iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

fe cu deposits in the kangdian region sw china a proterozoic iocg iron oxide copper gold metallogenic province numerous fe cu deposits are hosted in the late paleoproterozoic dongchuan and dahongshan groups in the kangdian region sw china the dongchuan group is composed of siltstone slate and dolostone with minor volcanic rocks whereas the dahongshan group has undergone lower amphibolite facies metamorphism and consists of quartz mica schist albitite quartzite marble and amphibolite with local migmatite deposits in the dongchuan group are commonly localized in the cores of anticlines in fault bends and intersections and at lithological contacts orebodies are closely associated with breccias which are locally derived from the host rocks fe oxides magnetite and or hematite and cu sulfides chalcopyrite bornite form disseminated vein like and massive ores and typically fill open spaces in the host rocks the deposits have extensive albite alteration and local k feldspar alteration overprinted by quartz carbonate sericite and chlorite deposits in the dahongshan group have orebodies sub parellel to stratification and show crude stratal partitioning of metals fe oxide ores occur as massive and or banded replacements within the breccia pipes whereas cu sulfide ores occur predominantly as disseminations and veinlets within mica schists and massive magnetite ores ore textures suggest that cu sulfides formed somewhat later than fe oxides but are possibly within the same mineralization event both ore minerals predated regional neoproterozoic metamorphism both orebodies and host rocks have undergone extensive alteration of albite scapolite amphibole biotite sericite and chlorite silica and carbonate alterations are also widespread ore hosting strata have a la icp ms zircon u pb age of 1681 13 ma and a dolerite dyke cutting the fe oxide orebodies has an age of 1659 16 ma thus the mineralization age of the dahongshan deposit is constrained at between the two all ores from the two groups have high fe and low ti with variable cu contents locally they are rich in mo co v and ree but all are poor in pb and zn sulfides from the fe cu deposits have 34s values mostly in the range of 2 to 6 per mil suggesting a mix of several sources due to large scale leaching of the strata with the involvement of evaporites isotopic dating and field relationships suggest that these deposits formed in the late paleoproterozoic ore textures mineralogy and alteration characteristics are typical of iocg type deposits and thus define a major iocg metallogenic province with significant implications for future exploration

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

late paleoproterozoic sedimentary and mafic rocks in the hekou area sw china implication for the reconstruction of the yangtze block in columbia abstract the paleoproterozoic hekou group in the western yangtze block is a volcano sedimentary succession that is intruded by gabbroic plutons sedimentary rocks in the group include slates marble and meta siltstones interlayered with felsic metavolcanic rocks metabasalts and metatuffs both the volcanic rocks of the hekou group and gabbros have undergone upper greenschist to lower amphibolite facies metamorphism metatuff samples from different layers have average zircon u pb ages of 1697 ma slightly older than the intruding gabbroic plutons with zircon u pb ages of 1684 ma both metabasalts and metagabbros have similar elemental and isotopic compositions indicative of a co magmatic origin they are rich in tio2 mostly 2 5 wt zr 94 5 347 ppm ta 0 48 3 00 ppm and th 1 05 7 61 ppm with high nb y ratios mostly 0 6 and lree enriched chondrite normalized ree patterns resembling within plate mafic rocks their positive whole rock nd t 0 2 to 3 4 and zircon hf t values 3 3 to 8 4 suggest contributions from a depleted mantle source the large range of nd t and hf t values and variable degrees of nb ta anomalies ta lapn 0 17 1 75 are indicative of crust contamination during magma ascending both the metabasalts and metagabbros are considered to have formed in a continental rift setting detrital zircon grains from meta siltstones in the hekou group have u pb age populations mainly at 2070 1880 ma 2330 2250 ma and 2900 2700 ma these age populations are comparable to those of the north australian and north china cratons in the columbia supercontinent however in terms of geochemical features the 1 7 ga within plate mafic rocks at hekou are similar to those from the 1 7 ga leichhardt and calvert superbasins of the north australian craton but different from those from the 1 7 1 2 ga zhaertai bayan obo rift zone of the north china craton it is thus suggested that the yangtze block was more likely linked with the north australian craton in columbia during the late paleoproterozoic these rifting basins and mafic rocks may record the initial break up of the columbia supercontinent

an intrusion related origin for cu au mineralization in iron oxide copper gold iocg provinces major cu au deposits of iron oxide copper gold iocg style are temporally associated with oxidized potassic granitoids similar to those linked to major porphyry cu au deposits stable and radiogenic isotope evidence indicates fluids and ore components were likely sourced from the intrusions iocg deposits form over a range of crustal levels because co2 rich fluids separate from the magmas at higher pressures than in co2 poor systems thereby promoting partitioning of h2o cl and metals to the fluid phase at deep levels the magma fluid system cannot generate sufficient mechanical energy to fracture the host rocks as in porphyry systems and the iocg deposits therefore form in a variety of fault related structural traps where the magmatic fluids may mix with other fluids to promote ore formation at shallow levels the iocg deposits form breccia and fracture hosted mineralization styles similar to the hydrothermal intrusive breccias and sulphide vein systems that characterize many porphyry cu au deposits the fluids associated with iocg deposits are typically h2o co2 salt fluids that evolve by unmixing of the carbonic phase and by mixing with fluids from other sources in contrast fluids in porphyry systems typically evolve by boiling of moderate salinity fluid to produce high salinity brine and a vapor phase commonly with input of externally derived fluids these different fluid compositions and mechanisms of evolution lead to different alteration types and parageneses in porphyry and iocg deposits porphyry cu au deposits typically evolve through potassic sericitic and intermediate and or advanced argillic stages while iocg deposits typically evolve through sodic calcic potassic and carbonate rich stages and at deeper levels generally lack sericitic and argillic alteration the common association of porphyry and iocg cu au deposits with potassic oxidized intermediate to felsic granitoids together with their contrasting fluid compositions alteration styles and parageneses suggest that they should be considered as part of the broad family of intrusion related systems but that they are typically not directly related to each other

tourmaline b isotopes fingerprint marine evaporites as the source of high salinity ore fluids in iron oxide copper gold deposits carajas mineral province brazil the carajas mineral province in northern brazil contains a variety of world class 100 mt ore iron oxide copper gold iocg deposits including the only archean examples of this deposit class e g the igarape bahia alemao and salobo deposits tourmaline of schorldravite composition a common gangue mineral in these deposits precipitated shortly prior to and after the ore assemblage a boron isotope study of texturally different tourmaline from three iocg deposits igarape bahia salobo and sossego using secondary ion mass spectrometry sims provides new evidence in the long standing debate of magmatic versus non magmatic sources for the high salinity up to 50 wt nacl equiv of ore fl uids in these deposits values of 11 b from 14 to 26 5 for the igarape bahia and salobo deposits confi rm marine evaporite derived brines in the ore fl uids whereas lower 11 b values for the igarape bahia deposit 5 8 to 8 8 suggest that these fl uids may have mixed with an isotopically different hydrothermal fl uid or one that had a mixed boron source more variable and isotopically lighter boron in tourmaline from the sossego deposit 8 to 11 is attributed to mixed sources including light boron leached from felsic intrusive and volcanic host rocks and heavy boron derived from marine evaporites the boron isotope data indicate that the characteristic high salinity of the ore fl uids in the carajas mineral province was acquired by the interaction of hydrothermal fl uids with marine evaporites for iocg deposits that contain tourmaline as a common gangue mineral boron isotopes offer a valuable tool to constrain the high salinity source problem which is a critical issue in metallogenesis of iocg deposits worldwide

reos and s isotopic constraints on the origins of two mineralization events at the tangdan sedimentary rock hosted stratiform cu deposit sw china abstract the tangdan stratiform cu deposit in the kangdian region of south china is hosted in sedimentary rocks of the late paleoproterozoic to early mesoproterozoic dongchuan group orebodies mainly occur in dolostone and black shale above a thick sequence of hematitic sandstone and siltstone mineralization consists mainly of bedding parallel stratiform ores with minor amounts of discordant vein type ores both stratiform and vein type ores are composed of bornite and chalcopyrite with minor chalcocite and digenite associated with gangue minerals including ankerite dolomite calcite and quartz cu sulfides from vein type ores contain 122 293 ppb re much higher than those of stratiform ores 0 6 14 ppb re they have highly radiogenic os with re os model ages ranging from 1413 to 1457 ma and a weighted mean re os model age of 1432 19 ma 2 mswd 0 30 which is within uncertainty in agreement with isochron ages of 1401 30 ma 2 mswd 0 67 and 1397 71 ma 2 mswd 0 22 using 187 re 188 os versus 187 os 188 os and 187 re versus 187 os regression respectively in contrast sulfides from stratiform ores did not yield meaningful model ages due to the extremely low concentrations of re and radiogenic os however early studies have shown that the stratiform ores were likely formed at 1700 ma during the diagenesis of the host strata sulfides from the vein type ores have 34 s values ranging from 15 to 8 significantly lower than those of stratiform ores 3 to 10 suggesting that organic matter may have been involved in the formation of the vein type ores contrasting re os and s isotopes suggest that the two types of ores at the tangdan deposit were likely formed from different ore forming fluids we propose that stratiform ores were precipitated from basinal fluids during the early evolution of the rift basin whereas the vein type ores were formed due to a much younger thermal event during which hydrothermal fluids interacted with overlying black shale to account for the high re and negative 34 s values this study demonstrates that re os isotopes of sulfides can be used to study the origin of hydrothermal system

sulfide re os and rb sr isotope dating of the kangdian iocg metallogenic province southwest china implications for regional metallogenesis the kangdian iron oxide copper gold iocg metallogenic province contains a number of economically important fe cu deposits in south china and northern vietnam due to the lack of precise mineralization ages the metallogenesis of this province has long been a matter of debate in this study molybdenite re os pyrite re os and rb sr isotope methods are used to date the yinachang and e touchang fe cu deposits in the central part of this province fine grained 0 1 mm molybdenite occurs as veinlets along bandings or fractures of magnetite ores and hydrothermal veins in the yinachang deposit molybdenite separates from magnetite ores have highly reproducible re os model ages of 1654 7 ma whereas those from hydrothermal veins have a much younger re os model age of 1451 6 ma euhedral pyrite grains occur locally along foliations of hematite ores and their proximal alteration assemblages in the e touchang deposit pyrite separates have an re os isochron age of 1487 110 ma and a single grain rb sr isochron age of 1453 28 ma both of which are compatible with the molybdenite re os age of hydrothermal veins from the yinachang deposit the molybdenite age of magnetite ores is in good agreement with zircon u pb ages of dolerite intrusions in the region and is considered to represent the timing of a major ore formation event at 1655 ma the younger re os and rb sr ages likely record a secondary hydrothermal overprint event at 1450 ma which has not been recognized before the mineralization potential and implications of this event need to be investigated in future studies our new isotopic data set hence demonstrates that the kangdian iocg deposits were likely formed at 1655 ma synchronous with the late paleoproterozoic intracontinental rifting event of the western yangtze block

in situ sr isotope analysis of apatite by la mc icpms constraints on the evolution of ore fluids of the yinachang fe cu ree deposit southwest china apatite is a ubiquitous accessory mineral in a variety of rocks and hydrothermal ores strontium isotopes of apatite are well known to retain petrogenetic information and have been widely used to investigate the origin of igneous rocks but such attempts have rarely been made to constrain ore forming processes of hydrothermal systems we here report in situ la mc icpms sr isotope data of apatite from the 1660 ma yinachang fe cu ree deposit southwest china the formation of this deposit was coeval to the emplacement of regionally distributed doleritic intrusions within a continental rift setting the deposit has a paragenetic sequence consisting of sodic alteration stage i magnetite mineralization stage ii cu sulfide and ree mineralization stage iii and final barren calcite veining stage iv the stage ii and iii assemblages contain abundant apatite allowing to investigate the temporal evolution of the sr isotopic composition of the ore fluids apatite of stage ii apt ii is associated with fluorite magnetite and siderite whereas apatite from stage iii apt iii occurs intimately intergrown with ankerite and cu sulfides apt ii has 87sr 86sr ratios varying from 0 70377 to 0 71074 broadly compatible with the coeval doleritic intrusions 0 70592 to 0 70692 indicating that ore forming fluids responsible for stage ii magnetite mineralization were largely equilibrated with mantle derived mafic rocks in contrast apt iii has distinctly higher 87sr 86sr ratios from 0 71021 to 0 72114 which are interpreted to reflect external radiogenic sr likely derived from the paleoproterozoic strata some apt iii crystals have undergone extensive metasomatism indicated by abundant monazite inclusions the metasomatized apatite has much higher 87sr 86sr ratios up to 0 73721 which is consistent with bulk rock rb sr isotope analyses of cu ores with 87sr 86sri from 0 71906 to 0 74632 the elevated 87sr 86sr values of metasomatized apatite and bulk cu ores indicate that later fluids were dominated by highly radiogenic sr equilibrated with the paleoproterozoic country rocks results of this study highlight the utilization of in situ sr isotope analysis of apatite in unraveling the evolution of hydrothermal systems

stable isotope evidence for the origin of the mesoproterozoic starra au cu deposit cloncurry district northwest queensland new stable isotope data are consistent with a metasomatic origin for the controversial mesoproterozoic ironstone hosted au cu deposit at starra in the cloncurry district of northwest queensland this supports textural and mineralogical evidence that the ore bearing ironstones formed after the peak of metamorphism and were strongly controlled by brittle ductile deformation three dominant paragenetic stages are recognized these are 1 early widespread na ca metasomatism quartz albite scapolite actinolite 2 localized k fe metasomatism biotite magnetite hematite quartz pyrite and 3 mineralization quartz anhydrite barite hematite calcite gold pyrite chalcopyrite bornite chalcocite chlorite muscovite crosscutting anhydrite veins associated with carbonate or hematite are rare in the upper parts of the system but more common at depths greater than 700 m stage 3 minerals demonstrate that the ore fluid was highly oxidized a restricted range of fe oxide delta 18 o implies isotopically similar fluids were responsible for the magnetite ironstones and later hematite alteration associated with gold and sulfides between 0 2 to 3 3ppm except for one magnetite at 5 4ppm sulfur isotope compositions suggest that pyrite 0 2 to 3 9ppm chalcopyrite 5 8 to 0 7 and 14 6ppm bornite 4 7ppm chalcocite 0 1ppm and anhydrite 1 1 2 4ppm all formed from the same sulfur source anhydrite delta 34 s falls within the sulfide range suggesting that the sulfate inherited its delta 34 s through hydrolytic processes similar to those of some porphyry environments delta 13 c of ore stage carbonates range from 7 3 to 2 2 per mil temperatures based on stage 2 quartz magnetite pairs imply 400 degrees to 500 degrees c for ironstone formation and stage 3 calcite hematite pairs indicate 180 degrees to 330 degrees c for mineralization stage 2 fluid inclusions have homogenization temperatures between 345 degrees and 615 degrees c and salinities of 34 to 52 wt percent nacl equiv stage 3 fluid inclusions homogenized between 225 degrees and 360 degrees c and have salinities of 30 to 42 wt percent nacl equiv calculated delta 18 o fluid compositions for magnetite quartz and hematite calcite average 7 8 per mil and 9 5 per mil respectively fluid compositions for stages 2 and 3 fall within the range for a magmatic or metamorphic fluid however combined stable isotope and fluid inclusion data and thermodynamic considerations suggest a magmatic metasomatic origin for both the magnetite ironstones and the highly oxidized mineral assemblage associated with high grade gold deposition

constraints of sr isotopic compositions of apatite and carbonates on the origin of fe and cu mineralizing fluids in the lala fe cu mo lree deposit sw china abstract numerous fe cu deposits with mineralization styles similar to iron oxide copper gold iocg deposits form the kangdian fe cu metallogenic province southwestern sw china as one of the largest deposits in the region the 1 0 ga lala fe cu deposit is hosted in a paleoproterozoic volcanic sedimentary succession named the hekou group which is alternately intruded by 1 0 ga doleritic plutons this deposit has a paragenetic sequence evolving from stage i of na alteration to stage ii of fe mineralization and finally to stage iii of cu mo ree mineralization coeval with mafic felsic intra plate magmatism in the region this study conducted in situ sr isotopic analyses on apatite and carbonate aiming to resolve the long controversial issue regarding the origin of the fe and cu mineralizing fluids in the deposit apatite of stage ii has 87sr 86sr ratios varying from 0 71380 to 0 72733 much higher than those of synchronous igneous rocks in the region 0 7074 to 0 7091 but similar to the paleoproterozoic host rocks 0 71368 to 0 71837 at 1 0 ga this similarity indicates that radiogenic sr of the fe mineralizing fluid was dominantly sourced from the host rocks apatite and calcites of stage iii have 87sr 86sr ratios 0 75758 0 79293 much higher than apatite of stage ii and the host rocks but similar to the archean basement rocks as high as 0 80 at 1 0 ga beneath the cover of the yangtze block suggesting that the highly radiogenic sr isotopic composition of the cu mineralizing fluid was mainly inherited from the old basement rocks in combination with previous c o s isotopic data indicating a magma hydrothermal origin it was suggested that the fe mineralizing fluid was exsolved from a mafic magma that generated the 1 0 ga doleritic plutons and inherited radiogenic sr from the host rocks during fluid rock interaction by contrast the cu mineralizing fluid might have been sourced from another pulse of magmatic cu mo ree and co2 rich fluid which have once interacted with archean basement rocks prior to mineralization the source of such a cu mo ree rich fluid was not well constrained in current study but was inferred to be exsolved from a hidden felsic magma we propose that intrusions of the bimodal magmas in kangdian are responsible for regional hydrothermal circulation which led to fe cu mo ree mineralization in the kangdian province

mixed messages in iron oxide copper gold systems of the cloncurry district australia insights from pixe analysis of halogens and copper in fluid inclusions proterozoic rocks of the cloncurry district in nw queensland australia are host to giant tens to hundreds of square kilometers hydrothermal systems that include 1 barren regional sodic calcic alteration 2 granite hosted hydrothermal complexes with magmatic hydrothermal transition features and 3 iron oxide copper gold iocg deposits fluid inclusion microthermometry and proton induced x ray emission pixe show that iocg deposits and the granite hosted hydrothermal complexes contain abundant high temperature ultrasaline complex multisolid type 1 inclusions that are less common in the regional sodic calcic alteration the latter is characterized by lower salinity three phase halite bearing type 2 and two phase type 3 aqueous inclusions copper contents of the type 1 inclusions 300 ppm is higher than in type 2 and 3 inclusions 1 000 ppm are found both in the granite hosted systems and in inclusions with br cl ratios that are consistent with a magmatic source the br cl ratios of the inclusions with lower cu contents are consistent with an evaporite related origin wide ranges in salinity and homogenization temperatures for fluid inclusions in iocg deposits and evidence for multiple fluid sources as suggested by halogen ratios indicate fluid mixing as an important process in iocg genesis the data support both leaching of cu by voluminous nonmagmatic fluids from crustal rocks as well as the direct exsolution of cu rich fluids from magmas however larger iocg deposits may form from magmatic derived fluids based on their higher cu content

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

detrital zircon u pb geochronological and lu hf isotopic constraints on the precambrian magmatic and crustal evolution of the western yangtze block sw china abstract in situ u pb geochronological and lu hf isotopic studies of detrital zircon from a variety of precambrian strata along the western margin of the yangtze block of south china show that the rocks have maximum depositional ages of ca 1000 740 ma all of the strata probably formed in a subduction related tectonic setting the kunyang group heishantou formation and huili group tongan formation have maximum depositional ages of 960 1000 ma and contain zircons whose ages are dominantly paleoproterozoic 2500 2300 1900 1700 and 1650 1500 ma the yanbian group has a zircon population ranging mainly from 860 to 1000 ma different from that of the bikou group with ages from 745 to 890 ma ages of zircons from the lieguliu and guanyinya formations range from 740 to 900 ma the paleoproterozoic detrital zircons commonly have negative or slightly positive hf values from 8 0 to 2 3 whereas most of the 1000 740 ma zircons have moderately to significantly high positive hf values from 0 3 to 13 0 the new detrital zircon u pb and lu hf isotopic dataset suggests four major episodes of magmatism in the region 2500 2300 1900 1700 1650 1500 and 1000 740 ma and the presence of widespread archean basement of the western yangtze block the data also suggest an important period of juvenile magmatism at 1000 740 ma our results favor a model in which continuous subduction 1000 740 ma along the western margin of the yangtze block lasted for 260 million years

a fluid inclusion study of the suicide ridge breccia pipe cloncurry district australia implication for breccia genesis and iocg mineralization abstract the suicide ridge barren breccia pipe 1527 4 ma is one of numerous breccia occurrences that characterize the cloncurry district australia interest in breccia systems in the cloncurry district is related to their possible link with iron oxide copper gold deposits the suicide ridge barren breccia pipe is temporally and spatially associated with a granite that outcrops at its southwestern boundary and which is ascribed to the williams and naraku magmatic event ca 1550 1500 ma the breccia is characterized by clasts of variable dimensions degree of rounding and composition that includes dominant calc silicate clasts of the corella formation that underlie rocks of the soldiers cap group that host the pipe indicating a dominant upward transport of the fragments other breccia fragments include granite bodies characterized by albite quartz mineralogy and textures typical of the magmatic hydrothermal transition these rocks are interpreted to have formed in a fractionated granite carapace during the exsolution and accumulation of volatiles associated with the cooling magma two dominant types of inclusions have been identified at the suicide ridge barren breccia pipe these include early primary and pseudosecondary carbonic fluid inclusions observed only in magmatic hydrothermal transitional textures of granite breccia clasts and secondary sodic calcic brine inclusions that occur in all the collected samples variable homogenization temperatures in the primary and pseudosecondary pure co2 fluid inclusions indicate that they were trapped under different pressure conditions pressures estimated from the primary co2 fluid inclusions suggest that they were trapped at 4 2 kbar at least 1 kbar above the inferred lithostatic pressure this likely represents the overpressuring produced by release of co2 rich volatiles during the crystallization of magma and which ultimately caused the subsequent brecciation estimated pressures for pseudosecondary co2 fluid inclusions indicate pressure entrapment conditions around 2 7 kbar similar to the lithostatic pressure and 1 5 kbar lower than pressures recorded by type ia fluid inclusions this significant drop of pressure likely represents the sudden pressure depression occurring in response to brecciation evidence from field relationships breccia characteristics mineralogy and textures of granite clasts within the pipe and fluid inclusion studies support an origin of the suicide ridge barren breccia pipe in response to overpressuring generated by the release expansion and possibly phase separation of fluids of dominant carbonic composition from a crystallizing magma beneath and adjacent to the pipe sodic calcic fluid inclusions represent a later influx of fluids in the breccia system that produced widespread albitization significantly high temperature ultrasaline multisolid fluid inclusions abundant in iocg deposits and considered to be samples of the mineralizing fluid were not observed at the suicide ridge breccia pipe their absence in the barren systems suggests that they were critical for the formation of iocg deposits

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

arc related sodic hydrothermal alteration in the western united states sodium rich hydrothermal alteration is widely developed in permian to jurassic arc igneous rocks of the western united states but it is rare in younger rocks na rich alteration reflects a paleogeographic control on development two varieties naca and na can be defined by mineralogic and compositional changes both are common in permian to jurassic arc plutonic and volcanic rocks and are accompanied by fe and cu zn mineralization geologic relations and mineralogic stable isotopic and fluid inclusion data indicate that the fluids responsible for sodium rich alteration were isotopically heavy moderately to highly saline fluids of marine formation and or meteoric origin with or without a magmatic component the transition away from widespread na ca rich alteration in the late mesozoic corresponds to and is consistent with the change from an early mesozoic marine and or arid rifted arc setting to a fully emergent continental arc environment in the cretaceous

noble gas and halogen constraints on fluid sources in iron oxide copper gold mineralization mantoverde and la candelaria northern chile the noble gas ar kr xe and halogen cl br i composition of fluid inclusions in hydrothermal quartz and calcite related to the hypogene iron oxide copper gold iocg mineralization at mantoverde and candelaria chile have been investigated to provide new insights of fluid and salinity sources in andean iocg deposits a combination of mechanical extraction by crushing and thermal decrepitation methods was applied and collectively indicate that fluid inclusions with salinities ranging from 3 4 up to 64 wt nacl equivalent have molar br cl and i cl ratios of between 0 5 10 3 and 3 0 10 3 and i cl of between 8 10 6 and 25 10 6 in the majority of samples with maximum values of 5 2 10 3 obtained for br cl and 64 10 6 for i cl in fluid inclusions within individual samples the fluid inclusions have age corrected 40ar 36ar ratios ranging from the atmospheric value of 296 up to 490 45 indicating the presence of crustal or mantle derived excess 40ar in the fluid inclusions of most samples the fluid inclusions have 84kr 36ar and 130xe 36ar ratios intermediate of air and air saturated water however 40ar 36ar is not correlated with either 84kr 36ar or 130xe 36ar and the fluid inclusion 36ar concentrations of 0 2 3 5 10 10 mol g calculated from measured cl 36ar and thermometric salinity measurements extend below the seawater value of 0 34 10 10 mol g suggesting that contamination with modern air is a minor artifact the range of fluid inclusion br cl and i cl ratios overlap those previously documented for the mantle and magmatic hydrothermal ore deposits and the fluids unusually low 36ar concentration is consistent with the involvement of magmatic hydrothermal fluids input of additional non magmatic fluid components is suggested by the spread in br cl and i cl to values characteristic of bittern brine sedimentary formation waters and near atmospheric 40ar 36ar these data are compatible with mixing of magmatic hydrothermal fluids and evaporated seawater which was modified by interaction with back arc basin sediments as the major control on ore formation low br cl 0 5 10 3 and i cl 5 0 10 6 values that would provide evidence for evaporite dissolution as an important source of fluid salinity were not detected

geology geochronology and geochemistry of the dahongshan fe cu au ag deposit southwest china implications for the formation of iron oxide copper gold deposits in intracratonic rift settings the large dahongshan fe cu au ag deposit in the kangdian iron oxide copper gold iocg metallogenic province southwest china contains approximately 458 3 mt of ore at 41 0 fe 1 35 mt cu metal at 0 78 cu and significant amounts of au 16 t ag 141 t co 18 156 t and pd pt 2 1 t the deposit consists mainly of two types of ores 1 lenses of massive or banded magnetite hematite hosted in extensively na metasomatized metavolcanic rocks metaarenite and brecciated rocks and 2 strata bound disseminated stockwork and banded magnetite chalcopyrite bornite in mica schist and marble both types of orebodies and country rocks underwent extensive hydrothermal alteration resulting in a similar paragenesis pervasive stage i sodic alteration formed widespread albite and local scapolite it was subsequently replaced by ca or k rich minerals represented by actinolite k feldspar biotite sericite and chlorite of stages ii and iii magnetite is slightly younger than and partly overlaps the sodic alteration assemblages hematite is texturally later than magnetite is locally abundant within the massive fe oxide orebody and is closely associated with sericite copper sulfides are coeval with quartz biotite sericite and chlorite in stage iii assemblages widespread siderite and ankerite predominate in stages ii and iii respectively quartz calcite veins mark the result of waning stage iv hydrothermal alteration in addition to widespread alteration during the major ore forming event the deposit has also undergone extensive overprinting and remobilization during post ore magmatic and metamorphic events the dahongshan orebodies are intimately associated with abundant doleritic dikes and sills that have hydrothermal mineral assemblages similar to those in the ore hosting rocks one dolerite sill that cuts a massive fe orebody has a laser ablation inductively coupled plasma mass spectrometry zircon u pb age of 1661 7 ma which is within uncertainty consistent with the age of 1653 18 ma determined for hydrothermal zircons from stockwork chalcopyrite magnetite ore the zircon u pb ages are thus considered to mark the timing of major mineralization that formed the dahongshan deposit post ore modification is recorded by an re os isochron age of 1026 22 ma for pyrite in discordant quartz carbonate sulfide veins and by younger neoproterozoic mineralization dated at ca 830 ma using re os isotopes on molybdenite the former age is contemporaneous with late mesoproterozoic magmatism in the region whereas the latter is coeval with regional neoproterozoic metamorphic events in southwest china carbon and oxygen isotope values of albitized marble are between those of mantle derived magmatic carbon and dolostone end members the ore forming fluids that equilibrated with stage ii magnetite have 18 o values of 9 1 to 9 5 whereas fluids linked to the deposition of quartz and ankerite during stages iii and iv have lower 18 o values of 2 9 to 7 3 the oxygen isotope data indicate that the ore forming fluids related to stage ii are chiefly magmatically derived and mixed with abundant basinal brine during stages iii and iv this interpretation is consistent with sulfur isotope values of sulfides in the deposits pyrite and chalcopyrite from the dahongshan deposit have a large range of 34 s values from 3 4 to 12 4 implying mixing of magmatic and external sulfur likely from basinal brines in sedimentary rocks the dahongshan deposit formed in an intracratonic rift setting due to underplating by mafic magmas that induced large scale fluid circulation and pervasive sodic calcic metasomatism in country rocks ore metals were derived mainly from a deep seated magma chamber and partly from country rocks hydrothermal brecciation of the country rocks formed at the top of the dolerite intrusions and along zones of weakness within the country rocks owing to overpressure imposed by the ore fluids magnetite and hematite precipitated early near the dolerite intrusions whereas cu sulfides formed later in country rocks where sulfide saturation was favored we propose that this genetic model may be widely applicable to precambrian iocg deposits elsewhere that formed in intracratonic rift settings

gravity and magnetic interpretation of the deer lake basin newfoundland detailed reconnaissance gravity surveys in the deer lake carboniferous basin have been conducted using a station spacing of 2 5 km the digitized aeromagnetic data for the basin were reduced to a 1 253 440 scale composite map these two data bases were used to determine the configuration of major features and the total sediment thickness at various locations in the basin preliminary seismic results from reflection and refraction seismic surveys planned on the basis of these results are discussed modelling of gravity and magnetic data indicates that the humber syncline contains approximately 1 2 km of sediments underlain on the west by rocks similar to the long range complex the eastern limb of the syncline is underlain by rocks similar to the gull pond igneous suite the howley formation is deduced to be approximately 1 5 km thick and floored by rocks similar to the topsails igneous suite

alteration paragenesis and mineral chemistry of the tjarrojakka apatite iron and cu au occurrences kiruna area northern sweden the northern norrbotten area in northern sweden is an important mining district and hosts several deposits of fe oxide cu au type one of the best examples of spatially and possibly genetically related apatite iron and copper gold deposits in the region is at tjarrojakka 50 km wsw of kiruna the deposits are hosted by strongly sheared and metamorphosed intermediate volcanic rocks and dolerites and show a structural control the tjarrojakka iron deposit is a typical apatite iron ore of kiruna type and the tjarrojakka copper occurrence shows the same characteristics as most other epigenetic deposits in norrbotten the host rock has been affected by strong albite and k feldspar alteration related to mineralisation resulting in an enrichment of na k and ba fe and v were depleted in the altered zones and added in mineralised samples ree were enriched in the system with the greatest addition related to mineralisation y was also mobile associated with albite alteration and copper mineralisation the tjarrojakka iron and copper deposits show comparable hydrothermal alteration minerals and paragenesis which might be a product of common host rock and similarities in ore fluid composition or overprinting by successive alteration stages mineralogy and mineral chemistry of the alteration minerals apatite scapolite feldspars amphiboles and biotite indicate a higher salinity and ba k ratio in the fluid related to the alterations in the apatite iron occurrence than in the copper deposit where the minerals are enriched in f and s the presence of hematite barite and in so4 in scapolite suggests more oxidising rich conditions during the emplacement of the tjarrojakka cu deposit from existing data it might be suggested that one evolving system created the two occurrences with the copper mineralisation representing a slightly later product

carbon and oxygen isotope constraints on fluid sources and fluid wallrock interaction in regional alteration and iron oxide copper gold mineralisation eastern mt isa block australia the source of metasomatic fluids in iron oxide copper gold districts is contentious with models for magmatic and other fluid sources having been proposed for this study 18o and 13c ratios were measured from carbonate mineral separates in the proterozoic eastern mt isa block of northwest queensland australia isotopic analyses are supported by petrography mineral chemistry and cathodoluminescence imagery marine meta carbonate rocks ca 20 5 18o and 0 5 13c calcite and graphitic meta sedimentary rocks ca 14 18o and 18 13c calcite are the main supracrustal reservoirs of carbon and oxygen in the district the isotopic ratios for calcite from the cores of na ca alteration systems strongly cluster around 11 18o and 7 13c with shifts towards higher 18o values and higher and lower 13c values reflecting interaction with different hostrocks na ca rich assemblages are out of isotopic equilibrium with their metamorphic hostrocks and isotopic values are consistent with fluids derived from or equilibrated with igneous rocks however igneous rocks in the eastern mt isa block contain negligible carbon and are incapable of buffering the 13c signatures of co2 rich metasomatic fluids associated with na ca alteration in contrast plutons in the eastern mt isa block have been documented as having exsolved saline co2 rich fluids and represent the most probable fluid source for na ca alteration intrusion proximal skarn like cu au orebodies that lack significant k and fe enrichment e g mt elliott display isotopic ratios that cluster around values of 11 18o and 7 13c calcite indicating an isotopically similar fluid source as for na ca alteration and that significant fluid wallrock interaction was not required in the genesis of these deposits in contrast k and fe rich intrusion distal deposits e g ernest henry record significant shifts in 18o and 13c towards values characteristic of the broader hostrocks to the deposits reflecting fluid wallrock equilibration before mineralisation low temperature low salinity low 18o 10 calcite and co2 poor fluids are documented in retrograde metasomatic assemblages but these fluids are paragenetically late and have not contributed significantly to the mass budgets of cu au mineralisation

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

external sulphur in iocg mineralization implications on definition and classification of the iocg clan abstract although the sources of the ore metals remain problematic in most iron oxide cu and au iocg deposits external sulphur either from surficial basinal brines and seawater e g central andean and carajas deposits or from formation water and metamorphic fluids e g the cloncurry deposits or introduced by magmatic assimilation of metasedimentary units e g phalaborwa has been documented in many major cu rich iocg centres however only the evaporite sourced fluids yield diagnostically high 34s values i e 10 while sedimentary formation water or metamorphic fluids commonly have lower values and are less clearly distinguishable from magmatic fluids as in the cloncurry deposits in which the involvement of external fluids is revealed by other evidence such as noble gas isotopes on the basis of these arguments iocg deposits could be redefined as a clan of cu au ag u deposits containing abundant hypogene iron oxide magnetite and or hematite in which externally derived sulphur probably plays an important role for the cu au ag u mineralization in this definition all kiruna type magnetite deposits hydrothermal iron deposits e g skarn fe deposits and magnetite rich porphyry cu au and skarn cu au deposits are excluded two subtypes of iocg deposits are recognized on the basis of the predominant iron oxide directly associated with the cu au mineralization whether magnetite or hematite neither magnetite nor hematite rich iocg deposits show any preference for specific host rocks and both range in age from neoarchean to pleistocene within a broad tectonic environment

paragenesis stable isotopes and molybdenite re os isotope age of the lala iron copper deposit southwest china the lala fe cu deposit in the kangdian iron oxide copper gold iocg metallogenic province sw china is hosted in the paleoproterozoic hekou group this volcanic sedimentary sequence has undergone upper greenschist lower amphibolite facies metamorphism at 850 ma the deposit contains more than 200 million metric tons mt of fe cu ores with an average grade of 13 wt fe and 0 92 wt cu orebodies are roughly strata bound but occur along foliation lithologic contacts and shear zones the paragenetic sequence of the lala deposit includes metamorphosed i ii and iii and unmetamorphosed iv and v stages stage i is characterized by extensively pervasive na alteration forming abundant albite but minor scapolite stage ii occurs as massive and banded replacements consists of ti v poor magnetite and apatite with minor disseminated sulfide minerals and was associated with pervasive k fe alterations forming k feldspar chlorite and actinolite stage iii occurs predominantly as bands and disseminations confined along foliations with minor veinlets cross cutting hosting rocks this stage is characterized by abundant fe cu mo sulfides intergrown with angular magnetite and minor titanite and allanite and is associated with alteration of carbonate quartz fluorite and mica stage iv has an assemblage dominated by chalcopyrite with variable pyrite and bornite occurring as veins of sulfides quartz calcite biotite muscovite fluorite stage v occurs chiefly as veins of hematite calcite quartz and also results in extensive hematization stages ii and iii have fluids with high 18 o 7 2 11 7 and 34 s values 0 4 indicative of a magmatic hydrothermal origin however the stage iii fluids have 34 c values 0 5 close to the least altered marble 0 2 of the hosting rocks indicating a possible contribution of strata sourced carbon the stage iv fluids have 34 c values similar to and 18 o 4 1 6 7 lower than the stage iii fluids and a wider range of 34 s values 9 0 to 10 5 consistent with significant contributions of strata sourced sulfur fluids of the late barren vein stage v have relatively low 34 c 4 0 to 2 4 and 18 o values 2 9 to 0 6 indicative of significant contributions of meteoric and oxidized fluids molybdenite from stage iii has an re os isotope age of 1086 8 ma providing tight constraints on the timing of the main stage of mineralization this age indicates that the lala deposit is coeval with the 1100 ma intraplate magmatism in the western yangtze block we propose that the majority of the fe cu deposits in the kangdian iocg metallogenic province may have formed in an intraplate extensional setting although it is possible that some of the deposits may have involved in multiple events including modification by the neoproterozoic metamorphism forming the mineral assemblages of stage iv