an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

sedimentology sequence stratigraphy and geochemical variations in the mesoproterozoic nonesuch formation northern wisconsin usa abstract we use core descriptions and portable x ray fluorescence analyses to identify lithofacies and stratigraphic surfaces for the mesoproterozoic nonesuch formation within the ashland syncline wisconsin we group lithofacies into facies associations and construct a sequence stratigraphic framework based on lithofacies stacking and stratigraphic surfaces the fluvial alluvial facies association upper copper harbor conglomerate is overlain across a transgressive surface by the fluctuating profundal facies association lower nonesuch formation the fluctuating profundal facies association comprises a retrogradational sequence set overlain across a maximum flooding surface by an aggradational progradational sequence set comprising fluctuating profundal fluvial lacustrine and fluvial alluvial facies associations middle nonesuch through lower freda formations lithogeochemistry supports sedimentologic and stratigraphic interpretations fe s molar ratios reflect the oxidation state of the lithofacies values are most depleted above the maximum flooding surface where lithofacies are chemically reduced and are greatest in the chemically oxidized lithofacies si al and zr al molar ratios reflect the relative abundance of detrital heavy minerals vs clay minerals greater values correlate with larger grain size vertical facies association stacking records depositional environments that evolved from fluvial and alluvial to balanced fill lake to overfilled lake and returning to fluvial and alluvial elsewhere in the basin where accommodation was greatest some volume of fluvial lacustrine facies is likely present below the transgressive stratigraphic surface this succession of continental and lake basin types indicates a predominant tectonic driver of basin evolution lithofacies distribution and geochemistry indicate deposition within an asymmetric half graben bounded on the east by a west dipping growth fault while facies assemblages are lacustrine and continental periodic marine incursions are probable especially across maximum transgressive surfaces we demonstrate a sequence stratigraphic approach may be applied to fine grained precambrian sediments using traditional rock description and supporting lithogeochemistry identification of a characteristic lithofacies succession in mesoproterozoic sediments demonstrates fundamental controls commonly interpreted for phanerozoic lake systems may be extended into the precambrian these controls result in a predictable association of lithofacies with distinct physical biological and geochemical properties this has regional significance for carbon sequestration and the distribution of mineral and hydrocarbon resources and broader significance for addressing mesoproterozoic paleogeographic reconstructions and questions related to the evolution of terrestrial life

paragenesis of cobalt and nickel in the black butte shale hosted copper deposit belt basin montana usa the black butte copper deposits formerly known as sheep creek are a group of sediment hosted laterally extensive cu co ag deposits hosted in dolomitic shale of the mid proterozoic newland formation copper cobalt mineralization occurs in zones of massive laminated pyrite that were locally reworked and infiltrated by cu rich fluids during early diagenesis cobalt along with substantial nickel and arsenic mainly occurs as impurities within early porous pyrite or as minute grains of sulpharsenides i e cobaltite glaucodot and or alloclasite later thermal events remobilized the co ni and as to form intergrowths of siegenite co ni 3s4 and tennantite the temperature of this later event is constrained by the mineralogical assemblage to have been relatively low between 125 and 225 c although many of the characteristics of sedex type deposits are present at black butte e g laterally extensive massive pyrite horizons interbedded black shales abundant barite and local phosphate horizons and rifted continental margin setting the lack of economic pb and zn mineralization in the main deposits and the abundance of cu with high co is more typical of sediment hosted stratiform copper deposits the neihart formation a hematitic quartz sandstone resting below the base of the belt supergroup may have been an important source bed for cu co ni ag fluids it is speculated that these fluids ideal for forming cu deposits were expelled along growth faults near the margin of the belt basin and deposited metals on or just below the sea floor in a setting that is typical of sedex deposits this unique mineral deposit model may have applications to other districts where cu co rich sulfides are deposited in an exhalative setting

populations of faults and fault displacements and their effects on estimates of fault related regional extension abstract measured populations of fault displacements derived from regional seismic oilfield seismic coalmine plans and outcrop data show a power law distribution with exponents s of 0 45 to 0 95 for singleline samples across an array of faults the more negative values indicate relatively larger numbers of smaller faults an expression for a population of active faults derived from the gutenberg richter magnitude frequency relation for earthquakes is log n a b d log d where d maximum displacement of a fault n number of faults of maximum displacement d or greater and b d 1 0 and has the same value as b for the corresponding earthquake population populations of dead faults existing at the end of a tectonic episode have been numerically derived using a fault growth model and satisfy the relation log n a e log d where e has a value between 1 6 and 2 0 numerically derived populations of fault displacements in a dead fault population have slopes of s where s e 1 the contribution of an individual fault to the regional strain varies with the lifetime seismic moment of the fault and is proportional to d 2 estimation of fault related extension by summing heaves on faults of a limited size range is valid only if the measured size range of faults accommodates most of the extension correction can be made if the s value of the fault displacement population is known

the north american midcontinent rift beneath lake superior from glimpce seismic reflection profiling the midcontinent rift system is a 1 1 b y old structure extending from kansas through the lake superior region and into southern michigan the rift is filled with thick sequences of basaltic volcanic rocks and clastic sediments for most of its extent it is buried beneath paleozoic rocks but can be traced by its strong gravity and magnetic anomalies the rocks of the rift system are exposed only in the lake superior region and comprise the keweenawan supergroup much of the geology of the keweenawan is beneath lake superior and has only been inferred from potential field studies and seismic refraction studies and extrapolation from on shore geology seismic reflection surveys by the great lakes international multidisciplinary program on crustal evolution in 1986 imaged much of the deep structure of the rift beneath the lake in detail the reflection profiles across the rift reveal a deep asymmetrical central graben whose existence and magnitude was not previously documented they show that in addition to crustal sagging documented by previous investigations normal faulting played a major role in subsidence of the axial region of the rift a sequence of volcanic and sedimentary rocks in places greater than 30 km thick fills the graben thinner volcanic and sedimentary units lie on broad flanks of the rift outside of the graben near the axis the prerift crust is thinned to about one fourth of its original thickness apparently by a combination of low angle extensional faulting and ductile stretching or distributed shear the sense of asymmetry of the central graben changes along the trend of the rift documenting the segmented nature of the structure and suggesting the existence of accommodation zones between the segments the location of the accommodation zones is inferred from abrupt disruptions in the bouguer gravity signature of the rift uplift of the central graben occurred when the original graben bounding normal faults were reactivated as high angle reverse faults with throws of 5 km or more in places the midcontinent rift has some striking similarities to some younger passive continental margins we propose that it preserves a record of nearly complete continental separation which had it not been arrested would have created a middle proterozoic ocean basin

geology and geochemistry of the sediment hosted cheshmeh konan redbed type copper deposit nw iran the several hundred m thick miocene upper red formation in northwestern iran hosts stratiform and fault controlled copper mineralization copper enrichment in the percent range occurs in dm thick carbonaceous sandstone and shale units within the clastic redbed sequence and consists of fine grained disseminated copper sulfides chalcopyrite bornite chalcocite and supergene alteration minerals covellite malachite and azurite the copper mineralization formed after calcite cementation of the primary rock permeability copper sulfides occur mainly as replacement of diagenetic pyrite which in turn replaced organic matter electron microprobe analysis on bornite chalcocite and covellite identifies elevated silver contents in these minerals up to 0 12 0 72 and 1 21 wt respectively whereas chalcopyrite and pyrite have only trace amounts of silver 0 26 and 0 06 wt respectively microthermometric data on fluid inclusions in authigenic quartz and calcite indicate that the cu mineralization is related to a diagenetic fluid of moderate to low temperature th 96 160 c but high salinity 25 38 wt cacl2 equiv the range of 34s in pyrite is 41 9 to 16 4 average 31 4 where framboidal pyrite shows the most negative values between 41 9 and 31 8 and fine grained pyrite has relatively heavier 34s values 29 2 to 16 4 consistent with a bacteriogenic derivation of the sulfur the cu sulfides chalcopyrite bornite and chalcocite show slightly heavier values from 14 6 to 9 0 and their sulfur sources may be both the precursor pyrite s and the bacterial reduction of sulfate bearing basinal brines carbonates related to the ore stage show isotopically light values of 13cv pdb from 8 2 to 5 1 and 18ov pdb from 10 3 to 7 2 indicating a mixed source of oxidation of organic carbon ca 20 and hco3 from seawater porewater ca 0 the copper mineralization is mainly controlled by organic matter content and paleopermeability intragranular space to large fracture patterns enhanced by feldspar and calcite dissolution the cheshmeh konan deposit can be classified as a redbed type sediment hosted stratiform copper ssc deposit

anisotropic features of geometry and permeability in fractured rock masses abstract a geometric anisotropy factor a f of two dimensional natural fracture systems has been defined according to fracture spacing and orientation in a given direction geometric anisotropy of fracture systems has a major effect on the percolation threshold the critical fracture density of fracture systems below which the overall permeability is zero a two dimensional distinct element code udec has been used to calculate directional flow rates of fracture systems simulated and natural fracture patterns sampled on outcrops in the lake district england have been tested to examine the relation between geometric anisotropy and permeability anisotropy which is demonstrated to have a power law form also the differential anisotropy factor a f results in different universal exponents which govern the relation between fracture density and flow rates

origin of hematite and its associated remanence in the copper harbor conglomerate keweenawan upper michigan to study further the origin remanence in red beds the volcanogenic copper harbor conglomerate has been investigated using both paleomagnetic and petrographic techniques paleomagnetic results suggest the presence of two magnetic components both possessing a westerly and shallow or normal keweenawan direction one component in the vicinity of declination 294 inclination 7 6 comprises approximately 30 of the total natural remanent magnetization is removed by alternating field demagnetization following chemical demagnetization and shows a consistent inclination error that is controlled in sense and amount by the dip of the cross beds in which the samples were taken the low coercivities of this component suggest that the magnetization resides in magnetite this and the inclination error due to the bedding indicate that the component is a detrital remanent magnetization the predominant component declination 286 5 inclination 0 0 based on six sites is removed by chemical demagnetization and shows no consistent relationship between inclination and dip of the cross beds which suggests that it is a postdepositional magnetization this component resides in hematite that is removed during the chemical demagnetization procedure petrographic studies show that hematite is present authigenically as pigment and as partly to wholly martitized grains martitization may have occurred before or after deposition petrographic results are at present inconclusive a pole position calculated from this postdepositional component 168 3 e 11 2 n is similar to poles from the overlying nonesuch shale and freda sandstone which suggests that the remanence was acquired before the end of freda deposition

genesis of copper lead mineralization in the regionally zoned agnigundala sulfide belt cuddapah basin andhra pradesh india shallow marine sandstone shale carbonate sedimentary rocks of the paleoproterozoic northern cuddapah basin host copper nallakonda deposit copper lead dhukonda deposit and lead mineralization bandalamottu deposit which together constitute the agnigundala sulfide belt the cu sulfide mineralization in sandstone is both stratabound and disseminated and pb sulfide mineralization occurs as stratabound fracture filling veins and or replacement veins within dolomite systematic mineralogical and sulfur carbon and oxygen isotope studies of the three deposits indicate a common ore fluid that deposited copper at nallakonda copper lead at dhukonda and lead at bandalamottu under progressive cooling during migration through sediments the ore fluid was of low temperature 200 c and oxidized thermochemical reduction of basinal water sulfate produced sulfide for ore deposition it is envisaged that basal red bed and evaporite bearing rift related continental to shallow marine sediments might have acted as the source for the metals rift related faults developed during sedimentation in the basin might have punctured the ore fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration the ore bearing horizons have participated in deformations during basin inversion without any recognizable remobilization

modes and mechanisms of sea surface temperature low frequency variations over the coastal china seas 1 in this paper low frequency variability of annual mean sea surface temperature in the coastal china seas is studied based on ocean and atmosphere reanalysis products there are two distinct low frequency modes a basin mode and a north south dipole mode the former is characterized by a uniform warming over the entire coastal oceans while the latter is characterized by a seesaw pattern over the shelf seas and the south china sea the basin mode is associated with global warming but it is primarily attributed to oceanic advection with surface heat flux playing a damping effect due to intensification of the latent heat loss the dipole mode varies coherently with the pacific decadal oscillation in contrast to the basin mode the dipole mode is broadly associated with the surface heat flux with oceanic advection acting to damp sea surface temperature sst in the shelf seas but sustain sst in the south china sea a further analysis indicates that the basin mode and the dipole mode derived from the annual mean sst remain robust in winter and summer despite some differences in the governing processes it is found that the summer dipole mode is associated with the atlantic multidecadal oscillation therefore sst over the coastal china seas may be used as a potential indictor of these global scale climate changes

district scale concentration of native copper lodes from a tectonically induced thermal plume of ore fluids on the keweenaw peninsula northern michigan economic native copper lodes in the lake superior district are confined to a 45 km long portion of the portage lake volcanics on the keweenaw peninsula despite similar host rocks extending for more than 1 000 km around lake superior the focus of ascending ore forming brine into a narrow segment of portage lake strata may be attributed to upward thrusting on the keweenaw fault during closure of the midcontinent rift forming anomalously hot steeply dipping aquifers on the keweenaw promontory and to the development of a single dominant thermal plume within the incipiently buoyant brine at the scale of the mine district on that promontory

abundance of co 2 rich fluid inclusions in a sedimentary basin hosted cu deposit at jinman yunnan china implications for mineralization environment and classification of the deposit the jinman cu deposit is hosted in sandstones and slates of the jurassic huakaizuo formation in the mesozoic to cenozoic lanping basin in western yunnan china despite the fact that cu mineralization occurs mainly in quartz carbonate veins controlled by faults and fractures the jinman deposit was classified as a sediment hosted stratiform cu deposit mainly because it is hosted in a sedimentary basin characterized by abundant red beds with many stratiform cu deposits a detailed petrographic and microthermometric study of fluid inclusions from the jinman deposit reveals the presence of abundant co2 rich fluid inclusions together with aqueous inclusions the co2 rich inclusions have co2 melting temperatures mainly from 58 0 c to 56 6 c homogenization temperatures of the carbonic phase mostly into the liquid phase mainly between 22 c and 30 c clathrate melting temperatures from 1 8 c to 9 2 c with corresponding salinities from 1 6 to 13 4 wt nacl equivalent and total homogenization temperatures from 226 c to 330 c the aqueous inclusions have first melting temperatures from 60 c to 52 c ice melting temperatures from 41 4 c to 2 3 c with salinities from 3 9 to 29 0 wt nacl equivalent and total homogenization temperatures mainly from 140 c to 250 c these fluid inclusion characteristics are comparable to those of orogenic or magmatic mineralization systems and are uncharacteristic of basinal mineralization systems suggesting that it is inappropriate to classify the jinman deposit as a sediment hosted stratiform cu deposit the results of this study together with geochemical data reported previously suggest that the jinman deposit formed in a hydrothermal system that involved both extra basinal deeply sourced co2 rich fluid and basinal aqueous fluid

latent volcanic heat and further unique aspects of early diagenetic stratiform copper mineralization in the white pine presque isle district northern michigan the curious occurrence of copper rich early diagenetic sediment hosted stratiform copper mineralization in the finest grained facies of nonesuch greybeds in northern michigan has been previously attributed to the warming of cupriferous brines in the footwall copper harbor conglomerate by latent volcanic heat from the subjacent porcupine volcanics shield volcano that anomalous footwall warming is employed here to explain other unique aspects of the white pine presque isle mineralization the abrupt downward sulfide zoning from disseminated pyrite to chalcocite across the top of the cupriferous zone the absence of bornite and chalcopyrite in the cupriferous zone proper and the essential absence of pseudomorphs after pyrite euhedra and framboidal aggregates within the cupriferous zone proper as well as the relatively coarse grained character of disseminated chalcocite in the cupriferous zone

crustal scale thrusting and origin of the montreal river monocline a 35 km thick cross section of the midcontinent rift in northern michigan and wisconsin a structurally simple 35 km thick north facing stratigraphic succession of late archean to middle proterozoic rocks is exposed near the montreal river which forms the border between northern wisconsin and michigan this structure the montreal river monocline is composed of steeply dipping to vertical sedimentary rocks and flood basalts of the keweenawan supergroup middle proterozoic along the south limb of the midcontinent rift and disconformably underlying sedimentary rocks of the marquette range supergroup early proterozoic these rocks lie on an archean granite greenstone complex about 10 km of which is included in the monocline this remarkable thickness of rocks appears to be essentially structurally intact and lacks evidence of tectonic thickening or repetition tilting to form the monocline resulted from southward thrusting on listric faults of crustal dimension the faults responsible for the monocline are newly recognized components of a well known regional fault system that partly closed and inverted the midcontinent rift system resetting of biotite ages on the upper plate of the faults indicates that faulting and uplift occurred at about 1060 20 ma and followed very shortly after extension that formed the midcontinent rift system

fractal and multifractal measures of natural and synthetic fracture networks we have analyzed the fractal and multifractal nature of a series of 17 natural fracture trace maps representing a wide variety of scales geological settings and lithologies as well as a number of typical synthetic fracture networks in which fracture locations orientations and lengths are drawn from various probability distribution functions recent studies have shown that multifractal methods can be used to investigate fracture networks at greater depth since the fractal dimension represents only part of the scaling spectrum characterizing each network we find that the real and synthetic fracture maps display fractal and multifractal properties moreover the properties of the synthetic networks are very similar to those of the real networks with nontrivial fractal dimensions and multifractal spectra we suggest that different fracturing mechanisms can lead to two or more distinct subranges over which a fractal dimension can be defined while the heterogeneity of the rock and the nature of the fracturing mechanisms lead to multifractal properties we also find that the fractal dimension of a synthetic fracture network is relatively insensitive to parameters such as fracture length and orientation but can be controlled by appropriate choice of the relative fracture density

relations between deformation and sediment hosted copper mineralization evidence from the white pine part of the midcontinent rift system detailed studies over the past decade have significantly extended and revised our knowledge of the geologic history of the well known white pine mining district of northern michigan and indicate that the location of faults exerted a strong control on copper mineralization in this part of the midcontinent rift system at white pine there is evidence for three episodes of faulting 1 synsedimentary faulting 2 subsequent high angle dominantly normal faulting and 3 thrusting two stages of copper mineralization are present at white pine and in the nearby presque isle syncline the first main stage mineralization formed a classic sediment hosted stratiform copper deposit during early diagenesis synsedimentary faults may have provided important conduits for cupriferous brines flowing from underlying red beds of the copper harbor conglomerate into the reduced silts and shales of the nonesuch formation where main stage copper sulfides and native copper were precipitated the second stage of copper mineralization was synchronous with thrusting and introduced additional copper to the white pine ore body and the presque isle syndine thrust faults and cogenetic tear faults provided conduits for second stage mineralizing fluids collectively these observations indicate strong control by regional deformation on fluid migration and mineralization in the rocks of the midcontinent rift similar to proposed relations between deformation and mineralization in other tectonic settings

the copper harbor conglomerate a late precambrian fining upward alluvial fan sequence in northern michigan the keweenawan copper harbor conglomerate exposed in northern michigan is part of a thick succession of volcanics and terrigenous clastics deposited in the keweenawan trough a failed intracontinental rift it is a fining upward wedge of volcanogenic conglomerate and sandstone deposited as proximal to distal braided stream and sheet flood facies on coalesced alluvial fans and sand flats this unit along with the lower portion of the overlying nonesuch shale consists of an alluvial fan shallow lake sequence that filled the rift during and following volcanic activity the fining upward nature of the sequence reflects a waning sediment supply probably due to lowering of the source area following faulting the copper harbor conglomerate exhibits attributes of both arid fan and humid fan alluvial models coarse grained facies are lithologically similar to alluvial fan units deposited in modern humid regions conversely finer distal copper harbor facies exhibit numerous features indicating flashy discharges and desiccation processes typical of deposition in modern arid regions ambiguity of sedimentary features useful for climatic inference probably reflects the limited applicability of holocene models to more ancient alluvial sequences because precambrian hydraulic regimes developed under various climatic settings may have differed from their holocene counterparts

the sediment hosted stratiform copper ore system sediment hosted stratiform copper deposits comprise disseminated to veinlet cu and cu fe sulfides in siliciclastic or dolomitic sedimentary rocks sediment hosted stratiform copper deposits are extremely common though economically significant deposits are rare they account for approximately 23 percent of the world s cu production and known reserves in addition to being significant sources of co and ag three sedimentary basins the paleoproterozoic kodaro udokan in siberia the neoproterozoic katangan in central africa and the permian basin of central europe contain supergiant 24 million metric tons mt contained cu deposits sediment hosted stratiform copper deposits are the products of evolving basin scale fluid flow systems that include source s of metal and s source s of metal and s transporting fluids the transport paths of these fluids a thermal and or hydraulic pump to collect and drive the fluids and the chemical and physical processes which result in precipitation of the sulfides metal sources are undoubtedly red bed sedimentary rocks containing fe oxyhydroxides capable of weakly binding metals sulfur may be derived from marine or lacustrine evaporites reduced seawater or hydrogen sulfide bearing petroleum metals appear to have been transported at low to moderate temperatures in moderately to highly saline aqueous fluids with the temperature of the fluid largely dependent on the time of fluid migration in the basin s burial history these basinal fluids were focused to potential metal precipitation sites by thinning of the red bed sequence at basin margins by faults by differentially permeable sedimentary units by paleotopography within the basin or along the margins of salt diapirs fluid movement produced widespread basin scale alteration that has commonly been overlooked but can form an important exploration guide sulfide precipitation occurred due to reduction typically caused by reaction with carbonaceous rocks or petroleum the amount of sulfides present at any deposit may be either metals or sulfide limited or could have been controlled by the amount of available reductant e g petroleum while understanding of sediment hosted stratiform copper ore genesis at the deposit scale is relatively robust there are still significant questions in regards its position in terms of basin evolution a wide variety of basin architectures and processes can lead to the formation of sediment hosted stratiform copper deposits despite general agreement that sulfides postdate sedimentation the absolute age of mineralization in many deposits has been difficult to document and the available evidence suggests that deposits can form throughout a basin s evolution from early diagenesis of ore host sediments to basin inversion and metamorphism supergiant and giant deposits formed in basins which underwent prolonged periods of fluid flow and in which unique conditions allowed for the accumulation of large amounts of metal bearing fluid sufficient reduced s and large amounts of reductants

role of indian ocean warming in the development of philippine sea anticyclone during enso 1 the anomalous low level anticyclone near the philippines and suppressed convection over the western pacific associated with the mature warm phase of el nino southern oscillation enso have been suggested as important elements in the interaction between enso and the east asian monsoon we examined the causes of these anomalies in the circulation and convection using a newly developed linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes a conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the philippine sea anticyclone from a series of the moist linear model experiments we found that the modest warming of the indian ocean in addition to the strong warming in the central eastern pacific and weak cooling in the western pacific is significant to suppress the convection over the maritime continent observed data also show a coincidence of the development between the philippine sea anticyclone indian ocean warming and the ascending motion over the indian ocean supporting the model results the above results indicate that the atmosphere ocean system in the indian ocean may be one of important factors to improve predictability of the east asian climate during enso

the midcontinent rift in the lake superior region with emphasis on its geodynamic evolution abstract the midcontinent rift is a middle proterozoic continental rift which records about 15 m y of extension subsidence and voluminous volcanism in the period 1109 1094 ma in the central part of north america during that time the crust was nearly totally separated and as much as 25 km of subaerial basalts accumulated in a deep central depression following extension and volcanism a longer period of subsidence resulted in development of a post rift sedimentary basin in which as much a 8 km of fluvial and lacustrine clastic rocks were deposited partial inversion of the central depression occurred about 30 50 m y after extension to produce the current configuration of a central horst composed mostly of thick volcanic accumulations between shallower flanking basins

indian ocean capacitor effect on indo western pacific climate during the summer following el nino significant climate anomalies persist through the summer june august after el nino dissipates in spring over the equatorial pacific they include the tropical indian ocean tio sea surface temperature sst warming increased tropical tropospheric temperature an anomalous anticyclone over the subtropical northwest pacific and increased mei yu baiu rainfall over east asia the cause of these lingering el nino effects during summer is investigated using observations and an atmospheric general circulation model gcm the results herein indicate that the tio warming acts like a capacitor anchoring atmospheric anomalies over the indo western pacific oceans it causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection emanating a baroclinic kelvin wave into the pacific in the northwest pacific this equatorial kelvin wave induces northeasterly surface wind anomalies and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone the gcm results support this kelvin wave induced ekman divergence mechanism in response to a prescribed sst increase over the tio the model simulates the kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest pacific an additional experiment further indicates that the north indian ocean warming is most important for the kelvin wave and northwest pacific anticyclone a result corroborated by observations these results have important implications for the predictability of indo western pacific summer climate the spatial distribution and magnitude of the tio warming rather than simply whether there is an el nino in the preceding winter affect summer climate anomalies over the indo western pacific and east asia

effect of potential vorticity flux on the circulation in the south china sea this study analyzes temperature and salinity products from the u s navy generalized digital environment model to avoid the fictitious assumption of no motion reference level a p vector inverse method is employed to derive geostrophic velocity line integral of geostrophic velocity shows evidence for the existence of a sandwiched circulation in the south china sea scs i e cyclonic circulation in the subsurface and deep layers and anticyclonic in the intermediate layer to reveal the factors responsible for the sandwiched circulation we derive the potential vorticity equation based on a four and a half layer quasi geostrophic model and apply theoretical potential vorticity constraint to density layers the result shows that the sandwiched circulation is largely induced by planetary potential vorticity flux through lateral boundaries mainly the luzon strait this dynamical mechanism lies in the fact that the net potential vorticity inflow in the subsurface and deep layers leads to a positive layer average vorticity in the scs basin yielding vortex stretching and a cyclonic basin wide circulation on the contrary the net potential vorticity outflow in the intermediate layer induces a negative layer average vorticity generating an anticyclonic basin wide circulation in the scs furthermore by illustrating different consequence from depth density layers we clarify that density layers are essential for applying theoretical potential vorticity constraint to the isolated deep scs basin

reos and s isotopic constraints on the origins of two mineralization events at the tangdan sedimentary rock hosted stratiform cu deposit sw china abstract the tangdan stratiform cu deposit in the kangdian region of south china is hosted in sedimentary rocks of the late paleoproterozoic to early mesoproterozoic dongchuan group orebodies mainly occur in dolostone and black shale above a thick sequence of hematitic sandstone and siltstone mineralization consists mainly of bedding parallel stratiform ores with minor amounts of discordant vein type ores both stratiform and vein type ores are composed of bornite and chalcopyrite with minor chalcocite and digenite associated with gangue minerals including ankerite dolomite calcite and quartz cu sulfides from vein type ores contain 122 293 ppb re much higher than those of stratiform ores 0 6 14 ppb re they have highly radiogenic os with re os model ages ranging from 1413 to 1457 ma and a weighted mean re os model age of 1432 19 ma 2 mswd 0 30 which is within uncertainty in agreement with isochron ages of 1401 30 ma 2 mswd 0 67 and 1397 71 ma 2 mswd 0 22 using 187 re 188 os versus 187 os 188 os and 187 re versus 187 os regression respectively in contrast sulfides from stratiform ores did not yield meaningful model ages due to the extremely low concentrations of re and radiogenic os however early studies have shown that the stratiform ores were likely formed at 1700 ma during the diagenesis of the host strata sulfides from the vein type ores have 34 s values ranging from 15 to 8 significantly lower than those of stratiform ores 3 to 10 suggesting that organic matter may have been involved in the formation of the vein type ores contrasting re os and s isotopes suggest that the two types of ores at the tangdan deposit were likely formed from different ore forming fluids we propose that stratiform ores were precipitated from basinal fluids during the early evolution of the rift basin whereas the vein type ores were formed due to a much younger thermal event during which hydrothermal fluids interacted with overlying black shale to account for the high re and negative 34 s values this study demonstrates that re os isotopes of sulfides can be used to study the origin of hydrothermal system

paleomagnetism of the native copper mineralization keweenaw peninsula michigan the age and genesis of michigan s world class native copper deposits are poorly constrained the copper is hosted by basaltic flow tops and conglomeratic interbeds of the 1095 2 ma keweenawan por

formation of sedimentary rock hosted stratiform copper deposits through earth history sedimentary rock hosted stratiform copper deposits form by movement of oxidized copper bearing fluids across a reduction front that results in the precipitation of copper sulfides large scale production of such oxidized fluids as well as the formation of mobile hydrocarbons oil has probably been common since the formation of the first red beds in the paleoproterozoic and deposits of this type occur in rocks from the paleoproterozoic to the tertiary however supergiant deposits are currently recognized in only three basins the paleoproterozoic kodaro udokan basin of siberia the neoproterozoic katangan basin of south central africa and the permian zechstein basin of northern europe the paucity of data regarding the udokan deposit makes understanding this system difficult in terms of earth history events both the neoproterozoic and the permian were times of supercontinent breakup with major landmasses at low latitudes this global tectonic framework favored the formation of failed rifts that subsequently became significant intracratonic basins with basal synrift red bed sequences overlain by marine and or lacustrine sediments and in some basins located at low latitudes by thick evaporitic strata the intracratonic setting of these basins allowed the development of a hydrologically closed basinal architecture in which highly oxidized and saline moderate temperature basinal brines were produced that were capable of supplying reduction controlled sulfide precipitation over very long time periods tens to hundreds of millions of years the length of time available for the mineralizing process may be the key factor necessary to form supergiant deposits however examination of the absolute ages for the kupferschiefer zechstein basin and katangan deposits allows speculation that other factors may also have been important both the neoproterozoic and permian were times of major glacial events glaciation may also be conducive for the formation of supergiant sediment hosted stratiform copper deposits glacial periods correspond to magnesium and sulfate rich oceans that could have been responsible for additional sulfur in basinal brines developed during evaporite formation and would then be available during the long mineralization process

closing of the midcontinent rift a far field effect of grenvillian compression the midcontinent rift formed in the laurentian supercontinent between 1109 and 1094 ma soon after rifting stresses changed from extensional to compressional and the central graben of the rift was partly inverted by thrusting on original extensional faults thrusting culminated at about 1060 ma but may have begun as early as 1080 ma on the southwest trending arm of the rift the crust was shortened about 30 km on the southeast trending arm strike slip motion was dominant the rift developed adjacent to the tectonically active grenville province and its rapid evolution from an extensional to a compressional feature at ca 1080 ma was coincident with renewal of northwest directed thrusting in the grenvllle probably caused by continent continent collision a zone of weak lithosphere created by rifting became the locus for deformation within the otherwise strong continental lithosphere stresses transmitted from the grenville province utilized this weak zone to close and invert the rift

origin of the nchanga copper cobalt deposits of the zambian copperbelt the zambian copperbelt forms the southeastern part of the 900 km long neoproterozoic lufilian arc and contains one of the world s largest accumulations of sediment hosted stratiform copper mineralization the nchanga deposit is one of the most significant ore systems in the zambian copperbelt and contains two major economic concentrations of copper and cobalt hosted within the lower roan group of the katangan supergroup a lower orebody copper only and upper orebody copper and cobalt occur towards the top of arkosic units and within the base of overlying shales the sulfide mineralogy includes pyrite bornite chalcopyrite and chalcocite although in the lower orebody sulfide phases are partially or completely replaced by malachite and copper oxides carrollite is the major cobalt bearing phase and is restricted to fault propagation fold zones within a feldspathic arenite hydrothermal alteration minerals include dolomite phlogophite sericite rutile quartz tourmaline and chlorite quartz veins from the mine sequence show halite saturated fluid inclusions ranging from 31 to 38 wt equivalent nacl with homogenisation temperatures thtot ranging between 140 and 180 c diagenetic pyrites in the lower orebody show distinct relatively low 34s ranging from 1 to 17 whereas arenite and shale hosted copper and cobalt sulfides reveal distinctly different 34s from 1 to 12 for the lower orebody and 5 to 18 for the upper orebody there is also a clear distinction between the 34s mean of 12 1 3 3 n 65 for the upper orebody compared with 5 2 3 6 n 23 for the lower orebody the 13c of dolomites from units above the upper orebody give 13c values of 1 4 to 2 5 consistent with marine carbon however dolomite from the shear zones and the alteration assemblages within the upper orebody show more negative 13c values 2 9 to 4 0 and 5 6 to 8 3 respectively similarly shear zone and upper orebody dolomites give a 18o of 11 7 to 16 9 compared to lower roan dolomites which show 18o of 22 4 to 23 0 two distinct structural regimes are recognized in the nchanga area a weakly deformed zone consisting of basement and overlying footwall siliciclastics and a moderate to tightly folded zone of meta sediments of the katangan succession the fold geometry of the lower roan package is controlled by internal thrust fault propagation folds which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the ne faulting and folding are considered to be synchronous as folding predominantly occurred at the tips of propagating thrust faults with local thrust breakthrough the data from nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the lufilian orogeny sulfides tend to be concentrated within arenites or coarser grained layers within shale units suggesting that host rock porosity and possibly permeability played a role in ore formation however sulfides are also commonly orientated along but not deformed by a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization the ore mineralogy hydrothermal alteration and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate and metal enriched hydrothermal fluid at the site of mineralization there is no evidence at nchanga for a contribution of bacteriogenic sulfide produced during sedimentation or early diagenesis to the ores

copper mineralization and alterations in gercus basalt within the gercus formation northern iraq abstract the gercus basalt is a recently discovered body within the gercus formation which is exposed on both limbs of the large double plunging nw se trending bekhair anticline to the north of duhok city northern iraq the basalt is mostly basanitic and alkaline in nature greenish to grayish black in color and very fine grained vesicular amygdaloidal and microscopically porphyritic in texture it consists of anorthoclase diopside forsterite and accessory titaniferous magnetite ilmenite and apatite as well as their alteration products the primary minerals are pervasively altered by calcitization zeolitization serpentinization chloritization silicification iddingsitization martitization and possibly anorthoclasization copper mineralization has taken place as veins and fracture joint filling which is mostly observed near the northwestern plunge of the anticline where the basalt attains its maximum thickness of about 16 m twelve copper minerals were found within veins and fractures including primary minerals bornite chalcopyrite and an unidentified sulfide cu2 3fes3 and their secondary alteration and replacement products represented by sulfides covellite digenite and chalcocite native copper cuprite carbonates malachite and azurite silicate chrysocolla and possibly sulfates the copper minerals are in many cases zonally arranged as spherules where the primary minerals acted as cores surrounded outward by secondary minerals primary copper mineralization is of late magmatic hydrothermal origin postdating the emplacement consolidation deuteric alterations and fracturing jointing of the gercus basalt followed by the formation of secondary supergene copper minerals as a result of alteration and replacement of the primary copper sulfides along mineralized veins and fractures joints due to chemical weathering by meteoric and or groundwater during eocene time

fracture spacing and orientation distributions for two dimensional data sets a new automated method is developed for the measurement and display of fracture spacing and orientation from two dimensional 2 d fracture maps separate histograms of fracture spacing are calculated at different orientations through the 2 d data set the histograms for all orientations are plotted together reducing the biasing effects associated with one dimensional 1 d sampling of a fracture population quantitative measurements of fracture strike anisotropy and fracture density are incorporated in the plot no prior measurements are needed of parameters such as fracture spacing orientation or width the data do not have to be preprocessed into a numerical vector format saving time and reducing user bias the method retains the relative frequency of different ranges of fracture spacings which are lost in other fracture frequency measures such as fracture intensity density thus the presence of any dominant rather than average fracture spacing and fracture clustering is highlighted the method provides a quantitative statistically unbiased representation of fracture orientation and spacing and is illustrated on synthetic and real fracture data sets at a range of scales from meters to tens of kilometers its application to a seismic energy scattering problem is also discussed

sulfur carbon hydrogen and oxygen isotope geochemistry of the idaho cobalt belt cobalt copper gold deposits of the idaho cobalt belt including the deposits of the blackbird district have been analyzed for their sulfur carbon hydrogen and oxygen isotope compositions to improve the understanding of ore formation previous genetic hypotheses have ranged widely linking the ores to the sedimentary or diagenetic history of the host mesoproterozoic sedimentary rocks to mesoproterozoic or cretaceous magmatism or to metamorphic shearing the 34 s values are nearly uniform throughout the blackbird district with a mean value for cobaltite coass the main cobalt mineral of 8 0 0 4 n 19 the data suggest that 1 sulfur was derived at least partly from sedimentary sources 2 redox reactions involving sulfur were probably unimportant for ore deposition and 3 the sulfur was probably transported to sites of ore formation as h 2 s hydrogen and oxygen isotope compositions of the ore forming fluid which are calculated from analyses of biotite rich wall rocks and tourmaline do not uniquely identify the source of the fluid plausible sources include formation waters metamorphic waters and mixtures of magmatic and isotopically heavy meteoric waters the calculated compositions are a poor match for the modified seawaters that form volcanogenic massive sulfide vms deposits carbon and oxygen isotope compositions of siderite a mineral that is widespread although sparse at blackbird suggest formation from mixtures of sedimentary organic carbon and magmatic metamorphic carbon the isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper so its significance for the ore forming event is uncertain from the stable isotope perspective the mineral deposits of the idaho cobalt belt contrast with typical vms and sedimentary exhalative deposits they show characteristics of deposit types that form in deeper environments and could be related to metamorphic processes or magmatic processes although the isotopic evidence for magmatic components is relatively weak

strata bound fe co cu au bi y ree deposits of the idaho cobalt belt multistage hydrothermal mineralization in a magmatic related iron oxide copper gold system mineralogical and geochemical studies of strata bound fe co cu au bi y rare earth element ree deposits of the idaho cobalt belt in east central idaho provide evidence of multistage epigenetic mineralization by magmatic hydrothermal processes in an iron oxide copper gold iocg system deposits of the idaho cobalt belt comprise three types 1 strata bound sulfide lenses in the blackbird district which are cobaltite and less commonly chalcopyrite rich with locally abundant gold native bismuth bismuthinite xenotime allanite monazite and the be rich silicate gadolinite y with sparse uraninite stannite and bi tellurides in a gangue of quartz chlorite biotite muscovite garnet tourmaline chloritoid and or siderite with locally abundant fluorapatite or magnetite 2 discordant tourmalinized breccias in the blackbird district that in places have concentrations of cobaltite chalcopyrite gold and xenotime and 3 strata bound magnetite rich lenses in the iron creek area which contain cobaltiferous pyrite and locally sparse chalcopyrite or xenotime most sulfide rich deposits in the blackbird district are enclosed by strata bound lenses composed mainly of cl rich fe biotite some deposits have quartz rich envelopes whole rock analyses of 48 co and or cu rich samples show high concentrations of au up to 26 8 ppm bi up to 9 16 wt y up to 0 83 wt rees up to 2 56 wt ni up to 6 780 ppm and be up to 1 180 ppm with locally elevated u up to 124 ppm and sn up to 133 ppm zn and pb contents are uniformly low 821 and 61 ppm respectively varimax factor analysis of bulk compositions of these samples reveals geochemically distinct element groupings that reflect statistical associations of monazite allanite and xenotime biotite and gold detrital minerals chalcopyrite and sparse stannite quartz and cobaltite with sparse selenides and tellurides significantly cu is statistically separate from co and as consistent with the general lack of abundant chalcopyrite in cobaltite rich samples paragenetic relations determined by scanning electron microscopy indicate that the earliest y ree be mineralization preceded deposition of co cu au and bi allanite xenotime and gadolinite y commonly occur as intergrowths with and inclusions in cobaltite the opposite texture is rare monazite in contrast forms a poikiloblastic matrix to cobaltite and thin rims on allanite and xenotime reflecting a later metamorphic paragenesis allanite and xenotime also show evidence of late dissolution and reprecipitation forming discordant rims on older anhedral allanite and xenotime and separate euhedral crystals of each mineral textural data suggest extensive deformation of the deposits by folding and shearing and by pervasive recrystallization all during cretaceous metamorphism sensitive high resolution ion microprobe u pb geochronology by aleinikoff et al 2012 supports these paragenetic interpretations documenting contemporaneous mesoproterozoic growth of early xenotime and crystallization of megacrystic a type granite on the northern border of the district these ages are used together with mineralogical and geochemical data from the present study to support an epigenetic iocg model for fe co cu au bi y ree deposits of the idaho cobalt belt a sulfide facies variant of iocg deposits is proposed for the blackbird district in which reducing hydrothermal conditions favored deposition of sulfide minerals over iron oxides this new model includes mesoproterozoic vein mineralization and related fe cl metasomatism that formed the biotite rich lenses a predominantly felsic magmatic source for metals in the deposits given their local abundance of y rees and be and a major sedimentary component in the hydrothermal fluids based on independent sulfur isotope and boron isotope data for sulfides and ore related tourmaline respectively

latent thermal effects from porcupine volcanics calderas underlying the white pine presque isle stratiform copper mineralization northern michigan economic stratiform copper mineralization in the fine grained carbonaceous basal nonesuch formation of the 50 km wide white pine presque isle mining district northern michigan has long been explained by the essentially vertical infiltration of cupriferous brine across the full width of basal nonesuch strata from the underlying copper harbor conglomerate aquifer followed by copper precipitation mainly by reactions with in situ iron sulfide based on that model why do lesser amounts of total copper measured in vertical sections occur in coarser grained presumably more permeable basal nonesuch strata situated laterally to the east and west of the mining district the answer may lie in increased infiltration rates for copper harbor hosted ore forming brine warmed locally by latent volcanic heat from a resurgent caldera or calderas located within the large porcupine volcanics dome underlying the mine district not only would caldera heat have warmed the brine and lowered its density but more importantly it would have produced a remarkable decrease in the brine viscosity an increase in temperature from 15 to 100 c could have increased the brine infiltration rate by more than four times in very early diagenetic time when the sediments were poorly compacted and highly porous because progressive compaction would have opposed the temperature effect a very early diagenetic timing is suggested for main stage copper mineralization over the porcupine volcanics caldera textural evidence has also long supported an early mineralization event at the rift basin scale the exceptionally rapid upward flux of warmed brine into fine grained nonesuch over the caldera would have required equivalent volumes of replacement brine which would in turn have required a lateral convergence of brine within the footwall copper harbor conglomerate aquifer toward the white pine presque isle district this lateral focus of brine toward the warm caldera area would have created a more efficient basin scale ore forming system than that resulting from a linear hydrogeologic flow most concepts described here deserve further evaluation through quantitative hydrogeologic modeling thermal effects on ore brine viscosities and densities developed here for the sediment hosted stratiform copper mineralization of the white pine presque isle district could be considered in genetic models for other deposits and deposit types the effects are especially strong for solutions warmed from low temperatures e g 20 c or lower to 100 c and could also be important to ore fluid flow for ores involving much higher hydrothermal temperatures if solutions with initially low temperatures played a role in their genesis

stable isotope and fluid inclusion study of sediment hosted stratiform copper deposits from the neuquen basin argentina the los chihuidos and el porvenir deposits of the neuquen basin are examples of sediment hosted stratiform cu deposits generated by interaction of hydrocarbons and formation water with host red beds and metal charged basinal brines during early diagenesis of red beds precipitated hematite kaolinite at 60 c from meteoric water followed by calcite 1 13c 8 to 3 3 and barite 34s 4 1 with increasing temperature 75 85 c from an evolved surface fluid 18ofluids 0 9 to 2 7 during the tertiary andean orogeny hydrocarbons and formation water migrated and reacted with the red beds resulting in bleaching of the sandstone smectite fluid 18o 2 2 and d 73 7 chlorite smectite mixed layer minerals fluid 18o 6 9 and d 84 pyrite 34s 10 2 and calcite 2 13c 12 9 to 6 8 formed as by product of the redox reactions calcite 2 formed from low salinity fluids 0 4 to 5 9 wt nacl equiv at slightly higher temperatures 125 145 c at el porvenir and at los chihuidos deposit 80 105 c during subsequent uplift metal charged basinal brines flowed into the bleached sandstone and precipitated chalcopyrite bornite 34s 12 3 followed by chalcocite spionkopite 34s 64 to 4 1 calcites 3a 13c 19 to 10 1 and 3b 13c 31 4 to 9 5 that accompanied fe cu and cu sulfides respectively formed from saline fluids up to 21 3 wt nacl equiv at temperatures of 159 70 c the 18o values 5 6 to 11 4 of fluids in equilibrium with calcite 3a are similar to oilfield and basinal brines fluids in equilibrium with calcite 3 in los chihuidos and calcite 3b in el porvenir show much lighter 18o values 7 3 to 4 6 and 0 6 to 2 3 respectively which suggests the involvement of methane as the main reductant and possibly meteoric water interaction

the genesis of the liancheng cu mo deposit in the lanping basin of sw china constraints from geology fluid inclusions and cu s h o isotopes abstract liancheng is an important cu mo deposit hosted by red beds in the mesozoic to cenozoic lanping basin located in the sanjiang tethyan orogen of sw china the deposit is fault controlled where it has been affected and enriched by four hydrothermal events indicated by four distinct sets of veins and their cross cutting relationships a detailed cu s h o isotopic study is reported here on the mineralization focusing on the source of the metals and fluid and on the mineralizing processes the first two hydrothermal events are characterised by co 2 and fluid rich inclusions with homogenisation temperatures of 124 446 c and salinities ranging from 0 4 to 24 6 wt nacl equiv the next two hydrothermal events are characterised by liquid rich fluid inclusions that homogenise at 145 256 c with salinities ranging from 1 4 to 22 9 wt nacl equiv the h o isotope values obtain from the fluid inclusions indicate that the first three hydrothermal events relate to mineralizing fluids derived from a metamorphic source but the last event includes a mixed metamorphic and meteoric source chalcopyrite tennantite and bornite from the deposit have 34 s values between 11 5 and 3 the 65 cu values for quartz cu sulfide mineralization associated with the second hydrothermal event range from 0 31 to 0 2 but carbonate cu sulfide mineralization associated with the third hydrothermal event ranges from 1 01 to 1 08 the combination of the cu and s isotopic values and field observations indicate that the controlling factors include structures the temperature of regional metamorphism and the ph of the mineralizing fluid the zation is therefore characteristic of an orogenic type deposit

magnetization age from paleomagnetism of the copper harbor red beds northern michigan usa and its keweenawan geologic consequences the copper harbor formation on lake superior s keweenaw peninsula records the transition from volcanic to sedimentary infilling of north america s 1 1 ga keweenawan rift radiometric dating shows t

different responses of sea surface temperature in the south china sea to various el nino events during boreal autumn abstractthis study investigates variations of sea surface temperature sst anomalies in the south china sea scs during developing autumn of various el nino events the warm sst anomalies are observed in the scs for canonical el nino and el nino modoki i whereas the cold sst anomalies are found for el nino modoki ii the ocean heat budget analyses show that the latent heat flux change induced by various types of el nino events is a major contributor to the scs sst variations an anomalous anticyclone resides near the philippine sea for canonical el nino and el nino modoki i which induces the southerly wind anomalies over the scs and thus weakens the climatological northeasterly in boreal autumn the weakened surface wind speed reduces heat loss from the ocean leading to a warmer state in the scs however for el nino modoki ii the anomalous anticyclone shifts westward to the west of the scs and thus the northeasterly wind anomalies appear in the scs the northeasterly anomalies enhance the climatol

red bed and basement sourced fluids recorded in hydrothermal mn fe as veins sailauf germany a la icpms fluid inclusion study the hydrothermal mn fe as vein mineralization at sailauf germany hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history the mineralization is related to a major unconformity that separates permian zechstein sedimentary rocks from underlying variscan crystalline basement the hydrothermal veins contain two principal mineralization stages which are mn oxides associated with calcite and hematite associated with mn calcite the fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography microthermometry and la icpms microanalysis coupled with stable isotope geochemistry of carbonate and oxide minerals the fluid inclusions are high salinity sodic calcic brines and the bulk fluid properties show no major differences between the mn oxide and the hematite stage la icpms analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their k li b pb and zn concentrations the fluid that precipitated the mn oxide stage has anomalous pb zn and li b ratios which closely resemble fluids found in fracture fillings in red beds of the permian rotliegend basin by contrast the fluids associated with the hematite stage have pb zn and li b ratios typical of crustal fluids that were derived from interaction with crystalline basement both fluids possess characteristic element ratios including cl br but variable absolute concentrations of most metals this suggests that both fluids were modified by mixing with a common metal depleted brine that had a similar cl br ratio most likely a formation water from the overlying zechstein sedimentary rocks the sailauf mineralization provides insight into the protracted post variscan fluid evolution at the basement cover interface the compositionally anomalous fluid that precipitated the mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of kupferschiefer type sediment hosted cu deposits conversely the fluid that deposited the hematite mineralization resembles fluids that typically form basement and sediment hosted pb zn deposits

the sandstone hosted stratiform copper mineralization at mwitapile and its relation to the mineralization at lufukwe lufilian foreland democratic republic of congo abstract the lufilian foreland is a triangular shaped area located in the se of the democratic republic of congo and to the ne of the lufilian arc which hosts the well known central african copperbelt the lufilian foreland recently became an interesting area with several vein type e g dikulushi and stratiform e g lufukwe and mwitapile copper occurrences the lufilian foreland stratiform cu mineralization is to date observed in sandstone rock units belonging to the nguba and kundelungu groups katanga supergroup the mwitapile sandstone hosted stratiform cu prospect is located in the north eastern part of the lufilian foreland the host rock for the cu mineralization is the sonta sandstone of the ngule subgroup kundelungu group a combined remote sensing petrographic and fluid inclusion microthermometric analysis was performed at mwitapile and compared with similar analysis previously carried out at lufukwe to present a metallogenic model for the mwitapile and lufukwe type stratiform copper deposits interpretation of etm satellite images for the mwitapile prospect and the surrounding areas indicate the absence of ne sw or ene wsw faults similar to those observed controlling the mineralization at lufukwe faults with these orientations are however present to the nw w sw and e of the mwitapile prospect at mwitapile the sonta sandstone host rock is intensely compacted arkosic to calcareous with high silica cementation first generation of authigenic quartz overgrowths in the sonta sandstone feldspar and calcite are present in disseminated banded and nodular forms intense dissolution of these minerals caused the presence of disseminated rectangular pipe like and nodular dissolution cavities sulfide mineralization is mainly concentrated in these cavities the hypogene sulfide minerals consist of two generations of pyrite chalcopyrite bornite and chalcocite separated by a second generation of authigenic quartz overgrowth the hypogene sulfide minerals are replaced by supergene digenite and covellite fluid inclusion microthermometry on the first authigenic quartz phase indicates silica precipitation from an h 2 o nacl cacl 2 fluid with a minimum temperature between 111 and 182 c and a salinity between 22 0 and 25 5 wt cacl 2 equiv microthermometry on the second authigenic quartz overgrowths and in secondary trails related to the mineralization indicate that the mineralizing fluid is characterized by variable temperatures th 120 to 280 c and salinities 2 4 to 19 8 wt nacl equiv and by a general trend of increasing temperatures with increasing salinities comparison between mwitapile and lufukwe indicates that the stratiform cu mineralization in the two deposits is controlled by similar sedimentary diagenetic and structural factors and likely formed from a similar mineralizing fluid a post orogenic timing is proposed for the mineralization in both deposits the main mineralization controlling factors are grain size clay and pyrobitumen content the amount and degree of feldspar and or calcite dissolution and the presence of ne sw to ene wsw faults the data support a post orogenic fluid mixing model for the mwitapile and lufukwe type sandstone hosted stratiform cu deposits in which the mineralization is related to the mixing between a cu rich hydrothermal fluid with a temperature up to 280 c and a maximum salinity of 19 8 wt nacl equiv with a colder low salinity reducing fluid present in the sandstone host rock the mineralizing fluid likely migrated upwards to the sandstone source rocks along ne sw to ene wsw orientated faults at lufukwe the highest copper grades at surface outcrops and boreholes were found along and near to these faults at mwitapile where such faults are 2 to 3 km away the cu grades are much lower than at lufukwe copper precipitation was possibly promoted by reduction from pre existing hydrocarbons and non copper sulfides and by the decrease in fluid salinity and temperature during mixing based on this research new cu prospects were proposed at lufukwe and mwitapile and a set of recommendations for further cu exploration in the lufilian foreland is presented

the spar lake strata bound cu ag deposit formed across a mixing zone between trapped natural gas and metals bearing brine ore formation at the spar lake red bed associated strata bound cu deposit took place across a mixing and reaction zone between a hot oxidized metals transporting brine and a reservoir of sour h2s bearing natural gas trapped in the host sandstones fluid inclusion volatile analyses have very high ch4 concentrations 1 mol in most samples and a sample from the fringe of the deposit has between 18 and 36 mol ch4 the ratio of ch4 co2 in fluid inclusions appears to vary regularly across the deposit with the lowest ch4 co2 ratios from high grade chalcocite bearing ore and the highest from the chalcopyrite bearing fringe the helium r ra isotope ratios 0 23 0 98 and concentrations define a mixture between crustal and atmospheric helium the volatiles in fluid inclusions ch4 co2 h2s so2 h2 h2o and other organic gases and values of f o2 and temperature calculated from the volatiles data all show gradations across the deposit that are completely consistent with such a mixing and reaction zone other volatiles from the fluid inclusions hcl hf 3he 4he n2 ar characterize the brine and give evidence for only shallow crustal fluids with no magmatic influences the brine entered the gas reservoir from below and along the axis of the deposit and migrated out along bedding to the southwest northeast and northwest metals transporting brines may have been fed into the host sandstones from the east fault but that remains uncertain abundant ore stage fe and mn calcite cements from the reduced fringe have 13c values as low as 18 4 and many values less than 10 which indicate that significant carbonate was generated by oxidation of organic carbon from the natural gas the zone of calcite cements with very low 13c values approximately envelopes chalcocite bearing ore sulfur isotope data of cu pb and fe sulfides and barite indicate derivation of roughly half of the orebody sulfide directly from sour gas h2s that sour gas h2s had developed in steps known from other sedimentary basins starting with 1 bacterial sulfate reduction bsr of seawater sulfate having 34s of about 20 and sequestering of the sulfide in organic matter in source rocks stratigraphically below the deposit host rocks followed by 2 maturation of the sulfide bearing organic matter into liquid petroleum with relatively homogeneous sulfide having 34s of 5 5 then by 3 thermal cracking of the oil to ch4 and h2s with relatively homogeneous sulfide having 34s closely distributed about 6 the ch4 and h2s migrated and were trapped in sandstones of the upper member of the revett formation where they were later met by the 200 c metals transporting brine there was additional contribution of sulfide to ore from later thermochemical sulfate reduction tsr operating on sulfate 34s of 20 to 29 in both formation waters and metals transporting solutions a large range of 34s in sulfides resulted as the 6 sour gas sulfide was supplemented with varying proportions of 20 to 29 sulfide from tsr

value of mineral deposits associated with mafic and ultramafic magmatism implications for exploration strategies abstract magmatic ore deposits associated with ultramafic and mafic magmatism modum include nickel sulfide deposits that are locally enriched in copper cobalt platinum group elements and gold a diverse range in platinum group element deposit types oxide and silicate related nickel cobalt laterite deposits formed by weathering of ultramafic bodies and massive and stratiform accumulations of chromite ilmenite and vanadium bearing magnetite magmatic ore deposits associated with ultramafic and mafic rocks span most of earth s history and are well represented on all continents and in all climatic zones and physiographic regions currently these deposits are estimated to account for approximately 7 of the total value of annual global metal and mineral mining they include the world s greatest concentration of metals the bushveld complex which has an estimated total metal endowment value representing past production and current reserves and resources of us 3 6 trillion recent trends in exploration spending for mafic to ultramafic magmatic ore deposits compared to commodity market size and production value indicate a significant under investment in exploration for magmatic chromite ilmenite vanadium and polymetallic disseminated copper nickel platinum group element sulfide deposits historically exploration of mafic to ultramafic magmatic belts has commonly involved a narrow range of deposit models geological environments and exploration methods a value based and more holistic approach to exploration for mafic to ultramafic magmatic ore deposits is proposed that captures a larger range of known mineralization styles settings and commodities a focus on high value deposits providing excellent operating margins and long mine life is recommended as a starting point for new programs however by recognizing the full range of possible mineralization styles and understanding mineral economic thresholds future explorers can expand the search area and methodology and increase the probability of discoveries that create value assuming that commodity prices continue to rise with declining average grades current global resources hosted by mafic to ultramafic magmatic ore deposits are adequate to meet global demand for nickel platinum group elements pge chromium and vanadium for many decades to come despite this the high net smelter return nsr value of many types of modum deposits provides ongoing economic motivation for both greenfields and brownfields exploration in these strategically important deposits furthermore the large range in producer costs for key modum commodities such as nickel copper and pge provides significant opportunities for new projects to displace existing higher cost operations on the industry cost curve the known clustering of high value deposits within discrete magmatic belts e g nickel sulfide and nickel laterite deposits is an additional motivation for exploration investment as it allows exploration to focus early in areas of higher mineral potential additional incentives for modum exploration include the cumulative size and maturity of modum commodities that reduce investment risk and thereby appeal to junior explorers mid cap explorers and developers and major multi national mining companies the economies of scales that were successfully applied to mining of large porphyry copper deposits for many decades could have a similar positive impact on a large number of advanced modum projects especially polymetallic sulfide deposits capable of generating high value concentrates having significant base metal and precious metal contents

enigmatic carbonates of the ombombo subgroup otavi fold belt namibia a prelude to extreme cryogenian anoxia abstract the ombombo subgroup of the otavi fold belt kaokoveld namibia preserves a succession of clastic and carbonate sediments with unusual sedimentary features the stratigraphy of these units is discussed here in detail for the first time since their initial definition with particular emphasis on the sedimentology of carbonate units early neoproterozoic shales of the beesvlakte formation equivalent to the zambian katangan copperbelt s lower roan formation host evaporitic lithologies and minor copper mineralisation the overlying dolomitic 760 ma devede formation contains carbonate platformal lithologies which are in many ways dissimilar to phanerozoic shallow water carbonates this includes unusual curl breccias sheet cavities carbonate shrubs and tepee carbonate lithologies which contain large quantities of fibrous cements curl breccias are defined here as distinctive curled intraclasts of laminated dolomite that often have shrinkage cracks in their margins and are cemented by fibrous dolomite cements fibrous cements take on two forms an early length fast fascicular optic dolomite and a later length slow phase with unit extinction the presence of overlying internal sediments the fibrous habit of these first generation cements as well as their preserved cathodoluminescent and optical character suggests that these cements originally precipitated as calcite and dolomite marine cements respectively after this initial marine calcite precipitation all components of devede formation carbonates have been mimetically dolomitised preserving original depositional fabrics combined with the presence of marine dolomite cements this style of dolomitisation is suggested to be syn sedimentary similar to that of some cryogenian dolomites suggesting unusual ocean conditions during the early neoproterozoic in particular the presence of dolomite marine cements which have been linked to ocean anoxia and high seawater mg ca conditions suggests that the onset of marine anoxia in the neoproterozoic may have occurred during the growth of the devede formation carbonate platforms prior to the sturtian glaciation this implies that glaciation may not be the sole cause for the development of marine anoxia during the neoproterozoic it is possible that marine anoxia in this southern african ocean basin may have contributed to a build up of metals in seawater perhaps pre enriching basinal fluids for large scale stratabound copper mineralisation

u th pb zircon ages of some keweenawan supergroup rocks from the south shore of lake superior new single crystal zircon u th pb ages for plutonic and rhyolitic keweenawan supergroup rocks from the south shore of lake superior provide geochronological constraints on magmatic evolution associated with the 1 1 ga midcontinent rift analyses of a granophyric phase of the mineral lake intrusion and the mellen granite both parts of the mellen intrusive complex and a laterally extensive rhyolite from the top of the kallander creek volcanics have weighted average 207pb 206pb ages of 1102 0 2 8 ma n 2 1100 9 1 4 ma n 5 and 1098 8 1 9 ma n 4 respectively analyses of a pyroclastic rhyolite flow at the top of the porcupine volcanics result in variable 207pb 206pb ages that range from 1080 to 1137 ma this rhyolite exhibits a continuum between morphologically complex and simpler prismatic zircon crystals the latter yielding concordant analyses having a weighted average 207pb 206pb age of 1093 6 1 8 ma n 2 four prismatic zircons from an aphyric rhyolite of the chengwatana volcani

the mesoproterozoic copperwood sedimentary rock hosted stratiform copper deposit upper peninsula michigan copperwood is located in gogebic county upper peninsula michigan within the porcupine mountains copper district it was discovered in 1956 and in 2008 orvana minerals corp began exploration and development work with production projected in the near future stratiform copper mineralization is hosted by gray to black shales and siltstones of the basal nonesuch formation copper mineralization is overlain by laminated gray siltstones of the nonesuch formation and is underlain by red bed sandstones conglomerates and minor siltstones of the copper harbor formation these rocks are part of a thick section of clastic sedimentary rocks that comprise the upper fill of the mesoproterozoic 1 1 1 0 ga midcontinent rift the copper deposit is a tabular body that averages 2 5 m thick lacks significant basal undulations and dips 8 to 12 northward on the southwest limb of the western syncline an open fold with a shallow plunge to the northwest chalcocite is the only cu bearing mineral in the orebody and occurs as concentrations along stratigraphic laminations and as disseminated grains within the orebody there is no mineral or metal zoning cu ag and s are strongly enriched zn is very slightly enriched and pb and co lack enrichment gangue minerals in the orebody are quartz clinochore muscovite illite plagioclase k feldspar calcite and hematite which are consistent with temperatures of less than 130 c only one significant fault a shallow nw dipping reverse fault with displacement of up to 7 m has disturbed the section the mineralized zone at copperwood is stratigraphically equivalent to that at the white pine mine but copperwood lacks the structural complexity and the hydrothermal overprint manifested by the native cu mineralization at white pine reported canadian national instrument 43 101 compliant measured indicated and inferred resources are 33 million metric tonnes mt of 1 60 cu and 4 1 ppm ag for total contained cu of about 1 165 billion lb and 4 32 moz of ag the characteristics of copperwood are consistent with those of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits the proposed genetic model is chalcocite replacement of pyrite in unlithified sediments during diagenesis as a result of emanating upward focused compaction driven cu bearing saline basinal waters with cu leached from the underlying red bed paleoquifer the simplicity of the mineralizing event and the undeformed nature of the deposit distinguish copperwood from most other examples of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits throughout the world

on the relationship between sst gradients boundary layer winds and convergence over the tropical oceans a linear mixed layer model that skillfully reproduces observed surface winds and convergence over the tropicaloceans is used to examine the relative influenceof boundarylayer and free tropospheric processes on the distribution of climatological surface winds and convergence the semiempirical model assumes a subcloud layer momentum force balance between pressure gradients coriolis acceleration linearized friction and downward momentum mixing and it utilizes boundary conditions from the 40 yr ecmwf re analysis era 40 observed pressure gradients are linearly decomposed into boundary layer defined as the region below 850 hpa and free tropospheric components and the surface winds and convergence associated with these components are computed results show that surface zonal winds are predominantly associated with a combination of free tropospheric pressure gradients and downward momentum mixing whereas the distribution of convergence is primarily due to boundary layer temperature gradients which are closely related to sst gradients the authors conclude that the climatological distribution of boundary layer convergence is primarily a function of the pattern of sst gradients and is better regarded as a cause rather than a consequence of deep convection

mineral deposits of the mesoproterozoic midcontinent rift system in the lake superior region a space and time classification abstract the mesoproterozoic midcontinent rift system mrs of north america hosts a diverse suite of magmatic and hydrothermal mineral deposits in the lake superior region where rift rocks are exposed at or near the surface historically hydrothermal deposits such as michigan s native copper deposits and the white pine sediment hosted stratiform copper deposit were major mrs metal producers on going exploration for and potential development of copper nickel sulfide deposits hosted by the duluth complex of minnesota and the opening of the eagle nickel mine in michigan indicate an expanding interest in mrs magmatic deposits mrs hydrothermal and magmatic mineral deposits many of which are significant past present and likely future providers of critical minerals here are placed into a space and time metallogenic framework to construct this framework regional mrs mineral deposits extracted from the u s geological survey mineral resources data system mrds and the ontario ministry of energy northern development and mines mineral deposit inventory mdi were supplemented by other known and recently recognized mineral deposits described in the literature all mineral deposits were classified by deposit type host rock age and type and estimated timing of mineralization deposits were then put into a tectonic evolutionary framework stages for the mrs which shows that deposits formed within discrete spatial and temporal stages of rift evolution each stage of rift evolution is characterized by specific mineral deposit types that are largely confined both by their physical location in rift rocks and type and timing of mineralization examples include mrs nickel rich conduit type magmatic sulfide deposits which are restricted to an early magmatic stage mrs history when magma compositions were characterized by ni rich picrites and high mg basalts in contrast contact type magmatic sulfide deposits with cu ni were derived from more evolved al rich tholeiitic magmas that dominated a later time of voluminous magmatic activity hydrothermal sediment hosted stratiform chalcocite mineralization along the margins of western lake superior in michigan is economic only where fluid flow through red beds was concentrated by structures along the margins of a post volcanic mrs sedimentary basin widespread native cu and native ag mineralization occurred about 40 million years after formation of host basalt lava flows and interflow sedimentary rocks these descriptions of the diverse mineral deposits in the lake superior region cataloged within the space of the local and regional geology and over the more than 60 million year mineralizing history of the mrs are indicative of the complex and at times overlapping magmatic and hydrothermal mineral systems that operated within this major large igneous province

fault spacing in the el teniente mine central chile evidence for nonfractal fault geometry we utilize the excellent rock exposure provided by the network of mining tunnels in el teniente mine central chile to test the applicability of fractal fault spacing laws to a 2 km 3 km 1 3 km body of crystalline rock in an andean shear zone fractal spacing laws can be particularly useful because they allow prediction of fault spacing at unsampled scales because of the restrictions of tunnel geometry in the mine we use only scanline one dimensional analyses the large number of parallel tunnels allows us to assess the consistency of one dimensional scanline samples over a two dimensional area we use two methods 1 an interval counting technique and 2 standard cumulative statistics to test the hypothesis of fractal fault geometry in the shear zone the interval counting method produces deceptively good fits to a fractal distribution in fact by analyzing the residuals and differential slopes of interval counting and cumulative statistical plots and by comparison with synthetic fractal negative exponential and log normal distribution data we conclude that a negative exponential distribution best describes fault spatial distribution at the mine we present three possible explanations for the negative exponential spacing distribution 1 the rock body is at the earliest stage in a deformational path that will produce varying spacing distributions as deformation proceeds 2 the spacing distribution is inherited through joint reactivation and 3 the present spacing distribution is the result of a superposition of two spacing distributions each of which is not necessarily negative exponential additionally we attempt to use the deviation of mean spacings in parallel scanlines after wu and pollard 1995 to further classify deformational maturity we show that this method cannot be used to compare population development in faults which follow a negative exponential spacing distribution because of the negative exponential s equivalence of mean and standard deviation instead we use a relative measure of parallel scanline deviation to compare regions the distinctly smaller standard deviation of mean spacings in one region the t3 isla region may be a signature of increased local finite strain accumulation

genesis of kupferschiefer cu ag deposits by convective flow of rotliegendes brines during triassic rifting extensive and rich cu ag sulfide mineralization occurs in poland across the contact between the upper permian zechstein restricted marine sequence and the lower permian rotliegende continental volcanic and clastic sequence geologic evidence suggests that the mineralization was formed during late diagenesis when metalliferous brines migrated through the rotliegende leaching metals from the volcanic detritus and up the flanks of basement highs possibly along fracture porosity to the pyritic kupferschiefer and zechstein limestone above thick evaporites in the lower zechstein preclude a vertical flow through model but metal zoning attitudes suggest that the brines overturned where the rotliegende pinched out against the highs and moved laterally along the base of the zechstein toward the basin centers presumably to sink back down into the rotliegende completing a convection cell a middle triassic paleomagnetic age for the metal zoning and kimmerian attitudes of dilatant sulfide veinlets indicate that the mineralizing event coincided with continental rifting associated with the opening of the tethys ocean slow unicellular convection may be commonplace in sandstone basins where small lateral temperature gradients delta t exist but greater velocities are necessary to form large orebodies an anomalous tensional and thermal event such as rifting can increase velocities by increasing permeability slope angle or delta t the paleothermal structure of southwestern poland was determined by modeling the conductive heat flow in 14 one dimensional geologic sections which described the evolution of the basin architecture for 10 m y in the early triassic rifting was simulated by increasing the lower boundary condition from 500 degrees to 1 000 degrees c at 25 km this thermal pulse produced a surprisingly high delta t of 25 degrees c across the lubin ore district solely from differences in thermal conductivities between the basement high 4 2 w m degrees c the sandstone 2 5 w m degrees c and the shale basin center 1 25 w m degrees c unicellular convection patterns would be induced by the lateral boundary conditions of warm basement highs and cold shale centers and by the greater horizontal permeability these cells were 15 to 20 km long 400 m high and subhorizontal a slope angle of 2 degrees and a permeability of 1 d produces a convection velocity of 13 cm yr which with a copper solubility of 1 000 mg kg in 20 to 30 percent ca na cl brines in equilibrium with hematite can form the lubin deposit in less than 6 m y using a fracture permeability of 2 d and a solubility of 300 mg kg the time needed is less than 10 m y the konrad mine can be formed in similar time periods without the continuous recycling of the brine inherent in convective flow 20 times or more the metal solubilities needed to form the lubin deposits by a flow through model would be unreasonably high natural gases likely migrated along with the metalliferous brines and helped convection by creating secondary porosity and increasing the buoyancy of the fluids because the fluids are recirculated and not expelled convection provides a way in which secondary migration of methane and petroleum can occur effectively in solution as well as in separate phases

age of native copper mineralization keweenaw peninsula michigan amygdaloidal flood basalts and conglomerates are the host for substantial deposits of native copper within the portage lake volcanics in the keweenaw peninsula of michigan a wide variety of gangue minerals are associated with the regional hydrothermal alteration mineralization event application of the rb sr method to amygdule filling microcline calcite epidote and chlorite suggests an age of mineralization between 1 060 and 1 047 m y or asymp 20 m y these results are supported by a fission track age on epidote of 1 044 or 169 m y the age of native copper mineralization determined in this study is consistent with geologic evidence which suggests that mineralization postdated the deposition of most or all of the overlying freda sandstone variable initial 87 sr 86 sr ratios between the low rb sr phases suggest mixing of isotopically distinct sources of sr during the generation and equilibration of the hydrothermal solutions

alteration halos in the tordillos sediment hosted copper deposit of the neuquen basin argentina abstract the tordillos sediment hosted cu deposit is located in the north central sector of the huincul high structure in the neuquen basin argentina it is hosted in sedimentary rocks of the huincul formation an upper cretaceous redbed sequence deposited in a fluvial environment field mapping petrography and chemical analysis of the authigenic clay sulfate carbonate and sulfide minerals at tordillos have identified systematic variation in alteration and paragenesis with time and with respect to the main feeder zones the alteration associated with cu mineralization provides evidence of a multistage infiltration of fluids spatially associated with paleo hydrocarbon migration driven by tertiary tectonism early diagenesis formed hematite kaolinite and calcite1 that have been preserved in the reddish brown mudstones later influx of hydrocarbons and warm reduced formation waters from deeper reservoir rocks is associated with dissolution of early cements and clasts and precipitation of new minerals in the thickest paleo channels of the huincul formation dissolution of early cements hematite kaolinite calcite1 and barite1 and clasts locally increased the porosity of sandstones up to 24 and destroyed hematite that changed sandstones and conglomerates from red to yellowish grey bitumen impregnations are abundant along with calcite2 3 and 4 pyrite minor montmorillonite quartz overgrowth and coarse barite2 crystals with primary organic fluid inclusions at the contact with hydrocarbon tubes the mno enrichment of calcite in stages 3 and 4 reflects their precipitation under reduced conditions grey and greenish grey sandstones with montmorillonite v hematite smectite chlorite group minerals and pyrite respectively are exposed between the reddish brown mudstones and the yellowish grey sandstones and conglomerates the grey and greenish grey horizons are representative of abrupt changes in eh ph conditions between regional early oxidizing solutions responsible for the formation of early diagenetic redbeds and later infiltration of reducing fluids responsible for alteration of sedimentary rocks copper mineralization is located inside the altered sandstones and conglomerates zones forming halos surrounding vertical tubes containing bitumen these tubes are interpreted as the conduits through which migrated hydrocarbons formation waters and subsequent chloride and metal rich fluids in these places pyrite calcite and barite cements of the altered rocks have been dissolved and replaced by copper rich sulfides and then by late supergene cu minerals interconnection among stacked permeable paleo channels in the mid section of the huincul formation facilitated the migration of several generations of fluids during early diagenesis hydrocarbon up flow and exhumation of the neuquen group resulting in the development of alteration halos and cu mineralization that can be used both in outcrop and drill core during exploration for sediment hosted cu mineralization

the precambrian nonesuch formation of the north american mid continent rift sedimentology and organic geochemical aspects of lacustrine deposition abstract the precambrian keweenawan trough in the lake superior region of north america is part of a failed intractonic rift that is filled with a thick sequence of volcanic and sedimentary rocks one unit in this sequence the none such formation is composed of black to green siltstones and shales and is conformable with the underlying alluvial copper harbor conglomerate and the overlying fluvial freda sandstone the formation is exposed as a lens in northern michigan and wisconsin and attains a maximum thickness of 200 m based on the integration of outcrop and core data nine facies have been recognized in the formation each has been assigned to one of three genetic facies assemblages a marginal lacustrine assemblage characterized by interbedded lithic sandstones siltstones mudstones and sandstone shale couplets is interpreted as a record of deposition on a sandflat mudflat complex a lacustrine assemblage is characterized by massive to well laminated dark shaly siltstones carbonate laminites shales siltstones and mudstones these sediments were probably deposited in a progressively shallowing perennial lake bottom conditions were anoxic and became increasingly more oxic as lake regression progressed a gradual transition from a lacustrine environment to a fluvial environment is represented by the red to brown massive horizontally laminated and rippled fine sandstones siltstones and mudstones of the fluvial lacustrine assemblage interactions among rates of subsidence rates of sedimentation fluctuations in lake level possible changes in climate and differences in tectonic setting controlled sedimentation in the nonesuch lake and resulted in variable vertical facies sequences total organic carbon toc analyses show a strong correlation between organic richness and the shale facies lacustrine assemblage and mudstone facies marginal lacustrine assemblage detailed petrographic analysis using incident white light and reflected blue light fluorescence revealed two prevalent organic petrographies which could be distinguished using combined pyrolysis gas chromatography mass spectrometry py gc ms and to a limited extent by stable carbon isotope mass spectrometry the geographic and stratigraphic distribution of rocks containing the two organic petrographies suggests that differential preservation e g microbial degradation accounts for the difference rather than maturity or variable source input

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

regional dynamics of seasonal variability in the south china sea abstract dynamics of the seasonal cycle of sea surface height ssh in the south china sea scs are studied using observations as well as numerical and theoretical models seasonal variability of the scs is interpreted in light of large scale dynamics and rossby waves it is found that the seasonal cycle over most of the scs basin is determined predominantly by the regional ocean dynamics within the scs the ssh variability is shown to be forced mainly by surface wind curl on baroclinic rossby waves annual baroclinic rossby waves cross the basin in less than a few months leaving the upper ocean in a quasi steady sverdrup balance an anomalous cyclonic anticyclonic gyre is generated in winter summer by the anomalous cyclonic anticyclonic wind curl that is associated with the northeasterly southwesterly monsoon in addition surface heat flux acts to enhance the wind generated variability the winter surface cooling warming cools warms the mixed layer especially in the central scs reducing

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

variation in the form and distribution of dykes in the mull swarm scotland the dykes of the mull swarm part of the british tertiary igneous province have been examined in a series of well exposed coastal sections traverses through the dyke swarm show systematic changes in the thickness and spacing of dykes both of which are typically log normally distributed both the geometric mean thickness and spacing of dykes increase with distance from the mull centre concordant with a decrease in crustal extension variations in the thickness and spacing result from changes in character of the magma flow it is inferred that the magma flux was fairly evenly distributed near the mull centre but farther away from the source it becomes focused into larger dykes the form orientation and opening direction are also observed to vary with distance away from the volcanic centre on mull the dykes intrude a range of pre existing fractures the range of fractures used decreases with distance from the centre this together with other features of the form of the dykes have been interpreted in terms of the varying magma pressure and regional stress which is expressed as the r ratio analysis of the variable strikes of fracture filled dykes is consistent with decreasing magma pressure with distance from the mull centre assuming that regional stresses were relatively invariant across the same distance

atmospheric dynamic and thermodynamic processes driving the western north pacific anomalous anticyclone during el nino part ii formation processes abstractin part i the authors showed that northerly anomalies associated with the rossby wave response to el nino heating anomalies in the equatorial central pacific lead to the southward advection of low moist enthalpy air forming the western north pacific anomalous anticyclone wnpac why does such a remote forcing not cause the formation of the anomalous anticyclone in el nino developing summer the physical mechanism responsible for the timing of the wnpac formation is investigated in part ii through both an observational analysis and idealized numerical model experiments the authors find that the onset timing of the wnpac relies on the following three factors the first is a sign change from positive to negative of the meridional gradient of background low level specific humidity over the key tropical western north pacific wnp region in november the second is a sign change from positive to negative of the meridional gradient of background relative vorticity which efficiently reduces the w

scaling systematics of fault sizes on a large scale range fault map abstract a large scale high quality fault map was produced for an intensively mined area of the u k south yorkshire coalfield this database has been used to investigate both the scaling properties of fault systems and the robustness of techniques for the prediction of sub resolution faulting the mapped area is 87 km 2 and contains 2257 individual fault traces with on average one throw reading available for every 82 m of fault trace recorded throw values range from 10 cm to 180 m and fault trace lengths from 10 m to 12 km two sets of normal faults nw and ne striking are present together with local wnw striking dextral strike slip zones size populations are power law over at least 2 5 orders of magnitude and the exponents of the throw maximum throw and fault trace length population curves are interrelated and taking into account the effects of resolution on trace length populations are internally consistent derivatives of the primary map reproduce resolutions typical of offshore seismics and illustrate the limitations of seismic data power law fault size distributions provide a basis for sub seismic fault prediction for this data set a fault throw resolution of better than 10 m would be required to provide an accurate prediction of the throw population down to ca 0 6m

how to measure the strength of the east asian summer monsoon defining the intensity of the east asian summer monsoon easm has been extremely controversial this paper elaborates on the meanings of 25 existing easm indices in terms of two observed major modes of interannual variation in the precipitation and circulation anomalies for the 1979 2006 period the existing indices can be classified into five categories the east west thermal contrast north south thermal contrast shear vorticity of zonal winds southwesterly monsoon and south china sea monsoon the last four types of indices reflect various aspects of the leading mode of interannual variability of the easm rainfall and circulations which correspond to the decaying el nino while the first category reflects the second mode that corresponds to the developing el nino the authors recommend that the easm strength can be represented by the principal component of the leading mode of the interannual variability which provides a unified index for the majority of the existing indices this new index is extremely robust captures a large portion 50 of the total variance of the precipitation and three dimensional circulation and has unique advantages over all the existing indices the authors also recommend a simple index the reversed wang and fan index which is nearly identical to the leading principal component of the easm and greatly facilitates real time monitoring the proposed index highlights the significance of the mei yu baiu changma rainfall in gauging the strength of the easm the mei yu which is produced in the primary rain bearing system the east asian ea subtropical front better represents the variability of the easm circulation system this new index reverses the traditional chinese meaning of a strong easm which corresponds to a deficient mei yu that is associated with an abnormal northward extension of southerly over northern china the new definition is consistent with the meaning used in other monsoon regions worldwide where abundant rainfall within the major local rain bearing monsoon system is considered to be a strong monsoon

sterane and triterpane biomarkers in the precambrian nonesuch formation north american midcontinent rift abstract molecular fossils and organic matter from microbial communities living around 1 1 ga ago are well preserved in the nonesuch formation of the us midcontinent rift system although some compound classes of biological markers have been recognized repeatedly in previous studies of nonesuch rocks and associated petroleums steranes and triterpanes have not been detected failure to detect these compounds was due primarily to instrumental limitations and the relatively high thermal maturity of samples collected within zones of copper mineralization our analyses of nonesuch samples from the white pine mine and nonmineralized localities in michigan and wisconsin reveal suites of c 26 c 30 steranes and c 27 c 35 pentacyclic triterpanes similar to those found in phanerozoic oils and sedimentary rocks of marine origin stereoisomeric distributions in the nonesuch samples are consistent with moderate thermal maturity except in the mineralized zone near white pine

refinements for footwall red bed diagenesis in the sediment hosted stratiform copper deposits model the emplacement of copper in sediment hosted stratiform copper deposits requires the circulation of a low temperature chloride rich brine in rift filling footwall red beds probably driven by meteoric recharge in adjacent highlands the descending oxygen rich meteoric water may become saline probably by leaching of footwall evaporites or possibly by mixing with brines draining down from contemporaneous evaporite pans and evolve toward a moderately oxidized brine as oxygen is consumed during the diagenetic reddening of the initially nonred coarse grained clastic rift sediments under these conditions the pore solution attains its maximum ability to leach and transport trace amounts of copper from the red beds sediment hosted stratiform copper deposits may form where the brine crosses a redox boundary into reduced sulfide rich gray beds with further consumption of oxygen during reddening the brine may become highly reduced and able to take iron into solution possibly explaining synsediment hosted stratiform copper iron oxide alterations and deposits the timing of copper deposition is clearly linked to the diagenetic reddening of immature footwall sediments in rift basins a process considered to extend over millions of years

late paleoproterozoic sedimentary rock hosted stratiform copper deposits in south china their possible link to the supercontinent cycle giant sedimentary rock hosted stratiform copper ssc deposits commonly occur in rift environments tem porally coincident with the breakup of the rodinia and pangea supercontinents however whether or not such deposits have also formed during the breakup of the paleo proterozoic columbia supercontinent is not well known a group of dolostone hosted cu deposits in late paleoproter ozoic rift related sedimentary sequences of the dongchuan group south china form one of the largest ssc districts in the world being one of the largest ssc deposits in the region the yinmin deposit has stratiform cu orebodies intruded by dolerite dykes one dyke has a sims zircon u pb age of 1 701 28 ma slightly younger than the ore hosting strata with a zircon u pb age of 1 742 13 ma for a tuff unit six chalcopyrite and bornite separates from strat iform orebodies contain highly radiogenic os and extremely low common os and yield a weighted mean re os model age of 1 666 82 ma and a 187 os 187 re errorchron age of 1 585 100 ma the present zircon u pb and sulfide re os ages thus constrain the timing of the mineralization at 1 700 ma the yinmin deposit and by inference other ssc deposits in the region arguably represent a large scale ssc mineralization event during the late paleoproterozoic the formation of these deposits was coeval with the initial breakup fragmentation of the columbia supercontinent this study highlights the temporal and likely genetic links between large sized ssc deposits and the supercontinent cycle

interannual variability of the south china sea throughflow inferred from wind data and an ocean data assimilation product 1 the luzon strait transport as an index for the south china sea throughflow has attracted much attention recently in this study the interannual variability of luzon strait transport is examined using the island rule and results from ocean data assimilation transport variability obtained from these two approaches is consistent with each other assessment of contribution from each integral segment involved in the island rule indicates that wind stress in the western and central equatorial pacific is the key factor regulating the interannual variability of the luzon strait transport whereas the effect of local wind stress in the vicinity of the luzon strait is secondary analysis also shows that when the westerly easterly wind anomalies in the tropical pacific break out the luzon strait transport increases decreases associated with the variations in the

four dimensional analysis of fracture arrays at theaspohard rock laboratory se sweden abstract during excavation and construction ofaspohrl an underground laboratory for the study of spent nuclear fuel geological information is systematically recorded and filed in a data base called geotab statistical analyses have been performed on fracture information from geotab and stochastically chosen outcrops have been mapped in detail based on systematic recording of crosscutting relations a succession of minerals and characteristics of decreasing age have been outlined these include epidote quartz oxidized walls iron oxides chlorite and calcite the sequential fragmentation of the rock mass is described in terms of evolution of fracture arrays in time a correction procedure for sampling biases has been performed and fracture characteristics have been analysed it is concluded that fracture lengths follow a lognormal distribution with mean mode and standard deviation estimated to 2 84 m 1 52 m and 1 43 m respectively spacing has been evaluated for different fracture sets and varies between 0 32 m 1 to 8 45 m 1 it is concluded that the fracture array consist of six sets with different kinematics fracture zones underground are compared to a fracture zone at the surface

genesis of native copper lodes in the keweenaw district northern michigan a hybrid evolved meteoric and metamophogenic model the keweenaw peninsula of northern michigan is well known for early diagenetic sulfide dominant sediment hosted stratiform copper mineralization hosted mainly by basal siltstone shale units of the nonesuch formation in the white pine district and later native copper lodes hosted mainly by flow top breccias and amygdaloidal portions of flood basalts and interbedded conglomerates of the stratigraphically lower portage lake volcanics the native copper mineralization is generally attributed to downdip burial metamorphism of the host strata an alternative model is proposed here involving a complementary influx of evolved meteoric water elevated in salinity and progressively equilibrating with its aquifers similar to the fluid which formed the white pine mineralization this model has several advantages over the metamorphogenic model alone it would provide the salinity by dissolution of evaporites and moderately oxidizing conditions as a result of hematitization i e reddening of coarse continental rift sediments necessary for copper transport and the evolved meteoric water would have been an important cupriferous brine owing to the leaching of trace amounts of copper from the voluminous aquifers further reduction of the evolved fluid would also explain the updip deposition of native copper in association with dehematitized pumpellyite and chlorite dominant i e reduced hydrothermal mineral assemblages at the same time this influx of meteoric water from highlands adjacent to the keweenaw rift basin would have provided a mechanism to move the deep seated hot dense ore brine upward along the aquifers of the portage lake volcanics on its ascent from deep portions of the rift basin the gravity driven evolved meteoric brine would have mixed with the fluid generated by burial metamorphism to form a hybrid evolved meteoric metamorphogenic oreforming hydrothermal brine

hybrid veins from the southern margin of the bristol channel basin uk sinistral and dextral en echelon hybrid calcite veins are exposed on the southern margin of the bristol channel basin north somerset on a liassic carbonate platform these hybrid veins are transitional between pure extensional mode i and shear fractures mode ii mode iii and experienced both extensional and shear displacements during their formation in the study area they occur in conjugate sets with the conjugate angle ranging between 10 and 50 based on the kinematic analysis of these veins a new model for the opening of the bristol channel is proposed

fractal dimension of fault systems in japan fractal structure in rock fracture geometry at various scales based on fault maps whether or not the fracture geometry of rocks is self similar was examined by using a box counting algorithm the statistical self similarity fractal structure of the fault fracture systems holds well at the scale of about 2 to 20 km the fractal dimension in japan varied from 1 05 to 1 60 the fractal dimension is about 1 5 1 6 at the central part of the japan arc and decreases with distance from the center at a smaller scale the fractal structure also holds well in the rock fracture geometry the fractal dimension of the north izu peninsula fault system branching faults is 1 49 at the scale of 0 625 to 10 km the fractal dimension of rock fracture geometry at the scale order of 10 1 to 10 2 meters is about 1 49 1 61 the upper limit of the fractal dimension of rock fracture geometry is about 1 6 judging from the estimation of fractal dimension on actual fracture geometry of rocks this value may impose a restraint on modeling of faulting and the fracture process of rocks

thickness and spatial distributions of clastic dykes northwest sacramento valley california abstract the geometry and distribution of the clastic dykes of the ono district north sacramento valley are examined within stream sections five traverses along dry stream beds provide good exposure allowing the spacing thickness and geometry of the dykes to be recorded the spatial and thickness distribution of the dykes are considered using cumulative frequency plots allowing a visual estimation of a best fit distribution dyke thickness conforms best to a log normal distribution there is also a characteristic minimum dyke thickness in a traverse and this is attributed to the minimum aperture that a fluid with sand clasts is able to exploit dyke spacing however shows a good correlation with a power law distribution for four traverses suggesting that there is a mechanistic control on the spatial distribution plotting dyke thickness against minimum dyke spacing reveals that thin dykes do not generally intrude in isolation unlike veins and igneous dykes clastic dykes continue to provide preferential pathways for fluid flow subsequent to their intrusion thus inhibiting intrusion in the area surrounding a pre existing dyke a combination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of clastic dykes seen in the ono district california

chemical and stable isotopic b h and o compositions of tourmaline in the maocaoping vein type cu deposit western yunnan china constraints on fluid source and evolution abstract this study determined the chemical and stable isotopic b h and o compositions of three stages of ore related hydrothermal tourmaline in the newly discovered maocaoping vein type cu deposit western yunnan china as well as the chemical and b isotopic compositions of magmatic tourmaline tourmaline g from a neighboring peraluminous granitic intrusion that is contemporaneous with the cu mineralization the objective was to constrain the source and evolution of the co 2 rich ore forming fluid the maocaoping cupriferous veins types v1 and v2 are hosted in mylonitized and metamorphosed jurassic sedimentary rocks early to late stage hydrothermal tourmaline occurs as vein related alteration halos tourmaline a in altered marble or schist as tourmaline v1 in type v1 veins and as tourmaline v2 in type v2 veins tourmaline a v1 and v2 belong to the alkalic group and consist mostly of dravite with 11 b values of 3 9 to 1 1 2 8 to 0 5 and 6 3 to 3 9 respectively tourmaline g belongs to the alkalic group and consists of schorl with 11 b values of 14 7 to 12 2 the similarities in chemical composition between marble and schist hosted tourmalines and between tourmalines in veins and alteration halos indicating their formation at different water rock ratios suggest that the compositions of the hydrothermal tourmaline at maocaoping were controlled mainly by the chemistry of ore fluid rather than that of the host rocks the similarities together with the lack of systematic variations in 11 b values in individual tourmaline grains imply that mixing of multiple fluids cannot be important during the mineralization the positive shift in 11 b values from tourmaline a to tourmaline v1 is interpreted to result from continuous precipitation of tourmaline in a closed fluid system relative to tourmaline a and v1 tourmaline v2 is fe rich al poor and 11 b depleted these differences may be explained by fluid phase separation and subsequent escape of the co 2 rich vapor phase during the formation of type v2 veins consistent with the observations that these veins are extensional contain large amounts of carbonate minerals and include fluid inclusions trapped in the vapor liquid two phase field the earliest tourmaline a records the initial ore fluid chemistry the calculated 11 b 18 o and d values of the initial ore fluid in equilibrium with tourmaline a at mineralization temperatures of 280 to 320 c are 0 3 to 3 0 10 7 to 11 8 and 110 to 84 respectively the 11 b values as well as the chemical compositions of tourmaline a are much different from those of tourmaline g suggesting that the ore fluid at maocaoping was not derived directly from the peraluminous granitic magma the b h o isotopic features as well as enrichment of co 2 in fluid inclusions also suggest the ore fluid cannot solely be derived from basinal fluid or meteoric water the simplest explanation is that the fluid was derived from a metamorphic fluid that had obtained isotopically lighter hydrogen via reaction with organic compounds e g ch 4 h 2 s alternatively the ore fluid sourced from the mixed metamorphic fluid and basinal brine meteoric water or degassed magmatic fluid it implies that the vein cu ore formation in the lanping basin is unlikely as a result of a sole magmatic or basinal fluid activity and it needs the involvement of metamorphic fluid process

relative role of dynamic and thermodynamic processes in the development of the indian ocean dipole an ogcm diagnosis 1 the relative role of oceanic dynamics and surface heat fluxes in the initiation and development of the indian ocean dipole was investigated by analyzing results from an oceanic general circulation model the model was forced by observed surface wind stress and heat flux fields for 1958 1997 the results show that it was capable of reproducing observed dipole events over the tropical indian ocean the diagnosis of the mixed layer heat budget indicates that the sst anomaly ssta in the east pole is primarily induced by anomalous surface latent heat flux and vertical temperature advection whereas in the west pole it is mainly caused by meridional and vertical temperature advection anomalies in both regions shortwave radiation anomalies tend to damp the ssta the ocean rossby waves are essential in linking the anomalous wind and sst off sumatra and subsurface temperature variations in southwest indian ocean

precambrian non marine stromatolites in alluvial fan deposits the copper harbor conglomerate upper michigan laminated cryptalgal carbonates occur in the precambrian copper harbor conglomerate of northern michigan which was deposited in the keweenawan trough an aborted proto oceanic rift this unit is composed of three major facies deposited by braided streams on a large alluvial fan complex coarse clastics were deposited in braided channels predominantly as longitudinal bars whereas cross bedded sandstones were deposited by migrating dunes or linguoid bars fine grained overbank deposits accumulated in abandoned channels gypsum moulds and carbonate filled cracks suggest an arid climate during deposition stromatolites interstratified with these clastic facies occur as laterally linked drapes over cobbles as laterally linked contorted beds in mudstone as oncolites and as poorly developed mats in coarse sandstones stromatolites also are interbedded with oolitic beds and intraclastic conglomerates stromatolitic microstructure consists of alternating detrital and carbonate laminae and open space structures radialfibrous calcite fans are superimposed on the laminae the laminae are interpreted as algal in origin whereas the origin of the radial fibrous calcite is problematic the stromatolites are inferred to have grown in lakes which occupied abandoned channels on the fan surface standing water on a permeable alluvial fan in an arid climate requires a high water table maintained by high precipitation or local elevation of the water table possibly due to the close proximity of a lake occurrence of stromatolites in the upper part of the copper harbor conglomerate near the base of the lacustrine nonesuch shale suggests that these depositional sites may have been near the nonesuch lake

why were the 2015 2016 and 1997 1998 extreme el ninos different subtle but important differences are identified between the 1997 1998 and 2015 2016 extreme el ninos that reflect fundamental differences in their underlying dynamics the 1997 1998 event is found to evolve following the eastern pacific el nino dynamics that relies on basin wide thermocline variations whereas the 2015 2016 event involves additionally the central pacific cp el nino dynamics that depends on subtropical forcing the stronger cp dynamics during the 2015 2016 event resulted in its sea surface temperature sst anomalies lingering around the international date line during the decaying phase which is in contrast to the retreat of the anomalies toward the south american coast during the decaying phase of the 1997 1998 event the different sst evolution excited different wave trains resulting in the western u s not receiving the same above normal rainfall during the 2015 2016 el nino as it did during the 1997 1998 el nino ensemble model experiments are conducted to confirm the different climate impacts of the two el ninos

the world s by product and critical metal resources part iii a global assessment of indium abstract indium has considerable technological and economic value to society due to its use in solar panels and liquid crystal displays for computers television and mobile devices yet without reliable estimates of known and potentially exploitable indium resources our ability to sustainably manage the supply of this critical metal is limited here we present the results of a rigorous deposit by deposit assessment of the global resources of indium using a new methodology developed for the assessment of critical metals outlined in part ii of this study werner et al 2017 we establish that at least 356 kt of indium are present within 1512 known mineral deposits of varying deposit types including vms skarn epithermal and sediment hosted pb zn deposits a total of 101 of these deposits have reported indium contents some 76 kt of contained in with the remaining 1411 deposits having mineralogical associations that indicate they are indium bearing yielding 280 kt of contained indium an additional 219 deposits contain known indium enrichments but have unquantifiable contents indicating that our global resource figure of 356 kt of contained indium is therefore most certainly a minimum a limited number of case studies also indicates that a further minimum of 24 kt indium is present in mine wastes a total that is undoubtedly smaller than reality given the minimal reporting of mine waste indium concentrations and the extensive volume of historical mine wastes these quantities are sufficient to meet demand for indium this century assuming current and projected levels of consumption however given indium s classification as a critical metal its supply still remains a concern and hence we have also discussed the economic viability and spatial distribution of the indium resources identified during this study to further our understanding of the geopolitical scarcity of this critical metal our results suggest that the global indium supply chain is fairly adaptable primarily as the spatial distribution of indium resources deviates significantly from the current supply chains for this metal our study provides a stronger basis for future studies of indium criticality provenance supply chain dynamics and stocks and flows in the fields of economic geology and industrial ecology

thermal variations in the south china sea associated with the eastern and central pacific el nino events and their mechanisms in this study we investigate the interannual variability of the sea surface temperature sst in the south china sea scs associated with two types of el nino namely the eastern pacific ep el nino and the central pacific cp el nino first double warm peaks can occur during both types of el nino events in the scs however the strong warm basin mode can only develop in the ep el nino while the warm semibasin mode exists during the cp el nino associated with an anomalous positive negative net surface heat flux in the ep cp el nino along with a shallower thermocline with weaker stronger northeasterly wind anomalies the sst anomalies become warmer cooler in the developing autumn over the background of cooling sst in autumn of cp el nino therefore only a weak warming can occur in the subsequent years which is limited in the western boundary area under the forcing of warm ocean advection second the sst oscillation periods are different in these two types of el nino the sst evolution in the ep el nino is negative positive with a quasi biennial oscillation but that in the cp el nino is positive negative positive negative with an annual oscillation it seems that the double cooling in the cp el nino is phase locked to the late autumn season

a process based approach to estimating the copper derived from red beds in the sediment hosted stratiform copper deposit model most estimates of the total tonnage of copper metal leached from footwall red beds to form sediment hosted stratiform copper deposits are based on the amounts of copper at ppm levels that might have been derived from the volume of red beds underlying given sediment hosted stratiform copper deposits that static calculation is replaced here with a process based approach in which the release of copper results from the progressive diagenetic alteration of the footwall aquifers by oxygen rich meteoric water driven by topographic recharge in highlands adjacent to the intracontinental rift basins hosting these deposits the total amount of liberated copper depends on the volume of meteoric water its oxygen content and the duration of the diagenetic leaching of copper estimates suggest that adequate amounts of copper may be derived from footwall red beds within reasonable periods of early and possibly more advanced diagenesis

extremely late onset of the 2018 south china sea summer monsoon following a la nina event effects of triple sst anomaly mode in the north atlantic and a weaker mongolian cyclone

fault length statistics and implications of graben sets at candor mensa mars abstract the lengths of individual martian grabens from three spatially and temporally distinct regional sets are analyzed by a two dimensional window sampling method length distributions are influenced by fault growth and coalescence processes image resolution window size and the post faulting geologic history of the region cumulative length frequency distributions can be linear for graben lengths between 30 and 100 km with slopes on the area plot of 2 suggesting self similar growth of the graben array post faulting geologic processes contribute to concave cumulative length distributions on the log log plot with curtailment and truncation biases producing strongly non linear distributions for smaller and longer lengths respectively recent evidence for a positive correlation between stratigraphic throw and graben length from analogous terrestrial grabens implies that the magnitudes of throw and extensional strain may also be dependent on relative position along the martian grabens

structural control on the dikulushi cu ag deposit katanga democratic republic of congo the dikulushi cu ag deposit is located in the kundelungu plateau region in the southeast katanga province of the democratic republic of congo the kundelungu plateau is a triangular shaped area to the north of the lufilian arc which contains part of the central african copperbelt the largest known sediment hosted copper province in the world the lufilian arc and the kundelungu plateau comprise neoproterozoic sedimentary rocks of the katanga supergroup that attain an overall thickness of more than 7 000 m the lufilian orogeny imposed a northeast directed shortening on the kundelungu plateau region forming several gentle northwest oriented anticlines above subparallel detachment surfaces at depth a north northwest oriented thrust is exposed in the western part of the dikulushi mine marked by ductile deformed shale that was transported upward and is in faulted contact with an overlying dolomite sandstone sequence this upward emplacement of the shale caused brecciation and the local development of kink folds in the dolomite sandstone sequence the brecciated layers in the west and nonbrecciated sandstone layers in the central part of the mine are crosscut by several east west and northeast oriented faults this complex set of faults produced a damage zone that was a favorable site for the migration of mineralizing fluids the faults and brecciated layers contain cu pb zn fe mineralization consisting of chalcopyrite bornite and chalcocite with minor pyrite arsenopyrite sphalerite and galena with dolomite calcite and quartz as gangue minerals the northeast oriented fault direction was reactivated several times with dextral strike and oblique slip fault movement these fault zones were sites of remobilization and enrichment of the previously deposited cu pb zn fe mineralization the remobilized sulfides consist of ag rich chalcocite with barite calcite and quartz as gangue minerals the study has shown that the deposit of dikulushi is structurally controlled by a crosscutting set of east west and northeast oriented faults similar structural settings in the mine and in the dikulushi region represent important future exploration targets

episodic basin wide fluid expulsion from geopressured shale sequences in the north sea basin a proposed general model for the episodic dewatering of thick shale successions is based on the recognition of a pervasive polygonal extensional fault network developed in the dominantly fine grained lower tertiary of the north sea basin seismic data show that the faults are arranged in stratigraphically bound structural units tiers that are delimited vertically by almost undeformed condensed sections and are restricted in distribution to the lowest permeability slope and basin floor facies i propose an episodic three stage mechanism to explain the fault genesis involving 1 the development of basin wide overpressured compartments 2 a density inversion between the overpres sured units and the overlying seal and 3 natural hydraulic fracturing pressure bleed off and resealing of the pressure compartment leading to a repeat of the cycle