irregular recurrence of paleoearthquakes along the central garlock fault near el paso peaks california 1 new investigations at the el paso peaks paleoseismic site have refined and extended the record of paleoearthquakes for the central garlock fault event evidence in the form of buried fissures scarps folds and upward terminations has allowed us to identify six well resolved earthquakes designated as events w u r q k and f within the last 7000 years the exposures that we excavated did not reveal additional evidence for three poorly resolved events reported by mcgill and rockwell 1998 evidence for event y identified in the previous study was reexamined and found not to be a paleoearthquake radiocarbon dates of detrital charcoal combined with a method of interpolating the event ages with revised sedimentation rates provide our preferred constraints on the timing of faulting events the most recent surface rupturing earthquake event w occurred between a d 1450 and 1640 the penultimate event u occurred between a d 675 and 950 event r which was unrecognized in the previous study occurred between a d 250 and 475 event q occurred relatively shortly before event r between a d 25 and 275 event k occurred between 3340 and 2930 b c the oldest identified paleoearthquake event f occurred between 5300 and 4670 b c the event ages indicate that earthquake recurrence is highly irregular at the el paso peaks site with individual preferred intervals ranging from as little as 215 years to as many as 3300 years the irregular recurrence of surface rupturing earthquakes along the central garlock fault may be related to temporal and spatial clustering of earthquakes proposed for faults in the eastern california shear zone

glacial stage ice core records from the subtropical dunde ice cap china the first ice core record of both the holocene and wisconsin wiirm late glacial stage lgs from the subtropics has been extracted from three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau ice thicknesses at the ice cap summit average 138 m the bedrock surface is relatively flat surface and basal temperatures are 7 3 and 4 7 c respectively and the ice cap exhibits radial flow away from the summit dome these records reveal a major change in the climate of the plateau 10 000 years ago and suggest that lgs conditions were colder wetter and dustier than holocene conditions this is inferred from the more negative 6180 ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes which characterize the lgs part of the cores total b radioactivity from shallow ice cores indicates that over the last 24 years the average accumulation rate has been 400 mm a 1 at the summit the ice cores have been dated using a combination of annual layers in the insoluble dust and 6180 in the upper sections of core visible dust layers which are annual and ice flow modeling the oxygen isotope record which serves as a temperature proxy indicates that the last 60 years have been the warmest in the entire record

subsurface imaging of the garlock fault cantil valley california imaging of the garlock fault from seismic reflection data tests tectonic models for the mojave desert region of southern california models developed from geologic and geodetic evidence of fault movement rates disagree on whether the garlock fault should dip north or south such models are further at odds with focal mechanism and dislocation analyses consistent with a vertical strike slip fault our analysis demonstrates a nonvertical southward dip for the garlock fault consortium for continental reflection profiling mojave line 5 collected seismic reflection data across the garlock in cantil valley where the 3 km deep cantil pull apart basin has developed between the southwest and east branches of the fault we analyze the reflection data for evidence of the fault s structure to 5 km depths garlock fault plane reflections on unprocessed shot gathers merge with the first arrival as the source progresses to the surface trace of the east branch explicitly tracing the garlock fault as a seismic reflector from depth to the mapped contemporary fault trace the apparent velocity of these reflections gives a 37 10 south dip for the east branch of the fault a prestack kirchhoff sum migration images the east branch reflector with a 45 south dip our migration process fully accounts for the bending of seismic rays through the strong lateral velocity variations in cantil basin the south dip of the garlock s east branch together with basement steps that decrease to the south suggest that cantil basin developed from a 0 4 1 mm yr component of extension normal to the fault development of the basin by detachment provides a mechanism to widen it as left lateral motion lengthens it allowing the pull apart to maintain the globally constant length to width ratio of 3 detachment by the garlock at cantil valley similarly requires 0 4 1 mm yr of dextral strike slip on a northwest striking fault such as the helendale that cuts the mojave between the garlock and pinto mountain faults such motion is consistent with regional tectonic models

understanding the evolution of magmatic hydrothermal systems based on microtextural relationships fluid inclusion petrography and quartz solubility constraints insights into the formation of the yulong cu mo porphyry deposit eastern tibetan plateau china the evolution of the magmatic hydrothermal system that formed the eocene yulong cu mo porphyry deposit of the eastern tibetan plateau china is reconstructed based on the study of the sequence of stockwork vein sets showing systematic crosscutting relationships in hand specimen early a veins associated with potassic alteration of the porphyritic host are composed of vitreous quartz that is extensively recrystallized and has a dark blue cathodoluminescence fluid inclusions contained in the quartz have been affected by post entrapment modification some of the a veins were reopened and contain ribbons of microscopic molybdenite flakes formation of the molybdenite was associated with recrystallization of the earlier formed quartz and concomitant with the development of a dark purple to brownish cathodoluminescence signature reopening of the early veins also resulted in the formation of ab veins containing euhedral quartz crystals that contain encapsulated molybdenite flakes and are intergrown with coarse laths of molybdenite these euhedral quartz crystals showing a dark purple to brownish cathodoluminescence host vapor rich intermediate density fluid inclusions as well as hypersaline liquid and vapor rich fluid inclusions indicating that fluid immiscibility at hydrostatic pressure conditions occurred during crystal growth later c veins that crosscut and commonly reopen the earlier a and ab veins lack quartz as a gangue mineral and consist entirely of chalcopyrite and pyrite with minor molybdenite sulfide formation was accompanied by chlorite or sericite alteration of the wall rocks late d veins containing quartz and pyrite with associated sericitic alteration of the porphyritic wall rocks crosscut all earlier vein types only minor amounts of molybdenite and chalcopyrite are present euhedral quartz crystals in the d veins contain liquid rich fluid inclusions that have not been affected by post entrapment modification the results of this study indicate that mo and cu mineralization at yulong was introduced by single phase intermediate density magmatic hydrothermal fluids as the porphyry system was transitioning from ductile to brittle conditions the bulk of the mo endowment predated cu mineralization and formed during the change from lithostatic to hydrostatic conditions and associated immiscibility of the magmatic hydrothermal fluids chalcopyrite precipitation followed as the single phase intermediate density magmatic hydrothermal fluids was escaping into the hydrostatic pressured regime cooling of the magmatic hydrothermal fluids appears to have been the principal control on metal precipitation

ages of late holocene earthquakes on the central garlock fault near el paso peaks california a trench across the central garlock fault within a small playa adjacent to el paso mountains revealed buried fissures and fault scarps that provide strong evidence for five surface rupturing earthquakes within the past 5 kyr weaker evidence suggested the possibility of three additional events within this same time period these observations indicate an average recurrence interval of 700 to 1200 years nearly all 28 radiocarbon dates on samples of detrital charcoal wood and shell are in correct stratigraphic order these dates constrain the ages of the individual faulting events and indicate that the recurrence interval is not periodic but is quite irregular individual recurrence intervals range from 190 to 1545 years if all eight events are actual earthquakes or from 190 to 3405 years if only the five well documented events represent earthquakes the two most recent earthquakes occurred within the past 550 years with preferred ages of about a d 1790 and a d 1600 the a d 1790 event ruptured a narrower width of the fault zone and may have been a smaller earthquake than the others the radiocarbon dates from the trench also indicate that the sedimentation rate on the playa has fluctuated within the past 5 kyr low sedimentation rates 0 1 to 0 35 mm yr and infrequent floods 1 per century prevailed from about 2000 b c to a d 100 and from a d 500 to 1300 during the remaining intervals within the past 5 kyr the sedimentation rate averaged 1 0 to 1 7 mm yr and major floods occurred two to four times per century the changes in sedimentation rate and flood frequency may reflect climatic changes or they may simply reflect changes in drainage patterns

holocene glacier advances in the headwaters of sredniaya avacha kamchatka russia abstract holocene glacial deposits in sredniya avacha headwaters are subdivided into three age groups events a b and c based upon geomorphic features tephrochronology and lichenometry tephras of opala volcano 1400 1500 yr b p ksudach volcano 1700 1800 and 6000 yr b p and zavaritskiy volcano 2800 yr b p are used as stratigraphic markers rhizocarpon geographicum l dc and rhizocarpon section alpicola growth curves are established using tephrochronologically dated and historical surfaces the age of event a pre hypsitermal moraines is constrained by an age of 6000 yr b p for overlying ksudach 2 tephra and an age of 7200 lichenometric l yr b p event b neoglaciation had a multiple nature with the most prominent advances at 4300 3500 3300 2800 2600 2100 1800 1400 and 1300 1100 l yr b p the culmination occurred before 2800 yr b p as suggested by a date for zavaritskiy volcano tephra found on the glacial and outwash deposits less extensive glacier advances of event c little ice age occurred at 800 600 500 200 180 110 and 90 40 l yr b p the ela depression was 200 250 100 150 30 70 m during the culmination of events a b and c respectively

compositions of biotite amphibole apatite and silicate melt inclusions from the tongchang mine dexing porphyry deposit se china implications for the behavior of halogens in mineralized porphyry systems abstract the dexing deposit located in the circum pacific ore belt is the largest porphyry copper deposit in eastern china it is composed of 3 separate plutons which host three mines tongchang fujiawu and zhushahong mines the porphyritic granodiorite samples studied in this investigation were collected from the tongchang ore forming pluton of this giant deposit this paper presents electron microprobe analyses of biotite apatite amphibole plagioclase potassium feldspar and rehomogenized glassy melt inclusions from the tongchang porphyritic granodiorites petrographic observations of the samples are consistent with portions of the granodioritic magma represented by our samples being overprinted by potassic hydrothermal fluid which variably altered these minerals all of the studied micas are mg rich biotites the biotites are separated into altered magmatic and secondary types based on their petrographic and geochemical characteristics the phlogopite components of the secondary biotites are typically higher than those of the altered magmatic biotites and the x mg values of all biotites correlate negatively with cl contents consistent with the mg cl avoidance principle the x mg values also correlate negatively with k 2 o na 2 o bao feo and tio 2 for both generations of biotites the calculated log f h 2 o f hcl values for 690 k of the coexisting potassic fluids which are determined from the altered magmatic biotite compositions range from 4 43 to 4 67 and are very similar to those of other major porphyry deposits however the log f h 2 o f hf and log f hf f hcl values for the same batch of hydrothermal fluids are significant higher and lower than those of these other porphyry deposits respectively the cl concentrations of amphiboles and melt inclusions range from 0 18 to 0 32 wt and 0 15 to 0 44 wt respectively most apatites trapped in biotite and plagioclase phenocrysts display a bimodal cl distribution 0 19 to 1 35 wt and 1 48 to 3 73 wt similarly the s contents of the apatite also show a distinct bimodal distribution reflecting the effects of variable anhydrite saturation during evolution of the tongchang melt and variable dissolution of anhydrite by saline aqueous fluids the cl contents of the apatites from the tongchang system are typically higher than those of other studied porphyry deposits furthermore the cl contents of the melt inclusions are at or very near the cl saturation levels 0 36 to 0 46 wt at 850 c and 50 mpa and 0 42 to 0 54 wt at 850 c and 200 mpa for these melt compositions at shallow crustal pressures these findings suggest that the area of the granodioritic magma represented by our samples and perhaps the bulk of the tongchang granodioritic magma was rich in cl the melt inclusion compositions are consistent with a high salinity hydrosaline liquid being exsolved directly from the granodioritic melt directly this high salinity hydrosaline liquid was likely very efficient at dissolving transporting and precipitating ore metals in the mineralizing magmatic hydrothermal system

controls of alteration and mineralization in the sungun porphyry copper deposit iran evidence from fluid inclusions and stable isotopes the sungun porphyry copper deposit is located in northwestern iran azarbaijan province and is associated with diorite granodiorite to quartz monzonite of miocene age which intruded eocene volcano sedimentary and cretaceous carbonate rocks copper mineralization was accompanied by both potassic and phyllic alteration field observations and petrographic studies demonstrate that emplacement of the sungun stock took place in several intrusive pulses each with associated hydrothermal activity molybdenum was concentrated at a very early stage in the evolution of the hydrothermal system and copper somewhat later four main vein groups have been identified i quartz molybdenite anhydrite or k feldspar with minor pyrite chalcopyrite and bornite ii quartz chalcopyrite pyrite or molybdenite iii quartz pyrite calcite or chalcopyrite or anhydrite gypsum or molybdenite and iv quartz or calcite or gypsum or pyrite early hydrothermal alteration produced a potassic assemblage orthoclase biotite in the central part of the stock propylitic alteration occurred contemporaneously with potassic alteration but in the peripheral parts of the stock and phyllic alteration occurred later overprinting the earlier alteration the early hydrothermal fluids are represented by high temperature 340 degrees 500 degrees c high salinity up to 60 wt nacl equiv liquid rich fluid inclusions and high temperature 320 degrees 550 degrees c low salinity vapor rich inclusions these fluids are interpreted to represent an orthomagmatic fluid which boiled episodically the brines are interpreted to have caused potassic alteration and deposition of group i and ii quartz veins containing molybdenite and chalcopyrite propylitic alteration is attributed to a liquid rich lower temperature 240 degrees 330 degrees c ca rich evolved meteoric fluid influx of meteoric water into the central part of the system and mixing with magmatic fluid produced deep albitization transition alteration and shallow phyllic alteration this influx also caused dissolution of early formed copper sulfides and remobilization of cu into the sericitic zone where it was redeposited in response to a boiling induced decrease in temperature supergene alteration was minor and restricted to a thin blanket of cu sulfides below an argillic cap

late holocene landscape reconstruction in the land of seven rivers kazakhstan abstract a landscape reconstruction for the late holocene was carried out in the land of the seven rivers kazakhstan to investigate the environmental conditions during the prehistoric nomadic occupation of the sakes 1st mill bc two sampling locations were sedimentologically analysed a radiocarbon dated late holocene colluvial deposits and b fluvial deposits of assumed late pleistocene to early holocene age the geochemical and mineralogical components icp element analysis carbon contents grain size distributions x ray diffractometry were investigated to identify synsedimentary weathering conditions a modified weathering index mcia was used to evaluate the weathering processes the mcia results were compared with the silt clay ratio as an additional indicator for post depositional soil forming processes differences within the silt clay ratios and mcia indexes revealed that during the late holocene increased erosion processes occurred in the catchment a first tentative geochronology is based on radiocarbon and luminescence ages ranging from 14 5 1 4 ka to 3 23 0 07 cal ka bp for the colluvial deposits this paleoenvironmental reconstruction is supplemented by a detailed geomorphological characterization of the present landscape relief landforms and landscape units close to the sakian graves

a review of intermediate sulfidation epithermal deposits and subclassification abstract intermediate sulfidation is veins is one of the subtypes of epithermal deposits formed in subduction related arc settings or post collisional orogenic belts the economic and scientific significance of is deposits has been highlighting importance in ag au pb zn exploration and study of porphyry epithermal systems this epithermal clan of deposits typically have a close relationship with andesitic dacitic volcanic subvolcanic rocks and formed at a depth of 0 3 to as much as 1 km is deposits are typically related to oxidized calcic to calc alkaline magmatism fluid homogenization temperatures and salinities range between 150 and 350 c and 0 and 23 wt nacl equivalent respectively the o and h isotope compositions are consistent with a mixture of magmatic and meteoric water with an increase in meteoric diluent as the hydrothermal system wanes most of the is deposits in the world particularly those in circum pacific metallogenic belts formed during cenozoic time several mesozoic and paleozoic is deposits in the central asian orogenic belt imply great exploration potential for pre cenozoic is deposits in this area the presence of mn carbonate such as rhodochrosite and manganocalcite locally mn silicate e g rhodonite helvite typically in mid to late hydrothermal stages is a common diagnostic feature to discern is from low sulfidation ls deposits in addition the occurrence of intermediate sulfidation state sulfides such as pyrite chalcopyrite sphalerite galena and tetrahedrite tennantite associations are another indicator of the is type light colored fe poor sphalerite is typical of is deposits consistent with relatively oxidized fluids elevated fluid salinity is another characteristic with maximum salinity values of base metal rich is veins usually 5 wt nacl equiv the reported is deposits worldwide show that they develop in compressional volcanic arcs as well as in some extensional settings in this review is deposits are subdivided into nc neutral compressional type is with a low ag au ratio 60 formed in extensional settings such as extensional intra arc post collisional orogenic belts and back arc settings another notable feature of e type is deposits is their large ag endowment compared to nc type is nc type is au ag deposits can be associated with porphyry cu au and or high sulfidation hs au cu deposits and their economic metals are mainly gold and or silver by contrast some e type is deposits can occur on the flanks of porphyry molybdenum deposits e type is veins can also occur together with ls precious metal veins in back arcs or extensional continental margins the most representative examples occurring in mexico the occurrence of the two subtypes of is are largely controlled by the parent magma with parent magma of nc type is primarily derived from depleted mantle or juvenile crust while parent magma of e type is mainly from ancient continental crust the occurrence of is deposits is presumably controlled by tectono magmatic settings and fluid evolution paths neutral to compressive stress regime relatively great depth to an exsolving magma 4 km and low exsolution rate of magmatic fluids plus the presence of syn ore dikes in conjunction with the development of interconnected fracture networks above the porphyry stock could be conducive for the occurrence of is and also hs au veins upon porphyry copper deposits pcds confirmation of sub types and variations of is veins can aid in exploration for spatially and genetic related mineralization types such as porphyry and hs deposits

porphyry epithermal au ag mo ore formation by vapor like fluids new insights from geochemical modeling shallow magmatic hydrothermal systems are characterized by steep gradients in temperature and pressure and because the fluid is of low density and highly compressible the solubility of ore minerals in these systems varies considerably as a function of both temperature and pressure we use novel pressure and temperature dependent experimentally derived thermodynamic data to geochemically model the transport and deposition of au ag and mo by vapor and low to intermediate density supercritical fluids in the context of au and mo porphyry and au ag epithermal ore formation the results show that there is a strong compositional control on the au mo ratio of the parental ore fluid which can explain au mo zoning in porphyry ore deposits and the formation of au rich and mo rich subtypes gold solubility reaches a maximum between 320 c and 500 c depending on the fluid density whereas mo and ag concentrations decrease with decreasing temperature and pressure these differences in mineral solubility help explain the fractionation of au from ag and mo and the preferential mobilization of au into sites of epithermal ore deposition application of this modeling of metal solubility in vapor like fluids offers an important opportunity for understanding individual ore forming hydrothermal systems and determining the limiting factors for metal enrichment

characteristics and genesis mechanism of ground fissures in taiyuan basin northern china abstract since the 1980s ground fissures in the taiyuan basin have experienced blowouts resulting in a significant but hidden danger to cities in the basin this paper describes the plane and damage characteristics of the ground fissures based on the findings of field investigations and mapping most ground fissures in the basin were determined as linear with pinch out reappearances on the surface they were characterized by both horizontal tension with maximum widths and vertical offsets of up to 40 and 15 cm respectively the ground fissure strikes in the basin were observed to be consistent with those of nearby active faults and the long axis direction of the groundwater depression funnel the roads and houses that lie across the fissures were determined to be the most affected by ground fissure disasters in the basin the primary damage modes for the roads were vertical offset and surface collapse whereas buildings experienced foundation failure and tensile damage profiles obtained through geological drilling and trench exploration further revealed obvious tension and synsedimentary characteristics of the ground fissures correlated with existing faults correlation analysis shows that the formation of ground fissures in taiyuan basin is mainly related to faults and excessive groundwater extraction theoretical analysis revealed that the size and activity of ground fissures in the basin were positively correlated with four factors the dip of faults in an area regional tensile stress difference between the thicknesses of aquifers on either side of a fault and groundwater exploitation the significant increase in ground fissure activity since the 1980s mainly reflects uncontrolled groundwater discharge hence prevention of excessive groundwater exploitation in the basin would mitigate the destructive effects of the ground fissures

the influence of late pleistocene geomorphological inheritance and holocene hydromorphic regimes on floodwater farming in the talgar catchment southeast kazakhstan central asia abstract in comparison to southwest asia and the indian subcontinent the relationship between holocene river dynamics climate change and floodwater farming in central asia is significantly under researched to address this a multi disciplinary research project was begun in 2011 centred on the talgar catchment a south bank tributary of the ili river southeast kazakhstan building on archaeological excavations and surveys conducted over the past 20 years we have undertaken investigations of holocene human adaptations to changing hydromorphic regimes in the tien shan piedmont region central asia fluvial geochronologies have been reconstructed over the last 20 000 years using optically stimulated luminescence and 14c dating and are compared with human settlement histories from the eneolithic to the medieval period phases of late pleistocene and holocene river aggradation at c 17 400 6420 4130 2880 and 910 500 cal bc and between the mid 18th and early 20th centuries were coeval with cooler and wetter neoglacial episodes entrenchment and floodplain soil development c 2880 2490 cal bc and cal ad 1300 1640 coincided with warmer and drier conditions prior to the modern period floodwater farming in the talgar river reached its height in the late iron age 400 cal bc cal ad 1 with more than 70 settlement sites and 700 burial mounds this period of agricultural expansion corresponds to a phase of reduced flooding river stability and glacier retreat in the tien shan mountains late iron age agriculturists appear to have been opportunistic by exploiting a phase of moderate flows within an alluvial fan environment which contained a series of partially entrenched distributary channels that could be easily engineered to facilitate floodwater farming holocene climate change was therefore not a proximate cause for the development and demise of this relatively short lived c 200 years period of iron age farming river dynamics in the tien shan piedmont are however strongly coupled with regional hydroclimatic fluctuations and they have likely acted locally as both push and pull factors for riparian agriculturists

climate changes reconstructed from a glacial lake in high central asia over the past two millennia abstract climatic changes in arid central asia aca over the past two millennia have been widely concerned however less attention has been paid to those in the high central asia hca where the asian water tower nurtures the numerous oases by glacier and or snow melt here we present a new reconstruction of the temperature and precipitation change over the past two millennia based on grain size of a well dated glacial lake sediment core in the central of southern tianshan mountains the results show that the glacial lake catchment has experienced cold wet climate conditions during the dark age cold period 300 600 ad dacp and the little ice age 1300 1870 ad lia whereas warm dry conditions during the medieval warm period 700 1270 ad mwp integration of our results with those of previously published lake sediment records stalagmite 18o records ice core net accumulation rates tree ring based temperature reconstructions and mountain glacier activities suggest that there has a broadly similar hydroclimatic pattern over the hca areas on centennial time scale during the past two millennia comparison between hydroclimatic pattern of the hca and that of the aca areas suggests a prevailing warm dry and cold wet hydroclimatic pattern over the whole westerlies dominated central asia areas during the past two millennia we argue that the position and intensity of the westerlies which are closely related to the phase of the north atlantic oscillation nao and the strength of the siberian high pressure sh could have jointly modulated the late holocene central asia hydroclimatic changes

the bingham canyon porphyry cu mo au deposit iii zoned copper gold ore deposition by magmatic vapor expansion fluid inclusion microthermometry and laser ablation icpms microanalysis are combined with geological and textural observations to reconstruct the spatial and temporal evolution of magmatic fluids that formed the subvolcanic porphyry cu au mo ore deposit at bingham canyon utah the bingham canyon orebody is exposed over 1 6 km vertically and has the shape of an inverted cup with distinct metal zoning fluid inclusions in the barren but highly veined and potassically altered deep center of the system have intermediate density 0 6 g cm 3 and a salinity of 7 wt percent nacl equiv they have subequal concentrations of na k fe and cu and contain minor co2 the intermediate density fluids were trapped as a single phase mostly at 500 c and 800 bars the au cu rich center near the top of the orebody contains low density vapor inclusions 0 2 g cm 3 coexisting with brine inclusions containing 45 wt percent nacl equiv the vertical transition of different inclusion types indicates phase separation of the single phase input fluid upon volume expansion associated with a pressure drop to 200 100 bars mass balance calculation based on all analyzed inclusion components indicates that the mass of the vapor phase exceeded that of the brine by 9 1 the vapor contained cu as its dominant cation 1 5 wt and contributed about 95 percent of the total amount of copper transported to the base of the orebody bornite chalcopyrite and native gold were precipitated in a narrow temperature interval from 430 to 350 c into secondary pore space created by local redissolution of vein quartz as a result of retrograde quartz solubility in the vapor dominated fluid system intermediate density fluid inclusions in the deepest parts of the peripheral copper ore zone have identical density and composition including similar gold contents as those in the deep center microthermometry and statistical estimation of phase proportions in the inclusions show that the vapor in the peripheral cu rich but au poor ore zone remained denser and the separating brine was less saline 36 wt nacl equiv compared to vapor and brine in the central au cu ore zone this indicates that the peripheral fluids experienced a lower degree of phase separation due to slightly higher fluid pressure at equivalent temperature compared to more strongly expanding fluids in the center of the system the systematic zoning of au cu within the ore shell despite compositionally similar input fluids is interpreted to have resulted from slightly different pressure temperature density evolution paths of magmatic fluids copper was selectively precipitated in the peripheral ore zone in contrast to complete coprecipitation of au and cu in the central upflow zone of the vapor plume the formation of particularly rich cu au ore in the center of the upward expanding fluid plume is consistent with published experimental data showing that the solubility of metals in hydrous vapor decreases sharply with falling pressure due to destabilization of the hydration shell around metal complexes in expanding vapor this interpretation supports the classic vapor plume model for porphyry copper ore formation but additionally emphasizes the role of sulfur bearing complexes as a key chemical control on magmatic hydrothermal metal transport and the deposition of cu and au in porphyry ores our interpretation of selective cu au precipitation as a function of vapor density can explain the more general observation that most gold rich porphyry copper deposits are formed in shallow sub volcanic environments whereas deeper seated porphyry cu mo deposits are generally gold poor

porphyry related polymetallic au ag vein deposit in the central city district colorado mineral paragenesis and pyrite trace element chemistry abstract the colorado mineral belt is a 500 km long segment of calc alkaline to alkaline laramide age intrusions and related porphyry and polymetallic vein deposits the central city historic au ag mining district in the front range of colorado usa has been one of the most productive au deposits in the colorado mineral belt with a total of 119 1 t of au produced between 1859 and 1959 development of ne trending laramide strike slip faults and re activation of pre existing proterozoic brittle structures in proterozoic gneiss provided the structural controls for the mineralization of au and ag in re opened pyrite quartz and base metal veins previous studies have related ore formation in the district to the emplacement of late cretaceous paleogene laramide porphyritic alkaline intrusions it remains however unclear how to reconcile the au ag enrichment of this deposit with the historic vein descriptions and the evolution of a deep magmatic hydrothermal porphyry system here we document the crosscutting relationships and the mineral paragenesis of the different vein types and use the trace element chemistry in pyrite to fingerprint au mineralization and the succession of different veining styles in the central city district based on comparisons to porphyry and polymetallic style veins worldwide a revised vein classification is proposed which distinguishes porphyry transitional pyrite quartz and polymetallic veining styles these veining styles led to the development of an almost concentric district wide metal zoning comprising a central and an intermediate zone both enriched in cu au ag grading into a peripheral zone enriched in zn pb ag rare porphyry style veins include k feldspar veins and quartz veins with molybdenite ribbons the transitional style veins include abundant pyrite quartz veins that crosscut the earlier formed porphyry style veins and disseminated pyrite accompanied by phyllic alteration formation of the au ag bearing polymetallic style veins was associated with the brecciation and re opening of pyrite quartz veins based on mineral paragenetic relationships the polymetallic style base metal veins can be subdivided into four subtypes comprising sphalerite chalcopyrite veins tetrahedrite veins enargite pyrite quartz veins and galena sphalerite carbonate veins the textures mineral inclusions and trace element concentrations in pyrite are distinct for the different vein types and associated alteration halos pyrite in pyrite quartz veins is enriched in co and ni and contains quartz inclusions in contrast pyrite in polymetallic base metal veins is characterized by elevated au 20 ppm cu as pb ag and sb concentrations and contains inclusions of electrum and galena the observed veining styles paragenetic relationships and associated pyrite chemistry in the central city district confirm that ore formation is porphyry related the central city district also shares several similarities with cordilleran polymetallic style cu zn pb ag vein deposits associated with cu mo porphyries however the high au and low cu mo grades make central city an example of a newly recognized porphyry related polymetallic au ag vein deposit type

hydrographic development of the aral sea during the last 2000 years based on a quantitative analysis of dinoflagellate cysts the aral sea basin is a critical area for studying the influence of climate and anthropogenic impact on the development of hydrographic conditions in an endorheic basin we present organic walled dinoflagellate cyst analyses with a sampling resolution of 15 to 20 years from a core retrieved at chernyshov bay in the nw large aral sea kazakhstan cysts are present throughout but species richness is low seven taxa the dominant morphotypes are lingulodinium machaerophorum with varied process length and impagidinium caspienense a species recently described from the caspian sea subordinate species are caspidinium rugosum romanodinium areolatum spiniferites cruciformis cysts of pentapharsodinium dalei and round brownish protoperidiniacean cysts the chlorococcalean algae botryococcus and pediastrum are taken to represent freshwater inflow into the aral sea the data are used to reconstruct salinity as expressed in lake level changes during the past 2000 years we quantify and date for the first time prominent salinity variations from the northern part of the large aral sea during high lake levels i caspienense representing brackish conditions with salinities of about 10 15 g kg or less prevails assemblages dominated by l machaerophorum document lake lowstands during approximately 0 425 ad or 100 bc 425 ad 920 1230 ad 1500 ad 1600 1650 ad 1800 ad and since the 1960s because salinity in the aral sea is mostly controlled by meltwater discharges from the syr darya and amu darya rivers we interpret changes in salinity levels as a proxy for temperature fluctuations in the tien shan mountains that control snow melt significant erosion of marine palaeogene and neogene deposits in the hinterland evidenced between 1230 ad and 1400 ad is regarded as sheet wash from shore this is controlled by the low pressure system that develops over the eastern mediterranean and brings moist air to the middle east and central asia during late spring and summer we propose that the recorded environmental changes are related primarily to climate but perhaps to a lesser extent by humancontrolled irrigation activities our results documenting climate change in western central asia are fairly consistent with reports elsewhere from central asia

development characteristics and mechanisms of damage causing urban ground fissures in datong city china abstract a set of widely developed ground fissures within the datong basin northern china have inflicted serious damage to farm fields roads houses and building foundations in datong city such emergence of large scale ground fissures is rare in urban areas the formation mechanisms of these features were therefore investigated in detail through surveying mapping trenching drilling and geophysical prospecting the 11 fissures in datong city are located on the hanging wall of the kouquan fault part of regional horst and graben terrain and run approximately parallel with a dominant strike of ne34 70 and a maximum length of 5 5 km these structures occur in clear zones with similar directions and lateral distributions on the surface they possess evident synsedimentary fault characteristics including y shaped trapezoidal and traction structures in their profiles the synergistic action of different tectonic factors and groundwater exploitation is responsible for fissure formation under the influences of regional tensile stress upper mantle uplift and fault block movement activity along local faults created hidden fracture systems within the hanging wall the over exploitation of groundwater in the region subsequently accelerated fracture growth and varying vertical compressibility of the strata on both sides of the local fault resulted in uneven subsidence on the surface generating tensile zones and promoting the appearance of fissures at the edges of settlement funnels

environmental change during the holocene in western china on a millennial timescale recent data on the evolution of the inland lakes loess palaeosol sequences and glacier variations in western china are briefly reviewed the lake history shows three distinct stages in the holocene i e low water levels before 7500 bp a stage of expansion during the climatic optimum between 7500 and 3500 bp and contraction after 3500 bp three stages wooded grassland mixed woodland wooded grassland becoming steppe also appear indicated by the holocene loess palaeosol sequence in the lanzhou region the optimal period for soil development being between 7500 and 3500 bp there were seven periods of glacier advance the continental glaciers advanced at about 8300 5700 4000 and 400 bp in northwestern china and the maritime glaciers advanced at about 3000 2000 1000 and 200 bp it is suggested that the climatic changes show two periodicities during the holocene namely at intervals of about 2500 and 1000 years

direct observation and measurement of au and ag in epithermal mineralizing fluids abstract colloidal gold particles have been observed in c 300 c low salinity fluids from the arapucandere intermediate sulphidation epithermal base metal au deposit in nw turkey this is the first time colloidal gold has been recorded in an ancient mineralizing fluid growth in veins of large euhedral quartz crystals after the deposition of sulphides occurred in a number of stages from the introduction of fresh pulses of fluid the quartz overgrowths have a fibrous texture which facilitated trapping of large elongate fluid inclusions between the quartz fibres which grew perpendicular to the crystal faces of the pre existing quartz episodic periods of intense trapping of fluid inclusions occurred throughout the growth of quartz trapped within primary fluid inclusions are numerous particles of gold the largest observed is c 1 m but most are smaller bse element mapping shows these to contain au ag cu hg la icp ms profiles of the fluid inclusions confirm au and ag is not present in solution being present as numerous particles we have quantified the concentration of gold in fluid inclusions which are orders of magnitude greater than has been previously measured or thought likely in crustal fluids the average ag concentration is c 32 ppm and au is c 41 ppm but the maximum concentrations of both may reach several 100 s to 1000 ppm calcite forms a coating on the inner surface of the inclusions and barite pyrite galena sphalerite and unidentified minerals are also present with the au ag particles it is clear that the au ag particles could not have precipitated in the fluid inclusions therefore they must have precipitated elsewhere and been carried with the hydrothermal fluid the high concentrations and their colloidal nature have implications for the enrichment of gold in mineral deposits

holocene and latest pleistocene activity on the mesquite lake fault near twentynine palms eastern california shear zone implications for fault interaction paleoseismic data from the mesquite lake fault reveal evidence for up to four prehistoric earthquakes since the latest pleistocene with three large surface rupturing events in about the past 10 2 ka three events were recorded in trenches excavated for this investigation on mesquite lake playa a buried fault scarp brack eted by accelerator mass spectrometer radiocarbon ages of detrital charcoal indicate that a mid to late holocene event occurred between about 2 7 and 7 4 ka most likely between about 3 9 and 4 6 ka an early holocene rupture defined by a subtle buried scarp and upward terminating fissures is bracketed between about 7 7 and 10 2 ka evidence for an inferred late pleistocene event prior to about 10 2 ka includes a subtle scarp upward termination of faults folding and in filled craters and fissures a previous paleoseismic investigation just south 2 km of the playa identified at least one event in the past 1 3 ka although this event was not identified in this study at the playa site apparent vertical offsets of about 1 0 m and 1 2 m for the last two events at the playa site suggest a sequence of similar serial ruptures these separa tions are comparable to the height of surficial scarps just south of the playa because the vertical separations produced by each event are similar the mesquite lake fault at least locally experiences similar slip per event since the initiation of holocene playa development just over 10 2 ka ago we estimate a horizontal slip rate of 0 7 0 9 mm yr 1 that is consistent with slip rates for other faults in the eastern california shear zone despite large uncertainties event stratigraphy at the playa site shows that periods of quiescence up to thousands of years separated large ruptures similar to other faults in the eastern california shear zone comparison of paleoseismic studies in the eastern california shear zone suggest that the mesquite lake and possibly the bullion and lavic lake faults in the eastern part of the shear zone may have failed during periods of seismic quiescence in the western part of the zone at about 1 5 ka this suggests that seismic strain release may vary spatially across the shear zone and that temporal clusters of earthquakes are not necessarily spatially limited to specific regions

record of glacier variations during the last glacial in the turkestan range of the pamir alay kyrgyz republic moraines in five valleys of the turkestan range of the pamir alay kyrgyz republic were analyzed based on their geographical position and elevation morphology and ecological characteristics the moraines represent four glacial advances turkestan stage i during the last glacial stage ii during the late holocene stage iii during the little ice age ad 1400 1900 and stage iv during the 20th century in turkestan stage i the glaciers expanded to about 5 10 km from their present termini during marine isotope stage mis 2 radiocarbon ages for several soil layers buried in a lateral moraine of the asan usin glacier frontal area indicate that glaciers shrank or stagnated between at least 48 and 42 kyr bp during the warm climate of mid mis 3 these findings suggest that the glacier expansion in mid mis 3 was relatively small compared to the glacier expansion of mis 2 during the last glacial

the origin and impact of the shizhuang ground fissure yingxian area datong basin china abstract the datong basin is part of the regionally extensive fenwei graben system a major tectonic zone impacted by active tectonics and the resulting damage to life and infrastructure the basin also contains the shizhuang ground fissure system in this study the likely origin surface extent and fissure subsurface characteristics are explored by traditional methods surveying mapping trenching drilling and seismic exploration the shizhuang ground fissure is located at the intersection of the xiaoshikou fault and the southern liuleng margin fault in yingxian county it has a length of 2 1 km excellent continuity and semi elliptical surface morphology the dislocation of strata induced by the fissure increases significantly as the depth increases the strata bend downward and form typical traction structures near the fissure plane indicating that the fissure has prominent synsedimentary fault characteristics the fissure causes serious damage to houses farmlands roads and public facilities featuring large tensile cracks and vertical dislocations the resulting data and interpretations indicate that 1 the ground fissures connect to two major subsurface active faults which lay the tectonic foundation for the fissure 2 accelerated groundwater extraction has reactivated the underlying faults and exacerbated fissure development and 3 mitigation is best achieved by cessation of excessive groundwater pumping appropriate engineering design and local avoidance for placement of critical structures this paper provides a heretofore generally unknown example promotes research on the mechanisms of fissures and has guiding significance for disaster prevention and reduction in this area

nearfield interseismic vertical strain on the central garlock fault southern california 1984 1991 repeated precise leveling of fault crossing arrays at two sites on the central and western parts of the garlock fault discloses minor height changes of a few centimeters across the fault in seven years during that time the seismicity of the fault has been very low relative to other parts of california although other investigators have measured a millimeter or two of horizontal displacement per year near each of the leveling arrays the vertical changes measured in this study probably result from nontectonic differential subsidence across the fault due to the effects of the 1985 1991 drought in southern california the vertical displacement at cameron could turn out to be tectonic but at the koehn lake site the subsidence may be related to nearby pumping of groundwater the changes and rates of heights reported here should not be extrapolated in time or space because of the relatively short period of observations and because these sites measure only minuscule parts of the 250 km long fault

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

limits to lichenometry abstract lichenometry is a straightforward and inexpensive method for dating holocene rock surfaces the rationale is that the diameter of the largest lichen scales with the age of the originally fresh rock surface that it colonised the success of the method depends on finding the largest lichen diameters a suitable lichen growth model and a robust calibration curve recent critique of the method motivates us to revisit the accuracy and uncertainties of lichenometry specifically we test how well lichenometry is capable of resolving the ages of different lobes of large active rock glaciers in the kyrgyz tien shan we use a bootstrapped quantile regression to calibrate local growth curves of xanthoria elegans aspicilia tianshanica and rhizocarpon geographicum and report a nonlinear decrease in dating accuracy with increasing lichen diameter a bayesian type of an analysis of variance demonstrates that our calibration allows discriminating credibly between rock glacier lobes of different ages despite the uncertainties tied to sample size and correctly identifying the largest lichen thalli our results also show that calibration error grows with lichen size so that the separability of rock glacier lobes of different ages decreases while the tendency to assign coeval ages increases the abundant young

formation and evolution of multistage ore forming fluids in the miocene bangpu porphyry skarn deposit southern tibet insights from la icp ms trace elements of quartz and fluid inclusions abstract the large bangpu mo cu pb zn deposit is a mo rich 0 089 cu poor 0 32 porphyry skarn deposit located in the northeastern gangdese porphyry copper belt gpcb southern tibet in this study la icp ms data for fluid inclusions and quartz formed during different stages of the mineralization are used to 1 constrain changes in fluid composition during mineralization 2 infer the origin transport pathways and conditions of ore precipitation and 3 explore the influence of magma chamber on fluid exsolution and shallow mineralization the cu content of the vapor rich vl inclusions is higher than that of the halite bearing lvh inclusions while the mo pb and zn contents of the vl and lvh inclusions are similar indicating that mo cu pb and zn had a common source which is inferred to be the intermediate level magma chamber the metal contents of fluid inclusions in the early stage potassic alteration related vein a vein and later stage sericitic alteration related vein b vein are similar but variable implying the intermediate level magma chamber was too small to form a large stable fluid system the enrichment of mo pb and zn in the bangpu deposit relative to other porphyry deposits in the gpcb is related to the participation of ancient crustal material a comparison of our results with those from super large porphyry cu deposits elsewhere indicates that metal rich fluids are not the sole factor to form ore deposits and the variability of metal contents in the early exsolved fluids is a better predictor of mineralization potential than absolute metal concentrations

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

modern ground failure in the garlock fault zone fremont valley california modern ground failures ranging from renewed displacement on 2 5 km long fault scarps to 1 km long tension cracks occur in fremont valley california most of the failures formed along pre existing holocene fault scarps that are part of the tectonically active garlock fault system the failures began to form in the 1960s and currently affect an area of 17 km 2 that is coincident with ground water level decline induced by pumping for crop irrigation several observations indicate that these failures were caused by water level decline rather than natural tectonism first modern ground failure began after water level started to decline and was restricted to the area affected by decline land subsidence was associated with this decline and appears to be caused by aquifer compaction second geodetic monitoring from 1977 to 1982 of faults near the center of the cone of depression demonstrated that fault creep occurred during periods of seasonal water level decline and stopped during periods of seasonal water level recovery by contrast faults near the margin of the cone of depression where water levels declined at a constant rate moved at a steady rate third surface strain fields near failures suggest that subsurface fault associated deformation was restricted to aquifer level depths and fourth seasonal rebound of the land surface across one fault was caused by elastic expansion of the aquifer system that was induced by large seasonal water level recovery

late holocene glacier variations in the frontal and inner ranges of the tian shan central asia evidence for the timing and extent of late holocene glacial advances in the tian shan mountains central asia is based on lichenometric and radiocarbon dating of end moraines three phases of glacial advance occurred at 1700 2100 and 1100 1300 lichenometric l years ago and then during the little ice age 150 700 l years ago differences in the pattern of glacier variations between the northwestern frontal and inner areas of the tian shan are reflected in the equilibrium line altitude ela depression of 23 glaciers studied at nine selected sites the peripheral glaciers appear to have been significantly more extensive during late holocene advances than the glaciers of the inner areas this difference seems to be explained by regional differences in humidification in the northwestern periphery of the tian shan the cold periods of the late holocene were more humid than the warm period of the mid holocene whereas in the inner areas the pattern of climate changes was the opposite a warm and hu

glacier variations mudflow activity and landscape development in the aksay valley tian shan during the late holocene the object of this paper is to reconstruct the history of glaciation and the dynamics of mudflow activity as part of the development of landscapes in the aksay valley kirgizsky ridge over the last 2000 years glacial mudflow and slope deposits were dated by lichenometry and the radiocarbon method the results of 14c dating of buried soils shows that at about 1700 bp a period of activization of slope processes took place in the valley the zone of alpine meadow was situated at that time at an elevation of about 2750 m and glacier termini were situated at about 3100 3200 m the oldest mudflow surface which was investigated by lichenometry dates from the same time new equations for the rate of growth of the lichens aspicilia tianshanica and rhizocarpon geographicum use the oldest mudflow surface as a control point two periods of reduced mudflow activity are identified by lichenometry i e 350 450 and 130 240 bp and the latter is confirmed by 14c dating of peat soil interlayers in a mudflow stratum w

lichenometric constraints on the age of the huashan grottoes east china abstract lichenometry is a method of dating that has been widely used in glaciated areas for determining the minimum age of exposure of a geomorphic landform during the late holocene this paper presents a regional calibration data set of lichen thallus sizes versus rock surface ages for the huashan area east china based on measurements of yellow green rhizocarpon lichens on the known age substrates at eight sites an empirical relationship between thallus sizes and rock surface ages was established using both the traditional regression and the bayesian approaches using the bayesian calibration the minimum age of the huashan grottoes was dated from 450 60 to 330 60 years ago corresponding to the late ming dynasty ad 1477 1632 these dates are generally consistent with those predicted from the regression based linear growth curve our results suggest that applications of this technique can be safely extended to the non glaciated areas

holocene glacier fluctuations and climate changes in the southeastern part of the russian altai south siberia based on a radiocarbon chronology abstract this study investigates glacier dynamic and climatic variations in the southeastern part of the russian altai se altai during the last 7000 years recent glacier retreats and ice melting in moraines has led to exhumation of organic material allowing the possibility of radiocarbon dating we report here 57 new radiocarbon dates from wood remains buried by moraines and from proglacial forefields from peat layers and lacustrine sediments that cover moraines from dead trees at the upper tree limit and from rock glaciers on trough slopes from six glacial valleys in the north chuya range se altai such a numerous dataset for the vast but unified in neotectonic and climatic conditions area is presented for the first time the history of research in the altai together with 62 previously published radiocarbon ages mainly of fossil soils and peat layers in the foot of the ranges in se altai they form the basis for understanding the relative magnitudes and timing of the most important glacial and climatic events of se altai new data refute the traditional concept of the russian altai holocene glaciations as a consecutive retreat of the late wurm glaciers and argue their complete degradation at the head of trough valleys at least 7000 cal years bp moraine complexes of three holocene glacial stages are morphologically expressed in trough valleys of the north chuya range they correlate with three identified periods of glacial advances from 4900 to 4200 cal years bp akkem stage from 2300 to 1700 cal years bp historical stage and in the 13th 19th centuries little ice age lia or aktru stage the coincident extremes of lowering temperature and increasing precipitation during the akkem stage led to abrupt glacier advances and forming of the most remote moraine complexes downstream in the valleys following glacier advances had distinctly smaller magnitudes in addition to the radiocarbon data the time limits of the historical stage were defined more precisely using dendrochronological and archaeological data from scythian burials of pazyryk culture in se altai repeated forest regrowth in the presently glaciatiated area indicates significant retreat or even complete glacier degradation during interstage warming the decreases of glacier length in the following stages argues for intensification of aridity in the se altai during the second half of the holocene the thermal minimum in the middle of 19th century the greatest in the last millennium did not positively influence the mass balance of glaciers which also supports this conclusion

late holocene variation of the raigorodskogo glacier and climate change in the pamir alai central asia during the late holocene the raigorodskogo glacier in the pamir alai central asia expanded before 3215 after 1545 and at 310 cal years bp as dated by the 14c calibrated ages of wood samples from moraine deposits and terrace exposures the glacier expansions which were accompanied by increased melt water run off over the terrace surface were confined to the proglacial area the terrace deposits with intercalated buried soil layers provide evidence of two obvious warm periods when the glacier abruptly retreated during the late holocene shortly before 1545 cal years bp and again sometime before ca 500 cal years bp fallen juniperus turkestanica broken by moraine deposits suggests that the largest glacial expansion during the little ice age occurred 310 cal years bp the glacier expansion in the little ice age was on roughly the same scale as that which occurred in the cold period after 1545 cal years bp observational records of the glacier terminus and moraine positions indicate that recent glacier advances occurred in the years 1908 1911 sometime in 1911 1934 and in 1960 1977 these advances were small while the glacier recessions were larger in the 1900s with large recessions also sometime in 1911 1934 and in 1977 1998 the glacier recession rate of 27 m year in 1911 1934 was faster than the rates of 13 m year in 1977 1990 and 21 m year in 1990 1998 however the glacier recession rate has been accelerating recently particularly after 1990 this recession reflects recent climate warming in inland asia

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

development characteristics and mechanisms of the taigu qixian earth fissure group in the taiyuan basin china since the 1980s increasing human activity and continuing over exploitation of groundwater resources have caused the earth fissures in the rift basin in shanxi china to enter an active phase buildings along these earth fissures have been seriously damaged four massive earth fissures that developed in the taigu and qixian areas of the eastern taiyuan basin endanger the operational safety of the high speed railway that passes through this region using field observations measurements and exploration we determined that the four earth fissures are parallel to each other have a northeast trend and are separated by approximately equal distances the rupture zones of these earth fissures are generally 10 50 m wide and are formed by the main fissures and secondary fissures the width of the zone affected by the earth fissures is 20 50 m based on deformation and the damage done to buildings these fissures formed on the earth s surface their hanging walls are lower than their foot walls forming normal faults and the ground surface around the fissures exhibits ridges and depressions the fissures are connected to deep hidden faults the fault displacement increases with increasing depth which is characteristic of syn sedimentary faults these earth fissures are characterized by vertical displacement and their average annual activity rate is 1 3 cm we believe that the formation of this large scale fissure group may be related to the tectonic structure of the hidden faults in the basin and may also be affected by the continuous regional extensional stress of the basin the current increased level of activity could be caused by the over exploitation of groundwater in the area

high temperature gold copper extraction with chloride flux in lava tubes of tolbachik volcano kamchatka subvolcanic environments in supra subduction zones are renowned for hosting epithermal deposits that often contain electrum and native gold including bonanza examples this study examined mineral assemblages and processes occurring in shallow crust volcanic settings using recent eruption 2012 2013 of the basaltic tolbachik volcano in the kamchatka arc the tolbachik eruptive system is characterized by an extensive system of lava tubes after cessation of magma input the tubes maintained the flow of hot oxidized gases that episodically interacted with the lava surfaces and sulphate chloride precipitates from volcanic gases on these surfaces the gas rock interaction had strong pyrometamorphic effects that resulted in the formation of molten salt oxidized tenorite hematite cu rich magnesioferrite and skarn like silicate mineral assemblages by analogy with experimental studies we propose that a combination of these processes was responsible for extraction of metals from the basaltic wall rocks and deposition of cu fe and cu fe oxides and native gold

analysis and comparison of two types of ground fissures in dali county in the weihe basin china dali county is located in the eastern weihe basin where frequent ground fissure disasters occur dali ground fissures are macroscopically part of the ground fissure group in the weihe basin and have caused serious damage to infrastructure and agricultural production in this area in this paper 25 ground fissures in dali county are identified through investigation and two typical ground fissures in fengcun and weizhuang are selected for research through field investigation trench excavation geophysical exploration soil water content tests and collapsibility coefficient tests the basic features shallow structural characteristics deep structural characteristics and genetic mechanisms of the two ground fissures are revealed the strike of the fengcun ground fissure is 45 almost parallel to the shuangquan linyi fault the length is 2 km and the profile is ladder like and extends deep with synsedimentary characteristics the weizhuang ground fissures are circular in plan view with a length of 315 m and trumpet shaped in profile they disappear in the paleosol layer the mechanism of the fengcun ground fissure is related to basin extension and fault activity the ground fissures are the surface reflections of deep faults the mechanism of the weizhuang ground fissures is related to loess collapsibility and seepage the malan loess has differential settlement in collapsible and noncollapsible areas and ground fissures are the boundary line for differential settlement of loess finally based on the genetic mechanisms of ground fissures dali ground fissures can be divided into two types tectonic and nontectonic

mid to late holocene climate driven regime shifts inferred from diatom ostracod and stable isotope records from lake son kol central tian shan kyrgyzstan abstract arid central asia represents a key region for understanding climate variability and interactions in the northern hemisphere patterns and mechanisms of holocene climate change in arid central asia are however only partially understood multi proxy data combining diatom ostracod sedimentological geochemical and stable isotope analyses from a ca 6000 year old lake sediment core from son kol central kyrgyzstan show distinct and repeated changes in species assemblages diatom and ostracod inferred conductivity shifts between meso euhaline and freshwater conditions suggest water balance and regime shifts organism derived data are corroborated by stable isotope mineralogical and geochemical records underlining that son kol was affected by strong lake level fluctuations of several meters the 13ccarb 18ocarb correlation shows repeated switchovers from a closed to an open lake system from 6000 to 3800 and 3250 to 1950 cal yr bp son kol was a closed basin lake with higher conductivities increased nutrient availability and a water level located below the modern outflow son kol became again a hydrologically open lake at 3800 and 1950 cal yr bp comparisons to other local and regional paleoclimate records indicate that these regime shifts were largely controlled by changing intensity and position of the westerlies and the siberian anticyclone that triggered changes in the amount of winter precipitation a strong influence of the westerlies ca 5000 4400 3800 3250 and since 1950 cal yr bp enhanced the amount of precipitation during spring autumn and winter whereas cold and dry winters prevailed during phases with a strong siberian anticyclone and southward shifted westerlies at ca 6000 5000 4400 3800 and 3250 1950 cal yr bp similarities between variations in winter precipitation at son kol and records of the predominant nao mode further suggest a teleconnection between wet dry winter climate in central asia and a positive negative nao mode thus this study identifies climate fluctuations as the main driver for hydrological regime shifts in son kol controlling physicochemical conditions and consequently causing abrupt species assemblage changes this emphasizes the importance of multi proxy approaches to identify triggers thresholds and cascades of aquatic ecosystem transformations

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

alpine glaciers and permanent ice and snow patches in western canada approach their smallest sizes since the mid holocene consistent with global trends most alpine glaciers in the northern hemisphere reached their maximum extents of the holocene between ad 1600 and 1850 since the late 1800s however glaciers have thinned and retreated mainly be

porphyry copper deposit density estimating numbers of undiscovered mineral deposits has been a source of unease among economic geologists yet is a fundamental task in considering future supplies of resources estimates can be based on frequencies of deposits per unit of permissive area in control areas around the world in the same way that grade and tonnage frequencies are models of sizes and qualities of undiscovered deposits to prevent biased estimates it is critical that for a particular deposit type these deposit density models be internally consistent with descriptive and grade and tonnage models of the same type in this analysis only deposits and prospects that are likely to be included in future grade and tonnage models are employed and deposits that have mineralization or alteration separated by less than an arbitrary but consistent distance 2 km for porphyry copper deposits are combined into one deposit only 286 deposits and prospects that have more than half of the deposit not covered by postmineral rocks sediments or ice were counted nineteen control areas were selected and outlined along borders of hosting magmatic arc terranes based on three main features 1 extensive exploration for porphyry copper deposits 2 definable geologic settings of the porphyry copper deposits in island and continental volcanic arc subduction boundary zones and 3 diversity of epochs of porphyry copper deposit formation porphyry copper deposit densities vary from 2 to 128 deposits per 100 000 km2 of exposed permissive rock and the density histogram is skewed to high values ninety percent of the control areas have densities of four or more deposits 50 percent have densities of 15 or more deposits and 10 percent have densities of 35 or more deposits per 100 000 km2 deposit density is not related to age or depth of emplacement porphyry copper deposit density is inversely related to the exposed area of permissive rock the linear regression line and confidence limits constructed with the 19 control areas can be used to estimate the number of undiscovered deposits given the size of a permissive area in an example of the use of the equations we estimate a 90 percent chance of at least four a 50 percent chance of at least 11 and a 10 percent chance of at least 34 undiscovered porphyry copper deposits in the exposed parts of the andean belt of antarctica which has no known deposits in a permissive area of about 76 000 km2 measures of densities of deposits presented here allow rather simple yet robust estimation of the number of undiscovered porphyry copper deposits in exposed or covered permissive terranes

causes for large scale metal zonation around mineralized plutons fluid inclusion la icp ms evidence from the mole granite australia detailed reconstruction of the fluid evolution in several ore deposits associated with the sn w and base metal mineralized mole granite shows that multiple factors contributed to the zonal metal distribution around this intrusion information about the mechanism of ore formation was obtained from field relationships detailed petrographic studies and laser ablation inductively coupled plasma mass spectrometry la icp ms microanalysis of single fluid inclusions premineralization fluid inclusions in sn deposits are characterized by high sn w ratios whereas early fluid inclusions from w deposits contain higher w concentrations and comparatively low sn w ratios this indicates that the metal ratio in these deposits already was predefined by the composition of the magmatic input fluid however in both types of deposits the input fluid actually contained much higher concentrations of base metals pb zn cu etc than sn and w demonstrating that metal precipitation was highly selective the metal zonation around the mole granite therefore reflects both a compositional variation of the source fluid as well as sequential metal precipitation from it an additional process contributing to metal fractionation occurred by phase separation of the hydrothermal fluid into saline brine and low density vapor whereby cu b li as s ag la preferentially partitioned into the vapor phase analyses on six assemblages of unambiguously coexisting vapor and brine inclusions allowed direct determination of vapor brine distribution coefficients for 24 elements

climatic changes in the qinghai xizang tibetan region of china during the holocene climatic changes in the qinghai xizang plateau of china were studied by analyzing the composition of peat and layers of sand and gravel distributed along the southern slopes of nianqing tanggula and gangdise mountains cross sections of deposits near a number of interior lakes in xizang past glacial variations on the southern slope of nianqing tanggula mountain and landform changes south of the yaluzangbu river such geologic evidence suggests a division of five climatic periods since the beginning of the holocene 1 the wumadung interval 10 000 7500 yr b p slightly cold and dry 2 qilongduo interval 7500 3000 yr b p warm and moist 3 the mid neoglacial period 3000 1500 yr b p cold except between 2500 and 200 yr b p when it was warmer 4 the dawelong interval 1500 300 yr b p mild and 5 the little ice age 300 0 yr b p cold these changes progressed in a similar but not identical pattern as those in the northeastern part of china and in the northern region of europe

a study of the symbiotic relationship between tectonic fissures and faults in the fenwei graben system china the fenwei graben system is an important extensional fault depression zone which is the tectonic boundary between the ordos block and the south china block and the north china block the graben system presents an s shape with a total length of 1200 km and a width of 30 60 km and an overall strike of nne due to complex tectonic background and active faults nearly 612 ground fissures develop in these basins and more than 90 of these ground fissures are tectonic fissures which are closely associated with fault activities to reveal the plane symbiotic phenomena profile symbiotic modes and symbiotic mechanism between tectonic fissures and faults in the fenwei graben system the developmental characteristics were investigated in detail by surveying mapping trenching and drilling in the study area the main conclusions are as follows 1 the tectonic fissures of the fenwei graben system are mainly distributed along the margin faults of basins the boundary faults between blocks and the hidden faults within blocks causing serious damages to farmlands houses and roads the symbiosis between these fissures and faults is obvious on the surface 2 the profile symbiotic morphology includes vertical extension type syncline and anticline y type and stepped type 3 the symbiotic mechanisms include vertical growth lateral rupture and clustery derivation 4 the activities of underlying faults give impetus to the formation and expansion of tectonic fissures the exposure of the fissures makes underlying faults continue to develop in the form of surface fractures

deformation across the western united states a local estimate of pacific north america transform deformation we obtain a locally based estimate of pacific north america relative motion and an uncertainty in this estimate by integrating deformation rate along three different paths leading west across southwestern north america from east of the rio grande rift to near the continental escarpment data are primarily quaternary geologic slip rate estimates and resulting deformation determinations therefore are instantaneous in a geologic sense but long term with respect to earthquake cycles we deduce a rate of motion of the pacific plate relative to north america that is 48 2 mm yr a rate indistinguishable from that predicted by the global kinematic models rm2 and nuvel 1 however we obtain an orientation that is 5 9 counterclockwise of these models a more westerly motion of the pacific plate with respect to north america is calculated from all three paths the relatively westerly motion of the pacific plate is accommodated by deformation in the north american continent that includes slip on relatively counterclockwise oriented strike slip faults including the san andreas fault which is especially relevant in and south of the transverse ranges and a margin normal component of net extension across the continent which is especially relevant north of the transverse ranges deformation of the sw united states occurs in regionally coherent domains within which the style of deformation is approximately uniform in the vicinity of the transverse ranges two important shear systems splay from the san andreas fault the eastern california shear zone trending nnw from the eastern transverse ranges and the trans peninsular faults trending sse from the western and central transverse ranges within the transverse ranges the right lateral san andreas fault steps left seemingly requiring large amounts of convergence there however most of this convergence is avoided through a funneling flow of the crust toward the western transverse ranges and into the relatively narrow central california coast ranges and the northern motion of the mojave the former process involves an alternation of rotation direction from counterclockwise in and south of the central transverse ranges to clockwise in the western transverse ranges

long dormancy low slip rate and similar slip per event for the emerson fault eastern california shear zone excavations in a playa along the 1992 rupture of the emerson fault reveal evidence of two paleoseismic events with only one large prehistoric rupture in the past 15 millennia accelerator mass spectrometer radiocarbon ages of charcoal from playa sediments and from fault scarp colluvium directly beneath the playa beds indicate that the last large prehistoric slip event occurred about 9000 ka trench wall exposures revealed clear evidence of at least one pre 9 ka rupture at the playa site the event horizon of this earthquake is between two pedogenic carbonate layers that have radiocarbon ages of 14 8 ka and 24 1 ka implying that the earthquake occurred about 20 000 years b p the actual bracketing ages for this rupture are likely a few thousand years older because of the mean residence time for the pedogenic carbonate and calibration of the 14c ages by 230th dating despite the large uncertainties a dormant period of at least 6 kyr to as much as 13 kyr separates the older event from the 9 ka event because the scarp formed by the penultimate event is similar in height to the scarp formed by the 1992 mw 7 3 landers earthquake the penultimate rupture was at least locally similar in size to the most recent rupture this similarity supports the concept of characteristic slip for the emerson fault preliminary results from paleoseismic studies at other sites on the 1992 rupture suggest that large ruptures occurred on other nearby faults within a few hundred years of this penultimate event on the emerson fault the interseismic period that preceded the 1992 earthquake on the emerson fault was about 40 times longer than the average interval between large events on the nearby san andreas fault therefore in comparison to events on the san andreas fault the 1992 landers earthquake was an exceedingly rare event

mechanism of fuping ground fissure in the weihe basin of northwest china fault and rainfall the special geological conditions of the weihe basin located in the southern fenwei graben system are the cause of many of the ground fissures developing in this area the tingzi ground fissure in fuping county is one of the typical and particular ground fissures found in the weihe basin the ground fissure is famous for its sudden appearance after heavy rainfall to explore the characteristics and mechanism of the fissure some geological methods were carried out in the study area for this study such as surveying mapping trenching drilling and seismic exploration the main conclusions are as follows 1 the fissure is located on the hanging side of the secondary fault of the liquan pucheng heyang fault with a ne40 ne75 strike and a length of 2 7 km 2 the fissure is steeply inclined and presents a funnel shape in the shallow strata there are many secondary cracks near the main fissure 3 the fissure is connected with underlying fault and possesses the characteristics of synsedimentary faults reflecting the historical stages of fissure activities 4 the fissure destroys farmlands and houses along the fissure and mainly causes tensile damage 5 the fissure was controlled by regional extension and fault and it was promoted and enlarged by rainfall and other influential factors

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

a typical earth fissure resulting from loess collapse on the loess plateau in the weihe basin china abstract earth fissures are major geological hazards that frequently occur in the weihe basin in northwestern china and can cause severe damage to infrastructure this paper reports a case study of earth fissures resulting from loess collapse in the village of xibai in the weihe basin a series of geological investigations consisting of a site investigation trench excavation geological drilling exploratory well drilling and geotechnical testing were conducted to determine and analyze the characteristics of the xibai village earth fissures as well as the physical characteristics of the loess in the earth fissure development area the earth fissures were parallel to the village sewage pit and had a total length of 800 m with a maximum depth of 8 5 m the xibai village earth fissures were nearly vertical comparing the results of self weight collapsibility coefficient and three parameters void ratio dry density and water content of loess at different distances from the sewage pit the collapsibility of malan loess in this area and the effects of leakage from the sewage pit were determined the results revealed that a tilted seepage line was generated and the loess below this seepage line underwent varying degrees of self weight collapse deformation the nonuniform collapse settlement and rotation deformation of loess above the seepage line were thus generated while tensile stress was created in the upper part of the loess this rotation of loess similar to the deformation of the cantilever beam caused the formation of the earth fissures at the site with higher tensile stress based on the rotation mechanism this study explained the development process of collapse earth fissures and predicted that the xibai village earth fissures would continue to develop outward in the future

palaeoenvironmental change and glacier fluctuations in the high tian shan mountains during the last millennium based on sediments from lake ala kol kyrgyzstan abstract a suite of limnological proxies measured in clastic sediments of the glacier fed lake ala kol ne kyrgyzstan document palaeoenvironmental change and glacier fluctuations in the central tian shan over the last millennium rock magnetic and geochemical data provide supporting evidence for three glacier expansion episodes occurring in 1200 1400 ce 1500 1850 ce and 1900 1950 ce and glacier retreat periods during 1000 1200 ce and the intervening periods the maximal glacier extent as inferred from high lf si inc coh ca inc coh and low arm30 arm is recorded between 1500 and 1850 ce and corresponds to cold and wet conditions during the little ice age in the high central tian shan periods of glacier waxing and waning recorded at lake ala kol present a close correspondence to ice accumulation rate in the northern tibetan plateau suggesting that precipitation changes are the main driver of glacier fluctuations in central tian shan during the last millennium although temperature may have exerted a more complex influence on centennial timescales

separation of molybdenum and copper in porphyry deposits the roles of sulfur redox and ph in ore mineral deposition at bingham canyon the giant bingham canyon porphyry cu mo au deposit utah is associated with eocene subvolcanic intrusions it shows a distinct metal zonation above a barren core with dominantly shallow cu au mineralization cu stage following the early quartz monzonite porphyry qmp intrusion and spatially deeper mo mineralization mo stage occurring in a separate vein set exclusively after a late quartz latite porphyry qlp intrusion that truncates earlier cu au veins to understand this metal separation and the geochemical process of molybdenite mineralization we investigated fluid inclusions by microthermometry raman spectroscopy and laser ablation inductively couple plasma mass spectrometry la icp ms microanalysis in low and high grade quartz veins of both mineralization stages in deep low grade quartz veins interpreted to represent the root zone of the cu stage we found high concentrations of cu s and mo in the fluid inclusions whereas in low grade mo stage veins we found lower cu but similar concentrations of s and mo compared to the inferred input fluids to the cu stage sulfur and copper concentrations were similar in intermediate density type fluid inclusions in deep low grade cu stage samples whereas intermediate density type inclusions in low grade mo stage veins have s contents that exceed their cu contents in high grade mo stage vein we found large variations of mo concentrations in coexisting brine and vapor inclusions compared to the p t conditions of the cu precipitation stage 90 260 bars and 320 430 c the mo precipitating fluids were trapped at higher pressures and temperatures of 140 to 710 bars and 360 to 580 c mass balance calculation based on the compositions of intermediate density inclusions and brine vapor assemblages interpreted to be derived by phase separation during decompression of the ascending single phase intermediate density fluid indicate that the mass of vapor phase exceeded that of brine by about 9 1 in both mineralization stages combining this mass balance with the analyzed vapor brine partitioning data indicates that more than 70 of mo and s by mass in the deposit were deposited from the vapor phase earlier cu au deposition was similarly dominated by vapor but recently published data about postentrapment cu diffusion in and out of fluid inclusions cast doubt on previous quantifications suggesting that almost none of the copper was deposited by brine mo is less likely to be modified by selective diffusion and high mo contents max 0 0054 mo na in intermediate density 380 g g mo in brine in the hydrothermal fluids were maintained from the early cu stage to the late mo stage this indicates that mo concentration was not the decisive factor for separate precipitation of late mo ore at bingham canyon instead the metal separation may be explained by a reduction in redox potential and an increase in acidity in the evolving source region of the fluids i e a large subvolcanic magma reservoir this is indicated by the stoichiometry of chalcopyrite and molybdenite precipitation reactions a tentative difference in the fe mn ratio in fluids of both veining stages incipient muscovite alteration along high temperature molybdenite veins and an increasing tendency for mo to fractionate from brine to vapor we suggest that the early cu stage fluids were slightly more oxidized and neutral allowing cu fe sulfides to saturate first while molybdenite saturation was suppressed and mo was lost from the early ore stage by contrast during the later mo stage the fluids were more reduced and acidic thereby allowing selective saturation of molybdenite as the first precipitating sulfide in the cooling and expanding two phase fluid consistent with textural observations this interpretation may imply more generally that small differences in redox potential and acid base balance of the magmatic source of porphyry mineralizing systems may be decisive in the temporal and spatial separation of the two metals

a high resolution diatom inferred palaeoconductivity and lake level record of the aral sea for the last 1600 yr formerly the world s fourth largest lake by area the aral sea is presently undergoing extreme desiccation due to large scale irrigation strategies implemented in the soviet era as part of the intas funded climan project into holocene climatic variability and the evolution of human settlement in the aral sea basin fossil diatom assemblages contained within a sediment core obtained from the aral sea have been applied to a diatom based inference model of conductivity r2 0 767 rmsep 0 469 log10 s cm 1 this has provided a high resolution record of conductivity and lake level change over the last ca 1600 yr three severe episodes of lake level regression are indicated at ca ad 400 ad 1195 1355 and ca ad 1780 to the present day the first two regressions may be linked to the natural diversion of the amu darya away from the aral sea and the failure of cyclones formed in the mediterranean to penetrate more continental regions human activity however and in particular the destruction of irrigation facilities are synchronous with these early regressions and contributed to the severity of the observed low stands