graphitization of carbonaceous matter during metamorphism with references to carbonate and pelitic rocks of contact and regional metamorphisms japan this study is an attempt to correlate the graphitization process of carbonaceous matter during metamorphism with metamorphic grade graphitization can be parameterized using crystal structure and chemical and isotopic compositions the extent of graphitization could be characterized mainly by temperature duration of metamorphism and rock composition we compared the graphitization trends for two metamorphic terrains a contact aureole of the kasuga area and a regional metamorphic terrain of high temperature low pressure type of the ryoke metamorphic terrain in northern kiso area central japan and for two different lithologies carbonate and pelite using x ray diffractogram dta tg analysis and chemical and stable isotope analyses during contact metamorphism graphitization and carbon isotopic exchange reactions proceeded simultaneously in pelitic and carbonate rocks the decreases in basal spacing d 002 of the carbonaceous matter in carbonate rocks is greatly accelerated at temperatures higher than about 400 c furthermore carbon isotopic ratios of graphite in carbonate rocks also change to 13c enriched values implying exchange with carbonates the beginning of this enrichment of 13c in the carbonaceous matter coincides with an abrupt increase of the graphitization processes carbon isotopic shifting up to 5 in pelites could be observed as metamorphic temperature increased probably by about 400 c carbonaceous matter in pelitic rocks is sometimes a mixture of poorly crystallized organic matter and well crystallized graphite detritus dta tg analysis is an effective tool for the distinction of detrital graphitic material two sources for the original carbon isotopic composition of carbonaceous matter in pelites in the kasuga contact aureole can be distinguished about 28 and 24 regardless of the presence of detrital graphite and were mainly controlled by depositional environment of the sediments graphitization in limestones and pelitic rocks in regional metamorphism proceeds further than in a contact aureole in the low temperature range the differences in extent of graphitization between the two metamorphic regions is large however at temperatures higher than 600 c the extent of graphitization in both regions is indistinguishable the degree of graphitization is different in limestones and pelitic rocks from the ryoke metamorphic terrain we demonstrate that the graphitization involves a progressive re construction process of the crystal structure the sequence of the first appearance of crystal inter planar spacing correlates with the metamorphic grade and indicates the crystal growth of three dimensional structured graphite

stable isotope evidence for limited fluid infiltration of deep crustal rocks from the ivrea zone italy isotopic and petrologic studies of the ivrea zone a segment of deep crustal high grade rocks suggest that metamorphism did not involve the transfer of large quantities of co sub 2 from mantle to crust high grade ivrea zone calcites may retain high delta sup 18 o up to 24 per thousand smow indicating little interaction with externally derived fluid graphite isotopic compositions delta sup 13 c 10 per thousand to 25 per thousand pdb that do not vary with grade are attributed to mixing between carbonate carbon and biogenic noncarbonate carbon calcites from high grade carbonate poor amphibolites have delta sup 13 c of about 1 per thousand pdb and sedimentary not infiltrative origins the general lack of carbon and oxygen isotopic homogenization suggests that fluid interactions may be explained in terms of fluid generated internally to the ivrea zone metasedimentary rocks

correlations between fluid composition and deep seated structural style in the footwall of the simplon low angle normal fault switzerland structural and fluid inclusion analyses reveal a correlated change in structural style and fluid composition along strike in footwall mylonites of the simplon low angle normal fault of switzerland in the south early postmylonitic structures are semibrittle shears and brittle faults synkinematic fluid inclusions within the faults contain a carbonic component whereas those in the shears lack co 2 to the north early postmylonitic structures are extension veins and kinkbands and synkinematic fluid inclusions are aqueous entrapment conditions for all fluid inclusions are estimated to be 500 c and 5 kbar we speculate that different wetting characteristics of carbonic versus aqueous fluids influenced the mechanical behavior of the rocks nonwetting carbonic fluids locally increased fluid pressure and induced brittle failure resulting in development of abundant closely spaced brittle faults in areas lacking carbonic fluids ductile deformation continued to lower pressures and temperatures

the early proterozoic birimian supergroup of ghana and some aspects of its associated gold mineralization abstract rocks of the birimian supergroup of early proterozoic age sm nd isochron age 2166 66 ma form part of the west african craton ghana contains the eastern portion of the birimian terrane five parallel evenly spaced several hundred kilometre long volcanic belts consisting mainly of low grade metamorphic tholeiitic lavas morb chemistry characterize the birimian supergroup of ghana the belts are separated by basins containing isoclinally folded dacitic volcaniclastics wackes and argillitic sediments as well as granitoids lavas and sedimentary rocks were deposited contemporaneously as lateral facies equivalents within the sedimentary basins various lithofacies are distinguished in the transition zone between belt volcanics and basin sediments a chemical facies occurs this is defined by cherts manganiferous and carbon rich sediments fe ca mg carbonates and sulphide mineral disseminations after their emplacement birimian lavas and sediments were folded in the course of the eburnean tectono thermal event intruded by various types of granitoids uplifted and eroded the erosion products were deposited as sediments of the tarkwaian group in long narrow intramontane grabens which formed due to rifting preferentially in the central portions of all five birimian volcanic belts tarkwaian sediments were deformed by gravity tectonics two major types of eburnean granitoids in ghana are characterized as follows basin granitoids cape coast type occur as synorogenic foliated batholiths chiefly in the central portions of birimian sedimentary basins they are peraluminous and generally granodioritic in composition belt granitoids dixcove type mostly form late orogenic unfoliated intrusions in volcanic belts they possess a metaluminous character and commonly are of tonalitic composition bongo granitoids are of post tarkwaian age and k rich in contrast to these granitoid types which have strong mantle affinities the winneba type had an archean sialic precursor a model involving small scale equidimensional parallel and contemporaneously operating convection cells in the upper mantle which caused rifting of a highly attenuated protocrust as well as linear eruptions of tholeiitic magmas is proposed recent sm nd pb pb and rb sr data of volcanic and plutonic rocks are incorporated most ghanaian birimian gold occurrences and mines are concentrated in narrow corridors of 10 15 km width in the transition zone between volcanic belts and sedimentary basins as are the chemical facies and regionally extensive shear zones at the volcanics sediment interface birimian gold in ghana is present as two major types 1 the disseminated sulphide type which is generally lithofacies controlled i e controlled by chemical sediments and to a lesser extent by selvages of gold quartz veins and 2 the quartz vein type which is exclusively structure controlled data on geochemical underground traverses across both types of gold mineralization are briefly summarized

a carbon isotope study of graphites from the kerala khondalite belt southern india evidence for co_ 2 infiltration in granulites field relations of arrested charnockite patches felsic pegmatite dikes and coarse cordierite graphite veins in the granulite facies supracmstal belt of southern kerala suggest paleo fluid channels we have investigated the stable isotopic composition of graphites associated with these structures as well as those in association with charnockites adjacent to calcsilicate horizons the remarkably high delta 13 c values displayed by graphites from the structurally controlled zones 8 6 to 13 4 o together with the narrow spread in individual localities pm 1 2 0 correlate with precipitation from isotopically homogeneous co 2 rich fluids that either infiltrated along structural pathways faults shears or were transferred through magmatic conduits graphites from charnockite calcsilicate associations show extreme 13 c enrichment delta 13 c up to 4 8 changing fluid regimes are detected from up to 5 0 variation in delta 13 c among graphites sampled adjace

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

graphite deformation in marble and mylonitic marble grenville province canadian shield in the southern grenville province of the canadian shield otter lake area high grade marble gneiss and amphibolite have been folded about north to north east trending axes mylonite zones parallel to layering and 0 1 10 cm wide are locally present in marble in nonmylonitic marble graphite occurs as c 1 mm hexagonal prisms which are commonly accompanied by a relatively few crystals that have been deformed resulting in cleavage separation and the formation of folds and kink bands fracture filled calcite contains less mg and fe than surrounding calcite e g 0 30 compared with 1 8 2 7 wt mgo and 0 02 0 12 compared with 0 13 0 18 wt feo the composition of fracture filled dolomite is similar to that of the surrounding dolomite in semimylonite graphite forms elongate streaks of fragmented crystals and in mylonite further fragmentation has occurred to produce extremely small particles the fragmentation has not destroyed the atomic structure hexagonal modification of graphite the behaviour of biotite was similar to that of graphite but extreme fragmentation did not occur dolomite was more rigid than calcite and in mylonite it occurs more commonly as relics amphibole and pyroxene crystals remained undeformed but are locally replaced by calcite the numerous microprocesses that have evidently occurred in marble and mylonitic marble of the study area are coarsening calcite graphite twinning calcite dolomite slip calcite dolomite graphite biotite strain induced recrystallization calcite microfolding and kink band formation graphite biotite fragmentation graphite and the pressure induced transport of calcite and dolomite to voids in graphite and biotite

the origin and hydrothermal mobilization of carbonaceous matter associated with paleoproterozoic orogenic type gold deposits of west africa abstract the chemical and physical properties of carbonaceous matter cm were studied in paleoproterozoic metasediment hosted orogenic type gold deposits in burkina faso the inata deposit in mali the syama deposit and in ghana the obuashi and bogoso deposits two types of cm occur in all the studied deposits metamorphosed and hydrothermal metamorphosed cm prevails in all the deposits hydrothermal cm occurs in small veinlets in hydrothermally altered rocks and in quartz veins or forms irregular accumulations parallel or sub parallel to c type cleavage within the shear zones the origin of hydrothermal cm which occurs in paragenesis with au bearing arsenopyrite or pyrite seems to have been due to supersaturation of hydrothermal fluids with carbon at the deeper or middle crustal levels the isotopic composition of carbon in bulk cm 33 1 to 26 2 vpdb indicates its biogenic origin the isotopic composition of carbon in hydrothermal carbonates ranges from 14 5 to 4 4 vpdb which suggest mixing of carbon derived from a deep seated source with carbon derived from an organic source the interaction of hydrothermal fluids with metamorphosed cm could be one of the causes of the reduction of hydrothermal fluids and formation of the respective mineralization the optical properties and raman spectra of the metamorphosed cm particles in the individual studied mineral deposits differ considerably the temperatures calculated on the basis of the raman spectra of metamorphosed cm vary between 280 and 440 c depending on the thermometer used and correspond to temperatures of metamorphism of upper sub grenschist and greenschist facies the temperatures calculated for hydrothermal cm at the individual deposits are only slightly lower compared to the metamorphosed cm at the same deposits which indicates approximately the same temperature of the metamorphic and hydrothermal processes

synmetamorphic carbon mobility and graphite enrichment in metaturbidites as a precursor to orogenic gold mineralisation otago schist new zealand the macraes orogenic gold deposit is hosted by a graphitic micaceous schist containing auriferous porphyroblastic sulphides the host rock resembles zones of unmineralised micaceous graphitic pyritic schists derived from argillaceous protoliths that occur locally in background pelitic otago schist metasediments this study was aimed at determining the relationship between these similar rock types and whether the relationship had implications for ore formation argillites in the protolith turbidites of the otago schist metamorphic belt contain minor amounts of detrital organic matter 50 million years of evolution of the metamorphic belt from development of sheared argillite in the jurassic to postmetamorphic ductile extension in the cretaceous introduced graphite is structurally controlled and occurs with metamorphic muscovite and chlorite as veins and slicken sided shears with some veins having 50 noncarbonate carbon graphitic foliation seams in low grade micaceous schist and metamorphic quartz veins contain equant graphite porphyroblasts up to 2 mm across that are composed of crystallographically homogeneous graphite crystals graphite reflectance is anisotropic and ranges from 1 to 8 green light texturally similar porphyroblastic pyrite has grown in micaceous schist up to 10 wt s metamorphic quartz veins and associated muscovite rich shears these pyritic schists are weakly enriched in arsenic up to 60 ppm the low grade metamorphic mobility and concentration of graphite in micaceous schists is interpreted to be a precursor process that structurally and geochemically prepared parts of the otago schist belt for later more restricted gold mineralisation economic amounts of gold and associated arsenic were subsequently introduced to carbonaceous sulphidic schists in the macraes gold deposit by a separate metamorphic fluid derived from high grade metaturbidites fluid flow at all stages in these processes occurred at metamorphic rates mm year and fluids were broadly in equilibrium with the rocks through which they were passing

carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan abstract carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan was separated from the host rocks and its x ray diffraction and chemical composition were studied its crystal structure and chemistry change continously with increasing metamorphic grade and approach those of well ordered graphite near the biotite isograd as graphitization is a rate process the temperature of complete graphitization differs from one metamorphic terrain to another as a function of the duration of metamorphism in an individual metamorphic terraan however the degree of graphitization is a useful indicator of relative metamorphic temperature in lower grade rocks

microscale chemical heterogeneity in groundwater ronen d magaritz m gvirtzman h and garner w 1987 microscale chemical hetereogeneity in groundwater j hydrol 92 173 178 large variations in the concentration of cl no a and so42 in the upper water layers of a polluted aquifer were found between samples that were vertically separated by as little as 3 cm this was disclosed when a multilayer dialysis cell device was used to obtain undisturbed real time samples from test wells this first time presentation of chemical fine structure provides new insights into mechanisms of contamination of an aquifer by surface inputs and raises the question of the validity of groundwater quality data based on single samples however obtained

shear induced graphitization of carbonaceous materials during seismic fault motion experiments and possible implications for fault mechanics abstract carbonaceous materials often concentrate in fault zones developed in pelitic rocks among carbonaceous minerals graphite is known as a lubricant and possibly plays a key role in frictional properties of the fault graphite reported from slip localized zones suggests that graphitization can occur during seismogenic fault motion thus we performed friction experiments on amorphous carbon and graphite to investigate how graphite forms in association with fault motion and how these carbonaceous minerals affect frictional properties of faults experiments were done at normal stresses of 0 5 2 8 mpa and slip rates of 50 m s to 1 3 m s in atmospheres of air and n 2 gas using rotary shear apparatuses xrd and tem analyses revealed that graphitization can indeed occur during seismogenic fault motion perhaps due to large shear strain short lived flash heating and stress concentration at asperity contacts even at low temperatures and pressures under anoxic environments we found large differences in steady state friction coefficient ss between graphite ss 0 1 and amorphous carbon ss 0 54 at low slip rate but amorphous carbon exhibits marked velocity weakening at slip rate above 10 mm s and its steady state friction reduces to the same level as that of graphite at a slip rate of 1 3 m s faults with amorphous carbon are not weak at low slip rates but they can become dynamically weak to foster fault motion during the generation of large earthquakes enriched graphite in fault zones can lubricate at all slip rates even at great depths and should receive more attention

geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock macraes gold mine otago schist new zealand abstract the macraes gold deposit in the otago schist new zealand formed during late metamorphic fluid flow through a lower greenschist facies shear zone mineralisation occurred near to the brittle ductile transition at about 300 c large volumes of host rock in a shear zone up to 120 m thick have been hydrothermally altered by this fluid activity most alteration is not structurally controlled apart from proximity to the shear zone ductile and brittle microshears traverse the most mineralised rocks and some structural control of fluid flow occurred as well fluid flow was slow similar to that in metamorphic rocks mm year and diffusion through interconnected fluid was a significant chemical process localised extensional hydrofractures m scale are filled with mineralised quartz most alteration of the host rocks was isochemical with respect to the lithophile elements and mineralised rocks have been variably enriched in as au sb w mo and bi but not co or cd addition of sulphur has occurred to both host rocks and mineralised rocks up to 1 wt above a background of 0 1 wt host rock sulphur is mainly pyritic and is not structurally controlled mineralised rocks have pyrite and arsenopyrite along microshears pyrite chalcopyrite sphalerite and galena have formed from sulphidation of silicates with no addition of metals graphite has been added to mineralised rocks along microshears up to 3 wt locally above a background of 0 1 wt noncarbonate carbon graphite deposition may have occurred as a result of mixing of two fluids water methane and water carbon dioxide graphitisation and sulphidation reactions released low d water which accumulated in the slow moving mineralising fluid distinction between this low d reaction water and meteoric water incursion is difficult

graphitization of organic matter and fluid deposited graphite in palaeoproterozoic birimian black shales of the kaya goren greenstone belt burkina faso west africa palaeoproterozoic black shales form an essential part of the birimian volcanosedimentary belt in burkina faso west africa the mean rmax values and the atomic h c values of the bulk carbonaceous matter bcm together with rock structures and mineral assemblages indicate that these carbon rich rocks were metamorphosed to sub greenschist and low grade greenschist facies x ray diffraction reveals that the 002 graphite peak width in half maximum fwhm ranges from 0 43 to 0 71 2 in sub greenschist facies and from 0 27 to 0 41 2 in greenschist facies rocks but the d 002 values in both groups of rocks are approximately the same 3 35 a the bcm of individual samples is composed of particles with very variable shape reflectance and raman spectra type i particles that predominate in sub greenschist facies are fine grained irregular or elongate bodies 1 to 3 m in size their maximum reflectance rmax ranges between 2 5 and 8 2 and raman parameters r1 and r2 range from 0 5 to 1 4 and 0 5 to 0 8 respectively type ii particles are lath shaped up to 40 m large bodies commonly arranged parallel to white mica flakes the number of these particles increases from sub greenschist to greenschist facies maximum reflectance varies between 6 and 11 2 and r1 and r2 raman parameters range from 0 05 to 0 7 and from 0 1 to 0 5 respectively type iii particles occur in hydrothermally altered and sheared rocks these are nodular aggregates composed of grains up to 10 m in size this type of particles has very high reflectance rmax 11 15 and its raman spectra indicate a very high degree of structural ordering corresponding to well ordered graphite type i particles represent original organic matter in the metasediments type ii particles are believed to have been formed either in situ by solid state transformation of type i particles or by crystallization from metamorphic fluids gradual graphitization of the type i organic particles and the growth of lath shaped type ii particles from a fluid phase is assumed to have taken place under the peak metamorphic conditions associated with the burial of birimian sediments during thrust tectonism progressive tectonic accretion and crustal thickening during the d1 event of the eburnean orogeny the growth of equant high reflectance postkinematic nodular aggregates of type iii particles is ascribed to the reduction of co2 rich fluids during a hydrothermal event associated with late eburnean d2 exhumation and strike slip movements type i carbonaceous particles were only slightly affected by high temperature low pressure contact metamorphism during intrusion of late eburnean magmatic bodies whereas formation of type ii or iii particles was not recorded in contact metamorphosed rocks at all

transcurrent tectonics and polycyclic evolution in the lower proterozoic of senegal mali abstract outcrops of the early proterozoic birimian series within the kedougou inlier straddling the mali senegal border have traditionally been described as being composed of a basal volcanic mako series overlain by a detrital carbonate dialle dalema series this geosynclinal context was later reinterpreted in terms of oceanization and subduction as the mako series contains successively basaltic pillow lavas of tholeiitic affinity and a calc alkaline complex however the sedimentary dialle dalema series lie in the core of a major anticlinorium and the rocks show overprinting of an earlier by a later tectonic phase the volcanic and sedimentary rocks of the mako series were affected only by the later tectonic phase in addition a fan delta deposit intercalated between the tholeiitic and calc alkaline rocks contains pebbles of schistose and folded sedimentary rock that clearly belong to the dialle dalema series these observations necessitate a complete revision of the local stratigraphy thus the clastic deposits of the dialle dalema are attributed to the lower birimian and are interpreted as having been deposited in intra cratonic basins the first tectonic phase took place before emplacement of the volcanic sereis which shows evidence of an extensional setting with major crustal fracturing the second deformation affected both the sedimentary and volcanic series structural analysis furthermore shows that the formation of the second cleavage s2 was contemporaneous with the emplacement of major granite bodies as well as with major transcurrent sinistral shear zones finally this evolution is shown to be comparable with that in other lower proterozoic terranes of the west african craton

organic alteration in hydrothermal sulfide ore deposits many ore deposits are enriched in transition metals especially iron whereas organic carbon is a minor component based on currently available analyses variations in bulk chemistry of organic matter in ore deposits correlates with differences in phase equilibria in the system fe s h 2 o in the pyrrhotite and magnetite stability fields extractable organic compositions are restricted to molecules with relatively few carbons organic matter in pyrite rich deposits reflects biochemical precursors pyrite also being the stable fe s phase in fossil fuels oxidation of relatively iron poor deposits results in microbial oxidation of the organic matter in iron copper deposits oxidation results in aromatization and the generation of organosulfurs in h 2 o dominated systems the fluid is a hydrogen source to the organic matter whereas organic products in co 2 dominated fluids are hydrogen depleted the organic matter in ore deposits therefore is often considered to be an alteration product reflecting the dominant iron phase temperature and the alteration fluid composition

lithogeochemical localisation of disseminated gold in the white river area yukon canada gold mineralisation in the white river area 80 km south of the highly productive klondike alluvial goldfield is hosted in amphibolite facies gneisses in the same permian metamorphic pile as the basement for the klondike goldfield hydrothermal fluid which introduced the gold was controlled by fracture systems associated with middle cretaceous to early tertiary extensional faults gold deposition occurred where highly fractured and chemically reactive rocks allowed intense water rock interaction and hydrothermal alteration with only minor development of quartz veins felsic gneisses were sericitised with recrystallisation of hematite and minor arsenic mobility and extensively pyritised zones contain gold and minor arsenic ca 10 ppm graphitic quartzites up to 5 wt carbon caused chemical reduction of mineralising fluids with associated recrystallisation of metamorphic minerals graphite pyrrhotite pyrite chalcopyrite in host rocks and veins and introduction of arsenic up to 1 wt to form arsenopyrite in veins and disseminated through host rock veins have little or no hydrothermal quartz and up to 19 wt carbon as graphite late stage oxidation of arsenopyrite in some graphitic veins has formed pharmacosiderite gold is closely associated with disseminated and vein sulphides in these two rock types with grades of up to 3 ppm on the metre scale other rock types in the white river basement rocks including biotite gneiss hornblende gneiss pyroxenite and serpentinite have not developed through going fracture systems because of their individual mineralogical and rheological characteristics and hence have been little hydrothermally altered themselves have little hydrothermal gold and have restricted flow of fluids through the rock mass some small post metamorphic quartz veins metre scale have been intensely fractured and contain abundant gold on fractures up to 40 ppm but these are volumetrically minor the style of gold mineralisation in the white river area is younger than and distinctly different from that of the klondike area some of the mineralised zones in the white river area resemble mineralogically and geochemically nearby coeval igneous hosted gold deposits but this resemblance is superficial only the white river mineralisation is an entirely new style of yukon gold deposit in which host rocks control the mineralogy and geochemistry of disseminated gold without quartz veins

fluid deposited graphitic inclusions in quartz comparison between ktb german continental deep drilling core samples and artificially reequilibrated natural inclusions we used raman microsampling spectroscopy rms to determine the degree of crystallinity of minute 2 15 m graphite inclusions in quartz in two sets of samples experimentally reequilibrated fluid inclusions in a natural quartz grain and biotite bearing paragneisses from the ktb deep drillhole in se germany our sequential reequilibration experiments at 725 c on initially pure co2 inclusions in a quartz wafer and the j krautheim 1993experiments at 900 1100 c on organic compounds heated in gold or platinum capsules suggest that at a given temperature 1 fluid deposited graphite will have a lower crystallinity than metamorphosed organic matter and 2 that the crystallinity of fluid deposited graphite is affected by the composition of the fluid from which it was deposited we determined that the precipitation of more crystalline graphite is favored by lower f h2 higher f o2 and that the crystallinity of graphite is established by the conditions including gas fugacities that pertain as the fluid first reaches graphite saturation graphite inclusions within quartz grains in the ktb rocks show a wide range in crystallinity index reflecting three episodes of carbon entrapment under different metamorphic conditions isolated graphite inclusions have the spectral properties of totally ordered completely crystalline graphite such crystallinity suggests that the graphite was incorporated from the surrounding metasedimentary rocks which underwent metamorphism at upper amphibolite facies conditions much of the fluid deposited graphite in fluid inclusions however shows some spectral disorder the properties of that graphite resemble those of experimental precipitates at temperatures in excess of 700 c and at elevated pressures suggesting that the inclusions represent precipitates from c o h fluids trapped under conditions near those of peak metamorphism at the ktb site in contrast graphite that is intimately associated with chlorite and other presumably low temperature silicates in inclusions is highly disordered and spectrally resembles kerogens this graphite probably was deposited during later greenschist facies retrograde metamorphism at about 400 500 c the degree of crystallinity of fluid deposited graphite is shown to be a much more complex function of temperature than is the crystallinity of metamorphic graphite to some extent experiments can provide temperature calibration of the crystallinity index however the difference in time scales between experimental runs and geologic processes makes it difficult to infer specific temperatures for naturally precipitated graphite

graphitization in a high pressure low temperature metamorphic gradient a raman microspectroscopy and hrtem study the graphitization of carbonaceous material cm in a high pressure metamorphic gradient is characterized along a cross section in the schistes lustres formation western alps along this 25 km cross section both the cm precursor and the host rock lithology are homogeneous and the prograde evolution of the pressure temperature metamorphic conditions from the lower blueschist facies 13 kbar 330 c to the eclogite facies 20 kbar 500 c is tightly constrained by literature data raman microspectroscopy shows that at the micrometre scale this process is progressive and continuous with increasing metamorphic grade and that the structure of cm is very sensitive to temperature variations at the nanometre scale hrtem the cm is composed of a mixture of a microporous phase and an onion ring like phase both known as non graphitizing under the effect of temperature at ambient pressure the hp lt graphitization produces structurally and microtexturally heterogeneous cm with increasing metamorphic grade the graphitization of the two types of cm proceeds up to the triperiodic graphite stage because of microtextural and structural changes that are specific to each type of cm the microporous material is progressively transformed into graphite through a macroporous transitional stage in this case graphitization mainly occurs on the pore walls as a result of pore growth in the case of concentric onion ring like material graphitization occurs in the regions with the largest radius of curvature i e on the outer part of the ring in comparison with 1 bar experiments pressure seems to induce microtextural changes which allows the subsequent structural modifications of the starting material

the role of carbonaceous indicator slates in the genesis of lode gold mineralization in the western lachlan orogen victoria southeastern australia indicator slates have long been considered to represent a useful exploration guide for turbidite hosted mesothermal lode gold mineralization in central victoria this assumption has been based on an apparent close spatial relationship between high gold grades and the proximity of thin commonly pyritic and carbon rich marker units detailed studies in a number of gold deposits throughout central victoria however reveal that highest gold grades do not necessarily coincide with the presence of carbonaceous units in many places where gold mineralization is associated with carbon rich matter the high c accumulations are the result of epigenetic remobilization during hydrothermal alteration and ore genesis petrographic geochemical and stable isotope c o s investigations into the origin and nature of the carbonaceous matter mainly amorphous bitumens and pyrobitumen of organic origin with biological fragments and rare graphite of both detrital and metamorphic origin demonstrate that black shales within the cambro ordovician succession in central victoria lacked the vital constituents to provide 1 a primary sink for precious metals and 2 whereas the presence of carbonaceous matter was likely to affect the evolution of epigenetic hydrothermal fluids and locally may have facilitated gold enrichment carbon rich sedimentary rocks were not crucial for ore genesis on the deposit scale instead the size of the hydrothermal cell physicochemical conditions of the ascending fluids and dynamic fault valve behavior played far more significant roles in controlling gold precipitation the importance of these processes has implications for exploration targeting sediment hosted lode and disseminated style gold mineralization in the western lachlan orogen and in slate belt provinces elsewhere

early proterozoic ore deposits and tectonics of the birimian orogenic belt west africa abstract the early proterozoic of the west african craton comprises a series of volcanic troughs and sedimentary basins the birimian with granitic terranes accreted on archean nuclei in the man and reguibat shields studies of the birimian of the man shield indicate a model of polycyclic evolution with a major collision event d 1 2 1 ga thrusting part of the proterozoic terrane over the archean before individualization of numerous volcanic troughs and clastic infill basins the proposed evolution for the birimian orogenic belt comprises 1 deposition of the sedimentary lower birimian b1 with minor tholeiitic volcano sedimentary intercalations containing chert and or mn formations and with most of the detritus being derived from early proterozoic sources apart from contamination near the proterozoic archean contact 2 pre b2 crustal thickening related to d 1 thrusting 3 formation over about 40 ma of the upper birimian b2 with numerous volcanic troughs of different composition tholeiitic and rare komatiitic bimodal tholeiitic to calc alkaline volcano plutonic and tarkwaian clastic infill basins and 4 major transcurrent tectonics with sinistral d 2 and dextral d 3 strike slip faults such a tectonic evolution from a collision d 1 phase to a transcurrent d 2 d 3 phase is typical of collision belts and in the present case the evolution of the birimian orogenic belt can be extended into guyana the metallogenic history of the birimian shows a three phase evolution coinciding with the orogenic evolution and extends over almost 150 ma from the perkoa massive zn ag sulfides 2 12 ga with a clear mantle affinity to the latemesothermal au quartz veins 2 ga with according to lead isotopes a high crustal participation the economic mineralization of belt thus consists of 1 1 pre orogenic pre d 1 deposits related to early extension zones this was diverse with stratiform au tourmalinite type 1 au loulo in mali dorlin in guyana stratiform fe cu faleme in senegal and mn nsuta in ghana tambao in burkina faso and a single massive zn ag sulfide deposit perkoa in burkina faso associated with regional volcanosedimentary variably tholeiitic stratigraphic marker beds 2 2 syn orogenic post d 1 to syn d 2 d 3 deposits with disseminated au sulfides type 2 au yaoure in the ivory coast in extensional zones of the b2 followed by auriferous paleoplacers type 3 au in b2 extensional zones tarkwaian banket conglomerate or syn d 2 transtensional zones debris flow of orapu in guyana 3 3 late orogenic post peak d 2 d 3 deposits with mesothermal au mineralization evolving from a disseminated gold bearing arsenopyrite and au quartz lode type type 4 au ashanti in ghana to a quartz vein type with free gold and cu pb zn ag bi paragenesis most of the gold in west africa comes from this phase finally the metallogeny of the birimian appears as rich in au and mn formations and poor in volcanogenic mineralization and bif it differs from the archean metallogeny of west africa and other regions through the presence of certain deposit types such as au stratiform tourmalinite gold bearing conglomerate with au and fe ti oxides but no uranium or sulfides and au arsenopyrite rich shear zone deposits that are very common in but not exclusive to the proterozoic and paleozoic

multistage graphite precipitation through protracted fluid flow in sheared metagranitoid digana sri lanka evidence from stable isotopes abstract the digana metagranitoid situated within the digana shear zone a critical junction between the highland and wanni complexes of sri lanka hosts a variety of graphite types with structural evidence showing formation during different stages prior to and after deformational events affecting this terrain here we discuss their occurrence association and stable isotopes the carbon isotopes of graphite reported in this study from the sri lankan high grade metamorphic terrain differ significantly from the composition of graphite reported elsewhere in other precambrian terrains the stable isotope composition from random crystals depicts an enriched carbon isotopic composition in the range 1 6 to 8 suggesting precipitation by reduction from co2 rich fluids intracrystalline microscale traverses made on graphite crystals indicate the 13c composition of the rims becoming progressively lighter in 13c in metagranitoid hosted samples with the variation reaching up to 1 5 consistent with the changing fluid regimes induced by decreasing temperature during the graphite growth and shows the preservation of core at higher temperatures a highly enriched carbon isotopic composition 0 6 with a rimward enrichment of 13c observed in migmatites contrary to the values in metagranitoid indicates preferential enrichment of heavy isotopes as a result of the partial melting and dissolution reprecipitation of graphite the oxygen isotopic composition of a quartz calcite vein show values in the range 18 5 to 20 typical for recycled crustal source the tight constraint in the isotopic data from different graphite types studied indicates a homogeneous fluid source for the deposits prolonged fluid flow in this region is envisaged in this study which is related to the multistage deformation of the crustal scale shear zone

gold mineralization without quartz veins in a ductile brittle shear zone macraes mine otago schist new zealand greenschist facies schist which hosts the macraes mine in east otago new zealand has been pervasively altered by post metamorphic lower greenschist facies fluids over a 120 m thick section perpendicular to foliation metamorphic titanite has been replaced by rutile and epidote has been replaced by a variety of metamorphic minerals including siderite chlorite muscovite and calcite the early stages of this alteration occurred during development of a ductile cleavage associated with kilometre scale recumbent folding the cleavage was widely overprinted by a subparallel set of spaced mm scale microshears which are locally enriched in rutile and hydrothermal graphite strain was then concentrated into narrow m scale zones where more intensely deformed portions of the rock are crossed and highly disrupted by closely spaced 100 m scale microshears the highly strained rocks show a combination of mylonitic and cataclastic microstructures including crystal plastic grain size reduction and recrystallization of micas to form a new foliation muscovite has grown at the expense of albite in the mylonitic cataclasites hydrothermal alteration was accompanied by addition of pyrite arsenopyrite and gold without development of quartz veins gold precipitated with sulphides during reduction of the fluid by hydrothermal graphite the whole altered rock sequence was later cut sporadically by mesothermal quartz veins which contain gold scheelite rutile pyrite and arsenopyrite this deposit displays a continuum of post metamorphic processes and hydrothermal fluid flow which occurred during uplift of the schist belt

evidence for the influence of fch 4 on the crystallinity of disseminated carbon in greenschist facies rocks rhode island usa disseminated carbon has been extracted from 19 samples of arkosic rocks from the chlorite biotite and garnet zones in the narragansett basin and analysed by x ray diffraction xrd and scanning electron microscopy sem xrd of these samples yields only the 002 peak which may be as much as four times wider than the silicon internal standard peak and is always skewed to low angles 2 all 002 peaks were digitized and the four moments calculated the results suggest that width at half height w1 2 provides a poorer estimate of peak shape than coefficients of skewness and kurtosis the positive correlation of these coefficients with grain size determined by sem in the range of 0 1 100 m suggest a direct relationship between peak shape and grain size

fluid characteristics of granitoid hosted gold deposits in the birimian terrane of ghana a fluid inclusion microthermometric and raman spectroscopic study fluid inclusions in vein quartz from 10 granitoid hosted gold deposits and prospects in the birimian terrane of ghana as well as from the sansu mine ashanti shear zone type and quartz veins in the nonmineralized princess town granodiorite were studied by microthermometry and raman microspectrometry fluid inclusions from the granitoid hosted gold deposits are dominated by aqueous h2o co2 nacl type 1 and liquid co2 n2 ch4 type 2 with minor 10 aqueous h2o nacl type 3 type 1 inclusions show large variations in co2 phase volume proportions 10 90 at 25 c and have salinities commonly between 0 and 6 wt percent nacl equiv their bulk densities fall in a major range from 0 62 to 1 11 g cm3 type 2 inclusions show no visible h2o phase at room temperature and have bulk densities between 0 30 and 0 92 g cm3 type 3 inclusions containing 10 to 20 vol percent h2o vapor have salinities of 1 to 8 wt percent nacl equiv and bulk densities of 0 77 to 1 03 g cm3 in most cases the three types of fluid inclusions coexist as groups in individual quartz grains of the samples studied these fluid inclusions are interpreted to be trapped during phase separation of an originally homogeneous h2o co2 fluid with low salinity 6 wt nacl equiv and moderate to high density 0 65 0 95 g cm3 the type 1 fluid inclusions are suggested to be heterogeneous mixtures of the two end members of type 2 and 3 inclusions fluid immiscibility is documented by petrographic characteristics and microthermometric results of the three types of inclusions trapping temperatures and pressures estimated from microthermometry of type 3 inclusions equation of state and the p t x nature of the h2o co2 nacl system are mainly between 200 and 350 cand 1 and 3 kbars for the gold deposits by contrast fluid inclusions in the sansu mine at ashanti mostly comprise the liquid co2 n2 ch4 type 2 the inclusions are considered to represent postentrapment modifications of trapped fluids in addition fluid inclusions in barren vein quartz from the princess town granodiorite comprise the low salinity commonly 6 wt nacl equiv h2o nacl type 3 raman microspectrometry shows that gaseous compositions of fluid inclusions from both granitoid and shear zone hosted gold deposits are mainly composed of co2 80 95 mol with significant amounts of n2 2 20 mol and ch4 0 10 mol the distinct low salinity h2o co2 rich fluids from the granitoid hosted gold deposits are comparable in composition to those from the major ashanti and tarkwaian types of gold deposits in the birimian terrane of ghana these fluids are most likely to be metamorphic in origin and associated with the waning stages of the regional birimian orogeny gold deposition within the birimian granitoids was related to fluid phase separation and sulfidization of host rocks during hydrothermal alteration and mineralization the present study together with previous publications suggests that fluid inclusions are characterized by h2o co2 nacl and or co2 n2 ch4 types in mineralized areas whereas h2o nacl fluid compositions dominate in barren areas fluid inclusion characteristics may therefore be a useful tool for regional gold exploration in the birimian terrane of ghana

raman spectroscopic carbonaceous material thermometry of low grade metamorphic rocks calibration and application to tectonic exhumation in crete greece we present new raman spectra data of carbonaceous material cm to extend the range of the raman spectra of cm thermometer rscm to temperatures as low as 100 8c previous work has demonstrated that raman spectroscopy is an excellent tool to describe the degree of graphitization of cm a process that is independent of pressure but strongly dependent on metamorphic temperature a linear relationship between temperature and the raman parameter r2 derived from the area of the defect band relative to the ordered graphite band forms the basis of a previous thermometer because r2 shows little variability in low temperature samples 330 8c serves as a lower limit on the existing thermometer herein we present raman spectra from a suite of low temperature 100 to 300 8c samples from the olympics mountains and describe other aspects of the raman spectra of cm that vary over this range in particular the raman parameter r1 the ratio of heights of the disordered peak to ordered peak varies regularly between 100 and 350 8c these data together with published results from higher temperature rocks are used to calibrate a modified rscm thermometer applicable from 100 to 700 8c application to low grade metasediments in the otago region in the south island of new zealand gives temperatures consistent with previous estimates demonstrating the reliability of the modified rscm thermometer we apply the modified rscm thermometer to 53 samples from crete to evaluate the role of the cretan detachment fault in exhuming miocene high pressure low temperature metamorphic rocks exposed there the metamorphic rocks below the detachment the plattenkalk and phyllite quartzite units give metamorphic temperatures that range from 250 to 400 8c consistent with previous petrologic estimates we also demonstrate that the tripolitza unit which lies directly above the detachment gives an average metamorphic temperature of about 260 8c the modest break in metamorphic temperature in central crete indicates that the cretan detachment accounts for only 5 to 7 km of exhumation of the underlying hp lt metamorphic rocks which were initially accreted at 35 km we argue that the bulk of the exhumation 28 km out of 35 km total occurred by pervasive brittle stretching and erosion of structural units above the detachment d 2005 elsevier b v all rights reserved

geological controls on refractory ore in an orogenic gold deposit macraes mine new zealand the macraes mine is hosted in an orogenic mesothermal gold deposit in metasedimentary rocks of the otago schist belt much gold occurs within altered schist with minimal silica addition and this study focuses on altered schist ore types the unmineralized host schists are chemically and mineralogically uniform in composition but include two end member rock types feldspathic schist and micaceous schist both rock types have undergone hydrothermal alteration along a shallow dipping foliation parallel shear zone but their different rheological properties have affected the style of mineralisation micaceous schist has been extensively recrystallized and hydrothermally altered during ductile deformation to form ores characterized by abundant disseminated millimetre scale pyrite cubes typically 1 2 wt s and minor silicification the earliest pyrite contained ni and or as in solid solution and no gold was imaged in these pyrites or later arsenopyrite grains the ore type is refractory and gold recovery by cyanide leaching is less than 50 with lowest recovery in rocks that have been less affected by later brittle deformation in contrast hydrothermally altered feldspathic schist is characterized by mineralised black microshears and veinlets formed during shear zone related brittle deformation microsheared ore has relatively low sulphur content 0 7 wt and muscovite has been illitised during hydrothermal alteration pyrite and arsenopyrite in microshears are fractured and deformed and contain 1 10 m blebs of gold later pyrite veinlets also contain micron to submicron scale inclusions of sphalerite chalcopyrite galena and gold 10 microns gold in microsheared ore is more readily recoverable than in the refractory ore although encapsulation of the fine gold grains inhibits cyanidation both microsheared ore and disseminated pyritic ore pass laterally into mineralised black shears which contain hydrothermal graphite and late stage cataclastic sulphides this black sheared ore releases gold readily but the gold is then adsorbed on to gangue minerals preg robbed and net cyanidation recovery can be less than 50 hence low gold recovery during cyanidation results from 1 poor liberation of gold encapsulated in microcrystalline quartz and unfractured sulphide grains and 2 preg robbing of liberated gold during cyanidation introduction of pressure oxidation of ore prior to cynidation has mitigated these issues

the association of poorly ordered graphite coke and bitumens in greenschist facies rocks of the ponikla group lugicum czech republic the result of graphitization of various types of carbonaceous matter greenschist facies rocks of the ponikla group ordovician silurian czech republic contain several types of carbonaceous matter that differ in their morphology texture reflectance and raman characteristics the first type consists of large up to 3 mm irregularly bound particles of low reflectance romin 0 9 romax 5 6 the area ratio of the 1585 cm 1 to 1350 cm 1 raman peaks 1 08 1 17 indicates an intermediate degree of graphitization the formation of this type of highly porous particle displaying a texture reminiscent of regular or needle coke is attributed to the thermal alteration of the amorphous structureless kerogen of the precursor sediments the second type consists of lamellar particles up to 30 m thick which can be associated with the latter or can occur independently in white mica rich laminae this type is characterized by high bireflectance romin 0 6 romax 11 9 and by lower ratios 0 70 0 82 of the raman peak areas these particles are interpreted as the product of solid state diffusion controlled graphitization of a chemically homogeneous organic material e g of graptolite periderms the third type consists of isometric up to 2 mm large commonly fractured grains and fragments which mainly occur in quartz rich laminae in reflected light the texture is either homogeneous or consists of various types of anisotropic mozaics the raman peak area ratios 0 75 1 14 indicate a highly variable degree of structural ordering these particles are considered as the remains of metamorphosed bitumens accumulated in the sandy laminae of the original sediments the fourth type consists of small particles of carbonaceous matter maximum length 25 m thickness 1 2 m which occur adjacent to crystal faces of white micas this type is probably the product of epitaxial growth of graphite from the gaseous phase the results of this work indicate that the differences in the degree of graphitization of the carbonaceous matter in low grade metamorphosed rocks can be mainly related to the initial nature of the sedimentary organic matter and to its premetamorphic history

conversion of carbonaceous material to graphite within the greywacke zone of the eastern alps morphology and reflectance of carbonaceous material cm in late carboniferous metasediments of the eastern greywacke zone eastern alps indicate a mixture of vitrinite grainy textured and lamellar shaped particles as imaged by high resolution atomic force microscopy vitrinite and the grainy textured particles show mesophase structures which can be described as facetted nanocrystals within the carbon matrix high resolution transmission electron microscopy has revealed two types of microtextures representing different degrees of graphitization the first type is characterized by elongated ring shaped microtextures whereas the second type is characterized by graphite lamellae and polygonal flakes with long range ordered aromatic layers in spite of the heterogeneity of the cms the geographical distribution of quantitative metamorphic parameter raman spectra parameter x ray diffraction pattern microscopic reflectance suggests a graphitization process which is promoted by advective heat transport during post collisional processes in a tentative pressure time path late cretaceous thrusting results in a turbostratic ordering of the aromatic layer ordering to long range ordered aromatic layers was achieved during the late cretaceous paleogene exhumation of mid crustal rocks beneath the eastern greywacke zone

stable carbon isotopes of amorphous kerogens from phanerozoic sedimentary rocks amorphous kerogens from phanerozoic sedimentary rocks may be divided into two groups on the basis of their 13c values h amorphous kerogens have isotopic values in the range of 24 to 20 per mil and l amorphous kerogens have isotopic values in the range of 35 to 26 per mil the occurrence of amorphous kerogens in the intermediate isotopic range from one rock unit in the data set suggests a weak continuum may exist between these two groups phytoplankton and to a lesser extent zooplankton and bacteria are considered to be the precursors for both kerogen types a plausible explanation for this dichotomy may be found in the source of co2 utilized by phytoplankton which is considered to be controlled by environmental factors h amorphous kerogens are expected to occur in silled basins that are overlain by expansive well circulated deep 500 m water where the prevailing source of carbon in the photic zone is atmospheric derived co2 conversely l amorphous kerogens are expected to occur in restricted basins that are overlain by stratified shallow 200 m water where the prevailing source of carbon in the photic zone may be organic derived co2

lithogeochemical and stratigraphic controls on gold mineralization within the metavolcanic rocks of the hoyle pond mine timmins ontario the hoyle pond gold deposit is hosted in complexly deformed mafic ultramafic volcanic rocks of the hersey lake and central formations tisdale assemblage in the porcupine gold camp located approximately 15 km northeast of timmins in the abitibi greenstone belt the deposit is hosted within a homoclinal sequence of south facing stacked volcanic flows of high mg tholeiitic basalt basaltic komatiite and komatiite flows and interbedded high mg tholeiitic basalt and fe rich tholeiitic basalts the bulk of the gold mineralization was emplaced at lithologic contacts along late shear zones associated with isoclinal folding and thrusting the mineralization is characterized by micron to centimeter sized flakes of free gold or veinlets in quartz carbonate dolomite and ferroan dolomite shear and extension vein arrays at the mine scale a broad carbonate alteration is evident two alteration zones surrounding the veins were mapped at the meter scale an inner sericite alteration zone composed of sericite muscovite fuchsite cr muscovite quartz arsenopyrite pyrite ferroan dolomite dolomite and graphite plus tourmaline and an outer zone of albite alteration consisting of albite quartz ferroan dolomite and dolomite geochemical analyses of 355 samples show that the ree zr al2o3 tio2 and y were largely immobile during alteration and mineralization co2 k2o na2o cr2o3 rb as b sio2 and cao and locally fe2o3 feo and mgo were mobile during alteration and mineralization the chromium enrichment is not primary and is interpreted to have been caused by remobilization from ultramafic rocks during mineralization in addition an intense graphite alteration originally derived from organic matter probably from sedimentary rocks and now associated with mineralization is present in zones that were porous and permeable at the time of mineralization in common with other mesozonal orogenic gold deposits gold was likely transported as a thio complex the cr enrichment in the wall rock indicates that cr was mobile most likely as cr6 because species such as cr6 are transported under oxidizing conditions and carbon and au hs species are transported under reduced conditions we suggest that more than one fluid was involved in the mineralization and or alteration mixing between reducing and oxidizing fluids is thought to have reduced cr6 to cr3 oxidized the organic matter to form graphite oxidized sulfur to form sulfides and precipitated au this is consistent with the observed para genesis reducing fluids rich in boron arsenic carbon and au may have been generated from sedimentary rocks porcupine assemblage at depth and expelled during orogenesis into syndeformation structures within overlying volcanic rocks where they mixed with oxidizing fluids containing cr k2o sio2 na2o and cao

organic geochemistry and mineralogy i characterisation of organic matter associated with metal deposits abstract as geochemical appraisals of mineral regions of commercial prospectivity evolve the organic matter associated with metal rich ores has attracted greater attention petroleum basin and modern seafloor hydrothermal vent studies have suggested that organic matter can have a significant influence on the behaviour of mineralising fluids there have been many isolated reports of certain organic compositional or morphological e g pyrobitumen features showing an apparent relationships with hydrothermal fluids or minerals raising expectations that organic based parameters might be useful to mineral exploration however the understanding of organic inorganic relationships in earth systems is far from complete for example the detailed mechanics of the interaction of organics with hydrothermal fluids over geological time remain largely undefined organic geochemistry studies have traditionally involved the measurement and interpretation of the hydrocarbon composition of sedimentary rocks here we review the types of aliphatic hydrocarbons aromatic hydrocarbons and metalloporphyrins often detected from organic geochemical investigations in mineral rich regions such molecular data can be particularly diagnostic of biochemical sources and the palaeo environments at the time mineral associated organic matter was deposited sub surface trends of hydrocarbon alteration may also reflect major biogeochemical processes such as thermal maturity and biodegradation organic geochemistry data can also occasionally provide information about the nature e g origin composition temperatures and migration pathways of hydrothermal fluids and can make a contribution to holistic ore genesis models the well preserved organic matter associated with the economic here s your chance pb zn ag mine paleoproterozoic barney creek formation mcarthur basin australia and the transition metal rich early permian kupferschiefer formation germany poland have attracted significant attention a more detailed summary of the organic character of these deposits is provided to highlight the contribution organic geochemistry can make to understanding mineralisation processes most organic geochemical studies of highly mineralised regions however have not adequately addressed the significance of organic matter to mineralisation a slightly different analytical focus than traditionally used for exploration appraisal of petroleum hydrocarbons may be required to properly evaluate the significance of organic species to the mobilisation transport and deposition of ore metals the characterisation and subsequent thermodynamic modeling of organic substances and complexes within metalliferous hydrothermal systems will contribute to a better understanding of the nature and role of organic inorganic fluids or other affiliated organics in ore systems

very low grade metamorphic evolution of pelitic rocks under high pressure low temperature conditions nw new caledonia sw pacific the p t gradient in a late eocene low t high p metamorphic belt in northern new caledonia increases from sw to ne metapelites in the pumpellyite prehnite and blueschist zones contain lawsonite mg carpholite fe stilpnomelane and fe glaucophane thermodynamic calculations indicate a progression of metamorphic conditions from less than 0 3gpa and 250 c in a kaolinitebearing rock in the sw up to 1 5gpa and 410 c in a lawsonite glaucophane bearing sample in the ne of the diahot terrane through a multi method investigation of phyllosilicates organic matter and fluid inclusions we demonstrate that the evolution of organic matter and illite crystallinity depends strongly on the evolution of the p t path with time in addition we show that the illite muscovite b cell dimension provides a robust estimate of maximum pressure reached in low temperature domains with polyphase metamorphic histories despite subsequent hightemperature low pressure events fluid inclusion study reveals an isothermal decompression in the diahot terrane

age constraints on gold mineralization and paleoproterozoic crustal evolution in the ashanti belt of southern ghana abstract u pb isotopic dating in the region of the ashanti belt in ghana has been carried out to improve understanding of crustal evolution and gold mineralization in this paleoproterozoic terrane a u pb zircon age of ca 2174 2 ma for a belt type granitoid from sekondi accords with previous ages on belt type plutons in ghana but metamorphic titanite within this granitoid gives an age of 2092 3 ma coeval with intrusion of the late basin type granitoids the within belt granitoid at banso village has an age close to 2097 3 ma which falls into the age range typical for basin type granitoids 2116 2088 ma these results indicate that widespread plutonism in the birimian sedimentary basins also produced magmatic and metamorphic effects within the volcanic belts most dated detrital zircons from birimian metasediment samples at the ashanti gold mine agree in age at 2155 2 ma with others that are slightly older this gives a maximum estimate for the depositional age of the sediments and for gold mineralization at the ashanti gold mine hydrothermally altered and auriferous granitoid plutons along the western flank of the ashanti belt at anyankyerim nhyiaso yaomensakrom and esuajah ayanfuri all have intrusion ages within error of 2105 2 ma this is also the age of metamorphic titanite in an unmineralized basin type granitoid at kwapia rutiles from the hydrothermally altered yaomensakrom and the mineralized esuajah ayanfuri granitoid were dated at 2098 7 and 2086 4 ma respectively and probably provide minimum ages on gold mineralization these data indicate a close temporal association among auriferous granitoid plutons near the western margin of the ashanti belt at 2105 ma gold mineralization may be only slightly younger than magmatic emplacement of the plutons granitic plutonism in the sedimentary basins metamorphism and hydrothermal gold mineralization in southern ghana are all part of a major crust formation event the eburnean orogeny that can be constrained to the time range 2120 2080 ma

c o h s fluid composition and oxygen fugacity in graphitic metapelites c 0 h fluid produced by the equilibration of hzo and excess graphite must maintain the atomic h o ratio of water 2 1 this constraint implies that all thermodynamic properties of the fluid are uniquely determined at isobaric isothermal conditions the o h20 and co fugacities j fhto and fc of such fluids have been estimated from equations of state and fit as a function of pressure and temperature these fugacities can be taken as characteristic for graphitic metamorphic systems in which the dominant fluid source is dehydration e g pelitic lithologies because there are no compositional degrees of freedom for graphite saturated fluids produced entirely by dehydration the variance of the dehydration process is not increased in comparison with that in non graphitic systems thus compositional buffering of c 0 h fluids by dehydration equilibria a common petrological model requires that redox reactions decarbonation reactions or external h o 2 fluid sources perturb the evolution of the metamorphic system such perturbations are not likely to be significant in metapelitic environments but their tendency will be to increase the fo of the fluid phase at high metamorphic grades pyrite desulphidation reactions may cause a substantial reduction of fhz0 and slight increases info and fcs relative to sulphur free fluid at low metamorphic grade sulphur solubility in h o s 2 fluids is so low that pyrite decomposition must occur by sulphurconserving reactions that cause iron depletion in silicates a common feature of sulphidic pelites with increasing temperature and sulphur solubility pyrite desulphidation may be driven by dehydration reactions or infiltration of h o rich fluids the absence of magnetite and the assemblages carbonate aluminosilicate or pyrite pyrrhotite ilmenite from most graphitic metapelites is consistent with an h o 2 model for gcoh s fluid for graphitic rocks in which such a model is inapplicable a phase diagram variable that defines the h o ratio of gcoh s fluid is more useful than the conventional

the rožna uranium deposit bohemian massif czech republic shear zone hosted late variscan and post variscan hydrothermal mineralization three major mineralization events are recorded at the ro na uranium deposit total mine production of 23 000 t u average grade of 0 24 u 1 pre uranium quartz sulfide and carbonate sulfide mineralization 2 uranium and 3 post uranium quartz carbonate sulfide mineralization 1 k ar ages for white mica from wall rock alteration of the pre uranium mineralization style range from 304 5 5 8 to 307 6 6 0 ma coinciding with the post orogenic exhumation of the moldanubian orogenic root and retrograde metamorphic equilibration of the high grade metamorphic host rocks the fluid inclusion record consists of low salinity aqueous inclusions together with h2o co2 ch4 co2 ch4 and pure ch4 inclusions the fluid inclusion paragenetic and isotope data suggest that the pre uranium mineralization formed from a reduced low salinity aqueous fluid at temperatures close to 300 c 2 the uraniferous hydrothermal event is subdivided into the pre ore ore and post ore substages k ar ages of pre ore authigenic k feldspar range from 296 3 7 5 to 281 0 5 4 ma and coincide with the transcurrent reorganization of crustal blocks of the bohemian massif and with late stephanian to early permian rifting massive hematitization albitization and desilicification of the pre ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the moldanubian domain the wide range of salinities of fluid inclusions is interpreted as a result of the large scale mixing of basinal brines with meteoric water the cationic composition of these fluids indicates extensive interaction with crystalline rocks chlorite thermometry yielded temperatures of 260 c to 310 c during this substage uranium was probably leached from the moldanubian crystalline rocks the hydrothermal alteration of the ore substage followed or partly overlapped in time the pre ore substage alteration k ar ages of illite from ore substage alteration range from 277 2 5 5 to 264 0 4 3 ma and roughly correspond with the results of chemical u pb dating of authigenic monazite 268 50 ma the uranium ore deposition was accompanied by large scale decomposition of biotite and pre ore chlorite to fe rich illite and iron hydrooxides therefore it is proposed that the deposition of uranium ore was mostly in response to the reduction of the ore bearing fluid by interaction with ferrous iron bearing silicates biotite and pre ore chlorite the th data on primary mostly aqueous inclusions trapped in carbonates of the ore substage range between 152 c and 174 c and total salinity ranges over a relatively wide interval of 3 1 to 23 1 wt nacl eq gradual reduction of the fluid system during the post ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite chlorite thermometry yielded temperatures of 150 c to 170 c solid bitumens that post date uranium mineralization indicate radiolytic polymerization of gaseous and liquid hydrocarbons and their derivatives the origin of the organic compounds can be related to the diagenetic and catagenetic transformation of organic matter in upper stephanian and permian sediments 3 k ar ages on illite from post uranium quartz carbonate sulfide mineralization range from 233 7 4 7 to 227 5 4 6 ma and are consistent with the early tethys central atlantic rifting and tectonic reactivation of the variscan structures of the bohemian massif a minor part of the late variscan uranium mineralization was remobilized during this hydrothermal event

graphite ch4 h2o co2 equilibria at low grade metamorphic conditions equilibrium calculations and published phase equilibria are used to show that at temperatures below 400 c and pressures above 300 bar the fluids coexisting with graphite in the c o h system consist either of co2 h2o mixtures or ch4 h2o mixtures bulk fluid compositions consisting of ch4 h2o will unmix to methane rich fluid and h2o rich liquid at temperatures below about 325 c compositions on the co2 h2o join will unmix only at temperatures below about 275 c oxygen fugacity in the ch4 h2o graphite three phase region is fixed at constant p and t and approximately equal to that of the quartz magnetite fayalite assemblage in the co2 h2o graphite three phase region oxygen fugacity is about three orders of magnitude greater from the end stages of diagenesis to temperatures of 300 c and possibly 400 c in salt rich systems many metamorphic rocks may contain ch4 h2o fluids rather than co2 h2o mixtures thus metamorphic reactions involving carbonate minerals would involve ch4 graphite and h2o rather than co2 the immiscibility between ch4 and h2o could result in the common occurrence of methane natural gas in low grade metamorphic terrains

timing and structural controls on gold mineralization at the bogoso gold mine ghana west africa the bogoso gold deposit comprises 20 open pits scattered along 18 km of a major fault zone which separates birimian supergroup turbiditic sedimentary rocks to the northwest from tarkwaian group rocks to the southeast individual pits are centered on 200 to 400 m long ore shoots which are located in three broad structural settings steeply pitching relatively high grade orebodies are commonly localized in left hand dilational jogs in the strike of the controlling faults these jogs often coincide with intersecting minor faults gold is largely confined to the graphitic mylonite which defines the fault and imbricated slices of carbonate altered rock gently dipping mineralized quartz vein stockworks and disseminated auriferous pyrite and arsenopyrite form broader zones between more steeply dipping bounding faults in the vicinity of right hand bends and splays in these faults smaller zones of disseminated sulfide mineralization coincide with areas where bedding and or foliation in the adjacent birimian sedimentary rocks is strongly discordant with the adjacent mineralized fault generally where the faults cut the short limbs of tight upright east trending folds approximately 75 percent of the gold extracted from the bogoso district has been mined from a cluster of pits that coincides with the densest and most highly connected concentration of larger faults in the bogoso concession the majority of ore shoots are located along the largest of these faults the narrower faults generally host smaller and less frequent ore shoots the fault network originated during an early episode of regional scale shortening involving thrusting and isoclinal folding the structural setting and geometry of the ore shoots implies that mineralization occurred during a later minor episode of sinistral strike slip movement on the controlling faults after development of the fault network the undeformed nature of the auriferous sulfides implies that this was the last phase of ductile brittle deformation on the host faults this conclusion is consistent with earlier work indicating that the giant ashanti deposit 150 km along strike from bogoso also developed during a period of small displacement sinistral offset late in the history of the host fault network

early proterozoic crustal evolution in the birimian of ghana constraints from geochronology and isotope geochemistry abstract representative suites of ghanaian granitoids metavolcanics and metasediments were selected from birimian rock units for rb sr pb pb and sm nd analyses isotopic data on the igneous rocks provide evidence for a major early proterozoic crust forming episode which took place over a maximum time interval from 2 3 to 2 0 ga by a differention from a depleted mantle source there is little evidence for the involvement of significantly older e g archaean crust in the genesis of the igneous rock units the only exception so far found is the winneba granitoid which appears to contain a magmatic contribution from presumably underlying archaean basement sm nd model ages indicates that birimian sediments were derived from adjacent penecontemporaneous volcanic belts the birimian of ghana forms part of a major proterozoic eburnean episode of juvenile crustal accretion which has been recognised in the surrounding areas of mauretania senegal ivory coast burkina faso mali and niger where it has been dated at 2 1 2 2 ga abouchami et al the birimian terranes bridge a major gap in mantle activity and associated crustal evolution for a period considered as quiescent on other continents

carbon isotopic study on coexisting calcite and graphite in the ryoke metamorphic rocks northern kiso district central japan carbon isotope fractionation between coexisting calcite and grpahite 13ccc gr has been determined in metamorphosed limestones and calc silicate rocks from the ryoke metamorphic belt in the northern kiso district in this district the ryoke metamorphic rocks ranging from the lower greenschist facies to the upper amphibolite facies are widely distributed the fractionation of 13c 12c between calcite and graphite decreases regularly with increasing metamorphic grade and is independent of absolute 13c values of calcite this evidence suggests that carbon isotopic exchange equilibrium has been attained during metamorphism even in the greenschist facies and isotopic modification possibly caused by retrogressive metamorphism is not distinguished for t 270 650 c the fractionation is expressed by the following equation 13ccc gr 8 9 106t 2 7 1 t in k

regional setting structure and descriptive geology of the middle proterozoic syama gold deposit mali west africa the syama gold deposit lies in a birimian 2 0 2 2 ga greenstone belt in southern mali gold mineralization is hosted by a thin 0 5 2 0 km but regionally extensive sequence of basalt and andesite interbedded graywacke and argillite and andesitic lamprophyric intrusions this sequence is bounded on the east by andesitic conglomerate and graywacke and on the west by interbedded graywacke and argillite in the syama mine area this ore bearing sequence is structurally layered overturned and east vergent massive competent basalt and conglomerate bound the hanging wall and footwall respectively of the mineralized interval lateritic weathering developed an oxide orebody that overlies sulfide mineralization the oxide orebody extends to 35 to 40 m below the surface sulfide mineralization extends to a depth of at least 500 m mineable oxide reserves are 3 0 million tons with an average grade of 3 20 g ton geologic sulfide reserves from the top of sulfides to 320 m below the surface are 21 million tons with an average grade of 4 02 g ton the oxide deposit was expressed on the surface as a series of 3 to 15 m deep ancient mine workings which extended 800 m along the strike of the deposit and sparse outcrops of silicified rock oxide ore occurs as two deposits a surficial deposit consisting of ancient tailings and dump material which are 0 1 to 5 m thick and extend up to 200 m away from the ancient workings and an in situ lode or saprolite deposit which lies immediately below the ancient workings and extends downward into sulfide mineralization the sulfide deposit consists of lenticular bodies of intense ankerite quartz veinlet stockworks zones of sheeted ankerite quartz veinlets and breccia bodies pyrite is the principal gold bearing mineral and occurs disseminated in veinlet halos and breccia clasts green chloritic basalt is the preferred but nonexclusive host of the mineralization it is commonly bleached by ankerite albite and sericite alteration in the pyritic gold bearing zones silica na 2 o au co 2 s and c have been added to mineralized zones hosted by basalt fe 2 o 3 al 2 o 3 and trace metals have been removed andesitic lamprophyric intrusions and graywacke argillite layers also host disseminated pyrite mineralization faulted beds of graphitic graywacke argillite and zones of silicification bound most individual orebodies the volcanic rocks at syama were probably originally deposited in a narrow rift or graben in an intra arc setting gold mineralization overlapped with compressional deformation and intrusive activity the mineralized horizons at syama lie within a sequence of rocks which has been either stacked or attenuated by layer parallel reverse faults these faults coincide with abrupt regional and mine scale contrasts in rock competency intrusive rocks form a volumetrically significant part of the mineralized sequence and may have aided hydrothermal alteration as a source of heat both the graywacke argillite layers and the altered basalt and intrusions may have been a source for some of the elements and fluids responsible for the mineralization and alteration the mineralization at syama is similar to other middle proterozoic gold deposits in the birimian shield of west africa and to archean gold deposits hosted by mafic volcanic rocks in terms of tectonic setting wall rock alteration form of mineralization and associated structures

seismic refraction studies of the afro arabian rift system a brief review abstract the crustal and uppermost mantle structure of major units of the afro arabian rift system has been consecutively investigated by seismic refraction surveys in the jordan dead sea rift the red sea the afar depression and the east african rift of kenya with the exception of the jordan dead sea transform the entire afro arabian rift system is underlain by anomalous mantle with pn velocities less than 8 km s while under the rift flanks the velocity is clearly equal to or above 8 0 km s various styles of rifting have been found oceanic crust floors the axial trough of the southern red sea rift thinned continental crust underlies the margins of the red sea as the afar depression and the northern kenya rift on the other hand 30 35 km thick continental crust is found both under the jordan dead sea rift where strike slip rifting is active and thinning towards the mediterranean occurs and under the central kenya rift where updoming is apparently the controlling feature while the transition from thinned continental to 5 6 km thick oceanic crust in the centre of the red sea appears to be more gradual the transition from rift related structure to undisturbed continental crust of 40 5 km thickness is mostly rather abrupt the seismic data indicate various stages of rifting evidenced by different styles of crustal strucre and they imply the presence of heated uppermost mantle under most parts of the rift system possibly related to plume activity local volcanism may disrupt and or underplate the crust in places altering in particular the structure of the lower crust progressive thickening of the rifted crust away from the oceanized centres in the southern red sea and gulf of aden towards north and south may be viewed as an evolutionary sequence which however may be difficult to explain when viewing the afro arabian rift system as an active rift controlled by plume activity

structural and geochemical controls on the development of turbidite hosted gold quartz vein deposits wattle gully mine central victoria australia gold quartz vein deposits in the wattle gully mine arefault related structures developed in a low grade metamorphosed ordovician quartz rich flysch sequence the major mineralization is associated with a high angle reverse fault wattle gully fault that has a maximum displacement of 40 m over 10 6 metric tons t of vein quartz averaging 10 5 g t au occur within a dilatant jog in this structure fold geometry has controlled fault geometry and resulted in the localization of the jog segment where the wattle gully fault traverses an east dipping fold limb to link two more steeply dipping bedding parallel fault sediments on adjacent west dipping fold limbs gold mineralization is also associated with several minor east clipping reverse faults and a bedding parallel fault whose development is related to flexural slip during fold tightening mineralization occurs within fault fill veins and extension veins adjacent to faults the geometry and internal structures of veins indicate that vein growth has been controlled by repeated fluctuations in fluid pressure and shear stress associated with fault valve behavior vein mineralogy is dominated by quartz with minor carbonates chlorite white mica albite and apatite arsenopyrite and pyrite are the major sulfide phases but sphalerite galena chalcopyrite and pyrrhotite are also present the highest au grades tend to be localised in vein systems that are in proximity to carbonaceous slates wall rock alteration is minor and restricted mainly to narrow zones adjacent to major vein systems sulfur isotope fractionation between galena and sphalerite indicates mineralization occurred at temperatures around 300 degrees c the delta 34 s compositions of pyrite and arsenopyrite are nearly uniform throughout the mine 1 5 2 8 but are generally not in equilibrium with the delta 34 s values of associated base metal sulfides 0 7 5 3 the delta 18 o values for vein quartz vary between 15 6 and 18 0 per mil and correspond to delta 18 o values

carbonaceous material in the ryoke metamorphic rocks kinki district japan abstract carbonaceous material in the ryoke pelitic metamorphic rocks in the wazuka area kinki district japan has been studied by x ray diffraction xrd analysis detrital graphite in the lower grade rocks is recognized in both x ray diffractograms and transmission electron micrographs progressive graphitization is considered to have proceeded continuously on the basis of the xrd data of the bulk concentrates of carbonaceous material and a conspicuous asymmetric shape of xrd peaks in lower grade samples is ascribed to the mixture of carbonaceous materials with different crystallinities fully ordered graphite does not occur until the highest grade part of the chlorite biotite zone the variation of degree of crystallinity of carbonaceous materials inferred from xrd data is consistent with the prograde mineral zones the temperatures for the development of fully ordered graphite are estimated to be between 410 and 440 c in regional metamorphism through comparing the xrd data from low medium and high pressure types of metamorphic terrains

key factors controlling massive graphite deposition in volcanic settings an example of a self organized critical system massive graphite deposition resulting in volumetrically large occurrences in volcanic environments is usually hindered by the low carbon contents of magmas and by the degassing processes occurring during and after magma emplacement in spite of this two graphite deposits are known worldwide associated with volcanic settings at borrowdale uk and huelma spain as inferred from the borrowdale deposit graphite mineralization resulted from the complex interaction of several factors so it can be considered as an example of self organized critical systems these factors in turn could be used as potential guides for exploration the key factors influencing graphite mineralization in volcanic settings are as follows 1 an unusually high carbon content of the magmas as a result of the assimilation of carbonaceous metasedimentary rocks 2 the absence of significant degassing related to the presence of sub volcanic rocks or hypabyssal intrusions acting as barriers to flow 3 the exsolution of a carbon bearing aqueous fluid phase 4 the local structural heterogeneity represented at borrowdale by the deep seated burtness comb fault 5 the structural control on the deposits implying an overpressured fluid rich regime favouring a focused fluid flow 6 the temperature changes associated with fluid flow and hydration reactions resulting in carbon supersaturation in the fluid and leading to disequilibrium in the system this disequilibrium is regarded as the driving force for massive graphite precipitation through irreversible mass transfer reactions therefore the formation of volcanic hosted graphite deposits can be explained in terms of a self organized critical system