evidence for proterozoic and late cretaceous early tertiary ore forming events in the coeur d alene district idaho and montana discussion

cordilleran epithermal cu zn pb au ag mineralization in the colquijirca district central peru deposit scale mineralogical patterns at colquijirca central peru a miocene diatreme dome complex is associated in space and time with several large epithermal polymetallic cu zn pb au ag deposits of the cordilleran class of these deposits smelter and colquijirca located in the northern sector of the district are part of a continuously mineralized northsouth corridor that extends for nearly 4 km outward from the diatreme dome complex and to depths of 1 km below surface this corridor is zoned from cu au ores in its inner parts smelter deposit to peripheral zn pb ag ores colquijirca deposit the smelter colquijirca corridor has undergone minor erosion providing a good example of a nearly intact paleo epithermal system of the cordilleran class this description of the hypogene mineralogical patterns of the smelter colquijirca corridor leads to the proposal that they are the result of superimposition in time and space of three main stages during an early quartzpyrite stage in which basically no economic ore deposition occurred carbonate rocks surrounding the marcapunta diatreme dome complex were replaced by quartz and pyrite this was followed by the main ore stage which was largely superimposed on the quartz pyrite replacements and produced zonation of ore minerals and metals along much of the smelter colquijirca corridor the zoning from cu ores to zn pb ores is complex and comprises a number of distinct and well defined zones that display abrupt or gradual interfaces between zones from internal to external parts these zones consist mainly of the following mineral associations and assemblages 1 enargite luzonite pyrite colusite tennantite goldfieldite ferberite gold silver tellurides bismuthinite gold alunite zunyite kaolinite dickite smectite illite sericite quartz 2 enargite pyrite quartz bismuthinite alunite dickite kaolinite smectite illite sericite 3 bornite pyrite quartz alunite dickite kaolinite barite 4 tennantite barite dickite kaolinite chalcopyrite bi and or ag bearing minerals 5 chalcopyrite sphalerite galena pyrite quartz dickite kaolinite barite 6 sphalerite galena pyrite hematite kaolinite siderite magnetite marcasite 7 zn bearing carbonate zone and 8 a barren outer zone consisting mainly of calcite the crosscutting relationships and zoning patterns indicate that during the main ore stage the inner cu zones progressively overprinted the zn pb zones evidence for the subsequent contraction of the mineralization front is also recognized a mainly fault controlled late ore stage was the last recognized episode of mineralization in the smelter colquijirca corridor related to the deposition of chalcocite digenite and covellite as veinlets cutting and replacing the different cu bearing zones of the main ore stage it is not economically important the different mineral associations and assemblages provide insights into the chemistry of the hydrothermal fluids particularly that of the main ore stage the acidity and oxidation state of the main ore stage fluids varied considerably prior to significant interaction with the host rock this is best observed in the enargite bearing zones in which most acidic fluids formed alunite zunyite enargite bearing assemblages and less acidic fluids formed smectite illite enargite and muscovite enargite bearing assemblages the common kaolinite dickite enargite assemblage was related to a fluid with intermediate character between these two end member styles the significant fluctuations in the acidity of the ore fluids in the central parts of the mineralizing system are interpreted to reflect mixing between variable amounts of acidic and oxidized magmatic vapor derived fluids and less acidic low to moderate saline ore forming fluids of magmatic origin

la cassiterite zonee du gisement de sokhret allal granite des zaer maroc central composition chimique et phases fluides associees la composition chimique d une cassiterite zonee provenant du gisement de tungstene etain de sokhret allal granite des zaer maroc central a ete analysee par microsonde electronique la zonation optique du mineral correspond a des variations en elements mineurs fe ti nb les bandes sombres apparaissent correlees a une augmentation en titane et fer tandis que les bandes claires sont plus pures les inclusions fluides contemporaines du depot de la cassiterite sont primaires et constituees de fluides typiquement aqueux de composition 97 a 99 moles h2o 3 a 1 moles equivalent nacl temperature 270 330 c et sont piegees en phase liquide la contribution de ces nouvelles donnees a la metallogenese w sn du maroc central est discutee

a descriptive model for silver lead zinc veins in clastic metasedimentary terranes a comparative study of selected geologic features from six classic districts the kokanee range and keno hill canada coeur d alne united states freiberg and the harz moun tains germany and pibram czechoslovakia demonstrates that silver lead zinc veins in clastic metasedimentary terranes form a distinct class of mineral deposits which can be typi fied by a descriptive model these silver lead zinc veins have characteristic metal ratios and are comprised of galena sphalerite and a diverse suite of silver and sulfosalt minerals in a gangue of siderite quartz or calcite the veins are typically enclosed by spatially restricted phyllic alteration silver lead zinc veins occur in various tectonic settings the veins are hosted by monotonous sequences ofclastic rocks intruded by gabbroic to granitic plutons and metamorphosed to at least the greenschist facies the veins are late features in the tectonic evolution of an orogen commonly occur near a crustal scale fault and are not genetically related to felsic intrusions mineralization occurs at temperatures near 250 o to 300oc from dilute to saline fluids at an average depth of 6 km precipitation results from district scale mixing of up to three distinct fluids and localized boiling these fluids include a deep seated hydrothermal fluid an upper crustal fluid of ultimate meteoric origin and a late stage meteoric dominated fluid sulfur is derived from the local country rocks whereas carbon is derived from organic and or deep seated sources pb is mainly derived from the local upper crustal country rocks

discovery of chalukou super large scale molybdenum polymetallic deposit northern daxing anlin mountain china and its significance the chalukou molybdenum polymetallic deposit located in north daxinganling district is a super large scale porphyry deposit with resource of 1 34 mt molybdenum 370 kt zinc lead and nearly 4 200 t silver the resource has exceeded that of jinduicheng molybdenum deposit and make it the largest scale molybdenum deposit in northern china the molybdenum mineralization occurs in the jurassic volcanic sedimentary rocks as veinlet veins and stockwork the quartz porphyry granite porphyry and explosive breccia show close space time relationship with the molybdenum mineralization preliminary result shows that geological setting geological feature petrological characteristics and hydrothermal alteration of chalukou molybdenum deposit are similar to climax molybdenum in west america which is the product of extensional environment after collage of north china mongolia block and siberia block in late mesozoic

evidence for proterozoic and late cretaceous early tertiary ore forming events in the coeur d alene district idaho and montana new 40 ar 39 ar age spectra on sericite and lead isotope data on tetrahedrite siderite galena bournonite and stibnite together with previously published isotopic geochemical and geologic studies provide evidence for two major vein forming events in the coeur d alene district and surrounding areas of the belt basin the data suggest that the zinc and lead rich veins e g bunker hill and star morning mines formed in the proterozoic 1 0 ga whereas the silver rich veins e g silver belt mines antimony veins e g u s antimony mine and gold bearing quartz veins murry subdistrict formed in late cretaceous to early tetitary time

geology of gold bearing skarn deposits in the middle and lower yangtze river valley and adjacent regions abstract the middle and lower yangtze river valley and adjacent regions are the most important metallogenic belt of gold and copper bearing skarn deposits in china the total gold reserves in this belt have been estimated at more than 600 t the gold bearing skarns are mainly distributed in the southeastern hubei tongling and northern anhui regions favorable tectonic settings are depressions and fold zones of the platforms i e mobile belts these skarns are hosted by platformal limestone dolomitic limestone and dolomite of the triassic carboniferous permian and middle to lower cambrian formations the related intrusions are yenshanian 180 to 113 ma calc alkaline quartz monzodiorite granodiorite quartz monzonite monzogabbro and their hybabyssal facies the intrusions have high fe2o3 feo 0 5 and intermediate initial 87 sr 86 sr ratios 0 7046 to 0 7087 their ree distribution patterns are lree enriched and exhibit smooth right dipping curves these suggest that the source materials mainly came from upper mantle with contamination by sialic crustal components the auriferous skarns are both calcic and magnesian but calcic skarns are most common the constituent minerals of the calcic skarns are diopside garnet wollastonite vesuvianite and scapolite whereas magnesian skarns are dominated by forsterite spinel diopside phlogopite chondrodite and clinohumite with abundant superimposed serpentine clinochlore and brucite the compositions of coexisting pyroxenes and garnets are diopside and andradite indicating the high oxygen fugacity and low acidity conditions gold is closely associated with cu pb zn sulfides and exists mainly in the form of native gold and electrum arsenides tellurides bismuthides and selenides are present in many ore deposits therefore cu as bi te ag pb zn se and co are the major metals present in the deposits and are important geochemical ore searching indicators in some au fe cu magnesian skarns magnesiomagnetite magnesioferrite and ludwigite are locally abundant the metasomatic zoning in many gold skarn deposits is very distinct consisting of an outward sequence of fe cu cu mo cu au au cu au pb zn the geologic characteristics of au cu skarn deposits that formed in the mobile platformal setting of china have distinct differences compared to au skarns formed in orogenic belts at convergent plate margins in british columbia and the western usa

morphology and origin of coastal karst landforms in miocene and quaternary carbonate rocks along the central western coast of sardinia italy in the area of punta funtanas arbus central west sardinia some small surfaces of miocene limestones crop out partially covered with quaternary calcarenites and plio quaternary basalts the biggest of these outcrops forms a fossil wave cut shore platform of up to 50 m wide with an altitude above sea level of approximately 4 5 m on this platform a wide variety of dissolution landforms can be observed these morphologies are related to the influence of the seawater zone of wave action marine splash and spray zone up to progressively more continental environments and to biokarst processes erosional action of marine organisms algae and micro organisms and are arranged in bands parallel to the coast corresponding to different morphological zones this paper describes all the karst landforms observed in this coastal area from a morphological and genetic point of view

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

silver lead zinc veins metamorphic core complexes and hydrologic regimes during crustal extension the kokanee range ag pb zn au vein and replacement deposits formed during eocene crustal extension and unroofing of the valhalla metamorphic core complex in the hanging wall of the transcrustal slocan lake fault the 34ssulfide 18oquartz 18osiderite and galena pb isotopic ratios for vein minerals display regional zonations revealing fluid flow paths of a large fossil hydrothermal system sulfur was derived from local country rocks but carbon was derived from a deep seated reservoir possibly the upper mantle lead is a mixture of local upper crustal pb with lower crustal and depleted upper mantle pb regional isotopic zonations were controlled by deep fracture zones such as the slocan lake fault which channeled lower crustal and mantle pb and mantle co2 to higher crustal levels where mixing occurred with highly evolved meteoric waters that had leached local sulfur and upper crustal ph this is the first ag pb zn vein district for which a genetic link between mineralization and metamorphic core complex unroofing is demonstrated

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

the pre devonian tectonic framework of xing an mongolia orogenic belt xmob in north china abstract a new tectonic division of the xing an mongolia orogenic belt xmob in north china has been presented according to our research and a lot of new data of tectonics geochronology and geochemistry four blocks and four sutures have been recognized in the xmob including the erguna eb xing an airgin sum xab songliao hunshandake shb and jiamusi jb and xinlin xiguitu xxs xilinhot heihe xhs mudanjiang ms and ondor sum yongji sutures oys the framework of the xmob is characterized by a tectonic collage of the blocks and orogenic belts between them different precambrian basements have been found in the blocks including the neoproterozoic metamorphic rocks and plutons in the eb the neoproterozoic metamorphic rocks in western and eastern of segments of the xab mesoproterozoic and neoproterozoic metamorphic rocks in middle segments of the xab respectively the neoproterozoic metamorphic rocks and mesoproterozoic volcanic rocks and plutons in the shb and neoproterozoic metamorphic rocks in the jb the xxs resulted from a northwestward subduction of the xab beneath the eb during the cambrian which was followed by the forming of the xhs and oys in the northwest and south margins of the shb in the silurian respectively the ms was caused by a westward subduction of the jb beneath the east margin of the shb during the middle devonian the three cambrian silurian and middle devonian events indicate that the xmob belongs to a pre middle devonian multiple orogenic belt in the central asian orogenic belt caob forming of the xmob suggests that the southeast part of the paleo asian ocean closed before the middle devonian

fluid seepage variability across the external northern apennines italy structural controls with seismotectonic and geodynamic implications abstract the relations between fluid seeps and tectonic structures have been targeted in some key areas of the axial sector and partly at the edge of the exposed northern apennines pede apennine margin in the axial zone fluid seepage is dominated by methane venting which may occur in the form of dry seeps or associated with mineral springs surface venting is linked to the presence of foreland dipping normal faults or related to reservoirs localised at inactive anticlines the pede apennine margin is instead dominated by thrusting and mud volcanism the two different categories of fluid seepage appear strongly coupled to the dissimilar stress fields compressional or extensional operating in these sectors pressure data inferred from deep wells delineate an overall fluid pressure increase from the axial zone toward the pede apennine margin possibly as a result of the growth of tectonic compaction in this direction the increase of fluid pressure at the pede apennine margin is thus interpreted as the primary control on the transition from dry vents to mud volcanism the intimate association between seepage modes and distinct tectonic structures involves relevant consequences on fluid fault interactions and seismotectonics and also shows connections with processes dictating the internal deformation of evolving fold and thrust belts

geochemical signature of the granitoids in the chalukou giant porphyry mo deposit in the heilongjiang province ne china abstract the chalukou porphyry mo deposit located in the northern great xing an range is the largest mo deposit in the xing an mongolia orogenic belt its ore bodies are mainly hosted in the intermediate felsic complex and jurassic volcanic sedimentary rocks of which late jurassic granite porphyry quartz porphyry and fine grained granite are closely associated with mo mineralization the middle jurassic monzogranite belongs to shoshonite series with sio2 and al2o3 contents of 69 48 to 74 98 and 12 35 to 14 48 respectively the total alkali k2o na2o content ranges from 7 67 to 10 42 with k2o na2o ratios between 1 07 and 2 81 these rocks are strongly enriched in rb and k but are depleted in ta nb p and ti with negative eu anomalies and positive ehf t the late jurassic granite porphyry quartz porphyry and fine grained granite are shoshonite or high k calc alkaline series their sio2 and al2o3 contents range from 73 87 to 78 95 and 10 35 to 13 47 respectively the total alkali k2o na2o contents range from 8 06 to 10 02 with k2o na2o ratios from 1 03 to 8 20 these rocks are strongly enriched in rb k and th but are depleted in p ti ba and sr indicating clear negative eu anomalies and positive ehf t the middle late jurassic granitoids in the chalukou deposit are highly fractionated i type granitoids and derived from juvenile lower crust materials that originated from the neoproterozoic depleted mantle these granitoids formed in the extension tectonic setting of the post collision stage of the mongol okhotsk orogenic belt probably superposed by the back arc extension related to the subduction of the paleo pacific plate

oxygen carbon and strontium isotope geochemistry of the sunshine mine coeur d alene mining district idaho the pb ag ores of the sunshine mine located in the coeur d alene mining district of northern idaho occur within steeply dipping tabular west northwest trending veins of siderite gangue that crosscut the overturned northern limb of the big creek anticline the delta 13 c pdb 9 9 to 6 4 and delta 18 o smow 13 1 17 7 values of the siderites vary in a proportion of about 1 2 but siderites with delta 18 o or 16 exhibit a slope close to the 1 4 trend expected for a system with variable temperature whereas no correlation is evident for siderites with delta 18 o 16 the delta 18 o values of crosscutting quartz veins 13 4 15 5 and the surrounding wall rocks 10 7 15 5 are several per mil too low to be in isotopic equilibrium with the siderite at the temperature of approximately 325 degrees c determined from fluid inclusion studies at this temperature the calculated delta 18 o values for the precipitating fluids range from 7 8 to 12 4 for the siderite and 6 9 to 8 9 for the quartz the high delta 18 o values calculated for these fluids reflect their exchange with the high 18 o metasedimentary rocks of the belt supergroup in higher temperature fluid source regions detailed sample traverses across two 1 to 3 m wide siderite veins show that 1 some veins are composite containing materials deposited at different times or in different places which were juxtaposed by subsequent vein parallel faulting 2 siderite in structurally simple veins is most enriched in 13 c and 18 o adjacent to the walls resulting in u shaped spatial trends and 3 the delta 18 o values of metasedimentary wallrocks are substantially lower than those of the siderite in the veins and increase adjacent to them these small scale variations account for the lack of a simple relationship between delta 18 o and depth in the vein systems these data also indicate that the vein fluids were hotter and considerably higher in 18 o than the fluids in equilibrium with adjacent wall rock the progressive 18 o decrease from the margins to the centers of the siderite veins further decreasing into the early crosscutting quartz veins probably represents a progressive increase in the temperature of deposition but could also represent variations in fluid source in an evolving system the dispersion of delta 12 c values for samples with delta 18 o 16 per mil may be the result of late stage explosive pressure release and co 2 effervescence during fluid decompression when fissure filling was nearly complete the structural simplicity of the veins and the primary hydrothermal character of the stable isotope variations argue against postdepositional deformation and metamorphism stable isotope and strontium isotope data support the interpretation that ore deposition occurred during the late cretaceous or early tertiary as the result of metamorphic hydrothermal processes associated with regional compression and the formation of major granitic batholiths

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

proterozoic pb isotope evolution in the belt purcell basin constraints from syngenetic and epigenetic sulfide deposits sediment hosted massive sulfide and ag pb zn veins are two major deposit types which contain large concentrations of lead in the middle proterozoic belt purcell basin new pb isotope data on the sullivan sediment hosted massive sulfide deposit and the st eugene ag pb zn vein deposit are combined with existing data to provide a comprehensive overview of proterozoic pb isotope evolution in the belt purcell basin the pb isotope ratios for sulfides in the sullivan deposit form a linear array the sullivan array bedded sulfides plot within this array and no systematic change in pb isotope ratios with stratigraphic position time is observed the sullivan array results from the mixing of leads from the upper crustal and or orogen pb reservoirs represented by metasedimentary rocks of the lower aldridge formation in the footwall of the sullivan deposit with perhaps leads derived from the precambrian basement of the belt purcell basin a zone within the massive sulfides of the sullivan deposit has been altered to chlorite pyrite calcite the center of the alteration zone is comprised of massive pyrite calcite which has more radiogenic pb isotope compositions the sullivan alteration the sullivan alteration apparently formed from the same pb reservoirs as the sullivan array perhaps as a product of the east kootenay orogeny 1370 ma after a period of up to 108 m y which allowed radiogenic pb growth ag pb zn occurrences in the belt purcell basin form an array in pb isotope space the coeur d alene array which is not collinear with the sullivan array it is characterized by pb isotope compositions less radiogenic than those of the sullivan array the coeur d alene array is a mixture of leads derived from the upper crustal and mantle pb reservoirs it is proposed that mantle lead was introduced into the belt purcell basin at 1468 ma by the mafic moyie sills leads in sediment hosted massive sulfide deposits in middle aldridge rocks and leads of the coeur d alene array in epigenetic veins formed after intrusion of the moyie sills but before east kootenay orogeny metamorphism

the early cretaceous weilasituo zn cu ag vein deposit in the southern great xing an range northeast china fluid inclusions h o s pb isotope geochemistry and genetic implications abstract the weilasituo vein type deposit hosted in hercynian middle to late paleozoic quartz diorite and palaeozoic gneiss occurs on the western slopes of the southern great xing an range in this paper we present results from fluid inclusion and isotope h o s pb investigations on the weilasituo deposit we identify three stages during the ore formation a barren pre ore stage stage 1 a main ore stage with economic grade cu zn ag mineralization stage 2 and a barren post ore stage stage 3 fluid inclusion and mineral thermometry constrain temperature intervals of approximately 243 to 333 c 192 to 425 c and 141 to 261 c for the three stages respectively fluids in the main ore stage are characterized by complex nacl h 2 o ch 4 co 2 low salinity 3 55 to 8 68 wt nacl equiv with isotopic signatures consistent with a magmatic source these fluids evolved by mixing with local meteoric water 18 o fluid 1 15 to 5 15 d fluid 139 4 to 88 2 measured and calculated sulfur isotope compositions of hydrothermal fluids 34 s fluid 3 0 to 3 4 indicate that the ore sulfur was derived mainly from a magmatic source the lead isotope ratios from the ores show mean values of 18 326 15 553 and 38 242 for 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb respectively indicating a mantle source our study shows that fluid mixing and or dilution played an important role in copper zinc and silver mineralization in the weilasituo deposit the weilasituo and bairendaba deposits represent a linked ore system genetically related to the late mesozoic magmatism the ore forming fluids associated with the early cretaceous mineralization in the southern great xing an range are of magmatic in origin and evolved by mixing with local meteoric water these deposits preserve the signature of a mantle source for lead however the deposits formed at ca 177 160 ma possess a dominantly magmatic signature with less radiogenic lead

fluid evolution in the w cu zn pb san cristobal vein peru fluid inclusion and stable isotope evidence abstract the zn pb ag cu san cristobal district is located 100 km east of lima in the western cordillera of peru it is centred around the chumpe intrusion and is composed of vein and carbonate replacement ore types the main san cristobal vein presents a paragenesis that can be divided into three stages a an early wolframite quartz pyrite stage b a quartz base metal stage and c a late quartz carbonate barite stage fluid inclusions in quartz from the tungsten stage are biphase lv at room temperature and homogenise to the liquid phase between 146 and 257 c their salinities range between 2 1 and 5 1 wt nacl equiv rare inclusions contain an additional crystal of halite and have salinities of 46 54 wt nacl equiv data of the first two stages show a decrease in homogenisation temperatures concomitant with a salinity decline fluid inclusions in quartz from the late stage homogenise at higher temperatures between 252 and 323 c with salinities ranging between 4 6 and 6 7 wt nacl equiv hydrogen and oxygen isotope data indicate a two stage evolution isotopic compositions of the fluid associated with the first two stages define a trend with constant 18 o values and decreasing d values 18 o 3 2 to 5 0 v smow and d 60 to 112 v smow which is interpreted as mixing of a dominantly magmatic component with minor meteoric water that had equilibrated with the host rocks this interpretation is supported by sulphur and lead isotopic data from previous studies by contrast the quartz carbonate barite stage bears isotopic characteristics defining a trend with a coupled decrease of 18 o and d 18 o 8 1 to 2 5 v smow and d 57 to 91 v smow and is explained by addition of meteoric water to the system and subsequent mixing with a less important magmatic component different fluid origins are confirmed by laser ablation icp ms analyses of the triphase lvh and biphase lv primary inclusions the concentrations of the major ore elements i e w cu zn and pb decrease throughout the paragenesis w and to a lesser extent cu show significant variations associated with a steep decrease in their concentration the decreasing concentrations can be explained by mineral deposition and dilution by the meteoric fluid differences in the rate of decrease indicate selective precipitation of w fluid inclusions of the quartz carbonate stages show an abrupt increase in ba and sr concentrations this is interpreted to reflect a higher volume of host rock silicate alteration probably due to the increasing size of the fluid flow cell and is explained by the input of a third fluid of unknown origin la icp ms analyses show that the fluids were already depleted in w and cu before reaching the emplacement of carbonate replacement ore type whereas zn and pb were still present in considerable amounts this is again due to selective precipitation and is consistent with the interpretation that the economically interesting metals were dominantly introduced by magmatic fluids

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

the genesis of metal zonation in the weilasituo and bairendaba ag zn pb cu sn w deposits in the shallow part of a porphyry sn w rb system inner mongolia china abstract the weilasituo and bairendaba zn pb ag cu sn w sulphide deposits are located in the southern part of great xing an range of inner mongolia in china the deposits are located at shallow depths in the newly discovered weilasituo porphyry hosting sn w rb mineralization the mineralization at weilasituo and bairendaba consist of zoned massive sulphide veins within fractures cutting the xilinhot metamorphic complex and quartz diorite the weilasituo deposit gradually zones from the cu rich zn cu sulphide mineralization in the west to zn rich zn cu sulphide mineralization in the east the bairendaba deposit has a cu bearing and zn rich core through a transitional zone devoid of copper to an outer zone of zn pb ag mineralization three main veins contain more than 50 wt of the contained metal in the two deposits with their metal ratios displaying a systematic and gradual increase in zn cu pb zn and ag zn ratios from the western part of weilasituo to the eastern part of bairendaba three stages of vein type mineralization are recognized early sub economic mineralization consists of a variable proportion of euhedral arsenopyrite pyrite quartz and rare wolframite scheelite cassiterite magnetite and cobaltite this was succeeded by main stage mineralization with economic concentration of zoned cu zn pb and ag sulphide minerals along strike within the veins the zones consist of the assemblages 1 pyrrhotite fe rich sphalerite chalcopyrite quartz fluorite at west weilasituo 2 pyrrhotite fe rich sphalerite chalcopyrite galena tetrahedrite quartz fluorite at east weilasituo 3 pyrrhotite fe rich sphalerite chalcopyrite galena tetrahedrite quartz fluorite in the centre of bairendaba 4 pyrrhotite fe rich sphalerite galena chalcopyrite tetrahedrite quartz fluorite in the transition zone of bairendaba and 5 pyrrhotite fe rich sphalerite galena tetrahedrite chalcopyrite falkmanite argentite pyrargyrite quartz fluorite in the outer zone at bairendaba post main ore stage is devoid of sulphides and characterized overprinting of fluorite sericite chlorite illite kaolinite and calcite zircon shrimp u pb dating zircon la icp ms u pb dating molybdenite re os isochron dating and muscovite ar ar dating indicate the beidashan granitic batholith was intruded at 140 3 ma mswd 3 3 the porphyritic monzogranite from marginal facies of the beidashan batholith was intruded at 139 2 ma mswd 0 75 the mineralized quartz porphyry was intruded at 135 2 ma mswd 0 91 the greisen mineralization occurred at 135 11 ma mswd 7 2 and the post main ore stage muscovite deposited at 129 5 0 9 ma the new geochronology data show the porphyry sn w rb and vein type sulphide mineralization are contemporaneous with granitic magmatism in the region the metal zonation at the weilasituo and bairendaba deposits is a result of progressive metal deposition this was during the evolution of a metal bearing fluid along the strike of the veins and during the main stage of ore formation at the upper part of the deep seated porphyry sn w rb system this progressive zonation indicates that the deposits represent end numbers formed from one ore forming fluid which moved from west to east from the porphyry the metal zonation patterns of the major veins are consistent with metal bearing fluid entering the system with the precipitation of chalcopyrite proximally and sphalerite galena and ag bearing minerals more distally we show that the mechanism of metal deposition is therefore controlled by thermodynamic conditions resulting in the progressive separation of sulphides from the metal bearing fluid the temperature gradient between the inflow zone and the outflow zone appears to be one of the key parameters controlling the formation of the metal zonation pattern the sulphide precipitation sequence is consistent with a low f s 2 and low f o 2 state of the acidic metal bearing fluid the metal zonation pattern provides helpful clues from which it is possible to establish the nature of fluid migration and metal deposition models to locate a possible porphyry mineralization at depth in the great xing an range which is consistent with the geology of the newly discovered porphyry sn w rb system

age and origin of base and precious metal veins of the coeur d alene mining district idaho ore bearing quartz carbonate veins of the coeur d alene mining district yield 87sr 86sr ratios of 0 74 to 1 60 for low rb sr carbonate gangue minerals similar to current ranges measured in middle proterozoic high rb sr rocks of the belt supergroup stable isotope and fluid inclusion studies establish a genetic relationship between vein formation and metamorphic hydrothermal systems of the region these extraordinary 87sr 86sr ratios require accumulation of radiogenic 87sr in a high rb sr system over an extended period prior to incorporation of sr into the hydrothermal veins evaluation of the age and composition of potential sources of highly radiogenic sr indicates that the ore bearing veins of the coeur d alene district formed during the cretaceous from components scavenged from rocks of the belt supergroup the primary host rocks of the district proterozoic pb isotope ratios observed in galena from many coeur d alene veins were established when pb separated from uranium during deposition or diagenesis of the belt supergroup at 1400 to 1500 ma possibly as disseminated syngenetic deposits k ar and rb sr apparent ages and 18o values of belt supergroup rocks decrease from the coeur d alene district toward the idaho and kaniksu batholiths approximately normal to the trends of metamorphic isograds fold axes foliation and the major reverse faults of the district isoclinal folding thrust faulting high temperature metamorphism granitic plutonism and regional scale metamorphic hydrothermal activity is documented in the region between 140 and 45 ma representing the only such combination of events in the coeur d alene region subsequent to about 1300 ma the sr and oxygen results and geologic evidence favor formation of the ore bearing carbonate veins by fluids related to a complex metamorphic hydrothermal system during the cretaceous pb with proterozoic isotopic compositions was probably mobilized and incorporated like other metals into the hydrothermal veins during this event the ore bearing veins were sheared and displaced during early tertiary northwest trending dextral strike slip faulting along the osburn fault and related structures of the lewis and clark line