the iberian type of volcano sedimentary massive sulphide deposits the iberian pyrite belt located in the sw iberian peninsula contains many paleozoic giant and supergiant massive sulphide deposits including the largest individual massive sulphide bodies on earth total ore reserves exceed 1500 mt distributed in eight supergiant deposits 100 mt and a number of other smaller deposits commonly with associated stockwork mineralizations and footwall alteration haloes massive sulphide bodies largely consist of pyrite with subordinated sphalerite galena and chalcopyrite and many other minor phases although substantial differences occur between individual deposits both in mineral abundance and spatial distribution these deposits are considered to be volcanogenic roughly similar to volcanic hosted massive sulphides vhms however our major conclusion is that the iberian type of massive sulphides must be considered as a vhms sub type transitional to shms

a case study of the internal structures of gossans and weathering processes in the iberian pyrite belt using magnetic fabrics and paleomagnetic dating in the rio tinto district of the iberian pryrite belt of south spain the weathering of massive sulfide bodies form iron caps i e true gossans and their subsequent alteration and re sedimentation has resulted in iron terraces i e displaced gossans to study the stucture and evolution of both types of gossans magnetic investigations have been carried out with two foci 1 the characterisation and spatial distribution of magnetic fabrics in different mineralised settings including massive sulfides gossans and terraces and 2 paleomagnetic dating hematite has been identified as the suceptibility carrier in all sites and magnetic fabric investigation of four gossans reveals a vertical variation from top to bottom with 1 a horizontal foliation refered to as mature fabric in the uppermost part of the primary gossans 2 highly inclined or vertical foliation interpreted as immature fabric between the uppermost and lowermost parts and 3 a vertical foliation interpreted to be inherited from hercynian deformation in the lowermost part of the profiles in terraces a horizontal foliation dominates and is interpreted to be a sedimentary fabric rock magnetic studies of gossan samples have identified goethite as the magnetic remanence carrier for the low temperature component showing either a single direction close to the present earth field pef direction or random directions maghemite hematite and occasionally magnetite are the remanence carriers for the stable high temperature component that is characterized by non pef directions with both normal and reversed magnetic polarities no reliable conclusion can be yet be drawn on the timing of terrace magnetization due to the small number of samples in gossans the polarity is reversed in the upper part and normal in the lower part this vertical distribution with a negative reversal test suggests remanence formation during two distinct periods remanence in the upper parts of the gossans is older than in the lower parts indicating that the alteration proceeded from top to bottom of the profiles in the upper part the older age and the horizontal mature fabric is interpreted to be a high maturation stage of massive sulfides alteration in the lower part the age is younger and the inherited imature vertical hercynian fabric indicates a weak maturation stage these two distinct periods may reflect changes of paleoclimate erosion and or tectonic motion

can biological toxicity drive the contrasting behavior of platinum and gold in surface environments abstract in spite of the similar chemical properties of gold au and platinum pt au is highly mobile in surface environments whereas pt appears to be far less so in this study we assess if geomicrobial processes are likely to cause these differences as the mobility of pt and au should differ little based on thermodynamic solubility alone to achieve an accurate comparison it is important that both metals occur in the same environment mineral and groundwater samples were obtained from the fifield pt au field in new south wales australia where pt and au nuggets occur in a series of tertiary eluvial and alluvial paleo placers in particular we studied the m scale dispersion of au and pt within an extraordinary 10 mm sized fragment of ferruginous paleochannel material which contained abundant native au and isoferroplatinum grains gold grains displayed complex secondary morphologies indicative of biogeochemical transformations whereas isoferroplatinum grains appeared smooth and well rounded and showed no signs of supergene transformation gold grains were surrounded by a dusting of highly pure metallic au particles 10 m in diameter whereas no metallic pt particles were detected a search for ionic pt was also unsuccessful a series of biotic and abiotic incubation experiments was conducted to investigate the hypothesis that these differences in mobility are driven by interactions with microbiota biofilms consisting of metallophilic bacteria formed on ultraflat au surfaces and caused significant surface transformations in contrast only subtle changes were observed on pt surfaces incubated under similar conditions minimal inhibitory concentrations for au complexes are more than an order of magnitude lower than those measured for pt complexes in cupriavidus metallidurans cells this higher cell toxicity of mobile au compared to pt complexes can lead to toxic levels of mobile au in the vicinity of au grain surfaces the elevated toxicity drives the formation of au detoxifying biofilms that catalyze the biomineralization of spheroidal nano particulate and bacteriomorphic au in contrast this does not occur on isoferroplatinum grains due to the lower toxicity of pt in conclusion these results are consistent with microbial adaptation to element toxicity driving the cycling of precious metals in surface environments

supergene gold in silcrete as a vector to the scuddles volcanic massive sulfides western australia this study reports data on the first occurrence of economic supergene au in a near surface silcrete horizon over the scuddles volcanic massive sulfide vms deposit in the golden grove district western australia a deep weathering profile was developed on dacite rhyodacite siltstone and breccia that host primary cu zn and pb sulfides with au ag ore from the base the weathering profile at scuddles is subdivided into five main zones 1 supergene sulfide enrichment zone 2 supergene oxide enrichment zone 3 ferruginous saprolite 4 leached zone of kaolinitic saprolite and silcrete and 5 lateritic zone of mottled clays ferruginous duricrust and gravels silcrete at scuddles hosts supergene au deposit that formed in two generations the first is intimately associated with ag halides during supergene enrichment of the primary vms and the second is associated with kaolinite in dissolution cavities inside ag halides during lateritic weathering these two au generations imply more than one mechanism of au remobilization and formation multiple fluid pathways and superimposed episodes of weathering under variable timing and climatic conditions gold grains are pure nanocrystalline up to 10 nm and clustered together forming microcrystalline aggregates a few au grains are residual in silcrete with ag sb rich cores and ag poor rims possibly formed during dealloying of ag and sb chemically au in silcrete is associated with a multi element concentration of ag i br cl sb sn bi hg mo w te and ge gold and ag in the supergene weathering profile were mobilized to silcrete as a halide complex under acidic and saline conditions generated during the oxidation of massive sulfides at depth the precipitation of au ag halides in the silcrete may have taken place in response to a rise in ph gold was likely remobilized with kaolinite from the surface lateritic zone facilitated by decays of plant roots and bioturbation the clustered spongy cube octahedral platy six sided dendritic and reniform like morphologies of au in cavities inside ag halides may indicate biogenic related processes in its precipitation recognizing au ag rich silcrete over the buried vms at scuddles highlights the significance of the silcrete in finding buried vms particularly if the gossan is absent

isotopic composition δ13c δ18o in wood and cellulose of siberian larch trees for early medieval and recent periods 1 we related tree ring width trw and isotopic composition 13c 18o of wood and cellulose from four larch trees larixcajanderi mayr to climate parameters the material was sampled in northeastern yakutia 70 n 148 e for the recent ad 1880 2004 and early medieval ad 900 1000 periods during the recent period june july and august air temperatures were positively correlated with 13c and 18o of wood and cellulose while july precipitation was negatively correlated furthermore the vapor pressure deficit vpd of july and august was significantly correlated with 13c of wood and cellulose but vpd had almost no influence on 18o comparative analyses between mean isotope values for the ad 900 1000 and ad 1880 2004 periods indicate similar ranges of climatic conditions with the exception of the period ad 1950 2004 while isotopic ratios in cellulose are reliably related to climatic variables during some periods those in whole wood showed even stronger relationships strong positive correlations between 18o of cellulose and greenland ice core gisp2 data were detected for the beginning of the medieval period r 0 86 p 0 05 indicating the reliability of isotope signals in tree rings for large scale reconstructions

the in vitro growth of gold grains gold colloids octahedral platelets and foils directly and indirectly formed from the reduction of soluble au i thiosulfate and au iii chloride complexes by iron oxidizing bacteria cyanobacteria and sulfate reducing bacteria were combined in an experimental system this system represented simplified biogeochemical conditions occurring within a fluvial environment in which placer au could occur in this study biofilm formation and physical aggregation i e sedimentation processes were critical for the accumulation of nanometer to micrometer sized au particles into grains 4 5 mm in size characterization of grain surface textures by scanning electron microscopy in association with monitoring soluble au concentrations over time suggested that dissolution and reprecipitation processes were occurring at the au grain fluid interface this laboratory model demonstrates that the biogeochemical cycling of au can contribute to the formation of anomalous enrichments such as placer au deposits

supergene gold transformation biogenic secondary and nano particulate gold from arid australia abstract biofilms on au grains from sub tropical and tropical sites promote the dispersion of gold au by continuously recycling coarse au and releasing nano particulate au in this study we investigated the influences of bio geochemical processes on the transformation of au grains in arid environments at these sites water and nutrient availability are limited and episodic hence abiogenic evaporative mechanisms were thought to control the formation of secondary and especially nano particulate au gold grains were collected from eight arid sites in three australian au provinces i e lawlers western australia tanami northern territory and flinders ranges south australia sites were chosen based on contrasting deposit styles i e primary underground and epithermal deposits as well as secondary eluvial colluvial and alluvial placers at increasing distances from primary mineralization gold grains were studied using optical microscopy feg sem fib sem edxa epma and pixe gold grains from all surface environments displayed supergene transformation features i e morphotypes indicative of au and ag dissolution au aggregation and au neoformation the latter included spheroidal and bacteriomorphic au which increased in abundance with distance to source viable biofilms containing abundant au nano particles and spheroidal au crystals were detected on all grains from the flinders ranges gold grains from the lawlers and the tanami provinces are covered by polymorphic layers containing abundant nano particulate spheroidal and bacteriomorphic au the polymorphic layers consist of vermiform clays and organic matter suggestive of remnant biofilms these results demonstrate that biofilms capable of transforming au grains develop episodically on au grains in arid environments in conclusion this study shows that microbial processes play a critical role for the transformation of au grains and contribute to the dispersion of au and the formation of geochemical anomalies in arid environments

messinian productivity changes in the northeastern atlantic and their relationship to the closure of the atlantic mediterranean gateway implications for neogene palaeoclimate and palaeoceanography the stable isotope composition of planktic and benthic foraminifera and the distribution of selected benthic foraminiferal species from a messinian record of the lower guadalquivir basin northeastern atlantic ocean show that regional productivity changes were linked to glacioeustatic fluctuations glacial periods were characterized by poorly ventilated bottom waters as a result of weak atlantic meridional overturning circulation amoc and by phases of high productivity related to intensified upwelling in contrast well ventilated bottom waters owing to strong amoc the presence of degraded organic matter in the upper slope and high input of degraded terrestrial organic matter derived from fluvial discharge to the outer shelf were recorded during interglacial periods before closure of the adjacent guadalhorce corridor at 6 18 ma which was the final active betic atlantic mediterranean gateway the study area was alternately influenced by well ventilated mediterranean outflow water mow and poorly ventilated atlantic upwelled water auw following closure of the corridor cessation of the mow reduced the amoc and promoted glacial conditions in the northern hemisphere resulting in the establishment of local upwelling cells

natural gold nanoparticles abstract the nanoparticulate gold component in ore deposits and exploration samples is yet to be fully realised but new methods of characterisation and analysis access to high grade gold samples and a strong focus on au nanoparticles in the manufacturing sector provide a new impetus to quantify its significance in geology nanoparticles are increasingly recognised as a fundamental step in geochemical reactions a critical component in weathering processes in biomineralisation and metal migration in ore systems the nanoparticulate population of au is a significant factor in the formation of economic deposits as a refractory component locked up in sulphides in secondary supergene enrichments the formation of surface geochemical anomalies and in the formation of high grade accumulations a better understanding and characterisation of this nanoparticulate gold could unlock hidden resources in known deposits through easier beneficiation and processing but also assist in the discovery of new deposits through advanced exploration methods

stability of climate signal in carbon and oxygen isotope records and ring width from scots pine pinus sylvestris l in finland four hundred year long records of carbon and oxygen stable isotope ratios and ring width were measured from scots pine pinus sylvestris l from sites in northern and eastern finland responses of isotope ratios to temperature and precipitation were analysed for the 20th century carbon isotope ratios responded strongly to summer temperature at both sites whereas an influence of precipitation on the record was observed only at the site in eastern finland oxygen isotope ratios were less responsive to climatic variation than carbon at the high frequency level to shed light on the role of the possible divergence problem during last decades the climate responses were studied separately in the first and in the second half of the 20th century the responses to temperature were stable in the north but in eastern finland the significant period of summer occurred earlier during the later half of the century relationships between records were studied during the 400 a period all proxies correlated positively with each other although temporal changes occurred common forcing discovered in northern finland between carbon isotope and ring width records was weaker in the earlier period studied three climate reconstructions were created temperature reconstruction for northern finland and temperature and precipitation reconstructions for eastern finland copyright 2009 john wiley sons ltd

supergene features and evolution of gossans capping massive sulphide deposits in the iberian pyrite belt abstract twelve massive sulphide deposits from the iberian pyrite belt ipb show well preserved iron caps some of which were mined during the last century to recover precious metals e g tharsis rio tinto san miguel field observations and correlation assays between the distinct mineral sequences at different deposits suggest that all the gossans were developed under similar conditions and have undergone the same geological events all the gossans have a mushroom like morphology in sharp contact with the underlying massive sulphide orebodies in most cases these are located over an apparent supergene enrichment zone rich in secondary sulphides some gossans extend into tongues of alluvial heterolithic breccias consisting of eroded transported gossans displaced as far as several hundred meters away from their sources the distribution of major minerals throughout the gossan profiles goethite hematite quartz and jarosite and the statistical analysis of the geochemical data distinguish three separate zones with gradual contacts roughly parallel to the current topography 1 the lower zone dominated by goethite and subordinate jarosite with significant enrichment in s as p pb sn sb ag and au 2 the middle or principal zone dominated by goethite and lacking jarosite which is depleted in s and as as well as heavy and precious metals and 3 the upper zone near the surface mainly composed of hematite and quartz with only weak anomalies in p pb and sn the origin and variations occurred in the profiles are explained by a three stage process this involves an initial acidic stage of gossan development centred on the oxidation of sulphides that lead to the formation of the first fe rich oxyhydroxides and sulphates mainly goethite and jarosite respectively over time a progressive stage of maturity is reached progressively downwards through the gossan profile due to the intensification of the oxidation and leaching processes the ongoing gossan formation produced alteration and reprecipitation of pre existing oxyhydroxides the loss of the majority of the previously sorbed heavy metals and a major dilution of trace elements especially in the zones near the surface the main results of this stage of formation are the production of heavy metal depleted oxyhydroxides most commonly goethite and hematite and the disappearance of jarosite subsequently local uplift of the gossanous rocks by neotectonic movements facilitated the rejuvenation of the oxidation of the ores this final stage complicated the previously developed zonation with the formation of jarosite in mature areas possible major breaks in this gossan development ocurred in messinian times 7 8 ma and at the beginning of the early quaternary 1 2 ma

bismuth and cobalt minerals as indicators of stringer zones to massive sulphide deposits iberian pyrite belt the stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the iberian pyrite belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides these are fairly rare cobalt sulphoarsenides cobaltite alloclasite galucodot that were formed at the beginning of the massive sulphide genesis and fairly common bismuth sulphides bismuthinite hammarite wittichenite cosalite kobellite joseite etc including species rare at world scale nuffieldite giessenite jaskolskiite that were deposited from last stage high temperature 300 c copper bearing fluids containing bi te se the last stage fluids precipitated chalcopyrite containing cu bi te se sulphosalts at the base of the sulphide mound to form a high cupriferous zone their interaction with the massive sulphides is reflected by the formation of an exchange zone a few metres thick showing chalcopyrite disease textures at the base of the mound this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals gold is undoubtedly in part if not totally related to this last phase the bismuth concentrations being equivalent in the massive sulphides and the stringers the presence of bismuth minerals in the stringer zones results from high temperature conditions combined with a rarity of galena which impedes absorption of available bi the distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone with a deep low as2 zone containing native bismuth and tellurides and a shallow higher as2 zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides these results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature and provide mineralogical criteria for the proximity of copper rich zones they enrich the very complex mineralogy of the iberian pyrite belt

the deposition of elemental gold from gold i thiosulfate complexes mediated by sulfate reducing bacterial conditions the role of sulfate reducing bacteria in the precipitation of elemental gold through a geologic stratum was investigated using column experiments the mixed culture dominated by sulfate reducing bacteria was isolated from the driefontein consolidated gold mine witwatersrand basin republic of south africa bacterially mediated gold precipitation from the gold i thiosulfate complex was more efficient than the corresponding abiotic experiments in the bacterial systems sulfate reducing bacteria i e desulfovibrio sp deposited gold inside the cells as spherical nanoparticles over time these nanoparticles of gold were released from the cells and deposited at cell surfaces and in the bulk solutions ultimately these nanoparticles of gold contributed to the formation of micrometer scale octahedral gold crystals occasional framboidlike structures 1 5 m diam and millimeter scale gold foils typically surrounding the silicate grains spherical gold particles 1 m diam were precipitated in the abiotic experiments and the formation of octahedral gold framboidlike structures and gold foils were not observed in these experiments the reduction and enrichment of elemental gold by sulfate reducing bacteria occurred without the concomitant death of the bacteria suggesting that in natural systems this process could go on over geologic time scales as long as nutrients and gold i thiosulfate were provided to the system

the las cruces deposit iberian pyrite belt spain abstract the las cruces deposit is located at the eastern margin of the iberian pyrite belt ipb beneath the neogene quaternary deposits of the guadalquivir basin these sediments covered and preserved the supergene profile somewhat after its generation until its recent discovering for this reason the las cruces ore deposits together with lagoa salgada in portugal are the only known deposits in the ipb that preserve the entire weathering profile including both the gossan and the enrichment zone in that sense the present study provides new data on the ipb ore deposits and their post palaeozoic evolution the primary mineralization consists of massive and semi massive polymetallic sulfides overlaying a cupriferous and pyritic stockwork the supergene enrichment extends from the primary zone to gossan and consists of a thick cementation zone characterized by intense replacement of part of the primary sulfides by cu rich supergene sulfides at present the only economic resource of las cruces is the cementation zone with initial reserves of 17 6 mt 6 2 cu but the orebody also includes significant contents of cu and zn within the primary mineralization and au ag and pb in the gossan mineralogical and geochemical data confirm that the primary mineralization at las cruces resembles other ipb deposits in terms of distribution and evolution however the gossan and cementation zone show an uncommon evolution for this kind of supergene profile the major singularity that makes the las cruces supergene mineralisation noticeably different from others in the ipb or elsewhere resides in its unusual mineralogical composition mostly comprised of newly formed siderite calcite fe sulfides and galena the genetic model proposed for the las cruces deposit includes three main stages 1 ore genesis and evolution of primary mineralization which seems to be comparable to other ipb deposits 2 genesis of cu rich secondary mineralization and gossan by weathering after miocene exhumation of the upper part of the massive sulfide deposit under oxidizing and acidic conditions and 3 late evolution of supergene profile below the carbonated rich sediments of the guadalquivir basin with the subsequent change in the redox conditions due to water rock interaction between the supergene profile and basinal fluids

insights into the causes of arc rifting from 2 d dynamic models of subduction author s billen mi abstract 2017 american geophysical union all rights reserved back arc spreading centers initiate as fore arc or arc rifting events when extensional forces localize within lithosphere weakened by hydrous fluids or melting two models have been proposed for triggering fore arc arc rifting rollback of the subducting plate causing trench retreat or motion of the overriding plate away from the subduction zone this paper demonstrates that there is a third mechanism caused by an in situ instability that occurs when the thin high viscosity boundary which separates the weak fore arc from the hot buoyant mantle wedge is removed buoyant upwelling mantle causes arc rifting drives the overriding plate away from the subducting plate and there is sufficient heating of the subducting plate crust and overriding plate lithosphere to form adakite or boninite volcanism for spontaneous fore arc arc rifting to occur a broad region of weak material must be present and one of the plates must be free to respond to the upwelling forces

iodine rich waters involved in supergene enrichment of the mantos de la luna argentiferous copper deposit atacama desert chile recent studies have suggested the involvement of highly saline deep formation waters that modified preexisting cu assemblages to form atacamite during supergene oxidation of cu deposits in the atacama region in this report we document the occurrence of ag i inclusions hosted by supergene chalcocite from mantos de la luna an argentiferous upper jurassic stratabound cu deposit in the coastal range of northern chile the presence of this unusual mineral assemblage indicates that iodargyrite precipitated from reducing iodine rich waters suggesting that the fluids involved in supergene enrichment of cu deposits in the coastal range were more complex than previously thought this suggests the prevalence of hyperarid conditions during the latest stages of supergene enrichment of the mantos de la luna cu deposit in the atacama region supporting the notion that supergene enrichment processes in hyperarid areas are dynamic in nature and do not exclusively require the presence of meteoric water

freshening anomalies in the indonesian throughflow and impacts on the leeuwin current during 2010 2011 during the 2010 2011 la nina and ningaloo nino excessive precipitations in the maritime continent and indonesian australian basin caused surface waters to freshen by 0 3 practical salinity unit in the southeast indian ocean the low salinity anomalies are observed to be carried westward by the indonesian throughflow and the south equatorial current and transmitted into the poleward flowing eastern boundary current the leeuwin current along the western australian coast low salinity anomalies contribute to about 30 of the anomalous increase of the southward leeuwin current transport during the evolution of the 2010 2011 ningaloo nino resulting in unprecedented warming off the coast of western australia episodical freshening of the leeuwin current has been observed at the rottnest coastal reference station of western australia during extended la nina conditions over the past several decades low salinity anomalies at the station during the 2010 2011 ningaloo nino are comparable with strong historical events

the lagoa salgada orebody iberian pyrite belt portugal the iberian pyrite belt is one of the most outstanding european ore provinces and hosts one of the largest concentrations of massive sulfide deposits today totaling 1 850 million metric tons mt in more than 90 deposits lagoa salgada is a small orebody estimated to have at least 4 mt and as yet an unexploited orebody found within this ore province it is located 80 km northwest of neves corvo and occurs 130 m beneath sediments of the sado tertiary basin limiting interpretation to drill hole data lagoa salgada is folded faulted and interpreted to occur mostly on the subvertical overturned and intensely faulted limb of a southwest verging anticline it is represented by a central stockwork zone and a massive sulfide lens zone in the northwestern part of the orebody mineralization is mainly composed of pyrite with minor sphalerite tetrahedrite tennantite arsenopyrite chalcopyrite galena stannite and supergene minerals the orebody is hosted by a volcanic succession of rhyodacitic composition these small orebodies and some of the other abandoned mines within the iberian pyrite belt may represent interesting and feasible mining projects as a result of the added value generated by the presence of trace metals such as in serving a significant future demand for the high tech industry lagoa salgada is one such case indium is a significant trace metal in the ores of lagoa salgada as indicated by whole rock analyses this element is preferentially contained by sphalerite electron probe microanalyses epma of in contents within sphalerite show a large variability ranging from below detection limits to an obtained maximum of 0 8 percent in discrete inclusions of in bearing minerals have not been observed thus favoring the idea that in occurs either dispersed or in nanodomains within the host mineral

tornetrask tree ring width and density ad 500 2004 a test of climatic sensitivity and a new 1500 year reconstruction of north fennoscandian summers this paper presents updated tree ring width trw and maximum density mxd from tornetrask in northern sweden now covering the period ad 500 2004 by including data from relatively young trees for the most recent period a previously noted decline in recent mxd is eliminated non climatological growth trends in the data are removed using regional curve standardization rcs thus producing trw and mxd chronologies with preserved low frequency variability the chronologies are calibrated using local and regional instrumental climate records a bootstrapped response function analysis using regional climate data shows that tree growth is forced by april august temperatures and that the regression weights for mxd are much stronger than for trw the robustness of the reconstruction equation is verified by independent temperature data and shows that 63 64 of the instrumental inter annual variation is captured by the tree ring data this is a significant improvement compared to previously published reconstructions based on tree ring data from tornetrask a divergence phenomenon around ad 1800 expressed as an increase in trw that is not paralleled by temperature and mxd is most likely an effect of major changes in the density of the pine population at this northern tree line site the bias introduced by this trw phenomenon is assessed by producing a summer temperature reconstruction based on mxd exclusively the new data show generally higher temperature estimates than previous reconstructions based on tornetrask tree ring data the late twentieth century however is not exceptionally warm in the new record on decadal to centennial timescales periods around ad 750 1000 1400 and 1750 were equally warm or warmer the 200 year long warm period centered on ad 1000 was significantly warmer than the late twentieth century p 0 05 and is supported by other local and regional paleoclimate data the new tree ring evidence from tornetrask suggests that this medieval warm period in northern fennoscandia was much warmer than previously recognized

tree rings δ13c and climate in picea glauca growing near churchill subarctic manitoba canada abstract white spruce picea glauca moench voss trees were sampled to investigate the relationship between ring width and 13c as well as between these descriptors and climate cross sections from eight white spruce trees growing in the hudson bay lowlands subartic manitoba with an establishment date prior to 1775 were selected from our archive for each cross section two radii were measured to produce ring width chronologies for stable carbon isotope measurements every fifth ring 2000 1995 1750 was analyzed separately from each tree whereas approximately equal masses from the eight trees were pooled into composite samples for each of the intermediate years mixing masses from each tree equal to that from the tree with the least amount alpha cellulose was extracted and 13c was determined using continuous flow mass spectrometry the ring width residual chronology derived from eight trees was highly correlated to that previously developed for the area a small but significant correlation was also found between the ring width and the 13c residual chronologies the climate signal contained in both ring width and the 13c residual chronologies suggests that warm early summers were conducive to larger rings whereas the 13c best reflects the overall growing season temperature precipitation relative humidity and or drought index have little to no association with either chronology significant correlations were observed between 13c and the historical ice records from the hudson bay co archive data suggesting that during long warm growing season the 13c content of alpha cellulose increases our results indicate that both ring width and 13c provide complementary information future work will involve looking at long term trends in carbon isotope ratios and the potential use of 13c for dendroclimatic reconstruction

recent hiatus caused by decadal shift in indo pacific heating recent modeling studies have proposed different scenarios to explain the slowdown in surface temperature warming in the most recent decade some of these studies seem to support the idea of internal variability and or rearrangement of heat between the surface and the ocean interior others suggest that radiative forcing might also play a role our examination of observational data over the past two decades shows some significant differences when compared to model results from reanalyses and provides the most definitive explanation of how the heat was redistributed we find that cooling in the top 100 meter layer of the pacific ocean was mainly compensated for by warming in the 100 to 300 meter layer of the indian and pacific oceans in the past decade since 2003

supergene enrichment of precious metals by natural amalgamation in the las cruces weathering profile iberian pyrite belt sw spain abstract natural au ag hg alloys occur in the las cruces ore deposit in the eastern part of the iberian pyrite belt they are mainly concentrated in the lower part of the gossan profile including a sheared black shale level where the gossan makes contact with a barren pyrite zone within the supergene cu rich mineralization drill core analyses show a heterogeneous distribution of au ag and hg within the weathering profile with mean values of 5 1 ppm 155 ppm and 52 ppm respectively in general the absolute tenures increase towards the bottom of the weathered profile mineralogical studies conducted on samples from the active mine workings indicate that hg and precious metals occur mainly as au ag hg alloys these associations constitute the best potential resource for precious metals at the las cruces deposit this paper describes how this unusual precious metal enrichment is produced along the weathering profile by supergene processes combining paragenetic information mineral chemistry and the data pertaining to the solubilities of au ag and hg in a weathering profile we suggest a two stage genetic model for the formation of the las cruces au ag hg mineralization 1 release of au ag and hg from the massive sulfide deposit by weathering processes during the gossan formation at ph 0 9 v conditions au ag and hg are mobilized downward through the weathering profile as chloride complexes and fixed as elemental au halides oxides and sulfates and 2 remobilization of hg ag and au in the gossan after the deposit was buried beneath the neogene carbonate rich sedimentary cover the buffering capacity of the percolating fluids due to their interaction with the carbonate rich sedimentary pile leads to significant mineralogical and geochemical changes at near neutral conditions ph 6 7 eh 0 v hg ag and au are newly remobilized as thiosulfate sulfate and hydroxide complexes and newly fixed by sorption during ferric hydroxide formation and as sulfates several cycles of dissolution precipitation of au ag and hg near the redox front occur by oscillations in the water table and changes in the ph eh conditions the interaction of downward migrating fluids with high reductant lithologies black shales and massive sulfides seems to be responsible for the reduction of different complexes and for the precipitation of cinnabar ag sulfides and sulfosalts as well as the precipitation of au ag hg amalgams

gold and pathfinder elements in ferricrete gold deposits of the yilgarn craton of western australia a review with new concepts abstract secondary mineral deposits have played an important role in the global mineral resource economy for over 50 years with lateritic au al fe and ni deposits having a significant input to global metal production and reserves in the yilgarn craton of western australia a deeply weathered mantle is commonly capped with 2 10 m of lateritic residuum residual lateritic gravels and duricrust and or ferricrete fe oxide cemented sediment which formed under seasonally humid tropical and sub tropical climates during the cenozoic the principal constituents of these units are goethite hematite maghemite kaolinite and quartz they are commonly overlain by younger 2 10 m thick transported cover deposited under later semi arid conditions both ferricrete and lateritic residuum may host exploitable secondary gold deposits typically small

robustness of observation based decadal sea level variability in the indo pacific ocean we examine the consistency of indo pacific decadal sea level variability in 10 gridded observation based sea level products for the 1960 2010 period decadal sea level variations are robust in the pacific with more than 50 of variance explained by decadal modulation of two flavors of el nino southern oscillation classical enso and modoki amplitude of decadal sea level variability is weaker in the indian ocean than in the pacific all data sets indicate a transmission of decadal sea level signals from the western pacific to the northwest australian coast through the indonesian throughflow the southern tropical indian ocean sea level variability is associated with decadal modulations of enso in reconstructions but not in reanalyses or in situ data set the pacific independent indian ocean decadal sea level variability is not robust but tends to be maximum in the southwestern tropical indian ocean the inconsistency of indian ocean decadal variability across the sea level products calls for caution in making definitive conclusions on decadal sea level variability in this basin

a chemical model for the concentration of gold in volcanogenic massive sulphide deposits abstract study and review of the gold distribution in selected volcanogenic massive sulphide deposits rosebery and hellyer in tasmania mt chalmers in queensland and millenbach in quebec indicates that gold has two distinct occurrences in these deposits 1 a gold zinc lead silver association which is commonly found in the upper part of zinc rich massive sulphide lenses e g rosebery and hellyer and 2 a gold copper association which is commonly present in the stringers and lower portions of copper rich deposits e g mt chalmers and millenbach in each deposit one of these occurrence dominates almost to the exclusion of the other thermodynamic modelling of the volcanogenic fluid which is based on previous work by large 1977 eldridge et al 1983 and pisutha arnond and ohmoto 1983 indicates that gold in the upper part of the zinc rich massive sulphide lenses was transported as au hs 2 while gold in the stringers and bases of copper rich massive sulphide deposits was transported as aucl 2 the ph and o 2 of the ore forming fluid have an important control on gold deposition and therefore gold grades high gold grades in zinc rich massive sulphide are promoted by near neutral oxidised and low temperature 150 c to 275 c fluids as indicated by the presence of barite carbonate feldspar gangue high gold grades in the copper rich stringers and base of the massive sulphide are promoted by higher temperatures 275 c to 350 c relatively oxidised fluids as indicated by bornite or by barite or hematite gangue and relatively acid fluids as indicated by kaolinite gangue in o 2 t space significant gold transport by au hs 2 occurs only in the pyrite stability field at relatively low temperatures 2 is not restricted by iron mineral equilibria but is greatest in the hematite magnetite and pyrite fields at high temperatures 300 c and high o 2 10 30 under conditions of au hs 2 transport bonanza type gold deposition may be found in areas where the hydrothermal fluids passed from the field of pyrite stability to that of hematite stability oxidation of hydrothermal fluids by seawater mixing and the rapid precipitation of sulphide minerals at the top of the massive sulphide lens may cause the precipitation of gold via the mechanisms of either h 2 s oxidation or sulphide gold coprecipitation other types of gold deposits may be classified into either the gold zinc or gold copper association the gold copper bismuth association is developed in higher temperature systems of moderate to high salinity where aucl 2 is the dominant complex e g porphyry cu au deposits and au rich skarns whereas the gold zinc lead silver association is developed in systems of low salinity and high h 2 s where au hs 2 is the dominant complex e g epithermal au ag and archean greenstone hosted au quartz

decadal phase change in large scale sea level and winds in the indo pacific region at the end of the 20th century 1 satellite observations of sea surface height ssh and wind stress for the period of 1993 2006 reveal a near coherent large scale decadal variability in much of the indo pacific region with a phase change at the turn of the 20th century trade wind variations in the tropical pacific and south indian ocean are anti correlated with each other as are ssh differences across these two basins implying anti correlated variation of the subtropical cells in the two oceans decadal changes in large scale ssh in the extra tropics are mostly associated with well defined patterns of wind stress curl indicating a near coherent decadal variation in the strength of subtropical and subpolar gyres together these variations reflect a linkage in the circulation of the pacific and indian oceans via atmospheric and oceanic bridges the phase change in the tropical pacific tends to occur earlier than elsewhere suggesting a potential role of the tropical pacific in regulating decadal variability of the entire region

pacific decadal oscillation documented in a coral record of north pacific winter temperature since 1873 1 the pacific decadal oscillation pdo the leading mode of sea surface temperature sst anomalies in the extratropical north pacific ocean has widespread impacts on precipitation in the americas and marine fisheries in the north pacific however marine proxy records with a temporal resolution that resolves interannual to interdecadal sst variability in the extratropical north pacific are extremely rare here we demonstrate that the winter sr ca and u ca records of an annually banded reef coral from the ogasawara islands in the western subtropical north pacific are significantly correlated with the instrumental winter pdo index over the last century the reconstruction of the pdo is further improved by combining the coral data with an existing eastern mid latitude north pacific growth ring record of geoduck clams the spatial correlations of this combined index with global climate fields suggest that sst proxy records from these locations provide potential for pdo reconstructions further back in time

july mean temperature and annual precipitation trends during the holocene in the fennoscandian tree line area pollen based climate reconstructions july mean temperature and annual precipipation during the last 9900 cal yr bp were recon structed from pollen assemblages preserved in a sediment core from northern finland quantitative recon structions were performed using a modern pollen climate calibration model based on weighted averaging partial least squares regression the predictive ability of the model was evaluated against modern meteoro logical data using leave one out cross validation the prediction error for july mean temperature is c 1 0 c and for annual precipitation 340 mm the july mean temperatures during the earliest holocene were low c 1 1 0 c and annual precipitation was high c 600 800 mm between 8200 and 6700 cal yr bp july mean temperatures reached their maxima 12 5 13 0 c which are c 1 4 1 7 c higher than at present at the same time precipitation decreased during the late holocene july mean temperatures declined and the last 2000 years have been the coolest since the early holocene precipitation has slightly increased the spatial coherence between our results and of several other climate reconstructions from northern europe indicates that the holocene climate was strongly influenced by north atlantic oceanic and atmospheric circulation patterns we propose that the distinctly oceanic climate of the early holocene was due to enhanced westerly latitudinal airflow which was replaced at c 8200 cal yr bp by a more meridional flow pattern and by the development of predominantly anticyclonic summer conditions

gold behavior in supergene profiles under changing redox conditions the example of the las cruces deposit iberian pyrite belt the las cruces deposit is in the eastern end of the iberian pyrite belt sw spain it is currently being mined by cobre las cruces s a the main operation is focused on the supergene cu enriched zone initial reserves of 17 6 mt 6 2 cu an au ag pb rich gossan resource 3 6 mt 3 3 pb 2 5 g t au and 56 3 g t ag occurs in the upper part of the deposit the au grade ranges from 0 01 ppm to 100 ppm and occurs as three different au ore types 1 au mineralization in the upper part of the gossan linked to fe oxides lithofacies 2 au concentration in the lower part of the gossan associated with leached black shales and 3 au ore in the cementation zone related to subvertical fractures a hydroseparation device has been used to obtain heavy mineral concentrates from selected samples of different ore types reflected light microscopy scanning electron microscopy energy dispersive spectroscopy sem eds and electron probe microanalysis epma were used to study the separated au particles significant differences between the defined ore types include the au bearing lithologies mineral associations textural features particle sizes morphologies and fineness au rich minerals include native au au ag electrum and au ag hg amalgams gold bearing mineral associations include pb oxihalides fe oxides galena pyrite cinnabar and ag sulfosalts the au enrichment mechanism in the supergene profile involves 1 dissolution of au from the primary sulfides as chloride rich ionic complexes during the weathering of the deposit under subaerial exposure dissolved au is transported downward through the supergene profile under acidic and oxidized conditions 2 destabilization of the au complexes by fe controlled redox reactions as a consequence coarse grained high fineness au particles precipitated in association with fe oxyhydroxides this resulted in secondary concentration in the upper gossan and 3 after deposition of cover sediments took place a progressive change in the system conditions resulting in a later au remobilization as hydroxidehalide hydroxide thiosulfate and bisulfide complexes in the lowermost gossan and cementation zone the main pathways for migration of enriched fluids to the cementation zone are secondary permeability zones linked to alpine reactivated faults deposition of au seems to be related to fluid interaction with reductant lithologies including black shales and the primary sulfides

platinum group minerals pgm in the falcondo ni laterite deposit loma caribe peridotite dominican republic two ni laterite profiles from the loma caribe peridotite dominican republic have been investigated for their platinum group element pge geochemistry and mineralogy one profile loma peguera i

gold nugget morphology and geochemical environments of nugget formation southern new zealand abstract gold nuggets centimetre scale have formed in a supergene alteration zone on hydrothermal gold deposits and occur intergrown with quartz and iron oxyhydroxide pseudomorphs after sulphide minerals and along fractures in quartz and host rocks the supergene alteration was driven by groundwater driven water rock interaction near to a regional unconformity beneath fluvial sediments and involved clay alteration and oxidation that extended up to 50 m below the unconformity oxidation of pyrite and arsenopyrite produced temporary thiosulphate ligands that mobilised microparticulate gold encapsulated in the sulphide minerals the nuggets have some crystalline form and internally they consist of anhedral grains elongated gold plates and intimate intergrowths of gold and iron oxyhydroxide nugget surfaces have further micron scale overgrowths of microparticulate gold gold plates and gold crystals nuggets were eroded and recycled into nearby proximal miocene quartz pebble conglomerates where they concentrated in placers near the basal unconformity later recycling transferred gold into pleistocene fluvial channels gold dissolution and redeposition as plates and crystals occurred on the exterior surfaces of placer gold particles with little change in mass all groundwater maintained high ph throughout the geological history because there was sufficient calcite in the basement rocks to neutralise any acid generated by pyrite oxidation hence gold mobility in sediments was driven by thiosulphate complexes as for the in situ nuggets albeit with lower dissolved sulphur concentrations despite aridification of the climate in the late cenozoic with resulting localised high dissolved chloride concentrations chloride complexation did not contribute to gold mobility

supergene gold transformation secondary and nano particulate gold from southern new zealand biogeochemical processes drive the transformation of gold au in surface environments in this study we assess the link between surface morphologies of au grains and supergene transformation processes with a focus on the formation of nano particulate au in temperate settings gold grains were collected from six localities across the south island of new zealand deposit styles vary from eluvial alluvial and beach placer deposits in areas of moderate to very high levels of precipitation gold grains were assessed using optical microscopy om field emission scanning electron microscopy feg sem focused ion beam scanning electron microscopy fib sem coupled with x ray dispersive analysis edxa and electron microprobe analyses epma morphologies indicative of au and ag dissolution e g grain boundary dissolution as well as abundant au neoformation and aggregation morphologies were observed on all grains the latter include a variety of secondary au morphotypes in particular nano particulate and crystalline forms as well as bacteriomorphic au sheet au and porous branched au networks pervasive dissolution features on grains from an outcropping quartz vein system as well as extensive nano particle formation on weathered quartz vein and placer grains from the west coast of new zealand s south island which is subject to very heavy orographic precipitation suggest that these climatic conditions enhance the transformation of au grains at these sites au nano particles are most abundant in the polymorphic layer i e a coating of biofilms secondary au siliceous and carbonaceous materials on the surface of transforming au grains and in soil materials associated with the grains nano particulate au is also highly abundant in carbonaceous likely exopolymeric coatings on au grains from orepuki beach suggesting that au dissolution in seawater and microbial biomineralization are important contributors to au alteration in beach placer deposits in conclusion surface morphologies of au grains from new zealand are the result of supergene transformations occurring in current environments the formation of nano particulate au which was previously thought to be evaporation driven is in these high rainfall environments likely due to other mechanisms such as biomineralization

the mobility of gold in tropical rain forest soils the complex mineralogical and chemical system of a tropical rain forest weathering profile at the ashanti mine ghana was characterized to evaluate the role of inorganic and organic processes with the potential to mobilize gold in the rain forest soils the concentration of gold has been measured in bulk saprolite soil samples and in pore water extractions from the saprolite and soil horizons from the sansu prospect at ashanti gold concentration in the ground waters varied from below the detection limit 0 01 mu g l to a maximum of 84 4 mu g l at the water table average gold concentration in the soil pore waters is 3 6 mu g l the gold in the pore waters is present as either soluble gold or as suspended particles less than 0 45 mu m in size despite the presence of significant gold concentrations in the soil pore waters gold concentration in soils over the auriferous shear zones is up to 400 times greater than over the nonauriferous country rocks suggesting a limited gold mobility similarly a close correlation between gold held in the solid soil fraction and in soil pore waters reveals very little in the way of supergene gold enrichment conversely the gold is dissolved and reprecipitated over a range of a few centimeters the high concentration of gold in the soil pore waters at ashanti is a reflection both of the high gold content of the hypogene ore and of the efficiency of supergene fluids in the tropical rain forest environment to leach the gold but not retain it in a mobile form solubility calculations indicate that gold complexing in the soils appears to be dominated by auoh h 2 o au cn 2 super au s 2 o 3 2 super 3 au nh 3 2 super and a gold fulvate complex selective extraction of gold from organic and inorganic soil fractions reveals that the element is largely concentrated as native gold a significant proportion up to 28 is concentrated in the light organic fraction of the near surface soils which is dominated by fulvic acid the role of gold adsorption by clays and hydrous fe mn oxides appears to be small with less than 1 percent of the gold being present in an easily exchangeable form gold appears relatively immobile in the lower saprolite with gold values in solution being below the detection limit 0 01 mu g l higher up in the saprolite gold appears to be dissolved by hydroxide and thiosulfate complexes in the upper saprolite and by fulvate cyanide and hydroxide complexes in the soils due to the in situ nature of gold dissolution and reprecipitation even short lived species such as thiosulfate and cyanide can play an important role in the supergene chemistry of gold in the ashanti soils halide complexes are not considered important owing to their low concentration in the ground waters cl 9 mg l and the unrealistically high eh low ph conditions required humic acids are also not considered important in the dissolution of gold as they are only sparingly soluble in the ph range of the ashanti soils 4 2 6 8

mineralogical evolution of the las cruces gossan cap iberian pyrite belt from subaerial to underground conditions abstract the las cruces vms deposit is located at the eastern corner of the iberian pyrite belt sw spain and is overlain by the neogene quaternary sediments of the guadalquivir foreland basin the deposit is currently exploited from an open pit by cobre las cruces s a being the supergene cu enriched zone the present mined resource the las cruces orebody is composed of a polymetallic massive sulfide orebody a cu rich stockwork and an overlying supergene profile that includes a cu rich secondary ore initial reserves of 17 6 mt 6 2 cu and a gossan cap initial reserves of 3 6 mt 3 3 pb 2 5 g t au and 56 3 g t ag the mineralogy of the las cruces weathering profile has been studied in this work textural relationships mineral chemistry deposition order of the minerals and genesis of the las cruces gossan are described and discussed in detail a complex mineral assemblage composed by the following minerals has been determined carbonates such as siderite calcite and cerussite fe sulfides including pyrite marcasite greigite and pyrrhotite pb sb sulfides and sulfosalts like galena stibnite fuloppite plagionite boulangerite plumosite and the jordanite geocronite series ag hg sb sulfides and sulfosalts including miargyrite pyrargyrite sternbergite acanthite freibergite cinnabar ag au hg amalgams and bi pb bi sulfides and sulfosalts such as bismuthinite galenobismutite others unidentified bi pb sulfosalts native bi and unidentified fe pb sb sulfosalts remains of the former oxidized assemblage appear as relicts comprised of hematite and goethite combining paragenetic information textures and mineral chemistry it has been possible to derive a sequence of events for the las cruces gossan generation and subsequent evolution in that sense the small amount of fe oxyhydroxides and their relict textures replaced by carbonates and sulfides suggest that the gossan was generated under changing physico chemical conditions it is proposed that the las cruces current gossan represents the modified residue of a former gossan mineralization where prolonged weathering led to dissolution and leaching out of highly mobile elements and oxidation of the primary sulfides later the gossan was subject to seawater gossan interaction and then buried beneath a carbonated rich cover the basinal fluids gossan interaction and the equilibration of fluids with the carbonated sediments brought to the carbonatization and sulfidation of the gossan and thus to the generation of fe carbonates and pb sb sulfides the las cruces mineral system likely represents a new category within the weathering class of ore deposits

pacific modulation of accelerated south indian ocean sea level rise during the early 21st century the south indian ocean has shown an unprecedented sea level rise during the early 21st century sea level rise in the south indian ocean is found to be 37 quicker than the global mean sea level during 2000 2015 observational datasets and long term proxy records identify pacific origin of the south indian ocean sea level rise our results indicate that co evolution of the cold phase of pacific decadal oscillation pdo and prolonged la nina like condition enhances the equatorial pacific easterlies stronger in phase association of these major pacific climate modes and equatorial pacific easterlies enhances the indonesian throughflow itf transporting fresh and warm water anomalies from western tropical pacific into the south indian ocean as a result south indian ocean sea level rise has accelerated more than the global with 40 contribution from the halosteric sea level primarily through the itf transport and a secondary from the local processes during 2000 2015 the co evolution of pdo and the south indian ocean sea level is also evident from the long term proxy records indicating that the association is part of an internal mode of variability modulated on decadal time scales the finding from the study cautions that accelerated heat and freshwater intrusion from the western pacific with the co evolution of pdo and la nina like condition may lead to the accelerated sea level rise and marine heat waves in the south indian ocean imposing threats to the life of coral reefs and marine ecosystems

forcing of recent decadal variability in the equatorial and north indian ocean recent decadal sea surface height ssh variability across the equatorial and north indian ocean enio north of 5 s is spatially coherent and related to a reversal in basin scale upper ocean temperature trends analysis of ocean and forcing fields from a data assimilating ocean synthesis eccov4 suggests that two equally important mechanisms of wind driven heat redistribution within the indian ocean account for a majority of the decadal variability the first is the cross equatorial cell cec forced by zonal wind stress curl at the equator the wind stress curl variability relates to the strength and position of the mascarene high which is influenced by the phase of the indian ocean subtropical dipole the second mechanism is deep 700 m upwelling related to zonal wind stress at the equator that causes deep cross equatorial overturning due to the unique geometry of the basin the cec acts to cool the upper ocean throughout most of the first decade of satellite altimetry while the deep upwelling delays and then amplifies the effect of the cec on ssh during the subsequent decade reversals in the forcing anomalies drive warming of the upper ocean and increasing ssh with the effect of the deep upwelling leading the cec this article is protected by copyright all rights reserved

naturally occurring gold nanoparticles and nanoplates during the weathering of gold deposits exceptionally pure 200 nm diameter nanoparticulate gold plates 6 nm thick are formed the particles display controlled growth of both size and shape and signs of assembly to form belts and sheets the gold is associated and intergrown with minerals formed by evaporation and is interpreted to have been deposited rapidly from saline groundwater during a drying event the size and morphology of the gold nanoparticles and nanoplates are identical to the products of experimentally manufactured gold colloids this represents the fi rst direct observation of colloidal nanoparticulate gold in nature confi rming this as an active mechanism of gold transport during the weathering of gold deposits

on the stability of gold silver alloys in the weathering environment thermodynamic analysis of the stability conditions for gold silver solid solutions reveals that the silver component is unstable with respect to chlorargyrite and silver sulfate in most weathering environments as a consequence supergene secondary gold and gold found in modern river placers detrital and authigenic tends to be pure impure detrital placer gold is subject to natural purification processes as evidenced by silver depleted spongey grain margins in contrast under hydrothermal conditions the silver content of primary gold can be controlled by equilibrium reactions with argentite

gold in the southwest of the iberian peninsula during the 3rd millennium bc abstract in the southwest of the iberian peninsula one of the main gold mining regions in western europe the presence of the first gold products are noted in the archaeological records of 3rd millennium bc megalithic tombs at some distance from the mining districts the lack of systematic programmes to analyse such archaeological gold finds has led them to being identified as ornamental finds of undetermined chronology linked to a simple manufacturing technology of hammering gold nuggets of an uncertain origin or from the eastern mediterranean as well as items with a purely symbolic or prestige value in the funerary practices of simple group oriented or collaborative chiefdoms but however the first documentation radiocarbon dating and systematic analysis of these products in settlement contexts has altered this interpretation the presence of gold manufactures during the third quarter of the 3rd millennium bc c 2500 2350 cal bc in the contexts of a settlement specialised in copper production such as cabezo jure in the south western mining region huelva spain and in the contexts of a huge central site such as valencina de la concepcion in the agrarian region of the lower guadalquivir basin seville spain points to the widespread social use of gold in the period of maximum expression of the inter settlement hierarchisation in the southwest of the iberian peninsula its link with the social spaces of inequality expression and their relationship with a complex production system geochemical characterization by la icp ms lead isotopes analysis by mc icp ms and metallographic study suggest two differentiated and independent supplies of raw material systems fluvial placers vs mines and local vs regional scale with at least four source areas the regional circulation of raw material or products and a manufacturing by a metallurgical technology linked to the copper production

weathering profile of the cerro de maimon vms deposit dominican republic textures mineralogy gossan evolution and mobility of gold and silver abstract cerro de maimon in the central dominican republic is currently the only vms deposit under production in the caribbean region it is hosted in the maimon formation of early cretaceous age which is part of the oldest and chemically most primitive island arc in the caribbean from bottom to top this deposit can be divided into i a primary sulfide zone ii a supergene enrichment zone and iii an oxidized zone this study reports new data on the textural and mineralogical characteristics of the oxidized zone gossan leached capping zone with emphasis in the au ag bearing phases the mineral paragenesis of the oxidized zone is essentially composed of goethite hematite quartz and barite botryoidal cellular and brecciated textures can be distinguished botryoidal and brecciated textures dominate in the upper parts of the oxidized zone whereas cellular textures are more common in the intermediate and lower parts however the weathering profile is very heterogeneous the leached capping profile shows evidence of both transported and indigenous gossans gold in the oxide paragenesis is extremely pure 99 au suggesting that chemical refining took place silver occurs mainly as iodargyrite agi and minor agbr agcl in botryoidal aggregates particles of au ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents chemical and biochemical that may exist simultaneously in the presence of halides gold and silver can be leached and transported in a wide range of ph eh conditions especially if iodine is present silver is leached more rapidly and over a broader range of ph eh conditions and is preferentially transported as iodine complexes than other halides the presence of iodargyrite in the cerro de maimon gossan fully developed under tropical conditions suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors iodargyrite occurrence would rather point to the presence of saline halide rich groundwater in oxide deposits

nanoparticle factories biofilms hold the key to gold dispersion and nugget formation biofilms living on gold au grains play a key role in the biogeochemical cycle of au by promoting the dispersion of au via the formation of au nanoparticles as well as the formation of secondary biomorphic au gold grains from queensland australia are covered by a polymorphic organic inorganic layer that is up to 40 m thick it consists of a bacterial biofilm containing au nanoparticles associated with extracellular polymeric substances as well as bacterioform au focused ion beam fib sectioning through the biofilm revealed that aggregates of nanoparticulate au line open spaces beneath the active biofilm layer these aggregates bacterioform au type 1 resulted from the reprecipitation of dissolved au and their internal growth structures provide direct evidence for coarsening of the au grains at the contact between the polymorphic layer and the primary au bacterioform au type 2 is present it consists of solid rounded forms into which crystal boundaries of underlying primary au extend and is the result of dealloying and ag dissolution from the primary au this study demonstrates that 1 microbially driven dissolution precipitation and aggregation lead to the formation of bacterioform au and contribute to the growth of au grains under supergene conditions and 2 the microbially driven mobilization of coarse au into nanoparticles plays a key role in mediating the mobility of au in surface environments because the release of nanoparticulate au upon biofilm disintegration greatly enhances environmental mobility compared to au complexes only

iodargyrite from zalas cracow area poland as an indicator of oligocene miocene aridity in central europe abstract iodargyrite the hexagonal silver iodide was found in the permian rhyodacite quarry at zalas near cracow southern poland in a fault zone cutting middle jurassic sandy limestone it occurs within a tectonic breccia encrusted by chalcopyrite pyrite ag containing chalcocite covellite galena native bismuth malachite cuprite fe and mn dominant oxides cu sulfates and barite the hydrothermal encrustacion is most likely connected with rejuvenation of old paleozoic faults in the sava phase of the alpine orogeny on the oligocene miocene boundary the periods of aridity when iodargyrite precipitated determined by evaporation of salt lakes or the inland miocene sea that delivered halide ions to the groundwater oxidation system or leaching of weathered ag containing mineralization by saline i rich deep formation waters derived from paleogene sediments during folding and formation of the carpathians nappe structure are connected rather with the low to middle miocene period at this time steppe areas with a dry climate existed on the north foreland of the carpathians in southern poland as a result of a displacement to the north of a dry subtropical zone because of uplift of the carpathians and regression of the inland miocene sea

geochemistry and mineralogy of contrasting supergene gold alteration zones southern new zealand abstract supergene alteration of gold deposits has had important geochemical effects that changed the mineralogy and textures of near surface exposures and can affect the economics of gold mines by enhancing gold liberation and increasing gold grades this study links observed mineralogy with 655 water analyses from environments relevant to supergene processes in the otago schist goldfield of southern new zealand and these analyses are used as proxies for past supergene processes there are two contrasting supergene alteration styles in otherwise identical host rocks and mineralisation zones in this area long term groundwater alteration of sediments and underlying basement near to a regional unconformity developed progressively since the cretaceous this alteration has affected orogenic gold deposits exposed at the unconformity and has resulted in supergene enrichment of gold with localised formation of centimetre scale gold nuggets alteration processes occurred under circumneutral ph conditions ph 6 8 5 and was accompanied by extensive oxidation and clay alteration of basement rocks and sediments gold was mobilised as thiosulphate and bisulphide complexes and was reprecipitated by redox changes near the unconformity the chemical processes of supergene enrichment were primarily abiotic with minor bacterial facilitation of late stage gold mobility at the micron scale in contrast supergene alteration of eroding freshly exposed mountain outcrops has occurred in the late cenozoic without au enrichment apart from liberation and minor particle size enhancement the ambient ph of the associated waters was also circumneutral but localised and temporary acidification to ph 3 has occured on the metre scale or less in sulphidic outcrops this supergene alteration was dominated by oxidation but some low redox minerals senarmontite and secondary stibnite have formed during the early stages of oxidation or subsequent reduction sulphide decomposition with associated localised acidification and gold remobilisation was probably enhanced by bacterial processes in these exposed outcrops

mobility of gold and silver in lateritic weathering profiles some observations from western australia experimental evidence suggests that very acid chloride solutions generated in lateritic profiles by ferrolysis oxidation and hydrolysis of iron are responsible for the dissolution of gold and silver au is subsequently reprecipitated by reduction of the aucl 4 super ion with fe super 2 reduction of the agcl complex does not similarly occur because of the relative redox potentials of fe super 2 fe super 3 and ag agcl thus chemical refinement of gold occurs during lateritization the development of low ph and the redistribution of gold and silver in lateritic weathering profiles appear to be more common over granitic and gneissic basement and may be inhibited by the presence of carbonate in the weathering zone of basic rock sequences modified journal abstract