sedimentary sequences is a giant deposit in the fe cu metallogenic province of southwestern china two ore types have been identified 1 massive and disseminated fe ores hosted dominantly in meta volcanic rocks and 2 disseminated and banded fe cu ores in meta sedimentary rocks magnetite presents in all orebodies and is dominant in the fe ores chemistry of magnetite suggest that the fluids for iron mineralization in the fe and fe cu orebodies are likely chemically similar and cogenetic minor sulfides e g molybdenite occur at the end of iron mineralization stage indicating the gradually decrease in oxygen fugacity for the mineralizing fluids with magnetite precipitation along with evolution mineralizing fluids generate magnetite with depletions in cr ni ga and v but enrichments in mn sn and co which are primarily reflective of the temperature decrease of fluids we have discovered some magnetite grains that are extremely rich in v 10000 ppm but low in ti and cr geochemical patterns suggest that they were formed by fluids similar to those of ordinary ores available knowledge about the unique high v magnetite indicates highly reduced marine environments for its generation ore bulk ree patterns showing remarkable positive eu anomalies and absence of obvious ce anomalies suggest a bif like marine environment consistent with the morphology of both fe and fe cu orebodies our results provide independent evidence for submarine environment in the formation of the giant precambrian stratiform fe cu ore deposit

trace elements in magnetite as petrogenetic indicators we have characterized the distribution of 25 trace elements in magnetite mg al si p ca sc ti v cr mn co ni cu zn ga ge y zr nb mo sn hf ta w and pb using laser ablation icp ms and electron microprobe from a variety of magmatic and hydrothermal ore forming environments and compared them with data from the literature we propose a new multielement diagram normalized to bulk continental crust designed to emphasize the partitioning behavior of trace elements between magnetite the melt fluid and co crystallizing phases the normalized pattern of magnetite reflects the composition of the melt fluid which in both magmatic and hydrothermal systems varies with temperature thus it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts the crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in ti or cu respectively the chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite e g si and ca magnetite formed from low temperature fluids has the lowest overall abundance of trace elements due to their lower solubility chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning which records the changing conditions and composition of the fluid during magnetite growth this new way of plotting all 25 trace elements on 1 diagram normalized to bulk continental crust and elements in order of compatibility into magnetite provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments it has applications in both petrogenetic and provenance studies such as in the exploration of ore deposits and in sedimentology

experimental effects of pressure and fluorine on apatite saturation in mafic magmas with reference to layered intrusions and massif anorthosites apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic complexes we investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes apatite saturation gives information about the formation of silicate rocks and is of interest in explaining the formation of apatite oxide rich rocks e g nelsonites comprising approximately one third apatite and two third fe ti oxide two models of formation are proposed for this rock type crystal fractionation followed by accumulation of apatite and fe ti oxides and liquid immiscibility new experiments carried out with mafic compositions at 500 mpa confirm that the most important variables on phosphate saturation are sio2 and cao fluorine addition leads to apatite saturation at lower sio2 and higher cao concentrations comparison of our results with those of previous experimental studies on liquid liquid immiscibility at upper to mid crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid liquid immiscibility in the petrogenesis of nelsonites and similar rocks the liquid line of descent of three natural examples studied the sept iles intrusive suite the anorthositic complex of the lac st jean and the skaergaard layered intrusion do not cross the liquid liquid immiscibility field before they reach apatite saturation thus the apatite oxide rich rock associated with these three intrusive suites are best explained by crystal fractionation followed by accumulation of apatite and fe ti oxides

in situ la icp ms trace element analysis of magnetite from mesozoic iron oxide apatite ioa deposits in the luzong volcanic basin eastern china abstract the iron copper gold belt in the middle and lower yangtze river region is among the most important metallogenic provinces in eastern china the luzong lujiang zongyang ore district hosts many significant iron deposits in the luzong basin and is an important part of this belt the yangshan deposit is hosted in the cretaceous volcanic rocks of the middle luzong basin the makou deposit in the southern central luzong basin has orebodies at the contact between gabbro diorite and volcanic rocks of the zhuanqiao formation there are three types of magnetite in these two deposits 1 magmatic magnetite from the makou gabbro diorite 2 hydrothermal magnetite from the makou deposit and 3 hydrothermal magnetite in the volcanic rocks from the yangshan deposit magmatic magnetite from gabbro diorite in the makou deposit has concentrations of elements mg al k sc ti v cr mn co ni and zn higher than hydrothermal magnetite magmatic magnetite from the makou deposit are the highest concentrations of cr sc ni al and zn but hydrothermal magnetite from this deposit has the lowest concentrations of these elements whereas hydrothermal magnetite from the yangshan deposit contains intermediate concentrations of these elements overall there are positive correlations between mg and al and ti and mn the makou and yangshan hydrothermal magnetite show highly variable mg values apparently influenced by clinopyroxene diopside crystallisation from hydrothermal fluids the ti ga and sn contents of the makou hydrothermal magnetite are generally higher than those from the yangshan deposit suggesting the makou magnetite formed under higher temperatures the formation of ival rich clinopyroxene in the yangshan deposit may have resulted in the low v content of magnetite whereas the high cr content may have been derived from the associated trachyandesite leaching of thick volcanic sequences via magmatic fluids may have led to the incorporation of certain elements into the ore forming fluids resulting in higher al mn and zn concentrations in the yangshan magnetite the makou hydrothermal magnetite has na and k contents similar but ca content higher than that of the magmatic magnetite indicating that na and k were retained in the melt but ca was enriched in the fluid both the makou and yangshan hydrothermal magnetites contain high v and low cr concentrations and resemble magnetite in ioa deposits elsewhere combined with the wall rocks and mineral assemblages the makou and yangshan deposits are best classified as magnetite apatite deposits intensive diopside alteration in these two deposits may be related to the marine sedimentary strata at the depth

defining early stages of iocg systems evidence from iron oxides in the outer shell of the olympic dam deposit south australia the iocg deposit at olympic dam south australia is hosted within the roxby downs granite which displays a weakly mineralised contact to the orebody hereafter outer shell in a mineralogical geochemical characterisation of fe oxides from the outer shell we show silician magnetite si magnetite and hfse bearing hematite define the early stages of alkali calcic alteration this association forms in the presence of hydrothermal k feldspar and calc silicates via overprinting of magmatic magnetite and ilmenite breakdown geochemical modelling at 400 c shows such reactions occur at ph fo2 conditions coinciding with shifts from k feldspar to sericite and ilmenite to rutile stability the subsequent si magnetite siderite association forms down t in the absence of k feldspar transition from granular to bladed morphologies in si magnetite is part of a series of fe oxide interconversions followed by formation of zoned u w sn mo bearing hematite enrichment in ree y and u in si magnetite and the prevalence of u w sn mo bearing hematite support a granite derived fluid combined petrographic and geochemical evidence show a transition among fe oxides from the outer shell to the orebody attributable to the evolution of the same fluid unusual massive magnetite intervals and fe oxide nodules in granite are considered due to either the presence of inherited lithologies metasomatic products or the result of magnetite rich crystal mush forming in the melt we propose a model corroborated by recently published data including high precision u pb dating of magmatic zircon and hydrothermal hematite in which an outer shell is initiated at the 6 8 km depth of granite emplacement during volatile release from fluids ponding at intrusion margins granite cupola collapse at shallower levels 2 3 km follows via uplift along faults facilitating intense brecciation and ore formation

dissolution reprecipitation process of magnetite from the chengchao iron deposit insights into ore genesis and implication for in situ chemical analysis of magnetite abstract magnetite formed in different environments commonly has distinct assemblages and concentrations of trace elements that can potentially be used as a genetic indicator of this mineral and associated ore deposits in this paper we present textural and compositional data of magnetite from the chengchao iron deposit daye district china to provide a better understanding in the formation mechanism and genesis of the deposit and shed light on analytical protocols for in situ chemical analysis of hydrothermal magnetite magnetite grains from the ore related granitoid pluton mineralized endoskarn magnetite dominated exoskarn and vein type iron ores hosted in marine carbonate intruded by the pluton were examined using scanning electron microscopy and analyzed for major and trace elements using electron microprobe back scattered electron images reveal that primary magnetite from the mineralized skarns and vein type ores were all partly reequilibrated with late stage hydrothermal fluids forming secondary magnetite domains that are featured by abundant porosity and have sharp contact with the primary magnetite these textures are interpreted as resulting from a dissolution reprecipitation process of magnetite which however are mostly obscure under optically primary magnetite grains from the mineralized endoskarn and vein type ores contain high sio 2 0 92 3 21 wt al 2 o 3 0 51 2 83 wt and low mgo 0 15 0 67 wt whereas varieties from the exoskarn ores have high mgo 2 76 3 07 wt and low sio 2 0 03 0 23 wt and al 2 o 3 0 54 1 05 wt this compositional contrast indicates that trace element geochemical composition of magnetite is largely controlled by the compositions of magmatic fluids and host rocks of the ores that have reacted with the fluids compared to its precursor mineral secondary magnetite is significantly depleted in most trace elements with sio 2 deceasing from 1 87 to 0 47 wt on average and al 2 o 3 from 0 89 to 0 08 wt in mineralized endoskarn and vein type ores and mgo from 2 87 to 0 60 wt in exoskarn ores on the contrary average content of iron is notably increased from 69 2 wt to 71 9 wt in the secondary magnetite grains the results suggest that the dissolution reprecipitation process has been important in significantly removing trace elements from early stage magnetite to form high grade high quality iron ores in hydrothermal environments the textural and compositional data confirm that the chengchao iron deposit is of hydrothermal origin rather than being crystallized from immiscible iron oxide melts as previously suggested this study also highlights the importance of textural characterization using various imaging techniques before in situ chemical analysis of magnetite as is the case for texturally complicated u th bearing accessory minerals that have been widely used for u pb geochronology study

partial least squares discriminant analysis of trace element compositions of magnetite from various vms deposit subtypes application to mineral exploration abstract the petrography and mineral chemistry of magnetite from fifteen volcanogenic massive sulfide vms deposits in canada and the lasail vms deposit in oman as well as from two vms associated banded iron formations bif austin brook new brunswick canada and izok lake nunavut canada were investigated using optical microscopy electron probe micro analyzer epma and laser ablation inductively coupled plasma mass spectrometry la icp ms the method of robust estimation for compositional data robcompositions was applied to investigate geochemical censored data among thirty seven elements analyzed by epma and or la icp ms in magnetite from the studied deposits bedrock lithologies only the results for si ca zr al mg ti zn co and ni contain pls da shows that variable compositions of magnetite slightly discriminate different studied deposits bedrock lithologies the geochemical observations suggest that the variation in magnetite chemistry from different vms settings might be sourced from differences in 1 the composition and temperature of parental magmas or hydrothermal fluids 2 the composition of host bedrocks 3 the composition of co forming minerals and 4 oxygen fugacity pls da distinguishes magnetite compositions from the studied vms deposits and bifs from that of the other ore deposit types including ni cu porphyry cu mo au iron oxide copper gold iron oxide apatite and the bayan obo ree fe nb deposit magnetite from the vms settings on average contains lower concentrations of si zr al mg ti zn co and ni relative to that from the other mineral deposit types pls da of magnetite data from vms deposits and bifs of the bathurst mining camp as well as pls da of magnetite compositions from various mineral deposit types yield discrimination models for application to mineral exploration for vms deposits using indicator minerals in quaternary lithified sedimentary rocks

nanogeochemistry of hydrothermal magnetite magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million ppm of elements such as ti si v al ca mg na which tend to either structurally incorporate into growth and sector zones or form mineral micro to nano sized particles here we report micro to nano structural and chemical data of hydrothermal magnetite from the los colorados iron oxide apatite deposit in chile where magnetite displays both types of trace element incorporation three generations of magnetites x z were identified with concentrations of minor and trace elements that vary significantly sio2 from below detection limit bdl to 3 1 wt al2o3 0 3 2 3 wt cao bdl 0 9 wt mgo 0 02 2 5 wt tio2 0 1 0 4 wt mno 0 04 0 2 wt na2o bdl 0 4 wt and k2o bdl 0 4 wt an exception is v2o3 which is remarkably constant ranging from 0 3 to 0 4 wt six types of crystalline nanoparticles nps were identified by means of transmission electron microscopy in the trace element rich zones which are each a few micrometres wide 1 diopside 2 clinoenstatite 3 amphibole 4 mica 5 ulvospinel and 6 ti rich magnetite in addition al rich nanodomains which contain 2 3 wt of al occur within a single crystal of magnetite the accumulation of nps in the trace element rich zones suggest that they form owing to supersaturation from a hydrothermal fluid followed by entrapment during continuous growth of the magnetite surface it is also concluded that mineral nps promote exsolution of new phases from the mineral host otherwise preserved as structurally bound trace elements the presence of abundant mineral nps in magnetite points to a complex incorporation of trace elements during growth and provides a cautionary note on the interpretation of micron scale chemical data of magnetite

tourmaline boron and strontium isotope systematics reveal magmatic fluid pulses and external fluid influx in a giant iron oxide apatite ioa deposit abstract tourmaline is a common boron bearing mineral in hydrothermal system and has been widely used as a mineral probe to reconstruct geological processes because of its broad range in composition and resistance to metasomatic alteration the origin of kiruna type iron oxide apatite ioa deposits commonly linked to andesitic subvolcanic or volcanic rocks is highly controversial constraints on the evolution of these mineralizing systems are needed to advance understanding of the ore forming process in this study we apply in situ elemental and combined b sr isotopic analyses of tourmaline to elucidate the nature and evolution of the subsurface hydrothermal system associated with ioa mineralization in the giant taocun deposit eastern china taocun is hosted at the top of a diorite intrusion and exhibits three stages of hydrothermal alteration that contain tourmaline pre ore na alteration tur i syn ore magnetite formation and associated ca fe alteration tur ii and post ore ca mg alteration with sulfide veins tur iii compositional data for each stage of tourmaline plot along the oxy dravite povondraite join which is indicative of precipitation from relatively oxidizing fluids ranges of sr isotopic compositions in tur i 0 7065 0 7078 and tur ii 0 7068 0 7076 are identical to those of the igneous host rocks indicating precipitation from magmatic hydrothermal fluids the range of b isotopic compositions in tur i 11b values of 6 3 to 1 2 is also consistent with a magmatic source higher 11b values 2 4 to 5 4 obtained from tur ii are mainly ascribed to rayleigh fractionation in the magmatic hydrothermal system as tourmaline precipitated post ore tur iii has a wide range of mostly lower b isotopic compositions 8 5 to 0 8 that record another pulse of magmatic fluid input this interpretation is supported by the enrichment of na li be w sn v and ti in tur iii relative to tur i and ii however the higher sr isotope composition 0 7076 0 7086 of tur iii and available o isotope composition 7 to 3 5 of fluids of this stage record the infiltration of meteoric ground water from adjacent sedimentary country rocks the results suggest that the taocun ioa deposit formed in a magmatic hydrothermal system characterized by two or more pulses of magmatic fluid discharge from subvolcanic diorite intrusions followed by the influx of external ground water as the system waned this study highlights the utility of tourmaline as a robust geochemical and isotopic monitor of ore forming processes in such systems

new field evidence bearing on the origin of the el laco magnetite deposit northern chile a reply the el laco magnetite deposit has been interpreted as lava flows and feeder dikes formed from iron oxide magma but more recently as a product of metasomatic replacement open pit exposure created at laco sur during the 1990s reveals that the massive magnetite contains magnetite veined blocks and smaller fragments of altered andesitic volcanic rock clearly supporting the replacement origin open space growth of magnetite and pyroxene along the walls of chimney structures and veins within magnetite indicates precipitation from aqueous fluid rather than from gas alone the native sulfur bearing cristobalite alunite alteration widespread at el laco and broadly contemporaneous with magnetite formation is recognized as part of a steam heated horizon generated in the vadose zone above a paleowater table consequently the magnetite replacement must have taken place beneath the paleowater table but probably 300 m beneath the paleosurface thus magnetite deposition at or immediately beneath the paleosurface is precluded the main outstanding question is how hot hypersaline brine the probable ore forming fluid at el laco attained such shallow crustal levels within a high volcanic edifice without undergoing the extensive groundwater dilution documented from most shallowly preserved hydrothermal systems

triple oxygen δ18o δ17o hydrogen δ2h and iron δ56fe stable isotope signatures indicate a silicate magma source and magmatic hydrothermal genesis for magnetite orebodies at el laco chile

the link between hydrothermal nickel mineralization and an iron oxide copper gold iocg system constraints based on mineral chemistry in the jatoba deposit carajas province abstract the jatoba deposit represents a specific portion of an archean paleoproterozoic iron oxide copper gold system notable due to its hydrothermal nickel rich zones neoarchean mafic and acid volcanic rocks of the itacaiunas supergroup host the mineralized zones pre syn and late shearing hydrothermal alteration associated with the canaa shear zone development was pervasive and intense early distal hydrothermal alteration encompasses potassic iron silica quartz biotite magnetite apatite sodic albite scapolite and sodic calcic ferro pargasite alteration the main syn tectonic hydrothermal alteration stage resulted in scapolite hastingsite biotite controlled by the mylonitic foliation syn deformation massive magnetite bodies represent proximal envelopes of the mineralized zones they were intercepted by actinolite apatite magnetite and potassic iron biotite magnetite alteration fronts late tectonic hydrothermal alteration comprises chlorite epidote quartz calcite fibrous scapolite veins and green biotite scapolite f cl apatite veinlets the copper nickel mineralized zones in the jatoba deposit were formed in four stages coeval to ductile and ductile brittle deformational events the mineralization stage i spatially related to massive magnetite apatite actinolite bodies has the highest nickel content it is characterized by ni pyrrhotite ni pyrite and subordinately co chalcopyrite ce allanite co pentlandite and ce monazite the mineralization style evolved from replacement fronts controlled by the mylonitic foliation to hydraulic breccia zones the mineralization stage ii was synchronous to the development of syn tectonic potassic iron alteration and co chalcopyrite ni pyrite ni pyrrhotite the mineralization stage iii controlled by ductile brittle and brittle structures enabled the formation of veins with typical open space filling textures infilled by paler brown or green biotite co chalcopyrite and siegenite co pyrite co magnetite cassiterite the late mineralization stage iv coeval to widespread chlorite alteration formed the most important copper mineralization at jatoba it is represented by branching veinlets and breccias with chalcopyrite co chalcopyrite co pyrite sphalerite molybdenite uraninite monazite w bearing hematite and rare earth carbonates bastnasite coskrenite and sahamalite the high chlorine contents of halogen rich minerals e g scapolite biotite apatite and amphibole imply the participation of highly saline supersaturated fluids in the system evolution metalliferous fluids were highly focused and mineralized zones represent the hotter hydrothermal centers the high v and ti contents in magnetite and its coexistence with hercynite and ilmenite indicate temperatures above 600 c these conditions would be similar to that of magnetite formed in the transition from magmatic to deep magmatic hydrothermal systems including the ioa deposits especially on the onset of the early nickel enriched mineralization stage such conditions enabled nickel leaching from mafic and mafic ultramafic rocks its transport in cl rich hydrothermal fluids and precipitation related to episodic decompression temperature decrease

oldest volcanic hosted submarine iron ores in south china evidence from zircon u pb geochronology and geochemistry of the paleoproterozoic dahongshan iron deposit abstract the dahongshan iron deposit is hosted in the paleoproterozoic submarine metavolcanic rocks of the dahongshan group in the yangtze block south china la icp ms dating of hydrothermal zircon grains from the genetically associated albitite and dolomite albitite show ca 2008 ma ages that are consistent with the zircon ages from the host metavolcanic rocks ca 2012 ma and postdated the post ore diabase dike ca 1724 ma marking the dahongshan iron deposit as the oldest submarine volcanic hosted deposit so far as known the ore hosting metavolcanic rocks in the dahongshan deposit have low ni 9 1 77 4 ppm cr 1 0 63 0 ppm and co contents 5 6 62 9 ppm suggesting the fractionation of olivine clinopyroxene and plagioclase within the magma chamber the major and trace element features of the alkaline to tholeiitic metavolcanic rocks are consistent with high degree partial melting of the mantle wedge metasomatized by melts enriched in high field strength elements hfses which were derived from the subducted slab in volcanic arc setting based on an evaluation of the morphology of orebody ore fabrics petrology and melt fluid inclusions as well as the geochemical characteristics of the major ore mineral magnetite we correlate the iron mineralization in the dahongshan deposit with hydrothermal process induced by the high temperature high salinity and fe rich brines derived through magmatic exsolution the similar characteristic of ce and eu anomalies of the dahongshan iron deposit and banded iron formations bifs suggest that the dahongshan deposit was formed in reducing environment although the two types of iron ores were generated through distinct processes with hydrothermal processes dominating for the submarine volcanic hosted iron deposits whereas the bifs were formed through chemical precipitation

differentiation of nelsonitic magmas in the formation of the 1 74 ga damiao fe ti p ore deposit north china the 1 74 ga damiao anorthosite complex north china is composed of anorthosite and leuconorite with subordinate melanorite mangerite oxide apatite gabbronorite perthite noritic i e jotunitic and ferrodioritic dykes the complex hosts abundant vein pod and lens like fe ti p ores containing variable amounts of apatite 10 60 modal and fe ti oxides in addition to fe ti p ores there are also abundant fe ti ores which are closely associated with fe ti p ores in the deposit most of fe ti p ores are dominated by fe ti oxides and apatite devoid of silicate minerals mineralogically similar to the common nelsonites elsewhere in contrast fe ti ores are dominated by fe ti oxides with minor apatite 5 modal the parental magma of these ores estimated from olivine and apatite compositions using mineral melt partition coefficients has composition similar to the ferrodioritic dykes fe ti p ores have variable fe ti oxides and apatite proportions indicating that they are cumulates their simple assemblage of fe ti oxides and apatite and local net texture suggest that the fe ti p ores in damiao have formed from nelsonitic melts immiscibly separated from the ferrodioritic magma during late stage differentiation fe ti ores are also cumulates and have mineral compositions similar to fe ti p ores the close association between fe ti and fe ti p ores indicates that the fe ti ores may have also formed from the nelsonitic melts we proposed that differentiation of nelsonitic melts accompanied by gravity settling is responsible for the formation of fe ti and fe ti p ores such a differentiation process in nelsonitic melts is well supported by variations of sr y th u ree and eu eu of apatite in fe ti p ores using oxides apatite ratio of 2 1 and compositions of apatite and calculated primary oxides we estimate the composition of the nelsonitic melt as 52 0 wt fe2o3t 18 5 wt cao 14 2 wt p2o5 8 7 wt tio2 4 0 wt al2o3 and 1 1 wt mgo with minor sio2 k2o na2o and f such a nelsonitic melt is suggested to be possibly conjugated with si rich melts compositionally similar to the damiao jotunitic dykes 50 wt sio2 and 15 wt fe2o3t which may subsequently evolve to mangeritic rocks in damiao our modeling also indicates that the onset of immiscibility occurs at a time when the evolved melt has 44 wt sio2 21 wt fe2o3t 3 0 wt tio2 and 2 6 wt p2o5 high oxygen fugacity and phosphorous content in magmas may play important roles in the immiscibility of nelsonitic magmas including promoting iron enrichments and widening the two liquid field

trends of atlantic wave extremes as simulated in a 40 yr wave hindcast using kinematically reanalyzed wind fields abstract in this study seasonal extremes of wave height in the north atlantic are analyzed the analysis is based on a 40 yr 1958 97 numerical wave hindcast using an intensive kinematic reanalysis of wind fields changes in the ocean wave extremes are identified by performing the mann kendall test and are further related to changes in the atmospheric circulation sea level pressure by means of redundancy analysis the relationship between sea level pressure and ocean wave extremes is also used to reconstruct the seasonal wave statistics for the last century back to 1899 consistent with previous studies this high resolution atlantic wave hindcast also shows that the northeast north atlantic ocean has experienced significant multidecadal variations in the last century and it has indeed roughened in winters of the last four decades the winter wave height increases are closely related to changes in the north atlantic oscillation during the last four decades while showing trend patterns similar to

high grade iron ore at windarling yilgarn craton a product of syn orogenic deformation hypogene hydrothermal alteration and supergene modification in an archean bif basalt lithostratigraphy banded iron formation bif hosted iron ore deposits in the windarling range are located in the lower greenstone succession of the marda diemals greenstone belt southern cross domain yilgarn craton and constitute a total hematite martite goethite ore resource of minimum 52 mt at 60 wt fe 0 07 p banded iron formation is interlayered with high mg basalts at windarling and precipitated during episodes of volcanic quiescence trace element content and the rare earth element ree ratios y ho 42 to 45 sm yb 1 5 together with positive la and gd anomalies in least altered hematite magnetite metachert bif indicate the precipitation from archean seawater that was fertilised by hydrothermal vent fluids with a basaltic hree y signature hypogene iron ore in sub greenschist facies metamorphosed bif formed during three distinct stages ore stage 1 was a syn to post metamorphic syn d1 fe ca mg ni co p ree metasomatism that produced local ni ree rich fe dolomite magnetite alteration in bif hydrothermal alteration was induced by hot fluid flow controlled by brittle ductile reactivation of bif basalt margins and crosscutting d1 faults the ni co rich content of dolomite and a shift in ree ratios in carbonate altered bif towards archean mafic rock signature y ho to 31 to 40 sm yb to 1 to 2 and gd gd to 1 2 to 1 4 suggest that high mg basalts in the windarling range were the primary source of introduced metals during ore stage 2 a syn deformational and likely acidic and oxidised fluid flow along bif basalt margins and within d1 faults leached carbonate and precipitated lepidoblastic and anhedral granoblastic hematite high grade magnetite hematite ore is formed during this stage ore stage 3 hydrothermal specular hematite spch fe dolomite quartz alteration was controlled by a late orogenic brittle compressional transpressional stage d4 the regional scale shear zone related d3 is not preserved in windarling this minor event remobilised iron oxides carbonate and quartz to form veins and breccia but did not generate significant volumes of iron ore ore stage 4 involved mesozoic to recent supergene oxidation and hydration in a weathering environment reaching down to depths of 100 to maximum 200 m below surface supergene ore formation involved goethite replacement of dolomite and quartz as well as martitisation important ground preparation for supergene modification and upgrade were mainly the formation of steep d1 to d4 structures steep bif basalt margins and particularly the syn d1 to syn d2 carbonate alteration of bif that is most susceptible to supergene dissolution the windarling deposits are structurally controlled supergene modified hydrothermal iron ore systems that share comparable physical chemical and ore forming characteristics to other iron ore deposits in the yilgarn craton e g koolyanobbing beebyn in the weld range mt gibson however the remarkable variety in pre syn and post deformational ore textures relative to d1 and d2 has not been described elsewhere in the yilgarn and are similar to the ore deposits in high strain zones such as of brazil quadrilatero ferrifero or iron quadrangle and nigeria the overall similarity of alteration stages i e the sequence of hydrothermal carbonate introduction and hypogene leaching with other greenstone belt hosted iron ore deposits supports the interpretation that syn orogenic bif alteration and upgrade was crucial in the formation of hypogene supergene iron ore deposits in the yilgarn craton and possibly in other archean paleoproterozoic greenstone belt settings worldwide

petrogenesis of a 900 ma mafic sill from xuzhou north china implications for the genesis of fe ti rich rocks abstract the niutishan sill one of the 900 ma mafic sills in xuzhou jiangsu province north china has a thickness of 30 m we have identified chemical parameters that define three differentiated interlayers from thirty eight samples in a 22 m profile the sill reveals a succession consisting of an upper border zone of fine grained dolerite uz a middle zone of quartz bearing gabbro mz a coarse grained apatite enriched gabbro lzc a layer of fe ti oxide enriched gabbro lzb and a deeper medium grained massive gabbro lza at the bottom of the lower zone capped by an uppermost chilled margin cm of plagioclase clinopyroxene porphyritic dolerite its significantly differentiated interlayers offer an opportunity to investigate the petrogenesis of high fe ti gabbro the chilled margin composition suggests a highly evolved ferro basaltic parental magma whole rock mg 39 with 2 9 wt tio2 and 14 2 wt feot which likely represents a residual magma derived from a deep seated magma chamber after significant removal of olivine the internal compositional variation was controlled by fractional crystallisation with successive presence of plagioclase and fe poor clinopyroxene followed by fe ti oxides plus fe rich clinopyroxene and finally apatite and albite oligoclase this sequence is consistent with the result of thermodynamic modelling of melts at a low h2o content of 0 2 wt and in a temperature range from 1200 to 780 c and at a pressure of 70 mpa the saturation of clinopyroxene before fe ti oxides in liquids is interpreted to imply low fo2 and water unsaturated conditions which led the residual magma to an fe ti enriched trend after the saturation and mechanical settling of clinopyroxene primocrysts from the parental magma large amounts of fe ti oxides crystallised from the evolved fe ti rich melt further crystallisation and solidification of the crystal mush led to the formation of the major fe ti oxide rich layer and expelled interstitial melt upward to mix with the more evolved residual melts leading to the saturation of apatite meanwhile the residual melts gradually tended to si enrichment which matches the observed compositions enriched incompatible elements of naturally occurring quartz gabbro in the mz as a result viscosity would increase trapping highly evolved melts and impeding liquid separation as exhibited by the silicic mesostasis of graphic intergrowths of quartz and alkali feldspar and occasionally calcite this sill is also characterized by considerable amounts of titanite at the bottoms of the uz and lz which was likely formed during the late evolutionary stages as products of reaction between the primary ti rich minerals and a late igneous fluid melt at temperature near 584 c the f rich and cl poor apatite xf 0 95 and ti rich magnetite 7 2 9 7 wt ti from fe ti p rich layers indicate a magmatic origin from high temperature fe ti rich melts it is thus concluded that the significantly differentiated niutishan sill was formed by the combined processes of fractionation accumulation and compaction under water unsaturated and low fo2 conditions which most likely occurred in an intra continental rather than a subduction related environment further synthetic analysis suggests conclusion that this magmatism may record a break up event

two tiered magmatic hydrothermal and skarn origin of magnetite from gol gohar iron ore deposit of se iran in situ la icp ms analyses abstract genesis of magnetite from gol gohar iron deposit ggid of southeastern iran is studied with reference to elemental composition more than 1 2 billion tonnes of magnetite ore at 58 total fe is hosted by greenschist to amphibolite facies metapelites and magnesian marbles the ggid occurs in the mainly metamorphic terrain of sanandaj sirjan geological province with continental margin tectonic setting the magnetite bearing ore is divided into two distinct types of massive and banded the latter hosted mainly by magnesian marbles both subtypes of the ore bodies are associated with mineral assemblages consisting of calcite dolomite forsterite tremolite actinolite talc serpentine and chlorite the ore minerals in both subtypes are magnetite hematite with minor amounts of pyrite pyrrhotite and chalcopyrite concentrations of temperature dependent elements ti al and ga in the two subtypes would suggest that temperature of formation was higher for the massive magnetite with ti 626 ppm al 69 ppm and ga 56 ppm on average and relatively lower for the banded magnetite with ti 60 ppm al 62 ppm and ga 4 ppm on average the multi element diagrams for massive magnetite show patterns closer to those of magmatic hydrothermel iron deposits kiruna type whereas patterns of the banded magnetite match better with those of skarn deposits particularly the magnesian skarns average concentrations of v 1000 ppm and cr 4 ppm of the massive subtype fall within the range of those of kiruna type deposits and the in average lower concentrations of v 10 ppm and cr 1 ppm of the banded magnetite match the values of skarn deposits the average v content of the massive magnetite 1342 ppm is consistent with the global range of magmatic hydrothermal magnetite up to 3880 ppm but different from global values of purely magmatic magnetites up to 6600 ppm the banded magnetites contain 0 21 25 ppm v which is only consistent with the lowest values of hydrothermal magnetites we contend that the massive magnetite was formed by magmatic hydrothermal processes i e kiruna type and the banded magnetites were generated via metasomatic reactions between iron rich residual magmatic fluids and the magnesian carbonate host rocks i e skarn type

alteration facies linkages among iron oxide copper gold iron oxide apatite and affiliated deposits in the great bear magmatic zone northwest territories canada high temperature metasomatism driven by ascent of voluminous saline fluid columns in the upper crust plays a major role in the genesis of iron oxide alkali alteration ore systems but fundamental questions remain on genetic linkages among iron oxide copper gold iocg iron oxide apatite ioa albitite hosted uranium and skarn deposits that they produce excellent surface exposures of such systems in the great bear magmatic zone of northernwestern canada record the depth to paleosurface prograde evolution of iron oxide alkali alteration facies and mineralization across the belt albitite corridors that are tens of kilometers in length record the earliest reactions between highly saline fluids and host rocks along fault zones and subvolcanic intrusions pervasive albitization partitioned metals from the host rocks into the ascending fluid column leaving behind structurally weakened corridors of porous albitite these corridors were cut replaced and overprinted by amphibole and magnetite bearing calcic iron alteration assemblages in extreme cases the discharge of calcium iron and specialized metals formed iron oxide apatite deposits vanadium rare earth elements while recharging the outgoing fluids in sodium potassium and base and precious metals as temperatures declined and fluid chemistry evolved through fluid rock reactions the formation of potassic iron alteration assemblages breccias and sulfides resulted in magnetite and hematite group iocg mineralization within carbonate units skarns formed prior to are replaced by and evolved to calcic iron alteration facies skarns can locally host base metal mineralization tectonically uplifted albitite breccias replaced by potassic iron alteration assemblages became a preferential host for uranium mineralization the results of this study also illustrate that permutations and cyclical build up of alteration products can arise from a combination of faulting differential uplift and renewed magmatism framed within an alteration facies deposit model alteration zones and mineral occurrences play a pivotal role in predicting the mineral potential of iron oxide and alkali altered systems at district to deposit scales

immiscible iron and silica rich melts and magnetite geochemistry at the el laco volcano northern chile evidence for a magmatic origin for the magnetite deposits abstract the pliocene el laco volcano northern chile hosts a large iron oxide deposit that occurs as stratiform bodies with underlying feeder zones dykes hosted by hydrothermally altered andesite lava flows phenocrysts in the andesite hosting the mineralization have abundant melt inclusions displaying strong evidence for melt immiscibility most of the pyroxene and the plagioclase phenocrysts contain abundant fe rich melt inclusions with low ti magnetite pyroxene apatite and minor anhydrite the glassy groundmass of these melt inclusions is chemically similar to sub alkaline rhyolitic rocks e g 70 sio 2 si al k na rich large resorbed plagioclase phenocrysts also host another group of melt inclusions with a similar silica rich groundmass but hosting evenly distributed immiscible and complex fe rich spheroidal globules that are enriched in ti p mg ca and s these immiscible globules and the ti poor magnetite daughter crystals in the melt inclusions in pyroxene phenocrysts are thought to be the parental iron oxide melt liquid after which their coalescence leads to the formation of magnetite melts from which the magnetite that formed the el laco iron oxide deposits crystallized and were emplaced the mineralogy and chemistry of these melt inclusions tracks the chemical evolution of the fe ox melts and supports a magmatic origin for the el laco magnetite this is mainly recognized by the continuum of compositions between volcanic separate immiscible fe oxide melts and magnetite ores the trace element composition of the fe rich melt inclusions and of the magnetite in the host andesite and the ore bodies reveals a systematic depletion in most of the elements that are compatible in magnetite the ti content of the magnetite also records the separation and crystallization of the iron rich melt typically the magnetite in the orebodies and the melt inclusions is ti poor compared with titanomagnetite found in the andesite groundmass and that hosted by the hydrothermally altered andesite that is interpreted as being attributed to its crystallization under oxidizing and sulfur rich conditions the cause of this unusual chemical behaviour is probably due to the mechanism s governing the crystallization of the iron rich melt including the temperature changes in chemistry prior to eruption and an increase in the redox conditions of the silicate melt magma oxidation facilitates the prevalence of ferric iron and formation of ti poor magnetite preventing the incorporation of ti in the exsolving iron rich melt the likely reason for the formation of these large ti poor magnetite deposits is likely the contamination of the parental andesitic magma by oxidized crustal rocks and concomitant crystallization of magnetite under oxidizing conditions something that had a significant impact on the elemental distribution

depositional sequences and stratigraphy of the colon carbonate platform bocas del toro archipelago panama abstract the colon platform located in the bocas del toro region of panama was studied as a near modern analog for buried reefal platforms the platform has an areal extent of 90 km2 and formed in a convergent tectonic setting backarc under a tropical climatic regime the attached platform formed as part of a discontinuously rimmed shelf along the caribbean side of the isthmus of panama and consisted of mixed carbonates and siliciclastics based on field relations and strontium isotope stratigraphy three depositional sequences were identified in the near surface deposits of the uplifted platform a miocene to late pliocene lithic sandstone unit sequence 1 old bank formation forms the foundation of the platform coral rich limestone and coral rich siliciclastic units were deposited during both the late pliocene sequence 2 isla colon formation and early pleistocene sequence 3 urraca formation in sequences 2 and 3 the sediment composition and fauna show distinct differences between the windward and leeward sides of the platform with the main lithologic variable being the amount of siliciclastic sediment that was admixed with the biogenic carbonate sediments the siliciclastic deposits mud rich in sequences 2 and 3 exhibit lower permeability and relatively minor diagenetic modification and they lack major karst features conversely the more carbonate rich deposits are well cemented and strongly affected by meteoric dissolution and karstification this facies selective dissolution occurred when middle pleistocene regional uplift exposed the platform to a tropical climate with high rainfall earthquakes and associated uplift of the platform over the past 1 myr intensely fractured the limestone fracture porosity has contributed to rapid infiltration of meteoric water and pervasive dissolution that resulted in numerous vertical sinks as well as an extensive network of horizontal conduits a large incised channel feature connects several of the pre existing caves and conduits the colon platform limestone is a product of an equatorial humid carbonate system and is of size similar to platforms of oligo miocene age near malaysia sarawak indonesia and farther north in the south china sea

a genetic link between iron oxide apatite and iron skarn mineralization in the jinniu volcanic basin daye district eastern china evidence from magnetite geochemistry and multi mineral u pb geochronology various styles of ore deposits may form from a single magmatic hydrothermal system identification of a possible genetic link between different ore types in a region is not only of critical importance for a better understanding of the magmatic hydrothermal processes but can also help in successful mineral exploration both iron oxide apatite ioa and iron skarn deposits are closely associated with intrusive rocks of intermediate to felsic in composition but whether these two ore types can form from the same magmatic intrusion remains poorly understood in this study we present a comparative study between a newly identified subsurface ioa ore body located at the apex of a diorite porphyry and the iron skarn ore bodies located immediately above it in the jinniu volcanic basin of the daye district middle lower yangtze river metal logenetic belt mlyrmb eastern china in order to highlight a genetic link between these two styles of mineralization the ioa ores are dominated by ti rich magnetite with variable amounts of fluorapatite diopside and actinolite this mineralogical assemblage is distinctly different from the iron skarn ores which consist mainly of ti depleted magnetite and subordinate pre ore garnet and diopside and post ore quartz chlorite calcite and pyrite in addition magnetite from the ioa ores is characterized by well developed ilmenite lamellae and has high concentrations of ni v co and ga consistent with high temperature crystallization whereas magnetite grains from the iron skarn ores usually exhibit oscillatory growth zones and contain much lower ni v co and ga indicating their formation under relatively low temperatures titanite and fluorapatite from the ioa ores have u pb ages of 132 5 2 4 ma to 128 4 3 0 ma which match a titanite u pb age for the associated iron skarn ores 1323 2 0 ma and are consistent with zircon u pb ages for the ore hosting diorite porphyry 130 4 0 7 ma to 130 3 0 5 ma this age consistency supports a possible genetic link among the diorite porphyry ioa ores and iron skarn ores we propose that the ioa and skarn ores are the products of two consecutive mineralization stages of the same magmatic hydrothermal system involving a high temperature hypersaline fluid coexisting with the diorite porphyry magma during emplacement and a subsequent low temperature diluted hydrothermal fluid other ioa and iron skarn deposits of similar ages 130 ma are found in a series of volcanic basins in the mlyrmb which forms one of the world s largest ioa metallogenic belts the close association of the two ore styles identified at daye provides a useful exploration guide for ioa and iron skarn deposits both on a local and regional scale

fe ti p oxide melts generated through magma mixing in the antauta subvolcanic center peru implications for the origin of nelsonite and iron oxide dominated hydrothermal deposits commingling and mixing of k rich basaltic absarokitic and partially crystallized strongly peraluminous s type monzogranitic rhyodacitic magmas have been documented in the 23 8 ma antauta hypabyssal complex of the picotani group puno southeastern peru magma mixing generated intermediate andesitic rocks hosting small volumes of sio2 poor 8 4 wt fe oxide rich melt with tio2 30 wt and p2o5 23 wt contents corresponding to those of the genetically problematic nelsonite ore type microscopic spheres of this composition are embedded in rhyolitic glass surrounding both extensively melted sieve textured plagioclase xenocrysts derived from the rhyodacitic magma and cognate orthopyroxene phenocrysts exhibiting replacive fe rich mantles the andesites also contain up to 15 modal percent of strongly resorbed granite derived quartz xenocrysts with glass orthopyroxene clinopyroxene coronas intense quasipervasive silicification of the fractionating mafic magma is inferred to have displaced the hybridized melt composition into the stable liquid immiscibility region of the na2o k2o mgo al2o3 feo tio2 mno cao p2o5 sio2 h2o system some fe ti p rich bodies have 30 to ca 55 wt percent sio2 and exhibit broadly linear trends of major oxides versus sio2 but the more sio2 deficient spheres exhibit extreme compositional scatter implying the existence of complex immiscibility fields within the parental protonelsonitic melt domain in contrast the predominant apparently conjugate silicate glass 70 78 wt sio2 is relatively consistent in composition and equivalent to a syenogranite and or rhyolite the extreme local variability in the composition of the oxide rich melt bodies may directly reflect their formation in a magma mixing environment in which temperature varied over at least 200 to 300 c such a compositional range also apparent in large scale nelsonite occurrences indicates that strong fractionation of mafic melts under conditions precluding ferroan spinel crystallization may not be a prerequisite for oxide silicate immiscibility and hence nelsonite formation specular hematite is widely disseminated in the glassy andesites commonly clustered around resorbed quartz xenocrysts and microscopic bodies of illite montmorillonite chlorite occur in contact with unaltered glass in unveined andesites implying endogenous sources of respectively iron and hydrothermal fluid moreover the upper paleozoic clastic sedimentary envelope of the antauta center at pucacancha hosts hydrothermal breccias and veins rich in hematite barite quartz chalcedony and epidote with lesser anhydrite and traces of u th ree rich allanite chalcopyrite and molybdenian scheelite this unambiguously hydrothermal mineralization is analogous to that of the iron oxide copper gold clan and we propose that the development of some deposits of this type may have been triggered by the formation and subsequent vesiculation of immiscible fe rich oxide melt during the mixing of mafic and felsic magmas

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

occurrence of apatite associated with magnetite in an ophiolite complex othrys greece small irregular to lens like occurrences maximum 0 5 1 m of apatite associated with magnetite and silicates are present in the agoriani area of the othrys ophiolite complex central greece the ano agoriani area is dominated by peridotite plagioclase lherzolite of the mantle sequence intruded by irregular bodies dikes and veins of gabbro as well as by dikes of pyroxenite and pegmatitic gabbro apatite occurs as large up to 3 cm long well formed crystals associated with magnetite the aggregates consist predominantly of apatite or massive magnetite with subordinate amounts of apatite apatite may also be accompanied by silicate minerals mainly chlorite and lesser amounts of serpentine tremolite and ni silicates nepouite pimelite and by ni sulfides pentlandite violarite heazlewoodite the apatite magnetite association from the agoriani area differs from nelsonite hosted by an orthosite suites with respect to 1 the host rock type ophiolites 2 the highly variable proportion between apatite magnetite 3 the large size up to 3 cm of the apatite crystals 4 the lack of fluorine 20 ppm f in the apatite 5 the presence of abundant liquid rich fluid inclusions in apatite and 6 the lack of ilmenite the high v content 700 1000 ppm of the magnetite from agoriani differs from that of disseminated fe ti mineralization ti magnetite ilmenite in the magmatic sequence of ophiolite complexes mainly hosted in gabbronorites as well as the pure massive magnetite associated with fe ni cu co sulfides found in shear zones in ophiolite complexes the composition of the apatite chlor hydroxylapatite the presence of abundant primary two phase aqueous fluid inclusions in the apatite and the composition of the associated magnetite and sulfides suggest that a hydrothermal system played an essential role in the formation of these deposits

combined igneous and hydrothermal source for the kiruna type bafq magnetite apatite deposit in central iran trace element and oxygen isotope studies of magnetite abstract the main deposits of the bafq district choghart se chahun and chadormalou deposits are magnetite apatite ore bodies with early cambrian age hosted by early cambrian volcano sedimentary rocks showing lava flow structure with miarolitic cavities and occasional brecciation the texture and geochemistry trace elements and o isotope of the studied magnetite crystals show three types of magnetite with different proportions in different parts of the district and the deposits these are primary ignious magnetite and high temperature hydrothermal magnetite in the massive parts of the deposits and foam like magnetite in the veins or in the fractures of the massive part the lack of zonation high ti fe ratios and 18o values 2 than the massive magnetites the magmatic origin for the main part of the ores in the bafq is more plausible contamination of the primary magmas of the bafq magmatic rocks with crustal phosphorus and evaporate units was the major agent for triggering iron rich melt immiscibility from the original magma concentration of volatiles in the iron rich melt involving in crystallization of the primary magnetite and nucleation of the aqueous fluid bubbles on magnetite surfaces led to ascending the buoyant fluid bubble magnetite aggregates this caused continuation of the magmatic magnetite microlites growth from the iron rich magmatic hydrothermal fluid and formed high temperature hydrothermal magnetite formation of hypersaline fluid due to crystallization of iron rich melt at shallow depth led to crystallization of titanite and th u ree bearing minerals and sodic calcic alteration related to magnetite mineralization microscopic evidence replacement of magnetite by hematite and filling of fractures of thorite by magnetite show that degassing continued at shallow depth which led to re crystallization of the primary magnetites and formation of the foam like magnetites

variation in trace element content of magnetite crystallized from a fractionating sulfide liquid sudbury canada implications for provenance discrimination abstract laser ablation icp ms analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination we have determined trace element concentrations of fe oxides in massive sulfides that form ni cu pge deposits at the base of the sudbury igneous complex in canada the samples represent the crystallization products of fractionating sulfide liquids and consist of early forming fe rich monosulfide solution mss cumulates and residual cu rich intermediate solid solution iss this study shows that fe oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and fe oxide phases in addition it is useful in determining the provenance of detrital fe oxide in a sulfide melt all lithophile elements cr ti v al mn sc nb ga ge ta hf w and zr are compatible into fe oxide the concentrations of these elements are highest in the early forming fe oxide titanomagnetite which crystallized with fe rich mss upon the continual crystallization of fe oxide from the sulfide liquid the lithophile elements gradually decrease so that late forming fe oxide magnetite which crystallized from the residual cu rich liquid is depleted in these elements this behavior is in contrast with fe oxides that crystallized from a fractionating silicate melt whereby the concentration of incompatible elements such as ti increases rather than decreases the behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only ni co zn mo sn and pb present above detection limit in magnetite nickel mo and co are compatible in fe rich mss and thus the co crystallizing fe oxide is depleted in these elements in contrast magnetite that crystallized later from the fractionated liquid with cu rich iss is enriched in ni mo and co because fe rich mss is absent the concentrations of sn and pb which are incompatible with fe rich mss are highest in magnetite that formed from the fractionated cu rich liquid at subsolidus temperatures ilmenite exsolved from titanomagnetite whereas al spinel exsolved from the cores of some magnetite locally redistributing the trace elements however during laser ablation icp ms analysis of these fe oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the fe oxide that crystallized from the sulfide melt

experiments on phosphate silicate liquid immiscibility with potential links to iron oxide apatite and nelsonite deposits the formation of phosphorus iron oxide p fe immiscible melts and their possible connection to the genesis of kiruna type and nelsonite deposits was experimentally investigated by adding phosphoric acid h3po4 water and sulfur to andesite at 100 450 mpa 500 900 c at the ninio and magnetite hematite fo2 buffers using internally heated gas vessels the addition of up to 8 02 wt of h3po4 to the andesite causes crystallization of apatite at higher concentrations of h3po4 whitlockite crystallizes and at concentrations above 11 4 h3po4 at 800 c 385 mpa an immiscible p fe melt forms adding sulfur at low fo2 ninio causes an additional immiscible fe s melt to form increasing the fo2 to the hematite magnetite buffer causes the sulfur rich melt to shift in composition to a ca s o melt and the coexisting p fe melt to incorporate large amounts of so4 immiscible p fe melts can form at temperatures above 1100 c down to 600 c at 400 mpa mass balance calculations show that some experimentally produced p fe rich immiscible liquids may result in mineral assemblages similar to those found at some kiruna type deposits such as actinolite rich dikes and apatite rich veins depending on the geological conditions and the composition the fractionation of a p fe melt may result in the formation of nelsonites at high pressures high temperatures and low fo2 or kiruna type deposits at lower temperatures and higher fo2

mineral equilibria and zircon garnet and titanite u pb ages constraining the ptt path of granite related hydrothermal systems at the big bell gold deposit western australia the big bell deposit 75 t gold is located in a narrow spur of the meekatharra greenstone belt yilgarn craton western australia two ore bodies are located in a calcic potassic contact alteration zone overprinting lineated granodiorite dykes and amphibolite almandine cummingtonite hornblende skarn 1 3 g t au 1700 g t as 330 g t w and the muscovite microcline gneiss 3 5 g t au 580 g t sb 620 g t w of the main lode genetic models vary from pre to post metamorphic replacement hornblende plagioclase pairs in amphibolite constrain peak metamorphic temperature to 670 50 c in contrast garnet biotite thermometry provides estimates of 578 50 and 608 50 c for garnet cordierite biotite schist bordering the skarn and enveloping the main lode garnet cordierite and garnet hornblende pairs extend the range of fluid temperature to 540 65 c well below peak metamorphic temperature at 540 600 c the alteration assemblage andalusite sillimanite constrains pressure to 300 400 mpa corresponding to 11 14 km crustal depth published u pb ages indicate that metamorphism took place in the aureole of the southeast granodiorite tonalite batholith 2740 2700 ma followed by gold mineralization at 2662 5 ma and by the emplacement of biotite granite and sn ta nb granite pegmatite dykes at 2625 2610 ma amphibolite xenoliths in granite northwest of the deposit record the lowest temperature 628 50 c suggesting it lacks a metamorphic aureole the rare metal dykes are spatially associated with epidote albite and andradite diopside skarns 1 5 g t au mined where enriched in the weathered zone we analysed hydrothermal zircon intergrown with andradite concordant u pb ages of 2612 7 and 2609 10 ma confirm the presence of a second granite related system the zircons display oscillatory zoning and have low th u ratios 0 05 0 08 low th titanite from an albite granite dyke has a concordant but reset u pb age of 2577 7 ma

geology petrography and mineral chemistry of iron oxide apatite occurrences ioa type western sector of the neoproterozoic santa quiteria magmatic arc ceara northeast brazil abstract iron oxide apatite ioa occurrences have recently been identified in the western sector of the neoproterozoic santa quiteria magmatic arc ceara state northeast brazil close to the boundary with the paleozoic parnaiba basin the ioa mineralization is hosted by albitized metadiorites and metavolcano sedimentary rocks which are crosscut by a late to post brasiliano pan african biotite granite intrusion with a u pb age approximately 548 4 ma within the metavolcano sedimentary sequence metavolcanic rocks are bimodal and consist of albitized metabasalt andesite and metarhyolites with a u pb age of 554 6 ma whereas the metasedimentary units are represented by calc silicate marble and pelitic gneisses the iron oxide apatite mineralization occurs as i banded stratabound lenses layers composed of magnetite 50 70 with or without ilmenite exsolution apatite 8 monazite and locally subordinate copper sulfides 2 ii massive magnetite specular hematite apatite bodies iii disseminated and vein magnetite apatite within albitized metadiorite iv massive rhombohedral hematite bodies and v garnet magnetite type the host rocks also display marialite diopside albite and epidote sodic calcic alteration biotite and k feldspar potassic alteration chlorite and epidote in lower t hydrothermal alteration assemblages mineral chemistry data reveal that i except for vein types apatite in all the other occurrences is f rich 2 4 f 4 4 and low in cl

magnetite chemistry as a provenance indicator in archean metamorphosed sedimentary rocks abstract conventional provenance studies of high grade e g amphibolite facies metamorphic sandstone are limited due to intense recrystallization destruction of original minerals and growth of new minerals magnetite is a heavy mineral common in a wide range of sedimentary rocks it can originate from a wide range of rock sources from high temperature to low temperature magmatic metamorphic or hydrothermal environments laser ablation la icp ms and electron microprobe analytical techniques allowed determination of a wide range of trace elements at sub ppm levels in magnetite to identify the provenance of two archean sedimentary formations in eeyou istchee baie james quebec canada results were plotted on multi element diagrams the most compatible elements in magnetite were identified as the most discriminant elements to differentiate four potential different rock sources for the magin formation overlap between the spectra of the magin and keyano formations substantiate the existence of a common source interbedded conglomerate magnetite bearing clasts were examined to determine potential source rocks mafic clasts apparently do not contain magnetite detrital magnetites analyzed have low ti values that would support either felsic to intermediate plutonic or a hydrothermal source the trace element spectra of detrital magnetite from the sandstone beds were compared to magnetite spectra from conglomerate clasts of banded iron formation and felsic to intermediate plutonic rocks only magnetites from felsic plutonic rocks have a signature similar to those from the sandstone to further substantiate a felsic plutonic source a detailed study of magnetite chemistry from ten felsic and intermediate regional plutons from a regional databank allowed us to recognize that each of these plutons has a particular signature on the basis of wide variations in ni and cr from this data base four individual plutons were identified as potential sources for the magin formation recently published magnetite discrimination diagrams proposed for mineral deposits can be applied to sedimentary magnetite provenance however our database shows the importance of identifying low ti magnetite from felsic rocks since these could be misidentified as low ti magnetite from hydrothermal mineral deposits thus we propose improvement to these diagrams by differentiating magnetite from felsic magmatic low ni cr and hydrothermal high ni cr sources before applying the mineral deposit discrimination diagrams