fluid inclusion characteristics of intrusion related gold mineralization tombstone tungsten magmatic belt yukon territory canada intrusion hosted low sulfide sheeted vein systems are common within many plutons and stocks of the middle cretaceous tombstone tungsten magmatic belt yukon territory and host significant gold mineralization fluid inclusion characteristics of five such systems namely emerald lake dublin gulch scheelite dome mike lake and mactung constrain the vein forming fluid composition formation temperatures and pressures hydrothermal fluid processes and potential fluid sources the veins contain a wide range of fluid inclusion types ubiquitous type 1a and 1b inclusions are low salinity 1a xnacl 1 kbar at emerald lake and dublin gulch and 2 kbar at mactung and scheelite dome that potentially control fluid composition and evolution a variety of fluid processes may have been responsible for gold precipitation including immiscibility and or release of an evolving magmatic fluid

the origin of hematite in high grade iron ores based on infrared microscopy and fluid inclusion studies the example of the conceicao mine quadrilatero ferrifero brazil petrographic and textural analysis combined with fluid inclusion studies by infrared microscopy of high grade 65 fe hematite ore samples from the conceicao deposit in the northeastern part of the quadrilatero ferrifero brazil indicate a complex process of oxidation and mineralization during two orogenic events each developed under different conditions and involving distinct fluids the earliest mineralization formed massive magnetite rich orebodies under relatively reducing conditions in the early stages of the transamazonian orogeny magnetite was oxidized martitized with the development of porous hematite crystals hematite i possibly during this stage new hematite crystals were also formed from low temperature low to medium salinity fluids as indicated by two phase fluid inclusions the origin of these fluids is still uncertain but tentatively interpreted as being modified surface water the fluids were transported along normal faults and fractures during post tectonic collapse following the transamazonian orogeny 2 1 2 0 ga and creation of the dome and keel structural pattern of the quadrilatero ferrifero these solutions were also likely responsible for the initial oxidation of the iron formations and the development of hematite i subsequent uplifted hot basement rocks or post tectonic plutons were probable heat sources for the regional metamorphism and development of a granoblastic fabric of hematite ii grains in the iron formations and high grade orebodies however the ore was only partially recrystallized as several relics of the early magnetite martite and hematite are still preserved in the granular hematite ii crystals during the brasiliano pan african orogeny 0 8 0 6 ga high salinity fluids with temperatures varying from 120 to a maximum of approximately 350 c penetrated the iron formations along shear zones crystallizing initially tabular and thereafter platy hematite crystals hematite iii and specularite forming schistose orebodies quartz veins that cut across the ore and envelop specularite plates and ore fragments formed from late stage high temperature and low salinity fluids containing co2 these later fluids did not alter the ore each of these stages of mineralization produced orebodies with distinct features recurrent hydrothermal mineralization is thought to have been responsible for the development of giant high grade iron ore deposits in structurally favorable sites fold hinges with enhanced permeability and deep faults able to conduct the fluids to the surface repeatedly over time should be important targets for exploration of new resources

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

wall rock alteration structural control and stable isotope systematics of the high grade copper orebodies of the kennecott district alaska the kennecott district alaska contained three important copper silver orebodies bonanza mother lode jumbo and erie and numerous other small occurrences from 1911 to 1938 the kennecott copper corporation recovered some 1 18 billion pounds blbs of copper and around 9 million ounces moz of silver from these deposits the host rocks for the kennecott deposits are part of the type section wrangellia terrane ore was hosted in the triassic carnian chitistone limestone most of it located 20 to 40 m above the contact with the native copper bearing triassic ladinian nikolai greenstone the bonanza mother lode and jumbo orebodies are upward tapering veins having wide bases controlled by one or more often subtle bedding parallel fault s they plunge downdip to the northeast with long axes approximately parallel to the direction of regional shortening the veins hosting the orebodies occupy ne striking oblique slip faults with dextral and normal kinematics that were probably formed between 155 to 110 ma during the docking of wrangellia with north america the deposits consist of a paragenetically early and volumetrically minor assemblage of chalcopyrite bornite luzonite covellite that precipitated between approximately 180 and 110 c a dominant stage of chalcocite djurleite that precipitated in the range of 110 to 90 c and a minor late assemblage of covellite digenite spionkopite yarrowite that probably precipitated at even lower temperatures wall rock alteration includes premineral hydrothermal dolomitization and synmineral dedolomitization hydrothermal dolomite occurs in replacement zones one to tens of meters wide along favorable structures and stratigraphic horizons whereas dedolomite is generally restricted to thin 1 m selvages along structures within breccias and adjacent to orebodies sulfur isotope measurements on samples collected from the bonanza and jumbo mines as well as from numerous smaller deposits and prospects in both the chitistone limestone and nikolai greenstone throughout the region indicate that 34 s generally becomes enriched through time and paragenesis sulfur for the deposits was probably derived from sulfate in both the nikolai greenstone and the basal chitistone limestone that was reduced during burial and diagenesis via thermochemical sulfate reduction tsr the extremely broad range 54 1 of sulfur isotope compositions including in the main stage chalcocite djurleite assemblage from 16 0 to 17 4 is probably due to tsr operating on two separate sources of sulfate and limited incorporation of bacteriogenic sulfide which was sourced from either early bacterial sulfate reduction bsr or from dissolution of diagenetic pyrite found in the lower chitistone limestone field and isotopic data support a model in which an oxidized fluid generated by dehydration reactions during prehnite pumpellyite metamorphism of the nikolai greenstone scavenged copper and possibly sulfur from the greenstone and then moved along faults into the overlying chitistone limestone where it mixed with an anoxic basinal brine containing reduced sulfur copper deposition was controlled fundamentally by redox reactions with main stage precipitation occurring at low temperatures 110 c important field criteria for the recognition of kennecott style deposits include any or all of the following baroque dolomite dedolomite and hydrothermal breccia particularly in association with faulted carbonate host rocks

the origin of the tongkeng changpo tin deposit dachang metal district guangxi china clues from fluid inclusions and he isotope systematics tongkeng changpo is the largest tin deposit within the giant dachang polymetallic tin ore field in guangxi southern china which is part of a large skarn system associated with cretaceous granitoids the tongkeng changpo mineralization consists of veins and stockworks in the upper levels and replacement stratiform orebodies mantos at lower levels based on textural relationships three major mineralizing stages can be recognized stage i with cassiterite sulphides stannite tourmaline and quartz stage ii with cassiterite sulphides sulphosalts quartz and calcite and stage iii with calcite as the main phase the study of fluid inclusions has shown that there are two main fluid types co2 and nacl h2o homogenization temperatures are 270 to 365 c 210 to 240 c and 140 to 190 c for stages i ii and iii respectively salinities range from 1 to 7 wt nacl equiv in the early ore stage and 3 to 10 wt nacl equiv in the late stages laser raman spectroscopy indicates that the inclusion fluids in stages i and ii were of carbono aqueous composition with minor amounts of ch4 and h2s whereas those in stage iii were aqueous helium isotopic analyses of inclusion fluids indicate that the 3he 4he ratios in the ore veins are in between 1 2 to 2 9 ra ra 1 4 10 6 modern atmospheric ratio and range from 1 6 to 2 5 ra in the stratiform orebodies this range of 3he 4he ratios is significantly higher than that of crustal fluids 0 01 0 05 ra the similar characteristics of fluid inclusions and their he isotopic composition as well as age constraints indicate that the ore veins and stratiform orebodies of the tongkeng changpo deposit formed from the same hydrothermal system likely related to granite intrusions of the mesozoic yanshanian tectono thermal event in addition the high r ra ratios indicate a mantle contribution in the ore fluids

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

geochemical evolution of the banded iron formation hosted high grade iron ore system in the koolyanobbing greenstone belt western australia the banded iron formation bif hosted iron ore deposits in the lower greenstone succession of the koolyanobbing greenstone belt 50 km north of southern cross in western australia are a 200 mt high grade fe 58 pre mining resource and represents one of the most important iron ore districts in the yilgarn craton four hypogene alteration ore forming stages and one supergene upgrading event took place 1 during ore stage 1 lree depleted transition metal enriched mg fe ca carbonates replaced quartz in bifs the deposit scale alteration was most likely induced by devolatilization of sea floor altered ca si depleted mafic rocks in the vicinity of the bif during early regional syn d 1 very low to low grade metamorphism and was most strongly developed on reactivated bif basalt contacts 2 ore stage 2 involved the formation of patchy magnetite ore by a syn d 2 to d 4 dissolution of early carbonate enrichment of fe 2o 3total in magnetite iron ore was by a factor of 2 to 2 4 and compatible trace elements in magnetite such as ga v and al were immobile a subdeposit scale ferroan talc footprint proximal to magnetite iron ore in the largest deposit k deposit was associated with ore stage 2 and resulted from dissolution of magnesite due to reaction with silica in the bif under greenschist facies conditions and potentially high fluid rock ratio 3 magnetite growth during ore stage 3 forming granular magnetite martite ore is related to a subsequent hydrothermal event occurring locally throughout the belt especially in d 2b faults 4 ore stage 4 was associated with fe ca p l ree y enriched hydrothermal fluids possibly from a magmatic source such as the postmetamorphic lake seabrook granite that crops out about 10 km west of the koolyanobbing deposits and at the southern margin of the greenstone belt these ca enriched fluids interacted with distal metamorphosed mafic rock and influenced the bif ore system in a small number of deposits they were channelled through regional d 4 faults and caused specularitedolomite quartz alteration resulting in fe grades of up to 68 5 supergene upgrade ore stage 5 by further gangue leaching in the weathering zone was most effective in carbonate altered bifs and magnetite ore this process together with supergene martitization and goethite replacement of magnetite led to the formation of high grade locally at k deposit high p goethite martite ore at koolyanobbing the two geochemically distinct stages of archean carbonate alteration clearly controlled the formation of hypogene magnetite specularite martite rich ore and recent supergene modification including the further upgrade of fe ore 2012 by economic geology

genesis of middle miocene yellowstone hotspot related bonanza epithermal au ag deposits northern great basin usa epithermal deposits with bonanza au ag veins in the northern great basin ngb are spatially and temporally associated with middle miocene bimodal volcanism that was related to a mantle plume that has now migrated to the yellowstone national park area the au ag deposits formed between 16 5 and 14 ma but exhibit different mineralogical compositions the latter due to the nature of the country rocks hosting the deposits where host rocks were primarily of meta sedimentary or granitic origin adularia rich gold mineralization formed where glassy rhyolitic country rocks host veins colloidal silica textures and precious metal colloid aggregation textures resulted where basalts are the country rocks clay rich mineralization with silica minerals adularia and carbonate developed oxygen isotope data from quartz originally amorphous silica and gels from super high grade banded ores from the sleeper deposit show that ore forming solutions had 18o values up to 10 heavier than mid miocene meteoric water the geochemical signature of the ores including their se rich nature is interpreted here to reflect a mantle source for the epithermal suite elements au ag se te as sb hg and that signature is preserved to shallow crustal levels because of the similar volatility and aqueous geochemical behavior of the epithermal suite elements a mantle source for the gold in the deposits is further supported by the pb isotopic signature of the gold ores apparently the host rocks control the mineralization style and gangue mineralogy of ores however all deposits are considered to have derived precious metals and metalloids from mafic magmas related to the initial emergence of the yellowstone hotspot basalt derived volatiles and metal loid s are inferred to have been absorbed by meteoric water dominated geothermal systems heated by shallow rhyolitic magma chambers episodic discharge of volatiles and metal loid s from deep basaltic magmas mixed with heated meteoric water to create precious metal ore forming fluids colloidal nanoparticles of au ag alloy electrum naumannite ag2se silica and adularia likely nucleated at depth traveled upward and deposited where they grew large enough to aggregate along vein walls silica and gold colloids have been reported in hot springs from yellowstone national park suggesting that such processes may continue to some extent to the present however it is possible that the initial development of the mantle plume led to a major but short lived distillation process which led to the mid miocene bonanza ore forming event

limestone assimilation and the origin of co2 emissions at the alban hills central italy constraints from experimental petrology abstract the alban hills volcanic region 20 km south of rome in the roman province emitted a large volume of potassic magmas 280 km 3 during the quaternary chemical interactions between ascending magmas and the 7000 8000 m thick sedimentary carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been frequently corroborated by geochemical surveys in this paper we characterize the effect of carbonate assimilation on phase relationships at 200 mpa and 1150 1050 c by experimental petrology calcite and dolomite addition promotes the crystallization of ca rich pyroxene and mg rich olivine respectively and addition of both carbonates results in the desilication of the melt furthermore carbonate assimilation liberates a large quantity of co 2 rich fluid a comparison of experimental versus natural mineral glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different alban hills eruptions a maximum of 15 wt assimilation is suggested by some melt inclusion and clinopyroxene compositions however most of the natural data indicate assimilation of between 3 and 12 wt carbonate current high co 2 emissions in this area most likely indicate that such an assimilation process still occurs at depth we calculate that a magma intruding into the carbonate basement with a rate of 1 2 10 6 m 3 year estimated by geophysical studies and assimilating 3 12 wt of host rocks would release an amount of co 2 matching the current yearly emissions at the alban hills our results strongly suggest that current co 2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate hosted reservoir at 5 6 km depth with important consequences for the present day volcanic hazard evaluation in this densely populated and historical area

oxygen isotope evidence for the mixing of magmatic and meteoric waters during tin mineralization in the mole granite new south wales australia oxygen isotope measurements of quartz in the tin mineralized permian mole granite new south wales support a model of progressive mixing of magmatic water and surface derived water of meteoric origin in mineralizing hydrothermal circulation systems the magmatic water observed as multiphase fluid inclusions in hydrothermal quartz biotite orthoclase topaz bearing pegmatites had a high temperature 550 degrees c high salinity 55 75 wt and a delta 18 o smow value of about 8 7 per mil the initial magmatic delta 18 o smow value of the granite is estimated to be about 9 per mil the meteoric water observed as liquid rich fluid inclusions in quartz from late veins of quartz sphalerite galena had a low temperature 250 degrees c low salinity 3 5 wt and a delta 18 o smow value of 15 per mil permian meteoric water is expected to be light isotopically owing to a near polar 70 degrees palcolatitude for the new england fold belt quartz from cassiterite quartz chlorite sericite ores has a wide range of delta 18 o values from 2 8 to 6 7 per mil this is intermediate between the values for quartz deposited from magmatic and from meteoric waters the fluid inclusions in these samples have homogenization temperatures of about 300 degrees c and a wide range of salinities 25 35 wt the variation in isotopic composition observed for quartz is attributed to a fluctuating isotopic composition of the hydrothermal solutions resulting from variable degrees of mixing of magmatic and meteoric water cassiterite has a narrow range of delta 18 o 5 9 7 2ppm which suggests precipitation of cassiterite over a narrow range of mixing of the hydrothermal fluids three cassiterite quartz mineral pairs with textures indicating synchronous crystallization imply cassiterite water fractionations of 2 2 per mil at 300 degrees c and 4 1 per mil at 370 degrees c hydrogen isotope data are less systematic due to postcrystallization isotopic exchange of hydrous minerals and the presence of younger fluids in secondary fluid inclusions in quartz

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

genesis of the jianzhupo sb pb zn ag deposit and formation of an ore shoot in the wuxu ore field guangxi south china abstract the jianzhupo sb pb zn ag deposit in the southeastern dachang sn polymetallic ore belt guangxi region south china is the largest deposit in the wuxu district and is hosted by devonian limestone and mudstone the deposit mainly comprises a stage i jamesonite sphalerite ore shoot and stage ii jamesonite sphalerite calcite quartz jscq veins we use homogenization temperatures salinities and the h o isotopic compositions of fluid inclusions from the jianzhupo deposit to constrain the genesis of the deposit and determine factors that controlled the formation of the ore shoot fluid inclusions from both stages of mineralization contain large volumes of co2 and minor bitumen c6h6 and ch4 fluid inclusions from the ore shoot yield homogenization temperatures of 120 c 290 c mainly 250 c 270 c and salinities of 3 4 13 6 wt nacl equiv fluid inclusions from the stage ii mineralization yield homogenization temperatures of 150 c 350 c mainly 240 c 310 c and salinities of 1 4 12 0 wt nacl equiv ore forming fluids of the jianzhupo deposit yield 18oh2o and dv smow values of 4 9 9 9 and 78 to 111 respectively and plot close to the composition of magmatic water on the dv smow vs 18oh2o diagram co2 in the ore forming fluids was likely generated through deep skarnization beneath the wuxu ore field rather than from metamorphism thermal degradation or the oxidization of organic matter h o isotopic compositions of ore forming fluids that contain large volumes of co2 with minor bitumen and c6h6 indicate that they were derived from magmatic water that was mixed with basin brines ore forming fluids of the stage i ore shoot yield lower 18oh2o values 4 9 6 7 than those associated with the stage ii mineralization 7 5 9 9 moreover ore forming fluids of the ore shoot and the jscq veins yield strongly and weakly positive correlations between homogenization temperature and salinity respectively this difference suggests that rapid and large scale mixing between magmatic water and basin brines was the key factor that controlled the formation of the ore shoot

sedimentology of the coal bearing mist mountain formation line creek southern canadian cordillera relationships to coal quality abstract a detailed sedimentological investigation of the jurassic cretaceous mist mountain formation in the southern canadian cordillera was undertaken to determine what if any sedimentological factors control coal quality and seam geometry in the line creek area the mist mountain formation is divisible into two units based on abundance and lateral continuity of facies the lower unit consists of alternating laterally extensive coal seams and thick widespread channel sandstones interspersed with crevasse splay and flood plain facies sediments the lower unit was deposited in an interdeltaic coastal plain environment protected from marine incursion by the beach ridge dune sandstones of the underlying morrissey formation the upper unit of the mist mountain formation was deposited in a distal alluvial fluvial flood plain environment and has similar facies to the lower unit but coal seams and channel sandstones are less laterally continuous and thinner than in the lower unit channel sandstones decrease in number and thickness up section and are replaced by an increasing abundance of coal seams flood plain and crevasse splay facies sediments seam geometry and ash data indicate that clastic sedimentation had only limited influence on peat coal accumulation in the mist mountain formation while the geometry of the seams reflects the proximity of under and overlying channel sandstones neither abundance nor mineralogy of the coal ash reflects changes in surrounding clastic sediments the mist mountain formation peat mires were thus not obviously influenced by coeval fluvial activity characteristics of the lower unit suggest peat mires developed only during hiatus in clastic deposition whereas upper unit coals appear to have formed in at least partially domed mires contemporaneous with clastic sedimentation the vitrinite content of the coal increases up section at the expense of semifusinite possibly reflecting an increase in the proportion of arborescent vegetation in the mire with time and a lower susceptibility to fires

the anatomy of a carboniferous epithermal ore shoot at pajingo queensland setting zoning alteration and fluid conditions the paleozoic scott lode gold silver epithermal deposit situated at pajingo northeast queensland is hosted by feldspathic volcanolithic sandstones quartzose sandstones ignimbrites andesitic voltanits with interbedded block and ash deposits lapilli tuffs and andesitic to dioritic intrusive rocks the scott lode deposit contains 1 23 million metric tons of 9 9 g t gold and 38 9 g t silver there are six principal types of alteration assemblages which are zoned with respect to the main vein structure propylitic potassic adularia intermediate argillic silicic kaolinitic and ferroan carbonate overprinting textural relationships indicate that the propylitic type is earliest progressively followed by potassic adularia then intermediate argillic and finally silicic alteration auriferous veins are largely coeval with the silicic and intermediate argillic alteration types kaolinitc and ferroan carbonate occur as late stage alteration products postdating the precious metal mineralization principal ore and sulfide minerals include pyrite sphalerite galena chalcopyrite hessitc tennantite tetrahedrite argentitc petzite electrum and native gold gangue minerals in the veins are quartz illitc adularia calcite and locally kaolinitc the main stage quartz is zoned with respect to mineralogy mineralization styles metal distribution patterns and vein textres three major zones can be recognized zone i an upper precious metal moss chalcedonic crustiform colloform quartz zone zone ii intermediate precious base metal crystalline quartz coarse grained sulfide dominated crustiform colloform quartz zone and zone iiideep sparse base metal weakly banded crystalline comb quartz zone the ore interval occurs in zones i and ii with the transition to zone iii effectively defining the limit of mineralization economic mineralization at the scott lode deposit was laid down from dilute fluids 0 7 2 5 wt nac1 equiv with a very low concentration of co2 homogenization temperatures of 170 o to 315oc exhibit vertical variation with higher temperatures at greater depth the presence of coexisting liquid and gas rich inclusions in mineralized quartz together with adularia vein brecciation and pronounced crustiform colloform banding indicates hydrothermal boiling as the principal precipitation mechanism for gold and silver deposition thermodynamic modeling of adiabatic boiling of a fluid with an initial concentration of 2 to 5 ppb gold at 300oc indicates that such a fluid can deposit ores containing 10 ppm gold and 260 ppm silver at the temperature intervals recorded by the fluid inclusion work

high grade ore shoots at the martha epithermal vein system deseado massif argentina the interplay of tectonic hydrothermal and supergene processes in ore genesis abstract the complexity of high grade ore shoot formation is addressed through a detailed study of the martha mine epithermal deposit deseado massif patagonia argentina the mine was active from 2002 to 2012 producing over 21 million oz of silver from an intermediate sulfidation vein system hosted in a pyroclastic sequence erupted during upper jurassic times 40ar 39ar age 157 6 1 ma the martha deposit is composed of more than 15 different veins 8 of which show high grade ore shoots locally up to 45 000 g t ag veins are hosted in a sinistral transtensive horst structure delimited by two nw se trending first order veins up to 600 m long and 5 m thick inside this horst a series of e w trending veins up to 450 m long and 2 5 m thick developed as second order structures in response to growth and linkage of the two overlapping first order vein structures ore is characterized by a complex paragenetic sequence of ag as sb sulfosalts and cu pb zn sulfides with an adularia quartz illite gangue hydrothermal alteration is zoned outward and rarely extends for more than 15 m away from the vein walls five alteration zones were defined an adularia zone close to the veins an intermediate halo characterized by illite and illite smectite zones and a distal smectite zone additionally a late and supergene kaolinite zone can be found near the surface in close association with the mineralized structures high grade bonanza ore shoots are the result of the interplay of a series of structural hydrothermal mostly physicochemical and supergene processes the mineralization evolved through three main phases a main hydrothermal tectonically controlled phase a late tectonic hydrothermal phase and a post mineral supergene phase the main hydrothermal phase was the result of mineral deposition from low salinity 0 5 to 3 5 wt nacl eq near neutral to weakly alkaline chloride aqueous hydrothermal solutions with estimated temperatures ranging from 215 5 c to 316 5 c and isotopic composition suggesting high proportions of meteoric waters 18oh2o from 8 1 to 2 7 relatively constant fluid inclusion liquid to vapor ratios and a trend of decreasing th and 18oh2o with increasing time suggest that cooling and dilution were the main mechanisms controlling ore deposition these physicochemical conditions combined with an efficient network of structural conduits vein intersections jogs and step over zones were the first step in the construction of the high grade ore shoots that characterize the vein system 40ar 39ar dating in adularia crystals constrains the hydrothermal activity to the upper jurassic 156 5 0 9 ma afterwards a late tectonic hydrothermal phase occurred through the development of irregularly shaped bodies of massive fault breccias and foliated cataclasites related to tectonic reactivations of the vein system in synchronism with the waning stages of the hydrothermal system the interplay between deformation and fluid circulation resulted in mechanical and chemical remobilization of the previously deposited ag rich sulfosalts by lower temperature 138 c to 168 c and higher salinity fluids 7 7 and 9 9 wt nacl eq possibly reflecting a late magmatic input into the waning system this late tectonic hydrothermal phase strongly contributes to increase the grades in some veins and therefore is considered an essential process in order to build the highest grade portions of the ore shoots found at the mine finally a post mineral supergene phase defined a 20 m thick oxidized zone close to the surface followed by a 20 30 m thick secondary enrichment zone below it developed in response to the circulation of descending cold meteoric waters despite its small size and vertical extension the secondary enrichment level at martha mine constitutes an important economic factor for the mining operations as it helped to increase the silver grades in the shallower portion of the vein system the martha mine vein system constitutes an excellent example of how the interplay of hydrothermal processes controlling mineral deposition structural factors building up an efficient plumbing system tectonic ore remobilization and late supergene secondary enrichment processes are combined in order to build bonanza grade ore shoots in the epithermal environment

fluid inclusion study of the nannihu giant porphyry mo w deposit henan province china implications for the nature of porphyry ore fluid systems formed in a continental collision setting abstract the nannihu mo w deposit located in the henan province of china is a giant porphyry deposit formed in the qinling orogen during the jurassic continental collision between the north china and yangtze cratons mo w mineralization is associated with the nannihu porphyritic monzogranite occurring as numerous stockwork veinlets in the altered wallrocks and the causative porphyry both the porphyry stock and wallrocks underwent intense hydrothermal alteration ranging outwardly from potassic to phyllic alteration and to carbonation zones with increasing distance from the intrusion the hydrothermal ore forming process can be divided into four stages characterized by veinlets from early to late 1 quartz potassic feldspar molybdenite pyrite 2 quartz molybdenite veins containing minor pyrite and chalcopyrite 3 quartz polymetal sulfide and 4 quartz carbonate fluorite most of the ores are formed during stages 2 and 3 four types of fluid inclusions fis are distinguished in this study based on petrographic and microthermometric criteria i e pure co 2 nacl h 2 o co 2 h 2 o and daughter mineral bearing fluid inclusions all of the four types of fis can be observed in the hydrothermal quartz formed in stages 1 2 and 3 while the stage 4 minerals contain only nacl h 2 o fluid inclusions fluid inclusions of stage 1 are mainly homogenized between 350 and 460 c with salinities ranging from 5 7 to 17 9 wt nacl equiv the stage 2 fis yield homogeneous temperatures of 300 380 c and salinities of 3 5 16 9 wt nacl equiv fis of stage 3 are homogenized between 250 and 370 c with salinities of 1 8 14 3 and 28 6 39 1 wt nacl equiv fis of stage 4 are homogenized at temperatures of 115 to 265 c yielding salinities of 0 5 to 1 2 wt nacl equiv daughter minerals such as halite chalcopyrite and some unknown minerals are frequently present in stage 3 fis which probably represent a reducing and oversaturated fluid system resulting from fluid boiling the daughter mineral bearing fis coexist with vapor and liquid rich nacl h 2 o fis that have contrasting salinities these fis are homogenized in divergent ways at similar temperatures suggesting that fluid boiling took place in stages 2 and 3 the estimated pressures range from 70 to 270 mpa in stage 1 through 30 150 mpa in stage 2 to 30 85 mpa in stage 3 corresponding to a depth of no less than 3 km in other words the ore forming fluids are characterized by high temperature high salinity high f o 2 and high co 2 content and fluid boiling resulted in co 2 release f o 2 decrease and ore mineral precipitation we suggest that the co 2 rich fluid is a distinctive feature of porphyry systems developed in continental collision setting in transitional compressional to extensional regime contrasting to the co 2 poor nacl h 2 o fluids observed in volcanic arcs

trace elements of indium bearing sphalerite from tin polymetallic deposits in bolivia china and japan a femto second la icpms study abstract indium bearing tin polymetallic base metal deposits in japan toyoha ashio and akenobe china dulong and dachang and bolivia potosi huari huari bolivar and porco were studied using femto second laser ablation icpms fsla icpms and epma analyses for major and minor elements in sphalerite paying special attention to in concentrations sphalerite is a principal mineral in these tin polymetallic deposits and a broad range of in concentration is measured in the ores there are distinct differences in mode of occurrence of the sphalerite and the distribution of in the highest in concentration up to 18 wt occur as a zn in mineral within black sphalerite zones in an oscillatory zoned sphalerite from the huari huari deposits additionally jamesonite from the huari huari deposit also contains anomalous in values ranging from several hundreds to thousands g g sphalerite from the toyoha and the other bolivian deposits are characterized by oscillatory and chemical zoning whereas those from akenobe and the chinese deposits are represented by homogeneous distribution of in the 1000in zn values of sphalerite are in good agreement with those of the ore grade for each of the selected tin polymetallic deposits indicating that sphalerite is the principal host of in the in bearing sphalerite principally involves the combined coupled substitutions 2zn2 cu in3 3zn2 cu ag sn4 and 3zn2 2cu sn4 the first of these is apparent in sphalerite from huari huari and bolivar whereas the second is prominent in sphalerite from toyoha ashio potosi porco and dachang akenobe and dulong sphalerite features the dominant coupled substitution of 2zn2 cu or ag in3 owing to their poor sn content occasionally sub micron inclusions of minerals such as stannite and pb sb bearing sulfides can occur in sphalerite contributing to high cu sn and high ag contents respectively the observed correlations of each element in the in cu ag sn bearing sphalerite can be proposed as a fundamental reason for the indium enrichment related to sulfur rich oxidized magmatism in addition the ag content in sphalerite is considered a possible indicator of formation depth which ranges from plutonic to subvolcanic environments

silica and gold textures in bonanza ores of the sleeper deposit humboldt county nevada evidence for colloids and implications for epithermal ore forming processes

on the occurrence and wider implications of anomalously low δd fluids in quartz veins south cornwall england a chemical and hydrogen isotopic study has been carried out on quartz hosted fluid inclusions from three different quartz carbonate sulphide sulphate veins from southwest england two fluid types have been identified in these veins by fluid inclusion microthermometry 1 a low temperature 80 150 c saline 20 27 wt nacl cacl2 equiv nacl cacl2 brine and 2 a moderate temperature 200 c low salinity 0 5 wt nacl equiv fluid d values for the brines range from 39 to 103 and values for the dilute fluids are in the range 46 to 79 both fluid types have at least some values of d which are defined as anomalous i e cannot be directly related to either a low d source fluid or to modification of a source fluid by common physicochemical processes such as evaporation or boiling examination of these data in the given geological context suggest the anomalously low values are unlikely to be attributable to analytical artifacts or post entrapment changes of the fluid inclusions similarly fluid interaction with a suitable mineral or organic phase cannot adequately explain the data we conclude that an as yet unidentified process is responsible for producing low d fluids in southwest england and that this may be a common phenomenon in low temperature basinal environments

oxygen isotope compositions of iron oxides from high grade bif hosted iron ore deposits of the central hamersley province western australia constraints on the evolution of hydrothermal fluids the hamersley province of northwest western australia is one of the world s premier iron ore regions with high grade martite microplaty hematite iron ore deposits mostly hosted within banded iron formation bif sequences of the brockman iron formations of the hamersley group these high grade iron ores contain between 60 and 68 wt percent fe and formed by the multistage interaction of hydrothermal fluids with the host bif formation the oxygen isotope compositions of magnetite and hematite from bif hydrothermal alteration assemblages and high grade iron ore were analyzed from the mount tom price paraburdoo and channar iron ore deposits the 18o values of magnetite and hematite from hydrothermal alteration assemblages and high grade iron ore range from 9 0 to 2 9 per mil a depletion of 5 to 15 per mil relative to the host bif the 18o values are spatially controlled by faults within the deposits a response to higher fluid flux and larger influence on the isotopic compositions by the hydrothermal fluids the oxygen isotope composition of hydrothermal fluids 18ofluid indicates that the decrease in the 18o content of iron oxides was due to the interaction of both basinal brines and meteoric fluids with the original bif late stage talc bearing ore at the mount tom price deposit formed in the presence of a pulse of 18o enriched basinal brine indicating that hydrothermal fluids may have repeatedly interacted with the bifs during the paleoproterozoic

porphyry copper gold mineralization at yulong china promoted by decreasing redox potential during magnetite alteration the yulong porphyry cu au deposit occurs on the eastern margin of the tibetan plateau and is one of the largest porphyry cu au deposits in china containing more than 6 million tons of cu metal similar to other porphyry cu deposits in the world the yulong porphyry is highly oxidized sulfate is the dominant sulfur species in fluid inclusions hosted by magmatic quartz phenocrysts and no sulfide is observed indicating an oxygen fugacity above the sso buffer during magmatic processes the sulfur species changed from sulfate dominant during magmatic processes to sulfide dominant during the main mineralization processes with sulfate and sulfide mineral assemblages observed in fluid inclusions in mineralized quartz veinlets and only sulfides in the orebodies corresponding to a decrease in redox potential from the porphyry to the hydrothermal fluid magnetite crystallization was coincident with the onset of major sulfate reduction indicating that magnetite isolated trivalent iron reducing sulfate and consequently leading to the formation of porphyry cu au mineralization most porphyry cu au ore deposits are spatially associated with and genetically related to oxidized felsic magmas our results indicate that sulfate reduction promoted by magnetite crystallization is essential for the final precipitation of cu au bearing sulfides i e decreasing redox potential of the fluid is the key to and direct cause of ore formation in yulong initial high redox potential is a prerequisite for and may be an indirect indicator of most mineralization of this kind because it enables efficient transportation of cu au redox potential fluctuations can be well preserved in zircon a resistant accessory mineral commonly found in porphyries which might be developed as a handy and reliable exploration tool for porphyry cu deposits associated with magnetite

fluid inclusion geochemistry of high grade vein hosted gold ore at the pamour mine porcupine camp ontario this study was undertaken to characterize fluid inclusions associated with high grade vein hosted gold at the pamour mine in the porcupine camp of ontario and to compare them with fluid inclusions in quartz veins associated with wall rock hosted gold which is much more common the pamour mine contains two principal types of orebodies metasediment hosted fracture zones and larger metavolcanic or metasediment hosted quartz carbonate veins gold in the veins is distributed erratically attains very high grades locally and increases in grade at higher levels zoned alteration around the veins is dominated by addition of k 2 o co 2 as s and cao and depletion of na 2 o k 2 o co 2 and s are concentrated in the hanging wall and the intensity of co 2 and h super metasomatism increases upward in the mine roughly parallel to the trend seen in gold values gold was introduced along with sphalerite galena calcite chlorite and chalcopyrite late in the paragenetic history after brittle deformation of earlier vein hosted quartz tourmaline feldspar and pyrite sphalerite that is directly associated with high grade gold contains two types of primary inclusions a co 2 ch 4 fluid 20 45 mole ch 4 and an h 2 o rich liquid with a carbonaceous phase co 2 ch 4 as well as muscovite and graphite daughter minerals aqueous phase salinity estimates range from 2 to 9 equiv wt percent nacl and sem analyses of evaporitic residues of thermally decrepitated inclusions contain nacl and cacl 2 with lesser amounts of kcl mgcl 2 s zn and fe these two inclusion types appear to represent immiscible fluids trapped along the solvus in the h 2 o co 2 ch 4 salt system at temperatures of 325 degrees or 25 degrees c and pressures of 1 to 2 kbars these fluids are similar to those observed in vein quartz at the mcintyre and hollinger deposits where most gold is hosted by wall rocks except that co 2 immiscibility appears to have been more widespread at pamour the separation of immiscible fluids of the type identified in this study would increase the f sub o 2 and ph of the residual fluid owing to the partitioning of h 2 s ch 4 and co 2 into the carbonaceous phase the net effect of these changes would be to decrease the solubility of bisulfide complexed gold suggesting that co 2 immiscibility is an important contributor to gold deposition within veins where wall rock interaction is limited it is not clear whether all vein hosted gold formed from such unmixing or only the higher grade ore shoots

colloidal transport of gold and silica in epithermal precious metal systems evidence from the sleeper deposit nevada bonanza vein gold ore from the sleeper deposit nevada was deposited at a depth of less than 500 m and exhibits a characteristic texture of alternating colloform bands of fine grained quartz and bands of opaline silica containing abundant electrum textural evidence indicates that the quartz bands recrystallized from a gel like amorphous precursor whereas the gold rich bands were deposited originally as amorphous precipitate formed by the coagulation of colloidal silica and gold particles gold and silica precipitated initially as colloidal particles at deeper levels in the hydrothermal system and were mechanically transported upward by the hydraulic action of the ore forming fluids coagulation of the colloidal particles may have been caused by solution cooling or boiling and catalyzed by hydrated polycationic al 3 aqueous species transport of gold as colloidal particles in epithermal systems indicates that at least in some instances higher gold content is possible than in true solution a gold enriched ore fluid appears necessary to explain the origin of the bonanza grade ore at the sleeper mine and the colloidal gold transport process locally might have played a role in the genesis of the more common disseminated epithermal precious metal deposits

emplacement depth and carbon dioxide rich fluid inclusions in intrusion related gold deposits phanerozoic intrusion related gold deposits have many consistent characteristics such as a spatial temporal and geochemical association with moderately reduced predominantly ilmenite series i type intrusions the deposits exhibit a range of characteristics that vary over a wide range of emplacement depths 7 km deposits in shallow crustal settings 5 km have characteristics of mesothermal environments and are hosted by plutons containing sheeted veins greissen and disseminated gold fluid characteristics also vary with depth deposits in shallow environments contain high temperature 350 c immiscible brine 30 wt nacl equiv and low salinity 5 wt nacl equiv vapor that commonly contains carbon dioxide deposits in deeper environments contain abundant low salinity carbon dioxide rich aqueous fluids 10 wt nacl equiv that in some deposits are postdated by moderate to high salinity brines 10 40 wt nacl equiv these contrasting fluid types are interpreted to be magmatic in origin and are the result of the complex interplay between exsolution of different volatiles carbon dioxide water and chlorine from felsic magmas emplaced at different crustal levels experimental studies have shown that carbon dioxide will exsolve from felsic magmas at much higher pressures than water and chlorine due to its lower solubility in the melt thus deposits formed from felsic magmas in deeper environments will contain abundant carbon dioxide rich fluids subsequent fluids released from the magma are likely to be water rich and more saline felsic magmas in shallow environments will contain lower concentrations of carbon dioxide that will partition into the vapor phase during phase separation between brine and vapor

an oxygen hydrogen sulfur and carbon isotope study of carbonate replacement skarn tin deposits of the dachang tin field china the dachang tin field located in guangxi province of southern china is one of the largest in the world it comprises the changpo bali and longtaoshan carbonate replacement tin deposits and the lamo cu zn skarn deposit these deposits are hosted by devonian carbonate rich sedimentary rocks which have been metamorphosed to calc silicate skarn and marble near the contact of the longxianggei granite calculated delta 18 o sub h 2 o values of the hydrothermal fluids in equilibrium with quartz cassiterite and calcite are 10 6 and 11 6 9 1 to 10 2 and 7 5 to 9 8 per mil respectively measured delta d values of fluid inclusion waters in cassiterite and calcite are 115 and 120 and 73 to 93 per mil respectively the decrease in the calculated delta 18 o sub h 2 o values from 11 6 to 7 5 per mil is attributed to increase in the co 2 content of the hydrothermal fluids the low delta d values of fluid inclusion waters in cassiterite may be the result of decreasing ch 4 co 2 as the originally magmatic fluid migrated from reducing conditions in carbonaceous black shale to oxidizing conditions in pure limestone oxygen and hydrogen isotope data indicate that the hydrothermal fluid was derived from the longxianggei granite variations in delta 13 c and delta 18 o values of calcite in orebodies altered limestone and marble are due to continuous isotopic exchange reaction between magmatic fluid and carbonate rocks at variable water to rock ratios between 300 degrees to 600 degrees c sulfur isotope data indicate that host rocks controlled the variations in sulfur isotope compositions of sulfide minerals in different deposits of the tin field with significant contribution of sulfur from magmatic fluids

internal vein texture and vein evolution of the epithermal shila paula district southern peru the epithermal shila paula au ag district is characterized by numerous veins hosted in tertiary volcanic rocks of the western cordillera southern peru field studies of the ore bodies reveal a systematic association of a main e w vein with secondary n55 60 w veins two directions that are also reflected by the orientation of fluid inclusion planes in quartz crystals of the host rock in areas where this pattern is not recognized such as the apacheta sector vein emplacement seems to have been guided by regional n40 e and n40 w fractures two main vein filling stages are identified stage 1 is a quartz adularia pyrite galena sphalerite chalcopyrite electrum mn silicate carbonate assemblage that fills the main e w veins stage 2 which contains most of the precious metal mineralization is divided into pre bonanza and bonanza substages the pre bonanza substage consists of a quartz adularia carbonate assemblage that is observed within the secondary n45 60 w veins in veinlets that cut the stage 1 assemblage and in final open space fillings the two latter structures are finally filled by the bonanza substage characterized by a fe poor sphalerite chalcopyrite pyrite galena tennantite tetrahedrite polybasite pearceite electrum assemblage the ore in the main veins is systematically brecciated whereas the ore in the secondary veins and geodes is characteristic of open space crystallization microthermometric measurements on sphalerite from both stages and on quartz and calcite from stage 2 indicate a salinity range of 0 to 15 5 wt nacl equivalent and homogenization temperatures bracketed between 200 and 330 c secondary co2 n2 and h2s bearing fluid inclusions are also identified the age of vein emplacement based on 40ar 39ar ages obtained on adularia of different veins is estimated at around 11 ma with some overlap between adularia of stage 1 11 4 0 4 ma and of stage 2 10 8 0 3 ma a three phase tectonic model has been constructed to explain the vein formation phase 1 corresponds to the assumed development of e w sinistral shear zones and associated n60 w cleavages under the effects of a ne sw shortening direction that is recognized at andean scale these structures contain the stage 1 ore assemblage that was brecciated during ongoing deformation phase 2 is a reactivation of earlier structures under a nw se shortening direction that allowed the reopening of the preexisting schistosity and the formation of scarce n50 e striking s2 cleavage planes filled by the stage 2 pre bonanza minerals phase 3 coincides with the bonanza ore emplacement in the secondary n45 60 w veins and also in open space in the core of the main e w veins our combined tectonic textural mineralogical fluid inclusion and geochronological study presents a complete model of vein formation in which the reactivation of previously formed tectonic structures plays a significant role in ore formation

late mesozoic metallogeny and intracontinental magmatism southern great xing an range northeastern china abstract mineral deposits are typically tied to plate margin processes such as accretion or rifting however some major deposits occur in plate interiors e g deposits in the southern great xing an range lacking a clear association with the supercontinent cycle intrusive activity in the southern great xing an range peaked in late mesozoic i e 155 120 ma simultaneously with large scale mineralization in this area in addition the late mesozoic granitoids show initial nd and hf isotopic signatures of depleted mantle possibly newly underplated basaltic materials with variable contamination from older crust and with model ages younger than 1 0 ga fluid inclusion waters extracted from ore minerals pyrite galena sphalerite and chalcopyrite associated with the late mesozoic mineralization have elevated 3he 4he ratios indicating a contribution of mantle derived helium stable isotopes of fluid inclusion waters hydrogen and oxygen and of sulfide minerals sulfur confirm a magmatic source for these components lead isotope data of ore minerals indicate a significant mantle lead contribution from the newly underplated material thus the southern great xing an range is best described as a typical late mesozoic intracontinental metallogenic belt related to magmatism with a significant mantle contribution the magmatism and mineralization took place in a setting of lithospheric extension and resulted because of the break off of the southerly dipping mongol okhotsk oceanic slab at depth during closure of the mongol okhotsk ocean which also restricted the westward movement of the paleo pacific oceanic plate this interplay between plate tectonic events and mantle dynamics provides a good example of the evolution of magmatism and hydrothermal activity in intracontinental settings