mapping geochemical anomalies related to fe polymetallic mineralization using the maximum margin metric learning method abstract geochemical anomaly identification is an important task in mineral exploration targeting this task can be regarded as a binary classification problem whereby the aim is to discriminate between anomalous and not anomalous i e background we can analyze geochemical data from the aspects of frequency distributions correlations and variances geometrical properties of geochemical anomalies and scale independence of geochemical patterns in this study we recognize geochemical anomalies based on the intrinsic relationship between geochemical elements which can be addressed by measuring their separation distance as a machine learning method metric learning aims at exploiting the statistical information between the geochemical features in limited training samples and developing a more suitable distance to evaluate the similarity of samples without priori distribution assumptions accordingly a metric learning method based on the maximum margin frame was applied to identify multivariate geochemical anomalies related to fe polymetallic mineralization in the southwestern fujian province of china the geochemical exploration data were firstly translated into a dimensional reduced subspace with the help of maximum margin metric learning mmml the adaptive coherence estimator ace detector from the field of target detection was then employed to identify geochemical anomalies the anomaly results obtained by this integrated procedure using a combination of mmml and ace were compared to those obtained by ace without metric learning using a receiver operating characteristic roc curve the area under the curve value implied superior performance using the combination of mmml and ace suggesting that this hybrid method can be effectively applied to recognize geochemical anomalies linked to mineralization

lateral variation of crustal structure and composition in the cathaysia block of south china and its geodynamic implications abstract in order to clarify lateral variations in the crustal structure and composition of the cathaysia block in south china which was affected by violent mesozoic and cenozoic tectono magmatic activities we studied the crustal thickness and the poisson s ratio in this region using the h stacking method of teleseismic receiver functions our results show that the poisson s ratio varies between 0 20 and 0 29 and the crustal thickness ranges from 26 to 34 km in the cathaysia block the crustal thickness and poisson s ratio show considerable variations across the lishui haifeng fault the southeast coast magmatic belt is characterized by poisson s ratios 0 25 and a crustal thickness of 28 33 km reflecting probably intermediate to mafic compositions of the crust the southwestern part of the cathaysia fold belt exhibits a crustal thickness of 27 30 km and poisson s ratios

shallow burial dolomitization and dedolomitization of cenozoic cool water limestones southern australia geochemistry and origin abstract the gambier limestone a bryozoan rich cool water carbonate of late eocene to early miocene age in the otway basin of southeastern australia is about one third variably dolomitized limestone and dolostone individual dolomite crystals range from 10 to 500 m and are of three types 1 silt size crystals 4 64 m diameters having a brightly luminescent core 10 20 m of nearly stoichiometric dolomite with 1 mol mnco3 and sio2 but no fe surrounded by a thin dull or alternating dark and bright cl cortex that is nonstoichiometric with 44 46 mol mgco3 but sharp to diffuse zoning in mn and fe 2 sand size crystals which also have a brightly luminescent and stoichiometric core and dark and bright non stoichiometric thin inner cortex but are mostly a thick outer cortex at ca 50 m diameter that is nonluminescent and nonstoichiometric with some fe but no mn and 3 identical sand size crystals with a variably leached core and inner cortex that is either a void or a void filled with late calcite cement these three crystal populations represent two distinct dolomites and their alteration product the smallest of the silt size crystals which are rarely preserved are also the cores of the larger crystals upon which grew an inner and outer cortex of somewhat different composition the 18o values of dolomite rhombs 1 6 to 2 9 correlate positively with 13c values 0 7 to 3 0 with the lowest values from silt size or small sand size crystals and the highest values from large sand size crystals with leached unfilled cores low and variable 18o and 13c values in conjunction with high and variable mn and fe contents in both the core and inner cortex of all crystals are consistent with formation from a mixture of brackish water and seawater higher values for the outer cortex in sand size crystals are typical of those expected for precipitation from normal or near normal seawater low sr mn and fe contents in the largest crystals in conjunction with fluid inclusions of seawater salinity in the outer cortex are also consistent with the bulk of the large crystals having precipitated from seawater using the sr isotope evolution curve for cenozoic seawater sr isotope ratios of the dolomites can be divided into four distinct groups which correspond to times of major transgressions this cenozoic example in which dolomite petrography and crystal chemistry can be explained in terms of simple transgression regression offers a simple sedimentological explanation for many similar dolomites where processes of formation cannot be so easily constrained

receiver operating characteristics roc as validation tool for prospectivity models a magmatic ni cu case study from the central lapland greenstone belt northern finland abstract a prospectivity model for magmatic ni cu deposits was created by integrating spatially referenced geophysical and geochemical datasets based on a simple and practical exploration model the study area is the central lapland greenstone belt northern fennoscandian shield finland magmatic nickel deposits are related to rock types that are typically characterized by local magnetic and gravity anomalies these deposit types can also be a source of nickel copper and cobalt anomalies in the overlying glacial till cover this straightforward exploration criterion was translated into a fuzzy logic prospectivity model the model validation is an essential step in justifying the validity of the prospectivity model this was accomplished by using receiver operating characteristics roc technique we used the known ni cu occurrences and deposits as true positive cases and other deposit type locations or random points as true negative cases in the validation process it appears that the roc technique provides a robust model validation and optimization technique providing that suitable validation data exists

chemistry and environments of dolomitization a reappraisal abstract dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain preservation or loss during the replacement process experimental data as well as textures and porosities of natural dolomites indicate that these reactions must include co 3 2 and or hco 3 supplied by the solution to the reaction site since dolomite formation is thermodynamically favoured in solutions of a low ca 2 mg 2 ratios b low ca 2 co 3 2 or ca 2 hco 3 ratios and c high temperatures the thermodynamic stability for the system calcite dolomite water is best represented in a diagram with these three parameters as axes kinetic considerations favour dolomitization under the same conditions and additionally at low as well as at high salinities if thermodynamic and kinetic considerations are combined the following conditions and environments are considered chemically conducive to dolomitization 1 environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite i e freshwater seawater mixing zones normal saline to hypersaline subtidal environments hypersaline supratidal environments schizohaline environments 2 alkaline environments i e those under the influence of bacterial reduction and or fermentation processes or with high input of alkaline continental groundwaters and 3 many environments with temperatures greater than about 50 c subsurface and hydrothermal environments whether or not massive replacive dolostones are formed in these environments depends on a sufficient supply of magnesium and thus on hydrologic parameters most massive dolostones particularly those consisting of shallowing upward cycles and capped by regional unconformities have been interpreted to be formed according to either the freshwater seawater mixing model or the sabkha with reflux model however close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive replacive dolostones commonly inferred to have been formed in these environments many shallowing upward sequences are devoid of dolomite it is therefore suggested that massive replacive dolomitization during exposure is rare if not impossible rather only small quantities of dolomite cement or replacement are formed which may act as nuclei for later subsurface dolomitization alternatively large scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity the integration of stratigraphic petrographic geochemical and hydrological parameters suggests that the only environments capable of forming massive replacive dolostones on a large scale are shallow hypersaline subtidal environments and certain subsurface environments

sandstone vs carbonate petroleum reservoirs a global perspective on porosity depth and porosity permeability relationships plots are presented comparing average porosity vs depth for 30 122 siliciclastic petroleum reservoirs and 10 481 carbonate petroleum reservoirs covering all petroleum producing countries except canada however separate plots cover 5534 siliciclastic and 2830 carbonate reservoirs of the alberta basin in canada average permeability vs average porosity is shown for the non canadian reservoirs key similarities and differences between sandstones and carbonates are noted and implications are discussed regarding the dominant factors controlling reservoir quality in each lithology trends of steadily decreasing median and maximum porosity with increasing depth reflect burial diagenetic porosity loss in response to increasing thermal exposure with depth these trends seem inconsistent with the suggestions that both sandstones and carbonates commonly increase in porosity by dissolution during deeper burial carbonate reservoirs have lower values of median and maximum porosity for a given burial depth probably because of greater chemical reactivity of carbonate minerals relative to quartz and the resulting lower resistance to chemical compaction and associated cementation relative paucity of low porosity 0 8 siliciclastic reservoirs at all depths compared with carbonates may reflect the more common occurrence of fractures in carbonates and the effectiveness of these fractures for facilitating economic flow rates in low porosity rock overall carbonate reservoirs do not have lower permeability for a given porosity compared with sandstones but do have strikingly lower proportions of both high porosity and high permeability values the data presented can serve as a general guide for the distribution of reservoir quality that can reasonably be expected in exploration wells drilled to any given depth in the absence of detailed geologic information such as burial and thermal history

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

cosmic ray exposure age and preatmospheric size of the bunburra rockhole achondrite abstract bunburra rockhole is the first meteorite fall photographed and recovered by the desert fireball network in australia it is classified as an ungrouped achondrite similar in mineralogical and chemical composition to eucrites but it has a distinct oxygen isotope composition the question is if achondrites like bunburra rockhole originate from the same parent body as the howardite eucrite diogenite hed meteorites or from several separate differentiated parent bodies to address this question we measured cosmogenic radionuclides and noble gases in the bunburra rockhole achondrite the short lived radionuclides 22na and 54mn confirm that bunburra rockhole is a recent fall the concentrations of 10be 26al and 36cl as well as the 22ne 21ne ratio indicate that bunburra rockhole was a relatively small object r approximately 15 cm in space consistent with the photographic fireball observations the cosmogenic 38ar concentration yields a cosmic ray exposure cre age of 22 3 myr whereas 21ne and 3he yield approximately 30 and approximately 60 lower ages respectively due to loss of cosmogenic he and ne mainly from plagioclase with a cre age of 22 myr bunburra rockhole is the first anomalous eucrite that overlaps with the main cre peak of the hed meteorites the radiogenic k ar age of 4 1 gyr is consistent with the u pb age while the young u th he age of approximately 1 4 gyr indicates that bunburra rockhole lost radiogenic 4he more recently

geology geochronology fluid inclusion and h o isotope geochemistry of the luoboling porphyry cu mo deposit zijinshan orefield fujian province china abstract the luoboling cu mo deposit in the zijinshan orefield fujian province southeastern china is a large porphyry deposit hosted by the sifang granodiorite and the luoboling granodiorite porphyry the largest cu mo orebody is saddle shaped with various types of hydrothermal veinlets intensive hydrothermal alteration in the deposit is characterized by outward zoning from potassic overprinted by phyllic alteration to phyllic and alunite dickite alteration based on the mineral assemblages and crosscutting relationships of veins the ore forming process can be divided into three stages namely an early stage k feldspar quartz magnetite molybdenite veins associated with potassic alteration a middle stage quartz molybdenite chalcopyrite pyrite veins in phyllic zone and a late stage quartz gypsum veins in the phyllic and alunite dickite alteration zones six molybdenite separates yield a re os isochron age 104 6 1 0 ma which is identical to the age of emplacement of the sifang and luoboling granodiorite porphyries three types of fluid inclusions fis were observed at the luoboling deposit 1 nacl h 2 o aqueous 2 daughter mineral bearing and 3 co 2 h 2 o fluid inclusions fis of the early and middle stages are predominantly vapor rich aqueous and daughter mineral bearing inclusions together with minor co 2 rich and liquid rich aqueous inclusions whereas the late stage minerals only contain liquid rich aqueous inclusions homogenization temperatures and salinities of fis trapped in the early stage minerals range from 420 to 540 c and 0 4 to 62 9 wt nacl equiv respectively fis of the middle stage yield homogenization temperatures of 340 to 480 c and salinities of 0 5 to 56 0 wt nacl equiv co 2 content and the oxygen fugacity indicated by daughter minerals of fis trapped in middle stage minerals are lower than those in the early stage the liquid rich aqueous inclusions of the late stage homogenize at temperatures of 140 to 280 c yielding salinities of 0 4 to 8 4 wt nacl equiv the minimum estimated pressures of the three stages are 30 70 mpa 10 40 mpa and 1 10 mpa respectively corresponding to minimum ore forming depths of 1 2 8 km fluids trapped in early middle and late stages yield d values of 67 to 54 54 to 70 and 62 and 18 o values of 5 4 to 6 7 2 8 to 4 2 and 2 1 respectively fluid boiling which resulted in the formation of stockworks and the precipitation of sulfides occurred in the early and middle stages the fluids subsequently evolved into a low temperature low salinity system in the late stage along with an input of meteoric water the luoboling porphyry cu mo system was developed in a transition from continental arc to back arc extension region which was related to the westward subduction of the paleo pacific plate beneath the huanan orogen

the relationship between joint aperture spacing distribution vertical dimension and carbonate stratification an example from the kimmeridgian limestones of pointe du chay france joint aperture and joint development have been studied in the kimmeridgian limestones of the pointe du chay at the northern boundary of the jurassic biscay basin france at belette outcrop in some layers the mean joint spacing of the n120 joint set is close to mean layer thickness there the classical spacing to thickness relationship appears to be valid in the competent carbonate layers that are included in a more argillaceous matrix at pillar outcrop the n10 joint set is characterised by a high level of joint density and a non saturated spacing distribution as indicated by the mode mean ratio values and the cv values cv is the ratio of standard deviation to mean fracture spacing the classical relationship between layer thickness and fracture spacing has not been observed at the pillar outcrop joint aperture reaches larger values at the pillar outcrop than at the belette outcrop where aperture is more homogeneously distributed almost all the joints are opened with moderate aperture values at belette outcrop whereas most joints with large vertical dimension have large apertures at pillar outcrop and smaller fractures are closed or poorly opened from two outcrops that have been subjected to the same geological conditions apertures of non stratabound joints appear to be controlled by the vertical dimension of the joints whereas stratabound joints are more regularly spaced and opened

early to late diagenetic dolomitization of platform carbonates lower ordovician ellenburger group permian basin west texas abstract pervasive early to late diagenetic dolomitization of lower ordovician ellenburger carbonates in the deep permian basin is recorded in core samples having present day burial depths of 1 5 to 7 0 km petrography geochemistry and paragenetic relation of dolomite rock textures indicate that ellenburger carbonate rocks were subjected to a complex diagenetic history ranging from early shallow subtidal dolomitization to late diagenetic deep burial dolomitization fine crystalline planar replacement dolomite of precursor lime muds formed during early diagenesis in a subtidal to peritidal setting under near surface low temperature conditions with mg2 supplied by diffusion from overlying seawater during intermediate burial 500 2000 m medium to coarse crystalline planar s dolomite replaced allochems and matrix or occurred as void filling planar e dolomite precipitated along walls of pores and fractures or formed porous mosaics of medium to coarse euhedral crystals nonplanar a dolomite replaced a precursor limestone dolostone only in zones that are characterized by original high porosity and permeability during deep burial 2000 m nonplanar dolomite cement saddle dolomite calcite and authigenic quartz precipitated i and occluded fractures and pore space the nonplanar dolomite cement is typically enriched in calcium mean 52 6 mole caco3 and iron mean 6635 ppm burial history and thermal maturation calculations suggest that deep burial dolomite cementation occurred during the late pennsylvanian early permian inter and intracrystalline dissolution surfaces are observed within the paragenetic sequence major truncation surfaces between early replacement dolomites and later void filling dolomites and between planar and nonplanar dolomite cements are evidence for dolomite dissolution deep discharge of meteoric fluids as a result of frequent periods of karsting in overlying strata and long distance fluid migration during the ouachita orogeny from foreland basins to the south are invoked for sources of undersaturated fluids causing dolomite dissolution and creating matrix porosity in the deep subsurface dissolution of precursor dolomite may also provide a source of mg2 for late stage dolomite cements similar diagenetic relationships have been described from deeply buried carbo ate rocks elsewhere indicating that trends and timing of dolomitization dissolution and porosity formation and cementation by late dolomite and calcite are intimately related to the evolution of sedimentary basins the origin of massive dolostones such as the ellenburger is best explained in the context of basin evolution rather than by a single model of dolomite formation

application of fuzzy logic and geometric average a cu sulfide deposits potential mapping case study from kapsan basin dpr korea abstract in this paper two kinds of knowledge driven methods one using the fuzzy logic and another using geometric average were applied to create the mineral potential maps for cu sulfide deposits in the greenfield kapsan basin dpr korea the ore geology studies for the study area have revealed that cu sulfide deposits of hydrothermal genesis in kapsan basin are closely associated with jurassic intrusions and faulting tectonics based on the conceptual model of cu sulfide deposits and the available spatial datasets in the study area we used five independent evidential maps for cu sulfide deposits potential mapping they include 1 faults 2 aeromagnetic anomaly 3 cu geochemical data 4 pb geochemical data and 5 zn geochemical data the evidential map values were transformed into continuous values of the 0 1 range using the non linear fuzzy membership functions logistic sigmoid and fuzzy gaussian functions because the fuzzy logic and geometric average methods can use the same fuzzification methodology based on suitable membership functions it is very economic and efficient to simultaneously apply two predictive models for mineral potential mapping of the study area the preparation of these evidential layers were performed using spatial analyses supported in arcgis 10 4 gis platform based on geological geophysical and geochemical spatial datasets the validation and comparative analysis results for the two predictive models demonstrated that most of known mineral occurrences are distributed in areas with high potential values the target areas classified by the fuzzy logic occupy 15 of the study area and contain 78 of the total number of known mineral occurrences compared with the fuzzy logic the resulting areas by the geometric average occupy 13 of the study area but contain 93 of the total number of known mineral occurrences although the total number of known mineral occurrences is relatively low for the application of roc receiver operating characteristics technique the areas under the roc curve auc obtained by two predictive models were greater than 0 5 suggesting that both predictive models and their resulting potential maps are useful for evaluating the prospectivity of cu sulfide deposits in kapsan basin

an active margin across the adriatic sea central mediterranean sea abstract new seismological and structural data from the central adriatic gargano promontory area demonstrate that the current models of an aseismic and slightly deformed adriatic block have to be revised a seismically active deformational belt is mapped along two main fault systems the tremiti islands and mattinata faults moreover geologic and geophysical evidence suggests that a more extensive lithospheric boundary may cut across the central italian peninsula to the tyrrhenian basin

discovery of a basaltic asteroid in the outer main belt visible and near infrared spectroscopic observations of the asteroid 1459 magnya indicate that it has a basaltic surface magnya is at 3 15 astronomical units au from the sun and has no known dynamical link to any family to any nearby large asteroid or to asteroid 4 vesta at 2 36 au which is the only other known large basaltic asteroid we show that the region of the belt around magnya is densely filled by mean motion resonances generating slow orbital diffusion processes and providing a potential mechanism for removing other basaltic fragments that may have been created on the same parent body as magnya magnya may represent a rare surviving fragment from a larger differentiated planetesimal that was disrupted long ago

the lohawat howardite mineralogy chemistry and cosmogenic effects the lohawat meteorite is a texturally heterogeneous breccia having a variety of mineral and lithic fragments among mineral fragments pyroxenes show a wide range of composition woo 17en0 37 78fs0 60 whereas plagioclase is anorthitic an0 92abo 070ro 007 abundant rounded chondrule like objects ranging in size up to 7 mm some with concentric layering have been observed petrographic features trace element composition and rare earth element patterns show the presence of eucritic and diogenitic components confirming that it is a typical howardite cosmogenic tracks rare gases he ne and ar and radionuclides 22na and 26a1 were measured track density in olivine and plagioclase varies between 0 7 to 6 x 106 cm2 38ar exposure age is estimated to be 1 10 ma being the highest among howardites the track production rates correspond to ablation of 9 to 15 cm implying a radius for its preatmospheric size of 27 cm 22na 26ai 1 as expected from the production models and solar modulation of galactic cosmic ray fluxes before its fall suggesting that the meteoroid did not undergo any fragmentation during the past 2 ma in interplanetary space the radiogenic age based on k ar method is 4 3 ga while the u th 4he age is 3 3 ga indicating partial loss of he

assessing geochemical anomalies using geographically weighted lasso abstract geochemical patterns in the surficial media are complex because of the various processes involved in their formation these processes may or may not relate to mineralization therefore geochemical anomalies identified are usually subject to uncertainty geographically weighted lasso gwl was adopted in this study to model the non stationary relationships between the geological geographical features and geochemical patterns in the surficial media the sparsity and reliability of regression coefficients in the gwl modeling renders it suitable for quantifying the controls that geological geographical features have on geochemical patterns this information can improve current knowledge about the complexity of geochemical patterns a case study in which the gwl model was established between geological geographical variables and the geochemical patterns of cu observed in stream sediments in the southwestern fujian province of china was presented the following findings were obtained 1 geological features show a major control on the geochemical patterns of cu in the studied area however the geochemical patterns of cu have been modified to some extent by secondary processes resulting in the relationships between geochemical signatures and mineralization becoming more complex and uncertain and 2 the gwl modeling can provide useful information for evaluating geochemical anomalies which can help reduce the uncertainty and benefit geochemical exploration at a later stage

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

gold and silver metallogeny of the south china fold belt a consequence of multiple mineralizing events abstract the south china fold belt is part of the south china block that is interpreted to be the result of multiple tectonic and magmatic events that formed a collage of accreted proterozoic and phanerozoic terranes the jurassic to early cretaceous yanshanian period 180 90 ma a time of major tectono thermal events that affected much of eastern and southeastern china is of great metallogenic importance in the fold belt this period is linked to subduction of the pacific plate beneath the eurasian continent and is manifested by voluminous volcano plutonic activity of predominantly calc alkaline affinity the distribution of gold and silver deposits in the south china fold belt indicates the presence of two distinct metallogenic provinces a region of basement uplifts which are controlled by shear zones and form neoproterozoic inliers of metamorphosed iron rich rock types defines the first province in this province orogenic lodes and volcanic related epithermal deposits represent the more significant precious metal mineralization the second province is essentially confined to a belt of yanshanian felsic intermediate volcanic and subvolcanic rocks that extends along most of the southeastern china coast in an area known as the coastal volcanic belt deposits in the coastal volcanic belt are silver and or copper rich volcanic hosted and epithermal in character the precious metal metallogeny of the south china fold belt is interpreted to have developed in at least three stages one as a result of collision events during the caledonian orogeny ca 400 ma the second during the indosinian orogeny ca 200 ma and the third during or soon after the formation of the yanshanian magmatic belt yanshanian orogeny 180 90 ma the latter was responsible for a hydrothermal event that affected large sections of the belt and its proterozoic substrate this may have resulted in the redistribution and enrichment of precious metals from preexisting orogenic gold lodes in neoproterozoic basement rocks which are now exposed as windows in zones of tectonic uplift the yanshanian hydrothermal activity was particularly widespread in the coastal volcanic belt and resulted in the formation of both low and high sulfidation epithermal gold and silver and locally copper and other base metal mineralization it is suggested that the coastal volcanic belt has greater potential for world class epithermal and porphyry deposits than previously realised

data driven predictive mapping of gold prospectivity baguio district philippines application of random forests algorithm the random forests rf algorithm has recently become a fledgling method for data driven predictive mapping of mineral prospectivity and so it is instructive to further study its efficacy in this particular field this study carried out using baguio gold district philippines examines a the sensitivity of the rf algorithm to different sets of deposit and non deposit locations as training data and b the performance of rf modeling compared to established methods for data driven predictive mapping of mineral prospectivity we found that rf modeling with different training sets of deposit non deposit locations is stable and reproducible and it accurately captures the spatial relationships between the predictor variables and the training deposit non deposit locations for data driven predictive mapping of epithermal au prospectivity in the baguio district we found that a the success rates of rf modeling are superior to those of weights of evidence evidential belief and logistic regression modeling and b the prediction rate of rf modeling is superior to that of weights of evidence modeling but approximately equal to those of evidential belief and logistic regression modeling therefore the rf algorithm is potentially much more useful than existing methods that are currently used for data driven predictive mapping of mineral prospectivity however further testing of the method in other areas is needed to fully explore its usefulness in data driven predictive mapping of mineral prospectivity

cosmogenic effects in mbale l5 6 chondrite measurements of particle tracks cosmogenic radionuclides and rare gas isotopes in mbale indicate that the meteoroid had a simple one stage exposure for 30 2 ma in interplanetary space on the basis of the measured track production rates and 60co and 26al activities the meteoroid is estimated to be a sphere with a radius of 36 cm the activities of several cosmogenic radionuclides i e 57co 54mn 22na 44ti and 26al in two fragments having different shielding as estimated by their track density and 60co activity provide the depth variation in their production rates cobalt 57 54mn and 22na activities agree with the production that is expected around the maximum of the solar cycle 22 as calculated from the sunspot numbers the u th 4he and k 40ar ages are measured to be 0 54 ga indicating a late thermal event which is in agreement with the thermal history of some other l group chondrites the trapped n has 15n of 57 4 o which is much lighter than the average l group chondrite value this indicates the presence of an isotopically anomalous light n component

data and knowledge driven mineral prospectivity maps for canada s north abstract data and knowledge driven techniques are used to produce regional au prospectivity maps of a portion of melville peninsula northern canada using geophysical and geochemical data these basic datasets typically exist for large portions of canada s north and are suitable for a greenfields exploration programme the data driven method involves the use of the random forest rf supervised classifier a relatively new technique that has recently been applied to mineral potential modelling while the knowledge driven technique makes use of weighted index overlay commonly used in gis spatial modelling studies we use the location of known au occurrences to train the rf classifier and calculate the signature of au occurrences as a group from non occurrences using the basic geoscience dataset the rf classification outperformed the knowledge based model with respect to prediction of the known au occurrences the geochemical data in general were more predictive of the known au occurrences than the geophysical data a data driven approach such as rf for the production of regional au prospectivity maps is recommended provided that a sufficient number of training areas known au occurrences exist

dolomitisation cementation and reservoir quality in three jurassic and cretaceous carbonate reservoirs in north western iraq abstract dolomitisation is a key diagenetic process commonly improving reservoir quality in carbonate rocks it is important in the jurassic and cretaceous carbonate reservoirs of north and north western iraq creating primary and secondary pays in many oilfields kirkuk ain zalah and butmah this paper addresses the impact of dolomitisation and cementation on the reservoir quality of three dolomitised carbonate formations butmah mauddud and wajnah three different dolomitisation types were recognised reflux dolomitisation mixing zone and burial dolomitisation extensive petrophysical measurements were carried out and have shown that differences in dolomite crystal size and cementation control the complexity of porosity pore and pore throat size distributions pore network connectivity and permeability reflux dolomitisation exhibits widely spread porosities and permeabilities compared to the other two characterised dolomitisation models indicating better reservoir properties wherever anhydride cement is either absent or subsequently dissolved as in the butmah formation mixing zone dolomitisation was encountered in the mauddud and wajnah formations providing moderate to good reservoir properties whereas burial dolomitisation generally provides poor to moderate reservoir properties in all three studied formations it was noted that dolomite cementation provides poor reservoir properties in both the butmah and mauddud formations both the mauddud and wajnah formations show poroperm relationships with the degree of scatter dependent on both differences in crystal size and pore connectivity indicating the degree of formation heterogeneity combined both quantitative and qualitative observations indicate that dolomitisation cannot be considered in isolation but is co active and co dependent upon dissolution cementation and fracturing all of these processes can both cause and amplify dolomitisation but can themselves be caused or amplified by dolomitisation we have combined all of our observations to propose a new model which relates different reservoir quality outcomes to the occurrence intensity and history of different diagenetic processes as a first step in the petrophysical quantification of the effect of diagenetic processes on reservoir quality

how fracture systems affect permeability development in shallow water carbonate rocks an example from the gargano peninsula italy abstract fracture networks control the permeability of many reservoirs since the fracture patterns of petroleum reservoirs in situ are difficult to study in detail field analogues are very important for understanding their fracture related permeability here we present the results of a study of the fracture system of carbonate rocks of lower cretaceous age in a quarry associated with the damage zone and fault core of a major fault zone on the gargano peninsula in south italy we measured the attitude of 1541 fractures and faults along several vertical and horizontal scan lines there are two main fracture sets one strikes between e w and ese wnw the other nne ssw a total of 675 fracture spacing measurements indicate log normal spacing distributions with an arithmetic mean fracture spacing of 0 29 m and a median of 0 15 m the data plotted on a log log plot suggest three main spacing subpopulations each of which follows approximately a power law with different fractal dimensions subpopulation 1 where the spacing ranges from 1 to 10 cm and the straight line slope d fractal dimension is 0 20 represents fractures confined to laminated carbonate mudstones multilayers that form the microbial mat deposits of a peritidal cycle subpopulation 2 where the spacing ranges from 11 to 55 cm and d is 0 77 represents fractures confined to thicker layers forming a part of a peritidal cycle the contacts of which are marked by stylolites subpopulation 3 where the spacing ranges from 56 to 243 cm and d is 2 81 represents fractures that dissect comparatively thick units of an entire peritidal cycle for the spacing the minimum coefficient of variation c v defined as standard deviation divided by the mean is 1 00 essentially randomly spaced fractures while its maximum c v is 1 62 suggesting that some fractures form clusters some clusters being denser than others the clusters composed of fractures with varying attitudes and therefore commonly intersecting are likely to contribute significantly to the overall permeability of the carbonate rock fracture aperture opening data n 324 also show a log normal size distribution with a mean opening of 1 01 cm and median of 0 29 cm log log plots indicate that a part of this data groups into two subpopulations i and ii each of which follows approximately a power law the straight line slope d the fractal dimension of subpopulation i is 0 46 whereas that of subpopulation ii is 1 49 we present boundary element models showing that laminated carbonate mudstones and their contacts modify the local stress fields so as to encourage fracture offset and commonly arrest our results also show that when a fluid driven subpopulation 2 fracture approaches subpopulation 1 fractures the induced tensile stresses may result in the opening up of many of the subpopulation 1 fractures directly above the tip of the subpopulation 2 fractures if in addition the contacts between the multilayers are weak they also tend to open up thus generating a large interconnected cluster of vertical fractures and horizontal contacts the results suggest that the tensile stresses induced by a comparatively large fluid driven subpopulation 2 fracture may contribute to the formation of an interconnected cluster of subpopulation 1 fractures and associated contacts thereby significantly increasing the permeability of the carbonate rock

dolomitization in a mixing zone of near seawater composition late pleistocene northeastern yucatan peninsula abstract patches of dolomite occur in cores of reefal limestone from the shallow subsurface on the northeastern coast of the yucatan peninsula this limestone accumulated during an interglacial high stand of sea level about 200 000 years ago dolomitization was preceded by freshwater diagenesis including precipitation of sparry calcite cement stabilization of mg calcitic skeletal fragments and partial dissolution of aragonitic components this suggests a predolomitization lowering of sea level with the consequent freshening of pore water the subsequent precipitation of dolomite indicates a return to high sea level with the consequent increase in mg ca ratio of pore water dolomitization took place during a brief high stand of sea level either shortly after deposition about 200 000 yr bp r more likely about 125 000 yr bp dolomite occurs both as microcrystalline replacement dolomite and as cement the cement is part of the following diagenetic sequence 1 limpid euhedral subhedral calcian dolomite crystals 2 zoned dolomite crystals with zones formed by variations of the calcium magnesium ratio in dolomite 3 layers of alternating calcian dolomite and magnesian calcite or calcite and 4 calcite this sequence represents the progressive freshening of ground water during the initial stage of a fall in sea level average cation composition of the limpid dolomite cement is ca57mg43 electron microprobe analysis zoned cement crystals are composed of ca57 59mg43 41 layers and ca62mg38 layers most of the higher calcium dolomite layers are dissolved forming hollow zone crystals in cement with alternating dolomite and calcite zones the calcite is ca99 97mg1 3 low mg calcite and ca96 93mg4 7 mg calcite the dolomite and mg calcite zones are partially to totally leached 18o compositions of yucatecan dolomite and of modern ground water suggest dolomite precipitation from mixed water ranging from about 75 seawater 25 freshwater to nearly all seawater isotope analyses are for the most stable calcian dolomites more soluble calcium rich dolomite presumably is analyzed with calcite and thought to be isotopically lighter than the less soluble dolomite in the cement sequence the most stable dolomite is followed by more soluble dolomite as ground water becomes less saline isotope analyses together with position of dolomite in the cement sequence suggest the most stable calcian dolomite including limpid dolomite precipitated from mixed water with large proportions of seawater and the less stable more calcian dolomite precipitated from fresher mixed water

classification and description of dolomitic fabrics of rocks from the floridan aquifer u s a abstract biozones of the lake city formation avon park formation and ocala limestone are characterized by interbedded massive fossiliferous carbonate rocks wackestones to grainstones and thinly bedded peloidal and carbonaceous rocks mudstones and wackestones several horizons have been partly or completely dolomitized a wide range of early to late stages of dolomitic fabrics are recognized the fabrics are classified descriptively as equigranular unimodal or inequigranular multimodal fabrics composed of crystals two processes of dolomitization are suggested a homogeneous dolomitization resulting in a single stage development of microtextured groundmass crystals

a machine learning based approach to exploration targeting of porphyry cu au deposits in the dehsalm district eastern iran abstract the dehsalm district in the central part of the lut block is an important polymetallic belt of eastern iran this study identifies the prospective areas for cu au porphyry deposits within the dehsalm district by integrating the outputs of the restricted boltzmann machine rbm and random forest rf models based on geological metallogenic and statistical analyses seven predictor maps namely proximity to faults and intrusive rocks to aeromagnetics anomalies to hydrothermal alterations argillic and fe oxide and two multivariate geochemical signatures of the stream sediments were generated to train the models to identify anomalies indicative of cu au porphyry mineralization from the rbm results the rf model was applied as a supervised machine learning algorithm the target areas delineated in the combined model occupy 4 2 of the study region and contain 82 of the known cu au occurrences the most prospective areas identified in the combined model extend along with structures that are spatially associated with known cu au occurrences and provide clear targets for future exploration

manetoe facies a gas bearing megacrystalline devonian dolomite yukon and northwest territories canada the manetoe facies is a broadly stratiform and regionally developed 38 000 km2 or 15 000 mi2 body of white sparry dolomite hosted in lower and middle devonian strata and is the northwestward continuation of the similar but better known presqu ile facies dolomite several large gas fields have been discovered within anomalously thick developments of the manetoe dolomite close to the northwest limit of the devonian elk point basin of alberta the external geometry of the manetoe facies indicates that it may have been a cavern or karst system excavated in the late middle devonian by a large vertically confined coastal aquifer the local regions of anomalously thick manetoe facies may have developed where the aquifer stoped upward into strata above the confining aquiclude of the headless formation shale dolomite cementation may have occurred during any of three possible episodes of large scale fluid movement fluid inclusion and strontium isotope data favor the hypothesis that manetoe dolomites precipitated from heated 150 210 c or 300 410 f hypersaline evaporitic brines that have interacted with the underlying precambrian crust probably in the late devonian lead isotope data support the general concept of pre mesozoic dolomite cementation and largely preclude a late early tertiary deep burial setting spectacular zones of detrital dolomite cement within the manetoe are most readily accommodated by a near surface very early middle devonian aquifer mixing model origin but the presence of these zones does not preclude the other possible origins carbon and xygen isotope data from the manetoe facies support the concept that the presqu ile and manetoe facies are physically continuous and had a common origin

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

itawa bhopji l3 5 chondrite regolith breccia fall classification and cosmogenic records a stony meteorite fell at itawa bhopji rajasthan india on 2000 may 30 this is the fifth recorded fall in a small area of rajasthan during the past decade the meteorite is an ordinary chondrite with light clasts in a dark matrix consisting of a mixture of equilibrated mainly type 5 and unequilibrated components olivine is fa24 26 and pyroxene fs20 22 but within the unequilibrated components olivine fa5 29 and low calcium pyroxene fs5 37 are highly variable based on petrographic studies and chemical analyses it is classified as l 3 5 regolith breccia studies of various cosmogenic records including several gamma emitting radionuclides varying in half life from 5 6 day 52mn to 0 73 ma 26al tracks and rare gases have been carried out the exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19 6 ma the track density varies by a factor of 3 from 4 to 12 x 10 6 cm 2 within the meteorite indicating a preatmospheric body of 9 cm radius corresponding to a meteoroid mass of 11 kg and small ablation 1 5 to 3 6 cm trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite large excess of neutron produced 82kr and 128xe in both the light and the dark lithology but very low 60co indicating low neutron fluxes received by the meteoroid in the interplanetary space are clear signatures of an additional irradiation on the parent body

modeling of cu au prospectivity in the carajas mineral province brazil through machine learning dealing with imbalanced training data abstract machine learning ml is becoming an appealing tool in various fields of earth sciences especially in mineral prospectivity mapping mpm to support mineral exploration ml algorithms are designed to assume a relatively balanced amount of training data for the estimation of the decision boundaries between the classes of interest i e in mpm mineralized and non mineralized locations however in mpm the numbers of mineralized and non mineralized locations are naturally imbalanced as the number of known mineral deposit occurrences as a proxy of mineralized or positive class are naturally much smaller than the number of non mineralized locations the negative class the use of imbalanced data leads to difficulties in the training of ml models for mpm due to the learning bias towards the features of the predominant i e negative class in the present study using support vector machine for cu au prospectivity modeling in the carajas mineral province brazil we evaluated the effects of synthetic minority over sampling technique smote which addresses the issue of imbalanced training data on the performance of mpm the original training data for the positive i e minority class was modified by over sampling the mineralized locations using smote and by randomly under sampling the non mineralized locations at different proportions producing 400 training datasets with proportions of mineralized to non mineralized samples ranging from 600 30 to 30 600 each of these individual training datasets was used to evaluate the performance of mpm under different proportions of mineralized to non mineralized samples the performance of each prospectivity model was objectively evaluated using the f1 score and the success rate curve the results show that smote can significantly increase the performance and the spatial efficiency of mpm the main differences between the performances of the derived prospectivity models illustrate the sensitivity of mpm to the number of samples and distribution of classes in the training data according to the results better performance is achieved using smote when the prospectivity models are trained with an equal number of mineralized and non mineralized samples the best prospectivity model trained with a modified dataset with 600 600 proportion of mineralized to non mineralized samples resulted in 100 classification of the training mineralized locations and almost 80 of the testing mineralized locations and outlined only 7 of the study area as prospective

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

from fractures to flow a field based quantitative analysis of an outcropping carbonate reservoir abstract fractures can play an important role in the fluid storage migration properties of fault damage zones in this present contribution we document the role exerted by fractures on fluid flow in carbonate damage zones of hydrocarbon bearing km long oblique slip normal faults with 10 s of m throw the carbonate fault damage zones were analysed by mean of scan line surveys conducted in both tar free and tar rich outcrops in this way the relationships among the individual fracture characteristics length spacing aperture orientation connectivity and distance from slip surfaces pertaining to small faults of the fault damage zones and hydrocarbons have been established data obtained by scan line surveys were also used to compute the amount of fracture porosity the degree of fracture connectivity and based upon simple assumptions the orientation of the local hmax at times of faulting additionally scan line surveys were also carried out along outcrops exposing unfaulted carbonate host rocks the results of our computation are consistent with a carbonate host rock made up of a quite isotropic fracture array comprised of isolated and coupled fractures in which individual fracture sets have negative exponential spacing distributions in terms of fluid flow the fracture array of the carbonate host rock enhances the fluid storage conversely the fracture array of the fault damage zones is characterized by a pronounced anisotropy due to interconnected fractures which enhance the fluid migration fractures in the fault damage zones include those inherited from background deformation and others related to the faulting processes the latter fracture sets are characterized by power law spacing distributions in conclusion counter intuitively both fracture length and fracture spacing do not have any correlation with hydrocarbons in the fault damage zones on the contrary fracture anisotropy fracture spread and fracture orientation are positively correlated with hydrocarbons

mechanism for joint saturation in mechanically layered rocks an example from southern israel abstract over 700 joint spacings were measured along a 190 m scanline within a single limestone bed of the turonian gerofit formation southern israel by investigating joints belonging to a single systematic set confined to a bed of uniform thickness one can factor out the major influences of bed thickness lithology and mechanical properties on joint set development joint spacing distributions and fracture spacing ratios fsr vary dramatically along the length of the scanline and correlate directly with throughgoing fracture zones belonging to the same tectonic stress regime regions cross cut by fracture zones display narrower median joint spacings fsr of 1 3 and unimodal joint spacing distributions where fracture zones are absent joint spacings have wider medians fsr of 0 8 and multimodal distributions because fracture zones most likely represent areas of high strain and laboratory experiments demonstrate a systematic decrease in fracture spacing with increasing strain regions of the bed cross cut by fracture zones are likely at a more advanced stage of joint set development and hence closer to saturation than other regions joint saturation in the gerofit formation may be achieved by a shift in scale from single layer to multi layer jointing as the development of throughgoing joints prevents the formation of additional bedding confined joints

dinosaurs re write the geodynamics of the eastern mediterranean and the paleogeography of the apulia platform abstract evidence of a sizeable population of large dinosaurs on the apulia carbonate platform calls for a revision of the current paleotectonic and paleogeographic scenario of the eastern mediterranean area a review of geophysical and geological data of the ionian sea and surrounding areas leads to envisage the late jurassic early cretaceous ionian sea region as a cul de sac type basin enclosed by shallow water carbonate banks connecting the apulia carbonate platform to peloponnesus northern cyrenaica cyrene seamount and medina ridge these banks were repeatedly and periodically exposed to subaerial conditions and offered vast land areas for migration of dinosaurs as regards the nature of the mesozoic ionian basin interpretations are quite controversial the continental vs oceanic crust debate will likely be solved only when the ionian basin crust will be reached by drilling the conclusion of the present review leads to consider adria as a true african promontory and the apulia platform as a sort of florida peninsula attached to north africa cyrenaica spur subdividing the oceanic mesozoic mediterranean into a western ionian basin and an eastern levantine basin

introduction to the special issue gis based mineral potential modelling and geological data analyses for mineral exploration this introduction provides an overview of the procedures involved in mineral potential modelling the papers included in this special issue are also summarized

a revised classification of limestones abstract the most widely used classifications of limestones are now thirty years old and our appreciation of the diagenetic effects on limestone textures is now much greater a revision of the classifications of dunham 1962 and embry and klovan 1971 is offered and new diagenetic categories are proposed the confusing term lime mudstone is replaced by calcimudstone two categories of diagenetic textures are recognized non obliterative and obliterative the former contains limestones which are almost wholly composed of diagenetic cement cementstones and those whose fabric is the result of intergranular pressure solution condensed and fitted grainstones obliterative categories include limestones and dolomites whose original fabric has been destroyed sub categories include sparstones or dolosparstones crystals 10 m in size and microsparstones dolomicrosparstones crystals 4 10 m in size and dolomicrostones crystals m in size many diagenetic processes can produce fabrics which mimic depositional ones and these are reviewed

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

tertiary geodynamic evolution of the southern adria microplate the southern adria microplate is the common foreland for the hellenide and southern apennine thrust belts the apulian platform dominates the microplate outcrop well and seismic data allow us to trace the carbonate platform edge whilst structural analysis geophysical and palaeomagnetic data provide important clues to the geodynamic evolution of the region the present structural fabric of apulia is dominated by several e w lineaments that divide the region into different blocks rospo plateau gargano promontory murge ridge salento peninsula apulian plateau one such lineament the pescara dubrovnik line a prominent feature traversing the adriatic sea between central italy and southern croatia has been active since the early mesozoic when it acted as a major transform fault controlling sedimentation along the northern margin of southern adria during the cenozoic the pescara dubrovnik underwent predominantly vertical and oblique movement due to a differential flexural response of the platform and the adjacent pelagic sequences to the thrust belt loading in tertiary time the southern adria microplate was partly involved in heilenide collision the apulian platform can be considered as an area of thicker crust more resistant to underthrusting than the surrounding basins during the orogenic events it acted as a passive rigid indentor causing local distortion of the most external hellenide structures the dextral transpressive activity recorded along the south east margin of this indentor kephallinia line can be interpreted as the result of the oblique collision between the margin of the thick apulian platform in this zone nne ssw striking and the nw se striking hellenic thrust belt horizontal stress generated during the collision was partly transmitted to the rigid foreland re activating palaeo e w faults within the south adria microplate in a dextral strike slip sense the clockwise rotation recorded in the salento peninsula can be explained by the rotation of several nw se striking faulted blocks the rotation was accompanied by the opening of small transtensional basins between blocks this block rotation was caused by the dextral shear that is expressed along the north and the south salento fault zones

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

machine learning predictive models for mineral prospectivity an evaluation of neural networks random forest regression trees and support vector machines abstract machine learning algorithms mlas such us artificial neural networks anns regression trees rts random forest rf and support vector machines svms are powerful data driven methods that are relatively less widely used in the mapping of mineral prospectivity and thus have not been comparatively evaluated together thoroughly in this field the performances of a series of mlas namely artificial neural networks anns regression trees rts random forest rf and support vector machines svms in mineral prospectivity modelling are compared based on the following criteria i the accuracy in the delineation of prospective areas ii the sensitivity to the estimation of hyper parameters iii the sensitivity to the size of training data and iv the interpretability of model parameters the results of applying the above algorithms to epithermal au prospectivity mapping of the rodalquilar district spain indicate that the rf outperformed the other mla algorithms anns rts and svms the rf algorithm showed higher stability and robustness with varying training parameters and better success rates and roc analysis results on the other hand all mla algorithms can be used when ore deposit evidences are scarce moreover the model parameters of rf and rt can be interpreted to gain insights into the geological controls of mineralization

mapping mineral prospectivity through big data analytics and a deep learning algorithm abstract identification of anomalies related to mineralization and integration of multi source geoscience data are essential for mapping mineral prospectivity in this study we applied big data analytics and a deep learning algorithm to process geoscience data to identify and integrate anomalies related to skarn type iron mineralization in the southwestern fujian metallogenic zone of china based on the geological setting and environment for the formation of skarn type iron mineralization 42 relevant variables including two geological one geophysical and 39 geochemical variables were analyzed and integrated for detecting anomalies related to mineralization using a deep autoencoder network the results indicate that the mapped prospectivity areas have a strong spatial relationship with the locations of known mineralization and demonstrate that big data analytics supported by deep learning methods is a potential technique to be considered for use in mineral prospectivity mapping

the vissannapeta eucrite a wholly encrusted single stone that fell in vissannapeta andhra pradesh india has been identified as a cumulate eucrite based on its primary texture and mineral composition anorthite an 92 4 94 6 orthopyroxene en 49 1 51 8 fs 44 2 49 7 wo 1 2 4 0 and clinopyroxene en 38 8 46 8 fs 14 8 33 6 wo 19 6 46 4 the stone is pyramidal in shape and the crust shows rib like flow features indicating that it had an oriented passage through the atmosphere towards the terminal stage of its flight conditions of its fall mineralogical characteristics and results of measurements of cosmogenic radioactivity 26 al 22 na and 54 mn and track density are described aluminum 26 and 22 na in vissannapeta are 75 of the expected values and also lower by a similar factor compared to the activities measured in piplia kalan another eucrite which fell 18 months before vissannapeta because higher activity of 22 na and 54 mn would be expected from solar cycle modulation of galactic cosmic rays these results as well as the track density gradient indicate that vissannapeta was a small body 120 kg in the interplanetary space wherein the nuclear cascade due to galactic cosmic rays did not develop fully tracks surface morphology and crustal features indicate at least two fragmentation events in the atmosphere

environmental and sequence stratigraphic implications of anhydrite textures a case from the lower triassic of the central persian gulf abstract the lower triassic kangan formation in the persian gulf south pars gas field and its adjacent areas are composed of carbonate evaporite sequences these sediments were deposited in a shallow marine homoclinal ramp study of the anhydrite bearing intervals shows various structures and textures the anhydrite structures are mainly bedded massive chicken wire and nodular type and the main textures are felted sparse crystal needle shape lath shape equant and fibrous pervasive and poikilotopic cement together with replacement and porphyroblastic gypsum are accounted as the most common diagenetic features in anhydrite evaluation of anhydrite occurrences and features support both primary and secondary formations the nodular to chicken wire anhydrite formed under synsedimentary sabkha conditions whereas anhydrite cements occurred during the late stages of diagenesis shallow burial stage massive to bedded anhydrite could have been formed under subaqueous conditions or originated by coalescing and continued growth of anhydrite nodules in the sabkha zone anhydrite fabrics impose a significant control on the reservoir quality of the kangan carbonates at the south pars gas field thick massive and bedded anhydrite could have been formed as an intraformational seals and anhydrite cements occluded pore spaces and reduced the poroperm values the sequence stratigraphic analysis revealed two depositional sequences in the studied intervals which are composed of tst and hst investigation of anhydrite throughout depositional sequences indicates a change in the content and style of anhydrite texture anhydrite content volume decreases upward through transgressive system tract sea level rise whereas it enhances during highstand system tract sea level fall pervasive and poikilotopic anhydrite cements together with replacement by anhydrite are prevalent features during transgressive and early highstand system tract at the late hst with a progradational stacking pattern anhydrite value increases and felted radial equant crystalline and mosaic texture are the most common anhydrite fabrics sequence boundaries that indicate maximum sea level fall and exposure of successions are marked by the broad anhydrite deposits with massive to bedded and chicken wire structures and various textures that located in late hst package there is an unambiguous relationship between the microfacies associations the evaporite textures and the sea level fluctuations this relationship could lead to a predictable pattern that can be of use as a general guide for the sequence stratigraphic interpretations in the area

mapping mineral prospectivity for cu polymetallic mineralization in southwest fujian province china abstract in this study both the fuzzy weights of evidence fwofe and random forest rf methods were applied to map the mineral prospectivity for cu polymetallic mineralization in southwestern fujian province which is an important cu polymetallic belt in china recent studies have revealed that the zijinshan porphyry epithermal cu deposit is associated with jurassic to cretaceous yanshanian intermediate to felsic intrusions and faulting tectonics evidence layers which are key indicators of the formation of zijinshan porphyry epithermal cu mineralization include 1 jurassic to cretaceous intermediate felsic intrusions 2 mineralization related geochemical anomalies 3 faults and 4 jurassic to cretaceous volcanic rocks these layers were determined using spatial analyses in support by geodas and arcgis based on geological geochemical and geophysical data the results demonstrated that most of the known cu occurrences are in areas linked to high probability values the target areas delineated by the fwofe occupy 10 of the study region and contain 60 of the total number of known cu occurrences in comparison with fwofe the resulting rf areas occupy 15 of the study area but contain 90 of the total number of known cu occurrences the normalized density value of 1 66 for rf is higher than the 1 15 value for fwofe indicating that rf performs better than fwofe receiver operating characteristics roc were used to validate the prospectivity model and check the effects of overfitting the area under the roc curve auc was greater than 0 5 indicating that both prospectivity maps are useful in cu polymetallic prospectivity mapping in southwestern fujian province

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

devgaon h3 chondrite classification and complex cosmic ray exposure history the devgaon meteorite fell in india on february 12 2001 and was immediately collected it is an ordinary chondrite having a number of sio2 rich objects and some ca al rich inclusions olivines fa17 19 are fairly equilibrated while pyroxenes fs4 20 are unequilibrated occasionally shock veins are visible but the bulk rock sample is very weakly shocked s2 chondrules and chondrule fragments are abundant based on chemical and petrological features devgaon is classified as an h3 8 group chondrite several cosmogenic radionuclides ranging in half lives from 5 6 d 52mn to 7 3 x 10 5 yr 26al noble gases he ne ar kr and xe and particle track density have been measured the track density in olivines from five spot samples varies between 4 6 to 9 x 10 6 cm 2 showing a small gradient within the meteorite the light noble gases are dominated by cosmogenic and radiogenic components large amounts of trapped gases ar kr and xe are present in addition n products from br and i are found in kr and xe respectively the average cosmic ray exposure age of 101 8 ma is derived based on cosmogenic 38ar 83kr and 126xe the track production rates correspond to shielding depths of about 4 9 to 7 8 cm indicating that the stone suffered type iv ablation low 60co high 22ne 21ne c and large neutron produced excesses at 80kr 82kr and 128xe indicate a complex exposure history of the meteoroid in the first stage a meter sized body was exposed for nearly 108 yr in the interplanetary space that broke up in 50 cm sized fragments about a million years ago stage 2 before it was captured by the earth

an aeromagnetic investigation of the dapai deposit in fujian province south china structural and mining implications abstract the dapai region is considered as one of the largest polymetallic reserves in fujian province south china as exploration advances so does the demand for prospecting the deeper concealed deposits in this place however in the past few years due to the rugged surface topography and dense vegetation few high precision and large scale ground surveys have been carried out in this area therefore the understanding of the overall structure and non exposed deposits remains insufficient to meet the challenges involved in deeper ore prospecting in the present study we applied a cost effective and high precision aeromagnetic survey to investigate the structural trends prevailing in the study area and delimit the areas with potential for finding deposits to achieve the aforementioned goals the tilt angle derivative was conducted on the pre processed magnetic anomalies to highlight any deeply seated structural features based on which reliability of the geologically inferred faults was analyzed and seven major faults and 22 minor faults were identified for the first time most of these deduced faults show an ns trend in the center part and an nw ne trend in other parts of the study area in addition 3d generalized physical property inversion of the obtained residual magnetic anomalies was implemented to delineate the potential ore bodies based on which an integrated prospecting target map was established our inversion results indicate that there are several isolated magnetic sources in the subsurface extending from a depth of a few hundred meters to no more than 3 km this presented study not only leads to a deeper understanding of the dapai deposit but also provides references for studying other similar deposits where large scale ground studies are hard to be executed

the quest for regolithic howardites part 2 surface origins highlighted by noble gases we report noble gas data of helium he neon ne argon ar krypton kr and xenon xe cosmic ray exposure cre ages and nominal gas retention k ar u th he ages for seven howardites cre 01400 eet 87513 eet 87518 eet 99400 gro 95535 gro 95602 san 03472 in continuing research to identify regolithic samples and better understand the vestan regolith in our previous work we found little correlation between suggested regolith parameters of ni 300 g g al 2o 3 8 9 wt and eucrite diogenite e d ratio of 2 1 warren et al 2009 and trapped solar wind sw fractionated solar wind fsw or planetary noble gas components from impacted material noble gas indicators of a regolithic origin here we have expanded our data set to include samples outside of these parameters to further explore composition and the differences in ni content as indicators for the presence of non vesta material in addition our sample set includes two potentially paired meteorites from the gro suite finally in our petrographic studies the samples selected showed no evidence for carbonaceous chondrite fragments which should reduce the effect of contamination by planetary noble gas components and will allow us to better identify sw fsw components where present of the samples studied here three howardites gro 95535 gro 95602 and eet 87513 show evidence for a regolithic origin with both isotopic and element noble gas ratios clearly pointing to the presence of trapped components similar to sw fsw or planetary the two gro howardites gro 95535 and gro 95602 show similar noble gas ratios to our previously defined sw fsw dominated regolithic group lew 85313 and met 00423 suggesting a surface origin for these samples however interestingly the gro samples show vastly different cosmogenic noble gas abundances and thus different cre ages which suggests that they are not paired for howardite eet 87513 the data hint to the presence of cm material with a neon release pattern similar to our defined planetary fsw dominated regolithic group cm rich samples pra 04401 sco 06040 our petrological investigations found no evidence for cm fragments within eet 87513 though a single clast was reported previously buchanan et al 1993 aside from the ne release pattern the remaining noble gas data show more similarity with sw fsw components the remaining four howardites cre 01400 eet 87518 eet 99400 and san 03472 and are dominated by cosmogenic noble gases and show no evidence for a regolithic origin our data suggest that a cm composition is likely present in all samples to some degree but that this can be overprinted by sw components or cosmogenic components obtained in situ on the vestan surface or during transit to earth respectively the presence of cm material is an important parameter for understanding the evolution of vesta s surface while we have uncovered three further regolithic howardites 13 regolithic total of 41 analysed further noble gas analysis of hed meteorites is needed to not only determine regolithic origins but to better characterise the abundance of carbonaceous chondrite material and its effect on the noble gas signatures of such samples

piplia kalan eucrite fall petrography and chemical characteristics two stones that fell near piplia kalan on 1996 june 20 are identified as ca rich achondrites belonging to the eucrite group the conditions of their fall are described the petrographic description texture and chemical composition the elemental ratios particularly k la and yb sc and relatively flat rare earth element ree patterns 6 8 chondrite of bulk samples without any significant eu anomaly all agree with the characteristic values found in eucrites a feldspar rich fraction shows a significant positive eu anomaly the presence of several different lithologies and clasts indicates that it is a texturally diverse breccia and the chemical analysis suggests that it belongs to the noncumulate group of eucrites falling in the nuevo laredo trend

gis based mineral prospectivity mapping using machine learning methods a case study from tongling ore district eastern china abstract predictive modelling of mineral prospectivity using gis is a valid and progressively more accepted tool for delineating reproducible mineral exploration targets in this study machine learning methods including support vector machine svm artificial neural networks ann and random forest rf were employed to conduct gis based mineral prospectivity mapping of the tongling ore district eastern china the mineral systems approach was used to translate our understanding of the skarn cu mineral system into mappable exploration criteria resulting in 12 predictor maps that represent source transport physical trap and chemical deposition processes critical for ore formation predictive svm ann and rf models were trained by way of predictor maps and corroborated using a 10 fold cross validation the overall performance of the resulting predictive models was assessed in both training and test datasets using a confusion matrix set of statistical measurements receiver operating characteristic curve and success rate curve the assessment results indicate that the three machine learning models presented in this study achieved satisfactory performance levels characterized by high predictive accuracy in addition all models exhibited well interpretability that provided consistent ranking information about the relative importance of the evidential features contributing to the final predictions in comparison the rf model outperformed the svm and ann models having achieved greater consistency with respect to variations in the model parameters and better predictive accuracy importantly the rf model exhibited the highest predictive efficiency capturing most of the known deposits within the smallest prospective tracts the above results suggest that the rf model is the most appropriate model for cu potential mapping in the tongling ore district and therefore was used to generate a prospectivity map containing very high high moderate and low potential areas in support of follow up exploration the prospective areas delineated in this map occupy 13 97 of the study area and capture 80 95 of the known deposits the fact that two newly discovered deposits occur within the prospective areas predicted by the prospectivity model indicates that the model is robust and effective regarding exploration target generation

origin and petrophysics of dolostone pore space abstract the common claim that dolomitization creates 12 porosity is based on the mole for mole replacement equation however in the past 50 years data have been collected demonstrating that dolomitization does not create porosity instead dolostones inherit the porosity and fabric of the precursor limestone and porosity is reduced by overdolomitization the porosity of the precursor limestone depends on the diagenetic history up to the time of dolomitization data show that 1 carbonates are born with high porosity and lose porosity gradually over a long period and 2 mud dominated fabrics compact more readily than grain dominated fabrics the problem of estimating the time of dolomitization is minimized by confining observations to young limestones and associated dolostones limited data from holocene dolomitic sediments suggest no change in porosity with dolomitization study of plio pleistocene carbonates in bonaire netherlands antilles demonstrates that precursor limestones are more porous than dolostones limestones average 25 porosity whereas dolostones average 11 porosity data from the neogene of the great bahama bank show that dolostones and adjacent limestones both have 40 porosity porosity studies of the jurassic arab d formation show that dolostones and associated grain dominated limestones have similar porosity ranges and that the decrease in porosity with increasing dolomitization results from compaction of the mud dominated fabrics these data suggest that porosity in dolostone is not created by a mole for mole replacement mechanism instead dolostone porosity is 1 inherited from the precursor limestone and 2 occluded by the process of overdolomitization palaeozoic dolostones however are commonly more porous than juxtaposed limestones the explanation for this observation is that limestones lose porosity through compaction and cementation whereas dolostones resist compaction and retain much of their porosity permeability studies have demonstrated that dolomitization of grain dominated limestones usually does not change porosity permeability relationships instead precursor limestone fabric controls pore size distribution the dolomite crystal size of a muddominated dolostone may however be larger than the carbonate mud size improving the porosity permeability relationship substantially hence there is a predictable relationship between interparticle grains or crystals porosity permeability precursor grain size and dolomite crystal size

from andesitic volcanism to the formation of a porphyry cu au mineralizing magma chamber the farallon negro volcanic complex northwestern argentina abstract the geological relations and geochemical composition of extrusive and subvolcanic intrusive rocks of the upper miocene farallon negro volcanic complex nw argentina were studied to reconstruct the evolution of a deeply eroded andesitic volcano over most its life history of some 3 5 my this paper is part of an integrated study of the processes that generate magmatic hydrothermal fluids responsible for the formation of porphyry cu au deposits here we present new data on bulk rock chemical and nd sr and pb isotopic compositions of unaltered volcanic and subvolcanic intrusive rocks for which geological relations and ages are constrained by field based stratigraphy and extensive ar ar geochronology the combined results indicate that voluminous volcanism started at ca 9 7 ma with the eruption of basaltic andesite to andesite lava flows and pyroclastic deposits this basic to intermediate volcanism persisted until 7 5 ma and was followed at 7 35 ma by the eruption of dacites as the last recorded major extrusive event the oldest andesitic intrusions emplaced at 9 0 ma were followed by hypabyssal intrusions of basaltic andesite andesite and dacite composition which intruded the volcanic sequence between 8 3 and 6 1 ma intrusions at 6 8 0 2 ma led to the formation of over 800 mt of porphyry cu au ore at bajo de la alumbrera it was formed by a large flux of magmatic hydrothermal fluids channeled through several phases of fractured dacitic porphyry which together with immediately following barren andesitic intrusions make up a composite stock after this magmatic hydrothermal event only minor rhyodacitic to rhyolitic intrusions were emplaced until magmatic activity ceased at 6 1 ma geochemical data for the magmatic rocks indicate that the evolution of the system was dominated by mixing of a mafic magma with a felsic magma that contained a component of crustal material as indicated by linear compositional correlations between compatible and incompatible elements initial strontium isotopic ratios vary between 0 7047 and 0 7118 while 143nd 144nd range from 0 5127 to 0 5124 and both isotopic variations correlate with each other and with sio2 content of the rocks after 8 5 ma a continuous increase in the silica content of intrusive rocks suggests the gradual formation of a magma chamber a substantial magma reservoir 7 km3 must have been established by the time of porphyry cu au mineralization to allow rapid release of a large volume of ore forming magmatic brine as a result of wholesale crystallization and de volatilization of the magma chamber

three dimensional facies modeling of carbonate sand bodies outcrop analog study in an epicontinental basin triassic southwest germany this article is the first part of an integrated study to characterize the anatomy and geometries of carbonate shoal reservoir bodies in epicontinental settings it is based on outcrop analog data from triassic layer cake carbonates in the south german basin which were deposited along an epicontinental very gently inclined carbonate ramp the database of this study consists of 56 measured sections supplemented by six shallow cores and wireline logs covering an area of 25 by 36 km 15 by 22 mi the potential reservoir bodies consist generally of midramp shoal and shoal fringe facies types which are composed of skeletal and oolitic carbonate packstones and grainstones with significant amounts of porosity the upper muschelkalk is composed of a lower transgressive and an upper regressive interval within these shoal bodies show not only similarities but also major differences in character geometry and distribution these reflect the conditions of an epeiric system which reacts strongly to small changes in accommodation the accommodation seems to be mainly triggered by the interaction of hierarchically organized large medium and small scale relative sea level changes and a subtle paleorelief at the level of medium scale cycles distinct two dimensional cyclicity styles can be differentiated which record the lateral facies distribution along the depositional gradient different styles of medium scale cycles include different types of shoal bodies 1 transgressive crinoidal shoal style shoal bodies mean width 21 km 13 mi mean length 37 km 23 mi mean thickness 4 2 m 13 7 ft with low facies differentiation deposited on top of subtle paleohighs 2 skeletal sheets style thin reservoir sheets mean width 5 1 km 3 1 mi mean length 11 1 km 6 8 mi mean thickness 0 3 m 0 9 ft of reservoir facies on top of the paleohighs 3 regressive oolitic shoal style shoal bodies mean width 14 6 km 9 0 mi mean length 20 8 km 12 9 mi mean thickness 0 69 m 2 2 ft with high facies differentiation on the flanks of paleohighs and 4 low accommodation style patchy and mosaic distribution of shoal bodies mean width 11 2 km 6 9 mi mean length 26 km 16 mi mean thickness 0 69 m 2 2 ft all data were loaded into three dimensional 3 d modeling software to distribute 14 facies types and model the 3 d stratigraphic architecture the resulting facies distribution implies that volume and dimensions of the shoal bodies are mainly controlled by the combination of stratigraphic cycles and a subtle paleorelief which is indicated by overall thickness changes of succession high energy shoal facies types occur only in and around areas with a reduced overall thickness whereas areas with a thicker development are dominated by low energy muddy facies types all observations combined point to the presence of a subtle paleorelief which could be induced by slight differential subsidence of inherited paleotectonic basement blocks on the kilometer to regional scale previous studies suggest simple layer cake stratal patterns however in the full 3 d view the apparent layer cake stratigraphy turned out to be a pseudolayer cake with very gentle 0 01 0 001 dip clinoform geometries these very subtle offlapping pinch out geometries may have been overlooked in epeiric reservoir systems elsewhere

petrophysical evaluation of a slope fan basin floor fan complex cherry canyon formation ward county texas the cherry canyon formation consists of a 925 ft 280 m thick section of up to 25 different sandstone and siltstone units that were deposited in deep water in the delaware basin lowstand sedimentation by fluid density currents with periodic turbidity currents resulted in a broad migrating channelized slope fan basin floor fan complex exhibiting a complex depositional architecture of reservoir sandstones original depositional fabric modified by diagenetic cements and authigenic clays create a range of petrophysical rock types type i reservoirs are found in channel sandstones beds of lesser reservoir quality type ii are present in laminated overbank interchannel sandstones a practical pore geometry classification scheme based on pore grain shapes and pore throat rad i is used to understand fluid saturations and predict well performance within the context of the depositional framework and structural relief pore geometry factors combine with insufficient structural closure to create high water saturations throughout the oil column type i macroporous reservoirs exhibit oil water transition zones and are interbedded with type ii mesoporous to microporous reservoirs which contain all or mostly water due to high capillarity associated with small pore throat size accurate reservoir water saturations can be derived using archie s equation when combined with a movable oil analysis and drainage relative permeability fractional flow curves initial watercuts can be predicted to maximize deliverability from optimal rock types high original water saturations in the transition zone decrease average water saturations behind the waterflood front resulting in inefficient secondary recovery a combined application of sedimentological petrophysical logging and reservoir engineering technologies is necessary to properly evaluate the cherry canyon reservoirs

the vestan cataclysm impact melt clasts in howardites and the bombardment history of 4 vesta crystalline impact melt samples were created in high temperature environments by relatively large craters and as such give additional constraints on the nature of the impacts that created them this article provides new 40ar 39ar ages of impact melt clasts in howardites and shows that these clasts formed on the hed parent body 4 vesta within the time period 3 3 3 8 ga rather than resulting from an increased number of impacts however impact melted material in howardites may result from unusually high velocity impacts occurring in the asteroid belt during this period this scenario is similar to the late heavy bombardment of the moon pointing to an unusual dynamical event at this time across the inner solar system therefore impact melt rocks in howardites uniquely record a vestan cataclysm

delineating and quantifying depositional facies patterns in carbonate reservoirs insight from modern analogs modern carbonate settings have long been used as analogs for interpreting various environments of deposition in subsurface data sets based on well log and core data and have provided examples of how these environments can be interrelated within a larger context this study focuses on carbonate sands in the exuma islands part of the great bahama bank to show how modern settings can be better used for reservoir analogs by emphasizing visualization and quantification techniques that conceptually delineate aspects of potential grainstone reservoir distribution and heterogeneity along the windward margin of the exumas the association of tidal deltas channels and islands forms an exploration scale linear belt of mostly ooid sand approximately 5 10 km 3 1 6 mi wide and 170 km 106 mi long paralleling the platform margin but set back from the platform edge the distribution of carbonate sands in the exumas was assessed with a digital elevation model and satellite imagery by selecting different water depth intervals parts of the sand belt were highlighted for visual analysis and extracted for measurements of size and shape for example 37 of the sand belt comprises shallowest sands in which the largest areas greater than 100 000 m2 1 07 million ft2 are highly sinuous and maintain connectivity the sand belt was also subdivided into various depositional settings flood tidal delta lobes comprise 85 of the sand belt tidal channels and islands add further heterogeneity to the sand belt channels average about 3 km 1 8 mi in length and have regular but locally variable spacing a representative island shows how the syndepositional topography of holocene ridges develops complexly around antecedent pleistocene topography

permeability prediction and diagenesis in tight carbonates using machine learning techniques abstract machine learning techniques have found their way into many problems in geoscience but have not been used significantly in the analysis of tight rocks we present a case study testing the effectiveness of artificial neural networks and genetic algorithms for the prediction of permeability in tight carbonate rocks the dataset consists of 130 core plugs from the portland formation in southern england all of which have measurements of klinkenberg corrected permeability helium porosity characteristic pore throat diameter and formation resistivity permeability has been predicted using genetic algorithms and artificial neural networks as well as seven conventional benchmark models with which the machine learning techniques have been compared the genetic algorithm technique has provided a new empirical equation that fits the measured permeability better than any of the seven conventional benchmark models however the artificial neural network technique provided the best overall prediction method quantified by the lowest root mean square error rmse and highest coefficient of determination value r2 the lowest rmse from the conventional permeability equations was from the rgpz equation which predicted the test dataset with an rmse of 0 458 while the highest rmse came from the berg equation with an rmse of 2 368 by comparison the rmse for the genetic algorithm and artificial neural network methods were 0 433 and 0 38 respectively we attribute the better performance of machine learning techniques over conventional approaches to their enhanced capability to model the connectivity of pore microstructures caused by codependent and competing diagenetic processes we also provide a qualitative model for the poroperm characteristics of tight carbonate rocks modified by each of eight diagenetic processes we conclude that for tight carbonate reservoirs both machine learning techniques predict permeability more reliably and more accurately than conventional models and may be capable of distinguishing quantitatively between pore microstructures caused by different diagenetic processes

fault controlled dolomitization in a rift basin there are numerous examples of fault controlled so called hydrothermal dolomite htd many of which host economic mineral deposits or hydrocarbons but there remains a lack of consensus as to how they form in particular multiple phases of diagenetic overprinting can obscure geochemical fingerprints study of a cenozoic succession with a relatively simple burial history here provides new insights into the development of differentially dolomitized beds the hammam faraun fault hff block within the suez rift egypt hosts both massive and stratabound dolostone bodies non fabric selective massive dolostone is limited to the damage zone of the fault while fabric selective stratabound dolostone bodies penetrate nearly 2 km into the footwall oligo miocene seawater is interpreted to have been drawn down discrete faults into a deep aquifer and convected upwards along the hff escape of fluids from the incipient hff into the lower thebes formation led to differential stratabound dolomitization once the hff breached the surface fluid circulation focused along the fault plane to form younger massive dolostone bodies this study provides a snapshot of dolomitization during the earliest phases of extension unobscured by subsequent recrystallization and geochemical modification contrary to many models stratabound dolomitization preceded non stratabound dolomitization fluids were hydrothermal but with little evidence for rapid cooling and brecciation common to many htd bodies these results suggest that many of the features used to interpret and predict the geometry of htd in the subsurface form during later phases of structural deformation perhaps overprinting less structurally complex dolomite bodies

a comparison study of the c a and s a models with singularity analysis to identify geochemical anomalies in covered areas abstract fractal multifractal modeling of geochemical data is an interesting topic in the field of applied geochemistry identification of weak anomalies for mineral exploration in covered areas is one of the most challenging tasks for utilization of geochemical data in this study three fractal models consisting of the concentration area c a spectrum area s a and singularity index models were applied to identify geochemical anomalies in the covered area located in the chaobuleng fe polymetallic district inner mongolia china the results show that 1 the grassland cover weakens the concentrations of geochemical elements 2 the c a model has a limitation to identify weak anomalies in covered areas 3 the s a model is a powerful tool to decompose mixed geochemical patterns into a geochemical anomaly map and a varied geochemical background map but suffers edge effects in an irregular shaped study area and 4 the singularity index is a useful tool to identify weak geochemical anomalies

maximum entropy modeling for orogenic gold prospectivity mapping in the tangbale hatu belt western junggar china abstract the tangbale hatu belt western junggar region located in the central asian orogenic belt caob has undergone complicated accretion and collision processes during the evolution of the paleo asian ocean the geological events contributed to orogenic gold mineral systems in the region in the present study mineral systems approach was employed to evaluate critical ore forming processes such as fluid migration pathways the formation of trap zones and deposition of metals by means of translating these critical processes into mappable ore controlling variables we attempt to establish a process based quantitative evaluation model a maximum entropy maxent model was proposed to predict the potential distribution of orogenic gold deposits based on known gold deposits occurrences and ore controlling variables nine ore controlling variables including fault intersection density fault linear density the first factor score map au singularity indices au regional anomaly au local anomaly proximity to ne trending faults proximity to intrusion contacts and proximity to stratigraphic contacts were selected to identify the most potential zones endowed with gold deposits the spatial association of individual ore controlling variable with the incidence of gold deposit occurrences was investigated by response curves and the relative importance of each ore controlling variable was determined by jackknife analysis in the maxent model the results indicate that au regional anomaly derived from spectrum area s a fractal model is the most important variable followed by the first factor score map and proximity to stratigraphic contacts the model accuracy was evaluated by roc curve giving a high predictive ability auc 0 915 favorable zones for gold mineralization illustrated by the prospectivity map are spatially coincident with known gold deposits occurrences and the main mineralized trends showing that the maxent model can be efficiently employed for spatial fusion analysis of multisource geospatial data to support conceptual mineral systems modeling of geologic controls on mineral deposit occurrences

early diagenetic dolomite cements examples from the permian lower magnesian limestone of england and the pleistocene carbonates of the bahamas abstract early diagenetic dolomite cements are found in the permian lower magnesian limestone of eastern england and the pleistocene carbonates of great abaco island bahamas in the lower magnesian limestone the dolospar occurs as isopachous rinds that have grown both centripetally and centrifugally on the dolomitized micrite envelopes of hollow centered allochems because compactional fractures penetrate both the allochem walls and the cement rinds dolomite cementation is inferred to have predated any significant sediment accumulation in the great abaco carbonates limpid dolomite forms isopachous rinds around inter and intragranular porosity and is postdated by meteoric calcite cement both examples of early diagenetic dolomite cement textures developed as a consequence of changes in pore fluid chemistry from marine to mixed meteoric marine to meteoric waters therefore the presence of this cement type may point toward aliagenetic environments resulting from marine regressions

permeability prediction from micp and nmr data using an electrokinetic approach theaccuratemodelingofoil gas andwaterreservoirsdependsfundamentallyuponaccesstoreliablerockpermeabilitiesthatcannotbeobtaineddirectlyfromdownholelogs instead a range of empirical models are usually employed we propose a new model that has been derived analytically from electrokinetic theory and is equally valid for all lithologies the predictions of the new model and four other common models kozeny carman berg swanson and van baaren have been compared using measurements carried out on fusedandunfusedglassbeadpacksaswellason91rocksamples representing 11 lithologies and three coring directions the new model provides the best predictions for the glass beadpacksaswellforallthelithologies thecruxofthenew modelistohaveagoodknowledgeoftherelevantmeangrain diameter forexample frommicpdata hence wehavealso predictedthepermeabilitiesof21northseawellcoresusing all five models and five different measures of relevant grain size these data show that the best predictions are provided by the use of the new model with the geometric mean grain size wehavealsoappliedthenewmodeltothepredictionof permeability from nmr data of a 500 m thick sand shale succession in the north sea by inverting the t2 spectrum to provide a value for the geometric mean grain size the new model shows a good match to all 348 core measurements fromthesuccession performingbetterthanthesdr timurcoates hscm andkozeny carmanpredictions

neogene to quaternary sedimentary basins in the south adriatic central mediterranean foredeeps and lithospheric buckling up to several kilometers deep sedimentary basins of neogene to quaternary age are found in the south adriatic between the apennines and the dinarides albanides they are the apennines foredeep the central adriatic basin and the south adriatic basin two regional seismic lines 260 and 170 km long across the entire system provide hitherto unavailable constraints on the kinematics and dynamics of basin development the apennine foredeep imaged along the lines formed in middle to late pliocene times through a rapid westward tilting of the basin floor a paleobathymetry of few kilometers was created in which allochthonous bodies were emplaced and sediments deposited unaffected by deformation and farther rotations the central and south adriatic basins formed in neogene to quaternary times and are both characterized by strong subsidence in their central parts gradually diminishing toward the edges in the sw and ne depocenters did not shift laterally through time subsidence rates increase through time and subsidence continued also following the end of main shortening episodes in the dinarides albanides the central and south adriatic basins form two crustal scale synclines with subsidence concentrated in their central parts basins geometries and subsidence patterns indicate that the adriatic crust has undergone episodes of buckling since miocene times wavelengths and amplitudes of such folds change along strike corresponding to mechanical changes of the folded medium

predicting landslides for risk analysis spatial models tested by a cross validation technique abstract a landslide hazard map is intended to show the location of future slope instability most spatial models of the hazard lack reliability tests of the procedures and predictions for estimating the probabilities of future landslides thus precluding use of the maps for probabilistic risk analysis to correct this deficiency we propose a systematic procedure comprising two analytical steps relative hazard mapping and empirical probability estimation a mathematical model first generates a prediction map by dividing an area into prediction classes according to the relative likelihood of occurrence of future landslides conditional by local geomorphic and topographic characteristics the second stage estimates empirically the probability of landslide occurrence in each prediction class by applying a cross validation technique cross validation a blind test here using non overlapping spatial or temporal subsets of mapped landslides evaluates accuracy of the prediction and from the resulting statistics estimates occurrence probabilities of future landslides this quantitative approach exemplified by several experiments in an area near lisbon portugal can accommodate any subsequent analysis of landslide risk