alteration zoning and primary geochemical dispersion at the bronzewing lode gold deposit western australia the late archaean bronzewing lode gold deposit is in the yandal greenstone belt western australia it is located in a 500 m wide n s trending structural corridor consisting of an anastomosing set of brittle ductile shear zones and is chiefly hosted by tholeiitic basalts which are metamorphosed at mid to upper greenschist facies syn peak metamorphic alteration surround all ore bodies and alteration extends laterally for 80 m from individual mineralised structures individual alteration haloes partially overlap and form a 1 5 km long and 300 m wide domain the alteration sequence studied here at 140 m below the present undisturbed surface comprises distal calcite chlorite albite quartz intermediate calcite dolomite chlorite muscovite albite quartz and proximal ankerite dolomite muscovite albite quartz pyrite zones mass transfer calculations indicate that chemical changes during alteration include enrichment of ag au ba bi co2 k rb s sb te and w and depletion of na sr and y the elements al ca cr cu fe mg mn ni p ti v zn and zr are immobile the degree of chemical change increases with proximity to gold ore zones in addition abundant quartz veins indicate substantial silica mobility during the hydrothermal event although there is no large relative silica loss or gain in the host rock the broadest anomaly surrounding the bronzewing gold deposit is defined by tellurium 10 ppb which if it is a hydrothermal anomaly extends beyond the 400 600 m study area anomalous values for co2 k rb and sb also define wider zones than does anomalous gold 4 ppb although even the lithogeochemical gold anomaly extends across strike for as much as 80 m away from ore and 600 m along the n s strike of the shear zone corridor also carbonation and sericitisation indices outline large exploration targets at the bronzewing deposit sericitisation indices define anomalies that extend for tens of metres beyond visible potassic alteration whereas the anomalies defined by the carbonation indices do not extend beyond visible carbonation none of the individual alteration indices or pathfinder elements are able to define consistent gradients towards ore however the respective dimensions of individual geochemical anomalies can be used as an extensive although stepwise vector towards ore this sequence is from species with broadest dispersion first as follows te co2 ca sb 3k al rb ti au w y ti depletion ag bronzewing ore

importance of depth and intensity of convection on the isotopic composition of water vapor as seen from iasi and tes δd observations abstract we use tropical observations of the water vapor isotopic composition derived from iasi and tes spaceborne measurements to show that the isotopic composition of water vapor in the free troposphere is sensitive to both the depth and the intensity of convection we find that for any given precipitation intensity vapor associated with deep convection is isotopically depleted relative to vapor associated with shallow convection the intensity of precipitation also plays a role as for any given depth of convection the relative enrichment of water vapor decreases as the intensity of precipitation increases shallow convection via the uplifting of enriched boundary layer air into the free troposphere and the convective detrainment enriches the free troposphere in contrast deep convection is associated with processes that deplete the water vapor in the free troposphere such as rain re evaporation the results of this study allow for a better identification of the parameters controlling the isotopic composition of the free troposphere and indicate that the isotopic composition of water vapor can be used to evaluate the relative contributions of shallow and deep convection in global models

the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

hydrothermal alteration and gold mineralization of the awak mas metasedimentary rock hosted gold deposit sulawesi indonesia abstract the awak mas gold deposit is hosted by phyllites and schists indicated and infered resource are around 38 4 mt at 1 41 g t au equaling to total resource of 1 74 moz gold hydrothermal alteration zones proximal to the gold bearing veins are characterized by the mineral assemblage albite ankerite pyrite and marked by elevated na al ratios and depleted 3 k al ratios these changes are manifested by the replacement of muscovite by albite carbonate alteration with ankerite and siderite occured simultaneous to albitization proximal to the veins distal alteration zones are characterized by chlorite albite in phyllites and albite quartz in schists there are two types of au mineralizing veins in the deposit namely quartz albite ankerite veins and quartz ankerite siderite veins gold occurs in pyrite as sub microscopic inclusions and as fracture fillings with a gold fineness of 925 935 and au ag ratios between 12 1 and 14 1 the aqueous ore fluid was co2 poor and of low salinity with homogenization temperatures between 275 and 325 c fluid inclusion leachates have br cl ratios between 1 0 and 2 0 10 3 and i cl ratios of 5 6 to 18 3 10 5 suggesting that the ore fluids were derived from metamorphic dewatering of organic rich marine sedimentary rocks on the other hand br cl ratios between 1 6 and 3 0 10 3 and i cl ratios from 5 1 to 10 6 10 5 in the non mineralized veins indicate an input of magmatic hydrothermal fluids the results of this study show that the awak mas deposit is an epigenetic orogenic gold deposit which developed at the transition between the epizone and the mesozone

geochemical comparison of reservoir solid bitumens with diverse origins abstract geochemical and petrologic comparison of solid bitumens with various origins from reservoirs in zaire canada and kazakhstan were studied to provide insight into their formation processes and their physical and chemical properties results of this study can help develop methods for treatment and removal of solid bitumen and evaluating producibility of associated hydrocarbon fluids characterization of these solid bitumens reveals a wide range in quantity and composition of extractables soluble material and in solid bitumen reflectance which indicate significant differences in formation processes hydrocarbon source and thermal maturity the zaire and kazakhstan samples represent end members of the spectrum of solid bitumens studied solid bitumens from the motoba field zaire are highly extractable and low in thermal maturity 0 2 0 3 bitumen reflectance reservoir mixing of a cretaceous lacustrine sourced oil and a tertiary marine sourced oil of different thermal maturities appears to be responsible for their formation in contrast solid bitumens from the tengiz field kazakhstan are characterized by their extremely low extractables high bitumen reflectance 1 and low atomic h c ratios

geographic variability in the export of moist static energy and vertical motion profiles in the tropical pacific 1 column integrated moist static energy mse budgets were calculated using daily data from three reanalyses 1998 2001 and isccp radiative cooling the mse export by the circulation was separated into vertical and horizontal mse advection components in order to examine how observationally derived vertical motion profiles affect gross moist stability calculations in a 2000 km wide region in the central eastern pacific itcz vertical motions import mse implying a negative gross moist stability horizontal mse advection is negative and of similar magnitude to vertical mse advection in rainy regions geographic differences in export of mse by the vertical circulation are primarily due to differences in the shape of the vertical motion profile in the west pacific warm pool rainy regions mean horizontal convergence extends up to 300 mb while in parts of the pacific itcz where meridional sst gradients are strong the vertical motion profile is bottom heavy with convergence below 800 mb and divergence above on daily timescales the mode of vertical motion variability has little dependence on precipitation rate and is consistent with observed regional differences in the vertical structure of trmm pr reflectivities

oxidized and reduced mineral assemblages in greenstone belt rocks of the st ives gold camp western australia vectors to high grade ore bodies in archaean gold deposits hydrothermal sulfide oxide gold mineral assemblages in gold deposits in the archaean st ives gold camp in western australia indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time reduced alteration assemblages pyrrhotite pyrite occur in deposits in the southwest of the camp e g argo junction deposits and moderately to strongly oxidized assemblages magnetite pyrite hematite pyrite occur in deposits in the central corridor in the northeast e g north orchin revenge deposits reduced mineral assemblages flank the central corridor of oxidized deposits and locally cut across it along e w trending faults oxidized mineral assemblages in the central corridor are focused on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1 000 m below present surface hydrothermal magnetite predates and is synchronous with early phases of gold associated albite carbonate pyrite biotite chlorite hydrothermal alteration later stage gold associated pyrite is in equilibrium with hematite the spatial distribution and temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly synchronous hydrothermal fluids with contrasting redox states sulfur isotope constraints support the argument that the different mineral assemblages reflect differences in redox conditions the 34s values for pyrite for the st ives gold camp range between 8 4 and 5 1 with the negative values occurring in oxidized magnetite rich domains and slightly negative or positive values occurring in reduced pyrrhotitic domains preliminary spatial and paragenetic analysis of the distribution of iron sulfides and oxides in the st ives camp suggests that gold grades are highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite pyrite to relatively oxidized magnetite pyrite and hematite pyrite both in space and time gold deposition is inferred to have occurred where fluids of contrasting redox state mixed

pennsylvanian coal and associated bitumen at johnson mills shepody bay new brunswick canada abstract pennsylvanian fluviatile sandstones at johnson mills new brunswick host fossil logs preserved as a result of the paragenetic succession pyritization carbonatization carbonization and overlapping bitumenization carbonatization is the dominant process the coalified material is all overmature as reflected by temperature of maximum pyrolysis tmax in a range of 460 464 c veinlets of once liquid now solid bitumen extend outward from the logs into the surrounding sandstones for several meters present in the bitumen are relict coal macerals that contribute to a microscopic distinctly structured coaly appearance of the material reflectance measurements of coal range from romax 0 78 to romin 0 61 two distinct populations of bitumens are recognized romax 0 78 to romin 0 65 for the main population romax 0 60 to romin 0 48 for the second population transmitted and reflected light microscopy long count energy dispersive spectroscopy eds and rock eval analysis indicate that bitumen was derived from the logs as a result of late stage diagenesis exsudatinite like material is the probable precursor of the bitumen thermal maturity of the bitumen increases directly with inferred migration distance from the logs across the spectrum solid bitumen closest to the logs and within the oil window is least mature tmax 449 c and bitumen furthest from the logs is most mature with tmax 493 c this phenomenon results from differences in the chemistry of the derivative bitumen which is relatively more aliphatic and nso enriched close to the log source and more aromatic distally these differences in bitumen composition may have arisen as a consequence respectively of pre gas and post gas generating conditions

source oil charging history and filling pathways of the ordovician carbonate reservoir in the halahatang oilfield tarim basin nw china abstract the ordovician reservoir in the halahatang depression is one of the most commercially prolific oil reservoirs in the tabei uplift of the tarim basin nw china for this study a total of 94 oil samples were collected from 88 exploration production wells in this oilfield all of the oils possess similar organic molecular compositions and belong to the same oil population oil to source correlation results indicate that oil accumulations discovered in halahatang oilfield were derived from the upper ordovician source rocks the homogenization temperatures of fluid inclusion in the ordovician reservoir in the halahatang oilfield range from 90 c to 100 c and from 140 c to 160 c the bimodal distribution pattern shown in a histogram of the homogenization temperatures indicates that the ordovician oil reservoir in the halahatang oilfield has been charged twice coupling this information with the reconstructed burial and geothermal histories by 1 d basin modeling the homogenization temperatures can be related to the relative geological ages of 419 ma to 410 ma and 16 ma to 8 ma namely the middle to late silurian and the middle miocene respectively representing the two phases of oil charging and entrapment the oil migration orientation and charging pathways can be traced using molecular indicators such as ts ts tm and tmnr parameters the overall oil migration orientation in the oilfield is generally from south to north therefore the source kitchen for the halahatang oilfield is predicted to be to the south side of the depression the southern part of the halahatang depression along the oil charging pathways is identified as the most promising region for oil exploration

proportions of convective and stratiform precipitation revealed in water isotope ratios distinguishing convective and stratiform rainfall is key to understanding how the water cycle responds to climate change an analysis of satellite and surface data shows that rain isotope ratios reflect the proportions of these types of rain

modeling the isotopic composition of precipitation the physics of the stable isotopes of water is incorporated into a two dimensional kinematic bulk cloud microphysical model the model is run for several idealized classical stratiform and convective storm situations and the resulting isotope ratios of precipitation and water vapor are diagnosed and compared to observations for stratiform snow the model produces low isotope ratios that decrease rapidly poleward of the warm front the lowest isotope ratios occur when the atmosphere is cold and when the vertical velocity attains its maximum value high in the troposphere for stratiform rains the model produces much higher isotope ratios without a significant poleward gradient as a result of isotope exchange between the falling rain and the surrounding vapor isotope ratios of rain are lowest when the melting level is near the ground and isotope exchange is minimized for air mass thunderstorms isotope ratios are uniformly high in warm air no matter what the cloud height unless hail approaches or reaches the ground the model also produces a significant amount effect for rain in which isotope ratios decrease with increasing rainfall totals isotope ratios are particularly low when the rain derives from a recirculation process in which air previously charged by vapor from falling rain subsequently rises under such conditions the model sometimes produces isotope ratios that decrease from the periphery to the core of the precipitation shield it is suggested that this recirculation process is responsible for extraordinarily low isotope ratios observed in some hurricanes and organized thunderstorms the dominant cloud microphysical processes can sometimes be inferred from isotope ratios of precipitation the model produces ice pellets with isotope ratios close to those of rain when the pellets are produced by homogeneous freezing of rain and close to those of snow when the pellets are produced by refreezing of partially melted snow a climatology of isotope values that matches the main features of the observed global data set and of a seven year record of storms at mohonk lake new york is generated by running the model for a wide range of conditions this includes the deuterium excess d d 8 18o for antarctic snows that increases markedly as d falls below 300 and the deuterium deficit observed for rain in warm dry regions

4d architecture and tectonic evolution of the laverton region eastern yilgarn craton western australia abstract the laverton region located in the eastern yilgarn craton eyc western australia is second only to the kalgoorlie region for gold endowment the integration of high density potential field data regional and camp scale seismic reflection data regional and mine scale structural analysis and geochronologically constrained stratigraphy provided new insights into the 4d architecture and tectonic evolution of laverton region at a regional scale the map patterns of laverton are dominated by the mt margaret dome in the northwest and the kirgella dome in the southeast these domes are flanked to the east and west by north northwest striking shear zones with the central zone between the two domes being dominated by north to north northeast striking sigmoidal shear zones these distinctly different strikes to the shear zones developed early in the tectonic evolution and resulted in a favourable architecture for late stage orogenic gold mineralisation a series of regional seismic reflection lines have imaged the sub surface architecture of the laverton region with a major crustal penetrating shear extending to the moho mapped as the laverton tectonic zone ltz the ltz consists of a basal fault the north northwest striking celia fault and a series of steeper faults for example the north to north northeast striking childe harold fault and far eastern fault which sole at depth into the celia fault beneath the laverton region lower angle faults imaged in the seismic reflection data develop parallel to granite gneiss domes that postdate the north northwest striking and north to northeast striking faults the construction and integration of the new 3d map with the structural stratigraphic and geochronological analysis has defined six main deformation events and their effects on the architectural evolution of the region this analysis suggests that early formed faults are genetically associated with late stage orogenic gold mineralisation regional and mine scale structural analysis at the wallaby and sunrise dam deposits indicate that gold deposition occurred synchronously during the d4b event in both deposits both mines are separated by the ltz which records sinistral and later d5 dextral movement the kinematic model which best describes the observed architecture is a restraining step over within a sinistral strike slip system a structural model consistent with analogue modelling of strike slip systems is proposed where two early extensional basement faults were reactivated during d4b northwest southeast contraction as low angle thrusts in a pop up zone this architecture has been mapped in 3d in the region between wallaby and sunrise dam where both deposits are located on the low angle thrusts on opposing sides of a sigmoidal structure developed during sinistral strike slip movement this strike slip step over architecture provided significant opportunity for dilation and fluid flow late dextral movement of the basement faults during northeast southwest contraction d5 reactivated the low angle thrusts at sunrise dam producing extensional movement and further dilation within the overall restraining step over this event is not significant at wallaby mine a detailed 3d stress analysis at sunrise dam revealed that the most favourable fault segments to reactivate during the d4b event were orientated at 30 towards 310 a comparison of the spatial distribution of gold defined from extensive production and resource estimation drilling with the favourably orientated segments of faults was confirmed the analysis also highlighted down dip extensions beyond the coverage of the drilling of favourably oriented segments which may provide additional targets during future near mine exploration the same approach was applied to the regional 3d map and new targets generated beneath the major salt lake between wallaby and sunrise dam

re assessment of chemical weathering indices case study on pyroclastic rocks of hong kong abstract quantitative and objective characterization of weathered states of rock by means of chemical weathering indices has significant potential in ground investigation practice this paper reviews more than thirty different chemical indices and re assesses their variations along a weathered profile developed over pyroclastic rocks under subtropical conditions chemical weathering indices are principally based on the basic assumption that distributions of chemical elements as well as loss on ignition loi content along the profile are mainly regulated by the degree of weathering however this study clearly demonstrates that the behavior of chemical elements and loi during weathering depend not only on the degree of weathering but also on microenvironmental conditions that control the type and abundance of clay minerals and sesquioxides and thus determine the level of heterogeneity of the profile it is suggested that signatures of chemical weathering should be used to establish a framework for the interpretation of the heterogeneity level and the prediction of variability in engineering properties rather than for quick classifications using chemical weathering indices

thermochronologic constraints on evolution of the linglong metamorphic core complex and implications for gold mineralization a case study from the xiadian gold deposit jiaodong peninsula eastern china abstract the nne trending linglong metamorphic core complex hosts the majority of the gold deposits in the jiaodong peninsula of eastern china many of the deposits are hosted by the 163 155 ma linglong granite in the footwall of the linglong detachment fault argon thermochronology suggests that the granite had cooled to 400 c by 143 1 5 ma possibly as a result of normal movement on the detachment nine zircon fission track zft ages from samples collected along a nw se transect perpendicular to the central part of the linglong detachment fault at the 652 m level in the xiadian deposit constrain the subsequent thermal evolution of linglong metamorphic core complex which overlapped the period of major gold deposition the zft ages vary from 136 9 3 3 ma 1 to 130 1 2 2 ma 1 the unaltered linglong granite in the footwall and amphibolite in the hangingwall have similar ages at 136 9 3 3 ma 1 and 135 0 3 0 ma 1 whereas ages for the disseminated and stockwork style ores appear to be younger at ca 131 130 ma although there is an overlap of ages when considering the 1 precision interestingly zft ages show no marked differences between the hangingwall and footwall of the linglong detachment fault although significant movement along the fault occurred the results are best interpreted to indicate that the linglong granite was emplaced at 160 ma and cooled to 240 50 c at 135 ma as recorded by unaltered rocks in the footwall hydrothermal alteration along the linglong detachment fault led to annealing of zircon fission tracks and the consistent younger ages of 131 ma quartz aggregates associated with gold mineralization show evidence of recrystallization suggesting that the hydrothermal event was initiated at temperatures of at least 300 350 c near the brittle ductile transition but cooled rapidly to zft closure temperatures within a country rock environment that was already relatively cool therefore these zft ages suggest that the timing of mineralization at the xiadian deposit was post 135 ma and likely very close to 131 ma the mineralization and cooling occurred in the footwall of a major detachment fault under an extensional regime possibly related to the progressive slab rollback of the paleo pacific plate and controlled by the linglong metamorphic core complex

late archean convergent margin tectonics and gold mineralization a new look at the norseman wiluna belt western australia on a world scale the most important hydrothermal gold deposits occur either in late archean ca 2700 ma greenstone belts or at late paleozoic to quaternary convergent plate boundaries in the latter environments epithermal and porphyry hosted deposits form during subduction related magmatism in volcanic arcs and deep level meso thermal deposits form during deformation in continental margin orogenic belts the mesothermal deposits are similar to archean gold deposits in greenstone belts such as the norseman wiluna belt in western australia we here suggest that this similarity exists because the norseman wiluna belt is an orogenic belt with a tectonic history similar to that of younger mineralized convergent margins such as the north american cordillera it is most likely that the norseman wiluna belt resulted from the interaction of lithospheric plates during the major period of continental growth and stabilization that occurred in the late archean the distribution of gold mineralization being controlled by convergent margin tectonics

gold hosting high ba sr granitoids in the xincheng gold deposit jiaodong peninsula east china petrogenesis and tectonic setting abstract the xincheng deposit is the only large gold deposit with a proven reserve of 200 t gold hosted by the early cretaceous granitoids in northwest jiaodong peninsula east china the granitoids hosting this ore deposit comprise an inner medium to fine grained quartz monzonite and an outer medium to coarse grained monzogranite with distinctive k feldspar megacrysts la icp ms zircon dating yields u pb ages of 128 1 to 132 1 ma and 127 2 to 129 1 ma for the quartz monzonite and the monzogranite respectively the early cretaceous ages obtained in our study are comparable with the 126 130 ma age range reported for the guojialing granitic suite the monzogranites typical high ba sr granites possess high sio2 70 89 73 35 k2o 3 85 4 32 total alkalis k2o na2o 8 08 8 68 sr 634 888 ppm ba 1395 2111 ppm and lree 59 43 145 88 with low hree and hfse contents and insignificant eu anomalies the rocks display markedly high sr y 114 297 and la yb n 20 79 ratios they have low mgo 0 23 0 62 cr 0 4 8 33 ppm and ni 0 47 2 92 ppm contents the typical high ba sr signatures of the outer acidic monzogranites are also shared by the inner intermediate acidic quartz monzonites with a relatively higher abundance of these elements the plagioclases in the quartz monzonites and monzogranites are oligoclase andesine with an contents of 11 7 44 5 and oligoclase with an contents of 12 9 29 3 respectively which both show the reverse zoning texture the quartz monzonites have zircon ehf t values of 21 3 to 13 9 average 18 7 which are less negative and show larger variations than those of the monzogranites ehf t 24 7 to 18 1 average 19 5 detailed elemental mineralogical and isotopic data suggest that the high ba sr quartz monzonites and monzogranites were most likely generated by partial melting of the basement rocks of the jiaobei terrane accompanied by crustal assimilation with minor addition of the intermediate magma derived from the partial melting of juvenile mafic lower crust formed by the earlier underplating of mantle magma and the quartz monzonites may represent the path of intermediate magma inputting into felsic magma in combination with previous investigations we suggest subduction of the paleo pacific slab beneath the north china craton ncc and associated asthenosphere upwelling were most likely the mechanism associated with the generation of the high ba sr granites

a review of the mesothermal gold deposits of the meguma group nova scotia canada abstract the gold province of the meguma terrane in nova scotia contains several classic examples of turbidite hosted mesothermal gold deposits there are over 300 gold occurrences and deposits hosted by the cambro ordovician meguma group rocks in southern nova scotia canada the meguma group consists of two formations 1 a lower sand dominated flysch goldenville formation and 2 an upper shaley flysch halifax formation subdivision of the goldenville formation into several map units is leading to a better understanding of the stratigraphic constraints on the gold mineralization although detailed stratigraphic investigations in all of the major gold producing areas is still ongoing it is evident that the steve s road beaverbank and the mt uniacke stratigraphic intervals contain most of the major past gold producers in the province the meguma group rocks are variably deformed into upright gently to moderately doubly plunging folds with multiple cleavages the strata are metamorphosed from greenschist to amphibolite facies and are subsequently intruded by ca 370 ma peraluminous granites and minor mafic intrusions the gold deposits can be divided into three main types 1 high grade approximately 15 g t au narrow gold bearing quartz veins 2 low grade 0 5 4 g t au slate argillite hosted and 3 low grade meta sandstone hosted a combination of two or more of the above can also occur almost all of the historic production 47 million g au has come from the high grade veins within 200 m of surface a variety of vein types occur although most of the gold produced came from bedding concordant stockwork and fissure veins isotopic investigations and dating of the vein minerals indicate that the mineralization was related to migration of metamorphic fluids from multiple reservoirs in the waning stages of the acadian orogeny disseminated low grade gold with minor electrum and associated intermetallic compounds and metal alloys have recently been recognized in host rocks at several of the former gold mining areas in nova scotia the presence of disseminated gold in combination with high grade vein mineralization greatly enhances the economic viability of gold deposits in the meguma group the association of disseminated gold and narrow vein hosted deposits has important exploration implications for similar mesothermal gold districts elsewhere

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

the vertical structure of the eastern pacific itczs and associated circulation using the trmm precipitation radar and in situ data the atmospheric circulation associated with the eastern pacific single and double itczs particularly its vertical structure is little known due to the sparce observations using precipitation profiles from the tropical rainfall measure mission trmm precipitation radar with approximations to the liquid water and energy budget equations we estimated vertical profiles of latent heating and vertical velocity in the far eastern pacific 95 w 85 w itczs in the 800 730 hpa layer we combined this with eastern pacific investigation of climate campaign epic2001 and other in situ data to produce a preliminary characterization of the meridional vertical circulation we found evidence of a double cell structure in boreal fall between the itcz and the equator with both shallow and upper level peaks in vertical velocity in spring the flow poleward of the two itczs has a single cell structure although around the equator it shows some hints of the double cells reanalysis and satellite based data are shown to be unreliable for describing the vertical structure of the circulation

hydrothermal alteration in metasedimentary rock hosted orogenic gold deposits reefton goldfield south island new zealand orogenic or mesothermal quartz lodes in lower palaeozoic greenland group metasedimentary rocks of the reefton area have produced 67 tonnes t of gold prior to 1951 and recent exploration has identified new gold resources in several deposits including the largest past producers blackwater and globe progress the metasedimentary rocks consist of alternating sandstone and mudstone beds that were metamorphosed to lower greenschist facies prior to being hydrothermally altered adjacent to the quartz lodes the sandstones are feldspathic litharenites averaging q65 f10 r25 with detrital grains of quartz rock fragments muscovite and plagioclase and biotite that were altered to albite and chlorite respectively during metamorphism accessory minerals are graphite apatite zircon tourmaline and titanite hydrothermal alteration of the sandstones has developed a mineral assemblage of k mica carbonate dolomite ankerite ferroan magnesite and magnesian siderite chlorite pyrite and arsenopyrite the abundance of hydrothermal chlorite is greater at blackwater than at the other prospects studied hydrothermal alteration associated with the quartz lodes is marked by bleaching magnesian siderite spots disseminated arsenopyrite and pyrite and thin carbonate quartz and sulphide veins these trends are accompanied by increasing concentrations of s as and sb and decreasing na and a decrease of fe and mg in k mica the alkali alteration indices 3k al representing k mica and na al representing albite generally show antipathetic trends with 3k al increasing near the lodes and na al decreasing these trends reflect the replacement of albite by k mica carbonate alteration indices co2 ca mg fe and co2 ca mg fe 0 5 s as quantify the abundance of hydrothermal carbonates but they show variable correlation with the lodes they increase the width of the alteration halo in the hanging wall of the lodes at the globe progress and general gordon prospects but the peak values are as far as 150 m from the lodes by contrast peak values of the carbonate alteration indices are within 10 and 2 m of the lodes respectively at the merrijigs and blackwater deposits data show that for deposits with wide hydrothermal alteration halos such as at the globe progress and general gordon prospects the use of a suite of geochemical indicators can assist exploration by indicating trends in hydrothermal alteration that provide vectors to mineralisation they also increase the size of the exploration target by contrast the alteration halo of the blackwater deposit is restricted to within less than 5 m of the quartz lode and therefore the geochemical indicators are of more limited assistance to exploration

ion microprobe upb zircon geochronology of granitic magmatism in the western province of the south island new zealand abstract zircon u pb isotopic systems are described for three mid palaeozoic and four late mesozoic granites from the western province of the south island new zealand the granites chosen are representative of the major plutons in this region two distinct episodes of palaeozoic magmatism have been identified middle devonian 380 ma and early carboniferous 330 ma the mesozoic granites are all mid cretaceous in age and range from 120 to 110 ma the o sullivans granite forming a large part of the karamea batholith has a crystallisation age of 377 7 4 1 ma and the windy point granite from the paparoa batholith has an age of 328 6 4 4 ma further west the granite at cape foulwind has a similar age of 327 3 6 2 ma from east to west the cretaceous granites appear to decrease in age the separation point batholith is dated at 118 ma the oldest phase at separation point gave an age of 116 6 1 9 ma and the youngest phase the pearse granodiorite gave the same age within error at 119 4 2 3 ma the mount olympus pluton in nw nelson gave an age of 111 4 2 0 ma and the same age is found for the buckland granite which forms most of the paparoa batholith at 109 6 1 7 ma inherited zircon components as old as 1700 ma have been identified in many of the granites and distinct components are present at 1000 and 500 600 ma this pattern of zircon ages has also been observed in granites from the lachlan fold belt and in ordovician sediments from se australia and new zealand however it is not clear whether the old zircons are derived from the lower crust from the incorporation of upper crustal material or both the palaeozoic granites can be broadly correlated with rocks of similar age in antarctica se australia and tasmania that formed part of the gondwana supercontinent the cretaceous granites are probably part of an extensive mesozoic magmatic arc that can be traced from south america through west antarctica and on into new zealand

a permeability model for naturally fractured carbonate reservoirs abstract based on a detailed structural study performed on a reservoir surface analogue a fracture permeability model for carbonate reservoirs is proposed this involves four hierarchical systems each one assumed to convey fluids exclusively to that of immediately higher order new basic equations are then provided simulating hydrodynamic reservoir response the large scale first order structures consist of faults to which high permeability structures damage zones are associated at the meter scale stratabound joint systems together with bedding joints bounding the mechanical layers form a connected network transporting fluids to the fault system at a lower scale down to crystal size non stratabound joints constitute a pervasive and capillary fracture network which conveys fluids within the rock mass the non fractured host rock constitutes the lower permeability system at the crystal scale as no published works include an effective integration of detailed structural and numerical models the present study aims at covering a significant gap in the literature also providing appropriate theoretical basis for subsequent studies on fracture network modeling and reservoir simulation besides its application in the field of reservoir development and management the illustrated model may also be useful in environmental studies involving ground fluids such as e g in the field of special toxic nuclear waste management

unique chemical and isotopic characteristics and origins of natural gases in the paleozoic marine formations in the sichuan basin sw china isotope fractionation of deep and high mature carbonate reservoir gases abstract large quantities of natural gases have recently been discovered in the marine carbonate formations in the sichuan basin southern china the origins and isotopic compositions of the gases are poorly understood and highly controversial we examined the chemical and isotopic compositions of the carbonate reservoir gases in marine formations from the sinian to lower triassic as well as shale gas from the silurian and cambrian formation in the sichuan basin it is found that the carbon isotopes of the carbonate reservoir gases had been evolved through three stages corresponding to pre rollover rollover and post rollover in the plot of 13c2 versus wetness which is consistent with that found in shale gas by tilley and muehlenbachs 2013 the unique carbon isotopic compositions indicate that both kerogen and oil cracking gas have contributed to the accumulation of the carbonate reservoir gases in the sichuan basin a mixing of two thermogenic gases with different maturities can cause the 13c reversal between methane and ethane which is commonly observed in the carbonate reservoir gases in the carboniferous permian and triassic formations and the shale gas in the silurian and cambrian formations in the sichuan basin we established two mixing models for quantitatively determining the contribution of each type gas for the natural gases in different formations kinetic extrapolation based on thermal history of the anyue gas field demonstrates that ethane cracking indeed occurred in the deep reservoir formations which may explain the disappearance of the 13c reversal for methane and ethane in the carbonate reservoir gases in the post rollover zone it is proposed that organic inorganic interactions may be responsible for the presence of d isotope rollover for methane in carbonate reservoir gases with ultra high maturity the organic inorganic interactions include thermal reactions between water and residual organic matters or carbons and hydrogen isotope exchange between water and methane and their mechanism needs further investigations in future

biomarker evidence for two sources for solid bitumens in the subu wells implications for the petroleum prospectivity of the east papuan basin abstract late cretaceous sandstones from the subu 1 and 2 wells aure scarp papua new guinea contain patchily distributed solid bitumens the solid bitumens vary in reflectance and geochemistry indicating that they formed by the biodegradation of two different families of crude oils termed family a and family b biomarker characteristics such as the high abundance of rearranged hopanes and steranes indicate that the family a solid bitumens were derived originally from a clay rich marine source rock low in sulphur which had significant input of terrestrial organic matter these correlate with oils from the iagifu 7x gobe 3x omati 1 and puri 1 wells that are believed to be generated from sources of jurassic age the family b solid bitumens and a fluid inclusion oil from subu 1 have a high abundance of 2 methylhopanes bisnorhopanes and dibenzothiophene and originated from a marine source rock with a calcareous component this source rock had a high proportion of prokaryotic organic matter input a greater sulphur content and a more reducing depositional environment than the jurassic source rocks the lack of correlation with other oils in papua new guinea suggests the presence of a second so far unidentified generative marine source rock in the east papuan basin the fine grained samples in the subu wells are thermally immature vre 0 5 0 6 organically lean and contain type iii organic matter with little hydrocarbon generation potential most of the solid bitumens have peak oil window thermal maturities vre 0 8 1 0 but some have lowered maturities that are interpreted to be due to co extraction of indigenous detrital low maturity organic matter low molecular weight n alkanes alkylcyclohexanes methylalkylcyclohexanes and alkylbenzenes in many of the samples are attributed to overprinting of pre existing variably biodegraded solid bitumens in the sandstones with pristine hydrocarbon charge with a condensate composition this condensate charge has not undergone any major biodegradation or water washing implying that it is a relatively recent event solid bitumen from a vein in a miocene volcanolithic sandstone from the ouha anticline was generated from an early mature palaeogene or late cretaceous source rock that contained predominantly terrestrial organic matter deposited in an oxic environment this sample proves the existence of a different oil generative source rock in the east papuan basin in addition to the two oil source rocks inferred from the subu data

vertical lithogeochemical halos and zoning vectors at goushfil zn pb deposit irankuh district southwestern isfahan iran implications for concealed ore exploration and genetic models abstract the vertical lithogeochemical halos of indicator elements in host rocks over a blind zn pb deposit are developed by upward migration of geochemical halos this may prove to be a useful exploration guide for targeting undiscovered zn pb mineral systems the main objective of this investigation is to assess the vertical distribution patterns of the composite lithogeochemical halos for detecting possible exploration guides as well as a possible genetic model of zn pb sulfide mineralization the goushfil zn pb deposit is one of the most important lower cretaceous carbonate and shale hosted deposit in the irankuh district west central iran the deposit contains about 4 3 million tonnes of sphalerite galena barite ore with an average grade of 8 zn and 2 4 pb in order to examine the exploration significance of the vertical lithogeochemical halos about 274 rock samples from 26 boreholes were sampled and analyzed by icp ms for a multi element package the results demonstrate that the highly anomalous values for ag 0 1 120 ppm as 3 1165 ppm ba 9 2820 ppm ca 0 07 25 cd 0 005 210 ppm hg 0 9 24 ppm mg 0 03 11 75 pb 15 15 000 ppm zn 65 15 000 ppm and sb 1 305 ppm are developed in faulted or fracture controlled hydrothermally dolomitized and jasperoid carbonates and shales the newly proposed multiphase composite geochemical halos defined by ratios of ag cd pb zn ag as pb zn ca mg pb zn sb as pb zn hg sb pb zn sb ba pb zn and ba ca pb zn correlate with three exploration zones at the average depth of 10 200 and 310 m above and below the main ore zone all the composite lithogeochemical halos in particular ag cd pb zn in both rock and soil samples tend to increase toward the shallow depths but decrease as they approach the main zn pb ore toward the deeper parts of the ore zone this geochemical response of the composite halos could be used for targeting undiscovered zn pb sulfide mineralization the low contents of cu and fe in the mineralized rocks indicate a low modal content of chalcopyrite and pyrite in the precursor sulfide ore which correlate with those of the mississippi valley type mvt zn pb deposits this is also highlighted on the log pb zn pb pb zn cu pb zn cu and homogenization temperature salinity variodiagrams on which the goushfil data plot close to the mvt type zn pb mineralization

mineralisation footprints and regional timing of the world class siguiri orogenic gold district guinea west africa siguiri is a world class orogenic gold district hosted in the weakly metamorphosed upper birimian to lower tarkwa group sedimentary rocks of the siguiri basin guinea the district is characterised by a protracted deformation history associated with four main deformation events d1s is a n s compression d2s is an e w compression progressively evolving into an early d3s transpression and then into a late d3s nnw sse transtension and d4s is a ne sw compression field observations petrography and geochemistry at three key deposits of the siguiri district bidini sintroko pb1 and kosise suggest a polyphase hydrothermal history that can be subdivided into four hydrothermal events the first hydrothermal event was associated with the development of barren bedding parallel and en echelon v2s quartz dominated pyrite veins the second hydrothermal event is characterised by the development of v3a pyrite ankerite veins late during d3s laser ablation icp ms data show that this vein set contains high gold contents of up to 43 3 ppm in substitution in pyrite crystal lattice representing a minor first gold mineralisation event the third and most prominently developed hydrothermal event is late d3s and represents the second and principal gold mineralisation event this mineralisation event led to two distinct mineralisation textures the first texture is best exposed in the kosise deposit and is characterised by gold bearing quartz ankerite arsenopyrite conjugate v3b veins although the bulk of the gold is hosted in native gold grains in v3b veins la icp ms analyses show that gold also substitutes in the arsenopyrite crystal lattice up to 55 5 ppm the second mineralisation texture is best expressed in the sanu tinti deposit and consists of disseminated barren pyrite hosted in a polymict conglomerate the second and third hydrothermal events are both structurally controlled by a series of early d3s n s ne sw wnw ese and e w sub vertical incipient structures expressed as fracture zones of higher v3s vein density a composite geochemical cross section across fracture zones from the kosise deposit indicates that gold mineralisation in the siguiri district is associated with enrichments in ag au as bi co mo sb s te and w relative to background geochemical variations associated with the ore shoots in the siguiri district are consistent with petrographic observations and highlight an albite carbonate sulphide sericite alteration the fourth and last hydrothermal event is associated with the development of a late penetrative s4s cleavage during d4s deformation which overprints all pre existing hydrothermal features and is associated with the deposition of free gold chalcopyrite and galena along fractures in v3a pyrite and v3b pyrite and arsenopyrite mineralogical and geochemical footprints as well as timing of the gold mineralising events in the siguiri district when compared with other deposits of the west african craton highlight the synchronicity of gold mineralisation in siguiri syn d3s and syn d4s events with other similar events in this part of the craton such as the early au sb bi te w mineralisation at the morila deposit in southeast mali our results support the hypothesis that late eburnean age gold mineralisation in the siguiri district and in the west african craton as a whole was polyphase

fluid chemical evolution as a factor in controlling the distribution of gold at the archean golden crown lode gold deposit murchison province western australia the golden crown lode gold deposit is one of a number of northwest southeast to north south trending quartz veins hosted by a steeply dipping 500 m thick differentiated dolerite sill the great fingall sill and adjacent graphitic shale in the day dawn district of the murchison province in the archean yilgarn craton western australia quartz veins of the golden crown deposit are shear zone hosted crosscut the dominant host rock stratigraphy at a high angle and are laminated partly boudinaged and generally bifurcate at their extremities veins are dominated by dark gray or milky white quartz with subordinate calcite and ankerite and in order of abundance arsenopyrite pyrrhotite pyrite galena chalcopyrite and minor sphalerite the vein sulfides coexist with native gold and are most abundant at vein margins textural evidence indicates that precipitation of the majority of these minerals overlapped and that most phases can be considered to have been in equilibrium during vein genesis mineral chemistry fluid inclusions alteration and ore assemblages show that there are significant systematic gradients in intensive variables within the golden crown deposit these are recorded over the approximately 450 m of vertical exposure of the vein system and over up to 30 m into the wall rocks based on proximal alteration assemblages and zoning patterns zoned wall rock alteration haloes are divisible into four sequences three of which are closely related to gold mineralization specific alteration sequences occur within different parts of the vein system biotite alteration predominates in the deeper portions whereas muscovite alteration characterizes the upper and southern portions of the system higher grade gold zones within the golden crown deposit are limited to the northern end of the system in the deeper portion of the veins and expand along strike to the south in the upper portions fluid inclusions interpreted to be trapped during gold mineralization are low salinity 10 wt nacl equiv h2o co2 ch4 inclusions with variable carbonic to aqueous contents that are interpreted to be due to fluid immiscibility inferred methane concentrations in the carbonic phase vary significantly from 19 7 mole percent in the vicinity of the shale contact to 5 2 mole percent in the shallower southern end of the deposit carbon and oxygen isotope compositions of carbonates 13ccalcite 10 5 to 1 9 13cankerite 5 3 to 4 1 18ocalcite 7 0 18 3 and 18oankerite 7 7 9 2 and oxygen isotope compositions of vein quartz 18oquartz 10 2 12 5 are well within the range of known archean orogenic lode gold deposits combining the results of all geothermometers and geobarometers a temperature of 300 to 400 c and pressure of 2 5 0 5 kbars are determined with temperature variations over the exposed quartz vein of less than 40 c the as content at of arsenopyrite and au ag ratios of native gold show significant compositional variation which appears to be controlled by parameters such as a h2s aq and f o2 not temperature gradients on the basis of the variations in fluid composition determined in the reefs the two major processes responsible for high grade gold mineralization are interpreted to have been phase separation in the deeper portions of the ore forming system approximately below 400 m level and above these levels mixing between two modified ore fluids one reduced fluid that had reacted with graphitic shale and a relatively oxidized fluid that had partly equilibrated with dolerite

predictive mapping of prospectivity for orogenic gold giyani greenstone belt south africa we present a mineral systems approach to predictive mapping of orogenic gold prospectivity in the giyani greenstone belt ggb by using layers of spatial evidence representing district scale processes that are critical to orogenic gold mineralization namely a source of metals fluids b active pathways c drivers of fluid flow and d metal deposition to demonstrate that the quality of a predictive map of mineral prospectivity is a function of the quality of the maps used as sources of spatial evidence we created two sets of prospectivity maps one using an old lithologic map and another using an updated lithological map as two separate sources of spatial evidence for source of metals fluids drivers of fluid flow and metal deposition we also demonstrate the importance of using spatially coherent or geologically consistent deposit occurrences in data driven predictive mapping of mineral prospectivity the best predictive orogenic gold prospectivity map obtained in this study is the one that made use of spatial evidence from the updated lithological map and spatially coherent orogenic gold occurrences this map predicts 20 of the ggb to be prospective for orogenic gold with 89 goodness of fit between spatially coherent inactive orogenic gold mines and individual layers of spatial evidence and 89 prediction rate against spatially coherent orogenic gold prospects in comparison the predictive gold prospectivity map obtained by using spatial evidence from the old lithological map and all gold occurrences has 80 goodness of fit but only 63 prediction rate these results mean that the prospectivity map based on spatially coherent gold occurrences and spatial evidence from the updated lithological map predicts exploration targets better i e 28 smaller prospective areas with 9 stronger fit to training gold mines and 26 higher prediction rate with respect to validation gold prospects than the prospectivity map based on all known gold occurrences and spatial evidence from the old lithological map

alteration of eocene lamprophyres in the zhenyuan orogenic gold deposit yunnan province china composition and evolution of ore fluids abstract the zhenyuan orogenic gold deposit 100 t au located in the northern part of the ailaoshan shear zone assz in south china is characterized by extensive alteration and mineralization in a variety of host rocks in the deposit abundant eocene lamprophyres have been infiltrated by ore fluids to produce carbonate veins with zones of disseminated fine grained gold bearing pyrite and arsenopyrite on both margins of the veins primary phlogopite k feldspar and magnetite have been altered to carbonate sericite and fuchsite carbonate minerals and sericite in altered lamprophyre have higher mg contents than in other host rocks reflecting the primitive geochemistry of the lamprophyres since carbonatization is the primary alteration type in the lamprophyres whose main primary components are low ca phlogopite and k feldspar the cao content of the lamprophyres reflects their degree of alteration as alteration increases incompatible element ratios remain essentially constant whereas sr is enriched with ca in addition au with co ni as ag sb and bi are enriched reflecting the addition of these metal elements during alteration of the lamprophyres altered lamprophyres have slightly lower 143nd 144nd t 0 51240 0 51253 and substantially higher 87sr 86sr t 0 70716 0 71234 than unaltered or weakly altered lamprophyres indicative of crustal contamination the auriferous ore forming fluids are thus interpreted to have migrated upwards and interacted with the sedimentary host rocks before altering the lamprophyres lamprophyres commonly show a close spatial and commonly temporal association with orogenic gold deposits worldwide at zhenyuan the lamprophyres shared a common deep source to the auriferous ore fluids but did not themselves contribute to this fluid or its gold content

the mobility of zirconium and other immobile elements during hydrothermal alteration abstract development of zircon and other zr phases in hydrothermal deposits indicates that zr can be highly mobile in these systems mobility is most common in but not restricted to f rich hydrothermal systems related to alkalic f rich igneous suites these suites can range from peralkaline through metaluminous to peraluminous a few examples are neither alkalic nor f rich three locations in the trans pecos magmatic province texas u s a demonstrate this hydrothermal zr mobility all three igneous systems are alkalic and f rich but vary in alkali al ratios peralkaline rhyolites and trachytes in the christmas mountains contain as much as 2100 ppm zr mostly in aegirine or arfvedsonite zircon is rare or absent fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38 000 ppm zr occurring as small disseminated zircons the deposits also are enriched in a variety of incompatible elements including be rare earth elements ree y nb mo hf pb th and u the sierra blanca intrusions a series of mildly peraluminous f rich rhyolite laccoliths contain as much as 1000 ppm zr mostly as zircon hydrothermal zircon occurs as overgrowths on magmatic grains as veinlets connected to overgrowths and in fluorspar replacement bodies in adjacent limestone the highest zr concentrations in fluorspar are 200 ppm metaluminous quartz monzonite from the infiernito caldera contains 400 600 ppm zr mostly as zircon euhedral zircon in quartz fluorite veins in the quartz monzonite indicates mobility of zr zirconium concentrations in the veins are unknown but the paucity of zircon suggests little zr enrichment relative to the host zircon and more rarely zirconolite occur in skarn in the ertsberg district of irian jaya indonesia unlike in texas related igneous rocks are metaluminous and the hydrothermal system was f poor worldwide hydrothermal zircon other zr phases and ti and al bearing phases occur in skarn epithermal precious metal veins volcanogenic massive sulfide deposits and mylonites we propose that differences in zr mineralogy of igneous source rocks is an important factor in determining the availability of zr to hydrothermal fluids although zr concentrations in the sierra blanca and christmas mountains rhyolites are similar zr enrichment in fluorspar was much greater in the christmas mountains we suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release zr but that zircon was only moderately attacked therefore far more zr was available for transport and subsequent deposition in the christmas mountains than at sierra blanca availability of other trace elements probably is also governed by their mineral host although zr mobility is most common in f rich hydrothermal systems related to alkalic and f rich igneous systems mobility at ertsberg may have been promoted by sulfate complexing

the global monsoon as seen through the divergent atmospheric circulation a comprehensive description is given of the global monsoon as seen through the large scale overturning in the atmosphere that changes with the seasons and it provides a basis for delimiting the monsoon regions of the world the analysis focuses on the mean annual cycle of the divergent winds and associated vertical motions as given by the monthly mean fields for 1979 93 reanalyses from the national centers for environmental prediction national center for atmospheric research ncep ncar and european centre for medium range weather forecasts ecmwf which are able to reproduce the dominant modes a complex empirical orthogonal function analysis of the divergent circulation brings out two dominant modes with essentially the same vertical structures in all months of the year the first mode which depicts the global monsoon has a simple vertical structure with a maximum in vertical motion at about 400 mb divergence in the upper troposphere that is strongest at 150 mb and decays to zero amplitude above 70 mb and convergence in the lower troposphere with a maximum at 925 mb ecmwf or 850 mb ncep however this mode has a rich three dimensional spatial structure that evolves with the seasons it accounts for 60 of the annual cycle variance of the divergent mass circulation and dominates the hadley circulation as well as three overturning transverse cells these include the pacific walker circulation an americas atlantic walker circulation both of which comprise rising motion in the west and sinking in the east and a transverse cell over asia the middle east north africa and the indian ocean that has rising motion in the east and sinking toward the west these exist year round but migrate and evolve considerably with the seasons and have about a third to half of the mass flux of the peak hadley cell the annual cycle of the two hadley cells reveals peak strength in early february and early august in both reanalyses a second monsoon mode which accounts for 20 of the variance features relatively shallow but vigorous overturning with the maximum vertical velocities near 800 mb outflow from 750 to 350 mb and inflow peaking at 925 mb it is especially strong over africa where the shallow mostly meridional overturning migrates back and forth across the equator with the seasons it influences the middle east has a signature over australia and is also an important component of the overturning in the tropical eastern pacific and atlantic and thus of the convergence zones in these regions the relationship of the global monsoon to the regional monsoons is described over six zonal sectors africa australia asia north america south america and the pacific and atlantic oceans only the two ocean areas do not undergo a seasonal reversal required for monsoons although they have direct overturning cells and they nevertheless participate in the global monsoon through the changes in large scale overturning the regional meridional cross sections highlight the importance of the shallow overturning cell in lower troposphere monsoon activity the steadiness of the overturning circulation is determined by comparing the signal of the seasonal mean vertical motions at 500 mb with the standard deviation of the transient daily variations locations where this signal exceeds 60 of the daily noise correspond closely with the regional centers of the monsoon

zircon solubility in alkaline aqueous fluids at upper crustal conditions field evidence and thermodynamic data at ambient conditions suggest that complexing of zr with hydroxyl ions at high ph enhances the solubility of zircon we tested this hypothesis by measuring the solubilities of the assemblages zircon zrsio 4 baddeleyite z b and zircon quartz z q in neutral to alkaline fluids at 0 2 gpa and 450 750 c in neutral to alkaline fluids 0 0 1 1m naoh zircon dissolved incongruently in quartz undersaturated fluids to form baddeleyite at 450 c various na zr silicates precipitated from fluids saturated and undersaturated in quartz we observed no significant dependence of solubility on temperature the measured solubilities of zircon in pure h 2o at 600 and 750 c are only slightly higher than the procedural blank of 3 3 10 7 m zr however the measured solubility of zircon increases with increasing aqueous silica suggesting that zirconium complexes with silica in the fluid at 600 c linear regression of experimental results yielded ln zr 0 25 2 9 ln si where terms in parentheses represent molal concentrations zircon solubility also seems to increase with increasing hydroxyl concentration in the fluid enhanced solubility in silica rich alkaline fluids may cause dissolution reprecipitation of zircon and resetting of its isotopic clocks suggesting that some zircon u pb ages may correspond to fluid events

a fractal measure of mass transfer in fluid rock interaction abstract exploring the mechanism of mass transfer is critical for characterizing geochemical behaviour of elements in fluid rock interaction and is useful for understanding the sequence of hydrothermal alteration the focus of this study is on identifying the spatial relationship between the concentration variation of elements and the distance of samples to the source of the hydrothermal fluid a mobility index mi was applied to represent the mass changes a value of mi 1 indicates gain of elements x from alteration to the source of hydrothermal fluids is observed for the enriched and depleted elements the relation can be expressed as mi cx d and mi cx d respectively where c is a constant and d is the fractal dimension such relations indicate a power law decrease increase of mi with the decreasing degree of alteration the fractal dimension provides an objective measure of the mass gain or loss the larger the fractal dimension the larger the mass change the fractal dimension sequence quantitatively reveals the activity of ore forming elements and the degree of mass changes in the process of hydrothermal fluid rock interaction which can provide critical information on hydrothermal alteration

predictive mineral discovery in the eastern yilgarn craton western australia an example of district scale targeting of an orogenic gold mineral system abstract the eastern yilgarn craton eyc is one of the world s premier gold provinces subject to over a century of mineral exploration prolonged interest in the terrane has led to the assembly of multiple world class data sets suitable for testing district scale targeting methodologies district scale targeting is concerned with identifying a mineral camp 60 km 60 km in size within a prospective region or province 1000 km 1000 km in size exploration at the district scale necessitates the development of predictive exploration models which can be applied to large regions recent advances in the study of the geodynamic evolution and 3d architecture of the eyc together with an understanding of their interrelationship with the orogenic gold mineral system has resulted in identification of critical mineralisation processes responsible for the region s rich gold endowment here we describe and map these critical processes using them as a basis for district scale targeting we relate gold mineralisation to three temporally constrained geodynamic periods integrated with regional hydrothermal alteration unlike many targeting methodologies this methodology does not incorporate the location of known gold deposits in the analysis yet it predicted 75 of known gold mineralisation in 5 of the area the methodology allows critical mineralisation processes to be identified and mapped through time and space these critical processes are mostly generic and can be applied to other granite greenstone orogenic gold regions such as the abitibi in canada an important outcome of this work for the eyc is the identification of a number of new target areas not known currently for significant gold mineralisation in what is otherwise thought to represent a mature terrane for gold exploration

an overview of timing and structural geometry of gold gold antimony and antimony mineralization in the jiangnan orogen southern china abstract the jiangnan orogen located between the yangtze and cathaysia blocks in southern china hosts significant gold and antimony resources long standing controversies over the number and precise timing of gold gold antimony and antimony mineralization event s and the genesis of these deposits limit the understanding and exploration of this giant gold and antimony system together with geological evidence a critical review of the published geochronological data of these deposits suggest that there were two gold events in the triassic 235 ma and early cretaceous 142 130 ma two gold antimony events in the early devonian 402 ma and late triassic middle jurassic 224 163 ma possibly equivalent to the two gold events and one antimony event in the early cretaceous 130 ma there are other possible gold events in the neoproterozoic or at an even older age and ordovician to early devonian which are constrained only by limited geological evidence and a few non robust isotopic ages the regional distribution of the gold gold antimony and antimony districts and deposits therein reveal a first order control on the mineralization by crustal scale faults which acted as ore forming fluid pathways connected to deep fluid and metal source areas second and third order faults that are situated along the jogs of the first order faults especially fault corridors defined by nne ne trending second order faults and third order nw to e w trending discontinuous oblique faults provided favorable locations for pre cretaceous gold antimony mineralization in addition ne trending open anticlines linked to deep crustal levels by first order faults host significant antimony and minor gold mineralization and the curvilinear fanjingshan detachment fault hosts some gold and antimony deposits locally at deposit to orebody scales pre ore barren quartz veins and magmatic dikes were the loci for mineralization in some gold antimony deposits the structural geometry of the pre cretaceous gold and gold antimony deposits suggests an early devonian orogenic gold antimony mineralization event during a transpressional tectonic regime related to coeval intracontinental orogeny between the yangtze and cathaysian blocks in contrast triassic orogenic gold and triassic middle jurassic orogenic gold antimony events are interpreted to relate to distal effects of the collision between the north and south china blocks the structurally contrasting major early cretaceous epizonal antimony mineralization event together with contemporaneous hydrothermal gold mineralization is interpreted to have been controlled by normal faults and pre ore open folds in an extensional tectonic regime related to the distal effects of rollback of the paleo pacific plate after 135 ma for future geoscience based exploration in the orogen documentation and interpretation of critical structural geometries of gold gold antimony and antimony deposits is a vital step towards successful target generation

origin and evolution of ore fluid and gold deposition processes at the giant taishang gold deposit jiaodong peninsula eastern china abstract the early cretaceous taishang gold deposit is the largest deposit in the linglong goldfield jiaodong peninsula with a pre mining endowment of 326 t of gold it is hosted in the 165 150 ma linglong biotite granite and controlled by the nee to ne trending potouqing fault near the northern end of the regional zhaoping fault system hydrothermal alteration is well developed in the footwall of the potouqing fault and is characterized by a narrow zone of sericitization followed by a wider zone of silicification and an even wider zone of potassic alteration the main orebodies no i orebody comprise disseminated and stockwork veinlet systems although about 5 of the resources are in larger quartz veins no ii orebody four stages have been identified for both styles of mineralization on the basis of cross cutting relationships and mineralogical and textural characteristics pyrite quartz sericite stage 1 quartz pyrite stage 2 quartz pyrite base metal sulfide stage 3 and quartz carbonate stage 4 gold was mainly deposited in stages 2 and 3 with minor amounts in stage 1 petrographical microthermometric and laser raman spectroscopic studies on fluid inclusion assemblages in quartz and calcite from the four stages reveal three types of primary fluid inclusions type 1 h 2 o rich aqueous carbonic type 2 co 2 rich aqueous carbonic and rare type 3 carbonic inclusions stage 1 quartz primary inclusions are only type 1 inclusions with an estimated composition of 88 h 2 o 10 co 2 4 5 wt nacl equiv and 0 5 ch 4 with trapping at 336 c and 1 7 kbars the gold rich stages 2 and 3 from both orebodies typically contain primary fluid inclusion assemblages with both type 1 and 2 inclusions which show similar phase transition temperatures and were trapped between 246 and 294 c the stage 4 quartz and calcite contain only primary type 1 inclusions which are estimated to have a composition of 93 h 2 o 6 0 co 2 3 6 wt nacl equiv and trace amount of ch 4 and were trapped at temperatures of 236 c the 34 s values of hydrothermal pyrite from the four stages have a narrow range from 4 5 to 8 0 and are within the ranges for whole rock sulfides from the archean jiaodong group and magmatic pyrite from mesozoic granitoid and intermediate basic dikes the 18 o values of hydrothermal quartz range mainly from 10 9 to 12 5 and remain constant for all four stages calculated fluid 18 o values are 1 3 10 0 the d water values calculated from hydrothermal sericite range from 60 to 45 considering the fluid inclusion compositions 18 o and d compositions of ore forming fluids and regional geological events the most likely ultimate potential fluid and metal reservoirs would be the paleo pacific oceanic slab and its overlying sediments which were thrust below the high grade metamorphic rocks of the jiaodong peninsula the initial ore forming fluids were medium high temperature co 2 rich and low salinity h 2 o co 2 nacl ch 4 homogeneous fluids over the duration of the hydrothermal system the fluid remained fairly consistent in p t x although becoming slightly more water rich during final post ore activity fluid immiscibility occurred during stages 2 and 3 ore deposition at pressures that fluctuated strongly from 1700 to 580 bars during hydrofracturing the hs 2 ion was the most probable gold transporting complex at taishang wall rock sulfidation and episodic pressure drops with associated fluid unmixing and other chemical changes were the two main mechanisms of ore deposition

structural controls on hydrothermal alteration and gold antimony mineralisation in the hillgrove area nsw australia the hillgrove gold antimony deposit is hosted in late palaeozoic biotite grade metasedimentary rocks and permo carboniferous granitoid intrusions of the new england orogen mineralisation occurred at a range of structural levels during rapid uplift in the orogen at 255 245 ma hydrothermal fluids were controlled by extensional faults in a regional scale sinistral strike slip fault system principal faults in this system were developed in and possibly evolved from mylonite zones which were active during late permian tectonics earliest mineralisation formed scheelite bearing quartz veins and these were followed by auriferous arsenopyrite pyrite quartz carbonate veins with minor base metal sulphides this latter type was accompanied by sericitisation and carbonation of the host rock with addition of sulphur arsenic and gold in zones up to 20 m from veins quartz stibnite veins with electrum gold aurostibite and arsenopyrite form a prominent and economically important hydrothermal type with little wall rock alteration but extensive hydrothermal breccia formation and local open space filling textures below a mining depth of 300 500 m this type passes over a short distance downwards into stibnite poor gold bearing veins late stage carbonate stibnite veins with gold and silver sulphosalts cut all earlier veins and have open space filling textures aspects of the hillgrove deposit have similarities to many other orogenic gold deposits in the sw pacific which have been formed at different structural levels hillgrove is distinctive in having evidence for mineralisation at this wide range of structural levels in the one deposit formed progressively during syn orogenic uplift

shallow meridional circulation in the tropical eastern pacific abstract based on four independent datasets this study presents observational evidence of a shallow meridional circulation cell in the eastern tropical pacific in this shallow meridional circulation cell the northerly cross equatorial return flow from the itcz into the southern hemisphere is found immediately above the atmospheric boundary layer in contrast to the classic concept of the hadley type deep meridional circulation whose northerly return flow resides in the upper troposphere the strength and depth of this shallow meridional circulation undergo a distinct annual cycle possible causes and climatic implications of this shallow meridional circulation are discussed

magnitudes spatial scales and processes of environmental antimony mobility from orogenic gold antimony mineral deposits australasia antimony sb is strongly concentrated into hydrothermal mineral deposits commonly with gold in metasedimentary sequences around the pacific rim these deposits represent potential point sources for sb in the downstream environment particularly when mines are developed this study documents the magnitude and scale of sb mobility near some mineral deposits in australia and new zealand two examples of new zealand historic mining areas demonstrate that natural groundwater dissolution of sb from mineral deposits dominates the sb load in drainage waters with sb concentrations between 3 and 24 g l in major streams mine related discharges can exceed 200 g l sb but volumes are small sb flux in principal stream waters is ca 1 14 mg s compared to mine tunnel fluxes of ca 0 001 mg s dissolved sb is strongly attenuated near some mine tunnels by adsorption on to iron oxyhydroxide precipitates similar sb mobilisation and attenuation processes are occurring downstream of the historic active hillgrove antimony gold mine of new south wales australia but historic discharges of sb bearing debris has resulted in elevated sb levels in stream sediments ca 10 100 mg kg and riparian plants up to 100 mg kg for ca 300 km downstream dissolution of sb from these sediments ensures that river waters have elevated sb ca 10 1 000 g l over that distance total sb flux reaching the pacific ocean from the hillgrove area is ca 8 tonnes year of which 7 tonnes year is particulate and 1 tonne year is dissolved

experimental simulation of element mass transfer and primary halo zone on water rock interaction abstract primary halo zone is an important theory for prospecting the deep blind ore body and predicting resource potential the common description of primary halo zone of multiple elements is based on their behaviors during hydrothermal alteration or mineralization a geofluid with multiple elements which are bi cu pb zn cd ag and as bearing ni and mo is prepared to simulate the dispersive transfer of elements in a hydrothermal fluid granite reaction at 15 mpa 100 c using a new constructed core flow through pressure vessel reactor core granite samples with 5 cm long after water rock reaction are cut into ten sections to analyze their major oxides and trace elements according to experiment results and the method of immobile plateau we determine that al and ti are immobile elements during the water rock reaction and the hydrothermal alteration of granite is a mass gained process the mobility index mi of each of experimental elements is calculated based on the immobile component al 2 o 3 the sequence of experimental elements is from as to ag pb zn cu bi ni cd and mo which are sorted on their values of mi in these reacted granite cores from near to far end respecting to the reaction fluid this result is consistent with the empirical sequence of zonation of primary halo elements which is derived from the statistical results from 58 gold deposits in china the denudation coefficient of primary halo zone zf or zfe is proposed to assess the degree of approaching to ore body on these experiments which is the averaged mi ratio of front halo elements to ore body halo elements the denudation coefficient of primary halo zone is applied on the cross section of gold ore body hosted in the granite of the linglong gold deposit located in the jiaodong peninsula of eastern china the degree of approaching to the gold ore body is clearly illustrated by the denudation coefficient of primary halo zone

indian monsoon precipitation isotopes linked with high level cloud cover at local and regional scales abstract precipitation stable isotopes preserve historic changes of evaporation in the source regions and precipitation processes therefore they can be used to reveal regional hydrological cycle dynamics and paleoclimate reconstructions in monsoon regions strong inverse impacts of convection on precipitation isotope ratios have created a debate regarding the interpretation of isotope records as local climate proxies the proportions of stratiform to convective precipitation on water isotopes together with the influence mechanisms on seasonal and interannual scales remain highly uncertain to further address the influence of precipitation patterns on water isotopes we used 10 yrs of precipitation isotope data from the southern tibetan plateau tp to explore the effects of large scale cloud cover and local climate on precipitation isotopes correlation analysis performed between local precipitation 18 o values and different level cloud data indicated significant negative correlations between precipitation isotopes and high level cloud cover on both seasonal and interannual time scales this result suggests that high level convection in the upper moisture transport stream is a main control on precipitation isotopes in the southern tp the clear and coherent variations of precipitation isotopes with the southern oscillation index and outgoing longwave radiation confirmed that strong convection activity in the moisture source region and during transport significantly depleted heavy isotopes in vapor producing substantially decreased precipitation 18 o in the study region these results agree with earlier findings of tree ring cellulose isotope records that correlate with cloud cover but we emphasized the important role of larger scale regional cloud cover we also delineated different maximum correlation zones for seasonal and interannual time scales likely due to different mechanisms these findings further improve the interpretation of paleoisotope records from the indian summer monsoon region

architecture and geodynamic evolution of the st ives goldfield eastern yilgarn craton western australia abstract a new structural evolution consisting of both extensional and contractional events has been defined for the st ives goldfield in the south central kalgoorlie terrane of the eastern yilgarn craton in western australia these events shaped the development of the fault architecture which controlled the location of the regional anticlines the magmatic centres and the deposition of the archaean greenstone successions the fundamental grain of the st ives goldfield is north northwest trending this trend is marked by faults which developed during d1 extension which was oriented east northeast west southwest across these faults we map major stratigraphic changes in the thickness and composition of units especially of the previously undivided black flag group volcaniclastic rocks the centre of the st ives goldfield is dominated by the kambalda anticline this north northwest trending regional fold was likely established early during the d1 extensional history and was fully established during subsequent east northeast oriented d2 contraction the regional anticline is an important architectural element because 1 magmatism and gold mineralising fluids were focussed into this domed region and 2 deformation was partitioned across the limbs and crest of this structure the d3 event involved regional uplift and extension resulting in the formation of late basins merougil conglomerate locally and the emplacement of granitoids sourced from a metasomatised mantle wedge mafic type porphyries the most significant gold event in terms of endowment occurred during d4b sinistral strike slip shearing and associated thrusting e g tramways and republican thrusts these thrusts were previously interpreted as the first contractional structures to deform the area d1 but are here reinterpreted as relatively late d4b in this d4b event the north northwest trending faults underwent sinistral strike slip shearing and were linked across the kambalda anticline by accommodation structures represented by generally east to east northeast trending thrusts reactivation of d1 transfer structures may have influenced the location of these later accommodation structures late stage mineralisation during d5 was the result of dextral strike slip brittle shearing

genesis of the shangxu orogenic gold deposit bangong nujiang suture belt central tibet china constraints from h o c si he and ar isotopes abstract shangxu is an orogenic gold deposit in the bangong nujiang suture zone central tibet china formed in the early cretaceous orogene related to convergence and collision between the qiangtang and lhasa terranes the mineralization at shangxu is hosted by jurassic turbidite sedimentary rocks of the mugagangri group and is associated with a regional fault system hydrothermal minerals develop muscovite carbonate sulfides and chlorite hydrothermal fluids record three main hydrothermal stages based on mineral paragenesis the earliest is barren quartz stage h1 which is pre ore during the early mineralization quartz pyrite stage h2a defined by massive quartz veins with minor euhedral pyrite and gold hydrothermal fluids had a 18ofluid of 6 1 6 4 d of 74 to 116 13cco2 of 5 4 to 7 6 and 30si of 0 1 in the quartz pyrite sulfides stage h2b characterized by abundant quartz granular pyrite muscovite with minor chalcopyrite galena sphalerite and gold fluids had a 18ofluid of 7 8 2 d of 109 to 120 13cco2 of 9 6 and 30si of 0 1 to 0 2 during the ankerite sulfide stage h3a distinguished by abundant ankerite muscovite sulfides with minor quartz and chlorite hydrothermal system had a fluid with 18ofluid of 4 9 5 3 d of 125 3 30si of 0 1 13cco2 of 12 4 in quartz inclusion fluid and 13cco2 of 2 7 in ankerite the calcite sulfide stage h3b is characterized by calcite sulfides with minor quartz and chlorite quartz formed earlier than calcite from a fluid having a 18ofluid of 6 4 d of 112 6 30si of 0 1 and 13cco2 of 7 4 after which calcite precipitated from a hydrothermal fluid with 18ofluid of 5 5 9 13cco2 of 0 5 to 2 8 hydrothermal fluids in h2b pyrite have 3he 4he ratios of 0 27 0 42ra and 40ar 36ar ratios of 313 372 the stable isotope composition of hydrothermal fluids from the shangxu gold deposit is similar to that of typical orogenic gold deposits the early stage h1 methane bearing fluids were probably sourced from the basin sediments leading to precipitation of early barren quartz veins and siderite alteration from the quartz sulfide stage h2 to carbonate sulfide stage h3 hydrothermal fluids were likely derived from dissolution of the marine carbonate cement from sedimentary host rocks during metamorphism at depth the decreasing d and 13c of the ore forming fluids from early to late suggests mixing with 13c depleted oxidized graphite in sedimentary rocks meteoric waters or reation between d depleted organic matters generally these fluids were likely generated at depth through prograde metamorphic devolatilization of hydrous minerals in the deeper equivalents of the sedimentary rocks of the mugagangri group sulfur and gold by inference likely originated from sedimentary diagenetic pyrite or the metasedimentary rocks between the greenschist and amphibolite facies and migrated with the metamorphic fluids during transportation to the site of deposition gold bearing fluids variably reacted with country rocks

whole rock δ o and δ h footprint of the canadian malartic gold deposit pontiac sub province quebec canada the canadian malartic gold deposit was produced by a hydrothermal system that altered the host metasedimentary rocks of the pontiac group metavolcanic rocks of the piche group and associated porphyritic intrusions and mafic dykes the isotopic footprint in pontiac metasedimentary rocks is marked by an increase in 2h values from 91 near mineralization to background values of ca 59 whereas 18o values remain relatively constant near 10 the isotopic footprint in mafic dykes is marked by an increase in 2h values from 84 near mineralization to background values of ca 73 and a decrease in 18o values from 9 8 near mineralization to background values of ca 8 3 kriging of oxygen and hydrogen isotopic compositions around the canadian malartic deposit delineates the isotopic footprint of the deposit in greywackes the 59 2h isopleth encircles the mineralized domain and is elongated towards the northwest and southeast in mafic dykes the 73 2h isopleth encircles the mineralized domain as well as a large area to the south and southeast whereas the 8 3 18o isopleth encircles the center of the mineralized system and extends over an area towards the southeast host rock oxygen and hydrogen isotope compositions therefore define a cryptic alteration footprint up to 2 5 km outside of the canadian malartic deposit the isotopic composition of the metamorphic fluid in equilibrium with the average least altered greywacke at upper greenschist to amphibolite conditions of ca 550 c is approximately 18o 8 6 and 2h 19 this is close to the composition of the mineralizing fluid at the canadian malartic deposit reported by previous studies fluid rock oxygen and hydrogen isotope exchange modeling indicate that the isotopic footprint formed at relatively low fluid rock ratios up to 0 5 at temperatures near 350 400 c

utilization of pre existing competent and barren quartz veins as hosts to later orogenic gold ores at huangjindong gold deposit jiangnan orogen southern china most if not all orogenic gold deposits form during the late stages of deformation in some cases there is barren pre mineralization hydrothermal alteration which may be part of a single progressive hydrothermal event or a temporally distinct event relative to deposition of gold at the huangjindong orogenic gold deposit in the jiangnan orogen of southern china there are two phases of vein generation the earlier of which is largely barren structural analysis petrography mineralogy and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms gold mapping of different generations of gold bearing sulfides reveal the relationship between different phases of hydrothermal alteration and quartz veins pre existing barren and brittle quartz veins which are controlled by tight folds and thrust faults provide favorable competent hosts for later overprinting by gold bearing ore bearing fluids that infiltrated during ongoing reverse sinistral fault movement these overpressured fluids caused hydrofracturing to complete brecciation of segments of the earlier quartz veins and associated pre existing breccias with deposition of auriferous quartz sulfide veins and breccia cements or matrices within them although fluid inclusion data are non definitive fluid pressure fluctuations are interpreted to have resulted in phase separation within the ore fluid which was primarily responsible for destabilization of gold complexes and deposition of native gold with other invisible gold bearing ore related sulfides formed by sulfidation reactions in hydrofractures and breccia matrices thus competent barren quartz veins in fold thrust belts may locally host superimposed gold mineralization and provide favorable targets for gold resources

pore system characterisation in heterogeneous carbonates an alternative approach to widely used rock typing methodologies abstract rock typing is used in carbonate reservoir characterisation to group petrophysically similar rocks for reservoir modelling purposes the focus is often upon bringing together samples with similar porosity permeability and capillary pressure to achieve this rock typing studies are usually conducted primarily on core plugs using routine core analysis data and thin sections however such an approach results in a tendency to focus on grouping samples with consistent petrophysical properties ignoring the geological controls on pore evolution this means that modelling rock types predicatively using 3d geocellular models is not easily accomplished furthermore where geological observations are made they tend to consider only depositional rock properties and not the effects of diagenesis in doing so a key control on the evolution of the carbonate pore network is ignored this paper addresses these issues using a giant carbonate reservoir in northern oman rock types were defined on the basis of pore geometry whilst retaining distinct geological descriptors the aim was to ensure that each rock type could be defined on the basis of both its petrophysical properties and behaviour during hydrocarbon recovery the results show that characterisation of pore heterogeneity is critical to the prediction of flow behaviour under reservoir conditions and that routine petrophysical parameters are often not good indicators of sweep efficiency

expanding the size of multi parameter metasomatic footprints in gold exploration utilization of mafic dykes in the canadian malartic district quebec canada ore forming hydrothermal fluids react differently with different country rocks but few studies have applied this knowledge with the specific goal of expanding the size of hydrothermal footprints in mineral exploration to develop this concept 122 metamorphosed mafic dykes from the world class canadian malartic gold district 18 6 moz au were sampled and analyzed for mineralogy physical properties and lithogeochemistry partial and total digestion the mafic dykes intrude mainly metasedimentary rocks post date d1 deformation and cross cut early d2 quartz monzodiorite intrusions but they were deformed and altered during d2 deformation mineralization and metamorphism they can be subdivided into three groups group 1 dykes are least altered characterized by amphibole rich regional metamorphic assemblages and distributed throughout the pontiac subprovince group 2 and 3 dykes underwent ore related hydrothermal biotite calcite pyrite alteration and are associated with density and volume adjusted concentration gains of over 100 in au w te c s ag cs mo cu k rb se u pb ba f bi sn they define a metasomatic footprint up to 6 km away from the deposit toward the se and up to 2 km away from the deposit toward the sw fifty eight variables that define halos around the canadian malartic deposit have been identified and integrated using principal component analysis pc1 explains 30 of the variance separates least mobile elements from ore related elements and is interpreted to reflect the ore forming alteration process pc2 and pc3 represent igneous processes pc4 highlights the calcite pyrite and biotite alteration spatial variations of the modal abundances of amphibole biotite calcite and pyrite are the simplest expression of the metasomatic footprint and they can easily be documented during exploration at the camp scale

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

origin of the jiaodong type xinli gold deposit jiaodong peninsula china constraints from fluid inclusion and c d o s sr isotope compositions abstract the xinli gold deposit within the sanshandao cangshang gold belt in the jiaodong gold province is a typical jiaojia type ore deposit with high grade quartz sulfide vein veinlet stockworks that cut mesozoic granodiorite four ore stages are distinguished in the following sequences i quartz k feldspar sericite pyrite ii quartz pyrite iii quartz polymetallic sulfide and iv quartz calcite pyrite fluid inclusions in quartz and calcite in the ores contain c o h fluids dominantly of six types with varied liquid vapor ratio ore fluid in the main ore stage is characterized by medium low temperature low salinity reducing condition and nacl h 2 o co 2 ch 4 in composition the 18 o water smow of quartz in ore stages ii and iii range from 2 82 to 5 34 and the d smow are between 69 6 and 88 3 both suggest that the ore fluid was dominantly magmatic water the 13 c pdb of the calcite are from 6 4 to 2 4 indicating mantle contribution to the ore fluid the pyrite 34 s cdt from four ore stages are basically similar varying from 9 42 to 11 62 which implies significant involvement of crustal materials the initial 87 sr 86 sr ratios in the calcite ranging from 0 710657 to 0 711542 also denote a crustal contribution the fluid composition and systematic h o c s sr isotopic data are explained by a model of slab subduction induced gold mineralization in the model the ore fluid and metals were considered to associate with the dehydration and desulfidation of the subducting paleo pacific slab and the subsequent devolatilization of enriched mantle wedge the h 2 o in the fluid might have been released from the devolatilization of enriched mantle wedge the co 2 could be from mantle wedge or subcontinental lithospheric mantle and the sulfur and strontium would be initially released from the subducted seafloor sediments this process was further supported by the geochemical features of intermediate basic dykes contemporaneous to the gold ore deposits the deposit features and ore forming process of the xinli gold deposit hardly concur those of the orogenic gold deposit and the pluton related gold deposit the study supports the argument of that the gold deposits in the jiaodong belong to a unique gold type related to a complex slab subduction related process the geodynamic engine of the jiaodong type gold deposit is specific i e the slab subduction coupling with the consequent lithospheric thinning and structure adjustment

a two stage model for the formation of the granite greenstone terrains of the kalgoorlie norseman area western australia abstract accurate dating of granites and greenstones from the kalgoorlie norseman area shows that there is considerable overlap in time between the formation of granites and greenstones however within any given area the oldest granites are always younger than the oldest greenstones it is suggested that the long lived 100 ma thermal anomaly in the uppermost asthenosphere that gave rise to the greenstones is also responsible for regional metamorphism and widespread crustal melting leading to the production of granites the time lag between greenstone and granite formation reflects the time taken to conduct heat from the mantle to the lower crust anatexis of the lower crust produces a layer of light granitic magma that may temporarily stop the ascent of basaltic magma where this happens the basaltic magma ponds at the base of the crust supplying additional heat and accelerating the melting process eventually the granitic melt layer becomes unstable and rises within the crust areas intruded by granite become topographic highs with topographic lows forming above areas where light melt has been withdrawn from the lower crust when the topographic highs protrude above sea level they are eroded to shed sediments into the topographic lows which contain the basaltic greenstones thus the change from a basalt dominated lower greenstone succession to a sediment and felsic volcanic dominated upper whitestone sequence seen in many granite greenstone terrains results from the intrusion of granitic magma into the upper crust the crust of the kalgoorlie norseman area formed in two distinct stages separated by a time break of up to 700 ma the first stage involved the formation of primitive crust probably above subduction zones this primitive crust was characterized by low rb sr and high sm nd ratios the second stage resulted from a major change in mantle convection that produced thermal upwellings in the mantle below the continents this led to the eruption of basaltic magmas and to metamorphism and anatexis of the lower crust to produce granitic magmas melting reset the rb sr sm nd and u pb systems giving the impression that the second event which occurred at 2 7 ga was a major crust forming event it was in fact a crustal reworking process although some basalt was added to the crust at this time although the two stage history of the kalgoorlie norseman area is clearly seen in the lead isotopes and in zircons it is not readily discernible from the rb sr and sm nd systematics due to mantle like ratios of those elements in the primitive crust

the influence of asphaltene on the interpretation of nmr measurement abstract in the middle south of sichuan province in china there are varying degrees of asphaltene found in the marine carbonate reservoir rock of the gaoshiti moxi longwangmiao formation this study verifies the effect of asphaltene on the interpretation of nuclear magnetic measurements and results are reported with 65 samples from the longwangmiao formation furthermore an additional 48 samples from the same well block in the shallower xixia formation and the deeper dengying formation are used in the experiment to study the influence of a different evolutionary degree of asphaltene on the nuclear magnetic signal the experimental results show that the asphaltene produces a certain amount of nuclear magnetic signals that impact the calculation of the nmr porosity the bound water saturation and the t2 cutoff values reservoirs at different depths have differing asphalt contents and differing degrees of carbonization due to thermal evolution at the real reservoir temperature the asphaltene t2 spectrum form becomes much wider and slower the effects of asphaltic magnetic signals on the calculation of porosity and the t2 cutoff value are much weaker in the deep dengying formation than they are in the shallow xixia formation in order to determine the bound water t2 cutoff the asphalt t2 cutoff is introduced to account for the asphaltene effect in nmr measurement the results also show that the calibrated nmr porosity the bound water saturation and the obtained t2 cutoff are closer to the actual values asphalting could affect nmr measurement and other parameters interpretation the method mentioned in this paper provides the basis for nmr measurement to study the asphaltene reservoir more accurately

evolving metalloid signatures in waters draining from a mined orogenic gold deposit new zealand abstract the globe progress gold mine has recently since 2007 been developed as an open pit on the site of historic underground mine workings on an orogenic type au deposit historic mines followed auriferous quartz veins with arsenopyrite and low sb content ore in the modern mine includes later stage cataclasite with abundant stibnite hence rock exposed in the area has evolved from sb as ratio hco 3 and so 4 both up to 300 mg l dissolved as in drainage waters was typically near 0 5 mg l or below but reached 1 mg l at times and sb reached 3 mg l the sb as ratio of mine drainage waters has evolved from

stable water isotopes and large scale vertical motions in the tropics a complete understanding of the interaction between convection and the large scale circulation in the tropics remains an outstanding problem although there is evidence that the vertical structure of convective heating has great influence in the large scale response and that this structure also presents considerable geographical variations more need to be done one of the questions that are still unanswered is how the vertical structure of the convective heating or similarly of vertical velocity varies across the tropical pacific here it is suggested that some light can be shed on this debate by considering stable water isotopes because these tend to be progressively less abundant with increasing height precipitation associated with top heavy profiles should be expected to be more depleted than that associated with bottom heavy profiles this claim is verified with a variety of data first using observations from iaea wmo global network of isotopes in precipitation stations then using a simple model based on the budget of water isotopes in precipitation finally using a more complex isotope enabled general circulation model evidence provided by these sources confirms that different structures of vertical velocities are associated with different isotopic abundances with top heavy profiles giving rise to more depleted rainfall finally the data from over the pacific although scarce seem to suggest that precipitation in the eastern part is more enriched than in the western thus hinting at velocity profiles over the east being more bottom heavy than over the west pacific

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

regional mineral resources assessment based on rasterized geochemical data a case study of porphyry copper deposits in manzhouli china abstract this study used regional geochemical survey data 1 200 000 scale from the manzouli area of china to assess mineral resources geochemical survey data was rasterized and a geochemical atlas was generated with the image pixel size determined according to geochemical exploration sample point spacing the wunugetushan babayi and badaguan porphyry copper deposits were selected as model areas for the assessment of copper mineral resources three parameters were considered for the calculation of the mineral resources an ore bearing hydrothermal alteration coefficient was determined based on geological characteristics and geochemical characteristics of the model area in order to determine alteration intensity a denudation coefficient was calculated to determine denudation extent and a mineralization intensity coefficient was calculated to determine the intensity of mineralization within each pixel resource estimation was conducted through regression analysis of model deposit resources and coefficients the results can be used to determine prospecting target areas based on frequency classification and can be used to estimate the number of ore deposits results show that resource estimation using rasterized geochemical data provides high prediction precision and accurate positioning

symplectite formation in the presence of a reactive fluid insights from hydrothermal experiments this study describes the microstructural and chemical development of symplectites obtained in fluid mediated mineral replacement experiments during the experiments polymineralic feldspar rich samples were exposed to aqueous na sio2 solution at 600 c and 2 kbar confining pressures for durations of 12 hr to 20 days the resulting reaction rims display high mineralogical and structural complexity and contain two varieties of symplectites represented by nanometre scale intergrowths of gehlenite zeolite and grossular zeolite grains the experimental fluid was enriched in 18o isotope in order to trace oxygen redistribution during the reaction the elevated 18o concentration in the reaction products and the heterogeneity in its distribution suggest that symplectite formation was controlled by dissolution precipitation mechanisms rather than volume diffusion processes microstructural and chemical observations suggest that symplectite formation occurred in multiple stages in response to spatially heterogeneous and temporarily evolving fluid composition at the reaction interfaces hence our results shed light on the fundamental processes involved in symplectite formation improving our ability to interpret symplectite microstructures this article is protected by copyright all rights reserved

hydrothermal alteration zoning and gold concentration at the kerr addison archean lode gold deposit kirkland lake ontario kerr addison a major archcan lode gold deposit of the abitibi belt with a production of approximately 10 x 10 6 oz au approximately 320 metric tons up to 1983 is localized in a zone of talc carbonate and chlorite carbonate rocks immediately south of a regional structural break the kirkland lake larder lake fault zone relict volcanic textures taken in conjunction with the ratios of diag nostic relatively less mobile elements collectively indicate that most of the wall rocks of the mine were originally mafic and ultramafic rocks along with their clastic derivatives regional greenschist facies metamorphism is locally superposed by a distinct zonation of gold associated hydrothermal alteration characterized by massive introduction of co 2 coupled with variable enrichments of alkali metals and calcium which produced systematic trends of alteration mineral assemblages alteration types of the initial stage contain chlorite which is replaced by muscovite or albite in the advanced stage of alteration with a concomitant increase in the proportion of carbonate minerals numerous generations of crosscutting veins are enveloped by alteration borders in which the sequence of the al bearing minerals namely albite mus covite and chlorite develop from the vein to the wall rocks always in a systematic sequence the same sequence is observed at a larger scale from the ore zone to the periphery of the mine area the intensity of alteration can be monitored by saturation indices co 2 ca fe mg for carbonates and 3k na al 3k al and na al for muscovite albite muscovite and albite respectively molar ratios plots of the moving averages of these indices across the 3 850 ft level of the mine reveal a remarkable correspondence to variations of gold abundance suggesting a genetic relationship of gold enrichment to hydrothermal alteration on a broad scale gold is concentrated to the south of the kirkland lake larder lake fault zone and at a more detailed scale in the transition zone between carbonate muscovite and carbonate albite alteration types during advanced alteration fluid x sub co 2 was approximately 0 1 and na k asymp 10 volcanics of the kinojevis and larder lake groups are 18 o enriched relative to pristine tholeiites and possess distinct mineral delta 18 o values probably due to different conditions of marine water alteration during or shortly after extrusion in domains of advanced alteration these are all shifted down to a common narrow bracket here 18 o 16 o and d h data indicate fairly constant temperatures 270 degrees 300 degrees c and a common isotopic composition of hydro thermal fluids delta 18 o 5ppm delta d 30 to 50ppm across the alteration zoning these results are in common with many other archcan lode gold deposits fe dolomite has a uniform delta 13 c value of 2 8 or 0 42 per mil 1sigma throughout the footwall and ore zones but it is enriched by approximately 1 per mil in the graphite free hanging wall rocks fluid delta 13 c value was 4 or 1 per mil reflecting either a magmatic carbon reservoir or mixtures of marine carbonate carbonaceous and magmatic sources the enrichment of gold at one side of the kirkland lake fault zone is interpreted to be the result of development of a metasomatic zoning induced by gradients in oxidation state the precious metal being concentrated in the reducing side zonation of alteration types south of the kirkland lake larder lake fault zone represents various steps of a continuous process of incremental changes of the rocks to adapt to the composition of an externally generated fluid successive generations of fracture arrays and veins have the same alteration patterns and thus the composition of the incoming hydrothermal fluid seems to have remained essentially unchanged through time gold mineralization at the kerr addison mine and its contiguous alteration halo are interpreted to be the result of repeated cycles of hydraulic fracturing fluid penetration and local reaction with rocks fluid rock interaction produced lateral variations of fluid composition which led to gold concentration probably due to gradients in ph preferentially at the interface between the carbonate muscovite and carbonate albite alteration types which is also the site of pyrite concentration the alteration assemblages and specific site of gold pyrite concentration at kerr addison are common to several other described archcan lode gold deposits

geology mineralogy and geochemistry of the shangxu orogenic gold deposit central tibet china implications for mineral exploration abstract shangxu is an orogenic gold deposit within the bangong nujiang suture zone central tibet china it is hosted by turbidite sedimentary rocks of the jurassic mugagangri group the host rocks were metamorphosed to subgreenschist facies prior to being hydrothermally altered adjacent to mineralization hydrothermal minerals in wall rocks consist of muscovite carbonate sulfides and chlorite whole rock geochemistry indicates hydrothermal alteration is characterized by the introduction of k2o co2 and s and leaching of na2o increasing 3 k al and decreasing na al alteration indexes approaching the ore correlate to muscovitization co2 concentration reflects the degree of carbonation which in conjunction with molar mn fe fe ca mg mn and co2 cao can be used to distinguish siderite from ankerite in carbonate alteration mass transfer analysis shows gains in as au co2 w ca cd ni cr sr rb k and losses in na pb cu during hydrothermal alteration in the muscovite alteration zone muscovite within shear zones ms1 shows an increase in fe mg and na towards the ore whereas metamorphic muscovite along cleavage planes and in pressure shadows ms2 and hydrothermal muscovite ms3 change in composition from phengitic mg fe distal to mineralization to paragonitic na adjacent to gold in carbonate alteration the composition in carbonate phases changes from early magnesian siderite to ankerite and then to calcite and dolomite during the evolution of the hydrothermal system siderite spots in host rocks and ankerite in veins wall rock or its replacement of siderite are all enriched in fe mn and depleted in mg from proximal to distal alteration zones pyrite is a dominant mineral in sulfide alteration of the shangxu deposit the earliest framboidal pyrite py1 formed during diagenesis and overprinted by py2 which is recrystallized pyrite associated with burial metamorphism py3 rims and enlarges previous pyrite aggregates or recrystallizes into cubic grains with cracks and quartz pressure shadows during deformation py4 is ore related euhedral pyrite disseminated near gold and formed in hydrothermal stage vein pyrite py5 coexists with marcasite and fills cracks in quartz veins hydrothermal alteration minerals form overlapping alteration haloes surrounding the main auriferous lodes distal muscovitization carbonatization and proximal sulfidation constitute a progressive alteration front from gold the alteration envelope is tabular in shape following the strike and dip of the mineralization and tends to be the widest around the thickest parts of the ore such that the occurrence and thickness of the alteration envelope can be used as an approximate guide to the size of gold mineralization shangxu shares many diagnostic features with turbidite hosted orogenic gold deposits such as bendigo reefton and meguma districts in deposit geology alteration mineralogy and lithogeochemistry

structural event framework for the eastern yilgarn craton western australia and its implications for orogenic gold abstract the nnw trending tectonic grain of the eastern yilgarn craton eyc was established as a result of predominantly ene wsw directed extension d1 and d3 and e ene w wsw d2 d4 to ne sw directed d5 contraction the result has been a succession of nnw striking temporally discrete fabric elements which can be difficult to interpret reliably at any single location despite this many past workers interpreted the nnw striking fabric as the result of only one regional contractional event and used it as a marker for correlating structural events across the region in order to unravel the complexity this paper presents a new sixfold d1 d6 deformation nomenclature based on 10 000 new mesoscale structural observations including their kinematic analysis and cross cutting relationships these mesoscale data were referenced with regional 3d map patterns stratigraphic magmatic metallogenic considerations and deep seismic reflection images this integrated geodynamic architectural approach is applicable to solving structural event histories in other polydeformed terrains gold mineralisation occurred during the first five events but was particularly concentrated from d3 onwards the d3 event marked the most profound change in the tectonic evolution of the eyc with changes in greenstones granites and tectonic mode lithospheric extension and core complexes with the first significant gold deposited within extensional shear zones that dissect the crust later contraction d4 was imposed at a high angle to the previously established anisotropic architecture the outcome was the creation of a new dynamic permeability framework which resulted in gold mineralisation during nnw striking sinistral strike slip faulting and associated thrusting a further stress switch d5 further modified the architecture resulting in n to nne striking dextral strike slip faulting and the final period of gold mineralisation before late stage extension d6

crustal structure of granite greenstone terranes in the eastern goldfields yilgarn craton as revealed by seismic reflection profiling abstract a deep crustal seismic reflection profile across granite greenstones of the eastern goldfields in the archaean yilgarn craton has revealed new constraints on upper crustal geometries the ida fault which forms the western boundary of the eastern goldfields is a 30 east dipping normal fault that can be traced to a depth of about 25 km a mid crustal boundary is displaced with a throw of some 5 km across this fault in a broad region below the ida fault the crust mantle boundary moho is gently warped from a depth of c 33 km in the west to a depth of c 38 km to the east greenstones of the eastern goldfields are underlain by a regional detachment outlined by prominent reflectors at depths between 4 and 7 km open anticlines of the greenstone succession are truncated against this basal detachment or against gently dipping reflectors that can be correlated with terrane and domain boundary faults identified during regional mapping these truncations are not associated with changes in thickness of the successions these geometries suggest several stages of large scale movement possibly including out of section north south movements unresolved by the east west seismic reflection line reflectors representing boundary faults mostly sole out into the basal detachment however the west dipping bardoc shear zone is continuous across the basal detachment and may have been reactivated as a conjugate fault to the late stage ida fault granite plutons are imaged as steep sided and flat bottomed opaque regions locally underlain by continuous reflectors indicating greenstone stratigraphy these geometries in combinations with the map observations suggest that the plutons were emplaced as elongate ovoid sheets presumably fed through fractures

shear strain and volume change associated with sigmoidal vein arrays in the boda claystone abstract the boda claystone formation a potential host rock for high level nuclear waste in hungary contains numerous sigmoidal vein arrays with angular vein terminations these veins are excellent strain markers and can be used in the interpretation of palaeo environments sigmoidal vein arrays were investigated in the baf 2 well which penetrates the formation to depths above 900 m with nearly 100 core recovery the veins have antitaxial growth morphologies and are filled by calcite anhydrite and barite celestine phases to estimate the volume change in shear zones we used geometric mass balance and density change calculations these methods exhibit different volume loss rates the geometric approach indicates a large amount of volume loss whereas the isocon method and density change approach suggest that volume loss in the shear zones was less than 10 we propose that the volume loss in the shear zone occurred because of tectonic compaction vein shapes indicate formation under compressional stress fields based on their intersections with other vein generations the sigmoidal en echelon vein generation is determined to be one of the youngest structures in the well which probably formed during a late cretaceous compression event

wallrock alteration in the bendigo gold ore field victoria australia uses in exploration the bendigo goldfield which has produced most of victoria s gold 22 million ounces 684 3 ton consists of numerous deposits located mainly along narrow parallel trending anticlinal domes separated by 100 to 400 m the individual domes are parts of a regional anticlinorium in lower ordovician sedimentary rocks highest gold ore values are generally located in the eastern limbs and particularly in the apical areas of the smaller individual anticlinal domes and in the central part of the more regional anticlinorium alteration present in metasandstone units in the nell gwynne anticline consists of phengitic sericite to 15 vol chlorite to 7 carbonates siderite sideroplesite ankerite and calcite to 10 and sulphides arsenopyrite pyrite chalcopyrite and sphalerite to 5 the alteration generally follows the trend of the structure extending upward and above mineralisation in anticlinal areas and below largely unmineralised synclinal areas phengitic sericite extends furthest to at least 150 m above mineralised saddle reef positions chlorite to 130 m sulphides to 80 m and carbonate to 50 m chlorite geothermometry suggests temperatures of 260 to 290 c for the alteration the sequence of carbonate precipitation generally is from siderite early sideroplesite ankerite and calcite the more fe rich carbonates tend to occur near the apical parts of the anticlinal domes arsenopyrite occurs within 10 m of the veins while hydrothermal pyrite chalcopyrite and sphalerite all extend to 50 m framboidal pyrite possibly greigite present in unaltered metasediments becomes progressively recrystallised and replaced by hydrothermal pyrite chalcopyrite and sphalerite as mineralisation is approached hydrothermal pyrite is generally euhedral and anomalous in having high as contents when compared to framboidal pyrite maximum au grades 205 ppm occur in the saddle reef position and below a thick shale unit lower grade mineralisation 0 5 6 0 ppm occurs above this in the overlying stratigraphy as and pb anomalies cross cut the alteration zoning and occur as plume like dispersion haloes above the mineralisation the au occurs in and near the as plume cu concentrations reach their maximum values adjacent to high au values measured co2 values confirm the observed carbonate distributions h2o and zn values in the section show relatively random distributions two separate stages of mineralisation are indicated the earlier localised within classic saddle reef structures and containing the highest au cu and some as and a later cross cutting stage of mineralisation associated with high as the alteration is mainly associated with the former

comparison of contrasting gold mine processing residues in a temperate rain forest new zealand abstract processing residues high in metallic elements are the legacy of historic gold processing sites concentrating naturally occurring metalloids in the ore as sb as well as chemicals and metals added during processing to recover the gold zn pb hg this study uses electron microscopy to investigate the link between variations in processing residue mineralogy and the processing technique used to extract the gold semi cemented amorphous ferric arsenate and as bearing iron oxyhydroxides attenuating as zn and pb are the products of the simplest processing technique of crushing sulphide concentration and gold recovery through hg amalgamation zinc pb and ca added during cyanidation form zn rich carbonate and zn oxide mineralogy ore roasting concentrates as to elevated levels 35 wt as well as concentrating sb from the ore and hg from the amalgamation process roasting rapidly oxidises sulphide concentrates producing toxic and highly mobile arsenolite as2o3 as3 roaster tailings processed by all of these techniques crushing roasting and cyanidation are largely comprised of as hematite and quartz mine residue weathering causes localised acidification and leaching of metallic elements along with the high rainfall on these site remobilising elements lime added during processing and the carbonate host rock neutralises this acidification the formation of secondary fe3 oxyhydroxide minerals formed during residue weathering and oxidisation sequesters as zn and pb redox conditions and the ph of a site will control the stability of these secondary minerals the toxicity of a site processing residue can be correlated to the processing technique used with characterisation of processing residue mineralogy having important implications for site remediation and management

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

behavior of major and trace elements during weathering of sericite quartz schist abstract two regolith profiles developed on the sericite quartz schist in subtropical humid environment were selected to investigate behaviors of major and trace elements during weathering in mengman gold deposit of yunnan province china one profile located in the mining district sheared by a fault and the other was outside the mining area which represented the normal weathering profile on the schist regolith samples were collected in both profiles sequentially thirteen major oxides and 23 trace elements including ree were analyzed and their behaviors were compared in these two profiles based on the idea that immobile element is just a relative notion we presented a method of immobile plateau to determine immobile elements during each stage in a progressive geochemical process and used mass ratio mr to calculate the percentage of gain or loss x gp of each element during the whole process in both profiles only tio 2 was immobile during the whole weathering the regolith profile formed on the mineralized schist recorded the weathering process more sensitively than the regolith profile on the normal schist ree was mobile and fractionated during the schist weathering lree was loss in mass during the soil development stage which resulted from the chemical leaching but was gain in mass during the pedogenesis stage because of the preferential absorption of soil to lree the lree depletion near the fault during weathering was the collective effects of chemical leaching and physical accumulation hfse were all mobile in the mineralized regolith profile especially near the fault but nb ta and zr hf were covariant in both profiles during the schist weathering

the use of lithogeochemistry in delineating hydrothermal fluid pathways and vectoring towards gold mineralization in the malartic district quebec abstract the world class oxidized intrusion related canadian malartic gold deposit with reserves estimated at 5 56 moz au grading 1 10 g t au and a total geological endowment of 16 3 moz au is one of the largest gold deposits in the archean superior province of canada the gold mineralization is hosted predominantly by pontiac group metasedimentary rocks piche group metavolcanic rocks and quartz monzodiorite to granodiorite porphyritic intrusions the ore takes the form of a low grade envelope of disseminated pyrite 0 35 to 1 g t au grading inwards into higher grade 1 g t au stockwork and breccia zones hydrothermal alteration in the metasedimentary rocks is zonally distributed around the fluid pathways proximal alteration is characterized by a microcline albite quartz replacement type assemblage with lesser phlogopite calcite fe dolomite pyrite and rutile the distal alteration assemblage comprises biotite microcline albite phengite quartz calcite pyrite and rutile in this study we assess the magnitude and distribution of fluid rock interaction in the metasedimentary rocks of the malartic district the metaturbidites are separated into four lithotypes based on grain size to reduce the effects of primary depositional processes on mass change calculations despite the variability in protolith composition the metasedimentary rocks define a geochemically consistent cogenetic sequence the results of the mass transfer calculations indicate progressive gains in co2 s k2o and loi as well as au te w ag as be sb bi mo and pb from background to distal and proximal alteration zones relative to the least altered samples molar element ratio analysis alkali aluminum indicates an increase in alkali metasomatism k and na adjacent to the main hydrothermal fluid pathways which is manifested by the progressive stabilization of microcline and albite at the expense of oligoclase biotite and white mica ore associated pathfinder elements delineate broad enrichment patterns around the deposit and are used to understand hydrothermal fluid circulation in the malartic district a statistical approach based on a comparison of the mass change results with the background composition provides robust constraints on the magnitude and extent of the lithogeochemical haloes generally the alteration forms envelopes that extend along the s2 fabric with the largest lithogeochemical anomalies e g au w te and ag reaching up to 10 km in length and 2 km in width the results of this study demonstrate that whole rock lithogeochemistry can provide a valuable tool with which to define vectors toward gold mineralization in a regional exploration context

alteration patterns linked to high grade gold mineralization at the wattle dam deposit western australia abstract sharp physio chemical gradients occur in archean gold systems yet they are often poorly defined these physio chemical gradients can provide windows into fluids that deposit high grade gold mineralization recognizing different alteration styles and fluid types in mineral systems helps define processes that led to the deposition of high grade gold here we report on the architecture and chemical gradients across the komatiite hosted wattle dam gold deposit in the eastern yilgarn craton western australia which is one of australia s highest grade gold deposits the deposit notably contains millimeter to centimeter thick gold only veins with an absence of quartz whole rock geochemistry shows that high grade gold veins are hosted in komatiite flow margins facies with olivine orthocumulate komatiites in the footwall interbedded graphitic shale close to the lode and komatiite basalt in the hangingwall the komatiite flow margin facies that hosts high grade gold veins have been pervasively altered by stage 1 biotite actinolite stage 2 gold veins cross cut the biotite actinolite altered komatiite and these veins contain thin

single grain pyrite rb sr dating of the linglong gold deposit eastern china abstract this study employs the single grain pyrite rb sr technique to date mineralization using the example of the linglong lode gold deposit jiaodong peninsula eastern china the gold deposits in this area are interpreted to have a consistent spatial temporal relationship with widespread late jurassic early cretaceous magmatism in eastern china likely related to lithospheric thinning around 120 ma pyrite of the linglong gold mine contains different types of mineral inclusions such as sericite and feldspar that cause distinguishable variations in rb and sr contents and rb sr ratios four pyrite samples from veins of different mineralization stages give an average isochron age of 120 6 0 9 ma analyses of one quartz and two sericite samples yield isochron ages between 122 ma and 120 ma dating of mineralization is often hampered by disequilibrium of isotopic systems and or the lack of suitable minerals for dating purposes hence the successful attempt of the single grain rb sr technique of pyrite which occurs as a common mineral phase in orebodies and is genetically related to the mineralization has great potential for precise geochronology of hydrothermal mineral deposits

geochemical behaviors of different element groups during shale weathering at the susquehanna shale hills critical zone observatory major and trace element concentrations were measured in bedrock regolith and stream sediments from a first order catchment developed entirely on grey shale in central pennsylvania usa these elements can be classified into five major groups based on statistical data analysis the presence of different elemental groups is due to the mineralogical origin cycling processes and geochemical properties of these elements during soil formation a better understanding of the behaviors of these elements during chemical weathering would allow for their possible use as natural tracers in critical zone processes

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

wallrock alteration associated with turbidite hosted gold deposits examples from the palaeozoic lachlan fold belt in central victoria australia abstract the study of wallrock alteration phenomena around slate belt hosted gold deposits can provide valuable information regarding the physico chemical conditions of the ore bearing fluids and the timing relationships between deformation peak metamorphism granitoid emplacement and mineralisation thus studying the processes involved in the interaction of the hydrothermal fluids with the host rock is critical in order to constrain genetic models and ultimately as a tool for exploration largely due to the characteristics of the host rocks turbidite hosted mesothermal gold deposits were historically believed to lack such diagnostic alteration haloes and their study has long been neglected however recent studies in the palaeozoic lachlan fold belt in southeastern australia and in similar tectonic settings elsewhere have demonstrated that alteration around many of these deposits is more widespread and pervasive than previously thought a review of existing information and new data strongly support the viability of studying hydrothermal alteration as a guide to turbidite hosted mineralisation and as an indicator of the character of the solutions associated with ore deposition characteristically the auriferous reef structures are surrounded by broad bleached zones while disseminations of carbonate spots pyrite and arsenopyrite porphyroblasts are the most obvious features of alteration depending on parameters such as fault geometry fluid pressure and reactivity and permeability of the host rocks these disseminations can occur up to a kilometre away from the auriferous structures sericitisation and carbonatisation are commonly discernible within 3 to 10 m wide haloes wallrock alteration chemistry of turbidite hosted gold deposits in the lachlan fold belt shows consistent enrichments of k2o co2 s and as and the anomalous values of these elements also provide the most useful dispersion haloes for turbidite hosted gold exploration due to both their regularity and extent

permeability prediction in tight carbonate rocks using capillary pressure measurements abstract the prediction of permeability in tight carbonate reservoirs presents ever more of a challenge in the hydrocarbon industry today it is the aim of this paper to ascertain which models have the capacity to predict permeability reliably in tight carbonates and to develop a new one if required this paper presents i the results of laboratory klinkenberg corrected pulse decay measurements of carbonates with permeabilities in the range 65 nd to 0 7 md ii use of the data to assess the performance of 16 permeability prediction models iii the development of an improved prediction model for tight carbonate rocks and iv its validation using an independent data set initial measurements including porosity permeability and mercury injection capillary pressure measurements micp were carried out on a suite of samples of kometan limestone from the kurdistan region of iraq the prediction performance of sixteen different percolation type and poiseuille type permeability prediction models were analysed with the measured data analysis of the eight best models is included in this paper and the analysis of the remainder is provided in supplementary material some of the models were developed especially for tight gas sands while many were not critically none were developed for tight gas carbonates predictably then the best prediction was obtained from the generic model and the rgpz models r 2 0 923 0 920 and 0 915 respectively with other models performing extremely badly in an attempt to provide a better model for use with tight carbonates we have developed a new model based on the rgpz theoretical model by adding an empirical scaling parameter to account for the relationship between grain size and pore throat size in carbonates the generic model the new rgpz carbonate model and the two original rgpz models have been tested against independent data from a suite of 42 samples of tight solnhofen carbonates all four models performed very creditably with the generic and the new rgpz carbonate models performing well r 2 0 840 and 0 799 respectively it is clear from this study that the blind application of conventional permeability prediction techniques to carbonates and particularly to tight carbonates will lead to gross errors and that the development of new methods that are specific to tight carbonates is unavoidable

multivariate anomaly modeling of primary geochemical halos by u spatial statistic algorithm development a case study from the sari gunay epithermal gold deposit iran abstract an accurate separation of anomalous areas values in primary geochemical halos with heterogeneous spatial variations requires an appropriate algorithm that considers the complex patterns and multivariate relationships of the input geochemical data there are several problems in multivariate modeling of geochemical compositional data because such data present spurious values of spatial correlation between the variables to address this problem this paper proposes an improved u spatial statistic algorithm for 3d multivariate anomaly modeling of the geochemical dataset with compositional nature at the sari gunay epithermal gold deposit nw iran to perform 3d multivariate modeling isometric logarithmic ratio ilr as an effective method to transform compositional data from the simplex to real space and minimum maximum autocorrelation factor maf as a multivariate geostatistical method were used in an integrated analysis in comparison to the other separation techniques this integrated approach has an advantage to control the heterogeneous spatial variations in the input data in this approach we improved the u spatial statistic method by using the variogram tool theory by using this approach we identified the primary geochemical haloes associated with au as sb hg front halo elements cu ag pb near ore halo elements and ni co tail halo elements at the sari gunay gold depsoit the results were validated by using contrast coefficient and exploratory index tools by examining the 3d multivariate primary anomalous geochemical halos zones of possible hidden epithermal gold and porphyry copper gold mineralizations were recognized at this deposit for future exploration