ore forming fluids associated with granite hosted gold mineralization at the sanshandao deposit jiaodong gold province china the sanshandao gold deposit with total resources of more than 60 t of gold is located in the jiaodong gold province the most important gold province of china the deposit is a typical highly fractured and altered disseminated gold system with high grade quartz sulphide vein veinlet stockworks that cut mesozoic granodiorite there are four stages of veins that developed in the following sequence 1 quartz k feldspar sericite 2 quartz pyrite arsenopyrite 3 quartz base metal sulfide and 4 quartz carbonate fluid inclusions in quartz and calcite in vein veinlet stockworks contain c o h fluids of three main types the first type consists of dilute co2 h2o fluids coeval with the early vein stage molar volumes of these co2 h2o fluid inclusions ranging from 50 60 cm3 mol yield estimated minimum trapping pressures of 3 kbar homogenization temperatures obtained mainly from co2 h2o inclusions with lower co2 concentration range from 267 375 c the second inclusion type with a co2 h2o ch4 composition was trapped during the main mineralizing stages these fluids may reflect the co2 h2o fluids that were modified by fluid rock reactions with altered wallrocks isochores for co2 h2o ch4 inclusions with homogenization temperatures ranging from 204 325 c and molar volumes from 55 to 70 cm3 mol provide an estimated minimum trapping pressure of 1 2 kbar the third inclusion type aqueous inclusions trapped in cross cutting microfractures in quartz and randomly in calcite are post mineralization and have homogenization temperatures between 143 228 c and salinities from 0 71 7 86 wt nacl equiv stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin most likely sourced from 120 126 ma mafic to intermediate dikes this is consistent with the carbonic nature of the fluid and the cross cutting nature of those deposits relative to the host mesozoic granitoid

pb isotope fingerprinting of mesothermal gold deposits from central victoria australia implications for ore genesis new pb isotope data from three major mesothermal lode gold deposits ballarat west tarnagulla maldon in central victoria support a model whereby the metals derived from a large reservoir with a long residence time in the crust below the palaeozoic lachlan fold belt the pb isotopic ratios of least radiogenic samples from these deposits are in close agreement with published pb signatures for turbidite hosted gold deposits and for devonian granites elsewhere in the lachlan fold belt despite their spatial distribution and variations in the geological setting the pb signatures point to the extraction and transport of metals from a crustal source area by long lasting large scale hydrothermal systems resulting in the prominent homogenisation of pb isotopic ratios the enduring interaction between large hydrothermal systems and an extensive crustal source reservoir were a vital pre requisite in the formation of the victorian gold province in this regard the prospectivity of victoria is analogous to world class ore provinces elsewhere such as the archaean yilgarn block in western australia

tectonic setting of synorogenic gold deposits of the pacific rim abstract more than 420 million oz of gold were concentrated in circum pacific synorogenic quartz lodes mainly during two periods of continental growth one along the gondwanan margin in the palaeozoic and the other in the northern pacific basin between 170 and 50 ma these ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary rock dominant terranes the auriferous veins contain only a few percent sulphide minerals have gold silver ratios typically greater than 1 1 show a distinct association with medium grade metamorphic rocks and may be associated with large scale fault zones ore fluids are consistently of low salinity and are co2 rich in the early and middle palaeozoic in the southern pacific basin a single immense turbidite sequence was added to the eastern margin of gondwanaland deformation of these rocks in southeastern australia was accompanied by deposition of at least 80 million oz of gold in the victorian sector of the lachlan fold belt mainly during the middle and late devonian lesser devonian gold accumulations characterized the more northerly parts of the gondwanan margin within the hodgkinson broken river and thomson fold belts additional lodes were emplaced in this flyschoid sequence in devonian or earlier palaeozoic times in what is now the buller terrane westland new zealand minor post devonian growth of gondwanaland included terrane collision and formation of gold bearing veins in the permian in australia s new england fold belt and in the jurassic early cretaceous in new zealand s otago schists collision and accretion of dozens of terranes for a 100 m y long period against the western margin of north america and eastern margin of eurasia led to widespread latest jurassic to eocene gold veining in the northern pacific basin in the former location late jurassic and early cretaceous veins and related placer deposits along the western margin of the sierra nevada batholith have yielded more than 100 million oz of gold additional significant ore forming events during the development of north america s cordilleran orogen included those in the klamath mountains region california in the late jurassic and early cretaceous the klondike district yukon by the early cretaceous the nome and fairbanks districts alaska and the bridge river district british columbia in the middle cretaceous and the juneau gold belt alaska in the eocene gold bearing veins deposited during the late jurassic and early cretaceous terrane collision that formed the present day russian far east have been the source for more than 130 million oz of placer gold the abundance of gold bearing quartz carbonate veins throughout the gondwanan north american and eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata the common temporal association between gold veining and magmatism around the pacific rim reflects these thermal episodes melting of the lower thickened crust during arc formation slab rollback and extensional tectonism and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore forming processes

fluid inclusions as tectonothermobarometers relation between pressure temperature history and reequilibration morphology during crustal thickening results of experimental reequilibration studies of natural primary aqueous inclusions in quartz under conditions of hydrostatic compressive loading at 1 2 3 4 and 5 kbar and 500 c indicate that the intensity of reequilibration features is inversely proportional to inclusion volume the smallest inclusions show the first evidence of reequilibration dissolution of inclusion walls after 1 8 kbar of effective pressure for effective pressures less than 3 8 kbar decrepitation of inclusions is probably controlled by the corrosive action of water on the inclusion walls at higher effective pressures decrepitation is related to high compressive stress and is less dependent on fluid interaction with the inclusion walls the observed correlation between inclusion size intensity of reequilibration features and amount of loading combined with paragenetic and microthermometric data for the inclusions may be used to determine the pressure temperature history of the inclusions and their host rocks

crustal outgassing and lile enrichment in major lithosphere structures archean abitibi greenstone belt evidence on the source reservoir from strontium and carbon isotope tracers major structural discontinuities in the abitibi greenstone belt acted as conduits for outgassing of the archean crust as reflected in fixation of a select group of lithophile elements including si c k rb ba li cs b and pb in metasomatized faults for two of the largest structures the destor porcupine dp and kirkland lake cadillac kc fault zones 6 1015 g si 3 1015 g co2 and 1015 g k were introduced into the faults during expulsion of an estimated 6 1018 g aqueous fluids strontium isotope ratios of tourmaline piemontite actinolite and scheelite mineral separates characterized by rb sr 0 02 are concordant with respect to 87sr 86sr initial ratios over local sectors of the faults the sr isotope data record geographic variations which from east to west on the kc fault is 0 7031 0 7041 val d or 0 7008 0 7022 bourlemaque 0 7017 0 7019 bousquet 0 7029 0 7031 noranda and 0 7013 to 0 7015 kirkland lake at timmins on the pd fault 87sr 86sr initial ratios cluster at 0 7010 to 0 7020 metasomatised fault zones are systematically more radiogenic than contiguous host lithologies and imply a source reservoir 0 7010 to 0 7041 generally more radiogenic than the upper mantle at 2690 ma 0 700 0 001 or contemporaneous volcanic rocks of mafic to ultramafic composition 0 700 to 0 7012 whereas certain minerals are concordant and retentive rb sr isochrons based on suites of rocks at progressive intensities of metasomatism have been systematically reset over an elpased time of 200 ma after termination of outgassing due to disturbance accompanying incremental displacements on structures

late paleocene to middle eocene calcareous nannofossil biochronology from the shatsky rise walvis ridge and italy abstract the precision of late paleocene to middle eocene nannofossil datums is investigated by means of quantitative methods and correlated to the magnetic polarity stratigraphy using sequences from the northwest pacific southeast atlantic and italy it is the rule rather than the exception to find tails of very reduced abundances prior to or after a range of consistent and higher abundances the absolutely first or final occurrence of a species therefore seldom provides a synchronous datum when material from different geographic areas are compared on the other hand synchroneity is often confirmed when the initial sharp rise or the final sharp decline in abundance is used as datum level the use of datums not employed in the two principal existing nannofossil zonal schemes can substantially improve the biostratigraphic resolution two established zonal markers show abundance patterns making them unsuitable as datums the first occurrences of ellipsolithus macellus base np4 diachronous and tribrachiatus nunnii base np10 and paleocene eocene boundary too rare and too short range in open ocean sections the first occurrence of either fasciculithus spp or sphenolithus spp is a better marker near the base of np4 the first occurrence of discoaster diastypus at 56 6 ma represents a suitable replacement for recognition of the paleocene eocene boundary

microthermometric laser raman spectroscopic and volatile ion chromatographic analysis of hydrothermal fluids in the paleozoic muruntau au bearing quartz vein ore field uzbekistan fluid inclusions in quartz and scheelite from flat steeply dipping central and stockwork type quartz veins within the muruntau au bearing quartz vein ore field have been investigated in a reconnaissance study using fluid inclusion mapping microthermometry laser raman spectroscopy and integrated gas and ion chromatography for bulk volatile and cation anion analysis muruntau central veins are dominated by inferred early co2 bearing fluid inclusions in contrast flat quartz veins contain considerable numbers of low density pure aqueous inclusions on deformation and recrystallization related microstructures fluid phase separation is indicated for samples from the muruntau central ore veins by fluid inclusion observational work as well as by microthermometry and bulk fluid geochemistry co2 ch4 co2 n2 and co2 c2 and c3 hydrocarbon ratios salinity data however in flat veins and all samples from the myutenbai deposit no evidence for fluid immiscibility could be found quartz microstructural results and fluid inclusion data suggest formation of the low grade mineralized flat veins before the main stage of hydrothermal activity and considerable variation in the geochemical conditions during fluid evolution in the muruntau and myutenbai deposits mixing of fluids from different sources in variable proportions may be inferred from halide geochemistry furthermore fluid inclusion br cl ratios differ significantly for samples from different vein types fluid phase separation is suggested as a mechanism for the precipitation of au from the hydrothermal fluid in the muruntau high grade au mineralized central veins

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

compositional polarity of triassic granitoids in the qinling orogen china implication for termination of the northernmost paleo tethys abstract the qinling orogen was formed from the closure of the northernmost paleo tethys sea and the tectonic suturing of the yangtze and north china cratons the timing of this collision and the tectonic framework are debated the widely developed triassic granitoids in the western qinling orogen offer a key to understand the tectonic evolution of this region here we compile the geological geochemical and geochronological data of the triassic granitoids from the qingling orogen and conclude that the granitoids north of the mian lue suture were emplaced in an active continental margin related to the northward subduction of the mian lue oceanic plate during 248 200 ma the granitoids can be classified into i and s types with the former constituting the major variety northward from the mian lue fault an s type granite belt appears followed by and locally overlapping with an i type granite belt the i type granite belt can be subdivided into four sub belts from south to north with increasing contents of k2o k2o na2o sio2 th and u and the ratios of k2o na2o rb sr and 87sr 86sr i but decreasing contents of na2o al2o3 mg and ehf t except for the northernmost belt which occurs in the huaxiong block of the north china craton this geochemical polarity of i type granitoids and the zoned distribution of s and i types granitoids cannot be explained through continental collision orogeny including syn to post collision but can be well interpreted by considering the progressive subduction of the northernmost branch of the paleo tethys as represented by the mian lue ocean thus the termination of the northernmost paleo tethys and the onset of the continental collision between the yangtze and the north china plates are considered to have occurred at about 200 ma during the transition from triassic to jurassic our model is also supported by the available data from other studies and provides a revised framework for the timing and tectonics of assembly of the yangtze and the north china cratons

development of the north china craton during the late archaean and its final amalgamation at 1 8 ga some speculations on its position within a global palaeoproterozoic supercontinent abstract new data obtained over the past few years indicate that by the end of the archaean the north china craton consisted of two major crustal entities identified as the eastern and western blocks the formation of island and magmatic arcs along the western margin of the eastern block record the latest archaean events so far identified the location of the western block at this time is unknown however the occurrence of palaeoproterozoic passive margin sediments similar in age to those occurring in the eastern block indicates essentially similar conditions and possible separation by an ocean of unknown dimensions re initiation of east dipping subduction beneath the western margin of the eastern block resulted in closure of this palaeoproterozoic ocean bringing the western block into close proximity continued subduction resulted in a major continental continental collision and the western margin of the eastern block was again reactivated leading to extensive thrusting high pressure metamorphism and the generation of crustal melts this occurred between 1 88 and 1 79 ga ago resulting in the formation of the trans north china orogen and final amalgamation of the north china craton although information is sparse to non existent we have reviewed the possible location of the north china craton at the time of collision and note a similarity in terms of age lithology and distribution of major crustal components between the north china craton and baltica although speculative we present this model in the hope that it will stimulate debate and lead to further research in these areas

geology fluid inclusion geochemistry and 40ar 39ar geochronology of the wulasigou cu deposit and their implications for ore genesis altay xinjiang china abstract the wulasigou cu deposit occurs as veins controlled by a nw trending structure in a devonian volcano sedimentary basin of the altay orogenic belt xinjiang china igneous and sedimentary rocks exposed in the area have undergone greenschist facies metamorphism the ore forming process can be divided into early middle and late stages represented by respectively pyrite quartz polymetallic sulfide quartz and carbonate quartz veins veinlets and or replacement bodies the early veins were deformed and brecciated during a compressional or transpressional event the middle stage veinlets filled fractures in the early stage vein and alteration assemblages and are undeformed suggesting a tensional shear setting the late stage veinlets are mainly open space fissure fillings that cut veins and replacement bodies formed in the earlier stages four types of fluid inclusions fis including aqueous w type mixed carbonic aqueous m type purely carbonic c type and daughter mineral bearing s type have been identified in copper related quartz and calcite from the wulasigou deposit the early stage quartz contains m and w type primary fis that completely homogenized at temperatures of 322 412 c with low salinities of 0 9 6 5 wt nacl equiv in contrast the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 101 234 c and salinities of 0 9 2 9 wt nacl equiv this indicates that the metallogenic system evolved from co 2 rich metamorphic to co 2 poor through input of meteoric fluids all four types of fis can only be observed in the middle stage minerals where they show evidence of vein formation during an episode of fluid immiscibility these fis homogenized at temperatures ranging mainly from 230 to 347 c with salinities clustering 2 7 10 2 wt nacl equiv for the w m and c types and 34 7 38 2 wt nacl equiv for the s type respectively the metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility episode the estimated trapping pressures for the middle stage fluids are 1 55 3 55 kbar suggesting an alternating lithostatic hydrostatic fluid system controlled by fault valve activity at a depth of 13 15 5 km muscovite separates from the middle stage polymetallic quartz veinlets yield a well defined 40 ar 39 ar isotopic plateau age of 219 41 2 10 ma and an 39 ar 36 ar 40 ar 36 ar isochron age of 219 73 2 17 ma this age postdates the final paleo asia ocean closure at ca 250 ma by about 30 ma and indicates that the cu mineralization at wulasigou has occurred in the triassic continental collision setting hence the wulasigou cu deposit may be the first example of orogenic lode cu deposits formed in accretionary orogeny or continental collision

lead isotope systematics and pyrite trace element geochemistry of two granitoid associated mesothermal gold deposits in the southeastern lachlan fold belt

fluid inclusion characteristics of mesothermal gold deposits in the xiaoqinling district shaanxi and henan provinces people s republic of china fluid inclusions were studied in quartz samples from early stage i gold poor quartz veins and later stage ii gold and sulphide rich quartz veins from the wenyu dongchuang qiangma and guijiayu mesothermal gold deposits in the xiaoqinling district china fluid inclusion petrography microthermometry and bulk gas analyses show remarkably consistent fluid composition in all studied deposits primary inclusions in quartz samples are dominated by mixed co2 h2o inclusions which have a wide range in co2 content and coexist with lesser primary co2 rich and aqueous inclusions in addition a few secondary aqueous inclusions are found along late healed fractures microthermometry and bulk gas analyses suggest hydrothermal fluids with typically 15 30 mol co2 in stage i inclusions and 10 20 mol co2 in stage ii inclusions estimates of fluid salinity decrease from 7 4 9 2 equivalent wt nacl to 5 7 7 4 equivalent wt nacl between stage i and ii primary aqueous inclusions in both stages show consistent salinity with but slightly lower th total than their coexistent co2 h2o inclusions the coexisting co2 rich co2 h2o and primary aqueous inclusions in both stage i and ii quartz are interpreted to have been trapped during unmixing of a homogeneous co2 h2o parent fluid the homogenisation temperatures of the primary aqueous inclusions give an estimate of trapping temperature of the fluids trapping conditions are typically 300 370 c and 2 2 kbar for stage i fluids and 250 320 c and 1 6 kbar for stage ii fluids the co2 h2o stage i and ii fluids are probably from a magmatic source most likely devolatilizing cretaceous yanshanian granitoids the study demonstrates that gold is largely deposited as pressures and temperatures fall accompanying fluid immiscibility in stage ii veins

isotope geochemistry of the tieluping silver lead deposit henan china a case study of orogenic silver dominated deposits and related tectonic setting the tieluping silver deposit which is sited along ne trending faults within the high grade metamorphic basement of the xiong er terrane in the qinling orogenic belt is part of an important recently discovered mesozoic orogenic type ag pb belt ore formation includes three stages an early barren quartz pyrite stage e an intermediate polymetallic sulfide ore stage m and a late barren carbonate stage l carbon sulfur and lead isotope systematics indicate that the e stage fluids are deeply sourced the l stage fluids are shallow sourced meteoric water whereas the m stage fluids are a mix of deep sourced and shallow sourced fluids sulfur and lead isotope data show that the ore forming fluids must have originated from a source with elevated radiogenic lead and low 34s values that differs significantly from exposed geologic units in the xiong er terrane the lower crust and the mantle this supports the view that the carbonate shale chert sequences of the guandaokou and luanchuan groups south of the machaoying fault might be the favorable sources although little is known about their isotopic compositions a tectonic model that combines collisional orogeny metallogeny and hydrothermal fluid flow is proposed to explain the formation of the tieluping silver deposit during the mesozoic collision between the north china craton and south china block early mid triassic indosinian orogeny crustal slabs containing the carbonate shale chert sequences of the guandaokou and luanchuan groups locally rich in organic matter carbonaceous shale were thrust northwards beneath the xiong er terrane along the machaoying fault metamorphic devolatilisation of this underthrust slab probably provided the ore forming fluids to develop the ag pb ore belt which includes the tieluping silver deposit fluids and magmas were emplaced during extensional stages related to the jurassic cretaceous yanshanian orogeny

metallogeny during continental outgrowth in the columbia supercontinent isotopic characterization of the zhaiwa mo cu system in the north china craton abstract the eastern qinling molybdenum belt eqmb in central china represents the largest mo province in the world located at the southern margin of the north china craton this mo province is largely associated with mesozoic granitoids here we report re os isochron age of 1761 33 ma 2 mswd 2 9 from molybdenite in the recently discovered zhaiwa porphyry mo cu system within the eqmb this age coincides with the peak eruption period 1 78 1 75 ga of the xiong er group volcanic rocks which unconformably overlie the taihua supergroup and are interpreted to have developed on a continental arc the re concentrations 1 to 43 ppm of the zhaiwa molybdenites are similar to those of typical porphyry cu mo au systems developed on continental arcs the 34 s values of the zhaiwa ores 2 7 7 3 average 5 2 suggest that the sulfur was mainly sourced from a magmatic system the sulfides from the ores yield sr i average of 0 70533 similar to that of the xiong er group 0 70547 albeit higher than that of the kuanping group 0 70334 and lower than the taihua supergroup 0 70763 suggesting a mixed source the average e nd 1 76 ga of the sulfides from the ores 0 9 falls between the averages of the taihua supergroup ca 6 8 and the kuanping group ca 7 4 the pb isotope ratios of the ores are similar to but slightly higher than those of the taihua supergroup reflecting preferential leaching of radiogenic pb from the taihua supergroup by magmatic fluids integrated data and interpretations constrain the zhaiwa mo cu deposit to be a porphyry mineral system developed within a ca 1 76 ga continental arc related to oceanic plate subduction beneath the southern margin of the north china craton a correlation between tectonic settings and metallogenic types clearly indicate that the xiong er group was formed in a volcanic arc confirming paleo mesoproterozoic continental outgrowth along the margins of the columbia supercontinent the isotopic characterization of the zhaiwa deposit provides new insights into the enigma of the widespread distribution of large and super large mo deposits of eqmb along the southern margin of the north china craton

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

pb sr nd isotope constraints on the fluid source of the dahu au mo deposit in qinling orogen central china and implication for triassic tectonic setting abstract the dahu au mo deposit is a structure controlled lode system occurring in the northern xiaoqinling terrane huaxiong block qinling orogen this paper reports a new sr nd pb isotope dataset obtained for ore sulfides and the hostrocks within the taihua supergroup in an attempt to constrain the source of the ore forming fluids from a new dimension 16 sulfide samples yield i sr ratios of 0 70470 0 71312 with an average of 0 70854 e nd t values between 13 5 and 18 1 with average of 15 1 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios of 17 033 17 285 15 358 15 438 and 37 307 37 582 with averages of 17 162 15 405 and 37 440 respectively 5 gneiss samples from the taihua supergroup yield i sr ratios of 0 70947 0 73201 averaging 0 72294 e nd t values of 20 0 to 31 1 averaging 25 1 and 206 pb 204 pb i 207 pb 204 pb i 208 pb 204 pb i ratios of 17 127 18 392 15 416 15 604 and 37 498 37 814 with averages of 17 547 15 470 and 37 616 respectively these data show that the ore sulfides have less radiogenic sr nd pb isotope systematics than the hostrocks and suggest that the ore forming fluids which interacted with the wallrocks to form ores must be sourced from a depleted mantle or a depleted subducted oceanic slab in combination with the spatial scenario and geochemical signatures of the triassic magmatites and mineral systems we argue that in the triassic the mianlue ocean was not completely closed and that the northward oceanic plate subduction still survived along the mian lue suture which caused the late triassic magmatism and associated mineralization in qinling orogen including the au mo dahu deposit

p t x conditions of hydrothermal fluids and precipitation mechanism of stibnite gold mineralization at the wiluna lode gold deposits western australia conventional and infrared microthermometric constraints the wiluna lode gold deposits are located in the archean wiluna greenstone belt in the northern sector of the norseman wiluna belt in the yilgarn craton of western australia they are hosted in subgreenschist facies meta basalts and controlled by the wiluna strike slip fault system and associated shear veins and breccias the 13 individual lode gold deposits have produced around 115 t au from 1901 to 1946 and 1986 to today historically they also produced 38 3 t as and 3 5 t sb gold formed in two stages stage 1 gold pyrite arsenopyrite is finely disseminated in the wallrock and breccia fragments whereas stage 2 gold stibnite is located in massive shear veins and breccia matrix as fracture fill and in banded colloform textured veins stibnite gold orebodies only occur in some of the deposits e g moonlight and northern part of the west lode and also display a restricted vertical extent being preserved only in the uppermost 200 m of stibnite bearing lodes petrographic conventional and infrared microthermometric and laser raman analysis on stibnite bearing quartz veins and breccias reveal that the antimony and gold rich hydrothermal fluid was of mixed h2o nacl co2 ch4 type microthermometric measurements reveal maximum homogenization temperatures of 340 c average 290 25 c and a wide range of salinities between 0 2 and 23 eq wt nacl aqueous carbonic fluid inclusions contain variable xco2 ch4 0 03 to 0 82 with the carbonic phase containing a maximum xch4 of 0 21 combined petrographic and microthermometric evidence suggests that the fluid inclusion properties reflect fluid immiscibility of a low salinity medium xco2 ch4 homogeneous parent fluid at about 290 c and pressures between 700 and 1 700 bar fluid immiscibility was triggered by cyclic pressure release during fault zone movement the decompression adiabatic cooling of the hydrothermal fluids shifted the ore fluid to lower temperatures significantly reduced the degree of stibnite undersaturation and caused stibnite to precipitate the deposition of stibnite reduced the ore fluid h2s concentration thereby destabilized gold bisulfide complexes in solution and caused gold precipitation locally this mechanism explains the intimate spatial association of stibnite and gold in quartz veins and breccias in the stibnite gold orebodies at wiluna

stable isotope o h s c and n systematics of quartz vein systems in the turbidite hosted central and north deborah gold deposits of the bendigo gold field central victoria australia constraints on the origin of ore forming fluids the central and north deborah gold deposits are located in one of 15 mining centers of the bendigo gold field central victoria australia a major world class gold province developed in a turbidite terrane gold mineralization occurs primarily within domes and reverse fault systems in multiply deformed lower ordovician metaturbidites deformation and thrusting occurred between 450 and 420 ma coevally with regional metamorphism at zeolite to greenschist facies in the central and north deborah deposits six stages of quartz veining each with characteristic geometry and mineral paragenesis developed sequentially stages 1 2 and 4 are gold bearing whereas stages 3 5 and 6 are barren gold related quartz veins were deposited at temperatures of 350 25 c based on oxygen isotope geothermometry of silicate phases quartz muscovite and sulfur isotope compositions of coexisting sulfide mineral pairs sphalerite galena this result is consistent with temperatures inferred from fluid inclusions the 18o values of gold bearing vein quartz and coexisting hydrothermal muscovite are uniform within and between the six vein stages ranging from 15 9 to 17 2 per mil and 11 6 to 12 8 per mil respectively the d values of hydrothermal muscovites are also uniform at 68 to 55 per mil ore fluids have calculated 18o values of 8 to 11 per mil and d values of 37 to 17 per mil pyrite of synsedimentary diagenetic origin in slate and sandstone displays sulfur isotope compositions of 23 5 to 8 0 per mil and 0 1 to 11 9 per mil respectively sulfides from gold bearing quartz veins have a range of 7 4 to 8 1 per mil median ca 2 5 the relatively uniform vein pyrites indicate a large uniform sulfur source most likely from desulfidation reactions of sulfide minerals interaction of the ore forming fluid with depleted sulfides at the site of deposition may have shifted the sulfur isotope signatures of source sulfides to more negative values carbon isotope compositions of carbonates range from 5 1 to 9 0 per mil median ca 6 5 nitrogen concentrations and nitrogen isotope compositions of hydrothermal muscovite from quartz veins are 652 to 895 ppm and 2 84 to 4 49 per mil respectively collectively the data define a band in n content vegh rsus 15n coordinate space from higher n and lower 15n in the phanerozoic metasedimenary hosted central and north deborah gold deposits to lower n and higher 15n in predominantly meta igneous hosted neoarchean gold provinces collectively the h o s c and n isotope compositions of ore related hydrothermal minerals indicate that the dilute aqueous carbonic and n bearing ore forming fluids were generated from metamorphic dehydration reactions at deeper crustal levels and were variably influenced by exchange with wall rocks during transport to the site of deposition this genetic model for the central and north deborah gold deposits is consistent with other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes in contrast these data are not consistent with either mantle derived fluids or magmatic fluids nor do they support a deeply circulated meteoric surface water model for vein formation

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

modification of fluid inclusions in quartz by deviatoric stress ii experimentally induced changes in inclusion volume and composition fluid inclusions in quartz are known to modify their densities during shear deformation modifications of chemical composition are also suspected however such changes have not been experimentally demonstrated their mechanisms remain unexplained and no criteria are available to assess whether deformed inclusions preserve information on paleofluid properties to address these issues quartz crystals containing natural co2 h2o nacl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90 250 mpa at 700 c and 600 mpa confining pressure the resulting microcracking of the inclusions leads to expansion by up to 20 producing low fluid densities that bear no relation to physical conditions outside the sample nevertheless the chemical composition of the precursor inclusions is preserved with time the microcracks heal and form swarms of tiny satellite inclusions with a wide range of densities the highest reflecting the value of the maximum principle stress 1 these new inclusions lose h2o via diffusion thereby passively increasing their salt and gas contents and triggering plastic deformation of the surrounding quartz via h2o weakening using microstructural criteria to identify the characteristic types of modified inclusions both the pre deformation fluid composition and syn deformation maximum stress on the host mineral can be derived from microthermometric analysis and thermodynamic modelling

paleoproterozoic positive δ13ccarb excursion in the northeastern sino korean craton evidence of the lomagundi event abstract the 2 33 2 06 ga positive 13 c carb excursion associated with environmental change and the breakup of the kenorland or superia supercontinent is called the lomagundi or jatulian event or great oxidation event and has been reported in many early precambrian cratons but not yet in the sino korean craton the guanmenshan formation of the liaohe group occurs in the northeastern part of the sino korean craton 13 c carb and 18 o values in 42 samples from this formation range from 3 5 5 9 v pdb and 15 4 24 8 v smow respectively showing a clear positive 13 c carb excursion that characterizes the lomagundi event thirty five of the 42 samples with less hydrothermal alteration have higher 13 c carb and 18 o carb values than the other 7 samples obviously affected by fluid flow confirming that it was fluid flow that reduced the 13 c carb and 18 o carb values this positive 13 c carb excursion places deposition of the guanmenshan formation within the age range of 2 33 2 06 ga

geology geochemistry and ore genesis of the wenyu gold deposit xiaoqinling gold field qinling orogen southern margin of north china craton abstract the wenyu giant gold deposit is hosted in the precambrian taihua supergroup metamorphic rocks within the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided into three stages quartz pyrite veins early quartz sulfide veins middle main and carbonate quartz veinlets late with gold being mainly introduced in main stage quartz formed in two earlier stages contains three compositional types of fluid inclusions i e pure co2 co2 h2o and nacl h2o but the late stage minerals only contain the nacl h2o inclusions the inclusions in quartz formed in the early main and late stages yield total homogenization temperatures of 262 417 c 236 407 c and 114 239 c respectively with salinities no higher than 13 wt nacl equiv trapping pressures estimated from co2 h2o inclusions are 139 399 mpa and 111 316 mpa in the early and main stages corresponding to mineralization depths of 14 km and 11 km respectively fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co2 rich to co2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18owater values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology fluid inclusion and c h o s pb isotope geochemistry we conclude that the wenyu gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

syn to late orogenic quartz veins marking a retrograde deformation path in a slate belt examples from the high ardenne slate belt belgium abstract an integrated structural petrographic and microthermometric methodology has been applied on syn to late orogenic quartz veins from the high ardenne slate belt belgium to define their relative timing the quartz precipitates which do not show any mutual cross cutting relationships represent the meso scale brittle accommodation during fold initiation amplification and locking crystal plastic deformation structures and p t trapping conditions indicate that the different processes accommodating folding occurred in a progressive manner along a retrograde deformation path associated with the gradual exhumation of the slate belt from ca 7 5 to 6 km depth successive veining occurred from peak metamorphic conditions ca 300 c and 190 mpa measured in extrados veins to subsequent lower p t conditions in the periphery of a lenticular vein ca 275 c and 180 mpa late orogenic saddle reef filling ca 245 c and 160 mpa and the core of a lenticular vein ca 220 c and 150 mpa open cavity growth and fluid assisted brecciation indicate that veining occurred under overpressured fluid conditions it is therefore fair to assume that the high ardenne slate belt acted at least episodically as a mid crustal overpressured fluid reservoir not only in the earliest and latest stages but also during the main stage of orogeny

giant mesozoic gold provinces related to the destruction of the north china craton abstract lode gold deposits in precambrian cratons represent the world s major gold source and were mostly generated during formation and stabilization of the cratons however there is an extraordinary exception in the north china craton ncc where lode gold deposits formed after prolonged stabilization of the craton molybdenite re os and hydrothermal sericite and biotite 40 ar 39 ar dating of major gold deposits from the xiaoqinling district southern ncc bracket their emplacement in the range of 154 1 1 1 to 118 9 1 2 ma n 23 postdating formation of the craton by more than 1 7 billion years fluid inclusions extracted from gold bearing pyrite have elevated 3 he 4 he ratios 1 52 0 22 ra and mantle like ne isotopes 20 ne 22 ne 10 02 9 22 and 21 ne 22 ne 0 033 0 027 indicating presence of mantle derived fluids in the ore system measured 34 s of pyrite and d and 18 o of hydrothermal micas and fluid inclusion waters in auriferous quartz further confirm a magmatic mantle source for sulfur and ore fluids gold deposits of similar ages also widely occur in the eastern and northern margins of the ncc which together with those in the xiaoqinling district have a total reserve of 2500 t gold forming the only known giant late mesozoic gold province in the world s precambrian cratons these deposits formed coevally with extensive felsic to mafic magmatism development of intracontinental rift basins and exhumation of metamorphic core complexes across the eastern ncc events interpreted as indicating thinning and destruction of the lithosphere beneath the craton rising of asthenosphere coupled with destruction of the lithosphere has generated voluminous mafic and felsic magmas that provided sufficient fluids sulfur and by inference other ore components to form the giant gold provinces

gravity modelling of the lherzolite body at lers french pyrenees some regional implications lherzolites outcrop throughout the north pyrenean zone of the pyrenees and are everywhere associated with metamorphosed carbonates it has been suggested that heat from the cooling of the lherzolites was responsible for the high temperature metamorphism of the carbonates a gravity survey reported here shows that the volume of the lherzolite body at lers is approximately 0 8 cubic km the maximum volume of carbonates that such a body could metamorphose is 3 2 cubic km this latter value is so much less than the volume of carbonates inferred from field mapping that the lherzolite body cannot have been the sole source of heat for metamorphism of the carbonates it has been suggested from seismic data that there is a step in the moho beneath the north pyrenean fault in the central pyrenees gravity anomalies reported here show that either the step is less than 10 km high or that the density contrast is very low at the base of the crust in the pyrenees

contrasting late carboniferous and late permian middle triassic intrusive suites from the northern margin of the north china craton geochronology petrogenesis and tectonic implications two contrasting intrusive suites have been identified from the northern margin of the north china craton a late carboniferous dioritegranodiorite suite mainly made up of quartz diorite diorite granodiorite tonalite and hornblende gabbro and a late permian middle triassic suite of granitoid intrusions consisting of monzogranite syenogranite and quartz monzonite plutons from the late carboniferous suite exhibit variable sio2 contents and calc alkaline or high k calc alkaline metaluminous geochemical features most have low negative whole rock nd t values where t is the crystallization age of 17 1 to 11 5 and zircon hf t values of 38 3 to 11 2 indicating that they were derived mainly from anatectic melting of the ancient lower crust with some involvement of mantle materials however an older pluton in the suite exhibits higher nd t values of 11 5 to 9 9 nd model ages of 1 82 1 64 ga lower initial 87sr 86sr ratios of 0 7046 0 7048 and it contains some zircon grains that are characterized by high negative to positive zircon hf t values of 8 7 to 1 2 indicating strong involvement of juvenile materials derived from the lithospheric mantle the late carboniferous plutons are interpreted as subduction related and to have been emplaced in an andean style continental margin arc during the southward subduction of the paleo asian oceanic plate beneath the north china craton rocks from the late permian middle triassic intrusive suite display geochemical signatures ranging from highly fractionated i type to a type they exhibit higher zircon hf t values of 14 9 to 6 7 whole rock nd t values of 10 6 to 8 8 and younger hf and nd model ages than most of the late carboniferous plutons indicating that they could have been produced by extreme fractional crystallization of hybrid magmas resulted from mixing of coeval mantle and crust derived melts they are interpreted as postcollisional postorogenic granitoids linked to lithospheric extension and asthenosphere upwelling due to slab break off and subsequent sinking after final collision and suturing of the mongolian arc terranes with the north china craton these two contrasting intrusive suites suggest that the final closure of the paleo asian ocean and collision between the mongolian arc terranes and the north china craton occurred during the late permian and these events were followed by postcollisional postorogenic extension large volume magmatism and significant continental growth no significant syncollisional crustal thickening high pressure metamorphism or s type granitoid magmatism occurred during the collision process

geology and fluid evolution of the wangfeng orogenic type gold deposit western tian shan china abstract the wangfeng gold deposit is located in western tian shan and the central section of the central asian orogenic belt caob the deposit is mainly hosted in precambrian metamorphic rocks and caledonian granites and is structurally controlled by the shenglidaban ductile shear zone the gold orebodies consist of gold bearing quartz veins and altered mylonite the mineralization can be divided into three stages quartz pyrite veins in the early stage sulfide quartz veins in the middle stage and quartz carbonate veins or veinlets in the late stage ore minerals and native gold mainly formed in the middle stage four types of fluid inclusions were identified based on petrography and laser raman spectroscopy co 2 h 2 o inclusions c type pure co 2 inclusions pc type nacl h 2 o inclusions w type and daughter mineral bearing inclusions s type the early stage quartz contains only primary co 2 h 2 o fluid inclusions with salinities of 1 62 to 8 03 wt nacl equivalent bulk densities of 0 73 to 0 89 g cm 3 and homogenization temperatures of 256 c 390 c vapor bubbles are composed of co 2 the middle stage quartz contains all four types of fluid inclusions of which the co 2 h 2 o and nacl h 2 o types yield homogenization temperatures of 210 c 340 c and 230 c 300 c respectively the co 2 h 2 o fluid inclusions have salinities of 0 83 to 9 59 wt nacl equivalent and bulk densities of 0 77 to 0 95 g cm 3 with vapor bubbles composed of co 2 ch 4 and n 2 fluid inclusions in the late stage quartz are nacl h 2 o solution with low salinities 0 35 3 87 wt nacl equivalent and low homogenization temperatures 122 c 214 c the coexistence of inclusions of these four types in middle stage quartz suggests that fluid boiling occurred in the middle stage mineralization trapping pressures estimated from co 2 h 2 o inclusions are 110 300 mpa and 90 250 mpa for the early and middle stages respectively suggesting that gold mineralization mainly occurred at depths of about 10 km in general the wangfeng gold deposit originated from a metamorphic fluid system characterized by low salinity low density and enrichment of co 2 depressurized fluid boiling caused gold precipitation given the regional geology ore geology fluid inclusion features and ore forming age the wangfeng gold deposit can be classified as a hypozonal orogenic gold deposit

genesis of the 1 76 ga zhaiwa mo cu and its link with the xiong er volcanics in the north china craton implications for accretionary growth along the margin of the columbia supercontinent abstract the east qinling molybdenum belt hosting numerous mesozoic magmatic hydrothermal mo deposits is one of the largest molybdenum provinces in the world the recently discovered zhaiwa mo cu deposit luoning county henan province occurs within the xiong er terrane of the east qinling orogenic belt the mo cu mineralization is associated with widespread stockworks or veinlets occurring within altered amphibolite here we investigate the characteristics of the ore mineralization through systematic fluid inclusion petrography microthermometry and laser raman spectroscopy the typical inclusions in the veins and stockworks are aqueous daughter mineral bearing and a subordinate co2 rich type the homogenization temperatures of the aqueous inclusions in quartz molybdenite veins are up to 370 c which together with some daughter mineral bearing inclusions homogenized by dissolution of halite at 500 c indicates that the ore forming fluids were derived from a hypothermal fluid system the daughter mineral bearing inclusions assign high salinities for the ore forming fluids correlating the ore deposit to a magmatic hydrothermal system we also present h o isotope systematics which support this interpretation the recently reported re os molybdenite age of 1 76 0 03 ga from this deposit is coeval to the xiong er group andesite dominated volcanic sequence 1 8 1 45 ga based on which we propose that the zhaiwa deposit represents the upper domain of a porphyry system developed within a subduction related setting with accretion to the southern margin of the north china craton our study provides new constraints on the outgrowth of the columbia supercontinent during paleoproterozoic

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

shrimp and la icp ms zircon geochronology of the xiong er volcanic rocks implications for the paleo mesoproterozoic evolution of the southern margin of the north china craton the paleo mesoproterozoic xiong er volcanic rocks along the southern margin of the north china craton are lithologically and geochemically similar to those formed in subduction related continental margin volcanic arcs the volcanic rocks are primarily composed of basaltic andesites and andesites with minor dacites and dacitic rhyolites traditionally the xiong er volcanic rocks have been divided from lower to upper into the xushan jidanping and majiahe formations but the ages of volcanic rocks in these formations have not been well constrained which has hindered further understanding the tectonic significance of the xiong er volcanic belt at the southern margin of the north china craton shrimp and la icp ms u pb zircon analyses combined with cathodeluminescence cl images have enabled resolution of xenocrystic and magmatic zircons that can be directed toward determination of the ages of the xiong er volcanic rocks shrimp and la icp ms u pb analyses on magmatic zircons from two basaltic andesite samples one dacite sample and one rhyolite sample of the xushan formation known as the lowest sequence of the xiong er volcanic rocks indicate that the volcanic eruption of this formation occurred at 1 78 ga but most xenocrystic inherited zircons in these samples yielded 207pb 206pb ages ranging from 2 55 ga to 1 91 ga of three samples collected from the jidanping formation two rhyolite samples 05xe015 and 05xe100 yielded weighted mean 207pb 206pb ages of 1778 5 5 ma and 1751 14 ma respectively similar to the ages of the volcanic rocks in the xushan formation whereas one dacite sample 05xe066 gave a weighted mean 207 pb

isotope systematics and fluid inclusion studies of the qiyugou breccia pipe hosted gold deposit qinling orogen henan province china implications for ore genesis abstract the qiyugou gold deposits henan province are hosted in breccia pipes within the xiong er terrane qinling orogen on the southern margin of the north china craton in these deposits three paragenetic assemblages have been recognized an early k feldspar epidote quartz pyrite a middle quartz polymetallic sulfide and a late quartz carbonate adularia in this paper we review and interpret fluid inclusion and stable and radiogenic isotopic data of host rocks and ores fluid inclusions in quartz and calcite include water rich co 2 rich and daughter crystal bearing the co 2 rich and daughter mineral bearing fluid inclusions are common in the early stage quartz and absent in the late stage quartz and calcite which only contain water rich fluid inclusions accordingly the early stage ore fluids are magmatic in origin and characterized by high temperature 350 c high salinity 30 wt nacl equiv and are co 2 rich fluid boiling in the middle ore stage resulted in co 2 release decreasing oxygen fugacity and rapid precipitation of ore materials the late stage fluids have low temperature low salinity are co 2 poor and lack daughter minerals these fluids are probably sourced from meteoric water h o c isotope systematics confirm that the ore fluid system evolved from magmatic to meteoric the carbon and lead isotope ratios indicate that the meso neoproterozoic sequence south of the xiong er terrane was the likely source of the ore forming materials the qiyugou breccia pipes and their associated gold ores were emplaced during an extensional regime following a transition from collision to rifting tectonics linked to collision and subduction of the yangtze plate beneath the north china craton geochronological studies show that mesozoic magmatism in the region occurred between the triassic and cretaceous the triassic to jurassic magmas were mostly derived from partial melting of ancient crust whereas the cretaceous magmas show juvenile signatures indicating mantle derived components processes of fragmentation of lithospheric roots crustal and lithospheric thinning extension and rifting were probably associated with the subducting pacific izanagi plate these crust mantle geodynamic processes were responsible for the development of anorogenic granitic melts that interacted with the meso neoproterozoic volatile rich sedimentary successions producing a flow of gas rich hydrothermal fluids that resulted in the emplacement of the qiyugou auriferous breccia pipes we conclude that the qiyugou gold deposits are intrusion related explosive breccia pipe type that evolved from hypothermal through mesothermal to epithermal

the shanggong gold deposit eastern qinling orogen china isotope geochemistry and implications for ore genesis abstract the shanggong au deposit in the xiong er terrane east qinling china has resources of about 30 ton au making it one of the largest orogenic mesothermal au deposits hosted in volcanic rocks of the mesoproterozoic xiong er group three stages of hydrothermal activity are recognized early middle and late of which two early and middle were ore producing and characterized by quartz pyrite and polymetallic sulfides respectively the third and late stage is represented by a carbonate quartz assemblage hydrogen oxygen and carbon isotope systematics of the shanggong deposit from a previous work suggest that the early stage fluids were derived from magmatic and or metamorphic devolatilization of sedimentary rocks at depth this is supported by new c s and published sr and pb isotopic data presented in this paper these new data 13c values ranging from 1 5 for early stage ankerite to 2 2 for late stage ankerite negative 34s values for sulfides from the middle stage 19 2 to 6 3 suggest a contribution from organic matter and that the ore fluid evolved from deeply sourced to shallowly sourced with those of the middle stage representing a mixture of these two fluid systems the comparison of the hydrogen oxygen carbon sulfur lead strontium isotope systematics between the shanggong deposit and the main lithologies in the xiong er terrane shows that neither these nor the underlying lower crust and mantle or combinations thereof could be considered as the source of ore fluids for the shanggong au deposit a likely source was a carbonaceous carbonate sandstone shale chert sequence in the underthrusted guandaokou and luanchuan groups exposed south of the xiong er terrane ar ar and rb sr isochron ages for mineral phases of the early middle and late stages together with geological field data constrain the timing of the hydrothermal activity and au metallogenesis at 242 10 167 7 and 112 7 ma respectively this metallogenesis and associated granitic magmatism can be related to the continental collision between the yangtze and north china cratons that resulted in the formation of the qinling orogen led to the different hydrothermal systems that were responsible for the three stages that formed the shanggong au deposit over a period of about 130 myrs

interpretation of post entrapment fluid inclusion re equilibration at the three mile hill marvel loch and griffins find high temperature lode gold deposits yilgarn craton western australia abstract fluid inclusions that are interpreted to be related to vein filling of quartz veins at the three mile hill and marvel loch gold deposits in amphibolite facies rocks and the griffins find deposits in granulite facies rocks in the yilgarn craton of western australia are dominantly low salinity h 2 o co 2 ch 4 mixtures or co 2 ch 4 fluids at each deposit inclusions have a wide range of compositions with respect to both the aqueous carbonic ratio and the co 2 ch 4 ratio of the carbonic phase and most fluids could not have been in equilibrium with the mineral assemblage in the vein and adjacent rock inclusion densities suggest a range of p t conditions of entrapment and are in general not consistent with the conditions of vein formation indicated by vein assemblages diffusional addition of h 2 into inclusions diffusional loss of h 2 o and reduction of inclusion volume are possible during cooling and uplift along the inferred p t path the inclusion populations could have been derived from an originally uniform population of low salinity aqueous dominated h 2 o co 2 inclusions by a combination of these processes inclusion modification as the cause of the complex inclusion populations is supported by relations of molar volume to composition and to an extent by variations in fluid salinity if inclusion re equilibration is the cause of inclusion variability it was of variable intensity within a single vein system and within individual clusters of inclusions in some samples and is suggested to have been a function of the local petrological and textural environment

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

evolution of ore forming fluids in the sawayaerdun gold deposit in the southwestern chinese tianshan metallogenic belt northwest china the sawayaerdun gold deposit was discovered in the early 1990s and is the largest orogenic gold deposit in the chinese tianshan gold mineralization occurs in quartz veins which are hosted in carbonaceous metasediments and controlled by faults and fractures three major hydrothermal events can be identified at sawayaerdun an early barren quartz vein stage middle stage quartz veins with pyrite and gold mineralization and late carbonate quartz veins fluid inclusion studies of quartz pyrite and carbonate formed during the major hydrothermal stagesshow distinct changes in fluid temperature composition and redox conditions occurred during fluid evolution three types of fluid inclusions have been identified at sawayaerdun h2o nacl l v h2o nacl co2 l v and co2 l v fluids trapped in early barren quartz have high temperatures 280 420 c low salinities 3 wt nacl equiv high cl and are co2 rich middle stage quartz contains fluids with lower temperatures 210 310 c and variable salinities 0 8 17 5 wt nacl equiv they are commonly s rich co2 containing and relatively reduced compared with early stage fluids in contrast hydrothermal pyrite hosted in middle stage quartz veins trapped fluids formed over a narrower temperature range 220 270 c more oxidized high co2 ch4 ratio and have higher ca k and mg than fluids in quartz late stage carbonate is dominated by fluids with low temperatures 200 c and low contents of cl s and k fluid immiscibility probably commenced at the onset of mineralization along with middle stage quartz formation resulting in the generation of coexisting fluid inclusions with distinguishable vapor liquid ratios and salinities the compositional difference between fluids trapped in pyrite and quartz indicate fluid mixing may have occurred during the mineralization stage the oxidized fluids probably a mixture of meteoric water and fluids generated during water host rock interaction emerged into the ore forming system to generate extensive metals precipitation the fluid immiscibility and fluid mixing are most likely caused by pressure decrease during late paleozoic uplift and erosion in the chinese southern tianshan area comparison of fluids between four major mineralization zones at sawayaerdun indicate that zone ii is similar to the most important zone iv and the order of similarity is probably zone ii xi i which could be applied to the future mineral exploration in this area

geodynamic settings and tectonic model of skarn gold deposits in china an overview seventy skarn type gold deposits including 1 super large 19 large and 24 medium sized are known from different geotectonic units of china they contain a total resource of approximately 1000 t of gold 625 t in south china and account for 20 of china s gold reserves these skarn deposits are sited in collisional orogenic belts fault controlled magmatic belts and reactivated cratonic margins all of the chinese skarn gold provinces were affected by phanerozoic collisional orogenesis the timing of the metallogenic events and the spatial temporal distribution of the chinese skarn gold deposits indicates that they were formed during ore forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen and not to subduction systems as is commonly advocated for porphyry copper systems around the pacific rim

gold precipitation by fluid mixing in bedding parallel fractures near carbonaceous slates at the cosmopolitan howley gold deposit northern australia the proterozoic cosmopolitan howley gold deposit consists of quartz veins on the steeply dipping limbs of the howley anticline and is hosted by pelitic metasediments within the high temperature metamorphic aureole of proterozoic granites in the pine creek province of northern australia ore is restricted to a stratigraphic contact always occurring within noncarbonaceous hornfels within 50 m of carbonaceous slates similar veins farther away from or within carbonaceous slates are abundant but barren a companion paper establishes that ore formation occurred in response to hydrothermal activity accompanying granite intrusion and contact metamorphism the involvement of a magmatic brine in ore genesis is referred on the basis of fluorine concentrations in biotite from the potassic alteration selvages of the gold bearing veins from stable isotopic data and from mutual crosscutting relations of veins and felsic dikes this paper focuses on the fluid flow and chemical processes that formed the gold bearing quartz veins it is argued that lateral focusing of fluid flow into the subvertical vein hosting fractures led to mixing of the ascending magmatic brine or some metamorphic fluid with hydrocarbon rich fluid advected through carbonaceous slate in the steeply dipping fold limbs crock seal textures in some of the gold quartz veins indicate that this fluid flow and mixing were locally episodic the magmatic brine involved in the mixing was expelled from a crystallizing i type granite at depth or 0 24 these features indicate a redox state of tile magmatic fluid at or above the nno buffer by contrast gold deposition occurred at 2 to 3 log f o2 units below nno a weakly acid ph of 4 3 to 4 7 550 degrees or 100 ppb at or 500 degrees c that gold availability in ordinary metasediments may be insufficient to generate an effective ore fluid for high temperature gold deposition by metamorphic devolatilization if correct these predictions further emphasize the inferred role of magmatic fluids in the formation of gold deposits within high grade contact metamorphic aureoles

metallogeny of the north china craton link with secular changes in the evolving earth abstract the north china craton ncc has experienced a complex geological evolution since the early precambrian and carries important records of secular changes in tectonics and metallogeny here we synthesize the salient geological and tectonic features of the evolution and destruction of the ncc vis a vis major metallogenic events and the formation of potential ore deposits we identify a close relationship between the major geological events in the ncc and those reported elsewhere on the globe we trace the records of a regular change in the pattern of metallogeny mineral deposit character spatial distribution and genetic mechanisms which closely match the timing and styles of the major geological and tectonic events in this craton the ncc went through five major tectonic cycles 1 neoarchean crustal growth and stabilization 2 paleoproterozoic rifting subduction accretion collision with imprints of the great oxidation event goe 3 late paleoproterozoic neoproterozoic multi stage rifting 4 paleozoic orogenesis at the margins of the craton and 5 mesozoic extensional tectonics associated with lithospheric thinning and decratonization coinciding with these major geological events are five major metallogenic systems identified as follows 1 an archean bif system 2 paleoproterozoic cu pb zn and mg b systems 3 a mesoproterozoic ree fe pb zn system 4 a paleozoic orogenic cu mo system and 5 mesozoic intracontinental au and ag pb zn and mo systems the ore deposit types in each of these metallogenic systems show distinct characteristics and tectonic affinities from early precambrian through late precambrian to paleozoic and mesozoic the ncc records a transition from primitive to modern style plate tectonics evidence for imbricated oceanic plate stratigraphy in a subduction accretion setting and collisional orogenesis along at least three major zones of ocean closure are documented major transitions in tectonic style and surface environmental changes recorded in other parts of the world are also reflected in the geological history and metallogenic events in the ncc large scale gold deposits formed through intraplate tectonics during the mesozoic provide important insights into mantle dynamics and crust mantle interaction associated with lithospheric thinning and craton destruction the ncc provides one of the best examples for documenting secular changes in the geological history and metallogenic epochs of an evolving earth

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

la icp ms trace element analysis of pyrite from the xiaoqinling gold district china implications for ore genesis abstract the xiaoqinling district the second largest gold producing district in china is located on the southern margin of the north china craton it consists of three ore belts namely the northern ore belt the middle ore belt and the southern ore belt pyrite from the dahu gold deposit in the northern ore belt and wenyu and yinxin gold deposits in the southern ore belt were investigated using a combination of ore microscopy and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms a range of trace elements was analyzed including au te ag pb bi cu co ni zn mo hg as and si the results show that there are no systematic differences between the trace element compositions of pyrite in the three deposits from different ore belts in general au concentrations in pyrite are low from 2 rich ore fluids spatial association with large scale compressional structures of the qinling orogen 18 o and d data suggestive of mixing between metamorphic and meteoric waters 34 s and pb isotopic data that point to a mixed crustal mantle source all point to typical orogenic type gold deposits high ni concentrations up to 8425 ppm of pyrite possibly linked to deep seated mafic ultramafic metamorphic rocks provide further evidence on the orogenic gold deposit affinity but against the model of a granitic derivation of the mineralizing fluid as previously suggested by some workers generally low au concentration in pyrite is also consistent with those from worldwide orogenic gold deposits therefore the gold mineralization in the xiaoqinling district is described as orogenic type and is probably related to indosinian collision between the north china craton and the yangtze craton

ore geology and fluid inclusion geochemistry of the tiemurt pb zn cu deposit altay xinjiang china a case study of orogenic type pb zn systems abstract the tiemurt pb zn cu deposit is hosted in a devonian volcanic sedimentary basin of the altay orogenic belt and is thus interpreted to have formed by sea floor hydrothermal exhalation in previous studies our investigation discovered that the deposit is not stratiform or stratabound but structure controlled instead the hydrothermal ore forming process can be divided into the early middle and late stage represented by pyrite quartz polymetallic sulfide quartz and carbonate quartz veinlets respectively the early stage veins and contained minerals are structurally deformed and brecciated suggesting a compressional or transpressional tectonic regime the middle stage veinlets intrude and infill the fissures of the early stage assemblages and show no deformation suggesting a tensional shear setting the late stage veinlets mostly infill open space fissures that crosscut veins and replacements formed in the earlier stages four types of fluid inclusions fis including aqueous type w carbonic aqueous type c pure carbonic type pc and solid bearing type s are identified at the tiemurt deposit the early stage minerals contain the c and w type primary fis that are totally homogenized at temperatures of 330 390 c with low salinities of 0 8 11 9 wt nacl eqv whilst the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 118 205 c and salinities of 1 4 3 4 wt nacl eqv this indicates that the ore fluid system evolved from co2 rich probably metamorphic to co2 poor meteoric fluids and that a significant co2 escape must have occurred all the four types of fis can be only observed in the middle stage minerals and even in a microscopic domain of a crystal representing an association trapped from a boiling fluid system these fis homogenize at temperatures ranging from 270 to 330 c with two salinity clusters of 1 9 14 5 and 37 4 42 4 wt nacl eqv respectively this implies that metal precipitation resulted from fluid boiling co2 escape and transient oversaturation the estimated trapping pressures of fis range from 130 to 380 mpa suggesting an alternating lithostatic hydrostatic fluid system controlled by a fault valve at the depth of 13 km therefore the tiemurt pb zn cu deposit is likely an example of orogenic pb zn cu systems formed in collision orogeny rather than a pre collision vms or sedex system developed in devonian and a new metallogenic model is proposed to interpret the formation of the tiemurt pb zn cu deposit

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

geology c h o s pb isotope systematics and geochronology of the yindongpo gold deposit tongbai mountains central china implication for ore genesis abstract the yindongpo gold deposit is located in the weishancheng au ag dominated polymetallic ore belt in tongbai mountains central china the ore bodies are stratabound within carbonaceous quartz sericite schists of the neoproterozoic waitoushan group the ore forming process can be divided into three stages represented by early barren quartz veins middle polymetallic sulfide veinlets and late quartz carbonate stockworks with most ore minerals such as pyrite galena native gold and electrum being formed in the middle stage the average 18owater values changed from 9 7 in the early stage through 4 9 in the middle stage to 5 9 in the late stage with the d values ranging between 65 and 84 the 13cco2 values of ore fluids are between 3 7 and 6 7 with an average of 1 1 the h o c isotope systematics indicate that the ore fluids forming the yindongpo gold deposit were probably initially sourced from a process of metamorphic devolatilization and with time gradually mixed with meteoric water the 34s values range from 0 3 to 5 2 with peaks ranging from 1 to 4 fourteen sulfide samples yield 206pb 204pb values of 16 990 17 216 207pb 204pb of 15 419 15 612 and208pb 204pb of 38 251 38 861 both s and pb isotope ratios are similar to those of the main lithologies of the waitoushan group but differ from other lithologic units and granitic batholiths in the tongbai area which suggest that the ore metals and fluids originated from the waitoushan group the available k ar and 40ar 39ar ages indicate that the ore forming process mainly took place in the period of 176 140 ma during the transition from collisional compression to extension and after the closure of the oceanic seaway in the qinling orogen the yindongpo gold deposit is interpreted as a stratabound orogenic style gold system formed during the transition phase from collisional compression to extension the ore metals in the waitoushan group were extracted transported and then accumulated in the carbonaceous sericite schist layer the carbonaceous sericite schist layer especially at the junction of collapsed anticline axis and fault structures became the most favorable locus for the ore bodies

textural evolution of synthetic fluid inclusions in quartz during reequilibration with applications to tectonic reconstruction experimental reequilibration of synthetic 10 wt nacl h2o inclusions in natural quartz reveals that reequilibration textures show distinct differences depending upon the p t path followed by the inclusion after formation these differences combined with other geological information may be used to determine whether the sample rock followed a dominantly isothermal or isobaricp t path following entrapment the intensity and style of inclusion reequilibration features is related to the direction and magnitude of the departure of thep t path from the original isochore for the inclusion thus fluid inclusion reequilibration textures not only permit inclusionists to determine whether the rocks followed an isothermal or isobaric retrogradep t path but also the magnitude of departure of this path from one that is isochoric

gold deposits in the xiaoqinling xiong ershan region qinling mountains central china the gold rich xiaoqinling xiong ershan region in eastern shaanxi and western henan provinces central china lies about 30 50 km inland of the southern margin of the north china craton more than 100 gold deposits and occurrences are concentrated in the xiaoqinling west xiaoshan middle and xiong ershan east areas late archean gneiss of the taihua group and middle proterozoic metavolcanic rocks of the xiong er group are the main host rocks for the deposits mesozoic granitoids ca 178 104 ma are present in most gold districts but deposits are typically hosted in the precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones deposits in the xiaoqinling and xiaoshan areas are best classified as orogenic gold deposits with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks alteration assemblages are dominated by quartz sericite pyrite and carbonate minerals the ore forming fluids were low salinity co2 rich and characterized by isotopically heavy 18o four deposits dongchuang wenyu yangzhaiyu and dahu in the xiaoqinling area each contain resources of about 1 moz au some of the gold deposits in the xiong ershan area represent more shallowly emplaced tellurium enriched orogenic systems which include resources of approximately 1 1 5 moz au at shanggong and beiling or tantou others are epithermal deposits e g qiyugou and dianfang that are hosted in volcanic breccia pipes isotopic dates for all gold deposits although often contradictory generally cluster between 172 99 ma and are coeval with emplacement of the post kinematic granitoids the gold deposits formed during a period of relaxation of far field compressional stresses clearly subsequent to the extensive paleozoic early mesozoic accretion of arc terranes and the yangtze craton onto the southern margin of the north china craton hydrothermal and magmatic events occurred locally where extension related precambrian basement uplifting took place along the craton margin fluids for the orogenic gold deposits in the xiaoqinling xiaoshan and xiong ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones alternatively for the epithermal gold deposits at shallower levels in the xiong ershan area gold transporting fluids were mainly exsolved from coeval magmas although meteoric water was also involved in these hydrothermal systems