thrust controlled sediments hosted pb zn ag cu deposits in eastern and northern margins of tibetan orogenic belt geological features and tectonic model numberous of pb zn ag cu ore deposits with significant economic values occur in lanping basin and yushu and tuotuohe areas on the eastern and northern margins of tibetan orogenic belt being hosted by sediments and having no obvious affinity to igneous activities these deposits occur in continent continent indo asian collisional orogen and are controlled by thrust nappe structures thus obviously different from the well known sediments hosted base metal deposits in the world they were formed in tertiary foreland basins developed from paleo tethyan rifting basins and mesozoic depression basins during mineralization thrust nappe structures juxtaposed mesozoic strata over tertiary strata through a series of parallel reverse thrust faults in the basins the deposits are strictly controlled by thrust nappe structures there exist four types of ore deposits the jinding type deposits is formed in a thrusting related dome structure combined with lithologic trap the hexi sanshan type deposit is controlled by a pop up structure the fulongchang type deposits are located in thrusting related second order faults within clastics and the dongmozhazhua type deposits are hosted by second order faults within limestone of the hanging walls of major thrust faults their ore bodies are controlled by faults where sandstone dolomitized limestone and structural cracking zones are favorable loci of ore concentration ores were mainly derived from open space filling and replacement resembling epigenetic mineralization metal sulfides are present as low fe sphalerite galena pyrite or cu sulfides tetrahedrite bornite chalcopyrite chalcocite ag bearing sulfides argentite freibergite ag tetrahedrite galena sphalerite gangue minerals are calcite fluorite barite dolomite celestine quartz with rare bitumen fluid inclusions contain mainly salt aqueous solutions and locally and subordinately co2 and hydrocarbons with homogenization temperatures predominately of 80 190 and salinities of 1 wt 28 wt nacl eq indicative of basinal brines meteoric water as the source of ore forming fluids studies show that the thrust nappe structures provided channelways for lateral and vertical migration of ore forming fluids as well as open space for ore accumulation isotope data suggest that ore forming materials were mainly derived from basinal sedimentary rocks with or without the contribution of mantle derived rocks metal composition and abundance of a deposit depend probably on types of rocks that the ore forming fluids encountered during their migration and accumulation in the ore district the existence of limestone generally corresponds to zn pb znpb mineralization whereas the occurrence of clastics especially for red bed corresponds to cu ag pb mineralization a preliminary metallogenic model for the pb zn ag cu deposits can be described as follows india asian collision led to the lifting of the orogenic belt relative to the tertiary foreland basins in the eastern and northern margins of the tibetan plateau and strong compression resulted in the thrusting of these basins consequently fluids generated from the orogen migrated laterally along gently dipping detachment faults of the thrust systems towards the basins and evolved into ore forming fluids through interaction with country rocks the ore forming fluids migrated vertically along major thrust faults and finally accumulated in the open spaces induced by thrust nappe structures at shallow levels to form ore deposits

ages of sediment hosted himalayan pb zn cu ag polymetallic deposits in the lanping basin china re os geochronology of molybdenite and sm nd dating of calcite abstract the lanping basin is a significant pb zn cu ag mineralization belt of the sanjiang tethyan metallogenic province in china over 100 thrust controlled sediment hosted himalayan base metal deposits have been discovered in this basin including the largest sandstone hosted pb zn deposit in the world jinding and several cu ag co deposits baiyangping baiyangchang and jinman these deposits with total reserves of over 16 0 mt pb zn 0 6 mt cu and 7000 t ag are mainly hosted in meso cenozoic mottled clastic rocks and strictly controlled by two cenozoic thrust systems developed in the western and eastern segments of the lanping basin to define the metallogenic history of the study area we dated nine calcite samples associated with copper sulfides from the jinman cu deposit by the sm nd method and five molybdenite samples from the liancheng cu mo deposit by the re os method the calcite sm nd age for the jinman deposit 58 5 ma and the molybdenite re os age for the liancheng deposit 48 2 ma together with previously published chronological data demonstrate 1 the cu ag mineralization in the western lanping basin mainly occurred in three episodes i e 56 54 51 48 and 31 29 ma corresponding to the main and late collisional stages of the indo asian orogeny and 2 the pb zn ag cu mineralization in the eastern lanping basin lacked precise and direct dating however the apatite fission track ages of several representative deposits 21 4 ma to 32 5 ma may offer some constraints on the mineralization age

genesis of the jinding zn pb deposit northwest yunnan province china constraints from rare earth elements and noble gas isotopes abstract the giant sediment hosted jinding zinc lead deposit is located in the lanping basin northwestern yunnan province china the genesis of the deposit has long been debated and the sources of the ore forming fluids and metals are controversial this study presents rare earth element ree and noble gas isotope data that constrain the origins of the ore fluids and the heat source driving the hydrothermal circulation the early stage sulfides are enriched in light rees and have high ree values 30 8 94 8 ppm and weakly negative eu eu 0 85 0 89 and ce anomalies ce 0 84 0 95 suggesting that the fluids were likely derived from dissolution of upper triassic marine carbonates with input of rees from aluminosilicate rocks in the basin in contrast the late stage sulfides have irregular ree patterns generally low ree values 0 24 10 8 ppm and positive eu eu 1 22 10 9 and weakly negative ce anomalies ce 0 53 0 90 which suggest that the ore forming fluids interacted with evaporite minerals the 3 he 4 he 0 01 0 04 r a and 40 ar 36 ar values 301 340 of the ore forming fluids indicate crustal and atmospheric origins for these noble gases these findings are in agreement with the published fluid inclusion microthermometry data and the results of h o c s pb and sr isotope studies our data in combination with published results support a two stage hydrothermal mineralization model involving early stage basinal brines and late stage meteoric water that acquired metals and heat from crustal sources

progressive 18o depletion during co2 separation from a carbon dioxide rich hydrothermal fluid evidence from the grey river tungsten deposit newfoundland oxygen isotope data for the grey river tungsten prospect newfoundland canada indicate a progressive depletion in 18ofluid during mineralization early veins with pegmatitic affinities were deposited at 470 c and pressures greater than 1 kbar 100 mpa from a fluid with a 18o composition of 7 4 presumed to be of magmatic origin successive vein deposition at progressively lower temperatures and pressures culminated in the precipitation of wolframite bearing veins at a temperature of 300 c and pressures of 150 320 bar 15 32 mpa from a low salinity fluid with a 18o composition in the range 3 2 1 6 low values of 18o and dfluid are recorded in many vein tungsten deposits and are normally interpreted as reflecting mixing of isotopically light meteoric fluids or formation brines with magmatic fluids however fluid inclusion evidence for the grey river mineralization indicates that a 40 mol co2 loss occurred by immiscibility and retrograde boiling of the hydrothermal fluid between 420 and 3

sanjiang tethyan metallogenesis in s w china tectonic setting metallogenic epochs and deposit types abstract tectonically the sanjiang tethyan metallogenic domain stmd is located within the eastern himalayan tibetan orogen in the sanjiang tethys southwestern china although this metallogenic domain was initiated in the early palaeozoic extensive metallogenesis occurred in the late palaeozoic late triassic and himalayan tertiary epochs corresponding tectonic settings and environments in the domain are an arc basin system related to the subduction of the palaeo tethyan oceanic slabs a post collision crustal extension setting caused by the lithospheric delamination or slab breakoff underneath the sanjiang tethys during the late triassic large scale strike slip faulting and thrusting systems due to the indo asian continent collision since the palaeocene in this metallogenic domain important gold copper base metals rare metals and tin ore belts incorporating a large number of giant deposits were developed the main types of deposits include 1 porphyry copper deposits controlled by a large scale strike slip fault system 2 vhms deposits mainly occurring in intra arc rift basins and post collision crustal extensional basins 3 shear zone type gold deposits in the ophiolitic melange zone along the thrusting shearing system 4 hydrothermal silver polymetallic deposits in the triassic intra continental rift basins and tertiary strike slip pull apart basins and 5 himalayan granite related greisen type tin and rare metallic deposits within the metallogenic epochs of the late palaeozoic to cenozoic the styles and types of the ore deposits changed from vhms types in the late palaeozoic through exhalative sedimentary type deposits in the late triassic to porphyry type copper deposits shear zone type gold deposits hydrothermal vein type silver polymetallic deposits greisen type tin and rare metal deposits in the cenozoic correspondingly ore forming metals also changed from a pb zn cu ag association through ag cu pb zn fe ag pb and ag au hg associations to ag cu pb zn cu mo au sn and li rb cs nb zr hf y ce sc associations

sediment hosted gold deposits in guizhou china products of wall rock sulfidation by deep crustal fluids sediment hosted gold deposits in guizhou china are hosted in late paleozoic and early mesozoic sedimentary rocks along the southwest margin of the precambrian yangtze craton they have characteristics similar to carlin type gold deposits in nevada and are notably enriched in as sb hg and tl the shuiyindong and yata deposits consist of disseminated strata bound sulfides in permian bioclastic limestone and fault controlled mineralization in middle triassic calcareous clastic rocks respectively mineralization in both deposits consists of barren milky quartz veins disseminated gold bearing arsenian pyrite and arsenopyrite stibnite realgar and orpiment the barren milky quartz veins occur in the ore controlling structures with an envelope of gold mineralization in the host rock consisting of disseminated gold bearing arsenian pyrite and arsenopyrite and replacement style quartz veinlets later drusy quartz stibnite realgar and orpiment fill fractures and vugs on the periphery of gold mineralization petrography microthermometry laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometric la icp ms analyses of fluid inclusions are used to characterize the chemical evolution of ore fluids at shuiyindong and yata early barren milky quartz veins trapped aqueous fluid with moderate salinity 6 0 wt nacl equiv and minor co2 2 4 mol at a temperature of 230 30 c this fluid contains measurable b na k cs sr as sb and au 3 8 0 5 5 7 2 3 g g determined by la icp ms and is interpreted to approximate the mineralizing fluid responsible for precipitation of early barren quartz veins low salinity 0 9 2 3 wt nacl equiv co2 bearing 6 3 8 4 mol aqueous fluids are recorded in replacement style quartz veinlets they formed gold bearing arsenian pyrite and arsenopyrite and quartz veinlets at a temperature of 210 20 c and pressures of 450 to 1 150 bars corresponding to depths between 1 7 and 4 3 km under lithostatic conditions fluid inclusions in late stibnite orpiment realgar quartz veins contain high co2 58 64 mol and n2 19 2 23 7 mol with trace ch4 up to 1 6 mol the increasing content of co2 and decrease in the concentrations of au and as in aqueous carbonic inclusions are interpreted to result from carbonate dissolution at the level of the deposits during gold mineralization covariance of au as sb and sr concentrations in the fluids is interpreted to reflect deposition of as and sb sulfides and gold concurrent with carbonate crystallization iron is below detection limit 400 g g in all fluid inclusion types suggesting that the ore fluids were fe poor but possibly sulfur rich possibly explaining their exceptionally high gold contents iron in sulfide minerals was probably derived from dissolution of ferroan minerals in the host rocks sulfidized by h2s rich fluids to precipitate arsenian pyrite arsenopyrite and gold pressure fluctuation induced by faulting resulted in local fluid immiscibility and led to late deposition of realgar orpiment stibnite and calcite hydrogen and oxygen isotope compositions of ore fluids d h2o 35 to 68 18o h2o 4 16 5 indicate a metamorphic origin possibly related to crustal thickening and prograde metamorphism during the late yanshanian orogeny

diffusion of cosmogenic3he in olivine and quartz implications for surface exposure dating abstract thein situ production of3he in surface rocks by cosmic ray induced nuclear reactions offers an important geochronological tool to evaluate helium loss problems in this technique cosmogenic3he diffusivities were measured in quartz and olivine by incremental heating at 150 600 c arrhenius temperature dependences were observed in both minerals with similar activation energies ea 25 4 kcal mole logd0 3 7 0 9 in olivine andea 25 2 0 9 logd0 0 2 0 4 in quartz and imply very low diffusivities when extrapolated to environmental temperatures less than 10 18 cm2 s in quartz and 10 22 cm2 s in olivine at 20 c these low diffusivities suggest helium loss will not significantly affect cosmogenic helium exposure dating for time scales on the order of 106 years in quartz and 109 years in olivine provided large 2 mm sample grains are used exposure ages obtained with smaller grains need to be corrected for diffusive helium loss and equations are provided for this purpose cosmogenic3he diffuses more than 100 times faster than trapped magmatic3he in olivine or radiogenic4he in quartz the mechanisms responsible for these differences have yet to be determined but may involve both trapping processes at mineral defects and enhanced mobility associated with spallation produced crystal damage therefore it is possible that helium diffusivities may depend on a sample s cosmic ray exposure or radiogenic production history whatever the precise mechanism the higher mobility of3he suggests that incremental heating will be useful in separating cosmogenic helium from magmatic or radiogenic helium in future studies comparison of the diffusivity results with total cosmogenic3he contents of different quartz size fractions for an antarctic quartzite suggests that he loss may have occurred more rapidly than predicted by the laboratory measurements nonetheless retention of cosmogenic3he is quite high equivalent to more than a million years of exposure and cosmogenic3he geochronology is feasible in this and other quartz containing rocks

link between gold provinces low salinity high temperature 200 degrees c reducing fluids are poorly represented in ore forming processes yet appear to account for 90 percent of the primary gold mined to date such fluids have been implicated in the formation of many archcan greenstone witwatersrand slate belt and epithermal gold deposits these low salinity auriferous fluids occur in variable time space lithological sequence and tectonic settings and are most easily explained by metamorphic devolatilization of mafic and or graywacke successions metamorphism of chlorite calcite albite quartz assemblages e g mafic or graywacke at the greenschist amphibolite facies boundary occurs around 480 degrees or 20 degrees c for 3 5 kbars and produces large volumes of low salinity h 2 o co 2 fluid similar in composition to those recorded in many gold deposits widespread pyrite in the above assemblage typically leads to elevated levels of dissolved sulfur such conditions are ideal for gold transport as a molecular au s complex and can lead to deposits rich in gold relative to silver and base metals deposition of gold occurs in the temperature range of 250 degrees to 400 degrees c and can be facilitated by lower temperature lower sulfur activity and changes in oxygen activity lower sulfur activity is most readily achieved by fluid interaction with fe rich host rocks with the formation of pyrite or pyrrhotite whereas lower oxygen activity is readily achieved by interaction with carbonaceous metasediments low salinity fluids produced by metamorphic devolatilization provide a common theme embracing the formation of many archcan greenstone slate belt witwatersrand and potentially epithermal gold deposits it involves the common features of high geothermal gradient low salinity fluid high au ag high au base metals and broad synchroneity with metamorphism it also accounts for the considerable variability in hosting structures detailed timing relations host rocks alteration assemblages and geologic age of different deposits interestingly the similarities are explained by deeper processes the differences by processes at or near the depositional sites

spatial temporal evolution of ore forming fluids and related mineralization in the western lanping basin yunnan province china abstract the lanping basin is a significant pb zn cu ag mineralization belt in the sanjiang tethyan metallogenic province a series of sediment hosted himalayan cu ag pb zn polymetallic deposits have been discovered in the western part of the basin controlled by a thrust nappe system in the thrust nappe system the cu orebodies mainly occur in the western and relatively deep part of the mineralization system the root zone whereas the pb zn ag cu orebodies occur in the eastern and relatively shallow part of the system the front zone both as vein type mineralization in this paper we present new data combined with existing data on fluid inclusions isotopes and geologic characteristics of representative deposits to provide the first study that contrasts mineralizing fluids in the cu ag mo and pb zn ag cu polymetallic deposits fluid inclusion and isotope studies show that the cu ag mo mineralization in the root zone formed predominantly from deep crustal fluids with the participation of basinal brines the deep crustal fluids are marked by high co2 content relatively high temperatures 280 to 340 c and low salinities 1 to 4 wt nacl equivalent whereas the basinal brine shows relatively low temperatures 160 c to 220 c and high salinities 12 to 22 wt nacl equivalent containing almost no co2 in comparison hydrothermal activity associated with the pb zn ag cu deposits in the front zone is characterized by basinal brine with relatively low temperatures 130 c to 180 c high salinities 9 to 24 wt nacl equivalent and low co2 concentrations although evolved meteoric waters have predominantly been proposed as the source for deep crustal fluids magmatic and metamorphic components cannot be completely excluded the basinal brine was predominantly derived from meteoric water the 34s values of sulfides from the cu ag mo deposits and pb zn ag cu deposits range from 17 9 to 16 3 and from 2 5 to 11 2 respectively these ranges may relate to variations in physicochemical conditions or compositional variation of the sources lead isotope compositions indicate that the ore forming metals were predominantly derived from sedimentary rocks of the lanping basin

n2 ar he compositions in fluid inclusions indicators of fluid source abstract a quadrupole mass spectrometer was used to measure bulk samples of conservative gas species n 2 ar and he in fluid inclusions from a variety of hydrothermal systems analyses of these tracer elements help determine 1 1 if gases extracted by bulk inclusion analyses can provide accurate measurement of n 2 ar he in active and fossil geothermal systems 2 2 if hydrothermal fluids associated with paleogeothermal systems in a continental setting follow n 2 ar he systematics similar to th the western pacific rim active geothermal systems specifically new zealand and 3 3 whether different deposit types systematically vary with regard to n 2 ar he the n 2 ar he ratios of fluid inclusion volatiles released from recently deposited minerals from the valles system are similar to those of present day valles thermal waters those inclusion samples from deep within the valles system below a regional aquitard increase in n 2 compositions for inclusions from the questa and copper flat porphyry deposits are n 2 rich similar to those of arc related volcanic gases whereas those from taylor creek sn deposit appear to be mixtures of magmatic and crustal components n 2 ar he ratios of the precambrian tribag deposit suggest a basalt source but significant levels of self generated he from u and th in the inclusion fluids are also possible inclusions from two epithermal deposits with low salinity inclusions have n 2 ar he ratios trending towards air saturated meteoric waters asw and those inclusions with higher salinities indicate minor to no asw component the n 2 ar he ratios in fresnillo and cochiti inclusions which have magmatic helium isotopic ratios indicate additions of magmatic gases to meteoric fluids inclusions from sediment hosted deposits that contain hydrocarbon bearing brines are he rich as are meteoric waters with a long residence time in the crust at relevant pressure temperature composition conditions henry s law constants of n 2 ar and he are similar and thus the relative amounts of these species trapped under boiling conditions will not vary appreciably from solubility controlled amounts in coexisting liquid furthermore there is no evidence of he loss or gain in inclusions by diffusion process data from the various systems that were examined indicate that fluid inclusion n 2 ar he compositions may be related to magmatic fluid sedimentary brine deep circulating meteoric fluid and shallow circulating meteoric fluid sources which we modified from those proposed by giggenbach 1986 relationships between the n 2 ar he tracer gases and other measurable quantities in fluid inclusions are indicated to be helpful in understanding fluid mixing processes in paleogeothermal systems

abundance of co 2 rich fluid inclusions in a sedimentary basin hosted cu deposit at jinman yunnan china implications for mineralization environment and classification of the deposit the jinman cu deposit is hosted in sandstones and slates of the jurassic huakaizuo formation in the mesozoic to cenozoic lanping basin in western yunnan china despite the fact that cu mineralization occurs mainly in quartz carbonate veins controlled by faults and fractures the jinman deposit was classified as a sediment hosted stratiform cu deposit mainly because it is hosted in a sedimentary basin characterized by abundant red beds with many stratiform cu deposits a detailed petrographic and microthermometric study of fluid inclusions from the jinman deposit reveals the presence of abundant co2 rich fluid inclusions together with aqueous inclusions the co2 rich inclusions have co2 melting temperatures mainly from 58 0 c to 56 6 c homogenization temperatures of the carbonic phase mostly into the liquid phase mainly between 22 c and 30 c clathrate melting temperatures from 1 8 c to 9 2 c with corresponding salinities from 1 6 to 13 4 wt nacl equivalent and total homogenization temperatures from 226 c to 330 c the aqueous inclusions have first melting temperatures from 60 c to 52 c ice melting temperatures from 41 4 c to 2 3 c with salinities from 3 9 to 29 0 wt nacl equivalent and total homogenization temperatures mainly from 140 c to 250 c these fluid inclusion characteristics are comparable to those of orogenic or magmatic mineralization systems and are uncharacteristic of basinal mineralization systems suggesting that it is inappropriate to classify the jinman deposit as a sediment hosted stratiform cu deposit the results of this study together with geochemical data reported previously suggest that the jinman deposit formed in a hydrothermal system that involved both extra basinal deeply sourced co2 rich fluid and basinal aqueous fluid

archean gold mineralization and oxidized hydrothermal fluids sulfate minerals hematite and isotopically fractionated sulfides are relatively rare in rocks of archean age several archean au deposits however contain one or more of these features indicative of oxidized hydrothermal fluids they include hemlo mcintyre hollinger macassa lake shore and ross which are all in ontario canada and kalgoorlie in australia examples of lesser deposits are in hislop township and in the matachewan area ontario canada with the exception of hemlo these are quartz carbonate vein deposits spatially and temporally associated with felsic plutonism because metamorphic fluids and archean surface waters were mostly reducing the most feasible general source for the fluids was felsic magmas parent magmas were relatively oxidized hydrous and co 2 rich the oxidized character may have favored the incorporation of au into the partial melt and its partitioning into magmatic aqueous fluids high contents of co 2 are conducive to the separation of an aqueous fluid from magma at greater depth than otherwise fluid inclusion data support the formation of major archean au vein deposits at deeper crustal levels than more recent magmatic hydrothermal mineralization such as porphyry cu deposits co 2 rich fluids can unmix into two phases at relatively high temperatures and pressures a saline aqueous liquid and a low salinity h 2 o co 2 liquid this can cause partitioning of cl complexed base metals from other metals including au sb and as the extensive carbonatization around most deposits has consistent delta 13 c values in the range of juvenile magmatic co 2

fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising fluids the naturally occurring noble gas isotopes 40ar 36ar 84kr and 129xe and halogens cl br i have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits pcd bingham canyon utah and silverbell ray mission pinto valley and globe miami in arizona in addition analyses of 3he 4he have been obtained from sulphide minerals hosted by the quartz veins at silverbell ray pinto valley and globe miami the majority of pcd fluids studied have br cl and i cl ratios that overlap those of fluids included in mantle diamond suggesting that the salinity had a juvenile origin the high i cl 121 10 6 mole m in samples from the propylitic zone of silverbell is attributed to the presence of sedimentary formation water 3he 4he ratios have r ra values in the range 0 3 to 1 72 and provide evidence for the involvement of a crustal component in addition to mantle volatiles 40ar 36ar ratios vary from meteoric values of 317 in the propylitic zone of bingham canyon and 323 in the skarn alteration of mission up to 3225 in the potassic zone of pinto valley fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end member comprising meteoric water and air and a high salinity end member consisting of a mixed mantle and crustal fluid the 40ar cl ratio of fluid inclusions at pinto valley 10 4 m is similar to values obtained previously for mantle fluids the 40ar cl value is two orders of magnitude lower at bingham canyon where a depleted 36ar concentration 0 2 10 6 cm3 g below that of air saturated water asw and a range of highly fractionated noble gas compositions f84kr 13 and f129xe 160 indicate that boiling and pulsed fluid flow have occurred

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr

scalability of the mineral prospectivity modelling an orogenic gold case study from northern finland abstract one of the key objectives for mineral exploration is to map the most prospective areas for the selected deposit type at a regional scale subsequently narrowing these down to camp size target areas and finally to individual prospects that can be developed into economic mines exploration targeting at all scales is constrained by conceptual mineral system models and requires the integration and interpretation of a variety of geophysical geological and geochemical data geographic information system gis applications are commonly used to integrate spatially referenced data sets to produce mineral prospectivity maps in support of the mineral exploration targeting process a knowledge driven fuzzy logic method is used in this work for data integration and prospectivity modelling for orogenic gold deposits in northern finland the modelling workflow is done in a stepwise manner at three scales each step simulates the successive stage used in mineral exploration from selecting the most prospective belt scale domain to the camp size target area and individual prospects new higher resolution data sets are added at each stage as is typically the case in mineral exploration northern finland was selected as the test area due to the regional scale coverage of publicly available geoscientific data and its proven orogenic gold potential the regional scale prospectivity map outlines the central part of the paleoproterozoic central lapland greenstone belt clgb as the most prospective area for orogenic gold in northern finland the belt scale model of the clgb improves the resolution mapping of several camp sized high prospectivity target areas the camp scale model of one of these a past producing mining camp further narrows down the high prospectivity zones into prospect size targets three models have score area under curve auc values between 0 839 and 0 930 from the receiver operating characteristic roc method validation technique indicating that the models are robust the stepwise approach presented confirms that prospectivity mapping using the knowledge driven fuzzy logic method is a scalable flexible and relatively fast method which can be used for decision making at different stages of the exploration targeting process adding new data and rerunning the prospectivity model with the new data is fast and easy the most important conclusion from the study is that remodelling individual regional and camp scale domains separately is highly recommended for mapping the most prospective target areas even if the data sets used are the same

metallogenesis in tibetan collisional orogenic belt ii mineralization in late collisional transformation setting the collisional processes established many paleo mountain belts are commonly divided by many geologists into two simple but distinct stages i e syn collisional and post collisional periods as the transition from late to post collisional is not clear and the definition of post and late collisions also is blurring however the tectonic evolution of the tibetan orogen underwent a complicate history which is divided into 1 syn collisional 65 41 ma 2 late collisional 40 26 ma and 3 post collisional 25 0 ma periods the orogeny during the late collisional period generally happened in a compressional regime resulted from successional convergence between indian and asian continents and is characterized by intra continental subduction underthrust crustal shortening large scale thrusting and strike slip faulting systems developed in the margins of the tibetan plateau which resulted in the development of potassic porphyry stocks and carbonatite alkalic complexes in the eastern tibet and potassic ultrapotassic volcanic rocks in the northern tibet at least four significant metallogenic events associated with the late collsional orogeny have been recognized in the eastern margin of the tibetan plateau a tectonic transformation belt they are 1 the porphyry cu mo au mineralization related to large scale strike slip faults system which controlled the localization of the yulong porphyry cu belt 40 36 ma in east tibet 2 the ree mineralization associated with carbonatite alkalic complexes formed the mianning dechang ree belt 40 27 ma in the western sichuan 3 the pb zn ag mineralization controlled by thrust faulting systems formed at least two large sized pb zn ag deposits 40 30 ma in the lanping strike slip pull apart basin western yunnan and 4 the au mineralization related to large scale shearing which produced the ailaoshan au belts composed of numerous shear type or orogenic type au deposits in the western sichuan and yunnan these data indicate that the late collisional metallogensis in the tibetan orogen were mainly developed in an intra continental transformation orogenic sdetting characterized by a series of large scale strike slip faulting thrusting and shearing systems developed in the late collisional period available data suggest that the metallogensis is probably controlled by a shared deep lithospheric process most likely related to upwelling of the asthenosphere triggered by face to face subduction of the yangtze and lhasa blocks continental slabs in the eastern margin of the tibetan plateau during the late collisional period

hydrothermal fluid origins in mississippi valley type ore districts combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the illinois kentucky fluorspar district viburnum trend and tri state districts midcontinent united states samples were selected from three of the classic mississippi valley type districts in the midcontinent area of north america the illinois kentucky fluorspar district belongs to the fluoritic subtype of mississippi valleytype districts and the ozark districts of the viburnum trend and tri state are representative of the pb rich and more typical zn rich subtypes of mississippi valley type mineralization respectively noble gas ar kr and halogen cl br i data have been obtained simultaneously by noble gas mass spectrometry of inclusion fluids released by in vacuo crushing of irradiated fluorite quartz carbonate and sphalerite samples additionally he analyses have been obtained from nonirradiated fluorite from the illinois kentucky fluorspar district fluorite from the illinois kentucky fluorspar district has a maximum 3 he 4 he ratio of 0 35 ra where ra atmospheric 3 he 4 he ratio of 1 4 10 6 higher than values typical of crustal fluids and confirming the presence of a minor mantle component equal to less than 6 percent of the total he in the fluids of the illinois kentucky fluorspar district the br cl mol ratios of all the deposits are with one exception higher than the value of seawater 1 54 10 3 ranging from 1 69 to 3 70 10 3 and indicating acquisition of salinity by the evaporation of seawater beyond the point of halite saturation late quartz from the tri state district contains a very minor component of halite dissolution water and has a br cl mol ratio of 1 46 10 3 the i cl mol ratios are typical of oil field brines and are ubiquitously higher than what is attainable by the evaporation of seawater alone i cl mol ratios are in the range of 6 to 270 10 6 indicating that the fluids have interacted with i rich organic matter present in sedimentary rocks in the ozark districts 40 ar 36 ar ratios vary between 320 and 345 in the tri state and between 350 and 420 in the viburnum trend in the illinois kentucky fluorspar district 40 ar 36 ar ratios reach values of 1 200 the corresponding concentrations of 40 arexcess 40 ar not attributable to radiogenic decay of 40 k or an atmospheric source are similarly elevated in the main stage fluorite mineralization of the illinois kentucky fluorspar district 6 8 18 2 10 4 cm 3 cm 3 h2o relative to the viburnum trend and tri state districts mostly 1 3 3 3 10 4 cm 3 cm 3 h2o and 0 3 1 4 10 4 cm 3 cm 3 h2o respectively together the noble gas and halogen data indicate the existence of three brine provinces 1 a regional tristate brine present throughout the ozark region 2 a viburnum trend brine and 3 an illinois kentucky brine furthermore in the viburnum trend the halogen composition of main stage dolomite is distinct from that of the main stage sphalerite but identical to the regional hydrothermal dolomite seen in the tri state district the data imply that mixing relationships in the viburnum trend are highly complex but are compatible with regional models in which the tri state brine present throughout the ozark region was sourced in the arkoma basin

fluid inclusion and noble gas studies of the dongping gold deposit hebei province china a mantle connection for mineralization the dongping gold deposit 100 t au occurs about 200 km inboard of the northern margin of the north china craton the deposit is mainly hosted by syenite of a middle paleozoic alkalic intrusive complex that was emplaced into late archean basement rocks both groups of rocks are intruded by late jurassic to early cretaceous crustal melt granite dikes and stocks some within a few kilometers of the deposit the gold ores were deposited during this latter magmatic period at about 150 ma a time that was characterized by widespread regional north south compression that formed the east west trending yanshan deformational belt the ores include both the telluride mineral bearing low sulfide quartz veins and the highly k feldspar altered syenite with most of the resource concentrated in two orebodies 1 and 70 fluid inclusion microthermometry indicates heterogeneous trapping of low salinity e g 5 7 wt nacl equiv fluids that varied from a few to 60 mole percent nonaqueous volatile species laser raman spectroscopy confirms that the vapor phase in these inclusions is dominated by co2 but may be comprised of as much as 9 mole percent h2s and 20 mole percent n2 methane concentrations in the vapor phase are consistently 1 mole percent the variable phase ratios are consistent with fluid immiscibility during ore formation fluid inclusion trapping conditions are estimated to be 250 to 375 c and 0 6 to 1 0 kbar helium isotope studies of fluid inclusions in ore stage pyrites indicate 3he 4he ratios of 2 1 to 5 2 ra ra 1 4 10 6 for air for orebody 1 and 0 3 to 0 8 ra for orebody 70 the former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1 the lower values for orebody 70 which is characterized by a more disseminated style of gold mineralization are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks which may have contributed additional 4he to the fluids a mantle source for at least some of the components of the gold forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool archean lithosphere beneath the craton during this time the dongping deposit is located along the 100 km wide north south gravity lineament which marks the western border of the thinned crust as both regional metamorphism of mesoproterozoic and younger cover rocks and widespread granite magmatism also occurred at ca 150 ma it is unclear as to whether one or both of these also contributed fluid and or metals to the hydrothermal system importantly these new data suggest that economically significant gold deposits of similar mineral style and fluid composition which are scattered along the margins of the craton may all be products of a fluid originally partly sourced within the mantle

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

archean lode gold deposits fluid flow and chemical evolution in vertically extensive hydrothermal systems abstract the range of conditions of formation of lode gold deposits from the sub greenschist to the lower granulite facies in archean greenstone belts and the generally steeply plunging vertically continuous pipe like or tabular geometries of individual deposits indicate long distance hydrothermal fluid advection along well defined channelways in the upper and middle crust from presently available gold solubility data destabilisation of gold bisulphide complexes through h 2 s loss from the fluid to the wallrock was the dominant gold precipitation mechanism within these hydrothermal systems as a whole this inference is supported by the s au ratios of ores sulphur and au precipitation in the hydrothermal system is estimated to be relatively inefficient with only 10 50 of s or au contained in the fluid precipitated over any kilometre length of fluid channelway the relative inefficiency of gold precipitation allowed mineralisation over a significant depth range in a crustal profile

fluid inclusion evidence for immiscibility in magmatic differentiation abstract after a brief review of recent work on melt inclusions in diamond and in normal magmatic environments the nature of the fluid inclusion evidence for various stages of magmatic immiscibility is summarized during magmatic differentiation by crystal fractionation from originally low volatile content silicate melts yielding normal plutonic rocks through hydrous silicate melts yielding pegmatites to late stage water rich fluids yielding quartz veins and ore deposits the composition of the residual liquid changes drastically in some geologic environments this change in composition of the residual liquid may be continuous with no phase change in the fluid part of the system under most natural conditions however it is far more likely to have one or more stages in the evolution during which globules of a separate new immiscible fluid phase exsolve the term immiscibility is used here in its more general sense to refer to the existence at equilibrium of two or more non crystalline polycomponent solutions fluids differing in properties and generally in composition i believe that the great bulk of the magmatic inclusions that are being studied today have come about through the intervention of one or more such stages of immiscible fluid separation i e magmatic differentiation by fluid immiscibility examples include silicate melt dense co2 fluid silicate melt sulfide melt silicate melt silicate melt silicate melt low density vapor i e vesiculation and as presented in more detail in this paper various stages of silicate melt hydrous saline melt aqueous fluid co2 fluid immiscibility generally only parts of these stages are recorded by the trapping of fluid inclusions and the interpretation of the inclusion record is commonly ambiguous and difficult particularly that stage between hydrous silicate melts and the hydrous saline melts and aqueous solutions responsible for many ore deposits the ambiguity results mainly from problems of inclusion origin and nonrepresentative trapping within any given individual inclusion thus the probability of trapping of only one vs various amounts of two immiscible fluids or of trapping solid phases along with the fluid present severe difficulties in addition there is the almost universal superposition of various stages of trapping of fluids within any given sample these problems can only be approached by very careful petrography and analysis of optimum material combined with field data and experimental p v t x studies of pertinent systems completely unequivocal statements of the course of evolution of the fluids in such natural systems may never be possible

noble gas and halogen constraints on mineralizing fluids of metamorphic versus surficial origin mt isa australia abstract the origin of hydrothermal fluids responsible for silica dolomite alteration associated with cu ore in the giant mt isa deposit of queensland north east australia has been investigated main stage quartz and dolomite veins and late to post ore quartz from the buck quartz fault in the orebody footwall plus the regional mt isa and railway faults contain two phase liquid vapour fluid inclusions with variable salinity fluid inclusion molar br cl values are mostly in the range 1 5 12 10 3 and molar i cl values are in the range 9 186 10 6 greater than seawater br cl and i cl values can characterise either sedimentary formation waters with a bittern brine origin by the sub aerial evaporation of surface water beyond the point of halite saturation or some metamorphic dehydration fluids with a deep crustal source we propose that these alternative origins can be distinguished in our samples based on the relationship between 40 ar 36 ar and 36 ar concentration metamorphic fluids formed by dehydration of crystalline rock are predicted to have low 36 ar concentrations with the salinity 40 ar 36 ar and 40 ar e cl values determined by the whole rock concentration of cl 36 ar oh k and age the main stage quartz and buck quartz fault samples host fluid inclusions with 36 ar 40 ar 36 ar in the range 10 000 28 000 and high 40 ar e cl values of 3 8 10 4 these values are consistent with metamorphic fluids sourced by devolatilisation of either the underlying eastern creek volcanics or the barramundi basement in contrast surface derived fluids acquire elevated 40 ar 36 ar values 296 through fluid rock interaction which leads to a simultaneous increase in 36 ar concentration the main stage ca rich dolomite fluid inclusions have high salinities close to the point of halite saturation 26 wt 1 7 5 5 ppb 36 ar 40 ar 36 ar in the range 1600 8400 and 40 ar e cl of 0 2 1 10 4 these values are most similar to those expected in an evolved bittern brine however the 36 ar concentration and 40 ar 36 ar value exhibit a weakly negative correlation which is the opposite to that expected in surface derived fluids only fluid inclusions in samples from the railway fault and some fluid inclusions in samples from the buck quartz fault have 36 ar concentrations of greater than air saturated water asw 1 3 2 7 ppb 36 ar up to 27 ppb and 40 ar 36 ar values of 1000 2500 that are expected for fluids with an exclusively sedimentary formation water origin fluid inclusions in the mt isa fault samples have the highest 36 ar concentrations of up to 100 ppb some of the lowest 40 ar 36 ar values and the highest br cl value of up to 30 10 3 these features distinguish it from all other sample groups in the mine area silica dolomite alteration and cu mineralization are interpreted to have resulted from mixing of the deeply derived metamorphic fluid best preserved in quartz fluid inclusions and a surface derived bittern brine partially preserved within the main stage dolomite fluid inclusions inflow of a second surficial fluid along regional faults and into the mine through the late to post d 3 buck quartz fault may have terminated mineralization the involvement of metamorphic fluids is compatible with the syn d 3 1530 ma timing of mineralization during the final stages of the isan orogeny