gold speciation and transport in geological fluids insights from experiments and physical chemical modelling this contribution provides an overview of available experimental thermodynamic and molecular data on au aqueous speciation solubility and partitioning in major types of geological fluids in the earth s crust from low temperature aqueous solution to supercritical hydrothermal magmatic fluids vapours and silicate melts critical revisions of these data allow generation of a set of thermodynamic properties of the auoh aucl 2 auhs and au hs 2 complexes dominant in aqueous hydrothermal solutions however other complexes involving different sulphur forms chloride and alkali metals may operate in high temperature sulphur rich fluids vapours and melts the large affinity of au for reduced sulphur is responsible for au enrichment in s rich vapours and sulphide melts which are important gold sources for hydrothermal deposits thermo dynamic speciation and partitioning data and their comparison with au and s contents in natural fluid inclusions from magmatic hydrothermal gold deposits provide new constraints on the major physical chemical parameters temperature pressure salinity acidity redox and ubiquitous fluid components sulphur carbon dioxide arsenic affecting au concentration transport precipitation and fractionation from other metals in the crust the availability and speciation of sulphur and their changes with the fluid and melt evolution are the key factors controlling gold behaviour in most geological situations

more than just nopcsa s transylvanian dinosaurs a look outside the haţeg basin abstract since the end of the 19th century the notorious palaeontologist baron nopcsa reported several late cretaceous small sized dinosaurs in the ha eg basin he explained their sizes as the consequence of unusual evolution on an island he named the ha eg island he found similar dinosaurs outside ha eg in other regions of transylvania near alba iulia or nearby jibou recent surveys carried out in these areas support nopcsa s presumptions even adding several new outcrops with dinosaur remains in s laj and cluj counties the dinosaur fossils are rather scarce but still obvious in the jibou formation in alba county the main outcrops are located between vurp r and ard on the right bank of the mures river but also between petresti and oarda de jos along the sebes valley the majority of the taxa from ha eg are also documented in these areas during the palaeogene and early miocene several of these mesozoic reptile bones were reworked to younger deposits another area with high potential for finding maastrichtian vertebrates is the rusca montan basin

the latest cretaceous fauna with dinosaurs and mammals from the haţeg basin a historical overview abstract research on the uppermost cretaceous continental deposits with dinosaur remains from the ha eg basin has behind it a history of more than 110 years the first studies were by franz nopcsa 1877 1933 who published between 1897 and 1929 a series of notes and papers on this fauna including five monographs dedicated to the ha eg dinosaurs nopcsa described 10 vertebrate taxa including dinosaurs crocodilians and turtles from the ha eg basin out of which 6 are still valid he recognized the primitiveness and the small size of most of the taxa from the ha eg palaeofauna characters that he related to the isolated island environment within which this fauna lived for a long time span after nopcsa systematic research on the ha eg fauna was interrupted for many decades being resumed after 1977 when d grigorescu leading a small group of students in geology started to explore the deposits outcropping along the sibisel valley near s npetru village from where nopcsa made most of his collection of fossil bones since then the fieldwork continued every summer until now numerous remains of dinosaurs crocodiles and turtles being unearthed the list of the maastrichtian fauna from ha eg currently includes 56 taxa from all vertebrate classes more than half of the recorded taxa were discovered in micropalaeontological samples through screen washing the most spectacular discoveries made after 1977 include a large variety of small theropods several sites with dinosaur egg clutches one of these also yielding hatchling remains one of the largest pterosaurs in the world representing a new genus and species hatzegopteryx thambema and several taxa of multituberculate mammals studies of the ha eg fauna were not restricted to systematic palaeontology but also covered all the fields that contribute together to an accurate reconstruction of the environment within which the maastrichtian fauna existed this overview includes a list of contributors to the actual knowledge on the ha eg fauna during the last 30 years divided by fields of scientific interest

boiling colloid nucleation and aggregation and the genesis of bonanza au ag ores of the sleeper deposit nevada a deep parent composition for bonanza oreforming fluids at the sleeper deposit was calculated by the computer program solveq using fluid inclusion microthermometric and gas data and by assuming equilibrium with the following minerals present in vein samples below the bonanza zones gold chalcedony adularia pyrite chalcopyrite and acanthite the calculated dissolved gold content of 295 ppb is approximately 2 orders of magnitude higher than that assumed for typical geothermal systems thus a gold enriched fluid appears to have been a principal factor in the genesis of bonanza au ag ores at the sleeper deposit geochemical modelling of possible ore forming processes using the computer program chiller with the reconstructed ore forming solution as a starting composition indicates that boiling most closely reproduces observed minerals and their relative abundances in bonanza ores the constraint imposed by the association of amorphous silica with gold precludes all of the mixing scenarios modelled such as mixing with cold and steam heated groundwaters acid sulfate co2 rich modelling indicates that boiling of a gold rich deep solution leads to rapid gold precipitation and that the amount of gold precipitated initially is large relative to other minerals these factors apparently led to nucleation of colloidal gold particles instead of in situ gold deposition or coprecipitation with other phases gold colloids apparently were entrained in the upward flowing hydrothermal solutions and grew as they travelled upon reaching a critical size 10 100 nm they were deposited due to orthokinetic aggregation at an elevation and temperature at which amorphous silica was nucleating and aggregating

origin of the columbia plateau and snake river plain deflection of the yellowstone plume previous models relating the snake river plain and columbia river basalt northwest united states to the yellowstone plume have not taken into account the effects of the subducted farallon and juan de fuca plates not only did subduction shield the surface from mantle plume activity but it deflected the plume in the direction of plate motion a variety of geophysical and geologic evidence suggests that the plume penetrated the subducted slab at 17 5 ma causing eruption of the columbia river basalt the plate boundary then migrated over the plume and the yellowstone plume has recovered to a more nearly vertical conduit forming the snake river plain and yellowstone plateau

sulfur and strontium isotopic study of epithermal mineralization a case study from the se afar rift djibouti epithermal mineralization was recently described in synrift volcanic rocks from the se afar rift in djibouti to infer fluid sources in this system coupled sulfur and strontium isotopic analyses were performed on mineralized samples from hydrothermal veins and stockwork zones mineralization includes gypsum and chalcedony and or quartz carbonate containing gold and sulfides sulfur isotopic compositions of sulfides and sulfates were determined using multicollector inductively coupled plasma mass spectrometer mc icpms laser ablation mc icpms and continuous flow elemental analyzer isotope ratio mass spectrometry while strontium isotopes were determined by thermal ionisation mass spectrometry tims methods sulfur isotopic composition of sulfides mainly pyrite varies from 9 2 to 6 6 these values are classically reported for hydrothermal sulfides resulting from the mixing of variable s sources such as seawater sulfate and magmatic source in addition individual pyrite grains within the same sample show both positive and negative 34s values suggesting multi phase mineralization processes coupled sulfur and strontium isotopic compositions of seven sulfate samples hosted in i gypsum mound ii evaporites iii stockwork veins in sediments or in volcanic rocks were also investigated to characterize the sources of sr and s the 34s values of the sulfate ranged from 0 8 to 14 3 while the 87sr 86sr ranged from 0 70389 to 0 70639 consistent with variable mixing ratios of sr and s derived from volcanic sources and seawater derived sulfate this study shows that although precious metal deposition is related to low sulfidation epithermal environment both acidic fluid of magmatic and saline origins contributed to the hydrothermal system in the se afar rift

cu rich scales in the reykjanes geothermal system iceland seawater dominated fluids discharge from the subaerial reykjanes geothermal system iceland there is a sharp pressure decrease in surface pipes at an orifice throttle point and cu rich scales deposit at this orifice that consist largely of bornite and digenite along with sphalerite and other sulfides the bornite and digenite form complex intergrowths with sphalerite and galena accompanied by high concentrations of gold and silver up to 590 ppm and 2 3 wt respectively the precipitates form in response to rapid boiling flashing of the hydrothermal fluids due to the sharp decrease in pressure 37 22 bars at the orifice downstream of the well head the boiling and concomitant separation of the vapor phase results in a temperature decrease from 252 to 220 c across this throttle over distances of centimeters there is a nearly quantitative deposition of metals from solution compared to concentrations in reservoir liquids resulting in formation of the metastable cu fes solid solution rich in silver and gold plus sphalerite and galena a high degree of supersaturation of metals in the quenched liquid is indicated by the very fine grain size of the sulfides and dendritic textures postdepositional cooling likely caused exsolution of bornite and digenite from the high temperature solid solution in addition silver was expelled from the cu fe s solid solution and remobilized into late fractures in the scales whereas the gold appears to have remained in solid solution or as submicroscopic inclusions in the bornite and digenite the observed mineral assemblage at reykjanes contrasts with that of sea floor black smokers despite similar fluid compositions the sea floor hydrothermal vents characteristically have cu rich linings composed predominantly of chalcopyrite which is precipitated by a combination of conductive cooling of high temperature 350 c hydrothermal fluids and mixing with seawater the difference in sulfide mineralogy between the reykjanes orifice scales with cu sulfides dominated by bornite and digenite and many sea floor vents may provide an indication of the subsea floor mineralization where fluids boil before discharging at sea floor vents

geochronology of the sleeper deposit humboldt county nevada epithermal gold silver mineralization following emplacement of a silicic flow dome complex the high grade gold silver deposits at the sleeper mine are low sulfidation quartz adularia type epithermal deposits formed during the final stages of igneous hydrothermal activity of a small middle miocene silicic flow dome complex in north central nevada potassiumargon and 40 ar 39 ar ages of alkali feldspar indicate that the rhyolitic flow dome complex was emplaced before about 16 5 ma hydrothermal alteration and mineralization followed lasting from about 16 2 to 14 ma based on ages of adularia associated with electrum there were multiple pulses of alteration and mineralization but all occurred within a period of less than 2 m y later supergene alteration formed opal and alunite about 5 4 ma but produced no au or ag mineralization other than some remobilization to produce locally rich pockets of secondary au and ag enrichment and is unrelated to the older magmatic hydrothermal system the sleeper deposit in the northern part of the great basin is genetically related to bimodal volcanism that followed a long period of arc related andesitic volcanism in the same general region

colloidal gold and silica in mesothermal vein systems some of the textural features of mesothermal gold quartz veins may be best explained by the initial precipitation of amorphous silica gel colloid which subsequently crystallizes to quartz this can occur in brittle ductile shear zones where a significant fluid pressure drop occurs during stick slip failure such a process rapidly supersaturates the hydrothermal fluid with respect to amorphous silica which precipitates instead of quartz owing to favorable kinetics depressurization also commonly leads to fluid unmixing and destabilization of soluble gold complexes however the presence of colloidal silica can stabilize gold colloid allowing further transport of particulate gold in suspension in the hydrothermal fluid silica gel would be highly unstable under mesothermal conditions and would undergo rapid syneresis and crystallization to form quartz solid impurities would tend to be expelled toward grain boundaries this model can account for the primary anhedral aggregate textures typical of mesothermal quartz veins the concentration of gold along grain boundaries and the formation of discrete gold nuggets and the rare occurrence of low order silica polymorphs and relict spheroidal structures the transport of gold in colloidal form may be one reason for the frequently consistent bulk grade distribution in gold quartz vein systems over many hundreds of metres in some cases kilometres of depth in addition the formation of charged colloidal particles may help to explain the attraction of gold grains to specific mineral surfaces

colloform gold in coal from southern wales geochemically significant concentrations of particulate gold in the westphalian coals of the south wales coalfield are situated on the coal cleat and are associated with a complex sulfide assemblage gold grains up to 100 mu m long and more than 20 mu m thick display a colloform microtexture suggesting an origin through late variscan low temperature ground water circulation these discoveries provide additional constraints on the timing and rates of coal evolution 14 refs 4 figs 1 tab

spatial resolution and repeatability of magsat crustal anomaly data over the indian ocean preliminary results from analysis of individual magsat tracks in the eastern indian ocean demonstrate the resolution capability and repeatability of these data spectrum analysis indicates that 250 km is the absolute lower limit for resolving crustal magnetic anomalies in magsat along track data spectral coherence analysis of closely spaced tracks shows that magnetic anomaly features with wavelengths greater than 700 km are highly repeatable from track to track

native gold and gold rich sulfide deposits in a submarine basaltic caldera higashi aogashima hydrothermal field izu ogasawara frontal arc japan sulfide deposits with extremely high au concentrations up to 275 ppm avg 102 ppm n 15 high au ag ratios 0 24 n 15 and low cu cu zn ratios 0 03 n 15 were discovered in 2015 in active hydrothermal fields at a water depth of 760 m in a basalt dominated submarine caldera in the izu ogasawara frontal arc japan native gold grains occur in massive sulfide fragments concretions and metalliferous sediments from a sulfide mound 40 m across and 20 m high with up to 30 m high black smoker chimneys tiny native gold grains up to 14 m in diameter are mainly present in sulfide fallouts from chimney orifices and plumes larger native gold grains up to 150 m long occur mostly as discrete particles and or with amorphous silica and sulfides the larger gold grains are interpreted to represent direct precipitation from au bearing hydrothermal fluids circulating in and or beneath the unconsolidated sulfide mound deposits sulfur isotope compositions from a limited number of sulfide separates n 4 range from 4 3 to 5 8 34s similar to the quaternary volcanic rocks of the arc barite separates have values of 22 2 and 23 1 close to modern seawater values and indicate probable seawater sulfate origin the cu zn and pb concentrations in bulk samples of sulfide rich rocks are similar to those of volcanogenic massive sulfides formed in continental crustal environments the gold is interpreted to have formed by low temperature hydrothermal activity perhaps genetically different from systems with documented magmatic contributions or from seafloor hydrothermal systems in other island arc settings its presence suggests that basalt dominated submarine calderas situated on relatively thick continental crust in an intraoceanic arc setting such as the higashi aogashima knoll caldera may be perspective for gold mineralization

heavy mineral distributions of maastrichtian deposits from the haţeg basin south carpathians tectonic and palaeogeographic implications abstract this study represents the first extensive investigation of source areas of the maastrichtian continental deposits of the ha eg basin using heavy mineral associations the heavy mineral associations consist of garnet hematite magnetite ilmenite rutile staurolite kyanite epidote apatite titanite tourmaline and zircon the general pattern indicates different source areas with contrasting metamorphic grades for the northern and southern parts of the basin the sediments of the northern and central sectors of the basin show a high proportion of garnet staurolite and kyanite and a low proportion of epidote suggesting an amphibolite facies metamorphic source which is compatible with the lithology of the getic upper plate on which the basin formed the samples with abundant amphibolite facies heavy mineral components have high proportions of magnetic fe ti oxides with complex exsolution intergrowth features these oxides belong chiefly to the hematite ilmenite solid solution series and indicate a high grade metamorphic and or igneous source area in the south the heavy mineral spectra change to epidote rich evidence of exhumation and erosion of the greenschist metamorphic rocks of the danubian lower plate during updoming and core complex formation the study shows that for the northern and central parts of the basin the getic plate is the main source for the sediments during the maastrichtian time due to increasing relief in the hinterland and exhumation of the lower plate the danubian unit fed the basin as recorded in the sediments situated along sibisel and r ul b rbat valley

stable isotope distribution in maastrichtian vertebrates and paleosols from the haţeg basin south carpathians abstract located in the south carpathians in romania the ha eg basin contains a thick sequence of maastrichtian continental deposits yielding a rich dinosaur and mammalian fauna stable isotope analyses of both calcretes and dinosaur crocodilian and turtle remains from two localities tustea and sibisel were integrated in order to reconstruct environmental conditions during maastrichtian time and to gain further insights into the metabolism and behaviour of the vertebrates the large difference observed between the 18o and 13c of the eggshells and the surrounding mudstones as well as the preservation of the 9 difference between the oxygen isotope composition of the telmatosaurus eggshell and tooth enamel indicate that diagenesis has not significantly altered the primary isotopic signal the presence of smectite in the fraction less than 2 m and the preservation of dinosaur eggshell structure also indicate that diagenesis was not significant in the studied outcrops stable isotope compositions of both calcretes and phosphatic remains suggest warmer conditions during the deposition of the tustea sequence mean annual temperature of around 14 c than during the deposition of the sibisel sequence mean annual temperature of 10 c the intra tooth 18o patterns for zalmoxes and allodaposuchus show different magnitudes of isotopic variation with lower values for tustea and higher for sibisel the calculated 18obody water enrichment for kallokibotion bajazidi is similar to that found in living turtle taxa by contrast in the case of allodaposuchus the isotopic enrichment is higher than for recent taxa this suggests that for allodaposuchus the body water was less buffered by a watery environment which probably indicates more time spent outside water i e more terrestrial habit the 18o values for the teeth of telmatosaurus and zalmoxes are similar to those of allodaposuchus suggesting that at the investigated sites the body temperature of both dinosaurs was similar to that of the crocodile the isotopic composition of calcretes teeth and eggshells indicates a c3 vegetation and diet with 13c values between 27 and 29 pdb and the absence of large scale habitat partitioning between the dinosaurs

boiling and dilution in the shallow portion of the waiotapu geothermal system new zealand abstract the waiotapu geothermal system is the largest in terms of surface extent and heat flow 17 km2 and 600 mw respectively of the 20 major geothermal systems in the taupo volcanic zone new zealand two extinct dacite cones and a rhyolite dome rise about 500 m above the waiotapu valley the majority of thermal features occurs in the valley over a relief of only 100 m and lies within coincident apparent resistivity and 30 m depth thermal anomalies thermal features comprise near neutral ph chloride springs often boiling acid sulfate springs and mud pools and mixed waters the latter including both bicarbonate chloride and acid sulfate chloride springs the majority of the sulfate discharges to the surface in the northern higher altitude area while most chloride that reaches the surface does so in the southern portion of the system comparison of measured and calculated surface chloride flux the latter from measured heat flow and reservoir chloride concentrations indicates that at least half of the deep chloride does not discharge at the surface but flows laterally to the south at shallow depths mixing with groundwater the composition of well discharges indicates a shallow 400 m reservoir of chloride fluid about 1350 mg cl kg at 230 c is diluted by a co2 rich steam heated water nil chloride at about 160 c the latter located on the margins of the system this same dilution trend is apparent from the compositional variation and k na and k mg geothermometry of hot spring waters however there is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels and very near the surface steam heated acid sulfate waters mix with the upflow boiling of the deep chloride fluids prior to dilution results in the stabilization of k feldspar in contrast dilution at shallower depths by the steam heated waters both co2 rich and acid sulfate leads to the water compositions initially shifting to k mica and interstratified clay stability and to kaolinite stability with further dilution and temperature decrease the composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core although boiling occurs at deeper levels and up to the surface in the upflow zone at waiotapu mixing is also common and is the dominant process on the margin and in the near surface portion of the system boiling of deep chloride fluid is very common in the upper 1 2 km of the upflow zone of most geothermal systems though it may be quenched by mixing with marginal waters either cold groundwater in high relief terrane or steam heated waters in areas of lower relief co2 rich steam heated waters are common on the margins of systems and will generally underlie the near surface acid sulfate steam heated waters interaction with co2 rich waters will form k mica and interstratified clays while acid sulfate waters cause kaolinite and even alunite to form the former assemblage is commonly associated with typical low sulfidation epithermal gold mineralization as wallrock alteration where gold bearing veins comprise adularia and illite in contrast kaolinite is rare and alunite absent from a direct spatial and genetic association with gold mineralization in this environment this implies that mixing of the deep neutral ph chloride fluid with surficial acid sulfate waters does not commonly lead to ore grade gold deposition mixing with and cooling by co2 rich steam heated waters leads to clay stability accounting for the large halos of clay alteration and low grade metal anomalies which often surround veins of high gold grade in contrast mixing with surficial acid sulfate waters is unlikely to cause precious metal mineralization because the chloride fluids have already lost the majority of their gold through deeper boiling and dilution

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

taphonomical and palaeoecological investigation of the late cretaceous maastrichtian tustea vertebrate assemblage romania haţeg basin insights into a unique dinosaur nesting locality abstract the tustea vertebrate locality at oltoane hill northwestern part of the ha eg basin romania has provided a rich and diverse assemblage of late cretaceous maastrichtian continental vertebrates more than 800 vertebrate fossils were recovered from this locality the isolated and associated remains represent 21 different taxa including amphibians turtles lizards snakes crocodyliforms pterosaurs dinosaurs and mammals the local assemblage is overwhelmingly dominated by dinosaurs with the rhabdodontid zalmoxes as the most abundant taxon the bonebeds that yielded this fossil material occur in a stacked series of mudstone calcrete units belonging to the middle member of the densus ciula formation the taphonomical investigations suggest that the tustea assemblage is made up of attritionally accumulated politaxic remains and that it is a parautochthonous assemblage with no evidence for significant bone transport or reworking according to the synthesis of all available field data two outstanding fossiliferous levels can be identified within the tustea locality where megaloolithus eggs and hadrosauroid hatchling material are preserved together recognized here as two superposed nesting grounds such co occurrence was considered controversial since there is a long standing and quasi general consensus that eggs of the megaloolithus oogenus were laid by titanosaurian sauropods we present several alternative scenarios to account for the co occurrence of telmatosaurus hatchling remains and megaloolithid eggs in the nesting horizons and explore these alternative hypotheses by weighing the arguments supporting or contradicting them the burden of evidence derived from our sedimentological taphonomical and palaeoecological investigations at tustea is still in favour of the autochthony of the hatchlings preserved within their own nesting grounds whereas there is no such support for a titanosaurian origin of the tu tea megaloolithid eggs

volatility of se and te during subduction related distillation and the geochemistry of epithermal ores of the western united states subduction partial melting of mantle and magma generation and ultimately magma degassing can lead to the preferential mobilization of volatile elements and compounds research indicates that devolatilization reactions in a subducted slab can cause the overlying mantle to be enriched in volatile ore forming constituents water co2 sulfur metal loid s this process of mantle enrichment plays an important role in subsequent magma generation and initiation of ore genesis furthermore the relative volatility of metal loid s appears to play a role in the ultimate geochemistry of shallow epithermal epizonal hydrothermal ores in the western united states for example there is a general west to east geographic zonation of tertiary ores from se rich to te rich it is proposed that this geographic geochemical zonation is the direct result of the higher geochemical volatility of se as compared to te previously au ag te se hg as sb and tl have been referred to as the epithermal suite of elements it is suggested here that their geochemical cycles are linked by their similar volatile behavior through subduction partial melting in the mantle and subsequent magma degassing processes essentially specific tectonomagmatic events that affected the western united states e g oligocene eocene magmatism in the great basin and southern rocky mountains mid miocene magmatism associated with the inception of the yellowstone hotspot in the pacific northwest were distillation events that drove devolatilization of fertile mantle after the laramide shallow slab event furthermore the metal loid volatility behavior likely occurs in other regions affected by subduction and may play a fundamental role in the metal endowment of these regions

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