isotope evidence for the involvement of recycled sediments in diamond formation diamonds as chemically robust containers of material from the mantle have provided important information regarding the evolution of the earth s interior1 yet despite much effort2 9 the origins of diamonds themselves have remained controversial10 13 sulphur isotope ratios measured in most mantle or meteoritic samples exhibit minimal deviation from the meteoritic standard whereas the ratios in crustal materials deviate by as much as 70 ref 14 for this reason isotopic studies of sulphide mineral inclusions in diamonds and mantle material are an attractive means of investigating the possible role of crust mantle interaction in the formation of diamonds15 recent ion microprobe studies have found departures from mantle values in the sulphur isotope compositions of individual diamond inclusions16 and some mantle rocks17 which would be consistent with subduction of altered ocean crust into the region of diamond growth here we present new sulphur and lead isotope data from diamond sulphide inclusions which suggest that sedimentary material might also be subducted into the mantle and that the crustal recycling process has been operative for at least 1 000 million years

the candelaria punta del cobre iron oxide cu au zn ag deposits chile several iron oxide rich cu au zn ag deposits define an approximately 5 km wide and at least 20 km long belt along the eastern margin of the coastal batholith near copiapo chile this belt includes the large candelaria mine and a group of middle and small sized mines in the punta del cobre district which is located about 3 km northeast of the candelaria deposit estimated geologic resources of the belt are on the order of 700 to 800 million metric tons mt at 1 0 percent cu the ore occurs in veins breccia and stringer bodies and in replacement bodies that are roughly concordant to bedding the orebodies are hosted mainly by volcanic and volcaniclastic rocks of the punta del cobre formation and in places also occur in volcaniclastic intercalations in the lower part of the overlying early cretaceous chanarcillo group most of the larger orebodies in the belt are located where northwest trending brittle faults intersect the contact between massive volcanic and volcaniclastic rocks these northwest faults and a major northeast trending ductile shear zone control portions of the ore of the candelaria deposit chalcopyrite is the only hypogene cu mineral the cu au ore is characterized by abundant magnetite and or hematite and by locally elevated concentrations of ag zn mo and light rare earth elements the ore is hosted mainly in zones with biotite potassium feldspar calcic amphibole epidote alteration at candelaria in the punta del cobre district ore in the deeper parts of the deposits is similarly associated whereas at shallow levels it occurs in zones of biotite potassium feldspar or albite chlorite calcite alteration mineralization at candelaria punta del cobre took place under relatively oxidized conditions manifested by the formation of specular hematite in parts of the district the pseudomorphic replacement of early specular hematite by magnetite during the main iron oxide formation marks a shift toward more reduced conditions or higher temperatures the bulk of the magnetite probably formed at temperatures of about 500 to 600 c the main sulfide stage followed with formation of pyrite and chalcopyrite at temperatures of 470 to 328 c subsequent martitization of the magnetite points to a temperature decrease cooling of the hydrothermal system is also indicated by the homogenization temperatures of 236 c of saline fluid inclusions in late stage calcite oxygen isotope combined with microthermometric data suggest that magmatic fluids or nonmagmatic fluids equilibrated with magmatic silicates were dominant during the main copper mineralization relatively light oxygen isotope signatures of fluids in equilibrium with late calcite suggest mixing with a nonmagmatic fluid e g basinal brines or meteoric waters during the late stages of hydrothermal activity sulfur isotope ratios of chalcopyrite pyrite pyrrhotite and sphalerite from the bronce candelaria las pintadas santos and socavon rampa deposits range from 34scdt values of 0 7 to 3 1 per mil this narrow range of sulfur isotope ratios near 0 per mil is consistent with sulfur of magmatic origin anhydrite from the candelaria mine paragenetically overlaps with chalcopyrite fluid inclusions in this anhydrite homogenize between 340 and 470 c and it has 34scdt values between 14 5 and 17 5 per mil a sulfate sulfide value of 13 4 per mil for a sample with coexisting anhydrite and chalcopyrite is consistent with sulfide sulfate fractionation at temperatures on the order of 400 c ore lead isotope signatures are homogeneous and similar to those of least altered volcanic host rocks and nearby intrusive rocks radiometric ages including new 40ar 39ar ages for hydrothermal alteration at candelaria point to a main cu au mineralization event at candelaria punta del cobre at around 115 ma the ages indicate that ore formation was broadly coeval with batholithic granitoid intrusions and with regional uplift they further imply that the cu au zn ag deposits formed at shallow crustal levels 3 km the stable isotope data the presence of previously reported hypersaline co2 rich fluid inclusions in the main cu ore stage and saline fluid inclusions in late stage calcite the oxidized character of the first ore fluid pulses and the mineralization age coeval with nearby intrusive activity are consistent with but not unequivocally evidence of magmatic fluid contribution into the hydrothermal system

tectonic transition in the aqishan yamansu belt eastern tianshan constraints from the geochronology and geochemistry of carboniferous and triassic igneous rocks abstract a combination of zircon u pb ages whole rock geochemistry sr nd isotopes and in situ zircon hf isotope for newly found felsic igneous rocks from the hongshanliang copper deposit district in the aqishan yamansu belt nw china are presented to investigate the petrogenesis and tectonic or even crustal evolution of the eastern tianshan during the late paleozoic to the early mesozoic zircon u pb ages show two phases of igneous activity in the early carboniferous 348 8 2 1 ma and 343 3 2 3 ma for rhyolite and granite porphyry and the triassic 250 2 3 5 ma and 235 7 2 4 ma for monzonitic granodiorite and monzogranite in the hongshanliang copper deposit district the carboniferous granitic rocks are enriched in rb ba and pb and depleted in nb and ta with low sr y ratios showing arc related affinities dominantly positive ehf t values 2 55 to 7 15 and 1 54 to 5 03 for the rhyolite and granite porphyry respectively crustally derived geochemical elements ratios e g nb ta th u ta u and th la and mg values

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

the middle permian hongshanliang manto type copper deposit in the east tianshan constraints from geology geochronology fluid inclusions and h o s isotopes abstract the hongshanliang copper deposit hosted in the tuff of the lower carboniferous yamansu formation is a typical copper deposit in the aqishan yamansu belt east tianshan based on crosscutting relationships of veins textural relationships and mineral assemblages five alteration mineralization stages at hongshanliang have been established chlorite sulfide stage stage i quartz pyrite stage stage ii quartz polymetallic sulfide stage stage iii late veins stage iv and supergene process stage v stage i has mineral assemblage of chlorite pyrite chalcopyrite quartz sericite and is commonly characterized by euhedral pyrite with silicates e g chlorite quartz and sericite and or chalcopyrite as its pressure shadow indicating an early mineralization event with apparent deformation stage ii is characterized by quartz pyrite chalcopyrite or locally quartz gypsum anhydrite pyrite veins cutting stage i chlorite pyrite the main mineralization stage stage iii at hongshanliang has typical mineral assemblages of quartz chalcopyrite chlorite calcite sericite quartz chalcopyrite sphalerite galena pyrite and quartz sphalerite galena chlorite with veins veinlets disseminations and local massive ore types similar to manto type copper deposits regarding mineralization and ore structures detailed fluid inclusion study shows temperature of fluids decreased from stage ii 307 484 c through stage iii peak at 160 180 c consistent with quartz chlorite oxygen isotope geothermometer of 190 c to stage iv 129 169 c with corresponding salinities of 2 7 26 2 wt nacl equiv peak at 8 wt 2 1 12 3 wt nacl equiv peak at 8 wt and 0 5 7 7 wt nacl equiv peaks at 4 6 wt respectively indicating an evolved hydrothermal ore forming system such fluid evolution can also be supported by h o isotopes during water rock reaction from stage ii 18ofluid 6 3 8 3 and dfluid 77 to 64 through stage iii 18ofluid 1 7 to 7 0 and dfluid 82 to 58 to stage iv 18ofluid 2 5 to 2 1 and dfluid 77 to 73 with a magmatic hydrothermal origin furthermore sulfur isotopes suggest that fluids of the two mineralization stages stage i and iii are predominantly magmatic hydrothermal with other influx contribution into the ore forming system i e minor early carboniferous seawater in stage i 34sfluid varying from 3 5 to 6 1 with peak at 0 and minor organic materials in stage iii 34sfluid varying from 6 5 to 4 1 with peak at 0 1 and detection of ch4 and c2h6 from fluid inclusions in combination of alteration paragenesis nature and source of ore forming fluids and comparison with other typical deposits we proposed that the hongshanliang copper deposit underwent two mineralization events with the main mineralization similar to manto type copper deposits 40ar 39ar dating of sericite from a massive chalcopyrite ore indicates the hongshanliang main mineralization formed at 269 0 0 4 ma generally coeval with regional k feldspar granite emplacement ca 272 ma integrating the regional tectonic setting magmatism and metallogenesis of the aqishan yamansu belt and the east tianshan we suggest that the aqishan yamansu belt has potential of mineral prospecting for the middle permian manto type copper deposits

geology geochronology and hf and pb isotope data of the raul condestable iron oxide copper gold deposit central coast of peru raul condestable is a 32 million metric ton mt iron oxide copper gold iocg deposit located on the peruvian coast 90 km south of lima the ore occurs as veins replacement mantos and disseminations consisting of a chalcopyrite pyrite pyrrhotite magnetite amphibole mineral association the geology of the studied area comprises a series of superposed volcanic edifices of late jurassic to early cretaceous age which are part of a larger volcanic island to continental arc system particularly good exposures of the tilted host sequence allow the mapping of the raul condestable iocg deposit in a nearly complete oblique cross section from its associated volcanic edifice down to a paleodepth of about 6 km u pb zircon ages indicate that in the deposit area felsic magmatic activity took place between 116 7 0 4 and 114 5 1 ma defining a new raul condestable superunit the oldest so far of the peruvian coastal batholith this superunit is located west of the main part of the batholith and includes a dacite andesite volcanic dome and a subvolcanic quartz diorite porphyry sill dike complex that were emplaced at 116 7 0 4 and 116 4 0 3 ma respectively followed by tonalite stocks and dikes emplaced between 115 1 0 4 and 114 5 1 ma all these rocks contain hornblende and or biotite but no pyroxene and correspond to silica and water rich magmas following a calcic differentiation trend hf isotope data on zircons ehf 115 ma 5 2 7 5 and pb isotope data on whole rock combined with lithogeochemical results suggest that magmas were generated by partial melting of the upper mantle enriched through hydrous metasomatism and or melting of subducted pelagic sediments the lack of zircon inheritance suggests that there was no direct involvement of continental crust the raul condestable iocg deposit is connected in space and time with the magmatism of the raul condestable superunit the mineralization was emplaced in the core of the dacite andesite volcanic dome at a paleodepth of 2 to 3 km surrounding two tonalitic intrusions formed at 115 1 0 4 and 114 8 0 4 ma the u pb age of hydrothermal titanite from iocg veins at 115 2 0 3 ma indicates that the mineralization was coeval with or more probably just followed the emplacement of the tonalites re os geochronology on molybdenite did not yield reliable ages due to apparent re loss copper ore is associated with a zoned alteration pattern which surrounds the tonalite intrusions it consists of a core of biotite alteration and quartz stockwork grading outward to actinolite magnetite chlorite titanite scapolite albite epidote and upward to sericite fe chlorite alteration an upper distal alteration halo consisting of hematite chlorite surrounds the sericite fe chlorite and actinolite alterations laterally most of the ore is spatially associated with the actinolite alteration and to a lesser extent with the sericite fe chlorite alteration the results of this study confirm that the 110 to 120 ma age range was a productive time period for andean iocg deposits the characterization of the hydrous intermediate magmatism related to the mineralization as well as the subvolcanic position of the deposit and its related alteration pattern provides further criteria that may be used when exploring for iocg deposits in a convergent plate tectonic setting

contrasting fluids and reservoirs in the contiguous marcona and mina justa iron oxide cu ag au deposits south central peru the marcona mina justa deposit cluster hosted by lower paleozoic metaclastic rocks and middle jurassic shallow marine andesites incorporates the most important known magnetite mineralization in the andes at marcona 1 9 gt at 55 4 fe and 0 12 cu and one of the few major iron oxide copper gold iocg deposits with economic cu grades 346 6 mt at 0 71 cu 3 8 g t ag and 0 03 g t au at mina justa the middle jurassic marcona deposit is centred in ica department peru and the lower cretaceous mina justa cu ag au prospect is located 3 4 km to the northeast new fluid inclusion studies including laser ablation time of flight inductively coupled plasma mass spectrometry la tof icpms analysis integrated with sulphur oxygen hydrogen and carbon isotope analyses of minerals with well defined paragenetic relationships clarify the nature and origin of the hydrothermal fluid responsible for these contiguous but genetically contrasted deposits at marcona early sulphide free stage m iii magnetite biotite calcic amphibole assemblages are inferred to have crystallized from a 700 800 c fe oxide melt with a 18o value from 5 2 to 7 7 stage m iv magnetite phlogopite calcic amphibole sulphide assemblages were subsequently precipitated from 430 600 c aqueous fluids with dominantly magmatic isotopic compositions 34s 0 8 to 5 9 18o 9 6 to 12 2 d 73 to 43 and 13c 3 3 stages m iii and m iv account for over 95 of the magnetite mineralization at marcona subsequent non economic lower temperature sulphide calcite amphibole assemblages stage m v were deposited from fluids with similar 34s 1 8 to 5 0 18o 10 1 to 12 5 and 13c 3 4 but higher d values average 8 several groups of lower 200 c fluids can be recognized in the main polymetallic cu zn pb sulphide stage m v and may record the involvement of modified seawater at mina justa early magnetite pyrite assemblages precipitated from a magmatic fluid 34s 0 8 to 3 9 18o 9 5 to 11 5 at 540 600 c whereas ensuing chalcopyrite bornite digenite chalcocite hematite calcite mineralization was the product of non magmatic probably evaporite sourced brines with 34s 29 18o 0 1 and 13c 8 3 two groups of fluids were involved in the cu mineralization stage 1 ca rich low temperature approx 140 c and high salinity plausibly a basinal brine and 2 na k dominant with a low temperature approx 140 c and low salinity probably meteoric water la tof icpms analyses show that fluids at the magnetite pyrite stage were cu barren but that those associated with external fluids in later stages were enriched in cu and zn suggesting such fluids could have been critical for the economic cu mineralization in andean iocg deposits

constraints on the timing of fe cu metallogenesis in the eastern aqishan yamansu shaquanzi metallogenic belt eastern tianshan nw china abstract the aqishan yamansu shaquanzi belt is a well known fe cu au metallogenic belt located in the central asian orogenic belt nw china numerous fe rich ores as well as polymetallic mineralization including cu pb zn and co and related magmatic hydrothermal alteration are hosted in volcanic rocks especially those in the eastern part of this metallogenic belt the complex geology of the belt and the divergent geochronological data obtained by different investigators and analytical methods have led to contrasting opinions on the deposit types and metallogenesis of the belt the present study focuses on the shaquanzi yamansu and heifengshan fe cu polymetallic deposits in the eastern part of the belt these deposits display fe dominated metallogenesis related to volcanic sedimentary exhalative processes and polymetallic metallogenesis related to volcanic hydrothermal metasomatism and skarnization caused by subsequent intrusion processes the shaquanzi yamansu and heifengshan deposits have undergone multiple periods of metallogenesis and contain late fe cu pb mo fe cu zn co and fe cu mineralization respectively using zircon u pb dating by laser ablation multi collector inductively coupled plasma mass spectrometry two rhyolite samples at the base and lower middle part of the tugutubulak formation and a basaltic andesite and a diorite dyke in the shaquanzi ore district yield concordant ages of 327 9 2 6 ma mean square of weighted deviates or mswd 0 015 327 8 1 4 ma mswd 1 03 285 9 2 0 ma mswd 0 81 and 276 3 1 4 ma mswd 0 21 respectively basaltic andesite from the upper yamansu formation in the yamansu deposit area yields a concordant age of 327 6 6 4 ma mswd 0 54 whereas rhyolite diorite dyke and granite stock from the heifengshan deposit give concordant ages of 285 7 1 3 ma mswd 0 01 273 7 1 6 ma mswd 1 2 and 274 4 2 5 ma mswd 0 20 respectively hydrothermal molybdenite in the shaquanzi deposit yields a weighted mean re os age of 314 6 1 7 ma mswd 0 29 and an isochron age of 316 6 ma mswd 0 46 a collation of previously reported ages and our new age data show that extensive magmatism occurred during the carboniferous early permian ca 350 270 ma in the aqishan yamansu shaquanzi belt with a peak period between ca 335 and ca 305 ma the yamansu formation and tugutubulak formation volcanic rocks formed at ca 348 334 ma early carboniferous and between ca 328 and ca 303 ma late early carboniferous to late carboniferous respectively in the eastern part of the belt fe dominated mineralization resulting from volcanic sedimentary exhalative processes e g ca 334 ca 322 and ca 286 ma and polymetallic mineralization resulting from volcanic hydrothermal metasomatism e g ca 334 323 ma as well as skarnization and magmtic hydrothermal caused by intrusions occurred at different stages e g ca 322 316 ca 299 and ca 274 ma leading to the superimposition of polymetallic mineralization between ca 334 and ca 273 ma

tracking meteoric infiltration into a magmatic hydrothermal system a cathodoluminescence oxygen isotope and trace element study of quartz from mt leyshon australia the oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope cathodoluminescence sem cl images and fluid inclusion properties to track fluid sources and hydrothermal processes in the mt leyshon an deposit australia oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections using secondary isotope mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms respectively with sem cl images obtained before analysis for petrographic context over the 280 to 650 degrees c quartz precipitation range suggested by fluid inclusion microthermometry delta o 18 quartz varies from 0 0 to 14 4 o corresponding to a wide range of equilibrium delta o 18 fluid values from 6 1 to 10 2 o vs v smow the delta o 18 quartz signature varies systematically among distinct sem cl quartz generations both within and between samples and can be correlated with variations in temperature and fluid composition but is independent of intra generational oscillatory zoning in contrast al and li concentrations correlate broadly with cl intensity in oscillatory quartz whereas their concentration is unpredictable in sealed fractures and overgrowths concentrations of b mg na p cl k ti mn fe ge and sn are independent of al li and oscillatory cl features but ti correlates with quartz precipitation temperature although no systematic correlation between delta o 18 quartz and trace element concentrations was found complementary patterns exist in narrow overgrowths of low delta o 18 quartz similar to 0 o and high al g 10 000 ppma these quartz zones likely formed during the incursion of o 18 depleted meteoric water into the magmatically dominated mt leyshon hydrothermal system we interpret the highest al concentrations as the result of high quartz precipitation rates triggered by depressurisation of the hydrothermal cell the decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that 1 under most circumstances temperature and fluid chemistry dominate delta o 18 quartz and 2 the trace element record and in particular al and li is influenced by the superimposed effects of quartz precipitation rate c 2007 elsevier b v all rights reserved

paragenesis and fluid evolution of the halasu iii porphyry cu deposit east junggar nw china implications for the paleozoic multiphase superimposing mineralization in the central asian orogenic belt abstract the halasu iii deposit an important cu deposit in the southernmost part of the halasu porphyry cu belt is situated in the east junggar block in nw china copper and mo sulfide mineralization commonly occurs as disseminations or veinlets and is mainly associated with devonian granodiorite porphyry our detailed field geological investigation identified late stage high grade cu sulfide bearing veining superimposed on the earlier porphyry cu mo mineralization four hydrothermal alteration and mineralization stages were identified namely the early epidote alteration stage i porphyry style alterations stage ii comprising ii a potassic ii b propylitic and ii c phyllic alteration sub stages late veining stage iii and supergene processes stage iv in the northern and southern mineralization zones at halasu iii multiphase granodiorite and alkali granite dykes intruded the beitashan formation volcanic rocks generating the early epidote alteration potassic alteration stage ii a occurred in and around the nnw treading granodiorite dykes while the propylitic alteration stage ii b occurred in the intrusions or volcanic wall rocks around the potassic zone these early alteration assemblages were overprinted by the subsequent structurally controlled phyllic alteration stage ii c confined within the granodiorite porphyry late veins stage iii include sulfide bearing stage iii a and sulfide barren stage iii b ones supergene process stage iv represented by hematite and jarosite replacing primary sulfides extends tens of meters down depth and is commonly fracture controlled three fluid inclusion fi types were recognized namely type a single phase b liquid vapor two phase and c liquid vapor solid three phase for type b fis those of potassic alteration homogenized at 183 347 c with corresponding salinities of 6 2 17 8 wt nacl equiv the propylitic and phyllic fis homogenized at 172 425 c and 231 352 c respectively with the corresponding salinities of 0 9 14 0 wt nacl equiv and 0 4 10 5 wt nacl equiv the sulfide bearing vein fis homogenized at 243 410 c stage iii a 1 260 362 c stage iii a 2 and 117 235 c stage iii a 3 along with the corresponding salinities of 1 9 9 2 wt nacl equiv 1 1 6 7 wt nacl equiv and 6 5 17 1 wt nacl equiv respectively the sulfide barren vein fis yielded homogenization temperatures of 260 380 c stage iii b 1 and 114 297 c stage iii b 2 with corresponding salinities of 1 7 9 8 wt nacl equiv and 0 2 13 6 wt nacl equiv respectively we suggest that hydrothermal veins at halasu iii may have undergone complex and superimposing alteration due to the episodic reopening of the preexisting veins with stage iii a 3 veining overprinting the phyllic alteration and stage iii a 2 veining stage iii b 2 veining superimposed on the potassic alteration as well as on stages iii a 1 and iii b 1 veining paragenetic sequence and fluid evolution at halasu iii indicate that these complex hydrothermal alteration stages were formed in accordance with the regional tectonic evolution these various alteration and mineralization stages at halasu iii deposit reveal a prolonged history of magmatic and hydrothermal processes extending episodically from the middle devonian to middle permian wherein early mineralization was overprinted by late hydrothermal events such superimposed mineralization may occur commonly in the paleozoic central asia orogenic belt

scanning electron microscope cathodoluminescence analysis of quartz reveals complex growth histories in veins from the butte porphyry copper deposit montana scanning electron microscope cathodoluminescence sem cl analysis of quartz reveals textures that cannot be observed using optical microscopy or backscattered electrons these cryptic textures yield insight into timing and physical conditions of quartz growth especially in environments with multiple quartz precipitation events hydrothermal quartz from quartz sulfide veins in the porphyry copper deposit in butte montana was analyzed by sem cl revealing the following textures euhedral growth zones wide nonluminescing bands that cut across multiple quartz grains rounded luminescent quartz grain cores with euhedral overgrowths nonluminescing splatters of quartz connected by networks of cobweb like nonluminescing quartz in otherwise luminescent quartz concentric growth zones and wide nonluminescent grain boundaries these textures indicate that many veins have undergone fracturing dilation growth of quartz into fluid filled space quartz dissolution and recrystallization of quartz precipitation and dissolution textures indicate that early quartz molybdenite veins formed as a result of pressure fluctuations between lithostatic and hydrostatic at high temperatures and later pyrite quartz veins formed near hydrostatic pressure in response to temperature decrease through and beyond the field of retrograde quartz solubility

hydrothermal alteration fluid inclusions and stable isotope characteristics of the shaquanzi fe cu deposit eastern tianshan implications for deposit type and metallogenesis abstract the shaquanzi fe cu deposit is an important fe cu deposit in the yamansu fe mineralization belt eastern tianshan five stage stage i to v hydrothermal alteration mineralization have been recognized the early skarn stage i and late skarn stage ii stages are featured by extensive garnet and amphibole alteration respectively magnetite mineralization stage stage iii is associated with pervasive k fe ca alteration forming magnetite mushketovite k feldspar epidote magnetite pyrite and quartz chalcopyrite mineralization stage stage iv has an ore mineral assemblage of chalcopyrite bornite acicular hematite and sphalerite accompanied with broad epidote chlorite calcite alteration the late veins stage stage v occurs mainly as epidote calcite veins crosscutting the host rocks and earlier stage minerals stage i hydrothermal fluids have high temperatures 600 c medium high salinities with magmatic 18ofluid 6 to 11 7 stage iii ore forming fluids are medium high temperature ca 470 570 c with medium salinity stage iii minerals were formed under dfluid 45 7 to 24 3 18ofluid 5 8 to 9 1 and 34sfluid 1 7 to 4 7 indicative of magmatic fluids mixed with minor seawater in contrast stage iv fluids have low temperatures ca 160 c medium low salinities and are ca rich with isotopic compositions reflecting basinal brine mixed with meteoric water 13cfluid 6 6 to 2 3 18ofluid 3 3 to 2 8 and 34sfluid 24 8 the shaquanzi diorite zircon u pb age 298 5 ma is broadly coeval with previous re os ages of the shaquanzi magnetite and pyrite 303 12 ma and 295 7 ma respectively indicating that the shaquanzi fe cu metallogeny may have been genetically linked to the regional magmatic hydrothermal activities led by the yamansu arc backarc basin inversion features of hydrothermal alterations mineral assemblages ore forming fluids and tectonic setting all suggest that the shaquanzi fe cu deposit is an iocg like deposit similar to those in the cenozoic central andes

magnitude frequency relation for small earthquakes a clue to the origin of ƒmax of large earthquakes in order to test the hyothesis that the max of large earthquakes is due to the source effect and is causally related to the corner frequency of small earthquakes when it becomes constant below magnitude about 3 we constructed the frequency magnitude relation for earthquakes with magnitude range from 1 3 to 4 recorded at a borehole seismograph station operated by the university of southern california at baldwin hills in the middle of the newport inglewood fault a procedure was developed for an accurate estimation of moment magnitude from the measurement of coda amplitude as a function of lapse time the cumulative number of earthquakes per unit time period and area was estimated by finding the detection limit for ts p for each magnitude we found a clear depature of the observed log frequency magnitude relation for m 3 the observed frequency of earthquakes with m 0 5 is almost 10 times less than that expected from the extrapolation of empirical relation for earthquakes with magnitudes larger than 3 we conclude that the observed frequency magnitude relation departs from self similarity for earthquakes with magnitude smaller than about 3 this departure coincides with the widely observed departure of the moment corner frequency relation from self similarity these observations are consistent with the interpretation of max of large earthquakes in terms of the slip weakening instability model in which the critical slip may be a few tenths of a meter to a few meters and the cohesive zone size may be a few hundred meters to a few kilometers

re os isotopic ages of pyrite and chemical composition of magnetite from the cihai magmatic hydrothermal fe deposit nw china the eastern tianshan orogenic belt of the central asian orogenic belt and the beishan terrane of the tarim block nw china host numerous fe deposits the cihai fe deposit 90 mt at 45 6 fe in the beishan terrane is diabase hosted and consists of the cihai cinan and cixi ore clusters ore minerals are dominantly magnetite pyrite and pyrrhotite with minor chalcopyrite galena and sphalerite gangue minerals include pyroxene garnet hornblende and minor plagioclase biotite chlorite epidotite quartz and calcite pyrite from the cihai and cixi ore clusters has similar re os isotope compositions with 14 to 62 ppb re and 10 ppt common os pyrrhotite has 5 to 39 ppb re and 0 6 ppb common os pyrite has a mean re os model age of 262 3 5 6 ma n 13 in agreement with the isochron regression of 187os vs 187re the re os age 262 ma for the cihai fe deposit is within uncertainty in agreement with a previously reported rb sr age 268 25 ma of the hosting diabase indicating a genetic relationship between magmatism and mineralization magnetite from the cihai deposit has mg al ti v cr co ni mn zn ga and sn more elevated than that of typical skarn deposits but both v and ti contents lower than that of magmatic fe ti v deposits magnetite from these two ore clusters at cihai has slightly different trace element concentrations magnetite from the cihai ore cluster has relatively constant trace element compositions some magnetite grains from the cixi ore cluster have higher v ti and cr than those from the cihai ore cluster the compositional variations of magnetite between the ore clusters are possibly due to different formation temperatures combined with regional tectonic evolution of the beishan terrane the re os age of pyrite and the composition of magnetite indicate that the cihai fe deposit may have derived from magmatic hydrothermal fluids related to mafic magmatism probably in an extensional rift environment

geochemistry mineralogy and genesis of the ayazmant fe cu skarn deposit in ayvalik balikesir turkey abstract the ayazmant fe cu skarn deposit is located approximately 20 km se of ayvalik or 140 km n of izmir in western turkey the skarn occurs at the contact between metapelites and the metabasites of the early triassic kinik formation and the porphyritic hypabyssal intrusive rocks of the late oligocene kozak intrusive complex the major trace and rare earth element geochemical analysis of the igneous rocks indicate that they are i type subalkaline calc alkaline metaluminous i type products of a high level magma chamber generated in a continental arc setting the 40 ar 39 ar isochron age obtained from biotite of hornfels is 20 3 0 1 ma probably reflecting the age of metamorphic bimetasomatic alteration which commenced shortly after intrusion into impure carbonates three stages of skarn formation and ore development are recognized 1 early skarn stage stage i consisting mainly of garnet with grossular rich gr 75 79 cores and andradite rich gr 36 38 rims diopside di 94 97 scapolite and magnetite 2 sulfide rich skarn stage ii dominated by chalcopyrite with magnetite andraditic garnet ad 84 89 diopside di 65 75 and actinolite and 3 retrograde alteration stage iii dominated by actinolite epidote orthoclase phlogopite and chlorite in which sulfides are the main ore phases 40 ar 39 ar age data indicate that potassic alteration synchronous or postdating magnetite pyroxene amphibole skarn occurred at 20 0 0 1 ma the high pyroxene garnet ratio plus the presence of scapolite in calc silicate and associated ore paragenesis characterized by magnetite hematite chalcopyrite and bornite suggests that the bulk of the ayazmant skarns were formed under oxidized conditions oxygen isotope compositions of pyroxene magnetite and garnet of prograde skarn alteration indicate a magmatic fluid with 18 o values between 5 4 and 9 5 on the basis of oxygen isotope data from mineral pairs the early stage of prograde skarn formation is characterized by pyroxene di 94 97 magnetite assemblage formed at an upper temperature limit of 576 c the lower temperature limit for magnetite precipitation is estimated below 300 c on the basis of magnetite calcite pairs either as fracture fillings or massive ore in recrystallized limestone marble the sulfide assemblage is dominated by chalcopyrite with subordinate molybdenite pyrite cubanite bornite pyrrhotite galena sphalerite and idaite gold copper mineralization formed adjacent to andradite dominated skarn which occurs in close proximity to the intrusion contacts native gold and electrum are most abundant in sulfides as fine grained inclusions grain size with varying from 5 to 20 m sulfur isotope compositions obtained from pyrrhotite pyrite chalcopyrite sphalerite and galena form a narrow range between 4 8 and 1 6 suggesting the sulfur was probably mantle derived or leached from magmatic rocks geochemical data from ayazmant shows that cu is strongly associated with au bi te se cd zn pb ni and co the ayazmant mineralizing system possesses all the ingredients of a skarn system either cogenetic with or formed prior to a porphyry cu au mo system the results of this study indicate that the aegean region of turkey has considerable exploration potential for both porphyry related skarns and porphyry cu and au mineralization

early neoproterozoic granitic gneisses in the chinese eastern tianshan petrogenesis and tectonic implications abstract early neoproterozoic granitic gneisses are known from several locations such as the xingxingxia alatage and baluntai areas in the central tianshan arc terrane of the chinese eastern tianshan which is one of several precambrian microcontinents within the southern central asian orogenic belt caob the petrogenesis and the tectonic significance of the early neoproterozoic granitic gneisses have not been well constrained yet resulting in an ambiguous understanding of the early tectonothermal evolution of the chinese eastern tianshan geochronological results suggest that the protoliths of these granitic gneisses formed during a relatively short time period between ca 970 and 915 ma mainly clustering at ca 940 ma these peraluminous to strongly peraluminous granitic rocks show a common geochemical s type granite affinity involving low cao na 2 o th and y contents zircon saturation thermometry and ti in zircon thermometry yielded a relatively low crystallization temperature of approximately 750 800 c for the magmatic protolith of the granitic gneisses zircon hf isotopic compositions of the xingxingxia and alatage granitic gneisses show e hf t values of 5 4 to 4 2 with t dm2 model ages of 1 53 2 14 ga indicating that their protoliths were derived by the recycling of older continental crust we suggest that the early neoproterozoic granitic rocks in the chinese eastern tianshan were formed along an active continental margin furthermore we propose that the central tianshan arc terrane was located at the periphery of rodinia and separated from the tarim craton terrane in the early neoproterozoic

discriminating hydrothermal fluid sources using tourmaline boron isotopes example from bailingshan fe deposit in the eastern tianshan nw china abstract tourmaline is an important b bearing mineral in many types of hydrothermal deposits and its chemical and boron isotopic signatures shed light on the nature and evolution of the metallogenic processes two generations of hydrothermal tourmaline in potassic altered rocks tourmaline i and subsequent veinlets tourmaline ii have been identified at the volcanic hosted bailingshan fe deposit in the chinese eastern tianshan nw china both tourmaline i and ii have low ca contents and x site occupancy and belong to the alkali group tourmaline i grains plot in the schorl field or between the dravite and schorl fields whereas tourmaline ii grains are largely mg rich dravitic mineral textural and geochemical features suggest that the compositions of tourmaline i and ii were mainly controlled by the host rock and hydrothermal fluid compositions respectively in situ b isotope analyses of tourmaline i yielded 11b values of 1 7 to 4 1 whereas tourmaline ii yielded slightly higher values of 3 5 to 6 6 calculated b isotope compositions 11bh2o of the hydrothermal fluids in equilibrium with tourmaline i are 3 3 to 5 7 at 550 c suggesting a mixed magmatic fluid major and basinal brine minor origin meanwhile tourmaline ii forming fluids yielded 11bh2o values of 6 2 to 9 3 at 400 c based on geological constraints and modal calculations we suggest that the observed b isotope variations from tourmaline i to ii are mainly controlled by rayleigh fractionation process and indicate that they may have crystallized from similar fluids the presence of basinal brine incursion into the k rich hydrothermal fluids and geological constraints lead us to suggest that the bailingshan deposit was likely formed in a paleozoic aqishan yamansu arc related basin in the eastern tianshan

genesis of permian granites along the kangguer shear zone jueluotage area northwest china geological and geochemical evidence abstract permian mafic and felsic intrusions occur along the kangguer shear zone ksz in the jueluotage area eastern tianshan northwest china this study focuses on the permian felsic intrusions 288 276 2 ma systematic geological and geochemical investigations show that granite plutons in the western ksz dikan guandao and hongshi have lower al and higher alkali contents than those in the eastern ksz longdong huangshan and baishandong the western granite plutons experienced higher degrees of crystal fractionation than the eastern granite plutons both of the western and eastern permian granite intrusions along ksz were derived from juvenile crust the nd pb isotopic characteristics of which exhibit mixed compositions of dm and emii type mantles both of the western and eastern permian granites along ksz were formed within post collision background the dikan guandao and hongshi plutons in the west ksz sector were formed in an extensional tectonic setting whereas the longdong huangshan and baishandong plutons in the east ksz formed in a compressional tectonic setting

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

epithermal deposits in north xinjiang nw china the north xinjiang region nw china is an important part of the central asia orogenic belt situated at the junction of siberia tarim and kazakhstan plates it is an area characterized by multiple stages of phanerozoic continental growth during which several porphyry and epithermal systems were formed the relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood in this paper we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in north xinjiang and classify them into high sulfidation and low sulfidation styles with the latter being predominant we have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail the deposit scale geology and geochemistry of epithermal systems in north xinjiang are essentially similar to those in other parts of the world all epithermal deposits in north xinjiang are hosted in volcanic rocks with ages ranging from devonian to triassic with the early carboniferous volcanic sequences being the most important followed by the permian and triassic the devonian early carboniferous host rocks belong to the calc alkaline series that developed in pre collisional arc back arc basin systems whereas the permian triassic host volcanic rocks of shoshonite series formed in post subduction regimes available isotopic ages of these epithermal systems cluster in two periods early carboniferous 320 ma and late carboniferous triassic 320 220 ma reflecting two metallogenic episodes that occurred during subduction related accretion and post subduction collision regimes respectively accordingly three groups of epithermal deposits in north xinjiang can be recognized as 1 pre collisional deposits without or with negligible collisional related modification 2 deposits formed in collision regime and 3 ore systems strongly overprinted by fluid flow in post subduction collision regime

genesis of the paleozoic aqishan yamansu arc basin system and fe cu mineralization in the eastern tianshan nw china abstract the formation of the eastern tianshan orogen northern xinjiang nw china with a number of ew trending mineralization belts was closely linked to the evolution of the junggar and south tianshan oceans probably part of the paleo asian ocean among these eastern tianshan mineralization belts the carboniferous aqishan yamansu fe cu belt hosts a total reserve of 207 mt fe and economic cu endowments for many deposits these fe cu deposits are hosted in submarine volcanic rocks lower carboniferous yamansu formation and upper carboniferous tugutublak formation and are featured by the presence of extensive skarn alteration without apparently causative intrusive rocks which leads to debates over their genesis in this paper we have summarized the ore deposit geology geochemistry and stable isotopes of the aqishan yamansu fe cu deposits and discuss their genesis under the regional tectonic framework we suggest that the carboniferous aqishan yamansu belt may have been a forearc basin formed by the south dipping subduction of the kangguer ocean beneath the central tianshan massif the yamansu formation volcanic rocks and some syngenetic fe deposits may have formed during the opening of the forearc basin the tugutublak formation volcanic rocks and most fe cu deposits may have formed during the subsequent late carboniferous basin inversion in these aqishan yamansu fe cu deposits the fe mineralization occurred earlier and was likely formed directly from the magmatic hydrothermal fluids whereas the subsequent cu mineralization was likely caused by the gradual increase of seawater or basinal brine influx into the fluid system external sulfur the probable external sulfur input the absence of clear plutonic link and the temporal coincidence of peak mineralization and basin inversion for the carboniferous aqishan yamansu fe cu mineralization are comparable to the mesozoic iocg mineralization in the central andes

age geochemistry and tectonic implications of a late paleozoic stitching pluton in the north tian shan suture zone western china the central asian orogenic belt is the largest tectonic assembly of continental and oceanic terranes on earth due to closure of the paleo asian ocean in the phanerozoic among major suture zones in the north xinjiang region of western china the north tian shan suture zone because of collision between the yili terrane in the south and the junggar terrane in the north contains the youngest ophiolitic rocks and may represent the terminal stage of development of the central asian orogenic belt in western china but the timing of the suture zone remains poorly constrained a sensitive high resolution ion microprobe shrimp zircon u pb age of 316 3 ma i e the beginning of the late carboniferous from the undeformed sikeshu pluton which crosscuts the suture zone places a crucial upperage bound for the time of collision between the yili and junggar terranes this event occurred later than or nearly concurrent with other accretion collision events in the north xinjiang region implying that fi nal terrane amalgamation was completed in the late carboniferous the sikeshu pluton shares geochemical characteristics of the widespread late carboniferous to permian postcollisional a type and i type granitoids with depleted mantle like sr nd isotopic signatures in the north xinjiang region they all occurred during a protracted ca 320 270 ma episode of postcollisional magmatism that may have been induced by basaltic under plating due to either slab breakoff or delamination of thickened mantle lithosphere beneath the central asian orogenic belt the same postcollisional magmatism also generated cu ni sulfi de bearing mafi c ultramafi c magmatic complexes adakites and porphyry type coppermolybdenum bearing magmatic rocks in the north xinjiang region

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

trace elements in hydrothermal quartz relationships to cathodoluminescent textures and insights into vein formation high resolution electron microprobe maps show the distribution of ti al ca k and fe among quartz growth zones revealed by scanning electron microscope cathodoluminescence sem cl from 12 hydrothermal ore deposits formed between 100 and 750 c the maps clearly show the relationships between trace elements and cl intensity in quartz among all samples no single trace element consistently correlates with variations in cl intensity however in vein quartz from five porphyry cu mo au deposits cl intensity always correlates positively with ti concentrations suggesting that ti is a cl activator in quartz formed at 400 c ti concentrations in most rutile bearing vein quartz from porphyry copper deposits indicate reasonable formation temperatures of 750 c using the titaniq geothermometer titanium concentrations of 10 ppm in all veins that formed at temperatures 350 c suggest a broad correlation between ti concentrations and temperature of quartz precipitation in quartz from most deposits formed at 2000 ppm but in high temperature quartz al concentrations are consistently in the range of several hundred ppm aluminum concentrations in quartz reflect the al solubility in hydrothermal fluids which is strongly dependent on ph aluminum concentrations in quartz therefore reflect fluctuations in ph that may drive metal sulfide precipitation in hydrothermal systems

geology and ore genesis of the late paleozoic heijianshan fe oxide cu au deposit in the eastern tianshan nw china abstract the heijianshan fe cu au deposit located in the aqishan yamansu belt of the eastern tianshan nw china is hosted in the mafic intermediate volcanic and mafic felsic volcaniclastic rocks of the upper carboniferous matoutan formation based on the pervasive alteration mineral assemblages and crosscutting relationships of veins six magmatic hydrothermal stages have been established including epidote alteration stage i magnetite mineralization stage ii pyrite alteration stage iii cu au mineralization stage iv late veins stage v and supergene alteration stage vi the stage i epidote calcite tourmaline sericite alteration assemblage indicates a pre mineralization ca mg alteration event stage ii fe and stage iv cu au mineralization stages at heijianshan can be clearly distinguished from alteration mineral assemblages and nature and sources of ore forming fluids homogenization temperatures of primary fluid inclusions in quartz and calcite from stage i 189 370 c ii 301 536 c iii 119 262 c and v 46 198 c suggest that fluid incursion and mixing probably occurred during stage i to ii and stage v respectively the stage ii magmatic hydrothermal derived fe mineralization fluids were characterized by high temperature 300 c medium high salinity 21 2 56 0 wt nacl equiv and being na ca mg fe dominated these fluids were overprinted by the external low temperature in situ sulfur isotopes also indicate that the sulfur sources vary in different stages viz stage ii magmatic hydrothermal iii basinal brine related and iv magmatic hydrothermal stage ii disseminated pyrite has 34 s fluid values of 1 7 4 3 comparable with sulfur from magmatic reservoirs 34 s fluid values 24 3 29 3 of stage iii type a pyrite coexists with hematite probably indicate external basinal brine involvement consistent with the analytical results of fluid inclusions with the basinal brines further interacting with volcanic volcaniclastic rocks of the carboniferous matoutan formation stage iii type b pyrite chalcopyrite pyrrhotite assemblage with low 34 s fluid values of 4 6 10 0 may have formed at low f o 2 and temperature 119 262 c the continuous basinal brine volcanic volcaniclastic rock interactions during the basin inversion 325 300 ma may have leached sulfur and copper from the rocks yielding magmatic like 34 s fluid values 1 5 4 1 such fluids may have altered pyrite and precipitated chalcopyrite with minor au in stage iv eventually the stage v low temperature 160 c and low salinity meteoric water may have percolated into the ore forming fluid system and formed late hydrothermal veins the similar alteration and mineralization paragenetic sequences ore forming fluid sources and evolution and tectonic settings of the heijianshan deposit to the mesozoic central andean iocg deposits indicate that the former is probably the first identified paleozoic iocg like deposit in the central asian orogenic belt

geology tectonic settings and iron ore metallogenesis associated with submarine volcanism in china an overview abstract submarine volcanogenic iron oxide svio deposits are one of the most important sources of high grade iron ores in china the spatial distribution of the deposits is controlled by the tectonic settings including arc back arc and rift environments with the svio deposits mostly concentrated in the western part of china namely the southwestern yangtze craton western and eastern tianshan and altay orogens and the kaladawan iron ore district in the eastern part of the altyn tagh region the chinese svio deposits range in age from paleoproterozoic to mesozoic and were formed during two main metallogenic epochs in the proterozoic and paleozoic more than 70 of the svio deposits formed in the paleozoic with three important svio metallogenic provinces recognized in the altay eastern and western tianshan orogens these svio deposits are hosted in lithofacies that are related to submarine magmatism such as lavas and associated pyroclastic and volcaniclastic sedimentary rocks the iron orebodies are hosted in different volcanic lithofacies with different features moreover the different volcanic lithofacies in which the fe ores are hosted also provide information as to their spatial relationship ranging from distal to proximal to the eruption center or vent many of these deposits are characterized by well developed skarns and could be interpreted either by a distal position of the ore system in question and or exposed igneous rocks or active magma chamber or a relationship to early metamorphism and continuous alteration at relatively high temperature followed by retrograde alteration as temperatures decline geological and geochemical evidence suggests that these deposits were formed as a result of submarine magmatic activity including subaqueous volcanic eruptions associated volcano sedimentary lithofacies and related post magmatic hydrothermal activity iron oxide ore probably formed the hydrothermal fluids which generated the skarns could be a mixture of evolved magma derived water and convecting sea water driven by the heat from the shallow active magma chamber whereas volcano sedimentary deposits could be formed by the fallout of the ore bearing materials to the sea floor emanating from submarine eruption columns or fractional precipitation of iron which had been introduced locally into the bottom water by volcanic origin hydrothermal solutions and by leaching from the relatively iron rich volcanic rocks the formation of these various styles of fe ore deposits is controlled by several key factors such as magma differentiation lithofacies of host rocks temperature and chemical compositions of hydrothermal fluids as well as the depth of sea water in combination with their geological characteristics geodynamic mechanisms and metallogenesis we propose a genetic model in which the origin of these deposits can be related to the space time evolution of the submarine volcanism and their relationship to volcanic lithofacies variation such as central proximal and distal environments of ore formation

the evolution of the hydrothermal iocg system in the mantoverde district northern chile new evidence from microthermometry and stable isotope geochemistry new microthermometric data combined with stable isotope geochemistry and paragenetic relationships support a previously suggested cooling mixing model for the iron oxide copper gold mineralization in the mantoverde district fluid inclusions show characteristics of a co2 bearing aqueous nacl cacl2 salt system the evolution of the mantoverde hydrothermal system is characterized by 1 an early hypersaline high to moderate temperature fluid 2 a moderate saline moderate temperature fluid and 3 a low saline moderate to low temperature fluid early magnetite formation took place at median temperatures of 435 0 c whereas hematite formed at median temperatures of 334 4 c the main sulfide mineralization texturally post dates the iron oxides and occurred before late stage calcite which developed at a median temperature of 244 8 c boiling occurs only locally and is of no relevance for the ore formation the microthermometric and stable isotope data are supportive for a fluid cooling and mixing model and suggestive for a predominantly magmatic hydrothermal fluid component during the iron oxide and main sulfide mineralization thereafter the incursion of a nonmagmatic fluid of ultimately meteoric or seawater gains more importance

fluid inclusion and isotopic constraints on the origin of the paleoproterozoic yinachang fe cu ree deposit southwest china the yinachang deposit in the kangdian fe cu metallogenic province southwest china contains approximately 20 mt ore 41 9 to 44 5 wt fe and 15 mt ore 0 85 to 0 97 wt cu with potentially significant rees orebodies are hosted in the late paleoproterozoic dongchuan group and consist mainly of massive and banded replacement ores the paragenetic sequence of this deposit includes pre ore na fe alteration stage i fe ree mineralization dominated by magnetite and siderite with subsidiary apatite and fluorite stage ii and cu ree mineralization with chalcopyrite ankerite biotite and subordinate apatite fluorite allanite and synchysite stage iii this sequence is similar to those of many iron oxide copper gold iocg deposits elsewhere there are two distinct types of fluid inclusions within apatite of both stages ii and iii type 1 fluid inclusions with liquid and vapor phases have relatively low homogenization temperatures 98 345 c and salinities 4 7 16 2 wt nacl equiv whereas type 2 fluid inclusions with one or more solid phases a liquid phase and a vapor phase have higher homogenization temperatures 273 500 c and salinities 36 2 59 8 wt nacl equiv fluids in sulfur isotope equilibrium with chalcopyrite of stages iii have 34 s cdt values ranging from 2 8 to 2 7 consistent with a magmatic origin for the sulfur thus sulfur isotopie compositions imply that magmatic hydrothermal fluids probably represented by the hot and saline type 2 fluid inclusions were involved in the ore forming process although 34 s close to 0 might also mean that sulfur was leached from igneous rocks by nonmagmatic fluids siderite of stage ii and ankerite of stage iii have 13 c pdb values ranging from 12 4 to 7 5 and from 8 5 to 4 4 respectively the large variation of 13 c pdb values reveals a strong interaction between the magmatic hydrothermal fluids and the dolostone in the ore hosting sequence calculated 18 o smow values of the fluids in stages ii and iii are broadly similar and vary from 11 1 to 17 1 avg 13 5 such values are higher than that of magmatic hydrothermal fluids and thus may indicate extensive fluid wall rock interaction and or mixing of magmatic hydrothermal fluids with shallow level nonmagmatic fluids this interpretation is consistent with the radiogenic sr isotope compositions of bulk ores 87 sr 86 sr i 0 710404 0 734034 and fluorite separated from ores 87 sr 86 sr i 0 709851 0 723658 these nonmagmatic fluids are probably representative of the type 1 fluid inclusions bulk ores and mineral separates have nd t values ranging from 8 1 to 0 4 mostly 0 9 to 0 4 similar to the coeval mafic intrusions in the region 2 0 to 2 8 this similarity suggests that rees in the yinachang deposit might have been derived dominantly from mantle derived magmas on the other hand relatively low nd t values 5 5 and 8 1 of some samples indicate insignificant ree contributions from wall rocks the yinachang deposit is temporally associated with regional mantle derived mafic magmatism and may have a genetic relationship with it fluids derived from deep seated magmas may have supplied abundant sulfur and carbon as well as some of the ore metals in this deposit the mafic magmatism could also have provided heat to induce the shallow level nonmagmatic fluids to interact with the sedimentary volcanic sequence thus leaching additional ore metals into the ore forming system fluid mixing can effectively trigger saturation and deposition of ore minerals our work highlights that nonmagmatic fluids are not a prerequisite for cu au ree mineralization but may facilitate metal deposition in magmatic hydrothermal iocg systems

the raul condestable iron oxide copper gold deposit central coast of peru ore and related hydrothermal alteration sulfur isotopes and thermodynamic constraints the iron oxide copper gold iocg raul condestable deposit is located 90 km south of lima peru and approximately 5 km from the pacific coast mineralization consists mainly of replacement mantos and disseminations within permeable volcaniclastic and carbonate rich rocks and structurally controlled veins surrounding a coeval and apparently causative intrusion of tonalitic composition emplaced in the core of a dacitic volcano potassic biotite grading upward to sericite chlorite alteration and a poorly developed almost sulfide free quartz stockwork closely border the tonalite affecting the basaltic to dacitic lower cretaceous volcano sedimentary host sequence ore is associated with a hydrated calc silicate mainly amphiboles alteration that surrounds the biotite alteration a hematite chlorite albite epidote calcite alteration affects the periphery of the system the main ore stage is characterized by two end member mineral associations that were formed according to 1 an oxidized deposition sequence hematite magnetite pyrite chalcopyrite occurring in and near feeder structures and 2 a reduced deposition sequence pyrrhotite pyrite chalcopyrite found in volcaniclastic rocks and veins early specular hematite of the oxidized sequence is transformed to magnetite mushketovite the main ore stage mineralization is cut by minor late stage calcite sulfide veins main ore stage sulfides have 34s values asymmetrically distributed from 1 0 to 26 3 per mil with a median at 6 6 per mil n 51 similar values are observed for pyrrhotite pyrite and chalcopyrite the 34s values depend on the stratigraphic position with deep seated vein samples normally distributed between 1 0 and 6 3 per mil avg about 3 5 n 13 and shallower samples from 2 7 to 26 3 per mil median around 7 5 n 39 sulfides found in late stage calcite sulfide veins show strongly negative 34s values ranging between 32 7 and 22 9 per mil n 6 indicating a possible biogenic source because no rock unit is known to occur in the internal parts of the deposit that could have oxidized fluids to the point of hematite stability the oxidized mineral sequence is best explained by magmatic brines following the so2 h2s gas buffer at high temperature 350 c and fluid rock ratio this is supported by the close to magmatic 34s values of sulfides from the deep parts of feeder veins mass balance calculation based on sulfur isotope data suggests that at the deposit scale the bulk of the sulfides is dominated by magmatic sulfur with sulfides of the oxidized minerals association having a larger component of magmatic sulfur than those of the reduced mineral association the deposition sequence from hematite to chalcopyrite reflects the cooling of the magmatic fluid and redox and ph buffering by the basaltic andesitic volcano sedimentary host rocks thus the occurrence of magnetite pseudomorphous after early hematite mushketovite paragenetically followed by iron bearing sulfides is interpreted to be direct field evidence for precipitation from oxidized magmatic brines the same sequence has been described in many iocg skarn and some porphyry copper deposits worldwide 34s values of sulfides ranging up to 26 3 per mil are found in what corresponded to a relatively shallow aquifer filled with evolved reduced seawater heavy sulfur in h2s was produced through thermochemical reduction of aptian seawater sulfate 34s 14 in the recharge zone which is interpreted to correspond to the hematitechlorite albite epidote calcite alteration present at the upper flanks of the hydrothermal system adjacent to the causative intrusion hematitization through oxidation resulted from the high fo2 of seawater and from the reduction of its sulfate to h2s by the fe2 contained in the rock in the core of the system the seawater derived fluids reached near chemical equilibrium with their actinolitized host rock at about 300 to 350 c in reduced rock dominated conditions mixing of these fluids with magmatic brines already partially or totally reduced through reaction with wall rock at medium to low magmatic fluid rock ratio can explain the large positive 34s scatter observed in sulfides of the reduced mineral association at stratigraphically shallow positions

paleozoic tectonic evolution of the tianshan orogen northwestern china abstract the chinese tianshan orogenic belt which extends west east for about 1500 km is one of the most important paleozoic orogenic belts in central asia it includes parts of the tarim yili central tianshan and junggar plates which are microcontinental blocks with precambrian basements and meso cenozoic depositional covers the tarim plate is separated from the yili central tianshan plate by the southern central tianshan suture early carboniferous ophiolitic melanges and blueschists are widespread in this suture and are believed to be produced by the collision between a passive continental margin on the north side of the tarim plate and an active continental margin on the south side of the yili central tianshan plate the collision occurred at the end of early carboniferous the yili central tianshan and the junggar plates are separated by the northern central tianshan suture also considered as an early carboniferous collisional zone along which the middle ordovician ophiolitic melanges blueschists and late devonian early carboniferous ophiolites are exposed in early paleozoic times the subduction of the paleo junggar ocean took place in an active margin on the north side of the yili central tianshan plate along the northern central tianshan suture at the end of early carboniferous the north side of the yili central tianshan plate collided with the north tianshan arc along this suture the paleo oceanic crust in the tianshan and adjacent region was entirely consumed at the end of early carboniferous meanwhile the tarim yili central tianshan and junggar plates were accreted to eurasia epicontinental sediments were then deposited throughout the tianshan region during the middle late carboniferous times in the early permian tianshan began to uplift with accompanying volcanic eruption and granitic intrusion the uplift was accelerated in the late permian and continental molasse was extensively deposited

mineral chemistry of ore and hydrothermal alteration at the sossego iron oxide copper gold deposit carajas mineral province brazil abstract the sossego iron oxide copper gold deposit in the carajas mineral province comprises two major orebodies sequeirinho and sossego sodic alteration albite hematite and sodic calcic alteration zones represented by albite ferro edenite hastingsite up to 3 8 wt cl actinolite magnesiohornblende magnetite titanite epidote and calcite are predominant at sequeirinho magnetite bodies with envelopes of apatite rich actinolitite were formed with the sodic calcic event at high temperatures 500 c at 1 4 kbar in the sossego orebody potassic alteration with orthoclase and cl rich biotite up to 3 1 wt and chloritization are the main alteration types mineralized breccias in both orebodies have coarse grained zoned actinolite ferro actinolite cl apatite and magnetite within the matrix sulfides occur in equilibrium with a paragenetically late calcite quartz chlorite epidote allanite assemblage the al iv contents of the chlorite indicate crystallization at temperatures below 300 c chalcopyrite occurs associated with pyrite up to 2 3 wt co and 0 2 wt ni native gold up to 14 9 wt ag siegenite millerite vaesite pd melonite and hessite dilution and cooling of the hot metalliferous fluid 500 c by mixing with meteoric fluids may have been the main mechanisms responsible for the deposition of metals transported as metal chloride complexes in both orebodies of the sossego deposit

age of mineralization of the candelaria fe oxide cu au deposit and the origin of the chilean iron belt based on re os isotopes re os isotopes are used to determine the age of iron oxide cu au mineralization at candelaria chile and to explore possible genetic links with the batholithic intrusions in the area re os ages calculated from molybdenite are 114 2 0 6 ma and 115 2 0 6 ma and they are interpreted to represent the age of mineralization these ages are consistent with previously reported ages for biotite alteration that range from 114 to 116 ma an isochron calculated by re os ratios from hydrothermal magnetite and sulfides constrains an initial 187 os 188 os ratio of 0 36 0 10 the initial 187 os 188 os ratio for sulfide from bronce mine a small satellite of the candelaria orebody is 0 33 0 01 these values are broadly similar to the calculated initial 187 os 188 os ratio for magmatic magnetite in nearby batholithic rocks that range from 0 20 to 0 41 the relatively radiogenic initial 187 os 188 os ratio represents a mixture of mantle and crustal components in the ores and batholitic rocks the similarity in initial 187 os 188 os ratio of the ore and magmatic oxides suggest that the granitic plutons could be the source of metals in the candelaria district these data are consistent with the existence of a significant magmatic fluid component in the hydrothermal system as suggested by previously published work in order to establish a regional perspective we analyzed ore minerals from other chilean deposits of the iron oxide cu u au rare earth elements ree class magnetite from the manto verde iron oxide cu au deposit has os and re concentrations of 11 to 17 parts per trillion ppt and 4 to 6 parts per billion ppb respectively the initial 187 os 188 os ratio is approximately 0 20 and is similar to that of ore minerals from candelaria and of the early cretaceous batholithic intrusions these data indicate a similar metal source for the mineralization at manto verde and candelaria magnetite from three magnetite apatite deposits of the chilean iron belt have re concentrations between 0 8 and 3 ppb and os concentrations between 11 and 76 ppt calculated initial 187 os 188 os ratios of these magnetites range from 1 2 to 8 4 and are distinctly different from those of the iron oxide cu au deposits the cause of the comparatively high radiogenic signatures in the magnetite apatite ores is probably related to fluid interactions with i e leaching the surrounding sedimentary rocks during their genesis in contrast to the iron oxide cu au systems the os in magnetite apatite ores could be derived from sedimentary rocks this evidence suggests that predominantly basin derived nonmagmatic brines formed these magnetite apatite deposits

trace element and ree geochemistry of minerals from heifengshan shuangfengshan and shaquanzi cu fe deposits eastern tianshan mountains located in the south of hami basin of xinjiang the heifengshan shuangfengshan and shaquanzi cu fe deposits are important deposits in the aqishan yamansu belt of eastern tianshan based on trace element and ree geochemistry this paper deals with the source and nature of the ore forming fluid and also discusses ore genesis of theses deposits la icp ms analyses show that magnetite contains low v cr and ti 68 10 6 13 10 6and 237 10 6on average respectively indicating that magnetite was derived from the hydrothermal process rather than from the magmatic differentiation the relatively high cu content in pyrite probably indicates cu bearing inclusionsin pyrite whereas low pb and zn concentrationsin pyrite may indicate the low abun dances of pb2 and zn2 in the ore forming fluids the co ni ratios of pyrite indicate that these deposits are of volcanic hydrothermal origin pyrite from these deposits is characterized by very low ree content ree 0 07 10 6 3 02 10 6 pyrite from the heifengshan fe deposit shows no obvious fractionation between lree and hree whereas pyrite from the shuangfengshan fe deposit and shaquanzi fe cu deposit shows significant lree enrichment with la yb nvalues being 3 51 13 4 and 2 76 17 2 respectively the different ree patterns of calcite for these deposits indicate different fluid compositions and mechanisms responsible for the formation of calcite there are no ce anomalies for both pyrite and calcite indicating the high t formation of these deposits pyrite and calcite from the heifengshan fe deposit show ree patterns with negative eu anomalies whereas those from the shuangfengshan and shaquanzi deposits show positive eu anomalies indicating that the ore forming fluids responsible for the heifengshan fe deposit were alkaline and those for the shuangfengshan and shaquanzi deposits were acid and reductive combined with previous studies the authors hold that these deposits may be of the volcanic hydrothermal infilling replacement type

a new attraction detachment model for explaining flow sliding in clay rich tephras altered pyroclastic tephra deposits are highly susceptible to landsliding leading to fatalities and property damage every year halloysite a low activity clay mineral is commonly associated with landslide prone layers within altered tephra successions especially in deposits with high sensitivity which describes the post failure strength loss however the precise role of halloysite in the development of sensitivity and thus in sudden and unpredictable landsliding is unknown here we show that an abundance of mushroom cap shaped mcs spheroidal halloysite governs the development of sensitivity and hence proneness to landsliding in altered rhyolitic tephras north island new zealand we found that a highly sensitive layer which was involved in a flow slide has a remarkably high content of aggregated mcs spheroids with substantial openings on one side we suggest that short range electrostatic and van der waals interactions enabled the mcs spheroids to form interconnected aggregates by attraction between the edges of numerous paired silanol and aluminol sheets that are exposed in the openings and the convex silanol faces on the exterior surfaces of adjacent mcs spheroids if these weak attractions are overcome during slope failure multiple weakly attracted mcs spheroids can be separated from one another and the prevailing repulsion between exterior mcs surfaces results in a low remolded shear strength a high sensitivity and a high propensity for flow sliding the evidence indicates that the attraction detachment model explains the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding in sensitive altered tephras rich in spheroidal halloysite

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

genesis of the aqishan skarn zn pb deposit in the eastern tianshan nw china constraints from geology geochronology and hf s pb isotopic geochemistry abstract the aqishan deposit located in the eastern tianshan xinjiang china is a newly discovered large scale zn pb deposit with a proven reserve of 1 94 mt pb and zn metal at an average grade of 1 05 the zn pb orebodies are tabular and lentoid in shape developed within skarnized carbonates and calcareous volcanoclastic rocks of the yamansu formation the skarn mineral assemblages are characterized by abundant garnet epidote chlorite actinolite calcite and quartz with minor amounts of pyroxene metallic minerals comprising sphalerite galena chalcopyrite pyrite pyrrhotite and arsenopyrite mainly occur as disseminations and irregular patches within the skarn re os dating of five syn ore stage pyrite samples yielded an isochron age of 301 13 ma which is in agreement with the 306 2 8 ma age obtained from the granodiorite porphyry occurring at southeast part of the aqishan zn pb deposit the ehf t values of zircon from the granodiorite porphyry vary from 9 62 to 14 69 suggesting a juvenile crust source the 34 sv cdt values of 22 sulfide samples range from 11 6 to 2 76 with an average of 5 08 the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 9 sulfide samples range from 18 102 to 18 336 15 539 to 15 655 and 37 929 to 38 479 respectively which are similar to the carboniferous grantoids of the aqishan area and partly overlap with the volcanoclastic rocks of the yamansu formation based on these data we propose that the aqishan deposit formed from magmatic hydrothermal fluids that emanated from the granodiorite porphyry much of the metals were derived from the magmatic intrusions with minor contributions from the volcanoclastic rocks whereas the sulfur may have been mainly extracted from the country rocks with slight contributions from a magmatic source the close genetic relationships between the carboniferous magmatism and skarn type zn pb mineralization in the aqishan area as well as other deposits in the region suggests a great potential of finding more analogous deposits in the eastern tianshan where carbonates or calcareous volcanoclastic rocks and plutons that related to the subduction of the northern tianshan oceanic slab beneath the yili central tianshan terrane during late paleozoic are well developed

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

isotopic footprints of the giant precambrian caixiashan zn pb mineralization system abstract carbonate replacement zn pb deposits are formed through fluid circulation within carbonate rocks and are an important global source of zn and pb the caixiashan carbonate replacement deposit is one of the largest zn pb systems in china the mesoproterozoic syn sedimentary stage i of the caixiashan deposit is characterized by sulfides with negative 34s values 25 3 to 8 6 generated by organic sulfate reduction which co precipitated with the host rocks the neoproterozoic main sulfide precipitation stage ii was caused by thermo sulfide reduction resulting in positive 34s values 7 9 12 3 carbonates from stage i have 13cpdb of 1 2 to 2 8 and 18osmow of 17 1 24 0 similar to those of marine carbonate rocks dolomite and calcite from stage ii have 13cpdb ranging from 5 1 to 0 2 and 18osmow of 14 1 19 7 consistent with dissolution of carbonate rock in contrast dolomite and calcite from stage iii have mantle c o signatures with the 13cpdb ranging from 7 5 to 0 4 and 18osmow from 5 8 to 13 2 c o isotopic signatures suggest that the original carbonates were dissolved by the acid generated from sulfide precipitation consistent with the sulfide precipitation process subsequent precipitation of carbonates created large volumes of dolomite alteration that coated the sulfides and possibly contributed to the preservation of the ore as dolomite would dissolve more slowly than calcite carboniferous magmatism stage iii resulted in a magmatic overprint on the stage ii sulfide the metal sources of these sulfide ore packets are mainly derived from the mesoproterozoic carbonate rocks as indicated by the lead isotopes of sulfides and also c o isotopes of carbonates the deposit is characterized by a complex paragenesis with multiple overprinting sources of hydrothermal fluids and sulfide over 700 m y the syn sedimentary stage 1019 ma and main mineralization stage 859 837 ma at caixiashan are chronologically and tectonically associated with the assembly and break up of the rodinia supercontinent whereas the magmatic hydrothermal modification stage 353 ma is associated with the closure of the paleo asian ocean during the early carboniferous

magnetite geochemistry of the heijianshan fe cu au deposit in eastern tianshan metallogenic implications for submarine volcanic hosted fe cu deposits in nw china abstract the heijianshan fe cu au deposit is located in the aqishan yamansu belt in eastern tianshan nw china as a typical fe cu deposit in the region heijianshan is hosted in the upper carboniferous matoutan formation submarine volcanic volcaniclastic rocks alteration styles mineral assemblages and vein crosscutting relationships divide the hydrothermal alteration and mineralization processes into seven stages namely the chromite stage i epidote stage ii magnetite stage iii pyrite stage iv cu au stage v late veins stage vi and supergene stage vii alteration mineralization stages magnetite mineralization comprises the hematite stage iii a and main magnetite stage iii b mineralization sub stages the heijianshan magnetite ores consist of massive with mushketovite mom or sulfides mos disseminated do and magnetite clasts with chromite mwc or without chromite mnc ores magnetite in massive and disseminated ores is featured by 1 depletion in zr nb and ta 2 low ti f o 2 increased which may represent the major controls on the formation of the various magnetite ore types compositions of the ore fluids and host rocks formation of coexisting minerals and other physicochemical parameters such as t and f o 2 may have variably influenced the magnetite geochemistry in the different heijianshan ore types with fluid compositions probably playing the most important role discrimination diagrams for instance cr vs co ni cr vs ti v vs cr and ni vs cr may be useful for magnetite mineralization type differentiation in other submarine volcanic hosted fe fe cu deposits in the aqishan yamansu belt geochemical discrimination diagrams alteration and mineralization paragenesis indicate that the heijianshan fe cu au deposit is best classified as an iocg like deposit which offers a new insight for classifying and characterizing ore genetic types for similar fe and fe cu deposits in eastern tianshan

an early paleozoic collisional event along the northern margin of the central tianshan block constraints from geochemistry and geochronology of granitic rocks abstract the tianshan orogen was formed by multiple stage accretionary events ophiolites exposed in the northern margin of the central tianshan block ctb indicate the existence of an early paleozoic ocean between the tuha terrane and the ctb i e the paleo tianshan ocean however the closing history of this ocean is still controversial granitoids exposed extensively in the ctb can place a good constraint for this collisional process in this study geochemical and geochronological analyses are carried out on four granitic plutons from the ctb one mylonitic granodiorite intruding the ctb basement has a zircon u pb age of ca 496 ma and shows geochemical affinity to adakite its formation can be attributed to the subduction of the paleo tianshan ocean the 426 ma old gneissic granite that intrudes the gangou ophiolitic zone presents geochemical features of a type granite and gives an upper limit for the closure time of the paleo tianshan ocean the metamorphic age of 430 5 4 6 ma of the zircons from the mylonitic granodiorite possibly represents the event caused by the collision two other granitic samples a granodiorite and a monzodiorite yield 330 ma and 319 ma in age and display the chemical characters of i type granites that indicates a magmatic arc setting mostly related to the subduction of another ocean called the north tianshan ocean