the fazenda nova gold deposit goias magmatic arc late neoproterozoic intrusion related auriferous mineralization controlled by intracontinental strike slip faulting abstract the fazenda nova gold deposit with an inferred resource of 650 koz at 4 0 g t au cut off grade of 2 0 g t au consists of stockwork au as mineralization hosted in late neoproterozoic dikes in the goias magmatic arc central brazil the dikes which host the mineralization consist of a set of post collisional ilmenite bearing gabbros dolerites trachyandesite porphyry trachyandesite and trachyte porphyry known as the bacil ndia intrusions u pb dating indicates at least two pulses of dike intrusions the first pulse consists of small volume dikes with ages varying from 593 5 to 590 5 ma and the second pulse comprises a large volume of dikes with ages from 574 7 to 572 5 ma three veining or hydrothermal alteration stages are identified in the fazenda nova deposit the first is the early or main stage which comprises the pervasive biotitization of mafic minerals and a stockwork of quartz associated with a disseminated sulfide assemblage of arsenopyrite pyrrhotite stibnite in addition to hydrothermal siderite scheelite rutile and apatite the most common sulfide in this stage is a fine grained acicular arsenopyrite hosting inclusions of gold galena and pyrite grains the temperature estimated for acicular arsenopyrite pyrrhotite and gold is 340 c based on the arsenopyrite geothermometry the intermediate stage is represented by a stockwork of calcite quartz veins associated with hydrothermal sericite chlorite tourmaline epidote and titanite and a sulfide assemblage of pyrrhotite arsenopyrite pyrite the arsenopyrite at this stage displays a tabular texture with no inclusions of sulfides or gold the crystallization temperature of the tabular arsenopyrite pyrite was estimated to be 305 c the c o isotope data from the calcite veins of the second stage provided 13c values ranging from 9 68 to 11 57 and 18o values range from 12 87 to 13 84 these values are equivalent to those of hydrothermal mantle magmatic carbonates the late stage is represented by veining and brecciation infilled by monotonous calcite ankerite with cockade and colloform vein textures and no gold mineralization the dikes and gold mineralization present a strong relationship with the crustal scale strike slip bacil ndia fault this is a second order crustal scale fault that branches out of the major crustal scale moipora novo brazil shear zone mnbsz along a nnw direction the bacil ndia fault played an important role in channeling melts and mineralizing hydrothermal fluids to the upper crust the major activity of this fault occurred at 572 ma with the emplacement of the second pulse of dikes and most likely the development of hydrothermal stages in the fazenda nova deposit the collectively evidence allows fazenda nova to be classified as an epizonal reduced intrusion related deposit following that i the mineralization developed in a post collisional tectonic setting above previously metasomatized subcontinental lithospheric mantle ii the dikes crystallized from metaluminous magmas with a primary oxidation state which formed the ilmenite series intrusions iii the ore deposition had relatively high temperatures 340 300 c and vein textures formed only at shallow depths

a synmetamorphic lateral fluid flow model for gold mineralization in the archean southern kalgoorlie and norseman terranes western australia gold deposits are widely distributed in the archean southern kalgoorlie and norseman greenstone terranes eastern goldfields superterrane western australia which have collectively produced more than 1 850 metric tons t of gold gold deposits occur in a variety of host rocks and structural settings but all are associated with quartz veins and or shear zones that formed during the latest stages of regional compression available data indicate a similar h 2 o co 2 ch 4 ore fluid at each deposit alteration assemblages vary with metamorphic grade in a manner which indicates that late tectonic regional metamorphic gradients were still in place when gold was deposited from hydrothermal fluids these late tectonic thermal gradients were related to differential uplift of deep hot crust at the margin of the greenstone belt accompanied by intrusion of voluminous monzogranite magma at this time the western margin of the greenstone belt was a zone of high heat flow as were intrusive centers in the northern part of the southern kalgoorlie terrane these spatial and temporal relationships in combination with the apparent absence of a viable local source for the ore fluid at most deposits suggest that gold was deposited from a small number of large synmetamorphic hydrothermal systems published thermal models predict up temperature lateral fluid flow toward zones of high heat flow under these circumstances a model involving up temperature lateral flow of metamorphic fluids overcomes some of the problems associated with deeply sourced and conventional metamorphic models for the ore fluids and is consistent with most of the features of gold deposits in the southern kalgoorlie and norseman terranes potassium metasomatism and radiogenic isotope signatures associated with gold mineralization are ascribed to a metamorphic fluid that was modified by exchange with biotite bearing felsic rocks granitoids felsic volcanic and volcaniclastic rocks in the course of lateral flow toward zones of high heat flow

gold graphite association in granulite terrains implications for ore genesis abstract the gold occurrences of sri lanka are closely associated with the graphite deposits and are genetically related the quartz graphite margins of the vein graphite are shown to be metal accumulating the movement of co 2 rich fluids formation of graphite and the concentration of au are closely related whereas the co 2 rich fluids may well be the carbon carriers in the formation of graphite the original source of co 2 is still debated hydrothermal solutions when in contact with the graphite tend to activate the carbon thereby producing sites for the enrichment of gold the genetic link between the graphite veins and gold deposition has useful implications in the investigation of ore genesis in high grade metamorphic terrains and the exploration for gold

lithologic succession in the path fork coal bed breathitt formation middle pennsylvanian southeastern kentucky abstract the path fork coal bed breathitt formation middle pennsylvanian westphalian b on the pine mountain thrust sheet in southeastern kentucky and adjacent portions of virginia exhibits a lithologic succession which is traceable for about 25 km lateral continuity of lithotypes within the bed can be demonstrated using organic petrography palynology and ash geochemistry the lithologic continuity is a consequence of the initial levelling of the pre peat topography and the interaction of the peat with growing anticlines and synclines

carbonatization of oceanic crust by the seafloor hydrothermal activity and its significance as a co2 sink in the early archean abstract early archean 3 46 ga hydrothermally altered basaltic rocks exposed near marble bar eastern pilbara craton have been studied in order to reveal geological and geochemical natures of seafloor hydrothermal carbonatization and to estimate the co2 flux sunk into the altered oceanic crust by the carbonatization the basaltic rocks are divided into basalt and dolerite and the basalt is further subdivided into type i having original igneous rock textures and type ii lacking these textures due to strong hydrothermal alteration primary clinopyroxene phenocrysts are preserved in some part of the dolerite samples and the alteration mineral assemblage of dolerite chlorite epidote albite quartz actinolite indicates that the alteration condition was typical greenschist facies in other samples all primary minerals were completely replaced by secondary minerals and the alteration mineral assemblage of the type i and type ii basalts chlorite k mica quartz carbonate minerals albite is characterized by the presence of k mica and carbonate minerals and the absence of ca al silicate minerals such as epidote and actinolite suggesting the alteration condition of high co2 fugacity the difference of the alteration mineral assemblages between basalt and dolerite is probably attributed to the difference of water rock ratio that in turn depends on their porosity carbonate minerals in the carbonatized basalt include calcite ankerite and siderite but calcite is quite dominant the 13c values of the carbonate minerals are 0 3 1 2 and mostly within the range of marine carbonate indicating that the carbonate minerals were formed by seafloor hydrothermal alteration and that carbonate carbon in the altered basalt was derived from seawater whole rock chemical composition of the basaltic rocks is essentially similar to that of modern mid ocean ridge basalt morb except for highly mobile elements such as k2o rb sr and ba compared to the least altered dolerite all altered basalt samples are enriched in k2o rb and ba and are depleted in na2o reflecting the presence of k mica replacing primary plagioclase in addition noticeable co2 enrichment is recognized in the basalt due to the ubiquitous presence of carbonate minerals but there was essentially neither gain nor loss of cao this suggests that the co2 in the hydrothermal fluid seawater was trapped by using ca originally contained in the basalt the cao co2 ratios of the basalt are generally the same as that of pure calcite indicating that ca in the basalt was almost completely converted to calcite during the carbonatization although mg and fe were mainly redistributed into noncarbonate minerals such as chlorite the carbon flux into the early archean oceanic crust by the seafloor hydrothermal carbonatization is estimated to be 3 8 1013 mol yr based on the average carbon content of altered oceanic crust of 1 4 10 3 mol g the alteration depth of 500 m and the spreading rate of 1 8 1011 cm2 yr this flux is equivalent to or greater than the present day total carbon flux it is most likely that the seafloor hydrothermal carbonatization played an important role as a sink of atmospheric and oceanic co2 in the early archean

composition and source of fluids in high temperature graphite bearing granitoids associated with granulites examples from the southern marginal zone limpopo complex south africa abstract p t conditions fluid regime and carbon isotope composition of graphite and fluid inclusions from garnet sillimanite bearing leucocratic tonalites trondhjemites and granites associated with orthopyroxene bearing granulite metapelites in the southern marginal zone smz of the limpopo complex south africa are presented in the paper re integrated compositions of perthitic alkali feldspars and antiperthitic plagioclase as well as p t and t xco2 phase equilibria modeling using perple x software indicate that the granitoids began to crystallize at temperatures of 900 940 c and pressures of 7 9 kbar and were equilibrated with a fluid phase with xco2 0 5 0 6 as is recorded in dense fluid inclusions in quartz a small fraction of a saline fluid accumulated during cooling only average 13cpdb values for graphite 6 52 to 8 65 and fluid inclusions 2 50 to 5 58 from the granitoids differ substantially from the values which have been obtained in previous studies for graphite from the surrounding smz metapelites isotope data thus indicate that fluids associated with the granitoid magmas of the smz originated from a source unrelated to the host metapelites in terms of the heavy isotope signatures of carbon the granitoids might carry fluids which have been produced during devolatilization of mafic rocks amphibolites interlayered with hydrothermal carbonate veins in the adjacent granite greenstone successions of the kaapvaal craton that have been buried underneath the smz granulites during their exhumation the cratonic rock could serve as a source for the trondhjemite magmas intruding the smz granulites in this scenario the studied granitoids crystallized from these magmas variously contaminated by metapelitic material graphite precipitated via reduction of co2 rich fluid as the result of dissolution of pyrrhotite rich metapelites in the magmas

regional metamorphic controls on alteration associated with gold mineralization in the eastern goldfields province western australia implications for the timing and origin of archean lode gold deposits alteration assemblages associated with archean epigenetic gold mineralization in the menzies kambalda area of the yilgarn craton western australia vary systematically with regional metamorphic grade up to and including upper amphibolite facies rocks k metasomatism is recorded by the presence of muscovite biotite and k feldspar at progressively higher metamorphic grades high metamorphic grades are commonly developed in broad thermal aureoles around fate syntectonic granitic intrusions metamorphic recrystallization of alteration assemblages is common in the thermal aureoles these relations suggest broad contemporaneity among granitoid intrusion regional metamorphism and mineralization during the final stages of the tectonic evolution of the granite greenstone terrain late syntectonic granitoids acted as centers of heat and fluid flux in large scale synmetamorphic hydrothermal systems that deposited gold possibly from modified mantle derived fluids

the multiple sulfur isotope architecture of the golden mile and mount charlotte deposits western australia the golden mile and mount charlotte deposits in the kalgoorlie terrane western australia display three main mineralization styles fimiston comprised of interconnected shear zones associated with ankerite pyrite hematite magnetite gold telluride alteration oroya made up of breccia bodies with v muscovite ankerite pyrite pyrrhotite gold telluride alteration and mount charlotte which consists of vein arrays with symmetrical ankerite sericite albite pyrite pyrrhotite gold alteration pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes the 34s 33s and 36s analyses on pyrite grains from the different mineralization styles including oxidized and reduced sulfide oxide assemblages reveal 1 a large variation in 34s from 12 6 to 23 5 and 2 a previously unrecognized occurrence of anomalous 33s and 36s signatures from 1 0 to 1 1 and from 2 3 to 0 9 respectively it is argued that the mineralizing fluids that formed the golden mile and mount charlotte deposits record mixing among three components mantle sulfur oxidized seawater sulfur e g so4 and reduced elemental sulfur e g s8 petrographic evidence in conjunction with 33s and 36s data suggest that mif s was acquired during the deposition of shales and basalts present in the kalgoorlie terrane and later mixed with mantle derived sulfur during the mineralization events the negative 34s values that predominate in fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore forming process as reflected by the presence of hematite pyrite magnetite gold assemblages conversely the positive 34s values that dominate in the mt charlotte and oroya mineralization styles reflect a reducing environment as reflected by the presence of pyrite pyrrhotite gold assemblages

palynologic and petrographic intervals in the upper pennsylvanian mcleansboro group western kentucky abstract the mcleansboro group formerly the sturgis formation in the western kentucky coal field spans the upper desmoinesian westphalian d and the missourian and virgilian series stephanian extensive drilling has demonstrated the lateral continuity of major and minor beds in the group making it possible to study vertical and lateral changes in palynology and petrology significant features of the mcleansboro group are the marine zones over most of the coals and paleochannels which are the only disruptions to the continuity of other lithologies the desmoinesian baker no 13 and wheatcroft no 13a coal beds were included in the study but the primary emphasis is on the missourian and virgilian coals patoka formation lower missourian coals are dominated by tree fern spores with lesser amounts of sphenopsids ferns and cordaites spores this is in marked contrast to the arborescent lycopod dominated desmoinesian coals only the no 15 coal bed exceeds 80 vitrinite the vitrinite content of the no 16 coal bed is less than 72 the lowest of any western kentucky humic coal the bond formation upper missourian represents a distinct floristic interval with a greater diversity of plant groups than in the patoka formation herbaceous lycopod spores which are relatively minor contributors to the patoka coals are common in the bond formation the coals generally exceed 80 vitrinite the mattoon formation virgillian coals have a variety of palynomorph assemblages the low sulfur geiger lake coal bed is dominated by tree fern spores with important contributions from other ferns and sphenopsids similar to the underlying tree fern interval vitrinite contents are less than 80 the uppermost mattoon coals are dominated by tree ferns and are notable in being the only coals more than 1 m thick in the stephanian portion of the section with the top coal being 4 3 m thick the uppermost coals generally contain more than 80 vitrinite the permian mauzy formation overlies the mcleansboro group the palynologic petrographic intervals appear to represent fluctuating dry low vitrinite and wet intervals within the stephanian which was itself drier than the westphalian d

structural setting and geochemistry of archaean i type granites in the bardoc coolgardie area of the norseman wiluna belt western australia abstract regional structures in the bardoc coolgardie area of the archaean norseman wiluna greenstone belt in western australia developed during early large scale thrusting followed by a transpressional regime characterized by enewsw shortening and large scale sinistral strike slip faults structural relationships between granites and greenstone successions indicate emplacement of granitic rocks throughout this deformation history emplacement mechanisms include solid or liquid state diapirism forceful dilation of country rocks and passive stoping i type granites are common and include early and late tectonic intrusions the widespread occurrence of i type granodiorite and monzogranite probably derived by partial melting of lower continental crust or subducted oceanic crust suggests a continental margin setting for the belt alkalic quartz diorite occurs as rounded enclaves in granodiorite and is enriched in ba rb sr ce la p and f which suggests a mantle derived volatile component these quartz diorite melts may have formed by partial melting of metasomatized mantle or alternatively mantle degassing may have lowered solidus temperatures in the source region and thus induced melting emplacement of hot volatilerich quartz diorite melts into the lower crust may have lowered solidus temperatures in the source rocks for granodiorite and monzogranite recent models for archaean gold mineralization suggest that auriferous fluids contained co 2 derived from lower crustal or mantle sources in the bardoc coolgardie area co 2 may have been flushed out during partial melting of the lower continental crust however the origin of the gold in the mineralizing fluids requires some other explanation because gold mineralization is generally a late stage event and took place over a considerably shorter time interval than the formation and emplacement of i type granites

isotope c and o composition of auriferous quartz carbonate veins central lode system gadag gold field dharwar craton india implications to source of ore fluids abstract carbon 13 c pdb and oxygen 18 o smow isotopic compositions of auriferous quartz carbonate veins qcvs of gold deposits from sangli kabuliyatkatti nagavi nabapur and mysore mining areas developed on the central lode system of the gadag gold field ggf in the neoarchaean gadag schist belt of the dharwar craton southern india have been examined for the first time to understand the origin of the mineralising fluids in majority of the samples 46 out of 49 13 c pdb of carbonates of the qcvs fall in the range from 2 2 to 9 7 and the 18 o values range from 12 0 to 30 5 smow the calculated fluid 13 c c compositions for these deposits range from 2 1 to 9 6 and 18 o h 2 o from 6 8 to 25 9 respectively carbonate 13 c and fluid 13 c c compositions of the carbonates of the qcvs of the ggf are not only distinct from the carbon isotope range of marine carbonates or meta sedimentary carbonates of the chitradurga schist belt but are consistent with c isotope values of magmatic 5 3 burrows et al 1986 and or mantle 6 2 ohmoto 1986 carbonates as dissolution decarbonation reactions during metamorphism of pre existing carbonate carbonated rocks produce co 2 with 13 c values similar to or more enriched than parent rock the carbonate or fluid 13 c ratios of the qcvs which fall in the compositional range of mantle magmatic derived co 2 or carbonates obtained in this work cannot be the result of metamorphism the present study corroborates our previous reports from ajjanahalli and g r halli gold deposits sarangi et al 2012 occurring in the vicinity of the southern extension of the same crustal scale shear zone on which all the ggf deposits are located the age of gold mineralisation in this area has been reported to be 2522 6 ma by sarma et al 2011 chardon et al 2011 have proposed large scale remobilization of the older gneissic basement as well as emplacement of juvenile granites between 2559 ma and 2507 ma close to the crustal scale shear zone along the eastern margin of the chitradurga schist belt based on these observations and our isotope studies it is proposed that gold mineralising fluids were derived from mantle juvenile magmatic melts and were channelled through crustal scale shear zones to give rise to the gold deposits in the ggf

geochemistry of precambrian carbonates i archean hydrothermal systems abstract carbonate rocks from the superior and slave provinces of canada kaapvaal craton of south africa and the pilbara block of australia considered of hydrothermal origin from field criteria have been characterized mineralogically isotopically sr o c and chemically major and trace elements in agreement with previous studies the bulk chemical composition suggests that the carbonate rocks originated by massive carbonatization silicification and k na metasomatism of intermediate to ultramafic silicate precursors the carbonate component itself defines two partially overlapping populations the ferroan dolomite breunnerite assemblage is confined mostly to shear zones conduits and stockworks while the calcite ferroan dolomite ankerite siderite mineral assemblage represents a wider regional halo this dichotomy may result from a multistory not necessarily coeval plumbing system of the volcanosedimentary piles with the regional halo population being a product of shallow circulation cells while the conduit assemblage probably formed from deeper focussed flows trace element chemistry of carbonates is consistent with their precipitation from relatively low salinity solutions 2 sea water and with derivation of solutes from the contemporaneous volcanosedimentary piles 87 sr 86 sr 0 7020 0 0008 the hydrothermal waters were derived either from metamorphic dewatering at the base of the piles or from a magmatic source with 18o of about 6 7 smow in contrast carbon dioxide in the regional and the conduit assemblages had dissimilar principal sources in the former it was derived from exogenic sources decarbonation of marine carbonates and thermal decomposition and oxidation of organic matter while in the latter the co2 was of mantle origin 13c of 2 to 10 and 4 2 pdb respectively

giant quartz vein systems in accretionary orogenic belts the evidence for a metamorphic fluid origin from δ 15 n and δ 13 c studies abstract nitrogen isotope compositions of hydrothermal micas in giant structurally hosted quartz vein systems place constraints on the origin of the hydrothermal fluids the vein systems are from neoarchean terranes in the superior province of canada and the norseman terrane western australia the four quartz vein systems studied in different terranes formed at metamorphic grades ranging from lower greenschist to lower amphibolite facies coevally with metamorphism of the host terrane nitrogen resides predominantly as nh 4 in hydrothermal mica for lower to upper greenschist facies quartz veins n contents and 15 n values of micas are between 40 and 200 ppm and 15 and 21 respectively whereas in quartz veins formed at the greenschist to amphibolite transition and lower amphibolite facies micas have n contents of 20 70 ppm and 15 n of 11 24 in contrast micas and k feldspars from granitoids in the neoarchean abitibi and red lake greenstone belts are characterized by systematically lower 15 n of 5 to 5 and generally lower n contents of 20 50 ppm comparable to other granitoids carbon and oxygen isotope compositions of hydrothermal ferroan dolomite and calcite show systematic depletions with increasing metamorphic grade the mean values range from 2 2 to 3 7 for 13 c and 13 8 to 12 3 for 18 o in veins formed at lower to upper greenschist facies but from 5 8 to 7 1 for 13 c and 11 4 to 9 8 for 18 o at higher metamorphic grades nitrogen isotope compositions rule out mantle 15 n mean 5 magmatic 15 n 5 to 15 n mean 4 4 2 0 for the quartz veins accordingly the results are consistent with fluids derived from metamorphic dehydration of oceanic crust and sediments within accretionary orogenic belts

molecular transformation and degradation of refractory dissolved organic matter in the atlantic and southern ocean more than 90 of the global ocean dissolved organic carbon doc is refractory has an average age of 4000 6000 years and a lifespan from months to millennia the fraction of dissolved organic matter dom that is resistant to degradation is a long term buffer in the global carbon cycle but its chemical composition structure and biochemical formation and degradation mechanisms are still unresolved we have compiled the most comprehensive molecular dataset of 197 fourier transform ion cyclotron resonance mass spectrometry ft icr ms analyses from solid phase extracted marine dom covering two major oceans the atlantic sector of the southern ocean and the east atlantic ocean ranging from 50 n to 70 s molecular trends and radiocarbon dating of 34 dom samples comprising 14c values from 229 to 495 were combined to model an integrated degradation rate for bulk doc resulting in a predicted age of 24 ka for the most persistent dom fraction first order kinetic degradation rates for 1557 mass peaks indicate that numerous dom molecules cycle on timescales much longer than the turnover of the bulk doc pool estimated residence times of up to 100 ka and the range of validity of radiocarbon dating changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks the combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the dom pool in our dataset a group of 361 molecular formulae represented the most stable composition in the oceanic environment island of stability these most persistent compounds encompass only a narrow range of the molecular elemental ratios h c average of 1 17 0 13 and o c average of 0 52 0 10 and molecular masses 360 28 and 497 51 da in the weddell sea doc concentrations in the surface waters were low 46 3 3 3 m while the organic radiocarbon was significantly more depleted than that of the east atlantic representing average surface water dom ages of 4920 180 a these results are in accordance with a highly degraded dom in the weddell sea surface water as also shown by the molecular degradation index ideg obtained from ft icr ms data further we identified 339 molecular formulae which probably contribute to an increased doc concentration in the southern ocean and potentially reflect an accumulation or enhanced sequestration of refractory doc in the weddell sea these results will contribute to a better understanding of the persistent nature of marine dom and its role as an oceanic carbon buffer in a changing climate

fluid inclusion and stable isotope o h c constraints on the genesis of the pedra branca gold deposit troia massif borborema province ne brazil an example of hypozonal orogenic gold mineralization abstract at the archean paleoproterozoic troia massif ne brazil two major paleoproterozoic greenstone belts are documented algodoes and serra das pipocas they share similar lithostratigraphic characteristics with other 2 2 2 1 ga greenstone belts of the surrounding cratonic domains e g guiana shield and west africa craton gold mineralization in the serra das pipocas greenstone belt is associated with a regional ne trending shear zone in the mineralized area the pedra branca gold deposit the main gold mineralization is found in association with quartz veins calc silicate alteration e g diopside k feldspar amphibole titanite biotite pyrite albite magnetite carbonates and albitization pyrrhotite is commonly found as inclusions in pyrite and late magnetite replaces pyrite suggesting progressive oxidation of the ore forming fluid free milling gold commonly precipitates at the late stages of alteration in close association with magnetite and tellurides the main tellurides found are hessite altaite sylvanite calaverite and tellurobismuthite two fluid inclusion assemblages were identified from mineralized quartz veins assemblage 1 is characterized by pseudo secondary trails that show the coexistence of co2 rich and low salinity 0 8 wt nacl equiv co2 h2o nacl and h2o nacl inclusions suggesting formation during phase separation fluid immiscibility assemblage 2 is represented by late secondary low temperature th

b_na rich palaeoproterozoic aravalli metasediments of evaporitic association nw india a new repository of gold mineralization we report field observations and preliminary petrochemical and stable isotopic compositions of the host rock and sulfide minerals for a recently discovered sulfide hosted gold deposit from the palaeoproterozoic aravalli rocks in northwestern india gold occurs associated with feascu co sulfides in lithofacies of diverse mineralogical composition dominated by amphibole bearing dolomitic marble and albite rich quartzo feldspathic rocks qfr the presence of vugs believed to be after dissolution of halite patches coupled with the development of scapolite bearing assemblages in dolomite marble occurrence of tourmaline rich mineralized rocks and very high na content of carbonates and qfr indicate hypersaline depositional environment for the host rock a narrow spread of 34 scdt values from 10 5 to 12 8 for stratiform arsenopyrite and remobilized pyrrhotite corroborates hypersaline to evaporitic depositional environment the 13 c values for gold bearing carbonates show bimodal distribution one population mean 0 4 v pdb is close to the sea water carbonate values while the other 3 l indicates probable mantle affinity the 18 o values for carbonates mean 18 4 v smow are not discriminative as they appear to have been modified by subsequent metamorphism and hydrothermal activity interpretation of mantellic source for carbon is borne out from the absence of biogenic activity and incompatibility of significantly negative 13 c values in the evaporitic setting of deposition of bhukia rocks we suggest that nab rich fluids channeled through rift related faults were responsible for creating hypersaline conditions that eventually evolved into an evaporitic environment mantle carbon through some still deeper faults was probably responsible for the gold transport and its subsequent deposition in an otherwise uncommon evaporitic repository of carbonates and qfr 2002 elsevier science b v all rights reserved

geochemistry of the pond creek coal bed eastern kentucky coalfield the pond creek coal bed middle pennsylvanian breathitt formation is an important low sulfur resource in pike and martin countries in the eastern kentucky coalfield the mined area is crossed by the n20 e trending belfry anticline the pond creek coal bed has a higher sulfur content on the west side of the anticline the vertical trends in the ash geochemistry also vary across the anticline the sites to the east of the anticline represent deposition of peat through periods of relative stability with slow deposition bright lithotypes interspersed with periods of relatively rapid clastic deposition dull lithotypes both generally removed from marine influence comparison of elemental trends between the lowest bright lithotype and the second bright lithotype suggest that the swamp became less acidic with time an upward decrease in minor element concentration may be related to the influx of clays and other silicates present in the bone lithotype this bone may have acted as a relatively low nutrient soil for the growth of the plants which contributed to the overlying bright lithotype the sites to the west of the anticline were subjected to a greater marine influence than the eastern sites high k2o al2o3 ratios at the bottom and top of the coal bed and a high tio2 zr dull clarain near the bottom of the coal point to clastic influences on the geochemistry the relatively high cao percentages in the middle third of the coal bed suggest deposition at near neutral ph the upper third of the coal bed was dominated by syngenetic and epigenetic pyrite emplacement

gold mineralization in the ashanti belt of ghana genetic constraints of the stable isotope geochemistry the ashanti belt of ghana is the key district of gold mineralization in the paleoproterozoic terrane of west africa the area considered in southwest ghana is covered by lithologies of the volcanic sedimentary birimian supergroup and the overlying elastic sedimentary tarkwaian group which were jointly folded and metamor phosed under greenschist facies conditions during the eburnean teetonothermal event at about 9 1 ga regional fotiation md subparallel shear zones hosting mesothermal gold mineralization developed during deformation coeval with metamorphism four major tsoes of primary gold mineralization are present in the ashanti belt 1 mesothermal generally steeply dipping quartz veins in shear zones mainly in birimian sedimentary rocks 9 sulfide ores with auriferous arsenopyrite and pyrite spatialty dosely associated with the quartz veins 3 sulfide disseminations and stockworks in granitoids and 4 paleoplaeers of the tarkwaian group this study concentrates on types 1 and 9 of the hydrotherlnal gold mineralization stable isotope analyses of host rock and ore components were performed with the ailn of obtaining parameters relevant to the origin and evolution of the fluids that produced gold mineralization carbonaeeous matter in the birimian metasediments displays 93c values ranging from 11 4 to 9 8 3 per mil relative to pdb indicating an organogenie origin carbonates display a unimodal distribution of 9ac values ranging from 9 9 to 17 0 per rail relative to pdb coz extracted from fluid inclusions in the auriferous quartz veins has 93c values ranging from 9 5 to 15 7 per mil relative to pdb it is proposed that these carbon isotope compositions of carbonates and coz reflect extensive interaction of the co 2 rieh hydrothermal fluids with reduced carbon in birimian sediments in the deeper parts of the hydrothermal systems carbonates and auriferous vein quartz have 6 so values ranging from 19 9 to 9 9 9 and 19 8 to 15 6 per mil relative to smow respectively carbonates and quartz were deposited in near isotopic equilibrium with respect to 6 so indicating fluid dominated conditions during ore formation from fluids of metamorphic or magmatie origin such an origin is corroborated bysd values of water extracted from fluid inclusions in vein quartz 37 to 53 relative to smoxv pyrite of synsedimentary diagenetie origin in birimian schists displays sulfur isotope compositions ranging from 7 3 to 9 0 9 per rail median ca 10 relative to cdt similar compositions and wide ranges are usually attributed to sulfide generation by bacterial sulfate reduction from seawater arsenopyrite and eogenetie pyrite from the sulfide ores generally have 534s values in the range 5 3 to 10 9 per rail relative to cdt the tight unimodal distribution of 534s values indicates a large homogeneous fluid reservoir the low 534s values are interpreted as source inherited not related to unusual ph eh temperature or depositional conditions sulfides in birimian sediments represent the most likely sulfur reservoir tapped by the fluid systems the c o h and s isotope compositions of ore related hydrothermal minerals and fluid inclusion compo nents indicate that the mineralizing fluids interacted extensively with the paleoproterozoie rocks especially birimian sediments at deeper crustal levels and at high temperatures the isotopic compositions are most compatible with the formation of fluids from devolatilization reactions invomng birimian strata during pro grade metamorphism at depth metamorphic fluids

crustal scale shear zones and their significance to archaean gold mineralization in western australia many large archaean epigenetic gold deposits show a broad spatial relationship to regional lineaments in greenstone belts although in detail they are sited in subsidiary brittle ductile fault structures fluids originating from a deep source follow a complex path and re equilibrate with different lithologies and with metamorphic fluid during migration to higher crustal levels temperature and pressure conditions at or below the amphibolite greenschist metamorphic boundary where most gold deposits are located favour the establishment of brittle ductile and brittle subsidiary structures the preferred structural setting of gold deposits physical gradients between the regional ductile structures and more brittle subsidiary structures ensure transient strongly localized fluid flow into the latter where lower temperatures and suitable host rocks with high fe fe mg ratios favour gold deposition the multi source origin and continuous re equilibration of the fluid with crustal rock which includes granitoid and greenstone belt lithologies of different ages is reflected in the diverse isotopic and geochemical signature of the gold deposits

redox effects on organic matter storage in coastal sediments during the holocene a biomarker proxy perspective coastal margins play a significant role in the burial of organic matter om on earth these margins vary considerably with respect to their efficiency in om burial and to the amounts and periodicity of their om delivery depending in large part on whether they are passive or active margins in the context of global warming these coastal regions are expected to experience higher water temperatures changes in riverine inputs of om and sea level rise low oxygen conditions continue to expand around the globe in estuarine regions i e hypoxic zones and shelf regions i e oxygen minimum zones which will impact the amounts and sources of om stored in these regions in this review we explore how these changes are impacting the storage of om and the preservation of sedimentary biomarkers used as proxies to reconstruct environmental change in coastal margins

petrology of the pond creek coal bed in eastern kentucky abstract the middle pennsylvanian breathitt formation pond creek coal bed was examined along two cross sections in pike and martin countries in the eastern kentucky coal field along the north south profile the sulfur content increased markedly to the top of the bed in the eastern portion of the east west profile the coal bed is marked by a high vitrinite high ash bone shaley coal lithotype within the top half of the bed and by a thin clarodurite vitrinertoliptite rich durain at the top of the bed a northeastward plunging anticline termed here the belfry anticline marks the boundary between the high sulfur coal beds in the west and the appearance of the bony horizon on the east the coal and the interval between the rider and the coal bed both thin across the anticline which was active at the time of deposition

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

metamorphism in archaean greenstone belts calculated fluid compositions and implications for gold mineralization an inescapable consequence of the metamorphism of greenstone belt sequences is the release of a large volume of metamorphic fluid of low salinity with chemical characteristics controlled by the mineral assemblages involved in the devolatilization reactions for mafic and ultramafic sequences the composition of fluids released at upper greenschist to lower amphibolite facies conditions for the necessary relatively hot geotherm corresponds to those inferred for greenstone gold deposits xco2 0 2 0 3 this result follows from the calculation of mineral equilibria in the model system cao mgo feo al2o3 sio2 h2o co2 using a new expanded internally consistent dataset greenstone metamorphism cannot have involved much crustal over thickening because very shallow levels of greenstone belts are preserved such orogeny can be accounted for if compressive deformation of the crust is accompanied by thinning of the mantle lithosphere in this case the observed metamorphism which was contemporaneous with deformation is of the low p high t type for this type of metamorphism the metamorphic peak should have occurred earlier at deeper levels in the crust i e the piezothermal array should be of the deeper earlier type however at shallow crustal levels the piezothermal array is likely to have been of deeper later type as a consequence of erosion thus while the lower crust reached maximum temperatures and partially melted to produce the observed granites mid crustal levels were releasing fluids prograde into shallow crustal levels that were already retrograde we propose that these fluids are responsible for the gold mineralization thus the contemporaneity of igneous activity and gold mineralization is a natural consequence of the thermal evolution and does not mean that the mineralization has to be a consequence of igneous processes upward migration of metamorphic fluid via appropriate structurally controlled pathways will bring the fluid into contact with mineral assemblages that have equilibrated with a fluid with significantly lower xco2 these assemblages are therefore grossly out of equilibrium with the fluid in the case of infiltrated metabasic rocks intense carbonation and sulphidation is predicted if as seems reasonable gold is mobilized by the fluid generated by devolatilization then the combination of processes proposed most of which are an inevitable consequence of the metamorphism leads to the formation of greenstone gold deposits predominantly from metamorphic fluids

late archean granitoid hosted lode gold deposits yilgarn craton western australia deposit characteristics crustal architecture and implications for ore genesis granitoid hosted lode gold deposits constitute a sub group of late archean lode gold deposits in the yilgarn craton of western australia they share a number of common characteristics including 1 a strong structural control on a variety of scales 2 in most instances the presence of mineralisation in adjacent supracrustal sequence 3 wallrock alteration and vein assemblages consistent with the addition of sio2 k2o co2 s na2o but dependent on the p t conditions of the host environment and ore fluid 4 a metal association comprising au ag as bi te w mo and low concentrations of cu pb and zn and 5 deposition from a low moderate salinity near neutral h2o co2 ch4 fluid over a temperature and pressure range from 250 to 600 c and 1 to 4 kbar which corresponds to a range of crustal environments from lower greenschist to upper amphibolite facies these characteristics suggest that the granitoid hosted lode gold deposits represent a coherent genetic group that is equivalent to the more abundant greenstone hosted lode gold deposits of the craton in combination lode gold deposits irrespective of their host rocks and host terrane formed over a range of crustal levels and developed late in the tectonic sequence of the craton granitoids which host lode gold mineralisation are older than the inferred age of mineralisation by at least 10 million years and in combination with thermodynamic and isotope studies indicate that the host granitoids are not the dominant source of the ore fluid however the host granitoids do provide a structural and to a lesser extent chemical trap for gold bearing fluids in combination trace element and isotope studies of greenstone and granitoid hosted deposits suggest that the ore fluid originated from a deep mid to lower crustal source and at least interacted with granitic rocks at some stage the ore fluid composition is quite constant over the range of crustal levels from deep to shallow implying that the extent of modification by interaction with fluid conduit rocks is variable but not substantial

genesis of the shangxu orogenic gold deposit bangong nujiang suture belt central tibet china constraints from h o c si he and ar isotopes abstract shangxu is an orogenic gold deposit in the bangong nujiang suture zone central tibet china formed in the early cretaceous orogene related to convergence and collision between the qiangtang and lhasa terranes the mineralization at shangxu is hosted by jurassic turbidite sedimentary rocks of the mugagangri group and is associated with a regional fault system hydrothermal minerals develop muscovite carbonate sulfides and chlorite hydrothermal fluids record three main hydrothermal stages based on mineral paragenesis the earliest is barren quartz stage h1 which is pre ore during the early mineralization quartz pyrite stage h2a defined by massive quartz veins with minor euhedral pyrite and gold hydrothermal fluids had a 18ofluid of 6 1 6 4 d of 74 to 116 13cco2 of 5 4 to 7 6 and 30si of 0 1 in the quartz pyrite sulfides stage h2b characterized by abundant quartz granular pyrite muscovite with minor chalcopyrite galena sphalerite and gold fluids had a 18ofluid of 7 8 2 d of 109 to 120 13cco2 of 9 6 and 30si of 0 1 to 0 2 during the ankerite sulfide stage h3a distinguished by abundant ankerite muscovite sulfides with minor quartz and chlorite hydrothermal system had a fluid with 18ofluid of 4 9 5 3 d of 125 3 30si of 0 1 13cco2 of 12 4 in quartz inclusion fluid and 13cco2 of 2 7 in ankerite the calcite sulfide stage h3b is characterized by calcite sulfides with minor quartz and chlorite quartz formed earlier than calcite from a fluid having a 18ofluid of 6 4 d of 112 6 30si of 0 1 and 13cco2 of 7 4 after which calcite precipitated from a hydrothermal fluid with 18ofluid of 5 5 9 13cco2 of 0 5 to 2 8 hydrothermal fluids in h2b pyrite have 3he 4he ratios of 0 27 0 42ra and 40ar 36ar ratios of 313 372 the stable isotope composition of hydrothermal fluids from the shangxu gold deposit is similar to that of typical orogenic gold deposits the early stage h1 methane bearing fluids were probably sourced from the basin sediments leading to precipitation of early barren quartz veins and siderite alteration from the quartz sulfide stage h2 to carbonate sulfide stage h3 hydrothermal fluids were likely derived from dissolution of the marine carbonate cement from sedimentary host rocks during metamorphism at depth the decreasing d and 13c of the ore forming fluids from early to late suggests mixing with 13c depleted oxidized graphite in sedimentary rocks meteoric waters or reation between d depleted organic matters generally these fluids were likely generated at depth through prograde metamorphic devolatilization of hydrous minerals in the deeper equivalents of the sedimentary rocks of the mugagangri group sulfur and gold by inference likely originated from sedimentary diagenetic pyrite or the metasedimentary rocks between the greenschist and amphibolite facies and migrated with the metamorphic fluids during transportation to the site of deposition gold bearing fluids variably reacted with country rocks

new constraints on fluid sources in orogenic gold deposits victoria australia fluid inclusion microthermometry raman spectroscopy and noble gas plus halogen geochemistry complemented by published stable isotope data have been used to assess the origin of gold rich fluids in the lachlan fold belt of central victoria south eastern australia victorian gold deposits vary from large turbidite hosted orogenic lode and disseminated stockwork gold only deposits formed close to the metamorphic peak to smaller polymetallic gold deposits temporally associated with later post orogenic granite intrusions despite the differences in relative timing metal association and the size of these deposits fluid inclusion microthermometry indicates that all deposits are genetically associated with similar low salinity aqueous co2 bearing fluids the majority of these fluid inclusions also have similar 40ar 36ar values of less than 1500 and 36ar concentrations of 2 6 58 ppb by mass that are equal to or much greater than air saturation levels 1 3 2 7 ppb limited amounts of nitrogen rich fluids are present at a local scale and have the highest measured 40ar 36ar values of up to 5 700 suggesting an external or distinct source compared to the aqueous fluids the predominance of low salinity aqueous carbonic fluids with low 40ar 36ar values in both orogenic and intrusion related gold deposits is attributed to fluid production from common basement volcano sedimentary sequences and fluid interaction with sedimentary cover rocks turbidites aqueous fluid inclusions in the stawell magdala deposit of western victoria including those associated with n2 preserve mantle like br cl and i cl values in contrast fluid inclusions in deposits in the eastern structural zones which contain more abundant shales have elevated molar i cl ratios with maximum values of 5 170 10 6 in the melbourne zone br i ratios in this zone range from 0 5 to 3 0 that are characteristic of fluid interaction with organic rich sediments the maximum i cl and characteristic br i ratios provide evidence for organic br and i released during metamorphism of the shales therefore the regional data provide strong evidence for the involvement of sedimentary components in gold mineralisation but are consistent with deeper metamorphic fluid sources from basement volcano sedimentary rocks the overlying sediments are probably involved in gold mineralisation via fluid rock interaction

two stages of co2 metasomatism at the munro mine munro township ontario evidence from fluid inclusion stable isotope and mineralogical studies the munro asbestos mine is hosted by a differentiated ultramafic sill of archean age localized carbonate alteration at the mine has resulted from two separate episodes of co2 metasomatism and the fluids were unrelated the first episode affected only the serpentinized peridotite and occurred at 250 c the fluid was a saline brine up to 24 wt nacl cacl2 and had an oxygen isotopic composition of 3 and 13c was equal to 7 8 calcite veins were emplaced into the overlying fractured pyroxenite at approximately 300 400 c during the second episode the salinity of this fluid was only 1 5 equiv wt nacl the oxygen isotopic composition was 7 5 and 13c equaled 3 to 5 the first episode was probably associated with burial metamorphism diagenesis and the second episode with regional metamorphism the widespread occurrence of two separate stages of co2 metasomatism in the abitibi belt and in other well documented archean terranes such as the norseman wiluna greenstone belt in western austra

archaean carbon reservoirs and their relevance to the fluid source for gold deposits it is commonly assumed1 2 that seawater derived carbon in altered volcanic rocks is the only major pre metamorphic carbon in carbonate reservoir in archaean greenstone belts thus carbonates from archaean gold deposits with stable isotope ratios too negative median 13c 3 to have been derived from such carbon 13c usually assumed to be near 0 have been interpreted as being derived from a local felsic magmatic source1 barley and groves3 however recognize two carbonate alteration styles that predate regional metamorphism and gold mineralization in the norseman wiluna greenstone belt of western australia evidence is summarized below these are seafloor alteration and fault controlled regional alteration which as shown below have completely different carbon isotope compositions the latter median 13c 4 8 implies a major juvenile carbon co2 flux from the mantle during greenstone belt evolution and is thus of fundamental importance in itself however here we show why the mere existence of two carbon in carbonate reservoirs and variation in carbon isotope ratios of carbonates between individual gold deposits in one area negate some of the fundamental assumptions used to support magmatic fluid models1

geochemistry of the blue gem coal bed knox county kentucky abstract the blue gem coal bed middle pennsylvanian westphalian b breathitt formation has low ash with some sample sites having less than 1 ash and low sulfur contents through parts of knox county kentucky most collection sites exhibit similar vertical elemental trends in ash geochemistry the relatively high ash 1 ash lower part of the bed displays enrichment in tio2 zr cr v and ni co zn rb and mn show enrichment at some sites a low ash 1 ash and a relative enrichment in sio2 k2o and rb and a relative decrease in cu ni co ba and mn when compared to the middle part of the bed principal components analysis indicates that the samples with an ash content 0 63 1 0 show associations for ni cu cr and co samples with between 1 01 2 0 ash display strong element associations that suggest increased clastic sediment contributions tio2 zr k2o rb sio2 the low ash content and the upwards decrease in trace concentrations both suggest that the blue gem peat swamp was ombrotrophic through at least a part of its geologic history

chemoautotrophy in the ocean are the most importantcontributors this input of new organic carbon to the oceanis similar to that supplied by world rivers and eventuallyburied in oceanic sediments chemoautotrophy driven byorganic carbon recycling is globally more important thanthat fuelled by water rock interactions and hydrothermalventsystems

coal facies studies in the eastern united states coals in the eastern united states east of the mississippi river have been the subject of a number of coal facies studies going back to the 19th century such studies would not necessarily fall within a strict modern classification of coal facies studies but if a study encompassed some aspects of paleobotany palynology petrology geochemistry or sedimentology we assumed that some data and interpretations may be of use in evaluations of the facies references are presented as a guide for further research with annotation in the tables

geology and alteration in the golden mile kalgoorlie the giant kalgoorlie gold deposit 1 200 metric tons au recovered is surrounded by a wide wall rock alteration halo 1 x 3 km this alteration primarily represents the selectively pervasive formation of carbonate chlorite and localized intense pyrite and muscovite alteration which all formed synchronously with gold mineralization the carbonate alteration halo is interpreted as epigenetic because of evidence that carbonate chlorite assemblages overprint regional metamorphic fabrics furthermore the geometry of the alteration zone boundaries is controlled by ductile shear zones formed during regional deformation and the geochemistry of all the alteration zones suggests that one fluid was responsible for all assemblages there is no evidence of intense premetamorphic carbonation in the kalgoorlie area kalgoorlie is situated in the highly auriferous eastern goldfields province of the yilgarn block within a narrow corridor rift zone that contains several large gold deposits regional metamorphism has produced upper greenschist facies assemblages but has retained original rock textures at kalgoorlie the most important gold host is the golden mile dolerite 80 of gold produced a differentiated tholeiitic sill intruded between a lower mafic ultramafic pile including the paringa basalt the next most important gold host and overlying felsic rocks and metasediments the kalgoorlie syncline is the dominant tectonic structure in the main gold producing area of the golden mile adjacent to this infold of metasediments the golden mile dolerite and paringa basalt are the site of a number of ductile shear zones which formed synchronously with the syncline these zones and the many smaller shear zones between them have provided fluid channelways throughout the golden mile and are the site of most economic gold mineralization three alteration zones have been mapped in the golden mile dolerite on the basis of the mineralogic siting of fe i e the chlorite carbonate and pyrite zones the additional actinolite zone representing the unaltered regional metamorphic mafic assemblage has been converted to chlorite zone assemblages throughout the mined areas of the golden mile the carbonate zone bleached dolerite can be traced for 2 km through the main mineralized parts of the golden mile and to the full depth of lake view mine the boundary between the chlorite and carbonate alteration zones is locally sharp and controlled by ductile shear zones but is generally strata bound and preferentially developed in the more fe rich parts of the dolerite the pyrite zone which includes all economically gold mineralized areas is the site of the strongest muscovite alteration and is most intense and continuous in ductile shear zones the chlorite zone chlorite calcite or ankerite forms from mild carbonation of actinolite zone assemblages the carbonate zone ankerite siderite is a more local expression of this carbonation even after extensive carbonate alteration relative major element abundances are little changed and the main added components are limited to co 2 s k and rb the pyrite zone i e the gold lodes has ankerite muscovite quartz albite pyrite and minor siderite bearing assemblages it represents significant addition of sulfur the three alteration zones not only reflect differing degrees of alteration intensity but are also strongly influenced by host rock fe mg and this ratio largely determines the stability of chlorite favored by low fe mg and thus the distribution of the carbonate zone favored by high fe mg progressive deformation within the shear zones reworked existing mineralization kalgoorlie fits a metamorphic replacement model of gold formation by auriferous metamorphic fluids interacting with fe rich host rocks its great size is a function of a very well developed fluid channelway system via ductile shear zones and later fault zones and the favorable chemical nature of the host rocks especially the golden mile dolerite the full width of carbonation chlorite and carbonate zones reflects overlapping alteration envelopes around the closely spaced fluid pathways the processes responsible for the formation of most of the gold at kalgoorlie were essentially similar to those at several other archean gold deposits but on a larger scale

archaean au ag mineralisation at racetrack near kalgoorlie western australia a high crustal level expression of the archaean composite lode gold system the racetrack au ag deposit in the archaean yilgarn block western australia is hosted by a porphyritic basalt in a low greenschist facies setting and is associated with a brittle strike slip fault system three distinct and successive stages of hydrothermal activity and late quartz carbonate veining resulted in multiple veining and or brecciation stages i and ii are au bearing whereas stage iii and late veins are barren the ore shows features of both classic epithermal and mesothermal deposits alteration assemblages typified by sericitization carbonization silicification and chloritization are similar to those of mesothermal gold deposits wheras the quartz vein textures including comb rosette plumose and banded ore mineralogyof arsenopyrite pyrite chalcopyrite sphalerite galena freibergite tetrahedrite tennantite fahlore electrum and gold and metal associations cu as ag sn sb w au and pb are more characteristics of epithermal deposits fluid inclusions related to stage ii are two phase and aqueous with 1 8 average 4 wt nacl equiv and co2 content of 0 85 molal pressure corrected homogenisation temperatures range from 190 c to 260 c mineral assemblages indicate that ore fluid ph ranged between 4 2 and 5 3 fo 2 between 10 38 8 and 10 39 6 bars and m s between 10 3 2 and 10 3 6 calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the mineralisation but evidence for deep crustal pb indicates that deeply sourced fluids were also involved the deposit is interpreted to have formed in a shallow environment via mixing of deeply sourced fluids from at least as deep as the base of the greenstone belt with surface waters it therefore represents the upper crustal end member of the crustal depth spectrum of archaean lode gold mineralisation

the role of fluids in the metamorphism of komatiites agnew nickel deposit western australia the agnew nickel sulfide deposit is spatially associated with a lenticular body of ultramafic rocks which shows a concentric zonation in metamorphic mineralogy olivine tremolite chlorite cummingtonite enstatite assemblages occur at the margin of the ultramafic lens giving way to olivine anthophyllite olivine talc and olivine antigorite assemblages successively inwards these rocks are interpreted as having crystallized from komatiitic lavas and exhibit a spectrum of compositions from those of original flow tops to pure olivine adcumulates the relative modal abundances of metamorphic olivine tremolite and chlorite reflect original proportions of cumulus olivine and komatiite liquid in the protolith peak metamorphic conditions are estimated at 550 c based on garnet biotite thermometry at a maximum pressure of 3 kb this temperature falls within the narrow range over which metamorphic olivine may co exist with enstatite anthophyllite talc or antigorite depending upon the fugacity of water in the metamorphic fluid the observed mineralogical zonation is therefore attributed to infiltration by co2 rich fluids generated by decarbonation of talc carbonate rocks formed during pre metamorphic marginal alteration of the ultramafic lens metamorphic fluids were essentially binary mixtures of water and co2 with minor h2s having a maximum partial pressure less than 1 percent of total pressure enstatite bearing assemblages formed in the presence of co2 rich fluids at fluid rock volume ratios close to one while anthophyllite talc and antigorite bearing assemblages formed in the presence of progressively more water rich fluids at progressively lower fluid rock ratios

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

geochemistry of fluid inclusions from the mcintyre hollinger gold deposit timmins ontario canada type 1 h 2 o co 2 type 2 h 2 o co 2 type 3 ch 4 co 2 h 2 o and type 4 ch 4 fluid inclusions type 1 type 3 and some type 2 inclusions are primary or pseudosecondary in origin whereas type 4 and most type 2 inclusions are secondary the primary or pseudosecondary type 1 and 2 inclusions homogenized at temperatures of 220 degrees to 385 degrees c secondary type 2 inclusions homogenized at 160 degrees to 215 degrees c crushing tests confirm the presence of co 2 in samples with type 1 and 2 inclusions visually estimated x co2 values in type 1 inclusions range from 3 to 24 mole percent with bulk molar volumes of 19 to 28 cm 3 mole mineralizing fluids were at equilibrium with graphite at temperatures of 380 degrees to 480 degrees c and pressures of 1 to 3 kb calculated oxygen fugacities lie near the quartz fayalite magnetite buffer the mineralizing fluids differ compositionally from fluids in other types of ore deposits but resemble fluids derived from metamorphic rocks and deep level felsic intrusions modified journal abstract

fluid sources and the role of abiogenic ch4 in archean gold mineralization constraints from noble gases and halogens abstract the st ives goldfield of western australia hosts high grade gold mineralization in a variety of lithologies within 2 7 ga greenstone belts the low salinity co 2 bearing fluids responsible for gold mineralization could have been generated either by metamorphic processes within the greenstones or from external magmatic sources and independently sourced abiogenic ch 4 has been suggested as an important control on gold mineralization in order to better constrain possible fluid sources we applied a combination of he ne ar kr xe isotope and cl br i analyses to quartz and carbonate veins containing h 2 o co 2 fluid inclusions pyrite magnetite hematite and quartz veins containing ch 4 rich fluid inclusions pyrrhotite pyrite samples containing h 2 o co 2 fluid inclusions have higher br cl and i cl values and less radiogenic noble gas isotope signatures than suggested for ch 4 rich fluid inclusions the samples containing ch 4 fluid inclusions have maximum 40 ar 36 ar of 50 000 20 ne 22 ne of 9 8 and maximum 21 ne 22 ne of 0 56 in contrast h 2 o co 2 fluid inclusions have maximum 40 ar 36 ar of only 20 000 and maximum 21 ne 22 ne of 0 14 the use of 40 ar 39 ar methodology to measure k simultaneously with 40 ar 36 ar enables us to show the highest 40 ar 36 ar ratios are representative of the fluids trapped at 2 65 ga and have not been significantly modified by post entrapment 40 ar r production 40 ar r radiogenic 40 ar furthermore the 40 ar 36 ar ratio is correlated with the 21 ne 22 ne and 136 xe 130 xe ratios demonstrating that other heavy noble gas isotope ratios are also close to their original composition the highly radiogenic noble gas isotope signatures are unlikely to have been generated within the greenstone host rocks because seawater altered volcanic rocks have high abundances of non radiogenic atmospheric noble gas isotopes in contrast the strongly radiogenic noble gas isotope signatures are likely to have been generated in ancient basement rocks underlying the greenstones at 2 65 ga the combined noble gas and halogen data are consistent with models in which redox reactions triggered by interaction of independently and distally sourced h 2 o co 2 and ch 4 localized high grade gold mineralization we suggest that the fluids were intimately associated with crustal magmatism in the st ives goldfield and that abiogenic ch 4 could be an important moderator of redox processes in other crustal environments

whole coal versus ash basis in coal geochemistry a mathematical approach to consistent interpretations abstract several standard methods require coal to be ashed prior to geochemical analysis researchers however are commonly interested in the compositional nature of the whole coal not its ash coal geochemical data for any given sample can therefore be reported in the ash basis on which it is analyzed or the whole coal basis to which the ash basis data are back calculated basic univariate mean variance distribution etc and bivariate correlation coefficients etc measures of the same suite of samples can be very different depending which reporting basis the researcher uses these differences are not real but an artifact resulting from the compositional nature of most geochemical data the technical term for this artifact is subcompositional incoherence since compositional data are forced to a constant sum such as 100 or 1 000 000 ppm they possess curvilinear properties which make the euclidean principles on which most statistical tests rely inappropriate leading to erroneous results applying the isometric logratio ilr transformation to compositional data allows them to be represented in euclidean space and evaluated using traditional tests without fear of producing mathematically inconsistent results when applied to coal geochemical data the issues related to differences between the two reporting bases are resolved as demonstrated in this paper using major oxide and trace metal data from the pennsylvanian age pond creek coal of eastern kentucky usa following ilr transformation univariate statistics such as mean and variance still differ between the ash basis and whole coal basis but in predictable and calculated manners further the stability between two different components a bivariate measure is identical regardless of the reporting basis the application of ilr transformations addresses both the erroneous results of euclidean based measurements on compositional data as well as the inconsistencies observed on coal geochemical data reported on different bases

chemoautotrophy in the redox transition zone of the cariaco basin a significant midwater source of organic carbon production during the cariaco time series program microbial standing stocks bacterial production and acetate turnover were consistently elevated in the redox transition zone rtz of the cariaco basin the depth interval 240 450 m of steepest gradient in oxidation reduction potential anomalously high fluxes of particulate carbon were captured in sediment traps below this zone 455 m in 16 of 71 observations here we present new evidence that bacterial chemoautotrophy fueled by reduced sulfur species supports an active secondary microbial food web in the rtz and is potentially a large midwater source of labile chemically unique sedimenting biogenic debris to the basin s interior dissolved inorganic carbon assimilation 27 159 mmol c m 22 d 21 in this zone was equivalent to 10 333 of contemporaneous primary production depending on the season however vertical diffusion rates to the rtz of electron donors and electron acceptors were inadequate to support this production therefore significant lateral intrusions of oxic waters mixing processes or intensive cycling of c s n mn and fe across the rtz are necessary to balance electron equivalents chemoautotrophic production appears to be decoupled temporally from short term surface processes such as seasonal upwelling and blooms and potentially is more responsive to longterm changes in surface productivity and deep water ventilation on interannual to decadal timescales findings suggest that midwater production of organic carbon may contribute a unique signature to the basin s sediment record thereby altering its paleoclimatological interpretation

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

carbon isotope studies of auriferous quartz carbonate veins from two orogenic gold deposits from the neoarchean chitradurga schist belt dharwar craton india evidence for mantle magmatic source of auriferous fluid abstract carbon and oxygen isotopic compositions of carbonates from auriferous quartz carbonate veins qcvs of two orogenic gold deposits ajjanahalli and guddadarangavvana halli g r halli from the neoarchean chitradurga schist belt of the dharwar craton southern india are examined to understand the origin of the mineralizing fluids the average carbonate carbon 13cpdb and oxygen 18osmow isotope compositions of qcvs of ajjanahalli are 5 5 1 3 and 14 1 2 7 respectively the same ratios for the qcvs of g r halli are 6 2 1 9 and 14 1 0 5 the corresponding average fluid 13c and 18o compositions are 5 81 1 14 13 78 5 1 for ajjanahalli and 4 64 0 7 6 50 0 6 for g r halli the 13cpdb of syn sedimentary carbonates of bif of ajjanahalli 1 8 0 1 carbonated metabasalts of ajjanahalli 1 4 and g r halli 1 3 fall in the compositional range of marine carbonates 0 2 as dissolution decarbonation reactions during metamorphism of pre existing carbonate carbonated rocks produce co2 with 13c values similar to or more enriched than parent rock the carbonate or fluid 13c ratios of the qcvs which fall in the compositional range of mantle magmatic derived co2 or carbonates obtained in this work cannot be the result of metamorphism it is proposed that gold mineralizing fluids were derived from juvenile magmatic melts and were channeled through crustal scale shear zones to give rise to the gold deposits

nature of ore forming fluid and formation conditions of bif hosted gold mineralization in the archean amalia greenstone belt south africa constraints from fluid inclusion and stable isotope studies abstract orogenic gold mineralization in the amalia greenstone belt is hosted by oxide facies banded iron formation bif hydrothermal alteration of the bif layers is characterized by chloritization carbonatization hematization and pyritization and quartz carbonate veins that cut across the layers the alteration mineral assemblages consist of ankerite ferroan dolomite minerals siderite chlorite hematite pyrite and subordinate amounts of arsenopyrite and chalcopyrite information on the physico chemical properties of the ore forming fluids and ambient conditions that promoted gold mineralization at amalia were deduced from sulfur oxygen and carbon isotopic ratios and fluid inclusions from quartz carbonate samples associated with the gold mineralization microthermometric and laser raman analyses indicated that the ore forming fluid was composed of low salinity h 2 o co 2 composition 3 wt nacl equiv the combination of microthermometric data and arsenopyrite pyrite geothermometry suggest that quartz carbonate vein formation gold mineralization and associated alteration of the proximal bif wall rock occurred at temperature pressure conditions of 300 30 c and 2 kbar thermodynamic calculations at 300 c suggest an increase in f o 2 10 32 10 30 bars and corresponding decrease in total sulfur concentration 0 002 0 001 m that overlapped the pyrite hematite magnetite boundary during gold mineralization although hematite in the alteration assemblage indicate oxidizing conditions at the deposit site the calculated low f o 2 values are consistent with previously determined high fe fe mg ratios 0 7 in associated chlorite absence of sulfates and restricted positive 34 s values in associated pyrite based on the fluid composition metal association and physico chemical conditions reported in the current study it is confirmed that gold in the amalia fluid was transported as reduced bisulfide complexes e g au hs 2 at amalia gold deposition was most likely a combined effect of increase in f o 2 corresponding to the magnetite hematite buffer and reduction in total sulfur contents due to sulfide precipitation during progressive fluid rock interaction the epigenetic features coupled with the isotopic compositions of the ore forming fluid 34 s s 1 8 to 2 3 18 o h2o 6 6 to 7 9 and 13 c c 6 0 to 7 7 at 300 330 c are consistent with an externally deep sourced fluid of igneous signature or and prograde metamorphism of mantle derived rocks

palynologic and petrographic variation in the pond creek coal bed pike county kentucky abstract recent studies of the petrology and ash geochemistry of the pond creek coal bed middle pennsylvanian breathitt formation in pike and martin countries kentucky have defined vertical and lateral trends that are related to the development of the northeast trending belfry anticline contemporaneous with the deposition of the pond creek peat to the northwest of the anticline the coal bed has a high caco3 middle zone and a high fe2o3 high sulfur upper zone to the east of the anticline particularly in the lick creek and jamboree 7 1 2 quadrangles the coal bed exhibits a distinctive petrographic zonation in the latter area the usual megascopic sequence is a basal durain followed by a bright clarain durain dull the palynology of the pond creek coal bed was investigated in six sets of bench lithotype samples from the lick creek and jamboree 7 1 2 quadrangles the low vitrinite basal durain zone 1 has a palynomorph assemblage which reflects the importance of tree ferns and herbaceous lycopods the easternmost site has a bright clarain below the durain the latter lithotype has a fair diversity of palynormph groups and also has the highest percentage of arborescent lycopod forms of any bench below the bone zone 5 the bright zone 2 above the durain has the greatest maceral group range and the greatest floral diversity of any of the lithotypes the zone 3 dull lithotype has increased amounts of herbaceous lycopods and decreased amounts of arborescent lycopods sphenopsids and tree ferns the zone 4 bright lithotypes are generally over 80 vitrinite and in general exhibit a dominance of arborescent lycopods although sphenopsid tree fern and small fern forms exhibit varying importance the high ash bone zone 5 has 71 6 77 0 vitrinite this lithotype is marked by a dominance of herbaceous lycopods at the expense of arborescent lycopods and sphenopsids the zone 6 bright clarian is marked by an increase in arborescent lycopods and a large decrease in herbaceous lycopods the low vitrinite terminal durain has an assemblage with high percentages of herbaceous lycopods and low percentages of arborescent lycopods as well as increase in tree fern spores over zone 6 in general the petrology and palynology trends are predictable dull lithotypes have abundant herbaceous lycopod representation and bright lithotypes have abundant arborescent lycopod representation the greatest deviation from this simple pattern is within the zone 4 bright lithotypes where diverse palynomorph assemblages occur among the high vitrinite benches overall the greatest floral diversity appears to have occurred near the base of the coal bed

age origin and significance of nodular sulfides in 2680 ma carbonaceous black shale of the eastern goldfields superterrane yilgarn craton western australia abstract sulfide nodules composed of pyrite occur within black shales in the lucky bay area of the bulong domain eastern goldfields superterrane yilgarn craton western australia that correlate with the neoarchean black flag group detailed petrography reveals a variety of shapes and textures from spherical to ovoid and zoned to uniform some nodules have recrystallized resulting in a later generation of pyrite all have been affected by post depositional metamorphism as evidenced by pressure shadows containing quartz mica carbonate assemblages la icp ms analyses show that these nodules are enriched in a range of trace elements including co ni cu ag sb te au tl pb and bi gold and te concentrations range from 0 3 to 1 ppm and 10 to 50 ppm respectively the black flag group equivalents stratigraphically and structurally underlie a younger basin east of lucky bay that contains turbidites sandy debris flows and bif the latter of which hosts several gold deposits at randalls 60 km se of kalgoorlie it is likely that the lateral equivalents of the nodular sulfide bearing black shale originally occurred stratigraphically beneath what is now the ore horizon at randalls given its anomalous au and te content this lithology is a potential contributor of gold to the bif hosted gold deposits of the randalls goldfield as well as other similar gold resources elsewhere in the eastern goldfields superterrane

the relationship of mantle derived fluids to gold metallogenesis in the jiaodong peninsula evidence from d o c s isotope systematics abstract the largest gold district in china is the jiaodong peninsula where three types of gold deposits are recognized quartz vein fracture altered and breccia types the first two developed along a group of ne trending faults and are hosted by granitic intrusions dated at 160 to 150 ma biotite granite and 130 to 126 ma granodiorite and by metamorphic rocks of the precambrian crystalline basement the breccia type gold system is mainly located around the northern margin of the jiaolai cretaceous basin where mineralisation is controlled by both detachment fractures and ne trending faults this study is based on stable isotope determinations from ten gold deposits including linglong jiaojia sanshandao cangshang wang ershan dayigezhuang denggezhuang pengjiakuang fayunkuang and dazhuangzi as well as the linglong jurassic biotite granite guojialing cretaceous granodiorite and archean gneiss the stable isotope systematics reflect the style of the three types of gold deposits but also show that they belong to the same metallogenic system in which the hydrothermal fluids were derived from a mantle fluid reservoir and mixed with crustal fluids the ore forming age is later than both the jurassic biotite granite and cretaceous granodiotite but overlaps with the 121 to 114 ma ages of lamprophyre and diabase dykes the hydrothermal fluids that were responsible for both gold mineralisation and the retrograde alteration of the diabase and lamprophyre dykes are similar and represent a co 2 and potassium rich system this fluid system is interpreted to be the consequence of cretaceous lithospheric thinning asthenospheric upwelling and mantle degassing in eastern china

lithophile element systematics of archean greenstone belt au ag vein deposits implications for source processes reply potassic alteration domains of greenstone belt lode gold deposits are characterized by systematic partitioning between lithophile elements k rb and ba are generally co enriched and linearly correlated over almost three orders of magnitude in abundance where k rb 220 400 and k ba 30 85 k cs 104 and k tl 2 104 are also correlated though more weakly lithium abundances and rb sr ratios are erratic in altered rocks these interelement trends collectively are present in deposits variously hosted by ultramafic mafic or felsic volcanic rocks and sediments or granitoids magmatic processes involving crystal fractionation of biotite k feldspar and plagioclase generate trends to systematically diminished k rb 50 k li k cs and k tl but enhanced k ba 8 103 and rb sr in most late stage differentiates such late stage trends are the rule in magmatophile deposits including the archean cadillac molybdenite deposit phanerozoic cu and mo porphyry deposits sn w greisens and most

the scale of ore depositional systems an important restraint on epigenetic vs remobilized syngenetic origins for archaean mesothermal gold deposits there is general consensus that the majority of gold deposits in the important group hosted by volcanic or intrusive host rocks within archaean granitoid greenstone terrains have an epigenetic origin however there is controversy surrounding those stratabound deposits hosted by fe rich sedimentary rocks such as banded iron formation bif for which epigenetic syngenetic and remobilized syngenetic lateral secretion origins have all been proposed in western australia such controversial gold deposits in fe rich sedimentary units have similar ore mineralogies ore element ratios and in places alteration assemblages and on the craton scale show very similar structural controls to the other deposits equivalent relationships are recorded for similar deposits in other cratons all western australian deposits occur along kilometre scale shear or fault zones linked to trans craton obliqueto strike slip shear zones that were a focus for i carbonation with a mantle like isotopic signature and ii emplacement of high level a and i type granitoids felsic porphyries and or calc alkaline lamprophyres the scale of the mineralizing systems and the broad contemporaneity of mineralization as indicated by radiogenic isotope studies is much larger than that envisaged in conceptual secretion models which involve volumetrically small locally enriched source rocks instead archaean gold mineralization in western australia at least is probably the result of high fluid flux during deformation hightemperature metamorphism and magmatism which may be related to tectonism at convergent plate margins as in modern examples there is strong evidence for similar tectonic and mineralizing processes from the canadian shield

stable isotopes c o and fluid inclusion study of quartz carbonate veins from the antimony line murchison greenstone belt in the homogeneously deformed murchison greenstone belt region fluids circulations were focused along a localized deformation brittle ductile zone and the so called antimony line in order to trace the origin of the fluid its composition the temperature of the precipitation along the antimony line we investigate the stable isotope oxygen and carbon and fluid inclusion compositions of the quartz carbonate veins as well as chemical analyses of the carbonates and 40ar 39ar dating on the fuchsite associated with the veins three types of fluid inclusions are recognized for the h2o co2 dominated plus minor ch4 n2 fluid s microthermometric measurements together with the paragenesis of the veins and host rocks indicate that the pressure temperature of the precipitation is 350 to 450 c 200 to 300 mpa which is an unusually high temperature for an antimony deposit the carbonates are fe mg rich and are characterized by flat mree and hree patterns with slight depletions in lree the oxygen isotope compositions of the quartz are rather homogeneous at the scale of the antimony line 18oquartz 10 9 14 3 in detail subtle differences in the 18o values for the quartz and carbonate exist depending on the sampling sites these differences are likely due to minor temperature and or host rock geochemistry variations along the antimony line data point to a metamorphic origin for the fluids responsible for the mineralization which likely escaped from the nearby greenstone lithologies finally we present an overview of the murchison greenstone belt geological evolution by integrating the antimony metallogeny of the antimony line which can be compared to that of an orogenic gold deposit

p t conditions mechanism and timing of the localized melting of metapelites from the petronella shear zone and relationships with granite intrusions in the southern marginal zone of the limpopo belt south africa

geology and fluid characteristics of the ulu sokor gold deposit kelantan malaysia implications for ore genesis and classification of the deposit abstract the ulu sokor gold deposit is one of the most famous and largest gold deposits in malaysia and is located in the central gold belt this deposit consists of three major orebodies that are related to ns and ne striking fractures within fault zones in permian triassic meta sedimentary and volcanic rocks of the east malaya block the faulting events represent different episodes that are related to each orebody and are correlated well with the mineralogy and paragenesis the gold mineralization consists of quartz dominant vein systems with sulfides and carbonates the hydrothermal alteration and mineralization occurred during three stages that were characterized by i silicification and brecciation ii carbonatization sericitization and chloritization and iii quartz carbonate veins fluid inclusions in the hydrothermal quartz and calcite of the three stages were studied the primary co 2 ch 4 h 2 o nacl fluid inclusions in stage i are mostly related to gold mineralization and display homogenization temperatures of 269 389 c salinities of 2 77 11 89 wt nacl equivalent variable co 2 contents typically 5 29 mol and up to 15 mol ch 4 in stage ii gold was deposited at 235 398 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 0 83 9 28 wt nacl equivalent variable co 2 contents typically 5 63 mol and up to 4 mol ch 4 the 18 o h 2 o and d values of the ore forming fluids from the stage ii quartz veins are 4 5 to 4 8 and 44 to 42 respectively and indicate a metamorphic hydrothermal origin oxygen fugacities calculated for the entire range of t p x co 2 conditions yielded log f o 2 values between 28 95 and 36 73 for stage i and between 28 32 and 39 18 for stage ii these values indicate reduced conditions for these fluids which are consistent with the mineral paragenesis fluid inclusion compositions and isotope values the presence of daughter mineral bearing aqueous inclusions is interpreted to be a magmatic signature of stage iiia combined with the oxygen and hydrogen isotopic compositions 18 o h 2 o 6 8 to 11 9 d 77 to 62 these inclusions indicate that the initial fluid was likely derived from a magmatic source in stage iiib the gold was deposited at 263 to 347 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 5 33 to 11 05 wt nacl equivalent variable co 2 contents typically 9 15 mol and little ch 4 the oxygen and hydrogen isotopic compositions of this fluid 18 o h 2 o 8 1 to 8 8 d 44 to 32 indicate that it was mainly derived from a metamorphic hydrothermal source the co 2 h 2 o ch 4 nacl fluids that were responsible for gold deposition in the stage iiic veins had a wide range of temperatures 214 483 c salinities of 1 02 to 21 34 wt nacl equivalent variable co 2 contents typically 4 53 mol and up to 7 mol ch 4 the oxygen and hydrogen isotopic compositions 18 o h 2 o 8 5 to 9 8 d 70 to 58 were probably acquired at the site of deposition by mixing of the metamorphic hydrothermal fluid with deep seated magmatic water and then evolved by degassing at the site of deposition during mineralization the log f o 2 values from 28 26 to 35 51 also indicate reduced conditions for this fluid in stage iiic moreover this fluid had a near neutral ph and 34 s values of h 2 s of 2 32 to 0 83 which may reflect the derivation of sulfur from the subducted oceanic lithospheric materials the three orebodies represent different gold transportation and precipitation models and the conditions of ore formation are related to distinct events of hydrothermal alteration and gold mineralization the gold mineralization of the ulu sokor deposit occurred in response to complex and concurrent processes involving fluid immiscibility fluid rock reactions and fluid mixing however fluid immiscibility was the most important mechanism for gold deposition and occurred in these orebodies which have corresponding fluid properties structural controls geologic characteristics tectonic settings and origins of the ore forming matter these characteristics of the ulu sokor deposit are consistent with its classification as an orogenic gold deposit while some of the veins are genetically related to intrusions

turbidite hosted gold mineralization at the dolaucothi gold mines dyfed wales united kingdom the dolaucothi gold deposit occurs in thin bedded turbidites of upper ordovician to basal silurian age deposited near the southern margin of the lower paleozoic welsh basin the host rocks were deformed during the caledonian orogeny 390 410 ma into a series of inclined asymmetrical commonly overturned tight southeast facing folds with associated cleavage reverse dip slip faults accompanied the folding and the whole area is cut by late tensional faults the mineralization is controlled by structures produced during the caledonian orogeny in particular a thrust fault which formed the host to the roman lode a flat lying auriferous quartz reef up to 6 m thick gold occurs in a variety of hosts including pyritic shales containing both euhedral and framboidal pyrite quartz carbonate stringer veins in steeply or gently inclined veins associated with shear zones and in planar quartz veins associated with the roman lode the mineralogy is simple with pyrite and arsenopyrite being the dominant sulfides ankeritic carbonates hydromuscovite and the lithium silicate cookeite are also present it is proposed that during prograde metamorphism associated with early stages of the caledonide orogeny fluids circulated through the basement below the southeast margin of the welsh basin and leached gold and associated metals from rocks of igneous or volcanic origin these overpressured fluids were released to high crustal levels during later orogenic movements and uplifts perhaps related to reactivation of such basement faults as the infra tywi fault geothermometric studies indicate that the host rocks experienced upper anchizone facies metamorphism whereas the temperatures of the mineralizing fluids were in the range of 345 degrees to 450 degrees c isotopic studies point to a common origin for the sulfides in both the shales and the veins and also indicate that the host rocks provided the source of the carbon now incorporated in the carbonates