lewis ponds a hybrid carbonate and volcanic hosted polymetallic massive sulphide deposit new south wales australia the lewis ponds zn pb cu ag au deposit located in the eastern lachlan fold belt central western new south wales exhibits the characteristics of both volcanic hosted massive sulphide and carbonate hosted replacement deposits two stratabound massive to disseminated sulphide zones main and toms occur in a tightly folded upper silurian sequence of marine felsic volcanic and sedimentary rocks they have a combined indicated resource of 5 7 mt grading 3 5 zn 2 0 pb 0 19 cu 97 g t ag and 1 9 g t au main zone is hosted by a thick unit of poorly sorted mixed provenance breccia limestone clast breccia and quartz crystal rich sandstone whereas toms zone occurs in the overlying siltstone pretectonic carbonate chalcopyrite pyrite and quartz pyrite stringer veins occur in the footwall porphyritic dacite south of toms zone strongly sheared dolomite chalcopyrite pyrrhotite veins directly underlie the toms massive sulphide lens the mineralized zones consist predominantly of pyrite sphalerite and galena paragenetically early framboidal dendritic and botryoidal pyrite aggregates and tabular pyrrhotite pseudomorphs of sulphate occur throughout the breccia and sandstone beds that host main zone but are rarely preserved in the annealed massive sulphide in toms zone main and toms zones are associated with a semi conformable hydrothermal alteration envelope characterized by texturally destructive chlorite dolomite and quartz rich assemblages dolomite chlorite quartz calcite and sulphides have selectively replaced breccia and sandstone beds in the main zone host sequence whereas the underlying porphyritic dacite is weakly sericite altered vuggy and botryoidal textures resulted from partial dissolution of the dolomite altered sedimentary rocks and unimpeded growth of base metal sulphides carbonate and quartz into open cavities the intense chlorite rich alteration assemblage underlying toms zone grades outward into a weak pervasive sericite quartz assemblage with distance from the massive sulphide lens limestone clasts and hydrothermal dolomite at lewis ponds are enriched in light carbon and oxygen isotopes the dolomite yielded 13cvpdb values of 11 to 1 and 18ovsmow values of 6 to 16 liquid vapour fluid inclusions in the dolomite have low salinities 1 4 7 7 equiv wt nacl and homogenization temperatures 166 232 c for 1 000 m water depth dolomitization probably involved fluid mixing or fluid rock interactions between evolved heated seawater and the limestone bearing facies prior to and during mineralization 34svcdt values range from 2 0 to 5 0 in the massive sulphide and 3 9 to 7 4 in the footwall carbonate chalcopyrite pyrite stringer veins indicating that the hydrothermal fluid may have contained mamgatic sulphur and a component of partially reduced seawater the sulphide mineral assemblages at lewis ponds are consistent with moderate to strongly reduced conditions during diagenesis and mineralization low temperature dolomitization of limestone bearing facies in the main zone host sequence created secondary porosity and provided a reactive host for fluid rock interactions main zone formed by lateral fluid flow and sub seafloor replacement of the poorly sorted breccia and sandstone beds base metal sulphide deposition probably resulted from dissolution of dolomite fluid mixing and increased fluid ph pyrite sphalerite and galena precipitated from a relatively low temperature 150 250 c hydrothermal fluid in contrast toms zone was emplaced into fine grained sediment at or near the seafloor above a zone of focused up flowing hydrothermal fluids copper rich assemblages were deposited in the toms zone footwall and massive sulphide lenses in main and toms zones as the hydrothermal system intensified during the d1 deformation fracture controlled fluids within the lewis ponds fault zone and adjacent footwall volcanic succession remobilized sulphides into syntectonic quartz veins lewis ponds is a rare example of a synvolcanic sub seafloor hydrothermal system developed within fossiliferous limestone bearing facies the close spatial association between limestone hydrothermal dolomite massive sulphide and dacite provides a basis for new exploration targets elsewhere in new south wales

the role of attenuation in 2d full waveform inversion of shallow seismic body and rayleigh waves abstractfull waveform inversion fwi of rayleigh waves is attractive for shallow geotechnical investigations due to the high sensitivity of rayleigh waves to the s wave velocity structure of the subsurface in shallow seismic field data the effects of anelastic damping are significant dissipation results in a low pass effect as well as frequency dependent decay with offset we found this by comparing recorded waveforms with elastic and viscoelastic wave simulation the effects of anelastic damping must be considered in fwi of shallow seismic rayleigh waves fwi using elastic simulation of wave propagation failed in synthetic inversion tests in which we tried to reconstruct the s wave velocity in a viscoelastic model to overcome this q values can be estimated from the recordings to quantify viscoelasticity waveform simulation in the fwi then uses these a priori values when inferring seismic velocities and density a source wavelet correction which is inevitable in fwi of field data can compensate a

an 8000 year history of landscape climate and copper exploitation in the middle east the wadi faynan and the wadi dana national reserve in southern jordan abstract investigations of geomorphology geoarchaeology pollen palynofacies and charcoal indicate the comparative scales and significance of palaeoenvironmental changes throughout the holocene at the junction between the hyper arid hot wadi arabah desert and the front of the mediterranean belt mountains of edom in southern jordan through a series of climatic changes and episodes of intense mining and smelting of copper ores early holocene alluviation followed the impact of neolithic grazers but climate drove fluvial geomorphic change in the late holocene with a major arid episode corresponding chronologically with the little ice age causing widespread alluviation the harvesting of wood for charcoal may have been sufficiently intense and widespread to affect the capacity of intensively harvested tree species to respond to a period of greater precipitation deduced for the roman byzantine period a property that affects both taphonomic and biogeographical bases for the interpretation of palynological evidence from arid lands with substantial industrial histories studies of palynofacies have provided a record of human and climatic causes of soil erosion and the changing intensity of the use of fire over time the patterns of vegetational climatic change and geomorphic changes are set out for this area for the last 8000 years

short wave infrared spectral and geochemical characteristics of hydrothermal alteration at the archean izok lake zn cu pb ag volcanogenic massive sulfide deposit nunavut canada application in exploration target vectoring short wave infrared swir field and laboratory spectra were used to identify and characterize hydrothermal alteration mineral chemical variability in host rocks proximal to the izok lake zn cu pb ag volcanogenic massive sulfide vms deposit in nunavut canada the deposit is hosted within a sequence of predominantly felsic pyroclastic rocks of archean age that are regionally metamorphosed to amphibolite facies these rocks are characterized by the muscovite biotite sillimanite and chlorite biotite cordierite mineral suite proximal to the deposit white micas are al rich to potassic muscovite and the biotite and chlorite are mg rich in areas that are immediately outboard of the proximal alteration zones rocks are altered to al poor muscovite and intermediate to fe rich biotite and chlorite outboard of this distal areas are characterized by potassic muscovite and mg rich biotite and chlorite the white micas and biotite chlorite group minerals display considerable variation in their al oh and fe oh absorption feature wavelength positions the variations in muscovite and biotite chlorite compositions as determined by the al oh and fe oh absorption feature wavelength positions broadly correlate with changes in hydrothermal alteration intensity as measured by the ishikawa and chlorite carbonate pyrite alteration indices our findings suggest that the large scale alteration intensity trends of the izok lake study area can be elucidated using the spectral properties of the hydrothermal alteration minerals

using physical volcanology chemical stratigraphy and pyrite geochemistry for volcanogenic massive sulfide exploration an example from the blake river group abitibi greenstone belt an innovative approach to enhance volcanogenic massive sulfide vms exploration in regions outside of mining camps is to first use physical volcanology with litho and chemostratigraphy to establish the location of effusive centers in the volcanic units and use pyrite geochemistry in sulfide bearing stratified intervals with whole rock geochemistry in the underlying volcanic units to identify hydrothermal upflow zones this methodology is illustrated by this study in the archean blake river group within the abitibi greenstone belt of quebec and ontario the blake river group contains numerous vms deposits yet large segments remain underexplored including the hebecourt formation which contains four tholeiitic units that range from basalt to rhyolite in composition effusive centers are located for three felsic units and subunits 1 low ti porphyritic subunit of the main rhyolite 2 high ti aphyric subunit of the main rhyolite and 3 the upper rhyolite and for a basaltic andesite unit stringer and disseminated zn cu mineralization occurs within the flank breccia of the low ti rhyolite dome an inferred vent area for an overlying basaltic andesitic unit has also been identified in this area illustrating the coincidence of hydrothermal upflow zones with volcanic vents la icp ms analysis of pyrite grains from several sulfide bearing stratified intervals indicates two broad areas of higher cu zn au and ag contents the eastern region corresponds to known volcanic vents and mineralization the western region also indicates upflow of cu bearing hydrothermal fluids and corresponds to a possible effusive center for the high ti subunit the western region does not contain known mineralization at lower stratigraphic positions but it has not been thoroughly explored

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

the precious metal rich south hercules mineralization western tasmania a possible subsea floor replacement volcanic hosted massive sulfide deposit south hercules is a newly delineated disseminated to semimassive base metal sulfide deposit with significant gold and silver grades the deposit lies a kilometer along strike south from the hercules mine a 2 0 mt polymetallic massive sulfide deposit in the mount read volcanics belt western tasmania the mineralization and alteration at the south hercules deposit has been divided into two major facies the mineralized sulfide facies and the carbonate facies the carbonate facies interfingers with and surrounds the upper part of the sulfide facies the mineralized sulfide facies includes three zones a massive pyrite or barite zone a siliceous or stringer sulfide zone and a sphalerite galena or pyrite zone the carbonate facies also consists of three zones a blebby carbonate chlorite zone a massive carbonate zone and a cherty carbonate zone the massive pyrite or barite zone contains significant gold grades and occurs mostly at the top of the sulfide facies this zone is characterized by colloform aggregates of pyrite and compact massive pyrite in chert the siliceous or stringer sulfide zone is a silicified and sericitized tuffaceous shale with disseminated to stringer pb zn mineralization the massive sphalerite galena or pyrite zone contains subordinate gold and silver and occurs as thin lenses toward the base of the sulfide facies significant zinc and lead values occur throughout the mineralized sulfide facies with the highest values occurring along stratigraphically controlled layers copper values are conspicuously low throughout the south hercules deposit rarely exceeding 0 5 percent the carbonate facies is conspicuous by its lack of significant precious metal and base metal grades mineragraphic investigations indicate that electrum occurs in two general associations with pyrite and with other sulfides such as sphalerite galena and tetrahedrite the electrum locked in the pyrite euhedra is generally fine grained 5 40 mu m whereas the electrum associated with other sulfides displays a range between 5 and 200 mu m microprobe analysis indicates that the fineness 1 000 au au ag wt for gold in the deposit ranges from 427 to 965 the delta 18 o isotope composition of the carbonate varies from 9 8 to 16 7 per mil and the delta 13 c values range from 3 5 to 0 6 per mil the calculated isotopic composition of the ore fluid at 150 degrees and 250 degrees c is consistent with derivation from evolved seawater sulfur isotope analyses of selected samples from the mineralized facies give delta 34 s values of 8 2 to 14 1 per mil which is in the same range as values from the rosebery deposit and consistent with values of sulfur derived from cambrian seawater the form texture mineralogy stable isotopes and fluid inclusion data for the south hercules deposit suggest that it was formed largely by a subsea floor replacement process from relatively low temperature 150 degrees 250 degrees c near neutral fluids the very low copper content and relatively high au ag pb zn ratio of the ores support a low temperature environment in which gold was transported as the au hs 2 super complex and pb and zn were transported as chloride complexes

regional alteration systems associated with volcanogenic massive sulfide mineralization at panorama pilbara western australia outstanding exposure across the panorama district of the archean pilbara block of western australia reveals a cross section through a ca 3 24 ga massive sulfide bearing volcanic pile and an underlying coeval subvolcanic intrusion in an area of low metamorphic grade and very low strain this has provided a rare opportunity to map a complete regional scale hydrothermal alteration system associated with volcanogenic massive sulfide mineralization and to assess the role of a subvolcanic intrusion in driving such a system four major alteration facies can be defined in the panorama district these are feldspar bearing background alteration and feldspar sericite quartz alteration and completely feldspar destructive sericite quartz and chlorite quartz alteration these alteration facies affect all of the volcanic pile and the upper parts of the underlying subvolcanic intrusion regional semiconformable alteration zones which are predominantly feldspar bearing are crosscut by broad corridors of transgressive feldspar destructive alteration a convective hydrothermal model is invoked to explain this distribution of alteration facies where semiconformable alteration zones represent seawater recharge and transgressive feldspar destructive alteration zones mark the path of evolved seawater discharging back to the sea floor the interpreted discharge sites are coincident with base metal sulfide deposits at the top of the volcanic pile geologic relationships and the distribution of alteration zones clearly implicate the strelley granite as the subvolcanic intrusion which drove the hydrothermal alteration systems granophyric textures and miarolitic cavities in the upper parts of the intrusion suggest that a magmatic fluid phase was exsolved early in its crystallization history granite hosted copper zinc tin veins near the top of the intrusion are interpreted to be a product of this magmatic fluid this raises the possibility of a substantial contribution of magmatically derived metal to the overlying volcanogenic massive sulfide hydrothermal alteration systems

hydrothermally precipitated mixed layer illite smectite in recent massive sulfide deposits from the sea floor mixed layer illite smectite i s in recent massive sulfide deposits from a seamount near the east pacific rise has been studied by x ray powder diffraction xrd and scanning and transmission electron microscopy sem tem the i s fills pore space between quartz and sulfides and xrd and tem analyses indicate that the i s contains 25 45 smectite with r1 type ordering isisis microprobe and analytical electron microscope analyses indicate a rectorite like composition k being the dominant interlayer cation the occurrence of the i s within a hydrothermally precipitated sulfide deposit the pore filling texture and the internal structure of the i s are all consistent with direct precipitation from hydrothermal solutions direct precipitation of i s from solution has two important implications first some sericite in ancient volcanogenic massive sulfide deposits may have similarly originated as hydrothermal precipitates rather than as alteration products with implications for mobility and transport of al second direct precipitation of r1 ordered i s from fluid implies that during diagenetic evolution of smectite to illite the sequence of smectite random i s ordered i s illite may not be followed

alteration mineralogy lithochemistry and stable isotope geochemistry of the murgul artvin ne turkey volcanic hosted massive sulfide deposit implications for the alteration age and ore forming fluids abstract the murgul artvin ne turkey massive sulfide deposit is hosted dominantly by late cretaceous calc alkaline to transitional felsic volcanics the footwall rocks are represented by dacitic flows and pyroclastics whereas the hanging wall rocks consist of epiclastic rocks chemical exhalative rocks gypsum bearing vitric tuff purple vitric tuff and dacitic flows multi element variation diagrams of the hanging wall and footwall rocks exhibit similar patterns with considerable enrichment in k rb and ba and depletion in nb sr ti and p the chondrite normalized rare earth element rees patterns of all the rocks are characterized by pronounced positive negative eu anomalies as a result of different degrees of hydrothermal alteration and the semi protected effects of plagioclase fractionation mineralogical results suggest illite illite smectite chlorite kaolinite and chlorite in the footwall rocks and illite smectite kaolinite and chlorite illite in the hanging wall rocks overall the alteration pattern is represented by silica sericite chlorite and chlorite carbonate epidote sericite and quartz albite zones increments of ishikawa alteration indexes resulting from gains in k 2 o and losses in na 2 o and the chlorite carbonate pyrite index towards to the center of the stringer zone indicate the inner parts of the alteration zones calculations of the changes in the chemical mass imply a general volume increase in the footwall rocks abnormal volume increases are explained by silica and iron enrichments and a total depletion of alkalis in silica zone relative k increments are linked to the sericitization of plagioclase and glass shards and the formation of illite smectite in the sericite zone in addition fe enrichment is always met by pyrite formation accompanied by quartz and chlorite illite is favored over chlorite smectite and kaolinite in the central part of the ore body due to the increase in the al k na ca ratio although the rees were enriched in the silicification zone light rees show depletion in the silicification zone and enrichment in the other zones in contrast to the heavy rees behavior hydrothermal alteration within the hanging wall rocks apart from the gypsum bearing vitric tuffs is primarily controlled by chloritization with proportional fe and mg enrichments and sericitization the 18 o and d values of clay minerals systematically change with increasing formation temperature from 6 6 to 8 7 and 42 to 50 for illites and 8 6 and 52 for chlorite respectively the o and h stable isotopic data imply that hydrothermal alteration processes occurred at 253 332 c for illites and 136 c for chlorite with a temperature decrease outward from the center of the deposit the positive 34 s values 20 3 to 20 4 for gypsum suggest contributions from seawater sulfate reduced by fe oxide hydroxide phases within altered volcanic units thus the hydrothermal alteration possibly formed via a dissolution precipitation mechanism that operated under acidic conditions the k ar dating 73 62 ma of the illites indicates an illitization process from the maastrichtian to early danian period

lateral resolution and lithological interpretation of surface wave profiling in civil engineering geological hazards can be in the form of both soft and hard zones soft zones notably sinkholes can lead to collapse structures reaching the surface and expensive damages during or after construction hard zones might be an impediment to excavation or if they are to be used as foundations it is desirable to know the thickness and strength

the geoarchaeology of waste heaps from the ancient mining and beneficiation of copper rich ores in the wadi khalid in southern jordan two main types of ancient mining waste spoil deposits were identified on the floor of the wadi khalid in the foothills of the mountains of edom near the ancient metallurgical centre of the khirbat faynan the khalid op beds are primarily the product of the purposeful breaking and selection of copper rich clasts of particular sizes as part of the beneficiation of the mined ores whereas the khalid w beds appear to be the result of the widespread discard of the more abundant final waste products geochemical studies of their surface copper contents by p xrf of both deposits at eroding exposures conform to these interpretations

hydrothermal alteration and volatile element halos for the rosebery k lens volcanic hosted massive sulfide deposit western tasmania a detailed study of alteration mineralogy mineral chemistry and lithogeochemistry in the host rocks surrounding the a b and k lenses at the north end of the rosebery mine has revealed a series of overlapping alteration halos with characteristic mineralogy and geochemistry the study involved logging and sampling from nine drill holes spaced at varying distances from the a b and k lenses the stratiform zn pb cu ore lenses have a sheetlike morphology and are hosted by a mixed sequence of rhyolitic to dacitic massive mediumgrained quartz porphyritic pumice breccia black mudstone and crystal rich volcaniclastic sandstone overlying a thick homogeneous sequence of rhyolitic pumice breccia the major alteration minerals at rosebery are arranged in a complex series of zones passing away from the deposit quartz sericite zone mn carbonate zone chlorite zone and outer sericite zone the chlorite zone is best developed in the immediate footwall below the copper pyrite rich ore lenses whereas the strongest mn carbonate alteration occurs in the immediate hanging wall volcanics or lateral to the ore lenses the outermost visible sericitic alteration extends about 60 to 100 m into the footwall 10 to 20 m into the hanging wall and over 500 m along the upper contact of the footwall pumice breccias thallium and antimony form the most extensive trace element halos related to the mineralization thallium forms a halo that extends 200 to 300 m into the overlying volcanics and 60 to 100 m into the footwall anomalously high thallium also occurs over 500 m along strike marking the contact between the footwall pumice breccias and the overlying volcaniclastic sandstones proximal to the ore lenses tl and sb values range from 10 to 100 ppm compared to the halo zone where they vary from around 1 to 10 ppm studies of alteration mineral chemistry at rosebery have revealed some important relationships that may assist exploration the mn content of alteration carbonate increases toward ore both along strike and across strike close to ore alteration carbonates contain 20 mole percent mnco3 kutnahorite rhodochrosite mn siderite and mn ankerite whereas at distances of 40 to 60 m across strike the mole percent mnco3 in carbonate drops to below 10 percent at greater than 80 m the carbonates are mn poor calcites and are commonly located in synmetamorphic structures white mica composition changes with stratigraphy and alteration assemblages and may be related to the mineralizing event although this has not been convincingly demonstrated proximal white mica contains minor ba substituting for octahedral al however except for their ba content these phengetic white micas are similar to those found in nonmineralized areas of the mount read volcanics sodic white mica with up to 0 35 na na k and a low phengite content 0 5 fe mg cations occurs in a zone of volcanic sandstones and black slates overlying the ore deposit this research has lead to the development of a series of proximal medial and distal vectors useful for both regional and mine scale exploration the most useful vectors listed from proximal to distal include zn ba content of white mica na2o k2o ishikawa alteration index ai s na2o ba sr mn content of carbonate tl and sb

palhydaf palaeohydrology in africa program objectives methods major results abstract the palhydaf program aims to reconstruct the late quaternary 130 ka b p to present environmental and hydrological changes of northwest africa and to interpret them in terms of palaeoclimate for testing coupled atmospheric ocean circulation models lacustrine sequences were obtained from closed basins which lie along two meridional transects southern tunisia southern niger and algeria mali particular attention is given to groundwater storage and periods of recharge of the aquifers the chronological framework is based on 14c dates conventional and ams methods and or the th u disequilibrium method in favourable cases e g mali correlations can be made between the chronology of surface palaeohydrology and that of aquifer recharge various environmental markers mineralogy elemental chemistry stable isotopes biological remains are used for palaeoenvironmental purposes quantitative estimates of palaeoclimatic variables e g air humidity may be attempted through the combination of geochemical and palaeobiological data the major results already obtained are summarized for the following individual sectors 1 southern tunisia 1 northern algeria 2 southern algeria 3 northern niger 3 mali 4 southern niger at the present stage of investigation the following new inferences can be drown one or several humid episode s occurred in the northern sahara between 150 and 75 ka b p several factors suggest that these humid conditions also affected lower latitudes although their southern extent cannot be given precisely at present the previously postulated existence of large lakes at 20 35 ka b p is not confirmed this time interval seems to coincide with raised water tables but not to a major humid phase in all cases the 14c chronologies obtained for the late pleistocene have to be checked by comparison with other dating methods e g th u disequilibrium after the arid period of the last glacial maximum the return of humid conditions occurred in two major steps at 12 and 9 5 9 ka b p for both the southern and the northern sahara

mineralogy and geochemical behavior of trace elements of hydrothermal alteration types in the volcanogenic massive sulfide deposits ne turkey abstract volcanogenic massive sulfide vms deposits of the eastern pontides turkey are hosted by the maastrichtian eocene dacite and rhyodacite series accompanied by lesser andesite and basalts as well as their pyroclastic equivalents with tholeiitic to calc alkaline affinity the ore mineral assemblages are chalcopyrite sphalerite galena chalcocite covellite bornite and tetrahedrite potassic phyllitic sericitic argillic kaolinitic and smectitic silicic propylitic and hematitic alteration is commonly associated with these deposits hfse lile trte and ree contents show strong variability in different alteration types resulting from interaction with acid or alkaline fluids sample groups showed chondrite normalized enrichment of lree relative to hree and sub parallel trends except for the hematitic and phyllitic alteration types mree are strongly depleted in the zones of most intense silicification and kaolinization most sample groups have strongly to slightly negative eu anomalies ranging from 0 35 to 0 88 mean hematitic 1 45 and propylitic altered rocks 1 11 have slightly to moderately positive anomalies the negative eu anomalies indicate the low temperatures of fluids 200 c no ce anomaly was observed except for phyllitic alteration where a slight positive anomaly was noted the chondrite normalized trace and ree patterns of the altered rocks are similar to each other suggesting that they were derived from a common felsic source the alteration groups formed from acid intermediate and alkaline hydrothermal solutions some transition base and precious metals and volatile elements were clearly enriched especially in the hematitic silicic kaolinitic and phyllitic altered samples the other elements exhibit different behaviors in different sample groups ree behavior is relatively immobile in the silicic hematitic kaolinitic and partially in moderately and propylitic altered rocks based on mass balance calculations lile and hfse appear mobile in the altered sample groups except in the propylitic altered rocks trte behave as relatively immobile in most of samples except in some of the silicic and phyllitic altered rocks and especially in the hematitic altered samples hfse most of the transition w mo cu and sb and some other trace elements pb as hg bi se and tl are enriched in the hematitic altered samples and in the some silicic altered samples the highest as bi mo se and hg concentrations in the hematite altered samples can be used to distinguish other alteration types and may be a useful indicator in a prospect scale base metal exploration

focus on land seismic technology the near surface challenge a new era in land seismic is at hand growing energy demand will spur greater efforts in exploration and development into regions of the world where hydrocarbons occur in land environments interpreters will require accurate near surface solutions for mapping low relief structures and stratigraphic traps and to improve data quality for placing horizontal wells this will require solutions to near surface challenges such as energy penetration scattering source generated noise surface generated multiples statics and source and receiver coupling solutions to these problems will become possible due to advances in seismic acquisition including simultaneous source acquisition and wireless seismic driven ultrahigh channel systems additionally advances in seismic processing technology for processing the resulting huge data volumes will be made possible by continual growth in computational capability these advances will for the first time allow acquisition of true 3d seismic data this will not only re

false pyroclastic textures in altered silicic lavas with implications for volcanic associated mineralization there is strong emphasis in recent literature that zn cu pb massive sulfide deposits associated with felsic volcanism the kuroko type deposits are directly related to submarine calderas formed by large submarine pyroclastic eruptions altered silicic volcanic rocks with the appearance of welded and nonwelded pyroclastic flow deposits volcaniclastic debris flows and massive to thin bedded tuffaceous rocks form a major component of a silurian succession that hosts zn cu pb massive sulfide deposits at benambra southeastern australia however critical evaluation of rock textures indicates that these silicic volcanic rocks are mainly lavas and associated autoclastic facies with remarkably deceptive false pyroclastic and volcaniclastic textures including apparent pumice fiamme and glass shards intercalated sediments indicate that most of the silicic volcanics were emplaced in subaqueous settings ranging from relatively shallow water to deep marine the false textures were produced mainly in originally glassy lava by the combined effects of devitrification perlitic fracture and pervasive hydrothermal alteration these processes are related to the emplacement and cooling history of individual lavas and to a regional essentially synvolcanic hydrothermal system tectonic foliation of the more altered and mechanically weakened rocks has led to partial dismembering of phenocrysts and groundmass fabrics thereby further enhancing clastic appearance subsequent to recognition of widespread false pyroclastic textures at benambra similar features have been identified in three other australian massive sulfide districts these results suggest that a reinvestigation of host rocks is warranted at other deposits where submarine pyroclastics are documented noncaldera settings combining subsidence in an extensional volcano tectonic basin passive submarine lava effusion within the basin and ambient sedimentation derived from basin margins including resedimented pyroclastic debris may be more relevant models in a number of massive sulfide districts

a wetter climate in eastern sudan 2 000 years ago within the past 15 years accurate radiocarbon dating and plant microfossil analysis of tropical lake sediments in africa and elsewhere have revealed that the early holocene 11 7 kyr was generally wetter than today throughout the tropics1 4 in contrast to last glacial maximum 18 2 kyr which was cool dry and windy5 6 desiccation beginning 4 5 kyr ago forced neolithic herders to abandon previously habitable old world deserts7 9 less well known is the climate of proto historic times 2 kyr ago when iron smelting became important in africa10 here we present the first evidence that the red sea hills were somewhat wetter at this time and suggest that this was also true of much of northern africa

the spectrum of ore deposit types volcanic environments alteration halos and related exploration vectors in submarine volcanic successions some examples from australia variations in shape metal content alteration mineralogy and volcanic host rocks of the ore deposits in the two major volcanic hosted massive sulfide vhms districts of eastern australia the cambrian mount read volcanics and the cambro ordovician mount windsor subprovince strongly reflect their volcanic environment conditions of ore formation and hydrothermal alteration processes lens and sheet style polymetallic zinc rich deposits such as rosebery hellyer que river and thalanga are considered to have formed in moderate to relatively deep water environments 500 1 000 m these deposits probably formed either on the sea floor e g hellyer que river or by replacement of porous volcaniclastic units directly below the sea floor e g rosebery the footwall alteration associated with these polymetallic vhms deposits was controlled by host rock permeability and porosity which are in turn related to volcanic facies type degree of fracturing and synvolcanic structural architecture focusing of hydrothermal fluids along synvolcanic structures has resulted in well zoned chlorite sericite footwall alteration pipes within footwall lavas at hellyer on the other hand diffuse fluid flow through very thick pumice breccia at rosebery and hercules has resulted in strata bound sericite dominated footwall alteration zones parallel to the paleosea floor and the ore lenses massive and disseminated pyritic cu au deposits such as those in the mount lyell field and at highway reward formed by subsea floor replacement and are associated with only minor zinc lead massive sulfide ore these deposits formed from higher temperature fluids 300 degrees c in which copper transport is enhanced and are commonly located in felsic volcanic centers dominated by shallow porphyritic intrusions e g highway reward the cu au ore lenses may be strata bound e g mount lyell or crosscutting pipes e g highway reward depending on the structure and permeability characteristics of the felsic volcanic host rocks the presence of high sulfidation alteration minerals e g pyrophyllite zunyite in some of the cu au deposits e g mount lyell field indicates that fluids were relatively acidic and suggests the possibility of magmatic fluid input into the hydrothermal system alteration zonation associated with the cu au vhms deposits is more symmetrical than that of the zn rich deposits with sericite rich alteration extending into the hanging wall in keeping with the subsurface replacement origin of these deposits synvolcanic gold rich deposits with high gold base metal ratios are less common than the cu au and zn rich vhms ore types the gold rich ores e g henty south hercules are strata bound in nature have low sulfide contents and are associated with central zones of intense silicification surrounded by envelopes of sericite pyrite and carbonate alteration volcanological and geochemical studies at henty indicate the gold rich ore formed by the replacement of particular volcanic units deposited in a relatively shallow water environment dominated by volcaniclastic facies lavas and limestones this spectrum of cu au zn rich and au only deposits in the mount read volcanics and the mount windsor subprovince is interpreted to represent a continuum from classic sea floor vhms ores toward those with features more akin to porphyry cu au and epithermal au ag deposits this spectrum relates to the interplay between factors in the submarine volcanic environment and the character of the hydrothermal fluid as follows 1 proportions of volcaniclastic lava and subvolcanic intrusive facies 2 depth of seawater 3 permeability and porosity of volcanic host rocks 4 balance between magmatic components and seawater components in the ore fluid and 5 temperature and acidity of the ore fluid mineralogical lithogeochemical and isotopic studies have revealed a range of alteration vectors useful in exploration for both the zn rich and cu au vhms deposits carbonate and white mica compositional variations are highlighted as important mineralogical vectors thallium and antimony halos may be useful trace element vectors and oxygen and sulfur provide important isotope vectors toward the center of the hydrothermal system

discovery of the west 45 volcanic hosted massive sulfide deposit using oxygen isotopes and ree geochemistry a number of innovative geochemical techniques were tested around the thalanga volcanic hosted massive sulfide vhms deposit in north queensland with the objective of being able to recognize a near miss in the exploration drilling in and around the mine whole rock oxygen isotope analyses were used to determine temperature gradients in the footwall rocks just beneath the ore horizon by assuming a water 6180 value of 0 per mil consistent with a seawater dominated hydrothermal system an alteration temperature was calculated for each sample a quantitative determination of the mineralogy was used to work out a weighted fractionation factor for each sample so that the variance attributable to differences in mineralogy could be taken into account comparison of the temperatures to a sodium depletion index indicates that the 6180 halo is comparable in size to an alteration mineralogy halo but the distribution of na is somewhat unpredictable in the distal parts of the hydrothermal system this study identified a hot spot i km west of the limit of the mine workings the mount windsor volcanics which host the thalanga deposit contain a large number of stratiform quartz hematite lenses red jaspers rather than drill test all of these occurrences a geochemical index was determined to assist in ranking them elevated ba s and pb along with positive chondrite normalized europium anomalies were found to be characteristics of proximal jaspers as compared to barren jaspers a red jasper outcrop west of thalanga coincident with the 6180 hot spot was the most anomalous sample in this study subsequent drill testing of this target led to the discovery of the west 45 vhms deposit

hydrothermal alteration in oceanic ridge volcanics a detailed study at the galapagos fossil hydrothermal field abstract the galapagos fossil hydrothermal field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern galapagos rift between 85 49 w and 85 55 w the discharge zone of the hydrothermal system is revealed along scarps thus providing an opportunity to examine the uppermost mineralized and highly altered interior parts of the crust altered rocks collected in situ by the submersible alvin show complex concentric alteration zones microsamples of individual zones have been analysed for major minor trace elements and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration interlayered chlorite smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene phenocrysts and matrix grains of plagioclase are unaffected during alteration using a modification of the gresens equation we demonstrate that the trivalent rare earth elements rees are relatively immobile and calculate degrees of enrichment and depletion in other elements strontium isotopic ratios increase as sr concentrations decrease from least altered cores to most altered rims and cross cutting veins in individual samples and can be modeled by open system behaviour under low fluid rock ratio

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

alteration of felsic volcanics hosting the thalanga massive sulfide deposit northern queensland australia and geochemical proximity indicators to ore thalanga is an early ordovician stratiform zn pb cu ag rich massive sulfide deposit in northern queensland australia with a total resource of 6 6 mt of ore the host rock succession consists of variably altered rhyolite in the footwall and a dacite dominated volcano sedimentary sequence in the hanging wall the sulfide deposit and the enclosing volcanic sequence were metamorphosed under upper greenschist conditions a laterally continuous footwall alteration zone extends beneath the entire deposit 3 000 m and to a stratigraphic depth of at least 300 m below the ore lenses the bulk of this zone is occupied by feldspar destructive muscovite biotite chlorite rich mottled alteration facies with disseminated pyrite representing the metamorphic equivalent of phyllosilicate dominated hydrothermal alteration discordant zones of intense quartz pyrite alteration represent the principal fluid pathways during mineralizing hydrothermal activity locally quartz k feldspar alteration facies exist on the fringes of the system and calcareous alteration and chlorite pyrite alteration facies exist in the upper part of footwall rhyolite proximal to sulfide lenses quartz feldspar porphyritic rhyolite laterally surrounding the footwall alteration zone and feldspar porphyritic dacite in the hanging wall are unaltered or weakly altered the compositional diversity of altered footwall rhyolite implies that hydrothermal alteration at thalanga was a complex processes this paper presents a model for the evolution of the footwall alteration zone calcareous alteration probably represents the initial phase of hydrothermal activity this was followed by diffuse upwelling of acidic seawater dominated fluids causing destruction of primary feldspar precipitation of pyrite and formation of hydrothermal sericite chlorite and clay minerals subsequent intense quartz pyrite alteration was directly associated with mineralization the thalanga footwall alteration zone has several geochemical characteristics that show systematic changes with increasing proximity to ore these include na depletion and elevated mg s alteration index ai chlorite carbonate pyrite index ccpi mo bi and as furthermore the x mg of chlorite and biotite increases systematically from values of 0 45 to 0 5 in least altered rhyolite to values 0 9 immediately below ore these geochemical features can be used in exploration for massive sulfide deposits as vectors to ore at the prospect scale and in discrimination of prospective hydrothermal from unprospective diagenetic alteration systems at the regional scale

quaternary palaeogeomorphologic evolution of the wadi faynan area southern jordan abstract the faynan area comprises a complex assemblage of deposits and landforms of varying nature age and position in the landscape the dominant facies are fluvial slope and aeolian at least eight palaeochannels are present at different heights within the wadis dana and ghuwayr fewer terraces are preserved in the wadi faynan planated surfaces leaving low gradient straths rock cut channels and fluvial deposits are all evident the continuing drop in regional base level as a result of subsidence of the dead sea trough has driven incision and aided in the retention of many of the terrace deposits as they have been abandoned as the wadi systems have eroded downwards calcretisation has enhanced the preservation potential of many of the fluvial deposits a large proportion of these deposits are comparable to those found in the modern wadi systems and it is thought that they formed under arid conditions similar to those that exist today two of the terrace deposits appear to reflect slightly wetter conditions as they consist of finer grained better sorted materials and display evidence of biological activity there are at least four distinct alluvial fan and slope deposits that have formed at the edge of various mountain fronts the fans have been entrenched to varying degrees and are likely to have formed at different times in the quaternary possibly when conditions were more humid or during periods of increased tectonic activity aeolian deposits indicate a marginally drier phase in the late glacial maximum and similar sediments of mid holocene age could either reflect increasing aridity at this time as has been suggested by frumkin et al 1991 and or be a result of the increasing impact of humans on the landscape many of the deposits are beyond the age range of optically stimulated luminescence osl and radiocarbon dating techniques but a proposed stratigraphy is supported by some numerical dates on the younger deposits and associated archaeological artefacts

early holocene environments in the wadi faynan jordan hunt c elrishi h gilbertson d grattan j mclaren s pyatt b rushworth g barker g early holocene environments in the wadi faynan jordan the holocene 2004 14 6 pp 921 930

the origin of chlorite tremolite carbonate rocks associated with the thalanga volcanic hosted massive sulfide deposit north queensland australia the thalanga polymetallic massive sulfide deposit is hosted by felsic volcanics of the cambro ordovician mount windsor subprovince in north queensland the sheetlike sulfide deposit consists of several semiconnected lenses totaling 6 6 million metric tons mt which lie at a single stratigraphic level between underlying subaqueously emplaced rhyolite and overlying dacitic to andesitic lavas sills and volcaniclastic rocks the ores and host rocks have been deformed and metamorphosed to upper greenschist facies associated with the west thalanga orebody are strata bound lenses composed of chlorite tremolite dolomite and calcite that previously have been interpreted as exhalites they extend up to a few hundred meters along the mineralized horizon and locally also exist in the stratigraphic footwall around the fringes of the deposit rhyolitic volcanics beneath the deposit are extensively altered a pervasive sericite chlorite pyrite zone that extends greater than 200 m into the footwall envelops semistratiform proximal quartz pyrite chlorite stringer zones major and trace element geochemical data indicate that zr ti and al remained essentially immobile in the footwall rocks despite intense hydrothermal alteration involving significant mass transfers of mobile elements the chlorite tremolite carbonate assemblages associated with ore lenses have immobile element ratios identical to those of the altered rhyolites carbonate rich assemblages retain some relict spheroidal and rhombic textures in dolomite which suggest formation at an early hydrothermal stage in a matrix of chlorite or in open spaces the chlorite tremolite carbonate rocks probably represent metamorphic equivalents of hydrothermal chlorite quartz dolomite calcite or mg smectite quartz dolomite calcite assemblages the formation of tremolite by metamorphic reaction of quartz and dolomite is consistent with regional metamorphic conditions with allowance for metamorphic decarbonation carbon and oxygen isotope data from dolomite and calcite are consistent with precipitation of primary dolomite at 170 to 250 c from seawater dominated fluid the chlorite tremolite carbonate rocks at thalanga are consequently reinterpreted as altered rhyolitic volcaniclastics containing variable proportions of hydrothermal carbonate they probably formed in a zone of mixing of hydrothermal fluid and seawater in a permeable substrate close to the paleosea floor siliceous ironstones that are present in distal parts of some thalanga ore lenses have very low immobile element contents and are probably true exhalites

rare earth element and isotopic evidence for the genesis of the prieska massive sulfide deposit south africa the prieska orebody is contained in high grade metamorphic peraluminous rocks birdwing shaped rare earth element profiles and high epsilon nd values are observed in rocks under the ore these characteristics are interpreted to reflect an early magmatic dominated alteration stage during which heavy rare earth elements and highly radiogenic nd were added to the rocks rocks studied above the ore display normal rare earth element profiles and country rock epsilon nd the generally high mg fe ratios of all the altered rocks are thought to indicate pervasive late alteration by seawater derived fluids the alteration processes appear to be linked to the cooling of a hypothetical high level intrusion derived from the depleted mantle the existence of this type of magmatism is also indicated by the occurrence of amphibolites higher up in the sequence which have flat rare earth element profiles and high epsilon nd

mass volume and chemical changes in the alteration zone at the norbec mine noranda quebec a funnel shaped alteration pipe in archean rhyolite and andesite below massive sulphide zn cu ores at the norbec mine in northwestern quebec was outlined from drill core samples geochemical parameters and normative alteration mineralogy the pipe has a mass of 37 9 million tonnes giving a volume of 13 106 m3 which represents volume increase of 10 relative to the unaltered host volcanic rocks a bulk chemical composition was calculated using weighting procedures for volumes of influence for the samples net mobile mass change or chemical flux for the alteration pipe was 5 8 106 tonnes inclusion of the massive ore lens yields a flux of 9 6 106 tonnes for the whole hydrothermal system the largest additions to the system in millions of tonnes were feo 4 2 sio2 3 8 s 1 8 k2o 0 55 and mgo 0 5 the only depletions were na2o 1 4 and cao 0 44 base and precious metals accounted for 3 4 of the total element flux

application of a complete workflow for 2d elastic full waveform inversion to recorded shallow seismic rayleigh waves abstractthe s wave velocity of the shallow subsurface can be inferred from shallow seismic rayleigh waves traditionally the dispersion curves of the rayleigh waves are inverted to obtain the local s wave velocity as a function of depth two dimensional elastic full waveform inversion fwi has the potential to also infer lateral variations we have developed a novel workflow for the application of 2d elastic fwi to recorded surface waves during the preprocessing we apply a line source simulation spreading correction and perform an a priori estimation of the attenuation of waves the iterative multiscale 2d elastic fwi workflow consists of the preconditioning of the gradients in the vicinity of the sources and a source wavelet correction the misfit is defined by the least squares norm of normalized wavefields we apply our workflow to a field data set that has been acquired on a predominantly depth dependent velocity structure and we compare the reconstructed s wave velocity model with the result

hydrothermal carbonates in altered wall rocks at the uwamuki kuroko deposits japan magnesite siderite and dolomite are characteristic alteration minerals occurring in miocene hanging wall rocks of dacitic composition which host the kuroko orebodies these carbonates generally occur in a more stratigraphically upper horizon than chlorite alteration zone surrounding the orebodies the mg mg fe ratios of the carbonates decrease from the central alteration zone to marginal zone the mg mg fe ratios of carbonates and chlorite positively correlate the 18o and 13c values of magnesite siderite and dolomite positively correlate with each other and lie between the igneous and marine carbonate values the petrographic isotopic and fluid inclusion characteristics and thermochemical modelling calculations indicate that magnesite and dolomite formed in the central zone close to the orebodies due to the interaction of hydrothermal solutions with the biogenic marine carbonates calcite formed further from the orebodies from hydrothermal fluids which did not contain a biogenic marine carbon component the compositional and textural relationships indicate that superimposed alterations chlorite alteration and carbonate alteration occurred in hanging wall rocks the mode of occurrences and the mg mg fe ratios of magnesite and dolomite occurring in hanging wallrocks are useful in the exploration for concealed volcanogenic massive sulfide sulfate deposits

mineral and whole rock compositions of seawater dominated hydrothermal alteration at the arctic volcanogenic massive sulfide prospect alaska the arctic volcanogenic massive sulfide prospect located in the ambler mineral district of northwestern alaska includes three types of hydrothermally altered rocks overlying underlying and interlayered with semimassive sulfide mineralization hydrothermal alteration of wall rocks and deposition of sulfide and gangue minerals were contemporaneous with late devonian or early mississippian basalt rhyolite volcanism whole rock analyses of altered rocks surrounding the prospect indicate that strong chemical gradients exist in major and minor oxides and volatiles these were not homogenized or overprinted by late jurassic to middle cretaceous greenschist to glaucophane schist facies metamorphism very low alkali contents and moderate to very high contents of ba f and mg are the major chemical characteristics of the pervasively altered rocks the strong mg metasomatism high ba contents and limited extent of altered rocks suggest a rapid influx of relatively cold seawater into a hot hydrothermal vent system alteration developed asymmetrically around a linear fissure suggesting fracture control of ore fluids rather than a point source micro probe analyses of phyllosilicates from the arctic area indicate two discrete mineral populations magnesian chlorite barian white mica and barian fiuorphlogopite in hydrothermally altered rocks have compositions distinct from similar minerals chlorite phengite biotite developed during high pressure metamorphism in metapelitic and metavolcanic lithologies these differences in mineral chemistry are the result of differences in protolith composition caused by hydrothermal alteration metasomatism without mineral composition data the contacts between some alteration assemblages and relatively unaltered metavolcanic and metasedimentary rocks with similar mineralogy cannot be determined

short wavelength infrared swir spectral analysis of hydrothermal alteration zones associated with base metal sulfide deposits at rosebery and western tharsis tasmania and highway reward queensland spectral analysis of rock samples by short wavelength infrared swir analysis using the portable infrared mineral analyzer pima spectrometer is a relatively new field method with applications in mineral exploration the technique allows rapid field based identification of hydrothermal alteration minerals and delineation of alteration zones variations in mineral composition crystallinity and relative abundance may also be determined phyllosilicates including white mica and chlorite are particularly amenable to short wavelength infrared analysis these are prominent alteration minerals in the felsic volcanic rocks in the mount read volcanics tasmania and the mount windsor subprovince north queensland they have regional distributions as diagenetic and metamorphic products and exist locally in alteration zones associated with volcanic hosted sulfide deposits a geochemical and spectral investigation of white micas in the least altered rocks in the mount read volcanics has shown considerable background compositional variations the white micas range from phengite to moderately sodic muscovite and swir spectral measurements provide reliable estimates of their compositions chlorites also have a broad compositional range in these rocks however swir spectral analysis has proven to be unreliable in determining chlorite composition in samples where chlorite exists in low proportions relative to white mica or in mixed assemblages with epidote white micas in footwall alteration zones of the rosebery stratiform zn pb deposit tasmania are variably phengitic similar to those in regional background volcanics a unit of relatively unaltered volcaniclastic sandstone in the rosebery hanging wall sequence contains anomalous sodic muscovite in proximity to ore lenses white micas associated with the disseminated to massive pyritic cu au deposits at western tharsis tasmania and highway reward north queensland range in composition from phengite to slightly sodic muscovite in these symmetrically zoned alteration systems white micas grade in composition from phengite in peripheral zones to slightly sodic muscovite in proximal zones near ore in all three cases the white mica compositional variation is a vector to ore that is effectively measured by swir spectrometry with particular application in prospect scale exploration chlorite compositions at rosebery are not strictly spatially related to ore but tend to be most magnesian in zones of high chlorite abundance in the outer alteration zone at western tharsis there is a faint proximal trend to iron rich chlorites however it does not represent a well defined vector to ore in either case attempts at quantitative estimation of the relative abundance of white mica and chlorite in mixed samples by spectral analysis have produced results that are imprecise in comparison to geochemically derived estimates the data scatter relates to the low proportions of chlorite in the majority of the samples analyzed resulting in weak chlorite absorptions better results may be obtainable in specific alteration or lithostratigraphic domains by use of customized spectral unmixing software this investigation has shown that pima based swir spectrometry is a potent field method of mapping compositional variations in white micas that represent empirical vectors to at least some types of volcanic hosted sulfide deposits it has also highlighted its effectiveness in field identification of megascopically difficult or indeterminate alteration minerals such as pyrophyllite zunyite and topaz which may have genetic implications and exploration significance

texture mineralogy and geochemistry of hydrothermally altered submarine volcanics recovered southeast of cheshire seamount western woodlark basin the western woodlark basin lies within a gold rich metallogenic province this area is characterized by detachment faults that record ongoing extension and act as major pathways for the circulation of hydrothermal fluids dredging from the flanks of a submarine ridge southeast of cheshire seamount western woodlark basin retrieved hydrothermally altered monomictic to polymictic crackle mosaic and chaotic breccias with at least 30 clasts n2 mmin diameter the precursor rocks are andesitic to rhyolitic in composition but have been intensely hydrothermally altered with about 90 of the volcanic glass replaced by secondaryminerals the breccias show five generations of quartz growth with the first being related to magmatic processes and the remaining four to alteration stages including silicification chloritization illitization sericitization albitization and sulfidation needle like crystals ofmordenite zeolite withmultiple growth centers growon the fourth generation of quartz notable textural variants in the breccias are vesicles perlitic cracks and zoned alteration halos that mantle the rims of clasts electron microprobe analyses on chlorite from breccia samples have identified clinochlore as the main chlorite type and indicate a formation temperature in the range of 210 304 c this and the elevated au as ag hg zn pb sb contents of a mineralized sample indicate hydrothermal alteration temperatures n200 c suggesting that these breccias may represent the upflow zone of a hydrothermal system and highlight the potential for seafloor massive sulfides in the area the breccias show elevated contents of immobile trace elements and lree as well as a depletion in ta and nb suggesting that the precursor rocks were formed in a rift related suprasubduction environment

horizontal resolution of multichannel analysis of surface waves abstractthe multichannel analysis of surface wave masw method has been effectively and widely used to determine near surface shear wave velocity horizontal resolution of the masw method represents the minimum horizontal length of recognizable geologic anomalous bodies on a pseudo 2d s wave velocity vs section accurately assessing the achievable lateral resolution is one of the main issues in lateral variation reconstruction using the masw method it is difficult to quantitatively estimate the horizontal resolution of the masw method because of the many influencing factors such as parameters of the observation system the depth of an anomalous body and the velocity contrast between the anomalous body and the surrounding rocks we first analyzed the horizontal resolution of the masw method based on numerical simulation experiments according to different influencing factors of the horizontal resolution we established different laterally heterogeneous models and observation systems and then simulated

the paleoproterozoic aripuana zn pb ag au cu volcanogenic massive sulfide deposit mato grosso brazil geology geochemistry of alteration carbon and oxygen isotope modeling and implications for genesis aripuana is a paleoproterozoic 1 76 1 75 ga stratiform volcanogenic zn pb ag au cu massive sulfide deposit has an estimated resource of 11 6 million metric tons mt of ore and is located on the south southwest border of the amazon craton brazil aripuana resides in a caldera composed of strongly fractionated felsic metavolcanic rocks transitional between calc alkaline and tholeiitic compositions the entire region was metamorphosed into lower greenschist facies 1 68 1 63 ga and the deposit was subsequently thermally metamorphosed and metasomatized 1 56 1 53 ga the mineralized bodies are lenticular and elongated they are located at the base of a sequence of turbidites which overlie dacitic and rhyolitic ignimbrites the rocks of the footwall are silicified sericitized and chloritized and the hanging wall rocks are carbonate rhythmites and turbidites hydrothermal marbles carbonate breccias and breccia like rocks carbonate talc tremolite chlorite rock talc tremolite and biotite rich rocks and carbonate and fluorite bearing cherts the deposit was formed during at least four submarine exhalative hydrothermal cycles in which siliceous marbles and marls represent the initial phase of each cycle followed by the coprecipitation of pyrite pyrrhotite sphalerite argentiferous galenas chalcopyrite which were disseminated in clay carbonate breccias or formed massive lenses this phase was followed by fluoritic cherts and argillites which were followed by carbonate and fluorite rhythmites and turbidites to close the cycle the variation in total rare earth element ree contents and in the eu and ce anomalies indicates that the original sediments were mixtures of hydrothermal carbonate and smectitic clay and were deposited below a redoxcline isotopic analysis identified 18osmow values between 8 and 13 and 13cpdb values between 7 and 1 modeling isotopic data showed that mineralizing fluids were distinct based on the proportion of magmatic fluid that mixed with the seawater carbonate rocks and sulfide minerals precipitated while hydrothermal activity and volcanism evolved from an exhalative to an exhalative explosive character with temperatures increasing between 100 and 200 c the regional metamorphism of the deposit formed carbonate talc tremolite chlorite rocks tremolite biotite and talc rich rocks it recrystallized the minerals foliated and folded all of the rocks and caused limited decarbonation at the sites where carbonate rocks contained silica and smectite however the original isotopic signatures were maintained the thermal metamorphism erased the metamorphic foliation and the metasomatism generated veinlets of chlorite with sulfides

geochemistry of the mount windsor volcanics implications for the tectonic setting of cambro ordovician volcanic hosted massive sulfide mineralization in northeastern australia the mount windsor subprovince is an important relic of upper cambrian to lower ordovician sedimentation and volcanism in the northern part of the tasman orogenic zone volcanic hosted massive sulfide mineralization occurs at several stratigraphic horizons within the volcano sedimentary package and one major mine is operational within the belt major and trace element data and nd isotope ratios are presented for the least altered coherent units from the three major volcanic bearing formations in the mount windsor subprovince the data are used to discriminate four major phases of volcanism and related intrusive activity derived from three isotopically discrete sources and to assess the geodynamic setting in which the volcanism occurred the earliest phase of mafic volcanism has minor and trace element characteristics suggesting an alkaline intraplate or rift association and it was probably produced by partial melting of attenuated subcontinental lithospheric mantle the overlying mount windsor formation silicic volcanics have nd isotope characteristics epsilon sub nd 480 ma 4 7 to 12 8 that suggest they were produced by partial melting of underlying precambrian crustal rocks mafic volcanics of the overlying trooper creek formation include a low tio 2 suite and a high tio 2 suite with a range of distinguishing chemical characteristics but similar nd isotope ratios epsilon sub nd 480 ma 3 8 2 3 which indicate derivation from relatively depleted asthenospheric mantle variably modified by subduction processes the high tio 2 suite is also represented by abundant intrusions within the underlying volcanic package the more silicic volcanics in the trooper creek formation appear to be cogenetic with their mafic associates but have varying nd isotope ratios which suggest progressive crustal interaction with increasing sio 2 content comparisons with modern volcanic compositions and ore depositional environments suggest that the volcanic and sedimentary units within the mount windsor subprovince were deposited in a back arc basin developed by extension of continental lithosphere along the eastern australian margin in the late cambrian and early ordovician mineralization and volcanic deposits of similar age farther north in the tasman orogenic zone suggest that this basin may have had a north south orientation although there is no clear evidence remaining of the original arc front deposits

braided rivers perspectives and problems progress towards a fuller understanding of the dynamics and deposits of braided rivers demands an interdisciplinary approach to a host of unresolved problems although many advances have been made within recent years in interpreting the mechanics of flow transport of sediment and sedimentary architecture of braided rivers many key issues remain to be addressed in particular several areas demand attention the mechanisms of braid bar initiation confluence diffluence dynamics the nature of sedimentary facies over a range of grain sizes and the influence of flow stage and aggradational regime upon the depositional architecture over a range of channel scales this paper focuses upon these issues and highlights several areas of fruitful future interdisciplinary collaboration 1993 the geological society

greenschist facies regional and contact metamorphism of the thalanga volcanic hosted massive sulfide deposit northern queensland australia the conditions of two separate greenschist facies metamorphic events have been reconstructed at the syn genetic thalanga massive sulfide deposit northern queensland australia using scarce garnet biotite and garnet chlorite bearing samples from the felsic volcano sedimentary host rock succession regional metamorphism peak temperature 440 to 480 c generated a foliation defined by aligned chlorite muscovite and biotite and rare euhedral spessartine almandine grossular rich garnets the emplacement of a post tectonic diorite pluton was associated with contact metamorphism and scarce anhedral spessartine almandine rich garnet poikiloblasts crystallized within a 650 m wide aureole at temperatures of 500 c both metamorphic stages occurred under pressure conditions of 3 5 kbar our study documents a useful method for geothermobarometric reconstruction of metamorphosed syn genetic ore deposits where calculations based on sulfide assemblages failed to produce unequivocal constraints furthermore we show that hydrothermally altered footwall rhyolite have higher rm x rm mg rm chlorite rm and rm x rm mg rm biotite than unaltered rocks which may help to identify fossil metamorphosed hydrothermal systems associated with massive sulfide deposits similar to thalanga

metamorphism of magnesium altered felsic volcanic rocks from bergslagen central sweden a transition from mg chlorite to cordierite rich rocks abstract the ca 1 9 ga old felsic volcanic rocks of the bergslagen province have been affected by synvolcanic hydrothermal mg metasomatism a spatial relationship exists between mg alteration zones and calc silicate carbonate banded iron mineralizations and a genetic link is suggested this is supported by the occurrence of the mg rich tourmaline dravite which exists in the mg alteration zones as well as in the wall rocks to iron oxide mineralizations following later regional metamorphism and deformation these rocks occur as large zones of mg rich schists parallel to sub parallel with the regional foliation s1 the dravite crystals have been affected by this regional deformation a second deformational episode folded s1 along steeply dipping fold axes locally this resulted in a crenulation cleavage and the development of a new generation of micas s2 crosscutting s1 in the westernmost areas the mg schists contain a fine grained network of mg chlorite and muscovite with little or no preferred orientation indicating low pressures and low grade metamorphic conditions the grade of recrystallization and deformation increase towards the east and a boundary between low and medium grade metamorphic terrains is crossed the metamorphic boundary is marked by the disappearance of chlorite and the appearance of cordierite in the mg schists porphyroblasts of mg chlorite or cordierite grew across s1 and cordierite porphyroblasts are transected by s2 micas this indicates that the peak of regional metamorphism occurred between the two deformational episodes retrogression of cordierite to chlorite and muscovite is confined to the vicinity of crosscutting s2 micas

geology and volcanic facies architecture of the lower ordovician waterloo massive sufide deposit australia the waterloo massive sulfide deposit occurs in the cambro ordovician seventy mile range group in the charters towers district in northern queensland one of the principal submarine successions in eastern australia that contains abundant volcanic hosted base metal deposits the deposit consists of several small dismembered stratiform blanketlike pyrite chalcopyrite sphalerite galena massive sulfide lenses hosted by intensely altered volcanic rocks the deposit and its host rocks have been deformed during regional deformation of the middle to late ordovcian and were affected by two subsequent events of brittle deformation the waterloo deposit formed on top of a lava dominated andesite succession comprising coherent volcanic units and related juvenile volcaniclastic rocks the hydrothermal activity leading to the deposition of massive sulfides commenced during the waning stages or after the cessation of the andesite volcanism the blanketlike mineralization is interpreted to have formed largely at or very close to the sea floor in a moderately deep to deep marine environment formation of the massive sulfides was accompanied by the mass flow deposition of coarse quartz feldspar crystal rich volcanic debris that records broadly contemporaneous probably explosive rhyolitic volcanism occurring outside the immediate study area this resedimented volcaniclastic unit retains a record of hanging wall alteration indicating that the waterloo hydrothermal system was operative during and after burial by the coarse volcaniclastic material the deposition of the coarse volcaniclastic rocks was followed by the intrusion of a feldspar porphyritic dacite cryptodome that was also subject to hydrothermal alteration associated with the massive sulfide formation facies relationships suggest that the cryptodome locally breached the wet and unconsolidated coarse volcaniclastic material to emerge on the sea floor the emplacement of the partially extrusive dacite cryptodome coincided with the waning of the waterloo hydrothermal system the subsequent period of relatively quiet sedimentation was occasionally interrupted by the emplacement of synsedimentary basalt and andesite sills as volcanism at waterloo shifted back to more mafic compositions this period was followed by the mass flow deposition of coarse feldspar quartz vitric volcanic debris and the onset of another period of intense basalt to andesite dominated volcanism geochemical analyses of volcanic rocks from the host rock succession of the waterloo deposit and correlation with regional data suggest that the massive sulfide deposits in the charters towers district formed during a specific period of cambro ordovician back arc basin development dominated by mantle derived volcanism comparison with the volcanic architecture of other known massive sulfide deposits in the district indicates that massive sulfide mineralization at charters towers is mainly associated with silicic shallow intrusion dominated volcanic centers and occurrences of this volcanic facies should be considered prospective for other deposits in the belt

the local and global dimensions of metalliferous pollution derived from a reconstruction of an eight thousand year record of copper smelting and mining at a desert mountain frontier in southern jordan abstract this paper establishes an eight thousand year history of anthropogenic metal pollution at one of the oldest most important and longest sustained sites of the extraction and smelting of copper ores in the old world the faynan orefield in jordan which is located between the hyper arid southern desert and the front of the wetter mountains of edom the modern land surface is shown in significant part to be a complex palimpsest of archaeological sites metal pollution of various ages and ore processing deposits quantitative and qualitative observations of the storage and cycling of heavy metals through the local natural and domestic systems have produced a body of information on processes with which the past has been interpreted heavy metal concentrations in semi continuous sedimentary bodies indicate that over the last 1500 years metals were removed by natural processes at a comparatively slow rate given the scale of the original anthropogenic metal burden the proportions of lead with respect to copper have increased as the overall metal burden has been lowered distinctive anthropogenic metal pollution signatures have been detected in ash and charcoal rich deposits that were discarded onto the banks of a perennial stream in the late neolithic at present the nature of the human activities that might have produced these pollution signatures is unknown substantial metal pollution from industrial scale smelting activity was present from the early bronze age the intensity of heavy metal pollution produced in classical times locally exceeded that recorded at major european copper smelting centres in the nineteenth century a d the pollution evidence indicates that intensive copper smelting at the immediate area took place until approximately the end of the byzantine period with the exception of one further minor episode of smelting radiocarbon dated to cal bp 530 330 an observed partial but perhaps significant parallelism is also noted between this local record and the records of the metal burdens of the northern hemisphere determined at mire or ice sheet sites at high altitudes or high latitudes the paper discusses the extent to which this parallelism might be a geochemical indicator of the actual existence of economic systems of a geographical scope and scale to have both exercised substantial pull upon the resources of such isolated and difficult locations at the wadi faynan and to have generated sufficient overall metal pollution to have materially altered the chemistry of the global atmosphere the comparative absence of quantitative information upon the nature spatial scale and impacts of human industrial and natural processes affecting metal pollution in other metal rich arid lands provides a significant impediment to such approaches that seek to research locally and think globally

holocene palaeoecology of the eastern sahara selima oasis buried lake sediments and tufa strandlines of holocene age provide evidence of a former lake in the selima oasis depression northwest sudan near the hyperarid core of the eastern sahara desert a 1 6 m section through laminated lake muds and precipitates has been analysed in detail and 30 radiocarbon dates geochemical sedimentological diatom and pollen analyses indicate that the unit dated from approximately 8 4 ka bp to 6 ka bp and was deposited in an environment that passed through one arid to humid to arid cycle the arid episodes from prior to 8 4 ka bp and subsequent to 7 ka bp are characterized by high caco3 deposition abundant diatom indicators of relatively high salinity and well developed periphytic communities and pollen spectra dominated by desert grassland indicators a humid period centered on 8 ka bp is indicated by low caco3 deposition high organic rich mud and al and si oxide deposition diatoms indicating a fresh deep 20 m lake and a pollen assemblage with maximum values for sahelo sudanian tree taxa suggesting a thorn tree and shrub savanna vegetational mosaic this reconstruction concordant with higher groundwater table and precipitation between 9 3 and 7 ka bp agrees with palaeoecological inferences from other sites in north africa

stratigraphy structure and volcanic hosted mineralization of the mount windsor subprovince north queensland australia the mount windsor subprovince contains a major belt of mineralized cambro ordovician subaqueous volcanogenic rocks at the northern end of the tasman orogenic belt the base of the stratigraphic sequence is a thick continent derived siliciclastic package intruded by alkali andesites typical of intraplate settings this is overlain by massive subaqueous rhyolitic units and then by a mixed association of basaltic andesitic dacitic and rhyolitic volcanics and volcaniclastics containing numerous small elongate pods of quartz hematite or magnetite exhalite the cessation in active volcanism is marked by a change to a sandstone siltstone unit dominated by volcanic sources the majority of volcanics form a coherent group of low to medium k calc alkaline lavas similar to those in modern island arc settings extensional growth faults produced local variation in the stratigraphic thickness the largest growth fault in the area is close to the reward highway and handcuff deposits the sequence has been multiply folded and faulted in the paleozoic but the large scale structure remains relatively simple volcanic hosted massive sulfide vhms deposits occur at the top of the massive rhyolite and in the mixed volcanic package above it with the exception of the reward pyrite pipe the mineralization occurs as blanketlike deposits with low thickness lateral extent ratios the thalanga reward and waterloo deposits are copper rich whereas agincourt magpie liontown handcuff and warrawee are zinc rich and copper poor with a significant barite component

genetic and exploration significance of the zinc ratio 100 zn zn pb in massive sulfide systems comparison of the 100 zn zn pb ratio zinc ratio of various styles of mineralization in the mount read volcanics of tasmania indicates that volcanogenic massive sulfide deposits have a restricted range of mean values 60 77 and low standard deviations less than 15 whereas other mineralization styles have a broader but lower range of mean values 39 61 and higher standard deviations greater than 26 thermochemical calculations on lead and zinc transport in saturated ore solutions show that the solution zinc ratio is controlled only by temperature and salinity and is independent of ph f sub o 2 and activity of dissolved sulfur zinc ratios calculated for saturated ore solutions at conditions typical of the deposition of sphalerite and galena in massive sulfide deposits 250 degrees 150 degrees c and 0 5 1 5 m nacl are very similar to those observed in polymetallic massive sulfide deposits in particular those of the rosebery hercules and hellyer deposits in western tasmania this similarity along with the shape of the pb vs zn plots suggests that zinc and lead as chloride complexes were saturated in the metal deficient m sub sigma metal m sub h 2 s hydrothermal fluid that formed the rosebery and hellyer ores variations in the zinc ratio between individual massive sulfide deposits in the mount read volcanics indicate that lead zinc saturation of the ore solution rather than lead zinc content in the footwall volcanic source rocks was the major control on the zinc ratio of the deposits however this is probably not the case for the pb poor cu zn type massive sulfides e g cyprus deposits canadian archean deposits and present day black smokers where low concentrations of lead in the basalt dominated source rocks result in complete undersaturation of lead in the hydrothermal solutions the low mean values and high standard deviations of cambrian vein deposits in the mount read volcanics and in ordovician and devonian deposits of the dundas trough may be explained by a lack of zinc lead saturation in the relevant hydrothermal fluids the characteristic zinc ratio of volcanogenic massive sulfide style mineralization can be used to distinguish these deposits from other mineralization types in the mount read volcanics effective use of this simple technique requires a reasonable number of anomalous samples minimum 15 and an unoxidized sample medium drill core samples are preferable in combination with geology and lead isotope studies the zinc ratio provides an excellent early screening of prospects