the presence of carbonic dominant volatiles during the crystallization of sulfide bearing mafic pegmatites in the north roby zone lac des iles complex ontario mafic pegmatites in the platinum group element pge mineralized roby zone lac des iles complex northwest ontario canada comprise dikes veins and irregular pods of coarse grained magnesiohornblende pyroxene and labradorite andesine with minor biotite apatite fe ti oxides and intercumulus quartz that grades into massive quartz or graphic quartz base metal sulfide vysotskite pd ni s intergrowth at their cores quartz apatite and magnesiohornblende host primary and secondary assemblages of one or two phase carbonic fluid co 2 up to 10 ch 4 minor h 2 o n 2 inclusions that contain ore metals ni cu pd bi te fe rare trails of late stage high salinity aqueous fluid inclusions are secondary in origin and therefore unrelated to the crystallization of the pegmatites assemblages of primary carbonic fluid inclusions show considerable variation in mode and temperature of homogenization reflecting large fluctuations in confining pressure at the time of quartz crystallization of as much as 1 kbar in single quartz crystals and 2 8 kbars all data independent thermobarometric methods constrain conditions for the following two stages of pegmatite formation and carbonic fluid entrapment 1 the crystallization of magnesiohornblende plagioclase intergrowth at t 650 to 850 c and p 1 to 3 kbars and 2 the crystallization of quartz at t 535 to 650 c and p 0 4 to 3 2 kbars setting the maximum depth of emplacement of the lac des iles complex north roby zone magma at 10 to 12 km the results indicate that aqueous dominant volatile phases were absent during the crystallization of pegmatitic gabbroic rocks at the lac des iles complex and that water poor carbonic fluid entrapment persisted to well below solidus conditions a role played by carbonic fluid as a potential transport medium for ligands involved in the precipitation and remobilization of the pge and base metals is strongly suggested and warrants further investigation

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

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

magnetostratigraphy of chinese loess paleosol sequences abstract as one of the longest and most continuously deposited terrestrial sedimentary archives in the world chinese loess paleosol sequences record paleoclimatic and paleomagnetic variations at a range of time scales magnetostratigraphic studies provide a first order chronological framework for chinese loess sequences in this review we highlight recent developments in loess magnetostratigraphy including pedostratigraphy based on magnetic susceptibility variations we highlight progress in understanding the mechanisms by which the natural remanent magnetization nrm is acquired and discuss in detail the fidelity of paleomagnetic recording in loess records including the recording of magnetic polarity reversals excursions and relative paleointensity variations finally we discuss future prospects for studies of loess nrm

the response of transitional pedogenic characteristics of loess in the yunxian basin to abrupt climatic events in the northern subtropics since the last glacial maximum abstract the transitional pedogenic characteristics of loess deposits in the yunxian basin have provided solid evidence for understanding the mechanisms of dust transportation deposition and detailed documentation of climate instability since the last glacial maximum lgm in the northern subtropics of china the heinrich stadial 1b hs 1b 16 9 14 7 ka b p event b lling aller d b a 13 9 13 ka b p period younger dryas yd 12 9 11 7 ka b p event and an environmental event 5 4 ka b p during the holocene optimum were imprinted by the high resolution multi proxy of loess paleosol in the yunxian basin china based on granularity and chemical analyses the loess in the yunxian basin can be classified as a fine clayey loess zone that experienced a moderate degree of chemical weathering the mechanism forming the transitional pedogenic characteristics was explained by the dust storm frequency data 1957 2007 particle size data and multi proxy records of chemical weathering extent which was mainly caused by the moderate transport distance from the common provenance and the transitional climatic characteristics of the northern subtropical zone

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

flash vaporization during earthquakes evidenced by gold deposits fluids flowing through cavities in earth s crust can deposit gold thermo mechanical modelling of a fluid filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously

gold and metal enrichment in natural granitic melts during fractional crystallization metal evolution in a composite granitic pluton was tracked by analyzing melt inclusions in 11 quartz samples from 7 zones at the timbarra gold deposit australia we present the first quantitative microanalyses of gold au in granitic silicate melt inclusions using laser ablation inductively coupled plasma mass spectrometry and show how au and other metals become enriched during fractional crystallization in a granite intrusion au was enriched during fractionation from a monzogranite to a highly fractionated alkali feldspar granite similar enrichment behavior for other metals implies that no gold enriched precursor melt is required and fractional crystallization can enrich the au concentration to economic levels the low content of accessory oxides and sulfides the absence of early cl bearing fluids the volatile content in the melt and a prolonged crystallization constitute important factors for extensive metal enrichment during crystal fractionation these characteristics play a crucial role in felsic highly fractionated plutons and their associated deposits such as intrusion related au deposits the gold enrichment during fractionation also implies that au is directly sourced from the granites

new magnetostratigraphic dates of lantian homo erectus skeletal remains of homo erectus found in pleistocene loess at two sites near lantian in central china are of greatly different geologic age the cranium found in the fossil bearing strata at gongwangling is about 1 15 myr old whereas the remains found at the chenjiawo locality in middle pleistocene loess are about 0 65 myr old the dating is based on new paleomagnetic polarity determinations and on the lithostratigraphic position of the fossils in the loess paleosol sequence our results confirm that both localities are older than the first occupation of zhoukoudian new dates palaeoenvironmental settings and morphological features of the hominids from lantian localities have significant bearing on the understanding of adaptive radiations of the middle and late hominids in asia

cyclic quaternary alluviation and terracing in a nonglaciated drainage basin on the north flank of the qinling shan central china abstract pleistocene alluvial terraces of the nonglaciated ba river drainage basin on the north flank of the qinling shan are capped by a succession of loess units and paleosols that correlate with the standard marine isotope chronology and are used to date the subjacent alluvial gravels alluvial fills were deposited during isotope stages 2 6 8 12 and 16 whereas terracing occurred during interglacial stages 1 5 7 11 and 15 the apparent absence of terraces dating to stage 14 and stage 4 may be due to the lesser intensity of these glaciations compared to that of stage 2 although disruption of the alluvial regime by local tectonism is a likely alternative for the lack of a stage 4 terrace a stage 10 terrace was not positively identified from available exposures its possible absence could be related to post stage 12 uplift aggradational episodes correlate with glaciations and loess deposition whereas degradational episodes correlate with interglaciations or interstades and soil formation implying that climate is the primary control on quaternary paleohydrology this in turn points to variations in the earth s orbital geometry as the major factor that modulates both climate and ultimately the fluvial system in the qinling shan in this region glaciations were dominated by a cold dry winter monsoon climate whereas during interstades and interglaciations a warmer and wetter climate prevailed implying strengthening of the summer monsoon both the loess paleosol and the alluvial records are consistent with climate model simulations spanning the last 18 000 yr that show a change from cold dry conditions during the last glacial maximum to a climate warmer and wetter than present during the first half of the holocene

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

hydrothermal transport and depositional processes in archean lode gold systems a review abstract compelling evidence now exists for the formation of archean lode gold deposits over a substantial range in metamorphic conditions and crustal depth the commonality of ore fluid isotopic and geochemical characteristics the extreme fluid rock ratios within actual ore zones and the observed depth continuity within individual orebodies all suggest that these deposits formed within vertically extensive crustal scale hydrothermal systems calculations based on new thermodynamic data and estimated ore fluid conditions suggest that gold would have been transported as au hs 2 over most of this range gold transport in the ore fluids that formed some diopside and diopside k feldspar class deposits t 550 c would have been as aucl2 whereas the au hs complex may have been significant in some of the lower temperature 270 c less alkaline ore fluids the high solubility of gold in lode gold ore fluids at amphibolite facies conditions 10 s to 1000 s ppb suggests that fluids may have been undersaturated in gold within their source regions promoting the ore fluid s capacity to retain gold in solution over the large transport distances involved ore depositional mechanisms were also likely to vary between crustal levels fluid rock interactions and wallrock sulphidation in particular appear to be the most important type of precipitation mechanism however with decreasing depth of formation the scope of other depositional mechanisms notably phase separation and fluid mixing becomes greater

tt osl and post ir irsl dating of the dali man site in central china abstract showing features associated with archaic homo sapiens and evolved homo erectus the dali skull is a key fossil for understanding human evolution in china various dating methods such as u series irsl tl esr esr u series and stratigraphical correlation with central loess plateau sequence were used to estimate the antiquity the dali man site with varying results in this study a total of 12 samples were taken in the sequence in the dali man site from the aeolian loess palaeosol sequence and underlying fluvial deposit layers including the palaeoanthropological level and dated by several optically stimulated luminescence osl methods coarse grained quartz sar osl thermally transferred osl tt osl and k feldspar post ir infrared ir stimulated luminescence post ir irsl pirir 290 methods results show that the tt osl and pirir 290 ages were consistent up to 100 ka for older samples the feldspar ages were significantly older these pirir 290 ages increased with the stratigraphy up to 310 ka the best age estimation of the dali man layer providing by the feldspar pirir 290 suggested that the dali man lived in late period of l3 mis 8 stage furthermore correlating the pirir 290 ages between 267 7 13 9 ka and 258 3 14 2 ka and new pollen analysis we proposed a new viewpoint that the dali man was likely to live during a transitional period from glacial to interglacial climate in the s2 l3 mis 7 8 stage

boiling and vertical mineralization zoning a case study from the apacheta low sulfidation epithermal gold silver deposit southern peru the au ag pb zn apacheta deposit is located in the shila district 600 km southeast of lima in the cordillera occidental of arequipa province southern peru the vein mineralization is found in early to middle miocene calc alkaline lava flows and volcanic breccias both gangue and sulfide mineralization express a typical low sulfidation system assay data show element zoning with base metals enriched at depth and higher concentrations of precious metals in the upper part of the veins three main deposition stages are observed 1 early pyrite and base metal sulfides with minor electrum 1 and acanthite 2 brecciation of this mineral assemblage and cross cutting veinlets with subhedral quartz crystals mn bearing calcite and rhombic adularia crystals and finally 3 veinlets and geodal filling of an assemblage of tennantite tetrahedrite colorless sphalerite 2 galena chalcopyrite electrum 2 fluid inclusions in the mineralized veins display two distinct types aqueous carbonic liquid rich lw c inclusions and aqueous carbonic vapor rich vw c inclusions microthermometric data indicate that the ore minerals were deposited between 300 and 225 c from relatively dilute hydrothermal fluids 0 6 3 4 wt nacl the physical and chemical characteristics of the hydrothermal fluids show a vertical evolution with in particular a drop in temperature and a loss of h2s the presence of adularia and platy calcite and of co existing liquid rich and vapor rich inclusions in the ore stage indicates a boiling event strong h2s enrichment in the vw c inclusions observed at 200 m the abundance of platy calcite and the occurrence of hydrothermal breccia at this level may indicate a zone of intense boiling the vertical element zoning observed in the apacheta deposit thus seems to be directly related to the vertical evolution of hydrothermal fluid characteristics precious metal deposition mainly occurred above the 200 m level below the present day surface in response to a liquid vapor phase separation due to an upward boiling front

the behaviour of metals and sulphur during the formation of hydrothermal mercury antimony arsenic mineralization uzon caldera kamchatka russia abstract uzon caldera located in the eastern volcanic belt of the kamchatka peninsula is a complicated structure of middle pleistocene age the composition of the co existing solid and fluid phases temperature and ph were determined with the aim of establishing the distribution of sulphur species as sb and the main ore forming metals in the solid samples the following sulphur bearing minerals were identified pyrite realgar orpiment alacranite as8s9 uzonite as4s5 amorphous as sulphide stibnite cinnabar and native sulphur the following sulphur bearing species h2s h2s2 s52 aq aqueous polysulphanes s0 aq so32 aq s2o32 so42 and total concentration of sulphur were determined in solutions eh ph and h2s concentration were measured potentiometrically in situ zero valent sulphur s0 aq h2s2 s52 aq predominates in uzon solutions the pair h2s scolloidal is eh determining in uzon solutions up to 75 85 c a quantitative thermodynamic model of the mineral deposition process at uzon was constructed using the collected data it was obtained that the composition of the hydrothermal solution and the precipitation of sb as hg species can be described using two only main factors the initial composition of fluid and the temperature variation

initial gold contents of silicic volcanic rocks bearing on the behavior of gold in magmatic systems many fresh silicic volcanic rocks have markedly lower initial gold contents than previously recognized of 129 carefully selected glassy silicic volcanic rocks analyzed 113 contain f o 2 more readily accommodate gold the mean of 23 relatively silicic intermediate rocks is 0 54 ppb au with tholeiitic andesites icelandites generally higher in gold than calc alkalic types there is little evidence that particular geologic regions are intrinsically richer in gold than others bulk composition melt structure and the amount and timing of separation of vapor mineral and sulfide and or metal melt phases would appear to largely determine the gold contents of silicic magmas the various lines of evidence for the removal of gold from magma by the separation of vapor crystalline and immiscible melt phases indicate that fresh volcanic rocks provide only minimum limits on magmatic gold concentrations in most cases magmatic values will be much higher elevated gold contents 0 3 to 1 0 ppm of some porphyry deposits suggest the existence of salic magmas containing gold in concentrations appreciably greater than the 1 2 ppb concentrations of basalts

mineralogic and stable isotope zonation at the surface over the el salvador porphyry copper deposit chile we examined in detail the mineralogic and stable isotope characteristics of alteration minerals exposed at the surface of the el salvador porphyry copper deposit a total of 276 samples was collected from 203 localities over an area of 5 km 2 at elevations between 2 900 and 3 300 m the alteration assemblages can be separated into two groups broadly corresponding to the stages previously identified from underground studies although the early stage k silicate alteration identified underground is not evident at the surface a transitional to late stage is characterized at the surface by assemblages of 1 muscovite andalusite with trace diaspore including some areas rich in andalusite and 2 muscovite with trace diaspore there is a sharp contact outward with a marginal propylitic assemblage chlorite calcite epidote pyrophyllite occurs as a retrograde overprint of muscovite in both of the transitional to late stage assemblages these assemblages are concentrically zoned and centered on a core of least altered granodiorite porphyry a late intramineral intrusion the muscovite andalusite assemblage occurs up to 500 m away from the granodiorite porphyry and andalusite rich zones are located near the brecciated margin of the porphyry further outward is the muscovite zone from 500 to 1 500 m wide the pyrophyllite overprint overlaps the contact of the muscovite andalusite and muscovite zones and occurs mainly above 3 000 m elevation such that its present distribution is controlled largely by topography very late alteration minerals occur in radial pebble dikes of hydrothermal breccia and their extensions and they are dominated by an advanced argillic assemblage of alunite aluminum phosphate sulfate minerals diaspore zunyite pyrophyllite dickite with residual muscovite in one case a breccia extends upward and appears to be the root of a 300 500 m outcrop 80 m thick of massive quartz alunite replacement of rhyolite pure mineral separates were prepared from these samples for o h and s isotope analysis including 48 samples of silicate minerals muscovite pyrophyllite dickite and supergene kaolinite and 20 samples of alunite some supergene in origin information on mineral assemblage was used to estimate temperatures of formation which then allowed calculation of the isotopic composition of associated hydrothermal fluids the fluid responsible for forming the muscovite had a relatively narrow range of isotopic composition 6 5 1 5 per mil 18 o and 40 10 per mil d the heaviest 18 o and d values about 8 and 35 per mil respectively were obtained from the samples with andalusite muscovite diaspore assemblage this composition is close to that expected for a magmatic fluid with 10 to 20 percent meteoric water component responsible for forming the other muscovite samples the fluid compositions calculated for the very late stage alunite range from 5 and 30 per mil to 1 and 40 per mil 18 o and d respectively this range in composition agrees with the trend predicted for magmatic vapor absorbed by local groundwater the latter similar in composition to that responsible for forming the supergene kaolinite there is no systematic spatial zonation of the alunite samples in terms of isotopic composition or paleotemperature the temperature estimates from s isotope geothermometry are higher than those based on mineral assemblage possibly caused by partial supergene replacement of some hypogene alunites there is no strong isotopic zonation of hydrothermal minerals from surface alteration assemblages at el salvador that can be applied to generate clear exploration guidelines by contrast mapping of alteration mineralogy in the field backed up by laboratory checking of mineralogy and examination of relict minerals and replacement textures in thin section clearly indicates the center of the late intramineral intrusion

pedostratigraphy of aeolian deposition near the yunxian man site on the hanjiang river terraces yunxian basin central china abstract since 2010 we have found stone artifacts at the houfang and dishuiyan loess sections on the second terrace of the hanjiang river and the wolonggang thick natural loess section on the fifth terrace of the same river near the xuetangliangzi site we dated dishuiyan and houfang loess sections by optically stimulated luminescence osl and thermally transferred osl tt osl methods respectively dating results showed that the loess paleosol deposited on the second hanjiang river terrace as l1 s1 l2 and s2 in sequence we dated the wolonggang loess section by high resolution paleomagnetostratigraphic analyses the jaramillo subchron was found at this section correlating with the central loess plateau we recognized the continuous loess paleosol sequence from l9 to l15 investigations showed that loess was continuously deposited on the terraces of the hanjiang river at yunxian basin since at least 1200 ka

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

fluid evolution in zoned cordilleran polymetallic veins insights from microthermometry and la icp ms of fluid inclusions abstract fluid inclusion analysis through the paragenetic sequence of one symmetrically zoned vein sample is used to reconstruct the p t x fluid evolution of a porphyry intrusion related cordilleran polymetallic vein from morococha central peru results record an evolution from initial deep seated precipitation of quartz pyrite and base metal sulphides to final near surface deposition of carbonates demonstrating progressive mineralisation during uplift and erosion this is the first detailed study addressing meso to epithermal zn pb ag cu rich ore in a magmatic hydrothermal system by combination of fluid inclusion microthermometry with laser ablation inductively coupled plasma mass spectrometry la icp ms quantifying metal as well as sulphur concentrations in the evolving hydrothermal fluid scanning electron microscopy cathodoluminescence sem cl imaging of quartz and detailed transmitted and reflected light petrography provide textural evidence that early moderately saline 4 5 wt nacl eq and co 2 bearing fluids with homogenisation temperatures of 340 380 c precipitate cu bearing minerals in this open hydrothermal system the fluids record decreasing salinities co 2 contents and temperatures while zn pb and ag sulphides precipitate fluids related to early precipitation in the vein have metal contents of several 1000 g g s and fe over 1000 g g cu 100 g g pb 10 g g ag and several 100 g g zn sulphur concentrations in the fluid are sufficiently high to precipitate all metals in solution as sulphides the latest generation of fluid inclusions associated with abundant carbonate precipitation in the centre of the vein has homogenisation temperatures ranging from 260 to 220 c low metal concentrations and no measurable co 2 during vein formation cooling and several kilometres of erosion resulted in telescoping of consecutively precipitated mineral assemblages the deep input fluid dominating in the early vein stage is interpreted to be of magmatic origin most likely a single phase magmatic fluid of intermediate salinity and density it cooled to an aqueous liquid separated minor co 2 rich vapour and was eventually diluted by meteoric water in the late stages of vein formation when the progressively eroded land surface was only several hundred meters above the vein location

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

luminescence dating of the stratzing loess profile austria testing the potential of an elevated temperature post ir irsl protocol abstract feldspar infrared stimulated luminescence irsl signals saturate at 2000 gy i e 500 700 ka assuming a dose rate of 3 4 gy ka typical for loess and it is therefore theoretically possible to date middle pleistocene loess however the accuracy of age estimates is hampered by anomalous fading which leads to significant age underestimation fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses as the growth curve approaches saturation recent studies have identified a post ir irsl signal that shows less fading and is thus less dependent on accurate fading corrections this study builds upon these investigations and applies a post ir irsl sar dating protocol to polymineral fine grain samples of the loess palaeosol sequence in stratzing lower austria after a preheat at 320 c 60 s and an ir bleach at 50 c 200 s irsl was measured at 290 c for 200 s the same set of conditions were used to measure the response to a test dose recycling ratios recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation although finite residual doses of up to 20 gy are observed for the oldest samples the natural signal is in or close to saturation indicating that fading is negligible in nature this observation is inconsistent with the measured laboratory fading rates of 1 1 5 decade and needs further investigation

modeling of gold scavenging by bismuth melts coexisting with hydrothermal fluids the effect of gold scavenging by bismuth melts is investigated using equilibrium thermodynamic modeling of an aqueous solution mineral melt system the calculations for the au bi na cl s h o system performed at temperatures between 300 and 450 c demonstrate that au concentrations in the melt are several orders of magnitude higher than in the coexisting fluid indicating the possible formation of economic gold deposits from undersaturated aqueous fluids in which mineralization would not be expected in the absence of a bismuth melt the model applies to any deposit where a bi melt is stable and coexists with a hydrothermal fluid examples of such deposits are known from skarn intrusion related orogenic and volcanogenic massive sulfide vms gold systems in sulfur poor systems the partitioning curves presented here can be used directly to correlate the gold concentration in the fluid and the au grade in the ore e g escanaba trough vms deposit these results also illustrate important principles generally applicable to understanding magmatic hydrothermal and metamorphic deposits that may have contained significant volumes of more complex polymetallic melts

astronomical calibration of loess paleosol deposits at luochuan central chinese loess plateau abstract the 140 m loess paleosol profile at luochuan in the central chinese loess plateau was sampled at 5 cm intervals in loess units and at 3 cm in paleosol units in order to obtain a high resolution climatic record covering the past 2 5 million years all samples were measured for magnetic susceptibility which is regarded as a good proxy index of the east asian summer monsoon strength on the basis of the astronomical theory of pleistocene climatic change an age model of the luochuan loess paleosol sequence was developed by tuning the magnetic susceptibility record to time series of insolation changes the results show that the ages of the boundaries between the malan and lishi and lishi and wucheng loess formations are 71 and 1320 kyr bp respectively the onset of loess accumulation is at 2470 kyr bp our age model was tested by comparing the orbitally derived ages with absolute age determinations of magnetic reversals and cross spectrum analyzing with solar radiation variations for summer at 65 n these indicate that the calibration provides a reliable time scale for the luochuan loess paleosol deposit

hominin distribution in glacial interglacial environmental changes in the qinling mountains range central china abstract the qinling mountain range qmr in central china encompasses innumerable paleolithic sites the hominin settlement in the qmr is comparable with that in the nihewan basin in northern china the recorded information on the loess deposition in the qmr include both hominin remains and environmental changes since 2004 geological geomorphological archaeological and chronological investigations were conducted by our team by systematically using luminescence paleomagnetic and 26al 10be burial dating methods to obtain age controls and by correlating the pedostratigraphy and magnetic susceptibility of the luochuan loess section we established the loess paleosol sequence and chronology of the lithic artifact levels for 35 paleolithic sites and spots in the qmr this work remarkable found shifts from glacial to interglacial driving hominin settlement patterns during the stage between 1 2 and 0 7 ma large drying events such as l15 mis 38 and l9 mis 22 23 and 24 may have driven hominin migrations when the loess plateau was depopulated moreover the southern qmr was a glacial refugium during the stage after 0 60 ma the contrasts between glacial and interglacial scales are the greatest furthermore longer and warmer humid interglacial environments were dominant s5 mis 13 14 15 and s1 mis 5 interglacial periods provided the optimal environments for hominin settlement and dispersal on the basis of investigations we also found that the hominin settlement is relatively continuous from 1 20 ma to 0 05 ma in the qmr the human occupation of the qmr decreased considerably after 0 05 ma probably because of changes in climate and human adaptations

multiphase timing of hominin occupations and the paleoenvironment in luonan basin central china thousands of paleolithic artifacts have been recovered from paleolithic sites in the luonan basin in the upper south luohe river of central china their discovery suggests that the basin was an important area for hominin settlement during the pleistocene however the initial timing of this occupation and the environmental conditions for this period are still largely unknown in addition the sediments are not well dated and most of the artifacts lie on the surface in an attempt to resolve these issues a new systemic paleomagnetic analysis was carried out on the loess deposits that contain in situ stone tools our detailed loess paleosol analyses of the stratigraphy of different sites in the basin and chinese loess plateau shows the accumulation of the loess since at least 1 1 million years ma ago moreover recently discovered in situ cores flakes and retouched stone tools in these deposits show that hominins used this region repeatedly from 0 8 0 7 ma to 0 4 0 3 and 0 2 0 1 ma pedostratigraphic analyses magnetic susceptibility and carbon isotope analyses also indicate that these hominins lived in a subtropical to warm temperate climate with broad needle leaf forest vegetation mixed with grasses c 2011 university of washington published by elsevier inc all rights reserved

tt osl dating of longyadong middle paleolithic site and paleoenvironmental implications for hominin occupation in luonan basin central china dating middle pleistocene hominin occupations alongside the reconstruction of paleoenvironments in china between 700 and 100 ka has always been a challenging task in this paper we report thermally transferred optically stimulated luminescence tt osl dating results for a middle paleolithic site in the luonan basin central china which we have named longyadong cave the results suggest that the age of cave infilling and the deposition of sediments outside the cave range between 389 18 and 274 14 ka these deposits are stratigraphically and geochronologically correlated with the l4 loess and s3 paleosol units of the typical loess paleosol sequence of the chinese loess plateau and with marine isotope stages mis 10 to 9 respectively on the basis of these new ages and the available paleoenvironmental data it is suggested that the longyadong hominins might have occupied the site both in glacial and interglacial periods demonstrating that they coped well with environmental change in this mountainous region in warm wet and cold dry climates the study further implies that the hominins abandoned the longyadong cave between 274 14 and 205 19 ka when it was sealed by alluvial and slope deposits c 2012 university of washington published by elsevier inc all rights reserved

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

zoned base metal mineralization in a porphyry system origin and evolution of mineralizing fluids in the morococha district peru porphyry related base metal vein and replacement mineralization i e cordilleran polymetallic mineralization in the morococha district central peru is part of a large magmatic hydrothermal system associated with the emplacement of several late miocene porphyry intrusions and formation of important cu mo mineralization zn pb ag cu veins overprint the giant toromocho porphyry cu mo deposit in the center of the district and display a typical concentric base metal zonation cu zn pb ag covering an area of approximately 50km2 a detailed fluid inclusion study supports the hypothesis that base metal mineralization precipitated from cooled and evolved metal rich intermediate density porphyry type fluids in early stages of cordilleran base metal vein formation fluid inclusions have low salinities of 2 to 5 wt nacl equiv co2 contents of 3 to 10mol and homogenization temperatures th of 380 to 340 c they are similar to intermediate density fluid inclusions trapped in a milky quartz vein predating cordilleran polymetallic mineralization with similar low salinities 3 0 3 8 wt nacl equiv and low co2 contents 6 5 8 mol but higher th of 420 to 410 c during cooling of the intermediate density fluids from 400 to 300 c the lithostatic pressure regime changed to a hydrostatic one the fluids underwent pressure drop as well as phase separation i e unmixing and lost most of their co2 they acquired moderate salinities in some cases intermediate up to 16 wt nacl to brine compositions however the bulk of the magmatic fluid retained low salinity while it continued to cool under open system conditions and precipitated tennantite tetrahedrite chalcopyrite enargite sphalerite and galena upon cooling below 270 c the fluids deposited abundant rhodochrosite and quartz while following the boiling curve toward lower p t conditions these data record an evolution of mineral precipitation from deep minimum depth of 2 1 5 km to shallow environments 300 800 m oxygen hydrogen and carbon stable isotope data indicate that the hydrothermal fluids have a dominantly magmatic signature and were diluted by meteoric waters during the carbonate stage copper 5 000 18 000 g g sulfur up to 12 000 g g and iron 2 100 6 000 g g concentrations in the intermediate density fluid inclusions in the milky quartz veins are approximately 5 to 10 times higher than in intermediate density inclusions of the early cordilleran base metal veins the base metals zn pb and mn have comparable concentrations between 100 and 1 000 g g for both types of fluid these findings suggest that the fluids identified in cordilleran polymetallic veins are compositionally similar to the porphyry type fluids and could have derived from the latter after precipitation of cu and fe bearing sulfides in a deeper porphyry environment the new data explain the commonly observed base and precious metal zonation patterns encountered in porphyry centered districts e g bingham butte and show that both porphyry and polymetallic mineralization can precipitate from similar magmatic hydrothermal fluid pulses

high cu concentrations in vapor type fluid inclusions an artifact abstract studies of natural fluid inclusions have shown that cu commonly occurs at higher concentrations in vapor type inclusions than in coexisting brine inclusions a phenomenon which has been interpreted to arise from copper partitioning into the vapor phase in the first part of this study we attempted to experimentally reproduce this behavior in hydrothermal experiments covering a range of p t conditions 600 800 c 70 130 mpa fluid compositions nacl kcl fecl 2 0 5 6 6 wt s fluid acidities quench fluid ph 0 3 10 and sulfur speciation h 2 s dominated to so 2 dominated however as in several other studies we did not succeed in reproducing conditions under which cu partitions into the vapor phase in view of recent observations that quartz hosted fluid inclusions can diffusively loose or gain cu after entrapment we set out to determine if the evidence from natural fluid inclusions could be compromised for this purpose we synthesized vapor and brine inclusions from cu h 2 o nacl s fluids at 800 c 130 mpa and re equilibrated them in slightly different fluids at 800 c 70 mpa measuring some inclusions by la icp ms after each step vapor inclusions indeed experienced a dramatic increase in cu from 0 3 0 03 to 5 7 3 3 wt while brine inclusions remained largely unmodified leading to a change in the partition coefficient d cu vap brine from a true value i e before re equilibration of 0 4 0 05 to an apparent value of 8 3 4 9 the requirements for substantial diffusional gain of cu in fluid inclusions are a change in the ph of the surrounding fluid from 1 to more neutral and the presence of s in the pre existing fluid inclusions these requirements are also fulfilled in nature cooling magmatic hydrothermal fluids experience a change from acidic to more neutral ph due to buffering along the feldspar mica join and natural vapor inclusions typically contain significant amounts of sulfur a reversal experiment performed on natural quartz hosted fluid inclusions from the erongo granite namibia showed that this process can be reversed with the measured d cu vap brine value of 11 9 3 being modified to 0 06 0 04 thus d cu vap brine values 1 measured on natural fluid inclusions in quartz are likely a secondary feature caused by post entrapment copper diffusion realistic d cu vap brine values in porphyry cu environments are between 0 11 and 0 15 and reconstructed vapor brine mass ratios are in the order of 4 9 this suggests that the main transporting agent of cu at the porphyry level are brines and that models based on copper into the vapor phase are incorrect

magnetostratigraphic dating of early humans in china abstract china is a key area for research into human occupation in the old world after the initial expansion of early humans out of africa reliable age determinations are pivotal for assessing the patterns of human evolution and dispersal in this region this paper reviews magnetostratigraphic studies of some early pleistocene strata bearing hominin remains and or artifact stone tools from northern to southern china the quality and reliability of the paleomagnetic dates are also evaluated new magnetostratigraphic results for the xihoudu paleolithic site in north central china are also presented among the few hominin or paleolithic sites in china from the early pleistocene five have been well investigated three of these are in northern china at xiaochangliang donggutuo and gongwangling the remaining two in southern china at longgupo and yuanmou considerable progress has been made during the past three decades towards paleomagnetically dating these sites indeed the age estimates at xiaochangliang and gongwangling have been widely accepted magnetostratigraphic consensus about the age of the donggutuo site has also been reached however the age determination for the two sites in southern china is still contested the integration of rock magnetic stratigraphy with magnetic polarity stratigraphy has resulted in a determined age of 1 36 ma for a stone tool containing layer of lacustrine sediments at the xiaochangliang site in the nihewan basin lithostratigraphic constraints have significantly contributed to determining the age of lantian homo erectus at gongwangling which occurred in a loess paleosol sequence of the southern loess plateau its age paleomagnetically derived is about 1 15 ma these two paleomagnetic ages suggest an expansion and flourishing of human groups from northern to north central china during the early pleistocene this suggestion has been reinforced by our new magnetostratigraphic age estimate of about 1 27 ma for the xihoudu site as will be presented in this paper however more work is needed for the age determinations of the hominin bearing strata at the longgupo and yuanmou sites in southern china finally we stress that it is necessary to combine biostratigraphy lithostratigraphy and rock magnetic stratigraphy with the traditional magnetic polarity stratigraphy in order to obtain reliable age determinations for strata bearing hominin remains or stone artifacts

age of the fossil dali man in north central china deduced from chronostratigraphy of the loess paleosol sequence dali man an archaic type of early homo sapiens is of great significance to the origin of homo sapiens achievements have been made during the past decades in the understanding of the fossil human skull as well as the accompanying mammalian fossils and stone artifacts however the absolute age of the fossil dali man still remains unclear based on the magnetic susceptibility of loess sediments and the relationship of terracing process with climatic condition we correlated the loess sequence and the subjacent terrace alluvium at the dali man site with the well studied loess paleosol sequence at luochuan in the central part of the chinese loess plateau the correlation indicates that the loess paleosol sequence at the dali man site extends down to the paleosol s2 and the underlying fluvial deposits correspond to the loess u because the dali man skull appears in the basal gravel layer of the terrace and because the deposition of the terrace gravels would occur during the transition from s3 paleosol formation to l3 loess accumulation the age of the fossil dali man is inferred to be ca 270 ka which is equivalent to the age of the boundary between the loess l3 and paleosol s3 on the magnetic susceptibility time series of the luochuan loess paleosol sequence c 2002 elsevier science ltd all rights reserved

the relation between cu au ratio and formation depth of porphyry style cu au mo deposits constraints on gold and copper ore grades in porphyry style cu au mo deposits are re examined with particular emphasis on published fluid pressure and formation depth as indicated by fluid inclusion data and geological reconstruction defining an arbitrary subdivision at a molar cu au ratio of 4 0 104 copper gold deposits have a shallower average depth of formation 2 1 km compared with the average depth of copper molybdenum deposits 3 7 km based on assumed lithostatic fluid pressure from microthermometry the correlation of cu au ratio with depth is primarily influenced by the variations of total au grade despite local mineralogical controls within some ore deposits the overall cu au ratio of the deposits does not show a significant correlation with the predominant type of cu fe sulfide i e chalcopyrite or bornite primary magma source probably contributes to metal endowment on the province scale and in some individual deposits but does not explain the broad correlation of metal ratios with the pressure of ore formation by comparison with published experimental and fluid analytical data the observed correlation of the cu au ratio with fluid pressure can be explained by dominant transport of cu and au in a buoyant s rich vapor coexisting with minor brine in two phase magmatic hydrothermal systems at relatively shallow depth approximately 3 km and greater confining pressure is likely to precipitate copper molybdenum only while sulfur complexed gold remains dissolved in the relatively dense vapor upon cooling this vapor may ultimately contract to a low salinity epithermal liquid which can contribute to the formation of epithermal gold deposits several kilometers above the au poor porphyry cu mo deposit these findings and interpretations imply that petrographic inspection of fluid inclusion density may be used as an exploration indicator low pressure brine vapor systems are favorable for coprecipitation of both metals leading to au rich porphyry copper gold deposits epithermal gold deposits may be associated with such shallow systems but are likely to derive their ore forming components from a deeper source which may include a deeply hidden porphyry copper molybdenum deposit exposed high pressure brine vapor systems or stockwork veins containing a single type of intermediate density inclusions are more likely to be prospective for porphyry copper molybdenum deposits

the role of sulfur in the formation of magmatic hydrothermal copper gold deposits abstract essential resources of many rare metals including copper zinc molybdenum silver and gold occur in natural sulfide mineral deposits understanding the origin of these metal resources has been limited by a lack of data about the geochemistry of sulfur the most important and abundant element of ore deposits we report the first directly measured sulfur concentrations in high temperature fluids together with their ore metal contents using a new method for sulfur quantification in fluid inclusions by laser ablation inductively coupled plasma mass spectrometry la icp ms co genetic brine and vapor inclusions from magmatic hydrothermal ore deposits and granitic intrusions show an excess of sulfur over ore metals as required for efficient ore mineral precipitation the results demonstrate that s cu and au are highly enriched in vapor like magmatic fluids implying that such low salinity fluids are the key agent for the formation of porphyry copper and epithermal gold deposits

luminescence dating of the jigongshan paleolithic site in hubei province southern china abstract the jigongshan jgs paleolithic site in the middle reaches of the yangtze river has two different cultural layers namely the upper flake tool industry and lower cobble tool industry cultural layers jgs site is also among the few upper paleolithic sites in the middle reaches of the yangtze river with an absolute age peking university has performed a preliminary 14c dating at the site and found that the upper culture layer is approximately 10 20 ka whereas the lower layer is older than 50 ka to date the lower culture layer precisely the standard quartz single aliquot regenerative sar dose based optically stimulated luminescence osl and thermally transferred osl tt osl methods were used in this study results showed that the age of the upper culture layer is approximately 23 2 38 3 ka whereas that of the lower culture layer is approximately 115 9 149 9 ka the 14c and osl dating methods showed huge differences in their results for the lower culture layer based on our dating results we propose that the main part of the upper culture layer corresponds to the late mis 3 to the early mis 2 stages during the glacial period in l1 unit in the chinese loess sequence whereas the lower culture layer corresponds to the late mis 6 and the early mis 5 stages during both glacial and interglacial periods in the upper l2 and the lower s1 units a cultural gap of nearly 100 ka was observed between these two cultural layers this gap is larger than what was expected

enhanced vapor phase transport of tin in hydrothermal systems or experimental artifacts comments on the role of vapor in the transportation of tin in hydrothermal systems experimental and case study of the dachang deposit china by zhang et al j volcanol geotherm res 173 2008 313 324

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

geochemistry of metallic trace elements in fumarolic condensates from nicaraguan and costa rican volcanoes metallic trace element composition of volcanic gas from cerro negro momotombo san cristobal telica and masaya volcanoes in nicaragua and poas volcano in costa rica is indicated by analyses of fumarolic condensates for alkalis alkaline earths transition elements precious metals halogens and sulphate the temperatures of the fumaroles varied from 85 to 852 c element concentrations range from 104 to 10 3 ppm statistical tests indicate that the trace element constituents of the condensates are log normally distributed although there are variations in element concentrations in individual condensates the general order of decreasing elemental abundances in nicaraguan and costa rican fumarolic gas is cl so4 certain igneous rock forming elements si al fe ti f and alkalis li na k alkaline earths mg ca ba br and transition elements cr mn co ni cu zn other ore forming elements mo cd sn pb semi metals as sb sc hg and precious metals au ag li mn cr and pb were found to be near or below detection limits in many of the condensates analyzed so4 ti al k na zn sn cr and br all tend to decrease in abundance as mean fumarolic temperature between volcanoes decreases the remaining elements remain constant in abundance or behave erratically the metallic trace element composition of the nicaraguan and costa rican fumarolic condensates is very similar to condensates from subduction zone volcanoes around the pacific margin and the mediterranean metals in volcanic gas are postulated to have been transported as halogen sulphate and oxide compounds chloride and fluoride compounds are considered to be the primary transporters of metals in volcanic gas correlations between metal and halogen content vary considerably between volcanoes statistically significant correlations between metal content and both chlorine and bromine are found in the cerro negro and between metal content and bromine and fluorine in the momotombo condensates metal bearing compounds in volcanic gas are postulated from correlation matrices bromine though seldom reported in condensates is a minor but important constituent of volcanic gas with concentrations similar to those of fluorine metal bromide compounds have higher volatilities than fluoride compounds and volatilities similar to chloride compounds significant correlations between bromine content and metal concentration suggests that bromide compounds play a role in the transportation of metals in volcanic gas

chronology and the upper dating limit for loess samples from luochuan section in the chinese loess plateau using quartz osl sar protocol abstract luminescence dating of loess older than 100 ka has long been a challenge it has been recently reported that using optically stimulated luminescence osl of fine grained quartz 4 11 m extracted from loess the range of luminescence dating could be pushed to 0 6 ma with osl ages being in agreement with independent ages watanuki t murray a s tsukamoto s 2005 quartz and polymineral luminescence dating of japanese loess over the last 0 6 ma comparison with an independent chronology earth and planetary science letters 240 774 789 the aim of this study is to provide a luminescence chronology 20 samples for the standard luochuan loess section and to further examine the upper limit of quartz osl dating for chinese loess the growth curve does not saturate at 700 gy and should allow reliable equivalent dose d e determination up to at least 400 gy however when compared with independent chronological control the d e that could be treated as reliable is less than 230 gy corresponding to 70 ka in age for chinese loess and the d e larger than 230 gy should be underestimated ages for samples from the lower part of palaeosol s1 are severely underestimated with the maximum age of 95 ka for a sample from the bottom of this palaeosol much younger than the expected age of 128 ka the maximum d e obtained for sample l9 m collected from loess layer l9 which is below the matuyama brunhes b m boundary whose age is 780 ka is only 403 gy which corresponds to an age of 107 ka the cause of underestimation is not yet clear the previous results by watunuki et al 2005 on the extension of osl dating of loess to 0 6 ma is not confirmed when evaluating the validity of osl ages in s1 another possibility is to question the already established chronological frame for luochuan section which is based on the hypothesis of continuous dust deposition the assumption of an erosion hiatus between l2 and s1 could make the osl ages look reasonable however if this is the case then it is difficult to explain why the age of sample l9 m is only 107 ka which could be treated as a saturation age while the osl can provide a correct age for loess as old as 94 9 ka for sample lc22 collected from the bottom of s1 much work is required to clarify these confusions

chronology of newly discovered paleolithic artifact assemblages in lantian shaanxi province central china abstract the homo erectus cranium mandible and hundreds of associated lithic artifacts found in lantian central china in the 1960s demonstrate that the area was important for hominin habitation during the early to middle pleistocene however the region which was not adequately researched until the early 2000s still poses several questions regarding hominin behavior and lithic technology development in this study three loess paleosol sequences the jijiawan ganyu and diaozhai sites from which in situ stone artifacts were recovered are investigated and dated by optically stimulated luminescence osl magnetostratigraphy and stratigraphic correlation the results demonstrate that the artifacts are located within paleosol layers s4 correlative with marine oxygen isotope stage mis 11 s3 mis 9 s2 mis 7 and s1 mis 5 and within loess layer l1 mis 2 4 the main stone knapping technique used was direct hard hammer percussion in addition the technological features of the stone tools found at these sites exhibit little variation indicating the presence of a long established stable technology in the lantian area our observations show that the ancient humans lived episodically on the terraces of the bahe river from the early pleistocene indicating a long history of hominin occupation of the region

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

native gold in a hawaiian alkalic magma native gold found in fresh basanite glass from the early submarine phase of kilauea volcano hawaii may be the first documented case of the transport of gold as a distinct precious metal phase in a mantle derived magma the gold bearing glass is a grain in bedded volcanic glass sandstone japan marine science and technology center jamstec sample s508 r3 collected by the submersible shinkai 6500 at 3879 m depth off kilauea south flank extensive outcrops there expose debris flow breccias and sandstones containing submarine erupted alkalic rock fragments and glasses from early kilauea precipitation of an immiscible gold liquid resulted from resorption of magmatic sulfides during crystallization differentiation with consequent liberation of sulfide hosted gold elevated whole rock gold concentrations to 36 ppb for fresh lavas and clasts from early kilauea further show that some magmas erupted at the beginning stages of hawaiian shield volcanoes were distinctly gold rich most likely owing to limited residual sulfide in their mantle source alkalic magmas at other ocean islands may also be gold rich and oceanic hot spot provinces may contain underappreciated gold resources

partitioning of palladium iridium platinum and gold between sulfide liquid and basalt melt at 1200 c abstract iron nickel monosulfide and basalt glass containing trace amounts of pge equilibrated at 1200 c and fo 2 10 9 2 close to the wustite magnetite buffer and fs 2 10 0 9 have been analyzed for noble metals by radiochemical and instrumental neutron activation analysis the average contents of pge in coexisting fe ni sulfide and basalt glass respectively are pd 50 ppm and 0 5 ppb ir 50 ppm and 0 5 ppb pt 100 ppm and 10 ppb and au 0 7 ppm and 0 8 ppb the sulfide liquid silicate melt partition coefficients d values for the noble metals are 9 7 10 4 for pd 1 0 7 10 5 for ir 9 6 10 3 for pt and 1 0 9 10 3 for au the noble metals are strongly partitioned into sulfide liquid but the affinity of pd and ir for sulfide liquid is about 50 times greater than that of pt and about 500 times greater than that of au the d values indicate that equilibrium partitioning between immiscible sulfide liquid and basalt magma would result in fractionation of the noble metals which differs significantly from that generally observed in nature

direct analysis of ore precipitating fluids combined ir microscopy and la icp ms study of fluid inclusions in opaque ore minerals laser ablation inductively coupled plasma mass spectrometry la icp ms in combination with near infrared microscopy of fluid inclusions hosted by ore minerals that are opaque to visible light can provide the composition of ore precipitating fluids we applied the two techniques to well constrained fluid inclusion assemblages hosted by pyrite enargite and quartz to trace the source and evolution of the fluids in high sulfidation epithermal veins overprinting a porphyry copper deposit at rosia poieni romania despite some analytical limitations caused by the sulfide host minerals the data demonstrate that fluids trapped in apparently cogenetic quartz and ore minerals are chemically different systematic changes in major and trace element ratios between liquid vapor vapor rich and brine fluid inclusion assemblages in the three minerals record an evolving fluid source at the porphyry to epithermal transition regarding their cs na k ratios most of epithermal quartz hosted fluid inclusion assemblages form a well defined cluster which coincides with the narrow range of the porphyry stage fluids trapped in early quartz of the porphyry stockwork veins their cu na k ratios are 10 to 100 times lower compared to the pyrite hosted inclusions and correspond to the lowest cu na k ratios recorded for the porphyry stage fluids by contrast pyrite hosted vapor rich fluid inclusions have the highest cu na k similar to the highest cu na k ratios measured in the porphyry stage fluid inclusions the results led to the conclusion that the gangue and ore minerals in the high sulfidation epithermal veins at rosia poieni formed by successive pulses of chemically distinct hydrothermal fluids that were successively exsolved from residual melt batches of a progressively crystallizing magma at greater depth these results are consistent with detailed textural observations but petrography alone could not have led to this unambiguous conclusion

new contributions to chinese plio pleistocene magnetostratigraphy abstract a new collection of over 500 orientated hand samples of which 180 are red clays from a 195 m loess red clay section near xian 109 12 e 34 12 n china has been dated by magnetic stratigraphy biostratigraphic and previous magnetostratigraphic investigations gave a maximum age for the chinese loess of 2 4 ma implying that the underlying red clay formation is pliocene in age the present study yields a clearly defined magnetic polarity stratigraphy in good agreement with a polarity time scale developed by earlier workers an interpretation of this magnetostratigraphy suggests a basal age for the loess series in this region of 2 5 ma and a minimum age for the base of the red clay formation which is also the base of the section of 5 0 ma